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Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 
Columbia  University  Libraries 


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MORRIS'S 

TEEATISE  ON  ANATOMY 

FIFTH  EDITION 


CONTRIBUTORS  TO  FIFTH  EDITION 


CHARLES  R.  BARDEEN,  University 
of  Wisconsin. 

ELIOT  R  CLARK,  Johns  Hopkins 
University. 

IRVING  HARDESTY,  Tulane  Uni- 
versity of  Louisiana. 

C.  M.  JACKSON,  University  of  Min- 
nesota. 

F.  W.  JONES,  London  School  of  Medi- 
cine for  Women. 

ABRAM  T.  KERR,  Cornell  University. 


J.  PLAYFAIR  McMURRICH,  Uni- 
versity of  Toronto. 

JOHN  MORLEY,  Manchester  Univer- 
sity. 

H.  D.  SENIOR,  University  and  Belle- 
vue  Hospital  Medical  College.,  N.  Y. 

R.  J.  TERRY,  Washington  University, 
St.  Louis. 

PETER  THOMPSON,  University  of 
Birriiingham. 

DAVID  WATERSTON,  King's  Col- 
lege, London. 


For  arrangement  of  subjects  and  authors  see  page  v. 


THIS  WORK  IS  ALSO  PUBLISHED  IN  FIVE  PARTS  AS  FOLLOWS: 


PART      I.  Morphogenesis.     Osteology.     Articulations.     Index.     $L50. 

PART  II.  Muscles.  Blood-Vascular  System.  Lymphatic  System.  Index. 
$2.50. 

PART  III.  Nervous  System.     Special  Sense  Organs.     Index.     $2.00. 

PART  IV.  Digestive  System.  Respiratory  System.  Skin,  Mammary  and  Duct- 
less Glands.     Urogenital  System.     Index.     $L50. 

PART     V.  Clinical  and  Topographical  Anatomy.     Index.     $1.50. 


MOEEIS'S 

HUMAN  ANATOMY 


A    COMPLETE    SYSTEMATIC    TREATISE 
BY  ENGLISH  AND  AMERICAN  AUTHORS 


EDITED    BY 

•  C.  M.  JACKSON,  M.  S.,  M.  D. 

PROFESSOR   AND  DIRECTOR  OF  THE  DEPARTMENT  OF  ANATOMY 
UNIVERSITT    OF  MINNESOTA 


ELEVEN  HUNDRED  AND  EIGHTY  TWO  ILLUSTRATIONS 
THREE  HUNDRED  AND  FIFTY  EIGHT  PRINTED  IN  COLOURS 


FIFTH  EDITION,  REVISED  AND  LARGELY  REWRITTEN 


PHILADELPHIA 

P.  BLAKISTON'S  SON  &  CO, 

1012  WALNUT  STREET 


Copyright,  1914,  by  P.  Blakiston's  Son  &  Co. 


hi  4 


.  YORK-   PA 


AREANGEMENT  OF  SUBJECTS  AND  AUTHORS 


The  names  of  the  more  recent  of  those  who  wrote  or  revised  articles  for 
previous  editions  have  been  retained  in  the  following  list  in  order  that  due  credit 
should  be  given  them  for  the  work  done  and  for  their  share  in  the  great  success 
which  Morris's  "Anatomy"  has  achieved. 

MORPHOGENESIS.     Revised  and  largely  rewritten  for  the  fifth  edition  by 

C.  M.  Jackson,  M.S.,  M.D.,  Professor  of  Anatomy  in  the  University  of  Minne- 
sota. Originally  written  by  J.  Playfair  McMurrich,  A.M.,  Ph.D.,  Professor  of 
Anatomy,  University  of  Toronto. 

OSTEOLOGY.  Revised  for  the  third,  fourth  and  fifth  editions  by  Peter 
Thompson,  M.D.,  Professor  of  Anatomy,  University  of  Birmingham;  Member 
of  Anatomical  Society  of  Great  Britain.  This  article  was  originally  written  by  Sir 
John  Bland  Sutton,  F.R.C.S. 

ARTICULATIONS.  Revised  for  the  fifth  edition  by  Frederic  Wood  Jones, 
D.Sc,  M.B.,  B.S.  (Lond.),  M.R.C.S.,  L.R.C.P.,  Head  of  the  Department  of 
Anatomy  and  Lecturer  in  the  London  School  of  Medicine  for  Women.  Originally 
written  by  Su-  Henry  Morris,  A.M.,  M.B. 

MUSCLES.  Rewritten  and  revised  for  the  fourth  and  fifth  editions  by 
Charles  R.  Bardeen,  A.B.,  M.D.,  Professor  of  Anatomy  in  the  University  of 
Wisconsin;  Member  Association  of  American  Anatomists;  Member  of  Editorial 
Board  of  "American  Journal  of  Anatomy." 

BLOOD-VASCULAR  SYSTEM.     Revised  and  in  part  rewritten  by  Harold 

D.  Senior,  M.B.,  F.R.C.S.,  Professor  of  Anatomy,  University  and  Bellevue  Hos- 
pital Medical  College.  The  section  on  Blood-vessels  was  formerly  revised  by 
Florence  R.  Sabin,  B.S.,  M.D.,  Associate  Professor  of  Anatomy,  Johns  Hopkins 
University. 

LYMPHATIC  SYSTEM.  Revised  and  partly  rewritten  for  the  fifth  edition 
by  Eliot  R.  Clark,  A.B.,  M.D.,  Associate  in  Anatomy,  Johns  Hopkins  Uni- 
versity.    Revised  for  previous  edition  by  Florence  R.  Sabin,  B.S.,  M.D. 

NERVOUS  SYSTEM.  Revised  and  largely  rewritten  for  the  fourth  and  fifth 
editions  by  Irving  Hardesty,  A.B.,  Ph.D.,  Professor  of  Anatomy,  Tulane 
University,  Louisiana;  Member  Association  of  American  Anatomists. 

SPECIAL  SENSE  ORGANS.  Revised  for  the  fifth  edition  by  David 
Waterston,  M.A.,  M.D.,  F.R.C.S.,  Professor  of  Anatomy  in  the  University  of 
London.  In  the  earlier  edition,  the  Ear,  Nose,  Tongue  were  revised  by  Abram 
T.  Kerr,  B.S.,  M.D. 

DIGESTIVE  SYSTEM.  Revised  and  largely  rewritten  for  the  fifth  edition 
by  C.  M.  Jackson,  M.S.,  M.D.,  Professor  of  Anatomy,  LTniversity  of  Minnesota. 
Revised  for  the  fourth  edition  by  G.  Carl  Huber,  M.D. 


vi  ARRANGEMENT  OF  SUBJECTS  AND  AUTHORS 

RESPIRATORY  SYSTEM.  Revised  for  the  fourth  and  fifth  editions  by 
R.  J.  Terry,  A.B.,  M.D.,  Professor  of  Anatomy,  Washington  University,  St. 
Louis;  Member  Association  of  American  Anatomists. 

UROGENITAL  SYSTEM.  Revised  for  the  fourth  and  fifth  editions  by 
J.  Playfair  McMurrich,  A.M.,  Ph.D.,  Professor  of  Anatomy,  University  of 
Toronto;  Member  Association  of  American  Anatomists. 

THE    SKIN  AND    MAMMARY   GLAND;    THE    DUCTLESS   GLANDS. 

By  Abram  T.  Kerr,  B.S.,  M.D.,  Professor  of  Anatomy,  Cornell  University; 
Member  Association  of  American  Anatomists,  etc.  The  article  on  the  Ductless 
Glands  was  originally  written  by  G.  Carl  Huber,  M.D. 

CLINICAL  AND  TOPOGRAPHICAL  ANATOMY.  By  John  Morley, 
Ch.M.,  F.R.C.S.,  Honorary  Surgeon,  Ancoats  Hospital,  Manchester,  and 
Lecturer  in  Clinical  Anatomy,  Manchester  University.  Originally  written  by 
W.  H.  A.  Jacobson,  F.R.C.S. 


EDITOR'S  PREFACE  TO  THE  FIFTH  EDITION 


One  criticism  upon  most  of  the  current  text-books  of  human  anatomy  is  that 
they  are  too  extensive  for  the  beginner.  Much  precious  time  is  wasted  by  him  in 
floundering  through  a  mass  of  details  which  obscure  the  fundamental  facts.  And 
yet  it  is  important  to  have  these  details  conveniently  accessible  for  both  present 
and  future  reference.  To  meet  this  difficulty,  the  attempt  is  made  in  this  edition 
to  discriminate  systematically  in  the  use  of  sizes  of  type.  The  larger  type  is  used 
for  the  more  fundamental  facts,  which  should  be  mastered  first,  and  the  smaller 
type  for  details.  While  it  has  been  found  difficult  to  apply  this  principle  uni- 
formly through  the  various  sections,  it  is  hoped  that  the  plan,  even  though  but 
imperfectly  realized,  will  prove  useful  to  the  beginner. 

In  the  illustrations  of  the  bones,  as  heretofore,  the  origins  of  muscles  are  in- 
dicated by  red  lines,  the  insertions  by  blue  lines,  and  the  attachments  of  ligaments 
by  dotted  black  lines. 

While  the  authors  of  the  present  edition  are  for  the  most  part  the  same  as  in 
the  previous  edition,  a  few  changes  have  been  made  as  noted  under  the  preceding 
section,  "Arrangement  of  Subjects  and  Authors."  Owing  to  the  retirement 
of  the  distinguished  originator  and  former  editor  of  this  work.  Sir  Henry  Morris, 
and  of  Professor  McMurrich  as  co-editor,  the  responsibility  for  the  general 
supervision  of  the  fifth  revision  has  fallen  to  the  present  editor. 

Each  author  is  alone  responsible  for  the  subject-matter  of  the  article  following 
his  name.  Care  has  been  exercised  on  the  part  of  the  editor,  however,  to  make 
the  whole  uniform,  complete  and  systematic. 

As  to  nomenclature,  the  Anglicised  form  of  the  BNA  has  been  continued, 
excepting  those  cases  where  the  Latin  form  is  adopted  into  English  (e.  g.,  most  of 
the  muscles),  and  rare  cases  where  the  BNA  term  seems  undesirable.  As  a  rule, 
the  Anglicised  form  where  first  used  is  followed  by  the  BNA  Latin  term  in 
brackets,  except  where  the  two  are  practically  identical.  For  convenience  of  refer- 
ence, some  of  the  commoner  synonyms  of  the  old  nomenclature  are  also  added  in 
parenthesis. 

The  previous  edition  of  Morris's  Anatomy  was  the  first  general  text-book  of 
anatomy  in  English  to  adopt  the  BNA.  During  the  past  few  years  the  merit  of 
this  system  of  nomenclature  has  become  so  widely  recognized  that  it  is  now  very 
generally  accepted  among  the  English-speaking  nations.  Lack  of  space  forbids 
the  enumeration  here  of  the  many  advantages  of  this  system,  not  the  least  of  which 
is  the  reduction  of  some  30,000  anatomical  terms  (including  synonyms)  to  5000. 
The  comparatively  few  defects  of  the  BNA  will  doubtless  be  remedied  by  revision 
(preferably  through  the  International  Anatomical  Congress).  For  a  full 
discussion  of  the  BNA  system,  with  complete  Hst  of  the  Latin  terms  and  English 
equivalents,  the  reader  is  referred  to  the  excellent  work  on  the  BNA  by  Professor 
L.  F.  Barker,  of  Johns  Hopkins  University. 

In  addition  to  the  bibliographical  references  scattered  throughout  the  text,  a 
brief  list  is  given  at  the  close  of  each  section.  These  brief  lists  of  carefully  selected 
references  are  intended  merely  as  a  guide  to  put  the  student  "on  track"  of  the 
original  literature. 


viii  EDITOR'S  PREFACE  TO  THE  FIFTH  EDITION 

In  addition  to  a  thorough  revision  of  the  various  sections,  there  has  also  been 
a  rearrangement  of  a  part  of  the  subject  matter  in  the  present  edition.  The  Teeth 
have  been  transferred  from  the  section  on  Osteology  to  the  Digestive  System. 
The  Tongue  and  Nose  are  transferred  to  the  Digestive  System  and  Respiratory 
System,  respectively,  excepting  those  portions  forming  the  organs  of  Taste  and 
Smell,  which  have  been  retained  in  the  section  on  Special  Sense  Organs.  The 
Pelvic  Outlet  has  been  discontinued  as  a  separate  section,  the  subject  matter 
being  divided  between  Musculature  and  Clinical  and  Topographical  Anatomy. 
The  Ductless  Glands  have  been  included  in  the  section  with  the  Skin  and  Mam- 
mary Glands. 

Due  credit  has  been  given  throughout  the  book  wherever  illustrations  have 
been  taken,  or  modified,  from  other  works.  Special  acknowledgment  should  be 
made  of  our  indebtedness  to  the  works  of  Toldt,  Rauber-Kopsch,  Poirier  and 
Charpy,  Henle  and  Spalteholz. 

The  number  of  figures  in  the  present  edition  has  been  increased  about  one 
hundred  and  sixty  and  in  addition  many  of  the  older  figures  have  been  improved 
or  replaced.  For  the  generosity  of  the  publishers  in  this  connection,  and  for  the 
hearty  cooperation  of  the  contributors  in  the  revision  of  the  various  sections,  the 
editor  desires  to  express  his  deep  indebtedness.  Valuable  assistance  has  been 
rendered  by  Mr.  Walter  E.  Camp  in  the  reading  of  proof  and  preparation  of 
the  index. 

C.  M.  Jackson. 
Minneapolis. 


CONTENTS 


Introduction. 


By  C.  M.  Jackson,  M.S.,  M.D. 
SECTION  I 


MORPHOGENESIS 
By  C.  M.  Jackson,  M.S.,  M.D. 


Segmentation  of  the  Ovum 9 

Embryonic  Disc  and  Derivatives 10 

Metamerism 15 ' 

Branchiomerism 16 


Viscera  and  Limbs 18 

Prenatal  Growth 22 

Variability 25 

References 25 


SECTION  II 


OSTEOLOGY 


By  Peter  Thompson,  M.D. 


The  Skeleton 27 

I.  The  Axial  Skeleton 29 

A.  The  Vertebral  Column 29 

The  Cervical  Vertebrae 31 

The  Thoracic  Vertebrae 36 

The  Lumbar  Vertebrae 37 

The  Sacrum 39 

The  Coccygeal  Vertebrae 42 

The  Vertebral    Column    as   a 

Whole 43 

B.  Bones  of  the  Skull 51 

The  Occipital 51 

The  Parietal 57 

The  Frontal 59 

The  Sphenoid 62 

The  Sphenoidal  Conchae 67 

The  Epipteric    and    Wormian 

Bones 68 

The  Temporal  Bone 68 

The  Tympanum 77 

The  Osseous  Labyrinth 80 

The  Ethmoid 81 

The  Inferior  Nasal  Concha.  .  .  84 

The  Lacrimal  Bone 85 

The  Vomer 85 

The  Nasal  Bones 86 

The  Maxilla  or  Upper  Jaw ...  87 

The  Palate  Bone 91 

The  Zygomatic  or  Malar  Bone  93 

The  Mandible  or  Lower  Jaw. .  95 

The  Hyoid  Bone 99 

The  Skull  as  a  Whole 100 

The  Orbits 109 


The  Nasal  Fossa 110 

The  Interior  of  the  Skull 112 

The  Morphology  of  the  Skull .  117 

The  Skull  at  Birth 120 

C.  The  Thorax 126 

The  Ribs 126 

The  Sternum 132 

The  Thorax  as  a  Whole 138 

The  Appendicular  Skeleton 139 

A,  Bones  of  the  Upper  Extremity.  139 

The  Clavicle 139 

The  Scapula 141 

The  Humerus 146 

The  Radius 152 

The  Ulna 165 

The  Carpus 159 

The  Metacarpals 164 

The  Phalanges 167 

B.  Bones  of  the  Lower  Extremity . .  169 

The  Coxal  Bone 169 

The  Pelvis 175 

The  Femur  or  Thigh  Bone...  178 

The  Patella 184 

The  Tibia 185 

The  Fibula 189 

The  Tarsus 191 

The  Metatarsus 200 

The  Phalanges 203 

The  Bones  of  the  Foot 205 

Homology  of  the  Bones  of  the 

Extremities 206 

References 209 


CONTENTS 


SECTION  III 


THE  ARTICULATIONS 
By  F.  W.  Jones,  D.  Sc,  M.  B.,  M.  R.  C.  S.,  L.  R.  C.  P. 


Constituents  of  an  Articulation 211 

Classifioation  of  Articulations 212 

Development  and  Morphology 213 

Movements  of  Joints 214 

Articulations  of  the  Skull 215 

Mandibular  Articulation 215 

Ligaments   and   Joints   between    the 

Skull  and  Vertebral  Column 218 

Articulations  of  Atlas  with  Occiput.  .  218 
Articulations  between  Atlas  and  Epis- 
tropheus   220 

Ligaments  uniting  the  Occiput  and 

Epistropheus 223 

Articulations  of  the  Trunk 224 

1.  The  Articulations  of  the  Verte- 

bral Column 225 

a.  The  Bodies  of  the  Verte- 

brffi 225 

6.  The  Articular  Processes  .  .  228 

c.  The  Lamina 229 

d.  The  Spinous  Processes  .  . .  229 

e.  The  Transverse    Processes  231 

2.  Sacro-vertebral  Articulations.  232 

3.  Articulations  of  the  Pelvis. . . .  234 

4.  Articulations  of  the  Ribs  with 

the  Vertebrfe 241 

5.  Articulations  at  the  Front  of 

the  Thorax 244 

Movements  of  the  Thorax 247 

The  Articulations    of    the    Upper    Ex- 
tremity   248 


PAGE 

1.  Sterno-costo-olavicular  Articu- 

lation     248 

2.  Scapulo-clavioular  Union  ....  250 

3.  Shoulder-joint 253 

4.  Elbow-joint 258 

5.  Union  of  Radius  with  Ulna.  .  261 

6.  Radio-carpal  Articulation. .  .  .  265 

7.  Carpal  Joints 268 

8.  Carpo-metacarpal  Joints 272 

9.  Intermetacarpal  Articulations.  273 

10.  Metacarpo-phalangeal  Joints.  274 

11.  Interphalangeal  Articulations.  276 
The  Articulations  of  the  Lower  Limb .  . .  276 

1.  Hip-joint 276 

2.  Knee-joint 284 

3.  Tibio-fibular  Union 295 

4.  Ankle-joint 297 

5.  Tarsal  Joints 301 

a.  The  Talo-calcaneal  Union..  301 

b.  Articulations    of    Anterior 

Part  of  Tarsus 303 

c.  Medio-tarsal     or      Trans- 

verse Tarsal  Joints 305 

6.  Tarso-metatarsal  Articulations  307 

7.  Intermetatarsal  Articulations.  309 

8.  Metatarso-phalangeal  Articu- 

lations   310 

9.  Interphalangeal  Joints 310 

References 311 


SECTION  IV 
THE  MUSCULATURE 


By  C.  R.  Bardeen,  A.B.,  M.D. 


General  Remarks  on  Muscles 313 

Muscle  Fasciae 313 

Gross  Structure 314 

Finer  Structure  of  Muscles 315 

Tendons 317 

Synovial  Bursse 318 

Synovial  Sheaths 318 

Nerves  and  Vessels 318 

Nomenclature 319 

Variation 320 

Physiology 320 

I.  Musculature  of  the  Head  and  Neck 

and  Shoulder  Girdle 323 

Physiological  and  Morphological. .  323 

1.  Facialis  Musculature 329 

2.  Cranio-mandibular     Muscula- 

ture   338 

3.  Supra-hyoid    Musculature....  343 

4.  Muscles  of  the  Tongue 345 

5.  Superficial     Shoulder     Girdle 

Musculature 347 

6.  Infrahyoid  Muscles 350 

7.  Scalene  Musculature 353 

8.  Prevertebral  Musculature ....  355 

9.  Anterior    and    Lateral    Inter- 

transverse Muscles 356 


10.  Deep     Musculature     of     the 

Shoulder  Girdle 356 

II.  Musculature  of  the  Upper  Limb.  .  360 

A.  Musculature  of  the  Shoulder. .  363 

B.  Pectoral  Muscles  and  Axillary 

Fascia 370 

C.  Musculature  of  the  Arm 374 

1.  Dorsal  or  Extensor  Group. .  377 

2.  Ventral  or  Flexor  Group ....  379 

D.  Musculature   of   the   Forearm 

and  Hand 383 

1.  Dorsal-Radial  Division 387 

a.  Superficial    Layer 387 

6.  Deep  Layer 392 

2.  Ulno-Volar  Division 395 

a.  First  Layer 395 

6.  Second  Layer 399 

c.  Third  Layer 401 

d.  Fourth  Layer 402 

3.  Musculature  of  the  Hand...  403 
III.  Spinal  Musculature 410 

A.  Superficial  Lateral  Dorsal  Sj's- 

tem 414 

B.  Deep  Lateral  Dorsal  Muscles.  417 

C.  Superficial  Medial  Dorsal  Sys- 

tem   417 


CONTENTS 


PAGE 

D.  Deep  Medial  Dorsal  System .  .  417 

E.  Suboccipital  Muscles 419 

IV.  Thoracic-abdominal  Musculature.  422 

A.  Ventral  Division 430 

B.  Lateral  Division 431 

1.  Serratus  Group 431   j 

2.  External  Oblique  Group....  432 

3.  Internal  Oblique  Group 433 

4.  Transverse  Group 434 

C.  Lumbar  Muscle 436 

D.  Diaphragm 436 

V.  Musculature  of  the  Pelvic  Outlet.  439 

A.  Muscles    of    the    Pelvic    Dia-  '• 

phragm,  Coccyx  and  Anus. .  448 

B.  Muscles     of     the     Urogenital 

Diaphragm 449   ' 

C.  External  Genital  Muscles 450   , 

VI.  Musculature  of  the  Lower  Limb .  .  452 

A.  Musculature  of  the  Hip 454  i 

1.  Ilio-femoral  Musculature. . .  454  i 

a.  Anterior  Group 455   i 


b.  Posterior  Group 457 

2.  Ischio-pubo-femoral  Muscu- 
lature of  the  Hip 463 

B.  Musculature  of  the  Thigh 464 

1.  Anterior  Group 468 

2.  Medial  (Adductor)  Group.  .  471 

3.  Posterior  (Hamstring) 

Group 474 

C.  Musculature  of  the  Leg 477 

1.  Muscles  of  the  Front  of  the 

Leg 480 

2.  Lateral  Musculature  of  the 

Leg 483 

3.  Musculature  of  the  Back  of 

the  Leg 484 

D.  Muscles  of  the  Foot 491 

1.  Muscle   of   the   Dorsum   of 

the  Foot 492 

2.  Muscles  of  the  Sole 493 

Muscles  Grouped  According  to  Function  500 

References 506 


SECTION  V 


BLOOD-VASCULAR  SYSTEM 
By  Harold  D.  Senior,  M.B.,  M.D. 


A.  The  Heart  and  Pericardium 508 

1.  The  Heart 508 

Exterior  of  the  Heart 509 

Atrial  Portion 511 

Atrio- Ventricular  Valves 515 

Ventricular  Portion 516 

Semilunar  Valves 517 

Architecture  of  the  Heart 518 

Vessels  and  Nerves 519 

2.  The  Pericardium 522 

3.  Surface  Relations 523 

4.  Morphogenesis 523 

B.  The  Arteries  and  Veins 527 

1.  Pulmonary  Arteries  and  Veins.  .  .  528 

2.  The  Systemic  Arteries 529 

The  Aorta 529 

Innominate  Artery 532 

Branches 532 

Common  Carotid  Arteries 533 

E.xternal  Carotid  Artery 536 

Branches 536 

Internal  Carotid  Artery 549 

Branches 552 

Subclavian  Artery 556 

Branches 658 

Axillary  Ai-tery 569 

Branches 570 

Brachial  Artery 573 

Branches 575 

Ulnar  Artery 576 

Branches 577 

Superficial  Volar  Arch 582 

Branches 582 

Radial  Artery 582 

Branches 583 

Deep  Volar  Arch 586 

Branches 586 

Descending  or  Thoracic  Aorta.  .  586 

Visceral  Branches 588 

Parietal  Branches 588 

Abdominal  Aorta 590 

Parietal  Branches 592 

Visceral  Branches 593 

Terminal  Branches 603 

Middle  Sacral  Artery 603 


Common  Iliac  Arteries 603 

Hypogastric  Artery 605- 

Parietal  Branches    606 

Visceral  Branches 609 

External  Iliac  Artery 614 

Branches 614 

Femoral  Artery 616 

Branches 618 

PopUteal  Artery 621 

Branches 622 

Posterior  Tibial  Artery 624 

Branches 626 

Lateral  Plantar  Artery 627 

Branches 628 

Medial  Plantar  Artery 629 

Branches 629 

Anterior  Tibial  Artery 629 

Branches 630 

Dorsahs  Pedis  Artery 632 

Branches 632 

Morphogenesis    and    Variations 

of  the  Arteries 633 

a.  Arteries   of    the   Head   and 

Trunk 6.33 

6.  Arteries  of  the  Extremities  639 

The  Systemic  Veins 640 

Veins   Emptying  into   the  Vena 

Cava  Superior 641 

Veins  of  the  Head  and  Neck 642 

Superficial  Veins  of  the  Head 

and  Neck 643 

Deep  Veins  of  the  Head  and 

Neck 648 

Veins  of  the  Thorax 662 

Superficial  Veins  of  the  Thorax.  662 

Deep  Veins  of  the  Thorax 662 

Veins  of  the  Upper  Extremity. .  .  667 
Superficial  Veins  of  Upper  Ex- 
tremity    667 

Deep  Vems  of  Upper  Extremity  670 
Veins   Emptying  into  the  Vena 

Cava  Inferior 672 

Portal  Vein  and  its  Tributaries.  675 

Common  lUao  Veins 679 

Hypogastric  Vein 679 


CONTENTS 


PAG£ 

External  Iliae  Vein 683 

Superficial  Veins  of  Abdominal 

Wall 683 

Veins  of  the  Lower  Extremity. . .  683 
Superficial  Veins  of  Lower  Ex- 
tremity   684 

Deep  Veins  of  Lower  Extremity  686 
Morphogenesis  and  Variations  of 

the  Veins 690 


PAGE 

a.  Vena    Cava     Superior    and 

Tributaries 690 

b.  Vena     Cava     Inferior     and 

Tributaries 693 

c.  Portal  System 694 

The  Foetal  Circulation 695 

References 696 


SECTION  VI 

THE  LYMPHATIC  SYSTEM 

By  Eliot  R.   Claek,  A.B.,  M.D. 


I .  General  Anatomy  of  the  Lymphatic 

System 697 

1.  Lymphatic  Capillaries 697 

2.  Lymphatic  Vessels 702 

3.  Lymphoid  Organs 704 

4.  Development    of    the    Lym- 

phatic System 706 

II.  Special  Anatomy  of  the  Lymphatic 

System 709 

A.  Lymphatics    of    the    Head    and 

Neck 709 

1.  Superficial  Nodes  of  Head  and 

Neck 709 

2.  Lymphatic  Vessels  of  the  Face     712 

3.  Deep  Lymphatic  Nodes  of  the 

Head  and  Neck 714 

4.  Deep   Lymphatic   Vessels   of 

the  Head  and  Neck 714 

B.  Lymphatics   of   the   Upper   Ex- 

tremity      719 

1.  Lymphatic  Nodes  of  the  Up- 

per Extremity 719 

2.  Lymphatic  Vessels  of  the  Up- 

per Extremity 721 

C.  Lymphatics  of  the  Thorax 723 

1.  Superficial  Lymphatic  Vessels 

of  the  Thorax 723 

2.  Lymphatic     Nodes     of     the 

Thorax 724 


3.  Deep  Lymphatics  of  the  Tho- 
rax      725 

Thoracic  Duct 726 

Right  Collecting  Ducts 728 

Deep  Lymphatic  Vessels 728 

D.  Lymphatics    of    Abdomen    and 

Pelvis 730 

1.  Lymphatic  Nodes  of  the  Ab- 

domen and  Pelvis 730 

2.  Lymphatic  Vessels  of  the  Ab- 

dominal WaUs 733 

3.  Visceral  Lymphatic  Vessels  of 

the  Abdomen  and  Pelvis .  .  .      733 
Lymphatics     of     Alimentary 

Tract 733 

Lymphatics  of  Excretory  Or- 
gans      737 

Lymphatics  of  Reproductive 
Organs 742 

E.  Lymphatics   of   the  Lower   Ex- 

tremity       746 

1.  Lymphatic     Nodes     of     the 

Lower  Extremity 746 

2.  Lymphatic     Vessels     of     the 

Lower  Extremity 748 

References 750 


SECTION  VII 
THE  NERVOUS  SYSTEM 


5y  Irving  Hardestt,  A.B.,  Ph.D. 


General  Considerations 751 

Central  Nervous  System 770 

I.  Spinal  Cord 771 

External  Morphology 771 

Internal  Structure 775 

II.  Brain  or  Encephalon 792 

General  Topography 793 

Rhombencephalon 799 

1.  Medulla  Oblongata 799 

2.  Pons  VaroUi 804 

3.  Cerebellum 804 

Cerebrum 833 

1.  Mesencephalon    (Mid-brain).  833 

2.  Prosencephalon    (Fore-brain)  843 

A.  Diencephalon(Inter-brain)  843 

B.  Telencephalon  (End-brain)  847 

III.  General     Summary     of     Principal 

Conduction    Paths    of    Nervous 

System 895 

IV.  Meninges 908 


The  Peripheral  Nervous  System 924 

I.  Cranial  Nerves 927 

Olfactory  Nerves 929 

Optic  Nerves 930 

Oculo-motor  Nerves 931 

Trochlear  Nerves 933 

Abducens  Nerves 934 

Trigeminal  Nerves 934 

Masticator  Nerves 942 

Facial  Nerves 943 

Glosso-palatine  Nerves 946 

Vestibular  Nerves 949 

Cochlear  Nerves 950 

Glosso-pharyngeal  Nerves 951 

Hypoglossal  Nerves 952 

Vagus  Nerves 954 

Spinal  Accessory  Nerves 958 

Gangliated  Cephalic  Plexus 959 

II.  Spinal  Nerves 964 

A.  Posterior  Primary  Divisions.  .  .  970 


CONTENTS 


xiu 


1.  Cervical  Nerves 971 

2.  Thoracic  Nerves 971 

3.  Lumbar  Nerves 973 

4.  Sacral  Nerves 973 

B.  Anterior  Primary  Divisions ....     973 

1.  Cervical  Nerves 974 

Cervical  Plexus 974 

Brachial  Plexus 980 

2.  Thoracic  Nerves 994 

3.  Lumbar  Nerves 996 

Lumbo-sacral  Plexus 996 

Lumbar  Plexus 998 

Lumbo-sacral  Trunk 1005 

4.  Sacral  Nerves 1006 

Sacral  Plexus 1006 

Pudendal  Plexus 1016 

Coccygeal  Plexus.  . 1018 

III.  Distribution     of     the     Cutaneous 

Branches 1018 

Cutaneous  Areas  of  Scalp 1018 

Cutaneous  Areas  of  Face 1018 


PAGE 

Cutaneous  Areas  of  Neck 1019 

Cutaneous  Areas  of  Trunk 1020 

Cutaneous  Areas  of  Limbs 1020 

The  Sympathetic  System 1026 

Sympathetic  Trunks 1032 

Cephalic  and  Cervical  Portions  of  the 

Sympathetic  Trunk 1033 

1.  Superior  Cervical  Ganglion 1035 

2.  Middle  Cervical  GangUon 1036 

3.  Inferior  Cervical  Ganghon 1036 

Thoracic     Portion     of     Sympathetic 

Trunk 1037 

Lumbar  Portion  of  Sympathetic 

Trunk 1039 

Sacral  Portion  of  Sympathetic  Trunk.  1040 

Great  Prevertebral  Plexuses 1040 

1.  Cardiac  Plexus 1041 

2.  CcEliac  Plexus 1043 

3.  Hypogastric  Plexus 1045 

References 1047 


SECTION  VIII 

SPECIAL  SENSE  ORGANS 

By  David  Waterston,  M.A.,  M.D.,  F.R.C.S. 


General  Considerations 1049 

I.  Olfactory  Organ 1049 

II.  Organ  of  Taste 1051 

III.  The  Eye 1051 

General  Surface  View 1052 

Examination  of  Eyeball 1055 

Cavity  of  Orbit 1066 

General  Arrangement 1066 

Optic  Nerve 1073 

Blood-vessels     and     Nerves     of 

Orbit 1074 


Eyelids 1076 

Lacrimal  Apparatus 1079 

Development  of  the  Eye 1080 

The  Ear 1082 

External  Ear 1082 

Middle  Ear 1086 

Internal  Ear 1092 

Development  of  the  Ear 1096 

References 1098 


SECTION  IX 
THE  DIGESTIVE  SYSTEM 
By.  C.  M.  Jackson,  M.S.,  M.D. 


The  Mouth 1100 

The  Lips  and  Cheeks 1102 

The  Palate 1104 

The  Tongue 1106 

The  Salivary  Glands 1113 

The  Teeth 1117 

The  Pharynx 1128 

The  (Esophagus 1138 

The  Abdomen 1142 

The  Peritoneum 1145 


The  Stomach 1151 

The  Small  Intestine 1161 

The  Duodenum 1161 

The  Jejunum  and  Ileum 1165 

The  Large  Intestine 1170 

The  Liver 1180 

The  Bile  Passages 1186 

The  Pancreas 1192 

References 1197 


SECTION  X 
THE  RESPIRATORY  SYSTEM 


By  R.  J.  Terry,  A.B.,  M.D. 


The  Nose 1200 

The  Larynx 1209 

Cartilages  of  Larynx.  . 1209 

Joints  and  Membranes  of  Larynx.  .  .  1213 

Muscles  of  Larynx 1218 

Cavity  of  Larynx  and  Mucosa 1220 


The  Trachea  and  Bronchi 1225 

The  Lungs 1228 

The  Thoracic  Cavitv, 1235 

The  Pleura; .' 1236 

Mediastinal  Septum 1239 

References 1240 


CONTENTS 


SECTION  XI 

UROGENITAL  SYSTEM 

By  J.  Playpair  McMubeich,  A.M.,  Ph.D. 


PAGE 

The  Urinary  Apparatus 1241 

The  Kidneys 1241 

The  Ureters 1247 

The  Urinary  Bladder 1249 

The  Male  Reproductive  Organs 1253 

The  Testes  and  Their  Appendages. . .  1254 

The  Scrotum 1254 

The  Testes  and  Epididymis 1255 

The  Ductus  Deferentes  and  Seminal 

Vesicles 1257 

The  Spermatic  Cord 1259 

The  Penis 1260 

The  Male  Urethra 1262 


PAGE 

The  Prostate 1264 

The  Bulbo-urethral  Glands 1265 

The  Female  Reproductive  Organs 1265 

The  Ovaries 1268 

The  Tuba;  Uterinas 1269 

The  Uterus 1271 

The  Vagina 1274 

Female  External  Genitalia  and  Ure- 
thra     1276 

Development  of  the  Reproductive  Or- 
gans     1278 

References 1280 


SECTION  XII 


THE  SKIN,  MAMMARY  AND  DUCTLESS  GLANDS 
By  Abeam  T.  Kerr,  B.S.,  M.D. 


The  Skin 1281 

Appendages  of  the  Skin 1290 

Hairs 1290 

Nails 1293 

Cutaneous  Glands 1296 

Mammary  Glands 1299 

The  Ductless  Glands 1306 

The  Spleen 1306 


The  Thyreoid  Gland 1312 

Parathyreoid  Glands 1318 

Thymus 1319 

Suprarenal    Glands 1323 

Glomus  Caroticum 1327 

Aortic  Paraganglia 1329 

Glomus   Coccygeum 1329 

References 1329 


SECTION  XIII 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 
By  John  Morley,  Ch.M.,  F.R.C.S. 


The  Head 1331 

The  Cranium 1333 

The  Bony  Sinuses 1335 

Cranio-cerebral  Topography 1338 

The  Hypophysis  Cerebri 1342 

The  Face 1342 

The  Orbit  and  Eye 1346 

The  Mouth 1349 

The  Nose 1352 

The  Neck 1354 

The  Thorax 1363 

The  Abdomen 1370 

The  Pelvis 1382 

Male  Pelvis 1382 

Female  Pelvis 1391 

Hernia 1394 

Inguinal  Hernia 1394 


Femoral  Hernia 1398 

Umbilical  Hernia 1402 

The  Back 1403 

The  Upper  Extremity 1409 

The  Shoulder  and  Arm 1409 

The  Elbow 1417 

The  Forearm 1419 

The  Wrist  and  Hand 1424 

The  Lower  Extremity 1434 

The  Hip  and  Thigh 1434 

The  Knee 1444 

Popliteal  Space 1451 

The  Leg 1453 

The  Ankle 1459 

The  Foot 1464 

Arches  of  the  Foot 1468 


Index 1471 


INTRODUCTION 

By  C.  M.  JACKSON,  M.S.,  M.D. 

PROFESSOR  OP   ANATOMY,   TJNrVEHSITT  OP  MINNESOTA. 


ANATOMY,  as  the  term  is  usually  employed,  denotes  the  study  of  the 
/-\  structure  of  the  human  body.  Properly,  however,  it  has  a  much  wider 
-^-*-  significance,  including  within  its  scope  not  man  alone,  but  all  animal  forms, 
and,  indeed,  plant  forms  as  well;  so  that,  when  its  application  is  limited  to  man, 
it  should  be  qualified  by  the  adjective  human.  Human  Anatomy,  then,  is  the 
study  of  the  structure  of  the  human  body,  and  stands  in  contrast  to,  or  rather  in 
correlation  with.  Human  Physiology,  which  treats  of  the  functions  of  the  human 
body,  the  two  sciences,  Anatomy  and  Physiology,  including  the  complete  study 
of  man's  organization  and  functional  activities. 

In  the  early  history  of  the  sciences  these  terms  sufficed  for  all  practical  needs, 
but  as  knowledge  grew,  specialization  of  necessity  resulted  and  new  terms  were 
from  time  to  time  introduced  to  designate  special  lines  of  anatomical  inquiry. 
With  the  improvement  of  the  microscope  a  new  field  of  anatomy  was  opened  up 
and  the  science  of  Histology  came  into  existence,  assuming  control  over  that 
portion  of  Anatomy  which  dealt  with  the  minuter  details  of  structure.  So,  too, 
the  study  of  the  development  of  the  various  organs  gradually  assumed  the 
dignity  of  a  more  or  less  independent  study  known  as  Embryology,  and  the  study 
of  the  structural  changes  due  to  disease  was  included  in  the  science  of  Pathology; 
so  that  the  term  Anatomy  is  sometimes  limited  to  the  study  of  the  macroscopic 
structure  of  normal  adult  organisms. 

It  is  clear,  however,  that  the  lines  of  separation  between  Anatomy,  Histology, 
Embryology,  and  Pathology  are  entirely  arbitrary.  Microscopic  anatomy 
necessarily  grades  ofi'  into  macroscopic  anatomy;  the  development  of  an  organism 
is  a  progressive  process  and  the  later  embryonic  or  foetal  stages  shade  gradually 
into  the  adult;  and  structural  anomalies  lead  insensibly  from  the  normal  to  the 
pathological  domains.  Furthermore  it  is  found  that  in  its  individual  develop- 
ment the  organism  passes  through  stages  corresponding  to  those  of  its  ancestry 
in  evolution;  in  other  words,  Ontogeny  repeats  Phylogeny.  A  comprehensive 
study  of  Anatomy  must  therefore  include  more  or  less  of  the  other  sciences,  and 
since  an  appreciation  of  the  significance  of  structural  details  can  only  be  obtained 
by  combining  the  studies  of  Anatomy,  including  Histology  and  Embryology, 
and  since,  further,  much  light  may  be  thrown  on  the  significance  of  embryological 
stages  by  comparative  studies,  Anatomy,  Embryology,  and  Comparative  Anatomy 
form  a  triumvirate  of  sciences  by  which  the  structure  of  an  organism,  the  signi- 
ficance of  that  structure,  and  the  laws  which  determine  it  are  elucidated.  For 
this  combination  it  is  convenient  to  have  a  single  term,  and  that  which  is  used  is 
Morphology,  a  word  meaning  literally  the  science  of  form. 

In  morphological  comparisons,  the  term  liomology  denotes  similarity  of  structure,  due  to  a 
common  origin  in  the  evolution  of  organs  or  parts;  while  analogy  denotes  merely  physiological 
correspondence  in  function.  Thus  the  arm  of  man  and  the  wing  of  a  bird  are  homologous,  but 
not  analogous,  structures;  on  the  other  hand,  the  wing  of  a  bird  and  the  wing  of  an  insect  are 
analgous,  but  not  homologous.  Serial  homology  refers  to  oorresp  ending  parts  in  successive 
segments  of  the  body. 

Nomenclature. — Formerly  there  was  much  confusion  in  the  anatomical 
nomenclature,  due  to  the  multiphcity  of  names  and  the  lack  of  uniformity  in 
using  them.  Various  names  were  applied  to  the  same  organs  and  great  diversity 
of  usage  prevailed,  not  only  between  various  countries,  but  also  even  among 
authors  of  the  same  country.  Recently,  however,  a  great  improvement  has  been 
made  by  the  general  adoption  of  an  international  sj^stem  of  anatomical  nomen- 


2  INTRODUCTION 

clature.  This  system  was  first  adopted  by  the  German  Anatomical  Society  at  a 
meeting  in  Basel,  in  1895,  and  is  hence  called  the  Basel  Nomina  Anatomica,  or 
briefly,  the  BNA.  The  BNA  provides  each  term  in  Latin  form,  which  is  es- 
pecially desirable  for  international  usage.  Each  nation,  however,  is  expected  to 
translate  the  terms  into  its  own  language,  wherever  it  is  deemed  preferable  for 
everyday  usage.  Thus  in  the  present  work  the  Anglicised  form  of  the  BNA  is 
generally  used.  Where  not  identical,  however,  the  Latin  form  is  added  once  for 
each  term  in  a  place  convenient  for  reference,  and  is  designated  by  enclosure  in 
brackets  [  ].     Where  necessary  the  older  terms  have  also  been  added  as  synonyms. 

The  Commission  by  whom  the  BNA  was  prepared  included  eminent  anatomists  represent- 
ing various  European  nations.  The  work  of  the  Commission  was  very  thorough  and  careful, 
and  extended  through  a  period  of  six  years.  Among  the  guiding  principles  in  the  difficult  task 
of  selecting  the  most  suitable  terms  were  the  following:  (1)  Each  part  should  have  one  name 
only.  (2)  The  names  should  be  as  short  and  simple  as  possible.  (3)  Related  structures 
should  have  similar  names.  (4)  Adjectives  should  be  in  opposing  pairs.  A  few  exceptions 
were  found  necessary,  however. 

On  account  of  its  obvious  merits,  the  BNA  system  has  been  generally  adopted  throughout 
the  civilised  world,  and  the  results  are  very  satisfactory.  Comparatively  few  new  terms  have 
been  thereby  introduced,  over  4000  of  the  4500  names  in  the  BNA  corresponding  almost  exactly 
to  older  terms  already  in  use  by  the  Enghsh-speaking  nations.  Certain  minor  defects  in  the 
system  have  been  criticised;  but  these  are  outweighed  by  the  advantages  of  this  uniform 
system. 

Abbreviations. — Certain  frequently  used  words  in  the  BNA  are  abbreviated  as  follows: 
a.,  arteria  (plural,  aa.,  arterise);  b.,  bursa;  g.,  ganglion;  gl.,  glandula;  lig.,  ligamentum  (plural, 
ligg.,  ligamenta);  m.,  musculus  (plural,  mm.,  muscuU);  n.,  nervus  (plural,  nn.,  nervi);  oss., 
ossis  (or  ossium);  proc,  processus;  r.,  ramus  (plural,  rr.,  rami);  v.,  vena  (plural,  vv.,  venae). 

Terms  of  position  and  direction. — The  exact  meaning  of  certain  fundamental 
terms  used  in  anatomical  description  must  be  clearly  understood  and  kept  in 
mind.  In  defining  these  terms,  it  is  supposed  that  the  human  body  is  in  an 
upright  position,  with  arms  at  the  sides  and  palms  to  the  front. 

The  three  fundamental  planes  of  the  body  are  the  sagittal,  the  transverse  and 
the  frontal.  The  vertical  plane  through  the  longitudinal  axis  of  the  trunk, 
dividing  the  body  into  right  and  left  halves,  is  the  median  or  mid-sagittal  plane; 
and  any  plane  parallel  to  this  is  a  sagittal  plane.  Any  vertical  plane  at  right 
angles  to  a  sagittal  plane,  and  dividing  the  body  into  front  and  rear  portions  is  a 
frontal  (or  coronal)  plane.  A  plane  across  the  body  at  right  angles  to  sagittal  and 
coronal  planes  is  a  transverse  or  horizontal  plane. 

Terms  pertaining  to  the  front  of  the  body  are  anterior  or  ventral;  to  the  rear, 
'posterior  or  dorsal]  upper  is  designated  as  superior  or  cranial]  and  lower  as  inferior 
or  caudal. 

The  term  medial  means  nearer  the  mid-sagittal  plane,  and  lateral,  further  from 
that  plane.  These  terms  should  be  carefully  distinguished  from  internal  (inner) 
and  external  (outer),  which  were  formerly  synonymous  with  them.  Internal,  as 
now  used  (BNA),  means  deeper,  i.  e.,  nearer  the  central  axis  of  the  body  or  part; 
while  external  refers  to  structures  more  superficial  in  position.  Proximal,  in 
describing  a  limb,  refers  to  position  nearer  the  trunk;  while  distal  refers  to  a  more 
peripheral  position. 

'Adverbial  forms  are  also  employed,  e.  g.,  anteriorly  or  ventrally  (forward,  before);  poster- 
iorly or  dorsally  (backward,  behind);  superiorly  or  cranially  (upward,  above);  and  inferiorly  or 
caudally  (downward,  below). 

It  should  also  be  noted  that  the  terms  ventral,  dorsal,  cranial  and  caudal  are  independent  of 
the  body  posture,  and  therefore  apply  equally  weU  to  corresponding  surfaces  of  vertebrates  in 
general  with  horizontal  body  axis.  On  this  account  these  terms  are  preferable,  and  wiU  doubt- 
less ultimately  supplant  the  terms  anterior,  posterior,  superior  and  inferior. 

The  discrimination  in  the  use  of  several  similar  terms  of  the  BNA  should  also  receive  atten- 
tion. Thus  medianus  (median)  refers  to  the  median  plane.  Medialis  (medial)  means  nearer 
the  median  plane  and  is  opposed  to  lateral,  as  above  stated.  Medius  (middle)  is  used  to  desig- 
nate a  position  between  anterior  and  posterior,  or  between  internal  and  external.  Between 
medialis  and  lateralis,  however,  the  term  intermedius  is  used.  Finally,  transversalis  means  trans- 
verse to  the  body  axis;  transversus,  transverse  to  an  organ  or  part;  and  iransversarius,  pertaining 
to  some  other  structure  which  is  transverse. 

Parts  of  the  body. — The  primary  divisions  of  the  human  body  (fig.  1)  are  the 
head,  neck,  trunk  and  extremities.  The  head  [caput]  includes  cranium  and  face 
[facies].  The  neck  [coUum]  connects  head  and  trunk.  The  trunk  [truncus] 
includes  thorax,  abdomen,  and  pelvis.  The  upper  extremity  [extremitas  superior] 
includes   arm    [brachium],  forearm   [antibrachium],    and    hand    [man us].     The 


INTRODUCTION 


lower  extremity  [extremitas  inferior]  includes  thigh  [femur],  leg  [crus],  and  foot 
[pes]. 

Each  of  the  parts  mentioned  has  further  subdivisions,  as  indicated  in  fig.  1. 
The  cranium  includes :  crown  [vertex] ;  hack  of  the  head  [occiput] ;  frontal  region 
[sinciput],  including  forehead  [frons];  temples  [tempora];  ears  [aures],  including 
auricles  [auriculfe]. 

Pig.  1. — Parts  op  the  Human  Body.     A,  Posterior  view.     B,  Anterior  view. 

ERTEXl 


EYE  [OCULUS] 
^EAR  [AURIS] 
NOSE  [NASUS] 
MOUTH  [OS] 


The  face  includes  the  regions  of  the  eye  [oculus],  nose  [nasus],  and  mouth  [os], 
the  subdivisions  of  which  will  be  given  later  under  the  appropriate  sections. 

The  thorax  includes:  hreast  [pectus];  mammary  gland  [mamma];  and  thoracic 
cavity  [cavum  thoracis].  The  hack  [dorsum]  includes  the  vertebral  column 
[columna  vertebralis].  The  abdomen  includes:  navel  [umbilicus] ;  ^awfc  [latus]; 
groin  [inguen];  loin  [lumbus];  and  the  abdominal  cavity  [cavum  abdominis].  The 
pelvis  includes:     "pelvic  cavity  [cavum  pelvis];  genital  organs  [organa  genitalia], 


4  INTRODUCTION 

buttocks  [nates],  separated  by  a  cleft  [crena  ani]  at  the  anus.  The  hip  [coxa] 
connects  the  pelvis  with  the  lower  extremity. 

In  the  lower  extremity,  the  thigh  is  joined  to  the  leg  by  the  knee  [genu].  The 
foot  includes:  heel  [calx];  sole  [planta];  instep  [tarsus];  metatarsus;  and  five  toes 
[digiti  I-V],  including  the  great  toe  [hallux]  and  little  toe  [digitus  minimus]. 

The  upper  extremity  is  joined  to  the  thorax  by  the  shoulder.  The  arm  is 
joined  to  the  forearm  at  the  elboiv  [cubitus].     The  hand  includes:     wrist  [carpus]; 

Fig.  2. — Section  of  the  Epidehmi.s  of  a  Finger,  prom  a  Human  Embryo  of  10.2  cm. 


metacarpus,  with  palm  [vola  or  palma]  and  back  [dorsum  manus].  The  five 
fingers  [digiti  I-V]  include:  thumb  [pollex],  index  finger  [index];  middle  finger 
[digitus  medius];  ring  finger  [digitus  annularis]  and  little  finger  [digitus  minimus]. 

Organ-systems. — Each  of  the  various  parts  of  the  body  above  outlined  is 
composed  of  various  organs,  and  the  groups  of  related  organs  make  up  organ- 
systems. 

The  various  organ-systems  are  treated  as  special  branches  of  descriptive 
anatomy.     The  study  of  the  bones  is  called  osteology;  of  the  ligaments  and  joints, 

Fig.  3. — Diagram  op  a  Typical  Cell.     (Szymonowicz.) 

'Granules 


Nuclear  membrane  ^ 


Nuclear  fluid' 
Interfibrillar  substanc 


"Fibrillar  substance 
-~^ —  Microsome 


syndesmology  for  arthrology);  of  the  vessels,  angiology;  of  the  muscles,  myology;  of 
the  nervous  system,  neurology;  and  of  the  viscera,  splanchnology.  Further  subdivi- 
sions are  also  made.  The  viscera,  for  example,  include  the  digestive  tract, 
respiratory  tract,  urogenital  tract,  etc. 

Tissues  and  cells. — The  body,  as  above  stated,  has  various  parts,  each  of  which  may  be 
subdivided  into  its  component  systems  and  organs.  A  further  analysis  reveals  a  continued 
series  of  structm'al  units  of  gradually  decreasing  complexity.  Thus  each  organ  is  found  to  con- 
sist of  a  number  of  tissues  (epithehal,  connective,  muscular  or  nervous).  Finally,  each  tissue  is 
composed  of  a  group  of  similar  units  called  cells  (figs.  2,  3)  which  are  the  ultimate  structural  units 


INTRODUCTION  5 

of  the  body.  The  body  may  therefore  be  regarded  as  composed  of  myriads  of  cell  units,  organ- 
ized into  units  of  gradually  increasing  complexity,  very  much  as  a  social  community  is  composed 
of  individuals  organized  into  trades,  municipalities,  etc. 

Most  of  the  individual  tissues  can  be  recognized  by  their  gross  appearance.  In  fact,  the 
principal  tissues  were  first  demonstrated  by  Bichat  through  skilful  dissection,  maceration,  etc., 
and  without  the  aid  of  the  microscope.  The  cellular  structure  of  the  tissues  was  later  discovered 
by  Schwann  in  1839. 

Each  cell  (fig.  3)  is  composed  of  a  material  called  ■protoplasm,  a  viscid  substance  variable  in 
appearance  and  exceedingly  complex  in  chemical  composition.  It  readily  breaks  down  into  sim- 
pler chemical  compounds,  whereby  energy  (chiefly  in  the  form  of  heat  and  mechanical  energy)  is 
liberated.  It  has  also  the  power  of  absorbing  nutritive  material  to  build  up  and  replace  what 
was  lost.  Its  decomposition  results  from  stimuli  of  various  kinds,  and  hence  it  is  said  to  be 
irritable.  The  mechanical  energy  which  it  liberates  is  manifested  by  its  contractihty,  especially 
in  the  muscle  cells.  It  excretes  the  waste  products  produced  by  its  decomposition.  Each  cell 
has  the  power,  under  favourable  conditions,  of  reproducing  itself  by  division.  Protoplasm  pre- 
sents, in  short,  all  the  forms  of  activity  manifested  by  the  body  as  a  whole;  and,  indeed,  the  ac- 
tivities of  the  body  are  the  sum  of  the  activities  of  its  constituent  cells. 

In  the  protoplasm  of  each  cell  is  a  specially  differentiated  portion,  the  nucleus  (fig.  3).  The 
nucleus  plays  an  important  part  in  regulating  the  activities  of  the  cytoplasm,  the  general  proto- 
plasm of  the  cell  body.  The  nucleus  differs  from  the  cytoplasm  both  structurally  and  chem- 
ically, and  contains  a  very  important  substance,  chromat^in,  which  during  cell  division  is  aggre- 
gated into  a  definite  number  of  masses  called  chromosomes.  The  cytoplasm  of  actively  growing 
cells  also  contains  the  archoplasm  and  centrosome,  structures  of  importance  in  the  process  of  cell 
division.  Further  details  concerning  the  cells  and  tissues  may  be  found  in  the  text-books  of 
cytology  and  histology. 

In  earher  days  Human  Anatomy  was  almost  entirely  a  descriptive  science,  but  little  atten- 
tion being  paid  to  the  significance  of  structure,  except  in  so  far  as  it  could  be  correlated  with 
physiological  phenomena  as  they  were  at  the  time  understood.  In  recent  years  attention  has 
been  largely  paid  to  the  morphology  of  the  human  body  and  much  valuable  information  as  to 
the  meaning  of  the  structure  and  relations  of  the  various  organs  has  resulted.  Since  the  form 
and  structure  of  the  body  are  the  final  result  of  a  series  of  complicated  developmental  changes, 
the  science  of  Embryology  has  greatly  contributed  to  our  present  knowledge  of  human  Mor- 
phology; and,  accordingly,  a  brief  sketch  of  some  of  the  more  important  phases  of  morphogenesis 
will  form  a  fitting  introduction  to  the  study  of  the  adult. 

References. — General:  For  looking  up  the  literature  upon  any  anatomical 
topic,  the  best  guide  is  the  "  Jahresbericht  ueber  die  Fortschritte  der  Anatomie 
und  Entwicldungsgeschichte,"  which  contains  classified  titles  and  brief  abstracts 
of  the  more  important  papers  in  gross  anatomy,  histology  and  embryology. 
Other  useful  aids  are  the  "Zentralblatt  fuer  normale  Anatomie,"  the  "Index 
Medicus"  and  the  catalogue  of  the  Surgeon  Genera  's  Library  of  the  War  Dep't. 
(Washington,  D.  C).  The  latter  two  contain  titles  only,  but  cover  the  whole 
field  of  medicine.  The  "Concilium  Bibliographicum"  also  provides  a  conveni- 
ent card-index  system  of  references  for  the  biological  sciences,  including 
Anatomy. 

For  nomenclature:  His,  Archiv  f.  Anat.,  1895  (BNA  system);  Barker,  Ana- 
tomical Nomenclature.  Cells  and  tissues:  Wilson,  The  Cell;  Hertwig,  Zelle  und 
Gewebe  (also  English  transl.) ;  Sehaefer,  Microscopic  Anatomy  (in  Quain's 
Anatomy,  11th  ed.) ;  Heidenhain,  Plasma  und  Zelle. 


SECTION  1 

MOEPHOGENESIS 

Revised  for  the  Fifth  Edition 
By  C.  M.  JACKSON,  M.S.,  M.D. 

PROFESSOR   OF   ANATOMY   IN  THE   tJNIVERaiTY   OF    MIN 


CHANGE  is  a  fundamental  characteristic  of  all  living  things.  The  human 
body  during  its  life  cycle  accordingly  passes  through  various  phases  of  form 
and  structure.  In  the  earliest  embryonic  phases  of  development  the 
changes  are  very  rapid,  decreasing  in  rapidity  during  the  later  foetal  stages,  but 
continuing  at  a  diminishing  rate  throughout  infancy,  childhood  and  youth  up  to 
the  adult.  Following  the  acme  of  maturity,  changes  continue  which  lead 
gradually  to  senescence  and  final  death  of  the  body. 

This  cycle  of  change  in  the  body  depends  upon  similar  changes  in  its  various  component 
organs,  each  having  its  own  characteristic  hfe  cycle.  In  a  few  of  the  organs  this  cycle  is  very 
short,  as  in  some  of  the  organs  of  the  embryo  (e.  g.,  mesonephros).  Other  organs  persist  only 
during  childhood  (e.  g.,  thymus);  while  the  majority  continue,  with  varying  degrees  of  change, 
throughout  postnatal  life.  The  final  death  of  the  body  is  due  to  the  breakdown  of  some  of  the 
essential  organs. 

A  further  analysis  reveals  the  fact  that  the  characteristic  life  cycles  of  the  organs  depend 
ultimately  upon  similar  changes  in  their  constituent  tissues  and  cells.  Every  ceU  has  a  definite 
life  cycle,  an  early  period  characterised  by  rapid  and  vigourous  changes,  later  periods  of  differen- 
tiation and  maturity,  followed  by  stages  of  degeneration  and  death.  This  cycle  of  cell  changes 
has  been  designated  by  Minot  as  cytomorphosis. 

Growth. — Associated  with  the  process  of  cell  differentiation  (cytomorphosis),  and  even 
more  important  as  a  factor  in  the  morphogenesis  of  the  body,  is  the  process  of  growth.  The 
developmental  changes  in  form  and  structure  of  the  body  are  due  largely  to  the  unequal  growth 
of  its  various  parts.  Growth,  like  other  changes  in  the  body  and  its  parts,  depends  ultimately 
upon  the  characteristics  of  the  constituent  cells. 

Fig.  4. — The  Ovum  op  a  New-bohn  Child,  with  Follicle  Cells.     (After  Mertens.) 
Nucleus 


The  cell  changes  during  growth  may  be  grouped  under  two  heads.  The  first,  or  growth 
proper,  involves  merely  the  enlargement  (hypertrophy)  of  the  individual  cells  and  intercellular 
products.  The  second  includes  the  muUiplication  (hyperplasia)  of  the  cells,  which  is  accom- 
plished by  mitotic  division.  Cell  division  is  necessary  in  ceU  growth,  for  otherwise  the  cell 
would  soon  reach  a  size  where  its  surface  (for  nutritive,  respiratory  and  excretory  purposes) 
would  be  inadequate  for  its  mass.  In  general,  however,  cell  division  is  most  active  in  the  earher 
embryonic  periods,  during  which  the  cells  remain  small.  Later,  cell  division  diminishes  or 
ceases,  and  growth  is  due  chiefly  to  enlargement  of  the  cells  already  present.  It  is  also  during 
the  later  period,  when  the  cells  have  ceased  rapid  division,  that  the  process  of  cell  differentiation 
and  tissue  formation  is  most  marked. 

The  principle  of  the  ratio  of  surface  to  mass  often  apphes  to  the  growing  organs  as  well  as  to 
the  individual  cells.  To  maintain  the  necessary  ratio,  the  surface  area  is  increased  by  the  for- 
mation, through  localised  unequal  growth,  of  projections  (e.  g.,  villi  or  folds)  or  invaginations 
(e.  g.,  glands)  from  surfaces.  Innumerable  modifications  of  this  principle  occur  throughout  the 
process  of  morphogenesis. 

7 


8  MORPHOGENESIS 

Fig.  5. — Ovum  fkom  Ovaey  of  a  Woman  Thibtt  Years  of  Age.  cr,  corona  radiata. 
n,  nucleus,  y,  yolk,  p,  clear  protoplasmic  zone,  ps,  perivitelline  space,  zp,  zona  pellucida. 
(McMurrich's  Embryology,  from  Nagel.) 


zp 


% 


;>s 


vJ 


^ 


~ii^\ 


Fig.  6. — Stages  of  Segmentation  in  the  Ovum  of  the  Mouse,     x,  polar  body. 
(McMurrich's  Embryology,  from  Sobotta.) 


SEGMENTATION  OF  THE  OVUM 


9 


While  the  present  work  deals  primarily  with  the  adult  human  organism  in  the 
stage  of  maturity,  reference  is  made  also  to  its  changes  according  to  age.  Although 
these  changes  for  the  various  systems  of  organs  are  described  under  the  ap- 
propriate sections,  it  is  desirable  to  consider  first  some  of  the  more  fundamental 
features  pertaining  to  the  body  as  a  whole.  This  apphes  particularly  to  the 
earlier  embryonic  period,  which  includes  the  more  general  phases  of  morpho- 
genesis. No  attempt  will  be  made  to  describe  fully  the  process  of  development, 
the  details  of  which  are  to  be  found  in  text-books  of  embryology. 

Segmentation  of  the  ovum. — The  human  body,  like  all  living  organisms,  arises 
from  a  single  cell,  the  egg-cell  or  ovum.  An  early  stage  in  the  development  of  the 
ovum  is  shown  in  fig.  4,  and  a  later  stage,  approaching  maturity,  in  fig.  5.  The 
mature  human  ovum  is  about  0.2  mm.  in  diameter.  In  the  uterine  (Tallopian) 
tube,  the  fertilised  ovum  undergoes  segmentation,  the  various  stages  of  which  are 
represented  in  figs.  6  and  7. 


Fig.  7. — Diagram  of  Section 
through  a  mammalian  ovum  at  the 
Morula  Stage. 


Fig.  8. — Diagram  of  Section  of 
A  Mammalian  Ovum  Showing  the 
Inner  Cell  Mass. 


fi 


0~ 

^ .,  J'\  ^  ^ 

i  — 

A^; 

\;^-:^ 

('**-•  -t^ 


While  the  processes  of  maturation,  fertilisation  and  segmentation  have  not  as  yet  been  ob- 
served in  the  human  ovum,  the  evidence  of  comparative  anatomy  makes  it  very  prolDable  that  in 
all  essential  respects  these  processes  are  like  those  found  in  other  mammals.  As  a  result  of  the 
successive  divisions  of  the  ovum  in  segmentation,  a  spherical  mass  of  cells,  the  morula  (fig.  7)  is 
formed.  In  this  mass,  an  excentric  cavity  forms  (fig.  8)  whereby  the  mass  is  transformed  into  a 
hollow  vesicle.  The  wall  of  this  vesicle  is  probably  formed  throughout  the  greater  part  of  its 
extent  by  a  single  layer  of  cejls;  but  at  one  point  of  the  circumference  there  is  a  group  of  cells 
termed  the  inner  cell  mass  (fig.  8).  Probably  about  this  time  the  ovum  enters  the  uterine  cavity, 
and  through  the  activity  of  the  outer  layer  of  ceUs  {trophoblasi)  becomes  embedded  in  the  uterine 
mucosa. 

Formation  of  the  embryonic  disc  and  germ  layers. — -In  the  earliest  human 
embryos  which  have  been  described,  development  has  already  proceeded  beyond 

Fig.  9. — Diagram  Showing  the  Relations  of  the  Germ  Layers  in  an  Early  EimRYO. 
Ac,  amniotic  cavity,  lined  by  ectoderm.  D,  yolk-sac,  lined  by  endoderm  (En).  Me, Me', 
mesoderm,  C,  extra,-embryonic  calom.     B,  chorion.     T,  trophoblast.     (McMurrich.) 


the  stage  represented  by  fig.  8,  and  has  reached  that  of  fig.  9.     Within  the  inner 
cell  mass,  two  cavities  have  appeared.     The  more  superficial  fac)  is  the  amniotic 


10 


MORPHOGENESIS 


■cavity;  the  deeper  (D)  is  the  cavity  of  the  yolk-sac;  while  between  them  is  a 
plate  of  cells  forming  the  embryonic  disc.  The  embryonic  disc  (figs.  9  and  10) 
contains  three  layers  of  cells, — the  fundamental  germ  layers, — ectoderm  (Ec), 
endoderm  (En),  &n.A  mesoderm. 

The  germ  layers  of  the  embryonic  disc  are  of  prime  importance  in  the  development  of  the 
body.  From  the  ectoderm,  which  hes  next  to  the  amniotic  cavity  and  represents  the  upper 
(later  outer)  germ  layer,  are  derived  the  epidermis  and  the  entire  nervous  system.  From  the 
■endoderm,  which  hes  next  to  the  yolk-sac,  and  represents  the  lower  (later  inner)  germ  layer,  is 
derived  the  epithehal  lining  of  the  digestive  mucosa  and  its  derivatives.  From  the  mesoderm,  or 
middle  germ  layer,  is  differentiated  the  remainder  of  the  body,  including  the  skeletal  and  sup- 
porting tissues,  vascular  system,  muscle  and  most  of  the  urogenital  organs. 

The  germ  layers  also  extend  beyond  the  embryonic  disc,  as  shown  in  figs.  9  and  10.  The 
yolk-sac  is  made  up  of  a  lining  of  endoderm  and  an  outer  layer  of  mesoderm.     The  amnion,  which 

Fig.  10. — Diagram  op  Section  of  a  Mammalian  Ovum  showing  the  Embryonic  Disc, 
Amniotic  Cavity  and  the  Germ  Layers. 


Endoderm 


later  becomes  separated  from  the  chorion,  is  composed  of  mesoderm  lined  by  endoderm.  The 
outer  cell  layers  form  the  chorion,  which  likewise  shows  two  layers,  the  outermost  of  which 
(trophoblast)  is  ectoderm,  the  inner,  mesoderm.  In  fig.  10  the  chorion  is  beginning  to  send  out 
root-like  projections  (villi)  which  invade  the  uterine  mucosa. 

It  is  thus  noteworthy  that  of  the  cells']derived  from  the  ovum  relatively  only  a  few — those  of 
the  embryonic  disc — enter  directly  into  the  formation  of  the  body.  The  yolk-sac,  a  rudimentary 
organ  of  phylogenetic  significance,  is  later  chiefly  absorbed,  although  the  proximal  portion  may 
enter  slightly  into  the  formation  of  the  intestinal  wall.  The  amnion  is  a  protective  membrane, 
while  the  chorion  forms  the  foetal  part  of  the  placenta. 

Development  of  the  embryonic  disc. — When  first  formed,  the  surface  of  the 
embryonic  disc  shows  no  trace  of  differentiation.  A  slightly  later  but  still 
comparatively  early  stage  in  its  development  is  shown  in  fig.  11.     It  is  here 

Fig.  11.- — Model  Showing  the  Embryonic  Disc  from  an  Embryo  1.17  mm.  In  Length. 
Viewed  from  above  and  laterally,  the  roof  of  the  amniotic  cavity  having  been  removed,  n, 
primitive  pit  (neurenteric  canal),  pg,  primitive  groove,  mg,  neural  groove,  b,  body-stalk. 
(McMurrich.  from  Frassi.) 


viewed  from  above,  the  amnion  having  been  removed.  The  disc  is  an  elliptical 
plate,  whose  long  axis  represents  the  mid-line  of  the  embryo.  Near  the  center 
is  a  small  rounded  depression,  the  primitive  pit.  Extending  backward  (toward  the 
tail  end  of  the  embryo)  from  this  is  a  dark  line,  the  'primitive  streak,  corresponding 
to  a  groove,  the  primitive  groove.  Extending  forward  from  the  primitive  pit  is  an 
indistinct  wide  shallow  groove,  the  neural  groove. 

At  an  earlier  stage,  the  primitive  streak  extends  further  forward,  possibly  to  the  anterior  end 
of  the  embryonic  disc  (Spee).     The  primitive  streak  and  groove  probably  con-espond  to  the 


TOPOGRAPHY  OF  THE  EMBRYONIC  DISC 


11 


fused  lips  of  a  primitive  blastopore.  They  represent  a  centre  of  proliferation  from  which  the 
mesoderm  is  budded  off  from  the  ectoderm  and  spreads  out  to  form  the  middle  germ  layer  of  the 
embryonic  disc. 

At  the  anterior  end  of  the  primitive  streak  this  proliferation  extends  forward  as  a  plate  of 
cells,  the  so-called  'head  process.'  The  axial  portion  of  this  process  is  the  anlage  of  the  rtoto- 
chord,  the  embryonic  skeletal  axis.  It  contains  a  canal,  which  opens  into  the  primitive  pit. 
The  notochordal  anlage  soon  fuses  with  the  underlyiag  endoderm,  and  its  canal  forms  the 
transient  neurenteric  canal. 

In  the  mid-line  anterior  to  the  primitive  streak  there  appears  the  shallow  neural  groove 
(fig.  11),  corresponding  to  a  thickened  plate  of  ectodermic  cells,  the  neural  plate.  The  neural 
groove  is  slightly  forked  at  its  posterior  extremity,  in  the  region  of  the  primiiive  node  (Hensen's 
node),  which  forms  the  dorsal  lip  of  the  primitive  pit.  As  development  proceeds,  the  neural 
plate  extends  posteriorly,  and  the  primitive  pit  is  accordingly  shifted  backward,  the  correspond- 
ing part  of  the  primitive  groove  being  converted  into  'head  process.'  The  primitive  streak  thus 
becomes  progressively  shortened  (cf.  figs.  11  and  13). 

Fig.  12. — Topogkapht  of  the  Embryonic  Disc.  Diagram  op  Relations  at  the  Length 
OF  ABOUT  1  MM.  ng,  neural  groove,  pn,  primitive  node,  pp,  primitive  pit.  U,  upper  limb. 
L,  lower  limb. 


Topography  of  the  embryonic  disc. — Although  only  slight  signs  of  differentia- 
tion are  visible  in  the  embryonic  disc  at  the  stage  shown  in  fig.  11,  it  is  already 
possible  to  map  out  more  or  less  definite  areas  corresponding  to  all  the  various 
regions  of  the  future  body,  as  shown  in  fig.  12. 

Beginning  anteriorly,  the  head  region  is  relatively  enormous  in  size,  occupying  at  this 
time  the  entire  portion  in  front  of  the  primitive  pit  and  forming  about  half  of  the  entire  disc. 
The  cervical,  thoracic,  lumbar  and  sacro-coccygeal  regions  appear  successively  smaller,  ap- 
proaching the  posterior  end  ('tail  bud')  of  the  primitive  streak.  It  is  also  a  striking  fact 
that  the  future  dorsal  region  of  the  body  wall,  corresponding  to  the  central  portion  of  the  disc, 
along  each  side  of  the  mid-line,  is  now  larger  than  the  ventro-lateral  regions,  which  occupy  a 
relatively  narrow  area  around  the  periphery  of  the  disc. 


12 


MORPHOGENESIS 


The  topography  of  the  germinal  areas  in  the  embryonic  disc  shown  in  fig.  12  is  based  partly 
upon  a  study  of  the  succeeding  stages  of  development,  and  partly  upon  the  results  of  experi- 
ments upon  the  germinal  disc  in  lower  forms,  especially  in  the  chick  (Assheton,  Peebles,  Kopsch). 

Law  of  developmental  direction. — In  the  relative  size  of  the  various  embryonic 
areas  is  foreshadowed  what  may  be  termed  the  law  of  direction  in  development. 
In  general  it  is  found  that  development  (including  growth  and  differentiation)  in 

Fig.  13. — Human  Embryo  1.54  mm.  long.     Viewed  from  above,  the  roof  of  the  amniotic 
cavity  having  been  removed.     (Minot,  after  Graf  Spee.) 


Neurenteric  canal 

Primitive  groove 
Body-stalk 


Chorion  with  villi 


the  long  axis  of  the  body  appears  first  in  the  head  region  and  progresses  toward 
the  tail  region.  Similarly  in  the  transverse  plane  development  begins  in  the 
mid-dorsal  region  and  progresses  latero-ventrally  (in  the  limbs,  proximo-distally). 
These  principles  are  of  great  importance  in  morphogenesis. 

Fig.  14. — Diagrams  Showing  the  Constriction  of  the  Embryo  prom  the  Yolk-sac. 
A  and  C,  longitudinal  sections;  B  and  D,  corresponding  cross-sections.     (McMurrich.) 


The  law  of  developmental  direction  is  also  probably  of  phylogenetic  significance.  The 
cranio-caudal  direction  of  development  is  in  accordance  with  the  theory  that  the  head  is  the  most 
primitive  portion  of  the  body,  and  hence  precocious  in  development.  The  trunk  is  perhaps  a 
secondary  acquisition,  hence  arising  as  an  extension  of  the  primitive  head  region. 


DERIVATION  OF  BODY  TUBE  FROM  EMBRYONIC  DISC        13 

The  dorso-ventral  direction  of  development,  together  with  the  plate-hke  form  of  the  embry- 
onic disc,  has  a  different  phylogenetio  significance.  Both  are  probably  inherited  from  an  ances- 
tral type  with  a  yolk-laden  ovum.  In  such  an  ovum,  with  the  meroblastic  type  of  segmentatien, 
the  flattened  embryonic  disc  gradually  spreads  from  the  dorsal  surface  in  a  ventral  direction 
around  the  underlying  yolk-mass. 

Derivation  of  body  tube  from  embryonic  disc. — ^The  primary  result  of  the 
precocious  growth  in  the  dorsal  region  of  the  embryonic  disc  is  the  conversion  of 
the  disc  into  the  body  tube,  curved  ventrally  in  its  long  axis  (fig.  14). 

Fig.  15. — ■Portion  op  Cross  Section  of  the  Embryo  shown  in  Fig.  13.  ch,  notochord. 
ct,  somatic  mesoderm,  df,  splanchnic  mesoderm,  g,  junction  of  extra-embryonic  somatic  and 
splanchnic  mesoderm,  ek,  ectoderm,  en,  endoderm.  me,  embryonic  mesoderm.  /,  neural 
groove,  p,  beginning  of  embryonic  coelom  (pericardial  cavity).     (Minot,  after  Graf  Spee.) 


As  a  result  of  the  more  rapid  expansion  of  the  germ  layers  (especially  the  ectoderm)  near 
the  mid-line,  the  dorsal  surface  of  the  embryonic  disc  in  general  becomes  convex,  with  a  depres- 
sion laterally  (where  growth  is  less  rapid)  forming  a  groove  at  the  line  of  attachment  of  the  am- 
nion (figs.  11,12,  13,  14  B).  The  unequal  growth  in  the  germ  layers  is  clearly  evident  in  the  cross 
section  shown  in  fig.  15.  By  a  continuation  of  this  process,  the  margins  of  the  embryonic  disc 
become  still  further  depressed  and  finally  folded  in  ventrally  so  as  to  transform  the  disc  into  a 
tube  (fig.  14  D).  Similarly,  by  a  more  rapid  expansion  of  the  dorsal  layer  of  the  disc  in  the  lon- 
gitudinal axis,  the  head  and  tail  ends  of  the  disc  are  folded  and  tucked  in  ventrally,  and  the 
primitive  body  tube  is  thus  correspondingly  curved  in  its  long  axis  (figs.  14  A,  14  C). 

Fig.  16. — Model  op  Human  Embryo  1.8  mm.  Long.  Viewed  from  above,  the  roof  of  the 
amniotic  cavity  having  veen  removed.  Near  the  caudal  end  of  the  neural  groove,  the  primitive 
pit  (opening  of  neurenteric  canal)  is  visible.  The  primitive  somites  are  appearing  in  the  occip- 
ital region,  the  fourth  corresponding  to  the  boundary  between  head  and  neck.  (McMurrich, 
from  Keibel  and  Elze.) 


The  embryonic  disc  is  thus  converted  into  a  tube  composed  of  an  outer  layer  of  ectoderm, 
a  middle  layer  of  mesoderm  and  an  inner  layer  of  endoderm.  The  yolk-sac  now  presents  an 
expanded  yolk-vesicle  fined  by  endoderm  which  is  still  continuous  through  the  constricted  yolk- 
stalk  with  the  endoderm  lining  the  primitive  enteric  cavity  (fig.  14  C).  The  enteric  cavity  (or 
archenteron)  has  a  bhnd  tubular  prolongation  (fore  gut)  into  the  head  region,  and  another  (hind 
gut)  into  the  tail  region.  From  the  latter  a  slender  diverticulum,  the  allantois,  extends  into  the 
body  stalk  (later  the  umbiUcal  cord).  The  allantois  is  an  organ  of  phylogenetic  importance, 
with  which  the  urinary  bladder  is  later  connected. 

Formation  of  the  neural  tube. — The  principle  of  unequal  growth  applies  to  the 
formation  not  only  of  the  body  as  a  whole,  but  also  of  its  constituent  parts. 
Thus  the  anlage  of  the  nervous  system  arises  from  the  ectoderm  as  a  wide  groove 


14  MORPHOGENESIS 

whose  edges  (neural  ridges)  by  local  growth  are  folded  upward  so  as  to  meet  in 
the  mid-line  where  they  fuse,  thus  transforming  the  groove  into  the  neural  tube 
(fi*gs.  11,  12,  13,  15,  16,  17,  18). 

The  closure  begins,  not  at  the  anterior  end  (as  might  be  expected  from  the  general  law  of 
cranio-oaudal  development),  but  in  the  cervical  region,  extending  forward  into  the  brain  region, 
and  backward  along  the  spinal  cord.  Thus  the  extreme  ends  (anterior  and  posterior  neuropores) 
are  the  last  to  close. 

The  precocious  and  energetic  growth  of  the  neural  anlage  is  largely  responsible  for  the  ven- 
tral flexure  of  the  embryonic  body  axis,  especially  in  the  head  region,  where  the  flexures  of  the 
brain  are  very  conspicuous  (figs.  22,  26). 

With  the  closure  of  the  neural  tube  dorsally  and  of  the  aUmentary  canal  ventraUy  the  human 
embryo  assumes  the  typical  vertebrate  form.  The  cyhndrioal  body  wall  now  encloses  two  tubes 
(neural  and  enteric)  with  the  longitudinal  axis  (notochord)  between  them  (figs.  18,  24). 

After  the  embryonic  disc  has  been  transformed  into  a  tube,  the  body  of  the  human  embryo 
in  cross  section  appears  not  circular  but  elongated  dorso-ventrally.  This  is  the  typical  form  for 
vertebrates  with  horizontal  body  axis.  In  later  foetal  stages,  the  body  becomes  more  rounded  in 
cross  section,  and  finally,  with  the  assumption  of  the  erect  posture  in  postnatal  life,  becomes 
decidedly  flattened  dorso-ventrally  (figs.  20,  21). 


Fia.  17. — A  HoMAN  Embryo  2.5  mm.  in  Length.     (After  Kollmann.) 


Mesodermic  somite 


Medullary  canal 


Development  of  the  mesoderm. — The  mesodermic  layer  on  each  side  of  the 
notochord  in  the  embryonic  disc  develops  in  two  divisions.  The  medial  (or 
dorsal)  divisions  form  a  series  of  hollow  segments,  the  somites  (figs.  16,  17,  18). 
The  lateral  (later  ventral)  divisions  each  spht  into  an  upper  (outer)  or  somatic  layer 
and  a  lower  (inner)  or  visceral  layer.  When  the  embryonic  disc  becomes  folded, 
the  corresponding  somatic  and  visceral  layers  unite  ventrally  and  enclose  between 
them  the  common  cmlom  or  primitive  body  cavity  (fig.  18). 

(As  previously  noted,  the  mesoderm  arises  chiefly  from  the  lateral  portions  of  the  'head 
process.'  A  comparatively  early  stage  before  the  appearance  of  the  somites  is  shown  m  cross 
section  in  fig.  15.  The  somites  appear  first  in  the  occipital  region,  and  rapidly  differentiate 
successively  in  the  cranio-oaudal  direction  (figs.  16,  17,  22).  In  embryos  7  or  8  mm.  in  length, 
about  40  somites  may  be  distinguished,  3  to  5  occipital,  8  cervical,  12  thoracic,  5  lumbar,  5  sacral 
and  5  or  6  coccygeal  (in  the  rudimentary  tail  region). 

The  cmlom  or  body  cavity  is  unsegmented.     Two.primitive  pericardial  cavities  appear  sepa- 


DEVELOPMENT  OF  THE  SOMITES 


15- 


rate  at  first,  but  soon  fuse  and  unite  with  the  general  coelom.     Later  the  general  ccelom  becomes 
secondarily  divided  into  the  permanent  pericardial,  pleural  and  peritoneal  cavities. 

The  outer  layer  of  the  lateral  mesodermic  division  forms  the  somatic  or  parietal  layer  of  the 
peritoneum,  etc.  The  inner  layer  forms  the  visceral  or  splanchnic  layer,  and  develops  not  only 
the  serous  membrane,  but  also  the  muscular  and  connective  tissue  of  the  walls  of  the  alimentarj' 
canal  and  its  derivatives. 

Development  of  the  somites.  Metamerism. — The  appearance  of  the  somites 
marks  the  beginning  of  nietdmerism,  the  arrangement  of  the  body  in  successive 

Fig.  18. — Diagram  of  a  Cross  Section  op  a  Human  Embryo. 

Spinal  cord 


Mesodermic  somite 


Intermediate  cell  i 


^'",,. 


Ventral  mesoderm,  visceral  layer 


/^^'SlLl^V entral  mesoderm, 
somatic  layer 


segments  or  metameres.  Each  somite  develops  a  primitive  muscle  segment, 
myotome,  and  a  skeletal  segment,  sclerotome  (figs.  18,  19).  Moreover,  the  cor- 
responding nerves  and  .blood-vessels  likewise  assume  a  metameric  arrangement. 
This  metamerism  persists  (more  or  less  modified)  in  the  adult  neck  and  trunk. 

The  differentiation  of  the  somites  is  illustrated  by  figs.  18  and  19.  The  medial  wall  of  each 
somite  forms  the  sclerotome.     Its  cells  migrate  to  form  the  corresponding  vertebra,  rib,  etc.,  as 

Fig.  19. — Diagrams  Illustrating  the  History  of  the  Mesoderm.  M,  myotome,  dM, 
dorsal  portion  of  myotome.  vM,  ventral  portion  of  myotome.  SC,  sclerotome,  gr,  genital 
ridge.  PFd,  Wolffian  duct.  iSm,  somatic  layer  of  mesoderm,  bto,  visceral  layer  of  mesoderm. 
mr,  membrana  reuniens.     I,  intestine.     A'',  neural  tube.     (MoMurrich.) 


well  as  the  mesenchyme  forming  the  various  connective  tissues  in  this  region.  The  remainder  of 
the  somite  forms  the  myotome,  from  which  the  voluntary  musculature  of  the  trunk,  the  neck  and 
(in  part)  the  head  is  derived.  The  dorsal  portions  of  the  myotomes  develop  the  muscle  in  the 
dorsal  region  of  the  trunk,  while  the  ventral  portions  extend  ventralward  to  form  the  muscula- 
ture of  the  latero-ventral  body  walls  (figs.  19,  20,  21,  23). 

At  the  junction  of  the  dorsal  and  ventral  divisions  of  the  mesoblast  is  a  group  ofJceUs  called 
the  intermediate  cell  mass.     This  mass  becomes  segmented  (corresponding  to  the  somites)  and 


16 


MORPHOGENESIS 


each  segment,  or  nephrotome,  gives  rise  to  a  portion  of  tlie  mesonephros,  the  provisional  kidney. 
Other  cells  of  the  mass  become  mesenchyme,  which  is  converted  into  blood-vessels,  connective 
tissue,  etc. 

As  development  proceeds,  the  metamerism  of  the  muscles  and  arteries  becomes  more  or  less 
obscured,  but  that  of  the  vertebrfe  and  nerves  is  fully  retained  even  in  the  adult.  In  the  case  of 
the  muscle  plates,  from  which  all  the  voluntary  musculature  of  the  trunk  is  derived,  great  modi- 
fications occur.  Extensive  fusion  of  successive  plates  occurs,  the  intervening  connective  tissue 
disappearing  more  or  less  completely;  associated  with  this  fusion  there  is  longitudinal  and  tan- 
gential splitting  of  the  somites  to  form  individual  muscles;  and  portions  of  some  of  the  plates  may 
wander  far  from  their  original  position.  But  notwithstanding  these  complicated  changes,  in- 
dications of  the  primary  metameric  arrangement  of  the  muscle  plates  are  abundant,  and  even  in 
the  most  e.xtreme  cases  of  modification  the  developmental  history  of  a  muscle  can  be  determined 
by  means  of  its  nerve  supply.  For  the  fibres  derived  from  each  plate  will  usually  retain,  up 
matter  what  changes  of  independence  or  position  they  may  undergo,  the  innervation  by  their 
originally  corresponding  segmental  nerve;  so  that  the  occurence  in  the  lumbar  region  of  the  body 
of  muscle-fibres  (the  diaphragm)  supplied  by  nerve-fibres  from  a  cervical  nerve  is  evidence  that 
the  muscle-fibres  have  been  derived  from  a  cervical  mesodermic  somite  and  have  subsequently 
migrated  to  the  position  they  finally  occupy. 

As  regards  the  arteries,  they  arise  primarily  from  a  longitudinal  stem,  the  aorta,  in  a  strictly 
segmental  manner,  each  metamere  having  distributed  to  it  two  pairs  of  arteries  and  a  single 
median  one  (fig.  20).  One  pair  of  arteries  supplies  the  body  wall,  and  these  retain  very  distinctly 
their  original  metameric  arrangement;  the  other  pair  passes  to  the  paired  viscera,  such  as  the 
lungs,  kidneys,  ovaries  (or  testes),  so  many  of  the  pairs  disappearing,  however,  that  their  meta- 
meric arrangement  is  not  very  evident  in  the  adult.  The  unpaired  vessels  supply  the  digestive 
tract  and  its  unpaired  appendages,  such  as  the  liver  and  pancreas,  and  undergo  great  modifica- 
tions, those  of  the  lower  thoracic  and  lumbar  regions  becoming  reduced  by  fusion  and  degenera- 
tion to  three  main  trunks. 

Fig.  20. — Diagram  of  a  Transvehsb  Section  through  the  Abdominal  Region. 


DORSAL   MUSCLES 


, =99aiv 

DORSAL   MUSCLES 


.\ 


HYPOSK.ELETAL 
MUSCLE 


VERTEBR.o, 


X_/ 


—  PERITONEUM 
\  PARIETAL  LAYER 


X. 


Branchiomerism. — Throughout  the  trunk  and  neck  regions,  then,  a  funda- 
mental metameric  plan  underlies  and  determines  the  arrangement  of  many  parts. 
In  the  head  there  is  also  evident  a  primary  arrangement  of  the  parts  in  succession; 
but  this  arrangement  appears  to  be  somewhat  different  from  that  of  the  trunk  in 
that  it  involves  the  ventral  instead  of  the  dorsal  mesoderm  and  is  associated  with 
the  occurrence  of  branchial  arches  rather  than  with  true  mesodermic  somites. 
It  is  consequently  termed  branchiomerism. 

Not  but  that  there  are  also  indications  of  metamerism  in  the  head,  the  muscles  of  the  orbit, 
and  the  majority  of  the  extrinsic  muscles  of  the  tongue,  together  with  the  nerves  supplying 
these  muscles,  being  apparently  metameric  structures,  but  the  metamerism  of  this  region  of  the 
body  is  largely  overshadowed  by  the  branchiomerism. 

If  an  embryo  of  about  the  fifth  week  of  development  (fig.  22)  be  examined,  there  will  be 
observed  on  the  surface  of  the  body  in  the  pharyngeal  region  three  or  four  linear  depressions, 


DEVELOPMENT  OF  THE  SOMITES 


17 


and  sections  will  show  that  similar  and  corresponding  grooves  also  occur  upon  the  inner  surface 
of  the  pharyngeal  wall.  These  are  the  branchial  grooves,  and  since  they  are  four  in  number 
(with  a  rudimentary  fifth)  in  the  human  embryo,  they  mark  off  five  branchial  (or  visceral)  arches, 
the  first  of  which  hes  between  the  oral  depression  and  the  first  branchial  groove,  while  the  fifth 
is  situated  behind  the  fourth  groove.  These  branchial  arches  are  so  named  because  they  repre- 
sent the  arches  which  (excepting  the  first)  support  the  gills  (branchise)  in  the  lower  vertebrates, 
the  grooves  representing  the  branchial  slits,  even  although  they  do  not  become  perforated  in 
the  human  embryo. 

Each  branchiomere  consists  of  an  axial  skeletal  structure,  of  muscles  which  act  on  this  skel- 
eton, of  a  nerve  which  supphes  the  muscles  and  the  neighbouring  integument  and  mucous  mem- 
brane, and  of  an  artery  which  carries  blood  to  all  these  structures.  The  arches,  however,  do 
npt  in  the  human  embryo  retain  their  original  branchial  function,  but  undergo  extensive  modi- 
fications, becoming  adapted  to  various  functions  and  showing  less  in  the  adult  of  their  originally 
simple  arrangement  than  do  the  metameres.  Nevertheless  no  matter  what  modifications  the 
musculature  of  any  arch  may  undergo,  it  will  retain  its  original  innervation  and,  to  a  large 
extent,  its  relations  to  the  skeletal  elements  of  its  arch;  and  even  the  arteries  in  their  distribu- 
tion show  clear  indications  of  being  arranged  in  correspondence  to  the  various  arches. 

Fig.  21. — Diagram  of  a  Transverse  Section  through  the  Thoracic  Region. 
(The  pleura  is  represented  in  blue  and  the  pericardium  in  red.) 


With  respect  to  the  fate  of  the  various  structures  pertaining  to  each  branchial  arch,  their 
general  arrangement  in  the  adult  body  may  be  stated  in  the  following  table: — 


Arch 


Relations  of  the  Branchial  Arches  in  the  Adult 
Skeleton  Muscles 


First  arch Mandible,  malleus  and 

'     incus. 
Second  arch Hyoid     (lesser    cornu), 

I    styloid     process     and 
stapes. 
Third  arch !  Hyoid  (greater  cornu), . 


Masticatory,  mylohoid  and  di- 
gastric (ant.),  tensor  tympani. 

Stylohyoid,  digastric  (post.), 
muscles  of  expression,  stape- 
dius. 

Pharyngeal 


Nerve 


Trigeminus. 
Facialis. 


Glossopharyn- 
geus. 

Fourth  and  fifth    Thyreoid  cartilage ;  Pharyngeal  and  laryngeal 1  Vagus. 

arches.  !  , 


» Branchial  grooves. — Of  the  external  branchial  grooves,  the  first  (lying  between  mandibular 
and  hyoid  arches)  becomes  deepened  to  form  the  external  auditory  meatus,  the  margins  becom- 
ing elevated  to  form  the  auricle  (fig.  26).  The  region  corresponding  to  the  second,  third  and 
fourth  external  grooves  becomes  depressed,  forming  the  sinus  cervicalis,  which  soon  closes  up 
and  disappears. 

The  internal  branchial  grooves  or  pouches  communicate  with  the  pharjTigeal  cavity  and  are 


18 


MORPHOGENESIS 


lined  with  endoderm.  The  first  internal  groove  becomes  transformed  into  the  auditory  (Eu- 
stachian) lube,  tympanic  cavity,  etc.  The  second  internal  groove  persists  in  part  as  the  fossa  of 
the  palatine  tonsil.  The  third  and  fourth  grooves  are  probably  represented  in  part  by  the 
vallecula  and  recessus  piriformis,  detached  portions  of  their  lining  endoderm  giving  rise  to  the 
thymus,  parathyreoid  glands,  etc.  The  rudimentary  fifth  groove  is  said  to  give  rise  to  the 
ultimobranchial  body,  a  structure  of  uncertain  significance  (fig.  27). 

Development  of  the  face, — -The  facial  region  is  at  first  relatively  small.  It  includes  the 
sense  organs  (eye,  ear,  nose)  and  mouth  region.  Some  of  the  more  important  developmental 
features  may  be  briefly  mentioned.  In  an  embryo  of  the  sixth  week  (fig.  28)  the  wide  mouth 
aperture  is  seen  to  be  bounded  below  (posteriorly)  by  the  lower  (mandibular)  portion  of  the 


Fig.  22. — Htjman  Embryo  of  4.2  mm.,  Showing  Three  Branchial  Grooves. 
(After  His.) 


tory  vesicle 
Branchial  grooves 


Mesodermic  somite 


first  arch,  laterally^by  the  upper  (maxillary)  process  of  the  first  arch.  Above  it  is  bounded  by  a 
median  plate,  the  nasal  process,  which  on  either  side  forms  a  protuberance,  the  globular  process. 
Lateral  to  the  globular  process  is  a  rounded  depression,  the  nasal  pit.  The  maxillary  process 
extends  forward  and  fuses  with  the  globular  process  to  form  the  upper  jaw  region  (failure  to 
unite  resulting  in  the  malformation  known  as  'hare-lip').  The  nose  is  at  first  broad,  due  to 
the  width  of  the  nasal  process,  which  later  becomes  the  nasal  septum  (fig.  29).  The  nasal  pits 
deepen  and  later  acquire  openings  into  the  primitive  mouth  cavity. 

The  viscera. — The  structures  so  far  considered  belong,  for  the  most  part,  to 
the  body  wall;  it  remains  to  consider  the  general  plan  of  arrangement  of  the 
viscera.  It  has  been  pointed  out  that  the  body  may  be  regarded  as  a  cylinder 
enclosing  two  tubes,  one  of  which  constitutes  the  central  nervous  system  and  the 


THE  VISCERA 


19 


other  the  digestive  tract.  The  latter  may  be  regarded  as  being  primarily  a 
straight  tube  traversing  lengthwise  the  body  cavity  enclosed  by  the  body  wall 
(figs.  18,  20).     The  layers  of  both  the  visceral  and  somatic  plates  which  im- 

FiG.  23. — Sagittal  Section  Showing  the  Primitive  Pericardial  and  Ccelomic  Com- 
munication, Septum  Transversum,  Liver,  etc.,  in  a  Human  Embryo  op  3  mm.  (After 
KoUmann,  from  a  model  by  His.) 

Truncus  aortse 
_  Mesocardium  posterius 

Pericardial  cavity  . 


Anterior  wall  of 
pericardium 


Septum  transversum  and  floor 
of  pericardium 


Venous  trunk  of  the  heart 

Mesocardium  laterale 

Ductus  Cuvieri 

v.  umbilicalis 

v.  omphalo-mesenterica 

Ccelomic  communication 
Peritoneal  cavity 

mediately  enclose  the  body  cavity  become  transformed  into  a  characteristic 
pleuro-peritoneal  membrane.  Near  the  mid-dorsal  line,  a  vertical  double  plate 
of  peritoneum  extends  ventrally  connecting  the  somatic  (parietal)  and  visceral 
layers  of  peritoneum,  and  constituting  what  is  termed  the  mesentery  (fig.  20). 

Fig.  24. — Diagram  Illustrating  the  Recession  of  the  JDiaphragm  (Septum  Trans- 
versum) IN  the  Human  Embryo.  On  the  right  are  indicated  the  vertebral  levels;  on  the 
left,  the  position  of  the  septum  transversum  in  a  series  of  embryos  from  2  mm.  (XII)  to 
24  mm.  (VI)  in  length,     pp,  pleuro-peritoneal  cavity.      (Mall.) 


'MtJuJ^ 


_  As  development  proceeds  the  digestive  tract  grows  in  length  more  rapidly  than  the  cavity 
which  contains  it,  and  so  gradually  becomes  thrown  into  numerous  coils  in  the  abdominal 
region,  these  changes  leading  to  numerous  modifications  of  the  original  arrangement  of  the  mes- 
entery. These  will  be  described  later  on  in  the  section  on  the  digestive  system.  Several  out- 
growths also  arise  from  the  primitive  digestive  tract,  to  form  important  organs,  such  as  the  lungs, 


20 


MORPHOGENESIS 


the  liver,  the  pancreas  and  the  urinary  bladder;  and,  with  the  exception  of  the  bladder,  each 
of^these  becomes  completely  invested  by  primitive  peritoneum.  In  the  case  of  the  liver  this 
original  condition  is  practically  retained,  but  the  investment  of  the  pancreas  later  becomes  a 
partial  one  on  account  of  the  modifications  which  ensue  in  the  mesentery.  The  bladder  has 
only  a  portion  of  its  surface  in  contact  with  the  peritoneum,  but  the  investment  of  the  lungs 
remains  complete,  each  lung,  indeed,  appropriating  to  itself  the  entire  visceral  layer' of  its  half 
of  the  thorax,  with  the  exception  of  a  small  ventral  portion  which  forms  the  investment  of  the 
heart.  Furthermore,  the  cavities  which  surround  each  of  the  three  organs  named,  the  two  lungs 
and  the  heart,  become  completely  separated  from  one  another;  and  since  each  investment  con- 
sists of  a  visceral  and  a  parietal  layer,  each  of  the  organs  is  enclosed  within  a  double-waUed 
sac,  which  in  the  case  of  each  lung  forms  its  pleura,  while  that  of  the  heart  is  known  as  the 
pericardium.  The  spaces  which  occur  within  the  thorax  between  the  pleurte  of  the  two  sides 
are  known  as  the  mediastina,  which  include  the  heart,  oesophagus,  etc.  (fig  21). 

Tn  addition  to  the  viscera  mentioned  there  are  some  organs,  such  as  the  spleen  and  genito- 
urinary organs,  which  are  developments  of  the  mesoderm,  the  spleen  arising  in  the  mesentery 
which  passes  to  the  stomach  and  the  genito-urinary  organs  primarily  from  the  intermediate 
cell  mass.  The  morphogeny  of  these  structures  and  also  of  the  vascular  system,  nervous  system, 
and  sense  organs  will  be  considered  later  in  connection  with  their  structure. 

Fig.  25. — Diagram  op  a  Cross  Section  of  the  Embetonic  Body  and  Limb.     (McMurrich, 

after  Kollman.) 


Dorsal  (posterior)  division  of 
spinal  nerre 


Ventral  (anterior)  division  of 
spinal  nerve 

Dorsal  limb  mus- 
culature 


Peritoneal  cavity  - 


Recession  of  the  diaphragm  and  heart. — In  the  early  stages  of  development 
the  heart  is  situated  far  forward,  in  what  will  eventually  be  the  pharyngeal 
region  (figs.  12,  17).  Just  behind  (caudal  to)  the  heart,  between  it  and  the  yolk- 
sac,  is  a  plate  of  connective  tissue,  the  septum  transversum,  which  serves  for  the 
passage  of  large  veins  from  the  body  wall  to  the  heart  (figs.  17,  23).  This  septum 
together  with  certain  accessory  structures  eventually  gives  rise  to  the  diaphragm, 
which  becomes  a  complete  partition  separating  the  thoracic  and  abdominal  por- 
tions of  the  body  cavity. 

The  diaphragm  and  heart  are  therefore  originally  situated  far  above  (cranial  to)  their 
final  position  and  recede  in  the  course  of  development,  producing  an  elongation  of  the  vessels 
and  nerves  associated  with  them  and  forcing  downward  such  organs  as  the  stomach  and  liver 
(fig.  24).  The  chief  factor  in  this  displacement  is  probably  the  ventral  head  flexion  and  the 
precocious  growth  and  expansion  of  the  organs  in  the  head  region.  The  effects  of  this  recession 
are  especially  noticeable  in  the  nerves,  these  passing  to  the  various  organs  concerned  arising 
from  a  much  higher  level  than  that  occupied  by  the  organs.  The  nerve  to  the  diaphragm,  for 
instance,  comes  from  the  fourth  cervical  segment,  those  passing  to  the  cardiac  and  pulmonary 
plexuses  from  the  cervical  region,  and  those  to  the  plexus  in  relation  with  the  stomach,  liver 
and  adjacent  organs  from  the  thoracic  region.  The  blood-vessels,  however,  may  shift  their 
origins  from  the  main  trunks  by  successive  anastomotic  roots,  so  that  in  general  they  keep  pace 
with  the  viscera  in  the  migration  caudalward. 

The  limbs. — Each  limb  at  its  first  appearance  (fig.  22)  is  a  flat,  plate-like 
outgrowth  from  the  side  of  the  body,  and  consists  of  an  axial  mass  (blastema)  of 
mesodermic  tissue  from  which  the  limb  skeleton  will  develop,  and,  surrounding 
this,  a  layer,  also  of  mesodermic  tissue,  from  which  the  muscles  and  blood-vessels 
will  arise.  It  is  as  yet  uncertain  whether  the  muscle  blastema  is  derived  from  the 
myotomes  (as  in  lower  vertebrates)  or  whether  it  develops  from  the  mesenchyme. 


THE  LIMBS 


21 


Fig.  26. 


-Lateral  View  of  a  Human  Embryo  18  mm.  Long,  Showing  the  Development  op 
THE  Extremities.     M,  mandibular  arch. 


Fig.  27. — Diagram  to  Show  the  Derivatives  op  the  Branchial  Clefts.  le,  lie,  Ille, 
IVe,  Ve,  external  branchial  grooves,  li,  Hi,  llli,  IVi,  Yi,  internal  branchial  grooves.  Tons., 
palatine  tonsil.  Ep  III,  Ep  IV,  epithelial  bodies.  Ub,  ultimobranchial  body.  Th.^  'thyreoid 
D.th.  gl.,  ductus  thyreoglossus.      (Modified  rom  Keibel  and  Mall.) 


Ub.    ^_^ 
Thymus 


22 


MORPHOGENESIS 


As  the  muscles  become  differentiated,  nerves  grow  to  ttiem  from  a  definite 
number  of  spinal  segments  (fig.  25). 

At  first  each  limb  plate  is  so  placed  that  one  of  its  surfaces  looks  dorsally  and  the  other  ven- 
trally,  and  one  border  (that  corresponding  to  the  thumb  or  great  toe)  is  anterior  (i.  e.,  cranial) 
and  the  other  posterior  (caudal).  Later,  however,  each  limb  becomes  bent  caudally  through 
about  ninety  degrees,  so  that  the  limbs  whose  long  axes  were  at  first  at  right  angles  to  the  long 
axis  of  the  body  come  to  he  parallel  to  that  axis.  In  addition  there  occurs  a  rotation  of  each 
fore-limb  in  such  a  manner  that  the  thumb  turns  latero-dorsally,  while  in  the  lower  Umb  the 
direction  of  the  movement  is  exactly  the  opposite,  the  great  toe  turning  ventro-medially.  As 
a  result  there  is  an  apparent  reversal  of  the  surfaces  in  the  two  limbs,  the  flexor  muscles  of  the 
arm  reaching  on  the  surface  which  is  directed  anteriorly,  while  in  the  lower  limb  the  corre- 
sponding muscles  occupy  the  posterior  surface.  The  dorsum  of  the  foot  and  the  great  toe  side 
correspond  respectively  to  the  back  and  thumb  side  of  the  hand,  the  tibia  corresponds  to  the 
radius  and  the  fibula  to  the  ulna.  The  limb  anlage  soon  becomes  divided  into  three  primary 
segments.  The  distal  segment  (hand  or  foot)  is  a  flattened  rounded  disc,  in  which  the  digits 
soon  appear  (fig.  26).  The  proximal  portion  forms  the  forearm  or  leg  and  the  arm  or  thigh. 
In  general,  the  extremities  follow  the  law  of  cranio-caudal  and  dorso-ventral  (proximo-distal) 
development. 


Fig.  28A. — Face  of  Human  Embryo  of 
ABOUT  8  MM.      (His.) 


"^Tasal  fossa 
Lateral  nasal  process 
^lobular  process 
Maxillary  process 
Mandibular  process 


Fig.  28B. — Face  of  Human  Embryo 
AT  Stage  Slightly  Later  than  28A. 
(After  Kallius.) 


Nasal  fossa 


Lateral  nasal 

process 
Globular  process 
Maxillary  process 


Prenatal  Growth  in  Length  and  Weight 


Age  in 
lunar 

Crown-rump  or 
sitting  height 

Crown-heel  or 
standing  height 

Weight  at  end  of 
month,  grams 

Ratio  of  increase 
to  weight  at  be- 

months 

(Mall),  cm. 

(Mall),  cm. 

ginning  of  month 

0 

(diameter  of  ovum 
=  0.2  mm.) 

(Ovum  =  0.000004  g.) 

I 

0.25 

0.25 

0.004 

999.0 

II 

2.5 

3.0 

2.0 

499.0 

III 

6.8 

9.8 

24.0 

11.0 

IV 

12.1 

18.0 

120.0 

4.0 

V 

16.7 

25.0 

330.0 

1.75 

VI 

21.0 

31.5 

600.0 

0.82 

VII 

24.5 

37.1 

1000.0 

0.67 

VIII 

28.4 

42.5 

1600.0 

O.BO 

IX 

31.6 

47.0 

2400.0 

0.50 

*x 

33.6 

50.0 

3200.0 

0.33 

Prenatal  growth. — The  prenatal  growth  of  the  human  body  in  length  and  weight  is  indi- 
cated in  the  preceding  table.  According  to  Hasse,  the  age  of  the  foetus  may  be  estimated  from 
its  total  length  as  follows.  Before  the  fifth  month,  the  square  of  the  age  in  (lunar)  months  gives 
the  length  in  centimetres.  After  this,  the  age  in  months  multiphed  by  five  gives  the  length. 
This  gives  approximate  results,  except  for  the  first  month. 

While  the  growth  in  absolute  weight  increases  from  month  to  month,  it  is  important  to  note 
that  the  real  (relative)  growth  rate  rapidly  diminishes.  The  ovum  increases  in  weight  during 
the  first  month  about  1000  times,  or  100,000  per  cent,  (not  including  the  extra-embryonic 
structures).  This  rate  diminishes  rapidly,  however,  so  that  the  increase  during  the  last  foetal 
month  is  only  about  33  per  cent. 

The  continuation  of  growth  in  length  and  weight  during  the  postnatal  period  is  shown  in 
the  following  chart  (fig.  30). 

The  following  chart  is  based  upon  data  from  Camerer  (1-5  yrs.).  Porter  (6-17  yrs.),  and 
Roberts  (18-20  yrs.),  showing  the  average  postnatal  growth  in  height  and  weight  by  sexes. 
The  average  height  at  birth  is  about  50  cm.  (20  inches) ;  weight,  about  3200  g.  (7  pounds).  The 
male  is  slightly  heavier  and  taller  than  the  female,  except  during  the  acceleration  at  the  period 

*  270  days  (Mall). 


PRENATAL  GROWTH 


23 


Fig.  29. — Face  op  a  Human  Embryo  after  Completion  of  the  Upper  Jaw.     (McMurrich 

from  His.) 


Fig.  30. — Chart  Showing  Average  Postnatal  Growth  in  Height  and  Weight. 


^ 

^ 

-X- 

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male 



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■"^ 

<^ 

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.... 

y^' 

**** 

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-'' 

V 

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<i^- 

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8  9  10  II  12  13         W  15  16  17 

"Years  of  age 


24 


MORPHOGENESIS 


of  puberty.  Puberty  occurs  earlier  in  the  female,  so  that  between  the  ages  of  12  and  15  the 
girls  exceed  the  boys  in  average  height  and  weight.  With  the  exception  of  this  period  of  accel- 
eration, the  (relative)  growth  rate  in  general  diminishes  steadily  from  birth,  and  has  practically 
ceased  at  20  years.  The  average  height  at  this  time  is  about  160  cm.  (5  ft.,  3  in.)  in  the  female, 
and  170  cm.  (5  ft.,  7  in.)  in  the  male;  average  weight,  about  56  kilograms  (126  lbs.)  in  the  female, 
and  65  kilograms  (146  lbs.)  in  the  male.  Under  favourable  conditions,  growth  in  height  may  con- 
tinue slowly  up  to  about  25  years,  and  in  weight  even  longer;  but  in  old  age  there  is  a  slight 
decrease  in  both  height  and  weight. 

The  following  measurements  (from  Holt,  "Diseases  of  Infancy  and  Childhood" 
may  be  taken  as  a  normal  average  standard  of  growth  during  the  first  three 
years.  The  weights  are  taken  without  clothing.  The  height  is  taken  by  plac- 
ing the  baby  on  a  perfectly  flat  surface  like  a  table,  and  having  some  one  hold 
the  child's  knee  down  so  that  he  hes  out  straight,  then  taking  a  tape-measure 
and  measuring  from  the  top  of  his  head  to  the  bottom  of  his  foot,  holding  the 
tape  line  absolutely  straight.  The  chest  is  measured  by  means  of  a  tape  line 
passed  directly  over  the  nipples  around  the  child's  body  and  midway  between 
full  inspiration  and  full  expiration.  The  head  measurement  is  taken  directly 
around  the  circumference  of  the  head,  over  the  forehead  and  occipital  bone. 


Weight, 
pounds 


Height, 
inches 


Chest, 
inches 


Head, 
inches 


Birth  ; 

6  months .  . 
12  months . 
18  months . 

2  Years .  .  . 

3  Years  .  . . 


7.56 
7.16 
16.0 
15.5 
20.5 
19.8 
22.8 
22.0 
26.5 
25.5 
31.2 
30.0 


20.6 
20.5 
25.4 
25.0 
29.0 
28.7 
30.0 
29.7 
32.5 
32.5 
35.0 
35.0 


13.4 
13.0 
16.5 
16.1 
18.0 
17.4 
18.5 
18.0 
19.0 
18.5 
20.1 
19.8 


13.9 
13.5 
17.0 
16.6 
18.0 
17.6 
18.5 
18.0 
18.9 
18.6 
19.3 
19.0 


Relative  growth  of  the  parts. — The  growth  of  the  body  is  not  uniform  in  the 
various  parts,  and  changes  in  proportions  therefore  occur  during  development,  as 

Fig.  31. — Figures  Illustrating  the  Changes  in  Proportion  During  Prenatal  and 
Postnatal  Growth.     (Stratz.) 


shown  in  fig.  31.  It  will  be  noted  that  the  changes  are  in  accordance  with  the 
law  of  developmental  direction  previously  explained,  the  growth  impulse  passing 
along  the  body  in  a  cranio-caudal  direction. 

The  head  is  therefore  largest  in  the  earlier  stages,  forming  about  half  the  body,  decreasing 
to  25  per  cent,  in  the  newborn,  and  to  7  or  8  per  cent,  of  the  body  in  the  adult.  The  upper 
limbs  increase  to  about  10  per  cent,  of  the  body  at  birth,  maintaining  thereafter  about  the  same 
relative  size.     The  trunk  as  a  whole  remains  of  about  the  same  relative  size  (about  45  per  cent.). 


VARIABILITY  25 

although  the  thoracic  portion  reaches  its  maximum  in  the  earher  stages,  and  the  pelvic  portion 
not  until  adult  life.  The  loiver  limbs,  Uke  the  pelvis,  develop  slowly,  forming  about  20  per  cent, 
of  the  body  at  birth  and  reaching  35  per  cent,  in  the  adult. 

Relative  growth  of  the  systems. — There  is  also  a  marked  difference  in  the  relative  growth 
of  the  various  systems.  Data  for  the  skin  and  skeleton  are  somewhat  scanty  and  unsatis- 
factory. The  musculature,  however,  is  relatively  small  in  the  embryo,  increasing  to  about  25 
per  cent,  of  the  body  in  the  newborn,  and  to  40  or  45  per  cent,  in  the  adult.  The  visceral  group 
(including  brain  and  spinal  cord),  on  the  other  hand,  is  relatively  largest  in  the  early  embryo, 
decreasing  from  about  35  per  cent,  of  the  body  to  about  24  per  cent,  in  the  newborn  and  to  about 
10  per  cent,  in  the  adult. 

Relative  growth  of  the  organs. — While  in  general,  the  individual  organs  follow  the  course 
of  relative  growth  of  the  visceral  group,  each  organ  has  its  own  characteristic  course  of  growth. 
As  a  rule,  after  its  appearance  in  the  embryo,  each  organ  increases  more  or  less  rapidly  to  its 
maximum  relative  size,  after  which,  although  increasing  in  absolute  size,  it  decreases  in  relative 
size  through  subsequent  prenatal  and  postnatal  life  up  to  the  adult. 

Thus  the  brain  in  the  embryo  of  the  second  month  forms  more  than  20  per  cent,  of  the  body, 
but  steadily  declines  to  about  13  or  14  per  cent,  in  the  newborn,  and  about  2  per  cent,  in  the 
adult.  The  spinal  cord  and  eyeballs  have  a  similar  course  of  growth.  The  heai-t  declines  from 
about  5  per  cent,  of  the  body  in  the  embryo  of  the  second  month  to  about  .75  per  cent,  in  the 
newborn  and  .46  per  cent,  in  the  adult.  The  liver  decreases  from  a  maximum  of  nearly  10  per 
cent,  in  the  thh-d  month  to  5  per  cent,  in  the  newborn  and  2.7  per  cent  in  the  adult.  The  supra- 
renal glands  decrease  from  about  .46  per  cent,  of  the  body  in  the  third  month  to  .23  per  cent, 
in  the  newborn  and  .01  per  cent,  in  the  adult.  The  lungs  decrease  from  3.3  per  cent,  in  the 
fourth  month  to  about  2  per  cent,  of  the  body  at  birth  and  1  per  cent,  (bloodless  weight)  in 
the  adult.  The  kidneys  reach  a  maximum  of  about  1  per  cent,  of  the  body  toward  the  end  of  the- 
fcetal  period,  decreasing  to  about  .46  per  cent,  in  the  adult.  The  thymus,  thyroid,  spleen  and 
alimentary  canal  likewise  reach  their  maximum  slowly,  being  probably  relatively  largest  about 
the  time  of  birth.  The  ovary  and  testis,  however,  appear  to  be  relatively  largest  during  the 
prenatal  period. 

Variability. — It  must  be  borne  in  mind  that  all  statements  concerning  struc- 
ture refer  to  the  average  or  norin,  and  are  always  subject  to  variation.  This  is. 
therefore  a  topic  of  importance  to  students  of  anatomy.  Variations  are  classified 
as  either  germinal  or  somatic. 

Germinal  variations  are  due  to  fundamental  differences  in  the  germ  plasm,  and  are  trans- 
mitted by  heredity.  These  include  many  of  the  characters  whereby  one  individual  differs  from 
another.  Variations  according  to  sex  are  included  under  this  class.  Variations  inherited  from, 
more  or  less  remote  ancestors  are  termed  atavistic  or  reversional. 

Somatic  variations,  or  'acquired  characters,'  are  due  to  environmental  influences,  such 
as  nutrition,  temperature,  shelter,  disease,  training,  etc.  While  somatic  variations  may  be 
very  great,  they  do  not  affect  the  germ  plasm  and  are  not  transmitted  by  heredity. 

In  many  cases  it  is  exceedingly  difficult  to  distinguish  germinal  from  somatic  variations 
Size,  for  example,  may  be  due  to  either  or  both.  Moreover,  somatic  variations  may  be  pro- 
duced at  any  time  after  the  fertilisation  of  the  ovum.  Very  slight  environmental  changes  are 
sometimes  sufficient  to  produce  a  marked  effect  upon  the  dehcately  balanced  mechanism  of 
the  developing  embryo.  Malformations  and  pathological  conditions  are  thus  often  to  be 
explained.  As  to  the  extent  of  variability,  some  characters  are  much  more  variable  than  others. 
Height,  for  exahiple,  is  less  variable  than  weight.  Moreover,  variability  differs  in  the  various 
parts  and  organs.  In  general,  the  head  and  head  organs  are  less  variable  than  the  remainder 
of  the  body.  The  skeleton  and  musculature  appear  less  variable  than  the  integument  and 
viscera. 

Details  concerning  variations  and  methods  for  their  measurement  may  be  found  in  works 
on  genetics  and  biometrical  statistics. 

'Reieiences.—Embnjology:  Keibel  and  Mall,  Human  Embryology  (2  vols.); 
Bryce,  Quain's  Anatomy,  11th  ed.,  vol.  1 ;  Minot,  Laboratory  Text-book  of  Embry- 
ology; McMurrich,  Development  of  the  Human  Body.  Growth:  Minot,  Age, 
Growth,  and  Death;  Jackson,  Amer.  Jour.  Anat.,  vol.  9;  Anat.  Record,  vol.  3. 
Heredity:  Davenport,  Heredity  and  Eugenics;  Walter,  Genetics.  Biometry: 
Davenport,  Statistical  Methods;  Yule,  Theory  of  Statistics. 


I 


S  E  C  T  I  O  N  1 1 

OSTEOLOGY 

Revised  for  the  Fifth  Edition 
By  peter  THOMPSON,  M.D., 

PROFESSOR    OF    ANATOMY   IN   THE    UNIVEIlSITr    OF  BIRMINQHAM;    EXAMINER   IN    ANATOMY,    THE   HNIVERSITY 
[^CAMBRIDGE;    FORMERLY    EXAMINER   IN   ANATOMY    FOR   THE    UNIVERSITIES    OF    LOMDON,    ABERDEEN,    MANC 
DUBLIN    AND    FOR  THE    CONJOINT  BOARD    OF    ENGLAND 


i 


THE  SKELETON 

THE  skeleton  forms  the  solid  framework  of  the  body,  and  is  composed  of 
bones,  and  in  certain  parts,  of  pieces  of  cartilage.  The  various  bones  and 
cartilages  are  united  by  means  of  ligaments,  and  are  so  arranged  as  to 
give  the  body  definite  shape,  protect  from  injury  the  more  important  delicate 
organs,  and  afford  attachment  to  the  muscles  by  which  the  various  movements  are 
accomplished. 

In  its  widest  acceptance,  the  term  skeleton  includes  all  parts  of  the  framework,  whether 
internal  or  external,  and  as  in  many  of  the  lower  animals  there  are,  in  addition  to  the  deeper 
osseous  parts,  hardened  structures  associated  with  the  integument,  it  is  convenient  to  refer  to 
the  two  groups  as  endoskeleton  and  exoskeleton  or  dermal  skeleton,  respectively.  All  verte- 
brate— i.  e.,  back-boned — animals  ])o,sscss  an  endoskeleton,  and  many  of  them  a  well-developed 
exoskeleton  also,  but  in  maniiiials,  the  highest  group  of  vertebrates,  the  external  skeleton,  when 
it  exists,  plays  a  relatively  subordinate  part.  In  most  of  the  invertebrates  the  endoskeleton  is 
absent  and  the  dermal  skeleton  alone  is  found. 

In  man  by  far  the  greater  part  of  the  endoskeleton  is  formed  of  bone,  a  tissue  of  definite 
chemical  composition,  being  formed  mainly  of  a  gelatine  basis  strongly  impregnated  with  lime 
salts. 

The  number  of  bones  in  the  skeleton  varies  at  different  ages,  some,  which  are 
originally  quite  independent,  becoming  united  as  age  advances.  They  are  ar- 
ranged in  an  axial  set,  which  includes  the  vertebral  column,  the  skull,  the  ribs, 
and  the  sternum,  and  an  appendicular  set,  belonging  to  the  limbs.  The  following 
table  shows  the  number  of  bones  usually  distinct  in  middle  Hfe,  excluding  the 
auditory  ossicles: — 

Bones. 

.    .  ,  f  The  vertebral  column 26 

™' ,  ,  The  skull 23 

bueieton  ^  r^j^^  ^.-^^^  ^^^  sternum 25 

Appendicular     /  The  upper  Umbs 64 

Skeleton  \  The  lower  limbs 62 

Total 200 

Several  of  the  skull  bones  are  compound,  i.  e.,  in  the  immature  skeleton  they  consist  of 
separate  elements  which  ultimately  unite  to  form  a  single  bone.  In  order  to  comprehend  the 
nature  of  such  bones  it  is  advantageous  to  study  them  in  the  various  stages  through  which 
they  pass  in  the  process  of  development  in  the  foetus  and  the  cliild.' 

It  follows,  therefore,  that  to  appreciate  the  morphology  of  the  skeleton — i.  e.,  the  history 
of  the  osteological  units  of  which  it  is  composed — the  osteogenesis  or  mode  of  development  of 
the  bones  must  be  studied,  as  well  as  their  topography  or  position. 

Some  bones  arise  by  ossification  in  membrane,  others  in  cartilage.  In  the  embryo,  many 
portions  of  the  skeleton  are  represented  by  cartilage  which  may  become  infiltrated  by  lime  salts 
— calcification.  This  earthy  material  is  taken  up  and  redeposited  in  a  regular  manner- 
ossification.     Portions  of  the  original  cartilage  persist  at  the  articular  ends  of  bones,  and,  in 

27 


I 


28  THE  SKELETON 

young  bones,  at  the  epiphysial  lines,  i.  e.,  the  lines  of  junction  of  the  main  part  of  a  bone  with  the 
extremities  or  epiphyses.  Long  bones  increase  in  length  at  the  epiphysial  cartilages,  and  increase 
in  thickness  by  ossification  of  the  deeper  layers  of  the  investing  membrane  or  periosteum. 
These  processes — intracartilaginous  and  intramembranous  ossification — proceed  concurrently 
in  the  limb-bones  of  a  young  and  growing  mammal. 

There  is  no  bone  in  the  human  skeleton  which,  though  pre-formed  in  cartilage,  is  perfected 
in  this  tissue.  The  ossification  is  completed  in  membrane.  On  the  other  hand,  there  are  nu- 
merous instances  in  the  skull,  of  bones  the  ossification  of  which  begins  in,  and  is  perfected  by,  the 
intramembranous  method.  Ossification  in  a  few  instances  commences  in  membrane,  but  later 
invades  tracts  of  cartilage;  occasionally  the  process  begins  in  the  perichondrium  and  remains 
restricted  to  it,  never  invading  the  underlying  cartilage,  which  gradually  disappears  as  the  result 
of  continued  pressure  exerted  upon  it  by  the  growing  bone.  The  vomer  and  nasal  bones  are 
the  best  examples  of  this  mode  of  development.  Further  details  of  development  and  ossification 
are  included  in  the  description  of  each  bone. 

The  limb-bones  differ  in  several  important  particulars  from  those  of  the  skull.  Some  of 
the  long  bones  have  many  centres  of  ossification,  but  these  have  not  the  same  significance  as 
those  of  the  skull.  It  is  convenient  to  group  the  centres  into  two  sets,  primary  and  secondary. 
The  primary  nucleus  of  a  long  bone  appears  quite  early  in  f  cetal  life,  and  the  main  part  (shaft) 
thus  formed  is  called  the  diaphysis.  In  only  three  instances  does  a  secondary  centre  appear 
before  birth,  e.  g.,  the  lower  end  of  the  femur,  the  head  of  the  tibia,  and  occasionally  the  head  of 
the  humerus.  Many  primary  ossific  nuclei  appear  after  birth,  e.  g.,  those  for  the  carpal  bones,  the 
cuneiform  and  navicular  bones  of  the  foot,  the  coracoid  process  of  the  scapula,  and  for  the  third, 
fourth,  and  fifth  pieces  of  the  sternum. 

When  a  bone  ossifies  from  one  nucleus  only,  this  nucleus  may  appear  before  or  after  birth. 
Examples:  the  talus  (astragalus)  at  the  seventh  month  of  foetal  life,  and  the  lesser  multangular 
(trapezoid)  at  the  eighth  year.  When  a  bone  possesses  one  or  more  secondary  centres,  the  pri- 
mary nucleus,  as  a  rule,  appears  early.  Examples:  the  femur,  humerus,  phalanges,  and  the 
calcaneus. 

Secondary  centres  which  remain  for  a  time  distinct  from  the  main  portion  of  a  bone  are 
termed  epiphyses.  An  epiphysis  may  arise  from  a  single  nucleus,  as  is  the  case  at  the  lower  end 
of  the  femur,  or  from  several,  as  at  the  upper  end  of  the  humerus.  Prominences  about  the  ends 
of  long  bones  may  be  capped  by  separate  epiphyses,  as  illustrated  at  the  upper  end  of  the  femur. 

According  to  Professor  F.  G.  Parsons,  there  are  at  least  three  kinds  of  epiphyses: — (1) 
Those  which  appear  at  the  articular  ends  of  long  bones,  which,  since  they  transmit  the  weight 
of  the  body  from  bone  to  bone,  may  be  termed  pressure  epiphyses.  (2)  Those  which  appear  as 
knob-like  processes,  where  important  muscles  are  attached  to  bones;  and  as  these  are  concerned 
with  the  pull  of  muscles,  they  may  be  described  as  traction  epiphyses.  (3)  The  third  kind 
includes  those  epiphyses  which  represent  parts  of  the  skeleton  at  one  time  of  functional  import- 
ance but  which,  having  lost  their  function,  have  now  become  fused  with  neighbouring  bones  and 
only  appear  as  separate  ossifications  in  early  life.  These  may  be  termed  atavistic  epiphyses 
and  include  such  epiphyses  as  the  tuberosity  of  the  ischium,  the  representative  of  the 
hypoischium  of  reptiles. 

The  epiphyses  of  bones  seem  to  follow  certain  rules,  thus: — 

1.  Those  epiphyses  whose  centres  of  ossification  appear  last  are  the  first  to  unite  with  the 
shaft.  There  is  one  exception,  however,  to  this  statement,  viz.,  the  upper  end  of  the  fibula, 
which  is  the  last  to  unite  with  the  shaft,  although  its  centre  appears  two  years  after  that  for  the 
lower  end.  This  may  perhaps  be  accounted  for  by  the  rudimentary  nature  of  the  proximal  end 
of  the  fibula  in  man  and  many  other  mammals. 

2.  The  epiphysis  toward  which  the  nutrient  artery  is  directed  is  the  first  to  be  united  with 
the  shaft.  It  is  also  found  that  while  the  increase  in  length  of  the  long  bones  takes  place  at  the 
epiphysiai  cartilages,  the  growth  takes  place  more  rapidly  and  is  continued  for  a  longer  period  at 
the  end  where  the  epiphysis  is  the  last  to  unite.  It  follows,  therefore,  that  the  shifting  of  the 
investing  periosteum,  which  results  from  these  two  factors,  leads  to  obliquity  of  the  vascular 
canal  by  drawing  the  proximal  portion  of  the  nutrient  artery  toward  the  more  rapidly  growing 
end.  Moreover,  when  a  bone  has  only  one  epiphysis,  the  nutrient  artery  will  be  directed  toward 
the  extremity  which  has  no  epiphysis. 

3.  The  centres  of  ossification  appear  earliest  in  those  epiphyses  which  bear  the  largest 
relative  proportion  to  the  shafts  of  the  bones  to  which  they  belong. 

4.  When  an  epiphysis  ossifies  from  more  than  one  centre,  the  various  nuclei  coalesce  before 
the  shaft  and  epiphysis  consolidate,  e.  g.,  the  upper  end  of  the  humerus. 

On  section,  the  shaft  of  a  f  cetal  long  bone  is  seen  to  be  occupied  by  red  marrow  lodged  in 
bony  cells  which  do  not  present  any  definite  arrangement.  In  an  adult  the  central  portion  of 
the  shaft  is  filled  with  fat  or  marrow  held  together  by  a  deUcate  reticulum  of  connective  tissue, 
whence  the  space  is  known  as  the  medullary  cavity.  The  expanded  ends  of  the  bones  contain  a 
network  of  cancellous  tissue,  the  intervals  being  filled  with  red  marrow.  This  cancellous  tissue 
differs  from  that  of  the  foetal  bone  in  being  arranged  in  a  definite  manner  according  to  the  direc- 
tion of  pressure  exerted  by  the  weight  of  the  body,  and  the  tension  produced  by  the  muscles. 
The  arrangement  of  the  cancelli  in  consequence  of  the  mechanical  conditions  to  which  bones  are 
subject  is  noticed  in  the  description  of  a  vertebra,  the  femur,  and  the  humerus. 

Bones  are  divisible  into  four  classes: — long,  short,  flat,  and  irregular.  The  long  bones, 
found  chiefly  in  the  limbs,  form  a  system  of  levers  sustaining  the  weight  of  the  trunk  and  provid- 
ing the  means  of  locomotion.  The  short  bones,  illustrated  by  those  of  the  carpus  and  tarsus, 
are  found  mainly  where  compactness,  elasticity,  and  Umited  motion  are  the  principal  require- 
ments. Flat  bones  confer  protection  or  provide  broad  surfaces  for  muscular  attachment,  as 
in  the  case  of  the  cranial  bones  and  the  shoulder-blade.  Lastly,  the  irregular  or  mixed  bones 
constitute  a  group  of  peculiar  form,  often  very  complex,  which  cannot  be  included  under  either 
of  the  preceding  heads.  These  are  the  vertebrae,  sacrum,  coccyx,  and  many  of  the  bones  of  the 
skull. 


THE  VERTEBRAL  COLUMN 


29 


The  shafts  ot  long  bones  at  the  time  of  birth  are  mainly  cylindrical  and  free  from  ridges. 
The  majority  of  the  lines  and  ridges  so  conspicuous  on  the  shafts  of  long  bones  in  adults  are  due 
to  the  ossification  of  muscle-attachments.  The  more  developed  the  muscles,  the  better  marked 
the  ridges  become. 

The  surfaces  of  bones  are  variously  modified  by  environing  conditions.  Pressure  at  the 
•extremities  causes  enlargement,  and  movement  renders  them  smooth.  The  two  causes  combined 
produce  an  articular  surface.  When  rounded  and  supported  upon  a  constricted  portion  of  bone, 
-an  articular  surface  is  termed  a  head,  sometimes  a  condyle ;  when  depressed,  a  glenoid  fossa. 
Blunt,  non-articular  processes  are  called  tuberosities;  smaller  ones,  tubercles;  sharp  projections, 
spines.     Slightly  elevated  ridges  of  bones  are  crests;  when  narrow  and  pronounced,  lines  and 

Fig.  32. — The  Tibia  and  Fibula  in  Section  to  show  the  Epiphyses. 


Centre  of  ossification  of  epiphysis 
Epiphysial  line 


i 


Shaft  of  fibula 


Shaft  of  tibia  in  section 


Epiphysis  of  tibia 
{J_    Epiphysis  of  fibula 


"borders.     A  shallow  depression  is  a  fossa;  when  narrow  and  deep,  a  groove;  a  perforation  is 
usually  called  a  foramen. 

In  addition  to  these,  other  terms  are  employed  which  do  not  require  any  e.xplanation,  such 
as  canal,  notch  or  incisura,  sulcus  or  furrow,  and  the  like. 


/.  THE  AXIAL  SKELETON 

A.  THE  VERTEBRAL  COLUMN 

The  vertebral  column  [columna  vertebralis]  consists  of  a  series  of  bones  called 
vertebrae,  closely  connected  by  means  of  fibrous  and  elastic  structures,  which 
allow  of  a  certain  but  limited  amount'  of  motion  between  them.     In  the  young 


30  THE  SKELETON 

subject  the  vertebrse  are  thirty-three  in  number.  Of  these,  the  upper  twenty- 
four  remain  separate  throughout  life,  and  are  distinguished  as  movable  or  true 
vertebrae.  The  succeeding  five  vertebrae  become  consolidated  in  the  adult  to  form 
one  mass,  called  the  sacrum,  and  at  the  terminal  part  of  the  column  are  four  rudi- 
mentary vertebrae,  which  also  tend  to  become  united  as  age  advances,  to  form  the 
coccyx.  The  lower  nine  vertebrae  thus  lose  their  mobihty  as  individual  bones, 
and  are  accordingly  known  as  the  fixed  or  false  vertebrae.  Of  the  true  vertebrae, 
the  first  seven  are  called  cervical  [cervicales],  the  succeeding  twelve  thoracic 
[thoracales]  or  dorsal,  and  the  remaining  five  lumbar  [lumbales]. 

Although  the  vertebrae  of  the  different  regions  of  the  coliunn  differ  markedly 
in  many  respects,  each  vertebra  is  constructed  on  a  common  plan,  which  is  more 
or  less  modified  in  different  regions  to  meet  special  requirements.  The  essential 
characters  are  well  seen  in  the  vertebrae  near  the  middle  of  the  thoracic  region,  and 
it  will  be  advantageous  to  commence  the  study  of  the  vertebral  structures  with 
one  selected  from  this  region. 

Description  of  a  thoracic  vertebra  (figs.  33,  34). — The  vertebra  consists  of  two 
essential  parts — a  body  in  front  and  an  arch  behind. 

Fia.  33. — -A  Thoracic  Vertebra.     (Side  view.) 

Superior  costal  pit  for  head  of  i 

Superior  articular  process 
Pedicle  (root  of 


Transverse  process 


Inferior  costal  pit  for 
head  of  rib 
Inferior  articular  process 


-Spinous  process 


The  body  [corpus  vertebrae]  or  centrum  is  a  soUd  disc  of  bone,  somewhat 
heart-shaped,  deeper  behind  than  in  front,  slightly  concave  on  its  superior  and  in- 
ferior surfaces,  and  wider  transversely  than  antero-posteriorly.  The  upper  and 
lower  surfaces  are  rough' for  the  intervertebral  discs  which  are  interposed  between 
the  bodies  of  the  vertebrae,  and  the  margins  are  slightly  lipped.  The  circum- 
ference of  the  body  is  concave  from  above  downward  in  front,  convex  fron  side  to 
side,  and  perforated  by  numerous  vascular  foramina.  Posteriorly  it  is  concave 
from  side  to  side  and  presents  one  or  two  large  foramina  for  the  exit  of  veins  from 
the  cancellous  tissue.  On  each  side  of  the  body,  at  the  place  where  it  joins  the 
arch,  are  two  costal  pits  (superior  and  inferior)  [fovea  costalis  superior;  inferior] 
placed  at  the  upper  and  lower  borders,  and  when  two  vertebrae  are  superimposed, 
the  adjacent  costal  pits  form  a  complete  articular  pit  for  the  head  of  a  rib.  The 
superior  and  inferior  costal  pits  were  formerly  designated  as  "  demi-f acets. " 

The  arch  [arcus  vertebrae]  is  formed  by  two  pedicles  and  two  laminae,  and 
supports  seven  processes — one  spinous,  two  transverse,  and  four  articular.  The 
pedicles  or  roots  of  the  vertebral  arch  [radices  arcus  vertebrae]  are  two  short,  con- 
stricted columns  of  bone,  projecting  horizontally  backward  from  the  posterior  sur- 
face of  the  body.  The  concavities  on  the  upper  and  lower  borders  of  each  pedicle, 
of  which  the  lower  is  much  the  deeper,  are  named  vertebral  notches  [incisurae],  and 
when  two  vertebrae  are  in  position,  the  notches  are  converted  into  intervertebral 
foramina  for  the  transmission  of  the  spinal  nerves  and  blood-vessels. 

The  laminae  are  two  broad  plates  of  bone  which  connect  the  spinous  process 
with  the  roots  (pedicles)  and  complete  the  arch  posteriorly.  The  superior  border 
and  the  lower  part  of  the  anterior  surface  of  each  lamina  is  rough  for  the  insertion  of 
the  ligamenta  flava.  The  upper  part  of  the  anterior  surface  is  smooth  where  it 
forms  the  posterior  boundary  of  the  vertebral  canal.     When  articulated,  the 


THE  CERVICAL  VERTEBRA  31 

laminse  in  the  thoracic  region  are  imbricated  or  sloped,  one  pair  over  the  other, 
somewhat  like  tiles  on  a  roof. 

The  spinous  process  [processus  spinosus],  long  and  three-sided,  projects  back- 
ward and  downward  from  the  centre  of  the  arch  and  terminates  in  a  slight  tubercle. 
It  gives  attachment  by  its  prominent  borders  to  the  interspinous  ligaments  and  by 
its  free  extremity  to  the  supraspinous  ligament.  It  serves  mainly  as  a  process  for 
muscular  attachment. 

The  transverse  processes  [processus  transversus]  are  two  in  number  and  extend 
laterally  from  the  arch  at  the  junction  of  the  pedicles  and  laminse.  They  are  long, 
thick,  backwardly  directed  columns  of  bone  terminating  in  a  clubbed  extremity, 
on  each  of  which  is  a  costal  pit  for  articulation  with  the  tubercle  of  a  rib.  The 
transverse  processes,  in  addition  to  supporting  the  ribs,  afford  powerful  leverage 
to  muscles. 

The  articular  processes,  two  superior  and  two  inferior,  project  upward  and 
downward  opposite  the  attachments  of  the  transverse  processes.  The  superior 
are  flat  and  bear  facets  or  surfaces  [facies  articulares  superiores]  which  are  directed 

Fig.  34. — A  Thoracic  Vertebra. 
Lamina 


Costal  pit  for  tubercle  of  rib 


i 


Pedicle  (root  of  arch) 
Costal  pit  for  head  of  rib 


Transverse  process 


upward,  backward,  and  laterally,  and  are  situated  a  little  in  advance  of  the  inferior, 
the  facets  of  which  [facies  articulares  inferiores]  are  oval,  concave,  and  directed 
downward,  forward,  and  medially. 

The  vertebral  foramen  is  bounded  anteriorly  by  the  body,  posteriorly  and  on 
each  side  by  the  arch.  It  is  nearly  circular,  and  is  smaller  than  in  the  cervical  or 
the  lumbar  region.  When  the  vertebrae  are  articulated,  the  series  of  rings  con- 
stitute the  spinal  or  vertebral  canal  [canalis  vertebralis],^in  which  is  lodged  the 
spinal  cord. 

THE  CERVICAL  VERTEBRA 

A  typical  cervical  vertebra  (from  the  third  to  the  sixth  inclusive)  presents  the 
following  characteristics  (fig.  35) : — The  body  is  smaller  than  in  other  regions  of 
the  column  and  is  of  oval  shape  with  the  long  axis  transverse.  The  lateral  mar- 
gins of  the  upper  surface  are  raised  into  prominent  lips,  so  that  the  surface  is 
concave  from  side  to  side;  it  is  also  sloped  downward  in  front.  The  inferior  sur- 
face, on  the  contrary,  projects  downward  in  front  and  is  rounded  off  at  the  sides 
to  receive  the  corresponding  lips  of  the  adjacent  vertebra.  It  is  concave  antero- 
posteriorly  and  convex  in  an  opposite  direction. 

The  roots  (pedicles)  are  directed  laterally  and  backward  and  spring  from  the 
body  about  midway  between  the  upper  and  lower  borders.  The  superior  and 
inferior  notches  are  nearly  equal  in  depth,  but  the  inferior  are  usually  somewhat 
deeper.  The  laminse  are  long,  narrow,  and  slender.  The  spinous  process  is 
short  and  bifid  at  the  free  extremity. 


32 


THE  SKELETON 


Articular  processes. — Both  the  superior  and  inferior  articular  processes  are 
situated  at  the  junction  of  the  root  with  the  lamina  and  they  form  the  upper  and 
lower  extremities  of  a  small  column  of  bone.  The  articular  surfaces  are  oblique 
and  nearly  flat,  the  superior  looking  backward  and  upward,  and  the  inferior 
forward  and  downward. 

The  transverse  process  presents  near  its  base  a  round  costo-transverse  foramen 
[foramen  transversarium]  for  the  transmission  of  the  vertebral  artery,  vein,  and  a 
plexus  of  sympathetic  nerves.  Moreover,  each  process  is  deeply  grooved  above 
for  a  spinal  nerve,  and  is  bifid  at  its  free  extremity,  terminating  in  two  tubercles — 
anterior  and  posterior.  The  costo-transverse  foramen  is  very  characteristic  of  a 
cervical  vertebra.  It  is  bounded  medially  by  the  pedicle,  posteriorly  by  the 
transverse  process  (which  corresponds  to  the  transverse  process  of  a  thoracic 
vertebra),  anteriorly  by  the  costal  process  (which  corresponds  to  the  rib  in  the 
thoracic  region),  and  laterally  by  the  costo-transverse  lamella.  The  latter  is  a 
bar  of  bone  joining  the  two  processes  and  directed  obliquely  upward  and  forward 
in  the  upper  vertebrae  and  horizontally  in  the  lower.  The  vertebral  foramen  is 
triangular  with  rounded  angles,  and  is  larger  than  in  the  thoracic  or  lumbra 
vertebrae. 


Fig.  35. — A  Cervical  Vertebra. 


Costal  process 

Costo-transverse   foramen 

Transverse  process 

Superior  articular  process 

Inferior  articular  process 
Lamina 


Spinous  process 


gvPedicle  (root  of  arch) 


Peculiar  cervical  vertebrae. — The  various  cervical  vertebrae  possess  distinguishing  features, 
though,  with  the  exception  of  the  first,  second,  and  seventh,  which  are  so  different  as  to  necessi- 
tate separate  descriptions,  these  are  largely  confined  to  the  direction  of  the  costo-transverse 
lamella,  and  the  size  and  level  of  the  anterior  and  posterior  tubercles.  In  the  third  the  anterior 
tubercle  is  higher  than  the  posterior  and  the  costo-transverse  lamella  is  obhque;  in  the  fourth  the 
anterior  tubercle  is  elongated  vertically,  so  that  its  lower  end  is  nearly  on  a  level  with  the 
posterior,  though  the  lamella  still  remains  oblique.  In  the  fifth  and  sixth  they  are  nearly  on 
the  same  level,  but  in  the  latter  the  anterior  tubercle  is  markedly  developed  to  form  the  carotid 
tubercle. 

The  Atlas  or  First  Cervical  Vertebra 

This  vertebra  (fig.  36)  is  remarkable  in  that  it  has  neither  body  nor  spinous 
process.  It  has  the  form  of  an  irregular  ring,  and  consists  of  two  thick  portions, 
the  lateral  masses,  united  in  front  and  behind  by  bony  arches.  The  anterior 
arch  joins  the  lateral  masses  in  front  and  constitutes  about  one-fifth  of  the  entire 
circumference  of  the  ring.  On  its  anterior  surface  it  presents  a  tubercle  for  the 
attachment  of  the  longus  colli  muscle  and  the  anterior  longitudinal  ligament, 
and  on  its  posterior  surface  a  circular  facet  [fovea  dentis]  for  articulation  with 
the  odontoid  process  [dens]  of  the  axis.  The  upper  and  lower  borders  serve  for 
the  attachment  of  ligaments  uniting  the  atlas  to  the  occipital  bone  and  axis 
respectively. 

The  lateral  masses  are  thick  and  strong,  supporting  the  articular  processes  above  and  below 
and  extending  laterally  into  the  transverse  processes.  The  superior  articular  surfaces  are 
elongated,  deeply  concave,  and  converge  in  front.  Directed  upward  and  mediaOy  they  receive 
the  condyles  of  the  occipital  bone,  and  occasionally  each  presents  two  oval  facets  united  by  an 
isthmus.  The  inferior  articular  surfaces  are  circular  and  almost  flat;  they  are  directed  down- 
ward and  medially  and  articulate  with  the  axis.  The  articular  processes,  like  the  superior 
articular  processes  of  the  axis,  differ  from  those  of  other  vertebrte  in  being  situated  in  front  of 
the  places  of  exit  of  the  spinal  nerves. 

Between  the  upper  and  lower  articular  surfaces  on  the  inside  of  the  ring  are  two  smooth 
rounded  tubercles,  one  on  each  side,  to  which  the  transverse  ligament  is  attached.     This  liga- 


THE  CERVICAL  VERTEBRA 


33 


ment  divides  the  interior  of  the  ring  into  a  smaller  anterior  part  for  the  dens  of  the  axis,  and  a 
larger  posterior  part,  corresponding  to  the  foramina  of  other  vertebrae,  for  the  spinal  cord  and 
its  membranes. 

The  transverse  processes  are  large  and  extend  farther  outward  than  those  of  the  vertebrae 
immediately  below.  They  are  flattened  from  above  downward  and  each  is  perforated  by  a  large 
costo-transverse  foramen;  the  extremity  is  not  bifid,  but,  on  the  contrary,  is  broad  and  rough 
for  the  attachment  of  numerous  muscles.  The  posterior  arch  unites  the  lateral  masses  behind 
and  forms  about  two-fifths  of  the  entire  circumference.  It  presents  in  the  rniddle  line  a  rough 
elevation  or  tubercle  representing  a  rudimentary  spinous  process.  At  its  junction  with  the 
lateral  mass  on  the  superior  surface  is  a  deep  groove,  the  sulcus  arteriee  vertebralis,  which 


Fig.  36. — The  First  Cervical  Vertebra  or  Atlas. 


Anterior  tubercle 
Superior  articular  process 

Costal  process 

Costo-transverse  foramen 

Transverse  process 

Groove  for  vertebral  artery- 


Posterior  tuberclt 


i 


lodges  the  vertebral  artery  and  the  sub-occipital  (first  spinal)  nerve.  The  groove  corresponds 
to  the  superior  notches  of  other  vertebrae  and  occasionally  it  is  converted  into  a  foramen  by  a 
bony  arch — the  ossified  oblique  ligament  of  the  atlas.  A  similar  but  much  shallower  notch  is 
present  on  the  inferior  surface  of  the  posterior  arch,  and,  with  a  corresponding  notch  on  the 
axis,  forms  an  intervertebral  foramen  for  the  exit  of  the  second  spinal  nerve.  The  upper  and 
lower  surfaces  of  the  areh  afford  attachment  to  Ugaments  uniting  the  atlas  to  the  occipital 
bone  and  the  axis. 

The  atlas  gives  attachment  to  the  following  muscles: — 

Anterior  arch Longus  colli. 

Posterior  arch Rectus  capitis  posterior  minor. 

Transverse  (process Rectus  capitis  anterior  (minor),  "rectus"'capitis  lateralis, 

obliquus  capitis  inferior,  obliquus  capitis  superior, 
splenius  cervicis,  levator  scapulae,  and  intertransver- 
sarii,  anterior  and  posterior. 

Fig.  37. — The  Epistropheus  or  Axis. 


Odontoid  process  (dens) 


Groove  for  transverse  ligament  - 
Lamina 


Facet  for  atlas 


Superior  articular  process 


Costo-transverse  foramen 


Body 

Costal  process 


Spinous  process         Inferior  articular  process 


The  Epistropheus  (Axis) 

The  epistropheus  (axis)  (fig.  37)  is  the  thickest  and  strongest  of  the  bones  of 
this  region,  and  is  so  named  from  forming  a  pivot  on  which  the  atlas  rotates, 
carrying  the  head.  It  is  easily  recognised  by  the  rounded  dens  (odontoid  process) 
which  surmounts  the  upper  surface  of  the  body.  This  process,  which  represents 
the  displaced  body  of  the  atlas,  is  large,  blunt,  and  tooth-Uke,  and  bears  on  its 
anterior  surface  an  oval  facet  for  articulation  with  the  anterior  arch  of  the  atlas; 
posteriorly  it  presents  a  smooth  groove  which  receives  the  transverse  ligament. 
To  the  apex  a  thin  narrow  fibrous  band  (the  apical  dental  ligament)  is  attached, 
and  on  each  side  of  the  apex  is  a  rough  surface  for  the  attachment  of  the  alar 


34 


THE  SKELETON 


ligaments  which  connect  it  with  the  occipital  bone.  The  enlarged  part  of  the 
process  is  sometimes  termed  the  head,  and  the  constricted  basal  part  the  neck. 
The  inferior  surface  of  the  body  resembles  that  of  the  succeeding  vertebrae  and 
is  concave  from  front  to  back  and  slightly  convex  from  side  to  side.  Its  anterior 
surface  is  marked  by  a  median  ridge  separating  two  lateral  depressions  for  the 
insertion  of  the  longus  colli. 

The  roots  (pedicles)  are  stout  and  broad;  the  laminae  are  thick  and  prismatic;  the  spinous 
process  is  large  and  strong,  deeply  concave  on  its  under  surface,  and  markedly  bifid;  the  trans- 
verse processes  are  small,  not  bifurcated  and  not  grooved.  The  costo-transverse  foramen  is 
directed  very  obliquely  upward  and  laterally  and  the  costal  process  is  larger  than  the  transverse. 

Fig.  38. — The  Cervical  Vertebra.     (Anterior  view.) 

Anterior  tubercle  of  atlas  to  which 
the  longus  colli  is  inserted 


Rectus  capitis  anterior 


The  upper  oblique 
portion  of  longus 
colli 


The  upper  oblique 
portion  of  longus 
colli  and  insertion 
of  inferior  oblique 
portion 


This  and  the  three  suc- 
ceeding processes  give 
origin  to  the  longus 
capitis  and  insertion 
to  the  scalenus  an- 
terior 


Origin  of  vertical  portion  of  the  longus  colli; 
its  insertion  is  into  the  second,  third,  and  fourth  vertebrae 

The  superior  articular  surfaces  are  oval,  and  directed  upward  and  laterally  for  articulation 
with  the  atlas.  They  are  remarkable  in  being  supported  partly  by  the  body,  and  partly  by  the 
pedicles,  and  in  being  situated  in  front  of  the  superior  notches.  The  inferior  articular  surfaces 
are  similar  in  form  and  position  to  those  of  the  succeeding  vertebrae. 

The  axis  gives  attachment  to  the  following  muscles: — 

Body Longus  coUi. 

Spinous  process Obliquus  capitis  inferior,  rectus  capitis  posterior  major 

semispinalis  cervicis,  interspinales,  multifidus. 
Transverse  process Splenius     cervicis,    intertransversarii,    levator    scapulae, 

longissimus  (transversahs)  cervicis,  scalenus  medius. 


The  Seventh  Cervical  Vertebra 

Situated  at  the  junction  of  the  cervical  and  thoracic  regions  of  the  vertebral 
column,  the  seventh  cervical  vertebra  (figs.  38,  39)  may  be  described  as  a  transi- 
tional vertebra — i.  e.,  possessing  certain  features  characteristic  of  both  regions. 

The  spinous  process  is  longer  than  that  of  any  of  the  other  cervical  vertebrae. 
It  is  not  bifurcated,  but  ends  in  a  broad  tubercle  projecting  beneath  the  skin, 


THE  CERVICAL  VERTEBRAE 


35 


whence  the  name  vertebra  prominens  has  been  applied  to  this  bone.  The  trans- 
verse process  is  massive;  the  costal  element  of  the  process  is  very  small,  but,  on 
the  other  hand,  the  posterior  or  vertebral  part  of  the  process  is  large  and  becom- 
ing more  like  the  transverse  process  of  a  thoracic  vertebra. 

The  costo-transverse  foramen  is  the  smallest  of  the  series  and  may  be  absent.  It  does  not, 
as  a  rule,  transmit  the  vertebral  artery,  but  frequently  gives  passage  to  a  vein.  Occasionally 
the  costal  process  is  segmented  off  and  constitutes  a  cervical  rib.  The  body  sometimes  bears 
on  each  side  near  the  lower  border  a  costal  pit  for  the  head  of  the  first  rib.  When  this  is  present, 
there  is  usually  a  well-developed  cervical  rib. 

Fig.  39. — The  Cervical  Vertebra.     (Posterior  view.) 
Rectus  capitis  posterior  minor 


Superior  oblique 
■  oblique 


Rectus  capitis  posterior  major 
(the  pointer  crosses  the  or- 
igin of  the  inferior  oblique) 
Semispinalis  cervicis- 


Semispinalis  cervicis. 


Longissimus  cervicis 
Iliocostalis  cervicis 
Semispinal: 


Levator  costse  (origin) 

Iliocostalis  dorsi  (insertion) 

Interspinales 


Interspinales 
Trapezius 

Rhomboideus  minor 
Serratus  posterior  superior 
Splenius 
Semispinalis  capitis 


Transverse  process 

of  atlas 
Levator    scapulae 

(origin) 
Splenius  cervicis 

(.insertion) 

Levator  scapulse 
-pie   ■ 

Scalenus  medius 
(insertion) 


Levator  scapulae 
'Splenius  cervicis 
Scalenus  medius 
Semispinalis  capitis 

Levator  scapulae 
Sple   ■ 

(sometimes) 
Scalenus  medius 


i 


Scalenus  medius 
Scalenus  posterior 

spinalis   and  lon- 
gissimus capitis 
Multifidus 

medius 
posterior 
spinalis  and   lon- 
gissimus capitis 
Multifidus 
Scalenus  medius  ' 
Scalenus  posterior 

Semispinalis  and  lon- 
gissimus capitis 

Multifidus  spinas 

(The  large  surface  isfor 
the  multifidus) 


Multifidus  (and  to  each 
spinous  process  as 
high  as  the  second) 


The  seventh  cervical  vertebra  gives  attachment  to  the  following  muscles: — 

Body Longus  coUi. 

Spinous  process Trapezius,  rhomboideus  minor,  serratus  posterior  supe- 
rior, splenius  capitis,  multifidus,  interspinales,  semi- 
spinalis dorsi. 

Transverse  process Intertransversarii,    levator     costse,    scalenus    posterior, 

iliocostahs  dorsi  (musculus  accessorius),  scalenus  me- 
dius, semispinalis  capitis  (complexus). 

Articular  process Multifidus,  longissimus  capitis  (trachelomastoid). 

The  cervical  vertebrae  exhibit  great  variation  in  regard  to  the  extremities  of  their  spinous 
processes.  As  a  rule  among  Europeans,  the  second,  third,  fourth,  and  fifth  vertebrae  possess 
bifid  spines.  The  sixth  and  seventh  exhibit  a  tendency  to  bifurcate,  their  tips  presenting  two 
small  lateral  tubercles;  sometimes  the  sixth  has  a  bifid  spine,  and  more  rarely  the  seventh  pre- 


86 


THE  SKELETON 


sents  the  same  condition.  Occasionally  all  the  cervical  spines,  with  the  exception  of  the  second, 
are  non-bifid,  and  even  in  the  axis  the  bifurcation  is  not  extensive.  In  the  lower  races  of  men 
the  cervical  spines  are  relatively  shorter  and  more  stunted  than  in  Europeans  generally  and, 
as  a  rule,  are  simple.  The  only  cervical  vertebra  which  presents  a  bifid  spine  in  all  races  is  the 
axis;  even  this  may  be  non-bifid  in  the  Negro,  and  occasionally  in  the  European.  (Owen, 
Turner,  Cunningham.) 

The  laminae  of  the  lower  cervical  vertebrae  frequently  present  posteriorly  distinct  tubercles 
from  which  fasciculi  of  the  muUifidus  muscle  arise.  They  are  usually  confined  to  the  sixth 
and  seventh  vertebrae,  but  are  fairly  frequent  on  the  fifth,  and  are  occasionally  seen  on  the 
fourth. 

Fig.  40. — Peculiar  Thoracic  Vertebra. 


An  entire  costal  pit 
above  a  half-pit 
below.  In  shape  the 
body  resembles  that 
of  a  cervical  vertebra 


Jsually  a  ha  If-pit 
above  (sometimes  't 
has  a  half-pit  below) 


Usually  an  entire  pit 
above .  Occasionally 
this  pit  is  incomplete 
The  pit  on  the  trans- 
verse process  is  usu- 
ally small 


An  entire  pit  above, 
no  pit  on  transverse 
process  which  is  tri- 
partite; body  large 
Inferior  articular  pro- 
cesses turn  lateral- 
ward  as  in  a  lumbar 
vertebra 


THE  THORACIC  VERTEBRA 

The  general  characters  of  the  thoracic  (or  dorsal)  vertebrae  have  already 
been  considered.  Their  most  distinguishing  features  are  the  pits  on  the  trans- 
verse processes  and  sides  of  the  bodies  for  the  tubercles  and  heads  of  the  ribs 
respectively. 

Peculiar  thoracic  vertebrae. — Several  vertebrae  in  this  series  differ  from  the 
typical  example.  The  exceptional  ones  are — the  first,  ninth,  tenth,  eleventh,  and 
twelfth  (fig.  40).  . 


THE  LUMBAR  VERTEBRM 


37 


The  first  thoracic  vertebra  is  a  transitional  vertebra.  The  body  in  its  general 
conformation  approaches  very  closely  the  seventh  cervical,  in  that  the  greatest 
diameter  is  transverse,  its  upper  surface  is  concave  from  side  to  side,  and  its  lateral 
margins  bear  two  prominent  lips.  On  each  side  is  an  entire  pit,  close  to  the  upper 
border,  for  the  head  of  the  first  rib,  and  a  very  small  pit  (inferior  costal  pit)  below 
for  the  head  of  the  second  rib.  The  spinous  process  is  thick,  strong,  almost  hori- 
zontal and  usually  more  prominent  than  that  of  the  seventh  cervical,  an  important 
point  to  remember  when  counting  the  spines  in  the  living  subject.  Occasionally 
the  transverse  process  is  perforated  near  the  root. 

The  ninth  has  superior  costal  pits,  and  usually  no  inferior;  when  the  inferior 
pits  are  present,  this  vertebra  is  not  exceptional. 

The  tenth  usually  has  an  entire  costal  pit  at  its  upper  border,  on  each  side,  but 
occasionally  only  a  superior  costal  pit.  It  has  no  lower  pits  and  the  pits  on  the 
transverse  processes  are  usually  small. 

The  eleventh  has  a  large  body  resembling  a  lumbar  vertebra.  The  pits  are  on 
the  pedicles  and  they  are  complete  and  of  large  size.  The  transverse  processes  are 
short,  show  evidence  of  becoming  broken  up  into  three  parts,  and  have  no  pits  for 
the  tubercles  of  the  eleventh  pair  of  ribs. 

In  many  mammals,  the  spines  of  the  anterior  vertebrae  are  directed  backward,  and  those 
of  the  posterior  directed  forward,  whilst  in  the  centre  of  the  column  there  is  usually  one  spine 
vertical.  The  latter  is  called  the  anti-clinal  vertebra,  and  indicates  the  point  at  which  the 
thoracic  begin  to  assume  the  characters  of  lumbar  vertebrae.  In  man  the  eleventh  thoracic  is 
the  anti-cUnal  vertebra. 

The  twelfth  resembles  in  general  characters  the  eleventh,  but  may  be  distin- 
guished from  it  by  the  articular  surfaces  on  the  inferior  articular  processes  being 
convex  and  turned  laterally  as  in  the  lumbar  vertebrfe.  The  transverse  process 
is  rudimentary  and  tripartite,  presenting  for  examination  three  tubercles,  superior, 
inferior,  and  lateral,  which  correspond  respectively  to  the  mammillary,  accessory, 
and  transverse  processes  of  the  lumbar  vertebra.  There  is  one  complete  pit  on 
the  root  (pedicle)  for  the  head  of  the  twelfth  rib. 

A  pecuUarity,  more  frequent  in  the  thoracic  and  lumbar  than  in  the  cervical  and  sacral 
regions  of  the  column,  is  the  existence  of  a  half-vertebra.  Such  specimens  have  a  wedge-shaped 
half-centrum,  to  which  are  attached  a  lamina,  a  transverse,  superior,  and  inferior  articular,  and 
half  a  spinous  process.     As  a  rule,  a  half-vertebra  is  ankylosed  to  the  vertebrae  above  and  below. 


THE  LUMBAR  VERTEBRAE 

The  lumbar  vertebrae  (figs.  41,  42)  are  distinguished  by  their  large  size  and  by 
the  absence  of  costal  articular  surfaces. 

The  body  is  somewhat  reniform,  with  the  greatest  diameter  transverse,  flat 
above  and  below,  and  generally  slightly  deeper  in  front  than  behind.     The  roots 


Fig.  41. — A  Lumbar  Vertebra. 


(Side  view.) 

-Superior  articular  process 


Mammillary  process 
Transverse  process 

Accessory  process 


Inferior  articular  process 


(pedicles)  are  strong  and  directed  straight  backward,  and  the  lower  vertebral 
notches  are  deep  and  large.  The  laminae  are  shorter  and  thicker  than  those  of 
the  thoracic  or  cervical  vertebrae,  and  the  vertebral  foramen  is  triangular,  wider 
than  in  the  thoracic,  but  smaller  than  in  the  cervical  region.     The  spinous  process, 


38 


THE  SKELETON 


thick,  broad,  and  somewhat  quadrilateral,  projects  horizontally  backward.  It  is 
thicker  below  than  above  and  terminates  in  a  rough  posterior  edge.  The  articular 
processes  are  thick  and  strong.  The  superior  articular  surface  is  concave  and 
directed  backward  and  medially;  the  inferior  is  convex  and  looks  forward  and 
laterally.  The  superior  pair  are  more  widely  separated  than  the  inferior  pair  and 
embrace  the  inferior  articular  processes  of  the  vertebra  above.  The  posterior 
margin  of  each  superior  articular  process  is  surmounted  by  the  mammillary 
process  or  tubercle  (metapophysis)  which  corresponds  to  the  superior  tubercle 
of  the  transverse  process  of  the  last  thoracic  vertebra.  In  man.  the  mammillary 
tubercles  are  rudimentary,  but  in  some  animals  they  attain  large  proportions,  as 
in  the  kangaroo  and  armadillo.  The  transverse  processes  are  long,  slender, 
somewhat  spatula-shaped,  compressed  from  before  backward,  and  directed 
laterally  and  a  little  backward.  They  are  longest  in  the  third  vertebra  and  dimin- 
ish in  the  fourth,  second,  and  fifth,  in  this  order,  to  the  first,  in  which  they  are 
shortest  of  all.  Their  extremities  are  in  series  with  the  lateral  tubercles  of  the 
transverse  processes  of  the  twelfth  thoracic  vertebra  and  also  with  the  ribs. 
With  the  latter  the  so-called  transverse  processes  in  the  lumbar  region  are  homol- 
ogous, and  hence  they  are  sometimes  called  the  costal  processes.  Occasionally 
the  costal  element  differentiates  and  becomes  a  well-developed  lumbar  rib. 

Fig.  42. — A  Ltjmbar  Vertebra. 
(Showing  the  compound  nature  of  the  transverse  process.     Upper  view.) 


Mammillary  process. 


Accessory  process 
or  tip  of  the  true 
transverse  pro- 
cess 

Costal  element 


Behind  the  base  of  each  transverse  or  costal  process  is  a  small  eminence,  directed  down- 
ward, which  corresponds  with  the  inferior  tubercle  of  the  lower  thoracic  transverse  process, 
and  with  the  transverse  processes  of  the  thoracic  vertebrae  above,  and  is  named  the  accessory 
process  (anapophysis).  The  accessory  process  represents  the  tip  of  the  partially  suppressed 
true  transverse  process  of  a  lumbar  vertebra.  It  is  well  developed  in  some  of  the  lower  animals, 
as  in  the  dog  and  cat. 

Each  of  the  five  lumbar  vertebrae  is  readily  recognized.  The  body  of  the  first 
is  deeper  behind  than  in  front;  the  body  of  the  second  is  equal  in  depth  in  front 
and  behind;  the  bodies  of  the  third,  fourth,  and  fifth  are  deeper  in  front  than 
behind,  but  the  third  has  long  transverse  processes  and  the  inferior  articular 
processes  are  not  widely  separated.  The  fourth  has  shorter  transverse  processes 
and  the  inferior  articular  processes  are  placed  more  widely  apart.  The  fifth 
lumbar  vertebra  deviates  in  some  of  its  features  so  widely  from  the  other  members 
of  the  series  that  special  prominence  must  now  be  given  them. 

The  fifth  lumbar  vertebra  is  massive,  and  the  body  is  much  thicker  in  front 


THE  SACRUM 


39 


than  behind  in  consequence  of  being  bevelled  off  to  form  with  the  sacrum  the  sacro- 
vertebral  angle.  The  transverse  processes  are  short,  thick,  conical,  and  spring 
from  the  body  as  well  as  from  the  roots  of  the  arch.  They  are  very  strong  for  the 
attachment  of  the  ilio-lumbar  ligaments.  The  spinous  process  is  smaller  than 
that  of  any  of  the  other  lumbar  vertebrse;  the  laminae  project  into  the  vertebral 
foramen  on  each  side;  and  the  roots  are  stout  and  flattened  from  above  down- 
ward. The  inferior  articular  processes  are  separated  to  such  a  degree  as  to  be 
wider  apart  than  the  superior,  and  they  articulate  with  the  first  sacral  vertebra. 

The  roots  of  the  arch  in  this  vertebra  are  liable  to  a  remarkable  deviation  from  the  condi- 
tions found  in  other  parts  of  the  spine.  The  peculiarity  consists  of  a  complete  solution  in  the 
continuity  of  the  arch  immediately  behind  the  superior  articular  processes.  In  such  speci- 
mens the  anterior  part  consists  of  the  body  carrying  the  roots,  transverse  and  superior  articu- 
lar processes;  whilst  the  posterior  segment  is  composed  of  the  laminae,  spine,  and  inferior  articu- 
lar processes.  The  posterior  segment  of  the  ring  of  this  vertebra  may  even  consist  of  two  pieces. 
There  is  reason  to  believe  that  this  abnormality  of  the  fifth  lumbar  vertebra  occurs  in  five  per 
cent,  of  aU  subjects  examined.  Sir  William  Turner,  in  his  report  on  the  human  skeletons  in 
the  Challenger  Reports,  found  seven  examples  among  thirty  skeletons  examined.  The  skeletons 
in  which  this  occurred  were: — a  Malay,  an  Andamanese,  a  Chinese,  two  Bushmen,  an  Eskimo, 
and  a  Negro.  Turner  has  also  seen  it  in  the  skeleton  of  a  Sandwich  Islander.  A  similar  con- 
dition is  occasionally  met  with  either  unilaterally  or  bilaterally  in  the  thoracic  vertebrae. 

THE    SACRUM 

The  five  sacral  vertebrse  (figs.  43,  44)  are  united  in  the  adult  to  form  the  os 
sacrum,  a  large,  curved,  triangular  bone,  firmly  wedged  between  the  innominate 
bones,  and  completing,  together  with  the  coccyx,  the  posterior  boundary  of  the 

Fig.  43. — The  Sacrum  and  Coccyx.     (Anterior  view.) 


Inferior  lateral 
angle 


minor  (or  small)  pelvis.  Of  the  five  vertebrae  which  compose  the  sacrum  the 
uppermost  is  the  largest,  the  succeeding  ones  become  rapidly  smaller,  and  the  fifth 
is  quite  rudimentary.  In  the  erect  posture  the  sacrum  lies  obliquely,  being  di- 
rected from  above  downward  and  backward,  and  forms  with  the  last  lumbar 
vertebra  an  anterior  projection  known  as  the  promontory.  The  sacrum  presents 
for  examination  a  pelvic  and  a  dorsal  surface,  two  lateral  margins,  a  base,  and 
an  apex. 

Surfaces. — The  pelvic  surface,  directed  downward  and  forward,  is  smooth, 
concave  from  above  downward  and  slightly  from  side  to  side.     It  is  crossed  in  the 


40 


THE  SKELETON 


middle  by  four  transverse  ridges  [lineae  transversee]  which  represent  the  ossified 
intervertebral  discs  and  separate  the  bodies  of  the  five  sacral  vertebrae.  Of  the 
bodies,  the  first  and  second  are  nearly  equal  in  size  and  are  larger  than  the  third, 
fourth,  and  fifth,  which,  in  vertical  depth,  are  also  nearly  equal  to  each  other.  At 
the  extremities  of  the  transverse  ridges  on  each  side  are  four  openings,  called  the 
anterior  sacral  foramina,  which  correspond  to  the  intervertebral  foramina  in  other 
regions  of  the  column,  and  transmit  the  anterior  divisions  of  the  first  four  sacral 
nerves ;  they  are  also  traversed  by  branches  of  the  lateral  sacral  arteries.  The  fora- 
mina are  separated  by  wide  processes,  representing  the  costal  processes  of  the 
vertebrae,  which  unite  laterally  to  form  the  lateral  portion  (or  mass)  [pars  lateralis]. 
The  latter  is  grooved  for  the  sacral  nerves,  and  rough  opposite  the  second,  third, 
and  fourth  sacral  vertebrae,  for  the  origin  of  the  piriformis  muscle.  The  lateral 
part  of  the  fifth  sacral  vertebra  gives  insertion  to  fibres  of  the  coccygeus. 

.  The  dorsal  surface  is  strongly  convex  and  rough.  The  middle  line  is  occu- 
pied by  four  eminences  representing  the  somewhat  suppressed  spinous  processes. 
Of  these  the  first  is  the  largest,  the  second  and  third  may  be  confluent,  and  the 
fourth  is  often  absent.     The  processes  are  united  to  form  an  irregular  ridge  or 


The  Sacrum.     (Posterior  view.) 


Articular  process 
Auricular  surface 


Articular   process' 
Transverse  process 


Sacral  foramen- 


Multifidus 
Sacro-spinalis 


Gluteus   maximus 


Notch  for  fifth  sacral 


crest  [crista  sacralis  media].  The  bone  on  each  side  of  the  spines  is  slightly 
hollowed  and  is  formed  by  the  united  laminae.  In  the  fourth  sometimes,  but 
always  in  the  fifth,  the  laminae  fail  to  meet  in  the  middle  line,  leaving  a  gap 
[hiatus  sacralis]  at  the  termination  of  the  spinal  canal,  the  lateral  margins  of  which 
are  prolonged  downward  as  the  sacral  cornua.  They  represent  the  lower  articular 
processes  of  the  fifth  sacral  vertebra  and  give  attachment  to  the  posterior  sacro- 
coccygeal ligaments.  Lateral  to  the  laminae  is  a  second  series  of  small  eminences 
which  represent  the  articular  and  mammillary  processes  of  the  vertebrae  above. 
The  first  pair  are  large  for  the  last  lumbar  vertebra,  the  second  and  third  are  small, 
and  the  fourth  and  fifth  are  inconspicuous.  Together  they  form  a  pair  of  irregular 
ridges  [cristae  sacrales  articulares]. 

Immediately  lateral  to  the  articular  processes  are  the  posterior  sacral  fora- 
mina, four  on  each  side;  they  are  smaller  than  the  anterior,  and  give  exit  to  the 
posterior  primary  divisions  of  the  first  four  sacral  nerves.  Lateral  to  the  fora^ 
mina  on  each  side  are  five  elevations  representing  the  transverse  processes.  The 
first  pair,  situated  at  the  junction  of  the  posterior  surface  with  the  base,  are  large 
and  conspicuous,  and  serve  all  for  the  attachment  of  ligaments  and  muscles. 


THE  SACRUM 


41 


Together  they  form  on  each  side  of  the  sacrum  an  irregular  ridge  [crista  saoralis  lateralis]. 
The  space  between  the  spinous  and  transverse  processes  presents  a  shallow  concavity  known  as 
the  sacral  groove,  continuous  above  with  the  vertebral  groove  of  the  movable  part  of  the 
column,  and,  like  it,  lodging  the  multifidus  muscle.  Bridging  across  the  groove  and  attached 
to  the  sacral  spines  medially,  and  to  the  lower  and  back  part  of  the  sacrum  laterally,  is  the  flat 
tendon  of  origin  of  the  sacro-spinalis  {erector  spince) .  The  gluteus  maximus  takes  origin  from  the 
back  of  the  lower  two  pieces  of  the  sacrum. 

The  base  or  upper  surface  of  the  sacrum  bears  considerable  resemblance  to  the 
upper  surface  of  the  fifth  lumbar  vertebra.  It  presents  in  the  middle  the  body,  of 
a  reniform  shape,  posterior  to  which  is  the  upper  end  of  the  sacral  canal  bounded 
by  two  laminae.  On  each  side  of  the  canal  are  two  articular  processes  bearing;well- 
marked  mammillary  tubercles.  The  conjoined  transverse  and  costal  processes 
form  on  each  side  a  broad  surface,  the  wing  or  ala  of  the  sacrum,  continuous  with 
the  iliac  fossa  of  the  hip  bone,  and  giving  attachment  to  a  few  fibres  of  the  iliacus. 

Fig.  45. — Left  Lateral  View  op  Sacrum  and  Coccyx. 


The  lateral  margins. — It  has  already  been  noted  that  the  lateral  portion  of 
the  sacrum  is  the  part  lateral  to  the  foramina.  It  is  broad  and  thick  above, 
where  it  forms  the  ala,  but  narrowed  below.  The  lateral  aspect  of  the  upper 
part  presents  in  front  a  broad  irregular  surface,  covered  in  the  recent  state  with 
fibro-cartilage,  which  articulates  with  the  ilium  and  is  known  as  the  auricular 
surface.  It  is  bounded  posteriorly  by  some  rough  depressions  for  the  attachment 
of  the  posterior  sacro-iliac  ligaments.  Below  the  auricular  surface,  the  lateral 
margin  is  rough  for  the  sacro-tuberous  (greater)  and  sacro-spinous  (lesser  sacro- 
sciatic)  ligaments,  and  terminates  in  the  projection  known  as  the  inferior  lateral 
angle.  Immediately  below  the  angle  is  a  notch,  converted  into  a  foramen  by  the 
transverse  process  of  the  first  coccygeal  vertebra,  and  a  ligament  connecting  this 
with  the  inferior  lateral  angle  of  the  sacrum.  Through  this  foramen  passes"  the 
anterior  branch  of  the  fifth  sacral  nerve. 

The  apex  is  directed  downward  and  forward  and  is  formed  by  the  inferior 
aspect  of  the  body  of  the  fifth  sacral  vertebra.     It  is  transversely  oval  and 


42 


THE  SKELETON 


articulates  by  means  of  an  intervertebral  disc  with  the  coccyx.     In  advanced 
life  the  apex  of  the  sacrum  becomes  united  to  the  coccyx  by  bone. 

The  sacral  canal  is  the  continuation  of  the  spinal  canal  through  the  sacrum. 
Like  the  bone,  it  is  curved  and  triangular  in  form  at  the  base  and  flattened  toward 
the  apex.  It  terminates  at  the  hiatus  sacralis  between  the  sacral  cornua,  where 
the  laminse  of  the  fourth  and  fifth  sacral  vertebrae  are  incomplete.  The  canal 
opens  on  the  surface  by  the  anterior  and  posterior  sacral  foramina  and  lodges  the 
lower  branches  of  the  cauda  equina,  the  filum  terminale,  and  the  lower  extremity 
of  the  dura  and  arachnoid.  The  sub-dural  and  sub-arachnoid  spaces  extend 
downward  within  the  canal  as  far  as  the  body  of  the  third  sacral  vertebra. 

Differences  in  the  two  sexes. — The  sacrum  of  the  female  is  usually  broader  in  proportion 
to  its  length,  much  less  curved,  and  directed  more  obliquely  backward  than  in  the  male.  The 
curvature  of  the  female  sacrum  belongs  chiefly  to  the  lower  part  of  the  bone,  whereas  in  the 
male  it  is  equally  distributed  over  its  whole  length;  but  the  curvature  is  subject  to  considerable 
variation  in  different  skeletons. 


Fig.  46. — Base  of  Sacrum. 

Spinous  process— j^fjf^ij 


cular  process 

Lamina 

Sacral  canal 


Racial  differences. — The  human  sacrum  is  characterised  by  its  great  breadth  in  comparison 
with  its  length,  though  in  the  lower  races  it  is  relatively  longer  than  in  the  higher.  The  propor- 
tion is  expressed  by  the  sacral  index  = . — — rr '     The  average  sacral  index  in  the  British 

male  is  112,  in  the  female  116.     Sacra  in  which  the  index  is  above  100  are  plaiyhieric,  as  in 
Europeans;  those  under  100  are  dolichohieric,  as  in  most  of  the  black  races  (Sir  W.  Turner). 

Fig.  47. — The  Coccyx.     A.  Posterior  view;  B.  Anterior  view. 
A.  B. 


THE  COCCYGEAL  VERTEBRiE 

The  four  coccygeal  vertebrae  are  united  in  the  adult  to  form  the  coccyx  [os 
coccygis]  (fig.  47).  While  four  is  the  usual  number  of  these  rudimentary  vertebrse, 
occasionally  there  are  five,  and  rarely  three.  In  middle  life  the  first  piece  is 
usually  separate,  and  the  original  division  of  the  remaining  portion  of  the  coccyx 


THE  VERTEBRAL  COLUMN  AS  A  WHOLE  43 

into  three  parts  is  indicated  by  transverse  grooves.  In  advanced  life  the  pieces 
of  the  coccyx,  having  previously  united  to  form  one  bone,  may  also  become 
joined  to  the  sacrum. 

The  first  piece  of  the  coccyx  is  much  broader  than  the  others.  It  consists  of  a  body, 
transverse  processes,  and  rudiments  of  a  neural  arch.  The  body  presents  on  its  upper  surface 
an  oval  facet  for  articulation  with  the  apex  of  the  sacrum.  On  each  side  of  the  body  a  trans- 
verse process  projects  laterally  and  is  joined  either  by  ligament  or  bone  to  the  inferior  lateral 
angle  of  the  sacrum,  forming  a  foramen  for  the  anterior  division  of  the  fifth  sacral  nerve.  From 
the  posterior  surface  of  the  body  two  long  coccygeal  cornua  project  upward  and  are  connected  to 
the  sacral  cornua  by  the  posterior  saero-coccygeal  ligaments,  enclosing  on  each  side  an  aperture 
— the  last  intervertebral  foramen — for  the  exit  of  the  fifth  sacral  nerve.  The  coccygeal  cornua 
represent  the  roots  and  superior  articular  processes  of  the  first  coccygeal  vertebra. 

The  second  piece  of  the  coccyx  is  much  smaller  than  the  first,  and  consists  of  a  body, 
traces  of  transverse  processes,  and  a  neural  arch,  in  the  form  of  slight  tubercles  at  the  sides  and 
on  the  posterior  aspect  of  the  body. 

The  third  and  fourth  pieces  of  the  coccyx,  smaller  than  the  second  piece,  are  mere  nodules 
of  bone,  corresponding  solely  to  vertebral  bodies. 

The  anterior  surface  of  the  coccyx  gives  attachment  to  the  anterior  sacro-coccygeal  ligament 
and  near  the  tip  to  the  levator  ani;  it  is  in  relation  with  the  posterior  surface  of  the  rectum. 

The  posterior  surface  of  the  coccyx  is  convex,  and  the  upper  three  pieces  afford  attachment 
to  the  gluteus  maximus  on  each  side,  and  the  last  piece  to  the  coccygeal  portion  of  the  sphincter 
ani  externus. 

The  lateral  margins  are  thin,  and  receive  parts  of  the  sacro-seiatio  ligaments,  of  the 
coccygei  muscles,  and  of  the  levatores  ani. 

THE  VERTEBRAL  COLUMN  AS  A  WHOLE 

The  vertebral  column  (fig.  48)  is  the  central  axis  of  the  skeleton  and  is  situated  in  the 
median  line  at  the  posterior  aspect  of  the  trunk.  Superiorly  it  supports  the  skull;  laterally  it 
gives  attachment  to  the  ribs,  through  which  it  receives  the  weight  of  the  upper  limbs,  and 
inferiorly  it  is  supported  by  the  hip  bones,  by  which  the  weight  of  the  trunk  is  transmitted  to 
the  lower  limbs.  Its  length  varies  in  different  skeletons,  but  on  an  average  it  measures  about 
70  cm.  (28  in.)  in  the  male  and  about  2.5  cm.  (1  in.)  less  in  the  female.  To  the  entire  length  the 
cervical  region  contributes  12.5  cm.  (5  in.),  the  thoracic  27.5  cm.  (11  in.),  the  lumbar  17.5  cm. 
(7  in.),  and  the  sacro-coccygeal  portion  the  remaining  12.5  cm.  (5  in.).  The  vertebral  column 
presents  a  series  of  curvatures,  four  when  viewed  in  profile  and  one  when  viewed  from  the  front 
or  back.  The  former  are  directed  alternately  forward  and  backward,  and  are  named,  from  the 
regions  of  the  column  in  which  they  occur,  cervical,  thoracic,  lumbar,  and  sacral.  The  fifth 
curve  is  lateral,  being  in  most  cases  directed  toward  the  right  side. 

The  cervical,  thoracic  and  lumbar  curvatures  pass  imperceptibly  into  one  another,  but  at 
the  junction  of  the  last  lumbar  vertebra  with  the  sacrum  a  well-marked  angle  occurs,  known  as 
the  sacro-vertebral  or  lumbo-sacral  angle,  with  the  result  that  the  promontory  of  the  sacrum 
overhangs  the  cavity  of  the  minor  (small)  pelvis  and  forms  a  portion  of  the  superior  aperture  of 
the  small  pelvis. 

The  thoracic  and  sacral  curves  have  their  concavities  directed  forward  and  are  developed 
during  intra-uterine  life.  They  are  in  obvious  relation  to  two  great  cavities  of  the  trunk, 
thoracic  and  pelvic,  and  may  be  regarded  as  primary  or  accommodation  curves,  for  the  thoracic 
and  pelvic  viscera.  The  thoracic  curve  extends  from  the  second  to  the  twelfth  thoracic  vertebra 
and  the  sacral  curve  coincides  with  the  sacrum  and  coccyx. 

The  cervical  and  lumbar  curves  have  their  convexities  directed  forward,  and  are  developed 
during  the  first  year  after  birth.  They  are  essentially  curves  of  compensation,  necessary  for 
the  maintenance  of  the  upright  posture,  and  are  brought  about  by  modifications  in  the  shape 
of  the  intervertebral  discs.  The  cervical  curve  is  formed  about  the  third  month,  or  as  soon  as 
the  infant  can  sit  upright.  The  great  pecuharity  of  the  curve  is  that  it  is  never  consolidated, 
being  present  when  the  body  is  placed  in  the  erect  position  and  obliterated  by  bending  the  head 
down  upon  the  chest.  The  lumbar  curve  is  developed  about  the  end  of  the  first  year  or  when  the 
child  begins  to  walk,  but  is  not  consolidated  until  adult  life.  (Symington.)  The  cervical  curve 
extends  from  the  atlas  to  the  second  thoracic  vertebra,  and  the  lumbar  curve  from  the  twelfth 
thoracic  to  the  promontory  of  the  sacrum. 

The  lateral  curve  is  situated  in  the  upper  thoracic  region,  and  when  directed  to  the  right  is 
probably  associated  with  the  greater  use  made  of  the  right  hand.  This  curve,  however,  is 
particularly  liable  to  modification  in  different  occupations  and  in  different  races. 

Viewed  from  the  front,  the  vertebral  column  presents  a  series  of  pyramids  due  to  the 
successive  increase  and  decrease  in  size  of  the  bodies.  These  become  broader  from  the  axis  to 
the  first  thoracic  vertebra  and  then  decrease  to  the  fourth  thoracic.  The  first  pyramid  therefore 
includes  all  the  cervical  vertebrae  except  the  atlas,  and  has  the  apex  directed  upward  and  its 
base  downward,  whilst  the  second  is  inverted  and  formed  by  the  first  four  thoracic  vertebrae. 
The  third  pyramid,  much  the  longest,  is  the  result  of  the  increase  in  size  from  the  fourth  thoracic 
to  the  fifth  lumbar  vertebra,  and  the  fourth,  which  is  inverted,  is  produced  by  the  rapid  contrae-  ■ 
tion  of  the  sacral  and  coccygeal  vertebriE. 

Viewed  from  behind,  the  spinous  processes  project  in  the  middle  Hne,  and  the  transverse 
processes  as  two  lateral  rows.  Of  the  spines,  those  of  the  axis,  seventh  cervical,  first  thoracic, 
and  the  lumbar  vertebrae  appear  most  prominent.  On  each  side  is  the  vertebral  groove,  the 
floor  of  which  is  formed  in  the  cervical  and  lumbar  regions  by  the  laminae  and  articular  processes, 


44 


THE  SKELETON 


Fig.  48. — Vertebral  Column.     (Lateral;  view.) ' 
Atlas ^«&a^^T 


Epistropheus  "- 


Vertebra  prominens  . 


Vff 


iin 


OSSIFICATION  OF  VERTEBRA 


45 


and  in  the  thoracic  region,  by  the  laminae  and  transverse  processes.  The  transverse  processes 
project  laterally  for  a  considerable  distance  in  the  atlas,  first  thoracic,  and  the  middle  of 
the  lumbar  series;  they  are  shortest  in  the  third  cervical  and  the  twelfth  thoracic. 

In  the  lateral  view,  the  intervertebral  foramina  appear  oval  in  shape,  and  are  small  in  the 
cervical,  larger  in  the  thoracic,  and  largest  in  the  lumbar  region. 

Structure  o£  a  vertebra. — The  bodies  of  the  vertebrae  are  largely  composed  of  cancellous 
tissue,  with  a  thin  outer  covering  of  compact  tissue.     In  a  vertical  section  through  the  centrum 

Fig.  49. — A  Divided  Thoracic  Vertebra.     (After  Turner-.) 


the  fibres  of  the  cancellous  tissue  are  seen  to  be  arranged  vertically  and  horizontally,  the  vertical 
fibres  being  curved  with  their  concavities  directed  toward  the  centre  of  the  bone.  The  hori- 
zontal fibres  are  slightly  curved  parallel  with  the  upper  and  lower  surfaces,  and  have  their  con- 
vexities toward  the  centre  of  the  bone.  They  are  not  so  well  defined  as  the  vertical  set. 
(Wagstaffe.) 

Ossification. — The  vertebrae  in  general. — The  ossification  of  each  vertebra  takes  place 
in   cartilage  from  three    primary   and  five  secondary   centres.     The  three    primary  centres 

Fig.   50. — A  Vertebral  Centrum  in  Section  to  Show  the  Pressure  Curves. 


appear,  one  in  the^body  and  two  in  the  arch,  about  the  seventh  week  of  intra-uterine  life. 
In  the  thoracic  region  the  nucleus  for  the  body  appears  first,  but  in  the  cervical  region  it  is  pre- 
ceded by  the  centres  for  the  arch.  The  nucleus  for  the  body  soon  becomes  bilobed,  and  this 
condition  is  sometimes  so  pronounced  as  to  give  rise  to  the  appearance  of  two  distinct  nuclei. 
Indeed,  the  nucleus  is  very  rarely  double  and  the  two  parts  of  the  body  may  remain  separate 
throughout  life  (fig.  49).  The  bilateral  character  of  the  nucleus  is  further  emphasised  by  the 
occasional  formation  of  half-vertebrje.     The  lateral  centres  are  deposited  near  the  bases  of  the 


Fig.  51. — A  Vertebra  at  Birth. 


Neuro-central  suture 
Centrum  or  body 


Superior  articular  processes  and  give  rise  to  the  roots,  laminae,  articular,  and  the  greater 
parts  of  the  tran8.verse  and  spinous  processes. 

At  birth  a  typical  vertebra  consists  of  three  osseous  pieces — a  body  and  two  lateral  masses, 
which  constitute  the  arch,  the  parts  being  joined  together  by  hyahne  cartilage.  The  line  of 
union  of  the  lateral  portion  with  the  body  is  known  as  the  neuro-ceniral  suture,  and  is  not  actually 
obliterated  for  several  years  after  birth.  In  the  thoracic  region  the  central  ossification  does  not 
pass  beyond  the  point  with  which  the  head  of  the  rib  articulates,  and  leaves  a  portion  of  the  bodj' 
on  each  side  formed  from  the  lateral  ossification.     A  thoracic  vertebra  at  the  fifth  year  shows 


46 


THE  SKELETON 


that  the  pits  for  the  heads  of  the  ribs  are  situated  behind  the  neuro-central  suture,  which  is 
directed  obhquely  backward  and  medially.  The  laminae  unite  during  the  first  year  after  birth; 
and  by  the  gradual  extension  of  ossification  into  the  various  processes,  the  vertebrae  have  at- 
tained almost  their  full  size  by  the  time  of  puberty.  Subsequently  the  secondary  centres 
appear  in  the  cartilaginous  extremities  of  the  spinous  and  transverse  processes,  and  in  the  carti- 


FiQ.  52.- 


-Cervical  Vertebra  showing  the  Epiphysial  Plate  on  the  Upper  Surface  op 
THE  Body. 


lage  on  the  upper  and  lower  surfaces  of  the  bodies,  forming  in  each  vertebra  two  annular  plates, 
thickest  at  the  circumference  and  gradually  thinning  toward  the  central  deficiency.  The 
epiphyses  appear  from  the  fifteenth  to  the  twentieth  year  and  join  with  the  vertebra  by  the 
twenty-fifth  year. 

Fig.  53. — Lumbar  Vertebra  at  the  Eighteenth  Year  with  Secondary  Centres. 
Epiphysial  plate  or  disc 


Mammillary  tubercle 
Transverse  process 
Spinous  process 


Epiphysial  plate 


In  several  vertebrae  the  mode  of  ossification  differs  from  the  account  given  above — in  some 
cases  considerably — and  necessitates  separate  consideration. 

Atlas. — The  lateral  portions  and  posterior  arch  are  formed  from  two  centres  of  ossification, 
which  correspond  to  the  lateral  centres  of  other  vertebrae  and  appear  about  the  seventh  week. 

Fig.  54. — Upper  Thoracic  Vertebra  with  an  Epiphysial  Plate  Removed  and  Drawn  at 

the  Side. 
The  plate  shows  the  characteristic  deficiency  in  the  centre.     (Natural  size.) 


The  anterior  arch  is  ossified  from  one  centre,  which,  however,  does  not  appear  until  a  few  months 
after  birth.  Union  of  the  lateral  parts  occurs  posteriorly  in  the  third  year,  being  sometimes 
preceded  by  the  appearance  of  a  secondary  centre  of  ossification  in  the  intervening  cartilage, 
and  the  union  of  the  lateral  parts  with  the  anterior  arch  occurs  about  the  sixth  year. 


EPISTROPHEUS 


47 


Epistropheus. — The  arch,  and  the  processes  associated  with  it,  are  formed  from  two  lateral 
centres  which  appear,  like  those  in  the  other  vertebras,  about  the  seventh  week.  The  common 
piece  of  cartilage  which  precedes  the  body  and  dens  is  ossified  from  four  (or  five)  centres,  one 
(or  two)  for  the  body  of  the  axis,  in  the  fourth  month,  two,  laterally  disposed,  for  the  dens,  a 

Fig.  55. — Immature  Atlas.     (Third  year.) 


few  weeks  later,  and  one,  for  the  apex  of  the  dens,  in  the  second  year.  The  two  collateral  centres 
for  the  main  part  of  the  dens  soon  coalesce,  so  that  at  birth  the  axis  consists  of  four  osseous  pieces 
— two  lateral  portions  which  constitute  the  arch,  the  body,  and  the  dens,  surmounted  by  a 
piece  of  cartilage.     During  the  third  or  fourth  year  the  dens  joins  with  the  body,  the  line  of 


i 


Fig. 

Suspensory  ligament 
Nucleus  for  tip  of  odontoid  dens- 
Lateral  centres  for  odontoid  dens' 


)iphysial  plate  or  disC' 
Pedicle 


■Development  of  the  Epistkopheus. 


Centrum  or  body. 
Epiphysial  plate 


union  being  indicated  even  in  advanced  life  by  a  small  disc  of  cartilage,  and  the  arch  unites  in 
front  and  behind  about  the  same  time  or  a  little  later.  The  apical  nucleus  of  the  dens,  which 
represents  an  epiphysis,  joins  the  main  part  about  the  twelfth  year  and  in  the  seventeenth  year 


Fig.  57.- 


-The  Epistropheus  at  Four  Years  op  Age,  showing  the  Size  and  Extent  of 
the  Dens.     (Natural  size.) 


an  epiphysial  plate  appears  for  the  lower  surface  of  the  body.     There  are   also  rudiments, 
adjoining  the  cartilaginous  disc,  of  the  upper  epiphysial  plate  of  the  body. 

Cervical  vertebrse. — In  the  cervical  vertebrae  the  lateral  centres  form  a  larger  share  of  the 
body  than  in  the  vertebrae  of  other  regions,  and  the  neuro-central  suture  runs  almost  in  a  sag- 

FiG.  58. — The  Epistropheus  (prom  an  Adult)  in  Sagittal  Section. 


Dens  (odontoid  process) 


Cartilage  representing  the  inter- 
vertebral  disc  between  the  dens 
and  the  body  of  the  epistropheus 


Body  of  epistropheus 


ittal  direction.  The  sixth,  seventh,  and  even  the  fifth  have  additional  centres  which  appear 
before  birth  for  the  anterior  or  costal  divisions  of  the  transverse  processes.  In  the  other  cer- 
vical vertebrae  the  costal  processes  are  ossified  by  extension  of  the  lateral  nuclei.  The  costal 
processes  of  the  seventh  cervical  sometimes  remain  separate,  constituting  cervical  ribs. 


48 


THE  SKELETON 


Lumbar  vertebrae. — In  the  lumbar  vertebrEe  the  neuro-oentral  suture  is  almost  transverse, 
and  to  the  usual  number  of  centres  of  ossification,  two  other  epiphyses  for  the  mammillary 
tubercles  are  added,  the  centres  appearing  about  puberty.  The  transverse  process  of  the  first 
lumbar  vertebra  is  occasionally  developed  from  an  independent  centre. 

The  fifth  lumbar  exhibits  in  some  cases  a  special  mode  of  ossification  in  the  arch.  Instead 
of  two  centres,  there  are  four — one  on  each  side  for  the  root,  transverse  process,  and  supe- 

FiG.  59. — An  Immature  Cervical  Vertebra. 


Neuro-central  suture 


rior  articular  process,  and  another  on  each  side  for  the  lamina,  inferior  articular  process,  and  the 
lateral  half  of  the  spinous  process  (fig.  60).  There  may  be  failure  of  union  of  roots  with  the 
laminae  or  of  the  laminae  with  one  another. 

Sacral  vertebree. — The  sacrum  ossifies  from  thirty-five  centres,  which  may  be  classified  as 
follows ; — In  each  of  the  five  vertebrae  there  are  three  primary  nuclei — one  for  the  body  and  two 
for  the  arch;  in  each  of  the  first  three  the  costal  element  of  the  lateral  mass  on  each  side  is 

Fig.  60. — Ossification  of  the  Fifth  Lumbar  Vertebra. 


Neuro-central  suture. 
Centrum^ 


formed  from  a  separate  nucleus;  associated  with  each  body  are  two  epiphysial  plates;  and  on 
each  lateral  margin  are  two  irregular  epiphyses,  one  for  the  auricular  surface  and  another  for 
the  rough  edge  below. 

The  centres  for  the  bodies  appear  about  the  eighth  or  ninth  week  and  for  the  vertebral 
arches  about  the  sixth  month.     The  arches  join  the  bodies  at  difi'erent  times  in  the  different 

Fig.  61. — Sacrum  at  Birth  to  show  Centres  op  Ossification.     (Enlarged  one-third.) 

Ossific  centre  in  the  body  of  first  sacral  vertebra. 
Beneath  this  are  seen  in  succession  the  centres  in  the 
bodies  of  the  second,  third,  fourth,  and  fifth  vertebras 


Ossific  centres  in  the  lateral  mass^      \         yi^\ 


vertebrae,  ranging  from  the  second  year  below,  to  the  fifth  or  sixth  year  above,  and  union  of  the 
laminae  takes  place  behind  some  years  later,  from  about  the  ninth  to  the  fifteenth  year. 

The  centres  for  the  costal  elements  appear  outside  the  anterior  sacral  foramina,  from  the 
fifth  to  the  seventh  month,  and  these  unite  with  the  bodies  somewhat  later  than  the  arches. 

The  centres  for  the  epiphysial  plates  appear  about  the  fifteenth  year,  and  for  the  auricular 
epiphyses  and  the  edges  below,  from  the  eighteenth  to  the  twentieth  year. 


COCCYGEAL  VERTEBRA 


49 


Consolidation  begins  soon  after  puberty  by  fusion  of  the  costal  processes,  and  this  is  followed 
by  ossification  from  below  upward  in  the  intervertebral  discs,  resulting  in  the  union  of  the 
adjacent  bodies  and  the  epiphysial  plates,  the  ossific  union  of  the  first  and  second  being  com- 
pleted by  the  twenty-fifth  year  or  a  little  later.     The  marginal  epiphyses  are  also  united  to  the 


Fig.  62.- 


-Thb  Sacrum  at  Four  Years  of  Age  (B).     The  Figure  at  the  Top  (A)  Shows 
THE  Base  Drawn  from  Above.     (Three-fourths  natural  size.) 


icle  and  transverse  proces 


Cartilage 
Costal  process 
Cartilage 


i 


Cartilage  covering  lateral  mass 


Cartilaginous  disc 


Ossification  in  first  piece  of  coccyx 


sacrum  by  the  twenty-fifth  year.     Even  in  advanced  life  intervertebral  discs  persist  in  the 
more  central  parts  of  the  bone  and  can  be  well  seen  in  sections. 

Coccygeal  vertebrae. — The  coccygeal  vertebrae  are  cartilaginous  at  birth  and  each  is  usually 
ossified  from  a  single  centre,  though  there  may  be  two  for  the  first  piece.  Ossification  be- 
gins soon  after  birth  in  the  first  segment,  and  in  the  second  from  the  fifth  to  the  tenth  year. 

Fig.  63. — Sacrum  at  about  Twenty-two  Years.     (Three-fifths'natural  size.) 

Epiphysial  plate  on  the  upper  surface  of  body  of  first  sacral  vertebra 


Lateral  epiphyses  appear  at  eighteen 
(    years  and  join  at  twenty-five 


The  centres  for  the  third  and  fourth  segments  appear  just  before,  and  after,  puberty  respec- 
tively. As  age  advances  the  various  pieces  become  united  with  each  other,  the  three  lower 
uniting  before  middle  life  and  the  upper  somewhat  later.  In  advanced  life  the  coccyx  maj'  join 
with  the  sacrum,  the  union  occurring  earUer  and  more  frequently  in  the  male  than  in  the  female. 


50 


THE  SKELETON 


The  Serial  Morphology  of  the  Vertebrae 

Although  at  first  sight  many  of  the  vertebrae  exhibit  peculiarities,  nevertheless  a  study 
of  the  mode  by  which  they  develop,  and  their  variations,  indicates  the  aerial  homology  of>  the 
constituent  parts  of  the  vertebrae  in  each  region  of  the  column. 

The  body  (centrum)  of  the  vertebra  is  that  part  which  immediately  surrounds  the  noto- 
chord.  This  part  is  present  in  all  the  vertebrae  of  man,  but  the  centrum  of  the  atlas  is  disso- 
ciated from  its  arch,  and  ankylosed  to  the  body  of  the  epistropheus.     The  reasons  for  regard- 


FiG.  64. — Morphology  of  the  Tkansverse  and  Articular  Processes. 


Cervical  vertebra 


Transverse  process 
Costo-transverse  foramen 


Transverse  process 
Costo-transverse  foramen 


Neuro-central  suture 
Rib 


.Transverse  process 
Lumbar  rib 


Sacral  vertebra 


Netiro-central  suture 
Costal  process 


ing  the  dens  as  the  body  of  the  atlas  are  these:  In  the  embryo  the  notochord  passes  through 
it  on  its  way  to  the  base  of  the  cranium.  Between  the  dens  and  the  body  of  the  axis  there  is 
a  swelling  of  the  notochord  in  the  early  embryo  as  in  other  intervertebral  regions.  This  swell- 
ing is  later  indicated  by  a  small  intervertebral  disc  hidden  in  the  bone,  but  persistent  even  in 
old  age.  Moreover,  the  dens  ossifies  from  primary  centres,  and  in  chelonians  it  remains  as  a 
separate  ossicle  throughout  life;  in  Ornithorhynchus  it  remains  distinct  for  a  long  time,  and  it 
has  been  found  separate  even  in  an  adult  man.     Lastly,  in  man  and  many  mammals,  an  epi- 


BONES  OF  THE  SKULL  51 

physial  plate  develops  between  it  and  the  body  of  the  axis.  The  anterior  arch  of  the  atlas 
represents  a  cartilaginous  hypochordal  bar,  which  is  present  in  the  early  stages  of  development 
of  the  vertebrae,  but  disappears  in  all  but  the  atlas  in  the  ossification  of  the  body. 

The  arches  and  spinous  processes  are  easily  recognised  throughout  the  various  parts  of  the 
column  in  which  complete  vertebrae  are  present. 

The  articular  processes  or  zygapophyses  are  of  no  morphological  value,  and  do  not  require 
consideration  here. 

•The  transverse  processes  offer  more  difficulty.  They  occur  in  the  simplest  form  in  the  tho- 
racic series.  Here  they  articulate  with  the  tubercles  of  the  ribs,  whence  the  term  tubercular 
processes  or  diapophyses  has  been  given  them  (the  place  of  articulation  of  the  head  of  the  rib 
with  the  vertebra  is  the  capitular  process  or  parapophysis),  and  the  transverse  process  and  the 
neck  of  the  rib  enclose  an  arterial  foramen  named  the  costo-transverse  foramen.  In  the  cer- 
vical region  the  costal  element  (pleur apophysis)  and  the  transverse  process  are  fused  together, 
and  the  conjoint  proce.ss  thus  formed  is  pierced  by  the  costo-transverse  foramen.  The  com- 
pound nature  of  the  process  is  indicated  by  the  fact  that  the  anterior  or  costal  processes  in  the 
lower  cervical  vertebrte  arise  from  additional  centres  and  occasionally  retain  their  independence 
as  cervical  ribs,  and  in  Sauropsida  (birds  and  reptiles)  these  processes  are  represented  by  free 
ribs.  In  the  lumbar  region,  the  compound  nature  of  the  transverse  process  is  further  marked. 
The  true  transverse  process  is  greatly  suppressed,  and  its  extremity  is  indicated  by  the  accessory 
tubercle.  Anterior  to  this  in  the  adult  vertebrae  a  group  of  holes  represents  the  costo-transverse 
foramen,  and  the  portion  in  front  of  this  is  the  costal  element.  Occasionally  it  persists  as  an 
independent  ossicle,  the  lumbar  rib. 

In  the  sacral  series  the  costal  elements  are  coalesced  in  the  first  three  vertebrae  to  form  the 
greater  portion  of  the  lateral  portion  for  articulation  with  the  ilium,  the  costo-transverse  fora- 
mina being  completely  obscured.  In  rare  instances  the  first  sacral  vertebra  will  articulate  with 
the  ilium  on  one  side,  but  remain  free  on  the  other,  and  under  such  conditions  the  free  process 
exactly  resembles  the  elongated  transverse  process  of  a  lumbar  vertebra.  The  first  three  sacral 
vertebrae  which  develop  costal  processes  for  articulation  with  the  ilium  are  termed  true  sacral 
vertebrae,  while  the  fourth  and  fifth  are  termed  pseudo-sacral.  A  glance  at  fig.  64  will  show  the 
homology  of  the  various  parts  of  a  vertebra  from  the  cervical,  thoracic,  lumbar,  and  sacral 
regions. 


B.  BONES  OF  THE  SKULL 

The  skull  is  the  expanded  upper  portion  of  the  axial  skeleton  and  is  supported 
on  the  summit  of  the  vertebral  column.  It  consists  of  the  cranium,  a  strong  bony 
case  enclosing  the  brain  and  made  up  of  eight  bones — viz.,  occipital,  tvs^o  parietal, 
frontal,  two  temporal,  sphenoid,  ethmoid;  and  the  bones  of  the  face,  surrounding 
the  mouth  and  nose,  and  forming  with  the  cranium  the  orbital  cavity  for  the 
reception  of  the  eye.  The  bones  of  the  face  are  fourteen  in  number — viz.,  two 
maxillae,  two  zygomatic  {malar),  two  nasal,  two  lacrimal,  two  palate,  two  inferior 
conchoe  {turbinates),  the  mandible,  and  the  vomer.  All  the  bones  enumerated 
above,  with  the  exception  of  the  mandible,  are  united  by  suture  and  are  therefore 
immovable.  The  proportion  between  the  facial  and  cranial  parts  of  the  skull 
varies  at  different  periods  of  life,  being  in  the  adult  about  one  (facial)  to  two 
(cranial),  and  in' the  new-born  infant  about  one  to  eight.  A  group  of  movable 
bones,  comprising  the  hyoid,  suspended  from  the  basilar  surface  of  the  cranium, 
and  three  small  bones,  the  incus,  malleus,  and  stapes,  situated  in  the  middle  ear  or 
tympanic  cavity,  is  also  included  in  the  enumeration  of  the  bones  of  the  skull. 

According  to  the  BNA  nomenclature,  the  term  cranium  is  used  in  a  wider  sense  as  synony- 
mous with  skull,  and  is  subdivided  into  cranium  cerebrate  (cranium  in  the  narrower  sense)  and 
cranium  viscerate  (facial  skeleton).  In  the  BNA,  seven  bones  above  listed  with  the  facial, — 
two  inferior  conchae,  two  lacrimal,  two  nasal  and  the  vomer — are  classed  with  the  cranium 
cerebrate. 

THE  OCCIPITAL 

The  occipital  bone  [os  occipitale]  (fig.  65)  is  situated  at  the  posterior  and 
inferior  part  of  the  cranium.  In  general  form  it  is  flattened  and  trapezoid  in 
shape,  curved  upon  itself  so  that  one  surface  is  convex  and  directed  backward 
and  somewhat  downward,  while  the  other  is  concave  and  looks  in  the  opposite 
direction.  It  is  pierced  in  its  lower  and  front  part  by  a  large  aperture,  the  foramen 
magnum,  by  which  the  vertebral  canal  communicates  with  the  cavity  of  the 
cranium. 

The  occipital  bone  is  divisible  into  four  parts,  basilar,  squamous,  and  two 
condylar,  so  arranged  around  the  foramen  magnum  that  the  basilar  part  lies  in 
front,  the  condylar  parts  on  either  side,  and  the  squamous  part  above  and  behind. 


52 


THE  SKELETON 


Speaking  generally,  this  division  corresponds  to  the  four  separate  parts  of  which  the  bone 
consists  at  the  time  of  birth  (fig.  69),  known  as  the  basi-occipital,  supra-occipital,  and  ex- 
occipital.  In  early  life  these  parts  fuse  together,  the  lines  of  junction  of  the  supra-occipital  and 
ex-occipitals  extending  lateralward  from  the  posterior  margin  of  the  foramen  magnum,  and 
those  of  the  ex-occipitals  and  basi-occipital  passing  through  the  condyles  near  their  anterior 
extremities.  It  must  be  noted,  however,  that  the  upper  portion  of  the  squamous  part  represents 
an  additional  bone,  the  interparietal. 

The  squamous  part  [squama  occipitalis]  (supra-occipital  and  interparietal) 
presents  on  its  convex  posterior  surface,  and  midway  between  the  superior  angle 
and  the  posterior  margin  of  the  foramen  magnum,  a  prominent  tubercle  known 
as  the  external  occipital  protuberance,  from  which  a  vertical  ridge — the  external 
occipital  crest — runs  downward  and  forward  as  far  as  the  foramen.  The  pro- 
tuberance and  crest  give  attachment  to  the  ligamentum  nuchse. 


Fig.  65. — The  Occipital.     (External  view.) 

External  occipital  protuberance 


Trapezius 
Semispinalis  capitis 


Area  covered  by 
scalp 


Rectus  capitis  anterior 
Longus  capitis 


'Attachment  of  superior  constrictor  of 
pharynx  to  pharyngeal  tubercle 


Arching  lateralward  on  each  side  from  the  external  occipital  protuberance 
toward  the  lateral  angle  of  the  bone  is  a  semicircular  ridge,  the  superior  nuchal 
line  [linea  nuchce  superior],  which  divides  the  surface  into  two  parts — an  upper 
[planum  occipitale]  and  a  lower  [planum  nuchale].  Above  this  line,  a  second  less 
distinctly  marked  ridge — the  highest  nuchal  line  [linea  nuchse  suprema] — is 
usually  seen.  It  is  the  most  curved  of  the  three  lines  on  this  surface  and  gives 
attachment  to  the  epicranial  aproneuosis  and  to  a  few  fibres  of  the  occipitalis 
muscle.  Between  the  superior  and  highest  curved  lines  is  a  narrow  crescentic 
area  in  which  the  bone  is  smoother  and  denser  than  the  rest  of  the  surface,  whilst 
the  part  of  the  bone  above  the  hnea  suprema  is  convex  and  covered  by  the  scalp. 

The  lower  part  of  the  surface  is  ver.y  uneven  and  subdivided  into  an  upper 
and  a  lower  area  by  the  inferior  nuchal  line,  which  runs  laterally  from  the  middle 
of  the  crest  to  the  jugular  process. 


THE  OCCIPITAL  BONE 


53 


The  curved  lines  and  the  areas  thus  mapped  out  between  and  below  them  give  attachment 
to  several  muscles.  To  the  superior  nuchal  line  are  attached,  medially  the  trapezius,  and 
laterally  the  occipitalis  and  sterno-cleido-mastoid;  the  area  between  the  superior  and  inferior 
curved  lines  receives  the  semispinalis  capitis  (complexus)  medially,  and  splenius  capitis  and 
ohliquus  capitis  superior  laterally;  the  inferior  nuchal  line  and  the  area  below  it  afford  insertion 
to  the  rectus  capitis  posterior  minor  and  major. 

The  anterior  or  cerebral  surface  is  deeply  concave  and  marked  by  two  grooved 
ridges  which  cross  one  another  and  divide  the  surface  into  four  fossse  of  which 
the  two  upper,  triangular  in  form,  lodge  the  occipital  lobes  of  the  cerebrum,  and 
the  two  lower,  more  quadrilateral  in  outline,  the  lobes  of  the  cerebellum.  The 
vertical  ridge  extends  from  the  superior  angle  to  the  foramen  magnum  and  the 
transverse  ridge  from  one  lateral  angle  to  the  other,  the  point  of  intersection  being 
indicated   by   the  internal   occipital   protuberance    [eminentia   cruciata].     The 

Fig.  66. — -Occipital  Bone,  Cerebral  Stjefacb. 

Superior  angle 


Cerebral  fossa 


Groove  for  transverse  sinus 


Lateral  angle 


Cerebellar  fossa 


Groove  for  transverse  smus 

Jugular  process 

For    petrosal 


i 


upper  part  of  the  vertical  ridge  is  grooved  [sulcus  sagittalis]  for  the  superior 
sagittal  {longitudinal)  sinus  and  gives  attachment,  by  its  margins,  to  the  falx 
cerebri;  the  lower  part  is  sharp  and  known  as  the  internal  occipital  crest,  and 
affords  attachment  to  the  falx  cerebelli.  Approaching  the  foramen  magnum 
the  ridge  divides,  and  the  two  parts  become  lost  upon  its  margin.  The  angle 
of  divergence  sometimes  presents  a  shallow  fossa  for  the  extremity  of  the  vermis 
of  the  cerebellum,  and  is  called  the  vermiform  fossa.  The  two  parts  of  the 
transverse  ridge  are  deeply  grooved  [sulcus  transversus]  for  the  transverse 
{lateral)  sinuses,  and  the  margins  of  the  groove  give  attachment  to  the  tentorium 
cerebelli.  To  one  side  of  the  internal  occipital  protuberance  is  a  wide  space, 
where  the  vertical  groove  is  continued  into  one  of  the  lateral  grooves  (more 
frequently  the  right),  and  this  is  termed  the  torcular  Herophili;  it  is  sometimes 
exactly  in  the  middle  line. 

The  squamous  portion  has  three  angles  and  four  borders.  The  superior  angle 
forming  the  summit  of  the  bone  is  received  into  the  space  formed  by  the  union  of 
the  two  parietals.  The  lateral  angles  are  ver}'  obtuse  and  correspond  in  situatio  n 
with  the  lateral  ends  of  the  transverse  ridges.  Above  the  lateral  angle  on  each 
side  the  margin  is  deeply  serrated,  forming  the  lambdoid  or  superior  border 
which  extends  to  the  superior  angle  and  articulates  with  the  posterior  border  of 
the  parietal  in  the  lambdoid  suture.     The  mastoid  or  inferior  border  extends 


54  THE  SKELETON 

from  the  lateral  angle  to  the  jugular  process  and  articulates  with  the  mastoid 
portion  of  the  temporal. 

The  condylar  or  lateral  portions  [partes  laterales]  (ex-occipitals)  form  the 
lateral  boundaries  of  the  foramen  magnum  and  bear  the  condyles  on  their  in- 
ferior surfaces.  The  condyles  are  two  convex  oval  processes  of  bone  with  smooth 
articular  surfaces,  covered  with  cartilage  in  the  recent  state,  for  the  superior 
articular  processes  of  the  atlas.  They  converge  in  front,  and  are  somewhat 
everted.  Their  margins  give  attachment  to  the  capsular  ligaments  of  the 
occipito-atlantal  joints  and  on  the  medial  side  of  each  is  a  prominent  tubercle 
for  the  alar  (lateral  odontoid)  ligament.  The  anterior  extremities  of  the  condyles 
extend  beyond  the  ex-occipitals  on  the  basi-occipital  portion  of  the  bone.  The 
hypoglossal  (anterior  condyloid)  foramen  or  canal  [canalis  hypoglossi]  perforates 
the  bone  at  the  base  of  the  condyle,  and  is  directed  from  the  interior  of  the 
cranium,  just  above  the  foramen  magnum,  forward  and  laterally;  it  transmits 
the  hypoglossal  nerve  and  a  twig  of  the  ascending  pharyngeal  artery. 

The  foramen  is  sometimes  double,  being  divided  by  a  delicate  spicule  of  bone.  Above  the 
canal  is  a  smooth  convexity  known  as  the  tuberculum  jugulare  sometimes  marked  by  an  oblique 
groove  for  the  ninth,  tenth  and  eleventh  cranial  nerves.     Posterior  to  each  condyle  is  a  pit,  the 

Fig.  67. — Cerebral  Surface  of  the  Occipital,  Showing  an  Occasional  Disposition  of 

THE  Channels. 


Vermiforin  fossa 


Condylar  foramen 
Hypoglossal  foramen. 


condylar  fossa,  which  receives  the  hinder  edge  of  the  superior  articular  process  of  the  atlas  when 
the  head  is  extended.  The  floor  of  the  depression  is  occasionally  perforated  by  the  condylar 
(posterior  condyloid)  canal  or  foramen  [canalis  condyloideus],  which  transmits  a  vein  from  the 
transverse  sinus.  Projecting  laterally  opposite  the  condyle  is  a  quadi'ilateral  portion  of  bone 
known  as  the  jugular  process,  the  extremity  of  which  is  rough  for  articulation  with  the  jugular 
facet  on  the  petrous  portion  of  the  temporal  bone.  Up  to  twenty-five  years  the  bones  are  united 
here  by  means  of  cartilage;  about  this  age  ossification  of  the  cartilage  takes  place,  and  the  jugular 
process  thus  becomes  fused  with  the  petrosal.  Its  anterior  border  is  deeply  notched  to  form  the 
posterior  boundary  of  the  jugular  foramen,  and  the  notch  is  directly  continuous  with  a  groove 
on  the  upper  surface  which  lodges  the  termination  of  the  transverse  sinus.  In  or  near  the  groove 
is  seen  the  inner  opening  of  the  condylar  foramen.  The  lower  surface  of  the  process  gives 
attachment  to  the  rectus  capitis  lateralis  and  the  oblique  occipito-atlantal  ligament.  Occa- 
sionally the  mastoid  air  cells  extend  into  this  process  and  rarely  a  process  of  bone,  representing 
the  paramastoid  process  of  many  mammals,  projects  downward  from  its  under  aspect  and  may 
be  so  long  as  to  join  or  articulate  with  the  transverse  process  of  the  atlas. 

The  basilar  portion  (basi-occipital)  is  a  quadrilateral  plate  of  bone  projecting 
forward  and  upward  in  front  of  the  foramen  magnum.  Its  superior  surface 
presents  a  deep  groove — the  basilar  groove  [chvus];  it  supports  the  medulla 
oblongata  and  gives  attachment  to  the  tectorial  membrane  (occipito-axial 
ligament).  The  lower  surface  presents  in  the  middle  line  a  small  elevation 
known  as  the  pharyngeal  tubercle  for  the  attachment  of  the  fibrous  raphe  of  the 
pharynx,  and  immediately  in  front  of  the  tubercle  there  is  frequently  a  shallow 


THE  OCCIPITAL  BONE 


55 


fossa — the   scaphoid   fossa — which   originally   received  the   primitive    anterior 
extremity  of  the  foregut. 

On  each  side  of  the  middle  line  are  impressions  for  the  insertions  of  the  longus  capitis  (rectus 
capitis  anterior  major)  and  rectus  capitis  anterior  (minor),  the  impression  for  the  latter  being 


Fig.  68. — The  Foramen  Magnum  at  the  Sixth  Year. 


Condylar  foramen 


Ex-occipital  portion  of  the 
condyle,  J 


Hypoglossal  foramen. 
Basi-occipital    portion'  I  of 
the  condyle 


i 


Basi-occipitaj 


nearer  to  the  condyle,  and  near  the  foramen  magnum  this  surface  gives  attachment  to  the 
anterior  occipito-atlantal  ligament.  Anteriorly  the  basilar  process  articulates  by  synchondrosis 
with  the  body  of  the  sphenoid  up  to  twenty  years  of  age,  after  which  there  is  complete  bony 
union.  Posteriorly  it  presents  a  smooth  rounded  border  forming  the  anterior  boundary  of 
the  foramen  magnum.     It  gives  attachment  to  the  apical  odontoid  ligament,  and  above  this 


Fig.  69. — The  Occipital  at  Birth.     (Anterior  view.) 


Interparietal     portion     (develops     in' 
membrane) 


The  interparietal  and  supra-occipital 
portions  form  the  squamous  portion 
of  the  adult 

Supra-occipital  portion  (develops  in 
cartilage) 


to  the  ascending  portion  of  the  crucial  ligament.  In  the  occipital  bone  at  the  sixth  year  the 
lateral  extremities  of  this  border  are  enlarged  to  form  the  basilar  portion  of  the  condyles.  The 
lateral  borders  are  rough  below  for  articulation  with  the  petrous  portion  of  the  temporal  bones, 
but  above,  on  either  side  of  the  basilar  groove,  is  a  half-groove,  which,  with  a  similar  half  -groove 
on  the  petrous  portion  of  the  temporal  bone,  lodges  the  inferior  petrosal  sinus. 


56 


THE  SKELETON 


The  foramen  magnum  is  oval  in  shape,  with  its  long  axis  in  a  sagittal  direc- 
tion. It  transmits  the  medulla  oblongata  and  its  membranes,  the  accessory 
nerves  (spinal  portions) ,  the  vertebral  arteries,  the  anterior  and  posterior  spinal 


Fia.  70. — The  Occipital  with  a  Separate  Interparietal. 


arteries,  and  the  tectorial  membrane  (occipito-axial  ligament).  It  is  widest 
behind,  where  it  transmits  the  medulla,  and  is  narrower  in  front,  where  it  is 
encroached  upon  by  the  condyles. 

Fig.  71. — Skull  showing  a  Pre-inteeparietal  Bone  (P.I.)- 


Occasionally  a  facet  is  present  on  the  anterior  margin,  forming  a  third  occipital  condyle  for 
articulation  with  the  dens.  Between  the  condyles  and  behind  the  margin  of  the  foramen  mag- 
num the  posterior  occipito-atlantal  ligament  obtains  attachment. 

Blood-supply. — The  occipital  bone  receives  its  blood-supply  from  the  occipital,  posterior 
auricular,  middle  meningeal,  vertebral  and  the  ascending  pharyngeal  arteries. 

Articulations. — The  occipital  bone  is  connected  by  suture  with  the  two  parietals,  the  two 
temporals,  and  the  sphenoid;  the  condyles  articulate  with  the  atlas,  and  exceptionally  the  occip- 
ital articulates  with  the  dens  of  the  epistropheus  by  means  of  the  third  occipital  condyle. 


THE  PARIETAL  BONE  57 

Ossification. — The  occipital  bone  develops  in  four  pieces.  The  squamous  portion  is  ossi- 
fied from  four  centres,  arranged  in  two  pairs,  which  appear  about  the  eighth  week.  The 
upper  pair  are  deposited  m  membrane,  and  this  part  of  the  squamous  portion  represents  the 
interparietal  bone  of  many  animals.  The  lower  oair,  deposited  in  cartilage,  form  the  true 
supra-ocoipital  element,  and  the  four  parts  quickly  coalesce  near  the  situation  of  the  future 
occipital  protuberance.  For  many  weeks  two  deep  lateral  fissures  separate  the  interparietal 
and  supraoccipital  portions,  and  a  membranous  space  extending  from  the  centre  of  the  squamous 
portion  to  the  foramen  magnum  partially  separates  the  lateral  portions  of  the  supra-occipital. 
This  space  is  occupied  later  by  a  spicule  of  bone,  and  is  of  interest  as  being  the  opening  through 
which  the  form  of  hernia  of  the  brain  and  its  rneninges,  known  as  occipital  meningocele  or  en- 
cephalocele,  occurs.  The  basi-occipital  and  the  two  ex-occipitals  are  ossified  each  from  a  single 
nucleus  which  appears  in  cartilage  from  the  eighth  to  the  tenth  week. 

At  birth  the  Ijone  consists  of  four  parts  united  by  strips  of  cartilage,  and  in  the  squamous 
portion  fissures  running  in  from  the  upper  and  lateral  angles  are  still  noticeable.  The  osseous 
union  of  the  squamous  and  ex-occipital  is  completed  in  the  fifth  year,  and  that  of  the  ex- 
occipitals  with  the  basi-occipital  before  the  seventh  year.  Up  to  the  twentieth  year  the  basi- 
occipital  is  united  to  the  body  of  the  sphenoid  by  an  intervening  piece  of  cartilage,  but  about 
that  date  ossific  union  begins  and  is  completed  in  the  course  of  two  or  three  years.  Occasionally 
the  interparietal  portion  remains  separate  throughout  Ufe  (fig.  70),  forming  what  has  been 
termed  the  inca  hone,  or  it  may  be  represented  by  numerous  detached  ossicles  or  Wormian 
bones.  In  some  cases  a  large  Wormian  bone,  named  the  pre-interparietal,  is  found,  partly 
replacing  the  interparietal  bone  (fig.  71).  A  pre-interparietal  bone  is  found  in  some  mammals, 
and  it  has  occasionally  been  observed  in  the  human  foetal  skull.  In  fig.  71  the  bone  is  seen  in 
an  adult  human  skull — a  distinctly  rare  condition. 
I 

THE  PARIETAL 

The  two  parietal  bones  (figs.  72,  73),  interposed  between  the  frontal  before 
and  the  occipital  behind,  form  a  large  portion  of  the  roof  and  sides  of  the  cranium. 
Each  parietal  bone  [os  parietale]  is  quadrilateral  in  form,  convex  externally, 
concave  internally,  and  each  presents  for  examination  two  surfaces,  four  borders, 
and  four  angles. 

The  parietal  surface  is  smooth  and  is  crossed,  just  below  the  middle,  by  two 
curved  lines  known  as  the  temporal  lines.  The  superior  line  gives  attachment 
to  the  temporal  fascia;  the  lower,  frequently  the  better  marked,  limits  the  origin 
of  the  temporal  muscle;  whilst  the  narrow  part  of  the  surface  enclosed  between 
them  is  smooth  and  more  poHshed  than  the  rest.  Immediately  above  the  ridges 
is  the  most  convex  part  of  the  bone,  termed  the  parietal  eminence  [tuber  parietale], 
best  marked  in  young  bones,  and  indicating  the  point  where  ossification  com- 
menced. Of  the  two  divisions  on  the  parietal  surface  marked  off  by  the  temporal 
lines,  the  upper  is  covered  by  the  scalp,  and  the  lower,  somewhat  striated,  ait'ords 
attachment  to  the  temporal  muscle.  Close  to  the  upper  border  and  near  to  the 
occipital  angle  is  a  small  opening — the  parietal  foramen — which  transmits  a  vein 
to  the  superior  sagittal  {longitudinal)  sinus. 

The  cerebral  surface  is  marked  with  depressions  corresponding  to  the  cerebral 
convolutions  and  by  numerous  deep  furrows,  running  upward  and  backward 
from  the  sphenoidal  angle  and  the  lower  border,  for  the  middle  meningeal  vessels 
(sinus  and  artery).  A  shallow  depression  running  close  to  the  superior  border 
forms,  with  the  one  of  the  opposite  side,  a  channel  for  the  superior  sagittal  sinus, 
at  the  side  of  which  are  small  irregular  pits  for  the  Pacchionian  bodies;  the  pits 
are  usually  present  in  adult  skulls,  but  are  best  marked  in  those  of  old  persons. 
The  margins  of  the  groove  for  the  superior  sagittal  sinus  give  attachment  to  the 
falx  cerebri. 

Borders. — The  sagittal  or  superior  border,  the  longest  and  thickest,  is  deeply 
serrated  to  articulate  with  the  opposite  parietal,  with  which  it  forms  the  sagittal 
suture.  The  frontal  or  anterior  border  articulates  with  the  frontal  to  form  the 
coronal  suture.  It  is  deeply  serrated  and  bevelled,  so  that  it  is  overlapped  by  the 
frontal  above,  but  overlaps  the  edge  of  that  bone  below.  The  occipital  or 
posterior  border  articulates  with  the  occipital  to  form  the  lambdoid  suture,  and 
resembles  the  superior  and  anterior  in  being  markedly  serrated.  The  squamosal 
or  inferior  border  is  divided  into  three  portions : — the  anterior,  thin  and  bevelled, 
is  overlapped  by  the  tip  of  the  great  wing  of  the  sphenoid;  the  middle  portion, 
arched  and  also  bevelled,  is  overlapped  by  the  squamous  part  of  the  tempora,l; 
and  the  posterior  portion,  thick  and  serrated,  articulates  with  the  mastoid 
portion  of  the  temporal  bone. 

Angles. — The  frontal  or  anterior  superior,  almost  a  right  angle,  occupies  that 
part  of  the  bone  which  at  birth  is  membranous  and  forms  part  of  the  anterior 


58 


THE  SKELETON 


fontanelle.  The  sphenoidal  or  anterior  inferior  angle  is  thin  and  prolonged 
downward  to  articulate  with  the  tip  of  the  great  wing  of  the  sphenoid.  Its  inner 
surface  is  marked  by  a  deep  groove,  sometimes  converted  into  a  canal  for  a  short 

Fig.  72. — The  Left  Parietal.     (Outer  surface.) 

Sagittal  border  Parietal  foramen 


Portion  covered  by 


Superior  temporal    line 


Inferior  temporal    line 

For  temporal  muscle, 
and  forms  part  of 
the  temporal  fossa 


Sphenoidal  angle' 


Fig.  73. — The  Left  Parietal.     (Inner  surface.) 
Parietal  foramen       Groove  for  superior  sagittal  sinus       Depressions  for  Pacchionian  bodies 


Groove  for  transverse 


Grooves  for  middle  meningeal  artery 


distance,  for  the  middle  meningeal  vessels  (chiefly  for  the  sinus).  The  occipital 
or  posterior  superior  angle  is  obtuse  and  occupies  that  part  which  during  foetal 
life  enters  into  formation  of  the  posterior  fontanelle.     The  mastoid  or  posterior 


THE  FRONTAL  BONE 


59 


inferior  angle  is  thick  and  articulates  with  the  mastoid  portion  of  the  temporal 
bone.  Its  inner  surface  presents  a  shallow  groove  which  lodges  a  part  of  the 
transverse  (lateral)  sinus. 

Blood-supply. — The  parietal  bone  receives  its  blood-supply  from  the  middle  meningeal, 
occipital,  and  supra-orbital  arteries. 

Articulations. — The  parietal  articulates  with  the  occipital,  frontal,  sphenoid,  temporal, 
its  fellow  of  the  opposite  side,  and  the  epipterio  bone  when  present.  Occasionally  the  temporal 
and  epipteric  bones  exclude  the  parietal  from  articulation  with  the  great  wing  of  the  sphenoid. 

Ossification. — The  parietal  ossifies  from  a  single  nucleus  which  appears  in  the  outer  layer 
of  the  membranous  wall  of  the  skull  about  the  seventh  week.  The  ossification  radiates  in 
such  a  way  as  to  leave  a  cleft  at  the  upper  part  of  the  bone  in  front  of  the  occipital  angle,  the 

Fig.  74. — Unusual  Form  op  Pabietal  Exhibiting  a  Horizontal  Suture  Separating  the 
Bone  into  Two  Pif.ces,  Upper  and  Lower. 


^f^^^^^^^sy^m 


cleft  of  the  two  side  forming  a  lozenge-shaped  space  across  the  sagittal  suture  known  as  the  sag- 
ittal fontanelle.  This  is  usually  closed  about  the  fifth  month  of  intra-uterine  life,  but  traces  may 
sometimes  be  recognised  at  the  time  of  birth,  and  the  parietal  foramina  are  to  be  regarded  as 
remains  of  the  cleft.  According  to  Dr.  A.  W.  W.  Lea,  a  well-developed  sagittal  fontanelle  is 
present  in  4 . 4  per  cent,  of  infants  at  birth.  In  such  cases  it  closes  within  the  first  two  months 
of  life,  but  at  times  it  may  remain  open  for  at  least  eight  months  after  birth  and  possibly  longer. 
Rarely  the  parietal  bone  is  composed  of  two  pieces  (fig.  74),  one  above  the  other,  and 
separated  by  an  antero-posterior  suture  (sub-sagittal  suture),  more  or  less  parallel  with  the 
sagittal  suture.     In  such  cases  the  parietal  is  ossified  from  two  centres  of  ossification. 


THE  FRONTAL 

The  frontal  bone  [os  frontale]  closes  the  cranium  in  front  and  is  situated  above 
the  skeleton  of  the  face.  It  consists  of  two  portions — a  frontal  {vertical)  portion 
[squama  frontalis],  forming  the  convexity  of  the  forehead,  and  an  orbital  {hori- 
zontal) portion,  which  enters  into  formation  of  the  roof  of  each  orbit. 

Frontal  {vertical)  portion. — The  frontal  surface  is  smooth  and  convex,  and 
usually  presents  in  the  middle  line  above  the  root  of  the  nose  some  traces  of  the 
suture  which  in  young  subjects  traverses  the  bone  from  the  upper  to  the  lower 
part.  This  suture,  known  as  the  frontal  or  metopic  suture,  indicates  the  line  of 
junction  of  the  two  lateral  halves  of  which  the  bone  consists  at  the  time  of  birth; 
in  the  adult  the  suture  is  usually  obliterated  except  at  its  lowest  part.  On  each 
side  is  a  rounded  elevation,  the  frontal  eminence  [tuber  frontale],  very  prominent 
in  young  bones,  below  which  is  a  shallow  groove,  the  sulcus  transversus,  separat- 
ing the  frontal  eminence  from  the  superciliary  arch.  The  latter  forms  an  arched 
pi^ojection  above  the  margin  of  the  orbit  and  corresponds  to  an  air-cavity  within 
the  bone  known  as  the  frontal  sinus;  it  gives  attachment  to  the  orbicularis  oculi 
and  the  corrugator  muscles.     The  ridges  of  the  two  sides  converge  toward  the 


' 


60 


THE  SKELETON 


median  line,  but  are  separated  by  a  smooth  surface  called  the  glabella  (nasal 
eminence).  Below  the  arch  the  bone  presents  a  sharp  curved  margin,  the  supra- 
orbital border,  forming  the  upper  boundary  of  the  circumference  of  the  orbit  and 
separating  the  frontal  from  the  orbital  portion  of  the  bone.  At  the  junction  of 
its  medial  and  intermediate  third  is  a  notch,  sometimes  converted  into  a  foramen, 
and  known  as  the  supra-orbital  notch  or  foramen ;  it  transmits  the  supra-orbital 
nerve,  artery,  and  vein,  and  at  the  bottom  of  the  notch  is  a  small  opening  for 
a  vein  of  the  diploe  which  terminates  in  the  supra-orbital.  Sometimes,  a  second 
less  marked  notch  is  present,  medial  to  the  supra-orbital,  and  known  as  the 
frontal  notch;  it  transmits  one  of  the  divisions  of  the  supra-orbital  nerve.  The 
extremities  of  the  supra-orbital  border  are  directed  downward  and  form  the 
medial  and  zygomatic  (lateral  angular)  processes.  The  prominent  zygomatic  proc- 
ess articulates  with  the  zygomatic  bone  and  receives  superiorly  two  well-marked 
lines  which  converge  somewhat  as  they  curve  downward  and  forward  across  the 
bone.     These  are  the  superior  and  inferior  temporal  lines,  continuous  with  the 


Fig.  75. — The  Frontal.     (Anterior  view.) 


'Temporal  line 


Supra-orbital  notch 
Zygomatic  process 


temporal  lines  on  the  parietal  bone,  the  upper  giving  attachment  to  the  temporal 
fascia  and  the  lower  to  the  temporal  muscle.  Behind  the  lines  is  a  slight  con- 
cavity which  forms  part  of  the  fioor  of  the  temporal  fossa  and  gives  origin  to  the 
temporal  muscle.  The  medial  angular  processes  articulate  with  the  lacrimals 
and  form  the  lateral  limits  of  the  nasal  notch,  bounded  in  front  by  a  rough, 
semilunar  surface  which  articulates  with  the  upper  ends  of  the  nasal  bones  and 
the  frontal  (nasal)  processes  of  the  maxillae. 

In  the  concavity  of  the  notch  hes  the  nasal  portion  of  the  frontal,  which  projects  somewhat 
beneath  the  nasal  bones  and  the  nasal  processes  of  the  maxillfe.  It  is  divisible  into  three  parts: 
— a  median  frontal  (nasal)  spine,  which  descends  in  the  nasal  septum  between  the  crest  of  the 
nasal  bones  in  front  and  the  vertical  plate  of  the  ethmoid  behind,  and,  on  the  posterior 
aspect  of  the  process,  two  alee,  one  on  either  side  of  the  median  ridge  from  which  the  frontal 
(nasal)  spine  is  continued.  Each  ala  forms  a  small  grooved  surface  which  enters  into  the 
formation  of  the  roof  of  the  nasal  fossa. 

The  cerebral  surface  presents  in  the  middle  line  a  vertical  groove — the  sagittal 
sulcus — which  descends  from  the  middle  of  the  upper  margin  and  lodges  the 
superior  sagittal  (longitudinal)  sinus.  Below,  the  groove  is  succeeded  by  the 
frontal  crest,  which  terminates  near  the  lower  margin  at  a  small  notch,  converted 
into  a  foramen  by  articulation  with  the  ethmoid. 


THE  FRONTAL  BONE 


61 


The  foramen  is  called  the  foramen  caecum,  and  is  generally  closed  below,  but  sometimes 
transmits  a  vein  from  the  nasal  fossje  to  the  superior  sagittal  (longitudinal)  sinus.  The  frontal 
crest  serves  for  the  attachment  of  the  anterior  part  of  the  falx  cerebri.  On  each  side  of  the 
middle  line  the  bone  is  deeply  concave,  presentino:  depressions  for  the  cerebral  convolutions 
and  numerous  small  furrows  which,  running  medially  from  the  lateral  margin,  lodge  branches  of 
the  middle  meningeal  vessels.  At  the  upper  part  of  the  surface,  on  either  side  of  the  frontal 
sulcus,  are  some  depressions  for  Pacchionian  bodies. 

The  horizontal  portion  consists  of  two  somewhat  triangular  plates  of  bone 
called  the  orbital  plates,  which,  separated  from  one  another  by  the  ethmoidal 

Fig.  76. — The  Frontal  Bone.    (Inferior  view.) 
Frontal  spine 

Articulation  with  nasal 

bone 
Articulation  with  max- 
illa ^<Jitf^'^-  -  '^^fst&i^li  l«Ktf\  iillillllWIIIIiillli 

Trochlear  fossa 

Lacrimal  fossa 

Orbital  surface 


ulation  with 
papyracea 
of  ethmoid 
Articulation  with 

zygomatic 
Articulation  with 

greater  wing  of 

sphenoid 
Articulation  with 

lesser  wing  of 

sphenoid 


{ 


Ethmoidal  notch 


notch  [incisura  ethmoidalis],  form  the  greater  part  of  the  roof  of  each  orbit.  When 
the  bones  are  articulated,  the  notch  is  filled  up  by  the  cribriform  plate  of  the 
ethmoid,  and  the  half -cells  on  the  upper  surface  of  the  lateral  mass  of  the  ethmoid 
are  completed  by,  the  depressions  or  half -cells  which  occupy  the  irregular  margins 
of  the  notch.  Traversing  these  edges  transversely  are  two  grooves  which  com- 
plete, with  the  ethmoid,  the  anterior  and  posterior  ethmoidal  canals.  The 
anterior  transmits  the  anterior  ethmoidal  nerve  and  vessels;  the  posterior  trans- 
mits the  posterior  ethmoidal  nerve  and  vessels,  and  both  canals  open  on  the 
medial  wall  of  the  orbit.  Farther  forward,  on  either  side  of  the  nasal  spine,  are 
the  openings  of  the  frontal  sinuses,  two  irregular  cavities  which  extend  within 

Fig.  77. — The  Frontal  Bone  at  Birth. 


the  bone  for  a  variable  distance  and  give  rise  to  the  superciliary  arches  (ridges) . 
Each  is  lined  by  mucous  membrane  and  communicates  with  the  nasal  fossa  by 
means  of  a  passage  called  the  infundibulum. 

The  inferior  surface  of  each  orbital  plate,  smooth  and  concave,  presents  im- 
mediately behind  the  lateral  angular  process  the  lacrimal  fossa,  for  the  lacrimal 
gland.  Close  to  the  medial  angular  process  is  a  depression  called  the  trochlear 
fossa  [fovea  trochlearis],  which  gives  attachment  to  the  cartilaginous  pulley  for 
the  superior  oblique  muscle.  The  superior  surface  of  each  plate  is  convex  and 
strongly  marked  by  eminences  and  depressions  for  the  convolutions  on  the  orbital 
surface  of  the  cerebrum. 


62 


THE  SKELETON 


Borders. — The  articular  border  of  the  frontal  portion  (parietal  margin)  forms  a  little  more 
than  a  semicircle.  It  is  thick,  strongly  serrated,  and  bevelled  so  as  to  overlap  the  parietal 
above  and  to  be  overlapped  by  the  edge  of  that  bone  below.  The  border  is  continued  inferiorly 
into  a  triangular  rough  surface  on  either  side,  which  articulates  with  the  great  wing  of  the  sphe- 
noid. The  posterior  border  of  the  orbital  portion  is  thin  and  articulated  with  the  lesser  wing 
of  the  sphenoid. 

Blood-supply. — The  blood-vessels  for  the  supply  of  the  vertical  portion  are  derived 
from  the  frontal  and  supra-orbital  arteries,  which  enter  on  the  outer  surface,  and  from  the 
middle  and  small  meningeal,  which  enter  on  the  cerebral  surface.  The  horizontal  portion 
receives  branches  from  the  ethmoidal,  and  other  branches  of  the  ophthalmic,  as  well  as  from 
the  meningeal. 

Articulations. — The  frontal  articulates  with  the  parietal,  sphenoid,  ethmoid,  lacrimal, 
zygomatic  (malar),  maxilla,  and  nasal  bones.  Also,  with  the  epipteric  bones  when  present, 
and  occasionally  with  the  squamous  portion  of  the  temporal,  and  with  the  sphenoidal  concha 
when  it  reaches  the  orbit. 

Fig.  78. — Unusually  Large  Frontal  Sinuses. 


Ossification. — The  frontal  is  ossified  from  two  nuclei  deposited  in  the  outer  layer  of  the 
membranous  wall  of  the  cranium,  in  the  situations  ultimately  known  as  the  frontal  eminences. 
These  nuclei  appear  about  the  eighth  week,  and  ossification  spreads  quickly  through  the  mem- 
brane. At  birth  the  bones  are  quite  distinct,  but  subsequently  they  articulate  with  each  other 
in  the  median  line  to  form  the  metopie  suture.  In  the  majority  of  cases  the  suture  is  obliter- 
ated by  osseous  union,  which  commences  about  the  second  year,  though  in  a  few  cases  the 
bones  remain  distinct  throughout  life. 

After  the  two  halves  of  the  bone  have  united,  osseous  material  is  deposited  at  the  lower 
end  of  the  metopie  suture  to  form  the  frontal  spine,  which  is  one  of  the  distinguishing  features 
of  the  human  frontal  bone.  The  spine  appears  about  the  twelfth  year,  and  soon  consolidates 
with  the  frontal  bone  above.  Accessory  nuclei  are  sometimes  seen  between  this  bone  and  the 
lacrimal  and  may  persist  as  Wormian  ossicles. 

The  frontal  sinuses  appear  about  the  seventh  year  as  prolongations  upward  from  the  hiatus 
semilunaris  and  increase  in  size  up  to  old  age.  As  they  grow  they  extend  in  three  directions, 
viz.,  upward,  laterally,  and  backward  along  the  orbital  roof.  A  bony  septum,  usually  com- 
plete, separates  the  sinuses  of  the  two  sides,  and  they  are  larger  in  the  male  than  in  the  female. 
The  supercihary  arches  are  not  altogether  reliable  guides  as  to  the  size  of  the  sinuses,  since 
examples  are  seen  in  which  the  arches  are  low  and  the  sinuses  large.  In  fig.  78  an  example 
of  unusually  large  sinuses  is  figured,  illustrating  the  extension  upward,  laterally,  and  backward. 


THE  SPHENOID 


The  sphenoid  [os  sphenoidale]  (figs.  79,  80,  81,  82)  is  situated  in  the  base  of 
the  skull  and  takes  part  in  the  formation  of  the  floor  of  the  anterior,  middle,  and 
posterior  cranial  fossae,  of  the  temporal  and  nasal  fossae,  and  of  the  cavity  of  the 
orbit.  It  is  very  irregular  in  shape  and  is  described  as  consisting  of  a  central 
part  or  body,  two  pairs  of  lateral  expansions  called  the  great  and  small  wings, 
and  a  pair  of  processes  which  project  downward,  called  the  pterygoid  processes. 

The  body,  irregularly  cuboidal  in  shape,  is  hollowed  out  into  two  large  cavities 
known  as  the  sphenoidal  sinuses,  separated  by  a  thin  sphenoidal  septum  and 
opening  in  front  by  two  large  apertures  into  the  nasal  fossae.     The  superior  sur- 


THE  SPHENOID 


63 


face  presents  the  following  points  for  examination:  In  front  is  seen  a  prominent 
spine,  the  ethmoidal  spine,  which  articulates  with  the  hinder  edge  of  the  cribri- 
form plate  of  the  ethmoid.  The  sm-face  behind  this  is  smooth  and  frequently 
presents  two  longitudinal  grooves,  one  on  either  side  of  the  median  line,  for  the 
olfactory  bulbs;  it  is  limited  posteriorly  by  a  ridge,  the  limbus  sphenoidalis, 
which  forms  the  anterior  border  of  the  narrow  transverse  optic  groove  [sulcus 
chiasmatis],  above  and  behind  which  lies  the  optic  commissure.  The  groove 
terminates  on  each  side  in  the  optic  foramen,  which  perforates  the  root  of  the 
small  wing  and  transmits  the  optic  nerve  and  the  ophthalmic  artery.  Behind  the 
optic  groove  is  the  tuberculum  sellae,  indicating  the  line  of  junction  of  the  two 
parts  of  which  the  body  is  formed  (pre-  and  post-sphenoid);  and  still  further 
back,  a  deep  depression,  the  hypophyseal  fossa  [sella  turcica],  which  lodges  the 
hypophysis  cerebri.  The  floor  of  the  fossa  presents  numerous  foramina  for 
blood-vessels,  and  at  birth  the  superior  orifice  of  a  narrow  passage  called  the 
basi-pharyngeal  canal  opens  on  the  tuberculum.  The  posterior  boundary  of  the 
fossa  is  formed  by  a  quadrilateral  plate  of  bone,  the  dorsum  sellae   (dorsum 

Fig.  79. — The  Sphenoid,  from  Above. 


Optic  groove    Ethmoidal  spine  .         .... 

Optic  Tuberculum  sellse      Superior  orbital  fissure 


Articulation 
with  frontal 


Articulation 
with  parietal 
Cerebral  surface 
of  great  wing 
Foramen  rotundum 

Foramen  Vesalii 


Foramen  spinosum 


Carotid  groove 
Posterior  petrosal  process 


Dorsum  sellae 
Posterior  clinoid  process 


ephippii),  the  posterior  surface  of  which  is  sloped  in  continuation  mth  the  basilar 
groove  of  the  occipital  bone.  The  superior  angles  of  the  plate  are  surmounted 
by  the  posterior  clinoid  processes,  which  give  attachment  to  the  tentorium  cere- 
belli  and  the  interclinoid  ligaments.  Below  the  clinoid  process,  on  each  side  of 
the  dorsum  sellffi  (sometimes  at  the  suture  between  the  sphenoid  and  apex  of 
petrosal),  a  notch  is  seen,  converted  into  a  foramen  by  the  dura  mater,  for  the 
passage  of  the  sixth  cranial  nerve,  and  at  the  inferior  angle  the  posterior  petrosal 
process,  which  articulates  with  the  apex  of  the  petrous  portion  of  the  temporal 
bone,  forming  the  inner  boundary  of  the  foramen  lacerum.  The  dorsum  sellse 
is  slightly  concave  posteriorly  (the  clivus)  and  supports  the  pons  Varolii  and  the 
basilar  artery. 

The  inferior  surface  presents  in  the  middle  line  a  prominent  ridge  known  as 
the  rostrum,  which  is  received  into  a  deep  depression  between  the  alee  of  the 
vomer.  On  each  side  is  the  vaginal  process  of  the  medial  pterygoid  plate, 
directed  horizontally  and  medially,  which,  with  the  alee  of  the  vomer,  covers  the 
greater  part  of  this  surface.  The  remainder  is  rough  and  clothed  by  the  mucous 
membrane  of  the   roof  of  the  pharynx. 

The  anterior  surface  is  divided  into  two  lateral  halves  by  the  sphenoidal 
crest,  a  vertical  ridge  of  bone  continuous  above  with  the  ethmoidal  spine,  below 
with  the  rostrum,  and  articulating  in  front  with  the  perpendicular  plate  of  the 
ethmoid.  The  surface  on  each  side  presents  a  rough  lateral  margin  for  articula- 
tion with  the  lateral  mass  of  the  ethmoid  and  the  orbital  process  of  the  palate 
bone.     Elsewhere  it  is  smooth,  and  enters  into  the  formation  of  the  roof  of  the 


64 


THE  SKELETON 


nasal  fossae,   presenting  superiorly  the  irregular   apertures  of  the  sphenoidal 
sinuses. 

The  body  is  not  hollowed  until  after  the  sixth  year,  but  from  that  time  the  sinuses  increase 
in  size  as  age  advances.  Except  for  the  apertures  just  mentioned,  they  are  closed  below  and 
in  front  by  the  two  sphenoidal  conchse  (turbinate  bones),  originally  distinct,  but  in  the  adult 
usually  incorporated  with  the  sphenoid. 

The  posterior  surface  is  united  to  the  basilar  process  of  the  occipital,  up  to 
the  twentieth  year,  by  a  disc  of  hyaline  cartilage  forming  a  synchondrosis,  but 
afterward  this  becomes  ossified  and  the  two  bones  then  form  one  piece. 

Fig.  80. — The  Left  Half  of  the  Sphenoid. 


Anterior  clinoid  process 

Middle  clinoid  process 

Posterior  clinoid  process 


Spine  of  sphenoid 

Lateral  pterygoid  plate- 

Hamular  process  of  medial  pterygoid  platt 


Ethmoidal  spine 

— -The  limbus 
Optic  groove 
Tuberculum  sella 


Dorsum  sellee 


The  lateral  surface  of  the  body  gives  attachment  to  the  two  wings,  and  its 
fore  part  is  free  where  it  forms  the  medial  boundary  of  the  superior  orbital  fissure  and 
the  posterior  part  of  the  medial  wall  of  the  orbit.  Above  the  line  of  attachment 
of  the  great  wing  is  a  broad  groove  which  lodges  the  internal  carotid  artery  and 
the  cavernous  sinus,  called  the  carotid  groove.  It  is  deepest  where  it  curves  behind 
the  root  of  the  process,  and  this  part  is  bounded  along  its  lateral  margin  by  a 
slender  ridge  of  bone  named  the  lingula,  which  projects  backward  in  the  angle 
between  the  body  and  the  great  wing. 

Fig.  81. — The  Sphenoid.     (Anterior  view.) 


Orbital  surface  (the  pointer"^ 
crosses  the  zygomatic 
border) 


Lateral  pterygoid  plate 
Pterygoid  notch, 
Hamular  process- 


Pterygo-palatine  groove 


The  small  or  orbital  wings  [alse  parvse]  are  two  thin,  triangular  plates  of  bone 
extending  nearly  horizontally  and  laterally  on  a  level  with  the  front  part  of  the 
upper  surface  of  the  body.  Each  arises  medially  by  two  processes  or  roots,  the 
upper  thin  and  flat,  the  lower  thick  and  rounded. 

Near  the  junction  of  the  lower  root  with  the  body  is  a  small  tubercle  for  the  attachment  of 
the  common  tendon  of  three  ocular  muscles — viz.,  the  superior,  medial,  and  upper  head  of 
lateral  rectus — and  between  the  two  roots  is  the  optic  foramen.  The  lateral  extremity,  slender 
and  pointed,  approaches  the  great  wing,  but,  as  a  rule,  does  not  actually  touch  it.  The  supe- 
rior surface,  smooth  and  slightly  concave,  forms  the  posterior  part  of  the  anterior  fossa  of  the 
cranium.     The  inferior  surface  constitutes  a  portion  of  the  roof  of  each  orbit  and  overhangs 


THE  SPHENOID  65 

the  superior  orbital  (or  sphenoidal)  fissure,  the  elongated  opening  between  the  small  and  great 
wings.  The  anterior  border  is  serrated  for  articulation  with  the  orbital  plate  of  the  frontal, 
and  the  posterior  border,  smooth  and  rounded,  is  received  into  the  Sylvian  fissure  of  the  cere- 
brum. Moreover,  the  posterior  border  forms  the  boundary  between  the  anterior  and  middle 
cranial  fossse  and  is  prolonged  at  its  medial  extremity  to  form  the  anterior  clinoid  process, 
which  gives  attachment  to  the  tentorium  cerebelli  and  the  interclinoid  ligaments.  Between 
the  tuberoulum  sellse  and  the  anterior  chnoid  process  is  a  semicircular  notch  which  represents 
the  termination  of  the  carotid  groOve.  It  is  sometimes  converted  into  a  foramen,  the  carotico- 
clinoid  foramen,  by  a  spicule  of  bone  which  bridges  across  from  the  anterior  clinoid  to  the  middle 
clinoid  process;  the  latter  is  a  small  tubercle  frequently  seen  on  each  side,  in  front  of  the  hypo- 
physeal fossa,  and  slightly  posterior  to  the  tuberculum  sellse;  the  foramen  transmits  the  internal 
carotid  artery,  and  the  spicule  of  bone  which  may  complete  the  foramen  is  formed  by  ossi- 
fication of  the  carotioo-clinoid  ligament. 

The  great  or  temporal  wings  [alse  magnse],  arising  from  the  lateral  surface  of 
the  body,  extend  laterally  and  then  upward  and  forward.  The  posterior  part 
is  placed  horizontally  and  projects  backward  into  the  angle  between  the  squamous 
and  petrous  portions  of  the  temporal  bone.  From  the  under  aspect  of  its  pointed 
extremity  the  spine,  which  is  grooved  medially  by  the  chorda  tympani  nerve 
(Lucas),  projects  downward.  The  spine  serves  for  the  attachment  of  the  spheno- 
mandibular  ligament  and  a  few  fibres  of  the  tensor  veli  -palatini.  Each  wing 
presents  for  examination  four  surfaces  and  four  borders. 

Fig.  82. — Right  Half  op  Sphenoid.     (Anterior  view.) 


Temporal  surface 


Ridge  which  forms  the  upper  bound- 
ary of  the  inferior  orbital  fissure 


Ext.  pterygoid  muscU 


Sphenoidal  crest 
Sphenoidal  sinus 


The  cerebral  or  superior  surface  is  smooth  and  concave.  It  enters  into  the 
formation  of  the  middle  cranial  fossa,  supports  the  temporo-sphenoidal  lobe  of 
the  cerebrum,  and  presents  several  foramina.  At  the  anterior  and  medial 
part  is  the  foramen  rotundum  for  the  second  division  of  the  fifth  nerve,  and 
behind  and  lateral  to  it,  near  the  posterior  margin  of  the  great  wing,  is  the  large 
foramen  ovale,  transmitting  the  third  division  of  the  fifth,  the  small  meningeal 
artery,  and  an  emissary  vein  from  the  cavernous  sinus. 

Behind  and  lateral  to  the  foramen  ovale  is  the  small  circular  foramen  spinosum,  sometimes 
incomplete,  for  the  passage  of  the  middle  meningeal  vessels,  and  the  recurrent  branch  of  the 
third  division  of  the  fifth.  Between  the  foramen  ovale  and  the  foramen  rotundum  is  the  incon- 
stant foramen  Vesalii,  which  transmits  a  small  emissary  vein  from  the  cavernous  sinus;  and  on 
the  plate  of  bone,  behind  and  medial  to  the  foramen  ovale  (spheno-petrosal  lamina),  a  minute 
canal  is  occasionally  seen — the  canaliculus  innominatus — -through  which  the  small  superficial 
petrosal  nerve  escapes  from  the  skull.  When  the  canaliculus  is  absent,  the  nerve  passes  through 
the  foramen  ovale. 

The  anterior  surface  looks  medially  and  forward  and  consists  of  two  divisions — 
a  quadrilateral  or  orbital  surface,  which  forms  the  chief  part  of  the  lateral  wall  of 
the  orbit,  and  a  smaller,  inferior  or  spheno-maxillary  surface,  situated  above  the 
pterygoid  process  and  perforated  by  the  foramen  rotundum;  this  inferior  part 
forms  the  posterior  wall  of  the  pterygo-palatine  fossa. 

The  lateral  or  squamo-zygomatic  surface  is  divided  by  a  prominent  infra- 
temporal ridge  into  a  superior  portion,  which  forms  part  of  the  temporal  fossa  and 
affords  attachment  to  the  temporal  muscle,  and  an  inferior  part,  which  looks 
downward  into  the  zygomatic  fossa  and  gives  attachment  to  the  external  pterygoid 
muscle;  the  inferior  part  joins  the  lateral  surface  of  the  lateral  pterygoid  plate, 
and  presents  the  inferior  orifices  of  the  foramen  ovale,  foramen  spinosum,  and 
foramen  of  Vesalius. 


66  THE  SKELETON 

Borders. — The  posterior  border  extends  from  the  body  to  the  spine.  By  its  lateral  third  it 
articulates  with  the  petrous  portion  of  the  temporal  bone,  whilst  the  medial  two-thirds  form  the 
anterior  boimdary  of  the  foramen  laoerum.  The  squamosal  border  is  serrated  behind  and 
bevelled  in  front  for  articulation  with  the  squamous  portion  of  the  temporal  bone,  whilst  its 
upper  extremity,  or  summit,  is  bevelled  on  its  inner  aspect,  for  the  anterior  inferior  angle  of  the 
parietal.  Immediately  in  front  of  the  upper  extremity  is  a  rough,  triangular,  sutural  area  for 
the  frontal,  the  sides  of  which  are  formed  by  the  upper  margins  of  the  superior,  anterior,  and 
lateral  surfaces  respectively.  The  zygomatic  or  anterior  border  separates  the  orbital  and  tem- 
poral surfaces  and  articulates  with  the  zygomatic,  and  by  its  lower  angle,  in  many  skulls,  also 
with  the  maxilla.  Below  the  anterior  border  is  a  short  horizontal  ridge,  non-articular,  which 
separates  the  spheno-maxillary  and  zygomatic  surfaces.  Above  and  medially,  where  the  orbital 
and  cerebral  surfaces  meet,  is  the  sharp  medial  border,  which  forms  the  lower  boundarj'  of  the 
superior  orbital  fissure,  serving  for  the  passage  of  the  third,  fourth,  three  branches  of  the  first 
division  of  the  fifth,  and  the  sixth  cranial  nerves,  the  orbital  branch  of  the  middle  meningeal 
artery,  a  recurrent  branch  from  the  lacrimal  artery,  some  twigs  from  the  cavernous  plexus  of 
the  sympathetic,  and  one  or  two  ophthalmic  veins.  Near  the  middle  of  the  border  is  a  small 
tubercle  for  the  origin  of  the  lower  head  of  the  lateral  rectus  muscle. 

The  pterygoid  processes  project  downward  from  the  junction  of  the  bodj'  and 
the  great  wings.  Each  consists  of  two  plates,  one  shorter  and  broader,  the  lateral 
pterygoid  plate  [lamina  lateralis],  the  other  longer  and  narrower,  the  medial 
pterygoid  plate  [lamina  medialis].  They  are  united  in  front,  but  diverge  behind 
so  as  to  enclose  between  them  the  pterygoid  fossa  in  which  lie  the  internal  "pterygoid 
and  tensor  palati  muscles.  The  lateral  pterygoid  plate  is  turned  a  httle  laterally 
and  by  its  lateral  surface,  which  looks  into  the  zygomatic  fossa,  affords  attach- 
ment to  the  ezteimal  pterygoid  muscle,  whilst  from  its  medial  surface  the  internal 
pterygoid  takes  origin. 

The  posterior  border  of  the  lateral  pterygoid  plate  frequently  presents  one  or  more  bony 
projections,  which  represent  ossified  parts  of  the  pterygo-spinous  ligaments,  and  occasionally 
one  may  extend  across  to  the  spine  and  complete  the  bony  boundary  of  the  pterygo- 
spinous  foramen.  The  medial  pterygoid  plate  is  prolonged  below  into  a  slender,  hook-like  or 
hamular  process,  smooth  on  the  under  aspect  for  the  tendon  of  the  tensor  palati,  which  plays 
round  it.  Superiorly,  the  medial  plate  extends  medially  on  the  under  surface  of  the  body, 
forming  the  vaginal  process,  which  articulates  with  the  ala  of  the  vomer  and  the  sphenoidal 
process  of  the  palate.  The  vaginal  process  presents,  on  the  under  surface,  a  small  groove 
which,  with  the  sphenoidal  process  of  the  palate,  forms  the  pharyngeal  canal  for  the  trans- 
mission of  branches  of  the  spheno-palatine  vessels  and  ganglion.  The  medial  surface  of 
the  medial  pterygoid  plate  forms  part  of  the  lateral  boundary  of  the  nasal  fossa,  and  the 
lateral  surface,  the  medial  boundary  of  the  pterygoid  fossa.  The  posterior  border  presents 
superiorly  a  well-marked  prominence,  the  pterygoid  tubercle,  above  and  to  the  lateral  side 
of  which  is  the  posterior  orifice  of  the  pterygoid  canal.  The  latter  pierces  the  bone  in  the 
sagittal  direction  at  the  root  of  the  medial  pterygoid  plate  and  transmits  the  Vidian  vessels 
and  nerve.  Some  distance  below  the  tubercle  is  a  projection,  called  the  processus  tubarius, 
which  supports  the  cartilage  of  the  tuba  auditiva  (Eustachian  tube).  From  the  lower  third 
of  the  posterior  border  and  from  the  hamular  process,  the  superior  constrictor  of  the  pharynx 
takes  origin,  and  from  the  depression  known  as  the  scaphoid  fossa,  situated  in  the  upper  part 
of  the  recess  between  the  two  pterygoid  plates,  the  tensor  palati  arises. 

Fig.  83. — The  Sphenoid  at  Birth. 


Pterygoid  canal 


In  front,  the  two  plates  are  joined  above,  but  diverge  below,  leaving  a  gap — 
the  pterygoid  notch — occupied,  in  the  articulated  skull,  by  the  pyramidal  process 
of  the  palate.  Superiorly,  they  form  a  triangular  surface  which  looks  into  the 
pterygo-palatine  fossa  and  presents  the  anterior  orifice  of  the  pterygoid  canal. 
The  anterior  border  of  the  medial  pterygoid  plate  articulates  with  the  posterior 
border  of  the  vertical  plate  of  the  palate. 

Blood-supply. — The  sphenoid  is  supplied  by  branches  of  the  middle  and  small  meningeal 
arteries,  the  deep  temporal  and  other  branches  of  the  internal  maxillary  artery — viz.,  the 
Vidian  and  spheno-palatine.     The  body  of  the  bone  also  receives  twigs  from  the  internal  carotid. 

Articulations. — The  sphenoid  articulates  with  all  the  bones  of  the  cranium — viz.,  occipital, 


THE  SPHENOIDAL  CONCHM 


67 


parietal,  frontal,  ethmoid,  temporal,  and  sphenoidal  conohfe.  Also  with  the  palate,  vomer, 
zygomatic,  epipteric  bone  when  present,  and  occasionally  with  the  maxilla. 

Ossification.^The  sphenoid  is  divided,  up  to  the  seventh  or  eighth  month  of  intra-uterine 
life,  into  an  anterior  or  pre-sphenoid  portion,  including  the  part  of  the  bddy  in  front  of  the  tub- 
erculum  sellai  and  the  small  wings,  and  a  post-sphenoid  portion,  the  part  behind  the  tuberculum 
sellae  including  the  hypophyseaf  fossa  and  the  great  wings.  The  two  portions  of  the  body  join 
together  before  birth,  but  in  many  animals  the  division  is  persistent  throughout  life. 

The  pre-sphenoid  portion  ossifies  in  cartilage  from  four  centres,  one  of  which  gives  rise  to 
each  lesser  wing  (orbito-sphenoid)  and  a  pair  to  the  body  of  the  pre-sphenoid. 

In  the  formation  of  the  post-sphenoidal  portion  both  cartilage  and  membrane  bone  partici- 
pate, the  pterygoid  plates  being  formed  in  membrane,  while  the  rest  of  the  portion,  together 
with  the  hamular  process,  ossifies  from  cartilage.      (Fawoett.)      At  about  the  eighth  week  a 

Fig.  84. — The  Jugum  Sphenoidale. 


centre  appears  at  the  base  of  each  greater  wing  (ali-sphenoid),  and  at  about  the  same  time  a 
pair  of  centres  appear  in  the  body  (basi-sphenoid)  and  later  one  in  each  hngula  (sphenotic). 
The  medial  pterygoid  plates  are  pre-formed  in  cartilage,  in  which  a  centre  appears  for  the 
hamular  process,  but  the  rest  of  the  plate  is  formed  from  membrane  bone  which  invests  the 
cartilage.  The  lateral  plate  is  formed  in  membrane  and  a  considerable  part  of  the  greater 
wing  is  also  membranous  in  origin  (see  epipteric  bone). 

At  birth  the  bone  consists  of  three  pieces.  The  median  piece  includes  the  basi-sphenoid 
and  Hngulse,  conjoined  with  the  pre-sphenoid,  carrying  the  orbito-sphenoids. 

The  two  lateral  pieces  are  the  ali-sphenoids,  carrying  the  medial  pterygoid  plates.  The 
dorsum  sellae  is  cartilaginous.     A  canal,  known  as  the  basi-pharyngeal  canal,  extends  into  the 


Pig.  85. — The  Inferior  Surface  op  Pre-sphenoid  at  the  Sixth  Year. 


Pre-sphenoid 
Pterygo-palatine  groove 


~  Vidian  canal 
Vaginal  process 


body  from  the  sella  turcica  and  sometimes  reaches  its  under  surface.  It  contains  a  process 
of  dura  mater,  and  represents  the  remains  of  the  canal  in  the  base  of  the  cranium,  through 
which  the  diverticulum  of  Rathke  extended  upward  to  form  part  of  the  hypophysis. 

The  great  wings  are  joined  to  the  lingulae  by  cartilage,  but  in  the  course  of  the  first  year 
bony  union  takes  place.  About  the  same  time  the  orbito-sphenoids  meet  and  fuse  in  the  mid- 
dle line  to  form  the  jugum  sphenoidale,  which  thus  excludes  the  anterior  part  of  the  pre-sphenoid 
from  the  cranial  cavity.  For  some  years  the  body  of  the  pre-sphenoid  is  broad  and  rounded 
inferiorly  (fig.  85).  The  posterior  clinoid  processes  chondrify  separately,  a  fact  which  throws 
some  hght  on  the  occasional  absence  of  these  processes. 


THE  SPHENOIDAL  CONCHA 

The  sphenoidal  conchEe  (or  turbinate  bones;  bones  of  Bertin)  (figs.  86,  87)  may  be  obtained 
as  distinct  ossicles  about  the  fifth  year,  and  resemble  in  shape  two  hollow  cones  flattened  in 
three  planes.  At  this  date  each  is  wedged  in  between  the  under  surface  of  the  pre-sphenoid 
and  the  orbital  and  sphenoidal  processes  of  the  palate  bone,  with  the  apex  of  the  cone  directed 
backward  as  far  as  the  vaginal  process  of  the  medial  pterygoid  plate.  Of  its  three  surfaces, 
the  lateral  is  in  relation  with  the  pterygo-palatine  fossa,  and  occasionally  extends  upward  be- 
tween the  sphenoid  and  the  lamina  papyracea  of  the  ethmoid,  to  appear  on  the  medial  wall  of 
the  orbit  (fig.  105).  The  inferior  surface  forms  the  upper  boundary  of  the  spheno-palatine 
foramen  and  enters  into  formation  of  the  posterior  part  of  the  roof  of  the  nasal  fossa.     The 


68  THE  SKELETON 

superior  surface  lies  flattened  against  the  under  surface  of  the  pre-sphenoid,  whilst  the  base  of 
the  cone  is  in  contact  with  the  lateral  mass  of  the  ethmoid. 

The  deposits  of  earthy  matter  from  which  the  sphenoidal  conchae  are  formed  appear  at  the 
fifth  month.  At  birth  each  forms  a  small  triangular  lamina  in  the  peiichondrium  of  the  ethmo- 
vomerine  plate  near  its  junction  with  the  presphenoid,  and  partially  encloses  a  small  recess  from 
the  mucous  membrane  of  the  nose,  which  becomes  the  sphenoidal  sinus.  By  the  third  year  the 
bone  has  surrounded  the  sinus,  forming  an  osseous  capsule,  conical  in  shape,  the  circular  orifice 
which  represents  the  base  becoming  the  sphenoidal  foramen.  As  the  cavity  enlarges  the 
medial  wall  is  absorbed,  and  the  medial  wall  of  the  sinus  is  then  formed  by  the  pre-sphenoid. 

Fig.  86. — The  Sphenoidal  Concha  at  the  Sixth  Year. 


The  bones  are  subsequently  ankylosed  in  many  skulls  with  the  ethmoid,  whence  they  are  often 
regarded  as  parts  of  that  bone.  More  frequently  they  fuse  with  the  pre-sphenoid,  and  less 
frequently  with  the  palate  bones.  After  the  twelfth  year  they  can  rarely  be  separated  from  the 
skull  without  damage.  In  many  disarticulated  skulls  they  are  so  broken  up  that  a  portion  is 
found  on  the  sphenoid,  fragments  on  the  palate  bones,  and  the  remainder  attached  to  the 
ethmoid.  Sometimes,  even  in  old  skulls,  they  are  represented  by  a  very  thin  triangular  plate 
on  each  side  of  the  rostrum  of  the  sphenoid  (fig.  87). 

Fig.  87. — The  Sphenoidal  Conch.s:  from  an  Old  Skull. 


Sphenoidal  concha 


Rostrum  of  sphenoid 


THE  EPIPTERIC  AND  WORMIAN  BONES 

The  epipterics  are  scale-like  bones  which  occupy  the  antero-lateral  fontanelles- 
Each  epipteric  bone  is  wedged  between  the  squamo-zygomatic  portion  of  the 
temporal,  frontal,  great  wing  of  sphenoid,  and  the  parietal,  and  is  present  in  most 
skulls  between  the  second  and  fifteenth  year.  After  that  date  it  may  persist  as  a 
separate  ossicle,  or  unite  with  the  sphenoid,  the  frontal,  or  the  squamo-zygomatic. 
The  epipteric  bone  is  pre-formed  in  membrane,  and  appears  as  a  series  of  bony 
granules  in  the  course  of  the  first  year. 

The  Wormian  or  sutural  bones  [ossa  suturarum]  are  small,  irregularly  shaped 
ossicles,  often  found  in  the  sutures  of  the  cranium,  especially  those  in  relation  with 
the  parietal  bones.  They  sometimes  occur  in  great  numbers;  as  many  as  a 
hundred  have  been  counted  in  one  skull.  They  are  rarely  present  in  the  sutures 
of  the  face. 

THE  TEMPORAL  BONE 

The  temporal  bone  [os  temporale],  situated  at  the  side  and  the  base  of  the 
cranium,  contains  the  organ  of  hearing  and  articulates  with  the  lower  jaw.  It  is 
usually  divided  into  three  parts — viz.,  the  squamous  portion,  forming  the  anterior 
and  superior  part  of  the  bone,  thin  and  expanded  and  prolonged  externally  into 
the  zygomatic  process;  the  mastoid  portion,  the  thick  conical  posterior  part, 
behind  the  external  aperture  of  the  ear;  and  a  pyramidal  projection  named  the 
petrous  portion,  situated  in  a  plane  below  and  to  the  medial  side  of  the  two  parts 
already  mentioned,  and  forming  part  of  the  base  of  the  skull. 

When  it  is  considered  in  reference  to  its  mode  of  development,  the  temporal  bone  is  found 
to  be  built  up  of  three  parts  (figs.  88,  89,  90),  which,  however,  do  not  altogether  correspond  to 
the  arbitrary  divisions  of  the  adult  bone.     The  three  parts  are  named  squamosal,  petrosal, 


THE  TEMPORAL  BONE 


69 


and  tympanic,  and  a  knowledge  of  their  arrangement  in  the  early  stages  of  growth  greatly 
faciHtates  the  study  of  the  fully  formed  bone. 

The  more  important  division  of  the  temporal  bone  is  the  petrous  portion.     It 
is  pyramidal  in  shape,  and  contains  the  essential  part  of  the  organ  of  hearing, 


Fig.  88. — -The  Temporal  Bone  at  Birth.         Fig. 


-Temporal  Bone  at  Birth. 
(Inner  view.) 


i 


Hiatus  canalis  facialis 

Floccular  fossa 
A.qu£eductus  vestibuli 
Internal  auditory 
meatus 


Fig.  90. — The  Temporal  Bone  at  Birth.     (Outer  view.) 


Post-glenoid  tubercle 

Petro-tympanic  fissure 

Tympanic  annulus 


Petro- squamous  suture 
Petrosal 


Stylo-mastoid  foramen 
Tympano-byal 


Carotid  canal 


Fig.  91. — Right  Temporal  Bone  at  about  Six  Years. 

The  tympanic  plate  has  been  separated  and  drawn  below.     A  portion  of  the  post-auditory 

process  of  the  squamosal  has  been  removed  to  show  the  mastoid  antrum. 


Position  of  lateral  semicircular  canal 


Mastoid  antrum 


Mastoid  process 
Fenestra  cocbleaa 


Fenestra  vestibuli 
Canal  for  tensor  tympani 
Promontory 


>y  Carotid  canal 


Non-ossified    area    of  tbe 
tympanic  plate 


around  which  it  is  developed  as  a  cartilaginous  capsule.     This  is  known  as  the 
periotic  capsule  or  petrosal  element,  and  its  base  abuts  on  the  outer  aspect  of  the 


70 


THE  SKELETON 


cranium,  where  it  forms  a  large  part  of  the  so-called  mastoid  portion  of  the 
temporal  bone.  Besides  containing  the  internal  ear,  it  bears  on  its  cranial  side  a 
foramen  for  the  seventh  and  eighth  cranial  nerves  (internal  auditory  meatus), 
and  on  its  outer  side  two  openings — the  fenestra  vestibuli  and  fenestra  cochleae 
(fig.  91).  The  squamosal  is  a  superadded  element  and  is  formed  as  a  membrane 
bone  in  the  lateral  wall  of  the  cranium.  It  is  especially  developed  in  man  in 
consequence  of  the  large  size  of  the  brain,  and  forms  the  squamous  division  of  the 
adult  bone,  and  by  a  triangular  shaped  process  which  is  prolonged  behind  the 
aperture  of  the  ear  it  also  contributes  to  the  formation  of  the  mastoid  portion. 
It  is  obvious,  therefore,  that  the  mastoid  is  not  an  independent  element,  but 
belongs  in  part  to  the  petrous,  and  in  part  to  the  squamous.  The  tympanic 
portion,  also  superadded,  is  a  ring  of  bone  developed  in  connection  with  the 
external  auditory  meatus,  and  eventually  forms  a  plate  constituting  part  of  the 
bony  wall  of  this  passage.  These  three  parts  are  easily  separable  at  birth,  but 
eventually  become  firmly  united  to  form  a  single  bone  which  affords  little  trace 
of  its  complex  origin.  Lastly  a  process  of  bone,  developed  in  the  second  visceral 
arch,  coalesces  with  the  under  surface  of  the  temporal  bone  and  forms  the  styloid 
process. 

Fig.  92. — The  Left  Temporal  Bone.     (Outer  view.) 


Zygomatic  process 


Tympanic  plati 

Stylo-pharyngeus 

Stylo-hyoid 

Stylo-glossus 


Styloid  process      Mastoid  process 


The  squamous  portion  [squama  temporalis]  is  flat,  scale-like,  thin,  and  trans- 
lucent. It  is  attached  almost  at  right  angles  to  the  petrous  portion,  forms  part 
of  the  side  wall  of  the  skull  and  is  limited  above  by  an  uneven  border  which 
describes  about  two-thirds  of  a  circle.  The  outer  surface  is  smooth,  slightly 
convex  near  the  middle,  and  forms  part  of  the  temporal  fossa.  Above  the 
external  auditory  meatus  it  presents  a  nearly  vertical  groove  for  the  middle 
temporal  artery.  Connected  with  its  lower  part  is  a  narrow  projecting  bar  of 
bone  known  as  the  zygomatic  process.  At  its  base  the  process  is  broad,  directed 
lateralljr,  and  flattened  from  above  downward.  It  soon,  however,  becomes 
twisted  on  itself  and  runs  forward,  almost  parallel  with  the  squamous  portion. 
This  part  is  much  narrower  and  compressed  laterally  so  as  to  present  medial 
and  lateral  surfaces  with  upper  and  lower  margins.  The  lateral  surface  is  sub- 
cutaneous; the  medial  looks  toward  the  temporal  fossa  and  gives  origin  to  the 
masseter  muscle.  The  lower  border  is  concave  and  rough  for  fibres  of  the  same 
muscle,  whilst  the  upper  border,  thin  and  prolonged  further  forward  than  the 
lower,  receives  the  temporal  fascia.  The  extremity  of  the  process  is  serrated  for 
articulation  with  the  zygomatic  bone.  At  its  base  the  zygomatic  process  presents 
three  roots — anterior,  middle,  and  posterior. 


THE  TEMPORAL  BONE 


71 


The  anterior,  continuous  with  the  lower  border,  is  short,  broad,  convex,  and  directed 
medially'  to  terminate  in  the  articular  tubercle,  which  is  covered  with  cartilage  in  the  recent 
state,  for  articulation  with  the  condyle  of  the  lower  jaw.  The  middle  root,  sometimes  very 
prominent,  forms  the  post-glenoid  process.  It  separates  the  articular  portion  of  the  man- 
dibular fossa  from  the  external  auditory  meatus  and  is  situated  immediately  in  front  of  the 
petro-tympanic  (Glaserian)  fissure.  The  posterior  root,  prolonged  from  the  upper  border,  is 
strongly  marked  and  extends  backward  as  a  ridge  above  the  external  auditory  meatus.  It  is 
called  the  temporal  ridge  (supra-mastoid  crest),  and  marks  the  arbitrary  line  of  division  be- 
tween the  squamous  and  mastoid  portions  of  the  adult  bone.  It  forms  part  of  the  posterior 
boundary  of  the  temporal  fossa,  from  which,  as  well  as  from  the  ridge,  fibres  of  the  temporal 
muscle  arise.  Where  the  anterior  root  joins  the  zygomatic  process  is  a  slight  tubercle — the 
preglenoid  tubercle — for  the  attachment  of  the  temporo-mandibular  ligament,  and  between  the 
anterior  and  middle  roots  is  a  deep  oval  depression,  forming  the  part  of  the  mandibular  fossa 
for  the  condyle  of  the  lower  jaw.  The  mandibular  fossa  is  a  considerable  hollow,  bounded  in 
front  by  the  articular  tubercle  and  behind  by  the  tympanic  plate  which  separates  it  from  the 
external  auditory  meatus.  It  is  divided  into  two  parts  by  a  narrow  slit — the  petro-tympanic 
(Glaserian)  fissure.  The  anterior  part  [facies  articularis],  which  belongs  to  the  squamous 
portion,  is  articular,  and,  like  the  articular  tubercle,  is  coated  with  cartilage.     The  posterior 

Fig.  93. — The  Left  Temporal  Bone.     (Seen  from  the  inner  side  and  above.) 
Squaipous  portion 


Meningeal  groove 


{ 


Zygomatic  process 


Eminentia  arcuata 


Sigmoid  groove 
Mastoid  foramen 


Masseter 
Hiatus  canalis  facialis 


Internal  auditory  meatus 


Aquasductus  vestibuli 

Fossa  subarcuata 

Mastoid  process  Aquaeductus  cochleaE 


Stylo-pharyngeus 
Styloid  process 


part,  formed  by  the  tympanic  plate,  is  non-articular  and  lodges  a  lobe  of  the  parotid  gland. 
Immediately  in  front  of  the  articular  tubercle  is  a  small  triangular  surface  which  enters  into 
the  formation  of  the  roof  of  the  zygomatic  fossa. 

The  inner  or  cerebral  surface  of  the  squamous  portion  is  marked  by  furrows  for  the  con- 
volutions of  the  brain  and  grooves  for  the  middle  meningeal  vessels.  At  the  upper  part  of  the 
surface  the  inner  table  is  deficient  and  the  outer  table  is  prolonged  some  distance  upward, 
forming  a  thin  scale,  with  the  bevelled  surface  looking  inward  to  overlap  the  corresponding 
edge  of  the  parietal.  Anteriorly  the  border  is  thicker,  serrated,  and  slightly  bevelled  on  the 
outer  side  for  articulation  with  the  posterior  border  of  the  great  wing  of  the  sphenoid.  Pos- 
teriorly it  joins  the  rough  serrated  margin  of  the  mastoid  portion  to  form  the  parietal  notch. 
The  line  separating  the  squamous  from  the  petrous  portion  is  indicated  at  the  lower  part  of 
the  inner  surface  by  a  narrow  cleft,  the  internal  petro-squamous  suture,  the  appearance  of 
which  varies  in  different  bones  according  to  the  degree  of  persistence  of  the  original  line  of 
division. 

The  mastoid  portion  [pars  mastoidea]  is  rough  and  convex.  It  is  bounded 
above  by  the  temporal  ridge  and  the  parieto-mastoid  suture;  in  front,  by  the 
external  auditory  meatus  and  the  tympano-mastoid  fissure;  and  behind,  by  the 
suture  between  the  mastoid  and  occipital.  As  already  pointed  out,  it  is  formed 
by  the  squamous  portion  in  front  and  by  the  base  of  the  petrosal  behind,  the 
line  of  junction  of  the  two  component  parts  being  indicated  on  the  outer  surface 
by  the  external  petro-squamous  suture  (squamo-mastoid).  The  appearance  of 
the  suture  varies,  being  in  some  bones  scarcely  distinguishable,  in  others,  a  series 


72  THE  SKELETON 

of  irregular  depressions,  whilst  occasionally  it  is  present  as  a  well-marked  fissure 
(fig.  92)  directed  obliquely  downward  and  forward.  The  mastoid  portion  is 
prolonged  downward  behind  the  external  acoustic  meatus  into  a  nipple-shaped 
projection,  the  mastoid  process,  the  tip  of  which  points  forward  as  well  as  down- 
ward. The  process  is  marked,  on  its  medial  surface,  by  a  deep  groove,  the 
mastoid  notch  (digastric  fossa),  for  the  origin  of  the  digastric  muscle,  and 
again  medially  by  the  occipital  groove  for  the  occipital  artery. 

The  outer  surface  is  perforated  by  numerous  foramina,  one,  of  large  size,  being  usually 
situated  near  the  posterior  border  and  called  the  mastoid  foramen.  It  transmits  a  vein  to  the 
transverse  (lateral)  sinus  and  the  mastoid  branch  of  the  occipital  artery.  The  mastoid  portion 
gives  attachment  externally  to  the  auricularis  posterior  (retrahens  aurem)  and  occipitalis,  and, 
along  with  the  mastoid  process,  to  the  sterno-mastoid,  splenius  capitis,  and  longissimus  capitis 
{trachelo-mastoid) .  Projecting  from  the  postero-superior  margin  of  the  external  auditory 
meatus  there  is  frequently  a  small  tubercle — the  supra-meatal  spine — behind  which  the  surface 
is  depressed  to  form  the  mastoid  (supra-meatal)  fossa. 

The  inner  surface  of  the  mastoid  portion  presents  a  deep  curved  sigmoid 
groove,  in  which  is  lodged  a  part  of  the  transverse  sinus ;  the  mastoid  foramen  is 
seen  opening  into  the  groove.  The  interior  of  the  mastoid  portion,  in  the  adult, 
is  usually  occupied  by  cavities  lined  by  mucous  membrane  and  known  as  the 
mastoid  air-cells  (fig.  97).  These  open  into  a  small  chamber — the  mastoid 
antrum — which  communicates  with  the  upper  part  of  the  tympanic  cavity.  The 
mastoid  cells  are  arranged  in  three  groups:  (1)  antero-superior,  (2)  middle,  and 
(3)  apical.  The  [apical  cells,  situated  at  the  apex  of  the  mastoid  process,  are 
small  and  usually  contain  marrow. 

Borders. — -The  superior  border  is  broad  and  rough  for  articulation  with  the  hinder  part  of 
the  inferior  border  of  the  parietal  bone.  The  posterior  border,  very  uneven  and  serrated, 
articulates  with  the  inferior  border  of  the  occipital  bone,  extending  from  the  lateral  angle  to 
the  jugular  process. 

The  petrous  portion  [pars  petrosa;  pyramis]  is  a  pyramid  of  very  dense  bone 
presenting  for  examination  a  base,  an  apex,  three  (or  four)  surfaces,  and  three  (or 
four)  borders  or  angles.  Two  sides  of  the  pyramid  look  into  the  cranial  cavity, 
the  posterior  into  the  posterior  cranial  fossa,  and  the  anterior  into  the  middle 
cranial  fossa.  The  inferior  surface  appears  on  the  under  surface  of  the  cranium . 
The  medial  and  posterior  walls  of  the  tympanic  cavity  in  the  temporal  bone 
are  sometimes  described  as  a  fourth  side  of  the  pyramid.  The  base  forms  a  part 
of  the  lateral  surface  of  the  cranium;  the  apex  is  placed  medially. 

The  posterior  surface  of  the  pyramid  is  triangular  in  form,  bounded  above  by 
the  superior  angle  and  below  by  the  posterior  angle  Near  the  middle  is  an 
obliquely  directed  foramen  [porus  acusticus  internus]  leading  into  a  short  canal — ■ 
the  internal  auditory  meatus — at  the  bottom  of  which  is  a  plate  of  bone,  pierced 
by  numerous  foramina,  and  known  as  the  lamina  cribrosa.  The  canal  transmits 
the  facial  and  auditory  nerves,  the  pars  intermedia,  and  the  internal  auditory 
artery.  The  bottom  of  the  internal  auditory  meatus  can  be  most  advantageously 
studied  in  a  temporal  bone  at  about  the  time  of  birth,  when  the  canal  is  shallow 
and  the  openings  relatively  wide. 

The  fundus  of  the  meatus  is  divided  by  a  transverse  ridge  of  bone,  the  transverse  crest,  into  a 
superior  and  inferior  fossa.  Of  these,  the  superior  is  the  smaller,  and  presents  anteriorly  the 
beginning  of  the  facial  canal  (aqueduct  of  Fallopius),  which  transmits  the  seventh  nerve.  The 
rest  of  the  surface  above  the  crest  is  dotted  with  small  foramina  (the  superior  vestibular  area) 
which  transmit  nerve-twigs  to  the  recessus  elliptious  (fovea  hemielliptica)  and  the  ampuUae 
of  the  superior  and  lateral  semicircular  canals  (vestibular  division  of  the  auditory  nerve). 
Below  the  crest  there  are  two  depressions  and  an  opening.  Of  these,  an  anterior  curled  tract 
(the  spiral  cribriform  tract)  with  a  central  foramen  (foramen  oentrale  cochleare)  marks  the 
base  of  the  cochlea;  the  central  foramen  indicates  the  orifice  of  the  canal  of  the  modiolus, 
and  the  smaller  foramina  transmit  the  cochlear  twigs  of  the  auditory  nerve.  The  posterior 
opening  (foramen  singulare)  is  for  the  nerve  to  the  ampulla  of  the  posterior  semicircular 
canal.  The  middle  depression  (inferior  vestibular  area)  is  dotted  with  minute  foramina  for 
the  nerve-twigs  to  the  saccule,  which  is  lodged  in  the  recessus  sphsericus  (fovea  hemisphaeri- 
ca).  The  inferior  fossa  is  subdivided  by  a  low  vertical  crest.  The  fossa  in  front  of  the  crest 
is  the  fossula  cochlearis,  and  the  recess  behind  it  is  the  fossula  vestibularis. 

Behind  and  lateral  to  the  meatus  is  a  narrow  fissure,  the  aquseductus  vestibuli,  covered  by 
a  scale  of  bone.  In  the  fissure  lies  the  ductus  endolymphaticus,  a  small  arteriole  and  venule, 
and  a  process  of  connective  tissue  which  unites  the  dura  mater  to  the  sheath  of  the  internal 
ear.  Occasionally  a  bristle  can  be  passed  through  it  into  the  vestibule.  Near  the  upper 
margin,  and  opposite  a  point  about  midway  between  the  meatus  and  the  aqueduct  of  the  vesti- 


THE  TEMPORAL  BONE  73 

bule,  is  an  irregular  opening,  the  fossa  subarcuata,  the  remains  of  the  floccular  fossa,  a  con- 
spicuous depression  in  the  foetal  bone.  In  the  adult  the  depression  usually  lodges  a  process  of 
dura  mater  and  transmits  a  small  vein,  though  in  some  bones  it  is  almost  obhterated. 

.The  anterior  surface  of  the  pyramid,  sloping  downward  and  forward,  forms 
the  back  part  of  the  floor  of  the  middle  fossa  of  the  cranium. 

Upon  the  anterior  surface  of  the  pyramid  will  be  found  the  following  points  of  interest, 
proceeding  from  the  apex  toward  the  base  of  the  pyramid: — (1)  a  shallow  trigeminal  im- 
pression for  the  semilunar  (Gasserian)  ganglion  of  the  trigeminal  nerve;  (2)  two  small  grooves 
running  backward  and  laterally  toward  two  small  foramina  overhung  by  a  thin  osseous  lip,  the 
larger  and  medial  of  which,  known  as  the  hiatus  canalis  facialis,  transmits  the  great  superfi- 
cial petrosal  nerve  and  the  petrosal  branch  of  the  middle  meningeal  artery,  whilst  the  smaller 
and  lateral  foramen  is  for  the  small  superficial  petrosal  nerve;  (3)  behind  and  lateral  to  these 
is  an  eminence — the  eminentia  arcuata — best  seen  in  young  bones,  corresponding  to  the  su- 
perior semicircular  canal  in  the  interior;  (4)  still  more  laterally  is  a  thin  transulcent  plate  of 
bone,  roofing  in  the  tympanic  cavity,  and  named  the  tegmen  tympani. 

Fig.  94. — The  Foramina  in  the  Fundtts  of  the  Left  Internal  Auditory  Meatus  op  a 

Child  at  Birth  (y).     (Diagrammatic.) 

Superior  fossa 


Superior  cribriform  area 


Foramen  singulare 


Entrance  to  the  facial  canal 


-  Transverse  crest 
Middle  cribriform  area \j,'^     j^^^g\  Orifice  of  the  canal  of  the  modiolus 


Spiral  cribriform  tract 


The  inferior  or  basilar  surface  of  the  pyramid  is  very  irregular.  At  the  apex 
it  is  rough,  quadrilateral,  and  gives  attachment  to  the  tensor  tympani,  levator 
veil  palatini,  and  the  pharyngeal  aponeurosis.  Behind  this  are  seen  the  large 
circular  orifice  of  the  carotid  canal  for  the  transmission  of  the  carotid  artery  and 
a  plexus  of  sympathetic  nerves,  and  on  the  same  level,  near  the  posterior  border, 
a  small  three-sided  depression,  the  canaliculus  cochleae,  which  transmits  a  small 
vein  from  the  cochlea  to  the  internal  jugular.  Behind  these  two  openings  is  the 
large  elliptical  jugular  fossa  which  forms  the  anterior  and  lateral  part  of  the 
bony  wall  of  the  jugular  foramen,  in  which  is  contained  a  dilatation  on  the 
commencement  of  the  internal  jugular  vein;  on  the  lateral  wall  of  the  jugular 
fossa  is  a  minute  foramen,  the  mastoid  canaliculus,  for  the  entrance  of  the 
auricular  branch  of  the  vagus  (Arnold's  nerve)  into  the  interior  of  the  bone. 
Between  the  inferior  aperture  of  the  carotid  canal  and  the  jugular  fossa  is  the 
sharp  carotid  ridge,  on  which  is  a  small  depression,  the  fossula  petrosa,  and  at  the 
bottom  of  this  a  minute  opening,  the  tympanic  canaliculus,  for  the  tympanic 
branch  of  the  glosso-pharyngeal  or  Jacobson's  nerve,  and  the  small  tympanic 
branch  from  the  ascending  pharyngeal  artery.  Behind  the  fossa  is  the  rough 
jugular  surface  for  articulation  with  the  jugular  process  of  the  occipital  bone,  on 
the  lateral  side  of  which  is  the  prominent  cylindrical  spur  known  as  the  styloid 
process  with  the  stylo-mastoid  foramen  at  its  base.  The  facial  nerve,  and 
sometimes  the  auricular  branch  of  the  vagus,  leave  the  skull,  and  the  stylo-mas- 
toid artery  enters  it  by  this  foramen.  Running  backward  from  the  foramen  are 
the  mastoid  and  occipital  grooves  already  described. 

The  tympanic  surface  of  the  pyramid,  forming  the  medial  and  posterior 
walls  [paries  labyrinthica]  of  the  tympanic  cavity,  is  shown  by  removing  the 
tympanic  plate  (fig.  91).  It  presents  near  the  base  an  excavation,  known  as  the 
tympanic  or  mastoid  antrum,  covered  by  the  triangular  part  of  the  squamous 
below  and  behind  the  temporal  line.  The  opening  of  the  antrum  into  the 
tympanic  cavity  is  situated  immediately  above  the  fenestra  vestibuli,  an  oval- 
shaped  opening  which  receives  the  base  of  the  stapes;  below  the  fenestra  vestibuli 
is  a  convex  projection  or  promontory,  marked  by  grooves  for  the  tympanic  plexus 
of  nerves  and  containing  the  commencement  of  the  first  turn  of  the  cochlea. 
In  the  lower  and  posterior  part  of  the  promontory  is  the  fenestra  cochlesB,  closed 
in  the  recent  state  by  the  secondary  membrane  of  the  tj^mpanum.  Running 
downward  and  forward  from  the  front  of  the  fenestra  vestibuli  is  a  thin  curved 
plate  of  bone  [septum  canalis  musculotubarii],  separating  two  grooves  converted 


74 


THE  SKELETON 


into  canals  by  the  overlying  tympanic  plate.  The  lower  is  the  groove  for  the 
Eustachian  tube  [semicanalis  tubse  audi tivse],  the  communicating  passage  between 
the  tympanum  and  the  pharynx ;  the  upper  is  the  semicanalis  m.  tensoris  tympani, 
and  the  lateral  apertures  of  both  canals  are  visible  in  the  retiring  angle,  b-etween 
the  petrous  and  squamous  portions  of  the  bone. 

The  apex  of  the  pyramid  is  truncated  and  presents  the  medial  opening  of  the 
carotid  canal.  The  latter  commences  on  the  inferior  surface,  and,  after  ascending 
for  a  short  distance,  turns  forward  and  medially,  tunnelling  the  bone  as  far  as 
the  apex,  and  finally  opens  into  the  upper  part  of  the  foramen  lacerum  formed 
between  the  temporal  and  sphenoid  bones.  One  or  two  minute  openings  in  the 
wall  of  the  carotid  canal,  known  as  the  carotico -tympanic  canaliculi,  transmit 
communicating  twigs  between  the  carotid  and  tympanic  plexuses.  The  upper 
part  of  the  apex  is  joined  by  cartilage  to  the  posterior  petrosal  process  of  the 
sphenoid. 

The  base  is  the  part  of  the  pyramid  which  appears  laterally  at  the  side  of 
the  cranium  and  takes  part  in  the  formation  of  the  mastoid  portion.  It  is 
described  with  that  chvision  of  the  bone. 


Fig.  95. — The  Left  Temporal  Bone.     (Inferior  view.) 


Carotid  canal- 
Tensor  tympani 

Levator  veil  palatini' 

Carotid  canal 

Tympanic  canaliculus 


Canalicul 

Mastoid  canaliculus 

Jugular  fossa 

Jugular  surface 


Zygomatic  process 
Masseter 

Articular  tubercle 

Mandibular  fossa 
■Petro-tympanic  fissure 

Tympanic  plate 
Styloid  process 
Stylo-pharyngeus 
Tympano-mastoid  fissure 
Stylo-mastoid  foramen 
Mastoid  process 
Digastric 
Occipital  groove 


Angles. — The  superior  angle  (border)  of  the  pyramid  is  the  longest  and  separates  the  pos- 
terior from  the  anterior  surface.  It  is  grooved  for  the  superior  petrosal  sinus,  gives  attachment 
to  the  tentorium  cerebelli,  and  presents  near  the  apex  a  semilunar  notch  upon  which  the  fifth 
cranial  nerve  lies.  Near  its  medial  end  there  is  often  a  small  projection  for  the  attachment 
of  the  petro-sphenoid.al  ligament,  which  arches  over  the  inferior  petrosal  sinus  and  the  sixth 
nerve.  The  posterior  angle  separates  the  posterior  from  the  inferior  surface,  and  when  ar- 
ticulated with  the  occipital,  forms  the  groove  for  the  inferior  petrosal  sinus,  and  completes  the 
jugular  foramen  formed  by  the  temporal  in  front  and  on  the  lateral  side,  and  by  the  occipital 
behind  and  on  the  medial  side.  The  jugular  foramen  is  divisible  into  three  compartments:  an 
anterior  for  the  inferior  petrosal  sinus,  a  middle  for  the  glossopharyngeal,  vagus  and  accessory 
cranial  nerves,  and  a  posterior  for  the  internal  jugular  vein  and  some  meningeal  branches 
from  the  occipital  and  ascending  pharyngeal  arteries.  The  anterior  angle  is  the  shortest 
and  consists  of  two  parts,  one  joined  to  the  squamous  in  the  petro-squamous  suture  and  a 
small  free  part  internally  which  articulates  with  the  sphenoid.  A  fourth  or  inferior  border  may 
be  distinguished,  which  runs  along  the  line  of  junction  with  the  tympanic  plate  and  is  continued 
on  to  the  rough  area  below  the  apex. 


THE  TEMPORAL  BONE  75 

The  tympanic  portion  [pars  tympanica]  is  quadrilateral  in  form,  hollowed  out 
above  and  behind,  and  nearly  flat,  or  somewhat  concave,  in  front  and  below.  It 
forms  the  whole  of  the  anterior  and  inferior  walls,  and  part  of  the  posterior  wall, 
of  the  external  auditory  meatus,  and  is  separated  behind  from  the  mastoid 
process  by  the  tympano-mastoid  (auricular)  fissure  through  which  the  auricular 
branch  of  the  vagus  in  some  cases  leaves  the  bone. 

In  front  it  is  separated  by  the  petro-tympanic  fissure  from  the  squamous  portion.  Through 
the  petro-tympanio  fissure  the  tympanic  branch  of  the  internal  maxillary  artery  and  the  so- 
called  laxator  tympani  pass.  The  processus  graoihs  of  the  malleus  is  lodged  within  it,  and  a 
narrow  subdivision  at  its  inner  end,  known  as  the  canal  of  Huguier,  transmits  the  chorda 
tympani  nerve.     The  tympanic  part  presents  for  examination  two  surfaces  and  four  borders. 

The  antero-inferior  surface,  directed  downward  and  forward,  lodges  part  of  the  parotid 
gland.  Near  the  middle  it  is  usually  very  thin,  and  sometimes  presents  a  small  foramen  (the 
foramen  of  Huschke),  which  represents  a  non-ossified  portion  of  the  plate.  The  postero- 
superior  surface  looks  into  the  external  auditory  meatus  and  tympanic  cavity,  and  at  its  medial 
end  is  a  narrow  groove,  the  sulcus  tympanicus,  deficient  above,  which  receives  the  membrana 
tympani. 

The  lateral  border  is  rough  and  everted,  forming  the  external  auditory  process  for  the 
attachment  of  the  cartilage  of  the  pinna;  the  superior  border  enters  into  the  formation  of  the 
petro-tympanic  fissure;  the  inferior  border  is  uneven  and  prolonged  into  the  vaginal  process 
[vagina  processus  styloideil  which  surrounds  the  lateral  aspect  of  the  base  of  the  styloid  process 
and  gives  attachment  to  the  front  part  of  the  fascial  sheath  of  the  carotid  vessels;  the  medial 
border,  short  and  irregular,  lies  immediately  below  and  to  the  lateral  side  of  the  opening  of  the 
Eustachian  tube,  and  becomes  continuous  with  the  rough  quadrilateral  area  on  the  inferior 
aspect  of  the  apex. 

The  external  auditory  meatus  is  formed  partly  by  the  tympanic  and  partly 
by  the  squamous  portion.  It  is  an  elliptical  bony  tube  leading  into  the  tym- 
panum, the  extrance  of  which  is  bounded  throughout  the  greater  part  of  its 
circumference  by  the  external  auditory  process  of  the  tympanic  plate.  Above, 
the  entrance  is  limited  by  the  temporal  ridge  or  posterior  root  of  the  zygomatic 
process. 

The  styloid  process  is  a  slender,  cylindrical  spur  of  bone  fused  with  the 
inferior  aspect  of  the  temporal  immediately  in  front  of  the  stylo-mastoid  foramen. 
It  consists  of  two  parts,  basal  (tympano-hyal),  which  in  the  adult  lies  under  cover 
of  the  tympanic  plate,  and  a  projecting  portion  (stylo-hyal) ,  which  varies  in  length 
from  five  to  fifty  millimetres.  When  short,  it  is  hidden  by  the  vaginal  process, 
but,  on  the  other  hand,  it  may  reach  to  the  hyoid  bone.  The  projecting  portion 
gives  attachment  to  three  muscles  and  two  ligaments. 

The  slylo-pharyngeus  arises  near  the  base  from  the  medial  and  slightly  from  the  posterior 
aspect;  the  slylo-hyoid  from  the  posterior  and  lateral  aspect  near  the  middle;  and  the  slylo- 
glossus  from  the  front  near  the  tip.  The  tip  is  continuoiis  with  the  stylo-hyoid  ligament,  which 
runs  down  to  the  lesser  cornu  of  the  hyoid  bone.  A  band  of  fibrous  tissue — the  stylo-mandibular 
ligament — passes  from  the  process  below  the  origin  of  the  stylo-glossus  to  the  angle  of  the  lower 
jaw. 

Blood-supply. — The  arteries  supplying  the  temporal  bone  are  derived  from  various  sources. 
The  chief  are: — 

Stylo-mastoid  from  posterior  auricular:  it  enters  the  stylo-mastoid  foramen. 

Anterior  tympanic  from  internal  maxillary:  it  passes  through  the  petro-tympanic  fissure. 

Superficial  petrosal  from  middle  meningeal:    transmitted  by  the  hiatus  canalis  facialis. 

Carotieo-tympanic  from  internal  carotid  whilst  in  the  carotid  canal. 

Internal  auditory  from  the  basilar:  it  enters  the  internal  auditory  meatus,  and  is  distributed 
to  the  cochlea  and  vestibule. 

Other  less  important  twigs  are  furnished  by  the  middle  meningeal,  the  meningeal  branches 
of  the  occipital,  and  by  the  ascending  pharyngeal  artery.  The  squamous  portion  is  supplied, 
on  its  internal  surface,  by  the  middle  meningeal,  and  externally  by  the  branches  of  the  deep 
temporal  from  the  internal  maxillary. 

Articulations. — The  temporal  bone  articulates  with  the  occipital,  parietal,  sphenoid, 
zygomatic,  and,  by  a  movable  joint,  with  the  mandible.  Occasionally  the  squamous  portion 
presents  a  process  which  articulates  with  the  frontal.  A  fronto -squamosal  suture  is  common 
in  the  skulls  of  the  lower  races  of  men,  and  is  normal  in  the  skulls  of  the  chimpanzee,  gorilla, 
and  gibbon. 

Ossification. — Of  the  three  parts  which  constitute  the  temporal  bone  at  birth,  the  squa- 
mosal and  tympanic  develop  in  membrane  and  the  petrosal  in  cartilage.  The  squamosal  is 
formed  from  one  centre,  which  appears  as  early  as  the  eighth  week,  and  ossification  extends 
into  the  zygomatic  process,  which  grows  concurrently  with  the  squamosal.  At  first  the  tym- 
panic border  is  nearly  straight,  but  soon  assumes  its  characteristic  horseshoe  shape.  At  birth 
the  post-glenoid  tubercle  is  conspicuous,  and  at  the  hinder  end  of  the  squamosal  there  is  a  pro- 
cess which  comes  into  relation  with  the  mastoid  antrum  The  centre  for  the  tympanic  ele- 
ment appears  about  the  twelfth  week.  At  birth  it  forms  an  incomplete  ring,  open  above,  and 
slightly  ankylosed  to  the  lower  border  of  the  squamosal.     The  anterior  extremity  terminates 


76 


THE  SKELETON 


in  a  small  irregular  process,  and  the  medial  aspect  presents,  in  the  lower  half  of  its  circumfer- 
ence, a  groove  for  the  reception  of  the  tympanic  membrane. 

Up  to  the  middle  of  the  fifth  month  the  periotio  capsule  is  cartilaginous;  it  then  ossifies 
so  rapidly  that  by  the  end  of  the  sixth  month  its  chief  portion  is  converted  into  porous  bone. 
The  ossifio  material  is  deposited  in  four  centres,  or  groups  of  centres,  named  according  to 
their  relation  to  the  ear-capsule  in  its  embryonic  position. 

The  nuclei  are  deposited  in  the  following  order; — 

1.  The  opisthotic  appears  at  the  end  of  the  fifth  month.  The  osseous  material  is  seen  first 
on  the  promontory,  and  it  quickly  surrounds  the  fenestra  cochleae  from  above  downward,  and 
forms  the  floor  of  the  vestibule,  the  lower  part  of  the  fenestra  vestibuli,  and  the  internal  au- 
ditory meatus;  it  also  invests  the  cochlea.  Subsequently  a  plate  of  bone  arises  from  it  to  sur- 
round the  internal  carotid  artery  and  form  the  floor  of  the  tympanum. 

2.  The  prootic  nucleus  is  deposited  behind  the  internal  auditory  meatus  near  the  medial 
limb  of  the  superior  semicircular  canal.  It  covers  in  a  part  of  the  cochlea,  the  vestibule,  and 
the  internal  auditory  meatus,  completes  the  fenestra  vestibuli,  and  invests  the  superior  semi- 
circular canal. 

3.  The  pterotic  nucleus  ossifies  the  tegmen  tympani  and  covers  in  the  lateral  semicircular 
canal;  the  ossific  matter  is  first  deposited  over  the  lateral  limb  of  this  canal. 

4.  The  epiotic,  often  double,  is  the  last  to  appear,  and  is  first  seen  at  the  most  posterior 
part  of  the  posterior  semicircular  canal. 

At  birth  the  bone  is  of  loose  and  open  texture,  thus  offering  a  striking  contrast  to  the  dense 
and  ivory-like  petrosal  of  the  adult.  It  also  differs  from  the  adult  bone  in  several  other  par- 
ticulars. The  floccular  fossa  is  widely  open  and  conspicuous.  VoltoUni  has  pointed  out  that 
a  small  canal  leads  from  the  floor  of  the  floccular  fossa  and  opens  posteriorly  on  the  mastoid 
surface  of  the  bone;  it  may  open  in  the  mastoid  antrum.     The  hiatus  canalis  facialis  is  unclosed 


Fig.  96. — -Temporal  Bone  at  the  Sixth  Year. 


External  auditory  meatus 

Non-ossified  area  of  the  tympanic  plate 

Petro-tympamc  fissure 


Wormian  bone  in 
parietal  notch 


and  the  tympanum  is  filled  with  gelatinous  connective  tissue.  The  mastoid  process  is  not 
developed,  and  the  jugular  fossa  is  a  shallow  depression. 

After  birth  the  parts  grow  rapidly.  The  tympanum  becomes  permeated  with  air,  the  var- 
ious elements  fuse,  and  the  tympanic  annulus  grows  rapidly  and  forms  the  tympanic  plate. 
Development  of  the  tympanic  plate  takes  place  by  an  outgrowth  of  bone  from  the  lateral 
aspect  of  the  tympanic  annulus.  This  outgro\vth  takes  place  most  rapidly  from  the  tubercles 
or  spines  at  its  upper  extremities,  and  in  consequence  of  the  slow  growth  of  the  lower  segment  a 
deep  notch  is  formed;  gradually  the  tubercles  coalesce,  lateral  to  the  notch,  so  as  to  enclose  a 
foramen  which  persists  until  puberty,  and  sometimes  even  in  the  adult.  In  most  skuUs  a  cleft 
capable  of  receiving  the  nail  remains  between  the  tympanic  element  and  the  mastoid  process; 
this  is  the  tympano-mastoid  fissure.  The  anterior  portion  of  the  tympanic  plate  forms  with 
the  inferior  border  of  the  squamosal  a  cleft  known  as  the  petro-tympanic  fissure,  which  is  sub- 
sequently encroached  upon  by  the  growth  of  the  petrosal.  As  the  tympanic  plate  increases  in 
size  it  joins  the  lateral  wall  of  the  carotid  canal  and  presents  a  prominent  lower  edge,  known  as 
the  vaginal  process  (sheath  of  the  styloid). 

The  mastoid  process  becomes  distinct  about  the  first  year,  coincident  with  the  obliteration 
of  the  petro-squamous  suture,  and  increases  in  thickness  by  deposit  from  the  periosteum. 
According  to  most  writers,  the  process  becomes  pneumatic  about  the  time  of  puberty,  but 
it  has  been  shown  by  Young  and  Milligan  that  the  mastoid  air-cells  develop  at  a  much 
earlier  period  than  is  usually  supposed.  These  writers  have  described  specimens  in  which  the 
air-cells  were  present,  as  small  pit-like  diverticula  from  the  mastoid  antrum,  in  a  nine  months' 
foetus  and  in  an  infant  one  year  old.  In  old  skulls  the  air-cells  may  extend  into  the  jugular 
process  of  the  occipital  bone. 

At  birth  the  mastoid  antrum  is  relatively  large  and  bounded  laterally  by  a  thin  plate  of 
bone  belonging  to  the  squamosal  (post-auditory  process).  As  the  mastoid  increases  in  thick- 
ness the  antrum  comes  to  lie  at  a  greater  depth  from  the  surface  and  becomes  relatively  smaller. 


THE  TYMPANUM 


77 


The  styloid  process  is  ossified  in  cartilage  from  two  centres,  one  of  which  appears  at  the 
base  in  the  tympano-hyal  before  birth.  This  soon  joins  with  the  temporal  bone,  and  in  the 
second  year  a  centre  appears  for  the  stylo-hyal,  which,  however,  remains  very  small  until  pu- 
berty. In  the  adult  it  usually  becomes  firmly  united  with  the  tympano-hyal,  but  it  may  remain 
permanently  separate. 


THE  TYMPANUM 

The  tympanum  (middle  ear)  includes  a  cavity  [cavum  tympani]  of  irregular 
form  in  the  temporal  bone,  situated  over  the  jugular  fossa,  between  the  petrous 
portion  medially  and  the  tympanic  and  squamous  portions  laterally.  When  fully 
developed,  it  is  completely  surrounded  by  bone  except  where  it  communicates 
with  the  external  auditory  meatus,  and  presents  for  examination  six  walls — 
lateral,  medial,  posterior,  anterior,  superior  (roof),  and  inferior  (floor).  The 
lateral  and  medial  wails  are  flat,  but  the  remainder  are  curved,  so  that  they  run 
into  adjoining  surfaces,  without  their  limits  being  sharply  indicated. 

The  roof  or  tegmen  tympani  [paries  tegmentalis]  is  a  translucent  plate  of  bone,  forming 
part  of  the  superior  surface  of  the  petrous  portion  and  separating  the  tympanum  from  the 
middle  fossa  of  the  skull.  The  floor  [paries  jugularis]  is  the  plate  of  bone  which  forms  the  roof 
of  the  jugular  fossa. 

The  medial  wall  [paries  labyrinthica]  is  formed  by  the  tympanic  surface  of  the  petrous 
portion.  In  the  angle  between  it  and  the  roof  is  a  horizontal  ridge  which  extends  backward  as 
far  as  the  posterior  wall  and  then  turns  downward  in  the  angle  between  the  medial  and  posterior 
walls.  This  is  the  facial  (Fallopian)  canal,  and  is  occupied  by  the  facial  nerve.  The  other 
features  of  this  surface — viz.,  the  fenestra  vestibuli,  the  fenestra  cochleae,  and  the  promontory 
— have  previously  been  described  with  the  anterior  surface  of  the  petrous  portion  of  the  temporal 
bone. 

The  posterior  wall  [paries  mastoidea]  of  the  tympanum  is  also  formed  by  the  anterior 
surface  of  the  petrous  portion.     At  the  superior  and  lateral  angle  of  this  wall  an  opening 

Fig.  97. — The  Medial  Wall  of  the  Tympanum. 


Carotid  canal 

Tensor  tympani 

Groove  for  Eustacliian. 

tube 

Levator  veli  palatini' 

Canal  for  small  deep. 

petrosal  nerve 


Stylo  pharyngeus 
Stylo-hyoxd 
Stylo  gl( 


Lateral  semicircular 

canal 
Mastoid  antrum 
Facial  canal 


Canal  for  chorda  tympani 
Stylo-mastoid  foramen 


leads  into  the  mastoid  antrum.  Immediately  below  this  opening  there  is  a  small  hoUow  cone, 
the  pyramidal  eminence,  the  cavity  of  which  is  continuous  with  the  descending  limb  of  the 
facial  canal.  The  cavity  is  occupied  by  the  stapedius  and  the  tendon  of  the  muscle  emerges 
at  the  apex.  One  or  more  bony  spicules  often  connect  the  apex  of  the  pyramid  with  the 
promontory. 

The  roof  and  floor  converge  toward  the  anterior  extremity  of  the  tympanum,  which  is,  in 
consequence,  very  low;  it  is  occupied  by  two  semicanals,  the  lower  for  the  Eustachian  tube,  the 
upper  for  the  tensor  tympani  muscle.  These  channels  are  sometimes  described  together  as  the 
canalis  musculo-tubarius.  In  carefully  prepared  bones  the  upper  semicanal  is  a  small  hori- 
zontal hollow  cone  (anterior  pyramid),  12  mm.  in  length;  the  apex  is  just  in  front  of  the  fenestra 
vestibuli,  and  is  perforated  to  permit  the  passage  of  the  tendon  of  the  muscle.  As  a  rule,  the 
thin  walls  of  the  canal  are  damaged,  and  represented  merely  by  a  thin  ridge  of  bone.  The 
posterior  portion  of  this  ridge  projects  into  the  tympanum,  and  is  known  as  the  processus 
cochleariformis.  The  thin  septum  between  the  semicanal  for  the  tensor  tympani  and  the 
tube  is  pierced  by  a  minute  opening  which  transmits  the  small  deep  petrosal  nerve. 

The  lateral  wall  [paries  membranaeea]  is  occupied  mainly  by  the  external  auditor}'  meatus. 
This  opening  is  closed  in  the  recent  state  by  the  tympanic  membrane.  The  rim  of  bone  to 
which  the  membrane  is  attached  is  incomplete  above,  and  the  defect  is  known  as  the  tympanic 
notch  (notch  of  Rivinus).  Anterior  to  this  notch,  in  the  angle  between  the  squamous  portion 
and  the  tympanic  plate,  is  the  petro-tympanic  (Glaserian)  fissure,  and  the  small  passage 
which  transmits  the  chorda  tympani  nerve,  known  as  the  canal  of  Huguier. 

Up  to  this  point  the  description  of  the  middle  ear  conforms  to  that  in  general  usage.  But 
Young  and  Milligan  have  laid  stress  on  the  fact  that  the  middle  ear  is  really  a  cleft,  named 
by  them  the  "middle-ear  cleft,"  which  intervenes  between  the  periotic  capsule,  on  the  one  hand, 
and  the  squamo-zygomatic  and  tympanic  elements  of  the  temporal  bone  on  the  other.  This 
cleft,  as  development  proceeds,  gives  rise  to  three  cavities: — -(1)  the  mastoid  antrum;  (2) 


78 


THE  SKELETON 


tympanum;  and  (3)  the  Eustachian  tube.  They  point  out  that  "the  cleft  is  primarily  con- 
tinuous, and  however  much  it  may  be  altered  in  shape  and  modified  in  parts  to  form  these  three 
cavities,  that  continuity  is  never  lost."  It  will  be  clear  that  the  mastoid  antrum,  according  to 
this  view,  is  not  an  outgrowth  from  the  tympanum,  but  is  simply  the  lateral  end  of  the  middle- 
ear  cleft. 

The  tympanic  cavity  may  be  divided  into  three  parts.  The  part  below  the 
level  of  the  superior  margin  of  the  external  auditory  meatus  is  the  tympanum 
proper ;  the  portion  above  this  level  is  the  epitympanic  recess  or  attic ;  it  receives 
the  head  of  the  malleus,  the  body  of  the  incus,  and  leads  posteriorly  into  the 
recess  known  as  the  mastoid  antrum.  The  third  part  is  the  downward  extension 
known  as  the  hypotympanic  recess. 

The  tympanic  or  mastoid  antrum. — The  air-cells  which  in  the  adult  are  found  in  the 
interior  of  the  mastoid  portion  of  the  temporal  bone  open  into  a  small  cavity  termed  the 
mastoid  antrum.  This  is  an  air-chamber,  communicating  with  the  attic  of  the  tympanum, 
and  separated  from  the  middle  cranial  fossa  by  the  posterior  portion  of  the  tegmen  tympani. 
The  floor  is  formed  by  the  mastoid  portion  of  the  petrosal,  and  the  lateral  wall  by  the  squamosal, 
below  the  temporal  ridge.  In  children  the  outer  wall  is  exceedingly  thin,  but  in  the  adult  it  ia 
of  considerable  thickness.     The  lateral  semicircular  canal  projects  into  the  antrum  on  its 


Fig.  98." 


-Temporal  Bone  at  Birth  Dissected  prom  above  and  behind  to  show  the  Semi- 
circular Canals  and  the  Mastoid  Antrum.     (Enlarged  \.) 


Opening  into  tympanura 


Superior  semicircular  canal 


Mastoid  antrum 


'Lateral  semicircular  canal 


Posterior  semicircular  canal 


medial  wall,  and  is  very  conspicuous  in  the  foetus.  Immediately  below  and  in  front  of  the 
canal  is  the  facial  nerve,  contained  in  the  facial  canal. 

The  mastoid  antrum  has  somewhat  the  form  of  the  bulb  of  a  retort  (Thane  and  Godlee) 
compressed  laterally,  and  opening  by  its  narrowed  neck  into  the  attic  or  epitympanic  recess. 
Its  dimensions  vary  at  different  periods  of  hfe.  It  is  well  developed  at  birth,  attains  its  maxi- 
mum size  about  the  third  year,  and  diminishes  somewhat  up  to  adult  life.  In  the  adult  the 
plate  of  bone  which  forms  the  lateral  wall  of  the  antrum  is  12  to  18  mm.  (|  to  J  in.)  in  thickness, 
whereas  at  bu-th  it  is  about  1.8  mm.  (j^  in.)  or  less.  The  deposition  of  bone  laterally  occurs, 
therefore,  at  average  rate  of  nearly  1  mm.  a  year  in  thickness.  In  the  adult  the  antrum  ia 
about  12  mm.  (i  in.)  from  front  to  back,  9  mm.  (f  in.)  from  above  downward,  and  4.5  mm. 
(j^V  in.)  from  side  to  side. 

A  canal  occasionally  leads  from  the  mastoid  antrum  through  the  petrous  bone  to  open  in 
the  recess  which  indicates  the  position  of  the  fioecular  fossa;  it  is  termed  the  petro-mastoid 
canal.     (Gruber.) 

The  facial  (Fallopian)  canal. — This  canal  begins  at  the  anterior  angle  of  the  superior  fossa 
of  the  internal  auditory  meatus,  and  passes  forward  and  laterally  above  the  vestibular  portion 
of  the  internal  ear  for  a  distance  of  1.5-2.0  mm.  At  the  lateral  end  of  this  portion  of  its  course 
it  becomes  dilated  to  accommodate  the  geniculate  ganglion,  and  then  turns  abruptly  back- 
ward and  runs  in  a  horizontal  ridge  on  the  medial  wall  of  the  tympanurn,  lying  in  the  angle 
between  it  and  the  tegmen  tympani,  immediately  above  the  fenestra  vestibuli,  and  extending 
as  far  backward  as  the  entrance  to  the  mastoid  antrum.  Here  it  comes  into  contact  with  the 
inferior  aspect  of  the  projection  formed  by  the  lateral  semicircular  canal,  and  then  turns  verti- 
cally downward,  running  in  the  angle  between  the  medial  and  posterior  walls  of  the  tympanum 
to  terminate  at  the  stylo-mastoid  foramen. 

The  canal  is  traversed  by  the  facial  nerve.  Numerous  openings  exist  in  the  walls  of  this 
passage.  At  its  abrupt  bend,  or  genu,  the  greater  and  smaller  superficial  petrosal  nerves  escape 
from,  and  a  branch  from  the  middle  meningeal  artery  enters,  the  canal,  and  in  the  vertical  part 
of  its  course  the  cavity  of  the  pyramid  opens  into  it.  There  is  also  a  small  orifice  by  which  the 
auricular  branch  of  the  vagus  joins  the  facial,  and  near  its  termination  the  iter  chordae  posterius 
for  the  chorda  tympani  nerve  leads  from  it  into  the  tympanum. 


THE  SMALL  BONES  OF  THE  TYMPANUM 


79 


The  small  bones  of  the  tympanum. — These  bones,  the  malleus,  incus  and 
stapes,  are  contained  in  the  upper  part  of  the  tympanic  cavity.  Together  they 
form  a  jointed  column  of  bone  connecting  the  membrana  tympani  with  the 
fenestra  vestibuli. 

The  malleus. — This  is  the  most  external  of  the  iiuditory  ossicles,  and  hes  in  relation  with  the 
tympanic  membrane.  Its  upper  portion,  or  head,  is  lodged  in  the  epitympanic  recess.  It  is 
of  rounded  shape,  and  presents  posteriorly  an  elliptical  depression  for  articulation  with  the 
incus.  Below  the  head  is  a  constricted  portion  or  neck,  from  which  three  processes  diverge. 
The  largest  is  the  handle  or  manubrium,  which  is  slightly  twisted  and  flattened.  It  forms  an 
obtuse  angle  with  the  head  of  the  bone,  and  lies  between  the  membrana  tympani  and  the 
mucous  membrane  covering  its  inner  surface.  The  tensor  tympani  tendon  is  inserted  into  the 
manubrium  near  its  junction  with  the  neck  on  the  medial  side. 


Fig.  99. — The  Bones  of  the  Ear.     (Modified  from  Henle.) 


Fossa  for  incus 


Posterior  crus 


■Head  of  malle 


Lateral  process 
Anterior  process 


Articular  surface  for  malleus 


Lenticular  process 


The  anterior  process  (processus  gracilis  or  Folii)  is  a  long,  slender,  dehoate  spiculum  of  bone 
(rarely  seen  of  full  length  except  in  the  fcetus),  projecting  nearly  at  right  angles  to  the  anterior 
aspect  of  the  neck,  and  extending  obliquely  downward.  It  lies  in  the  petro-tympanic  fissure, 
and  in  the  adult  usually  becomes  converted  into  connective  tissue,  except  a  small  basal  stump. 
The  lateral  process  is  a  conical  projection  from  the  lateral  aspect  of  the  base  of  the  manu- 
brium. Its  apex  is  connected  to  the  upper  part  of  the  tympanic  membrane,  and  its  base  receives 
the  lateral  ligament  of  the  malleus.  The  malleus  also  gives  attachment  to  a  superior  hgament 
and  an  anterior  ligament,  the  latter  of  which  was  formerly  described  as  the  laxator  tymipani 
muscle. 

The  incus. — This  bone  is  situated  between  the  malleus  externally  and  the  stapes  internaUy. 
It  presents  for  examination  a  body  and  two  processes.  The  body  is  deeply  excavated  anteriorly 
for  the  reception  of  the  head  of  the  malleus.  The  short  process  projects  backward,  and  is 
connected  by  means  of  ligamentous  fibres  to  the  posterior  wall  of  the  tympanum,  near  the 
entrance  to  the  mastoid  antrum.  The  long  process  is  slender,  and  directed  downward  and  in- 
ward, and  lies  parallel  with  the  manubrium  of  the  maUeus.  On  the  medial  aspect  of  the  distal 
extremity  of  this  process  is  the  lenticular  process  (orbicular  tubercle),  separate  in  early  life,  but 


80 


THE  SKELETON 


subsequently  joined  to  the  process  by  a  narrow  neck.  Its  free  surface  articulates  with  the  head 
of  the  stapes. 

The  stapes  is  the  innermost  ossicle.  It  has  a  head  directed  horizontally  outward,  capped 
at  its  outer  extremity  by  a  disc  resembling  the  head  of  the  radius.  The  cup-shaped  depression 
receives  the  lenticular  process  of  the  incus.  The  base  occupies  the  fenestra  vestibuli,  and  like 
this  opening,  the  inferior  border  is  straight,  and  the  superior  curved.  The  base  is  connected 
with  the  head  by  means  of  two  crura,  and  a  narrow  piece  of  bone  called  the  neck.  Of  the  two 
crura,  the  anterior  is  the  shorter  and  straighter.  The  crura  with  the  base  form  a  stirrup-shaped 
arch,  of  which  the  irmer  margin  presents  a  groove  for  the  reception  of  the  membrane  stretched 
across  the  hollow  of  the  stapes.  In  the  early  embryo  this  hollow  is  traversed  by  the  stapedial 
artery.  The  neck  is  very  short,  and  receives  on  its  posterior  border  the  tendon  of  the  stapedius 
muscle. 

Development. — The  tympanic  cavity  represents  the  upper  extremity  of  the  first  endodermal 
branchial  groove,  which  becomes  converted  into  a  blind  pouch,  the  communication  of  which 
with  the  pharyngeal  cavity  is  the  tuba  auditiva  (Eustachian  tube).  The  thin  membrane  which 
separates  the  endodermal  from  the  ectodermal  groove  becomes  the  tympanic  membrane,  and 
it  is  from  the  upper  extremities  of  the  axial  skeletons  of  the  first  and  second  branchial  arches, 
which  bound  the  groove  anteriorly  and  posteriorly,  that  the  auditory  ossicles  are  formed,  the 
malleus  and  incus  belonging  to  the  first  arch  and  the  stapes  to  the  second  (Reichert).  The 
ossicles  consequently  lie  originally  in  the  walls  of  the  cavity,  but  they  are  surrounded  by  a  loose 
spongy  tissue,  which,  on  the  entrance  of  air  into  the  cavity,  becomes  compressed,  allowing  the 
cavity  to  enfold  the  ossicles.  These  therefore  are  enclosed  within  an  epithelium  which  is  con- 
tinuous medially  with  that  lining  the  posterior  tympanic  wall,  and  laterally  with  that  lining 
the  internal  surface  of  the  tympanic  membrane. 

The  mastoid  cells  are  outgrowths  of  the  cavity  into  the  adjacent  bone,  and  are  therefore 
lined  with  an  epithelium  continuous  with  that  of  the  cavity. 

THE  OSSEOUS  LABYRINTH 

The  osseous  labyrinth  [labyrinthus  osseus]  (fig.  100)  is  a  complex  cavity 
hollowed  out  of  the  petrous  portion  of  the  temporal  bone  and  containing  the 
membranous  labyrinth,  the  essential  part  of  the  organ  of  hearing.  It  is  in- 
completely divided  into  three  parts,  named  the  vestibule,  the  semicircular  canals, 
and  the  cochlea. 


Fig.  100. — The  Left  Osseous  L.\byrinth.     (After  Henle.     From  a  cast.) 

Superior  semicircular  caaal 

Lateral  semicircular  canal 

Posterior  semicircular  canal 
Fenestra  cochleae       Fenestra  vestibul: 

The  vestibule. — This  is  an  oval  chamber  situated  between  the  base  of  the  internal  auditory 
meatus  and  the  medial  wall  of  the  tympanum,  with  which  it  communicates  by  way  of  the 
fenestra  vestibuh.  Anteriorly,  the  vestibule  leads  into  the  cochlea,  and  posteriorly  it  receives 
the  extremities  of  the  semicircular  canals.  It  measures  about  3  mm.  transversely,  and  is  some- 
what longer  antero-posteriorly. 

Its  medial  wall  presents  at  the  anterior  part  a  circular  depression,  the  spherical  recess 
(fovea. hemispherica),  which  is  perforated  for  the  passage  of  nerve-twigs.  This  recess  is  sepa- 
rated by  a  vertical  ridge  (the  crista  vestibuli)  from  the  vestibular  orifice  of  the  aquseductus 

Fig.  101. — The  Cochlea  in  S.agittal  Section.     (After  Henle.) 


Internal  auditory  meritus 
The  spiral  canal 


vestibuli,  which  passes  obhquely  backward  to  open  on  the  posterior  surface  of  the  petrosal. 
The  roof  contains  an  oval  depression — the  elliptical  recess  (fovea  hemielUptioa). 

The  semicircular  canals  are  three  in  number.  Arranged  in  different  planes,  each  forms 
about  two-thirds  of  a  circle.     One  extremity  of  each  canal  is  dilated  to  form  an  ampulla.  _ 

The  superior  canal  lies  transversely  to  the  long  axis  of  the  petrosal,  and  is  nearly  vertical; 


i 


THE  ETHMOID  81 

its  highest  limb  makes  a  projection  on  the  superior  surface  of  the  bone.  The  ampulla  is  at  the 
lateral  end;  the  medial  end  opens  into  the  vestibule  conjointly  with  the  superior  limb  of  the 
posterior  canal. 

The  posterior  canal  is  nearly  vertical  and  lies  in  a  plane  nearly  parallel  to  the  posterior  sur- 
face of  the  petrosal.  It  is  the  longest  of  the  three;  its  upper  extremity  joins  the  medial  hmb 
of  the  superior  canal,  and  opens  in  common  with  it  into  the  vestibule.  The  lower  is  the  ampul- 
lated  end. 

The  lateral  canal  is  placed  horizontally  and  arches  laterally;  its  lateral  limb  forms  a 
prominence  in  the  mastoid  antrum.  This  canal  is  the  shortest;  its  ampulla  is  at  the  lateral  end 
near  the  fenestra  vestibuli. 

The  cochlea. — This  is  a  cone-shaped  cavity  lying  with  its  base  upon  the  internal  auditory 
meatus,  and  the  apex  directed  forward  and  laterally.  It  measures  about  five  millimetres  in 
length,  and  the  diameter  of  its  base  is  about  the  same.  The  centre  of  this  cavity  is  occupied  by 
a  column  of  bone — the  modiolus — around  which  a  canal  is  wound  in  a  spiral  manner,  making 
about  two  and  a  half  turns.  This  is  the  spiral  canal  of  the  cochlea;  its  first  turn  is  the  largest 
and  forms  a  bulging,  the  promontory,  on  the  medial  wall  of  the  tympanum. 

Projecting  into  the  canal  throughout  its  entire  length  there  is  a  horizontal, shelf-like  lamella, 
the  lamina  spiralis,  which  terminates  at  the  apex  of  the  cochlea  in  a  hook-like  process,  the 
hamulus.  The  free  edge  of  the  lamina  spiralis  gives  attachment  to  the  membranous  cochlea, 
a  canal  having  in  section  the  form  of  a  triangle  whose  base  is  attached  to  the  lateral  wall  of  the 
spiral  canal.  By  this  the  spiral  canal  is  divided  into  a  portion  above  the  lamina  spiralis,  termed 
the  scaia  vestibuli,  which  communicates  at  its  lower  end  with  the  osseous  vestibule,  and  a  portion 
below,  termed  the  scala  tympani,  which  abuts  at  its  lower  end  upon  the  fenestra  cochlea.  The 
two  scalae  communicate  at  the  apex  of  the  cochlea  by  the  helicotrema.  Near  the  commencement 
of  the  scala  tympani,  and  close  to  the  fenestra  rotunda,  is  the  cochlear  orifice  of  the  canaliculus 
cochlese  (ductus  perilymphaticus).  In  the  adult  this  opens  below,  near  the  middle  of  the  pos- 
terior border  of  the  petrous  bone,  and  transmits  a  small  vein  from  the  cochlea  to  the  jugular 
fossa. 

Measurements  of  the  principal  parts  connected  with  the  auditory  organs: — 
Internal  auditory  meatus Length  of  anterior  wall,  13-14  mm. 

Length  of  posterior  waU,  6.7  mm. 

External  auditory  meatus 14^16  mm.     (Gruber.) 

Tympanum Length,  13  mm. 

Height  in  centre  of  cavity,  15  mm. 

Width  opposite  the  membrana  tympani,  2  mm. 

Width  opposite  the  tubal  orifice,  3-4  mm.     (Von  Troltsch.) 

The  capsule  of  the  osseous  labyrinth  is  in  length  22  mm.     (Schwalbe.) 

Superior  semicircular  canal  measures  along  its  convexity  20  mm. 

The  posterior  semicircular  canal  measures  along  its  convexity  22  mm. 

The  lateral  semicircular  canal  measures  along  its  convexity  15  mm. 

The  canal  is  in  diameter  1.5  mm.     (Huschke.) 

The  ampulla  of  the  canal,  2.5  mm. 

Development. — The  membranous  internal  ear  arises  in  the  embryo  as  a  depression  of  the 
ectoderm  of  the  surface  of  the  head  opposite  the  fifth  neuromere  of  the  hind-brain  and  later 
becomes  a  sac-like  cavity,  the  otocyst,  which  separates  from  its  original  ectodermal  connec- 
tions and  sinks  deeply  into  the  subjacent  mesoderm,  a  part  of  which  becomes  incorporated  with 
it.  The  rest  of  the  mesodermal  tissue  which  surrounds  the  otocyst  becomes  later  the  petrous 
portion  of  the  temporal  bone,  the  perilymph  and  the  internal  periosteal  layer;  the  osseous 
labyrinth  is  therefore  merely  the  portions  of  the  petrous  which  enclose  the  cavity  occupied  by 
the  membranous  internal  ear. 

THE  ETHMOID 

The  ethmoid  [os  ethmoidale]  is  a  bone  of  delicate  texture,  situated  at  the  an- 
terior part  of  the  base  of  the  cranium  (figs.  102,  103,  104).  Projecting  downward 
from  between  the  orbital  plates  of  the  frontal,  it  enters  into  the  formation  of  the 
orbital  and  nasal  fossae.  It  is  cubical  in  form,  and  its  extreme  lightness  and 
delicacy  are  due  to  an  arrangement  of  very  thin  plates  of  bone  surrounding 
irregular  spaces  known  as  air-cells.  The  ethmoid  consists  of  four  parts:  the  hori- 
zontal or  cribriform  plate,  the  ethmoidal  labyrinth  on  each  side,  and  a  perpen- 
dicular plate. 

The  cribriform  plate  [lamina  cribrosa]  forms  part  of  the  anterior  cranial  fossa, 
and  is  received  into  the  ethmoidal  notch  of  the  frontal  bone.  It  presents  on  its 
upper  surface,  in  the  median  line,  the  intra-cranial  portion  of  the  perpendicular 
plate,  known  as  the  crista  galli,  a  thick,  vertical,  triangular  process  with  the  high- 
est point  in  front,  and  a  sloping  border  behind  which  gives  attachment  to  the  f alx 
cerebri.  The  anterior  border  is  short  and  in  its  lower  part  broadens  out  to  form 
two  alar  processes  which  articulate  with  the  frontal  bone  and  complete  the 
foramen  caecum.  The  ci'ista  galli  is  continuous  behind  with  a  median  ridge, 
and  on  each  side  of  the  middle  line  is  a  groove  which  lodges  the  olfactory  bulb. 


82 


THE  SKELETON 


The  cribriform  plate  is  pierced,  on  each  side,  by  numerous  foramina,  arranged  in  two  or 
three  rows,  which  transmit  the  filaments  of  the  olfactory  nerves  descending  from  the  bulb. 
Those  in  the  middle  of  the  groove  are  few  and  are  simple  perforations,  through  which  pass  the 
nerves  to  the  roof  of  the  nose;  the  medial  and  lateral  series  are  more  numerous  and  constitute 
the  upper  ends  of  small  canals,  which  subdivide  as  they  course  downward  to  the  upper  parts 
of  the  septum  and  the  lateral  wall  of  the  nasal  fossa.  At  the  front  part  of  the  cribriform  plate 
is  a  narrow  longitudinal  sht,  on  each  side  of  the  crista  gaUi,  which  transmits  the  anterior  eth- 
moidal (nasal)  branch  of  the  ophthalmic  division  of  the  fifth  nerve.  The  posterior  border 
articulates  with  the  ethmoidal  spine  of  the  sphenoid. 


Fig. 


102. — Section  through  the  Nasal  Fossa  to  show  the  Mesethmoid 
(Lamina  Perpendiculaeis). 


Crest  of  sphenoid 


-palatine  nerve: 


Crest  of  maxilla 


The  perpendicular  plate  (mesethmoid)  [lamina  perpendicularis  is  directly 
continuous  with  the  crista  galli  on  the  under  aspect  of  the  cribriform  plate,  so 
that  the  two  plates  cross  each  other  at  right  angles.  The  larger  part  of  the 
perpendicular  plate  is  below  the  point  of  intersection  and  forms  the  upper  third 
of  the  septum  of  the  nose.     It  is  quadrangular  in  form  with  unequal  sides. 


Fig.  103. — The  Ethmoid.     (Lateral  view.) 
-Crista  galli 


Anterior  ethmoidal  groove  — - 


Uncinate  process 


Inferior  nasal  concha 


Jt'osterior  ethmoidal  groove 
' -|- Lamina  papyracea 


Sphenoidal  concha 
Middle  nasal  concha 


The  anterior  border  articulates  with  the  spine  of  the  frontal  and  the  crest  of  the  nasal  bones. 
The  inferior  border  articulates  in  front  with  the  septal  cartilage  of  the  nose  and  behind  with  the 
anterior  margin  of  the  vomer.  The  posterior  margin  is  very  thin  and  articulates  with  the  crest 
of  the  sphenoid.  This  plate,  which  is  generally  deflected  a  little  to  one  side,  presents  above  a 
number  of  grooves  and  minute  canals  which  lead  from  the  inner  set  of  foramina  in  the  cribri- 
form plate  and  transmit  the  olfactory  nerves  to  the  septum. 

The  labyrinth  (lateral  mass)  is  oblong  in  shape  and  suspended  from  the  under 
aspect  of  the  lateral  part  of  the  cribriform  plate.     It  consists  of  two  scroll-like 


THE  ETHMOID 


83 


pieces  of  bone,  the  superior  and  middle  nasal  conchse  (turbinate  bones),  and 
encloses  numerous  irregularly  shaped  spaces,  known  as  the  ethmoidal  cells. 
These  are  arranged  in  three  sets — anterior,  middle,  and  posterior  ethmoidal  cells 
— and,  in  the  recent  state,  are  lined  with  prolongations  of  the  nasal  mucous 
membrane.  Laterally  the  labyrinth  presents  a  thin,  smooth,  quadrilateral  plate 
of  bone — the  lamina  papyracea  (os  planum) — which  closes  in  the  middle  and 
posterior  ethmoidal  cells  and  forms  a  large  part  of  the  medial  wall  of  the  orbit. 

By  its  anterior  border  it  articulates  with  the  lacrimal,  and  by  its  posterior  border  with  the 
sphenoid;  the  inferior  border  articulates  with  the  medial  margin  of  the  orbital  plate  of  the 
maxilla  and  the  orbital  process  of  the  palate  bone,  whilst  the  superior  border  articulates  with 
the  horizontal  plate  of  the  frontal.  Two  notches  in  the  superior  border  lead  into  grooves 
running  horizontally  across  the  lateral  mass  to  the  cribriform  plate,  which  complete,  with  the 
frontal  bone,  the  ethmoidal  canals.  The  anterior  canal  transmits  the  anterior  ethmoidal  ves- 
sels and  (nasal)  nerve;  the  posterior  transmits  the  posterior  ethmoidal  vessels  and  nerve. 


Fig. 


104. — Section  THRonGH  the  Nasal  Fossa  to  show  the  Labyrinth  of  .the  Ethmoid. 
It  shows  also  the  lateral  wall  of  the  left  nasal  fossa. 

Superior  nasal  concha 
Probe  in  sphenoidal  foran 
Sphenoidal  sinus 
Sella  turcica 


{ 


Superior  meatus 

Spheno-palatine 

foramen 


Uncinate  process  of  ethmoid 

Medial  pterygoid  plate 

Palate  bone 

Probe  in  posterior  palatine  canal 


Agger  nasi 

Lacrimal  bone 

Lower  end  of  bristle 
in  middle  meatus 
Middle  meatus 

Inferior  nasal 
concha 

Probe  at  lower  end 
of  naso-lacrimal 
canal     where      it 
opens  into  inferior 
meatus 

Incisive  canal 


At  the  lower  part  of  the  lateral  surface  is  a  deep  groove,  which  belongs  to 
the  middle  meatus  of  the  nose,  and  is  bounded  below  by  the  thick  curved  margin 
of  the  inferior  nasal  concha.  Anteriorly  the  middle  meatus  receives  the  in- 
fundibulum,  a  sinuous  passage  which  descends  from  the  frontal  sinus  through  the 
anterior  part  of  the  labyrinth.  The  anterior  ethmoidal  cells  open  into  the  lower 
part  of  the  infundibulum,  and  in  this  way  communicate  with  the  nose,  whereas 
the  middle  ethmoidal  cells  open  directly  into  the  middle  or  horizontal  part  of  the 
meatus.  In  front  of  the  lamina  papyracea  are  seen  a  few  broken  cells,  which 
extend  under,  and  are  completed  by,  the  lacrimal  bone  and  the  frontal  process 
of  the  maxilla;  from  this  part  of  the  labyrinth  an  irregular  lamina,  known  as  the 
uncinate  process,  projects  downward  and  backward.  The  uncinate  process 
articulates  with  the  ethmoidal  process  of  the  inferior  nasal  concha  and  forms  a 
small  part  of  the  medial  wall  of  the  maxillary  sinus. 

Medially  the  labyrinth  takes  part  in  the  formation  of  the  lateral  wall  of  the 
nasal  fossa,  and  presents  the  superior  and  middle  nasal  conchae  (turbinate 
processes),  continuous  anteriorly,  but  separated  behind  by  a  space  directed  for- 
ward from  the  posterior  margin.  This  channel  is  the  superior  meatus  of  the  nose 
and  communicates  with  the  posterior  ethmoidal  cells.     The  conchse  are  covered 


84 


THE  SKELETON 


in  the  recent  state  with  mucous  membrane  and  present  numerous  foramina  for 
blood-vessels  and,  above,  grooves  for  twigs  of  the  olfactory  nerves.  Each 
concha  has  an  attached  upper  border  and  a  free,  slightly  convoluted,  lower 
border,  and  in  the  case  of  the  middle  concha,  the  lower  margin  has  already  been 
noticed  on  the  outer  aspect,  where  it  overhangs  the  middle  meatus  of  the  nose. 
The  posterior  extremity  of  the  labyrinth  articulates  with  the  anterior  surface 
of  the  body  of  the  sphenoid  and  is  commonly  united  with  the  sphenoidal  concha. 

A  rounded  prominence  on  the  lateral  wall  of  the  middle  meatus  is  known  as  the  bulla 
ethmoidalis.  Antero-inferior  to  the  bulla  is  a  large  semilunar  depression  [hiatus  semilunaris] 
which  corresponds  to  the  lower  aperture  of  the  infundibulum. 

Man}'  of  the  ethmoidal  cells  are  imperfect  and  are  completed  by  adjacent  bones.  Those 
along  the  superior  edge  of  the  lateral  mass  are  the  fronto-ethmoidal;  those  at  the  anterior 
border,  usually  two  in  number,  are  known  as  lacrimo-ethmoidal.  Those  along  the  lower 
edge  of  the  lamina  papyraoea  are  the  maxillo-ethmoidal;  and  posteriorly,  are  the  spheno- 
ethmoidal, completed  by  the  sphenoidal  concha,  and  a  palate -ethmoidal  cell.  The  anterior 
extremity  presents  one  or  two  incomplete  cells  closed  by  the  nasal  process  of  the  maxilla. 

Blood-supply. — The  ethmoid  receives  its  blood-supply  from  the  anterior  and  posterior 
ethmoidal  arteries  and  from  the  spheno-palatine  branch  of  the  internal  maxillary. 

Articulations. — With  the  frontal,  sphenoid,  two  palate  bones,  two  nasals,  vomer,  two 
inferior  nasal  conchae,  two  sphenoidal  oonohse,  two  maxills,  and  two  lacrimal  bones.  The 
posterior  surface  of  each  labyrinth  is  in  relation  with  the  sphenoid  on  each  side  of  the  crest  and 
rostrum,  and  helps  to  close  in  the  sphenoidal  sinus. 

Ossification. — The  ethmoid  has  three  centres  of  ossification.  Of  these,  a  nucleus  appears 
in  the  fourth  month  of  intra-uterine  hfe  in  each  labyrinth,  first  in  the  lamina  papyraoea  and 
afterward  extending  into  the  middle  concha.  At  birth  each  lateral  portion  is  represented  by 
two  scroll-like  bones,  very  delicate  and  covered  with  irregular  depressions,  which  give  it  a  worm- 
eaten  appearance.  Six  months  after  birth  a  nucleus  appears  in  the  ethmo-vomerine  cartilage  lor 
the  vertical  plate  which  gradually  extends  into  the  crista  galU,  and  the  cribriform  plate  is  formed 
by  ossification  extending  laterally  from  this  centre,  and  medially  from  the  labyrinth.  The 
three  parts  coalesce  to  form  one  piece  in  the  fifth  or  sixth  year. 

The  ethmoid.al  cells  make  their  appearance  about  the  third  year,  and  gradually  invade 
the  labyrinths.  In  many  places  there  is  so  much  absorption  of  bone  that  the  cells  perforate 
the  ethmoid  in  situations  where  it  is  overlapped  by  other  bones.  Along  the  lower  border,  near 
its  articulation  with  the  maxilla,  the  absorption  leads  to  the  partial  detachment  of  a  narrow 
strip  known  as  the  uncinate  process.  Sometimes  a  second  but  smaller  hook-like  process  is 
formed,  above  and  anterior  to  this,  so  fragile  that  it  is  difficult  to  preserve  it  in  disarticulated 
bones.  The  relations  of  the  uncinate  process  are  best  studied  by  removing  the  lateral  wall  of 
the  maxillary  sinus. 


THE  INFERIOR  NASAL  CONCHA 

The  inferior  nasal  concha  (inferior  turbinate)  (fig.  105)  is  a  slender,  scroll-Hke 
lamina,  attached  by  its  upper  margin  to  the  lateral  wall  of  the  nasal  fossa,  and 
hanging  into  the  cavity  in  such  a  way  as  to  separate  the  middle  from  the  inferior 

Fig.  105. — The  Inferior  Concha,  Adult  Sphenoidal  Turbinate,  and  Lacrimal  Bones. 


The  crest  of  lacrimal 
Tensor  tarsi 
The  orbital  surface 
Lacrimal  groove 


Hamular  process, 

Conchal  process 

The    lacrimal    process 

The  ethmoidal  process 


The  maxillary  process 


Middle  nasal  concha 


meatus  of  the  nose.  It  may  be  regarded  as  a  dismemberment  of  the  ethmoidal 
labyrinth,  with  which  it  is  closely  related.  It  presents  for  examination  two 
surfaces,  two  borders,  and  two  extremities. 

The  lateral  surface  is  concave,  looks  toward  the  lateral  wall  of  the  nasal  fossa, 


THE  LACRIMAL  85 

and  is  overhung  by  the  maxillary  process.  The  medial  surface  is  convex,  pitted 
with  depressions,  and  grooved  for  vessels,  which,  for  the  most  part,  run  longi- 
tudinally. The  superior  or  attached  border  articulates  in  front  with  the  conchal 
crest  of  the  maxilla,  then  ascends  to  form  the  lacrimal  process,  which  articulates 
with  the  lacrimal  bone  and  forms  part  of  the  wall  of  the  lacrimal  canal.  Behind 
this,  it  is  turned  downward  to  form  the  maxillary  process,  already  mentioned, 
which  overhangs  the  orifice  of  the  maxillary  sinus  and  serves  to  fix  the  bone  firmly 
to  the  lateral  wall  of  the  nasal  fossa.  The  projection  behind  the  maxillary  process 
is  the  ethmoidal  process,  joined  in  the  articulated  skull  with  the  uncinate  process 
of  the  ethmoid  across  the  opening  of  the  maxillary  sinus.  Posteriorly  the  upper 
border  articulates  with  the  conchal  crest  of  the  palate.  The  inferior  border 
is  free,  rounded,  and  somewhat  thickened.  The  anterior  extremity  is  blunt  and 
flattened,  and  broader  than  the  posterior  extremity,  which  is  elongated,  narrow, 
and  pointed. 

Articulations. — With  the  maxilla,  lacrimal,  palate,  and  ethmoid. 

Ossification. — The  inferior  nasal  conotia  is  ossified  in  cartilage  from  a  single  nucleus  which 
appears  in  the  fifth  month  of  intra-uterine  life.  At  birth  it  is  a  relatively  large  bone  and  filla 
up  the  lower  part  of  the  nasal  fossa. 

THE  LACRIMAL 

The  lacrimal  bone  [os  lacrimale]  (fig.  105)  is  extremely  thin  and  delicate, 
quadrilateral  in  shape,  and  situated  at  the  anterior  part  of  the  medial  wall  of  the 
orbit.     It  is  the  smallest  of  the  facial  bones. 

The  orbital  surface  is  divided  by  a  vertical  ridge,  the  posterior  lacrimal 
crest,  into  two  unequal  portions.  The  anterior,  smaller  portion  is  deeply  grooved 
to  form  the  lacrimal  groove,  which  lodges  the  lacrimal  sac  and  forms  the  com- 
mencement of  the  canal  for  the  naso-lacrimal  duct.  The  portion  behind  the 
ridge  is  smooth,  and  forms  part  of  the  medial  wall  of  the  orbit.  The  ridge  gives 
origin  to  the  orbicularis  oculi  (pars  lacrimalis)  muscle  and  ends  below  in  a  hook-like 
process,  the  lacrimal  hamulus,  which  curves  forward  to  articulate  with  the  lacrimal 
tubercle  of  the  maxilla  and  completes  the  superior  orifice  of  the  naso-lacrimal 
canal.  The  medial  surface  is  in  relation  with  the  two  anterior  cells  of  the  ethmoid 
(lacrimo-ethmoidal),  forms  part  of  the  infundibulum,  and  inferiorly  looks  into 
the  middle  meatus  of  the  nose.  The  superior  border  is  short,  and  articulates 
with  the  medial  angular  process  of  the  frontal.  The  inferior  border  posterior  to 
the  crest  joins  the  medial  edge  of  the  orbital  plate  of  the  maxilla.  The  narrow 
piece,  anterior  to  the  ridge,  is  prolonged  downward  as  the  descending  process 
to  join  the  lacrimal  process  of  the  inferior  nasal  concha.  The  anterior  border 
articulates  with  the  posterior  border  of  the  frontal  process  of  the  maxilla  and  the 
posterior  border  with  the  lamina  papyracea  of  the  ethmoid. 

The  vessels  of  the  lacrimal  bone  are  derived  from  the  infra-orbital,  dorsal  nasal  branch  of 
the  ophthalmic,  and  anterior  ethmoidal  arteries. 

Articulations. — The  lacrimal  articulates  with  the  ethmoid,  maxilla,  frontal,  and  inferior 
nasal  concha. 

Ossification. — This  bone  arises  in  the  membrane  overlying  the  cartilage  of  the  fronto-nasal 
plate,  and  in  its  mode  of  ossification  is  very  variable.  As  a  rule,  it  is  formed  from  a  single 
nucleus  which  appears  in  the  third  or  fourth  month  of  intra-uterine  life.  Not  infrequently,  the 
hamulus  is  a  separate  element,  and  occasionally  the  bone  is  divided  by  a  horizontal  cleft,  a  pro- 
cess of  the  lamina  papyracea  projecting  between  the  two  halves  to  join  the  frontal  process  of 
the  maxilla.  More  rarely  the  bone  is  represented  by  a  group  of  detached  ossicles  resembling 
Wormian  bones. 

The  hamular  process  is  regarded  as  representing  the  remains  of  the  facial  part  of  the 
lacrimal  seen  in  lower  animals. 

THE  VOMER 

The  vomer  (fig.  106)  (ploughshare  bone)  is  an  unpaired  flat  bone,  which  lies 
in  the  median  plane  and  forms  the  lower  part  of  the  nasal  septum.  It  is  thin  and 
irregularly  quadrilateral  in  form,  and  is  usually  bent  somewhat  to  one  side, 
though  the  deflection  rarely  involves  the  posterior  margin.  Each  lateral  surface 
is  covered  in  the  recent  state  by  the  mucous  membrane  of  the  nasal  cavity,  and  is 
traversed  by  a  narrow  but  well-marked  groove,  which  lodges  the  naso-palatine 
nerve  from  the  spheno-palatine  ganglion. 


i 


86 


THE  SKELETON 


The  superior  border,  by  far  the  thickest  part  of  the  bone,  is  expanded  laterally 
into  two  alse.  The  groove  between  them  receives  the  rostrum  of  the  sphenoid, 
and  the  margin  of  each  ala  comes  into  contact  with  the  sphenoidal  process  of  the 
palate  and  the  vaginal  process  of  the  medial  pterygoid  plate.  The  inferior  border 
is  uneven  and  lies  in  the  groove  formed  by  the  crests  of  the  maxillary  and  palate 
bones  of  the  two  sides.  The  anterior  border  slopes  downward  and  forward  and  is 
grooved  below  for  the  septal  cartilage  of  the  nose;  above  it  is  united  with  the 
perpendicular  plate  of  the  ethmoid.  The  posterior  border,  smooth,  rounded,  and 
covered  by  mucus  membrane,  separates  the  posterior  nares.  The  anterior  and 
inferior  borders  meet  at  the  anterior  extremity  of  the  bone  which  forms  a  short 
vertical  ridge  behind  the  incisor  crest  of  the  maxillae.  From  near  the  anterior 
extremity,  a  small  projection  passes  downward  between  the  incisive  foramina. 


Fig.  106.— The  Vomer.     (Side  view.) 


Anterior  border 


-palatine  nerve 


Groove  for  septal  cartilage — ^^^f\^ 
Inferior  border 


Blood-supply. — The  arterial  supply  of  the  vomer  is  derived  from  the  anterior  and  posterior 
ethmoidal  and  the  spheno-palatine  arteries.  Branches  are  also  derived  from  the  posterior 
palatine  through  the  foramen  incisivum. 

Ossification. — The  vomer  is  ossified  from  two  centres  which  appear  about  the  eighth  week 
in  the  membrane  investing  the  ethmo-vomerine  cartilage.  The  two  lamellae  unite  below  during 
the  third  month  and  form  a  shallow  bony  trough  in  which  the  cartilage  lies.  In  the  process 
of  growth  the  lamells  extend  upward  and  forward  and  gradually  fuse  to  form  a  rectangular 
plate  of  bone,  the  cartilage  enclosed  between  them  undergoing  absorption  at  the  same  time. 
The  alae  on  the  superior  margin  and  the  groove  in  front  are  evidence  of  the  original  bilaminar 
condition. 

THE  NASAL 

The  nasal  (figs.  107  and  108)  are  two  small  oblong  bones  situated  at  the  upper 
part  of  the  face  and  forming  the  bridge  of  the  nose.  Each  bone  is  thicker  and 
narrower  above,  thinner  and  broader  below,  and  presents  for  examination  two 
surfaces  and  four  borders. 


Fig.  107. — The  Left  Nasal  Bone, 
Facial  Surface. 

Superior  borde 


Medial  border 
Lateral  border- 
Inferior  border' 


Fig.  108. — The  Left  Nasal  Bone, 
Nasal  Surface. 

Medial   border 


The  facial  surface  is  concave  from  above  downward,  convex  from  side  to  side, 
and  near  the  centre  is  perforated  by  a  small  foramen,  which  transmits  a  small 
tributary  to  the  facial  vein.  The  posterior  or  nasal  surface,  covered  in  the  recent 
state  by  mucous  membrane,  is  concave  laterally,  and  traversed  by  a  longitudinal 
groove  [sulcus  ethmoidalis]  for  the  anterior  ethmoidal  branch  of  the  ophthalmic 
division  of  the  fifth  nerve.  The  short  superior  border  is  thick  and  serrated  for 
articulation  with  the  medial  part  of  the  nasal  notch  of  the  frontal.  The  inferior 
border  is  thin,  and  serves  for  the  attachment  of  the  lateral  nasal  cartilage.  It 
is  notched  for  the  external  nasal  branch  of  the  anterior  ethmoidal  nerve.  The 
nasal  bones  of  the  two  sides  are  united  by  their  medial  borders,  forming  the  inter- 
nasal  suture.  The  contiguous  borders  are  prolonged  backward  to  form  a  crest 
which  rests  on  the  frontal  spine  and  the  anterior  border  of  the  perpendicular 
plate  of  the  ethmoid.  The  lateral  border  articulates  with  the  frontal  process 
of  the  maxilla. 


THE  MAXILLA  87 

Blood-supply. — Arteries  are  supplied  to  this  bone  by  the  nasal  branch  of  the  ophthalmic, 
the  frontal,  the  angular,  and  the  anterior  ethmoidal  arteries. 

Articulations. — With  the  frontal,  maxilla,  ethmoid,  and  its  fellow  of  the  opposite  side. 

Ossification. — Each  nasal  bone  is  developed  from  a  single  centre  which  appears  about  the 
eighth  week  in  the  membrane  overlying  the  fronto-nasal  cartilage.  The  cartilage,  which  is 
continuous  with  the  ethmoid  cartilage  above  and  the  lateral  cartilage  of  the  nose  below,  sub- 
sequently undergoes  absorption  as  a  result  of  the  pressure  caused  by  the  expanding  bone.  A.t 
birth  the  nasal  bones  are  nearly  as  wide  as  they  are  long,  whereas  in  the  adult  the  length  is 
three  times  greater  than  the  width. 

THE  MAXILLA 

The  maxilla  or  upper  jaw-bone  (figs.  109,  110,  111)  is  one  of  the  largest  and 
most  important  of  the  bones  of  the  face.  It  supports  the  maxillary  teeth  and 
takes  part  in  the  formation  of  the  orbit,  the  hard  palate,  and  the  nasal  fossa. 
It  is  divisible  into  a  body  and  four  processes,  of  which  two — the  frontal  and 
zygomatic — belong  to  the  upper  part,  and  the  palatine  and  alveolar  to  the  lower 
part  of  the  bone. 

The  body  is  somewhat  pyramidal  in  shape  and  hollowed  by  a  large  cavity 
known  as  the  sinus  maxillaris  (antrum  of  Highmore) ,  lined  by  mucous  membrane 
in  the  recent  state,  and  opening  at  the  base  of  the  pyramid  into  the  nasal  cavity, 
the  zygomatic  process  forming  the  apex.  The  anterior  (or  facial)  surface 
looks  forward  and  outward  and  is  marked  at  its  lower  part  by  a  series  of  eminences 
which  indicate  the  positions  of  the  fangs  of  the  teeth.  The  eminence  produced 
by  the  fang  of  the  canine  tooth  is  very  prominent  and  separates  two  fossa. 
That  on  the  medial  side  is  the  incisive  fossa,  and  gives  origin  to  the  alar  and 
transverse  portions  of  the  nasalis,  and  just  above  the  socket  of  the  lateral  incisor 
tooth,  to  a  slip  of  the  orbicularis  oris;  on  the  lateral  side  is  the  canine  fossa,  from 
which  the  caninus  {levator  anguli  oris)  arises.  Above  the  canine  fossa,  and  close 
to  the  margin  of  the  orbit,  is  the  infra-orbital  foramen,  through  which  the  terminal 
branches  of  the  infra-orbital  nerve  and  vessels  emerge,  and  from  the  ridge  im- 
mediately above  the  foramen  the  quadratus  labii  superioris  takes  origin.  The 
medial  margin  of  the  anterior  surface  is  deeply  concave,  forming  the  nasal  notch, 
and  is  prolonged  below  into  the  anterior  nasal  spine. 

A  ridge  of  bone  extending  upward  from  the  socket  of  the  first  molar  tooth 
separates  the  anterior  from  the  infratemporal  (zygomatic)  surface.  This  latter 
surface  is  convex  and  presents  near  the  middle  the  orifices  of  the  posterior 
alveolar  canals,  transmitting  the  posterior  alveolar  vessels  and  nerves.  The 
posterior  inferior  angle,  known  as  the  tuberosity  [tuber  maxillare],  is  rough  and  is 
most  prominent  after  eruption  of  the  wisdom  tooth.  It  gives  attachment  to  a 
few  fibres  of  the  internal  pterygoid  muscle  and  articulates  with  the  tuberosity  of 
the  palate. 

The  orbital  surface  [planum  orbitale]  is  smooth,  irregularly  triangular,  and 
forms  the  greater  part  of  the  floor  of  the  orbit. 

Anteriorly,  it  is  rounded  and  reaches  the  orbital  circumference  for  a  short  distance  at  the 
root  of^the  nasal  process;  lateraUy  is  the  rough  surface  for  the  zygomatic  bone.  The  posterior 
border,  smooth  and  rounded,  forms  the  inferior  boundary  of  the  inferior  orbital  fissure.  The 
medial  border  is  nearly  straight  and  presents  behind  the  frontal  process,  a  smooth  rounded 
angle  forming  part  of  the  circumference  of  the  orbital  orifice  of  the  naso-lacrimal  canal,  and  a 
notch  which  receives  the  lacrimal  bone.  The  rest  of  the  medial  border  is  rough  for  articulation 
with  the  lamina  papyracea  of  the  ethmoid  and  orbital  process  of  the  palate  bone. 

The  orbital  surface  is  traversed  by  the  infra-orbital  groove,  which,  com- 
mencing at  the  posterior  border,  deepens  as  it  passes  forward  and  finally  becomes 
closed  in  to  form  the  infra-orbital  canal.  It  transmits  the  second  division  of  the 
fifth  nerve  and  the  infra-orbital  vessels  and  terminates  on  the  anterior  surface 
immediately  below  the  margin  of  the  orbit.  From  the  infra-orbital,  other  canals 
— the  anterior  and  middle  alveolar — run  downward  in  the  wall  of  the  antrum  and 
transmit  the  anterior  and  middle  alveolar  vessels  and  nerves.  Lateral  to  the 
commencement  of  the  lacrimal  canal  is  a  shallow  depression  for  the  origin  of 
the  inferior  oblique. 

The  nasal  surface  takes  part  in  the  formation  of  the  lateral  wall  of  the  nasal 
fossa.  It  presents  a  large  irregular  aperture  which  leads  into  the  antrum  and, 
immediately  in  front  of  this,  the  lacrimal  groove,  directed  downward,  backward, 
and  laterally  into  the  inferior  meatus  of  the  nose.     The  groove  is  converted 


( 


THE  SKELETON 


into  a  canal  by  the  lacrimal  and  inferior  nasal  concha  and  transmits  the  naso- 
lacrimal duct. 

In  front  of  the  groove  is  a  smooth  surface  crossed  obhquely  by  a  ridge,  the  concbal  crest, 
for  articulation  with  the  inferior  nasal  concha.  The  surface  below  the  crest  is  smooth,  concave, 
and  belongs  to  the  inferior  meatus;  the  surface  above  the  crest  extends  on  to  the  lower  part  of 
the  frontal  process  and  forms  the  wall  of  the  atrium  of  the  middle  meatus.  Behind  the  open- 
ing of  the  antrum  the  surface  is  rough  for  articulation  with  the  vertical  plate  of  the  palate 
bone,  and  crossing  it  obliquely  is  a  smooth  groove  converted  by  the  ipalate  into  the  pterygo- 
palatine canal  for  the  passage  of  the  (descending)  palatine  nerves  and  the  descending  palatine 
artery. 

Fig.  109. — The  Left  Maxilla.     (Outer  view.) 


Infra-orbital  foramen- 
Nasal  notch. 
Canine  fossa' 
al  spine 


Canin 


eminence 


Border  of  inferior  orbital  fissure 
For  sphenoid 
Zygomatic  surface 
Zygomatic  process 
Posterior  alveolar  canals 


W   ,    It       /J -Tuberosity 


The  frontal  process,  somewhat  triangular  in  shape,  rises  vertically  from  the 
angle  of  the  maxilla.  Its  lateral  surface  is  continuous  with  the  anterior  surface 
of  the  body,  and  gives  attachment  to  the  orbicularis  oculi,  the  medial  palpebral 
ligament  and  the  quadratus  labii  superioris  {caput  angular e).  The  medial  sur- 
face forms  part  of  the  lateral  boundary  of  the  nasal  fossa  and  is  crossed  obliquely 
by  a  low  ridge,  known  as  the  agger  nasi,  limiting  the  atrium  of  the  middle  meatus. 

The  hinder  part  of  this  surface  rests  on  the  anterior  extremity  of  the  labyrinth  of  the  eth- 
moid and  completes  the  maxillo-ethmoidal  cells.  The  superior  border  articulates  with  the 
frontal;  the  anterior  border  articulates  with  the  nasal  bone;  the  posterior  border  is  thick  and 
vertically  grooved,  in  continuation  with  the  lacrimal  groove,  and  lodges  the  lacrimal  sac. 
The  medial  margin  of  the  groove  articulates  with  the  lacrimal  bone,  and  the  junction  of  its 
lateral  margin  with  the  orbital  surface  is  indicated  by  the  lacrimal  tubercle. 

Fig.  110. — The  Left  Maxilla.     (Inner  view.) 


'Frontal  process 


Posterior  palatine  groove 
Palatine  process 


The  zygomatic  process,  rough  and  triangular,  forms  the  summit  of  the 
prominent  ridge  of  bone  separating  the  anterior  and  infratemporal  surfaces.  It 
articulates  above  with  the  zygomatic,  and  from  its  inferior  angle  a  few  fibres  of 
the  masseter  take  origin.  The  anterior  and  posterior  surfaces  are  continuous 
with  the  anterior  and  infratemporal  surfaces  of  the  body. 

The  palatine  process  projects  horizontally  from  the  medial  surface  and,  with 
the  corresponding  process  of  the  opposite  side,  forms  about  three-fourths  of  the 
hard  palate.     The  superior  surface  is  smooth,  concave  from  side  to  side,  and 


THE  MAXILLA  89 

constitutes  the  larger  part  of  the  floor  of  the  nasal  fossa.  The  inferior  surface  is 
vaulted,  rough,  and  perforated  with  foramina  for  nutrient  vessels.  Near  its 
lateral  margin  is  a  longitudinal  groove  for  the  transmission  of  the  vessels  and 
nerves  which  issue  at  the  posterior  palatine  canal  and  course  along  the  lower 
aspect  of  the  palate.  When  the  bones  of  the  two  sides  are  placed  in  apposition,  a 
large  orifice  may  be  seen  in  the  middle  line  immediately  behind  the  incisor  teeth. 
This  is  the  incisive  foramen,  at  the  bottom  of  whjch  are  four  foramina.  Two  are 
small  and  arranged  one  behind  the  other  exactly  in  the  meso-palatine  suture. 
These  are  the  foramina  of  Scarpa  and  transmit  the  naso-palatine  nerves,  the  left 


Fig.  111. — Section  op  Maxilla  to  show  the  Floor  op  the  Maxillary  Antrum. 
(Reduced  J.) 


( 


passing  through  the  anterior  and  the  right  through  the  posterior  aperture.  The 
lateral  and  larger  orifices  are  the  foramina  of  Stenson,  representing  the  lower 
apertures  of  two  passages  by  which  the  nose  communicates  with  the  mouth ;  they 
transmit  some  terminal  branches  of  the  descending  palatine  artery  to  the  nasal 
fossae,  and  lodge  recesses  of  the  nasal  mucous  membrane  and  remnants  of 
Jacobson's  organs. 


Fig.  112. — Maxilla  and  Zygomatic  Bone,  to  show  Muscular  Attachments. 

Inferior  oblique 


(Poirier.) 


Quadrate  muscle, 
zygomatic  head 


Orbicularis  oculi 


Quadrate  muscle, 
angular  head 


Dilator  narisposterii 


Nasalis  (alar  portion) 


Running  laterally  from  the  incisive  foramen  to  the  space  between  the  second  incisor  and 
canine  tooth,  an  indistinct  suture  may  sometimes  be  seen,  indicating  the  hne  of  junction  of  the 
maxillary  and  pre-maxillary  portions  of  the  bone.  The  premaxilla  or  incisive  bone  is  the  part 
which  bears  the  incisor  teeth  and  in  some  animals  exists  tliroughout  life  as  an  independent 
element.    The  posterior  border  of  the  palate  process  is  rough  and  serrated  for  articulation  with 


90 


THE  SKELETON 


the  horizontal  plate  of  the  palate  bone  which  completes  the  hard  palate.  The  medial  border 
joins  with  its  fellow  to  form  the  nasal  crest  upon  wliich  the  vomer  is  received.  The  more 
elevated  anterior  portion  of  this  border  is  known  as  the  incisor  crest,  and  is  continued  forward 
into  the  anterior  nasal  spine.  The  septal  cartilage  of  the  nose  rests  on  its  summit  and  the  anterior 
extremity  of  the  vomer  lies  immediately  behind  it.  At  the  side  of  the  incisor  crest  is  seen  the 
upper  aperture  of  the  canal  leading  from  the  nose  to  the  mouth  (Stenson's  canal),  which  in  its 
course  downward  becomes  a  groove  by  a  deficiency  of  its  medial  wall.  Thus  when  the  two  bones 
are  articulated  a  canal  is  formed  (incisive)  with  the  lower  ends  of  two  canals  opening  into  it. 

The  alevolar  process  is  crescentic  in  shape,  spongy  in  texture,  and  presents 
cavities  [alveoli  dentales]  in  which  the  upper  teeth  are  lodged.     When  complete 


there  are  eight  tooth-cavities  (alveoli),  with  wide  mouths,  gradually  narrowing 
as  they  pass  into  the  substance  of  the  bone,  and  forming  exact  impressions  of  the 
corresponding  fangs  of  the  teeth.  The  pit  for  the  canine  tooth  is  the  deepest; 
those  for  the  molars  are  the  widest,  and  present  subdivisions.  Along  the  lateral 
aspect  of  the  alveolar  process  the  buccinator  arises  as  far  forward  as  the  first  molar 
tooth. 

The  maxillary  sinus  or  antrtma  of  Highmore,  as  the  air-chamber  occupying 
the  body  of  the  bone  is  called,  is  somewhat  pyramidal  in  shape,  the  base  being 
represented  by  the  nasal  or  medial  surface,  and  the  apex  corresponding  to  the 
zygomatic  process.  In  addition  it  has  four  walls:  the  superior  is  formed  by  the 
orbital  plate,  and  the  inferior  by  the  alveolar  ridge.  The  anterior  wall  corre- 
sponds to  the  anterior  surface  of  the  maxilla,  and  the  posterior  is  formed  by  the 
infratemporal  surface.     The  medial  boundary  or  base  presents  a  very  irregular 


Fig.  113. — The  Maxilla  at  Birth. 
Premaxillary  portion 


Inferior  view 


orifice  at  its  posterior  part;  this  is  partially  filled  in  by  the  vertical  plate  of  the 
palate  bone,  the  uncinate  process  of  the  ethmoid,  the  maxillary  process  of  the 
inferior  nasal  concha,  and  a  small  portion  of  the  lacr'mal  bone.  Even  when  these 
bones  are  in  their  relative  positions,  the  orifice  is  very  irregular  in  shape,  and 
requires  the  mucous  membrane  to  form  the  definite  rounded  aperture  (or  apertures, 
for  they  are  often  multiple)  known  as  the  opening  of  the  sinus  through  which 
the  cavity  communicates  with  the  middle  meatus  of  the  nose. 

The  cavity  of  the  sinus  varies  considerably  in  size  and  shape.  In  the  young,  it  is  small  and 
the  walls  are  thick:  as  life  advances  it  enlarges  at  the  expense  of  its  walls,  and  in  old  age  they  are 
often  extremely  thin,  so  that  occasionally  the  cavity  extends  even  into  the  substance  of  the 
zygomatic  bone.  The  floor  of  the  sinus  is  usually  very  uneven,  due  to  prominences  corre- 
sponding to  the  roots  of  the  molar  teeth.  In  most  oases  the  bone  separating  the  teeth  from 
the  sinus  is  very  thin,  and  in  some  cases  the  roots  project  into  it.  The  teeth  which  come  into 
closest  relationship  with  the  sinus  are  the  first  and  second  molars,  but  the  sockets  of  any  of 
the  teeth  lodged  in  the  maxilla  may,  under  diseased  conditions,  communicate  with  it.  As  a 
rule,  the  cavity  of  the  sinus  is  single,  but  occasionally  specimens  are  seen  in  which  it  is  divided 
by  bony  septa  into  chambers,  and  it  is  not  uncommon  to  find  recesses  separated  by  bony 
processes.  The  roof  of  the  sinus  presents  near  its  anterior  aspect  what  appears  to  be  a  thick 
rib  of  bone;  this  is  hollow  and  corresponds  to  the  infra-orbital  canal. 

The  most  satisfactory  method  of  studying  the  relation  of  the  bones  closing  in  the  base  of 
the  antrum  is  to  cut  away  the  lateral  wall  of  the  cavity  (see  fig.  128). 

Blood-supply. — The  maxilla  is  a  very  vascular  bone  and  its  arteries  are  numerous  and 
large.  They  are  derived  from  the  infra-orbital,  alveolar,  descending  palatine,  spheno-pala- 
tine,  ethmoidal,  frontal,  nasal,  and  facial  vessels. 

Articulations. — With  the  frontal,  nasal,  lacrimal,  ethmoid,  palate,  vomer,  zygomatic, 
inferior  nasal  concha  and  its  fellow  of  the  opposite  side.  Occasionally  it  articulates  with  the 
great  wing,  and  the  pterygoid  process,  of  the  sphenoid. 


THE  PALATE  BONE 


91 


Ossification. — The  maxilla  is  developed  from  several  centres  which  are  deposited  in  mem- 
brane during  the  second  month  of  intrauterine  life.  Several  pieces  are  formed  which  speedily 
fuse,  so  that  at  birth,  with  the  exception  of  the  incisor  fissure  separating  the  maxilla  from  the 
premaxiUa,  there  is  no  trace  of  the  composite  character  of  the  bone.  The  centres  of  ossification 
comprise — (1)  the  malar,  which  gives  rise  to  the  portion  of  bone  outside  the  infra-orbital  canal; 

(2)  the  maxillary,  from  which  the  greater  part  of  the  body  and  the  frontal  process  are  developed; 

(3)  the  palatine,  forming  the  hinder  three-fourths  of  the  palatal  process  and  adjoining  part 
of  the  nasal  wall;  (-1)  the  premaxiilary,  giving  rise  to  the  independent  premaxiUary  bone  (os 
incisivum),  which  lodges  the  incisor  teeth  and  completes  the  anterior  fourth  of  the  hard  palate. 
In  the  early  stages  of  growth  the  premaxiUa  may  consist  of  two  pieces  arising  from  two  centres 
of  ossification  which  AJbrecht  has  named  as  follows: — the  endognathion,  or  medial  division  for 

Fig.  114. — Maxilla  at  the  end  op  the  First  Dentition  in  both  op  which  the  Sutures 
BETWEEN  Maxilla  and  Premaxilla,  and  between  the  two  Parts  op  the  Prbmaxilla, 

ARE   seen. 


£ndo-mesognathic  suture 
Meso-exognatliic  suture 


{ 


the  central  incisor,  and  the  mesognathion,  or  lateral  division  for  the  lateral  incisor;  the  rest 
of  the  maxilla  is  named  the  exognathion;  (5)  the  prepalatine,  corresponding  to  the  infra-vomerine 
centre  of  Rambaud  and  Renault,  forms  a  portion  of  bone  interposed  between  the  premaxiUary 
in  front  and  the  palatine  process  behind.  It  gives  rise  to  a  part  of  the  nasal  surface  and  com- 
pletes the  medial  waU  of  the  incisive  canal. 

At  birth  the  sinus  is  narrow  from  side  to  side  and  does  not  extend  laterally  to  any  appre- 
ciable extent  between  the  orbit  and  the  alveoli  of  the  teeth.  During  the  early  years  of  life  it 
graduaUy  enlarges,  but  does  not  attain  its  fuU  growth  untU  after  the  period  of  the  second 
dentition. 


THE  PALATE 

The  palate  bone  [os  palatinum]  (figs.  115,  116)  forms  the  posterior  part  of  the 
hard  palate,  the  medial  wall  of  the  nasal  fossa  between  the  maxilla  and  the 
medial  pterygoid  plate,  and,  by  its  orbital  process,  the  hinder  part  of  the  floor 
of  the  orbit.  It  is  somewhat  L-shaped  and  presents  for  examination  a  horizontal 
part  and  a  perpendicular  part;  at  their  point  of  junction  is  the  pyramidal  process, 
and  surmounting  the  top  of  the  vertical  plate  are  the  orbital  and  sphenoidal 
processes,  separated  by  the  spheno-palatine  notch. 

The  horizontal  part  resembles  the  palatine  process  ofthe  maxilla,  but  is  much 
shorter.  The  superior  surface  is  smooth,  concave  from  side  to  side,  and  forms 
the  back  part  of  the  floor  of  the  nasal  fossa;  the  inferior  surface  completes  the 
hard  palate  behind  and  presents  near  its  prosterior  border  a  transverse  ridge 
which  gives  attachment  to  the  tensor  veli  'palatini  muscle. 

The  anterior  border  is  rough  for  articulation  with  the  palatine  process  of  the  maxiUa;  the 
posterior  is  free,  curved,  and  sharp,  giving  attachment  to  the  soft  palate.  MediaUy  it  is  thick 
and  broad  for  articulation  with  its  fellow  of  the  opposite  side,  forming  a  continuation  of  the 
crest  of  the  palatal  processes  of  the  maxiUae  and  supporting  the  vomer.  The  posterior  extremity 
of  the  crest  is  the  posterior  nasal  spine,  from  which  the  azygos  uvulce  arises.  LateraUy,  at  its 
junction  with  the  perpendicular  part,  it  is  grooved  by  the  lower  end  of  the  pterygo-palatine 
canal. 

The  perpendicular  part  is  longer  and  thinner  than  the  horizontal  plate.  The 
lateral  surface  is  in  relation  with  the  maxilla  and  is  divided  into  two  parts  by 


92 


THE  SKELETON 


a  vertical  groove  which  forms  with  the  maxilla  the  pterygo -palatine  canal  for 
the  transmission  of  the  anterior  palatine  nerve  and  the  descending  palatine 
artery.  The  part  of  the  surface  in  front  of  the  groove  articulates  with  the  nasal 
surface  of  the  maxilla  and  overlaps  the  orifice  of  the  antrum  by  the  maxillary 
process,  a  variable  projection  on  the  anterior  border.  Behind  the  groove  the 
surface  is  rough  for  articulation  with  the  maxilla  below  and  the  medial  pterygoid 
plate  above. 

Fig.  115. — Palate  Bone  (Left).     (Medial  view.) 


Sphenoidal  process. 

-palatine     notcli     (when 

complete  in  the  palate 
bone,  it  is  due  to  ankylosis  with 
sphenoidal  concha) 


Orbital  process  (ethmoidal  surfaced 

Superior  meatus 
■Ethmoidal  crest 

Middle  meatus 

Conchal  crest 
Inferior  meatus 


The  medial  or  nasal  surface  presents  two  nearly  horizontal  ridges  separating 
three  shallow  depressions.  Of  the  depressions,  the  lower  forms  part  of  the  inferior 
meatus  of  the  nose,  and  the  limiting  ridge  or  conchal  (inferior  turbinate)  crest 
articulates  with  the  inferior  nasal  concha.  Above  this  is  the  depression  forming 
part  of  the  middle  meatus,  and  the  ridge  or  ethmoidal  (superior  turbinate)  crest, 
constituting  its  upper  boundary,  articulates  with  the  middle  nasal  concha. 


Fig.  116. — Palate  Bone.     (Posterior  view.) 


Orbital  surface 


Zygomatic  surface 


Spheno-palatine   foramen    (usually  a 
notch) 


Groove  for  external  pterygoid- 

Groove  for  pterygoid  fo 
Groove  for  internal  pterygoid 


Tuberosity- 


Orbital  process 


Sphenoidal  process 


The  upper  groove  is  narrower  and  deeper  than  the  other  two  and  forms  a  large  part  of  the 
superior  meatus  of  the  nose.  The  anterior  border  of  the  vertical  plate  is  thin  and  bears  the 
maxillary  process,  a  tongue-like  piece  of  bone,  which  e.xtends  over  the  opening  of  the  maxillary 
sinus  from  behind.  This  border  is  continuous  above  with  the  orbital  process.  The  posterior 
border  is  rough  and  articulates  with  the  anterior  border  of  the  medial  pterygoid  plate.  It  is 
continuous  superiorly  with  the  sphenoidal  process. 

The  pyramidal  process  or  tuberosity  fits  into  the  notch  between  the  lower  extremities  of 
the  pterygoid  plates  and  presents  posteriorly  three  grooves.  The  middle,  smooth  and  concave, 
completes  the  pterygoid  fossa,  and  gives  origin  to  a  few  fibres  of  the  internal  -pterygoid;  the 
medial  and  lateral  grooves  are  rough  for  articulation  with  the  anterior  border  of  the  correspond- 
ing pterygoid  plate.  Inferiorly,  close  to  its  junction  with  the  horizontal  plate,  are  the  openings 
of  the  greater  palatine  and  smaller  palatine  canals,  of  which  the  latter  are  the  smaller  and  less 
constant;  they  transmit  the  palatine  nerves.  Medially  the  pyramidal  process  gives  origin  to  a 
few  fibres  of  the  superior  constrictor  of  the  pharynx,  and  laterally  a  small  part  appears  in  the 
zygomatic  fossa  between  the  tuberosity  of  the  maxilla  and  the  pterj'goid  process  of  the  sphenoid. 

The  sphenoidal  process,  the  smaller  of  the  two  processes  surmounting  the  vertical  part, 
curves  upward  and  medially  and  presents  three  surfaces  and  two  borders.  The  superior  sur- 
face is  in  contact  with  the  body  of  the  sphenoid,  and  the  top  of  the  medial  pterygoid  plate,  where 
it  completes  the  pharyngeal  canal.     The  medial  or  inferior  surface  forms  part  of  the  lateral 


THE  ZYGOMATIC  BONE  93 

wall  and  roof  of  the  nasal  fossa,  and  at  its  medial  end  tounhes  the  ala  of  the  vomer.  The 
lateral  surface  looks  forward  and  laterally  into  the  pterygo-palatine  (spheno-maxillary)  fossa. 
Of  the  two  border3,the  posterior  is  thin  and  articulates  with  the  medial  pterygoid  plate;  the 
anterior  border  forms  the  posterior  boundary  of  the  spheno-palatine  foramen. 

The  orbital  process  is  somewhat  pyramidal  in  shape,  and  presents  for  examination  five 
surfaces,  three  of  which — the  posterior,  anterior,  and  medial — are  articular  and  the  rest  non- 
articular.  The  posterior  or  sphenoidal  surface  is  small  and  joins  the  anterior  surface  of  the 
body  of  the  sphenoid;  the  medial  or  ethmoidal  articulates  with  the  labyrinth  of  the  ethmoid; 
and  the  anterior  or  maxillary,  which  is  continuous  with  the  lateral  surface  of  the  perpendicular 
part,  is  joined  with  the  maxilla.  Of  the  two  non-articular  surfaces,  the  superior  or  orbital, 
directed  upward  and  laterally,  is  slightly  concave,  and  forms  the  posterior  angle  of  the  floor 
of  the  orbit;  the  lateral  or  zygomatic,  smooth  and  directed  lateral,  looks  into  the  pterygo- 
palatine (spheno-maxillary)  and  zygomatic  fossse,  and  forms  the  anterior  boundary  of  the 
spheno-palatine  foramen.  The  process  is  usually  hollow  and  the  cavity  completes  one  of  the 
posterior  ethmoidal  cells  or  communicates  with  the  sphenoidal  sinus. 

Fig.  117. — Maxilla  and  Palate  Bones  showing  how  the  Inpha-okbital  Groove 
Runs  Outwakd  almost  at  Right  Angles  phom  the  Neighbourhood  op  the  Spheno- 
palatine Foramen  on  the  Back  of  the  Maxilla  and  the  Orbital  Process  op  the 
Palate.    Posterior  View.     (E.  Fawcett.) 


.Infra-orbital  groove 


Between  the  orbital  and  sphenoidal  processes  is  the  spheno-palatine  notch,  converted  by 
the  body  of  the  sphenoid,  into  a  complete  foramen.  It  leads  from  the  pterygo-palatine  fossa 
into  the  back  part  of  the  nasal  cavity  close  to  its  roof,  and  transmits  the  medial  branches  from 
the  spheno-palatine  ganglion  and  the  spheno-palatine  vessels. 

Blood-supply. — The  palate  bone  receives  branches  from  the  descending  palatine  and  the 
spheno-palatine  arteries. 

Articulations. — With  the  sphenoid,  maxilla,  vomer,  inferior  nasal  concha,  ethmoid,  and  its 
fellow  of  the  opposite  side. 

Ossification. — The  palate  is  ossified  in  membrane  from  a  single  centre  which  appears  about 
the  eighth  week  at  the  angle  between  the  horizontal  and  perpendicular  parts.  At  birth  the 
two  parts  are  nearly  equal  in  length,  but  as  the  nasal  fossae  increase  in  vertical  depth,  the 
perpendicular  part  is  lengthened  until  it  becomes  about  twice  as  long  as  the  horizontal  part. 

THE  ZYGOMATIC 

The  zygomatic  [os  zygomaticum]  or  malar  bone  (fig.  118)  forms  the  promi- 
nence known  as  the  cheek  and  joins  the  zygomatic  process  of  the  temporal  with  the 
maxilla.  It  is  quadrangular  in  form  with  the  angles  directed  vertically  and 
horizontally.  The  malar  (or  external)  surface  is  convex  and  presents  one  or  two 
small  orifices  for  the  transmission  of  the  zygomatico-facial  nerves  and  vessels. 
It  is  largely  covered  by  the  orbicularis  oculi  and  near  the  middle  is  slightly  ele- 
vated to  form  the  malar  tuberosity,  which  gives  origin  to  the  zygomaticus  and 
zygomatic  head  of  quadrate  muscle  of  upper  lip. 

The  temporal  (or  internal)  surface  is  concave  and  looks  into  the  temporal 
and  infratemporal  fossae;  it  is  excluded  from  the  orbit  by  a  prominent  curved  plate 


94 


THE  SKELETON 


of  bone,  the  orbital  process,  which  forms  the  anterior  boundary  of  the  temporal 
fossa.  The  upper  part  gives  origin  to  a  few  fibres  of  the  temporal  muscle,  while 
at  the  lower  part  is  a  large  rough  area  for  articulation  with  the  zygomatic  process 
of  the  maxilla. 

The  orbital  process  is  placed  at  right  angles  to  the  remaining  part  of  the  bone 
and  forms  the  anterior  portion  of  the  lateral  wall  of  the  orbit.     On  the  orbital 

Fig.  118. — The  Left  Ztgoma.tic  Bone. 
A,  the  malar  surface.     B,  the  temporal  and  orbital  surfaces. 


Frontal  process 


Frontal  process 


Orbital  border 


Malar  canal 


Processus  marginalis        Temporal  — 

Temporal  border  Temporal  border 
Zygomatic  process 


Infra- 
orbital 
process 
Intraorbital  head      ^'^ 
of  quadrate  muscle    X-^ 
Maxillary 
border 

Zygomatic  head 
of  quadrate  muscle 

Zygomaticus 


Masseter 
Malar  tubercle 


Malar  tubercle 


surface  of  the  process  are  seen  the  foramina  of  two  zygomatico -orbital  canals, 
which  transmit  the  zygomatico-facial  and  zygomatico-temporal  branches  of  the 
zygomatic  branch  of  the  fifth,  together  with  two  small  arteries  from  the  lacri- 
mal. In  some  cases,  however,  the  canal  is  single  at  its  commencement  on  the 
orbital  plate  and  bifurcates  as  it  traverses  the  bone.     The  rough  free  edge  of  the 

Fig.  119. — Skull  showing  the  Right  Malar  Bone  DrviDED  into  Two  Parts  by  a  Hori- 
zontal Suture.     (From  a  specimen  in  the  Museum  of  University  College,  London.) 


process  articulates  above  with  the  zygomatic  border  of  the  great  wing  of  the 
sphenoid,  and  below  with  the  maxilla.  When  the  orbital  process  is  large,  it 
excludes  the  great  wing  of  the  sphenoid  from  articulation  with  the  maxilla, 
and  the  border  then  presents  near  the  middle  a  short,  non-serrated  portion 


THE  MANDIBLE  95 

which  closes  the  anterior  extremity  of  the  inferior  orbital  (spheno-maxillary) 
fissure. 

All  the  four  angles  of  the  zygomatic  bone  have  distinguishing  featm-es.  The  superior, 
forming  the  fronto-sphenoidal  process,  is  the  most  prominent,  and  is  serrated  for  articulation 
with  the  zygomatic  process  of  the  frontal;  the  anterior  or  infra-orbital  process,  sharp  and 
pointed,  articulates  with  the  maxilla  and  occasionally  forms  the  superior  boundary  of  the  infra- 
orbital foramen;  the  posterior  or  temporal  process  is  blunt  and  serrated  rnainly  on  its  medial 
aspect  for  articulation  with  the  zygomatic  process  of  the  temporal;  the  inferior  angle,  blunt 
and  rounded,  is  known  as  the  malar  tubercle. 

Of  the  four  borders,  the  orbital  is  the  longest  and  extends  from  the  fronto-sphenoidal  to  the 
infra-orbital  process.  It  is  thick,  rounded,  and  forms  more  than  one-third  of  the  circumference 
of  the  orbit;  the  temporal  border,  extending  from  the  fronto-sphenoidal  to  the  temporal  process, 
is  sinuously  curved  and  gives  attachment  to  the  temporal  fascia.  Near  the  frontal  .angle  is 
usually  seen  a  sHght  elevation,  the  processus  marginalis,  to  which  a  strong  shp  of  the  fascia  is 
attached;  the  masseteric  border,  thick  and  rough,  completes  the  lower  edge  of  the  zygomatic 
arch  and  gives  origin  to  the  anterior  fibres  of  the  masseler;  the  maxillary  border,  rough  and  eon- 
cave,  is  connected  by  suture  with  the  maxilla,  and  near  the  margin  of  the  orbit  gives  origin  to 
the  infra-orbital  head  of  the  guadratus  Inbii  svperioris. 

Blood-supply. — The  arteries  of  the  zygomatic  are  derived  from  the  ^infra-orbital,  lacrimal, 
transverse  facial,  and  deep  temporal  arteries. 

Articulations. — With  the  maxilla,  frontal,  temporal,  and  sphenoid. 

Ossification. — The  zygomatic  is  ossified  in  membrane  from  three  centres  which  appear  in 
the  eighth  week  of  intra-uterine  life.  The  three  pieces,  which  have  received  the  names  of  ■pre- 
violar,  poslmalar,  and  hypnmalar,  unite  .about  the  fifth  month.  Occasionally  the  primary  nuclei 
fail  to  coalesce,  and  the  bone  is  then  represented  in  the  adult  by  two  or  three  portions  sepa- 
rated by  sutures.  In  those  cases  in  which  the  premalar  and  postmalar  unite  and  the  hypo- 
malar  remains  distinct,  the  suture  is  horizontal;  if  the  independent  portion  is  the  premalar, 
then  the  suture  is  vertical.  The  bipartite  zygomatic  has  been  observed  in  skulls  obtained  from 
at  least  a  dozen  different  races  of  mankind,  but  because  of  the  greater  frequency  in  which  it 
occurs  in  the  crania  of  the  Japanese  (seven  per  cent.),  the  name  of  o.«  Japonicum  has  been 
given  to  it. 

THE  MANDIBLE 

The  mandible  [mandibula]  or  lower  jaw-bone  (figs.  120,  121)  is  the  largest  and 
strongest  bone  of  the  face.  It  supports  the  mandibular  teeth,  and  by  means  of  a 
pair  of  condyles,  moves  on  the  skull  at  the  mandibular  fossse  of  the  temporal 
bones.  It  consists  of  a  horizontal  portion — the  body- — strongly  curved,  so  as  to 
somewhat  resemble  in  shape  a  horseshoe,  from  the  ends  of  which  two  branches 
or  rami  ascend  almost  at  right  angles. 

The  body  is  marked  in  the  middle  line  in  front  by  a  faint  groove  which  in- 
dicates the  symphysis  or  place  of  union  of  the  two  originally  separate  halves 
of  the  bone.  This  ends  below  in  the  elevation  of  the  chin  known  as  the  mental 
protuberance,  the  lowest  part  of  which  is  slightly  depressed  in  the  centre  and 
raised  on  each  side  to  form  the  mental  tubercle.  Each  half  of  the  mandible 
presents  two  surfaces  and  two  borders.  On  the  lateral  surface,  at  the  side  of 
the  symphysis,  and  below  the  incisor  teeth,  is  a  shallow  depression,  the  incisor 
fossa,  from  which  the  vientalis  and  the  incisivus  labii  inferioris  muscle  arise;  and 
more  laterally,  opposite  the  second  bicuspid  tooth,  and  midway  between  the 
upper  and  lower  margins,  is  the  mental  foramen,  which  transmits  the  mental 
nerve  and  vessels.  Below  the  foramen  is  the  oblique  line,  extending  backward 
and  upward  from  the  mental  tubercle  to  the  anterior  border  of  the  rairius;  it 
divides  the  body  into  an  upper  or  alveolar  part  and  a  lower  or  basilar  part,  and 
affords  attachment  to  the  quadratus  labii  inferioris  and  the  triangularis  oris. 

The  medial  surface  presents  at  the  back  of  the  symphysis  four  small  pro- 
jections, called  the  mental  spine  (genial  tubercles).  These  are  usually  arranged 
in  two  pairs,  one  above  the  other;  the  upper  comprising  a  pair  of  prominent 
spines,  gives  origin  to  the  genio-glossi,  and  the  lower,  represented  in  some  bones 
by  a  median  ridge  or  only  a  slight  roughness,  gives  origin  to  the  genio-hyoid  muscles. 
At  the  side  of  the  symphysis  near  the  inferior  margin  is  an  oval  depression,  the 
digastric  fossa,  for  the  insertion  of  the  digastric  muscle.  Commencing  below 
the  mental  spine,  and  extending  upward  and  backward  to  the  ramus,  is  the 
mylo-hyoid  line,  which  becomes  more  prominent  as  it  approaches  ,the  alveolar 
border;  it  gives  attachment  along  its  whole  length  to  the  mylo-hyoid  muscle, 
at  its  posterior  fifth  to  the  superior  constrictor  of  the  pharynx,  and  at  the  pos- 
terior extremity  to  the  pterygo-mandibular  raphe.  Above  this  line  at  the  side 
of  the  symphysis  is  a  smooth  depression  [fovea  sublingualis]  for  the  sublingual 
gland,  and  below  it,  farther  back,  is  another  for  the  submaxillary  gland. 


96 


THE  SKELETON 


The  alveolar  part  or  superior  border  is  hollowed  out  into  eight  sockets  or 
alveoli.  These  are  conical  in  shape  and  form  an  exact  counterpart  of  the  roots- 
of  the  teeth  which  they  contain.  From  the  lateral  aspect  of  the  alveolar  process, 
as  far  forward  as  the  first  molar  tooth,  the  buccinator  muscle  takes  origin. 

The  base  or  inferior  border  is  thick  and  rounded.  In  the  anterior  part  of  its 
extent  it  gives  attachment  to  the  platysma,  and  near  its  junction  with  the  ramus 
is  a  groove  for  the  external  maxillary  artery  which  here  turns  upward  into  the  face. 

The  ramus  is  thinner  than  the  body  and  quadrilateral  in  shape.  The  lateral 
surface  is  flat,  gives  insertion  to  the  masseter,  and  at  the  lower  part  is  marked  by 
several  oblique  ridges  for  the  attachment  of  tendinous  bundles  in  the  substance 
of  the  muscle.  The  medial  surface  presents  near  the  middle  the  mandibular 
(inferior  dental)  foramen,  leading  into  the  mandibular  (inferior  dental)  canal 
which  traverses  the  bone  and  terminates  at  the  mental  foramen  on  the  lateral 
surface  of  the  body.  From  the  canal,  which  in  its  posterior  two-thirds  is  nearer  to 
the  medial,  and  in  its  anterior  third  nearer  to  the  lateral,  surface  of  the  mandible, 


Fig.  120.^The  Mandible.     (Lateral  view.) 


Coronoid 
Temporal       process 


Mandibular 

notch      External  pterygoid 


Plat\  sma 

Triangularis'  oris  Groove  for  external  maxillary  artery 

External  oblique  line 


a  series  of  small  channels  pass  upward  to  the  sockets  of  the  posterior  teeth  and 
transmit  branches  of  the  inferior  alveolar  (dental)  vessels  and  nerve;  in  front  of 
the  mental  foramen  a  continuation  of  the  canal  extends  forward  and  conveys  the 
vessels  and  nerves  to  the  canine  and  incisor  teeth.  The  mandibular  foramen  is 
bounded  medially  by  a  sharp  margin  forming  the  lingula  (mandibular  spine), 
which  gives  attachment  to  the  spheno-mandibular  ligament. 

The  posterior  margin  of  the.  lingula  is  notched.  This  notch  forms  the 
commencement  of  a  groove,  the  mylo-hyoid  groove  [sulcus  mylohyoideus], 
which  runs  obliquely  downward  and  forward  and  lodges  the  mylo-hyoid  nerve 
and  artery,  and,  in  the  embryo,  Meckel's  cartilage.  Behind  the  spine  is  a  rough 
area  for  the  insertion  of  the  internal  pterygoid  muscle. 

The  posterior  border  of  the  ramus  is  thick  and  rounded,  and  in  meeting  the 
inferior  border  of  the  ramus  forms  the  angle  of  the  jaw,  which  is  rough,  obtuse, 
usually  everted,  and  about  122°  in  the  adult;  the  angle  gives  attachment  to  the 
stylo-mandibular  ligament.  The  inferior  border  is  thick,  rounded,  and  continu- 
ous with  the  base.  The  anterior  border  is  continuous  with  the  oblique  line, 
whilst  the  upper  border  presents  two  processes  separated  by  a  deep  concavity,  the 
mandibular  (sigmoid)  notch.  Of  the  processes,  the  anterior  is  the  coronoid;  the 
posterior,  the  condylar. 


THE  MANDIBLE 


97 


The  condylar  process  consists  of  the  condyle  [capitulum  mandibulse]  and  the 
narrowed  portion  by  which  it  is  supported,  the  neck.  The  condyle  is  oval  in 
shape,  with  its  long  axis  transverse  to  the  upper  border  of  the  ramus,  but  oblique 
with  regard  to  the  median  axis  of  the  sicull,  so  that  the  lateral  extremity,  which 
presents  the  condylar  tubercle  for  the  temporo-mandibular  ligament  of  the 
temporo-mandibular  articulation,  is  a  little  more  forward  than  the  medial  ex- 
tremity.    The  convex  surface  of  the  condyle  is  covered  with  cartilage  in  the  recent 

Fig.  121. — The  Mandible.     (Medial  view.) 


Lin^ula 

Mandibular 

foramen 

Spheno-mandib- 

ular  ligament 

Superior 

constnctor 

Mylo-hyoid 

groove 

Internal 
pterygoid 

Stylo-mandibular 
ligament 


^  >  "  tii  { — Groove  for  sub- 
lingual gland 
Genio-glossus 

Genio-hyoid 

Digastric 

Mylo-hyoid  Groove  for  submaxillary  gland 

Mylo-hyoid  line 

state,  and  rests  in  the  mandibular  fossa;  the  neck  is  flattened  from  before  back- 
ward, and  presents,  in  front,  a  depression  [fovea  pterygoidea]  for  the  insertion 
of  the  external  pterygoid  muscle. 

The  coronoid  process,  flattened  and  triangular,  is  continued  upward  from  the 
anterior  part  of  the  ramus.  The  lateral  surface  is  smooth  and  gives  insertion 
to  the  temporal  and  masseter  muscles;  the  medial  surface  is  marked  by  a  ridge 
which  descends  from  the  tip  and  becomes  continuous  with  the  posterior  part  of 
the  mylo-hyoid  line.     On  the  medial  surface,  as  well  as  on  the  tip  of  the  coronoid 


Fig  122 — Mandiblb  showing  Relations  op  Meckel's  Cartilage  in  Human  Fcetus  op 
8  CM.  Cbown-Rump  Length.     (After  KoUmann,  Handatlas  der  Entwickelungsgeschichte.) 


Groove  for  teeth 


Meckel's  cartilage 


AnniUus  tym- 
panicus 


process,  the  temporal  muscle  is  inserted.  The  mandibular  notch,  the  deep  semi- 
lunar excavation  separating  the  coronoid  from  the  condylar  process,  is  crossed 
by  the  masseteric  nerve  and  vessels. 

Blood-supply. — Compared  with  other  bones,  the  superficial  parts  of  the  mandible  are  not 
so  freely  supplied  with  blood.     The  chief  artery  is  the  inferior  alveolar  which  runs  in  the  man- 
dibular canal,  and  hence,  as  the  bone  is  exposed  to  injury  and  sometimes  actually  laid  bare  in 
its  alveolar  portion,  it  often  necroses,  especially  if  the  artery  is  involved  at  the  same  time. 
7 


98  THE  SKELETON 

Ossification. — The  mandible  is  mainly  formed  by  ossification  in  the  fibrous  tissue  investing 
the  cartilage  of  the  first  branchial  arch  or  Meckel's  cartilage,  although  a  small  portion  of  the 
cartilage  itself  is  directly  converted  into  bone. 

It  is  now  generally  admitted  that  the  lower  jaw  is  developed  in  membrane  as  a  single  skel- 
etal element.  The  centre  of  ossification  appears  in  the  outer  aspect  of  Meckel's  cartilage  and 
gives  rise  to  the  bony  plate  known  as  the  dentary.  This  plate  extends  forward  right  up  to  the 
middle  line  in  front,  and  from  it  a  shelf  grows  upward  for  the  support  of  the  tooth  germs. 

Fig.  123. — The  Mandible  at  Birth. 


Meckel's  cartilage  lies  below  and  medial  to  the  dentary  plate,  and  the  inferior  alveolar  nerve 
passes  forward  between  the  two  structures.  Meckel's  cartilage  itself  takes  some  small  part  in 
the  formation  of  the  lower  jaw.  Ossification  from  the  primary  nucleus  invades  the  cartilage 
at  a  point  opposite  the  interval  between  the  first  and  second  tooth  germs,  and  the  resulting 
bone  contributes  to  the  formation  of  the  alveolar  margin  opposite  these  two  teeth.  Behind 
this  point  the  cartilage  atrophies  except  in  so  far  as  it  helps  to  form  the  spheno-mandibular 
ligament  and  the  malleus  and  incus.  Behind  the  symphysis  the  anterior  extremity  of  the 
cartilage  does  not  enter  into  the  formation  of  the  jaw,  but  it  usually  persists  throughout  foetal 

Fig.  124. — The  Skull  op  a  Woman  Eighty-three  Years  Old,  to  show  the  Changes  in 
THE  Mandible  and  Maxilla 


life  as  one  or  two  small,  rounded,  cartilaginous  masses.  Occasionally  they  become  ossified 
and  give  rise  to  accessory  ossicles  in  this  situation.  The  lamella  of  bone  situated  on  the  medial 
side  of  Meckel's  cartilage,  corresponding  to  the  distinct  splenial  element  in  some  animals,  arises 
in  man  as  an  extension  from  the  dentary  element. 

In  connection  with  the  condylar  and  coronoid  processes,  cartilaginous  masses  are  developed. 
These  do  not,  however,  indicate  separate  elements,  but  are  adaptations  to  the  growth  of  the 
lower  jaw.     'They  are  ossified  by  an  extension  from  the  surrounding  membrane  bone. 


THE  HYOID  BONE 


The  process  of  ossification  of  the  lower  jaw  commences  very  early,  between  the  sixth  and 
eighth  week,  and  proceeds  rapidly,  so  that  by  the  fourth  month  the  various  parts  are  formed. 

Age-changes. — At  birth  the  mandible  is  represented  by  two  nearly  horizontal  troughs  of 
bone,  lodging  unerilpted  teeth,  and  joined  at  the  symphysis  by  fibrous  tissue.  The  body 
is  mainly  alveolar,  the  basal  part  being  but  little  developed;  the  condyle  and  the  upper  edge 
of  the  symphysis  are  nearly  on  a  level;  the  mental  foramen  is  nearer  the  lower  than  the  upper 
margin,  and  the  angle  is  about  175°.  The  inferior  alveolar  nerve  lies  in  a  shallow  groove 
between  the  spleuial  and  dentary  plates. 

During  the  first  year  osseous  union  of  the  two  halves  takes  place  from  below  upward,  but 
is  not  complete  until  the  second  year.  After  the  first  dentition,  the  ramus  forms  with  the  body 
of  the  mandible  an  angle  of  about  140°,  and  the  mental  foramen  is  situated  midway  between 
the  upper  and  lower  borders  of  the  bone  opposite  the  second  milk-molar.  In  the  adult,  the 
angle  formed  by  the  ramus  and  body  is  nearer  to  a  right  angle,  and  the  mental  foramen  is  oppo- 
site the  second  bicuspid,  so  that  its  relative  position  remains  unaltered  after  the  first  dentition. 
In  old  age,  after  the  fall  of  the  teeth,  the  alveolar  margin  is  absorbed,  the  angle  formed  by  the 
ramus  and  body  is  again  increased,  and  the  mental  foramen  approaches  the  alveolar  margin. 
In  a  young  and  vigorous  adult  the  mandible  is,  with  the  exception  of  the  petrous  portion  of  the 
temporal,  the  densest  bone  in  the  skeleton;  in  old  age  it  becomes  exceedingly  porous,  and  often 
so  soft  that  it  may  easily  be  broken. 


( 


THE  HYOID  BONE 

The  hyoid  bone  [os  hyoideum]  or  os  linguae  (fig.  125),  situated  in  the  anterior 
part  of  the  neck  between  the  chin  and  the  thyreoid  cartilage,  supports  the  tongue 
and  gives  attachment  to  numerous  muscles.  It  is  suspended  from  the  lower 
extremities  of  the  styloid  processes  of  the  temporal  bones  by  two  slender  bands 
known  as  the  stylo-hyoid  ligaments,  and  is  divisible  into  a  body  and  two  pairs  of 
processes,  the  greater  and  lesser  cornua. 

The  body,  constituting  the  central  portion  of  the  bone,  is  transversely  placed 
and  quadrilateral  in  form.  It  is  compressed  from  before  backward  and  lies 
obliquely  so  that  the  anterior  surface  looks  upward  and  forward  and  the  posterior 
surface  in  the  opposite  direction. 

The  anterior  surface  is  convex  and  divided  by  a  horizontal  ridge  into  a  superior 
and  an  inferior  portion.  Frequently  it  also  presents  a  vertical  ridge  crossing  the 
former  at  right  angles,  and  just  above  the  point  of  intersection  is  the  glosso-hyal 


Fig.  125. — The  Hyoid  Bone.     A,  Male,  B,  Female  (Natural  Size) 


process,  the  vestige  of  a  well-developed  process  in  this  situation  in  the  hyoid 
bone  of  some  of  the  lower  animals  (reptiles  and  the  horse).  In  this  way  four 
spaces  or  depressions  for  muscular  attachments  are  marked  off,  two  on  either 
side  of  the  middle  line.  The  posterior  surface  is  deeply  concave  and  separated 
from  the  epiglottis  by  the  thyreo-hyoid  membrane,  and  by  some  loose  areolar 
tissue.  The  membrane  passes  upward  from  the  thyreoid  cartilage  to  be  attached 
to  the  superior  border,  and  interposed  between  it  and  the  concavit.y  on  the 
back  of  the  body  is  a  small  synovial  bursa.  The  inferior  border,  thicker  than 
the  upper,  gives  insertion  to  muscles.  The  lateral  borders  are  partly  in  relation 
with  the  greater  cornua,  \vith  which  they  are  connected,  up  to  middle  life,  by 
synchondrosis,  but  after  this  period,  usually  by  bone. 


100 


THE  SKELETON 


The  greater  cornua  projects  upward  and  backward  from  the  sides  of  the  body. 
They  are  flattened  from  above  downward,  thicker  near  their  origin,  and  terminate 
posteriorly  in  a  rounded  tubercle  to  which  the  thyreo-hyoid  ligament  is  attached. 

The  lesser  cornua  are  small  conical  processes  projecting  upward  and  back- 
ward opposite  the  lines  of  junction  between  the  body  and  the  greater  cornua, 
and  by  their  apices  give  attachment  to  the  stylo-hyoid  ligaments;  they  are 
connected  to  the  body  by  fibrous  tissue.  Professor  Parsons  has  shown  that  a 
joint  with  a  synovial  cavity  is  common  between  the  smaller  and  geater  cornua. 
The  lesser  cornua  are  sometimes  partly  or  even  completely  cartilaginous  in  the 
adult. 


Fig.  126. — Hyoid  Bone  Enlarged  to  show  Muscular  Attachments.     (After 
F.  G.  Parsons.) 


Greater  cornu' 


Attachment  to 
digastric  tendon 


Hyo-glossus 


The  muscles  attached  to  each  half  of  the  hyoid  bone  may  be  enumerated  as  follows: — 

Body Genio-hyoid,   genio-glossus,   mylo-hyoid,   sterno-hyoid,  omo-hyoid,  stylo- 
hyoid, thyreo-hyoid  and  hyo-glossus. 

Greater  cornu Thyreo-hyoid,  middle  constrictor,  hyo-glossus,  and  digastric. 

Lesser  cornu Chondro-glossus,  and  middle  constrictor. 

Ossification. — In  the  early  months  of  intra-uterine  life  the  hyoid  bone  is  composed  of 
hyahne  cartilage  and  is  directly  continuous  with  the  styloid  processes  of  the  temporal  bones. 
Ossification  takes  place  from  six  centres,  of  which  two  appear  in  the  central  piece  of  cartilage, 
one  on  either  side  of  the  middle  line,  either  just  before  or  just  after  birth;  soon  after  their 
appearance,  however,  they  coalesce  to  form  the  body  of  the  bone  (basi-hyal).  The  centre  for 
each  of  the  greater  cornua  (thyreo-hyals)  appears  just  about  the  time  of  birth,  and  for  each 
of  the  lesser  cornua  (oerato-hyals)  some  years  after  birth,  even  as  late  as  puberty.  (F.  G. 
Parsons.)  The  greater  cornua  and  the  body  unite  in  middle  life;  the  lesser  cornua  rarely  anky- 
lose  with  the  body  and  only  in  advanced  age.  Professor  Parsons  has  shown,  however,  that  the 
lesser  cornua  more  frequently  unite  with  the  greater  cornua. 


THE  SKULL  AS  A  WHOLE 

The  skull,  formed  by  the  union  of  the  cranial  and  facial  bones  already  de- 
scribed, may  now  be  considered  as  a  whole.  Taking  a  general  view,  it  is  spheroidal 
in  shape,  smooth  above,  compressed  from  side  to  side,  flattened  and  uneven 
below,  and  divisible  into  six  regions :  a  superior  region  or  vertex,  a  posterior  or 
occipital  region,  an  anterior  or  frontal  region,  an  inferior  region  or  base,  and  two 
lateral  regions. 

(1)  The  Superior  Region 

Viewed  from  above  {norma  verticalis)  the  skull  presents  an  oval  outline  with 
the  broader  end  behind,  and  includes  the  frontal,  parietals,  and  the  interparietal 
portion  of  the  occipital.  In  a  skull  of  average  width  the  zygomatic  arches  are 
visible,  but  in  very  broad  skulls  they  are  obscured. 


THE  SKULL  AS  A  WHOLE  101 

The  sutures  of  the  vertex  are : — 

The  metopic,  which  is,  in  most  skulls,  merely  a  median  fissure  in  the  frontal  bone  just 
above  the  glabella;  occasionally  it  involves  the  whole  length  of  the  bone.  It  is  due  to  the 
persistence  of  the  fissure  normally  separating  the  two  halves  of  the  bone  in  the  infant. 

The  sagittal  is  situated  between  the  two  parietals,  and  extends  from  the  bregma  to  the 
lambda. 

The  coronal  lies  between  the  frontal  and  parietals,  and  extends  from  pterion  to  pterion. 

The  lambdoid  is  formed  by  the  parietals  and  interparietal  portion  of  the  occipital.  It 
extends  from  asterion  to  asterion. 

The  occipital  suture  is  only  present  when  the  interparietal  exists  as  a  separate  element 
(figs.  70  and  71). 

The  more  important  points  are: — 

The  bregma,  which  indicates  the  situation  of  the  frontal  (gi-eater)  fontanelle,  and  marks 
the  confluence  of  the  coronal,  the  sagittal,  and,  when  present,  the  metopic  sutures. 

The  lambda,  where  the  sagittal  enters  the  lambdoid  suture;  it  marks  the  situation  of  the 
occipital  (lesser)  fontanelle. 

The  obelion,  a  little  anterior  to  the  lambda,  is  usually  indicated  by  a  median  or  two  lateral 
foramina. 

(2)  The  Posterior  Region 

Viewed  from  behind  {norma  occipitalis)  the  skull  is  somewhat  pentagonal  in 
form.  Of  the  five  angles,  the  superior  or  median  is  situated  in  the  line  of  the 
sagittal  suture;  the  two  upper  lateral  angles  coincide  with  the  parietal  eminences 
and  the  two  lower  with  the  mastoid  processes  of  the  temporal  bones.  Of  the 
sides,  four  are  somewhat  rounded,  and  one,  forming  the  basal  line,  running 
between  the  mastoid  processes,  is  flattened. 

The  centre  is  occupied  by  the  lambda,  and  radiating  from  this  point  are  three  sutures, 
the  sagittal,  and  the  two  parts  of  the  lambdoid.  Each  half  of  the  lambdoid  suture  bifurcates 
at  the  mastoid  portion  of  the  temporal  bone,  the  two  divisions  constituting  the  parieto-mastoid 
and  occipito-mastoid  sutures;  the  point  of  bifurcation  is  known  as  the  asterion. 

In  the  lower  part  of  the  view  is  seen  the  external  occipital  protuberance  (inion),  the  occipital 
crest,  and  the  thi-ee  pairs  of  nuchal  lines,  which  give  it  a  rough  and  uneven  appearance.  The 
occipital  point  is  the  point  of  the  occiput  furthest  from  the  glabella  in  the  median  plane.  It 
is  situated  above  the  external  occipital  protuberance. 

(3)  The  Lateral  Region 

The  lateral  region  (norma  lateralis)  (fig.  127)  is  somewhat  triangular  in  shape, 
being  bounded  above  by  a  line  extending  from  the  zygomatic  process  of  the 
frontal,  along  the  temporal  line  to  the  lateral  extremity  of  the  superior  nuchal  line 
of  the  occipital  bone;  this  forms  the  base  of  the  triangle.  The  two  sides  are 
represented  by  lines  drawn  from  the  extremities  of  the  base  to  the  angle  of  the 
jaw.  It  is  divisible  into  two  portions,  one  in  front,  the  other  behind,  the  emi- 
nentia  articularis  [tuberculum  articulare].  The  posterior  portion  presents,  in  a 
horizontal  line  from  behind  forward,  the  mastoid  portion  of  the  temporal,  with 
its  process  and  foramen,  the  external  auditory  meatus,  the  centre  of  which  is 
known  as  the  atiricular  point,  the  mandibular  fossa,  and  the  condyle  of  the  mandible. 

In  the  anterior  portion  are  three  fossaj,  (a)  temporal,  (b)  infratemporal,  (c) 
pterygo-palatine  (spheno-maxillary),  and  two  fissures,  the  inferior  orbital  (spheno- 
maxillary) and  pterygo-palatine. 

(a)  The  temporal  fossa,  somewhat  semilunar  in  shape,  is  bounded  above  and  behind  by  the 
temporal  line,  in  front  by  the  frontal,  zygomatic,  and  great  wing  of  sphenoid,  and  laterally  by 
the  zygomatic  arch,  by  which  it  is  separated  superficially  from  the  infratemporal  fossa;  more 
deeply  the  infratemporal  ridge  separates  the  two  fossae. 

The  fossa  is  formed  by  parts  of  five  bones,  the  zygomatic,  temporal,  parietal,  frontal, 
great  wing  of  sphenoid,  and  is  traversed  by  six  sutures,  coronal,  spheno-zygomatic,  sphcno- 
sc(uamosal,  spheno-parietal,  squamosal,  and  spheno-frontal.  The  point  where  the  temporal 
ridge  is  crossed  by  the  coronal  suture  is  the  stephanion,  and  the  region  where  the  frontal, 
sphenoid,  temporal,  and  parietal  meet  is  the  pterion.  The  latter  is  frequently  occupied  in  the 
adult  by  the  epipteric  bone. 

The  temporal  fossa  is  concave  in  front,  convex  behind,  filled  by  the  temporal  muscle,  and 
roofed  in  by  a  strong  glistening  aponeurosis,  the  temporal  fascia,  which  serves  to  bind  down 
the  muscle. 

(b)  The  infratemporal  fossa  (zygomatic  fossa),  irregular  in  shape,  is  situated  below  and 
to  the  medial  side  of  the  zj'goma,  covered  in  part  by  the  ramus  of  the  mandible.  It  is  bounded 
in  front  by  the  lower  part  of  the  medial  surface  of  the  zygomatic,  and  by  the  infratemporal 
surface  of  the  maxilla,  on  which  are  seen  the  orifices  of  the  posterior  superior  alveolar  canals; 
behind  by  the  posterior  border  of  the  lateral  pterygoid  plate,  the  spine  of  the  sphenoid,  and  the 
articular  tubercle;  above  by  the  infratemporal  ridge,  a  small  part  of  the  squamous  portion  of 


102 


THE  SKELETON 


the  temporal,  the  great  wing  of  the  sphenoid  perforated  by  the  foramen  ovale  and  foramen 
spinosum;  helow  by  the  alveolar  border  of  the  maxilla;  laterally  by  the  ramus  of  the  mandible 
and  the  zygoma  formed  by  zygomatic  and  temporal;  medially  by  the  lateral  pterygoid  plate,  a 
line  from  which  to  the  spine  of  the  sphenoid  separates  the  infratemporal  fossa  from  the  base  of 
the  skull.  It  contains  the  lower  part  of  the  temporal  muscle  and  the  coronoid  process  of  the 
mandible,  the  external  and  internal  pterygoids,  the  internal  maxillary  vessels,  and  the  mandibular 
division  of  the  fifth  nerve  with  numerous  branches.  At  its  upper  and  medial  part  are  seen  the 
inferior  orbital  and  pterygo-palatine  fissures. 

The  inferior  orbital  (or  spheno-maxillary)  fissure  is  horizontal  in  position,  and  lies  between 
the  maxQla  and  the  great  wing  of  the  sphenoid;  laterally  it  is  usually  completed  by  the  zygo- 
matic, though  in  some  cases  the  sphenoid  joins  the  maxilla,  and  in  this  way  excludes  the  zygo- 
matic bone  from  the  fissure;  medially  it  is  terminated  by  the  infratemporal  surface  of  the  orbital 
process  of  the  palate  bone.  Through  this  fissure  the  orbit  communicates  with  the  pterygo- 
palatine (spheno-maxillary),  infratemporal,  and  temporal  fossae.  It  transmits  the  infra- 
orbital nerve  and  vessels,  the  zygomatic  nerve,  ascending  branches  from  the  spheno-palatine 
ganglion  to  the  orbit,  and  a  communicating  vein  from  the  ophthalmic  to  the  pterygoid  plexus. 

Fig.  127.^The  Skull.     (Norma  lateralis.) 


The  pterygo-palatine  (pterygo-maxillary)  fissure  forms  a  right  angle  with  the  inferior 
orbital  fissure  and  is  situated  between  the  maxilla  and  the  anterior  border  of  the  pterygoid 
process  of  the  sphenoid.  At  its  lower  angle,  where  the  two  lips  of  the  fissure  approximate,  the 
lateral  pterj'goid  plate  occasionally  articulates  with  the  maxilla,  but  they  are  usually  separated 
by'  a  thin  portion  of  the  pyramidal  process  of  the  palate.  The  pterygo-palatine  fissure,  which 
serves  to  connect  the  infratemporal  fossa  with  the  pterygo-palatine  fossa,  is  bounded  medially 
by  the  perpendicular  part  of  the  palate;  it  transmits  branches  of  the  internal  maxillary  artery, 
and  the  corresponding  veins,  to  and  from  the  pterygo-palatine  fossa. 

(c)  The  pterygo-palatine  (spheno-maxillary)  fossa  is  a  small  space,  of  the  form  of 
an  inverted  pyramid,  situated  at  the  angle  of  junction  of  the  inferior  orbital  (spheno-maxil- 
lary) with  the  pterygo-palatine  (pterygo-maxillary)  fissure,  below  the  apex  of  the  orbit.  It  is 
bounded  infroid  by  the  infratemporal  surface  of  the  maxilla;  behind,  by  the  base  of  the  pterygoid 
process  and  the  lower  part  of  the  anterior  surface  of  the  great  wing  of  the  sphenoid;  medially 
by  the  perpendicular  part  of  the  palate  with  its  orbital  and  sphenoidal  processes;  above  by  the 
lower  surface  of  the  body  of  the  sphenoid.  Three  fissures  terminate  in  it — viz.,  the  superior 
orbital,  pterygo-palatine,  and  inferior  orbital;  through  the  superior  orbital  fissuje  it  communi- 
cates with  the  cranium,  through  the  pterygo-palatine  fissure  with  the  infratemporal  fossa, 
through  the  inferior  orbital  fissure  with  the  orbit,  and  throagh  the  spheno-palatine  foramen 
on  the  medial  wall  it  communicates  with  the  upper  and  back  part  of  the  nasal  fossa.     In- 


THE  SKULL  AS  A  WHOLE 


103 


eluding  the  spheno-palatine  foramen  sL\  foramina  open  into  the  fossa.  Of  these,  three  are  on 
the  posterior  wall:  enumerated  from  without  inward,  and  from  above  downward,  they  are  the 
foramen  rotundum,  the  pterygoid  (Vidian)  canal,  and  the  pharyngeal  (pterygo-palatine) 
canal.  The  apex  of  the  pyramid  leads  below  into  the  pterygo-palatine  canal  and  the  accessory 
palatine  canals  which  branch  from  it;  and  anteriorly  is  the  orifice  of  the  infra-orbital  canal. 
The  fossa  contains  the  spheno-palatine  ganglion,  the  maxillary  nerve,  and  the  terminal  part  of 
the  internal  maxillary  artery,  and  the  various  foramina  and  canals  in  relation  with  the  fossa 
serve  for  the  transmission  of  the  numerous  branches  which  these  vessels  and  nerves  give  off. 


Fig.  128. — A  Section  of  the  Skull,  showing  the  Medial  Wall  of  the   Orbit,  the  Medial 
Wall  of  the  Antrum,  and  the  Pterygo-palatine  Fossa. 


Frontal  sinus 


Frontal  process  of  maxilla  ~7 
Lacrimal  -— 


Lacrimal  canal 


Orifice  of  antrum 

Inferior  nasal  concha 

Palate  bone 

Anterior  nasal  spine 


Anterior  ethmoid  canal 
Posterior  ethmoid  canal 


Spheno-palatine  foramen 

Pterygoid     canal,     leading     into     the 

pterygo-palatine  fossa 
Sphenoid 


Lateral  pterygoid  plate 


(4)  Inferior  Region  or  External  Base  of  Skull 

The  external  base  of  the  skull  {norma  basilaris)  (figs.  130,  131)  extends  from 
the  incisor  teeth  to  the  occipital  protuberance,  and  is  bounded  on  each  side  by 
the  alveolar  arch,  the  zygomatic,  the  zygoma,  the  temporal,  and  the  superior 
nuchal  line  of  the  occipital  bone.  It  is  very  uneven  and,  excluding  the  lower 
jaw,  divisible  into  three  portions:  (a)  anterior,  (b)  middle  or  subcranial,  and  (c) 
posterior  or  suboccipital. 


Fig.  129. — Hard  Palate  of  a  Child  Five  Years  Old. 


Palate  bonet^ 


L^f'Cc  ^ Palate  process  of  maxilla 


Greater  palatine  foramen 
Lesser  palatine  foramen 


(a)  The  anterior  division  consists  of  the  hard  palate,  the  alveolar  arch,  and 
the  choanse  (posterior  nares). 

When  the  skull  is  inverted,  the  hard  palate  stands  at  a  higher  level  than  the 
rest,  and  is  bounded  anteriorly  and  laterally  by  the  alveolar  ridges  containing  the 
teeth.  The  bones  appearing  in  the  intermediate  space  are  the  premaxillary  and 
palatine  portions  of  the  maxillse  and  the  horizontal  parts  of  the  palate  bones. 


104 


THE  SKELETON 


Fig    130  — The  Skull      (Norma  basilaris.) 


Tensor  veli  palatini 
Azygos  uvulee 

Superior  constrictor 

Internal  pterygoid 

Tensor  veli  palatini 

Tensor  tympani 
Levator  veli  palatini 

Longus  capitis 
Superior  constrictor 
Rectus  capitis  anterior 

Anterior  longitudinal  ligament  of  spine 
Vertical  part  of  crucial  ligament 

Alar  ligament 
Articular  capsule 


Posterior  occipito-atlantal  membrane 
Superior  oblique 

Rectus  capitis  posterior  major 
Rectus  capitis  posterior  minor 


f-  -   Ligamentum  nuchse 
Trapezius 


THE  SKULL  AS  A  WHOLE 


105 


Fig.  131. — The  Skull.     (Norma  basilaris.) 


Scarpa^s  foramen 

Stenson's  foramen 

Scarpa's  foramen 

:  fossa 


Palatine  groove 

Posterior  palatine  foramen 

Spine  of  the  palate  bone 

Hamular  process 


VO\ER 

Sphenoidal  process  of  palate  bone 


Foramen  lacerum 


Pharyngeal  tubercle 
Carotid  canal 


Tubercle  for  alar  ligament 


Condylar  foramen' 


External  occipital  crest 


External  occipital  protuberance 


106 


THE  SKELETON 


They  are  rough  for  the  attachment  of  the  muco-periosteum,  and  near  the  posterior 
margin  is  the  ridge  for  the  fibrous  expansion  of  the  tensor  veli  'palatini.  The  fol- 
lowing points  are  readily  recognised  (fig.  129) : — 

The  meso-palatine  suture  commences  at  the  alveolar  point,  traverses  the  incisive  fossa,  and 
terminates  at  the  posterior  nasal  spine. 

The  transverse  palatine  suture,  between  the  palate  bones  and  palatine  processes  of  the 
maxiUae. 

In  young  skulls  the  incisive  sutures,  and  behind  the  incisor  teeth  four  small  openings 
known  aS  the  gubemacular  canals  (see  figs.  114  and  129). 

The  incisive  fossa  containing  the  termination  of  four  canals:  two  small  orifices,  foramina  of 


Fig.  1.32. — The  Skull.     (Norma  facialis.) 


Quadratus  lahii  superions 
(zygomatic  head) 


Orbicularis  oculi 


Quadratus  labii  superioris 
(ancular  head) 


Quadratus  labii  superiosis 
(infraorbital  head) 


Nasalis  (transverse 
portion) 


Nasalis  (alar  portion) 
Orbicularis  oris 


Scarpa,  situated  one  behind  the  other  in  the  meso-palatine  suture;  and  two  larger  openings, 
the  foramina  of  Stenson.  The  foramina  of  Scarpa  transmit  the  naso-palatine  nerves,  and  those 
of  Stenson  are  in  relation  (embryonic)  with  the  organs  of  Jacobson. 

At  the  posterior  angles  of  the  hard  palate  are  the  greater  palatine  foramina,  through  which 
the  descending  palatine  vessels  and  the  anterior  palatine  nerves  emerge  on  to  the  palate;  a  thin 
lip  of  bone  separates  them  from  the  lesser  palatine  foramen  in  the  tuberosity  of  the  palate  bone 
on  each  side,  for  the  posterior  palatine  nerve. 

The  hamular  process  of  the  medial  pterygoid  plate  is  the  most  posterior  limit  of  the  hard 
palate. 

At  the  posterior  extremity  of  each  alveolar  ridge  is  the  tuberosity  of  the  maxilla,  and  between 
it  and  the  palate  bone  is  a  foramen  (variable  in  size  and  sometimes  absent),  the  middle  palatine 
foramen,  for  the  middle  palatine  nerve.  This  foramen  is  often  included  under  the  lesser  pala- 
tine foramina  (BNA). 


THE  SKULL  AS  A  WHOLE 


107 


Behind  the  hard  palate  are  the  choanae  (posterior  nares),  separated  from  each  other  by  the 
vomer.  Each  is  bounded  laterally  by  the  medial  pterygoid  plate;  below  by  the  horizontal 
plate  of  the  palate  bone;  above  by  the  under  surface  of  the  body  of  the  sphenoid,  with  the  ala 
of  the  vomer  and  a  portion  of  the  sphenoidal  process  of  the  palate  bone. 

Lateral  to  the  choanae  there  is  on  each  side  a  vertical  fossa  lying  between  the  pterygoid 
plates.  It  extends  upward  to  the  under  surface  of  the  great  wings  of  the  sphenoid;  it  is  com- 
pleted anteriorly  by  the  coalescence  of  the  pterygoid  plates  and  below  by  the  pyramidal  process 
of  the  palate  bone.     It  contains  the  following  points  of  interest: — 

An  elongated  furrow,  the  scaphoid  fossa,  for  the  tensor  veli  palatini  muscle  and  the  carti- 
lage of  the  Eustachian  tube. 

The  general  cavity  of  the  pterygoid  fossa  which  lodges  the  tensor  veli  palatini  and  internal 
pterygoid  muscles. 


Fig.  133. — ^The  Skuli,.     (Norma  facialis.) 


Ophryoa 

Superciliary   arch 

Glabella 

Nasion 


Nasal  (piriform) 
apertxire 


Subnasal  point 
Canine  fossa 

Canine  eminence 
Alveolar  point 


( 


Frequently  there  is  a  notch  in  the  lateral  pterygoid  plate  close  beside  the  foramen  ovale. 
The  posterior  termination  of  the  pterygoid  (Vidian)  canal. 

If  a  line  be  drawn  across  the  base  of  the  skull  from  one  preglenoid  tubercle  to 
the  other,  it  will  fall  immediately  behind  the  lateral  pterygoid  plate  and  bisect 
the  foramen  spinosum  on  each  side.  A  second  transverse  line,  drawn  across  the 
opisthion  or  posterior  margin  of  the  foramen  magnum,  will  fall  behind  the 
mastoid  processes.  The  space  between  these  arbitrary  lines  may  be  called  the 
subcranial  region;  that  behind  the  second  hne,  the  suboccipital  region. 

(b)  The  subcranial  region  is  separated  from  the  infratemporal  fossa  by  a  line 
drawn  from  the  posterior  margin  of  the  lateral  pterygoid  plate  to  the  spine  of  the 


108  THE  SKELETON 

sphenoid.  It  is  formed  by  the  inferior  surface  of  the  basilar  process  of  the 
occipital  and  the  body  of  the  sphenoid,  the  petrous  portion  of  the  temporal  bone, 
a  small  piece  of  the  squamosal  portion,  the  posterior  part  of  the  great  wing  of  the 
sphenoid,  and  the  condylar  portions  of  the  occipital  bone.  It  presents  the 
following  points  for  examination  (Figs.  95,  131): — 

The  pharyngeal  tubercle. 

The  foramen  magnum  and  the  occipital  condyles.  The  most  anterior  point  of  the  foramen 
is  termed  the  basion,  and  the  most  posterior  point  the  opisthion. 

On  each  side  will  be  seen: — The  hypoglossal  foramen  for  the  hypoglossal  nerve  and  a  men- 
ingeal branch  of  the  ascending  pharyngeal  artery. 

The  condylar  fossa  with  the  condylar  foramen  (this  foramen  is  not  constant). 

The  under  aspect  of  the  jugular  process,  from  which  the  rectus  capitis  lateralis  takes  origin. 

The  foramen  lacerum  and  the  orifice  of  the  pterygoid  (Vidian)  canal. 

The  canalis  musculo -tubarius  for  the  tensor  tympani  muscle  and  Eustachian  tube. 

The  carotid  canal. 

The  quadrilateral  area  for  the  origin  of  the  levator  veli  palatini  and  tensor  tympani  muscles. 

The  canaliculus  cochleae,  or  ductus  perilymphaticus. 

The  jugular  foramen  and  fossa  for  the  glosso-pharyngeal,  vagus,  and  spinal  accessory 
nerves,  the  internal  jugular  vein,  and  a  meningeal  branch  of  the  ascending  pharyngeal  artery. 

The  tympanic  canaliculus  for  Jacobson's  nerve  (tympanic  branch  of  glossopharyngeal). 

The  spine  of  the  sphenoid;  this  is  sometimes  fifteen  miUimetres  in  length. 

The  mandibular  fossa  with  the  petro-tympanic  fissure.  This  lodges  the  anterior  process 
of  the  malleus,  the  tympanic  twig  of  the  internal  maxillary  artery.  A  small  passage  beside 
it,  the  canal  of  Huguier,  conducts  the  chorda  tympani  nerve  from  the  tympanum. 

The  external  auditory  meatus. 

The  auricular  or  tympano-mastoid  fissure. 

The  tympanic  plate  and  vaginal  process. 

The  styloid  process. 

The  stylo -mastoid  foramen  for  the  stylo-mastoid  artery  and  the  exit  of  the  facial  nerve 
and,  in  some  cases,  the  auricular  branch  of  the  vagus. 

The  mastoid  process  with  the  digastric  and  occipital  grooves. 

(c)  The  suboccipital  region  is  largely  formed  by  the  tabular  portion  of  the 
occipital  bone  with  its  ridges  and  areas  for  muscular  attachment.  Laterally  a 
small  part  of  the  mastoid  portion  of  the  temporal  is  seen,  pierced  by  a  small 
foramen,  of  variable  size,  the  mastoid  foramen,  which  transmits  a  vein  from  the 
transverse  (lateral)  sinus  and  a  meningeal  branch  of  the  occipital  artery. 

(5)  The  Anterior  Region 

The  anterior  region  {norma  facialis)  (figs.  132,  133)  comprises  the  anterior 
end  of  the  cranium  or  forehead,  and  the  skeleton  of  the  face;  also  the  cavities 
known  as  the  orbits,  formed  by  the  junction  of  the  two  parts  of  this  region,  and 
the  nasal  fossae,  situated  on  either  side  of  the  septum  of  the  nose. 

The  upper  part  or  forehead,  narrowest  between  the  temporal  crests  about 
half  an  inch  above  the  zygomatic  processes  of  the  frontal,  presents  at  this  level 
the  two  transverse  sulci ;  above  are  the  frontal  eminences,  below  the  superciliary 
arches,  and  still  lower  the  supra-orbital  margins,  interrupted  near  their  medial 
ends  by  the  supra-orbital  notches. 

Below  the  forehead  are  the  openings  of  the  orbits,  bounded  laterally  by  the 
zygomatic  bones  constituting  the  prominences  of  the  cheeks,  and  between  them 
the  bridge  of  the  nose,  formed  by  the  nasal  bones  and  the  frontal  processes  of  the 
maxillae.  Below  the  nasal  bones  is  the  apertura  piriformis  or  anterior  nasal 
aperture,  leading  into  the  nasal  fossse.  The  teeth  form  a  conspicuous  feature 
in  this  view  of  the  skull,  the  outline  of  which  is  completed  below  by  the  mandible. 

The  bones  entering  into  formation  of  the  norma  facialis  are: — the  frontal,  nasals,  lacrimals, 
orbital  surfaces  of  the  small  and  the  great  wings,  and  a  portion  of  the  body  of  the  sphenoid, 
the  laminas  papjrraceoB  of  the  ethmoids,  the  orbital  processes  of  the  palate  bones,  the  zygomatics, 
maxillse,  inferior  nasal  conchae,  and  the  mandible. 

The  sutures  are  numerous,  and  for  the  most  part  unimportant: — 

The  transverse  sutiu-e  (fig.  133)  extends  from  one  zygomatic  process  of  the  frontal  to  the 
other.  The  upper  part  of  the  suture  is  formed  by  the  frontal  bone;  below  are  the  zygomatic, 
great  and  small  wings  of  the  sphenoid,  lamina  papyracea,  lacrimal,  maxillary,  and  nasal  bones. 
A  portion  of  this  complex  suture,  lying  between  the  sphenoidal  and  frontal  bones,  appears  in 
the  anterior  cranial  fossa. 

Other  fissures  are  the  internasal,  naso-maxillary,  inter-maxillary  and  zygomatioo-maxillary. 
The  small  sutures  seen  in  the  orbit  are  described  with  that  cavity. 

The  foramina  are: — the  supra-orbital,  infra-orbital,  optic,  zygomatico-facial,  and  mental; 
the  naso-lacrimal  canal;  the  ethmoidal  canals;  and  the  inferior  and  superior  orbital  fissures. 


THE  ORBITS 


109 


The  following  points  may  also  be  noticed: — 

The  glabella,  a  smooth  space  between  the  converging  superciliary  arches. 
The  ophryon,  the  most  anterior  point  of  the  metopic  suture. 
The  nasion,  the  middle  of  the  naso-frontal  sutui'e. 

The  subnasal  point,  the  middle  of  the  inferior  border  of  the  pyriform  aperture  at  the  base 
of  the  nasal  spine. 

The  alveolar  point,  the  centre  of  the  anterior  margin  of  the  upper  alveolar  arch. 

THE  ORBITS 

The  orbits  [orbitse]  (fig.  134)  are  two  cavities  of  pyramidal  shape,  with  their 
bases  directed  forward  and  laterally  and  their  apices  backward  and  medially; 
their  medial  walls  are  nearly  parallel,  but  their  lateral  walls  diverge  so  as  to  be 
nearly  at  right  angles  to  each  other.  Each  cavity  forms  a  socket  for  the  eyeball 
and  the  muscles,  nerves,  and  vessels  associated  with  it. 

Seven  bones  enter  into  formation  of  its  walls,  viz.,  the  frontal,  zygomatic, 
sphenoid,  ethmoid,  lacrimal,  palate,  and  maxilla;  but  as  three  of  these — the 
frontal,  sphenoid,  and  ethmoid — are  single  median  bones  which  form  parts  of 
each  cavity,  there  are  only  eleven  bones  represented  in  the  two  orbits.  Each 
orbit  presents  for  examination  four  walls,  a  circumference  or  base,  and  an  apex. 

The  superior  wall  or  roof,  vaulted  and  smooth,  is  formed  mainly  by  the  orbital  plate  of  the 
frontal  and  is  completed  posteriorly  by  the  small  wing  of  the  sphenoid.  At  the  lateral  angle 
it  presents  the  lacrimal  fossa  for  the  lacrimal  gland,  and  at  the  medial  angle  a  depression  or  a 
spine  for  the  puOey  of  the  superior  oblique  muscle. 


Fig.  134. — The  Medial  Wall  of  the  Orbit. 


Frontal  process  of  maxilla     /       V 
T.arrimfll-     /— 


Lacrimal  canal 

Orifice  of  antrum 
Inferior  nasal  concha 

Palate  b( 
Anterior  nasal  spine 


Anterior  ethmoid  canal 
Posterior  ethmoid  canal 

Optic  foramen 

Lamina  papyracea  of  ethmoid 

\      r^Spheno-palatine  foramen 
?^— ^Pterygoid     canal,     leading    into     the 
^^^  pterygo -palatine  fossa 

Sphenoid 

External  pterygoid  plate 


The  inferior  wall  or  floor  is  directed  upward  and  laterally  and  is  not  so  large  as  the  roof. 
It  is  formed  by  the  orbital  plate  of  the  maxilla,  the  orbital  process  of  the  zygomatic,  and  the 
orbital  process  of  the  palate  bone.  At  its  medial  angle  it  presents  the  naso-laorimal  canal,  and 
near  this,  a  depression  for  the  origin  of  the  inferior  oblique  muscle.  It  is  marked  near  the  middle 
by  a  furrow  for  the  infra-orbital  artery  and  the  second  division  of  the  fifth  nerve,  terminating 
anteriorly  in  the  infra-orbital  canal,  through  which  the  nerve  and  artery  emerge  on  the  face. 
Near  the  commencement  of  the  canal  a  narrow  passage,  the  anterior  alveolar  canal,  runs  for- 
ward and  downward  in  the  anterior  wall  of  the  antrum,  transmitting  nerves  and  vessels  to  the 
incisor  and  canine  teeth. 

The  lateral  wall,  directed  forward  and  medially,  is  formed  by  the  orbital  surface  of  the 
great  wing  of  the  sphenoid,  and  the  zygomatic.  Between  it  and  the  roof,  near  the  apex,  is  the 
superior  orbital  (sphenoidal)  fissure,  by  means  of  which  the  third,  fourth,  ophthalmic  division 
of  the  fifth,  and  sixth  nerves  enter  the  orbit  from  the  cranial  cavity;  it  also  transmits  some 
filaments  from  the  cavernous  plexus  of  the  sympathetic,  the  orbital  branch  of  the  middle  men- 
ingeal artery,  recurrent  branches  of  the  lacrimal  artery,  and  an  ophthalmic  vein.  The  lower 
margin  of  the  fissure  presents  near  the  middle  a  small  tubercle,  from  which  the  inferior  head  of 
the  lateral  rectus  muscle  arises.  Between  the  lateral  wall  and  the  floor,  near  the  apex,  is  the 
inferior  orbital  (spheno-maxiUary)  fissure,  tlu-ough  which  the  second  division  of  the  fifth  and 
the  infra-orbital  vessels  pass  from  the  pterygo-palatine  fossa  to  enter  the  infra-orbital  groove. 
At  the  anterior  margin  of  the  fissure  the  sphenoid  occasionally  articulates  with  the  maxilla,  but 


no 


THE  SKELETON 


the  two  are  usually  separated  by  the  orbital  plate  of  the  zygomatic,  and  on  the  latter  are  seen 
the  orifices  of  the  zygomatico-temporal  and  zygomatico-facial  canals,  which  traverse  the 
zygomatic  bone.  The  commencement  of  the  zygomatico-temporal  canal  is  sometimes  seen  in 
the  spheno-zygomatic  sutm-e  connecting  the  sphenoid  and  zygomatic  bones. 

The  medial  wall,  narrow  and  nearly  vertical,  is  formed  from  before  backward  by  the 
frontal  process  of  the  maxilla,  the  lacrimal,  the  lamina  papyracea  of  the  ethmoid,  and  the 
body  of  the  sphenoid.  At  the  junction  of  the  medial  wall  with  the  roof,  and  in  the  suture 
between  the  ethmoid  and  frontal,  are  seen  the  orifices  of  the  anterior  and  posterior  ethmoidal 
canals,  the  anterior,  transmitting  the  anterior  ethmoidal  vessels  and  nerve;  and  the  posterior, 
the  posterior  vessels  and  nerve.  Anteriorly  is  the  lacrimal  groove  for  the  lacrimal  sac,  and 
behind  this  the  lacrimal  crest,  from  which  the  tensor  tarsi  arises.  The  medial  wall,  which  is 
the  smallest  of  the  four,  is  traversed  by  three  vertical  sutures: — one  between  the  frontal  process 
of  the  maxilla  and  the  lacrimal,  a  second  between  lacrimal  and  lamina  papyracea,  and  a  third 
between  the  lamina  papyracea  and  the  sphenoid.  Occasionally  the  sphenoidal  concha  appears 
in  the  orbit  between  the  ethmoid  and  the  body  of  the  sphenoid. 

The  apex  of  each  orbit  corresponds  to  the  optic  foramen,  a  circular  orifice  which  transmits 
the  optic  nerve  and  ophthalmic  artery.  The  base  or  circumference  is  quadrilateral  in  form 
and  is  bounded  by  the  frontal  bone  above,  the  frontal  process  of  the  maxilla  and  the  medial 
angular  process  of  the  frontal  on  the  medial  side,  the  zygomatic  bone  and  the  zygomatic  process 
of  the  frontal  on  the  lateral  side,  and  by  the  zygomatic  and  the  body  of  the  maxilla  below. 
The  following  points  may  also  be  noted: — The  suture  between  the  zygomatic  process  of  the 
frontal  bone  and  the  zygomatic;  the  supra-orbital  notch  (sometimes  a  complete  foramen); 
the  sutiu'e  between  the  frontal  bone  and  the  frontal  process  of  the  maxilla;  and  in  the  lower 
segment,  the  zygomatico-maxillary  suture. 

The  orbit  communicates  with  the  cranial  cavity  by  the  optic  foramen  and  superior  orbital 
fissure;  with  the  nasal  fossa,  by  means  of  the  naso-lacrimal  canal;  with  the  zygomatic  and 
ptery go-palatine  fossae,  by  the  inferior  orbital  fissure.  In  addition  to  these  large  openings,  the 
orbit  has  five  other  foramina — the  infra-orbital,  zygomatico-orbital,  and  the  anterior  and 
posterior  ethmoidal  canals — opening  into  it  or  leading  from  it. 

The  following  muscles  arise  within  the  orbit : — the  four  recti,  the  -tuperior  oblique,  and 
levator  palpebrce  superioris,  near  the  apex;  the  inferior  oblique  on  the  floor  of  the  orbit  lateral 
to  the  naso-lacrimal  canal;  and  the  tensor  tarsi  from  the  lacrimal  crest.  The  margins  of  the 
inferior  orbital  fissure  give  attachment  to  the  orhitalis  muscle. 

THE  NASAL  FOSS^ 

The  nasal  fossae  (figs.  135,  136)  are  two  irregular  cavities  situated  on  each 
side  of  a  median  vertical  septum.  They  open  in  front  by  the  piriform  aperture 
and  communicate  behind  with  the  pharynx  by  the  choanse.     They  are  somewhat . 

Fig.  135. — Section  through  the  Nasal  Fossa  to  show  the  Septum.     Left  Half,  with 
Septum  looking  toward  Right  Nasal  Fossa. 


Crest  of  sphenoid—^ 

';4 


Groove  for  naso-palatine  nerve 


Crest  of  maxilla 


oblong  in  transverse  section,  and  extend  vertically  from  the  anterior  part  of  the 
base  of  the  cranium  above  to  the  superior  surface  of  the  hard  palate  below. 
Their  transverse  extent  is  very  limited,  especially  in  the  upper  part.  Each  fossa 
presents  for  examination  a  roof,  floor,  medial  and  lateral  walls,  and  communicates 
with  the  sinuses  of  the  frontal,  sphenoid,  maxilla,  and  ethmoid  bones. 


THE  NASAL  FOSSAE 


111 


The  roof  is  horizontal  in  the  middle,  but  sloped  downward  in  front  and  behind.  The 
anterior  slope  is  formed  by  the  posterior  surface  of  the  nasal  bone  and  the  nasal  process  of  the 
frontal;  the  horizontal  portion  corresponds  to  the  cribriform  plate  of  the  ethmoid  and  the  sphe- 
noidal concha;  the  posterior  slope  is  formed  by  the  inferior  surface  of  the  body  of  the  sphenoid, 
the  ala  of  the  vomer,  and  a  small  portion  of  the  sphenoidal  process  of  the  palate.  The  sphe- 
noidal sinus  opens  at  the  upper  and  back  part  of  the  roof  into  the  spheno-ethmoidal  recess, 
above  the  superior  meatus. 

The  floor  is  concave  from  side  to  side,  and  in  the  transverse  diameter  wider  than  the  roof. 
It  is  formed  mainly  by  the  palatine  process  of  the  maxilla  and  completed  posteriorly  by  the  hori- 
zontal part  of  the  palate  bone.  Near  its  anterior  extremity,  close  to  the  septum,  is  the  incisive 
canal. 

The  septum  or  medial  waO  is  formed  by  the  perpendicular  plate  of  the  ethmoid,  the  vomer, 
the  rostrum  of  the  sphenoid,  the  crest  of  the  nasal  bones,  the  frontal  spine,  and  the  rnedian 
crest  formed  by  the  apposition  of  the  palatine  processes  of  the  maxilte  and  the  horizontal 
parts  of  the  palate  bones.  The  anterior  border  has  a  triangular  outline  limited  above  by  the 
perpendicular  plate  of  the  ethmoid  and  below  by  the  vomer,  and  in  the  recent  state  the  defi- 
ciency is  filled  up  by  the  septal  cartilage  of  the  nose.     The  posterior  border  is  formed  by  the 


Fig.  136.- 


-Section  throctgh  the  Nasal  Fossa  to  show  the  Lateral  Wall  with 
THE  Meatuses. 


Superior  nasal  concha 
Probe  in  sphenoidal  foramen 
Sphenoidal  sinus 
Sella  turcica 


Superior  meatus 
Spheno-palatine 


Uncinate  process  of  ethmoid 

Internal  pterygoid  plate 

Palate  bone 

Probe  in  posterior  palatine  canal 


Probe  in  naso- 
lachrymal  canal 


Frontal  sinus 


Agger  nasi 

?r — Lachrymal  bone 
■*■       Lower  end  of  bristle 
in  middle  meatus 
Middle  meatus 

r  nasal 
concha 
Probe  at  lower  end 
of  naso-lachrymal 
canal     where      it 
opens  into  inferior 
meatus 
Incisive  canal 


pharyngeal  edge  of  the  vomer,  which  separates  the  two  choanaj.  The  septum,  which  is  usually 
deflected  from  the  middle  line  to  one  side  or  the  other,  is  occasionally  perforated,  and  in  some 
cases  a  strip  of  cartilage,  continuous  with  the  triangular  cartilage,  extends  backward  between 
the  vomer  and  perpendicular  plate  of  the  ethmoid  (posterior  or  sphenoidal  process). 

The  lateral  wall  is  the  most  extensive  and  the  most  comphcated  on  account  of  the  forma- 
tion of  the  meatuses  of  the  nose.  It  is  formed  by  the  frontal  process  and  the  medial  surface  of 
the  maxilla,  the  lacrimal,  the  superior  and  inferior  conchse  of  the  ethmoid,  the  inferior  nasal 
concha,  the  vertical  part  of  the  palate  bone,  and  the  medial  surface  of  the  medial  pterygoid 
plate.  The  three  conchae,  which  project  medially,  overhang  the  three  recesses  known  as  the 
meatuses  of  the  nose.  The  superior  meatus,  the  shortest  of  the  three,  is  situated  between  the 
superior  and  middle  nasal  conch®,  and  into  it  open  the  orifice  of  the  posterior  ethmoidal  cells 
and  the  spheno-palatine  foramen.  The  middle  meatus  lies  between  the  middle  and  inferior 
conchse.  At  its  fore  part  it  communicates  with  the  frontal  sinus  by  means  of  the  infundibulum, 
and  near  the  middle  with  the  maxillary  sinus  (antrum);  the  communication  with  the  sinus  is 
very  irregular  and  sometimes  represented  by  more  than  one  opening  (fig.  136).  Two  sets  of 
ethmoidal  cells — the  middle  and  anterior — also  open  into  the  middle  meatus,  the  anterior  in 
common  with  the  infundibulum,  the  middle  on  an  elevation  known  as  the  bulla  ethmoidalis. 
The  inferior  meatus,  longer  than  either  of  the  preceding,  is  situated  between  the  inferior  nasal 
concha  and  the  floor  of  the  fossa,  and  presents,  near  the  anterior  part,  the  lower  orifice  of  the 
canal  for  the  naso-lacrimal  duct. 


112 


THE  SKELETON 


The  nasal  fossae  open  on  the  face  by  means  of  the  apertura  piriformis,  a  heart-shaped  or 
piriform  opening  whose  long  axis  is  vertical  and  whose  broad  end  is  below.  The  orifice  is 
bounded  above  by  the  lower  borders  of  the  nasal  bones,  laterally  by  the  maxillae,  inferiorly 
by  the  premaxillary  portions  of  the  maxiUae,  and  in  the  recent  state  the  orifice  is  divided  by  the 
septal  cartilage.  Below,  where  the  lateral  margins  slope  inward  to  meet  in  the  middle  line, 
is  the  anterior  nasal  spine. 

The  choanae  (posterior  nares)  are  bounded  superiorly  by  the  alae  of  the  vomer,  the  sphe- 
noidal processes  of  the  palate,  and  the  inferior  surface  of  the  body  of  the  sphenoid;  laterally 
by  the  lateral  pterygoid  plates;  and  inferiorly  by  the  posterior  edge  of  the  horizontal  plates  of 
the  palate  bones.     They  are  separated  from  each  other  by  the  posterior  border  of  the  vomer. 

The  nasal  fossae  communicate  with  all  the  more  important  fossae  and  the  air-sinuses  of  the 
skull.     By  means  of  the  foramina  in  the  roof  they  are  in  connection  with  the  cranial  cavity; 


Fig.  137. — The  Choan^.    Veiwed  from  behind. 
Pharyngeal  canals 


Pterygoid  canal 


Foramen  ovale 


Scaphoid  fossa 


Pterygoid  fossa 
Lateral  pterygoid  plate 

Tuberosity  of  palate  bone 


Medial   pterygoid  plate 


Hamular  process 


by  the  infundibulum  each  fossa  is  in  communication  with  the  frontal  and  anterior  ethmoidal 
cells;  the  posterior  ethmoidal  cells  open  into  the  superior  meatuses  and  the  sphenoidal  sinuses 
into  the  recesses  above;  the  spheno-palatine  foramina  connect  them  with  the  pterygo-palatine 
fossae,  and  by  means  of  an  irregular  orifice  in  each  lateral  wall  they  communicate  with  the  max- 
illary sinuses.  The  canals  for  the  naso-lacrimal  ducts  connect  them  with  the  orbits,Jand  the 
incisive  canals  with  the  oral  cavity. 


THE  INTERIOR  OF  THE  SKULL 

In  order  to  study  the  interior  of  the  skull  it  is  necessary  to  make  sections  in 
three  directions — sagittal,  coronal,  and  horizontal.  This  enables  the  student  to 
examine  the  various  points  with  facility,  and  displays  the  great  proportion  the 
brain  cavity  bears  to  the  rest  of  the  skull.  The  sagittal  section  (fig.  138)  should 
be  made  slightly  to  one  side  of  the  median  line,  in  order  to  preserve  the  nasal 
septum.  The  black  line  (fig.  138)  drawn  from  the  basion  (anterior  margin  of 
the  foramen  magnum)  to  the  gonion  (the  anterior  extremity  of  the  sphenoid) 
represents  the  basi-cranial  axis ;  whilst  the  line  drawn  from  the  gonion  to  the 
subnasal  point  lies  in  the  basi-facial  axis.  These  two  axes  form  an  angle  termed 
the  cranio -facial,  which  is  useful  in  making  comparative  measurements  of  crania. 
A  line  prolonged  vertically  upward  from  the  basion  will  strike  the  bregma.  This 
is  the  basi-bregmatic  axis,  and  gives  the  greatest  height  of  the  cranial  cavity. 
A  line  drawn  from  the  ophryon  to  the  occipital  point  indicates  the  greatest  length 
of  the  cranium. 

Near  its  middle,  the  cranial  cavity  is  encroached  upon  by  the  petrous  portion 
of  the  temporal  bone  on  each  side;  the  walls  are  channelled  vertically  by  narrow 
grooves  for  the  middle  and  small  meningeal  vessels,  and  toward  the  base  and  at 
the  vertex  are  broader  furrows  for  the  venous  sinuses. 

The  coronal  section  is  most  instructive  when  made  in  the  basi-bregmatic 
axis.  The  section  will  pass  through  the  petrous  poition  on  each  side  in  such  a 
way  as  to  traverse  the  external  auditory  passage  and  expose  the  tympanum  and 
vestibule,  and  will  also  partially  traverse  the  internal  auditory  meatus.     Such 


THE  INTERIOR  OF  THE  SKULL 


113 


a  section  will  divide  the  parietal  bones  slightly  posterior  to  the  parietal  eminences, 
and  a  line  drawn  transversely  across  the  section  at  the  mid-point  will  give  the 
greatest  transverse  measurement  of  the  cranial  cavity.  A  skull  divided  in  this 
way  facilitates  the  examination  of  the  parts  about  the  choanse  (posterior  nares) . 

The  horizontal  section  (figs.  139,  140)  of  the  skull  should  be  made  through  a 
line  extending  from  the  ophiyon  to  the  occipital  point,  passing  laterally  a  few 
millimetres  above  the  pterion  on  each  side.  It  is  of  great  advantage  to  study  the 
various  parts  on  the  floor  of  the  cranial  cavity  in  a  second  skull  in  which  the  dura 
mater  and  its  various  processes  have  not  been  removed. 

The  floor  [basis  cranii  interna]  of  the  cranial  cavity  presents  three  irregular 
depressions  termed  the  anterior,  middle,  and  posterior  fossse  (figs.  139  and  140). 

The  Anterior  Cranial  Fossa. — The  floor  of  this  fossa  is  on  a  higher  level 
than  the  rest  of  the  cranial  floor.  It  is  formed  by  the  horizontal  plate  of  the 
frontal  bone,  the  cribriform  plate  of  the  ethmoid,  and  the  lesser  wings  of  the 


Fig.  138. — The  Skull  in  Sagittal  Section. 

Bregma 


Ophryon 


sphenoid,  which  meet  and  exclude  the  body  of  the  sphenoid  from  the  anterior 
fossa.  The  free  margins  of  the  lesser  wings  and  the  anterior  margin  of  the  optic 
groove  mark  the  limits  of  this  fossa  posteriorly.  The  central  portion  is  depressed 
on  each  side  of  the  crista  galli,  presents  the  numerous  apertures  of  the  cribriform 
plate,  and  takes  part  in  the  formation  of  the  roof  of  the  nasal  fossse;  laterally, 
the  floor  of  the  anterior  cranial  fossa  is  convex;  it  forms  the  roof  of  the  orbits, 
and  is  marked  by  irregular  furrows.  It  supports  the  frontal  lobes  of  the  cerebrum. 
The  sutures  traversing  the  floor  of  the  fossa  are  the  fronto-ethmoidal,  forming 
three  sides  of  a  rectangle,  that  portion  of  the  transverse  facial  suture  which  tra- 
verses the  roof  of  the  orbit,  and  the  ethmo-sphenoidal  suture,  the  centre  of  which 
corresponds  to  the  gonion.     The  other  points  of  interest  in  the  fossa  are:^ 

A  groove  for  the  superior  sagittal  sinus. 

The  foramen  caecum  which  frequently  transmits  a  small  vein  to  the  nasal  cavity. 

The  crista  galli.    • 

The  ethmoidal  fissure  for  the  anterior  ethmoida,l  branch  of  the  fifth  nerve. 

The  cranial  orifice  of  the  anterior  ethmoidal  canal,  transmitting  the  anterior  ethmoidal 
branch  of  the  fifth  nerve,  and  a  meningeal  branch  of  the  anterior  ethmoidal  artery. 

The  cranial  orifice  of  the  posterior  ethmoidal  canal,  transmitting  a  meningeal  branch  of  the 
posterior  ethmoidal  artery. 

The  ethmoidal  spine  of  the  sphenoid. 

Furrows  for  meningeal  vessels. 


114 


THE  SKELETON 


Fig.  139. — The  Skull  in  Horizontal  Section. 


Ethmoidal    fissure   for    anterior    eth- 


Ethmoidal     foramina     for     olfactory 

nerve 
Ethmoid 


Optic  foramen    (for 
optic   nerve) 


Foramen     ovale     (third     divis 

trigeminus 
Notch  for  abducens  nerve 


Interior     auditory     meatus     (facial 
and  auditory  nerves) 


Jugular   foramen    (glosso-^  haryngeal 
vagus  and  accessary  nerves) 


Hypoglossal  foramen  (hypoglossal  nervo 


THE  INTERIOR  OF  THE  SKULL 


115 


Fig.   140. — The  Skull  in  Horizontal  Section. 

Frontal  bo 


Ridge  for  falx  cerebri 
Crista  galli 

Anterior  fossa 
Cribriform  plate 


Lesser  wing  of  sphenoid 
The  limbus 
Optic  groove- 
Pituitary  fossa- 

Dorsum  sellae. 
Petro-sphenoidal  proces 


Internal  occipital  crest 


Internal  occipital  protuberance 


Foramen  magnum 


116  THE  SKELETON 

The  Middle  Cranial  Fossa,  situated  on  a  lower  level  than  the  anterior, 
consists  of  a  central  and  two  lateral  portions.  In  front  it  is  limited  by  the  posterior 
borders  of  the  lesser  wings  of  the  sphenoid  and  the  anterior  margin  of  the  optic 
groove,  behind  by  the  dorsum  sellse  and  the  upper  angle  of  the  petrous  portion 
of  both  temporal  bones.  Laterally  it  is  bounded  on  each  side  by  the  squamous 
portion  of  the  temporal,  the  great  wing  of  the  sphenoid,  and  the  parietal  bone, 
whilst  the  floor  is  formed  by  the  body  and  great  wings  of  the  sphenoid  and  the 
anterior  surface  of  the  petrous  portion  of  the  temporals.  It  contains  the  follow- 
ing sutures: — spheno-parietal,  petro-sphenoidal,  squamo-sphenoidal,  squamous, 
and  a  part  of  the  transverse  suture.  The  central  portion  of  the  fossa  presents 
from  before  backward : 

The  optic  groove,  above  and  behind  which  is  the  optic  chiasma. 

The  optic  foramen  on  each  side,  transmitting  the  optic  nerve  and  ophthalmic  artery. 

The  tuberculum  sellae,  indicating  the  hne  of  junction  of  pre-  and  post-sphenoid  elements. 

The  anterior  clinoid  processes. 

The  fossa  hypophyseos  or  sella  turcica,  with  the  middle  clinoid  processes,  and  grooves  for 
the  internal  carotid  arteries.  The  dorsum  sellse,  with  the  posterior  clinoid  processes,  and 
notches  for  the  sixth  pair  of  cranial  nerves. 

The  central  portion  is  in  direct  relation  with  the  parts  of  the  brain  within  the  circle  of 
Willis. 

The  lateral  portions  are  of  considerable  depth  and  marked  by  numerous  elevations  and 
depressions  corresponding  to  the  convolutions  of  the  temporal  lobes  of  the  brain,  and  by  grooves 
for  the  branches  of  the  middle  and  small  meningeal  vessels.  The  following  foramina  are  seen 
on  each  side: — 

The  superior  orbital  (sphenoidal)  fissure,  leading  into  the  orbit  and  transmitting  the  third, 
fom-th,  three  branches  of  the  ophthalmic  division  of  the  fifth  and  sixth  cranial  nerves,  some 
filaments  from  the  cavernous  plexus  of  the  sympathetic,  an  ophthalmic  vein,  the  orbital  branch 
of  the  middle  meningeal,  and  a  recurrent  branch  of  the  lacrimal  artery. 

The  foramen  rotundum,  for  the  passage  of  the  second  division  of  the  fifth  nerve  into  the 
pterygo-palatine  fossa. 

The  foramen  ovale,  which  transmits  the  third  division  of  the  fifth  nerve  with  its  motor 
root  (mandibular  nerve),  the  small  meningeal  artery,  and  the  small  superficial  petrosal  nerve. 

The  foramen  Vesalii  (not  always  present)  for  a  small  vein. 

The  foramen  spinosum,  for  the  middle  meningeal  artery  and  its  venae  comitantes;  also  the 
N.  spinosus. 

The  foramen  lacerum  is  the  irregular  aperture  between  the  body  and  great  wing  of  the 
sphenoid,  and  the  apex  of  the  petrous  portion  of  the  temporal.  In  the  recent  state  it  is  closed 
below  by  a  layer  of  fibro-cartilage  which  is  perforated  by  the  Vidian  nerve,  a  meningeal  branch 
of  the  ascending  pharynge.<!l  artery,  and  an  emissary  vein.  The  carotid  canal  opens  on  its 
lateral  wall  and  the  pterygoid  (Vidian)  canal  in  front. 

On  the  anterior  surface  of  the  petrous  portion  of  the  temporal  bone  are  seen: — 

A  depression  which  lodges  the  semilunar  (Gasserian)  ganglion. 

The  hiatus  canalis  facialis  for  the  great  superficial  petrosal  nerve  and  the  petrosal  branch 
of  the  middle  meningeal  artery. 

The  accessory  hiatus  for  the  small  superficial  petrosal  nerve. 

A  minute  foramen  for  the  external  superficial  petrosal  nerve. 

The  eminentia  arcuata,  formed  by  the  superior  semicircular  canal. 

Anterior  and  slightly  lateral  to  the  eminentia  arcuata  the  bone  is  exceedingly  thin  and 
translucent,  forming  the  roof  of  the  tympanum  (tegmen  tympani).  When  the  dura  mater  is 
in  situ,  the  depression  lodging  the  semilunar  ganglion  is  converted  into  a  foramen,  traversed  by 
the  fifth  nerve,  and  in  the  same  way  the  notch  on  the  side  of  the  dorsum  sellae  is  converted  into 
a  foramen  for  the  sixth  nerve.  In  many  skulls  the  middle  clinoid  process  is  prolonged  toward 
the  anterior  clinoid  process,  with  which  it  may  be  joined  to  complete  a  foramen  for  the  internal 
carotid  artery.  The  grooves  for  the  middle  meningeal  vessels  are  sometimes  converted  into 
canals  or  tunnels  for  a  short  distance,  especially  in  old  skulls.  The  bones  most  deeply  marked 
are  the  squamous  portion  of  temporal,  the  great  wing  of  the  sphenoid,  and  the  parietal. 

The  Posterior  Cranial  Fossa  is  the  deepest  and  largest  of  the  series.  It  is 
bounded  in  front  by  the  dorsum  sellse  of  the  sphenoid  and  on  each  side  by  the 
superior  border  of  the  petrosal,  and  the  mastoid  portion  of  the  temporal  bone,  the 
posterior  inferior  angle  of  the  parietal,  and  the  groove  on  the  occipital  bone  for 
the  transverse  sinus;  each  of  the  bones  mentioned  takes  part  in  the  formation  of 
its  floor. 

In  the  recent  state  the  fossa  lodges  the  cerebellum,  pons,  and  medulla,  and  is 
roofed  in  by  the  tentorium  cerebelli,  a  tent-like  process  of  the  dura  mater  attached 
to  the  ridges  limiting  the  fossa  above.  It  communicates  with  the  general  cranial 
cavity  by  means  of  the  foramen  ovale  of  Pacchionius,  a  large  opening  bounded 
in  front  by  the  clivus  (basilar  groove)  and  behind  by  the  anterior  free  edge  of  the 
tentorium. 


THE  MORPHOLOGY  OF  THE  SKULL  117 

The  posterior  fossa  is  marlced  by  several  sutures,  viz.,  petro-occipital,  occipito-mastoid, 
parieto-mastoid,  and  in  young  skulls  the  basilar  (occipito-sphenoidal).  In  addition,  the  follow- 
ing points  may  be  noted: — 

The  clivus,  extending  from  the  dorsum  selte  to  the  anterior  margin  of  the  foramen  magnum, 
and  in  relation  with  the  basilar  artery,  the  pons,  the  medulla,  the  sixth  nerves,  and  the  basilar 
sinus. 

The  foramen  magnum,  occupied  in  the  recent  state  by  the  lower  end  of  the  medujla  oblon- 
gata and  its  membranes,  the  vertebral,  anterior  spinal  and  posterior  spinal  arteries,  the  accessory 
(eleventh)  cranial  nerves,  and  the  tectorial  membrane. 

The  hypoglossal  canal  (foramen) ,  sometimes  divided  by  a  spicule  of  bone  into  two  divisions, 
for  the  two  parts  of  the  hypoglossal  nerve  and  a  meningeal  branch  of  the  ascending  pharyngeal 
artery. 

The  internal  occipital  crest,  behind  the  foramen  magnum,  for  the  attachment  of  the  falx 
cerebelli.     It  sometimes  presents  a  depression  known  as  the  vermiform  fossa. 

The  internal  auditory  meatus,  for  the  seventh  and  eighth  cranial  nerves,  the  pars  inter- 
media, and  the  internal  auditory  vessels. 

The  jugular  foramen  (foramen  laoerum  posterius),  somewhat  pyriform  in  shape,  and  divis- 
ible into  three  compartments.  The  anterior  division,  placed  somewhat  medially,  transmits 
the  inferior  petrosal  sinus  and  is  sometimes  completely  separated  by  an  iutra-jugular  process  of 
bone;  the  middle  division  transmits  three  cranial  nerves,  the  ninth,  tenth,  and  eleventh;  and,  in 
the  posterior  division,  placed  somewhat  laterally,  the  transverse  sinus  becomes  continuous  with  the 
internal  jugular  vein.  A  meningeal  branch  of  the  ascending  pharyngeal  or  occipital  artery 
enters  the  cranium  through  this  division  of  the  foramen. 

The  termination  of  the  groove  for  the  transverse  sinus  with  the  internal  orifice  of  the  mas- 
toid foramen. 

The  aquseductus  vestibuli  and  the  fossa  subarcuata,  on  the  posterior  surface  of  the  petrous 
portion  of  the  temporal. 

The  cranium  of  an  average  European  has  a  capacity  of  1450  c.c.  The  circumference,  taken 
in  a  plane  passing  through  the  ophryon  in  front,  the  occipital  point  behind,  and  the  pterion  at 
the  side,  is  52  cm.  The  length  from  the  ophryon  to  the  occipital  point  is  17  cm.,  and  the  width 
between  the  parietals  at  the  level  of  the  zygomata  is  12.5  cm.  The  proportion  of  the  greatest 
width  to  the  length  is  known  as  the  cephalic  index,  i.  e.,  index  of  breadth.  A  skull  with  an  aver- 
age cephalic  index  is  mesaticephalic.  When  the  index  is  above  the  average,  it  is  brachycephalic 
(short  and  broad),  and  when  below  the  average,  dolichocephalic  (long  and  narrow).  The  height 
from  the  basion  to  the  bregma  is  nearly  the  same  as  the  width  at  the  level  of  the  zygomata. 
The  cranio-facial  angle  is  about  96°. 


THE  MORPHOLOGY  OF  THE  SKULL 

In  man  the  skull  during  development  passes  thi-ough  three  stages.  At  first  the  brain  vesi- 
cles are  enclosed  in  a  sac  of  indifferent  tissue  which  ultimately  becomes  tough  and  fibrous  to  form 
the  membranous  cranium.  This,  in  turn,  is  partly  converted  into  the  membrane  or  roof  bones 
of  the  cranium,  whilst  the  remainder  is  represented  in  the  adult  by  the  dura  mater.  At  the 
sides  and  base  of  the  membranous  cranium,  however,  cartilage  is  deposited,  chondro -cranium, 
in  which,  as  well  as  in  the  membranous  tracts,  osseous  tissue  appears  in  due  course.  Eventually, 
as  osseous  box  is  formed,  consisting  of  membrane  bones  and  cartilage  bones  intricately 
interwoven. 

A  study  of  the  skull  in  the  chondral  stage  is  very  instructive.  It  consists  of  two  parts: 
(1)  The  skull  proper  and  (2)  the  appendicular  elements. 

(1)  The  skull  proper  consists  of  three  regions: — 

(a)  The  notochordal  region,  which  ultimately  gives  rise  to  the  chief  parts  of  the  occipital 

bone  and  a  part  of  the  sphenoid.     It  is  named  notochordal  because  the  notochord  runs 

in  it  as  far  as  the  anterior  extremity,  i.  e.,  the  level  of  the  fossa  hypophyseos  (sella  turcica.) 

(6)   Anterior  to  the  notochordal  is  the  trabecular  region,  from  which  the  remainder  of  the 

sphenoid  is  developed. 

(c)   The  most  anterior  part  of  the  prechordal  portion  of  the  base  is  the  ethmo-vomerine 

region,  from  which  the  nasal  septum  and  its  cartilages  arise.     These  thi-ee  parts  continue 

forward  the  line  of  the  vertebral  a.xis,  and  constitute  a  cranio-facial  axis  terminating,  in 

front,  in  the  premaxilk;.     Finally,  wedged  in  on  each  side,  between  the  notochordal  and 

trabecular  regions,  is  the  complicated  periotic  capsule. 

The  chondro-cranium  at  the  thii-d  month  presents  the  following  parts.     Seen  from  above, 

the  cartilage  extends  from  the  cranial  base  to  a  spot  midway  between  the  base  and  the  vertex, 

shading  off  indefinitely  on  the  membranous  wall.     The  oval  masses  on  each  side  are  the  periotic 

cartilages,  in  which  the  fossae  subarouatEe  are  conspicuous  objects.     Each  periotic  cartilage  is 

joined  to  the  sphenoid  by  a  strip,  termed  the  sphenotic  cartilage,  which  usually  persists  in  the 

adult  skuU.     The  cartilage  for  the  orbito-sphcnoid  (the  small  wing)  is  co-extensive  with  the 

aU-sphenoid,  and  forms  part  of  the  lateral  wall  of  the  skuU.     The  snout-like  appearance  of  the 

anterior  part  of  the  skull  is  caused  bj'  thefronto-nasal  plate.    On  each  side  of  the  ethmo-vomerine 

plate,  near  its  anterior  termination,  are  two  small  concave  pieces  of  cartilage  for  Jacobson's 

organs.     They  are  sometimes  referred  to  as  the  ploughshare  cartilages,  owing  to  their  shape. 

Further  details  are  given  in  fig.  141. 

(2)  The  appendicular  elements  of  the  skull  are  a  number  of  cartilaginous  rods  surrounding 
the  visceral  cavity — i.  e.,  nose,  mouth,  and  pharymx — which  undergo  a  remarkable  metamor- 
phosis, and  are  represented  in  the  adult  by  the  ear  bones,  the  styloid  process,  and  the  hyoid  bone. 


118 


THE  SKELETON 


Fig.    141. — Model   of  the  Chondro-cranium    of    a    Human  Fcetus    8   cm.   in    Length. 
Cartilage  in  Blue.    Viewed  from  Above.     (After  O.  Hertwig.) 


Crista  galli 


Lamina  cribrosa 


Ala  orbitalis 
Foramen  opticum 
Ala  temporalis 

Sella  turcica 
Dorsum  sellas 

Facial  nerve  and  canal 
Auditory  capsule 


Foramen  magnum 


Tectum  synoticum 


Fig.  142. — An  Enlarged  Portion  of  the  Same  Model  of  the  Chondro-cranium  as  Shown 

IN  Fig.   141.     Viewed  From  the  Right  Side,  Showing  the  Skeleton   of  the  Auditory 

Region.     Cartilage  in  Blue.     (After  O.  Hertwig.) 


Facial  nerve 


Pars  mastoidea 


—  Pars  petrosa 


Styloid  process 


J 


THE  MORPHOLOGY  OF  THE  SKULL  119 

Metamorphosis  of  the  Branchial  or  Visceral  Bars 

These  rods  of  cartilage  are  named,  f  om  before  backward,  the  mandibular,  hyoid,  and 
thyreoid  bars.  They  may  with  care  be  easily  dissected  in  the  foetus  between  the  third  and  fourth 
months.     Their  metamorphosis  is  as  follows: — • 

The  two  extremities  of  the  mandibular  bar  (cartilago  Meckehi)  ossify;  the  distal  end  ulti- 
mately forms  a  portion  of  the  mandible  near  to  the  symphysis  (see  p.  98);  the  pro.ximal  end 
ossffies  as  the  malleus  and  incus.  The  intermediate  portion  disappears;  the  only  vestige  is  a 
band  of  fibrous  tissue,  the  spheno-mandibular  ligament,  extending  from  the  spine  of  the  sphenoid 
to  the  spine  of  the  mandible. 

In  the  connective  tissue  surrounding  the  bar  there  appear,  however,  ossifications,  one  of 
which  invests  the  bar  to  form  the  dentary  plate;  while  a  second,  situated  more  proximally,  forms 
the  tympanic  bone. 

The  hyoid  bar  fuses  distaUy  with  the  thyreoid  bar,  and  forms  part  of  the  hyoid  bone.  Its 
proximal  end  becomes  the  stapes,  the  tympano-hyal  portion  of  the  styloid  process  (fused  with 
the  petro-mastoid),  and  the  stylo-hyal  or  free  portion  of  the  process.  The  succeeding  portion 
(epl-hyal  segment)  is  represented  in  the  adult  by  the  stylo-hyoid  ligament,  and  the  lowest  seg- 
ment, or  cerato-hyal,  by  the  small  cornu  of  the  hyoid. 

The  thyreoid  bar  forms  the  great  cornu  of  the  hyoid  bone  (thyreo-hyal).  The  body  of  the 
hyoid  (basi-hyal)  is  regarded  as  representing  the  fused  ventral  ends  of  the  hyoidean  and  thy- 
reoidean  arches. 

In  addition  to  these  structures  ossifications  occur  in  the  connective  tissue  of  the  maxillary 
process,  a  structure  which  may  be  regarded  as  forming  the  anterior  part  of  the  first  branchial 
arch,  and  in  the  fronto-nasal  process.  The  ossifications  in  the  maxillary  process  give  rise  to 
the  pterygoid  (medial  pterygoid  process  of  the  sphenoid),  the  palate,  the  maxiUa,  and  the 
zygomatic,  while  that  in  the  fronto-nasal  process  forms  the  premaxilla. 

The  bony  elements  of  the  head  may  therefore  be  arranged,  according  to  their  origin,  in  the 
following  table: — 

I.  Basilar  Bones  Developed  in  the  Cartilaginous  Cranium 

Basi-occipital Basilar  portion  of  the  occipital  bone. 

Exoccipitals Condylar  parts  of  the  occipital  bone. 

Supra-occipital Lower  part  of  the  squamous  portion  of  the  occipital. 

Pre-s^  henoW^  } Constituting  the  body  of  the  sphenoid. 

Ali-sphenoids Greater  wings  and  lateral  pterygoid  plates. 

Orbito-sphenoids  Lesser  wings. 

Petro-mastoids Petrous    and     mastoid    portions   (excepting    post-auditory 

processes)  of  the  temporal  bones. 

II.  Roof  Bones  Developed  in  the  Membranous  Cranium 

Squamosals Squamous  portions  of  temporals. 

Parietals The  two  parietal  bones. 

Frontals United  to  form  a  median  frontal  bone. 

Interparietal Upper  part  of  squamous  portion  of  occipital. 

Epipterics The  epipteric  bones. 

III.  Bones  of  the  Nasal  Region 

Mesethmoid Vertical  plate  of  ethmoid  developed  in  the  cartilage  of  the 

cranio-facial  axis. 

Ethmo-turbinals Superior  and  inferior  conchal  processes  of  ethmoid. 

Maxillo-turbinals The  inferior  nasal  conohaj. 

Cribriform  lamina Cribriform  plate  of  ethmoid. 

These  elements  are  developed  in  the  cartilage  of  the  lateral  nasal  process. 

Sphenoidal  turbinals Sphenoidal  conchse.     These  are  derivatives  of  the  ethmo- 
turbinals. 

Lacrimals The  lacrimal  bones  1      Developed   in   the   membrane   over 

Nasals The  nasal  bones       J  the  lateral  nasal  process. 

Vomer The  vomer.     Ossified  in  the  membrane  investing  the  carti- 
lage of  the  cranio-facial  axis. 

IV.  Facial  Bones 

MaxillEe The  maxillse 1      Developed  in  the  connective  tissue 

Zygomatics The  zygomatic  bones  /  of  the  maxillary  process. 

Premaxillae The  incisor  parts  of  the  maxilLe.     Formed  at  the  anterior 

extremity  of  the  cranio-facial  axis  in  the  tissue  of  the 
fronto-nasal  process  (proc.  globulares). 


120  THE  SKELETON 

V.  AppENDicnLAR  Elements  (Bones  of  the  Visceral  Arches) 

(A)  Cartilaginous 
Malleus,        Incus,        and 

Stapes The  ossicula  auditus. 

Mento-Meckelian    portion 

of  the  lower  jaw Small  part  on  either  side  near  to  the  symphysis  menti. 

Tympano-hyals  and  Stylo- 

hyals Styloid  processes  of  the  temporal  bones. 

Epihyals Stylo-hyoid  ligaments. 

Cerato-hyals Lesser  cornua  of  hyoid  bone. 

Thyreo-hyals Greater  cornua  of  hyoid  bone. 

Basi-hyals Body  of  hyoid  bone. 

(B)  Membranous 

Mandible The  lower  jaw  excluding  a  small  portion  near  symphysis. 

Tympanies The  tympanic  plates. 

Pterygoids The  medial  pterygoid  plates. 

Palatals The  palate  bones. 

The  Skull  at  Birth 

The  skull  at  birth  presents,  when  compared  with  the  adult  skull,  several  important  and 
interesting  features.  Its  peculiarities  may  be  considered  under  three  headings: — The  pecuhar- 
ities  of  the  fcetal  skuU  as  a  whole;  the  construction  of  the  individual  bones;  the  remnants  of 
the  chondral  skull. 

(1)   The  General  Characters  of  the  Fcetal  Skull 

l-The  most  striking  featm'es  of  the  skull  at  birth  are,  its  relatively  large  size  in  comparison 
with  the  body,  and  the  predominance  of  the  cranial  over  the  facial  portion  of  the  skull  (8_to  1) ; 
the  latter  is,  in  fact,  very  smaU. 

Fig.  143. — The  Cranium  at  Birth.     (Viewed  from  above.) 


\ 


\ 


The  frontal  and  parietal  eminences  are  large  and  conspicuous;  the  sutures  are  absent;  the 
adjacent  margins  of  the  bones  of  the  vault  are  separated  by  septa  of  fibrous  tissue  continuous 
with  the  dura  mater  internally  and  the  pericranium  externally;  hence  it  is  difficult  to  separate 
the  roof  bones  from  the  underlying  dura  mater,  each  being  lodged,  as  it  were,  in  a  dense  mem- 
branous sac.  The  bones  of  the  vault  consist  of  a  single  layer  without  any  diploe,  and  their 
cranial  surfaces  present  no  digital  impressions.  Six  membranous  spaces  e.xist,  named  fonta- 
neUes:  two  are  median,  the  frontal  [fonticulus  frontalis;  major]  being  anterior  and  the  occipital 
[fonticulus  occipitahs;  minor]  posterior.  Two  exist  on  each  side,  termed  anterior  [fonticulus 
sphenoidalis]  and  posterior  [fonticulus  mastoideiis]  lateral  fontanelles.  Each  angle  of  the  pari- 
etal bones  is  in  relation  with  a  fontanelle.  The  anterior  fontanelle  is  lozenge-shaped,  the  poste- 
rior triangular.  The  lateral  fontanelles  are  nregular  in  outUne.  The  lateral  fontanelles  close 
soon  after  birth;  the  occipital  fontanelle  closes  in  the  first  year,  and  the  frontal  during  the  second 
year. 


THE  MORPHOLOGY  OF  THE  SKULL 


121 


Turning  to  the  base  of  the  skull,  the  most  striking  points  are  the  absence  of  the  mastoid 
processes,  and  the  large  angle  which  the  pterygoid  plates  form  with  the  skull-base,  whereas  in 
the  adult  it  is  almost  a  right  angle.  The  base  of  the  skull  is  relatively  short,  and  the  lower 
border  of  the  mental  symphysis  is  on  a  level  with  the  occipital  condyles. 

The  facial  skeleton  is  relatively  smaU  in  consequence  of  the  small  size  of  the  nasal  fossae, 
the  small  size  of  the  maxiUary  sinus,  and  the  rudimentary  condition  of  the  alveolar  borders 

Fig.  144. — The  Cranium  at  Birth.     (Lateral  view.) 


of  the  maxiUse  and  mandible;  the  nasal  fossce  are  as  wide  as  they  are  high,  and  are  almost  fiUed 
with  the  conchje. 

Growth  takes  place  rapidly  in  the  first  seven  years  after  birth.  There  is  a  second  period 
of  rapid  growth  at  puberty,  when  the  air  sinuses  develop,  and  this  affects  especially  the  face 
and  frontal  portion  of  the  cranium. 

Fig.  145. — The  Cranium  at  Birth  in  Sagittal  Section.     (Sphenoidal  concha 
indicated  by  a  *) 


(2)   The  Peculiarity  o/  Individual  Bones  at  Birth 

The  occipital  bone  consists  of  four  distinct  parts,  which  have  already  been  described. 
Compared  with  the  adult  bone,  the  following  are  the  most  important  points  of  distinction: — ■ 
There  is  no  pharyngeal  tubercle  or  jugular  process ;  the  squamous  portion  presents  two  deep 
fissures  separating  the  interparietal  from  the  supra-occipital  portion  and  extending  medially 


122 


THE  SKELETON 


as  far  as  the  occipital  protuberance.     The  grooves  for  the  transverse  (lateral)  sinuses  are 
absent. 

The  sphenoid  in  a  macerated  foetal  skuU  falls  into  three  pieces:  (1)  united  pre-  and  post- 
sphenoids,  orbito-sphenoids,  and  lingulse,  and  (2  and  3)  the  ali-sphenoids.  The  pre-sphe- 
noid  is  quite  solid  and  connected  with  the  ethmo-vomerine  cartilage,  and  presents  no  traces  of 
the  air  sinuses  which  occupy  this  part  in  the  adult  skull.  The  pre-sphenoid  by  its  upper  surface 
forms  part  of  the  anterior  cranial  fossa,  from  which  it  is  subsequently  excluded  by  the  growth 
of  the  orbito-sphenoids.     The  optic  foramina  are  large  and  triangular  in  shape.     The  lingulae 


Fig.   146.— The  Occipital  at  Birth. 


Interparietal     portion     (develops     in — ^' 
membrane) 


The  interparietal  and  supra-occipital 
portions  form  the  squamous  portion 
of  the  adult 

Supra-occipital    portion    (develops 
cartilage) 


stand  out  from  the  basi-sphenoid  as  two  lateral  buttresses,  and  at  the  tuberculum  sellse  is  the 
basi-pharyngeal  canal,  which  in  the  recent  bone  is  occupied  by  fibrous  tissue.  The  dorsum 
sellae  is  still  cartilaginous.  The  ali-sphenoids  with  the  pterygoid  processes  are  separated^from 
the  rest  of  the  bone  by  cartilage.  The  foramen  rotundum  is  complete,  but  the  future  foramen 
ovale  is  merely  a  deep  notch  in  the  posterior  border  of  the  great  wing,  and  there  is  no  foramen 
spinosum.  The  pterygoid  processes  are  short,  and  each  medial  pterygoid  plate  presents  a  broad 
surface  for  articulation  with  the  lingula.  The  pterygoid  canal  is  a  groove  between  the  medial 
pterygoid  plate,  the  lingula,  and  great  wing. 


Fig.  147. — The  Sphenoid  at  Birth. 


Pterygoid  canal  Lingula 


The  temporal  bone  at  birth  consists  of  three  elements,  the  petrosal,  squamosal,  and  tym- 
panic. The  petrosal  presents  a  large  and  conspicuous  floccular  fossa;  the  hiatus  Fallopii  is 
a  shallow  bay  lodging  the  geniculate  gangUon  of  the  facial  nerve.  There  is  a  relatively  large 
mastoid  antrum,  but  no  mastoid  process.  The  styloid  process  is  unossified,  but  the  tympano- 
hyal  may  be  detected  as  a  minute  rounded  nodule  of  bone  near  the  stylo-mastoid  foramen. 

The  squamosal  has  a  very  shallow  mandibular  fossa  and  a  relatively  large  post-glenoid 
tubercle.  The  posterior  part  of  the  inferior  border  is  prolonged  downward  into  an  uncinate 
process  {post-auditory  process)  which  closes  the  mastoid  antrum  laterally. 


THE  MORPHOLOGY  OF  THE  SKULL 


123 


The  tympanic  bone  or  annulus  is  a  delicate,  horseshoe-shaped  ossicle,  attached  by  its  ante- 
rior and  posterior  extremities  to  the  inferior  border  of  the  squamosal 

The  ear -bones  are  chiefly  of  interest  from  their  size,  for  they  are  as  large  at  birth  as  in  the 
adult.     The  anterior  process  (Fohan  process)  may  be  2  cm.  in  length. 


Fig.  149. — Temporal  Bone  at  Bibth. 
Fig    148. — The  Temporal  Bone  at  Birth.  (Medial  view.) 


Squamosal 


Hiatus  canalis  facialis 

Floccular  fossa 
Aquseductus  vestibuU 
Internal  auditory 
meatus 


Post-glenoid  tubercle 
Petro-tympanic  fi 

Tympanic  annulus 


(Lateral  view.) 


Petro-squamous  suture 
Petrosal 

Stylo-mastoid  foramen 
Tympano-hyal 


•Carotid  canal 


The  frontal 'consists  of  two  bones  separated  by  a  median  vertical  (metopic)  suture.  The 
frontal  eminence  is  very  pronounced,  but  the  superciliary  arche=i  and  frontal  sinuses  are  wanting. 
The  frontal  spine,  which  later  becomes  one  of  the  most  conspicuous  features  of  this  bone,  is 
absent.     There  is  no  temporal  line.  gil 


Fig.  151. — The  Frontal  Bone  at  Birth. 


The  parietal  is  simply  a  quadrilateral  lamina  of  bone,  concave  on  its  inner  and  convex  on 
the  outer  surface.  The  parietal  eminence,  which  indicates  the  spot  in  which  the  ossification  of 
the  bone  commenced,  is  large  and  prominent.     The  grooves  for  blood-sinuses,  as  in  other  cranial 


124 


THE  SKELETON 


bones,  are  absent.  Each  angle  of  the  parietal  is  in  relation  with  a  fontanelle.  As  in  the  adult, 
the  anterior  inferior  angle  of  the  bone  is  prolonged  downward  toward  the  aU-sphenoid. 

The  ethmoid  consists  of  two  lateral  portions  separated  by  the  still  cartilaginous  ethmo- 
vomerine  plate.  The  ethmoid  cells  are  represented  by  shallow  depressions,  and  the  uncinate 
process  is  undeveloped. 

The  sphenoidal  conchae  are  two  small  triangular  pieces  of  bone  lying  in  the  perichondrium 
on  each  side  of  the  ethmo-vomerine  plate  near  its  junction  with  the  pre-sphenoid.  (Indicated 
by  the  *  in  fig.  145.) 

The  maxilla  presents  the  following  characters: — The  incisive  suture  is  visible  on  the  palatine 
aspect  of  the  bone.     The  alveolar  border  presents  five  sockets  for  teeth.     The  infra-orbital 


Fig. 


152. — The  Maxilla  at  Birth. 
Premaxillary  portion 


Inferior  view. 


Medial  view. 


foramen  communicates  with  the  floor  of  the  orbit  by  a  deep  fissure;  this  fissure  sometimes  per- 
sists in  the  adult.     The  sinus  is  a  shallow  depression. 

The  mandible  at  birth  consists  of  two  halves  united  by  fibrous  tissue  in  the  fine  of  the  future 
symphysis.  Each  half  is  a  bony  trough  lodging  teeth.  The  trough  is  divided  by  thin  osseous 
partitions  into  five  compartments:  of  these,  the  fifth  is  the  largest,  and  is  often  subdivided  by 
a  ridge  of  bone.  The  floor  is  traversed  by  a  furrow  as  far  forward  as  the  fourth  socket  (that 
for  the  first  milk  molar),  where  it  turns  outward  at  the  mental  foramen.  This  furrow  lodges 
the  inferior  alveolar  nerve  and  artery,  which  enter  by  the  large  mandibular  foramen.  The  con- 
dyle is  on  a  level  with  the  upper  border  of  the  anterior  extremity  of  the  bone. 

The  palate  bones  differ  mainly  from  those  in  the  adult  in  that  the  vertical  and  horizontal 
plates  are  of  the  same  length;  thus  the  nasal  fossae  in  the  foetus  are  as  wide  as  they  are  high, 
whereas  in  the  adult  the  height  of  each  nasal  fossa  greatly  exceeds  the  width. 

Concerning  the  remaining  bones  little  need  be  said.  The  vomer  is  a  delicate  trough  of 
bone  for  the  reception  of  the  inferior  border  of  the  ethmo-vomerine  plate;  its  inferior  border, 

Fig.  153. — The  Mandible  at  Bikth. 


which  rests  upon  the  hard  palate,  is  broad,  and  the  bone  presents  quite  a  different  appearance 
from  that  in  the  adult.  The  nasal  bones  are  short  and  broad;  the  zygomatics  and  inferior 
conchae  are  relatively  very  large;  and  the  lacrimals  are  thin,  frail,  and  dehoate  lamellae. 

The  hyoid  consists  of  five  parts.     There  is  a  median  nucleus  for  the  basi-hyal,  and  one  on 
each  side  for  the  greater  cornua  (thyreo-hyals).     The  lesser  oornua  are  cartilaginous. 


(3)  Remnants  of  the  Cartilaginous  Cranium 

It  has  aheady  been  pointed  out  that  at  an  early  date  the  base  of  the  skull  and  the  face  are 
represented  by  hyahne  cartilage,  which  for  the  most  part  is  replaced  by  bone  before  birth. 
Even  at  birth  remnants  of  this  primitive  chondral  skull  are  abundant.  In  the  cranium,  carti- 
laginous tracts  exist  between  the  various  portions  of  the  occipital  bone,  as  well  as  at  the  line  of 


THE  MORPHOLOGY  OF  THE  SKULL  125 

junction  of  the  occipital  with  the  petrosal  and  sphenoid.  The  dorsum  sellae  is  entirely  carti- 
laginous at  birth,  and  the  last  portion  of  this  cartilage  disappears  with  the  ankylosis  of  the 
basi-occipital  and  basi-sphenoid  about  the  twentieth  year.  A  strip  of  cartilage  unites  the  ali- 
sphenoids  with  the  hngulae,  and  for  at  least  a  year  after  bu-th  this  cartilage  is  continuous  with 
that  which  throughout  life  occupies  the  foramen  lacerum.  A  strip  of  cartilage  exists  along  the 
posterior  border  of  the  orbito-sphenoid,  and  not  unfrequently  extends  lateralward  to  the 
pterion.     In  the  adult  skull  it  is  replaced  by  ligamentous  tissue. 

The  ethmo-vomerine  plate  is  entkely  cartilaginous,  and  near  the  end  of  the  nose  supports 
the  lateral  nasal  cartilages,  remnants  of  the  fronto-nasal  plate.  The  fate  of  the  ethmo-vomerine 
plate  is  instructive.  The  upper  part  is  ossified  to  form  the  mesethmoid;  the  lower  part  atro- 
phies from  the  pressure  exerted  by  the  vomer;  the  anterior  end  remains  as  the  septal  cartilage. 
The  lateral  snout-like  extremities  of  the  fronto-nasal  plate  persist  as  the  lateral  cartilages  of  the 

Among  the  appendicular  elements  of  the  skull,  the  styloid  process  and  a  large  portion  of  the 
hyoid  are  cartilaginous  at  birth. 

The  Nerve-foramina  of  the  Skull 

The  various  foramina  and  canals  in  the  skull  which  give  passage  to  nerves  may  be  arranged 
in  two  groups,  primary  and  secondary.  Primary  foramina  indicate  the  spots  where  the  nerves 
leave  the  general  cavity  of  the  dura  mater,  and  as  this  membrane  indicates  the  limit  of  the 
primitive  cranium,  a  cranial  nerve,  in  a  morphological  sense,  becomes  extra-cranial  at  the  point 
where  it  pierces  this  membrane.  In  consequence  of  the  complicated  and  extraordinary  modifica- 
tions the  vertebrate  skull  has  undergone,  many  nerves  traverse,  in  the  adult  skull,  bony  tunnels 
and  canals  which  are  not  represented  in  the  less  complex  skulls  of  low  vertebrates,  such  as 
sharks  and  rays.     To  such  foramina  and  canals  the  terms  secondary  or  adventitious  may  be 


Nerve-foramina  are  further  interesting  in  that  they  occupy  sutm-es,  or  indicate  the  points 
of  union  of  two  or  more  ossific  centres.  To  this  rule  the  foramen  rotundum  is  the  only  excep- 
tion in  the  human  skull. 

The  Primary  Foramina 

1.  Foramen  magnum. — This  is  bounded  by  four  distinct  centres,  the  supra-,  basi-,  and 
two  ex-ocoipitals.  It  transmits  the  accessory  (eleventh)  pair  of  cranial  nerves,  the  vertebral 
arteries  and  their  anterior  and  posterior  spinal  branches,  the  medulla  oblongata  and  its  mem- 
branes, and  the  membrana  tectoria. 

2.  The  hypoglossal. — At  birth  this  is  a  deep  notch  in  the  anterior  extremity  of  the  ex- 
ocoipital,  and  becomes  a  complete  foramen  when  the  basi-  and  ex-occipitals  fuse.  Occasionally 
it  may  be  complete  in  the  ex-occipital,  but  it  indicates  accurately  the  line  of  union  of  these  two 
elements  of  the  occipital  bone.  It  transmits  the  hypoglossal  nerve,  the  meningeal  branch  of  the 
ascending  pharyngeal  artery,  and  its  venae  comitantes. 

3.  Jugular  foramen. — This  occupies  the  petro-occipital  suture,  and  is  formed  by  the  basi- 
and  ex-occipital  in  conjunction  with  the  petrosal.  It  transmits  the  glosso-pharyngeal,  vagus, 
and  accessory  nerves,  a  meningeal  branch  of  the  ascending  pharyngeal  artery,  and  receives  the 
transverse  and  inferior  petrosal  sinuses. 

4.  Auditory. — This  marks  the  point  of  confluence  of  the  groups  of  centres  termed  pro-otic 
and  opisthotic.  It  transmits  the  facial  and  auditory  nerves,  the  pars  intermedia,  and  the  au- 
ditory twig  of  the  basilar  artery. 

5.  Trigeminal. — This  is  only  a  foramen  when  the  dura  mater  is  present  in  the  skull.  It 
is  a  notch  at  the  apex  of  the  petrosal  converted  into  a  foramenby  the  tentorium.  The  main 
trunk  of  the  trigeminal  nerve,  with  the  small  motor  root  (masticator  nerve),  traverses  it. 

6.  Petro-sphenoidal. — This  is  a  notch  between  the  side  of  the  dorsum  sellae  and  apex  of 
the  petrosal  which  becomes  converted  into  a  foramen  by  dura  mater. 

7.  Optic. — This  foramen  is  formed  by  the  confluence  of  the  orbito-  and  pre-sphenoidal 
centres.     It  opens  into  the  orbit  and  transmits  the  optic  nerve  and  ophthalmic  artery. 

The  Secondary  Nerve -foramina 

Foramina  transmitting  the  various  subdivisions  of  the  trigeminal  nerve. — The  primary 
foramen  of  exit  for  the  trigeminal  nerve  is  formed  partly  of  bone  and  partly  of  membrane  at 
the  apex  of  the  petrosal.     The  three  divisions  of  the  nerve  issue  through  secondary  foramina. 

(a)  The  superior  orbital  (sphenoidal)  fissure  is  an  elongated  chink,  bounded  above  by 
the  orbital  wing  and  below  by  the  great  wing  of  the  sphenoid,  medially  by  the  body  of  the 
sphenoid,  and  laterally  by  the  frontal.  It  opens  into  the  orbit,  and  transmits  the  third,  fourth, 
first  (ophthalmic)  division  of  the  trigeminal  and  abducens  nerves,  also  the  ophthalmic  vein  or 
veins. 

(6)  The  foramen  rotundum  is  the  only  exception  to  the  ru,le  relating  to  the  formation  of 
nerve-foramina;  it  is  probably  a  segment  of  the  superior  orbital  fissure.  The  foramen  is  really 
a  canal  running  from  the  middle  cranial  fossa  to  the  pterygo-palatine  fossa,  and  transmits  the 
second  or  maxillary  division  of  the  trigeminal. 

(c)  The  foramen  ovale  at  birth  is  a  gap  in  the  hinder  border  of  the  great  wing  (ali-sphe- 
noid)  of  the  sphenoid,  and  is  converted  into  a  foramen  by  the  petrosal;  subsequently  it  becomes 
complete  in  the  sphenoid.  It  transmits  the  thii'd  or  mandibular  division  of  the  trigeminal  and 
the  small  or  motor  root,  the  small  superficial  petrosal  nerve  (which  occasionally  passes  thi-ough 
a  separate  foramen),  and  the  small  meningeal  artery  with  its  venae  comitantes. 


126  THE  SKELETON 

The  ethmoidal  canals. — These  commence  in  the  suture  between  the  lamina  papyracea  and 
the  frontal  bone,  and  traverse  the  space  between  the  upper  surface  of  the  lateral  mass  of  the 
ethmoid  and  the  horizontal  plate  of  the  frontal,  to  emerge  on  the  cribriform  plate;  they  are 
situated  outside  the  dura  mater.  The  anterior  foramen  transmits  the  anterior  ethmoidal 
branch  of  the  ophthalmic,  which  subsequently  gains  the  nasal  cavity  by  passing  through  the 
ethmoidal  fissure  by  the  side  of  the  crista  galli. 

The  infra-orbital  canal  indicates  the  line  of  confluence  of  the  maxillary  and  malar  centres 
of  the  maxilla;  occasionaOy  it  is  completed  by  the  zygomatic;  rarely  it  is  incomplete  above, 
and  communicates  by  a  narrow  fissure  with  the  orbit.  It  lodges  the  infra-orbital  nerve  and 
artery. 

The  zygomatico-temporal  foramen  is  situated  in  the  suture  between  the  zygomatic  and 
the  greater  wing  of  the  sphenoid  (ali-sphenoid) ;  it  transmits  the  temporal  branch  of  the  zygo- 
matic nerve  and  a  branch  of  the  lacrimal  artery.  In  the  adult  this  foramen  may  be  wholly 
confined  to  the  zygomatic  bone. 

The  zygomatico -facial  canals  traverse  the  zygomatic  bone,  and  indicate  the  line  of  con- 
fluence of  the  two  chief  centres  for  this  bone.  The  facial  twigs  of  the  zygomatic  nerve  issue 
from  them  accompanied  by  arterial  twigs. 

The  spheno-palatine  foramen  is  a  deep  groove  between  the  orbital  and  sphenoidal  pro- 
cesses of  the  palate  bone,  converted  into  a  foramen  by  the  sphenoidal  concha.  It  is  traversed 
by  the  naso-palatine  nerve  and  artery  as  they  enter  the  nasal  from  the  pterygo-palatine  fossa. 

Scarpa's  foramina  are  two  minute  openings  in  the  meso-palatine  suture  where  it  is  in 
relation  with  the  incisive  fossa.     They  are  traversed  by  the  naso-palatine  nerves. 

The  pharyngeal  foramen  is  situated  between  the  sphenoidal  process  of  the  palate  bone, 
the  medial  pterygoid  plate  of  the  sphenoid,  and  the  sphenoidal  concha.  The  pharyngeal 
branch  of  the  spheno-palatine  ganghon  and  a  branch  of  the  spheno-palatine  artery  pass 
through  it. 

The  pterygoid  (Vidian)  canal  is  trumpet-shaped:  the  narrower  end  is  situated  in  the  foramen 
lacerum;  the  broader  orifice  opens  on  the  posterior  wall  of  the  pteryo-palatine  fossa.  The  canal 
is  10  mm.  long;  in  the  fcetal  skull  it  is  a  chink  between  the  base  of  the  medial  pterygoid  plate, 
the  ah-sphenoid,  and  the  lingula  of  the  sphenoid.  The  canal  is  traversed  by  the  Vidian  branch 
of  the  spheno-palatine  ganglion  and  the  Vidian  artery. 

The  posterior  (greater)  palatine  canal  is  a  passage  left  between  the  maxilla,  the  vertical 
plate  and  tuberosity  of  the  palate  bone  and  the  medial  pterygoid  plate;  it  commences  on  the 
hard  palate  by  the  greater  palatine  foramen.  The  descending  palatine  nerve  and  artery  trav- 
erse this  canal.  Several  foramina  open  from  it.  In  the  suture  between  the  vertical  plate  of  the 
palate  bone  and  the  maxilla,  two  small  openings  allow  minute  nerves  to  issue  for  the  middle  and 
inferior  nasal  conchae.  In  the  fissures  between  the  tuberosities  of  the  palate  and  maxillee,  and 
the  pterygoid  plates,  the  posterior  and  middle  palatine  nerves  issue.  These  are  sometimes  called 
the  posterior  and  middle  (smaller)  palatine  canals. 

The  mandibular  or  inferior  dental  canal  runs  in  the  mandible  between  the  dentary  and 
Meckel's  cartilage  of  the  mandible.  The  posterior  orifice  of  the  canal  is  the  mandibular  (infe- 
rior dental)  foramen;  the  anterior  orifice  is  the  mental  foramen.  The  inferior  alveolar  nerve 
and  artery  enter  the  canal  at  its  posterior  orifice;  the  mental  foramen  allows  the  mental  nerve 
to  escape  from  the  canal  accompanied  by  the  mental  artery. 

Foramina  transmitting  the  facial  nerve  and  its  branches. — The  main  trunk  of  the  facial 
enters  the  internal  auditory  meatus  and  traverses  the  facial  canal.  In  the  early  embryo  the 
nerve  lies  on  the  petrosal,  and  is  not  covered  in  with  bone  until  the  fifth  month  of  foetal  life. 
The  terminal  orifice,  the  stylo-mastoid  foramen,  is  situated  between  the  tympanic,  tympano- 
hyal,  and  epiotic  elements  of  the  complex  temporal  bone. 

The  'iter  chorda  posterius'  is  a  chink  between  the  squamosal  and  the  tympanic  elements, 
and  allows  the  chorda  tympani  nerve  to  enter  the  tympanum.  The  fissure  of  exit  for  this  nerve 
is  the  subdivision  of  the  petro-tympanic  fissure  termed  the  canal  of  Huguier,  or  'iter  chordae 
anterius.'  The  petro-tympanic  fissure  lies  between  the  tympanic  plate  and  the  squamosal. 
It  transmits  the  tympanic  branch  of  the  internal  maxillary  artery,  and  lodges  the  anterior  proc- 
ess of  the  malleus. 

The  inferior  orbital  (spheno-maxillary)  fissure  is  situated  between  the  posterior  border 
of  the  orbital  plate  of  the  maxilla  and  a  smooth  ridge  on  the  orbital  surface  of  the  great  wing 
of  the  sphenoid.  It  transmits  the  superior  maxillary  division  (second)  of  the  fifth  nerve,  the 
zygomatic  nerve,  branches  of  the  spheno-palatine  ganglion  to  the  orbit,  and  a  communicating 
vein  from  the  ophthalmic  to  the  pterygoid  plexus. 

C.     THE  THORAX 

The  thorax  is  a  bony  cage  formed  by  the  thoracic  vertebrte  already  described, 
the  ribs  with  their  costal  cartilages,  and  the  sternum. 

THE  RIBS 

The  ribs  [costse]  (figs.  154,  155)  twelve  in  number  on  each  side,  constitute  a 
series  of  narrow,  flattened  bones,  extending  from  the  sides  of  the  thoracic  vertebrae 
toward  the  median  line  on  the  anterior  aspect  of  the  trunk.  The  anterior  ends 
of  the  first  seven  pairs  are  connected,  by  means  of  their  costal  cartilages,  with  the 
sides  of  the  sternum,  and  on  this  account  the  first  seven  ribs  on  each  side  are 


THE  RIBS  127 

termed  true  or  sternal  ribs.  The  remaining  five  pairs,  known  as  false  or  asternal 
ribs,  may  be  arranged  in  two  sets: — one,  including  the  eighth,  ninth,  and  tenth 
ribs,  in  which  the  cartilages  of  the  anterior  extremities  are  connected  together, 
and  the  other,  including  the  eleventh  and  twelfth,  in  which  the  anterior  extremi- 
ties, tipped  with  cartilage,  are  free.  The  eleventh  and  twelfth  are  known,  in 
consequence,  as  the  floating  ribs.  Thus,  the  first  seven  are  vertebro -sternal; 
the  eighth,  ninth,  and  tenth,  vertebro -chondral;  the  eleventh  and  twelfth, 
vertebral  ribs. 

The  ribs  increase  in  length  from  the  first  to  the  seventh,  and  decrease  from  the 
seventh  to  the  twelfth.  They  also  vary  in  their  direction,  the  upper  ones  being 
less  oblique  than  the  lower.  The  obliquity  is  greatest  at  the  ninth  rib  and  gradu- 
ally decreases  from  the  ninth  to  the  twelfth. 

Typical  characters  of  a  rib  (fig.  154). — The  seventh  is  regarded  as  the  most 
typical  rib.  It  presents  for  examination  a  vertebral  extremity  or  head;  a  narrow 
portion  or  neck;  a  sternal  extremity;  and  an  intermediate  portion,  the  body  or 
shaft. 

The  head  [capitulum  costse]  presents  an  articular  surface  made  up  of  two 
articular  facets  separated  by  a  horizontal  crest  [crista  capituh].  The  crest  is 
connected  by  an  interarticular  ligament  with  an  intervertebral  disc,  and  the  facets 
articulate  with  the  costal  pits  on  the  sides  of  the  bodies  of  two  vertebrae  (sixth  and 
seventh) .  As  a  rule,  the  lower  facet  is  the  larger,  and  articulates  with  the  thoracic 
vertebra,  to  which  the  rib  corresponds  in  number.  This  is  the  primary  facet,  and 
is  the  one  represented  in  those  ribs  which  possess  only  a  single  facet  on  the  rib-head. 
The  anterior  margin  is  lipped  for  the  attachment  of  the  radiate  ligament. 

The  neck  [coUum  costae]  is  that  portion  of  the  rib  extending  from  the  head  to 
the  tubercle.  It  is  flattened  from  before  backward  and  the  posterior  surface  is 
in  relation  with  the  transverse  process  of  the  lower  of  the  two  vertebrae  with  which 
the  head  articulates;  it  forms  the  anterior  boundary  of  the  costo-transverse  fora- 
men, and  is  rough  where  it  is  attached  to  the  neck  (middle  costo-transverse) 
ligament.  The  anterior  surface  is  flat  and  smooth.  The  superior  border  of  the 
neck,  continuous  with  the  corresponding  border  of  the  shaft,  presents  a  rough 
crest  [crista  colli]  for  the  anterior  costo-transverse  ligament.  The  inferior  bor- 
der of  the  neck  is  rounded  and  continuous  with  the  ridge  of  the  costal  groove. 
This  difference  in  the  relation  of  the  neck,  to  the  upper  and  lower  borders  of  the 
rib-shaft,  is  useful  in  determining  to  which  side  a  rib  belongs. 

The  tubercle,  situated  behind  at  the  junction  of  the  neck  with  the  shaft,  con- 
sists of  an  upper  and  lateral  part,  rough  for  the  attachment  of  the  posterior  costo- 
transverse ligament,  and  a  lower  and  medial  part,  bearing  a  facet  for  articulation 
with  a  pit  near  the  tip  of  the  transverse  process.  The  tubercle  projects 
below  the  lower  edge  of  the  rib  to  form  a  crest,  marking  the  beginning  of  the  costal 
groove. 

The  body  is  strongly  curved  and  presents  for  examination  two  surfaces  and 
two  borders.  At  first  the  curve  is  in  the  same  plane  as  the  neck,  but  it  quickly 
turns  forward  at  a  spot  on  the  posterior  surface  of  the  shaft  known  as  the  angle, 
where  it  gives  attachment  to  the  ilio-costalis  muscle  and  some  of  its  subdivisions. 
The  rib  has  also  a  second  or  upward  curve,  beginning  at  the  angle.  These  curves 
are  expressed  by  describing  the  main  curve  as  disposed  around  a  vertical,  and  the 
second  or  upward  curve  around  a  second  transverse  axis. 

When  a  rib,  except  the  first,  second,  and  twelfth,  is  laid  with  its  lower  border  upon  the  table, 
the  rib-head  rises  and  the  rib  touches  the  table  at  two  places,  viz.,  at  the  anterior  end,  and  in  the 
neighbourhood  of  the  angle. 

Besides  the  two  curves  now  described,  the  rib  is  slightly  twisted  on  itself,  so  that  the  sur- 
faces which  look  medially  and  laterally  behind  are  placed  obhquely  in  front  and  look  downward 
as  well  as  medially,  and  upward  as  well  as  laterally. 

The  external  sui-face  of  the  rib  is  convex,  and  gives  attachment  to  muscles.  Near  its  an- 
terior extremity  it  forms  a  somewhat  abrupt  curve,  indicated  by  a  ridge  on  the  bone,  which  gives 
attachment  to  the  serratus  anterior  (niagnus)  muscle,  and  is  sometimes  called  the  anterior 
angle. 

The  internal  surface  is  concave  and  presents  near  its  inferior  border  the 
costal  groove  [sulcus  costae].  The  groove  is  best  marked  near  the  angle,  and 
gradually  becomes  shallower  toward  the  anterior  extremity  of  the  rib,  where  it 
is  finally  lost;  it  lodges  the  intercostal  vessels  and  nerve.     The  ridge  limiting  the 


128 


THE  SKELETON 


groove  above  is  continuous  with  the  inferior  border  of  the  neck  of  the  rib,  and 
gives  attachment  to  the  internal  intercostal  muscle. 

The  superior  border  is  rounded,  and  affords  attachment  to  the  internal  and 
external  intercostal  muscles.  The  inferior  border  commences  abruptly  near  the 
angle,  and  gives  attachment  to  the  external  intercostal  muscle. 

The  sternal  end  of  the  shaft  is  cupped  for  the  reception  of  the  costal  cartilage. 


Fig.  154. — The  Seventh  Rib  of  the  Left  Side.     (Seen  from  below.) 


Tubercle 


Costal  groove 


sternal  end  for  costal 
cartilage 


Blood-supply. — -The  ribs  are  very  vascular  and  derive  numerous  branches  from  the  inter- 
costal arteries.  The  branches  in  the  shaft  run  toward  the  vertebral  end,  whilst  those  in  the 
head  and  neck  run,  as  a  rule,  toward  the  shaft.  In  the  neighbourhood  of  the  tuberosity  the 
vessels  do  not  seem  to  have  any  constant  arrangement. 

Peculiar  ribs  (figs.  155,  156). — Several  of  the  ribs  present  certain  pecuUarities  and  differ 
in  many  particulars  from  the  general  description  given  above.  These  are  the  first,  second,  tenth, 
eleventh,  and  twelfth. 

The  first  rib  is  the  broadest,  flattest,  strongest,  shortest,  and  most  curved  of  all  the  series. 
It  is  not  twisted,  and  is  so  placed  that  its  superior  sm-face  looks  forward  as  well  as  upward,  and 
its  inferior  surface  backward  as  well  as  downward.     The  head  is  small,  and  as  a  rule  is  furnished 


THE  RIBS 


129 


with  only  one  articular  facet.  The  neck,  longer  than  that  of  most  of  the  ribs,  is  slender  and 
rounded.  The  tubercle  is  large  and  prominent.  The  shaft  lies  for  its  whole  extent  nearly  in 
one  plane,  has  no  angle,  and  is  curved  in  one  du'eotion  only,  i.  e.,  around  a  vertical  axis.  The  su- 
perior surface  presents  two  shallow  grooves,  separated  near  the  inner  border  by  a  rough  surface 
(scalene  tubercle  or  tubercle  of  Lisfranc)  for  the  scalenus  anterior  muscle.  The  groove  in 
front  of  this  surface  is  for  the  subclavian  vein,  and  the  groove  behind  it  is  for  the  subclavian 
artery  and  a  nerve  trunl;;  passing  to  the  brachial  plexus.  Between  the  groove  for  the  artery  and 
the  tubercle  is  a  rough  surface  for  the  insertion  of  the  scalenus  medius,  and  between  the  groove 
and  the  outer  margin  is  an  area  for  the  origin  of  the  serratus  anterior  {magnus).  The  inferior 
surface  is  uniformly  flat  and  lacks  a  subcostal  groove.  By  the  lateral  portion,  which  is  rough, 
it  gives  attachment  to  the  internal  intercostal  muscle;  the  remainder  of  the  inferior  surface  is  in 
relation  to  pleura  and  lung.  The  lateral  border  is  thick  and  rounded,  and  gives  attachment 
to  the  external  intercostal  muscle,  whilst  the  medial  border,  thin,  sharp,  and  concave,  receives 
the  attachment  of  the  fascia  (Sibson's)  covering  the  dome  of  the  plem-a.  The  anterior  extrem- 
ity is  thick  and  broad,  and  its  upper  margin,  as  well  as  the  cartilage  to  which  it  is  joined,  afford 
attachment  to  the  costo-olavicular  ligament  and  the  subclavius  muscle.  The  costal  cartilage 
of  this  rib  is  du-ectly  united  to  the  manubrium  sterni,  and  occasionally  the  cartilage  and  the 
adjoining  part  of  the  anterior  extremity  of  the  rib  are  replaced  by  fibrous  tissue. 

Fig.  155. — Fikst  and  Second  Ribs.     (Viewed  from  above.) 


Scalenus  anterior" 

lOve  for  subclavian 
vein 


Levator  costEe 
Ilio-costalis  d( 

(insertion) 
Ilio-costali 

(origin) 
Serratus  posteri 

superior 

(insertion) 
Scalenus  posteri 


External  intercostals 


The  rib  derives  its  nutrition  mainly  from  the  superior  intercostal  branch  of  the  subclavian 
artery. 

The  second  rib'is  much  longer  than  the  first,  and  although  like  it  in  being  strongly  curved 
round  a  vertical  axis,  in  its  form  and  general  characters  there  is  a  closer  resemblance  to  the 
ribs  lower  down  in  the  series.  The  head  is  round  and  presents  two  facets,  the  costal  groove  is 
present,  though  faintly  marked,  and  an  angle  is  situated  near  the  tubercle.  The  specially  dis- 
tinguishing featm-e  of  the  rib,  however,  is  a  well-marked  tuberosity  on  its  outer  surface  some- 
what near  the  middle,  for  the  origin  of  a  part  of  the  first  digitation,  and  the  whole  of  the  second 
digitation  of  the  serratus  anterior  {magnus).  Between  the  tuberosity  and  the  tubercle  the  outer 
surface  is  smooth  and  rounded  and  gives  attachment  to  the  scaletius  posterior,  the  serratus 
posterior  superior,  the  ilio-costalis  cervicis  {cervicalis  ascendens),  and  the  ilio-costalis  dorsi  (acces- 
sorius) .  The  internal  sm-face  is  smooth  and  in  relation  to  the  pleura.  The  borders  give  attach- 
ment to  the  intercostal  muscles,  the  upper,  to  those  of  the  first  space,  the  lower,  to  those  of  the 
second.  The  shaft  of  the  second  rib  is  not  twisted  on  its  own  axis,  so  that  both  ends  can  he  fiat 
on  the  table.  The  second  rib  receives  vessels  from  the  superior  intercostal  branch  of  the 
subclavian  artery  and  the  first  aortic  intercostal. 

The  tenth  rib  is  distinguished  by  a  single  facet  on  the  head  for  articulation  with  the  body 
of  the  tenth  thoracic  vertebra.  Occasionally  there  are  two  facets,  in  which  case  the  rib  articu- 
lates also  with  the  ninth  thoracic  vertebra.  The  tenth  rib,  like  the  ribs  immediately  above,  is 
long,  curved,  presents  a  deep  costal  groove,  a  well-marked  tuberosity  and  an  angle.     It  may 

9 


130 


THE  SKELETON 


be  noted,  however,  that  the  distance  between  the  tubercle  and  the  angle  in  this  rib  is  greater 
than  in  the  ribs  above.  Speaking  generally,  the  distance  between  these  points  increases  from 
above  downward — a  disposition  which  is  useful  in  at  once  determining  if  any  given  rib  belongs 
to  the  upper  or  lower  end  of  the  series. 

The  eleventh  rib  is  peculiar  in  that  it  has  a  single  facet  on  the  head,  a  feebly  marked  angle 
some  distance  from  the  head,  a  shallow  costal  groove,  no  tubercle,  and  no  neck.  The  tubercle 
is  sometimes  represented  by  a  slight  elevation  or  roughness  without  any  articular  facet.  The 
anterior  extremity  is  pointed. 

The  twelfth  rib  has  a  large  head  furnished  with  one  facet  for  articulation  with  the  root 
(pedicle)  of  the  tweUth  thoracic  vertebra.  The  shaft  is  narrow  and  extremely  variable  in  length 
(3  to  20  cm.).  It  is  usually  somewhat  longer  than  the  first  rib,  but  it  may  be  shorter.  There 
is  no  tubercle,  no  angle,  no  neck,  no  costal  groove.  The  anterior  extremity  is  pointed.  Poste- 
riorly, the  upper  border  is  smooth  and  somewhat  rounded;  the  lower  border  is  sharp  and 
rough. 

The  costal  cartilages  are  bars  of  hyaline  cartilage  attached  to  the  anterior  extremities  of  the 
ribs,  and  may  be  regarded  as  representing  unossified  epiphyses.  Like  the  shaft  of  a  rib,  each 
cartilage  has  an  outer  and  inner  surface.  The  outer  surfaces  give  origin  and  insertion  to  large 
muscles,  and  the  inner  surfaces,  from  the  second  to  the  sixth  inclusive,  are  in  relation  with  the 
transversus  thoracis  {triangularis  sterni) .  The  upper  and  lower  borders  serve  for  the  attachment 
of  the  internal  intercostal  muscles.  The  upper  seven  cartilages,  and  occasionally  the  eighth, 
are  connected  with  the  sternum.  Of  these,  the  first  fuses  with  the  manubrium  sterni  and  the 
remaining  six  are  received  into  small  articular  concavities,  and  retained  by  means  of  ligaments. 


Fig.   156. — The  Vertebral  Ends  of  Tenth,  Eleventh,  and  Twelfth  Ribs. 

Angle 


Single     facet    (sometimes 
two   facets   are  present) 


Single  facet  (this  rib  has 
an  angle,  but  no  tuber- 
osity and  no  neck) 


Single  facet  (this  rib  has 
neither  tuberosity,  angle, 
nor  neck) 


xn 


The  cartilages  of  the  vertebro-ohondral  ribs  are  united  to  one  another  and  to  the  seventh  costal 
cartilage  by  ligaments  (sometimes  by  short  vertical  bars  of  cartilage),  while  those  of  the  verte- 
bral ribs  form  no  such  attachment,  but  lie  between  the  abdominal  muscles.  The  inner  surfaces 
of  the  lower  six  costal  cartilages  afford  attachment  to  the  diaphragrn  and  the  transversalis  muscle. 

Each  of  the  second,  third,  fourth,  and  fifth  costal  cartilages  articulates  with  the  side  of  the 
sternum,  at  a  point  corresponding  to  the  junction  of  two  sternebrse.  The  sixth  and  seventh 
(and  eighth  when  this  reaches  the  sternum)  are  arranged  irregularly.  As  a  rule,  the  sixth  lies 
in  a  recess  at  the  side  of  the  fifth  sternebra;  the  seventh  corresponds  to  the  line  of  junction  of 
the  meso-  and  metasternum;  and  the  eighth  articulates  with  the  metasternum  (see  figs.  158, 
161). 

Blood-supply. — The  costal  cartilages  derive  their  blood-supply  from  the  terminal  twigs  of 
the  aortic  intercostals  and  from  the  internal  mammary  arteries. 

Ossification. — At  the  eighth  week  of  intra-uterine  life  the  ribs  are  cartilaginous.  About 
this  date  a  nucleus  appears  near  the  angle  of  each  rib,  and  spreads  with  great  rapidity  along'the 
shaft,  and  by  the  fourth  month  reaches  as  far  as  the  costal  cartilage.  At  this  date  the  length  of 
rib-shaft  bears  the  same  proportion  to  that  of  the  costal  cartilage  as  in  adult  life.  Whilst  the 
ribs  are  in  a  cartilaginous  condition,  the  first  eight  reach  to  the  side  of  the  sternum,  and  even 
after  ossification  has  taken  place,  the  costal  cartilage  of  the  eighth  rib,  in  many  instances,  retains 
its  articulation  with  the  sternum  up  to  as  late  as  the  eighth  month  (fig.  158).  This  relationship 
may  persist  through  life,  but  usually  the  cartilage  retrogresses,  and  is  replaced  by  ligamentous 
tissue.  About  the  fifteenth  year  a  secondary  centre  appears  for  the  head  of  each  rib,  and  a 
little  later  one  makes  its  appearance  for  the  tubercle,  except  in  the  eleventh  and  tweKth  ribs. 
Frequently  epiphyses  are  developed  on  both  parts  of  the  tubercle  (see  figs.  159  and  160).     The 


THE  RIBS 


131 


epiphyses  fuse  with  the  ribs  about  the  twenty-third  year.     The  rib-shaft  increases  in  length 
mainly  at  its  line  of  junction  with  the  costal  cartilage. 

Variations  in  the  Number  and  Shape  of  the  Ribs 

The  ribs  may  be  increased  in  number  by  addition  either  at  the  cervical  or  lumbar  end  of  the 
series,  but  it  is  extremely  rare  to  find  an  additional  rib  or  pair  of  ribs  in  both  the  cervical  and 
lumbar  regions  in  the  same  subject. 


Fig.  157. — RtB  at  Puberty. 


The  cartilaginous  siiaft  commences  to 
ossify  at  the  eighth  week  of  intra- 
uterine life 


Fig.  158. — The  Thorax  at  the  Eighth  FfETAL  Month. 
(On  the  left  side  eight  cartilages  reach  the  sternum.) 


Cervical  ribs  are  fairly  common;  as  a  rule,  they  are  of  small  size  and  rarely  extend  more  than 
a  few  millimeters  beyond  the  extremity  of  the  transverse  process  (see  p.  35).  Rarely 
they  exceed  such  insignificant  proportions  and  reach  as  far  as  the  sternum;  between  these  two 
extremes  many  varieties  occur.  In  one  case  Tui'ner  was  able  to  make  a  thorough  dissection  of 
a  specimen  in  which  a  complete  cervical  rib  existed.     Its  head  articulated  with  the  body  of  the 


132  THE  SKELETON 

seventh  cervical  vertebra  and  had  a  radiate  ligament.  The  tubercle  was  well  developed,  and 
articulated  with  the  transverse  process.  The  costal  cartilage  blended  with  that  of  the  first 
thoracic  rib,  and  gave  attachment  to  the  costo-clavicular  ligament.  Between  it  and  the  first 
thoracic  rib  there  was  a  well-marked  intercostal  space  occupied  by  intercostal  muscles.  It 
received  the  attachment  of  the  scalenus  anterior  and  meditis  muscles,  and  it  was  crossed  by  the 
subclavian  artery  and  vein.  The  nerves  of  the  intercostal  space  were  supplied  by  the  eighth 
cervical  and  first  thoracic.  The  artery  of  the  space  was  derived  from  the  dee)]  cervical,  which, 
with  the  superioi  intercostal,  arose  from  the  root  of  the  vertebral.  The  head  of  the  first  thoracic 
rib  in  this  specimen  articulated  with  the  seventh  cervical,  as  well  as  with  the  first  thoracic 
vertebra.  An  interesting;  fact  is  also  recorded  in  the  careful  account  of  this  specimen.  There 
was  no  movable  twelfth  thoracic  rib  on  the  same  side  as  this  well-developed  cervical  rib,  and  the 
twelfth  thoracic  vertebra  had  mammillary  and  accessory  processes,  and  a  strong  elongated 
costal  process,  and  was  in  linear  series  with  the  lumbar  transverse  processes. 

Fig.  159. — Posterioe  Pohtion  op  the  Sixth  Rro  in  the  Fifteenth  Year. 
(After  Toldt.) 

Epiphysis  of  non-articular  portion  of  the  tubercle 


Epiphysis  of  head 


Articular  facet 


Gruber  and  Turner,  from  a  careful  and  elaborpte  study  of  this  question,  summarise  the  varia- 
tions in  the  cervical  rib  thus: — It  may  be  very  short  and  possess  only  a  bead,  neck,  and  tubercle. 
When  it  extends  beyond  the  transverse  process,  its  shaft  may  end  freely  or  join  the  first  thoracic 
rib:  this  union  may  be  effected  by  bone,  cartilage,  or  ligament.  In  very  rare  instances  it  may 
have  a  costal  cartilage  and  join  the  manubrium  of  the  sternum.  Net  unfrequently  a  process, 
or  eminence,  exists  on  the  first  thoracic  rib  at  the  spot  where  it  articulates  with  a  cervical  rib. 

Lumbar  ribs  are  of  less  significance  than  cervical  ribs  and  rarely  attain  a  great  length. 
Their  presence  is  easily  accounted  for,  as  they  are  the  differentiated  costal  elements  of  the  trans- 
verse processes.  They  are  never  so  complete  as  the  cervical  ribs,  and  articulate  only  with 
the  transverse  processes;  the  head  never  reaches  as  far  as  the  body  of  the  vertebra,  and  there  is 
no  neck  or  tubercle.     An  extra  levator  costce  muscle  is  associated  with  a  lumbar  rib. 

Fig.  160. — Posterior  Portion  of  the  Sixth  Rib  in  the  Eighteenth  Year. 
(After  Toldt.) 

Non-articular  portion  of  tubercle 


Epiphysis  of  head 


Epiphysis  of  the  articular  facet  of  the  tubercle 


Not  the  least  interesting  variation  of  a  rib  is  that  known  as  the  bicipital  rib.  This  condition 
is  seen  exclusively  in  connection  with  the  first  thoracic  rib.  The  vertebral  end  consists  of  two 
Hmbs  which  lie  in  different  transverse  planes.  These  bicipital  ribs  have  been  especially  studied 
in  whales  and  man.  This  abnormality  is  due  to  the  fusion  of  two  ribs,  either  of  a  cervical  rib 
with  the  shaft  of  the  first  thoracic;  or  the  more  common  form,  the  fusion  of  the  first  and  second 
true  ribs. 

Among  unusual  variations  of  ribs  should  be  mentioned  the  replacement  of  the  costal  carti- 
lage and  a  portion  of  the  rib-shaft  by  fibrous  tissue,  a  process  which  occurs  normally  in  the  case 
of  the  eighth  rib  during  its  development. 

Sometimes  the  shafts  of  two  or  more  ribs  may  become  united  by  small  quadrilateral  plates 
of  bone  extending  across  the  intercostal  spaces. 

THE  STERNUM 

The  sternum  (figs.  161,  162)  is  a  flat,  oblong  plate  of  bone,  situated  in  the 
anterior  wall  of  the  thorax,  and  divisible  into  three  parts,  called  respectively — (1)' 
the  manubrium  sterni  (presternum),  (2)  the  gladiolus  (mesosternum),  constitut- 
fng  the  body  of  the  bone,  and  (3)  the  xiphoid  (or  ensiform)  process  (metasternura). 
In  the  young  subject  it  consists  of  six  pieces  or  segment  (sternebrae) .  Of  these, 
the  first  remains  separate  throughout  life  and  forms  the  manubrium;  the  sue- 


THE  STERNUM  133 

ceeding  four  segments  fuse  together,  forming  the  body ;  whilst  the  lowest  segment, 
also  distinct  until  middle  life,  is  represented  by  the  xiphoid  process. 

In  its  natural  position  the  sternum  is  inclined  obliquely  from  above  downward  and  forward, 
and  corresponds  in  length  to  the  spine  from  the  third  to  the  ninth  thoracic  vertebra.  It  is  not 
of  equal  width  throughout,  being  broader  above  at  the  manubrium  and  narrow  at  the  junction 
of  this  piece  with  the  body.  Toward  the  lower  part  of  the  body  the  sternum  again  widens,  and 
then  suddenly  contracts  at  its  junction  with  the  xiphoid  process  which  constitutes  the  narrowest 
part. 

The  manubrium  or  first  piece  of  the  sternum  forms  the  broadest  and  thickest 
part  of  the  bone,  and  is  of  a  somewhat  triangular  form  with  the  base  directed  up- 
ward and  the  apex  downward.  It  presents  for  examination  two  surfaces  and  four 
borders.  The  anterior  surface  [planum  sternale]  is  largely  subcutaneous.  It  is 
slightly  convex  and  directed  obhquely  upward  and  forward,  is  smooth  and 
gives  origin  on  each  side  to  the  sternal  head  of  the  sterno-mastoid  and  the  pedoralis 
major.  The  posterior  surface,  almost  flat,  and  directed  downward  and  backward, 
affords  origin  near  the  lateral  margins  on  each  side;  to  the  sterno-hyoid  muscle 
above  and  the  sterno-thyreoid  muscle  below.  Of  the  four  borders,  the  superior 
is  the  longest  and  much  the  thickest.  In  the  middle  is  a  curved,  non-articular 
depression,  called  the  jugular  (interclavicular)  notch,  to  which  the  fibres  of  the 
interclavicular  ligament  are  attached,  and  at  either  end  is  an  oval  articular 
surface  [incisura  clavicularis],  somewhat  saddle-shaped  and  directed  upward, 
backward,  and  lateral^  for  the  reception  of  the  medial  end  of  the  clavicle.  The 
circumference  of  the  articular  surface  gives  attachment  to  the  sterno-clavicular 
ligaments.  The  lateral  borders  slope  from  above  downward  and  medially  and 
each  presents  an  irregular  surface  above  for  the  first  costal  cartilage  and  a  small 
facet  below,  which,  with  an  adjoining  facet  on  the  body,  forms  a  notch  for  the 
second  costal  cartilage.  The  two  articular  surfaces  are  separated  by  a  narrow 
curved  edge  in  relation  with  the  internal  intercostal  muscle  of  the  first  space.  The 
lower  border  is  thick  and  short  and  presents  an  oval  rough  surface  which  articu- 
lates with  the  upper  border  of  the  body,  forming  the  sternal  S3aichondrosis. 
The  two  opposed  surfaces  are  separated  by  a  fibro-cartilaginous  disc,  which  may, 
however,  become  partially  ossified  in  advanced  age,  and  at  the  position  of  the 
joint  there  is  usually  an  angle — the  angle  of  the  sternum — which  can  be  felt  as  a 
transverse  ridge  beneath  the  skin.  This  is  useful  in  locating  the  position  of  the 
second  rib  in  the  living  subject. 

The  body  (gladiolus)  or  second  piece  of  the  sternum  is  longer,  narrower,  and 
thinner  than  the  manubrium.  It  is  widest  opposite  the  notches  for  the  fifth 
costal  cartilages  and  becomes  narrower  above  and  below.  The  anterior  surface 
is  flat,  directed  upward  and  forward,  and  marked  by  three  transverse  elevations 
which  indicate  the  lines  of  junction  of  its  four  component  parts.  It  gives  attach- 
ment on  each  side  to  fibres  of  the  pectoralis  major,  and  occasionally  presents  a 
foramen — the  sternal  foramen — situated  at  the  junction  of  the  third  and  fourth 
pieces  of  the  bone.  The  posterior  surface  is  slightly  concave,  marked  by  lines 
corresponding  to  those  on  the  anterior  surface,  and  below  gives  attachment  on 
each  side  to  fibres  of  the  transversus  thoracis  {triangularis  sterni).  The  lateral 
borders  present  four  whole  notches  [incisure  costse]  and  two  half-notches  on 
each  side,  which  articulate  with  the  costal  cartilages  of  the  second  to  the  seventh 
ribs  inclusive;  the  two  half-notches  are  completed  by  corresponding  notches  on 
the  manubrium  and  the  xiphoid  process.  Between  the  articular  depressions  the 
lateral  border  is  curved  and  in  relation  to  the  internal  intercostal  muscles. 

In  order  to  appreciate  the  nature  of  these  articular  notches,  it  is  advantageous  to  study 
the  sternum  in  a  young  subject.  Each  typical  sternebra  presents  four  angles  at  each  of  which  is 
a  demi-notch.  Between  every  two  sternebrae  there  is  an  intersternebral  disc  so  that  when  in 
position,  each  notch  for  a  costal  cartilage  is  formed  by  a  sternebra  above  and  below  and  an  inter- 
sternebral disc  in  the  middle,  thus  repeating  the  relation  of  the  rib-head  to  the  vertebral  centre. 
Later  in  life  these  fuse  more  or  less  together,  except  in  the  case  of  the  first  and  second  sternebrae, 
which  usually  remain  separate  to  the  end  of  life.  The  first  (pre-sternum)  is  the  most  modified 
of  all  the  sternebrae,  and  differs  from  them  in  the  fact  that  the  costal  cartilage  of  the  first  rib 
is  continuous  with  it,  and  in  fact  that  it  supports  the  clavicles.  Occasionally  a  rounded  pisi- 
form bone  is  seen  on  each  side,  medial  to  the  articular  notch  for  the  clavicle;  these  are  the 
supra-sternal  bones. 

The  superior  border  of  the  sternal  body  presents  an  oval  facet  for  articulation 
(synchondrosis)  with  the  manubrium.     The  inferior  border  is  short  and  articu- 


134 


THE  SKELETON 


lated  with  the  xiphoid  process,  forming  the  meso-metasternal  joint,  the  two 
opposed  surfaces  being  separated  by  a  layer  of  cartilage  so  long  as  they  are  not 
united  by  bone. 

The  xiphoid   (ensiform)  process  is  the  thin,  elongated  process  projecting 
downward  between  the  cartilages  of  the  seventh  ribs.     It  is  the  least  developed 


Fig.  161. — The  Sternum.     (Anterior  view.) 
Jugular  notch 


Clavicular  notch 


For  first  costal  cartilage 


Xiphoid  foramen' 


Sterno-mastoid 


Pectoralis  major 


Body  or  mesostetnum 


Rectus  abdominis 


metasternum 


part  of  the  sternum  and  is  subject  to  many  variations  in  form,  being  sometimes 
pointed,  broad  and  thin,  occasionally  bifid  or  perforated  by  a  foramen,  and  some- 
times bent  forward,  backward,  or  deflected  to  one  side.  In  structure  it  is  carti- 
laginous in  early  life,  partially  ossified  in  the  adult,  but  in  old  age  it  tends  to  be- 
come ossified  throughout  and  to  fuse  with  the  body. 

The  anterior  surface  of  the  xiphoid  process  gives  attachment  to  a  few  fibres  of  the  rectus 
ahdominis  muscle  and  the  chondro-xiphoid  ligament,  the  posterior  surface  to  the  sternal  fibres 
of  the  diaphragm,  and  the  lowest  fibres  of  the  transversus  thoracis  {triangularis  sterni),  whilst 


THE  STERNUM 


135 


the  lateral  margins  receive  the  aponeuroses  of  the  abdominal  muscles.     Its  tip  is  directly  con-r 
tinuous  with  the  linea  alba. 

Differences  according  to  sex. — The  sternum  differs  somewhat  in  the  two  sexes.  The  female 
sternum  is  relatively  shorter,  the  diminution  being  almost  confined  to  the  body.  In  the  male 
the  body  is  more  than  twice  as  long  as  the  manubrium,  whereas  in  the  female  it  is  usually  less 
than  twice  the  length  of  the  first  piece. 


Fig.  162. — The  Stbhnttm.     (Posterior  view.) 


Clavicular  notch 
Sterno-hyoid 

Sterno-thyreoid 


Transversus  thoracis 


For  first  costal  cartilage 


Second 


Diaphragm 


Structurally  the  sternum  is  composed  of  cancellous  tissue  covered  with  an  outer  layer  of 
compact  tissue.  Its  arterial  supply  is  derived  mainly  from  the  sternal  and  perforating  branches 
of  the  internal  mammary. 

Development  of  the  sternum. — -The  osseous  sternum  is  preceded  by  a  continuous  or  non- 
segmented  central  sternal  cartilage  formed  in  the  following  way  When  the  cartilaginous  ribs 
first  appear  in  the  embryo,  their  anterior  or  ventral  ends  fuse  together  on  either  side  of  the  mid- 
dle fine.  For  some  time  a  median  fissure  is  present,  bordered  by  two  sagittaUy  directed  strips 
of  cartilage  with  each  of  which  at  first  nine  ribs  are  joined.  As  development  proceeds  the  two 
strips  come  into  contact  in  the  middle  line  and  fuse  from  before  backward  to  form  a  median 
sternal  cartilage.  The  eighth  cartilage  generally  loses  its  sternal  attachment,  although  in  some 
cases  it  remains  permanently  articulated  with  the  side  of  the  ensiform  process.     The  ninth 


136 


THE  SKELETON 


costal  cartilage  becomes  subdivided,  one  part  remaining  attached  to  the  sternum  and  forming  the 
xiphoid  process,  whilst  the  end  still  continuous  with  the  rib  acquires  a  new  attachment  to  the 
eighth  cartilage.  The  ends  adherent  to  the  sternum  may  remain  separate  and  give  rise  to  a 
bifid  xiphoid  process,  though  much  more  frequently  they  unite,  leaving  a  small  foramen. 

At  first,  therefore,  the  sternum  and  costal  cartilages  are  continuous.  A  joint  soon  forms 
between  the  presternum  and  mesosternum,  and  others  between  the  costal  cartilages  and  the 
sternum  (except  in  the  case  of  the  first)  quickly  follow.  The  division  of  the  mesosternum  into 
segments  is  a  still  later  formation  and  arises  during  the  process  of  ossification. 


Fig.  163. — Posteeior  Surface  of  the  Manubrium  (Pre-sternum),  with  Sternal  Ends 
OF  Clavicles  and  the  First  Costal  Cartilages. 


Sterno-hyoid       Sterno-thyreoid 


On  the  other  hand,  a  view  has  been  advanced  by  Professor  A.  M.  Paterson  that  the  sternum 
is  not  a  bilateral  structure,  but  is  laid  down,  as  shown  in  human  sterna  of  the  third  month,  as  a 
simple  median  band  of  hyahne  cartilage,  in  complete  fusion  with  the  costal  cartilages  on  each 
side  and  presenting  no  differentiation  of  its  component  parts.  From  a  study  of  the  earliest 
stages  of  the  development  of  the  sternum,  its  comparative  anatomy  and  structure,  Professor 
Paterson  has,  moreover,  brought  forward  evidence  which  indicates  its  independence  in  the  first 
instance  of  costal  elements  and  its  genetic  association  with  the  shoulder  girdle. 

Ossification. — The  ossification  of  the  sternutn  is  slow  and  irregular.  The  process  begins 
in  the  presternum  (manubrium)  by  a  single  centre  about  the  sixth  month  of  intra-uterine  life, 
though  occasionally  other  accessory  centres  are  superadded. 


Fig.  164. — Two  Stages  in  the  Formation  of  the  Cartilaginous  Sternum.     (After  Huge.) 


The  mesosternum  (body)  usually  ossifies  from  seven  centres.  The  upper  segment  ossifies 
from  a  single  median  nucleus  about  the  eighth  month,  and  below  this,  three  pairs  of  ossific 
nuclei  appear,  which  may  remain  for  a  long  time  separate.  Of  these,  two  parrs  for  the  second 
and  third  segments  are  visible  at  birth,  and  those  for  the  lower  segment  make  their  appearance 
toward  the  end  of  the  first  year.  The  various  lateral  centres  unite  in  pairs,  so  that  at  the  sixth 
year  the  sternum  consists  of  six  sternebra3,  the  lowest  (metasternum)  being  cartilaginous. 
Very  often,  however,  there  are  only  four  centres  of  ossification  in  the  gladiolus,  as  shown  in 
fig.  165.     Gradually  the  four  pieces  representing  the  mesosternum  fuse  with  one  another,  and 


THE  STERNUM 


137 


Fig.  165. — Ossification  of  the  Sternum. 

A,  common  arrangement  of  the  ossific  centres.     B,  showing  accessory  centre  in  the  manubrium 

sterni,  and  bilateral  centres  in  the  second,  third,  and  fourth  pieces  of  the  body. 


Single  centre  for  each 
of  the  four  pieces  of 
the  body 


Single  centre  f^ -_^ 

xiphoid  process         ^*^. 


Accessory  centre 


Single  centre  for  first 
piece  of  body 


Bilateral  centres  for 
second,  third,  and 
fourth  pieces  of  body 


Single  centre  for 
xiphoid  process 


Fig.  166.— The  Thorax.     (Front  view.) 

Superior  thoracic  aperture 


' >False  ribs 


138 


THE  SKELETON 


at  twenty-five  they  form  a  single  piece,  but  exhibit,  even  in  advanced  hfe,  traces  of  their  original 
separation.  A  sternal  foramen  is  usually  the  result  of  non-union  across  the  middle  line  or  a 
defect  of  ossification. 

The  metasternum  is  always  imperfectly  ossified,  and  does  not  join  with  the  mesosternum 
till  after  middle  life.  The  presternum  and  mesosternum  rarely  fuse.  The  dates  given  above 
for  the  various  nuclei,  and  for  the  union  of  the  various  segments,  are  merely  approximate,  hence 
the  sternum  affords  very  uncertain  data  as  to  age. 

Abnormalities  of  the  Sternum. — The  mode  of  development  of  the  sternum  as  described 
above  is  of  importance  in  connection  with  some  deviations  to  which  it  is  occasionally  subject. 
In  rare  instances  the  two  lateral  halves  fail  to  unite,  giving  rise  to  the  anomaly  of  a  completely 
cleft  sternum.  The  union  of  the  two  halves  may  occur  in  the  region  of  the  manubrium  and  fail 
below,  whilst  in  other  cases  the  upper  and  lower  parts  have  fused  but  remain  separate  in  the 
middle.  The  clefts  are  in  many  instances  so  small  as  not  to  be  of  any  moment,  and  are  not 
even  recognised  until  the  skeleton  is  prepared.  In  a  few  individuals,  however,  they  have  been 
so  extensive  as  to  allow  the  pulsation  of  the  heart  to  be  perceptible  to  the  hand,  and  even  to 
the  eye,  through  the  skin  covering  the  defect  in  the  bone. 

A  common  variation  in  the  sternum  is  asymmetry  of  the  costal  cartilages.  Instead  of  cor- 
responding, the  cartilages  may  articulate  with  the  sternum  in  an  alternating  manner.  The 
cause  of  this  asymmetry  is  not  known. 

THE  THORAX  AS  A  WHOLE 

The  bony  thorax  (fig.  166)  is  somewhat  conical  in  shape,  deeper  behind  than  in  front 
and  compressed  antero-posteriorly,  so  that  in  the  adult  it  measures  less  in  the  sagittal  than  in 
the  transverse  axis.     The  posterior  wall,  formed  by  the  thoracic  vertebrae  and  the  ribs  as  far 


Fig.  167.- 


-The   Thorax.     (Posterior  view.)     The  scapulae   are  drawn  from   an   X-ray 
photograph  of  a  man  33  years  old. 


outward  as  their  angles,  is  convex  from  above  downward,  and  the  backward  curve  of  the  ribs 
produces  on  each  side  of  the  vertebrae  a  deep  furrow,  the  costo-vertebral  groove,  in  which  the 
sacro-spinalis  (erector  spinoe)  muscle  and  its  subdivisions  are  lodged.  The  anterior  wall  is  formed 
by  the  sternum  and  costal  cartilages.  It  is  slightly  convex  and  inchned  forward  in  its  lower 
part,  forming  an  angle  of  about  20°  with  the  vertical  plane.  The  lateral  walls  are  formed  by 
the  ribs  from  the  angles  to  the  costal  cartilages.  The  top  of  the  thorax  presents  an  elUp- 
tical  aperture,  the  superior  thoracic  aperture,  which  measures  on  an  average  12.5  centimetres  (5 


THE  CLAVICLE  139 

inches)  transversely  and  6.2  centimetres  (2J  inches)  in  its  sagittal  axis.  It  is  bounded  by  the 
first  thoracic  vertebra  behind,  the  upper  margin  of  the  manubrium  sterni  in  front,  and  the  first 
rib  on  each  side.  As  the  upper  margin  of  the  manubrium  sterni  is  oftenest  on  a  level  with 
the  disc  between  the  second  and  third  thoracic  vertebrae,  it  follows  that  the  plane  of  the  open- 
ing is  directed  obliquely  upward  and  forward.  The  angle  of  the  sternum  {angulus  Ludovici)  is 
usually  opposite  the  body  of  the  fifth  thoracic  vertebra  and  the  xiphi-sternal  junction  corre- 
sponds to  the  disc  between  the  ninth  and  tenth  thoracic  vertebrae.  The  lower  aperture  of  the 
thorax  is  very  irregular,  and  is  formed  by  the  twelfth  thoracic  vertebra  behind,  the  twelfth  ribs 
laterally,  and  in  front  by  two  curved  lines,  ascending  one  on  either  side  from  the  last  rib,  along 
the  costal  margin  to  the  lower  border  of  the  gladiolus.  The  two  borders  form  the  costal  arch, 
which  in  the  median  line  below  the  sternum  forms  the  infrasternal  angle.  From  this  angle  the 
xiphoid  process  projects  downward.  The  intervals  between  the  ribs  are  the  intercostal  spaces, 
and  are  eleven  in  number  on  each  side. 

The  ratio  of  the  sagittal  and  the  transverse  diameter  of  the  thorax  forms  the  thoracic  index, 
which  is  higher  in  the  female  and  in  children,  in  whom  the  thorax  is  more  rounded.  In  the 
embryo,  the  index  is  very  much  higher,  the  sagittal  diameter  being  greater  than  the  transverse. 
In  the  early  embryo,  the  index  is  nearly  200;  at  birth  it  is  about  90.  In  the  adults  it_ varies 
from  70  to  75,  averaging  2  or  3  per  cent,  lower  in  the  male  than  in  the  female.  It  is  also 
lower  in  the  negro  than  in  the  white  race.     (Rodes,  Zeitschr.  f.  Morph.  u.  Anthrop.,  Bd.  9.) 


//.  THE  APPENDICULAR  SKELETON 
A.  BONES  OF  THE  UPPER  EXTREMITY 

The  bones  of  the  upper  extremity  may  be  arranged  in  four  groups  correspond- 
ing to  the  division  of  the  limb  into  four  segments.  In  the  shoulder  are  the 
clavicle  and  the  scapula,  which  together  constitute  the  pectoral  or  shoulder  girdle; 
in  the  arm  is  the  humerus;  in  the  forearm  are  the  radius  and  ulna;  and  in  the  hand 
the  carpus,  the  metacarpus,  and  the  phalanges. 

THE  CLAVICLE 

The  clavicle  [clavicula]  or  collar  bone  (figs.  168,  169)  is  situated  immediately 
above  the  first  rib  and  extends  from  the  upper  border  of  the  manubrium  sterni, 
laterally  and  backward  to  the  acromion  process  of  the  scapula.  It  connects  the 
upper  limb  with  the  trunk,  and  is  so  arranged  that  whilst  the  medial  end  rests  on 
the  sterniun  and  first  costal  cartilage,  the  lateral  end  is  associated  with  the  scapula 
in  all  its  movements,  supporting  it  firmly  in  its  various  positions  and  preventing  it 
from  falling  inward  on  the  thorax. 

The  clavicle  is  a  long  bone,  and  when  viewed  from  the  front  presents  a  double 
curvature,  so  that  it  somewhat  resembles  in  shape  the  italic  letter  /.  The  medial 
curve,  convex  forward,  extends  over  two-thirds  of  the  length  of  the  bone;  the 
lateral,  concave  forward,  is  smaller  and  confined  to  the  lateral  part.  For  descrip- 
tive purposes  the  clavicle  may  be  divided  into  a  medial  prismatic  portion,  a 
lateral  flattened  portion,  and  two  extremities. 

Prismatic  portion. — The  medial  two-thirds  of  the  bone,  extending  from  the 
sternal  extremity  to  a  point  opposite  the  coracoid  process  of  the  scapula,  has  the 
form  of  a  triangular  prism.  This  portion,  however,  is  subject  to  considerable 
variations  of  form,  being  more  cylindrical  in  ill-developed  specimens  and  be- 
coming almost  quadrangular  when  associated  with  great  muscular  development. 
In  a  typical  specimen  it  is  marked  by  three  borders  separating  three  surfaces. 
Of  these,  the  anterior  surface  is  convex  and  divided  near  the  sternal  end  by  a 
prominent  ridge  into  two  parts,  a  lower,  giving  origin  to  the  clavicular  portion  of 
the  pectoralis  major;  an  upper,  for  the  clavicular  portion  of  the  sterno-cleido- 
mastoid.  Near  the  middle  of  the  shaft  the  ridge  disappears,  the  surface  is  smooth, 
and  is  covered  by  the  platysma  myoides.  Occasionally  this  surface  is  pierced  by  a 
small  canal,  transmitting  a  cutaneous  nerve  from  the  cervical  plexus.  The 
posterior  surface  is  concave,  forming  an  arch  over  the  brachial  plexus  and  the 
subclavian  artery,  broadest  medially  and  smooth  in  its  whole  extent.  It 
gives  origin  near  the  sternal  extremity  to  a  part  of  the  sterno-hyoid  and  occasion- 
ally to  a  few  fibres  of  the  sterno-thyreoid.  Somewhere  near  the  middle  of  this 
surface  is  a  small  foramen,  directed  laterally,  for  the  chief  nutrient  artery  of  the 
bone,  derived  from  the  transverse  scapular  (suprascapular)  artery.     Sometimes  the 


140 


THE  SKELETON 


foramen  is  situated  on  the  inferior  surface  of  the  bone,  in  the  subclavian  groove. 
On  the  inferior  surface  near  the  sternal  end  is  a  rough  area,  the  costal  tuberosity, 
about  three-quarters  of  an  inch  in  length,  for  the  attachment  of  the  costo- 
clavicular ligament,  by  which  the  clavicle  is  fixed  to  the  first  rib.  More  laterally 
is  a  longitudinal  groove  for  the  subclavius,  bordered  by  two  lips,  to  which  the  sheath 
of  the  muscle  is  attached.  To  the  posterior  of  the  two  lips  the  layer  of  deep  cer- 
vical fascia  which  binds  down  the  posterior  belly  of  the  omo-hyoid  to  the  clavicle 
is  also  attached. 

Of  the  three  borders,  the  superior  separates  the  anterior  and  posterior  surfaces.  Be- 
ginning at  the  sternal  end,  it  is  well-marked,  becomes  rounded  and  indistinct  in  the  middle, 
whilst  laterally  it  is  continuous  with  the  posterior  border  of  the  outer  third.  The  posterior 
border  separates  the  inferior  and  posterior  surfaces  and  forms  the  posterior  lip  of  the  subclavian 


Fig.  168. — The  Left  Clavicle. 
Anterior 


(Superior  surface.) 

Pectoralis  major 


Epiphysial  line 


groove.  It  begins  at  the  costal  tuberosity  and  can  be  traced  laterally  as  far  as  the  coracoid 
tubercle,  an  eminence  on  the  under  aspect  of  the  bone  near  the  junction  of  prismatic  and  flat- 
tened portions.  The  anterior  border  is  continuous  with  the  anterior  border  of  the  flattened 
portion  and  separates  the  anterior  and  inferior  surfaces.  Medially,  it  forms  the  lower  boundary 
of  the  elliptical  area  for  the  origin  of  the  pecloralis  major,  and  approaches  the  posterior  border. 
Near  the  middle  of  the  bone  it  coincides  with  the  anterior  lip  of  the  subclavian  groove. 

Flattened  portion. — The  lateral  third  of  the  bone,  extending  from  a  point 
opposite  the  coracoid  process  of  the  scapula  to  the  acromial  extremity,  is  flat- 


Oblique 
line  for 
Articular     trapezoid 
capsule      ligament 


Fig.  169. — The  Left  Clavicle. 
Posterior 

Coracoid 
tubercle  for 
conoid  ligament     Subclavius 


(Inferior  surface.) 


Costo -clavicular 
ligament  and 
sterno- 
hyoid     Sterno-thyreoid  (occasional) 
Facet  for  first 
•costal  cartilage 


sternal  facet 


Acromial  facet 


tened  from  above  downward  and  presents  two  surfaces  and  two  borders.  The 
superior  surface  is  rough  and  looks  directly  upward  and  gives  attachment  to  the 
trapezius  behind  and  the  deltoid  in  front;  between  the  two  areas  the  surface  is 
subcutaneous.  On  the  inferior  surface,  near  the  posterior  border,  is  a  rough 
elevation,  the  coracoid  (conoid)  tubercle ;  it  overhangs  the  coracoid  process  and 
gives  attachment  to  the  conoid  ligament.  From  the  coracoid  tubercle,  a  promi- 
nent ridge,  the  trapezoid  or  oblique  line,  runs  laterally  and  forward  to  near 
the  lateral  end  of  the  bone.  To  it  the  trapezoid  ligament  is  attached.  The 
conoid  and  trapezoid  ligaments  are  the  two  parts  of  the  coraco-clavicular  liga- 
ment which  binds  the  clavicle  down  to  the  coracoid  process. 

The  anterior  border  is  sharp,  gives  origin  to  the  deltoid  muscle,  and  frequently  presents 
near  the  junction  of  the  flattened  and  prismatic  portions  a  projection  known  as  the  deltoid 
tubercle.  The  posterior  border  is  thick  and  rounded,  and  receives  the  insertion  of  the  upper 
fibres  of  the  trapezius. 


THE  SCAPULA  141 

Extremities. — The  sternal  extremity  of  the  clavicle  presents  a  triangular 
articular  surface,  directed  medially,  downward,  and  a  little  forward,  slightly 
concave  from  before  backward  and  convex  from  above  downward,  which  articu- 
lates with  a  facet  on  the  upper  border  of  the  manubrium  sterni  through  an 
interposed  interarticular  fibro-cartilage. 

Of  the  three  angles,  one  is  above  and  two  below.  The  postero-inferior  angle  is  prolonged 
backward,  and  so  renders  this  surface  considerably  larger  than  that  with  which  it  articulates; 
the  superior  angle  receives  the  attachment  of  the  upper  part  of  the  fibro-cartilage.  The  lower 
part  of  the  surface  is  continuous  with  a  facet  on  the  under  aspect  of  the  bone,  medial  to  the 
costal  tuberosity,  for  the  first  costal  cartilage.  The  circumference  of  the  extremity  is  rough, 
and  gives  attachment  to  the  interclavicular  ligament  above  and  the  anterior  and  posterior 
sterno-clavicular  ligaments  in  front  and  behind. 

The  acromial  extremity  presents  a  smooth,  oval,  articular  facet,  flattened  or 
convex,  directed  shghtly  downward  for  the  acromion;  its  border  is  rough,  for  the 
attachment  of  the  capsule  of  the  acromio-clavicular  joint. 

Structure. — The  clavicle  consists  e.\ternally  of  a  compact  layer  of  bone,  much  thicker  in 
the  middle  and  thinning  out  gradually  toward  the  two  extremities.     There  is  no  true  medullary 

Fig.  170. — The  Sternal  Ends  op  Two  Clavicles  with  Epiphyses. 

A,  right  clavicle  from  below  and  behind.     B,  left  clavicle  from  below  and  behind. 

(From  Royal  College  of  Surgeons  Museum.) 

Sternal  epiphyses 


cavity,  for  the  interior  is  occupied  from  end  to  end  by  cancellous  tissue,  the  amount  in  the  vari- 
ous parts  of  the  bone  being  in  inverse  proportion  to  the  thickness  of  the  outer  compact  shell 
Ossification. — From  observations  made  by  F.  P.  Mall,  D.  C.  L.  Fitzwilliams,  and  E.  Faw- 
cett  it  seems  almost  certain  that  there  are  two  centres  of  ossification  of  the  shaft  of  the  clavicle, 
at  the  juncture  of  the  middle  and  lateral  thirds.  They  appear  very  early,  about  the  fifth  week 
of  embryonic  life,  and  rapidly  fuse.  The  ossific  process  extends  medially  and  laterally  along  the 
shaft  toward  the  medial  and  lateral  extremities,  respectively.  About  the  eighteenth  year  a 
secondary  centre  appears  at  the  sternal  end  and  forms  a  small  epiphysis  which  joins  the  shaft 
about  the  twenty-fifth  year. 

THE  SCAPULA 

The  scapula  (figs.  171,  172)  is  a  large  flat  bone,  triangular  in  shape,  situated 
on  the  dorsal  aspect  of  the  thorax,  between  the  levels  of  the  second  and  seventh 
ribs.  Attached  to  the  trunk  by  means  of  the  clavicle  and  various  muscles  it 
articulates  with  the  lateral  end  of  the  clavicle  at  the  acromio-clavicular  joint, 
and  with  the  humerus  at  the  shoulder-joint.  The  greater  part  of  the  bone  con- 
sists of  a  triangular  plate  known  as  the  body,  from  which  two  processes  are 
prolonged:  one  anterior  in  position,  is  the  coracoid;  the  other,  posterior  in  posi- 
tion, is  the  spine,  which  is  continued  laterally  into  the  acromion. 

The  body  presents  for  examination  two  surfaces,  three  borders,  and  three 
angles.  The  costal  (anterior)  surface,  or  venter,  looks  considerably  medialward, 
is  deeply  concave,  forming  the  subscapular  fossa,  and  marked  by  several  oblique 
lines  which  commence  at  the  posterior  border  and  pass  obliquely  upward  and 
laterally;  these  lines  or  ridges  divide  the  surface  into  several  shallow  grooves, 
from  which  the  suhscapularis  takes  origin,  whilst  the  ridges  give  attachment  to 
the  tendinous  intersections  of  that  muscle.  The  lateral  third  of  the  surface  is 
smooth  and  overlapped  by  the  subscapularis,  whilst  medially  are  two  small  flat 
areas  in  front  of  the  upper  and  lower  angles  respectively,  but  excluded  from  the 
subscapular  fossa  by.  fairly  definite  lines  and  joined  by  a  ridge  which  runs  close 
to  the  vertebral  border.  The  ridge  and  its  terminal  areas  serve  for  the  insertion 
of  the  serratus  anterior  {magnus). 

The  dorsal  (posterior)  surface  is  generally  convex  and  divided  by  a  prominent 
plate  of  bone — the  spine — into  two  unequal  parts.  The  hollow  above  the  spine 
is  the  supraspinous  fossa  and  lodges  the  supraspinatus  muscle.     The  part  below 


142 


THE  SKELETON 


the  spine  is  the  infraspinous  fossa;  it  is  three  times  as  large  as  the  supraspinous 
fossa,  is  alternately  concave  and  convex,  and  gives  origin  to  the  infraspinatus. 
The  muscle  is  attached  to  its  medial  three-fourths  and  covers  the  lateral  fourth, 
without  taking  origin  from  it. 

The  infraspinous  fossa  does  not  extend  as  far  as  tlie  axillary  border,  but  is  limited  laterally 
by  a  ridge — the  oblique  hne— Which  runs  from  the  glenoid  cavity — the  large  articular  surface 
for  the  head  of  the  humerus — downward  and  backward  to  join  the  posterior  border  a  short  dis- 
tance above  the  inferior  angle.  Tliis  line,  which  gives  attachment  to  a  stout  aponeurosis,  cuts 
ofi  an  elongated  surface,  narrow  above  for  the  origin  of  the  teres  minor,  and  crossed  near  its 
middle  by  a  groove  for  the  circumflex  (dorsal)  artery  of  the  scapula;  below,  the  surface  is  broader 
for  the  origin  of  the  teres  major  and  occasionally  a  few  fibres  of  the  latissimus  dorsi.  The  two 
areas  are  separated  by  a  line  which  gives  attachment  to  an  aponeurotic  septum  situated 
between  the  two  teres  muscles. 


Fig.  171. — The  Left  Scapula.     (Dorsal  surface.) 
Coraco-acromial  ligament  Omo-hyoid  and  the  superior  transverse  ligament 


Superior  angle 


Rhomboideus 
major 


Teres  ma  jo 


The  supra-  and  infraspinous  fossa  communicate  through  the  great  scapular 
notch  at  the  lateral  border  of  the  spine,  and  through  the  notch  the  suprascapular 
nerve  and  transverse  scapular  artery  are  transmitted  from  one  fossa  to  the  other. 

Borders. — The  three  borders  of  the  scapula  are  named  superior,  vertebral, 
and  axillary.  The  superior  is  short  and  thin  and  extends  from  the  upper  angle 
to  the  coracoid  process.  Laterally  it  presents  a  deep  depression,  the  scapular 
notch,  to  the  extremities  of  which  the  superior  transverse  ligament  is  attached. 


Not  infrequently  the  notch  is  replaced  by  a  scapular  foramen,  and  it  is  interesting  to  note 
that  a  bony  foramen  occurs  normally  in  some  animals,  notably  the  great  ant-eater  (Myrmeco- 
phaga  jubata).  The  notch  or  foramen  transmits  the  suprascapular  nerve,  whilst  the  transverse 
scapular  artery  usually  passes  over  the  ligament.  From  the  adjacent  margins  of  the  notch  and 
from  the  ligament  the  posterior  belly  of  the  omo-hyoid  takes  origin. 


THE  SCAPULA 


143 


The  vertebral  border  (sometimes  called  the  base)  is  the  longest,  and  extends 
from  the  upper  or  medial  to  the  lower  angle  of  the  bone.  It  is  divisible  into  three 
parts,  to  each  of  which  a  muscle  is  attached:  an  upper  portion,  extending  from 
the  medial  (superior)  angle  to  the  spine,  for  the  insertion  of  the  levator  scapulae; 
a  middle  portion,  opposite  the  smooth  triangular  area  at  the  commencement 
of  the  spine,  for  the  rhomhoideus  minor;  and  the  lowest  and  longest  portion, 
extending  below  this  as  far  as  the  inferior  angle,  for  the  rhomhoideus  major, 
the  attachment  of  which  takes  place  through  the  medium  of  a  fibrous  arch. 

The  axillary  border  is  the  thickest,  and  extends  from  the  lower  margin  of 
the  glenoid  cavity  to  the  inferior  angle  of  the  bone.  Near  its  junction  with  the 
glenoid  cavity  there  is  a  rough  surface,  about  2.5  cm.  (1  in.)  in  length  the  in- 
fraglenoid  tubercle,  from  which  the  long  head  of  the  triceps  arises,  and  below 

Fig.  172. — The  Left  Scapula.     (Ventral  surface.) 

Trapezoid  ligament  Pectoralis  minor 

Scapular  notch         Conoid  lig 


Serratus  anten 


Coraco-acromial 
ligament 

Biceps  and  coraco- 

brachialis 
Clavicular  facet 


Glenoid  fossa 


Articular  capsule 


Triceps  (middle  or  long  head) 


the  tubercle  is  the  groove  for  the  circumflex  (dorsal)  artery  of  the  scapula. 
The  upper  two-thirds  of  the  border  is  deeply  grooved  on  the  ventral  aspect  and 
gives  origin  to  a  considerable  part  of  the  subscapidaris. 

Angles. — The  three  angles  are  named  medial,  inferior,  and  lateral. 

The  medial  (or  superior)  angle,  forming  the  highest  part  of  the  body,  is  thin,  smooth,  and 
either  rounded  or  approximating  a  right  angle.  It  is  formed  by  the  junction  of  the  superior 
and  vertebral  borders  and  gives  insertion  to  a  few  fibres  of  the  levator  scapula.  The  inferior 
angle,  constituting  the  lowest  part  of  the  body,  is  thick,  rounded,  and  rough.  It  is  formed  by 
the  junction  of  axillary  and  vertebral  borders,  gives  origin  to  the  teres  major,  and  is  crossed 
liorizontally  by  the  upper  part  of  the  lalissimus  dorsi,  the  latter  occasionally  receiving  from  it 
a  small  slip  of  fleshy  fibres. 

The  lateral  angle  forms  the  expanded  portion  of  the  bone  known  as  the  head, 
bearing  the  glenoid  cavity,  and  supported  by  a  somewhat  constricted  neck.     The 


144  THE  SKELETON 

glenoid  cavity  is  a  wide,  shallow,  pyriform,  articular  surface  for  the  head  of  the 
humerus,  directed  forward  and  laterally,  with  the  apex  above  and  the  broad  end 
below.  Its  margin  is  raised,  and  affords  attachment  to  the  glenoid  ligament, 
which  deepens  its  concavity.  The  margin  is  not,  however,  of  equal  prominence 
throughout,  being  somewhat  defective  where  it  is  overarched  by  the  acromion, 
notched  anteriorly,  and  emphasised  above  to  form  a  small  eminence,  the  supra- 
glenoid  tubercle,  for  the  attachment  of  the  long  head  of  the  biceps. 

The  circumference  and  adjoining  part  of  the  neck  give  attachment  to  the  articular  capsule 
of  the  shoulder-joint,  and  the  anterior  border  to  the  three  accessory  ligaments  of  the  capsule, 
known  as  the  superior,  middle,  and  inferior  gleno-humeral  folds.  The  superior  fold  (Flood's 
ligament)  is  attached  above  the  notch  near  the  upper  end;  of  the  two  remaining  folds,  which 
together  constitute  Schlemm's  ligament,  the  middle  is  attached  immediately  above  the  notch 
and  the  inferior  below  the  notch.  In  the  recent  state  the  glenoid  fossa  is  covered  with  hyaline 
cartilage.  The  neck  is  more  prominent  behind  than  before  and  below  than  above,  where  it 
supports  the  coracoid  process.     It  is  not  separated  by  any  definite  boundary  from  the  body. 

Processes. — The  spine  is  a  strong,  triangular  plate  of  bone  attached  obliquely 
to  the  dorsum  of  the  scapula  and  directed  backward  and  upward.  Its  apex  is 
situated  at  the  vertebral  border;  the  base,  corresponding  to  the  middle  of  the  neck, 
is  free,  concave,  and  gives  attachment  to  the  inferior  transverse  ligament,  which 
arches  over  the  transverse  scapular  (suprascapular)  vessels  and  suprascapular 
nerve.  Of  the  two  borders,  one  is  joined  to  the  body,  whilst  the  other  is  free, 
forming  a  prominent  subcutaneous  crest.  The  latter  commences  at  the  vertebral 
border,  in  a  smooth  triangular  area,  over  which  the  tendon  of  the  trapezius  glides, 
usually  without  the  intervention  of  a  bursa,  as  it  passes  to  its  insertion  into  a 
small  tubercle  on  the  crest  beyond.  Further  laterally,  this  border  is  rough,  and 
presents  two  lips — a  superior  for  the  insertion  of  the  trapezius  and  an  inferior  for 
the  origin  of  the  deltoid.    Laterally  the  crest  is  continued  into  the  acromion. 

The  spine  has  two  sm-faces,  the  superior,  which  also  looks  medialward  and 
forward,  is  concave,  contributes  to  the  formation  of  the  supraspinous  fossa,  and 
gives  origin  to  the  supraspinatus  muscle;  the  inferior  surface,  also  slightly  concave, 
is  directed  lateralward  and  backward,  forms  part  of  the  infraspinous  fossa,  and 
affords  origin  to  the  infraspinatus  muscle.  On  both  surfaces  are  one  or  more 
prominent  vascular  foramina. 

The  acromion,  a  process  overhanging  the  glenoid  cavity,  springs  from  the 
angle  formed  by  the  junction  of  the  crest  with  the  base  of  the  spine.  Somewhat 
crescentic  in  shape,  it  forms  the  summit  of  the  shoulder  and  is  compressed  from 
above  downward  so  as  to  present  for  examination  two  surfaces,  two  borders,  and 
two  extremities. 

The  posterior  part  sometimes  terminates  laterally  in  a  prominent  acromial  angle  (meta- 
cromion)  and  the  process  then  assumes  a  more  or  less  triangular  form.  Of  the  two  extremities, 
the  posterior  is  continuous  with  the  spine,  whilst  the  anterior  forms  the  free  tip.  The  upper 
surface,  directed  upward,  backward,  and  slightly  lateralward,  is  rough  and  convex,  and  affords 
origin  at  its  lateral  part  to  a  portion  of  the  deltoid;  the  remaining  part  of  this  surface  is  sub- 
cutaneous. The  lower  surface,  directed  downward,  forward,  and  slightly  medialward,  is  con- 
cave and  smooth.  The  medial  border,  continuous  with  the  upper  lip  of  the  crest,  presents, 
from  behind  forward,  an  area  for  the  insertion  of  the  trapezius;  a  small,  oval,  concave  articular 
facet  for  the  lateral  end  of  the  clavicle,  the  edges  of  which  are  rough  for  the  acromio-clavioular 
ligaments;  and,  beyond  this,  the  anterior  extremity  or  tip,  to  which  is  attached  the  apex  of  the 
coraco-acromial  ligament.  The  lateral  border,  continuous  with  the  inferior  lip. of  the  crest,  is 
thick,  convex,  and  presents  three  or  four  tubercles  with  intervening  depressions;  from  the 
tubercles  the  tendinous  septa  in  the  acromial  part  of  the  deltoid  arise,  and  from  the  depressions, 
some  fleshy  fibres  of  the  same  muscle. 

Projecting  upward  from  the  neck  of  the  scapula  is  the  coracoid  process,  bent 
finger-like,' pointing  forward  and  laterally.  It  consists  of  two  parts,  ascending 
and  horizontal,  arranged  at  almost  a  right  angle  to  each  other. 

The  ascending  part  arises  by  a  wide  root,  extends  upward  and  medially  for  a  short  distance, 
and  is  compressed  from  before  backward;  it  is  continuous  above  with  the  horizontal  part  and 
below  with  the  neck  of  the  scapula;  the  lateral  border  lies  above  the  glenoid  cavity  and  gives 
attachment  to  the  coraco-humeral  ligament;  the  medial  border,  which  forms  the  lateral  boundary 
of  the  scapular  notch,  gives  attachment  to  the  conoid  ligament  above  and  the  transverse  liga- 
ment below.  Its  anterior  and  posterior  surfaces  are  in  relation  with  the  subscapularis  and 
supraspinatus  respectively.  The  horizontal  part  of  the  process  runs  forward  and  lateralward;  it 
is  compressed  from  above  downward  so  as  to  present  two  borders,  two  surfaces,  and  a  free 
extremity.  The  medial  border  gives  insertion  along  its  anterior  half  to  the  pectoralis  minor  and 
nearer  the  base  to  the  oosto-coracoid  membrane;  the  lateral  border  is  rough  for  the  coraco- 
acromial  and  coraco-humeral  ligaments  ;_the  upper  surface  is  irregular  and  gives  insertion  in 


THE  SCAPULA 


145 


front  to  the  ■pectoralis  minor,  and  behind  to  the  trapezoid  ligament;  the  inferior  surface  is  smooth 
and  directed  toward  the  glenoid  cavity,  which  it  overhangs;  the  free  extremity  or  apex  gives 
origin  to  the  conjoined  coraco-brachialis  and  short  head  of  the  biceps. 

The  greater  part  of  the  body  of  the  scapula  and  the  central  parts  of  the  spinous  process 
are  thin  and  transparent.  The  coracoid  and  acromion  processes,  the  crest  of  the  spine  and  in- 
ferior angle,  the  head,  neck,  and  axillary  border,  are  thick  and  opaque.  The  young  bone  consists 
of  two  layers  of  compact  tissue  with  an  intervening  cancellous  layer,  but  in  the  transparent 
parts  of  the  adult  bone  the  middle  layer  has  disappeared.  The  vascular  foramina  on  the  costal 
surface  transmit  twigs  from  the  subscapular  and  transverse  scapular  (suprascapular)  arteries; 
those  in  the  infraspinous  fossa,  twigs  from  the  circumflex  (dorsal)  and  transverse  scapular 
(suprascapular)  arteries,  the  latter  also  giving  off  vessels  which  enter  the  foramina  in  the  supra- 
spinous fossa.  The  acromion  is  supplied  by  branches  from  the  thoraco-acromial  (acromio- 
thoracic)  artery. 

The  line  of  attachment  of  the  spinous  process  to  the  dorsum  of  the  scapula  is  known  as  the 
morphological  axis,  and  the  obtuse  angle  in  the  subscapular  fossa  opposite  the  spine  as  the 

Fig.  173. — Ossification  op  the  Scapula. 

The  right  Scapula  at  the  twelfth  year,  showing  the 

subcoracoid  element  (a  little  larger  than  half 

the  natural  size,  i.  e.  ^). 


Acromial  cartilage 


Subcoracoid  element 


The  Scapula  at  the  third  year, 
showing  the  caracoid  element.    (Anterior  view.) 


Tee  Scapula  at  birth.    (Anterior  view.) 
A 


B 


subscapular  angle.  From  the  axis  three  plates  of  bone  radiate  as  from  a  centre,  the  prescapula 
forward,  the  mesoscapula  laterally,  and  the  postscapula  backward,  being  named  in  accordance 
with  the  long  axis  of  the  body  in  the  horizontal  position.  In  the  human  subject  the  postscapula 
is  greatly  developed,  and  this  is  associated  with  the  freedom  and  versatility  of  movement 
possessed  by  the  upper  limb. 

Ossification. — The  scapula  is  ossified  from  nine  centres.  Of  these,  two  (for  the  body  of  the 
scapula  and  the  coracoid)  may  be  considered  as  primary,  and  the  remainder  as  secondary. 
The  centre  for  the  body  appears  in  a  plate  of  cartilage  near  the  neck  of  the  scapula  about  the 
eighth  week  of  intra-uterine  life,  and  quickly  forms  a  triangular  plate  of  bone,  from  which  the 
spine  appears  as  a  slight  ridge  about  the  middle  of  the  third  month.  At  birth  the  glenoid  fossa 
and  part  of  the  scapular  neck,  the  acromion  and  coracoid  processes,  the  vertebral  border  and 
inferior  angle,  are  cartilaginous.  During  the  first  year  a  nucleus  appears  for  the  coracoid,  and 
at  the  tenth  year  a  second  centre  appears  for  the  base  of  the  coracoid  and  the  upper  part  of  the 
glenoid  cavity  (subcoracoid,  fig.  173). 

During  the  fifteenth  year  the  coracoid  unites  with  the  scapula,  and  about  this  time  the  other 
secondary  centres  appear.  Two  nuclei  are  deposited  in  the  acromial  cartilage,  and  fuse  to  form 
the  acromion,  which  joins  the  spine  at  the  twentieth  year.  The  union  of  spine  and  acromion 
may  be  fibrous,  hence  the  latter  is  sometimes  found  separate  in  macerated  specimens.  The 
cartilage  along  the  vertebral  border  ossifies  from  two  centres,  one  in  the  middle,  and  another  at 
the  inferior  angle.     A  thin  lamina  is  added  along  the  upper  surface  of  the  coracoid  process  and 


146 


THE  SKELETON 


occasionally  another  at  the  margin  of  the  glenoid  cavity.     These  epiphyses  join  by  the  twenty- 
fifth  year. 

The  occurrence  of  a  special  primary  centre  for  the  coracoid  process  is  of  morphological  im- 
portance in  that  the  process  is  the  representative  of  what  in  the  lower  vertebrates  is  a  distinct 
coracoid  hone.  This  primarily  takes  part  in  the  formation  of  the  glenoid  cavity  and  extends 
medially  to  articulate  with  the  sternum.  In  man  and  all  the  higher  mammals  only  the  lateral 
portion  of  the  bone  persists. 

THE  HUMERUS 

The^humerus  (figs.  174,  175,  176)  is  the  longest  and  largest  bone  of  the  upper 
limb,  and  extends  from  the  shoulder  above,  where  it  articulates  with  the  scapula. 

Fig.  174. — The  Left  Humerxts.     (Anterior  view.) 


Subscapularis- 
Latissimus  dorsi- 


Teres  major 


-Intertubercular  groove 
Pectoralis  major 


Coraco-brachialis  - 


-Brachio-radialis 


'  carpi  radialis  longus 


iiKl 


Pronator  teres- 

Fexor  carpi  radialis  . 

Palmaris  longus 

Flexor  digitorum  sublimis 

Flexor  carpi  ulnaris 


I  Extensor  carpi  radialis  brevis 
J  Extensor  digitorum  communis 
F  Extensor  digiti  quinti  proprius 

Extensor  carpi  ulnaris 

Supinator 


to  the  elbow  [cubitus]  below,  where  it  articulates  with  the  two  bones  of  the  fore- 
arm [anti-brachium].  It  is  divisible  into  a  shaft  and  two  extremities;  the  upper 
extremity  includes  the  head  [caput],  neck  [collum],  and  two  tuberosities — great 
and  small;  the  lower  extremity  includes  the  articular  surface  ^\dth  the  surmounting 
fossae  in  front  and  behind,  and  the  two  epicondyles. 


THE  HUMERUS 


147 


Upper  extremity. — The  head  forms  a  nearly  hemispherical  articular  surface, 
cartilage-clad  in  the  recent  state  and  directed  upward,  medially,  and  backward 
toward  the  glenoid  cavity.  Below  the  head  the  bone  is  rough  and  somewhat 
constricted,  constituting  the  anatomical  neck,  best  marked  superiorly,  where  it 
forms  a  groove  separating  the  articular  surface  from  the  two  tuberosities.  The 
circumference  of  the  neck  gives  attachment  to  the  capsule  of  the  shoulder-joint 
and  the  gleno-humeral  folds,  the  upper  of  which  is  received  into  a  depression  near 
the  top  of  the  intertubercular  (bicipital)  groove.     The  lowest  part  of  the  capsule 


Fig.  175. — The  Left  HuMERtrs.     (Posterior  view.) 


Articular  capsule 
Infraspinatus 


Triceps    (lateral  head)- 


Groove  for  radial  nerve- 


Triceps  (medial  bead)- 


Articular  capsule 
1  fossa- 


Lateral  epicondyle 
Anconeus  and  radial  collateral  ligament 


-Medial   epicondyle 


descends  upon  the  humerus  some  distance  from  the  articular  margin.  Laterally 
and  in  front  of  the  head  are  the  two  tuberosities,  separated  by  a  deep  furrow.  The 
greater  tuberosity  [tuberculum  majus],  lateral  in  position  and  reaching  higher  than 
the  lesser  tuberosity  [tuberculum  minus},  is  marked  by  three  facets  for  the 
insertion  of  muscles:  an  upper  one  for  the  supraspinatus,  a  middle  for  the  in- 


148 


THE  SKELETON 


fraspinatiis,  and  a  lower  for  the  teres  minor.  The  lesser  tuberosity  is  situated  in 
front  of  the  head  and  is  the  more  prominent  of  the  two ;  it  receives  the  insertion  of 
the  subscapularis.  The  furrow  between  the  tuberosities  lodges  the  long  tendon 
of  the  biceps  and  forms  the  commencement  of  the  intertubercular  (bicipital) 
groove,  which  extends  downward  along  the  shaft  of  the  humerus.  Between  the 
tuberosities  the  transverse  humeral  ligament  converts  the  upper  end  of  the  groove 
into  a  canal.     In  addition  to  the  long  tendon  of  the  biceps  and  its  tube  of  synovial 

Fig.   176. — The  Left  Humerus  with  a  Suphacondyloid  Process  and  some  Irregular 
Muscle  Attachments.     (Anterior  view.) 


Lesser  tuberosity_ 

Subscapula 
Capsular  ligament- 

brevis       (Rotator_ 


-  Greater  tuberosity 
-Transverse  humeral  ligament 


-Fourth  head  of  biceps 


Intertubercular  groove- 


Coraco-brachialis- 


-Rough  surface  for  deltoid 


Third  head  of  biceps- 


.  The  lateral   condylar  ridge 


Pronator  teres- 


Medial  epicondyle 
Ulnar  collateral  ligament  ~ 
Trochlea  - 


-Radial  fossa 
^"I'i-  Lateral    epicondyle 
ip-  Capitulum 


membrane,  the  groove  transmits  a  branch  of  the  anterior  circumflex  artery. 
Immediately  below  the  two  tuberosities  the  bone  becomes  contracted  and  forms 
the  surgical  neck. 

The  shaft  or  body  [corpus  humeri]  is  somewhat  cylindrical  above,  flattened 
and  prismatic  below.     Three  borders  and  three  surfaces  may  be  recognised. 

Borders. — The  anterior  border  commences  above  at  the  greater  tuberosity, 
and  its  upper  part,  forming  the  crest  of  this  tuberosity  [crista  tuberculi  majoris], 


THE  HUMERUS  149 

receives  the  pectoralis  major.  In  the  middle  of  the  shaft  it  is  rough  and  prominent 
and  gives  insertion  to  fibres  of  the  deltoid;  below  it  is  smooth  and  rounded,  giviiig 
origin  to  fibres  of  the  brachialis,  and  finally  it  passes  along  lateral  to  the  coronoid 
fossa  to  become  continuous  with  the  ridge  separating  the  capitulum  and  trochlea. 
It  separates  the  antero-medial  from  the  antero-lateral  surface.  The  lateral 
margin  extends  from  the  lower  and  posterior  part  of  the  greater  tuberosity  to  the 
lateral  epicondyle.  Smooth  and  indistinct  above,  it  gives  attachment  to  the 
teres  minor  and  the  lateral  head  of  the  triceps;  it  is  interrupted  in  the  middle  by 
the  groove  for  the  radial  nerve  (musculo-spiral  groove),  but  the  lower  third 
becomes  prominent  and  curved  laterally  to  form  the  lateral  supracondylar 
ridge,  which  affords  origin  in  front  to  the  brachio-radialis  and  the  extensor  carpi 
radialis  longus;  behind  to  the  medial  head  of  the  triceps,  and  between  these 
muscles  in  front  and  behind  to  the  lateral  intermuscular  septum.  It  separates 
the  antero-lateral  from  the  posterior  surface.  The  medial  border  commences 
at  the  lesser  tuberosity,  forming  its  crest  which  receives  the  insertion  of  the 
teres  major,  and  continuing  downward  to  the  medial  epicondyle.  Near  the 
middle  of  the  shaft  it  forms  a  ridge  for  the  insertion  of  the  coraco-brachialis  and 
presents  a  foramen  for  the  nutrient  artery,  directed  downward  toward  the 
elbow-joint.  Below  it  forms  a  distinct  medial  supracondylar  ridge,  curved 
medially,  which  gives  origin  to  the  brachialis  in  front,  the  medial  head  of  the 
triceps  behind,  and  the  medial  intermuscular  septum  in  the  interval  between 
the  muscles.     This  border  separates  the  antero-medial  from  the  posterior  surface. 

Fig.  177. — A  Diagram  showing  Prbssuee  and  Tension  Curves  in  the  Head 
OF  THE  Humerus.     (After  Wagstaffe.) 


Surfaces. — The  antero-lateral  surface  is  smooth  above,  rough  in  the  middle, 
forming  a  large  impression  for  the  insertion  of  the  deltoid,  below  which  is  the 
termination  of  the  groove  for  the  radial  nerve.  The  lower  part  of  the  surface 
gives  origin  to  the  lateral  part  of  the  brachialis.  The  antero-medial  surface  is 
narrow  above,  where  it  forms  the  floor  of  the  intertubercular  (bicipital)  groove, 
and  receives  the  insertion  of  the  latissimus  dor  si.  Near  the  junction  of  the  upper 
and  middle  thirds  of  the  bone  the  groove,  gradually  becoming  shallower,  widens 
out  and,  with  the  exception  of  a  rough  impression  near  the  middle  of  the  shaft 
for  the  coraco-brachialis,  the  remaining  part  of  the  antero-medial  surface  is  flat 
and  smooth,  and  gives  origin  to  the  brachialis. 

Occasionally,  a  prominent  spine  of  bone,  the  supracondylar  process,  projects  downward 
from  the  medial  border  about  5  cm.  (2  in.)  above  the  medial  epicondyle,  to  which  it  is  joined  by 
a  band  of  fibrous  tissue.  Through'  the  ring  thus  formed,  which  corresponds  to  the  supracon- 
dylar foraman  in  many  of  the  lower  animals,  the  median  nerve  and  brachial  artery  are  trans- 
mitted, though  in  some  cases  it  is  occupied  by  the  nerve  alone.  The  process  gives  origin  to  the 
pronator  teres,  and  may  afford  insertion  to  a  persistent  lower  part  of  the  coraco-brachialis. 

The  posterior  surface  is  obliquely  divided  by  a  broad  shallow  groove,  which 
runs  in  a  spiral  direction  from  behind  downward  and  forward  and  transmits  the 
radial  (musculo-spiral)  nerve  and  the  profunda  artery.  The  lateral  part  of  the 
surface  above  the  groove  gives  attachment  to  the  lateral  head,  and  the  part 
below  the  groove,  to  the  medial  head  of  the  triceps. 

The  lower  extremity  of  the  humerus  is  flattened  from  before  backward,  and 
terminates  below  in  a  sloping  articular  surface,  subdivided  by  a  low  ridge  into  the 


150 


THE  SKELETON 


trochlea  and  the  capitulum.  The  trochlea  is  the  pulley-hke  surface  which  extends 
over  the  end  of  the  bone  for  articulation  with  the  semilunar  notch  (great  sigmoid 
cavity)  of  the  ulna.  It  is  constricted  in  the  centre  and  expanded  laterally  to  form 
two  prominent  edges,  the  medial  of  which  is  thicker,  descends  lower,  and  forms  a 
marked  projection;  the  lateral  edge  is  narrow  and  corresponds  to  the  interval 
between  the  ulna  and  radius.  Above  the  trochlea  are  two  fossae :  on  the  anterior 
surface  is  the  coronoid  fossa,  an  oval  pit  which  receives  the  coronoid  process  of 


Fig.  178.- 


-ossification  of  the  humerus ;  the  figure  also  shows  the  relations  of  the 
Epiphysial  and  Capsular  Lines 


nites  with  the  shaft  at  the  twentieth 
year.  The  upper  epiphysis  is 
formed  by  the  union  of  the  nucleus- 
for  the  head,  greater  tuberosity, 
and  that  for  the  lesser  tuberosity. 
These  form  a  common  epiphysis 
before  uniting  with  the  shaft 

Capsular  line^ 


Shaft  begins  to  ossify  in  the  eighth 
week  of  intra-uterine  life 


1 


r#^ 


Capsular  line 

Nucleus  for  the  medial  epicondyle  i 
appears  at  fifth,  fuses  at  ***"  ' 
eighteenth  year 

Nucleus  for  trochlea  appears  at  the - 
tenth  year 


Nucleus  for    lateral     epicondyle  ap- 
pears at  fourteenth  year 

_  Nucleus  for  capitulum  appears  in  the 
third  year 


The  centres  for  the  radial  epicondyle, 
trochlea,  and  capitulum  unite  to- 
gether and  form  an  epiphysis  which 
fuses  with  the  shaft  at  the  seven- 
teenth year 


the  ulna  when  the  forearm  is  flexed;  on  the  posterior  aspect  is  the  olecranon  fossa, 
a  deep  hollow  for  the  reception  of  the  anterior  extremity  of  the  olecranon  in  exten- 
sion of  the  forearm.  These  fossae  are  usually  separated  by  a  thin,  translucent 
plate  of  bone,  sometimes  merely  by  fibrous  tissue,  so  that  in  macerated  specimens 
a  perforation,  the  supratrochlear  foramen,  exists.  The  capitulum,  or  radial  head, 
is  much  smaller  than  the  trochlea,  somewhat  globular  in  shape,  and  limited  to 
the  anterior  and  inferior  surfaces  of  the  extremity.     It  articulates  with  the  con- 


THE  HUMERUS  151 

cavity  on  the  summit  of  the  radius.  The  radial  fossa  is  a  slight  depression  on  the 
front  of  the  bone,  immediately  above  the  capitulum,  which  receives  the  anterior 
edge  of  the  head  of  the  radius  in  complete  flexion  of  the  forearm,  whilst  between 
the  capitulum  and  the  trochlea  is  a  shallow  groove  occupied  by  the  medial  margin 
of  the  head  of  the  radius. 

In  the  recent  state  the  inferior  articular  surface  is  covered  with  cartilage,  the  fossae  are  lined 
by  synovial  membrane,  and  their  margins  give  attachment  to  the  capsule  of  the  elbow-joint. 
Projecting  on  either  side  from  the  lower  end  of  the  humerus  are  the  two  epicondyles.  The 
medial  one  is  large  and  by  far  the  more  prominent  of  the  two,  rough  in  front  and  below,  smooth 
behind,  where  there  is  a  shallow  groove  for  the  ulnar  nerve.  The  rough  area  serves  for  origin 
of  the  pronator  teres  above,  the  common  tendon  of  origin  of  the  flexor  carpi  radialis,  palmaris 
longus,  flexor  digitorum  sublimis  and  flexor  carpi  ulnaris  in  the  middle,  and  the  ulnar  collateral 
ligament  below.  The  lateral  epicondyle  is  flat  and  irregular.  Above,  it  gives  attachment  to  a 
common  tendon  of  origin  of  the  extensor  carpi  radialis  brevis,  extensor  digitorum  communis, 
extensor  quinti  digiti  proprius,  extensor  carpi  ulnaris,  and  supinator;  to  a  depression  near  the  outer 
margin  of  the  capitulum,  the  radial  collateral  ligament  is  attached,  and  from  an  area  below  and 
behind,  the  anconeus  takes  origin. 

Architecture. — The  interior  of  the  shaft  of  the  humerus  is  hollowed  out  by  a  large  medullary 
canal,  whereas  the  extremities  are  composed  of  cancellated  tissue  invested  by  a  thin  compact 
layer.  The  arrangement  of  the  cancellous  tissue  at  the  upper  end  of  the  humerus  is  shown 
in  fig.  177.  The  lamellae  converge  to  the  axis  of  the  bone  and  form  a  series  of  superimposed 
arches  which  reach  upward  as  far  as  the  epiphysial  line.  In  the  epiphyses  the  spongy  tissue 
forms  a  fine  network,  the  lamellae  resulting  from  "pressure"  being  directed  at  right  angles  to 
the  articular  surface  of  the  head  and  to  the  great  tuberosity. 

Blood-supply. — The  foramina  which  cluster  round  the  circumference  of  the  head  and  tuber- 
osities transmit  branches  from  the  transverse  scapular  (suprascapular)  and  anterior  and  pos- 
terior circumflex  arteries.     At  the  top  of  the  intertubercular  groove  is  a  large  nutrient  foramen 


Fig.  179. — The  Head  of  the  Humebus  at  the  Sixth  Year.     (In  section.) 

The  centre  for  the  head  appears 
during  the  first  year;  it  is  some- 
times present  at  birth 

The  centre  for  the  greater  tuberosity 
appears  in  the  third  year 


for  a  branch  of  the  anterior  circumflex  artery  which  supplies^the  head.  The  nutrient  artery  of 
the  shaft  is  derived  from  the  brachial,  and  in  many  cases,  an  additional  branch,  derived  from  the 
profunda  artery,  enters  the  foramen  in  the  groove  for  the  radial  nerve  (musculo-spiral  groove) . 
The  lower  extremity  is  nourished  by  branches  derived  from  the  profunda  (superior  profunda) , 
the  superior  and  inferior  ulnar  collateral  (inferior  profunda  and  anastomotic),  and  the  recurrent 
branches  of  the  radial,  ulnar,  and  interosseous  arteries. 

Ossification. — The  humerus  is  ossified  from  one  primary  centre  (diaphysial)  and  six  second- 
ary centres  (epiphysial).  The  centre  for  the  shaft  appears  about  the  eighth  week  of  intra- 
uterine life  and  grows  very  rapidly.  At  birth  only  the  two  extremities  are  cartilaginous,  and 
these  ossify  in  the  following  manner:  Single  centres  appear  for  the  head  in  the  first  year,  for 
the  greater  tuberosity  in  the  third  year,  and  for  the  lesser  tuberosity  in  the  fifth  year,  though 
sometimes  the  latter  ossifies  by  an  extension  from  the  greater  tuberosity.  These  three  nuclei 
coalesce  at  six  years  to  form  a  single  epiphysis,  which  joins  the  shaft  about  the  twentieth  year. 

The  inferior  extremity  ossifies  from  four  centres:  one  for  the  capitulum  appears  in  the  third 
year,  a  second  for  the  medial  epicondyle  in  the  fifth  year,  a  third  for  the  trochlea  in  the  tenth 
year,  and  a  fourth  for  the  lateral  epicondyle  in  the  fourteenth  year.  The  nuclei  for  the  capitu- 
lum, trochlea,  and  lateral  epicondyle  coalesce  to  form  a  single  epiphysis  which  joins  the  shaft 
in  the  seventeenth  year.  The  nucleus  of  the  medial  epicondyle  joins  the  shaft  independently 
at  the  age  of  eighteen  years. 

A  study  of  the  upper  end  of  the  humeral  shaft  before  its  union  with  the  epiphysis  is  of  interest 
in  relation  to  what  is  known  as  the  neck  of  the  humerus.  The  term  neck  is  appUed  to  three 
parts  of  this  bone.  The  anatomical  neck  is  the  constriction  to  which  the  articular  capsule  is 
mainly  attached,  and  its  position  is  accurately  indicated  by  the  groove  which  Ues  internal  to 
the  tuberosities.  The  upper  extremity  of  the  humeral  shaft,  before  its  union  with  the  epiphysis , 
terminates  in  a  low  three-sided  pyramid,  the  surfaces  of  which  are  separated  from  one  another 
by  ridges.  The  medial  of  these  three  surfaces  underlies  the  head  of  the  bone,  and  the  two 
lateral  surfaces  underhe  the  tuberosities.  The  part  supporting  the  head  constitutes  the  morpho- 
logical neck  of  the  humerus,  whilst  the  surgical  neck  is  the  indefinite  area  below  the  tuberosities 
where  the  bone  is  liable  to  fracture. 


152 


THE  SKELETON 
THE  RADIUS 


The  radius  (figs.  180-185)  is  the  lateral  and  shorter  of  the  two  bones  of  the 
forearm.  Above,  it  articulates  with  the  humerus;  below,  with  the  carpus;  and 
on  the  medial  side  with  the  ulna.  It  presents  for  examination  a  shaft  and  two 
extremities. 

The  upper  extremity,  smaller  than  the  lower,  includes  the  head,  neck,  and 
tuberosity.  The  head  [capitulum],  covered  with  cartilage  in  the  recent  state,  i& 
a  circular  disc  forming  the  expanded,  articular  end  of  the  bone.  Superiorly  it 
presents  the  capitular  depression  [fovea  capituli]  for  the  reception  of  the  capitulum 

Fig.  180. — The  Left  Ulna  and  Radius.     (Antero-medial  view.) 

Articular  capsule"         ^^*-      %;^ 


Ulnar  collateral  ligament^ 

Tubercle  for  the  flexor  digitorum  sublimis — 

Ulnar  collateral  ligament  — 

Brachialis  — 

Pronator  teres  (lesser  head)  — 

Flexor  pollicis  longus  (accessory  head)  — 


Interosseous  membrane. 


Flexor  digitorU|BU  profundu 


"'Semilunar  notch 

^Head  of  radius 
"Neck  of  radius 
"Lower  Umit  of  annular  ligament 

-Oblique  ligament 
-  Tuberosity 

"Oblique  ligament 
-Supinator 

Flexor  sublimis  digitorum 

ObUque  line 
Radius 

■  Pronator  teres 
Flexor  pollicis  longus 


Pronator  quadratus  . 


Anterior  radio-ulnar  ligament- 
Ulnar  collateral  ligament' 


Pronator  quadratus 


Interarticular  fibro-cartilage 


Brachio-radialis 

Radial  collateral  ligament 

Anterior  radio-carpal  ligament 


of  the  humerus;  its  circumference  [circumferentia  articularis],  deeper  on  the 
medial  aspect,  articulates  with  the  radial  notch  (lesser  sigmoid  cavity)  of  the  ulna, 
and  is  narrow  elsewhere  for  the  annular  ligament  by  which  it  is  embraced.  Below 
the  head  is  a  short  cylindrical  portion  of  bone,  somewhat  constricted,  and  known 
as  the  neck.  The  upper  part  is  surrounded  by  the  hgament  which  embraces  the 
head,  and  below  this  it  gives  insertion  antero-laterally  to  the  supinator.  Below 
the  neck,  at  the  antero-medial  aspect  of  the  bone,  is  an  oval  eminence,  the  radial 
tuberosity,  divisible  into  two  parts:  a  rough  posterior  portion  for  the  insertion  of 


THE  RADIUS 


153 


the  tendon  of  the  biceps,  and  a  smooth  anterior  surface  in  relation  with  a  bursa 
which  is  situated  between  the  tendon  and  the  tuberosity. 

The  body  [corpus  radii]  or  shaft  is  somewhat  prismatic  in  form,  gradually  in- 
creasing in  size  from  the  upper  to  the  lower  end,  and  slightly  curved  so  as  to  be 
concave  toward  the  ulna.  Three  borders  and  three  surfaces  may  be  recognised. 
Of  the  borders,  the  medial  or  interosseous  crest  [crista  interossea]  is  best  marked. 
Commencing  at  the  posterior  edge  of  the  tuberosity,  its  first  part  is  round  and  in- 
distinct, and  receives  the  attachment  of  the  oblique  cord  of  the  radius;  it  is  con- 

FiG.  181. — The  Left  Ulna  and  Radius.     (Postero-lateral  view.) 

Triceps -yjy^^^ 

Articular  capsule ^^mMi Olecranon 

Subcutaneous  surface 


Lower  limit  of  annular  ligament  " 


Abductor  pollicis  longus- 


Extensor  pollicis  brevis- 


-Abductor  pollicis  longus 


An  aponeurosis  is  attached  to  this 
border  from  which  the  flexor  and 
extensor  carpi  ulnaris,  and  flexor 
digitorum  profundus  arise 


-  Extensor  polHcis  longus 


Ulna 
-Extensor  indicis  proprius 


Grooves  for  abductor  longus  and  ex- 
tensor pollicis  hrevis 
For    extensor    carpi    radialis    longus^ 
and  brevis  ~~ 

Extensor  pollicis  longus- 


-Ettensor  quinti  digiti  proprius 
-iiixtensor  carpi  ulnaris 


^Ulnar  collateral  ligament 


Extensor    digitorum    communis    and    Posterior      Posterior  radio-ulnar  ligament 
extensor  indicis  proprius  radio-carpal 

ligament 


tinned  as  a  sharp  ridge  which  divides  near  the  lower  extremity  to  become  continu- 
ous with  the  anterior  and  posterior  margins^of  the  ulnar  notch  (sigmoid  cavity). 
The  prominent  ridge  and  the  posterior  of  the  two  lower  lines  give  attachment  to 
the  interosseous  membrane,  whilst  the  triangular  surface  above  the  ulnar  notch 
receives  a  part  of  the  pronator  quadratus.  The  interosseous  crest  separates  the 
volar  from  the  dorsal  surface.  The  volar  border  [margo  volaris]  runs  from  the 
tuberosity  obliquely  downward  to  the  lateral  side  of  the  bone  and  then  descends 
vertically  to  the  anterior  border  of  the  styloid  process.     The  upper  third,  consti- 


154 


THE  SKELETON 


tuting  the  oblique  line  of  the  radius,  gives  origin  to  the  radial  head  of  the  flexor 
digitorum  suhlimis,  limits  the  insertion  of  the  supinator  above,  and  the  origin 
of  the  flexor  pollicis  longus  below.  The  volar  border  separates  the  volar  from 
the  lateral  surface.  The  dorsal  border  extends  from  the  back  of  the  tuberosity  to 
the  prominent  middle  tubercle  on  the  posterior  aspect  of  the  lower  extremity. 
Separating  the  lateral  from  the  dorsal  surface,  it  is  well  marked  in  the  middle 
third,  but  becomes  indistinct  above  and  below. 

Surfaces. — The  volar  (or  anterior)  surface  is  narrow  and  concave  above;  broad, 
flat,  and  smooth  below.  The  upper  two-thirds  is  occupied  chiefly  by  the  flexor 
pollicis  longus  and  a  little  less  than  the  lower  third  by  the  pronator  quadratus.    Near 


Fig.  182. — Articulae  Facets  on  the  Lower  End  op  Left  Radius  and  Ulna. 

Posterior 


For  naviculi 
For  Iunat( 


styloid  process  of  ulna 


Head  of  ulna :  it  articulates  with 
the  interarticular  fibro-cartilage 
of  the  wrist-joint 


the  junction  of  the  upper  and  middle  thirds  of  the  volar  surface  is  the  nutrient  fora- 
men, directed  upward  toward  the  proximal  end  of  the  bone.  It  transmits  a 
branch  of  the  volar  interosseous  artery.  The  lateral  surface  is  rounded  above 
and  affords  insertion  to  the  supinator;  marked  near  the  middle  by  a  rough,  low, 
vertical  ridge  for  the  pronator  teres;  smooth  below,  where  the  tendons  of  the  exten- 
sor carpi  radialis  longus  and  brevis  lie  upon  it,  and  where  it  is  crossed  by  the 
abductor  pollicis  longus  and  extensor  pollicis  brevis.  The  dorsal  (or  posterior) 
surface,  smooth  and  rounded  above,  is  covered  by  the  supinator;  grooved  longi- 
tudinally in  the  middle  third  for  the  abductor  pollicis  longus  and  the  extensor  pollicis 


Fig.  183. — Dorsal  View  op  the  Lower  End  op  the  Radius  and  Ulna. 


Insertion  of  brachio -radialis 
Abductor   pollicis  longus   and 

ext.  pollicis  brevis  i 

Extensor  carpi  radialis  longus      | 

and  brevis  r 

Tubercle  for  posterior  annular- — p-j 
ligament  fcii^ 

Extensor  pollicis  longus      \\j 

styloid  process 


Ext.  digitorum  communis  and 
extensor  indicis  proprius 

Extensor  quinti  digiti  proprius 
lies  in  the  groove  between  the 
radius  and  ulna 

Extensor  carpi  ulnaris 

Styloid  process 


brevis;  the  lower  third  is  broad,  rounded,  and  covered  by  tendons.  The  line  which 
forms  the  upper  limit  of  the  impression  for  the  abductor  pollicis  longus  is  known 
as  the  posterior  oblique  line. 

The  lower  extremity  of  the  radius  is  quadrilateral;  its  carpal  surface  [facies 
articularis  carpea]  is  articular  and  divided  by  a  ridge  into  a  medial  quadrilateral 
portion,  concave  for  articulation  with  the  lunate  bone;  and  a  lateral  triangular 
portion,  extending  onto  the  styloid  process  for  articulation  with  the  navicular 
(scaphoid)  bone.  The  medial  surface,  also  articular,  presents  the  ulnar  notch 
(sigmoid  cavity)  for  the  reception  of  the  rounded  margin  of  the  head  of  the  ulna. 
To  the  border  separating  the  ulnar  and  carpal  articular  surfaces  the  base  of  the 


THE  ULNA 


155 


articular  disc  is  attached,  and  to  the  anterior  and  posterior  borders,  the  anterior 
and  posterior  radio-ulnar  ligaments  respectively.  The  anterior  surface  is  raised 
into  a  prominent  area  for  the  anterior  ligament  of  the  wrist-joint.  The  lateral 
surface  is  represented  by  the  styloid  process,  a  blunt  pyramidal  eminence,  to  the 
base  of  which  the  hrachio-radialis  is  inserted,  whilst  the  tip  serves  for  the  attach- 
ment of  the  radial  (external)  collateral  ligament  of  the  wrist.  Its  lateral  surface 
is  marked  by  two  shallow  furrows  for  the  tendons  of  the  abductor  pollicis  longus 
and  extensor  pollicis  brevis.  The  posterior  surface  is  convex,  and  marked  by  three 
prominent  ridges  separating  three  furrows.  The  posterior  annular  ligament  is 
attached  to  these  ridges,  thus  forming  with  the  bone  a  series  of  tunnels  for  the 
passage  of  tendons. 

The  most  lateral  is  broad,  shallow,  and  frequently  subdivided  by  a  low  ridge.  The  lateral 
subdivision  is  for  the  extensor  carpi  radialis  longus,  the  medial  for  the  extensor  carpi  radialis 
brevis  The  middle  groove  is  narrow  and  deep  for  the  tendon  of  the  extensor  pollicis  longus. 
The  most  medial  is  shallow  and  transmits  the  extensor  indicts  proprius,  the  extensor  digitorum 
communis,  the  dorsal  branch  of  the  interosseous  artery,  and  the  dorsal  interosseous  nerve. 
When  the  radius  and  ulna  are  articulated,  an  additional  groove  is  formed  for  the  tendon  of  the 
extensor  quinti  digiti  proprius. 

Ossification. — The  radius  is  ossified  from  a  centre  which  appears  in  the  middle  of  the  shaft 
in  the  eighth  week  of  intra-uterine  hfe  and  from  two  epiphysial  centres  which  appear  after  birth. 
The  nucleus  for  the  lower  end  appears  in  the  second  year,  and  that  for  the  upper  end,  which 
forms  simply  the  disc-shaped  head,  in  the  fifth  year.  The  head  unites  with  the  shaft  at  the 
seventeenth  year,  whilst  the  inferior  epiphysis  and  the  shaft  join  about  the  twentieth  year. 


THE  ULNA 

The  ulna  (figs.  180,  181,  189)  is  a  long,  prismatic  bone,  thicker  above  than 
below,  on  the  medial  side  of  the  forearm  and  parallel  with  the  radius,  which  it 


Fig.  184. — Upper  End  of  Left  Ulna.     (Lateral  view.) 

Olecranon- 


Semilunar  notch 


Coronoid  process 


Annular  ligament 


Flexor  digitorum  profundu 


Radial  notch 


Oblique  ligament iPilI)      HI    S Supinator 


Interosseous  membn 


exceeds  in  length  by  the  extent  of  the  olecranon  process.  It  articulates  at  the 
upper  end  with  the  humerus,  at  the  lower  end  indirectly  \vith  the  carpus,  and  on 
the  lateral  side  with  the  radius.  It  is  divisible  into  a  shaft  and  two  extremities. 
The  upper  extremity  is  of  irregular  shape  and  forms  the  thickest  and  strongest 
part  of  the  bone.  The  superior  articular  surface  is  concave  from  above  dowTiward, 
convex  from  side  to  side,  and  transversely  constricted  near  the  middle.     It  belongs 


156 


THE  SKELETON 


partly  to  the  olecranon,  the  thick  upward  projection  from  the  shaft,  and  partly 
to  the  coronoid  process,  whicli  projects  horizontally  forward  from  the  front  of  the 
ulna.  This  semilunar  excavation  forms  the  semilunar  notch  (greater  sigmoid 
cavity)  and  articulates  with  the  trochlear  surface  of  the  humerus.  The  olecranon 
is  the  large  curved  eminence  forming  the  highest  part  of  the  bone. 

The  superior  surface  of  the  olecranon,  uneven  and  somewhat  quadrilateral  in  shape,  receives 
behind,  where  there  is  a  rough  impression,  the  insertion  of  the  triceps,  and  along  the  anterior 
margin  the  articular  capsule  of  the  elbow-joint.  The  posterior  surface,  smooth  and  triangular 
in  outline,  is  separated  from  the  skin  by  a  bursa.  The  anterior  surface,  covered  with  cartilage 
in  the  recent  state,  is  dii'ected  downward  and  forward,  and  its  margins  give  attachment  to  the 
articular  capsule  of  the  elbow-joint.  This  surface,  as  already  noticed,  forms  the  upper  and  back 
part  of  the  semilunar  notch.  On  the  medial  surface  of  the  olecranon  is  a  tubercle  for  the  origin 
of  the  ulnar  head  of  the  flexor  carpi  ulnaris,  and  in  front  of  this  a  fasciculus  of  the  ulnar  collateral 
ligament  of  the  elbow-joint  is  attached  to  the  bone;  the  lateral  surface  is  rough,  concave,  and 
gives  insertion  to  a  part  of  the  anconeus.  The  extremity  of  the  olecranon  lies  during  extension 
of  the  elbow  in  the  olecranon  fossa  of  the  humerus. 


Fig.  185. — Ossification  of  the  Radius  and  Ulna;  the  Figure  also  shows  the  Relations 
OP  THE  Epiphysial  and  Capsular  Lines. 


Appears  at  the  fifth  year ;  fuses  at  the 
seventeenth  year 


Appears  at  the  second  year;  fuses  at 
the  twentieth  year 


The  coronoid  process,  forming  the  lower  and  anterior  part  of  the  semilunar 
notch,  has  a  superior  articular  surface  continuous  with  the  anterior  surface  of  the 
olecranon,  and,  like  it,  covered  with  cartilage.  The  inferior  aspect  is  rough  and 
concave,  and  gives  insertion  to  the  brachialis. 

It  is  continuous  with  the  volar  surface  of  the  shaft,  and  near  the  junction  of  the  two  is  a 
rough  eminence,  named  the  tuberosity  of  the  ulna,  which  receives  the  attachment  of  the  obhque 
cord  of  the  radius  and  the  insertion  of  the  brachialis.  The  medial  side  presents  above  a  smooth 
tubercle  for  the  origin  of  the  ulnar  portion  of  the  flexor  digitorum  suhlimis,  and  a  ridge  below 
for  the  lesser  head  of  the  pronator  teres  and  the  rounded  accessory  bundle  of  the  flexor  pollicis 
longus,  whilst  immediately  behind  the  subhmis  tubercle  there  is  a  triangular  depressed  surface 
for  the  upper  fibres  of  the  flexor  digitorum  profundus. 


THE  ULNA 


157 


On  the  lateral  surface  is  the  radial  notch  (lesser  sigmoid  cavity),  an  oblong 
articular  surface  which  articulates  with  the  circumference  of  the  head  of  the  radius, 
the  anterior  and  posterior  margins  of  which  afford  attachment  to  the  annular 
ligament  and  the  radial  collateral  ligament  of  the  elbow-joint.  In  flexion  of  the 
elbow  the  tip  of  the  process  is  received  into  the  coronoid  fossa  of  the  humerus. 

The  body  [corpus  ulnae]  or  shaft  throughout  the  greater  part  of  its  extent  is 
three-sided,  but  tapers  toward  the  lower  extremity,  where  it  becomes  smooth  and 
rounded.  It  has  three  borders  and  three  surfaces.  Of  the  three  borders,  the 
lateral,  the  interosseous  crest,  is  best  marked.  In  the  middle  three-fifths  of  the 
shaft  it  is  sharp  and  prominent,  but  becomes  indistinct  below;  above  it  is  contin- 
ued by  two  lines  which  pass  to  the  anterior  and  posterior  extremities  of  the  radial 
notch  and  enclose  a  depressed  triangular  area  (bicipital  hollow),  the  fore  part  of 
which  lodges  the  tuberosity  of  the  radius  and  the  insertion  of  the  biceps  tendon 
during  pronation  of  the  hand,  while  from  the  posterior  part  the  supinator  takes 
origin.  The  interosseous  crest  separates  the  volar  from  the  dorsal  surface  and 
gives  attachment  by  the  lower  four-fifths  of  its  extent  to  the  interosseous  mem- 
brane. The  volar  border  is  directly  continuous  with  the  medial  edge  of  the  rough 
surface  for  the  brachialis  and  terminates  inferiorly  in  front  of  the  styloid  process. 


Fig.  186. — Upper  End  of  Ulna  Showing  Two  Epiphyses.     (E.  Faweett.) 

"  Beak  centre 

Scale  on  summit  of  olecranon 

t^^WMwk 1 

Semilunar  notch 


Throughout  the  greater  part  of  its  extent  it  is  smooth  and  rounded,  and  affords 
origin  to  the  flexor  digitorum  profundus  and  the  pronator  quadratus.  It  separates 
the  volar  from  the  medial  surface.  The  dorsal  border  commences  above  at  the 
apex  of  the  triangular  subcutaneous  area  on  the  back  of  the  olecranon,  and  takes  a 
sinuous  course  to  the  back  part  of  the  styloid  process.  The  upper  three-fourths 
gives  attachment  to  an  aponeurosis  common  to  three  muscles,  viz.,  the  flexor  and 
extensor  carpi  ulnaris  and  the.  flexor  digitorum  profundus.  This  Isorder  separates 
the  medial  from  the  dorsal  surface. 

Surfaces. — The  volar  (or  anterior)  surface  is  grooved  in  the  upper  three- 
fourths  of  its  extent  for  the  origin  of  the  flexor  digitorum  profundus,  narrow  and 
convex  below,  for  the  origin  of  the  pronator  quadratus.  The  upper  limit  of  the 
area  for  the  latter  muscle  is  sometimes  indicated  by  an  oblique  line — the  pronator 
ridge.  Near  the  junction  of  the  upper  and  middle  thirds  of  the  anterior  surface  is 
the  nutrient  foramen,  directed  upward  toward  the  proximal  end  of  the  bone.  It 
transmits  a  branch  of  the  volar  interosseous  artery.  The  medial  surface,  smooth 
and  rounded,  gives  attachment,  on  the  upper  two-thirds,  to  the  flexor  digitorwn 
profundus,  whereas  the  lower  third  is  subcutaneous.  The  dorsal  (or  posterior) 
surface,  directed  laterally  as  well  as  backward,  presents  at  its  upper  part  the 
oblique  line  of  the  ulna  running  from  the  posterior  extremity  of  the  radial  notch 
to  the  dorsal  border. 


158 


THE  SKELETON 


The  oblique  line  gives  attachment  to  a  few  fibres  of  the  supinator  and  marks  off  the  posterior 
surface  into  two  unequal  parts.  That  above  the  hne,  much  the  smaDer  of  the  two,  receives  the 
insertion  of  the  anconeus.  The  more  extensive  part  below  is  subdivided  by  a  vertical  ridge 
into  a  medial  portion,  smooth,  and  covered  by  the  extensor  carpi  ulnaris,  and  a  lateral  portion 
which  gives  origin  to  three  muscles,  viz.,  the  abductor  pollicis  longus,  the  extensor  pollicis  longus 
and  the  extensor  indicis  proprius,  from  above  downward. 

The  lower  extremity  of  the  uhia  is  of  small  size  and  consists  of  two  parts,  the 
head  and  the  styloid  process,  separated  from  each  other  on  the  inferior  surface  by  a 
groove  into  which  the  apex  of  the  articular  disc  is  inserted.  That  part  of  the  head 
adjacent  to  the  groove  is  semilunar  in  shape  and  plays  upon  the  articular  disc 
which  thus  excludes  the  ulna  from  the  radio-carpal  or  wrist-joint.  The  margin  of 
the  head  is  also  semilunar,  and  is  received  into  the  ulnar  notch  of  the  radius.  The 
styloid  process  projects  from  the  medial  and  back  part  of  the  bone,  and  appears 
as  a  continuation  of  the  dorsal  border.  To  its  rounded  summit  the  ulnar  collateral 
ligament  of  the  wrist-joint  is  attached,  and  its  dorsal  surface  is  grooved  for  the 
passage  of  the  tendon  of  the  extensor  carpi  ulnaris.  Immediately  above  the 
articular  margin  of  the  head  the  anterior  and  posterior  radio-ulnar  ligaments  are 
attached  in  front  and  behind. 

Fig.  187. — The  Left  Radius  and  Ulna  in  Pronation.     (Anterior  view.) 


Ossification. — The  ulna  is  ossified  from  three  centres.  The  primary  nucleus  appears  near 
the  middle  of  the  shaft  in  the  eighth  week  of  intra-uterine  life.  At  birth  the  inferior  extremity 
and  the  greater  portion  of  the  olecranon  are  cartilaginous.  The  "nucleus  for  the  lower  end  ap- 
pears during  the  fourth  year  and  the  epiphysis  joins  with  the  shaft  from  the  eighteenth  to  the 
twentieth  year.  The  greater  part  of  the  olecranon  is  ossified  from  the  shaft,  but  an  epiphysis 
is  subsequently  formed  from  a  nucleus  which  appears  in  the  tenth  year. 

The  epiphysis  varies  in  size,  and  may  be  either  scale-like  and  form  a  thin  plate  on  the  sum- 
mit, or  involve  the  upper  fourth  of  the  olecranon  and  the  corresponding  articular  surface.  In 
the  latter  case  the  epiphysis  is  probably  composed  of  two  parts  fused  together:  (1)  The  scale 
on  the  summit  of  the  olecranon  process,  and  (2)  the  beak  centre  which  enters  into  the  formation 
of  the  upper  end  of  the  semilunar  notch  (see  fig.  186).  The  epiphysis  unites  to  the  shaft  in  the 
sixteenth  or  seventeenth  year. 


THE  CARPUS 


159 


THE  CARPUS 

The  carpus  (figs.  188,  189)  consists  of  eight  bones,  arranged  in  two  rows,  four 
bones  in  each  row.  Enumerated  from  the  radial  to  the  ulnar  side,  the  bones  of 
the  proximal  row  are  named  navicular  (scaphoid),  lunate  (semilunar),  triquetral 
(cuneiform),  and  pisiform;  those  of  the  distal  row,  greater  multangular  (trape- 
zium), lesser  multangular  (trapezoid),  capitate  (os  magnum),  and  hamate 
(unciform) . 

When  the  bones  of  the  carpus  are  articulated,  they  form  a  mass  somewhat  quad- 
rangular in  outline,  wider  below  than  above,  and  with  the  long  diameter  trans- 
verse. The  dorsal  surface  is  convex  and  the  volar  surface  concave  from  side  to 
side.     The  concavity  is  increased  by  four  prominences,  which  project  forward,  one 


Fig.  188. — Bones  of  the  Left  Hand.     (Dorsal  surface.) 
Lunate 


Extensor  carpi 
radialis  longus 
Extensor  carpi, 
radialis  brevis 


Extensor  digitorum  communis 


Extensor  digitorum  communis 
Third,  ungual,  or  terminal  phalanx 


from  each  extremity  of  each  row.  On  the  radial  side  are  the  tuberosity  of  the 
navicular  and  the  ridge  of  the  greater  multangular;  on  the  ulnar  side,  the  pisiform 
and  the  hook  of  the  hamate.  Stretched  transversely  between  these  prominences, 
in  the  recent  state,  is  the  transverse  carpal  ligament  forming  a  canal  for  the  passage 
of  the  flexor  tendons  and  the  median  nerve  into  the  palm  of  the  hand.  The  proxi- 
mal border  of  the  carpus  is  convex  and  articulates  with  the  distal  end  of  the 
radius  and  the  articular  disc.  The  pisiform,  however,  takes  no  share  in  this  ar- 
ticulation, being  attached  to  the  volar  surface  of  the  triquetral.  The  distal  border 
forms  an  undulating  articular  surface  for  the  bases  of  the  metacarpal  bones.     The 


160 


THE  SKELETON 


line  of  articulation  between  the  two  rows  of  the  carpus  is  concavo-convex  from  side 
to  side,  the  lateral  part  of  the  navicular  being  received  into  the  concavity  formed 
by  the  greater  multangular,  lesser  multangular,  and  capitate,  and  the  capitate 
and  hamate  into  that  formed  by  the  navicular,  lunate,  and  triquetral  bones. 

Fig.  189. — -Bones  of  the  Left  Hand.     (Volar  surface.) 
Adductor  poUicis  obliquus  Abductor  polUcis  brevis 


Flexor  carpi  ulnaris 

Abductor  digiti 

quinti 

Flexor    brevis    and 

opponens     digiti 

quinti 

Flexor  carpi  ulnaris 


Adductor  pollicis 

transversus 

Opponens  digiti 

quinti 


Opponens  and  flexor  brevis  pollicis 
Occasional     insertion     into     greater 

multangular 
Abductor  pollicis  longus 
carpi  radialis 

ep  head  of  flexor  pollicis  brevis 

(ist  volar  interosseus) 

Opponens  pollicis 


iexor  brevis  and 

abductor  poUicis 

Abductor  pollicis  and 

ist  volar  interosseus 


Abductor  and 
flexor  brevis 
digiti      quinti 


The  individual  carpal  bones  have  several  points  of  resemblance.  Each  bone 
(excepting  the  pisiform)  has  six  surfaces,  of  which  the  anterior  or  volar  and  poste- 
rior or  dorsal  are  rough  for  the  attachment  of  ligaments,  the  volar  surface  being 
the  broader  in  the  proximal  row,  the  dorsal  surface  in  the  distal  row.  The  supe- 
rior and  inferior  surfaces  are  articular,  the  former  being  generally  convex  and  the 
latter  concave.  The  lateral  surfaces,  when  in  contact  with  adjacent  bones,  are 
also  articular,  but  otherwise  rough  for  the  attachment  of  ligaments.  Further, 
the  whole  of  the  carpus  is  cartilaginous  at  birth  and  each  bone  is  ossified  from  a 
single  centre. 

The  Navicular 

The  navicular  [os  naviculare]  or  scaphoid  (fig.  190)  is  the  largest  bone  of  the 
proximal  row,  and  so  disposed  that  its  long  axis  runs  obhquely  downward  and 
lateralward. 

The  superior  surface  is  convex  and  somewhat  triangular  in  shape  for  articulation  with  the  • 
lateral  facet  on  the  distal  end  of  the  radius.     The  inferior  surface,  smooth  and  convex,  is  divided 


THE  CARPUS 


161 


into  two  parts  by  a  ridge  running  from  before  backward.  The  lateral  part  articulates  with  the 
greater  multangular,  the  medial  with  the  lesser  multangular.  The  volar  surface,  rough  and  con- 
cave above,  is  elevated  below  into  a  prominent  tubercle  for  the  attachment  of  the  transverse 
carpal  ligament  and  the  abductor  pollicis  brevis.     The  dorsal  surface  is  narrow,  being  reduced 


Fig.  190. — The  Left  Naviculae 

For  lunate 


For  ligament 

For  greater  multangular 

For  lesser  multangular- 


to  a  groove  running  the  whole  length  of  the  bone;  it  is  rough  and  serves  for  the  attachment 
of  the  dorsal  radio-carpal  ligament.  The  medial  surface  is  occupied  by  two  articular  facets, 
of  which  the  upper  is  crescentio  in  shape  for  the  lunate  bone,  whilst  the  lower  is  deeply  concave 
for  the  reception  of  the  head  of  the  capitate.  The  lateral  surface  is  narrow  and  rough  for  the 
attachment  of  the  radial  collateral  ligament  of  the  wTist-joint. 

Articulations. — With  the  radius  above,  greater  and  lesser  multangular  below,  lunate  and 
capitate  medially. 

The  Lunate 

The  lunate  [os  luuatum]  or  semilunar  (fig.  191),  placed  in  the  middle  of  the 
proximal  row  of  the  carpus,  is  markedly  crescentic  in  outline. 

The  superior  surface  is  smooth  and  oonve.x  and  articulates  with  the  medial  of  the  two  facets 
on  the  distal  end  of  the  radius.  The  inferior  surface  presents  a  deep  concavity  divided  into  two 
parts  by  a  line  running  from  before  backward.  Of  these,  the  lateral  and  larger  articulates  with 
the  capitate;  the  medial  and  smaller  with  the  hamate.     The  volar  surface  is  large  and  convex, 


Fig.  191. — The  Left  Lunate. 

For  triquetral- 


the  dorsal  surface  narrow  and  flat,  and  both  are  rough  for  the  attachment  of  ligaments.  The 
medial  surface  is  marked  by  a  smooth  quadrilateral  facet  for  the  base  of  the  triquetral.  The 
lateral  surface  forms  a  narrow  crescentic  articular  surface  for  the  lunate. 

Articulations. — With  the  radius  above,  capitate  and  hamate  below,  navicular  laterally 
and  triquetral  medially. 

The  Triquetral 

The  triquetral  [os  triquetrum]  or  cuneiform  (fig.  192)  is  pyramidal  in  shape 
and  placed  obliquely,  so  that  its  base  looks  upward  and  laterallj^  and  the  apex 
downward  and  medially. 

Fig.  192. — The  Left  Triquetral. 

For  lunate  " 
For  pisiform 

For  hamate 


The  superior  surface  presents  laterally  near  the  base  a  small,  convex  articular  facet  which 
plays  upon  the  articular  disc  interposed  between  it  and  the  distal  end  of  the  ulna,  and  medially 
a  rough  non-articular  portion  for  ligaments.  The  inferior  surface  forms  a  large,  triangular 
undulating  facet  for  articulation  with  the  hamate.  The  volar  surface  can  be  readily  recognised 
by  the  conspicuous  oval  facet  near  the  apex  for  the  pisiform  bone.  The  dorsal  surface  is  rough 
for  the  attachment  of  ligaments.  The  medial  and  lateral  surfaces  are  represented  by  the  base 
and  the  apex  of  the  pyramid.  The  base  is  marked  by  a  flat  quadrilateral  facet  for  the  lunate. 
The  apex  forms  the  lowest  part  of  the  bone  and  is  roughened  for  the  attachment  of  the  ulnar 
collateral  ligament  of  the  WTist. 

Articulations. — With  the  pisiform  in  front,  lunate  laterally,  hamate  below,  articular  disc 
above. 


162  THE  SKELETON 

The  Pisiform 

The  pisiform  [os  pisiform e]  (fig.  193),  the  smallest  of  the  carpal  bones,  is  in 
many  of  its  characters  a  complete  contrast  to  the  rest  of  the  series.  It  deviates 
from  the  general  type  in  its  shape,  size,  position,  use,  and  development.  Forming 
a  rounded  bony  nodule  with  the  long  axis  directed  vertically,  it  is  situated  on  a 
plane  in  front  of  the  oth^r  bones  of  the  carpus. 

Fig.  193. — The  Left  Pisiform. 

For  triquetral- 


On  the  dorsal  surface  is  a  single  articular  facet  for  the  triquetral  which  reaches  to  the  upper 
end  of  the  bone,  but  leaves  a  free  non-articular  portion  below.  The  volar  surface,  rough  and 
rounded,  gives  attachment  to  the  transverse  carpal  ligament,  the  flexor  carpi  ulnaris,  the  ab- 
ductor quinti  digiti,  the  piso-metacarpal  and  the  piso-hamate  ligaments.  The  median  and  lateral 
surfaces  are  also  rough  and  the  lateral  presents  a  shallow  groove  for  the  ulnar  artery.  It  is 
usually  considered  that  the  pisiform  is  a  sesamoid  bone  developed  in  the  tendon  of  the  ^ea;or 
carpi  ulnaris,  though  by  some  writers  it  is  regarded  as  part  of  a  rudimentary  digit. 

The  Greater  Multangular 

The  greater  multangular  [os  multangulum  ma  jus]  or  trapezium  (fig.  194), 
situated  between  the  navicular  and  first  metacarpal,  is  oblong  in  form  with  the 
lower  angle  prolonged  downward  and  medially. 

Fig.  194. — The  Left  Greater  Multangular. 

-The  ridge 


For  navicular 
For  lesser  multangular 
For  second  metacarpal 


■Groove  for  flexor  carpi  radialis 
'For  first  metacarpal 


The  superior  surface  is  concave  and  directed  upward  and  medially  for  articulation  with  the 
lateral  of  the  two  facets  on  the  distal  surface  of  the  navicular,  and  on  the  inferior  surface  is  a 
saddle-shaped  facet  for  the  base  of  the  first  metacarpal.  The  volar  surface  presents  a  prominent 
ridge  with  a  deep  groove  on  its  medial  side  which  transmits  the  tendon  of  the^exor  carpi  radialis. 
The  ridge  gives  attachment  to  the  transverse  carpal  ligament,  the  abductor  pollicis  brevis,  the 
opponens  pollicis,  and  occasionally  a  tendinous  slip  of  insertion  of  the  abductor  pollicis  longus. 
The  dorsal  and  lateral  surfaces  are  rough  for  ligaments.  The  medial  surface  is  divided  into 
two  parts  by  a  horizontal  ridge.  The  upper  and  larger  portion  is  concave  and  articulates  with 
the  lesser  multangular;  the  lower — a  small  flat  facet  on  the  projecting  lower  angle — articulates 
with  the  base  of  the  second  metarcarpal. 

Articulations. — With  the  navicular  above,  first  metacarpal  below,  the  lesser  multangular 
and  second  metacarpal  on  the  medial  side. 

The  Lesser  Multangular 

The  lesser  multangular  [os  multangulum  minus]  or  trapezoid  (fig.  195),  the 
smallest  of  the  bones  in  the  distal  row,  is  somewhat  wedge-shaped,  with  the 
broader  end  dorsally  and  the  narrow  end  ventrally. 

Fig.  195. — The  Left  Lesser  Multangular. 
Volar  surface. 

For  greater  multangular 
For  second  metacarpal 


The  superior  surface  is  marked  by  a  small,  quadrilateral,  concave  facet,  for  the  media 
of  the  two  facets  on  the  lower  surface  of  the  navicular.  The  inferior  surface  is  convex  from  side 
to  side  and  concave  from  before  backward,  forming  a  saddle-shaped  articular  surface  for  the 
base  of  the  second  metacarpal.    Of  the  volar  and  dorsal  surfaces,  the  former  is  narrow  and  rough. 


THE  CARPUS 


163 


the  latter  broad  and  rounded,  constituting  the  widest  sui-face  of  the  bone,  and  both  are  rough 
for  the  attachment  of  ligaments.  The  lateral  surface  slopes  downward  and  medially  and  is 
convex  for  articulation  with  the  corresponding  sm-face  of  the  greater  multangular.  On  the 
medial  surface  in  front  is  a  smooth  flat  facet  for  the  capitate;  elsewhere  it  is  rough  for  ligaments. 
Articulations. — With  the  navicular  above,  second  metacarpal  below,  greater  multangular 
laterally,  and  the  capitate  medially. 

The  Capitate 

The  capitate  [os  capitatum]  or  os  magnum  (fig.  196)  is  the  largest  bone  of  the 
carpus.  Situated  in  the  centre  of  the  wrist,  the  upper  expanded  portion,  globular 
in  shape  and  known  as  the  head,  is  received  into  the  concavity  formed  above  by 
the  navicular  and  lunate.  The  cubical  portion  below  forms  the  body,  whilst  the 
intermediate  constricted  part  is  distinguished  as  the  neck. 


For  lunati 
For  navicular' 


Fig.  196. — The  Left  Capitate. 


tacarpal 


Of  the  six  surfaces,  the  superior  is  smooth  and  convex,  elongated  from  before  backward 
for  articulation  with  the  concavity  of  the  lunate  bone.  The  inferior  surface  is  divided  into 
three  unequal  parts  by  two  ridges.  The  middle  portion,  much  the  larger,  articulates  with  the 
base  of  the  third  metacarpal;  the  lateral,  narrow  and  concave,  looks  lateral  as  well  as  downward 
to  articulate  with  the  second  metacarpal,  whilst  the  medial  portion  is  a  small  facet,  placed  on  the 
projecting  angle  of  the  bone  dorsally,  for  the  fom'th  metacarpal  bone.  The  volar  surface  is 
convex  and  rough,  giving  origin  to  fibres  of  the  oblique  adductor  pollicis;  the  dorsal  surface  is 
broad  and  deeply  concave.  Thelateral  surface  presents,  from  above  downward: — (1)  a  smooth 
convex  sm-face,  forming  the  outer  aspect  of  the  head,  with  the  superior  surface  of  which  it  is 
continuous,  for  articulation  with  the  navicular;  (2)  a  groove  representing  the  neck,  indented 
for  hgaments;  (3)  a  small  facet,  flat  and  smooth,  for  articulation  with  the  lesser  multangular. 
Behind  this  facet  is  a  rough  area  for  attachment  of  an  interosseous  ligament.  The  medial 
surface  has  extending  along  its  whole  hinder  margin  an  oblong  articular  surface  for  the  hamate; 
the  lower  part  of  this  smooth  area  sometimes  forms  a  detached  facet.  The  volar  part  of  the 
surface  is  rough  for  an  interosseous  ligament. 

Articulations. — With  the  lunate  and  navicular  above,  second,  third,  and  fourth  meta- 
carpals below,  lesser  multangular  laterally,  and  hamate  medially. 


The  Hamate 

The  hamate  [os  hamatum]  or  unciform  (fig.  197)  is  a  large  wedge-shaped  bone, 
bearing  a  hook-like  process,  situated  between  the  capitate  and  triquetral,  with 
the  base  directed  downward  and  resting  on  the  two  medial  metacarpals. 

Fig.  197. — The  Left  Hamate. 

Hamulus— 


Fifth  metacarpal- 
Fourth  metacarpal- 


The  apex  of  the  wedge  forms  the  narrow  superior  surface,  directed  upward  and  laterally 
for  articulation  with  the  lunate.  The  inferior  surface  or  base  is  divided  bj'  a  ridge  into  two 
(juadrilateral  facets  for  the  fourth  and  fifth  metacarpal  bones.  The  volar  svu-face  is  triangular 
in  outline  and  presents  at  its  lower  part  a  prominent  hamulus  (unciform  process),  a  hook-like 
eminence,  projecting  forward  and  curved  toward  the  carpal  canal.  It  is  flattened  from  side 
to  side  so  as  to  present  two  surfaces,  two  borders,  and  a  free  extremity.  To  the  latter  the  trans- 
verse carpal  ligament  and  the  flexor  carpi  ulnaris  (by  means  of  the  piso-hamate  ligament)  are 
attached,  whilst  the  medial  surface  affords  origin  to  the  flexor  brcvis  and  the  opponens  digili  quinli. 
The  lateral  surface  is  concave  and  in  relation  to  the  flexor  tendons.  The  dorsal  surface  is 
triangular  and  rough  for  ligaments.     The  lateral  surface  has  extending  along  its  upper  and 


164 


THE  SKELETON 


hinder  edges  a  long  flat  surface,  wider  above  than  below,  for  articulation  with  the  capitate. 
In  front  of  this  articular  facet  the  surface  is  rough  for  the  attachment  of  an  interosseous  liga- 
ment. The  medial  surface  is  oblong  and  undulating,  i.  e.,  concavo-conve.x  from  base  to  apex, 
for  articulation  with  the  triquetral. 

Articulations. — With  the  triquetral,  lunate,  capitate,  and  the  fourth  and  fifth  metacarpal 
bones. 

Ossification  of  the  Carpal  Bones 


Capitate first  year 

Hamate second  year 

Triquetral third  year 

Lunate fourth  year 


Greater  multangular fifth  year 

Navicular sixth  }rear 

Lesser  multangular eighth  year 

Pisiform twelfth  year 


Additional  carpal  elements  are  occasionally  met  with.  The  os  centrale  occurs  normally  in  the 
carpus  of  many  mammals,  and  in  the  human  fcetus  of  two  months  it  is  present  as  a  small  carti- 
laginous nodule  which  soon  becomes  fused  with  the  cartilage  of  the  navicular.  Failure  of 
fusion,  with  subsequent  ossification  of  the  nodule,  leads  to  the  formation  of  an  os  centrale  in 
the  human  carpus  which  is  then  found  on  the  dorsal  aspect,  between  the  navicular,  capitate, 
and  lesser  multangular.  In  most  individuals,  however,  it  coalesces  with  the  navicular  or  under- 
goes suppression. 

An  additional  centre  of  ossification,  leading  to  the  formation  of  an  accessory  carpal  element, 
occasionally  appears  in  connection  with  the  greater  multangular  and  the  hamate.  An  accessory 
element  {os  Vesalianum)  also  occurs  occasionally  in  the  angle  between  the  hamate  and  the  fifth 
metacarpal,  and  others  occur  between  the  second  and  third  metacarpals  and  the  lesser  multan- 
gular and  capitate. 

THE  METACARPALS 

The  metacarpus  (figs.  188,  189)  consists  of  a  series  of  five  cylindrical  bones 
[ossa  metacarpalia],  well  described  as  'long  bones  in  miniature.'  Articulated 
with  the  carpus  above,  they  descend,  slightly  diverging  from  each  other,  to  sup- 
port the  fingers,  and  are  numbered  from  the  lateral  to  the  medial  side.  With 
the  exception  of  the  first,  which  in  some  respects  resembles  a  phalanx,  they  con- 
form to  a  general  type. 

A  typical  metacarpal  bone  presents  for  examination  a  shaft  and  two  extrem- 
ities. The  body  or  shaft  is  prismatic  and  curved  so  as  to  be  slightly  convex 
toward  the  back  of  the  hand.     Of  the  three  surfaces,  two  are  lateral  in  position, 

Fig.  198. — The  First  (Left)  Metacarpal. 


separated  in  the  middle  part  of  the  shaft  by  a  prominent  palmar  ridge,  and  con- 
cave for  the  attachment  of  interosseous  muscles.  The  third  or  dorsal  surface 
presents  for  examination  a  large,  smooth,  triangular  area  with  the  base  below  and 
apex  above,  covered  in  the  recent  state  by  the  extensor  tendons  of  the  fingers,  and 
two  sloping  areas,  near  the  carpal  extremity,  also  for  interosseous  muscles.  The 
triangular  area  is  bounded  by  two  hnes,  which  commence  below  in  two  dorsal 
tubercles,  and,  passing  upward,  converge  to  form  a  median  ridge  situated  be- 
tween the  sloping  areas  on  either  side.  A  little  above  or  below  the  middle  of  the 
shaft,  and  near  the  volar  border,  is  the  medullary  foramen,  entering  the  bone 
obliquely  upward.  The  base  or  carpal  extremity,  broader  behind  than  in  front, 
is  quadrilateral,  and  both  palmar  and  dorsal  surfaces  are  rough  tor  hgaments;  it 
articulates  above  with  the  carpus  and  on  each  side  with  the  adjacent  metacarpal 
bones.  The  head  [capitulum]  or  digital  extremity  presents  a  large  rounded  ar- 
ticular surface,  extending  further  on  the  palmar  than  on  the  dorsal  aspect,  for 


THE  METACARPALS 


165 


articulation  with  the  base  of  the  first  phalanx.  The  volar  surface  is  grooved  for 
the  flexor  tendons  and  raised  on  each  side  into  an  articular  eminence.  On  each 
side  of  the  head  is  a  prominent  tubercle,  and  immediately  in  front  of  this  a  well- 
marked  fossa,  to  both  of  which  the  collateral  hgament  of  the  metacarpo-phalangeal 
joint  is  attached. 

Fig.  199. — The  Second  (Left)  Metacarpal. 


For  greater  multangular 


I  h 


For  third  metacarpal 
■For  capitate 


The  second  is  the  longest  of  all  the  metacarpal  bones,  and  the  third,  fourth, 
and  fifth  successively  decrease  in  length.  The  several  metacarpals  possess  dis- 
tinctive characters  by  which  they  are  readily  identified. 

The  first  metacarpal  (fig.  198)  is  the  shortest  and  widest  of  the  series.  Diverging  from  the 
carpus  more  widely  than  any  of  the  others  the  palmar  surface  is  directed  medially  and  marked 


Fig.  200. — The  Third  (Left)  Metacarp.^.l. 


For  second  metacarpal 


For  fourth  metacarpal 


Styloid  process 


bj'  a  ridge  placed  nearer  to  the  medial  border.  The  lateral  portion  of  the  surface  slopes  gently 
to  the  lateral  border  and  gives  attachment  to  the  opponens  poUicis;  the  medial  portion,  the 
smaller  of  the  two,  slopes  more  abruptly  to  the  medial  border,  is  in  relation  to  the  deep  head  of 
the  flexor  pollicis  brevis,  and  presents  the  nutrient  foramen,  directed  downward  toward  the 
head  of  the  bone  and  transmitting  a  branch  of  the  arteria  princeps  poUicis.  The  dorsal 
surface,  wide  and  flattened,  is  in  relation  to  the  tendons  of  the  extensor  poUicis  longus  and  brevis. 


166 


THE  SKELETON 


The  base  presents  a  saddle-shaped  articular  surface  for  the  greater  multangular,  prolonged  in 
front  into  a  thin  process.  There  are  no  lateral  facets,  but  laterally  a  small  tubercle  receives 
the  insertion  of  the  abductor  pollicis  longus.  Medially  is  a  rough  area  from  which  fibres  of  the 
inner  head  of  the  flexor  pollicis  brevis  take  origin.  The  margin  of  the  articular  surface  gives 
attachment  to  the  articular  capsule  of  the  carpo-metacarpal  joint.  The  inferior  extremity  or 
head  is  rounded  and  articular,  for  the  base  of  the  first  phalanx;  the  greatest  diameter  is  from 
side  to  side  and  the  surface  is  less  convex  than  the  corresponding  surface  of  the  other  metacarpal 
bones.  On  the  volar  surface  it  presents  two  articular  eminences  corresponding  to  the  two 
sesamoid  bones  of  the  thumb.  Of  the  two  margins,  the  medial  gives  origin  to  the  lateral 
head  of  the  first  dorsal  interosseous,  the  lateral  receives  fibres  of  insertion  of  the  opponens  pollicis. 


Fig.  201. — The  Fouhth  (Left)  Metacarpal. 


For  third  metacarpal 
For  capitate 


For  fifth  metacarpal 


The  second  metacarpal  (fig.  199). — The  distinctive  features  of  the  four  remaining  meta- 
carpals are  almost  exclusively  confined  to  the  carpal  extremities.  The  second  is  easily  recog- 
nised by  its  deeply  cleft  base.  The  terminal  surface  presents  three  articular  facets,  arranged 
as  follows,  from  lateral  to  medial  border : — (1)  a  small  oval  facet  for  the  greater  multangular;  (2) 
a  hollow  for  the  lesser  multangular;  and  (3)  an  elongated  ridge  for  the  capitate.  The  dorsal 
surface  is  rough  for  the  insertions  of  the  extensor  carpi  radialis  longus  and  a  part  of  the  extensor 
carpi  radialis  brevis;  the  palmar  surface  receives  the  insertion  of  the  flexor  carpi  radialis  and 
gives  origin  to  a  few  fibres  of  the  oblique  adductor  pollicis.  The  lateral  aspect  of  the  extremity 
is  rough  and  non-articular;  the  medial  surface  bears  a  bilobed  facet  for  the  third  metacarpal. 


Fig.  202. — The  Fifth  (Left)  Metacarpal. 


Fourth  metacarpal' 


The  shaft  of  the  second  metacarpal  gives  attachment  to  three  interosseous  muscles,  and  the 
nutrient  foramen,  directed  upward  on  the  ulnar  side,  transmits  a  branch  of  the  second  volar 
metacarpal  artery. 

The  third  metacarpal  (fig.  200)  is  distinguished  by  the  prominent  styloid  process  projecting 
upward  from  the  lateral  and  posterior  angle  of  the  base.  Immediately  below  it,  on  the  dorsal 
surface,  is  a  rough  impression  for  the  extensor  carpi  radialis  brevis.  The  carpal  surface  is 
concave  behind  and  convex  in  front,  and  articulates  with  the  middle  of  the  three  facets  on  the 
inferior  surface  of  the  capitate.  On  the  lateral  side  is  a  bilobed  articular  facet  for  the  second 
metacarpal,  and  on  the  medial  side  two  small  oval  facets  for  the  fourth  metacarpal.  The  volar 
a.spect  of  the  base  is  rough  and  gives  attachment  to  fibres  of  the  oblique  adductor  pollicis  and 


THE  PHALANGES 


167 


sometimes  a  slip  of  insertion  of  the  flexor  carpi  radialis.  The  shaft  of  the  third  metacarpal 
serves  for  the  origin  of  the  transverse  adductor  pollicis  and  two  interosseous  muscles.  The 
nutrient  foramen  is  directed  upward  on  the  radial  side  and  transmits  a  branch  of  the  second 
volar  metacarpal  artery. 

The  fourth  metacarpal  (fig.  201)  has  a  small  base.  The  carpal  surface  presents  two  facets: 
a  medial,  large  and  flat,  for  articulation  with  the  hamate,  and  a  small  facet,  at  the  lateral  and 
posterior  angle,  for  the  capitate.  On  the  lateral  side  are  two  small  oval  facets  for  the  correspond- 
ing surfaces  on  the  third  metacarpal  and  a  single  concave  facet  on  the  medial  side  for  the  fifth 
metacarpal.  The  shaft  of  the  fourth  metacarpal  gives  attachment  to  three  interosseous  muscles, 
and  the  nutrient  foramen,  directed  upward  on  the  radial  side,  transmits  a  branch  of  the  third 
volar  metacarpal  artery. 

The  fifth  metacarpal  (fig.  202)  is  distinguished  by  a  semilunar  facet  on  the  lateral  side  of 
the  base  for  the  fourth  metacarpal,  and  a  rounded  tubercle  on  the  medial  side  for  the  extensor 
carpi  ulnaris,  in  place  of  the  usual  medial  facet.  The  carpal  surface  is  saddle-shaped  for  the 
hamate;  the  palmar  surface  is  rough  for  ligaments  including  the  piso-metacarpal  prolongation 
from  the  flexor  carpi  ulnaris.  The  dorsal  surface  of  the  shaft  presents  an  oblique  line  separating 
a  lateral  concave  portion  for  the  fourth  dorsal  interosseous  muscle  from  a  smooth  medial  por- 
tion covered  by  the  extensor  tendons  of  the  little  finger.  The  palmar  surface  gives  attachment 
laterally  to  the  third  palmar  interosseous  muscle  and  medially  to  the  opponens  digili  quinti.  The 
nutrient  foramen  is  directed  upward  on  the  radial  side  and  transmits  a  branch  of  the  fourth 
volar  metacarpal  artery. 

THE  PHALANGES 

The  phalanges  (fig.  203)  are  the  bones  of  the  fingers,  and  number  in  all  fourteen. 
Each  finger  consists  of  three  phalanges  distinguished  as  first  or  proximal,  second 


Fig.  203. — The  Phalanges  op  the  Third  Digit  op  the  Hand.     (Dorsal  view.) 
[The  arrows  indicate  the  direction  of  the  nutrient  canals.] 


Third  terminal  or  ungual   phalanx 


Second  phalanx 


or  middle,  and  third  or  distal.  In  the  thumb,  the  second  phalanx  is  wanting. 
Arranged  in  horizontal  rows,  the  phalanges  of  each  row  resemble  one  another 
and  differ  from  those  of  the  other  two  rows.  In  all  the  phalanges  the  nutrient 
canal  is  directed  downward,  toward  the  distal  extremity. 

First  phalanx, — The  shaft  of  a  phalanx  from  the  first  row  is  flat  on  the  palmar  surface, 
smooth  and  rounded  on  the  dorsal  surface,  i.  e.,  semi-cyUndrical  in  shape.  The  borders  of  the 
palmar  surface  are  rough  for  the  attachment  of  the  sheaths  of  the  flexor  tendons.  The  base 
or  metacarpal  extremity  presents  a   single   concave  articular  surface,  oval  in  shape,  for  the 


168 


THE  SKELETON 


convex  head  of  the  metacarpal  bone.  The  distal  extremity  forms  a  pulley-like  surface,  grooved 
in  the  centre  and  elevated  at  each  side  to  form  two  miniature  condyles,  for  articulation  with 
the  base  of  a  second  phalanx. 

Second  phalanx. — The  second  phalanges  are  four  in  number  and  are  shorter  than  those  of 
the  first  row,  which  they  closely  resemble  in  form.  They  are  distinguished,  however,  by  the 
articular  surface  on  the  proximal  extremity,  which  presents  two  shallow  depressions,  separated 
by  a  ridge  and  corresponding  to  the  two  condyles  of  the  first  phalanx.  The  distal  end  for  the 
base  of  the  third  phalanx  is  trochlear  or  pulley-like,  but  smaller  than  that  of  the  first  phalanx. 
The  palmar  surface  of  the  shaft  presents  on  each  side  an  impressionSfor  the  tendon  of  the  flexor 
digitorum  sublimis,  and  the  dorsal  aspect  of  the  base  is  marked  by  a  projection  for  the  insertion 
of  the  extensor  digitorum  communis. 

Third  phalanx. — A  third  phalanx  is  readily  recognised  by  its  small  size.  The  proximal 
end  is  identical  in  shape  with  that  of  a  second  phalanx,  and  bears  a  depression  in  front  for  the 
tendon  of  the  flexor  digitorum  profundus.  The  free,  flattened  and  expanded  distal  extremity 
presents  on  its  palmar  surface  a  rough  semilunar  elevation  for  the  support  of  the  pulp  of  the 
finger.  The  somewhat  horseshoe-shaped  free  extremity  is  known  as  the  ungual  tuberosity 
[tuberositas  unguicularis],  and  the  bone  is  accordingly  referred  to  as  the  ungual  phalanx. 

Ossification  of.  the  Metacarpus  and  Phalanges 

Each  of  the  metacarpal  bones  and  phalanges  is  ossified  from  a  primary  centre  for  the  greater 
part  of  the  bone,  and  from  one  epiphysial  centre.  The  primary  nucleus  appears  from  the  eighth 
to  the  tenth  week  of  intra-uterine  life.     In  four  metacarpal  bones  the  epiphysis  is  distal,  whilst 


Fig.  204. — Ossification  of  the  Metacarpals  and  Phalanges. 


Appears  in  th 
Consolidates  i 
year 


Epiphysis  for  base- 


Metacarpal  of  thum^ 


Epiphysis  for  head 


1  Appear  in  the  third,  and  con- 
J     soiidate  in  the  twentieth  year 


Appear  between  the  third  and 
fifth  year.  Consolidate  in 
the  eighteenth  year 


in  the  first  metacarpal  bone,  and  in  all  the  phalanges,  it  is  proximal.  The  epiphysial  nuclei 
appear  from  the  third  to  the  fifth  year  and  are  united  to  their  respective  shafts  about  the  twen- 
tieth year.  In  many  cases  the  first  metacarpal  has  two  epiphyses,  one  for  the  base  in  the  third 
year  and  an  additional  one  for  the  head  in  the  seventh  year,  but  the  latter  is  never  so  large  as 
in  the  other  metacarpal  bones.  The  third  metacarpal  occasionally  has  an  additional  nucleus 
for  the  prominent  styloid  process  which  may  remain  distinct  and  form  a  styloid  bone,  and  traces 
of  a  proximal  epiphysis  have  been  observed  in  the  second  metacarpal  bone.  In  many  of  the 
Cetacea  (whales,  dolphins,  and  porpoises)  and  in  the  seal,  epiphyses  are  found  at  both  ends  of 
the  metacarpal  bones  and  phalanges  (Flower). 

The  ossification  of  a  terminal  phalanx  is  peculiar.  Like  the  other  phalanges,  it  has  a  pri- 
mary nucleus  and  a  secondary  nucleus  for  an  epiphysis.  But  whereas  in  other  phalanges  the 
primary  centre  appears  in  the  middle  of  the  shaft,  in  the  case  of  the  distal  phalanges  the  earthy 
matter  is  deposited  in  the  free  extremity. 


Sesamoid  Bones 

The  sesamoid  bones  are  small  and  rounded  and  occur  imbedded  in  certain  tendons  where 
they  exert  a  considerable  amount  of  pressure  on  subjacent  bony  structures.  In  the  hand  five 
sesamoid  bones  are  of  almost  constant  occurrence,  namely,  two  over  the  metacarpo-phalangeal 
joint  of  the  thumb  in  the  tendons  of  the  flexor  pollicis  brevis,  one  over  the  interphalangeal  joint 
of  the  thumb,  and  one  over  the  metacarpo-phalangeal  joints  of  the  second  and  fifth  fingers. 


THE  COXAL  BONE  169 

Occasionally  sesamoids  occur  over  the  metacarpo-phalangeal  joint  of  the  third  and  fourth  digits, 
and  an  additional  one  may  occur  over  that  of  the  fifth. 

Very  rarely  a  sesamoid  is  developed  in  the  tendon  of  the  biceps  over  the  tuberosity  of  the 
radius. 

B.  THE  BONES  OF  THE  LOWER  EXTREMITY 

The  bones  of  the  lower  extremity  may  be  arranged  in  four  groups  correspond- 
ing to  the  division  of  the  limb  into  the  hip,  thigh,  leg,  and  foot.  In  the  hip  is  the 
coxal  or  hip-bone,  which  constitutes  the  pelvic  girdle  [cingulum  extremitatis 
inferioris],  and  contributes  to  the  formation  of  the  pelvis;  in  the  thigh  is  the  femur; 
in  the  leg,  the  tibia  and  fibula,  and  in  the  foot  the  tarsus,  metatarsus,  and  phalanges. 
Associated  with  the  lower  end  of  the  femur  is  a  large  sesamoid  bone,  the  patella 
or  knee-cap. 

THE  COXAL  BONE 

The  coxal  (innominate)  bone  or  hip-bone  [os  coxse]  (figs.  205,  206)  is  a  large, 
irregularly  shaped  bone  articulated  behind  'with  the  sacrum,  and  in  front  with  its 
fellow  of  the  opposite  side,  the  two  bones  forming  the  anterior  and  side  walls  of 
the  pelvis.  The  coxal  bone  consists  of  three  parts,  named  ilium,  ischium,  and 
pubis,  which,  though  separate  in  early  life,  are  firmly  united  in  the  adult.  The 
three  parts  meet  together  and  form  the  acetabulum  (or  cotyloid  fossa),  a  large, 
cup-like  socket  situated  near  the  middle  of  the  lateral  surface  of  the  bone  for 
articulation  with  the  head  of  the  femur. 

The  ilium  [os  ilium]  is  the  upper  expanded  portion  of  the  bone,  and  by  its 
inferior  extremity  forms  the  upper  two-fifths  of  the  acetabulum.  It  presents  for 
examination  three  borders  and  two  surfaces. 

Borders. — When  viewed  from  above,  the  thick  crest  [crista  iliaca]  or  superior 
border  is  curved  somewhat  like  the  letter  /,  being  concave  medially  in  front  and 
concave  laterally  behind.  Its  anterior  extremity  forms  the  anterior  superior 
iliac  spine,  which  gives  attachment  to  the  inguinal  (Poupart's)  ligament  and  the 
sartorius;  the  posterior  extremity  forms  the  posterior  superior  iliac  spine  and 
affords  attachment  to  the  sacro-tuberous  (great  sacro-sciatic)  ligament,  the  pos- 
terior sacro-iliac  ligament,  and  the  multifidus.  The  crest  is  narrow  in  the  middle, 
thick  at  its  extremities,  and  may  be  divided  into  an  inner  lip,  an  outer  lip,  and  an 
intermediate  line.  About  two  and  a  half  inches  from  the  anterior  superior  spine 
is  a  prominent  tubercle  on  its  external  lip. 

The  external  lip  of  the  crest  gives  attachment  in  front  to  the  tensor  fascia  latw;  along  its 
whole  length,  to  the  fascia  lata;  along  its  anterior  half  to  the  external  oblique;  and  behind  this, 
for  about  an  inch,  to  the  latissimus  dorsi.  The  anterior  two-thirds  of  the  intermediate  line 
gives  origin  to  the  internal  oblique.  The  internal  lip  gives  origin,  by  its  anterior  two-thirds,  to 
the  iransversus;  behind  this  is  a  small  area  for  the  quadratus  lumborum,  and  the  remainder 
is  occupied  by  the  sacro-spinalis  (erector  spince).  The  internal  lip,  in  the  anterior  two-thirds, 
also  serves  for  the  attachment  of  the  iliac  fascia. 

The  anterior  border  of  the  ilium  extends  from  the  anterior  superior  iliac  spine 
to  the  margin  of  the  acetabulum.  Below  the  spine  is  a  prominent  notch  from 
which  fibres  of  the  sartorius  arise,  and  this  is  succeeded  by  the  anterior  inferior 
iliac  spine,  smaller  and  less  prominent  than  the  superior,  to  which  the  straight 
head  of  the  rectus  and  the  ilio-femoral  ligament  are  attached.  On  the  medial  side 
of  the  anterior  inferior  spine  is  a  broad,  shallow  groove  for  the  ilio-psoas  as  it 
passes  from  the  abdomen  into  the  thigh,  limited  below  by  the  ilio-pectineal 
eminence,  which  indicates  the  point  of  union  of  the  ilium  and  pubis. 

The  posterior  border  of  the  ilium  presents  the  posterior  superior  iliac  spine, 
and  below  this,  a  shallow  notch  terminating  in  the  posterior  inferior  iliac  spine 
which  corresponds  to  the  posterior  extremity  of  the  auricular  surface  and  gives 
attachment  to  a  portion  of  the  sacro-tuberous  (great  sacro-sciatic)  hgament. 
Below  the  spine  the  posterior  border  of  the  ilium  forms  the  upper  limit  of  the 
greater  sciatic  notch. 

Surfaces. — The  external  surface  or  dorsum  is  concave  behind,  convex  in  front, 
limited  above  by  the  thick  superior  border  or  crest,  and  traversed  by  three  gluteal 
lines. 


170 


THE  SKELETON 


The  posterior  gluteal  line  commences  at  the  crest  about  two  inches  from  the  posterior 
superior  iliac  spine  and  curves  downward  to  the  upper  margin  of  the  greater  sciatic  notch. 
The  space  included  between  this  ridge  and  the  crest  affords  origin  at  its  upper  part  to  the 
gluteus  maximus,  and  at  its  lower  part,  to  a  few  fibres  of  the  piriformis,  while  the  intermediate 
portion  is  smooth  and  free  from  muscular  attachment.  The  anterior  gluteal  line  begins  at 
the  crest,  one  inch  behind  its  anterior  superior  iliac  spine,  and  curves  across  the  dorsum  to 
terminate  near  the  lower  end  of  the  superior  line,  at  the  upper  margin  of  the  greater  sciatic 
notch.  The  surface  of  bone  between  this  line  and  the  crest  is  for  the  origin  of  the  gluteus 
medius.     The  inferior  gluteal  line  commences  at  the  notch  immediately  below  the  anterior 


Fig.  205." 

Insertion  of  external  oblique 
Internal  oblique 

Tensor  fasicEe  latee 
Sartorius 


-The  Left  Coxal  or  Hip-bone.     (Lateral  view.) 

Posterior  limit  of  external  oblique 


Latissimus  dorsi 


Crest  of  ilium 


Posterior 

superior  iliac 
spine 


•informis 
Posterior  inferior 
iliac  spine 


Greater  sciatic  (ilio-sci- 
atic)  notch 


Pectineus 
Rectus 

abd 

Pyramidali 

Adducto 

longu 

Adducto 

brevi 

Descending  ramus  of 

pubis 

Gracilis 


Ramus  of  ischium       Obturator  externus 


superior  iliac  spine  and  terminates  posteriorly  at  the  front  part  of  the  greater  sciatic  notch- 
The  space  between  the  anterior  and  inferior  gluteal  lines,  with  the  exception  of  a  small  area 
adjacent  to  the  anterior  end  of  the  spine  for  the  tensor  fasciw  latce,  gives  origin  to  the  gluteus 
minimus.  Between  the  inferior  gluteal  line  and  the  margin  of  the  acetabulum  the  surface 
affords  attachment  to  the  capsule  of  the  hip-joint,  and  on  a  rough  area  (sometimes  a  depression) 
toward  its  anterior  part,  to  the  reflected  tendon  of  the  rectus  femoris. 

The  internal  surface  presents  in  front  a  smooth  concave  portion  termed  the 
iliac  fossa,  which  lodges  the  iliacus  muscle.  The  fossa  is  limited  below  by  linea 
arcuata,  the  iliac  portion  of  the  terminal  (iho-pectineal)  line.  This  is  a  rounded 
border  separating  the  fossa  from  a  portion  of  the  internal  surface  below  the  line, 
which  gives  attachment  to  the  obturator  internus  and  enters  into  the  formation  of 
the  minor  (true)  pelvis.     Behind  the  iliac  fossa  the  bone  is  uneven  and  presents 


THE  COXAL  BONE 


171 


an  auricular  surface,  covered  with  cartilage  in  the  recent  state,  for  articulation 
with  the  lateral  aspect  of  the  upper  portion  of  the  sacrum;  above  the  auricular 
surface  are  some  depressions  for  the  posterior  sacro-iliac  ligaments  and  a  rough 
area  reaching  as  high  as  the  crest,  from  which  parts  of  the  sacro-spinalis  {erector 
spince)  and  vmltifidus  take  origin.  The  rough  surface  above  the  auricular  facet  is 
known  as  the  tuberosity  of  the  ilium. 

The  ischium  [os  ischii]  consists  of  a  body,  a  tuberosity,  and  a  ramus.     The 
body,  which  has  somewhat  the  form  of  a  triangular  pyramid,  enters  superiorly  into 


Fig.  206. — The  Left  Coxal  or  Hip-bone.     (Medial  aspect.) 

Quadratus  lumborum 


Transversus  muscle  and 
iliac  fasica 


Auricular  surface 


Ant.  inf.  spine  of  ilium 


Symphysial  surface 
Levator  ani 


Junction  of  pubis       Cms  penis  and    Sphincter     Arcuate 
and  ischium  Ischio-  urethra      ligament 

cavernosas    membranacese 


the  formation  of  the  acetabulum,  to  which  it  contributes  a  little  more  than  two- 
fifths,  and  forms  the  chief  part  of  the  non-articular  portion  or  floor.  The  inner 
surface  forms  part  of  the  minor  (true)  pelvis  and  gives  origin  to  the  obturator  in  - 
ternus.  It  is  continuous  with  the  ilium  a  little  below  the  terminal  (ilio-pectineal) 
line,  and  with  the  pubis  in  front,  the  line  of  junction  with  the  latter  being  fre- 
quently indicated  in  the  adult  bone  by  a  rough  line  extending  from  the  ilio-pec- 
tineal eminence  to  the  margin  of  the  obturator  foramen.  The  outer  surface  in 
eludes  the  portion  of  the  acetabulum  formed  by  the  ischium.  The  posterior  sur- 
face is  broad  and  bounded  laterally  by  the  margin  of  the  acetabulum  and  behind 


172  THE  SKELETON 

by  the  posterior  border.  The  capsule  of  the  hip-j  oint  is  attached  to  the  lateral  part 
and  the  -pirijorniis,  the  great  sciatic  and  posterior  cutaneous  nerves,  the  inferior 
gluteal  (sciatic)  artery,  and  the  nerve  to  the  quadratus  femoris  lie  on  the  surface 
as  they  leave  the  pelvis.  Inferiorly  this  surface  is  limited  by  the  obturator  groove, 
which  receives  the  posterior  fleshy  border  of  the  obturator  externus  when  the  thigh 
is  flexed.  Of  the  three  borders,  the  external,  forming  the  prominent  rim  of  the 
acetabulum,  separates  the  posterior  from  the  external  surface  and  gives  attach- 
ment to  the  glenoid  lip.  The  inner  border  is  sharp  and  forms  the  lateral 
boundary  of  the  obturator  foramen.  The  posterior  border  is  continuous  with  the 
posterior  border  of  the  ilium,  with  which  it  joins  to  complete  the  margin  of  the 
great  sciatic  notch  [incisura  ischiadica  major].  The  notch  is  converted  into  a 
foramen  by  the  sacro-spinous  (small  sacro-sciatic)  ligament,  and  transmits  the 
piriformis  muscle,  the  gluteal  vessels,  the  superior  and  inferior  gluteal  nerves,  the 
sciatic  and  posterior  cutaneous  nerves,  the  internal  pudic  vessels  and  nerve,  and 
the  nerves  to  the  obturator  internus  and  quadratus  femoris.  Below  the  notch  is 
the  prominent  ischial  spine,  which  gives  attachment  internally  to  the  coccygeus 
and  levator  ani,  externally  to  the  gemellus  superior,  and  at  the  tip  to  the  sacro- 
spinous  ligament.  Below  the  spine  is  the  small  sciatic  notch  [incisura  ischiadica 
minor],  covered  in  the  recent  state  with  cartilage,  and  converted  into  a  foramen  by 
the  sacro-tuberous  (great  sacro-sciatic)  ligament.  It  transmits  the  tendon  of  the 
obturator  internus,  its  nerve  of  supply,  and  the  internal  pudic  vessels  and  nerve. 

The  rami  form  the  flattened  part  of  the  ischium  which  runs  first  downward, 
then  upward,  forward  and  medially  from  the  tuberosity  toward  the  inferior 
ramus  of  the  pubis,  with  which  it  is  continuous.  The  rami  together  form  an  L- 
shaped  structure  with  an  upper  vertical  ramus  [ramus  superior]  and  a  lower 
horizontal  ramus  [ramus  inferior].  The  outer  surface  of  the  rami  gives  origin  to 
the  adductor  magyius  and  obturator  externus;  the  inner  surface,  forming  part  of  the 
anterior  wall  of  the  pelvis,  receives  the  crus  penis  (or  clitoridis)  and  the  ischio- 
cavernosus,  and  gives  origin  to  a  part  of  the  obturator  internus.  Of  the  two  borders, 
the  upper  is  thin  and  sharp,  and  forms  part  of  the  boundary  of  the  obturator 
foramen;  the  lower  is  rough  and  corresponds  to  the  inferior  ramus.  It  is  some- 
what everted  and  gives  attachment  to  the  fascia  of  Colles,  and  the  transversus 
perinei.  To  a  ridge  immediately  above  the  impression  for  the  cms  penis  (or 
clitoridis)  and  the  ischio-cavernosus ,  the  urogenital  trigone  (triangular  ligament) 
is  attached.  The  posterior  and  inferior  aspect  of  the  superior  ramus  is  an  ex- 
panded area  forming  the  tuberosity  [tuber  ischiadicum]. 

The  tuberosity  is  that  portion  of  the  ischium  which  supports  the  body  in  the  sitting  posture. 
It  forms  a  rough,  thick  eminence  continuous  with  the  inferior  border  of  the  infeiior  ramus, 
and  is  marked  by  an  oblique  line  separating  two  impressions,  an  upper  and  lateral  for  the 
semimembranosus,  and  a  lower  and  medial  for  the  common  tendon  of  the  biceps  and  semitendi- 
nosus,  while  the  lower  part  is  markedly  uneven  and  gives  origin  to  the  adductor  magnus.  The 
upper  border  gives  origin  to  the  inferior  gemellus;  the  inner  border,  sharp  and.  prominent,  re- 
ceives the  sacro-tuberous  (great  sacro-sciatic)  ligament,  while  the  surface  of  the  tuberosity 
immediately  in  front  is  in  relation  with  the  internal  pudic  vessels  and  nerve.  The  outer 
border  gives  origin  to  the  quadratus  femoris. 

The  pubis  [os  pubis]  consists  of  a  body  and  two  rami — superior  and  inferior. 
The  body  is  somewhat  quadrilateral  in  shape  and  presents  for  examination  two 
surfaces  and  three  borders.  The  anterior  surface  looks  downward,  forward  and 
slightly  outward,  and  gives  origin  to  the  adductor  longus,  the  adductor  brevis,  the 
obturator  externus,  and  the  gracilis.  The  posterior  surface  is  smooth,  looks  into 
the  pelvis,  and  affords  origin  to  the  levator  ani,  the  obturator  internus,  and  the  pubo- 
prostatic ligaments.  The  upper  border  or  crest  of  the  body  is  rough  and  presents 
laterally  a  prominent  bony  point,  known  as  the  tubercle  [tuberculum  pubicum] 
or  spine,  for  the  attachment  of  the  inguinal  (Poupart's)  ligament.  The  upper 
border  extends  from  the  pubic  tubercle  medialward  to  the  upper  end  of  the 
symphysis,  with  which  it  forms  the  angle  of  the  pubis.  The  upper  border  is  a 
short  horizontal  ridge,  which  gives  attachment  to  the  rectus  abdominis  and  pyram- 
idalis.  The  medial  border  is  oval  in  shape,  rough,  and  articular,  forming  with 
the  bone  of  the  opposite  side  the  symphysis  pubis  [facies  symphyseos].  The 
lateral  border  is  sharp  and  forms  part  of  the  boundary  of  the  obturator  foramen. 

The  inferior  ramus,  like  the  inferior  ramus  of  the  ischium,  with  which  it  is 
continuous,  is  thin  and  flattened.     To  its  anterior  surface  are  attached  the 


THE  COXAL  BONE 


173 


adductor  hrevis,  adductor  magnus,  and  obturator  externus.  The  posterior  surface 
is  smooth  and  gives  attachment  to  the  crus  penis  or  clitoridis,  the  sphincter  urethrce 
(urogenitalis) ,  the  obturator  internus,  and  the  urogenital  trigone  (triangular  liga- 
ment). The  lateral  border  forms  part  of  the  circumference  of  the  obturator 
foramen,  and  the  medial  border  forms  part  of  the  pubic  arch  and  gives  attach- 
ment to  the  gracilis. 

The  superior  ramus  extends  from  the  body  of  the  pubis  to  the  ilium,  forming 
by  its  lateral  extremity  the  anterior  one-fifth  of  the  articular  surface  of  the  acetab- 
ulum. It  is  prismatic  in  shape  and  increases  in  size  as  it  passes  laterally.  Above 
it  presents  a  sharp  ridge,  the  pecten  or  pubic  portion  of  the  terminal  (ilio-pectineal) 
line  continuous  with  the  iliac  portion  at  the  ilio-pectineal  eminence,  and  affording 


Fig.  207. — An  Immature  Coxal  (Innominate)  Bone,  showing  a  Cotyloid  Bone. 


Tha  cotyloid  bone 


attachment  to  the  conjoined  tendon  [falx  aponeurotica  inguinalis],  the  lacunar 
(Gimbernat's)  hgament,  the  reflected  inguinal  ligament  (fascia  triangularis), 
and  the  pubic  portion  of  the  fascia  lata;  the  ihac  portion  of  the  terminal  (ilio- 
pectineal)  line  gives  attachment  to  the  psoas  minor,  the  iliac  fascia,  and  the  pelvic 
fascia.  Immediately  in  front  of  the  pubic  portion  of  the  line  is  the  pectineal 
surface;  it  gives  origin  at  its  posterior  part  to  the  pectineus,  and  is  limited  below 
by  the  obturator  crest,  which  extends  from  the  pubic  tubercle  to  the  acetabular 
notch.  The  inferior  surface  of  the  ascending  ramus  forms  the  upper  boundary 
of  the  obturator  foramen  and  presents  a  deep  groove  [sulcus  obturatorius]  for  the 
passage  of  the  obturator  vessels  and  nerve.  The  posterior  surface  is  smooth, 
forms  part  of  the  anterior  wall  of  the  pelvic  cavity,  and  gives  attachment  to  a 
few  fibres  of  the  obturator  internus. 

According  to  the  BNA,  the  body  [corpus  ossis  pubis]  is  the  portion  corresponding  to  the 
acetabulum.  The  remainder  of  the  bone  is  described  as  consisting  of  the  ramus  superior  and 
the  ramus  inferior,  which  meet  at  the  symphysis.  Thus  the  divisions  according  to  the  BNA 
are  different  from  those  in  the  description  above  given. 

The  acetabulum  is  a  circular  depression  in  which  the  head  of  the  femur  is 
lodged  and  consists  of  an  articular  and  a  non-articular  portion.  The  articular 
portion  is  circumferential  and  semilunar  in  shape  [facies  lunata],  with  the  defi- 
ciency in  the  lower  segment.  One-fifth  of  the  acetabulum  is  formed  bj^  the  pubis, 
two-fifths  by  the  ischium,  and  the  remaining  two-fifths  are  formed  by  the  ilium. 
In  rare  instances  the  pubis  may  be  excluded  by  a  fourth  element,  the  cotyloid 
bone.  The  non-articular  portion  [fossa  acetabuli]  is  formed  mainly  by  the 
ischium,  and  is  continuous  below  with  the  margin  of  the  obturator  foramen. 
The  articular  portion  presents  a  lateral  rim  to  which  the  glenoid  lip  is 
attached,  and  a  medial  margin  to  which  the  synovial  membrane  which  excludes 


174 


THE  SKELETON 


the  ligamentum  teres  from  the  synovial  cavity  is  connected.  The  opposite 
extremities  of  the  articular  lunate  surface  which  limit  the  acetabular  notch  are 
united  by  the  transverse  ligament,  and  through  the  acetabular  foramen  thus 
formed  a  nerve  and  vessels  enter  the  joint. 

The  obturator  (thyreoid)  foramen  is  sHuated  between  the  ischium  and  pubis. 
Its  margins  are  thin,  and  serve  for  the  attachment  of  the  obturator  membrane. 
At  the  upper  and  posterior  angle  it  is  deeply  grooved  for  the  passage  of  the  obtu- 
rator vessels  and  nerve. 


Fig.  208. — The  Pelvis  of  a  Fcetus  at  Birth,  to  show  the  Three  Portions  of  the 

CoxAL  Bones. 


The  nucleus  for  the  pubis  appears 
bout  the  end  of  the  fourth  month 
3  nucleus  for  the  ischium  appears 
Q  the  third  month 


Blood-supply. — The  chief  vascular  foramina  of  the  coxal  bone  are  found  where  the  bone  is 
thickest.  On  the  inner  surface,  the  ilium  receives  twigs  from  the  ilio-lumbar,  deep  circumflex 
iliac,  and  obturator  arteries,  by  foramina  near  the  crest,  in  the  iliac  fossa,  and  below  the  terminal 
line  near  the  greater  sciatic  notch.  On  the  outer  surface  the  chief  foramina  are  found  below 
the  inferior  gluteal  line  and  the  nutrient  vessels  are  derived  from  the  gluteal  arteries.  The 
ischium  receives  nutrient  vessels  from  the  obturator,  internal  and  external  circumflex  arteries, 
and  the  largest  foramina  are  situated  between  the  acetabulum  and  the  ischial  tuberosity.  The 
pubis  is  supplied  by  twigs  from  the  obturator,  internal  and  external  circumflex  arteries,  and 
from  the  pubic  branches  of  the  common  femoral  artery. 

Fig.  209. — Coxal  or  Hip-bone,  showing  Secondary  Centres. 

Appears  at  fifteen.     Unites  at  twenty- 


Appears  at  fifteen.     Unites  at  twenty. 


Appears  at  fifteen.     Fuses  at  twenty 


Fuses  at  twenty 


Ossification. — The  cartilaginous  representative  of  the  hip-bone  consists  of  three  distinct 
portions,  an  iliac,  an  ischiatic,  and  a  pubic  portion;  the  iliac  and  ischiatio  portions  first  unite 
and  later  the  pubic  portion,  so  that  eventually  there  is  found  a  single  cartilaginous  mass.  Early 
in  the  second  month  a  centre  of  ossification  appears  above  the  acetabulum  for  the  ilium.  A 
little  later  a  second  nucleus  appears  below  the  cavity  for  the  ischium,  and  this  is  followed  in 
the  fourth  month  by  a  deposit  in  the  pubic  portion  of  the  cartilage.     At  birth,  the  three  nuclei 


THE  PELVIS 


175 


are  of  considerable  size,  but  are  surrounded  by  relatively  wide  tracts  of  cartilage;  ossification 
has,  however,  extended  into  the  margin  of  the  acetabulum.  In  the  eighth  j^ear  the  rami  of  the 
pubis  and  ischium  become  united  by  bone,  and  in  the  tweKth  year  the  triradiate  cartilage  which 
separates  the  three  segments  of  the  bone  in  the  acetabulum  begins  to  ossify  from  several  centres. 
Of  these,  one  is  more  constant  than  the  others  and  is  known  as  the  acetabular  nucleus.  The 
triangular  piece  of  bone  to  which  it  gives  rise  is  regarded  as  the  representative  of  the  cotyloid 
or  acetabular  bone,  constantly  present  in  a  few  mammals.  It  is  situated  at  the  medial  part  of 
the  acetabulum  and  is  of  such  a  size  as  to  exclude  entirely  the  pubis  from  the  cavity.  With 
this  bone,  however,  it  eventually  fuses,  and  afterward  becomes  joined  with  the  ilium  and 

Fig.  210. — Coxal  or  Hip-bone  (Inner  Surface)  at  the  Eighth  Year. 


ischium,  so  that  by  the  eighteenth  or  twentieth  year  the  several  parts  of  the  acetabulum  have 
become  united.  In  the  fifteenth  year  other  centres  appear  in  the  cartilage  of  the  crest  of  the 
ilium,  the  anterior  inferior  iliac  spine,  the  tuberosity  of  the  ischium,  and  the  pubic  pecten.  The 
epiphyses  fuse  with  the  main  bone  about  the  twentieth  year.  The  fibrous  tissue  connected 
with  the  tubercle  of  the  pubis  represents  the  epipubio  bones  of  marsupials. 


THE  PELVIS 

The  pelvis  (figs.  211,  212,  213,  214)  is  composed  of  four  bones:  the  two  coxal 
or  hip-bones,  the  sacrum,  and  the  coccyx.  The  hip-bones  form  the  lateral  and 
anterior  boundaries,  meeting  each  other  in  front  to  form  the  pubic  symphysis 
[symphysis  ossium  pubis];  posteriorly  they  are  separated  by  the  sacrum.  The 
interior  of  the  pelvis  is  divided  into  the  major  and  minor  pelvic  cavity. 

The  major  (or  false)  pelvis  is  that  part  of  the  cavity  which  lies  above  the  ter- 
minal (ihopectineal)  lines  and  between  the  iliac  fossse.  This  part  belongs  really  to 
the  abdomen,  and  is  in  relation  with  the  hypogastric  and  iliac  regions. 

The  minor  (or  true)  pelvis  is  situated  below  the  terminal  (ilio-pectineal)  lines. 
The  upper  circumference,  known  as  the  superior  aperture  (inlet  or  brim)  of  the 
pelvis,  is  bounded  anteriorly  by  the  tubercle  and  pecten  of  the  pubis  on  each  side, 
posteriorly  by  the  anterior  margin  of  the  base  of  the  sacrum,  and  laterally  by  the 
terminal  lines.  The  inlet  in  normal  pelves  is  heart-shaped,  being  obtusely  pointed 
in  front;  posteriorly  it  is  encroached  upon  by  the  promontory  of  the  sacrum.  It 
has  three  principal  diameters;  of  these,  the  antero-posterior,  called  the  conjugate 
diameter  [conjugata],  is  measured  from  the  sacro-vertebral  angle  to  the  symphj^sis. 
The  transverse  diameter  represents  the  greatest  width  of  the  pelvic  cavity.  The 
oblique  diameter  is  measured  from  the  sacro-iliac  synchondrosis  of  one  side  to  the 
ilio-pectineal  eminence  of  the  other. 

The  cavity  of  the  minor  (true)  pelvis  is  bounded  in  front  by  the  pubes,  behind 
bjr  the  sacrum  and  coccj^x,  and  laterally  by  a  smooth  wall  of  bone  formed  in  part 
by  the  ilium  and  in  part  by  the  ischium.  The  cavity  is  shallow  in  front,  where  it 
is  formed  by  the  pubes,  and  is  deepest  posteriorly. 


176 


THE  SKELETON 


The  inferior  aperture,  or  outlet,  of  the  minor  pelvis  is  verj'  irregular,  and  en- 
croached upon  by  three  bony  pi'ocesses:  the  posterior  process  is  the  coccyx,  and 
the  two  lateral  processes  are  the  ischial  tuberosities.  They  separate  three  notches. 
The  anterior  notch  is  the  pubic  arch,  and  is  bounded  on  each  side  by  the  conjoined 
rami  of  the  pubes  and  ischium.     Each  of  the  two  remaining  gaps,  bounded  by  the 


Fig.  211.— The  Male  Pelvis. 


ischium  anteriorly,  the  sacrum  and  coccjrx  posteriorly,  and  the  ilium  above,  cor- 
responds to  the  greater  and  lesser  sciatic  notches.  These  are  converted  into 
foramina  bj^  the  sacro-tuberous  (great  sacro-sciatic)  and  sacro-spinous  (small 
sacro-sciatic)  ligaments. 

The  position  of  the  pelvis. — In  the  erect  position  of  the  skeleton  the  plane  of  the  pelvic 
inlet  forms  an  angle  with  the  horizontal  plane,  which  varies  in  indi%dduals  from  50°  to  60°. 


212. — The  Female  Pelvis. 


The  base  of  the  sacrum  in  an  average  pelvis  lies  nearly  ten  centimetres  (four  inches)  above  the 
upper  margin  of  the  symphysis  pubis. 

The  axis  of  the  pelvis.— This  is  an  imaginary  curved  line  drawn  through  the  minor  pelvis 
at  right  angles  to  the  planes  of  the  inlet,  cavity,  "and  outlet  through  then  central  points. 

As  the  posterior  wall,  formed  by  sacrum  and  coccyx,  is  nearly  five  inches  long  and  concave, 
and  the  anterior  waU  at  the  symphysis  pubis  one  one  and  a  half  to  two  inches  long,  it  follows 
that  the  axis  must  be  cm-ved. 


THE  PELVIS 


177 


The  average  measurements  of  the  diameters  of  the  minor  pehas  in  the  three  planes  are 
given  below: — 


Inlet... 
Cavit}' . 
Outlet . 


Conjugate  or 
axtero-posterior. 
a  inches  (10.6  cm.) 
4i      "       (11.8  cm.) 
3f      "       (9.0  cm.) 


Oblique. 
o    inches  (12.5  cm.) 
5i      "       (13.0  cm.) 
4i      "        (11.2  cm.) 


Thaxsverse. 
5t  inches  (13.0  cm.) 
4J      "       (11.8  cm.) 
4i      "       (10.6  cm.) 


Fig.  213. — M.^le  Pewis.     (Lateral  view.) 


Fig.  214. — Female  PEL-\as.     (Lateral  view.) 


There  is,  however,  a  difference  between  the  sexes,  the  diameters  of  the  male  pelvis  in 
general  averaging  slighth-  less,  and  those  of  the  female  sUghtly  greater  than  the  figures  above 
given. 

Differences  according  to  sex. — There  is  a  marked  difference  in  the  size  and  form  of  the 
male  and  female  pelvis,  the  pecularities  of  the  latter  being  necessary  to  qualify  it  for  its  func- 
tions in  partm-ition.     The  various  points  of  divergence  may  be  tabulated  as  follows: — 


M.\.LE. 

Bones  heavier  and  rougher. 

Ilia  less  vertical. 

Iliac  fossEB  deeper. 

Major  pehds  relatively  wider. 

Minor  pelvis  deeper. 

"         "        narrower. 
Superior  aperture  move  heart-shaped. 
Symphysis  deeper. 
Tuberosities  of  ischia  inflexed. 
Pubic  angle  narrow  and  pointed. 
Margins  of  ischio-pubic  rami  more  everted. 
Obturator  foramen  oval. 
Sacrum  narrower  and  more  curved. 
Capacity  of  minor  pelvis  less. 


Female. 
Bones  more  slender. 
Ilia  more  vertical. 
Iliac  fossae  shallower. 
Major  pelvis  relatively  narro'srer. 
Minor  pelvis  shallower. 

"         "        wider. 
Superior  aperture  more  oval. 
Symphj'sis  shallower. 
Tuberosities  of  ischia  everted. 
Pubic  arch  wider  and  more  rounded. 
Margins  of  ischio-pubic  rami  less  everted. 
Obturator  foramen  triangular. 
Sacrum  wider  and  less  curved. 
Capacity  of  minor  pelvis  greater. 


The  sexual  characters  of  the  pelvis  as  shown  by  A.  Thomson  are  manifest  as  early  as  the 
fourth  month  of  fcetal  life. 

Quite  recently  attention  has  been  drawn  by  D.  Derry  to  some  special  points  in  which  the 
OS  coxaj  differ  in  the  two  sexes,  and  two  figures  are  shown  here  in  which  one  of  these  points  is 
clearly  brought  out.  It  will  be  seen  that  the  great  sciatic  notch  is  larger  in  the  female,  and 
that  the  sacrum  projects  less  forward  at  its  apex.  Moreover  the  facies  auricularis  is  smaller 
whilst  below  and  in  front  of  this  surface,  the  sulcus  preauricularis,  a  depression  for  the  attach- 
ment of  the  ligamenta  sacroiliaca  anteriora,  is  usualh-  more  pronounced. 

In  comparison  with  the  pelves  of  lower  animals,  which,  speaking  generally,  are  elongated 
and  narrow,  the  human  pelvis  is  characterised  by  its  breadth,  shallowness,  and  great  capacity. 
Differences  are  also  to  be  recognised  in  the  form  of  the  pelvis  in  the  various  races  of  mankind,  the 
most  important  being  the  relation  of  the  antero-posterior  to  the  transverse  diameter,  measured 

at  the  inlet.    This  is  expressed  bj'  the  pelmc  index  = —^^-^r. 

transverse  diameter 
In  the  average  European  male  the  index  is  about  80;  in  the  lower  races  of  mankind,  90  to  95. 
Pelves  with  an  index  below  90  are  platypellic,  from  90  to  95  are  mesatipellic,  and  above  95 
dolichopellic.     (Sir  WiUiam  Turner.) 


178  THE  SKELETON 

THE  FEMUR 

The  femur  or  thigh  bone  (figs.  215,  216)  is  the  largest  and  longest  bone  in  the 
skeleton,  and  transmits  the  entire  weight  of  the  trunk  from  the  hip  to  the  tibia. 
In  the  erect  posture  it  inclines  from  above  downward  and  medially,  approaching 
at  the  lower  extremity  its  fellow  of  the  opposite  side,  but  separated  from  it  above 
by  the  width  of  the  true  pelvis.  It  presents  for  examination  a  superior  extremity, 
including  the  head,  neck,  and  two  trochanters,  an  inferior  extremity,  expanded 
laterally  into  two  condyles,  and  a  shaft. 

The  upper  extremity  is  surmounted  by  a  smooth,  globular  portion  called  the 
head,  forming  more  than  half  a  sphere,  directed  upward  and  medially  for  articu- 
lation with  the  acetabulum.  With  the  exception  of  a  small  rough  depression,  the 
fovea,  for  the  ligamentum  teres,  a  little  below  and  behind  the  centre  of  the  head, 
.  its  surface  is  covered  with  cartilage  in  the  recent  state.  The  head  is  connected 
with  the  shaft  by  the  neck,  a  stout  rectangular  column  of  bone  which  forms  with 
the  shaft,  in  the  adult,  an  angle  of  about  125*.  Its  anterior  surface  is  in  the  same 
plane  with  the  front  aspect  of  the  shaft,  but  is  marked  off  from  it  by  a  ridge  to 
which  the  capsule  of  the  hip-joint  is  attached.  The  ridge,  which  commences  at 
the  great  trochanter  in  a  small  prominence,  or  tubercle,  extends  obliquely  down- 
ward, and  winding  to  the  back  of  the  femur,  passes  by  the  lesser  trochanter  and 
becomes  continuous  with  the  medial  lip  of  the  linea  aspera,  on  the  posterior  aspect 
of  the  shaft.  This  ridge  forms  the  intertrochanteric  line  or  spiral  line  of  the  femur. 
The  intertrochanteric  line  receives  the  bands  of  the  ilio-femoral  thickening  of  the 
capsule  of  the  hip-joint.  The  posterior  surface  of  the  neck  is  smooth  and  concave 
and  its  medial  two-thirds  is  enclosed  in  the  capsule  of  the  hip-joint.  The  superior 
border  of  the  neck,  perforated  by  large  nutrient  foramina,  is  short  and  thick,  and 
runs  downward  to  the  great  trochanter.  The  inferior  border,  longer  and  narrower 
than  the  superior,  curves  downward  to  terminate  at  the  lesser  trochanter. 

The  trochanters  are  the  prominences  which  afford  attachment  to  the  rotator 
muscles  of  the  thigh;  they  are  two  in  number — great  and  lesser. 

The  great  trochanter  is  a  thick,  quadrilateral  process  surmounting  the  junction 
of  the  neck  with  the  shaft,  and  presents  for  examination  two  surfaces  and  four 
borders.  The  lateral  surface  is  broad,  rough,  and  continuous  with  the  lateral 
surface  of  the  shaft.  It  is  marked  by  a  diagonal  ridge  running  from  the  postero- 
superior  to  the  antero-inferior  angle,  which  receives  the  insertion  of  the  gluteus 
medius.  The  ridge  divides  the  surface  into  two  triangular  areas :  an  upper,  cov- 
ered by  the  gluteus  medius,  and  occasionally  separated  from  it  by  a  bursa,  and  a 
lower,  covered  by  a  bursa  to  permit  the  free  gliding  of  the  tendon  of  the  gluteus 
maximus.  Of  the  medial  surface  the  lower  and  anterior  portion  is  joined  with 
the  rest  of  the  bone;  the  upper  and  posterior  portion  is  free,  concave,  and  presents 
a  deep  depression,  the  trochanteric  or  digital  fossa,  which  receives  the  tendon  of 
the  obturator  externus.  The  fore  part  of  the  surface  is  marked  by  an  impression 
for  the  insertion  of  the  obturator  internus  and  two  gemelli. 

Of  the  four  borders,  the  superior,  thick  and  free,  presents  near  the  centre  an  oval  mark  for 
the  insertion  of  the  -piriformis;  the  anterior  border,  broad  and  irregular,  receives  the  gluteus 
minimus;  the  posterior  border,  thick  and  rounded,  is  continuous  with  the  intertrochanteric 
crest,  the  prominent  ridge  uniting  the  two  trochanters  behind.  Above  the  middle  of  this  line  is 
an  elevation,  termed  the  tubercle  of  the  quadratus,  for  the  attachment  of  the  upper  part  of  the 
quadralus  femoris.  The  inferior  border  corresponds  with  the  line  of  junction  of  the  base  of 
the  trochanter  with  the  shaft;  it  is  marked  by  a  prominent  ridge  for  the  origin  of  the  upper  part 
of  the  vastus  lateralis. 

The  lesser  trochanter  is  a  conical  eminence  projecting  medially  from  the  poste- 
rior and  mecUal  aspect  of  the  bone,  where  the  neck  is  continuous  with  the  shaft. 
Its  summit  is  rough  and  gives  attachment  to  the  tendon  of  the  ilio-psoas.  The 
fibres  of  the  iliacus  extend  beyond  the  trochanter  and  are  inserted  into  the  surface 
of  the  shaft  immediately  below. 

The  body  or  shaft  of  the  femur  is  almost  cylindrical,  but  is  slightly  flattened  in 
front  and  strengthened  behind  by  a  projecting  longitudinal  ridge,  the  linea  aspera, 
for  the  origin  and  insertion  of  muscles.  The  linea  aspera  extends  along  the  middle 
third  of  the  shaft  and  presents  a  medial  lip  and  a  lateral  lip  separated  by  a  narrow 
interval.  When  followed  into  the  upper  third  of  the  shaft,  the  three  parts  diverge. 
The  lateral  lip  becomes  continuous  with  the  gluteal  tuberosity  and  ends  at  the 
base  of  the  great  trochanter.     The  ridge  affords  insertion  to  the  gluteus  maximus, 


THE  FEMUR 


179 


Fig.  215. — The  Left  Femur.     (Anterior  view.) 

Greater  trochanter 


Superior  cervical  tubercl 


Adductor  tubercl 
Adductor  magnu; 


Capsular  line  — ^ 


Piriformis 

Obturator  internus  and  gemelli 


Gluteus  minimus 


Vastus  lateralis 


Fibular  collateral  ligament 
Popliteus 


Literal  condyle 


180 


THE  SKELETON 


Fro.  216. — The  Left  Femur.     (Posterior  view.) 
Obturator  externus 


.  Fovea  for  ligamentum  teres 


Gluteus  medius 


-^'^ 


Quadratus  femoris 


Capsule 
-Intertrochanteric  crest 


Vastus  lateralis  - 

Gluteal  tuberosity 

Gluteus  maximus       |r~ 


-Psoas 

-Lesser  trochante 

-Iliacus 
-Pectineus 


-Adductor  brevis 


Adductor  magnus 


Lateral  lip  of  the  Hnea  aspera 
Biceps 


Vastus  laterahs  - 


Vastus  intermedn 


Intervening  space  of  the  linea  aspera 
"Adductor  longus 


Vastus  medialis 
"Medial lip  of  the  linea  aspera 


.  Nutrient  foramen 


-  For  femoral  artery 


Plantaris  _ 
Gastrocnemius- 


Anterior  crucial  ligament- 
Intercondylar  fossa- 


l« 


pCapsule 

-Tibial  collateral  ligament 


Lateral  condyle 


Posterior  crucial  ligament 


'  Medial  condyle 


THE  FEMUR 


181 


and  when  very  prominent  is  termed  the  third  trochanter.  The  medial  Hp  curves 
medialward  below  the  lesser  trochanter,  where  it  becomes  continuous  with  the 
intertrochanteric  line;  the  intervening  portion  bifurcates  and  is  continued  upward 
as  two  lines,  one  of  which  ends  at  the  small  trochanter,  and  receives  some 
fibres  of  the  iliacus,  whilst  the  other  is  the  linea  pectinea  and  marks  the  insertion 
of  the  pectineus  muscle. 

Toward  the  lower  third  of  the  shaft  the  medial  and  lateral  lips  of  the  linea 
aspera  again  diverge,  and  are  prolonged  to  the  condyles  by  the  medial  and  lateral 
supra-condylar  lines,  enclosing  between  them  a  triangular  surface  of  bone,  the 
popliteal  surface  [planum  popliteum]  of  the  femur,  which  forms  the  upper  part  of 
the  floor  of  the  popliteal  space.  The  lateral  line  is  the  more  prominent  and  ter- 
minates below  in  the  lateral  epicondyle.  The  medial  one  is  interrupted  above, 
where  the  femoral  vessels  are  in  relation  with  the  bone,  better  marked  below, 
where  it  terminates  in  the  adductor  tubercle,  a  small  sharp  projection  at  the  sum- 
mit of  the  medial  epicondyle,  which  affords  attachment  to  the  tendon  of  the  ad- 
ductor magnus. 

Fig.  217. — A  Diagram  to  show  the  Pressure  and  Tension  Curves  of  the  Femur. 
(After  Wagstaffe.) 


Near  the  centre  of  the  linea  aspera  is  the  foramen  for  the  medullary  artery,  directed  upward 
toward  the  head  of  the  bone. 

From  the  medial  lip  of  the  linea  aspera  and  the  lower  part  of  the  int-ertrochanteric  line 
arises  the  vastus  medialis  (internus),  and  from  the  lateral  lip  and  the  side  of  the  gluteal  ridge 
arises  the  vastus  lateralis  (externus).  The  adductor  magnus  is  inserted  into  the  medial  lip  of 
the  linea  aspera,  from  the  medial  side  of  the  gluteal  tuberosity  above,  and  the  medial  supra- 
condylar line  below.  Between  the  adductor  magnus  and  vastus  medialis  (internus)  four  muscles 
are  attached:  the  pectineus  and  iliacus  above,  then  the  adductor  brevis,  and  lowest  of  all,  the 
adductor  longus.  Above,  in  the  interval  between  the  adductor  magnus  and  the  vastus  lateralis 
(externus),  the  gluteus  maximus  is  inserted;  in  the  interval  lower  down  is  the  short  head  of 
the  biceps,  taking  origin  from  the  lower  two-thirds  of  the  lateral]  lip  of  the  linea  aspera  and  the 
upper  two-thirds  of  the  lateral  supra-condylar  line.  On  the  popliteal  surface  of  the  bone,  just 
above  the  condyles,  are  two  rough  areas  from  which  fibres  of  the  two  heads  of  the  gastrocnemius 
take  origin.  Above  the  area  for  the  lateral  head  of  the  gastrocnemius  is  a  slight  roughness  for 
the  plantaris. 

For  purposes  of  description  it  is  convenient  to  regard  the  shaft  of  the  femur  as 
presenting  anterior,  medial,  and  lateral  surfaces,  although  definite  borders  separat- 
ing the  surfaces  from  one  another  do  not  exist.  All  three  surfaces  are  smooth 
and  the  anterior  is  not  separated  from  the  lateral  by  ridges  of  any  kind.  In  the 
middle  third  of  the  shaft  the  medial  and  lateral  surfaces  approach  one  another 
behind,  being  separated  by  the  linea  aspera. 


182 


THE  SKELETON 


The  shaft  is  overlapped  on  its  medial  side  by  the  vastus  medialis  (internus) ,  and 
on  its  lateral  side  by  tlie  vastus  lateralis  (externus).  The  upper  three-fourths  of 
the  anterior  and  lateral  surfaces  afford  origin  to  the  vastus  intermedius  (crureus), 
and  the  lower  fourth  of  the  anterior  surface,  to  the  articularis  genu  (sub-crureus) . 
The  medial  surface  is  free  from  muscular  attachment. 


Fig.  218. — Transverse  Section  op  Shaft  of 
Femtjr  to  show  the  Medttllary  Cavity. 


Fig.  219. — Section  of  Upper  End  of  Femur 
to  show  the  Calcar  Femorale. 


Lateral  lip  Linea  aspera  Medial  Up 

.  Nutrient  canal 


Lateral  surface 


Medial  surf  ace 


Anterior  surface 


Fig.  220. — The  Femur  at  Birth. 


The  lower  extremity  presents  two  cartilage-covered  eminences  or  condyles, 
separated  behind  by  the  intercondyloid  fossa.  The  lateral  condyle  is  wider 
than  its  fellow  and  more  prominent  anteriorly;  the  medial  condyle  is  narrower, 
more  prominent,  and  longer,  to  compensate  for  the  obliquity  of  the  shaft.  When 
the  femur  is  in  the  natural  position,  the  inferior  surfaces  of  the  condyles  are  on  the 


THE  FEMUR 


183 


same  plane,  and  almost  parallel,  for  articulation  with  the  upper  surfaces  on  the 
head  of  the  tibia.  The  two  condyles  are  continuous  in  front,  forming  a  smooth 
trochlear  surface  [facies  patellaris]  for  articulation  with  the  patella.  This  surface 
presents  a  median  vertical  groove  and  two  convexities,  the  lateral  of  which  is 
wider,  more  prominent,  and  prolonged  farther  upward.  The  patellar  surface  is 
faintly  marked  off  from  the  tibial  articular  surfaces  by  two  irregular  grooves, 
best  seen  while  the  lower  end  is  still  coated  with  cartilage.  The  lateral  groove 
commences  on  the  medial  margin  of  the  lateral  condyle  near  the  front  of  the 
intercondylar  fossa,  and  extends  obliquely  forward  to  the  lateral  margin  of  the 
bone.  The  general  direction  of  the  medial  groove  is  from  front  to  back,  turning 
medially  in  front  and  extending  backward  as  a  faint  ridge  which  marks  off  from  the 


Fig.  221. — The  Left  Femur  at  the  Twentieth  Year.     (Posterior  view ,) 
The  figure  shows  the  relations  of  the  epiphysial  and  capsular  lines. 


Appears  in  the  firsts  and  fuses  in  the 
nineteenth  year 


the  f  ourth,  and  unites 
the  e  ighteenth  year 


Appears  in  the  fourteenth,  and  unite 
in  the  seventeenth  year 


Appears  early  in  the  ninth  month  of, 
intra-uterine  life,  and  unites  at 
the  twentieth  year 


rest  of  the  medial  condyle  a  narrow  semilunar  facet  for  articulation  with  the 
medial  perpendicular  facet  of  the  patella  in  extreme  flexion.  The  grooves  receive 
the  semilunar  menisci  in  the  extended  position  of  the  joint.  The  tibial  surfaces 
are  almost  parallel  except  in  front,  where  the  medial  turns  laterally  to  become 
continuous  with  the  patellar  surface. 

The  opposed  surfaces  of  the  two  condyles  form  the  boundaries  of  the  inter- 
condylar fossa  and  give  attachment  to  the  crucial  ligaments  which  are  lodged 
within  it.  The  posterior  crucial  ligament  is  attached  to  the  fore  part  of  the  lateral 
surface  of  the  medial  condyle  and  the  anterior  crucial  ligament  to  the  back  part  of 
the  medial  surface  of  the  lateral  condyle.  The  two  remaining  surfaces  of  the 
condyles  are  broad  and  convex,  and  each  presents  an  epicondyle  (tuberosity)  for 
the  attachment  of  lateral  ligaments.  The  medial  epicondyle,  the  larger  of  the 
two,  is  surmounted  by  the  adductor  tubercle,  behind  which  is  an  impression  for 


184 


THE  SKELETON 


the  medial  head  of  the  gastrocnemius  on  the  upper  aspect  of  the  condyle;  below 
and  behind  the  lateral  epicondyle  is  a  deep  groove  which  receives  the  tendon  of 
the  popliteus  muscle  when  the  knee  is  flexed,  and  its  anterior  end  terminates  in 
a  pit  from  which  the  tendon  takes  origin.  Above  the  lateral  epicondyle  is  a 
rough  impression  for    the  lateral  head  of  the  gastrocnemius. 

The  interior  of  the  shaft  of  the  femur  is  hollowed  out  by  a  large  medullary  canal,  and  the 
extremities  are  composed  of  cancellated  tissue  invested  by  a  thin  compact  la3'er.  The  arrange- 
ment of  the  cancelli  in  the  upper  end  of  the  bone  forms  a  good  illustration  of  the  effect  produced 
by  the  mechanical  conditions  to  which  bones  are  subject.  In  the  upper  end  of  the  bone  the 
cancellous  tissue  is  arranged  in  divergent  curves.  One  system  springs  from  the  lower  part  of 
the  neck  and  upper  end  of  the  shaft  medially  and  spreads  into  the  great  trochanter  ('pressure 
lamellae').  A  second  system  springs  from  the  lateral  part  of  the  shaft  and  arches  upward  into 
the  neck  and  head  ('tension  lamelte'),  crossing  the  former  almost  at  right  angles.  A  second  set 
of  pressure  lamellae  springs  from  the  lower  thick  wall  of  the  neck,  and  extends  into  the  upper 
part  of  the  head  to  end  perpendicularly  in  the  articular  surface  mainly  along  the  lines  of  greatest 
pressure.  A  nearly  vertical  plate  of  compact  tissue  (calcar  femorale)  projects  into  the  neck 
of  the  bone  from  the  inferior  cervical  tubercle  toward  the  great  trochanter.  This  is  placed  in 
the  line  through  which  the  weight  of  the  body  falls,  and  adds  to  the  stability  of  the  neck  of  the 
bone;  it  is  said  to  be  liable  to  absorption  in  old  age.  In  the  lower  end  of  the  bone  the  vertical 
and  horizontal  fibres  are  so  disposed  as  to  form  a  rectangular  meshwork. 

Blood-supply. — The  head  and  neck  of  the  femur  receive  branches  from  the  inferior  gluteal, 
obturator,  and  circumflex  arteries,  and  the  trochanters  from  the  circumflex  arteries.  The 
nutrient  vessel  of  the  shaft  is  derived  from  either  the  second  or  third  perforating  artery,  or 
there  may  be  two  nutrient  vessels  arising  usually  from  the  first  and  third  perforating.  The 
vessels  of  the  inferior  extremity  arise  from  the  articular  branches  of  the  popliteal  and  the 
anastomotic  branch  of  the  femoral  (supremagenu). 

Ossification. — The  femur  is  ossified  from  one  primary  centre  for  the  shaft  and  from  four 
epiphysial  centres.  The  shaft  begins  to  ossify  in  the  seventh  week  of  intra-uterine  life.  Early 
in  the  ninth  month  a  nucleus  appears  for  the  lower  extremity.  During  the  first  year  the  nucleus 
for  the  head  of  the  bone  is  visible,  and  in  the  fourth  year  that  for  the  trochanter  major.  The 
centre  for  the  lesser  trochanter  appears  about  the  thirteenth  or  fourteenth  year.  The  lesser 
trochanter  joins  the  shaft  at  the  seventeenth,  the  great  trochanter  at  the  eighteenth,  the  head 
about  the  nineteenth,  and  the  lower  extremity  at  the  twentieth  year. 

The  neck  of  the  femur  is  an  apophysis,  or  outgrowth  from  the  shaft.  The  line  of  fusion  of 
the  condylar  epiphysis  with  the  shaft  passes  through  the  adductor  tubercle. 

The  morphological  relation  of  the  patellar  facet  to  the  tibial  portions  of  the  condyles  is 
worthy  of  notice.  In  a  few  mammals,  such  as  the  ox,  this  facet  remains  separated  from  the 
condyles  by  a  furrow  of  rough  bone, 

The  angle  which  the  neck  of  the  femur  forms  with  the  shaft  at  birth  measures,  on  an  average, 
160°.  In  the  adult  it  varies  from  110°  to  140°;  hence  the  angle  decreases  greatly  during  the 
period  of  growth.  When  once  growth  is  completed,  the  angle,  as  a  rule,  remains  fixed. 
(Humphry.) 

THE  PATELLA 

The  patella  (fig.  222)  or  knee-pan,  situated  in  front  of  the  knee-joint,  is  a  sesa- 
moid bone,  triangular  in  shape,  developed  in  the  tendon  of  the  quadriceps  femoris. 
Its  anterior  surface,  marked  by  numerous  longitudinal  striae,  is  slightly  convex,  and 


Fig.  222.- 

Anterior  surface 


-The  Left  Patella. 


perforated  by  small  openings  which  transmit  nutrient  vessels  to  the  interior  of  the 
bone.  It  is  covered  in  the  recent  state  by  a  few  fibres  prolonged  from  the  com- 
mon tendon  of  insertion  (supra-patellar  tendon)  of  the  quadriceps  femoris,  into  the 
ligamentum  patellae  (infra-patellar  tendon),  and  is  separated  from  the  skin  by  one 


THE  TIBIA  185 

or  more  bursse.  The  posterior  surface  is  largely  articular,  covered  with  cartilage 
in  the  recent  state,  and  divided  by  a  slightly  marked  vertical  ridge,  corresponding 
to  the  groove  on  the  trochlear  surface  of  the  femur,  into  a  lateral  larger  portion 
for  the  lateral  condyle,  and  a  medial  smaller  portion  for  the  medial  condyle. 
Close  to  the  medial  edge  a  faint  vertical  ridge  sometimes  marks  off  a  narrow  articu- 
lar facet,  for  the  lateral  margin  of  the  medial  condyle  of  the  femur  in  extreme 
flexion  of  the  leg.  Below  the  articular  surface  is  a  rough,  non-articular  depression, 
giving  attachment  to  the  ligamentum  patellae,  and  separated  by  a  mass  of  fat  from 
the  head  of  the  tibia. 

The  base  or  superior  border  is  broad,  sloped  from  behind  downward  and  for- 
ward, and  affords  attachment,  except  near  the  posterior  margin,  to  the  common 

Fig.  223. — The  Superior  Border  or  Base  of  the  Left  Patella. 
Anterior  surface 


tendon  of  the  quadriceps.  The  borders,  thinner  than  the  base,  converge  to  the 
apex  below,  and  receive  parts  of  the  two  vasti  muscles.  The  apex  forms  a  blunt 
point  directed  downward,  and  gives  attachment  to  the  ligamentum  patellae,  by 
which  the  patella  is  attached  to  the  tibia. 

Structurally  the  patella  consists  of  dense  cancellous  tissue  covered  by  a  thin  compact  layer, 
and  it  receives  nutrient  vessels  from  the  articular  branch  of  the  suprema  genu  (anastomotic), 
the  anterior  tibial  recurrent,  and  the  inferior  articular  branches  of  the  popliteal. 

Ossification. — The  cartilaginous  deposit  in  the  tendon  of  the  quadriceps  muscle  takes  place 
in  the  fourth  month  of  intra-uterine  life.  Ossification  begins  from  a  single  centre  during  the 
third  year,  and  is  completed  about  the  age  of  puberty. 

THE  TIBIA 

The  tibia  (figs.  224,  225)  or  shin-bone  is  situated  at  the  front  and  medial  side 
of  the  leg  and  nearly  parallel  with  the  fibula.  Excepting  the  femur,  it  is  the 
largest  bone  in  the  skeleton,  and  alone  transmits  the  weight  of  the  trunk  to  the 
foot.  It  articulates  above  with  the  femur,  below  \vith  the  tarsus,  and  laterally 
with  the  fibula.     It  is  divisible  into  two  extremities  and  a  shaft. 

The  upper  extremity  (or  head)  consists  of  two  lateral  eminences,  or  condyles. 
Their  superior  articular  surfaces  receive  the  condyles  of  the  femur,  the  articular 
parts  being  separated  by  a  non-articular  interval,  to  which  ligaments  are  attached. 
The  medial  articular  surface  is  oval  in  shape  and  concave  for  the  medial  condyle 
of  the  femur.  The  lateral  articular  surface  is  smaller,  somewhat  circular  in  shape, 
and  presents  an  almost  plane  surface  for  the  lateral  condyle.  The  peripheral 
portion  of  each  articular  surface  is  overlaid  by  a  fibro-cartilaginous  meniscus  of 
semilunar  shape,  connected  with  the  margins  of  the  condyles  by  bands  of  fibrous 
tissue  termed  coronary  ligaments.  Each  semilunar  meniscus  is  attached  firmly 
to  the  rough  interval  separating  the  articular  surfaces.  This  interval  is  broad 
and  depressed  in  front,  the  anterior  intercondyloid  fossa,  where  it  affords  attach- 
ment to  the  anterior  extremities  of  the  medial  and  lateral  menisci  and  the  anterior 
crucial  ligament;  elevated  in  the  middle  to  form  the  intercondyloid  eminence  or 
spine  of  the  tibia,  a  prominent  eminence,  presenting  at  its  summit  two  compressed 
intercondyloid  tubercles,  on  to  which  the  condylar  articular  surfaces  are  prolonged ; 
the  posterior  aspect  of  the  base  of  the  eminence  affords  attachment  to  the  posterior 
extremities  of  the  lateral  and  medial  semilunar  menisci,  and  limits  a  deejj  notch, 
inclined  toward  the  medial  condyle,  known  as  the  posterior  intercondyloid  fossa 
or  popliteal  notch.  It  separates  the  condyles  on  the  posterior  aspect  of  the  head 
and  gives  attachment  to  the  posterior  crucial  ligament,  and  part  of  the  posterior 
ligament  of  the  knee-joint.  Anteriorly,  the  two  condyles  are  confluent,  and  form 
a  somewhat  flattened  surface  of  triangular  outline,  the  apex  of  which  forms  the 
tuberosity  of  the  tibia.     The  tuberosity  is  divisible  into  two  parts.     The  upper 


186 


THE  SKELETON. 


part,  rounded  and  smooth,  receives  the  attachment  of  the  ligamentum  patellse. 
The  lower  part  is  rough,  and  into  its  lateral  edges  prolongations  of  the  ligamentum 
patella  are  inserted.  A  prominent  bursa  intervenes  between  the  ligament  and 
the  anterior  aspect  of  the  upper  extremity  of  the  bone. 

Fig.  224. — -The  Left  Tibia  and  Fibitla.     (Anterior  view.) 
Intercondyloid  eminence 


Medial  meniscus 
Coronary  ligament 
Anterior  crucial  ligament- 
Medial  condyle 

Tibial  collateral  ligament 
Ligamentum  patellge 

Gracilis 
Sartorius 


border  of  crest  of  the  tibi 


Medial  surface  of  tibia, 


Interosseous  membrane- 


Anterior  ligament  of  ankle-joint 

Deltoid  ligament- 
Medial  malleolus- 


Lateral    meniscus 
Capsule 
Lateral  condyle 
Biceps  and  the  anterior 
tibio-fibular  ligament 

Fibular  collateral  ligament 


Extensor  digitorum  longus 


Peroneus  longus 


Peroneus  brevis 


Extensor  digitorum  longus 


Peroneal  surfa.ce  of  fibula 


Extensor  surface  of  fibula 
Extensor  hallucis  longus 


Peroneus  tertius 


Subcutaneous  portion 


Anterior  tibio-fibular  ligament 


Lateral  malleolus 

Anterior  talo-fibular  ligament 


The  medial  condyle  is  less  prominent  though  more  extensive  than  the  lateral,  and  near  the 
posterior  part  of  its  circumference  is  a  deep  horizontal  groove  for  the  attachment  of  the 
central  portion  of  the  semimembranosus  tendon.     The  margins  of  this  groove,  and  the  surface 


THE  TIBIA 


187 


of  bone  below,  give  attachment  to  the  tibial  (internal)  lateral  ligament  of  the  knee.  On  the 
under  aspect  of  the  lateral  condyle  is  a  rounded  articular  facet  for  the  head  of  the  fibula,  flat 
and  nearly  circular  in  outline,  directed  downward,  backward,  and  laterally.  The  circumfer- 
ence of  the  facet  is  rough  and  gives  attachment  to  the  ligaments  of  the  superior  tibio-fibular 
joint,  while  above  and  in  front  of  the  facet,  at  the  junction  of  the  anterior  and  lateral  surfaces 

Fig.  225. — The  Left  Tibia  and  Fibula.     (Posterior  view.) 

Posterior  intercondyloid  notch 
Lateral  meniscus ^^__^  ~f^  1  iV^-= ^ Medial    meniscus 

Capsule 3(f*^*«io«.»    ^*      '*!>uui»--i^'ir^ Capsule 

Posterior  crucial  ligament V^g,;  •  ■■  vyf^in.      kT  vJ 

j^pgx ^      \'      ^.L-w    ^  J£Buff'*'w**>Kk*^ 'Semimembranosus 

Posterior  tibio-fibular  ligament' 


Flexor  hallucis  longus- 


Flexor  surface  of  fibula 


Nutrient  foramen' 


Peroneus  brevis 


Posterior  tibio-fibular  ligament' 
Groove  for  flexor  hallucis  longus- 

Posterior  talo-fibular  ligament 
Calcaneo-fibular  ligament 


Nutrient  foramen 


flexor  digitorum  longus 


Groove  for  tibialis  posterior 
and  flexor  digitorum  longus 


Deltoid  ligament 


Posterior  ligament  of  ankle-joint 


of  the  condyle,  is  a  ridge  for  the  ilio-tibial  band.  A  slip  from  the  tendon  of  the  biceps  and  parts 
of  the  extensor  longus  digitorum  and  peroneus  longus  muscles  are  attached  to  the  head  below 
the  ilio-tibial  band. 


188 


THE  SKELETON 


The  shaft  or  body  [corpus]  of  the  tibia,  thick  and  prismatic  above,  becomes 
thinner  as  it  descends  for  about  two-thirds  of  its  length,  and  then  gradually  ex- 
pands toward  its  lower  extremity.  It  presents  for  examination  three  borders  and 
three  surfaces.  The  anterior  border  is  very  prominent  and  known  as  the  anterior 
crest  of  the  tibia.  It  commences  above  on  the  lateral  edge  of  the  tuberosity  and 
terminates  below  at  the  anterior  margin  of  the  medial  malleolus.  It  runs  a  some- 
what sinuous  course,  and  gives  attachment  to  the  deep  fascia  of  the  leg.  The 
medial  border  extends  from  the  back  of  the  medial  condyle  to  the  posterior  margin 
of  the  medial  malleolus,  and  affords  attachment  above,  for  about  three  inches,  to 


Fig.  226. — The  Tibia  and  Fibula  at  the  Sixteenth  Yeae. 
The  figure  shows  the  relations  of  the  epiphysial  and  capsular  lines. 


apsule 
.Appears   at  birth;   unites  at  twenty- 
one  :  but  union  is  sometimes  delayed 
to  twenty-five 

Appears  at  the  fourth  year;  unites  at 
twenty -four 


Capsule 
Appears  at  the 
twenty 


cond  year;  unites  at 


the  tibial  (internal)  lateral  ligament  of  the  knee-joint  and  in  the  middle  third,  to 
the  soleus.  The  interosseous  crest  or  lateral  border,  thin  and  prominent,  gives 
attachment  to  the  interosseous  membrane.  It  commences  in  front  of  the  fibular 
facet,  on  the  upper  extremity,  and  toward  its  termination  bifurcates  to  enclose  a 
triangular  area  for  the  attachment  of  the  interosseous  ligament  uniting  the  lower 
ends  of  the  tibia  and  fibula. 

The  medial  surface  is  bounded  by  the  medial  margin  and  the  anterior  crest;  it 
is  broad  above,  where  it  receives  the  insertions  of  the  sartorius,  gracilis,  and  semi- 
tendinosus;  convex  and  subcutaneous  in  the  remainder  of  its  extent.  The  lateral 
surface  lies  between  the  crest  of  the  tibia  and  the  interosseous  crest.  The  upper 
two-thirds  presents  a  hollow  for  the  origin  of  the  tibialis  anterior;  the  rest  of  the 


THE  FIBULA  189 

surface  is  convex  and  covered  by  the  extensor  tendons  and  the  anterior  tibial 
vessels.  The  posterior  surface  is  limited  by  the  interosseous  crest  and  the  medial 
border.  The  upper  part  is  crossed  obliquely  by  a  rough  popliteal  line,  extending 
from  the  fibular  facet  on  the  lateral  condyle  to  the  medial  border,  a  little  above  the 
middle  of  the  bone. 

The  popliteal  line  gives  origin  to  the  soleus  and  attachment  to  the  popliteal  fascia,  while 
the  triangular  surface  above  is  occupied  by  the  popliieus  muscle.  Descending  along  the 
posterior  surface  from  near  the  middle  of  the  popliteal  line  is  a  vertical  ridge,  well  marked  at 
its  commencement,  but  gradually  becoming  indistinct  below.  The  portion  of  the  surface 
between  the  ridge  and  the  medial  border  gives  origin  to  the  flexor  digilorum  longus;  the  lateral 
and  narrower  part,  between  the  ridge  and  the  interosseous  border,  to  fibres  of  the  tibialis 
posterior.  The  lower  third  of  the  posterior  surface  is  covered  by  flexor  tendons  and  the  posterior 
tibial  vessels.  Immediately  below  the  popliteal  line  and  near  the  interosseous  border  is  the  large 
medullary  foramen  directed  obliquely  downward. 

The  lower  extremity,  much  smaller  than  the  upper,  is  quadrilateral  in  shape 
and  presents  a  strong  process  called  the  medial  malleolus,  projecting  downward 
from  its  medial  side.  The  anterior  surface  of  the  lower  extremity  is  smooth  and 
rounded  above,  where  it  is  covered  by  the  extensor  tendons,  rough  and  depressed 
below  for  the  attachment  of  the  anterior  ligament  of  the  ankle-joint.  It  some- 
times bears  a  facet  for  articulation  with  the  neck  of  the  talus  (astragalus) .  (A. 
Thomson.)  The  posterior  surface  is  rough  and  is  marked  by  two  grooves.  The 
medial  and  deeper  of  the  two  encroaches  on  the  malleolus,  and  receives  the  tendons 
of  the  tibialis  posterior  and  flexor  digitorum  longus;  the  lateral,  very  shallow  and 
sometimes  indistinct,  is  for  the  tendon  of  the  flexor  hallucis  longus.  The  lateral  sur- 
face is  triangular  and  hollowed  for  the  reception  of  the  lower  end  of  the  fibula  and 
rough  for  the  interosseous  ligament  which  unites  the  two  bones,  except  near  the 
lower  border,  where  there  is  usually  a  narrow  surface,  elongated  from  before  back- 
ward, covered  with  cartilage  in  the  recent  state  for  articulation  with  the  fibula. 
The  lines  in  front  of  and  behind  the  triangular  surface  afford  attachment  to  the 
anterior  and  posterior  ligaments  of  the  inferior  tibio-fibular  articulation.  The 
medial  surface,  prolonged  downward  on  the  medial  malleolus,  is  rough,  convex, 
and  subcutaneous.  The  lateral  surface  of  this  process  is  smooth  and  articulates 
with  the  facet  on  the  medial  side  of  the  talus  (astragalus).  Its  lower  border  is 
notched,  and  from  the  notch,  as  well  as  from  the  tip  and  anterior  border,  the  fibres 
of  the  deltoid  Hgament  of  the  ankle-joint  descend.  The  inferior  or  terminal 
surface,  by  which  the  tibia  articulates  with  the  talus,  is  of  quadrilateral  form, 
concave  from  before  backward,  wider  in  front  than  behind,  and  laterally  than 
medially  where  it  is  continuous  with  the  lateral  surface  of  the  malleolus. 

The  occasional  facet  on  the  anterior  siu'face  of  the  lower  extremity  of  the  tibia  is  a  pressure 
facet,  produced  by  extreme  flexion  of  the  ankle  joint.  It  is  therefore  sometimes  designated  as 
the     squatting  facet."     (See  fig.  333.) 

Blood-supply. — The  tibia  is  a  very  vascular  bone.  The  nutrient  artery  of  the  shaft  is 
furnished  by  the  posterior  tibial,  and  is  the  largest  of  its  kind  in  the  body.  The  head  of  the 
bone  receives  numerous  branches  from  the  inferior  articular  arteries  of  the  popliteal  and  the 
recurrent  branches  of  the  anterior  and  posterior  tibial.  The  lower  extremity  receives  twigs 
from  the  posterior  and  anterior  tibial,  the  peroneal,  and  the  medial  malleolar  arteries. 

Ossification. — The  tibia  is  ossified  from  one  principal  centre  for  the  shaft,  which  appears 
in  the  eighth  week  of  intra-uterine  life,  and  two  epiphyses,  the  centres  for  which  appear  in  the 
cartilaginous  head  of  the  bone  toward  the  end  of  the  ninth  month,  and  in  the  lower  extremity 
during  the  second  year.  The  latter  unites  with  the  shaft  at  eighteen,  but  the  union  of  the  head 
with  the  shaft  does  not  take  place  until  the  twenty-first  year,  and  it  may  even  be  delayed  until 
twenty-five.  The  upper  part  of  the  tubercle  of  the  tibia  is  ossified  from  the  upper  epiphysis, 
and  the  lower  part  from  the  diaphysis. 

THE  FIBULA 

The  fibula  (figs.  224,  225)  is  situated  on  the  lateral  side  of  the  leg  and,  in 
proportion  to  its  length  is  the  most  slender  of  all  the  long  bones.  It  is  placed 
nearly  parallel  to  the  tibia  with  which  it  is  connected  above  and  below.  In  man 
it  is  a  rudimentary  bone  and  bears  none  of  the  weight  of  the  trunk,  but  is  retained 
on  account  of  the  muscles  to  which  it  gives  origin  and  its  participation  in  the 
formation  of  the  ankle-joint.  Like  other  long  bones,  it  is  divisible  into  a  shaft 
and  two  extremities. 

The  head  [capitulum  fibulae],  or  upper  extremity,  is  a  rounded  prominence. 
Its  upper  surface  presents  laterally  a  rough  eminence  for  the  attachment  of  the 


190  THE  SKELETON 

biceps  tendon  and  the  fibular  (long  external)  collateral  ligament  of  the  knee-joint, 
medially  it  presents  a  round  or  oval  facet  [fades  articularis  capituli],  directed 
upward,  forward,  and  medially,  for  articulation  with  the  lateral  condyle  (tuber- 
osity) of  the  tibia.  The  margin  of  the  facet  gives  attachment  to  the  articular 
capsule  of  the  superior  tibio-fibular  articulation.  Posteriorly,  the  head  rises  into 
a  pointed  apex  (styloid  process),  which  affords  attachment  to  the  short  lateral 
ligament  of  the  knee-joint,  and  on  the  lateral  side,  to  part  of  the  biceps  tendon. 

The  posterior  aspect  of  the  head  gives  attachment  to  the  soleus,  the  lateral  aspect,  extend- 
ing also  in  front  of  the  eminence  for  the  biceps,  to  the  peroneus  longus;  from  the  anterior  aspect 
fibres  of  the  extensor  digiiorum  longus  arise,  whilst  the  medial  side  lies  adjacent  to  tlie  tibia. 

The  shaft  [corpus  fibulse],  in  its  upper  three-fourths,  is  quadrangular,  possessing 
four  borders  and  four  surfaces,  whereas  its  lower  fourth  is  flattened  from  side  to 
side,  so  as  to  be  somewhat  triangular.  The  borders  and  surfaces  vary  exceed- 
ingly so  that  their  description  is  difficult.  The  anterior  crest  (or  antero-lateral 
border)  commences  in  front  of  the  head  and  terminates  below  by  dividing  to 
enclose  a  subcutaneous  surface,  triangular  in  shape,  immediately  above  the 

Fig.  227. — The  Upper  End  of  the  Left  Flbtjla  to  show  Musculae  and  Ligamentous 
Attachments  X  2.     (G.  J.  Jenkins.) 


Fibular  collateral  ligament 


Biceps ^  V^^^^^^^-  9  JBt — Capsule  of  superior  tibio- 

^  '  fibular  joint 


Styloid  process 


Posterior   superior   tibio- 
fibular  ligament 

lateral  malleolus.  It  gives  attachment  to  a  septum  separating  the  extensor 
muscles  in  front  from  the  peronei  muscles  on  the  lateral  aspect.  The  interosseous 
crest  (or  antero-medial  border),  so  named  from  giving  attachment  to  the  interos- 
seous membrane,  also  commences  in  front  of  the  head,  close  to  the  anterior  crest, 
and  terminates  below  by  dividing  to  enclose  a  rough  triangular  area  immediately 
above  the  facet  for  the  talus  {astragalus) ;  this  area  gives  attachment  to  the  inferior 
interosseous  ligament,  and  may  present  at  its  lower  end  a  narrow  facet  for  articula- 
tion with  the  tibia.  The  medial  crest  (or  postero-medial  border),  sometimes 
described  as  the  oblique  line  of  the  fibula,  commences  at  the  medial  side  of  the 
head  and  terminates  below  by  joining  the  interosseous  crest,  in  the  lower  fourth 
of  the  shaft.  It  gives  attachment  to  an  aponeurosis  separating  the  tibialis 
posterior  from  the  soleus  and  flexor  hallucis  longus.  The  lateral  crest  (or  postero- 
lateral border)  runs  from  the  back  of  the  head  to  the  medial  border  of  the  peroneal 
groove  on  the  back  of  the  lower  extremity;  it  gives  attachment  to  the  fascia  sepa- 
rating the  peronei  from  the  flexor  muscles. 

The  anterior  or  extensor  surface  is  the  interval  between  the  interosseous  and 
anterior  crests.  In  the  upper  third  it  is  extremely  narrow,  but  broadens  out 
below,  where  it  is  slightly  grooved  longitudinally.  It  affords  origin  to  three 
muscles :  laterally,  in  the  upper  two-thirds,  to  the  extensor  digitorum  longus,  and,  in 
the  lower  third,  to  the  peroneals  tertius;  medially,  in  the  middle  third,  also  to  the 
extensor  hallucis  longus.  The  medial  surface,  situated  between  the  interosseous 
and  medial  crests,  is  narrow  above  and  below,  and  broadest  in  the  middle.  It 
is  grooved  and  sometimes  crossed  obliquely  by  a  prominent  ridge,  the  secondary 
oblique  line  of  the  fibula;  the  surface  gives  origin  to  the  tibialis  posterior,  and  the 
ridge  to  a  tendinous  septum  in  the  substance  of  the  muscle.     The  posterior  surface 


THE  TARSUS  191 

is  the  interval  between  the  medial  and  lateral  crests,  and  is  somewhat  twisted  so 
as  to  look  backward  above  and  medially  below.  It  serves,  in  its  upper  third,  for 
the  origin  of  the  soleus,  and  in  its  lower  two-thirds  for  the  flexor  hallucis  longus. 
Near  the  middle  of  the  surface  is  the  medullary  foramen,  directed  downward 
toward  the  ankle.  The  lateral  surface,  situated  between  the  anterior  and  lateral 
crests,  is  also  somewhat  twisted,  looking  laterally  above  and  backward  below, 
where  it  is  continuous  with  the  groove  on  the  back  of  the  lateral  malleolus. 
The  surface  is  often  deeply  grooved  and  is  occupied  by  the  peroneus  longus  in  the 
upper  two-thirds  and  by  the  peroneus  brevis  in  the  lower  two-thirds. 

The  lateral  malleolus  or  lower  extremity  is  pyramidal  in  form,  somewhat 
flattened  from  side  to  side,  and  joined  by  its  base  to  the  shaft.  It  is  longer,  more 
prominent,  and  descends  lower  than  the  medial  malleolus.  Its  lateral  surface  is 
convex,  subcutaneous,  and  continuous  with  the  triangular  subcutaneous  surface 
on  the  shaft,  immediately  above.  The  medial  surface  is  divided  into  an  anterior 
and  upper  area  [facies  articularis  malleoli],  triangular  in  outline  and  convex  from 
above  downward  for  articulation  with  the  lateral  side  of  the  talus  (astragalus),  and 
a  lower  and  posterior  excavated  area,  the  digital  fossa,  in  which  are  attached  the 
transverse  iriferior  tibio-fibular  ligament  and  the  posterior  talo-fibular  (posterior 
fasciculus  of  the  external  lateral)  ligament  of  the  ankle.  The  anterior  border  is 
rough  and  gives  attachment  to  the  anterior  talo-fibular  (anterior  fasciculus  of  the 
external  lateral)  ligament  of  the  ankle,  and  the  anterior  inferior  tibio-fibular  liga- 
ment. The  posterior  border  is  grooved  for  the  peronei  tendons,  and  near  its 
upper  part  gives  attachment  to  the  posterior  inferior  tibio-fibular  ligament.  The 
apex  or  summit  of  the  process  affords  attachment  to  the  calcaneo-fibular  (middle 
fasciculus  of  the  external  lateral)  ligament  of  the  ankle. 

Blood-supply. — The  shaft  of  the  fibula  receives  its  nutrient  artery  from  the  peroneal 
branch  of  the  posterior  tibial.  The  head  is  nourished  by  branches  from  the  inferior  lateral 
articular  branch  of  the  popliteal  artery,  and  the  lateral  malleolus  is  supplied  mainly  by  the 
peroneal,  and  its  perforating  and  malleolar  branches. 

Ossification. — The  shaft  of  the  fibula  commences  to  ossify  in  the  eighth  week  of  intra- 
uterine life.  A  nucleus  appears  for  the  lower  extremity  in  the  second  year,  and  one  in  the  upper 
extremity  during  the  fourth  or  fifth  year.  The  lower  extremity  fuses  with  the  shaft  about 
twenty,  but  the  upper  extremity  remains  separate  until  the  twenty-second  year  or  even  later. 

It  is  interesting,  in  connection  with  the  times  of  appearance  of  the  two  epiphyses  of  the 
fibula,  to  note  that  the  ossification  of  the  lower  epiphysis  is  contrary  to  the  general  rule — viz., 
that  the  epiphysis  toward  which  the  nutrient  artery  is  directed  is  the  last  to  undergo  ossification. 
This  is  perhaps  explained  by  the  rudimentary  nature  of  the  upper  extremit}'.  In  birds  the  head 
of  the  bone  is  large  and  enters  into  the  formation  of  the  knee-joint;  and  in  human  embryos, 
during  the  second  month,  the  fibula  is  quite  close  up  to  the  femur. 

The  human  fibula  is  characterised  by  the  length  of  its  malleolus,  for  in  no  other  vertebrate 
does  this  process  descend  so  far  below  the  level  of  the  tibial  malleolus.  On  the  other  hand,  in 
the  majority  of  mammals  the  tibial  descends  to  a  lower  level  than  the  fibular  malleolus.  In 
the  human  embryo  of  the  third  month,  the  lateral  is  equal  in  length  to  the  medial  malleolus. 
At  the  fifth  month  the  lateral  malleolus  exceeds  the  medial  by  1.5  mm.;  at  birth,  the  lateral 
malleolus  is  still  longer;  and  by  the  second  year  it  assumes  its  adult  proportion. 


THE  TARSUS 

The  tarsal  bones  [ossa  tarsi]  (figs.  228,  229)  are  grouped  in  two  rows: — a 
proximal  row,  consisting  of  the  talus  and  calcaneus,  and  a  distal  row,  consisting 
of  four  bones  which,  enumerated  from  tibial  side,  are  the  first,  second,  and  third 
cuneiform  bones  and  the  cuboid.  Interposed  between  the  two  I'ows  on  the  tibial 
side  of  the  foot  is  a  single  bone,  the  navicular ;  on  the  fibular  side  the  proximal  and 
distal  rows  come  into  contact. 

Compared  with  the  carpus,  the  tarsal  bones  present  fewer  common  characters, 
and  greater  diversity  of  size  and  form,  in  consequence  of  the  modifications  for  sup- 
porting the  weight  of  the  trunk.  On  each,  however,  six  surfaces  can  generally  be 
recognised,  articular  when  in  contact  with  neighbouring  bones,  elsewhere  sub- 
cutaneous or  rough  for  the  attachment  of  ligaments.  As  regards  ossification,  they 
correspond  in  the  main  with  that  of  the  bones  of  the  carpus.  Each  tarsal  bone  is 
ossified  from  a  single  centre,  but  the  calcaneus  has,  in  addition,  an  epiphysis  for  a 
large  part  of  its  posterior  extremity,  and  the  talus,  an  occasional  centre  for  the  os 
trigonum. 


192 


THE  SKELETON 


The  Talus 

The  talus  (or  astragalus)  (figs.  230,  231)  is,  next  to  the  calcaneus,  the  largest 
of  the  bones  of  the  tarsus.  Above  it  supports  the  tibia,  below  it  rests  on  the  cal- 
caneus, at  the  sides  it  articulates  with  the  two  malleoli,  and  in  front  it  is  received 
into  the  navicular.  For  descriptive  purposes,  it  may  be  divided  into  a  head,  neck, 
and  body. 

Fig.  228. — The  Left  Foot.     (Superior  surface.) 


Tendo  Achill 


Extensor  digitorum  brevis 


Peroneus  brevis 
Peroneus  tertius 


Metatarsus 


|\    [I First  phalanx 

Second  phalam 
l.h Third  phalanx 


Extensor  digitorum  longus 


The  body  is  somewhat  quadrilateral  in  shape.  The  upper  surface  presents  a  broad,  smooth 
surface  for  the  tibia,  slightly  concave  from  side  to  side,  convex  from  before  backward,  and 
wider  in  front  than  behind.  "The  diminution  in  width  posteriorly  is  associated  with  an  obliquity 
of  the  lateral  margin,  which  is  directed  medially  as  well  as  backward  and  downward.  The 
inferior  surface  is  occupied  by  a  transversely  disposed  oblong  facet  [taoies  articularis  calcanea 


THE  TARSUS 


193 


posterior],  deeply  concave  from  side  to  side,  which  articulates  with  a  corresponding  surface 
on  the  calcaneus.  Of  the  malleolar  sm-faces,  the  lateral  is  almost  entirely  occupied  by  a  large 
triangular  facet,  broad  above,  where  it  is  continuous  with  the  superior  surface,  concave  from 
above  downward,  for  articulation  with  the  lateral  malleolus;  on  the  medial  malleolar  surface 
is  a  pyriform  facet  continuous  with  the  superior  surface,  broad  in  front  and  narrow  behind, 
which  articulates  with  the  medial  malleolus.  Below  this  facet  the  medial  surface  is  rough  for 
the  attachment  of  the  deep  fibres  of  the  deltoid  (internal  lateral)  ligament  of  the  ankle.     The 


Fig.  229. — The  Left  Foot.     (Plantar  surface.) 


Abductor  digiti  quinti 
Abductor  ossis  metatarsi  quiati 


Quadratus  plantae  (lateral  head) 


Flexor  hallucis  brevis 
Abductor  ossis  metatarsi  quinti 
Flexor  brevis  digiti  quinti 

Adductor  hallucis 
Third  plantar  interosseous 

Second  plantar  interosseous 
First  plantar  interosseou 


Flexor  brevis  digiti  quinti 

Abductor  digiti  quinti 

Third  plantar  interosseous 


Second  plantarinterosseous' 
First  plantar  interosseouE. 


Flexor  digitorum  brevis. 


Flexor  digitorum  longus 


Abductor  hallucis 
Flexor  digitorumi  brevis 


Quadratus  plantce  (medial head) 


Tibiahs  posterior 


Tibialis  anterior 
Peroneus  longus 


Abductor  hallucis 
Flexor  hallucis  brevis 

(medial)  portion) 
Flexor  hallucis  brevis 

(lateral)  portion) 
Adductor  hallucis 
Transversus  pedis 


Flexor  hallucis  longus 


superior  surface  and  the  two  malleolar  surfaces  together  constitute  the  trochlea.  The  poste- 
rior Surface  is  of  small  extent  and  marked  by  a  groove  which  lodges  the  tendon  of  the  flexor 
hallucis  longus.  Bounding  the  groove  on  either  side  are  two  tubercles,  of  which  the 
lateral  [processus  posterior  tali]  is  usually  the  more  prominent,  for  attachment  of  the  posterior 
talo-fibular  ligament  of  the  ankle-joint;  the  medial  tubercle  gives  attachment  to  the  medial 
talo-calcaneal  ligament.     Continuous,  with  the  anterior  aspect  of  the  body  is  the  neck,  a  con- 


194 


THE  SKELETON 


strioted  part  of  the  bone  supporting  the  head.  Above  it  is  rough,  and  perforated  by  numerous 
vascular  foramina.  Below,  it  presents  a  deep  groove  [sulcus  tali],  directed  from  behind  forward 
and  lateralward.  When  the  talus  is  articulated  with  the  calcaneus,  this  furrow  is  converted 
into  a  canal  [sinus  tarsi]  in  which  is  lodged  the  interosseous  talo-calcaneal  ligament.  The  head 
is  the  rounded  anterior  end  of  the  bone,  and  its  large  articular  surface  is  divisible  into  three 
parts:  in  front,  a  smooth,  oval  convex  area,  directed  downward  and  forward  for  the  navicular 
bone;  below,  an  elongated  facet,  convex  from  front  to  back,  for  articulation  with  the  sustentacu- 
lum taJi  of  the  calcaneus;  and  between  these,  is  a  small  facet  which  rests  on  the  calcaneo- 

FiG.  230. — The  Left  Talus.     (Plantar  view.) 


Groove  for  the  flexor  hallucis  longus 


For  calcaneus 


■For  the  sustentaculum  tall 


For    the    calcaneo-navicular    (or    the 
spring)  ligament 


For  navicular 


navicular  ligament,  separated  from  it  by  the  synovial  membrane  of  the  talo-calcaneo-navicular 
joint. 

Articulations. — The  talus  articulates  with  four  bones  and  two  ligaments.  Above  and 
medially  with  the  tibia,  below  with  the  calcajieus,  in  front  with  the  navicular,  laterally  with  the 
fibula.  The  head  articulates  with  the  calcaneo-navicular  ligament  and  the  lateral  border  of 
the  superior  surface,  at  its  posterior  part,  with  the  transverse  ligament  of  the  inferior  tibio- 
fibular joint. 

The  talus  is  a  very  vascular  bone  and  is  nourished  by  the  dorsalis  pedis  artery  and  its  tarsal 
branch.     It  gives  attachment  to  no  muscles. 

Fig.  231. — A  Talus  with  the  Os  Trigonum. 
Os  trigonum 


Ossification. — The  talus  is  ossified  from  one,  occasionallj*  from  two,  nuclei.  The  principal 
centre  for  this  bone  appears  in  the  middle  of  the  cartilaginous  talus  at  the  seventh  month  of 
intra-uterine  life.  The  additional  centre  is  deposited  in  the  posterior  portion  of  the  bone,  and 
forms  the  lateral  posterior  tubercle  which  may  remain  separate  from  the  rest  of  the  bone  and 
form  the  os  trigonum.  At  birth,  the  talus  presents  some  important  peculiarities  in  the  disposi- 
tion of  the  articular  facet  on  the  tibial  side  of  its  body,  and  in  the  obliquity  of  its  neck.  If,  in  the 
adult  talus,  a  line  be  drawn  through  the  middle  of  the  superior  trochlear  surface  parallel  with 
its  medial  border,  and  a  second  line  be  drawn  along  the  lateral  side  of  the  neck  of  the  bone  so  as 
to  intersect  the  first,  the  angle  formed  by  these  two  lines  will  express  the  obliquity  of  the  neck 
of  the  bone.     This  in  the  adult  varies  greatly,  but  the  average  may  be  taken  as  10°.     In  the 


THE  TARSUS 


195 


foetus  at  birth  the  angle  averages  35°,  whilst  in  a  young  orang  it  measures  45°.  In  the  normal 
adult  talus  the  articular  surface  on  the  tibial  side  is  limited  to  the  body  of  the  bone.  In  the 
foetal  talus  it  extends  for  some  distane  on  to  the  neck,  and  sometimes  reaches  almost  as  far 
forward  as  the  navicular  facet  on  the  head  of  the  bone.  This  disposition  of  the  medial  malleolar 
facet  is  a  characteristic  feature  of  the  talus  in  the  chimpanzee  and  the  orang.  It  is  related  to 
the  inverted  position  of  the  foot  which  is  found  in  the  human  foetus  almost  up  to  the  period  of 
birth,  and  is  of  interest  to  the  surgeon  in  connection  with  some  varieties  of  club-foot.  (Shattock 
and  Parker.) 

The  Calcaneus 

The  calcaneus  (or  os  calcis)  (figs.  232,  233)  is  the  largest  and  strongest  bone  of 
the  foot.  It  is  of  an  elongated  form,  flattened  from  side  to  side,  and  expanded  at 
its  posterior  extremity,  which  projects  downward  and  backward  to  form  the  heel. 
It  presents  six  surfaces,  superior,  inferior  lateral,  medial,  anterior  and  posterior. 

The  superior  surface  presents  in  the  middle  a  large,  oval,  convex,  articular  facet  for  the 
under  aspect  of  the  body  of  the  talus.     In  front  of  the  facet  the  bone  is  marked  by  a  deep 

Fig.  232. — The  Left  Calcaneus.    (Dorsal  view.) 


Media]  process 


Calcaneal  groove' 


Peroneal  tubercle 


Facet  for  talus 


depression,  the  floor  of  which  is  rough  for  the  attachment  of  ligaments,  especially  the  talo- 
calcaneal,  and  the  origin  of  the  extensor  digitorum  hrevis  muscle;  when  the  calcaneus  and  talus 
are  articulated,  this  portion  of  the  bone  forms  the  floor  of  a  cavity  called  the  sinus  tarsi.  Medi- 
ally, the  upper  surface  of  the  bone  presents  a  well-marked  process,  the  sustentaculum  tali, 
furnished  with  an  elongated  concave  facet,  occasionally  divided  into  two,  for  articulation  with 
the  under  aspect  of  the  head  of  the  talus.  The  posterior  part  of  the  upper  surface  is  non- 
articular,  convex  from  side  to  side,  and  in  relation  with  a  mass  of  fat  placed  in  front  of  the 
tendo  Aohillis. 

The  inferior  surface  is  narrow,  rough,  uneven,  and  ends  posteriorly  in  two  processes:  the 
medial  is  the  larger  and  broader,  the  lateral  is  narrower  but  prominent.  The  medial  process 
affords  origin  to  the  abductor  hallucis,  the  flexor  digitorum  brevis,  and  the  abductor  digiti  quinti; 
the  last  muscle  also  arises  from  the  lateral  process  and  from  the  ridge  of  bone  between.  The 
rough  surface  in  front  of  the  tubercles  gives  attachment  to  the  long  plantar  ligament  (calcaneo- 
cuboid) and  the  lateral  head  of  the  quadratus  plantoe.  Near  its  anterior  end  this  surface  forms 
a  rounded  eminence,  the  anterior  tubercle,  from  which  (as  well  as  from  the  shallow  groove  in 
front)  the  plantar  (short)  calcaneo-cuboid  ligament  arises.  (According  to  the  BNA  nomen- 
clature, the  medial  and  lateral  processes  belong  to  the  tuber  calcanei  or  the  posterior  extremity 
of  the  bone.) 

The  lateral  surface  is  broad,  flat,  and  slightly  convex.  It  represents  near  the  middle  a  small 
eminence  for  the  calcaneo-fibular  ligament  of  the  ankle-joint.  Below  and  in  front  of  this  is  a 
well-marked  tubercle — the  trochlear  process  [processus  trochlearis]  (or  peroneal  tubercle), 
separating  two  grooves,  the  upper  for  the  peroneus  brevis  and  the  lower  for  the  peroneiis  longus. 

The  medial  surface  is  deeply  concave,  the  hollow  being  increased  by  the  prominent  medial 
process  behind  and  the  overhanging  sustentaculum  tali  in  front.  The  latter  forms  a  promi- 
nence of  bone  projecting  horizontally,  concave  and  articular  above,  grooved  below  for  the 
tendon  of  the  flexor  hallucis  longus,  and  giving  attachment  to  a  slip  of  the  tendon  of  the  tibialis 
posterior,  the  inferior  calcaneo-navicular  ligament,  and  some  fibres  of  the  deltoid  ligament  of 
the  ankle-joint.  The  hollow  below  the  process  receives  the  plantar  vessels  and  nerves  and  its 
lower  part  gives  attachment  to  the  medial  head  of  the  quadratus  planice. 


196 


THE  SKELETON 


The  anterior  surface  is  somewhat  quadrilateral  in  outline  with  rounded  angles,  and  presents 
a  saddle-shaped  articular  surface  for  the  cuboid. 

The  posterior  surface  is  oval  in  shape,  rough,  and  convex.  It  is  divided  into  three  parts: — 
an  upper,  smooth  and  separated  by  a  bursa  from  the  tendo  Aohillis;  a  middle  part  giving 
attachment  to  the  tendo  Achillis  and  the  plantaris,  and  a  lower  part  in  relation  to  the  skin  and 
fat  of  the  heel.     The  expanded  posterior  extremity  of  the  bone  is  known  as  the  tuber  calcanei. 

Articulations. — The  calcaneus  articulates  with  two  bones,  the  talus  above  and  the  cuboid 
in  front. 

Blood-supply. — The  calcaneus  is  nourished  by  numerous  branches  from  the  posterior  tibial 
and  the  medial  and  lateral  malleolar  arteries.  They  enter  the  bone  chiefly  on  the  inferior 
and  medial  surfaces. 


Fig.  233. — The  Calcaneus  at  the  Fifteenth  Year,  showing  the  Epiphysis. 


Appears  at  the  tenth,  and  unites  at  the  sixteenth  year 


Ossification. — The  primary  nucleus  appears  in  the  sixth  month  of  intra-uterine  life.  The 
epiphysis,  for  its  posterior  extremity,  begins  to  be  ossified  in  the  tenth  year  and  is  united  to 
the  body  of  the  bone  by  the  sixteenth  year.  It  may  extend  over  the  whole  of  the  posterior 
surface,  as  shown  in  fig.  233,  or  over  the  lower  two-thirds  only,  leaving  a  part  above  in  relation 
to  the  bursa  beneath  the  tendo  Achillis,  which  is  formed  from  the  primary  nucleus.  The 
medial  and  lateral  processes  are  formed  by  the  epiphysis. 

The  Naviculae 

The  navicular  [os  naviculare  pedis]  (figs.  234,  235)  is  oval  in  shape,  flattened 
from  before  backward,  and  situated  between  the  talus  behind  and  the  three 
cuneiform  bones  in  front.     It  is  characterised  by  a  large  oval,  concave,  articular 


Fig.  234. — The  Left  Navicular.     (Anterior  view.) 


For  first  cuneiform' 

Medial  border 

Tuberosity 


■For  second  cuneiform 

Lateral  border 
■For  third  cuneiform 


facet  on  the  posterior  surface,  which  receives  the  head  of  the  talus;  a  broad,  rough, 
rounded  eminence  on  the  medial  surface,  named  the  tuberosity  of  the  navicular, 
the  lower  part  of  which  projects  downward  and  gives  insertion  to  the  tendon  of 


Fig.  235. — The  Left  Navicular,  showing  a  Facet  for  the  Cuboid. 


For  first  cuneif' 


For  second  cuneiform 

■For  third  cuneiform 
For  cuboid 


the  tibialis  posterior;  and  an  oblong-shaped  anterior  surface,  convex  and  chvided 
by  two  vertical  ridges  into  three  facets  which  articulate  with  the  three  cuneiform 
bones.     The  superior  (dorsal)  surface  is  rough,  convex,  and  slopes  downward  to 


THE  TARSUS  197 

the  tuberosity;  the  inferior  (plantar)  surface  is  irregular  and  rough  for  the  attach- 
ment of  the  inferior  cAlcaneo-navicular  ligament,  and  the  lateral  surface  is  rough 
and  sometimes  presents  a  small  articular  surface  for  the  cuboid. 

Articulations. — With  the  talus  behind,  with  the  three  cuneiform  bones  in 
front,  and  occasionally  with  the  cuboid  on  its  lateral  aspect. 

Ossification. — The  nucleus  for  the  navicular  appears  in  the  course  of  the  fourth  year.  The 
tuberosity  of  the  navicular,  into  which  the  tibialis  posterior  acquires  its  main  insertion,  occasion- 
ally develops  separately,  and  sometimes  remains  distinct  from  the  rest  of  the  bone. 

The  Cuneiform  Bones 

Of  the  three  cuneiform  bones,  the  first  is  the  largest,  the  second  is  the  smallest, 
and  the  third  intermediate  in  size.  They  are  wedge-shaped  bones  placed  between 
the  navicular  and  the  first,  second  and  third  metatarsal  bones.  Posteriorly,  the 
ends  of  the  bones  lie  in  the  same  transverse  line,  but  in  front,  the  first  and  third 
project  farther  forward  than  the  second,  and  form  the  sides  of  a  deep  recess  into 
which  the  base  of  the  second  metatarsal  bone  is  received. 

Fig.  236. — The  Left  First  Cuneiform.     (Medial  surface.) 


For  first  metatarsal 


The  first  cuneiform  [os  cuneiforme  primum]  (figs.  236,  237)  is  distinguished  by  its  large 
size  and  by  the  fact  that  when  articulated,  the  base  of  the  wedge  is  directed  downward  and  the 
apex  upward.  The  posterior  surface  is  concave  and  pyritorm  for  articulation  with  the  medial 
facet  on  the  anterior  surface  of  the  navicular.  The  anterior  surface  forms  a  reniform  articular 
facet  for  the  base  of  the  first  metatarsal.  The  medial  surface  is  rough,  and  presents  an  oblique 
groove  for  the  tendon  of  the  tibialis  anterior;  this  groove  is  limited  inferiorly  by  an  oval  facet 
into  which  a  portion  of  the  tendon  is  inserted.  The  lateral  surface  is  concave  and  presents  along 
its  superior  and  posterior  borders  a  reversed  L-shaped  facet  for  articulation  with  the  second 
cuneiform,  and,  at  its  anterior  extremity,  with  the  second  metatarsal.  Anteriorly  it  is  rough 
for  ligaments.  The  inferior  surface  is  rough  for  the  insertion  of  the  peroneus  longus,  tibialis 
anterior,  and  (usually)  the  tibialis  posterior.  The  superior  surface  is  the  narrow  part  of  the 
wedge  and  is  directed  upward. 

FiQ  237. — The  Left  First  Cuneiform.     (Lateral  aspect.) 

For  second  metatarsal 

For  second  cuneiform 


Articulations. — With  the  navicular  behind,  second  cuneiform  and  second  metatarsal  on 
its  lateral  side,  and  first  metatarsal  in  front. 

Ossification. — From  a  single  nucleus  which  appears  in  the  course  of  the  third  year. 

The  second  cuneiform  [os  cuneiforme  secundum]  (figs.  238,  239)  is  placed  with  the  broad 
extremity  upward  and  the  narrow  end  downward,  and  is  readily  recognised  by  its  nearly 
square  base.  The  posterior  surface,  triangular  and  concave,  articulates  with  the  middle  facet 
on  the  anterior  surface  of  tlie  navicular.  The  anterior  surface,  also  triangular,  but  narrower 
than  the  posterior  surface,  articulates  with  the  base  of  the  second  metatarsal.  The  medial 
surface  has  a  reversed  L-shaped  facet  running  along  its  superior  and  posterior  margins  for 
articulation  with  the  corresponding  facet  on  the  first  cuneiform,  and  is  rough  elsewhere  for  the 


198 


THE  SKELETON 


attachment  of  ligaments.  On  the  lateial  surface  near  its  posterior  border  is  a  vertical  facet, 
sometimes  bilobed,  for  the  third  cuneiform,  and  occasionally  a  second  facet  at  the  anterior 
inferior  angle.  The  superior  surface  forms  the  square-cut  base  of  the  wedge  and  is  rough  for 
the  attachment  of  ligaments.  The  inferior  surface  is  sharp  and  rough  for  ligaments  and  a  slip 
of  the  tendon  of  the  tibialis  posterior. 


Fig.  238. — The  Left  Second  Cuneiform.     (Medial  sm-face.) 


For  first  cuneiform 
For  second  metatarsal 


Articulations. — With  the  navicular  behind,  second  metatarsal  in  front,  third  cuneiform  on 
the  lateral  side,  and  first  cuneiform  on  the  medial  side. 

Ossification. — From  a  single  nucleus  which  appears  in  the  fourth  year. 

The  third  cuneiform  bone  (figs.  240,  241)  also  placed  with  the  broad  end  directed  upward 
and  the  narrow  end  downward,  is  distinguished  by  the  oblong  shape  of  its  base.     Like  the 


Fig.  239. — The  Left  Second  Cuneiform.     (Lateral  surface.) 

-For  third  cuneiform 
For  navicular 

jional  facet  for  third  cuneiform 


second  cuneiform,  the  posterior  surface  presents  a  triangular  facet  for  the  navicular;  and  the 
anterior  surface  a  triangular  facet,  longer  and  narrower,  for  the  third  metatarsal.  The  medial 
surface  has  a  large  facet  extending  along  the  posterior  border  for  the  second  cuneiform,  and 
along  the  anterior  border  a  narrow  irregular  facet  for  the  lateral  side  of  the  base  of  the  second 
metatarsal.     Occasionally,  a  small  facet  is  present  near  the  anterior  inferior  angle  for  the  second 


Fig.  240. — The  Left  Third  Cuneiform      (Medial  surface.) 

For  second  cuneiform  - 


For  navicular 


Foi  second  metatarsal.  The  circular 
facet  near  the  inferior  angle  is  for 
the  second  cuneiform 


cuneiform.  The  lateral  surface  has  a  large  distinctive  facet  near  its  posterior  superior  angle 
for  the  cuboid,  and  at  the  anterior  superior  angle  there  is  usually  a  small  facet  for  the  medial 
side  of  the  base  of  the  fourth  metatarsal.  The  superior  surface,  oblong  in  shape,  is  rough  for 
ligaments,  and  the  inferior,  forming  a  rounded  margin,  receives  a  slip  of  the  tibialis  posterior 
and  gives  origin  to  a  few  fibres  of  the^e:!;or  hallucis  brevis. 


Fig.  241. — The  Left  Third  Cuneiform.     (Lateral  surface.) 

T^      z      ..t-       1.  4.        ,  i     T.  =^  ^1  i^-rt-t-i — For  cuboid 

For  fourth  metatarsal  i      v,.^   -«i  i  ,    >•  i 

For  third  metatarsal 


Articulations. — With  the  navicular  behind,  third  metartarsal  in  front,  cuboid  and  fourth 
metatarsal  on  the  lateral  side,  .second  cuneiform  and  second  metatarsal  on  the  me'dial  side. 
Ossification. — A  single  nucleus  appears  in  the  course  of  the  first  year. 


THE  TARSUS  199 

The  Cxiboid 

The  cuboid  (figs.  242,  243,  244),  irregularly  cubical  in  shape,  is  placed  on  the 
lateral  aspect  of  the  foot,  forming  a  continuous  line  with  the  calcaneus  and  the 
fourth  and  fifth  metatarsals. 

Its  posterior  surface  is  somewhat  quadrangular  with  rounded  angles  and  presents  a  saddle- 
shaped  articular  surface  for  the  calcaneus.  Its  lower  and  medial  angle  is  somew-hat  prolonged 
backward  beneath  the  sustentaculum  tali  (calcaneal  process  of  the  cuboid),  an  arrangement  to 
oppose  the  upward  or  outward  movement  of  the  bone.     This  process  occasionally  terminates 

Fig.  242. — The  Left  Cdboid.     (Medial  view.) 

For  third  cuneiform j|^iq5\-J —  J'''',  'A — For  fourth  metatarsal 

For  calcaneus 

Groove   for   tendon   of   the    per 

longus  "■ ■-  - 

in  a  rounded  facet  which  plays  on  the  head  of  the  talus  lateral  to  the  facet  for  the  calcaneo 
navicular  ligament.  The  anterior  surface  is  smaller  and  divided  by  a  vertical  ridge  into  two 
articular  facets,  a  lateral  for  the  base  of  the  fifth,  and  a  medial  for  the  base  of  the  fourth  meta- 
tarsal. The  superior  surface  is  rough,  non-articular,  and  directed  obliquely  upward.  The 
inferior  surface  presents  a  prSminent  ridge  for  the  attachment  of  the  long  plantar  (calcaneo- 
cuboid) ligament,  in  front  of  which  is  a  deep  groove — the  peroneal  groove — running  obliquely 
forward  and  medially  and  lodging  the  tendon  of  the  peroneiis  longus.  The  ridge  terminates 
laterally  in  an  eminence,  the  tuberosity  of  the  cuboid,  on  which  there  is  usually  a  facet  for  a 
sesamoid  bone  of  the  tendon  contained  in  the  groove.  The  part  of  the  surface  behind  the  ridge 
is  rough  for  the  attachment  of  the  plantar  (short)  calcaneo-cuboid  ligament,  a  slip  of  the  tibialis 
posterior,  and  a  few  fibres  of  the  flexor  hallucis  hrevis. 


Fig.  243.- 

-The  Left  Cuboid.     (Medial  view.) 

For  third  cuneiform 
For  calcaneus 

-fSpTM 

For  navicular  (occasional) 

"z/^vA  .^^v-^'Il 

Groove   for   tendon   of   the    peroneus_ 
longus 

^^^^ 

The  medial  surface  presents,  near  its  middle  and  upper  part,  an  oval  facet  for  articulation 
with  the  third  cuneiform  bone  (fig.  242);  behind  this,  a  second  facet  for  the  navicular  is  fre- 
quently seen  (fig.  243).  Generally  the  two  facets  are  confluent  and  then  form  an  elliptical 
surface  (fig.  244).  The  remainder  of  this  surface  is  rough  for  the  attachment  of  strong  inter- 
osseous ligaments. 

The  lateral  surface,  the  smallest  and  narrowest  of  all  the  surfaces,  presents  a  deep  notch 
which  leads  into  the  peroneal  groove. 

Articulations. — With  the  calcaneus  behind,  fourth  and  fifth  metatarsals  in  front,  third 
cuneiform  and  frequently  the  navicular  on  the  medial  side;  occasionally  also  the  talus. 

Fig.  244. — The  Left  CtTBOiD.     (Medial  view.) 

For  third  cuneiform 
For  navicular 


Ossification. — The  cuboid  is  ossified  from  a  single  nucleus  which  appears  about  the  time 
of  birth. 

Accessory  tarsal  elements. — As  in  the  carpus,  a  number  of  additional  elements  may 
occur  in  the  tarsus.  The  most  frequent  of  these  is  the  os  trigonum,  which  has  already  been 
noticed.  Ne.\t  in  frequency  is  an  additional  first  cuneiform,  resulting  from  the  ossification  of 
the  plantar  half  of  that  bone  independently  of  the  dorsal  half,  so  that  the  bone  is  represented 
by  a  plantar  and  a  dorsal  first  cuneiform.  Other  additional  elements  may  occasionally  occur 
at  the  upper  posterior  angle  of  the  sustentaculum  tali;  at  the  anterior  superior  angle  of  the  cal- 
caneus, between  that  bone  and  the  navicular;  in  the  angle  between  the  first  cuneiform  and  the 
first  and  second  metatarsals;  and  in  the  fibular  angle  between  the  fifth  metatarsal  and  the 
cuboid  (os  Vesalianum). 


200 


THE  SKELETON 


The  fibular  portion  of  the  navicular  is  sometimes  united  to  the  cuboid  and  quite  separate 
from  the  rest  of  the  navicular,  the  cuboid  in  such  eases  articulating  with  the  talus.  This  con- 
dition suggests  the  recognition  of  the  fibular  portion  of  the  navicular  as  a  distinct  accessory 
tarsal  element,  the  cuboides  secundarium,  though  it  has  not  yet  been  observed  as  an  inde- 
pendent bone  in  the  human  foot. 

THE  METATARSUS 

The  metatarsus  [ossa  metatarsalia]  consists  of  a  series  of  five  somewhat 
cylindrical  bones.  Articulated  with  the  tarsus  behind,  they  extend  forward, 
nearly  parallel  with  each  other,  to  their  anterior  extremities,  which  articulate 
with  the  toes,  and  are  numbered  according  to  their  position  from  great  toe  to  small 
toe.  Like  the  corresponding  bones  in  the  hand,  each  presents  for  examination  a 
three-sided  shaft,  a  proximal  extremity  termed  the  base,  and  a  distal  extremity  or 
head.  The  shaft  tapers  gradually  from  the  base  to  the  head,  and  is  slightly 
curved  longitudinally  so  as  to  be  convex  on  the  dorsal  and  concave  on  the  plantar 
aspect. 

A  typical  metatarsal  bone. — The  shaft  [corpus]  is  compressed  laterally  and 
presents  for  examination  three  borders  and  three  surfaces.  The  two  borders,  dis- 
tinguished as  medial  and  lateral,  are  sharp  and  commence  behind,  one  on  each  side 
of  the  dorsal  aspect  of  the  tarsal  extremity,  and,  gradually  approaching  in  the 
middle  of  the  shaft,  separate  at  the  anterior  end  to  terminate  in  the  corresponding 


Fig.  245. — The  First  (Left)  Metatarsal. 


For  peroneus  longus 
Facet  for  second  meta- 
tarsal (occasional) 


tubercles.  The  inferior  border  is  thick  and  rounded  and  extends  from  the  under 
aspect  of  the  tarsal  extremity  to  near  the  anterior  end  of  the  bone,  where  it  bi- 
furcates, the  two  divisions  terminating  in  the  articular  eminences  on  the  plantar 
aspect  of  the  head.  Of  the  three  surfaces,  the  dorsal  is  narrow  in  the  middle  and 
wider  at  either  end.  It  is  directed  upward  and  is  in  relation  -with  the  extensor 
tendons.  The  medial  and  lateral  surfaces,  more  extensive  than  the  dorsal, 
corresponding  with  the  interosseous  spaces,  are  separated  above,  but  meet  to- 
gether at  the  inferior  border;  they  afford  origin  to  the  interosseous  muscles.  The 
base  is  wedge-shaped,  articulating  by  its  terminal  surface  with  the  tarsus,  and  on 
each  side  with  the  adjacent  metatarsal  bones.  The  dorsal  and  plantar  surfaces 
are  rough  for  the  attachment  of  ligaments.  The  head  presents  a  semicircular 
articular  surface  for  the  base  of  the  first  jjhalanx,  and  on  each  side  a  depression, 
surmounted  by  a  tubercle,  for  the  attachment  of  the  lateral  ligaments  of  the 
metatarso-phalangeal  joint.  The  inferior  surface  of  the  head  is  grooved  for  the 
passage  of  the  flexor  tendons  and  is  bounded  by  two  eminences  continuous  with 
the  terminal  articular  surface. 

The  several  metatarsals  possess  distinctive  characters  by  which  they  can  be 
readily  recognised. 


THE  METATARSUS 


201 


The  first  metatarsal  (fig.  245)  is  the  most  modified  of  all  the  metatarsal  bones,  and  deviates 
widely  from  the  general  description  given  above.  It  is  the  shortest,  the  thickest,  the  strongest, 
and  most  massive  of  the  series.  The  base  presents  a  large  reniform,  slightly  concave  facet 
for  the  first  cuneiform  and  projects  downward  into  the  sole  to  form  the  tuberosity,  a  rough 
eminence  into  which  the  peroneus  longus  and  a  slip  of  the  tibialis  anterior  are  inserted.     A  little 

Fig.  246. — The  Second  (Left)  Metatarsal. 


Medial  side 


An  occasional  facet  for  the  first 

metatarsal  / 

First  cuneiform  — 


Facets  for  third  metatarsal 
Facets  for  third  cuneiform 


above  the  tuberosity,  on  its  lateral  side,  there  is  occasionally  a  shallow,  but  easily  recognised 
facet,  for  articulation  with  the  base  of  the  second  metatarsal.  The  head  is  marked  on  the  plan- 
tar surface  by  two  deep  grooves,  separated  by  a  ridge,  in  which  the  two  sesamoid  bones  of  the 
flexor  hallucis  brevis  glide.  The  shaft  is  markedly  prismatic.  The  dorsal  surface  is  smooth, 
broad,  and  convex,  directed  obliquely  upward;  the  plantar  surface  is  concave  longitudinally 

Fig.  247 — The  Third  (Left)  Metatarsal. 


Facets  for  second  metatarsal 


Facets  for  second  metatarsal 


Facet  for  fourth  metatarsal 


and  covered  by  the  flexor  hallucis  longus  and  brevis,  whilst  the  lateral  surface  is  triangular  in 
outline,  almost  vertical,  and  in  relation  with  the  first  dorsal  interosseous  and  adductor  hallucis 
obliquus.  A  few  fibres  of  the  medial  head  of  the  fii'st  dorsal  interosseous  occasionally  arise  from 
the  hinder  part  of  the  surface  adjoining  the  base,  or  from  the  border  separating  the  lateral  from 
the  dorsal  surface.  Somewhere  near  the  middle  of  the  shaft,  and  on  its  fibular  side,  is  the 
nutrient  foramen,  directed  toward  the  head  of  the  bone. 


202 


THE  SKELETON 


The  second  metatarsal  (fig.  246)  is  the  longest  of  the  series.  Its  base  is  prolonged  back- 
ward to  occupy  the  space  between  the  first  and  third  cuneiform,  and  accordingly  it  is  marlced 
by  facets  for  articulation  with  each  of  these  bones.  The  tarsal  surface  is  triangular  in  outline, 
with  the  base  above  and  apex  below,  and  articulates  with  the  second  cuneiform  bone.  On  the 
tibial  side  of  the  base,  near  the  upper  angle,  is  a  small  facet  for  the  first  cuneiform,  and  occa- 

FiG.  248. — The  Fourth  (Left)  Metatarsal. 


Facet  for  third  metatarsal 


Facet  for  third  metatarsal 
Facet  for  third  cuneiform 


-  Facet  for  fifth  metatarsal 


sionally  another  for  the  first  metatarsal  a  little  lower  down.  The  fibular  side  of  the  base  pre- 
sents an  upper  and  a  lower  facet,  separated  by  a  non-articular  depression,  and  each  facet  is 
divided  by  a  vertical  ridge  into  two,  thus  making  four  in  all.  The  two  posterior  facets  articu- 
late with  the  third  cuneiform  and  the  two  anterior  with  the  third  metatarsal.  The  base  gives 
attachment  to  a  slip  of  the  tibialis  posterior  and  the  adductor  hallucis  obliquus,  whilst  from  the 

Fig.  249. — The  Fjfth  (Left)  Metatarsal. 


Tibial 
Medial  side 


Fourth  metatarsal 


Fibular 

lateral  side 


shaft  the  first  and  second  dorsal  interosseous  muscles  take  origin.  The  nutrient  foramen  is 
situated  on  the  fibular  side  of  the  shaft  near  the  middle  and  is  directed  toward  the  base  of  the 
bone. 

The  third  metatarsal  (fig.  247),  a  little  shorter  than  the  second,  articulates  by  the  tri- 
angular surface  of  its  base  with  the  third  cuneiform.  On  the  medial  side  are  two  small  facets, 
one  below  the  other,  for  the  second  metatarsal,  and  on  the  lateral  side,  a  single  large  facet  for 
the  fourth  metatarsal.  The  base  gives  attachment  to  a  slip  of  the  tibialis  posterior  and  the 
adductor  hallucis  obliquus,  and  from  the  shaft  three  interosseous  muscles  take  origin.  The 
nutrient  foramen  is  situated  on  the  tibial  side  of  the  shaft  and  is  directed  toward  the  base. 


THE  PHALANGES 


203 


The  fourth  metatarsal  (fig.  248),  smaller  in  size  than  the  preceding,  is  distinguished  by 
the  quadrilateral  facet  on  the  base,  for  the  cuboid.  The  medial  side  presents  a  large  facet 
•divided  by  a  ridge  into  an  anterior  portion  for  articulation  with  the  third  metatarsal  and  a, 
posterior  portion  for  the  third  cuneiform.  Occasionally  the  cuneiform  part  of  the  facet  is 
wanting.  On  the  lateral  side  of  the  base  is  a  single  facet  for  articulation  with  the  fifth 
metatarsal. 

The  fifth  metatarsal  (fig.  249),  is  shorter  than  the  fourth,  but  longer  than  the  first.  It  is 
recognised  by  the  large  nipple-shaped  process,  known  as  the  tuberosity,  which  projects  on  the 
lateral  side  of  the  base.  It  constitutes  the  hindmost  part  of  the  bone  and  gives  insertion  to 
the  -peroneus  brevis  on  the  dorsal  aspect,  and  flexor  brevis  digili  quinli  and  the  occasional 
■abduclor  ossis  metatarsi  quinli  on  the  plantar  aspect.  The  fifth  metatarsal  articulates  behind 
by  an  obliquely  directed  triangular  facet  with  the  cuboid,  and  on  the  medial  side  with  the 
fourth  metatarsal.  The  plantar  aspect  of  the  base  is  marked  by  a  shallow  groove  which 
lodges  the  tendon  of  the  abductor  digili  quinli,  and  the  dorsal  surface,  continuous  with  the 
superior  surface  of  the  shaft,  receives  the  insertion  of  the  peroneus  terlius.  The  head  is  small 
and  turned  somewhat  laterally  in  consequence  of  the  curvature  of  the  shaft  in  the  same 
direction.  The  shaft  differs  from  that  of  any  of  the  other  metatarsals  in  being  compressed 
from  above  downward,  instead  of  from  side  to  side,  so  as  to  present  superior,  inferior,  and 
medial  surfaces.  It  gives  origin  to  the  lateral  head  of  the  fourth  dorsal  interosseous  and  the 
third  plantar  interosseous  muscles.  The  nutrient  foramen  is  situated  on  its  tibial  side  and  is 
directed  toward  the  base. 

Ossification. — Each  metatarsal  ossifies  from  two  centres.  The  primary  nucleus  for  the 
shaft  appears  in  the  eighth  week  of  embryonic  life  in  the  middle  of  the  cartilaginous  metatarsal. 
At  birth,  each  extremity  is  represented  by  cartilage,  and  that  at  the  proximal  end  is  ossified  by 
extension  from  the  primary  nucleus',  except  in  the  case  of  the  first  metatarsal.  For  this,  a 
nucleus  appears  in  the  third  year. 

The  distal  ends  of  the  four  lateral  metatarsals  are  ossified  by  secondary  nuclei  which  make 
their  appearance  about  the  third  year.  Very  frequently  an  epiphysis  is  found  at  the  distal  end 
of  the  first  metatarsal  as  well  as  at  its  base.  The  shafts  and  epiphyses  consolidate  at  the  twen- 
tieth year.  The  sesamoids  belonging  to  the  flexor  hallucis  brevis  begin  to  ossify  about  the  fifth 
year. 

THE  PHALANGES 

The  phalanges  (fig.  250)  are  the  bones  of  the  toes,  and  number  in  all  fourteen. 
Except  the  great  toe,  each  consists  of  three  phalanges,  distinguished  as  first 
(proximal),  second  and  third  (distal) ;  in  the  great  toe  the  second  phalanx  is  absent. 

Fig.  250. — The  Phalanges  of  the  Middle  Toe. 

5?1 


There  is  thus  a  similarity  as  regards  number  and  general  arrangement  with  the 
phalanges  of  the  fingers.  With  the  exception  of  the  phalanges  of  the  great  toe, 
which  are  larger  than  those  of  the  thumb,  the  bones  of  the  toes  are  smaller  and 
more  rudimentary  than  the  corresponding  bones  of  the  fingers.  In  all  the  pha- 
langes, the  nutrient  foramen  is  directed  toward  the  distal  extremity. 

The  phalanges  of  the  first  row  are  constricted  in  the  middle  and  expanded  at  either  ex- 
tremity.    The  shafts  are  narrow  and  laterally  compressed,  rounded  on  the  dorsal  and  concave 


204 


THE  SKELETON 


on  the  plantar  aspects.  The  base  of  each  presents  a  single  oval  concave  facet  for  the  convex 
head  of  the  corresponding  metatarsal,  whilst  the  head  forms  a  pulley-like  surface  [trochlea 
phalangis],  grooved  in  the  centre  and  elevated  on  each  side  for  the  second  phalanx. 

The  phalanges  of  the  second  row  are  stunted,  insignificant  bones.  Their  shafts,  besides 
being  much  shorter,  are  flatter  than  those  of  the  first  row.  The  bases  have  two  depressions, 
separated  by  a  vertical  ridge,  and  the  heads  present  trochlear  surfaces  for  the  ungual  phalanges. 

The  third,  or  ungual  phalanges  are  easily  recognised.  The  bases  articulate  with  the  second 
phalanges;  the  shafts  are  expanded,  forming  the  ungual  tuberosities  which  support  the  nails, 
and  their  plantar  surfaces  are  rough  where  they  come  into  relation  with  the  pulp  of  the  digits. 

The  muscles  attached  to  the  various  phalanges  may  be  tabulated  thus: — 

The  first  phalanx  of  the  hallux  gives  insertion  to  the  flexor  haUucis  brevis;  abductor  halluois; 
adductor  hallucis  transversus  and  obliquus;  extensor  digitorum  brevis. 

The  first  phalanx  of  second  toe :    The  first  and  second  dorsal  interosseous. 

The  first  phalanx  of  third  toe :   Thii'd  dorsal  interosseous;  first  plantar  interosseous. 

The  first  phalanx  of  fourth  toe :   Second  plantar  interosseous;  fourth  dorsal  interosseous. 

The  first  phalanx  of  fifth  toe:  Third  plantar  interosseous;  flexor  digiti  quinti  brevis;  and 
abductor  digiti  quinti. 

The  terminal  phalanx  of  hallux:    Flexor  hallucis  longus;  extensor  hallucis  longus. 


Fig.  251. — A  Longitudinal  Section  of  the  Bones  of  the  Lower  Limb  at  Birth. 


The  centre  for  the  lower  extremity  of 
the  femur  appears  early  in  the 
ninth  month 


The  centre  for  the  upper  end  of  the 
tibia  appears  about  a  week  before 


The  centre  for  the  navicular  appears  in  the  fourth  year 
For  the  first  cuneiform  appears  in  the  third  year 


First  phalanx  of  hallux 

Second  phalanx  of  hallux 


The  second  phalanges  of  the  remaining  toes :  Dorsal  expansion  of  the  extensor  tendons, 
including  extensor  digitorum  longus,  extensor  digitorum  brevis  (except  in  the  case  of  the  fifth 
toe),  and  expansions  from  the  interossei  and  lumbricales. 

The  third  phalanges :  Flexor  digitorum  longus;  dorsal  expansion  of  the  extensor  tendon 
with  the  associated  muscles. 

Ossification, — Like  the  corresponding  bones  of  the  fingers,  the  phalanges  of  the  toes  ossify 
from  a  primary  and  a  secondary  nucleus.  In  each,  the  centre  for  the  shaft  appears  during  the 
eighth  or  ninth  week  of  embryonic  life.  The  secondai-y  centre  forms  a  scale-like  epiphysis  for 
the  proximal  end  between  the  fourth  and  eighth  years,  and  union  takes  place  in  the  eighteenth 
or  nineteenth  year — i.  e.,  earlier  than  the  corresponding  epiphj'ses  in  the  fingers.  The  primary 
centres  for  the  third  phalanges  appear  at  the  distal  extremities  of  the  bones. 

Sesamoid  Bones 


In  the  foot  a  pah-  of  sesamoid  bones  is  constant  over  the  metatarso-phalangeal  joint  of  the 
great  toe  in  the  tendons  of  the  flexor  hallucis  brevis.  One  sometimes  occurs  over  the  inter- 
phalangeal  joint  of  the  same  toe  and  over  the  metatarso-phalangeal  joints  of  the  second  and 
fifth  and  rarely  of  the  third  and  fourth  toes. 


BONES  OF  THE  FOOT  AS  A  WHOLE 


205 


A  sesamoid  also  occurs  in  the  tendon  of  the  peroneus  longus,  where  it  glides  over  the  groove 
in  the  cuboid;  another  may  be  found,  especially  in  later  life,  in  the  tendon  of  the  tibialis  anterior 
over  the  first  cuneiform  bone,  and  another  in  the  tendon  of  the  tibialis  posterior  over  the  medial 
surface  of  the  head  of  the  talus.  Further  a  sesamoid,  the  fabella,  sometimes  occurs  in  the 
lateral  head  of  the  gastrocnemius,  and  another  may  be  found  in  the  tendon  of  the  ilio-psoas 
over  the  pubis. 

BONES  OF  THE  FOOT  AS  A  WHOLE 

Although  the  foot  is  constructed  on  the  same  general  plan  as  the  hand,  there 
is  a  marked  difference  in  its  architecture  to  qualify  it  for  the  different  functions 
which  it  is  called  upon  to  perform.  When  in  the  erect  posture,  the  foot  forms  a 
firm  basis  of  support  for  the  rest  of  the  body,  and  the  bones  are  arranged  in  an 
elliptical  arch,  supported  on  two  pillars,  a  posterior  or  calcaneal  pillar  and  an 

Fig.  252. — The  Secondary  Ossific  Centres  op  the  Foot. 
The    centre    for    the     epiphysis    for 
calcaneus  appears  at  the  tenth  year 
consolidates  at  the  sixteenth  year 


The  centre  for  the  epiphysis  for  the 
metatarsal  of  the  hallux  appears  at 
the  third  year;  consolidates  at  the 
twentieth  year 


The  centres  for  the  base  of  the  ter- 
minal phalanges  appear  at  sixth 
year,  and  consolidate  at  the  eight- 
eenth year 


The'centres  for  the  heads  of  the  metatarsals 
appear'atlthelthird  year,  and  consoUdate  at  the  twentieth  year 

anterior  or  metatarsal  pillar.  It  is  convenient,  however,  to  regard  the  anterior 
part  of  the  arch  as  consisting  of  two  segments,  corresponding  to  the  medial  and 
lateral  borders  of  the  foot  respectively.  The  medial  segment  is  made  up  of  the 
three  metatarsal  bones,  the  three  cuneiform,  the  navicular,  and  talus;  the  lateral 
segment  is  made  up  of  the  fourth  and  fifth  metatarsal  bones,  the  cuboid,  and  the 
calcaneus,  and  both  segments  are  supported  behind  on  a  common  calcaneal  pillar. 
The  division  corresponds  to  a  difference  in  function  of  the  two  longitudinal  arches. 
Both  are  intimately  concerned  in  ordinarj-  locomotion.  In  addition,  the  medial, 
characterised  by  its  great  curvature  and  remarkable  elasticitj^,  sustains  the  more 
violent  concussions  in  jumping  and  similar  actions,  whereas  the  lateral,  less  curved, 
more  rigid,  and  less  elastic  arch  forms,  with  the  pillars  in  front  and  behind,  a 
firm  basis  of  support  in  the  upright  posture. 

Both  arches  are  completed  and  maintained  by  strong  ligaments  and  tendons. 
The  weakest  part  is  the  joint  between  the  talus  and  navicular  bone,  and  special 


206 


THE  SKELETON 


provision  is  accordingly  made,  by  the  addition  of  a  strong  calcaneo-navicular  liga- 
ment, for  the  support  of  the  head  of  the  talus.  This  ligament  is  in  turn  supported 
by  its  union  with  the  deltoid  ligament  of  the  ankle,  and  by  the  tendon  of  the 
tibialis  posterior  which  passes  beneath  it  to  its  insertion. 

Besides  being  arched  longitudinally,  the  foot  presents  a  transverse  arch  formed 
by  the  metatarsal  bones  in  front  and  the  distal  row  of  the  tarsus  behind.  It  is 
produced  by  the  marked  elevation  of  the  central  portion  of  the  medial  longitudinal 
arch  above  the  ground,  whereas  the  lateral  longitudinal  arch  is  much  less  raised, 
and  at  its  anterior  end  becomes  almost  horizontal.  Both  the  longitudinal  and 
transverse  arches  serve  the  double  purpose  of  increasing  the  strength  and  elasticity 
of  the  foot  and  of  providing  a  hollow  in  which  the  muscles,  nerves,  and  vessels  of 
the  sole  may  lie  protected  from  pressure. 

Homology  of  the  Bones  of  the  Limbs 

That  there  is  a  general  correspondence  in  the  plan  of  construction  of  the  two  extremities  is 
apparent  to  a  superficial  observer,  and  this  becomes  more  marked  when  a  detailed  examination 
of  the  individual  bones,  their  forms  and  relations,  their  embryonic  and  adult  peculiarities,  is 
systematically  carried  out.  In  each  limb  there  are  four  segments,  the  shoulder  girdle  corre- 
sponding to  the  pelvic  girdle,  the  arm  to  the  thigh,  the  forearm  to  the  leg,  and  the  hand  to  the 
foot.  These  parts  have  been  variously  modified,  in  adaptation  to  the  different  functions  of  the 
two  limbs,  particularly  as  regards  the  deviations  or  changes  from  what  is  regarded  as  their  primi- 


FiG.  253.- 


Subscapular  fo 


-Diagrammatic  Representation  op  the  Bones  op  the  Two  Limbs,  to 
SHOW  Homologous  Parts.     (Modified  from  Flower.) 
Iniiaspinous  fossa 


Great  trochanti 


^^' 
'^V. 


tive  position,  and  as  a  knowledge  of  these  changes  is  essential  to  a  clear  understanding  of  the 
homologous  bones,  it  will  be  advantageous  to  refer  briefly  to  the  relations  of  the  limbs  in  the 
earliest  stages  of  development. 

The  limbs  first  appear  as  flattened,  bud-like  outgrowths  from  the  sides  of  the  trunk.  Each 
presents  a  dorsal  or  extensor  surface,  and  a  ventral  or  flexor  surface,  as  well  as  two  borders, 
an  anterior,  or  cephalic,  directed  toward  the  head  end  of  the  embryo,  and  a  posterior  or  caudal, 
du-ected  toward  the  tail  end.  In  reference  to  the  axis  of  the  limb  itself,  the  borders  have 
been  called  pre-axial  and  post-axial,  respectively.  When,  somewhat  later,  the  various  divisions 
of  the  limb  make  their  appearance,  it  is  seen  that  the  gi-eater  tuberosity,  the  lateral  epicondyle, 
the  radius,  and  the  thumb  he  on  the  pre-axial  border  of  the  anterior  extremity,  and  the  small 
trochanter,  the  medial  condyle,  the  tibia,  and  the  great  toe  on  the  pre-axial  border  of  the 
posterior  extremity.  Further  on  the  post-axial  border  of  the  anterior  extremity  are  seen  the 
lesser  tuberosity,  the  medial  epicondyle,  the  ulna,  and  little  finger,  whilst  on  the  corresponding 
border  of  the  posterior  limb  are  the  great  trochanter,  the  lateral  condyle,  the  fibula,  and  the 
little  toe.  The  parts  now  enumerated  on  the  corresponding  borders  of  the  two  limbs  must 
therefore  be  regarded  as  serially  homologous  (fig.  253). 


HOMOLOGY  OF  THE  BONES  OF  THE  LIMBS  207 

It  is  necessary  to  trace  next  the  further  changes  which  take  place  in  the  segments  of  the  limbs 
up  to  the  time  when  they  assume  their  permanent  positions.  They  may  be  arranged  in  stages 
as  follows: — 

(1)  Each  segment  of  the  limb  is  bent  upon  the  one  above  it.  The  humerus  and  femur 
remain  unchanged.  The  forearm  segment,  however,  is  bent  so  that  the  ventral  surface  looks 
medially  and  the  dorsal  surface  laterally.  Moreover,  the  joints  between  these  segments — i.  e., 
elbow  and  knee — form  marked  projections.  The  terminal  segments  (hand  and  foot)  are  bent 
in  the  opposite  direction  to  the  middle  one,  so  that  the  primitive  position  is  retained,  and  the 
ends  of  the  digits  directed  laterally.  It  will  be  noticed  that  in  this  series  of  changes  the  relations 
of  the  pre-axial  and  post-axial  borders  of  the  limbs  remain  as  before. 

(2)  This  stage  consists  in  a  rotation  of  the  whole  limb  from  the  proximal  end,  though  in  an 
exactly  opposite  direction  in  each  case.  The  anterior  extremity  is  rotated  backward  so  that  the 
humerus  lies  parallel  with  the  trunk;  the  elbow  is  directed  toward  the  caudal  end,  the  pre-axial 
(radial)  border  becomes  lateral,  and  the  post-axial  border  medial.  The  ends  of  the  digits  point 
backward.  The  posterior  extremity  undergoes  a  rotation  forward  to  the  same  extent,  so  that 
the  femur  is  also  nearly  parallel  with  the  trunk;  the  knee  is  directed  toward  the  head  end,  the 
pre-axial  (tibial)  border  becomes  medial,  and  the  post-axial  border  lateral.  The  tibia  and 
fibula  are  parallel,  the  ends  of  the  digits  are  directed  forward,  the  gi-eat  toe  is  on  the  pre-axial 
and  the  Uttle  toe  on  the  post-axial  border  of  the  Umb,  and  in  this  position  the  posterior  extremity 
remains,  the  changes  being  finally  completed  by  the  extension  of  the  Hmb  at  the  hip-joint  as  the 
body  attains  its  full  development. 

(3)  This  stage  affects  the  anterior  extremity  alone  and  consists  in  a  rotation  of  the  radius, 
carrying  the  hand  round  the  ulna  so  that  the  digits  are  brought  round  from  the  back  to  the  front 
of  the  limb,  and  in  many  animals  the  maOus  is  thus  placed  permanently  in  the  prone  position. 
But  in  man,  in  whom  the  capacity  for  pronation  and  supination  is  highly  developed,  the  hand 
can  assume  either  position  at  will.  In  his  case  the  final  change  is  the  extension  which  takes  place 
at  the  shoulder-joint  with  the  assumption  of  the  upright  posture,  the  limb  dropping  loosely  at 
the  side  of  the  body,  and  being  endowed  with  the  greatest  freedom  of  movement. 

Homological  comparison  of — 

I.  The  shoulder  and  pelvic  girdles. — Primarily  the  lateral  half  of  each  girdle  consists 
of  a  curved  bar  or  rod  of  cartilage  placed  at  right  angles  to  the  longitudinal  axis  of  the  trunk  and 
divisible  into  a  dorsal  segment,  and  a  ventral  segment,  the  point  of  division  corresponding 
to  the  place  of  articulation  with  the  limb-stalk — i.  e.,  the  glenoid  and  acetabular  cavities.  In 
the  fore-limb  the  dorsal  segment  is  the  scapula,  and  the  ventral  segment  the  coracoid,  whilst 
in  the  hind-hmb  the  dorsal  segment  is  the  iUum  and  the  ventral  segment  the  ischium  and 
pubis. 

The  dorsal  segments  of  the  two  girdles — i.  e.,  scapula  and  ihum — are  accordingly  regarded 
as  homologous  bones,  the  chief  difference  being  that  whereas  the  scapula  is  free  from  articulation 
with  the  vertebral  column,  the  ilium  is  firmly  jointed  to  the  rib  elements  (lateral  mass)  of  the 
sacrum.  But  the  correspondence  is  not  quite  so  clear  with  regard  to  the  ventral  segments.  In 
the  primitive  condition  the  coracoid  articulates  with  the  side  of  the  sternum,  an  arrangement 
which  persists  throughout  hfe  in  certain  animals,  such  as  reptiles  and  Ornithorhynchus.  But  in 
aU  the  higher  mammals  it  undergoes  reduction,  withdrawing  from  the  side  of  the  sternum,  and 
eventually  forming  a  more  or  less  rudimentary  process  attached  to  the  scapula.  In  the  more 
generahsed  form  of  shoulder  girdle  the  ventral  bar  is  double,  consisting  of  coracoid  and  pre- 
coracoid  elements,  the  latter  being  situated  in  front  and  almost  parallel  with  the  coracoid.  The 
pre-coracoid  in  mammals  is  largely  replaced  by  the  development  over  it  of  the  clavicle,  a  dermal 
or  membranous  splint-bone  which  eventually  invades  the  underlying  cartilage.  Parts,  however, 
remain  distinct  and  form  the  sternal  epiphysis  of  the  clavicle,  the  inter-articular  cartilage 
between  it  and  the  sternum,  the  supra-sternal  bones,  and  the  inconstant  inter-articular  cartilage 
in  the  acromio-clavicular  joint. 

It  has  already  been  noticed  that  in  the  hip  girdle  the  ventral  segment  also  consists  of  two 
elements,  the  pubis  and  ischium.  Both  take  part  in  the  formation  of  the  acetabular  cavity,  and 
the  pubis  meets  in  the  ventral  median  line  the  corresponding  segment  of  the  opposite  side. 

It  is  generally  agreed  that  the  coracoid  and  ischium  are  homologous  structures.  The  pubic 
portion  of  the  ventral  segment  appears  to  correspond  most  closely  with  the  pre-coracoid  element 
of  reptiles,  so  that  there  is  no  true  homologue  of  the  clavicle  in  the  pelvis.  If,  however,  the 
clavicle  corresponds  to  the  reptilian  pre-coracoid,  as  believed  by  many  anatomists,  it  then  be- 
comes the  representative  of  the  pubis, 

From  a  consideration  of  the  condition  in  oranio-cleido-dysostosis,  Mr.  FitzwiUiams  has 
put  forward  the  following  views  regarding  the  homology  of  the  shoulder  girdle: — Coracoid  bar 
is  represented  by  (a)  medial  two-thu'ds  of  clavicle;  (b)  coraco-clavicular  ligaments;  and  (c) 
sub-coracoid  centre  of  coracoid  process.  The  clavicula,  a  membranous  bone,  is  represented 
by  the  lateral  third  of  adult  clavicle.  The  pre-coracoid  bar  is  represented  by: — (a)  the  coracoid 
process  (less  the  sub-coracoid  centre) ;  and  (b)  the  costo-coracoid  ligament.  The  epi-coracoid 
is  represented  by  the  meniscus  of  the  sterno-clavicular  joint. 

Moreover,  it  is  possible  to  establish  a  comparison  between  the  individual  parts  of  the  ilium 
and  scapula.  A  reference  to  fig.  253  shows  that  both  the  scapula  and  ilium  may  be  resolved  into 
three-sided  prismatic  rods,  each  of  which  has  thi-ee  surfaces  and  three  borders.  In  the  primitive 
position  of  the  limb  one  surface — the  internal — is  turned  toward  the  vertebral  column,  the 
remaining  surfaces  are  external,  and  named  -pre-axial  and  post-axial,  corresponding  to  the  borders 
of  the  limb.  The  borders  separating  the  internal  from  the  external  surfaces  are  antero-internal 
(terminating  in  the  acromion  or  pubis)  and  postero-internal  (terminating  in  the  coracoid  or 
ischium).  The  two  external  surfaces  are  separated  by  a  ridge,  terminating  below  at  the  upper 
margin  of  the  glenoid  cavity  or  acetabulum  (glenoid  and  cotyloid  borders). 

The  primitive  arrangement  is  lost  by  the  marked  growth  of  the  borders  of  the  rods  leading 
to  the  formation  of  fossae  and  by  the  rotation  of  each  rod,  the  scapula  laterally  and  the  ihum 
medially,  in  association  with  the  rotation  which  takes  place  in  the  free  part  of  the  limb,  so  that 


208 


THE  SKELETON 


the  inner  surface  of  the  one  comes  to  correspond  with  the  outer  surface  of  the  other.  It  results 
that  the  primitive  vertebral  surface  of  the  scapula  is  now  the  pre-scapular  or  supraspinous 
fossa,  and  the  corresponding  surface  in  the  ilium  is  the  sacral,  which,  on  account  of  its  close  con- 
nection with  the  vertebral  column,  undergoes  but  little  change  in  position.  Further,  the  primi- 
tive pre-axial  surfaces  are  the  infraspinous  fossa  and  the  iliac  fossa,  which  accordingly  are  to 
be  regarded  as  homologous,  as  well  as  the  two  post-axial  surfaces,  the  subscapular  fossa  and  the 
dorsum  ilii.  The  correspondence  between  the  various  parts  of  the  scapula  and  ilium  is  shown 
in  the  appended  table  (after  Flower). 


I.  Surfaces  • 

II.  Borders: 


ScAPUIiA 

Supraspinous  fossa. 
Infraspinous  fossa. 
Subscapular  fossa. 
Axillary  or  glenoid. 

Spine. 

Superior  or  coracoid. 

Base. 


Primitive 
Arrangement 

Vertebral. 
Pre-axial. 
Post-axial. 
External. 

Antero-internal. 
Postero-internal. 
Dorsal  extremity. 


Ilium 

Sacral  surface. 
Iliac  fossa. 
Gluteal  surface. 
Cotyloid  or  anterior 

border. 
Terminal  line. 
Posterior  border. 
Crest  of  ilium. 


II.  Bones  of  the  arm  and  thigh,  forearm,  and  leg. — It  has  already  been  pointed  out  in 
describing  the  deviation  of  the  limbs  from  the  primitive  position  that  the  humerus  corresponds 
to  the  femur,  the  radius  to  the  tibia,  and  the  ulna  to  the  fibula;  also  that  in  consequence  of  the 
rotation  backward  of  the  fore-limb,  and  forward  of  the  hind-limb,  the  lateral  side  of  the  humerus 
corresponds  with  the  medial  aide  of  the  femur,  the  radial  border  of  the  forearm  to  the  tibial 
border  of  the  leg,  and  the  ulnar  (border  of  the  forearm)  to  the  fibular  border  of  the  leg.  The 
corresponding  parts  are  tabulated  below: — 


Fore-Limb 
Humerus 

Greater  tuberosity 

Lesser  tuberosity 

Lateral  epicondyle  and  capitulum 

Medial  epicondyle  and  trochlea 
Radius 
Ulna 
Not  represented 


Hind-Limb 
Femur 

Lesser  Trochanter 
Great  Trochanter 
Medial  Condyle 
Lateral  Condyle 

Tibia 

Fibula 

Patella 


III.  Bones  of  the  hand  and  foot. — It  is  obvious  that  the  carpus  and  tarsus,  the  meta- 
carpus and  metatarsus,  and  the  various  digits,  commencing  at  the  thumb,  in  the  hand,  and  at 
the  great  toe,  in  the  foot,  are  serially  homologous. 

Fig.  254. — Dorsal  Surface  of  the  Right  Manus  of  a  Water-tortoise,  Chelydra  serpentina. 
("After  Gegenhaur.l 


In  order  to  trace  the  correspondence  between  the  various  elements  of  the  carpus  and  tarsus 
it  is  convenient  to  refer  in  the  first  place  to  the  primitive  type  of  hand  and  foot  as  found  in  the 
water-tortoise  and  the  lizard  (fig.  254).  In  each  segment  nine  elements  may  be  recognised, 
arranged  in  a  proximal  row  of  three,  named  respectively  radiate  or  tibiale,  intermedium,  and 
ulnare,  or  flbulare,  a  distal  row  of  five  carpalia,  or  tarsalia,  numbered  from  one  to  five,  commenc- 
ing at  the  pre-axial  border,  and  between  the  two  rows  an  os  cenlrale. 

In  man  the  carpus  is  derived  from  the  typical  form  in  the  following  manner:  The  radiale 
forms  the  navicular,  intermedium  the  lunate,  and  the  ulnare,  the  triquetral;  carpale  I  forms 
the  greater  multangular,  oarpale  II  the  lesser  multangular,  carpale  III  the  capitate,  whilst  car- 
paha  IV  and  V  coalesce  to  form  the  hamate.  The  os  centrale  is  present  in  the  human  carpus 
at  an  early  stage,  but  in  the  second  month  it  joins  the  navicular.  It  is  occasionally  separate — 
a  normal  arrangement  in  most  of  the  primates. 


HOMOLOGY  OF  THE  BONES  OF  THE  LIMBS 


209 


In  the  tarsus,  the  tibiale  and  intermedium  coalesce  to  form  the  talus,  and  the  fibulare 
becomes  the  calcaneus.  It  is  interesting  to  note  that  although  in  the  human  subject  there  are 
three  bones  in  the  first  row  of  the  carpus  and  two  in  the  first  row  of  the  tarsus,  in  carnivores  the 
navicular  and  lunate  are  united  to  form  a  naviculo-lunate  bone — the  homologue  of  the  talus. 
In  the  human  tarsus  the  intermedium  occasionally  remains  distinct  as  the  os  trigonum. 

Tarsale  I  forms  the  first  cuneiform,  tarsale  11  the  second  cuneiform,  tarsale  III  the  third 
cuneiform,  and  tarsale  IV  and  V  are  joined  to  form  the  cuboid.  The  os  centrale  forms  the 
navicular. 

In  addition  to  the  carpal  and  tarsal  elements  enumerated  above,  brief  mention  must  now 
be  made  of  the  sesamoid  bones  of  the  two  segments,  which  are  regarded  by  many  anatomists 
as  vestiges  of  suppressed  digits.  In  the  hand  are  the  ulnar  and  radial  sesamoids,  the  ulnar 
being  represented  by  the  pisiform  and  the  radial  probably  by  the  tuberosity  of  the  navicular. 
(In  the  mole  and  other  aUied  species  with  fossorial  habits,  the  radial  sesamoid  is  greatly  de- 
veloped to  form  a  sickle-shaped  bone  which  has  received  the  name  of  os  falciforme.) 

The  corresponding  structures  in  the  foot  are  the  tibial  and  fibular  sesamoids,  the  tibial 
being  most  nearly  represented  by  the  tuberosity  of  the  navicular  and  the  fibular  by  the  tuber 
of  the  calcaneus. 


Table  Showing  the  HoMOLOGOtis  Bones  op  the  Carpus  and  Tarsus. 

in  Quain's  Anatomy.) 


[After  G.  D.   Thane 


Carpus 


Priaiitive  Names 


Tarsus 

>  Calcaneus 
I  Talus 

>  Navicular 

First  cuneiform 
Second  cuneiform 
Third  cuneiform 

}  Cuboid 

References. — ^For  the  development  of  the  skeleton,  consult  the  bibliography 
in  Bardeen's  article  in  Keibel  and  Mall's  '  Human  Embryology,'  Vol.  1.  For 
further  references  concerning  the  adult  structure  and  morphology  of  the  skeleton, 
the  sections  on  osteology  in  the  larger  works  on  human  anatomy  by  Quain,  von 
Bardeleben,  Rauber-Kopsch.  Poirier-Charpy,  etc.,  should  be  consulted.  Refer- 
ences to  the  most  recent  literature  may  be  found  in  Schwalbe's  Jahresbericht, 
the  Index  Medicus,  and  in  the  various  anatomical  journals. 


Triquetral 

Ulnare 

Fibulare 

Pisiform 

Ulnar  sesamoid 

Fibular  sesamoid 

Lunate 

Intermedium 

Intermedium 

■  Radiale 

Tibiale 

Navicular 

Radial  sesamoid 

Tibial  sesamoid 

Centrale 

Centrale 

Greater  multangular 

Carpale     I 

Tarsale     I 

Lesser  multangular 

II 

II 

Capitate 

"       III 

"       III 

Hamate 

r     "     IV 

(       "         V 

"       IV 

V 

I 


SECTION    III 

THE  ARTICULATIONS 


Revised  for  the  Fifth  Edition 
By  FREDERIC  WOOD  JONES,  D.Sc,  M.B.,  B.S.(Lond.),  M.R.C.S.,L.R.C.P. 

HEAD  OF  THE  DEPARTMENT  OF  ANATOMY  AND  LECTURER  IN  THE  LONDON  SCHOOL  OP  MEDICINE  FOR  WOMEN. 


THE  CONSTITUENTS  OF  AN  ARTICULATION 

THE  section  devoted  to  the  Articulations  or  Joints  deals  with  the  union  of  the 
various  and  dissimilar  parts  of  the  human  skeleton.     The  followiing  struc- 
tures enter  into  the  formation  of  joints. 
Bones  constitute  the  basis  of  most  joints.     The  long  bones  articulate  by  their 
ends,  the  flat  by  their  edges,  and  the  short  at  various  parts  on  their  surfaces.     The 
articular  ends  are  usually  expanded,  and  are  composed  of  cancellous  tissue,  sur- 
rounded by  a  dense  and  strong  shell  of  compact  tissue. 

This  shell  has  no  Haversian  canals  (the  vessels  of  the  cancellous  tissue  turn  back  and  do 
not  perforate  it),  or  large  lacunae,  and  no  canaliculi,  and  is  thus  well  adapted  to  bear  pressure. 
This  "osteoid"  layer  may  represent  in  part  calcified  cartilage  rather  than  true  bone. 

The  cartilage  which  covers  the  articular  ends  of  the  bones  is  called  articular, 
and  is  of  the  hyaline  variety.  It  is  firmly  implanted  on  the  bone  by  one  surface, 
while  the  other  is  smooth,  polished,  and  free,  thus  reducing  friction  to  a  minimum, 
while  its  slight  elasticity  tends  to  break  jars.  It  ends  abruptly  at  the  edge  of  the 
articulation,  and  is  thickest  over  the  areas  of  greatest  pressure. 

Another  form  of  cartilage,  the  white  fibrous,  is  also  found  in  joints: — 

(i)  As  inlerarlicular  cartilage  in  diarthrodial  joints — viz.,  in  the  knee,  mandibular, 
sterno-clavicular,  radio-carpal,  and  occasionally  in  the  acromio-clavicular  joint.  It  is  interposed 
between  the  ends  of  the  bones,  partially  or  completely  dividing  the  synovial  cavity  into  two. 
It  serves  to  adjust  dissimilar  bony  surfaces,  adding  to  the  security  of,  while  it  increases  the 
extent  of  motion  at,  the  joint;  it  also  acts  as  a  buffer  to  break  shocks. 

(ii)  As  circumferential  or  marginal  iibro-cartilages,  which  serve  to  deepen  the  sockets 
for  the  reception  of  the  heads  of  bones — e.  g.,  the  glenoid  ligaments  of  the  shoulder  and  hip. 
Another  form  of  marginal  plate  is  seen  in  the  accessory  volar  ligaments  of  the  fingers 
and  toes,  which  deepen  the  articulations  of  the  phalanges  and  add  to  their  security. 

(iii)  As  connecting  fibro-cartilage.  The  more  pliant  and  elastic  is  the  more  cellular  form, 
and  is  found  in  the  intervertebral  discs;  while  the  less  yielding  and  more  fibrous  form  is  seen  in 
the  sacro-iliac  and  pubic  articulations,  where  there  is  little  or  no  movement. 

The  ligaments  which  bind  the  bones  together  are  strong  bands  of  white  fibrous 
tissue,  forming  a  more  or  less  perfect  capsule  [capsula  articularis],  round  the  articu- 
lation. They  are  pliant  but  inextensile,  varying  in  shape,  strength,  and  thick- 
ness according  to  the  kind  of  articulation  into  which  they  enter.  They  are  closely 
connected  with  the  periosteum  of  the  bones  they  unite.  In  some  cases — as  the 
ligamenta  flava  which  unite  parts  not  in  contact — they  are  formed  of  j'ellow 
elastic  tissue. 

The  synovial  membrane  [stratum  synoviale]  lines  the  interior  of  the  fibrous 
ligaments,  thus  excluding  them,  as  well  as  the  cushions  or  pads  of  fatty  tissue 
situate  within  and  the  tendons  which  perforate  the  fibrous  capsule,  from  the 
articular  cavity.  It  is  a  thin,  delicate  membrane,  frequently  forming  folds  and 
fringes  which  project  into  the  cavity  of  the  joint;  or,  as  in  the  knee,  stretches  across 
the  cavity,  forming  a  so-called  synovial  ligament.  In  these  folds  are  often  found 
pads  of  fatty  tissue,  which  fill  up  interstices,  and  form  soft  cushions  between  the 
contiguous  bones.  The  amount  of  fat  that  is  normally  present  within  a  joint 
varies  greatly.    It  is  an  old  observation  that  although  there  is  always  fat  in  the  hip- 

211 


I 


212  THE  ARTICULATIONS 

and  knee-joints,  there  is  usually  none  within  the  shoulder-joint.  Sometimes 
these  fringes  become  villous  and  pedunculated,  and  cause  pain  on  movement  of 
the  joints.  They  contain  fibro-fatty  tissue,  with  an  isolated  cartilage  cell  or  two. 
The  synovial  membrane  is  well  supplied  with  blood,  especially  near  the  margins  of 
the  articular  cartilages  and  in  the  fringes.  It  secretes  a  thick,  glairy  fluid  like 
white  of  egg,  called  synovia,  which  lubricates  the  joint.  Another  variety  of 
synovial  membrane  is  seen  in  the  bursas,  which  are  interposed  between  various 
moving  surfaces.  In  some  instances  bursas  in  the  neighbourhood  of  a  joint  may 
communicate  with  the  synovial  cavity  of  that  joint. 

CLASSIFICATION  OF  ARTICULATIONS 

Joints  may  be  classified: — (a)  From  an  anatomical  point  of  view,  with  regard 
to  the  substances  and  the  arrangement  of  the  substances  by  which  the  constituent 
parts  are  united.  (6)  From  a  physiological  standpoint,  with  regard  to  the  greater 
or  smaller  mobility  at  the  seat  of  union,  (c)  From  a  physical  standpoint,  either 
the  shapes  of  the  portions  in  contact  being  mainly  considered  or  the  axes  round 
which  movement  can  occur.  Or  again  (d)  a  combination  of  the  preceding  methods 
may  be  adopted,  and  this  is  the  plan  most  generally  followed.  None  of  the  classi- 
fications hitherto  used  is  quite  satisfactory,  but  perhaps,  on  the  whole,  that 
suggested  by  Prof.  Alex.  Macalister  is  the  least  open  to  objection,  and  therefore 
with  slight  modification  it  is  utilised  here. 

There  are  three  chief  groups  of  joints: — 

1.  Synarthroses.     In  joints  of  this  class  the  bones  are  united  by  fibrous  tissue. 

2.  Synchondroses.  Or  joints  in  which  the  uniting  substance  intervening  be- 
tween the  bones  is  cartilage. 

3.  Diarthroses.  The  constituent  parts  of  joints  of  this  class  are  (a)  two  or  more 
bones  each  covered  by  articular  hyaline  cartilage ;  (6)  a  fibrous  capsule  uniting  the 
bones,  and  (c)  a  synovial  membrane  which  lines  the  fibrous  capsule  and  covers 
any  part  of  bone  enclosed  in  the  capsule  and  not  covered  with  articular  cartilage. 
An  interarticular  plate  of  cartilage  may  or  may  not  be  present. 

Synarthroses. — 

(a)  Sutures  or  immovable  joints,  in  which  the' fibrous  tissue  between  the  bones  is  too 
small  in  amount  to  allow  movement. 

(1)  Harmonic.     The  edges  of  the  bones  are  comparatively  smooth  and  are  in  even 
apposition,  e.  g.,  vertical  plate  of  palate  and  maxilla. 

(2)  Squamous.     The  margin  of  one  bone  overlaps  the  other,  e.  g.,  temporal  and 
parietal. 

(3)  Serrate.     The  opposed  edges  interlock  by  processes  tapering  to  a  point. 

(4)  Dentate.     The  opposed  edges  are  dovetailed,  e.  g.,  occipital  and  parietal. 

(5)  Limbous.     The  opposed  edges  alternately  overlap,  e.  g.,  parietal  and  frontal. 

(6)  Schindylesis.     A  ridge  or  flattened  process  is  received  into  a  corresponding 
socket,  e.  g.,  rostrum  of  sphenoid  and  vomer. 

(7)  Gotnphosis.     A  peg-like  process  is  lodged  in  a  corresponding  socket,  e.  g.,  the 
fangs  of  the  teeth. 

(6)  Syndesmoses.  Movable  joints  in  which  the  fibrous  tissue  between  bones  or  carti- 
lages is  sufficiently  lax  to  allow  movement  between  the  connected  parts,  e.  g., 
thyreo-hyoid  membrane.     Interosseous  membranes  of  forearm  and  leg. 

2.  Synchondroses. — In  all  synchondroses  a  certain  amount  of  movement  is  possible,  and 

they  are  often  called  amphiarthroses. 

(1)  True  synchondroses.  The  cartilage  connecting  the  bones  is  the  remains  of  the  bar 
in  which  the  bones  were  ossified,  e.  g.,  occipito-sphenoidal  joint. 

(2)  False  synchondroses.  The  plate  of  cartilage  intervening  between  and  connecting 
the  bones  is  fibro-cartilage  and  is  not  part  of  the  cartilage  in  which  the  bones  were 
ossified,  but  is  developed  separately,  e.  g.,  intervertebral  joint  and  pubic  sym- 
physis. The  articular  end  of  each  bone  may  be  covered  with  hyaUne  cartilage 
and  there  may  be  a  more  or  less  well-marked  cavity  in  the  intervening  plate  of 
fibro-cartilage. 

3.  Diarthroses. — In  diarthrodial  joints  the  surfaces  in  contact  may  be  equal  and  similar 

or  unequal  and  dissimilar.     In  the  former  case  the  joints  are  homomorphic;  in  the 
latter,  heteromorphic. 
(A)  HomomorTphic. 

(a)  Plane    or   arlhrodial.     Flat    surfaces,     admitting     gliding    movement,  e.    g., 

intercarpal  and  acromio-clavicular  joints. 
(6)  Ephippial.     Saddle-shaped  surfaces  placed  at  right  angles  to  each  other,  ad- 
mitting free   movement  in   all   directions,   e.  g.,  metacarpo-phalangeal  joint 
of  thumb. 


DEVELOPMENT  OF  JOINTS 


213 


(B)  Heteromorphic. 

(a)  Enarlhrodial.     Ball-and-socket,  allowing  the  most  free  movement,  e.  g.,  hip- 

and  shoulder-joints. 
(6)   Condylarlhroses.     The  convex  surface  is  ellipsoidal,  and  fits  into  a  corresponding 

concavity,  e.  g.,  wrist  and  metacarpo-phalangeal  joints, 
(c)   Ginglymi.     One  surface  consists  of  two  conjoined  condyles  or  of  a  segment  of 
a  cone  or  cylinder,  and  the  opposite  surface  has  a  reciprocal  contour.     In  these 
joints  movement  is  only  permitted  round  one  axis,  which  may  be  transverse; 
e.  g.,  elbow,  ankle;  or  it  may  be  vertical,  in  which  case  the  joint  is  trochoid; 
e.  g.,  odontoid  process  of  axis  with  atlas,  radius  with  ulna. 
Such  a  classification  should  be  considered  as  being  purely  academic  and  the  student  must 
always  remember  that  it  is  not  enough  to  discuss  a  joint  by  assigning  it  to  a  particular  class  in 
any  scheme;  for  he  must  be  familiar  with  the  actual  conditions  present  in  every  joint.     No 
classification,  however  perfect,  must  be  taken  as  final,  and  each  joint  should  be  studied  as  a 
separate  thing  altogether  apart  from  any  general  systematic  arrangement. 


DEVELOPMENT  AND  MORPHOLOGY  OF  JOINTS 

The  arrangement  of  the  various  parts  which  constitute  an  articulation  is  best  appreciated 
by  a  study  of  the  development  of  the  various  types  of  joints.  In  this  way  it  is  easy  to  recog- 
nise a  primitive  condition  typical  of  each  class;  but  it  must  be  remembered  that  various  modi- 
fications take  place  during  growth,  that  these  modifications  vary  in  the  individual  joints,  and 
produce  adult  departures  from  the  primitive  arrangement  which  are  peculiar  to  each  joint  and 
which  must  be  studied  separately. 

In  the  case  of  bones  ossifying  in  membrane  the  articulation  will  be  a  suture,  the  ossifications 
from  neighbouring  centres  extending  until  they  practically  come  into  contact. 

Fig.  255. — Development  of  Joints 

A.  Stage  in  which  primary  embryonic  tissue  separates  the  developing  cartilages. 

B.  Primary  embryonic  tissue  transformed  into  cartilage  (synchondrosis),  or  fibrous  connec- 
tive tissue  (syndesmosis). 

C.  Degeneration  of  embryonic  tissue  with  production  of  a  joint  cavity  (diarthrosis). 


tWith  cartOage  bones  the  articulation  may  be  either  a  syndesmosis,  a  synchondrosis,  or  a 
diarthrosis.  The  embryonic  tissue  in  which  the  cartilage  is  to  develop  is  at  first  continuous; 
centres  of  chondrification,  corresponding  in  number  to  the  bony  elements  which  are  destined  to 
be  formed,  appearing  in  it.  As  the  chondrifications  approach  each  other  a  small  portion  of  the 
primary  embryonic  tissue  persists  between  them  (fig.  255),  and  it  is  the  subsequent  fate  of 
this  intermediate  tissue  that  determines  the  nature  of  the  articulation. 

(1)  When  the  ossification  of  the  cartilage  occurs  to  form  the  articulating  bones,  the  inter- 
mediate tissue  may  undergo  transformation  into  cartilage  (fig.  255),  a  synchondrosis  being 
thus  produced.     (2)  Or  the  intermediate  tissue  may  be  converted  into  fibrous  connective-tissue 


I 


214  THE  ARTICULATIONS 

(fig.  255),  the  result  being  a  syndesmosis.  (3)  Or,  finally,  the  central  portion  of  the  inter- 
mediate tissue  may  degenerate,  so  that  an  articular  cavity  is  produced,  the  peripheral  portions 
being  converted  into  connective  tissue,  forming  a  sleeve-like  capsule  surrounding  the  cavity, 
continuous  at  either  extremity  with  the  periosteum  of  the  articulating  bones  (fig.  255).  This 
is  the  articular  capsule,  and  the  connective-tissue  cells  arranging  themselves  in  a  layer  upon 
its  inner  surface  give  rise  to  a  synovial  membrane.  As  the  result  of  these  processes  a  diarthrosis 
is  produced,  and  from  its  mode  of  formation  it  is  clear  that  the  cavity  of  such  an  articulation  is 
completely  closed. 

In  a  typical  diarthrosis  there  is  therefore  a  ligamentous  capsule  which  entirely  encloses  the 
joint  cavity,  which  is  continuous  with  the  periosteum  of  the  bones  entering  into  the  articulation 
but  which  is  not  attached  to  nor  reflected  onto  the  cartilaginous  ends  of  the  bones  which  consti- 
tute the  articulating  surfaces.  Such  a  capsule  constitutes  the  primitive  bond  between  the  articu- 
lating bones  and  furnishes  a  complete  lubricating  bag  in  which  these  smooth  cartilaginous 
ends  gKde  over  one  another.  This  primitive  capsule,  however,  becomes  modified  in  most  adult 
joints,  (1)  by  unequal  development  of  various  parts  of  the  capsule;  and  (2)  by  the  more  or  less 
complete  incorporation  of  other  structures  which  are  developmentaUy  separate  from  the  capsule. 
Under  the  first  heading  come  specially  thickened  bands  which  may  be  so  distinctly  marked  off 
from  the  rest  of  the  capsule  as  to  be  named  as  separate  hgaments  (e.  g.,  the  temporo-mandibular 
ligament  of  the  mandibular  joint).  Again  certain  thickened  bands  of  capsule  may,  with 
alteration  of  joint  contour,  take  up  anatomical  positions  which  are  apparently  separated  from 
the  rest  of  the  capsule;  advanced  examples  of  this  process  are,  in  all  probability,  seen  in  the 
ligamentum  teres  of  the  hip-joint  and  the  crucial  ligaments  of  the  knee.  Under  the  second 
heading  comes  a  series  of  ligaments  derived  from  a  gi'eat  variety  of  soirrces;  the  most  common 
origin  being  from  the  divorced  or  rearranged  tendons  of  the  muscles  around  the  joint. 

Muscles  arising  from,  or  inserted  into,  bones  in  the  immediate  vicinity  of  a  joint  tend  to 
become  metamorphosed  into  tendon  near  their  attachments,  and  a  comprehensive  study  of 
myology  in  low  vertebrate  forms  indicates  that  there  is  associated  with  this  tissue-change  a 
tendency  for  the  muscle  to  alter  its  point  of  attachment;  hence  a  muscle  originally  inserted  below 
a  joint  may  eventually  come  to  have  its  insertion  above  the  joint.  In  the  same  way,  a  muscle 
arising  above  a  joint  may,  as  a  result  of  altered  environment,  shift  its  origin  to  some  point  below 
the  joint.  To  this  change  of  position  the  term  migration  of  muscles  has  been  applied.  In 
many  instances  a  portion  of  the  muscle  equivalent  to  the  distance  between  the  original  and  the 
acquired  attachment  persists  as  a  fibrous  band  and  fulfils  the  function  of  a  Ugament.  This  is  well 
seen  in  the  knee-joint,  where  the  tibial  collateral  ligament  is  derived  from  the  adductor  magnus, 
this  muscle  having  shifted  its  insertion  from  the  tibia  to  the  femur.  In  the  same  way  the 
fibular  collateral  ligament  represents  the  tendon  of  the  peroneus  longus,  which  has  migrated 
from  the  femur  to  the  head  of  the  fibula. 

Among  other  ligaments  derived  in  a  similar  way  from  muscles  may  be  mentioned  the  sacra- 
tuberous  ligament.  This  was  originally  the  tendon  of  origin  of  the  biceps  femoris.  (H.  Morris, 
Med.  Times  and  Gazette,  1877,  p.  361.)  The  sacro-spinous  is  derived  from  the  fibrous  retro- 
gression of  portions  of  the  coccygeus.  The  sacro-coccygeal  ligaments  represent  the  muscles 
which  lift,  depress,  and  wag  the  tail  in  those  mammals  furnished  with  such  an  appendage; 
indeed,  these  ligaments  are  occasionally  replaced  by  muscle-tissue. 

The  coraco-humeral  ligament  is  derived  from  the  original  tendon  of  insertion  of  the  pectorahs 
minor,  and  not  unfrequently  the  muscle  is  inserted  into  the  lesser  tuberosity  of  the  humerus,  the 
ligament  being  then  replaced  by  the  tendon  of  the  muscle.  The  coraco-clavicular,  rhomboid,  and 
gleno-humeral  ligaments  are  probably  derived  from  modifications  of  the  subclavius  muscle. 

Other  anatomical  structures  besides  muscles  may,  when  degenerated  or  functionally 
altered,  form  the  basis  of  ligaments  in  connection  with  joints.  The  spheno-mandibular  ligament 
is  the  fibrous  remnant  of  the  cartilaginous  mandibular  bar. 

The  pulpy  substance  in  the  centre  of  each  interoertebral  disc  is  derived  from  the  notochord; 
the  apical  ligament  passing  from  the  tip  of  the  dens  to  the  anterior  margin  of  the  foramen 
magnum  is  a  remnant  of  the  sheath  of  the  notochord,  and  indicates  its  position  as  it  passed 
from  the  vertebral  column  into  the  base  of  the  cranium.  The  transverse  ligament  of  the  atlas 
(as  pointed  out  by  Professor  Cleland)  is  a  persistent  and  functional  form  of  the  posterior  conjugal 
ligament  uniting  the  rib-heads  in  seals  and  many  other  mammals,  whilst  the  interosseous 
ligament  of  the  head  of  a  rib  in  man  is  the  feeble  representative  of  this  structure  in  the  thoracic 
region  of  the  spine.  The  ligamentum  conjugate  costarum  was  described  by  Mayer  in  1834 
(Mtiller's  Archiv  fiir  Anatomie).  According  to  Luschka's  account  of  this  ligament  it  would 
seem  as  though  the  posterior  superior  fibres  of  the  capsule  of  the  costo-central  joint  represented 
it  in  man,  rather  than  the  interosseous  ligament. 

THE  MOVEMENTS  OF  JOINTS 

The  movements  which  may  take  place  at  a  joint  are  either  gliding,  angular, 
rotatory,  or  circumductorJ^ 

The  gliding  motion  is  the  simplest,  and  is  common  to  aU  diarthrodial  joints;  it  consists  of  a 
simple  sliding  of  the  apposed  surfaces  of  the  bones  upon  one  another,  without  angular  or  rotatory 
motion.  It  is  the  only  kind  of  motion  permitted  in  the  carpal  and  tarsal  joints,  and  in  those 
between  the  articular  processes  of  the  vertebne. 

The  angular  motion  is  more  elaborate,  and  increases  or  diminishes  the  angle  between  difi'er- 
ent  parts.  There  are  four  varieties,  viz.,  flexion  and  extension,  which  bend  or  straighten  the 
various  joints,  and  take  place  in  a  forward  and  backward  direction  (in  a  perfect  hinge-joint  this 
is  the  only  motion  permitted) ;  and  adduction  and  abduction,  which,  except  in  the  case  of  the  fin- 
gers.and  toes,  signifies  an  approach  to,  or  deviation  from,  the  median  plane  of  the  body.     In  the 


ARTICULATIONS  OF  THE  SKULL  215 

case  of  the  hand,  the  line  to  or  from  which  adduction  and  abduction  are  made  is  drawn  through 
the  middle  finger,  while  in  the  foot  it  is  through  the  second  toe. 

Rotation  is  the  revolution  of  a  bone  about  its  own  axis  without  much  change  of  position. 
It  is  only  seen  in  enarthrodial  and  trochoidal  joints.  The  knee  also  permits  of  slight  rotation  in 
certain  positions,  which  is  a  distinctive  feature  of  this  articulation. 

Circumduction  is  the  movement  compounded  of  the  four  angular  movements  in  quick 
succession,  by  which  the  moving  bone  describes  a  cone,  the  proximal  end  of  the  bone  forming  the 
apex,  while  the  distal  end  describes  the  base  of  the  cone.  It  is  seen  in  the  hip  and  shoulder,  as 
well  as  in  the  carpo-metacarpal  joint  of  the  thumb,  which  thus  approximates  to  the  ball-and- 
socket  joint. 

In  some  situations  where  a  variety  of  motion  is  required,  strength,  security,  and  celerity 
are  obtained  by  the  combination  of  two  or  more  joints,  each  allowing  a  different  class  of  action, 
as  in  the  case  of  the  wrist,  the  ankle,  and  the  head  with  the  spine.  Many  of  the  long  muscles, 
which  pass  over  two  or  more  joints,  act  on  all,  so  tending  to  co-ordinate  their  movements  and 
enabhng  them  to  be  produced  with  the  least  expenditure  of  power.  Muscles  also  act  as  elastic 
ligaments  to  the  joints;  and  when  acting  as  such,  are  diiJusers  and  combiners,  not  producers 
of  movement;  the  short  muscles  producing  movement,  the  long  diffusing  it,  and  thus  allowing 
the  short  muscles  to  act  on  more  than  one  joint. 

Muscles  are  so  disposed  at  their  attachments  near  the  joints  as  never  to  strain  the  Uga- 
ments  by  tending  to  pull  the  bones  apart,  but,  on  the  contrary,  they  add  to  the  security  of  the 
joint  by  bracing  the  bones  firmly  together  during  their  action. 

The  articulations  may  be  divided  for  convenience  of  description  into  those:  1 . 
of  the  Skull;  2.  of  the  Trunk;  3.  of  the  Upper  Limb;  and  4.  of  the  Lower  Limb. 

THE  ARTICULATIONS  OF  THE  SKULL 

The  movable  articulations  of  the  skull  comprise  (1)  the  mandibular;  and  (2) 
those  between  the  skull  and  the  vertebral  column,  namely  (a)  between  the  occiput 
and  atlas ;  (6)  between  the  atlas  and  epistropheus  (axis) ;  and  (c)  the  ligaments 
which  connect  the  occiput  and  epistropheus. 

The  union  of  the  atlas  and  epistropheus  is  described  in  this  section  because, 
(1)  there  is  often  a  direct  communication  between  the  synovial  cavity  of  the  trans- 
verse epistrophic  and  the  occipito-atlantal  joints;  (2)  the  rotatory  movements  of 
the  head  take  place  around  the  dens  (odontoid  process) ;  and  (3)  important  liga- 
ments from  the  dens  pass  over  the  atlas  to  the  occiput. 

(1)  THE  MANDIBULAR  ARTICULATION 

Class. — Diarthrosis.  Subdivision. — Condylarthrosis. 

The  parts  entering  into  the  formation  of  this  joint  (figs.  256,  257)  are: — the 
anterior  portion  of  the  mandibular  fossa  and  glenoid  ridge  (eminentia  articularis) 
of  the  temporal  bone  above,  and  the  condyle  of  the  lower  jaw  below.  Both  are 
covered  with  articular  cartilage,  which  extends  over  the  front  of  the  glenoid  ridge 
to  facilitate  the  play  of  the  interarticular  cartilage.  The  ligaments  which  unite 
the  bones  are: 

1.  Articular  capsule.  3.  Spheno-mandibular. 

2.  Articular  disc.  4.  Stylo-mandibular. 

The  articular  capsule  is  often  described  as  consisting  of  four  portions,  anterior, 
posterior,  lateral  and  medial,  which  are,  however,  continuous  with  one  another 
around  the  articulation. 

1.  The  anterior  portion  consists  of  a  few  stray  fibres  connected  with  the  anterior  margin 
of  the  articular  disc,  and  attached  below  to  the  anterior  edge  of  the  condyle,  and  above  to  the 
front  of  the  articular  eminence.  Some  fibres  of  insertion  of  the  external  pterygoid  pass  between 
them  to  be  inserted  into  the  margin  of  the  articular  disc. 

2.  The  posterior  portion  is  attached  above,  just  in  front  of  the  petro-tympanic  {Glaserian) 
fissure,  and  is  inserted  into  the  back  of  the  jaw  just  below  its  neck. 

3.  The  lateral  portion  or  temporo-mandibular  (external  lateral)  ligament  (fig.  256)  is  the 
strongest  part  of  the  capsule.  It  is  broader  above,  where  it  is  attached  to  the  lower  edge  of 
the  zygoma  in  nearly  its  whole  length,  as  well  as  to  the  tubercle  at  thu  point  where  the  two 
roots  of  the  zygoma  meet.  It  is  inoUned  downward  and  backward,  to  be  inserted  into  the 
condyle  and  neck  of  the  mandible  laterally.  Its  fibres  diminish  in  obliquity  and  strength  from 
before  backward,  those  coming  from  the  tubercle  being  short  and  nearly  vertical. 

4.  The  medial  portion  (or  short  internal  lateral  ligament)  (fig.  257)  consists  of  well-defined 
fibres,  having  a  broad  attachment,  above  to  the  lateral  side  of  the  spine  of  the  sphenoid  and 
medial  edge  of  the  mandibular  fossa;  and  below,  a  narrow  insertion  to  the  medial  side  of  the  neck 


216 


THE  ARTICULATIONS 


of  the  condyle.     Fatty  and  cellular  tissue  separate  it  from  the  spheno-mandibular  ligament 
which  is  medial  to  it. 

The  articular  disc  (fig.  258)  is  an  oval  plate  of  fibro-cartilage  interposed  between 
and  adapted  to  the  two  articular  surfaces.  It  is  thinner  at  the  centre  than  at  the 
circumference,  and  is  thicker  behind,  where  it  covers  the  thin  bone  at  the  bottom 
of  the  mandibular  fossa  which  separates  it  from  the  dura  mater,  than  in  front, 
where  it  covers  the  articular  eminence. 


Fig.  256. — Lateral  View  op  the  Mandebtjlar  Joint. 


I 


Temporo  mandibular 
ligament 


mandibular  ligament 


Fig.  257. — Medial  View  of  the  Mandibijlar  Joint. 


Stylo-hyoid, 
ligament 


Its  inferior  surface  is  concave  and  fits  on  to  the  condyle  of  the  lower  jaw;  while  its  superior 
surface  is  concavo-convex  from  before  backward,  and  is  in  contact  with  the  articular  surface 
of  the  temporal  bone.  It  divides  the  joint  into  two  separate  synovial  cavities,  but  is  occasion- 
ally perforated  in  the  centre,  and  thus  allows  them  to  communicate.  It  is  connected  with  the 
articular  capsule  at  its  circumference,  and  has  some  fibres  of  the  exiernallpterygoid  muscle 
inserted  into  its  anterior  margin. 

There  are  usually  two  synovial  membranes  (fig.  258),  the  superior  being  the 
larger  and  looser,  passing  down  from  the  margin  of  the  articular  surface  above,  to 
the  upper  surface  of  the  articular  disc  below;  the  lower  and  smaller  one  passes 


THE  MANDIBULAR  JOINT 


217 


from  the  articular  disc  above  to  the  condyle  of  the  jaw  below,  extending  somewhat 
further  down  behind  than  in  front.  When  the  disc  is  perforated,  the  two  sacs 
communicate. 

The  spheno-mandibular  ligament  (long  internal  lateral)  (fig.  257)  is  a  thm, 
loose  band,  situated  some  little  distance  from  the  joint.  It  is  attached  above  to 
the  spine  of  the  sphenoid  and  contiguous  part  of  the  temporal  bone,  and  is  inserted 
into  the  lingula  of  the  lower  jaw. 

It  covers  the  upper  end  of  the  mylo-hyoid  groove,  and  is  here  pierced  by  the  mylo-hyoid 
nerve.  Its  origin  is  a  little  medial  to,  and  immediately  behind,  the  origin  of  the  medial  por- 
tion of  the  capsule.  It  is  separated  from  the  joint  and  ramus  of  the  jaw  by  the  external  ■ptery- 
goid muscle,  the  internal  maxillary  artery  and  vein,  the  inferior  alveolar  {dental)  nerve  and 
artery,  the  auriculo-temporal  nerve,  and  the  middle  meningeal  artery.  It  is  really  the  fibrous 
remnant  of  a  part  of  the  mandibular  (Meckelian)  bar. 

The  stylo -mandibular  ligament  (stylo-maxillary)  (figs.  256  and  257)  is  a 
process  of  the  deep  cervical  fascia  extending  from  near  the  tip  of  the  styloid  proc- 
ess to  the  angle  and  posterior  border  of  the  ramus  of  the  jaw,  between  the  masseter 
and  internal  ■pterygoid  muscles.  It  separates  the  parotid  from  the  submaxillary 
gland,  and  gives  origin  to  some  fibres  of  the  st^ylo-glossus  muscle. 

Fig.  258. — Sagittal  Section  through  the  Condyle  op  Jaw  to  show  the  Two  Synqviai. 
Sacs  and  the  Articular  Disc. 


Articular  disc  -l^j^ftr  •rr  _^  r 
Section  through  condyle^ —    ->     — i-4- 
Posterior  portion  of         -ji/lTiN     u 
capsule  \»4T^^ 


Spheno-mandibular  hgament 


Stylo-mandibular  hgament 


The  arterial  supply  of  the  mandibular  joint  is  derived  from  the'temporal,  middle  meningeal 
and  ascending  pharyngeal  arteries,  and  from  the  latter  by  its  branches  to  the  Eustachian  tube. 

The  nerves  are  derived  from  the  masseteric  and  auriculo-temporal. 

Movements. — The  chief  movement  of  this  joint  is  of  (i)  a  ginglymoid  or  hinge  character, 
accompanied  by  a  slight  gliding  action,  as  in  opening  or  shutting  the  mouth.  In  the  opening 
movement  the  condyle  turns  like  a  hinge  on  the  articular  disc,  while  at  the  same  time  the  ar- 
ticular disc,  together  with  the  condyle,  glides  forward  so  as  to  rise  upon  the  eminentia  articularis, 
reaching  as  far  as  the  anterior  edge  of  the  eminence,  which  is  coated  with  articular  cartilage 
to  receive  it;  but  the  condyle  never  reaches  quite  so  far  as  the  summit  of  the  eminence.  Should 
the  condyle,  however,  by  excessive  movement  (as  in  a  convulsive  yawn),  glide  over  the  summit, 
it  slips  into  the  zygomatic  fossa,  the  mandible  is  dislocated,  and  the  posterior  portion  of  the 
capsule  is  torn.  In  the  shutting  movement  the  condyle  revolves  back  again,  and  the  articular 
disc  glides  back,  carrying  the  condyle  with  it.  This  combination  of  the  hinge  and  gUding 
motions  gives  a  tearing  as  well  as  a  cutting  action  to  the  incisor  teeth,  without  any  extra  muscu- 
lar exertion. 

There  is  (ii)  a  horizontal  gliding  action  in  an  antero-posterior  direction,  by  which  the  lower 
teeth  are  thrust  forward  and  drawn  back  again:  this  takes  place  almost  entirely  in  the  upper 
compartment,  because  of  the  closer  connection  of  the  articular  disc  with  the  condyle  than  with 
the  squamosal  bone,  and  also  because  of  the  insertion  of  the  external  pterygoid  into  both  bone 
and  cartilage.  In  these  two  sets  of  movements  the  joints  of  both  sides  are  simultaneously  and 
similarly  engaged. 

The  third  form  of  movement  is  called  (iii)  the  oblique  rotatory,  and  is  that  by  which  the 
grinding  and  chewing  actions  are  performed.     It  consists  in  a  rotation  of  the  cond3'le  about 


I 


218  THE  ARTICULATIONS 

the  vertical  axis  of  its  neck  in  the  lower  compartment,  while  the  cartilage  glides  obUquely  for- 
ward and  inward  on  one  side,  and  backward  and  inward  on  the  other,  upon  the  articular  surface 
of  the  squamosal  bones,  each  side  acting  alternately.  If  the  symphysis  be  simply  moved  from 
the  centre  to  one  side  and  back  again,  and  not  from  side  to  side  as  in  grinding,  the  condyle  of 
that  side  moves  round  the  vertical  axis  of  its  neck,  and  the  opposite  condyle  and  cartilage  ghde 
forward  and  inward  upon  the  mandibular  fossa.  But  in  the  ordinary  grinding  movement,  one 
condyle  advances  and  the  other  recedes,  and  then  the  first  recedes  while  the  other  advances, 
slight  rotation  taking  place  in  each  joint  meanwhile. 

Relations. — The  chief  relations  are:  Behind,  and  overlapping  the  lateral  side,  the  parotid 
gland.  Laterally,  the  superficial  temporal  artery.  Medially,  the  internal  maxillary  artery 
and  auriculo-temporal  nerve.     In  front,  the  nerve  to  the  masseter  muscle. 

Muscles  acting  on  the  joint. — Elevators  of  the  mandible. — temporals,  masseters,  int. 
pterygoids. 

Depressors. — -Mylo-hyoids,  digastrics,  genio-hyoid,  muscles  connecting  the  hyoid  bone  to 
lower  points.     Ext.  pterygoids.     The  weight  of  the  jaw. 

Protractors. — Ext.  pterygoids,  superficial  layer  of  masseters,  anterior  fibres  of  temporals. 

Retractors. — Posterior  fibres  of  temporals,  slightly  by  the  int.  pterygoids  and  deep  layer  of 
the  masseters. 

(2)  THE   LIGAMENTS   AND   JOINTS   BETWEEN   THE   SKULL   AND 

VERTEBRAL   COLUMN,   AND   BETWEEN  THE   ATLAS  AND 

EPISTROPHEUS 

(a)  The  Articulation  of  the  Atlas  with  the  Occiput 

Class. — Diarthrosis.         Subdivision. — Double  Condylarthrosis. 

This  articulation  [articulatio  atlanto-occipitalis]  consists  of  a  pair  of  joints 
symmetrically  situated  on  either  side  of  the  middle  line.  The  parts  entering  into 
their  formation  are  the  cup-shaped  superior  articular  processes  of  the  atlas  and 
the  condyles  of  the  occipital  bone.     They  are  united  by  the  following  ligaments : — 

1.  Anterior  atlanto-occipital.         3.  Two  articular  capsules. 

2.  Posterior  atlanto-occipital.        4.  Two  anterior  oblique. 

The  anterior  atlanto-occipital  ligament  [membrana  atlanto-occipitalis  anterior] 
(fig.  259)  is  less  than  an  inch  (about  2  cm.)  wide,  and  is  composed  of  densely 
woven  fibres,  most  of  which  radiate  slightly  lateralward  as  they  ascend  from  the 
front  surface  and  upper  margin  of  the  anterior  arch  of  the  atlas  to  the  anterior 
border  of  the  foramen  magnum;  it  is  continuous  at  the  sides  with  the  articular 
capsules,  the  fibres  of  which  overlap  its  edges,  and  take  an  opposite  direction 
medially  and  upward. 

The  central  fibres  ascend  vertically  from  the  anterior  tubercle  of  the  atlas  to  the  pharyn- 
geal tubercle  on  the  occipital  bone;  they  are  thicker  than  the  lateral  fibres,  and  are  continuous 
below  with  the  superficial  part  of  the  anterior  atlanto-epistrophic  ligarnent,  and  through  it 
with  the  anterior  longitudinal  ligament  of  the  vertebral  column.  It  is  in  relation,  in  front, 
with  the  recti  capitis  anteriores;  and  behind,  with  the  apical  dental  or  suspensory  ligament. 

The  posterior  atlanto-occipital  ligament  (fig.  260)  is  broader,  more  mem- 
branous, and  not  so  strong  as  the  anterior.  It  extends  from  the  posterior  surface 
and  upper  border  of  the  posterior  arch  of  the  atlas  to  the  posterior  margin  of  the 
foramen  magnum  from  condyle  to  condyle;  being  incomplete  on  either  side  for  the 
passage  of  the  vertebral  artery  into,  and  suboccipital  nerve  out  of,  the  canal.  It  is 
somewhat  thickened  in  the  middle  line  by  fibres,  which  pass  from  the  posterior 
tubercle  of  the  atlas  to  the  lower  end  of  the  occipital  crest. 

It  is  not  tightly  stretched  between  the  bones,  nor  does  it  limit  their  movements;  it  corre- 
sponds with  the  position  of  the  ligamenta  flava,  but  has  no  elastic  tissue  in  its  composition. 
It  is  in  relation  in  front  with  the  dura  mater,  which  is  firmly  attached  to  it;  and  behind  with  the 
recti  capitis  posteriores  minores,  and  enters  into  the  floor  of  the  suboccipital  triangle.  Its 
lateral  margins,  which  do  not  reach  the  occipital  bone  but  terminate  on  the  posterior  end  of 
the  superior  articular  processes  of  the  atlas,  form  the  so-called  oblique  ligaments  of  the  atlas. 
The  lateral  margins  of  these  ligaments  are  free  and  they  form  the  posterior  boundaries  of  the 
apertures  through  which  the  vertebral  arteries  enter  and  the  suboccipital  nerves  leave  the 
vertebral  canal. 

The  atlanto-occipital  articular  capsules  (figs.  259  and  260)  are  very  distinct 
and  strongly  marked,  except  on  the  medial  side,  where  they  are  thin  and  formed 
only  of  short  membranous  fibres.  They  are  lax,  and  do  not  add  much  to  the 
security  of  the  joint. 


ARTICULATION  OF  ATLAS  WITH  OCCIPUT 


219 


In  front,  the  capsule  descends  upon  the  atlas,  to  be  attached,  some  distance  below  the 
articular  margin,  to  the  front  surface  of  the  lateral  mass  and  to  the  base  of  the  transverse  proc- 
ess ;  these  fibres  take  an  obUque  course  upward  and  medialward,  overlapping  the  anterior  atlan to- 
occipital.  At  the  sides  and  behind,  the  capsule  is  attached  above  to  the  margins  of  the  occipital 
condyles;  below,  it  skirts  the  medial  edge  of  the  foramen  for  the  vertebral  artery,  and  behind 
is  attached  to  the  prominent  tubercle  overhanging  the  groove  for  that  vessel;  these  latter  fibres 
are  strengthened  by  a  band  running  obliqviely  upward  and  medialward  to  the  posterior  margin 
of  the  foramen  magnum. 

The  anterior  oblique  or  lateral  occipito-atlantal  ligament  is  an  accessory 
band  which  strengthens  the  capsule  laterally  (fig.  259).  It  is  an  oblique,  thick 
band  of  fibres,  sometimes  quite  separate  and  distinct  from  the  rest,  passing 
upward  and  medialward  from  the  upper  surface  of  the  transverse  process  beyond 
the  costo-transverse  foramen  to  the  jugular  process  of  the  occipital  bone. 

The  synovial  membrane  of  these  joints  occasionally  communicates  with  the 
synovial  sac  between  the  dens  (odontoid  process)  and  the  transverse  ligament. 

The  arterial  supply  is  derived  from  twigs  of  the  vertebral,  and  occasionally  from  twigs 
from  the  meningeal  branches  of  the  ascending  pharyngeal. 

Fig.  259. — Anteriok  View  of  the  Upper  End  of  the  Vertebral  Column. 


Continuation  of 
tiie    anterior 
longitudinal 
ligament   of 

Atlanto-         V        ,/^       '^'  A  '  '  '    /K H_  '^  'he   vertebral 

occipital" ^~\         ^  /y^^a      1%"'K  ^  I  column 

articular  ^j;  \  i  '<ii£l^a    L£ZZZ.  »X  ,     ,         Anterior  atlanto- 

capsule  N^\  Z5  I  *■'  /    '  occipital  liga- 

ment 


The  anterior  oblique  or  —  ,   ,, 

lateral      occipitoatlantal  //// 
ligament 

Atlanto-epistroph:  _  ^  

articular  capsule     ]^  /^      ii]i\'J~,         I  ^  J^ ''* 


Articular  capsules  of  arti- 
cular processes  between 
axis  and  the  third,  the 
third  and  fourth,  and 
the  fourth  and  fifth  cer- 
vical vertebrae 


Anterior  atlanto- 
-^■*   epistrophic  ligament 


Short  vertebral 
ligament 


Anterior  longitudinal 
*^  ligament 


The  nerve-supply  comes  from  the  anterior  division  of  the  suboccipital  nerve. 

Movements. — By  the  symmetrical  and  bilateral  arrangement  of  these  joints,  security  and 
strength  are  gained  at  the  expense  of  a  very  small  amount  of  actual  articular  surface;  the  basis 
of  support  and  the  area  of  action  being  equal  to  the  width  between  the  most  distant  borders 
of  the  joint. 

The  principal  movement  permitted  at  these  joints  is  of  a  ginglymoid  character,  producing 
flexion  and  extension  upon  a  transverse  axis  drawn  across  the  condyles  at  their  slightly  con- 
stricted parts. 

In  flexion,  the  forehead  and  chin  drop,  and  what  is  called  the  nodding  movement  is  made; 
in  extension,  the  chin  is  elevated  and  the  forehead  recedes. 

There  is  also  a  slight  amount  of  gliding  movement,  either  directly  lateral,  the  lateral  edge 
of  one  condyle  sinking  a  little  within  the  lateral  edge  of  the  socket  of  the  atlas,  and  that  of  the 
opposite  condyle  projecting  to  a  corresponding  degree.  The  head  is  thus  tilted  to  one  side,  and 
it  is  even  possible  that  the  weight  of  the  skull  may  be  borne  almost  entuely  on  one  joint,  the 
articular  surfaces  of  the  other  being  thrown  out  of  contact. 

Or  the  movement  may  be  obliquely  lateral,  when  the  lower  side  of  the  head  will  be  a  trifle 


220 


THE  ARTICULATIONS 


in  advance  of  the  elevated  side.  In  this  motion,  which  takes  place  on  the  antero-posterior  axis, 
one  condyle  advances  slightly  and  approaches  the  middle  line,  while  the  other  recedes.  This  is 
of  the  nature  of  rotation,  though  there  is  no  true  rotation  round  a  vertical  axis  possible  between 
the  occiput  and  atlas. 

These  lateral  movements  are  checked  by  the  alar  ligaments  and  the  lateral  part  of  the 
capsules;  extension  is  checked  by  the  anterior  atlanto-oocipital  and  anterior  oblique  ligaments, 
and  flexion  by  the  posterior  part  of  the  capsule  and  the  tectorial  membrane. 

Muscles  acting  upon  the  occipito-atlantal  joint. — Flexion  whereby  the  chin  is  approxi- 
mated toward  the  sternum  is  produced  by  the  weight  of  the  anterior  part  of  the  head  and  by 
all  muscles  which  are  attached  to  the  hyoid  bone  or  to  the  bones  of  the  skuU  in  front  of  a  trans- 
verse axis  between  the  two  condyles.  These  muscles  take  their  fixed  point  below  either  from 
the  vertebral  columir,  the  sternum,  or  the  bones  of  the  shoulder  girdle.  Before  those  connected 
with  the  mandible  can  act  that  bone  must  be  fixed  by  the  muscles  of  mastication  which,  there- 
fore, also  take  part  in  the  movements.  It  must  be  noted  that  the  sterno-mastoid  muscles  are 
powerful  flexors,  although  a  part  of  their  insertion  is  behind  the  transverse  axis  between  the 
two  condyles. 

Extension  is  due  to  the  action  of  muscles  or  portions  of  muscles  inserted  into  the  skull 
behind  the  transverse  axis  above  mentioned,  and  connected  below  either  with  the  vertebral 
column,  shoulder  girdle,  or  sternum. 

Lateral  movement  is  produced  by  the  anterior  and  posterior  groups  of  muscles  on  the  same 
side  acting  simultaneously  and  aided  by  the  rectus  capitis  lateralis  of  that  side. 


I 


Fig.  260. — Median  Sagittal  Section  of  Yektebral  Column  showing  Ligaments. 


Transverse  ligament 


Inner   part   of    capsular   ligament    of 
atlanto-occipital  joint 


Posterior  atlanto-occipital 
ligament 


Descending  portion  of  crucial 

ligament 
Posterior  atlanto-epistrophic 

ligament 


Interspinous  ligament 


Ligamentum  flavum 


-Apical     dental    ligament 
Anterior  atlanto-occipital 
\\  ligament 

\_      Atlanto-dental  synovial 


(b)  The  Articulations  between  the  Atlas  and    Epistropheus    (Axis). 


1.  The  Lateral  Atlanto-epistrophic  Joints. 

2 .  The  Central  Atlanto-epistrophic  Joint  or 

The  Atlanto-dental. 


Class. — Diarthrosis. 
Subdivision. — Arthrodia. 
Class. — Diarthrosis. 
\  Subdivision. — Trochoides. 


The  bones  that  enter  into  the  formation  of  the  lateral  joints  are  the  inferior 
articular  processes  of  the  atlas  and  the  superior  of  the  epistropheus  (axis);  the 
central  joint  is  formed  by  the  dens  (odontoid  process)  articulating  in  front  with 
the  atlas,  and  behind  with  the  transverse  ligament. 


ATLANTO-EPISTROPHIC  JOINTS 


221 


The  ligaments  which  unite  the  epistropheus  and  atlas  are : — 

1.  The  anterior  atlanto-epistrophic.        3.  Two  articular  capsules   (for  lateral 

joints). 

2.  The  posterior  atlanto-epistrophic.      4.  The  transverse  ligament. 


5.  The  atlanto-dental  articular  capsule. 

The  anterior  atlanto-epistrophic  ligament  (figs.  259  and  260)  is  a  narrow  but 
strong  membrane  filling  up  the  interval  between  the  lateral  joints.  It  is  attached 
above  to  the  front  surface  and  lower  border  of  the  anterior  arch  of  the  atlas,  and 
below  to  the  transverse  ridge  on  the  front  of  the  body  of  the  epistropheus.  Its 
fibres  are  vertical,  and  are  thickened  in  the  median  line  by  a  dense  band  which  is 
a  continuation  upward  of  the  anterior  longitudinal  ligament  of  the  vertebral 
column. 

This  band  is  fixed  above  to  the  anterior  tubercle  of  the  atlas,  where  it  becomes  continuous 
with  the  central  part  of  the  anterior  atlanto-oocipital  ligament  (fig.  259) ;  it  is  sometimes  sepa- 
rated by  an  interval  from  the  deeper  ligament,  and  is  often  described  as  the  superficial  atlanto- 
epistrophic  ligament.     It  is  in  relation  with  the  longus  colli  muscle. 

The  posterior  atlanto-epistrophic  ligament  (fig.  260)  is  a  deeper,  but  thinner 
and  looser  membrane  than  the  anterior.  It  extends  from  the  posterior  root  of  the 
transverse  process  of  one  side  to  that  of  the  other,  projecting  laterally  beyond 
the  posterior  part  of  the  capsules  which  are  connected  with  it.  It  is  attached 
above  to  the  posterior  surface  and  lower  edge  of  the  posterior  arch  of  the  atlas, 
and  below  to  the  superior  edge  of  the  laminae  of  the  epistropheus  on  their  dorsal 
aspect. 

It  is  denser  and  stronger  in  the  median  line,  and  has  a  layer  of  elastic  tissue  on  its  anterior 
surface  like  the  ligamenta  flava,  to  which  it  corresponds  in  position.  It  is  connected  in  front 
with  the  dura  mater;  behind,  it  is  in  relation  with  the  inferior  oblique  muscles,  and  is  perforated 
at  each  side  by  the  second  cervical  nerve. 

1.  The  Lateral  Atlanto-epistrophic  Joints  are  provided  with  short, 
ligamentous  fibres,  forming  ari:icular  capsules  (fig.  259),  which  completely  sur- 
round the  lateral  articular  facets.  Lateral  to  the  canal  they  are  attached  some 
little  distance  from  the  articular  margins,  extending  along  the  roots  of  the 

Pig.  261. — Horizontal  Section  through  the  Lateral  Masses  of   the   Atlas  and  the 
Top  of  the  Dens  (Odontoid  Process). 


Atlanto-dental 
synovial  sac 


Transverse  dental 
synovial  sac 


Atlanto-dental 
articular  capsule 
Transverse 

ligament 
Posterior  longitud- 
inal   ligament    and 
tectorial  membrane 


transverse  processes  of  the  epistropheus  nearly  to  the  tips,  but  between  the  roots 
they  skirt  the  medial  edge  of  the  costo-transverse  foramina.  They  are  strength- 
ened in  front  and  behind  by  the  atlanto-epistrophic  hgaments. 

Medially  each  capsule  is  thinner,  and  attached  close  to  the  articular  mai'gins,  being  strength- 
ened behind  by  a  strong  band  of  slightly  oblique  fibres  passing  upward  along  the  lateral  edge  of 
the  tectorial  membrane  from  the  body  of  the  epistropheus  to  the  lateral  mass  of  the  atlas  behind 
the  transverse  ligament;  some  of  these  fibres  pass  on,  thickening  and  blending  with  the  atlanto- 
oocipital  capsule,  to  be  inserted  into  the  margin  of  the  foramen  magnum.  This  band  is  some- 
times called  the  accessory  band  (fig.  263). 

There  is  a  synovial  membrane  for  each  joint. 

2.  The  Central  Atlanto-epistrophic  Joint,  although  usually  described  as 
one,  is  composed  of  two  articulations,  which  are  quite  separate  from  one  another : 


> 


222  THE  ARTICULATIONS 

an  anterior  between  the  dens  and  the  arch  of  the  atlas,  and  a  posterior  between 
the  dens  and  the  transverse  hgament. 

The  transverse  ligament  (figs.  260,  261,  and  263)  is  one  of  the  most  important 
structures  in  the  body,  for  on  its  integrity  and  that  of  the  alar  ligaments  our 
lives  largely  depend.  It  is  a  thick  and  very  strong  band,  as  dense  and  closely 
woven  as  fibro-cartilage,  about  a  quarter  of  an  inch  (6  mm.)  deep  at  the  sides, 
and  somewhat  more  in  the  middle  line.  Attached  at  each  end  to  a  tubercle  on 
the  inner  side  of  the  lateral  mass  of  the  atlas,  it  crosses  the  ring  of  this  bone  in  a 
curved  manner,  so  as  to  have  the  concavity  forward;  thus  dividing  the  ring  into 
a  smaller  anterior  portion  for  the  dens  and  a  larger  posterior  part  for  the  spinal 
cord  and  its  membranes,  and  the  spinal  accessory  nerves. 

It  is  flattened  from  before  backward,  being  smooth  in  front,  and  covered  by  synovial  mem- 
brane to  allow  it  to  glide  freely  over  the  posterior  facet  of  the  dens.  Where  it  is  attached  to  the 
atlas  it  is  smooth  and  well  rounded  off  to  provide  an  easy  floor  of  communication  between  the 
transverso-dental  and  occipito-atlantal  joints. 

To  its  posterior  surface  is  added,  in  the  middle  line,  a  strong  fasciculus  of 
vertical  fibres,  passing  upward  from  the  root  of  the  dens  to  the  basilar  border  of 
the  foramen  magnum  on  its  cranial  aspect.  Some  of  these  fibres  are  derived 
from  the  transverse  ligament.  These  vertical  fibres  give  the  transverse  liga- 
ment a  cruciform  appearance;  hence  the  name,  the  crucial  ligament  (figs.  260 
and  263)  applied  to  the  whole. 

The  atlanto-dental  articular  capsule  (fig.  261)  is  a  tough,  loose  membrane, 
completely  surrounding  the  apposed  articular  surfaces  of  the  atlas  and  dens. 

At  the  dens  it  blends  above  with  the  front  of  the  alar  and  central  occipito-odontoid  liga- 
ments, and  arises  also  along  the  sides  of  the  articular  facet  as  far  as  the  neck  of  the  dens;  the 
fibres  are  thick,  and  blend  with  the  capsules  of  the  lateral  joint.  At  the  atlas  they  are  attached 
to  the  non-articular  part  of  the  anterior  arch  in  front  of  the  tubercles  for  the  transverse  liga- 
ment, blending,  above  and  below  the  borders  of  the  bone,  with  the  anterior  atlanto-occipital 
and  atlanto-epistrophic  ligaments,  as  well  as  with  the  medial  portion  of  the  articular  capsules. 
It  holds  the  dens  to  the  anterior  arch  of  the  atlas  after  aU  the  other  ligaments  have  been  divided. 

The  synovial  membranes  (figs.  260  and  261)  are  two  in  number: — one  for  the 
joint  between  the  dens  and  atlas;  and  another  (transverso-dental)  for  that 
between  the  transverse  ligament  and  the  dens.  This  last  often  communicates 
with  the  atlanto-occipital  articulations;  it  is  closed  in  by  membranous  tissue 
between  the  borders  of  the  transverse  ligament  and  the  margin  of  the  facet  on 
the  dens,  and  is  separated  from  the  front  sac  by  the  atlanto-dental  articular 
capsule. 

The  arterial  supply  is  from  the  vertebral  artery,  aiid  the  nerve-supply  from  the  loop  between 
the  first  and  second  cervical  nerves. 

Movements. — The  chief  and  characteristic  movement  at  these  joints  is  the  rotation,  in  a 
nearly  horizontal  plane,  of  the  collar  formed  by  the  atlas  and  transverse  ligament,  round  the 
dens  as  a  pivot,  which  is  extensive  enough  to  allow  of  an  all-round  view  without  twisting  the 
trunk.  Partly  on  account  of  its  ligamentous  attachments,  and  partly  on  account  of  the  shape 
of  the  articular  siirfaces,  the  cranium  must  be  carried  with  the  atlas  in  these  movements.  The 
rotation  is  checked  by  the  ligaments  passing  from  the  dens  to  the  occiput  (alar  ligarnents),  and 
also  by  the  atlanto-epistrophic.  Owing  to  the  fact  that  the  facets  of  both  atlas  and  epistropheus, 
which  enter  into  the  formation  of  the  lateral  atlanto-epistrophic  articulations,  are  convex  from 
before  backward,  and  have  the  articular  cartilage  thicker  in  the  centre  than  at  the  circumfer- 
ence, the  motion  is  not  quite  horizontal  but  slightly  curvilinear.  In  the  erect  position,  with  the 
face  looking  directly  forward,  the  most  convex  portions  of  the  articular  surfaces  are  alone  in 
contact,  there  being  a  considerable  interval  between  the  edges;  dm-ing  rotation,  therefore,  the 
prominent  portions  of  the  condyles  of  the  atlas  descend  upon  those  of  the  epistropheus,  dimin- 
ishing the  space  between  the  bones,  slackening  the  ligaments,  and  thus  increasing  the  amount  of 
rotation,  without  sacrificing  the  security  of  the  joint  in  the  central  position. 

Besides  rotation,  forward  and  backward  movements  and  some  lateral  flexion  are  permitted 
between  the  atlas  and  epistropheus,  even  to  a  greater  extent  than  in  most  of  the  other  vertebral 
joints. 

The  muscles  acting  upon  the  atlanto-epistrophic  joints. — The  muscles  capable  of  producing 
rotation  at  the  atlanto-epistrophic  joints  are  those  which  take  origin  from  near  the  mesial  plane 
either  in  front  or  behind  and  which  are  attached  above  either  to  the  atlas  or  the  skull,  lateral 
to  the  atlanto-epistrophic  joints.  When  the  muscles  which  lie  at  the  back  of  the  joint  on  one 
side  act  they  will  turn  the  head  to  the  same  side  and  will  be  aided  by  the  muscles  in  front  on  the 
opposite  side.  If  the  muscles  in  front  and  behind  on  the  same  side  act  simultaneously,  they  will 
pull  down  the  head  to  that  side  and  will  be  aided  by  muscles  which  pass  more  or  less  vertically 
from  the  transverse  process  of  the  atlas  to  points  below. 


LIGAMENTS  OF  OCCIPUT  AND  EPISTROPHEUS 


223 


(c)  The  Ligaments  uniting  the  Occiput  and  Epistropheus 

The  following  ligaments  unite  bones  not  in  contact,  and  are  to  be  seen  from 
the  interior  of  the  canal  after  removing  the  posterior  arches  of  the  epistropheus 
and  atlas  and  posterior  ring  of  the  foramen  magnum : — 


1.  The  tectorial  membrane. 

2.  The  crucial  ligament. 


3.  Two  alar  (or  check)  ligaments. 

4.  The  apical  dental  ligament. 


The  tectorial  membrane  (occipito-cervical  hgament)  (figs.  261,  262,  and  263) 
consists  of  a  very  strong  band  of  fibres,  connected  below  to  the  upper  part  of 
the  body  of  the  third  vertebra  and  lower  part  of  the  body  of  the  epistropheus 
as  far  as  the  root  of  the  dens.  It  is  narrow  below,  but  widens  out  as  it  ascends, 
to  be  fastened  to  the  basilar  groove  of  the  occiput.  Laterally,  it  is  connected 
with  the  accessory  fibres  of  the  atlanto-epistrophic  capsule.  It  is  really  only 
the  upward  prolongation  of  the  deep  stratum  of  the  posterior  longitudinal 
ligament,  the  superficial  fibres  of  which  run  on  to  the  occipital  bone  without 
touching  the  epistropheus,  thus  giving  rise  to  two  strata.  It  is  in  relation  in 
front  with  the  crucial  ligament. 

Fig.  262. — The  Superficial  Layer  of  the  Posteeioe  Longitudinal  Vertebral  Liga- 
ment HAS  BEEN  Removed  to  show  its  Deep  oh  Short  Fibres.  These  Deep  Fibres 
FORM  the  Tectorial  Membrane.     Viewed  from  behind. 


$/  Membrana  tectoria,  i.  e.^ 
the  deep  stratum  of  the 
posterior  longitudinal 
vertebral  hgament 


Transverse  process  of  atlas 


The  crucial  ligament  has  been  already  described  (see  p.  222). 

The  alar  (or  check)  ligaments  (figs.  260  and  263)  are  two  strong  rounded 
cords,  which  extend  from  the  sides  of  the  apex  of  the  dens,  transversely  lateral- 
ward  to  the  medial  edge  of  the  anterior  portion  of  the  occipital  condyles. 

They  are  to  be  seen  immediately  above  the  upper  border  of  the  transverse  ligament,  which 
they  cross  obliquely  owing  to  its  forward  curve  at  its  attachments  to  the  atlas.  Some  of  their 
fibres  occasionally  run  across  the  middle  line  from  one  alar  ligament  to  the  other.  At  the  dens 
they  are  connected  with  the  atlan to-dental  capsule,  and  at  the  condyles  they  strengthen  the 
atlanto-occipital  articular  capsule. 

The  apical  dental  or  suspensory  ligament  (figs.  260  and  263)  consists  of  a 
slender  band  of  fibres  ascending  from  the  summit  of  the  dens  to  the  lower  surface 
of  the  occipital  bone,  close  to  the  foramen  magnum.  It  is  best  seen  from  the 
front,  after  removing  the  anterior  atlanto-occipital  ligament,  or  from  behind  by 
drawing  aside  the  crucial  ligament. 


224 


THE  ARTICULATIONS 


The  apical  ligament  is  tightened  by  extension  and  relaxed  by  flexion  or  nodding;  the  alar 
ligaments  not  only  limit  the  rotatory  movements  of  the  head  and  atlas  upon  the  epistropheus, 
but  by  binding  the  occiput  to  the  pivot,  round  which  rotation  occurs,  they  steady  the  head 
and  prevent  its  undue  lateral  inclination  upon  the  vertebral  column.  (See  Transverse 
Ligament,  p.  222.) 

By  experiments,  it  has  been  proved  that  the  head,  when  placed  so  that  the  orbits  look  a 
little  upward,  is  poised  upon  the  occipital  condyles  in  a  line  drawn  a  little  in  front  of  their 
middle;  the  amount  of  elevation  varies  slightly  in  different  cases,  but  the  balance  is  always  to 
be  obtained  in  the  human  body — it  is  one  of  the  characteristics  of  the  human  figm'e.  It  serves 
to  maintain  the  head  erect  without  undue  muscular  effort,  or  a  strong  ligamentum  nuchse 
and  prominent  dorsal  spines  such  as  are  seen  in  the  lower  animals.  Disturb  this  balance,  and 
let  the  muscles  cease  to  act,  the  head  will  either  drop  forward  or  backward  according  as  the 
centre  of  gravity  is  in  front  or  behind  the  balance  line.  The  ligaments  which  pass  over  the  dens 
to  the  occiput  are  not  quite  tight  when  the  head  is  erect,  and  only  become  so  when  the  head  is 
flexed;  if  this  were  not  so,  no  flexion  would  be  allowed;  thus,  muscular  action,  and  not  liga- 
mentous tension,  is  employed  to  steady  the  head  in  the  erect  position.  It  is  through  the  com- 
bination of  the  joints  of  the  atlas  and  epistrophaus,  and  occiput  and  epistropheus  (consisting  of 
two  paii-s  of  joints  placed  symmetrically  on  either  side  of  the  median  line,  while  through  the 
median  line  there  passes  a  pivot,  also  with  a  pair  of  joints),  that  the  head  enjoys  such  freedom 
and  celerity  of  action,  remarkable  strength,  and  almost  absolute  security  against  violence, 
which  could  only  be  obtained  by  a  ball-and  socket  joint;  but  the  ordinary  ball-and-socket 
joints  are  too  prone  to  dislocations  by  even  moderate  twists  to  be  reliable  enough  when  the 
life  of  the  individual  depends  on  the  perfection  of  the  articulation:  hence  the  importance 
of  this  combination  of  joints. 


> 


Fig.  263. — Coronal    Section   of    the    Vertebral    Column    and    the   Occipital    Bone 

TO  SHOW  Ligaments. 
(The  tectorial  membrane  (1),  though  shown  as  a  distinct  stratum,  is  really  the  deeper  part  of 
the  posterior  longitudmal  ligament  (2)      The  upper  ends  have  been  reflected 
upward    the  lower  downward      Viewed  from  behind.) 


Vertical  portion  of  crucial 

ligament 
Apical    dental    ligament 


Accessory  ^  band    of   atlanto 
epistropbic  capsules 


Atlanto -epistrophic  joint 

Tectorial  membrane 
Posterior  longitudinal  ligament 


THE  ARTICULATIONS  OF  THE  TRUNK 

These  may  be  divided  into  the  following  sets: — 

1.  Those  of  the  vertebral  column.     Joints  and  ligaments  connecting: 


(a)  The  bodies. 

{h)  The  articular  processes. 

(c)  The  laminae. 

2.  Vertebral  column  with  the  pelvis. 

3.  Pelvis. 


(d)  The  spinous  processes. 

(e)  The  transverse  processes. 


(o)  Sacro-iliac 

(b)  Sacro-coccygeal. 


(c)  Intercoccygeal. 

(d)  Symphysis  pubis. 


'ARTICULATIONS  OF  VERTEBRAL  COLUMN  225 

4.  Ribs  with  the  vertebral  column. 

5.  The  articulations  at  the  front  of  the  thorax. 

(a)  Costal  cartilages  with  the  sternum. 

(6)  Costal  cartilages  with  the  ribs. 

(c)  Sternal. 

(d)  Certain  costal  cartilages  with  each  other. 

1.  THE  ARTICULATIONS  OF  THE  VERTEBRAL  COLUMN 
There  are  two  distinct  sets  of  articulations  in  the  vertebral  column : — 

(a)  Those  between  the  bodies  and  intervertebral  discs  which  form  synchon- 
droses and  which  are  amphiarthrodial  as  regards  movement. 
(6)  Those  between  the  articular  processes  which  form  arthrodial  joints. 

The  ligaments  which  unite  the  various  parts  may  also  be  divided  into  two 
sets,  viz. — immediate,  or  those  that  bind  together  parts  which  are  in  contact; 
and  intermediate,  or  those  that  bind  together  parts  which  are  not  in  contact. 

Immediate. 

(a)  Those  between  the  bodies  and  discs. 
(6)  Those  between  the  articular  processes. 

Intermediate. 

(c)  Those  between  the  laminae. 

(d)  Those  between  the  spinous  processes. 

(e)  Those  between  the  transverse  processes. 

Fig.  264. — Horizontal  Section  through  an  Intervektebbal  Fibro-cartilage  and 
THE  Corresponding  Ribs. 

Fibrous  ring  of  intervertebral 
fibro-cartilage 


Tubercular  ligament 


(a)  The  Aeticxtlations  of  the  Bodies  of  the  Vertebra 

Class. — False  Synchondrosis. 
The  ligaments  which  unite  the  bodies  of  the  vertebrae  are : — 


Intervertebral  fibro-cartilages. 
Short  lateral  ligaments. 


Anterior  longitudinal. 
Posterior  longitudinal. 


The  intervertebral  fibro-cartilages  (figs.  260  and  264)  are  tough,  but  elastic 
and  compressible  discs  of  composite  structure,  which  serve  as  the  chief  bond  of 
union  between  the  vertebrae.  They  are  twenty-three  in  number,  and  are  inter- 
posed between  the  bodies  of  all  the  vertebrae  from  the  epistropheus  to  the  sacrum 
(figs.  260  and  271).  Similar  discs  are  found  between  the  segments  of  the  sacrum 
and  coccyx  in  the  younger  stages  of  life,  but  they  undergo  ossification  at  their 
surfaces  and  often  throughout  their  whole  extent. 


226 


THE  ARTICULATIONS 


Each  disc  is  composed  of  two  portions — a  circumferential  laminar,  and  a  central  pulpy 
portion;  the  former  tightly  surrounds  and  braces  in  the  latter,  and  forms  somewhat  more  than 
half  the  disc.  The  fibrous  ring  [annulus  fibrosus]  or  laminar  portion  consists  of  alternating 
layers  of  fibrous  tissue  and  fibro-oartilage;  the  component  fibres  of  these  layers  are  firmly  con- 
nected with  two  vertebriE,  those  of  one  passing  obliquely  down  and  to  the  right,  those  of  the 
next  down  and  to  the  left,  malving  an  X -shaped  arrangement  of  the  alterriate  layers.  A  few 
of  the  superficial  lamellie  project  beyond  the  edges  of  the  bodies,  their  fibres  being  connected 
with  the  edges  of  the  anterior  and  lateral  surfaces;  and  some  do  not  completely  siu-round  the 
rest,  but  terminate  at  the  intervertebral  foramina,  so  that  on  horizontal  section  the  circum- 
ferential portion  is  seen  to  be  thinner  posteriorly.  The  more"  central  lamellae  are  incomplete, 
less  firm,  and  not  so  distinct  as  the  rest;  and  as  they  near  the  pulp  they  gradually  assume  its 
characters,  becoming  more  fibro-cartilaginous  and  less  fibrous,  and  have  cartilage  cells  in  their 
structure. 

The  pulpy  nucleus  [nucleus  pulposus]  or  central  portion  is  situated  somewhat  behind  the 
centre  of  the  disc,  forming  a  baU  of  very  elastic  and  tightly  compressed  material,  which  bulges 
freely  when  the  confining  pressure  of  the  laminar  portion  is  removed  by  either  horizontal  or 
vertical  section.  Thus,  it  has  a  constant  tendency  to  spring  out  of  its  confinement  in  the 
direction  of  least  resistance,  and  constitutes  a  pivot  round  which  the  bodies  of  the  vertebrae 
can  twist,  tilt,  or  incline.     It  is  yellowish  in  colour,  and  is  composed  of  fine  white  and  elastic 


Fig.  265. — The  Anterior  Longitudinal  Ligament,  the  Radiate,  the    Interarticular, 
AND  THE  Anterior  Costo-transverse  Ligaments. 


The  interarticular  ligament 


The       anterior       costo- 
transverse ligaments 


The  radiate  ligament 


fibres  amidst  which  are  ordinary  connective-tissue  cells,  and  pecuhar  cells  of  various  sizes  which 
contain  one  or  more  nuclei.  Together  with  the  most  central  laminee,  it  is  separated  from  im- 
mediate contact  with  the  bone  by  a  thin  plate  of  articular  cartilage.  The  central  pulp  of  the 
intervertebral  substance  is  the  persistent  part  of  the  notochord. 

The  intervertebral  substances  vary  in  shape  with  the  bodies  of  the  vertebrae  they  unite, 
and  are  widest  and  thickest  in  the  lumbar  region.  In  the  cervical  and  lumbar  regions  they  are 
thicker  in  front  than  behind,  and  cause,  the  convexity  forward  of  the  cervical,  and  increase  that 
of  the  lumbar;  the  curve  in  the  thoracic  region,  almost  entirely  due  to  the  shape  of  the  bodies, 
is,  however,  somewhat  increased  by  the  discs.  Without  the  discs  the  column  loses  a  quarter 
of  its  length,  and  assumes  a  curve  with  the  concavity  forward,  most  marked  a  little  below  the 
mid-thoracic  region.  Such  is  the  curve  of  old  age,  which  is  due  to  the  shrinking  and  drying 
up  of  the  intervertebral  substances.  The  disc  between  the  epistropheus  and  third  cervical  is 
the  thinnest  of  all  (fig.  260) ;  that  between  the  fifth  lumbar  and  sacrum  is  the  thickest,  and  is 
much  thicker  in  front  than  behind  (fig.  271).  The  intervertebral  discs  are  in  relation,  in  front 
with  the  anterior  longitudinal  ligament;  behind,  with  the  posterior  longitudinal  ligament; 
laterally,  with  the  short  lateral;  and  in  the  thoracic  region,  with  the  interarticular  and  radiate 
ligaments. 

In  the  cervical  region  lateral  diarthrodial  joints  are  placed  one  on  each  side  of  the  inter- 
vertebral discs.  They  are  of  small  extent  and  are  confined  to  the  intervals  between  the  promi- 
nent lateral  lips  of  the  upper  surface  of  the  body  below  and  the  bevelled  lateral  edges  of  the  lower 
surface  of  the  body  above.  Situated  in  front  of  the  issuing  spinal  nerves  and  between  those 
parts  of  the  bodies  formed  from  the  neural  arches,  they  are  homologous  with  the  joints  between 
the  atlas  and  epistropheus,  and  between  the  atlas  and  occipital  bone. 


VERTEBRAL  LIGAMENTS 


227 


The  anterior  longitudinal  ligament  (figs.  259  and  265)  commences  as  a  narrow 
band  attached  to  the  inferior  surface  of  the  occipital  bone  in  the  median  line, 
just  in  front  of  the  atlanto-occipital  Ugament,  of  which  it  forms  the  thickened 
central  portion.  Attached  firmly  to  the  tubercle  of  the  atlas,  it  passes  down  as 
the  central  portion  of  the  atlanto-epistrophic  ligament,  in  the  mid-line,  to  the 
front  of  the  body  of  the  epistropheus.  It  now  begins  to  widen  out  as  it  descends, 
until  it  is  nearly  two  inches  (5  cm.)  wide  in  the  lumbar  region.  Below,  it  is  fixed 
to  the  upper  segment  of  the  sacrum,  becoming  lost  in  periosteum  about  the 
middle  of  that  bone;  but  is  again  distinguishable  in  front  of  the  sacro-coccygeal 
joint,  as  the  anterior  sacro-coccygeal  ligament. 

Its  structure  is  bright,  pearly-white,  and  gUstening.  Its  lateral  borders  are  separated 
from  the  lateral  bands  by  clefts  through  which  blood-vessels  pass;  they  are  frequently  indistinct 
and  are  best  marked  in  the  thoracic  region.  It  is  thickest  in  the  thoracic  region,  and  thicker  in 
the  lumbar  than  the  cervical.  It  is  firmly  connected  with  the  bodies  of  the  vertebra,  and  is 
composed  of  longitudinal  fibres,  of  which  the  superficial  extend  over  several,  while  the  deeper 
pass  over  only  two  or  three  vertebrae.  It  is  connected  with  the  tendinous  expansion  of  the  pre- 
vertebral muscles  in  the  cervical,  and  the  crura  of  the  diaphragm  are  closely  attached  to  it  in 
the  lumbar  region. 

Fig.  266. — Posterior    Longitudinal    Ligament.     (Thoracic  region.) 
(Pedicles  cut  through,  and  posterior  arches  of  vertebrae  removed.) 


The  posterior  longitudinal  ligament  (figs.  263,  266,  267,  and  274)  extends 
from  the  occipital  bone  to  the  coccyx.  It  is  wider  above  than  below,  and  com- 
mences by  a  broad  attachment  to  the  cranial  surface  of  the  basi-occipital.  In  the 
cervical  region  it  is  of  nearly  uniform  width,  and  extends  completely  across  the 
bodies  of  the  vertebrae,  upon  which  it  rests  quite  flat.  It  does,  however,  extend 
slightly  further  laterally  on  each  side  opposite  the  intervertebral  discs.  In  the 
thoracic  and  lumbar  regions  it  is  distinctly  dentated,  being  broader  over  the  inter- 
vertebral substances  and  the  edges  of  the  bones  than  over  the  middle  of  the 
bodies,  where  it  is  a  narrow  band  stretched  over  the  bones  without  resting  on 
them,  the  anterior  internal  vertebral  venous  plexus  being  interposed.  The 
narrow  median  portion  consists  of  longitudinal  fibres,  some  of  which  are  super- 
ficial and  pass  over  several  vertebrae;  and  others  are  deeper,  and  extend  only  from 
one  vertebra  to  the  next  but  one  below. 

The  dentated  or  broader  portions  (fig.  267)  are  formed  by  oblique  fibres  which,  springing 
from  the  bodies  near  the  intervertebral  foramina,  take  a  curved  course  downward  and  back- 


228 


THE  ARTICULATIONS 


ward  over  an  intervertebral  fibro-cartilage,  and  reach  the  narrow  portion  of  the  ligament  on  the 
centre  of  the  vertebra  next  below;  they  then  diverge  to  pass  over  another  intervertebral  dies 
to  end  on  the  body  of  the  vertebra  beyond,  near  the  intervertebral  notch.  They  thus  pass 
over  two  discs  and  three  vertebrae.  Deeper  still  are  other  fibres  thickening  these  expansions 
of  the  longitudinal  hgament,  and  extending  from  one  bone  to  the  next. 

The  last  well-marked  expansion  is  situated  between  the  first  two  segments  of  the  sacrum: 
'below  this,  the  ligament  becomes  a  deUcate  central  band  with  rudimentary  expansions,  being 
more  pronounced  again  over  the  sacro-coccygeal  joint,  and  losing  itself  in  the  ligamentous 
tissue  at  the  back  of  the  coccyx.  The  dura  mater  is  tightly  attached  to  it  at  the  margin  of  the 
foramen  magnum  and  behind  the  bodies  of  the  upper  cervical  vertebrae,  but  is  separated  from 
it  in  the  rest  of  its  extent  by  loose  cellular  tissue  which  becomes  condensed  in  the  sacral  region 
to  form  the  sacro-dural  ligament.  The  filum  terminale  becomes  blended  with  it  at  the  lower 
part  of  the  sacrum  and  back  of  the  coccyx. 

Fig.  267. — Postbbior  Longitudinal  Ligament.     (Lumbar  region.) 


Median  band 
Expanded  lateral  portion 


The  lateral  (or  short)  vertebral  ligaments  (fig.  265)  consist  of  numerous  short 
fibres  situated  between  the  anterior  and  posterior  longitudinal  ligaments,  and 
passing  from  one  vertebra  over  the  intervertebral  disc,  to  which  it  is  firmly 
adherent,  to  the  next  vertebra  below. 

The  more  superficial  fibres  are  more  or  less  vertical,  but  the  deeper  decussate  and  have  a 
crucial  arrangement.  They  are  connected  with  the  deep  surface  of  the  anterior  longitudinal 
ligament,  and  so  tie  it  to  the  edges  of  the  bodies  of  the  vertebrae  and  to  the  intervertebral  discs. 
They  blend  behind  with  the  expansions  of  the  posterior  longitudinal  ligament,  and  so  complete 
the  casing  round  each  amphiarthrodial  joint.  In  the  thoracic  region,  they  overlie  the  radiate 
ligament,  and  in  the  lumbar  they  radiate  toward  the  transverse  processes.  In  the  cervical 
region  they  are  less  well  marked. 


(b)  The  Ligaments  Connecting  the  Articular  Processes 
Class. — Diarthrosis.     Subdivision. — Arthrodia. 

The  articular  capsules  (fig.  259)  which  unite  these  processes  are  composed 
partly  of  yellow  elastic  tissue  and  partly  of  white  fibrous  tissue.  In  the  cervical 
region  only  the  medial  side  of  the  capsule  is  formed  by  the  ligamenta  flava,  which 
in  the  thoracic  and  lumbar  regions,  however,  extend  anteriorly  to  the  margins 
of  the  intervertebral  foramina. 

The  part  formed  of  white  fibrous  tissue  consists  of  short,  well-marked  fibres,  which  in  the 
cervical  region  pass  obhquely  downward  and  forward  over  the  joint,  between  the  articular  proc- 


VERTEBRAL  LIGAMENTS 


229 


esses  and  the  posterior  roots  of  the  transverse  processes  of  two  contiguous  vertebra.  In  the 
thoracic  region  the  fibres  are  shorter,  and  vertical  in  direction,  and  are  attached  to  the  bases 
of  the  transverse  processes;  in  the  lumbar,  they  are  obhquely  transverse.  The  articular 
capsules  in  the  cervical  region  are  the  most  lax,  those  in  the  lumbar  region  are  rather  tighter, 
and  those  in  the  thoracic  region  are  the  tightest. 

There  is  one  s3movial  membrane  to  each  capsule. 


(c)  The  Ligaments  uniting  the  Lamina 

The  ligamenta  flava  (fig.  268)  are  thick  plates  of  closely  woven  yellow  elastic 
tissue,  interposed  between  the  laminae  of  two  adjacent  vertebrae.  The  first  con- 
nects the  epistropheus  with  the  third  cervical,  and  the  last  the  fifth  lumbar  with 


Fig.  268.- 
Canal. 


-Ligamenta  Flava  in  the  Lumbar  Region,  seen  from  within  the  Vertebral 


Portion  of  ligamentu 
flavum    removed   to 
show    the     articular 
cavity 


Ligamentum  flavum 


the  sacrum.  Each  ligament  extends  from  the  medial  and  posterior  edge  of  the 
intervertebral  foramen  on  one  side  to  a  corresponding  point  on  the  other ;  above, 
it  is  attached  close  to  the  inner  margin  of  the  inferior  articular  process  and  to  a 
well-marked  ridge  on  the  inner  surface  of  the  laminae  as  far  as  the  root  of  the 
spine;  below,  it  is  fixed  close  to  the  inner  margin  of  the  superior  articular  process 
and  to  the  dorsal  aspect  of  the  upper  edge  of  the  laminae. 

Thus  each  ligamentum  flavum,  besides  filling  up  the  interlaminar  space,  enters  into  the 
formation  of  two  articular  capsules;  they  do  so  to  a  greater  extent  in  the  thoracic  and  lumbar 
regions  than  in  the  cervical,  where  the  articular  processes  are  placed  wider  apart.  When  seen 
from  the  front  after  removing  the  bodies  of  the  vertebrae,  they  are  concave  from  side  to  side, 
but  convex  from  above  downward;  they  make  a  more  decided  transverse  curve  than  the  arches 
between  which  they  are  placed.  This  concavity  is  more  marked  in  the  thoracic,  and  still  more 
in  the  lumbar  region  than  in  the  cervical;  in  the  lumbar  region  the  hgamenta  flava  extend  a 
short  distance  between  the  roots  of  the  spinous  process,  blending  with  the  interspinous  ligament, 
and  making  a  median  sulcus  when  seen  from  the  front;  there  is,  however,  no  separation  between 
the  two  parts.  In  the  cervical  region,  where  the  spines  are  bifid,  there  is  a  median  fissure  in  the 
yellow  tissue  which  is  filled  up  by  fibro-areolar  tissue.  The  ligaments  are  thickest  and  strongest 
in  the  lumbar  region;  narrow  but  strong  in  the  thoracic;  thinner,  broader,  and  more  membranous 
in  the  cervical  region. 

(d)  The  Ligaments  connecting  the  Spinous  Processes 

These  include  supraspinous  ligament,  interspinous  ligaments,  and  the  liga- 
mentum nuchae. 


230 


THE  ARTICULATIONS 


The  supraspinous  ligament  (fig.  270)  extends  without  interruption  as  a 
well-marked  band  of  longitudinal  fibres  along  the  tips  of  the  spines  of  the  vertebrae 
fromthat  of  the  seventh  cervical  downward  till  it  ends  on  the  median  sacral  crest. 


Fig.  269. — Side  View  op  Ligamentum  Nuch^. 


Ligamentum  auchs 
First  iuterspinalis  muscle' 


Fig.  270.  —The  Interspinous  and  Supraspinous  Ligaments  in  the  Lumbar  Region. 


-The  interspinous  ligament 


jttJ — The  supraspinous  ligament 


Its  more  superiioial  fibres  are  much  longer  than  the  deep.  The  deeper  fibres  pass  over 
adjacent  spines  only,  while  the  superficial  overlie  several.  It  is  connected  laterally  with  the 
aponeurotic  structures  of  the  back;  indeed,  in  the  lumbar  region,  where  it  is  well  marked,  it 


VERTEBRAL  LIGAMENTS  231 

appears  to  result  from  the  interweaving  of  the  tendinous  fibres  of  the  several  muscles  which  are 
attached  to  the  tips  of  the  spinous  processes.  In  the  dorsal  region  it  is  a  round  slender  cord 
which  is  put  on  the  stretch  in  flexion  and  relaxed  in  extension  of  the  back. 

The  ligamentum  nuchse,  or  the  posterior  cervical  ligament  (fig.  269),  is  the 
continuation  in  the  neck  of  the  supraspinous  ligament,  from  which,  however,  it 
differs  considerably.  It  is  a  slender  vertical  septum  of  an  elongated  triangular 
form,  extending  from  the  seventh  cervical  vertebra  to  the  external  protuberance 
and  the  crest  of  the  occipital  bone.  Its  anterior  border  is  firmly  attached  to  the 
tips  of  the  spines  of  all  the  cervical  vertebrte,  including  the  posterior  tubercle  of 
the  atlas,  as  well  as  to  the  occiput.  Its  posterior  border  gives  origin  to  the 
trapezii,  with  the  tendinous  fibres  of  which  muscle  it  blends.  Its  lateral,  tri- 
angular surfaces  afford  numerous  points  of  attachment  for  the  posterior  muscles 
of  the  head  and  neck. 

In  man  it  is  rudimentary,  and  consists  of  elastic  and  white  fibrous  tissues.  As  seen  in  the 
horse,  elephant,  ox,  and  other  pronograde  mammals,  it  is  a  great  and  important  elastic  ligament, 
which  even  reaches  along  the  thoracic  part  of  the  spinal  column.     In  these  animals  it  serves 

to  support  the  head  and  neck,  which  otherwise  from  their  own  weight  would  hang  down.  Its 
rudimentary  state  in  man  is  the  direct  consequence  of  his  erect  position. 

The  interspinous  ligaments  (fig.  270)  are  thin  membranous  structures  which 
extend  between  the  spines,  and  are  connected  with  the  ligamenta  flava  in  front, 
and  the  supraspinous  ligament  behind. 

The  fibres  pass  obliquely  from  the  root  of  one  spine  to  the  tip  of  the  next;  they  thus  decus- 
sate. They  are  best  marked  in  the  lumbar  region,  and  are  replaced  by  the  well-developed 
inierspinales  muscles  in  the  cervical  region. 

(e)  The  Ligaments  connecting  the  Transverse  Processes 
The  intertransverse  ligaments  are  but  poorly  developed. 

In  the  thoracic  region  they  form  small  rounded  bundles,  and  in  the  lumbar  they  are  flat 
membranous  bands,  unimportant  as  bonds  of  union.  They  consist  of  fibres  passing  between 
the  apices  of  the  transverse  processes.  In  the  cervical  region  they  are  replaced  by  the  inter- 
transversarii  muscles. 

The  arterial  supply  for  the  column  comes  from  twigs  of  the  vertebral,  ascending  pharyn- 
geal, ascending  cervical,  superior  and  aortic  intercostals,  lumbar,  iUo-lumbar,  and  lateral  sacral. 

The  nerve-supply  comes  from  the  spinal  nerves  of  each  region. 

Movements. — The  vertebral  column  is  so  formed  of  a  number  of  bones  and  intervertebral 
discs  as  to  serve  many  purposes.  It  is  the  axis  of  the  skeleton;  upon  it  the  skull  is  supported; 
and  with  it  the  cavities  of  the  trunk  and  the  limbs  are  connected,  As  a  fixed  column  it  is  capable 
of  bearing  great  weight,  and,  through  the  elastic  intervertebral  substances,  of  resisting  and 
breaking  the  transmission  of  shocks.  Moreover,  it  is  flexible.  Now,  the  range  of  movements 
of  the  column  as  a  whole  is  very  considerable;  but  the  movements  between  any  two  vertebrae 
are  slight,  so  that  motions  of  the  spine  may  take  place  without  any  change  in  the  shape  of  the 
column,  and  without  any  marked  disturbance  in  the  relative  positions  of  the  vertebrae.  It  is 
about  the  pulpy  part  of  the  intervertebral  discs,  which  form  a  central  elastic  pivot  or  ball,  upon 
which  the  middle  of  the  vertebras  rest,  that  these  movements  take  place. 

The  amount  of  motion  is  everywhere  limited  by  the  common  vertebral  Ugaments,  but  it 
depends  partly  upon  the  width  of  the  bodies  of  the  vertebrae,  and  partly  upon  the  depth  of  the 
discs,  so  that  in  the  loins,  where  the  bodies  are  large  and  wide,  and  the  discs  very  thick,  free 
motion  is  permitted;  in  the  cervical  region,  though  the  discs  are  thinner,  yet,  as  the  bodies  are 
smaller,  almost  equally  free  motion  is  allowed.  As  the  ball-Uke  pulpy  part  of  the  intervertebral 
disc  is  the  centre  of  movement  of  each  vertebra,  it  is  obvious  that  the  motion  would  be  of  a 
rolUng  character  in  any  direction  but  for  the  articular  processes,  wtiich  serve  also  to  give  steadi- 
ness to  the  column  and  to  assist  in  bearing  the  superincumbent  weight.  Were  it  not  for  these 
processes,  the  column,  instead  of  being  steady,  endowed  with  the  capacity  of  movement  by 
muscular  agency,  would  be  tottering,  requiring  muscles  to  steady  it.  The  influence  of  the 
articular  processes  in  limiting  the  direction  of  incUnation  will  appear  from  a  study  of  the 
movements  in  the  three  regions  of  the  spine. 

In  the  neck  all  movements  are  permitted  and  are  free,  except  between  the  second  and  third 
cervical  vertebrje,  where  they  are  slight,  owing  to  the  shallow  intervertebral  disc  and  the  great 
prolongation  of  the  anterior  hp  of  the  inferior  surface  of  the  body  of  the  epistropheus,  which 
checks  forward  flexion  considerably.  On  the  whole,  however,  extension  and  lateral  inclination 
are  more  free  and  extensive  in  this  than  in  any  other  region  of  the  column,  whilst  flexion  is  more 
limited  than  in  the  lumbar  region.  Rotatory  movements  are  also  free,  but  take  place,  on  ac- 
count of  the  position  and  inclination  of  the  articular  facets,  not,  as  in  the  thoracic  region,  round 
a  vertical  axis,  but  round  an  oblique  axis,  the  articular  process  of  one  side  gliding  upward  and 
forward  and  that  of  the  opposite  side  downward  and  backward. 

In  the  thoracic  region,  especially  near  its  middle,  antero-posterior  flexion  and  extension 
are  very  slight;  and,  as  the  concavity  of  the  curve  here  is  forward,  the  flat  and  nearly  vertical 
surfaces  of  the  articular  processes  prevent  anything  like  sliding  in  a  curvilinear  manner  of  the 


232  THE  ARTICULATIONS 

one  set  of  processes  over  the  sharp  upper  edges  of  the  other,  which  would  be  necessary  for 
forward  flexion.  A  fair  amount  of  lateral  inclination  would  be  permitted  but  for  the  impedi- 
ment offered  by  the  ribs;  while  the  position  and  direction  of  the  articular  processes  allows  rota- 
tion round  a  vertical  axis  which  passes  through  the  centres  of  the  bodies  of  the  vertebrae.  This 
rotation  is  not  very  great,  and  is  freer  in  the  upper  than  in  the  lower  part  of  the  thoracic 
region. 

In  the  lumbar  region,  extension  and  flexion  are  very  free,  especially  between  the  third  and 
fourth  and  fourth  and  fifth  vertebrae,  where  the  lumbar  curve  is  sharpest;  lateral  inclination 
is  also  very  free  between  these  same  vertebrae.  It  has  been  stated  that  the  shape  and  position 
of  the  articular  processes  of  the  lumbar  and  the  lower  two  or  three  dorsal  are  such  as  to  prevent 
any  rotation  in  these  regions;  but,  owing  to  the  fact  that  the  inferior  articular  processes  are  not 
tightly  embraced  by  the  superior,  so  that  the  two  sets  of  articular  processes  are  not  in  contact 
on  both  sides  of  the  bodies  at  the  same  time,  there  is  always  some  space  in  which  horizontal 
motion  can  occur  round  an  axis  drawn  through  the  central  part  of  the  bodies  and  interverte- 
bral discs,  but  it  is  very  slight.  Thus,  the  motions  are  most  free  in  those  regions  of  the  column 
which  have  a  convex  curve  forward,  due  to  the  shape  of  the  intervertebral  discs,  where  there 
are  no  bony  waOs  surrounding  solid  viscera,  where  the  spinal  canal  is  largest  and  its  contents 
are  less  firmly  attached,  and  where  the  pedicles  and  articular  processes  are  more  nearly  on  a 
transverse  level  with  the  posterior  surface  of  the  bodies  of  the  vertebrae. 

Nor  must  the  uses  of  the  ligamenta  flava  be  forgotten:  these  useful  structures — (1)  com- 
plete the  roofing-in  of  the  vertebral  canal,  and  yet  at  the  same  time  permit  an  ever-changing 
variation  in  the  width  of  the  interlaminar  spaces  in  flexion  and  extension;  (2)  they  also  restore 
the  articulating  surfaces  to  their  normal  position  with  regard  to  each  other  after  movements 
of  the  column;  (3)  and  by  forming  the  medial  portion  of  each  articular  capsule,  they  take  the 
place  of  muscle  in  preventing  it  from  being  nipped  between  the  articular  surfaces  during 
movement. 

Muscles  which  take  part  in  the  movements  of  the  vertebral  column. — Flexors :  When  acting 
with  their  fellows  of  the  opposite  side.  Rectus  abdominis,  infra-hyoid  muscles  (slightly) 
sterno-mastoid,  external  oblique,  internal  obHque,  intercostals,  scalenus  anterior,  psoas 
major  and  minor,  longus  colli,  longus  capitis  (rectus  capitis  anterior  major). 

Extensors :  When  acting  with  their  fellows  of  the  opposite  side.  Sacro-spinalis,  quadratus 
lumborum,  semispinalis,  multifidus,  rotatores,  interspinales,  serrati  posteriores,  the  splenius, 
and  with  the  scapula  fixed  the  levator  scapulae  and  the  upper  fibres  of  the  trapezius. 

Muscles  which  help  to  incline  the  column  to  their  own  side. — Sacro-spinaUs,  quadratus 
lumborum,  semispinalis,  multifidus,  the  intercostals  helping  to  fix  the  ribs,  the  external  and 
internal  oblique  muscles,  levatores  costarum,  serrati  posteriores,  the  scalenes,  splenius  cervicis, 
longus  coUi  (oblique  part),  rotatores,  intertransversales,  psoas,  and  with  the  scapula  fixed  the 
levator  scapulae  and  the  upper  and  lower  fibres  of  the  trapezius. 

Muscles  which  rotate  the  column  and  turn  the  body  to  their  own  side. — Splenius  cervicis, 
internal  oblique  (the  ribs  being  fixed),  serratus  posterior  inferior,  and  with  the  scapula  fixed 
the  lower  fibres  of  the  trapezius. 

Muscles  which  rotate  the  column  and  turn  the  body  to  the  opposite  side. — Multifidus, 
semispinalis,  external  oblique,  the  lower  oblique  fibres  of  the  longus  colli,  and  with  the  scapula 
and  humerus  fixed  the  latissimus  dorsi  and  trapezius. 

2.  THE  SACRO-VERTEBRAL  ARTICULATIONS 

(a)  Class. — False  Synchondrosis. 

(b)  Class. — Diarthrosis.     Subdivision. — Arihrodia. 

As  in  the  intervertebral  articulations,  so  in  the  union  of  the  first  portion  of  the 
sacrum  with  the  last  lumbar  vertebra,  there  are  two  sets  of  joints — viz.  (a)  a 
synchondrosis,  between  the  bodies  and  intervertebral  disc;  and  (6)  a  pair  of 
arthrodial  joints,  between  the  articular  processes.  The  union  is  effected  by  the 
following  ligaments,  which  are  common  to  the  vertebral  column: — (i)  anterior, 
and  (ii)  posterior  longitudinal;  (iii)  lateral  or  short  vertebral;  (iv)  capsular;  (v) 
ligamenta  flava;  (vi)  supraspinous  and  (vii)  interspinous  ligaments.  Two 
special  accessory  ligaments  on  either  side,  viz.,  the  sacro-lumbar  and  the  ilio- 
lumbar, connect  the  pelvis  with  the  fourth  and  fifth  lumbar  vertebrae. 

The  sacro-lumbar  ligament  (fig.  271)  is  strong,  and  triangular  in  shape.  Its 
apex  is  above  and  medial,  being  attached  to  the  whole  of  the  lower  border  and 
front  surface  of  the  transverse  process  of  the  fifth  liunbar  vertebra,  as  well  as  to 
the  pedicle  and  body.  It  is  intimately  blended  with  the  ilio-lumbar  ligament. 
Below,  it  has  a  wide,  fan-shaped  attachment,  extending  from  the  edge  of  the  ilio- 
lumbar ligament  forward  to  the  brim  of  the  true  pelvis;  blending  with  the  perios- 
teum on  the  base  of  the  sacrum  and  in  the  iliac  fossa,  and  with  the  superior  sacro- 
iliac ligament. 

By  its  sharp  medial  border  it  Umits  laterally  the  foramen  for  the  last  lumbar  nerve.  It  is 
pierced  by  two  large  foramina,  which  transmit  arteries  to  the  saoro-iliac  synchondrosis.  This 
ligament  is  in  series  with  the  intertransverse  ligaments  of  the  spinal  column.  It  is  sometimes 
described  as  a  part  of  the  ilio-lumbar  ligament. 


SACRO-VERTEBRAL  ARTICULATIONS 


233 


The  ilio-lumbar  ligament  (fig.  271)  is  a  strong,  dense,  triangular  ligament 
connecting  the  fourth  and  fifth  lumbar  vertebrae  with  the  iliac  crest. 

It  springs  from  the  front  surface  of  the  transverse  process  of  the  fifth  lumbar  vertebra  as 
far  as  the  body,  by  a  strong  fasciculus  from  the  posterior  surface  of  the  process  near  the  tip, 
and  also  from  the  front  surface  and  lower  edge  of  the  transverse  process  and  pedicle  of  the  fourth 
lumbar  vertebra,  as  far  medialward  as  the  body.  Between  these  two  lumbar  vertebrae  it  is 
inseparable  from  the  intertransverse  hgament. 

At  its  origin  from  the  transverse  process  of  the  fifth  lumbar  vertebra  it  is  closely  inter- 
woven with  the  sacro-lumbar  ligament,  and  some  of  its  iibres  spread  downward  on  to  the  body 
of  the  fifth  vertebra,  while  others  ascend  to  the  disc  above.  At  the  pelvis  it  is  attached  to  the 
inner  lip  of  the  crest  of  the  ilium  for  about  two  inches  (5  cm.) .  The  highest  fibres  at  the  column 
form  the  upper  edge  of  the  ligament  at  the  pelvis,  those  which  come  from  the  posterior  portion 
of  the  transverse  process  of  the  fifth  lumbar  vertebra  forming  the  lower,  while  the  fibres  from 
the  front  of  the  same  process  pass  nearly  horizontally  lateralward.     Near  the  column  the  surfaces 


Fig.  271. — Anterior  View  of  the  Ligaments  between  Vertebra  and  Pelvis. 


anterior  primary  branch  of  fourth 


Foramen  for  last 
lumbar  nerve 
Intervertebral  disc 
between  last  lum- 
bar and  first  sacral 
vertebrae 


The  ilio-lumbar 
ligament 


The  sacro-luml 
ligament 

Superior  sacro- 
ligament 

Anterior  sacro- 
ligament 


Sacro-tuberous 
ligament 


Sacro-spinous  ligament 


look  directly  backward  and  forward,  but  at  the  ilium  the  ligament  gets  somewhat  twisted,  so 
that  the  posterior  surface  looks  a  little  upward,  and  the  anterior  looks  a  Mttle  downward. 
The  anterior  surface  forms  part  of  the  posterior  boundary  of  the  major  (false)  pelvis,  and  over- 
lies the  upper  part  of  the  posterior  sacro-iliao  ligament;  the  posterior  surface  forms  part  of  the 
floor  of  the  spinal  groove,  and  gives  origin  to  the  mullifidus  muscle.  Of  the  borders,  the  upper 
is  oblique,  has  the  anterior  lamella  of  the  lumbar  fascia  attached  to  it,  and  gives  origin  to  the 
quadralus  lumborum;  the  lower  is  horizontal,  and  is  adjacent  to  the  upper  edge  of  the  sacro- 
lumbar  ligament;  while  the  medial  is  crescentic,  and  forms  the  lateral  boundary  of  a  foramen 
through  which  the  fourth  lumbar  nerve  passes. 

The  arterial  supply  is  very  free,  and  comes  from  the  last  lumbar,  ilio-lumbar,  and  lateral 
sacral. 

The  nerve-supply  is  from  the  sympathetic,  as  well  as  from  twigs  from  the  fourth  and  fifth 
lumbar  nerves. 

Movements. — The  angle  formed  by  the  sacrum  with  the  spinal  column  is  called  the  sacro- 
vertebral  angle.  The  pelvic  inclination  does  not  depend  entirely  upon  this  angle,  but  in  great 
part  upon  the  obUquity  of  the  co.xal  (innominate)  bones  to  the  sacrum,  so  that  in  males  in  whom 
the  average  pelvic  obliquity  is  a  Uttle  greater,  the  average  sacro-vertebral  angle  is  considerably 
less  than  in  females. 

The  sacro-vertebral  angle  in  the  male  shows  that  there  is  a  greater  and  more  sudden  change 
in  direction  at  the  sacro-vertebral  union  than  in  the  female.  A  part  of  this  change  in  direction 
is  due  to  the  greater  thickness  in  the  anterior  part  of  the  intervertebral  fibro-cartilage  between 
the  last  lumbar  vertebra  and  the  sacrum.    Owing  to  the  greater  thickness  of  the  intervertebral 


234  THE  ARTICULATIONS 

disc  here  than  elsewhere,  the  movements  permitted  at  this  joint  are  very  free,  being  freer  than 
those  between  any  two  lumbar  vertebrEe.  As  the  diameter  of  the  two  contiguous  bones  is  less 
in  the  sagittal  than  in  the  frontal  plane,  the  forward  and  backward  motions  are  much  freer  than 
those  from  side  to  side.  The  backward  and  forward  motions  take  place  every  time  the  sitting 
is  exchanged  for  the  standing  position,  and  the  standing  for  the  sitting  posture;  in  rising,  the 
back  is  extended  on  the  sacrum  at  the  sacro-lumbar  union;  in  sitting  down  it  is  flexed. 

The  articular  processes  provide  for  the  ghding  movement  incidental  to  the  extension, 
flexion,  and  lateral  movements;  they  also  allow  some  horizontal  movement,  necessary  for  the 
rotation  of  the  vertebral  column  on  the  pelvis,  or  pelvis  on  the  column.  The  inferior  articular 
processes  of  the  fifth  differ  considerably  from  the  inferior  processes  in  the  rest  of  the  lumbar 
vertebrae,  and  in  direction  they  resemble  somewhat  those  of  the  cervical  vertebrae;  while  the  su- 
perior articular  processes  of  the  sacrum  differ  in  a  similar  degree  from  the  superior  processes  of 
the  lumbar  vertebrae.     This  difference  allows  for  the  freer  rotation  which  occurs  at  this  joint. 

The  sacro-vertebral  angle  averages  117°  in  the  male,  and  130°  in  the  female;  while  the 
pelvic  incKnation  averages  155°  in  the  male,  and  150°  in  the  female. 

As  already  stated,  the  movements  at  the  sacro-vertebral  joint  are  the  same  as  those  in  other 
parts  of  the  spinal  column,  but  more  extensive,  and  the  muscles  which  produce  the  movements 
are  those  mentioned  in  the  preceding  groups  which  cross  the  plane  of  the  articulation. 

3.  THE  ARTICULATIONS  OF  THE  PELVIS 

This  group  may  again  be  subdivided  into — - 

(a)  The  sacro-iliac. 

(6)  The  sacro-coccygeal. 

(c)  The  intercoccygeal. 

(d)  The  symphysis  pubis. 

(a)  The  Sacro-iliac  Articulation  and  Sacro-sciatic  Ligaments 

Class. — Diarthrosis.     Subdivision. — Arthrodia. 

It  is  now  generally  admitted  that  the  sacro-iliac  joint  is  a  diarthrosis,  the 
articular  surface  of  each  bone  being  covered  with  a  layer  of  cartilage,  whilst  the 
cavity  of  the  joint  is  a  narrow  cleft  and  the  capsule  is  extremely  thick  posteriorly. 
The  cartilage  on  the  sacrum  is  much  thicker  than  that  on  the  ilium  and  the 
cartilages  are  sometimes  bound  together  here  and  there  by  fibrous  strands. 
The  different  character  of  the  joint  in  the  two  sexes  should  be  noted.  Briefly, 
the  female  joint  has  strong  ligamentous  bonds  with  but  little  bony  apposition, 
while  the  male  joint  gains  its  strength  by  virtue  of  extensive  areas  of  bony 
contact  and  a  slighter  development  of  ligaments.  This  difference  is,  of  course, 
a  physiological  one;  for  some  laxity  of  the  joint  is  demanded  during  pregnancy 
and  labour.  The  bones  which  enter  into  the  joint  are  the  sacrum  and  ilium, 
and  they  are  bound  together  by  the  following  ligaments: — 

Anterior  sacro-iliac.  Superior  sacro-iliac. 

Posterior  sacro-iliac.  Inferior  sacro-iliac. 

Interosseous. 

The  anterior  sacro-iliac  ligament  (figs.  271  and  272)  consists  of  well-marked 
glistening  fibres  which  pass  above  into  the  superior,  and  below  into  the  inferior, 
ligaments.  It  extends  from  the  first  three  bones  of  the  sacrum  to  the  ilium 
between  the  brim  of  the  pelvis  minor  and  the  great  sciatic  notch,  blending  with  the 
periosteum  of  the  sacrum  and  ilium  as  it  passes  away  from  the  united  edges  of 
the  bones. 

The  superior  sacro-iliac  ligament  (figs.  271  and  272)  extends  across  the 
upper  margins  of  the  joint,  from  the  ala  of  the  sacrum  to  the  iliac  fossa,  being 
well  marked  along  the  brim  of  the  pelvis,  where  it  is  thickened  by  some  closely 
packed  fibres.  Behind,  it  is  far  stronger,  especially  beneath  the  transverse  process 
of  the  fifth  lumbar  vertebra.  This  ligament  is  connected  with  the  strong  sacro- 
lumbar  ligament,  which  spreads  lateralward  and  forward  over  the  joint  to  reach 
the  iliac  fossa  and  terminal  line.  By  some  authors  it  is  described  as  a  part  of  the 
ilio-lumbar  ligament. 

The  posterior  sacro-iliac  ligament  is  extremely  strong  and  consists  essentially 
of  two  sets  of  fibres,  deep  and  superficial.  The  deep  fibres  (short  posterior  sacro- 
iliac ligament)   pass  downward  and  medialward  from  the  rough  area  of  the 


PELVIC  ARTICULATIONS 


235 


ilium  behind  the  auricular  surface  to  the  back  of  the  lateral  mass  of  the  sacrum, 
both  lateral  to  and  between  the  upper  foramina  and  to  the  upper  sacral  articular 
process,  and  the  area  between  it  and  the  first  sacral  foramen.  The  deepest  fibres 
of  this  group  constitute  the  so-called  interosseous  ligament.  The  more  superficial 
fibres  (long  posterior  sacro-iliac  ligament)  are  oblique  or  vertical,  and  pass  from 
the  posterior  superior  iliac  spine  to  the  second,  third,  and  fourth  tubercles  on 
the  back  of  the  sacrum,  a  more  or  less  well-defined  band  which  goes  to  the  third 
and  fourth  sacral  tubercles  being  called  sometimes  the  oblique  saero-iliac  band 
and  sometimes  the  long  straight  band. 

The  inferior  sacro-iliac  ligament  (fig.  272)  is  covered  behind  by  the  upper 
end  of  the  sacro-tuberous  ligament;  it  consists  of  strong  fibres  extending  from 
the  lateral  border  of  the  sacrum  below  the  articular  facet  to  the  posterior  iliac 
spines;  some  of  the  fibres  are  attached  to  the  deep  surface  of  the  ilium  and  join 
the  interosseous  ligament. 


Fig.  272. — Median  Sagittal  Section  op  the  Pelvis,  Showing  Ligaments. 


Anterior  sacro-iliac  liga- 
ment 

Inferior  sacro-iliac  liga- 
ment 


Sacro-spinous  ligament 
Sacro-tuberous  ligament 


i 


The  interosseous  ligament  is  the  strongest  of  all,  and  consists  of  fibres  of 
different  lengths  passing  in  various  directions  between  the  two  bones.  Imme- 
diately above  the  interspinous  notch  of  the  ilium  the  fibres  of  this  ligament  are 
very  strong,  and  form  an  open  network,  in  the  interstices  of  which  is  a  quantity 
of  fat  in  which  the  articular  vessels  ramify. 

Tlie  ear-shaped  cartilaginous  plate,  which  unites  the  bones  firmly,  is  accu- 
rately applied  to  the  auricular  surfaces  of  the  sacrum  and  ilium.  It  is  about 
one-twelfth  of  an  inch  (2  mm.)  thick  in  the  centre,  but  becomes  thinner  toward 
the  edges.  Though  closely  adherent  to  the  bones,  it  tears  away  from  one  entirely, 
or  from  both  partially,  on  the  application  of  violence,  sometimes  breaking  irregu- 
larly so  that  the  greater  portion  remains  connected  with  one  bone,  leaving  the 
other  bone  rough  and  bare.  It  is  usually  one  mass,  and  is  only  occasionally 
formed  of  two  plates  with  a  synovial  cavity  between  them. 

Because  of  the  occasional  presence  of  a  more  or  less  extensive  synovial  ca^dty  within  the 
fibro-cartilage,  and  also  of  a  synovial  lining  to  the  Ugaments  passing  in  front  and  behind  the 
articulation,  the  term  'diarthro-amphiarthrosis'  has  been  given  to  this  joint,  and  also  to  the 
sympliysis  pubis.  Testut  mentions  certain  folds  of  sjiiovial  membrane  filling  up  gaps  which 
here  and  there  occur  at  the  margin  of  the  fibro-cartilage  but  they  are  not  usually  seen. 

The  sacro-tuberous  (great  sciatic)  ligament  (figs.  271,  272,  and  273)  is  at- 
tached above  to  the  posterior  extremity  of  the  crest  of  the  ilium  and  the  lateral 
aspect  of  the  posterior  iliac  spines.     From  this  attachment  some  of  its  fibres 


236 


THE  ARTICULATIONS 


pass  downwai'd  and  backward  to  be  attached  to  the  lateral  borders  and  posterior 
surfaces  of  the  lower  three  sacral  vertebrae  and  upper  two  segments  of  the  coccyx; 
while  others,  after  passing  for  a  certain  distance  backward,  curve  forward  and 
downward  to  the  ischium,  forming  the  anterior  free  margin  of  the  ligament 
where  it  limits  posteriorly  the  sciatic  foramina.  These  fibres  are  joined  by  others 
which  arise  from  the  posterior  surfaces  of  the  lower  three  sacral  vertebrse  and 
upper  pieces  of  the  coccyx.  At  the  ischium  it  is  fixed  to  the  medial  border  of  the 
tuberosity,  and  sends  a  thin  sharp  process  upward  along  the  ramus  of  the 
ischium  which  is  called  the  falciform  process  (fig.  273),  and  is  a  prolongation  of 
the  posterior  edge  of  the  ligament. 

A  great  many  fibres  pass  on  directly  into  the  tendon  of  the  biceps  muscle,  so  that  traction 
on  this  muscle  braces  up  the  whole  ligament,  and  the  coccyx  is  thus  made  to  move  on  the  sacrum. 
The  ligament  may  not  unfairly  be  described  as  a  tendinous  expansion  of  the  muscle,  whereby 
its  action  is  extended  and  a  more  advantageous  leverage  given.  It  is  broad  and  flat  at  its 
attached  ends,  but  narrower  and  thicker  in  the  centre,  looking  like  two  triangular  expansions- 

Fig.  273. — Sacro-tuberous  and  Sacro-spinous  Ligaments.     (Posterior  view.) 


Falciform  process   of  sacro-tuberous 
ligament 


joined  by  a  flat  band,  the  larger  triangle  being  at  the  ilium,  and  the  smaller  at  the  ischium^ 
The  fibres  of  the  ligament  are  twisted  upon  its  axis  at  the  narrow  part,  so  that  some  of  the- 
superior  fibres  pass  to  the  lower  border. 

The  posterior  surface  gives  origin  to  the  gluteus  maximus  muscle,  and  on  it  ramify  the  loop; 
from  the  posterior  branches  of  the  sacral  nerves;  its  anterior  surface  is  closely  connected  at  its 
origin  ,with  the  sacro-spinous  ligament,  and  some  fibres  of  the  piriformis  muscle  arise  from  its 
below  the  obturator  internus  passes  out  of  the  pelvis  under  its  cover,  and  the  internal  pudic 
vessels  and  nerve  pass  in.  At  the  ilium,  its  posterior  edge  is  continuous  with  the  vertebra, 
aponeurosis;  while  to  the  anterior  edge  is  attached  the  thick  fascia  covering  the  gluteus  mediusl 
The  obturator  fascia  is  attached  to  its  falciform  edge.  It  is  pierced  by  the  coccygeal  branches  of 
the  inferior  gluteal  {sciatic)  artery  and  the  inferior  clunial  {perforating  cutaneous)  nerve  from  the 
second  and  third  sacral. 

The  sacro-spinous  (small  sciatic)  ligament  (figs.  271,  272,  and  273)  is  tri- 
angular and  thin,  springing  by  a  broad  base  from  the  lateral  border  of  the  sacrum 
and  coccyx,  from  the  front  of  the  sacrum  both  above  and  below  the  level  of  the 
fourth  sacral  foramen,  and  from  the  coccyx  nearly  as  far  as  its  tip.  By  its  apex 
it  is  attached  to  the  front  surface  and  the  borders  of  the  ischial  spine  as  far  out- 
ward as  its  base.  Its  fibres  decussate  so  that  the  lower  ones  at  the  coccyx  be- 
come the  highest  at  the  ischial  spine;  muscular  fibres  are  often  seen  intermingled 
with  the  ligamentous. 

The  sacro-spinous  ligament  is  situated  in  front  of  the  sacro-tuberous  Hgament,  with  which 
it  is  closely  connected  at  the  sacrum,  and  separates  the  greater  from  the  lesser  sciatic  foramen. 


SACRO-COCCYGEAL  ARTICULATION 


237 


Its  front  surface  gives  attachment  to  the  coccygeus  muscle,  which  overlies  it.  Behind,  it  is 
connected  with,  and  hidden  by,  the  sacro-tuberous  ligament,  so  that  only  the  lateral  inch  or 
less  (2  cm.)  and  a  small  part  of  its  attachment  to  the  coccyx  can  be  seen;  the  internal  pudic 
nerve  also  passes  over  the  posterior  surface. 

The  arterial  supply  of  the  sacro-Uiac  joint  comes  from  the  superior  gluteal,  ilio-lumbar,  and 
lateral  sacral. 

The  nerve-supply  is  from  the  superior  gluteal,  sacral  plexus,  and  external  twigs  of  the 
posterior  divisions  of  the  first  and  second  sacral  nerves. 

Movements. — Recent  investigations  have  shown  that  in  spite  of  the  interlocking  of  the 
articular  surfaces  and  the  strong  ligaments  connecting  the  bones  together  a  slight  amount  of 
movement,  both  a  gUding  and  rotatory,  does  occur  at  the  sacro-iliac  joint.  The  gliding  move- 
ment is  both  up  and  down,  and  forward  and  backward,  and  the  latter  is  associated  with  a  slight 
rotation  round  a  transverse  axis  which  passes  through  the  upper  tubercles  on  the  back  of  the 
sacrum.     The  movement  is  but  small  in  extent,  nevertheless  as  the  base  of  the  sacrum  moves 

Fig.  274. — Ligaments  connecting  Sacrum  and  Coccyx  posteriorly. 


Superficial  part  of 
the  supraspinous 
ligament,   turned 


Deep  part  of  the  su- 
praspinous ligament 
turned  up 


Lateral  sacro-coccygeaL 
ligament 


The  deep  posterior  sacro- 
cocygeal  ligament,  or  the 
lower  end  of  the  poste- 
rior longitudinal  liga- 
ment 

The  superficial  posterior 
sacro-coccygeal  1 i  g  a  - 
ment  connecting  the 
cornus  of  the  sacrum 
and  coccyx,  cut  and 
turned  down 


downward  and  forward  the  conjugate  (antero-posterior)  diameter  of  the  pelvic  inlet  is  diminished 
and  at  the  same  time,  as  the  coccyx  moves  up  and  back,  the  conjugate  diameter  of  the  outlet 
is  increased.  This  rotatory  movement  is  limited  principally  by  the  sacro-sciatic  (sacro- 
tuberous  and  sacro-spinous)  Ugaments  which  prevent  any  extensive  upward  and  backward 
movement  of  the  coccyx  and  lower  part  of  the  sacrum. 

Downward  displacement  of  the  sacrum  when  the  body  is  in  the  sitting  posture  is  prevented 
not  only  by  the  surrounding  hgaments,  but  also  by  the  wedge-like  character  of  the  sacrum, 
which  is  broader  above  than  below.  Downward  and  forward  displacement  of  the  sacrum  in 
the  erect  posture  is  prevented  by  the  ligaments  and  more  particularly  by  the  posterior  sacro- 
iliac bands,  while  backward  displacement  would  be  hindered  by  the  breadth  of  the  anterior  as 
contrasted  with  the  posterior  part  of  the  sacrum  as  well  as  by  the  anterior  ligaments. 

Relations. — The  sacro-ihac  joint  is  in  relation  above  with  psoas  and  iUaous.  In  front  it 
is  in  relation  at  its  upper  part  with  the  hypogastric  vessels  and  obturator  nerve,  and  at  its 
lower  part  with  the  piriformis  muscle. 

(b)  The  Sacro-coccygeal  Articulation 
Class. — False  Synchondrosis. 

The  last  piece  of  the  sacrum  and  first  piece  of  the  coccyx  enter  into  this  union 
[symphysis  sacrococcygea]  and  are  bound  together  by  the  following  ligaments : — 
Anterior  sacro-coccygeal.  Deep  posterior  sacro-coccygeal. 

Superficial  posterior  sacro-coccygeal.     Lateral  sacro-coccygeal. 
Intervertebral  substance. 


238  THE  ARTICULATIONS 

The  intervertebral  fibro -cartilage  is  a  small  oval  disc,  three-quarters  of  an 
inch  (about  2  cm.)  wide,  and  a  little  less  from  before  backward,  closely  con- 
nected with  the  surrounding  ligaments.  It  resembles  the  other  discs  in  struc- 
ture, but  is  softer  and  more  jelly-like,  though  the  laminse  of  the  fibrous  portion 
are  well  marked. 

The  anterior  sacro-coccygeal  ligament  is  a  prolongation  of  the  glistening 
fibrous  structure  on  the  front  of  the  sacrima.  It  is  really  the  lower  extremity  of 
the  anterior  longitudinal  ligament,  which  is  thicker  over  this  joint  than  over 
the  central  part  of  either  of  the  bones. 

The  posterior  sacro-coccygeal  ligament  (fig.  274)  is  divided  into  two  layers 
of  which  one  (the  deep)  is  a  direct  continuation  of  the  posterior  longitudinal 
ligament  of  the  column,  consisting  of  a  narrow  band  of  closely  packed  fibres, 
which  become  blended  at  the  lower  border  of  the  first  segment  of  the  coccyx 
with  the  filum  terminate  and  deep  posterior  ligament. 

The  superficial  layer  of  the  posterior  sacro-coccygeal  ligament  (or  supra- 
cornual  ligament),  (fig.  274)  is  the  prolongation  of  the  supraspinous  which  be- 
comes inseparably  blended  with  the  aponeurosis  of  the  sacro-spinalis  (erector 
spince)  opposite  the  laminse  of  the  third  sacral  vertebra,  and  is  thus  prolonged 
downward  upon  the  back  of  the  coccyx,  passing  over  and  roofing  in  the  lower 
end  of  the  spinal  canal  where  the  laminge  are  deficient. 

The  median  fibres  (the  supraspinous  ligament)  extend  over  the  back  of  the  coccyx  to  its 
tip,  blending  with  the  deep  fibres  of  the  posterior  sacro-coccygeal  ligament  and  filum  terminale; 
the  deeper  fibres  run  across  from  the  stunted  laminae  on  one  side  to  the  next  below  on  the  oppo- 
site side,  and  from  the  sacral  cornua  on  one  side  to  the  coccygeal  on  the  opposite,  some  passing 
between  the  two  cornua  of  the  same  side,  and  bridging  the  aperture  through  which  the  fifth 
sacral  nerve  passes.     Its  posterior  surface  gives  origin  to  the  gluteus  inaximus  muscle. 

The  lateral  sacro-coccygeal  or  intertransverse  ligament  (fig.  274)  is  merely  a  quantity  of 
fibrous  tissue  which  passes  from  the  transverse  process  of  the  coccyx  to  the  lateral  edge  of  the 
sacrum  below  its  angle.  It  is  connected  with  the  saerosciatic  ligaments  at  their  attachments, 
and  the  fifth  sacral  nerve  escapes  behind  it.  It  is  perforated  by  twigs  from  the  lateral  sacral 
artery  and  the  coccygeal  nerve. 

The  arterial  supply  of  the  sacro-coccygeal  joint  is  from  the  lateral  sacral  and  middle  sacral 
arteries. 

The  nerves  come  from  the  fourth  and  fifth  sacral  and  coccygeal  nerves. 

The  movements  permitted  at  this  joint  are  of  a  simple  forward  and  backward,  or  hinge- 
like character.  In  the  act  of  defecation,  the  bone  is  pushed  back  by  the  faecal  mass,  and,  in 
parturition,  by  the  foetus;  but  this  backward  movement  is  controlled  by  the  upward  and  forward 
puU  of  the  levator  ani  and  Qoccygeus.  The  external  sphincter  also  tends  to  puU  the  coccyx 
forward. 

(c)  Intercoccygeal  Joints 

The  several  segments  of  the  coccyx  are  held  together  by  the  anterior  and 
posterior  longitudinal  ligaments,  which  completely  cover  the  bony  nodules  on 
their  anterior  and  posterior  aspects.  Laterally,  the  sacro-sciatic  ligaments, 
being  attached  to  nearly  the  whole  length  of  the  coccyx,  serve  to  connect  them. 
Between  the  first  and  second  pieces  of  the  coccyx  there  is  a  very  perfect  amphiar- 
throdial  joint,  with  a  well-marked  intervertebral  substance. 

Movements. — But  Uttle  movement  occurs  as  a  rule  at  the  sacro-coccygeal  and  inter- 
coccygeal joints,  but  when  the  head  of  the  child  is  passing  through  the  pelyic  outlet  at  birth, 
the  tip  of  the  coccyx  is  displaced  backward,  it  may  be  to  the  extent  of  one  inch. 

(d)  The  Symphysis  Pubis 

Class. — False  Synchondrosis. 
The  bones  entering  into  this  joint  are  the  pubic  portions  of  the  hip-bones. 
This  joint  is  shorter  and  broader  in  the  female  than  in  the  male.     The  ligaments, 
which  completely  surround  the  articulation,  are : — 

Superior.  Anterior. 

Arcuate.  Posterior. 

Interpubic  cartilage. 

The  superior  ligament  (figs.  275  and  276)  is  a  well-marked  stratum  of  yellowish 
fibres  which  extends  lateralward  along  the  crest  of  the  pubis  on  each  side,  blending 
in  the  middle  line  with  the  interosseous  cartilage. 


SYMPHYSIS  PUBIS 


23& 


It  is  continuous  in  front  with  the  deep  traverse  fibres  of  the  anterior  ligament,  and  be- 
hind with  the  posterior  ligament.     It  gives  origin  to  the  rectus  abdominis  tendon. 

The  posterior  ligament  (fig.  277)  is  slight,  and,  excepting  above  and  below, 
consists  of  little  more  than  thickened  periosteum. 

Near  the  uipper  part  is  a  band  of  strong  fibres,  reaching  the  whole  width  of  the  pubic  bones, 
and  continuous  with  the  thickened  periosteal  fibres  along  the  terminal  line.  Below,  many  of  the 
upper  and  superficial  fibres  of  the  arcuate  ligament  ascend  over  the  back  of  the  joint,  and 
interlace  across  the  median  line  with  fibres  from  the  opposite  side  nearly  as  high  as  the  middle 
of  the  symphysis. 

Fig.  275. — Anteeiob  View  of  the  Symphysis  Pubis  (Male),  showing  the  Decussation 
OF  THE  Fibres  of  the  Anterior  Ligament. 
Superior  pubic  ligament 

X 


Arcuate  ligament 

The  anterior  ligament  (figs.  275  and  276)  is  thick  and  strong,  and  is  closely 
connected  with  the  fascial  covering  of  the  muscles  arising  from  the  body  of  the 
pubis.  It  consists  of  several  strata  of  thick,  decussating  fibres  of  different  de- 
grees of  obliquity,  the  superficial  being  the  most  oblique,  and  extending  lowest 
over  the  joint. 

The  most  superficial  descending  fibres  extend  from  the  upper  border  of  the  pubis,  cross 
others  from  the  opposite  side  about  the  middle  of  the  symphysis,  and  are  attached  to  the  ramus 
of  the  opposite  bone.     The  most  superficial  ascending  fibres  come  from  the  arcuate  ligament, 

Fig.  276. — Anterior  View  of  the  Symphysis  Pubis  (Female),   showing   greater   Width 
between  the  Bones. 

Superior  pubic  ligament 


Arcuate  ligament 


arch  upward,"and  decussate  with  other  fibres  across  the  middle  line,  and  are  lost  on  the  oppo- 
site side  beneath  the  descending  set.  There  is  another  deeper  set  of  descending  fibres  which 
arise  below  the  angle,  but  do  not  descend  so  far  as  the  superficial;  and  a  deeper  set  of  ascending, 
which  decussate,  and  reach  higher  than  the  superficial  set,  and  are  connected  with  the  arcuate 
ligament.  Some  few  transverse  fibres  pass  from  side  to  side,  especially  above  and  below^the 
points  of  decussation. 

The  arcuate  (inferior  or  subpubic)  ligament  (figs.  275,  276,  and  277)  is  a 
thick,  arch-like  band  of  closety  packed  fibres  which  fills  up  the  angle  between  the 
pubic  rami,  and  forms  a  smooth,  rounded  summit  to  the  pubic  arch.  On  section, 
it  is  yellowish  in  colour  and  three-eighths  of  an  inch  (1  cm.)  thick  in  the  middle 
line;  it  is  inseparably  connected  with  the  interpubic  cartilage. 


240 


THE  ARTICULATIONS 


Both  on  the  front  and  back  aspects  of  the  joint  it  gives  off  decussating  fibres,  which,  by  their 
interlacement  over  the  anterior  and  posterior  ligaments  of  the  symphysis,  add  very  materi- 
ally to  its  security.  In  fact,  the  ligament  may  be  said  to  split  superiorly  into  two  layers,  one 
passing  over  the  front,  and  the  other  over  the  back,  of  the  articulation. 

The  interpubic  fibro -cartilage  varies  in  thickness  in  different  subjects,  but 
is  thicker  in  the  female  than  in  the  male.  It  is  thicker  in  front  than  behind, 
and  projects  beyond  the  edges  of  the  bones,  especially  posteriorly  (see  fig.  277), 
blending  intimately  with  the  ligaments  at  its  margins.  It  is  sometimes  uninter- 
ruptedly woven  throughout,  but  at  others  has  an  elongated  narrow  fissure, 
partially  dividing  the  cartilage  into  two  plates,  with  a  little  fluid  in  the  interspace 

Fig.  277. — Posterior  View  of  the  Symphysis  Pubis,  showing  the  Decussation  op  the 
Fibres  prom  the  Arcuate  Ligament. 


Arcuate  ligament 


(fig.  278).  This  is  situated  toward  the  upper  and  posterior  aspects,  but  does 
not  usually  reach  either;  it  generally  extends  about  half  the  length  of  the 
cartilage. 

When  this  cavity  is  large,  especially  if  it  reaches  or  approaches  very  near  to  the  circumfer- 
ence of  the  cartilage  (which,  however,  it  very  rarely  does),  it  is  thought  by  some  anatomists 
that  it  more  nearly  resembles  a  diarthrodial  than  an  amphiarthrodial  joint,  and  it  is  then  classed 
with  the  sacro-Uiac  joint  under  similar  conditions,  as  'diarthroamphiarthrosis.'  The  interos- 
seous cartilage  is  intimately  adherent  to  the  layer  of  hyaline  qartUage  which  covers  the  medial 
surface  of  each  pubic  bone;  the  osseous  surface  is  ridged  to  give  a  firmer  attachment;  and,  on 
forcing  the  bones  apart,  it  does  not  frequently  spht  into  two  plates,  but  is  torn  from  the  bone 
on  one  side  or  the  other. 

Fig.  278. — Section  of  Symphysis  to  show  the  Synovial  Cavity. 


The  arterial  supply  of  the  interpubic  joint  is  from  twigs  of  the  internal  pudic,  pubic  branches 
of  the  obturator  and  epigastric,  and  ascending  branches  of  the  internal  circumflex  and  super- 
ficial external  pudic. 

The  nerve-supply  has  not  been  satisfactorily  made  out,  but  it  probably  comes,  m  part, 
from  the  internal  pudic  and  in  part  from  the  ilio-hypogastric  and  Uio-inguinal. 

The  movements  amount  only  to  a  slight  yielding  of  the  cartilage;  neithermuscular  force 
nor  extrinsic  forces  produce  any  appreciable  movement  in  the  ordinary  condition.  Occasion- 
ally, as  the  result  of  child-bearing,  the  joint  becomes  unnaturally  loose,  and  then  waMng  and 
standing  are  painfully  unsteady.     It  is  known  that,  during  pregnancy  and  parturition,  the 


COSTO-VERTEBRAL  ARTICULATIONS 


241 


symphyseal  cartilage  becomes  softer  and  more  vascular,  so  as  to  permit  the  temporary  enlarge- 
ment of  the  pelvis;  but  it  must  be  remembered  that  the  fibres  of  the  obhque  muscles  decussate 
and  thus,  during  labour,  while  they  force  the  head  of  the  fcetus  down,  they  strengthen  the  joint 
by  bracing  the  bones  more  tightly  together. 

Relations. — The  interpubic  joint  is  in  relation  above  with  the  Unea  alba.  Behind  with 
the  prostate  and  the  anterior  border  of  the  bladder.  In  front  with  the  suspensory  ligament 
of  the  penis  or  chtoris  and  below  with  the  dorsal  vein  of  the  penis  or  clitoris  and  the  upper 
border  of  the  urogenital  trigone  (triangular  ligament). 


4.  THE  COSTO-VERTEBRAL  ARTICULATIONS 
These  consist  of  two  sets,  viz. : — ■ 

(a)  The  capitular  (costo-central) :  i.  e.,  the  articulation  of  the  head  of  the  rib 
with  the  vertebrae. 

(6)  The  costo-transverse,  or  the  articulation  of  the  tubercle  (of  each  of  the 
first  ten  ribs)  with  the  transverse  process  of  the  lower  of  the  two  vertebree,  with 
which  the  head  of  the  rib  articulates:  i.e.,  the  one  bearing  its  own  number,  as 
the  first  rib  with  the  first  thoracic  vertebra,  the  second  rib  with  the  second  thoracic 
vertebra,  and  so  on. 

Fig.  279. — -The  Capsular  Ligaments  op  the  Costo-vertebral  Joints. 


Capsular    ligament     of 
capitular    joint 


(a)  The  Capitular  (Costo-central)  Articulation 

Class. — Diarthrosis.  Subdivision. — Condylarthrosis. 

It  is  a  very  perfect  joint,  into  the  formation  of  which  the  head  of  the  rib  and 
two  vertebrae,  with  the  intervertebral  disc  between  them,  enter.  In  the  case  of 
the  first,  tenth,  eleventh,  and  twelfth  ribs,  it  is  formed  by  the  head  of  the  rib 
articulating  with  a  single  vertebra. 


The  ligaments  are : — 

Articular  capsule. 


Interarticular. 


Radiate. 


The  articular  capsule  (fig.  279)  consists  of  short,  strong,  woolly  fibres,  com- 
pletely surrounding  the  joint,  which  are  attached  to  the  bones  and  intervertebral 
substances,  a  little  beyond  their  articular  margins. 

At  its  upper  part  it  reaches  through  the  intervertebral  foramen  toward  the  back  of  the 
bodies  of  the  vertebrae,  being  strengthened  here  by  fibres  which  at  intervals  connect  the  anterior 
with  the  posterior  longitudinal  ligaments.  The  lower  fibres  extend  downward  nearly  to  the 
demi-faoet  (costal  pit)  of  the  rib  below;  behind,  it  is  continuous  with  the  neck  ligament,  and 
in  front  is  overlaid  by  the  radiate. 

The  interarticular  ligament  (fig.  280)  consists  of  short,  strong  fibres,  closely 
interwoven  with  the  outermost  ring  of  the  intervertebral  disc,  and  attached  to 
the  transverse  ridge  separating  the  articular  facets  on  the  head  of  the  rib.  It 
completely  divides  the  articulations  into  two  parts,  but  does  not  brace  the  rib 
tightly  to  the  spine,  being  loose  enough  to  allow  a  moderate  amount  of  rotation 


242 


THE  ARTICULATIONS 


on  its  own  axis.     There  is  no  interarticular  ligament  in  the  costo-vertebral  joints 
of  the  first,  tenth,  eleventh,  and  twelfth  ribs. 

The  radiate  (or  stellate)  ligament,  a  thickening  of  the  anterior  part  of  the 
capsule  (figs.  280  and  281),  is  the  most  striking  of  all,  and  consists  of  bright, 
pearly-white  fibres  attached  to  the  anterior  surface,  and  upper  and  lower  borders 
of  the  neck  of  the  rib,  a  little  way  beyond  the  articular  facet;  from  this  they 
radiate  upward,  forward,  and  downward,  so  as  to  form  a  continuous  layer  of 
distinct  and  sharply  defined  fibres. 

The  middle  fibres  run  straight  forward  to  be  attached  to  the  intervertebral  disc;  the  upper 
ascend  to  the  lower  half  of  the  lateral  surface  of  the  vertebra  above,  and  the  lower  descend  to 
the  upper  half  of  the  vertebra  below.  The  radiate  ligament  is  overlapped  on  the  vertebral 
bodies  by  the  lateral  (short)  vertebral  ligaments. 

In  the  case  of  the  first,  tenth,  eleventh,  and  twelfth  ribs,  each  of  which  articulates  with  one 
vertebra,  the  ligament  is  not  quite  so  distinctly  radiate,  but  even  in  these  the  ascending  fibres 
reach  the  vertebra  above  that  with  which  the  rib  articulates. 

Fig.  280. — Showing  the  Anterior  Longitudinal  Ligament,  and  the  Connection  op  the 
Ribs  with  the  Vertebra. 


The  interarticular  ligament 


The  costo-transverse  ligaments 


^ — The  radiate  ligament 


The  synovial  membranes  (fig.  281)  consist  of  two  closed  sacs  which  do  not 
communicate:  one  above,  and  the  other  below,  the  interarticular  ligament.  In 
the  case  of  the  first,  tenth,  eleventh,  and  twelfth  articulations,  there  is  but  one 
synovial  membrane,  as  these  joints  have  no  interarticular  ligament. 

The  arterial  supply  is  from  the  intercostal  arteries,  the  twigs  piercing  the  radiate  and 
capsular  ligaments. 

The  nerve -supply  comes  from  the  anterior  primary  branches  of  the  intercostal  nerves. 

These  joints  approach  most  nearly  in  their  movements  to  the  condylarthroses. 

The  movements  are  ginglymoid  in  character,  consisting  of  a  slight  degree  of  elevation  and 
depression  around  an  obliquely  horizontal  axis  corresponding  with  the  interarticular  ligament; 
there  is  also  a  slight  amount  of  forward  and  backward  gliding;  and  a  slight  degree  of  screwing  or 
rotatory  movement  is  also  possible .  There  is  a  considerable  difference  in  the  degree  of  mobility  of 
the  different  ribs,  for  while  the  first  rib  is  almost  immobile  except  in  a  very  deep  inspiration, 
the  mobility  of  the  others  increases  from  the  second  to  the  last;  the  two  floating  ribs  being  the 
most  mobile  of  all.  The  head  of  the  rib  is  the  most  fixed  point  of  the  costal  arch,  and  upon 
it  the  whole  arch  rotates;  the  interarticular  ligament  allows  only  a  very  limited  amount  of 
flexion  and  extension  (i.  e.,  elevation  and  depression),  and  of  gliding.  Gliding  is  checked  by 
the  radiate  ligament. 

In  inspiration,  the  rib  is  elevated,  and  glides  forward  in  its  socket,  too  great  elevation 
being  checked  not  only  by  the  ligaments,  but  also  by  the  overhanging  upper  edge  of  the  cavity 
itself.     In  expiration,  the  rib  is  depressed,  and  glides  backward  in  its  cavity. 


COSTO-TRANSVERSE  ARTICULATIONS 


243 


(6)  The  Costo-transvehse  Articulation 


Class. — Diarthrosis. 


Subdivision. — Arthrodia. 


This  joint  is  formed  by  the  tubercle  of  the  rib  articulating  with  the  anterior 
part  of  the  tip  of  the  transverse  process.  The  eleventh  and  twelfth  ribs  are 
devoid  of  these  joints,  for  the  tubercles  of  these  ribs  are  absent,  and  the  transverse 
processes  of  the  eleventh  and  twelfth  thoracic  vertebrae  are  rudimentary. 


The  ligaments  of  the  union  are  :- 

Articular  capsule. 
Neck  ligament. 


Tubercular  ligament. 
Costo-transverse  ligaments. 


The  articular  capsule  (figs.  279  and  281)  forms  a  thin,  loose,  fibrous  envelope  to 
the  synovial  membrane.  Its  fibres  are  attached  to  the  bones  just  beyond  the 
articular  margins,  and  are  thickest  below,  where  they  are  not  strengthened  by 
any  other  structure.  It  is  connected  medially  with  the  neck  ligament,  above 
with  the  costo-transverse,  and  laterally  with  the  tubercular  (posterior  costo- 
transverse) ligaments.  The  eleventh  and  twelfth  ribs  are  unprovided  with  costo- 
transverse capsules. 


Fig.  281. — Horizontal  Section  through  the  Inteevertebeal  Disc  and  Ribs. 


Fibrous  ring  of  intervertebral 

fibro-cartilage 


Radiate  ligament 


i 


Costo-transverse  synovial  sac 


Tubercular  ligament 


The  neck  ligament  [lig.  colli  costae]  (middle  costo-transverse,  or  interosseous 
ligament)  (fig.  281),  consists  of  short  fibres  passing  between  the  back  of  the  neck 
of  the  rib  and  front  of  the  transverse  process,  with  which  the  tubercle  articulates. 
It  extends  from  the  capsule  of  the  capitular  joint  to  that  of  the  costo-transverse. 
It  is  best  seen  on  horizontal  section  through  the  bones.  In  the  eleventh  and 
twelfth  ribs  this  ligament  is  rudimentary. 

The  tubercular  ligament  (posterior  costo-transverse)  (fig.  281)  is  a  short  but 
thick,  strong,  and  broad  ligament,  which  extends  laterally  and  upward  from  the 
extremity  of  the  transverse  process  to  the  non-articular  surface  of  the  tubercle 
of  the  corresponding  rib.  The  eleventh  and  twelfth  ribs  have  no  posterior 
ligament. 

The  (superior)  costo-transverse  ligament  (fig.  280)  is  a  strong,  broad  band  of 
fibres  which  ascends  laterally  from  the  crest  on  the  upper  border  of  the  neck 
of  the  rib,  to  the  lower  border  of  the  transverse  process  above.  A  few  scattered 
posterior  fibres  pass  upward  and  medially  from  the  neck  to  the  transverse  process. 
The  costo-transverse  ligament  is  subdivided  into  a  stronger  anterior  portion 
(anterior  costo-transverse  ligament)  best  seen  from  the  front  (fig.  280) ,  and  a 
weaker  posterior  portion  (posterior  costo-transverse  ligament).  Its  medial 
border  bounds  the  foramen  through  which  the  posterior  branches  of  the  inter- 
costal vessels  and  nerves  pass.     To  the  lateral  border  is  attached  the  thin  aponeu- 


I 


244  THE  ARTICULATIONS 

rosis  covering  the  external  intercostals.  Its  anterior  surface  is  in  relation  with  the 
intercostal  vessels  and  nerve;  the  posterior  with  the  longissimus  dor  si.  The 
first  rib  has  no  (superior)  costo-transverse  ligament. 

The  synovial  membrane  (fig.  281)  is  a  single  sac. 

The  arterial  and  nerve  supplies  come  from  the  posterior  branches  of  the  intercostal  arteries 
and  nerves. 

The  movements  which  take  place  at  these  joints  are  limited  to  a  gliding  of  the  tubercle  of 
the  rib  upon  the  transverse  process.  The  exact  position  of  the  facet  on  the  transverse  process 
varies  slightly  from  above  downward,  being  placed  higher  on  the  processes  of  the  lower  vertebrae. 
The  plane  of  movement  in  most  of  the  costo-transverse  joints  is  inclined  upward  and  backward 
in  inspiration,  and  downward  and  forward  in  expiration.  The  point  round  which  these  move- 
ments occur  is  the  head  of  the  rib,  so  that  the  tubercle  of  the  rib  gUdes  upon  the  transverse 
process  in  the  circumference  of  a  circle,  the  centre  of  which  is  at  the  capitular  joint. 

5.  THE  ARTICULATIONS  AT  THE  FRONT  OF  THE  THORAX 
These  may  be  divided  into  four  sets,  viz.: — ■ 

(a)  The  intersternal  joints,  or  the  union  of  the  several  parts  of  the  sternum 
with  one  another. 

(6)  The  costo -chondral  joints,  or  the  union  of  the  ribs  with  their  costal 
cartilages. 

(c)  The  chondro-stemal  joints,  or  the  junction  of  the  costal  cartilages  with 
the  sternum. 

(d)  The  interchondral  joints,  or  the  union  of  five  costal  cartilages  (sixth, 
seventh,  eighth,  ninth,  and  tenth)  with  one  another. 

(a)  The  Intersternal  Joints 

The  sternum  being  composed,  in  the  adult,  of  three  distinct  pieces — the 
manubrium,  body,  and  the  xiphoid  process — has  two  articulations,  viz.,  the 
superior,  which  unites  the  manubrium  with  the  body  (gladiolus),  and  the  inferior, 
which  unites  the  body  with  the  xiphoid. 

1.  The  Superior  Intersternal  Articulation 
Class. — False  Synchondrosis. 

The  lower  border  of  the  manubrium  and  the  upper  border  of  the  body  of  the 
sternum  present  oval-shaped,  fiat  surfaces,  with  their  long  axes  transverse,  and 
covered  with  a  thin  layer  of  hyaline  cartilage.  An  interosseous  fibro-cartilage 
is  interposed  between  the  bony  surfaces:  it  corresponds  exactly  in  shape  and 
intimately  adheres  to  them.  At  each  lateral  border  this  fibro-cartilage  enters 
into  the  formation  of  the  second  chondro-sternal  articulation  (fig.  282). 

In  consistence  it  varies,  being  in  some  oases  uniform  throughout,  in  others  softer  in  the 
centre  than  at  the  circumference,  and  in  others  again  an  oval-shaped  synovial  cavity  is  found 
toward  its  anterior  part.  When  such  a  cavity  exists  in  the  fibro-cartilage  this  joint  has  a 
remote  resemblance  to  the  diarthroses,  and  is  classed,  with  the  sacro-iliac  joint  and  the  symphy- 
sis pubis  under  similar  conditions,  as  'diarthro-amphiarthrosis.' 

The  periosteum  passes  uninterruptedly  over  the  joint  from  one  segment  of  the  sternum  to 
the  other,  forming  a  kind  of  capsular  ligament  [membrana  sterni].  This  capsule  is  strength- 
ened, especially  on  its  pos'erior  aspect,  by  longitudinal  ligamentous  fibres  as  well  as  by  the 
radiating  and  decussating  fibres  of  the  chondro-sternal  ligaments. 

In  some  instances  the  fibro-cartilage  is  replaced  by  short  bundles  of  fibrous  tissue  which 
unite  the  cartilage-coated  articular  bony  sm'faces. 

2.  The  Inferior  Intersternal  Articulation 
Class. — False  Synchondrosis. 

The  gladiolus  is  joined  to  the  xiphoid  cartilage  by  a  thick  investing  mem- 
brane, by  anterior  and  posterior  longitudinal  fibres,  and  by  radiating  fibres  of  the 
sixth  and  seventh  chondro-sternal  ligaments.  The  costo-xiphoid  ligament  also 
connects  the  xiphoid  with  the  anterior  surface  of  the  sixth  and  seventh  costal 
cartilages,  and  thus  indirectly  with  the  gladiolus;  and  some  fine  fibro-areolar 
tissue  also  connects  the  xiphoid  with  the  back  of  the  seventh  costal  cartilage. 


STERNO-COSTAL  ARTICULATIONS  245 

The  junction  of  the  xiphoid  with  the  sternum  is  on  a  level  somewhat  posterior  to  the  junc- 
tion of  the  seventh  costal  cartilage  with  the  sternum.  The  union  is  a  synchondrosis,  each  bone 
being  covered  by  hyahne  cartilage  which  is  connected  with  the  intervening  fibro-cartilage  plate. 

(b)  The  Costo-chondral  Joints 

Class. — Synarthrosis. 

The  extremity  of  the  costal  cartilage  is  received  into  a  cup-shaped  depression 

at  the  end  of  the  rib,  which  is  somewhat  larger  than  the  cartilage.     The  two  are 

joined  together  by  the  continuity  of  the  investing  membranes,  the  periosteum  of 

the  rib  being  continuous  with  the  perichondrium  of  the  cartilage. 

(c)  The  Steeno-costal  Articulations 
Class. — Diarthrosis.  Subdivision — Ginglymus. 

These  articulations  are  between  the  lateral  borders  of  the  sternum  and  the 
ends  of  the  costal  cartilages.  The  union  of  the  first  rib  with  the  sternum  is 
synchondrodial,  and  therefore  forms  an  exception  to  the  others.  From  the  second 
to  the  seventh  inclusive,  the  articulations  have  the  following  ligaments,  which 
together  form  a  complete  capsule: — 

Radiate  (anterior)  sterno-costal.  Superior  sterno-costal. 

Posterior  sterno-costal.  Inferior  sterno-costal. 

The  radiate  (anterior)  sterno-costal  ligament  (fig.  282)  is  a  triangular  band 
composed  of  strong  fibres  which  cover  the  medial  half-inch  of  the  front  of  the 
costal  cartilage,  and  radiate  upward  and  downward  upon  the  front  of  the  sternum. 
Some  of  the  fibres  decussate  across  the  middle  line  with  fibres  of  the  opposite 
ligament.  At  its  upper  and  lower  borders  it  is  in  contact  with  the  superior  and 
inferior  ligaments  respectively. 

The  posterior  sterno-costal  ligament  consists  of  little  more  than  a  thickening 
of  the  fibrous  envelopes  of  the  bone  and  cartilage,  the  joint  being  completed 
behind  by  a  continuity  of  perichondrium  with  periostemn. 

The  superior  and  inferior  ligaments  are  strong,  well-marked  bands,  which 
pass  from  the  upper  and  lower  borders  respectively  of  the  costal  cartilage  to  the 
lateral  edges  of  the  sternum.  The  sixth  and  seventh  cartilages  are  so  close  that 
the  superior  ligament  of  the  seventh  is  blended  ^^^th  the  inferior  of  the  sixth  rib. 

Deeper  than  the  fibres  of  these  ligaments  are  short  fibres  passing  from  the  margins  of  the 
sternal  facets  to  the  edges  of  the  facets  on  the  cartilages;  they  are  most  distinct  in  the  front 
and  lower  part  of  the  joint,  and  may  encroach  so  much  upon  the  synovial  cavity  as  to  reduce 
it  to  a  very  small  size,  or  almost  obliterate  it.  This  occurs  mostly  in  the  case  of  the  sixth  and 
seventh  joints,  especially  the  latter. 

The  interarticular  ligament  (fig.  282)  is  by  no  means  constant,  but  is  usually 
present  in  the  second  joint  on  one,  if  not  on  both  sides  of  the  same  subject.  It 
consists  of  a  strong  transverse  bundle  of  fibres  passing  from  the  ridge  on  the  facet 
on  the  cartilage  to  the  fibrous  substance  between  the  manubrium  and  body; 
sometimes  the  upper  part  of  the  synovial  cavity  is  partially  or  entirely  obliterated 
by  short,  fine,  ligamentous  fibres. 

The  costo-xiphoid  ligament  (fig.  282)  is  a  strong  flat  band  of  fibres  passing 
obliquely  upward  and  laterally  from  the  front  surface  of  the  xiphoid  cartilage  to 
the  anterior  surface  of  the  sternal  end  of  the  seventh  costal  cartilage,  and  most 
frequently  to  that  of  the  sixth  also. 

Synovial  membranes. — -The  union  of  the  first  cartilage  with  the  sternum  being  synchondro- 
dial, it  has  no  synovial  membrane;  the  second  has  usually  two,  separated  by  the  interarticular 
Ugament.  The  rest  usually  have  one  synovial  membrane,  which  may  occasionally  be  subdivided 
into  two  (fig.  2S2). 

The  arterial  supply  is  derived  from  perforating  branches  of  the  internal  mammary;  and 
the  nerves  come  from  the  anterior  branches  of  the  interoostals. 

Movements. — -Excepting  the  first,  the  chondro-sternal  joints  are  ginglymoid,  but  the 
motion  of  which  they  are  capable  is  verj'  limited.  It  consists  of  a  hinge-like  action  in  two  direc- 
tions: first,  there  is  a  slight  amount  of  elevation  and  depression  which  takes  place  round  a 
transverse  axis,  and,  secondly,  there  is  some  forward  and  backward  movement  round  an  ob- 
liquely vertical  axis.  In  inspiration  the  cartilage  is  elevated,  the  lowest  part  of  its  articular 
facet  is  pressed  into  the  sternal  socket,  and  the  sternum  is  thrust  forward  so  that  the  upper 


i 


246 


THE  ARTICULATIONS 


aad  front  edges  of  the  articular  surfaces  separate  a  little;  in  expiration  the  reverse  movement 
takes  place.  Thus  the  two  extremities  of  the  costal  arches  move  in  their  respective  sockets  in 
opposite  directions. 

This  difference  results  necessarily  from  the  fact  that  the  costal  arch  moves  upon  the  verte- 
bral column,  and,  having  been  elevated,  it  in  its  turn  raises  the  sternum  by  pushing  at  upward 
and  forward. 

The  costo-.xiphoid  ligament  tends  to  prevent  the  xiphoid  cartilage  from  being  drawn  back- 
ward by  the  action  of  the  diaphragm. 

Fig.  282. — The  Articulation  at  the  Front  of  the  Thorax. 
(Left  side,  showing  ligaments,  right  side,  the  synovial  cavities.) 


For  clavicle  and  first  rib 


The  plate  of  fibre-  -  -,^.3 

cartilage  betW' ^^"  '  '^ 

manubriuDi     i 
body 


^^Radiate  sterno- 
costal ligameat 


(d)  The  Interchondral  Articulations 
Class. — Diarthrosis.  Subdivision. — Arthrodia. 

A  little  in  front  of  the  point  where  the  costal  cartilages  bend  upward  toward 
the  median  line  the  sixth  is  united  with  the  seventh,  the  seventh  with  the  eighth, 
the  eighth  with  the  ninth,  and  the  ninth  with  the  tenth. 

At  this  point  each  of  the  cartilages  from  the  sixth  to  the  ninth  inclusive  is  deeper  than 
elsewhere,  owing  to  the  projection  downward  from  its  lower  edge  of  a  broad  blunt  process, 
which  comes  into  contact  with  the  cartilage  next  below.    Each  of  the  apposed  surfaces  is  smooth. 


MOVEMENTS  OF  THE  THORAX 


247 


and  they  are  connected  at  their  margins  by  ligamentous  tissue,  which  forms  a  complete  capsule 
for  the  articulation,  and  is  hned  by  a  synovial  membrane  (fig.  282).  The  largest  of  these  cavi- 
ties is  between  the  seventh  and  eighth;  those  between  the  eighth  and  ninth,  and  ninth  and  tenth, 
are  smaller,  and  are  not  free  to  play  upon  each  other  in  the  whole  of  their  extent,  being  held 
together  by  ligamentous  tissue  at  theii'  anterior  margins.  Sometimes  this  fibrous  tissue  com- 
pletely obliterates  the  synovial  cavity. 

The  arteries  are  derived  from  the  musoulo-phrenio,  and  the  nerves  from  the  intercostals. 

Movements. — -By  means  of  the  costal  cartilages  and  interchondral  joints,  strength  with 
elasticity  is  given  to  the  wall  of  the  trunk  at  a  part  where  the  cartilages  are  the  only  firm  struc- 
tures in  its  composition;  while  a  slight  gliding  movement  is  permitted  between  the  costal  carti- 
lages themselves,  which  takes  place  round  an  axis  corresponding  to  the  long  axis  of  the  cartilages. 
By  this  means,  the  outward  projection  of  the  lower  part  of  the  thoracic  wall  is  increased  by  deep 
inspiration. 

MOVEMENTS  OF  THE  THORAX  AS  A  WHOLE 

Before  describing  these  movements  as  a  <vhole,  it  must  be  premised  that  there  are  somt 
few  modifications  in  the  movements  of  certain  ribs  resulting  from  their  shape.  Thus  the  firs 
rib  (and  to  a  less  extent  the  second  also),  which  is  flat  on  its  upper  and  lower  surfaces,  revolves 
on  a  transverse  axis  drawn  through  the  oosto-vertebral  and  costo-transverse  joints.  During 
inspiration  and  expiration,  the  anterior  extremities  of  the  first  pair  of  costal  arches  play  up  and 
down,  the  tubercles  and  the  heads  of  the  ribs  acting  in  a  hinge-like  manner,  the  latter  having 
also  a  sHght  screwing  motion.  By  this  movement  the  anterior  ends  of  the  costal  arches  are 
simply  raised  or  depressed,  and  the  sternum  pushed  a  little  forward;  it  may  be  likened  to  the 
movement  of  a  pump-handle,  as  in  fig.  283,  a,  b. 

The  movements  of  the  other  ribs,  particularly  in  the  mid-region  of  the  thorax,  are  more 
complex,  for,  besides  the  elevation  of  the  anterior  extremities,  the  bodies  and  angles  of  the 

Fig.  283. — Diagram  op  Axis  op  Rib-movement.     (After  Kirkes.) 


ribs  rise  nearly  as  much  as  the  extremities  themselves.  In  this'movement  the  tubercles  of  the 
ribs  glide  upward  and  backward  in  inspiration,  and  downward  and  forward  in  expiration;  and 
the  movement  may  be  likened  to  that  of  a  bucket  handle,  as  in  fig.  283,  A,  B. 

During  inspiration,  the  cavity  of  the  thorax  is  increased  in  every  direction.  The  antero- 
posterior diameter  is  increased  by  the  thrusting  forward  of  the  sternum,  caused  by  the  eleva- 
tion of  the  costal  cartilages  and  fore  part  of  the  ribs,  whereby  they  are  brought  to  nearly  the 
same  level  as  the  heads  of  the  ribs.  The  transverse  diameter  is  increased:  (i)  Behind,  by  the 
elevation  of  the  middle  part  of  the  ribs;  for  when  at  rest  the  mid-part  of  the  rib  is  on  a  lower 
level  than  either  the  costo-vertebral  or  chondro-sternal  articulations.  Owing  to  this  obUquity 
the  transverse  diameter  is  increased  when  the  rib  is  raised,  and  the  increase  is  proportionate 
to  the  degree  of  obliquity,  (ii)  By  the  eversion  of  the  lower  border  of  the  costal  arch,  which 
tuTns  outward  as  the  arch  is  raised,  (iii)  The  transverse  diameter  is  increased  in  front  by  the 
abduction  of  the  anterior  extremity  of  the  rib  at  the  same  time  as  it  is  elevated  and  thrust 
forward. 

The  increase  in  the  vertical  diameter  of  the  thorax  is  due  to  the  elevation  of  the  ribs,  espe- 
cially the  upper  ones,  and  the  consequent  widening  of  the  intercostal  spaces;  but  the  chief 
increase  in  this  direction  is  due  to  the  descent  of  the  diaphragm. 

The  greatest  increase  both  in  the  antero-posterior  and  transverse  diameters  takes  place 
where  the  ribs  are  longest,  most  oblique,  and  most  curved  at  theu'  angles,  and  where  the  bulkiest 
part  of  the  lung  is  enclosed.     This  is  on  a  level  with  the  sixth,  seventh,  and  eighth  ribs. 

At  the  lower  part  of  the  thorax,  where  the  ribs  have  no  relation  to  the  lungs,  and  do  not 
affect  respiration  directly  by  their  movements,  it  is  important  that  the  costal  arches  should 
be  thrown  well  outward  in  order  to  counteract  the  compression  of  the  abdominal  viscera  by  the 
contraction  of  the  diaphragm. 

By  widening  and  steadying  the  lower  part  of  the  thorax  during  inspiration,  the  attachments 
ofjthe  muscular  fibres  of  the  diaphi-agm  are  widened,  and  their  power  increased. 

Muscles  which  take  part  in  the  movements  of  inspiration. — (a)  Ordinary  inspiration;  The 
scalenes,  serratus  posterior  superior,  the  external  and  internal  (?)  intercostals,  the  diaphragm; 
the  quadratus  lumborum  and  serratus  posterior  inferior  fixing  the  lower  ribs,  possibly  the  poste- 
rior fibres  of  the  external  oblique  also  helping  to  fix  the  lower  ribs,  (b)  Extraordinary  inspira- 
tion: The  superior  extremities  are  raised  and  fixed.  The  cervical  part  of  the  vertebral  column 
and  the  head  are  extended,  and  in  addition  to  the  muscles  of  ordinary  inspiration,  the  following 


> 


248  THE  ARTICULATIONS 

muscles  also  come  into  play:  The  pectoralis  minor,  the  muscles  which  extend  the  head  and  the 
cervical  part  of  the  vertebral  column,  the  sterno-mastoid  and  the  supra-  and  infra-hyoid  mus- 
cles, the  lower  fibres  of  the  pectoralis  major,  some  of  the  lower  fibres  of  the  serratus  anterior,  and, 
when  the  clavicle  is  fixed,  the  subclavius. 

Expiration  is  produced  by  the  elasticity  of  the  lungs  and  the  weight  of  the  thorax,  aided 
by  the  elastic  reaction  and  contraction  of  the  external  and  internal  oblique  muscles,  the  recti 
and  pyramidales,  the  transversus  abdominis,  and  the  levatores  ani  and  coccygei.  In  forcible 
expiration  all  muscles  which  depress  the  ribs  and  reduce  the  dimensions  of  the  abdomen  are 
thrown  into  action.  The  internal  interoostals  probably  tend  to  contract  the  thorax,  excepting, 
the  parts  between  the  costal  cartilages,  which  tend  to  expand  the  thorax. 

THE  ARTICULATIONS  OF  THE  UPPER  EXTREMITY 

The  articulations  of  the  upper  extremity  are  the  following: — 

1.  The  stemo-costo -clavicular. 

2.  The  scapulo-clavicular  union. 

3.  The  shoulder-joint. 

4.  The  elbow-joint. 

5.  The  radio-ulnar  union. 

6.  The  radio-carpal  or  wrist-joint. 

7.  The  carpal  joints. 

8.  The  carpo-metacarpal  joints. 

9.  The  intermetacarpal  joints. 

10.  The  metacarpo-phalangeal  joints. 

11.  The  interphalangeal  joints. 

1.  THE  STERNO-COSTO-CLAVICULAR  ARTICULATION 
Class. — Diarthrosis.  Subdivision. — Condylarthrosis. 

At  this  joint  the  large  medial  end  of  the  clavicle  is  united  to  the  superior  angle 
of  the  manubrium  sterni,  the  first  costal  cartilage  also  assisting  to  support  the 
clavicle.  It  is  the  only  joint  between  the  upper  extremity  and  the  trunk,  and 
takes  part  in  all  the  movements  of  the  upper  limb.  Looking  at  the  bones,  one 
would  say  that  they  were  in  no  waj^  adapted  to  articulate  with  one  another,  and 
yet  they  assist  in  constructing  a  joint  of  security,  strength,  and  importance. 
The  bones  are  nowhere  in  actual  contact,  being  completely  separated  by  an 
articular  disc.  The  interval  between  the  joints  of  the  two  sides  varies  from  one 
inch  to  an  inch  and  a  half  (2.5-4  cm.).     The  ligaments  of  this  joint  are: — 

(1)  Articular  capsule.  (3)  Articular  disc. 

(2)  Interclavicular.  (4)  Costo-clavicular. 

The  articular  capsule  (fig.  284)  consists  of  fibres,  having  varying  directions 
and  being  of  various  strength  and  thickness,  which  completely  surround  the 
articulation,  and  are  firmly  connected  with  the  edges  of  the  interarticular  fibro- 
cartilage. 

The  fibres  at  the  back  of  the  joint,  sometimes  styled  the  posterior  stemo-clavicular  liga- 
ment, are  stronger  than  those  in  front  or  below,  and  consist  of  two  sets:  a  superficial,  passing 
upward  and  laterally  from  the  manubrium  sterni,  to  the  projecting  posterior  edge  of  the  end  of 
the  clavicle,  a  few  being  prolonged  onward  upon  the  posterior  surface  of  the  bone.  A  deeper 
set  of  fibres,  especiallj^  thick  and  numerous  below  the  clavicle,  connect  the  interarticular  car- 
tilage with  the  clavicle  and  with  the  sternum,  but  do  not  extend  from  one  bone  to  the  other. 
The  fibres  in  front,  the  anterior  sterno -clavicular  ligament,  are  well  marked,  but  more  lax  and 
less  tough  than  the  posterior,  and  are  overlaid  by  the  tendinous  sternal  origin  of  the  sterno- 
mastoid,  the  fibres  of  which  run  parallel  to  those  of  the  ligament.  They  extend  obliquely  up- 
ward and  laterally  from  the  margin  of  the  sternal  facet  to  the  anterior  surface  of  the  clavicle 
some  little  distance  from  the  articular  margin.  The  fibres  which  cover  in  the  joint  below  are 
short,  woolly,  and  consist  more  of  fibro-areolar  tissue  than  true  fibrous  tissue;  they  extend  from 
the  upper  border  of  the  first  costal  cartilage  to  the  lower  border  of  the  clavicle  just  lateral  to 
the  articular  margin,  and  fill  up  the  gap  between  it  and  the  costo-clavicular  ligament.  The 
superior  portion  consists  of  short  tough  fibres  passing  from  the  sternum  to  the  articular  disc; 
and  of  others  welding  the  fibro-cartilage  to  the  upper  edge  of  the  clavicle,  onlj'  a  few  of  them 
passing  from  the  clavicle  direct  to  the  sternum. 

The  interclavicular  ligament  (fig.  284)  is  a  strong,  concave  band,  materially 
strengthening  the  superior  portion  of  the  capsule.     It  is  nearly  a  quarter  of  an 


STERNO-COSTO  CLAVICULAR  JOINT 


249 


inch  (6  mm.)  deep  with  the  concavity  upward,  its  upper  border  tapering  to  a 
narrow,  almost  sharp  edge.  It  is  connected  with  the  posterior  superior  angle  of 
the  sternal  extremity  of  each  clavicle,  and  with  the  fibres  which  weld  the  inter- 
articular  cartilage  to  the  clavicle;  and  then  passes  across  from  clavicle  to  clavicle 
along  the  posterior  aspect  of  the  upper  border  of  the  manubrium  sterni.  The 
lowest  fibres  are  attached  to  the  sternum,  and  join  the  posterior  fibres  of  the 
capsule  of  each  joint.  In  the  middle  line,  between  the  ligament  and  the  sternum, 
there  is  an  aperture  for  the  passage  of  a  small  artery  and  vein. 

In  addition  to  the  interclavicular  ligament  Mr.  Carwardine  ("Journal  of  Anatomy  and 
Physiology,"  vol.  7,  new  series,  p.  232)  has  described  a  special  band  of  the  upper  portion  of  the 
sterno-clavioular  capsule  which  he  proposes  to  name  the  'suprasternal  hgament.'  It  descends 
from  the  upper  border  of  the  sternal  end  of  the  clavicle  to  the  upper  border  of  the  sternum,  and 
is  of  special  importance  as  it  encloses  the  suprasternal  bones,  when  these  rudiments  are  present. 

The  costo -clavicular  or  rhomboid  ligament  (fig.  284)  is  a  strong  dense  band, 
composed  of  fine  fibres  massed  together  into  a  membranous  structure.  It 
extends  from  the  upper  (medial)  border  of  the  first  costal  cartilage  (and  rib), 

Fig.  284.^Posteeior  View  op  the   Stbrno-costo-claviculak  Joint. 


upward,  backward,  and  distinctly  laterally  to  the  costal  tuberosity  on  the  under 
surface  of  the  medial  extremity  of  the  clavicle,  to  which  it  is  attached  just  lateral 
to  the  lower  part  of  the  capsule.  Frequently  some  of  the  lateral  fibres  pass  up- 
ward and  medially  behind  the  rest,  and  give  the  appearance  of  decussating.  It 
is  from  half  to  three-quarters  of  an  inch  (1.5-2  cm.)  broad. 

The  articular  disc  (fig.  285)  is  a  flattened  disc  of  nearly  the  same  size  and 
outline  as  the  medial  articular  end  of  the  clavicle,  which  it  fairly  accurately 
fits.  It  is  attached  above  to  the  upper  border  of  the  posterior  edge  of  the  clavicle ; 
and  below  to  the  cartilage  of  the  first  rib  at  its  union  with  the  sternum,  where  it 
assists  in  forming  the  socket  for  the  clavicle.  At  its  circumference  it  is  connected 
with  the  articular  capsule,  and  this  connection  is  very  strong  behind,  and  still 
stronger  above,  where  it  is  blended  with  the  interclavicular  ligament. 

It  is  usually  thinnest  below,  where  it  is  connected  with  the  costal  cartilage.  It  varies  in 
thickness  in  different  parts,  sometimes  being  thinner  in  the  centre  than  at  the  circumference 
sometimes  the  reverse,  and  is  occasionally  perforated  in  the  centre.  It  divides  the  joint  into 
two  compartments. 

There  are  two  synovial  membranes  (fig.  285) ;  a  lateral  one,  which  is  reflected 
from  the  clavicle  and  capsule  over  the  lateral  aspect  of  the  disc  and  is  looser 
than  the  medial  one;  the  medial  is  reflected  from  the  sternum  over  the  medial 
side  of  the  articular  disc,  costal  cartilage,  and  capsule.  Occasionally  a  communi- 
cation takes  place  between  them. 

The  arterial  supply  is  derived  from  branches — (1)  from  the  internal  mammary;  (2)  from 
the  superior  thoracic  branch  of  the  axillary;  (3)  twigs  of  a  muscular  branch  often  arising  from 
the  subclavian  artery  pass  over  the  interclavicular  notch;  (4)  twigs  of  the  transverse  scapular 
(suprascapular)  artery. 

The  nerve-supply  is  derived  from  the  nerve  to  the  subclavius  and  sternal  descending  branch 
of  the  cervical  plexus. 


250 


THE  ARTICULATIONS 


Relations. — In  front  of  the  joint  is  the  sternal  head  of  the  sterno-mastoid.  Behind  it  are 
the  sterno-hyoid  and  sterno-thyreoid  muscles.  Still  further  back,  on  the  right  side,  are  the 
innominate  and  internal  mammary  arteries,  and,  on  the  left  side,  the  left  common  carotid,  the 
left  subclavian,  and  the  internal  mammary  arteries.  Above  and  behind,  between  the  sterno- 
mastoid  and  s terno-hyoid  muscles,  the  anterior  jugular  vein  passes  back  and  laterally  toward  the 
posterior  triangle. 

The  movements  permitted  at  this  joint  are  various  though  limited,  owing  to  the  capsular 
ligament  being  moderately  tense  in  every  position  of  the  clavicle.  Motion  takes  place  in 
nearly  every  direction — viz.,  upward,  downward,  forward,  backward,  and  in  a  circumductory 
manner.  The  upward  and  downward  motions  occur  between  the  clavicle  and  the  articular 
disc;  during  elevation  of  the  arm  the  upper  edge  of  the  clavicle  with  its  attached  articular  disc 
is  pressed  into  the  sternal  socket,  and  the  lower  edge  gUdes  away  from  the  disc;  during  depression 
of  the  limb,  the  lower  edge  of  the  clavicle  presses  on  to  the  disc,  while  the  rest  of  the  articular 
surface  of  the  clavicle  inclines  laterally,  bringing  with  it  to  a  slight  degree  the  upper  edge  of 
the  articular  disc.  These  movements  occur  on  an  antero-posterior  axis  drawn  through  the 
outer  compartment  of  the  joint.  The  forward  and  backward  motions  take  place  between  the 
articular  disc  and  sternum,  the  clavicle  with  the  disc  gUding  backward  upon  the  sternum  when 
the  shoulder  is  brought  forward,  and  forward  when  the  shoulder  is  forced  backward;  these 
movements  odcur  round  an  axis  drawn  nearly  vertically  through  the  sternal  socket. 

FiQ.  285. — Anterior  View  of  Stbrno-costo-clavicular  Joint,  with  Section 
SHOWING  Cavities  opened  on  the  Right  Side. 


Interclavicular  ligament 


Joint  between  ster- 
num and  second  cos- 
tal cartilage 


The  articular  disc  serves  materially  to  bind  the  bones  together,  and  to  prevent  the  media 
and  upward  displacements  of  the  clavicle.  It  also  forms  an  elastic  lauffer  which  tends  to  break 
shocks.  The  capsule,  by  being  moderately  tight,  tends  to  limit  movements  in  all  directions, 
while  the  interclavicular  ligament  is  a  safeguard  against  upward  displacement  during  depression 
of  the  arm.  Tlie  costo-clavicular  ligament  prevents  dislocation  upward  during  elevation  of  the 
arm,  and  resists  displacements  backward. 

Muscles  which  move  the  clavicle  at  the  sterno-clavicular  joint. — Elevators. — Trapezius, 
clavicular  part  of  sterno-mastoid,  levator  scapulae,  omo-hyoid,  rhomboids. 

Depressors. — Subclavius,  pectoraUs  minor,  lower  fibres  of  trapezius  and  serratus  anterior 
(magnus).     Depression  is  aided  by  the  weight  of  the  upper  extremity. 

Protractors. — PectoraUs  major  and  minor.     Serratus  anterior  (magnus). 
-Latissimus  dorsi,  trapezius. 


2.  THE  SCAPULO-CLAVICULAR  UNION 

The  scapula  is  connected  with  the  clavicle  by  a  synovial  joint  with  its  liga- 
ments at  the  acromio-clavicular  articulation;  and  also  by  a  set  of  ligaments  pass- 
ing between  the  coracoid  process  and  the  clavicle.     So  that  we  have  to  consider — 

(a)  The  acromio-clavicular  articulation. 
lb)  The  cor aco -clavicular  ligaments. 

(c)  The  proper  scapular  ligaments  are  also  best  described  in  this  section — 
viz.,  the  coraco-acromial  and  transverse. 


COROCO-CLAVICULAR  UNION  251 

(a)  The  Acromio-claviculae  Joint 
Class. — Diarthrosis.         Subdivision. — Arthrodia. 

The  acromio-clavicular  joint  is  surrounded  by  an  articular  capsule  and  fre- 
quently contains  an  articular  disc. 

The  articular  capsule  (figs.  287  and  290)  completely  surrounds  the  articular 
margins,  and  is  composed  of  strong,  coarse  fibres  arranged  in  parallel  fasciculi, 
of  fairly  uniform  thickness,  which  are  attached  to  the  borders  as  well  as  the 
surfaces  of  the  bones.  It  is  somewhat  lax  in  all  positions  of  the  joint,  so  that  the 
clavicle  is  not  tightly  braced  to  the  acromion.  The  fibres  extend  three-quarters 
of  an  inch  (2  cm.)  along  the  clavicle  posteriorly,  but  only  a  quarter  of  an  inch 
(6  mm.)  anteriorly.  Superiorly,  they  are  attached  to  an  oblique  line  joining 
these  two  points,  while  inferiorly  they  reach  to  the  ridge  for  the  trapezoid  liga- 
ment with  which  they  blend. 

At  the  acromion  they  extend  half  way  across  the  upper  and  lower  surfaces,  but  at  the 
anterior  and  posterior  limits  of  the  joint  they  are  attached  close  to  the  articular  facet.  The 
anterior  fibres  become  blended  with  the  insertion  of  the  eoraco-acromial  ligament.  The 
fibres  are  strengthened  above  by  the  aponeuroses  of  the  trapezius  and  deltoid  muscles;  and  all 
run  from  the  acromion  to  the  clavicle  medially  and  backward. 

The  articular  disc  is  occasionally  present,  but  is  usually  imperfect,  only  oc- 
cupying the  upper  part  of  the  joint;  it  may  completely  divide  the  joint  into  two 
cavities,  or  be  perforated  in  the  centre.  It  is  usually  thicker  at  the  edge  than 
in  the  centre,  and  some  of  the  fibres  of  the  articular  capsule  are  blended  with  its 
edges. 

The  synovial  membrane  lining  the  joint  is  occasionally  either  partially  or 
entirely  divided  into  two  by  the  articular  disc. 

Relations. — Superiorly  skin  and  fascia  and  the  tendinous  intersection  between  the  deltoid 
and  the  trapezius.  Inferiorly,  the  eoraco-acromial  ligament  and  supraspinatus.  Anteriorly, 
part  of  the  origin  of  the  deltoid.     Posteriorly,  part  of  the  insertion  of  the  trapezius. 

Movements. — A  certain  amount  of  gliding  movement  occurs  at  this  joint,  but  the  most 
important  movement  is  a  rotation  of  the  scapula  whereby  the  glenoid  cavity  is  turned  forward 
and  upward,  or  downward.  As  these  movements  occur  the  inferior  angle  of  the  scapula  moves 
forward  as  the  glenoid  cavity  turns  upward  and  the  superior  angle  recedes. 

The  forward  movement  of  the  inferior  angle  is  produced  mainly  by  the  inferior  fibres  of 
the  serratus  anterior  (magnus),  aided  by  the  inferior  fibres  of  the  trapezius,  and  it  is  by  this 
movement  that  the  arm  is  raised  above  the  level  of  the  shoulder  forward. 

The  reverse  movement  is  produced  mainly  by  the  rhomboideus  major  aided  by  the  latissimus 
dorsi. 

(6)  The  Coraco-clavicular  Union 

The  coraco-clavicular  ligament  (figs.  286,  287,  and  290)  consists  of  two  parts, 
the  conoid  and  the  trapezoid  ligaments. 

The  conoid  ligament  is  the  medial  and  posterior  portion,  and  passes  upward 
and  laterally  from  the  coracoid  process  to  the  clavicle. 

It  is  a  very  strong  and  coarsely  fasciculated  band  of  triangular  shape,  the  apex  being 
fixed  to  the  medial  and  posterior  edge  of  the  root  of  the  coracoid  process  just  in  front  of  the 
scapular  notch,  some  fibres  joining  the  transverse  ligament.  Its  base  is  at  the  clavicle,  where 
it  widens  out,  to  be  attached  to  the  posterior  edge  of  the  inferior  surface,  as  well  as  to  the  cora- 
coid tubercle.  It  is  easily  separated  from  the  trapezoid,  without  being  absolutely  distinct.  A 
small  bursa  often  exists  between  it  and  the  coracoid  process;  medially,  some  of  the  fibres  of  the 
subclavius  muscle  are  often  attached  to  it. 

The  trapezoid  ligament  is  the  anterior  and  lateral  portion  of  the  coraco- 
clavicular  ligament.  It  is  a  strong,  flat,  quadrilateral  plane  of  closely  woven 
fibres,  the  surfaces  of  which  look  upward  and  medially  toward  the  clavicle,  and 
downward  and  laterally  over  the  upper  surface  of  the  coracoid  process. 

At  the  coracoid  it  is  attached  for  about  an  inch  (2.5  cm.)  to  a  rough  ridge  which  runs 
forward  from  the  angle,  along  the  anterior  border  of  the  process.  At  the  clavicle  it  is  attached 
to  the  oblique  ridge  which  runs  laterally  and  forward  from  the  coracoid  tubercle,  reaching  as 
far  as,  and  blending  with  the  inferior  part  of  the  acromio-clavicular  ligament.  Its  anterior 
edge  is  free,  and  overlies  the  eoraco-acromial  Ugament;  the  posterior  edge  is  shorter  than  the 
anterior,  and  is  in  contact  with  the  posterior  and  lateral  portion  of  the  conoid  hgament. 

The  arterial  supply  is  derived  from  the  transverse  scapular  (suprascapular),  acromial 
branches  of  the  thoraco-acromial,  and  the  anterior  circumflex. 

The  nerve-supply  is  derived  from  the  suprascapular  and  axillary  (circumflex)  nerves. 


252 


THE  ARTICULATIONS 


Movements. — In  the  movements  of  the  shoulder  girdle,  the  scapula  moves  upon  the  lateral 
end  of  the  clavicle,  and  the  clavicle,  in  turn,  carried  by  the  uniting  Ugaments,  moves  upon  the 
sternum;  so  that  the  entire  scapula  moves  in  the  arc  of  a  circle  whose  centre  is  at  the  sterno- 
clavicular joint,  and  whose  radius  is  the  clavicle.  The  scapula,  in  moving  upon  the  clavicle, 
also  moves  upon  the  thorax  forward  and  backward,  upward  and  downward,  and  also  in  a  rota^ 
tory  direction  upon  an  axis  drawn  at  right  angles  to  the  centre  of  the  bone.  Throughout  these 
movements  the  inferior  angle  and  base  of  the  scapula  are  kept  in  contact  with  the  ribs  by  the 

Fig.  286.— Anterior  View  op  Shoulder,  showing  also  Coraco-clavicular  and 
cohaco-acromial  ligaments. 

Conoid  ligament 
Superior  transverse  scapular  ligament  t 


Coraco-acromial  ligament 


> 


Short  head  of  biceps 
'Subscapular  tendon 


Capsule  of  shoulde 


Long  tendon  of  biceps 


latissimus  dorsi,  which  straps  down  the  former,  and  the  rhomboids  and  serratus  anterior  {magnus), 
which  brace  down  the  latter.  The  glenoid  cavity  could  not  have  preserved  its  obUquely 
forward  direction  had  there  been  no  acromio-clavicular  joint,  but  would  have  shifted  round  a 
vertical  axis,  and  thus  the  shoulder  would  have  pointed  medialward  when  the  scapula  was 
advanced,  and  lateralward  when  it  was  drawn  backward.  By  means  of  the  acromio-clavicular 
joint,  the  scapula  can  be  forcibly  advanced  upon  the  thorax,  the  glenoid  cavity  all  the  time 
keeping  its  face  duly  forward.  Thus  the  muscles  of  the  shoulder  and  forearm  can  be  with 
advantage  combined,  as,  for  example,  in  giving  a  direct  blow.  The  acromio-clavicular  joint 
also  permits  the  lower  angle  of  the  scapula  to  be  retained  in  contact  with  the  chest  wall  during 
the  rising  and  faUing  of  the  shoulder,  the  scapula  turning  in  a  hinge-like  manner  round  the 
horizontal  axis  of  the  joint. 

There  are  no  actions  in  which  the  scapula  moves  on  a  fixed  clavicle,  or  the  clavicle  ona 
fixed  scapula;  the  two  bones,  bound  together  by  their  connecting  ligament,  must  move  in 
unison. 

(c)  The  Phoper  Scapular  Ligaments 

There  are  three  proper  ligaments  of  the  scapula,  which  pass 
portions  of  the  bone,  viz. — 

Coraco-acromial.  Superior  transverse. 

Inferior  transverse. 

The  coraco-acromial  ligament  (figs.  286  and  290)  is  a  flat,  triangular  band 
with  a  broad  base,  attached  to  the  lateral  border  of  the  coracoid  process,  and  a 
blunt  apex  which  is  fixed  to  the  tip  of  the  acromion.  It  is  made  up  of  two  broad 
marginal  bands,  and  a  smaller  and  thinner  intervening  portion.  The  anterior 
band,  which  arises  from  the  anterior  portion  of  the  coracoid  process,  is  the 
stronger,  and  some  of  its  marginal  fibres  can  often  be  traced  into  the  short  head 
of  the  biceps,  which  can  then  make  tense  this  edge  of  the  ligament.  The  pos- 
terior band,  coming  from  the  posterior  part  of  the  coracoid  process,  is  also  strong. 


between  different 


THE  SHOULDER-JOINT 


253 


The  intermediate  part,  of  variable  extent,  is  thin  and  membranous,  containing 
but  few  ligamentous  fibres;  it  is  often  incomplete  near  the  coracoid  process, 
leaving  a  small  gap  (fig.  286). 

The  superior  surface  of  the  ligament  looks  upward  and  a  little  forward,  and  is  covered  by 
the  deltoid  muscle;  the  inferior  looks  downward  and  a  little  backward,  and  is  separated  from 
the  capsule  of  the  shoulder-joint  by  a  bursa  and  the  tendons  of  the  supraspinatus  and  sub- 
scapularis  muscles.  At  the  coracoid  process  it  overlies  the  coraco-humeral  ligament.  It  is 
barely  one-third  of  an  inch  (8  mm.)  above  the  capsule  of  the  shoulder,  and  in  the  undissected 
state  there  is  scarcely  a  quarter  of  an  inch  (6  mm.)  interval.  The  anterior  band  projects  over 
the  centre  of  the  head  of  the  humerus,  and  is  continued  into  a  tough  fascia  under  the  deltoid; 
the  posterior  band  is  continuous  with  the  fascia  over  the  supraspinatus  muscle.     It  binds  the 

Fig.  287. — Posterior  View  of   the   Shoulder-joint,    showing   also   the    Acromio-ola- 
vicuLAR  Joint  and  the  Special  Ligaments  or  the  Scapula. 
Superior  transverse  ligament 


Conoid  ligament 

Acromio-clavicular 
ligament 


Tendon  of   infra 
spinatus    and 
teres  minor 
Inferior  transverse 
ligament 

Capsule  of  shoulder 


two  processes  firmly  together,  and  so  strengthens  each;  it  holds  the  deltoid  off  the  capsule  of 
the  shoulder,  and  protects  the  joint  from  slight  injuries  directed  downward  and  backward 
against  it. 

The  superior  transverse  (coracoid,  or  suprascapular)  ligament  (figs.  286, 
287,  and  288)  is  a  small  triangular  band  of  fibrous  tissue,  the  surfaces  of  which 
look  forward  and  backward;  and  its  edges,  which  are  thin  and  sharp,  are  turned 
upward  and  downward.  It  continues  the  superior  border  of  the  scapula,  bridging 
over  the  scapular  notch. 

It  is  broader  medially,  where  it  springs  from  the  upper  border  of  the  scapula  on  its  dorsal 
surface;  and  narrow  laterally,  where  it  is  attached  to  the  base  of  the  coracoid  process;  some  of 
its  fibres  are  inserted  under  the  edge  of  the  trapezoid  ligament,  and  others  pass  upward  with 
the  conoid  to  reach  the  clavicle.  The  transverse  scapular  {suprascapular)  artery  passes  over  it, 
and  the  suprascapular  nerve  beneath  it.  Medially,  some  fibres  of  the  omo-hyoid  muscle  arise 
from  it. 

The  inferior  transverse  (spino-glenoid)  ligament  (fig.  287)  reaches  from  the  lateral 
border  of  the  spine  of  the  scapula  to  the  margin  of  the  glenoid  cavity,  and  so  forms  a  foramen 
under  which  the  transverse  scapular  (suprascapular)  vessels  and  suprascapular  nerve  gain  the 
infraspinous  fossa.  It  is  usually  a  weak  membranous  structure  with  but  few  ligamentous 
fibres. 


3.  THE  SHOULDER-JOINT 
Class. — Diarthrosis.  Subdivision. — Enarthrodia. 

The  shoulder  [articulatio  humeri]  is  one  of  the  most  perfect  and  most  movable 


254 


THE  ARTICULATIONS 


of  joints,  the  large  upper  end  of  the  humerus  playing  upon  the  shallow  glenoid 
cavity.  Like  the  hip,  it  is  a  ball-and-socket  joint.  It  is  retained  in  position 
much  less  by  ligaments  than  by  muscles,  and,  owing  to  the  looseness  of  its  cap- 
sule, as  well  as  to  all  the  other  conditions  of  its  construction  and  position,  it  is 
exceedingly  liable  to  be  displaced;  on  the  other  hand,  it  is  sheltered  from  violence 
by  the  two  projecting  processes — the  acromion  and  coracoid. 
The  ligaments  of  the  shoulder-joint  are: — - 


Articular  capsule. 
Gleno-humeral. 


Coraco-humeral. 
Glenoid: 


The  articular  capsule  (figs.  286,  287,  and  288)  is  a  loose  sac,  insufficient  in 
itself  to  maintain  the  bones  in  contact.  It  consists  of  fairly  distinct  but  not 
coarse  fibres,  closely  woven  together,  and  directed,  some  straight,  others  ob- 
liquely, between  the  two  bones,  a  few  circular  ones  being  interwoven  amongst 
them.     At  the  scapula,  it  is  fixed  on  the  dorsal  aspect  to  the  prominent  rough 

Fig.  288. — Vertical  Section  through  the  Shoulder-joint  to  show  the  Gleno-humeral 

Ligament. 
(The  joint  is  opened  from  behind.) 


Supraspinatus  muscle 

Subacromial  bursa 

Tendon  of  biceps  with 

gleno-humeral  liga- 


Articular  capsule 


Superior  trans- 
verse ligament 


Glenoid  ligament  (lip) 
Articular  capsule 

surface  around  the  margin  of  the  glenoid  cavity,  reaching  as  far  as  the  neck  of 
the  bone.  Superiorly,  it  is  attached  to  the  root  of  the  coracoid  process;  an- 
teriorly, to  the  ventral  surface,  at  a  variable  distance  from  the  articular  margin, 
often  reaching  half  an  inch  (12  mm.)  upon  the  neck  of  the  bone,  and  thus  allow- 
ing the  formation  of  a  pouch;  it  may  not,  however,  extend  for  more  than  a 
quarter  of  an  inch  (6  mm.)  beyond  the  articular  margin;  inferiorly,  it  blends  with 
the  origin  of  the  long  head  of  the  triceps.  At  the  humerus,  the  superior  half  is 
fixed  to  the  anatomical  neck,  sending  a  prolongation  downward  between  the  two 
tuberosities  which  attenuates  as  it  descends,  and  covers  the  transverse  hmneral 
ligament.  The  lower  half  of  the  capsule  descends  upon  the  hmnerus  further 
from  the  articular  margin,  some  of  the  deeper  fibres  being  reflected  upward  so 
as  to  be  attached  close  to  the  articular  edge,  thus  forming  a  kind  of  fibrous  in- 
vestment for  the  neck  of  the  humerus.  This  ligament  is  more  uniform  in  thickness 
than  that  of  the  hip. 

Gleno-humeral  bands  of  the  capsule  (figs.  288  and  289) . — There  are  three 
accessory  bands,  known  as  the  superior,  middle  and  inferior  gleno-humeral  bands, 
which  project  toward  the  interior  of  the  joint  from  the  fore  part  of  the  capsule 
and  are  consequently  best  seen  when  the  joint  is  opened  from  behind. 

The  middle  band  reaches  from  the  anterior  margin  of  the  glenoid  cavity  along  the  lower 
border  of  the  subscapularis  tendon  to  the  lower  border  of  the  lesser  tuberosity,  and  the  inferior 
band  from  the  inferior  part  of  the  glenoid  cavity  to  the  inferior  part  of  the  neck  of  the  humerus. 


THE  SHOULDER-JOINT  255 

The  superior  band,  known  also  as  the  gleno -humeral  ligament,  runs  from  the  edge  of  the  glenoid 
cavity  at  the  root  of  the  coracoid  process,  just  medial  to  the  origin  of  the  long  tendon  of  the 
biceps,  and,  passing  laterally  and  downward  at  an  acute  angle  to  the  tendon,  for  which  it  forms 
a  slight  groove  or  sulcus,  is  fixed  to  a  depression,  the  fovea  capitis  humeri,  above  the  lesser 
tuberosity  of  the  humerus.  It  is  a  thin,  ribbon-hke  band,  of  which  the  superior  surface  is 
attached  to  the  capsule,  while  the  inferior  is  free  and  turned  toward  the  joint.  In  the  foetus 
it  is  often,  and  in  the  adult  occasionally,  quite  free  from  the  capsule,  and  may  be  as  thick  as 
the  long  tendon  of  the  biceps  (fig.  289). 

The  tendons  of  the  supra-  and  infraspinatus,  teres  minor,  and  subscapularis  muscles 
strengthen  and  support  the  capsule,  especially  near  their  points  of  insertion,  and  can  be  with 
difficulty  dissected  off  from  it.  The  long  head  of  the  triceps  supports  and  strengthens  the 
capsule  below.  The  capsule  also  receives  an  upward  sUp  from  the  pectoralis  major.  The 
supraspinatus  often  sends  a  shp  into  the  capsule  from  its  upper  edge  (fig.  288). 

The  coraco-humeral  ligament  (fig.  290)  is  a  strong  broad  band,  which  is 
attached  above  to  the  lateral  edge  of  the  root  and  horizontal  limb  of  the  coracoid 
process  nearly  as  far  as  the  tip.  From  this  origin  it  is  directed  backward  along 
the  line  of  the  biceps  tendon  to  blend  with  the  capsule,  and  is  inserted  into 
the  greater  tuberosity  of  the  humerus. 

Seen  from  the  back,  it  looks  like  an  uninterrupted  continuation  of  the  capsule,  while  from 
the  front  it  looks  like  a  fan-shaped  prolongation  from  it  overlying  the  rest  of  the  ligament.  At 
its  origin  there  is  sometimes  a  bursa  between  it  and  the  capsule. 

The  glenoid  ligament  or  lip  [labrum  glenoidale]  (figs.  288  and  292)  is  a  narrow 
rim  of  dense  fibro-cartilage,  which  surrounds  the  edge  of  the  glenoid  socket  and 
deepens  it.  It  is  about  a  quarter  of  an  inch  (6  mm.)  wide  above  and  below,  but 
less  at  its  sides.     Its  peripheral  edge  is  inseparably  welded,  near  the  bone,  with 

Fig.  289. — Fcbtal  Shoulder-joint,  showing  the  Glbno-humeeal  Ligament,  and  also  the 
Short  Head  op  the  Biceps,  being  continuous  wtith  the  Coraco-acromial  Ligament. 


Short   tendon   of   biceps   running 


-Long  tendon  of  biceps 
nto'anterior  ba'nd'of  coraco-       |                        "     iiiBS//^''\i\\\\)/  H/'^ — Gleno-humeral  ligament 
acromial  Ugament  I    ,  |,«!#^^  ILlUW^Iil^ Capsule  of  shoulder,  turned  back 


the  articular  capsule.  Its  structure  is  almost  entirely  fibrous,  with  but  few 
cartilage  cells  intermixed.  At  the  upper  part  of  the  fossa  the  biceps  tendon  is 
prolonged  into  the  glenoid  ligament,  the  tendon  usually  dividing  and  sending 
fibres  right  and  left  into  the  ligament,  which  may  wind  round  nearly  the  whole 
circumference  of  the  socket.  It  may,  however,  send  fibres  into  one  side  only, 
usually  into  the  lateral. 

The  articular  cartilage  covering  the  glenoid  fossa  is  thicker  at  the  circumfer- 
ence than  in  the  centre,  thus  tending  to  deepen  the  cavity.  It  is  usually  thickest 
at  the  lower  part  of  the  fossa;  over  the  head  of  the  humerus  the  cartilage  is  thickest 
at  and  below  the  centre. 

The  synovial  membrane  lines  the  glenoid  ligament,  and  is  then  refiected  over 
the  capsule  as  far  as  its  attachment  to  the  humerus,  from  which  it  ascends  as 
far  as  the  edge  of  the  articular  cartilage.  The  tendon  of  the  biceps  receives  a 
long  tubular  sheath,  which  is  continuous  with  the  synovial  membrane,  both  at 
its  attached  extremity  and  at  the  bicipital  groove,  but  is  free  in  the  rest  of  its 
extent.  The  synovial  cavity  almost  always  communicates  with  the  bursa  under 
the  subscapularis,  and  sometimes  with  one  under  the  infraspinatus  muscle. 

It  also  sends  a  pouch-like  prolongation  beneath  the  coracoid  process  when  the  fibrous 
capsule  is  attached  wide  of  the  margin  of  the  glenoid  fossa.  A  few  fringes  are  seen  near  the 
edge  of  the  glenoid  cavity,  and  there  is  often  one  which  runs  down  the  medial  edge  of  the 
biceps  tendon,  extending  slightly  below  it  and  making  a  slight  groove  for  the  tendon  to   lie  in. 


256 


THE  ARTICULATIONS 


The  transverse  humeral  Ugament  (fig.  290)  is  so  closely  connected  with  the 
capsule  of  the  shoulder  that,  although  it  is  a  proper  hgament  of  the  humerus,  it 
may  well  be  described  here.     It  is  a  strong  band  of  fibrous  tissue,  which  extends 

Fig.  290. — Lateral  View  of  the  Shoulder-joint,   showing  the  Coraco-humbral  and 
Transverse  Humeral  Ligaments. 


Capsule  of  the  acromio-cla- 

vicular  joint 
Coraco-acromial  ligament 

Coraco-humeral  ligament 


-Transverse  humeral  ligament 


Tendon  of  biceps 


Fig.  291. — The  Upper  Extremity  or  the  Humerus,  Anterior  View,  to  Show  the  Rela- 
tion OF  THE  Articular  Capsule  of  the  Shoulder-joint  (in  red)   to  the  Epiphysial  Line. 


between  the  two  tuberosities,  roofing  in  the  intertubercular  (bicipital)  groove.  It 
is  covered  by  a  thin  expansion  of  the  capsule.  It  is  limited  to  the  portion  of  the 
bone  above  the  line  of  the  epiphysis. 


THE  SHOULDER-JOINT 


257 


Relations. — -The  following  muscles  are  in  contact  with  the  capsule  of  the  shoulder-joint. 
In  front,  the  subscapularis;  above,  the  supraspinatus;  above  and  behind,  the  infraspinatus; 
behind,  the  teres  minor;  below,  the  long  head  of  the  triceps  and  the  teres  major.  In  the  interval 
between  the  subscapularis  and  the  supraspinatus  the  subacromial  bursa  is  close  to  the  capsule 
and  occasionally  its  cavity  communicates  with  the  cavity  of  the  joint. 

The  axillary  (circumflex)  nerve  and  posterior  circumfle.x  artery  pass  beneath  the  capsule 
in  the  intei'val  between  the  long  head  of  the  triceps,  the  humerus,  and  the  teres  major.     When 
the  arm  is  abducted,  the  long  head  of  the  triceps  and  the  teres  major  are  drawn  into  closer  rela-  , 
tion  with  the  capsule  and  help  to  prevent  dislocation  of  the  humerus. 

The  axillary  vessels,  the  great  nerves  of  the  axilla,  the  short  head  of  the  biceps,  and  the 
coraco-brachialis  are  separated  from  the  joint  by  the  subscapularis,  whilst  the  deltoid  forms  a 
kind  of  cap,  which  extends  from  the  front  to  the  back  over  the  more  immediate  relations. 

The  arterial  supply  is  derived  from  the  transverse  scapular  (suprascapular),  anterior  and 
posterior  circumflex,  subscapular,  circumflex  scapular  (dorsalis  scapulae),  and  a  branch  from  the 
second  portion  of  the  axiUary  artery. 

The  nerve-supply  is  derived  from  the  suprascapular,  by  branches  in  both  fossse;  and  from 
the  axillary  (circumflex)  and  subscapular  nerves. 

The  movements  of  the  shoulder-joint  consist  of  flexion,  extension,  adduction,  abduction, 
rotation  and  circumduction. 

Flexion  is  the  swinging  forward,  extension  the  swinging  backward,  of  the  humerus;  abduc- 
tion is  the  raising  of  the  arm  from,  and  adduction  depression  of  the  arm  to,  the  side.  In  flexion 
and  extension  the  head  of  the  humerus  moves  upon  the  centre  of  the  glenoid  fossa  round  an 


Fig.  292. — Biceps  Tendon,  Bifukcating  and  Blending  on  each  Side  with  the  Glenoid 

Ligament. 


Tendon  of  biceps- 


Tendon  of  biceps  blended  with  glenoid, 
ligament 


oblique  line  corresponding  to  the  axis  of  the  head  and  neck  of  the  humerus,  flexion  being  more 
free  than  extension,  and  in  extreme  flexion  the  scapula  follows  the  head  of  the  humerus,  so  as 
to  keep  the  articular  surfaces  in  apposition.  In  extension  the  scapula  moves  much  less,  if 
at  all. 

In  abduction  and  adduction  the  scapula  is  fixed,  and  the  humerus  roUs  up  and  down  upon 
the  glenoid  fossa;  during  abduction  the  head  descends  until  it  projects  beyond  the  lower  edge 
of  the  glenoid  cavity,  and  the  greater  tuberosity  impinges  against  the  arch  of  the  acromion; 
during  adduction,  the  head  of  the  humerus  ascends  in  its  socket,  the  arm  at  length  reaches  the 
side,  and  the  capsule  is  completely  relaxed. 

In  circumduction,  the  humerus,  by  passing  quickly  through  these  movements,  describes 
a  cone,  whose  apex  is  at  the  shoulder-joint,  and  the  base  at  the  distal  extremity  of  the  bone 
or  hmb. 

Rotation  takes  place  round  a  vertical  axis  drawn  through  the  extremities  of  the  humerus 
from  the  centre  of  the  head  to  the  inner  condyle;  in  rotation  forward  (that  is,  medialward)  the 
head  of  the  bone  rolls  back  in  the  socket  as  the  great  tuberosity  and  shaft  are  turned  forward; 
in  rotation  backward  (that  is,  lateral  ward)  the  head  of  the  bone  glides  forward,  and  the  tuber- 
osity and  shaft  of  the  humerus  are  turned  backward,  i.  e.,  lateralward. 

Great  freedom  of  movement  is  permitted  at  the  shoulder,  and  this  is  increased  by  the 
mobility  of  the  scapula.  Restraint  is  scarcely  exercised  at  all  upon  the  movements  of  the 
shoulder  by  the  ligaments,  but  chiefly  by  the  muscles  of  the  joint. 

In  abduction,  the  lower  part  of  the  capsule  is  somewhat,  and  in  extreme  abduction  con- 
siderably, tightened;  and  in  rotation  medialward  and  lateralward,  the  upper  part  of  the  capsule 
is  made  tense,  as  is  also,  in  the  latter  movement,  the  coraco-humeral  ligament. 

The  movements  of  abduction  and  extension  have  a  most  decided  and  definite  resistance 
offered  to  them  other  than  by  muscles  and  ligaments,  for  the  greater  tuberosity  of  the  humerus, 
by  striking  against  the  acromion  process  and  coraco-acromial  ligament,  stops  short  any  further 
advance  of  the  bone  in  these  directions,  and  thus  abduction  ceases  altogether  as  soon  as  the  arm 


258  THE  ARTICULATIONS 

is  raised  to  a  right  angle  with  the  trunk,  and  extension  shortly  after  the  humerus  passes  the  Hne 
of  the  trunk. 

Further  elevation  of  the  arm  beyond  the  right  angle,  in  the  abducted  or  extended  position, 
is  effected  by  the  rotation  of  the  scapula  round  its  own  axis  by  the  action  of  the  trapezius  and 
serratus  anterior  muscles  upon  the  sterno-clavioular  and  acromio-clavicular  joints  respectively. 

The  acromion  and  coracoid  process,  together  with  the  coraco-acromial  ligament,  form  an 
arch,  which  is  separated  by  a  bursa  and  the  tendon  of  the  supraspinatus  from  the  capsule  of 
the  shoulder.  Beneath  this  arch  the  movements  of  the  joint  take  place,  and  against  it  the  head 
and  tuberosities  are  pressed  when  the  weight  of  the  trunk  is  supported  by  the  arms;  the  greater 
tuberosity  and  the  upper  part  of  the  shaft  impinge  upon  it  when  abduction  and  extension  are 
carried  to  their  fullest  extent. 

No  description  of  the  shoulder-joint  would  be  complete  without  a  short  notice  of  the  peculiar 
relation  which  the  biceps  tendon  bears  to  the  joint.  It  passes  over  the  head  of  the  humerus  a 
little  to  the  medial  side  of  its  summit,  and  lies  free  within  the  capsule,  surrounded  only  by  a 
tubular  process  of  synovial  membrane.  It  is  fiat,  with  the  surfaces  looking  upward  and  down- 
ward, until  it  reaches  the  intertubercular  (bicipital)  groove,  when  it  assumes  a  rounded  form. 
It  strengthens  the  articulation  along  the  same  course  as  the  coraco-humeral  hgament,  and  tends 
to  prevent  the  head  of  the  humerus  from  being  pulled  upward  too'.forcibly  against  the  inferior 
surface  of  the  acromion.  It  also  serves  the  purpose  of  a  ligament  by  steadying  the  head  of  the 
humerus  in  various  movements  of  the  arm  and  forearm,  and  to  this  end  is  let  into  a  groove  at 
the  upper  end  of  the  bone,  from  which  it  cannot  escape  on  account  of  the  abutting  tuberosities 
and  the  strong  transverse  humeral  ligament  which  binds  it  down.  Further,  it  acts  Uke  the  four 
shoulder  muscles  which  pass  over  the  capsule,  to  keep  the  head  of  the  humerus  against  the  glen- 
oid socket;  and,  moreover,  it  resists  the  tendency  of  the  pecloralis  major  and  latissimus  dorsi 
muscles,  in  certain  actions  when  the  arm  is  away  from  the  side  of  the  body,  to  pull  the  head  of 
the  humerus  below  the  lower  edge  of  the  cavity. 

Muscles  which  act  upon  the  shoulder-joint.- — Flexors  or  protractors. — Deltoid  (anterior 
fibres),  peotoralis  major  (clavicular  fibres),  coraco-brachiahs,  biceps  (short  head),Eubscapularis 
(upper  fibres). 

Extensors  or  retractors. — ^Latissimus  dorsi,  deltoid  (posterior  fibres),  teres  major,  teres  minor, 
infraspinatus  (lower  fibres). 

[Abductors. — Deltoid,  supraspinatus,  biceps  (longhead). 

Adductors. — Pectorahs  major,  latissimus  dorsi,  subscapularis,  infraspinatus,  teres  major, 
teres  minor,  coraco-brachiahs,  biceps  (short  head),  triceps  (lower  head). 

Medial  rotators. — Pectoralis  major,  latissimus  dorsi,  teres  major,  subscapularis,  deltoid 
(anterior  fibres). 

Lateral  rotators. — Deltoid  (posterior  fibres),  infraspinatus,  teres  minor. 

Circumductors. — The  above  groups  acting  consecutively. 

4.  THE  ELBOW-JOINT 
Class. — Diarthrosis.  Subdivision. — Ginglymus. 

The  elbow  [articulatio  cubiti]  is  a  complete  hinge,  and,  unlike  the  knee, 
depends  for  its  security  and  strength  upon  the  configuration  of  its  bones  rather 
than  on  the  number,  strength,  or  arrangement  of  its  ligaments.  The  bones 
composing  it  are  the  lower  end  of  the  humerus  above,  and  the  upper  ends  of  the 
radius  and  ulna  below;  the  articular  surface  of  the  humerus  being  received 
partly  within  the  semilunar  notch  (great  sigmoid  cavity)  of  the  ulna,  and  partly 
upon  the  cup-shaped  area  (fovea)  of  the  radial  head.  The  ligaments  form  one 
large  and  capacious  capsule  [capsula  articularis],  which,  by  blending  with  the 
annular  ligament,  and  then  passing  on  to  be  attached  to  the  neck  of  the  radius, 
embraces  the  elbow  and  the  superior  radio-ulnar  joints,  uniting  them  into  one. 
Laterally,  it  is  considerably  strengthened  by  superadded  fibres  arising  from  the 
epicondyles  of  the  humerus  and  inseparably  connected  with  the  capsule.  For 
convenience  of  description  it  will  be  spoken  of  as  consisting  of  four  portions:- — 

Anterior.  Medial. 

Posterior.  Lateral. 

The  anterior  portion  (fig.  293)  is  attached  to  the  front  of  the  humerus  above 
the  articular  surface  and  coronoid  fossa,  in  an  inverted  V-shaped  manner,  to  two 
very  faintly  marked  ridges  which  start  from  the  front  of  the  medial  and  lateral 
epicondyles,  and  meet  a  variable  distance  above  the  coronoid  fossa.  Below,  it  is 
fixed,  just  beyond  the  articular  margin,  to  the  front  of  the  coronoid  process  and  it 
is  intimately  blended  with  the  front  of  the  annular  ligament,  a  few  fibres  passing 
on  to  the  neck  of  the  radius. 

It  varies  in  strength  and  thickness,  being  sometimes  so  thin  as  barely  to  cover  the  syriovial 
membrane;  at  others,  thick  and  strong,  and  formed  of  coarse  decussating  fibres,  the  majority 
of  which  descend  from  the  medial  side  laterally  to  the  radius. 


THE  ELBOW-JOINT 


259 


The  posterior  portion  (fig.  294),  thin  and  membranous,  is  attached  superiorly 
to  the  humerus,  in  much  the  same  inverted  V-shaped  way  as  the  anterior;  ascend- 
ing from  the  medial  epicondyle,  along  the  medial  side  of  the  olecranon  fossa 
nearly  to  the  top;  then,  crossing  the  bottom  of  the  fossa, it  descends  on  the  lateral 
side,  skirting  the  lateral  margin  of  the  trochlear  surface,  and  turns  laterally  along 
the  posterior  edge  of  the  capitulum.     Inferiorly,  it  is  attached  to  a  slight  groove 

Fig.  293. — Medial  View  of  the  Elbow-joint. 


Anterior  ligament 


Ulnar  collateral- 
ligament 


Annular  ligament 
—  Tendon  ot  biceps 

Oblique  ligament 

Upper  edge  of  in- 
terosseous mem- 
brane 


along  the  superior  and  lateral  surfaces  of  the  olecranon,  and  the  rough  surface  of 
the  ulna  just  beyond  the  radial  notch,  and  to  the  annular  ligament,  a  few  fibres 
passing  on  to  the  neck  of  the  radius. 

It  is  composed  of  decussating  fibres,  most  of  which  pass  vertically  or  obliquely  downward,  a 
few  taking  a  transverse  course  at  the  summit  of  the  olecranon  fossa  where  the  ligament  is  usually 
thinnest. 

Fig.  294. — Lateral  View  of  the  Elbow-joint. 


Annular  ligament 


■Radial  collateral  ligment 


■Posterior  ligament 


The  medial  portion,  the  ubiar  collateral  ligament  (fig.  293),  is  thicker,  stronger, 
and  denser  than  either  the  anterior  or  posterior  portions.  It  is  triangular  in 
form,  its  apex  being  attached  to  the  anterior  and  under  aspect  of  the  medial 
epicondyle,  and  to  the  condyloid  edge  of  the  groove  between  the  trochlea  and  the 
condyle.  The  fibres  radiate  downward  from  this  attachment,  the  anterior 
passing  forward  to  be  fixed  to  the  rough  overhanging  medial  edge  of  the  coronoid 


260 


THE  ARTICULATIONS 


process ;  the  middle  descend  less  obliquely  to  a  ridge  running  between  the  coronoid 
and  olecranon  processes,  while  the  posterior  pass  obliquely  backward  to  the 
medial  edge  of  the  olecranon  just  beyond  the  articular  margin. 

Fig.  295. — Lower  Extremity  of  the  Humerus,  to  show  the  Relation  of  the  Articu- 
lar Capsule  of  the  Elbow-joint  (in  red)  to  the  Epiphysial  Lines. 


Fig.  296. — The  Upper  Extremity  of  the  Ulna,  to  show  the  Relation  of  the  Articu- 
lar Capsule  of  the  Elbow-joint  (in  red)  to  the  Epiphysial  Lines. 


An  oblique  band  (the  oblique  ligament  of  Sir  Astley  Cooper)  connects  the  margin  of  the 
olecranon  process  with  the  margin  of  the  coronoid  process.  It  lies  superficial  to  the  posterior 
fibres  of  the  ulnar  collateral  ligament.  The  anterior  fibres  are  the  thickest,  strongest,  and  most 
pronounced. 


RADIO-ULNAB  JOINTS  26L 

The  lateral  portion,  the  radial  collateral  ligament  (fig.  294),  is  attached  above 
to  the  lower  part  of  the  lateral  epicondyle,  and  from  this  the  fibres  radiate  to 
their  attachment  into  the  lateral  side  of  the  annular  ligament,  a  few  fibres  being 
prolonged  to  reach  the  neck  of  the  radius.  The  anterior  fibres  reach  further 
forward  than  the  posterior  do  behind.  It  is  strong  and  well-marked,  but  less 
so  than  the  medial  portion. 

The  synovial  membrane  lines  the  whole  of  the  capsule,  and  extends  into  the 
superior  radio-ulnar  joint,  lining  the  annular  ligament. 

Outside  the  synovial  membrane,  but  inside  the  capsule,  are  often  seen  some  pads  of  fatty 
tissue;  one  is  situated  on  the  medial  side  at  the  base  of  the  olecranon,  another  is  seen  on  the 
lateral  side  projecting  into  the  cavity  between  the  radius  and  ulna;  this  latter,  with  a  fold  of 
synovial  membrane  opposite  the  front  of  the  lateral  hp  of  the  trochlea,  suggests  the  division  of 
the  joint  into  two  parts — one  medially  for  the  ulna,  and  another  laterally  for  the  radius. 
There  are  also  pads  of  fatty  tissue  at  the  bottom  of  the  olecranon  and  coronoid  fossas,  and  at 
the  tip  of  the  olecranon  process. 

The  arterial  supply  is  derived  from  each  of  the  vessels  forming  the  free  anastomosis  around 
the  elbow,  and  there  is  also  a  special  branch  to  the  front  and  lateral  side  of  the  joint,  from  the 
brachial  artery,  and  the  arterial  branch  to  the  brachialis  also  feeds  the  front  of  the  joint. 

The  nerve-supply  comes  chiefly  from  the  musculo-cutaneous;  the  ulnar,  median,  and  radial 
(musculo-spiral)  also  give  fUaments  to  the  joint. 

Relations. — In  front  of  the  joint,  and  in  immediate  relation  with  the  capsule,  are  the 
brachiahs,  the  superficial  and  deep  branches  of  the  radial  (musculo-spiral)  nerve,  the  radial  re- 
current artery,  and  the  brachio-radiahs.  The  brachial  artery,  the  median  nerve,  and  the  pro- 
nator teres  are  separated  from  the  capsule  by  the  brachiahs.  Directly  behind  the  capsule 
are  the  triceps,  the  anconeus,  and  the  posterior  interosseous  recurrent  artery.  On  the  medial 
side  are  the  ulnar  nerve,  the  superior  ulnar  collateral  (posterior  ulnar  recurrent)  artery,  and  the 
upper  parts  of  the  flexor  carpi  ulnaris  and  flexor  digitorum  subhmis.  On  the  lateral  side  lie 
the  extensor  carpi  radiahs  longus  and  the  upper  part  of  the  common  tendon  of  origin  of  the 
superficial  extensors  of  the  wrist  and  fingers. 

The  movements  permitted  at  the  elbow  are  those  of  a  true  hinge  joint,  viz.,  flexion  and 
extension.  These  movements  are  oblique,  so  that  the  forearm  is  inclined  medially  in  flexion, 
and  laterally  in  extension ;  they  are  limited  by  the  contact  respectively  of  the  coronoid  and  ole- 
cranon processes  of  the  ulna  with  their  corresponding  fossae  on  the  humerus,  and  their  extent  is 
determined  by  the  relative  proportion  between  the  length  of  the  processes  and  depth  of  the 
fossae  which  receive  them,  rather  than  by  the  tension  of  the  ligaments,  or  the  bulk  of  the  soft 
parts  over  them.  The  anterior  and  posterior  portions  of  the  capsule,  together  with  the  corres- 
ponding portions  of  the  collateral  ligament,  are  not  put  on  the  stretch  during  flexion  and  exten- 
sion; but,  although  they  may  assist  in  checking  the  velocity,  and  thus  prevent  undue  force  of 
impact,  they  do  not  control  or  determine  the  extent  of  these  movements.  The  limit  of  exten- 
sion is  reached  when  the  ulna  is  nearly  in  a  straight  line  with  the  humerus;  and  the  limit  of 
flexion  when  the  ulna  describes  an  angle  of  from  30°  to  40°  with  the  humerus. 

The  obliquity  of  these  movements  is  due  to  the  lateral  inclination  of  the  upper  and  back 
part  of  the  trochlear  surface,  and  the  greater  prominence  of  the  medial  lip  of  the  trochlea  below; 
thus  the  plane  of  motion  is  directed  from  behind  forward  and  medially,  and  carries  the  hand 
toward  the  middle  third  of  the  clavicle.  The  obliquity  of  the  joint,  the  twist  of  the  shaft  of 
the  humerus,  and  the  backward  direction  of  its  head,  all  tend  to  bring  the  hand  toward  the  mid- 
line of  the  body,  under  the  immediate  observation  of  the  eye,  whether  for  defence,  employment, 
or  nourishment.  This  is  in  striking  contrast  to  the  lower  limb,  where  the  direction  of  the  foot 
diverges  from  the  median  axis  of  the  trunk,  thus  preventing  awkwardness  in  locomotion.  In 
flexion  and  e.xtension,  the  cup-like  depression  of  the  radial  head  glides  upon  the  capitulum,  and 
the  medial  margin  of  the  radial  head  travels  in  the  groove  between  the  capitulum  and  the 
trochlea.  This  allows  the  radius  to  rotate  upon  the  humerus  while  following  the  ulna  in  all 
its  movements.  In  full  extension  and  supination,  the  head  of  the  radius  is  barely  in  contact 
with  the  inferior  surface  of  the  capitulum,  and  projects  so  much  backward  that  its  posterior 
margin  can  be  felt  as  a  prominence  at  the  back  of  the  elbow.  In  full  flexion  the  anterior  edge 
of  the  radial  head  is  received  into,  and  checked  against,  the  depression  above  the  capitulum ; 
while  in  mid-flexion  the  cup-like  depression  is  fairly  received  upon  the  capitulum,  and  in  this 
position,  the  radius  being  more  completely  steadied  by  the  humerus  than  in  any  other,  pro- 
nation and  supination  take  place  most  perfectly. 

Muscles  which  act  upon  the  elbow-joint. — Flexors. — Brachialis,  biceps,  brachio-radialis, 
pronator  teres,  flexor  carpi  radialis,  palmaris  longus,  flexor  digitorum  sublimis,  flexor  carpi 
ulnaris. 

Extensors. — Triceps,  anconeus,  and  the  muscles  which  spring  from  the  lateral  epico  ndyle 

5.  THE  UNION  OF  THE  RADIUS  WITH  THE  ULNA 

The  radius  is  firmly  united  to  the  ulna  by  two  joints,  and  an  intermediate 
fibrous  union,  viz. : — • 

(a)  The  superior  radio-ulnar — whereat  the  head  of  the  radius  rotates  within 
the  radial  notch  and  annular  ligament. 

(b)  The  union  of  the  shafts — the  mid  radio-ulnar  union. 

(c)  The  inferior  radio-ulnar — whereat  the  lower  end  of  the  radius  rolls  round 
the  head  of  the  ulna. 


262 


THE  ARTICULATIONS 


.   (a)  The  Superior  Radio-ulnar  Joint 

Class. — Diarthrosis.  Subdivision. — Trochoides. 

The  bones  which  enter  into  this  joint  (which  is  often  included  with  the  elbow- 
joint)  are,  the  ulna  by  its  radial  notch  and  the  radius  by  the  smooth  vertical  border 
or  rim  on  its  head.     There  is  but  one  ligament  special  to  the  joint,  viz.: — 

Annular. 

The  annular  ligament  consists  of  bands  of  strong  fibres,  somewhat  thicker 
than  the  capsule  of  the  elbow-joint,  which  encircle  the  head  of  the  radius,  re- 
taining it  against  the  side  of  the  ulna.  The  bulk  of  these  fibres  forms  about  three- 
fourths  of  a  circle,  and  they  are  attached  to  the  anterior  and  posterior  margins 
of  the  radial  notch;  some  few  are  continued  round  below  the  radial  notch,  and 
form  a  complete  ligamentous  circle. 

The  ligament  is  inseparably  connected  along  its  upper  edge  and  lateral  (i.  e.,  its  non- 
articular)  surface  with  the  anterior,  posterior,  and  lateral  portions  of  the  capsule  of  the  elbow, 
a  few  of  the  fibres  of  these  portions,  especially  of  the  lateral,  descending  to  be  attached  to  the 
necli  of  the  radius.  The  lower  part  of  the  articulation  is  covered  in  anteriorly,  posteriorly,  and 
laterally  by  a  thin  independent  membranous  layer,  which  passes  from  the  lower  edge  of  the 
annular  ligament  to  the  neck  of  the  radius,  strengthened  on  the  lateral  side  by  those  fibres 
passing  down  from  the  capsule.     They  are  loose  enough  to  allow  the  bone  to  rotate  upon  its 

Fig.  297. — Annular  Ligament. 

(The  head  of  the  radius  removed  to  show  the  membranous  connection  of  this  ligament 

with  the  radius.) 


Capsule  of  elbow-joint 

CusMon  of  fatty  tissue 

Membranous  tissue  joining  the  an- 
nular ligament  to  the  neck  of  the 
radius 

Radius 

Annular  ligament 


own  axis  (fig.  297).  Medially  and  below  the  cavity  is  closed  in  by  a  loose  membrane,  the  liga- 
mentum  quadratum,  which  passes  from  the  lower  border  of  the  radial  notch  to  the  neck  of  the 
radius. 

The  synovial  membrane  is  the  same  as  that  of  the  elbow-joint,  and,  after 
lining  the  annular  ligament,  passes  on  to  the  neck  of  the  radius,  and  thence  up  to 
the  lower  margin  of  the  articular  cartilage. 

The  arterial  and  nerve -supply  are  the  same  as  those  to  the  lateral  part  of  the  elbow-joint. 
Relations. — Behind  lies  the  anconeus  and  in  front  the  lateral  border  of  the  brachiaUs. 


(b)  The  Mid  Radio-ulnar  Union 

Class. — Synarthrosis.  Subdivision. — Syndesmosis. 

There  are  two  interosseous  ligaments  which  pass  betweeen  the  shafts  of  the 
bones  and  unite  them  firmly  together,  viz. : — 

Oblique  cord.  Interosseous  membrane. 

The  oblique  cord  [chorda  obliqua]  (figs.  293  and  298)  is  a  fairly  strong,  narrow 
band,  which  passes  from  the  lower  end  of  the  rough  lateral  border  of  the  coronoid 


RADIO-ULNAR  JOINTS 


263 


process,  downward  and  laterally  to  be  attached  to  the  posterior  edge  of  the 
lower  end  of  the  tuberosity  of  the  radius  and  the  vertical  ridge  running  from  it 
to  the  medial  border  of  the  bone. 

Some  of  its  fibres  blend  with  the  fibres  of  insertion  of  the  biceps  tendon;  behind,  it  is  in 
close  contact  with  the  supinator;  below,  a  thin  membrane  passes  off  from  it  to  the  upper  edge 
of  the  interosseous  membrane;  the  posterior  interosseous  vessels  pass  in  the  space  between  it 
and  the  interosseous  membrane;  occasionally  a  slip  is  continued  into  the  annular  ligament  of  the 
superior  radio-ulnar  articulation  (see  fig.  298). 

The  interosseous  membrane  (fig.  293)  is  attached  to  the  ulna  at  the  lowest 
part  of  the  ridge  in  front  of  the  depression  for  the  supinator,  and  along  the  whole 
length  of  the  interosseous  border  as  far  as  the  inferior  radio-ulnar  articulation, 
approaching  the  front  of  the  bone  in  the  lower  part  of  its  attachment.  To  the 
radius  it  is  attached  along  the  interosseous  border,  from  an  inch  (2.5  cm.)  below 
the  tuberosity  to  the  ulnar  notch  for  the  lower  end  of  the  ulna. 

It  is  strongest  and  broadest  in  the  centre,  where  the  fibres  are  dense  and  closely  packed ; 
it  is  also  well  marked  beneath  the  pronator  quadratus,  and  thickens  considerably  at  the  lower  end, 
forming  a  strong  band  of  union  between  the  two  bones.  Its  fibres  pass  chiefly  downward 
and  medially,  from  the  radius  to  the  ulna,  though  some  take  the  opposite  direction;  at  the  lower 
end  some  are  transverse.  On  the  posterior  surface  are  one  or  two  bands,  which  pass  downward 
and  laterally  from  the  ulna  to  the  radius,  and  frequently  there  is  a  strong  bundle  as  large  as  the 

Fig.  298. — Upper  Portions  of  Left  Ulna  and  Radius,  to  show  an  Occasional  Slip  prom 
THE  Oblique  Cohd  to  the  Lower  Part  op  the  Annular  Ligament.  This  condition  is 
present  in  the  spider  monkey  (Ateles),  which  has  no  external  thumb  but  only  rudimentary 
bones  of  one. 

(From  a  dissection  by  Mr.  W.  Pearson,  Royal  CoUege  of  Surgeons,  England.) 


Annular  ligament 


Occasional  slip  from  oblique  cord 
to  annular  ligament 


Oblique  cord 


oblique  cord;  this,  which  may  be  called  the  inferior  oblique  ligament  (fig.  303),  stretches  from 
the  ulna,  an  inch  and  a  half  above  its  lower  extremity,  downward  and  laterally  to  the  ridge 
above  and  behind  the  ulnar  notch  of  the  radius. 

At  its  attachment  to  the  bones,  the  interosseous  membrane  blends  with  the  periosteum. 
Its  upper  border  is  connected  with  the  oblique  cord  by  a  thin  membrane,  which  is  pierced  by 
the  posterior  interosseous  vessels;  and  the  lower  border,  which  stretches  across  between  the  two 
bones  just  above  the  inferior  radio-ulnar  articulation,  assists  in  completing  the  capsule  of  that 
joint.  Its  anterior  surface  is  iii  relation  with  the  flexor  digitorum  profundus  and  flexor  pollids 
longus  in  the  upper  three-quarters,  the  lower  fourth  being  in  relation  with  the  pronator  quadratus. 
The  anterior  interosseous  vessels  and  nerve  descend  along  the  middle  of  the  membrane,  the 
artery  being  bound  down  to  it.  About  an  inch  from  the  lower  end  it  is  pierced  by  the  anterior 
interosseous  artery.  The  posterior  surface  is  in  relation  with  the  supinator,  abductor  pollids 
longus  (extensor  ossis  metacarpi  pollids),  extensor  pollids  longus  and  brevis,  and  the  extensor 
indids  proprius;  at  its  lower  part,  also  with  the  posterior  branch  of  the  anterior  interosseous 
artery,  and  the  deep  branch  of  the  radial  nerve  (posterior  interosseous). 


(c)  The  Inferior  Radio-xjlnar  Joint 

Class. — Diarthrosis.  Subdivision. — Trochoides. 

This  is,  in  one  respect,  the  reverse  of  the  superior;  for  the  radius,  instead  of 
presenting  a  circular  head  to  rotate  upon  the  facet  on  the  ulna,  presents  a  concave 
facet  which  rolls  round  the  ulna.     The  articulation  may  be  said  to  consist  of  two 


264 


THE  ARTICULATIONS 


parts  at  right  angles  to  each  other;  one  between  the  radius  and  ulna,  and  the 
other  between  the  ulna  and  the  articular  disc  (triangular  fibro-cartilage) . 


Anterior  radio-ulnar. 


The  ligaments  are: 
Articular  disc. 


Posterior  radio-ulnar. 


The  articular  disc  (triangular  fibro-cartilage)  (figs.  303  and  304)  assists  the 
radius  in  forming  an  arch  under  which  is  received  the  first  row  of  carpal  bones. 
Its  base  is  attached  to  the  margin  of  the  radius,  separating  the  ulnar  notch  from 
the  articular  surface  for  the  carpus,  while  its  apex  is  fixed  to  the  fossa  at  the  base 
of  the  styloid  process  of  the  ulna.  It  gradually  and  uniformly  diminishes  in 
width  from  base  to  apex,  becoming  rounded  where  it  is  fixed  to  the  ulna;  it  is 
joined  by  fibres  of  the  ulnar  collateral  ligament  of  the  wrist. 

The  articular  disc  is  about  three-eighths  of  an  inch  (1  cm.)  wide,  and  the  same  from  base  to 
apex;  thicker  at  the  circumference  than  in  the  centre;  smooth  and  concave  above  to  adapt 

Fig.  299. — ^Lower  Extremities  op  the  Radius  and  Ulna  to  Show  the  Relation  op 
THE  Articulab  Capsule  OP  THE  Wrist  Joint  (In  red)  to  the  Epiphysial  Lines.  Note  the 
upward  extension  of  the  membrana  saccLformis. 


itself  to  the  ulna,  and  smooth  and  slightly  concave  below  to  fit  over  the  triquetral  bone.  Its 
anterior  and  posterior  borders  are  united  to  the  anterior  and  posterior  radio-ulnar  and  radio- 
carpal ligaments.  It  is  the  most  important  structure  in  the  inferior  radio-carpal  articulation, 
as  it  is  a  very  firm  bond  of  union  between  the  lower  ends  of  the  bones,  and  serves  to  hmit  their 
movements  upon  one  another  more  than  any  other  structure  in  either  the  upper  or  lower  radio- 
ulnar joints.  Its  structure  is  fibrous  at  the  circumference,  while  in  the  centre  there  is  a  prepon- 
derance of  cells.  It  differs  from  all  other  fibro-cartilages  in  entering  into  two  distinct  articula- 
tions; and  separates  entirely  the  synovial  membrane  of  the  radio-ulnar  joint  from  that  of  the 
wrist. 

The  lower  end  of  the  interosseous  membrane  extends  between  the  ulna  and 
radius  immediately  above  their  points  of  contact.  Transverse  fibres  between  the 
two  bones  form  a  sort  of  arch  above  the  concave  articular  facet  of  the  radius,  and, 
joining  the  anterior  and  posterior  radio-ulnar  ligaments,  complete  the  articular 
capsule  of  the  inferior  radio-ulnar  joint.  The  ligaments  represent  merely 
thickenings  of  the  capsule. 

The  anterior  radio-ulnar  ligament  (fig.  300)  is  attached  by  one  end  to  the  anterior  edge 

of  the  ulnar  notch  of  the  radius,  and  by  the  other  to  the  rough  bone  above  the  articular  surface 
of  the  ulna  as  far  mediaDy  as  the  notch,  as  well  as  into  the  anterior  margin  of  the  trianguar 
cartOage  from  base  to  apex. 

The  posterior  radio-ulnar  ligament  (fig.  301)  is  similarly  attached  to  the  posterior  margin 
of  the  ulnar  notch  at  one  end,  and  at  the  other  to  the  rough  bone  above  the  articular  surface  of 
the  extremity  of  the  ulna  as  far  medially  as  the  groove  for  the  extensor  carpi  ulnaris,  with  the 
sheath  of  which  it  is  connected,  as  well  as  into  the  whole  length  of  the  posterior  margin  of  the 
articular  disc.     Both  the  radio-ulnar  ligaments  consist  of  thin,  almost  scattered,  fibres. 


THE  WRIST-JOINT  265 

The  synovial  membrane,  sometimes  called  the  membrana  sacciformis,  is 
large  and  loose  in  proportion  to  the  size  of  the  joint.  It  is  not  onty  interposed 
between  the  radial  and  ulnar  articular  surfaces,  but  lines  the  terminal  articular 
surface  of  the  ulna  and  the  upper  surface  of  the  articular  disc. 

The  arterial  supply  is  derived  from  the  volar  interosseous  artery  and  branches  of  the 
volar  carpal  rate. 

The  nerve-supply  comes  from  the  volar  interosseous  of  the  median,  and  the  deep  branch 
of  the  radial  (posterior  interosseous). 

Relations. — Behind  hes  the  tendon  of  the  extensor  digiti  quinti  proprius  and  in  front  the 
flexor  digitorum  profundus. 

The  movements  of  the  radius. — The  upper  end  of  the  radius  rotates  upon  an  axis  drawn 
through  its  own  head  and  neck  within  the  coUar  formed  b}'  the  radial  notch  and  the  annular 
ligament,  while  the  lower  end,  retained  in  position  by  the  articular  disc,  rolls  round  the 
head  of  the  ulna.  This  rotation  is  called  pronation,  when  the  radius  from  a  position  nearly 
parallel  to  the  ulna  turns  medialward  so  as  to  lie  obliquely  across  it;  and  supination,  when  the 
radius  turns  back  again,  so  as  to  uncross  and  lie  nearly  parallel  with  the  ulna.  In  these  move- 
ments the  radius  carries  with  it  the  hand,  which  rotates  on  an  axis  passing  along  the  ulnar  side 
of  the  hand;  thus,  the  hand  when  pronated  hes  with  its  dorsum  upward,  as  in  playing  the 
piano,  whUe  when  supinated,  the  palm  lies  upward — the  attitude  of  a  beggar  asking  alms. 
Ward  thus  expresses  the  relations  of  the  two  extremities  of  the  radius  in  pronation  and  supina- 
tion: 'The  head  of  the  radius  is  so  disposed  in  relation  to  the  sigmoid  cavitj'  (ulnar  notch)  at 
the  lower  end  that  the  axis  of  the  former  if  prolonged  falls  upon  the  centre  of  the  circle  of  which 
the  latter  is  a  segment;'  the  axis  thus  passes  through  the  lower  end  of  the  ulna  at  a  point  at 
which  the  articular  disc  is  attached,  and  if  prolonged  further,  passes  through  the  ring  finger. 
Thus  the  radius  describes,  in  rotating,  a  blunt-pointed  cone  whose  apex  is  the  centre  of  the  radial 
head,  and  whose  base  is  at  the  wrist;  partial  rotation  of  the  bone  being  unaccompanied  by  anj' 
hinge-like  or  antero-posterior  motion  of  its  head,  and  pronation  and  supination  occurring  with- 
out disturbance  to  the  parallelism  of  the  bones  at  the  superior  radio-ulnar  joint.  Associated 
with  this  rotation  in  the  ordinary  way,  there  is  some  rotation  of  the  humero-ulnar  shaft,  which 
causes  lateral  shifting  of  the  hand  from  side  to  side;  thus,  with  pronation  there  is  some  abduc- 
tion, and  with  supination  some  adduction  combined,  so  that  the  hand  can  keep  on  the  same 
superficies  in  both  pronation  and  supination.  The  power  of  supination  in  man  is  much  greater 
than  pronation,  owing  to  the  immense  power  and  leverage  obtained  by  the  cm-ve  of  the  radius, 
and  bj'  the  attachment  of  the  biceps  tendon  to  the  back  of  the  tuberosity.  For  this  reason  all 
our  screw-driving  and  boring  tools  are  made  to  be  used  bj-  supination  movements. 

In  the  undissected  state,  the  amount  of  rotation  it  is  possible  to  obtain  is  about  135°,  so 
that  neither  the  palm  nor  the  fore  part  of  the  lower  end  of  the  radius  can  be  turned  completely 
in  opposite  directions;  j-et  in  the  hving  subject  this  amount  can  be  greatly  increased  by  rotation 
of  the  humero-ulnar  shaft  at  the  shoulder-joint. 

Pronation  is  checked  in  the  living  subject  by  (a)  the  posterior  inferior  radio-ulnar  ligament, 
which  is  strengthened  by  the  connection  of  the  sheath  of  the  extensor  tendons  with  it;  (b)  the 
lowermost  fibres  of  the  interosseous  membrane;  (c)  the  back  part  of  the  ulnar  collateral  and 
adjacent  fibres  of  the  posterior  hgament  of  the  wrist,  and  (d)  the  meeting  of  the  soft  parts  on 
the  front  of  the  forearm. 

Supination  is  checked  mainly  (a)  by  the  medial  ulnar  collateral  ligaments  of  the  wrist,  but 
partly  also  by  (b)  the  oblique  cord;  (c)  the  anterior  inferior  radio-ulnar  hgament,  and  (d)  the 
lowest  fibres  of  the  interosseous  membrane. 

The  interosseous  membrane  serves,  from  the  direction  of  its  fibres  downward  and  medially 
from  the  radius  to  the  ulna,  to  transmit  the  weight  of  the  body  from  the  ulna  to  the  radius  in 
the  extended  position  of  the  elbow,  as  in  pushing  forward  with  the  arms  extended,  or  in  support- 
ing one's  own  weight  on  the  hands,  the  ulna  being  in  intimate  contact  with  the  humerus,  but 
not  at  all  with  the  carpus;  whOe  the  area  of  contact  of  the  radius  with  the  humerus  is  small, 
and  that  of  the  radius  with  the  carpus  large.  Hence  the  weight  transmitted  bj'  the  ulna  is 
communicated  to  the  radius  by  the  tightening  of  the  interosseous  membrane.  Conversely,  in 
falls  upon  the  hand  with  the  arm  extended,  the  interosseous  membrane  acts  as  a  sUng  to  break 
the  violence  of  the  shock,  and  prevents  the  whole  force  of  the  impact  from  expending  itself 
directly  upon  the  capitulum. 

Muscles  which  act  upon  the  radio-ulnar  joints.— Pronators. — Pronator  teres,  pronator 
quadratus,  flexor  carpi  radiahs,  palmaris  longus. 

Supinators. — Biceps,  supinator,  extensor  poUicis  longus. 

The  brachio-radialis  is  chiefly  a  flexor  of  the  elbow-joint,  but  it  takes  part  in  the  initiation 
of  the  movement  of  supination  when  the  hand  is  fully  pronated  and  of  pronation  when  the  hand 
is  fully  supinated. 

6.  THE  RADIO-CARP.\L  OR  WRIST-JOINT 
Class. — Diarthrosis.  Subdivision. — Condylarthrosis. 

The  wrist-joint  is  formed  by  the  imion  of  the  radius  and  articular  disc  above, 
articulating  -^vith  the  navicular,  lunate,  and  triquetral  bones  below;  the  ulna 
being  excluded  by  the  intervention  of  the  articular  disc.  The  radius  and  disc 
together  present  a  smooth  surface,  slightly  concave  both  from  before  backward, 
and  from  side  to  side,  whilst  the  three  bones  of  the  carpus  present  a  smooth, 


266 


THE  ARTICULATIONS 


convex  surface,  made  uniformly  even  by  the  interosseous  ligaments  which  bind 
them  together. 

The  capsule  of  the  wrist-joint  has  been  usually  described  as  four  separate  liga- 
ments, and  it  will  be  convenient  for  the  sake  of  a  complete  description  to  follow 
this  method;  but  it  must  be  understood  that  these  four  portions  are  continuous 
around  the  joint,  extending  from  styloid  process  to  styloid  process  on  both  its 
aspects. 

The  four  portions  are : — 


Volar  radio-carpal. 
Dorsal  radio-carpal. 


Ulnar  collateral. 
Radial  collateral. 


The  volar  (or  anterior)  radio-carpal  (fig.  300)  is  a  thick  strong  ligament,  at- 
tached superiorly  to  the  radius  immediately  above  the  anterior  margin  of  the 
terminal  articular  facet,  to  the  curved  ridge  at  the  root  of  the  styloid  process  of 
the  radius,  and  to  the  anterior  margin  of  the  articular  disc,  blending  with  some 
fibres  of  the  capsule  of  the  inferior  radio-ulnar  joint.  It  passes  downward  and 
in  a  medial  direction  to  be  attached  to  both  rows  of  carpal  bones,  especially  the 
second,  and  to  the  volar  intercarpal  ligament. 

Fig.  300.- — Anterior  View  op  Wrist. 


Ulnar  radio-ulnar 
ligament 

Ulnar  collateral  liga- 
ment of  wrist 
Flexor  carpi  ulnaris 


Volar  radio-carpal 

ligament 
Tendon  of  flexor  carpi 
radialis 

Capsular  ligament  of  first 
carpo-metacarpal  joint 


The  strongest  and  most  oblique  fibres  arise  from  the  root  of  the  styloid  process  of  the  radius, 
and  pass  obhquely  over  the  navicular,  with  which  only  a  few  fibres  are  connected,  to  be  inserted 
into  the  lunate,  capitate,  and  triquetral  bones.  Another  set,  less  oblique,  passes  from  the  margin 
of  the  facet  for  the  lUnate  to  be  attached  to  the  adjacent  parts  of  the  capitate,  hamate,  and  tri- 
quetral bones.     Between  the  two  sets  of  fibres,  small  vessels  pass  into  the  joint. 

The  dorsal  (or  posterior)  radio-carpal  ligament  (fig.  301)  is  attached  above 
to  the  dorsal  edge  of  the  lower  end  of  the  radius,  the  back  of  the  styloid  process, 
and  the  posterior  margin  of  the  fibro-cartilage.  It  passes  downward  and  in  a 
medial  direction  to  be  connected  with  the  first  row  of  the  carpal  bones,  chiefly 
with  the  lunate  and  triquetral,  and  the  dorsal  intercarpal  ligament.  This 
ligament  is  thin  and  membranous. 

It  is  strengthened  by  (i)  strong  fibres  passing  from  the  back  of  the  articular  disc  where 
they  are  blended  with  the  posterior  inferior  radio-ulnar  ligament,  and,  from  the  edge  of  the  radius 
just  behind  the  ulnar  notch,  to  the  triquetral  bone;  (ii)  from  the  ridge  and  groove  for  the  extensor 
pollicis  longus  to  the  back  of  the  lunate  and  triquetral  bones;  and  (iii)  from  the  groove  for  the 
radial  e.xtensors  to  the  back  of  the  navicular  and  lunate.  It  is  in  relation  with,  and  strengthened 
by,  the  extensor  tendons  which  pass  over  it. 

The  ulnar  collateral  ligament  (fig.  301)  is  fan-shaped,  with  its  apex  above,  at 
the  styloid  process  of  the  ulna,  to  which  it  is  attached  on  all  sides,  blending  with 


THE  WRIST-JOINT 


267 


the  apex  of  the  articular  disc.  Some  of  the  fibres  pass  forward  and  laterally  to 
the  base  of  the  pisiform  bone  and  to  the  medial  part  of  the  upper  border  of  the 
transverse  carpal  ligament,  where  it  is  attached  to  the  pisiform  bone;  they  form 
a  thick,  rounded  fasciculus  on  the  front  of  the  wrist.  Other  fibres  descend 
vertically  to  the  medial  side  of  the  triquetral  bone,  and  others  again  laterally  to 
the  dorsal  surface  of  the  triquetral.  The  tendon  of  the  extensor  carpi  ulnaris  is 
posterior  to,  and  passes  over,  part  of  the  fibres  of  the  ligament. 

The  radial  collateral  ligament  (fig.  300)  consists  of  fibres  which  radiate  from 
the  fore  part  and  tip  of  the  styloid  process  of  the  radius.  Some  pass  downward 
and  medially,  in  front,  to  the  navicular  and  adjacent  edge  of  the  capitate;  some 
downward,  a  little  forward  and  medially,  to  the  tubercle  of  the  navicular  and 
ridge  of  the  greater  multangular;  and  others  downward  and  laterally  to  the 
rough  dorsal  surface  of  the  navicular. 

The  fibres  of  this  ligament  are  not  so  long  and  strong,  nor  do  they  radiate  so  much  as  those 
of  the  ulnar  collateral  ligament.  It  is  in  relation  with  the  radial  artery,  and  the  abductor  pollicis 
longus  {extensor  ossis  metacarpi  pollicis)  and  extensor  pollicis  brevis,  the  artery  separating  the 
tendons  from  the  ligament. 

Fig.  301. — Posterior  View  op  Whist. 


Dorsal  radio-carpal  ligament 


Posterior  radio-ulnar  ligament 


Ulnar  collateral  ligament  of 
wrist 


The  synovial  membrane  is  extensive,  but  does  not  usually  communicate  with 
the  synovial  membrane  of  the  inferior  radio-ulnar  joint,  being  shut  out  by  the 
articular  disc.  It  is  also  excluded,  in  almost  every  instance,  from  that  of 
the  carpal  joints  by  the  interosseous  ligaments  between  the  first  row  of  carpal 
bones.  The  styloid  process  of  the  radius  is  cartilage-covered  medially,  and 
forms  part  of  the  articular  cavity,  while  that  of  the  ulna  does  not. 

The  arterial  supply  is  derived  from  the  anterior  and  posterior  carpal  rami,  the  dorsal 
division  of  the  volar  interosseous,  and  from  twigs  direct  from  the  radial  and  ulnar  arteries. 

The  nerve -supply  is  derived  from  the  ulnar  and  median  in  front,  and  the  deep  branch  of 
the  radial  (posterior  interosseous)  behind. 

Relations. — In  front  of  the  radio-carpal  joint  are  the  tendons  of  the  flexor  muscles  of  the 
wrist  and  fingers,  the  synovial  sheaths  associated  with  thern,  the  radial  and  ulnar  arteries,  and 
the  median  and  ulnar  nerves. 

Behind  the  joint  are  the  majority  of  the  tendons  of  the  extensor  muscles  of  the  wrist  and 
fingers,  with  their  synovial  sheaths,  the  terminal  part  of  the  anterior  and  posterior  interosseous 
arteries,  and  the  deep  branch  of  the  radial  nerve  (posterior  interosseous).  On  the  radial  side 
lie  the  tendons  of  the  abductor  pollicis  longus  {extensor  ossis  metacarpi  pollicis)  and  the  extensor 
pollicis  brevis.  On  the  ulnar  side  the  joint  is  subcutaneous  and  it  is  crossed  by  the  dorsal 
cutaneous  branch  of  the  ulnar  nerve. 

Movements. — The  wrist  is  a  condyloid  joint,  the  carpus  forming  the  condyle.  It  allows 
of  movements  upon  a  transverse  axis,  i.  e.,  flexion  and  extension;  and  around  an  antero-pos- 
terior  axis,  i.  e.,  abduction  and  adduction;  together  with  a  combination  of  these  in  quick  succes- 


268 


THE  ARTICULATIONS 


sion — oiroumduction.  Lacking  only  rotation  on  a  vertical  axis,  it  thus  possesses  most  of  the 
movements  of  a  ball-and-socket  joint,  without  the  weakness  and  liability  to  dislocation  which 
are  peculiar  to  these  joints.  This  deficiency  of  rotation  is  compensated  for  by  the  movements 
of  the  radius  at  the  radio-ulnar  joints,  viz.,  supination  and  pronation.  Its  strength  depends 
chiefly  upon  the  number  of  tendons  which  pass  over  it,  and  the  close  connection  which  exists 
between  the  fibrous  tissue  of  their  sheaths  and  the  capsule  of  the  wrist;  also  upon  the  proximity 
of  the  medio-carpal  and  carpo-metacarpal  joints,  which  permits  shocks  and  jars  to  be  shared 
and  distributed  between  them;  another  source  of  strength  is  the  absence  of  any  long  bone  on  the 
distal  side  of  the  joint.  In  flexion  and  extension  the  carpus  rolls  backward  and  forward,  respec- 
tively, beneath  the  arch  formed  by  the  radius  and  articular  disc;  flexion  being  limited  by  the 
dorsal  ligament  and  dorsal  portions  of  the  collateral;  extension  by  the  volar,  and  volar  portions 
of  the  collateral  ligaments.  In  adduction  and  abduction  the  carpal  bones  ghde  from  the  ulnar 
to  the  radial  side  and  from  the  radial  to  the  ulnar  side,  respectively.  Abduction  is  more  limited 
than  adduction,  and  is  checked  by  the  ulnar  collateral  hgament  and  by  contact  of  the  styloid 
process  of  the  radius  with  the  greater  multangular;  adduction  is  checked  by  the  radial  collateral 
ligament  alone.     One  reason  for  adduction  being  more  free  than  abduction  is  that  the  ulna  does 

Fig.  302. — Front  of  Wrist  with  Transverse  Carpal  Ligament. 


ulnar  collateral  ligament  of 
wrist  with  slip  to  annu- 
lar ligament 

Pisiform- 


Transverse  carpal  ligament' 


Volar  radio-carpal  ligament 


not  reach  so  low  down  as  the  radius,  and  the  yielding  articular  disc  allows  of  greater  movement 
upward  of  the  ulnar  end  of  the  carpus.  In  circumduction  the  hand  moves  so  as  to  describe  a 
cone,  the  apex  of  which  is  at  the  wrist.  These  movements  are  made  more  easy  and  extensive 
by  the  slight  gliding  of  the  carpal  bones  upon  one  another,  and  the  comparatively  free  motion 
at  the  medio-carpal  joint.  The  oblique  direction  of  the  fibres  of  the  collateral  hgaments  pre- 
vents any  rotation  at  the  radio-carpal  joint,  while  it  permits  considerable  freedom  of  abduction 
and  adduction. 

Muscles  which  act  upon  the  radio-carpal  joint. — Flexors. — The  flexors  of  the  carpus  and 
the  long  flexors  of  the  fingers  and  the  thumb,  and  the  pahnaris  longus.  Extensors. — The  exten- 
sors of  the  carpus  and  fingers.  Abductors. — Extensor  carpi  radialis  longus,  the  abductor  pol- 
licis  longus  (extensor  ossis  metacarpi  poUicis.  Adductors. — Flexor  carpi  ulnaris,  extensor  carpi 
ulnaris. 

7.  THE  CARPAL  JOINTS 

The  joints  of  the  carpus  may  be  subdivided  into — • 
(a)  The  joints  of  the  first  row. 
(6)  The  joints  of  the  second  row. 
(c)  The  medio-carpal,  or  junction  of  the  two  rows  with  each  other. 


THE  CARPAL  JOINTS 


269 


(a)  The  Joints  of  the  First  Row  of  Carpal  Bones 
Class. — Diarthrosis.  Subdivision. — Arthrodia. 

The  bones  of  the  first  row,  the  pisiform  excepted,  are  united  by  two  sets  of 
ligaments  and  two  interosseous  fibro-cartilages. 


Dorsal. 


Volar. 


Interosseous. 


The  two  dorsal  intercarpal  ligaments  extend  transversely  between  the  bones,  and  connect 
the  navicular  with  the  lunate,  and  the  lunate  with  the  triquetral.  Their  posterior  siu-faces  are 
in  contact  with  the  posterior  ligament  of  the  -nTist. 

The  two  volar  intercarpal  ligaments  extend  nearly  transversely  between  the  bones  connect- 
ing the  navicular  with  the  lunate,  and  the  lunate  with  the  triquetral.  They  are  Wronger  than 
the  dorsal  ligaments,  and  are  placed  beneath  the  anterior  ligament  of  the  wrist. 

The  two  interosseous  intercarpal  ligaments  (fig.  304)  are  interposed  between  the  navicular 
and  lunate,  and  the  lunate  and  triquetral  bones,  reaching  from  the  dorsal  to  the  volar  surfaces. 

Fig.  303. — Posterior  View  op  the  Wrist,  with  Capsule  cut  to  show  Articular  Surfaces, 

'll^^ — ^J Lower  end  of  interosseous  ligament 


Inferior  oblique  ligament 


Articular  disc 

Band  of  posterior   ligament   of   wrist 
i^ujH  .,,,,,     n^  ..  V  >,i|i  left  to  keep  bones  in  situ 

Transverse  dorsal  ligament  v*w».«™/    ^     


/   Tendon  flexor  carpi  ulnaris 


and  being  connected  with  the  dorsal  and  volar  ligaments.  They  are  narrow  fibro-cartilages 
which  extend  between  small  portions  only  of  the  osseous  surfaces.  They  help  to  form  the 
convex  carpal  surface  of  the  radio-carpal  joint,  and  are  somewhat  wedge-shaped,  their  bases 
being  toward  the  wrist,  and  their  thin  edges  between  the  adjacent  articular  surfaces  of  the  bones. 

The  synovial  membrane  is  a  prolongation  from  that  of  the  medio-oarpal  joint. 

The  arterial  and  nerve-supplies  are  the  same  as  for  the  medio-carpal  joint. 


The  Joint  of  the  Pisiform  Bone  with  the  Triquetral 

This  is  an  arthrodial  joint  which  has  a  loose  fibrous  capsule  attached  to  both 
the  pisiform  and  triquetral  bones  just  beyond  the  margins  of  their  articular 
surfaces. 

It  is  lined  by  a  separate  synovial  membrane.  Two  strong  rounded  or  flattened  bands  pass 
downward  from  the  pisiform,  one  to  the  process  of  the  hamate  [Ug.  pisohamatum],  and  the 
other  [Ug.  pisometacarpeum]  to  the  bases  of  the  third  to  fifth  metacarpals;  these  are  regarded  as 
prolongations  of  the  tendon  of  the  flexor  carpi  ulnaris,  and  the  pisiform  bone  may  be  looked 
upon  in  the  light  of  a  sesamoid  bone  developed  in  that  tendon. 

(b)  The  Joints  of  the  Second  Row  of  Carpal  Bones 

Class. — Diarthrosis.  Subdivision. — Arthrodia. 

The  four  bones  of  this  row  are  united  by  three  dorsal,  three  palmar,  and  three 
interosseous  ligaments. 


270  THE  ARTICULATIONS 

The  three  dorsal  ligaments  (fig.  303)  extend  transversely  and  connect  the  greater  with  the 
lesser  multangular,  the  lesser  multangular  with  the  capitate,  and  the  capitate  with  the  hamate. 

The  three  volar  ligaments  are  stronger  than  the  dorsal,  and  are  deeply  placed  beneath  the 
mass  of  flexor  tendons;  they  extend  transversely  between  the  bones  in  a  similar  manner  to  the 
dorsal  ligaments. 

Three  interosseous  ligaments  connect  the  bones  of  the  lower  row  of  the  carpus  together. 
Two  are  connected  with  the  capitate,  one  uniting  it  with  the  hamate  (fig.  304)  and  the  other 
binding  it  to  the  lesser  multangular.     The  third  Mgament  joins  the  greater  and  lesser  multangular. 

The  synovial  membrane  is  a  prolongation  of  that  lining  the  medio-carpal  joint. 

The  arterial  and  nerve -supplies  are  the  same  as  for  the  medio-carpal  joint. 

(c)  The  Medio-carpal  Joint,  or  the  Union  op  the  Two  Rows  of  the  Carpus 

WITH    EACH    other 

(I)  Class. — Diarthrosis.  Subdivision. — Arthrodia. 

(II)  Class.- — Diarthrosis.  Subdivision. — Condylarthrosis. 

The  inferior  surfaces  of  the  bones  of  the  first  row  are  adapted  to  the  superior 
articular  surfaces  of  the  bones  of  the  second  row.  The  line  of  this  articulation  is 
concavo-convex  from  side  to  side,  and  is  sometimes  described  as  having  the  course 
of  a  Roman  S  placed  horizontally,  co ,  a  resemblance  by  no  means  strained,  (i) 
The  lateral  part  of  the  first  row  consists  of  the  navicular  alone;  it  is  convex,  and 
bears  the  greater  and  lesser  multangulars.  (ii)  Then  follows  a  transversely 
elongated  socket  formed  by  the  medial  part  of  the  navicular,  the  lunate,  and 
triquetral,  into  which  are  received — (a)  the  head  of  the  capitate,  which  articulates 
with  the  navicular  and  lunate;  (6)  the  upper  and  lateral  angle  of  the  hamate,  which 
articulates  with  the  navicular;  and  (c)  the  upper  convex  portion  of  the  medial 
surface  of  the  hamate,  which  articulates  with  the  lateral  and  concave  portion  of 
the  inferior  surface  of  the  triquetral,  (iii)  The  medial  part  of  the  inferior  sur- 
face of  the  triquetral  bone  is  convex,  and  turned  a  little  backward  to  fit  into  the 
lower  portion  of  the  medial  surface  of  the  hamate,  which  is  a  little  concave  and 
turned  forward  to  receive  it.  The  central  part,  which  forms  a  socket  for  the  capi- 
tate and  hamate,  has  somewhat  the  character  of  a  condyloid  joint,  the  capitate 
and  hamate  being  the  condyle,  to  fit  into  the  cavity  formed  by  the  navicular, 
lunate,  and  triquetral;  the  other  portions  are  typically  arthrodial.  The  liga- 
ments are: — (1)  radiate  or  anterior  medio-carpal;  (2)  posterior  medio-carpal; 
(3)  transverse  dorsal. 

The  radiate,  anterior  or  volar  medio-carpal  is  a  ligament  of  considerable  strength,  consisting 
mostly  of  fibres  which  radiate  from  the  capitate  to  the  navicular,  lunate,  and  triquetral;  some 
few  fibres  connect  the  greater  and  lesser  multangular  with  the  navicular,  and  others  pass  between 
the  hamate  and  triquetral.  It  is  covered  over  and  thickened  by  fibrous  tissue  derived  from  the 
sheaths  of  the  flexor  tendons  and  the  fibres  of  origin  of  the  small  muscles  of  the  thumb  and  httle 
finger. 

The  posterior  or  dorsal  medio-carpal  ligament,  consists  of  fibres  passing  obliquely  from  the 
bones  of  the  first  row  to  those  of  the  second.  It  is  stronger  on  the  ulnar  side  than  on  the  radial, 
but  is  not  so  strong  as  the  volar  ligament. 

The  transverse  dorsal  ligament  (fig.  303)  is  an  additional  band,  well  marked  and  often  of 
considerable  strength,  which  passes  across  the  head  of  the  capitate  from  the  navicular  to  the 
triquetral  bone;  besides  binding  down  the  head  of  the  capitate,  it  serves  to  fix  the  upper  and  lat- 
eral angle  of  the  hamate  in  the  socket  formed  by  the  first  row. 

The  dorsal  ligaments,  like  the  volar,  are  strengthened  by  a  quantity  of  fibrous  tissue  belong- 
ing to  the  sheaths  of  the  extensor  tendons,  and  by  an  extension  of  some  of  the  fibres  of  the  capsule 
of  the  wrist.  There  are  no  proper  collateral  medio-carpal  hgaments;  they  are  but  prolongations 
of  the  collateral  ligaments  of  the  wrist. 

The  synovial  membrane  (fig.  304)  of  the  carpus  is  common  to  all  the  joints  of  the  carpus, 
and  extends  to  the  bases  of  the  four  medial  metacarpal  bones.  Thus,  besides  hning  the  inter- or 
medio-carpal  joint,  it  sends  two  processes  upward  between  the  three  bones  of  the  first  row,  and 
thi'ee  downward  between  the  contiguous  surfaces  of  the  lesser  and  greater  multangular,  the  lesser 
multangular  and  capitate,  and  capitate  and  hamate.  From  these  latter,  prolongations  extend 
to  the  four  medial  carpo-metacarpal  joints  and  the  three  intermetacarpal  joints. 

The  arterial  supply  is  derived  from — (a)  the  volar  and  dorsal  carpal  rami  of  the  radial 
and  ulnar  arteries;  (b)  the  carpal  branch  of  the  volar  interosseous;  (c)  the  recurrent  branches 
from  the  deep  palmar  arch.  The  terminal  twigs  of  the  volar  and  dorsal  interosseous  arteries 
supply  the  joint  on  its  dorsal  aspect. 

The  nerve -supply  comes  from  the  ulnar  on  the  ulnar  side,  the  median  on  the  radial  side,  and 
the  deep  branch  of  the  radial  (posterior  interosseous)  behind. 

Relations. — The  relations  of  this  joint  are  practically  the  same  as  those  of  the  radio-carpal 
joint,  except  that  the  flexor  carpi  ulnaris  does  not  cross  the  front,  the  ulnar  artery  is  separated 


THE  CARPAL  JOINTS 


271 


from  it  by  the  transverse  carpal  ligament,  and  the  radial  artery  passes  across  its  lateral  border 
instead  of  in  front. 

The  movements  of  the  carpal  articulations  between  bones  of  the  same  row  are  very  hmited 
and  consist  only  of  slight  gliding  upon  one  another;  but,  slight  as  they  are,  they  give  elasticity 
to  the  carpus  to  break  the  jars  and  shocks  which  result  from  blows  or  falls  upon  the  hand. 

The  movements  of  one  row  of  bones  upon  the  other  at  the  medio-carpal  joint  are  more 
extensive,  especially  in  the  direction  of  flexion  and  extension,  so  that  the  hand  enjoys  a  greater 
range  of  these  movements  than  is  permitted  at  the  wrist-joint  alone.  At  the  wrist,  extension  is 
more  free  than  flexion;  but  this  is  balanced  by  the  greater  freedom  of  flexion  than  of  extension 
at  the  medio-carpal  joint,  and  by  flexion  at  the  carpo-metacarpal  joint,  so  that  on  the  whole- the 
range  of  flexion  of  the  hand  is  greater  than  that  of  extension. 

Fig.  304. — Synovial  Membranes  of  Wri&t    Hand,  and  Fingers. 


Synovial  sac  of  the  wrist-joint 


Synovial  sac  of  the  carpus 


Synovial  sac,  occasionally 
separate,  for  the  fourth 
and  fifth  metacarpal  bones 


.Synovial   sac  of  the   carpo-meta- 
carpal joint  of  the  thumb 


Collateral  ligaments  of  the  metacarpo- 
pha  angeal      and      interphalangeal 


A  slight  amount  of  side  to  side  motion  accompanied  by  a  limited  degree  of  rotation  also 
takes  place;  this  rotation  consists  in  the  head  of  the  capitate  and  the  superior  and  lateral  angle 
of  the  hamate  bone  rotating  in  the  socket  formed  by  the  three  bones  of  the  upper  row,  and  in^a 
gliding  forward  and  backward  of  the  greater  and  lesser  multangular  upon  the  navicular. 

In  addition  to  the  ligaments,  the  undulating  outUne  and  the  variety  of  shapes  of  the  apposed 
facets  render  this  joint  very  secure. 

Bearing  in  mind  the  mobility  of  this  medio-carpal  joint  and  of  the  carpo-metacarpal,  we  see 
at  once  the  reason  for  the  radial  and  ulnar  flexors  and  extensors  of  the  carpus  being  prolonged 
down  to  their  insertion  into  the  base  of  the  metacarpus,  for  they  produce  the  combined  effect 
of  motion  at  each  of  the  three  transverse  articulations: — (1)  at  the  wrist;  (2)  at  the  medio-carpal; 
(3)  at  the  carpo-metacarpal  joints. 

Muscles  which  act  upon  the  mid-carpal  joint. — The  muscles  which  act  upon  this  joint  are 
the  same  as  those  which  act  upon  the  radio-carpal  joint,  except  the  flexor  carpi  ulnaris,  which  is 
inserted  into  the  pisiform  bone. 


272  THE  ARTICULATIONS 

8.  THE  CARPO-METACARPAL  JOINTS 
These  may  be  divided  into  two  sets,  namely: — 

(a)  The  carpo-metacarpal  joints  of  the  four  medial  fingers. 
(6)  The  carpo-metacarpal  joints  of  the  thumb. 

The  inferior  surfaces  of  the  bones  of  the  second  row  of  the  carpus  present  a 
composite  surface  for  the  four  medial  metacarpal  bones ;  the  greater  multangular 
presents  in  addition  a  distinct  and  separate  saddle-shaped  surface  for  the  base  of 
the  metacarpal  bone  of  the  thumb. 

(a)  The  Four  Medial  Carpo-metacarpal  Joints 

Class. — Diarthrosis.  Subdivision. — Arthrodia. 

These  joints  exist  between  the  greater  and  lesser  multangular,  capitate,  and 
hamate  bones  above,  and  the  four  medial  metacarpal  bones  below.  The  liga- 
ments which  unite  them  are,  dorsal,  volar,  and  interosseous. 

The  dorsal  ligaments  (fig.  303). — Three  dorsal  ligaments  pass  to  the  second  metacarpal 
bone:  one  from  each  of  the  carpal  bones  with  which  it  articulates,  viz.,  the  greater  and  lesser 
multangular,  and  capitate.  Two  dorsal  bands  pass  from  the  capitate  to  the  third  metacarpal 
bone.  Two  dorsal  bands  pass  to  the  fourth  bone:  viz.,  one  from  the  hamate,  and  another  from 
the  capitate;  the  latter  is  sometimes  wanting.  The  fifth  bone  has  only  one  band  passing  to  it 
from  the  hamate. 

The  volar  ligaments  (fig.  300). — One  strong  band  passes  from  the  second  metacarpal  bone 
to  the  greater  multangular  medial  to  the  ridge  for  the  transverse  carpal  ligament;  it  is  covered 
by  the  sheath  of  the  flexor  carpi  radialis. 

Three  bands  pass  from  the  third  metacarpal:  one  laterally  to  the  greater  multangular,  a 
middle  one  upward  to  the  capitate,  and  a  third  medially  over  the  fourth  to  reach  the  fifth  meta- 
carpal and  the  hamate  bones. 

One  ligament  connects  the  fourth  bone  to  the  hamate. 

One  ligament  connects  the  fifth  bone  to  the  hamate,  the  fibres  extending  medially,  and  con- 
necting the  dorsal  and  volar  ligaments.  The  ligament  to  the  fifth  bone  is  strengthened  in  front 
by  the  prolonged  fibres  of  the  flexor  carpi  ulnaris  and  the  strong  medial  sUp  of  the  ligament  of 
the  third  metacarpal  bone;  and  posteriorly,  by  the  tendon  of  the  extensor  carpi  ulnaris. 

The  interosseous  ligament  (fig.  304)  is  Hmited  to  one  part  of  the  articulation,  and  consists 
of  short  fibres  connecting  the  contiguous  angles  of  the  hamate  and  capitate  with  the  third  and 
fourth  metacarpal  bones  toward  their  volar  aspect.  There  is,  however,  a  thick  strong  ligament 
connecting  the  edge  of  the  greater  multangular  with  the  lateral  border  of  the  base  of  the  second 
metacarpal  bone;  it  helps  to  separate  the  carpo-metacarpal  joint  of  the  thumb  from  the  common 
carpo-metacarpal  joint,  and  to  close  in  the  radial  side  of  the  latter  joint. 

The  synovial  membrane  is  a  continuation  of  the  medio-carpal  joint;  occasionally  there  is 
a  separate  membrane  between  the  hamate  and  fourth  and  fifth  metacarpal  bones  (fig.  304) ; 
while  that  between  the  fourth  and  capitate  is  lined  by  the  synovial  sac  of  the  common  joint. 

The  arteries  to  the  four  medial  carpo-metacarpal  joints  are  as  follows: — 

(1)  For  the  index  finger:  twigs  are  supphed  by  the  trunk  of  the  radial  on  the  dorsal  and  volar 
aspects,  and  by  the  dorsal  and  volar  metacarpal  branches. 

(2)  For  the  middle  finger:  the  first  dorsal  metacarpal  by  the  branch  which  passes  upward 
to  join  the  dorsal  carpal  arch,  and  a  branch  from  the  deep  volar  arch  which  joins  the  volar  carpal 
arch. 

(3)  For  the  ring  finger:  the  deep  volar  arch  and  recurrent  twigs  from  the  second  dorsal 
metacarpal  in  the  same  manner  as  for  the  middle  finger. 

(4)  For  the  little  finger:  the  ulnar  and  its  deep  branch;  also  twigs  from  the  second  dorsal 
metacarpal. 

The  nerves  are  supplied  to  these  joints  by  the  deep  volar  branch  of  the  ulnar,  the  deep  branch 
of  the  radial  (posterior  interosseous),  and  the  median. 

Relations. — In  front  of  the  four  medial  carpo-metacarpal  joints  are  the  flexors  of  the 
fingers  with  their  synovial  sheath.  The  flexor  carpi  radialis  crossing  in  front  of  the  lateral  part 
of  the  joint  and  the  fibres  of  the  oblique  adductor  poUicis  which  spring  from  the  capitate  and 
lesser  multangular  are  also  anterior  relations.  Behind  the  joints  are  the  extensors  of  the  wrist 
and  fingers  with  their  synovial  sheaths  and  the  dorsal  metacarpal  arteries.  At  the  lateral  border 
of  the  joints  between  the  index  and  lesser  multangular  hes  the  radial  artery. 

The  movements  permitted  at  these  joints,  though  slight,  serve  to  increase  those  of  the 
medio-carpal  and  wrist-joints.  The  joint  between  the  fifth  metacarpal  and  the  hamate  bones 
approaches  somewhat  in  shape  and  mobihty  the  first  carpo-metacarpal  joint;  it  has  a  greater 
range  of  flexion  and  extension,  but  its  side  to  side  movement  is  nearly  as  limited  as  that  of  the 
three  other  metacarpal  bones;  the  process  of  the  hamate  bone  hrnits  its  flexion.  Motion  toward 
the  ulnar  side  is  checked  by  the  strong  palmar  band  which  unites  the  base  of  the  fifth  meta- 
carpal to  the  base  of  the  third,  and  the  strong  transverse  ligament  at  the  head  of  the  bones. 
The  mobility  of  the  second,  third,  and  fourth  metacarpal  bones  is  very  limited,  and  consists 
almost  entirely  of  a  slight  gliding  upon  the  carpal  bones,  i.  e.,  flexion  and  extension;  that  of  the 
third  and  fourth  bones  is  extremely  slight,  as  there  is  no  long  flexor  attached  to  either;  but, 


INTERMETACARPAL  JOINTS  273 

owing  to  the  close  connection  of  the  bases  of  the  metacarpal  bones,  the  radial  and  ulnar  flexors 
and  extensors  of  the  carpus  act  on  all  by  their  pull  on  the  particular  bone  into  which  they  are 
inserted. 

Abduction,  or  movement  toward  the  radial  side,  is  prevented  by  the  impaction  of  the  second 
bone  against  the  greater  multangular;  a  little  adduction  is  permitted,  and  is  favoured  by  the 
slope  given  to  the  hamate  and  fifth  metacarpal  bones. 

There  is  also  a  slight  gliding  between  the  fourth  and  fifth  bones,  when  the  concavity  they 
present  toward  the  palm  is  deepened  to  form  the  'cup  of  Diogenes.' 

Muscles  which  act  upon  the  four  medial  carpo-metacarpal  joints  are  the  flexors  and  ex- 
tensors of  the  wrist  and  fingers,  except  the  flexor  carpi  ulnaris. 

(6)  The  Carpo-metacarpal  Joint  of  the  Thumb 

Class. — Diarthrosis.  Subdivision. — Saddle-shaped    Arthrodia. 

The  bones  entering  into  this  joint  are  the  base  of  the  first  metacarpal  and  the 
greater  multangular.  The  first  metacarpal  bone  diverges  from  the  other  four, 
contrasting  very  strongly  with  the  position  of  the  great  toe.  It  is  due  to  this 
divergence  that  the  thumb  is  able  to  be  opposed  to  each  and  all  the  fingers. 
The  ligament  which  unites  the  bones  is  the 

Articular  capsule. 

The  articular  capsule  (figs.  300  and  301)  consists  of  fibres  which  pass  from 
the  margin  of  the  articular  facet  on  the  greater  multangular,  to  the  margin  of 
the  articular  facet  at  the  base  of  the  first  metacarpal  bone. 

The  fibres  are  stronger  on  the  dorsal  than  on  the  palmar  aspect.  They  are  not  tense 
enough  to  hold  the  bones  in  close  contact,  so  that  while  they  restrict  they  do  not  prevent  motion 
in  any  direction.     The  medial  fibres  are  stronger  than  the  lateral. 

The  synovial  membrane  is  lax,  and  distinct  from  the  other  synovial  membranes  of  the 
carpus. 

The  arteries  of  the  carpo-metacarpal  joint  of  the  thumb  are  derived  from  the  trunk  of  the 
radial,  the  first  volar  metacarpal,  and  the  dorsahs  pollicis. 

The  nerves  are  supplied  by  the  branches  of  the  median  to  the  thumb. 

Relations. — Behind  are  the  long  and  short  extensor  tendons  of  the  thumb,  and  behind 
and  laterally  the  tendon  of  the  abductor  pollicis  longus  (extensor  ossis  metacarpi  pollicis). 
The  tendon  of  the  flexor  pollicis  longus  is  in  front  and  fibres  of  the  flexor  pollicis  brevis  and  op- 
ponens  pollicis  muscles  are  also  anterior  relations.  To  the  medial  side  is  the  radial  artery  as 
it  passes  forward  into  the  palm  of  the  hand. 

The  movements  of  this  joint  are  regulated  by  the  shape  of  the  articular  surfaces,  rather 
than  by  the  ligaments,  and  consist  of  flexion,  extension,  abduction,  adduction,  and  circum- 
duction, but  not  rotation.  In  flexion  and  extension  the  metacarpal  bone  slides  to  and  fro  upon 
the  multangular;  in  abduction  and  adduction  it  slides  from  side  to  side  or,  more  correctly,  re- 
volves upon  the  antero-posterior  axis  of  the  joint.  The  power  of  opposing  the  thumb  to  any 
of  the  fingers  is  due  to  the  forward  and  medial  obliquity  of  its  flexion  movement,  which  is  by 
far  its  most  extensive  motion.  Abduction  is  very  free,  while  adduction  is  limited  on  account 
of  the  proximity  of  the  second  metacarpal  bone.  The  movement  of  the  greater  multangular 
upon  the  rest  of  the  carpus  somewhat  increases  the  range  of  all  the  movements  of  the  thumb. 

Muscles  which  act  upon  the  carpo-metacarpal  joint  of  the  thumb. — Flexors. — Flexor 
pollicis  brevis,  flexor  pollicis  longus,  opponens  pollicis.  Extensors. — Extensores  pollicis  brevis 
and  longus  and  abductor  pollicis  longus.  Ahduclors. — Abductores  pollicis  longus  and  brevis. 
Adductors. — The  transverse  and  oblique  adductor  pollicis,  opponens,  fii'st  dorsal  interosseous. 
Muscles  "producing  opposition. — Opponens,  flexor  brevis,  oblique  adductor. 

9.  THE  INTERMETACARPAL  ARTICULATIONS 

Class. — Diarthrosis.        ■  Subdivision. — Arthrodia. 

The  metacarpal  of  the  thumb  is  not  connected  with  any  other  metacarpal 
bone.  The  second,  third,  fourth,  and  fifth  metacarpal  bones  are  in  actual 
contact  at  their  bases,  and  are  held  firmly  together  by  the  following  ligaments 
(in  addition  to  the  articular  capsule) : — 

Dorsal.  Volar. 

Interosseous  hgaments. 

The  dorsal  ligaments  (fig.  302)  are  layers  of  variable  thickness  of  strong,  short  fibres,  which 
pass  transversely  from  bone  to  bone,  filUng  up  the  m-egularities  on  the  dorsal  surfaces. 

The  volar  ligaments  are  transverse  layers  of  hgamentous  tissue  passing  from  bone  to  bone; 
they  cannot  be  well  differentiated  from  the  other  ligaments  and  fibrous  tissue  covering  the  bones. 

The  interosseous  ligaments  (fig.  304)  pass  between  the  apposed  surfaces  of  the  bones,  and 
are  attached  to  the  distal  sides  of  the  articular  facets,  so  as  to  close  in  the  synovial  cavities  on 


274 


THE  ARTICULATIONS 


this  aspect;  where  there  are  two  articular  facets,  the  fibres  extend  upward  between  them  nearly 
as  far  as  their  carpal  facets.     That  between  the  fourth  and  fifth  is  the  weakest. 

The  synovial  membrane  is  prolonged  downward  from  the  common  carpal  sac. 

The  arteries  to  the  intermetacarpal  joints  are  twigs  from  the  volar  and  dorsal  metacarpal 
arteries;  the  twigs  pass  upward  between  the  interosseous  muscles. 

The  nerves  are  derived  from  the  ulnar  and  the  deep  branch  of  radial  (posterior  interosseous). 

The  Union  of  the  Heads  of  the  Metacarpal  Bones 

The  distal  extremities  of  these  bones  are  connected  together  on  their  palmar  aspects  by 
what  is  called  the  transverse  ligament  [lig.  capitulorum].  This  consists  of  three  short  bands 
of  fibrous  tissue,  which  unite  the  second  and  third,  third  and  fourth,  and  the  fourth  and  fifth 
bones.  They  are  rather  more  than  6  mm.  (J  in.)  deep,  and  rather  less  in  width,  and  limit  the 
distance  to  which  the  metacarpal  bones  can  be  separated.  They  are  continuous  above  with  the 
fascia  covering  the  interosseous  muscles;  below,  they  are  connected  with  the  subcutaneous 
tissue  of  the  web  of  the  hand.  They  are  on  a  level  with  the  front  surface  of  the  bones,  and  are 
blended  on  either  side  with  the  edges  of  the  glenoid  hgament  in  front,  with  the  lateral  Ligaments 

Fig.  305. — Anterior  and  Posterior  Views  of  Ligaments  of  the  Fingers. 


Transverse      ligament 
between    the    heads 

■    of     the      metacarpal 

!    bones 

_  Accessory  volar  ligament 
-Collateral  ligament 


Areolar  tissue  . 

capsule 

Collateral  ligament  - 


noid  ligament 
-Collateral  ligament 

-Flexor  tendon 


Areolar  tissue 

capsule 

Collateral  ligament  — ^ 

Extensor  tendon 


-Flexor  tendon 


of  the  metacarpo-phalangeal  joint,  and  also  with  the  sheaths  of  the  tendons.  In  front,  a  lum- 
brical  muscle  passes  with  the  digital  arteries  and  nerves;  while  behind,  the  interossei  muscles 
pass  to  their  insertions. 

10.  THE  METACARPO-PHALANGEAL  JOINTS 
(a)  The  Metacarpo-phalangeal  Joints  of  the  Four  Medial  Fingers 

Class.- — Diarthrosis.  Subdivision. — Condylarihrosis. 

In  these  joints  the  cup-shaped  extremity  of  the  base  of  the  first  phalanx  fits 
on  to  the  rounded  head  of  the  metacarpal  bone,  and  is  united  by  the  following 
ligaments  (in  addition  to  the  articular  capsule) : — 


Collateral. 


Volar  accessory. 


The  volar  accessory  (or  glenoid)  ligament  (fig.  305)  is  a  fibro-cartilaginous  plate  which 
seems  more  intended  to  increase  the  depth  of  the  phalangeal  articular  facet  in  front,  than  to 
unite  the  two  bones.  It  is  much  more  firmly  attached  to  the  margin  of  the  phalanx  than  to  the 
metacarpal  bone,  being  only  loosely  connected  with  the  palmar  surface  of  the  latter  by  some 
loose  areolar  tissue  which  covers  in  the  synovial  membrane,  here  prolonged  some  little  distance 
upon  the  surface  of  the  bone.     At  the  sides,  it  is  connected  with  the  collateral  ligaments  and  the 


METACARPO-PHALANGEAL  JOINTS  275 

transverse  metacarpal  ligament.  It  corresponds  to  the  sesamoid  bones  of  the  thumb;  a  sesa- 
moid bone  sometimes  exists  at  the  medial  border  of  the  joint  of  the  little  finger. 

The  collateral  ligaments  (304  and  305)  are  strong  and  firmly  connect  the  bones  with  one 
another;  each  is  attached  above  to  the  corresponding  tubercle,  and  to  a  depression  in  front 
of  the  tubercle,  of  the  metacarpal  bone.  From  this  point  the  fibres  spread  widely  as  they  de- 
scend on  either  side  of  the  base  of  the  phalanx;  the  anterior  fibres  are  connected  with  the  glenoid 
ligament;  the  posterior  blend  with  the  tendinous  expansion  at  the  back  of  the  joint. 

The  joint  is  covered  in  posteriorly  by  the  expansion  of  the  extensor  tendon,  and  some  loose 
areolar  tissue  passing  from  its  under  surface  to  the  bones  (fig.  305). 

The  synovial  membrane  is  loose  and  capacious,  and  invests  the  inner  surface  of  the  liga- 
ments which  connect  the  bones. 

The  arteries  come  from  the  digital  or  volar  metacarpal  vessels  of  the  deep  arch. 

The  nerves  are  derived  from  the  digital  branches,  or  from  twigs  of  the  branches  of  the  ulnar 
to  the  interosseous  muscles. 

Relations. — I.  The  metacarpo-phalangeal  joints  of  the  middle  three  digits.  In  front, 
the  tendons  of  the  flexor  profundus  and  flexor  subhmis  digitorum.  On  the  radial  side,  a  lum- 
brical,  an  interosseous  muscle,  and  digital  nerves  and  vessels;  on  the  ulnar  side,  an  interosseous 
muscle  and  digital  vessels  and  nerves.  Behind,  the  common  extensor  tendon  and  in  the  case 
of  the  index  digit  the  tendon  of  the  extensor  indicis. 

II.  The  metacarpo-phalangeal  joint  of  the  little  finger.  In  front,  the  flexor  quinti  digiti 
brevis  and  the  tendons  of  the  flexor  profundus  and  subhmis  digitorum  muscle  which  go  to 
this  digit.  Behind,  the  extensor  digiti  quinti  to  a  slip  of  the  extensor  digitorum  communis 
sometimes.  On  the  radial  side,  a  lumbrical,  the  third  palmar  interosseous  muscle,  digital  ves- 
sels and  nerves.     On  the  ulnar  side,  digital  vessels  and  nerves. 

The  movements  permitted  at  these  joints  are  flexion,  extension,  abduction,  adduction,  and 
circumduction.  Flexion  is  the  most  free  of  all  and  may  be  continued  until  the  phak  nx  is  at 
a  right  angle  with  the  metacarpal  bone.  It  is  on  this  account  that  the  articular  surface  of  the 
head  of  the  bone  is  prolonged  so  much  further  on  the  palmar  aspect,  and  that  the  synovial 
membrane  is  here  so  loose  and  ample.  Extension  is  the  most  limited  of  the  movements,  and  can 
only  be  carried  to  a  little  beyond  the  straight  line.  Abduction  and  adduction  are  fairlj'  free, 
but  not  so  free  as  flexion.  Flexion  is  associated  with  adduction,  and  extension  with  abduction. 
This  may  be  proved  by  opening  the  hand,  when  the  fingers  involuntarily  separate  as  they 
extend,  while  in  closing  the  fist  they  come  together  again.  The  free  abduction,  adduction,  and 
circumduction  which  are  permitted  at  these  joints  are  due  to  the  fact  that  the  long  axes  of  the 
articular  facets  are  at  right  angles  to  one  another. 

Muscles  acting  on  the  middle  three  digits. — Flexors. — Flexor  digitorum  profundus,  flexor 
digitorum  sublimis.  Extensors. — Extensor  digitorum  communis  and  on  the  index  digit  the 
extensor  indicis.     Abductors. — Dorsal  interossei.     Adductors. — Volar  interossei. 

Muscles  acting  on  the  metacarpo-phalangeal  joint  of  the  little  finger. — Flexors. — Flexor 
quinti  digiti  brevis,  flexor  digitorum  sublimis,  flexor  digitorum  profundus.  Extensors. — Exten- 
sor digitorum  communis,  extensor  quinti  digiti.  Abductor. — Abductor  quinti  digiti.  Adductor. 
— Third  volar  interosseous. 

(6)  The  Metacarpo-phalangeal  Joint  of  the  Thumb 
Class. — Diarthrosis.  Subdivision. — Condylarthrosis. 

The  head  of  the  metacarpal  bone  of  the  thumb  differs  considerably  from  the 
corresponding  ends  of  the  metacarpal  bones  of  the  fingers.  It  is  less  convex,  wider 
from  side  to  side,  the  palmar  edge  of  the  articular  surface  is  raised  and  irregular, 
and  here  on  either  side  of  the  median  line  are  the  two  facets  for  the  sesamoid 
bones.  The  base  of  the  first  phalanx  of  the  thumb,  too,  is  more  like  the  base  of 
the  second  phalanx  of  one  of  the  other  fingers.     The  ligaments  are : — 

Collateral.  Dorsal. 

Articular  capsule. 

The  collateral  ligaments  are  short,  strong  bands  of  fibres,  which  radiate  from  depressions 
on  either  side  of  the  head  of  the  metacarpal  bone  to  the  base  of  the  first  phalan.x  and  sesamoid 
bones.  As  they  descend  they  pass  a  little  forward,  so  that  the  gi'eater  number  are  inserted  in" 
front  of  the  centre  of  motion. 

The  dorsal  ligament  consists  of  scattered  fibres  which  pass  across  the  joint  from  one  col- 
lateral Ugament  to  the  other,  completing  the  articular  capsule  and  protecting  the  synovial  sac. 

The  sesamoid  bones  are  two  in  number,  situated  on  either  side  of  the  middle  fine,  and  con- 
nected together  by  strong  transverse  fibres  which  form  the  floor  of  the  groove  for  the  long 
flexor  tendon;  they  are  connected  with  the  base  of  the  phalanx  and  head  of  the  metacarpal  bone 
by  strong  fibres.  Anteriorly  they  give  attachment  to  the  short  muscles  of  the  thumb,  and  pos- 
teriorly are  smooth  for  the  purpose  of  gliding  over  the  facets.  The  collateral  ligaments  are  partly 
inserted  into  their  sides. 

The  arteries  and  nerves  come  from  the  digital  branches  of  the  thumb. 

Relations. — Of  the  metacarpo-phalangeal  joint  of  the  thumb:  In  front  and  externally 
abductor  poUicis  brevis  and  superficial  head  of  flexor  poUicis  brevis.  In  front  and  medially 
oblique  and  transverse  adductors  and  deep  head  of  flexor  poUicis  brevis.  Directly  in  front 
flexor  pollicis  longus  and  terminal  branches  of  first  volar  metacarpal  artery.  Behind,  extensor 
pollicis  brevis  and  longus  tendons.  On  either  side,  the  dorsal  digital  vessels  and  the  digital 
nerves. 


276  THE  ARTICULATIONS 

The  movements  are  chiefly  flexion  and  extension,  very  little  side  to  side  movement  being 
permitted,  and  that  only  when  the  joint  is  slightly  bent.  Thus  this  joint  more  nearly  approaches 
the  simple  hinge  character  than  the  corresponding  articulations  of  the  fingers.  The  thumb 
gets  its  freedom  of  motion  at  the  carpo-metacarpal  joint;  the  fingers  get  theirs  at  the  meta- 
carpo-phalangeal,  but  they  are  not  endowed  with  so  much  freedom  as  the  thumb  enjoys. 

Muscles  which  act  upon  the  metacarpo-phalangeal  joint  of  the  thumb. — Flexors. — Flexor 
poUicis  brevis,  flexor  pollicis  longus.  Extensors. — Extensor  poUicis  brevis,  extensor  pollicis 
longus. 

11.  THE  INTERPHALANGEAL  ARTICULATIONS 

Class. — Diarthrosis.  Subdivision. — Ginglymus . 

The  ligaments  which  unite  the  phalanges  of  the  thumb  and  of  the  fingers  are 
(in  addition  to  the  articular  capsule) : — 

Accessory  volar.  Collateral. 

The  accessory  volar  (or  glenoid)  ligament  (fig.  305),  sometimes  called  the  sesamoid  body, 
is  very  firmly  connected  with  the  base  of  the  distal  bone,  and  loosely,  by  means  of  fibro-areolar 
tissue,  with  the  head  of  the  proximal  one.  It  blends  with  the  collateral  ligaments  at  the  sides, 
and  over  it  pass  the  flexor  tendons.  Occasionally  a  sesamoid  bone  is  developed  in  the  cartilage 
of  the  interphalangeal  joint  of  the  thumb. 

The  collateral  ligaments  (figs.  304  and  305)  are  strong  bands  which  are  attached  to  the  rough 
depressions  on  the  sides  of  the  upper  phalanx,  and  to  the  projecting  margins  of  the  lower  phalanx 
of  each  joint.  They  are  tense  in  every  position,  and  entirely  prevent  any  side  to  side  motion; 
they  are  connected  posteriorly  with  the  expansion  of  the  extensor  tendon. 

Dorsally  (fig.  305)  the  joint  is  covered  in  by  the  deep  surface  of  the  extensor  tendon,  and  a 
little  fibro-areolar  tissue  extends  from  the  tendon,  and  thickens  the  posterior  portion  of  the 
synovial  sac,  completing  the  articular  capsule. 

The  synovial  membrane  is  loose  and  ample,  and  extends  upward  a  little  way  along  the  shaft 
of  the  pro.ximal  bone. 

The  arteries  and  nerves  come  from  their  respective  digital  branches. 

The  relations  of  the  interphalangeal  joints  are  the  flexor  and  extensor  tendons  and  the 
digital  vessels  and  nerves. 

The  movements  are  limited  to  flexion  and  extension.  Flexion  is  more  free,  and  can  be 
continued  till  one  bone  is  at  a  right  angle  to  the  other,  and  is  most  free  at  the  junction  of  the 
first  and  second  bones;  the  second  phalanx  can  be  flexed  on  the  first  through  110°  to  115°  when 
the  latter  is  not  flexed.  The  greater  freedom  of  flexion  is  due  to  the  greater  extent  of  the  articu- 
lar surface  in  front  of  the  heads  of  the  proximal  bones,  and  to  the  direction  of  the  flbres  of  the 
collateral  hgaments,  which  pass  a  little  forward  to  their  insertion  into  the  distal  bone. 

The  muscles  which  act  upon  the  interphalangeal  joints  are  the  extensors  and  flexors  of 
the  digits. 

THE  ARTICULATIONS  OF  THE  LOWER  LIMB 

The  articulations  of  the  lower  limb  are  the  following : — 

1.  The  hip-joint. 

2.  The  knee-joint. 

3.  The  tibio-fibular  union. 

4.  The  ankle-joint. 

5.  The  tarsal  joints. 

6.  The  tarso -metatarsal  joints. 

7.  The  intermetatarsal  joints. 

8.  The  metatarso-phalangeal  joints. 

9.  The  interphalangeal  joints. 

1.  THE  HIP-JOINT 
Class. — Diarthrosis.  Subdivision. — Enarthrodia. 

The  hip  is  the  most  typical  example  of  a  ball-and-socket  joint  in  the  body,  the 
round  liead  of  the  femur  being  received  into  the  cup-shaped  cavity  of  the  acetab- 
ulum. Both  articular  surfaces  are  coated  with  cartilage,  that  covering  the  head 
of  the  femur  being  thicker  above  where  it  has  to  bear  the  weight  of  the  body,  and 
thinning  out  to  a  mere  edge  below;  the  pit  for  the  ligamentum  teres  is  the  only 
part  uncoated,  but  the  cartilage  is  somewhat  heaped  up  around  its  margin. 
Covering  the  acetabulum,  the  cartilage  is  horseshoe-shaped,  and  thicker  above 
than  below,  being  deficient  over  the  depression  at  the  bottom  of  the  acetabulum, 


THE  HIP-JOINT 


277 


where  a  mass  of  fatty  tissue — the  so-called  synovial  or  Haversian  gland — is 
lodged. 

The  ligaments  of  the  joint  are: — 

Articular  capsule.  Ligamentum  teres. 

Transverse.      .  Glenoid  lip. 

The  articular  capsule  is  one  of  the  strongest  ligaments  in  the  body.  It  is 
large  and  somewhat  loose,  so  that  in  every  position  of  the  body  some  portion  of  it 
is  relaxed.  At  the  pelvis  it  is  attached,  superiorly,  to  the  base  of  the  anterior 
inferior  iliac  spine;  curving  backward,  it  becomes  blended  with  the  deep  surface 
of  the  reflected  tendon  of  the  rectus  Jemoris;  posteriorly,  it  is  attached  a  few 
millimetres  from  the  acetabular  rim ;  and  below,  to  the  upper  edge  of  the  groove 
between  the  acetabulum  and  tuberosity  of  the  ischium.     Thus  it  reaches  the 

Fig.  306. — Anterior  View  of  the  Articitlar  Capsule  op  the  Hip-joint. 


■Tendon  of  rectus  pulled  up 


Tendino-trochanteric  band  passing  between  rectus 
and  vastus  lateralis 

Placed  on  the  weak  spot  of  capsule,  which  is  some- 
times perforated  to  allow  the  bursa  under  psoas  to 
communicate  with  joint 

Ilio-f  emoral  ligament 

■Pubo-capsular  ligament 


transverse  ligament,  being  firmly  blended  with  its  outer  surface,  and  frequently 
sends  fibres  beyond  the  notch  to  blend  with  the  obturator  membrane.  Anteriorly 
it  is  attached  to  the  pubis  near  the  obturator  notch,  to  the  ilio-pectineal  eminence 
and  thence  backward  to  the  base  of  the  inferior  iliac  spine. 

A  thin  strong  stratum  is  given  off  from  its  superficial  aspect  behind;  this  extends  beneath 
the  gluteus  minimus  and  small  rotators,  to  be  attached  above  to  the  dorsum  of  the  ihum  higher 
than  the  reflected  tendon  of  the  rectus,  and  posteriorly  to  the  ilium  and  ischium  nearly  as  far 
as  the  sciatic  notch.  As  this  expansion  passes  over  the  long  tendon  of  the  rectus,  the  tendon 
may  be  described  as  being  in  part  contained  within  the  substance  of  the  capsule. 

At  the  femur,  the  capsule  is  fixed  to  the  anterior  portion  of  the  upper  border 
of  the  great  trochanter  and  to  the  cervical  tubercle.  Thence  it  runs  down, 
the  intertrochanteric  line  as  far  as  the  medial  border  of  the  femur,  where  it  is  on  a  level 
with  the  lower  part  of  the  lesser  trochanter.  It  then  runs  upward  and  backward 
along  an  oblique  line  about  1.6  cm.  (f  in.)  in  front  of  the  lesser  trochanter,  and  con- 
tinues its  ascent  along  the  back  of  the  neck  nearly  parallel  to  the  intertrochanteric 
crest,  and  from  12  to  16  mm.  (|  to  f  in.)  above  it;  finally,  it  passes  along  the  medial 
side  of  the  trochanteric  fossa  to  reach  the  anterior  superior  angle  of  the  great 
trochanter. 


278 


THE  ARTICULATIONS 


On  laying  open  the  capsule,  some  of  the  deeper  fibres  are  seen  reflected  upward  along  the 
neck  of  the  femur,  to  be  attached  much  nearer  the  head:  these  are  the  retinacula.  One  corre- 
sponds to  the  upper,  and  another  to  the  lower,  part  of  the  intertrochanteric  line;  a  third  is  seen 
at  the  upper  and  back  part  of  the  neck.     They  form  flat  bands,which  lie  on  the  femoral  neck. 

Superadded  to  the  capsule,  and  considerably  strengthening  it,  are  three  auxil- 
iary bands,  whose  fibres  are  intimately  blended  with,  and  in  fact  form  part  of, 
the  capsule,  viz.,  the  ilio-femoral,  ischio-capsular,  and  pubo-capsular  ligaments. 

The  ilio-femoral  ligament  (fig.  306)  is  the  longest,  widest,  and  strongest  of  the  bands. 
It  is  of  triangular  shape,  with  the  apex  attached  above  to  a  curved  line  on  the  iUum  immediately 
below  and  behind  the  anterior  inferior  spine,  and  its  base  below  to  the  anterior  edge  of  the 
greater  trochanter  and  to  the  spiral  line  as  far  as  the  medial  border  of  the  shaft.  The  highest  or 
most  lateral  fibres  are  coarse,  almost  straight,  and  shorter  than  the  rest;  the  most  medial  fibres 
are  also  thick  and  strong,  but  obhque.  This  varying  obliquity  of  the  fibres,  and  their  accumula- 
tion at  the  borders,  explain  why  this  band  has  been  described  as  the  Y-shaped  ligament;  but  it 

Fig.  307. — Upper  Extremity  of  the  Femur  (Anterior  View),  to  snow  the  Relation 
OP  THE  Articular  Capsule  op  the  Hip-joint  (in  red)  to  the  Epiphysial  Lines. 


should  be  noted  that  the  Y  is  inverted.  About  the  centre  of  its  base,  near  the  femoral  attach- 
ment, is  an  aperture  transmitting  an  articular  twig  from  the  ascending  branch  of  the  external 
circumflex  artery. 

The  ischio-capsular  ligament  (fig.  308)  is  formed  of  very  strong  fibres  attached  all  along 
the  upper  border  of  the  groove  for  the  external  obturator,  and  to  the  ischial  margin  of  the  ace- 
tabulum above  the  groove.  The  highest  of  these  incline  a  little  upward  as  they  pass  laterally 
to  be  fixed  to  the  greater  trochanter  in  front  of  the  insertion  of  the  piriformis  tendon,  while  the 
other  fibres  curve  more  and  more  upward  as  they  pass  laterally  to  their  insertion  at  the  inner 
side  of  the  trochanteric  fossa,  blending  with  the  insertion  of  the  external  rotator  tendons.  When 
the  joint  is  in  flexion,  these  fibres  pass  in  nearly  straight  lines  to  their  femoral  attachment,  and 
spread  out  uniformly  over  the  head  of  the  femur;  but  in  extension  they  wind  over  the  back  of 
the  femur  in  a  zonular  manner  [zona  orbicularis],  embracing  the  posterior  aspect  of  the  neck 
of  the  femur. 

The  pubo-capsular  (pectineo-femoral)  band  (fig.  306)  is  a  distinct  but  narrow  set  of  fibres 
which  are  individually  less  marked  than  the  fibres  of  the  other  two  bands;  they  are  fixed  above 
to  the  obturator  crest  and  to  the  anterior  border  of  the  iUo-pectineal  eminence,  reaching  as  far 
down  as  the  pubic  end  of  the  acetabular  notch.  Below,  they  reach  the  neck  of  the  femur,  and 
are  fixed  above  and  behind  the  lowermost  fibres  of  the  iho-femoral  band,  with  which  they  blend. 


THE  HIP'JOINT 


279 


In  thickness  and  strength  the  capsule  varies  greatly;  thus,  if  two  lines  be 
drawn,  one  from  the  anterior  inferior  spine  to  the  medial  border  of  the  femur  near 
the  lesser  trochanter,  and  the  other  from  the  anterior  part  of  the  groove  for  the 

Fig.  308. — Posterior  View  of  the  Articular  Capsule  of  the  Hip-joint. 


The  reflected  tendon  of  the 
rectus  and  the  triangular  ilio- 
trochanteric '  band 


Ischio-capsular  ligament 
This  is  placed  on  the  weak  portion 
of  the  capsule 


Fig.  309. — Section   through   the   Hip-joint,   showing  the   Glenoid  Lip,    Ligamentum 
Teres,  and  Retinacula. 


Ligamentum  teres. 
The  upper  line  is 
placed  on  the  fem- 
oral, the  lower  on 
the  ischial,  attach- 
ment 


Articular  capsule 
Reflected  fibres  of 
capsule       (retin- 
acula) 


Reflected  fibres 
of  capsule 


external  obturator  to  the  trochanteric  fossa,  all  the  ligament  between  these  lines 
on  the  lateral  and  upper  aspects  of  the  joint  is  very  thick  and  strong,  while  that 
below  and  to  the  medial  side,  except  at  the  narrow  pubo-capsular  ligament,  is 


280 


THE  ARTICULATIONS 


thin  and  weak,  so  that  the  head  of  the  bone  can  be  seen  through  it.  The  capsule 
is  thickest  in  the  course  of  the  iho-femoral  ligament,  toward  the  lateral  part  of 
which  it  measures  over  6  mm.  (J  in.).  Between  the  ilio-femoral  and  ischio-cap- 
sular  ligaments  the  capsule  is  very  strong,  and  with  it  here,  near  the  acetabulum, 
is  incorporated  the  reflected  tendon  of  the  rectus,  and  here  also  a  triangular  band 
of  fibres  runs  downward  and  forward  to  be  attached  by  a  narrow  insertion  to 
the  ridge  on  the  front  border  of  the  greater  trochanter  near  the  gluteus  minimus 
(the  ilio-trochanteric  band)  (fig.  308). 

The  capsule  is  strengthened  also  at  this  point  by  a  strong  band  from  the  under  surface  of 
the  gluteus  minimus,  and  by  the  tendino-trochanteric  band  which  passes  down  from  the  reflected 
tendon  of  the  rectus  to  the  vastus  lateralis  (externus)  (fig.  306).  This  is  closely  blended  with 
the  capsule  near  the  lateral  edge  of  the  ilio-femoral  Ugament. 

The  thinnest  part  of  the  capsule  is  between  the  pubo-capsular  and  ilio-femoral 
ligaments;  this  is  sometimes  perforated,  allowing  the  bursa  under  the  psoas  to 
communicate  with  the  joint.  The  capsule  is  also  very  thin  at  its  attachment  to 
the  back  of  the  femoral  neck,  and  again  opposite  the  acetabular  notch. 


Pig.  310.- 


-Hip-joint  after  Dividing  the  Aeticulab  Capsule  and  Disarticulating  the 
Femur. 


Articular  capsule,  cut 
Glenoid  lip 


Articular  capsule 


Ligamentum  teres 
Articular  capsule 


The  ligamentum  teres  (figs.  309  and  310)  is  an  interarticular  flat  band  which 
extends  from  the  acetabular  fossa  to  the  head  of  the  femur,  and  is  usually  about 
3.7  cm.  (1|  in.)  long.  It  has  two  bony  attachments,  one  on  either  side  of  the 
acetabular  notch  immediately  below  the  articular  cartilage,  while  intermediate 
fibres  spring  from  the  lower  surface  of  the  transverse  ligament.  The  ischial 
portion  is  the  stronger,  and  has  several  of  its  fibres  arising  outside  the  cavity, 
below  and  in  connection  with  the  origin  of  the  transverse  ligament,  where  it  is 
also  continuous  with  the  capsule  and  periosteum  of  the  ischium.  At  the  femur 
it  is  fixed  to  the  front  part  of  the  depression  on  the  head,  and  to  the  cartilage  round 
the  margin  of  the  depression. 

It  is  covered  by  a  prolongation  of  synovial  membrane,  which  also  covers  the  cushion  of  fat 
in  the  recess  of  the  acetabulum;  the  portion  of  the  membrane  reflected  over  the  fatty  tissue  does 
not  cling  closely  to  the  round  hgament,  but  forms  a  triangular  fold,  the  apex  of  which  is  at  the 
femur. 

The  transverse  ligament  (fig.  311)  passes  across  the  acetabular  notch  and 
converts  it  into  a  foramen;  it  supports  part  of  the  glenoid  fibro-cartilage,  and  is 
connected  with  the  ligamentum  teres  and  the  capsule.  It  is  composed  of  decus- 
sating fibres,  which  arise  from  the  margin  of  the  acetabulum  on  either  side  of 
the  notch,  those  coming  from  the  pubis  being  more  superficial,  and  passing  to  form 


THE  HIP-JOINT 


281 


the  deep  part  of  the  ligament  at  the  ischium,  while  those  superficial  at  the  ischium 
are  deep  at  the  pubis.     It  thus  completes  the  rim  of  the  acetabulum. 

The  glenoid  lip  (cotyloid  fibro-cartilage)  (figs.  309  and  310)  is  a  yellowish- 
white  structure,  which  deepens  the  acetabulum  by  surmounting  its  margin.     It 


Fig.  311.- 


-PoETiONS  OP   Ischium  and    Pubis,  showing  the  Acetabular  Notch  and  the 

LiGAMENTUM   TeBES   ATTACHED    OUTSIDE    THE    ACETABULUM. 


Transverse  ligament 


^>^^^ 


Transverse  ligament 


Ligamentum  teres  at- 
tached to  ischium  out- 
side the  acetabulum 


varies  in  strength  and  thickness,  but  is  stronger  at  its  iliac  and  ischial  portions 
than  elsewhere.  Its  base  is  broad  and  fixed  to  the  bony  rim  as  well  as  to  the 
articular  cartilage  of  the  acetabulum  on  the  inner,  and  the  periosteum  on  the 
outer,  side  of  it,  and  blends  inseparably  with  the  transverse  ligament  which 
supports  it  over  the  acetabular  notch. 

Fig.  312. — The  Uppek  Extremity  op  the  Femur  (Posterior  View),  to  show  the  Rela- 
tion OP  the  Articular  Capsule  op  the  Hip-joint  (in  red)  to  the  Epiphysial  Lines. 


Its  free  margin  is  thin;  on  section  it  is  somewhat  lunated,  having  its  outer  surface  convex  and 
its  articular  face  concave  and  very  smooth  in  adaptation  to  the  head  of  the  bone,  which  it 
tightly  embraces  a  little  beyond  its  greatest  circumference.  It  somewhat  contracts  the  aper- 
ture of  the  acetabulum,  and  retains  the  head  of  the  femur  within  its  grasp  after  division  of  the 
muscles  and  capsular  hgament.     It  is  covered  on  both  aspects  by  synovial  membrane. 


282 


THE  ARTICULATIONS 


The  synovial  membrane  lines  the  capsule  and  both  surfaces  of  the  glenoid 
lip,  and  passes  over  the  border  of  the  acetabulum  to  reach  and  cover  the  fatty 
cushion  it  contains.  The  part  covering  the  fatty  cushion  is  unusually  thick,  and 
is  attached  round  the  edges  of  the  rough  bony  surface  on  which  the  cushion  rests. 
The  membrane  is  loosely  reflected  off  this  on  to  the  ligamentum  teres,  along 
which  it  is  prolonged  to  the  head  of  the  femur;  thus  the  fibres  of  the  round  liga- 
ment are  shut  out  from  the  joint  cavity.  From  the  capsule  the  synovial  mem- 
brane is  also  reflected  below  on  to  the  neck  of  the  femur,  whence  it  passes  over 
the  retinacula  to  the  margin  of  the  articular  cartilage.  A  fold  of  synovial  mem- 
brane on  the  under  aspect  of  the  neck  often  conveys  to  the  head  of  the  femur  a 
branch  of  an  artery — generally  a  branch  of  the  medial  circumflex. 

The  arterial  supply  comes  from — (a)  the  transverse  branches  of  the  medial  and  lateral 
circumflex  arteries;  (6)  the  lateral  branch  of  the  obturator  sends  a  branch  through  the  acetabular 
notch  beneath  the  transverse  ligament,  which  ramifies  in  the  fat  at  the  bottom  of  the  ace- 
tabulum, and  travels  down  the  round  ligament  to  the  head  of  the  femur;  (c)  the  inferior  branch  of 
the  deep  division  of  the  superior  gluteal;  and  (d)  the  inferior  gluteal  (sciatic)  arteries.  The 
branch  from  the  obturator  to  the  ligamentum  teres  is  sometimes  very  large  when  the  branch 
from  the  medial  circumflex  does  not  also  supply  the  hgament. 

The  superior  and  inferior  gluteal  send  several  branches  through  the  innominate  attachment 

Fig.  313. — ^Ligamentum  Teres,  lax  in  Flexion. 


of  the  articular  capsule:  these  anastomose  freely  beneath  the  capsule  around  the  outer  aspect 
of  the  acetabulum,  and  supply  some  branches  to  enter  the  bone,  and  others  which  enter  the 
substance  of  the  glenoid  lip.  There  is  quite  an  arterial  crescent  upon  the  posterior  and  postero- 
superior  portions  of  the  acetabulum;  but  no  vessels  are  to  be  seen  on  the  inner  aspect  of  the 
glenoid  lip. 

The  nerve-supply  comes  from — (a)  femoral  (anterior  crural),  (6)  anterior  division  of  the 
obtm-ator,  (c)  the  accessory  obturator,  and  (d)  the  sacral  plexus,  by  a  twig  from  the  nerve  to 
the  quadratus  femoris,  or  from  the  upper  part  of  the  great  sciatic,  or  from  the  lower  part  of  the 
sacral  plexus. 

Relations. — In  front  and  in  contact  with  the  capsule  are  the  psoas  bursa,  the  tendinous 
part  of  the  psoas  magnus,  and  the  Uiacus.  StiU  more  anteriorly  and  not  in  contact  are  the 
femoral  artery,  the  femoral  (anterior  crural)  nerve,  the  rectus  femoris,  the  sartorius,  and  the 
tensor  fasciae  latse. 

Above  and  in  close  relation  with  the  capsule  are  the  piriformis,  the  obturator  internus  and 
the  gemelli,  and  the  reflected  head  of  the  rectus  femoris,  whilst  more  superficially  lie  the  gluteus 
minimus  and  medius. 

Behind  and  in  close  relation  with  the  capsule  are  the  obturator  externus,  the  gemeUi  and 
obturator  internus,  and  the  piriformis.  More  superficially  he  the  quadratus  femoris,  the  sciatic 
nerves,  and  the  gluteus  maximus. 

Below  the  obturator  externus,  the  pectineus,  and  the  medial  circumflex  artery  are  in  close 
relation  with  the  capsule. 

The  movements. — The  hip-joint,  like  the  shoulder,  is  a  ball-and-socket  joint,  but  with  a 
much  more  complete  socket  and  a  corresponding  limitation  of  movement.  Each  variety  of 
movement  is  permitted,  viz.,  flexion,  extension,  abduction,  adduction,  circumduction,  and  rota- 
tion; and  any  two  or  more  of  these  movements  not  being  antagonistic  can  be  combined,  i.  e., 
flexion  or  extension  associated  with  abduction  or  adduction  can  be  combined  with  rotation  in 
or  out. 


THE  HIP-JOINT 


283 


It  results  from  the  obliquity  of  tne  neck  of  the  femur  that  the  movements  of  the  head  in 
the  acetabulum  are  always  more  or  less  of  a  rotatory  character.  This  is  more  especially  the  case 
during  flexion  and  extension,  and  two  results  follow  from  it.  First,  the  bearing  surfaces  of  the 
femur  and  acetabulum  preserve  their  apposition  to  each  other,  so  that  the  amount  of  articular 
surface  of  the  head  in  the  acetabulum  does  not  sensibly  diminish  pari  passu  with  the  transit  of 
the  joint  from  the  extended  to  the  flexed  position,  as  would  necessarily  be  the  case  if  the  move- 
ment of  the  femoral  head,  like  that  of  the  thigh  itself,  was  simply  angular,  instead  of  rotatory 
and  angular.  Secondly,  as  rotation  of  the  head  can  continue  until  the  ligaments  are  tight  with- 
out being  checked  by  contact  of  the  neck  of  the  thigh  bone  with  the  rim  of  the  acetabulum, 
flexion  of  the  thigh  so  far  as  the  joint  is  concerned  is  practically  unlimited.  Flexion  is  the  most 
important,  most  frequent,  and  most  extensive  movement,  and  in  the  dissected  limb,  before  the 
ligaments  are  disturbed,  can  be  carried  to  160°,  and  is  then  checked  by  the  lower  fibres  of  the 
ischio-capsular  ligament.  In  the  living  subject  simple  flexion  can  continue  until  checked  by  the 
contact  of  the  soft  parts  at  the  groin,  if  the  knee  be  bent;  if  the  knee  be  straight,  flexion  of  the 
hip  is  checked  in  most  persons  by  the  hamstring  muscles  at  nearly  a  right  angle.  This  is  very 
evident  on  trying  to  touch  the  ground  with  the  fingers  without  bending  the  knees,  the  chief  strain 
being  felt  at  the  popliteal  space.  This  is  due  to  the  shortness  of  the]  hamstrings.  Extension 
is  limited  by  the  ilio-femoral  ligament. 

Fig.  314. — ^Ligamentum  Teres,  vekt  lax  in   Complete  Extension. 


Abduction  and  lateral  rotation  can  be  performed  freely  in  every  position  of  flexion  and 
extension — abduction  being  limited  by  the  pubo-capsular  hgament;  lateral  rotation  by  the 
ilio-femoral  Ugament,  especially  its  medial  portion,  during  extension;  but  by  the  lateral  portion, 
as  well  as  by  the  ligamentum  teres,  during  flexion. 

Adduction  is  very  limited  in  the  extended  thigh  on  account  of  the  contact  with  the  opposite 
limb.  In  the  slightly  flexed  position  adduction  is  more  free  than  in  extension,  and  is  then  limited 
by  the  lateral  fibres  of  the  ilio-femoral  band  and  the  superior  portion  of  the  capsule.  In  flexion 
the  range  is  still  greater,  and  limited  by  the  ischio-capsular  hgament,  the  hgamentum  teres  being 
also  rendered  nearly  tight.  Medial  rotation  in  the  extended  position  is  limited  by  the  lower 
fibres  of  the  ilio-femoral  ligament;  and  in  flexion  by  the  ischio-capsular  ligament  and  the  portion 
of  the  capsule  between  it  and  the  ilio-femoral  band. 

The  ilio-femoral  band  also  prevents  the  tendency  of  the  trunk  to  roU  backward  on  the  thigh 
bones  in  the  erect  posture,  and  so  does  away  with  the  necessity  for  muscular  power  for  this  pur- 
pose; it  is  put  on  stretch  in  the  stand-at-ease  position. 

The  ligamentum  teres  is  of  little  use  in  resisting  violence  or  in  imparting  strength  to  the 
joint.  It  assists  in  checking  lateral  rotation,  and  adduction  during  flexion.  A  ligament  can 
only  be  of  use  when  it  is  tight,  and  it  was  found  by  trephining  the  bottom  of  the  acetabulum, 
removing  the  fat,  and  threading  a  piece  of  whipcord  round  the  ligament,  that  the  ligament  was 
slack  in  simple  flexion,  and  very  loose  in  complete  extension,  but  that  its  most  slack  condition 
was  in  abduction.  It  is  tightest  in  flexion  combined  with  adduction  and  lateral  rotation  and 
almost  as  tight  in  flexion  with  lateral  rotation  alone,  and  in  flexion  with  adduction  alone  (flgs. 
313-315). 

Muscles  which  act  upon  the  hip-joint. — Flexors. — The  psoas  and  iliacus,  the  rectus  femoris, 
the  pectineus,  the  adductors,  the  sartorius,  the  tensor  fasciae  latse,  and  the  gluteus  medius. 


284 


THE  ARTICULATIONS 


Fig.  315. — Ligamentum    Teres,    drawn    Tight   in   I'lexion   Combined     with   Lateral 
Rotation  and  Adduction. 


Extensors. — The  gluteus  maximus,  the  posterior  fibres  of  the  glutei  medius  and  miQimus,  the 
biceps,  the  semitendinosus,  the  semimembranosus,  and  the  ischial  fibres  of  the  adductor  magnus; 
also  (slightly)  the  piriformis,  obturator  internusand  gemelli.  Abductors. — Gluteus  maximus 
(upper  fibres),  tensor  fasciae  latae,  gluteus  medius,  gluteus  minimus,  and,  when  the  joint  is 
flexed,  the  pii-iformis,  obturator  internus,  the  gemelli,  and  the  sartorius  also  become  abductors. 
Adductors. — Adduotores  magnus,  longus,  brevis,  and  minimus,  semitendinosus,  biceps^  the 
gracilis,  the  peotineus,  the  quadratus  femoris,  and  the  lower  fibres  of  the  gluteus  maxunus. 
Medial  rotators. — Psoas  (slightly),  adductor  magnus,  semimembranosus,  the  anterior  fibres 
of  the  gluteus  medius  and  minimus,  and  the  tensor  fascise  latae.  Lateral  rotators. — Gluteus 
maximus,  posterior  fibres  of  gluteus  medius  and  minimus,  the  adductors,  obturator  extemus, 
quadratus  femoris,  obturator  internus,  the  gemelli,  and  the  piriformis  when  the  joint  is  extended. 


2.  THE  KNEE-JOINT 


Class. — Diarthrosis. 


Subdivision. — Ginglymus. 


The  knee  is  the  largest  joint  in  the  body.  It  is  rightly  described  as  a  gingly- 
moid  joint,  but  there  is  also  an  arthrodial  element;  for,  in  addition  to  flexion  and 
extension,  there  is  a  sliding  backward  and  forward  of  the  tibia  upon  the  femoral 
condyles,  as  well  as  slight  rotation  round  a  vertical  axis.  It  is  one  of  the  most 
superficial,  and,  as  far  as  adaptation  of  the  bony  surfaces  goes,  one  of  the  weakest 
joints,  for  in  no  position  are  the  bones  in  more  than  partial  contact.  Its  strength 
lies  in  the  number,  size,  and  arrangement  of  the  ligaments,  and  the  powerful 
muscles  and  fascial  expansions  which  pass  over  the  articulation  and  enable  it  to 
withstand  the  leverage  of  the  two  longest  bones  in  the  bodj\  It  may  be  said'to 
consist  of  two  articulations  with  a  common  synovial  membrane — the  patello- 
femoral  and  the  tibio-femoral,  the  latter  being  double.  It  is  composed  of  the 
condyles  and  trochlear  surface  of  the  femur,  the  condyles  of  the  tibia,  and  the 
patella,  united  by  the  following  ligaments,  which  may  be  divided  into  an  external 
and  internal  set: — 


External 

(1)  Fibrous  expansion  of  the  extensors. 

(2)  Articular  capsule. 

(3)  Oblique  popliteal  ligament. 

(4)  Fibular  collateral. 

(5)  Tibial  collateral. 

(6)  Ligamentum  patellae 


Internal 

(1)  Anterior  crucial. 

(2)  Posterior  crucial. 

(3)  Medial  meniscus. 

(4)  Lateral  meniscus. 

(5)  Coronary. 

(6)  Transverse. 


THE  KNEE-JOINT 


285 


External  Ligaments 

Superficial  to  the  fibrous  expansion  of  the  quadriceps  extensor  tendons  the 
fascia  lata  of  the  thigh  covers  the  front  and  sides  of  the  knee-joint. 

The  deep  fascia  of  the  thigh,  as  it  descends  to  its  attachment  to  the  tuberosity  and  oblique 
lines  of  the  tibia,  not  only  overhes  but  blends  with  the  fibrous  expansion  of  the  extensor  tendons. 
The  oblique  lines  of  the  tibia  curve  upward  and  backward  from  the  tuberosity  on  each  side 
to  the  postero-lateral  part  of  the  condyles.  The  process  of  fascia  attached  to  the  lateral  ridge 
of  the  tibia  and  to  the  head  of  the  fibula  descends  from  the  tensor  fascise  latas  and  is  very  thick 
and  strong.  It  is  firmly  blended  with  the  tendinous  fibres  of  the  vastus  laterahs.  The  fascia 
lata,  on  the  medial  side  of  the  patella,  besides  being  attached  to  the  medial  oblique  ridge  of  the 
tibia,  sends  some  longitudinal  fibres  lower  down  to  become  blended  with  the  fibrous  expansion 
of  the  sartorius.  The  fascia  is  much  thinner  on  the  medial  side  of  the  patella  than  on  the  lateral, 
and  blends  much  less  with  the  tendon  of  the  vastus  niedialis  than  the  lateral  part  of  the  fascia 
does  with  the  vastus  lateralis.  A  thin  layer  of  the  fascia  lata  in  the  form  of  transverse  or  aroi- 
form  fibres  passes  over  the  front  of  the  joint.  These  fibres  are  speciaUy  well  marked  over  the 
ligamentum  patellae,  and  blend  here  with  the  central  portion  of  the  quadriceps  extensor  fibres. 

Fig.  316. — The  Lower  Extremity  of  the  Femur  (Posterior  View),  to  show  the  Rela- 
tion OP  the  Articular  Capsule  of  the   Knee-joint  (in  red)  to  the   Epiphysial  Line. 


The  fibrous  expansion  of  the  extensor  tendons  consists — (1)  of  a  central 
portion,  densely  thick  and  strong,  3.7  cm.  (1|  in.)  broad,  which  is  inserted  into 
the  anterior  two-thirds  of  the  upper  border  of  the  patella,  many  of  its  superficial 
fibres  passing  over  the  subcutaneous  surface  of  the  bone  into  the  ligamentum 
patellfe;  (2)  of  two  side  portions  thinner,  but  strong. 

The  side  portions  are  inserted  into  the  patella  along  its  upper  border  on  either  side  of  the 
central  portion  and  also  into  its  medial  and  lateral  borders,  nearer  the  anterior  than  the  posterior 
surface,  as  low  down  as  the  attachment  of  the  ligamentum  patellar;  passing  thence  along  the 
sides  of  the  ligamentum  patelte  to  the  tibia,  they  are  attached  to  the  obhque  lines  which  extend 
from  the  tuberosity  to  the  medial  and  lateral  condyles,  and  reach  as  far  as  the  tibial  and  fibular 
collateral  ligaments.  On  the  lateral  side,  the  fibres  blend  with  the  ilio-tibial  band  of  the  fascia 
lata,  and  on  the  medial  they  extend  below  the  oblique  line  to  blend  with  the  periosteum  of  the 
shaft.  Thus  there  is  a  large  hood  spread  over  the  whole  of  the  front  of  the  joint,  investing  the 
patella,  and  reaching  from  the  sides  of  the  ligamentum  pateUse  to  the  collateral  ligaments,  at- 
tached below  to  the  tibia,  and  separated  everywhere  from  the  synovial  membrane  by  a  layer 
■of  fatty  tissue. 

The  ligamentum  patellae  (fig.  320)  is  the  continuation  in  line  of  the  central 
portion  of  the  conjoined  tendon,  some  fibres  of  which  are  prolonged  over  the  front 


286 


THE  ARTICULATIONS 


of  the  patella  into  the  ligament.  It  is  an  extremely  strong,  flat  band,  attached 
above  to  the  lower  border  of  the  patella;  below,  it  is  fixed  to  the  lower  part  of  the 
tuberosity  and  upper  part  of  the  crest  of  the  tibia,  somewhat  obliquely,  being 
prolonged  downward  further  on  the  lateral  side,  so  that  this  border  is  fully  2.5 
cm.  (1  in.)  longer  than  the  medial,  which  measures  6.7  cm.  {2\  in.)  in  length. 
Behind,  it  is  in  contact  with  a  mass  of  fat  which  separates  it  from  the  synovial 
membrane,  and  a  small  bursa  intervenes  between  it  and  the  head  of  the  tibia. 
In  front,  a  large  bursa  separates  it  from  the  subcutaneous  tissue,  and  at  the  sides 
it  is  continuous  with  the  fibrous  expansion  of  the  extensors. 

The  tibial  (internal)  collateral  ligament  (fig.  317)  is  a  strong,  flat  band,  which 
extends  from  the  depression  on  the  tubercle  on  the  medial  side  of  the  medial 

Fig.  317. — Posterior  View  op  the  Knee-joint. 


Plantaris 
Lateral  head  of  gastrocnemius 


Fibular  collateral  ligament 
anterior  portion 


Posterior  part  of  fibular 
collateral  ligament 
Tendon  of  popliteus 

Tendon  of  biceps 

Superior   posterior   tibio- 
fibular ligament 


Tendon  of  adductor  magaus 


Medial  head  of  gastrocnemius 


Tendon  of  semimembra- 
nosus with  its  slip  to 
thicken  the  oblique  pop- 
liteal ligament 


Tibial  collateral  ligament 


epicondyle  of  the  femur,  to  the  medial  border  and  medial  surface  of  the  shaft  of 
the  tibia,  3.7  cm.  (1|  in.)  below  the  condyle.  It  is  8.7  cm.  (3|  in.)  long,  well 
defined  anteriorly,  where  it  blends  with  the  expansion  of  the  conjoined  extensor 
tendons;  but  not  so  well  defined  posteriorly,  where  it  merges  into  the  oblique 
popliteal  ligament. 

Some  of  the  lower  fibres  blend  with  the  descending  portion  of  the  semimembranosus  tendon. 
Its  deep  surface  is  firmly  adherent  to  the  edge  of  the  medial  meniscus  and  coronary  ligament, 
while  part  of  the  semimembranosus  tendon  and  inferior  medial  articular  vessels  and  nerve  pass 
between  it  and  the  bone.  Superficially,  a  bursa  separates  it  from  the  tendons  of  the  gracilis 
and  semitendinosus  muscles  and  from  the  aponeurosis  of  the  sartorius  muscle. 

The  fibular  (external)  collateral  ligament  (fig.  317)  consists  of  two  portions: 
the  anterior,  which  is  the  longer  and  better  marked,  is  a  strong,  rounded  cord, 
about  5  cm.  (2  in.)  long,  attached  above  to  the  tubercle  on  the  lateral  side  of  the 
lateral  epicondyle  of  the  femur,  just  below  and  in  front  of  the  origin  of  the  lateral 
head  of  the  gastrocnemius,  whilst  the  tendon  of  the  popliteus  arises  from  the 
groove  below  and  in  front  of  it.  Below,  it  is  fixed  to  the  middle  of  the  lateral 
surface  of  the  head  of  the  fibula,  1.25  cm. (J)  in.  or  more  anterior  to  the  apex. 

Superficially  is  the  tendon  of  the  biceps,  which  sphts  to  embrace  its  lower  extremity;  while 
beneath  it  pass  the  popliteus  tendon  in  its  sheath,  and  the  inferior  lateral  articular  vessels  and  nerve. 


THE  KNEE-JOINT 


287 


Some  fibres  of  the  peroneus  longus  occasionally  arise  from  the  lower  end  of  the  ligament.  The 
posterior  portion  is  8  mm.  (\  in.)  behind  the  anterior.  It  is  broader  and  less  defined;  fixed  below 
to  the  apex  of  the  fibula,  it  inclines  upward  and  somewhat  backward,  and  ties  down  the  popliteus 
against  the  lateral  condyle  of  the  tibia,  blending  beneath  the  lateral  head  of  the  gastrocnemius 
with  the  oblique  popliteal  ligament  of  the  knee,  of  which  it  is  really  a  portion. 

The  oblique  popliteal  ligament  or  ligamentum  Winslowii  (fig.  317)  is  a  broad 
dense  structure  of  interlacing  fibres,  with  large  orifices  for  vessels  and  nerves. 
It  is  attached  above  to  the  femur  close  to  the  articular  margins  of  the  condyles, 
stretching  across  the  upper  margin  of  the  intercondyloid  fossa,  to  which  it  is 
connected  by  fibro-fatty  tissue;  it  thus  reaches  across  from  the  tibial  to  the 
fibular  collateral  ligaments.  Below,  it  is  fixed  to  the  border  of  the  lateral  condyle 
of  the  tibia,  to  the  bone  just  below  the  posterior  intercondyloid  notch,  and  to  the 
shaft  of  the  tibia  below  the  medial  condyle,  blending  with  the  descending  slip  of 
the  semimembranosus  and  tibial  collateral  ligament. 

Superficially,  an  oblique  fasciculus  from  the  semimembranosus  runs  across  the  centre,  passing 
upward  and  laterally  from  near  the  back  part  of  the  medial  condyle  of  the  tibia  to  the  lateral 

Fig.  318. — The  Lower  Extremity  op  the  Femur  (Anterior  View)  to  show  the  Rela- 
tion OP  THE  Articular  Capsule  op  the  Knee-joint  (in  red)  to  the  Epiphysial  Line. 


epicondyle  of  the  femur,  where  it  joins  the  lateral  head  of  the  gastrocnemius,  a  sesamoid  plate 
being  sometimes  developed  at  the  point  of  junction.  This  slip  greatly  strengthens  the  oblique 
pophteal  ligament,  of  which,  if  not  the  chief  constituent,  it  is  at  least  a  very  important  part. 

Its  deep  surface  is  closely  connected  with  the  semilunar  menisci  (especially  the  medial)  and 
coronary  ligaments,  and  in  the  interval  between  the  cartilages  with  the  posterior  crucial  ligament 
and  fibro-fatty  tissue  within  the  joint.  Superficially  it  forms  part  of  the  floor  of  the  popHteal 
space.  A  special  band,  the  arcuate  ligament,  is  sometimes  found  extending  from  the  lateral 
epicondyle  to  the  oblique  ligament. 

The  articular  capsule  (fig.  319)  is  thin  but  strong,  covering  the  synovial 
membrane,  and  looking  like  a  loose  sac.  It  is  attached  to  the  femur  near  the 
articular  margin  on  the  medial  side,  but  further  away  on  the  lateral;  it  passes 
beneath  the  fibular  collateral  ligament  to  join  the  sheath  of  the  popliteus.  Medi- 
ally it  joins  the  tibial  collateral  ligament.  Below,  it  is  fixed  to  the  upper  as  well 
as  the  medial  and  lateral  borders  of  the  patella  and  the  anterior  border  of  the 
head  of  the  tibia.  It  is  strengthened  superficially  between  the  femur  and  patella 
by  an  expansion  from  the  articularis  genu  {suh-crureus)  and  is  separated  from 


288 


THE  ARTICULATIONS 


the  fibrous  expansion  of  the  extensor  tendon  by  a  layer  of  fatty  tissue.  The 
synovial  membrane  lines  its  deep  surface,  and  holds  it  against  the  borders  of  the 
semilunar  menisci;  it  is  also  attached  to  the  coronary  ligaments. 

Internal  Ligaments 

The  anterior  crucial  ligament  (figs.  319  and  320)  is  strong  and  cord-like.  It 
is  attached  to  the  medial  half  of  the  fossa  in  front  of  the  intercondyloid  eminence 
of  the  tibia,  and  to  the  lateral  border  of  the  medial  articular  facet  as  far  back  as 
the  medial  intercondyloid  tubercle.  It  passes  upward,  backward,  and  laterally 
to  the  back  part  of  the  medial  surface  of  the  lateral  condyle  of  the  femur.     To 

Fig.  319. — Anterior  View  of  the  Internal  Ligaments  op  the  Knee-joint. 


Aperture  leading  into  the 
bursa  beneath  the  quadri  ' 
ceps  extensor 


Attachment    of    articular, 
capsule    to    femur 


Posterior  crucial  ligament 


Medial    meniscus 


Transverse  ligament 
Coronary  ligament 


Anterior  crucial  ligament' 
Lateral 

Coronary  ligament 


the  tibia,  it  is  fixed  behind  the  anterior  extremity  of  the  medial  semilunar  menis- 
cus. Behind  and  to  the  lateral  side  it  has  the  anterior  extremity  of  the  lateral 
meniscus,  a  few  fibres  of  which  blend  with  the  lateral  edge  of  the  ligament. 

Its  anterior  fibres  at  the  tibial  end  are  strongest  and  longest;  being  fixed  highest  on  the 
femur;  while  the  posterior,  springing  from  the  intercondyloid  eminence,  are  shorter  and  more 
oblique.     Near  the  spine,  a  slip  is  sometimes  given  off  to  the  posterior  crucial  hgament. 

The  posterior  crucial  ligament  (fig.  319,  320,  and  322)  is  stronger  and  less 
oblique  than  the  anterior.  It  is  fixed  below  to  the  greater  portion  of  the  fossa 
behind  the  intercondyloid  eminence  of  the  tibia,  especially  the  lateral  and  pos- 
terior portion,  and  then  medially  along  the  posterior  intercondyloid  fossa;  being 
joined  by  fibres  which  arise  between  the  intercondyloid  tubercles,  it  ascends 
to  the  anterior  part  of  the  lateral  surface  of  the  medial  condyle  of  the  femur, 
having  a  wide  crescentic  attachment  1.5  cm.  (f  in.)  in  extent  just  above  the 
articular  surface. 

Behind,  it  is  connected  at  the  tibia  directly  with  the  posterior  Ugament,  and  a  little  higher 
up  by  means  of  a  quantity  of  interposed  areolar  tissue.     In  front  it  rests  upon  the  posterior 


THE  KNEE-JOINT 


289 


horn  of  the  medial  semilunar  meniscus,  and  receives  a  large  slip  from  the  lateral  meniscus, 
which  ascends  along  it,  either  in  front  or  behind,  to  the  femur;  higher  up  in  front  it  is  connected 
with  the  anterior  crucial  hgament. 

Until  they  rise  above  the  intercondyloid  eminence  of  the  tibia  the  two  crucial  ligaments 
are  closely  bound  together,  so  that  no  interspace  exists  between  their  tibial  attachments  and 
the  point  of  decussation;  the  only  space  between  them  is  therefore  a  v-shaped  one  correspond- 
ing to  the  upper  half  of  their  x-shaped  arrangement,  and  this  is  a  mere  chink  in  the  undissected 
state,  and  can  be  seen  from  the  front  only,  owing  to  the  fatty  tissue  beneath  the  synovial  mem- 
brane which  sm-rounds  their  femoral  attachment. 

The  interarticular  menisci  or  semilunar  fibro-cartilages  (figs.  319  and  320) 
are  two  crescentic  discs  resting  upon  tlie  circumferential  portions  of  the  articular 
facets  of  the  tibia,  and  moving  with  the  tibia  upon  the  femur.  They  some- 
what deepen  the  tibial  articular  surfaces,  and  are  dense  and  compact  in  structure, 
becoming  looser  and  more  fibrous  near  their  extremities,  where  they  are  firmly 
fixed  in  front  of  and  behind  the  intercondyloid  eminence  of  the  tibia.  The 
circumferential  border  of  each  is  convex,  thick,  and  somewhat  loosely  attached  to 
the  borders  of  the  condyles  of  the  tibia  by  the  coronary  ligaments  and  the  re- 
flexion of  the  synovial  membrane.  The  inner  border  is  concave,  thin,  and  free. 
Half  an  inch  (1.3  cm.)  broad  at  the  widest  part,  they  taper  somewhat  toward  their 

Fig.  320. — Strtjctuhes  lying  on  the  Head  op  the  Tibia.     (Right  knee.) 
Ligamentum  pateUee yiTTTiTT  nt  J'ili] 


Transverse  ligament 


Lateral  meniscus 


Anterior  crucial  ligament 


Medial  meniscus — W- \ 


Posterior  crucial  ligament 


Tendon  of  biceps 


Fibulai*  collateral 
ligament 


extremities,  and  cover  rather  less  than  two-thirds  of  the  articular  facets  of  the 
tibia.  Their  upper  surfaces  are  slightly  concave,  and  fit  on  to  the  femoral 
condyles,  while  the  lower  are  flat  and  rest  on  the  head  of  the  tibia;  both  surfaces 
are  smooth  and  covered  by  synovial  membrane. 

The  lateral  meniscus  (fig.  320)  is  nearly  circular  in  form  and  less  firmly  fixed  than  the 
medial,  and  consequently  slides  more  freely  upon  the  tibia.  Its  anterior  cornu  is  attached  to  a 
narrow  depression  along  the  lateral  articular  facet,  just  in  front  of  the  lateral  intercondyloid 
tubercle  of  the  tibia,  close  to,  and  on  the  lateral  side  of,  the  anterior  crucial  hgament;  a  small  slip 
from  the  cornu  is  often  fixed  to  the  tibia  in  front  of  the  crucial  ligament.  The  posterior 
cornu  is  firmly  attached  to  the  tibia  behind  the  lateral  intercondyloid  tubercle,  blending  with  the 
posterior  crucial  ligament,  and  giving  off  a  well-marked  fasciculus,  which  runs  up  along  the 
anterior  border  of  the  ligament  to  be  attached  to  the  femur  (ligament  of  Wrisberg).  It  also 
sends  a  narrow  slip  into  the  back  part  of  the  anterior  crucial  ligament.  Its  outer  border  is 
grooved  toward  its  posterior  part  by  the  popliteus  tendon,  which  is  held  to  it  by  fibrous  tissue 
and  synovial  membrane,  and  separates  it  from  the  fibular  collateral  hgament.  From  its  anterior 
border  is  given  off  the  transverse  hgament. 

The  medial  meniscus  (fig.  320)  is  a  segment  of  a  larger  circle  than  the  lateral,  and  has  an 
outline  more  oval  than  cuxular.  Its  anterior  cornu  is  wide,  and  has  a  broad  and  oblique  attach- 
ment to  the  anterior  margin  of  the  head  of  the  tibia.  It  reaches  from  the  margin  of  the  condyle 
toward  the  middle  of  the  fossa  in  front  of  the  intercondyloid  eminence,  being  altogether  in  front 
of  the  anterior  crucial  ligament.  The  posterior  cornu  is  firmly  fixed  by  a  broad  insertion  in  an 
antero-posterior  line  along  the  medial  side  of  the  posterior  intercondyloid  fossa,  from  the  medial 
tubercle  to  the  posterior  margin  of  the  head  of  the  tibia.  Its  convex  border  is  connected  with 
the  tibial  collateral  ligament  and  the  seviimeinhrmiosus  tendon. 

The  transverse  ligament  (figs.  319  and  320)  is  a  rounded,  slender,  short  cord, 
which  extends  from  the  convex  border  of  the  lateral  meniscus  to  the  concave 
border  or  anterior  cornu  of  the  medial,  near  which  it  is  sometimes  attached  to  the 
bone.  It  is  an  accessory  band  of  the  lateral  meniscus,  and  is  situated  beneath 
the  synovial  membrane. 


290 


THE  ARTICULATIONS 


The  coronary  ligaments  (fig.  319)  connect  the  margins  of  the  semilunar 
discs  with  the  head  of  the  tibia.  The  lateral  is  much  more  lax  than  the  medial, 
permitting  the  lateral  disc  to  change  its  position  more  freely  than  the  medial. 
They  are  not  in  reality  separate  structures,  but  consist  of  fibres  of  the  several 
surrounding  ligaments  of  the  knee-joint  which  become  attached  to  the  margins 
of  the  discs  as  they  pass  over  them. 

The  synovial  membrane  (fig.  324)  of  the  knee  forms  the  largest  synovial  sac 
in  the  body.  Bulging  upward  from  the  patella,  it  follows  the  capsule  of  the  joint 
into  a  large  cul-de-sac  beneath  the  tendon  of  the  extensor  muscles  on  the  front  of 
the  femur.  It  reaches  some  distance  beyond  the  articular  surface  of  the  bone,  and 
communicates  very  frequently  with  a  large  bursa  interposed  between  the  tendon 
and  the  femur  above  the  line  of  attachment  of  the  articular  capsule.  After 
investing  the  circumference  of  the  lower  end  of  the  femur,  it  is  reflected  upon  the 

Fig.  321. — The  Uppee  Extremity  of  the  Tibia  (Anterior  View),  to  show  the  Rela- 
tion OP  THE  Articular  Capsule  op  the  Knee-joint  (in  red)  to  the  Epiphysial  Line. 


fibrous  envelope  of  the  joint  formed  by  the  capsular,  posterior,  and  collateral 
ligaments. 

The  synovial  membrane  covers  a  great  portion  of  the  crucial  ligaments,  but  leaves  uncovered 
the  back  of  the  posterior  crucial  where  the  latter  is  connected  with  the  posterior  hgament,  and 
the  lower  part  of  both  crucial  ligaments  where  they  are  united.  Thus  the  hgaments  are  com- 
pletely shut  out  of  the  synovial  cavity.  Along  the  fibrous  envelope  the  synovial  membrane  is 
conducted  down  to  the  semilunar  menisci,  over  both  surfaces  of  which  it  passes,  and  is  reflected 
off  the  under  surface  on  to  the  coronary  ligaments,  and  thence  down  to  the  head  of  the  tibia, 
around  the  circumference  of  which  it  extends  a  short  way.  It  dips  down  between  the  external 
meniscus  and  the  head  of  the  tibia  as  low  as  the  superior  tibio-fibular  ligament,  reaching  inward 
nearly  as  far  as  the  intercondyloid  notch,  and  forming  a  bursa  for  the  play  of  the  popliteal 
tendon. 

At  the  back  of  the  joint  two  pouches  are  prolonged  beneath  the  muscles,  one  on  each  side 
between  the  condyle  of  the  femur  and  the  origin  of  the  gastrocnemius.  Large  processes  of  syno- 
vial membrane  also  project  into  the  joint,  and  being  occupied  by  fat  serve  as  padding  to  fill  up 
spaces.  The  chief  of  these  processes,  the  patellar  synovial  fold  (ligamentum  mucosum)  (figs. 
322  and  324),  springs  from  the  infrapatellar  fatty  mass.  This  so-called  ligament  is  the  central 
portion  of  the  large  process  of  synovial  membrane,  of  which  the  alar  folds  form  the  free  margins. 
It  extends  from  the  fatty  mass,  below  the  patella,  backward  and  upward  to  the  intercondyloid 
notch  of  the  femur,  where  it  is  attached  in  front  of  the  anterior  crucial,  and  lateral  to  the  poste- 
rior crucial  ligament.  Near  the  femur  it  is  thin  and  transparent,  consisting  of  a  double  fold  of 
synovial  membrane,  but  near  the  patella  it  contains  some  fatty  tissue.  Its  anterior  or  upper 
edge  ia  free,  and  fully  2.6  cm.  (an  inch)  long;  the  posterior  or  lower  edge  is  half  the  length,  and 
is  attached  to  the  crucial  ligaments  above,  but  is  free  below. 


THE  KNEE-JOINT 


291 


Passing  backward  from  the  capsule  on  each  side  of  the  patella  is  a  prominent  crescentic 
fold  formed  by  reduplications  of  the  synovial  membrane — these  are  the  alar  folds  (fig.  3?2). 
Their  free  margins  are  concave  and  thin,  and  are  lost  below  in  the  patellar  fold.  There  is  a 
slight  fossa  above  and  another  below  each  Ligament. 

Fig.  322.— Anterior  View  of  the  Knee-joint,  showing  the  Stnoviai,  Ligaments. 
(Anterior  portion  of  capsule  with  the  extensor  tendon  thrown  downward.) 


Posterior  crucial  ligament 


Synovial     pouch     under     tendon 
quadriceps  femoris 


Fig.  323. — The  Upper  Extremity  op  the  Tibia  (Posterior  View),  to  show  the  Relation 
OF  THE  Articular  Capsule  op  the  Knee-joint  (in  red)  to  the  Epiphysial  Line. 


The  arterial  supply  is  derived  from  the  art.  genu  suprema  (anastomotica) ;  the  superior  ajid 
inferior  medial  and  lateral  articular;  the  medial  articular;  the  descending  branch  of  the  lateral 
circumflex;  the  anterior  recurrent  branch  from  the  anterior  tibial;  and  the  posterior  tibial 
recurrent. 


292 


THE  ARTICULATIONS 


The  nerve-supply  comes  from  the  great  sciatic,  femoral,  and  obturator  sources.  The 
great  sciatic  pves  off  the  tibial  and  common  peroneal;  the  tibial  sends  tAvo,  sometimes  three 
bi'anches — one  with  the  medial  articular  artery;  one  with  the  inferior  medial,  and  sometimes 
one  with  the  superior  medial  articular  artery;  the  common  peroneal  gives  a  branch  which  accom- 
panies the  superior,  and  another  which  accompanies  the  inferior  articular  artery,  and  a  recurrent 
branch  which  follows  the  course  of  the  anterior  recm-rent  branch  of  the  anterior  tibial  artery. 
The  femoral  sends  an  articular  branch  from  the  nerve  to  the  vastus  lateralis;  a  second  from  the 
nerve  to  the  vastus  mediaiis;  and  sometimes  a  third  from  that  to  the  vastus  intermedins.  Thus 
there  are  three  articular  twigs  to  the  knee  derived  from  the  muscular  branches  of  the  femoral. 
The  obturator  by  its  deep  division  sends  a  branch  through  the  adductor  magnus  on  to  the  pop- 
liteal artery,  which  enters  the  joint  posteriorly. 


Fig.  324. — Sagittal  Section  of  the  Knee-joint. 
(The  bones  are  somewhat  drawn  apart.) 


Fatty  tissue 
Opening  in  synovial  mem- 
brane     behind     crucial 
ligament     leading     into 
inner  half  of  joint 
Synovial     membrane    re- 
flectedoff  crucialligaments 
Cut  end  of  anterior  crucial 

ligament 
Posterior  crucial  ligament 

Oblique  popliteal  ligament 


Muscular  fibres  of  quadriceps 
femoris 


(,.     Extension  of  synovial  sac  of  knee 
I    \\\  upon  femur 


\V.\\  .Tendon  of  quadriceps    femoris, 

'H\ 


l\^  forming  fibrous  capsule  of  joint 


Patella 
Pre-patellar  bursa 


Condyle  of  femur 
^medial) 

Patellar  synovial  fold 


Fatty  tissue  between 
ligamentum  patellas 
and  synovial  sac 


Bursa  beneath  ligamentum 
patellas 


Relations. — Anteriorly  and  at  the  sides  the  knee-joint  is  merely  covered  and  protectedlby 
skin,  fascia,  and  the  tendinous  expansions  of  the  quadriceps  extensor  muscle.  Laterally  and 
posteriorly  it  is  crossed  by  the  biceps  tendon.  Medially  and  posteriorly  lie  the  sartorius  and 
the  tendons  of  the  gracilis  and  seinitendinosus  muscles.  Posteriorly  it  is  in  relation  with  the 
popliteal  vessels  and  nerves,  the  semimembranosus,  the  two  heads  of  the  gastrocnemius,  and  the 
plantaris.  The  tendon  of  the  popliteus  pierces  the  capsule  behind  and  medial  to  the  biceps 
tendon. 

The  movements  which  occur  at  the  knee-joint  are  flexion  and  extension,  with  some  slight 
amount  of  rotation  in  the  bent  position.  These  movements  are  not  so  simple  as  the  correspond- 
ing ones  at  the  elbow,  for  the  knee  is  not  a  simple  hinge  joint.  The  movements  of  rotation 
instead  of  occurring  between  tibia  and  fibula,  as  between  radius  and  ulna,  are  movements  of  the 
tibia  with  the  fibula  upon  the  condyles  of  the  femur. 

The  knee  differs  from  a  true  hinge  joint,  like  the  elbow  or  ankle,  in  the  following  par- 
ticulars:— 

1.  The  points  of  contact  of  the  femur  with  the  tibia  are  constantly  changing.     Thus,  in 


THE  KNEE-JOINT 


293 


the  flexed  position,  the  posterior  part  of  the  articular  surface  of  the  tibia  is  in  contact  with  the 
rounded  bacli  part  of  the  femoral  condyles;  in  the  semiflexed  position  the  middle  parts  of  the 
tibial  facets  Articulate  with  the  anterior  rounded  part  of  the  condyles;  while  in  the  fully  extended 
position  the  anterior  and  middle  parts  of  the  tibial  facets  are  in  contact  with  the  anterior  flat- 
tened portion  of  the  condyles.  So  with  the  patella:  in  extreme  flexion  the  medial  articular  facet 
rests  on  the  lateral  part  of  the  medial  condyle  of  the  femur;  in  flexion  the  upper  pair  of  facets 
rests  on  the  lower  part  of  the  trochlear  surface  of  the  femur;  in  mid-flexion  the  middle  pan- 
rests  on  the  middle  of  the  trochlear  surface;  while  in  extension  the  lower  pair  of  facets  on  the 
patella  rests  on  the  upper  portion  of  the  trochlear  surface  of  the  femur. 

Fig.  325. — The  Collateral  Ligaments  op  the  Knee  in  Flexion  and  Extension. 


This  difference  may  be  described  as  the  shifting  of  the  points  of  contact  of  the  articular 
surface. 

2.  It  differs  from  a  true  hinge  in  that,  in  passing  from  a  state  of  extension  to  one  of  flexion, 
the  tibia  does  not  revolve  round  a  single  transverse  axis  drawn  through  the  lower  end  of  the 
femur,  as  the  ulna  does  round  the  lower  end  of  the  humerus.  The  articular  surface  of  the 
tibia  slides  forward  in  e.xtension  and  backward  in  flexion;  thus  the  axis  round  which  the  tibia 
revolves  upon  the  femur  is  a  shifting  one,  as  is  seen  by  reference  to  fig.  325,  B,  C,  D. 

3.  Another  point  of  difference  is  that  extension  is  accompanied  by  lateral  rotation,  and 
flexion  by  medial  rotation.  This  rotation  occurs  round  a  vertical  axis  drawn  through  the  middle 
of  the  lateral  condyle  of  the  femur  and  the  lateral  condyle  of  the  tibia,  and  is  most  marked  at 
the  termination  of  extension  and  at  the  commencement  of  flexion.  This  rotation  of  the  leg  at 
the  knee  is  a  true  rotation  about  a  vertical  axis,  and  thus  differs  from  the  obliquity  of  the  flexion 


294 


THE  ARTICULATIONS 


and  extension  movements  at  the  elbow  wMcIi  is  due  to  the  oblique  direction  of  the  articular 
surfaices  of  the  bones. 

4.  The  antero-posterior  spiral  curve  of  the  femoral  condyles  is  such  that  the  anterior  part 
is  an  arc  of  a  greater  circle  than  the  posterior;  hence  certain  ligaments  which  are  tightened  during 

Fig.  326. — Section  op  Knee,  showing  Crucial  Ligaments  in  Extension. 


Anterior  crucial  ligament 

Intercondyloid  eminence  of  tibia 

Transverse  ligament 


Slip  from  lateral  meniscus  to    femur 

(ligament  of  Wrisberg) 
Posterior  crucial  ligament 

Latetal  meniscus 


Coronary  ligament 

Anterior  tibio-fibular  ligament 


extension  are  relaxed  during  flexion,  and  thereby  a  considerable  amount  of  rotatory  movement 
is- permitted  in  the  flexed  position.  The  axis  of  this  rotation  is  vertical,  and  passes  through  the 
medial  intercondyloid  tubercle  of  the  tibia,  so  that  the  lateral  condyle  moves  in  the  arc  of  a 
larger  circle  than  does  the  medial,  and  is  therefore  required  to  move  more  freely  and  easily; 

Fig.  327. — Crucial  Ligaments  in  Flexion. 


Posterior  crucial 


Anterior  crucial 
Medial  meniscus 

Transverse  ligament 


Slip  from  lateral  cartilage  to  femur 
Lateral  meniscus 


Coronary  ligament 

Anterior  tibio-fibular  ligament 


hence  the  shape  of  the  lateral  articular  facet  and  the  loose  connection  of  the  lateral  meniscus 
which  is  adapted  to  it. 

In  extension,  all  the  ligaments  are  on  the  stretch  with  the  exception  of  the  ligamentum 
patellae  and  front  of  the  capsule.  Extension  is  checked  by  both  the  crucial  ligaments  and  the 
cSlateral  ligaments  (figs.  325,  A,  B,  and  326). 


THE  KNEE-JOINT  295 

In  flexion  the  ligamentum  patellae  and  anterior  portion  of  the  capsule  are  on  the  stretch; 
so  also  is  the  posterior  crucial  in  extreme  flexion,  though  it  is  not  quite  tight  in  the  semiflexed 
state  of  the  joint.  All  the  other  ligaments  are  relaxed  (fig.  325,  C,  D),  although  the  relaxation 
of  the  anterior  crucial  ligament  is  slight  in  extreme  flexion  (fig.  327).  Flexion  is  only  checked 
during  hfe  by  the  contact  of  the  soft  parts,  i.  e.,  the  calf  with  the  back  of  the  thigh. 

Rotation  medially  is  checked  by  the  anterior  crucial  ligament;  the  collateral  ligaments 
being  loose. 

Rotation  laterally  is  checked  by  the  collateral  Ugaments;  the  crucial  hgaments  have  no 
controlling  effect  on  it,  as  they  are  untwisted  by  it. 

Sliding  movements  are  checked  by  the  crucial  and  collateral  ligaments — sliding  forward 
especially  by  the  anterior,  and  sliding  backward  by  the  posterior  crucial. 

Muscles  which  act  upon  the  knee-joint. — Flexors. — Biceps,  semimembranosus,  semiten- 
dinosus,  sartorius,  gastrocnemius,  plantaris,  and  pophteus.  Extensor. — Quadriceps  extensor. 
Medial  Bolators. — Sartorius,  gracilis,  semitendinosus,  semimembranosus,  popliteus.  Lateral 
Rotator. — Biceps. 

3.  THE  TIBIO-FIBULAR  UNION 

The  fibula  is  connected  with  the  tibia  throughout  its  length  by  an  interosseous 
membrane,  and  at  the  upper  and  lower  extremities  by  means  of  two  joints. 
Very  little  movement  is  permitted  between  the  two  bones. 

(a)  The  superior  tibio-fibular  joint. 
(6)  The  middle  tibio-fibular  union. 
(c)  The  inferior  tibio-fibular  joint. 

(a)  The  Superior  Tibio-fibular  Joint 

Class. — Diarthrosis.  Subdivision. — Arthrodia. 

The  superior  tibio-fibular  joint  is  about  6  mm. (J  in.)  below,  and  quite  distinct 
from,  the  knee  at  its  upper  and  anterior  part;  but  at  its  posterior  and  superior 
aspect,  where  the  border  of  the  lateral  condyle  of  the  tibia  is  bevelled  by  the  pop- 
liteus muscle,  the  joint  is  in  the  closest  proximity  to  the  bursa  beneath  the  tendon 
of  that  muscle,  and  is  only  separated  from  the  knee-joint  by  a  thin  septum  of 
areolar  tissue.  There  is  often  a  communication  between  the  synovial  cavities  of 
the  two  joints.     The  ligaments  uniting  the  bones  are: — 

Articular  capsule.  Anterior  tibio-fibular. 

Posterior  tibio-fibular. 

The  articular  capsule  is  a  well-marked  fibro-areolar  structure;  it  is  attached 
close  round  the  articular  margins  of  the  tibia  and  fibula.  In  front  it  is  shut  off 
completely  from  the  knee-joint  by  the  capsule  of  the  knee  and  the  coronary  liga- 
ment; but  behind,  it  is  often  very  thin,  and  may  communicate  with  the  bursa 
under  the  pophteus  tendon. 

The  anterior  tibio-fibular  (capitular)  ligament  (fig.  326)  consists  of  a  few  fibres 
which  pass  upward  and  medially  from  the  fibula  to  the  tibia.  It  lies  beneath  the 
anterior  portion  of  the  tendon  of  the  biceps. 

The  posterior  tibio-fibular  (capitular)  ligament  (fig.  317)  consists  of  a  few  fibres 
which  pass  upward  and  medially  between  the  adjacent  bones,  from  the  head  of 
the  fibula  to  the  lateral  condyle  of  the  tibia. 

The  superior  interosseous  ligament  consists  of  a  mass  of  dense  yellow  fibroareolar  tissue, 
binding  the  opposed  surfaces  of  the  bones  together  for  2  cm.  (f  in.)  below  the  articular  facets. 
It  is  continuous  with  the  interosseous  membrane  along  the  tibia. 

The  biceps  tendon  is  divided  by  the  fibular  collateral  ligament  of  the  knee;  of  the  two 
divisions  the  anterior  is  by  far  the  stronger,  and  is  inserted  into  the  lateral  condyle  of  the  tibia 
as  well  as  to  the  front  of  the  head  of  the  fibula,  and  thus  the  muscle,  acting  on  both  bones,  tends 
to  brace  them  more  tightly  together;  indeed,  it  holds  the  bones  strongly  together  after  all  other 
connections  have  been  severed. 

The  synovial  membrane  which  lines  the  joint  sometimes  communicates  with  the  knee-joint 
through  the  bursa  beneath  the  popliteus  tendon. 

The  arterial  supply  is  from  the  inferior  lateral  articular  and  recurrent  tibial  arteries. 

The  nerve-supply  is  from  the  inferior  lateral  articular,  and  also  from  the  recurrent  branch 
of  the  common  peroneal. 

Relations. — In  front,  the  upper  ends  of  the  tibialis  anterior,  the  extensor  digitorum  longus, 
and  the  peroneus  longus.  Behind,  the  tendon  of  the  popliteus  overlapped  by  the  lateral  head 
of  the  gastrocnemius.  Laterally,  the  biceps  tendon  and  the  common  peroneal  nerve.  Below 
and  medially,  the  anterior  tibial  vessels. 

The  movements  are  but  slight,  and  consist  merely  of  a  gliding  of  the  two  bones  upon  each 
other.     The  joint  is  so  constructed  that  the  fibula  gives  some  support  to  the  tibia  in  transmitting 


296 


THE  ARTICULATIONS 


the  weight  to  the  foot.  The  articular  facet  of  the  tibia  overhangs,  and  is  received  upon  the 
articular  facet  of  the  head  of  the  fibula  in  an  oblique  plane.  This  joint  allows  of  slight  yielding 
of  the  lateral  malleolus  during  flexion  and  extension  of  the  ankle-joint,  the  whole  fibula  gUding 
slightly  upward  in  flexion,  and  downward  in  extension,  of  the  anlde. 


(6)  The  Middle  Tibio-fibular  Union 


Class. — Synarthrosis. 


Subdivision. — Syndesmosis. 


The  interosseous  membrane  is  attached  along  the  lateral  border  of  the  tibia 
and  the  interosseous  border  of  the  fibula.  It  is  deficient  above  for  about  2.5  cm. 
(1  in.)  or  more,  measured  from  the  under  aspect  of  the  superior  joint.  Its  upper 
border  is  concave,  and  over  it  pass  the  anterior  tibial  vessels. 

The  membrane  consists  of  a  thin  aponeurotic  and  translucent  lamina,  formed  of  oblique 
fine  fibres,  some  of  which  run  from  the  tibia  to  the  fibula,  and  some  from  the  fibula  to  the  tibia, 
but  all  are  inchned  downward.  They  are  best  marked  at  their  attachment  to  the  bones,  and 
gradually  grow  denser  and  thicker  as  they  approach  the  inferior  interosseous  ligament.     The 


Fig.  328. — Lower  Ends  op  Left  Tebia  and  Fibula,  showing  the  Ligaments.     The  synovial 
fold  between  these  bones  has  been  removed  to  show  the  transverse  ligament  forming  part 
of  the  capsule  of  the  joint,  and  the  deeper  fibres  of  the  anterior  lateral  malleolar  hgament 
which  come  into  contact  with  the  talus. 
(From  a  dissection  by  Mr.  W.  Pearson,  of  the  Royal  College  of  Surgeons'  Museum.) 


Deltoid  ligament 


Anterior  lateral  malle- 
_  /        olar  ligament 


Lateral  ligament 

Transverse  ligament 
Posterior  lateral  malle- 
olar ligament 


chief  use  of  the  membrane  is  to  afford  a  surface  for  the  origin  of  muscles.    It  is  continuous  below 
with  the  inferior  interosseous  ligament. 

In  front  of  the  interosseous  membrane  lie  the  tibialis  anterior,  the  extensor  digitorum  longus, 
the  extensor  hallucis  longus,  and  the  anterior  tibial  vessels  and  nerves.  Behind  it  is  in  relation 
with  the  tibialis  posterior,  the  flexor  hallucis  longus,  and  the  peroneal  artery. 

(c)  The  Inferior  Tibio-fibular  Articulation 
Class. — Diarihrosis.  Subdivision. — Arthrodia. 


This  junction  is  formed  by  the  lower  ends  of  the  tibia  and  fibula.  The  rough 
triangular  surface  on  each  of  these  bones  formed  by  the  bifurcation  of  their 
interosseous  lines  is  closely  and  firmly  united  by  the  inferior  interosseous  liga- 
ment. The  fibula  is  in  actual  contact  with  the  tibia  by  an  articular  facet,  which 
is  small  in  size,  crescentic  in  shape,  and  continuous  with  the  articular  facet  of 
the  malleolus. 

The  ligaments  which  unite  the  bones  are: — • 

1.  Anterior  lateral  malleolar  ligament. 

2.  Posterior  lateral  malleolar  ligament. 

3.  Transverse  ligament. 

4.  Inferior  interosseous  ligament. 

The  anterior  lateral  malleolar  ligament  (anterior  inferior  tibio-fibular  liga- 
ment) (figs.  328  and  334)  is  a  strong  triangular  band  about  2  cm.  (f  in.)  wide, 
and  is  attached  to  the  lower  extremity  of  the  tibia  at  its  anterior  and  lateral 
angle,  close  to  the  margin  of  the  facet  for  the  talus  and  passes  downward  and 


THE  ANKLE-JOINT  297 

laterally  to  the  anterior  border  and  contiguous  surface  of  the  lower  end  of  the 
fibula,  some  fibres  passing  along  the  edge  nearly  as  far  as  the  origin  of  the  anterior 
talo-fibular  ligament. 

The  fibres  increase  in  length  from  above  downward.  In  front  it  is  in  relation  with  the 
peroneus  tertius  and  deep  fascia  of  the  leg,  and  gives  origin  to  fibres  of  the  anterior  Kgament  of 
the  ankle-joint.  Behind,  it  Lies  in  contact  with  the  interosseous  Ugament,  and  comes  into  con- 
tact with  the  articxilar  surface  of  the  talus  (see  figs.  328  and  329). 

The  posterior  lateral  malleolar  ligament  (figs.  328  and  334)  is  very  similar 
to  the  anterior,  extending  from  the  posterior  and  lateral  angle  of  the  lower  end 
of  the  tibia  downward  and  laterally  to  the  lowest  1.5  cm.  (|  in.)  of  the  border 
separating  the  medial  from  the  posterior  surface  of  the  shaft  of  the  fibula,  and  to 
the  upper  part  of  the  posterior  border  of  the  lateral  malleolus.  It  is  in  relation 
in  front  with  the  interosseous  ligament;  below,  it  touches  the  transverse  ligament. 

The  inferior  interosseous  ligament  is  a  dense  mass  of  short,  felt-like  fibres,  passing  trans- 
versely between  and  firmly  uniting  the  opposed  rough  triangular  surfaces  at  the  lower  ends  of  the 

Fig.  329. — Right  Ankle-joint,  showing  the  Ligaments. 
(From  dissection  by  Mr.  W.  Pearson,  of  the  Royal  College  of  Surgeons'  Museum.) 


Superficial   fibres   of   anterior 
lateral  malleolar  ligament 
Deep  fibres  of  anterior  lateral. 
malleolar  Ugament 


Anterior  talo-fibular  ligament  — 

Posterior  talo-fibular  ligament  — 

Calcaneo-fibular  ligament — 


Deltoid  ligament 


tibia  and  fibula,  except  for  1  cm.  (f  in.)  at  the  extremity,  where  there  is  a  synovial  cavity.  It 
extends  from  the  anterior  to  the  posterior  lateral  malleolar  hgaments,  reaching  upward  4  cm. 
(l-J-  in.)  in  front,  but  only  half  this  height  behind. 

The  transverse  ligament  (fig.  331)  is  a  strong  rounded  band,  attached  to  nearly  the  whole 
length  of  the  inferior  border  of  the  posterior  svu-face  of  the  tibia,  just  above  the  articular  facet 
for  the  talus.  It  then  inclines  a  little  forward  and  downward,  to  be  attached  to  the  medial 
surface  of  the  lateral  malleolus,  just  above  the  fossa,  and  into  the  upper  part  of  the  fossa  itself. 

The  synovial  membrane  is  continuous  with  that  of  the  ankle-joint;  it  projects  upward 
between  the  bones  beyond  their  articular  facets  as  high  as  the  inferior  interosseous  ligament. 

The  nerve-supply  is  the  same  as  that  of  the  ankle-joint;  the  arterial  supply  is  from  the 
peroneal  and  the  anterior  peroneal,  and  sometimes  from  the  anterior  tibial,  or  its  lateral  malleolar 
branch. 

Relations. — In  front  of  the  inferior  tibio-fibular  joint  are  the  anterior  peroneal  artery  and 
the  tendon  of  the  peroneus  tertius,  and  behind  it  are  the  posterior  peroneal  artery  and  the  pad 
of  fat  which  Ues  La  front  of  the  tendo  Achillis. 

The  movement  permitted  at  this  joint  is  a  mere  gliding,  chiefly  in  an  upward  and  downward 
direction,  of  the  fibula  on  the  tibia.  The  bones  are  firmly  braced  together  and  yet  form  a  slightly 
yielding  arch,  thus  allowing  a  slight  side  to  side  expansion  during  extreme  flexion,  when  the 
broad  part  of  the  talus  is  brought  under  the  arch,  by  the  upward  gliding  of  the  fibula  on  the 
tibia.  To  this  end  the  direction  of  the  fibres  of  the  lateral  malleolar  ligaments  is  downward 
from  tibia  to  fibula.  This  mechanical  arrangement  secures  perfect  contact  of  the  articular 
surfaces  of  the  ankle-joint  in  all  positions  of  the  foot. 

4.  THE  ANKLE-JOINT 

Class. — Diarthrosis.  Subdivision. — Ginglymus. 

The  ankle  [articulatio  talo-cruralis]  is  a  perfect  ginglymus  or  hinge  joint. 
The  bones  which  enter  into  its  formation  are:  the  lower  extremity  and  medial 
malleolus  of  the  tibia,  and  the  lateral  malleolus  of  the  fibula,  above;  and  the  upper 


298 


THE  ARTICULATIONS 


and  lateral  articular  surfaces  of  the  talus  (astragalus)  below, 
(supplementing  the  articular  capsule)  uniting  the  bones  are: — 


The  ligaments 


Anterior. 
Posterior. 


Deltoid. 
Lateral  ligament. 


The  anterior  ligament  (fig.  334)  is  a  thin,  membranous  structure,  which 
completes  the  capsule  in  front  of  the  joint.  It  is  attached  above  to  the  anterior 
border  of  the  medial  malleolus,  to  a  crest  of  bone  just  above  the  transverse  groove 
at  the  lower  end  of  the  tibia,  to  the  anterior  lateral  malleolar  ligament,  and  to  the 
anterior  border  of  the  lateral  malleolus.  Below,  it  is  attached  to  the  rough  upper 
surface  of  the  neck  of  the  talus  (astragalus).  Medially  it  is  thicker,  and  is  fixed 
to  the  talus  close  to  the  facet  for  the  medial  malleolus,  being  continuous  with  the 
deltoid  ligament,  and  passing  forward  to  blend  with  the  talo-navicular  ligament. 
Laterally  it  is  attached  to  the  talus,  just  below  and  in  front  of  the  angle  between 
the  superior  and  lateral  facets,  close  to  their  edges,  and  joins  the  anterior  talo- 
fibular ligament. 

It  is  in  relation,  in  front  with  the  tibialis  anterior  muscle,  the  anterior  tibial  vessels  and  nerve, 
the  extensor  tendons  0/  the  toes,  and  the  peroneus  tertius;  and  behind  with  a  mass  of  fat  and  syno- 
vial membrane. 

Fig.  330. — Medial  View  of  the  Ankle  and  the  Tarsus,  showing  the  Groove  for  the 
Tendon  of  the  Tibialis  Posterior. 


Plantar  calcaneo-cuboid  ligament       Long  plantar  ligament 


The  posterior  ligament  (fig.  331)  is  a  very  thin  and  disconnected  membranous 
structure,  connected  above  with  the  lateral  malleolus,  medial  to  the  peroneal 
groove;  to  the  posterior  margin  of  the  lower  end  of  the  tibia  lateral  to  the  groove 
for  the  tibialis  posterior;  and  to  the  posterior  lateral  malleolar  ligament.  Below, 
it  is  attached  to  the  posterior  surface  of  the  talus  from  the  deltoid  to  the  lateral 
ligaments.  The  passage  of  the  flexor  hallucis  longus  tendon  over  the  back  of 
the  joint  serves  the  purpose  of  a  much  stronger  posterior  ligament. 

The  deltoid  ligament  (fig.  330)  is  attached  superiorly  to  the  medial  malleolus 
along  its  lower  border,  and  to  its  anterior  surface  superficial  to  the  anterior  liga- 
ment; some  very  strong  fibres  are  fixed  to  the  notch  in  the  lower  border  of  the 
malleolus,  and,  getting  attachment  below  to  the  rough  depression  on  the  medial 
side  of  the  talus,  form  a  deep  portion  to  the  ligament.  The  ligament  radiates; 
the  posterior  fibres  are  short,  and  incline  a  little  backward  to  be  fixed  to  the  rough 
medial  surface  of  the  talus,  close  to  the  superior  articular  facet,  and  into  the 


THE  ANKLE-JOINT 


299 


tubercle  to  the  medial  side  of  the  flexor  hallucis  longus  groove.  The  fibres  next 
in  front  are  numerous  and  form  a  thick  and  strong  mass,  filling  up  the  rough 
depression  on  the  medial  surface  of  the  talus,  whilst  some  pass  over  the  talo- 
calcaneal  joint  to  the  upper  and  medial  border  of  the  sustentaculum  tali.  The 
fibres  which  are  connected  above  with  the  anterior  surface  of  the  malleolus  pass 
downward  and  somewhat  forward  to  be  attached  to  the  navicular  and  to  the 
margin  of  the  calcaneo-navicular  ligament. 

The  lateral  ligament  (figs.  329  and  334)  consists  of  three  distinct  slips  (fas- 
ciculi). The  anterior  talc -fibular  ligament  (anterior  fasciculus),  is  ribbon-like 
and  passes  from  the  anterior  border  of  the  lateral  malleolus  near  the  tip  to  the 
rough  surface  of  the  talus  in  front  of  the  lateral  facet,  and  overhanging  the  sinus 
pedis.  The  calcaneo -fibular  ligament  (middle  fasciculus) ,  is  a  strong  roundish 
bundle,  which  extends  downward  and  somewhat  backward  from  the  anterior 
border  of  the  lateral  malleolus  close  to  the  attachment  of  the  anterior  fasciculus, 
and  from  the  lateral  surface  of  the  malleolus,  just  in  front  of  the  apex,  to  a  tuber- 
cle on  the  middle  of  the  lateral  surface  of  the  calcaneum.     The  posterior  talo- 

FiG.  331. — Ligaments  seen  from  the  Back  of  the  Ankle-joint. 


Posterior  ligament  of  ankle-joim 


Posterior  part  of  the  deltoid 
ligament 


Transverse  ligament  of  inferior 
tibio-fibular  joint 


Posterior  talo-fibular  ligament 
Calcaneo-fibular  ligament 


fibular  ligament  (posterior  fasciculus),  is  almost  horizontal;  it  is  a  strong,  thick 
band  attached  at  one  end  to  the  posterior  border  of  the  malleolus,  and  slightly  to  the 
fossa  on  the  medial  surface;  and  at  the  other  end  to  the  talus,  behind  the  articular 
facet  for  the  fibula,  as  well  as  to  a  tubercle  on  the  lateral  side  of  the  groove  for 

the  flexor  hallucis  longus. 

The  middle  fasciculus  is  covered  by  the  tendons  of  the  peronei  longus  and  brevis;  and  in 
extension,  the  posterior  fasciculus  is  received  into  the  pit  on  the  medial  surface  of  the  lateral 
malleolus. 

The  synovial  membrane  is  very  extensive.  Besides  lining  the  ligaments  of 
the  ankle,  it  extends  upward  between  the  tibia  and  fibula,  forming  a  short  cul- 
de-sac  as  far  as  the  interosseous  ligament.  Upon  the  anterior  and  posterior  liga- 
ments it  is  very  loose,  and  extends  beyond  the  limits  of  the  articulation.  It  is 
said  to  contain  more  synovia  than  any  other  joint. 

The  nerve -supply  is  from  the  saphenous,  posterior  tibial,  and  the  lateral  division  of  the 
anterior  tibial. 


300 


THE  ARTICULATIONS 


The  arterial  supply  comes  from  the  anterior  tibial,  the  anterior  peroneal,  the  lateral  malleolar, 
the  posterior  tibial,  and  posterior  peroneal. 

Relations. — In  front  and  in  contact  with  the  anterior  hgament,  from  medial  to  lateral 
aspects,  are  the  tendons  of  the  tibiahs  anterior,  the  tendon  of  the  extensor  haUucis  longus,  the 
anterior  tibial  vessels,  the  anterior  tibial  nerve,  the  tendons  of  the  extensor  digitorum  longus, 
and  the  tendon  of  the  peroneus  tertius.  To  the  medial  side  of  the  tibiahs  anterior  and  to  the 
lateral  side  of  the  peroneus  tertius  the  joint  is  subcutaneous  anteriorly.  Behind  and  laterally 
are  the  tendons  of  the  peroneus  longus  and  brevis.  Behind  and  medially,  from  medial  to 
lateral  side,  are  the  tendon  of  the  tibialis  posterior,  the  tendon  of  the  flexor  digitorum  longus, 
the  posterior  tibial  vessels,  the  posterior  tibial  nerve,  and  the  tendon  of  the  flexor  hallucis  longus. 
Directly  behind  is  a  pad  of  fat  which  intervenes  between  the  tendo  Achillis  and  the  joint. 
Below  and  on  the  lateral  side,  crossing  the  middle  fasciculus  of  the  lateral  ligament,  are  the 
tendons  of  the  peroneus  longus  and  brevis.  Below  and  on  the  medial  side,  crossing  the  deltoid 
ligament,  are  the  tendons  of  the  tibialis  posterior  and  the  flexor  digitorum  longus. 

Movements. — This  being  a  true  hinge  joint,  flexion  and  extension  are  the  only  movements 
of  which  it  is  capable,  there  being  no  side  to  side  motion,  except  in  extreme  extension,  when  the 
narrowest  part  of  the  talus  is  thrust  forward  into  the  widest  part  of  the  tibio-fibular  arch. 

Fig.  332. — Tne  Lower  Extremity  op  the  Tibia  (Anterior  view),  to  Show  the  Relation 
OP  the  Articular  Capsule  op  the  Ankle-joint  (in  red)  to  the  Epiphysial  Line. 


In  flexion  the  talus  is  tightly  embraced  by  the  malleoli,  and  side  to  side  movement  is  impossible. 
Flexion  of  the  ankle-joint  is  hmited  by: — (i)  nearly  the  whole  of  the  fibres  of  the  deltoid  ligament, 
none  but  the  most  anterior  being  relaxed;  (ii)  the  posterior  and  middle  portions  of  the  lateral  liga- 
ment, especially  the  posterior;  (iii)  the  posterior  ligament  of  the  ankle.  It  is  also  hmited  by  the 
neck  of  the  talus  abutting  on  the  edge  of  the  tibia. 

In  most  European  ankle-joints  the  anterior  edge  of  the  lower  end  of  the  tibia  is  kept  from 
actual  contact  with  the  neck  of  the  talus  in  positions  of  extreme  flexion  by  the  intervention  of  a 
pad  of  fat  situated  beneath  the  anterior  extension  of  the  anterior  hgament.  In  races  which 
adopt  a  squatting  posture,  however,  an  actual  articulation  may  be  developed  between  these  two 
bony  surfaces,  a  facet  being  present  both  upon  the  anterior  margin  of  the  tibia  and  upon  the  neck 
of  the  talus.  These  facets  are  known  as  "squatting  facets"  (fig.  333,  A)  and  are  of  common 
occurrence  in  ancient  bones  and  in  the  bones  of  modern  oriental  people. 

Extension  of  the  ankle-joint  is  limited  by: — (i)  the  anterior  fibres  of  the  deltoid  ligament; 
(ii)  the  anterior  and  middle  portions  of  the  lateral  hgament;  (ui)  the  medial  and  stronger  fibres 
of  the  anterior  hgament.  It  is  also  limited  by  the  posterior  portion  of  the  talus  meeting  with  the 
tibia.  Thus  the  middle  portion  of  the  lateral  ligament  is  always  on  the  stretch,  owing  to  its 
obliquely  backward  direction,  whereby  it  hmits  flexion;  and  its  attachment  to  the  fibula  in  front 
of  the  malleolar  apex,  whereby  it  prevents  over-extension  as  soon  as  the  foot  begins  to  twist 


THE  TARSAL  JOINTS 


301 


medialward.  .This  medial  twisting,  or  adduction  of  the  foot,  is  partly  due  to  the  greater  pos- 
terior length  of  the  medial  border  of  the  superior  articular  surface  of  the  talus,  and  to  the  less 
proportionate  height  posteriorly  of  the  lateral  border  of  that  surface,  but  chiefly  to  the  side  to 
side  movement  in  the  talo-calcaneal  joints.  Fle.xion  and  extension  take  place  round  a  transverse 
axis  drawn  through  the  body  of  the  talus.  The  movement  is  not  in  a  direct  antero-posterior 
plane,  but  on  a  plane  inclined  forward  and  laterally  from  the  middle  of  the  astragalus  to  the 
intermetatarsal  joint  of  the  second  and  third  toes. 

Muscles  which  act  on  the  ankle-joint. — Flexors. — Tibialis  anterior,  extensor  hallucis  longus, 
extensor  digitorum  longus,  peroneus  tertius.  Extensors. — Tibialis  posterior,  flexor  digitorum 
longus,  flexor  hallucis  longus,  peroneus  longus,  peroneus  brevis,  soleus,  gastrocnemius,  plantaris. 


Fig.  333. — Anterior  Aspect  of  the  Lower  Extremity  op  the  Tibia. 
In  A,  the  articular  surface  is  prolonged  upward  in  front,  forming  a  "squatting  facet"  which 
articulates  with  a  corresponding  facet  on  the  neck  of  the  talus.     In  B  (the  usual  condition)  the 
articular  surface  is  confined  to  the  lower  aspect  of  the  bone. 


5.  THE  TARSAL  JOINTS 
These  may  be  divided  into  the  following  sub-groups : — 

(a)  The  talo-calcaneal  union. 

(b)  The  articulations  of  the  anterior  portion  of  the  tarsus. 

(c)  The  medio-tarsal  joint. 

(a)  The  Talo-calcaneal  Union 

There  are  two  joints  which  enter  into  this  union — viz.,  an  anterior  and  a 
posterior. 


(i)   The  Posterior  Talo-calcaneal  Joint 

Class. — Diarthrosis.  Subdivision. — Arthrodia. 

'.  The  calcaneus  articulates  with  the  talus  by  two  joints,  the  anterior  and 
posterior:  the  former  communicates  with  the  medio-tarsal;  the  posterior  is 
separate  and  complete  in  itself.  At  the  latter  joint  the  two  bones  are  united  by 
an  articular  capsule  with  the  following  ligaments: — 


Interosseous. 

Posterior  talo-calcaneal. 


Lateral  talo-calcaneal. 
Medial  talo-calcaneal. 


The  interosseous  ligament  (figs.  334  and  335)  is  a  strong  band  connecting 
the  apposed  surfaces  of  the  calcaneus  and  talus  along  their  oblique  grooves.  It 
is  composed  of  several  vertical  laminae  of  fibres,  with  some  fatty  tissue  in  between. 


302  THE  ARTICULATIONS 

It  is  better  marked,  deeper,  and  broader  laterally.  Strong  laminse  extend  from  the  rough 
inferior  and  lateral  sm-faces  of  the  neck  of  the  talus  to  the  rough  superior  surface  of  the  calcaneus 
anteriorly,  forming  the  posterior  boundary  of  the  anterior  talo-caloaneal  joint;  these  have  been 
described  as  the  anterior  (interosseous)  ligament.  The  posterior  lamina  extend  from  the  roof 
of  the  sinus  pedis  to  the  calcaneus  immediately  in  front  of  the  lateral  facet,  thus  forming  the 
anterior  part  of  the  capsule  of  the  posterior  joint. 

The  lateral  talo-calcaneal  ligament  (fig.  334)  extends  from  the  groove  just  below  and  in 
front  of  the  lateral  articular  facet  of  the  talus,  to  the  calcaneus  some  little  distance  from  the  articu- 
lar margin.  Its  fibres  are  nearly  parallel  with  those  of  the  calcaneo-fibular  ligament  of  the 
ankle,  which  passes  over  it  and  adds  to  its  strength.  It  fiUs  up  the  interval  between  the  calcaneo- 
fibular  and  anterior  talo-fibular  ligaments,  a  considerable  bundle  of  its  fibres  blending  with  the 
anterior  border  of  the  calcaneo-fibular. 

The  posterior  talo-calcaneal  ligament  passes  from  the  lateral  tubercle  of  the  talus  and  lower 
edge  of  the  groove  for  the  flexor  haUucis  longus  to  the  calcaneus,  a  variable  distance  from  the 
articular  margin. 

The  medial  talo-calcaneal  ligament  includes  two  portions.  The  first  is  a  narrow  band  of 
well-marked  fibres  passing  obliquely  downward  and  forward  from  the  medial  tubercle  of  the 
talus,  just  behind  the  medial  end  of  the  sinus  tarsi,  to  the  calcaneus  behind  the  sustentaculum 
tali,  thus  completing  the  floor  of  the  groove  for  the  flexor  hallucis  longus  tendon.  The  second 
portion,  which  is  often  considered  a  separate  ligament,  is  described  below  with  the  anterior 
talo-calcaneal  joint. 

The  synovial  sac  is  distinct  from  any  other. 

The  nerve-supply  is  from  the  posterior  tibial  or  one  of  its  plantar  branches. 

The  arteries  are,  a  branch  from  the  posterior  tibial,  which  enters  at  the  medial  end  of  the 
sinus  pedis;  and  twigs  from  the  tarsal,  lateral  malleolar,  and  the  peroneal,  which  enter  at  the 
lateral  end  of  the  sinus. 

(ii)  The  Anterior  Talo-calcaneal  Joint 

Class. — Diarthrosis.  Subdivision. — Arthrodia. 

This  joint  is  formed  by  the  anterior  facet  on  the  upper  surface  of  the  calcaneus 
and  the  facets  on  the  lower  surface  of  the  neck  and  head  of  the  talus;  it  is  bounded 
on  the  sides  and  behind  by  ligaments,  and  communicates  anteriorly  with  the 
talo-navicular  joint.     The  ligaments  are: — 

Interosseous.  Medial  talo-calcaneal. 

Lateral  calcaneo-navicular. 

The  interosseous  ligament  by  its  anterior  laminae  limits  this  joint  posteriorly.  It  has  been 
already  described. 

The  medial  talo-calcaneal  ligament  (second  portion;  see  above)  consists  of  short  fibres  at- 
tached above  to  the  medial  surface  of  the  neck  of  the  talus,  and  below  to  the  upper  edge  of  the 
free  border  of  the  sustentaculum  tali,  blending  posteriorly  with  the  medial  extremityof  the  inter- 
osseous ligament,  and  anteriorly  with  the  upper  border  of  the  plantar  calcaneo-navicular  liga- 
ment. It  is  strengthened  by  the  deltoid  ligament,  the  anterior  fibres  of  which  are  also  attached 
to  the  plantar  calcaneo-navicular  ligament. 

The  lateral  calcaneo-navicular  (figs.  334  and  335)  limits  this,  as  well  as  the  talo-navicular 
joint,  on  the  lateral  side.  It  is  a  strong,  well-marked  band,  extending  from  thorough  upper  sur- 
face of  the  calcaneus,  lateral  to  the  anterior  facet,  to  a  slight  groove  on  the  lateral  surface  of 
the  navicular  near  the  posterior  margin.  It  blends  below  with  the  plantar  calcaneo-navicular, 
and  above  with  the  talo-navicular  ligament.  Its  fibres  run  obliquely  forward  and  medially. 
The  deltoid  ligament  and  middle  fasciculus  of  the  lateral  ligament  of  the  ankle-joint  also  add 
to  the  security  of  these  two  joints,  and  assist  in  limiting  movements  between  the  bones  by  pass- 
ing over  the  talus  to  the  calcaneus. 

The  synovial  membrane  is  the  same  as  that  of  the  talo-navicular  joint.  The  arteries  and 
nerves  are  derived  from  the  same  sources  as  those  of  the  medio-tarsal  joints. 

The  movements  of  which  these  two  joints  are  capable  are  adduction  and  abduction,  with 
some  amount  of  rotation.  Adduction,  or  inclination  of  the  sole  medialward,  is  combined  with 
some  medial  rotation  of  the  toes,  and  some  lateral  rotation  of  the  heel;  while  abduction,  or  in- 
clination of  the  foot  lateralward,  is  associated  with  turning  of  the  toes  laterally  and  the  heel 
medially.  Thus  the  variety  and  the  range  of  movements  of  the  foot  on  the  leg,  which  at  the  ankle 
are  almost  limited  to  flexion  and  extension,  are  increased.  The  cuboid  moves  with  the  calca- 
neus, while  the  navicular  revolves  on  the  head  of  the  talus. 

In  walking,  the  heel  is  first  placed  on  the  ground;  the  foot  is  slightly  adducted;  but  as  the 
body  swings  forward,  first  the  latei-al  then  the  medial  toes  touch  the  ground,  the  talus  presses 
against  the  navicular  and  sinks  upon  the  plantar  calcaneo-navicular  ligament;  the  foot  then 
becomes  slightly  abducted.  When  the  foot  is  firmly  placed  on  the  ground,  the  weight  is  trans- 
mitted to  it  obliquely  downward  and  medially,  so  that  if  the  ligaments  between  the  calcaneus 
and  talus  did  not  check  abduction,  medial  displacement  of  the  talus  from  the  tibio-fibular  arch 
would  only  be  prevented  by  the  tendons  passing  round  the  medial  ankle  (especially  the  tibialis 
posterior).  If  the  ligaments  be  too  weak  to  limit  abduction,  the  weight  of  the  body  increases  it, 
and  forces  the  medial  malleolus  and  talus  downward  and  medially,  giving  rise  to  flat  foot. 

The  advantages  of  the  obhquity  and  pecuUar  arrangement  of  the  posterior  talo- 
calcaneal  articulation  are  seen  in  walking: — (i)  for  the  posterior  facet  of  the  calcaneus  receives 


THE  TARSAL  JOINTS 


303 


the  whole  weight  of  the  body  when  the  heel  is  first  placed  on  the  ground;  (ii)  by  the  upward 
pressure  of  this  facet  against  the  talus  it  transfers  the  weight  to  the  ball  of  the  toes  as  the  heel 
is  raised,  the  posterior  edge  of  the  sustentaculum  tali  and  the  anterior  and  lateral  part  of  the 
upper  surface  of  the  calcaneus  preventing  the  talus  from  being  displaced  too  far  forward  by 
the  superincumbent  weight;  and  (iii)  the  calcaneus  serves  to  suspend  the  talus  when,  with  the 
heel  raised  by  muscular  action,  the  other  foot  is  being  swung  forward. 

Fig    334  — ^Lateral  View  of  the  Ligaments  op  the  Foot  and  Ankle. 


Posterior  lateral  malleolar 
ligament 


Anterior  lateral  malleolar  bgament 


Anterior  (mterosseous)  talo- 
calcaneal  ligament 
Lateral  calcaneo  navic 
ular  ligament 


Posterior  talo-fibular  ligament 


JJorsal  cuboideo  navicular  \ 

ligament  I 

Medial  calcaneo-cuboid       Dorsal     Lateral     Calcaneo-fibular  ligament 
calcaneo-      talo- 
cuboid     calcaneal 
ligament 

(b)  The  Articulations  of  the  Anterior  Part  of  the  Tarsus 

These  include   (i)   the  cuboideo-navicular;   (ii)  cuneo-navicular;   (iii)  inter- 
cuneiform; and  (iv)  cuneo-cuboid  joints. 


(i)  The  Cuboideo-navicular  Union 

Class. — Diarthrosis.  Subdivision. — A  rthrodia . 

The  joint  cavity  is  only  occasionally  present  and  this  joint  is  often  included 
in  the  transverse  tarsal. 

The  ligaments  which  unite  the  cuboid  and  navicular  are: — 


Dorsal. 


Plantar. 


Interosseous. 


The  dorsal  cuboideo-navicular  ligament  (fig.  334)  runs  forward  and  laterally  from  the 
lateral  end  of  the  dorsal  surface  of  the  navicular  to  the  middle  third  of  the  medial  border  of  the 
cuboid  on  its  dorsal  aspect,  passing  over  the  posterior  lateral  angle  of  the  third  cuneiform  bone. 
It  is  wider  laterally. 

The  plantar  cuboideo-navicular  ligament  is  a  well-marked  strong  band,  which  runs  forward 
and  laterally,  from  the  plantar  surface  of  the  navicular  to  the  depression  on  the  medial  siurface 
of  the  cuboid,  and  slightly  into  the  plantar  surface  just  below  it. 

The  interosseous  cuboideo-navicular  ligament  is  a  strong  band  which  passes  between  the 
apposed  surfaces  of  these  bones  from  the  dorsal  to  the  plantar  ligaments.  Some  of  its  posterior 
fibres  reach  the  plantar  surface  of  the  foot  behind  the  cuboideo-navicular  ligament,  and  radiate 
laterally  and  backward  over  the  medial  border  of  the  cuboid  to  blend  with  the  anterior  ex- 
tremity of  the  plantar  calcaneo-cuboid  ligament. 


304  THE  ARTICULATIONS 

(ii)  The  Cuneo-navicular  Articulation 

Class. — Diarthrosis.  Subdivision. — Arthrodia. 

The  ligaments  uniting  tlie  navicular  with  the  three  cuneiform  bones  are : — 

Dorsal.  Plantar. 

Medial. 

The  dorsal  cuneo-navicular  ligament  is  very  strong,  and  stretches  as  a  continuous  structure 
on  the  dorsal  surface  of  the  navicular,  between  the  tubercle  of  the  navicular  on  the  medial  side, 
and  the  dorsal  cuboideo-navicular  ligament  laterally,  passing  forward  and  a  little  laterally  to 
the  dorsal  surfaces  of  the  three  cuneiform  bones. 

The  medial  cuneo-navicular  ligament  is  a  very  strong  thick  band  which  connects  the  tuber- 
cle of  the  navicular  with  the  medial  surface  of  the  first  cuneiform  bone.  It  is  continuous 
with  the  dorsal  and  plantar  ligaments.  Its  lower  border  touches  the  tendon  of  the  tibialis 
posterior. 

The  plantar  cuneo-navicular  ligament  forms,  like  the  dorsal,  a  continuous  structure  ex- 
tending between  the  plantar  surfaces  of  the  bones.  Its  fibres  pass  forward  and  laterally.  It 
is  in  relation  below  with  the  tendon  of  the  tibialis  posterior. 

It  must  be  noticed  that  the  expanded  tendon  of  insertion  of  the  tibialis  posterior,  and  the 
ligaments  uniting  the  navicular  with  the  cuboid  and  cuneiform  bones,  pass  forward  and  later- 
aUy,  while  the  peroneus  longus  tendon  and  the  ligaments  uniting  the  first  and  second  rows  of 
bones,  except  the  medial  half  of  the  dorsal  talo-navicular  ligaments,  pass  forward  and  medially. 
This  arrangement  is  admirably  adapted  to  preserve  the  arches  of  the  foot,  and  especially  the 
transverse  arch.  Had  these  tendons  and  ligaments  run  directly  forward,  all  the  strain  on  the 
transverse  arch  would  have  fallen  on  the  interosseous  ligaments,  but  as  it  is,  the  arch  is  braced 
up  by  the  above-mentioned  structures. 

(iii)  The  Intercuneiform  and  (iv)  The  Cuneo-cuboid  A^'ticulations 
Class. — Diarthrosis.  Subdivision — Arthrodia. 

The  uniting  ligaments  of  these  bones  are  divided  into  three  sets : — 

Dorsal.  Plantar. 

Interosseous. 

The  dorsal  ligaments  are  three  in  number,  two,  the  dorsal  intercuneiform,  connecting  the 
three  cuneiform  bones,  and  a  thhd,  the  dorsal  cuneo-cuboid,  uniting  the  third  cuneiform  with 
the  cuboid.  They  pass  between  the  contiguous  margins  of  the  bones,  and  are  blended  behind 
with  the  dorsal  ligaments  of  the  cuboideo-navicular  and  cuneo-navicular  joints. 

The  plantar  ligaments  are  two  in  number:  a  very  strong  one,  the  plantar  intercuneiform, 
passes  laterally  and  forward  from  the  lateral  side  of  the  base  of  the  first  cuneiform  to  the  apex 
of  the  second  cuneiform,  winding  somewhat  to  its  lateral  side.  The  second,  the  plantar  cuneo- 
cuboid,  connects  the  apex  of  the  third  cuneiform  with  the  anterior  half  of  the  medial  surface  of 
the  cuboid  along  its  plantar  border,  joining  with  the  plantar  cuboideo-navicular  hgament 
behind. 

The  interosseous  ligaments  are  three  in  number.  They  are  strong  and  deep  masses  of 
ligamentous  tissue  which  connect  the  second  cuneiform  with  the  first  and  third  cuneiform  bones, 
and  the  third  cuneiform  with  the  cuboid;  occupying  all  the  non-articular  portions  of  the  apposed 
surfaces  of  the  bones.  The  ligaments  extend  the  whole  vertical  depth  between  the  second  cunei- 
form and  the  third,  and  the  third  cuneiform  and  the  cuboid,  and  blend  with  the  dorsal  and 
plantar  ligaments;  they  are  situated  in  front  of  the  articular  facets,  and  completely  shut  off 
the  synovial  cavity  behind  from  that  in  front.  The  hgament  between  the  first  and  second  cunei- 
form bones  occupies  the  inferior  and  anterior  two-thirds  of  the  apposed  surfaces,  and  does  not 
generally  extend  high  enough  to  separate  the  synovial  cavity  of  the  anterior  tarsal  joint  from  that 
of  the  second  and  third  metatarsal  and  cuneiform  bones.  If  it  does  extend  to  the  dorsal  sur- 
face, it  divides  the  facets  completely  from  one  another,  making  a  seventh  synovial  sac  in  the 
foot. 

The  synovial  cavity  will  be  described  later  on. 

The  arterial  supply  is  from  the  metatarsal  and  plantar  arteries. 

The  nerves  are  derived  from  the  deep  peroneal  and  medial  and  lateral  plantar. 
The  movement  permitted  in  these  joints  is  very  limited,  and  exists  only  for  the  purpose  of 
adding  to  the  general  pliancy  and  elasticity  of  the  tarsus  without  allowing  any  sensible 
alteration  in  the  position  of  the  dilferent  parts  of  the  foot,  as  the  medio-tarsal  and  talo-cal- 
caneal  joints  do.  It  is  simply  a  gUding  motion,  and  either  deepens  or  widens  the  transverse 
arch.  The  third  cuneiform  being  wedged  in  between  the  others  is  less  movable,  and  so  forms 
a  pivot  upon  which  the  rest  can  move.  The  movement  is  more  produced  by  the  weight  of 
the  body  than  by  direct  muscular  action;  and  of  the  muscles  attached  to  this  part  of  the 
tarsus,  all  deepen  the  arch  save  the  tibiahs  anterior,  which  pulls  the  first  cuneiform  up,  and 
so  tends  to  widen  it. 


THE  TARSAL  JOINTS 


305 


(c)  The  Tbansverse  Tarsal  Joints 

The  articulations  of  the  anterior  and  posterior  portions  of  the  tarsus,  although 
in  the  same  transverse  line,  consist  of  two  separate  joints,  viz.,  (i)  a  medial,  the 
talo-navicular,  which  communicates  with  the  anterior  talo-calcaneal  articulation; 
and  (ii)  a  lateral,  the  calcaneo-cuboid,  which  is  complete  in  itself.  The  move- 
ments of  the  anterior  upon  the  posterior  portions  of  the  foot  take  place  at  these 
joints  simultaneously.  It  will  be  most  convenient  to  deal  with  the  joints  sepa- 
rately as  regards  the  ligaments;  while  the  arteries,  nerves,  and  movements  will 
be  considered  together. 


(i)  The  Talo-navicular  Articulation 

Class. — Diarthrosis.  Subdivision. — Enarthrodia. 

This  is  the  only  ball-and-socket  joint  in  the  tarsus.  It  communicates  with 
the  anterior  talo-calcaneal  articulation,  and  two  of  the  ligaments  which  close  it  in 
do  not  touch  the  talus,  but  pass  from  the  calcaneus  to  the  navicular.  The  uniting 
ligaments  include,  in  addition  to  the  articular  capsule,  the  following: — 


Lateral  calcaneo-navicular. 


Plantar  calcaneo-navicular 


Talo-navicular. 

The  lateral  calcaneo-navicular  has  been  already  described  (p.  302). 

The  plantar  calcaneo-navicular  ligament  (figs.  335  and  336)  is  an  exceedingly  dense,  thick 
plate  of  fibro-elastio  tissue.  It  extends  from  the  sustentaculum  tali  and  the  under  surface  of 
the  calcaneus  in  front  of  a  ridge  curving  laterally  to  the  anterior  tubercle  of  that  bone,  to  the 

Fig.  335. — View  of  the  Foot  from  above,  with  the  Talus  removed  to  show  the  Plantar 
AND  Lateral  Calcaneo-navicular  Ligamenti? 


Dorsal  cuboideo-navicular  ligament 

Dorsal  calcaneo-cuboid  ligament' 

Medial  calcaneo-cuboid  ligament* 

Lateral  calcaneo-navicular  ligament' 

Plantar  calcaneo-navicular 

ligament 
Tendon  of  tibialis  posterior 

Cut  edge  of  interosseous  ligament' 


whole  width  of  the  inferior  surface  of  the  navicular,  and  also  to  the  medial  surface  of  the  navicular 
behind  the  tubercle.  Medially  it  is  blended  with  the  anterior  portion  of  the  deltoid  ligament  of 
the  ankle,  and  laterally  with  the  lower  border  of  the  lateral  calcaneo-navicular  hgament.  It 
is  thickest  along  the  medial  border.  Its  upper  surface  loses  the  well-marked  fibrous  appear- 
ance which  the  ligament  has  in  the  sole,  and  becomes  smooth  and  faceted.  In  contact 
with  the  under  surface  of  the  ligament  the  tendon  of  the  libialis  posterior  passes,  giving  consider- 
able support  to  the  head  of  the  talus  by  assisting  the  power  and  protecting  the  spring  of  the 
ligament.  The  fibres  of  the  ligament  run  forward  and  mediaUy.  On  account  of  its  elasticity  it 
is  sometimes  termed  the  spring  ligament. 


306 


THE  ARTICULATIONS 


The  talo -navicular  ligament  is  a  broad,  thin,  but  well-marked  layer  of  fibres  which  passes 
from  the  dorsal  and  lateral  surfaces  of  the  neck  of  the  talus  to  the  whole  length  of  the  dorsal 
surface  of  the  navicular.  Many  of  the  fibres  converge  to  their  insertion  on  the  navicular.  The 
fibres  low  down  on  the  lateral  side  blend  a  little  way  from  their  origin  with  the  upper  edge  of 
the  lateral  calcaneo-navicular  ligament,  and  then  pass  forward  and  medially  to  the  navicular; 
those  next  above  pass  obliquely  and  with  a  distinct  twist  over  the  upper  and  lateral  side  of  the 
head  of  the  talus  to  the  centre  of  the  dorsum  of  the  navicular,  overlapping  fibres  from  the  medial 
side  of  the  talus  as  well  as  some  from  the  anterior  ligament  of  the  ankle-joint. 

Synovial  membrane. — The  talo-navicular  is  lined  by  the  same  synovial  membrane  as  the 
anterior  talo-calcaneal  joint. 


(ii)  The  Calcaneo-cuboid  Articulation    - 


Class. — Diarthrosis. 


Subdivision. — Saddle-shaped  Arthrodia. 


The  ligaments  which  are  supplementary  to  the  articular  capsule  and  unite 
the  bones  forming  the  outer  part  of  the  medio-tarsal  joint  are: — 


Medial  calcaneo-cuboid. 
Long  plantar. 


Dorsal  calcaneo-cuboid. 
Plantar  calcaneo-cuboid. 


The  medial  calcaneo-cuboid  ligament  (fig.  335)  is  a  strong  band  of  fibres  attached  to  the 
calcaneus  along  the  medial  jiiirt  ol'  the  non-articular  ridge  above  the  articular  facet  for  the  cuboid, 
and  also  to  the  upper  part  of  tlie  medial  surface  close  to  the  articular  margin,  and  passes  forward 
to  be  attached  to  the  depression  on  the  medial  surface  of  the  cuboid,  and  also  to  the  rough  angle 


Fig.  336. — Ligaments  op  the  Sole  of  the  Left  Foot. 


Long  plantar  ligament 


Tendon  of  peroneuslongus 


Groove  for  flexor  hallucis  longus 


Plantar  calcaneo-navicular  ligament 


_U ^Plantar    calcaneo-cuboid 

(short  plantar)  ligament 


'    "A — Tubercle  of  navicular 

"".if 


Medial    cuneiform 


Insertion  of  peroneus  longus 


between  the  medial  and  inferior  surfaces.  At  the  calcaneus  this  ligament  is  closely  connected 
with  the  lateral  calcaneo-navicular  Mgament.  Toward  the  sole  it  is  connected  with  the  plantar 
calcaneo-cuboid  ligament,  and  superiorly  with  the  dorsal  calcaneo-cuboid. 

The  dorsal  calcaneo-cuboid  (fig.  335)  is  attached  to  the  dorsal  surfaces  of  the  two  bones, 
extending  low  down  laterally  to  blend  with  the  lateral  part  of  the  plantar  calcaneo-cuboid 
ligament.  Over  the  medial  half,  or  more,  the  ligament  stretches  some  distance  beyond  the  mar- 
gins of  the  articular  surfaces,  reaching  well  forward  upon  the  cuboid  to  be  attached  about 
midway  between  its  anterior  and  posterior  borders;  but  toward  the  lateral  side,  the  ligament 
is  much  shorter,  and  is  attached  to  the  cuboid  behind  its  tubercle. 


TARSO-METATARSAL  JOINTS  307 

The  long  plantar  ligament  (fig.  336)  is  a  strong,  dense  band  of  fibres  which  is  attached  pos- 
teriorly to  the  whole  of  the  inferior  surface  of  the  calcaneus  between  the  posterior  tubercles  and 
the  rounded  eminence  (the  anterior  tubercle)  at  the  anterior  end  of  the  bone.  Most  of  its  fibres 
pass  directly  forward,  and  are  fixed  to  the  lateral  two-thirds  or  more  of  the  oblique  ridge  behind 
the  peroneal  groove  on  the  cuboid,  while  some  pass  further  forward  and  medially,  expanding 
into  a  broad  layer,  and  are  inserted  into  the  bases  of  the  second,  thu-d,  fourth,  and  medial  half 
of  the  fifth  metatarsal  bones.  This  anterior  expanded  portion  completes  the  canal  for  the 
peroneus  hiugiiK  tvndnn,  and  from  its  under  surface  arise  the  oblique  adductor  hallucis  and  the 
flexor  quinii  iliijili  lircris  muscles. 

The  plantar  calcaneo-cuboid  (short  plantar)  (fig.  336)  is  attached  to  the  rounded  eminence 
(anterior  tubercle)  at  the  anterior  end  of  the  under  surface  of  the  calcaneus,  and  to  the  bone  in 
front  of  it,  and  then  takes  an  oblique  course  forward  and  medially,  and  is  attached  to  the  whole 
of  the  depressed  inferior  surface  of  the  cuboid  behind  the  oblique  ridge,  except  its  lateral  angle. 
It  is  strongest  near  its  lateral  edge,  and  is  formed  by  dense  strong  fibres. 

The  synovial  membrane  is  distinct  from  that  of  any  other  tarsal  joint. 

The  arterial  supply  of  the  medio-tarsal  joints  is  from  the  anterior  tibial,  from  the  tarsal 
and  metatarsal  branches  of  the  dorsalis  pedis,  and  from  the  plantar  arteries. 

The  nerve-supply  of  the  medio-tarsal  joints  is  from  the  lateral  division  of  the  deep 
peroneal,  and  occasionally  from  the  superficial  peroneal  or  lateral  plantar. 

Relations. — On  the  dorsal  aspect  of  the  mid-tarsal  joint  lie  the  tendons  of  the  tibialis 
anterior,  extensor  hallucis  longus,  extensor  digitorum  longus,  and  peroneus  tertius,  the  muscular 
part  of  the  extensor  digitorum  brevis,  the  dorsalis  pedis  artery,  and  the  anterior  tibial  nerve. 
On  its  plantar  aspect  are  the  tendons  of  the  flexor  digitorum  longus  and  hallucis  longus,  quadratus 
plantse  (accessorius),  and  the  medial  and  lateral  plantar  vessels  and  nerves.  It  is  crossed  later- 
ally by  the  tendons  of  the  peroneus  longus  and  brevis  and  medially  by  the  tendon  of  the  tibialis 
posterior. 

The  movements  which  take  place  at  the  medio-tarsal  joints  are  mainly  flexion  and  extension, 
with  superadded  side-to-side  and  rotatory  movements.  Flexion  at  these  joints  is  simultaneous 
with  extension  of  the  ankle,  and  vice  versa.  Flexion  and  extension  do  not  take  place  upon  a 
transverse,  but  round  an  oblique,  axis  which  passes  from  the  medial  to  the  lateral  side,  and  some- 
what backward  and  downward  through  the  talus  and  calcaneus. 

Combined  with  flexion  and  extension  is  also  some  rotatory  motion  round  an  antero-posterior 
axis  which  turns  the  medial  or  lateral  border  of  the  foot  upward.  There  is  also  a  fail'  amount 
of  side-to-side  motion  whereby  the  foot  can  be  inclined  medially  (i.  e.,  adducted)  or  laterally 
(i.  e.,  abducted). 

These  movements  of  the  medio-tarsal  joint  occur  in  conjunction  with  those  of  the  ankle' 
a,nd  talo-calcaneal  joints.  Rotation  at  the  talo-calcaneal  joint  is,  however,  round  a  vertical 
axis  in  a  horizontal  plane,  and  so  turns  the  toes  medially  or  laterally;  whereas  at  the  medio- 
tarsal  union  the  axis  is  antero-posterior  and  the  medial  or  lateral  edge  of  the  foot  is  turned  up- 
ward. Gliding  at  the  talo-calcaneal  joint  elevates  or  depresses  the  edge  of  the  foot,  while  at 
the  medio-tarsal  it  adducts  or  abducts  the  toes  without  altering  the  relative  position  of  the  cal- 
caneus to  the  talus. 

Thus  flexion  at  the  medio-tarsal  joint  is  associated  with  adduction  and  medial  rotation 
of  the  foot,  occurring  simultaneously  with  extension  of  the  ankle;  and  extension  at  the  medio- 
tarsal  joint  is  associated  with  abduction  and  lateral  rotation,  occurring  simultaneously  with 
flexion  of  the  ankle. 

Flexion  and  medial  rotation  are  far  more  free  than  extension  and  lateral  rotation,  which 
latter  movements  are  arrested  by  the  ligaments  of  the  sole  as  soon  as  the  foot  is  brought  into  the 
position  in  which  it  rests  on  the  ground. 

Although  the  talo-navicular  is  a  baU-and-socket  joint,  yet,  owing  to  the  union  of  the 
navicular  with  the  cuboid,  its  movements  are  limited  by  the  shape  of  the  calcaneo-cuboid  joint; 
this  latter  being  concavo-convex  from  above  downward,  prevents  rotation  round  a  vertical  axis, 
and  also  any  side-to-side  motion  except  in  a  direction  obliquely  downward  and  mediaUy,  and 
upward  and  laterally.  This  is  also  the  direction  of  freest  movement  at  the  talo-navicular  joint. 
Movement  is  also  limited  by  the  ligamentous  union  of  the  calcaneus  with  the  navicular.  The 
twisting  movement  of  the  foot,  such  as  turning  it  upon  its  medial  or  lateral  edge,  and  the  increase 
or  diminution  of  the  arch,  take  place  at  the  tarsal  joints,  especially  the  medio-tarsal  and  talo- 
calcaneal  articulations.  Here  too  those  changes  occur  which,  owing  to  paralysis  of  some  mus- 
cles or  contraction  of  others,  result  in  talipes  equino-varus,  or  valgus. 

Muscles  which  act  on  the  mid-tarsal  joint. — Medial  rotators. — Tibialis  anterior  and  posterior 
acting  simultaneously;  they  are  aided  by  the  flexor  digitorum  longus  and  flexor  hallucis  longus. 
Lateral  rotators. — The  peronei  longus,  brevis,  and  tertius,  acting  simultaneously.  They  are 
aided  by  the  extensor  digitorum  longus. 

6.  THE  TARSO-METATARSAL  ARTICULATIONS 

There  may  be  said  to  be  three  articulations  between  the  tarsus  and  metatarsus, 
viz. : — 

(a)  The  medial,  bet'ween  the  first  cuneiform  and  first  metatarsal  bones. 

(6)  The  intermediate,  between  the  three  cuneiform  and  second  and  third 
metatarsal  bones. 

(c)  The  lateral,  or  cubo-metatarsal,  between  the  cuboid  and  fourth  and  fifth 
metatarsal  bones. 


308  THE  ARTICULATIONS 

(a)  The  Medial  Taeso-metatarsal  Joint 

Class. — Diarthrosis.  Subdivision. — Arthrodia. 

A  complete  articular  capsule  unites  the  first  metatarsal  with  the  first  cunei- 
form, the  fibres  of  which  are  very  thick  on  the  inferior  and  medial  aspects;  those 
on  the  lateral  side  pass  from  behind  forward  in  the  interval  between  the  interos- 
seous ligaments  which  connect  the  two  bones  forming  this  joint  with  the  second 
metatarsal.  The  ligament  on  the  plantar  aspect  is  by  far  the  strongest,  and 
blends  at  the  cuneiform  bone  with  the  cuneo-navicular  ligament. 

(6)  The  Intermediate  Taeso-metatarsal  Joint 
Class. — Diarthrosis.  Subdivision. — Arthrodia. 

Into  this  union  there  enter  the  three  cuneiform  and  second  and  third  meta- 
tarsal bones,  which  are  bound  together  by  the  following  ligaments  (supplementary 
to  the  articular  capsule) :  dorsal,  plantar,  interosseous. 

The  dorsal  ligaments. — 1.  Some  short  fibres  cross  obliquely  from  the  lateral  edge  of  the 
first  cuneiform  bone  to  the  medial  border  of  the  base  of  the  second  metatarsal  bone;  they  take 
the  place  of  a  dorsal  metatarsal  hgament,  which  is  wanting  between  the  first  and  second  meta- 
tarsal bones. 

2.  Between  the  second  cuneiform  and  the  base  of  the  second  metatarsal  bone  some  fibres 
run  directly  forward. 

3.  The  third  cuneiform  is  connected  with  (1)  the  lateral  corner  of  the  second  metatarsal 
bone  by  a  narrow  band  passing  obliquely  medially;  (2)  with  the  third  metatarsal  by  fibres 
passing  directly  forward;  and  (3)  with  the  fourth  metatarsal  by  a  short  band  passing  obUquely 
laterally  to  the  medial  edge  of  its  base. 

The  plantar  ligaments. — A  strong  hgament  unites  the  first  cuneiform  and  the  bases  of  the 
second  and  third  metatarsal  bones.  The  tibialis  posterior  is  inserted  into  these  bones  close 
beside  it.  Other  slender  ligaments  connect  the  second  cuneiform  with  the  second,  and  the  third 
cuneiform  with  the  third  metatarsal  bones. 

The  interosseous  ligaments. — (1)  A  strong  broad  interosseous  hgament  extends  between 
the  lateral  surface  of  the  first  cuneiform  and  the  medial  surface  of  the  base  of  the  second  meta- 
tarsal bone.  It  is  attached  to  both  bones  below  and  in  front  of  the  articular  facets,  and  sepa- 
rates the  intermediate  [from  the  medial  tarso-metatarsal  joint.  (2)  A  second  band  is  attached 
behind  to  a  fossa  on  the  anterior  and  lateral  edge  of  the  third  cuneiform  and  to  the  interosseous 
ligament  between  it  and  the  cuboid,  and  passes  horizontally  forward  to  be  attached  to  the  whole 
depth  of  the  fourth  metatarsal  bone  behind  its  medial  facet,  and  to  the  opposed  surfaces  of  the 
third  and  fourth  below  the  articular  facets  upon  their  sides.  It  separates  the  middle  tarso- 
metatarsal, and  intermetatarsal  between  the  third  and  fourth  bones,  from  the  oubo-metatarsal 
joint.  It  is  more  firmly  connected  with  the  third  bone  than  with  the  fourth.  (3)  A  slender 
ligament  composed  only  of  a  few  fibres  often  passes  from  a  small  tubercle  on  the  medial  and  an- 
terior edge  of  the  third  cuneiform  to  a  groove  on  the  lateral  edge  of  the  second  metatarsal  bone 
between  the  two  facets  upon  then-  sides. 

The  synovial  membrane  is  prolonged  forward  from  that  of  the  naviculari-cuneiform  and 
inter-cuneiform  articulations. 

The  arteries  for  the  tarso-metatarsal  joints  are  derived: — (1)  for  the  medial,  from  the  dor- 
saUs  pedis  and  medial  plantar;  (2)  for  the  rest,  twigs  from  the  arcuate  and  deep  plantar  arch. 

The  nerve-supply  comes  from  the  deep  peroneal  and  plantar  nerves. 

The  movements  permitted  at  these  joints  are  flexion  and  extension  of  the  metatarsus  on 
the  tarsus;  and  at  the  medial  and  lateral  divisions,  slight  adduction  and  abduction.  In  the 
lateral,  the  side-to-side  motion  is  freer  than  in  the  medial  joint,  and  freest  between  the  fifth 
metatarsal  bone  and  the  cuboid.  In  the  medial  joint,  flexion  is  combined  with  sUght  abduction 
and  extension  with  abduction. 

There  is  also  a  little  gliding,  which  aflows  the  transverse  arch  to  be  increased  or  diminished 
in  depth;  the  medial  and  lateral  two  bones  sliding  downward,  and  the  two  middle  a  little 
upward,  when  the  arch  is  increased;  and  vice  versa  when  the  arch  is  flattened. 

(c)  The  Lateral  or  Cubo-metatarsal  Joint 

Class. — Diarthrosis.  Subdivision. — Arthrodia. 

The  bones  comprising  this  joint  are  the  fourth  and  fifth  metatarsal  and  the 
anterior  surface  of  the  cuboid,  firmly  connected  on  all  sides  by  the  articular  cap- 
sule, strengthened  by  the  following  ligaments: — 

Dorsal.  Plantar.  Interosseous. 

The  plantar  cubo-metatarsal  ligament  is  a  broad,  well-marked  ligament,  which  extends 
from  the  cuboid  behind  to  the  bases  of  the  fourth  and  fifth  metatarsal  bones  in  front.     It  is 


INTERMETATARSAL  JOINTS 


309 


continuous  along  the  groove  at  the  base  of  the  fifth  metatarsal  bone  with  the  dorsal  ligament, 
and  as  it  passes  round  the  lateral  border  of  the  foot  it  is  somewhat  thickened,  and  may  be  de- 
scribed as  the  lateral  cubo-metatarsal  ligament.  On  its  medial  side  it  joins  the  interosseous 
ligaments,  thus  completing  the  capsule  below.  It  is  not  a  thick  structure,  and  to  see  it  the  long 
plantar  ligament,  the  peroneus  longus,  and  lateral  slip  of  the  tibialis  posterior  must  be  removed; 
the  attachment  of  these  structures  to  the  fourth  and  fifth  metatarsal  bones  considerably  assists 
to  unite  them  with  the  tarsus. 

The  dorsal  cubo-metatarsal  ligament  is  composed  of  fibres  which  pass  obliquely  outward 
and  forward  from  the  cuboid  to  the  bases  of  the  fourth  and  fifth  metatarsal  bones.  They  com- 
plete the  capsule  above,  and  are  continuous  laterally  with  the  lateral  cubo-metatarsal  hgament. 

The  interosseous  ligament  shuts  off  the  cubo-metatarsal  from  the  middle  tarso-metatarsal 
joint.  It  is  attached  to  the  third  cuneiform  behind,  and  to  the  whole  depth  of  the  fourth  meta- 
tarsal behind  its  medial  facet,  and  to  the  apposed  surfaces  of  the  third  and  fourth  bones  below 
their  articular  facets.     It  is  continuous  below  with  the  plantar  ligament. 

The  synovial  membrane  is  separate  from  the  other  synovial  sacs  of  the  tarsus,  and  is  con- 
tinued between  the  fourth  and  fifth  metatarsal  bones. 

Relations. — The  line  of  the  tarso-metatarsal  joints  is  crossed  dorsally  by  the  tendons  of 
the  long  and  short  extensor  muscles  of  the  toes  and  the  tendon  of  the  peroneus  tertius.  On 
the  plantar  aspect  it  is  in  relation  with  the  obUque  adductor  of  the  great  toe,  the  short  flexor 
of  the  great  toe,  the  lateral  plantar  artery,  and  the  tendon  of  the  peroneus  longus.  Its  medial 
end  is  subcutaneous  except  that  it  is  crossed,  near  the  plantar  surface,  by  a  slip  of  the  tendon 
of  the  tibialis  anterior,  and  its  lateral  end  is  crossed  by  the  tendon  of  the  peroneus  brevis. 

Fig.  337. — Section  to  show  the  Synovial  Cavities  op  the  Foot. 


7.  THE  INTERMETATARSAL  ARTICULATIONS 


Class. — Diarthrosis. 


Sub  division. — A  rthrodia . 


The  bases  of  the  metatarsal  bones  are  firmly  held  in  position  by  dorsal,  plantar, 
and  interosseous  ligaments,  supplementing  the  articular  capsules.  The  first 
occasionally  articulates  by  means  of  a  distinct  facet  with  the  second  metatarsal 
(figs.  245  and  246). 

The  dorsal  ligaments  are  broad,  membranous  bands  passing  between  the  four  lateral  toes 
on  their  dorsal  aspect;  but  in  place  of  one  between  the  first  and  second  metatarsal  bones,  a 
ligament  extends  from  the  first  cuneiform  to  the  base  of  the  second  metatarsal  bone. 

The  plantar  ligaments  are  strong,  thick,  well-marked  ligaments  which  connect  the  bones  on 
their  plantar  aspect. 

The  interosseous  ligaments  are  three  in  number,  very  strong,  and  are  situated  at  the  points 
of  union  of  the  shaft  with  the  bases  of  the  bones,  and  fill  up  the  sulci  on  their  sides.  They  limit 
the  synovial  cavities  in  front  of  the  synovial  facets. 

The  common  synovial  membrane  of  the  tarsus  extends  between  .the  second  and  third,  and 
third  and  fourth  bones;  that  of  the  cubo-metatarsal  joint  extending  between  the  fourth  and  fifth. 

The  arterial  and  nerve-supply  is  the  same  as  for  the  tarso-metatarsal  joints. 

The  movements  consist  merely  of  gliding,  so  as  to  allow  the  raising  or  widening  of  the 
transverse  arch.  Considerable  flexibihty  and  elasticity  are  thus  given  to  the  anterior  part  of 
the  foot,  enabling  it  to  become  moulded  to  the  irregularities  of  the  ground. 


The  Union  of  the  Heads  of  the  Metatarsal  Bones 

The  heads  of  the  metatarsal  bones  are  connected  on  their  plantar  aspect  by 
the  transverse  ligament  [Ligg.  capitulorum  transversa],  consisting  of  four  bands 


310  THE  ARTICULATIONS 

.  of  fibres  passing  transversely  from  bone  to  bone,  blending  witli  the  fibro-cartilagi- 
nous  or  sesamoid  plates  of  the  metatarso-phalangeal  joints,  and  the  sheaths  of  the 
flexor  tendons  where  they  are  connected  witli  the  fibro-cartilages.  It  differs 
from  the  corresponding  ligament  in  the  hand  by  having  a  band  from  the  first  to 
the  second  metatarsal  bone. 

8.  THE  METATARSO-PHALANGEAL  ARTICULATIONS 

(0)  The  Metatarso-phalangeal  Joints  op  the  Four  Lateral  Toes 

Class. — Diarthrosis.  Subdivision. — Condylarthrosis. 

These  joints  are  formed  by  the  concave  proximal  ends  of  the  first  phalanges 
articulating  with  the  rounded  heads  of  the  metatarsal  bones,  and  united  by 
articular  capsules  strengthened  by  the  following  ligaments: — 

Collateral.  Dorsal.  Plantar  accessory. 

The  two  collateral  ligaments  are  strong  bands  passing  from  a  ridge  on  each  side  of  the  head 
of  the  metatarsal  bone  to  the  sides  of  the  proximal  end  of  the  first  phalanx,  and  also  to  the  sides 
of  the  sesamoid  plate  which  unites  the  two  bones  on  their  plantar  surfaces.  On  the  dorsal 
aspect  they  are  united  liy  the  dorsal  ligament. 

The  dorsal  ligament  consists  of  loose  fine  fibres  of  areolo-fibrous  tissue,  extending  between 
the  collateral  ligaments,  thus  completing  a  capsule.  It  is  connected  by  fine  fibres  to  the  \inder 
surface  of  the  extensor  tendons,  which  pass  over  and  considerably  strengthen  this  portion  of  the 
capsule. 

The  plantar  accessory  ligament  or  sesamoid  plate  helps  to  deepen  the  shallow  facet  of  the 
phalanx  for  the  head  of  the  metatarsal  bone,  and  corresponds  to  the  accessory  volar  ligament  of 
the  fingers.  It  is  firmly  connected  to  the  collateral  Ugaments  and  the  transverse  ligament,  and 
is  grooved  inferiorly  where  the  flexor  tendons  pass  over  it.  It  serves  to  prevent  dorsal  disloca- 
tion of  the  phalanx. 

The  second  metatarso-phalangeal  joint  is  6  mm.  (J  in.)  in  front  of  both  the  first  and  third 
metatarso-phalangeal  joints. 

The  third  metatarso-phalangeal  joint  is  6  mm.  (J  in.)  in  front  of  the  foui-th,  and  the  fourth 
9  mm.  (I  in.)  in  front  of  the  fifth. 

The  head  of  the  fifth  metatarsal  is  in  line  with  the  neck  of  the  fourth. 

Thus  the  lateral  side  of  the  longitudinal  arch  of  the  foot  is  shorter  than  the  medial,  it  is 
also  distinctly  shallower. 

(b)  The  Metatarso-phalangeal  Joint  of  the  Great  Toe 

The  metatarso-phalangeal  joint  of  the  great  toe  differs  from  the  rest  in  the 
folloTftdng  particulars : — 

(1)  The  bones  are  on  a  larger  scale,  and  the  articular  surfaces  are  more  extensive. 

(2)  There  are  two  grooves  on  the  plantar  surface  of  the  metatarsal  bone,  one  on  each  side 
of  the  median  hne,  for  the  sesamoid  bones. 

(3)  The  sesamoid  bones  replace  the  accessory  plantar  ligament  (sesamoid  plate).  They 
are  two  small  hemispherical  bones  developed  in  the  tendons  of  the  flexor  hallucis  brevis,  convex 
below,  but  flat  above  where  they  play  in  grooves  on  the  head  of  the  metatarsal  bone;  they  are 
united  by  a  strong  transverse  hgamentous  band,  which  is  smooth  below  and  forms  part  of  the 
channel  along  which  the  long  flexor  tendon  plays.  They  are  firmly  united  to  the  base  of  the 
phalanx  by  strong  short  fibres,  but  to  the  metatarsal  bone  they  are  joined  by  somewhat  looser 
fibres.  At  the  sides  they  are  connected  with  the  collateral  ligaments  and  the  sheath  of  the  flexor 
tendon.  They  provide  shifting  leverage  for  the  flexor  hallucis  brevis  as  well  as  for  the  flexor 
hallucis  longus. 

The  arteries  come  from  the  digital  and  metatarsal  branches ;  and  the  nerves  from  the  cuta- 
neous digital,  or  from  small  twigs  of  the  nerves  to  the  interossei  muscles. 

The  movements  permitted  are:  flexion,  extension,  abduction,  adduction,  and  circumduction. 

Flexion  is  more  free  than  extension,  and  is  limited  by  the  extensor  tendons  and  dorsal  liga- 
ments; extension  is  limited  by  the  flexor  tendons,  the  plantar  fibres  of  the  collateral  ligaments, 
and  the  sesamoid  plates.  The  side-to-side  motion  is  possible  from  the  shape  of  the  bony  surfaces, 
but  is  very  limited,  being  most  marked  in  the  great  toe.  It  is  limited  by  the  collateral  ligaments 
and  sesamoid  plates. 

9.  THE  INTERPHALANGEAL  JOINTS 

Class. — Diarthrosis.  Subdivision. — Ginglymus. 

The  articulations  between  the  first  and  second  and  second  and  third  phalanges 
of  the  toes  are  similar  to  those  of  the  fingers,  with  this  important  difference,  that 


INTERPHALANGEAL  JOINTS  311 

the  bones  are  smaller  and  the  joints,  especially  between  the  second  and  third 
phalanges,  are  often  ankylosed.  The  ligaments  which  unite  them  include,  in 
addition  to  the  articular  capsule : — 

Collateral.  Dorsal.  Accessory  plantar. 

The  two  collateral  ligaments  are  well  marked,  and  pass  on  each  side  of  the  joints  from  a 
little  rough  depression  on  the  head  of  the  proximal,  to  a  rough  border  on  the  side  of  the  base  of 
the  distal  phalanx  of  the  joint. 

The  dorsal  ligament  is  thin  and  membranous,  and  extends  across  the  joint  from  one  col- 
lateral ligament  to  the  other  beneath  the  extensor  tendon,  with  the  deep  surface  of  which  it  is 
connected  and  by  which  it  is  strengthened. 

The  accessory  plantar  ligament  covers  in  the  joint  on  the  plantar  surface.  It  is  a  fibro- 
cartilaginous plate,  connected  at  the  sides  with  the  collateral  hgaments,  and  with  the  bones  by 
short  ligamentous  fibres;  the  plantar  surface  is  smooth,  and  grooved  for  the  flexor  tendons. 

The  arteries  and  nerves  are  derived  from  the  corresponding  digital  branches. 

The  only  movements  permitted  at  these  joints  are  flexion  and  extension. 

At  the  interphalangeal  joint  of  the  great  toe  there  is  very  frequently  a  small  sesamoid  bone 
which  plays  on  the  plantar  surface  of  the  first  phalanx,  in  the  same  way  as  the  sesamoid  bones 
of  the  metatarso-phalangeal  joint  play  upon  the  plantar  surface  of  the  head  of  the  metatarsal 
bone. 

Relations  of  the  muscles  acting  on  the  metatarso-phalangeal  and  interphalangeal  joints 
of  the  foot. — If  the  student  will  refer  to  the  accounts  given  of  the  relations  of  the  corresponding 
joints  in  the  hand  and  of  the  actions  of  the  muscles  upon  those  joints,  and  if  he  contrasts  and 
compares  the  muscles  of  the  hand  with  those  of  the  foot,  he  will  readily  be  able  to  construct 
tables  of  the  relations  of  the  metatarso-phalangeal  and  interphalangeal  joints  of  the  foot,  and 
tables  of  the  muscles  acting  upon  the  joints. 

References. — A  complete  bibliography  for  the  joints  is  given  in  the  "Hand- 
buch  der  Anatomie  und  Mechanik  der  Gelenke,"  by  Professor  Rudolf  Tick  (in  von 
Bardeleben's  Handbuch  der  Anatomie).  References  are  also  given  in  the  larger 
works  on  human  anatomy  by  Quain,  Rauber-Kopsch,  Poirier-Charpy,  etc. 
References  to  the  most  recent  literature  may  be  found  in  Schwalbe's  Jahres- 
bericht,  the  Index  Medicus  and  the  various  anatomical  journals. 


SECTION    IV 

THE  MUSCULATURE 

Revised  fob  the  Fifth  Edition 
By  C.  R.  BARDEEN,  A.B.,  M.D. 

PROFESSOR    OF    ANATOMY    IN   THE    UNIVERSITT    OF   WISCON  SIN 


MUSCLES,  the  movements  of  which  are  under  the  control  of  the  will,  almost 
completely  envelope  the  skeletal  framework  of  the  body;  close  in  the  oral, 
abdominal,  and  pelvic  cavities;  separate  the  thoracic  from  the  abdominal 
cavity;  surround  the  pharynx  and  the  upper  portion  of  the  cesophagus;  and  are 
found  connected  with  the  eye,  ear,  larynx,  and  other  organs.  They  constitute 
about  two-fifths  to  three-sevenths  of  the  weight  of  the  body. 

In  this  section  an  account  is  given  of  the  gross  anatomy  of  the  musculature 
attached  to  the  skeleton  and  the  skin,  with  the  exception  of  certain  of  the 
muscles  which  are  more  conveniently  treated  in  connection  with  the  organs  to 
which  they  are  appended.  Thus,  the  muscles  of  the  eye,  the  ear,  the  pharynx, 
the  larynx,  and  the  intrinsic  muscles  of  the  tongue  are  described  in  the  sections 
devoted  to  those  structures. 

Relations  to  the  skin. — Beneath  the  skin  is  a  sheet  of  connective  tissue,  the 
tela  subcutanea.  In  this,  in  some  regions  of  the  body  (the  head,  neck,  and  palm), 
thin,  flat,  subcutaneous  muscles  are  embedded.  Superficial  muscles  of  this  kind 
constitute  a  panniculus  carnosus,  much  more  extensive  in  the  lower  mammals  than 
in  man.  The  tela  subcutanea  is  separated  from  the  more  deeply  seated  muscu- 
latiu-e  by  areolar  tissue,  which,  in  most  places,  is  loose  in  texture  over  the  muscles. 
In  some  regions,  as  over  the  upper  part  of  the  back,  the  tela  subcutanea  is  firmly 
united  to  the  underlying  musculature  and  is  less  freely  movable.  In  the  tela  sub- 
cutanea more  or  less  fat  is  usually  embedded.  This  constitutes  the  panniculus 
adiposus,  which  varies  greatly  in  thickness  in  different  parts  of  the  body.  As  a 
rule,  it  is  much  more  developed  over  muscles  than  over  those  regions  where  bone 
and  joints  lie  beneath  the  skin.  From  the  tela  subcutanea  of  the  eyelids,  penis, 
and  scrotum  fat  is  absent.  The  deeper  layer  of  the  tela  subcutanea  is  more  or  less 
free  from  fat,  and  in  it  run  the  main  trunks  of  the  cutaneous  nerves  and  vessels. 
In  some  regions,  as  over  the  lower  part  of  the  abdomen,  one  or  more  fibrous  mem- 
branes are  differentiated  in  this  deeper  layer. 

To  the  tela  subcutanea  the  term  superficial  fascia  has  been  commonly  applied,  but  since 
this  leads  to  a  confusion  with  the  superficial  fascia;  which  immediately  invest  the  muscles,  it 
seems  better  to  restrict  the  term  fascia  to  the  membranes  connected  with  the  muscular  system, 
and  to  use  the  term  tela  subcutanea  for  the  layer  of  connective  tissue  which  underlies  the  skin 
and  is  continuous  over  the  whole  surface  of  the  body. 

In  several  places  where  the  skin  overlies  bony  prominences  well-marked 
synovial  bursse,  or  sacs  (bursae  mucosae),  are  developed  in  the  tela  subcutanea. 

Since  the  skin  and  the  subcutaneous  tissue  must  be  removed  in  order  to  study 
the  muscles  of  various  regions,  the  tela  subcutanea  and  subcutaneous  bm-sse  may 
be  conveniently  described  in  connection  with  the  muscles,  and  brief  references  will, 
therefore,  be  made  to  them  in  connection  with  the  musculature  of  various  regions. 

Muscle  fasciae. — The  musculature  of  the  body,  with  the  exception  of  some  of 
the  subcutaneous  muscles,  is  ensheathed  by  fibrous  tissue,  which,  in  certain  regions 
forms  distinct  membranes,  while  in  other  regions  it  is  delicate  and  not  clearly  to  be 
distinguished  from  the  superficial  connective  tissue  of  the  muscles,  the  perimy- 

313 


I 


314  THE  MUSCULATURE 

sium  externum.  The  membranes,  or  muscle  fasciae,  are  united  to  various  parts 
of  the  skeleton,  eitlaer  directly  or  by  means  of  intermuscular  septa,  and,  where 
strong,  keep  the  underlying  musculature  in  place.  In  some  regions  they  are  united 
to  the  muscles;  in  others  they  are  separated  from  the  underlying  musculature  by 
loose  areolar  tissue,  which  allows  free  movement  between  the  surface  of  the  mus- 
cles and  the  overlying  fascia.  The  best  example  of  a  strong  fascia  of  this  nature 
is  that  which  envelopes  the  extensor  muscles  of  the  thigh.  Where  the  fasciee  are 
well  developed,  the  main  bundles  of  constituent  fibres  take  a  course  directly  or 
obliquely  transverse  to  the  direction  of  the  underlying  muscles.  They  may  be 
composed  of  several  successive  layers  of  fibrous  tissue,  the  fibres  of  one  layer  tak- 
ing a  different  direction  from  those  of  the  next  layer. 

The  function  of  the  fascicS  is  the  mechanical  one  of  restraining  or  modifying  muscle  action. 
The  direction  of  the  main  component  fibre-bundles  indicates  the  direction  of  the  greatest  stress 
to  which  the  fascia?  are  subjected.  Indirectly  the  fasciae  promote  the  circulation  of  the  blood 
and  lymph  in  places  where  the  vessels  lie  between  the  contracting  muscles  and  the  overlying 
fascia. 

Intermuscular  septa. — Muscle  fasciae  enclose  not  only  the  external  layer 
of  the  musculature  of  the  body,  but  also  the  various  groups  of  more  deeply 
seated  muscles.  In  addition,  between  the  individual  muscles,  and  between  the 
different  layers  and  groups  of  muscles,  there  intervenes  a  greater  or  less  amount  of 
connective  tissue,  sometimes  loose  in  texture,  sometimes  dense  in  structure.  In 
these  intermuscular  septa  run  the  chief  nerves  and  blood-vessels  of  the  region  in 
which  the  musculature  lies. 

Gross  structure  of  the  muscles. — The  muscles  are  composed  of  bundles  of  red- 
dish fibres  surrounded  by  a  greater  or  less  extent  of  white  and  glistening  connective 
tissue.  They  are  attached  by  prolongations  of  this  tissue  in  the  form  of  tendons 
or  aponeuroses  usually  to  the  bony  skeleton,  but  also  in  places  to  cartilages,  as  in 
the  thorax  and  larynx;  to  the  skin,  as  in  the  face;  to  mucous  membranes,  as  in  the 
tongue  and  cheeks;  to  the  tendons  of  other  muscles,  as  in  the  case  of  the  lumbrical 
muscles;  to  muscle  fasciae,  as  in  the  case  of  the  oblique  and  transverse  muscles  of 
the  abdomen;  and  to  other  structures,  as,  for  instance,  to  the  eyeball. 

The  fleshy  portion  of  the  muscle  is  called  the  belly.  The  belly  is  usually 
attached  at  one  extremity  to  a  portion  of  the  skeleton  or  to  some  other  structure 
which  serves  as  a  support  for  its  action  on  the  structures  to  which  its  other  ex- 
tremity is  attached.  The  attachment  to  the  more  fixed  part  is  called  the  origin  of 
the  muscle;  the  attachment  to  the  structure  chiefly  acted  on  is  called  the  insertion. 
Thus  the  origin  of  the  biceps  muscle,  the  chief  flexor  of  the  forearm  at  the  elbow, 
is  from  the  scapula;  the  insertion  is  into  the  radius  and  into  the  fascia  of  the  fore- 
arm. The  part  of  the  muscle  attached  to  the  origin  is  called  the  head  of  the  mus- 
cle. The  part  attached  to  the  insertion  is  sometimes  called  the  tail,  but  this  term 
is  much  less  frequently  used  than  the  former. 

The  muscles  vary  greatly  in  size  and  form.  Thus  the  stapedius  muscle  of  the 
middle  ear  is  a  slender  little  structure,  only  a  few  millimetres  long,  while  the  glu- 
teus maximus  muscle  of  the  hip  is  a  large,  rhomboid  structure  often  several  centi- 
metres thick  and  with  a  surface  area  of  over  500  square  centimetres.  The  length 
of  a  muscle  from  origin  to  insertion  may  be  much  less  than  the  width  of  the  muscle, 
as  in  the  intercostal  muscles;  or  much  greater  than  the  width,  as  in  most  of  the 
long  muscles  of  the  limbs.  The  thickness  of  a  muscle  is  usually  less  than  the  width 
— so  much  so  in  some  instances  that  the  muscle  is  described  as  flat,  sheet-like,  or 
ribbon-like;  while  in  other  instances  the  belly  is  cylindrical.  In  flat  muscles  the 
general  outline  is  usually  quadrilateral  or  triangular.  In  triangular  muscles  in 
most  instances  one  angle  of  the  triangle  marks  the  insertion  of  the  muscle,  while 
the  opposite  side  marks  the  origin.  In  cylindrical  muscles  the  belly  usually  has  a 
somewhat  fusiform  shape,  and  grows  smaller  both  toward  the  origin  and  the  in- 
sertion of  the  muscle. 

Some  muscles  are  divided  by  tendons  transverse  to  the  long  axis  of  the  muscle. 
When  one  such  tendon  exists,  the  muscle  is  called  digastric  (fig.  348) ;  when  sev- 
eral, polygastric,  e.  g.,  rectus  abdominis  (fig.  388). 

Two  muscle  masses  with  separate  origins  may  have  a  common  insertion.  Such 
muscles  are  usually  designated  bicipital  muscles  (biceps  muscles  of  the  arm  and 
thigh).  Other  muscles  have  three  heads  (the  triceps  muscle  of  the  arm)  or  four 
(the  quadriceps  muscle  of  the  thigh).     In  the  latter  case  special  names  are  given 


FINER  STRUCTURE  OF  MUSCLES  315 

to  the  four  parts  or  muscles  which  constitute  the  quadriceps  as  a  whole.  In  ad- 
dition to  these  comparatively  simple  compound  muscles  there  are  others  in  which 
the  various  component  fasciculi  and  the  tendons  of  origin  and  insertion  are  numer- 
ous and  complexly  interrelated.  The  intrinsic  muscles  of  the  back  offer  good 
illustrations  of  muscles  of  this  nature. 

In  addition  to  muscles  with  distinct  regions  of  origin  and  insertion,  there  are  a 
few  voluntary  muscles  which  surround  hollow  viscera  or  their  orifices  and  have  a 
circular  or  tube-like  form  (sphincter  muscles,  voluntary  muscles  of  the  oesophagus, 
■etc.). 

Number  of  muscles. — A  logical  constancy  does  not  appear  always  to  have  been 
followed  in  the  commonly  accepted  division  of  the  musculature  into  muscles  indi- 
vidually designated.  Most  of  the  muscles  are  symmetrically  placed  in  pairs,  one 
on  each  side  of  the  body.  Authors  not  only  vary  in  the  extent  to  which  they  carry 
the  subdivisions  of  the  musculature  on  each  side  of  the  body  into  individual 
muscles,  but  also  in  describing  muscles  placed  near  the  median  line  either  as  single 
muscles  with  bilateral  halves  or  as  paired  muscles.  In  addition  some  muscles  are 
not  constantly  present,  and  there  are  differences  of  opinion  as  to  which  of  these  less 
constant  muscles  should  be  classed  with  the  normal  musculature.  The  BNA 
recognises  347  paired  and  two  unpaired  skeletal  muscles,  and  47  paired  and  two 
unpaired  muscles  belonging  to  the  visceral  system  and  organs  of  special  sense. 
Of  the  skeletal  muscles  the  head  has  25  paired  and  one  unpaired;  the  neck  16 
paired;  the  back  112  paired;  the  thorax  52  paired,  one  unpaired;  the  abdomen  and 
pelvis  8  paired;  the  upper  extremity,  52  paired;  the  lower  extremity,  62  paired 
(Eisler). 

Finer  structure  of  muscles. — While  no  attempt  can  be  made  here  to  describe  in  detail  the 
finer  microscopic  features  of  muscle  structure,  some  of  the  more  general  features  of  muscle 
architecture  may  be  briefly  mentioned. 

The  contractile  cells  of  voluntary  muscle  are  long,  slender,  multinucleated  'fibres,'  the  pro- 
toplasm of  which  exhibits  both  cross  and  longitudinal  striation.  The  longitudinal  striation 
is  due  to  the  presence  of  fibrils  situated  in  the  sarcoplasma.  The  cross  striation  is  due  to  alter- 
nate segments  of  singly  and  doubly  refracting  substance  in  these  fibrils.  The  length  of  these 
fibres  in  the  human  body  varies  from  a  few  millimetres  to  sixteen  centimetres  or  more,  and  the 
thickness  from  ten  to  eighty  microns.  Each  muscle-fibre  is  surrounded  by  an  especially  differ- 
entiated sheath,  the  sarcolemma.  Outside  of  this  is  a  layer  of  delicate  connective  tissue,  the 
perimysium  internum  or  endomysium,  the  fibres  of  which  are  in  part  inserted  into  the  sarco- 
lemma. This  connective  tissue,  which  is  especially  developed  at  the  ends  of  the  fibres,  serves  to 
.attach  them  either  directly  to  the  structures  on  which  the  muscle  acts  or  to  the  skeletal  frame- 
work of  the  muscle. 

In  the  simplest  mammalian  muscles  the  muscle-fibres  take  a  parallel  course  from  tendon  to 
tendon,  and  are  not  definitely  bound  into  secondary  groups.  An  example  may  be  seen  in  fig. 
338,  a,  which  represents  two  segments  of  the  rectus  abdominis  muscle  of  a  mouse.  More  often, 
however,  the  individual  fibres  do  not  run  the  entu-e  distance  from  tendon  to  tendon,  but  instead 
.  they  interdigitate,  and  the  interdigitating  fibres  are  bound  up  into  secondary  and  tertiary 
anastomosing  fibre-bundles  by  connective  tissue,  in  which  there  is  usually  a  considerable  amount 
of  elastic  tissue.  Fig.  338,  b,  represents  diagrammatically  this  interdigitation  of  fibre-bundles  as 
seen  in  the  abdominal  musculature  of  one  of  the  larger  mammals. 

In  most  of  the  flat  muscles  of  the  body  the  fibre-bundles  either  take  a  nearly  parallel  course 
from  tendon  to  tendon  or  they  converge  from  the  tendon  of  origin  toward  the  tendon  of  insertion 
(see  fig.  338,  c-e).  The  gi-eater  the  distance  from  tendon  to  tendon,  the  more  marked  is  the 
interdigitation  of  the  constituent  fibre-bundles. 

In  elongated  muscles  the  tendons  of  origin  and  insertion  may  either  arise  near  the  extremities 
of  the  muscle  or  may  extend  for  a  considerable  distance  on  the  surface  or  within  the  substance  of 
the  muscle.  In  the  former  case  the  belly  of  the  muscle  is  composed  of  bundles  of  interdigitating 
fibres  which  take  a  course  parallel  with  the  long  axis  of  the  muscle.  This  is  shown  diagi'ammatic- 
ally  in  fig.  338,  f.  An  example  may  be  seen  in  the  sartorius  muscle  of  the  thigh  (fig.  411). 
When  the  tendons  extend  far  on  the  surface  or  within  the  substance  of  the  muscle,  the  con- 
stituent fibre-bundles  take  a  course  oblique  to  the  long  axis  of  the  muscle.  When  they  take  a 
course  from  a  tendon  of  origin  on  one  side  toward  a  tendon  of  insertion  on  the  other,  the  muscle 
is  called  unipenniform  (see  fig.  338,  g,  and  the  extensor  digitorum  longus,  fig.  415).  In  other 
instances  the  fibre-bundles  converge  from  two  sides  toward  a  central  tendon.  Such  a  muscle 
is  called  bipenniform  (see  fig.  338,  h,  and  the  flexor  hallucis  longus,  fig.  416).  When  there 
are  several  tendons  in  the  muscle  between  which  the  fibre-bundles  run  obliquely,  the  muscle 
is  called  multipenniform.  In  fusiform  muscles  the  tendons  usually  either  embrace  the  ex- 
tremity of  the  muscle  like  a  hollow  cone,  or  they  extend  far  on  the  surface  or  within  the  sub- 
stance of  the  muscle.  In  such  muscles  the  fibre-bundles  take  a  curved  course  from  one  tendon 
to  the  other.  The  bundles  which  arise  highest  on  one  tendon  are  inserted  highest  on  the  other, 
and  the  fibre-bundles  of  lowest  origin  have  the  lowest  insertion.  This  structm-e  is  diagram- 
matically shown  in  fig.  338,  i.  A  good  example  may  be  found  in  the  rectus  femoris  muscle 
(fig.  411). 

Many  other  arrangements  of  the  fibre-bundles  are  found,  and  the  arrangements  here  shown 
may  be  variously  combined.     In  most  muscles  the  architecture  is  decidedly  complex.     In  the 


316 


THE  MUSCULATURE 


more  complex  muscles  dense  connective-tissue  septa,  or  intramuscular  fasciae,  serve  to  separate 
different  regions  of  the  muscle  from  one  another.  In  general  there  are  groups  of  muscle  fibre- 
bundles  surrounded  by  a  greater  amount  of  connective  tissue,  or  perimysium  internum,  than  that 
surrounding  the  individual  fibre-bundles,  and  the  latter  are  surrounded  by  a  denser  connective 

Fig.  338. — Diagrammatic  Outlines  to  Illustrate  Various  Types  op  Muscle  Archi- 
tecture AND  THE  Relations  of  the  Main  Nerve  Branches  to  the  Fibre-bundles  op 
THE  Muscle. 

a.  Two  segments  of  the  rectus  abdominis  muscle  of  a  small  mammal,  b.  Portion  of  sheet-like 
muscle  with  two  nerve-branches  and  intramuscular  nerve  plexus,  c.  Typical  quadrilateral 
muscle  with  nerve  passing  across  the  muscle  about  midway  between  the  tendons,  d  and  e. 
Two  triangular  muscles  with  different  types  of  innervation,  f.  Long  ribbon-like  muscle 
with  interdigitating  fibre-bundles,  g.  Unipenniforra  muscle,  h.  Bipenniform  muscle, 
i.  Typical  fusiform  muscle.  The  main  intramuscular  nerve-branches  are  distributed  to  the 
fibre-bundles  about  midway  between  their  origins  and  insertions,     n.  nerve. 


> 


V 


tissue  than  that  surrounding  the  component  muscle-fibres.  The  muscles  are  surrounded  exter- 
nally by  a  more  or  less  dense  sheet  of  connective  tissue  called  the  perimysium  externum,  or 
epimysium,  which  is  continuous  with  the  connective  tissue  within  the  muscle,  the  perimysium 
internum.  In  the  following  pages  'muscle  fibre-bundle'  is  used  to  denote  small  groups  of 
muscle-fibres,  'fasciculus'  to  denote  large,  more  or  less  isolated,  groups  of  fibre-bundles. 

Embryonic  development  of  muscles. — The  voluntary  muscles  are  of  mesodermal  origin. 
The  muscles  of  the  trunk  arise  chiefly  from  the  myotomes,  those  of  the  head  and  limbs  chiefly 
from  the  mesenchyme  in  these  regions.  New  muscle  fibres  are  formed  mainly  before  birth. 
After  birth,  growth  of  muscles  depends  on  growth  of  individual  muscle  fibres. 


TENDONS  317 

Tendons. — Muscles  vary  not  only  in  general  form  and  in  the  relations  of  the 
constituent  fibre-bundles  to  the  intrinsic  skeletal  framework,  but  also  in  the  mode 
of  attachment  to  the  parts  on  which  they  act.  In  many  instances  the  fibre-bun- 
dles impinge,  perpendicularly  or  obliquely,  directly  upon  a  bone  or  cartilage. 
The  tendinous  tissue  arising  from  the  fibre-bundles  of  the  muscle  here  is  attached 
to  the  periosteum  or  perichondrium  or  to  the  bone  directly.  A  broad  attachment 
is  thus  offered  the  muscle.  Instances  of  this  mode  of  attachment  may  be  seen  in  the 
attachment  of  the  intercostal  muscles  and  of  many  of  the  muscles  attached  to  the 
shoulder  and  hip  girdles. 

In  the  case  of  most  thin,  flat  muscles  the  muscle  is  continued  at  one  or  both 
extremities  into  thin,  tendinous  sheets  called  aponeuroses,  composed  of  connective 
tissue.  Well-marked  instances  may  be  seen  in  the  transverse  muscle  of  the  abdo- 
men (fig.  390),  and  the  trapezius  and  latissimus  dorsi  muscles  of  the  back  (fig.  355) . 
The  extent  of  development  of  these  aponeuroses  is  generally  inversely  proportional 
to  the  development  of  the  muscle — the  more  extensively  developed  the  muscle  is 
in  a  given  individual,  the  less  extensive  the  aponeurotic  sheet.* 

Most  muscles  are  continue,d  at  one  or  both  extremities  into  dense,  tendinous 
bands  which  may  be  comparatively  short  and  thick,  like  the  tendon  of  Achilles 
(fig.  413) ,  or  very  long  and  narrow,  like  the  tendon  of  the  palmaris  longus  (fig.  370) . 
In  this  latter  case  the  tendon  represents  in  part  the  remnants  of  musculattu-e 
more  highly  developed  in  the  lower  vertebrates.  In  most  instances,  however, 
the  tendons  are  structures  specifically  differentiated  for  definite  functions  and  are 
composed  of  bundles  of  parallel  connective-tissue  fibrils  held  together  by  an  inter- 
lacing fibrous-tissue  framework.  The  tendons  usually  contain  a  relatively  small 
amount  of  elastic  tissue. 

The  tendons  are  attached  to  the  skeleton  early  in  embryonic  development. 
As  the  bones  enlarge  the  tendons  become  in  part  incorporated  in  the  substance  of 
the  bone  and  ossified. 

In  some  tendons  sesamoid  bones  are  developed  in  the  neighbourhood  of  joints 
over  which  the  tendons  pass.  Examples  of  these  are  the  patella  at  the  knee-joint 
(fig.  412)  and  the  sesamoid  bones  of  the  thumb  and  great  toe. 

Where  muscles  or  tendons  closely  envelope  a  joint,  there  is  usually  formed  a 
close  union  between  the  connective  tissue  of  the  capsule  of  the  joint  and  that  of  the 
muscle  or  the  tendon.  Special  bands  may  develop  in  the  direction  of  the  pull 
of  the  muscle  (lig.  popliteum  obhquum). 

Where  tendons  run  for  some  distance  across  or  beneath  a  fascia,  they  are 
usually  either  bound  to  the  fascia  by  a  special  investment,  as  near  the  wrist  and 
knee  (fig.  366  and  fig.  414),  or  are  fused  with  the  fascia,  as  in  the  case  of  the  ilio- 
tibial  band.  Fibrous  tracts  in  the  fascia  may  indicate  stress  under  muscle  con- 
traction (the  lacertus  fibrosus  of  the  fascia  of  the  forearm) . 

Often  in  broad  aponeurotic  attachments  of  muscles  there  is  formed  in  the  ten- 
don near  the  attachment  a  fibrous  archway  [arcus  tendineus]  for  the  passage  of 
blood-vessels,  nerves,  muscles,  or  tendons.  The  tendinous  arch  is  either  fastened 
at  both  ends  to  the  bone,  or  at  one  end  it  is  connected  with'a  joint  capsule  or  other 
membrane.  The  dorsal  attachment  of  the  diaphragm  (fig.  391)  and  that  of  the 
adductor  magnus  to  the  femur  (fig.  409)  offer  good  examples  of  tendon  arches. 

In  digastric  and  polygastric  muscles  the  transverse  tendons  which  separate 
the  bellies  are  often  composed  of  narrow,  incomplete  bands  of  fibrous  tissue. 
Such  a  transverse  band  is  called  an  inscriptio  tendinea  (see  Rectus  Abdominis 
Muscle,  fig.  388). 

Tendon  sheaths. — The  tendons  are  held  in  place  by  sheaths  composed  of  dense 
connective  tissue.  These  sheaths  vary  in  different  regions.  In  the  most  com- 
plete form  they  confine  tendons  in  osseous  grooves  which  they  convert  into  osteo- 
fibrous  canals  on  the  flexor  surface  of  the  digits.  The  sheath  is  here  called  a 
vagina  fibrosa  tendinis.  It  is  strengthened  by  tendinous  bands  (vaginal  liga- 
ments). In  other  regions  special  dense  bands  or  ligaments,  retinacula  tendinum, 
confine  a  series  of  tendons  in  place,  as  at  the  ankle  (fig.  417),  or  fasciae  may  be 
modified  for  this  purpose,  as  at  the  back  of  the  wrist  (fig.  366) .     A  tendinous  loop, 

*  The  terms  fascia  and  aponeurosis  are  often  loosely  and  interchangeably  used.  It  seems 
best  to  make  a  distinction  by  restricting  the  term  fascia  to  membranous  sheets  of  investment, 
and  aponeurosis  to  broad  tendons.  The  latter  may,  however,  be  inserted  into  and  form  a  part 
of  the  former. 


> 


318  THE  MUSCULATURE 

annulus  fibrosus,  may  hold  a  tendon  in  place,  as,  for  instance,  the  trochlea  of  the 
tendon  of  the  superior  oblique  muscle  of  the  eye. 

Synovial  bursas  [bursae  mucosae]. — Where  there  is  freedom  of  action  between 
muscles  and  tendons  and  the  surrounding  parts,  there  intervenes  a  loose  connective 
tissue.  In  regions  where  the  pressure  is  great  or  considerable  friction  would  re- 
sult were  these  conditions  retained,  there  are  developed  special  cavities  with 
smooth  surfaces  and  containing  fluid.  Most  of  these  bursas  are  developed  from 
the  intervening  connective  tissue  at  a  period  in  embryonic  life  preceding  muscular 
activity,  but  special  bursas  may  later  be  developed  as  the  result  of  unusual  pressure 
or  muscular  activity  after  birth.  An  instance  of  a  bursa  lying  in  a  region  of  fric- 
tion may  be  seen  in  the  bur?a  intervening  between  the  tendinous  posterior  surface 
of  the  ilio-psoas  muscle  and  the  ilio-femoral  ligament.  As  an  instance  of  a  bursa 
lying  in  a  region  of  intermittent  pressure  may  be  cited  that  between  the  tendon  of 
Achilles  and  the  calcaneus. 

Most  synovial  burste  intervene  between  a  tendon  and  a  bone,  a  tendon  and  a 
ligament,  or  between  two  tendons  (subtendinous  bursse  mucosae).  Others  lie  be- 
tween two  muscles,  a  muscle  and  some  skeletal  part,  or  between  a  muscle  and  a 
tendon  (submuscular  bursae  mucosae) ;  or  below  a  fascia  (subfascial  bursae  mu- 
cosas). Subcutaneous  bm-sse  have  been  referred  to  in  connection  with  the  tela 
subcutanea  (see  p.  313).  Most  bursas  are  developed  near  joints.  The  bursae  may 
so  expand  during  active  life  that  they  come  to  communicate  with  other  bursae  or 
with  a  neighbouring  joint  cavity. 

Synovial  sheaths  [vaginae  mucosae  tendinum]. — Synovial  sheaths  are  developed 
about  tendons  where  the  latter  are  confined  in  osteo-fibrous  canals,  as  in  the 
fingers.  The  wall  of  the  canal  and  the  enclosed  tendon,  or  tendons,  are  each 
covered  by  a  smooth  membrane  which  at  the  extremities  of  the  canal  is  reflected 
from  the  wall  to  the  tendon.  Between  the  membrane  covering  the  tendon  and 
that  lining  the  canal  is  a  sjaiovial  cavity.  An  interesting  feature  of  these  tendon- 
sheaths  is  the  presence  of  mesotendons,  delicate  bands  of  vascular  connective 
tissue  which  run  in  places  from  the  osseous  groove  to  the  tendon  and  carrj^  blood- 
vessels and  nerves. 

Trochlese. — Where  a  tendon  passes  at  an  angle  about  a  bone,  the  tissue  in  the  groove  in 
which  the  tendon  runs  frequently  is  composed  of  hj'aUne  cartilage  instead  of  bone.  An  example 
may  be  seen  in  the  trochlear  process  of  the  calcaneus. 

Nerves. — To  each  muscle  of  the  body  a  nerve  containing  motor  and  sensory 
fibres  is  distributed.  A  few  muscles  receive  two  or  more  nerves.  Sherrington  has 
estimated  that  in  the  muscle-nerves  of  the  cat  two-fifths  of  the  fibres  are  sensory 
and  thi-ee-fifths  motor. 

The  muscles  of  the  liead  and  in  part  those  of  the  neck  are  supplied  by  branches 
of  the  cranial  nerves.  The  intrinsic  muscles  of  the  neck,  back,  thorax,  and  abdo- 
men are  supplied  by  branches  which  arise  fairljr  directty  from  the  spinal  nerves. 
The  muscles  of  the  limbs  are  supplied  by  branches  from  nerve-trunks  which  arise 
from  plexuses  formed  by  the  spinal  nerves  in  the  regions  near  which  the  limbs 
are  attached. 

The  main  nerve-trunks  lie  beneath  the  superficial  muscles.  They  usually  run  in  the 
intermuscular  septa  which  separate  the  deeper  groups  of  muscles  from  one  another  and  from 
the  superficial  muscles.  The  nerve-branches  which  enter  a  given  muscle  usually  pass  in  where 
the  larger  intramuscular  septa  approach  the  surface  of  the  muscle,  and  then  ramify  tlu-ough 
the  perimysium  internum,  the  smaller  branches  being  distributed  in  the  finer  layers  of  connective 
tissue  which  surround  and  separate  the  primary  muscle  fibre-bundles,  to  the  constituent  muscle- 
fibres  of  which  terminal  branches  are  given.  Special  sensory  end  organs  are  distributed  chiefly 
in  the  large  intramuscular  septa,  in  the  tendons  and  in  the  muscles  near  the  tendons.  Simple 
sensory  endings  are  found  on  the  muscle  fibres. 

The  size  of  a  nerve  supplying  a  muscle  is  not  proportional  to  the  size  of  the  latter,  but 
rather  to  the  comple.xity  of  movements  in  which  the  muscle  plays  a  part. 

Muscles  receive  then-  nerve  supply  early  in  development.  During  later  development  the 
muscle  may  wander  a  considerable  distance  from  its  place  of  origin  and  carry  its  nerve  with  it. 
The  diaphragm,  innervated  by  cervical  nerves,  is  a  good  example. 

The  distribution  of  the  motor  nerves  varies  according  to  the  architectm-e  of  the  muscle,  but 
in  general  it  appears  that  the  nerves  are  so  distributed  as  to  carry  the  main  branches  of  distri- 
bution most  directly  to  the  middle  of  the  constituent  fibre-bundles.  This  is  seen  most  clearly  in 
muscles  with  comparatively  short  fibre-bundles,  where  the  individual  muscle-fibres  run  nearly 
or  quite  the  entire  distance  from  tendon  to  tendon  (fig.  338  a,  c,  d,  e,  g,  h,  and  i).  When  the 
distance  is  long,  a  marked  plexiform  arrangement  is  found  (fig'.  338,  b  andf).    To  each  muscle 


NOMENCLATURE  319 

fibre  there  is  distributed  a  terminal  nerve-fibre  which  passes  through  the  sarcolemma  and  ends 
in  a  motor  end  organ  (muscle  plate) .  Occasionally  there  are  two  such  nerve-fibres  to  one  muscle- 
fibre. 

Vessels. — The  muscles  are  richly  supplied  with  blood.  In  many  instances  the 
larger  blood-vessels  accompany  the  larger  nerve-trunks  as  they  enter  the  muscle, 
and  their  primary  branches  are  distributed  in  the  larger  intramuscular  septa. 
Often,  however,  the  main  blood-vessels  approach  a  muscle  from  a  direction  dif- 
ferent from  that  taken  by  the  nerves.  Each  muscle  has,  however,  its  own  blood 
supply.  There  is  little  anastomosis  between  the  blood-vessels  of  a  muscle  and 
those  of  a  neighbouring  structure,  but  the  anastomosis  between  the  vessels  within 
the  muscle  is  exceedingly  rich.  Veins,  as  a  rule,  accompany  all  but  the  smallest 
arteries  within  the  muscle.  The  veins  are  richly  supplied  with  valves,  so  that 
muscle  contraction  promotes  the  flow  of  blood  through  the  muscle.  Rich  cap- 
illary plexuses  sm-round  the  muscle-fibres.  The  capillaries  are  of  unusually 
small  diameter. 

During  contraction,  the  blood  is  forced  from  the  muscles;  during  expansion 
it  rushes  in  through  dilated  arteries  which  furnish  five  or  six  times  as  much 
blood  to  muscles  during  exercise  as  that  supplied  to  them  during  rest. 

The  connective-tissue  sheaths,  the  larger  intramuscular  septa,  and  the  tendons 
of  muscles  are  richly  supplied  vnih.  lymphatics.  There  are  no  lymphatics  within 
the  muscle  bundles  or  in  small  muscles. 

Nomenclature. — The  names  of  the  various  muscles  and  their  classification  are 
less  satisfactory  than  is  desirable.  The  muscular  system  was  first  carefully 
studied  in  the  human  body,  and  names  based  sometimes  upon  the  shape,  structure, 
size,  or  position,  at  other  times  upon  the  supposed  function  or  other  associated 
facts,  were  applied  to  the  muscles  found  in  various  regions.  Sometimes  two  or 
more  names  were  applied  to  a  muscle  to  indicate  several  of  these  factors.  Thus 
trapezius  and  triangularis  indicate  the  shape  of  the  corresponding  muscles;  biceps 
or  triceps  indicates  the  origin  by  two  or  three  heads;  rectus,  obliquus,  and  irans- 
versus  represent  the  direction  taken  by  a  muscle  or  its  constituent  fibre-bundles; 
viagnus  and  minimus  indicate  size;  sublimis  (superficial)  and  profundus  (deep) 
represent  the  relative  positions  occupied;  sterno-cleido-mastoid  indicates  structures 
to  which  the  muscle  is  attached;  flexor  and  extensor  indicate  function;  and  sar- 
torius  indicates  that  the  corresponding  muscle  was  supposed  to  be  of  use  to  tailors. 

Since  careful  study  has  been  devoted  to  the  comparative  anatomy  of  the  muscles  in 
various  vertebrates,  it  has  become  apparent  that  a  simple  and  more  consistent  nomenclature 
applicable  to  corresponding  muscles  found  in  various  animals  would  be  of  great  value.  A 
satisfactory  nomenclature  of  this  sort  has  not,  however,  as  yet  been  devised  and  adopted  in 
comparative  anatomy,  and  the  established  usage  of  the  terms  now  familiarly  apphed  to  the 
muscles  of  the  human  body  makes  it  seem  improbable  that  even  if  such  a  system  were  devised 
for  comparative  anatomy  it  could  be  brought  into  extensive  use  in  human  anatomy.  For 
many  of  the  muscles  in  the  human  body  various  synonyms  have  been  in  use  in  different  countries. 
The  Anatomical  Congress  assembled  at  Basel  in  1895,  to  simpUf}'  the  nomenclature  of  human 
anatomy,  adopted  in  large  part  the  terms  in  familiar  use  in  England  and  America.  In  the 
following  pages  the  terms  approved  by  the  Congress  wiU  be  employed,  but  where  they  differ 
materially  from  those  previously  in  use,  the  synonym  wUl  be  given  in  parentheses. 

Classification. — The  muscles  are  usually  treated  strictly  according  to  the  region  of  the  body 
in  which  they  are  found.  This  method  of  consideration  is  still  of  value  in  a  dissector's  guide  and 
in  text-books  of  topographical  anatomy.  But  in  studying  the  muscles  scientifically  it  is  of 
importance  also  to  consider  them  in  their  more  fundamental  genetic  relationships  to  one  another 
and  to  the  nervous  system.  Embryology  and  comparative  anatomy  have  proved  of  the  greatest 
value  in  revealing  these  relationships.  Studies  of  this  nature  have  revealed  well-marked  rela- 
tionships in  the  adult  human  musculature  which  are  of  practical  as  well  as  scientific  importance 
The  voluntary  musculature  may  be  broadly  divided  into  that  of  the  skeletal  axis,  the  limbs,  and 
the  visceral  orifices.  The  musculature  of  each  of  these  divisions  has  a  different  and  in  general 
simpler  form  in  the  lower  than  in  the  higher  vertebrates,  and  in  the  embryos  of  the  higher 
vertebrates  than  in  the  adult.  The  musculature  of  the  spinal  region  of  the  body  axis  of  fishes, 
the  tailed  amphibia,  and  all  vertebrate  embryos  is  metamerically  segmented;  that  is,  it  is  divided 
along  the  axis  of  the  body  into  a  series  of  components  corresponding  with  the  segmentation  of 
the  vertebral  column.  Although  marked  alterations  take  place  in  the  subsequent  ontogenetic 
differentiation  in  higher  vertebrates,  traces  of  this  primitive  segmentation  are  still  to  be  found 
in  the  adult;  in  man,  for  instance,  in  the  intercostal  muscles  and  the  segments  of  the  rectus  ab- 
dominis. In  the  region  of  the  head  conditions  are  complex,  owing  to  the  concurrent  presence 
of  muscles  which  primitively  correspond  in  nature  with  the  segmental  spinal  musculature,  and 
muscles  non-segmental  in  character,  which  surround  the  visceral  orfices.  This  also  is  true  of 
the  anus  and  external  genitalia,  where,  however,  the  conditions  are  simpler.  Embrj'ology  and 
comparative  anatomy  have  done  much  to  clear  up  puzzling  features  in  both  regions. 

■  The  muscles  of  the  hmbs  are  metamerically  arranged  in  no  adult  vertebrate.     In  some  of  the 
lower  forms  a  series  of  axial  muscle  segments,  myotomes,  fm-nishes  material  from  which  the 


320  THE  MUSCULATURE 

musculature  of  the  limbs  is  differentiated.  In  the  mammals  this  appears  not  to  be  the  case,  and 
the  muscles  are  differentiated  from  the  non-segmental  tissue  of  the  hmb-buds. 

Where  mammalian  musculature  is  primitively  segmental,  each  segment  becomes  associated 
with  a  corresponding  spinal  nerve  or,  in  the  head,  with  a  nerve  which  corresponds  in  series  with  a 
spinal  nerve.  Even  when  subsequent  differentiation  brings  about  marlied  alterations  in  the 
axial  musculature,  the  nerves  maintain  to  a  considerable  degree  a  segmental  distribution. 

Into  each  of  the  limbs,  where  the  intrinsic  musculature  is  at  no  time  segmental,  there  extends 
during  embryonic  development  a  series  of  segmental  spinal  nerves,  so  that  in  them,  as  in  the 
region  of  the  body  axis,  a  certain  segmentation  in  the  nerve-supply  can  be  made  out  in  the  adult. 
That  part  of  the  limb  nearest  the  head  in  early  embryonic  development  has  its  muscles  supplied 
by  the  most  cranial,  that  part  nearest  the  caudal  extremity  of  the  body  by  the  most  caudal, 
of  the  nerves  which  supply  the  hmb  musculature.  There  is  here,  however,  considerable  over- 
lapping of  the  segmental  areas. 

Variation. — In  man  some  variation  in  the  arrangement  of  the  muscles  is  met 
with  in  every  individual,  and  often  marked  deviations  from  the  normal  conditions 
are  found.  The  muscles  vary  in  their  mode  of  origin  or  insertion,  and  in  the  ex- 
tent to  which  muscles  of  a  given  group  are  fused  with  one  another  or  to  which  the 
chief  parts  of  a  complex  muscle  are  isolated  from  one  another.  Some  muscles, 
like  the  palmaris  longus  and  the  plantaris,  are  frequently  entirely  absent,  and 
other  muscles  generally  absent  are  frequently  present. 

In  addition  to  these  frequent  variations  there  are  others  so  rare  that  many  authors  prefer 
to  speak  of  them  as  anomalies  rather  than  variations.  Sometimes  muscles  may  be  found 
doubled  by  longitudinal  division,  or  two  or  more  muscles  normally  present  may  be  fused  into 
a  single  indivisible  muscle.  Occasionally  there  occur  muscles  constantly  present  in  some  of 
the  lower  animals,  but  normally  not  met  with  in  the  human  body  (anomalies  of  reversion  or  of 
convergence).  In  such  instances  the  muscle  may  be  normally  represented  by  a  tendon  or  fascia. 
At  times  the  anomalies  are  supposed  to  be  not  a  reversion  to  an  ancestral  condition,  but  a  dis- 
tinct step  in  advance.  This,  however,  is  difficult  to  prove.  At  other  times  no  phylogenetic 
relation  is  apparent,  and  the  anomaly  is  looked  upon  as  a  monstrous  sport  or  as  the  result  of 
somepathological  condition. 

The  nerve-supply  of  the  muscles  is  of  value  in  the  study  of  muscle  variations. 
There  is,  however,  not  infrequent  variation  in  the  nerves  with  relation  to  the 
supply  of  the  muscles. 

Physiology. — From  the  standpoint  of  morphology  the  muscles  are  grouped 
according  to  their  intimate  relations  to  one  another  and  to  the  peripheral  nerves, 
relations,  as  noted  above,  that  are  made  more  clear  by  a  study  of  comparative 
anatomy  and  embryology.  From  the  physiological  aspect  a  different  grouping  of 
the  muscles  is  required,  because  muscles  belonging  morphologically  in  one  group 
may  have  different  physiological  functions  in  the  animal  body.  The  chief  features 
of  the  mechanical  action  of  muscles  may  be  briefly  considered  here. 

Most  muscles  act  on  the  bones  as  levers.  In  physics  three  types  of  levers 
are  recognised  In  levers  of  the  first  type  (fig.  339,  I)  the  fulcrum  (F)  lies  be- 
tween the  place  where  power  (P)  is  exerted  on  the  lever  and  the  point  of  resist- 
ance or  load  (L) .  Levers  of  this  kind  are  frequently  met  with  in  the  body. 
A  good  example  is  seen  in  the  attachment  of  the  skull  to  the  vertebral  column. 
The  fulcrum  lies  at  the  region  of  attachment;  the  weight  of  the  skull  tends  to 
bend  the  head  forward,  while  the  force  exerted  by  the  dorsal  muscles  of  the 
neck  serve  to  keep  the  head  upright  or  to  bend  it  back. 

In  levers  of  the  second  class  (fig.  339 II)  the  point  on  which  power  is  exerted 
moves  through  a  greater  distance  than  the  point  of  resistance.  Speed  of  move- 
ment is  thus  sacrificed  to  power.  Levers  of  this  type  are  exceedingly  rare  in 
the  animal  body.  An  example  in  the  human  body  is  the  foot  when  the  body  is 
raised  on  the  toes. 

In  levers  of  the  third  class  (fig.  339,  III)  the  point  on  which  force  is  exerted 
moves  a  less  distance  than  the  point  of  resistance.  Power  is  thus  sacrificed  to 
speed.  This  is  the  common  form  of  leverage  found  in  the  body.  A  good  ex- 
ample is  found  in  the  action  of  the  muscles  which  flex  the  forearm  on  the  arm. 
The  region  in  which  the  biceps  and  brachialis  are  attached  is  but  a  short  dis- 
tance from  the  elbow-joint  or  fulcrum,  while  the  hand  may  be  looked  upon  as 
the  region  of  resistance  to  the  force  exerted.  A  movement  of  the  point  P 
through  a  short  distance  will  cause  L  to  move  through  a  great  distance. 

The  more  the  angle  between  a  muscle  or  its  tendon  and  the  bone  on  which  it  acts  approaches 
a  right  angle,  the  greater  is  the  power  of  movement  exerted  by  the  muscle.  The  arm  in  fig.  339, 
III,  is  in  the  position  of  greatest  advantage  for  the  action  of  the  biceps  on  the  forearm.  All 
boys  know  that  it  is  easier  to  'chin'  oneself  after  the  arm  is  partly  bent  than  when  hanging 


PHYSIOLOGY 


321 


straight  from  a  bar.  Many  of  the  muscles  run  nearly  parallel  with  the  parts  on  which  they  act, 
but  the  tendons  before  their  attachment  are  usually  either  carried  over  a  bony  prominence  or 
some  fascia  or  hgament  acts  as  a  pulley  so  that  tlie  tendon  is  inserted  at  an  oblique  angle. 
At  other  times  a  process  for  the  attachment  of  the  tendon  projects  from  the  bone  and  causes 
the  force  of  the  contracting  muscle  to  be  more  advantageously  exerted  on  the  bone.  It  may, 
of  course,  readily  be  seen  that  the  greater  the  distance  of  the  attachment  of  a  muscle  from  the 
joint  over  which  it  acts,  the  greater  will  be  the  power  exerted  by  the  muscle. 

In  considering  the  movements  of  the  body,  it  is  convenient  to  recognise  two 
groups,  simple  and  complex.  To  the  former,  which  alone  can  be  considered  in 
a  text-book  of  anatomy,  belong  such  movements  as  flexion,  extension,  adduc- 
tion, rotation,  etc.,  while  to  the  latter  belong  those  associated  movements  which 
give  rise  to  changes  in  the  positions  of  the  body  as  a  whole  or  of  extensive 
regions  of  the  body. 

In  flexion  the  extremities  of  the  trunk  or  limbs  or  special  portions  of  these 
regions  are  bent  near  to  one  another;  in  extension  the  reverse  movement  is 
brought  about.  The  parts  are  straightened  or  even  bent  beyond  the  straight 
position  (over-extension). 

Fig.  339. — Thbee  Diagrams  (after  Testut)  to  Illustrate  Different  Types  of  Levers  in 
THEIR  Relations  to  the  Mechanical  Action  of  the  Muscles. 


m 

In  abduction  transverse  movements  are  made,  a  part  being  bent  away  from 
the  median  line  of  the  body  or  limb;  in  adduction  the  reverse  movement  is 
brought  about. 

In  rotation  a  part  is  turned  on  its  longitudinal  axis.  The  rotation  of  the 
femur  at  the  hip-joint  is  called  medial  rotation  when  the  toes  are  turned  medial- 
ward,  lateral  rotation  when  the  toes  are  turned  lateralward.  Rotation  at  the 
shoulder-joint  is  called  medial  when  the  thumb  is  turned  forward  and  medial- 
ward  toward  the  body,  lateral  when  the  reverse  movement  takes  place.  These 
movements  are  also  carried  out  at  the  elbow-joint,  but  here  medial  rotation  is 
called  pronation,  lateral  rotation,  supination.  Fick  prefers  these  terms  also  for 
the  rotation  at  other  joints  as  at  the  shoulder,  hip  and  knee. 

At  the  shoulder- joint  the  swinging  of  the  arm  toward  the  back  is  called  exten- 
sion; toward  the  front,  flexion;  and  from  the  side,  abduction.  Moving  the  arm 
toward  the  mid-dorsal  or  mid-ventral  line  is  called  adduction. 

Taking  the  body  as  a  whole  the  musculature  may  be  divided  into  two  main 
divisions,  an  ex-pander  division  and  a,  contractor  division.  In  general  the  extensors, 
abductors  and  lateral  rotators  expand,  the  flexors,  adductors  and  medial  rota- 
tors contract. 

In  the  most  expanded  condition  the  head  and  spine  are  extended  or  even  sUghtly  hyper- 
extended  (flexed  dorsally),  and  the  limbs  project  laterally  from  the  body  with  the  backs  of  the 
hands  and  feet  facing  dorsalward,  the  palms  and  soles  ventral  ward,  and  the  digits  spread  out. 
In  the  fully  formed  human  body  it  is  not  possible  to  put  the  lower  extremity  in  the  completely 
expanded  position,  although  it  is  in  this  position  early  in  embryonic  development.  As  develop- 
ment proceeds  the  lower  extremity  is  adducted  and  rotated  medialward  and  the  girdle  is  so  fixed 
that  full  abduction  becomes  no  longer  possible.  In  many  of  the  lower  vertebrates  full  abduction 
is  possible  throughout  life  in  the  lower  extremities  just  as  it  is  throughout  life  in  the  upper 
extremities  in  man.  Full  extension  of  the  spinal  column  in  man  is  also  hindered  in  the  thoracic 
region  by  the  thorax,  and  in  the  sacro-coccygeal  region  by  the  osseous  union  of  the  vertebrae 
with  one  another  as  well  as  by  the  attachment  of  the  hip  girdles.  The  lumbar  region  in  man  is 
in  a  condition  of  permanent  hyper-extension. 


322  THE  MUSCULATURE 

In  the  fully  contracted  condition  the  head  and  spinal  column  are  strongly  flexed,  and  the 
digits  are  adducted,  the  various  segments  of  the  Hmbs  are  flexed  and  the  Umbs  are  adducted, 
flexed  and  rotated  medialward  toward  the  middle  of  the  trunk.  The  body  approaches  a  ball 
in  form.  It  is  the  position  taken  by  a  gymnast  when  turning  a  somerset  in  the  air,  and  is  in 
marked  contrast  to  the  fuUy  expanded  condition  which  would  be  assumed  could  man  fly  Mke  a 
bat  or  glide  Uke  a  flying  squirrel. 

In  general,  the  muscles  which  tend  to  put  the  body  or  a  part  of  the  body  into  the 
expanded  position  form  a  distinct  group  as  contrasted  with  those  which  tend  to  put  the  body 
into  the  contracted  position.  The  chief  musculature  which  extends  the  head  and  trunk  lies 
dorso-lateral  to  the  spinal  column  and  is  supplied  by  the  dorsal  divisions  of  the  spinal  nerves. 
The  chief  musculature  which  flexes  the  head  and  trunk  lies  ventro-lateral  to  the  spinal  column 
and  is  supplied  by  ventro-lateral  divisions  of  the  spinal  nerves.  The  chief  muscles  which 
abduct,  extend  and  rotate  the  limbs  lateralward  arise  during  embryonic  development  on  the 
dorsal  sides  of  the  limb  buds  and  are  innervated  by  branches  from  the  dorsal  sides  of  the  brachial 
and  lumbo-sacral  nerve  plexus.  The  chief  muscles  which  flex,  adduct  and  rotate  the  Hmbs 
medialward  arise  on  the  ventral  sides  of  the  Umb  buds  and  are  supphed  by  nerves  which  arise 
from  the  ventral  sides  of  the  hmb  plexuses.  To  these  general  rules  there  are  some  exceptions, 
the  most  marked  of  which  is  at  the  hip-joint  where  rotation  of  the  girdle  has  brought  about  a 
condition  in  which  the  primitive  action  of  the  flexor  and  extensor  groups  is  partly  reversed.  The 
chief  flexors  (the  ilio-psoas  and  rectus  femoris)  belong  to  the  dorsal  division  and  some  of  the  chief 
extensors  (the  hamstring  muscles)  belong  to  the  ventral  division.  At  the  ankle-joint  the  ex- 
ception is  more  apparent  than  real.  What  is  usually  called  flexion  at  the  ankle-joint  is  really 
hyper-extension  and  the  reverse  movement  is  the  nearest  we  can  come  to  real  flexion.  In 
the  extremelj'  contracted  position  of  the  body  as  a  whole  the  feet  are  extended  (flexed  plantar- 
ward)  at  the  ankle-joint. 

Muscles  which  produce  a  movement  in  a  common  direction  are  called 
S3aiergists,  while  those  whose  contraction  produces  opposite  movements  are 
called  antagonists;  e.  g.,  the  flexors  and  extensors  are  antagonists.  In  the 
actual  working  of  the  muscular  system,  however,  when  a  set  of  muscles  is 
contracting  to  produce  a  movement,  the  antagonists  also  contract  to  a  .;ertain 
degree.  The  movement  is  the  result  of  nerve /^impulses^  sent  simultaneously  to 
all  the  muscles  which  act  on  the  part  moved. | 

The  relation  of  the  internal  architecture  of  a  muscle  to  the  movements  to  which  its  contrac- 
tion gives  rise  is  a  complex  subject,  the  details  of  which  cannot  be  entered  into  here.  In  general 
it  may  be  said  that  when  the  fibre-bundles  run  directly  from  one  attachment  to  the  other,  as  in 
fig.  338,  a  and  f,  the  force  exerted  by  the  contraction  of  the  individual  muscle-fibres  is  most 
efficiently  utilised  and  the  extent  of  the  movement  varies  directly  as  the  length  of  the  fibres, 
while  the  force  exerted  varies  directly  with  the  number  of  the  fibres. 

In  muscles  of  the  types  indicated  in  fig.  338,  g,  h,  i,  a  certain  amount  of  the  extent  of  move- 
ment and  of  the  force  exerted  by  the  contraction  of  the  individual  fibres  is  not  effectively 
exerted  on  the  parts  moved  by  the  muscles,  as  may  be  seen  by  applying  to  this  action  the  laws 
of  the  parallelogram  of  forces.  In  such  muscles,  however,  the  great  number  of  short  muscle- 
fibres  composing  them  makes  possible  the  exertion  of  great  power  with  some  loss  of  speed  of 
contraction  in  the  muscle  as  a  whole. 

The  direction  of  the  movements  which  result  from  muscular  contraction  is  in  large  part 
determined  by  the  shape  of  the  articular  surfaces,  none  of  which  are  to  be  looked  upon  as  simple 
fulcra,  but  instead,  during  a  given  movement,  the  fulcrum  shifts  from  one  region  to  another  of 
the  joint. 

In  different  muscles  the  extent  of  contraction  of  the  constituent  fibre-bundles  during 
activity  varies  considerably.  While  usually  the  length  of  the  contracted  fibre-bundles  is 
half  that  of  those  in  the  extended  state,  the  amount  of  shortening  in  some  muscles  is  only  25 
to  35  per  cent. 

Functional  activity  is  necessary  for  the  fuU  development  or  for  the  maintenance  of  develop- 
ment in  muscles.  Muscles  atrophy  if  their  nerve  supply  is  injured  or  if  they  are  passively 
prevented  from  contracting. 

Order  of  treatment. — The  muscles  and  fascia  are  here  treated  in  the  following 
order : — (1)  those  of  the  head  and  neck  and  shoulder  girdle  (p.  323) ;  (2)  those  of  the 
upper  extremity  (p.  360);  (3)  those  of  the  back  (p.  410);  (4)  those  of  the  thorax 
and  abdomen  (p.  422);  (5)  those  of  the  pelvic  outlet  (p.  439);  (6)  those  of  the 
lower  extremity  (p.  452).  The  reason  for  taking  up  the  musculature  in  the  order 
named  is,  that  during  embryonic  development  musculature  belonging  primitively 
to  the  head  comes  to  overlap  that  of  the  neck;  that  of  the  neck  spreads  over  the 
region  of  the  back  and  thorax,  and  becomes  attached  to  the  shoulder  girdle; 
that  of  the  arm  extends  over  the  region  of  the  thorax,  abdomen,  and  back;  that 
of  the  back  partially  over  the  region  of  the  thorax;  while  that  of  the  abdomen 
enters  into  intimate  relation  with  the  pelvic  girdle.  So  far  as  practicable  the 
musculature  of  these  various  regions  will  be  taken  up  according  to  fundamental 
morphological  relationships. 

Since  a  morphological  grouping  of  the  muscles  does  not  accord  perfectly  with 
a  physiological  grouping,  there  is  given  at  the  end  of  this  section  a  table  showing 
what  muscles  are  concerned  in  performing  the  simpler  voluntary  movements. 


HEAD,  NECK  AND  SHOULDER  GIRDLE 


323 


The  topographical  relations  of  the  muscles  in  various  regions  of  the  body  are 
illustrated  in  the  series  of  cross-sections  given  for  each  region. 

Tables  illustrating  the  relations  of  the  central  nervous  system  and  the  per- 
ipheral nerves  to  the  muscles  are  given  in  the  section  on  the  nervous  system 
(Section  VI). 

Fig.  340.— Human  Embryo  (Le)  42  mm.  Long.      (After  His.) 


Auditory  sac 
Branchial  clefts 


Upper  limb 

First  thoracic  myotome 


Sixth  thoracic  myoton 


First  Ijimbar  myotome 


I.    MUSCULATURE   OF   THE   HEAD,  NECK  AND 
SHOULDER  GIRDLE 


PHYSIOLOGICAL  AND  MORPHOLOGICAL  ASPECTS 

The  head,  situated  at  the  anterior  end  of  the  trunk  in  bilaterally  symmetrical 
animals,  is  primitively  that  part  of  the  body  first  brought  into  contact  with  new 
surroundings  as  the  animal  moves  forward.  We  therefore  find  developed  here 
the  most  highly  differentiated  organs  of  .special  sense,  those  of  vision,  hearing, 
and  smell,  through  which  the  animal  is  put  in  touch  with  an  environment  more  or 
less  removed  from  immediate  contact  with  the  body.     In  connection  with  these 


324  THE  MUSCULATURE 

organs  of  special  sense,  the  brain  is  developed.  In  most  animals  the  head  also 
is  the  chief  organ  for  the  prehension  of  food  and  for  attack  and  defense.  The 
neck  is  a  part  of  the  trunk  differentiated  to  give  freedom  to  the  movements  of  the 
head.  The  forelimbs,  relatively  unimportant  as  the  forefins  in  the  fishes,  become 
important  organs  of  locomotion  in  the  land  animals.  In  the  fishes  there  is  no 
true  neck,  but  the  forefins  are  developed  at  the  sides  of  the  cervical  part  of  the 
trunk.  In  the  higher  vertebrates  the  forelimbs  are  also  first  differentiated  at  the 
sides  of  the  cervical  region  (fig.  340)  but,  as  embryonic  development  goes  on,  they 
shift  caudalward  to  the  sides  of  the  cranial  (anterior)  part  of  the  thorax.  The 
cervical  region  is  thus  left  free  for  movement  but  the  musculature  and  nerves  of 
the  upper  extremity  remain  intimately  related  to  it. 

In  man,  with  the  assumption  of  the  erect  posture,  the  head  no  longer  has  to 
bear  the  brunt  of  the  new  surroundings  as  the  body  moves  forward.  There  is, 
however,  a  distinct  advantage  in  having  those  organs  of  special  sense,  which  put 
the  individual  into  touch  with  the  more  distant  parts  of  the  environment,  situated 
high  above  the  ground,  and  a  motile  neck  is  of  great  value  in  directing  the 
organs  of  special  sense  toward  various  parts  of  the  environment.  The  develop- 
ment of  the  superior  extremities  as  organs  for  the  prehension  of  food  and  as 
organs  of  attack  and  defense  reduces  the  value  of  the  head  for  these  purposes,  but 
still  leaves  it  the  important  functions  of  the  reception  of  food  and  air  and  the 
preparation  of  food  for  gastric  and  intestinal  digestion.  The  head,  furthermore, 
assumes  a  new  and  most  important  function  as  an  organ  for  the  expression  of  the 
emotions  and  of  speech. 

The  expression  of  the  emotions,  such  as  anger,  fear,  affection  and  the  like,* 
is  brought  about  largely  through  the  action  of  flat,  subcutaneous  "facialis" 
muscles  which  underlie  most  of  the  skin  of  the  face  and  head  and  extend  down 
under  that  of  the  neck  (figs.  341  and  344).  They  also  line  the  mucous  membrane 
of  the  lips  and  cheeks.  Most  of  them  arise  from  the  surface  of  the  skull  and  are 
inserted  into  the  skin,  which  they  pull  in  various  directions  causing  it  to  become 
smooth  or  twinkled,  according  to  the  direction  of  the  pull.  The  various  muscles 
are  grouped  about  the  buccal,  nasal  and  aural  orifices  and  about  the  orbit  of  the 
eye.  Some  of  the  fibre-bundles  are  arranged  so  as  to  constrict  the  orifices,  others 
radiate  out  so  as  to  dilate  them. 

The  chief  groups  of  muscles  of  the  head  and  neck,  in  addition  to  the  facialis 
group  just  mentioned,  are  the  muscles  of  the  orbit  and  middle  ear,  the  muscles 
used  in  mastication  and  swallowing  (cranio-mandibular,  supra-  and  infrahyoid 
groups,  muscles  of  the  tongue,  soft  palate  and  pharj^nx),  the  muscles  of  the 
larynx,  and  the  ventral  and  dorsal  groups  of  muscles  which  lie  in  the  region  of 
neck,  extend  over  the  thorax  and  move  the  head,  neck  and  shoulder  girdle.  A 
brief  summary  of  these  groups  will  be  given  before  proceeding  to  a  more 
detailed  account. 

Facialis  group. — The  muscles  are  especially  well  developed  about  the  mouth,  a 
sphincter  muscle  {orbicularis  oris)  serving  to  close,  the  radiating  muscles  to  open  the  lips 
{quadratus  labii  superioris  and  inferioris),  to  pull  the  corners  ot  the  mouth  in  various  directions, 
as,  for  instance,  upward  to  express  bitterness  {caninus)  or  pleasure  {zygomaticus) ,  or  lateral- 
ward  and  downward  to  express  grief  or  pain  (risorius,  triangularis,  plalysma)  or  to  protrude  the 
lips  as  in  pouting  {mentalis  and  incisive  muscles).  The  buccinator,  which  radiates  out  from  the 
corner  of  the  mouth  and  hues  the  mucous  membrane  of  the  cheek,  is  used  in  mastication  and 
whisthng. 

About  the  orbit  and  in  the  eyelids  a  circulai-  musculature  {orbicularis  oculi)  is  broadly 
developed.  It  is  usedto  close  the  eyes,  and  to  contract  the  skin  about  the  orbit.  Associated 
with  the  orbicularis  are  muscles  which  produce  perpendicular  furrows  in  the  skin  of  the  fore- 
head above  the  nose  (procerus,  corrugator).  The  skin  is  drawn  upward  from  the  orbit  and 
horizontal  furrows  are  caused  in  the  skin  ot  the  forehead  by  muscles  attached  to  the  scalp 
(epicranius).  Two  of  these  muscles,  the  occipitales,  arise  one  on  each  side  from  the  occipital 
bone  and  are  attached  to  an  aponeurosis  which  lies  beneath  the  scalp  to  which  it  is  firmly 
united.  Two  of  the  muscles,  the  frontales,  extend  one  on  each  side  from  this  aponein-osis  to  the 
skin  above  the  eyebrows. 

About  the  nasal  orifices  there  are  weak  constrictors  (alar  part  of  the  nasalis,  depressor  aloe 
nasi)  and  dilators  (dilator  naris  anterior  and  posterior,  transverse  part  of  the  nasalis,  angular 
head  of  the  quadratus  labii  superioris).  From  the  ear  (auricle)  three  flat  muscles  radiate, 
one  backward  (auricularis  posterior),  one  upward  (auricularis  superior)  and  one  forward 
(auricularis  anterior).  These  muscles  are  seldom  functionally  developed.  They  pull  the 
auricle  in  their  respective  directions.  They  may  be  looked  upon  as  (primitively)  dilators 
of  the  aural  orifice.  On  the  cartilage  of  the  auricle  are  several  rudimentary  "  intrinsic  "  muscles 
which  may  be  looked  upon  as  remnants  of  a  constrictor  of  this  orifice. 

*See  Darwin:  The  Expression  of  the  Emotions  in  Man  and  Animals. 


GROUPS  OF  MUSCLES  325 

In  the  orbital  cavity  there  are  six  muscles  which  are  attached  to  and  move  the 
eyeball  and  one  muscle  (the  levator  palpehroe  superioris)  which  extends  into  and  raises  the 
upper  lid  (fig.  341) .  Of  the  muscles  which  move  the  eyebaU  five  arise  hke  the  levator  of  the  lid, 
from  the  back  of  the  orbit.  Four  of  these,  the  rectus  muscles,  are  inserted  respectively  into  the 
superior,  inferior,  medial  and  lateral  sides  of  the  eyeball  and  direct  the  pupil  upward, 
downward,  medialward  and  lateralward.  One,  the  superior  oblique,  sends  a  tendon  through 
a  loop  at  the  upper,  front  part  of  the  nasal  side  of  the  orbit  and  thence  to  the  upper  surface 
of  the  eyeball.  Another  muscle,  the  mferior  oblique,  arises  from  the  nasal  side  of  the  front  of 
the  lower  part  of  the  orbit  and  is  attached  to  the  lower  part  of  the  eyebaU.  The  obUque 
muscles  prevent  the  rectus  muscles  from  rotating  the  eyeball.  These  muscles  are  supphed 
by  the  third,  fourth  and  sixth  cranial  nerves.  They  are  described  in  the  section  on  the  eye,  p. 
1067.  In  the  middle  ear  are  two  small  muscles  (the  tensor  tympani  and  the  stapedius)  attached 
respectively  to  the  malleus  and  stapes  and  supplied  by  fifth  and  seventh  cranial  nerves.  They 
are  described  in  the  section  on  the  ear,  p.  1091. 

Mastication  and  swallowing. — The  complex  musculature  used  in  biting,  masticating  and 
swallowing  food  is  used  also  in  speech  in  conjunction  with  the  muscles  of  the  larynx  and  the  lips. 
The  two  movable  bones  of  the  skull  concerned  with  these  functions  are  the  mandible  and  the  hyoid 
bone.  The  mandible  articulates  with  the  skull  on  each  side,  just  in  front  of  the  external  audi- 
tory meatus.  The  hyoid  bone  is  connected  on  each  side  by  the  stylo-hyoid  ligament  with  the 
styloid  process  of  the  temporal  bone,  which  descends  just  behind  the  external  auditory  meatus. 
A  powerful  group  of  muscles,  the  cranio -mandibular  muscles  (figs.  344,  345,  346,  347  c),  or 
muscles  of  mastication,  arise  from  the  temporal  fossa  {temporal  muscle),  the  zygomatic  arch 
[masseter  muscle)  and  the  pterygoid  process  (external  and  internal  pterygoid  muscles)  and  are 
inserted  into  the  coronoid  process  of  the  mandible  [temporal  muscle),  the  outer  side  of  the 
ramus  {masseter  muscle),  the  inner  side  of  the  ramus  {internal  pterygoid),  and  into  the  condyle 
of  the  jaw  {external  pterygoid).  These  muscles  raise  the  jaw,  move  it  forward  and  from  side 
to  side,  and  are  used  in  biting  and  chewing  the  food.  They  are  innervated  by  the  fifth  cranial 
(masticator)  nerve. 

Another  less  powerful  group  of  muscles,  the  suprahyoid  group  (fig.  348),  is  divisible  into 
two  subdivisions,  hyo-mandibular  which  extends  in  front  between  the  hyoid  bone  and  the 
ramus  of  the  jaw  (anterior  belly  of  the  digastric,  genio-hyoid,  mylo-hyoid)  and  a  hyo-temporal 
group  which  extends  between  the  hyoid  bone  and  the  temporal  bone  back  of  the  external  audi- 
tory meatus  {stylo-hyoid,  posterior  belly  of  the  digastric).  Two  of  the  hyo-mandibular  muscles 
(the  anterior  belly  of  the  digastric  and  the  mylo-hyoid)  are  innervated  by  the  trigeminal;  the 
genio-hyoid  by  the  hypoglossal  nerve.  The  two  hyo-temporal  muscles  (posterior  belly 
of  the  digastric  and  stylo-hyoid)  are  innervated  by  the  facial  nerve.  Morphologically 
therefore,  as  indicated  by  this  innervation,  the  muscles  of  this  group  are  diverse.  Physiolog- 
ically they  are  closely  united.  The  group,  acting  as  a  whole,  elevates  the  hyoid  bone  and  with 
this  the  larynx  and  the  tongue.  If,  however,  the  hyoid  bone  be  fixed  by  contraction  of  the 
neck  muscles  (infrahyoid  muscles)  attached  to  its  lower  border,  the  suprahyoid  muscles  act 
as  antagonists  of  the  cranio-mandibular  muscles  and  depress  the  jaw.  The  hyo-mandibular 
muscles  form,  together  with  the  tongue,  the  muscular  floor  of  the  mouth.  When  acting  with 
the  hyo-temporal  muscles  they  help  the  tongue  to  pass  food  into  the  pharynx.  When  acting 
alone  the  hyo-mandibular  muscles  draw  forward  the  hyoid  bone  and  with  it  the  base  of  the  tongue 
and  the  larynx  and  thus  open  the  passage  from  the  pharynx  into  the  oesophagus.  The  two 
hyo-temporal  muscles,  acting  in  conjunction  with  the  middle  and  inferior  constrictors  of  the 
pharynx,  draw  the  hyoid  bone  and  larynx  backward,  as  well  as  upward,  and  thus  constrict  the 
pharynx  while  giving  free  passa'_e  for  air  from  the  naso-pharynx  into  the  larynx.  The  chief 
functions  of  the  suprahyoid  group  are,  therefore,  to  play  a  part  in  deglutition  and  respiration. 
Closely  associated  with  the  muscles  of  the  suprahyoid  group  in  the  performance  of 
these  important  functions  are  the  muscles  of  the  tongue,  the  pharynx  and  the  soft  palate. 
The  bulk  of  the  tongue  (fig.  349)  is  made  up  of  muscles  which  have  their  origin  on  each  side  from 
the  inner  surface  of  the  front  part  of  the  mandible  {genio-glossus) ,  the  hyoid  bone  {hyo-glossus 
and  chondro-glossus)  and  the  styloid  process  of  the  temporal  bone  {stylo-glossus) .  Muscles 
also  connect  the  tongue  with  the  palate  (glosso-palatinus)  and  with  the  pharynx  {glosso-pharyn- 
geus).  These  muscles,  together  with  intrinsic  longitudinal,  transverse  and  perpendicular 
fibre-bundles,  enable  the  tongue  to  perform  the  complex  activities  associated  with  mastication 
and  swallowing  and  with  speech.  During  mastication  the  tongue  passes  the  food  from  side  to 
side  between  the  teeth.  When  the  food  has  been  masticated  the  tongue  forms  a  bolus  of  it 
and  then  this  is  passed  into  the  pharynx  by  a  sudden  elevation  of  the  dorsum  of  the  tongue 
produced  in  part  by  the  muscles  of  the  tongue,  in  part  by  the  suprahyoid  group  of  muscles. 
The  muscles  of  the  tongue  are  described  on  p.  345. 

The  pharynx  is  the  dilated  upper  part  of  the  alimentary  canal  into  which  open  the  Eus- 
tachian tubes,  the  nasal  passages,  the  mouth  and  the  larynx.  The  walls  of  the  side  and  back 
of  the  pharynx  are  composed  mainly  of  muscular  tissue.  The  chief  muscles  are  three  "  con- 
strictor "  muscles  on  each  side,  a  superior,  a  middle  and  an  inferior,  and  an  elevator  and  dilator, 
the  stylO'pharyngeus  (fig.  894).  The  three  constrictor  muscles  are  attached  to  the  median 
raphe*  which  extends  in  front  of  the  spinal  column  from  the  base  of  the  occipital  bone  to  the 
sixth  cervical  vertebra.  The  superior  constrictor  muscle  is  attached  to  the  pterygoid  process, 
the  pterygo-mandibular  ligament,  the  mandible  and  the  side  of  the  root  of  the  tongue  (fig.  343) ; 
the  middle  constrictor  to  the  hyoid  bone ;  and  the  inferior  constrictor  to  the  larynx.  These  muscles 
constrict  the  pharyngeal  orifice  and  thus  force  food  into  the  oesophagus.  The  stylo-pharyngeal 
muscle,  which  extends  from  the  styloid  process  into  the  lateral  wall  of  the  pharynx,  serves  to 

*  The  attachments  to  the  raphe  are  usually  spoken  of  as  the  insertions,  those  to  the  bones 
in  front  as  the  origins  of  these  muscles.  The  raphe  is,  however,  a  more  fixed  structure  than 
most  of  the  structm'es  to  which  the  constrictors  are  attached  in  front. 


326  THE  MUSCULATURE 

elevate  and  dilate  the  pharynx  and  elevate  the  larynx.  The  muscles  of  the  pharynx  are  de- 
scribed on  page  1134. 

The  orifices  of  the  various  passages  into  the  pharynx  are  dilated  or  constricted  by  muscular 
action.  The  orifices  of  the  nasal  passages,  the  Eustachian  tubes,  and  the  mouth  are  controlled 
mainly  by  the  musculature  of  the  soft  palate  and  pharynx.  The  orifice  of  the  larynx  is  con- 
trolled by  special  muscles  which  act  in  conjunction  with  those  of  the  suprahyoid  group,  the 
tongue,  and  the  pharynx. 

The  soft  palate  is  a  muscular  partition  which  is  continued  backward  from  the  hard  palate 
between  the  buccal  cavity  and  the  naso-pharyngeal  orifice  and  then  bends  downward  between 
the  back  part  of  the  mouth  and  the  nasal  part  of  the  pharynx,  terminating  in  a  median  pro- 
jection, the  uvula.  Above,  on  each  side,  back  of  the  fold  of  tissue  {plica  salpingo-palatinus) 
which  descends  from  the  ventral  border  of  the  orifice  of  the  Eustachian  tube  and  which  marks 
laterally  the  passage  from  the  nose  into  the  pharynx,  there  is  a  muscle,-  the  levator  veli  palatini 
(fig.  343~>.  This  arises  from  the  petrous  portion  of  the  temporal  bone  and  from  the  Eustachian 
tube  descends  to  the  middle  of  the  side  of  the  soft  palate  and  then  spreads  out  broadly  on  its 
dorsal  side.  The  muscle  from  each  side  interdigitates  to  some  extent  with  that  of  the  other 
side.  These  muscles  raise  the  soft  palate  toward  the  upper  part  of  the  posterior  wall  of  the  naso- 
pharynx and  thus  shut  off  the  nose  from  the  buccal  portion  of  the  pharynx  during  deglutition. 
The  sides  of  this  portion  of  the  pharynx  are,  meanwhile,  constricted  by  the  superior  constrictors 
of  the  pharynx  and  by  the  pharyno-palatinus  muscles  described  below.  Contraction  of  the 
levator  veli  palatini  tends  to  cause  folds  of  tissue  to  close  firmly  the  opening  of  the  Eustachian 
tube.  This  is  counteracted  by  the  tensor  veli  palatini  muscles  (fig.  343).  One  of  these  arises 
on  each  side  from  the  pterygoid  region  of  the  sphenoid  bone,  and  is  inserted  into  the  anterior 
part  of  the  soft  palate  by  a  tendon  which  passes  beneath  the  hamular  process  of  the  pterygoid 
process.  Contraction  of  this  pair  of  muscles  flattens  the  anterior  part  of  the  soft  palate  and 
exerts  a  traction  which  dilates  the  orifice  of  the  Eustachian  tube.  Most  authorities  state  that 
the  Eustachian  tube  is  thus  opened  each  time  we  swaUow.  As  air  is  admitted  into  the  middle 
ear  the  tensor  tympani  muscle  contracts  so  as  to  prevent  too  sudden  an  effect  on  the  ear  drum 
(Jonnesco.) 

Dorsal  to  the  fibres  of  the  elevator  of  the  palate  in  the  soft  palate  next  the  median  line  on 
each  side  there  extends  from  the  hard  palate  into  the  uvula  a  small  muscle,  the  muscle  of  the 
uvula,  which  lifts  the  tip  of  this  and  shortens  the  soft  palate  from  front  to  back  thus  enlarging 
the  opening  from  the  mouth  into  the  pharynx.  On  each  side  of  the  uvula  the  posterior  edge  of 
the  soft  palate  is  continued  backward  and  downward  into  a  fold,  the  arcus  pharyngo-palatinus, 
which  contains  a  muscle,  the  pharyngo-palatinus  (fig.  865).  This  arises  from  the  soft  palate, 
gasses  downward  and  backward  on  the  inner  side  of  the  lateral  wall  of  the  pharynx  and  divides 
iato  two  fasciculi,  one  of  which  is  attached  to  the  larynx,  the  other  to  the  median  raphe.  The 
muscle  constricts  the  pharynx  at  the  junction  between  the  nasal  and  buccal  portions  and  elevates 
the  larynx.  As  the  bolus  of  food  is  passed  from  the  dorsum  of  the  tongue  into  the  pharynx 
the  bucco-pharyngeal  opening  is  dilated  by  the  contraction  of  the  elevators  of  the  palate  and 
uvular  muscles  and  the  opening  into  the  naso-pharynx  is  closed  not  only  by  the  soft  palate 
being  raised  against  the  posterior  wall  of  the  naso-pharynx  but  also  by  the  lateral  folds  raised 
on  each  side  by  the  pharyngo-palatinus  against  the  uvula.  Meanwhile  the  larynx  is  raised  by 
the  pharyngo-palatinus  and  the  stylo-pharyngeus,  as  well  as  by  the  suprahyoid  muscles,  and 
carried  forward  by  the  hyo-mandibular  subdivision  of  the  latter  muscles  so  that  the  opening 
from  the  pharynx  into  the  cesophagus  is  dilated  for  the  passage  of  food.  At  the  same  time  the 
opening  into  the  larynx  is  constricted  from  above,  the  larynx  being  carried  forward  beneath  the 
tongue  so  that  the  epiglottis  slants  somewhat  backward.  This  backward  slant  is  aided  by  the 
constriction  of  the  thjTeo-hyoid  muscle  which  raises  the  thyreoid  cartilage  toward  the  hyoid 
bone  and  by  the  stylo-glossus  muscle  whioh  pulls  the  tongue  backward  over  the  larynx.  The 
opening  into  the  larynx  is  constricted  at  the  sides  and  behind  by  the  contraction  of  muscles 
which  run  in  the  aryepiglottic  folds  and  by  the  thyreo-arytenoid  and  transverse  arytenoid 
muscles.  At  the  end  of  deglutition  the  larynx  is  puUed  back  from  beneath  the  base  of  the 
tongue  by  the  middle  and  inferior  constrictors  of  the  pharynx  and  the  opening  is  again  dilated. 
The  buccal  cavity  may  be  shut  off  from  the  pharynx  by  the  action  of  the  muscles  which  pass 
in  the  glosso-palatal  folds  from  the  soft  palate  to  the  mouth  in  front  of  the  tonsils.  These 
glosso-palatal  muscles  elevate  the  folds  in  which  they  he,  depress  the  soft  palate,  and,  if  the 
dorsum  of  the  tongue  be  raised,  shut  oft'  the  buccal  cavity.  The  muscles  of  the  soft  palate  are 
described  on  p.  1134. 

The  uvular  muscle,  the  levator  veU  palaini,  the  glosso-palatinus  and  the  pharyngo- 
palatinus  muscles  are  supphed  by  the  pharyngeal  plexus.  The  tensor  veU  palatini  is  sup- 
plied by  the  mandibular  division  of  the  fifth  nerve.  The  pharyngeal  muscles  are  supplied 
by  the  glosso-pharyngeal,  the  vagus,  and  the  spinal  accessory  cranial  nerves. 

The  larynx  lies  in  the  neck,  but  since  the  intrinsic  muscles  of  the  larynx  from  the  standpoint 
of  embryology  and  comparative  anatomy  belong  with  the  musculature  of  the  head,  it  is  con- 
venient to  refer  to  them  briefly  here  rather  than  to  treat  of  them  with  the  intrinsic  muscles  of  the 
neck.  A  full  description  of  the  laryngeal  muscles  is  given  in  the  section  on  the  larynx  (fig.  981) . 
They  develop  from  tissue  which  corresponds  with  that  which  in  fishes  gives  rise  to  the  muscles 
of  the  gills  and  are  innervated  by  the  nerves  which  in  the  fishes  innervate  the  gills,  the  tenth 
pair  (vagus)  of  cranial  nerves.  The  movements  of  the  laryngeal  cartilages  are  such  as  to 
approximate  or  draw  apart  the  vocal  cords  and  to  loosen  or  make  them  tense.  The  approxi- 
mation of  the  vocal  cords  is  produced  by  the  rotation  medialward  of  the  vocal  processes  of  the 
arytenoid  cartilages  brought  about  by  the  lateral  crico-arytcnoid  and  transverse  arytenoid 
muscles.  The  drawing  apart  of  the  vocal  cords  is  produced  by  the  posterior  crico-arytenoids. 
The  vocal  cords  are  made  long,  thin  and  tense  by  the  crico-thyreoid.  They  are  shortened  and 
thickened  by  the  thyreo-arytenoid  (externus)  and  the  vocalis.     The  inferior  laryngeal  branch  of 


GROUPS  OF  MUSCLES  327 

the  vagus  supplies  all  the  muscles  but  the  crioo-thyreoid.  This  is  supplied  by  the  superior 
laryngeal  branch  of  the  vagus. 

Metamerism. — The  muscles  thus  far  considered  are  essentially  visceral  muscles,  although 
all  are  composed  of  striated  muscle  cells  and  all  are  more  or  less  directly  under  the  control  of 
the  will.  From  the  morphological  standpoint  the  muscles  of  the  orbit,  the  tensor  tympani, 
the  muscles  of  mastication,  the  hyo-mandibular  muscles  and  the  muscles  of  the  tongue  have 
been  grouped  with  the  ordinary  voluntary  skeletal  muscles  while  the  facialis  musculatm'e,  the 
stapedius,  the  hyo-temporal  muscles  and  the  muscles  of  the  soft  palate,  pharyn.x  and  larynx 
are  looked  upon  as  of  a  more  purely  visceral  origin.  A  primitive  characteristic  of  the  voluntary 
skeletal  muscles  is  metameric  segmentation.  This  is  maintained  through  life  in  the  trunk 
musculature  of  fishes  and  of  tailed  amphibia  and  is  passed  through  as  a  temporary  stage  in 
aU  the  higher  vertebrates.  The  embryonic  segmented  muscles  are  caDed  myotomes  (see  fig. 
340).  In  some  regions  the  metamerism  is  retained  throughout  life  even  in  the  higher  forms, 
as,  for  instance,  in  the  intercostal  muscles  and  the  intertransverse  muscles.  But  for  the  most 
part  the  primitive  metamerism  is  so  lost  during  the  differentiation  of  the  definitive  trunk 
musculature  that  only  traces  of  it  remain  here  and  there  as,  for  instance,  in  the  segments  of  the 
rectus  abdominis  muscle.  In  the  lower  forms  the  myotomes  give  rise  during  embryonic 
development  to  material  utilized  in  the  formation  of  the  limb  musculature,  but  even  in  the 
fishes  all  traces  of  trunk  metamerism  are  lost  in  the  differentiated  limb  musculature  and  in  the 
higher  forms,  as  in  man,  the  limb  musculature  appears  to  differentiate  directly  from  the  un- 
segmented  tissue  in  the  hmb-buds.  In  the  head  the  musculature  is  differentiated  directly,  as 
in  the  limbs,  without  undergoing  a  preliminary  metameric  or  myotomic  stage.  Attempts 
have  been  made  to  show  that  in  primitive  forms  the  cranial  voluntary  skeletal  musculature,  in 
the  narrower  morphological  sense  mentioned  above,  passes  through  a  metameric  stage  com- 
parable with  the  myotomic  metamerism  of  the  trunk.  This  attempt  has  been  partially  success- 
ful as  regards  the  development  of  the  muscles  of  the  eye  in  some  of  the  lower  forms.  There 
is  also  good  evidence  that  the  spinal  region  of  the  skull  and  associated  structures  represent  a 
part  of  the  metameric  trunk  fused  with  a  more  primitive  head  so  that  the  musculature  of  the 
tongue  and  the  hyo-mandibular  muscles  belongs  morphologically  with  the  primitively  metameric 
trunk  musculature.  The  rest  of  the  cranial  musculature  gives  little  evidence  of  a  primitive 
metameric  segmentation  and  hence  is  probably  to  be  classed  morphologically  with  the  unseg- 
mented  visceral  musculature. 

Of  the  muscles  of  the  neck,  the  most  superficial,  the  platysma  (fig.  341),  is  a  subcutaneous 
muscle  belonging  to  the  facialis  group  of  the  head  from  which  it  grows  down  during  embryonic 
development.  It  is  supplied  by  the  seventh  cranial  (facial)  nerve.  It  extends  from  the  corner 
of  the  mouth  and  the  side  of  the  mandible  over  the  clavicle.  It  depresses  the  corner  of  the 
mouth,  wrinkles  up  the  skin  of  the  neck  and  aids  the  circulation  by  reUeving  pressure  on  the 
uiiderlying  veins. 

Beneath  the  platysma  there  lies  a  layer  composed  of  two  flat  muscles  (fig.  344)  which 
extend  from  the  base  of  the  skull  behind  the  ear  to  the  shoulder  girdle.  One  of  these  muscles, 
the  sterno-cleido-mastoid,  arises  in  front  from  the  sternum  and  clavicle  and  is  inserted  into  the 
m.istoid  process  of  the  temporal  bone  and  the  skull  behind  this.  The  other,  the  trapezius,  arises 
from  the  base  of  the  skull,  and  from  the  ligamentum  nuohfe  and  vertebral  spines  of  the  cervical 
and  thoracic  regions,  and  is  inserted  into  the  spine  of  the  scapula,  the  acromion  and  the  lateral 
third  of  the  clavicle.  These  two  muscles  constitute  the  superficial  shoulder -girdle  musculature. 
They  extend  the  head,  bend  it  toward  the  same  side  and  rotate  it  toward  the  opposite  side. 
The  sterno-cleido-mastoid  and  the  upper  part  of  the  trapezius  raise  the  shoulder  girdle  and 
thorax  and  hence  are  of  use  in  forced  inspiration.  The  trapezius  draws  the  scapula  toward  the 
spine  and  rotates  the  inferior  angle  of  the  scapula  lateralward.  The  lower  part  of  the  trapezius 
acting  alone  draws  the  scapula  downward  and  dorsalward  while  rotating  the  inferior  angle 
lateralward.  The  trapezius  is  therefore  used  when  the  arm  is  raised  high  or  carried  backward. 
The  two  muscles  of  this  group  are  innervated  partly  by  the  spinal  accessory,  and  partly  by  the 
ventral  divisions  of  the  second,  third  and  fourth  cranial  nerves.  They  represent  in  part 
musculature  which  in  the  lower  vertebrates  is  associated  with  the  visceral  musculature  of  the 
gills  (hence  the  innervation  by  the  spinal  accessory,  a  derivative  of  the  vagus  nerve)  and  in 
part  metameric  musculature  of  the  second,  third,  and  fourth  cervical  segments.  During 
embryonic  development  this  musculature  therefore  spreads  out  widely  from  its  origin,  the  upper 
cervical  region.  The  lower  part  of  the  trapezius  varies  greatly  in  the  extent  of  its  development 
caudalward.  It  may  reach  only  half  way  down  the  thoracic  region  or  it  may  extend  into  the 
lumbar  region.     The  deeper  musculature  of  the  neck  is  derived  from  the  cervical  myotomes. 

The  primitive  segmental  musculature  of  the  neck,  hke  that  of  the  whole  trunk,  becomes 
divided  at  an  early  embryonic  stage  into  two  divisions,  a  dorsal,  supplied  by  the  dorsal  divisions 
of  the  spinal  nerves,  and  a  ventro-lateral  supplied  by  the  ventral  divisions.  The  trapezius, 
although  it  covers  the  intrinsic  dorsal  musculature  of  the  cervical  region,  insofar  as  it  is  of 
cervical  origin,  belongs  to  the  ventro-lateral  musculature  and  is  derived,  apparently,  from  the 
first  three  cervical  myotomes.  There  is  also  a  deeper  layer  of  muscles  attached  to  the  shoulder 
girdle  which  arise  from  the  ventro-lateral  divisions  of  the  lower  five  or  six  cervical  myotomes 
but  which,  with  one  exception,  the  levator  scapulm  (fig.  353),  wander  over  the  thorax  during 
embryonic  development.  This  group  is  described  below  as  the  deep  shoulder-girdle  muscula- 
ture. The  rest  of  the  muscles  derived  from  the  ventro-lateral  divisions  of  the  cervical  myo- 
tomes are  divisible  into  three  gi'oups,  the  infra-hyoid,  the  scalene  and  the  prevertebral. 

The  infra-hyoid  group  hes  at  the  front  of  the  neck,  superficial  to  the  larynx  and  trachea 
(fig.  348),  and  is  composed  of  four  flat  muscles,  the  sterno-hyoid,  sterno-thyreoid,  thyreo-hyoid 
and  omo-hyoid  (scapulo-hyoid),  the  names  of  which  indicate  the  origin  and  insertion.  The 
chief  function  of  this  group  of  muscles  is  to  depress  the  hyoid  bone,  the  larynx  and  the  as- 
sociated structures.  When  the  supra-hyoid  group  of  muscles  contracts  at  the  same  time,  the 
infra-hyoid  muscles  help  to  depress  the  lower  jaw,  or  if  this  in  turn  is  fixed  by  the  cranio-man- 
dibular  group,  to  flex  the  head.     The  muscles  of  this  group  are  derived  from  the  ventral  portions 


328  THE  MUSCULATURE 

of  the  first  three  cervical  myotomes  and  are  innervated  by  the  first  three  cervical  nerves  through 
the  ansa  hypoglossi.  The  primitive  segmental  origin  of  these  muscles  is  frequently  indicated 
by  transverse  tendons  (inscriptiones  tendineae).  They  correspond  morphologically  with  the 
rectus  abdominis  musculature. 

The  scalene  group  (fig.  352)  lies  at  the  side  of  the  neck  and  extends  to  the  first  and 
second  ribs  from  the  transverse  processes  of  the  lower  six  cervical  vertebrae.  The  muscles  of  this 
group  bend  the  neck  toward  the  side,  or  if  the  neck  be  fixed,  elevate  the  thorax.  They  come 
from  the  lateral  parts  of  the  ventro-lateral  divisions  of  the  lower  five  cervical  myotomes  and  are 
innervated  by  the  lower  five  cervical  nerves.  They  correspond  morphologically  with  the 
intercostal  and  with  the  lateral  abdominal  musculature. 

The  prevertebral  group  lies  back  of  the  pharynx  and  oesophagus  and  in  front  of  the  bodies 
and  transverse  processes  of  the  cervical  veitebrae.  The  muscles  of  this  gi-oup  arise  not  only 
from  the  transverse  processes  and  bodies  of  the  cervical  vertebrae,  but  also  in  part  from  the 
bodies  of  the  first  three  thoracic  vertebrae  and  are  inserted  in  part  into  the  cervical  vertebrae 
(?or!(/MS  coiM)  and  in  part  into  the  base  of  the  occipital  bone  {longus  capitis).  This  musculature 
flexes  the  neck  and  the  head.  When  acting  on  one  side  it  rotates  the  head  toward  the  same 
side.     It  is  innervated  by  the  first  six  cervical  nerves. 

The  deep  shoulder-girdle  musculature. — This  becomes  differentiated  from  the  ven- 
tro-lateral divisions  of  the  lowei  five  or  six  cervical  myotomes.  Like  the  muscles  of  the 
superficial  layer  those  of  the  deeper  layer  spread  out  widely  from  their  origin.  There  are  four 
muscles  in  the  deeper  group,  all  of  which  become  attached  to  the  dorsal  border  of  the  scapula. 
Of  these,  one,  the  levator  scapulce  (fig.  353),  remains  in  the  cervical  region,  extending  from 
the  upper  cervical  transverse  processes  to  the  medial  angle  of  the  scapula.  Two,  the  rhomboids 
(fig.  353),  extend  over  the  intrinsic  dorsal  musculature  and  are  attached  to  the  upper  thoracic 
and  lower  cervical  vertebral  spines;  while  the  fourth,  the  serratus  anterior  (fig.  354),  extends 
over  the  side  of  the  upper  part  of  the  thorax  beneath  the  scapula  and  is  attached  to  the  first 
nine  ribs.  These  muscles  all,  however,  through  their  innervation,  reveal  in  the  adult  their 
primitive  cervical  origin.  They  are  supplied  by  branches  from  the  third  to  the  seventh  cervical 
nerves.  The  levator  scapulae  elevates  the  scapula,  the  rhomboid  muscles  retract  it  and  the  serratus 
anterior  draws  it  forward.  The  levator  and  rhomboid  muscles  rotate  the  shoulder  girdle  so 
as  to  depress  the  shoulder,  the  serratus  anterior,  like  the  trapezius,  rotates  it  so  as  to  raise 
the  shoulder.  The  two  former  muscles  are  an  aid  in  extending  the  arm,  the  latter  in  flexing 
and  abducting  it.  When  the  group,  as  a  whole,  contracts  action  is  exerted  on  the  ribs  so  that 
the  group  is  of  use  in  forced  inspiration. 

The  intrinsic  dorsal  musculature  of  the  neck,  innervated  by  the  dorsal  divisions  of  the 
cervical  nerves,  is  separated  from  the  scalene  muscles  by  the  levator  scapula.  Dorsally  it  is 
covered  by  the  trapezius  and  the  rhomboid  muscles.  It  is  to  be  looked  upon  as  a  specialized 
portion  of  the  system  of  intrinsic  dorsal  muscles  which  extend  from  the  sacrum  to  the  base  of 
the  skull  on  each  side  of  the  vertebral  column.  The  primary  function  of  this  muscle  system 
is  to  extend  and  to  rotate  the  spine  and  the  skuU.  In  the  thoracic  region  three  main  subdivi- 
sions may  be  recognised,  a  lateral,  the  ilio-costal;  an  intermediate,  the  longissimus;  and  a  medial, 
the  transverse-spinal  group  (fig.  381).  In  the  cervical  region  these  three  groups  may  hkewise 
be  recognised  and,  in  addition,  there  is  a  superficial  group,  the  splenius  (fig.  380) ,  not  represented 
in  the  lower  thoracic  region.  The  splenius  arises  from  the  upper  thoracic  and  lower  cervicla 
spines  and  is  inserted  into  the  transverse  processes  of  the  upper  cervical  vertebrae  and  into  the 
mastoid  processes  of  the  temporal  bone  and  the  neighbouring  part  of  the  occipital.  It  acts  with 
the  sterno-cleido-mastoid,  by  which  it  is  crossed  near  the  head,  in  extending  the  head,  bending 
it  toward  the  side,  but  tends  to  rotate  it  toward  the  same  side  instead  of  toward  the  opposite 
side.  Laterally  beneath  the  splenius  the  ilio-costalis  cervicis  extends  from  the  upper  part 
of  the  thorax  to  the  transverse  processes  of  the  sixth  to  the  fourth  cervical  vertebrae,  and  the 
longissimus  cervicis  and  capitis  extend  from  the  same  region  to  the  transverse  processes  of  the 
mid-cervical  vertebrae  and  to  the  mastoid  process  of  the  temporal  bone  (fig.  381).  These 
muscles  likewise  extend  and  bend  the  head  and  neck  laterally  and  rotate  it  toward  the  same 
side.  Medially  on  each  side  the  strong  semispinalis  capitis  (fig.  381),  arises  from  the  upper 
thoracic  and  the  lower  cervical  vertebrae,  spreads  out  and  is  inserted  into  the  squamous  portion 
of  the  occipital  bone.  It  is  a  powerful  extensor  of  the  head.  Beneath  it  numerous  fasciculi 
extend  from  the  transverse  proceses  to  the  spines  of  the  cervical  vertebrae.  These  fascicuh, 
the  more  superficial  of  which  are  the  Ion',  est,  constitute  the  Scmispinales  cervicis,  muliifidus, 
and  roiatores  muscles.     They  extend  and  rotate  the  neck. 

Between  the  successive  spines  and  the  transverse  process  there  are  short  muscles  (inler- 
spinales,  intertransversares) .  The  rectus  capitis  anterior  and  the  rectus  capitis  lateralis  between 
the  transverse  process  of  the  atlas  and  the  lateral  part  of  the  occipital  belong  with  the  latter 
series. 

Between  the  base  of  the  skull  behind  and  the  first  two  vertebrae  there  are  four  deep-seated 
specialized  muscles  which  constitute  the  suboccipital  group  (fig.  382).  The  rectus  capitis 
posterior  major  and  minor  spread  out  respectively  from  the  spines  of  the  atlas  and  epistropheus 
and  are  inserted  beneath  the  inferior  nuchal  line  of  the  occipital.  The  obliquvs  capitis  inferior 
arises  from  the  spine  of  the  epistropheus  and  is  inserted  into  the  transverse  process  of  the 
atlas;  the  obliquvs  capitis  superior  arises  from  this  and  is  inserted  into  the  lateral  part  of  the 
inferior  nuchal  line  of  the  occipital.  These  muscles  extend  and  rotate  the  head.  A  detailed  de- 
scription of  the  intrinsic  muscles  of  the  back  is  given  on  page  410. 

The  muscle  fasciae  in  the  head  and  neck  are  well  developed  in  connection  with  most  of 
the  groups  of  muscles  except  the  facialis  group  and  are  described  in  detail  in  connection  with 
each  of  these  groups.  In  the  head  we  may  here  call  attention  merely  to  the  dense  temporal 
fascia  which  covers  over  the  temporal  fossa  and  hides  from  view  the  temporal  muscle.  In 
the  neck  the  fasciae  are  of  considerable  practical  importance.  It  is  convenient  to  think  of  them 
as  divisible  into  several  layers  although  the  various  layers  fuse  to  some  extent.  The  external 
layer  (fig.  350)  may  be  looked  upon  as  completely  ensheathing  the  neck  and  as  dividing  on  each 


FACIALIS  MUSCULATURE  329 

side  into  two  layers  which  ensheath  the  sterno-cleido-mastoid  and  trapezius  muscles.  As  a 
free  fascia  it  is  attached  to  the  lower  jaw,  to  the  clavicle  and  sternum,  and  to  the  hyoid  bone 
which  divides  it  into  a  submaxillary  and  an  infra-hyoid  portion.  It  is  connected  with  the  fibrous 
sheath  of  the  parotid  and  submaxillary  glands.  The  middle  layer  of  cervical  fascia  is  composed 
of  two  laminae,  one  extending  between  the  sterno-hyoid  and  omo-hyoid  and  another  more  deli- 
cate one  beneath  this,  ensheathing  the  thyreo-hyoid  and  sterno-thyreoid  muscles  and  fused  with 
the  fibrous  sheath  which  encloses  the  carotid  artery,  internal  jugular  vein  and  the  vagus  nerve. 
The  deeper  muscles  of  the  side  and  front  of  the  neck  and  the  intrinsic  muscles  of  the  back  of 
the  neck  are  hkewise  ensheathed  by  muscle  fasciae. 

Of  the  various  groups  of  muscles  mentioned  above,  some,  for  the  sake  of  con- 
venience, are  treated  in  connection  with  the  organs  to  which  they  belong.  Thus 
the  muscles  of  the  eye  and  ear  are  taken  up  in  Section  VIII;  those  of  the  palate, 
pharynx  and  larynx  in  Sections  IX  and  X;  the  deep  dorsal  musculature  of  the 
neck  will  be  taken  up  in  the  section  on  the  intrinsic  muscles  of  the  back,  p.  410, 
The  remaining  groups  of  muscles  will  be  taken  up  in  the  following  order: — 

1.  The  facial  group  p.  329. 

2.  The  cranio-mandibular  group  p.  338. 

3.  The  supra-hyoid  musculature  p.  343. 

4.  The  muscles  of  the  tongue  p.  345. 

5.  The  superficial  shoulder-girdle  musculature  p.  347. 

6.  The  infra-hyoid  musculature  p.  350. 

7.  The  scalene  musculature  p.  353. 

8.  The  prevertebral  musculature  p.  355. 

9.  Anterior  and  lateral  intertransverse  muscles  p.  356.   ■ 
10.  Deep  musculature  of  the  shoulder  girdle  p.  356.* 

1.  THE  FACIALIS  MUSCULATURE 

(Figs.  341,  344) 

The  muscles  of  this  group  are  intimately  connected  with  the  scalp,  with  the 
skin  of  the  face  and  neck,  and  with  the  mucous  membrane  lining  the  lips  and  the 
cheeks.  Most  of  the  muscles  have  an  osseous  origin  and  a  cutaneous  insertion, 
but  there  are  exceptions.  Both  origin  and  insertion  may  be  cutaneous,  or  the 
attachment  may  be  to  an  aponeurosis  instead  of  directly  to  the  skin.  The 
deeper  musculature  about  the  mouth  is  attached  to  the  mucous  membrane. 

The  muscles  are  composed  of  interdigitating  muscle-fibres  which  are  grouped 
in  bundles  that  take  a  nearly  parallel  or  slightly  converging  course  and  give  rise 
to  thin  muscle-sheets.  The  extent  of  development  of  the  various  muscles  of  the 
group  and  their  independence  varies  greatly  in  different  individuals. 

The  region  from  which  the  facial  musculature  originates  in  the  embryo  is,  in  the  main  at 
least,  that  of  the  hyoid  arch  immediately  below  the  ear.  From  here  the  musculature  spreads 
with  the  development  of  the  facial  nerve,  dorsally  to  the  occipital  region  behind  the  ear,  distally 
over  the  neck,  ventrally  over  the  face,  and  upward  toward  the  eye,  forehead,  and  the  side  of 
the  skull.  The  course  of  the  development  is  indicated  by  the  branches  of  the  facial  nerve.  A 
somewhat  similar  phylogenetic  development  is  indicated  by  conditions  found  in  the  inferior 
mammals  and  lower  vertebrates.  According  to  Ruge  and  Gegenbam-,  the  facial  musculature 
is  to  be  looked  upon  as  derived  from  two  muscle-sheets,  of  which  in  man  the  deeper  has  dis- 
appeared in  the  region  of  the  neck  while  it  is  differentiated  into  the  deeper  facial  muscles  in  the 
region  of  the  head.  The  deeper  layer  of  transverse  fibres  in  the  neck,  the  sphincter  colli,  is  found 
in  several  of  the  mammals.  The  complex  development  of  the  facial  muscles  in  man  is  char- 
acteristic of  the  human  species,  and  is  associated  with  the  use  of  these  muscles  as  a  means  of 
expression  of  the  emotions,  a  physiological  function  superadded  to  the  primitive  function  of 
opening  and  closing  visceral  orifices.  There  is  much  individual  variation  in  the  differentiation 
of  the  muscles. 

Fasciae. — The  skin  of  the  head  and  neck  is,  in  most  regions,  firmly  fused  with  the  tela 
subcutanea.  This  is  composed  of  a  dense  fibrous  tissue  united  by  a  looser  areolar  tissue  to  the 
underlying  structures.  But  a  slight  amount  of  fat  is  embedded  in  the  subcutaneous  ti.ssue  of 
the  scalp,  forehead,  and  nose.  Considerable  fat  may  be  embedded  in  the  region  of  the  cheeks, 
the  back  of  the  neck,  and  the  under  surface  of  the  chin  (double  chin).  The  constantly  repeated 
action  of  various  muscles  of  the  facialis  group  usually  results  by  middle  Hfe  in  the  production 
of  permanent  wrinkles  due  to  alterations  in  the  structure  of  the  tela  subcutanea  and  the  cutis. 

The  subcutaneous  muscles  of  the  cranial  vault  and  the  neck  are  invested  with  fascial 
membranes.     That  covering  the  cranial  musculature  externally  is  firmly  fused  to  the  subcutane- 

*  The  pectoral  muscles  and  the  latissimus  dorsi,  which  extend  from  the  skeleton  of  the  hmb 
to  the  front  and  side  of  the  thorax  and  the  lower  part  of  the  back,  arise  from  the  hmb-bud  during 
embryonic  development,  are  innervated  through  the  brachial  plexus,  and  wiU,  therefore,  be  taken 
up  in  considering  the  intrinsic  musculature  of  the  upper  Imrb,  p.  360. 


330 


THE  MUSCULATURE 


ous  tissue  of  the  scalp.  That  covering  the  subcutaneous  muscle  of  the  neck  is  less  firmly  fused 
with  the  subcutaneous  tissue.  In  the  facial  region  the  more  superficial  muscles  are  so  closely 
embedded  in  the  subcutaneous  tissue  that  no  distinct  fasciae  intervening  between  the  muscles 
and  the  skin  can,  as  a  rule,  be  distinguished.  Of  the  deeper  muscles  of  the  facialis  group,  the 
buccinator  alone  possesses  a  distinct  fascia.  This  muscle  lies  upon  the  mucous  membrane  of  the 
lateral  wall  of  the  mouth,  and  is  covered  externally  by  a  fascia  continued  into  the  fascia  investing 
the  superior  constrictor  of  the  pharynx. 

Bursse. — Bursa  subcutanea  prementalis.  Between  the  periosteum  at  the  tip  of  the  chin 
and  the  overlying  tissue.  Bursa  subcutanea  prominentias  laryngese.  In  front  of  the  junction 
of  the  right  and  left  laminae  of  the  thyreoid  cartilage. 

Fig.  341.^The  Superficial  Muscles  of  the  Head  and  Neck. 


Orbicularis  oculi 


Procerus 

Quadr.  labii  sup 

caput  angulare 

Nasalis,  pars  transversa 

Dilator  naris  anterior-, 

Dilator  naris  posterior^ 

Quadr.  labii  sup. 
caput  infraorbitale 

Caput  zygomaticum 


Orbicularis  oris 


Quadratus  labii  infenoris 
Triangularis 


Auricularis 
superior 


MUSCLES 

The  muscles  of  the  faciahs  group  may  be  conveniently  subdivided  as  follows: — 
(a)  Cervical :  the  platysma.  (&)  Oral :  the  orbicularis  oris  and  the  incisivus 
labii  superioris  and  inferioris;  the  quadratus  labii  superioris  and  inferioris;  the 
caninus,  zygomaticus,  risorius,  and  triangularis;  and  the  buccinator,  (c) 
Mental,  (d)  Nasal:  the  nasalis,  depressor  septi,  and  the  dilatores  naris.  (e) 
Periorbital:  the  orbicularis  oculi,  corrugator,  and  procerus.  (/)  Epicranial:  the 
frontalis  and  occipitalis,  with  the  galea  aponeurotica.  (g)  Auricular:  anterior, 
superior,  and  posterior.     With  these  the  temporalis  superficialis  is  also  described. 


(o)  CERVICAL  MUSCLE 

The  platysma  is  a  large,  thin,  quadrangular  muscle  which  runs  obliquely  from 
the  chin,  the  corner  of  the  mouth,  and  the  lower  part  of  the  cheek  across  the 


ORAL  MUSCLES  331 

mandible  and  the  neck  to  the  proximal  part  of  the  thorax  and  shoulder.  The 
muscles  of  each  side  interdigitate  across  the  chin.  A  short  distance  below  the 
chin,  in  the  neck,  the  ventral  margins  diverge  (fig.  341). 

Origin. — From  the  tela  suboutanea  by  somewhat  scattered  bundles — (1)  along  a  Une  ex- 
tending from  the  cartilage  of  the  second  rib  to  the  acromion,  and  (2)  along  the  dorsal  margin  of 
the  muscle. 

Insertion. — Into — (1)  the  mental  protuberance  of  the  mandible  and  the  inferior  margin 
of  the  mandible;  and  (2)  into  the  skin  of  the  lower  part  of  the  cheek  and  at  the  corner  of  the 
mouth,  where  it  fuses  more  or  less  with  the  quadratus  labii  inferioris  and  the  orbicularis  oris. 

Nerve-supply. — The  cervical  branch  (ramus  colh)  of  the  seventh  cranial  nerve  forms  beneath 
the  muscle  a  plexus  to  which  the  cutaneus  colh  nerve  contributes  sensory  branches. 

Relations. — The  muscle  is  situated  beneath  the  panniculus  adiposus,  to  which  in  the  neck  it 
is  not  very  firmly  attached.  For  the  most  part  it  is  separated  from  the  external  layer  of  the 
cervical  fascia  by  loose  areolar  tissue.  The  main  cutaneous  rami  of  the  cervical  plexus  and  the 
external  jugular  vein  lie  beneath  the  muscle. 

Action. — It  wrinkles  up  the  skin  of  the  neck,  depresses  the  corner  of  the  mouth,  and  thus 
plays  a  part  in  expression  of  sadness,  fright,  and  suffering.  It  aids  the  circulation  by  relieving 
pressure  on  the  underlying  veins. 

Variations. — Either  the  facial  or  the  distal  development  of  the  muscle  may  be  more  exten- 
sive than  that  described  above.  On  the  other  hand,  it  ma.y  be  less  developed  than  usual,  and 
rarely  it  is  absent.  Accessory  shps  have  been  seen  going  to  the  zygoma,  the  auricle,  or  the 
mastoid  process,  etc.,  and  to  the  clavicle  and  sternum.  Rarely  a  deep  transverse  layer  is  found 
in  man. 

Fig.  342. — Diagram  to  Illustkate  the  Architecture  op  the  Orbicularis  Oris. 
(After  T.  D.  Thane.) 

Depressor  septi  nasi-^ 


Incisivus  sup.  ~ 


(b)  ORAL  MUSCLES 

The  muscles  of  the  mouth  belonging  to  the  facialis  system  include  several 
intralabial  muscles: — a  sphincter,  the  orbicularis  oris;  a  transverse,  the  com- 
pressor labii;  and  four  deep  submucous  muscles  which  pass  from  the  sides  of 
the  lips  to  the  alveolar  juga  of  the  upper  canine  and  lower  lateral  incisor  teeth,  the 
incisivi  labii  superioris  and  inferioris.  From  each  corner  of  the  mouth  there 
radiate  out  several  muscles;  the  caninus  and  zygomaticus  upward  to  the  maxilla 
and  zygomatic  bone;  the  risorius  lateral  ward  over  the  cheek;  the  platysma  and 
the  triangularis  downward  over  the  side  of  the  jaw;  and  the  buccinator,  lateral- 
ward  over  the  side  of  the  oral  cavity.  From  each  of  these  fibre-bundles  are 
continued  into  the  more  peripheral  and  superficial  portions  of  the  orbicularis. 
In  addition  to  these  muscles  there  are  two  retractors  or  quadrate  muscles,  one  of 
which,  the  quadratus  labii  superioris,  extends  from  the  upper  lip  medial  to  the 
angle  to  the  bridge  of  the  nose,  the  lower  margin  of  the  orbit,  and  the  zygo- 
matic bone;  while  the  other,  the  quadratus  labii  inferioris,  extends  from  a  corre- 
sponding position  in  the  lower  lip  to  the  side  of  the  chin.  The  orbicularis  oris, 
compressor  labii,  and  incisive  muscles  close  the  lips;  the  other  muscles  open  them 
and  pull  them  in  various  directions.  The  buccinator,  however,  plays  a  part  in  the 
closing  of  the  mouth  by  offering  support  for  the  orbicularis. 

Intralabial  Muscles 

The  orbicularis  oris  (figs.  308,  341,  342,  343)  is  a  complex  muscle  which  surrounds  the  oral 
orifice  and  forms  the  chief  intrinsic  musculature  of  the  Ups.  Immediately  about  the  orifice, 
and  on  the  deep  surface  of  the  muscle,  is  a  fairly  well-defined  sphincter,  although  at  the  corners 
of  the  mouth  the  fibre-bundles  of  one  hp  cross  those  of  the  other  and  are  inserted  into  the 
mucosa,  and  to  a  less  extent  into  the  skin.  In  the  mid-line  the  fibre-l^undles  end  partly  in  the 
perimysium,  partly  in  the  skin.     About  this  sphincter  area  and  between  its  outer  margin  and 


332  THE  MUSCULATURE 

the  skin  is  a  complex  musculature  comprised  partly  of  fibre-bundles  prolonged  from  the  muscles 
which  radiate  from  the  corners  of  the  mouth.  The  more  superficial  portion  of  the  muscle  in 
the  upper  Up  is  composed  of  fibre-bundles  from  the  triangularis  (depressor  anguU  oris),  the  more 
superficial  portion  of  that  in  the  lower  lip  by  fibre-bundles  from  the  caninus  (levator  anguli  oris). 
These  fibre-bundles  form  commissures  at  the  angles  of  the  mouth  and  extend  toward  the  median 
line,  where  many  of  them  interdigitate  with  those  of  the  opposite  side,  and  are  attached  to  the 
skin  of  the  lips.  The  deeper  portions  are  partly  formed  by  fibre-bundles  prolonged  from  the 
buccinator,  the  mandibular  fibre-bundles  of  the  latter  muscle  going  mainly  to  the  upper  lip, 
the  maxillary  fibre-bundles  mainly  to  the  lower  hp.  These  fibre-bundles  are  attached  chiefly 
to  the  mucosa,  near  the  corners  of  the  mouth. 

The  compressor  labii,  or  muscle  of  Klein,  is  composed  of  bundles  of  fibres  which  take  a 
course  transverse  to  those  of  the  orbicularis,  and  pass  obhquely  from  the  skin  surrounding  the 
oral  orifice  toward  the  mucosa  which  bounds  its  inner  margin.  It  is  said  to  be  best  marked 
in  infants. 

The  incisivus  labii  superioris  is  a  small  muscle-bundle  which  passes  from  the  alveolar  jugum 
of  the  upper  canine  tooth  to  the  back  of  the  orbicularis  near  the  corner  of  the  mouth. 

The  incisivus  labii  inferioris  passes  similarly  from  the  alveolar  jugum  of  the  lower  lateral 
incisor  tooth  to  the  back  of  the  orbicularis  in  the  lower  lip. 

Nerve-supply. — These  muscles  are  suppUed  by  the  buccal  branches  of  the  facial  nerve  which 
enter  the  orbicularis  on  the  lateral  border. 

Relations. — The  main  mass  of  intrinsic  musculature  of  the  lips  is  placed  slightly  nearer  the 
mucosa  than  the  skin.     On  its  deep  surface  lie  the  labial  arteries. 

Action. — The  orbicularis  draws  the  upper  lip  downward,  the  lower  lip  upward.  The 
incisive  muscles  draw  the  corners  of  the  lips  medialward,  and  the  compressor  flattens  the  lips. 
Together  they  serve  to  close  the  mouth.  Acting  separately  they  may  draw  different  parts  of 
it  in  the  directions  indicated  by  their  structure.  The  circumferential  portion  of  the  orbicularis 
acting  with  the  incisive  muscles  makes  the  lips  protrude.  The  central  portion  of  the  orbicularis 
draws  the  lips  together,  and  when  the  buccinator  also  acts,  draws  them  against  the  teeth.  It 
is  this  portion  of  the  muscle  that  has  chiefly  to  do  with  nutritive  functions.  The  more  peripheral 
parts  of  the  muscle  are  chiefly  utilised  in  the  expression  of  the  emotions. 

Retractors  op  the  Lips  or  Quadrate  Muscles 
(Fig.  341) 

The  quadratus  labii  superioris  is  a  thin,  quadrangular  muscle  with  three  heads,  all  of 
which  are  inserted  into  the  skin  and  musculature  of  the  upper  lip. 

The  caput  zygomaticum  (zygomaticus  minor)  is  long  and  slender  and  arises  from  the  lower 
part  of  the  external  surface  of  the  zygomatic  bone  beneath  the  lower  border  of  the  palpebral 
portion  of  the  orbicularis  oculi.  It  passes  obliquely  forward  over  the  caninus  and  orbicularis 
oris  muscles,  and  extends  to  a  cutaneous  and  muscular  insertion  in  the  upper  hp  medial  to  the 
corner  of  the  mouth.     It  lies  medial  to  the  zygomaticus. 

The  caput  infraorbitale  (levator  labii  superioris),  a  broad,  flat  muscle,  arises  from  the  infra- 
orbital margin  of  the  maxilla,  where  it  is  concealed  by  the  orbicularis  oculi.  It  extends  obhquely 
forward  over  the  caninus  and  beneath  the  caput  angulare  to  the  skin  and  musculature  of  the 
lateral  half  of  the  upper  hp. 

The  caput  angulare  (levator  labii  superioris  alseque  nasi)  arises  from  the  root  of  the  nose, 
where  it  is  fused  with  the  frontalis.  As  it  descends  it  divides  into  two  fasciculi,  one  of  which  is 
attached  to  the  skin  and  the  alar  cartilage  of  the  nose;  the  other  passes  obliquely  downward 
over  the  caput  infraorbitale  to  the  skin  and  musculature  of  the  lateral  half  of  the  upper  hp. 

Nerve-supply. — The  zygomatic  ramus  of  the  seventh  nerve  sends  branches  to  enter  the  deep 
surface  of  each  of  the  divisions  of  the  muscle. 

Actions. — It  raises  the  lateral  hah  of  the  upper  lip  and  the  wing  of  the  nose.  It  is  of  value 
in  inspiration,  serves  to  express  the  emotion  of  discontent,  and  comes  into  play  in  violent  weep- 
ing. 

Variations. — The  caput  zygomaticum  is  often  absent.  It  may  be  fused  with  the  zygoma- 
ticus (major).  It  may  be  doubled.  Its  origin  may  extend  to  neighbouring  structures.  The 
other  heads,  though  more  stable,  vary  considerably,  especiafly  in  the  extent  of  their  fusion  with 
neighbouring  muscles. 

The  quadratus  labii  inferioris  (depressor  labii  inferioris)  is  a  thin,  rhomboid  muscle  which 
arises  below  the  canine  and  bicuspid  teeth  from  the  base  of  the  mandible,  between  the  mental 
protuberance  and  the  mental  foramen,  and  extends  obhquely  upward  in  a  medial  direction  to  the 
orbicularis  oris,  through  which  its  fibre-bundles  pass.  Its  more  medial  fibres  cross  at  their 
insertion  with  those  of  the  muscle  of  the  other  side.  It  is  attached  to  the  skin  and  mucosa  of 
the  lower  lip.  It  is  essentially  a  part  of  the  platysma,  and  is  superficially  united  to  the  skin 
except  where  covered  by  the  triangularis  (depressor  anguh  oris).  It  crosses  the  mental  vessels 
and  nerves  and  a  part  of  the  mentalis  (levator  menti). 

Nerve-supply. — The  mandibular  branch  of  the  facial  sends  twigs  into  its  deep  surface  near 
the  lateral  border. 

Action. — It  draws  down  and  everts  the  lower  Up.  It  is  an  antagonist  of  the  mentahs 
(levator  menti).  It  plays  a  part  in  the  expression  of  terror,  irony,  great  anger,  and  similar 
emotions. 

Muscles  of  the  Angle  of  the  Mouth 

(Figs.  341,  342,  344,  345) 

The  caninus  (levator  anguli  oris)  is  a  flat,  quadrilateral  muscle  which  arises  from  the  canine 
fossa  of  the  maxilla  and  runs  beneath  the  quadratus  (levator)  labii  superioris  to  the  corner  of 


ORAL  MUSCLES 


333 


the  mouth,  where  it  becomes  attached  to  the  skin  and  sends  some  fasciculi  into  the  orbicularis  of 
the  lower  lip.  Between  the  caninus  and  the  quadratus  labii  superioris  there  is  a  certain  amount 
of  fatty  areolar  tissue  through  which  the  infraorbital  vessels  and  nerves  run.  Its  deep  surface 
extends  over  the  canine  fossa,  the  buccinator  muscle,  and  the  mucosa  of  the  Up.  The  external 
maxillary  (facial)  artery  passes  over  its  inferior  extremity. 

The  zygomaticus  (z.  major)  is  a  long,  ribbon-shaped  muscle  which  arises  by  short  tendinous 
processes  from  the  zygomatic  bone  near  the  temporal  suture  under  cover  of  the  orbicularis  oculi. 
It  passes  obliquely  to  the  corner  of  the  mouth,  where  it  is  attached  to  the  skin  and  mucosa. 
The  body  of  the  muscle  is  subcutaneous  and  is  usually  surrounded  by  fat.  It  crosses  the 
masseter  and  buccinator  muscles  and  the  anterior  facial  vein. 

The  risorius  is  a  thin,  triangular,  subcutaneous  muscle  which  extends  across  the  middle  of 
the  cheek  and  lies  in  a  more  superficial  plane  than  the  platysma,  with  which  it  is  often  fused.  It 
arises  from  the  tela  subcutanea  above  the  parotid  fascia.  Its  fibres  converge  across  the  masseter 
muscle  toward  the  angle  of  the  mouth  and  are  attached  to  the  skin  and  mucosa  in  this  vicinity. 
It  lies  above  the  anterior  facial  vein  and  external  maxillary  artery. 

The  platysma  has  been  described  above. 

The  triangularis  (depressor  anguli  oris)  is  a  broad,  flat,  well-developed,  subcutaneous  muscle 
which  arises  from  the  base  and  external  surface  of  the  body  of  the  mandible  below  the  canine, 
bicuspid,  and  first  molar  teeth.  From  here  its  fibres  converge  toward  the  corner  of  the  mouth, 
where  they  are  in  part  inserted  into  the  skin  and  in  part  are  continued  into  the  orbicularis  oris 
of  the  upper  hp.  It  overUes  the  buccinator  and  the  quadratus  (depressor)  labii  inferioris 
muscles.     Not  infrequently  (58  out  of  92  bodies — LeDouble)  some  fascicuh  are  continued  into 

Fig.  343.    (After  Eisleh.)    Buccinator  Muscle  and  Ptertgomandibular  Raphe, 

as  seen  from  the  buccal  side. 
The  alveolar  processes  of  both  jaws  have  been  removed  in  the  region  of  the  molar  teeth. 
The  soft  palate  and  its  muscles  have  been  removed. 


Auditory 

(Eustachian) 

.tube 


Mylo-hyoid 

Buccinator 


Internal  pterygoid 


the  neck  as  the  transversus  menti,  a  fibro-musoular  band  formed  by  the  interdigitation  of  the 
slips  prolonged  from  each  side  below  the  chin  and  superficial  to  the  platysma.  Santorini 
described  the  transversus  menti  as  an  independent  though  inconstant  muscle.  According  to 
Eisler  the  true  transversus  menti  muscle  is  to  be  distinguished  from  aberrent  slips  of  the  tri- 
angularis or  of  the  platysma  in  this  region.  In  one  instance  Eisler  found  a  slender  nerve 
emerging  through  the  platysma  and  passing  to  this  muscle. 

Nerue-supply. — The  zygomatic  branch  of  the  seventh  nerve  supphes  the  canine  (levator 
anguli  oris)  and  zygomatic  (major)  muscles.  Branches  enter  the  middle  of  the  deep  surface  of 
the  latter  muscle  and  the  superficial  surface  of  the  former  near  its  lateral  border.  The  risorius 
is  suppUed  by  branches  from  the  buccal  rami  of  the  seventh  nerve,  which  enter  its  deep  sur- 
face. The  triangularis  (depressor  anguh  oris)  is  supplied  by  the  buccal  branch  through  branches 
which  enter  its  deep  surface  near  the  posterior  margin. 

Action. — The  caninus  (levator  anguli  oris)  and  zygomatic  (z.  major)  muscles  raise  the  corner 
of  the  mouth,  the  former  at  the  same  time  drawing  it  medially,  the  latter,  laterally.  The 
caninus  gives  rise  to  expression  of  bitterness  or  menace.  The  zygomaticus  is  active  in  smihng  or 
laughing.  When  contracted  greatly  it  elevates  the  cheek  and  the  lower  eyehd  and  produces 
crow's-foot  wrinkles  at  the  corner  of  the  eye.  The  risorius  draws  the  angle  of  the  mouth  later- 
ally. ^  In  spite  of  its  name  it  is  not  used  to  express  pleasure,  but  instead  gives  rise  to  an  expression 
of  pain.  The  triangularis  (depressor  anguli  oris)  depresses  the  corner  of  the  mouth  and  draws 
it  laterally,  giving  rise  to  the  expression  of  grief. 


334  THE  MUSCULATURE 

Variations. — The  risorius  is  very  inconstant  in  its  development,  and  in  its  relations  to- 
neighbouring  muscles,  and  is  not  infrequently  quite  small.  The  zygomaticus  is  rarely  absent 
Its  origin  may  extend  to  the  temporal  or  masseteric  fascias.  It  may  be  doubled  throughout  its 
length  or  at  one  extremity.     Frequently  the  triangularis  is  divided  into  three  fasciculi. 

The  buccinator  (fig.  343)  arises  from — (1)  the  molar  portion  of  the  alveolar  process  of  the 
maxilla;  (2)  the  buccinator  crest  of  the  mandible,  and  (3)  the  pterygo-mandibular  raphe  of  the 
bucco-pharyngeal  fascia.  This  narrow  fibrous  band,  which  separates  the  buccinator  from  the 
superior  constrictor  of  the  pharynx,  extends  from  the  pterygoid  hamulus  to  the  buccinator  crest 
of  the  mandible.  The  fibre-bundles  are  divisible  into  four  sets.  The  most  cranial  extend 
directly  into  the  orbicularis  of  the  upper  lip.  The  next  pass  through  the  commissure  at  the 
corner  of  the  lips  into  the  orbicularis  of  the  lower  lip;  the  third  through  the  commissure  into  the 
orbicularis  of  the  upper  hp,  and  the  fourth  directly  into  the  orbicularis  of  the  lower  lip.  The 
muscle  is  attached  chiefly  to  the  mucosa  of  the  lips  near  the  angle  of  the  mouth.  Some  fibre- 
bundles  extend  to  the  more  medial  portion  of  the  mucosa  and  some  through  the  orbicularis  to 
the  skin. 

Nerve-supply. — By  the  buccal  branch  of  the  facial  nerve  through  filaments  which  enter  the 
posterior  half  of  its  outer  surface. 

Relations. — The  muscle  is  covered  externally  by  the  thin  bucco-pharyngeal  fascia;  internally 
by  the  mucosa  of  the  mouth.  Above  its  outer  surface  lie  the  zygomatic  (z.  major),  risorius,  and 
masseter  muscles."  Between  the  last  and  the  buccinator  lies  a  large  pad  of  fat  (the  buccal  fat 
pad).  The  parotid  duct  passes  forward  over  the  muscle,  and  slightly  in  front  of  its  centre 
pierces  it  and  passes  into  the  mouth.  It  is  crossed  by  the  external  maxillary  (facial)  artery  and 
anterior  facial  vein  and  by  the  buccal  artery  and  nerve. 

Actions. — It  draws  the  corner  of  the  mouth  laterally,  pulls  the  lips  against  the  teeth,  and 
flattens  the  cheek.  It  is  of  use  in  mastication,  swallowing,  whistling,  and  blowing  wind- 
instruments. 

Variations. — Occasionally  it  consists  of  two  laminse,  a  condition  found  in  many  mammals. 
It  may  be  continuous  in  part  with  the  superior  constrictor  of  the  pharynx,  as  in  the  cat. 

(c)  MENTAL  MUSCLE 

The  mentalis  (levator  menti)  (fig.  343)  is  a  short,  thick  muscle  which  arises  from  the  alveolar 
jugum  of  the  lower  lateral  incisor  tooth  and  the  neighbouring  region  of  the  mandible  under 
cover  of  the  quadratus  (depressor)  labii  inferioris  and  beneath  the  oral  mucosa,  where  this  is 
reflected  from  the  lips  to  the  gums.  It  extends  to  the  chin,  where  it  is  fused  with  the  muscle 
of  the  opposite  side  and  is  attached  to  the  skin  of  the  chin. 

Nerve-supply. — The  mandibular  branch  of  the  seventh  nerve  sends  terminal  twigs  into  this 
muscle. 

Actions. — It  draws  up  the  skin  of  the  chin  and  thus  indirectly  causes  the  lower  lip  to  pro- 
trude. It  is  of  use  in  articulation,  in  forcing  bits  of  food  from  between  the  gums,  and  in  the 
expression  of  various  emotions  (muscle  of  pride) . 

Variations. — It  varies  greatly  in  size  and  generally  is  fused  with  the  platysma. 

{d)  NASAL  MUSCLES 
(Figs.  341  and  344) 

Toward  the  nasal  apertures  several  muscles  converge.  Those  extending  from 
above  elevate  and  dilate,  those  from  below  depress  and  contract,  the  nostrils. 
To  the  former  belongs  the  pars  transversa  of  the  nasalis  (compressor  naris),  a 
triangular  muscle  extending  from  the  bridge  of  the  nose  to  the  naso-labial  sulcus; 
the  caput  angulare  of  the  quadratus  labii  superioris  (levator  labii  superioris 
alaeque  nasi),  which  arises  from  the  root  of  the  nose  and  sends  a  fasciculus  to  the 
wing  of  the  nose;  and  the  dilatores  naris,  described  below;  to  the  latter,  the 
pars  alaris  of  the  nasalis  (depressor  alas  nasi),  which  extends  from  the  alveolar 
juga  of  the  upper  lateral  incisor  and  canine  teeth  to  the  dorsal  margin  of  the 
nostril;  and  the  small  depressor  septi  nasi. 

The  nasalis  consists  of  two  parts,  the  pars  transversa  and  the  pars  alaris.  The  pars  trans- 
versa (compressor  naris)  is  triangular.  It  lies  on  the  side  of  the  nose  above  the  wing.  Its 
fibre-bundles  arise  from  an  aponeurosis  which  overlies  the  bridge  of  the  nose,  is  adherent  to  the 
skin,  and  is  not  closely  attached  to  the  underlying  cartilage.  From  this  aponeurosis  the  fibre- 
bundles  converge  toward  the  back  of  the  wing,  where  they  are  attached  to  the  skin  along  the 
fine  which  separates  the  wing  from  the  cheek  (naso-labial  sulcus).  Its  insertion  is  covered  by 
the  nasal  proce.ss  of  the  caput  angulare  (levator  labii  superioris  alseque  nasi)  of  the  quadratus 
labii  superioris  (p.  332),  with  which  its  fibres  interdigitate.  An  attachment  (origin)  is  also 
described  by  many  as  taking  place  in  the  lower  part  of  the  canine  fossa  of  the  maxilla. 

The  pars  alaris  (depressor  ala;  nasi)  (fig.  343),  is  a  small  quadrangular  muscle  situated  below 
the  aperture  of  the  nose,  between  this  and  the  alveolar  portion  of  the  maxilla.  It  is  covered  by 
the  mucosa  of  the  gum,  by  the  orbicularis  oris  and  the  quadratus  (levator)  labii  superioris,  aad 
laterally  is  fused  with  the  pars  transversa  (compressor  naris).  It  arises  from  the  alveolar  juga 
of  the  lateral  incisor  and  the  canine  teeth.  Its  fibre-bundles  extend  vertically  to  the  skin  of 
the  dorsal  margin  of  the  nostril,  from  the  dorsal  part  of  the  cartilage  of  the  wing  to  the  septum 

The  depressor  septi  is  a  flat,  triangular  muscle  which  extends  from  the  orbicularis  oris  to 
the  lower  edge  of  the  nasal  septum.     It  may  arise  from  the  jugum  alveolare  of  the  medial 


PERIORBITAL  MUSCLES 


335 


The  dilator  naris  posterior  is  a  thin,  triangular  muscle  which  lies  on  the  side  of  the  wing 
of  the  nose.  It  arises  from  the  skin  of  the  naso-labial  groove  and  is  attached  to  the  inferior 
border  of  the  wing  of  the  nose. 

The  dilator  naris  anterior  is  a  very  small,  thin  muscle  which  runs  from  the  lower  margin 
of  the  cartilage  at  the  front  of  the  wing  of  the  nose  to  the  skin.     It  is  not  usually  clearly  marked. 

Nerve-supply. — The  muscles  of  this  gi'oup  are  supphed  by  the  infra-orbital  and  buccal 
branches  of  the  facial  nerve. 

Actions. — The  transverse  portion  of  the  nasalis  (compressor  naris)  acts  with  the  angular 
head  (levator  labii  superioris  alaeque  nasi)  of  the  quadratus  labii  superioris  in  drawing  lateral- 


FiG.  344. — The  Deeper  Muscles  op  the  Face  and  Neck. 


Procerus 
Quadr.  labii 
sup.  caput 
angulare 
Caput  infra- 
orbitale 
Nasalis,  pars 
transversa 
Cani 
Depressor 
septi  nasi 
Nasalis,  pars 
alaris 
Orbicularis  oris 
Buccinator 

Triangularis 
Quadratus  la- 
bii inferions 
M  entails 
Mylo-hyoid 
Anterior  belly 
of  digastric 


-  Temporal 


_  Posterior  belly 
of  digastric 


'  Splenius  capitis 
-  Stylo-hyoid 


Scalenus  anterior 


•  '■  %\ 


ward  and  up  the  lateral  margin  of  the  wings  of  the  nose,  and  gives  rise  to  the  expression  of  sen- 
suaUty.  (Poirier.)  This  accords  with  the  electrical  experiments  of  Duchenne.  However, 
acting  in  conjunction  with  the  alar  portion,  the  transverse  portion  of  the  nasalis  may  constrict 
the  nostrils.  The  alar  portion  (depressor  alae  nasi)  of  the  nasalis  and  the  depressor  septi  nasi 
draw  down  the  nostril.  The  former  tends  to  contract  it  from  side  to  side,  the  latter  from  front 
to  back,  and  at  the  same  time  to  depress  the  tip  of  the  nose.  They  play  a  part  in  the  expression 
of  anger  and  of  pain.     The  functions  of  the  other  muscles  are  indicated  by  then'  names. 

Variations. — The  muscles  of  the  nose  vary  considerably  in  extent  of  development,  and  one 
or  more  may  be  absent.  Authors  differ  considerably  in  their  description  of  several  of  the 
muscles.  The  anomalus  is  a  longitudinal  muscle  strip  occasionally  found  running  from  the 
frontal  process  to  the  body  of  the  maxilla  near  the  lateral  margin  of  the  nasal  aperture. 


(e)  PERIORBITAL  MUSCLES 
(Figs.  341,  344) 

The  muscles  which  encircle  the  orbit  constrict  the  entrance  of  the  orbit  so  as 
to  shut  out  light  and  protect  the  eye  against  foreign  bodies.     To  these  belong 


336  THE  MUSCULATURE 

the  orbicularis  oculi,  the  corrugator,  and  the  procerus.  The  orbicularis  oculi  is  a 
large,  flat,  elliptical  muscle  which  lies  in  the  eyelids  and  over  the  bone  surrounding 
the  orbit.  Three  parts  are  recognised,  a  palpebral,  an  orbital  and  a  lacrimal. 
The  quadrangular  corrugator  extends  from  the  nasal  portion  of  the  frontal  bone 
to  the  skin  of  the  middle  half  of  the  eyebrow;  the  narrow  procerus  (pyramidaHs 
nasi)  from  the  bridge  of  the  nose  to  the  skin  at  the  root.  The  muscles  which 
have  an  antagonistic  action  are  the  levator  palpebrse  superioris  and  the  epicranius. 
The  levator  palpebrse  is  described  in  the  chapter  on  the  Eye  (see  Section  VIII), 
the  epicranius  in  the  following  subsection. 

The  orbicularis  oculi. — The  palpebral  portion  arises  from  the  ventral  surface  and  margins 
of  the  lateral  portion  of  the  medial  palpebral  hgament  (tendo  oculi),  and  from  the  covering  of  the 
lacrimal  sac.  The  fibre-bundles  spread  out  as  they  pass  into  the  eyelids  and  again  are  con- 
centrated toward  their  insertion  into  the  outer  surface  of  the  lateral  palpebral  ligament.  Many 
of  the  fibre-bundles  interdigitate  here  without  being  inserted  into  the  ligament.  The  muscle 
in  each  eyelid  lies  between  the  tarsal  plate  and  the  skin,  separated  from  both  by  loose  tissue. 
The  superficial  muscle-fibres  nearest  the  margin  of  the  hds  constitute  the  ciliary  muscle,  or  muscle 
of  Riolan.  They  are  very  small  fibres  and  probably  act  on  the  eyelashes  and  Meibomian 
glands. 

The  orbital  portion  arises  by  a  superior  origin  from  the  medial  palpebral  ligament  (tendo 
ocuU),  the  nasal  portion  of  the  frontal  bone,  and  the  anterior  lacrimal  crest  of  the  maxilla,  and 
by  an  inferior  origin  from  the  medial  palpebral  hgament  and  the  medial  portion  of  the  inferior 
rim  of  the  orbit.  The  fibre-bundles  form  a  flat  ring  which  surrounds  the  orbit  for  a  consider- 
able distance,  especially  inferiorly.  The  muscle  is  adherent  to  the  overlying  skin.  It  hes  over 
the  bones  surrounding  the  margin  of  the  orbit  and  over  the  attachments  of  several  of  the  facial 
muscles  attached  to  these  bones.  With  these  muscles  some  of  the  fibre-bundles  are  usually 
continuous. 

The  lacrimal  portion  (tensor  tarsi  or  Horner's  muscle)  arises  from  the  posterior  lacrimal 
crest  of  the  lacrimal  bone  and  passes  down  on  the  dorsal  surface  of  the  lacrimal  sac  and  the 
medial  palpebral  ligament  (tendo  oculi).  It  bifurcates  and  furnishes  a  fasciculus  attached  to 
each  tarsal  plate.  Some  of  the  fibre-bundles  surround  the  lacrimal  canaliculi  and  some 
surround  the  ducts  of  the  tarsal  glands  and  the  roots  of  the  eyelashes. 

The  corrugator  arises  from  the  frontal  bone  near  the  fronto-nasal  suture.  It  extends 
obliquely  upward  to  be  inserted  into  the  skin  of  the  middle  half  of  the  eyebrow.  The  fibre- 
bundles  of  insertion  interdigitate  with  those  of  the  frontahs.  The  muscle  hes  relatively  deep. 
It  is  covered  by  the  procerus  (pyramidahs  nasi),  the  frontalis,  and  the  orbicularis.  Under  it 
lie  the  supra-orbital  vessels  and  nerves. 

The  procerus  (p3rramidalis  nasi)  overlies  the  nasal  bone.  It  arises  from  the  lateral  cartilage 
of  the  nose  through  a  fibrous  membrane  and  also  directly  from  the  nasal  bone,  and  is  attached 
to  the  skin  over  the  root  of  the  nose,  where  its  fibres  interdigitate  with  those  of  the  frontalis. 
The  medial  margins  of  the  muscles  on  each  side  are  more  or  less  fused. 

Nerve-supply. — The  muscles  of  this  group  are  supphed  by  temporal  and  infraorbital  branches 
of  the  facial  nerve  which  enter  the  deep  surfaces  near  the  lateral  margins. 

Action. — The  palpebral  portion  of  the  orbicularis  closes  the  eyehds,  of  which  the  upper 
moves  more  freely  than  the  lower.  It  also  serves  to  dilate  the  lacrimal  sac  and  allow  the 
tears  to  flow  away  readily.  The  tensor  tarsi  probably  contracts  the  sac  and  forces  the  tears 
into  the  nose.  The  upper  half  of  the  orbital  portion  of  the  orbicularis  contracts  and  depresses 
the  tissue  overhanging  the  orbit,  and  stretches  the  skin  of  the  forehead.  The  corrugator  draws 
the  skin  of  the  brow  downward  and  medially,  thus  aiding  the  preceding  muscle.  It  causes  the 
perpendicular  furrows  characteristic  of  frowning.  The  procerus  (pyramidahs  nasi)  draws  down 
the  skin  of  the  forehead  and  wrinkles  the  skin  across  the  root  of  the  nose.  The  lower  half  of 
the  orbital  portion  of  the  orbicularis  raises  the  skin  of  the  cheek,  causing  the  wrinkles  seen  to 
radiate  from  the  corner  of  the  eye.  The  whole  set  of  muscles  comes  into  play  in  the  forcible 
closure  of  the  eyes.  In  case  of  violent  expiratory  efforts,  as  in  shouting,  sneezing,  coughing, 
etc.,  the  eye  is  thus  usually  forcibly  closed.  The  pressure  thus  exerted  on  the  eyeball  prevents 
a  too  violent  flow  of  blood  to  the  vessels  of  the  eye.  Pressure  is  thought  at  the  same  time  to 
be  exerted  on  the  lacrimal  gland  so  as  to  cause  the  excessive  flow  of  tears  often  experienced  at 
such  times. 

Variations. — The  muscles  of  this  group  vary  in  extent  and  differentiation,  and  may  be  more 
or  less  fused  with  one  another  or  with  neighbouring  muscles.  The  orbital  portion  of  the  or- 
bicularis, the  corrugator,  and  the  procerus  have  been  found  absent. 

(/)  THE  EPICRANIAL  MUSCULATURE 
(Fig.  341) 

The  epicranius  (occipito-frontalis)  is  formed  of  the  two  frontal  muscles,  which 
lie  on  each  side  of  the  forehead,  the  two  occipital  muscles,  which  occupy  corre- 
sponding positions  on  the  occipital  bone,  and  of  the  epicranial  aponeurosis,  the 
galea  aponeurotica,  which  extends  between  these.  The  occipital  muscles  arise 
from  the  supreme  nuchal  line  and  are  inserted  into  the  galea  aponeurotica.  The 
frontal  muscles  arise  from  the  latter  and  are  inserted  into  the  skin  near  the  eye- 
brows.    The  chief  function  of  these  muscles  is  to  elevate  the  brows.     The 


AURICULAR  MUSCLES  337 

muscles  and  the  intervening  aponeurosis  lie  between  two  layers  of  fascia,  the 
external  of  which  is  fused  to  the  skin,  while  the  internal  moves  freely  over  the 
periosteum,  to  which  it  is  loosely  attached.  Hsemorrhages  and  abscesses 
spread  freely  between  the  deep  layer  of  fascia  and  the  periosteum. 

The  frontalis  is  a  large,  thin  muscle  with  convex  upper  and  concave  lower  border.  It  arises 
from  the  epicranial  aponeurosis  midway  between  the  coronal  suture  and  the  orbital  arch,  and  is 
inserted  into  the  skin  of  the  eyebrow  and  of  the  root  of  the  nose.  The  medial  fibre-bundles  take 
a  sagittal  direction;  the  lateral  converge  obhquelj'  toward  the  brow.  The  medial  margins  of 
the  muscles  of  each  side  are  approximated  near  the  attachment.  The  more  medial  fibre-bundles 
are  continuous  with  those  of  the  procerus  (pyramidahs  nasi)  and  the  angular  portion  (levator 
labii  superioris  alasque  nasi)  of  the  quadratus  labii  superioris;  the  more  lateral  interlace  with  those 
of  the  corrugator  and  orbicularis  muscles.  The  branches  of  the  vessels  and  nerves  of  the  frontal 
region  pierce  the  muscle  and  are  distributed  between  it  and  the  skin. 

The  occipitalis,  flat  and  quadrangular,  lies  on  the  occipital  bone  above  the  supreme  nuchal 
line.  It  rises  by  tendinous  fibres  from  the  lateral  two-thirds  of  this  line  and  from  the  posterior 
part  of  the  mastoid  process  of  the  temporal  bone,  and  is  inserted  into  the  epicranial  aponeurosis. 
The  medial  fibre-bundles  run  sagitaUy,  while  the  lateral  run  obliquely  forward.  The  occipital 
artery  and  nerve  lie  between  the  muscle  and  the  skin.  The  lateral  border  of  the  muscle  comes 
in  contact  with  the  posterior  auricular  muscle.  The  muscles  of  each  side  are  usually  separated 
by  a  strip  of  aponeurosis. 

The  galea  aponeurotica  (epicranial  aponeurosis)  is  a  fibrous  membrane  which  extends  be- 
tween the  occipital  muscles  and  from  them  anteriorly  to  the  frontal  muscles.  In  the  area  be- 
tween these  two  sets  of  muscles  it  is  composed  largely  of  sagitahy  running  fibres  into  which 
coronal  fibres  radiate  from  the  region  of  the  muscles  of  the  ear.  Between  the  two  occipital 
muscles  the  aponeurosis  is  attached  to  the  supreme  nuchal  line  and  external  occipital  protuber- 
ance. Laterally  the  fascia  covering  it  is  continued  as  a  special  investment  of  the  auricular 
muscles,  beyond  which  it  is  attached  to  the  mastoid  process,  the  zygoma,  and  to  the  external 
cervical  and  the  masseteric  fasciae. 

Nerve-supply. — The  frontahs  is  suppUed  by  the  temporal  branches  of  the  facial  nerve,  the 
occipitalis  by  the  posterior  auricular  branch.  The  branches  enter  the  deep  surface  of  each  of 
these  muscles  near  its  lateral  border. 

Action. — The  occipitalis  serves  to  draw  back  and  to  fix  and  make  tense  the  epicranial  ap- 
oneurosis. The  frontalis,  with  its  aponeurotic  extremity  fixed,  elevates  the  brows  and  throws 
the  skin  of  the  forehead  into  transverse  wrinkles  as  in  the  expression  of  attention,  surprise,  or 
horror.  When  both  muscles  contract  forcibly  there  is,  in  addition,  a  tendency  to  make  the 
hair  stand  on  end  because  the  hair-bulbs  of  the  occipital  region  slant  forward,  those  of  the  frontal 
region  backward.     The  frontalis  when  fixed  below  puUs  the  scalp  forward. 

Variations. — The  ocoipitahs  is  occasionally  absent,  a  condition  normal  in  ruminants.  The 
muscles  of  the  two  sides  may  be  fused  in  the  median  line  (normal  in  dogs).  It  may  be  fused 
with  the  posterior  auricular.  The  frontalis  is  rarely  missing.  The  frontalis  may  send  shps 
to  the  medial  or  lateral  angles  or  the  orbital  arch  of  the  frontal  bone,  to  the  nasal  process  of  the 
maxilla  or  to  the  nasal  bone.  The  fibre-bundles  of  the  frontalis  may  interdigitate  across  the 
median  line. 

The  transversus  nuchas,  or  occipitaUs  minor,  is  a  small  muscle,  frequently  present  (27  per 
cent.,  Le  Double),  which  runs  from  the  occipital  protuberance  toward  the  posterior  auricular 
muscle,  with  which  it  may  be  fused.     It  may  He  over  or  under  the  trapezius. 

(g)  AURICULAR  MUSCLES 
(Fig.  341) 

The  intrinsic  muscles  of  the  auricle  are  described  in  Section  VIII.  There  are 
three  'extrinsic^  auricular  muscles  which  converge  from  regions  anterior,  superior, 
and  posterior  to  the  auricle  and  are  inserted  into  it. 

The  auricularis  anterior  (attrahens  aurem)  is  a  small,  flat,  triangular  muscle  which  arises 
between  the  two  layers  of  the  fascia  of  the  galea  aponem-otica,  extends  over  the  zygomatic  arch, 
and  is  attached  to  the  ventral  end  of  the  helix.  The  fibre-bundles  converge  from  the  origin 
toward  a  tendon  of  insertion.  The  area  of  origin  of  this  muscle  is  often  marked  by  a  fibrous 
band  tangential  to  its  component  fibres.  From  this  band  muscle  fibre-bundles  radiate  out 
toward  the  frontal  region  of  the  skull.  To  the  muscle  formed  of  these  radiating  fibres  the  names 
epicranio-temporalis  (Henle),  temporalis  superficialis  (Sappey)  and  auriculo-frontalis  (Gegen- 
baur)  have  been  given. 

The  auricularis  superior  (attoDens  aurem)  is  a  large,  tliin,  triangurar  muscle  which,  from 
its  tendinous  insertion  on  the  eminence  of  the  triangular  fossa  of  the  ear,  radiates  upward  into ' 
the  fascia  of  the  galea  aponeurotica,  between  the  layers  of  which  it  takes  oigin  near  the  temporal 
ridge.     It  lies  over  the  temporal  fascia  and  the  periosteum  of  the  parietal  bone. 

The  auricularis  posterior  (retrahens  aurem)  is  a  thin,  band-like  muscle  which  extends  over 
the  insertion  of  the  sterno-cleido-mastoid  from  the  base  of  the  mastoid  process  and  the  ap- 
oneurosis of  the  sterno-cleido-mastoid  muscle  to  the  convexity  of  the  concha,  where  it  has  a  ten- 
dinous insertion.  It  is  usually  composed  of  two  fasciculi,  and  is  contained  between  two  layers 
of  fascia  derived  from  the  galea  aponeurotica. 

Nerve-supply. — The  aiu-icularis  anterior  and  superior  are  supphed  by  the  temporal  branch 
of  the  facial,  the  auricularis  superior  and  posterior  by  the  posterior  am-icular  branch.  The 
twigs  of  supply  run  to  the  deep  surface  of  the  muscles. 


338 


THE  MUSCULATURE 


Relations. — The  superficial  ascending  branch  of  the  auriculo-temporal  nerve  usually  runs 
superficial  to  the  anterior  and  superior  auricular  muscles.  The  superficial  temporal  vessels  run 
at  first  beneath  these  muscles  and  the  lateral  expansion  of  the  galea  aponeurotica,  then  between 
the  two  fascial  layers  which  enclose  the  muscles.  Their  branches  of  distribution  finally  come 
to  lie  between  the  muscles  and  aponeurosis  and  the  skin.  The  posterior  auricular  artery  and 
nerve  usually  run  under  cover  of  the  auricularis  posterior. 

Action. — The  anterior  muscle  is  a  protractor,  the  superior  an  elevator,  and  the  posterior  a 
retractor  of  the  ear,  but  usually  in  man  they  are  inactive. 

Variations. — These  muscles  vary  much  in  development.  The  most  constant  of  them  is 
the  superior.  The  posterior  frequently  is  increased  in  size  and  may  be  fused  with  the  occipitalis, 
which  originally  was  probably  an  ear  muscle.  From  the  anterior  muscle  a  special  deep  fasciculus 
is  occasionally  isolated.  Each  of  the  muscles  is  occasionally,  though  rarely,  absent,  the  anterior 
most  frequently.  An  inferior  auricular  muscle  is  very  rarely  found  in  man,  though  present  in 
many  of  the  lower  mammals.  A  slip  of  the  posterior  auricular  may  run  beneath  the  ear  to  the 
parotid  fascia. 

Fig.  345. — The  Temporal  Muscle. 


2.  CRANIO-MANDIBULAR  MUSCULATURE 
(Figs.  344,  345,  346,  and  347) 

The  cranio-mandibular  muscles,  or  muscles  of  mastication,  pass  from  the  base 
of  the  skull  to  the  lower  jaw.  They  are  represented  in  the  selachians  by  a  single 
muscle  mass,  the  adductor  mandibulee  (Gegenbaur),  but  in  the  higher  vertebrates 
this  muscle  mass  becomes  variously  subdivided  during  embryonic  development. 
The  muscles  are  innervated  by  the  masticator  nerve  (motor  root  of  the  tri- 
geminal cranial  nerve,  the  nerve  of  the  mandibular  arch).  In  man  four  muscles 
are  recognised,  the  temporal,  masseter,  and  internal  and  external  pterygoids. 

The  temporal  and  masseter  muscles  are  situated  on  the  lateral  sm-face  of  the 
skull,  partly  under  cover  of  muscles  of  the  facialis  group.  The  temporal  muscle 
(fig.  345),  which  resembles  the  quadrant  of  a  circle,  arises  from  the  temporal 
fossa  and  is  inserted  into  the  coronoid  process  of  the  mandible;  the  thick,  quad- 
rilateral masseter  (fig.  344)  muscle  arises  from  the  zygomatic  arch  and  is  in- 
serted into  the  lateral  surface  of  the  ramus  and  angle  of  the  mandible.  The 
pterygoids  (fig.  346)  are  more  deeply  seated.  The  cone-shaped  external  pterygoid 
arises  from  the  lateral  side  of  the  pterygoid  process  and  lower  surface  of  the  great 
wing  of  the  sphenoid  and  is  inserted  into  the  condyloid  process  of  the  mandible 
and  the  capsule  of  the  joint.  The  thick,  quadrilateral  internal  pterygoid  parallels 
the  masseter.  It  arises  from  the  pterygoid  fossa  of  the  sphenoid  and  is  inserted 
into  the  inner  side  of  the  angle  of  the  mandible.     It  will  be  noted  that  the  tem- 


FASCIJE 


339 


poral,  masseter,  and  internal  pterygoid  muscles  have  approximately  vertical  axes 
of  contraction  and  adduet  the  lower  jaw,  while  the  external  pterygoid-  has  an 
approximately  horizontal  axis  of  contraction  and  draws  the  jaw  forward  and, 
when  acting  on  one  side,  toward  the  opposite  side. 


Fig.  346. — The  Pterygoid  Muscles. 


External  pterygoid 


Internal  pterygoid 


FASCI.E 

The  temporal  fascia  arises  from  the  temporal  line  of  the  frontal  bone  and  from  the  superior 
temporal  line  of  the  parietal  and  the  periosteum  immediately  below  this.  It  extends  to  the 
zygomatic  arch.  In  its  inferior  quarter  the  fascia  divides  into  two  lamellae,  one  of  which  passes 
to  the  outer,  the  other  to  the  inner,  surface  of  the  arch,  but  at  the  superior  margin  of  the  arch 
these  two  lamelte  are  united  by  dense  fibrous  tissue.  Between  the  two  lamella?  above  the 
arch  hes  a  fatty  areolar  tissue  in  which  the  middle  temporal  artery  often  runs.  The  outer  sur- 
face of  the  fascia  is  covered  by  the  superficial  temporal  and  anterior  and  superior  auricular 
muscles,  and  by  a  thin  layer  of  fascia  from  the  galea  aponeurotica,  with  which,  toward  the  zygo- 
matic arch,  it  becomes  merged.  The  superficial  temporal  artery  and  auriculo-temporal  nerve 
cross  it. 

The  masseteric  fascia  represents  essentially  a  continuation  of  the  temporal  fascia  from  the 
inferior  margin  of  the  zygomatic  arch  over  the  masseter  muscle  which  it  covers.  It  is  less  thick 
than  the  temporal  fascia,  but  is  firm  and  strong.  It  is  attached  dorsally  to  the  dorsal  margin 
of  the  mandible,  mferiorly  to  the  inferior  margin,  and  ventrally  to  the  body  and  to  the  ventral 
majgin  of  the  ramus  and  the  coronoid  process  of  the  mandible.  In  part  it  extends  over  the  fat 
pad  of  the  cheek  to  the  buccinator  fascia.  The  parotid  gland,  covered  by  the  parotid  extension 
of  the  external  cervical  fascia,  extends  over  the  posterior  portion  of  this  fascia.  The  parotid 
fascia  becomes  fused  to  its  external  surface  at  the  anterior  margin  of  the  gland.  Over  it  lie 
the  parotid  duct,  the  transverse  facial  artery,  branches  of  the  facial  nerve,  the  zygomaticus 
(major),  risorius,  and  platysma  muscles. 

The  pterygoid  muscles  are  each  surrounded  by  a  dehcate  membrane.  In  addition  an 
mterpterygoid  fascia  separates  the  two  muscles.  This  arises  from  the  sphenoidal  spine  and 
toUows  the  internal  surface  of  the  external  pterygoid  to  the  mandible.  MediaUy  it  is  attached 
to  the  lateral  lamella  of  the  pterygoid  process;  posteriorly  and  laterally  it  presents  a  free  margin 
which  forms  with  the  neck  of  the  mandibular  condyle,  an  orifice  for  the  passage  of  the  internal 
maxillary  artery,  the  auriculo-temporal  nerve,  and  several  veins.  Its  posterior  margin  is 
strengthened  into  the  spheno-mandibular  ligament,  which  runs  from  the  spine  of  the  sphenoid 
to  the  lingula  of  the  mandible. 

The  pharyngeal  region  is  separated  from  the  pterygoid  by  a  dense  membrane,  the  lateral 
pharyngeal  fascia.  This  extends  from  the  depth  of  the  pterygoid  fossa  to  the  prevertebral 
tascia,  a,nd  separates  the  tensor  veh  palatini  from  the  internal  pterygoid  muscle.  It  is  attached 
above  along  a  Ime  extending  from  the  external  margin  of  the  carotid  canal  to  the  internal  margin 
ot  the  oval  foramen. 


i 


340 


THE  MUSCULATURE 


Fig.  347. 


CRANIO-MANDIBULAR  MUSCLES  341 

The  sigmoidal  septum  is  a  thin  membrane  which  occupies  the  incisura  mandibulae  and  sepa- 
rates the  masseter  from  the  external  pterygoid  muscle. 

MUSCLES 

The  temporalis  (fig.  345). — Origin. — (1)  From  the  whole  of  the  temporal  fossa,  with  the 
exception  of  that  part  formed  by  the  body  and  temporal  process  of  the  zygomatic  (malar)  bone; 
and  (2)  from  the  fascia  covering  the  fossa.  Insertion  is  into  the  tip,  dorsal  and  ventral  borders, 
and  the  whole  internal  surface  of  the  coronoid  process  of  the  mandible  and  the  ventral  portion 
of  the  medial  surface  of  the  ramus. 

In  structure,  the  muscle  is  thin  near  its  superior  margin,  but  becomes  thick  as  its  insertion 
is  approached.  The  fibre-bundles  arising  from  the  medial  surface  of  the  fossa  and  from  the 
fascia  converge  upon  the  medial  and  lateral  surfaces  and  the  margins  of  a  thick,  broad  tendon 
which  begins  very  high  in  the  muscle,  becomes  visible  laterally  some  distance  above  the  zygo- 
matic arch,  and  is  inserted  into  the  tip,  edges,  and  internal  surface  of  the  coronoid  process.  On 
the  ventral  and  dorsal  margins  of  the  tendon  the  insertion  of  fibre-bundles  continues  to  the  coro- 
noid process,  while  medially  the  insertion  of  the  fibre-bundles  is  continued  on  the  medial  surface 
of  the  coronoid  process  and  often  on  the  ramus  as  far  as  the  body  of  the  bone. 

Nerve-supply. — Usually  three  branches  from  the  anterior  branch  of  the  mandibular  division 
of  the  fifth  nerve  curve  upward  over  the  temporal  surface  of  the  great  wing  of  the  sphenoid  and 
enter  the  deep  surface  of  the  muscle.  The  posterior  and  middle  nerves  pass  above  the  external 
pterygoid;  the  anterior,  which  springs  from  the  buccinator  nerve,  passes  between  the  two  heads 
of  the  external  pterygoid  before  curving  upward. 

Relations. — The  muscle  is  covered  by  the  temporal  fascia  and  the  zygomatic  arch.  Below 
the  temporal  fossa  the  pterygoid  muscles  and  the  buccinator  lie  medial  to  it.  The  temporal 
fossa  in  front  of  the  muscle  is  filled  with  a  fatty  areolar  tissue  and  this  also  extends  between  the 
muscle  and  the  temporal  fascia.  Fatty  tissue  hkewise  lies  between  the  muscle  and  the  buccina- 
tor. Medial  to  the  muscle  run  the  deep  temporal  vessels  and  nerves,  the  buccinator  nerve 
and  the  spheno-mandibular  ligament.  The  masseteric  nerve  passes  lateralward  behind  and 
below  the  tendon. 

The  masseter  (fig.  343)  is  composed  of  two  layers.  The  superficial  layer  arises  by  an  apo- 
neurosis from  the  anterior  two-thirds  of  the  lower  border  of  the  zygomatic  (malar)  bone.  The 
fibre-bundles  arise  from  the  deep  surface  of  this  aponeurosis  and  its  tendinous  prolongations 
pass  obliquely  downward  and  backward,  and  are  inserted  into  the  lower  half  of  the  external 
surface  of  the  ramus,  into  the  angle,  and  into  the  neighbouring  portion  of  the  body  of  the  man- 

FiG.  347.* — A  AND  B  ARE  Transvehsb  Sections  and  C  (after  Testut),  a  Frontal  Section 

THROUGH   the   LeFT    SiDE    OF   THE    HeAD,    IN   THE    REGIONS    INDICATED    IN   THE    DIAGRAM. 

a  and  b  in  the  diagram  indicate  the  regions  through  which  pass  sections  A  and  B,  fig.  351;  and 
a',  section  A,  fig.  357. 

1.  Adipose  tissue.  2.  Arteria  temporalis  superfioialis.  3.  A.  carotis  externa.  4.  A.  car- 
otis  interna.  5a.  A.  maxillaris  externa  (facial).  56.  A.  maxillaris  interna.  6.  A.  verte- 
bralis.  7.  Atlas.  8.  Cerebellum.  9.  Epistropheus  (axis).  10.  Fascia  buccopharyngea. 
11.  F.  cervicalis,  a  (superficial  layer),  6,  deep  parotid  process.  12.  F.  interpterygoidea. 
13.  F.  masseterioa.  14.  F.  nuchie.  15.  F.  pharyngobasilaris.  16.  F.  pharyngis  lateralis. 
17.  F.  temporaHs.  18.  Galea  aponeurotica.  19.  Glandula  parotica.  20.  Ligamentum  stylo- 
mandibularis.  21a.  Mandible,  capitulum;  b,  coronoid  process.  22.  Meatus  acusticus 
ext.  23.  Medulla  oblongata.  24.  MeduUa  spinalis  (spinal  cord).  25.  Musculus  auricu- 
laris  posterior  (retractor  auris).  26.  M.  buccinator.  27.  M.  caninus  (levator  anguli 
oris).  28.  M.  constrictor  pharyngis  medius.  29.  M.  constrictor  pharyngis  superior.  30. 
M.  digastricus.  31.  M.  genio-glossus.  32.  M.  hyo-glossus.  33.  M.  incisivus  labii 
inferioris.  34.  M.  levator  veli  palatini.  35.  M.  longus  capitis  (rectus  capitis  anticus 
major).  36.  M.  longissimus  capitis  (trachelo-mastoid).  37.  M.  longitudinalis  inferior. 
38. _M.  masseter.  39.  M.  mylo-hyoideus.  40.  M.  nasalis  (alar  portion).  41.  M. 
obhquus  ca,pitis  inferior.  42.  M.  obUquus  capitis  superior.  43.  M.  pterygoideus  externus 
— a,  superior  fasciculus;  6,  inferior  fasciculus.  44.  M.  pterygoideus  internus.  45.  M. 
quadratus  (levator)  labii  superioris.  46.  M.  rectus  capitis  anterior  (minor).  47.  M. 
rectus  capitis  posterior  major.  48.  M.  rectus  capitis  posterior  minor.  49.  M.  rectus 
capitis  laterahs.  50.  M.  semispinalis  capitis  (complexus).  51.  M.  splenius  capitis. 
52.  M.  sterno-cleido-mastoideus.  53.  M.  stylo-glossus.  54.  M.  stylo-hyoideus.  55. 
M._  stylo-pharyngeus.  56.  M.  temporalis  (a,  fasciculus  from  zygoma).  57.  M.  tensor 
veli  palatini.  58.  M.  trapezius.  59.  M.  zygomaticus  (major).  60.  Nervus  accessorius 
(spinal  accessory).  61.  N.  alveolaris  inferior  (dental).  62.  N.  alveolaris  posterior  superior 
(dental).  63.  N.  auriculo-temporalis.  64.  N.  buccinatorius.  65.  N.  canalis  pterygoidei 
(Vidian  nerve).  66.  N.  glosso-pharyngeus.  67.  N.  hypoglossus.  68.  N.  Ungualis. 
69.  N.  mandibularis.  70.  N.  masseteric  nerve.  71.  N.  maxillary  nerve.  72.  N.  mylo- 
hyoid nerve.  73.  N.  palatinus.  74.  Sympathetic  trunk.  75.  N.  temporalis  profundus. 
76.  N.  vagus.  77.  Os  occipitale — a,  basilar  portion;  b,  external  protuberance.  78.  Os 
sphenoidale.  79.  Os  temporale — o,  processus  zygomaticus;  b,  tubercle.  80.  Os  zygo- 
maticum  (malar).  81.  Pharyngeal  orifice  of  tuba  auditiva  (Eustachian  tube).  82. 
Palatum  durum  (hard  palate).  83.  Pharynx — a,  oral  portion;  b,  nasal  portion.  84. 
Pharyngeal  recess.  85.  Sinus  maxillaris  (antrum  of  Highmore).  86.  Sinus  transversus 
(lateral).  87.  Tonsila  palatina.  88.  Uvula.  89.  Vena  facialis  posterior  (temporo- 
maxillary).  90.  V.  jugularis  interna. 
*  This  and  the  following  series  of  cross-sections  are  taken  from  a  thin,  not  very  muscular, 

adult  male.     The  fasciae  are  represented  in  most  instances  disproportionately  thick. 


342  THE  MUSCULATURE 

dible — the  more  anterior  directly,  the  posterior  by  means  of  an  aponeurosis.  The  deep  layer 
arises  from  the  lower  border  and  internal  surface  of  the  zygomatic  arch.  The  fibre-bundles 
pass  neai'ly  vertically  downward,  and  are  inserted  upon  the  upper  hah  of  the  external  surface 
of  the  ramus.  The  origin  and  insertion  are  by  tendinous  bands,  to  which  the  fibre-bundles  are 
attached  in  a  multipenniform  manner.  The  two  layers  are  fused  near  the  origin  and  insertion 
and  in  front.  From  the  temporal  surface  of  the  zygomatic  bone  and  the  neighbouring  part  of 
the  deep  layer  of  the  temporal  fascia  there  arises  a  fasciculus  which  is  separated  by  a  pad  of 
fat  from  the  main  body  of  the  temporal  muscle,  and  is  inserted  into  the  lateral  sm-faoe  of  the 
lower  extremity  of  the  tendon  of  the  temporal  muscle  and  into  the  ventro-lateral  surface  of  the 
tip  of  the  coronoid  process.  This  fasciculus,  sometimes  described  as  a  part  of  the  temporal 
muscle,  is  innervated  by  the  masseteric  nerve. 

Nerve-supply. — The  branch  arises  in  common  with  the  posterior  nerve  to  the  temporal 
muscle  from  the  motor  root  of  the  trigeminal  (the  masticator  nerve).  It  passes  above  the 
external  pterygoid,  through  the  mandibular  (sigmoid)  notch,  and  enters  the  deep  surface  of 
the  muscle  near  the  dorsal  margin. 

•  I  Relations. — It  is  covered  by  the  masseteric  fascia  (see  above).  It  lies  upon  the  ramus  of 
the  jaw  and  ventrally  is  separated  by  a  pad  of  fat  from  the  buccinator  muscle.  At  the  mandibu- 
lar (sigmoid)  notch  the  sigmoid  septum  separates  it  from  the  external  pterygoid  muscle. 
The  parotid  gland  partly  overlaps  its  posterior  border. 

The  pterygoideus  externus  (figs.  343-346)  consists  of  two  fasciculi.  Each  is  thick  and  tri- 
angular. The  superior  is  flattened  in  a  horizontal,  the  inferior  in  a  vertical,  plane.  At  their 
origin  they  are  separated  by  a  narrow  cleft.  Near  the  insertion  they  become  more  or  less  fused. 
The  superior  fasciculus  arises  by  short  tendinous  processes  from  the  infratemporal  (pterygoid) 
crest  and  from  the  neighbouring  portion  of  the  under  surface  of  the  great  wing  of  the  sphenoid. 
Its  fibre-bundles  converge  toward  the  insertion,  which  takes  place  by  short  tendinous  processes 
into — (1)  the  capsular  ligament  in  front  of  the  articular  disc  and  (2)  the  upper  third  of  the  front 
of  the  neck  of  the  condyle.  The  inferior  fasciculus  is  the  larger.  It  arises  by  short  tendinous 
processes  from  the  lateral  surface  of  the  lateral  lamina  of  the  pterygoid  process,  from  the  pyrami- 
dal process  of  the  palate  bone,  and  from  the  adjacent  portions  of  the  maxillary  tuberosity. 
The  fibre-bundles  converge  toward  their  insertion  into  a  depression  on  the  front  of  the  neck  of 
the  condyle. 

Nerve-supply. — A  branch  from  the  masticator  nerve  (mot6r  root  of  the  trigerninus)  ap- 
proaches the  muscle  near  the  upper  border  of  the  medial  surface  of  the  superior  fasciculus  and 
gives  branches  to  both  portions. 

Relations. — It  is  partly  covered  by  the  maxillary  fasciculus  of  the  internal  pterygoid  and  by 
the  temporal  and  masseter  muscles.  Medial  to  it  lies  the  chief  fasciculus  of  the  internal  ptery- 
goid muscle.  The  masseteric  and  the  posterior  and  middle  temporal  nerves  usually  pass  above 
the  muscle,  the  anterior  temporal  and  the  buccinator  nerves  and  frequently  the  internal  maxil- 
lary artery  between  the  two  fasciculi.  The  internal  maxillary  vessels  usually  pass  below  the 
lower  border  of  the  muscle  and  across  its  external  surface;  and  the  auriculo-temporal,  lingual, 
and  infei-ior  alveolar  (dental)  nerves  cross  the  deep  surface  of  the  muscle. 

The  pterygoideus  internus  (fig.  346). — Origin. — From  (1)  the  pterygoid  fossa,  and  (2)  from 
the  maxillary  tuberosity  and  the  pyramidal  process  of  the  palatine,  where  these  adjoin. 

Structure  and  Insertion. — From  the  medial  and  lateral  lamins  of  the  pterygoid  process 
there  ai-ise  aponeuroses  and  from  the  palatine  bone  at  the  lower  margin  of  the  fossa,  and  from 
the  maxillary  tuberosity  and  palatine  bone  in  front  of  the  external  pterygoid,  there  arise  short 
tendons.  From  these  aponeuroses  and  tendons  and  directly  from  the  fossa  the  fibre-bundles 
take  a  nearly  parallel  course  downward,  backward,  and  outward,  and  are  inserted  in  part  in  a 
multi-penniform  manner  into  the  lower  half  of  the  internal  surface  of  the  ramus  of  the  mandible. 
The  insertion  extends  to  the  mylo-hyoid  ridge.  The  muscle  is  divided  at  its  origin  into  two 
fascicuh  by  the  distal  margin  of  the  external  pterygoid. 

Nerve-supply. — The  internal  pterygoid  nerve  arises  from  the  back  of  the  mandibular  nerve 
near  the  foramen  ovale.  It  passes  near  or  through  the  otic  ganglion,  and  thence  to  the  medial 
surface  of  the  muscle  near  the  dorsal  edge.  Both  the  buccinator  and  lingual  nerves  are  also 
described  as  sending  filaments  to  this  muscle. 

Relations. — Laterally  the  muscle  is  covered  by  the  interpterygoid  fascia  and  the  spheno- 
mandibular  ligament,  the  external  pterygoid,  temporal,  and  masseter  muscles,  and  the  ramus 
of  the  mandible.  The  inferior  alveolar  (dental)  and  Ungual  nerves  and  the  corresponding  vessels 
run  across  this  surface.  Medial  to  the  muscle  lie  the  lateral  pharyngeal  fascia,  the  tensor  veh 
palatini  muscle,  and  the  superior  constrictor  of  the  pharynx. 

Action. — The  muscles  of  this  group  adduct  the  lower  jaw  and  serve  to  carry  it  forward  and 
backward  and  from  side  to  side.  The  elevation  is  produced  by  the  masseter,  temporal,  and 
internal  pterygoid  muscles.  The  suprahyoid  muscles  and  the  external  pterygoid  are  the  feeble 
antagonists.  T?he  forward  movement  of  the  jaw  is  produced  by  the  simultaneous  action  of  the 
two  external  pterygoids  (slightly  by  the  superficial  layer  of  the  masseter,  and  the  anterior 
fibres  of  the  temporal)  while  the  inferior  posterior  portions  of  the  temporal  muscles  carry  the 
jaw  at  the  temporo-discoidal  joint  somewhat  backward.  Oblique  lateral  rotator}'  movements 
are  produced  chiefly  by  the  action  of  one  of  the  external  pterygoids.  The  alternate  action  of 
these  two  msucles  associated  with  the  elevating  action  of  the  other  muscles  of  the  group, 
gives  rise  to  the  grinding  movement  of  the  molar  teeth.  Purely  lateral  movements  of  the  jaw 
may  be  produced  by  the  internal  pterygoids,  acting  alternately.  Lord  (Anat.  Rec,  vol.  7,  p. 
355,  1913)  states  that  in  ordinary  opening  of  the  mouth  the  external  pterygoids  pull  the 
articular  discs  and  condyles  forward  while  the  jaw  rotates  about  an  axis  passing  through 
the  insertions  of  the  stylo-mandibular  ligaments. 

Variations. — The  temporal  muscle  may  have  a  more  extensive  cranial  origin  than  usual. 
It  may  be  formed  of  two  superimposed  layers.  It  may  be  more  or  less  fused  with  the  external 
pterygoid,  or  send  a  fasciculus  to  the  coronoid  process.     The  masseter  may  be  completely 


SUPRAHYOID  MUSCULATURE 


343 


divided  into  two  fasciculi,  a  condition  normal  in  many  mammals.  A  special  fasciculus  may 
arise  from  the  temporo-mandibular  articulation  or  from  the  zygomatic  (malar)  bone.  Its 
deepest  fibres  may  be  fused  with  the  temporal  muscle.  The  two  fasciculi  of  the  external 
pterygoid  may  be  distinct,  as  in  the  horse.  It  has  been  seen  fused  with  the  temporal  and  with 
the  digastric  muscle.  The  internal  pterygoid  may  send  a  fasciculus  to  the  masseter.  It  may 
give  origin  to  the  stylo-glossus.  Inconstant  fasoiouh  (accessory  pterygoids)  extending  from  the 
body  of  the  sphenoid  to  the  pterygoid  process  represent  perhaps  remnants  of  the  muscles  which 
act  on  the  movable  pterygoids  possessed  by  many  inferior  vertebrates. 

3.  SUPRAHYOID  MUSCULATURE 

(Fig.  348) 

From  the  hyoid  bone  there  extend  to  the  base  of  the  skull  on  each  side  four 
muscles  which  form  a  fairly  well-defined  group.     They  are  situated  external  to 

Fig.  348. — Antebioe  and  Lateral  Cervical  Muscles. 


stylo-glossus 
Hyo-glossus 

Mylo-hyoid 

Anterior  belly  of_£j 

digastric 

Raphe  of  mylo-, 

hyoid 


Inferior  constrictor 
Anterior  belly  of  omo- 
hyoid 
Sterno-hyoid 

Sterno-thyreoid 


Thyreo-hyoid 


the  musculature  of  the  tongue  and  pharynx.  They  elevate  the  hyoid  bone  and 
larynx  and  depress  the  mandible.  The  most  superficial  of  the  group  is  the 
slender,  fusiform  stylo-hyoid,  which  arises  from  the  styloid  process  of  the  temporal 
bone  and  is  inserted  into  the  body  of  the  hyoid.  Immediately  behind  this  is  the 
flattened  posterior  belly  of  the  digastric,  which  extends  from  its  origin  in  the 
mastoid  notch  to  a  tendon  that  runs  between  two  divisions  of  the  tendon  of  the 
stylo-hyoid  and  is  attached  to  the  hyoid  bone  by  an  aponeurotic  process.  From 
the  digastric  tendon  the  flat,  triangular  anterior  belly  is  continued  to  the  back 
of  the  ventral  portion  of  the  inferior  margin  of  the  mandible.  Internal  to  this 
anterior  belly  the  thin,  quadrangular  mylo-hyoid  arises  from  the  inner  surface  of 
the  body  of  the  mandible  and  is  inserted  into  a  median  raphe  extending  from  the 
mandible  to  the  hyoid.  Still  more  internally  the  triangular  genio-hyoid  extends 
from  the  hyoid  to  the  mental  spine  of  the  mandible.  The  last  two  muscles  form 
the  muscular  floor  of  the  mouth.     The  motor  innervation  of  the  posterior  belly 


344  THE  MUSCULATURE 

of  the  digastric  and  of  the  stylo-hyoid  is  from  the  seventh  cranial  nerve,  the 
sensory  innervation  probably  from  the  glosso-pharyngeal  cranial  nerve.  The 
mylo-hyoid  and  the  anterior  belly  of  the  digastric  are  supplied  by  the  masticator 
(fifth)  cranial  nerve;  the  genio-hyoid  from  the  hypoglossal  by  a  branch,  the 
fibres  of  which  are  possibly  derived  through  anastomosis  from  the  first  cervical 
nerve. 

From  the  morpliological  standpoint,  therefore,  the  stylo-hyoid  and  the  posterior  belly  of 
the  digastric  belong  to  the  faciahs  group;  the  anterior  belly  of  the  digastric  and  the  mylo-hyoid 
to  the  group  of  mandibular  muscles,  and  the  genio-hyoid  to  the  muscles  of  the  tongue  inner- 
vated by  the  hypoglossal,  or,  if  we  consider  the  nerve-fibres  of  the  nerve  to  the  genio-hyoid  as 
derived  from  the  first  cervical  nerve,  to  the  same  group  as  the  infra-hyoid  muscles.  It  is  con- 
venient, however,  to  follow  the  usual  custom  of  considering  these  muscles  as  a  suprahyoid  group. 

FASCIA 

The  muscles  of  this  group  he  internal  to  that  portion  of  the  external  cervical  fascia  which 
extends  above  the  hyoid  bone.  This  fascia,  which  is  described  on  p.  347,  comes  into  contact 
merely  with  the  tendon,  the  anterior  belly,  and  to  a  slight  extent  with  the  posterior  belly  of  the 
digastric  muscle.  Above  the  tendon  it  sends  inward  a  process  which  curves  down  internal  to 
the  tendon,  and  is  inserted  into  the  external  surface  of  the  hyoid  bone.  The  individual  muscles 
of  the  group  are  covered  by  dehcate  adherent  membranes.  An  aponeurotic  membrane  usually 
extends   between  the  anterior  bellies  of  the  digastric  muscles  of  each  side. 

MUSCLES 
(Fig.  348) 

The  stylo-hyoideus. — Origin. — From  the  lateral  and  dorsal  part  of  the  base  of  the  styloid 
process  by  a  rounded  tendon  which  soon  becomes  a  hollow  cone  to  the  internal  surface  of  which 
the  fibre-bundles  of  the  muscle  are  attached.  Structure  and  Insertion. — The  fibre-bundles  are 
inserted  on  both  sides  of  a  slender  tendon  which  divides  to  let  the  tendon  of  the  digastric  pass 
through  and  then  is  attached  to  the  ventral  surface  of  the  body  of  the  hyoid  bone  near  its  junc- 
tion with  the  great  cornu. 

Nerve-su-pply. — From  the  facial  nerve  as  it  emerges  from  the  stylo-mastoid  foramen  a  small 

twig  is  given  off  which  enters  the  proximal  third  of  the  deep  surface  of  the  muscle.  The  glosso- 
pharyngeal nerve  also  gives  to  it  a  small  twig,  probably  sensory. 

Relations. — It  descends  immediately  in  front  of  the  posterior  belly  of  the  digastric.  Ex- 
ternally lie  the  parotid  and  submaxillary  glands.  Medially  it  crosses  the  internal  and  ex-ternal 
carotid  artery,  the  hypoglossal  nerve,  the  stylo-pharyngeus  muscle,  the  superior  constrictor 
of  the  pharynx,  and  the  hyo-glossus  muscle.  The  posterior  auricular  artery  passes  between  it 
and  the  posterior  belly  of  the  digastric  and  the  external  maxillary  artery  crosses  over  it. 

The  digastricus. — The  posterior  belly  arises  by  tendinous  processes  from  the  mastoid 
(digastric)  notch  of  the  temporal  bone.  The  fibre-bundles  form  a  ribbon-)ike  belly  which  con- 
verges on  the  intermediate  tendon.  This  begins  as  a  semiconical  laminar  process  on  the  outer 
surface  of  the  muscle  a  short  distance  above  the  hyoid  bone.  The  anterior  belly  arises  by  short 
tendinous  processes  from  the  digastric  fossa  of  the  mandible.  This  attachment  is  often  de- 
scribed as  an  insertion.  The  fibres  converge  on  both  surfaces  of  the  flattened  anterior  end  of 
the  intermediate  tendon.  The  intermediate  tendon  hes  a  variable  distance  above  the  hyoid 
bone,  usually  less  than  a  centimetre.  It  curves  upward  toward  each  belly  of  the  muscle.  It 
is  united  to  the  outer  surface  of  the  body  and  to  the  base  of  the  great  cornu  of  the  hyoid  bone 
by  an  aponeurotic  expansion  from  its  inferior  margin.  Other  expansions  are  usually  continued 
into  the  interdigastric  aponeurotic  membrane.  Occasionally  the  intermediate  tendon  of  the 
digastric  is  bound  to  the  hyoid  bone  by  a  fibrous  loop  which  allows  the  tendon  free  play. 

Nerve-supply. — The  facial  nerve  near  the  stylo-mastoid  foramen  gives  off  a  branch  which 
enters  the  proximal  third  of  the  anterior  margin  of  the  muscle.  From  this  a  ramus  may  be 
continued  through  the  muscle  to  the  glosso-pharyngeal  nerve.  The  anterior  belly  is  supplied 
by  a  branch  of  the  nerve  to  the  mylo-hyoid  muscle.  This  enters  the  middle  of  the  lateral  part 
of  the  deep  surface.  Very  rarely  the  vagus  may  supply  the  anterior  belly,  the  hypoglossal, 
the  posterior  belly. 

Relations. — The  posterior  belly  of  the  digastric  lies  internal  to  the  mastoid  process  and 
the  longissimus  capitis  (trachelo-mastoid),  splenius,  and  sterno-cleido-mastoid  muscles.  Pos- 
teriorly near  its  origin  are  the  rectus  capitis  lateralis  and  obliquus  cap.  sup.  muscles,  the  occip- 
ital artery  and  the  spinal  accessory  nerve.  It  helps  to  form  the  deep  wall  of  the  cavity  in  which 
the  parotid  gland  is  placed.  Internally  it  crosses  the  origin  of  the  styloid  muscles,  the  carotid 
arteries,  the  internal  jugular  vein,  and  the  twelfth  cranial  nerve.  The  intermediate  tendon 
of  insertion  hes  below  the  inferior  margin  of  the  submaxillary  gland,  and  crosses  the  hyo- 
glossus  and  mylo-hyoid  muscles.  The  relations  to  the  stylo-hyoid  muscle  have  been  described 
above.  The  anterior  belly  lies  on  the  mylo-hyoid  and  is  covered  by  the  external  cervical  fascia 
and  the  platysma. 

The  mylo-hyoideus. — Origin. — From  the  mylo-hyoid  ridge  of  the  mandible.  Structure 
and  Insertion. — Its  fibre-bundles  take  an  oblique  course  and  are  inserted  into — (1)  a  median 
raphe  extending  from  the  middle  of  the  ventral  surface  of  the  hyoid  bone  nearly  or  quite  to  the 


MUSCLES  OF  THE  TONGUE  345 

dorsal  surface  of  the  inferior  margin  of  the  mandible,  and  (2)  into  the  ventral  surface  of  the  hyoid 
bone.  Some  of  the  fibre-bundles  may  cross  the  median  line.  The  muscles  of  the  two  sides 
form  a  sheet  with  a  downward  convexity  which  lies  between  the  inner  surface  of  the  body  of 
the  mandible  and  the  hyoid  bone.     On  the  diaphragm  thus  formed  rests  the  tongue. 

Nerve-supply. — From  the  mylo-hyoid  branch  of  the  inferior  alveolar  (dental)  nerve  several 
filaments  enter  the  under  surface  of  the  muscle. 

Relations. — The  mylo-hyoid  muscle  is  covered  externally  by  the  submaxillary  gland,  the 
anterior  belly  of  the  digastric,  and  the  external  cervical  fascia.  It  is  crossed  by  the  submental 
artery.  With  the  genio-hyoid  and  the  genio-glossus  muscles  it  helps  to  bound  a  cornpartment 
in  which  are  lodged  the  sublingual  gland,  the  duct  of  Wharton,  and  the  deep  portion  of  the 
submaxillary  gland.  Its  deep  surface  also  faces  the  stylo-glossus  and  hyo-glossus  muscles,  the 
lingual  and  hypoglossal  nerves,  and  to  a  slight  extent  the  buccal  mucosa. 

The  genio-hyoideus  (fig.  349). — Origin. — By  short  tendinous  fibres  from  the  mental  spine 
of  the  mandible.  Structure  and  Insertion. — The  fibre-bundles  diverge  and  are  inserted  into  the 
ventral  surface  of  the  body  of  the  hyoid  bone.  Usually  a  special  fasciculus  goes  to  the  great 
cornu  of  the  hyoid  bone. 

Nerve-supply. — The  hypoglossal  nerve  sends  a  filament  to  the  middle  third  of  the  deep 
surface  of  the  muscle.  The  nerve-fibres  are  thought  to  be  derived  chiefly  from  the  first 
cervical  nerve. 

Relations. — It  lies  between  the  genio-glossus  and  mylo-hyoid  muscles.  It  adjoins  its 
fellow  of  the  opposite  side  and  is  often  fused  with  it.  Lateral  to  it  he  the  subhngual  and  sub- 
maxillary glands  and  the  hypoglossal  nerve. 

Action. — The  muscles  of  this  group  all  elevate  the  hyoid  bone  and,  through  this,  the  larynx 
and  inferior  part  of  the  pharynx,  and  thus  play  a  part  in  the  act  of  swallowing.  The  stylo- 
hyoid and  posterior  belly  of  the  digastric  serve  also  to  draw  the  hyoid  bone  in  a  dorsal  direction; 
the  ventral  belly  of  the  digastric  and  the  genio-hyoid,  in  a  ventral  direction.  The  digastric, 
genio-hyoid,  and  mylo-hyoid  depress  the  mandible,  when  the  hyoid  bone  is  fixed.  The 
posterior  belly  of  the  digastric  has  a  slight  power  to  bend  the  head  backward. 

Variations. — The  stylo-hyoid  tendon  frequently  passes  entirely  in  front  of  and  less  frequently 
entirely  behind  the  digastric  muscle.  Its  insertion  may  be  of  greater  extent  than  usual.  A 
special  fasciculus  to  the  lesser  cornu  is  not  very  infrequent;  more  rarely  one  extends  to  the  angle 
of  the  jaw  or  to  other  regions.  The  muscle  may  arise  from  the  petrous  portion  of  the  tem- 
poral or  from  the  occipital  bone,  as  in  some  lower  vertebrates.  It  may  be  doubled  or  absent, 
or  fused  with  the  posterior  belly  of  the  digastric.  The  anterior  belly  of  the  digastric  may  be 
missing;  the  posterior  belly  may  be  inserted  into  the  angle  of  the  jaw.  The  intermediate  ten- 
dons of  the  digastric  of  each  side  may  be  connected  by  a  fibrous  arch.  The  anterior  bellies  of 
the  muscles  of  each  side  may  be  united  by  a  fasciculus  or  fused.  The  anterior  belly  is  frequen  tly 
doubled.  The  posterior  belly  may  be  divided  by  a  tendinous  inscription.  Fasciculi  may  pass 
from  either  belly  to  neighbouring  structures.  The  mylo-hyoid  may  not  extend  quite  to  the 
hyoid  bone.  It  may  be  more  or  less  fused  with  neighbouring  muscles.  Rarely  it  is  absent. 
The  genio-hyoid  is  frequently  more  or  less  fused  with  the  muscles  of  the  tongue  or  with  the  genio- 
hyoid of  the  opposite  side.  A  considerable  number  of  infrequently  found  muscles  have  been 
described  superficial  to  the  stylo-hyoid  and  digastric  muscles.  Most  of  them  are  innervated 
by  the  glosso-pharyngeal  nerve  or  by  the  facial  nerve. 

4.  MUSCLES  OF  THE  TONGUE 

(Fig.  349) 

The  tongue  is  a  flexible  organ,  composed  chiefly  of  various  muscles,  some  of 
which  lie  entirely  within  its  substance,  while  others  extend  to  be  attached  to 
neighbouring  parts  of  the  skeleton.  To  the  former  the  term  intrinsic,  to  the 
latter  the  term  extrinsic,  is  frequently  applied.  In  this  section  the  extrinsic 
muscle  will  alone  be  taken  up.  The  intrinsic  muscles  are  described  in  the 
section  on  the  Digestive  System.  Certain  pharyngeal  and  palatal  muscles 
which  are  continued  into  the  tongue  are  described  in  connection  ^vith  the 
pharynx.  The  extrinsic  musculature  of  the  tongue  is  concealed  below  by  the 
suprahyoid  musculature  and  the  sublingual  gland.  It  is  covered  on  the  free 
surface  of  the  tongue  by  the  mucosa. 

The  musculature  of  the  tongue  is  supplied  by  the  hypoglossal  nerve,  which  is 
in  series  with  the  motor  roots  of  the  spinal  nerves.  It  is,  primitively  at  least, 
derived  from  the  ventral  portion  of  mj'^otomes  in  series  with  the  spinal  myotomes. 

Four  extrinsic  muscles  are  recognised  on  each  side.  The  stylo-glossus  is  a 
slender  muscle,  which  arises  from  the  styloid  process  and  is  inserted  into  the  side 
of  the  tongue.  It  is  cylindrical  near  its  origin,  flat  and  triangular  near  its  inser- 
tion. The  thin,  quadrilateral  hyo-glossus  arises  from  the  body  and  great  cornu 
of  the  hyoid  bone  and  is  inserted  into  the  dorsum  of  the  tongue.  The  chondro- 
glossus  arises  from  the  lesser  cornu  of  the  hyoid  bone  and  joins  the  superior  and 
inferior  longitudinal  muscles  of  the  tongue.  The  genio-glossus  (genio-hyo- 
glossus),  which  forms  the  main  part  of  the  body  of  the  tongue,  arises  from  the 
mental  spine  of  the  mandible,  from  which  the  fibre-bundles  radiate  out  toward  the 
whole  length  of  the  dorsum  of  the  tongue  and  to  the  hj'oid  bone. 


346 


THE  MUSCULATURE 


Under  the  mucous  membrane  of  the  tongue  is  a  dense  layer  of  fibrous  tissue, 
the  lingual  fascia.  In  the  body  of  tlie  tongue  there  is  a  sagittal  septum  linguae, 
which  separates  the  two  genio-glossus  muscles.  A  transverse  fibrous  lamella, 
the  hyo-glossal  membrane,  helps  to  unite  the  tongue  to  the  hyoid  bone.  Delicate 
membranes  invest  the  free  portions  of  the  extrinsic  muscles  of  the  tongue. 


MUSCLES 

The  stylo -glossus. — This  arises  from  the  front  of  the  lower  end  of  the  styloid  process  of 
the  temporal  bone  and  from  the  upper  part  of  the  stylo-mandibular  ligament.  Insertion. — It 
runs  obliquely  downward,  forward,  and  medially,  with  slightly  diverging  fibre-bundles,  to  the 
lateral  margin  of  the  tongue,  where  it  gives  rise  near  the  anterior  pillar  of  the  fauces  to  two 
fasciculi.  The  larger,  lateral,  longitudinal  fasciculus  runs  superficially  along  the  lateral  margin 
of  the  tongue  to  the  tip.  The  fibre-bundles  are  attached  to  the  overlying  mucosa  and  under- 
lying musculature.  The  smaller,  inferior,  transverse  fasciculus  gives  rise  to  diverging  fibre- 
bundles  which  pass  medially  through  the  hyo-glossus  into  the  base  of  the  tongue.  The  most 
posterior  of  these  diverging  bundles  may  extend  to  the  hyoid  bone. 

The  hyo-glossus. — This  arises  from — (1)  the  lateral  part  of  the  ventral  surface  of  the  body 
of  the  hyoid  bone  and  (2)  from  the  upper  border  of  the  great  cornu.  The  fibre-bundles  take  a 
nearly  parallel  course  upward,  diverging,  however,  slightly.     Near  the  upper  margin  of  the  back 

Fig.  349. — Side  View  op  the  Muscles  op  the  Tongue. 


> 


Glosso-palatinus 
Stylo-glossus 


-hyoid 
Anterior  belly  of  - 
digastric 


part  of  the  tongue  they  curve  mcdianward  and  interlace  with  the  intrinsic  musculature  of  this 
region.  The  dorsal  fibre-bundles  pass  transversely,  the  middle  obliquely,  the  ventral  longi- 
tudinally. They  are  inserted  into  the  fibrous  tissue  which  forms  the  skeletal  framework  of  the 
tongue. 

The  chondro-glossus  is  a  small  muscle  which  arises  from  the  lesser  cornu  of  the  hyoid  bone 
and  gives  rise  to  fasciculi  which  join  the  longitudinalis  inferior  and  the  longitudinalis  superior 
of  the  tongue  described  in  Section  IX. 

The  genio-glossus. — This  arises  from  the  mental  (genial)  suine  of  the  mandible  partly 
directly,  partly  by  means  of  a  short,  triangular  tendon.  The  more  inferior  fibre-bundles  radiate 
toward  the  tip  of  the  tongue;  the  intermediate  extend  directly  toward  the  dorsum  of  the  tongue, 
where  they  are  inserted  into  the  lingual  fascia  and  skeletal  framework.  The  inferior  curve 
back  to  be  inserted  on  the  median  part  of  the  superior  border  of  the  hyoid  bone. 

Nerve-supply. — Twigs  from  the  hypoglossal  nerve  enter  the  lateral  surfaces  of  the  muscles 
of  this  group. 

Action. — The  chief  of  the  muscles,  the  genio-glossus,  performs  various  services  according  to 
the  part  which  contracts.  The  anterior  portion  serves  to  withdraw  the  tongue  into  the  mouth 
and  depress  the  tip;  the  middle  portion  to  draw  the  base  of  the  tongue  forward,  depress  the 
median  portion  of  the  tongue,  and  make  the  tongue  protrude  from  the  mouth;  the  inferior  fibres 
to  elevate  the  hyoid  bone  and  carry  it  forward.  The  stylo-glossus  retracts  the  tongue,  elevates 
its  margin,  and  raises  the  hyoid  bone  and  base  of  the  tongue.  The  hyo-glossus  draws  down  the 
sides  of  the  tongue  and  is  also  a  retractor.     The  chondro-glossus  aids  in  both  these  movements. 

Relations. — The  main  portion  of  the  tongue  is  composed  of  the  two  genio-glossus  muscles, 
which  are  separated  in  the  median  line  by  the  hngual  septum.  The  genio-glossus  is  covered 
inferiorly  by  the  genio- hyoid  and  the  mylo-hyoid  muscles;  along  the  lateral  margin  of  the  tongue 
by  the  glosso-palatinus,  the  stylo-glossus,  the  longitudinalis  inferior,  and  the  glosso-pharyngeus 


CERVICAL  FASCIA  347 

muscles;  and  posteriorly  by  the  hyo-glossus,  and  the  chondro-glossus.  Below  it  forms  a  part  of 
the  medial  wall  of  the  space  in  which  the  sublingual  gland  is  lodged.  Over  the  dorsum  and  tip 
of  the  tongue  it  is  covered  by  the  mucosa.  This  likewise  covers  laterally,  in  the  region  of  the 
base  of  the  tongue,  the  stylo-glossus,  hyo-glossus,  and  the  longitudinalis  inferior.  The  lingual 
artery  runs  between  the  hyo-glossus  and  the  genio-glossus,  and  along  the  boundary  between  the 
longitudinalis  inferior  and  the  genio-glossus  to  the  tip  of  the  tongue.  The  lingual  vein,  which 
lies  lateral  to  the  hyo-glossus  muscle,  takes  a  similar  although  much  more  irregular  course. 
The  glosso-pharyngeal  nerve  passes  down  medial  to  the  stylo-glossus  muscle  to  the  root  of  the 
tongue.  The  hngua!  nerve  passes  along  the  lateral  margin  of  the  tongue  external  to  the  stylo- 
glossus, hyo-glossus,  and  inferior  longitudinal  muscles.  The  hypoglossal  nerve  hes  lateral  to 
the  inferior  portion  of  the  hyo-glossus  muscle  and  then  sinks  into  the  genio-glossus. 

The  hyo-glossus  muscle  is  covered  laterally  below  the  free  portion  of  the  tongue  by  the  mylo- 
hyoid, digastric,  and  stylo-hyoxd  muscles  and  by  the  deep  part  of  the  submaxillary  gland. 
Medially  it  covers  in  part  the  middle  constrictor  of  the  pharynx. 

The  stylo-glossus  muscle  above  the  tongue  hes  medial  to  the  stylo-hyoid  and  the  internal 
pterygoid  muscles  and  the  parotid  gland,  and  between  the  internal  and  external  carotid  arteries. 
It  lies  lateral  to  the  superior  constrictor  of  the  pharynx. 

Variations. — The  genio-glossus  often  sends  a  slip  to  the  epiglottis  (levator  epiglottidis) . 
It  may  send  some  bundles  into  the  superior  constrictor  of  the  pharynx  (genio-pharyngeus)  or 
to  the  stylo-hyoid  hgament.  Various  parts  of  the  muscle  may  be  more  or  less,  isolated.  Of 
these,  a  fasciculus  from  the  mental  (genial)  spine  to  the  tip  of  the  tongue  is  the  most  frequent 
(longitudinalis  linguae  inferior  medius).  The  hyo-glossus  exhibits  considerable  variation  in 
structure.  Some  authors  consider  the  chondro-glossus  but  a  portion  of  this  muscle,  while 
Poirier  considers  it  merely  the  origin  of  the  longitudinalis  inferior.  The  stylo-glossus  may  be 
absent  on  one  side  or  on  both.  Its  origin  varies  considerably  and  may  be  from  the  angle  of  the 
jaw.     The  muscle  may  be  doubled. 

5.  SUPERFICIAL  MUSCULATURE  OF  THE  SHOULDER 
GIRDLE  AND  THE  EXTERNAL  CERVICAL  FASCIA 

(Figs.  348,  355) 

The  stemo-cleido-mastoid  is  a  strong,  band-shaped  muscle,  bifurcated  below, 
which  arises  from  the  medial  third  of  the  clavicle  and  the  front  of  the  manubrium 
and  is  inserted  into  the  mastoid  process  of  the  temporal  bone  and  the  neigh- 
bouring part  of  the  occipital.  The  large,  fiat,  triangular  trapezius  arises  from  the 
occipital  bone  and  the  spines  of  the  cervical  and  thoracic  vertebrae  and  is  in- 
serted into  the  lateral  third  of  the  clavicle  and  into  the  acromion  and  spine  of 
the  scapula.  The  two  muscles  lie  in  a  well  defined  layer  of  fascia  which  ensheaths 
the  neck  beneath  the  platysma,  the  external  cervical  fascia.  Both  muscles  bend 
the  head  and  neck  toward  the  shoulder,  rotate  and  extend  the  head,  and  raise 
the  shoulder.  The  sterno-cleido-mastoid  also  elevates  the  thorax  and  flexes 
the  neck. 

These  two  superficially  placed  muscles  represent  differentiated  portions  of  a  musculature 
found  in  elasmobranchs  and  in  the  amphibia  and  all  higher  vertebrates.  In  sharks  this  muscula- 
ture is  associated  with  the  musculature  of  the  branchial  arches,  and,  hke  them,  is  innervated 
by  the  vagus  nerve.  In  the  higher  vertebrates  it  is  innervated  by  the  vagus  or  by  the  spinal 
accessory  nerve,  developed  in  connection  with  the  vagus.  To  this  innervation  by  a  cranial 
nerve,  innervation  by  cervical  nerves  is  added  in  those  higher  vertebrates  in  which  the  muscula- 
ture is  more  extensively  developed.  In  the  human  embryo  the  muscles  migrate  from  their 
origin  in  the  upper  lateral  cervical  region  to  the  positions  found  in  the  adult. 

FASCIA 

The  fascise  of  the  neck  and  the  relations  of  the  muscles  are  shown  in  cross-section  in  figs. 
347,  and  351. 

The  tela  subcutanea  of  the  head  and  neck  in  the  upper  dorsal  region  is  thick,  fibrous,  and 
closely  adherent  to  the  underlying  muscle  fascia.  Ventrally  in  the  cervical  region  it  contains 
the  platysma. 

The  external  cervical  fascia  (fig.  350)  lies  beneath  the  subcutaneous  tissue  and  the  platysma, 
completely  invests  the  neck  and  extends  cranialward  over  the  parotid  gland  to  the  zygoma  and 
the  masseteric  fascia.  The  trapezius  hes  between  two  closely  adherent  lamince  of  the  fascia. 
From  the  ventral  margin  of  the  trapezius  it  is  continued  as  a  thin  but  strong  membrane  across 
the  posterior  triangle  of  the  neck,  between  this  muscle  and  the  sterno-  cleido-mastoid,  and  is 
attached  below  to  the  clavicle.  It  invests  the  sterno-cleido-mastoid  with  two  adherent  laminse 
and  extends  from  the  ventral  margin  of  this  muscle  across  the  anterior  triangle  to  the  mid-line 
where  it  is  continued  into  that  of  the  opposite  side.  In  this  triangle  the  fascia  is  bound  to  the 
hyoid  bone,  and  is  thus  divided  into  a  submaxillary  and  an  infrahyoid  portion.  The  infrahyoid 
portion  is  simple  and  is  attached  below  to  the  front  of  the  manubrium.  The  submaxillary 
portion  is  attached  to  the  inferior  margin  of  the  mandible.  It  covers  the  submaxillary  gland, 
and  along  the  inferior  margin  gives  rise  to  a  strong,  membranous  'process  which  passes  inward 
below  the  gland  and,  after  extending  around  the  tendon  of  the  digastric  muscle,  becomes  united 


348 


THE  MUSCULATURE 


to  the  superior  margin  of  the  hyoid  bone.  This  process  ventrally  becomes  fused  with  the  peri- 
mysium of  the  ventral  belly  of  the  digastric.  Dorsally  it  extends  over  the  posterior  end  of  the 
submaxillary  gland  and  becomes  attached  to  the  angle  of  the  jaw.  Here  it  is  strengthened  by 
fibrous  tissue  which  extends  in  from  the  ventral  margin  of  the  sterno-cleido-mastoid  and  serves 
to  separate  the  parotid  from  the  submaxillary  gland.  This  'mandibular  process'  is  continued 
into  the  stylo-mandibular  ligament. 

Fig.  350. — Fascia  op  the  Neck.  (After  Eisler.)  The  superficial  fascia  has  been  removed 
in  places  in  order  to  show  the  deeper  fasciaj;  the  sterno-cleido-mastoid  has  been  partly  removed; 
the  submaxillary  gland,  almost  wholly;  the  parotid  gland,  as  far  as  the  duct. 

1.  Submaxillary  space.  2.  Parotid  space.  3.  Sterno-cleido-mastoid.  4  Supra-clavicular 
fossa.  5.  Supra-sternal  space.  6.  External  jugular  vein.  7.  Anterior  jugular  vein.  8.  Median 
colU  vein.  9.  N  occipitaUs  minor.  10.  N.  aurioularis  magnus.  11.  Deltoid.  12.^Proc. 
coracoideus.     13,    Fascia   ooraco-clavieularis. 


The  parotid  gland  is  enclosed  between  two  laminae  of  the  external  cervical  fascia.  These 
are  continued  over  the  gland  from  the  fascial  investment  of  the  sterno-cleido-mastoid,  and  unite 
ventrally  to  become  fused  to  the  masseteric  fascia  along  the  anterior  margin  of  the  gland. 
They  unite  below  the  inferior  margin  of  the  gland,  and  are  continued  into  the  rnandibular  process 
mentioned  above.  The  external  layer,  which  is  the  thicker  and  stronger,  is  attached  above 
to  the  cartilage  of  the  auditory  canal  and  to  the  zygoma.      The  inner  lamina  is  attached  above 


TRAPEZIUS  349 

to  the  base  of  the  temporal  bone.  It  is  incomplete  and  is  more  or  less  fused  to  the  posterior 
belly  of  the  digastric  muscle,  the  styloid  process,  and  the  muscles  arising  from  this  process. 
Between  the  styloid  process  and  the  angle  of  the  jaw  this  lamina  is  strengthened  to  form  the 
stylo-mandibular  ligament. 

In  the  back,  beyond  the  spine  of  the  scapula,  the  fascia  arising  from  the  investing  adherent 
fascial  sheath  of  the  trapezius  muscle  is  continued  laterally  across  the  fascia  investing  the  infra- 
spinatus muscle,  and  becomes  fused  with  the  most  superficial  layer  of  this  fascia  and  more 
djstally  with  that  of  the  latissimus  dorsi  muscle.  Near  this  lateral  line  of  fusion  it  is  usually 
closely  adherent  to  the  tela  subcutanea. 

MUSCLES 

The  sterno-cleido-mastoideus  (fig.  348). — Origin. — By  a  medial  (sternal)  head  from  the 
front  of  the  manubrium  and  by  a  lateral  (clavicular)  head  from  the  upper  border  of  the  median 
third  of  the  clavicle.  Between  the  two  origins  there  intervenes  a  triangular  area  covered  by 
the  external  cervical  fascia.  Its  insertion  is — (1)  on  the  anterior  border  and  outer  surface  of 
the  mastoid  process,  and  (2)  on  the  lateral  half  of  the  superior  nuchal  line  of  the  occipital  bone. 

Structure. — The  tendons  are  comparatively  short,  the  longest  being  that  on  the  anterior 
surface  of  the  sternal  attachment.  The  fibre-bundles  of  the  muscle  take  a  nearly  parallel 
course  from  origin  to  insertion.  Five  fasciculi  may  be  more  or  less  clearly  recognised.  In  a 
superficial  layer — (1)  a  superficial  sterno-mastoid;  (2)  a  sterno-occipital;  and  (3)  a  cleido- 
occipital.     In  a  deep  layer — (4)  a  deep  sterno-mastoid  and  (5)  a  cleido-mastoid. 

Nerve-supply. — (1)  From  the  spinal  accessory  nerve,  which  gives  it  branches  during  its 
course  through  the  deep  portion  of  the  muscle,  and  (2)  by  branches  from  the  anterior  primary 
divisions  of  the  second  and  third  (?)  cervical  nerves.  These  branches  enter  the  deep  surface 
of  the  upper  half  of  the  muscle. 

Action. — To  bend  the  head  and  neck  toward  the  shoulder  and  rotate  the  head  toward  the 
opposite  side.  When  both  muscles  act,  the  neck  is  flexed  toward  the  thorax  and  the  chin  is 
raised;  or,  with  fixed  head,  the  sternum  is  raised,  as  in  forced  respiration.  When  the  head  is 
bent  back,  the  two  muscles  may  further  increase  the  hyperextension. 

Relations. — The  muscle  and  its  sheath  are  covered  externally  by  the  tela  subcutanea,  which 
here  contains  the  platysma  and  the  external  jugular  vein,  as  well  as  the  superficial  branches  of 
the  cervical  plexus.  Beneath  the  muscle  lie  the  sterno-hyoid,  sterno-thyreoid,  omo-hyoid. 
levator  scapuliE,  scaleni,  splenius,  and  digastric  muscles,  the  cervical  plexus,  the  common  carotid 
artery,  internal  jugular  vein,  and  the  vagus  nerve.  The  spinal  accessory  nerve  usually  runs 
through  its  deep  cleido-mastoid  portion. 

Variations. — There  is  considerable  variation  in  the  extent  of  independence  of  the  main 
fasciculi  of  the  muscle.  In  many  of  the  lower  animals  the  cleido-mastoid  portion  of  the  muscle 
is  quite  distinct  from  the  sterno-mastoid  portion,  and  this  condition  is  frequently  found  in 
man.  The  cleido-occipital  portion  of  the  muscle  is  that  most  frequently  absent  (Wood  found 
it  present  in  37  out  of  102  instances).  The  clavicular  portion  of  the  muscle  varies  greatly  in 
width.  The  sternal  head  has  been  seen  to  e.xtend  as  far  as  the  attachment  of  the  fifth  rib. 
Slips  from  the  muscle  may  pass  to  various  neighbouring  structures.  The  main  fascicuU  of  the 
muscle  may  be  doubled.  Sometimes  one  or  more  tendinous  inscriptions  cross  a  part  or  the 
whole  of  the  superficial  layer  of  the  muscle. 

The  trapezius  (fig.  355). — Origin. — By  aflat  aponeurosis  from  the  superior  nuchal  fine  and 
external  protuberance  of  the  occipital  bone,  the  ligamentum  nuchte,  and  the  vertebra!  spines 
and  supraspinous  ligament  from  the  seventh  cervical  to  the  twelfth  thoracic  vertebra.  The 
aponeuroses  of  the  right  and  left  muscles  are  continuous  across  the  middle  fine.  Between  the 
middle  of  the  ligamentum  nuchae  and  the  second  thoracic  vertebra,  the  aponeuroses  give  rise 
to  an  extensive  quadrilateral  tendinous  area.  At  the  distal  extremity  of  the  muscle  they  are 
also  weU  developed. 

Structure  and  Insertion. — The  superior  fibre-bundles  pass  obliquely  downward,  lateralward, 
and  forward  to  the  postero-superior  aspect  of  the  lateral  third  of  the  clavicle;  the  middle  fibre- 
bundles,  transversely  to  the  medial  edge  of  the  acromion  and  the  upper  border  of  the  spine  of  the 
scapula;  the  lower  fibre-bundles,  obliquely  upward  and  laterally  to  terminate  thi'ough  a  flat, 
triangular  tendon  on  a  tubercle  at  the  medial  end  of  the  spine  of  the  scapula. 

Nerve-supply. — The  external  branch  of  the  spinal  accessory  nerve  descends  for  a  distance 
near  the  superior  border  of  the  trapezius  muscle  and  then  along  the  ventral  surface.  Soon  it 
gives  rise  to  ascending  branches  for  the  superior  portion  of  the  muscle  and  descending  branches 
for  the  middle  and  inferior  portions.  The  main  branches  of  distribution  run  about  midway 
between  the  origin  and  insertion  of  the  fibre-bundles.  The  branches  from  the  second  (?),  third 
and  fourth  cervical  nerves  anastomose  with  the  trunk  of  the  spinal  accessory,  sometimes  as  it 
passes  along  the  margin  of  the  muscle,  at  other  times  within  the  substance  of  the  upper  portion 
of  the  muscle. 

Action. — When  the  whole  muscle  contracts,  it  draws  the  scapula  toward  the  spine  and 
turns  it  so  that  the  inferior  angle  points  laterally,  the  lateral  angle  upward.  In  addition  the 
upper  portion  draws  the  point  of  the  shoulder  upward,  and  with  the  scapula  fixed  extends  the 
head,  bends  the  neck  toward  the  same  side,  and  tm'ns  the  face  to  the  opposite  side.  The  lower 
portion  of  the  muscle  tends  to  draw  the  scapula  downward  and  inward  and  at  the  same  time  to 
rotate  the  inferior  angle  of  the  scapula  outward. 

Relations. — It  is  covered  merely  by  skin  and  fascia.  It  Ues  external  to  the  semispinahs, 
splenii,  rhomboidei,  latissimus  dorsi,  levator  scapute,  supraspinatus,  and  a  small  portion  of  the 
infraspinatus  muscles. 

Variations. — The  lower  limit  of  attachment  of  the  muscle  may  be  as  high  as  the  fourth 
thoracic  vertebra.  The  right  and  left  muscles  are  seldom  symmetrical.  The  upper  attach- 
ment may  not  extend  to  the  skull.     The  clavicular  attachment  may  be  much  more  extensive 


> 


350  THE  MUSCULATURE 

than  normal  or  may  be  missing.  The  attachments  to  the  scapula  show  considerable  variations. 
Occasionally  the  cervical  and  thoracic  portions  are  separate,  a  condition  normal  in  many 
mammals.  VentraUy  the  trapezius  may  become  continuous  with  the  sterno-cleido-mastoid 
in  the  neck,  or  send  a  fasciculus  to  it  or  to  the  sternum.  Aberrant  fasciculi  are  not  infrequent. 
Rarely  a  transverse  tendinous  inscription  is  found  in  the  cervical  or  in  the  thoracic  portion  of 
the  muscle.  Sometimes  a  fasciculus  is  sent  into  the  deltoid.  The  innervation  of  either  the 
sterno-cleido-mastoid  or  the  trapezius  may  be  by  cervical  nerves  only.  The  omo-cervicalis 
{levator  claviculce)  is  a  fasciculus  frequent  in  the  lower  mammals,  but  rarely  found  in  man. 
It  usually  extends  from  the  acromial  end  of  the  clavicle  to  the  atlas  and  axis,  but  may  extend 
to  more  distal  cervical  vertebrae.  It  is  innervated  by  a  ramus  from  the  cervical  branches  to  the 
trapezius.  The  supra-clavicularis  proprius  is  a  muscle  rarely  found.  It  extends  on  the  cranial 
surface  of  the  clavicle  from  the  sternal  to  the  acromial  end  and  is  innervated  by  the  third  cervical 
nerve.     It  is  said  to  make  tense  the  superficial  layer  of  the  cervical  fascia. 

A  bursa  is  often  found  between  the  base  of  the  spine  of  the  scapula  and  the  tendon  of  inser- 
tion of  the  thoracic  portion  of  the  trapezius.  Another  bursa  is  also  frequently  found  between 
the  insertion  of  the  transverse  portion  and  the  supraspinous  fascia. 

6.  INFRAHYOID  MUSCULATURE 

(Figs.  348  and  351) 

The  four  infrahyoid  muscles  constitute  a  well-defined  group  of  muscles  which 
depress  the  hyoid  bone,  the  larynx,  and  the  associated  structures.  They  lie 
beneath  the  sterno-cleido-mastoid  muscle  and  the  external  cervical  fascia.  Two 
strata  may  be  recognised.  In  the  superficial  stratum  are  comprised  the  omo- 
hyoid, a  narrow,  ribbon-like  digastric  muscle  which  arises  from  the  superior 
margin  of  the  scapula  and  is  inserted  into  the  hyoid  bone;  and  the  thin,  quad- 
rangular sterno-hyoid,  which  arises  from  the  superior  margin  of  the  sternum  and 
the  medial  end  of  the  clavicle  and  is  inserted  into  the  hyoid  bone.  Between 
these  two  muscles  is  an  aponeurotic  membrane  which  constitutes  the  main  part 
of  the  middle  layer  of  the  cervical  fascia,  and  represents  possibly  a  retrograde 
portion  of  a  single  muscle,  of  which  the  two  above  named  are  but  the  ventral  and 
dorsal  margins.  Beneath  this  superficial  musculature  the  thin,  quadrangular 
thyreo-hyoid  descends  from  the  hyoid  bone  to  the  thyreoid  cartilage,  and  the 
ribbon-like  stemo-thyreoid  arises  from  the  dorsal  surface  of  the  manubrium 
and  is  inserted  into  the  thyreoid  cartilage. 

All  these  muscles  are  supplied  by  branches  from  the  ansa  hypoglossi.  The 
nerve-fibres  arise  from  the  first  three  cervical  nerves. 

The  muscles  of  this  group  are  derived  from  the  ventral  portions  of  the  ventro-lateral  divi- 
sions of  the  first  three  cervical  myotomes,  and  correspond  with  the  rectus  abdominis  muscle, 
which  is  derived  from  the  ventral  portions  of  the  eighth  to  the  tweUth  thoracic  myotomes. 
This  musculature  is  characterised  by  metameric  segmentation,  which  may  be  more  or  less  ob- 
scured, and  by  a  general  longitudinal  direction  taken  by  the  component  fibre-bundles.  The 
course  of  the  fibres  in  the  omo-hyoid  may  be  looked  upon  as  a  secondary  condition  due  to  the 
shifting  laterally  of  the  distal  attachment  of  the  muscle.  Musculature  of  this  nature  is  not 
derived  from  the  lower  cervical  and  upper  thoracic  myotomes  in  man,  but  in  some  of  the  lower 
vertebrates  it  forms  a  continuous  ventral  band.  Even  in  man  occasional  traces  of  this  ventral 
musculature  may,  however,  be  seen  as  muscular  and  aponeurotic  slips  on  the  upper  part  of  the 
thoracic  wail,  above  the  ribs  and  the  aponeurosis  of  the  external  intercostal  muscles. 

FASCIA 
(Figs.  351  and  357) 

The  middle  cervical  fascia  is  composed  of  two  laminae.  Of  these,  the  superficial,  which 
ensheaths  the  sterno-hyoid  and  omo-hyoid  muscles  and  fills  in  the  intervening  area,  is  much  the 
stronger  and  better  differentiated.  The  more  delicate  deep  lamina  ensheaths  the  thyreo-hyoid 
and  sterno-thyreoid  muscles,  and  laterally  extends  out  to  become  fused  with  the  superficial 
lamina.  It  is  also  more  or  less  closely  bound  to  the  sheath  which  covers  the  internal  jugular 
vein,  carotid  artery,  and  vagus  nerve. 

The  middle  cervical  fascia  is  attached  above  to  the  hyoid  bone.  Beyond  the  lateral  edge 
of  the  omo-hyoid  it  becomes  fused  with  the  deep  lamina  of  the  external  layer  of  the  cervical 
fascia,  beneath  the  sterno-cleido-mastoid.  Posterior  to  this  muscle  it  usually  terminates  along 
the  cranial  margin  of  the  omo-hyoid  in  the  areolar  tissue  of  the  neck.  Its  distal  attachment 
takes  place  into  the  dorsal  surface  of  the  upper  margin  of  the  sternum,  and  from  here  a  process 
is  sent  over  the  left  innominate  vein  to  the  pericardium.  Lateral  to  the  sternum  the  fascia  is 
attached  for  some  distance  to  the  inner  margin  of  the  clavicle,  and  gives  rise  to  processes,  one  of 
which  extends  to  the  fascia  of  the  subclavius  muscle,  while  the  others  pass  on  each  side  of  the 
subclavian  vein  to  the  first  rib.  Still  more  laterally  the  fascia  is  fused  along  the  lower  margin 
of  the  scapular  belly  of  the  omo-hyoid  to  the  underlying  dense,  fatty  areolar  tissue. 


INFRA-HYOID  MUSCLES  351 

MUSCLES 
(Figs.  348  and  351) 

The  sterno-hyoideus. — Origin. — From  (1)  the  deep  surface  of  the  medial  extremity  of  the 
clavicle;  (2)  the  costo-clavicular  (rhomboid)  ligament;  and  (3)  the  neighbouring  part  of  the 
sternum.  The  origin  may  extend  to  the  cartilage  of  the  first  rib.  Structure  and  insertion — 
The  fibre-bundles  take  a  nearly  parallel  course  upward.  The  muscle  belly,  however,  contract, 
slightly  in  width  and  increases  slightly  in  thickness  and  slants  somewhat  toward  the  median 
Hne.  The  insertion  takes  place  directly  upon  the  inferior  margin  of  the  body  of  the  hyoid 
lateral  to  the  mid-line.  Not  infrequently  a  tendinous  inscription  near  the  junction  of  the  middle 
and  inferior  thirds  more  or  less  completely  divides  the  muscle  into  two  portions.  A  second 
inscription  is  sometimes  found  at  the  level  of  the  oblique  line  of  the  thyreoid  cai'tilage.  Nerve- 
supply. — One  or  more  branches  from  the  ansa  hypoglossi  enter  the  lateral  margin  of  the  muscle. 
Frequently  one  goes  to  the  upper  third,  another  to  the  lower  third,  of  the  muscle. 

The  omo-hyoideus. — Origin. — From  the  superior  margin  of  the  scapula  near,  and  occa- 
sionally also  from,  the  superior  transverse  ligament  of  the  scapula.  Insertion. — The  lower 
border  of  the  hyoid  bone  lateral  to  the  sterno-hyoid  muscle.  Structure. — The  inferior  belly  of 
the  muscle  near  its  origin  is  thick  and  fleshy.  It  contracts  as  it  passes  ventrally  across  the 
posterior  triangle  of  the  neck.  Beneath  the  sterno-cleido-mastoid  it  is  attached  to  a  short  ten- 
don from  which,  as  it  bends  upward  toward  the  hj-oid  bone,  the  superior  belly  takes  origin  and 
thence  expands  toward  the  insertion.  The  tendon  of  attachment  is  short.  The  fibre-bundles 
of  both  bellies  take  a  nearly  parallel  course.  The  central  tendon  of  the  muscle  is  held  in  place 
by  a  strong  process  in  the  middle  layer  of  the  cervical  fascia.  This  process  is  attached  to  the 
dorsal  surface  of  the  clavicle  and  to  the  first  rib.  Nerve-supply. — The  superior  belly  is  supphed 
by  a  branch  which  enters  its  deep  surface  near  the  medial  margin  somewhat  below  the  centre; 
the  inferior  by  a  branch  which  enters  the  proximal  third  of  its  deep  surface.  These  branches 
arise  from  the  ansa  hypoglossi. 

jjThe  sterno-thyreoideus. — Origin. — Partly  directly,  partly  by  tendinous  fibres,  from — (1) 
the  dorsal  surface  of  the  manubrium  from  the  middle  line  to  the  notch  for  the  first  rib;  (2)  the 
dorsal  surface  of  the  cartilage  of  the  first  rib.  Occasionally  also  from  the  back  of  the  cartilage 
of  the  second  rib  or  from  the  clavicle.  Structure  and  insertion. — The  fibre-bundles  take  a  nearly 
parallel  course  upward  and  shghtly  lateralward.  The  muscle  is  inserted  by  short  tendinous 
fibres  into  the  oblique  hne  on  the  lamina  of  the  thyreoid  cartilage.  A  transverse  tendinous 
inscription  near  the  upper  border  of  the  interclavicular  hgament  not  infrequently  divides  the 
belly  of  the  muscle  more  or  less  completely  into  two  parts.  Sometimes  a  second  transverse 
inscription  is  found  at  the  level  of  the  lower  margin  of  the  thyreoid  cartilage.  Nerve-supply. — 
By  one  or  two  branches  from  the  ansa  hypoglossi,  which  enter  the  ventral  surface  of  the  muscle 
near  the  lateral  margin.  One  branch  usually  goes  to  the  upper,  another  to  the  lower,  third  of 
the  muscle. 

The  thyreo-hyoideus. — Origin. — From  the  oblique  line  on  the  lamina  of  the  thyreoid 
cartilage.  Structure  and  insertion. — The  fibre-bundles  take  a  parallel  course  and  are  inserted 
on  the  inferior  margin  of  the  lateral  third  of  the  body  of  the  hyoid  bone  and  the  external  surface 
of  the  great  cornu.  Many  fibre-bundles  are  continuous  with  those  of  the  sterno-thyreoid. 
Nerve-supply. — By  a  branch  of  the  hypoglossal  which  enters  the  muscle  near  the  middle  of  its 
lateral  border.     The  fibres  are  said  to  be  derived  from  the  first  cervical  nerve. 

Action. — The  sterno-hyoid  and  omo-hyoid  depress  the  hyoid  bone;  the  sterno-thyreoid 
depresses  the  thyreoid  cartilage;  and  the  thyreoid-hyoid  approximates  the  bone  to  the  cartilage. 
The  omo-hyoid  tends  to  draw  the  hyoid  bone  somewhat  laterally.  In  this  it  is  aided  by  the 
posterior  bell}'  of  the  digastric  and  the  stylo-hyoid  and  is  opposed  by  the  sterno-thyreoid 
and  thyreo-hyoid  muscles,  and  the  anterior  belly  of  the  digastric. 

Relations. — The  muscles  of  this  group  he  beneath  the  external  cervical  fascia.  The  sterno- 
cleido-mastoid  muscle  crosses  the  omo-hyoid,  the  sterno-hyoid,  and  sterno-thyreoid  muscles. 
The  latter  two'muscles  extend  for  a  distance  behind  the  manubrium  of  the  sternum.  The  omo- 
hyoid is  partly  covered  by  the  trapezius,  crosses  the  scalene  muscles,  the  brachial  plexus,  the 
internal  jugular  vein,  carotid  artery,  and  the  sterno-thyreoid  and  thyreo-hyoid  muscles.  The 
sterno-hyoid  extends  over  the  sterno-thyreoid  muscle,  the  thyreoid  gland,  crico-thyreoid 
muscle,  and  the  thyi'eoid  cartilage.  The  sterno-thyreoid  Ues  over  the  innominate  veui,  the 
trachea,  and  thyreoid  gland.  It  is  partly  covered  by  the  sterno-hyoid  and  omo-hyoid  muscles. 
The  thyreo-hj'oid  is  largely  covered  by  the  omo-hyoid  and  sterno-hyoid  muscles,  and  lies  upon 
the  hyo-thyreoid  membrane  and  the  upper  part  of  the  thyreoid  cartilage. 

Variations. — The  muscles  vary  in  extent  of  development  and  may  be  more  or  less  fused 
with  one  another.  The  sternal  attachment  of  the  sterno-hyoid  is  more  frequently  absent  than 
the  clavicular  attachment.  The  region  between  the  omo-hyoid  and  sterno-hyoid  may  be  com- 
posed of  muscle  instead  of  fascia.  Each  of  the  muscles  may  be  longitudinally  divided  into  two 
distinct  fascicuh,  may  send  fascicuU  to  one  another  or  to  the  middle  layer  of  the  cervical  fascia, 
or  may  have  an  abnormal  origin  or  insertion.  The  omo-hyoid  is  the  one  of  the  group  most 
frequently  absent.  One  of  the  bellies  is  much  more  frequently  absent  than  both.  The  inter- 
mediate tendon  of  the  omo-hyoid  may  be  reduced  to  a  tendinous  inscription  or  even  disappear 
entirely.  The  distal  attachment  maj'  take  place  on  the  scapular  spine,  the  acromion,  the  cora- 
coid  process,  or  even  the  first  rib  or  clavicle.  An  extra  fasciculus  from  the  clavicle  is  found  in 
3  per  cent,  of  instances.  (Le  Double.).  Not  very  infrequently  a  muscle  innervated  by  a 
branch  of  the  descendens  hypoglossi  is  found  extending  from  the  sternum  to  the  clavicle  behind 
the  origin  of  the  sterno-cleido-mastoid.  It  may  also  extend  from  the  sternum  or  clavicle  in 
various  directions  upward  toward  the  head. 


352 


THE  MUSCULATURE 


Fig.  351,  A  and  B. — Tbansverse  Sections  Through  the  Left  Side  of  the  Neck  and 

Shoulder  in  the  Regions  indicated  in  the  Diagram. 
a  and  6  in  the  diagram  indicate  sections  A  and  B  of  fig.  347  (p.  340).     a,  that  of  section  A,  fig. 

357  (p.  366). 


41    63  35  5G  36  60  30  H  28  29 


SCALENE  MUSCLES  353 

BURS^ 

The  bursa  m.  sterno-hyoidei  is  in  constantly  found  between  the  lower  margin  of  the  hyoid 
bone  and  median  hyo-thyreoid  ligament  and  the  sterno-hyoid  muscle  and  external  cervical 
fascia.  It  is  better  developed  in  men  than  in  women  and  is  found  either  on  each  side  of  the 
median  line  or  fused  in  the  median  line. 

The  bursa  m.  thyreo-hyoidei  is  frequently  found  between  the  greater  cornu  of  the  hyoid 
bone  and  hyo-thyreoid  membrane  and  the  thyreo-hyoid  muscle. 

7.  SCALENE  MUSCULATURE 

(Figs.  348  and  352) 

The  three  muscles  which  form  this  group  constitute  a  triangular  mass  which 
extends  in  front  of  the  levator  scapulae  and  intrinsic  dorsal  musculature  and 
behind  the  prevertebral  musculature  from  the  first  two  ribs  to  the  transverse 
processes  of  the  cervical  vertebrae.  They  cover  laterally  the  apex  of  the  pleural 
cavity.  They  bend  the  neck  and  fix  the  first  two  ribs  or  raise  the  thorax.  In 
front  lies  the  scalenus  anterior,  which  extends  from  the  first  rib  to  the  fourth  to 
skth  vertebrae.  Behind  this  the  scalenus  medius  extends  from  the  first  rib  to  the 
lower  six  vertebrae.  The  most  dorsal  of  the  group,  the  scalenus  posterior, 
extends  from  the  second  rib  to  the  fifth  and  sixth  vertebrae. 

These  muscles  are  supplied  by  direct  branches  of  the  cervical  nerves.  They  are  probably 
derived  from  the  lateral  portions  of  the  cervical  myotomes.  According  to  Gegenbaur,  the  two 
more  ventral  are  homologous  with  intercostal  muscles,  the  dorsal  with  the  levatores  costarum. 
It  is  to  be  noted,  however,  that  the  anterior  muscle  lies  in  front  of  the  brachial  plexus,  i.  e.,  in 
a  position  similar  to  that  of  the  subcostal  musculature.  The  scalene  musculature  is  morpho- 
logically closely  related  to  the  deep  shoulder-girdle  musculature,  p.  356. 

FASCIA 
(Figs.  351,  357) 

From  the  front  of  the  bodies  of  the  cervical  vertebrae  the  prevertebral  fascia  is  continued 
laterally  over  the  longus  colli  and  the  scalene  muscles,  and  extends  dorsally  into  the  fascia 
covering  the  levator  scapulae.  Between  the  muscles  fascial  processes  are  sent  in  to  become 
attached  to  the  cervical  vertebras.     Interiorly  the  fascia  extends  to  the  outer  surface  of  the  thorax. 

MUSCLES 
(Fig.  352) 

The  scalenus  anterior. — This  arises  from  the  ventral  part  of  the  inferior  border  of  the 
transverse  processes  of  the  fourth,  fifth,  and  sixth  cervical  vertebrae,  usually  also  from  the  third, 
rarely  from  the  seventh,  by  means  of  long,  slender  tendinous  processes.  From  each  tendon 
arises  a  fasciculus  composed  of  nearly  parallel  fibre-bundles.  The  fasciculi  soon  fuse  to  form  a 
muscle  belly  which  contracts  somewhat  toward  the  insertion.     This  takes  place  by  means  of 

1.  Arteria  carotis  communis.  2a.  A.  cervicalis  profunda.  2b.  A.  cervicalis  superficiaUs 
3.  A.  thoracoacromialis  (acromial  branch).  4a.  A.  thyreoidea  inferior.  4b.  A.  thyreoidea 
superior.  5.  A.  transversa  colli.  6.  A.  transversa  scapulae.  7.  A.  vertebralis.  8.  Bursa 
m.  subscapularis.  9.  Cartilago  arytenoidea.  10.  Cartilago  thyreoidea.  11.  Clavicle. 
12.  Costa  I.  13.  Costa  II.  14.  Fascia  cervicalis — a,  superficial  layer;  b,  middle  layer. 
15.  Deep  or  prevertebral  layer.  16.  Fascia  coraco  clavicularis.  17.  Fascia  nuchas. 
IS.  Glandula  thyreoidea.  19.  Humerus.  20.  Ligamentum  coracohumerale.  21.  Med- 
ulla spinalis  (spinal  cord).  22.  Musculus  arytenoideus  transversus.  23.  M.  biceps  brachii, 
tendon  long  head.  24.  M.  constrictor  pharyngis  inferior.  25.  M.  deltoideus.  26.  M. 
Uio-costalis.  27.  M.  infraspinatus.  28.  M.  levator  scapulae.  29.  M.  longissimus  capitis 
(trachelo-mastoid).  30.  M.  longissimus  cervicis.  31a.  M.  longus  colli.  31b.  M.  longus 
capitis  (rectus  capitis  anticus  major).  32.  M.  omo-hyoideus.  33.  M.  platysma.  34.  M. 
rhomboideus  minor.  35.  M.  scalenus  anterior.  36.  M.  scalenus  medius.  37.  M.  semi' 
spinalis  capitis  (oomplexus).  38.  M.  serratus  anterior.  39.  M.  serratus  posterior  superior. 
40.  M.  splenius.  41.  M.  sterno-cleido-mastoideus.  42.  M.  sterno-hyoideus.  43.  M. 
sterno-thyreoideus.  44.  M.  subclavius.  45.  M.  subscapularis;  a,  tendon.  46.  M. 
thyreo-arytenoideus  (and  vocalis).  47.  M.  thyreo-hyoideus.  48.  M.  transverso-spinales. 
49.  M.  trapezius.  50.  Nervous  accessorius.  51.  N.  cervicalis  IV.  52.  N.  laryngeus 
inferior.  53.  N.  descendens  hypoglossi.  54.  Sympathetic  trunk.  55.  N.  thoracaUs  I. 
56.  N.  vagus.  57.  (Esophagus.  58.  Plexus  brachialis.  59.  Scapula — a,  glenoid  cavity; 
b,  ooracoid  process;  c,  spine.  60.  Trachea.  61.  Vena  transversa  colli.  62.  V.  jugularis 
externa.  6.3.  V.  jugularis  interna.  64.  Vertebra  cervicalis  V.  65.  Vertebra  cervicalis 
VII.  66.  Vertebra  thoracalis  I,  arch.  67.  Vertebra  thoracalis  II — a,  spine;  b,  transverse 
process. 


354 


THE  MUSCULATURE 


a  tendon  which  sends  a  fibrous  lamina  a  short  distance  upward  on  the  outer  surface  of  the  muscle. 
The  tendon  is  inserted  into  the  scalene  tubercle  on  the  upper  surface  of  the  body  of  the  first  rib. 

The  scalenus  medius. — This  arises  usually  from  the  third  to  the  seventh,  sometimes  from 
aU  seven  or  from  merely  the  last  four  or  five  cervical  vertebrrs.  The  origin  takes  place  from  the 
posterior  part  of  the  lateral  border  of  the  transverse  processes  by  means  of  a  slender  tendon  from 
each  of  the  upper  and  directly  by  a  muscular  fasciculus  from  each  of  the  lower  vertebrae.  The 
.fasciculi  become  combined  into  a  compact  muscle  belly  which  is  inserted  in  a  manner  similar  to 
the  scalenus  anterior  into  the  upper  surface  of  the  fu-st  rib  behind  the  subclavian  groove.  The 
insertion  usually  extends  to  the  second  rib. 

The  scalenus  posterior  arises  by  short  tendons  from  the  posterior  tubercles  of  the  transverse 
processes  of  the  fifth  and  sixth  cervical  vertebrae.  The  origin  may  extend  as  high  as  the  fourth 
vertebra,  or  as  low  as  the  seventh.  It  is  inserted  by  a  short  tendon  into  the  lateral  surface 
of  the  second  rib.     Occasionally  it  extends  to  the  third  rib. 


Fig.  352  — The  Deep  Ventral  Muscles  op  the  Neck. 


Rectus  capitis  anterior 
Rectus  capitis  lateralis 


Orgin  of  tlie  longus 
capitis 


Scalenus  medius 


Scalenus  anterior 


Scalenus  posterior 


Rectus   capitis   la- 
teralis 
Rectus  capitis 
anterior 


Intertransversus 
posterior 


Nerve-supply. — The  scalenus  anterior  is  innervated  by  branches  from  the'fifth,  sixth,  and 
seventh  cervical  nerves;  the  middle  by  the  fourth,  fifth,  sixth,  seventh,  and  eighth  cervical 
nerves;  the  posterior  by  the  seventh  or  eighth  nerves. 

Action. — With  the  thorax  fixed  the  scalene  muscles  bend  the  neck  to  the  side  and  sUghtly 
forward  and  turn  it  sUghtly  toward  the  opposite  side.  With  the  neck  fixed  they  serve  to  lift 
the  first  two  ribs  and  are  of  use  in  enforced  inspiration.  In  quiet  inspiration  they  serve  to 
fix  the  first  two  ribs. 

Relations. — The  longus  colli  lies  medial  to  the  scalenus  anterior.  DorsaUy  the  scalene 
muscles;  medially  the  pharynx,  thyreoid  gland,  and  trachea;  ventro-lateraUy  the  sterno-cleido- 
mastoid,  infra-hyoid,  and  subclavius  muscles  and  the  clavicle  bound  a  space  filled  with  dense 
fatty  areolar  tissue  in  which  are  contained  the  subclavian  and  carotid  arteries,  the  subclavian 
and  internal  jugular  veins,  the  vagus,  phrenic,  and  sympathetic  nerves,  and  numerous  smaller 
blood-vessels  and  nerves.  The  main  branches  of  the  lower  five  cervical  nerves  pass  laterally 
between  the  scalenus  anterior  and  medius.  The  subclavian  artery  passes  behind,  the  sub- 
clavian vein  in  front,  of  the  attachment  of  the  scalenus  anterior.  The  scalenus  medius  above 
and  the  scalenus  posterior  below  enter  into  relations  dorsally  with  the  levator  scapulae  and  the 
intrinsic  dorsal  musculature,  from  which  they  are  separated  by  fascial  septa. 


PREVERTEBRAL  MUSCLES  355 

Variations. — The  scaleni  present  numerous  variations  in  the  extent  of  the  costal  and  ver- 
tebral attachments.  The  degree  of  fusion  of  the  various  fasciculi  likewise  varies  so  much  that 
diiferent  authors  have  described  varying  numbers  of  muscles  into  which  the  scalenus  mass 
should  be  subdivided.  A  muscle  frequently  present  is  the  scalenus  minimus.  This  arises 
from  the  anterior  tubercle  of  the  sixth  or  sixth  and  seventh  cervical  vertebrte,  and  is  inserted 
into  the  first  rib  behind  the  sulcus  for  the  subclavian  artery.  It  sends  a  process  (Sibson's 
fascia)  to  the  pleural  cupola  and  serves  to  make  the  pleura  tense.  Zuckerkandl  found  it  in 
22  out  of  60  bodies  on  both  sides;  12  times  on  the  right  side  only,  9  times  on  the  left.  It  is 
innervated  by  the  eighth  cervical  nerve.  When  absent,  a  ligamentous  band  takes  its  place. 
An  intertransversarius  lateralis  longus,  may  extend  from  the  posterior  tubercles  of  the  3-5 
transverse  processes  to  the  tip  of  the  seventh  transverse  process  and  divide  the  muscle  fasciculi 
near  their  origin  into  dorsal  and  ventral  divisions. 

8.  THE  PREVERTEBRAL  MUSCULATURE 

(Fig.  352) 

This  deep-seated  musculature  extends  along  tiie  ventro-Iateral  sm-faces  of  the 
three  upper  thoracic  and  the  cervical  vertebrEe  to  the  skull.  It  is  composed  of 
two  muscles.  The  longus  colli  arises  from  the  bodies  of  the  three  thoracic  and 
from  the  bodies  and  transverse  processes  of  the  third  to  the  sixth  cervical  verte- 
brae, and  is  inserted  into  transverse  processes  and  bodies  of  the  cervical  vertebrae. 
The  longus  capitis  (rectus  capitis  anterior  major)  arises  from  the  transverse 
processes  of  the  fourth,  fifth,  and  sixth  cervical  vertebrae,  and  is  inserted  into  the 
basilar  process  of  the  occipital  bone.  These  muscles  flex,  abduct,  and  rotate 
the  head  and  neck.  All  of  them  are  supplied  by  direct  branches  from  the  anterior 
divisions  of  the  cervical  nerves.  They  are  probably  specialised  from  the  ventro- 
lateral portions  of  the  cervical  myotomes.  Similar  muscles  are  found  in  all 
vertebrates  with  well-developed  necks.  The  rectus  capitis  anterior  (minor) 
represents  an  anterior  cervical  intertransverse  muscle. 

FASCIA 

(Figs.  351,  357) 

The  muscles  are  firmly  bound  to  the  vertebral  column  by  the  prevertebral  fascia  described 
in  connection  with  the  scalene  muscles  and  by  the  septa  which  extend  in  between  the  muscles 
of  this  group  and  between  them  and  the  scalenus  anterior. 

MUSCLES 

(Fig.  352) 

The  longus  colli. — This  muscle  may  be  compared  to  a  triangle,  the  base  of  which  extends 
from  the  anterior  tubercle  of  the  atlas  to  the  body  of  the  third  thoracic  vertebra  and  the  apex 
of  which  is  the  transverse  process  of  the  fifth  cervical  vertebra.  The  complex  construction  of 
the  muscle  makes  it  advisable  to  consider  it  as  divided  into  three  parts. 

The  supero-lateral  portion  consists  of  fasciculi  which  arise  from  the  anterior  tubercles  of 
the  transverse  processes  of  the  third,  fourth,  fifth,  and  sixth  cervical  vertebrse  and  from  the  body 
of  the  third  thoracic  and  become  fused  into  a  belly  which  is  inserted  into  the  anterior  tubercle 
of  the  atlas. 

The  median  portion  is  formed  of  muscle  fasciculi  which  arise  from  the  antero-lateral  p.irts 
of  the  bodies  of  the  first  three  thoracic  vertebrae  and  the  last  three  cervical  vertebrae  by  tendin- 
ous processes.  These  fasciculi  fuse  into  a  belly  which  terminates  by  three  flat  tendinous  fas- 
ciculi on  the  antero-lateral  surfaces  of  the  bodies  of  the  second,  third,  and  fourth  cervical 
vertebras. 

The  infero -lateral  portion  is  applied  to  the  inferior  lateral  surface  of  the  median  portion. 
It  arises  from  the  lateral  parts  of  the  bodies  of  the  first  three  thoracic  vertebrae  and  is  inserted 
by  tendinous  processes  into  the  transverse  processes  of  the  fifth  and  sixth  cervical  vertebrae. 

Nerve-supply. — By  branches  from  the  second  to  sixth  cervical  nerves  which  send  rami 
to  the  various  constituent  fasciculi  of  the  muscle. 

The  longus  capitis  (rectus  capitis  anterior  major). — Origin. — By  cylindrical  tendons  from 
the  tips  of  the  anterior  tubercles  of  the  third,  fourth  fifth,  and  sixth  cervical  vertebras.  The 
tendons  send  up  aponeurotic  expansions  on  the  outside  of  the  fasciculi,  which  arise  from  them. 
These  fasciculi  fuse  into  a  dense  muscular  belly  to  which  is  usually  added  a  fasciculus  from  the 
longus  colli.  The  insertion  takes  place  into  the  impression  on  the  inferior  sui'face  of  the  basilar 
portion  of  the  occipital  bone,  extending  lateral  to  the  pharyngeal  tubercle  outward  and  for- 
ward. The  insertion  of  the  fibre-bundles  from  the  third  vertebra  is  direct;  the  other  fibre- 
bundles  are  inserted  largely  into  a  tendinous  lamina  which  covers  the  middle  of  the  ventral 
surface  of  the  muscle  and  from  which,  in  turn,  other  fibre-bundles  arise.  It  is  an  incomplete 
digastric  muscle.  Nerve-supply. — The  first,  second,  third,  and  fourth  cervical  nerves  send 
branches  into  the  ventral  surface  of  the  muscle. 


356  THE  MUSCULATURE 

Actions. — The  longus  colli  serves  to  bend  the  neck  forward;  the  supero-lateral  portion,  when 
acting  on  one  side  only,  serves  slightly  to  bend  the  neck  toward  that  side  and  to  rotate  it;  the 
infero-lateral  portion  serves  especially  to  prevent  hyperextension.  The  longus  capitis  bends  the 
head  forward;  one  side  acting  alone  rotates  the  head  toward  that  side. 

Variations. — There  is  considerable  variation  in  the  number  of  vertebrje  to  which  the  ten- 
dons of  origin  and  insertion  of  the  longus  colh  and  longus  capitis  may  be  attached  and  in  the 
extent  of  fusion  of  the  different  fasciculi  composing  them.  There  may  be  fusion  with  the  scale- 
nus anterior.  The  atlantico-hasilaris  internus  in  4  per  cent,  of  cases  extends  from  the  anterior 
tubercle  of  the  atlas  to  the  base  of  the  skull. 

9.  ANTERIOR  AND  LATERAL  INTERTRANSVERSE 
MUSCLES 

(Fig.  352) 

The  anterior  intertransverse  muscles  extend  successively  between  the  anterior 
tubercles  of  the  cervical  vertebrte.  They  lie  in  front  of  the  anterior  divisions  of 
the  cervical  nerves  and  are  supplied  by  branches  from  these  divisions.  They 
are  usually  more  or  less  bound  up  with  the  insertions  of  the  scalene  and  pre- 
vertebral muscles  into  these  tubercles.  The  muscle  between  the  atlas  and  epi- 
stropheus is  frequently  missing;  when  present,  it  passes  in  front  of  the  lateral 
articulation  between  these  vertebrte.  The  rectus  capitis  anterior  (minor)  may 
be  considered  a  continuation  of  the  series.  The  lowest  muscle  may  extend 
between  the  seventh  cervical  vertebra  and  the  first  rib.  The  lateral  intertrans- 
verse muscles  lie  immediately  behind  the  ventral  divisions  of  the  spinal  nerves  and 
lateral  to  the  dorsal  divisions  and  are  supplied  by  branches  from  the  ventral 
divisions.  The  rectus  capitis  laterahs  belongs  to  this  series.  The  rectus  capitis 
anterior  (minor)  arises  from  the  lateral  mass  of  the  atlas  and  is  inserted  into 
the  base  of  the  occipital  bone.  The  rectus  capitis  lateralis  runs  from  the 
transverse  process  of  the  atlas  to  the  lateral  part  of  the  occipital.  For  the 
posterior   intertransverse  muscles  see  p.  417. 

The  rectus  capitis  anterior  (minor). — This  arises  from  the  upper  surface  of  the  lateral  mass 
of  the  atlas  in  front  of  the  articular  process  and  partly  from  the  neighbouring  transverse  proc- 
ess. From  a  tendon  the  fibre-bundles  extend  in  a  nearly  parallel  direction  upward  and  medially 
to  be  inserted  on  the  inferior  surface  of  the  basilar  portion  of  the  occipital  bone  in  front  of  the 
condyle  Nerve-supply. — From  the  first  (and  second)  cervical  nerves.  Action. — The  rectus 
capitis  anterior  (minor)  serve  to  bend  the  head  forward  and,  when  the  muscles  on  one  side 
only  are  contracted,  to  rotate  the  head  toward  the  same  side. 

Relations. — The  muscles  of  this  group  are  closely  apphed  to  the  vertebral  column.  Be- 
tween the  fascia  covering  them  and  the  fascia  surrounding  the  pharynx  which  lies  in  front  is 
a  region  in  which  merely  a  slight  amount  of  loose  areolar  tissue  is  found.  Dorso-mediaUy  the 
longus  colli  below  and  the  longus  capitis  above  help  to  bound  the  space  in  which  the  chief  ves- 
sels and  nerves  extend  between  the  thorax  and  the  head. 

The  rectus  capitis  lateralis  (fig.  352). — Origin. — From  the  upper  surface  of  the  transverse 
process  of  the  atlas. 

Structure  and  insertion. — The  fibre-bundles  give  rise  to  a  quadrilateral  sheet  which  passes 
upward  to  be  inserted  on  the  under  surface  of  the  pars  lateralis  of  the  occipital  bone. 

Nerve-supply. — The  ventral  branch  of  the  suboccipital  (first  cervical)  nerve  gives  twigs 
to  its  ventral  surface. 

Action. — To  flex  the  head  laterally. 

Relations. — In  front  lie  the  anterior  primary  division  of  the  suboccipital  nerve  and  the 
internal  jugular  vein.  Behind  the  muscle  lie  the  superior  oblique  and  the  longissimus  capitis 
(trachelo-mastoid)  muscles  and  the  atlanto-occipital  joint. 

10.  DEEP  MUSCULATURE  OF  THE  SHOULDER   GIRDLE 

(Figs.  348,  353,  354,  388) 

To  this  group  belong  four  muscles  which  arise  in  the  lateral  cervical  region 
during  embryonic  development  and  become  secondarily  attached  to  the  vertebral 
margin  of  the  scapula.  One  of  these  muscles,  the  band-like  levator  scapulae 
(fig.  353),  remains  in  the  cervical  region.  It  extends  beneath  the  sterno-cleido- 
mastoid,  the  trapezius,  and  the  intervening  fascia  from  the  transverse  processes 
of  the  first  four  cervical  vertebrae  to  the  medial  angle  of  the  scapula.  A  second, 
the  large,  quadrilateral  serratus  anterior  (magnus)  (fig.  354),  comes  to  lie  beneath 
the  blade  of  the  scapula  and  wanders  with  this  to  the  thoracic  region.  It  arises, 
in  the  adult,  from  the  first  nine  ribs  and  is  inserted  into  the  vertebral  margin  of 
the   scapula.     The   flat,  quadrangular   rhomboideus    major    and  rhomboideus 


DEEP  SHOULDER  MUSCLES 


357 


minor  (fig.  353)  arise  from  the  spines  of  the  last  cervical  and  first  four 
or  five  thoracic  vertebrae,  pass  obliquely  downward  across  the  deep  dorsal 
muscles  beneath  the  trapezius  and  are  inserted  into  the  vertebral  margin 
of  the  scapula.     The  third  to  the  seventh  cervical  nerves  supply  this  set  of 

Fig.  353. — The  Levator  Scapul*  and  Rhomboidbi. 


Semisplnalis  capitis 
Spleiiius  capitis 

Levator  scapulae 
Serratus  posterior  superior 

Rhomboideus  minor 

Splenius  cervicis 
Rhomboideus  major 


Supraspinatusp"" 


Serratus  posterior  inferior 


Obliquus  internus' 


muscles.  The  levator  scapulae  is  supplied  by  the  third  and  fourth  cervical 
nerves,  the  rhomboids  by  the  fifth  (dorsal  scapular),  the  serratus  anterior  by 
the  fifth  to  the  seventh  (long  thoracic  nerve).  The  muscles  of  this  group  ele- 
vate the  scapula,  rotate  it,  and  draw  it  backward  (rhomboidei)  or  forward 
(serratus  anterior).     When  all  contract  together  they  raise  the  thorax. 


358 


THE  MUSCULATURE 


The  levator  soapulse  and  the  serratus  anterior  (magnus)  are  two  differentiated  parts  of  a 
muscle  which  is  a  continous  mass  in  many  of  the  lower  mammals.  A  muscle  corresponding 
to  the  rhomboideus  is  found  in  some  of  the  reptiles  and  many  of  the  higher  vertebrates.  In 
some  of  the  mammals  it  has  a  more  extensive  cervical  attachment  than  in  man. 

FASCIiE 

The  fasciae  investing  these  muscles  are  shown  in  cross-section  in  fig.  357. 

The  levator  seapulEc  is  invested  by  fascial  membranes,  the  external  and  stronger  of  which 
is  continued  dorsaUy  from  the  fascial  investment  of  the  scalene  muscles.  The  thinner  layer 
on^its  deep  surface  Hes  next  the  fascial  investment  of  the  intrinsic  muscles  of  the  back.  Cranial- 
ward  from  the  rhomboid  muscles  the  fascial  investment  of  the  levator  scapulse  is  fused  dorsally 
with  the  fascia  covering  the  splenius  cervicis.  Where  the  dorsal  margin  of  the  levator  comes 
in  contact  with  the  rhomboideus  minor,  the  fascia  is  continued  over  into  the  thin  fascial  mem- 

FiQ.  354, — SERKATtrs  Anterioh. 


brane  which  invests  both  surfaces  of  the  rhomboidei.  Similarly  the  investing  fascia  of  the  leva- 
tor is  continued  ventrally  into  the  fascia  investing  both  sm'faces  of  the  serratus  anterior  (mag- 
nus). Within  the  internal  fascial  investment  of  this  group  of  muscles,  near  the  insertion  of 
the  levator,  run  the  transversa  coUi  artery  and  the  dorsal  scapular  nerve. 


MUSCLES 

The  rhomboideus  minor  (fig.  353). — Origin. — ^Lower  part  of  the  ligamentum  nuchse,  the 
spines  of  the  seventh  cervical  and  first  thoracic  vertebrae,  and  the  intervening  supraspinous  Uga- 
ment.     Insertion. — Vertebral  border  of  the  scapula  near  the  spine. 

The  rhomboideus  major  (fig.  353). — Origin. — Spines  of  the  fii'st  four  or  five  thoracic  ver- 
tebrae.    Insertion. — Vertebral  border  of  the  scapula  opposite  the  infraspinous  fossa. 

Structure. — The  two  muscles  are  included  between  two  adherent  fascial  layers  which  bridge 
over  the  greater  or  less  space  that  may  intervene  between  them.  The  fibre-bundles  take  a 
parallel  course  obliquely  downward  and  lateralward  from  the  vertebrae.  From  the  vertebral 
spines  the  muscles  arise  by  an  aponeurosis  which  varies  in  width.  The  attachment  to  the  scap- 
ula is  by  short  tendinous  processes.  The  attachment  of  the  rhomboideus  major  is  firmest  to- 
ward the  inferior  angle  of  the  scapula. 

Nerve-supply. — The  dorsal  scapular  nerve,  which  usually  arises  chiefly  from  the  fifth 
cervical  nerve,  enters  the  superior  margin  of  the  rhomboideus  minor  and  then  courses  distaUy 
near  the  deep  ventral  surface  of  the  two  muscles  and  about  midway  between  the  tendons  of 
origin  and  insertion. 


SERRATUS  ANTERIOR  359 

Action. — The  two  muscles  draw  the  scapula  upward  and  medialward  toward  the  spine  and 
rotate  it  so  as  to  depress  the  shoulder. 

Relations. — Over  the  muscles  lies  the  trapezius.  Under  them  he  the  serratus  posterior 
superior  and  the  splenius  cervicis,  the  longissimus  dorsi,  the  iho-costalis,  serratus  posterior 
superior  and  external  intercostal  muscles.  The  descending  ramus  of  the  transversa  ooUi 
artery  descends  on  the  deep  surface.  Blood-vessels  for  the  trapezius  pass  to  this  muscle  between 
the  two  rhomboids. 

Variations. — There  is  much  variation  in  the  extent  of  the  vertebral  attachment.  The 
minor  is  frequently,  the  major  occasionally,  absent.  The  two  rhomboids  are  frequently  fused 
with  one  another  or  may  be  divided  into  several  distinct  fascicuU.  Frequently  (SO  per  cent., 
Balli)  a  fasciculus  extends  obliquely  on  the  deep  surface  of  the  R.  major  from  the  cranial  part 
of  the  origin  to  the  distal  part  of  the  insertion.  Shps  may  be  sent  to  the  latissimus  dorsi  or 
the  teres  major.  An  accessory  slip  may  pass  between  the  trapezius  and  splenius  muscles  to 
the  occipital  bone  (occipito-scapularis).  A  muscle  corresponding  to  this  fasciculus  is  normally 
found  in  many  mammals. 

The  levator  scapulae  (figs.  353,  388). — Origin. — By  short  tendons  from  the  dorsal  tubercles 
of  the  transverse  processes  of  the  first  four  cervical  vertebras,  between  the  attachments  of  the 
splenius  cervicis  and  scalenus  medius  muscles.  The  tendons  from  the  third  and  fourth  cervical 
vertebrae  are  fused  for  a  short  distance  with  those  of  the  longissimus  cervicis.  Structure  and 
insertion. — The  fibres  run  in  parallel  bundles  in  a  dorso-lateral  direction  downward  to  the  ver- 
tebral border  of  the  scapula  opposite  the  supraspinous  fossa.  The  fibre-bundles  are  inserted 
directly  into  the  periosteum.  As  a  rule,  the  flat  fasciculi  arising  from  the  different  vertebrae 
are  easily  separated. 

Nerve-supply. — By  rami  chiefly  from  the  third  and  fourth  cervical  nerves.  These  rami  enter 
the  ventral  margin  of  the  muscle  and  extend  obhquely  across  the  dorsal  surface  of  the  constituent 
fascicuh  about  midway  between  the  tendons  of  origin  and  insertion.  Frequently  anastomosing 
branches  pass  between  the  nerves.  The  lowest  fasciculus  is  usually  supplied  by  branches  from 
the  nerve  to  the  rhomboid  muscles  (dorsal    scapular). 

Action. — Draws  the  scapula  upward  and  tends  to  rotate  it  so  that  the  inferior  angle 
approaches  the  spine.  When  the  scapula  is  fixed,  the  muscle  serves  to  bend  the  neck  laterally 
and  slightly  to  rotate  it  toward  the  same  side  and  extend  it. 

Relations. — Externally  the  sterno-cleido-mastoid  and,  in  part,  the  splenius  capitis  cover  it 
above;  the  trapezius,  below;  and  the  external  cervical  fascia,  its  middle  portion.  Internally 
lie  the  splenius  cervicis,  longissimus  and  ilioeostaUs  cervicis  (transversalis  cervicis),  and 
serratus  posterior  superior  muscles  and  the  ramus  descendens  of  the  transversa  colU  artery. 
In  front  lie  the  scalene  muscles. 

Variations. — The  number  of  cervical  vertebrae  from  which  the  muscle  springs  varies  from 
two  to  seven.  The  most  constant  are  the  slips  of  origin  from  the  fii'st  two  vertebrae.  The 
muscle  may  send  slips  to  the  temporal  or  the  occiptal  bone  or  to  the  trapezius,  the  serratus 
anterior  (magnus),  serratus  posterior  superior,  and  other  muscles,  or  to  the  clavicle,  first  or 
second  rib,  etc.  Often  the  parts  of  the  muscle  running  to  each  vertebra  are  separated  for  the 
whole  distance.  A  bundle  of  fibres  that  appears  to  be  a  detached  shp  of  the  levator  scapulae 
may  run  from  the  first  two  or  from  lower  cervical  vertebrae  to  the  lateral  end  of  the  clavicle  and 
to  the  acromion.  This  represents  the  levator  claviculae  found  normally  in  many  vertebrates. 
According  to  Le  Double,  it  is  innervated  by  a  branch  from  the  cervical  branches  to  the  trapezius 
group. 

The  serratus  anterior  (magnus)  (figs.  354,  388). — First  Pari. — The  origin  is  by  two  digita- 
tions  from  the  first  and  second  ribs  and  from  a  fibrous  arch  uniting  these  two  attachments. 
The  fibre-bundles  converge  to  be  inserted  on  an  oval  space  on  the  costal  surface  of  the  scapula 
near  its  medial  angle.  Second  Part. — This  arises  by  two  or  three  digitations  from  the  second, 
third,  and  sometimes  the  fourth  ribs.  The  fibre-bundles  spread  out  into  a  thin  sheet  which  is 
inserted  along  the  vertebral  border  of  the  scapula.  Third  Part. — This,  the  strongest  part  of  the 
muscle,  arises  by  digitations  from  the  fourth  or  fifth  to  the  eighth  or  ninth  ribs.  The  attach- 
ments of  the  digitations  are  longest  on  the  upper  border  of  each  rib.  The  interdigitate  with  the 
attachments  of  the  external  oblique  muscle  of  the  abdomen.  The  fibre-bundles  converge  to  be 
inserted  on  the  large  oval  space  on  the  costal  surface  near  the  inferior  angle  of  the  scapula. 

Nerve-supply. — From  the  proximal  portions  of  the  anterior  divisions  of  the  fifth,  sixth, 
seventh,  and  sometimes  the  eighth  cervical  nerves  branches  arise  which  fuse  into  the  long 
thoracic  nerve.  This  nerve  usually  passes  laterally  through  or  behind  the  scalenus  medius 
muscle,  courses  along  the  outer  surface  of  the  serratus  anterior  midway  between  the  origin  and 
insertion,  and  gives  rise  to  numerous  twigs  to  supply  the  various  divisions.  The  fibres  to  the 
upper  portion  come  mainly  from  the  fifth  cervical  nerve;  those  to  the  middle  from  the  fifth 
and  sixth;  and  those  to  the  lower  from  the  sixth  and  seventh. 

Action. — -The  muscle  holds  the  scapula  against  the  thorax  and  draws  it  forward  and  later- 
ally and,  by  its  highly  developed  inferior  portion,  rotates  the  bone  so  as  to  raise  the  point  of 
the  shoulder.  It  is  of  especial  importance  in  abduction  of  the  arm.  It  also  aids,  to  a  slight 
degree,  in  forced  inspiration. 

Relations. — Superficial  to  the  muscle  lie  the  peotoralis  major  and  minor,  subscapularis, 
teres  major,  and  latissimus  dorsi  muscles,  the  subclavian  and  axillary  vessels,  and  the  brachial 
plexus.  Between  the  latissimus  dorsi  and  pectoral  muscles  it  is  covered  by  skin  and  fascia 
inferiorly,  and  superiorly  by  the  fatty  areolar  tissue  of  the  axiUary  fossa.  Under  it  he  the  ex- 
ternal intercostal,  serratus  posterior  superior,  and  the  lower  extremity  of  the  scalenus  medius 
and  posterior  muscles. 

Variations. — -The  digitations  may  extend  to  the  tenth  or  only  to  the  seventh  rib.  The 
muscle  may  be  continuous  with  the  levator  scapulae  as  it  is  in  the  carnivora,  or  some  of  its 
upper  digitations  may  be  wanting.  Slips  may  be  continued  into  neighbouring  muscles.  The 
lower  digitations  may  be  partially  replaced  by  digitations  innervated  by  intercostal  nerves. 


360  THE  MUSCULATURE 

II.  MUSCULATURE  OF  THE  UPPER  LIMB 

The  upper  limbs  in  man,  relieved  of  the  function  of  locomotion  which  is  their 
chief  office  in  most  of  the  lower  mammals,  have  become  endowed  with  great 

Fig.  355. — First  Layer  of  Muscles  of  the  Back. 


Sterno-cleido-mastoid 


Triceps 


Rhomboideus  major 
Pectoralis  major 


Gluteus  medius 


Gluteus  maximus 


MUSCLES  OF  UPPER  LIMB  361 

freedom  of  movement  which  permits  their  developing  many  important  functions. 
Primitively  of  value  in  climbing,  in  seizing  food,  preparing  it  for  eating  and 
carrying  it  to  the  mouth,  in  attack  and  defense,  their  importance  has  been  greatly 
increased  through  the  invention  and  use  of  tools,  at  first  simple  but  constantly 
increasing  in  complexity.  They  are  also  used  as  a  means  of  social  expression,  as 
seen  primitively  in  the  shrugging  of  the  shoulders,  or  in  the  varied  movements  of 
the  arms  which  accompany  heated  discourse,  and  as  finally  developed  in  the  art  of 
writing.  In  order  to  understand  the  muscles  which  are  called  into  play  in  the 
performance  of  these  varied  functions  it  is  necessary  to  consider  the  various  types 
of  movement  which  take  place  at  each  of  the  joints.  Since,  however,  most 
muscles  act  on  more  than  one  joint  and  the  different  parts  of  a  muscle  may  act 
differently  on  the  same  joint,  it  is  convenient  to  take  up  the  muscles  of  each 
region  of  the  limb  in  groups,  based  not  so  much  upon  the  action  of  the  muscles  on 
any  one  joint  as  upon  the  development  of  the  group  and  the  innervation  of 
the  muscles  composing  it. 

Movement  of  the  scapula  is  of  essential  importance  in  the  movements  of  the  arm.  The 
scapula  is  kept  against  the  thorax  by  muscular  attachments  and  atmospheric  pressure,  but  it 
may  be  moved  forward,  backward,  upward,  and  downward,  and  may  be  rotated  so  that  the 
glenoid  fossa,  with  which  the  head  of  the  humerus  articulates,  is  pointed  forward  when  the  arms 
are  carried  forward,  lateralward  when  the  arms  are  abducted,  upward  when  the  arms  are  raised 
high  and  somewhat  downward  when  the  arms  are  carried  backward,  thus  greatly  increasing  the 
extent  of  movement  in  these  various  directions.  The  acromio-clavicular,  and  sterno-clavieular 
joints  both  allow  hmited  movements  in  various  directions  so  that  they  resemble  physiologically 
limited  ball  and  socket  joints.  The  part  played  by  the  superficial  and  deep  shoulder-girdle 
muscles  in  the  various  movements  has  been  described  above,  p.  356,  in  connection  with  these 
groups  of  muscles.  The  action  of  these  muscles  is  aided  by  the  "pectoral  muscles,"  (figs.  360, 
388)  and  by  the  latissimus  dorsi  (fig.  355)  described  below.     These  muscles  depress  the  scapula* 

At  the  humero-scapular  or  shoulder-joint  the  arm  may  be  carried  outward  or  abducted, 
bodyward  or  adducted,  forward  or  flexed  and  backward  or  extended.  The  last  is  much  more 
hmited  in  degree  than  the  other  two.  The  arm  may  also  be  partially  rotated  at  this  joint. 
These  various  movements  are  brought  about  by  the  scapulo-humeral  muscles  (figs.  355, 356, 363) 
and  by  the  latissimus  dorsi  (fig.  355)  and  the  pectoralis  major,  (fig.  360)  assisted  by  the  muscles 
of  the  arm  which  arise  from  the  scapula.  They  are  produced  in  association  with  the  movements 
of  the  scapula  described  above.  At  the  ulno-humeral  joint  the  movements  are  relatively 
simple,  consisting  of  flexion  and  extension.  Extension  is  produced  at  the  elbow  by  the  dorsal 
muscles  of  the  arm  (fig.  363),  flexion  is  produced  not  only  by  the  ventral  muscles  of  the  arm, 
which  are  inserted  into  the  radius  and  ulna  (fig.  364),  but  also  by  the  more  superficial  of  both 
the  main  groups  of  muscles  of  the  forearm.  The  pronation  of  the  forearm,  whereby  the  palm  is 
turned  downward,  and  supination,  whereby  it  is  turned  upward,  take  place  in  the  joints  be- 
tween the  radius  and  ulna  at  each  extremity  and  between  the  radius  and  the  lower  end  of  the 
humerus.  At  the  upper  radio-ulnar  joint  the  radius  is  turned  on  its  long  axis,  at  the  lower 
joint  it  is  carried  about  the  lower  end  of  the  ulna.  Pronation  is  produced  chiefly  by  muscles 
belonging  to  the  ulno-volar  group  of  forearm  muscles  (fig.  370) ;  supination  is  produced  by  the 
biceps  of  the  arm  (fig.  364)  in  conjunction  with  some  of  the  muscles  of  the  radio-dorsal  group 
of  the  forearm  (fig.  367).  At  the  wrist  joints  (radio-carpal,  intercarpal),  the  movements  are 
those  of  flexion,  extension,  radial  abduction  and  ulnar  abduction.  Volar  flexion  takes  place 
chiefly  at  tlie  radio-carpal  joint,  dorsal  flaxion  at  the  intercarpal  joint  (Frohse).  Extension 
is  produced  by  those  muscles  of  the  radio-dorsal  group  of  the  forearm,  which  send  tendons 
to  the  wrist  and  digits,  flexion  by  the  corresponding  muscles  of  the  ulno-volar  group,  radial 
abduction  is  produced  by  the  radial  carpal  extensors  (fig.  367),  and  flexor  ulnar  abduction 
by  the  ulnar  carpal  extensor  and  flexor  (fig.  370).  The  varied  movements  of  the  thumb 
and  fingers,  flexion,  extension,  abduction,  and  adduction  are  produced  partly  by  muscles  of 
the  two  chief  groups  of  forearm  muscles,  partly  by  the  intrinsic  muscles  of  the  hand.  Of 
chief  interest  here  are  the  free  movements  of  the  metacarpal  of  the  thumb  and  the  hmited 
movements  of  the  other  metacarpals,  that  of  the  little  fingers  being  the  most  movable, 
as  seen  in  spreading  or  cupping  the  hand.  In  flexion  and  extension  of  the  metacarpal 
of  the  thumb  the  movement  is  such  as  to  bring  the  thumb  into  opposition  to  the  fingers.  In  the 
metaoarpo-phalangeal  joints  those  of  the  fingers  admit  of  much  greater  freedom  of  movement, 
flexion,  extension,  abduction,  and  adduction,  than  that  of  the  thumb.  The  interphalangeal 
joints  are  pure  hinge  joints  and  permit  merely  flexion  and  extension. 

Divisions. — The  muscles  described  in  this  section  as  the  muscles  of  the  upper 
limb  are  all  differentiated  from  the  blastema  of  the  embryonic  limb  bud.  Most 
of  them  are  differentiated  in  connection  with  the  skeleton  of  the  limb  and  extend 
between  the  various  bones  which  compose  it,  but  a  few  grow  out  from  the  limb 
bud  over  the  trunk  and  become  secondarily  attached  at  one  extremity  to  the 
trunk,  while  the  other  extremitj'  remains  attached  to  the  skeleton  of  the  limb. 
Thus  the  pectoral  muscles  (fig.  360),  extend  from  the  limb  bud  over  the  front  of 
the  thorax  and  the  latissimus  dorsi  extends  over  the  side  and  back  of  the  trunk 

*  The  upper  sternal  part  of  the  pectoralis  major,  however,  acting  alone  elevates  the  scapula, 
and  the  glenoid  fossa,  the  latissimus  dorsi  draws  the  scapula  backward,  tlie  pectoral  muscles 
draw  it  forward. 


362  .    THE  MUSCULATURE 

as  far  as  the  iliac  crest  (fig.  355).  The  muscles  of  the  limb  may  be  divided  into 
two  great  divisions,  a  dorsal  division,  innervated  by  nerves  arising  from  the  back  of 
the  brachial  plexus  (supra-  and  subscapular,  axillary  and  radial  nerves)  and  a 
ventral  division  innervated  by  nerves  arising  from  the  front  of  the  plexus  (sub- 
clavian, anterior  thoracic,  musculo-cutaneous,  median  and  ulnar).  The  former, 
which  correspond  with  the  musculature  on  the  back  of  the  shark's  fin,  are  in  the 
main  extensors;  the  latter,  which  correspond  with  the  musculature  on  the  front 
of  the  shark's  fin  are  in  the  main  flexors.  The  bellies  of  the  muscles  of  each 
division  are  found  in  the  region  of  the  shoulder  and  thorax,  the  arm,  the  forearm, 
and  the  hand. 

The  shoulder  muscles  belong  to  the  dorsal  division.  They  arise  from  the 
lateral  third  of  the  clavicle  and  from  both  surfaces  of  the  scapula  and  are  inserted 
into  the  upper  part  of  the  humerus.  They  include  the  deltoid  (fig.  355),  the  chief 
abductor  of  the  arm;  the  supraspinatus,  the  infraspinatus  and  the  teres  minor 
(fig.  363),  all  lateral  rotators;  the  subscapularis  (fig.  356),  the  chief  medial  rotator; 
and  the  teres  major  (fig.  355) ,  a  medial  rotator  and  adductor.  With  these  may 
be  classed  the  latissimus  dorsi  (a  medial  rotator,  adductor  and  extensor)  (fig. 
355),  which  arises  from  the  dorsolumbar  fascia  and  the  crest  of  the  ilium  and  is 
inserted  into  the  upper  part  of  the  shaft  of  the  humerus.  These  muscles  are  sup- 
plied by  the  suprascapular,  the  subscapular,  and  the  axillary  nerves. 

The  pectoral  group  belongs  to  the  ventral  division.  It  includes  the  pedoralis 
major  (fig.  360) ,  a  powerful  flexor  and  adductor  of  the  arm  arising  from  the  anterior 
chest  wall  and  inserted  into  the  shaft  of  the  humerus;  the  pectoralis  minor  (fig. 
388),  which  arises  from  the  chest  wafl  and  is  inserted  into  the  coracoid  process  of 
the  scapula,  and  the  subclavius  (fig.  361),  which  extends  from  the  first  rib  to  the 
clavicle.  These  muscles  are  supplied  by  the  subclavian  and  the  anterior  thoracic 
nerves. 

In  the  arm  the  dorsal  division  is  represented  by  the  triceps  and  anconeus, 
(fig.  363).  The  triceps  arises  from  the  scapula  and  the  back  of  the  humerus  and  is 
inserted  into  the  olecranon  process  of  the  ulna.  The  anconeus  arises  from  the 
radial  epicondyle  of  the  humerus  and  is  inserted  into  the  olecranon  process.  Both 
muscles  extend  the  forearm.  The  triceps  also  adducts  the  arm.  They  are 
supplied  by  the  radial  nerve. 

The  ventral  division  is  made  up  of  the  coraco-brachialis  (fig.  365) ;  the  biceps 
(fig.  364);  and  the  brachialis  (fig.  365).  The  coraco-brachialis  (fig.  365),  arises 
from  the  tip  of  the  coracoid  process  of  the  clavicle  and  is  inserted  into  the  shaft  of 
the  humerus.  It  adducts  and  flexes  the  arm.  The  biceps  (fig.  364),  arises  by  a 
short  head  from  the  coracoid  process  and  by  a  long  head  from  the  scapula  above 
the  glenoid  fossa  and  is  inserted  into  the  radius  and  the  fascia  of  the  forearm.  It 
flexes  and  supinates  the  forearm.  The  long  head  is  an  abductor,  the  short  head 
an  adductor  and  flexor  of  the  arm.  The  brachialis  (fig.  365),  arises  from  the 
lower  part  of  the  shaft  of  the  humerus  and  is  inserted  into  the  ulna.  It  is  a 
flexor  of  the  forearm. 

The  two  main  divisions  of  the  musculature  of  the  forearm  give  rise  to  the 
prominences  on  each  side  of  the  elbow-joint.  Their  peculiar  arrangement  with 
respect  to  the  humerus  is  because  in  man,  as  in  most  tetrapods,  the  normal  posi- 
tion of  the  forearm  is  one  of  pronation  and  in  this  position  the  back  of  the  forearm 
is  in  line  with  the  radial  epicondyle,  the  front  with  the  ulnar  epicondyle.  The 
dorsal  or  extensor  muscles,  springing  from  the  lower  end  of  the  humerus  (fig.  367), 
get  the  most  direct  purchase  when  attached  to  the  radial  epicondyle,  and  the 
ventral  or  flexor  muscles  (fig.  370),  the  most  direct  purchase  when  attached  to  the 
ulnar  epicondyle.  The  two  divisions  of  the  musculature  may  therefore  here  be 
designated  the  radio-dorsal  and  the  ulno-volar  or  volar  divisions.  The  main 
bulk  of  the  musculature  is  found  in  the  upper  part  of  the  forearm.  At  the  wrist 
numerous  tendons  pass  over  to  the  wrist,  palm  and  digits.  This  arrangement 
facilitates  movement  of  the  hand. 

The  muscles  of  the  dorsal  division  (figs.  367,  368,  369),  are  divisible  into  two 
groups,  a  superficial  and  a  deep  group.  Those  of  the  superficial  group  arise 
from  the  radial  side  of  the  lower  end  of  the  humerus  and  are  inserted  into  the  dorsal 
end  of  the  radius  (brachio-radialis) ,  the  radial  and  ulnar  sides  of  the  metacarpus 
{extensor  carpi  radialis  longus  and  b7-evis  and  extensor  carpi  ulnaris)  and  into  the 
backs  of  the  digits  {extensores  digitorum) .     The  deeper  muscles  arise  chiefly  from 


MUSCLES  OF  SHOULDER  363 

the  ulna  and  are  inserted  into  the  radius  (supinator),  the  thumb  (abductor  pollicis 
longus,  extensor  pollicis  loncjus  and  brevis)  and  index-finger  (extensor  indicis  pro- 
prius,  fig.  369) .  All  are  supplied  by  the  radial  nerve.  The  chief  function  of  the 
brachio-radialis  is  to  flex  the  forearm.  The  chief  functions  of  the  other  muscles 
are  indicated  by  their  names. 

The  volar  musculature  (figs.  370,  371,  372,  375)  arises  from  the  medial  side 
of  the  lower  end  of  the  humerus  and  from  the  front  of  the  radius  and  ulna  and  is 
divisible  into  four  planes.  The  muscles  of  the  most  superficial  plane,  pronator 
teres,  flexor  carpi  radialis,  palmaris  longus,  and  flexor  carpi  ulnaris,  arise  from  the 
humerus  and  are  inserted  respectively  into  the  radius,  the  radial  side  of  the  meta- 
carpus, the  palmar  fascia  and  the  ulnar  side  of  the  metacarpus.  In  the  second 
layer  the  flexor  digitorum  sublimis  arises  from  the  humerus  and  the  upper  part  of 
the  radius  and  ulna  and  sends  tendons  to  the  second  row  of  phalanges  of  the  fin- 
gers. In  the  third  layer  the  flexor  digitorum  profundus  and  flexor  pollicis  longus 
arise  from  the  radius  and  ulna  and  send  tendons  to  the  terminal  row  of  phalanges. 
In  the  fourth  layer  a  single  muscle,  the  pronator  quadratus  (fig.  377),  extends  in 
the  lower  part  of  the  forearm  from  the  radius  to  the  ulna.  These  muscles  are 
supplied  mainly  by  branches  of  the  median  nerve  but  the  ulnar  nerve  supplies 
the  flexor  carpi  ulnaris  and  a  part  of  the  flexor  profundus  digitorum.  The  chief 
functions  of  these  muscles  are  indicated  bj^  their  names. 

In  the  hand  (figs.  368,  375,  376,  377,  379)  there  are  several  sets  of  intrinsic 
muscles.  About  the  metacarpal  of  the  thumb  is  grouped  a  set  of  muscles  which 
arise  from  the  carpus  and  metacarpus  and  are  inserted  into  the  metacarpal  and 
first  phalanx  of  the  thumb  (flexor  brevis  pollicis,  opponens  pollicis,  abductor  pollicis 
brevis,  adductor  pollicis) .  A  similar  set  of  muscles  is  grouped  about  the  metacarpal 
of  the  little  finger  (abductor  digiti  quinti,  opponens  digiti  quinti,  flexor  brevis  digiti 
quinti) .  These  sets  of  muscles  give  rise  respectively  to  the  thenar  and  hypothenar 
eminences.  Between  the  metacarpals  two  sets  of  interosseous  muscles  arise;  a 
volar,  adductor  toward  the  middle  finger  and  a  dorsal,  abductor  group.  They  are 
inserted  into  the  sides  of  the  bases  of  the  first  row  of  phalanges  and  into  the 
extensor  tendons.  They  also  flex  the  first  row  of  phalanges  and  extend  the  other 
two  rows.  From  the  tendons  of  the  deep  flexor  muscle  of  the  fingers,  a  series 
of  lumbrical  muscles  extends  to  the  radial  sides  of  the  extensor  tendons.  They 
flex  the  first  row  of  phalanges  and  extend  the  other  two.  Over  the  thenar  emi- 
nence there  is  a  subcutaneous  muscle,  the  palmaris  brevis.  The  muscles  of  the 
hand  are  supplied  by  the  ulnar  nerve,  with  the  exception  of  the  two  more  radial 
lumbricals  and  the  abductor,  opponens,  and  flexor  brevis  of  the  thumb,  which  are 
supplied  by  the  median  nerve. 

Fasciae. — The  muscle  fascise  of  the  upper  extremities  are  well  developed.  The  deltoid 
and  latissimus  dorsi  are  contained  in  a  fascial  sheet  which  extends  between  them.  The  deeper 
muscles  which  arise  from  the  scapula  are  covered  by  strong  fascia.  Of  the  pectoral  muscles  the 
pectorahs  major  is  covered  by  a  delicate  fascia,  while  the  subclavius  and  pectoralis  minor  are 
contained  within  the  dense  cosio-coracoid  membrane  (fig.  358)  which  extends  into  the  fascia 
covering  the  axillary  fossa.  The  latter  (fig.  359),  is  thin  and  is  intimately  fused  to  the  tela 
subcutanea.  The  muscles  of  the  arm  are  enveloped  in  a  cylindrical  sheath  which  in  the  lower 
half  of  the  arm  is  united  to  the  humerus  by  intermuscular  septa. 

In  the  forearm  near  the  wrist  and  on  the  back  of  the  hand  the  tela  subcutanea  contains 
little  fat.  The  antibrachial  fascia  forms  a  cylindrical  enclosure  for  the  muscles  of  the  forearm. 
Near  the  wrist  it  becomes  strengthened  dorsally  to  form  the  dorsal  ligament  of  the  carpus 
(posterior  annular  ligament).  This  ligament  converts  the  grooves  on  the  back  of  the  radius 
into  canals  for  the  tendons  of  the  extensors  of  the  wrist  and  fingers.  On  the  back  of  the  hand 
and  fingers  the  fascia  is  intimately  connected  with  these  tendons.  On  the  volar  side  near  the 
wrist  the  fascia  is  strengthened  to  form  the  volar  hgament  of  the  carpus.  Beneath  the  ligament 
hes  the  transverse  hgament  of  the  carpus  which  extends  from  the  pisiform  and  hamate  bones  to 
the  tuberosities  of  the  navicular  and  greater  multangular  bones.  It  completes  an  osteo-fibrous 
canal  for  the  tendons  of  the  long  flexors  of  the  fingers.  On  the  palm  of  the  hand  the  fascia  is 
firmly  bound  to  the  bones  by  intermuscular  septa,  which  separate  the  thenar  and  hypothenar 
regions  from  a  central  palmar  region.  On  the  volar  sides  of  the  fingers  the  fascia  forms  the 
vaginal  ligaments  of  the  flexor  tendons. 

A.   MUSCULATURE  OF  THE  SHOULDER 

(Figs.  355,  356,  357,  363,  388) 

The  muscles  belonging  to  this  group  are  the  deltoid,  the  teres  minor,  the  infra- 
and  supraspinatus,  the  latissimus  dorsi,  the  teres  major,  and  the  subscapularis. 


364 


THE  MUSCULATURE 


The  deltoid  (fig.  355)  is  a  large,  shield-shaped  muscle  which  covers  the  shoulder. 
It  arises  from  the  spine  of  the  scapula,  the  acromion,  and  lateral  third  of  the 
clavicle  and  is  inserted  into  the  deltoid  tubercle  of  the  humerus.  It  abducts  the 
arm. 

The  teres  minor,  infra-  and  supraspinatus  form  a  group  of  muscles  (fig.  363) 
which  arise  from  the  back  of  the  scapula,  pass  over  the  capsule  of  the  shoulder- 
joint,  to  which  their  tendons  are  adherent,  and,  under  cover  of  the  deltoid,  are 
inserted  into  the  top  and  the  dorsal  margin  of  the  great  tubercle  of  the  humerus. 
The  band-like  teres  minor  arises  from  the  upper  two-thirds  of  the  axillary  border 
of  the  scapula,  and  has  the  lowest  insertion  on  the  tubercle.  The  triangular 
infraspinatus  (fig.  363)  arises  from  the  whole  infraspinous  fossa  except  the  axillary 
border,  and  is  inserted  above  the  teres  minor.  The  pyramidal  supraspinatus 
(fig.  363)  arises  under  cover  of  the  trapezius  from  the  supraspinous  fossa,  and 
has  the  highest  insertion  on  the  tubercle.  The  teres  minor,  supraspinatus  and 
infraspinatus  act  as  lateral  rotators  of  the  arm,  the  supraspinatus  also  as  an 
abductor. 

The  latissimus  dorsi,  the  teres  major,  and  the  subscapularis  form  a  group  of 
muscles  attached  to  the  lesser  tubercle  of  the  humerus  and  to  the  crest  which 


Fig.  356. — Front  View  of  the  Scapular  Muscles. 


Clavicle 

Coracoid  process 

Supraspinatus 


Deltoid 

Coraco  bracliialis  and 
sliort  head  of  biceps 


Pectoralis  major 


extends  distally  from  this  on  the  medial  side  of  the  intertubercular  (bicipital) 
groove.  The  latissimus  dorsi  (figs.  355,  356)  is  a  large,  flat,  triangular  muscle, 
which  arises  from  an  aponeurosis  covering  the  lumbar  and  the  lower  half  of  the 
thoracic  regions  of  the  back  and  from  the  posterior  part  of  the  iliac  crest,  and  is 
inserted  into  the  intertubercular  (bicipital)  groove.  The  teres  major  (figs. 
355,  356)  is  a  thick,  ribbon-shaped  muscle  which  arises  from  the  dorsal  surface  of 
the  inferior  angle  of  the  scapula  and  is  inserted  behind  the  latissimus  dorsi  into 
the  distal  two-thirds  of  the  crest  of  the  small  tubercle  of  the  humerus.  The 
subscapularis  (fig.  355)  is  a  thick,  triangular  muscle  which  extends  from  the 
subscapular  fossa  to  the  small- tubercle  of  the  humerus.  These  muscles  adduct 
the  arm  and  rotate  it  medialward.  The  latissmus  dorsi  is  also  the  chief  extensor 
of  the  arm. 

Near  their  humeral  attachments  these  two  groups  of  muscles  are  separated 
below  by  the  long  head  of  the  triceps.  The  supraspinatus  is  separated  from  the 
subscapularis  by  the  base  of  the  coracoid  process  and  by  the  intertubercular 
(bicipital)  groove.  The  tendons  of  the  latissimus  dorsi,  teres  major,  and  sub- 
scapularis are  crossed  ventrally  by  the  main  vessels  and  nerves  of  the  arm  and  by 
the  short  head  of  the  biceps  and  the  coraco-brachialis. 

The  supra-  and  infraspinatus  muscles  are  supplied  by  the  suprascapular  nerve. 
The  deltoid  and  the  teres  minor  are  supplied  by  the  axillary  (circumflex).  The 
subscapularis,  the  teres  major,  and  the  latissimus  dorsi  are  supplied  by  subscapular 
nerves.     That  to  the  latissimus  dorsi  is  called  the  dorsal  thoracic  nerve. 


DELTOIDS  us  365 

The  deltoid  in  many  of  the  mammals  and  the  lower  vertebrates  is  represented  by  separate 
scapulo-humeral  and  cleido-humeral  portions.  The  cleido-mastoid  in  some  mammals  is  con- 
tinued into  the  deltoid.  The  teres  minor,  which  is  innervated  by  the  same  nerve,  may  be  looked 
upon  as  a  derivative  of  the  deltoid,  although  in  man  it  is  anatomically  more  intimately  connected 
with  the  infraspinatus.  The  teres  major  may  be  looked  upon  as  a  speciahsed  portion  of  the 
more  primitive  latissimus  dorsi.  The  comparative  anatomy  of  the  shoulder  muscles  through- 
out the  vertebrate  series  is  a  somewhat  intricate  subject,  owing  to  the  great  variations  exhibited 
in  the  form  and  attachment  of  the  shoulder  girdle. 

The  muscles  of  this  group  show  more  or  less  marked  resemblances  to  certain  muscles  of  the 
lower  limb.  The  deltoid  and  the  teres  minor  probably  represent  the  tensor  fascise  latEe,  the  glu- 
teal fascia,  and  the  upper  part  of  the  gluteus  maximus;  the  latissimus  dorsi  and  teres  major, 
the  lower  portion  of  the  gluteus  maximus;  and  the  subscapularis,  the  gluteus  medius  and  mini- 
mus, and  the  piriformis.  The  subscapular  and  axillary  nerves,  which  supply  the  arm  muscles 
mentioned,  therefore  represent  in  the  main  the  nerves  to  the  gluteal  muscles,  and  the  gluteal 
branch  of  the  posterior  cutaneous  nerve  of  the  thigh.  The  infraspinatus  muscle  probably 
represents  the  ihacus;  the  supraspinatus  possibly  the  pectineus  muscle  of  the  lower  limb. 

FASCIA 
(Figs.  351,  357,  359,  362) 

The  tela  subcutanea  covering  the  regions  occupied  by  these  muscles  contains  considerable 
fat.  In  most  regions  it  is  not  readily  separable  into  two  distinct  layers.  In  the  neighbourhood 
of  the  shoulder-joint  it  is  adherent  to  the  underlyingmusculatureand  the  axillary  fasciie.  Over 
the  acromion  there  is  a  well-marked  subcutaneous  bursa,  bursa  subcutanea  acromialis. 

Muscle  fasciae. — The  deltoid  and  latissimus  dorsi  muscles  are  throughout  the  greater  part 
of  their  extent  superficially  placed.  They  are  covered  by  an  adherent  fascial  layer,  which, 
above,  is  attached  to  the  clavicle  and  to  the  spine  of  the  scapula.  VentraUy  it  is  continued  over 
and  fuses  with  the  fascia  covering  the  pectoralis  major,  serratus  anterior,  and  external  oblique 
muscles.  On  the  back  it  extends  as  a  thin  sheet  between  the  dorsal  margin  of  the  deltoid  and 
the  upper  margin  of  the  latissimus  dorsi,  and  is  continued  dorsaUy  into  the  fascial  investment 
of  the  rhomboid  muscles.  The  lateral  fascial  extension  of  the  trapezius  becomes  fused  to  the 
dorsal  surface  of  this  sheet.  Toward  the  armpit  the  fascial  investment  of  the  deltoid  and  latiss- 
imus dorsi  muscles  is  continued  into  the  axillary  fascia,  and  on  the  back  of  the  arm  it  is  con- 
tinued into  the  fascial  investment  of  the  triceps. 

The  supraspinatus  muscle  lies  beneath  the  trapezius.  It  is  covered  by  a  dense  adherent 
fascial  layer  which  is  separated  from  the  trapezius  by  loose  connective  tissue  which  usually 
contains  a  considerable  amount  of  fat. 

The  infraspinatus  and  the  two  teres  muscles  lie  beneath  the  musculo-fascial  layer  composed 
of  the  deltoid,  the  latissimus  dorsi,  and  the  fascial  sheet  described  above.  Each  of  the  three 
muscles  has  a  special  fascial  investment  which  is  bound  to  the  scapula  about  the  region  of  attach- 
ment of  the  muscle  to  the  bone.  Where  two  of  the  muscles  adjoin,  their  fasciae  gives  rise  to 
intermuscular  septa.  Septa  of  this  nature  are  found  between  the  infraspinatus  and  each  of  the 
teres  muscles,  and  between  the  teres  minor  and  the  teres  major.  The  intermuscular  septum 
between  the  infraspinatus  and  teres  minor  muscles  is  often  incomplete.  The  fascia  covering 
the  teres  major  is  so  delicate  as  hardly  to  deserve  the  name,  except  near  the  origin  of  the  muscle. 
Near  the  spine  the  fascia  covering  the  deep  surface  of  the  deltoid  is  often  fused  to  that  covering 
the  infraspinatus. 

The  subscapularis  muscle  is  invested  by  a  moderately  dense  fascia  which  is  bound  to  the 
scapula  along  the  periphery  of  the  attachment  of  the  muscle.  For  a  short  distance  this  fascia 
is  fused  with  the  fascial  investment  of  the  teres  major  near  the  origin  of  the  latter  muscle,  so  that 
an  intermuscular  septum  is  formed.  From  the  ventro-lateral  margin  of  the  fascia  covering  the 
subscapularis  muscle  a  sheet  of  fascia  is  continued  below  the  axillary  fascia  into  the  fascia  cover- 
ing the  serratus  anterior  (magnus). 

MUSCLES 

The  deltoideus  (figs.  355,  356,  360). — Origin. — Fleshy  from  the  lateral  border  and  upper 
surface  of  the  acromion  and  from  the  ventral  border  and  upper  surface  of  the  lateral  third  of  the 
clavicle,  and  tendinous  from  the  spine  of  the  scapula.  Some  fibre-bundles  also  at  times  arise 
from  the  deep  fascia  of  the  muscle  where  it  overlies  and  is  fused  to  the  fascia  of  the  infraspinatus 
muscle  near  the  spine. 

Insertion. — Into  the  deltoid  tuberosity  of  the  humerus  by  a  strong  tendon  arising  from 
numerous  tendinous  bands  within  the  muscle  (fig.  364). 

Structure. — In  structure  the  deltoid  muscle  is  complex.  Three  portions  may  be  recognised: 
— a  clavicular,  an  acromial,  and  a  spinous.  The  first  and  last  are  composed  of  long  fibre-bundles 
which  take  a  slightly  converging  course  and  are  inserted  by  aponeurotic  tendons  respectively 
on  the  front  and  back  of  the  V-shaped  area  of  insertion  of  the  muscle.  The  acromial  portion, 
on  the  other  hand,  is  multipenniform  in  composition.  Four  or  five  tendinous  expansions  descend 
into  the  muscle  from  the  acromion,  and  three  up  into  the  muscle  from  the  tendon  of  insertion. 
From  the  acromion  and  from  the  descending  tendinous  processes  fibre-bundles  run  to  be  inserted 
on  the  sides  of  the  ascending  processes  and  into  the  tendons  of  insertion  of  the  clavicular  and 
spinous  portions  of  the  muscle. 

N eroe-supply . — The  axillary  (circumflex)  nerve  passes  across  the  costal  surface  of  the 
muscle  near  the  tendon  of  insertion  and  gives  off  rami  which  enter  lateral  to  the  middle  of  the 
muscle.     The  nerve  fibres  are  derived  from  the  (foiu-th),  fifth,  and  sixth  cervical  nerves. 

Action. — When  the  whole  muscle  contracts,  the  arm  is  abducted  (raised  lateralhO  to  a 


366 


THE  MUSCULATURE 


TERES  MINOR  367 

horizontal  position.  When  the  clavicular  and  acromial  parts  act,  the  arm  is  raised  and  flexed 
(brought  forward  toward  the  chest).  When  the  acromial  and  spinous  parts  act,  the  arm  is 
raised  and  extended  (carried  toward  the  back),  but  in  this  instance  the  arm  is  not  brought  to  a 
level  with  the  shoulder-joint,  but  only  about  45°  from  the  hanging  position.  The  inferior  part 
of  the  serratus  anterior  and  the  trapezius  act  in  conjunction  with  the  deltoid  in  abduction. 
Abduction  is  greatest  when  the  arm  is  rotated  lateralward.  The  ventral  portion  rotates  the 
arm  medially,  the  dorsal  portion  laterally.  When  the  arm  is  fixed,  the  deltoid  tends  to  carry 
the  inferior  angle  of  the  scapula  toward  the  spinal  column  and  away  from  the  thorax. 

Relations. — On  its  ventral  border  the  deltoid  is  in  contact  with  the  pectoralis  major  muscle. 
Near  the  clavicle  the  cephalic  vein  and  a  small  artery  pass  between  the  two  muscles.  Its  dorsal 
border  is  continued  into  a  dense  fascial  sheet  which  overlies  the  infraspinatus  muscle.  Its 
tendon  of  insertion  passes  between  the  biceps  and  triceps  muscles.  The  deltoid  overhes  the 
coracoid  process  and  upper  extremity  of  the  humerus,  the  coraco-olavicular  and  coraco-acromial 
hgaments,  and  the  insertions  of  the  supraspinatus,  infraspinatus,  and  teres  minor  muscles,  the 
origins  of  the  biceps  and  coraco-brachiahs,  and  a  part  of  the  long  and  lateral  heads  of  the  triceps. 
Beneath  it  run  the  posterior  circumflex  artery  and  axillary  (circumflex)  nerve. 

Variations. — The  clavicular  portion  is  frequently  separate  from  the  rest  of  the  muscle.  The 
three  portions  may  be  distinctly  separate — a  condition  normal  in  some  of  the  lower  mammals. 
The  clavicular  and  acromial  portions  have  been  found  missing.  The  deep  portion  of  the  muscle 
may  be  separated  as  a  distinct  layer  and  inserted  either  into  the  capsule  of  the  joint  or  into  the 
humerus.  Accessory  fasciculi  may  pass  into  the  muscle  from  the  fascia  over  the  infraspinatus 
and  from  the  vertebral  and  axillary  borders  of  the  scapula.  Not  infrequently  fasciculi  are  con- 
tinued into  the  muscle  from  the  trapezius — a  condition  normal  in  animals  with  ill-developed 
clavicles.  An  accessory  tendon  of  insertion  may  extend  to  the  radial  side  of  the  forearm. 
Bundles  of  fibres  from  the  axillai'y  border  of  the  scapula  have  been  seen  to  cross  the  deep  sm^face 
of  the  deltoid  and  be  inserted  into  the  deltoid  fascia.  The  deltoid  may  be  fused  with  neighbour- 
ing muscles,  the  pectoralis  major,  trapezius,  infraspinatus,  brachialis,  brachio-radiahs. 

The  teres  minor  (fig.  363). — Origin. — From  the  upper  two-thirds  of  the  axillary  border  of 
the  infraspinous  fossa,  and  from  the  septa  lying  between  it  and  the  infraspinatus  on  the  one 
side  and  the  teres  major  and  subscapularis  on  the  other.  The  origin  is  in  part  fleshy,  in  part 
from  an  aponeurotic  band  on  its  ventral  surface  toward  the  subscapularis  muscle. 

Structure  and  insertion. — The  fibre-bundles  from  this  origin  take  a  slightly  converging  course 
toward  a  tendon  of  insertion  which  extends  for  some  distance  on  the  dorsal  surface  of  the 
muscle.  The  muscle  is  adherent  to  the  capBule  of  the  joint,  and  terminates  on  the  inferior  of 
the  three  facets  of  the  great  tubercle  of  the  humerus  and  the  postero-lateral  aspect  of  that 
bone  for  two  or  three  centimetres  below  the  facet. 

Nerve-supply. — From  a  branch  of  the  axillary  (circumflex)  nerve  which  enters  the  muscle  on 
its  lateral  margin  about  midway  between  its  extremities.  A  'ganglion'  is  usually  found  upon 
this  nerve.  A  branch  from  the  nerve  to  the  teres  major  has  also  been  reported.  The  nerve 
fibres  are  derived  from  the  fifth  cervical  nerve. 

Action. — It  acts  conjointly  with  the  infraspinatus  to  rotate  the  arm  laterally.  It  is  a 
flexor  when  the  arm  is  down  and  an  extensor  when  it  is  abducted.     It  is  also  an  adductor. 

Relations. — The  muscle  is  in  part  covered  by  the  deltoid.  Ventrally  it  enters  into  relations 
with  the  long  head  of  the  triceps,  the  teres  major,  and  the  subscapularis.  Superiorly,  the  cir- 
cumflex (dorsal)  scapular  vessels  run  between  it  and  the  axillary  border  of  the  scapula. 

Fig.  357.  A  and  B. — Transverse  Sections  through  the  Left  Shoulder  in  the  Regions 

INDICATED   IN   THE    DIAGRAM. 

In  the  neighbourhood  of  the  brachial  plexus  in  each  section  some  of  the  adipose  and  lymphatic 
tissue  has  been  removed.  In  section  B  the  fascia  covering  the  apex  of  the  axillary  fossa 
is  thus  revealed  from  above,  a  and  6  in  the  diagram  indicate  the  regions  through  which 
pass  sections  A  and  B,  fig.  351  (p.  352);  a'  and  b',  the  regions  through  which  pass 
sections  A  and  B,  fig.  362  (p.  375). 

1.  Aorta.  2.  Arteria  brachiaUs.  3.  A.  circumflexa  scapulae  (dorsahs  scapulse).  4.  A.  carotis 
communis.  5.  A.  mammaria  interna.  6.  A.  subclavia.  7.  A.  thoracahs  lateralis  (long 
thoracic).  8.  Costa  I.  9.  Costa  II.  10.  Costa  III.  11.  Costa  IV.  12.  Costa  V. 
13.  Costa  VI.  '  14.  Clavicle.  15.  Fibrocartilago  intervertebrahs  (intervertebral  disc). 
16.  Fascia  axillaris.  17.  Fascia  cervicalis  (superficial  layer).  18.  Middle  layer.  19.  F. 
coraco-clavicularis.  20.  F.  lumbo-dorsahs.  21.  Fascia  of  posterior  serrati.  22.  Humerus. 
23.  Medulla  spinalis  (spinal  cord).  24.  Musculus  biceps — a,  long  head;  6,  short  head; 
c,  tendon  of  short  head.  25.  M.  coraco-brachialis.  26.  M.  deltoideus.  27.  M.  infraspin- 
atus. 28.  M.iho-costahsdor^i  (accessorius).  29.M.intercostalesexterni.  30.  M.intercostales 
interni.  31.  M.  latissimus  dorsi,  tendon.  32.  M.  levator  costs.  33.  M.  longissimus  dorsi. 
34.  M.  longus  oolU.  35.  M.  pectorahs  major.  36.  M.  pectorahs  minor.  37.  M.  platysma. 
38.  M.  rhomboideus  major.  39.  M.  scalenus  anterior.  40a.  M.  serratus  anterior.  406, 
M.  serratus  posterior  superior.  41.  M.  sterno-mastoideus.  42.  M.  cleido-mastoideus. 
insertion.  43.  M.  sterno-hyoideus.  44.  M.  sterno-thyreoideus.  45.  M.  subclavius.  46. 
M.  subscapularis.  47.  M.  teres  major.  48.  M.  teres  minor.  49.  M.  trapezius.  50. 
M.  transverso-spinales.  51.  M.  triceps — a,  long  head;  6,  lateral  head.  52.  Nervus  axillaris 
53.  N.  cutaneus  antebrachii  medialis  (internal  cutaneous).  54.  a-e,  Nn.  intercostales 
I-V.  55.  N.  medianus.  56.  N.  phrenicus.  57.  N.  musculocutaneus.  58.  N.  radiaUs 
(musoulo-spiral).  59.  N.  recurrens.  60.  N.  subscapularis.  61.  Sj'mpathetic  trunk. 
62.  N.  thoracalis  anterior.  63.  N.  thoracalis  longus.  64.  N.  thoracodorsaUs  (long 
subscapular).  65.  N.  ulnaris.  66.  N.  vagus.  67.  CEsophagus.  68.  Plexus  brachialis — 
a,  lateral  fasciculus;  6,  medial;  c,  posterior.  69.  Scapula.  70.  Sternum.  71.  Trachea. 
72.  Venae  brachiales.  73.  V.  cephaUca.  74.  V.  jugularis  anterior.  75.  V.  jugularis 
inferior.  76.  V.  subclavia.  77.  Vertebra  I.  78.  Vertebra  II.  79.  Vertebra  III.  80. 
Vertebra  IV.     81.  Vertebra  V.     82.  Vertebra  VI. 


368  THE  MUSCULATURE 

Variations. — Aside  from  its  frequent  fusion  with  the  infraspinatus,  there  has  also  been 
reported  an  isolation  of  a  special  fasciculus  to  the  subtubercular  attachment. 

The  infraspinatus  (fig.  363). — Origin. — From  the  vertebral  three-fourths  of  the  infra- 
spinous  fossa,  from  the  under  surface  of  the  spine,  from  the  enveloping  fascia  and  from  inter- 
muscular septa  between  it  and  the  two  teres  muscles. 

Structure  and  insertion. — The  fibre-bundles  converge  toward  the  lateral  angle  of  the  scapula 
to  be  attached  to  a  deep-seated  tendon  which  is  adherent  to  the  capsule  of  the  joint  and  is 
attached  to  the  middle  facet  of  the  great  tubercle.  The  fibre-bundles  arising  from  the  inferior 
surface  of  the  spine  and  the  fascia  near  this  form  a  distinct  fasciculus  which  descends  on  and 
covers  the  tendon  of  insertion. 

Nerve-supply. — From  the  suprascapular  nerve,  which  passes  beneath  the  supraspinatus 
muscle  and  enters  the  deep  surface  of  the  infraspinatus  in  the  lateral  part  of  the  midde  third 
of  its  upper  margin.  From  here  rami  spread  out  toward  the  vertebral  border  of  the  muscle 
and  toward  the  humeral  insertion.  The  nerve  fibres  are  derived  from  the  fifth  and  sixth 
cervical  nerves. 

Action. — This  muscle  is  the  chief  lateral  rotator  of  the  arm,  a  movement  that  can  be 
carried  through  90°.  The  upper  part  of  the  muscle  is  an  abductor,  the  lower  part  an  adductor 
of  the  arm.     The  muscle  is  also  a  flexor. 

Relations. — The  deltoid  and  trapezius,  and  sometimes  the  latissimus  dorsi  muscles,  cover 
a  portion  of  the  dorsal  surface.  Over  most  of  it  extends  the  complex  fascia  described  above. 
Laterally  it  adjoins  the  teres  minor  and  major  muscles.  Under  the  muscle  he  the  transverse 
(suprascapular)  and  circumflex  (dorsal)  scapular  vessels. 

Variations. — These  are  rare,  aside  from  a  greater  or  less  independence  of  the  bundles  arising 
from  the  spine  and  a  greater  or  less  complete  fusion  with  the  teres  minor.  A  fasciculus  has 
been  seen  extending  to  the  muscle  from  the  deltoid. 

The  supraspinatus  (fig.  363). — Origin. — Fleshy  from  the  medial  two-thirds  of  the  supra- 
spinous fossa  and  from  the  deep  surface  of  the  enveloping  fascia  near  the  vertebral  end. 

Structure  and  insertion. — The  fibre-bundles  converge  upon  a  deep-seated  tendon  nearly  to  its 
attachment  into  the  highest  of  the  three  facets  on  the  great  tubercle  of  the  humerus. 

Nerve-supply. — Two  branches  from  the  suprascapular  nerve  enter  the  middle  third  of  the 
deep  surface  of  the  muscle.     The  nerve  fibres  are  derived  from  the  fifth  cervical  nerve. 

Action. — It  aids  the  deltoid  in  abducting  the  arm.  It  is  also  a  weak  lateral  rotator  and 
flexor.     It  keeps  the  head  of  the  humerus  in  place  during  abduction  of  the  arm. 

Relations. — The  muscle  is  covered  by  the  trapezius,  the  acromion,  and  the  coraco-acromial 
hgament.  Beyond  the  base  of  the  spine  of  the  scapula  it  comes  into  contact  with  the  infra- 
spinatus muscle.  Beneath  the  muscle  pass  the  suprascapular  nerve  and  transverse  scapular 
(suprascapular)  vessels. 

Variations. — The  muscle  shows  slight  variations.  Its  tendon  may  be  fused  with  that  of 
the  infraspinatus.  Its  belly  may  be  reinforced  by  fibre-bundles  from  the  coraco-acromial 
ligament. 

The  latissimus  dorsi  (figs.  355,  356,  387,  388). — Origin. — (1)  From  an  aponeurosis  at- 
tached to  the  spines  and  interspinous  ligaments  of  the  five  or  six  last  thoracic  and  the  upper 
lumbar  vertebra,  to  the  lumbo-dorsal  fascia,  and  to  the  posterior  third  of  the  external  lip  of  the 
crest  of  the  ilium;  (2)  from  the  external  surface  and  upper  margin  of  the  last  three  or  four  ribs 
by  muscular  slips  which  interdigitate  with  those  of  the  external  oblique.  In  the  lumbar  region 
the  aponeuroses  of  the  right  and  left  muscles  are  connected  by  fibrous  fascicuh  which  cross  the 
mid-dorsal  line  above  the  supraspinous  ligament. 

Structure  and  insertion. — From  this  extensive  area  of  the  origin  fibre-bundles  converge 
toward  the  tendon  of  insertion.  In  the  region  of  the  dorsal  wall  of  the  axillary  fossa  the  muscle 
is  concentrated  into  a  thick,  ribbon-like  band  which  winds  about  the  teres  major  and  passes  to 
the  ventral  surface  of  that  muscle.  As  this  takes  place  the  fibre-bundles  become  apphed  to  each 
surface  of  a  flat  tendon,  which,  after  emerging  from  the  muscle,  is  six  to  eight  cm.  long  and  three 
to  five  cm.  broad,  and  is  inserted  into  the  ventral  side  of  the  crest  of  the  lesser  tubercle  of  the 
humerus  and  into  the  depth  of  the  intertubercular  (bicipital)  groove  immediately  ventral  to 
the  tendon  of  the  teres  major.  With  this  it  is  more  or  less  closely  bound,  although  between 
the  tendons  there  lies  a  serous  bursa.  Some  of  the  fasciculi  of  the  tendon  extend  to  the  crest 
of  the  greater  tubercle.  Frequently  a  tendon  slip  passes  from  the  inferior  margin  of  the  ten- 
don to  the  tendon  on  the  posterior  surface  of  the  long  head  of  the  triceps  or  into  the  brachial 
fascia  (see  lalissirno-condyloideus,  p.  379). 

Like  the  teres  major,  with  which  it  is  closely  associated,  the  latissimus  dorsi  muscle  under- 
goes a  torsion  between  its  origin  and  its  insertion,  so  that  the  dorsal  surface  of  the  muscle  is 
continued  into  the  ventral  surface  of  the  tendon  and  the  most  cranially  situated  of  the  fibre- 
bundles  are  most  distally  attached  to  the  humerus,  and  vice  versa.  The  muscle  either  directly 
or  through  its  fascial  extension  is  often  adherent  to  the  inferior  angle  of  the  scapula. 

Nerve-supply. — From  the  dorsal  thoracic  (long  subscapular)  nerve  (from  the  sixth,  seventh 
and  eighth  cervical  nerves) .  This  nerve,  which  may  arise  in  conjunction  with  the  axillai'y  nerve, 
passes  to  the  deep  surface  of  the  muscle  in  the  lower  part  of  the  axilla,  and  here  gives  rise  to 
rami  which  diverge  as  the  muscle  expands  toward  its  tendons  of  origin.  Though  soon  embedded 
in  the  muscle  substance,  two  main  branches  may  be  followed  for  a  considerable  distance  near 
the  deep  surface  of  the  muscle.  One  usually  extends  near  the  lateral,  the  other  near  the  supe- 
rior, border  of  the  muscle,  and  from  these  large  rami  pass  into  the  intervening  region.  Branches 
of  the  dorsal  thoracic  artery  and  vein  accompany  the  nerve. 

Action. — With  the  trunk  fixed,  the  latissimus  dorsi  draws  the  raised  arm  down  and  back- 
ward and  rotates  it  medialward  (swimming  movement).  When  the  arm  is  hanging  by  the  side, 
the  action  of  the  muscle  is  on  the  scapula.  The  upper  third  of  the  muscle  draws  the  scapula 
toward  the  spine,  the  inferior  two-thirds  depress  the  shoulder.  When  the  humerus  is  fi^ed, 
the  latissimus  serves  to  lift  the  trunk  and  pelvis  forward,  as  in  climbing.  It  also  aids  in  forced 
inspiration  through  its  costal  attachments. 


BURSJE  369 

^Relations. — The  trapezius  covers  a  small  portion  of  the  muscle  in  the  mid-thoracic  region 
of  the  back.  Over  a  large  area  it  is  subcutaneous,  and  its  fascial  investment  is  adherent  to 
the  skin.  As  it  winds  about  the  teres  major  its  tendon  comes  to  lie  behind  the  coraco-brachialis 
muscle.  The  main  nerves  and  vessels  of  the  arm  here  pass  across  its  ventral  surface.  The 
muscle  covers  in  part  the  rhomboideus  major,  the  infraspinatus,  teres  major,  serratus  posterior 
inferior,  the  lower  ribs,  the  external  intercostal  muscles,  the  dorsal  border  of  the  external  and 
internal  oblique  muscles,  and  the  lower  dorsal  part  of  the  serratus  anterior  (magnus). 

Variations. — It  may  show  considerable  variation  in  the  extent  of  its  fleshy  portion  and  in 
the  attachment  of  its  aponeurosis  to  the  vertebral  column,  crest  of  the  ilium,  the  ribs,  and  the 
scapula.  Its  origin  may  be  merely  from  the  ribs.  It  maj'  be  divided  into  separate  fasciculi. 
Frequently  a  fasciculus  arises  from  the  inferior  angle  of  the  scapula.  The  muscle  is  often  inti- 
mately united  to  the  teres  major.  For  an  account  of  the  muscular  slip  which  extends  from  the 
latissimus  dorsi  across  the  axillary  fossa  to  the  tendon  of  the  pectoralis  major  near  the  inter- 
tubercular  (bicipital)  groove  see  the  latter  muscle  (p.  .374);  and  for  the  slip  continued  from  the 
tendon  of  the  latissimus  dorsi  to  the  olecranon  see  the  Triceps  Muscle  (p.  .379). 

The  teres  major  (figs.  356,  388). — Origin. — Directly  from  the  dorsal  surface  of  the  inferior 
angle  of  the  scapula  and  from  the  septa  which  lie  between  this  muscle  and  the  subscapularis, 
teres  minor,  and  infraspinatus  muscles. 

Insertion. — For  about  five  or  six  cm.  from  the  lower  border  of  the  small  tubercle  of  the 
humerus,  along  the  medial  lip  of  the  intertubercular  (bicipital)  groove.  ProximaUy  the  fibre- 
bundles  are  attached  directly  to  the  tubercle;  more  distally  the  attachment  is  by  means  of  a  flat 
tendon  which  extends  for  some  distance  on  the  dorsal  surface  of  the  muscle. 

Structure. — The  nearly  paraOel  fibre-bundles  pass  upward  in  a  spiral  direction  so  that  the 
muscle  undergoes  a  torsion  on  its  axis.  The  fibre-bundles  which  have  the  highest  attachment 
to  the  scapula  have  the  lowest  humeral  attachment,  and  vice  versa. 

Nerue-supply. — By  a  branch  of  the  lower  subscapular  nerve  which  enters  the  muscle  near 
the  middle  of  its  scapular  border.  The  nerve  fibres  are  derived  from  the  fifth,  sixth  (and  seventh) 
cervical  nerves. 

Action. — It  aids  the  latissimus  dorsi  in  adducting  the  arm,  and  in  some  positions  of  the  arm 
acts  as  a  medial  rotator  and  as  an  extensor. 

Relations. — Dorsally  the  muscle  is  covered  by  the  latissimus  dorsi  and  by  the  fascia  which 
extends  from  this  muscle  to  the  deltoid  and  rhomboid  muscles.  It  is  also  crossed  by  the  long 
head  of  the  triceps.  Its  lower  border  and  ventral  surface  are  largely  covered  by  the  latissimus 
dorsi  and  its  tendon.  Its  upper  border  helps  to  bound  a  triangular  space  the  other  sides  of 
which  are  the  borders  of  the  scapula  and  the  humerus.  In  front  lies  the  subscapularis,  and 
behind,  the  teres  minor.  Across  this  space  passes  the  long  head  of  the  triceps.  Lateral  to  this 
head  lie  the  humeral  circumflex  vessels  and  axillary  (circumflex)  nerve;  and  medial,  the  circum- 
flex (dorsal)  scapular  artery. 

Variations. — The  teres  major  may  be  connected  with  the  latissimus  dorsi  by  a  fasciculus, 
or  it  may  be  fused  with  that  muscle  or  its  tendon.  Slips  have  also  been  seen  extending  to  the 
triceps  and  into  the  fascia  of  the  arm.     The  muscle  is  rarely  absent. 

The  subscapularis  (figs.  356,  388). — Origin. — The  fibre-bundles  spring — (1)  directly  and 
by  means  of  tendinous  bands  from  the  costal  surface  of  the  scapula,  except  near  the  neck  and 
at  the  upper  and  lower  angles;  and  (2)  from  intermuscular  septa  between  it  and  the  teres  major 
and  teres  minor  muscles. 

Insertion. — The  tendon  of  insertion  as  it  passes  over  the  capsule  of  the  joint  is  intimately 
bound  to  this.  It  is  inserted  into  the  lesser  tubercle  of  the  humerus  and  into  the  shaft  im- 
mediately below  this. 

Structure. — The  fibre-bundles  arising  from  the  tendinous  bands  attached  to  the  bone  con- 
verge upon  several  tendinous  laminee  which  extend  into  the  muscle  from  the  tendon  of  insertion, 
thus  forming  small  pennif orm  fasciculi.  The  fibre-bundles  arising  directly  from  the  bone  con- 
verge toward  the  extremities  of  the  tendinous  lamina;,  thus  forming  triangular  bundles  inter- 
digitating  with  the  penniform  fasciculi.  The  fasciculus  which  arises  highest  on  the  axillary 
border  goes  directly  to  the  humerus. 

Nerve-supTply. — By  two  or  three  subscapular  branches  from  the  back  of  the  brachial  plexus. 
One  or  more  of  these  may  arise  in  association  with  the  axillary  (circumflex)  nerve.  From  the 
main  nerves  rami  spread  out  to  enter  the  ventral  surface  of  the  muscle  near  the  junction  of  the 
lateral  and  middle  thirds.     The  nerve  fibres  come  from  the  fifth  and  sixth  cervical  nerves. 

Action. — It  is  the  chief  medial  rotator  of  the  arm.  It  strengthens  the  shoulder-joint  by 
drawing  the  humerus  against  the  glenoid  cavity.  It  is  an  extensor  when  the  arm  is  at  the  side, 
a  flexor  when  the  arm  is  abducted.  The  upper  portion  of  the  muscle,  however,  acts  as  a 
flexor  in  both  positions.  The  upper  part  acts  as  an  abductor  but  when  the  arm  is  abducted  the 
muscle  is  an  adductor. 

Relations. — Ventrally  it  forms  the  greater  part  of  the  posterior  wall  of  the  axillary  fossa, 
and  enters  into  relation  with  the  serratus  anterior  (magnus)  and  the  combined  tendon  of  the 
coraco-brachiaUs  and  biceps.  On  it  lie  the  axillary  vessels,  the  brachial  plexus,  and  numerous 
lymph-vessels  and  glands.  At  its  lateral  border  lie  the  teres  major,  the  humeral  cu-cumflex 
vessels,  axillary  (circumflex)  nerve,  and  circumflex  (dorsal)  scapular  vessels.  Behind  it  he  the 
long  head  of  the  triceps  and  the  teres  minor  muscle. 

Variations. — It  may  be  divided  into  several  distinct  segments.  A  fasciculus  may  be  sent 
to  the  tendon  of  the  latissimus  dorsi  and  another  to  the  brachial  fascia.  The  subscapularis 
minor  arises  from  the  axillary  border  of  the  scapula  and  is  inserted  into  the  articular  capsule 
(capsular  hgament)  of  the  shoulder-joint  or  into  the  crest  of  the  lesser  tubercle  of  the  humerus. 

BURS^ 

B.  subacromialis. — A  large  bursa,  nearly  constantly  found,  between  the  acromion  and 
coraco-acromial  ligament  and  the  insertion  of  the  supraspinatus  muscle  and  capsule  of  the  joint. 


370 


THE  MUSCULATURE 


Processes  extend  over  the  greater  and  lesser  tubercles. 

B.  supracoracoidea. — A  bursa  sometimes  found  between  the  coracoid  process  and  the 
clavicle  and  the  deltoid  muscle. 

B.  m.  subscapularis. — Between  the  glenoid  border  of  the  scapula  and  the  subscapularis 
muscle.  Communicates  with  the  joint  cavity.  A  small  portion  of  this  bursa  may  be  isolated 
adjacent  to  the  base  of  the  coracoid  process  (6.  subcoracoidea) . 

B.  m.  infraspinati. — Between  the  tendon  of  the  infraspinatus  and  the  capsule  of  the  joint 
or  the  great  tubercle. 

B.  m.  latissimi  dorsi. — Constant  between  the  tendons  of  the  latissimus  dorsi  and  the  teres 
major. 

B.  m.  teretis  majoris. — Under  the  insertion  of  the  tendon  of  the  teres  major  muscle. 

B.  PECTORAL  MUSCLES  AND  AXILLARY  FASCIA 

(Pigs.  357,  358,  360,  361,  388) 

The  muscles  belonging  to  this  group  are  the  pectoralis  major,  pectoralis 
minor,  and  the  subclavius.     Of  these,  the  largest  and  most  superficial  is  the 

Fig.  358. — Deep  Fascia  of  the  Breast.  (After  Eisler).  The  Pectoralis  Major  Has 
Been  in  Large  Part  Removed.  1,  Deltoid;  .2,  Pectoralis  Major,  Abdominal  Past;  3, 
Pectoralis. Minor;  4,  Coraco-Brachialis. 


triangular  pectoralis'major  (fig.  360),  which  arises  from  the  second  to  the  sixth 
ribs,  the  sternum,  and  the  medial  half  of  the  clavicle  and  is  inserted  into  the  crest 
of  the  greater  tubercle  of  the  humerus  (pectoral  ridge).  Its  lateral  margin  adjoins 
the  ventral  margin  of  the  deltoid.  Beneath  this  muscle  the  much  smaller  triangu- 
lar pectoralis  minor  (fig.  388)  extends  from  near  the  ends  of  the  second,  third, 
fourth,  and  fifth  ribs  to  the  tip  of  the  coracoid  process,  while  the  small  subclavius 
(fig.  361)  extends  from  the  first  rib  upward  and  lateralward  to  the  clavicle. 

The  pectoral  muscles  and  the  subclavius  play  a  part  in  forced  inspiration. 
The  pectoralis  major  also  serves  to  adduct  and  flex  the  arm-  and  rotate  it 
medialward. 

Of  the  muscles  included  in  this  group,  the  two  pectoral  muscles  are  morphologically  the  most 
closely  related.  They  receive  a  nerve-supply  from  the  same  set  of  nerves,  the  anterior  thoracic 
With  them  the  subclavius,  which  has  a  separate  nerve  of  its  own,  is  closely  associated.     Cor- 


F  ASCIIS 


371 


responding  musculatui-e,  although  variously  modified  in  different  forms,  is  found  tlii'oughout  the 
vertebrate  series.  In  the  lower  forms  it  se"ems  to  be  differentiated  directly  from  the  segmental 
trunk  musculature  and  secondarily  attached  to  the  shoulder  girdle,  like  the  superficial  and  deep 
musculature  of  the  shoulder  girdle  previously  described.  In  man,  however,  the  muscle  mass 
from  which  these  muscles  arise  is  at  all  times  in  intimate  union  with  the  skeleton  of  the  upper 
limb,  and  the  nerves  which  supply  it  are  in  much  more  intimate  union  with  the  brachial  plexus 
than  are  those  of  the  shoulder-girdle  muscles.  For  these  reasons  the  three  muscles  are  classed 
with  the  intrinsic  muscles  of  the  arm.  They  have  no  certain  representatives  in  the  lower  hmb, 
although  the  clavicular  portion  of  the  pectoralis  major  is  considered  by  some  to  represent  certain 
adductor  muscles  of  the  thigh.  Possibly  they  correspond  in  their  embryonic  origin  with  the 
obturator  internus  group  of  the  lower  hmb. 

In  many  of  the  mammals  a  subcutaneous  muscle  arises  from  the  pectoral  muscle  mass  and 
extends  over  the  axUla  and  the  trunk.  In  man  this  musculature  is  frequently  represented  by 
abnormal  shps  of  muscles,  of  which  the  'axillary  arch'  and  possibly  the  'sternalis'  are  representa- 
tives. A  list  of  some  of  the  abnormal  muscles  which  are  innervated  from  the  anterior  thoracic 
nerves  and  are  evidently  derivatives  of  the  pectoral  muscle  mass  is  given  at  the  end  of  this  section 

Fig.  359. —  (After  Eisler).      Fascia  of  the  Axillary  Fossa. 


FASCIiE 

In  the  tela  subcutanea  of  the  pectoral  region  the  mammary  gland  is  embedded  between 
two  layers  which  ensheath  the  gland  and  are  connected  by  dense  fibre-bands.  To  a  greater 
or  less  extent  the  platysma  extends  into  the  tela  of  this  region  from  above  the  clavicle. 

Muscle  fasciae. — The  pectorahs  major  is  invested  with  a  thin,  adherent  membrane,  fascia 
pectoralis,  attached  to  the  clavicle  and  the  sternum  and  continued  into  the  fascial  invest- 
ment of  the  external  obUque,  the  serratus  anterior  (magnus),  and  the  deltoid  muscles, 
and  in  to  the  axillary  fascia.  More  important  is  the  coraco-clavicular  (costo-coracoid)  fascia 
fig.  358.  This  arises  from  two  fascial  sheets  which  invest  the  subclavius  muscle  and  are  at- 
tached to  the  clavicle.  From  the  inferior  margin  of  this  muscle  the  membrane  is  continued 
to  the  superior  margin  of  the  pectoralis  minor.  Between  the  coracoid  process  and  the  first 
costal  cartilage  it  is  strengthened  to  form  the  costo-coracoid  ligament.  Between  this  and  the 
pectorahs  minor  it  is  thin.  At  the  superior  margin  of  this  muscle  it  again  divides  to  form  two 
adherent  fascial  sheets,  which,  at  the  axillary  margin  of  the  muscle,  once  more  unite  to  form  a 
fii'm  membrane  continued  into  the  fascial  investment  of  the  coraco-brachiahs  and  short  head  of 
the  biceps  and  into  the  axiUai'y  fascia.  Above,  dorsally,  the  membrane  is  adherent  to  the  sheath 
of  the  axillary  vessels  and  nerves. 

Axillary  fascia  (fig.  359). — The  arm-pit,  or  axillary  fossa,  is  a  pyramidal  space  bounded 
by  the  pectoralis  major  and  minor  and  coraco-brachialis  muscles  in  front;  by  the  latissimus 


372 


THE  MUSCULATURE 


dorsi,  teres  major,  and  subsoapularis  muscles  behind;  by  the  subscapularis  muscle  toward  the 
joint;  and  by  the  serratus  anterior  (magnus)  toward  the  thoracic  wall.  In  the  groove  between 
the  coraco-brachiaUs  and  the  subscapularis  and  tendons  of  the  latissimus  dorsi  and  teres  major 
muscles  run  the  main  nerves  and  vessels  of  the  arm.  These  are  surrounded  by  a  considerable 
amount  of  connective  tissue  in  which  numerous  blood-  and  lymph-vessels,  lymph-nodes, 
nerves,  and  masses  of  fat  are  embedded. 

Fig.  360. — The  Pectoralis  Major  and  Deltoid. 

Sterno-cleido- 
mastoid 


■Aponeurosis  of  external  oblique 


External  intercostal 


Over  this  connective  tissue  the  fascia  covering  the  musculature  of  the  neighbouring  portion 
of  the  shoulder  and  thorax  is  continued  into  the  fascia  covering  the  musculature  of  the  medial 
side  of  the  arm.  Thus  the  fascia  covering  the  pectoralis  minor,  the  coraco-clavicular  fascia, 
strengthened  by  a  reflection  of  the  fascial  investment  of  the  pectorahs  major  and  deltoid  muscles- 
is  continued  across  the  ventral  margin  of  the  arm-pit  into  the  fascia  which  covers  the  coraco- 
brachialis  and  biceps  muscles  in  the  arm.  Similarly,  dorsally,  the  fascia  Covering  the  latissimus 
dorsi  and  teres  major  is  continued  over  the  arm-pit  into  that  covering  the  long  head  of  the  triceps 
in  the  arm.  The  ventral  is  connected  with  the  dorsal  fascia  by  a  thin  membrane  which  is 
adherent  to  the  connective  tissue  filling  the  axillary  space  and  to  the  subcutaneous  tissue. 
On  the  trunk  this  membrane,  the  fascia  axillaris,  becomes  fused  below  the  axillary  fossa  with 
the  fascia  of  the  serratus  anterior  (magnus).  In  the  arm  it  becomes  fused  with  the  fascia  over 
the  biceps  muscle.  Owing  to  its  adherence  to  the  skin  and  the  connective  tissue  of  the  axillary 
fossa,  investigators  have  dissected  out  and  figured  the  axillary  fascia  in  different  ways. 


MUSCLES 

The  pectoralis  major  (fig.  360). — Origin. — (1)  From  the  medial  half  of  the  clavicle;  (2) 
from  the  side  and  front  of  the  sternum  as  far  as  the  sixth  costal  cartilage;  (3)  from  the  front  of 
the  cartilages  of  the  second  to  the  sixth  ribs;  and  (4)  from  the  upper  part  of  the  aponeurosis  of 
the  external  oblique  where  this  extends  over  the  rectus  abdominis  muscle.  The  costal  origin 
may  in  part  take  place  from  the  osseous  extremities  of  the  sixth  and  seventh  ribs. 

Insertion. — Crest  of  the  greater  tubercle  (outer  lip  of  the  bicipital  groove)  of  the  humerus 
from  the  tubercle  to  the  insertion  of  the  deltoid  (fig.  174).  Some  of  the  tendon  fibres  are  also 
continued  into  the  tendon  of  the  deltoid  and  adjacent  fibrous  septa  and  into  the  fibrous  lining 
of  the  intertubercular  sulcus. 

Structure. — The  muscle  is  divisible  into  a  series  of  overlapping  layers  spread  out  hke  a  fan. 
Of  these,  the  clavicular  portion  forms  the  most  cranial  and  superficial  layer,  and  the  portion  of 
the  muscle  springing  from  the  aponeurosis  of  the  external  oblique,  the  most  caudal  and  deepest 
layer.     This  last  layer  has  a  special  tendon,  while  the  other  layers  are  inserted  into  a  combined 


SUBCLAVIUS 


373 


tendon  lying  ventral  to  this.  The  two  tendons  are  continuous  at  their  distal  margins.  (W.  H. 
Lewis.) 

Neroe-supply. — From  the  external  and  internal  anterior  thoracic  nerves,  branches  of  which 
enter  the  sterno-costal  portion  of  the  muscle  about  midway  between  the  tendons  of  origin 
and  insertion,  and  the  clavicular  portion  in  the  proximal  third.  The  nerve  fibres  are  derived 
from  the  (fifth),  si.xth,  seventh  and  eighth  cervical  and  first  thoracic  nerves. 

Action. — With  the  thorax  fixed,  the  muscle  adducts  and  flexes  the  arm  and  rotates  it  medial- 
ward.  The  clavicular  portion  draws  the  arm  forward,  upward,  and  medialward;  the  sterno- 
costal portion  draws  the  arm  downward,  medialward,  and  forward.  When  the  arm  is  pendent, 
the  upper  portion  elevates,  the  lower  depresses,  the  shoulder.  With  the  arm  fixed,  the  muscle 
draws  the  chest  upward  toward  it.     It  is  of  value  in  forced  inspii'ation. 

Relations. — It  lies  over  the  coracoid  process,  the  subclavius,  pectoralis  minor,  intercostal, 
and  serratus  anterior  (magnus)  muscles,  the  coraco-clavicular  (costo-coracoid)  fascia,  and  the 
thoraco-aoromial  vessels.  It  forms  the  main  part  of  the  ventral  wall  of  the  axillary  fossa,  and 
laterally  it  enters  into  relation  with  the  deltoid,  biceps,  and  coraco-brachialis  muscles. 

Variations. — In  considering  variations  the  muscle  may  be  looked  upon  as  composed  of 
four  portions — a  clavicular,  a  sternal,  a  costal,  and  an  abdominal,  the  last  being  that  portion 
which  arises  from  the  aponeurosis  of  the  external  obhque.  These  portions  vary  in  the  extent 
of  their  attachments  and  in  the  degree  of  separation  which  they  present.  The  abdominal  por- 
tion may  extend  to  the  umbilicus.  Huntington  considers  this  portion  a  derivative  of  the  pan- 
nicular  muscle  of  the  lower  mammals.  On  the  sternum  the  muscles  of  the  two  sides  may  de- 
cussate across  the  middle  line.  The  sterno-costa!  portions  of  the  muscle  are  more  frequently 
deficient  or  missing  than  the  clavicular,  but  in  rare  cases  the  entire  muscle  is  absent.  The 
clavicular  portion  of  the  muscle  may  be  fused  with  the  deltoid.  The  sterno-costal  may  extend 
laterally  to  the  latissimus  dorsi.  There  may  be  an  intimate  fusion  of  the  abdominal  portion 
with  the  rectus  abdominis  or  the  external  oblique.  Sometimes  a  slip  may  run  from  the  pec- 
toralis major  to  the  biceps,  the  pectoralis  minor,  coracoid  process,  capsule  of  the  joint,  or 
brachial  fascia. 

The  pectoralis  minor  (fig.  388). — Origin. — By  aponeurotic  slips  from  the  second,  third, 
fourth,  and  fifth  ribs  near  the  costal  cartilages. 


Fig.  361. — The  Subclavius  and  the  Upper  Portion  op  the  Serratus  Anterior. 


Serratus  anterior 


Structure  and  insertion. — The  fibre-bundles  converge  upward  and  outward  to  a  flattened 
tendon  which  is  attached  to  the  medial  border  and  upper  surface  of  the  coracoid  process  of 
the  scapula. 

Nerve-supply. — From  the  internal  anterior  thoracic  nerve  which  enters  the  upper  part  of 
the  middle  third  of  the  deep  surface  by  several  branches.  Some  of  the  branches  extend  through 
to  the  pectoralis  major.     The  nerve  fibres  arise  from  the  seventh  and  eighth  cervical  nerves. 

Action. — When  the  thorax  is  fixed,  the  pectoraUs  minor  pulls  the  scapula  forward,  the 
lateral  angle  of  the  bone  downward,  and  the  inferior  angle  dorsalward  and  upward.  When 
the  scapula  is  fixed,  the  muscle  aids  in  forced  inspiration. 

Relations. — It  is  covered  by  the  pectorahs  major.  Near  its  insertion  the  fibrous  investment 
of  the  chief  nerves  and  vessels  of  the  arm  is  adherent  to  its  enveloping  fascia. 

Variations. — The  origin  may  extend  to  the  sixth  rib  or  may  be  reduced  to  one  or  two  ribs. 
In  the  primates  below  man  the  insertion  of  the  muscle  takes  place  normally  into  the  humerus. 
In  man  its  insertion  may  be  continued  (in  more  than  15  per  cent,  of  bodies — Wood)  over  the 
coracoid  process  to  the  coraco-acromial  or  coraco-humeral  ligaments,  to  the  tendon  of  the  sub- 
scapularis  muscle,  or  to  the  great  tubercle  of  the  humerus.  It  may  be  divided  into  two  super- 
imposed fasciculi.  Fasciculi  may  extend  from  the  muscle  to  the  subclavius  or  the  pectoralis 
major. 

The  subclavius  (fig.  361). — Origin. — From  a  flat  tendon  attached  to  the  fii-st  rib  and  its 
cartilage  near  their  junction. 

Structure  and  insertion. — The  fibre-bundles  arise  in  a  penniform  manner  from  the  tendon 
of  origin  which  extends  for  some  distance  along  the  lower  border  of  the  muscle.  They  are 
inserted  in  a  groove  which  lies  on  the  lower  sm'face  of  the  clavicle  between  the  costal  tuberosity 
and  the  coracoid  tuberosity.  The  medial  fibre-bundles  are  inserted  directly,  the  lateral  by  a 
strong  tendon. 

Nerve-supply. — By  a  branch  which  arises  usually  from  the  fifth  or  fifth  and  sixth  cervical 
nerves  and  enters  the  middle  of  the  back  part  of  the  muscle. 

Action. — When  the  first  rib  is  fixed,  the  subclavius  depresses  the  clavicle  and  the  point  of 


374  THE  MUSCULATURE 

the  shoulder.  When  the  clavicle  is  fixed,  the  muscle  aids  in  forced  inspiration.  It  also  serves 
to  keep  the  clavicle  against  the  sternum. 

Relations. — It  is  concealed  by  the  clavicle  and  peotorahs  major  muscle.  Behind  it  lie  the 
subclavian  vessels  and  the  brachial  plexus. 

Variations. — It  may  be  replaced  by  a  ligament  or  by  a  peotoralis  minimus  muscle  (see  below). 
It  may  be  doubled  or  may  be  inserted  into  the  coracoid  process,  ooraco-aoromial  hgament,  the 
acromion,  or  the  humerus.  The  subclavius  posticus  arises  near  the  subolavius,  passes  backward 
over  the  subclavian  vessels  and  brachial  plexus  and  is  inserted  into  the  cranial  margin  of  the 
scapula  near  the  base  of  the  coracoid  process. 

Abnormal  Muscles  of  the  Pectoral  Group 

The  following  muscles  are  usually  innervated  by  the  anterior  thoracic  nerves  and  are 
probably  generally  abnormal  derivatives  of  the  pectoral  mass.  Frequently  they  represent 
muscles  normally  found  in  lower  mammals. 

The  sternalis. — A  flat  muscle  somewhat  frequently  seen  on  the  surface  of  the  pectoralis 
major,  usually  nearly  parallel  to  the  sternum.  It  arises  from  the  sheath  of  the  rectus  and  from 
some  of  the  costal  cartilages  (third  to  seventh)  and  terminates  on  the  sterno-oleido-mastoid, 
on  the  sternum,  or  on  the  fascia  covering  the  pectoraUs  major.  When  present  on  both  sides, 
the  two  muscles  may  be  fused  across  the  sternum.  This  muscle  is  found  in  4  per  cent,  of 
normal  individuals  and  48  per  cent,  of  anencephalic  monsters.  (Eisler.)  Rarely,  corresponding 
muscle  slips  have  been  found  innervated  by  the  intercostal  nerves.  These  probably  represent 
remains  of  a  thoracic  'rectus'  muscle. 

The  pectoro-dorsalis  (axillary  arch). — This  muscle  in  its  most  complete  form  extends  from 
the  tendon  of  the  pectoralis  major  over  the  axillary  fossa  to  the  tendon  of  the  latissimus  dorsi, 
to  the  fascia  covering  the  latissimus  dorsi,  to  the  teres  major  or  even  more  distaUy.  It  may, 
however,  be  more  or  less  fused  with  either  of  the  last  two  muscles  mentioned,  and  it  presents  a 
great  variety  of  forms.  It  may  extend  from  the  latissimus  dorsi  to  the  brachial  fascia  over  the 
coraco-brachialis  or  biceps,  to  the  long  tendon  of  the  biceps,  to  the  axillary  fascia,  to  the  axillary 
margin  of  the  pectoralis  minor,  or  to  the  coracoid  process,  etc.  It  is  found  in  about  7  per  cent, 
of  bodies.  (Le  Double.)  When  supplied  from  the  anterior  thoracic  nerves,  it  probably  rep- 
resents a  portion  of  the  thoraco-humeral  subcutaneous  (pannicular)  muscle  of  the  lower 
primates.  It  is  also  sometimes  supplied  by  the  medial  brachial  cutaneous  or  the  intercosto- 
brachial  (humeral)  nerve  and  frequently  is  partly  or  wholly  supplied  by  the  dorsal  thoracic  (long 
subscapular)  nerve.  The  part  of  the  muscle  supphed  by  the  dorsal  thoracic  nerve  is  probably 
derived  from  the  latissimus  dorsi  musculature. 

The  costo-coracoideus. — A  muscular  slip  which  arises  from  one  or  more  ribs  or  from  the 
aponeurosis  of  the  external  oblique  between  the  pectoralis  major  and  latissimus  dorsi  muscles, 
and  is  inserted  in  the  coracoid  process. 

The  chondro-humeralis  (epitrochlearis). — This  is  a  slip  which  springs  from  one  or  two  rib 
cartilages  or  from  the  thoraco-abdominal  fascia  beneath  the  pectoralis  major,  or  from  its  lower 
border  or  tendon,  and  extends  on  the  medial  side  of  the  arm  to  the  intertubercular  (bicipital) 
groove,  the  brachial  fascia,  the  intermuscular  septum,  or  the  medial  epicondyle.  It  is  found  in 
12  to  20  per  cent,  of  bodies  (Le  Double),  and  occurs  normally  in  many  of  the  lower  mammals. 

The  pectoralis  minimus  (sterno-chondro-scapularis). — From  the  cartilage  of  the  first  rib 
and  sternum  to  the  coracoid  process. 

The  sterno-clavicularis. — From  the  manubrium  of  the  sternum  to  the  clavicle  between  the 
pectoralis  major  and  the  coraco-clavicular  (costo-coracoid)  fascia.  In  2  per  cent,  to  3  per  cent 
of  bodies.     (Gruber.) 

The  scapulo-clavicularis. — From  the  coracoid  process  of  the  scapula  to  the  outer  third  of 
the  clavicle. 

The  infra-clavicularis. — From  above  the  clavicular  part  of  the  pectoralis  major  to  the 
fascia  over  the  deltoid. 

BURSiE 

B.  m.  pectoralis  majoris. — Between  the  tendon  of  insertion  of  the  pectoralis  major  and 
the  long  head  of  the  biceps.     Frequent. 

C.  MUSCULATURE  OF  THE  ARM 

(Figs.  355,  356,  362,  363,  364,  365,  367,  370,  372) 

The  muscles  included  in  this  section  are  the  triceps  and  anconeus,  coraco- 
brachialis,  biceps,  and  brachialis.  The  triceps  and  anconeus  (fig.  363)  constitute 
a  mass  of  musculature  extending  along  the  back  of  tlie  arm  from  the  scapula  and 
humerus  to  the  olecranon  of  the  ulna.  The  coraco-brachialis,  biceps,  and  brachialis 
(figs.  364,  365)  constitute  a  similar  mass  of  musculature  extending  along  the  front 
of  the  arm  from  the  scapula  and  the  humerus  to  the  humerus,  and  to  the  radius 
and  ulna  near  the  elbow.  In  the  upper  half  of  the  arm  the  two  groups  are 
separated  on  the  lateral  side  of  the  arm  by  the  deltoid,  pectoralis  major,  teres 
minor,  supra-  and  infraspinatus  muscles,  and  by  the  greater  tubercle  of  the 
humerus.     On  the  medial  side  they  are  separated  the  by  chief  nerves  and  blood- 


MUSCLES  OF  THE  ARM 


375 


Fig.  362,  A-D. — Transverse  Sections  through  the  Left  Arm  in  the  Regions  shown  in 

THE  Diagram. 
o  and  6  in  the  diagram  indicate  the  regions  through  which  pass  sections  A  and  B,  fig.  351 

(p.  352);  a'  and  b',  the  regions  through  which  pass  sections  A  and  B,  fig.  367  (p.  366);  and 

a"  the  region  thi-ough  which  passes  section  A,  fig.  366  (p.  385). 

1.  Arteria  brachialis.  2.  Bursa  subcutanea  olecrani.  3.  Fascia  brachiahs.  4.  Humerus.  5. 
Musculus  anconeus.  6.  M.  biceps — a,  long  head;  b,  short  head;  c,  tendon  of  insertion. 
7.  M.  brachiahs.  8.  M.  brachio-radialis.  9.  M.  coraco-brachialis.  10.  M.  deltoideus. 
11.  M.  e.xtensor  carpi  radiahs  brevis.  12.  M.  extensor  carpi  radialis  longus.  13  M. 
extensor  digitorum  communis.  14.  M.  flexor  carpi  radialis.  15.  M.  flexor  carpi  ulnaris..  16. 
M.  flexor  digitorum  subhmis.  17.  M.  flexor  digitorum  profundus.  18.  M.  palmaris 
longus.  19.  M.  pronator  teres.  20.  M.  triceps — a,  lateral  head;  b,  long  head;  c,  medial 
head.  21a.  N.  cutaneus  antibrachii  medialis  (internal  cutaneous).  216.  N.  cutaneus 
antibrachii  dorsalis.  22.  N.  musculo-cutaneus.  23.  N.  medianus.  24.  N.  radialis^a, 
muscular  branch.  25.  N.  ulnaris.  26.  Lymphatic  gland.  27.  Olecranon.  28.  Septum 
intermusculare  laterale.  29.  Septum  intermusculare^mediale.  30.  Vena  cephalica.  31. 
V.  basilica.     32.  Vv.  brachiales. 


9   2,1''  23  32.2,5        24°- 


376 


THE  MUSCULATURE 


MUSCLES  OF  THE  ARM  377 

vessels  of  the  arm  and  by  the  tendons  of  the  latissimus  dorsi,  teres  major,  and 
subscapularis  muscles.  In  the  distal  half  of  the  arm  they  are  separated  medially 
by  the  medial  intermuscular  septum  (described  below)  and  by  the  medial  epicon- 
dyle  and  the  ulno-volar  group  of  muscles  of  the  forearm.  On  the  lateral  side 
of  the  arm  they  are  separated  by  the  lateral  intermuscular  septum,  by  the 
lateral  epicondyle,  and  by  the  brachio-radialis  and  the  extensor  muscles  of  the 
forearm  which  take  origin  from  the  lateral  epicondyle. 


FASCIA 

The  fasciae  and  the  general  relations  of  the  muscles  of  the  arm  are  shown  in  the  cross- 
sections  in  fig.  362. 

The  tela  subcutanea  of  the  arm  is  fairly  well  developed  and  contains  a  considerable  amount 
of  fat,  especially  near  the  shoulder.  It  is  but  loosely  bound  to  the  muscle  fascia,  except  near 
the  insertion  of  the  deltoid,  where  the  union  may  be  more  intimate. 

Bursse. — B.  subcutanea  epicondyli  lateralis. — Between  the  lateral  epicondyle  and  the  skin. 
Rare.  B.  subcutanea  epicondyli  medialis. — Between  the  medial  epicondyle  and  the  skin. 
Inconstant.  B.  subcutanea  olecrani. — Between  the  olecranon  process  of  the  ulna  and  the 
skin.     Nearly  constant. 

The  brachial  fascia  forms  a  cylindrical  sheath  about  the  muscles  of  the  arm.  It  contains 
circular  and  longitudinal  fibres,  the  former  being  the  better  developed.  The  fascia  is  strong 
over  the  dorsal  muscles,  especially  near  the  two  epicondyles  of  the  humerus.  Proximally  the 
fascia  of  the  arm  is  continued  into  the  axillary  fascia  and  into  the  fascial  investment  of  the  pec- 
toralis  major,  deltoid,  and  latissimus  dorsi  muscles;  distally  it  is  continued  into  the  fascial 
investment  of  the  forearm.  It  is  intimately  bound  to  the  epicondyles  and  to  the  dorsal  surface 
of  the  olecranon.  It  is  separated  by  loose  areolar  tissue  from  the  beUies  of  the  muscles  which  it 
covers.  From  the  tendons  of  the  deltoid,  pectoralis  major,  teres  major,  and  latissimus  dorsi 
muscles,  however,  fibrous  bundles  are  continued  into  the  brachial  fascia.  There  are  a  number 
of  orifices  in  the  fascia  for  the  passage  of  nerves  and  blood-vessels.  Of  these,  the  largest  is 
that  for  the  basilic  vein  and  two  or  three  large  branches  of  the  medial  antibrachial  (internal) 
cutaneous  nerve.  This  lies  on  the  ulnar  margin  of  the  arm  in  the  lower  third.  On  the  radial 
margin  lie  the  cephalic  vein  in  a  double  fold  of  the  fascia,  orifices  for  branches  of  the  musculo- 
cutaneous nerve,  and  more  dorsally  orifices  for  branches  of  the  radial.  From  the  fascia  septa 
descend  between  the  muscles  which  it  invests.  Of  these  septa,  the  most  important  are  the  medial 
and  lateral  intermuscular  septa,  which  separate  the  dorsal  group  of  muscles  from  the  ventral 
in  the  distal  half  of  the  arm.  The  medial  intermuscular  septum  is  the  stronger.  It  is  attached 
to  the  medial  epicondyle  and  to  the  medial  margin  of  the  humerus  proximal  to  this,  It  is 
continued  proximally  into  the  tendon  of  insertion  of  the  coraco-brachialis  and  the  investing 
fascia  of  this  muscle.  Into  it  longitudinal  bundles  of  fibres  descend  from  the  tendon.  It 
separates  the  brachiaUs  and  pronator  teres  muscles  from  the  medial  head  of  the  triceps.  The 
lateral  intermuscular  septum  is  attached  to  the  lateral  epicondyle  and  to  the  lateral  margin 
of  the  humerus.  It  is  continued  proximally  into  the  dorsal  surface  of  the  tendon  of  insertion 
of  the  deltoid  muscle,  and  into  the  septa  between  the  deltoid  and  the  triceps.  It  separates 
the  triceps  from  the  brachialis  in  the  third  quarter  of  the  arm  and  from  the  brachio-radi- 
alis and  extensor  carpi  radialis  longus  in  the  distal  quarter.  The  median  nerve  and  brachial 
vessels  lie  in  front  of  the  medial  septum.  The  ulnar  nerve  and  the  superior  ulnar  collateral 
(inferior  profunda)  artery  are  bound  to  its  dorsal  surface. 


MUSCLES 
1.  Dorsal  or  Extensor  Group 

Two  muscles  are  included  in  this  group,  the  triceps  brachii  and  the  anconeus. 
The  triceps  is  a  complex  muscle  in  which  proximally  three  heads,  a  long  or  scapu- 
lar, a  lateral  humeral,  and  a  medial  humeral,  may  be  distinguished.  The  long 
head  arises  from  the  infraglenoid  tuberosity  of  the  scapula,  the  lateral  head  from 
the  humerus  above  and  laterally  to  the  groove  for  the  radial  nerve  fmusculo- 
spiral  groove),  the  medial  head  from  the  lower  half  and  medial  margin  of  the 
posterior  surface  of  the  humerus.  Distally  these  heads  fuse  and  are  inserted 
by  a  common  tendon  into  the  olecranon  of  the  ulna.  The  anconeus  lies  chiefly 
in  the  forearm,  but  physiologically  and  morphologically  it  belongs  with  the  triceps, 
and  hence  is  described  in  connection  with  the  muscles  of  the  arm.  It  is  a  tri- 
angular muscle,  which  arises  from  the  lateral  epicondyle  and  is  inserted  into  the 
olecranon  and  adjacent  part  of  the  shaft  of  the  ulna.     Both  muscles  are  supplied 


378 


THE  MUSCULATURE 


by  branches  of  the  radial  (musculo-spiral)  nerve.     They  extend  the  forearm. 
The  long  head  is  also  an  adductor  of  the  arm. 

The  triceps,  variously  modified,  is  found  in  the  amphibia  and  all  higher  vertebrates.  The 
anconeus  is  found  in  the  prosimians  and  all  higher  forms.  The  triceps  muscle  is  homologous 
with  the  quadriceps  of  the  thigh.  The  long  head  is  equivalent  to  the  rectus  femoris.  The 
anconeus  is  not  represented  in  the  lower  limb. 

The  triceps  brachii  (figs.  355,  356,  363). — The  long  head  arises  from  the  infraglenoid  tuber- 
osity of  the  scapula  by  a  strong,  broad  tendon,  some  of  the  fibres  of  which  are  connected  with 
the  inferior  portion  of  the  capsule  of  the  shoulder-joint.  The  tendon  soon  divides  into  two 
lamellse,  which  extend  distally,  one  a  short  distance  on  the  deep  surface,  the  other  much  farther 

Fig.  363. — Dorsal  View  op  the  Scapular  Muscles  and  Triceps. 


Supraspinatus 


Infraspinatus 
Teres  minor 


Long  bead  of  triceps 


Lateral  head  of  triceps 


Medial  head  of  triceps 


on  the  superficial  surface  of  this  head.  The  parallel  fibre-bundles  which  arise  from  these 
lamellae  form  a  thick  muscle-baud  which  twists  upon  itself  so  that  the  ventral  surface  at  the 
origin  becomes  dorso-medial  at  the  insertion.  At  the  insertion  the  long  head  becomes  ap- 
plied to  an  aponeurosis  which  extends  upward  from  the  main  tendon  of  insertion  of  the  triceps. 
The  fibre-bundles  extend  for  some  distance  on  the  medial  side  of  this  tendon  and  terminate 
about  three-fourths  of  the  way  down  the  arm. 

'  The  lateral  head  has  a  tendinous  origin  from  the  superior  lateral  portion  of  the  posterior 
surface  of  the  humerus  along  a  line  extending  from  the  insertion  of  the  teres  minor  as  far  as  the 
groove  for  the  radial  (musoulo-spkal)  nerve,  and  from  the  aponeurotic  arch  formed  by  the 
lateral  intermuscular  septum  as  it  crosses  this  groove.  The  constituent  fibre-bundles  descend, 
the  superior  vertically,  the  inferior  obliquely,  to  be  inserted  on  the  dorsal  and  ventral  surfaces 
of  the  proximo-lateral  margin  of  the  common  tendon  of  insertion  of  the  triceps. 

The  medial  head  has  a  fleshy  origin  from  the  posterior  surface  of  the  humerus  below  the 
radial  (musculo-spiral)  groove  and  from  the  dorsal  surfaces  of  the  medial  and  lateral  intermus- 
cular septa.  The  greater  part  of  the  fibre-bundles  arising  from  this  extensive  area  are  inserted 
into  the  deep  surface  of  the  common  tendon,  but  some  extend  directly  to  the  olecranon  and  the 
articular  capsule  of  the  elbow.  The  slip  attached  to  the  capsule  is  sometimes  called  the 
subanconeus  muscle. 


FLEXORS  OF  THE  ARM  379 

Insertion. — The  tendon  of  insertion  of  the  triceps  forms  a  flat  band  covering  the  dorsal 
surface  of  the  distal  two-fifths  of  the  muscle.  It  also  extends  proximally  between  the  long  and 
lateral  heads  and  on  the  deep  surface  of  the  former.  This  tendon  is  inserted  into  the  olecranon 
and  laterally,  by  a  prolongation  over  the  anconeus,  into  the  dorsal  fascia  of  the  forearm. 

Neroe-supply. — From  the  radial  (musculo-spiral)  nerve.  The  branch  to  the  long  head  arises 
in  the  arm-pit  and  enters  that  margin  of  the  muscle  which  is  prolonged  down  from  the  lateral 
edge  of  the  tendon,  but  which,  because  of  the  torsion  of  the  muscle,  comes  to  he  on  the  medial 
side.  The  nerve  usually  enters  through  several  rami  about  the  middle  of  the  free  portion  of  the 
long  head.  Somewhat  more  distally  the  radial  nerve  gives  off  a  branch  that  enters,  by  two  or 
three  branches,  the  proximal  portion  of  the  medial  head.  A  similar  branch  is  given  to  the 
lateral  head  and  other  branches  are  given  to  the  lateral  and  medial  heads  from  that  portion  of 
the  radial  (musculo-spiral)  nerve  lying  in  the  radial  (musculo-spiral)  groove."  The  nerve  fibres 
arise  from  the  sixth,  seventh,  and  eighth  cervical  nerves. 

Relations. — Near  the  shoulder  the  triceps  is  covered  by  the  deltoid  muscle.  The  long  head 
passes  between  the  teres  major  and  teres  minor  muscles.  The  circumflex  (dorsal)  scapular 
vessels  here  pass  medial,  the  circumflex  humeral  vessels  and  the  axillary  (circumflex)  nerve 
lateral,  to  this  head.  More  distally  the  muscle  lies  beneath  the  brachial  fascia.  It  covers  the 
radial  groove  of  the  humerus,  in  which  run  the  radial  (musculo-spiral)  nerve  and  (superior)  pro- 
funda brachii  artery.  Ventro-lateral  to  the  muscle  he  the  deltoid,  brachialis,  brachio-radialis, 
and  extensor  carpi  radiaUs  muscles;  ventro-medial,  the  coraco-brachiahs,  biceps,  and  brachialis 
muscles. 

Action. — It  extends  the  forearm.  The  leverage  is  of  such  a  nature  that  force  is  sacrificed 
for  speed  of  movement.  The  long  head  of  the  triceps  also  serves  to  extend  and  to  adduct  the 
arm  and  to  hold  the  head  of  the  humerus  in  the  glenoid  cavity. 

Variations. — The  scapular  attachment  may  extend  for  a  considerable  distance  down  the 
axillary  border  of  the  scapula.  Each  of  the  heads  may  be  more  or  less  fused  with  neighbouring 
muscles.  Frequently  a  fourth  head  is  found.  This  may  arise  from  the  humerus,  from  the 
axillary  margin  of  the  scapula,  from  the  capsule  of  the  shoulder-joint,  from  the  coracoid  process, 
or  from  the  tendon  of  the  latissimus  dorsi. 

The  latissimo-condyloideus  (dorso-epitrochlearis).^This  muscle  is  found  in  about  5  per 
cent,  of  bodies.  When  well  developed,  it  extends  from  the  tendon  of  the  latissimus  dorsi  to  the 
brachial  fascia,  the  triceps  muscle,  the  shaft  of  the  humerus,  the  lateral  epicondyle,  the  olec- 
ranon, or  the  fascia  of  the  forearm.  It  is  innervated  by  a  branch  of  the  radial  (musculo-spiral) 
nerve.  It  is  a  muscle  normally  present  in  some  one  of  the  forms  above  mentioned  or  in  some 
similar  form,  in  a  large  number  of  the  inferior  mammals.  In  the  human  body  it  is  normally 
represented  by  a  fascial  slip  from  the  tendon  of  the  latissimus  to  the  long  head  of  the  triceps  or 
the  brachial  fascia. 

The  anconeus. — Origin. — By  a  short  narrow  tendon  from  the  distal  part  of  the  back  of  the 
lateral  epicondyle  and  the  adjacent  part  of  the  capsular  hgament  of  the  elbow-joint. 

Structure  and  insertion. — The  tendon  of  origin  is  prolonged  on  the  deep  surface  and  lateral 
border  of  the  muscle.  From  this  the  fibre-bundles  spread,  the  proximal  transversely,  the  more 
distal  obliquely,  to  be  inserted  into  the  radial  side  of  the  olecranon  and  an  adjacent  impres- 
sion on  the  shaft  of  the  ulna.  Its  superior  fibre-bundles  are  usually  continuous  with  those  of 
the  medial  head  of  the  triceps. 

Nerve-supply. — By  a  long  branch  which  arises  in  the  radial  (musculo-spiral)  groove  from  the 
radial  (musculo-spiral)  nerve,  passes  through  the  medial  head  of  the  triceps,  to  which  it  gives 
branches,  and  enters  the  proximal  border  of  the  anconeus.  The  nerve  fibres  arise  from  the 
seventh  and  eighth  cervical  nerves. 

Action. — It  aids  the  triceps  in  extending  the  forearm  and  draws  the  ulna  laterally  in  prona- 
tion of  the  hand. 

Relations. — The  muscle  hes  immediately  beneath  the  antibrachial  fascia.  It  extends  over 
the  head  of  the  supinator  (brevis)  and  the  elbow-joint  and  upper  radio-ulnar  joint. 

Variations. — The  extent  of  fusion  of  .the  muscle  with  the  medial  head  of  the  triceps  varies 
a  good  deal.  It  may  also  be  fused  with  thfe  extensor  carpi  ulnaris.  It  has  been  reported 
missing. 


P^P^*^  ^>> 


B.  intratendinea  olecrani. — Within  the  tendon  of  the='triceps  near  its  insertion.  JVIore 
frequent  than  the  following: —  -   ,' 

B.  subtendinea  olecrani. — Between  the  tendon  of  the  trffeopS;  and  the  olecranon  and  dorsal 
ligament  of  the  elbow-joint.     Inconstant. 

B.  epicondyli  medialis  dorsalis. — Between  the  medial  epicondyle,  the  edge  of  the  triceps, 
and  the  ulnar  nerve.     Rare.  jiC- 

B.  m.  anconei. — Between  the  tendon  of  origin  of  the  muscle  and  the  head  of  the  raditi^'* 
Frequent. 

2.  Ventral  or  Flexor  Group 

(Figs.  364,  365,  370,  372) 

The  muscles  of  this  group  are  the  coraco-brachialis,  the  biceps,  and  the  brachi- 
alis. The  coraco-brachialis  (fig.  365)  is  a  band-like  muscle  which  arises  from 
the  coracoid  process  and  is  inserted  into  the  middle  third  of  the  shaft  of  the 
humerus.  The  biceps  (fig.  364)  arises  by  two  heads:  a  short  head,  closely  as- 
sociated with  the  coraco-brachialis,  fi"om  the  coracoid  process;  a  long  head,  by  an 


380 


THE  MUSCULATURE 


extended  tendon,  from  the  supraglenoid  tuberosity  of  the  scapula.  The  fusiform 
belly  whicli  arises  from  the  fusion  of  these  two  heads  is  inserted  into  the  radius  and 
into  the  fascia  of  the  forearm.  The  brachialis  (fig.  365)  extends  under  cover  of 
the  biceps  from  the  lower  three-fifths  of  the  shaft  of  the  humerus  to  the  coronoid 
process  of  the  ulna.  The  muscles  of  this  group  are  supplied  by  the  musculo- 
cutaneous nerve.  The  brachialis  also  usually  receives  a  branch  from  the  radial 
nerve.  The  coraco-brachialis  and  short  head  of  the  biceps  flex  and  adduct  the 
arm  at  the  shoulder;  the  biceps  and  brachialis  flex  the  forearm  at  the  elbow.  The 
long  head  of  the  biceps  abducts  the  arm  at  the  shoulder. 


Fig.  364. — Superficial  Muscles  of  the  Front  of  the  Ahm. 


Pectoralis  minor 


Coraco-brachiali; 


Long  head  of  triceps 


Tendons    of    insertion    of  _  pectoralis 
major  and  deltoid 


Lateral  head  of  triceps 


Medial  head  of  triceps 


Semilunar  fascia 
(lacertus  fibrosus) 


Extensor  carpi  radialis  iongus 


Brachio-radialis 


The  muscles  of  this  group  are  found  in  most  of  the  hmbed  vertebrates.  In  many  of  the 
lower  forms  the  coraco-brachialis,  which  appears  farther  down  in  the  vertebrate  series  than  the 
biceps,  has  a  more  extensive  insertion  than  in  man.  It  may  extend  to  the  ulna  (lizards)  and 
may  be  subdivided  into  various  muscles  which  correspond  with  the  adductors  of  the  thigh.  The 
biceps,  the  place  of  which  is  taken  in  the  lower  vertebrates  by  a  coraco-radial  muscle,  in  most 
of  the  mammals  presents  two  heads,  the  more  lateral  of  which  is  attached  by  a  tendon  to  the 
scapula  above  the  shoulder-joint.  This  long  tendon  of  the  biceps  lies  primitively  outside  the 
capsule  of  the  shoulder-joint,  but  in  some  of  the  higher  mammals  has  come  to  lie  within  the 
capsule.  In  the  biceps  four  elements  mayberecogni.sed; — a  coraco-radial,  coraco-ulnar,  gleno- 
radial,  and  gleno-ulnar.  (Krause.)  The  development  of  these  elements  varies  in  different 
mammals 


CORA  CO-BRA  CHIALIS 


381 


The  coraco-brachialis  (fig.  365). — Origin. — (1)  By  a  short  tendon  from  the  tip  of  the  cora- 
coid  process  of  the  scapula  and  (2)  from  the  tendon  of  the  short  head  of  the  biceps. 

Insertion. — (1)  By  means  of  a  strong  tendon  into  the  medial  surface  of  the  humerus  im- 
mediately proximal  to  the  middle  of  the  shaft,  and  (2)  often  above  this  also  into  an  aponeurotic 
band  which  e.xtends  from  the  tendon  along  the  medial  margin  of  the  humerus,  arches  over  the 
tendons  of  the  latissimus  dorsi  and  teres  major,  and  is  attached  to  the  lesser  tubercle  of  the 
humerus.  When  the  attachment  to  the  tubercle  does  not  take  place,  the  band  becomes  closely 
applied  to  the  deep  surface  of  the  muscle. 

Structure. — From  the  tendons  of  origin,  which  are  usually  closely  associated,  the  fibre- 
bundles  take  an  oblique,  nearly  parallel,  course  and  are  attached  to  the  aponeurotic  band  above 


Fig.  365. — Deep  Muscle.?  of  the  Front  of  the  Arm. 


Pectoralis  minor 


Short  head  of  biceps 


Coraco-brachiahs 


Long  head  of  triceps 


Medial  head  of  triceps 


Medial  intermuscular  septi 


rLong  head  of  biceps 


— r~ — -Insertion  of  pectoralis  major 


Insertion  of  deltoid 


J-  Lateral  part  of  brachialis 


Insertion  of  biceps 


mentioned  and  to  both  surfaces  of  the  flat  tendon  of  insertion.  This  extends  high  into  the 
muscle.  The  belly  of  the  muscle  usually  shows  some  separation  into  a  superficial  and  a  deep 
portion,  between  which  runs  the  musculo-cutaneous  nerve.  When  this  separation  is  well 
marked,  the  tendon  of  origin  of  the  superior  fasciculus  may  be  distinct  from  that  of  the  inferior 
fasciculus  and  the  short  head  of  the  biceps,  and  the  tendon  of  insertion  may  give  a  separate 
lamina  to  each  fasciculus. 

Nerve-supply. — A  branch  of  the  musculo-cutaneous  nerve,  or  of  the  brachial  plexus  near 
the  origin  of  this  nerve,  enters  the  upper  third  of  the  medial  border  of  the  muscle,  and  passes 
across  the  constituent  fibre-bundles  about  midway  between  their  attachments.  The  nerve 
fibres  arise  from  the  sixth  and  seventh  cervical  nerves. 

Action. — Adducts  and  flexes  the  arm  at  the  shoulder  and  helps  to  keep  the  head  of  the 
humerus  in  the  glenoid  fossa.  When  the  arm  has  been  rotated  lateralward,  it  acts  as  a  medial 
rotator. 

Relations. — The  coraco-brachialis  is  largely  covered  by  the  deltoid  and  pectoralis  major 
muscles.     Below  the  inferior  border  of  the  latter  it  becomes  superficial.     Near  its  origin  it  lies 


382  THE  MUSCULATURE 

between  the  pectoralis  minor  and  the  subscapularis  muscles.  More  distally  it  lies  medial  to  the 
humerus  and  in  front  of  the  chief  brachial  vessels  and  nerves.  The  musculo-cutaneous  nerve 
usually  runs  through  it. 

Variations. — The  humeral  insertion  of  the  muscle  varies  considerably.  According  to  Wood, 
the  coraco-braohialis  consists  primitively  of  three  parts,  which  arise  from  the  coraooid  process 
and  are  inserted  respectively  into  the  upper,  the  middle,  and  the  distal  part  of  the  humerus 
along  the  medial  side.  The  superior  division  is  most  deeply,  the  inferior  the  most  superficially, 
placed.  In  man  the  muscle  is  composed  of  parts  of  the  middle  and  inferior  divisions.  The 
inferior  division  may  be  completely  developed  as  far  as  the  medial  epicondyle.  The  superior 
division  of  the  muscle  is  occasionally  found.  Slips  from  the  coraco-brachialis  to  the  brachiahs 
have  been  seen.     Complete  absence  of  the  muscle  has  been  recorded. 

The  biceps  brachii  (figs.  364,  370). — The  short  head  arises  by  a  flat  tendon  closely  asso- 
ciated with  that  of  the  coraco-brachialis  from  the  coracoid  process.  From  the  dorso-medial 
surface  of  this  tendon  the  fibre-bundles  descend  nearly  vertically,  though  increasing  in  num- 
ber, toward  their  attachment  to  the  tendon  of  insertion.  The  fibre-bundles  which  arise  highest 
on  the  tendon  of  origin  are  inserted  highest  on  the  tendon  of  insertion,  while  those  which  have 
the  lowest  origin  have  the  lowest  insertion. 

The  long  head  arises  from  the  supraglenoid  tuberosity  and  from  the  glenoid  ligament 
by  a  long  tendon  (9  cm.)  bifurcated  at  its  origin.  The  tendon  at  first  passes  over  the  head 
of  the^humerus  within  the  capsule  of  the  joint,  and  then  passes  into  the  intertubercular  (bicipital) 
groove,  which  is  covered  by  the  capsule  of  the  joint  and  an  expansion  from  the  tendon  of  the 
pectoralis  major.  To  this  point  the  tendon  is  surrounded  by  the  synovial  membrane  of  the 
joint.  After  emerging  from  this  the  tendon  slowly  expands  and  from  its  dorsal  concave  surface 
arise  fibre-bundles  which,  increasing  in  number,  extend,  somewhat  obliquely,  toward  the  ten- 
don of  insertion.  As  in  case  of  the  short  head,  here  also  the  fibre-bundles  which  arise  highest  on 
the  tendon  of  origin  have  the  highest  insertion. 

Insertion. — The  tendon  of  insertion  begins  usually  in  the  distal  quarter  of  the  arm  as  a 
vertical  septum  between  the  two  heads  of  the  muscle.  More  distally  this  broadens  out  on  each 
side  into  a  flattened  aponeurosis.  The  fibre-bundles  are  inserted  into  the  sides  of  the  septum 
and  on  each  surface  of  the  aponeurosis — those  of  the  long  head  chiefly  on  the  deep  surface,  those 
of  the  short  head  chiefly  on  the  superficial  surface.  The  aponeurosis  is  continued  into  a  strong, 
flattened  tendon  which  descends  between  the  brachio-radialis  and  pronator  teres  muscles  to  be 
inserted  on  the  dorsal  half  of  the  bicipital  tuberosity  of  the  radius.  From  the  medial  border 
of  the  tendon  an  aponeurotic  expansion,  the  lacertus  fibrosus  (semilunar  fascia),  is  continued 
into  the  fascia  of  the  ulnar  side  of  the  forearm. 

Nerve-supply. — By  a  branch  from  the  musculo-cutaneous  nerve  for  each  head.  These 
branches  may  be  bound  in  a  common  trunk  for  some  distance.  They  enter  the  deep  surface  of 
the  muscle  in  the  proximal  part  of  the  middle  third  of  each  belly  often  by  several  rami.  Usually 
there  is  a  distinct  intramuscular  fissure  for  the  reception  of  the  branches  to  each  head  and  the 
blood-vessels  which  accompany  them.  The  nerve  fibres  come  from  the  fifth  and  sixth  cervical 
nerves. 

Action. — It  is  a  chief  flexor  of  the  arm  at  the  elbow  and  is  also  a  supinator  of  the  forearm. 
This  last  action  is  most  marked  when  the  forearm  is  flexed  and  pronated.  Both  heads  are 
flexors  and  medial  rotators  of  the  arm  at  the  shoulder.  The  long  head  is  an  abductor  and 
so  also  is  the  short  head  when  the  arm  is  greatly  abducted,  otherwise  the  short  head  is  an 
adductor. 

Relations. — The  tendons  of  origin  are  concealed  by  the  pectoralis  major  and  deltoid  muscles. 
Beyond  this  the  muscle  is  covered  by  the  fascia  brachii.  In  the  lower  part  of  the  ai-m  it  lies 
upon  the  brachialis  muscle.  Upon  the  medial  margin  lie  the  coraco-brachialis  muscle,  the 
brachial  vessels,  and  the  median  nerve. 

Variations. — Variations  are  frequent.  The  whole  muscle  or  either  head  may  be  missing, 
but  such  cases  are  rare.  The  long  head  may  extend  only  to  the  bicipital  groove.  Frequently 
the  muscle  is  partially  divided  into  the  four  primitive  portions  mentioned  above.  The  two 
heads  may  be  separate  from  origin  to  insertion.  There  may  be  an  accessory  head  (1  in  10 
subjects — Le  Double)  which  arises  from  the  coracoid  process,  the  capsule  of  the  joint,  the  tendon 
of  the  pectoralis  major,  or  the  shaft  of  the  humerus  near  the  insertion  of  the  coraco-brachialis. 
In  most  instances  the  origin  takes  place  above  the  origin  of  the  brachialis  from  the  humerus. 
Sometimes  several  accessory  heads  are  seen.  Marked  vai-iation  of  insertion  is  less  frequent, 
but  occasionally  a  supernumerary  slip  may  go  to  the  medial  intermuscular  septum  or  the  medial 
epicondyle.  The  fusion  of  the  biceps  with  neighbouring  muscles  (pectoralis  major  and  minor, 
coraco-brachialis,  brachialis,  palmaris  longus,  pronator  teres,  brachio-radialis)  by  means  of 
tendinous  or  muscular  slips  has  been  frequently  reported. 

The  brachialis  (fig.  365). — Origin. — (1)  From  the  distal  three-fifths  of  the  front  of  the 
humerus,  (2)  from  the  medial  intermuscular  septum,  and  (3)  from  the  lateral  intermuscular 
septum  proximal  to  the  heads  of  the  brachio-radialis  and  extensor  carpi  radiaUs  longus.  Proxi- 
mally  it  sends  up  a  pointed  process  on  the  lateral  side  of  the  insertion  of  the  deltoid  and  another 
between  the  insertions  of  the  deltoid  and  the  coraco-braohiahs.  Distally  the  area  of  origin 
stops  a  little  above  the  capitulum  and  the  trochlea. 

Structure  and  Insertion. — The  fibre-bundles  arise  directly  from  this  area  of  origin,  except 
near  the  insertion  of  the  deltoid  and  on  the  medial  margin,  where  tendinous  bands  are  developed. 
The  fibre-bundles  descend,  the  middle  vertically,  the  medial  obliquely  lateralward,  the  lateral 
still  more  obliquely  medialward.  The  tendon  of  insertion  appears  on  the  dorsal  side  of  the 
lateral  edge  of  the  muscle  in  its  lower  fourth.  Continuous  with  this  stronger  lateral  portion  of 
the  tendon  more  distally  a  thinner  band  appears  upon  the  ventral  surface  of  the  muscle  above 
the  joint.  The  tendon  becomes  thick  as  it  passes  distally,  is  closely  united  to  the  capsule  of  the 
elbow-joint,  and  is  attached  to  the  ulnar  tuberosity.  In  addition  to  the  main  tendon,  some  of 
the  deeper  fibre-bundles  of  the  muscle  and  some  of  those  coming  from  the  lateral  intermuscular 
septum  are  attached  by  short  tendinous  bands  to  the  coronoid  process. 


MUSCLES  OF  FOREARM  AND  HAND  383 

Neri/e-supply. — From  the  museulo-cutaneous  nerve  by  a  branch  which  enters  the  ventral 
surface  of  the  muscle  near  the  junction  of  the  upper  and  middle  thirds  of  the  medial  border. 
In  addition  the  radial  (musculo-spiral)  nerve  usually  sends  a  small  branch  into  the  distal  lateral 
portion  of  the  muscle.  A  branch  from  the  median  nerve  frequently  supplies  the  medial  side  of 
the  muscle  near  the  elbow-joint  (Frohse). 

Action. — To  flex  the  forearm. 

Relations. — It  lies  behind  the  biceps,  on  each  side  of  which  it  projects.  The  distal  lateral 
portion  of  the  muscle  is  grooved  by  the  brachio-radialis,  which  here  is  closely  apphed  to  it. 
The  radial  (musculo-spiral)  nerve  runs  between  these  two  muscles.  On  the  medial  side  run  the 
brachial  vessels  and  median  nerve. 

Variations. — It  may  be  divided  into  two  distinct  heads  continuous  with  the  projections  on 
each  side  of  the  deltoid  tuJjerosity.  A  great  number  of  supernumerary  slips  have  been  recorded. 
These  may  be  attached  to  the  radius,  ulna,  fascia  of  the  forearm,  capsule  of  the  joint,  brachio- 
radialis,  and  extensor  carpi  radialis  muscles.  It  may  be  partially  fused  with  neighbouring 
muscles.     It  has  also  been  reported  absent. 

BURS^ 

B.  m.  coraco-brachialis. — Between  the  subscapularis  muscle,  the  tendon  of  the  coraco- 
brachialis,  and  the  coracoid  process.     Frequent. 

B.  bicipito-radialis. — Between  the  ventral  half  of  the  radial  tuberosity  and  the  tendon  of 
the  biceps.     Constant. 

B.  cubitalis  interossea. — Between  the  tendon  of  the  biceps  and  the  ulna  and  the  neighbour- 
ing muscles.     Frequent. 

D.  MUSCULATURE  OF  THE  FOREARM  AND  HAND 

(Figs.  366-379) 

The  muscles  of  the  forearm  arise  in  part  from  the  humerus,  in  part  from  the 
radius  and  ulna.  Their  bellies  lie  chiefly  in  the  proximal  half  of  the  forearm. 
They  are  divisible  into  two  groups: — a  radio-dorsal,  composed  of  extensors  of  the 
hand  and  fingers  and  supinators  of  the  forearm;  and  an  ulno-volar,  composed  of 
flexors  of  the  hand  and  fingers  and  pronators  of  the  forearm.  The  brachio- 
radialis,  which  belongs  morphologically  with  the  former  group,  is  physiologically 
a  flexor  of  the  forearm. 

The  two  groups  are  separated  on  the  medial  side  of  the  back  of  the  forearm 
by  the  dorsal  margin  of  the  ulna  (figs.  366,  369).  Ventrally  they  are  separated 
by  the  insertions  of  the  biceps  and  brachialis  and  by  an  intermuscular  septum 
(figs.  366,  370). 

In  the  hand,  in  addition  to  the  tendons  of  the  muscles  of  the  forearm  mentioned 
above  (fig.  376),  there  are  several  sets  of  intrinsic  muscles.  About  the  meta- 
carpal of  the  thumb  (figs.  375,  376,  377)  is  grouped  a  set  of  muscles  which  arise 
from  the  carpus  and  metacarpus  and  are  inserted  into  the  metacarpal  and  first 
phalanx  of  the  thumb.  A  similar  set  of  muscles  is  grouped  about  the  metacarpal 
of  the  little  finger  (figs.  375,  376).  These  sets  of  muscles  give  rise  respectively 
to  the  thenar  and  hypothenar  eminences.  Between  the  metacarpals  lies  a  series 
of  dorsal  and  palmar  interosseous  muscles  (figs.  377,  378,  379)  which  are  inserted 
into  the  first  row  of  phalanges  and  into  the  extensor  tendons.  From  the  tendons 
of  the  deep  flexor  of  the  fingers  a  series  of  lumbrical  muscles  passes  to  the  radial 
side  of  the  extensor  tendons  (figs.  373,  375).  These  various  muscles  abduct, 
adduct,  flex,  and  extend  the  digits.  In  addition  to  these  deeper  skeletal  muscles 
of  the  hand  there  is  a  subcutaneous  muscle  over  the  hypothenar  eminence  (fig. 
375).  Of  the  muscles  of  the  hand,  all  are  supplied  by  the  ulnar  nerve  except 
most  of  those  of  the  thumb  and  the  two  more  radial  lumbricals,  which  are 
supplied  by  the  median  nerve. 

An  arrangement  of  the  muscles  of  the  forearm  in  which  the  dorsal  extensor-supinator  mus- 
culture  extends  proximally  on  the  radial  side  of  the  arm  to  the  distal  extremity  of  the  humerus, 
and  the  volar  flexor-pronator  musculature  similarly  on  the  ulnar  side,  is  characteristic  of  all 
limbed  vertebrates  and  is  associated  with  the  pronate  position  of  the  forehmb  characteristic  of 
quadrupeds.  In  ampliibia  and  reptiles  the  musculature  terminates  distaUy  on  the  carpus  and 
in  the  aponeuroses  of  the  hand.  In  the  higher  forms  special  tendons  are  differentiated  for  those 
muscles  of  the  forearm  which  act  on  the  fingers.  On  the  back  of  the  hand  in  many  vertebrates 
short  extensor  muscles  are  found  running  from  the  carpus  to  the  phalanges.  On  the  volar 
surface  a  complex  musculature  is  found  in  all  forms  which  have  freely  movable  fingers.  In 
animals  which  walk  on  the  ends  of  the  fingers,  especially  in  the  hoofed  animals,  the  intrinsic 
musculature  of  the  hand  is  greatly  reduced.     The  phylogenetic  development  of  the  muscles  of 


384  THE  MUSCULATURE 

the  forearm  and  hand  is  too  complex  a  subject  to  be  briefly  summarised.  The  phylogeny  of  the 
forearm  flexors  and  the  palmar  musculature  has  been  studied  by  McMurrich.  In  his  papers  a 
summary  of  the  hterature  on  the  subject  may  be  found. 

FASCIA 

The  fasciae  and  the  general  relations  of  the  musculature  of  the  forearm  and  hand  may  be 
followed  in  the  cross-sections  fig.  366. 

The  tela  subcutanea  contains  a  moderate  amount  of  fat  in  the  upper  part  of  the  forearm. 
This  grows  less  in  amount  as  the  wrist  is  approached.  On  the  back  of  the  hand  it  contains 
little  fat.  In  the  palm  and  on  the  volar  surface  of  the  fingers  a  moderate  amount  of  fat  is 
embedded  between  dense  vertical  bundles  of  fibres  which  unite  the  skin  to  the  fascia.  Except 
on  the  volar  surface  of  the  hand  and  on  the  backs  of  the  terminal  phalanges,  the  tela  is  but 
loosely  united  to  the  underlying  fascia. 

The  bursa  subcutanea  olecrani  lies  over  the  dorsal  surface  of  the  olecranon.  Subcutaneous 
bursiE  are  also  frequently  found  over  the  knuckles  (b.  subcutanese  metacarpophalangeae 
dorsales)  and  the  proximal  joints  of  the  fingers  (b.  subcutanese  digitorum  dorsales). 

The  antibrachial  fascia  encloses  the  muscles  of  the  forearm  in  a  cylindrical  sheath,  composed 
in  the  main  of  circular  fibre-bundles,  but  strengthened  by  longitudinal  and  obhque  bundles 
extending  in  from  the  epicondyles  of  the  humerus,  the  olecranon,  the  lacertus  fibrosus  of  the  bi- 
ceps, and  the  tendon  of  the  triceps.  The  fascia  of  the  forearm  is  attached  to  the  dorsal  surface 
of  the  olecranon  and  to  the  subcutaneous  margin  of  the  ulna.  Above,  it  is  continued  into  the 
fascia  of  the  arm;  below,  into  the  fascia  of  the  hand.  From  the  antibrachial  fascia  in  the  upper 
half  of  the  foreai-m  a  fibrous  septum  extends  between  the  radio-dorsal  and  the  ulno-volar 
muscle  group  to  the  radius.  In  the  radial  septum  below  the  elbow  a  branch  of  communica- 
tion extends  between  the  superficial  and  deep  veins  of  the  arm.  That  part  of  the  fascia  over- 
lying the  radio-dorsal  group  of  muscles  is  much  denser  than  that  covering  the  volar  group, 
except  where  the  latter  is  strengthened  by  the  lacertus  fibrosus.  In  addition  to  the  main 
radial  septum  other  septa  descend  between  the  underlying  muscles  from  the  antibrachial 
fascia.  These  septa  are  best  marked  near  the  attachment  of  the  muscles  to  the  humerus. 
Here  the  fascia  is  firmly  fused  to  the  muscles. 

Dorsally  the  antibrachial  fascia  is  strengthened  at  the  wrist  by  transverse  fibres  which 
extend  from  the  radius  to  the  styloid  process  of  the  ulna,  the  triquetrum  (cuneiform),  and 
pisiform,  and  give  rise  to  the  dorsal  ligament  of  the  carpus  (posterior  annular  ligament).  From 
this  ligament  septa  descend  to  the  radius  and  ulna  and  convert  the  grooves  in  these  bones  into 
osteo-fibrous  canals  which  lodge  the  tendons  of  the  various  muscles  extending  to  the  wrist  and 
hand. 

On  the  back  of  the  hand  there  is  spread  a  fascia  composed  of  two  thin  fascial  sheets  between 
which  the  extensor  tendons  are  contained.  Between  the  tendons  these  sheets  are  more  or  less 
fused.  On  the  backs  of  the  fingers  the  fascia  blends  with  the  extensor  tendons  and.the  associated 
aponeurotic  expansions  from  the  interosseous  and  lumbrical  muscles.  Between  the  fingers 
it  is  continued  into  the  transverse  fasciculi  of  the  palmar  aponeurosis.  At  the  sides  of  the  hand 
the  fascia  is  continued  into  the  thenar  and  hypothenar  fasciae.  Each  dorsal  interosseous 
muscle  is  covered  by  a  special  fascial  membrane  which  is  separated  by  loose  tissue  from  the 
fascia  investing  the  e.xtensor  tendons. 

Fig.  366,  A-H. — Transverse  Sections  through  the  Llpt  Forearm  and  Hand. 

H.  Transverse  section  through  the  first  phalanx  of  the  middle  finger,  diagrammatic,  with  the 
cavity  of  the  synovial  sheath  of  the  flexor  tendons  distended. 
The  regions  through  which  these  sections  pass  are  indicated  in  the  diagram,     c  and  d  in  the 
diagram  show  the  regions  through  which  pass  sections  C  and  D,  fig.  362  (p.  375). 

1.  Aponeurosis  palmaris.  2.  Arteria  radialis.  3.  A.  ulnaris.  4.  Bursa  bicipito-radiahs.  5 
Discus  articularis.  6.  Ligamentum  carpale  dorsale.  7.  L.  carpi  transversum.  8.  L. 
carpi  volare.  9.  Fascia  antibrachii.  10.  Musculus  abductor  pollicis  brevis.  11.  M. 
abductor  pollicis  longus — a,  tendon.  12.  M.  abductor  digiti  quinti.  13.  M.  adductor 
polhcis.  14.  M.  anconeus.  15.  M.  biceps,  tendon.  16.  M.  brachialis,  tendon.  17.  M. 
braohio-radialis — a,  tendon.  18.  M.  extensor  carpi  radiahs  brevis — a,  tendon.  19.  M. 
extensor  carpi  radiahs  longus — a,  tendon.  20.  M.  extensor  carpi  ulnaris.  21.  M.  ex- 
tensor digitorum  communis — a,  tendon  for  second  finger;  b,  tendon  for  the  third  finger;  c, 
tendon  for  fourth  finger;  d,  tendon  for  fifth  finger;  e,  digital  aponeurosis.  22.  M.  extensor 
digiti  quinti  proprius.  23.  M.  extensor  indicis  proprius.  24.  M.  extensor  polhcis  brevis 
— a,  tendon.  25.  M.  extensor  poUicis  longus — a,  tendon.  26.  M.  flexor  carpi  radialis — 
a,  tendon.  27.  M.  flexor  carpi  ulnaris — a,  tendon.  28.  M.  flexor  digitorum  profundus — 
a,  tendon  for  second  finger;  b,  tendon  for  third  finger;  c,  tendon  for  fourth  finger;  d,  tendon 
for  fifth  finger.  29.  M.  flexor  digitorum  sublimis — a,  tendon  for  second  finger;  b,  tendon 
for  third  finger;  c,  tendon  for  fourth  finger;  d.  tendon  for  fifth  finger.  30.  M.  flexor  digiti 
quinti  brevis.  31.  M.  flexor  pollicis  brevis.  32.  M.  flexor  pollicis  longus — a,  tendon. 
33.  M.  interossei  dorsales.  34.  M.  intero.ssei  volares.  35.  M.  lumbricales.  36.  M.  op- 
ponens  polhcis.  37.  M.  opponens  digiti  quinti.  38.  M.  palmaris  brevis.  39.  M.  palmaris 
longus — a,  tendon.  40.  M.  pronator  quadratus.  41.  M.  pronator  teres.  42.  M.  supi- 
nator. 43.  N.  cutaneus  antibrachii  lateralis.  44.  N.  medianus.  45.  N.  radialis — a, 
deep  radial  nerve;  b,  superficial  radial  nerve.  46.  N.  ulnaris.  47.  Os  capitatum 
(magnum).  48.  Os  hamatum  (unciform).  49.  Os  lunatum  (semilunar).  50.  Os  meta- 
carpal, I.  51.  Os  metacarpale,  II.  52.  Os  metacarpale.  III.  53.  Os  metacarpale,  IV. 
54.  Os  metacarpale,  V.  55.  Os  multangulum  majus  (trapezium).  56.  Os  naviculare. 
57.  Ossa  sesamoidea  of  fifth  digit.  58.  Radius.  59.  Ulna.  60.  Vagina  fibrosa  (tendon- 
sheath)  of  the  long  digital  flexors.  61.  Vagina  fibrosa  (tendon-sheath)  of  the  flexor 
pollicis  longus.     62.  Vagina  fibrosa  (tendon-sheath  in  digit).     63.  Vena  cephalica. 


MUSCLES  OF  FOREARM  AND  HAND 


385 


44      2        9 


d 
A 


-~. 


4^i 


42    ^1      4-5»2a       JO         9 


H 


386 


THE  MUSCULATURE 
D 


28°    28*  28'     2t2Z   ai'     3f   2\^ 
F 


RADIO-DORSAL  DIVISION  387 

On  the  volar  side  of  the  forearm  for  some  distance  above  the  wrist  the  tendons  of  the 
flexor  carpi  radialis,  tlie  palmaris  longus,  and  the  flexor  carpi  ulnaris  run  between  two  layers  of 
the  fascia.  The  fascia  is  much  strengthened  at  the  wrist  by  transverse  fibres  which  give  rise 
to  the  volar  ligament  of  the  carpus.  Beneath  it  hes  the  transverse  ligament  of  the  carpus 
(anterior  annular  hgament).  This  dense  band  is  broader  than  the  volar  ligament  but  like  it 
extends  from  the  pisiform  bone  and  the  hamulus  of  the  hamatura  (unciform)  to  the  tuberosity 
of  the  navicular  and  the  tuberosity  of  the  greater  multangular  (trapezium).  It  serves  to 
complete  an  osteo-fibrous  canal  through  which  pa.ss  the  flexor  tendons  of  the  fingers.  Between 
the  two  ligaments  which  are  partially  fused  with  one  another  run  the  ulnar  artery  and  nerve. 

On  the  palm  of  the  hand  the  ensheathing  fascia  presents  three  distinct  areas — a  central, 
a  lateral,  and  a  medial. 

The  central  portion,  the  palmar  aponeurosis,  is  composed  chiefly  of  bundles  of  fibrous 
tissue  which  radiate  superficially  toward  the  fingers  from  the  tendon  of  the  palmaris  longus  or 
from  a  corresponding  region  of  the  forearm  fascia  when  this  muscle  is  absent.  Between  these 
bundles  are  others  which  arise  from  the  transverse  ligament.  The  deep  surface  of  the  fascia  is 
composed  of  a  thin  incomplete  layer  of  transverse  fibres  which  continue  the  transverse  fibres  of 
the  forearm  fascia.  Near  the  capitula  of  the  metacarpals  this  layer  becomes  much  stronger 
and  constitutes  a  ligamentous  band  (superficial  transverse  ligament  of  Poirier).  Near  the  bases 
of  the  digits  bundles  of  transverse  fibres  (fasciculi  transversi)  lie  in  the  webs  of  the  fingers  and 
constitute  an  incomplete  transverse  ligament  separated  by  a  distinct  interval  from  the  super- 
ficial transverse  ligament. 

From  the  palmar  aponeurosis  processes  are  sent  in  toward  the  deeper  structures.  Of  these, 
the  most  important  are  those  continued  into  a  fibrous  sheath  which  surrounds  the  space  con- 
taining the  long  flexor  tendons  and  the  lumbrical  muscles.  This  dense  fibrous  sheath  is  united 
by  fibrous  processes  to  the  third,  fourth,  and  fifth  metacarpals.  As  the  flexor  tendons  diverge 
and  the  ends  of  the  metacarpals  are  approached,  numerous  processes  descend  from  the  palmar 
aponeurosis  to  the  transverse  capitular  ligament.  These  hold  the  tendons  in  place.  On  the 
volar  surface  of  the  fingers  the  fascia  serves  to  complete  osteo-fibrous  canals  for  the  long  flexor 
tendons.  The  ventral  surface  of  the  first  and  second  phalanges  of  each  finger  is  slightly  grooved. 
The  fascia  is  firmly  united  on  each  side  to  the  margin  of  the  groove,  and  over  the  groove  forms 
a  semicyhndrical,  strong,  fibrous  sheath,  the  vaginal  ligament  of  the  finger.  This  sheath  is 
strengthened  by  transverse  bands  over  the  bases  of  the  first  and  second  phalanges  (annular 
ligaments)  and  by  cruciate  bands  over  the  shafts  of  the  phalanges  (cruciate  ligaments).  Over 
the  interphalangeal  joints  the  sheath  is  thin,  but  is  strengthened  by  crucial  bands  which  permit 
of  freedom  of  motion. 

The  thenar  fascia  is  a  thin  membrane  covering  the  short  muscles  of  the  thumb.  It  is  con- 
tinued above  into  the  fascia  of  the  forearm,  medially  is  fused  with  the  tendon  of  the  palmaris 
longus  and  the  palmar  aponeurosis,  and  extends  as  a  septum  to  be  attached  to  the  third  meta- 
carpal. Laterally  it  is  attached  to  the  first  metacarpal  and  is  continued  into  the  dorsal  fascia 
of  the  hand.  It  is  fused  with  an  aponeurosis  from  the  tendon  of  the  abductor  poUicis  longus. 
Distally  it  is  continued  into  the  vaginal  ligament  of  the  long  flexor  of  the  thumb.  Superficially 
it  is  closely  adherent  to  the  skin. 

The  hypothenar  fascia  invests  the  palmar  muscles  of  the  little  finger.  It  is  continued 
from  the  ulnar  margin  of  the  fifth  metacarpal  over  the  muscles  of  the  little  finger  to  the  palmar 
aponeurosis,  and,  by  means  of  a  septum,  to  the  radial  side  of  the  fifth  metacarpal.  Proximally, 
it  is  attached  to  the  hamatum  (unciforn?^  and  extends  into  the  fascia  of  the  forearm,  distally, 
it  extends  into  the  vaginal  ligament  of  the  tendon  of  the  fifth  digit. 

A  deeply  seated  suprametacarpal  fascial  layer,  or  deep  palmar  fascia,  covers  the  inter- 
osseous muscles  and  is  attached  to  the  volar  surface  of  the  metacarpal  bones. 

In  addition  to  the  fasciae  mentioned,  intermuscular  septa  serve  to  separate  mjre  or  less 
completely  the  various  intrinsic  muscles  of  the  hand. 

MUSCLES 
1.  Radio-Dorsal  Division 

The  muscles  of  this  group  lie  in  two  chief  layers,  a  superficial  and  a  deep. 

a.  Superficial  Layer 

(Figs.  367,  370,  371), 

The  muscles  of  this  laj^er,  closely  associated  at  their  origins,  extend  from  the 
radial  .side  of  the  distal  end  of  the  humerus  to  the  distal  extremity  of  the  radius, 
the  carpus,  and  the  fingers.  They  are  divisible  into  a  radial,  an  intermediate, 
and  an  ulnar  set. 

Radial  set. — To  this  belong  three  muscles,  the  brachio-radialis,  extensor  carpi 
radialis  longus  and  brevis.  The  brachio-radialis  (fig.  370),  a  forearm  flexor,  is  a 
superficial  fusiform  muscle  which  arises  from  the  lateral  epicondylar  ridge  of  the 
humerus  and  is  inserted  into  the  base  of  the  styloid  process  of  the  radius.  The 
extensor  carpi  radialis  longus  (fig.  371)  is  a  narrow,  fusiform  muscle  which  extends 


388  THE  MUSCULATURE 

along  the  radial  margin  of  the  forearm,  partly  under  cover  of  the  brachio-radialis. 
It  arises  from  the  lateral  epicondylar  ridge  of  the  humerus,  and  is  inserted  into 
the  second  metacarpal  bone.  The  extensor  carpi  radialis  brevis  (fig.  367)  is  a 
band-like  muscle  more  dorsally  placed  than  the  last  at  the  radial  side  of  the  arm. 
It  arises  from  the  lateral  epicondyle  and  is  inserted  into  the  bases  of  the  second 
and  third  metacarpals.  These  muscles  are  supplied  by  branches  of  the  radial 
nerve  which  arise  proximal  to  the  passage  of  the  deep  radial  (posterior  inter- 
osseous) through  the  supinator  muscle.  Distally  this  set  of  muscles  is  separated 
from  the  intermediate  set  by  the  long  abductor  and  the  extensors  of  the  thumb, 
which  pass  from  an  origin  under  the  latter  set  over  the  tendons  of  the  radial 
extensors  to  the  thumb. 

The  intermediate  set. — This  consists  of  the  thick,  flattened  extensor  digitorum 
communis  and  the  slender  extensor  digiti  quinti  proprius  (fig.  367).  They  arise 
from  the  lateral  epicondyle,  and  are  inserted  into  the  backs  of  the  fingers. 

The  ulnar  set  consists  of  one  muscle,  the  fusiform  extensor  carpi  ulnaris, 
which  arises  from  the  lateral  epicondyle  of  the  humerus  and  is  inserted  into  the 
back  of  the  base  of  the  fifth  metacarpal. 

The  intermediate  and  ulnar  sets  of  muscles  are  supplied  by  branches  from  the 
ramus  profundus  of  the  radial  nerve  after  this  has  passed  through  the  supinator 
muscle. 

In  the  leg  the  lateral  set  of  the  superficial  layer  is  represented  by  the  tibialis  anterior.  The 
intermediate  set  is  represented  by  the  long  extensors  of  the  toes.  The  single  muscle  which 
constitutes  the  medial  set  is  represented  by  the  peroneal  muscles. 

The  brachio-radialis  (supinator  radii  longus)  (figs.  367,  370). — Origin. — From  the  upper 
two-thirds  of  the  lateral  epicondylar  ridge  of  the  humerus  and  from  the  front  of  the  lateral 
intermuscular  septum. 

Insertion. — Into  the  lateral  side  of  the  base  of  the  styloid  process  of  the  radius. 

Structure. — The  constituent  fibre-bundles  arise  directly  from  the  septum  and  by  short 
tendinous  bands  from  the  epicondylar  ridge,  extend  downward  and  ventrally,  and  terminate 
in  a  penniform  manner  on  a  tendon  which  extends  high  on  the  deep  surface  of  the  muscle. 
This  tendon  becomes  free  about  the  middle  of  the  forearm  as  a  broad,  flat  band.  This  be- 
comes narrow  as  the  tendon  winds  about  the  radius  from  the  volar  to  the  lateral  surface. 
Before  its  insertion  it  expands  laterally  and  is  connected  with  neighbouring  ligaments.  The  free 
surface  of  the  muscle  faces  laterally  at  its  origin,  but,  owing  to  the  torsion,  ventrally  in  the 
forearm.  The  tendon,  however,  is  turned  again  so  that  at  the  insertion  it  faces  laterally  once 
more. 

Nerve-supply. — From  a  branch  of  the  radial  nerve  (musculo-spiral)  which  enters  the 
proximal  third  of  the  muscle  on  its  deep  surface.  The  nerve  fibres  arise  from  the  fifth  and  sixth 
cervical  nerves. 

Action. — To  flex  the  forearm.  This  action  is  strongest  when  the  forearm  is  pronated. 
It  acts  as  a  supinator  only  when  the  arm  is  extended  and  pronated.  It  then  serves  to  put  the 
arm  in  a  state  of  semi-pronation.     When  the  forearm  is  flexed,  it  acts  as  a  pronator. 

Relations. — The  muscle  is  superficially  placed  on  the  ventro-lateral  surface  of  the  forearm. 
Its  tendon  of  insertion,  however,  is  covered  by  the  long  abductor  and  the  short  extensor  of  the 
thumb.  Near  its  origin  (fig.  367)  it  lies  lateral  to  the  brachialis.  In  the  intervening  tissue  run 
the  radial  nerve  and  the  terminal  branch  of  the  profunda  brachii  artery.  Dorsally  and  laterally 
lieslthe  medial  head  of  the  triceps.  More  distally  the  muscle  overlies  the  extensor  carpi  radialis 
longus.  It  crosses  the  supinator,  pronator  teres,  and  flexor  pollicis  longus  muscles.  Beneath 
its  medial  edge  lie  the  radial  vessels  and  nerve. 

Variations. — The  humeral  origin  may  extend  half-way  up  the  shaft.  The  radial  insertion 
may  be  as  high  as  the  middle  of  the  shaft  or  descend  to  the  lesser  multangular,  navicular,  or 
third  metacarpal.  In  about  7  per  cent,  of  bodies  (Le  Double)  the  tendon  of  insertion  divides 
into  two  or  three  slips  which  are  inserted  on  the  styloid  process  of  the  radius.  Occasionally 
the  radial  nerve  passes  between  these  slips.  An  accessory  slip  may  pass  to  the  fascia  of  the 
forearm.  The  muscle  may  be  doubled  throughout  its  length  and  it  may  be  missing.  It  may  be 
connected  by  accessory  slips  with  neighbouring  muscles,  the  deltoid,  brachialis,  long  abductor  of 
the  thumb,  or  long  radial  carpal  extensor.     The  slip  most  frequently  found  goes  to  the  brachiahs. 

The  extensor  carpi  radialis  longus  (figs.  367,  368,  371.) — Origin. — From  the  lower  third 
of  the  lateral  epicondylar  ridge,  the  lateral  intermuscular  septum,  and  from  the  front  of  the 
tendons  of  the  extensor  carpi  radialis  brevis  and  the  extensor  communis  digitorum  which  arise 
from  the  lateral  epicondyle. 

Structure  and  insertion. — The  fibre-bundles  are  inserted  in  a  penniform  manner  on  both 
surfaces  of  a  tendon  which  first  appears  on  the  lateral  border  of  the  deep  surface  of  the  muscle, 
becomes  free  above  the  middle  of  the  forearm,  and  descends,  closely  applied  to  the  tendon  of 
the  short  radial  carpal  extensor,  to  the  second  compartment  beneath  the  dorsal  carpal  ligament, 
through  which  it  passes  to  its  insertion  into  the  base  of  the  second  metacarpal  near  the  radial 
border.     The  outer  surface  of  the  muscle  faces  at  first  laterally,  then  ventrally. 

Nerve-supply. — By  one  or  two  branches  which  arise  from  the  radial  (musculo-spiral)  nerve 
as  it  passes  between  the  brachialis  and  brachio-radialis.  The  nerve  enters  the  deep  surface 
of  the  muscle  in  the  proximal  third.  The  nerve  fibres  arise  from  the  (fifth),  sixth  and  seventh 
cervical  nerves. 

Action. — To  extend  and  abduct  the  hand.     It  steadies  the  wrist  when  the  flexors  act  on 


EXTENSOR  CARPI  RADIALIS  BREVIS 


389 


the  fingers.     It  is  a  flexor  of  the  forearm;  a  supinator  when  the  forearm  is  extended,  a  pronator 
when  it  is  flexed. 

Relations. — It  is  covered  by  the  brachio-radialis  near  the  elbow.  Below  it  becomes  super- 
ficial except  where  crossed  by  the  tendons  of  the  muscles  of  the  thumb.  (For  the  relations  to 
the  short  radial  carpal  extensor  see  below.) 

Fig.  367. — Muscles  of  the  Radial  Side  and  the  Back  of  tee  Foeearm. 


Brachlalis 
Brachio-radialis 


Extensor  carpi  radialis  longus 


Extensor  digitorum  communis 


Extensor  carpi  radialis  brevis 


Abductor  pollicis  longus 
Extensor  pollicis  brevis 


Extensor  pollicis  longus 


Flexor  carpi  ulnaris 


Extensor  carpi  ulnaris 


Extensor  digiti  quinti  propnus 


Variaiions. — The  humeral  attachment  may  be  more  extensive  than  that  indicated  above. 
The  tendon  of  insertion  may  send  a  band  to  the  third  or  to  the  fourth  metacai'pal  or  to  the  mul- 
tangulum  majus  (trapezium).  The  muscle  may  be  fused,  partly  or  completely,  with  the  short 
radial  extensor.     It  may  send  a  slip  to  the  abductor  pollicis  longus  or  to  some  of  the  interossei. 

The  extensor  carpi  radialis  brevis  (figs.  367,  368). — Origin. — From  a  band  which  descends 
on  its  deep  surface  from  the  common  extensor  tendon  attached  to  the  lateral  epicondyle,  from 
the  intermuscular  septa  surrounding  its  head,  and  from  the  radial  collateral  ligament  of  the 
elbow-joint. 


390 


THE  MUSCULATURE 


Structure  and  insertion. — The  fibre-bundles  converge  obliquely  toward  a  tendon  which 
appears  high  up  on  the  dorso-lateral  surface  of  the  muscle.  Toward  the  lower  third  of  the 
forearm  this  tendon  becomes  a  free,  strong  band  closely  apphed  to  the  under  surface  of  the 
tendon  of  the  long  radial  extensor,  and  with  this  passes  through  the  second  compartinent  be- 
neath the  dorsal  ligament  of  the  carpus,  diverging  as  it  does  so  toward  its  insertion  into  the 
back  of  the  bases  of  the  second  and  third  metacarpal  bones. 


Fig.  368  — Tendons  upon  the  Dobsum  of  the  Hand. 


Abductor  poUicis  longus 


Extensor  polUcis  brevii 


Dorsal  carpal  ligament 


Extensor  carpi  ulnans 


^^^  Extensor  digitorum  communis 


Extensor  digiti  quinti 


Extensor  indicts  proprius 


Attachment  of  extensor 
digitorum 
to  third  phalanx 


Nerve-supply. — A  branch  is  supplied  to  the  muscle  from  the  deep  radial  (posterior  interos- 
seous) nerve  before  this  enters  the  supinator  (brevis).  The  branch  enters  the  middle  third  of 
the  medial  margin  of  the  muscle  by  several  rami.  The  nerve  fibres  arise  from  the  (fifth), 
sixth  and  seventh  cervical  nerves. 

Action. — To  extend  the  hand  and,  to  a  slight  extent,  to  flex  the  forearm. 

Relations. — In  its  proximal  portion  the  muscle  is  placed  with  a  medial  surface  toward 
the  common  extensor,  a  deep  toward  the  supinator  (brevis)  and  pronator  teres,  and  a  dorso- 
lateral toward  the  long  radial  extensor.  More  distally  the  muscle  and  its  tendon  become 
flattened  about  the  radius  and  partly  covered  by  the  long  radial  extensor  and  its  tendon. 


EXTENSOR  CARPI  ULNARIS  391 

In  the  distal  quarter  of  the  forearm  the  tendons  of  these  two  muscles  are  crossed  by  the  long 
abductor  and  the  short  extensor  of  the  thumb.  Beneath  the  dorsal  carpal  ligament  the  tendon 
of  the  short  radial  extensor  is  crossed  by  the  tendon  of  the  long  extensor  of  the  thumb. 

Variations. — The  tendon  often  sends  no  slip  to  the  second  metacarpal.  Fusion  of  the  two 
radial  extensors  is  frequent.  The  fused  muscle  may  have  from  one  to  four  tendons.  The 
extensor  carpi  radialis  intermedius  of  Wood  is  a  muscle  which  arises,  rarely  directly  from  the 
humerus,  but  not  infrequently  as  a  slip  from  one  or  both  radial  extensors.  It  is  inserted  into 
the  second  or  third  metacarpal  bone  or  into  both.  The  extensor  carpi  radialis  accessorius  is  a 
muscle  which  has  an  origin  like  the  extensor  intermedius,  but  which  terminates  on  the  base  of 
the  metacarpal  or  first  phalanx  of  the  thumb,  the  short  abductor  of  the  thumb,  or  some  neigh- 
bouring structure. 

The  extensor  digitorum  communis  (figs.  367,  368). — Origin. — From  a  tendon  attached  to 
the  lateral  epicondyle,  and  from  intermuscular  septa  which  lie  between  the  head  of  the  muscle 
and  the  short  radial  extensor,  the  extensor  of  the  Uttle  finger,  and  the  supinator  muscle. 

Insertion. — By  four  tendons  into  the  bases  of  the  phalanges  of  the  fingers. 

Structure. — The  fibre-bundles  arise  from  the  interior  of  the  pyramidal  case  formed  by  the 
tendon,  the  fascia,  and  intermuscular  septa,  and  pass  distally  to  converge  on  four  tendons  which 
begin  in  the  middle  of  the  forearm,  become  free  a  little  above  the  wrist,  pass  under  the  dorsal 
carpal  ligament  in  a  groove  common  to  them  and  the  tendon  of  the  extensor  indicis  proprius,  and 
diverge  to  the  backs  of  the  fingers.  Opposite  the  metacarpo-phalangeal  joint  each  tendon  gives 
rise  on  its  under  surface  to  a  band  which  becomes  attached  to  the  base  of  the  first  phalanx  of  its 
respective  digit.  The  tendon  is  also  closely  bound  to  the  joint  by  fibrous  bands  connected 
with  the  palmar  fascia.  On  the  dorsum  of  the  first  phalanx  the  tendon  expands  and  is  bound 
to  an  aponeurotic  extension  from  the  interosseous  and  lumbrical  muscles.  The  tendon  divides 
into  three  bands.  The  middle  band  passes  to  the  base  of  the  second  phalanx,  the  lateral  bands 
pass  laterally  around  the  joint  to  be  inserted  into  the  back  of  the  base  of  the  third  phalanx. 
The  lateral  bands  are  bound  to  the  second  joint  by  a  thin  layer  of  transverse  and  oblique  fibres. 

An  obliquely  transverse  band  usually  passes  from  the  tendon  of  the  index  to  that  of  the 
middle  finger  above  the  heads  of  the  metacarpals.  The  tendon  to  the  index  finger  is  united  to 
the  tendon  of  the  extensor  indicis  proprius  opposite  the  metacarpo-phalangeal  articulation. 
The  tendon  to  the  ring  finger  usually  sends  a  slip  to  join  the  tendon  of  the  middle  finger.  The 
fourth  tendon  lies  near  that  of  the  ring  finger  and  divides  into  two  shps,  one  of  which  joins  the 
tendon  of  the  ring  finger  and  one  goes  to  the  little  finger  to  join  the  tendon  of  the  extensor  digiti 
quinti  proprius. 

Nerve-supply. — From  a  branch  which  arises  from  the  deep  radial  (posterior  interosseous) 
nerve  as  it  emerges  from  the  supinator  (brevis)  muscle.  From  this  several  twigs  enter  the  deep 
surface  of  the  middle  third  of  the  belly.  Often  the  nerve  is  bound  up  with  the  nerve  to  the 
extensor  of  the  little  finger  and  the  ulnar  extensor.  On  the  other  hand,  there  may  be  several 
separate  branches  to  the  muscle.  The  nerve  fibres  arise  from  the  sixth,  seventh,  and  eighth 
cervical  nerves. 

Action. — The  muscle  extends  the  two  terminal  phalanges  on  the  basal,  the  basal  on  the 
metacarpus,  and  the  hand  at  the  wrist.  The  extensor  action  is  strongest  on  the  first  phalanx. 
The  cross-bands  between  the  tendons  hinder  ^Jie  independent  extension  of  the  middle  and  ring 
fingers,  while  the  special  extensors  of  the  index  and  little  fingers  makes  the  movements  of  these 
fingers  freer.  When  the  hand  is  abducted  toward  the  radial  side,  the  extensor  muscles  tend  to 
draw  the  fingers  ulnarward.  When  the  hand  is  abducted  toward  the  ulnar  side,  the  muscles 
tend  to  draw  the  fingers  toward  the  thumb.  When  the  hand  is  in  the  mid-position  the  ring 
finger  and  little  finger  are  abducted  and  the  index-finger  is  adducted.     (Frohse.) 

Relations. — It  is  superficially  placed.  Under  it  lie  the  deep  muscles  of  the  back  of  the 
forearm,  the  interosseous  vessels,  and  the  deep  radial  (posterior  interosseous)  nerve.  It  lies 
between  the  short  radial  carpal  extensor  and  the  extensor  of  the  little  finger. 

Variations. — There  is  considerable  variation  in  the  extent  of  isolation  of  the  parts  going 
to  the  various  fingers.  That  to  the  index-finger  is  the  one  most  frequently  isolated.  At  times 
the  tendon  to  the  index  or  httle  finger  may  be  wanting.  More  frequently  one  or  more  of  the 
tendons  subdivides  to  be  attached  to  two  or  more  fingers  or  to  the  thumb.  The  connections 
between  the  tendons  on  the  back  of  the  hand  vary  greatly. 

The  extensor  digiti  quinti  proprius  (extensor  minimi  digiti)  (figs.  367,  368). — Origin. — 
Chiefly  from  the  septum  between  it  and  the  common  extensor,  but  also  in  part  from  the  septum 
between  it  and  the  extensor  ulnaris  and  from  the  overlying  fascia. 

Structure  and  insertion. — The  fibre-bundles  descend  in  a  narrow  band  which  begins  near 
the  neck  of  the  radius.  They  are  inserted  into  the  side  of  a  tendon  which  begins  high  on  the 
ulnar  margin  of  the  muscle.  The  most  distal  fibre-bundles  extend  nearly  to  the  wrist-joint. 
The  tendon  passes  through  the  fifth  compartment  beneath  the  dorsal  carpal  ligament,  and 
extends  on  the  back  of  the  fifth  metacarpal  to  the  base  of  the  first  phalanx  of  the  little  finger, 
where  it  is  joined  by  a  shp  from  the  fourth  tendon  of  the  common  extensor.  The  insertion  of 
the  tendon  is  Uke  that  of  the  tendons  of  the  common  extensor. 

Nerve-supply. — By  a  branch  or  branches  from  the  deep  radial  (posterior  interosseous),  nerve. 
The  nerve  filaments  enter  the  middle  third  of  the  fleshy  portion  of  the  muscle  on  its  deep 
surface.     The  innervation  of  this  muscle  is  intimately  related  to  that  of  the  preceding. 

Action. — It  acts  as  a  portion  of  the  common  extensor,  but,  owing  to  its  separation,  in- 
dependent movement  of  the  Little  finger  is  possible. 

Relations. — It  Ues  between  the  common  extensor  and  the  ulnar  extensor  and  upon  the  deep 
muscles  of  the  back  of  the  forearm. 

Variations. — Absence  is  not  very  frequent;  blending  with  the  common  extensor  is  frequent. 
Its  tendon  often  divides  into  two  or  more  slips.  The  belly  may  also  be  doubled.  It  may  have 
a  supplementary  origin  from  the  ulna.     A  tendon  shp  to  the  ring-finger  is  frequently  found. 

The  extensor  carpi  ulnaris  (figs.  367,  368). — Origin. — By  two  heads:  one  from  the  inferior 
dorsal  portion  of  the  epicondyle  by  an  aponeurotic  band  attached  below  the  tendon  of  the 


392  THE  MUSCULATURE 

common  extensor,  from  the  enveloping  fascia,  and  from  the  septa  between  it  and  the  extensor 
digitiquinti,  anconeus,  and  supinator  (brevis);  the  other  from  the  proximal  three-fourths  of 
the  dorsal  border  of  the  ulna. 

Structure  and  insertion. — The  fibre-bundles  descend  in  an  osteo-fascial  compartment 
bounded  by  the  dorsal  surface  of  the  ulna,  the  fascia  of  the  forearm,  the  dense  fascia  overlying 
the  ulnar  origin  of  the  muscles  of  the  thumb,  and  the  origin  of  the  extensor  indicis.  The  tendon 
commences  high  in  the  muscle  and  appears  on  the  radial  border  of  the  middle  third  of  the  back 
of  its  belly.  The  fibre-bundles  are  inserted  in  a  penniform  manner  on  the  ulnar  border  and 
deep  surface  of  the  tendon  as  far  as  the  wrist.  Here  the  tendon  enters  the  sixth  osteo-fibrous 
canal  beneath  the  dorsal  carpal  Ugament  in  a  special  groove  on  the  outer  side  of  the  styloid 
process  of  the  ulna.     It  is  inserted  into  the  base  of  the  fifth  metacarpal. 

Nerve-supply. — By  a  branch  which  arises  from  the  deep  radial  (posterior  interosseous)  nerve 
as  this  emerges  from  the  supinator  (brevis)  muscle.  Several  filaments  enter  the  deep  surface 
of  the  muscle  in  the  middle  third.  The  nerve  fibres  arise  from  the  sixth,  seventh  and  eighth 
cervical  nerves. 

Action. — To  extend  and  abduct  the  hand  ulnarward. 

Relations. — It  occupies  a  superficial  position  on  the  ulnar  side  of  the  extensors  of  the  fore- 
arm. Beneath  it  he  the  deep  muscles  of  the  back  of  the  forearm  and  the  posterior  surface  of 
the  ulna. 

Variations. — It  may  receive  a  slip  from  the  triceps  or  be  fused  with  the  anconeus  or  with 
the  extensor  of  the  little  finger.  More  frequently  it  is  doubled,  partially  or  completely.  An 
accessory  tendon  may  go  to  the  first  phalanx  of  the  little  finger,  to  the  head  of  the  fifth  meta- 
carpal, to  the  fourth  metacarpal,  to  the  extensor  tendon  of  the  little  finger,  or  to  the  fascia  over 
the  opponens  digiti  quinti.  The  muscle  may  be  reduced  to  a  fibrous  band.  The  ulnaris  digiti 
quinti  is  a  rare  muscle  arising  from  the  dorsal  surface  of  the  ulna  and  inserted  into  the  base  of 
the  first  phalanx  of  the  httle  finger.  It  may  be  represented  by  a  fasciculus  or  an  extra  tendon 
from  the  ulnar  extensor. 

b.  Deep  Layer 

(Fig.  369) 

The  muscles  of  this  group  extend  from  the  ulna  to  the  radius,  thumb,  and  index- 
finger.  They  are  the  supinator,  abductor  pollicis  longus,  extensor  pollicis  longus 
and  brevis,  and  extensor  indicis  proprius.  The  supinator  is  a  rhomboid  muscle 
which  arises  from  the  lateral  epicondyle  of  the  humerus  and  the  supinator  crest  of 
the  ulna  winds  laterally  around  the  radius  and  is  inserted  into  its  volar  surface. 
The  abductor  pollicis  longus  is  a  fusiform  muscle  which  arises  from  the  middle 
third  of  the  ulna,  the  interosseous  membrane,  and  the  radius,  and  is  inserted 
into  the  base  of  the  first  metacarpal.  The  extensor  pollicis  brevis  arises  from  the 
radius  distal  to  the  preceding  muscle,  and  is  inserted  into  the  base  of  the  first 
phalanx  of  the  thumb.  The  extensor  pollicis  longus  is  a  narrow  muscle  which 
arises  from  the  middle  third  of  the  dorsal  surface  of  the  ulna  and  is  inserted  into 
the  base  of  the  second  phalanx  of  the  thumb.  The  extensor  indicis  proprius  is  a 
narrow,  fusiform  muscle  arising  from  the  shaft  of  the  ulna  and  inserted  into  the 
dorsal  aponeurosis  of  the  index-finger.  These  muscles  are  supplied  from  branches 
of  the  deep  radial  (posterior  interosseous)  nerve  while  this  is  passing  through  or 
after  its  exit  from  the  supinator. 

The  extensor  pollicis  longus  is  represented  by  the  extensor  hallucis  longus  of  the  leg.  The 
abductor  pollicis  longus  and  extensor  pol'icis  brevis  are  represented  by  the  abnormal  abductor 
hallucis  longus  and  extensor  primi  internodii  hallucis  muscles,  the  rudiments  of  which  are 
perhaps  normally  present  in  the  tibialis  anterior.  The  supinator  and  the  extensor  indicis 
muscles  are  not  represented  in  the  leg.  On  the  other  hand,  the  extensor  digitorum  brevis, 
norma!  in  the  foot,  is  only  occasionally  found  on  the  back  of  the  hand. 

The  supinator  (brevis)  (figs.  366,  369,  372). — Origin. — From  (1)  the  inferior  dorsal  portion 
of  the  lateral  epicondyle  by  a  tendinous  band  which  is  adherent  to  the  deep  surface  of  the 
tendons  of  origin  of  the  radial  and  common  extensors  and  to  the  radial  collateral  ligament  of 
the  joint;  and  (2)  the  ulna  by  a  superficial  aponeurosis  and  by  fibre-bundles  attached  directly 
to  the  depression  below  the  radial  notch  and  to  the  supinator  crest. 

Insertion. — The  lateral  and  volar  surfaces  of  the  radius  from  the  tuberosity  to  the  attach- 
ment of  the  pronator  teres. 

Structure. — From  their  origin  the  fibre-bundles  descend  spirally  in  a  muscular  sheet  which 
enwraps  the  radius  (fig.  366).  The  attachment  extends  to  the  oblique  Une.  The  muscle  is 
divided  into  a  superficial  and  a  deep  plane  by  a  septum  in  which  the  deep  radial  (posterior 
interosseous)  nerve  runs.  The  radial  attachments  of  these  two  portions  are  separated  by  an 
osseous  area  into  which  no  fibre-bundles  are  inserted.  The  fibre-bundles  of  the  superficial  layer 
have  a  much  more  vertical  course  and  are  longer  than  those  of  the  deep  layer. 

Nerve-supply. — By  branches  which  arise  from  the  deep  radial  (posterior  interosseous) 
nerve  before  it  passes  between  the  two  layers  of  the  supinator  muscle.  The  nerve  fibres  arise 
from  the  fifth,  sixth,  and  seventh  cervical  nerves. 

Action. — To  supinate  the  forearm. 

Relations. — The  supinator  is  covered  by  the  superficial  group  of  extensor  muscles  above 
described  and  by  the  anconeus. 


ABDUCTOR  POLLICIS  LONGUS 


393 


'  Variations. — The  extent  of  separation  of  the  muscles  into  two  portions  varies.  Accessory 
fasciculi  of  origin  are  not  uncommon.  These  may  spring  from  the  annular  ligament,  tensor  liga- 
menti  annularis  anterior  (5  per  cent,  or  more  of  bodies — Le  Double),  the  lateral  epicondyle, 
the  tendon  of  the  bi  ceps,  the  tuberosity  of  the  radius,  etc.  A  sesamoid  bone  may  lie  in  the 
tendon  of  origin.  The  tensor  ligamenti  annularis  posterior  is  a  sUp  generally  present  and 
often  independent  of  the  supinator.  It  runs  from  the  ulna  behind  the  radial  notch  to  the  annular 
ligament  of  the  radio-ulnar  joint. 

The  abductor  polUcis  longus  (extensor  ossis  metacarpi  poUicis)  (fig.  369). — Origin. — From 
(1)  the  lateral  margin  of  the  dorsal  surface  of  the  ulna  in  the  proximal  portion  of  the  middle  third. 

Fig.  369. — The  Deep  Muscles  of  the  Back  of  the  Forearm. 


Abductor  pollicis  longus 


Extensor  poUicis  brevis 
Extensor  poUicis  longus 


Radial  extensors 


Flexor  carpi  ulnaris 


Flexor  digitorum  profundus 


Extensor  indicis  proprius 
Extensor  carpi  ulnaris 


and  the  adjacent  interosseous  membrane,  (2)  the  dorsal  surface  of  the  radius  distal  and  medial 
to  the  attachment  of  the  supinator,  and  (3)  at  times,  from  the  septa  lying  between  it  and  the 
supinator,  extensor  carpi  ulnaris,  and  extensor  polUcis  longus. 

Structure  and  insertion. — The  fibre-bundles  from  this  extensive  area  of  origin  converge  in 
a  bipenniform  manner  upon  a  tendon  which  appears  as  an  aponeurosis  on  the  deep  surface  of 
the  muscle  about  the  middle  of  the  forearm.  The  tendon  as  it  descends  becomes  rounded. 
The  insertion  of  fibre-bundles  continues  nearly  to  the  wrist.  Here,  together  with  the  tendon 
of  the  short  extensor,  it  enters  the  first  osteo-fibrous  canal  beneath  the  dorsal  carpal  ligament 
upon  the  lateral  surface  of  the  distal  extremity  of  the  radius.  Upon  leaving  this  canal  the 
tendon  extends  to  be  inserted  on  the  radial  side  of  the  base  of  the  first  metacarpal  bone. 

Nerve-supply. — By  one  or  more  branches  from  the  deep  radial  (posterior  interosseous)  nerve 


394  THE  MUSCULATURE 

after  it  has  emerged  from  the  supinator.  The  branches  enter  the  muscle  on  the  superficial 
surface  in  the  proximal  third.  The  nerve  fibres  come  from  the  sixth,  seventh  (and  eighth) 
cervical  nerves. 

Action. — It  carries  the  first  metacarpal  radialward  and  forward.  At  the  height  of  its 
contraction  it  flexes  and  abducts  the  hand  at  the  wrist. 

Relations. — Near  its  origin  the  muscle  is  covered  by  the  superficial  extensors  of  the  forearm. 
More  distally,  accompanied  by  the  short  extensor,  it  passes  radially,  becomes  superficial,  and 
crosses  the  tendons  of  the  two  radial  carpal  extensors. 

Variations. — The  muscle  or  its  tendon  may  be  doubled.  An  accessory  tendon  may  be 
applied  to  the  multangulum  majus  (trapezium),  the  transverse  ligament  of  the  carpus,  the 
superficial  muscles  of  the  thenar  eminence,  or  the  first  metacarpal.  Of  these,  the  attachment 
to  the  short  abductor  and  short  flexor  is  the  most  frequent  (7  out  of  36  bodies — Wood).  There 
may  be  three  or  more  tendons.     The  muscle  may  be  fused  with  the  short  extensor. 

The  extensor  poUicis  brevis  (fig.  369). — Origin. — From  the  distal  part  of  the  middle 
third  of  the  medial  portion  of  the  dorsal  surface  of  the  radius  and  from  the  neighbouring  portion 
of  the  interosseous  membrane.     Rarely  its  origin  extends  to  the  ulna. 

Structure  and  insertion. — The  fibre-bundles  converge  on  a  tendon  which  appears  on  the 
radial  border.  The  fibres  are  inserted  as  far  as  the  dorsal  carpal  (posterior  annular)  ligament. 
The  tendon  hes  parallel  to  the  ulnar  side  of  that  of  the  abductor  poUicis  longus,  and,  in  close 
connection  with  it,  passes  through  the  first  compartment  beneath  the  dorsal  carpal  ligament, 
and  crosses  the  metacarpo-phalangeal  joint  on  the  radial  side  of  the  long  extensor  tendon.  It 
is  inserted  on  the  base  of  the  first  phalanx  of  the  thumb  or  into  the  capsule  of  the  metacarpo- 
phalangeal joint. 

Nerve-supply. — From  a  branch  derived  from  the  deep  radial  (posterior  interosseous)  nerve. 
This  branch  is  usually  given  off  in  common  with  or  near  the  nerve  to  the  abductor  pollicis 
longus,  and  many  traverse  that  muscle  to  reach  the  extensor  pollicis  brevis,  which  it  enters  in 
the  proximal  third  of  its  radial  border.  The  nerve  fibres  come  from  the  sixth,  seventh  (and 
eighth)  cervical  nerves. 

Action. — To  extend  the  thumb  at  the  metacarpo-phalangeal  joint  and  to  abduct  the  first 
metacarpal.     It  likewise  acts  as  a  weak  supinator  of  the  forearm. 

Relations. — It  hes  between  the  abductor  pollicis  longus  and  the  extensor  pollicis  longus, 
by  which  its  origin  is  partly  overlapped.  In  company  with  the  former  muscle  it  passes  medially 
from  beneath  the  common  extensor  of  the  fingers  and  over  the  tendons  of  the  radial  carpal 
extensors  to  reach  its  osteo-fibrous  canal  under  the  dorsal  carpal  hgament. 

Variations. — The  head  of  the  mu3cle  may  be  fused  with  the  long  abductor.  Its  tendon 
of  insertion  may  give  rise  to  a  sUp  inserted  on  the  first  metacarpal  (in  2  out  of  85  bodies — Le 
Double)  or  into  the  terminal  phalanx.  Its  tendon  is  often  united  with  that  of  the  long  extensor. 
It  may  be  fused  with  the  long  abductor  of  the  thumb  and  has  been  found  missing.  It  may  be 
doubled. 

The  extensor  pollicis  longus  (fig.  369). — Origin. — From  the  middle  third  of  the  lateral 
part  of  the  dorsal  surface  of  the  ulna;  from  the  neighbouring  part  of  the  interosseous  membrane; 
and  from  the  septa  between  it  and  the  extensor  indicis  proprius,  and  the  extensor  carpi  ulnaris. 

Structure  and  insertion. — The  fibre-bundles  converge  in  a  bipenniform  manner  on  the  two 
sides  of  a  tendon  which  appears  high  on  the  dorsal  surface  of  the  muscle.  They  extend  as  far 
as  the  dorsal  carpal  (posterior  annular)  hgament.  The  fusiform  body  of  the  muscle  descends 
somewhat  obliquely  on  the  dorsal  surface  of  the  forearm.  The  tendon  enters  the  third  osteo- 
fibrous  canal  beneath  the  dorsal  carpal  (posterior  annular)  Hgament.  On  emerging  from  the 
canal  it  passes  very  obliquely  across  the  dorsal  surface  of  the  carpus,  over  the  tendons  of 
the  radial  extensors,  to  the  ulnar  side  of  the  first  metacarpal.  It  passes  along  this  and  on  the 
dorsal  surface  of  the  first  phalanx,  expands  to  be  inserted  into  the  base  of  the  second  phalanx. 
The  aponeurosis  of  insertion  receives  tendinous  slips  from  the  short  muscles  of  the  volar  surface 
of  the  thumb. 

Nerve-supply. — By  a  twig  from  the  deep  radial  (posterior  interosseous)  nerve.  The  branch 
gives  rise  to  twigs  which  enter  the  proximal  third  of  the  radial  border  of  the  muscle.  The 
fibres  arise  from  the  sixth,  seventh,  and  eighth  cervical  nerves. 

Action. — To  extend  the  second  phalanx  on  the  first,  and  this  on  the  metacarpal.  It  also 
draws  the  whole  thumb  when  extended  toward  the  second  metacarpal.  It  may  have  a  sUght 
supinator  action  on  the  forearm. 

Relations. — The  head  of  the  muscle  is  partly  overlapped  by  the  long  abductor  of  the  thumb. 
It  lies  between  this  and  the  extensor  pollicis  brevis  on  one  side,  and  the  extensor  indicis  proprius 
on  the  other.     Over  it  lie  the  extensors  of  the  fingers  and  the  ulnar  carpal  extensor. 

Variations. — The  tendon  may  give  a  slip  to  the  base  of  the  first  phalanx  of  the  thumb, 
to  the  dorsal  carpal  hgament,  or  to  the  index  finger.  It  may  receive  an  accessory  slip  from  the 
common  extensor  of  the  fingers  or  the  short  extensor  of  the  thumb.  It  is  frequently!  doubled. 
An  additional  extensor  is  found  in  about  6  per  cent,  of  bodies  between  the  extensor!  of  the  index 
finger  and  that  of  the  thumb.  It  has  a  double  tendon  and  insertion  into  both  digits  (extensor 
communis  pollicis  et  indicis). 

The  extensor  indicis  proprius  (fig.  369). — Origin. — From  the  proximal  part  of  the  distal 
third  of  the  posterior  surface  of  the  ulna,  medial  and  distal  to  that  of  the  preceding  muscle,  from 
the  adjacent  interosseous  membrane,  and  from  the  septum  between  it  and  the  extensor  pollicis 
longus. 

Structure  and  insertion. — The  fibre-bundles  are  inserted  on  a  tendon  which  first  appears  on 
the  radial  border  of  the  muscle.  The  insertion  of  fibre-bundles  extends  nearly  to  the  dorsal 
carpal  (posterior  annular)  ligament.  Here  the  tendon  passes  beneath  that  of  the  extensor 
of  the  little  finger  and  enters  the  fourth  osteo-fibrous  canal  beneath  the  lateral  tendons  of  the 
common  extensor.  It  passes  across  the  wrist  beneath  the  tendon  from  the  extensor  communis 
to  the  index  finger,  and  is  inserted  on  the  ulnar  side  of  this  into  the  dorsal  aponeurosis  of  the 
index  finger  opposite  the  base  of  the  first  phalanx. 


ULNO-VOLAR  DIVISION  395 

Nerve-supply. — By  a  twig  from  the  deep  radial  (posterior  interosseous)  nerve.  This  twig 
enters  the  proximal  third  of  the  radial  border  of  the  muscle.  It  frequently  arises  from  a  branch 
to  the  extensor  pollicis  longus.  The  nerve  fibres  come  from  the  sixth,  seventh,  eighth  cervical 
nerves. 

Ac! ion. — To  extend  the  first  phalanx  on  the  metacarpal.  Like  the  common  extensor 
it  has  a  limited  action  on  the  two  terminal  phalanges.  It  also  adducts  the  index  finger  and  is  a 
weak  supinator  of  the  forearm. 

Relations. — It  is  covered  by  the  superficial  extensor  group. 

Variations. — These  are  frequent.  It  may  be  absent.  There  may  be  two  heads,  or  the 
muscle  may  be  completely  doubled.  It  may  receive  an  accessory  slip  from  the  ulna  or  the 
carpus.  The  tendon  may  give  accessory  slips  to  the  middle  finger,  the  ring  finger,  or  the  thumb. 
The  accessory  tendon  to  the  middle  finger  is  the  most  frequent.  The  tendon  to  the  index 
finger  may  be  inserted  on  the  metacarpus. 

Abnormal  Muscles  of  the  Back  of  the  Wrist  and  Hand 

The  extensor  medil  digiti  is  a  small  muscle  which  arises  from  the  ulna  beneath  the  extensor 
of  the  index  finger,  with  which  it  is  more  or  less  fused.  It  sends  a  tendon  to  the  extensor 
aponeurosis  of  the  middle  finger  or  slips  both  to  this  finger  and  the  index  finger.  It  is  present 
in  about  10  per  cent,  of  bodies  (Le  Double). 

The  extensor  digiti  annularis  is  a  muscle  similar  to  the  extensor  medii  digiti,  but  much 
rarer . 

The  extensor  digitorum  brevis,  which  resembles  the  muscle  of  corresponding  name  on  the 
dorsum  of  the  foot,  may  have  from  one  to  four  fascicuU,  but  most  frequently  one.  The  most 
common  fasciculus  is  one  which  sends  a  tendon  to  the  extensor  tendon  of  the  index  finger.  One 
for  the  middle  finger  is  nearly  as  frequent.  Others  are  rare.  A  fasciculus  for  the  thumb  has  not 
been  reported.  (Le  Double.)  The  fasciculi  usually  arise  from  the  bones  of  the  ulnar  half  of 
the  carpus — lunatum  (semilunar),  triquetrum  (cuneiform),  hamatum  (unciform),  and  capitatum 
(magnum),  and  from  the  dorsal  ligaments  uniting  these  bones.  The  tendons  are  inserted  either 
into  the  corresponding  extensor  tendons  or  into  the  metacarpals.  The  muscle  is  found  in  about 
10  per  cent,  of  bodies  (Wood). 

BurSjB 

B.  m.  extensoris  carpi  radialis  brevis. — Between  the  tendon  and  the  base  of  the  third 
metacarpal. 

B.  m.  abductoiis  pollicis  longi. — Between  the  tendons  of  the  long  and  short  radial  extensors 
and  the  tendons  of  the  abductor  pollicis  longus  and  extensor  pollicis  brevis.  Another  bursa 
lies  beneath  the  tendon  of  insertion  of  the  abductor. 

B.  intermetacarpo-phalangeae. — Between  the  laXeral  surfaces  of  the  heads  of  the  meta- 
carpal bones  of  neighbouring  fingers  dorsal  to  the  transverse  capitular  ligament. 

B.  tendinum  m.  extensoris  digitorum  communis. — Small  bursae  are  sometimes  found  beneath 
the  tendons  to  the  index  and  little  fingers  near  where  they  begin  to  diverge  from  the  common 
tendon. 

B.  m.  extensoris  carpi  ulnaris. — A  small  bursa  may  be  found  under  the  tendon  of  origin 
of  this  muscle. 

B.  m.  supinatoris. — Between  the  supinator  and  the  tendon  of  the  extensor  muscles. 

B.  m.  extensoris  pollicis  longi. — Between  the  tendon  and  the  first  metacarpal. 

Synovial  Tendon-sheaths 

Vagina  tendinum  mm.  extensorum  carpi  radialium. — Synovial  sheaths  cover  the  tendons 
of  the  two  radial  carpal  extensors  as  they  pass  beneath  the  dorsal  carpal  (posterior  annular) 
ligament.  In  the  adult  these  sheaths  usually  are  more  or  less  fused  and  communicate  with  the 
sheath  of  the  extensor  pollicis  longus  where  this  crosses  them. 

Vagina  tendinum  mm.  extensoiis  digitorum  communis  et  extensoris  indicis. — A  synovial 
sheath  surrounds  the  tendons  of  these  muscles  as  they  pass  beneath  the  dorsal  carpal  (posterior 
annular)  ligament.     This  sheath  extends  for  some  distance  on  the  tendons  as  they  diverge. 

Vagina  tendinis  m.  extensoris  digiti  quinti. — A  synovial  sheath  extends  on  the  tendon  of 
this  muscle  from  above  the  dorsal  carpal  (posterior  annular)  ligament  to  the  base  of  the  meta- 
carpal. 

Vagina  tendinis  m.  extensoris  carpi  ulnaris. — This  sheath  commences  above  the  carpal 
(posterior  annular)  ligament  and  extends  to  the  insertion  of  the  tendon. 

Vagina  tendinum  mm.  abductoris  pollicis  longi  et  extensoris  pollicis  brevis. — The  sheaths 
which  surround  these  two  tendons  beneath  the  dorsal  carpal  (posterior  annular)  Ugament 
usually  communicate  freely. 

Vagina  tendinis  m.  extensoiis  pollicis  longi. — A  long  synovial  sheath  surrounds  this 
tendon.  Where  it  crosses  the  tendons  of  the  radial  extensors,  a  communication  is  found  with  the 
sheath  of  the  latter. 

2.  Ulno-Volar  Division 

The  muscles  on  the  volar  side  of  the  forearm  lie  in  four  layers. 

a.  First  Layer 
(Fig.  370) 

Of  the  four  muscles  of  associated  ulnar  epicondylar  origin  which  constitute 
this  layer  the  pronator  teres  is  a  strong,  band-like  muscle  which  is  inserted  into 


396 


THE  MUSCULATURE 


the  lateral  surface  of  the  middle  third  of  the  shaft  of  the  radius;  the  fusiform 
flexor  carpi  radialis  sends  a  tendon  to  the  base  of  the  second  metacarpal;  the 
slender  palmaris  longus  is  inserted  into  the  palmar  fascia;  and  the  medially 
situated,  fusiform  flexor  carpi  ulnaris  into  the  pisiform  bone  and  the  palmar 
fascia.     The  pronator  teres  is  the  most  powerful  pronator  of  the  forearm.     When 

Fig.  370. — Front  of  the  Forearm    First  Laier  of  Muscles. 


Pronator  teres 


Flexor  carpi  radialis  — 


Palmaris  longus 


Flexor  carpi  ulnaris 


Flexor  digitorum  sublimis 


Brachio-radialis 


Flexor  poUicis  longus 


the  hand  is  slightly  flexed  the  ulnar  carpal  flexor  abducts  ulnarward.  When  the 
hand  is  greatly  flexed  lateral  movement  is  difficult.  The  ulnar  flexor  is  supplied 
by  the  ulnar  nerve,  the  other  muscles  by  the  median. 

The  pronator  teres  probably  corresponds  with  the  pophteus  of  the  leg.  The  flexor  carpi 
radialis  and  flexor  carpi  ulnaris  probably  represent  in  the  main  the  two  heads  of  the  gastroc- 
nemius, and  the  palmaris  longus,  the  plantaris. 

The  pronator  teres  (fig.  370}. — Origin. — By  two  heads: — (1)  The  humeral  or  chief  head 
arises  by  a  tendon  from  the  superior  half  of  the  ventral  surface  of  the  medial  epioondyle  and 
directly  from  the  overlying  fascia  and  from  the  intermuscular  septa  between  it  and  the  medial 


PRONATOR  TERES 


397 


head  of  the  triceps  and  the  flexor  carpi  radialis.  (2)  The  ulnar,  deep  or  accessory,  head  arises 
by  an  aponeurotic  band  attached  to  the  inner  border  of  the  coronoid  process  medial  to  the 
tendon  of  the  brachialis.  Between  the  humeral  and  ulnar  heads  is  a  fibrous  arch  beneath 
which  the  median  nerve  passes. 

Structure  and  insertion. — The  fibre-bundles  of  the  humeral  head  are  inserted  in  a  penniform 
manner  on  a  tendon  which  begins  near  the  middle  of  the  belly  of  the  muscle  on  the  superficial 

Fig.  371. — Front  of  the  Forearm:  Second  Layer  op  Muscles. 


Muscles  of  first  layer 
Brachialis 


Flexor  digitorum  subli: 


Flexor  carpi  ulnans 


Flexor  carpi  radialis 
Palmaris  longus 


Brachio-radialis 


Extensor  carpi  radialis  longus 
Supinator 


Brachio-radialis 

Flexor  pollicis  longus 

Abductor  pollicis  longus 
Extensor  pollicis  brevis 


surface  along  the  radial  border.  The  tendon  gradually  becomes  broader,  winds  about  the  volar 
surface  of  the  radius,  and  is  inserted  into  the  middle  third  of  its  lateral  surface.  The  attach- 
ment of  fibre-bundles  continues  nearly  to  this  insertion.  The  fibre-bundles  of  the  ulnar  head 
form  a  slender  fasciculus  which  is  inserted  into  the  radial  side  of  the  deep  surface  of  the  humeral 
head. 

Nerve-supply. — By  a  branch  derived  from  the  median  nerve  before  it  passes  between  the  two 
heads  of  the  muscle.  The  nerve  enters  the  proximal  part  of  the  middle  third  of  the  main  belly 
of  the  muscle  on  its  deep  surface  near  the  radial  border.  The  branch  to  the  ulnar  head  usually 
enters  this  portion  of  the  muscle  somewhat  proximal  to  its  fusion  with  the  humeral  head. 
The  nerve  fibres  arise  from  the  sixth  and  seventh  cervical  nerves. 

Action. — To  pronate  and  flex  the  forearm. 


398  THE  MUSCULATURE 

Relations. — The  muscle  is  superficially  placed.  Near  its  origin  it  is  covered  by  the  lacertus 
fibrosus  of  the  biceps,  and  near  its  insertion  by  the  radial  vessels  and  nerve  and  the  brachio- 
radialis  and  radial  extensor  muscles.  It  is  the  most  radial  of  the  group  of  muscles  under  con- 
sideration. The  radial  border  helps  to  bound  an  angular  space,  the  cubital  fossa,  in  which  lie 
the  brachial  vessels,  median  nerve,  and  the  tendon  of  the  biceps.  The  median  nerve  passes 
between  its  humeral  and  ulnar  heads.  The  muscle  overlies  the  supinator,  the  brachialis,  and 
the  radial  origin  of  the  flexor  digitorum  sublimis  muscles  and  the  ulnar  artery. 

Variations. — Supplementary  fasciculi  may  arise  from  the  humerus,  the  medial  intermuscular 
septum  of  the  arm,  the  flexor  carpi  radialis,  the  flexor  sublimis,  or  the  brachiahs  muscles.  The 
two  portions  of  the  muscle  may  be  distinct  from  origin  to  insertion.  Either  part  of  the  muscle 
may  be  doubled.  The  ulnar  head  may  be  absent.  The  radial  insertion  may  be  extensive. 
Fasciculi  may  extend  to  the  long  flexor  of  the  thumb.  There  may  be  a  sesamoid  bone  in  the 
tendon  of  origin  from  the  humerus. 

The  flexor  carpi  radialis  (fig.  370). — Origin. — From  (1)  the  common  tendon  attached 
to  the  medial  epicondyle;  and  (2)  the  septa  between  its  head  and  the  pronator  teres,  the  flexor 
sublimis,  and  the  palmaris  longus. 

Structure  and  insertion. — The  fibre-bundles  descend  to  converge  upon  a  tendon  at  first  intra- 
muscular, but  which  in  the  middle  of  the  arm  appears  on  the  vblar  surface  of  the  muscle  and  soon 
becomes  free  from  the  attachment  of  fibre-bundles.  The  fibre-bundles  from  the  epicondyle 
descend  nearly  vertically  to  the  front  and  sides  of  the  tendon,  while  those  from  the  intermus- 
cular septa  take  an  oblique  course  to  the  deep  surface  of  the  tendon.  The  tendon  is  at  first 
flat,  but  soon  becomes  cylindrical,  bound  to  the  superficial  muscle  fascia,  and  enters  the  hand 
through  a  special  osteo-fibrous  canal  formed  mainly  by  the  groove  in  the  os  multangulum 
majus  (trapezium)  and  the  transverse  carpal  (anterior  annular)  ligament.  It  is  inserted  into 
the  base  of  the  second  metacarpal.     It  usually  also  sends  a  tendon  slip  to  the  third. 

Nerve-supply. — By  a  branch  from  the  median  nerve  which  divides  into  several  twigs  that 
enter  the  muscle  near  the  junction  of  its  proximal  and  middle  thirds  on  the  deep  surface.  The 
nerve  usually  arises  near  the  elbow.  The  nerve  fibres  arise  from  the  sixth,  seventh  (and  eighth) 
cervical  nerves. 

Action. — To  flex  the  hand  at  the  wrist.  To  a  slight  extent  it  may  also  act  as  a  pronator 
of  the  forearm  and  a  flexor  of  the  forearm  on  the  arm. 

Relations. — It  is  superficial  except  near  its  insertion.  The  belly  of  the  muscle  lies  between 
the  pronator  teres  and  the  palmaris  longus  and  upon  the  flexor  digitorum  sublimis.  The  tendon 
of  the  muscle  passes  over  the  flexor  poUicis  longus,  and  near  the  wrist  is  a  guide  to  the  radial 
artery,  which  here  lies  lateral  to  it.  In  the  hand  the  tendon  lies  beneath  the  thenar  muscles 
and  is  crossed  by  the  tendon  of  the  long  flexor  of  the  thumb. 

Variations. — It  may  receive  a  fasciculus  from  the  brachiahs  or  biceps  muscles  or  from  the 
radius  or  ulna.  It  may  send  tendon  slips  to  the  multangulum  majus  (trapezium),  navicular, 
the  transverse  carpal  (anterior  annular)  hgament,  or  the  fourth  metacarpal.  The  insertion 
may  take  place  variously  into  these  structures. 

The  palmaris  longus  (fig.  370). — Origin. — From  the  common  tendon  attached  to  the 
medial  epicondyle  and  from  the  surrounding  intermuscular  septa. 

Structure  and  insertion. — The  fibre-bundles  take  a  nearly  parallel  course  to  a  tendon  which 
appears  high  in  the  middle  third  of  the  forearm  on  the  volar  surface  of  the  muscle.  In  the 
middle  of  the  forearm  the  attachment  of  fibre-bundles  usually  ceases,  the  tendon  becomes 
bound  to  the  overlying  fascia,  and  descends  paraUel  with  that  of  the  radial  flexor.  Near  the 
proximal  border  of  the  transverse  carpal  (anterior  annular)  ligament  the  tendon  expands  into 
radiating  bundles  of  fibres  of  which  the  medial  and  lateral  are  attached  to  the  fascia  over  the 
intrinsic  muscles  of  the  thumb  and  little  finger,  while  the  middle,  much  more  developed,  con- 
stitute the  chief  portion  of  the  palmar  aponeurosis. 

Nerve-supply. — From  a  branch  which  usually  arises  in  company  with  the  nerve  to  the 
proximal  part  of  the  flexor  sublimis.  It  frequently  traverses  the  superficial  fibres  of  the  flexor 
sublimis.     The  nerve  enters  the  middle  third  of  the  muscle. 

Action. — To  flex  the  hand.     It  is  also  a  weak  flexor  and  pronator  of  the  forearm. 

Relations. — It  is  placed  between  the  radial  and  ulnar  flexors  over  the  flexor  sublimis. 
In  the  distal  part  of  the  forearm  the  tendon  lies  over   the  median  nerve. 

Variations. — It  is  absent  in  11.2  per  cent,  of  instances  (Le  Double).  It  may  be  highly 
developed  or  reduced  to  a  tendinous  band.  The  belly  of  the  muscle  may  lie  in  the  distal  instead 
of  in  the  proximal  part  of  the  forearm.  It  may  be  digastric.  It  may  be  fused  with  neighbouring 
muscles.  It  may  arise  from  the  medial  intermuscular  septum  of  the  arm  or  from  the  lacertus 
fibrosus,  from  the  radius,  from  the  coronoid  process,  from  the  radial  or  ulnar  flexor,  or  from  the 
flexor  sublimis  muscles.  The  tendon  may  terminate  in  the  fascia  of  the  forearm,  the  thenar 
eminence,  the  carpus,  or  the  abductor  of  the  thumb.  The  muscle  may  be  partly  or  wholly 
doubled. 

The  flexor  carpi  ulnaris  (fig.  370). — Origin. — By  two  heads: — (1)  the  humeral  head  arises 
from  the  common  flexor  tendon  attached  to  the  lower  ventral  part  of  the  medial  epicondyle 
Fibre-bundles  of  this  head  are  also  attached  to  the  surrounding  intermuscular  septa  and  the 
deep  fascia  of  the  forearm.  (2)  The  ulnar  head  arises  by  short  tendinous  fibres  from  the  medial 
side  of  the  olecranon  and  by  an  aponeurotic  band  common  to  it  and  the  flexor  digitorum  pro- 
fundus from  the  upper  two-thirds  of  the  dorsal  border  of  the  ulna.  Proximally  the  two  heads 
of  the  muscle  are  united  by  a  fibrous  arch  extending  from  the  olecranon  to  the  medial  epi- 
condyle. Beneath  this  band  pass  the  ulnar  nerve  and  the  dorsal  recurrent  ulnar  artery.  (See 
Epitrochleo-olecranonis,  p.  402.) 

Structure  and  insertion. — The  fibre-bundles  of  the  humeral  head  descend  nearly  vertically, 
those  of  the  ulnar  head  obliquely  distally  in  a  radial  direction.  They  are  iiiserted  in  a  penniform 
manner  on  a  tendon  which  appears  in  the  proximal  part  of  the  middle  third  of  the  belly  of  the 
muscle  on  the  radial  margin  of  the  deep  surface,  and  in  the  distal  third  of  the  forearm  forms  the 
radial  border  of  the  muscle.     On  the  ulnar  side  the  insertion  of  fibre-bundles  continues  nearly 


FLEXOR  DIGITORUM  SUBLIMIS  399 

to  the  pisiform  bone.  The  insertion  of  the  tendon  takes  place  chiefly  into  the  pisifoi'in  bone, 
but  from  it  tendinous  bundles  extend  to  the  palmar  aponeurosis,  volar  ligament  of  the  carpus, 
to  the  pisohamate  ligament  (pisi-unciform),  and  to  the  bases  of  the  fifth,  fourth,  and  third 
metacarpals. 

Nerve-supply. — From  two  or  three  branches  of  the  ulnar  nerve,  the  most  pro.ximal  of  which 
arises  near  the  elbow-joint.  These  branches,  which  may  arise  by  a  single  trunk,  enter  the  deep 
surface  of  the  proximal  third  of  the  muscle  and  send  long  twigs  distally  across  the  middle  third 
of  the  constituent  fibre-bundles.  The  nerve  fibres  arise  from  the  seventh  and  eighth  cervical 
and  first  thoracic  nerves. 

Action. — To  flex  the  hand  and  to  abduct  the  hand  ulnarward. 

Relations. — It  is  superficially  placed.  Its  aponeurotic  origin  is  adherent  to  the  fascia 
of  the  forearm.  It  lies  medial  to  the  palmaris  longus  and  flexor  sublimis  and  upon  the  flexor 
profundus.  Beneath  the  muscle  lies  the  ulnar  nerve.  The  ulnar  artery  extends  along  the 
radial  border  of  the  tendon  near  the  wrist. 

Variations. — These  are  rare.  Slips  from  the  tendon  may  pass  to  the  metacarpo-phalangeal 
articulation  of  the  little  finger.     (See,  however.  Abnormal  Muscles,  p.  402.) 

b.  Second  Layer 

This  is  composed  of  one  muscle,  the  flexor  digitorum  sublimis,  which, 
although  in  part  covered  by  the  muscles  of  the  preceding  layer,  is  in  part  super- 
ficial. It  arises  from  the  medial  epicondyle  of  the  humerus,  and  from  the  radius 
and  the  ulna,  and  sends  tendons  to  the  second  row  of  phalanges  of  the  fingers. 
It  corresponds  probably  with  the  soleus  and  the  tendons  of  the  flexor  digitorum 
brevis  in  the  leg  and  foot. 

The  flexor  digitorum  sublimis  (figs.  371,  373,  375). — Origin. — By  two  heads:  the  ulnar 
or  chief  head  arises  (1)  by  the  tendon  common  to  it  and  the  superficial  group  of  muscles  from 
the  medial  epicondyle,  and  by  short  tendinous  bands  from  the  ventral  surface  of  the  epicondyle; 
(2)  from  the  ulnar  collateral  ligament  of  the  elbow,  the  ulnar  tuberosity,  the  medial  border  of 
the  coronoid  process,  and  the  inferior  extremity  of  the  tendon  of  the  brachialis;  and  (3)  from 
the  intermuscular  septum  between  the  flexor  subhmis  and  the  overlying  muscles.  The  radial 
head  arises  from  an  oblique  line  on  the  volar  surface  of  Ijje  radius,  and  from  the  middle  third 
of  the  anterior  border. 

Insertion. — Into  the  sides  of  the  volar  surface  of  the  shafts  of  the  second  row  of  phalanges  of 
the  fingers. 

Structure. — The  fibre-bundles  of  the  ulnar  head  and  the  upper  part  of  the  radial  head  con- 
verge, the  ulnar  fibre-bundles  nearly  vertically,  the  radial  obliquely,  to  form  a  common  belly 
the  deep  surface  of  which  on  the  ulnar  side  is  backed  by  a  dense  tendinous  band.  On  the  radial 
side  of  this  a  less  dense  membrane  covers  over  an  oval  canal  which  passes  distally  along  the 
line  of  junction  of  the  two  heads  and  lodges  the  ulnar  artery  and  the  median  nerve. 

The  fibre-bundles  of  the  ulnar  head  form  a  superficial  and  a  deep  group.  The  superficial 
portion  near  the  middle  of  the  forearm  divides  into  a  lateral  and  a  medial  division,  the  former 
being  inserted  on  a  tendon  that  goes  to  the  middle  and  the  latter  on  one  that  goes  to  the  ring 
finger.  The  fibre-bundles  of  the  radial  head  join  with  the  lateral  division  of  the  superficial 
layer  of  the  ulnar  head  and  are  inserted  on  the  tendon  of  the  middle  finger  nearly  as  far  as  the 
wrist.  A  small  muscle  fasciculus  of  the  superficial  portion  of  the  ulnar  head  is  usually  united 
by  a  tendon  to  the  long  flexor  of  the  thumb. 

The  deep  portion  of  the  ulnar  head  about  the  middle  of  the  forearm  terminates  in  large  part 
on  the  volar  surface  of  the  dense  tendinous  band  above  mentioned.  From  this  in  turn  two 
muscle  bellies  arise.  One  of  these  is  inserted  in  a  bipenniform  manner  on  a  tendon  going  to 
the  index  finger,  the  other  on  a  tendon  going  to  the  little  finger.  A  muscle  fasciculus  also  usually 
passes  from  the  region  of  the  tendon  band  to  that  portion  of  the  superficial  fasciculus  which 
terminates  on  the  tendon  of  the  ring  finger. 

The  four  tendons  pass  together  through  the  carpal  canal  under  the  transverse  carpal 
(anterior  annular)  ligament,  those  to  the  middle  and  ring  fingers  lying  at  first  superficial  to  the 
other  two.  The  tendons  then  diverge,  and  each  tendon,  together  with  and  above  a  tendon  of 
the  flexor  profundus,  passes  over  the  metacarpo-phalangeal  joint  into  an  osteo-fibrous  canal  on 
the  palmar  surface  of  the  first  phalanx  of  the  finger  for  which  it  is  destined.  Here  the  tendon 
becomes  flattened  about  the  round  tendon  of  the  flexor  profundus.  Opposite  the  middle  of  the 
phalanx  the  tendon  divides  into  two  slips,  between  which  the  tendon  of  the  flexor  profundus 
passes.  The  divided  halves  of  the  sublimis  tendon  fold  about  the  profundus  tendon  so  that  their 
lateral  edges  come  to  meet  in  the  mid-line  beneath  this  tendon  opposite  the  phalangeal  joint 
(figs.  375,  376).  They  then  again  separate,  extend  distally,  and  are  attached  one  on  each  side 
into  a  ridge  at  the  middle  of  the  lateral  border  of  the  second  phalanx.  The  tendons  are  also 
attached  by  vincula  tendinum,  a  ligamentum  breve,  between  the  tendon  and  the  head  of  the 
first  phalanx  and  the  joint,  and  a  ligamentum  longum,  between  the  tendon  and  the  volar  surface 
of  the  first  phalanx. 

Nerve-supply. — Before  the  median  nerve  passes  between  the  two  heads  of  the  pronator 
teres  a  branch  arises  which  accompanies  the  nerve  through  the  pronator  and  sends  several 
branches  into  the  proximal  third  of  the  ulnar  head  of  the  muscle.  As  the  median  nerve  passes 
beneath  the  muscle,  one  or  more  branches  are  given  to  the  radial  head,  and  a  long  branch  is  given 
to  the  fasciculus  of  the  second  and  from  this  one  to  that  of  the  fifth  digit.  Occasionally,  the 
median  nerve  in  the  distal  third  of  the  forearm  gives  rise  to  branches  for  these  fasciculi.  The 
nerve  fibres  arise  from  the  seventh  and  eighth  cervical  and  first  thoracic  nerves. 

Action. — Chiefly  to  flex  the  second  phalanx  of  each  finger  on  the  first;  secondarily,  to  flex 
the  fingers  on  the  hand  and  the  hand  on  the  forearm. 


400 


THE  MUSCULATURE 


Relations. — The  belly  of  the  muscle  is  covered  by  the  pronator  teres,  flexor  carpi  radialis, 
and  palmaris  longus,  but  is  superficial  along  a  narrow  strip  between  the  flexor  carpi  ulnaris  and 
the  palmaris  longus,  and  on  each  side  of  the  tendon  of  the  flexor  carpi  radialis.  The  muscle 
rests  on  the  flexor  pollieis  longus  and  flexor  digitorum  profundus,  the  median  nerve  (see  de- 
scription given  above)  and  ulnar  vessels.  The  median  nerve  emerges  from  beneath  the  radial 
border  of  the  muscle  in  the  lower  third  of  the  forearm.     In  the  palm  the  tendons  lie  beneath  the 

Fig.  372. — Front  of  the  Forearm:  Third  Later  of  Muscles. 


Brachio-radialis 


Muscles  of  the  first  and  second  ,^</J 
layers  \  li 


Flexor  digitorum  profundus. 


Pronator  quadratus 


Brachialis 

Extensor  carpi  radialis  longus 
Supinator 


■Flexor  pollieis  longus 


■Brachio-radialis 


■Abductor  pollieis  longus 


■Extensor  pollieis  brevis 


pahnar  aponeurosis,  the  superficial  palmar  arch,  and  the  branches  of  the  median  nerve,  while 
they  lie  in  front  of  the  tendons  of  the  fle.xor  profundus,  with  which  they  are  closely  associated 
into  a  common  bundle  by  loose  fibrous  tissue.  The  digital  relations  of  the  tendons  are  described 
above. 

Variations. — The  whole  muscle  may  be  rendered  digastric  by  a  transverse  tendon.  A 
fasciculus  of  the  flexor  sublimis  may  replace  the  palmaris  longus  or  the  two  may  coexist.  A 
fasciculus  may  terminate  in  the  fascia  of  the  forearm  or  in  the  transverse  carpal  ligament,  the 
palmar  aponeurosis,  etc.  Various  parts  of  the  muscle  may  be  absent  or  more  independent  than 
usual.  The  extent  of  the  radial  attachment  varies  greatly  and  may  be  missing.  A  special 
fasciculus  may  be  received  from  the  coronoid  process  of  the  ulna.  A  fasciculus  may  be  sent  to 
the  flexor  profundus  or  to  other  muscles.  There  may  be  some  fusion  with  neighbouring 
muscles. 


FLEXOR  DIGITORUM  PROFUNDUS  401 

c.  Third  Layer 
(Figs.  372-376) 

The  two  muscles  which  constitute  this  layer  may  be  looked  upon  as  differen- 
tiated from  a  single  deep  flexor  muscle.  The  flexor  digitorum  profundus  is  a 
strong,  broad  muscle  which  arises  from  the  upper  three-fourths  of  the  volar  surface 
of  the  ulna  and  gives  rise  to  tendons  which  are  inserted  into  the  bases  of  the  third 
row  of  phalanges  of  the  fingers.  The  flexor  pollicis  longus,  likewise  broad  and  flat, 
arises  from  the  volar  surface  of  the  radius  and  is  inserted  into  the  base  of  the 
second  phalanx  of  the  thumb.  Both  muscles  are  supplied  by  the  median  nerve 
and  the  flexor  profundus  is  also  supplied  by  the  ulnar  nerve. 

These  muscles  correspond  to  the  flexor  digitorum  longus  and  the  flexor  hallu- 
cis  longus  of  the  leg. 

The  flexor  digitorum  profundus  (figs.  372-,376). — Origin. — (1)  Through  an  aponeurotic 
septum  between  it  and  the  fiexor  earpi  ulnaris  from  the  dorsal  border  of  the  ulna;  (2)  directly 
from  the  proximal  two-thirds  of  the  medial  surface  and  the  proximal  three-fourths  of  the  volar 
surface  of  the  uhia  and  from  the  adjacent  interosseous  membrane;  and  (3)  inconstantly,  from  a 
small  area  on  the  radius  below  the  bicipital  tuberosity. 

Structure  and  insertion. — The  fibre-bundles  descend  nearly  vertically  and  give  rise  to  a 
common  belly  which  soon  divides  into  four  portions,  each  of  which  is  attached  about  midway 
down  the  forearm  in  a  semipennif orm  manner  to  the  dorsal  surface  of  a  tendon.  The  attachment 
of  fibre-bundles  continues  nearly  to  the  wrist.  The  digital  divisions  of  the  muscle  vary  in  the 
height  to  which  they  extend.     That  belonging  to  the  index  finger  is  usually  the  one  most  exten- 

FiG.  373. — Insertions  of  the  Tendons  of  the  Muscles  which  act  on  the  Fingee. 
(After  Toldt,  Atlas  of  Human  Anatomy,  Rebman,  London  and  New  York.) 


dOD  of  fiexor  digitorum  sublin 


sively  isolated,  and  that  to  the  little  finger  is  the  next  most  so.  The  tendons  pass  side  by  side 
under  the  transverse  carpal  (anterior  annular)  ligament,  and  then  diverge  to  the  bases  of  the 
fingers.  At  the  metacarpo-phalangeal  joints,  they  enter  the  osteo-fibrous  canals  described 
above  (p.  387).  On  the  volar  surface  of  the  first  phalanx  each  tendon  passes  through  the  sht 
in  the  subhmis  tendon.  The  tendon  then  is  continued  over  the  second  phalanx  to  the  base  of  the 
third.  Vincula  tendinum  are  described  passing  to  the  capsule  of  the  second  interphalangeal  joint 
(ligamentum  breve)  and  to  the  tendon  of  the  flexor  subhmis  (ligamentum  longum).  The 
lumbrical  muscles  arise  from  the  tendons  while  they  are  in  the  palm. 

Nerve-supply. — The  interosseous  branch  of  the  median  nerve  arises  usually  before  the 
nerve  passes  through  the  pronator  teres  and  accompanies  the  main  trunk.  This  branch  as  it 
passes  beneath  the  flexor  sublimis  gives  off  a  branch  (or  two)  from  which  several  twigs  spring. 
These  twigs  enter  the  muscle  near  the  radial  border  and  pass  in  across  the  middle  third  of  the 
constituent  fibre-bundles  of  the  fasciculi  to  the  index  and  middle  fingers.  The  ulnar  nerve  near 
the  elbow  gives  rise  to  a  branch  which  enters  the  volar  surface  of  the  muscle  near  the  junction 
of  the  proximal  and  middle  thirds  of  that  portion  of  the  belly,  giving  tendons  to  the  ring  and 
little  fingers.  There  is  some  variation  in  the  extent  of  the  innervation  by  the  branches  of  the 
ulnar  and  those  of  the  median  nerve.  To  a  greater  or  less  extent  through  anastomosis  their 
territories  overlap.  The  nerve  fibres  arise  from  the  seventh  and  eighth  cervical  and  first 
thoracic  nerves. 

Action. — To  flex  the  terminal  phalanx  of  each  finger  on  the  second  and  the  second  on 
the  first,  while  that  of  the  superficial  flexor  is  to  flex  the  second  phalanx  on  the  first.  The 
action  of  the  two  flexors  on  the  first  phalanx  is  somewhat  more  limited.  The  interosseous 
muscles,  aided  by  the  lumbricals,  are  the  chief  flexors  of  the  first  row  of  phalanges.  The  flexor 
profundus  acts,  though  not  powerfully,  as  a  flexor  of  the  wrist. 

Relations. — The  flexor  profundus  muscle  lies  beneath  the  flexor  sublimis  and  the  flexor  carpi 
ulnaris  muscles,  the  median  nerve,  and  the  ulnar  vessels  and  nerve.  Under  the  muscle  lie  the 
ulna,  the  interosseous  membrane,  and  the  pronator  quadratus  muscle.  Under  the  transverse 
carpal  (anterior  annular)  ligament  the  tendons  lie  beneath  those  of  the  flexor  sublimis  in  the 
same  synovial  sac.  In  the  palm  the  tendons  with  the  associated  lumbrical  muscles  lie  upon  the 
interosseous  muscles,  the  adductor  of  the  thumb,  and  the  deep  palmar  arch,  and  beneath  the 
flexor  sublimis  tendons.     For  the  relations  to  the  synovial  bursse  see  p.  403. 


402  THE  MUSCULATURE 

Variations. — There  is  considerable  variation  in  the  extent  of  the  radial  origin  and  in  the 
extent  of  the  independence  and  fusion  of  the  different  fasciculi.  In  the  prosimians  a  common 
tendon  extends  as  far  as  the  hand.  The  division  in  the  higher  forms  is  associated  with  refine- 
ment of  movements  of  the  fingers.  One  or  more  special  fasciculi  not  infrequently  join  the 
muscle  from  the  flexor  sublimis,  the  flexor  pollicis  longus,  the  medial  epicondyle,  or  the  ulna. 
The  accessorius  ad  flexorem  digitorum  profundum  is  a  fasciculus  which  arises  from  the  coro- 
noid  process  of  the  ulna  and  sends  a  tendon  to  join  the  tendon  of  one  of  the  fingers,  most  fre- 
quently the  middle  or  index.     It  is  found  in  20  per  cent,  of  bodies. 

The  flexor  pollicis  longus  (fig.  372). — Origin. — The  attachment  extends  along  the  oblique 
line  and  the  ventral  border  of  the  radius  from  slightly  below  the  bicipital  tuberosity  to  within 
5  cm.  of  the  wrist.  Medially  it  is  continued  into  the  interosseous  membrane.  Proximally  the 
tendon  frequently  extends  to  the  distal  radial  margin  of  the  coronoid  process  of  the  ulna  and 
gives  rise  to  fibre-bundles  connected  with  the  muscle,  as  well  as  to  a  fasciculus  of  the  flexor 
profundus. 

Structure  and  insertion. — The  fibre-bundles  descend  obliquely  to  be  inserted  in  a  penni- 
form  manner  on  a  tendon  which  begins  high  up  on  the  volar  surface  near  the  ulnar  border 
of  the  muscle,  and  descends  as  a  broad  band  which  near  the  wrist  becomes  cyhndroid.  The 
insertion  of  fibres  continues  nearly  to  the  point  where  the  tendon  passes  under  the  transverse 
carpal  ligament.  Here  the  tendon  enters  the  carpal  canal  radial  to  the  tendons  of  the  flexor 
profundus,  and  passes  beneath  the  superficial  head  of  the  short  flexor  of  the  thumb,  then  between 
the  thumb  sesamoids  into  the  osteo-fibrous  canal  of  the  thumb,  in  which  it  is  continued  to  the 
base  of  the  terminal  phalanx. 

Nerve-supply. — Usually  from  two  branches  of  the  volar  interosseous  ramus  of  the  median 
nerve.  These  enter  the  proximal  half  of  tlie  ulnar  margin  of  the  muscle.  The  nerve  fibres 
arise  from  the  sixth,  seventh  (and  eighth)  cervical  nerves. 

Action. — It  is  a  strong  flexor  of  the  second  phalanx  on  the  first  and  has  less  powerful  action 
.  on  the  metacarpo-phalangeal  joint  and  on  the  wrist. 

Relations. — It  lies  beneath  the  flexor  subhmis,  the  flexor  carpi  radialis  and  brachio-radialis 
muscles,  and  the  radial  artery.  Near  the  wrist  it  crosses  over  the  insertion  of  the  pronator 
quadratus.  In  the  hand  the  tendon  runs  beneath  the  opponens  pollicis  and  the  superficial  head 
of  the  flexor  brevis,  and  across  the  deep  head  of  the  latter. 

Variations. — It  may  be  fused  or  united  by  fasciculi  with  the  flexor  profundus,  the  flexor 
subhmis,  or  the  pronator  teres.  It  may  be  partially  doubled,  giving  rise  to  an  accessory  ten- 
don which  extends  to  the  index  finger.  The  origin  may  extend  to  the  medial  epicondyle  of 
the  humerus  (epitrochlear  bundle). 

d.  Fourth  Layer 

This  layer  consists  of  a  single  quadrilateral  muscle  which  passes  transversely 
across  the  lower  part  of  the  forearm  from  the  ulna  to  the  radius.  In  the  leg  there 
is  no  corresponding  muscle. 

The  pronator  quadratus  (fig.  377). — Origin. — Medial  side  of  the  volar  sm-face  of  the  lower 
fourth  of  the  ulna. 

Structure  and  insertion. — From  the  ulna  a  strong  aponeurosis  extends  a  third  of  the  way 
across  the  volar  surface  of  the  muscle.  From  this  membrane  and  from  the  bone  fibre-bundles 
extend  transversely  to  be  inserted  on  the  distal  quarter  of  the  volar  surface  of  the  radius  and  on 
the  triangular  area  above  the  ulnar  notch.  The  deeper  fibre-bundles  which  arise  directly  from 
the  ulna  are  inserted  into  the  radius  by  means  of  an  aponeurosis.  The  superficial  and  deep 
portions  of  the  muscle  are  often  separated.     The  muscle  is  thicker  distally  than  proximally. 

Nerve-supply. — The  volar  interosseous  nerve  descends  along  the  interosseous  membrane, 
passes  behind  the  middle  of  the  proximal  margin  of  the  muscle,  and  sends  branches  into  its 
deep  surface.  The  nerve  fibres  arise  from  the  (sixth),  seventh  and  eighth  cervical  and  first 
thoracic  nerves. 

Action. — To  pronate  the  forearm. 

Relations. — The  muscle  lies  immediately  beneath  the  muscles  of  the  third  layer  and  upon 
the  radius  and  ulna,  the  interosseous  membrane,  and  radio-ulnar  joint.  The  radial  artery  and 
ulnar  nerve  pass  in  front  of  it,  the  volar  interosseous  artery  behind  it. 

Variations. — It  may  be  missing  or  may  extend  further  up  the  forearm  than  usual  or  down 
upon  the  carpus.  It  may  be  triangular  or  divided  into  parts  the  fibre-bundles  of  which  take 
different  directions.  It  may  send  fasciculi  to  the  carpus  or  metacarpus  or  be  fused  with  the 
flexor  carpi  radialis  brevis  (see  below). 

Abnormal  Muscles  of  the  Volar  Side  of  the  Forearm  and  Wrist 

The  epitrochleo-olecranonis  (anconeus  internus). — A  muscle  fasciculus,  distinct  from 
the  distal  margin  of  the  triceps,  which  runs  from  the  medial  epicondyle  to  the  olecranon  over 
the  groove  for  the  ulnar  nerve,  by  a  branch  of  which  it  is  supplied.  It  takes  the  place  of  the 
fibrous  arch  normally  extending  between  the  epicondylar  and  ulnar  heads  of  the  flexor  carpi 
ulnaris.  It  occurs  in  about  25  per  cent,  of  bodies  (Testut),  and  represents  an  adductor  of  the 
olecranon  of  the  lower  mammals.  Occasionally  the  medial  head  of  the  triceps  may  descend 
over  the  ulnar  groove,  but  this  forms  another  type  of  muscle  variation. 

The  flexor  carpi  ulnaris  brevis  (ulno-carpeus). — An  abnormal  muscle  which  arises  from 
the  distal  quarter  of  the  volar  surface  of  the  ulna  and  is  inserted  into  the  hamatum  (unciform), 
the  pisiform,  the  abductor  of  the  little  finger,  or  the  superior  extremity  of  the  fifth  metacarpal. 


MUSCLES  OF  THE  HAND 


403 


The  unci-pisiformis. — A  short,  thick  band  of  muscle  which  runs  from  the  pisiform  to  the 
tip  of  the  hamulus  of  the  os  hamatum  (unciform)  parallel  with  the  pisohamate  (pisi-unciform) 
ligament.     It  is  innervated  by  the  ulnar  nerve. 

The  flexor  carpi  radialis  brevis  (radio-carpeus). — An  abnormal  muscle  found  in  about  5  per 
cent,  of  bodies  (Le  Double).  It  arises  from  the  lateral  or  the  volar  surface  of  the  distal  half 
of  the  radius.  Some  of  the  fibre-bundles  may  spring  from  the  pronator  quadratus,  the  fascia 
of  the  forearm,  or  the  ulna.  It  is  inserted  into  the  carpus  or  metacarpus,  and  occasionally  even 
into  the  first  phalanx  of  the  index  finger,  etc.  It  is  supplied  by  a  branch  of  the  volar  interosse- 
ous nerve.     It  serves  to  flex  the  wrist.     It  is  said  to  represent  the  tibialis  posterior  of  the  leg. 

BURS^ 

B.  m.  flexoris  carpi  ulnaris. — Between  the  tendon  of  this  muscle  and  the  pisiform  bone. 
B.  m.  flexoris  carpi  radialis. — Between  the  tendon  of  this  muscle  and  the  tubercle  of  the 
navicular  bone. 

Fig.  374. — Synovial  Sheaths  of  the  Tendons  op  the  Long  Flexors  op  the  Fingers 
A.  Frequent  type;  B.  normal  type;  C.  foetal  type.     (After  Poirier  and  Charpy.) 


A  bursa  is  often  found  between  the  tendon  of  the  deep  flexor  of  the  index  finger  and  the 
carpus.     This  bursa  is  frequently  in  communication  with  the  radial  and  ulnar  tendon  sheaths. 
A  bursa  is  also  often  found  between  the  deep  and  superficial  tendons  of  the  index  finger. 


Synovial  Tendon  Sheaths 
(Figs.  366  and  374) 

Vagina  tendinis  m.  flexoris  carpi  radialis. — About  the  tendon  as  it  passes  beneath  the 
transverse  carpal  ligament. 

Vaginae  tendinum  mm.  flexorum  digitorum. — The  osteo-fibrous  canals  of  the  digits  are 
lined  by  a  synovial  membrane  which  is  reflected  by  means  of  a  fold  (oul-de-sac)  to  the^tendons  at 
each  end  and  over  the  vincula  tendinum,  in  which  blood-vessels  and  nerves  for  the  tendons  are 
contained.  The  synovial  cavity  of  the  first  and  usually  that  of  the  fifth  digit  communicate 
with  those  of  the  palm. 

In  the  wrist  and  palm  two  large  synovial  sacs  may  usually  be  recognized,  although  the 
number  may  be  raised  to  five  or  reduced  to  one. 

The  radial  sac,  vagina  tendinis  m.  flexoris  pollicis  longi,  surrounds  the  long  flexor  tendon 
of  the  thumb  in  the  wrist  and  palm  and  usually  communicates  with  that  of  the  thumb.  In  the 
palm  a  well-marked  mesotendon  usually  extends  to  the  deep  ulnar  side  of  the  tendon  from  the 
parietal  layer  of  the  sheath. 

The  ulnar  sac,  vagina  tendinum  mm.  flexorum  communium,  surrounds  the  tendons  of  the 
long  flexors  of  the  fingers.  It  begins  proximal  to  the  transverse  carpal  ligament  and  extends 
nearly  or  quite  to  the  synovial  sheath  of  the  little  finger  on  the  ulnar  side  and  on  the  radial 
side  to  the  centre  of  the  palm. 

3.  Musculature  of  the  Hand 

(Figs.  366,  368,  375-379) 

The  intrinsic  muscles  of  the  hand  are  taken  up  in  the  following  groups : — 

a  The  subcutaneous  muscle  of  the  palm. 

b  The  muscles  of  the  little  finger, 

c  The  muscles  of  the  thumb. 

d  The  lumbrical  muscles, 

e  The  interosseous  muscles. 


404  THE  MUSCULATURE 

The  ulnar  nerve  supplies  the  muscles  of  the  little  finger,  the  interossei,  the 
medial  lumbrical  muscles,  and  two  of  the  muscles  of  the  thumb;  the  median 
nerve  supplies  most  of  the  muscles  of  the  thenar  region  and  the  lateral  lumbrical 
muscles. 

(a)  Subcutaneous  Muscle 
(Fig.  375) 

The  palmaris  brevis  is  a  small,  trapezoid  sheet  situated  between  the  hypothe- 
nar  fascia  and  the  skin.  It  arises  at  the  lateral  edge  of  the  palmar  aponeurosis 
from  tendinous  slips  which  may  be  traced  through  the  aponeurosis  to  the  navicular 
and  greater  multangular.  It  is  composed  of  nearly  parallel  fibre-bundles,  and  ex- 
tends into  the  deep  surface  of  the  skin  along  the  ulnar  border  of  the  palm.  It  is 
generally  taken  to  be  a  subcutaneous  muscle  like  the  superficial  muscles  of  the 
head  and  neck.  It  has,  however,  been  suggested  that  it  represents  the  remnants 
of  a  short  flexor  of  the  digits  corresponding  with  the  flexor  digitorum  brevis  of  the 
foot. 

Nerve-supply. — The  superficial  branch  of  the  palmar  division  of  the  ulnar  nerve  gives  rise 
to  a  twig  which  enters  the  deep  surface  of  the  muscle.  The  fibres  come  from  the  (seventh  and) 
eighth  cervical  and  first  thoracic  nerves. 

Action. — The  action  of  the  muscle  is  to  draw  the  skin  of  the  ulnar  side  of  the  hand  toward 
the  centre  of  the  palm.  It  is  said  that  it  thus  helps  to  form  a  cup-shaped  hollow  when  the  hand 
conveys  fluid  to  the  mouth.  The  contraction  of  the  muscle  by  raising  a  ridge  over  the  ulnar 
nerve  and  artery  when  an  object  is  grasped  hard  serves,  according  to  Henle,  to  protect  these 
structures. 

Variations. — It  varies  in  size.  In  about  2  per  cent,  of  bodies  it  is  absent  (Le  Double). 
It  may  send  tendinous  slips  to  the  pisiform  bone.  (For  a  thenar  subcutaneous  muscle,  see 
variations  of  the  abductor  polhcis  brevis.) 

(h)  Muscles  of  the  Little  Finger 
(Figs.  375,  376,  377) 

In  the  hypothenar  eminence  are  three  muscles,  the  abductor,  the  flexor  brevis, 
and  the  opponens  digiti  quinti.  The  abductor  digit!  quinti  is  a  flat,  fusiform 
muscle  which  arises  from  the  pisiform  and  is  inserted  into  the  ulnar  border  of  the 
first  phalanx  and  into  the  dorsal  aponeurosis  through  which  it  helps  to  flex  the 
first  and  extend  the  second  and  third  phalanges  of  the  little  finger.  The  fusiform 
flexor  brevis  arises  from  the  hamatum  (unciform)  and  adjacent  part  of  the  trans- 
verse carpal  (anterior  annular)  ligament  and  is  inserted  into  the  ulnar  side  of  the 
base  of  the  first  phalanx.  The  triangular  opponens  likewise  arises  from  the  hama- 
tum (unciform)  and  the  transverse  (anterior  annular)  ligament.  It  is  inserted 
into  the  ulnar  border  and  the  head  of  the  fifth  metacarpal. 

The  abductor  of  the  little  finger  corresponds  with  that  of  the  little  toe.  A  part  of  the  oppo- 
nens beneath  the  ulnar  nerve  corresponds  with  that  of  the  little  toe,  while  the  more  superficial 
portion  is  unrepresented  in  the  foot.  The  flexor  brevis  of  the  httle  toe  corresponds  with  a  part 
of  the  deep  portion  of  the  opponens  of  the  little  finger.  The  flexor  brevis  of  the  httle  finger 
is  unrepresented  in  the  foot.     (Cunningham.) 

The  abductor  digiti  quinti  (figs.  375,  376). — Origin.— Yrom  the  distal  half  of  the  pisiform, 
the  ligaments  between  this  and  the  hamatum,  the  tendon  of  the  flexor  cai'pi  ulnaris,  and  often 
from  the  transverse  carpal  (anterior  annular)  ligament. 

Structure  and  insertion. — The  fibre-bundles  descend  vertically,  at  first  increasing  in  number 
and  then  concentrated,  toward  two  short  tendons  one  of  which  is  inserted  into  the  ulnar  border 
of  the  first  phalanx  of  the  little  finger  and  the  other  into  the  aponeurosis  of  the  extensor  tendon 
of  the  httle  finger. 

Nerve-suppbj. — From  the  deep  palmar  division  of  the  ulnar  nerve  before  it  passes  through 
the  opponens,  or  from  the  superficial  palmar  branch,  arise  one  or  more  twigs  which  enter  the 
radia)  side  of  the  muscle  on  its  deep  sm'face  in  the  proximal  third.  The  nerve  fibres  arise  from 
the  (seventh  and)  eighth  cervical  and  fu'st  thoracic  nerves. 

Action. — To  abduct  the  little  finger,  flex  the  first  phalanx,  and  extend  the  last  two. 

Relations. — It  overlies  the  opponens  and  flexor  brevis.  Superficially  it  is  covered  by  fascia 
and  the  palmaris  brevis  muscle.  Along  the  proximal  part  of  its  radial  margin  run  the  deep 
palmar  branches  of  the  ulnar  artery  and  nerve. 

Variations. — It  may  be  missing  or  doubled.  It  may  be  fused  with  the  short  flexor  or 
receive  fasciculi  from  the  palmaris  longus,  the  ulnar  flexor,  the  fascia  of  the  forearm,  etc. 

The  flexor  digiti  quinti  brevis  (figs.  376,  377). — Origin. — By  a  short  tendon  from  the  hook  of 
the  hamatum  (unciform)  and  from  the  adjacent  parts  of  the  transverse  carpal  (anterior  annular) 
ligament. 

Structure  and  insertion. — The  fibre-bundles  take  a  nearly  parallel  com'se  and  are  inserted 


MUSCLES  OF  LITTLE  FINGER 


405 


by  a  short  tendon  which  is  fused  with  that  of  the  abductor  and  is  inserted  into  the  ulnar  side  of 
the  base  of  the  first  phalanx  of  the  little  finger.     A  sesamoid  bone  may  lie  in  the  tendon. 

Nerve-supply. — A  branch  from  the  superficial  or  deep  palmar  division  of  the  ulnar  nerve 
enters  the  deep  surface  of  the  muscle  in  its  proximal  half.  The  nerves  to  the  abductor  and  flexor 
may  arise  in  common  from  the  ulnar.  The  nerve  fibres  arise  from  the  (seventh  and)  eighth 
cervical  and  first  thoracic  nerves. 


Fig.  375. — The  Superficial  Muscles  of  the  Palm  of  the  Hand. 


Flexor  carpi  radialis 


Abductor  poUicis  longus 


Flexor  digitorum' 
profundus 


Action. — To  flex  the  first  phalanx  of  the  little  finger.  When  it  sends  a  tendon  slip  to  the 
aponeurosis  of  the  extensor  of  the  finger  it  helps  to  extend  the  two  terminal  phalanges. 

Relations. — The  muscle  closely  adjoins  and  is  partly  covered  by  the  abductor.  The  pal- 
maris  brevis  and  the  lateral  volai'  digital  artery  to  the  fifth  finger  lie  superficial  to  it.  Under  it 
lies  the  opponens. 

Variations. — The  muscle  may  be  wanting  or  may  be  closelj'  fused  with  the  abductor  or  the 
opponens.  It  may  receive  an  accessory  slip  from  the  forearm  fascia.  It  may  give  a  tendon 
sUp  to  the  extensor  aponeurosis  or  to  the  head  of  the  fifth  metacarpal. 

The  opponens  digiti  quinti  (fig.  377). — Origin. — Partly  tendinous,  from  the  distal  ulnar 
border  of  the  hook  of  the  hamatum  (unciform)  and  from  the  adjacent  transverse  carpal  (anterior 
annular)  ligament. 


406 


THE  MUSCULATURE 


Structure  and  insertion. — The  fibre-bundles  diverge,  the  proximal  short  and  horizontal,  the 
distal  long  and  oblique,  and  are  inserted  on  the  whole  of  the  ulnar  border  and  on  a  part  of  the 
head  of  the  fifth  metacarpal.  Often  the^musole  is  divisible  into  two  portions  between  which  the 
ulnar  nerve  runs. 

Nerve-supply. — Before  the  deep  palmar  branch  passes  through  the  muscle  it  gives  rise  to 
a  twig  which  enters  its  volar  surface  in  the  middle  third  near  the  ulnar  margin.  The  nerve 
fibres  arise  from  the  (seventh  and)  eighth  cervical  and  first  thoracic  nerves. 

Action. — To  flex,  adduct,  and  slightly  rotate  the  fifth  metacarpal;  as,  for  example,  in  'cup- 
ping' the  hand  to  drink  from  it. 

Relations. — The  opponens  lies  beneath  the  abductor  and  flexor  brevis  muscles.  The  deep 
branches  of  the  ulnar  nerve  and  artery  pass  through  the  opponens  near  its  carpal  origin  and 
then  under  it  extend  into  the  palm. 

Fig    376  — The  Debpek  Muscles  op  the  Palm  of  the  Hand. 


Abductor  poUicis  longus 
Flexor  carpi  radialis 
Extensor  polUcis  brevis 

Abductor  pollicis  brevis 


Opponens  pollicis 


Flexor  digitorum.^5^ 
profundu 


Abductor  pollicis 

brevis 
Flexor  pollicis 
brevis 

Adductor  pollicis 


Variations. — -It  may  be  fused  with  neighbouring  muscles  or  receive  accessory  slips. 

The  tensor  capsularis  articulationis  metacarpo-phalangei  digiti  quinti  is  a  slender  muscle 
which  arises  from  the  ligaments  which  unite  the  pisiform  to  the  hamatum,  and  is  inserted  into 
the  volar  surface  of  the  metacarpo-phalangeal  joint  of  the  little  finger. 

(c)  Muscles  of  the  Thumb 

(Figs.  375,  376,  377) 

In  the  therar  region  there  are  four  muscles.  Of  these,  the  abductor  pollicis 
brevis  is  the  most  superficial.  Then  come  the  opponens  pollicis  and  the  short 
flexor,  and  beneath  the  last  the  adductor  pollicis.  All  are  triangular  in  form. 
The  abductor  pollicis  brevis  arises  from  the  radial  side  of  the  volar  surface  of  the 


MUSCLES  OF  THE  THUMB 


407 


carpus  and  is  inserted  into  the  radial  side  of  the  base  of  the  first  phalanx  of  the 
thumb.  The  opponens  is  a  thick  muscle  extending  from  the  transverse  carpal 
(anterior  annular)  ligament  to  the  radial  side  of  the  first  metacarpal.  The  flexor 
poUicis  brevis  arises  by  two  heads,  a  "deep"  and  a  "superficial"  from  the  carpus 
and  is  inserted  into  the  radial  side  of  the  base  of  the  first  phalanx.  The  adduc- 
tor poUicis  arises  from  the  carpus  and  the  second  and  third  metacarpals  and  is 
inserted  into  the  ulnar  side  of  the  first  phalanx  of  the  thumb.  From  the  ten- 
dons of  insertion  of  the  abductor  and  flexor  brevis  slips  are  continued  into  the 
dorsal  aponeurosis  of  the  thumb  so  that  they  aid  in  extending  the  second 
phalanx. 

In  the  foot  an  opponens  halluois  occurs  as  an  abnormal  muscle.     The  abductor,  flexor  brevis 
and  adductor  ot  the  thumb  are  represented  by  the  corresponding  muscles  of  the  big  toe,  although 


Fig.  377. — The  Pronator  Quadratus  and  Deep  MtrscLEs  op  the  Palm. 


Pronator  quadratus 


Flexor  carpi  ulnarl 


Abductor  digiti  V. 


Abductor  pollicis  brevis 


Deep  head  of  flex- 
or poUicis  brevis 

Opponens  pollicis 

I  Volar  inter- 
osseous 

Adductor  pollicis, 
oblique  head 


Fourth  dorsal 
interosseous 
Third  volar  interosseous 


Third  dorsal  interosseous 


Second  volar  interosseous 
Second  dorsal  interosseous 


the  last  two  muscles  are  not  perfectly  homologous  in  the  hand  and  foot. 

The  abductor  pollicis  brevis  (fig.  375). — Origin. — From  the  volar  surface  of  the  transverse 
carpal  (anterior  annular)  ligament,  and  from  the  greater  multangular  bone  (trapezium).  Also 
often  from  the  navicular  bone  and  from  a  tendon  slip  of  the  long  abductor. 

Structure  and  insertion. — The  fibre-bundles  converge  upon  a  flat  tendon  with  two  lamellae, 
the  deeper  of  which  is  inserted  into  the  radial  side  of  the  base  of  the  first  phalanx  of  the  thumb 
and  the  superficial  into  the  aponeurosis  of  the  extensor  poUicis  longus. 

Neroe-supply. — By  a  branch  ot  the  first  volar  digital  ramus  of  the  median  nerve.  This 
branch  passes  over  or  through  the  flexor  brevis  and  enters  the  muscle  on  the  volar  surface  in 
the  middle  third  near  its  ulnar  border. 

Action. — To  abduct  the  thumb,  flex  the  first  phalanx,  and  extend  the  terminal  phalanx. 

Relations. — It  lies  beneath  the  thenar  fascia  lateral  to  the  superficial  head  of  the  flexor 
brevis  and  over  the  opponens.     The  superficial  volar  artery  usually  perforates  the  muscle. 

Variations. — It  may  be  wanting  or  may  be  divided  into  two  divisions.  The  origin  may 
extend  to  the  fascia  of  the  forearm  or  styloid  process  of  the  radius.  It  may  receive  an  accessory 
slip  from  the  long  radial  extensor,  the  opponens,  or  the  short  extensor  of  the  thumb.  A  thenar 
subcutaneous  muscle  is  occasionally  present.  It  is  narrow,  is  closely  associated  with  the  short 
abductor  of  the  thumb,  and  extends  from  the  radial  side  of  the  base  of  the  first  metacarpal  into 
the  skin  of  the  thenar  eminence. 


408  THE  MUSCULATURE 

The  opponens  poUicis  (fig.  377). — Origin. — From  the  volar  surface  of  the  transverse  carpa 
(anterior  annular)  ligament  and  from  the  tubercle  of  the  greater  multangular  bone  (trapezium). 

Structure  and  Insertion, — The  fibre-bundles  extend  obliquely  in  a  nearly  parallel  direction 
to  their  insertioB  along  the -whole  lateral  border  of  the  volar  surface  of  the  shaft  and  the  head  of 
the  first  metacarpal. 

Nerve-supply. — By  a  branch  of  the  first  volar  digital  ramus  of  the  median  nerve.  This 
branch  passes  over  or  through  the  superficial  division  of  the  flexor  brevis  near  the  origin  of  the 
muscle.  One  or  two  twigs  enter  the  deep  surface  of  the  proximal  third  of  the  opponens  near 
its  ulnar  border.     The  nerve  fibres  arise  from  the  sixth  and  seventh  cervical  nerves. 

Action. — To  flex,  adduct,  and  rotate  medialward  the  first  metacarpal  bone.  The  volar 
surface  of  the  thumb  is  thus  brought  to  face  the  volar  surface  of  the  other  digits. 

Relations. — It  lies  beneath  the  thenar  fascia  and  the  abductor  brevis.  The  flexor  brevis 
overlies  its  ulnar  border. 

Variations. — It  may  be  absent  or  it  may  be  divided  into  two  heads.  It  is  usually  more  or 
less  fused  with  the  short  flexor. 

The  flexor  poUicis  brevis  (figs.  376,  377). — The  muscle  is  divided  by  the  tendon  of  the 
long  flexor  into  a  superficial  and  a  deep  portion.  The  superficial  head  arises  from  the  greater 
multangular  bone  (trapezium),  the  adjacent  part  of  the  transverse  carpal  (anterior  annular) 
ligament,  and  the  tendon  sheath  of  the  flexor  carpi  radialis.  The  fibre-bundles  descend  closely 
applied  to  the  opponens,  and  terminate  by  a  tendon  which  is  attached  to  the  lateral  side  of  the 
front  of  the  base  of  the  first  phalanx.  Over  the  joint  a  sesamoid  bone  lies  in  the  tendon.  The 
deep  head  has  a  tendinous  origin  from  the  os  multangulum  minus  (trapezoid)  and  the  os  capi- 
tatum  (magnum).  The  fibre-bundles  take  an  oblique  course,  to  be  inserted  into  the  tendon  of 
the  superficial  part.  A  muscle  fasciculus  which  arises  from  the  ulnar  side  of  the  base  of  the  first 
metacarpal  and  the  neighbouring  carpal  ligaments  and  is  inserted  on  the  ulnar  side  of  the  base 
of  the  first  phalanx,  is  sometimes  considered  to  be  the  deep  head  of  the  flexor  brevis.  It  is 
closely  bound  up  with  the  carpal  head  of  the  adductor  poUicis  and  they  have  a  common  tendon. 
Some  fibres  of  the  medial  division  of  the  tendon  may  be  traced  into  the  aponeurosis  of  the  exten- 
sor tendon.  It  is  probable  that  this  portion  of  the  muscle  represents  a  first  volar  interosseous, 
and  it  is  so  described  later  with  the  interosseous  muscles.  There  is  much  dispute  as  to  what 
fascicuU  should  be  included  in  the  flexor  brevis. 

Nerve-supply. — The  muscle  is  usually  suppUed  by  twigs  derived  from  a  branch  from  the 
first  volar  digital  ramus  of  the  median  nerve  as  this  branch  passes  through  its  substance,  and 
by  twigs  from  the  deep  branch  of  the  ulnar.  Brookes  found  this  supply  in  19  out  of  29  instances, 
in  5  by  the  median  alone,  and  in  5  by  the  ulnar  alone.  The  nerve  fibres  come  from  the  sixth 
and  seventh  cervical  nerves. 

Action. — To  flex,  adduct,  and  rotate  medialward  the  metacarpal  of  the  thumb;  flex  the  first 
phalanx;  and  extend  the  second  phalanx. 

Relations. — Proximally  the  short  flexor  is  grooved  for  the  tendon  of  the  long  flexor,  beneath 
which  more  distally  the  deep  head  of  the  muscle  passes  laterally.  The  superficial  portion  of 
the  muscle  lies  beneath  the  skin.  The  ulnar  border  of  the  deep  head  is  fused  prOximaUy  with 
the  adductor. 

Variations. — The  deep  head  may  be  absent.  Either  or  both  heads  may  be  double.  The 
superficial  head  may  be  fused  with  the  abductor  brevis,  and  is  usually  more  or  less  fused  with 
the  opponens. 

The  adductor  poUicis  (fig.  377).- — Origin. — By  two  heads.  The  carpal  or  oblique  head 
arises  from  the  deep  carpal  ligaments,  the  capitatum  and  the  bases  of  the  second  and  third 
metacarpals;  the  metacarpal  or  transverse  head,  from  the  crest  of  the  third  metacarpal,  from 
the  suprametacarpal  fascia  of  the  third  interspace,  and  sometimes  also  from  that  of  the  fourth 
interspace  and  from  the  capsules  of  the  second,  third,  and  fourth  metacarpo-phalangeal  articu- 
lations. 

Structure  and  insertion. — The  fibre-bundles  converge  toward  a  tendon  which  is  inserted 
into  the  ulnar  side  of  the  front  of  the  base  of  the  first  phalanx  of  the  thumb.  A  sesamoid  bone 
lies  in  the  tendon  over  the  joint. 

Nerve-supply. — One  or  more  twigs  from  the  deep  palmar  branch  of  the  ulnar  enter  the  middle 
third  of  the  muscle  on  its  deep  surface.  There  may  also  be  an  anastomosing  branch  from  the 
median  nerve.  The  nerve  fibres  come  from  the  sixth,  seventh  and  eighth  cervical  and  first 
thoracic  nerves. 

Action. — To  adduct  and  flex  the  first  metacarpal  and  flex  the  first  phalanx  of  the  thumb. 
When  the  thumb  is  in  an  extreme  position  of  apposition,  it  acts  as  an  abductor. 

'  Relations. — Superficial  to  the  muscle  lie  some  of  the  tendons  of  the  deep  flexor  of  the  fingers 
and  the  first  two  lumbrical  muscles.  It  extends  over  the  two  more  lateral  intermetacarpal 
spaces,  and  is  in  part  subcutaneous  on  the  dorsal  surface.  The  deep  palmar  arch  extends 
between  the  two  heads  and  beneath  the  oblique  head.  The  oblique  head  of  the  muscle  is  closely 
united  to  the  first  volar  interosseous,  so  that  the  latter  by  some  is  considered  a  part  of  the 
adductor. 

Variations. — The  extent  of  the  attachments  of  origin  of  the  muscle  vary  considerably. 
The  two  heads  of  the  muscle  may  be  more  or  less  completely  separated  from  one  another.  Each 
may  be  divided  into  separate  fasciculi. 

(d)  Lumbrical  Muscles 

From  the  deep  flexor  tendons  in  the  palm  of  the  hand  arise  the  lumbrical 
muscles,  four  in  number,  which  are  attached  by  small  tendons  to  the  radial  side  of 
the  extensor  tendons  (figs.  373,  375).  These  lumbrical  muscles  have  homologues 
in  the  sole  of  the  foot. 


INTEROSSEOUS  MUSCLES 


409 


The  lumbricales  (figs.  375,  376). — Origin. — The  two  lateral  arise  from  the  radial  side  of 
the  volar  aspect  of  the  first  and  second  tendons  of  the  flexor  digitorum  profundus;  the  two 
medial  arise  from  the  adjacent  sides  of  the  second  and  third  and  third  and  fourth  tendons. 

Structure  and  insertion. — The  fibre-bundles  of  each  muscle  arise  directly  from  the  flexor 
tendons  near  the  distal  border  of  the  transverse  carpal  (anterior  annular)  ligament.  They 
converge  as  far  as  the  metacarpo-phalangeal  joint,  upon  a  small  tendon  which  begins  about  the 
middle  of  the  muscle.  The  tendon  passes  out  between  the  palmar  aponeurosis  and  the  trans- 
verse capitular  ligament,  winds  about  the  metacarpo-phalangeal  joint,  expands,  and  is  attached 
along  the  side  of  the  first  phalanx  to  the  radial  border  of  the  tendon  of  the  extensor  digitorum 
communis.  .  j-  ,  ,       , 

NerBe-supply. — Branches  from  the  median  nerve  enter  the  middle  third  of  the  radial  border 
of  the  first  two  or  three  lumbrical  muscles.  The  last  one  or  two  are  supplied  by  branches  from 
the  deep  volar  branch  of  the  ulnar  nerve,  which  enter  the  middle  third  of  the  deep  surface.  The 
third  lumbrical  and  sometimes  one  or  more  of  the  others  may  receive  a  branch  from  both  nerves. 
The  nerve  fibres  come  from  the  eighth  cervical  and  first  thoracic  nerves. 

Action. — Together  with  the  interosseous  muscles  they  flex  the  basal  phalanges  on  the  meta- 
carpal bones  and  extend  the  terminal  and  middle  phalanges.  They  also  adduct  the  fingers 
toward  the  thumb. 

Relations. — The  muscles  run  between  the  tendons  of  the  flexor  profundus  and  beneath  the 
palmar  aponeurosis.  They  lie  upon  the  fascia  covering  the  interosseous  muscles,  the  capitular 
ligaments,  and  the  septum'  over  the  adductor  and  deep  head  of  the  flexor  pollicis  brevis. 

Variations. — These  are  very  frequent,  especially  in  case  of  the  third  and  fourth.  Each 
may  be  doubled  or  missing.  They  may  arise  from  the  tendons  of  the  flexor  subhmis  or  from 
the  belly  of  the  deep  flexor.  The  first  lumbrical  may  come  from  the  tendon  of  the  long  flexor, 
from  the  opponens,  or  the  metacarpal  of  the  thumb.  The  tendon  of  insertion  may  go  to  the 
ulnar  side  of  the  base  of  the  digit  opposite  that  to  which  the  tendon  Is  usually  attached,  or  the 
tendon  may  divide  and  go  to  the  adjacent  sides  of  two  fingers.  Kopsch  has  found  that  in  110 
bodies  all  four  lumbricals  were  inserted  on  the  radial  side  of  their  respective  digits  in  39  per  cent. 
In  35  per  cent,  the  first,  second,  and  fourth  were  so  inserted,  while  the  third  sent  slips  to  the 
adjacent  sides  of  the  middle  and  ring  fingers.  An  accessory  fasciculus  has  been  found  to  arise 
from  the  tendon  of  the  flexor  poUicis  longus  and  go  to  the  base  of  the  index  finger. 

(e)  Interosseous  Muscles  (figs.  377,  378,  379) 

These  muscles  lie  between  the  metacarpal  bones  and  are  covered  dorsally  and 
ventrally  by  fasciae  attached  to  the  metacarpals.  In  each  interspace  are  two  mus- 
cles, a  dorsal  and  a  palmaw    The  volar  interossei  are  inserted  into  all  the  fingers 

Fig.  378. — The  Volar  Interossei. 


except  the  middle  finger,  and  are  adductors  toward  an  axis  passing  through  the 
middle  finger;  the  dorsal  interossei  are  inserted  into  both  sides  of  the  middle  finger 
and  into  the  radial  side  of  the  second  and  the  ulnar  side  of  the  fourth  finger,  and 
are  abductors.  All  also  serve  as  flexors  of  the  first  row  of  phalanges  and  extensors 
of  the  second  and  third.  In  the  foot  the  axis  to  and  from  which  the  interosseous 
muscles  adduct  and  abduct  the  toes  passes  through  the  second  toe. 

The  interossei  volares  arise  from  the  sides  toward  the  middle  finger  and  the  front  of  the 
shafts  of  the  first,  second,  fourth,  and  fifth  metacarpals.     The  first  arises  from  near  the  base,  the 


410 


THE  MUSCULATURE 


others  from  three-fourths  of  the  shaft.  The  fibre-bundles  of  each  muscle  converge  in  a  penni- 
form  manner  upon  a  tendon  which  is  inserted  into  the  aponeurosis  of  the  digital  extensor  tendon 
and  the  base  of  the  first  phalanx  on  the  middle  finger  side  of  the  corresponding  digit  (see  fig.  373). 
The  first  volar  interosseous  is  often  described  as  a  division  of  the  flexor  poUicis  brevis  or  of  the 
adductor  poOicis. 

The  interossei  dorsales  arise  from  the  adjacent  sides  of  the  metacarpal  bones  in  each  inter- 
space. On  the  sides  nearest  the  middle  finger  they  cover  three-fourths  of  the  bone,  on  the 
opposite  sides  much  less.  The  fibre-bundles  converge  in  a  bipenniform  manner  upon  a  tendon 
which  begins  high  in  the  muscle  and  is  inserted  into  the  aponeurosis  of  the  extensor  muscles 
and  the  base  of  the  first  phalanx  on  each  side  of  the  middle  finger,  on  the  thumb  side  of  the 
index  finger,  and  the  ulnar  side  of  the  ring  finger.  The  interosseous  muscle  in  the  first  interspace 
is  thick  and  strong  and  forms  with  the  adductor  poUicis  the  fleshy  web  between  the  base  of  the 
thumb  and  the  palm. 

Nerve-supply. — By  branches  of  the  deep  palmar  division  of  the  ulnar  nerve.  As  a  rule,  a 
branch  to  each  volar  interosseous  enters  the  proximal  third  of  the  muscle.  To  each  dorsal  inter- 
osseous a  branch  is  given  which  enters  between  the  two  heads.  These  branches  may  be  variously 
combined  before  entering  the  interosseous  muscles.  The  nerve  fibres  arise  from  the  eighth 
cervical  and  first  thoracic  nerves. 


Fig.  379. — The  Dorsal  Interossei 


Action, — To  move  the  fingers  toward  the  radial  and  ulnar  sides,  to  flex  the  first  phalanx 
and  extend  the  second  and  third.  The  volar  interossei  move  the  fingers  toward  the  median 
axis,  the  dorsal  from  it. 

Relations. — The  volar  interossei  lie  volarward  from  the  dorsal  interossei.  The  two  sets 
of  muscles  are  bound  in  place  by  the  dorsal  and  volar  metacarpal  fascise.  The  tendons  pass  out 
on  the  dorsal  side  of  the  transverse  capitular  ligament  and  are  closely  apphed  to  the  metacarpo- 
phalangeal joints.  The  muscles  of  the  first  two  interspaces  lie  immediately  dorsal  to  the  adduc- 
tor of  the  thumb;  the  others  dorsal  to  the  flexor  tendons. 

Variations. — The  tendon  slip  from  an  interosseous  muscle  to  the  base  of  the  first  phalanx 
of  a  digit  may  be  missing.  This  is  more  frequent  in  case  of  the  volar  than  in  that  of  the  dorsal 
interossei,  and  in  the  medial  than  the  lateral  muscles.  Either  a  volar  or  a  dorsal  interosseous 
muscle  may  be  double  or  missing.  Rarely  the  insertions  of  the  interosseous  muscles  character- 
istic of  the  foot  (see  p.  499)  may  be  found  in  the  hand. 


III.  SPINAL  MUSCULATURE 

(Figs.  380,  381,  382,  383) 

The  spinal  (vertebral)  column  is  of  special  interest  as  the  segmented  longitudi- 
nal axial  support  of  the  body  vsrhich  has  given  rise  to  the  term  "vertebrates"  as 
applied  to  the  class  of  animals  of  which  man  is  the  highest  form.  The  segmenta- 
tion in  fishes  permits  the  lateral  movements  of  the  body  which  are  their  chief 
means  of  propulsion.  In  the  land  vertebrates,  with  the  exception  of  snakes,  the 
limbs  are  developed  as  the  chief  organs  of  propulsion  but  flexibility  of  the  column 


SPINAL  MUSCULATURE  411 

is  retained  for  the  sake  of  freedom  of  movement.  In  man  the  spinal  column,  with 
the  exception  of  the  sacral  region,  may  be  readily  extended  (bent  backward)  and 
flexed  (bent  forward),  abducted  (bent  to  the  side)  and  rotated.  Freedom  of 
movement  is  greatest  in  the  cervical  and  lumbar  regions  and  is  restricted  by  the 
thorax  in  the  thoracic  region.  The  cervical  region  allows  considerable  flexion, 
extension  and  rotation,  but  a  more  limited  abduction.  In  the  thoracic  region 
rotation  and  abduction  are  freer  than  flexion  and  extension.  The  lumbar  region 
is  that  in  which  the  chief  flexion  and  extension  of  the  trunk  takes  place,  but  abduc- 
tion and  rotation  are  limited,  especially  the  latter.  In  the  isolated  articulated 
spinal  column  freedom  of  movement  of  the  various  parts  depends  chiefly  upon  the 
thickness  and  elasticity  of  the  intervertebral  discs,  upon  the  conformation  of  the 
articulat  processes,  and  upon  the  elasticity  or  arrangement  of  the  various  liga- 
ments uniting  the  vertebrae.  In  the  living  body  freedom  of  movement  is  further 
restricted  by  the  musculature  and  skeletal  apparatus  attached  to  the  column. 
There  is  much  individual  variation  in  the  flexibility  of  the  vertebral  column. 

The  various  movements  ot  the  column  are  produced  partly  by  muscles  which  act  directly  on 
it  and  partly  by  muscles  which  act  on  it  through  the  head,  thorax  or  pelvis.  Most  of  the  muscles 
which  act  on  it  directly  belong  to  the  intrinsic  dorsal  musculature;  that  is,  to  musculature  which 
is  derived  from  the  dorsal  divisions  of  the  myotomes  and  is  innervated  by  the  dorsal  divisions 
of  the  spinal  nerves.  This  musculature  extends  from  the  sacrum  to*the  skull  and  is  closely 
applied  on  each  side  of  the  mid-dorsal  line  of  the  body  to  the  backs  of  the  vertebrae  and  the  back 
of  the  thorax  (fig.  381).  Its  chief  function  is  to  extend  the  spinal  column  and  head,  hence  the 
old  term  applied  to  the  superficial  portion  of  this  musculature  "erector  spinas. "  During  the 
development  of  the  body,  muscles  belonging  to  the  ventro-lateral  thoracic  musculature  and  to 
the  upper  extremity  come  to  overlie  in  part  the  intrinsic  dorsal  musculature.  The  trapezius 
and  rhomboid  muscles  which  cover  it  in  the  cervical  and  thoracic  regions,  and  the  latissimus 
dorsi  which  covers  it  in  the  thoracic  and  lumbar  regions  belong  to  the  shoulder  girdle  and  arm 
and  have  already  been  described,  p.  360.  The  serratus  posterior  superior,  which  overlaps  it 
in  the  upper  thoracic  region,  and  the  serratus  posterior  inferior,  which  overlaps  it  at  the  junction 
of  the  thoracic  and  lumbar  regions,  are  derived  from  the  intercostal  musculature  which  is  de- 
scribed below,  p.  422  (fig.  380).  All  of  these  muscles  are  innervated  by  the  ventro-lateral  divi- 
sions of  the  spinal  nerves.  The  levatores  costarum  (fig.  380),  which  extend  from  the  transverse 
process  of  the  thoracic  vertebrae  to  the  ribs,  and  which,  in  spite  of  their  name,  act  chiefly  on 
the  spinal  column,  are  derived  from  the  external  intercostal  musculature  and  are  innervated  by 
the  intercostal  nerves. 

Ventral  to  the  spinal  column  and  closely  applied  to  it  there  are  a  few  muscles,  the  chief 
function  of  which  is  to  flex  the  column.  All  are  supplied  by  branches  from  the  ventro-lateral 
divisions  of  the  spinal  nerves.  Of  these  the  longissimus  colli  and  longissimus  capitis  and  scalene 
muscles  have  been  described  in  connection  with  the  muscles  of  the  neck,  p.  353.  In  the  thoracic 
region  there  are  no  muscles  of  this  type.  In  the  lumbar  region  there  are  four  muscles  on  each 
side,  the  pillars  of  the  diaphragm,  fig.  391,  the  psoas  minor,  fig.  391,  the  psoas  major,  fig.  391, 
and  the  quadralus  lumborum,  fig.  391.  All  of  these  muscles  are  flexors  of  the  spine^  except  the 
quadratus,  which  is  an  extensor.  The  psoas  major  muscle  is  also  a  flexor  of  the  thigh.  Even 
more  powerful  flexors  of  the  column  than  those  above  mentioned  are  some  of  those  which  work 
indirectly  upon  it  through  the  leverage  offered  by  the  skull  (sterno-cleido-mastoid  described 
above,  p.  347),  and  the  thorax  (the  ventro-lateral  abdominal  musculature). 

Abduction  and  rotation  of  the  spine  are  produced  by  contraction  of  muscles  on  one  side 
while  the  corresponding  muscles  on  the  other  side  are  relaxed.     See  Table,  p.  502. 

In  the  present  section  we  shall  confine  our  attention  to  the  intrinsic  dorsal  musculature, 
leaving  for  consideration  elsewhere  the  other  musculature  which  acts  on  the  vertebral  column. 

The  intrinsic  dorsal  musculature  is  attached  to  the  sacrum,  to  the  ilium,  to  the 
spines,  transverse,  and  articular  processes  and  laminae  of  the  lumbar,  thoracic,  and 
cervical  vertebrae,  to  the  backs  of  the  ribs  and  to  the  base  of  the  skull.  Two  great 
longitudinal  subdivisions  may  be  recognised,  a  lateral,  supplied  by  lateral  branches 
of  the  posterior  divisions  of  the  spinal  nerves,  and  a  medial,  supplied  by  medial 
branches.  The  lateral  portion  is  further  divisible  into  a  superficial  division,  con- 
sisting chiefly  of  systems  of  muscles  extending  laterally  from  the  spines  of  the  verte- 
hv3d  upward  toward  the  transverse  processes  of  the  vertebrae,  the  ribs,  and  the 
mastoid  process  of  the  skull;  and  a  deep  division,  consisting  of  muscles  which  ex- 
tend between  successive  transverse  processes.  The  medial  portion  likewise  con- 
sists of  two  parts;  a  superficial  medial  composed  of  fasciculi  extending  from  in- 
ferior to  superior  spines,  best  developed  in  the  dorsal  region,  and  a  deep  portion 
consisting  mainly  of  muscle  fasciculi  which  pass  from  the  transverse  processes  up- 
ward toward  the  spines  of  vertebrae  situated  more  cranially.  In  the  neck  the  more 
superficial  extend  to  the  base  of  the  skull.  Between  the  base  of  the  skull  and  the 
first  two  vertebrae  there  are  several  specialised  muscles.  There  is  also  frequently 
present  the  rudimentary  sacro-coccygeus  posterior  described  on  p.  448,  which 
represents  an  extension  into  the  caudal  region  of  the  intrinsic  dorsal  musculature. 


412  THE  MUSCULATURE 

The  superficial  lateral  dorsal  musculature  consists  of  the  splenius  and  the  sacro- 
spinalis.  The  splenius  (fig.  380)  is  a  flat,  somewhat  triangular  muscle,  which 
extends  from  the  cervical  and  upper  thoracic  spines  to  the  upper  cervical  trans- 
verse processes  and  to  the  mastoid  process  of  the  temporal  bone  and  the  neighbour- 
ing part  of  the  occipital.  The  sacro-spinalis  (erector  spinte)  (fig.  381)  is  the  name 
given  to  a  mass  of  musculature  which  takes  its  origin  from  the  ihum,  the  sacrum, 
and  the  lumbar  spines.  In  the  lumbar  region  this  muscle  divides  into  its  two  chief 
portions,  the  ilio-costalis  and  the  longissimus.  The  ilio-costalis  (fig.  382)  is 
attached  to  the  lumbar  transverse  processes  and  to  the  ribs  near  the  angles,  and  is 
continued  upward  by  accessory  fasciculi  along  the  back  of  the  thorax  to  the  trans- 
verse processes  of  the  cervical  vertebrae.  The  longissimus  (fig.  382)  extends  up- 
ward between  the  ilio-costalis  and  the  spines  of  the  lumbar  and  thoracic  vertebree. 
It  is  attached  to  the  transverse  processes  of  the  lumbar  and  thoracic  vertebrae  and 
to  the  ribs  lateral  to  the  transverse  processes.  It  is  continued  to  the  transverse 
processes  of  the  cervical  vertebrae  and  to  the  skull  by  accessory  muscle  slips. 

The  deep  lateral  dorsal  musculature  consists  of  the  dorsal  intertransverse 
muscles.  The  intertransverse  muscles  are  best  developed  in  the  cervical  and  lum- 
bar regions.  In  the  cervical  region  intertransverse  muscles  belonging  to  the  dor- 
sal musculature  extend  between  the  successive  dorsal  tubercles,  while  intertrans- 
verse muscles  belonging  to  the  ventral  musculature  extend  between  the  ventral 
tubercles.  The  latter,  as  well  as  the  rectus  capitis  anterior  and  rectus  capitis 
lateralis,  which  belong  in  the  series,  have  been  described  above  (p.  356).  In  the 
lumbar  region  there  are  also  two  sets  of  intertransverse  muscles,  one  belonging  to 
the  ventral  and  one  to  the  dorsal  musculature. 

The  superficial  medial  dorsal  musculature  consists  of  the  spinalis  dorsi  and 
cervicis.  The  spinalis  dorsi  (fig.  381)  is  intimately  fused  with  the  longissimus.  It 
extends  from  the  lower  to  the  upper  thoracic  spines,  and  is  derived  from  the  medial 
dorsal  musculature.  The  inconstant  spinalis  cervicis,  which  extends  from  the 
upper  thoracic  to  the  lower  cervical  spines,  is  likewise  derived  from  the  medial 
dorsal  musculature,  but  is  less  intimately  related  to  the  longissimus. 

The  deep  medial  dorsal  musculature  (fig.  383)  lies  in  the  groove  between  the 
transverse  processes  and  the  spines  of  the  sacral,  lumbar,  thoracic,  and  cer- 
vical vertebrae.  It  extends  from  the  sacrum  to  the  skull,  and  is  best  developed  in 
the  lumbar  and  cervical  regions.  It  is  subdivided  into  a  vertebro-occipital  muscle 
(semispinalis  capitis),  a  transverso-spinal  group,  and  the  interspinal  muscles. 
The  semispinalis  capitis  (complexus)  (fig.  381)  arises  from  the  transverse  processes 
of  the  third  cervical  to  the  sixth  thoracic  vertebrae  and  from  the  spines  of  the  upper 
thoracic  vertebrae  and  is  inserted  into  the  base  of  the  skull.  The  transverso-spinal 
group  (fig.  383)  extends  from  the  sacrum  to  the  second  cervical  vertebra.  It  is 
more  or  less  artificially  divisible  into  several  layers.  In  the  superficial  layer,  the 
semispinalis  dorsi  et  cervicis,  which  extends  from  the  twelfth  thoracic  to  the  second 
cervical  vertebra,  the  constituent  fasciculi  extend  from  the  transverse  process  of 
one  vertebra  to  the  spine  of  a  vertebra  four  to  six  segments  above.  In  the  middle 
layer,  the  multifidus,  the  fasciculi  extend  over  from  two  to  four  vertebrae.  In  the 
deepest  layer,  the  rotatores,  the  fasciculi  extend  to  the  ne.xt  vertebra  (short  rotators) 
or  to  the  second  vertebra  above  (long  rotators).  The  interspinal  muscles  extend 
between  successive  spines. 

The  muscles  which  pass  from  the  first  two  vertebrae  to  the  base  of  the  skull 
behind,  or  suboccipital  muscles  (fig.  382),  consist  of  the  rectus  capitis  posterior 
minor,  from  the  spine  of  the  atlas  to  beneath  the  inferior  nuchal  line  of  the  occip- 
ital and  rectus  capitis  posterior  major,  from  the  spine  of  the  epistropheus  (axis)  to 
beneath  the  inferior  nuchal  line,  lateral  to  the  preceding;  of  the  obliquus  capitis 
inferior,  from  the  spine  of  the  epistropheus  (axis)  to  the  transverse  process  of  the 
atlas,  and  the  obliquus  capitis  superior,  from  the  transverse  process  of  the  atlas  to 
the  base  of  the  lateral  part  of  the  inferior  nuchal  line  of  the  occipital  above  the 
rectus  major. 

The  primitive  condition  of  the  dorsal  musculature  is  one  of  metameric  segmentation.  This 
is  characteristic  of  fishes,  many  amphibia,  and  of  the  embryos  of  all  higher  vertebrates.  In 
the  tailless  amphibia,  however,  a  partial  differentiation  of  the  dorsal  musculature  takes  place  dur- 
ing embryonic  development,  and  in  all  higher  forms  a  differentiation  takes  place  which  corre- 
sponds in  many  ways  to  that  described  above  for  man.  According  to  Favaro,  the  splenius  is 
differentiatied  from  the  medial  dorsal  system,  but  its  innervation  should  place  it  with  the  lateral 
system.  In  the  human  embryo  the  dorsal  segmental  musculature  extends  into  the  tail  region, 
but  afterward  here  undergoes  retrograde  metamorphosis. 


FASCIA 


413 


The  intrinsic  musculature  of  the  back  serves  to  extend,  bend  from  side  to  side,  and  to  rotate 
the  spinal  column  and  head.     The  muscles  attached  to  the  ribs  depress  the  thorax. 

Fig.  380. — The  Third  and  Fourth  Layers  of  the  Muscles  op  the  Back. 
(Intrinsic  Dorsal  Musculature) 


Semispinalis  capitis 
Splenius  capitis 


Splenius  cervici 


Serratus  posterior  superior 


Lumbo-dorsal  fascia 


Serratus  posterior  inferior 


Obliquus  internus 
Origin  of  latissimus  dorsi 


Seventh  cervical  vertebra 


Twelfth  thoracic  vertebra 


3 Fifth  lumbar  vertebra 


FASCIA 

The  fasciae  and  the  general  relations  of  the  muscles  of  the  back  may  be  followed  in  the  cross- 
sections  shown  in  figs.  347,  351,  357,  384,  and  407. 

The  tela  subcutanea  of  the  upper  dorsal  region  has  been  described  in  connection  with  the 
muscles  of  the  shoulder  girdle  (p.  347).     It  is  thick,  fibrous,  and  adherent.     In  the  lower  dorsal 


414  THE  MUSCULATURE 

region  it  is  somewhat  less  compact,  but  is  thicker  and  contains  more  fat.  It  is  usually  divisible 
into  two  layers,  of  which  the  deeper  is  adherent  to  the  lumbodorsal  fascia. 

The  splenius  (fig.  380)  is  enveloped  in  a  thin,  adherent  fascial  covering.  The  saoro-spinalis 
is  covered  by  a  fascia,  the  fascia  lumbo-dorsalis  (fig.  380),  which  inferiorly  is  attached  to  the 
iliac  crest,  the  distal  and  lateral  margins  of  the  sacrum,  and  the  sacral  spines.  In  the  lumbar 
and  thoracic  regions  it  is  attached  medially  to  the  vertebral  spines.  Laterally,  in  the  lumbar 
region,  it  is  reflected  around  the  muscle  to  its  ventral  surface,  where  a  'ventral'  or  'deep' 
layer  forms  an  intermuscular  septum  (fig.  384)  between  the  quadratus  lumborum  and  the  sacro- 
spinalis.  This  intermuscular  septum  (fig.  383)  extends  from  the  twelfth  rib  to  the  iliac  crest 
and  the  ilio-lumbar  ligament,  and  is  attached  medially  to  the  transverse  processes  of  the  lumbar 
vertebra,  from  which  fibre-bands  extend  laterally  into  it.  It  is  strengthened  above  by  fibre- 
bundles  which  pass  from  the  first  and  second  lumbar  vertebrce  to  the  twelfth  rib  (lumbo-costal 
ligament).     (For  the  relation  of  the  abdominal  muscles  to  this  fascia  see  p.  328.) 

In  the  thoracic  region  (fig.  384)  the  lumbo-dorsal  fascia  is  attached  to  the  ribs  lateral  to 
the  iho-costal  muscle.  In  the  cervical  region  (fig.  351)  the  fascia  is  continued  into  the  inter- 
muscular septa  which  surround  the  muscles  of  this  group  in  the  neck. 

The  transversospinal  muscles  are  covered  throughout  their  extent  by  a  fascial  membrane 
which  serves  to  separate  them  from  the  longissimus  in  the  sacral,  lumbar,  and  thoracic  regions. 

In  the  dorsal  region  of  the  neck  (figs.  347,  351,  357)  the  muscles  are  covered  on  each  surface 
by  adherent  fascial  sheets,  fascia  nuchas,  and  are  arranged  in  several  concentric  layers,  each 
of  which  is  separated  from  its  neighbour's  by  dense  fatty  areolar  tissue.  The  deepest  of  the 
layers  is  formed  by  the  muscles  of  the  transverso-spinal  group.  This  is  covered  by  a  dense  mem- 
brane, and  is  separated  from  the  semispinalis  capitis  (complexus)  by  a  thick  layer  of  areolar 
tissue  containing  the  chief  blood-vessels  and  nerves  of  the  neck.  The  semispinalis  capitis 
(complexus)  is  covered  on  each  surface  by  a  more  delicate  adherent  membrane,  and  is  separated 
from  the  splenius  by  loose  tissue.  The  splenius  has  a  somewhat  denser  adherent  fascial  cover- 
ing into  which  the  fascia  of  the  levator  scapulse  is  continued.  Separated  from  this  by  areolar 
tissue  lies  the  trapezius.  The  cervical  and  thoracic  portions  of  the  semispinalis  are  separated 
by  delicate  membranous  septa  from  the  semispinalis  capitis  (complexus),  the  levator  scapute, 
and  the  splenius.  The  muscles  of  each  side  are  separated  in  the  dorsal  median  plane  by  the 
dense  ligamentum  nuchae,  into  which  the  various  cervical  septa  and  fasciie  extend.  The  sub- 
occipital muscles  are  covered  by  fascial  sheaths  which  are  so  fused  as  to  constitute  a  special 
fascia  for  these  muscles.  Distally  this  is  continued  into  the  fascia  of  the  transversospinal 
muscles. 

MUSCLES 

A.  Superficial  Lateral  Dorsal  System 

The  splenius  (fig.  380). — The  two  parts  of  which  this  muscle  is  composed  may  be  separately 
considered. 

The  splenius  cervicis. — Origin. — By  a  narrow  aponeurotic  band  from  the  spinous  processes 
and  the  supraspinous  ligament  of  the  third  to  the  sixth  thoracic  vertebrae. 

Structure  and  insertion. — The  fibre-bundles  extend  upward  and  laterally  and  give  rise  to  a 
flat  muscle  sheet  from  which  fascicuh  arise  that  are  inserted  by  short  tendinous  processes  on  the 
posterior  tubercles  of  the  transverse  processes  of  the  first  two  or  three  cervical  vertebrae.  The 
processes  are  often  united  with  those  of  the  levator  scapula?  and  the  longissimus  cervicis. 

The  splenius  capitis. — Origin. — Froin  the  ligamentum  nuchae  in  the  region  of  the  third 
to  the  seventh  cervical  vertebrae  and  from  the  spinous  processes  and  the  supraspinous  ligament 
of  the  first  two  to  five  thoracic  vertebrae. 

Structure  and  insertion. — The  fibre-bundles  form  a  sheet  which  continues  cranialward 
that  of  the  splenius  cervicis.  The  fibre-bundles  converge  somewhat  and  are  inserted  by  a 
short,  broad,  thick  tendon  into — (1)  the  back,  the  side,  and  the  tip  of  the  mastoid  process  below 
the  sterno-cleido-mastoid  muscle,  and  (2)  into  the  neighbouring  part  of  the  occipital  bone. 

Relations. — The  splenius  lies  dorsal  to  the  semispinalis  capitis  (complexus)  and  to  the 
cervical  (transversalis  cervicis)  and  the  cranial  (trachelo-mastoid)  portions  of  the  longissimus 
and  the  cervical  portion  (cervicalis  ascendens)  of  the  ilio-costalis  and  to  the  levator  scapulae,  and 
is  partly  covered  by  the  trapezius,  sterno-cleido-mastoid,  serratus  posterior  superior,  and  the 
rhomboids.  In  the  triangle  bounded  by  the  trapezius,  sterno-cleido-mastoid,  and  the  levator 
scapulae  it  is  subcutaneous. 

Nerve-supply. — The  lateral  branches  of  the  posterior  divisions  of  the  second,  third  and  fourth 
(sometimes  also  of  the  first,  the  fifth  and  the  sixth)  cervical  nerves  give  off  rami  which  enter  the 
deep  surface  of  the  muscle. 

Action. — To  incline  and  rotate  the  head  and  neck  toward  the  side  on  which  the  muscle  is 
placed.     When  both  muscles  act,  the  head  and  neck  are  extended. 

Variations. — The  extent  of  separation  and  of  fusion  of  the  two  muscles  varies.  Absence 
of  either  muscle  is  rare.  The  splenius  capitis  may  be  divided  into  mastoid  and  occipital  portions. 
The  attachment  of  the  muscle  also  varies  somewhat.  Occasionally  the  spinal  origin  of  the 
splenius  may  extend  to  the  cranial  end  of  the  ligamentum  nuchae.  The  origin  may  extend  later- 
ally over  the  fascia  covering  the  deeper  dorsal  muscles.  An  accessory  slip,  the  splenius  cervicis 
accessorius,  separated  from  the  main  muscle  by  the  tendon  of  the  serratus  posterior  superior, 
is  frequently  (8  per  cent,  of  instances,  LeDouble)  found  to  run  from  the  lower  cervical  or  upper 
thoracic  vertebrae  to  the  transverse  process  of  the  atlas. 

The  sacro -spinalis  (erector  spinas). — Origin. — (1)  From  a  strong  aponeurosis  attached  to 
the  spines  of  the  lumbar,  and  the  sacral  vertebrae,  to  the  ligament  passing  from  the  sacrum  to  the 
coccyx,  to  the  lateral  sacral  crest,  the  sacro-tuberous  ligament,  the  long  posterior  sacro-ihac 
ligament,  and  to  the  dorsal  fifth  of  the  iliac  crest;  (2)  directly  from  the  iliac  crest  in  front  of 
and  lateral  to  the  attachment  of  the  aponeurosis;  and  (3)  from  the  short  posterior  sacro-iliac 


MUSCLES  OF  THE  BACK 


415 


ligaments.  The  aponeurosis  covers  the  muscles  of  the  sacral  region  and  is  there  united  to 
the  overlying  fascia  by  more  or  less  dense  areolar  tissue.  Opposite  the  iliac  crest  fibre-bundles 
begin  to  take  origin  from  the  lateral  margin  of  the  dorsal  surface  as  well  as  from  the  deep  or 

Fig.  381. — The  Fifth  Layer  of  the  Muscles  of  the  Back. 


Semispinalis  capitis 
Longissimus  capitis 


Longissimus  cervicis 
Ilio-costalis  cervicis 


Longissimus  dorsi 


Ilio-costalis  dorsi 


Spinalis  dur  i  — 


nio-costalis  lumborum 


Obliquus  internus- 


SacrospinaliS' 


Seventh  cervical  vertebra 


Twelfth  thoracic  vertebra 


Fifth,  lumbar  vertebra 


ventral  surface  of  the  aponeurosis  of  origin,  and  gradually  the  line  of  dorsal  attachment  extends 
medially  until,  in  the  lower  thoracic  region,  the  tendon  becomes  completely  embedded  in  the 
muscle-fasciculi  which  take  their  origin  from  it.  The  aponeurosis,  which  is  the  strongest  in 
the  lower  lumbar  region,  is  composed  chiefly  of  fibres  which  take  a  direction  upward  and  some- 
what lateralward. 


416  THE  MUSCULATURE 

In  the  lower  lumbar  region  the  sacro-spinalis  (erector  spinae)  muscle  begins  to  show  a 
distinct  division  into  its  two  chief  component  parts,  the  ilio-costalis  and  the  longissimus. 
The  parts  of  which  the  ilio-costalis  and  longissimus  are  composed  will  be  taken  up  separately. 
The  ilio-costalis  lumborum  (figs.  381,  382). — Origin. — (1)  Chiefly  from  the  back  of  the 
sacrospinal  aponeurosis,  medial  to  and  cranialward  from  the  iliac  crest,  and  (2)  from  the  iliac 
crest  directly.  The  deep  medial  surface  of  the  muscle  is  closely  united  in  the  lumbar  region 
to  the  longissimus. 

Structure  and  insertion. — From  the  mass  of  fibre-bundles  which  compose  the  muscle,  fas- 
ciculi are  given  off  which  are  attached  chiefly  by  tendinous  slips  to — (l)the  tips  of  the  transverce 
processes  of  the  lumbar  vertebrse;  (2)  the  fibrous  processes  which  extend  lateralward  from  the 
tips  of  the  transverse  processes  of  the  upper  lumbar  vertebrte  into  the  anterior  layer  of  the  lumbo- 
dorsal  fascia;  (3)  the  inferior  margin  of  the  last  six  or  seven  ribs  near  the  angles.  The  inser- 
tions into  the  lumbo-dorsal  fascia  and  the  twelfth  rib  are  usually  fleshy.  The  portions  attached 
to  the  lumbar  vertebrse  are  by  some  considered  to  belong  to  the  longissimus  (Eisler). 

Relations. — The  muscle  lies  on  the  lateral  margin  of  the  longissimus  and  upon  the  ribs  and 
the  external  intercostal  and  levatores  costarum  muscles,  and  under  the  axio-appendicular 
muscles  described  above. 

The  ilio-costalis  dorsi  (accessorius). — Origin. — By  fleshy  fasciculi  from  the  superior  borders 
of  the  lower  seven  ribs  medial  to  the  angles. 

Structure  and  insertion. — The  slips  of  origin  lie  beneath  the  preceding  portion  of  the  muscle, 
pass  medial  to  and  partly  fuse  with  it,  and  give  rise  to  a  belly  from  which  tendinous  shps  extend 
to  be  inserted  into  the  upper  seven  ribs  near  their  angles  and  to  the  transverse  process  of  the 
seventh  cervical  vertebra. 

Relations. — The  muscle  Ues  upon  the  ribs  and  the  external  intercostal  muscles  lateral  to  the 
longissimus. 

The  ilio-costalis  cervicis  (cervicalis  ascendens). — Origin. — By  fleshy  shps  from  the  upper 
borders  near  the  angles  of  the  seventh  to  the  third  (sometimes  to  the  second  or  first)  ribs. 

Structure  and  insertion. — The  slips  of  origin  are  covered  by  the  slips  of  insertion  of  the  dorsal 

portion  (accessorius).     They  emerge  medial  to  them  and  give  rise  to  a  fleshy  beUy  from  which 

tendons  pass  to  the  backs  of  the  transverse  processes  of  the  sixth  to  the  fourth  cervical  vertebrse. 

Relations. — The  scalenus  posterior  hes  in  front,  the  levator  scapulse  at  the  side,  and  the 

splenius  and  longissimus  (transversalis)  cervicis  medial  to  this  muscle. 

A  bursa  is  frequently  found  between  the  muscle  and  the  tubercle  of  the  first  rib. 
The  longissimus  dorsi  (figs.  381,  382). — Origin. — (1)  From  the  deep  surface  of  the  sacro- 
spinal aponeurosis;  (2)  from  the  short  posterior  sacro-iliac  ligaments;  and  (3)  through  accessory 
slips  which  arise  from  the  transverse  processes  of  the  first  two  lumbar  and  the  last  five  or  six 
thoracic  vertebrse.     In  the  lumbar  region  it  is  fused  dorso-laterally  with  the  ilio-costalis. 

Structure  and  insertion. — From  the  muscle  mass  arise  fasciculi  which  are  inserted  partly 
directly,  partly  by  means  of  tendons,  into — (1)  the  lower  border  of  the  back  of  the  transverse 
processes  of  the  lumbar  vertebrse  and  the  inferior  margins  of  the  ribs  lateral  to  the  tubercles;  and 
(2)  the  accessory  tubercles  of  the  lumbar  and  the  tips  and  inferior  margins  of  the  transverse 
processes  of  the  thoracic  vertebra.  The  attachment  to  the  first  rib  is  usually  wanting.  The 
attachment  to  the  first  five  ribs  may  fail.  The  medial  attachments  seldom  extend  to  the  first 
vertebra. 

Relations. — The  lateral  margin  of  the  muscle  is  covered  by  the  ilio-costahs.  Medially  it 
overlies  the  transverso-spinal  muscles.  The  lateral  branches  of  the  dorsal  veins,  arteries,  and 
nerves  pass  mainly  in  the  fibrous  tissue  which  separates  the  longissimus  from  the  ilio-costalis, 
the  medial  branches  chiefly  between  the  longissimus  and  the  transverso-spinal  muscles.  The 
relations  to  the  axio-appendicular  muscles  and  to  the  dorsal  fascia  have  been  pointed  out  above. 
Ventrally  it  lies  upon  the  intertransverse  muscles,  the  external  intercostals,  and  the  levatores 
costarum. 

The  longissimus  cervicis  (transversalis  cervicis). — Origin. — By  tendinous  slips  from  the 
transverse  processes  of  the  first  four  to  six  thoracic  vertebrse. 

Structure  and  insertion. — The  fasciculi  which  arise  from  these  slips  give  rise  to  a  muscle  belly 
from  which  tendons  of  insertion  extend  to  the  posterior  tubercles  of  the  transverse  processes  of 
the  mid-cervical  (second  to  sixth)  vertebrse. 

Relations. — This  muscle  lies  between  the  longissimus  dorsi  and  capitis  with  which  it  is  to 
some  extent  fused  and  the  ilio-costahs  dorsi  (accessorius)  and  cervicis  (cervicalis  ascendens) 
muscles. 

The  longissimus  capitis  (trachelo-mastoid). — Origin. — By  tendinous  slips  from  the  trans- 
verse processes  of  the  first  three  or  four  thoracic  vertebrse  and  the  articular  processes  of  the  last 
four  cervical. 

Structure  and  insertion. — The  muscle  fasciculi  arising  from  these  tendons  form  a  belly  which 
is  united  to  the  mastoid  process  by  a  short  tendon.  A  tendinous  inscription  often  crosses  the 
muscle. 

Relations. — It  lies  ventral  to  the  splenius  capitis,  lateral  to  the  semispinalis  capitis  (com- 
plexus)  and  medial  to  the  longissimus  cervicis  (cervicalis  ascendens). 

Nerve-supply  of  the  sacro-spinalis. — From  the  lateral  branches  of  the  posterior  divisions  of 
the  spinal  nerves.  The  exact  distribution  of  these  branches  is  too  complex  to  be  treated  here. 
The  nerves  for  the  ilio-costalis  arise  from  the  eighth  cervical  to  the  first  lumbar,  those  for  the 
longissimus  from  the  first  cervical  to  the  fifth  lumbar. 

Action  of  the  sacro-spinalis. — The  sacro-spinalis  serves,  when  acting  on  one  side,  to  bend 
the  spinal  column  toward  that  side,  and  when  acting  on  both  sides,  to  extend  the  spinal  column. 
The  cranial  portions  of  the  muscle  serve  to  inchne  the  head  toward  the  same  side,  and  when 
both  muscles  act  they  serve  to  extend  the  head.  The  ilio-costalis  muscle  has  the  greatest  power 
for  producing  lateral  inclination.  The  ilio-costalis  lumborum  depresses  the  ribs,  while  the 
ilio-costalis  cervicis  (cervicalis  ascendens)  may  aid  in  elevating  them.  The  spinahs  muscle 
serves  merely  as  an  extensor. 


MUSCLES  OF  THE  BACK  417 

Variations  of  the  sacro-spinalis. — The  slips  of  origin  and  insertion  of  the  various  parts  of 
this  muscle  and  the  extent  of  fusion  of  the  various  parts  vary  greatly.  Statistical  data  from 
which  the  most  frequent  conditions  might  be  determined  are  wanting.  Tendinous  inscriptions 
may  extend  across  the  longissimus  cervicis  and  other  parts  of  the  sacro-spinaUs. 

B.  Deep  Lateral  Dorsal  System 

The  intertransversarii. — These  are  vertical  bands  composed  of  short  bundles  which  pass 
between  the  transverse  processes  of  the  cervical,  lumbar,  and  the  lower  thoracic  vertebrae. 

(a)  Ceroical  (fig.  349). — Ventral,  lateral  and  dorsal  muscles  are  found  in  the  cervical  region. 
The  ventral  and  lateral  muscles  run  between  the  ventral  tubercles  and  tips  of  the  transverse 
processes  of  the  vertebrae,  are  homologous  with  the  intercostal  muscles,  are  supplied  by  branches 
from  the  anterior  divisions  of  the  corresponding  spinal  nerves,  and  have  been  described  above 
(p.  356).  The  dorsal  muscles  run  between  the  dorsal  tubercles  and  belong  to  the  intrinsic 
dorsal  musculature.  They  are  supplied  by  the  lateral  branches  of  the  posterior  divisions  of  the 
cervical  nerves.*  The  three  sets  of  muscles  are,  however,  more  or  less  fused.  The  first  pair 
of  muscles  extends  between  the  atlas  and  axis,  the  lowest  passes  to  the  transverse  process  of  the 
first  thoracic  vertebra,  or  to  the  first  rib  close  to  this.  The  obliquus  capitis  superior  (described 
later)  belongs,  however,  to  the  posterior  set  of  muscles,  the  rectus  capitis  laigralis  (p.  356)  to 
the  lateral  set.  The  vertebral  artery  runs  vertically  between  each  pair  of  muscles  above  the 
sixth,  and  the  anterior  division  of  each  cervical  nerve  passes  laterally  between  the  artery  and  the 
dorsal  muscle  in  each  space,  and  then  out  between  the  ventral  and  lateral  muscles.  The  pos- 
terior division  of  each  cervical  nerve  passes  medial  to  each  dorsal  muscle. 

(b)  Thoracic. — Small  muscle  f  ascicuh  may  extend  between  the  transverse  processes  of  the 
thoracic  vertebrae  and  between  the  last  thoracic  and  first  lumbar.  They  are  most  frequent  in 
the  upper  and  lower  thoracic  regions.  Often  they  are  replaced  by  tendinous  bands.  In  the 
second  interspace  the  insertion  may  extend  to  the  rib  near  the  transverse  process.  The  inner- 
vation is  from  the  lateral  branches  of  the  posterior  divisions  of  the  spinal  nerves. 

(c)  Lumbar  (fig.  383). — In  the  lumbar  region  there  is  a  lateral  set  of  muscles  connecting 
the  adjacent  margins  of  the  transverse  processes  and  a  medial  connecting  the  mammary  tubercle 
of  one  vertebra  to  the  mammary  or  the  accessory  tubercle  of  the  vertebra  next  above.  They 
extend  between  each  two  of  the  five  lumbar  vertebrae  and  sometimes  also  to  the  first  sacral. 
They  lie  between  the  sacrospinalis  and  psoas  muscles.  The  medial  muscles  are  supplied  by 
the  lateral  branches  of  the  posterior  divisions  of  the  spinal  nerves.  The  lateral  muscles  are 
supplied  by  branches  from  the  junction  between  the  two  divisions  of  the  corresponding  spinal 
nerves.     These  branches  probably  belong  to  the  anterior  divisions. 

Action. — The  intertransverse  muscles  bend  the  spinal  column  laterally,  and  when  acting 
on  both  sides,  make  it  rigid. 

Variations. — The  number  of  intertransverse  spaces  occupied  by  the  muscles  varies,  espe- 
cially in  the  thoracic  region.     They  may  be  doubled  or  extend  over  more  than  one  interspace. 

C.  Superficial  Medial  Dorsal  System 

The  spinalis  dorsi. — Origin. — By  tendinous  bands  from  the  tips  of  the  two  upper  lumbar 
and  the  last  two  thoracic  spines. 

Structure  and  insertion. — From  the  deep  surface  of  the  tendinous  bands  there  arises  a  long 
slender  muscle  belly  which  is  fused  laterally  with  the  longissimus  dorsi.  It  is  attached  by 
tendinous  processes  to  the  spines  of  the  upper  thoracic  vertebrae,  usually  the  second  or  third  to 
the  ninth. 

Nerve-supply. — From  the  medial  divisions  of  the  sixth  to  ninth  thoracic  nerves. 

The  spinalis  cervicis. — A  muscle  of  inconstant  development  which  arises  from  the  spines 
of  the  two  upper  thoracic  and  two  lower  cervical  vertebrae  and  extends  to  the  spines  of  the  second 
to  the  fourth  cervical  vertebrae.  The  nerve  supply  is  from  the  dorsal  divisions  of  the  lower  cer- 
vical nerves. 

Action. — To  extend  the  vertebral  column. 

Variation. — There  is  great  variation  in  the  development  of  the  spinaUs  muscles.  Similar 
fasciculi  are  sometimes  found  in  the  lumbar  region  and  in  the  cervical  region  sometimes  extend 
to  the  skull. 

D.  Deep  Medial  Dorsal  System 

1.  Vertebro-occipital  Muscle 

The  semispinalis  capitis  (complexus)  (fig.  381). — This  muscle  is  usually  separated  from  the 
semispinalis  muscles  of  the  back  and  neck  by  a  well-marked  septum  and  has  a  distinctive 
structure. 

Origin. — (1)  By  long  tendinous  fasciculi  from  the  tips  of  the  transverse  processes  of  the 
upper  five  or  six  thoracic  vertebrae  and  of  the  seventh  cervical  vertebra;  (2)  by  short  fleshy 
processes  from  the  articular  processes  and  bases  of  the  transverse  processes  of  the  third  to  the 
sixth  cervical  vertebrae;  and  (3)  by  delicate  fleshy  fasciculi  from  the  spinous  processes  of  the 
upper  thoracic  vertebrae. 

Structure  and  insertion. — The  sUghtly  diverging  fibre-bundles  form  a  long,  flat  belly  which 
is  inserted,  partly  by  means  of  an  aponeurosis  which  covers  the  muscle  laterally,  into  the  lower 

*  According  to  Lickley,  both  sets  of  cervical  intertransverse  muscles  are  supphed  by  the 
anterior  divisions  of  the  spinal  nerves. 


418 


THE  MUSCULATURE 


surface  of  the  squamous  portion  of  the  occipital,  between  the  superior  and  inferior  nuchal  hnes. 
There  is  often  a  transverse  tendinous  inscription  across  the  muscle  opposite  the  sixth  cervical 
vertebra,  and  less  frequently  one  between  the  upper  and  middle  thirds  of  the  muscle.     These 


Fig.  382. — The  Fifth  Layer  of  the  Muscles  of  the  Back,  after  separating  the  Longis- 

SIMUS   AND    IlIO-COSTALIS    DIVISIONS. 


Obliquus  superior 
Rectus  capitis  posterior  major 

Obliquus  capitis  inferior  — 
Longissimus  capitis 

Longissimus  cervicis 
Ilio-costalis  cervicis 


Ilio-costalis  dorsi 


Ilio-costalis  lumborum 


Insertion  of  ilio-costalis  upon    lum- 
bar transverse  processes 


Rectus  capitis  posterior 


Seventh  cervical  vertebra 


—  Longissimus  dorsi 


Twelfth  thoracic  vertebra 


Fifth  lumbar  vertebra 
Sacrospinalis 


are  best  marked  in  the  medial  portion  of  the  muscle,  which  comes  from  the  thoracic  vertebra 
and  is  sometimes  separately  designated  as  the  spinalis  capitis  {hiventer  cervicis). 

Nerve-supply. — It  is  suppUed  chiefly  by  the  medial  branches  of  the  posterior  divisions  of  the 
first  four  or  five  cervical  nerves.     The  muscle  also  gets  some  twigs  from  the  lateral  branches. 


SUBOCCIPITAL  MUSCLES  419 

Relations. — It  lies  dorso-lateral  to  the  suboccipital  muscles  and  to  the  semispinalis  cervieis. 
From  this  latter  it  is  separated  by  a  septum  containing  the  descending  branch  of  the  occipital 
artery,  the  deep  cervical  artery,  and  the  medial  dorsal  branches  of  the  cervical  nerves.  It  is 
covered  laterally  by  the  longissimus  capitis  (trachelo-mastoid),  and  dorsally  by  the  splenius, 
and  above  the  upper  margin  of  the  splenius  by  the  trapezius. 

Action. — To  extend  the  head  and  to  inchne  it  slightly  toward  the  same  side. 

Variations. — The  origin  of  the  muscle  may  extend  to  the  eighth  thoracic  vertebra  or  merely 
to  the  first  thoracic.  It  may  be  fused  with  the  longissimus  (transversahs)  cervieis.  A  special 
fasciculus  may  run  beneath  the  muscle  from  the  upper  thoracic  vertebrse  to  the  head.  The  ori- 
gin from  the  spinous  processes  of  the  thoracic  vertebrse  is  not  constant.  The  part  of  the  muscle 
arising  from  this  origin  may  be  looked  upon  as  a  spinalis  capitis. 

2.  Transversospinal  Muscles 

The  semispinalis  dorsi  et  cervieis  (fig.  383). — This  superficial  transverso-spinal  muscle  sheet 
extends  from  the  twelfth  thoracic  to  the  second  cervical  vertebra.  The  fasciciili  which  compose 
it  arise  by  short  tendons  from  the  backs  of  the  transverse  processes,  and  are  inserted  by  short 
tendons  into  the  spines. 

The  semispinalis  dorsi. — Origin. — From  the  sixth  to  the  tenth  or  twelfth  thoracic  vertebrae. 

Insertion. — The  upper  four  to  six  thoracic  and  the  last  two  cervical  vertebrae.  The  fas- 
cicuh  extend  over  four  to  six  vertebrae. 

Nerve-supply. — Third  to  sixth  thoracic. 

The  semispinalis  cervieis. — Origin. — From  the  upper  five  or  six  thoracic  vertebrse. 

Insertion. — Into  the  fifth  to  the  second  cervical  vertebrae.  The  fascicuU  extend  over  four 
.  to  five  vertebrae. 

Nerve-supply. — Third  to  sixth  cervical. 

Relations. — This  muscle  lies  beneath  the  longissimus  dorsi  and  the  semispinalis  capitis 
(complexus)  and  over  the  following  musculature. 

Variations. — A  semispinalis  lumborum  is  a  muscle  rarely  found  extending  from  the  lumbar 
to  the  lower  thoracic  vertebras. 

The  multifidus  (fig.  383). — This  second  layer  of  transverso-spinal  musculature  extends  from 
the  sacrum  to  the  second  cervical  vertebra.  It  is  best  developed  in  the  lumbar  region  and  least 
so  in  the  thoracic. 

Origin. — (1)  From  the  groove  on  the  back  of  the  sacrum  between  the  spines  and  the  ar- 
ticular elevations,  from  the  dorsal  sacro-iliao  ligaments,  from  the  dorsal  end  of  the  Uiac  crest,  and 
from  the  deep  surface  of  the  aponeurosis  of  the  sacrospinal  muscle;  (2)  from  the  mammary  and 
accessory  processes  of  the  lumbar  vertebrae;  (3)  from  the  backs  of  the  transverse  processes  of  the 
thoracic  vertebrae;  and  (4)  from  the  articular  processes  of  the  fourth  to  the  seventh  cervical 
vertebrae  and  the  back  of  the  transverse  process  of  the  seventh. 

Insertion. — Spinous  processes  of  the  lumbar,  thoracic,  and  lower  six  cervical  vertebrae. 

Structure. — The  more  superficial  fasciculi  arise  by  short  tendinous  processes,  the  deeper 
ones  directly.  The  more  superficial  fasciculi  extend  to  the  fourthor  fifth  vertebra  above,  the 
middle  to  the  third,  and  the  deepest  to  the  second  above. 

The  rotatores. — These,  the  third  layer  of  transverso-spinal  muscles,  extend  from  the  sa- 
crum to  the  second  cervical  vertebra.  They  are  composed  of  short  fleshy  fascicuh  which  ex- 
tend to  the  second  vertebra  above  (rotatores  longi)  and  to  the  first  above  {rotatores  breves).  The 
fasciculi  arise  from  the  back  and  upper  borders  of  the  transverse  processes  or  their  homologues, 
and  are  inserted  into  the  laminae  of  the  preceding  vertebrae.  They  are  best  developed  in  the 
thoracic  region.  Some  authors  consider  the  rotatores  breves  confined  to  the  thoracic  region. 
In  the  cervical  region  the  fascicuU  usually  run  from  articulai-  processes  to  the  bases  of  the  spines, 
in  the  lumbar  region  from  the  mammary  processes  to  the  caudal  margin  of  the  laminae  of  the 
arches. 

3.  The  Interspinal  Muscles 

The  interspinales  consist  of  short  fasciculi  which  extend  from  the  upper  surface  of  the  spiae 
of  each  vertebra  near  its  tip  to  the  lower  surface  of  the  spine  of  the  vertebra  above.  In  the 
neck  the  muscles  lie  in  pairs  between  the  bifid  extremities  of  the  vertebrae.  In  the  lumbar 
region  they  form  broad  bands  attached  to  the  whole  length  of  the  spinous  processes  and  are 
separated  by  the  interspinous  hgaments.     In  the  thoracic  region  they  usually  are  undeveloped. 

Nerve-supply  of  medial  dorsal  muscles. — These  are  all  supplied  by  the  medial  branches 
of  the  posterior  divisions  of  the  spinal  nerves. 

Action  of  medial  dorsal  muscles. — These  muscles  extend  the  spinal  column  when  acting  on 
both  sides.  When  acting  on  one  side,  they  produce  a  movement  of  rotation  toward  the  opposite 
side. 

E.  StTBOCCiPiTAL  Muscles 
(Figs.  382,  383) 

The  rectus  capitis  posterior  major. — Origin. — From  the  upper  surface  of  the  spine  of  the 
epistropheus. 

Structure  and  insertion. — The  muscle-fibres  diverge  to  form  a  broad  triangular  band  which 
is  inserted  into  the  lateral  half  of  the  inferior  nuchal  line  of  the  occipital  bone  and  the  area 
below  it.     Its  insertion  is  immediately  below  that  of  the  obliquus  superior. 

The  rectus  capitis  posterior  minor. — Origin. — From  the  upper  part  of  the  side  of  the  posterior 
tubercle  of  the  atlas. 


420 


THE  MUSCULATURE 


Structure  and  insertion.— The  fibre-bundles  diverge  to  form  a  flat,  triangular  sheet  inserted 
below  the  medial  third  of  the  inferior  nuchal  line  of  the  occipital  bone  on  the  mfenor  surface  ot 
the  squama  occipitalis.  .^  ,  ,     „  ^-^       -j       c  4.1.         ■ e 

The  obliquus  capitis  inferior.— Origrm.— From  the  upper  part  of  the  side  ot  the  spme  01 
the  epistropheus  (axis).  ,     .,         ,    ,,        ,  .  1    •    ■        ^  j  1. 

Structure  and  i«se»«io?i.— The  fibre-bundles  form  a  fusiform  beUy  which  is  inserted  by  a 
short  tendon  into  the  lower  part  of  the  tip  of  the  transverse  process  of  the  atlas. 

Fig.  383. — The  Tkansverso-spinalis. 


Obliquus  capitis  superior 
Rectus  capitis  posterior  major 

Obliquus  capitis  inferior mi 

Multifidus  spinsE' 


Semispmalis  cerviciS' 
Ilio-costalr 


Longissimus  dorsi. 


Levator  costee 


Longissimus  dorsi- 
Ilio-costalii 


Obliquus  internuS' 


Seventh  cervical  vertebra 


Semispinalis  dorsi 


Twelfth  thoracic  vertebra 


Fifth  lumbar  vertebra 


Multifidus 


The  obliquus  capitis  superior.— Onffiw.— From  the  back  of  the  upper  part  of  the  trans- 
verse process  of  the  atlas.  n  ^   ^  ■         1      ^  .„„i„   ,-r. 

Structure  and  insertion.— The  fibre-bundles  diverge  to  form  a  flat,  triangular  muscle  in- 
serted into  the  lateral  third  of  the  inferior  nuchal  line  of  the  occipital  bone,  and  above  the  lateral 
part  of  the  insertion  of  the  rectus  capitis  posterior  major. 


MUSCLES  OF  THE  BODY  WALL 


421 


Fig.  384,  A  and  B. — Sections  through  the  Left  Side  op  the  Trunk  in  the  Regions  shown 

IN  THE  Diagram. 

The  muscles  of  the  body  wall  have  been  sUghtly  pulled  apart  in  order  to  reveal  the  relations 
of  muscles,  fasciae,  and  aponeuroses,  a  and  6  in  the  diagram  indicate  sections  A  and  B, 
fig.  351  (p.  352);  a-  and  6^,  sections  A  and  B,  fig.  357  (p.  366);  a^"  and  6',  sections  A  and  B, 
fig.  407  (p.  458): 

1.  Aorta.  2.  Arteria  mammaria  interna.  3.  Costa  VI — a,  cartilage.  4.  Costa  VII — a, 
cartilage.  5.  Costa  VIII.  6.  Costa  IX.  7.  Costa  X.  8.  Costa  XI.  9.  Descending 
colon.  10.  Diaphragm — a,  costal  portion;  b,  lumbar  portion;  c,  sternal  portion;  d,  cen- 
trum tendineum.  11.  Fascia  lumbodorsalis — a,  anterior  layer;  b,  posterior  layer.  12. 
Fascia  transversalis.  13.  Flexura  colica  sinstra  (splenic  flexure).  14.  Kidney.  15. 
Liver.  16.  Linea  alba.  17.  Musculi  intercostales  externi — a,  ligament.  18.  Mm. 
intercostales  interni.  19.  M.  iho-costalis.  20.  M.  latissimus  dorsi.  *  21.  M.  levator  costee. 
22.  M.  longissimus  dorsi.  23.  M.  obUquus  abdominis  externus.  24.  M.  obhquus 
abdominis  internus.  25.  M.  psoas  major.  26.  M.  quadratus  lumborum.  27.  M.  rectus 
abdominis.  28.  M.  serratus  posterior  inferior.  29.  M.  subcostalis.  30.  M.  transversus 
thoracis.  31.  M.  transversus  abdominis.  32.  Mm.  transverso-spinales.  33.  M.  trape- 
zius. 34.  Nervus  lumbalis  I.  35.  N.  thoracalis  VI.  36.  N.  thoracalis  VII.  37.  N. 
thoracalis  VIII.  38.  N.  thoracahs  IX.  39.  N.  thoracalis  X.  40.  N.  thoracaUs  XI. 
41.  N.  thoracalis  XII.  42.  Sympathetic  trunk — a,  great  splanchnic  nerve.  43.  Omen- 
tum majus.  44.  CEsophagus.  45.  Scarpa's  fascia.  46.  Spleen.  47.  Stomach.  48. 
Ureter.     49.  Vertebra  lumbalis  II.     50.  Vert,  lumbalis  III.     51.  Vert,  thoracalis  X. 


4     36181723  5   371817 


142    14  49  48  2534  SO  47  32 


422  THE  MUSCULATURE 

Nerve-supply.- — These  muscles  are  all  supplied  by  the  posterior  branch  of  the  suboccipital 
(first  cervical)  nerve.  The  branch  to  the  two  rectus  muscles  passes  across  the  dorsal  surface 
of  the  major  rectus  and  supphes  branches  to  the  middle  of  the  dorsal  surface  of  each  muscle. 
The  branch  to  the  superior  oblique  muscle  enters  the  middle  of  the  medial  margin,  that  to 
the  inferior  oblique  about  the  middle  of  its  superior  margin.  The  inferior  oblique  and  major 
rectus  muscles  usually,  the  other  muscles  occasionally,  receive  branches  from  the  second  cervical 
nerve. 

Relations. — The  two  oblique  muscles  with  the  rectus  major  serve  to  bound  a  small  tri- 
angular space,  the  suboccipital  triangle,  through  which  pass  the  dorsal  division  of  the  sub- 
occipital nerve  and  the  vertebral  artery.  The  two  minor  recti  lie  on  the  atlanto-occipital 
membrane  in  the  upper  part  of  the  space  bounded  by  the  major  recti.  The  muscles  are  covered 
medially  by  the  semispinalis  capitis  (complexus),  laterally  by  the  longissimus  and  splenius 
capitis.  In  front  of  the  two  oblique  muscles  and  the  major  rectus  runs  the  vertebral  artery. 
The  great  occipital  nerve  runs  between  the  semispinalis  capitis  (complexus)  and  the  inferior 
oblique  and  the  two  recti  in  a  dense  fatty  connective  tissue  containing  the  extensive  sub- 
occipital venous  plexus. 

Action. — The  rectus  muscles  and  the  superior  oblique  draw  the  head  backward.  The 
rectus  major  and  the  inferior  obUque,  when  acting  on  one  side,  rotate  the  face  toward  that  side. 

Variations. — Each  of  these  muscles  may  be  doubled  by  longitudinal  division.  Accessory 
sUps  may  connect  the  two  recti  with  the  semispinahs  capitis.  The  atlanto -mastoid  is  a  small 
muscle  frequently  found.  It  passes  from  the  transverse  process  of  the  atlas  to  the  mastoid 
process. 

IV.  THE  THORACIC-ABDOMINAL  MUSCULATURE 

The  thoracic  and  abdominal  viscera  are  contained  within  cavities,  the  ventro- 
lateral walls  of  which  may  be  contracted  and  expanded  by  muscular  action.  The 
skeletal  support  for  the  intrinsic  musculature  of  these  walls  consists  of  the  ribs, 
the  sternum  and  the  vertebral  column  and  the  pelvis.  The  intrinsic  musculature 
in  the  thoracic  walls  is  situated  chiefly  between  the  ribs  {intercostal  muscles,  figs. 
385,  386)  while  in  the  region  of  the  abdomen  it  extends  in  broad  sheets  from  the 
lower  part  of  the  thorax  to  the  pelvis  (the  quadratus  lumborum  and  the  external 
and  internal  oblique,  transverse,  and  reciws  muscles,  figs.  387,  388,  390,  406).  Be- 
tween the  two  cavities,  attached  to  the  lower  part  of  the  thorax  and  to  the  lumbar 
vertebrae  lies  the  dome-shaped  diaphragm  (fig.  391).  The  thoracic  cavity  ex- 
tends on  each  side  slightly  above  the  first  rib.  The  abdominal  cavity  extends 
downward  and  backward  into  the  pelvis,  as  the  pelvic  cavity. 

The  function  of  the  intercostal  muscles  is  to  expand  and  contract  the  thoracic  cavity  for 
the  sake  of  respiration.  The  shape  of  the  ribs  and  their  articulations  with  the  vertebrae  are 
such  that  a  slight  rotation  of  the  neck  of  each  rib  will  cause  the  shaft  to  swing  outward  and  up- 
ward or  in  the  reverse  direction.  The  costal  cartilages  are  elastic  enough  to  permit  this  move- 
ment, and  at  the  same  time  are  strong  enough  to  make  the  thorax  an  effective  skeletal  apparatus. 
Ninety  joints  are  called  into  play  in  the  movements  of  the  thorax  (24  between  the  heads  of 
the  ribs  and  the  vertebrte,  20  between  the  tuberosities  and  the  transverse  processes  of  the  ver- 
tebras, 24  between  the  ribs  and  costal  cartilages,  14  between  the  costal  cartilages  and  the  sternum, 
6  between  the  costal  cartilages  and  2  intrasternal).  When  the  shafts  of  ribs  are  swung  outward 
and  upward  the  thorax  is  enlarged  in  the  antero-posterior  and  transverse  axes.  In  the  adult 
when  standing  the  sternum  may  be  raised  nearly  3  cm.,  and  protruded  1  cm.  The  cartilages 
of  the  lower  ribs  may  be  raised  4  to  5  cm.  The  side  of  the  thorax  at  the  level  of  the  second 
rib  may  be  protruded  3  cm.,  and  at  the  level  of  the  eighth  rib  nearly  as  far.  This  extent  of 
movement,  however,  is  found  only  in  forced  respiration.  In  ordinary  quiet  respiration  it  is 
far  less,  the  sternum  being  raised  merely  3  or  4  mm.  and  protruded  2  mm.,  and  the  thorax  is 
enlarged  at  the  side  merely  5  mm.  (R.  Fick).  The  chief  muscles  used  in  quiet  inspiration  are 
the  external  intercostals  and  the  intercartOaginous  parts  of  the  internal  intercostals. 

During  inspiration  the  diaphragm  contracts  so  that  the  thoracic  cavity  is  further  enlarged 
perpendicularly.  The  extent  of  movement  of  the  upper  part  of  the  diaphragm  is  estimated  by 
R.  Fick  at  from  14-3  cm. 

The  ventro-lateral  abdominal  muscles  contract  the  thoracic  cavity  by  depressing  the 
thorax  and  by  pushing  the  diaphragm  upward.  They  directly  contract  the  abdominal  cavity. 
Contraction  of  the  abdominal  cavity  is  of  aid  in  defecation  and  parturition.  The  abdominal 
muscles  are  also  of  value  in  flexion,  abduction,  and  rotation  of  the  vertebral  column  and  pelvis. 

The  thorax,  with  its  intrinsic  musculature,  is  in  large  part  covered  by  the  musculature 
which  extends  from  the  tnmk  to  the  shoulder  girdle  and  arm;  dorsally  by  the  trapezius  and 
rhomboids,  ventrally  by  the  pectoral  muscles,  and  laterally  by  the  serratus  anterior  and  the 
latissimus  dorsi,  as  well  as  by  the  scapula  and  the  muscles  which  pass  from  it  to  the  humerus. 
The  upper  extremity  on  each  side  is  largely  supported  from  the  spine  by  the  trapezius,  rhomboid 
and  levator  scapulae  muscles  but  it  none  the  less  exerts  some  pressure  on  the  thorax  and  inter- 
feres to  some  extent  with  respiration.  If  the  girdle  and  arm  are  fixed  or  raised  the  muscles 
which  pass  from  them  to  the  thorax  are  an  aid  in  forced  inspiration.  Advantage  of  this  is 
taken  when  in  artificial  respiration  the  arms  are  raised  so  as  to  hft  the  ribs  through  traction 
by  the  latissimus  dorsi,  the  pectoralis  muscles  and  the  subclavius.  Some  of  the  muscles  of  the 
neck,  especially  the  scalene  muscles  and  the  sterno-cleido-mastoid,  are  Ukewise  of  value  in  forced 
inspiration. 


THORACIC-ABDOMINAL  MUSCLES  423 

Expiration  is  produced  not  only  by  the  part  ofthe  internal  intercostals  which  lie  between  the 
bony  ribs,  and  by  the  abdominal  muscles,  but  also  by  the  lumbar  ilio-costales  and  by  the  quad- 
ratus  lumborum. 

The  intrinsic  muscles  of  the  thorax  and  abdomen  are  derived  from  the  twelve 
thoracic  myotomes  and  the  first  one  or  two  lumbar  and  are  innervated  by  the 
corresponding  nerves,  while  the  musculature  of  the  shoulder  girdle  and  arm  which 
covers  the  intrinsic  muscles  of  the  thorax  is  of  cervical  origin  an  d  is  innervated 
by  cervical  nerves.  The  diaphragm  is  likewise  of  cervical  origin  and  is  innervated 
by  the  phrenic  nerve  from  the  cervical  plexus.  ., 

The  intrinsic  muscles  of  the  back  extend  over  the  thoracic  musculature  (ex- 
ternal intercostals  and  levators  of  the  ribs,  fig.  383)  and  in  turn  are  in  part  covered 
by  muscles  which  extend  dorsally  from  the  thoracic  region  (posterior  serrate 
muscles,  fig.  380). 

The  intrinsic  thoracic-abdominal  muscles  are  composed  laterally  of  three  layers 
of  sheet-like  muscles. 

In  the  external  layer  the  fibre  bundles  run  downward  and  ventralward.  This 
layer  is  represented  in-  the  thoracic  region  by  the  external  intercostal  muscles,  the 
levators  of  the  ribs  and  the  posterior  serrate  muscles.  The  fibre-bundles  of  the 
external  intercostals  (fig.  385),  extend  between  each  pair  of  ribs  but  between  the 
costal  cartilages  are  replaced  by  fibrous  tissue,  the  external  intercostal  ligaments. 
The  levatores  costarum  (fig.  383),  extend  from  the  transverse  process  of  one 
vertebra  to  the  rib  which  articulates  with  the  next  vertebra  below  and  in  some 
instances  the  fibre  bundles  are  continued  to  the  second  rib  below. 

The  serratus  posterior  superior  and  inferior  (fig.  380) ,  are  derivatives  of  the 
external  oblique  which  during  development  wander  in  part  over  the  intrinsic 
dorsal  musculature.  The  superior  serrate  arises  from  the  spines  of  the  last  two 
cervical  and  first  two  thoracic  vertebrae  and  is  inserted  into  the  second  to  the 
fifth  ribs.  The  inferior  serrate  muscle  arises  from  the  spines  of  the  last  two  tho- 
racic and  first  two  lumbar  spines  and  is  inserted  into  the  last  four  ribs.  The  fibre- 
bundles  of  this  muscles  therefore  take  a  direction  opposite  to  that  of  the  other 
muscles  of  the  group.  The  muscles  aid  in  inspiration.  In  the  abdominal  region 
the  external  layer  is  represented  by  the  external  oblique  muscle  (fig.  387).  This 
arises  by  digitations  from  the  last  seven  ribs  and  is  inserted  into  the  crest  of  the 
ilium  and  by  means  of  a  broad  flat  aponeurosis  into  the  Hnea  alba  in  the  mid- 
ventral  fine  and  into  the  inguinal  Hgament  below.  The  external  intercostal, 
levatores  costarum,  and  posterior  serrate  muscles  are  innervated  from  branches 
which  arise  near  the  tubercles  of  the  ribs.  The  external  oblique  muscles  are  inner- 
vated by  branches  which  in  large  part  arise  in  conjunction  with  or  from  the  lateral 
branches  of  the  anterior  divisions  of  the  last  seven  thoracic  nerves  and  frequently 
also  by  branches  from  the  ilio-hypogastric. 

The  middle  layer  of  the  lateral  thoraco-abdominal  musculature  is  composed  of 
fibre-bundles  which  run  downward  and  backward  obliquely  across  the  fibre-bundles 
of  the  external  layer.  In  the  thoracic  region  it  is  represented  by  the  internal 
intercostal  and  subcostal  muscles.  The  internal  intercostal  (fig.  385)  muscles  lie 
between  the  costal  cartilages  and  between  the  ribs  as  far  dorsalward  as  the  angles, 
beyond  which  they  are  replaced  by  membranous  tissue  and  by  the  subcostal 
muscles.  The  latter,  instead  of  extending  from  one  rib  to  the  next  rib  below,  ex- 
tend to  the  second  or  third  rib  below.  They  are  best  developed  in  the  lower  part 
of  the  thoracic  cavity.  In  the  abdominal  region  the  middle  layer  is  represented  by 
the  internal  oblique  muscle  (fig.  388) .  This  arises  from  the  lumbo-dorsal  fascia, 
the  crest  of  the  ilium  and  the  inguinal  ligament  and  is  inserted  into  the  sheath  of 
the  rectus  abdominis  muscle  and  into  the  inferior  margins  of  the  ventral  extremi- 
ties of  the  three  lower  ribs.  The  aponeurosis,  which  helps  to  form  the  sheath  of 
the  rectus,  divides  in  the  upper  abdominal  region  into  two  layers,  one  of  which 
passes  in  front  and  the  other  of  which  passes  behind  the  rectus  to  be  inserted  into 
the  linea  alba  in  the  mid-ventral  line.  In  the  lower  third  of  the  ventral  abdominal 
wall  both  layers  pass  in  front  of  the  rectus.  The  fibre-bundles  which  compose  the 
internal  obUque  muscles  do  not  all  follow  the  usual  course  of  the  fibre-bundles  of 
this  layer.  At  the  level  of  the  iliac  crest  they  pass  nearly  transversely  across  the 
body  and  below  here  they  slant  downward  and  forward.  Just  above  the  in- 
guinal ligament  and  medial  to  its  centre  the  internal  oblique  muscle  is  continuous 
with  the  thin  cremaster  muscle  (fig.  389),  which  is  prolonged  over  the  spermatic 
cord  and  the  tunica  vaginalis  of  the  testis  and  epididymis  in  the  male  and  over  the 


424  THE  MUSCULATURE 

ligamentum  teres  in  the  female.  The  cremaster  muscle  is  attached  laterally 
to  the  inguinal  ligament,  medially  to  the  outer  layer  of  the  sheath  of  the  rectus 
near  the  insertion  of  the  latter. 

The  inner  layer  of  the  thoraco-abdominal  musculature  is  composed  of  fibre 
bundles  which  take  a  course  transversely  across  the  body.  In  the  thoracic  region 
it  is  represented  by  the  transversus  thoracis  (fig.  386) ,  a  slightly  developed  muscle 
which  arises  from  the  costal  cartilages  of  the  third  to  sixth  ribs  and  is  inserted  into 
the  lower  part  of  the  sternum  and  into  the  xiphoid  process.  In  the  upper  portion 
of  the  muscle  the  fibre-bundles  extend  obliquely  downward  and  forward  instead  of 
transversely.  In  the  abdomen  this  layer  is  represented  by  the  transversus 
abdominis  (fig.  390)  which  arises  from  the  cartilages  of  the  lower  seven  ribs,  from 
the  lumbo-dorsal  fascia,  the  iliac  crest  and  lateral  part  of  the  inguinal  ligament  and 
is  inserted  into  the  linea  alba  by  means  of  an  aponeurosis  which  lies  behind  the 
rectus  in  the  upper  two-thirds  of  the  ventral  wall  of  the  abdomen  and  in  front  in 
the  lower  third.  It  is  intimately  fused  with  the  aponeurosis  of  the  internal 
oblique. 

The  main  trunks  of  the  anterior  divisions  of  the  last  five  or  six  thoracic  nerves 
give  rise  to  branches  which  supply  the  muscles  both  of  the  middle  and  inner  layers 
of  the  lateral  thoraco-abdominal  musculature.  In  the  abdominal  region  these 
trunks  run  in  the  main  between  the  two  layers.  Some  muscular  branches  are 
usually  also  supplied  from  the  ilio-hypogastric  and  ilio-inguinal  nerves.  In  the 
thoracic  region  the  intercostal  nerves  run  external  to  the  subcostal  muscles, 
through  the  substance  of  the  costal  part  of  the  internal  intercostal  muscles,  and 
internal  to  the  parts  of  the  internal  intercostals  which  lie  between  the  costal 
cartilages.  Eisler  includes  the  subcostal  muscles  and  that  part  of  the  internal 
intercostals  which  lies  internal  to  the  nerve  trunk,  with  the  inner  rather  than  with 
the  middle  layer  of  the  thoracic  musculature. 

The  ventral  part  of  the  muscular  thoraco-abdominal  wall  is  represented  by  a 
single  muscle  on  each  side,  the  rectus  abdominis  muscle,  except  just  above  the 
symphysis  pubis  where  the  rudimentary  pyramidalis  is  usually  found.  The  rec- 
tus abdominis  muscle  (fig.  388),  is  a  band-like  muscle  which  arises  from  the  ventral 
surfaces  of  the  fifth  to  the  seventh  costal  cartilages  and  from  the  xiphoid  process 
and  is  inserted  into  the  superior  ramus  of  the  pubis.  It  is  ensheathed  by  the  ap- 
oneuroses of  the  lateral  abdominal  musculature  described  above.  The  component 
fibre-bundles  run  nearly  parallel  with  the  mid-sagittal  line.  Transverse  inscrip- 
tions partially  divide  the  muscles  into  segments.  It  is  innervated  by  the  last  six 
or  seven  thoracic  nerves.  The  pyramidalis  (fig.  388)  is  a  small  muscle  which 
arises  from  the  superior  pubic  ramus  and  is  inserted  into  the  linea  alba  for  about  a 
third  of  the  distance  to  the  umbilicus. 

The  lateral  intertransverse  muscles  of  the  lumbar  region  described  on  p.  417 
probably  belong  to  the  ventro-lateral  musculature  of  the  trunk.  The  nerves 
supplying  them  come  from  the  junction  between  the  posterior  and  anterior 
divisions  of  the  spinal  nerves. 

The  inguinal  (Poupart's)  ligament  and  the  inguinal  canal,  described  in  detail 
below,  are  of  considerable  practical  interest  because  of  the  frequency  of  hernias 
in  this  region.  In  the  quadrupeds  the  pressure  of  the  weight  of  the  abdominal 
viscera  centres  toward  the  umbilicus  while  in  man  it  centres  toward  the  ventral 
part  of  the  line  of  attachment  of  the  abdominal  wall  to  the  pelvis.  The  lower 
margin  of  the  aponeurosis  of  the  external  oblique  muscle  is  here  strengthened  to 
form  the  inguinal  (Poupart's)  ligament  which  extends  from  the  anterior  superior 
iliac  spine  to  the  pubic  tubercle.  Near  the  latter  it  is  reflected  (curves  medial- 
ward)  to  the  pubic  crest  forming  the  triangular  lacunar  ligament  (Gimbernart's). 
The  medial  half  of  the  inguinal  ligament  helps  to  bound  a  slit-hke  space,  inguinal 
canal  through  which  in  the  male  the  spermatic  cord  passes  to  the  scrotum,  and  in 
the  female,  the  round  ligament  passes  to  the  labium  majus.  This  canal  begins  on 
the  inner  side  at  the  (internal)  abdominal  ring,  which  is  situated  above  and  medial 
to  the  centre  of  the  inguinal  ligament.  The  canal,  which  is  about  4  cm.  long, 
extends  medialward  and  downward  to  the  subcutaneous  (external  abdominal) 
ring,  a  slit-like  opening  in  the  aponeurosis  of  the  external  oblique  just  above  the 
inguinal  ligament.     The  canal  is  bounded  ventrally  by  the  aponeurosis  of  the  ex- 


FASGIM  425 

ternal  oblique  and  the  cremaster  muscle,  below  by  the  reflected  portion  of  the  in- 
guinal ligament,  dorsally  by  the  transversalis  fascia  and  above  by  the  transversus, 
internal  oblique,  and  cremaster  muscles. 

The  quadratus  lumborum  (fig.  406),  which  extends  from  the  twelfth  rib  to  the 
ilium  and  ilio-lumbar  ligament,  is  supplied  by  direct  branches  of  the  lumbar  nerves 
in  series  with  the  nerves  supplying  the  musculature  of  the  abdominal  wall.  It 
will,  therefore,  be  taken  up  with  the  intrinsic  thoraco-abdominal  muscles.  It 
depresses  the  thorax  and  abducts  and  extends  the  spine.  The  psoas- muscle,  on 
on  the  other  hand,  which  also  lies  at  the  back  of  the  abdominal  cavity,  represents 
an  extension  of  the  intrinsic  musculature  of  the  limb  to  the  spinal  column  (see 
p.  455). 

The  diaphragm  (fig.  391),  a  dome-shaped  muscle  which  is  attached  to  the  distal 
margin  of  the  thorax  and  to  the  upper  lumbar  vertebrae,  and  separates  the  thoracic 
and  abdominal  cavities,  arises  in  the  embryo  in  the  region  of  the  neck,  and  main- 
tains cervical  relations  through  its  innervation  by  the  phrenic  nerves,  which  spring 
one  on  each  side  usually  from  the  third  to  fifth  cervical  nerves.  It  does  not  belong 
morphologically  with  the  other  muscles  considered  in  this  section,  but  is  here 
included  because  of  its  physiological  and  anatomical  relations  and  the  convenience 
of  treating  it  in  connection  with  the  intrinsic  thoraco-abdominal  muscles.  A 
diaphragm  completely  separating  the  thoracic  from  the  abdominal  cavities  is 
found  only  in  the  mammals.  The  central  portion  of  the  diaphragm  is  an  aponeu- 
rosis or  central  tendon  with  a  convex  ventral  and  concave  dorsal  margin.  Into 
this  tendon  is  inserted  the  musculature  which  arises  on  each  side  from  the  xiphoid 
cartilage,  the  cartilages  and  tips  of  the  last  six  or  seven  ribs  and  by  means  of  three 
crura  from  the  sides  of  the  first  four  lumbar  vertebras. 

In  fishes  and  tailed  amphibians  the  musculature  of  the  body  wall  is  composed  of  meta- 
merically  segmented  musculature.  In  all  higher  vertebrates  it  is  hkewise  at  an  early  embryonic 
stage  segmental,  being  composed  of  the  ventro-lateral  portions  of  the  myotomes.  The  ventral 
ends  of  the  myotomes  give  rise  to  a  ventral  longitudinal  muscle  which  runs  on  each  side  of  the 
body  next  the  mid-hne  in  front,  and  retains  more  or  less  of  the  primitive  segmentation.  The 
rectus  abdominis  and  the  infrahyoid  muscles  represent  this  system  in  man.  Very  frequently 
traces  of  the  system  may  also  be  seen  on  the  upper  thoracic  wall  in  the  form  of  slerider  muscular 
and  aponeurotic  slips.  The  rectus  muscle  in  man  is  usually  developed  from  the  last  seven  tho- 
racic myotomes.  The  pyramidalis  becomes  spht  ofT  from  its  lower  end.  The  lateral  part  of 
the  ventro-lateral  portions  of  the  thoracic  myotomes  usually  gives  rise  to  several  strata  of  mus- 
cles which  vary  somewhat  in  different  vertebrates,  although  quite  similar  among  the  mammals. 
In  man  the  twelve  thoracic  and  first  two  lumbar  myotomes  give  rise  to  the  lateral  musculature 
of  the  thoraco-abdominal  wall. 

The  quadratus  lumborum  represents  the  ventro-lateral  portions  of  the  lumbar  myotomes 
with  the  exception  of  that  portion  of  the  first  two  which  enter  into  the  lateral  abdominal  mus- 
culature and  of  the  fifth,  which  probably  undergoes  retrograde  metamorphosis. 

It  will  be  noted  that  the  abdominal  wall  is  composed  of  musculature  which  has  an  origin 
chiefly  from  the  thoracic  myotomes.  At  an  early  stage  of  embryonic  development  both  the 
thoracic  and  the  abdominal  viscera  are  covered  by  a  non-muscular  membrane.  The  myotomes 
extend  into  this  from  the  thoracic  region,  and  as  the  musculature  is  differentiated,  it  approaches 
the  median  fine  in  front  and  extends  distally  to  the  pelvis.  Owing  to  the  rotation  of  the  limbs 
the  abdominal  musculature  is  stretched  ventrally  over  an  area  corresponding  to  the  lumbar 
and  sacra!  regions  dorsally.  The  last  part  of  the  thoraco-abdominal  wall  to  be  furnished  with 
musculature  is  that  about  the  umbilicus.  Occasionally  the  process  fails  to  be  completed  in  this 
region. 

Each  spinal  nerve  suppUes  primarily  the  musculature  derived  from  the  myotome  which  lay 
caudal  to  it,  and  at  first  the  musculature  lies  wholly  superficial  to  the  nerves.  With  subsequent 
differentiation  the  metamerism  is  somewhat  obscured  by  anastomosis  of  nerves  and  fusion  of 
myotomes;  and  a  part  of  the  internal  oblique  layer  and  all  the  transverse  layer  of  the  lateral 
musculature  comes  to  he  on  the  inner  side  of  the  main  nerve-trunks. 

FASCIA 

The  fasciae  and  the  topographical  relations  of  the  thoraco-abdominal  muscles  may  be  fol- 
lowed in  the  sections  shown  in  figs.  357,  384,  and  407. 

Tela  subcutanea. — As  mentioned  above,  most  of  the  intrinsic  thoracic  musculature  is  cov- 
ered by  other  muscles,  while  the  superficial  layer  of  the  abdominal  musculature  is  subcutaneous. 
A  panniculus  adiposus,  Camper's  fascia,  in  which  much  fat  may  be  deposited  is  usualh'  easily 
distinguishable,  especially  in  the  lower  part  of  the  ventral  wall  of  the  abdomen,  from  a  membran- 
ous fascial  sheet  which  is  loosely  attached  to  the  underlying  fascial  envelopment  of  the  muscles. 
To  this  membrane  has  been  applied  the  term  Scarpa's  fascia.  Near  the  groin  it  is  separated 
from  the  panniculus  adiposus  by  blood-vessels  and  lymphatic  glands.  It  is  closely  bound  to  the 
linea  alba  between  the  two  rectus  muscles,  to  the  fibrous  structures  in  front  of  the  pubic  bone, 
to  the  fascia  lata  below  the  inguinal  ligament,  and  to  the  crest  of  the  ihum. 

Over  the  scrotum  of  the  male  and  vulva  of  the  female  both  layers  of  the  tela  subcutanea  are 
continued.     In  the  male  the  fat  of  the  more  superficial  layer  disappears  and  the  two  layers 


426 


THE  MUSCULATURE 


blend  with  the  fundiform  (suspensory)  hgament  and  fascia  of  the  penis  and  the  dartos  and  sep- 
tum of  the  scrotum. 

Muscle  fascias  and  sheaths. — The  posterior  serrate  muscles  (fig.  380)  are  enveloped  by  two 
adherent  layers  of  an  aponeurotic  sheet  that  extends  as  a  single  membrane  between  them  and  is 
attached  lateralward  to  the  ribs  and  medialward  to  the  spines  of  the  thoracic  vertebrae.  The 
membrane  between  the  muscles  may  represent  the  rudiment  of  a  primitive  continuous  muscle 
such  as  is  found  in  some  lower  vertebrates.  This  membrane  may  usually  be  easily  separated 
from  the  aponeurosis  of  the  latissimus  dorsi  on  its  superficial  surface  and  the  lumbo-dorsal 
fascia  beneath. 

The  intercostal  muscles  are  covered  by  delicate,  adherent  membranes  on  each  surface. 
The  e.xternal  intercostal  muscles  are  continued  as  aponeurotic  bands  between  thCjCostal  cartil- 
ages.    These  serve  here  as  fasciae  for  the  internal  intercostals. 

Fig.  385. — The  Intercostal  Muscles. 


The  external  obhque  muscle  is  covered  externally  by  a  dense,  adherent  membrane  and  in- 
ternally by  a  more  delicate  membrane  except  where  the  muscle  is  attached  to  the  ribs  or  fused 
with  the  external  intercostal  muscles.  VentraUy  and  distally  these  membrau'es  are  fused  be- 
yond the  fleshy  portion  of  the  muscle  to  the  broad  aponeurosis  that  serves  to  ensheath  the  rectus 
muscle  and  cover  the  lower  part  of  the  abdominal  wall  (fig.  389).  Dorsally  i,he  membranes 
are  in  part  attached  to  the  ribs  and  in  part  are  fused  to  form  a  membrane  whioh  becomes  ad- 
herent to  the  deep  surface  of  the  latissimus  dorsi  in  the  thoracic  region  and  to  th(3  lumbo-dorsal 
fascia  in  the  lumbar  region. 

The  internal  oblique  muscle  and  the  transversus  abdominis  have  similar  membranous 
coverings  which  are  fused  to  the  aponeuroses  of  origin  and  insertion  of  these  njusoles.  The 
membranes  on  the  muscles  are,  however,  much  more  delicate  than  that  of  the  extt;rnal  obhque. 
More  or  less  fusion  between  the  two  muscles  with  disappearance  of  the  membrfj,nes  covering 
the  opposing  surfaces  takes  place,  especially  in  the  lower  part  of  the  abdominal  wall.  The  super- 
ficial muscle  fasciae  of  the  external  oblique  and  the  fasciae  of  the  internal  oblique  iire  continued 
into  the  thin  cremasteric  fascia  which  covers  the  cremasteric  muscle,  spermatic  corci  and  testis. 

The  diaphragm  is  covered  on  each  surface  by  a  more  or  less  weD-marked  adherent  membrane. 

The  transversalis  fascia  is  a  thin  membrane  which  lies  external  to  the  peritoneum  of  the  ab- 
dominal wall.  It  covers  the  peritoneal  surface  of  the  transversus  muscle  and  its  aponeurosis. 
Ventrally  it  is  continued  across  the  median  line  internal  to  the  rectus  abdominis.  In  the  lum- 
bar region  the  fascia  divides  at  the  lateral  margin  of  the  quadratus  lumborum  (fig.  384),  one 
lamina  of  it  passing  dorsal  to  this  muscle  to  be  attached  to  the  lumbo-dorsal  fascia.  The  other 
lamina  extends  over  the  ventral  surface  of  the  quadratus  and  becomes  fused  with  the  psoas 
fascia.     Proximally  the  transversalis  fascia  becomes  fused  with  the  fascial  mernbrane  adherent 


FASCIA 


427 


to  the  diaphragm.  In  the  region  of  the  ihac  fossa  the  transversalis  fascia  is  reflected  from  the 
transversus  muscle  to  the  ilio-psoas  fascia,  with  which  it  usually  becomes  fused.  Sometimes, 
however,  it  may  be  traced  as  a  very  delicate  membrane  over  the  iliac  artery  and  vein.  As 
these  vessels  pass  below  the  inguinal  ligament  a  process  from  the  transversalis  fascia  is  usually 
reflected  into  their  sheath. 

The  sheath  of  the  rectus  (figs.  384,  407)  is  formed  externally  in  the  upper  portion  of  its 
extent  by  the  aponeurosis  of  the  external  oblique  which  fuses  distal  to  the  costal  margin  with 
the  external  layer  of  the  aponeurosis  of  the  internal  oblique.  In  the  lower  portion  of  the  abdo- 
men this  fusion  takes  place  nearer  the  linea  alba  than  in  the  upper  portion.  In  the  lewer  third 
of  its  extent  the  rectus  is  covered  ventrally  by  the  fused  aponeuroses  of  the  two  oblique  muscles 
conjoined  with  that  of  the  transversus.  Internally  the  rectus  is  covered  in  the  upper  two-thirds 
of  the  abdomen  by  the  inner  layer  of  the  aponeurosis  of  the  internal  oblique  conjoined  with  that 
of  the  transversus  and  by  the  transversalis  fascia.  In  the  lower  thkd  of  the  abdomen  the  ap- 
oneurosis of  the  internal  obhque,  together  with  that  of  the  transversus,  passes  in  front  of  the 
rectus,  leaving  the  rectus  in  this  portion  of  its  abdominal  surface  covered  merely  by  the  trans- 
versahs  fascia  and  the  peritoneum.  The  line  which  marks  the  lower  limit  of  the  dorsal  ensheath- 
ment  of  the  rectus  by  the  aponeurosis  of  the  transversus  muscle  is  called  the  linea  semicircularis, 

Fig.  386. — The  Muscles  attached  to  the  Back  op  the  Sternum. 


Sterno-hyoid 


Stemo-thyreoid 


Transversus  abdominis 


or  fold  of  Douglas.  Between  the  transversalis  fascia  and  the  rectus  just  above  the  pubis 
there  is  a  space  filled  with  loose  connective  tissue  or  with  fat. 

The  pyramidalis  lies  beneath  the  ventral  layer  of  the  sheath  of  the  rectus.  From  the  latter 
it  is  sometimes  separated  by  a  distinct  fascial  layer. 

Between  the  rectus  muscles  of  each  side  the  investing  aponeuroses  are  firmly  united  into 
a  dense  tendinous  band,  the  linea  alba  (fig.  389).  This  is  broadest  opposite  the  umbilicus. 
Above  this  it  gradually  grows  narrower  toward  the  xiphoid  process  to  the  ventral  surface  of 
which  it  is  attached.  From  the  tip  of  the  xiphoid  process  it  is  often  separated  by  a  bursa. 
Toward  the  symphysis  pubis  it  extends  as  a  narrow  line.  Just  above  the  symphysis  it  divides 
to  be  attached  on  each  side  to  the  tubercle  (spine)  of  the  pubis.  Behind  it  broadens  into  the 
adminiculum  linem  alboe  which  is  attached  on  each  side  to  the  pubis.  The  linea  alba  is  composed 
mainly  of  the  interlacing  of  the  fibres  which  pass  into  it  from  the  aponeurotic  sheaths  of  the 
rectus  abdominis.  From  it  and  Scarpa's  fascia,  a  few  centimetres  above  the  symphysis,  there 
arises  a  broad  elastic  band,  the  fundiform  ligament  (superficial  suspensory  ligament)  of  the  penis, 
which  sends  a  fasciculus  on  each  side  of  the  penis.  Below  the  penis  these  fasciculi  unite.*  At 
the  umbilicus  there  is  a  circular  opening  encircled  by  dense  fibrous  tissue  and  filled  with  a  thick 
connective  tissue,  extending  from  the  tela  subcutanea  to  the  subserosa. 

*  Alex.  Hagenton  has  shown  that  the  linea  alba  varies  much  in  width.  It  is  relatively  wide 
in  fat  people  and  in  foetuses. 


428 


THE  MUSCULATURE 


The  ventral  layer  of  the  lumbo-dorsal  fascia  and  its  relations  to  the  abdominal  muscles  also 
merit  attention.  This  lies  between  the  intrinsic  dorsal  musculature  and  the  quadratus  lum- 
borum  muscle  and  extends  from  the  twelfth  rib  to  the  ilio-lumbar  ligament.  It  is  strengthened 
by  the  lumbo-costal  ligament,  which  extends  between  the  transverse  processes  of  the  first  and 

Fig.  387. — Superficial  Musculature  op  Abdomen  and  Thigh. 


Pectoralis  major 


)rigin  of  pectoralis 
major  from  aponeu- 
rosis of  obliquus  ex- 
ternus 


Obliciuus  externus 


Linea  semilunaris 


Tensor  fasciae  latae 


Ilio-tibial  band 


Trapezius 
Serratus  anterior 


Latissimus  dorsi 


Gluteus  maximum 


Tendon  of  biceps 


second  lumbar  vertebras  and  the  twelfth  rib,  and  by  fibrous  processes  which  extend  into  it 
from  the  transverse  processes  of  the  lumbar  vertebras  to  which  it  is  attached.  With  the  lateral 
margin  of  this  ventral  layer  the  dorsal  layer  of  the  lumbo-dorsal  fascia  is  fused.  The  dorsal 
aponeurosis  of  the  transversus  muscle  is  united  to  the  lumbo-dorsal  fascia  at  the  line  of  junction 
of  the  ventral  and  dorsal  layers.  The  internal  oblique  muscle,  covered  externally  by  a 
fascia  continued  dorsally  from  the  external  obhque,  arises  in  part  from  the  dorsal  layer  of  the 
lumbo-dorsal  fascia  near  the  junction  of  the  two  layers. 


INGUINAL  LIGAMENT 


429 


The  inguinal  ligament  (Poupart's  ligament)  (figs.  387,  389,  390)  is  a  strong  band  which 
extends  along  the  distal  margin  of  the  aponeurosis  of  the  external  oblique  from  the  anterior 
superior  iliac  spine  to  the  pubic  tubercle.  Internally  the  iliac  fascia  is  fused  to  it.  Distally 
the  fascia  lata  of  the  thigh  is  attached  to  it.     The  deeper  lateral  abdominal  muscles  m  part 

Fig.  388. — The  Pectoralis  Minor,  Obliquus  Internus,  Ptramidalis,  and  Rectus 
Abdominis. 


Subscapularis 

Pectoralis  minor 
Latissimus  dorsi 


Pectoralis  major 
Teres  major 


Obliquus  internus 


Pyramidalis 
Falx  inguinalis 


arise  from  it.  Medially  near  the  attachment  of  the  hgament  to  the  pubic  tubercle  (spine) 
diverging  fibres  are  given  otT  which  pass  inward  and  upward  to  the  pecten  (crest)  of  the  pubis 
and  give  rise  to  the  triangular  lacunar  ligament  (Gimbernat's  ligament).  This  is  fused  with  the 
fascia  of  the  peotineus  muscle  and  bounds  the  femoral  ring.  Above  the  inguinal  ligament  near 
its  medial  extremity  lies  the  external  opening  of  the  inguinal  canal,  the  subcutaneous  (external) 


430  THE  MUSCULATURE 

inguinal  ring  [annulus  inguinalis  subcutaneus].  This  opening  is  formed  by  the  diverging  of 
the  lower  medial  fibres  which  compose  the  aponeuroiss  of  the  external  oblique  muscle.  The  supe- 
rior fibres  form  the  upper  boundary,  superior  crus,  of  the  ring  and  pass  to  the  front  of  the  sym- 
physis pubis.  The  inferior  fibres  form  the  inferior  boundary,  inferior  crus,  of  the  ring  and  pass 
to  the  pubic  tubercle  (spine).  Between  these  two  fibre  bands  intercrural  (intercolumnar) 
fibres  arch  about  the  lateral  boundary  of  the  ring  and  serve  to  strengthen  the  anterior  and  infe- 
rior walls  of  the  inguinal  canal.  Some  of  the  fibres  of  the  superior  crus,  intermingled  with  other 
fibres  cross  to  the  opposite  side  of  the  body  and  are  inserted  into  the  tubercle  (spine)  and 
crest  of  the  pubis  and  into  the  superior  crus  of  the  opposite  side.  The  structure  thus  formed 
is  called  the  reflected  inguinal  ligament  (CoUes's  ligament,  or  triangular  fascia). 

Inguinal  canal  [canalis  inguinalis]. — This  term  is  apphed  to  the  slit  in  the  lower  margin  of 
the  abdominal  wall  through  which,  in  the  male,  the  spermatic  cord  passes,  and  in  the  female,  the 
hgamentum  teres.  It  is  not  a  true  canal.  The  inner  end  begins  at  the  (internal)  abdominal 
ring  [annulus  inguinalis  abdominahs].  This  is  situated  just  above  and  slightly  medial  to  the 
middle  of  the  inguinal  (Poupart's)  ligament.  Below  the  hgament  in  this  region  lies  the  femoral 
canal  through  which  the  femoral  vessels  pass  into  the  thigh.  The  (internal)  abdominal  ring 
is  covered  by  the  peritoneum  and  the  transversalis  fascia.  The  latter  here  sends  a  shallow 
funnel-like  extension  outward  to  be  attached  to  the  spermatic  cord.  The  base  of  this  funnel- 
Hke  depression  toward  the  inguinal  (Poupart's)  ligament  is  formed  by  a  thickened  band  of 
tissue,  the  tractus  ilio-pubicus.  Medially  and  laterally  the  bundles  of  fibrous  tissue  which  con- 
stitute this  tract  spread  out  fan-like,  medially  over  the  sheath  of  the  rectus  and  toward 
the  pubis,  lateraUy  over  the  transversus  muscle  and  toward  the  crest  of  the  ilium.  The  trans- 
verse abdominal  muscle  arises  from  the  inguinal  ligament  nearly  as  far  as  the  lateral  margin  of 
the  abdominal  ring.  The  fibre-bundles  of  this  portion  of  the  muscle  course  ventralward  above 
the  base  of  the  funnel  mentioned  above  and  are  inserted  by  tendons  forming  a  more  or  less 
complete  aponeurosis,  the  "conjoined  tendon"  [falx  inguinalis],  common  to  it  and  the  internal 
obhque  into  the  ventral  sheath  of  the  rectus  abdominis  muscle,  into  the  tubercle,  crest  and 
pecten  of  the  pubis  and  sometimes  into  the  pectineal  fascia  or  the  lacunar  (Gimbernat's) 
ligament.  Tendinous  bands  from  the  transversahs  muscle  curve  downward  medial  to  the 
(internal)  abdominal  ring  and  help  to  strengthen  the  transversalis  fascia  here.  These  bands 
constitute  the  interfoveolar  ligament  [ligamentum  interfoveolare,  Hesselbachij.  The  fibrous 
bands  constituting  this  ligament  are  attached  to  the  lacunar  ligament  and  the  pectineal  fascia. 

From  the  internal  ring  the  spermatic  cord  (or  in  the  female  the  hgamentum  teres)  passes 
downward  and  forward  in  a  space  (inguinal  canal)  about  4  cm.  long  and  then  through  the  sub- 
cutaneous (external  abdominal)  ring  which  has  been  described  in  connection  with  the  inguinal 
ligament.  The  ventral  wall  of  the  inguinal  canal  is  composed  of  the  aponeurosis  of  the  external 
oblique,  the  intercrural  fibres,  and  the  cremaster  muscle.  Laterally  it  is  also  covered  by  the 
caudal  portions  of  the  internal  oblique  and  transversus  muscles.  The  caudal  wall  or  floor  of 
the  space  is  formed  chiefly  by  the  lacunar  (Gimbernat's)  hgament  and  laterally  also  by  the  iho- 
pubic  tract.  Cranialward  the  lateral  part  of  the  space  is  covered  by  the  transversus  and  internal 
oblique  muscles,  the  medial  part  by  the  cremaster  muscle.  The  dorsal  (internal)  wall  is  formed 
mainly  by  the  transversalis  fascia.  IMedially  the  lacunar  (Gimbernat's)  ligament  and  the  con- 
joined tendon  (falx  inguinahs),  when  this  is  well  developed,  help  to  form  the  dorsal  wall. 
Lateral  to  these  structures  the  dorsal  wall  is  thinner  but  may  be  strengthened  by  a  well  developed 
ilio-pubic  tract.  Near  the  (internal)  abdominal  ring  it  is  strengthened  by  the  interfoveolar 
ligament,  and  sometimes  by  muscle  slips  (interfoveolar  muscle). 

Abdominal  fossae  in  the  inguinal  region. — The  hernias  so  frequent  in  this  region  make  a 
special  study  of  the  inner  surface  of  the  abdominal  wall  of  considerable  practical  importance. 
Medial  to  the  abdominal  (internal)  inguinal  ring  the  inferior  internal  epigastric  vessels  give  rise 
to  a  shght  fold  (plica  epigasirica)  which  slants  medialward  and  upward  toward  the  rectus  muscle. 
From  the  lateral  margin  of  the  tendon  of  insertion  of  the  rectus  muscle  upward  toward  the 
umbilicus  over  the  obliterated  umbilical  artery  there  extends  a  better  marked  fold,  the  plica 
umbilicalis  lateralis.  Lateral  to  the  plica  epigastrica  lies  the  fovea  inguinalis  lateralis,  with  the 
internal  inguinal  ring.  Between  the  phca  epigastrica  and  the  phca  umbihcalis  laterahs  lies  the 
fovea  inguinalis  medialis.  In  the  latter  region  the  fascia  transversalis  which  here  forms  the 
inner  wall  of  the  inguinal  canal  is  strengthened  by  two  longitudinal  fibrous  bands  belonging  to 
the  aponeurosis  of  the  transversalis  muscle  and  described  above,  the  hgament  interfoveolare 
at  the  medial  side  of  the  (internal)  abdominal  ring,  and  the  falx  inguinalis  (conjoined  tendon) 
lateral  to  the  rectus  muscle.  These  bands  vary  in  width.  When  they  are  narrow  the  part  of 
the  internal  wall  of  the  inguinal  canal  covered  merely  by  the  thin  transversalis  fascia  and  the 
peritoneum  is  relatively  large  and,  since  this  region  hes  behind  the  subcutaneous  (external 
abdominal)  ring,  opportunity  is  offered  for  direct  inguinal  hernia. 

JVIUSCLES 
A.  Ventral  Division 

The  rectus  abdominis  (fig.  388). — Origin — Ventral  surface  of  the  fifth  to  seventh  costal 
cartilages,  the  xiphoid  process,  and  the  costo-xiphoid  ligament. 

-    Insertion. — The  upper  border  of  the  body  of  the  pubis  and  the  ventral  surface  of  the 
symphysis. 

Structure. — The  muscle  is  long,  flat,  and  somewhat  triangular  in  form.  Cranialward  it  is 
broad  and  thin;  caudalward  it  becomes  thicker  as  it  converges  toward  the  insertion.  The 
fibre-bundles  of  the  muscle  have  a  longitudinal  course.  It  is  crossed  by  several  incomplete, 
zigzag,  transverse  tendinous  bands,  inscriptiones  tendinese,  better  developed  on  the  ventral 
than  on  the  dorsal  surface  of  the  muscle  and  intimately  united  to  the  ventral  sheath  of  the  rectus. 
One  of  these,  corresponding  segmentally  to  the  tenth  rib,  is  usually  situated  opposite  the  um- 


SERRATUS  MUSCLES  431 

bilicus.  Another,  corresponding  to  the  ninth  rib,  is  situated  midway  between  this  and  the  lower 
margin  of  the  thoracic  wall,  and  one  corresponding  to  the  seventh  rib  is  found  at  the  level  of  the 
xiphoid  process.  Between  this  and  the  one  corresponding  to  the  ninth  rib  an  additional  inscrip- 
tion is  frequently  found.  Below  the  umbilicus  an  inscription  corresponding  with  the  eleventh 
rib  is  often  found  (30  per  cent.).  In  these  inscriptions  many  of  the  fibre-bundles  have  their 
origin  and  insertion.  The  thoracic  attachments  take  place  by  means  of  band-like  fascicuU 
which  extend  upward  from  the  highest  inscription,  the  fibre-bundles  of  these  fasciculi  being 
inserted  by  short  tendinous  bands.  The  pubic  attachment  of  the  muscle  takes  place  by  a* 
short,  thick  tendon,  usually  divisible  into  two  portions,  of  which  the  broader,  lateral  portion  is 
inserted  into  a  rough  area  extending  from  the  pubic  tubercle  (spine)  to  the  symphysis,  while  the 
more  slender  medial  portion  is  attached  to  the  fascise  in  front  of  the  symphysis  pubis,  where  its 
fibres  interdigitate  with  those  of  the  opposite  side.  In  addition  to  the  attachments  mentioned, 
some  of  the  fibre-bundles  are  attached  to  the  sheath  of  the  rectus  and  many,  after  interdigitating, 
terminate  in  the  intramuscular  framework. 

Nerve-supply. — The  anterior  branches  of  the  six  or  seven  lowermost  intercostal  nerves 
enter  the  deep  surface  of  the  muscle  neai^its  lateral  edge.  The  cutaneous  branches  pass 
obliquely  through  its  substance,  while  the  muscular  branches  give  rise  to  an  intramuscular 
plexus.  As  a  rule,  the  chief  ventral  branch  of  the  tenth  thoracic  nerve  enters  the  substance 
of  the  muscle  slightly  below  the  umbilical  transverse  inscription.  The  branches  of  the  eleventh 
and  twelfth  nerves  enter  at  a  lower  level.  The  main  branch  of  the  ninth  nerve  enters  slightly 
below  the  preumbilical  inscription;  the  eighth  nerve,  between  this  and  the  lower  margin  of 
the  thorax.  Either  the  sixth  or  seventh  nerve  may  supply  the  fascicuh  of  origin.  In  addition 
to  the  main  branches  other  smaller  branches  of  the  nerves  of  the  abdominal  wall  are  also  usually 
distributed  to  the  muscle.  Each  segment,  either  directly  or  through  intramuscular  plexuses, 
has  a  supply  from  more  than  one  spinal  nerve. 

Action. — To  depress  the  thorax  and  flex  the  spinal  column.  When  the  thorax  is  fixed  the 
rectus  serves  to  flex  the  pelvis  upon  the  trunk. 

Relations. — It  lies  between  the  transversalis  fascia  and  the  tela  subcutanea  and  is  ensheathed 
by  the  aponeuroses  of  the  lateral  abdominal  muscles,  as  above  described.  The  epigastric  artery 
runs  on  its  deep  surface. 

Variations. — The  rectus  muscle  varies  in  the  number  of  its  tendinous  inscriptions  and  in 
the  extent  of  its  thoracic  attachment.  It  may  extend  farther  than  usual  on  the  thorax.  Fre- 
quently aponeurotic  slips  or  slips  of  muscle  on  the  upper  part  of  the  thorax  indicate  a  more 
primitive  condition  in  which  the  muscle  extended  to  the  neck.  Absence  of  a  part  or  the  whole 
of  the  muscle  has  been  noted.  The  muscles  of  the  two  sides  may  be  separated  by  a  considerable 
interval  in  the  neighbourhood  of  the  umbiUcus.  The  muscle  is  relatively  thicker  in  men  than 
in  women.. 

The  pyramidalis  (fig.  388). — Origin. — Upper  border  of  the  body  of  the  pubis. 

Structure  and  insertion. — The  fibre-bundles  extend  toward  and  are  inserted  into  the  hnea 
alba  for  about  a  third  of  the  distance  to  the  umbilicus,  and  give  rise  to  a  flat,  triangular  belly. 

Nerve-supply. — Usually  through  a  branch  of  the  twelfth  thoracic,  which  may  extend  into 
the  muscle  through  the  rectus  abdominis.  Not  infrequently  a  special  branch  extends  into  the 
muscle  from  the  iho-hypogastric  or  ilio-inguinal  or,  rarely,  from  the  genito-femoral. 

Action. — -To  draw  down  the  hnea  alba  in  the  median  line. 

Relations. — It  hes  between  two  lamina;  of  the  anterior  layer  of  the   sheath  of  the  rectus. 

Variations. — It  is  missing  in  about  16  per  cent,  of  instances  (Le  Double).  Dwight  has 
found  it  absent  in  81  out  of  450  males  and  in  60  out  of  223  females  dissected  at  the  Harvard 
Medical  School.  It  may  extend  upward  to  the  umbilicus  or  be  but  very  shghtly  developed. 
It  may  be  double.  In  many  of  the  mammals  it  is  missing.  It  is  well  developed  in  the  marsu- 
pials and  monotremes. 

B.  Lateral  Division 

1.  Serratus  Group  (fig.  380) 

The  serratus  posterior  superior. — Origin. — By  a  broad,  thin  aponeurosis  from  the  liga- 
mentum  nuchfe  and  the  spines  of  the  last  one  or  two  cervical  and  the  first  two  or  three  thoracic 
vertebrae.  • 

Structure  and  insertion. — The  fibre-bundles  take  a  nearly  parallel  course  downward  and 
lateralward  and  give  rise  to  a  flat  belly  which  ends  by  four  fasciculi  on  the  upper  margin  of 
the  second  to  the  fifth  ribs,  lateral  to  the  ilio-costahs. 

Neroe-supply. — Through  branches  from  the  first  four  intercostal  nerves.  These  nerves 
give  rise  to  a  plexus  which  passes  across  the  deep  surface  of  the  muscle  in  the  middle  third  be- 
tween the  tendons  of  origin  and  insertion. 

Action.— To  elevate  the  ribs  to  which  the  muscle  is  attached,  and  through  them  to  enlarge 
the  thorax. 

Relations. — It  lies  upon  the  wall  of  the  thorax  and  the  intrinsic  dorsal  musculature  and 
beneath  the  levator  scapulae,  rhomboids,  serratus  anterior,  and  trapezius.  Its  fascicuh  extend 
on  the  ribs  to  those  of  the  serratus  anterior  (magnus). 

The  serratus  posterior  inferior. — Origin. — Through  an  aponeurosis,  fused  medially  and 
inferiorly  with  the  lumbo-dorsal  fascia,  from  the  last  two  or  three  thoracic  and  first  two  or  three 
lumbar  spines. 

Structure  and  insertion. — From  the  aponeurosis  arise  four  flat  bands  which  are  successively 
attached  to  the  inferior  margins  of  the  last  four  ribs,  lateral  to  the  iho-costalis. 

Nerve-supply. — From  the  ninth  to  eleventh  intercostal  nerves  arise  branches  which  form  a 
plexus  that  extends  across  the  deep  surface  of  the  muscle  in  the  middle  third  between  the  ten- 
dons of  origin  and  insertion. 

Action. — To  depress  and  draw  outward  the  four  lower  ribs  and  through  them  to  enlai'ge 


432  THE  MUSCULATURE 

the  thorax.  Together  with  the  serratus  posterior  superior  and  the  connecting  aponeurotic 
fascia  it  aids  in  keeping  the  intrinsic  dorsal  muscles  in  place. 

Relations. — It  lies  upon  the  intrinsic  dorsal  musculature,  the  lower  dorsal  part  of  the 
thorax,  and  the  lumbo-dorsal  fascia,  and  beneath  the  latissimus  dorsi,  the  trapezius,  and  their 
aponeuroses. 

Variations. — The  fasciculi  of  both  muscles  vary  in  number  and  may  be  replaced  by  ap- 
oneurotic slips.  Aberrant  muscle  fasciculi,  supracostales  posteriores,  may  be  found  in  the  fascia 
which  connects  the  two  muscles.  In  several  of  the  lower  mammals  the  two  muscles  are  nor- 
mally continuous. 

2.  External  Oblique  Group 

The  intercostales  extern!  (fig.  385). — These  muscles  extend  in  the  intercostal  spaces  from 
the  tubercles  of  the  ribs  to  the  costal  cartilagess.  The  intermediate  muscles  do  not,  however, 
often  quite  reach  the  cartilages.  The  first  intercostal  muscle  may  extend  to  the  sternum.  The 
others  are  continued  through  the  intercostal  region  by  thin  aponeuroses,  the  external  inter- 
costal ligaments,  the  fibres  of  which  have  a  direction  corresponding  to  that  of  the  muscle  fibre- 
bundles.  Dorsally  the  muscles  are  fused  with  the  levatores,  and  ventrally  the  lower  seven 
muscles  are  more  or  less  fused  with  the  corresponding  fasciculi  of  the  external  oblique. 

Origin. — From  the  lower  margin  of  each  rib  external  to  the  costal  sulcus. 

Structure  and  insertion. — The  fibre-bundles  take  a  parallel  course  obliquely  forward  and 
downward  to  the  upper  margin  of  the  next  rib.  The  proximal  fibre-bundles  are  more  obhque 
than  the  distal,  and  the  muscles  are  best  developed  in  the  dorsal  part  of  the  intercostal  spaces. 

Nerve-supply. — By  several  branches  from  the  corresponding  intercostal  nerves. 

Action. — To  elevate  the  ribs  and  enlarge  the  thorax. 

Relations. — They  are  covered  externally  by  the  pectoral  muscles,  the  serratus  anterior, 
and  serrati  posteriores,  the  levatores  costarum,  the  sacro-spinalis  (erector  spinae),  and  the 
external  obhque  muscles.  Internally  they  are  separated  by  a  slight  amount  of  loose  tissue  from 
the  internal  intercostals,  the  membranes  which  continue  these  muscles  medially,  and  from  the 
subcostal  muscles. 

Variations. — When  the  twelfth''rib  is  very  small  or  is  lacking,  the  eleventh  intercostal 
muscle  may  be  missing.  When  there  is  a  supernumerary  cervical  or  thirteenth  thoracic  rib, 
there  may  be  an  extra  external  intercostal  muscle.  Next  to  the  first  intercostal,  the  fourth 
most  frequently  reaches  the  sternum. 

The  levatores  costarum  (fig.  383). — These  consist  of  a  series  of  flat,  triangular  muscles, 
each  of  which  arises  from  the  tip  and  inferior  margin  of  a  transverse  process  and  extends  later- 
ally with  diverging  fibre-bundles  to  be  inserted  into  the  dorsal  surface  of  the  rib  below,  from 
the  tubercle  to  the  angle.  The  fb'st  extends  from  the  transverse  process  of  the  seventh  cervical 
vertebra  to  the  first  rib.  They  increase  successively  in  size  from  this  to  the  last,  which  is  at- 
tached to  the  twelfth  rib.  Those  arising  from  the  transverse  processes  of  the  eighth  to  the  elev- 
enth thoracic  vertebrse  send  their  more  medial  fibre-bundles  across  the  rib  below  to  join  the 
lateral  margin  of  the  succeeding  muscle  (levatores  longi).  The  levatores  costarum  are  closely 
united  to  the  external  intercostals  and  are  innervated  by  the  'ntercostal  nerves  which  pass  for- 
ward in  the  corresponding  intercostal  spaces.  The  first  muscle  is  innervated  by  the  eighth 
cervical  nerve. 

Action. — To  bend  laterally  and  extend  the  spinal  column. 

Relations. — They  are  covered  dorsally  by  the  longissimus  dorsi  and  the  ilio-costahs. 

Variations. — The  first  levator  may  be  continued  into  the  scalenus  posterior.  When  greatly 
developed,  the  series  of  levators  forms  a  serrate  muscle. 

■  The  obliquus  abdominis  externus  (fig.  387). — Origin. — By  eight  fleshy  digitations  from 
the  external  surface  of  the  lower  eight  ribs  immediately  lateral  to  where  they  join  the  cartilages. 
The  fu'st  five  slips  interdigitate  with  the  serratus  anterior  (magnus),  the  last  three  with  the 
latissimus  dorsi. 

Insertion. — (1)  By  a  strong  aponeurosis  which  extends  over  the  rectus  to  the  hnea  alba, 
where  the  more  superficial  fibres  interdigitate  across  the  median  line,  and  to  the  inguinal  (Pou- 
part's)  ligament;  and  (2)  directly  into  the  outer  hp  of  the  crest  of  the  ilium.  The  aponeurosis 
over  the  rectus  is  usually  partly  fused  with  the  aponeurosis  of  the  internal  obhque. 

Structure. — The  fibre-bundles  which  compose  the  flat  fasciculi  of  origin  diverge  shghtly 
as  they  pass  forward  and  downward,  and  by  fusion  of  their  edges  give  rise  to  a  flat  sheet  of 
muscle.  The  fasciculus  taking  origin  from  the  fifth  rib  passes  nearly  directly  ventrally,  but 
the  succeeding  fasciculi  incline  somewhat  downward,  those  from  the  seventh  to  the  ninth  ribs 
showing  the  greatest  downward  inclination.  The  lower  margin  of  the  fasciculus  which  arises  from 
the  seventh  rib  terminates  opposite  the  umbilicus,  that  from  the  ninth  rib  extends  toward  the 
anterior  superior  spine  of  the  ilium,  and  those  from  the  last  three  ribs  descend  to  the  ihac  crest. 
The  first  two  fasciculi  extend  over  the  lateral  margin  of  the  rectus,  the  next  two  to  its  lateral 
edge.  The  fourth  and  fifth  usually  terminate  along  a  line  extending  ventrally  from  the  anterior 
superior  iliac  spine  toward  the  rectus. 

Nerve-supply. — The  external  oblique  is  supplied  by  rami  from  the  lateral  branches  of  the 
lower  seven  intercostal  nerves  and  usually  from  the  ilio-hypogastric  as  well.  The  rami  of  the 
first  two  or  three  nerves  usually  extend  on  the  external  surface  of  the  muscle,  while  the  others 
extend  on  the  deep  surface  of  the  muscle  as  the  cutaneous  branches  are  passing  through  it  to- 
ward the  skin.  The  nerves  of  the  external  oblique  take  a  more  transverse  direction  than  the 
fasciculi  of  the  muscle.  Thus  the  branch  from  the  tenth  intercostal  nerve  extends  toward  the 
umbilicus  and  that  of  the  twelfth  toward  a  point  midway  between  the  umbilicus  and  the  sym- 
physis pubis.  The  nerves  have  a  segmental  distribution  corresponding  with  the  primitive 
segmental  condition  of  the  muscle. 

Action. — (1)  To  compress  the  abdomen;  (2)  to  depress  the  thorax;  (3)  to  flex  the  spinal 


INTERNAL  OBLIQUE  GROUP 


433 


column;  and  (4)  to  rotate  the  column  toward  the  opposite  side.  With  the  thorax  fixed  it 
serves  to  flex  and  rotate  the  pelvis. 

Relations. — It  lies  superficial  to  the  lower  ventro-lateral  margin  of  the  thorax  and  the 
internal  oblique  muscle.  It  is  partly  covered  by  the  latissimus  dorsi  muscle  behind.  Other- 
wise it  is  subcutaneous.  • 

Variations. — It  may  have  a  more  or  less  extensive  origin  from  the  ribs.  Broad  fasciculi 
not  infrequently  are  separated  by  loose  tissue  from  the  main  belly  of  the  muscle  either  on  its 
deep  or  superficial  surface.  Occasionally  tendinous  inscriptions  are  found.  These  transverse 
inscriptions  are  constant  in  many  of  the  smaller  mammals.  The  supracostalis  anterior  is  a 
rare  fasciculus  sometimes  found  on  the  upper  portion  of  the  thoracic  wall.  It  is  usually  suppUed 
by  branches  of  the  upper  thoracic  nerves  and  seems  to  be  a  continuation  upward  of  the  external 
oblique  muscle.  In  some  prosimians  the  external  oblique  extends  normally  to  the  first  or  sec- 
ond rib. 

3.  Internal  Oblique  Group 

The  intercostales  interni  (figs.  385,  386,  388). — These  extend  in  the  intercostal  spaces  from 
the  angles  of  the  ribs  to  the  sternal  ends  of  the  spaces.  The  upper  and  lower  muscles  are  usually 
continued  dorsally  slightly  beyond  the  angles  of  the  ribs,  while  the  intermediate  muscles  fre- 
quently do  not  quite  reach  them.     Dorso-medially  the  internal  intercostals  are  continued  in 


Aponeurosis 
of  obliquus 
externus         Ky'l 
Spermatic  cord~^ 

Origin  of 
cremaster 
Ligament' 

reflexum 

Origi 
cremaster 


xum  h 
n  of  4 


Inguinal  ligament 


the  form  of  thin  fascial  sheets  across  the  inner  surface  of  the  external  intercostals  and  become 
fused  with  the  subcostals. 

Origin. — Near  the  angles  of  the  ribs  they  arise  from  the  internal  lip  of  the  costal  sulcus. 
More  ventraUy  they  arise  mainly  from  the  external  lip  of  the  sulcus,  but  also  in  part  from  the 
internal  lip. 

Structure  and  insertion. — The  fibre-bundles  take  a  parallel  course  downward  and  dorsal- 
ward  to  the  upper  margin  of  the  rib  below.  They  are  less  obliquely  placed  than  those  of  the 
external  intercostals.  The  muscles  are  thicker  in  front  and  grow  thinner  dorsaUy.  They  con- 
tain less  fibrous  tissue  than  the  e.xternal  intercostals. 

Nerve-supply. — From  numerous  branches  of  the  corresponding  intercostal  nerves. 

Action. — Investigators  disagree  as  to  the  functions.  It  is  probable  that  the  portions  of 
the  muscles  between  the  ribs  serve  to  contract,  those  between  the  costal  cartilages  to  expand, 
the  thorax. 

Relations. — Between  the  ribs  they  are  covered  by  the  external  intercostal  muscles  and  be- 
tween the  costal  cartilages  by  the  external  intercostal  ligaments.  Between  the  internal  and 
external  muscles  there  is  some  loose  areolar  tissue.  Proximally,  for  a  short  distance,  the  inter- 
costal nerve  in  each  interspace  runs  between  the  external  and  internal  intercostal  muscles,  but 
more  distally  it  runs  first  in  the  substance  of  and  then  on  the  internal  surface  of  the  internal 
intercostal.  Eisler  distinguishes  that  portion  of  the  internal  intercostal  muscle  which  lies 
external  to  the  nerve  as  the  intercostalis  intermedius,  that  which  lies  internal  as  the  true  in- 
ternal intercostal.  The  terminal  branches  of  the  fii'st  six  nerves,  however,  pass  through  the 
muscle  on  their  way  to  the  skin,  while  the  last  six  pass  beneath  the  inferior  margin  of  the  thorax. 
Internal  to  the  internal  intercostal  muscles  lie  the  transversus  (triangularis  sterni)  and  sub- 


434  THE  MUSCULATURE 

costal  muscles,  the  diaphragm,  and  the  pleural  membranes.  The  more  distal  internal  inter- 
costal muscles  are  continuous  with  the  internal  obUque  and  the  subcostal  muscles. 

Variations. — The  tenth  and  eleventh  internal  intercostal  muscles  normally  are  but  sHghtly 
developed  and  often  may  be  wanting.  The  internal  intercostals  of  the  first  three  spaces  may 
extend  to  the  vertebrae. 

The  subcostales  (fig.  385). — These  muscles  are  due  to  an  extension  over  two  or  more  inter- 
costal spaces  of  those  fibre-bundles  of  the  internal  intercostal  muscles  which  lie  in  the  proximal 
part  of  the  interspaces.  They  arise  near  the  angles  of  the  ribs,  and  are  usually  well  developed 
only  in  the  lower  part  of  the  thorax.  The  component  fibre-bundles  keep  the  general  direction 
of  the  internal  intercostals,  but  they  converge  toward  the  tendons  of  insertion,  which  are  at- 
tached in  each  case  to  the  second  or  third  rib  below,  between  the  angle  and  the  neck. 

Nerve-supply. — The  main  nerve  of  supply  for  each  muscle  comes  from  the  intercostal  nerve 
running  below  the  rib  from  which  the  muscle  takes  origin. 

Action. — To  depress  the  ribs  and  contract  the  thorax. 

Relations. — They  lie  on  the  inner  side  of  the  internal  and  external  intercostals  and  the  ribs, 
and  are  covered  by  the  pleural  membranes. 

Variations. — They  vary  much  in  development.  Next  to  the  lower  fasciculi,  the  fasciculi 
in  the  cranial  part  of  the  thorax  are  those  usually  best  developed. 

The  obliquus  abdominis  internus  (fig.  388). — Origin. — From  the  lumbo-dorsal  fascia  the 
intermediate  lip  of  the  ventral  two-thirds  of  the  iliac  crest,  and  the  lateral  half  of  the  inguinal 


Structure  and  insertion. — From  the  origin  the  fibre-bundles  radiate  forward  in  a  flat  sheet. 
The  most  dorsal  extend  to  the  lower  three  ribs,  where  they  become  continuous  with  the  internal 
intercostals.  The  rest  extend  toward  the  lateral  margin  of  the  rectus,  the  upper  ones  toward 
the  xiphoid  process,  the  intermediate  toward  the  umbilicus,  the  lower  ones  somewhat  obhquely 
downward  across  the  lower  part  of  the  abdomen.  The  fibre-bundles  which  extend  toward  the 
rectus  terminate  in  an  aponeurosis  which  in  its  upper  two-thirds  divides  into  two  layers,  one 
of  which  passes  in  front  of  and  the  other  behind  the  rectus  muscle  to  the  linea  alba.  In  the 
lower  third  the  aponeurosis  passes  as  a  single  membrane  in  front  of  the  rectus.  In  the  neigh- 
bourhood of  the  subcutaneous  inguinal  (external  abdominal)  ring  the  muscle  is  continued  into 
the  cremaster.  Medial  to  the  ring  some  fasciouh  are  attached  to  the  tubercle  of  the  pubis 
and  to  the  symphysis. 

Nerve-supply. — From  branches  of  the  last  three  intercostal  and  the  ilio-hypogastric,  ilio- 
inguinal and  genito-femoral  (?)  nerves  as  these  pass  between  this  muscle  and  the  transversus. 

Action. — To  depress  the  thorax,  flex  the  vertebral  column,  and  bend  and  rotate  it  toward 
the  side  on  which  the  muscle  is  placed.  When  the  thora.x  is  fixed,  the  muscle  serves  to  flex  and 
rotate  the  pelvis. 

Relations. — It  hes  between  the  external  obhque  and  the  transversus.  The  trigonum  lum- 
bale  (triangle  of  Petit)  is  an  area,  variable  in  size,  between  the  posterior  margin  of  the  external 
obUque,  the  lateral  margin  of  the  latissimus  dorsi,  and  the  crest  of  the  ihum.  In  this  area  the 
internal  obhque  is  subcutaneous. 

Variations. — The  attachments  and  the  extent  of  development  of  the  fleshy  part  of  the 
muscle  vary  considerably.  Occasionally  tendinous  inscriptions  are  found  in  the  muscle  which 
indicate  a  primitive  segmental  condition. 

The  cremaster  (fig.  389). — The  cremaster  muscle  is  found  well  developed  only  in  the  male. 
It  represents  an  extension  of  the  lower  border  of  the  internal  obhque  muscle  and  possibly  also 
of  the  transverse  over  the  testis  and  spermatic  cord. 

Origin. — (1)  Lateral,  thick  and  fleshy,  from  about  the  middle  of  the  upper  border  of  the 
inguinal  hgament,  and  (2)  medial,  thin  and  tendinous,  from  the  sheath  of  the  rectus  muscle  and 
the  tubercle  (spine)  of  the  pubis. 

Structure. — The  lateral  head  is  apphed  to  the  lateral  side,  the  medial  head  to  the  medial  side, 
of  the  spermatic  cord.  Both  pass  with  this  through  the  subcutaneous  (external  abdominal) 
ring  of  the  inguinal  canal  and  become  spread  in  loops  over  the  testis.  Ensheathing  the  muscle 
and  between  the  somewhat  scattered  fibre-bundles  which  compose  it,  there  extends  a  thin, 
membranous  layer  of  connective  tissue,  the  cremasteric  (Cowper's)  fascia. 

Nerve-supply. — The  genital  nerve  (external  spermatic),  usually  joined  by  a  ramus  from  the 
inguinal  nerve,  gives  rise  to  branches  which  spread  over  the  muscle. 

Action. — To  lift  the  testis  toward  the  subcutaneous  inguinal  (external  abdominal)  ring. 

Relations. — It  is  covered  by  the  aponeurosis  of  the  external  oblique,  the  cremasteric  fascia, 
the  dartos,  and  the  skin.     It  covers  the  spermatic  cord  and  the  testis. 

Variations. — In  the  female  the  muscle  is  represented  by  a  few  fasciculi  on  the  round  hga- 
ment. It  may  arise  whoUy  from  the  transversalis  fascia  or  be  somewhat  fused  with  the  trans- 
versus muscle.     The  latter  condition  is  espeoiaUy  frequent  in  muscular  individuals. 

4.  Transversus  Group 

The  transversus  thoracis  (triangularis  sterni)  (fig.  386). — Origin. — By  aponeurotic  bands 
from  the  dorsal  surface  of  the  lower  half  of  the  body  of  the  sternum  and  the  xiphoid  process. 

Structure  and  insertion. — The  muscle  is  composed  of  several  flat,  thin  fasciculi,  partly 
fibrous,  more  or  less  isolated,  which  are  inserted  by  aponeurotic  bands  into  the  dorsal  surface 
of  the  cartilages  of  the  second  or  third  to  the  sixth  ribs,  and  occasionally  also  into  the  tips  of 
the  bony  portions  of  the  ribs.  The  lower  fasciculus  is  closely  related  to  the  cranial  margin  of 
the  transversus  abdominis. 

Nerve-supply. — By  rami  from  the  ventral  portions  of  the  second  to  the  sixth  intercostal 
nerves.  These  nerves  give  rise  to  a  longitudinal  plexus  across  the  deep  surface  of  the  muscle 
near  the  middle  of  the  constituent  fasciculi. 


TRANSVERSUS  ABDOMINIS 


435 


Action. — To  depress  the  ribs  in  expiration. 

Relations. — The  sternum,  the  costal  cartilages,  internal  intercostal  muscles,  and  the  internal 
mammary  vessels  lie  in  front  and  the  pleura  and  pericardium  behind  the  muscle. 

Variations. — It  is  an  exceedingly  variable  muscle,  both  in  the  extent  of  its  attachments 
and  in  the  development  of  the  individual  fasciouh.  The  fasciculi  vary  in  number  from  one  to 
six.  With  this  muscle  Eisler  would  class  the  subcostal  muscles  and  those  portions  of  the  internal 
intercostal  muscles  which  lie  internal  to  the  intercostal  nerves. 

The  transversus  abdominis  (figs.  386,  390). — Origin. — Directly  from — (1)  the  inner  side 
of  the  cartilages  of  the  lower  six  ribs  by  dentations  which  interdigitate  with  the  attachments  of 
the  diaphragm;  (2)  the  internal  lip  of  the  iliac  crest  and  lateral  half  of  the  inguinal  ligament; 
and  (3)  through  an  aponeurosis  from  the  lumbo-dorsal  fascia. 

Structure  and  insertion. — The  fibre-bundles  give  rise  to  a  broad,  thin  belly  and  take  a  nearly 
transverse  course  across  the  inner  side  of  the  abdominal  wall.  The  most  distal  fibres,  however, 
are  inclined  obliquely  toward  the  pubis.  The  fleshy  portion  of  the  muscle  terminates  in  a 
strong  aponeurosis  along  a  curved  line,  which  extends  above  well  under  the  rectus  and  emerges 


Fig.  390.- 


-Teansversus  Abdominis  and  Sheath  op  Rectus. 


External  intercostal — fe 


Internal  intercostal 


Transversus  abdomims 


Rectus  abdominis  — %C" 

Iliacus 

Transversalis  fascia 

Falx  inguinalis 

Inguinal  ligament 

Lacunar  ligament 


Serratus  anterior 


lateral  to  the  rectus  opposite  the  umbilicus,  whence  it  extends  toward  the  middle  of  the  inguinal 
ligament.  In  the  upper  two-thirds  of  the  abdomen  the  aponeurosis  extends  behind  the  rectus 
to  the  linea  alba  and  fuses  with  the  inner  lamina  of  that  of  the  internal  oblique.  In  the  lower 
third  of  the  abdomen  it  extends  in  front  of  the  rectus  to  the  hnea  alba,  and  is  here  also  fused 
with  the  aponeurosis  of  the  internal  obhque.  Some  of  the  fibres  are  continued  into  the  aponeu- 
rosis of  the  muscle  of  the  opposite  side.  The  lower  attachment  of  the  muscle  is  somewhat 
more  complex.  The  fibre-bundles  here  bend  around  the  spermatic  cord,  on  the  medial  side  of 
which  they  are  spread  out  to  be  attached  to  the  lacunar  (Gimbernat's)  ligament  and  pectineal 
fascia,  the  pubis,  and  the  sheath  of  the  rectus.  The  attachment  to  the  lacunar  ligament  and 
pectineal  fascia  takes  place  by  means  of  an  aponeurotic  band,  the  more  lateral  fibres  of  which 
are  dense  and  curve  below  the  spermatic  cord  to  the  lacunar  hgament  and  the  pectineal  fascia 
below  this.  This  band  is  caOed  the  interfoveolar  ligament.  It  is  composed  partly  of  bundles  of 
fibres  prolonged  from  the  aponeurosis  of  the  opposite  transversus,  and  bounds  the  abdominal  ring 
medially  and  below.  Medially  the  transversus  is  united  to  the  upper  part  of  the  os  pubis,  and 
to  the  sheath  of  the  rectus  by  an  aponeurotic  band,  the  falx  inguinalis  (conjoined  tendon). 
Between  the  interfoveolar  ligament  and  the  falx  inguinalis  the  transversalis  fascia  forms  the 
posterior  wall  of  the  inguinal  canal.  In  this  area  a  detached  band  of  muscle-fibres  is  sometimes 
found.     This  is  called  the  musciilus  interfoveolaris. 

Nerve-supply. — The  transversus  is  supphed  with  nerves  by  the  last  five  or  six  thoracic  and 


436 


THE  MUSCULATURE 


the  ilio-hypogastric,  inguinal  and  genito-femoral  nerves  as  these  course  forward  between  this 
muscle  and  the  internal  oblique. 

Action. — The  chief  function  is  to  compress  the  abdominal  viscera.  Through  the  portions 
extending  between  the  lower  margins  of  the  thorax  on  each  side  it  serves  to  contract  the  thorax 
and  so  may  aid  in  expiration. 

Relations. — It  lies  on  the  inner  side  of  the  lower  ribs,  the  internal  oblique  and  rectus  muscles, 
and  is  covered  on  the  deep  surface  by  the  transversalis  fascia. 

Variations. — It  is  very  rarely  absent.  It  shows  considerable  variation  in  the  extent  of  its 
development.  The  pubo-peritonealis  is  a  similar  muscle  which  may  pass  from  the  pubic  crest 
to  the  transversus  near  the  umbilicus.  The  pubo-transversalis  is  a  small  muscle  which  may 
extend  from  the  superior  ramus  of  the  pubis  to  the  transversalis  fascia  near  the  abdominal 
inguinal  ring.  The  tensor  laminae  posterioris  vaginae  musculi  recti  abdominis,  essentially  like 
the  preceding,  may  e.xtend  from  the  inguinal  ligament  to  the  rectus  sheath  on  the  deep  surface 
of  the  rectus  muscle  near  the  umbilicus.  The  tensor  laminae  posterioris  vaginae  musculi 
recti  et  fasciae  transversalis  abdominis  likewise  extends  from  the  transversalis  fascia  near  the 
abdominal  inguinal  ring  to  the  fold  of  Douglas. 

C.  LuMBAE  Muscle 

The  quadratus  lumborum  (fig.  406). — Origin. — From — (1)  the  internallip  of  the  iliac  crest 
near  the  junction  of  the  middle  and  dorsal  thirds,  and  the  iliolumbar  ligament;  (2)  the  transverse 
processes  of  the  three  or  four  lower  lumbar  vertebra;  and  (3)  the  lumbo-dorsal  fascia. 


Fig.  391. — Diaphkagm. 


(£  sophagus 

Left  division 

of  tendon 
Costal  origin 


Left  crus 

Lateral  lumbo- 
costal arch 
Transverse  pro- 
cess of  second 
lumbar  vertebra 
Fourth  lumbar 
vertebra 


Structure  and  insertion. — From  the  origins  there  arises  a  complex  quadrangular  muscle 
belly  from  which  spring  the  fasiouli  of  termination.  These  extend  to — (1)  the  transverse 
processes  of  the  upper  three  or  four  lumbar  vertebrae;  (2)  to  the  fibre-bands  which  extend  out 
laterally  in  the  lumbar  fascia  from  the  transverse  processes;  and  (3)  to  the  medial  part  of  the 
lower  border  of  the  twelfth  rib. 

Nerve-supply. — Through  du-eot  branches  from  the  first  three  or  four  lumbar  nerves. 

Action. — It  serves  primarily  to  produce  lateral  flexion  of  the  spinal  column.  When  both 
muscles  act  together,  they  produce  extension  of  the  column.  The  muscle  also  serves  to  depress 
and  fix  the  twelfth  rib. 

Relations. — It  rests  posteriorly  on  the  lumbo-dorsal  fascia  and  the  transverse  processes  of 
the  lumbar  vertebrae.  Its  medial  edge  is  partly  covered  by  the  psoas.  In  front  of  it  also  he 
the  kidney,  the  intestines,  and  the  lumbar  arteries  and  nerves.  It  is  ensheathed  by  membranes 
continued  over  each  surface  from  the  transversalis  fascia.  Of  these,  the  anterior  is  the  better 
marked  and  is  called  the  lumbar  fascia. 

Variations. — There  is  much  individual  variation  in  the  internal  structure  of  the  muscle  and 
in  its  attachments.     Its  insertion  may  e.xtend  to  the  eleventh  rib. 

The  psoas  major  and  minor  belong  essentially  to  the^musculature  of  the  lower  limb  and  are 
there  described  (p.  455). 

D.  The  Diaphragm 

The  diaphragm  (figs.  386,  391). — This  dome-shaped  musculo-membranous  sheet  has,  when 
seen  from  above,  something  of  the  outline  of  a  kidney.  It  consists  of  a  pair  of  muscles  which 
arise  one  on  each  side  from  the  thoracic  wall  and  are  inserted  into  a  central  tendon.     Lateral 


THE  DIAPHRAGM 


437 


to  the  tendon  the  diaphragm  projects  higher  into  the  thoracic  cavity  than  in  the  central  area. 
On  the  right,  in  moderate  expiration,  it  extends  in  adults  to  the  height  of  the  medial  extremity 
of  the  fifth  rib,  and  on  the  left  to  the  fifth  interspace. 

Origin. — On  each  side  from — (1)  the  lower  border' and  back  of  the  .xiphoid  process  and  the 
adjacent  aponeurosis  of  the  transversus  abdominis  or  from  the  tendinous  arch  extending  from 
the  tip  of  the  xiphoid  process  to  the  cartilages  of  the  fifth  and  sixth  ribs,  {sternal  portion) ;  (2) 
the  lower  border  and  inner  surfaces  of  the  cartilages  of  the  seventh  and  eighth  ribs,  the  cartilages 
and  osseous  extremity  of  the  ninth  rib  and  the  osseous  extremities  of  the  last  three  ribs  [costal 
portion);  and  (3)  from  the  lumbar  vertebrae  (lumbar  portion).  The  lumbar  portion  is  divided 
somewhat  irregularly  into  three  crura,  between  which  pass  blood-vessels  and  nerves. 

The  lateral  crus  arises  from  the  lateral  surface  of  the  bodies  of  the  first  two  lumbar  vertebrae 
and  from  fibrous  thickenings  of  the  fascia  over  the  psoas  and  quadratus  lumborum  muscles. 
Of  these,  one,  the  medial  lumbo-costal  arch  (internal  arcuate  Ugament),  extends  from  the  body 
of  the  second  lumbar  vertebra  to  the  transverse  process  of  the  same  vertebra;  the  other,  the 
lateral  lumbo-costal  arch  (external  arcuate  hgament),  extends  from  the  tip  of  the  transverse 


Fig.  392.- 


-The  Perineal  Muscles  in  the  Female. 
Pubis 


Vagina 


Superficial  layer  of 
urogenital  trigone 


Sphincter  ani  exter- 
nus  profundus 

Pubo-coccygeus 


Ilio-coccygeus 

Sphincter  ani  exter- 

nus  subcutaneus 

Sphincter  ani  exter- 

nus  superficialis 


Coccyx 


process  of  the  second  lumbar  vertebra  to  the  twelfth  rib.  The  lateral  crus  is  only  inconstantly 
attached  to  this.  The  intermediate  crus  arises  from  the  ventro-lateral  surface  of  the  body  of 
the  second  lumbar  vertebra  from  the  sides  of  the  bodies  of  the  first  two  lumbar  vertebrae  and 
from  the  intervening  discs.  The  medial  crus  arises  from  the  front  of  the  bodies  of  the  third  and 
the  fourth  lumbar  vertebrae.  On  the  left  side  it  usually  extends  only  to  the  third  vertebra, 
and  it  does  not  always  extend  to  the  fourth  on  the  right.  The  extremity  and  medial  margin 
of  this  crus  are  tendinous,  the  lateral  portion  fleshy.  On  the  second,  third,  and  fourth,  and  the 
lower  part  of  the  first  lumbar  vertebrae  the  medial  crus  of  each  side  is  separated  from  its  fellow 
by  the  hiatus  aorticus  (for  the  aorta  and  thoracic  duct).  Over  the  first  lumbar  vertebra  they 
are  fused  by  a  process  which  extends  from  the  right  crus  into  the  lower  ventral  sm'face  of  the 
left.  Above  here  the  right  crus  may  be  divided  into  two  parts,  one  of  which,  fused  with  the 
left  crus,  passes  on  the  left  of  the  hiatus  oesophageus,  while  the  other  passes  on  the  right.  Some- 
times the  hiatus  oesophageus  lies  between  the  right  and  left  crura.  Frequently  the  left  crus  gives 
off  a  slip  which  passes  to  the  ventral  surface  of  the  right  below  the  hiatus. 

The  costal  portion  arises  by  a  series  of  dentations  which  do  not  correspond  perfectly  in 
number  with  the  ribs.  Some  costal  cartilages  have  two  dentations  attached  to  them.  It 
interdigitates  with  the  transversus  abdominis  but  in  part  arises  from  tendinous  arches  which 
bridge  the  origin  of  the  transversus  in  the  last  three  interspaces. 

Slructiire  and  insertion. — The  central  tendon  has  somewhat  the  shape  of  a  trifoliate  leaf, 


438 


THE  MUSCULATURE 


the  place  of  the  stem  being  taken  by  the  region  occupied  by  the  vertebral  column,  one  leaflet 
lying  on  each  side  of  this  and  one  in  front.  The  ventral  part  is  usually  placed  somewhat  to  the 
left  and  is  more  or  less  completely  fused  with  the  left  leaflet.  Between  the  ventral  and  the  right 
leaflets  there  is  a  large  opening  through  which  passes  the  inferior  vena  cava,  the  foramen  venae 
cavae.     The  leaflets  are  fused  in  front  and  behind  this. 

Fig.  393.— Ventr.4l  Coccygeal  Muscles  (After  Eisler.)— 1.  M.  sacrococcygeus  anterior. 
2.  M.  coccygeus.  3.  M.  piriformis.  4.  M.  obturator  internus'  5.  Fascia  iUaca,  above  the  ilio- 
psoas. 6.  Fibrocartilago  intervertebralis  lumbosacralis.  7.  Ventral  trunk  of  first  sacral  nerve. 
8.  Sacral  plexus. 


The  fleshy  portion  of  the  muscle  is  composed  of  fibre-bundles  which  pass  at  first  nearly 
vertically  upward  and  then  arch  over  to  be  attached  to  the  margins  of  the  central  tendon.  The 
sternal  portion  of  the  muscle  is  the  shortest.  It  is  often  separated  from  the  costal  portion  by  a 
small  space  through  which  the  superior  epigastric  vessels  pass. 

Nerve-supply. — From  the  phrenic  nerves,  one  of  which  arises  on  each  side  from  the  third  to 
the  fifth  cervical  nerves.  Each  nerve  penetrates  the  diaphragm  lateral  to  the  central  tendon 
and  breaks  up  into  an  extensive  plexus  on  the  inferior  surface  of  the  muscle.  Some  of  the  lower 
intercostal  nerves  also  contribute  to  the  sensory  innervation  of  the  margin  of  the  muscle  and  pos- 
sibly also  slightly  to  the  motor  innervation.  The  sympathetic  nerves  furnish  fibres  for  the 
blood-vessels. 

Action. — To  enlarge  the  thoracic  cavity  and  thus  cause  inspiration.  According  to  R.  Fick, 
however,  the  diaphragm  plays  a  less  important  part  in  inspiration  than  is  usuaUv  assumed  for 
it.  The  middle  part  of  the  central  tendon  is  united  to  the  pericardium  and  through  this  to 
the  cervical  fascia,  and  is,  therefore,  not  very  movable.  In  the  contraction  of  the  muscle  it  is 
the  dorsal  and  lateral  portions  which  in  the  main  are  flattened.  The  diaphragm  aids  in  defeca- 
tion, parturition  and  vomiting,  by  the  pressure  it  exerts  on  the  abdominal  viscera.  It  also 
acts  as  a  constrictor  of  the  oesophagus. 

Relations. — Above  lie  the  heart  and  the  lungs;  below  he  the  Uver,  stomach,  duodenum, 
pancreas,  spleen,  kidneys,  and  suprarenal  bodies. 

Variations. — The  sternal  portion  of  the  muscle  is  frequently  absent.  Infrequently  the 
diaphragm  is  incompletely  developed  dorsally  on  the  left  side.  This  condition  is  rarer  on  the 
right  side.  The  extent  of  the  various  insertions  of  the  diaphragm  shows  considerable  individual 
differences.  The  vertebral  portion  of  the  muscle  may  be  slightly  fused  with  the  psoas  or  with  the 
quadi-atus  lumborum.     Some  fusion  of  the  ventral  portion  of  the  muscle  with  the  transversus 


MUSCLES  OF  PELVIC  OUTLET 


439 


thoracis  has  also  been  seen.    Small  fasciculi  may  pass  to  neighbouring  structures :  the  oesophagus, 
stomach,  liver,  mesentery,  etc.     Muscle  fasciculi  are  frequently  found  in  the  central  tendon. 

V.    MUSCULATURE  OF  THE  PELVIC  OUTLET 

In  order  to  understand  the  musculature  of  the  pelvic  outlet  it  is  necessary  first 
to  consider  briefly  the  structure  of  the  pelvis.  It  is  bounded  laterally  and  in  front 
by  the  ilium  below  the  terminal  (ilio-pectineal)  line,  the  ischium  and  the  pubis,  and 
by  the  obturator  membrane  and  the  sacro-spinous  (small  sciatic),  sacro-tuberous 
(great  sciatic)  and  the  interpubic  hgaments.  The  pubis,  ischium  and  the  obturator 
membrane  are  covered  by  the  obturator  internus  muscle  (figs.  392,  401)  which  here 
takes  its  origin  and  which  converges  toward  and  passes  through  the  lesser  sciatic 
notch  on  its  way  to  its  insertion  on  the  great  trochanter  of  the  femur.  The  piri- 
formis muscle  (figs.  393,  396),  which  arises  from  the  sides  of  the  pelvic  surface  of 


Fig.  394. — The  Male  Perineum.     (Modiiied  from  Hirschfeld  and  LeveiUd.) 
Bulbo-cavernosus 

Superficial  layer  of  uro-genital  trigone 
Iscliio-cavernosus 

Muscles  of  thigh 


Posterior  femoral  cutaneous  ner 

Perineal  nerve 
Inferior  haemorrhoidal  nerve 
Cutaneous  branch  of  fourth  sacral 


Gluteus  maximus 
Tuberosity  of  ischium 
Sacro-tube 
Levator  ani 
Superficial  transversus  perinei 
Sphincter  ani 


the  sacrum,  from  the  posterior  border  of  the  great  sciatic  notch  and  the  neighbour- 
ing part  of  the  sacro-tuberous  (great  sciatic)  ligament  nearly  fills  up  the  great 
sciatic  notch  on  its  way  to  its  insertion  on  the  great  trochanter.  The  walls  of  the 
pelvis  are  thus  padded  by  muscles  which  belong  to  the  limb.  The  muscles  are 
covered  by  fascia  best  developed  over  the  obturator  internus  muscle  as  the 
obturator  fascia.  The  gluteus  maximus  muscle  (figs.  392,  394,  400,  401),  which 
arises  from  the  back  of  the  ilium,  the  sacrum,  and  the  coccj^x,  and  is  inserted  into 
the  femur  and  the  fascia  of  the  thigh  overlaps  to  some  extent  the  sacro-tuberous 
ligament,  and  in  the  standing  position  the  tuberosity  of  the  ischium  so  that  its 
lower  margin  forms  an  accessory  boundar}'  to  the  pelvic  outlet. 


440 


THE  MUSCULATURE 


The  outlet  of  the  pelvis  thus  bounded  by  bone,  ligaments  and  by  muscles  be- 
longing to  the  lower  extremity  presents  two  triangles  (figs.  392, 394),  an  anterior  or 
urogenital  triangle,  with  the  base  between  the  two  ischial  tuberosities  and  the  apex 
below  the  symphysis  pubis,  and  a  posterior  or  rectal  with  the  base  between  the 
ischial  tuberosities  and  the  apex  at  the  coccyx  which  projects  into  it  here.  The 
outlet  is  closed  by  a  special  musculature  divisible  into  three  groups  of  muscles  and 
fascia;  those  of  the  pelvic  diaphragm  and  anus,  those  of  the  urogenital  diaphragm, 
and  those  of  the  external  genitalia. 

The  pelvic  diaphragm  [diaphragma  pelvis]  extends  from  the  upper  part  of  the 
pelvic  surface  of  the  pubis  and  ischium  to  the  rectum  which  passes  through  it  to  be 
surrounded  by  the  external  sphincter.  The  urogenital  trigone  or  urogenital  dia- 
phragm [diaphragma  urogenitale]  lies  between  the  ischio-pubic  rami  superficial  to 
the  pelvic  diaphragm  and  surrounds  the  membranous  urethra  and  in  the  female 
also  the  vagina.     The  external  genital  muscles  lie  superficial  to  the  trigone. 

The  muscles  of  the  pelvic  diaphragm  are  two  in  number  on  each  side,  the  coccy- 
geus,  and  the  levator  ani  (figs.  395,  396,  397).     The  coccygeus  arises  from  the 

;     Fig.  395. — The  Pelvic  Diaphragm  in  the  Female,  fkom  below  and  behind. 


ischial  spine  and  is  inserted  into  the  lateral  margin  of  the  lower  sacral  and  the 
upper  coccygeal  vertebrae.  It  is  closely  applied  to  the  pelvic  surface  of  the  sacro- 
spinous  (small  sciatic)  ligament.  In  so  far  as  it  is  active  it  flexes  and  abducts  the 
coccyx. 

The  levator  ani  arises  (figs.  395,  396,  397)  from  the  inner  side  of  the  pubis, 
along  a  line  extending  laterally  from  the  inferior  margin  of  the  symphysis  to  the 
obturator  canal,  and  from  the  obturator  fascia  along  a  line,  the  arcus  tendineus, 
extending  from  the  pubis  to  the  spine  of  the  ischium.  The  levator  ani  is  inserted 
into  the  median  raphe  back  of  the  anus,  the  ano-coccygeal  raphe,  into  the  tip  and 
sides  of  the  coccyx  and  into  an  aponeurosis,  which  is  attached  to  the  anterior 
sacrococcygeal  ligament.  It  is  divisible  into  three  portions,  a  pubo-coccygeal,  an 
iliococcygeal,  and  a  pubo-rectal.  The  levator  ani  muscles  of  the  two  sides  are  sepa- 
rated by  a  slit  which  extends  from  the  rectum  to  the  symphysis  pubis  and  in  which 
in  the  male  lie  the  lower  part  of  the  prostate,  and  the  membranous  urethra  (fig. 
396),  and  in  the  female  the  vagina  and  urethra  (fig.  395).  Back  of  the  rectum 
some  of  the  fibre-bundles  from  the  muscles  of  the  two  sides  interdigitate,  while 


ISCHIO-RECTAL  FOSSA 


441 


others  terminate  in  the  ano-coccygeal  raphe.  A  few  fibre-bundles  also  inter- 
digitate  across  the  median  line,  in  front  of  the  rectum  (pubo-coccygeal,  fig.  395) 
and  some  are  inserted  into  the  walls  of  the  rectum.  The  levator  ani  and  coccygeal 
muscles  of  the  two  sides  form  a  funnel-shaped  muscular  support  for  the  pelvic 
viscera  (fig.  399).  When  the  abdomino-thoracic  diaphragm  contracts,  as  during 
inspiration,  the  pressure  on  the  viscera  is  transmitted  to  the  pelvic  diaphragm 
which  resists  the  pressure  and  elevates  the  viscera  when  the  abdomino-thoracic 
diaphragm  relaxes.  The  levator  ani  muscle  also  constricts  the  rectum  and  pulls 
it  forward  and  in  the  female  constricts  the  vagina  from  side  to  side. 

As  it  passes  through  the  pelvic  diaphragm,  the  rectum  for  about  two  and  a 
half  centimetres  is  surrounded  by  a  special  external  sphincter  muscle  ffigs. 
393,  394,  397),  divisible  into  three  concentric  layers  as  described  below.  This 
muscle,   especially  differentiated  from  the  primitive  sphincter  of  the  cloaca, 


Fig.  396. — ^Lateral  View  of  Muscles  of  the  Flooh  op  the  Pelvis. 
(A  portion  of  the  ischial  and  pubic  bones  sawn  away.) 


Aperture  for  superior 
gluteal  vessels  and 
nerve 

Sacrum 


Aperture  for  inferior 
gluteal  and  pudic 
vessels  and  nerve 
and  sciatic  nerve 

Ischial  spine 

Coccyx 

Coccygeus 

Hindmost  fibres  of 

levator  ani 


White  line  farcus 
tendineus")  of 
levator  ani 


serves  to  close  the  rectum.  It  is  supplemented  by  a  sphincter  of  smooth  muscle 
which  lies  immediately  beneath  the  mucous  membrane  of  the  anus.  It  is  attached 
behind  to  the  coccygeus,  and  in  front  to  the  central  tendon  of  the  perineum 
described  below. 

The  lateral  origin  of  the  levator  ani,  as  above  described  and  as  shown  in  figs. 
396  and  399,  is  considerably  above  the  osseous  and  muscular  margin  of  the  pelvic 
outlet.  The  muscles  of  each  side  converge  toward  the  post-anal  region  so  that  a 
space  is  left  between  the  lateral  wall  of  the  pelvis,  and  the  levator  ani  and  external 
sphincter  (fig.  399).  This  space,  the  ischio-rectal  fossa,  is  filled  with  fat  (fig.  400, 
401,  402).  It  is  deepened  laterally  by  the  lower  margin  of  the  gluteus  maxim  us 
muscle  (fig.  400).     In  the  fascial  canal  (Alcock's  canal)  in  the  lateral  wall  of  the 


442 


THE  MUSCULATURE 


fossa  run  the  internal  pudic  vessels  and  nerves  (fig.  401).  Above  the  pelvic 
diaphragm  in  the  median  part  of  the  pelvic  cavity  are  found  the  bladder,  the 
ampulla  of  the  rectum,  and  the  prostate  gland  (in  the  male)  or  the  vagina  and 
uterus  (in  the  female).  Laterally  on  each  side  there  is  a  subperitoneal  space,  filled 
with  connective  tissue  and  containing  blood-vessels  and  nerves  (fig.  402) .  Fasciae 
invest  each  surface  of  the  pelvic  diaphragm  {diaphragmatic  fascia)  and  extend 
about  the  viscera  [endo-pelvic  fascia) . 


Fig.  397.- 


-SAGITT.4.L  Section  op  the  Pelvis  to  Show  the  Pelvic  Diaphragm  and  External 
Sphincter  Ani. 


Tendinous    aponeu- 
of  pubo- 
coccygeus 
Raphe  formed  by 
iho-coccygei 
Sphincter  recti 

Sphincter  ani  ext.  profundus 


Sphincter  ani  externus  subcutaneus 


The  muscular  apparatus  of  the  anterior  or  urogenital  triangle  of  the  pelvic 
outlet  is  much  more  complicated  than  that  of  the  posterior  or  rectal  triangle  just 
described.  We  have  seen  that  between  the  levator  ani  muscles  of  each  side  in 
front  of  the  rectum  there  is  a  slit  which  extends  to  the  symphysis  pubis  and  that 
through  it,  the  lower  part  of  the  prostate  and  the  urethra  extend  in  the  male,  the 
urethra  and  the  vagina  in  the  female.  Between  the  ischio-pubic  rami  there  is 
stretched  a  triangular  muscular  and  fibrous  membrane,  which  likewise  surrounds 
these  urogenital  ducts  and  which  serves  to  strengthen  the  pelvic  wall  in  this 
region.  This  structure  is  known  as  the  urogenital  trigone  (figs.  398,  400,  403). 
The  musculature  within  it,  called  by  Holl  the  accessorj^  or  urogenital  diaphragm, 
includes  two  muscles  (fig.  398),  the  sphincter  urogenitalis  (urethraj)  and  the  deep 
transverse  perineal  muscle.  The  sphincter  embraces  the  urethra  and  associated 
structures.  The  component  fibre-bundles  arise  chiefly  from  the  fibrous  tissue  in 
the  angle  beneath  the  symphysis  pubis,  but  partly  also  from  the  descending  pubic 
rami.  They  pass  analward  and  medialward  on  each  side  of  the  urethra  and  then 
partly  interdigitate  across  the  median  line,  partly  terminate  in  a  median  raphe. 
Some  fibre-bundles  embrace  in  the  male  the  lower  part  of  the  prostate  and 
Cowper's  gland.  In  the  female  the  fibre-bundles  of  the  sphincter  partly  terminate 
in  the  wall  of  the  vagina.  Some  of  them  are  continued  downward  on  each  side  of 
the  vagina  and  interdigitate  with  fibre-bundles  from  the  deep  transverse  perineal 
muscle.  The  deep  transverse  perineal  muscle  (fig.  398)  arises  on  each  side  from 
the  ischio-pubic  ramus.     It  constitutes  a  flat  band  of  muscle,  the  fibre-bundles  of 


B  ULBO-CA  VERNOS  US 


443 


which  in  part  interdigitate  across  the  median  line,  and  in  part  are  inserted  into  a 
median  raphe. 

The  musculature  of  the  urogenital  diaphragm  is  enclosed  between  two  well 
marked fasciallayers  (fig.  400,  403),  the  deep  (superior)  and  superficial  (inferior) 
layers  of  the  urogenital  trigone  (triangular  ligament).  The  anterior  margins  of 
the  two  fascial  layers  are  fused  to  form  the  transverse  ligament  of  the  pelvis 
which  extends  between  the  inferior  pubic  rami,  beneath  the  dorsal  nerves  and 
veins  of  the  penis  (clitoris).  At  the  anal  margin  of  the  musculature  these  two 
layers  are  also  fused  with  one  another.  The  deep  layer  of  the  urogenital  trigone 
forms  the  floor  of  the  anterior  recess  of  the  ischio-rectal  fossa  (fig.  400). 

Superficial  to  the  urogenital  trigone  lie  the  external  genitalia  (figs.  392,  394). 
Voluntary  muscle  is  here  found  in  connection  with  the  crura  of  the  penis  (clitoris) 
and  the  bulb  of  the  penis  (vestibule).  Although  the  musculature  in  the  two  sexes 
is  fundamentally  similar,  neverthel^gs,  owing  to  the  differences  in  the  structure  of 
the  genitalia  in  the  two  sexes,  it  is  convenient  to  take  up  first  the  external  genital 
musculature  in  the  male  and  then  that  in  the  female. 


Fig.  398. — Muscles  between  the  Two  Layers  of  the  Urogenital  Trigone  (Male.) 


Corpus  cavernosum 


Dorsal  vein  of 
penis 

Transverse    liga- 
ment of  pelvis 

Urethra,  sur- 
rounded by 
sphincter 


Transversus    urethra 


Transversus  perinei  profundus 


In  the  male  the  crus  penis,  the  posterior  part  of  the  corpus  cavernosum,  is 
relatively  large.  It  lies  in  the  groove  between  the  ischio-pubic  ramus  and  the 
urogenital  trigone  (fig.  398),  to  the  former  of  which  it  is  firmly  united.  It  is 
enwrapped  on  its  free  medial  surface  by  the  ischio-cavernosus  muscle  (erector 
penis)  (figs.  398,  402).  The  fibre-bundles  of  this  muscle  arise  from  the  ischial 
tuberosity  and  from  the  ischio-pubic  ramus  on  each  side  of  the  attachment  of  the 
crus.  It  is  inserted  into  the  medial  and  ventral  surfaces  of  the  crus  near  the 
attachment  of  the  suspensory  ligament.  Some  of  the  fibre-bundles  may  fre- 
quently be  traced  to  the  dorsal  surface  of  the  root  of  the  penis  (levator  penis 
muscle). 

The  corpus  spongiosum  [corpus  cavernosum  urethrae]  terminates  posteriorly 
in  the  bulb  which  lies  on  the  urogenital  trigone  between  the  two  crura  (figs.  394, 
402).  It  is  united  to  the  superficial  layer  of  the  trigone  (fig.  402).  It  is  envel- 
oped by  the  bulbo-cavernosus  muscle,  composed  of  right  and  left  halves  united  by 
a  median  raphe  on  the  superficial  surface  of  the  bulb  (fig.  394).  Each  half  con- 
sists of  several  superimposed  laj^ers  of  fibre-bundles  described  below.  The 
component  fibre-bundles  arise  from  the  superficial  layer  of  the  urogenital  trigone, 
from  fibrous  tissue  on  the  dorsum  of  the  bulb  in  the  angle  between  the  two  crura, 
from  the  lateral  surface  of  the  corpus  cavernosum  penis  in  front  of  the  ischio- 
cavernosus  and  from  the  dorsal  surface  of  the  penis.  It  is  inserted  into  a  tendi- 
nous structure  situated  in  front  of  the  anus,  the  central  tendon  of  the  perineum, 


444 


THE  MUSCULATURE 


and  into  the  median  raphe  on  the  free  surface  of  the  bulb.  By  its  contraction  the 
bulbo-cavernosus  forces  semen  or  urine  from  the  bulbous  part  of  the  urethra. 

The  superficial  transverse  muscle  of  the  perineum  (figs.  392,  394)  arises  on 
each  side  from  the  ascending  ramus  of  the  ischium  and  is  inserted  into  the  central 
tendon  of  the  perineum.  It  is  frequently  weakly  developed.  It  acts  with  the 
deep  transverse  perineal  muscle  in  fixing  the  perineum  and  thus  offering  support 
for  the  action  of  otiier  muscles. 

In  the  female  (fig.  392)  the  ischio-cavernosus  does  not  differ  markedly  from  that 
in  the  male  although  usually  it  is  smaller.  The  superficial  transverse  muscles  are, 
on  the  other  hand,  usually  relatively  better  developed.  The  central  tendon  of 
the  perineum  is  likewise  usually  better  developed  in  women  and  is  more  elastic,  a 
characteristic  of  value  in  childbirth. 

The  chief  difference  in  the  musculature  in  the  two  sexes  is  found  in  the 
bulbo-cavernosus  (fig.  392) .  This,  in  the  female,  arises  from  the  back  of  the  clitoris, 
the  corpus  cavernosum  and  the  trigone.  It  covers  the  outer  side  of  the  bulb  of 
the  vestibule  and  the  gland  of  Bartholin.  It  is  inserted  into  the  central  tendon  of 
the  perineum.     The  chief  function  of  the  pair  of  muscles  is  to  constrict  the  vagina. 

The  external  genital  muscles  are  covered  by  a  deep  layer  of  the  tela  subcutanea, 

Fig.  399. — Diagram   to   show  the   Fascia   op  the   Pelvis   in   Section.     (After  HoU.) 


Endo- 
pelvic 
fascia 


Ischio-rectal  fossa 


Colles'  fascia,  which  is  firmly  fused  with  the  two  layers  of  the  urogenital  trigone 
at  the  anal  margin  of  the  latter. 


MORPHOLOGICAL  REMARKS 

While  the  shoulder-girdle  and  the  muscles  which  extend  from  this  and  from  the  trunk  to  the 
upper  extremity  are  superficially  placed  with  respect  to  the  trunk,  and  do  not  interrupt  the  trunk 
musculature  the  reverse  is  true  of  the  hip-girdle  and  the  musculature  of  the  lower  extremity. 
The  hip-girdle  is  firmly  united  to  the  spinal  column  at  the  sacrum.  The  muscles  which  arise 
from  the  trunk  and  are  attached  to  the  lower  limbs  are  few  in  number  compared  with  those  of 
the  upper  extremity  and,  unhke  the  latter,  are  deeply  placed.  Thus  the  psoas  major  muscle 
(fig.  406)  arises  on  each  side  of  the  lumbar  region  of  the  spinal  column  at  the  back  of  the  ab- 
dominal cavity  and  is  inserted  into  the  femur  and  the  piriformis  (fig.  406)  arises  from  the  front 
of  the  sacrum  at  the  back  of  the  pelvic  cavity  and  is  inserted  into  the  great  trochanter  of  the 
femur.  The  skeleton  and  musculature  of  the  lower  extremity,  furthermore,  markedly  inter- 
fere with  the  continuity  of  the  trunk  musculature  which  in  the  lower  vertebrates  and  in  the  hu- 
man embryo  may  be  followed  continuously  to  the  caudal  end.  The  interruption  is  much  less 
marked  behind  than  in  front.  The  intrinsic  dorsal  spinal  musculature  extends  well  down  over 
the  back  of  the  sacrum,  but  on  the  back  of  the  lower  end  of  the  sacrum  and  on  the  back  of  the 
coccyx  there  is  found  merely  the  inconstant  sacro-coccygeus  posterior.  Of  the  ventro-lateral 
musculature  the  musculature  of  the  abdominal  wall,  as  is  indicated  by  its  innervation,  is  de- 
rived from  the  lower  thoracic  and  the  first  one  or  two  lumbar  myotomes;  thequadratus  lum- 
borum,  at  the  back  of  the  abdominal  cavity  (fig.  406),  from  the  first  three  or  four  lumbar  myo- 


FASCIA 


445 


tomes.  Beyond  here  there  is  an  interruption  until  we  come  to  the  musculature  of  the  pelvic 
outlet  which,  in  part,  may  be  looked  vipon  as  modified  trunk  musculature  belonging  to  the  last 
three  sacral  myotomes.  The  intervening  region  is  "cut  out"  for  the  reception  of  the  base  of  the 
lower  extremity. 

It  is  of  interest  to  note  that  more  and  more  of  the  ventro-lateral  wall  of  the  trunk  is  "cut 
out"  as  the  mid-ventral  line  is  approached.  Thus  while  the  quadratus  lumborum  behind 
represents  spinal  segments  as  far  caudal  as  the  third  or  fourth  lumbar,  the  rectus  abdominis 
in  front  represents  segments  merely  as  far  caudal  as  the  twelfth  thoracic.     Similarly  while  the 


Fig.  400. — Sagittal  Section"  through  the  Urogenital  Trigone  and  Ischio-rbctal  Fossa 
TO  the  Left  op  the  Middle  Line.     (Diagrammatic.) 


Obturator  fascia 


Subperitoneal  tissue 
Fascia  transversalis 


f  Os  pubis 
Obturator  internus 


Fascia  lata  of  thigh 
Muscles  of  thigh 


Nerves 

Sacro-tuberous  ligament 

Sacro-spinous  ligament 


Gluteus 

Levator  ani  with  its  fascia 

Ischio-rectal  fossa 

Deep   perineal   interspace 

with  sphincter    urethree, 

etc. 
Superficial  fascia  of 

urogenital  trigone 


coccygeus  at  the  back  part  of  the  pelvic  outlet  represents  the  third  and  fourth  sacral  segments, 
the  levator  ani  at  the  front  represents  chiefly  the  fourth. 

The  musculature  which  in  the  tailed  mammals  is  used  to  move  the  tail  as  well  as  to  wall  off 
the  pelvic  cavity  and  close  rectal  and  urogenital  openings,  in  man  is  modified  whoUy  for  the  latter 
functions.     It  constitutes  the  pelvic  diaphragm. 

The  musculature  of  the  urogenital  diaphragm  of  the  external  genitalia  and  anus  in  man  is 
differentiated  from  the  primitive  sphincter  of  the  cloaca. 


FASCI.E 

The  tela  subcutanea  in  the  male  perineal  region  contains  many  bundles  of  smooth  muscle 
fibres  continuous  with  and  similar  to  the  dartos  of  the  scrotum  (corrugator  cutis  ani).  At  the 
sides  where  it  passes  over  the  lower  margin  of  the  gluteus  maximus  it  contains  a  large  amount  of 
fat,  but  in  the  dorsal  region  over  the  coccyx  and  sacrum,  as  in  the  mid-perineal  region,  the  fat 
is  limited  in  amount.  In  the  labia  majora  of  the  female  perineum  there  is  much  fat  in  the  tela 
subcutanea. 

The  ischio-rectal  fossa  (figs.  401,  402)  is  bounded  laterally  by  the  obturator  internus  muscle 
and  fascia,  the  tuberosity  of  the  ischium  and  the  ischio-pubic  ramus,  medially  by  the  levator  ani 
and  coccygeus  muscles  and  fasoise,  ventraUy  by  the  dorsal  aspect  of  the  urogenital  trigone  and 
dorsaUy  by  the  gluteus  maximus  muscle.  An  anterior  recess  extends  forward  well  toward  the 
body  of  the  pubis  between  the  levator  ani,  the  ischio-pubic  ramus  and  the  urogenital  trigone. 
A  posterior  recess  may  likewise  be  traced  backward  covered  by  the  lower  edge  of  the  gluteus 
maximus  (figs.  400,  401).  The  fossa  is  filled  with  loose  fatty  tissue  continuous  with  that  of 
the  tela  subcutanea.  Through  it  pass  the  hemorrhoidal,  and  long  and  short  perineal  branches 
of  the  pudic  artery  and  nerve.  The  main  trunks  of  these  vessels  and  nerves  lie  in  a  special 
fascial  compartment  (Alcook's  canal)  in  the  lateral  wall  (fig.  401). 

The  external  genital  organs  are  covered  by  a  special  deep  layer  of  the  tela  subcutanea,  the 
superficial  perineal  (CoUes')  fascia  (fig.  402).  This  is  attached  on  each  side  to  the  lower  margin 
of  the  ischio-pubic  ramus  and  to  the  ischial  tuberosity.  At  the  posterior  margin  of  the  superficial 
transverse  perineal  muscle  it  fuses  with  the  two  fascial  layers  of  the  trigone.  It  is  adherent  to 
the  central  tendon  of  the  perineum  and  to  the  raphe  of  the  bulb.  Anteriorly  it  is  continuous 
with  the  deep  layer  of  the  tela  subcutanea  covering  the  scrotum,  the  penis,  and  the  lower  part 
of  the  abdominal  wall.  In  rupture  of  the  urethra  urine  is  prevented,  by  the  attachments  of  the 
tela,  from  getting  further  back  than  the  posterior  edge  of  the  trigone,  but  anteriorly  it  may 
extend  to  the  surface  of  the  abdomen.  Here  it  may  extend  upward  for  a  considerable  distance, 
but  it  is  kept  from  the  thighs  by  the  attachment  of  the  deep  laj'er  of  the  tela  subcutanea  (Scarpa's 
fascia)  to  the  inguinal  ligament.     Beneath  the  superficial  perineal  fascia  are  found  the  crura  of 


446 


THE  MUSCULATURE 


the  penis  and  their  muscles,  the  bulb  of  the  corpus  spongiosum  and  its  muscles,  the  superficial 
transverse  perinei  muscles,  and  the  perineal  vessels  and  nerves  (fig.  402). 

Muscle  fasGise. — The  muscles  of  the  urogenital  diaphragm,  the  urogenital  (urethral)  sphincter 
and  the  transversus  perinei  profundus,  are  contained  between  two  fascia  layers  which  constitute 
the  superficial  (inferior)  and  deep  (superior)  layers  of  the  urogenital  trigone  (the  superficial 
or  inferior  and  the  deep  or  superior  layers  of  the  triangular  ligament). 

Fig.  401. — Section  showing  the  Ischio-bectal  Fossa  in  its  Relations  to  the  Pelvic 

Viscera. 


Symphysis  pubis 


Pubo-prostatic  ligaments 

Prostatic  plexus 

Prostate 

Capsule  of  prostate  formed  by 

endopelvic  fascia 
Fat 


Rectum  invested  by  er.do- 
pelvic  fascia 


'ith  its  fasciae 
Obturator  internu 

Internal  pudic  vessels  and        /%//    ^r* 

nervesin  obturator  fascia  ^"g,/  'g'*"4^o,''i^bft 

Tuber  ischii /  ^^"«*-\  \1 

Ischio-rectal  fossa  with  its  an- I  '•UOr*^  r  vt 

teriorand  posterior  recesses 


The  superficial  (inferior)  layer  (figs.  392,  394,  400,  402,  403)  which  lies  between  the  external 
genitalia  and  the  urogenital  diaphi-agm,  is  composed  of  strong  bands  of  fibrous  tissue  which  extend 
■  transversely  across  the  subpubic  arch  and  are  attached  to  a  ridge  on  the  ischio-pubic  rami.  It 
is  separated  from  the  arcuate  (subpubic)  ligament  by  a  mass  of  fibrous  tissue  through  which  the 
dorsal  veins  and  nerves  of  the  penis  (clitoris)  run,  and  in  which  there  is  a  venous  plexus. 


Fig.  402. — Vertical  Frontal  Section  of  the  Pelvis,  showing  Fascia. 
(Modified  from  Braune.) 


Tendinous  arch 


Subperitoneal  fat 

Obturator  internus 
/  ij'fjf  ^^S7~  Ischio-rectal  fascia 
^^^~-  Os  innominatum 

Endopelvic  fascia  and 

prostatic  sheath 

^v^'sT      Obturator  fascia 

—  Obturator  membrane 


Levator  am 

Prostate 

Colli  cuius  seminalis 


Bulbo-cavernosus 
with  its  fa; 
Integument  o£- 
peri 


Ischio-rectal  fossa 
Superior  layer  of 

trigone 
Deep  transversus 

perinei 
Inferior  layer  of  uro- 
genital trigone 
Muscles  of  thigh 
Ischio-cavernosus 


Muscles  of  thigh 


Beneath  this  tissue  a  fibrous  band,  the  transverse  ligament  of  the  pubis,  extends  between  the 
descending  pubic  rami.  This  represents  a  region  of  fusion  of  the  deep  and  superficial  layers  of 
the  fascia  of  the  trigone.  Posterior  to  the  deep  transverse  muscle  the  two  layers  are  likewise 
fused.  The  superficial  layer  is  better  developed  in  the  front  than  in  the  back  part  of  the  space. 
It  is  pierced  by  the  urethra  (about  3  cm.  below  the  symphysis)  by  the  ducts  of  the  bulbo-urethral 


PELVIC  FASCIA 


447 


(Cowper's)  glands,  the  arteries  of  the  bulb,  and  the  dorsal  nerves  and  arteries  of  the  penis. 
In  the  female  it  is  pierced  by  the  vagina  as  well  as  by  the  structures  mentioned  above. 

Beneath  the  superficial  layer  of  the  fascia  of  the  trigone,  in  addition  to  the  muscles  of  the 
urogenital  diaphragm,  there  are  found  the  membranous  uretlira,  the  bulbo-urethral  glands 
(Cowper's),  the  internal  pudic  arteries  and  the  pudic  nerves  (in  part). 

The  dee-p  (superior)  layer  of  the  urogenital  trigone  (figs.  400,  402,  403)  lies  between  the  muscles 
of  the  urogenital  diaphragm  and  the  ischio-rectal  fossa  and  levator  ani.  It  may  be  looked  upon 
as  a  continuation  of  the  obturator  fascia  across  the  pubic  arch.  Posterior  to  the  deep  transverse 
perineal  muscle  it  fuses  with  the  superficial  layer  of  the  fascia  of  the  urogenital  trigone.  In 
this  region  in  the  male  it  fuses  with  a  fascial  membrane,  the  prostaiico-perineal  fascia,  which 
extends  upward  between  the  rectum  and  prostate,  and  is  attached  to  the  posterior  wall  of  the 
latter.  In  the  female  it  is  fused  with  the  fibrous  tissue  which  lies  between  the  vagina  and  the 
rectum. 

The  muscle  fasciae  of  the  pelvis  (figs.  399,  400,  401,  402,  407,  B)  have  been  described  in 
various  ways  by  different  authors.     They  may  be  subdivided  into  parietal  and  diaphragmatic. 


Fig.  403. — Diagram  of  the  Supehpicial  and  Deep  Layers  op  the  Urogenital  Trigone. 


Arcuate  ligament 

Apertures  for  dorsal  artery  and 
nerve  of  the  penis 


Crus  penis 

Aperture  for  deep  artery  of  penis 

Superficial  layer  of  urogenital 

trigone 

Ischio-cavernosus 

Aperture  for  artery. &__. , 

to  bulb  M& 

Urethral  aperture 
Aperture  for  bulbo 


Apertures  for  peri 
neal  vessels  and 
nerve 


Tela  subcutanea  of, 
perineum  turned 
backwards 


Aperture  for  dorsal  vein  of  the  penis 


1  nerve 
Superficial  layer  of  urogenital 

trigone  (reflected) 
Dorsal  artery  of  penis 

Deep  layer  of  urO' 

genital  trigone 
Deep  artery  of 
penis 

Artery  to  bulb 


Position  of  bulbo-ure- 
thral gland 
Internal  pudic  artery 


Junction  of  urogen- 
ital trigone  with 
tela  subcutanea  of 


The  parietal  fasciae  (fig.  399)  cover  the  muscles  which  extend  from  the  interior  of  the  pelvis 
to  the  thigh  (the  obturator  internus  and  piriformis  muscles).  Above,  the  fascia  on  each  side 
is  attached  to  the  linea  terminalis  and  is  continuous  with  the  fascia  transversalis  and  the  iliac 
fascia.  It  is  attached  to  the  margins  of  the  greater  and  lesser  sciatic  notches  and  to  the  ischio- 
pubic  ramus  and  the  body  of  the  pubis.  Between  the  ischio-pubic  rami  it  is  stretched  across 
the  subpubic  arch  and  forms  the  superior  or  deep  layer  of  the  urogenital  trigone  described  above. 
The  portion  of  parietal  pelvic  fascia  over  the  obturator  internus  muscle  is  called  the  obturator 
fascia. 

The  diaphragmatic  pelvic  fasciae  cover  both  surfaces  of  the  pelvic  diaphragm  and  are  re- 
flected upon  the  viscera.  The  fascia;  covering  the  two  surfaces  of  the  levator  ani  are  attached 
to  the  parietal  (obturator)  fascia  along  the  line  of  origin  of  the  muscle. 

The  line  of  attachment  of  the  levator  ani  divides  the  obturator  fascia  into  two  parts  (fig. 
399),  a  pelvic  part  above  the  line  of  attachment,  covered  by  peritoneum,  and  an  ischio-rectal 
part  below  the  line  of  attachment.  The  latter  bounds  the  lateral  wall  of  the  ischio-rectal  fossa. 
The  former  part  is  much  the  thicker.  It  consists  morphologically  of  two  fused  membranes,  the 
obturator  fascia  proper  and  the  aponeurosis  of  the  ilio-coccygeal  portion  of  the  levator  ani, 
which  although  usually  fused  with  the  obturator  fascia,  may  frequentlj'  be  traced  to  the  term- 
inal (ilio-pectineal)  line  from  which  in  tailed  mammals  this  portion  of  the  levator  takes  origin. 
The  two  layers  of  fascia  also  become  continuous  at  the  medial  margin  of  the  muscle  where  this 
faces  the  urogenital  passage  (fig.  399).  Posteriorly,  the  inner  layer  fuses  with  the  tendinous 
insertion  of  the  pubo-coocygeus  portion  of  the  muscle  and  the  fasciae  of  the  muscles  of  each  side 
are  continuous.     It  also  fuses  with  a  fascia  covering  the  coccygeus  muscle. 

The  thin  perineal  layer  of  the  levator  fascia  behind  the  rectum  fuses  with  that  of  the  opposite 
side  and  is  attached  to  the  coccyx  and  the  ano-coccygeal  raphe.  About  the  anus  it  helps  to 
form  a  covering  for  the  external  sphincter.  Ventrally  it  is  attached  to  the  ischio-pubic  rami. 
It  forms  the  medial  wall  of  the  ischio-rectal  fossa. 

Endo-pelvic  fascia  (figs.  401,  402), — The  peritoneum  is  reflected  from  the  pelvic  wall  onto 
the  viscera  much  higher  up  than  the  level  at  which  the  viscera  are  attached  to  the  pelvic  dia- 
phragm. Between  the  pelvic  fascia  covering  the  deep  surface  of  the  pelvic  diaphragm  (levator 
ani  and  coccygeus  muscles)  and  the  peritoneum  there  is  thus  left  a  space,  subperitoneal  space 
(fig.  467  B).  In  the  median  plane  in  this  region  in  the  male  are  found  the  bladder,  prostate, 
seminal  vesicles,  the  ureter  and  ductus  deferens  in  their  course  near  the  bladder,  and  the  am- 
pulla of  the  rectum.  In  the  female  we  find  here  the  bladder,  the  vagina,  the  uterus,  and  the  am- 
pulla of  the  rectum.     Between  these  medially  placed  viscera  and  the  lateral  wall  of  the  pelvis 


448  THE  MUSCULATURE 

there  is  an  irregularly  shaped  space,  cavum  pelvis  subperitoneale,  bounded  above  by  peritoneum, 
below  by  the  fascia  covering  the  pelvic  diaphragm  and  filled  with  connective  tissue  of  varying 
density.  The  tissue  in  this  space  in  the  female  is  continuous  with  that  between  the  two  per- 
itoneal surfaces  of  the  broad  ligament.  Between  the  viscera  in  the  subperitoneal  region  and 
about  their  walls  tlie  connective  tissue  is  more  or  less  definitely  condensed  into  membranes 
which  constitute  the  endopelvio  fascia,  variously  described  by  different  authors.  The  fascia 
covering  the  pelvic  diaphragm,  especiaOy  that  on  the  deep  surface,  is  fused  to  the  endopelvic 
fascia  where  the  viscera  pass  through  the  pelvic  diaphragm.  In  the  connective  tissue  of  the 
subperitoneal  space  are  found  the  hypogastric  artery  and  vein  and  their  chief  branches,  and 
various  visceral  nerves.  The  subperitoneal  space  above  the  pelvic  diaphragm  is  to  be  compared 
with  the  subcutaneous  space  below  the  pelvic  diaphragm  known  as  the  ischio-rectal  fossa  and 
described  above. 

MUSCLES 
A.  Muscles  of  the  Pelvic  Diaphragm,  Coccyx,  and  Anus 

The  coccygeus  (figs.  393,  396,  397,  400). — Origin. — From  the  ischial  spine  and  the  neigh- 
bouring margin  of  the  great  sciatic  notch.  Structure  and  insertion. — The  fibre-bundles  diverge 
to  be  inserted  partly  directly,  partly  by  means  of  an  aponeurosis,  into  the  lateral  margin  of  the 
fourth  and  fifth  sacral  vertebrse  and  of  the  coccyx.  Usually  the  muscle  is  composed  in  consider- 
able part  of  tendinous  connective  tissue,  especially  on  the  dorsal  side  of  the  cranial  portion,  and 
the  ventral  side  of  the  caudal  portion. 

Nerve-supply. — From  the  pudendal  plexus  several  small  nerves  enter  the  cranial  margin 
and  pelvic  surface  of  the  muscle.  They  arise  usually  from  the  third  and  fourth  sacral  nerves. 
Action. — Insofar  as  the  muscle  is  active  it  flexes  and  abducts  the  coccyx. 
Relations. — Ventrally  the  muscle  bounds  the  pelvic  cavity,  from  which  it  is  separated  by 
the  pelvic  fascia,  beneath  which  runs  the  nerve  to  the  levator  ani  muscle.  The  dorsal  surface 
is  partly  covered  by  the  sacro-spinous  (lesser  sciatic)  ligament  and  helps  to  bound  the  ischio- 
rectal fossa  (posterior  recess). 

Variations. — The  muscle  varies  greatly  in  the  extent  of  its  fleshy  development.  It  may  be 
doubled.     It  may  be  partially  fused  with  the  levator  ani.     Occasionally  it  is  absent. 

The  sacro-coccygeus  anterior  (fig.  393). — This  inconstant  muscle,  when  well  developed, 
arises  from  the  sides  of  the  fourth  and  fifth  sacral  and  from  the  front  of  the  fii'st  coccygeal  ver- 
tebra and  from  the  sacro-spinous  ligament.  The  short  fibre-bundles  which  compose  it  make  up 
a  somewhat  irregular  beDy  which  is  inserted  into  the  anterior  sacro-coccygeal  ligament  and  into 
the  second  to  fourth  coccygeal  vertebrse  dorsal  to  the  insertion  of  the  levator  ani.  The  innerva- 
tion is  from  the  fourth  and  fifth  sacral  nerves. 

The  sacrococcygeus  posterior  is  an  inconstant  muscle  consisting  of  a  few  muscle  bundles 
which  extend  from  the  dorsal  surface  of  the  lower  sacral  vertebrae  or  from  the  posterior  Oiac 
spine  to  the  dorsal  surface  of  the  coccyx.  It  hes  beneath  the  superficial  layer  of  the  sacro- 
tuberous  (great  sciatic)  ligament. 

The  levator  ani  (figs.  392,  394,  395,  396,  399,  401)  is  divisible  into  three  portions,  the  iUo- 
coccygeus,  the  pubo-coccygeus  and  the  pubo-rectahs. 

The  ilio-coccygeus  (fig.  397)  arises  from  the  ischial  portion  of  the  arcus  tendinous  (white 
line).  This  extends  from  the  iscliial  spine  and  posterior  part  of  the  arcuate  line  to  the  superior 
ramus  of  the  pubis  near  the  obturator  canal,  curving  downward  for  a  variable  distance  below 
the  obturator  canal.  The  constituent  fibre-bundles  form  a  muscular  sheet  which  is  inserted 
into  the  side  of  the  coccyx  and  into  the  median  raphe  (ano-coccygeal)  which  extends  from  the 
tip  of  the  coccyx  to  the  rectum.     Many  fibre-bundles  cross  the  median  hne. 

The  pubo-coccygeus  (figs.  395,  397)  arises  from  the  inner  surface  of  the  os  pubis,  along 
a  line  extending  from  the  lower  margin  of  the  symphysis  pubis  to  the  obturator  canal,  and  from 
the  arcus  tendineus  as  far  backward  as  the  origin  of  the  ilio-coccygeus.  The  fibre-bundles 
form  a  sheet  of  muscle  which  passes  backward,  downward,  and  medialward  past  the  urogenital 
organs  and  the  rectum  on  each  side  and  is  inserted  by  means  of  an  aponeiu:osis  into  the  anterior 
sacro-coccygeal  hgament.  Back  of  the  rectum  some  of  the  fibre-bundles  of  the  muscle  sheets 
of  each  side  interdigitate  across  the  median  line.  Some  of  the  more  superficial  fibres  are  in- 
serted into  the  deep  part  of  the  ano-coccygeal  raphe.  Some  of  the  fibre-bundles  which  arise 
nearest  the  symphysis  are  inserted  on  each  side  into  the  rectum.  The  pubo-coccygeus  lies  to 
some  extent  on  the  pelvic  surface  of  the  insertion  of  the  ilio-coccygeus. 

The  pubo-rectalis  (fig.  395)  arises  (a)  from  the  body  and  descending  ramus  of  the  pubis 
beneath  the  origin  of  the  pubo-coccygeus,  (b)  from  the  neighbom'ing  part  of  the  obturator  fascia 
and  (c)  from  the  fascia  covering  the  pelvic  surface  of  the  urogenital  trigone.  The  fibre-bundles 
form  a  thick  band  on  each  side  of  the  rectum  behind  which  those  of  each  side  are  inserted  into 
the  ano-coccygeal  raphe.  Many  fibre-bundles  may  be  traced  into  the  muscle  of  the  opposite 
side.  Some  of  the  more  superficial  fibre-bundles  are  reflected  medialward  in  front  of  rectum 
and  may  be  followed  into  the  superficial  transverse  perineal  muscle,  others  may  be  followed  into 
the  sphincter  ani  externus,  or  even  to  the  skin. 

Nerve-supply. — By  a  special  nerve  which  arises  usually  from  the  fourth  sacral,  runs  across 
the  pelvic  surface  of  the  muscle  and  gives  a  special  branch  to  each  portion. 

Action. — To  flex  the  coccyx,  raise  the  anus  and  constrict  the  rectum.  It  resists  the  down- 
ward pressure  which  the  thoraco-abdominal  diaphragm  exerts  on  the  viscera  during  inspiration. 
Relations. — Between  the  right  and  left  muscles  in  front  lie  the  m-ethra  and  the  lower  part 
of  the  prostate  in  the  male,  the  urethra  and  vagina  in  the  female.  In  the  triangle  between  the 
ischio-pubic  rami  of  each  side  lies  the  urogenital  diaphragm  separated  from  the  pubo-rectal  part 
of  the  muscle  by  the  deep  layer  of  the  trigone  from  which  some  of  the  fibres  of  the  latter  arise. 
Back  of  the  iirogenital  diaphragm  the  muscle  helps  to  bound  the  ischio-rectal  fossa. 


UROGENITAL  DIAPHRAGM  449 

Variations. — The  muscle  shows  great  individual  variation  in  structure  which  causes  it  to 
be  variously  described  by  different  authors. 

The  sphincter  ani  externus  (figs.  392,  394,  396,  397,  399)  is  made  up  of  bundles  of  muscle 
fibres  which  surround  the  anus  for  nearly  two  centimetres.  It  is  elliptical  in  form.  Behind 
the  anus  the  fibre-bundles  of  each  side  in  part  interdigitate,  forming  a  ring.  They  are  attached 
to  the  skin,  and  in  part  are  attached  through  a  tendon,  the  ligamentum  ano-coccygeum,  to  the 
back  of  the  coccyx.  In  front  of  the  anus  the  fibre-bundles  also  in  part  interdigitate  with  one 
another,  in  part  are  inserted  into  the  skin  and  in  part  interdigitate  with  the  fibre-bundles  of  the 
transverse  perineal  and  bulbo-cavernosus  muscles.  At  the  point  where  these  muscles  meet, 
about  two  and  a  half  centimetres  in  front  of  the  anus,  there  may  be  a  visible  mass  of  fibrous 
tissue,  the  central  tendon  of  the  -perineum,  but  this  is  not  always  distinct.  It  is  usually  better  de- 
veloped in  the  female  than  in  the  male  perineum.  The  external  sphincter  is  divisible  into  three 
portions,  a  subcutaneus,  a  superficial  and  a  deep  (fig.  397).  The  thi-ee  parts  are  connected  by 
fibre-bundles,  and  are  not  always  distinct.  The  subcutaneous  division  is  small  and  immediately 
encircles  the  anal  orifice.  The  superficial  division  lies  external  to  the  subcutaneous  ring  and  de- 
scends further  toward  the  rectum.  It  is  shown  in  figs.  392,  394.  It  is  the  only  part  attached 
to  the  coccyx.  In  front  it  is  attached  to  the  central  tendon  of  the  perineum,  but  some  fibres 
are  continued  into  the  bulbo-cavernosus.  The  deep  portion  forms  a  heavy  ring  above  the  rec- 
tum beneath  the  superficial  part.  It  is  distinctly,  though  not  completely,  separated  from  the 
pubo-rectal  portion  of  the  levator  ani  by  fascial  tissue  containing  the  inferior  haemorrhoidal 
vessels.  Some  of  the  fibre-bundles  of  the  deep  portion  may  be  traced  in  front  of  the  anus 
across  the  mid-line  to  the  ascending  ramus  of  the  opposite  side  and  form  part  of  the  superficial 
transverse  perineal  muscle. 

Nerve-supply. — From  the  inferior  haemorrhoidal  branches  of  the  pudendal  (internal  pudic) 
and  frequently  also  by  a  perineal  branch  from  the  fourth  sacral. 

Action. — To  keep  the  anus  closed. 

Relations. — Externally  it  is  surrounded  by  the  fat  of  the  ischio-rectal  fossa,  internally  near 
the  skin  it  surrounds  the  sphincter  ani  internus,  composed  of  smooth  muscle,  deeper  it  lies 
next  the  mucous  membrane,  for  a  distance  of  two  centimetres  from  the  skin. 

Variations. — The  muscle  shows  considerable  individual  variation  in  structure. 

The  recto-coccygeus  or  muscle  of  Treitz,  is  a  triangular  bundle  of  smooth  muscle  fibres. 
The  origin  of  the  muscle  is  from  the  second  and  third  coccygeal  vertebrse.  It  is  inserted  by 
its  apex  into  the  posterior  wall  of  the  rectum  and  the  perirectal  fascia.  It  retracts  and  elevates 
the  rectum. 

B.  Muscles  of  the  Urogenital  Diaphragm 

The  urogenital  diaphragm  is  composed  of  two  closely  united  muscles,  the  deep  transverse 
perineal  muscle  and  the  urogenital  sphincter. 

The  transversus  perinei  profundus  (fig.  398)  is  a  flat  muscle  which  arises  from  the  inner  side 
of  the  inferior  ischial  ramus  and  is  inserted  into  the  median  raphe.  Many  of  the  fibre-bundles 
interdigitate  with  those  of  the  opposite  side  and  some  may  be  followed  into  the  external  sphinc- 
ter of  the  anus  and  into  the  urogenital  spincter  and  other  perineal  muscles. 

Nerve-supply. — By  the  perineal  branch  of  the  pudendal  (internal  pudic). 

Action. — The  pair  of  muscles  draw  back  and  fix  the  central  tendon  of  the  perineum  and  thus 
give  firm  support  for  the  action  of  the  urogenital  sphincter. 

Relations. — The  inferior  surface  is  separated  (often  incompletely)  by  the  inferior  layer  of 
the  urogenital  trigone  from  the  superficial  transverse  perineal  muscle.  The  superior  surface 
is  covered  by  the  deep  layer  of  the  urogenital  trigone,  into  which  the  superficial  layer  is  reflected 
about  the  anal  margin  of  the  muscle. 

Variations. — The  muscle  is  variable  in  structure  and  may  be  absent.  (It  is  more  frequently 
absent  in  the  female  than  in  the  male.) 

The  sphincter  urogenitalis  differs  in  the  male  and  female  owing  to  the  passage  of  the  vagina 
through  the  perineum  in  the  latter.  In  each  sex  it  is  convenient  to  consider  the  muscle  as 
divided  into  two  parts,  a  peri-urethral  and  an  infra-urethral  (vaginal). 

In  the  male  (fig.  398)  the  peri-urethral  part,  the  m.  sphincter  urethros  memhranacece  is  com- 
posed of  fibre-bundles  which  are  circularly  placed  about  the  membraneous  urethra.  The  more 
external  fibre-bundles  are  attached  to  the  crura  of  the  penis  near  their  junction,  to  the  trans- 
verse ligament  of  the  pubis  and  to  the  fasciae  of  the  trigone.  Some  of  them  partially  ensheath 
the  lower  part  of  the  prostate,  and  others  envelop  the  bulbo-urethral  (Cowper's)  glands.  Some 
of  the  fibre-bundles  take  a  longitudinal  course  along  the  urethra.  Bundles  of  smooth  muscle 
fibres  are  intermingled  with  the  striated,  and  the  fibrous  framework  of  the  musculature  is  marked 
by  the  large  amount  of  elastic  tissue  which  it  contains.  The  infra-urethral  part,  the  m.  trans- 
versus urethrce,  is  closely  associated  with  the  urethral  part.  The  fibre-bundles  arise  on  each  side 
from  the  inferior  ramus  of  the  pubis.  They  pass  for  the  greater  part  beneath  the  urethra  and 
interdigitate  with  that  of  the  opposite  side  or  are  inserted  into  a  median  raphe.  A  few  fibre- 
bundles  may  pass  above  instead  of  below  the  urethra.  The  transverse  urethral  muscle,  first 
described  by  Guthrie  (On  the  anatomy  and  diseases  of  the  neck  of  the  bladder,  London,  1834) 
is  inconstant.  Its  existence  as  a  normal  constituent  of  the  male  perineal  musculature  has  been 
disputed  by  Delbet  (Poirier  and  Charpy)  and  others. 

In  the  female  the  peri-urethral  part,  .•sphincter  urethrce,  differs  in  no  essential  respects  from 
the  corresponding  muscle  in  the  male.  Some  of  the  fibre-bundles  form  a  true  sphincter  about 
the  uretlu-a.  The  infra-urethral  part,  on  the  other  hand,  seems  to  vary  gi'eatly  in  different  indi- 
viduals so  that  the  descriptions  given  by  different  authors  are  somewhat  contradictory.  It  is 
better  developed  in  women  who  have  not  borne  children  than  in  those  who  have.  It  may  be 
looked  upon  as  composed  of  two  portions,  a  m.  transversus  vagina  and  an  m.  constrictor  vagince. 


450 


THE  MUSCULATURE 


The  iransversus  vagince  arises  from  the  ischio-pubic  rami  and  is  inserted  into  the  lateral  wall  of 
the  vagina.  Some  of  the  fibre-bundles  pass  above  and  some  below  the  vagina.  This  muscle 
corresponds  with  the  transversus  urethrce  of  the  male  but  is,  apparently,  seldom  fully  developed. 
The  m.  constrictor  vagince,  on  the  other  hand,  seems  to  be  more  constant.  It  is  composed  of 
fibre-bundles  which  embrace  the  lateral  wall  of  the  vagina  and  are  inserted  above  into  the  peri- 
urethral framework,  below  into  the  raphe  between  the  two  deep  transverse  perineal  muscles. 
Some  of  the  fibre-bundles  are  attached  to  the  vaginal  waU.  Some  interdigitate  With  the  sphinc- 
ter urethrae,  others  with  the  deep  transverse  perineal  muscle  and  with  the  transversus  vaginse. 

Nerve-supply. — By  a  branch  from  the  perineal  nerve. 

Action. — To  compress  or  close  the  urethra  and  in  the  male  to  compress  the  prostate  and 
Cowper's  glands,  in  the  female  to  compress  the  vagina  and  BarthoUn's  glands. 

Relations. — On  the  pelvic  side  it  is  separated  from  the  levator  ani  by  the  deep  layer  of  the 
urogenital  trigone,  and  on  the  perineal  side  it  is  separated  from  the  superficial  muscles  by  the 
superficial  layer  of  the  trigone.  Toward  the  anus  it  is  closely  associated  with  the  deep  trans- 
verse perineal  muscle.  Venous  plexuses  are  well  developed  near  the  sphincter  urethral  in  both 
sexes,  but  especially  in  the  female. 


Fig.  404. — Buibo-cavernostjs  in  the  Male. 
The  two  halves  have  been  reflected  from  the  median  raphe,  and  the  bulb  turned  downward  after 
division  of  the  corpus  spongiosum.     (The  isohio-bulbosus  is  not  present  on  the  right  side.) 


Corpus  cavernosum  penis 


Median  aponeurosi: 


Cut  surface   of  corpus 
cavernosum  urethra 


Corpus  cavernosum  urethrse 
(corpus  spongiosum) 


Constrictor  radicis  penis 


Ischio-bulbosus 


Compressor  bulbi  proprius 


Variations. — It  has  already  been  pointed  out  that  there  is  considerable  variation  in  the 
muscles  composing  urogenital  sphincter.  Occasionally  a  rudimentary  ischio-puhicus  is  found 
arising  from  the  ischio-pubic  ramus  and  terminating  in  a  tendon  which  unites  with  that  of  the 
opposite  side  beneath  the  dorsal  vein  of  the  penis  (clitoris).  The  tendon  may  be  present  as 
the  transverse  ligament  of  the  pelvis  when  the  muscle  itseH  is  absent.  It  represents  the  com- 
pressor of  the  dorsal  vein  found  in  lower  mammals. 

C.  External  Genital  Muscles 


The  bulbo-cavernosus  (figs.  394,  404)  in  the  male  ensheaths  the  bulb.  The  fibre-bundles 
arise  from  the  dense  tissue  covering  the  corpus  cavernosum  at  the  root  of  the  penis  and  from  the 
subpubic  connective  tissue  dorsal  to  the  bulbar  part  of  the  urethra  and  are  inserted  into  its  median 
raphe  on  the  ventral  side  of  the  bulb  and  into  the  central  tendon  of  the  perineum.  Several 
parts  may  be  more  or  less  clearly  distinguished. 

1.  The  constrictor  radicis  penis  arises  usually  from  the  lateral  surface  of  the  corpus  caver- 
nosum penis  at  the  base  of  the  penis,  but  may  arise  from  the  under  surface  or  from  the  dorsal 
surface,  or  even  from  the  suspensory  ligament  of  the  penis.  The  fibre-bundles  pass  obliquely 
backward  and  medialward  and  are  inserted  into  the  median  raphe  on  the  perineal  surface  of  the 
bulb. 

2.  The  compressor  bulbi  proprius  arises  (1)  from  a  strong  fibrous  aponeurosis  situated 
between  the  corpus  spongiosum  and  the  united  crura  of  the  penis  and  firmly  adherent  to  the 
former,  and  (2)  from  the  superficial  layer  of  the  trigone.  The  fibre-bundles  ensheath  the  bulb 
aim  are  inserted  into  the  posterior  part  of  the  median  raphe  and  into  the  central  tendon  of  the 


ISCHIO-CA  VERNOS  US 


451 


perineum.     To  a  greater  or  less  extent,  depending  on  the  development  of  the  two  muscles,  the 
compressor  covers  the  more  posterior  part  of  the  constrictor. 

3.  The  compressor  hemisphcerium  bulbi  arises  from  a  tendon  common  to  the  muscles  of  the 
two  sides  on  the  dorsum  of  the  bulbous  part  of  the  uretlira  near  the  membranous  part.  The 
fibre-bundles  embrace  the  hemisphere  of  the  bulb  and  are  inserted  into  the  median  raphe.  This 
muscle  is  covered  by  the  preceding.  It  not  only  compresses  the  bulb,  but  also  is  a  sphincter 
of  the  urethra. 

4.  The  ischio-bulbosus  is  placed  by  Holl  in  this  group.  It  arises  from  the  pelvic  surface  of 
the  tuberosity  and  of  the  inferior  ramus  of  the  ischium  and  when  well  developed  is  inserted  into 
the  median  raphe,  superficial  to  the  compressor  bulbi  proprius  or  the  constrictor  radicis  pro- 
prius.  Frequently,  however,  it  does  not  extend  over  the  bulb  but  is  inserted  into  the  inferior 
surface  of  the  corpus  cavernosum.     It  is  more  frequently  absent  than  present.     (See  fig.  404.) 

Nerve-supply. — The  perineal  division  of  the  pudic  nerve  sends  several  branches  to  the  bulbo- 
cavernosus. 

Action. — It  compresses  the  bulb  and  at  the  same  time  the  bulbous  portion  of  the  urethra. 
The  turgescence  of  the  penis  is  thus  increased  and  urine  or  semen  is  expelled  from  this  portion 
of  the  urethra. 

Relations. — It  lies  beneath  the  skin  and  subcutaneous  tissue. 

Variations. — The  muscle  is  variable  in  structure  as  is  indicated  by  the  different  descriptions 
given  by  different  authors.     The  compressor  vence  dorsalis  described  by  Houston  is  composed  of 

Fig.  405. — Diagrammatic  Representation  op  the  Perineal  Structures  in  the  Female. 


Iscbio-pubic  arch 


Bulbo-cavernosus 
covering  bulbus 
vestibuli 


Inferior  layer  of  urO' 
genital  trigone 


Glans    clitoridis    with 
prepuce 

Pars  intermedia 
Mucous  membrane  of 
vestibule 

Urethral  orifice 


Bulbus  vestibuli 


External  sphincter  ani 


a  few  fasciculi  which  arise  from  the  sheath  of  the  corpus  spongiosum,  and  from  the  median 
raphe  and  are  united  to  those  of  the  opposite  side  by  a  tendon  which  passes  over  the  dorsal  vein. 

The  hulbo-cavernosus  (sphincter  vagince)  (fig.  392,  405)  in  the  female  arises  (1)  from  fibrous 
tissue  dorsal  to  the  clitoris,  (2)  from  the  tunica  fibrosa  of  the  corpus  cavernosum  and  from  the 
superficial  layer  of  the  urogenital  trigone  in  the  angle  between  the  crura  of  the  ohtoris.  The 
fibre-bundles  form  a  band  of  tissue  about  two  centimetres  wide  at  the  side  of  the  vagina  and  are 
inserted  into  the  posterior  part  of  the  superficial  (inferior)  layer  of  the  trigonum  and  into  the 
central  tendon  of  the  perineum  where  some  of  the  fibre-bundles  interdigitate  with  those  of  other 
muscles  attached  here.  The  fibre-bundles  arising  from  the  back  of  the  clitoris  correspond  with 
those  of  the  constrictor  radicis  penis  in  the  male.  The  other  fibre-bundles  correspond  with  those 
of  the  compressor  bulbi  proprius  in  the  male. 

Nerve-supply. — From  the  perineal  division  of  the  pudic. 

Action. — To  compress  the  vagina. 

Relations. — It  covers  the  bulb  of  the  vestibule  and  the  great  vestibular  gland  (Bartholin's). 
It  is  covered  by  skin  and  superficial  fascia. 

The  ischio-cavernosus  (figs.  398,  405)  (erector  penis  or  clitoridis)  arises  from  the  pelvic 
surface  of  the  tuberosity  and  inferior  ramus  of  the  ischium,  back  and  on  each  side  of  the  attach- 
ment of  the  crus.  The  fibre-bundles  form  a  thin  sheet  which  is  spread  over  the  crus  into  the 
medial  and  inferior  surfaces  of  which  it  is  inserted  near  the  symphysis  pubis.  It  is  better  devel- 
oped in  the  male  than  in  the  female. 

Nerve-supply. — By  branches  of  the  perineal  nerve. 

Action. — By  constricting  the  crus  to  maintain  turgescence  of  the  penis  or  chtoris. 

Relations. — Superficially  it  is  covered  by  skin  and  subcutaneous  tissue.  Laterally  it  lies 
next  the  ischio-pubic  ramus.  Medially  it  bounds  a  space  lying  between  the  crus  and  the  bulb 
and  filled  with  fat. 


452  THE  MUSCULATURE 

Variations. — The  muscle  in  the  male  is  much  larger  than  in  the  female.  Some  of  the  more 
anterior  fibre-bundles  may  extend  to  the  dorsal  surface  of  the  penis  (chtoris)  and  form  a  'puho- 
cavernosus  or  levator  penis  muscle. 

The  transversus  perinei  superficialis  (figs.  392,  394,  405)  arises  from  the  inferior  ischial 
ramus.  The  fibre-bundles  extend  in  front  of  the  rectum  superficial  to  the  deep  transverse  mus- 
cle and  are  inserted  into  the  central  tendon  of  the  perineum.  Some  cross  to  the  opposite  side. 
Some  of  the  fibre-bundles  are  continuous  with  those  of  the  external  sphincter  or  of  the  pubo- 
rectalis  of  the  opposite  side. 

Action. — It  acts  with  the  deep  transverse  muscle  in  fixing  the  central  part  of  the  perineum. 

Nerve-supply. — By  a  branch  _from  the  perineal  division  of  the  pudic. 

Variations. — It  is  frequently  absent  or  poorly  developed. 

VI.  THE  MUSCULATURE  OF  THE  LOWER  LIMB 

The  lower  limbs  are  used  chiefly  for  the  support  and  propulsion  of  the  body. 
Variety  of  movement  is  subordinated  to  strength  and  precision.  In  contrast  with 
the  upper  limbs,  which  perform  a  vast  variety  of  complex  movements  under 
conscious  control,  the  lower  limbs  are  called  upon  to  perform  chiefly  the  relatively 
simple  movements  which  are  used  in  walking  or  running,  without  our  paying  much 
attention  to  them. 

The  contrast  between  the  two  extremities  is  best  marked  in  the  girdles,  the  relations  of 
which  to  the  trunk  have  already  been  described,  p.  444.  The  shoulder  girdle  is  constantly 
called  upon  for  movements  in  various  directions  which  increase  the  freedom  of  action  of  the  whole 
extremity.  The  sterno-clavicular  and  acromio-clavicular  joints  are  movable  so  that  the  scapula 
can  be  carried  in  various  directions  over  the  thorax.  The  bones  of  the  hip-girdle  on  each  side, 
on  the  other  hand,  are  ossified  into  a  single  hip-bone  (os  innominatum).  The  two  hip-bones  are 
almost  immovably  united  to  one  another  in  front  by  the  symphysis  pubis  and  behind  each  is 
united  to  the  sacrum  by  a  joint  which,  although  a  diarthrosis,  likewise  permits  but  sUght  move- 
ment. The  sacrum  in  turn  is  composed  of  vertebrre  firmly  ossified  together.  The  pelvis, 
composed  of  the  two  hip-bones  and  the  sacrum  forms  a  strong  support  for  the  trunk.  Such 
movements  as  it  makes  are  due  chiefly  to  the  lumbo-sacral  joint  and  to  a  less  extent  to  the  joints 
between  the  lumbar  vertebrae.  These  joints  permit  the  pelvis,  in  a  limited  manner,  to  be  flexed 
and  extended,  abducted,  adducted,  and  rotated.  Flexion  is  produced  by  the  rectus  and  the 
oblique  muscles  of  the  abdomen  (fig.  387)  and  by  the  psoas  muscles  (fig.  406),  extension  is  pro- 
duced by  the  quadratus  lumborum  (fig.  406)  and  the  sacrospinahs  (fig.  381).  Rotation  and 
abduction  are  produced  when  these  muscles  act  on  one  side  only.  The  weight  of  the  body  in 
the  sitting  posture  is  transmitted  through  the  sacrum  and  hip-bones  to  the  ischial  tuberosities. 
In  this  position  the  pelvis  is  flexed.  The  weight  of  the  body  in  the  standing  position  is  trans- 
mitted to  the  femora  through  the  acetabulum  on  each  side.  In  this  position  the  pelvis  is  ex- 
tended.    In  walking  the  pelvis  is  rotated  forward  toward  the  limb  that  is  being  advanced. 

The  hip-joint  is  a  true  ball-and-socket  joint,  but  freedom  of  movement  is  greatly  limited 
by  the  powerful  musculature  which  surrounds  it,  as  well  as  by  the  ligaments.  Movements 
here,  however,  are  freer  than  at  the  shoulder-joint,  if  the  shoulder  girdle  be  left  out  of  considera- 
tion. At  the  hip-joint  the  most  frequent  and  most  free  movements  are  those  of  flexion  and 
extension,  the  main  movements  in'walking  or  running;  but  abduction,  adduction,  circumduction, 
and  rotation  are  of  the  greatest  importance  in  balancing  the  body. 

At  the  knee-joint  the  main  movements  are  also  those  of  flexion  and  extension  and  the  mus- 
culature is  so  arranged  that  the  chief  flexors  of  the  knee  which  lie  at  the  back  of  the  thigh  are 
extensors  of  the  hip  (fig.  408)  while  the  extensor  musculature  of  the  knee  which  lies  at  the  front 
of  the  thigh  flexes  the  hip  (fig.  411).  Flexion  of  the  hip,  however,  through  the  action  of  gravity 
on  the  foot  passively  brings  about  flexion  at  the  knee,  while  flexion  of  the  knee  likewise  passively 
brings  about  flexion  of  the  hip,  since  the  flexed  knee  tends  to  swing  forward.  These  passive 
movements,  due  to  gravity,  are  of  importance  in  walking.  The  gastrocnemius  (fig.  413),  the 
most  powerful  extensor  of  the  ankle-joint,  is  also  a  powerful  flexor  of  the  knee-joint.  At  the 
knee-joint,  in  addition  to  flexion  and  extension,  some  rotation  is  possible,  best  marked  when 
the  knee  is  flexed.  This  rotation  is  of  value  in  walking  over  rough  ground  in  that  it  helps 
to  accommodate  the  foot  to  the  ground.  It  is  also  of  value  in  sitting  on  a  flat  surface.  Whfle 
there  is  thus  some  rotation  at  the  knee-joint  not  found  at  the  elbow-joint,  the  free  movement 
of  the  radius  about  the  ulna  which  accompanies  pronation  and  supination  in  the  forearm,  is 
unrepresented  in  the  leg  where  the  fibula  is  firmly  united  to  the  tibia  at  each  end. 

The  joint  between  the  bones  of  the  leg  and  the  tarsus  permits  merely  of  flexion  and  exten- 
sion in  contrast  to  the  wrist-joint  which  also  permits  of  adduction  and  abduction.  Flexion 
and  extension  are  also  more  limited  iit  the  ankle  than  at  the  wrist.  On  the  other  hand,  the 
movements  of  inversion  and  eversion  which  take  place  in  the  intertarsal  joints  are  not  needed 
in  the  wrist  because  of  the  pronation  and  supination  of  the  forearm.  Inversion  and  eversion 
of  the  foot  are  of  value  in  walking  on  rough  ground. 

The  movements  of  the  toes  resemble  those  of  the  fingers  except  that  they  are,  in  most 
individuals,  far  more  restricted.  The  greatest  restriction  is  seen  at  -the  joint  between  the 
metatarsal  of  the  big  toe  and  the  tarsus,  as  compared  with  that  between  the  metatarsal  of  the 
thumb  and  the  carpus. 

The  musculature  of  the  inferior  extremity,  like  that  of  the  superior,  can  be 
divided  according  to  its  development  and  innervation  into  two  great  subdivisions 


MUSCLES  OF  LOWER  LIMB  453 

which  correspond  with  the  musculature  on  the  dorsal  and  ventral  sides  of  the 
(shark's  fin.  The  dorsal  musculature  is  supplied  by  nerve  branches  which  arise 
from  the  back  of  the  lumbo-dorsal  plexus  ("femoral,  gluteal,  and  peroneal  nerves), 
the  ventral  musculature  by  branches  which  arise  from  the  front  of  the  plexus 
obturator  and  tibial  nerves).  Owing,  however,  to  the  rotation  which  the  limb 
makes  during  embryonic  development,  the  musculature  which  primitively  lies  on 
the  dorsal  side  of  the  limb-bud  comes  to  lie  on  the  front  and  lateral  side  of  the 
extremity  and  the  musculature  of  the  ventral  side  of  the  limb-bud  comes  to  lie 
on  the  back  and  medial  side  of  the  extremity  or  in  the  sole  of  the  foot.  The  side 
of  the  limb  which  primitively  was  toward  the  head  becomes  the  medial  side 
of  the  limb,  and  that  which  faced  caudalward  comes  to  lie  laterally.  While 
this  makes  the  primitive  relations  of  the  musculature  of  the  limb  at  first  somewhat 
confusing,  it  is  possible  to  approximate  these  primitive  conditions  by  abducting 
the  limb  and  rotating  it  so  that  the  sole  of  the  foot  faces  forward.  An  under- 
standing of  the  innervation  of  the  limb  is  thus  greatly  facilitated. 

In  the  region  of  the  hip  the  musculature  of  the  dorsal  division  is  that  which 
arises  from  the  spinal  column  and  ilium  and  is  inserted  into  the  upper  part  of  the 
femur  and  into  the  fascia  of  the  thigh.  It  includes  the  chief  flexor  of  the  thigh, 
the  ilio-psoas  (fig.  406),  and  the  most  powerful  extensor,  the  gluteus  maximus 
(fig.  413),  as  well  as  several  important  rotators  and  abductors,  gluteus  medius  and 
minimus,  piriformis  and  tensor  fascice  latce  (fig.  408) .  The  ilio-psoas  is  innervated 
by  nerves  from  the  back  of  the  lumbar,  the  other  muscles  by  nerves  from  the  back 
of  the  sacral  plexus.  The  musculature  of  the  ventral  division  arises  from  the 
pubis  and  ischium,  is  inserted  into  the  femur  near  the  great  trochanter  and  serves 
to  adduct  the  thigh  and  rotate  it  lateralward,  obturator  internus,  gemelli,  quadratus 
femoris  (fig.  408)  and  obturator  externus  (fig.  406).  The  obturator  externus  is 
innervated  by  the  obturator  nerve  from  the  front  of  the  lumbar  plexus,  the  other 
muscles  by  special  branches  from  the  front  of  the  sacral  plexus. 

In  the  thigh  there  are  three  well-marked  groups  of  muscles,  an  anterior  or 
extensor  group  (fig.  411),  a  medial  or  adductor  group  (fig.  411),  and  a  posterior  or 
flexor  group  (fig.  408).  The  anterior  group  belongs  to  the  primitive  dorsal 
division,  the  other  two  groups  to  the  ventral  division. 

The  muscles  of  the  anterior  group  (fig.  411)  the  sartorius  and  quadriceps  arise 
from  the  ilium  and  the  shaft  of  the  femur  and  are  inserted  into  the  tibia.  The 
quadriceps  flexes  the  thigh  and  extends  the  leg.  The  sartorius  flexes  both  the 
thigh  and  the  leg  and  rotates  the  former  lateralward,  the  latter  medialward. 
They  are  innervated  by  the  femoral  nerve.  The  muscles  of  the  medial  group 
(fig.  411),  gracilis,  pectineus,  adductor  brevis,  longus,  and  magnus,  arise  from  the 
pubis  and  the  inferior  ramus  of  the  ischium  and  are  inserted  into  the  shaft  of  the 
femur.  They  adduct  and  fiex  the  thigh.  They  are  innervated  by  the  obturator 
nerve.  The  adductor  magnus  gets  part  of  its  nerve-supply  from  the  sciatic. 
The  pectineus  usually  gets  all  or  most  of  its  supply  from  the  femoral.  The  rea- 
sons for  including  it  in  this  group  are  given  below.  The  posterior  group  (fig.  408) 
consists  of  the  semitendinosus  and  semimembranosus,  which  arise  from  the  ischial 
tuberosity,  and  of  the  biceps,  one  head  of  which  also  arises  from  the  ischial  tuber- 
osity while  the  other  arises  from  the  shaft  of  the  femur.  The  semimembranosus 
and  semitendinosus  are  inserted  into  the  tibia,  the  biceps  into  the  fibula.  They 
are  innervated  by  branches  of  the  sciatic.  They  extend  the  thigh  and  flex  the 
knee.     The  semitendinosus  rotates  the  leg  medialward,  the  biceps  lateralward. 

In  the  leg  there  are  also  three  groups  of  muscles,  an  anterior,  a  lateral  and  a 
posterior.  The  two  former  belong  to  the  dorsal  division  and  are  innervated  by 
the  peroneal  nerve.  The  last  belongs  to  the  ventral  division  and  is  innervated  by 
the  tibial  nerve.  The  muscles  of  the  anterior  group  (fig.  415),  the  tibialis  anterior, 
extensor  digitorum  longus,  peroneus  tertius  and  extensor  hallucis  longus,  arise  from 
the  tibia  and  fibula  and  are  inserted  into  first  and  fifth  metatarsals  and  into  the 
two  distal  rows  of  phalanges.  They  flex  the  ankle  and  extend  the  toes.  The 
extensor  digitorum  longus  and  peroneus  tertius  evert  the  foot.  The  muscles  of 
the  lateral  group  (fig.  415),  the  peroneus  longus  and  brevis,  arise  from  the  fibula, 
send  tendons  behind  the  lateral  malleolus  and  are  inserted  respectively  into  the 
first  and  the  fifth  metatarsals.  Thej^  extend  and  evert  the  foot.  The  posterior 
group  (figs.  413,  416)  may  be  separated  into  two  subdivisions,  a  superficial  and  a 
deep.     The  superficial  subdivision  (fig.  413)  consists  of  the  gastrocnemius,  which 


454  THE  MUSCULATURE 

arises  from  the  two  epicondyles  of  the  femur,  and  the  soleus  which  arises  from  the 
tibia  and  fibula.  These  powerful  extensors  of  the  ankle  are  inserted  by  means  of 
the  tendon  of  Achilles  into  the  calcaneus.  The  gastrocnemius  is  a  flexor  of  the 
knee  as  well  as  an  extensor  of  the  ankle.  A  rudimentary  muscle,  the  plantaris, 
arises  near  the  lateral  head  of  the  gastrocnemius  and  is  inserted  into  the  fibrous 
tissue  of  the  heel. 

The  deep  group  ("fig.  416)  consists  of  one  muscle,  the  popliteus,  a  medial 
rotator  and  flexor  of  the  leg,  which  arises  from  the  lateral  condyle  of  the  femur  and 
is  inserted  into  the  tibia;  and  of  three  muscles,  the  ^exor  digitorum  longus,  flexor 
hallucis  longus  and  tibialis  posterior,  which  arise  from  the  tibia  and  fibula,  send 
tendons  behind  the  medial  malleolus  and  are  inserted  into  the  plantar  surface  of 
the  tarsus  and  into  the  terminal  phalanges  of  the  toes.  They  invert  the  foot  and 
fiex  the  toes. 

In  the  foot  one  muscle  on  the  dorsum  represents  the  primitive  dorsal  division, 
the  extensor  digitorum  brevis  (fig.  418),  supplied  by  a  branch  from  the  peroneal 
nerve.  On  the  other  hand  the  primitive  ventral  division  is  well  represented  in 
the  sole  of  the  foot,  not  only  by  the  muscles  associated  with  the  long  flexor  tendons, 
quadratus  plantae,  lumbricales  (fig.  420),  but  also  by  the  short  flexor  of  the  toes 
(fig.  419),  by  the  special  musculature  of  the  big  and  little  toes  (fig.  421)  and  by  the 
interosseous  muscles  (fig.  422).  The  flexor  digitorum  brevis  (fig.  419),  the  most 
superficial  of  these  muscles,  arises  from  the  calcaneus  and  is  inserted  into  the 
second  row  of  phalanges  of  the  four  more  lateral  toes.  The  quadratus  plantce 
arises  from  the  calcaneus  and  is  inserted  into  the  tendon  of  the  long  extensor  of 
the  toes.  It  makes  the  action  of  the  tendon  on  the  digits  more  direct.  The  four 
lumbrical  muscles  run  from  this  tendon  to  the  medial  sides  of  the  four  lateral  toes. 
They  flex  the  digits.  Of  the  intrinsic  muscles  of  the  great  toe  (figs.  419,  421), 
the  abductor  arises  from  the  calcaneus;  the  flexor  brevis  from  the  cuneiform 
bones;  and  the  adductor,  by  one  head  from  the  long  plantar  ligament,  by  the  other 
from  the  capsules  of  the  metatarso-phalangeal  joints.  All  are  inserted  into  the 
base  of  the  first  phalanx.  Of  the  muscles  of  the  little  toe  (figs.  419-421),  the  abduc- 
tor arises  from  the  calcaneus,  the  flexor  and  opponens  from  the  cuboid.  The  two 
former  are  attached  to  the  base  of  the  first  phalanx,  the  last  to  the  fifth  metatarsal. 
The  interosseous  muscles  which  arise  between  the  metatarsals  are  so  arranged 
that  the  three  plantar  abduct  and  the  four  dorsal  adduct  the  four  lateral  toes  to 
and  from  an  axis  passing  through  the  second  toe.  The  muscles  of  the  sole  of  the 
foot  which  send  tendons  to  the  sides  of  the  bases  of  the  first  row  of  phalanges  help 
to  flex  the  digits  on  the  metatarsals  and  to  extend  the  toes  at  the  first  row  of  inter- 
phalangeal  joints.  These  are  much  less  effective  extensors  of  the  phalanges  than 
are  the  corresponding  muscles  of  the  hand  and,  unlike  the  latter,  seem,  in  most 
individuals,  to  exert  but  little  extensor  action  on  the  third  row  of  phalanges. 
The  muscles  of  the  sole  of  the  foot  are  supplied  by  the  lateral  and  medial  plantar 
branches  of  the  tibial  nerve. 

The  muscle  fasciae  of  the  inferior  extremity  are  well  developed.  The  fascia  lata,  which 
•encloses  the  musculature  of  the  back  of  the  hip  and  the  musculature  of  the  thigh,  is  especially 
strong  on  the  lateral  side  where  it  includes  the  longitudinal  bundles  of  fibres  which  compose 
the  iho-tibial  band.  From  the  fascia  lata  strong  intermuscular  septa  extend  on  each  side  of  the 
quadriceps  group  of  muscles  to  the  femur.  Medially  beneath  the  sartorius  muscle  (fig.  410), 
septa  help  to  bound  Hunter's  canal  in  which  lies  the  femoral  artery  on  its  way  to  the  pophteal 
space  behind  the  knee.  In  the  leg  there  is  hkewise  a  strong  cylindrical  fascial  sheath  which 
encloses  the  musculature  and  sends  septa  on  each  side  of  the  peroneal  group  to  the  fibula.  A 
transverse  septum  also  separates  the  deep  from  the  superficial  muscles  of  the  calf.  The  fascia 
of  .the  leg  is  especially  well  developed  near  the  anlde  where  it  helps  to  hold  in  place  the  tendons 
which  pass  from  the  muscles  of  the  leg  into  the  foot.  Muscle  fasciae  are  well  developed  both  on 
the  dorsum  and  in  the  sole  of  the  foot. 

A.  MUSCULATURE  OF  THE  HIP 

1.  Ilio-Femoeal  Musculature 

The  ihac  blade  divides  these  muscles  into  an  anterior  group  (ilio-psoas), 
supplied  by  nerves  from  the  lumbar  plexus,  and  a  posterior  group  (the  gluteal 
muscles,  piriformis,  and  tensor  fasciae  latse,  supplied  by  nerves  from  the  sacral 
plexus. 


MUSCLES  OF  HIP  455 

In  most  of  the  limbed  vertebrates  these  two  groups  of  muscles  are  represented,  but  they 
present  marked  specific  variations  in  the  different  forms.  Primitively,  the  iliacus  group  lies 
on  the  proximal  portion  of  the  lateral  surface  of  the  iUum. 

(a)  Anterior  Grottp 
■  (Figs.  406,  411) 

The  fan-shaped  iliacus  muscle  arises  from  the  iliac  fossa.  The  fusiform  psoas 
major  muscle  arises  from  the  sides  of  the  last  thoracic  and  of  the  lumbar  vertebrae 
and  extends  along  the  medial  margin  of  the  iliacus  muscle.  The  two  muscles  are 
inserted  by  a  common  tendon  into  the  lesser  trochanter  of  the  femur.  Together 
they  constitute  the  ilio-psoas  muscle.  The  small,  flat,  fusiform  psoas  minor  lies 
on  the  medial  surface  of  the  psoas  major  and  extends  from  the  twelfth  thoracic 
vertebra  to  the  ilio-pectineal  eminence.  The  ilio-psoas  flexes  the  thigh  at  the  hip 
and  the  pelvis  on  the  trunk.     The  psoas  minor  aids  in  flexing  the  pelvis. 

The  ilio-psoas  muscle  arises  in  the  human  embryo  from  a  blastema  which  at  first  surrounds 
the  femoral  nerve  and  later  extends  proximally  over  the  ihum  (iliacus)  and  toward  the  lumbar 
vertebrae  (psoas).  The  iliacus  is  phylogenetically  the  more  primitive.  In  the  shoulder  it  is 
probably  represented  by  the  infraspinatus.  The  psoas  minor  is  much  better  developed  in  many 
of  the  lower  mammals  than  in  man. 

FASCIA 

The  fasciae  and  the  relations  of  these  muscles  are  shown  in  figs.  384  and  407. 

The  iUac  and  psoas  muscles  are  covered  by  a  dense  fascia  which  is  but  sHghtly  adherent 
to  the  underlying  muscles.  It  is  best  developed  in  the  pelvic  region,  where  it  extends  from  the 
iliac  crest  and  ilio-lumbar  ligament  to  the  iliac  portion  of  the  linea  arcuata  and  is  called  the  iliac 
fascia.  Superiorly  it  is  continued  over  the  psoas  muscle  as  the  psoas  fascia  and  is  attached 
medially  to  the  sacrum  and  the  lumbar  region  of  the  spinal  column.  Laterahj'  it  unites  with 
the  lumbar  fascia  and  superiorlj'  it  is  strengthened  to  form  the  medial  lumbo-cosfal  arch  (fig. 
391).  Infiriorly  the  ilio-pectineal  fascia  extends  over  the  iUo-psoas  muscle  to  its  femoral  inser- 
tion. It  is  firmly  united  on  each  side  of  the  muscle  to  the  capsule  of  the  hip-joint  and  to  the 
femur.  As  it  passes  beneath  the  inguinal  ligament  it  is  united  to  this  by  tendinous  processes. 
Beyond  the  ligament  it  is  less  dense  than  in  the  pelvic  region. 

MUSCLES 

The  psoas  major  (figs.  406,  411). — Origin. — (1)  By  a  series  of  thick  fascicuh  from  the  inter- 
vertebral discs  between  the  tweKth  thoracic  and  the  fifth  lumbar  vertebra,  from  the  adjacent 
parts  of  the  bodies  of  these  vertebrae  and  from  tendinous  arches  which  bridge  over  the  middle 
of  the  sides  of  the  first  four  lumbar  vertebrae ;  and  (2)  by  a  series  of  more  slender  fascicuh  from 
the  lower  borders  and  ventral  surfaces  of  the  transverse  processes  of  the  lumbar  vertebrae. 

Structure  and  insertion. — From  these  origins  parallel  fibre-bundles  descend  nearly  vertically 
and  give  rise  to  a  fusiform  muscle  which  hes  at  the  side  of  the  vertebral  bodies  and  extends  along 
the  border  of  the  true  pelvis  toward  its  insertion.  A  tendon  arises  deep  in  the  muscle  near 
the  last  lumbar  vertebra,  and  becomes  free  on  its  dorso-lateral  surface  slightly  above  the  inguinal 
(Poupart's)  ligament.  On  the  medial  side  the  attachment  of  fibre-bundles  continues  to  the 
insertion  of  the  muscle  into  the  small  trochanter.  The  Uiacus  muscle  is  attached  to  the  lateral 
side  of  the  tendon  from  near  the  ilio-pectineal  eminence  downward. 

Nerve-supply. — Delicate  branches  pass  into  the  psoas  muscle  from  the  trunks  which  unite 
to  form  the  femoral  (anterior  crural)  nerve,  i.  e.,  from  the  fourth,  third,  second,  and  often  the 
first  lumbar  nerves. 

The  iliacus  (figs.  406,  411). — Origin. — (1)  From  the  iliac  crest,  the  ilio-lumbar  hgament, 
and  the  greater  part  of  the  iliac  fossa,  the  anterior  sacro-iliac  ligaments,  and  often  from  the 
sacrum,  and  (2)  from  the  ventral  border  of  the  ilium  between  the  two  anterior  spines. 

Structure  and  insertion. — From  these  areas  of  origin  the  fibre-bundles  pass  to  be  inserted — 
(1)  in  a  penniform  manner  on  the  lateral  surface  of  the  tendon  which  emerges  from  the  psoas 
above  the  inguinal  (Poupart's)  ligament,  and  (2)  directly  on  the  femur  immediately  distal  to  the 
small  trochanter.  The  lateral  portion  of  the  muscle  arise  from  the  ventral  border  of  the  ilium 
and  is  adherent  to  the  direct  tendon  of  the  rectus  femoris  and  the  capsule  of  the  hip-joint.  It  is 
sometimes  more  or  less  isolated  (m.  iliacus  minor,  ilio-capsulo-trochantericus,  etc.). 

Nerve-supply. — Nerve  branches,  often  united  in  a  plexiform  manner,  arise  from  the  femoral 
(anterior  crural)  nerve  and  pass  across  the  surface  of  the  Uiacus  muscle  about  midway  between 
the  crest  of  the  ilium  and  the  combined  iUo-psoas  tendon.  Special  nerve  branches  are  usually 
likewise  distributed  from  the  main  trunk  of  the  femoral  nerve  to  the  fleshy  portion  of  the  muscle 
which  extends  over  the  acetabulum  and  the  head  of  the  femur. 

Relations. — The  psoas  major  lies  lateral  to  the  lumbar  vertebrae  and  in  front  of  the  quad- 
ratus  lumborum  and  intertransverse  muscles.  The  psoas  minor  passes  downward  across  its  ventral 
surface.  Both  psoas  muscles  are  crossed  by  the  crura  of  the  diaphragm.  The  kidney  with  its 
adipose  capsule  lies  lateral  to  them  opposite  the  first  two  lumbar  vertebriB.  For  the  rest,  their 
fascia  is  covered  ventro-laterally  by  retro-intestinal  and  retro-peritoneal  tissue  in  which  the 
vena  cava  inferior  runs  in  front  of  them  on  the  right  side,  the  inferior  mesenteric  vein  in  front 
of  them  on  the  left  side,  and  the  ureter,  the  spermatic  or  ovarian,  and  the  renal  and  colic  vessels 
on  each  side.  The  external  iliac  artery  lies  medial  to  the  psoas  major  in  the  pelvis,  and  beyond 
the  inguinal  (Poupart's)  ligament  the  femoral  artery  hes  ventral  to  it.     The  lumbar  plexus  arises 


456 


THE  MUSCULATURE 


between  its  origins  from  the  vertebral  bodies  and  discs  and  those  from  the  transverse  processes. 
The  nerves  springing  from  the  lumbar  plexus  take  courses  subject  to  much  individual  variation 
through  the  muscle  on  the  way  to  their  destinations.  Fasciculi  of  the  muscle  may  thus  be 
separated  by  the  femoral  (anterior  crural)  nerve  or  other  branches  of  the  lumbar  plexus. 

The  iliacus  muscle  in  the  region  of  the  pelvis  is  covered  by  retro-peritoneal  fat.  The  psoas 
muscle  crosses  its  medial  margin  and  from  between  the  two  muscles  the  femoral  nerve  usuaUy 
emerges  to  pass  into  the  thigh  above  the  iliacus.  Beyond  the  inguinal  ligament  the  iliacus  lies 
in  front  of  the  capsule  of  the  hip-joint  and  the  straight  tendon  of  the  rectus  femoris,  and  is 
crossed  by  the  sartorius. 

Fig.  406 — Pscis,  Iliacus,  and  Quadratus  Lumborum. 


Quadratus  lumborum 


■Quadratus  lumborum 


Action. — The  ilio-psoas  is  a  powerful  flexor  of  the  thigh  at  the  hip  and  a  weak  medial 
rotator  and  adductor.     It  also  serves  to  flex  the  lumbar  region  of  the  spine. 

Variations. — The  psoas  muscle  may  be  separated  from  the  Uiacus  as  far  as  the  femoral 
insertion.  The  part  of  the  psoas  arising  from  the  distal  lumbar  vertebrae  may  form  a  distinct 
muscle.  Slips  may  pass  from  the  psoas  major  to  the  psoas  minor.  A  separate  lamina  of  the 
iliacus  muscle  may  be  attached  to  the  iliac  fascia.  From  the  anterior  inferior  iliac  spine  a  small 
muscle  slip  may  run  to  the  intertrochanteric  line  or  the  ilio-femoral  ligament.  To  this  slip  the 
term  iliacus  minor  has  been  applied  as  well  as  to  the  larger  fasciculus  mentioned  above. 

The  psoas  minor  (fig.  406). — Origin. — From  the  twelfth  thoracic  and  first  lumbar  vertebrae 
and  the  intervening  disc. 

Structure  and  insertion. — The  fibre-bundles  pass  to  be  attached  as  far  as  the  level  of  the  fifth 
lumbar  vertebra  to  a  flat  tendon  which  appears  about  the  mid-lumbar  region  and  is  inserted 
into  the  ilio-pectineal  eminence.     It  is  intimately  united  to  the  iUac  fascia. 

Nerve-supply. — The  branch  to  the  psoas  minor  arises  usually  from  the  first  and  second  lum- 
bar nerves,  often  in  company  with  the  genito-femoral  (genito-crural). 

Action. — To  flex  the  pelvis. 

Relations. — It  is  closely  applied  to  the  ventral  surface  of  the  psoas  major. 

Variations. — The  muscle  is  inconstant  in  development  and  is  frequently  absent.  Gruber 
has  found  it  absent  on  both  sides  in  183  out  of  450  bodies,  on  one  side  in  69. 

BuRS^ 

B.  iliopectinea. — A  large  bursa  between  the  ilio-psoas  muscle,  the  ilio-pectineal  eminence, 
and  the  capsule  of  the  hip-joint.  B.  iliaca  subtendinea. — A  small  bursa  between  the  tendon 
of  insertion  of  the  ilio-psoas  and  the  lesser  trochanter. 


FASCIAE  457 

(6)  Posterior  Group 
(Figs.  387,  407,  408,  413) 

The  muscles  of  this  group  arise  from  the  ilium  and  sacrum,  cover  the  dorso- 
lateral surface  of  the  hip,  and  are  inserted  into  the  great  trochanter  and  shaft 
of  the  femur  and  into  the  iho-tibial  band.  They  lie  in  three  planes.  In  the  first 
layer  (fig.  387)  are  the  flat,  quadrilateral  tensor  fasciae  latae,  which  arises  from 
the  front  of  the  crest  of  the  ilium  and  is  inserted  into  the  ilio-tibial  band,  and  the 
thick,  rhomboid  gluteus  maximus,  which  arises  from  the  dorsal  portion  of  the 
ihac  ala,  the  lumbo-dorsal  fascia,  the  sacrum  and  coccyx,  and  the  sacro-tuberous 
(great  sacro-sciatic)  ligament,  and  is  inserted  in  part  into  the  ilio-tibial  bandand 
in  part  into  the  back  of  the  upper  part  of  the  shaft  of  the  femur.  The  ilio-tibial 
band  is  a  flat  tendon  which  descends,  closely  fused  with  the  fascia  lata,  to  the 
lateral  side  of  the  upper  extremity  of  the  tibia.  In  the  second  layer  (fig.  408) 
are  the  flat,  thick,  triangular  gluteus  medius  and  the  'pear-shaped'  piriformis 
The  former  arises  from  the  upper  and  back  part  of  the  outer  surface  of  the  ala  of 
the  ilium,  the  latter  from  the  ventral  surface  of  the  sacrum  and  the  posterior 
border  of  the  great  sciatic  notch.  Both  are  inserted  into  the  top  of  the  great 
trochanter.  The  third  layer  (fig.  409)  is  composed  of  the  triangular  gluteus 
minimus,  which  arises  from  the  inferior  ventral  portion  of  the  outer  surface  of 
the  ala  of  the  ilium,  and  is  inserted  into  the  front  of  the  great  trochanter  of  the 
femur. 

The  muscles  of  this  group  extend,  flex,  abduct,  and  rotate  the  thigh  at  the  hip. 
The  gluteus  maximus  and  medius  are  in  part  extensors,  the  gluteus  minimus 
and  the  tensor  fasciae  latae  are  flexors  of  the  hip-joint.  All  the  muscles  serve  to 
abduct,  the  gluteus  maximus  acting  thus  when  the  hip  is  flexed.  When  the  thigh 
is  extended  the  lower  part  of  the  gluteus  maximus  is  an  adductor.  The  gluteus 
maximus  and  posterior  part  of  the  gluteus  medius  and  the  piriformis  act  as 
lateral,  the  anterior  part  of  the  gluteus  medius,  the  gluteus  minimus,  and  the 
tensor  fasciae  latae  as  medial,  rotators.  The  gluteus  maximus  and  the  tensor 
fasciae  latae  through  the  iho-tibial  band  keep  the  extended  knee-joint  firna. 
The  gluteus  maximus  is  supphed  by  the  inferior  gluteal  nerve,  the  piriformis 
by  special  nerves,  and  the  other  muscles  of  the  group  by  the  superior  gluteal 
nerve.  All  these  nerves  arise  from  the  upper  part  of  the  back  of  the  sacral 
plexus. 

The  gluteus  medius,  gluteus  minimus,  and  piriformis  form  a  group  of  muscles  which  in  the 
embryo  have  a  common  origin  and  are  more  or  less  fused  in  the  adult.  The  gluteus  maximus 
arises  in  two  distinct,  though  associated,  portions,  and  the  tensor  fasciae  latae  as  another^  dis- 
tinct portion.  The  two  muscles,  however,  are  probably  to  be  considered  as  parts  of  a  primitive 
caudo-pelvo-tibial  musculature,  while  the  gluteus  medius  group  is  represented  in  the  lower  forms 
by  an  iho-femoral  musculature.  The  former  group  is  often  closely  associated  with  the  extensor 
muscles  of  the  thigh  in  the  lower  forms  (frog),  and  in  some  of  the  lower  mammals  extends  its 
insertion  to  the  plantar  fascia  (ornithorhynchus).  In  the  arm  this  group  is  perhaps  represented 
by  the  deltoid,  the  latissimus  dorsi,  and  the  teres  major,  while  the  gluteus  medius  group  is 
represented  by  the  subscapularis. 

FASCIA 

The  tela  subcutanea  of  the  gluteal  region  is  very  thick,  contains  much  fat,  and  is  often 
divisible  into  two  layers,  of  which  the  deeper  is  closely  adherent  to  the  fascia  lata  and  through 
this  to  the  gluteus  maximus.  Over  the  great  trochanter  a  subcutaneous  bursa  is  usually  found 
(bursa  trochanterica  subcutanea). 

Muscle  fascia. — The  muscles  of  the  hip  and  thigh  are  enclosed  in  a  dense  fascia,  the  fascia 
lata  (figs.  387,  407).  This  arises  from  the  tuber  isohii,  the  sacro-tuberous  (great  sacro-sciatic) 
ligament,  the  back  of  the  sacrum  and  the  coccyx,  the  crest  of  the  iUum,  the  inguinal  (Poupart's) 
ligament,  and  the  pubic  and  ischial  rami,  and  extends  to  the  tibia  and  the  fascia  covering  the 
muscles  of  the  leg.  It  is  composed  mainly  of  bundles  of  fibres  running  transversely  to  the  long 
axis  of  the  limb.  In  the  region  of  the  gluteal  groove  it  is  strengthened  by  a  transverse  fibrous 
band  which  arises  from  the  tuberosity  of  the  ischium  and  arches  upward  over  the  lower  border 
of  the  gluteus  maximus  muscle. 

In  the  region  of  the  hip  the  fascia  lata  invests  both  surfaces  of  the  tensor  fasciae  latae  and 
the  gluteus  maximus,  and  is  closely  bound  to  these  muscles  through  intramuscular  septa. 
Between  these  two  muscles  the  fascia  covers  the  fascia  of  the  gluteus  medius,  to  which  it  is 
adherent  near  the  ihac  crest,  but  from  which  it  is  sejjarated  by  loose  tissue  more  distally.  Anter- 
iorly the  fascia  is  fused  with  the  IMo-pectineal  fascia  and  the  inguinal  (Poupart's)  ligament. 


458 


THE  MUSCULATURE 


More  distally  the  tendons  of  the  tensor  fasciae  latse  and  of  the  superficial  portion  of  the 
gluteus  maximus  become  incorporated  with  the  deep  surface  of  the  fascia  lata  and  give  rise  to 
the  ilio -tibial  band  [tractus  iliotibialis]. 

Fig.  407,  A  and  B. — Tbansveesb  Sections  through  the  Left  Side  of  the  Pelvis  in  the 
Regions  Indicated  in  the  Diagram. 

C.  Section  through  the  muscles  of  the  left  inguinal  region  parallel  to  the  inguinal  (Poupart's) 
ligament  (after  Spalteholz).  h  in  the  diagram  indicates  Section  B,  fig.  384,  p.  421;  a' 
and  h'  indicate  sections  A  and  B,  fig.  410,  p.  465.     (For  legends,  see  p.  459.) 


The  gluteus  medius  and  minimus  muscles  are  invested  by  adherent  fascial  sheets  which, 
ventrally  between  the  two  muscles,  may  be  combined  into  an  intermuscular  septum  or  be  so 
shghtly  developed  that  the  muscles  are  fused.  The  fascial  sheet  covering  the  gluteus  medius 
toward  the  iliac  crest  is  fused  with  the  deep  surface  of  the  fascia  lata.  This  fusion  results  in  the 
formation  of  septa  between  the  gluteus  medius  and  the  gluteus  maximus  and  tensor  fasciae  latae. 


GLUTEUS  MAXIM  US  459 

The  piriformis  in  the  pelvic  cavity  is  covered  on  the  anterior  surface  by  a  special  slightly 
developed  fascia.  This  fascia  also  covers  the  pelvic  surface  of  the  sacral  plexus.  Outside  the 
pelvis  the  piriformis  is  covered  by  an  adherent  membrane  which  usually  is  separated  by  loose 
tissue  from  the  surrounding  structures. 

MUSCLES 
I.  First  Layer 

The  tensor  fascise  latae  (figs.  387,  411). — Origin. — (1)  By  a  tendinous  band  from  the  external 
lip  of  the  iliac  crest,  and  the  upper  part  of  the  notch  between  the  anterior  superior  and  anterior 
inferior  spines  of  the  ilium,  and  (2)  from  the  septum  between  it  and  the  gluteus  medius. 

Structure  and  insertion. — The  nearly  parallel  fibre-bundles  pass  distally  and  laterally  and  are 
united  to  tendon  fasciculi  which  become  incorporated  with  the  ilio-tibial  band  (traotus  ilio- 
tibiaUs)  about  one-third  of  the  way  down  the  thigh. 

Nerve-supply. — The  superior  gluteal  nerve  sends  a  branch  through  the  ventral  margin  of 
the  gluteus  minimus  to  terminate  in  the  middle  third  of  the  deep  surface  of  the  tensor  fasciae 
latae  near  its  dorsal  border. 

Action. — To  rotate  medially,  flex,  and  abduct  the  thigh,  and  to  make  tense  the  fascia  lata. 

Relations. — It  lies  over  the  gluteus  medius,  the  proximal  part  of  the  rectus  femoris,  and  the 
vastus  laterahs. 

Variations. — It  may  be  divided  into  two  parts,  one  rising  from  the  anterior  superior  spine, 
the  other  from  the  iliac  crest.  Accessory  slips  may  arise  from  the  inguinal  ligament,  the  crest 
of  the  ilium,  or  the  fascia  over  the  lower  part  of  the  abdominal  wall.  Union  of  the  muscle  with 
the  gluteus  maximus  has  been  observed,  thus  making  a  muscle  much  resembling  the  deltoid  of 
the  shoulder.  By  some  the  fascia  lata  between  the  tensor  and  the  gluteus  maximus  is  considered 
an  atrophied  part  of  a  deltoid  of  the  hip. 

The  gluteus  maximus  (figs.  387,  413). — Origin. — (1)  From  the  dorsal  fifth  of  the  outer  lip 
of  the  iliac  crest,  the  outer  surface  of  the  ilium  dorsal  to  the  posterior  gluteal  line,  the  lumbo- 
dorsal  fascia  between  the  posterior  superior  spine  of  the  ilium,  and  the  side  of  the  sacrum,  and 
(2)  from  the  lateral  portions  of  the  fourth  and  fifth  sacral  and  the  coccygeal  vertebrae  and  from 
the  back  of  the  sacro-tuberous  (great  sacro-sciatic)  ligament. 

Insertion. — Into  (1)  the  ilio-tibial  band;  (2)  the  gluteal  tuberosity  of  the  femur  and  the 
adjacent  part  of  the  tendinous  origin  of  the  vastus  lateralis  (fig.  407). 

Structure. — The  large  fibre-bundles  of  which  the  muscle  is  composed  take  a  somewhat 
parallel  course  from  origin  to  insertion.  From  the  areas  of  origin  and  the  enveloping  fascia 
fibrous  bands  extend  into  the  muscle.  The  belly  is  divisible  into  two  portions,  a  superficial  and 
a  deep.  The  division  may  be  much  more  clearly  recognised  in  the  embryo  than  in  the  adult. 
The  superficial  portion  is  the  larger,  and  includes  all  of  that  part  of  the  muscle  which  springs 
from  the  ilium  and  the  more  superficial  portion  of  that  arising  from  the  sacrum  and  the  upper 
part  of  the  coccyx.  The  deep  portion  includes  that  part  of  the  muscle  attached  to  the  side  of 
the  sacrum  and  the  coccyx,  and  to  the  sacro-tuberous  ligament.  The  superficial  portion  and 
some  of  the  fibre-bundles  of  the  deep  portion  terminate  in  the  iho-tibial  band  along  a  line 
extending  from  the  great  trochanter  to  the  end  of  the  upper  third  of  the  femur.  The  deep  por- 
tion is  inserted  chiefly  by  a  flat  tendon  into  the  gluteal  tuberosity,  and  also  directly  into  the 
adjacent  portion  of  the  origin  of  the  vastus  lateralis. 

Nerve-supply. — Two  branches  (inferior  gluteal)  arising  from  the  sacral  plexus  either  separately 
or  united,  are  usually  given  to  the  muscle.  One  of  these  curves  anteriorly  across  the  deep 
surface  of  the  proximal  superficial  portion  of  the  muscle  in  the  middle  third  between  the  tendons 

1.  Acetabulum.     2.  Annulus  femoralis.     3.  Annulus  inguinalis  subcutaneous  (ext.  abdominal 
ring).    4.  Arteria  femorahs.     4a.  A.  profunda  femoris.     46.  A.  ciroumflexa  femoris  medialis. 

5.  A.  glutea  inferior.  6.  A.  hypogastrica  (internal  iliac).  7.  A.  ihaca  externa.  8.  A. 
pudena  interna  (pudic) .  9.  Bursa  iho-peotinea.  10.  B.  trochanterica  m.  glutaei  maximi. 
11.  Eminentia  iliopectinea.  12.  Fascia  iliaca.  13.  F.  ilio-pectinea.  14.  F.  lata — a,  iho- 
tibial  band.  15.  F.  obturatoria.  16.  F.  pectinea.  17.  F.  transversahs.  18.  Femur — a, 
trochanter  major;  b,  trochanter  minor.  19.  Funiculus  spermaticus  (spermatic  cord). 
20. — Lacuna  vasorum.  21.  Ligamentum  ilio-femorale.  22.  L.  inguinale  (Poupart's 
ligament).  23.  L.  lacunare  (Gimbernat's).  24.  L.  saoro-tuberosum  (great  sciatic).  25. 
Musoulus  adductor  brevis.  26.  M.  adductor  longus.  27.  M.  coccygeus.  28.  M.  gemel- 
lus inferior.  29.  M.  gluteus  maximus.  30.  M.  gluteus  medius.  31.  M.  gluteus 
minimus.  32.  M.  iliopsoas — a,  psoas;  6.  iliacus.  33.  M.  levator  ani.  34.  M. 
obliquus  abdominis  externus,  aponeurosis.  35.  M.  obhquus  abdominis  internus. 
36.  M.  obturator  externus.  37.  M.  obturator  internus.  38.  M.  pectineus.  39.  M. 
quadratus  femoris.  40.  M.  rectus  femoris.  41.  iVI.  sartorius.  42.  M.  tensor  fasciaj 
latae.  43.  M.  transversus  abdominis.  44.  M.  transverso-spinales  (multifidus).  45.  M. 
vastus  lateralis.  46.  N.  cutaneus  femoris  anterior  (middle  cutaneous).  47.  N.  cutaneous 
femoris  posterior  (small  sciatic).  48.  N.  femoralis  (anterior  crural).  49.  N.  gluteus 
superior.      50.   N.  ischiadicus  (great  sciatic) — a,  peronaeus  communis  (external  popliteal) ; 

6,  tibialis  (internal  popliteal).  51.  N.  obturatorius.  52.  N.  pudendus.  53.  N.  sacralis 
I.  54.  N.  sacralis  II.  55.  N.  saphenus.  56.  Os  ilium^a,  spina  anterior  superior;  6, 
spina  anterior  inferior.  57.  Os  ischium.  58.  Os  pubis — a,  spina  (tubercle).  59.  Pros- 
tata. 60.  Truncus  lumbo-saeralis.  61.  Vena  femoralis.  62.  V.  saphena  magna.  63. 
V.  iliaca  e.xterna.  64.  V.  hypogastrica  (internal  iliac).  65.  Vertebra  sacralis  I.  66. 
Vertebra  sacralis  II. 


460 


THE  MUSCULATURE 


of  origin  and  insertion,  the  other  descends  to  enter  the  middle  third  of  the  distal  deep  portion 
of  the  muscle. 

Action. — It  is  the  most  powerful  extensor  of  the  thigh.  It  also  serves  slightly  to  rotate  the 
limb  lateralward  and  to  make  tense  the  fascia  lata,  and  through  the  iho-tibial  band  to  keep  the 
extended  knee-joint  steady.  When  the  thigh  is  extended  the  major  part  of  the  muscle  is  an 
adductor  but  the  upper  part  is  a  weak  abductor.  The  whole  muscle  is  an  abductor  when  the 
thigh  is  flexed.     It  is  brought  powerfully  into  play  in  cUmbing  and  in  walking  up  hiU. 


Fig.  408. — The  Lateral  Rotators  and  the  Hamstring  Muscles. 


Gluteus  mediu 
Piriformi 
Gemellus  superior] 
Gemellus  infer: 
Quadratus  femoris 


Obturator  internus 


Gluteus  maximus 


Vastus  lateralis 
Biceps 


Vastus  intermedius 

Short  head  of  biceps 

Plantaris 


Gastrocnemius 


Semi-membranosus 

Sartorius 

Semi-tendinosus 


Relations. — It  is  covered  by  the  fatty  superficial  tissue  of  the  buttock.  It  extends  over  the 
posterior  portion  of  the  ilium,  the  lateral  surface  of  the  sacrum  and  coccyx,  the  sacro-tuberoua 
ligament,  and  the  great  trochanter.  It  covers  the  tuber  of  the  ischium  in  the  standing  but  not 
in  the  sitting  position.  Immediately  beneath  the  muscle  lie  portions  of  the  gluteus  medius, 
piriformis,  obturator  internus,  gemelH,  quadratus  femoris,  obturator  externus,  and  hamstring 
muscles,  and  of  the  gluteal  vessels  and  nerves  and  the  sciatic  nerve. 

Variations. — Few  anomahes  are  recorded.  The  deep  distal  portion  of  the  muscle  may  be 
more  isolated  than  normal  in  the  adult.  A  special  coccygeo-femoral  muscle  may  run  from  the 
coccyx  to  the  Unea  aspera,  or  from  the  sacro-tuberous  ligament  to  the  fascia  of  the  leg.     A 


GLUTEUS  MINIMUS  461 

special  fasciculus,  the  ischio-femoralis,  may  arise  from  the  tuberosity  of  the  ischium  and  become 
inserted  into  the  lower  border  of  the  muscle  near  the  great  trochanter.  The  sacral,  ischial,  or 
coccygeal  origin  may  be  lacking,  or  the  origin  of  the  muscle  may  be  from  the  sacrum  only. 

II.  Second  Layer 

The  muscles  of  this  layer  are  the  gluteus  medius  and  the  piriformis. 

The  gluteus  medius  (fig.  408). — Origin. — From  (1)  the  ventral  three-fourths  of  the  ihac 
crest,  and  the  outer  surface  of  the  ilium  between  the  anterior  and  posterior  gluteal  hnes  and  (2) 
the  investing  fascia. 

Structure  and  insertion. — The  fibre-bundles  converge  upon  both  surfaces  of  a  broad  tendon 
nearly  to  its  insertion  on  an  oblong  impression  on  the  postero-superior  angle  and  the  external 
surface  of  the  great  trochanter.  The  more  posterior  fibre-bundles  of  the  superficial  stratum 
of  the  ventral  portion  of  the  muscle  cross  obliquely  those  of  the  deeper  dorsal  portion  near 
the  tendon  of  insertion.  From  the  tendon  an  aponeurotic  extension  is  usually  continued  into 
the  tendon  of  the  vastus  lateraUs. 

Nerve-supply. — From  the  superior  gluteal  nerve  a  branch  passes  to  the  dorsal  portion  of  the 
muscle  and  one  or  more  twigs  of  the  branch  to  the  tensor  f ascise  latse  enter  the  ventral  portion  of 
the  muscle.  The  branches  enter  the  middle  third  of  the  muscle  between  its  tendons  of  origin 
and  insertion.  The  nerve-fibres  arise  usually  from  the  fourth  and  fifth  lumbar  and  first  sacral 
nerves.  The  branch  to  the  dorsal  portion  of  the  muscle  has  a  lower  spinal  origin  than 
those  to  the  ventral  portion. 

Action. — To  abduct  the  thigh.  The  anterior  portion  of  the  muscle  is  a  flexor  and  a  medial 
rotator,  the  posterior  a  lateral  rotator  and  an  extensor.  When  the  muscle  acts  as  a  whole,  it  is 
a  medial  rotator. 

Relations. — Upon  the  muscle  lie  the  tensor  fasciae  latas  and  gluteus  maximus  muscles  and  the 
fascia  lata;  beneath  it  lie  the  gluteus  minimus  muscle,  the  superior  gluteal  nerve  and  vessels, 
and  the  great  trochanter. 

Variations. — It  may  be  divided  into  two  distinct  portions,  or  it  may  be  fused  with  the 
piriformis  or  the  gluteus  minimus  or  botli.  A  special  fasciculus  may  extend  to  the  superior 
portion  of  the  great  trochanter. 

The  piriformis  (fig.  408). — Origin. — From  (1)  the  lateral  part  of  the  ventral  surface  of  the 
second,  third,  and  fourth  sacral  vertebrae;  (2)  the  posterior  border  of  the  great  sciatic  notch; 
and  (3)  the  deep  surface  of  the  sacro-tuberous  (great  sacro-sciatic)  ligament  near  the  sacrum. 

Structure  and  insertion. — The  fibre-bundles  converge  upon  a  tendon  which  is  inserted  upon 
the  anterior  and  inner  portion  of  the  upper  border  of  the  great  trochanter.  The  insertion  of 
fibre-bundles  continues  nearly  to  the  great  trochanter.  An  accessory  shp  of  insertion  may  pass 
to  the  gluteus  minimus. 

Nerve-supply. — From  a  nerve  which  arises  either  directly  from  the  first  or  second  sacral 
nerve  or  from  a  loop  between  them.  The  nerve  enters  the  deep  surface  of  the  muscle  in  its 
middle  third.     There  may  be  two  or  more  nerves. 

Action. — It  is  an  extensor,  abductor,  and  lateral  rotator  of  the  thigh.  It  causes  medial  rota- 
tion when  the  hip  is  flexed. 

Relations. — Its  ventral  surface  faces  the  sacral  plexus,  the  rectum,  and  the  hip-joint.  It  is 
covered  dorsaUy  by  the  gluteus  maximus.  It  hes  between  the  gluteus  medius  and  the  superior 
gemellus.  Between  the  piriformis  and  the  superior  gemellus  the  sciatic  nerve  usually  passes 
into  the  thigh.  The  superior  gluteal  nerve  and  vessels  pass  dorsall}'  above  its  superior  margin; 
the  inferior  nerve  and  vessels  beneath  its  inferior  margin. 

Variations. — It  is  rarely  absent.  The  origin  may  extend  to  the  first  sacral  or  to  the  fifth 
sacral  vertebra  and  the  coccyx.  It  may  be  fused  with  the  gluteus  medius  or  minimus  or  more 
rarely  with  the  superior  gemellus.  Its  tendon  of  insertion  may  be  fused  with  that  of  the  gluteus 
medius  or  the  obturator  internus.  In  about  20  per  cent,  of  bodies  it  is  divided  partly  or  com- 
pletely into  two  portions,  between  which  the  sciatic  nerve  or  its  peroneal  (external  popliteal) 
division  usually  passes.  Rarely  the  tibial  instead  of  the  peroneal  portion  may  pass  between  the 
two  fascicuh,  or  the  muscle  may  be  divided  into  three  or  more  fasciculi,  between  which  the 
branches  of  the  sciatic  nerve  pass. 

III.  Third  Layer 

The  gluteus  minimus  (fig.  409). — Origin. — From  the  outer  surface  of  the  ilium  between 
the  anterior  and  inferior  gluteal  lines;  (2)  from  the  septum  between  it  and  the  gluteus  medius 
near  the  anterior  superior  ihac  spine;  and  (3)  from  the  capsule  of  the  hip-joint. 

Structure  and  insertion. — The  fibre-bundles  converge  upon  a  tendon  which  appears  on  the 
middle  of  the  ventral  border  and  gradually  spreads  over  the  lateral  surface.  The  muscle  is 
thickest  in  front,  where  it  is  usually  bound  by  an  intermuscular  septum  to  the  gluteus  medius. 
The  tendon  is  inserted  into  the  ventral  surface  of  the  great  trochanter  of  the  femur. 

Nerve-supply. — From  twigs  of  the  branch  of  the  superior  gluteal  nerve  which  goes  to  the 
tensor  fasciae  latae.  These  twigs  enter  the  middle  third  of  the  muscle  as  the  tensor  branch  passe.i 
across  it. 

Action. — -To  abduct  the  thigh  and  rotate  it  medialward.  The  anterior  part  of  the  muscle 
is  a  flexor,  the  posterior  an  extensor. 

Relations. — It  is  covered  by  the  gluteus  medius  and  piriformis  muscles.  Beneath  it  lie  the 
inferior  part  of  the  iliac  ala,  the  hip-joint  (to  the  capsular  ligament  of  which  it  is  bound),  and  the 
direct  tendon  of  the  rectus  femoris  muscle. 

Variations. — It  may  be  fused  with  the  gluteus  medius  or  the  piriformis.  It  vaay  send  a 
slip  to  the  fascia  lata  or  the  vastus  lateralis.     It  may  be  divided  into  two  distinct  divisions, 


462 


THE  MUSCULATURE 


an  anterior  and  a  posterior.  Very  frequently  from  the  anterior  margin  of  the  muscle  a  special 
fasciculus  is  more  or  less  isolated  (the  scansorius,  invertor  femoris,  small  anterior  gluteal,  etc.). 
The  accessorius  of  the  gluteus  minimus  is  a  small  muscle  fasciculus  which  may  lie  under  cover 
of  the  gluteus  minimus  and  extend  to  be  inserted  into  the  capsule  of  the  hip-joifit. 

BuRS^ 

B.  ischiadica  m.  glutei  maximi. — A  small  inconstant  bursa  between  the  tuber  ischii  and 
the  gluteus  maximus  muscle.     B.  trochanterica  m.  glutei  maximi. — A  large  bursa  constantly 


Fig.  409 — The  Deep  Muscles  of  the  Back  op  the  Thigh. 


Gluteus  minimus- 


Obturator  externus 


Gluteus  maximus 


Vastus  lateral! 
Short  head  of  biceps 


Vastus  intermedius- 


Tendon  of  biceps- 


Obturator  internus 


Adductor  magnus 


Vastus  medialis 


present  between  the  fascial  tendon  of  the  gluteus  maximus  and  the  posterior  lateral  surface 
of  the  great  trochanter  and  the  origin  of  the  vastus  lateralis  muscle.  B.  gluteofemorales. — 
Two  or  three  small  burste  on  each  side  of  the  tendon  of  attachment  of  the  gluteus  maximus  to 
the  femur.  B.  trochanterica  m.  glutei  medii  anterior. — A  small  bursa  constantly  present 
between  the  tendon  of  the  gluteus  medius  muscle  and  the  lateral  surface  of  the  great  trochanter. 
B.  trochanterica  m.  glutei  medii  posterior. — A  small  bursa  frequently  present  between  the 
tendons  of  the  piriformis  and  the  gluteus  medius.  B.  trochanterica  m.  glutei  minimi. — A 
fairly  large  bursa  generally  present  between  the  margin  of  the  great  trochanter  and  the  tendon 
of  this  muscle.  B.  m.  piriformis. — A  small  bursa  frequently  present  between  the  tendons  of 
the  piriformis  and  superior  gemellus  muscles  and  the  femur. 


OBTURATOR  INTERNUS  463 

2.    ISCHIO-PUBO-FEMORAL  MUSCULATURE  OF  THE  HiP 

The  muscles  belonging  to  this  group  (the  obturator  internus,  the  two  gemelli, 
the  quadratus  femoris  and  the  obturator  externus,  extend  from  the  pubis  and 
ischium  across  the  back  of  the  hip-joint  to  the  great  trochanter  and  the  neigh- 
bouring part  of  the  shaft  of  the  femur.  They  are  powerful  lateral  rotators  of 
the  thigh.  The  obturator  internus  (fig.  409),  a  large,  flat,  triangular  muscle, 
arises  from  the  pelvic  surface  of  the  innominate  bone  and  from  the  obturator 
membrane.  At  the  lesser  sciatic  notch  its  tendon  is  joined  by  the  two  gemelli 
(fig.  408),  one  of  which  arises  on  each  side  from  the  bony  projections  which  make 
the  notch,  and  the  combined  tendon  is  inserted  into  the  trochanteric  (digital) 
fossa.  The  quadratus  femoris  (fig.  408)  passes  from  the  tuber  of  the  ischium  to 
the  femur  behind  and  below  the  great  trochanter.  These  muscles  are  supplied 
by  special  nerves  which  arise  from  the  front  of  the  sacral  plexus  and  enter  the 
deep  surfaces  of  the  muscles.  A  fifth  muscle,  attached  to  the  greater  trochanter 
and  associated  with  this  group,  the  obturator  externus,  is  differentiated  near  the 
adductor  muscles  of  the  thigh  and  is  supplied  by  a  branch  from  the  obturator 
nerve.  It  arises  from  the  outer  surface  of  the  bones  bounding  the  ventral  two- 
thirds  of  the  obturator  foramen  and  is  inserted  by  a  tendon  into  the  trochanteric 
(digital)  fossa. 

These  muscles  seem  to  have  no  certain  representatives  in  the  arm,  where  the  shoulder-ioint 
is  entirely  ensheathed  by  the  dorsal  musculature.  It  is  possible  that  the  pectoral  group  has  a 
corresponding  embryonic  origin.  The  group  is  represented,  with  marked  variations,  in  the  lower 
extremities  of  amphibia  and  aU  higher  vertebrates. 

FASCIA 

Within  the  pelvis  the  obturator  internus  hes  on  the  obturator  membrane.  It  is  covered 
by  the  obturator  fascia,  which  is  attached  to  the  body  of  the  pubis,  to  the  iliac  portion  of  the 
arcuate  line,  to  tlie  ventral  margin  of  the  great  sciatic  notch,  to  the  ischial  spine,  to  the  sacro- 
tuberous  (great  sacro-sciatic)  ligament,  and  with  the  falciform  process  of  that  Ugament,  to  the 
ischial  and  pubic  rami.  Near  the  upper  part  of  the  obturator  foramen  the  fascia  instead  of  being 
attached  to  bone  is  reflected  over  the  muscle  and  attached  to  the  obturator  membrane.  It  here 
helps  to  bound  the  canal  for  the  obtiu-ator  vessels  and  nerve.  The  upper  part  of  the  fascia  lies 
beneath  the  pelvic  peritoneum  and  the  levator  ani.  The  lower  part  forms  the  outer  boundary  of 
the  ischio-rectal  fossa.  The  fascia  is  continued  as  a  thin,  adherent  membrane  over  the  obturator 
internus  and  the  gemellus  muscles  to  their  attachment.  The  quadratus  femoris  is  invested  by 
a  thin  adherent  fascial  sheet. 

MUSCLES 

The  obturator  internus  (fig.  409). — Origin. — From  (1)  the  pelvic  surface  of  the  pubic  rami 
near  the  obturator  foramen;  (2)  the  pelvic  surface  of  the  iscliium  between  the  foramen  and  the 
great  sciatic  notch;  (3)  the  deep  surface  of  the  obturator  internus  fascia;  (4)  the  fibrous  arch 
which  bounds  the  canal  for  tlie  obturator  vessels  and  nerve;  and  (5)  the  pelvic  surface  of  the 
obturator  membrane  except  in  the  lower  part. 

Structure  and  insertion. — From  this  extensive  area  of  origin  the  fibre-bundles  converge 
toward  the  lesser  sciatic  notch  and  become  applied  to  the  broad  tendon  of  insertion.  At  the 
notch  the  muscle  curves  laterally  and  extends  outward  and  upward  to  its  insertion  into  the  fore 
part  of  the  trochanteric  fossa  of  the  femur.  The  tendon  is  formed  of  five  or  six  bands  which 
begin  high  in  the  muscle  and  converge  into  a  common  tendon  situated  on  the  deep  surface 
of  the  muscle  as  the  latter  curves  about  the  ischium.  The  tendon  bands  at  first  throw  the  ten- 
don into  folds  which  run  in  ridges  in  the  fibro-cartilage  which  lines  the  notch.  The  attachment 
of  fibre-bundles  continues  upon  the  dorsal  surface  of  the  tendon  to  half  way  between  the  lesser 
sciatic  notch  and  the  great  trochanter. 

Nerve-supply. — A  special  nerve  to  the  obturator  internus  arises  from  the  front  of  the  sacral 
plexus,  usually  from  the  lumbo-sacral  cord  and  the  first  and  second  sacral  nerves.  This  nerve 
passes  lateral  to  the  sacro-spinous  (lesser  sciatic)  ligament,  then  re-enters  the  pelvis  through 
the  lesser  sciatic  notch  and  sends  out  branches  of  distribution  on  the  pelvic  surface  of  the  obtu- 
rator internus. 

Action. — This  muscle  with  its  two  companions,  the  gemelli,  is  a  powerful  lateral  rotator 
of  the  thigh.     It  is  also  an  extensor  and  abductor  when  the  thigh  is  bent  at  a  right  angle. 

Relations. — The  chief  pelvic  relations  have  been  described  in  connection  with  the  obturator 
fascia  which  completely  covers  the  medial  surface  of  the  muscle.  The  muscle  passes  out  be- 
tween the  two  sacro-ischial  (sacro-sciatic)  ligaments.  Outside  the  pelvis  the  gemellus  muscles 
run  on  each  side  of  the  tendon,  which  is  here  closely  applied  to  the  capsule  of  the  joint.  Dorsal 
to  it  lie  the  gluteus  maximus,  the  sacro-tuberous  (great  sacro-sciatic)  ligament,  the  inferior 
gluteal  (sciatic)  vessels,  and  the  sciatic  and  posterior  cutaneous  nerves.  The  nerve  of  the  quad- 
ratus femoris  runs  beneath  the  obturator  internus  and  gemellus  muscles. 

Variations. — It  varies  in  the  extent  of  its  insertions.     It  may  be  divided  into  two  parts, 


464  THE  M  USC  ULA  T  URE 

a  pubic  and  an  ischial.  Fasciculi  may  be  sent  to  the  postero-inferior  part  of  the  ilio-pectineal 
eminence,  the  tendon  of  the  psoas  minor,  the  tuber  ischii,  the  sacro-tuberous  (great  sacro-sciatic) 
ligament,  the  ischial  spine,  etc. 

The  gemellus  superior  (fig.  408). — Origin. — From  the  outer  surface  of  the  ischial  spine 
and  the  neighbouring  edge  of  the  lesser  sciatic  notch. 

Structure  and  insertion. — The  fibre-bundles  encircle  the  upper  border  and  ventral  aspect  of 
the  tendon  of  the  obturator  internus.  They  are  inserted  into  the  upper  border  of  this  tendon, 
and  sometimes  also  into  the  trochanteric  fossa. 

Nerve-supply. — From  a  small  nerve  which  arises  either  directly  from  the  plexus  or  as  a 
branch  of  the  nerve  to  the  obturator  internus  or  of  that  to  the  quadratus  femoris.  This  nerve 
usually  enters  the  deep  surface  of  the  muscle  near  the  junction  of  its  ischial  and  middle  thirds. 

Action. — It  is  essentially  a  part  of  the  obturator  internus. 

Relations. — It  hes  between  the  piriformis  and  the  tendon  of  the  obturator  internus.  Proxi- 
mally  it  adjoins  its  fellow  beneath  this  tendon;  distally,  the  two  gemeUi  enclose  the  tendon  in  a 
musculo-tendinous  sheath. 

Variations. — It  may  be  wanting  or  may  have  a  more  extensive  origin  than  usual.  It 
may  be  joined  to  the  piriformis  or  to  the  gluteus  minimus  or  be  joined  more  closely  than  usual 
to  the  obturator  tendon. 

The  gemellus  inferior. — Origin. — From  the  upper  part  of  the  inner  border  of  the  tuberosity 
of  the  ischium,  the  sacro-tuberous  (great  sacro-sciatic)  ligament  and  from  the  neighbouring  edge 
of  the  lesser  sciatic  notch. 

Structure  and  insertion. — The  fibre-bundles  converge  upon  the  inferior  border  of  the  tendon 
of  the  obturator  internus,  and  are  inserted  by  tendon-fibres  into  this  or  into  the  great  trochanter 
below  the  obturator  internus  tendon. 

Nerve-supply. — From  a  branch  of  the  nerve  to  the  quadratus  femoris.  This  branch  enters 
the  deep  sm-face  of  the  muscle  near  the  junction  of  the  ischial  with  the  middle  third. 

Action. — -It  is  essentially  a  part  of  the  obturator  internus. 

Relations.— \t  lies  between  the  quadratus  femoris  and  the  tendon  of  the  obturator  internus. 

Variations. — It  is  rarely  absent.  It  may  be  joined  to  the  quadratus  femoris.  It  is  fre- 
quently closely  bound  up  with  the  obturator  internus.     It  may  be  doubled. 

The  quadratus  femoris  (fig.  408)  .^rOrijin. — From  the  upper  part  of  the  outer  border  of  the 
tuber  of  the  ischium. 

Structure  and  insertion. — The  fibre-bundles  take  a  nearly  parallel  course  and  are  inserted 
into  the  vertical  ridge  which  terminates  above  on  the  inferior  dorsal  angle  of  the  great  trochanter. 

Nerve-supply. — ^From  a  nerve  which  arises  usually  from  the  lumbo-sacral  cord  and  the  first 
sacral  nerve  and  passes  under  the  gemelli  and  the  tendon  of  the  obturator  internus.  The  nerve 
enters  the  deep  surface  of  the  muscle  near  the  junction  of  the  ischial  and  middle  thirds. 

Action. — It  is  a  powerful  lateral  rotator  and  a  weak  adductor  of  the  thigh. 

Relations. — -It  is  covered  by  the  gluteus  maximus.  Between  this  muscle  and  the  quadratus 
femoris  runs  the  sciatic  nerve.  The  obturator  externus  muscle  lies  in  front.  The  inferior 
gemellus  extends  along  its  superior  border.     The  adductor  minimus  adjoins  it  distally. 

Variations. — It  is  absent  in  from  1  to  2  per  cent,  of  instances.  (Schwalbe  and  Pfitzner.) 
It  may  be  double  near  its  femoral  insertion.  It  may  be  fused  with  the  inferior  gemellus  or  the 
adductor  magnus.     It  may  send  a  fasciculus  to  the  semimembranosus. 

The  obturator  externus  (figs.  407,  409). — Origin. — From  the  lateral  surface  of  the  pubic 
and  ischial  rami,  where  they  bound  the  obturator  foramen,  and  from  the  surface  of  the  obtu- 
rator membrane. 

Structure  and  insertion. — ^Often  the  muscle  is  distally  divided  into  three  fasciculi,  a  superior 
from  the  superior  pubic  ramus,  a  middle  from  the  inferior  pubic  ramus  and  the  obturator  mem- 
brane, and  an  inferior  from  the  ischium.  The  fibre-bundles  converge  upon  a  tendon  which  is  at 
first  deeply  buried,  then  appears  on  the  lateral  surface  of  the  muscle  and  is  continued  as  a 
rounded  tendon  over  the  capsule  of  the  joint  to  its  insertion  into  the  dorsal  part  of  the  trochan- 
teric fossa. 

Nerve-supply. — -The  obturator  nerve  gives  rise,  usually  in  the  obturator  canal,  to  a  branch 
which  bifurcates  to  enter  the  superior  border  and  ventral  surface  of  the  muscle  in  its  middle 
third. 

Action. — It  is  a  powerful  lateral  rotator  of  the  thigh  and  is  also  a  weak  adductor. 

Relations. — It  is  covered  by  the  pectineus,  the  ilio-psoas,  and  the  adductor  magnus  muscles 
in  front,  and  by  the  quadratus  femoris  behind  near  its  insertion.  It  covers  over  the  obturator 
membrane.     The  obturator  nerve  passes  either  above  the  muscle  or  through  its  upper  portion. 

Variations. — The  reported  variations  are  few.  It  may  be  joined  by  a  slip  from  the  ad- 
ductor brevis. 

BURS^ 

B.  m.  obturatoris  interni. — A  fairly  large  bursa  constantly  present  between  the  tendon  of 
the  obturator  internus  muscle  and  the  lesser  sciatic  notch.  It  may  extend  on  each  side  be- 
neath the  gemellus  muscles.  B.  m.  quadrati  femoris. — A  small  bursa  frequently  found  between 
this  muscle  and  the  small  trochanter.  B.  m.  obturatoris  externi. — A  bursa  is  sometimundes  of 
between  the  tendon  of  this  muscle  and  the  capsule  of  the  joint. 

B.  MUSCLES  OF  THE  THIGH 

In  the  thigh  three  groups  of  muscles  may  be  recognised,  an  anterior  or  ex- 
tensor (figs.  411,  412),  a  medial  or  adductor  (figs.  409,  411,  412),  and  a  posterior, 
flexor  or  hamstring  group  (figs.  408,  413). 


MUSCLES  OF  THIGH 


465 


Fig.  410,  A-D. — Transverse  Sections  through  the  Left  Thigh  in  the  Regions  indicated 
IN  the  Diagram. 


466  THE  MUSCULATURE 

In  the  proximal  part  of  the  thigh  the  anterior  group  of  muscles  is  separated 
from  the  medial  group  by  the  ilio-psoas  muscle  (fig.  411)  and  by  the  femoral 
blood-vessels  and  nerve,  and  from  the  posterior  group  by  the  gluteus  maximus 
(fig.  413).  More  distally  it  is  separated  from  the  medial  group  by  the  medial 
intermuscular  septum  and  from  the  posterior  by  the  lateral  intermuscular  septum 
(see  p.  468).  The  medial  and  posterior  groups  are  closely  associated.  The 
adductor  magnus  belongs  ontogenetically  to  both. 

The  three  groups  of  muscles,  with  numerous  modifications,  are  represented  in  the  thighs 
of  amphibia  and  all  higher  vertebrates.  In  the  human  arm  they  are  likewise  represented,  the 
adductor  group  in  a  much  reduced  form  by  the  coraco-brachialis.  The  quadriceps  is  represented 
by  the  triceps  in  the  arm,  the  long  head  of  the  triceps  corresponding  with  the  rectus  femoris. 
The  hamstring  muscles  are  represented  by  the  biceps  and  the  braohiahs. 

FASCIA 

The  fascise  and  the  relations  of  the  musculature  of  the  thigh  may  be  followed  in  the  cross- 
sections  figs.  407,  410,  414. 

The  tela  subcutanea  of  the  thigh  varies  considerably  in  thickness  in  different  regions, 
but  is  well  developed  throughout  and  contains  a  considerable  amount  of  fat.  Over  the  front 
of  the  thigh,  especially  in  the  upper  medial  region,  one  or  more  deeper  membranous  layers 
may  usually  be  separated  from  the  superficial  adipose  layer.  Between  the  former  and  the 
latter  are  situated  the  inguinal  lymphatic  nodes  and  the  saphenous  vein.  The  deepest  layer 
near  the  inguinal  (Poupart's)  Ugament  is  fused  with  the  fascia  lata  (see  below).  Medially  it 
is  attached  to  the  pubic  arch.  Thus  fluids  beneath  the  tela  subcutanea  of  the  abdomen  and 
perineum  do  not  readily  pass  into  the  region  of  the  thigh. 

Over  the  lower  half  of  the  patella  a  'subcutaneous  bursa  (b.  praepatellaris  subcutanea)  is 
found.  Another  is  usually  found  over  the  upper  end  of  the  patellar  ligament  (b.  infrapatellaris 
subcutanea). 

The  muscles  of  the  thigh  are  enclosed  in  a  dense  fascial  sheet,  the  fascia  lata  (figs.  387,  410). 
The  gluteal  portion  of  this  and  the  ilio-tibial  band  have  already  been  described  (p.  457).  The 
ventral  portion  of  the  fascia,  composed  chiefly  of  transverse  fibres,  is  a  dense,  fibrous  membrane. 
Above  it  is  attached  to  the  inguinal  Hgament  from  the  anterior  superior  spine  to  the  pubic 
tubercle.  Below  it  extends  over  the  knee,  where  it  is  united  to  the  capsule  of  the  joint  and  is 
strengthened  by  expansions  from  the  vastus  lateraUs  and  mediahs.  Between  the  front  of  the 
patella  and  the  fascia  is  a  bursa  (b.  praspatellaris  subfascialis).  Above  the  knee  the  fascia  is 
strengthened  by  an  arciform  process  which  extends  obliquely  distally  across  the  fascia  from  the 
ilio-tibial  band  to  the  capsule  of  the  knee.  This  gives  rise  to  a  fold  in  the  skin  when  the  leg  is 
extended  and  the  muscles  are  not  tense.  Over  the  medial  and  posterior  regions  of  the  thigh 
the  fascia  is  less  dense.  It  extends  from  the  body  and  inferior  ramus  of  the  pubis,  the  inferior 
ramus  and  tuber  of  the  ischium,  and  the  sacro-tuberous  ligament  into  the  fascia  of  the  back 
of  the  leg.  Above  the  popUteal  space  it  is  strengthened  by  a  transverse  band  of  fibres.  Near 
the  knee  the  tendons  of  the  quadriceps,  sartorius,  gracihs,  and  semitendinosus  become  bound 
to  the  fascia  by  membranous  laminse. 

The  relations  of  the  fascia  lata  to  the  inguinal  ligament  and  the  iliac  fascia  are  somewhat 
complex.  The  fascia  of  the  ilio-psoas  muscle  extends  over  the  muscle  to  its  femoral  insertion. 
Above  the  inguinal  ligament  this  fascia  is  called  the  fascia  iliaca;  below  the  ligament,  the  fascia 
ilio-pectinea.  This  fascia  is  firmly  united  to  the  lateral  extremity  of  the  inguinal  ligament. 
The  pectineus  muscle  is  likewise  invested  with  a  fascial  membrane  which  extends  over  the 
muscle  from  the  pubis  to  the  femur  and  is  fused  laterally  with  that  of  the  ilio-psoas.  This 
combined  fascia  is  firmly  bound  between  the  two  muscles  to  the  ilio-pectineal  eminence.  The 
ilio-pectineal  fascia  divides  the  space  beneath  the  inguinal  ligament  into  a  lateral  lacuna 
musculorum,  which  contains  the  iUo-psoas  muscle  and  the  femoral  (anterior  crural)  nerve,  and 
a  medial  lacuna  vasorum,  which  contains  the  femoral  artery  and  vein.  Medial  to  the  vein 
is  the  femoral  ring,  bounded  medially  by  the  lacunar  (Gimbernat's)  ligament.  This  is  closed 
off  from  the  abdominal  cavity  by  a  septum  derived  from  the  transversahs  fascia,  the  femoral 
septum,  but  offers  passage  for  lymph-vessels. 

a  and  6  in  the  diagram  indicate  the  regions  through  which  pass  sections  A  and  B,  fig.  407  (p.  458) ; 
1.  Arteria  circumflexa  femoris  lateralis.  2.  A.  circumflexa  femoris  medialis.  3.  A.  fem- 
oraUs.  4.  A.  femoralis  profunda.  5.  A.  glutea  inferior  (sciatic).  6.  A.  poplitea.  7.  Bursa 
praepatellaris  subfascialis.  8.  Adductor  (Hunter's)  canal.  9.  Fascia  lata.  10.  Femur — a, 
distal  extremity.  11.  Funiculus  spermaticus  (spermatic  cord).  12.  Musculus  adductor 
brevis.  13.  M.  adductor  longus.  14.  M.  adductor  magnus.  15.  M.  biceps  femoris — a, 
long  head;  b,  tendon  of  origin;  c,  short  head.  16.  M.  gastrocnemius — a,  lateral  head;  b,  medial 
head.  17.  M.  gluteus  maximus.  18.  M.  gracihs — a,  tendon.  19.  M.  rectus  femoris — a, 
tendon.  20.  M.  sartorius.  21.  M.  semimembranosus — a,  tendon.  22.  M.  semitendinosus 
• — a,  tendon.  23.  M.  sphincter  ani.  24.  M.  vastus  intermedins  (orureus) — a,  tendon.  25. 
M.  vastus  lateralis — a,  tendon.  26.  M.  vastus  medialis — a,  tendon.  27.  Nervus  cutaneous 
femoris  anterior.  28.  N.  cutaneous  femoris  posterior  (small  sciatic).  29.  N.  gluteus  inferior. 
30.  N.  obturatorius — a,  superficial  branch;  b,  deep  branch.  31.  N.  peroneus  communis 
(external  popliteal).  32.  N.  saphenus  (great  saphenous).  33.  N.  tibialis  (internal  pophteal). 
34.  Patella.  35.  Septum  intermusculare  laterale.  36.  Septum  intermusculare  mediale.  37. 
Tractus  iliotibialis  (ilio-tibial  band).  38.  Vena  femoralis.  39.  Vena  poplitea.  40.  V. 
saphena  magna  (great  saphenous  vein). 


FASCIA 


467 


Beyond  the  inguinal  ligament  the  fasciae  of  the  ilio-psoas  and  pectineal  muscles  line  a 
triangular  space,  the  ilio-pectineal  fossa,*  through  which  run  the  femoral  vessels  (fig.  407). 
The  sartorius  muscle  partly  overlies  the  distal  lateral  margin  of  this  fossa.  The  fascia  lata  is 
here  reflected  from  the  surface  of  the  sartorius  to  the  ilio-psoas  fascia,  and  becomes  fused  with 
it.  From  the  medial  margin  of  the  sartorius  a  process  of  the  fascia  is  continued  over  the  lateral 
and  upper  part  of  the  fossa,  and  is  attached  to  the  inguinal  and  lacunar  (Gimbernat's)  liga- 

FiG.  411. — Muscles  of  the  Front  op  the  Thigh. 


Adductor  brevis. 


Adductor  longus 


Adductor  magnus 


Vastus  medians 


Tendon  of  sartorius' 


Gluteus  medius 


Gluteus  minimus 
Tensor  fascia  latat 


Rectus  femoris 


Ilio-tibial  band 


Vastus  lateralis 


Ligamentum  patellse 


ments  (fig.  389).  Over  the  lower  extremity  of  the  fossa  a  process  is  continued  medially  into 
the  pectineal  fascia.  On  the  medial  margin  of  the  fossa  the  fascia  lata  is  continued  directly 
into  the  pectineal  fascia.  The  lateral  concave  margin  of  the  fascia  overlying  the  fossa  is  called 
the  falciform  margin;  the  upper  extremity  of  this,  the  superior  cornu;  the  distal  extremity,  the 
inferior  cornu.  The  oval  space  bounded  by  the  margo  falciformis  is  called  the  fossa  ovalis 
(saphenous  opening).     This  is  covered  by  the  fascia  cribrosa,  which  some  consider  a  deep  layer 

*  This  lies  within  Scarpa's  Iriangle  [trigonum  femorale],  a  space  bounded  by  the  inguinal 
(Poupart's)  ligament  and  the  sartorius  and  long  adductor  muscles. 


468  THE  MUSCULATURE 

of  the  tela  suboutanea  and  others  a  portion  of  the  fascia  lata.  This  fascia  cribrosa  contains 
many  openings  for  the  passage  of  blood-vessels  and  lymphatics.  The  space  which  lies  medial 
to  the  femoral  vessels  between  the  femoral  ring  and  the  fossa  ovahs  is  called  the  femoral  canal 
(crural  canal). 

From  the  fascia  intermuscular  septa  descend  in  between  the  underlying  muscles.  Of 
these,  the  medial  and  lateral  intermuscular  septa  are  the  best  marked  (fig.  410). 

The  lateral  intermuscular  septum  separates  the  extensor  muscles  from  the  hamstring 
group.  It  extends  from  the  tendon  of  the  gluteus  maximus  to  the  lateral  epicondyle.  It  is 
composed  chiefly  of  longitudinal  fibres  and  is  thickest  distaUy.  The  vastus  lateraUs  is  united 
to  its  ventro-lateral  surface;  the  short  head  of  the  biceps,  to  its  dorso-medial  surface. 

It  will  be  noted  that  this  septum  serves  to  divide  primarily  ventral  from  primarQy  dorsal 
musculature,  with  the  exception  of  the  short  head  of  the  biceps,  which,  though  primarily  dorsal, 
occupies  a  position,  perhaps  secondarily  acquhed,  with  the  primarily  ventral  muscles. 

The  medial  intermuscular  septum  serves  to  divide  the  anterior  extensor  from  the  medial 
adductor  musculature.  It  is  perhaps  simplest  in  the  region  immediately  distal  to  the  ilio- 
pectineal  fossa  (fig.  410  B).  Here  a  well-marked  septum  may  be  seen  extending  to  the  femur 
between  the  sartorius  and  quadriceps  on  the  one  side,  and  the  adductor  longus  and  brevis  on 
the  other.  The  septum  here,  next  the  muscles,  has  on  each  side  a  membranous  lamina.  Be- 
tween the  two  laminae  there  is  a  looser  tissue  in  which  run  blood-vessels  and  nerves.  A  fibrous 
membrane  extends  between  the  rectus  and  sartorius  to  the  septum. 

More  distally  the  sartorius  comes  to  overlie  the  septum  (fig.  410  C).  The  sheath  of  the 
sartorius  on  the  lateral  margin  becomes  fused  with  the  fascia  of  the  vastus  mediahs,  and  on 
the  medial  margin  to  a  membrane  that  covers  the  ventral  surfaces  of  the  adductor  longus  and 
magnus.  Beneath  the  sartorius  and  between  the  adductor  longus  and  the  vastus  medialis  is  a 
triangular  space  bounded  by  the  sheaths  of  these  muscles,  and  fiUed  with  a  loose  areolar  tissue 
in  which  run  the  chief  blood-vessels  of  the  thigh.  This  space,  first  described  by  John  Hunter, 
is  known  as  Hunter's  canal,  or  the  adductor  canal.  Still  more  distally  the  vessels  with  their 
surrounding  fibrous  tissue  pass  through  the  hiatus  tendinous,  between  the  long  tendon  of  the 
adductor  magnus  and  the  femur,  to  the  back  of  the  thigh.  The  septum  here  passes  behind  the 
posterior  surface  of  the  vastus  medialis  to  the  femur. 

MUSCLES 

1.  The  Anterior  Group 

(Figs.  411,  412) 

This  group,  which  forms  a  semi-conical  mass  pointed  upward,  is  composed  of 
the  quadriceps  femoris  and  the  sartorius  muscles,  innervated  by  the  femoral 
nerve. 

The  sartorius  is  a  long,  ribbon-like  muscle  which  arises  from  the  anterior 
superior  spine  of  the  ilium  and  extends  along  the  medial  margin  of  the  quadriceps, 
passing  obliquely  across  the  upper  part  of  the  thigh,  and  then  descending  to  the 
dorse-medial  side  of  the  knee,  whence  its  tendon  curves  forward  to  be  inserted 
into  the  ventro-medial  surface  of  the  superior  extremity  of  the  tibia. 

The  quadriceps  femoris  is  composed  of  four  muscles  differentiated  from  a  com- 
mon embr3'onic  origin.  Of  these,  the  rectus  femoris,  which  arises  from  the 
ventro-lateral  margin  of  the  ilium  by  two  tendons,  is  the  most  superficial  and 
the  most  completely  differentiated.  The  vastus  lateralis,  which  arises  from  the 
superior  e.xtremity  of  the  ventral  surface  of  the  shaft  of  the  femur  and  from  the 
lateral  lip  of  the  linea  aspera;  the  vastus  medialis,  which  arises  from  the  medial 
lip  of  the  linea  aspera  and  from  the  intertrochanteric  line;  and  the  vastus  inter- 
medius  (crureus),  which  arises  between  these  two  and  beneath  the  rectus  from  the 
surface  of  the  femur,  are  less  distinctly  differentiated  from  one  another.  The 
vastus  intermedius  and  vastus  laterahs  are  partly  fused  at  the  insertion,  the 
intermedins  and  medialis  at  their  origins.  From  the  four  muscles  arises  a  tendon 
which  is  inserted  into  the  tuberosity  of  the  tibia.  In  this  tendon,  which  is 
closely  applied  to  the  capsule  of  the  knee-joint,  lies  a  sesamoid  bone,  the  patella. 

The  sartorius  and  the  rectus  flex  the  thigh;  the  quadriceps  extends 
the  leg;  the  sartorius  flexes  the  leg  and  rotates  the  thigh  lateralward  and  the 
leg  medialward. 

In  the  embryo  the  sartorius  has  an  origin  distinct  from  that  of  the  quadriceps.  In  the 
anthropoid  apes  it  is  much  more  developed  than  in  man. 

In  addition  to  supplying  the  muscles  of  this  group,  the  femoral  nerve  also  gives  branches 
to  the  iliaous  muscle  (p.  4.55)  and  the  pectineus  muscle  (p.  472). 

The  sartorius  (fig.  411). — Origin. — From  the  anterior  superior  spine  of  the  iUum  and  the 
area  immediately  below  this. 

Insertion. — Into  the  medial  surface  of  the  tibia  near  the  tuberosity  and  into  the  neighbour- 
ing fascia  of  the  leg. 


SARTORIUS 


469 


Structure. — The  muscle  arises  by  short  tendinous  strands.  The  fibre-bundles  take  a  nearly 
parallel  course.  The  component  muscle-fibres  are  said  to  be  the  longest  in  the  body.  Near  the 
medial  epicondyle  of  the  femur  the  tendon  of  insertion  makes  its  appearance  on  the  deep  as- 
pect of  the  muscle.  On  the  superficial  surface  of  the  tendon  the  muscle-fibres  are  inserted 
as  far  as  the  distal  margin  of  the  knee-joint.  From  there  the  tendon  turns  forward  to  its 
insertion. 

Nerve-supply. — Usually  two  branches  enter  the  deep  surface  of  the  proximal  third  of  the 
sartorius.     One  or  both  of  them  may  be  bound  up  with  an  anterior  cutaneous  nerve  passing 

Fig.  412. — The  Deep  Muscles  of  the  Front  op  the  Thigh. 


Obturator  externus 


Adductor  longu: 


Adductor  magnu£ 


Adductor  longus 
Vastus  intermedius 


Vastus  mediali! 


Rectus  femoris 


Ligamentum  patellae 


Rectus  tendon 


Gluteus  medius 
[—  Gluteus  minimus 


Adductor  brevis 


Vastus  lateralis 


Biceps 


Ilio-tibial  band 


through  the  muscle.  The  first  of  the  branches  is  distributed  chiefly  to  the  lateral  and  proximal, 
the  second  to  the  medial  and  distal,  portions  of  the  muscle.  Within  the  muscle  is  a  complex 
plexus. 

Action. — (1)  To  flex  the  thigh  at  the  hip,  abduct  and  rotate  it  lateralward;  (2)  to  flex  the  leg 
and  rotate  it  slightly  medialward;  (3)  to  make  tense  the  medial  part  of  the  fascia  lata. 

Relations. — The  sartorius  lies  in  a  fascial  canal  bounded  by  the  fascia  lata  and  by  inter- 
muscular septa  which  descend  from  this.     It  crosses  the  rectus  femoris,  ilio-psoas,  the  adductor 


d70  THE  MUSCULATURE 

longus  and  magnus,  and  the  vastus  medialis  muscles,  the  femoral  vessels  and  nerve,  and  the 
knee-joint.     At  its  insertion  its  tendon  covers  the  gracilis  and  semitendinosus. 

Variations. — It  may  arise  from  the  inguinal  ligament  or  be  inserted  into  the  fascia  lata, 
the  medial  epicondyle,  or  the  capsule  of  the  knee-joint.  It  may  be  longitudinally  divided  into 
two  parts.  The  tendon  of  the  secondary  slip  is  in  such  instances  usuaOy  attached  to  the  capsule 
of  the  knee-joint,  but  sometimes  is  attached  to  the  fascia  over  the  vastus  medialis  or  to  the 
anterior  wall  of  the  adductor  canal.  More  frequently  the  muscle  is  partly  divided  proximally 
or  distaUy.  The  secondary  tendon  of  origin  may  arise  from  the  anterior  inferior  spine,  the 
ilio-pectineal  eminence,  etc.  The  muscle  is  very  rarely  absent.  It  may  be  crossed  by  a  ten- 
dinous inscription,  or  more  rarely  it  is  rendered  digastric  by  an  intervening  tendon. 

The  quadriceps  femoris  (figs.  411,  412). — This,  as  pointed  out  above,  is  composed  of  the 
rectus  femoris  and  the  vastus  lateralis,  intermedins,  and  medialis. 

The  rectus  femoris  (fig.  411). — Origin. — By  two  tendons.  The  anterior  'straight'  tendon 
is  attached  to  the  anterior  inferior  spine  of  the  ilium;  the  posterior  'reflected'  tendon  to  the 
postero-superior  surface  of  the  rim  of  the  acetabulum.  The  two  tendons  unite  so  as  to  form 
a  small  arch  above  the  capsule  of  the  joint. 

Structure  and  insertion. — From  this  arch  an  aponeurotic  expansion  descends  upon  the  front 
of  the  muscle  nearly  to  the  middle  of  the  thigh.  This  expansion  is  broad  above,  becomes 
narrower  as  it  descends,  and  is  continued  a  short  distance  as  a  narrow  intramuscular  tendon 
after  it  disappears  from  the  surface.  The  tendon  of  insertion  begins  on  the  back  of  the  muscle 
above  the  middle  of  the  thigh,  expands  into  a  broad  aponeurosis,  and  finally  becomes  a  strong 
band  which  is  inserted  into  the  proximal  border  of  the  patella.  The  fibre-bundles  pass  in  a  bi- 
penniform  manner  from  the  back  and  sides  of  the  tendon  of  origin  to  the  front  and  sides  of  the 
tendon  of  insertion. 

Nerve-swpply. — As  a  rule,  two  branches  enter  the  muscle.  One  of  these  enters  the  deep 
surface  of  the  muscle  in  its  upper  fourth,  and  is  distributed  mainly  to  the  proximal  part  of  the 
lateral  half.  The  other  enters  the  medial  margin  of  the  muscle  near  the  junction  of  the  proxi- 
mal and  middle  thirds,  and  is  distributed  chiefly  to  the  medial  half  and  distal  portion  of  the 
muscle. 

The  vastus  lateralis  (vastus  externus)  (fig.  412). — Origin. — From — (1)  the  shaft  of  the 
femur  along  the  antero-inferior  margin  of  the  great  trochanter  and  in  front  of  the  gluteal  tuber- 
osity; and  (2)  the  lateral  intermuscular  septum  along  the  upper  half  of  the  linea  aspera. 

Insertion. — By  a  flat  tendon  into — (1)  the  proximo-lateral  border  of  the  patella;  and  (2)  the 
front  of  the  lateral  condyle  of  the  tibia  and  the  fascia  of  the  leg. 

Structure. — The  fibre-bundles  arise  partly  from  the  bone,  partly  from  an  aponeurosis  which 
covers  the  proximal  two-thirds  of  the  muscle,  and  from  the  lateral  intermuscular  septum.  They 
take  a  parallel  course  distally  in  a  ventro-medial  direction,  and  are  inserted  into  an  aponeurosis 
which  lies  on  the  deep  surface  of  the  muscle  and  receives  fibres  until  within  a  few  centimetres 
of  the  patella.  Ventrally  this  aponeurosis  fuses  with  the  rectus  tendon,  laterally  with  that  of 
the  vastus  medialis,  and  dorsally  it  receives  some  of  the  fibre-bundles  of  the  vastus  intermedins. 
Commonly  the  muscle  is  distinctly  divisible  for  the  greater  part  of  its  course  into  two  sheets, 
a  superficial  and  a  deep.     The  deep  sheet  is  often  subdivided  into  two  laminae. 

NerBe-supply. — Usually  there  are  three  nerves,  one  of  which,  accompanied  by  blood-vessels, 
runs  on  the  inner  surface  of  the  superficial  sheet  midway  between  the  tendons  of  origin  and 
insertion,  the  second  between  the  two  laminae  of  the  deep  layer,  and  the  third  passes  through 
the  innermost  lamina  to  be  distributed  in  part  to  the  vastus  intermedins  (crureus)  muscle. 

The  vastus  medialis  (vastus  internus)  (fig.  412). — Origin. — From  the  whole  extent  of  the 
medial  lip  of  the  linea  aspera  and  from  the  distal  half  of  the  intertrochanteric  line.  The  origin 
takes  place  by  means  of  an  aponeurosis  which  is  adherent  to  the  tendons  of  insertion  of  the 
adductor  muscles. 

Structure  and  insertion. — The  fibre-bundles  arise  from  the  deep  surface  of  this  aponeurosis 
and  are  inserted  on  the  medial  surface  and  margin  of  a  tendon  which  begins  on  the  deep  surface 
of  the  muscle  about  its  middle  near  the  lateral  margin.  On  the  distal  lateral  border  of  the 
muscle  it  is  inserted  into  the  medial  half  of  the  proximal  margin  of  the  patella  and  into  the 
medial  condyle  of  the  tibia  and  the  fascia  of  the  leg.  For  some  distance  near  the  knee  the 
lateral  margin  of  the  tendon  is  united  to  those  of  the  vastus  intermedins  (crureus),  lateralis 
(externus)  and  the  rectus. 

Nerve-supply. — The  nerve  to  this  muscle  descends  on  its  medial  surface,  often  bound  up 
with  the  saphenous  nerve  for  a  part  of  its  course.  It  gives  off  successive  branches  and  finally 
sinks  into  the  muscle  substance.  These  branches  enter  about  midway  between  the  origin  and 
insertion  of  the  fibre-bundles  of  the  muscle. 

The  vastus  intermedins  (crureus)  (figs.  409,  412). — Origin. — From  (1)  the  distal  half  of  the 
lateral  margin  of  the  linea  aspera  and  its  lateral  bifurcation;  (2)  the  antero-lateral  siu'face  of  the 
shaft  of  the  femur.  Between  the  origin  of  the  vastus  intermedins  (crureus)  and  that  of  the 
vastus  medialis  the  shaft  of  the  femui'  is  free  from  muscle  attachment. 

Structure  and  insertion. — On  the  ventral  surface  of  the  muscle  lies  an  aponeurosis  which 
extends  from  its  proximal  fourth  to  the  proximal  margin  of  the  patella.  The  fibre-bundles  of 
the  muscle  are  inserted  into  the  deep  surface  of  this  and  into  the  deep  surface  of  the  aponeurosis 
of  insertion  of  the  vastus  lateralis.  The  proximal  fibre-bundles  descend  vertically,  the  medial 
and  lateral,  especially  the  latter,  obliquely  to  their  insertion.  Medially  the  tendon  is  more  or 
less  fused  with  that  of  the  vastus  medialis,  and  laterally  with  that  of  the  vastus  lateralis.  The 
muscle  is  composed  of  muscle  lamelto  superimposed  concentrically  about  the  shaft  of  the  femur. 
The  deepest,  most  distal  of  these  is  called  the  articularis  genu  (subcrureus).  The  fibre-bundles 
of  this  layer  are  inserted  into  the  capsule  of  the  joint  or  into  the  superior  margin  of  the  pateUa. 

Nerve-supply. — Several  branches  are  usually  distributed  to  this  muscle.  To  the  lateral 
region  a  branch  from  the  nerve  to  the  vastus  lateralis  is  usually  given;  to  the  middle  of  the 
muscle  another  branch  descends  from  the  femoral  (anterior  crural)  nerve;  to  the  medial  portion 
there  extend  several  twigs  from  the  nerve  to  the  vastus  medialis. 


ADDUCTOR  MUSCLES  471 

Tendon  of  the  quadriceps. — The  quadriceps  tendon  may  be  more  or  less  distinctly  divided 
into  layers,  of  which  the  superficial  layer  belongs  to  the  rectus,  the  deep  to  the  vastus  inter- 
medins, and  the  intermediate  to  the  vastus  lateralis  and  medialis.  Some  of  the  more  superficial 
fibres  of  the  tendons  of  the  two  vasti,  however,  cross  in  front  of  the  rectus  tendon.  The  com- 
bined tendon  of  the  quadriceps  is  in  part  attached  to  the  superior  and  lateral  margins  of  the 
patella,  and  in  part  extends  over  the  patella  into  the  patellar  ligament.  A  part  of  the  tendon 
fibres  of  the  vastus  laterahs  and  medialis  run  on  each  side  of  the  patella  to  the  ventral  surface  of 
the  condyles  of  the  tibia.  These  form  the  retinacula  patellse  mediate  and  laterale.  The  medial 
is  the  broader  and  better  developed.  With  the  retinacula  are  included  bundles  of  fibres  which 
run  from  the  epicondyles  to  the  patella  and  into  which  some  muscle  fibre-bundles  are  inserted. 
From  the  apex  of  the  patella  to  the  tuberosity  of  the  tibia  the  quadriceps  tendon  is  continued 
as  the  patellar  ligament  (fig.  415). 

Nerve-supply. — The  relations  of  the  branches  of  distribution  to  the  various  parts  of  the 
muscle  have  been  pointed  out  above  in  connection  with  each  head.  The  general  relations  of 
these  branches  of  the  femoral  nerve  are  as  follows: — From  the  femoral  nerve  near  the  proximal 
end  of  the  vastus  medialis  the  branches  for  the  vastus  lateralis,  vastus  intermedins  (crureus),  and 
rectus  pass  distally  and  laterally  between  the  rectus  and  vastus  intermedins  (crureus)  to  be 
distributed  to  the  muscles  named,  while  the  chief  nerve  for  the  vastus  mediahs  descends  on  the 
medial  side  of  this  muscle  in  company  with  the  saphenous  nerve.  The  branches  to  the  vastus 
lateralis  and  intermedins  are  commonly  bound  up  in  a  single  nerve-trunk  for  some  distance. 
The  branches  to  the  rectus  are  usually  bound  up  with  this  trunk  for  a  shorter  distance.  The 
nerve  to  the  vastus  medialis  may  be  united  to  this  trunk  for  a  slight  distance,  but  more 
frequently  it  is  more  or  less  bound  up  with  the  saphenous  nerve. 

Action. — The  quadriceps  is  the  extensor  of  the  leg.  The  rectus  femoris  also  flexes  the  thigh 
at  the  hip  and  is  a  weak  abductor  of  the  thigh.  The  articularis  genu  makes  tense  the  capsule 
of  the  knee-joint. 

Relations. — The  quadriceps  is  covered  ventrally  immediately  by  the  fascia  lata.  The 
sartorius  runs  along  its  medial  margin;  the  tensor  fasciee  latse  lies  over  the  proximal  quarter 
of  its  lateral  surface.  Dorsal  to  the  vastus  lateralis  lie  the  gluteus  maximus  and  biceps;  dorso- 
medial  to  the  vastus  medialis,  the  three  adductor  muscles  and  the  semimembranosus.  Next 
the  vastus  medialis  lies  the  adductor  canal  with  the  femoral  vessels  and  the  saphenous  nerve. 

Variations. — The  variations  of  this  muscle,  aside  from  a  greater  or  less  fusion  of  its  parts, 
are  not  marked.  The  attachment  of  the  rectus  femoris  to  the  anterior  inferior  spine,  which 
takes  place  in  the  embryo  later  than  its  insertion  above  the  acetabulum,  may  be  wanting.  On 
the  other  hand,  this  tendon  may  extend  to  the  anterior  superior  spine.  Occasionally  the  deep 
reflected  tendon  may  be  wanting.  The  rectus  accessorius  is  a  fasciculus  rarely  found,  which 
arises  by  a  tendon  from  the  rim  of  the  acetabulum  and  is  inserted  into  the  ventral  edge  of  the 
vastus  lateralis.     It  is  innervated  by  a  twig  from  the  branch  to  the  rectus. 

BURS^ 

B.  m.  recti  femoris  (superior). — A  small  bursa  between  the  deep  tendon  of  the  rectus 
femoris  and  the  edge  of  the  acetabulum.  Rare.  B.  m.  recti  femoris  (inferior). — Between 
the  tendon  of  the  rectus  and  the  combined  tendon  of  the  vastus  lateralis  and  medialis.  Oc- 
casional. B.  praepatellaris  subtendinea. — A  bursa  between  the  tendon  of  the  quadriceps 
and  the  periosteum  of  the  patella.  Of  the  three  prepatellar  bursK — the  subcutaneous,  sub- 
fascial, and  subtendinous — as  a  rule  only  one  occurs.  When  two  or  three  exist,  they  usually 
communicate  freely  with  one  another.  B.  suprapatellaris. — A  bursa  between  the  anterior 
surface  of  the  lower  end  of  the  femur  and  the  tendon  of  the  quadriceps.  It  usually  communi- 
cates with  the  joint  cavity.  B.  infrapatellaris  profunda. — A  bursa  between  the  patellar  liga- 
ment and  the  tibia.  It  seldom  communicates  with  the  joint  cavity.  B.  m.  sartorii  propria. 
— A  bursa,  fairly  large,  between  the  tendon  of  the  sartorius  and  the  tendons  of  the  semitendi- 
nosus  and  gracilis  muscles.     This  usually  communicates  with  the  bursa  anserina  (see  p.  474). 

2.  The  Medial  (Adductor)  Group 

(Figs.  409,  411,  412) 

To  this  group  of  muscles  belong  the  gracilis,  the  pectineus,  the  adductors  brevis, 
longus,  and  magnus,  and  the  obturator  externus.  The  most  superficial  of  the 
group  is  the  gracilis  (figs.  408,  411).  This  ribbon-shaped  muscle  arises  from  the 
inferior  pubic  and  ischial  rami,  extends  along  the  medial  side  of  the  thigh,  and 
gives  rise  to  a  tendon  which  curves  forward  from  behind  the  medial  condyle  of 
the  femur  to  be  inserted  under  the  tendon  of  the  sartorius  into  the  medial  side  of 
the  upper  extremity  of  the  tibia.  The  quadrilateral  pectineus  arises  from  the 
body  and  superior  ramus  of  the  pubis;  the  triangular  adductor  longus  from  the 
superior  ramus  medial  to  this  (fig.  411).  The  pectineus  is  inserted  into  the 
pectineal  line  of  the  femur;  the  adductor  longus  into  the  middle  third  of  the  linea 
aspera.  The  triangular  adductor  brevis  (fig.  412)  arises  from  the  inferior  pubic 
ramus  below  the  adductor  longus.  It  is  inserted  into  the  pectineal  line  and  the 
upper  third  of  the  linea  aspera.  The  large,  triangular  adductor  magnus  (figs. 
409,  412)  arises  from  the  inferior  ramus  and  the  tuber  of  the  ischium  and  is 


472  THE  MUSCULATURE 

inserted  behind  the  short  and  long  adductors  into  the  whole  length  of  the  linea 
aspera,  and  by  a  special  tendon  into  the  adductor  tubercle  of  the  femur.  The 
deepest  muscle  of  the  group,  the  obturator  externus,  which  arises  from  the  outer 
surface  of  the  bones  bounding  the  ventral  two-thirds  of  the  obturator  foramen, 
and  is  inserted  by  a  tendon  into  the  trochanteric  (digital)  fossa,  has  been  described 
in  connection  with  the  ischio-pubo-femoral  muscles  of  the  hip. 

All  the  muscles  of  this  group  adduct  the  thigh.  The  gracilis,  obturator  ex- 
ternus, adductor  brevis  and  the  lower  part  of  the  adductor  magnus  (when  the 
thigh  is  extended)  rotate  it  lateralward.  The  pectineus,  adductor  longus,  and 
the  adductor  magnus  rotate  it  medialward.  Those  attached  to  the  pubis  flex 
the  thigh.  The  gracilis  flexes  the  leg  and  rotates  it  medialward.  The  inferior 
part  of  the  adductor  magnus  extends  the  thigh. 

The  muscles  of  this  group  are  supplied  by  the  obturator  nerve,  except  the 
pectineus,  which  usually  gets  its  whole  supply  from  the  femoral  (anterior  crural) 
nerve,  and  the  adductor  magnus,  which  gets  a  part  of  its  supply  from  the  sciatic 
nerve. 

In  embryonic  development  the  pectineus  arises  in  close  conjunction  with  the  obturator 
group,  and  in  the  adult  it  may  get  the  wliole  or  a  part  of  its  nerve-supply  from  the  obturator 
nerve  or  from  the  accessory  obturator  nerve.  In  the  lower  mammals  the  nerve-supply  may 
come  from  the  femoral  (anterior  crural)  or  the  obturator  nerve  or  from  both.  It  is  not  certain 
whether  the  innervation  from  the  femoral  nerve  indicates  that  the  muscle  belongs  phylo- 
genetically,  if  not  ontogenetically,  with  the  primitive  dorsal  musculature  of  the  limb.  By 
some  it  is  considered  to  be  derived  in  part  from  the  primitive  dorsal,  in  part  from  the  primitive 
ventral,  musculature.  The  adductor  magnus  arises  in  the  embryo  as  two  distinct  portions,  one 
connected  with  the  flexor  group  of  muscles,  the  other  with  the  adductor  group.  These  two 
portions  later  become  fused.  Primitively  the  sciatic  portion  of  the  adductor  magnus  and  the 
semimembranosus  constitute  a  single  medial  flexor  muscle. 

The  gracilis  (figs.  408,  411). — Origin. — By  a  flat  tendon  from  the  medial  margin  of  the 
inferior  ramus  of  the  pubis  and  the  pubic  extremity  of  the  inferior  ramus  of  the  ischium. 

Structure  and  insertion. — The  nearly  parallel  fibre-bundles  which  arise  between  two  laminse 
of  the  tendon  form  a  thin  band  of  muscle  which  is  narrower  and  thicker  distaUy  than  proximally. 
They  are  inserted  on  a  tendon  which  begins  as  an  aponeurosis  on  the  posterior  border  and  medial 
surface  of  the  muscle  in  the  distal  third  of  the  thigh,  becomes  free  as  a  rounded  cord  a  little 
proximal  to  the  medial  condyle  of  the  femur,  runs  behind  the  condyle,  and  then  turns  forward 
to  be  inserted  by  an  expanded  process  into  the  tibia  below  the  medial  condyle. 

Nerve-supply. — The  nerve  enters  the  deep  surface  of  the  muscle  near  the  junction  of  the 
superior  and  middle  thirds. 

Action. — To  adduct,  flex  and  (sUghtly)  rotate  the  thigh  lateralward,  and  flex  the  leg. 
With  the  knee  flexed,  it  acts  as  a  medial  rotator  of  the  leg. 

Relations. — It  occupies  a  position  beneath  the  fascia  lata  and  superficial  to  the  adductor 
brevis,  longus,  and  magnus  muscles.  DistaUy  the  sartorius  lies  in  front,  the  semimembranosus 
behind.  Its  tendon  crosses  the  tibial  collateral  Ugament  of  the  knee-joint  and  the  tendons 
of  the  semitendinosus  and  the  semimembranosus,  and  is  overlapped  by  that  of  the  sartorius. 

Variations. — The  pubic  Origin  of  the  muscle  may  be  much  reduced  or  may  be  double. 
Its  tendon  of  insertion  may  give  rise  to  an  accessory  fasciculus  which  extends  distaUy  in  the 
leg.     In  some  of  the  apes  the  tendon  descends  normally  much  farther  down  the  leg  than  in  man. 

The  pectineus  (fig.  411.) — Origin. — (1)  From  the  peoten  (crest)  of  the  os  pubis,  the  bone 
in  front  of  this,  and  the  pectineal  fascia  near  this  origin;  and  (2)  from  the  anterior  margin  of 
the  obturator  sulcus  and  from  the  pubo-capsular  hgament.  Laterally  the  two  areas  of  origin 
are  usually  separated  by  most  of  the  superior  surface  of  the  body  of  the  pubis.  Medially _they 
come  together. 

Structure  and  insertion. — From  each  area  of  origin  a  separate  lamina  arises.  The  fibre- 
bundles  of  each  layer  take  a  nearly  parallel  course  and  terminate  between  two  tendinous  lameUfe 
which  fuse  to  be  inserted  into  the  upper  half  of  the  pectineal  line  behind  the  small  trochanter. 
The  fibre-bundles  of  the  superficial  layer  cross  those  of  the  deep  slightly  obliquely.  The  muscle 
faces  ventraUy  at  its  origin,  laterally  at  its  insertion. 

Nerve-supply. — From  a  branch  of  the  femoral  (anterior  crural)  nerve,  which  passes  behind 
the  femoral  artery  and  vein  and  through  the  pectineal  fascia  to  enter  the  ventral  surface  of  the 
muscle.  It  may  also  be  supplied  by  the  accessory  obturator  nerve,  when  present,  or  by  a  branch 
from  the  obturator.  When  both  the  femoral  (anterior  crura!)  and  obturator  nerves  supply  this 
muscle,  the  femoral  supphes  the  superficial,  the  obturator,  the  deep  lamina  (Paterson). 

Action. — To  flex  and  adduct  the  thigh  (as  in  crossing  the  legs). 

Relations. — It  is  covered  by  the  pectineal  fascia,  lies  between  the  ilio-psoas  and  the  adductor 
longus  muscles,  and  crosses  the  obturator  externus  and  adductor  brevis  muscles.  The  medial 
circumflex  artery  runs  between  it  and  the  ilio-psoas,  the  deep  femoral  artery  between  it  and  the 
adductor  longus. 

Variations. — The  extent  of  the  division  of  the  pectineus  into  superficial  and  deep  portions 
varies  considerably.  It  may  also  be  divided  into  a  lateral  and  a  medial  division.  Often  the 
pectineus  is  fused  with  the  adductor  longus.  It  may  receive  an  accessory  fasciculus  from  the 
capsule  of  the  hip-joint,  the  iliacus  muscle,  the  obturator  externus,  or  the  adductor  brevis 
muscles,  or  the  small  trochanter.     It  may  send  a  fasciculus  to  the  sartorius. 

The  adductor  longus  (fig.  411). — Origin. — From  the  medial  corner  of  the  superior  ramus 


ADDUCTOR  LONGUS 


473 


of  the  pubis  by  a  strong  tendon  which  extends  for  some  distance  on  the  medial  border  of  the 
Structure  and  insertion. — From  this  tendon  the  fibre-bundles  diverge  toward  then-  insertion. 
Fig.  413. — Superficial  Muscles  op  the  Back  of  the  Thigh  and  Leg. 


Gluteus  medius- 


Fascial  insertion  of  gluteus  maximus" 


-Gluteus  maximus 


"Semi-membranosus 


Vastus  lateralis- 


Gastrocnemius- 


"Semi-tendinosus 


"Gracilis 

-Tendon  of  semi-membranosus 


Peroneus  longus" 


-Flexor  digitorum  longus 


■'Tendo  Achillis 


This  takes  place  between  two  lamellae  of  a  short  tendon  attached  to  the  middle  third  of  the  linea 
aspera.  The  tendon  is  usually  fused  to  the  medial  intermuscular  septum  and  sends  an  expansion 
to  the  long  tendon  of  the  adductor  magnus. 


474  THE  MUSCULATURE 

Nerve-supply. — A  branch  from  the  anterior  division  of  the  main  obturator  trunk  gives  off 
several  twigs  which  enter  the  middle  third  of  the  deep  surface  of  the  muscle.  Occasionally  a 
small  branch  from  the  femoral  (anterior  crural)  nerve  enters  the  muscle.  This  is  probably 
sensory  in  nature. 

Action. — To  adduct  and  flex  the  thigh,  and  rotate  it  medialward. 

Relations. — The  sartorius,  the  vastus  medialis,  and  the  femoral  vessels  he  antero-lateral 
to  it.  Behind  it  lie  the  adductor  brevis  and  adductor  magnus  muscles.  Between  these  and 
the  longus  run  the  profunda  vessels.  Its  lateral  border  touches  the  pectineus  above,  but  is 
separated  from  it  toward  the  insertion. 

Variations. — It  may  be  fused  with  the  other  adductors,  including  the  pectineus.  It  may 
be  doubled.     The  femoral  insertion  may  extend  to  the  medial  epioondyle. 

The  adductor  brevis  (fig.  412). — Origin. — From  the  medial  part  of  the  outer  surface  of  the 
inferior  ramus  of  the  pubis  directly,  and  by  means  of  short  tendinous  processes  or  a  short  flat 
tendon. 

Structure  and  insertion. — From  their  origin  the  fibre-bundles  diverge  into  a  sheet  which  is 
inserted  by  short  tendinous  bands  into  the  distal  two-thirds  of  the  pectineal  line  and  the  upper 
third  of  the  hnea  aspera.  The  muscle  is  more  or  less  completely  divided  into  two  fasoiouU  near 
its  insertion.  The  place  of  division  is  near  where  the  intertrochanteric  fine  curves  away  from 
the  linea  aspera. 

Nerve-supply. — Usually  from  the  anterior  but  also  sometimes  from  the  posterior  branch 
of  the  main  obturator  trunk.  The  rami  enter  the  middle  third  of  the  muscle  near  the  proximal 
border. 

Action. — It  is  chiefly  an  adductor  and  to  a  less  extent  a  flexor  and  a  lateral  rotator  of  the 
thigh. 

Relations. — In  front  he  the  pectineus  and  adductor  longus;  behind,  the  obturator  externus 
quadratus  femoris  and  adductor  magnus.  It  is  crossed  by  the  profunda  artery.  The  first 
perforating  artery  passes  usually  between  the  two  fasciouh  of  the  insertion. 

Variations. — It  may  be  fused  with  other  members  of  the  group.  It  may  be  divided  com- 
pletely into  two  fasciculi,  rarely  into  three. 

The  adductor  magnus  (figs.  409,  412). — The  origin  of  this  muscle  begins  on  the  inferior 
ramus  of  the  pubis  posterior  to  the  origins  of  the  adductor  brevis  and  gracilis  muscles.  From 
here  it  extends  backward  along  the  inferior  margin  of  the  ventro-lateral  surface  of  the  ischium 
to  the  tuberosity.  The  muscle  in  passing  from  this  curved  origin  to  its  extensive  femoral  in- 
sertion presents  posteriorly  a  longitudinal  groove  in  which  rest  the  hamstring  muscles.  The 
adductor  magnus  is  composed  of  three  superimposed  fasciculi,  of  which  the  first  is  frequently 
fairly  distinct  and  is  called  the'.adductor  minimus,  while  the  other  two  are  normally  fused,  but 
are  occasionally  distinct. 

The  superior  fasciculus  (adductor  minimus)  arises  directly  from  the  inferior  rami  of  the 
pubis  and  ischium.  From  here  the  fibres  diverge  to  form  a  thin  sheet  inserted  by  tendinous 
bands  to  the  medial  side  of  the  gluteal  ridge  and  the  superior  part  of  the  hnea  aspera.  The 
middle  fasciculus  arises  dii'ectly  from  the  inferior  margin  of  the  ventro-lateral  surface  of  the 
inferior  ramus  and  the  tuber  of  the  ischium,  and  from  a  tendon  which  descends  along  the  dorso- 
medial  margin  of  the  muscle  from  the  tuber  ischti.  The  fibre-bundles  diverge  to  be  inserted 
between  the  lamellae  of  a  narrow  flat  tendon  attached  to  the  distal  three-fourths  of  the  linea 
aspera.  This  tendon  is  pierced  by  the  perforating  vessels.  The  inferior  fasciculus  arises 
dorsal  to  and  in  common  with  the  middle  fasciculus.  The  fibre-bundles  converge  toward  a 
strong  tendon  which  begins  in  the  distal  third  of  the -thigh  and  is'inserted  into  a  tubercle  at  the 
distal  end  of  the  medial  supracondylar  ridge. 

Nerve-supply. — The  chief  nerve-supply  is  from  the  posterior  ramus  of  the  obturator. 
This  enters  by  one  or  more  branches  the  proximal  portion  of  the  ventral  surface  of  the  muscle 
about  midway  between  its  pubic  and  femoral  attachments.  It  also  receives  a  branch  from 
the  sciatic  which  enters  the  dorsal  surface  of  the  muscle  in  the  middle  third  of  the  thigh.  To 
the  adductor  minimus  a  branch  may  be  sent  from  the  nerve  to  the  quadratus  femoris. 

Action. — It  is  the  strongest  of  the  adductors.  The  superior  and  middle  fasciculi  rotate 
the  thigh  medialward  and  flex  it;  the  inferior  rotate  it  lateralward  when  the  thigh  is  extended, 
but  medialward  when  the  thigh  is  flexed.     The  latter  also  extend  the  thigh. 

Relations. — In  front  are  the  pectineus,  the  short  and  long  adductor  and  the  vastus  medialis 
muscles,  and  the  profunda  artery.  Behind  lie  the  hamstring  muscles  and  the  gluteus  maximus. 
Medially  lies  the  gracilis  muscle.  The  femoral  and  perforating  arteries  pass  through  its  attach- 
ment to  the  shaft  of  the  femur. 

Variations. — The  divisions  of  the  muscle  may  be  more  or  less  distinct.  It  may  be  partly 
fused  or  exchange  fasciculi  with  neighbouring  muscles — the  semimembranosus,  quadratus 
femoris,  adductor  brevis,  and  adductor  longus. 

BxmsM 

B.  m.  pectinei. — A  small  bursa  frequently  present  between  this  muscle  and  the  iUo-psoas 
and  small  trochanter.  B.  anserina. — A  fairly  large  bursa  which  lies  between  the  tendons  of 
the  sartorius,  gracUis,  and  semitendinosus  muscles  and  the  tibial  collateral  hgament  of  the  knee- 
joint.     (See  also  B.  M.  Sartorii  Propria,  p.  471.) 

3.  The  Posterior  (Hamstring)  Group 

(Figs.  408,  413) 

The  muscles  of  this  group  are  the  semitendinosus,  semimembranosus,  and 
biceps.     They  flex  the  leg  and  extend  and  adduct  the  thigh.     The  semitendinosus 


HAMSTRING  GROUP  475 

and  semimembranosus  rotate  the  thigh  and  the  leg  medialward;  the  biceps, 
lateralward.  The  semitendinosus  and  the  long  head  of  the  biceps  constitute  a 
superficial  layer;  the  semimembranosus  and  the  short  head  of  the  biceps  a  deep 
layer.  The  semitendinosus  and  the  long  head  of  the  biceps  arise  by  a  common 
tendon  from  the  tuber  of  the  ischium.  The  somewhat  fusiform  semitendinosus 
gives  rise  to  a  tendon  in  the  lower  half  of  the  thigh.  The  tendon  curves  forward 
behind  the  knee  to  be  inserted  under  that  of  the  sartorius  into  the  medial  side  of 
the  tibia.  The  penniform  short  head  of  the  biceps  arises  from  the  linea  aspera 
in  the  lower  part  of  the  thigh,  and  is  inserted,  together  with  the  fusiform  long 
head,  into  a  tendon  that  passes  over  the  lateral  side  of  the  knee  and  is  attached 
to  the  head  of  the  fibula.  The  semimembranosus  arises  from  the  tuber  ischii 
through  a  long,  flat,  triangular  tendon.  The  belly  of  the  muscle  increases  in 
thickness  toward  the  knee.  It  is  inserted  by  a  strong  tendon  on  the  back  of  the 
medial  condyle  of  the  tibia.  From  the  tendons  of  all  the  hamstring  muscles 
expansions  are  sent  into  the  crural  fascia. 

The  muscles  of  this  group  are  all  supplied  by  the  tibial  portion  of  the  sciatic, 
except  the  short  head  of  the  biceps,  which  is  suppUed  from  the  peroneal  portion. 

The  femoral  head  of  the  biceps  is  characteristic  of  the  anthropoid  apes  and  man.  In  many- 
mammals  its  place  is  taken  by  a  slender  muscle,  the  tenuissimus,  which  extends  from  the  caudal 
vertebraj,  the  sacro-tuberous  (great  sacro-sciatic)  ligament,  or  the  gluteal  fascia  to  the  fascia 
of  the  back  of  the  leg.  In  some  forms  this  muscle  is  broad  instead  of  slender.  According  to 
Testut,  the  long  head  of  the  biceps  may  be  looked  upon  as  arising  by  two  fasciculi,  one  primi- 
tively attached  to  the  posterior  part  of  the  ihum,  the  other  to  the  caudal  vertebrse  or  coccyx. 
The  sacro-tulserous  (great  sacro-sciatic)  ligament  represents  the  reduced  upper  portion  of  this 
muscle.  In  the  foetus  the  origin  of  the  muscle  extends  higher  on  the  sacro-tuberous  Ugament 
than  in  the  adult.  In  many  of  the  lower  mammals  the  origins  of  the  semimembranosus  and 
semitendinosus  take  place  in  part  from  the  sacro-caudal  vertebras. 

In  the  mammals  below  man  the  insertion  of  the  biceps,  gracilis,  and  semitendinosus  takes 
place  chiefly  into  the  fascia  of  the  back  of  the  leg,  and  extends  more  distally  than  in  man.  This 
insertion  of  these  flexor  muscles  is  associated  with  a  permanent  position  of  flexion  of  the  leg  at  the 
knee.  In  the  human  embryo  likewise  these  muscles  are  inserted  more  distally  than  in  the  adult. 
In  the  lower  primates  the  semimembranosus  is  chiefly  a  medial  rotator  of  the  leg. 

Biceps  femoris  (Figs.  408,  413). — Long  head. — Origin. — From  a  tendon  common  to  it  and 
the  semitendinosus.  This  tendon  arises  from  the  more  medial  of  the  two  facets  on  the  back  of 
the  tuber  of  the  ischium  and  from  the  sacro-tuberous  (great  sacro-sciatic)  ligament.  It  is 
continued  for  a  third  of  the  distance  to  the  knee  as  a  septum  between  the  biceps  and  the  semi- 
tendinosus, and  for  a  short  distance  as. an  aponeurotic  sheath  on  the  deep  surface  of  the  biceps. 

Structure  and  insertion. — The  fibre-bundles  begin  to  arise  from  the  tendon  some  distance 
from  the  ischium.  They  form  a  thick  fusiform  belly  which  is  inserted  into  the  deep  surface  of 
a  tendon  that  begins  laterally  on  the  back  of  the  muscle  about  the  middle  of  the  thigh.  The 
insertion  of  the  fibre-bundles  of  the  long  head  continues  on  the  medial  margin  of  the  deep  surface 
of  the  tendon  nearly  as  far  as  the  lateral  condyle  of  the  femur. 

Short  head. — Origin. — By  short  tendinous  fibres  from  the  lateral  lip  of  the  linea  aspera  of 
the  femur  from  the  middle  of  the  shaft  to  the  bifurcation  of  this  line,  the  proximal  two-thirds 
of  the  supracondylar  ridge,  and  the  lateral  intermuscular  septum. 

Structure  and  insertion. — ^The  fibre-bundles  take  a  nearly  parallel  course,  to  be  inserted  on 
the  deep  surface  of  the  common  tendon  of  insertion.  The  most  distal  fibres  are  inserted  nearly 
to  the  skeletal  attachment  of  the  tendon.  The  tendon  is  inserted  into  the  superior  extremity 
of  the  head  of  the  fibula,  into  the  lateral  condyle  of  the  tibia,  and  into  the  fascia  of  the  leg. 

Nerve-supply. — Commonly  two  branches  are  given  to  the  long  head  of  the  biceps.  One 
of  these  branches  is  given  off  proximal  to  the  ischium,  and  enters  the 'proximal  third  of  the  deep 
surface  of  the  muscle.  The  other  is  given  off  more  distally  and  usually  enters  the  middle  third. 
Either  or  both  branches  may  be  doubled  or  the  two  may  be  combined  for  some  distance  in  a 
common  trunk.  The  nerve-fibres  arise  usually  from  the  first,  second,  and  third  sacral  nerves. 
The  branch  to  the  short  head  arises  from  the  peroneal  (external  pophteal)  portion  of  the  sciatic 
nerve  about  the  middle  of  the  thigh.  It  enters  the  posterior  surface  near  the  lateral  margin  of 
the  muscle,  and  passes  distaUy  across  the  muscle  bundles  about  midway  between  the  tendons  of 
origin  and  insertion.  The  nerve-fibres  come  chiefly  from  the  fifth  lumbar,  first  and  second 
sacral  nerves. 

Action. — To  extend  and  adduct  the  thigh  and  flex  the  leg.  The  short  head  acts  only  on  the 
leg.     The  long  head  acts  as  a  lateral  rotator  of  the  thigh,  and  of  the  leg  when  flexed. 

Relations. — The  upper  extremity  of  the  muscle  is  covered  by  the  gluteus  maximus.  Below 
this  the  long  head  and  tendon  of  insertion  lie  beneath  the  fascia  lata  and  overhe  the  short  head. 
Ventral  to  the  muscle  lie  the  tendon  of  origin  of  the  semimembranosus,  the  adductor  magnus 
and  vastus  lateralis  muscles,  and  the  lateral  head  of  the  gastrocnemius.  The  medial  border  is 
in  contact  with  the  semitendinosus  and  semimembranosus.  Distally  it  forms  the  upper  lateral 
border  of  the  pophteal  space.     The  sciatic  nerve  runs  between  it  and  the  adductor  magnus. 

Variations. — The  short  head  is  rarely  absent.  It  may  be  more  isolated  from  the  long 
head  than  usual,  and  at  times  has  a  separate  tendon  of  insertion.  It  may  itself  be  divided  into 
two  distinct  laminae.  Its  origin  may  take  place  higher  up  on  the  femur  than  usual  or  from  the 
fascia  lata.     Variations  of  this  sort  suggest  the  tenuissimus  muscle  of  some  of  the  lower  mammals 


476  THE  MUSCULATURE 

(see  above).  The  long  head  of  the  biceps  may  receive  accessory  fasciculi  from  the  coccyx, 
sacrum,  sacro-tuberous  (great  sacro-sciatic)  ligament,  tuber  of  the  ischium,  or  the  deep  surface 
of  the  gluteus  maximus.  These  fasciculi  suggest  the  iliac  and  sacro-coccygeal  origin  of  the 
muscle  found  in  lower  vertebrates  (see  above).  Inferiorly,  a  muscle  fasciculus  may  take 
the  place  of  the  fibrous  prolongations  from  the  tendon  of  the  biceps  into  the  sural  fascia  (the 
tensores  fasciae  suralis).  This  may  extend  to  the  tendon  of  Achilles.  The  long  head  may 
have  a  tendinous  inscription  similar  to  that  of  the  semitendinosus. 

The  semitendinosus  (figs.  408,  413). — Origin. — Partly  from  a  medio-dorsal  facet  on  the 
distal  margin  of  the  tuber  of  the  ischium  by  direct  implantation  of  the  fibre-bundles,  and 
partly  from  the  medial  surface  of  the  tendon  common  to  it  and  the  long  head  of  the  biceps. 

Structure  and  insertion. — The  fibre-bundles  spread  out  to  form  a  flat,  fusiform  belly  which, 
about  the  middle  of  the  thigh,  again  contracts  toward  the  tendon  of  insertion.  This  begins  on 
the  medial  margin  and  dorsal  surface  of  the  muscle,  becomes  free  from  the  muscle  slightly  above 
the  medial  condyle  of  the  femur,  passes  behind  this  and  curves  forward  to  be  inserted  by  a  trian- 
gular expansion  into  the  proximal  part  of  the  medial  surface  of  the  tibia  behind  and  distal  to 
the  insertion  of  the  gracilis.  An  aponeurotic  expansion  is  continued  into  the  fascia  of  the  leg. 
About  the  middle  of  the  muscle  a  narrow  irregular  tendinous  inscription  more  or  less  completely 
divides  the  belly  into  proximal  and  distal  divisions. 

Nerve-supply. — To  the  muscle  two  nerves  are  commonly  given.  One  arises  from  the  sciatic 
nerve  or  directly  from  the  plexus,  proximal  to  the  tuber  of  the  ischium,  sometimes  in  com- 
pany with  a  branch  to  the  long  head  of  the  biceps.  It  enters  the  middle  third  of  the  deep  surface 
of  the  proximal  portion  of  the  muscle.  The  other  branch  arises  from  the  sciatic  nerve,  usually 
distal  to  the  ischial  tuber,  sometimes  in  common  with  a  nerve  to  the  biceps  or  the  semimem- 
branosus. It  enters  about  the  middle  of  the  deep  surface  of  the  distal  half  of  the  muscle. 
Either  or  both  branches  may  be  represented  by  two  nerves.  The  nerve  fibres  of  the  first 
branch  arise  chiefly  from  the  first  and  second  sacral  nerves,  those  of  the  second  from  the  fifth 
lumbar  and  first  sacral  nerves. 

Action. — To  extend  and  adduct  the  thigh  and  rotate  it  medialward  and  to  flex  the  leg, 
and  with  knee  flexed,  to  rotate  the  leg  medialward. 

Relations. — It  is  covered  by  the  gluteus  maximus  and  fascia  lata;  on  the  lateral  side  lies 
the  biceps;  and  in  front,  the  semimembranosus  and  adductor  magnus. 

Variations. — It  may  be  completely  separated  from  the  biceps  at  its  origin.  It  may  be 
fused  with  neighbom'ing  muscles.  There  may  be  two  tendinous  inscriptions.  It  may  have  a 
femoral  head  (a  condition  characteristic  of  many  birds).  A  muscle  fasciculus  may  extend  from 
the  body  of  the  muscle  to  the  fascia  of  the  back  of  the  leg. 

The  semimembranosus  (fig.  408). — Origin. — By  a  long,  flat  tendon  which  lies  beneath  the 
proximal  half  of  the  semitendinosus,  and  which  arises  from  the  more  lateral  of  the  two  facets 
on  the  back  of  the  tuber  of  the  ischium,  between  the  tendons  of  the  biceps  and  the  quadratus 
femoris.  The  tendon  is  at  first  adherent  to  the  tendon  of  the  adductor  magnus  in  front  and 
to  that  of  the  biceps  and  semitendinosus  behind.     It  descends  to  the  middle  of  the  muscle. 

Structure  and  insertion. — From  both  surfaces  of  the  medial  side  and  distal  extremity 
of  the  tendon  of  origin  fibre-bundles  arise  which  take  an  oblique  course  to  their  insertion  on  the 
aponeurosis  of  the  tendon  of  insertion.  This  appears  on  the  deep  surface  and  medial  margin 
of  the  muscle  opposite  the  end  of  the  tendon  of  origin  and  descends  on  the  medial  side  and  deep 
surface  of  the  muscle.  Near  the  back  of  the  medial  condyle  of  the  femur  the  insertion  of  muscle- 
fibres  ceases  and  the  tendon  is  inserted  directly  on  the  back  of  the  medial  condyle  of  the  tibia, 
and  by  aponeurotic  expansions  into  the  capsule  of  the  joint,  into  the  lateral  condyle  of  the  femur, 
into  the  tibial  collateral  ligament,  and  into  the  fascia  of  the  pophteus  muscle. 

Nerve-supply. — By  several  branches  from  the  sciatic  nerve,  which  usually  arise  from  a 
common  trunk  in  company  with  the  branches  to  the  adductor  magnus.  These  branches  enter 
the  deep  surface  of  the  muscle  about  midway  between  the  origin  and  insertion  of  the  constituent 
fibre-bundles. 

Action. — To  flex  the  leg  and  rotate  it  medialward  and  to  extend  and  adduct  the  thigh  and 
rotate  it  medialward. 

Relations. — It  is  covered  by  the  gluteus  maximus,  the  long  head  of  the  biceps,  the  semi- 
tendinosus, and  the  fascia  lata.  It  lies  dorsal  to  the  quadratus  femoris,  the  adductor  magnus, 
and  the  knee-joint. 

Variations. — It  may  be  fused  with  the  semitendinosus  or  the  adductor  magnus.  It  may 
be  doubled.  Its  tendons  may  have  a  more  extensive  attachment  than  usual.  The  extent  of 
the  belly  of  the  muscle  varies  con.siderably.  A  muscle  fasciculus  may  be  sent  into  the  popUteal 
space.    An  extra  head  may  arise  from  the  ischial  spine. 


BURS^ 

B.  m.  bicipitis  femoris  superior. — A  fair-sized  bursa  which  frequently  lies  between  the 
tendon  of  origin  of  the  long  head  of  the  biceps  and  semitendinosus  and  the  tendon  of  the  semi- 
membranosus and  the  ischial  tuber.  B.  m.  bicipitis  femoris  inferior. — A  small  bursa  which 
separates  the  tendon  of  insertion  from  the  fibular  collateral  ligament  of  the  knee-joint.  B.  m. 
bicipitis  gastrocnemialis. — A  bm-sa  infrequently  found  between  the  tendon  of  the  biceps  and 
the  tendons  of  origin  of  the  lateral  head  of  the  gastrocnemius  and  the  plantaris  muscles.  B. 
m.  semimembranosus. — This  is  a  large  double  bursa  constantly  present.  One  part  extends 
between  the  semimembranosus,  the  medial  head  of  the  gastrocnemius,  and  the  knee-joint. 
With  the  cavity  of  the  joint  it  frequently  communicates.  The  other  part  extends  between  the 
tendon  of  the  semimembranosus  and  the  medial  condyle  of  the  tibia. 


MUSCLES  OF  LEG  477 

C.  MUSCULATURE  OF  THE  LEG 

(Figs.  413-422) 

The  musculature  of  the  leg  arises  in  part  from  the  distal  end  of  the  femur, 
but  in  the  main  from  the  tibia  and  fibula.  The  muscle-bellies  are  best  developed 
in  the  proximal  half  of  the  leg,  where  they  give  rise  to  the  '  calf  behind  and  to  less 
well-marked  ventral  and  lateral  protrusions.  Toward  the  ankle  the  muscle- 
bellies  give  way  to  tendons  which  attach  the  muscles  of  the  leg  to  the  skeleton  of 
the  foot. 

The  musculature  is  divisible  into  an  anterior,  a  lateral  and  a  posterior  group  of 
muscles.  The  anterior  and  lateral  groups  are  separated  from  one  another  by  an 
intermuscular  septum.  The  antero-lateral  groups  are  separated  from  the  pos- 
terior group  by  the  tibia  and  fibula,  the  interosseous  membrane,  and  by  an 
intermuscular  septum  which  extends  from  the  lateral  margin  of  the  shaft  of  the 
fibula  to  the  fascia  enveloping  the  leg.  Medially  the  separation  is  well  marked 
by  the  broad  medial  surface  of  the  tibia.  Laterally  the  line  of  division  is  not  so 
clearly  marked  externally.  In  the  proximal  part  of  the  leg  the  dorsal  musculature 
protrudes  somewhat  ventrally;  in  the  distal  part  the  lateral  musculature  passes 
dorsal  to  the  lower  end  of  the  fibula.  The  posterior  group  is  divided  by  a  trans- 
verse septum  into  superficial  and  deep  divisions. 

While  in  the  forearm  the  extensor-supinator  muscles  extend  proximally  on  the  radial  side 
of  the  arm  to  the  humerus,  and  the  flexor-pronator  muscles  on  the  ulnar  side,  in  the  leg  both 
of  the  corresponding  sets  of  muscles  extend  primitively  on  the  fibular  side  of  the  leg  to  the  femur. 
In  the  higher  vertebrates  the  superficial  layer  of  the  flexor  musculature  of  the  leg  takes  origin 
from  both  sides  of  the  distal  extremity  of  the  femur,  and  the  origin  of  the  extensor  musculature 
ceases  to  extend  to  the  femur.  The  crural  musculatiu'e  is  primitively  inserted  into  the  bones  of 
the  leg,  the  tarsus,  and  the  aponeuroses  of  the  foot.  On  the  extensor  side  of  the  leg  the  muscula- 
ture ultimately  becomes  attached  wholly  to  the  foot  by  means  of  tendons  differentiated,  in  part 
at  least,  from  the  dorsal  aponeurosis.  The  lateral  portion  of  the  extensor  musculature,  which 
primitively  extends  from  the  femur  to  the  fibula,  in  the  higher  vertebrates  extends  from  the 
fibula  to  the  tarsus  and  metatarsus  (peroneal  musculature).  On  the  flexor  side  of  the  leg  the 
more  superficial  musculature  maintains  a  tarsal  attachment  through  the  tendon  of  Achilles. 
The  deeper  musculature  in  part  extends  from  the  femur  and  fibula  to  the  tibia,  in  part  arises 
from  the  fibula  and  tibia,  and  is  inserted  into  the  metatarsus  and  the  digits  through  tendons 
differentiated  from  the  plantar  aponeuroses.  The  musculature  of  the  sole  of  the  foot  is  highly 
developed  in  five-toed  vertebrates,  but  in  those  which  walk  on  the  toes,  and  especially  in  hoofed 
animals,  it  is  very  greatly  reduced. 

FASCIiE  OF  THE  LEG 

The  tela  subcutanea  of  the  leg  contains  a  considerable  amount  of  fat  where  it  overlies  the 
muscles,  but  less  where  it  overhes  the  bones  and  joints.  Subcutaneous  bursas  are  found  over 
the  tuberosity  of  the  tibia  (b.  subcutanea  tuberositatis  tibiae)  and  over  each  of  the  malleoU 
(b.  subcutanea  malleoli  medialis  et  lateralis).  Over  the  dorsum  of  the  foot  the  tela  contains 
comparatively  little  fat,  but  on  the  sole  of  the  foot  and  plantar  surface  of  the  toes  it  contains 
much  fat  interposed  between  dense  fibrous  tissue.  The  b.  subcutanea  calcanea  hes  beneath 
the  tuber  calcanei. 

The  crural  fascia,  or  external  layer  of  fascia  of  the  leg,  extends  from  the  knee  to  the  ankle. 
It  forms  an  enveloping  cone-Hke  sheath  for  the  muscles  and  is  adherent  to  the  periosteum  of 
the  medial  surface  of  the  tibia.  It  is  formed  of  transverse,  oblique,  and  longitudinal  fibres 
and  is  thickest  in  front. 

Ventrally  the  fascia  of  the  thigh,  to  which  the  tendons  of  the  quadriceps,  sartorius,  graciUs, 
semitendinosus,  and  biceps  muscles  and  the  ilio-tibial  band  are  closely  united,  becomes  attached 
with  these  tendons  to  the  tibia  and  fibula.  From  these  attachments,  therefore,  the  fascia  of 
the  front  of  the  leg  may  be  said  to  arise.  Into  it  extend  processes  from  the  tendons  men- 
tioned. DorsaUy  the  fascia  of  the  thigh  is  continued  uninterruptedly  into  that  of  the  leg. 
Distally  the  crural  fascia  is  attached  to  the  two  malleoli  and  to  the  posterior  surface  of  the 
calcaneus. 

In  the  proximal  part  of  the  leg  in  front  the  underlying  muscles  in  part  take  origin  from  the 
fascia;  in  other  places  the  fascia  is  separated  from  the  underlying  muscles  by  loose  tissue. 

From  the  fascia  two  main  intermuscular  septa  arise.  One,  the  anterior  intermuscular 
septum,  extends  between  the  extensor  digitorum  longus  and  peroneal  muscles  to  the  anterior 
crest  of  the  fibula;  the  other,  the  posterior  intermuscular  septum,  between  the  peroneal  muscles 
and  the  soleus  to  the  lateral  crest  of  the  fibula.  These  septa  separate  compartments  for  the 
anterior,  lateral,  and  posterior  groups  of  muscles. 

As  the  heads  of  the  gastrocnemius  pass  over  the  back  of  the  knee  they  are  held  in  place  by  a 
special  deep  lamina  of  the  fascia  lata,  which  distally  becomes  fused  with  the  crural  fascia  (fig. 
414  A). 


478 


THE  MUSCULATURE 


Fig.  414,  A-F. — TransybbseISections  thhough  the  Left  Leg  in  the  Regions  shown  in 

THE  Diagram. 

d  In  the  diagram  indicates'the  region  through  which  passes  section  D,  fig.  410  (p.  465) ;  a',  6',  c', 
d',  the  regions  through  which  pass  sections  A,  B,  C,  D,  fig.  417  (p.  488). 

1.  Arteria  peronea.  2.  A.  pophtea.  3.  A.  tibialis  anterior.  4.  A.  tibialis  posterior.  5 
Bursa  anserina.  6.  Bursa  m.  sartorii  propria.  7.  Fascia  cruralis.  8.  Fibula.  9 
Ligamentum  crurale  transversum.  10.  Lig.  patellse.  11.  Membrana  interossea.  12 
Musculus  biceps  femoris — tendon.  13.  M.  e.xtensor  digitorum  longus — a,  tendon.  14.  M 
extensor  hallucis  longus.  15.  M.  flexor  digitorum  longus.  16.  M.  flexor  hallucis  longus 
17.  M.  gastrocnemius — a,  lateral  head;  b,  medial  head.  18.  M.  graciUs,  tendon.  19 
M.  peroneus  brevis.  20.  M.  peroneus  longus — a,  tendon.  21.  M.  peroneus  tertius, 
22.  M.  plantaris — a,  tendon.  23.  M.  pophteus.  24.  M.  sartorius,  tendon.  25.  M 
I  semimembranosus,  tendon.  26.  M.  semitendinosus,  tendon.  27.  M.  soleus — a,  fasciculus 
accessorius.  28.  M.  tibialis  anterior — a,  tendon.  29.  M.  tibialis  posterior — a,  tendon. 
30.  N.  cutaneus  surse  lateralis.  31.  N.  cutaneus  surse  medialis.  32.  N.  peroneus 
communis  (external pophteal).  33.  N.  peroneus  profundus  (anterior  tibial).  34.  N.  pero- 
neus superficiales  (musculo-cutaneus) .  35.  N.  plantaris  laterahs  (external  plantar).  36. 
N.  plantaris  medialis  (internal  plantar).  37.  N.  suralis  (external  saphenous).  38.  N. 
tibialis  (posterior  tibial).  39.  Septum  intermusculare  (anterior).  40.  S.  intermusculare 
(posterior).  41.  S.  surse  transversum.  42.  Tendo  Achilhs  (calcanei).  43.  Tibia.  44. 
Vena  saphena  magna.     45.  V.  saphena  parva. 


FASCIA 


479 


I  The  semimembranosus  has  a  special  fascial  investment  which,  on  the  back  of  the_knee 
becomes  bound  on  each  side  of  the  muscle  and  its  tendon  to  the  capsule  of  the  joint.  This 
fascia  extends  into  a  transverse  septal  membrane  which  is  continued  over  the  deep  muscles  of 
the  back  of  the  leg  to  the  ankle.  It  is  united  on  one  side  to  the  tibia,  on  the  other  to  the  fibula. 
Proximally  the  fibres  are  continued  into  it  from  the  tendon  of  the  semimembranosus.  Over 
the  back  of  the  tibia  the  septum  is  interrupted  by  the  attachment  of  the  soleus  to  the  pophteal 
line.  Beyond  the  tibial  origin  of  the  soleus  it  is  fused  on  the  medial  side  of  the  flexor  digitorum 
longus  to  the  crural  fascia. 

In  addition  to  the  two  intermuscular  septa  and  the  longitudinal  transverse  septum,  other 
septa  serve  to  separate  the  individual  muscles  of  the  different  groups. 

Above  the  ankle  the  fascia  is  enforced  by  bands  of  tissue  so  that  ligaments  are  formed 
which -serve  to  retain  in  position  the  various  tendons  which  pass  from  the  leg  into  the  foot. 

The  transverse  crural  ligament  (upper  part  of  anterior  annular  ligament)  (fig.  415)  lies 
on  the  front  of  the  lower  part  of  the  leg  above  the  ankle.  It  is  composed  of  fascia  strengthened 
by  transverse  bundles  which  pass  from  the  medial  side  of  the  tibia  to  the  ventral  margin  of  the 
fibula.  From  its  deep  surface  a  strong,  broad  septum  descends  to  the  tibia  and  divides  the 
underlying  space  into  two  osteo-fibrous  canals,  a  medial  for  the  tibialis  anterior  and  a  lateral 
for  the  long  extensor  muscles.  The  lateral  compartment  is  further  subdivided  by  a  sUghtly 
marked  septum  into  a  medial  division  for  the  extensor  hallucis  longus  and  a  lateral  for  the  ex- 
tensor digitorum  longus  and  the  peroneus  tertius. 

The  cruciate  ligament  (lower  part  of  anterior  annular  ligament)  (fig.  415)  serves  to  hold 
the  tendons  of  the  anterior  muscle  group  in  place  as  they  pass  to  the  dorsum  of  the  foot.  In 
part  it  is  formed  by  a  dense  fibrous  band  lying  in  the  fascia  over  the  ankle,  in  part  of  a  liga- 
ment which  passes  from  the  bones  of  the  ankle  to  the  deep  surface  of  this  band.  The  superficial 
band  is  V-shaped.  It  arises  from  the  lateral  surface  of  the  body  of  the  calcaneus  and  passes 
across  the  dorsum  of  the  foot,  one  arm  of  the  V  going  to  the  medial  malleolus,  the  other  to  the 
side  of  the  foot,  where  it  terminates  in  the  fascia  over  the  first  cuneiform  bone.  The  apex  of 
the  V  lies  over  the  tendons  of  the  extensor  digitorum  longus  and  peroneus  tertius  muscles. 
The  distal  arm  extends  over  the  tendons  of  the  extensor  hallucis  longus  and  tibialis  anterior 


480  THE  MUSCULATURE 

muscles.  The  proximal  arm  passes  over  the  tendon  of  the  extensor  hallucis  longus  and  then 
divides  into  two  layers,  between  which  the  tendon  of  the  tibialis  anterior  passes.  The  deeper 
ligament  mentioned  above  arises  from  deep  within  the  tarsal  sinus,  some  of  its  fibres  even 
from  the  sustentaculum  tali.  It  then  passes  forward  and  medially  beneath  the  long  extensor 
tendons,  and  divides  into  two  parts,  one  of  which  curves  about  the  medial  margin  of  the  ten- 
don of  the  extensor  digitorum  longus,  the  other  about  the  extensor  hallucis  longus  tendon  to 
the  under  surface  of  the  proximal  arm  of  the  V-shaped  band. 

The  peroneal  retinacula  are  strengthened  regions  in  the  fascia  which  serve  to  hold  the 
tendons  of  the  peroneal  muscles  in  place.  The  superior  extends  from  the  lateral  malleolus  into 
the  fascia  on  the  back  of  the  leg,  and  to  the  lateral  surface  of  the  calcaneus.  The  inferior 
overlies  the  tendons  on  the  lateral  surface  of  the  calcaneus,  and  is  attached  to  this  bone  on 
each  side  of  them.  Between  the  tendons  it  sends  a  septum  to  the  bone.  It  is  connected  with 
the  superficial  layer  of  the  cruciate  ligament. 

The  laciniate  ligament  (internal  annular)  (fig.  416)  is  found  on  the  medial  side  of  the  ankle. 
Here  the  fascia  is  strengthened  by  fibre-bands  which  form  a  well-marked  ligament  that  holds 
in  place  the  tendons  of  the  deep  dorsal  cruro-pedal  muscles.  This  ligament  extends  from  the 
dorsal  and  distal  margins  of  the  medial  malleolus  to  the  calcaneus.  It  is  closely  bound  to  the 
tibia  and  the  talo-tibial  (tibio-astragaloid)  ligament  until  the  tendon  of  the  tibialis  posterior  is 
reached.  It  passes  over  this  and  becomes  bound  to  the  bony  structures  on  the  posterior 
margin  of  the  tendon.  From  tjiis  attachment  two  layers,  a  deep  and  a  superficial,  extend 
backward.  The  superficial  layer  extends  to  the  tuber  calcanei,  and  is  connected  superiorly 
with  the  crural  fascia.  The  deep  layer,  which  represents  a  continuation  distally  of  the  trans- 
verse septum,  extends  over  the  tendons  of  the  flexor  digitorum  longus  and  flexor  hallucis  longus 
to  the  medial  surface  of  the  calcaneus,  and  is  closely  united  to  the  underlying  bone  on  each 
side  of  these  tendons,  thus  giving  rise  to  osteo-fibrous  canals. 

MUSCLES 

1.  Muscles  of  thf  Front  of  the  Leg 

(Figs.  415,  418) 

The  anterior  musculature  of  the  leg  consists  of  four  muscles,  the  tibialis 
anterior,  extensor  digitorum  longus,  peroneus  tertius,  and  extensor  hallucis 
longus.  The  tibialis  anterior  has  a  quadrangular  prismatic  belly  which  arises 
from  the  lateral  side  of  the  tibia  and  adjacent  interosseous  membrane  in  the 
proximal  half  of  the  leg.  The  tendon  passes  over  the  front  of  the  tibia  to  the 
first  metatarsal.  The  extensor  digitorum  longus  is  a  transversely  flattened, 
fusiform  muscle,  which  arises  from  the  superior  extremity  of  the  tibia,  the  anterior 
crest  of  the  fibula,  and  the  adjacent  interosseous  membrane,  and  gives  rise  to  a 
tendon  which  passes  over  the  front  of  the  distal  extremity  of  the  tibia  and  sends 
tendons  to  the  two  terminal  phalanges  of  the  four  more  lateral  toes.  The 
peroneus  tertius  represents  a  more  or  less  completely  differentiated  portion  of 
the  preceding  muscle.  Its  tendon  passes  laterally  through  the  same  osteo- 
fibrous  canal  in  the  same  synovial  sheath  and  terminates  on  the  fifth  metatarsal. 
The  extensor  hallucis  longus  is  a  narrow  muscle  which  arises  from  the  distal  half 
of  the  medial  surface  of  the  fibula  and  the  interosseous  membrane.  Its  tendon 
extends  over  the  ankle  to  the  great  toe.  The  tendons  of  these  muscles  are  held 
in  place  by  the  transverse  and  cruciate  ligaments  described  above. 

All  the  muscles  of  this  group  flex  the  foot.  The  extensors  extend  the  toes;  the 
peroneus  tertius  and  the  extensor  digitorum  longus  evert  the  foot.  The  nerve 
supply  is  from  the  deep  peroneal  (anterior  tibial)  nerve. 

The  tibialis  anterior  is  represented  in  the  arm  probably  by  the  braohio-radialis  and  the  two 
radial  extensors;  the  extensor  digitorum  longus  by  the  extensor  digitorum  communis  and 
extensor  digiti  quinti  proprius;  and  the  extensor  hallucis  longus  by  the  extensor  poUicis  longus. 
Two  abnormal  muscles  not  infrequently  found,  the  abductor  hallucis  longus  and  extensor  primi 
internodii  hallucis,  represent  probably  the  corresponding  normal  muscles  of  the  hand. 

The  tibialis  anterior  (fig.  415). — Origin. — From  the  distal  surface  of  the  lateral  condyle 
of  the  tibia,  and  the  lateral  surface  of  the  proximal  half  of  the  shaft  of  the  tibia,  the  adjacent 
interosseous  membrane,  the  overlying  fascia  near  the  condyle  (tuberosity)  of  the  tibia,  and  the 
intermuscular  septum  between  it  and  the  extensor  digitorum  longus. 

Structure. — Bipenniform.  The  fibre-bundles  converge  upon  a  flat  tendon  which  begins 
high  in  the  muscle  and  emerges  on  the  anterior  margin  of  the  muscle  about  the  middle  of  the  leg. 
On  the  deep  surface  the  implantation  of  fibre-bundles  continues  to  the  transverse  crural  (anterior 
annular)  ligament. 

Insertion. — The  tendon  passes  over  the  front  of  the  tibia  to  the  medial  side  of  the  foot, 
where  it  is  inserted  into  the  medial  surface  of  the  first  cuneiform  and  the  base  of  the  first 
metatarsal. 

Nerve-supply. — As  a  rule,  a  branch  from  the  common  peroneal  (external  popUteal)  nerve 
enters  the  proximal  portion  of  the  muscle  by  several  twigs,  and  another  from  the  deep  peroneal 
(anterior  tibial)  enters  near  the  middle  of  the  belly  on  the  lateral  edge. 


EXTENSOR  DIGITORUM  LONGUS 


481 


Relations. — In  the  proximal  half  of  the  leg  the  extensor  digitorum  longus  hes  lateral  to  it; 
and  between  the  two  muscles,  the  anterior  tibial  artery  and  vein.  It  is  covered  by  the  crural 
fascia  and  rests  on  the  interosseous  membrane.  Distally  it  lies  over  the  extensor  hallueis 
longus.  The  tendon  passes  in  special  compartments  beneath  the  transverse  and  the  cruciate 
(anterior  annular)  hgaments. 


Fig.  415. — The  Muscles  of  the  Front  of  the  Leg. 

ill     J 


Ligamentum  patellae 


Gastrocnemius 


Extensor  hallueis  longus 
Transverse  crural  ligament 


Dorsal  interossei 


Peroneus  longus 


Tibialis  anterior 


Peroneus  tertius 


Extensor  digitorum  longus 


Peroneus  tertius 


Cruciate  ligament 


Extensor  digitorium  brevis 


f^'  u^^*^°^°^  digitorum  longus  (fig.  4:1 5). —Grig  171. —From  the  lateral  condyle  of  the 
tibia,  the  anterior  crest  (surface)  of  the  fibula,  the  intermuscular  membrane  between  it  and 
the  tibiahs  anterior,  the  lateral  margin  of  the  interosseous  membrane,  the  septum  between 
it  and  the  peroneus  longus,  and  the  fascia  of  the  leg  near  the  tibial  origin. 

Structure. — Penniform.     The  fibre-bundles  converge  upon  the  posterior  surface  of  a  tendon 
which  begins  at  the  middle  of  the  leg.     The  implantation  of  fibres  continues  nearly  to  the 


482  THE  MUSC  ULA  T  URE 

ankle.  Usually  at  the  distal  margin  of  the  transverse  (anterior  annular)  Hgament  the  tendon 
divides  into  two  parts  which  pass  between  the  two  layers  of  the  cruciate  (lower  part  of  an- 
terior annular)  ligament,  and  then  each  divides  again  into  two  parts,  thus  giving  rise  to  four 
slips,  one  for  each  of  the  four  lateral  toes. 

Insertion. — Each  tendon  on  the  dorsal  surface  of  the  toe  to  which  it  goes  divides  into  three 
fasciculi:  an  intermediate,  which  is  attached  to  the  dorsum  of  the  base  of  the  second  phalanx; 
and  two  lateral,  which  converge  to  the  dorsum  of  the  base  of  the  third  phalanx.  The  margins 
of  the  tendon  are  also  bound  by  fibrous  tissue  to  the  sides  of  the  back  of  the  first  phalanx. 

Nerve-supply. — Most  frequently  two  branches  of  the  deep  peroneal  (anterior  tibial)  enter 
the  deep  surface  of  the  muscle,  one  near  its  tibial  origin,  one  about  the  centre  of  the  belly. 

Relations. — In  the  proximal  half  of  the  leg  it  lies  on  the  interosseous  membrane,  and  beneath 
the  fascia  of  the  leg,  and  adjoins  medially  the  tibialis  anterior,  laterally  the  peroneus  longus. 
DistaUy  it  lies  over  the  extensor  hallucis  longus  and  adjoins  laterally  the  peroneus  brevis.  The 
tendon  passes  beneath  the  transverse  crural  and  the  superficial  layer  of  the  cruciate  (anterior 
annular)  ligaments  and  over  the  extensor  digitorum  brevis  muscle.  The  superficial  peroneal 
(musculo-cutaneous)  nerve  runs  in  the  septum  between  it  and  the  peroneal  muscles;  the  anterior 
tibial  artery  and  deep  peroneal  nerve  pass  beneath  the  head  of  the  muscle,  and  then  between 
it  and  the  tibialis  anterior. 

The  peroneus  tertius  (fig.  415). — Origin. — From  the  distal  third  of  the  medial  surface 
of  the  fibula,  the  neighbouring  interosseous  membrane,  and  the  anterior  intermuscular  septum. 

Structure. — It  is  essentially  a  fasciculus  of  the  extensor  digitorum  longus,  from  which  it  is 
seldom  completely  differentiated.  The  fibre-bundles  descend  obliquely  forward  to  be  inserted 
In  a  penniform  manner  on  a  tendon  which  runs  along  the  lateral  margin  of  the  tendons  of  the 
extensor  digitorum.  The  attachment  of  fibre-bundles  continues  to  the  cruciate  ligament  (lower 
part  of  anterior  annular  ligament). 

Insertion. — On  the  base  of  the  fifth  metatarsal  and  often  also  on  the  base  of  the  fourth. 

Nerve-supply. — The  more  distal  nerve  to  the  extensor  digitorum  continues  into  this  muscle. 

Relations. — It  lies  lateral  to  the  extensor  digitorum  longus.  Its  tendon  passes  into  the  foot 
beneath  the  transverse  crural  and  the  superficial  layer  of  the  cruciate  hgament  in  the  same 
compartments  with  those  of  the  extensor  longus. 

The  extensor  hallucis  longus  (fig.  415). — Origin.- — From  the  middle  two-fo\irths  of  the 
medial  surface  of  the  fibula  near  the  interosseous  crest,  and  from  the  distal  half  of  the  interos- 
seous membrane. 

Structure. — Penniform.  The  fibre-bundles  are  attached  as  far  as  the  cruciate  ligament 
to  the  back  and  sides  of  a  tendon  which  begins  on  the  antero-medial  margin  of  the  distal 
third  of  the  muscle. 

Insertion. — On  the  base  of  the  second  phalanx  of  the  big  toe.  On  the  back  of  the  first 
phalanx  the  margins  of  the  tendon  are  attached  to  the  bone  by  bands  of  fibres. 

Nerve-supply. — As  a  rule,  a  branch  from  the  deep  peroneal  (anterior  tibial)  nerve  enters 
the  deep  surface  of  the  muscle  near  the  junction  of  the  upper  and  middle  thirds,  and  passes 
distally  across  the  middle  of  the  obliquely  running  muscle  fibre-bundles. 

Relations. — It  lies  on  the  distal  half  of  the  interosseous  membrane,  partly  covered  by  the 
extensor  digitorum  longus  and  the  tibiaUs  anterior  muscles.  Its  tendon  passes  over  the  front 
of  the  distal  extremity  of  the  tibia  and  the  medial  side  of  the  dorsum  of  the  foot  and  is  held  in 
place  by  the  transverse  and  cruciate  ligaments  and  by  a  strengthening  band  in  the  fascia  over 
the  base  of  the  first  metatarsal.  In  the  distal  part  of  the  leg  the  anterior  tibial  artery  and  the 
deep  peroneal  (anterior  tibial)  nerve  pass  beneath  the  muscle  to  enter  the  foot  on  the  lateral 
side  of  its  tendon. 

Actions. — The  muscles  of  this  group  all  flex  the  ankle.  The  tibiahs  anterior  and  extensor 
hallucis  longus  evert  the  foot  at  the  talo-calcaneo-navicular  joints,  and  invert  it  at  the  talo- 
navicular, calcaneo-cuboid  joints.  In  certain  positions  the  tibialis  anterior  may,  however, 
invert  the  foot  at  these  joints.  The  peroneus  tertius  and  the  long  extensor  evert  the  foot. 
The  force  of  the  extensor  hallucis  longus  is  exerted  powerfully  on  the  first  phalanx  and  weakly 
on  the  second.  The  short  muscles  of  the  big  toe  aid  in  extending  the  second  phalanx.  The 
extensor  digitorum  longus  extends  the  first  phalanx  of  each  toe  powerfully,  but  exerts  less 
force  on  the  second  and  third.     The  lumbrical  muscles  assist  in  extending  the  last  two  phalanges. 

Variations. — The  origin  of  the  tibialis  anterior  may  extend  to  the  femur.  Its  tendon  of 
insertion  may  give  accessory  slips  to  the  cuneiforms,  metatarsals,  and  phalanges.  ^  More  rarely 
its  belly  is  divided  into  two  portions,  one  of  which  sends  a  tendon  to  the  first  cuneiform  and  one 
to  the  first  metatarsal.  A  slip,  the  tensor  fascise  dorsalis  pedis  (Wood),  may  pass  to  the  dorsal 
fascia  of  the  foot.  Another,  the  tibio -astragalus  anticus  (Gruber),  to  the  talus  (astragalus) 
or  calcaneus.  The  bellies  or  the  tendons  of  the  extensor  hallucis  and  extensor  digitorum  may 
be  more  or  less  completely  fused,  or  tendon  slips  may  pass  from  the  tendon  of  one  muscle  to  that 
of  the  other.  Tendon  slips  may  pass  to  the  metatarsal  bones  or  from  the  tendon  of  one  toe  to 
that  of  a  neighbouring  toe.  The  tendon  to  each  toe  may  be  doubled.  The  belly  of  the  extensor 
digitorum  longus  may  be  more  or  less  completely  subdivided  to  correspond  with  the  tendons 
to  individual  toes.  The  peroneus  tertius  is  frequently  fused  with  the  long  extensor.  It  may 
be  doubled.  More  often  its  tendon  may  bifurcate  or  trifurcate  and  be  inserted  into  the  extensor 
tendons  of  the  fifth  toe  or  into  the  fourth  or  third  metatarsal.  It  is  absent  in  about  8.5  per  cent, 
of  bodies  (Le  Double). 

Abnormal  Muscles. — The  abductor  hallucis  longus  is  rarely  found  as  a  completely  in- 
dependent muscle.  It  usually  arises  as  a  fasciculus  of  the  e.xtensor  digitorum  longus,  extensor 
hallucis  longus,  or  the  tibialis  anterior.  It  is  inserted  into  the  base  of  the  first  metatarsal.  The 
extensor  primi  internodii  hallucis  (extensor  hallucis  brevis)  has  an  origin  similar  to  that  of  the 
long  abductor  above  described.  It  is  inserted  into  the  dorsum  of  the  base  of  the  first  phalanx 
of  the  big  toe.  It  is  not  to  be  confounded  with  that  portion  of  the  extensor  digitorum  brevis 
connected  with  the  great  toe  and  also  sometimes  called  the  extensor  hallucis  brevis. 


PERONEI  MUSCLES  483 

BnRSiE 

B.  subtendinea  m.  tibialis  anterioris. — A  small  bursa  between  the  medial  surface  of  the 
first  cuneiform  bone  and  the  tendon  of  the  tibialis  anterior.  B.  subtendinea  m.  extensoris 
hallucis  longi. — A  small  bursa  beneath  the  tendon  near  the  tarso-metatarsal  articulation.  It 
may  communicate  with  the  synovial  sheath  of  the  tendon.  B.  sinus  tarsi. — A  large  bursa  in 
the  sinus  tarsi  and  on  the  lateral  surface  of  the  neck  of  the  talus  (astragalus)  beneath  the  tendons 
of  the  extensor  digitorum  longus  and  the  fibrous  bands  between  the  talo-calcaneal  and  the 
cruciate  ligaments.  It  extends  back  to  the  talo-crural,  forward  to  the  talo-navioular  joint, 
and  may  communicate  with  the  joint  cavity  of  the  latter. 

Synovial  Tendon-sheaths 

Vagina  tendinis  m.  tibialis  anterioris. — This  sheath  surrounds  the  tendon  from  above 
the  transverse  crural  ligament  to  the  talo-navicular  joint.  Vagina  tendinis  m.  extensoris 
hallucis  longi. — The  sheath  begins  above  the  proximal  arm  of  the  cruciate  ligament,  and 
ends  near  the  tarso-metatarsal  joint  beneath  a  band-Uke  thickening  of  the  dorsal  fascia  of  the 
foot.  Vagina  tendinum  m.  extensoris  digitorum  longi. — This  sheath  surrounds  the  tendons 
of  the  long  digital  extensor  and  the  peroneus  tertius  from  above  the  cruciate  ligament  to  the 
middle  of  the  third  cuneiform  bone. 

2.  Lateral  Musculature  op  the  Leg 

(Figs.  416,  422) 

The  lateral  muscles  consist  of  the  peroneus  longus  and  the  peroneus  brevis. 
They  extend  and  evert  the  foot.  The  thick  prismatic  belly  of  the  peroneus  longus 
arises  from  the  proximal  half  of  the  lateral  surface  of  the  fibula  and  from  neigh- 
bouring structures,  while  the  smaller  belly  of  the  peroneus  brevis  arises  from  the 
middle  third  of  the  lateral  surface  of  this  bone.  The  peroneus  longus  partly 
covers  the  peroneus  brevis.  The  tendons  of  the  two  muscles  pass  behind  the 
lateral  malleolus,  held  in  place  by  special  retinacula  (p.  480).  There  the  tendon 
of  the  peroneus  longus  lies  at  first  lateral  to  and  then  crosses  behind  that  of  the 
peroneus  brevis  and  curves  about  the  lateral  side  of  the  calcaneus  and  across  the 
sole  of  the  foot  closely  applied  to  the  cuboid  and  to  the  tarso-metatarsal  articula- 
tions, and  terminates  on  the  base  of  the  first  metatarsal.  The  tendon  of  the 
peroneus  brevis  terminates  on  the  lateral  side  of  the  foot  at  the  base  of  the  fifth 
metatarsal.  The  nerve  supply  is  from  the  superficial  peroneal  (musculo-cuta- 
neous)  nerve. 

The  two  muscles  are  probably  represented  in  the  arm  by  the  extensor  carpi  ulnaris.  In 
some  of  the  lower  animals  the  head  of  the  peroneus  longus  extends  to  the  femur.  The  fibular 
collateral  ligament  of  the  knee-joint  probably  represents  in  man  the  femoral  head  of  the 
peroneus  longus. 

The  peroneus  longus  (figs.  416,  422). — Origin. — Anterior  head:  tendinous  from  the  anterior 
tibio-fibular  ligament,  the  neighbouring  part  of  the  lateral  condyle  of  the  tibia,  and  the  head  of 
the  fibula;  fleshy  from  the  proximal  third  of  the  anterior  intermuscular  septum  and  the  crural 
fascia  near  the  tibia.  Posterior  head :  fleshy  from  the  proximal  half  of  the  lateral  surf ace^of  the 
shaft  of  the  fibula  and  from  the  posterior  intermuscular  septum. 

Structure. — Bipenniform.  The  fibre-bundles  converge  upon  a  tendon  which  begins  high  in 
the  muscle.  The  constituent  fibre-bundles  of  the  anterior  head  are  long  and  take  a  nearly 
vertical  course.  The  fibre-bundles  of  the  posterior  head  take  a  more  obhque  course  and  their 
attachment  extends  more  distally  on  the  tendon.  The  tendon  emerges  on  the  surface  of  the 
muscle  in  the  distal  half  of  the  leg.  The  fibre-bundles  of  the  posterior  head  extend  to  within 
a  few  centimetres  of  the  lateral  malleolus.  The  tendon  passes  through  the  retro-malleolar 
groove,  passes  across  the  lateral  face  of  the  calcaneus,  to  and  through  the  peroneal  groove  of 
the  cuboid,  and  crosses  the  second  and  third  tarso-metatarsal  joints.  Where  the  tendon  enters 
the  groove  in  the  cuboid  it  contains  a  fibro-cartilaginous  nodule  which  may  become  a  sesamoid 
bone. 

Insertion. — On  the  inferior  surface  of  the  first  cuneiform  and  on  the  supero-lateral  border 
and  base  of  the  first  metatarsal.  From  the  region  of  the  fibro-cartilaginous  nodule  above  men- 
tioned a  fibrous  slip  is  usually  sent  to  the  base  of  the  fifth  metatarsal. 

Nerve-supply. — Most  commonly  the  peroneal  (external  pophteal)  nerve  before  dividing 
gives  off  two  branches.  One  of  these  enters  the  deep  surface  of  the  middle  third  of  the  anterior 
head,  the  other  passes  across  the  middle  third  of  the  constituent  bundles  of  the  posterior  head. 
The  latter  branch  may  arise  from  the  superficial  peroneal  (musculo-cutaneous)  nerve,  and  it 
may  extend  to  supply  the  peroneus  brevis. 

The  peroneus  brevis  (fig.  416). — Origin. — From  the  middle  third  of  the  lateral  surface 
of  the  fibula;  (2)  from  the  septa  which  separate  it  from  the  anterior  and  posterior  groups 
of  muscles. 

Structure. — Penniform.  The  fibre-bundles  converge  upon  a  tendon  which  begins  high  in 
the  muscle  and  becomes  visible  on  the  lateral  surface  of  the  distal  half  of  the  belly.  Behind  the 
lateral  malleolus  the  tendon  becomes  free,  then  passes  forward  below  the  malleolus  and,  across 
the  calcaneus  and  cuboid. 


484  THE  MUSCULATURE 

Insertion. — Into  the  tip  of  the  tuberosity  of  the  fifth  metatarsal. 

Nerve-supply. — The  nerve  arises  from  the  superficial  peroneal  (musculo-cutaneous)  nerve, 
or  from  a  branch  to  the  peroneus  longus.  It  enters  the  proximal  margin  of  the  muscle  and 
passes  distally  across  its  constituent  fibre-bundles. 

Relations. — The  peroneal  muscles  in  the  leg  are  contained  in  a  compartment  bounded  by 
the  anterior  and  posterior  intermuscular  septa,  by  the  fibula,  and  by  the  fascia  of  the  leg.  The 
peroneus  longus  to  a  considerable  degree  overlies  the  peroneus  brevis.  Beneath  the  upper  part 
of  the  peroneus  longus  the  peroneal  (external  popliteal)  nerve  bifurcates  into  its  two  chief 
branches.  The  deep  peroneal  (anterior  tibial)  nerve  passes  medially  beneath  the  anterior  head 
of  the  muscle.  The  superficial  peroneal  (musculo-cutaneous)  nerve  extends  in  the  interval 
between  the  areas  of  the  attachment  of  the  two  heads  of  the  peroneus  longus,  and  along  the  an- 
terior margin  of  the  peroneus  brevis  to  the  anterior  intermuscular  septum,  through  which  it 
passes  to  its  superficial  distribution.  The  tendon  of  the  peroneus  longus  at  first  lies  lateral  to 
and  slightly  overlaps  that  of  the  peroneus  brevis.  Toward  the  tip  of  the  malleolus  it  lies  almost 
directly  posterior  to  this  tendon.  On  the  lateral  surface  of  the  calcaneus  the  tendon  of  the 
brevis  lies  superior  to  that  of  the  longus,  from  which  it  is  separated  by  a  bony  spine,  the  processus 
trochlearis  of  the  calcaneus.  The  tendon  of  the  longus  is  separated  from  the  deep  surface  of  the 
abductor  of  the  little  toe,  and  is  held  in  place  in  the  groove  in  the  cuboid  by  the  long  plantar 
ligament. 

Action. — The  peroneus  brevis  everts  the  foot.  The  peroneus  longus  extends,  abducts,  and 
everts  the  foot,  and  supports  the  arch  of  the  foot.  The  peroneus  brevis  also  extends  the  foot 
when  this  is  greatly  flexed. 

Variations. — The  two  peroneal  muscles  may  be  more  or  less  fused.  The  origin  of  the 
peroneus  longus  may  extend  to  the  femur.  The  two  heads  of  origin  may  be  fused.  Its  tendon 
of  insertion  may  send  slips  to  the  second,  third,  and  rarely  to  the  fourth  and  fifth  metatarsals. 
The  tendon  may  be  united  to  that  of  the  tibialis  posterior  (12  out  of  45  bodies — Picou).  Sesa- 
moid cartilages  or  bones  are  occasionally  found  in  the  retro-malleolar  and  calcaneal  portions  of 
the  tendon.  The  tendon  of  the  peroneus  brevis  may  send  a  slip  to  the  second  or  third  phalanx 
or  to  the  head  of  the  metatarsal  of  the  fifth  toe,  to  its  extensor  tendon,  or  to  the  cuboid.  It  may 
also  send  a  fasciculus  to  the  fourth  metatarsal  or  the  extensor  tendon  of  the  fourth  toe. 

Accessory  peroneals. — Poirier  considers  these  all  varieties  of  a  muscle  which  in  its  simplest 
form  arises  from  the  distal  fourth  of  the  fibula  and  is  inserted  by  a  tendon  into  the  fifth  toe.  A 
corresponding  muscle  is  normally  found  in  many  of  the  monkeys  (peroneus  digiti  quinti).  In 
man  in  one  form  or  another  it  is  a  frequent  anomaly.  It  may  be  so  fused  with  the  peroneus 
brevis  that  only  its  tendon  of  insertion  is  apparent.  It  may  appear  as  a  special  muscle  fasciculus 
of  the  peroneus  longus  or  brevis.  It  may  be  merely  a  tendinous  band,  or  it  may  be  tendinous 
at  origin  and  insertion,  with  an  intermediate  belly.  Instead  of  being  attached  to  the  fifth  toe, 
it  may  be  inserted  into  the  fifth  metatarsal,  the  cuboid,  the  tendon  of  the  peroneus  longus,  the 
calcaneus,  lateral  malleolus,  or  posterior  talo-fibular  hgament. 

Synovial  Tendon-sheaths 

Vagina  tendinum  peroneorum  communis. — There  is  a  double  sheath  for  the  tendons  of 
the  peroneal  muscles  as  they  pass  back  of  the  lateral  malleolus.  From  this  region  of  union  the 
sheath  sends  processes  along  each  tendon  proximally  above  the  malleolus  and  distally  over  the 
lateral  surface  of  the  calcaneus.  This  process  on  the  tendon  of  the  peroneus  longus  often 
communicates  with  the  following  sheath.  Vagina  tendinis  m.  peronaei  longi  plantaris. — 
This  sheath  begins  in  the  peroneal  groove  of  the  cuboid  and  ends  near  the  medial  border  of  the 
long  plantar  hgament. 

3.  Musculature  of  the  Back  op  the  Leg 

a.  Superficial  Group  (fig.  413) 

To  this  group  belong  the  gastrocnemius,  soleus,  and  plantaris  muscles.  They 
extend  the  foot  and  flex  the  leg.  The  two  ovoid  heads  of  the  gastrocnemius  arise 
one  on  each  side  from  above  the  condyles  of  the  femur,  extend  about  to  the  middle 
of  the  back  of  the  leg,  and  are  inserted  into  the  posterior  surface  of  the  tendon  of 
Achilles,  and  through  this  into  the  back  of  the  calcaneus.  The  broad,  flat,  ovoid 
soleus  arises  beneath  the  gastrocnemius  from  the  tibia  and  fibula,  and  is  in- 
serted into  the  deep  surface  of  the  tendon  of  Achilles  as  far  as  the  ankle.  The 
two  heads  of  the  gastrocnemius  and  the  soleus  constitute  the  triceps  surag.  The 
plantaris  is  a  slender  muscle  which  passes  along  the  medial  margin  of  the  lateral 
head  of  the  gastrocnemius  and  beneath  the  medial  head,  where  it  gives  rise  to  a 
slender  tendon  that  runs  between  the  gastrocnemius  and  soleus  and  along  the 
medial  margin  of  the  tendon  of  Achilles  to  the  fatty  fibrous  tissue  of  the  heel. 
The  nerve-supply  is  from  the  tibial  nerve. 

The  muscles  of  this  group  have  a  common  embryonic  origin,  and  are  first  differentiated 
on  the  fibular  side  of  the  leg,  whence  they  extend  over  the  posterior  tibial  vessels  and  nerve  to 
their  medial  attachments.  The  gastrocnemius  corresponds  with  the  flexor  carpi  radialis  and 
ulnaris,  the  plantaris  with  .the  palmaris  longus,  the  soleus  with  a  portion  of  the  flexor  digitorum 


PLANTARIS  485 

sublimis  of  the  forearm.     In  many  of  the  monkeys  and  in  the  prosimians  the  plantaris  is  much 
more  developed  than  in  man. 

The  gastrocnemius  (fig.  413). — Medial  head. — Origin. — From  a  facet  on  the  back  of  the 
medial  condyle  of  the  femur  above  the  articular  surface,  from  an  area  on  the  back  of  the  femur 
superior  and  lateral  to  this,  and  from  the  femoral  margin  of  the  capsule  of  the  knee-joint. 
Lateral  head. — Origin. — From  a  facet  on  the  proximal  portion  of  the  postero-lateral  surface 
of  the  lateral  condyle  of  the  femur  and  from  a  rough  area  situated  more  medially  and  at  a 
greater  distance  from  the  joint. 

Structure  and  insertion. — The  heads  of  the  gastrocnemius  are  similar  in  structure.  From  the 
condylar  facets  there  descend  aponeurotic  bands,  one  oh  the  medial  margin  and  the  medial  side 
of  the  posterior  surface  of  the  medial  head,  the  other  on  the  lateral  margin  and  the  lateral  side 
of  the  posterior  surface  of  the  lateral  head.  These  bands  descend  about  two-thirds  of  the  way 
down  the  muscle.  In  the  tendon  of  the  lateral  head  a  sesamoid  bone  is  frequently  found.  The 
fibre-bundles  of  the  muscle  pass  obhquely  from  the  supracondylar  areas  of  origin  and  from  the 
deep  surface  of  the  aponeurosis  on  each  side  to  the  tendon  of  insertion.  This  tendon  begins  as 
a  septum  between  the  two  heads,  and  as  a  lamina  on  the  deep  surface  of  each  head.  The  septum 
and  laminae  soon  fuse  with  the  broad  aponeurosis  which  covers  the  dorsal  surface  of  the  soleus. 
The  attachment  of  fibre-bundles  continues  to  about  the  middle  of  the  back  of  the  leg.  The 
attachment  of  the  medial  head  extends  more  distaUy  than  that  of  the  lateral  head.  As  a  rule, 
the  medial  head  is  also  the  broader  and  thicker  of  the  two. 

The  soleus. — Origin. —  (1)  By  a  fibular  head  from  the  back  of  the  head  and  the  proximal 
third  of  the  posterior  surface  of  the  shaft  of  the  fibula,  and  from  the  intermuscular  septum 
between  it  and  the  peroneus  longus;  and  (2)  by  a  tibial  head  from  the  transverse  septum  over  the 
distal  margin  of  the  pophteus,  from  the  popliteal  line,  and  from  the  middle  third  of  the  medial 
border  of  the  tibia. 

Structure  and  insertion.'- — From  the  fibular  and  tibial  origins  arise  broad  aponeuroses  which 
unite  proximally  on  the  deep  surface  of  the  muscle  so  as  to  form  a  fibrous  arch  over  the  pos- 
terior tibial  vessels  and  nerves.  DistaUy  they  diverge  and  become  more  narrow,  but  the  fibular 
aponeurosis  is  continued  on  the  fibular  side  and  the  tibial  aponeurosis  on  the  tibial  side  of 
the  muscle  as  far  as  the  distal  quarter  of  the  leg.  The  main  portion  of  the  belly  of  the  muscle 
is  formed  by  fibre-bundles  which  arise  from  the  posterior  surface  of  these  aponeuroses  and 
pass  obliquely  to  be  inserted  in  a  bipenniform  manner  on  the  deep  surface  of  the  tendon  of 
Achilles.  This  tendon  begins  as  a  broad  aponeurosis  which  covers  the  greater  part  of  the 
posterior  surface  of  the  muscle,  and  gradually  converges  into  a  heavy  fibrous  band  that  is  in- 
serted into  the  calcaneus.  The  bundles  of  fibres  of  the  tendon  take  a  slightly  spiral  course. 
Those  on  the  posterior  surface  run  from  the  medial  margin  toward  the  lateral  surface  of  the 
calcaneus;  those  on  the  anterior  surface  in  a  reverse  direction.  The  attachment  of  the  fibre- 
bundles  continues  to  within  a  short  distance  of  the  heel.  A  few  of  the  fibre-bundles  arise 
directly  from  the  fibula  and  the  posterior  intermuscular  septum.  On  the  deep  surface  of  the 
belly  of  the  muscle  there  is  an  accessory  fasciculus  which  is  formed  by  fibre-bundles  that  spring 
on  each  side  from  the  anterior  surface  of  the  aponeuroses  of  origin  of  the  muscle  and  have  a 
bipenniform  insertion  on  each  side  of  a  thin,  obUque  tendinous  lamina  which  inferiorly  becomes 
united  to  the  deep  surface  of  the  tendon  of  Achilles. 

The  plantaris  (fig.  413). — This  muscle  arises  from  the  distal  part  of  the  lateral  line  of 
bifurcation  of  the  Unea  aspera,  in  close  association  with  the  lateral  head  of  the  gastrocnemius. 
The  fibre-bundles  give  rise  to  a  flat,  short,  fusiform  belly,  and  are  united  to  a  narrow  tendon 
which  extends  along  the  medial  edge  of  the  tendon  of  Achilles  to  the  lateral  part  of  the  dorsal 
surface  of  the  calcaneus,  where  it  terminates  in  the  neighbouring  fibrous  tissue. 

Nerve-supply. — From  the  tibial  (internal  pophteal)  part  of  the  sciatic  nerve  in  the  popliteal 
space  nerves  arise  for  each  head  of  the  gastrocnemius.  Each  nerve  enters  the  middle  third  of  the 
deep  surface  of  the  head  near  the  proximal  margin.  The  nerve-supply  for  the  soleus  is  from  two 
sources.  One  nerve  arises  in  the  pophteal  space,  often  in  company  with  the  nerve  to  the  lateral 
head  of  the  gastrocnemius.  It  enters  the  posterior  surface  of  the  muscle  near  the  proximal 
border  and  divides  into  two  branches,  one  for  each  head  of  the  muscle.  The  tibial  (posterior 
tibial)  nerve  gives  rise  to  a  branch  which,  about  half-way  down  the  leg,  enters  the  deep  surface 
of  the  muscle  and  furnishes  branches  for  the  deep  portion  of  the  muscle  on  each  side.  The 
nerve-supply  of  the  plantaris  is  by  a  branch  from  the  tibial  (internal  popliteal)  portion  of 
the  sciatic.     This  arises  in  the  popliteal  space  and  enters  the  deep  surface  of  the  muscle. 

Relations. — The  semimembranosus  winds  about  the  medial  margin  of  the  medial  head  of 
the  gastrocnemius  to  its  deep  surface.  The  biceps  passes  to  the  lateral  side  of  the  lateral  head 
of  the  gastrocnemius,  and  the  plantaris  along  its  mecUal  margin.  The  semimembranosus  and 
biceps  above,  the  medial  head  of  the  gastrocnemius  and  the  plantaris  below,  bound  the  ponUteal 
space.  The  peroneal  (external  popliteal)  nerve  passes  from  the  popliteal  space  obliquely  across 
the  plantaris  and  the  lateral  head  of  the  gastrocnemius.  The  medial  sural  (short  saphenous) 
nerve  and  the  small  saphenous  vein  pass  between  the  heads  of  the  gastrocnemius  to  the  surface 
and  thence  to  the  lateral  side  of  the  ankle.  From  the  peroneal  (external  pophteal)  nerve  in  the 
popliteal  space  the  lateral  sural  (communicans  peronei)  nerve  extends  distaUy  over  the  calf. 
The  (posterior)  tibial  nerve  and  posterior  tibial  artery  and  vein  run  between  the  two  heads  of  the 
gastrocnemius,  and  then  beneath  the  soleus  to  the  medial  side  of  the  ankle.  In  the  region  of  the 
tendon  of  Achilles  a  considerable  space  filled  with  fatty  tissue  intervenes  between  the  tendon 
and  the  transverse  septum. 

Action. — The  contraction  of  the  triceps  surte  produces  extension,  adduction,  and  inversion 
of  the  foot.  The  gastrocnemius  is  also  a  flexor  of  the  leg.  The  plantaris  has  no  known  function 
in  man.     In  some  animals  it  is  an  extensor  of  the  plantar  fascia. 

Variations. — There  is  considerable  variation  in  the  extent  of  the  separation  of  the  different 
parts  of  the  triceps  sura;.  The  tendons  of  the  three  heads  may  be  separate  nearly  to  the  heel. 
Either  or  both  heads  of  the  gastrocnemius  or  the  soleus  may  be  doubled.     A  shp  from  the  biceps 


486  THE  MUSCULATURE 

or  semimembranosus,  from  the  linea  aspera,  or  popliteal  space  may  join  the  triceps  and  give 
rise  to  a  quadriceps  surse.  On  the  other  hand,  one  of  the  heads  of  the  gastrocnemius  or  the 
tibial  head  of  the  soleus  may  be  missing.  A  supernumerary  fasciculus  may  extend  from  the 
deep  surface  of  the  soleus  to  the  calcaneus.  The  plantaris  is  exceedingly  variable  in  origin, 
structure,  and  insertion.  The  origin  may  be  from  the  capsule  of  the  knee-joint,  the  fascia  of  the 
leg,  or  from  the  tibia.  Its  tendon  may  terminate  at  almost  any  part  of  its  course  in  neighbouring 
structures.  It  may  be  represented  by  a  fibrous  band.  It  is  absent  in  about  7  per  cent,  of 
instances  (Le  Double). 

BURS^ 

B.  m.  gastrocnemii  lateralis. — A  bursa  is  often  found  between  the  tendon  of  the  lateral 
head  of  the  gastrocnemius  and  the  capsule  of  the  joint.  It  may  communicate  with  the  joint 
cavity.  B.  m.  gastrocnemii  mediaUs. — A  bursa  usually  hes  between  the  tendon  of  origin  of 
the  medial  head  of  the  gastrocnemius,  the  condyle  of  the  humerus,  and  the  capsule  of  the  joint. 
Another  bursa  (b.  m.  semimembranosi)  extends  between  the  semimembranosus  and  the  medial 
head  of  the  gastrocnemius  muscle.  The  two  bursaj  frequently  communicate  with  one  another 
and  with  the  joint.  B.  tendinis  calcanei. — This  lies  between  the  tendon  of  AchiUes  and  the 
upper  part  of  the  back  of  the  calcaneus.  Between  the  back  of  the  tendon  and  the  crural  fascia 
another  bursa  is  frequently  present. 

h.  Deep  Group 

The  deep  posterior  musculature  is  separated  from  the  superficial  by  the  trans- 
verse septum  described  above  (p.  479).  The  muscles  covered  by  this  septal  fascia 
are  the  popliteus,  the  flexor  digitorum  longus,  the  flexor  hallucis  longus,  and 
the  tibialis  posterior.  An  intermuscular  septum  between  the  popliteus  and  the 
tibialis  posterior,  and  the  attachment  of  the  soleus  to  the  popliteal  line  on  the 
back  of  the  tibia  serve  to  separate  the  popliteus  from  the  other  deep  posterior 
muscles  which  lie  distal  to  this  region  and  send  tendons  into  the  sole  of  the  foot 
The  deep  posterior  musculature  may  thus  be  considered  as  divided  into  a  proximal 
femoro-tibial  and  a  distal  cruro-pedal  group.  Both  sets  of  muscles  are  supplied 
by  branches  of  the  tibial  nerve. 

Femoro-tibial  Muscle 

The  popliteus  (fig.  416). — A  triangular  muscle  which  arises  from  an  ovoid 
facet  at  the  inferior  extremity  of  the  groove  on  the  outer  side  of  the  lateral  condyle 
of  the  femur  and  is  inserted  into  the  proximal  lip  of  the  popliteal  line  of  the  tibia 
and  the  surface  of  the  shaft  of  the  tibia  proximal  to  this.  It  rotates  the  leg 
medialward  and  flexes  it. 

Structure. — From  the  origin  a  broad  tendon  ghdes  over  the  condyle  within  the  capsule  of 
the  joint,  then  over  the  lateral  fibro-cartilage  and  through  a  groove  on  the  back  of  the  tibio-fibu- 
lar  articulation.  From  both  surfaces  of  this  tendon,  fibre-bundles  diverge  toward  the  area  of 
insertion.  The  tendon  is  more  or  less  intimately  united  to  several  structures  with  which  it 
comes  in  contact  about  the  joint.  Rarely  it  contains  a  sesamoid  bone.  The  fibres  of  insertion 
terminate  in  part  in  the  fascia  covering  the  muscle.  The  pophteus  is  homologous  with  the 
pronator  teres  of  the  arm,  or,  according  to  some  investigators,  with  the  deep  portion  of  that 
muscle. 

Nerve-supply. — -A  nerve  which  arises  either  independently  or  in  conjunction  with  that  to 
the  posterior  tibial  muscle  enters  the  popliteus  near  the  middle  of  its  distal  edge.  Sometimes 
a  branch  from  the  chief  nerve  to  the  knee-joint  enters  the  proximal  edge  of  the  muscle. 

Action. — To  flex  and  rotate  the  leg  medially. 

Relations. — The  popliteus  lies  within  a  compartment  bounded  by  the  transverse  septum, 
the  capsules  of  the  knee  and  superior  tibio-fibular  joints,  the  back  of  the  tibia,  and  a  septum 
extending  to  the  pophteal  line  (see  above).  On  the  transverse  septum  run  the  popliteal  vessels 
and  the  tibial  nerve.  The  proximal  margin  of  the  soleus  overlaps  the  distal  margin  of  the 
popliteus.  The  synovial  membrane  of  the  knee-joint  sends  a  prolongation  between  its  tendon 
and  the  back  of  the  lateral  condyle  of  the  tibia. 

Variations. — It  is  rarely  absent.  An  accessory  head  may  arise  from  the  medial  side  of 
the  lateral  condyle  or  from  some  neighbouring  structure.  The  fibulo-tibialis  (peroneo-tibiaUs) 
is  a  small  muscle  found  by  Gruber  in  one  body  in  seven.  It  arises  from  the  medial  side  of  the 
head  of  the  fibula  and  is  inserted  into  the  posterior  surface  of  the  tibia  beneath  the  popliteus. 

Cruro-pedal  Muscles  (figs.  416,  420) 

Of  the  three  muscles  of  this  group,  the  flexor  digitorum  longus  lies  on  the 
tibial  side  of  the  leg,  the  flexor  hallucis  longus  on  the  fibular  side,  and  the  tibialis 
posterior  upon  the  interosseous  membrane,  partly  covered  by  the  other  two 


CRURO-PEDAL  MUSCLES 


487 


muscles,  beneath  the  former  of  which  it  crosses,  distally,  to  the  tibial  side  of  the 
leg.  Septa  separate  the  flexor  muscles  from  the  tibialis.  The  tendons  of  the 
three  muscles  pass  behind  the  medial  malleolus,  held  in  place  by  the  transverse 
septum  and  the  deep  layer  of  the  laciniate  (internal  annular)  ligament.     They  lie 

Fig.  416. — The  Deep  Muscles  op  the  Back  of  the  Leg. 


Lateral  head  of  gastrocnemius t-r-     ?  *«)   i  ,     I  t~^/  J 


y-^-\ —  Medial  head  of  gastrocnemius 


Peroneus  longus 


Flexor  hallucis  longus 


Peroneus  brevis 


Tendon  of  semi-membranosus 


Tibialis  posterior 


Flexor  digitorum  longus 


Tibialis  posterior 
Laciniate  ligament 

Tendo  Achillis 


in  compartments  divided  by  septa  which  descend  to  the  tibia.  The  compart- 
ment for  the  tibialis  posterior  is  the  most  medial.  It  is  partly  overlapped  by 
that  for  the  flexor  digitorum.  At  the  ankle  the  tendon  of  the  tibialis  passes 
above,  the  tendon  of  the  flexor  digitorum  medial  to,  and  that  of  the  flexor  hallucis 
below,  the  sustentaculum  tall,  each  in  a  separate  osteo-fibrous  canal  bounded 


488 


THE  MUSCULATURE 


Fig.  417.  A-D. — Transverse  Sections  through  the  Foot  in  the  Regions  Shown  in  the 

Diagram. 

/in  the  diagram  indicates  the  region  through  which  passes  section  F,  fig.  414  (p.  478). 
1.  Arteria  peronea.  2.  A.  plantaris  mediaUs  (internal).  3.  A.  plantaris  lateralis  (external). 
4.  A.  tibiahs  anterior.  5.  Aponeurosis  plantaris.  6.  Calcaneus.  7.  Fascia  pedis  dorsalis. 
8.  F.  plantaris — a,  lateral;  b,  intermediate;  c,  medial.  9.  Ligamentum  cruciatum  (anterior 
annular).  10.  L.  laciniatum  (internal  annular).  11.  Malleolus  lateralis  (external).  12. 
Malleolus  medialis  (internal).  13.  Musculus  abductor  hallucis — a,  tendon.  14.  M. 
abductor  quinti  digiti — a,  insertion.  15.  M.  adductor  hallucis —  a,  oblique  head,  origin; 
b,  transverse  head.  16.  M.  extensor  digitorum  brevis — a,  tendons.  17.  M.  extensor  digi- 
torum  longus,  tendons.  18.  M.  extensor  hallucis  longus,  tendon.  19.  M.  flexor  digitorum 
brevis — a,  tendon.  20.  M.  flexor  digiti  quinti  brevis — a,  tendon.  21.  M.  flexor  digitorum 
longus,  tendon.  22.  M.  flexor  hallucis  brevis  tendon.  23.  M.  flexor  hallucis  longus. 
24.  M.  interossei  dorsales.  25.  M.  interossei  plantares.  26.  M.  lumbricales.  27.  M. 
peroneus  brevis.  28.  M.  peroneus  longus.  29.  M.  peroneus  tertius — a,  tendon.  30. 
M.  planaris,  tendon.  31.  M.  quadratus  plantae.  32.  M.  tibialis  anterior,  tendon.  33. 
M.  tibialis  posterior,  tendon.  34.  Nervus  peroneus  profundus.  35.  N.  peronsus  superficialis 
(musculo-cutaneous).  36.  N.  plantaris  medialis  (internal).  37.  N.  plantaris  laterahs 
(external).  38.  N.  surahs  (external  saphenous) .  39.  Os  cuneiform  I,  40.  Os  cuneiform 
III.  41.  Os  cuboid.  42.  Osmetacarpalel.  43.  Os  metacarpalell.  44.  Os  metacarpale 
III.  45.  Os  metacarpale  IV.  46.  Os  metacarpale  V.  47.  Os  naviculare.  48.  Ossa 
sesamoidea.  49.  Os  talus  (astragalus).  50.  Tendo  Achillis  51.  Retinacula  mm. 
peroneorum.  52.  Septum  intermusculare  laterale.  53.  S.  intermusculare  mediale.  54. 
Vena  saphena  magna. 


FLEXOR  DIGITORUM  LONGUS 

29  17 


externally  by  the  laciniate  (internal  annular)  ligament.  In  the  sole  the  tendon  of 
the  long  flexor  of  the  big  toe  passes  under  (deeper  than)  the  tendon  of  the  flexor 
digitorum,  to  which  it  gives  a  slip,  and  is  inserted  into  the  terminal  phalanx  of 
the  big  toe.  The  tendon  of  the  long  flexor  of  the  toes  passes  obliquely  across  the 
sole,  is  joined  by  the  quadratus  plantae  (flexor  accessorius),  and  gives  rise  to  a 
tendon  for  the  terminal  phalanx  of  each  of  the  four  lateral  toes.  From  these 
tendons  the  lumbrical  muscles  arise.  The  tibialis  posterior  has  an  extensive 
insertion  on  the  plantar  surface  of  the  tarsus. 

The  long  flexors  act  chiefly  on  the  toes.  Together  with  the  tibialis  posterior 
they  invert  and  extend  the  foot. 

The  long  flexors  of  the  toes  probably  represent  the  flexor  profundus  and  the  flexor  polhcis 
longus  of  the  forearm.  The  tendons  of  the  deep  flexors  of  the  forearm  do  not,  however,  cross 
like  those  of  the  long  flexors  of  the  toes.  In  the  lower  mammals  there  is  much  variation  in  the 
toes  to  which  the  tibial  and  fibular  flexors  are  distributed.  The  tibiahs  posterior  has  no  certain 
representative  in  the  forearm.     The  rare  ulno-carpeus  may  represent  it. 

The  flexor  digitorum  longus  (figs.  416,  420). — Origin. — From  the  popUteal  line,  the  medial 
side  of  the  second  quarter  of  the  dorsal  surface  of  the  tibia,  the  fibrous  septum  between  the 
muscle  and  the  tibiahs  posterior,  and  the  fascia  covering  its  proximal  extremity. 

Structure  and  insertion. — From  these  areas  of  origin  the  fibre-bundles  run  obUquely  to  be 
inserted  in  a  penniform  manner  on  a  tendon  which  begins  in  the  proximal  quarter  of  the 
muscle  as  a  narrow  septum,  and  more  distally  becomes  a  strong  band  on  the  medial  margin. 
The  insertion  of  the  fibre-bundles  continues  nearly  to  the  medial  maUeolus.  From  here  the 
tendon  passes  behind  the  medial  malleolus,  dorso-lateral  to  the  tendon  of  the  tibiahs  posterior, 
crosses  the  posterior  talo-tibial  ligament,  and  passes  along  the  medial  margin  of  the  sustenta- 
culum tali  into  the  sole  of  the  foot.  Here  it  crosses  the  tendon  of  the  flexor  hallucis  longus, 
from  which  it  receives  a  tendinous  slip,  and  divides  into  four  parts,  which  pass  to  the  second  to 
the  fifth  toes.  Each  tendon  is  bound  to  the  phalanges  of  the  toe  to  which  it  passes  by  a  fibrous 
sheath.     Superficial  to  it  in  the  sheath  lies  a  tendon  of  the  flexor  digitorum  brevis,  which  the 


490  THE  MUSCULATURE 

,  flexor  longus  tendon  perforates  as  it  passes  to  the  base  of  the  terminal  phalanx.     The  tendon 
is  connected,  like  those  of  the  fingers,  by  vincula  tendinum,  to  the  phalanges  of  the  toes. 

Nerve-supply. — From  the  tibial  (posterior  tibial)  nerve  a  branch  arises,  often  in  company 
with  nerves  to  some  other  or  others  of  the  muscles  of  this  group.  The  nerve  divides  into  two 
branches,  one  of  which  passes  to  the  lateral  side  of  the  muscle,  where  it  extends  along  near  the 
middle  of  the  fibre-bundles  of  that  side,  while  the  other  branch  passes  along  near  the  middle 
of  the  fibre-bundles  of  the  medial  side  of  the  muscle. 

Relations. — In  the  proximal  half  of  the  leg  it  lies  on  the  tibia,  in  the  distal  half  on  the 
posterior  tibial  muscle.  Between  it  and  the  flexor  hallucis  lie  the  posterior  tibial  vessels  and 
nerve.  Near  the  ankle  the  plantar  vessels  and  nerves  cross  the  tendon  of  the  muscle,  separated 
from  it  by  the  deep  layer  of  the  laciniate  (internal  annular)  ligament.  In  the  upper  two-thirds 
of  its  extent  it  is  covered  by  the  triceps  surte.  In  the  lower  third  of  the  leg  it  emerges  medial  to 
the  soleus  and  the  tendon  of  Achilles.  The  relations  of  its  tendon  at  the  ankle  have  been  de- 
scribed above.  The  tendon  Ues  beneath  the  origin  of  the  abductor  hallucis  muscle  and  in  the 
sole  is  covered  by  the  flexor  digitorum  brevis,  crosses  the  tendon  of  the  long  flexor  and  the 
oblique  adductor  of  the  big  toe  and  the  interosseous  muscles,  is  joined  by  the  quadratus  plantse 
(flexor  accessorius),  and  gives  origin  to  the  lumbrical  muscles. 

The  flexor  hallucis  longus  (figs.  416,  420). — Origin. — From  the  distal  two-thirds  of  the 
posterior  surface  of  the  fibula,  the  septa  between  it  and  the  tibialis  posterior  and  peroneal 
muscles,  and  the  fascia  above  its  proximal  extremity. 

Structure  and  insertion. — The  fibre-bundles  converge  upon  a  tendon  which  begins  in  the 
second  quarter  of  the  muscle,  within  its  substance,  and  emerges  upon  the  postero-medial  margin 
in  its  distal  half.  The  insertion  of  the  fibre-bundles  continues  to  the  end  of  the  tibia.  From 
here  the  tendon  passes  over  the  dorsal  talo-tibial  (tibio-astragaloid)  ligament,  and  through  the 
groove  on  the  posterior  surface  of  the  talus  and  the  under  surface  of  the  sustentaculum  tali, 
where  it  lies  on  the  fibular  side  of  the  tendon  of  the  flexor  digitorum  longus.  It  then  crosses 
the  deep  surface  of  this  tendon,  to  which  it  gives  a  slip,  passes  over  the  plantar  surface  of  the 
medial  head  of  the  flexor  hallucis  brevis,  and  between  the  sesamoid  bones  of  this  muscle  into 
the  osteo-fibrous  canal  on  the  plantar  surface  of  the  big  toe.  It  is  inserted  into  the  base  of 
the  terminal  phalanx  of  the  big  toe. 

Nerve-supply. — The  nerve  arises  from  the  tibial  (posterior  tibial)  nerve,  often  in  company 
with  the  nerve  to  the  flexor  digitorum  longus  or  the  other  muscles  of  the  group.  It  runs 
along  the  deep  surface  of  the  muscle  and  sends  twigs  into  the  middle  third  of  its  constituent 
fibre-bundles.     Sometimes  two  nerves  are  furnished  to  the  muscle. 

Relations. — It  hes  on  the  fibular  side  of  the  distal  two-thirds  of  the  leg.  ProximaUy  it 
diverges  from  the  preceding  muscle  so  as  to  disclose  the  tibiahs  posterior,  which  is  more  deeply 
situated.  Between  it  and  the  tibialis  posterior  he  the  peroneal  vessels.  Distally  its  tibial 
margin  approaches  the  flexor  digitorum  longus,  but  between  them  lie  the  posterior  tibial  vessels 
and  nerve.  Lateral  to  it  lie  the  peroneal  muscles.  It  is  covered  in  the  leg  by  the  soleus.  In 
the  distal  part  of  the  leg  its  tendon  hes  medial  to  the  tendon  of  Achilles.  On  entering  the  foot 
the  tendon  crosses  beneath  the  abductor  hallucis  muscle  and  the  lateral  plantar  vessels  and 
nerve.     The  other  relations  of  the  tendon  have  been  described  above. 

The  tibialis  posterior  (figs.  416,  422). — Origin. — From — (1)  the  lateral  half  of  the  distal 
margin  of  the  popliteal  line  and  the  middle  third  of  the  posterior  surface  of  the  tibia;  (2)  the 
medial  side  of  the  head  and  of  that  part  of  the  body  of  the  fibula  next  the  interosseous  mem- 
brane in  the  proximal  two-thirds;  (3)  from  the  whole  of  the  proximal  and  the  lateral  portion  of 
the  distal  part  of  the  posterior  surface  of  the  interosseous  membrane;  and  (4)  from  the  septa 
between  its  proximal  portion  and  the  long  flexor  muscles. 

Structure. — From  this  extensive  area  of  origin  the  fibre-bundles  converge  upon  a  tendon 
which  is  at  first  deep  seated  within  the  muscle-belly,  but  about  the  middle  of  the  leg  emerges 
on  the  medial  margin  of  the  muscle.  The  fibular  portion  of  the  muscle  is  much  more  extensive 
than  the  tibial.  The  proximal  fibres  take  a  nearly  perpendicular,  the  most  distal  (from 
the  fibula)  a  nearly  transverse,  course.  The  insertion  of  fibres  stops  a  little  proximal  to 
the  medial  malleolus.  The  tendon  then  extends  to  the  medial  side  of  the  tendon  of  the  long 
flexor  of  the  toes,  passes  through  the  groove  on  the  back  of  the  malleolus,  across  the  medial 
talo-tibial  (tibio-astragaloid)  ligament,  and  above  the  sustentaculum  tali  to  the  sole. 

Insertion. — The  tendon  divides  into  two  chief  divisions,  a  deep  and  a  superficial.  (1) 
The  deep  portion  becomes  attached  chiefly  to  the  tubercle  of  the  navicular  bone,  and  usually 
in  part  also  to  the  first  cuneiform.  (2)  The  superficial  spreads  out  to  be  attached  chiefly  to  the 
third  cuneiform  and  the  base  of  the  fourth  metatarsal,  but  also  in  part  to  the  second  cuneiform, 
to  the  capsule  of  the  naviculo-cuneiform  joint,  to  the  sulcus  of  the  cuboid,  and  usually  also  to 
the  origin  of  the  short  flexor  of  the  big  toe  and  the  base  of  the  second  metatarsal.  Shps  may, 
however,  also  be  given  to  other  structures.  A  sesamoid  bone  is  usuaUy  found  in  the  tendon 
either  near  the  calcaneo-navicular  hgament  or  the  navicular  bone. 

Nerve-supply. — The  nerve  arises  from  the  tibial  (posterior  tibial)  in  company  often  with 
branches  to  the  other  muscles  of  the  group.  It  enters  the  posterior  surface  of  the  muscle  in  its 
proximal  third,  and  gives  off  one  or  two  branches  for  the  tibial  fasciculus.  The  main  trunk 
descends  across  the  middle  third  of  the  fasciculi  arising  from  the  fibula. 

Relations. — The  muscle  covers  the  posterior  surface  of  the  interosseous  membrane,  and 
extends  distally  over  the  posterior  surface  of  the  tibia  beneath  the  flexor  digitorum  longus.  It 
is  covered  proximally  by  the  soleus,  distally  by  the  two  long  digital  flexors.  The  posterior 
tibial  and  peroneal  arteries  and  the  tibial  (posterior  tibial)  nerve  run  upon  its  posterior  surface. 
The  tendon  in  the  sole  is  under  cover  of  the  origin  of  the  plantar  muscles  of  the  big  toe. 

Action. — The  tibialis  posterior  adducts  the  foot  and  slightly  inverts  it.  The  flexor  digi- 
torum longus  flexes  the  terminal  phalanx  on  the  second  and  the  second  on  the  first,  and  at  the 
height  of  its  contraction  the  first  on  the  metatarsals.  It  also  rotates  medially  to  some  extent 
the  ends  of  the  fourth  and  fifth  toes,  and  inverts  the  foot.     The  flexor  haUucis  longus  flexes 


MUSCLES  OF  FOOT  491 

the  second  phalanx  of  the  big  toe  on  the  first,  and,  less  energetically,  the  first  on  the  metatarsal. 
It  also  inverts  the  foot.  All  three  muscles  extend  the  foot.  The  flexor  haUucis  is  the  strongest 
of  the  three  in  this  respect. 

Variations. — The  muscles  of  the  group  may  be  more  or  less  fused  with  one  another  or  be 
united  by  fascicuh.  This  is  especially  common  between  the  two  flexors  of  the  toes.  The 
individual  muscles  vary  in  development.  The  flexor  digitorum  longus  may  be  more  or  less 
divided  into  separate  fasciculi  for  the  individual  toes.  The  slip  from  the  flexor  haUucis  longus 
to  the  flexor  digitorum  longus  varies  greatly  in  extent,  but  usually  passes  mainly  to  the  second 
and  third  toes,  more  rarely  to  the  second,  third,  and  fourth,  and  very  rarely  to  the  fifth.  In 
most  of  the  apes  the  tibial  flexor  (flexor  digitorum)  sends  tendons  to  the  second  and  fifth,  the 
fibular  flexor  (flexor  haUucis)  to  the  first,  third,  and  fourth  toes.  This  condition  is  also  some- 
times found  in  man.  A  slip  may  pass  from  the  tendon  of  the  flexor  digitorum  to  that  of  the 
flexor  haUucis  longus.  There  may  be  a  sesamoid  bone  in  the  tendon  of  the  flexor  haUucis 
longus  as  it  passes  over  the  talus  (astragalus)  and  calcaneus.  The  tibiahs  posterior  may  be 
doubled.  Aberrant  fasciculi  may  arise  from  various  regions  on  the  back  of  the  leg  and  join  any 
one  of  the  three  muscles  of  the  group. 

Abnormal  muscles. — The  soleus  accessorius. — Arises  by  a  tendon  from  the  head  of  the  fibula 
beneath  the  soleus.  It  is  usually  a  slender  muscle  inserted  into  the  medial  surface  of  cal- 
caneus. The  tibialis  secundus  (tensor  of  capsule  of  ankle-joint). — A  smaU  muscle  which 
arises  from  the  tibia  beneath  the  flexor  digitorum  and  is  inserted  into  the  capsule  of  the  ankle- 
joint.  The  fibulo-calcaneus  medialis  (peroneo-oalcaneus  internus  of  MacAlister,  flexor 
accessorius  long.  dig.  long.,  etc.). — A  fasciculus  which  arises  from  the  lower  third  of  the  body  of 
the  fibula  and  gives  rise  to  a  tendon  which  passes  beneath  the  laciniate  hgament  to  the  quadratus 
plantse  or  to  the  tendon  of  the  flexor  digitorum  longus. 

BURS^ 

B.  subtendinea  m.  tibialis  posterioris. — A  smaU  bursa  between  the  navicular  fibro-cartilage 
and  the  tendon. 

Synovial  Tendon-sheaths 

Vagina  m.  flexoris  digitorum  longi. — The  tendon  is  surrounded  by  a  synovial  sheath 
from  the  back  of  the  medial  malleolus  to  where  it  crosses  the  tendon  of  the  flexor  haUucis  longus 
below  the  navicular  bone.  It  may  communicate  with  the  sheath  of  the  tibialis  anterior  or  with 
that  of  the  flexor  haUucis  longus.  Vaginae  tendinum  digitales. — The  tendons  of  the  long 
flexor,  together  with  those  of  the  short  flexor,  are  surrounded  by  synovial  sheaths  from  the 
heads  of  the  metatarsals  to  the  insertions  of  the  tendons.  In  structure  these  resemble  those 
of  the  fingers.  Vagina  m.  flexoris  haUucis  longi. — The  tendon  is  surrounded  by  a  sheath 
from  the  back  of  the  medial  malleolus  to  the  crossing  of  the  tendon  of  the  flexor  digitorum 
longus.  Another  sheath  surrounds  the  tendon  from  the  middle  of  the  first  metatarsal  to  its 
insertion.  Vagina  m.  tibialis  posterioris. — The  tendon  is  surrounded  by  a  synovial  sheath  ex- 
tending from  a  region  proximal  to  the  medial  malleolus  to  the  insertion  of  the  tendon. 

D.  MUSCULATURE  OF  THE  FOOT 

On  the  dorsum  of  the  foot  there  is  a  muscle  not  represented  in  the  hand,  the 
extensor  digitorum  brevis  (fig.  418).  In  the  sole  of  the  foot  there  is  a  highly 
developed  musculature  which  may  be  subdivided  into  the  flexor  digitorum  brevis 
(fig.  419);  the  muscles  connected  with  the  long  extensor  of  the  toes,  quadratus 
plantse  and  lumbricales  (fig.  420);  the  intrinsic  muscles  of  the  great  toe,  (figs. 
419,  421);  the  intrinsic  muscles  of  the  little  toe  (figs.  419,  421);  and  the  inter- 
osseous muscles  (fig.  422).  These  muscles  abduct  and  adduct  the  toes,  flex  them 
at  the  metacarpophalangeal  joints  and  flex  and  extend  them  at  the  first  row  of 
interphalangeal  joints.  On  the  second  row  of  interphalangeal  joints  they  seem 
to  exert  relatively  little  action.  All  the  movements,  excepting  flexion,  are  weak 
in  most  individuals.  The  extensor  digitorum  brevis  is  innervated  by  the  deep 
peroneal  (anterior  tibial)  nerve.  The  muscles  of  the  sole  of  the  foot  are  all 
innervated  by  the  lateral  (external)  plantar,  except  the  flexor  digitorum  brevis, 
the  most  medial  of  the  lumbrical  muscles,  and  the  abductor  and  flexor  brevis  of 
the  great  toe,  which  are  innervated  by  the  medial  (internal)  plantar. 

FASCIiE 

Tela  subcutanea. — Over  the  dorsum  of  the  foot  the  tela  subcutanea  contains  Uttle  fat.  On 
the  sole  of  the  foot  and  the  plantar  surface  of  the  toes  it  contains  much  fat  embedded  in 
dense  fibrous  tissue. 

Muscle  fasciae. — Over  the  dorsum  of  the  foot  a  fascial  membrane  extends  from  the 
cruciate  ligament  mentioned  above  to  the  toes,  where  it  is  continued  as  fibrous  sheaths  for 
the  extensor  tendons.     Laterally  and  mediaUy  it  is  continued  into  the  plantar  fascia.     Where 


492  THE  MUSCULATURE 

it  overlies  skeletal  structures  it  becomes  adherent  to  them.  In  the  main  this  fascial  sheet  is 
thin.  Over  the  base  of  the  first  metatarsal  it  is  strengthened  by  a  band  which  runs  from  the 
medial  side  of  this  bone  over  the  extensor  tendons  of  the  big  toe  to  the  base  of  the  second 
metatarsal.  The  extensor  digitorum  brevis  is  covered  by  an  adherent  fascial  sheet.  The 
dorsal  surface  of  each  dorsal  interosseous  muscle  is  likewise  covered  by  an  adherent  membrane. 

The  plantar  surface  of  the  foot  is  invested  by  a  fascia  in  which  three  distinct  regions  may 
be  observed,  a  central,  a  lateral,  and  a  medial.  The  central  region  is  greatly  thickened  by 
bands  of  fibrous  tissue,  the  plantar  aponeurosis,  which  diverge  toward  the  toes  from  the  medial 
half  of  the  tuber  calcanei.  These  bands  become  distinct  from  one  another  as  the  toes  are 
approached,  and  each  finally  terminates  partly  in  the  skin  over  the  head  of  the  corresponding 
metatarsal  and  in  the  digital  sheath  of  the  flexor  tendons.  Some  of  the  fibres  are  continued 
into  the  transverse  capitular  ligaments,  the  others  extend  through  near  the  metatarsophalangeal 
articulation  to  the  dorsum  of  the  foot.  Broader,  thicker  bands  go  to  the  three  middle  toes 
than  to  the  big  and  little  toes.  At  the  margins  of  this  central  area  some  fibres  radiate  into 
the  fascia  of  the  lateral  and  medial  area,  some  extend  lateraUy  into  the  skin,  and  some  sink 
into  the  intermuscular  septa  described  below.  Near  the  toes  well-marked  transverse  bundles 
of  fibres  may  be  seen  between  the  digital  bands.  The  central  area  of  the  plantar  fascia  is  not 
densely  adherent  to  the  skin. 

The  digital  sheaths  of  the  flexor  tendons  of  the  toes  correspond  essentially  with  those 
previously  described  (p.'  387)  for  the  fingers. 

The  medial  plantar  fascia  is  thin  and  adherent  to  the  skin.  It  extends  between  the  central 
plantar  and  the  dorsal  fascia  over  the  intrinsic  muscles  of  the  big  toe.  The  lateral  plantar 
fascia  is  thick  and  well  developed  near  the  heel,  thin  as  the  little  toe  is  approached.  A  dense 
band,  the  calcaneo -metatarsal  ligament,  strengthens  it  between  the  calcaneus  and  the  tuberosity 
of  the  fifth  metatarsal. 

At  the  junction  of  the  lateral  with  the  central  region  of  the  plantar  fascia  the  lateral  inter- 
muscular septum  sinks  in  to  be  attached  to  the  first  cuneiform,  the  navicular  and  the  tendon 
of  the  posterior  tibial.  A  similar  medial  intermuscular  septum  sinks  in  between  the  medial  and 
central  regions  of  the  plantar  fascia  and  is  attached  to  the  long  plantar  hgament,  the  tendon 
sheath  of  the  peroneus  longus  and  the  base  of  the  fifth  metatarsal.  The  fascia  of  each  of  these 
regions  in  considerable  part  extends  into  these  septa  instead  of  becoming  continuous  across  them. 

The  sole  is  thus  divided  into  three  great  fascial  compartments  by  these  septa,  a  lateral,  a 
central,  and  a  medial.  In  the  lateral  fie  the  intrinsic  pedal  muscles  of  the  little  toe;  in  the 
medial,  the  abductor  and  the  flexor  brevis  of  the  big  toe  and  the  distal  end  of  the  tendon  of 
the  flexor  hallucis  longus.  The  central  compartment  is  subdivided  by  transverse  septa  into 
several  sub-compartments.  In  the  most  superficial  compartment  lies  the  flexor  digitorum 
brevis;  in  the  second,  the  tendons  of  the  flexor  digitorum  longus  and  its  associated  muscles, 
the  quadratus  plantse  (flexor  accessorius)  and  the  lumbrical  muscles;  in  the  third,  the  adductor 
muscles  of  the  big  toe;  and  in  the  fourth,  the  interosseous  muscles. 

The  first  two  sub-compartments  are  most  clearly  marked  in  the  region  of  the  tarsus. 
Distally  they  become  merged  by  the  disappearance  of  the  intervening  transverse  septum,  and 
longitudinaUy  subdivided  by  fibrous  septa  which  serve  to  make  a  complete  sheath  over  each 
digit  for  the  flexor  tendons.  The  sheath  over  the  adductor  muscle  of  the  big  toe  is  a  thin  mem- 
brane continued  laterally  from  the  medial  intermuscular  septum.  Where  the  two  heads  of  the 
adductor  muscle  advance  upon  their  tendon  of  insertion,  the  medial  septum  has  no  skeletal  at- 
tachment, so  that  the  adductor  sub-compartment  of  the  middle  fascial  compartment  com- 
municates freely  with  the  medial  compartment.  Over  the  cuneiform  bones  the  tendon  of 
the  flexor  hallucis  longus  passes  from  the  long  flexor  region  of  the  middle  compartment  into 
the  medial  compartment.  Here  the  medial  intermuscular  septum  divides  into  two  layers, 
which  form  a  sheath  for  the  tendon  as  it  passes  to  the  plantar  surface  of  the  flexor  hallucis 
brevis. 

MUSCLES 

1.  Muscle  of  the  Dorsum  of  the  Foot 

The  extensor  digitorum  brevis  (fig.  418). — This  muscle  is  broad  and  thin, 
lies  beneath  the  tendons  of  the  long  extensor  muscle  on  the  tarsus,  lateral  to  the 
navicular  and  the  head  of  the  talus,  and  sends  tendons  to  the  four  more  medial 
toes.     It  arises  from  the  calcaneus.     Its  nerve-supply  is  from  the  deep  peroneal. 

Origin. — From  the  lateral  and  superior  surfaces  of  the  body  of  the  calcaneus  and  from  the 
apex  of  the  cruciate  hgament. 

Structure  and  insertion. — The  fibre-bundles  arise  directly  from  the  hgament,  and  by  short 
tendinous  bands  from  the  bone.  As  they  extend  distally  they  become  grouped  into  four  beUies. 
Those  of  the  most  medial  and  largest  beUy,  the  extensor  hallucis  brevis,  become  inserted  in  a 
bipenniform  manner  on  the  lateral  and  medial  margins  of  a  tendon  which  begins  opposite  the 
cuboid.  The  insertion  of  fibre-bundles  continues  to  the  base  of  the  first  metatarsal.  The  in- 
sertion of  the  fibre-bundles  of  the  other  belUes,  which  are  seldom  so  distinctly  isolated  as  the 
first,  takes  place  in  a  penniform  manner  into  their  respective  tendons,  but  the  exact  mode  of 
attachment  is  subject  to  great  individual  variations.  The  tendon  of  the  first  digit  is  inserted 
mainly  into  the  middle  of  the  back  of  the  base  of  the  first  phalanx,  but  it  is  often  also  united 
to  the  tendon  of  the  long  extensor.  The  other  three  tendons  are  fused  with  the  lateral  margins 
of  the  corresponding  tendons  of  the  long  extensor  near  the  bases  of  the  three  middle  digits. 
They  also  usually  give  shps  to  the  bases  of  the  first  phalanges  of  the  corresponding  toes. 


MUSCLES  OF  THE  SOLE 


493 


Nerve-stipply. — The  deep  peroneal  (anterior  tibial)  nerve,  which,  accompanied  by  the 
anterior  tibial  artery,  passes  beneath  the  medial  beUy  of  the  muscle,  gives  off  a  branch  which 
passes  transversely  across  the  middle  of  the  deep  surface  of  the  muscle  and  sends  twigs  into  it. 

Relaiions. — It  lies  on  the  lateral  side  of  the  tarsus,  beneath  the  long  extensor  tendons  of  the 
toes.     The  relations  of  its  tendons  have  been  described  above. 

Action. — It  aids  the  long  extensors  in  extending  the  first  phalanx  of  each  of  the  four  medial 
digits.  It  has  but  a  limited  action  on  the  second  and  third  phalanges.  It  serves  also  to  pull 
the  ends  of  the  toes  to  which  its  tendons  go  toward  the  little  toe. 

Fig.  418. — The  Muscle  of  the  Dorsum  of  the  Foot. 


Transverse  crural  ligament 


Extensor  digitorum  longus  — -f—  ::^ ^ 


Extensor  digitorum  brevis 


Extensor  hallucis  longus 


Peroneus  brev 


Cruciate  ligament 


Peroneus  tertius 


Flexor  digit!  V  brevis 


Variations. — The  muscle  shows  great  variation  in  development.  Rarely  the  whole  muscle, 
more  frequently  one  or  more  of  its  digital  divisions,  may  be  missing.  On  the  other  hand,  it  may 
be  more  highly  developed  than  usual.  Accessory  fasoicuh  vary  greatly  in  origin  and  termi- 
nation. Most  frequently  their  tendons  go  to  a  metacarpo-phalangeal  articulation  or  to  the 
second  or  the  fifth  toe. 

2.   Muscles  of  the  Sole  of  the  Foot 

a.  Flexor  Digitorum  Brevis  (fig.  419) 

The  flexor  digitorum  brevis,  the  most  superficially  placed  of  the  plantar 
muscles,  lies  in  the  mid-plantar  region  beneath  the  plantar  fascia  and  over  the 
tendons  of  the  long  flexor  of  the  toes  and  its  associated  muscles.  It  arises  from 
the  calcaneus,  and  has  a  flat,  elongated  belly,  which  toward  the  middle  of  the  sole 
is  prolonged  into  four  processes,  each  of  which  has  a  special  tendon  that  is  inserted 
into  the  second  phalanx  of  one  of  the  four  lateral  toes.  The  tendons  of  the  muscle 
correspond  to  those  of  the  flexor  sublimis  in  the  palm.     The  belly  of  the  flexor 


494 


THE  MUSCULATURE 


The  nerve  supply  is  from 


sublimis  is  supposed  to  be  represented  by  the  soleus. 
the  medial  (internal)  plantar. 

Origin. — From  (1)  the  medial  process  of  the  tuber  calcanei;  (2)  the  posterior  third  of  the 
plantar  aponeurosis;  and  (3)  the  medial  and  lateral  intermuscular  septa. 

Structure. — The  constituent  fibre-bundles  pass  distally  in  a  compact  mass.  The  tendons 
of  insertion  begin  within  the  muscle  substance,  and  as  the  fibre-bundles  become  inserted  on 
them,  the  separate  fascicuh  become  more  and  more  distinct.  The  fascicuU  for  the  second  and 
third  toes  are  larger  and  arise  more  superficially  than  those  for  the  fourth  and  fifth  toes.  The 
fasciculus  for  the  fifth  toe  is  often  very  small,  and  its  tendon  takes  an  obhque  course  to  the 
insertion. 

Insertion. — The  tendons  of  the  short  flexor  pass  superficial  to  those  of  the  long  flexor  into 
the  osteo-fibrous  canals  on  the  flexor  surface  of  the  digits.  Upon  the  first  phalanx  of  each  toe 
the  tendon  of  the  short  flexor  divides  and  forms  an, opening  (chiasma  tendinis)  through  which 

Fig.  419. — First  Layer  op  the  Muscles  of  the  Sole 


Abductor  digiti  V 


Flexor  digiti  V  brevis> 


Tendon  of  flexor  digitorumlongus 


Flexor  digitorum  brevis 


Abductor  hallucis 


Flexor  hallucis  longus 

Flexor  hallucis  brevis 
First  lumbrical 

Tendon  of  adductor  hallucis 


^-i-W...!.^ 


the  tendon  of  the  long  flexor  passes,  while  the  tendon  of  the  short  flexor  becomes  attached  to  the 
base  of  the  second  phalanx.  The  arrangement  is  essentially  Uke  that  described  at  length  for 
the  flexors  of  the  fingers  (p.  401). 

Nerve-supply. — From  the  medial  plantar  nerve  by  a  branch  which  enters  the  middle  third 
of  the  deep  surface  near  the  medial  margin  of  the  muscle. 

Action. — It  is  a  strong  flexor  of  the  second  row  of  phalanges. 

Relations. — The  short  flexor  is  sejiarated  from  the  abductors  of  the  big  toe  and  little  toe 
by  strong  intermuscular  septa  (p.  492),  and  from  the  long  flexor  tendons  and  the  quadratus 
plantaj  (flexor  accessorius)  by  a  transverse  septum  in  which  the  lateral  plantar  vessels  and 
nerve  cross  the  foot.  In  its  distal  two-thirds  it  is  separated  from  the  plantar  fascia  by  loose 
tissue. 

Variations.— The  muscle  shows  a  tendency  toward  reduction,  one  or  more  of  its  fasciculi 
being  frequently  absent,  and  occasionally  the  whole  muscle.  The  fasciculus  for  the  fifth  toe 
is  absent  in  about  20  per  cent,  of  bodies  (Le  Double).  When  a  fasciculus  is  absent,  its  tendon  is 
usually  replaced  by  an  accessory  tendon  from  the  long  flexor.  The  muscle  or  its  tendons  may 
be  more  or  less  fused  to  the  tendons  of  the  flexor  digitorum  longus. 


MUSCLES  OF  GREAT  TOE  495 

b.  Muscles  Attached  to  the  Tendons  op  the  Flexor  Digitoeum 
LoNGUs  (fig.  420) 

The  muscles  belonging  in  this  group  are  the  quadratus  plantae  (flexor  ac- 
cessorius),  a  flat,  quadrangular,  bicipital  muscle  which  runs  from  the  medial  and 
plantar  surface  of  the  body  of  the  calcaneus  to  the  dorso-lateral  margin  and  deep 
surface  of  the  long  flexor  tendon;  and  the  lumbrlcales,  four  slender  bipinnate 
muscles  which  run  from  the  medial  sides  of  the  digital  slips  of  the  tendon  to  the 
medial  sides  of  the  four  more  lateral  toes.  The  quadratus  aids  the  long  flexor 
muscle;  the  lumbricales  extend  the  last  two  phalanges  and  flex  the  first  phalanx 
of  each  of  the  digits  to  which  they  pass.  The  lumbrical  muscles  correspond  to 
those  of  the  hand.  The  quadratus  is  not  there  represented.  The  nerve-supply 
is  from  the  lateral  (external)  plantar  nerve  except  that  for  the  first  lumbrical 
muscle  which  gets  its  supply  from  the  medial  (internal)  plantar. 

The  quadratus  plantae  (flexor  accessorius)  (fig.  420). — This  muscle  arises  by  two  heads- 
The  lateral  head  springs  by  an  elongated  tendon  from  the  calcaneus  in  front  of  the  lateral 
process  of  the  tuber,  and  from  the  lateral  margin  of  the  long  plantar  hgament.  The  medial  head 
arises  directly  from  the  medial  surface  of  the  body  of  the  calcaneus  as  far  back  as  the  medial 
process  of  the  tuber  calcanei,  and  from  neighbouring  hgaments. 

Structure  and  insertion. — The  two  heads  are  separated  at  their  origin  by  a  short  triangular 
space.  They  soon  fuse  to  form  a  single  beUy,  but  the  fibre-bundles  of  each  head  in  the  main 
are  separately  inserted.  Those  from  the  lateral  head  diverge  to  be  attached  to  the  lateral 
margin  of  the  flexor  tendon.  Those  from  the  medial  head  are  inserted  on  a  tendon  that  begins 
on  the  medial  margin  and  deep  surface  of  this  head,  becomes  broader,  and  is  inserted  as  a 
flat  aponeurosis  on  the  deep  surface  of  the  flexor  tendon.  There  are  great  individual  varia- 
tions in  the  structure  of  this  muscle.  The  flbres  of  either  part  may  be  inserted  with  those  of 
the  other  part. 

Nerve-supply. — From  a  branch  of  the  lateral  plantar  nerve  which  passes  obliquely  across 
the  superficial  surface  of  the  muscle  parallel  with  the  tendon  of  the  flexor  digitorum  longus.  _ 

Relations. — The  muscle  Ues  in  a  fascial  compartment  with  the  long  flexor  tendons.  This 
compartment  is  bounded  on  each  side  by  intermuscular  septa,  deeply  by  the  tarsus,  and  plantar- 
ward  by  a  septum  which  intervenes  between  it  and  the  flexor  digitorum  brevis,  and  in  which  the 
lateral  plantar  nerve  and  vessels  cross  to  the  lateral  side  of  the  foot. 

Action. — It  assists  the  long  flexor  tendon  in  flexing  the  toes.  It  makes  the  direction  of 
traction  on  the  toes  parallel  with  the  long  axis  of  the  foot. 

Variations. — It  is  frequently  reduced  in  size.  The  lateral  head  is  not  infrequently  missing, 
the  medial  head  or  the  whole  muscle  much  more  rarely.  The  mode  of  attachment  to  the  tendon 
varies.  It  may  be  inserted  in  part  or  wholly  into  the  long  flexor  of  the  great  toe.  It  may 
receive,  in  about  one  body  in  twenty  (Wood),  an  accessory  slip  of  origin  from  the  fibula,  one  of 
the  muscles  of  the  leg,  the  fascia  of  the  leg  or  foot,  or  the  medial  surface  of  the  calcaneus,  etc. 

The  lumbricales. — The  three  lateral  muscles  arise  from  the  contiguous  sides  of  the  digital 
tendon-slips  of  the  flexor  digitorum  longus  in  the  angles  of  division.  The  first  lumbrical  arises 
on  the  medial  margin  of  the  tendon  to  the  second  toe.  The  fibre-bundles  of  each  muscle  con- 
verge on  both  sides  of  a  tendon  which  becomes  free  near  the  metatarso-phalangeal  joint  and  is 
attached  to  the  medial  side  of  the  first  phalanx  of  the  toe  to  which  the  muscle  belongs.  A  tendi- 
nous expansion  is  sent  into  the  aponeurosis  of  the  extensor  muscle. 

Nerve-supply. — The  three  lateral  lumbrical  muscles  are  most  frequently  supplied  by 
branches  of  the  deep  ramus  of  the  lateral  plantar  nerve,  the  medial  by  the  first  common  plantar 
digital  branch  of  the  medial  plantar  nerve.  The  latter  nerve  may  supply  the  two  more  medial 
muscles  or  the  more  medial  muscles  may  receive  a  double  supply.  The  branches  of  the  lateral 
plantar  nerve  enter  the  deep  surfaces  of  the  muscles  in  the  middle  third.  The  branches  of  the 
medial  plantar  enter  the  medial  borders  of  the  muscles  near  the  junction  of  the  proximal  and 
middle  thirds. 

Relations. — The  lumbrical  muscles  lie  in  a  plane  with  the  long  flexor  tendons  deeper  than 
the  flexor  brevis  tendons  and  superficial  to  the  adductor  hallucis.  The  deep  branches  of  the 
lateral  plantar  nerve  and  vessels  pass  across  their  deep  surface;  superficial  branches  of  both 
plantar  nerves  across  the  superficial  surface. 

Action. — To  extend  the  last  two  phalanges  of  the  toes  and  to  flex  the  first. 

Variations. — One  or  more  of  the  muscles  may  be  absent.  Sometimes  a  muscle  is  doubled. 
This  is  more  frequently  the  case  with  the  third  and  fourth  muscles.  The  first  may  arise 
wholly  from  the  tendon  of  the  posterior  tibial  muscle  or  from  this  and  the  Ions  flexor  of  the 
big  toe.  The  third  lumbrical  may  arise  from  the  flexor  digitorum  brevis.  The  second  and 
fourth  lumbricals  may  be  inserted  into  the  tendons  of  the  flexor  digitorum  brevis. 

c.  Intrinsic  Muscles  of  the  Great  Toe  (figs.  419-421) 

These  muscles  are  the  abductor,  flexor  brevis,  and  adductor.  Of  the  three 
muscles,  the  first  two  lie  in  the  medial  fascial  compartment,  while  the  last  lies  in 
the  middle  compartment  covered  by  the  flexor  digitorum  longus  and  its  associated 
muscles. 


496 


THE  MUSCULATURE 


The  abductor  hallucis  (fig.  419),  the  largest  and  most  superficial  of  these 
muscles,  lies  on  the  border  of  the  sole  medial  to  the  short  flexor  muscle.  It  passes 
from|the  calcaneus  across  the  tendons  of  the  long  flexor  muscles,  and  is  inserted 
into  the  medial  side  of  the  base  of  the  first  phalanx  of  the  great  toe  and  into  the 
medial  side  of  the  long  extensor  tendon.  It  is  partly  fused  to  the  medial  belly  of 
the  flexor  hallucis  brevis.  The  flexor  hallucis  brevis  (fig.  421)  is  a  bicaudal 
muscle  which  lies  over  the  first  metatarsal.  It  arises  in  the  region  of  the  cune- 
iform bones  and  is  inserted  on  each  side  of  the  base  of  the  first  phalanx.     Between 

Fig.  420. — Second  Layer  of  the  Muscles  op  the  Sole. 


Origin  of  abductor  digit!  V 


Part  of  abductor  digiti  V 


Flexor  digiti  V  \<\ 

Abductor  digiti  V 
Lumbricales 


Flexor  digitorum  brevis 
Abductor  hallucis 


Quadratus  plantEe 


Flexor  digitorum  longus 


Flexor  hallucis  longus 
Flexor  hallucis  brevis 
Adductor  hallucis 
Abductor  hallucis 


Tendon  of  flexor  digitorum  brevis 


its  two  bellies  and  insertions  runs  the  tendon  of  the  long  flexor  of  the  great  toe. 
Proximally  and  medially  the  flexor  brevis  is  crossed  by  the  abductor  hallucis. 
Its  tendons  are  fused  with  those  of  the  abductor  and  the  oblique  head  of  the  ad- 
ductor. The  adductor  hallucis  (fig.  421)  is  composed  of  two  distinct  heads,  an 
oblique  and  a  transverse.  The  oblique  head  extends  from  the  long  plantar  liga- 
ment under  cover  of  the  tendons  of  the  flexor  digitorum  longus  and  the  lumbrical 
muscles  to  the  lateral  side  of  the  base  of  the  first  phalanx  of  the  great  toe.  Its 
tendon  of  insertion  is  joined  by  the  transverse  head,  which  arises  from  the  capsules 
of  the  third  to  the  fifth  metatarso-phalangeal  joints.  Beneath  the  adductor  lie 
the  more  medial  interosseous  muscles. 

These  muscles  perform  not  only  the  functions  indicated  by  their  names,  but 
also  extend  the  second  phalanx.  They  correspond  fairly  well  with  those  of  the 
thumb.  The  opponens  is  not  normally  present  in  the  foot.  The  nerve  supply  for 
the  adductor  is  from  the  lateral  (external)  plantar  nerve;  that  for  the  other  muscles 
is  from  the  medial  (internal)  plantar. 


The  abductor  hallucis   (fig.  419). — Origin. — From   (1)  the  medial  process  of  the  tuber 
calcanei;  (2)  the  deep  surface  of  the  neighbouring  plantar  fascia;  (3)  the  laoiniate  (internal 


FLEXOR  HALLUCIS  BREVIS 


497 


annular)  ligament;  (4)  the  septum  between  the  muscle  and  the  flexor  digitorum  brevis;  and 
(5)  a  fibrous  arch  which  extends  on  the  deep  surface  of  the  muscle  over  the  plantar  vessels  and 
nerves  and  the  long  flexor  tendons  from  the  calcaneus  to  the  navicular  bone. 

Structure. — From  the  medial  process  of  the  tuber  calcanei  a  tendinous  band  passes  to  the 
deep,  lateral  side  of  the  muscle.  Numerous  tendinous  bands  arise  from  the  other  areas  of  origin. 
The  fibre-bundles  arise  from  these  tendons  and  directly  from  the  fibrous  arch.  They  are 
attached  in  a  penniform  manner  to  numerous  tendinous  slips  which  extend  far  up  in  the  muscle. 
These  slips  become  graduahy  fused  into  a  tendon  which  appears  on  the  superficial  plantar  aspect 
of  the  muscle.  Opposite  the  distal  half  of  the  first  metatarsal  bone  the  tendon  leaves  the 
belly  of  the  muscle  and  becomes  closely  bound  to  the  medial  belly  of  the  flexor  hallucis  brevis. 

Fig.  421. — Third  Layer  of  the  Muscles  op  the  Sole. 


Part  of  abductor  digiti  V 


Flexor  digiti  V  brevi: 


Tendon  of  flexor  digitorum  longus. 


Flexor  hallucis  longus 
Flexor  digitorum  longus 
Tibialis  posterior 


Flexor  hallucis  brevis 

Adductor  hallucis  (caputobliquum) 


Insertion. — In  conjunction  with  the  tendon  of  the  medial  belly  of  the  flexor  brevis  into  the 
base  of  the  first  phalanx.     It  usually  sends  an  expansion  to  the  extensor  tendon. 

Nerve-supply. — A  branch  from  the  medial  plantar  nerve  usually  enters  near  the  middle  of 
the  lateral  border  of  the  muscle. 

Relations. — It  is  covered  by  the  plantar  fascia  and  is  separated  from  the  muscles  of  the 
median  compartment  by  the  medial  intermuscular  septum.  It  crosses  the  tendons  of  the  tibialis 
anterior,  tibiahs  posterior,  flexor  digitorum  longus,  and  flexor  hallucis  longus  muscles  and  the 
plantar  vessels  and  nerves. 

The  flexor  hallucis  brevis  (fig.  421). — Origin. — From  a  tendon  attached  to  the  first  (in- 
ternal), second  and  third  cuneiform  bones.  The  more  lateral  of  its  fibres  are  continued  into 
the  plantar  calcaneo-cuboid  Ugament  and  the  more  medial  into  the  expansion  of  the  tendon  of 
the  posterior  tibial  muscle. 

Structure  and  insertion. — The  fibre-bundles  give  rise  to  two  belHes,  a  medial  and  a  lateral. 
Those  of  the  medial  belly  pass  obUquely  medially  to  be  inserted  into  the  tendon  of  the  abductor 
hallucis,  and  by  a  short  tendon  fused  with  this  into  the  medial  side  of  the  plantar  surface  of  the 
base  of  the  first  phalanx.  This  tendon  contains  a  sesamoid  bone.  Those  of  the  lateral  converge 
upon  the  tendon  of  the  oblique  head  of  the  adductor,  and  the  two  muscles  are  inserted  by  a 
common  tendon,  which  contains  a  sesamoid  bone,  into  the  lateral  side  of  the  plantar  surface 
of  the  base  of  the  first  phalanx. 


498  THE  MUSCULATURE 

Nerve-suy-ply. — A  branch  from  the  medial  plantar  (or  first  plantar  digital)  nerve  divides  over 
the  plantar  surface  of  the  muscle  and  gives  a  twig  to  each  belly  near  the  middle  third.  Rarely 
the  lateral  belly  may  receive  a  branch  from  the  lateral  plantar  nerve. 

Relations. — The  abductor  halluois  covers  it  medially;  the  tendon  of  the  flexor  hallucis 
longus  passes  between  its  two  heads.  Branches  of  the  medial  plantar  vessels  and  nerve  lie 
on  its  superficial  surface. 

The  adductor  hallucis  (fig.  421). — The  oblique  head. — Origin. — From  (1)  the  tuberosity 
of  the  cuboid  and  the  sheath  over  the  tendon  of  the  peroneus  longus  muscle;  (2)  the  plantar 
calcaneo-cuboid  hgament;  (3)  the  third  cuneiform;  (4)  the  bases  of  the  second  and  third  meta- 
tarsals and  (5)  a  fi^brous  arch  which  extends  from  the  plantar  calcaneo-cuboid  Ugament  to  the 
interosseous  fascia. 

Structure  and  insertion. — From  short  tendon-slips  the  fibre-bundles  pass  forward  to  form  a 
thick,  fusiform  belly  which  is  attached  in  a  bipeuniform  manner  to  a  flat  tendon.  The  tendon 
begins  about  the  middle  of  the  plantar  surface  of  the  muscle  and  is  inserted  in  common  with  that 
of  the  flexor  brevis  into  the  lateral  side  of  the  plantar  surface  of  the  base  of  the  first  phalanx, 
and  by  a  sUp  into  the  aponeurosis  of  the  long  e.xtensor  muscle  on  the  back  of  the  big  toe. 

Nerve-supply. — A  branch  from  the  deep  ramus  of  the  lateral  plantar  nerve  enters  the  middle 
third  of  the  lateral  border  of  the  muscle  on  its  deep  surface. 

The  transverse  head  arises  from  the  joint-capsules  of  the  third,  fourth,  and  fifth  metatarso- 
phalangeal joints  and  from  the  transverse  capitular  hgaments. 

Structure  and  insertion. — Of  the  three  fasciculi,  that  to  the  little  toe  Hes  nearest  the  heel, 
that  to  the  middle  toe  the  most  distally.  The  fibre-bundfes  take  a  nearly  parallel  course  to  be 
attached  to  tendon-shps  which  are  fused  into  a  common  tendon  that  sphts  and  passes  on  each 
side  of  the  tendon  of  the  obUque  head  and  is  inserted  into  the  sheath  of  the  tendon  of  the  long 
flexor  of  the  great  toe  (Leboucq). 

Nerve-supply. — A  branch  from  the  deep  ramus  of  the  lateral  plantar  nerve  enters  the  middle 
third  of  the  deep  surface  of  the  muscle. 

Relations. — The  adductor  hallucis  is  crossed  superflciaUy  by  the  tendons  of  the  flexor 
digitorum  longus  and  by  the  lumbrical  muscles.  On  its  deep  surface  he  the  interosseous  muscles, 
and  the  deep  plantar  vessels  and  nerves. 

Action. — The  actions  of  the  muscles  of  this  group  are  indicated  by  the  names  of  the  individ- 
ual muscles.  The  abductor  and  the  obhque  head  of  the  adductor  are  also  flexors  of  the  first 
phalanx.  All  the  muscles  of  the  group  aid  in  extending  the  second  phalanx.  The  transverse 
head  of  the  adductor  serves  to  draw  together  the  heads  of  the  metatarsals  after  they  have  been 
separated  by  the  weight  of  the  body  during  the  tread. 

Variations. — The  extent  of  fusion  of  the  abductor  and  adductor  with  the  two  heads  of  the 
short  flexor  varies  considerably.  The'  abductor  may  receive  an  accessory  fasciculus  from  the 
medial  border  of  the  foot.  Either  the  adductor  or  the  flexor  brevis  may  send  a  tendon  to  the 
base  of  the  first  phalanx  or  to  the  short  flexor  tendon  of  the  second  toe.  The  adductor  shows 
frequent  variations  in  relation  to  its  metatarsal  attachments,  owing  to  the  fact  that  originally 
a  fasciculus  from  the  body  of  the  second  (and  third)  metatarsal  was  probably  normally  present 
and  the  transverse  head  was  more  developed  (Leboucq).  The  opponens  hallucis  is  a  fasciculus 
occasionally  found  which  extends  from  the  short  flexor  or  the  medial  intermuscular  septum  to 
the  body  of  the  first  metatarsal.  This  muscle  is  normal  in  some  monkeys.  An  adductor  digiti 
secundi  has  been  seen  to  arise  from  various  sources  and  become  attached  to  the  lateral  side  of 
the  plantar  sm-face  of  the  base  of  the  first  phalanx  of  the  second  toe.  This  muscle  may  be  fused 
with  the  oblique  adductor.  A  corresponding  muscle  is  found  normally  in  some  apes,  and  in 
some  of  the  lower  animals  there  is  a  special  adductor  for  each  toe. 

d.  Intrinsic  Muscles  of  the  Little  Toe   (figs.  419-421) 

In  this  group  belong  three  muscles,  an  abductor,  a  flexor  and  an  opponens. 
The  largest  of  these,  the  abductor  digiti  quinti  (fig.  419),  extends  superficially  over 
the  lateral  margin  of  the  foot  from  the  lateral  side  of  the  tuber  calcanei  to  the 
base  of  the  little  toe.  The  flexor  digiti  quinti  brevis  (fig.  421)  is  a  small,  flat 
muscle  ,which  lies  on  the  plantar  surface  of  the  fifth  metatarsal.  The  opponens 
is  a  small  muscle  lying  lateral  to  this.  The  two,  which  are  often  fused,  arise  from 
the  cuboid.  The  flexor  brevis  is  inserted  into  the  plantar  side  of  the  base  of  the 
first  phalanx  of  the  little  toe.  The  opponens  is  inserted  into  the  lateral  surface 
of  the  metatarsal.  The  abductor  corresponds  with  the  abductor  of  the  little 
finger.  The  opponens  and  flexor  brevis  correspond  probably  with  the  deep 
part  of  the  opponens  of  the  little  finger.  The  nerve  supply  is  from  the  lateral 
plantar  nerve. 

The  abductor  digiti  quinti  (fig.  419). — -Origin. — From  (1)  the  lateral  process  of  the  tuber 
calcanei  and  the  lateral  and  plantar  surface  of  the  body  of  the  bone  in  front  of  this;  (2)  the  lateral 
intermuscular  septum;  (3)  the  deep  surface  of  the  lateral  plantar  fascia,  including  the  fibrous 
band  extending  from  the  calcaneus  to  the  lateral  side  of  the  base  of  the  fifth  metatarsal  bone. 

Structure. — The  fibre-bundles  run  obhquely  to  a  flat  tendon  of  insertion.  This  begins  within 
the  muscle  near  the  calcaneo-cuboid  joint,  soon  emerges  on  the  medial  side  of  the  deep  surface, 
and  becomes  free  near  the  metatarso-phalangeal  joint.  Considerable  individual  variation  in 
structure  is  found. 

Insertion.- — On  the  lateral  surface  of  the  first  phalanx  of  the  httle  toe  and  the  metatarso- 
phalangeal capsule.     Often  a  shp  is  sent  to  the  extensor  tendon.     While  usually  the  muscle 


INTEROSSEUS  MUSCLES  499 

glides  over  the  tuberosity  of  the  fifth  metatarsal,  it  frequently  sends  a  second  fasciculus  to  be 
attached  to  this  bone  (abductor  ossis  metatarsi  quinti) .  A  special  fasciculus  from  the  tuberosity 
often  constitutes  the  lateral  margin  of  the  muscle. 

Nerve-supply. — The  nerve  arises  from  the  lateral  plantar.  It  may  be  distributed  either 
near  the  deep  or  the  superficial  surface  of  the  muscle.  The  former  appears  to  be  the  case  when 
the  muscle  is  slightly  developed.  The  chief  intramuscular  branches  then  extend  across  the 
middle  third  of  the  constituent  fibre-bundles  near  the  deep  surface.  In  case  the  calcaneo-meta- 
tarsal  bundles  are  well  developed,  the  nerve  enters  the  proximal  margin  of  the  muscle  and  its 
chief  branches  extend  across  the  middle  third  of  the  more  superficial  muscle-bundles,  finally 
terminating  in  the  distal  margin  of  the  muscle. 

Relations. — It  is  ensheathed  by  the  plantar  fascia  and  the  lateral  intermuscular  septum. 
It  lies  superficial  to  the  quadratus  plantoe  (flexor  accessorius),  the  opponens  and  flexor  Ijrevis 
of  the  Mttle  toe,  the  long  plantar  hgament,  and  the  tendon  of  the  peroneus  longus  muscle. 

The  flexor  digiti  quinti  brevis  (fig.  421). — Origin. — From  the  sheath  of  the  peroneus  longus, 
the  tuberosity  of  the  cuboid,  and  (3)  the  base  of  the  fifth  metatarsal. 

Structure  and  insertion. — The  fibre-bundles  take  a  nearly  parallel  course,  although  the  belly 
is  slightly  fusiform.  They  are  attached  by  short  tendinous  bands  to  the  base  of  the  first 
phalanx  of  the  little  toe,  the  capsule  of  the  corresponding  joint,  and  the  aponeurosis  on  the 
dorsal  surface  of  the  toe. 

Nerve-supply. — A  branch  of  the  superficial  ramus  of  the  lateral  plantar  nerve  sends  twigs 
to  the  middle  third  of  the  plantar  surface  of  this  and  the  following  muscle. 

Relations. — It  is  covered  medially  by  the  plantar  fascia,  laterally  by  the  abductor  of  the 
fifth  toe.     Medially  it  lies  superficial  to  the  third  plantar  interosseous  muscle. 

The  opponens  digiti  quinti. — This  muscle  arises  from  the  sheath  of  the  peroneus  longus 
and  the  tuberosity  of  the  cuboid  by  a  slender  tendon  which  passes  over  the  tuberosity  of  the 
fifth  metatarsal  and  gives  rise  to  fibre-bundles  which  are  inserted  on  the  lateral  surface  of  the 
fifth  metatarsal. 

Nerve-supply. — From  branches  of  the  nerve  to  the  flexor  brevis. 

Relations. — It  is  covered  by  the  abductor  of  the  fifth  toe. 

Actions. — The  abductor  and  flexor  brevis  abduct  the  little  toe  and  flex  the  first  phalanx. 
They  act  as  extensors  of  the  second  phalanx.  The  opponens  serves  to  draw  the  little  toe  medi- 
ally in  a  plantar  direction. 

Variations. — The  muscles  of  this  group  may  be  more  or  less  completely  fused.  The  abduc- 
tor, in  addition  to  the  variations  mentioned  above,  may  send  tendons  to  the  third  and  fourth 
metatarsals.  The  opponens  is  frequently  missing.  The  abductor  accessorius  digiti  quinti  is 
a  rare  muscle  which  arises  from  the  lateral  process  of  the  tuber  of  the  calcaneus  and  is  inserted 
into  the  lateral  surface  of  the  base  of  the  first  phalanx  of  the  httle  toe. 

e.  The  Interosseous  Muscles  (fig.  422) 

Two  groups  of  interosseous  muscles  are  recognised,  a  dorsal  and  a  plantar. 
The  dorsal  are  the  larger  and  fill  the  interspaces.  The  first  two  are  inserted  into 
each  side  of  the  base  of  the  first  phalanx  of  the  second  toe;  the  third  and  fourth 
into  the  lateral  sides  of  the  bases  of  the  first  phalanges  of  the  third  and  fourth  toes. 
The  plantar  interossei  lie  on  the  medial  side  of  the  ventral  surfaces  of  the  third, 
fourth,  and  fifth  metatarsals,  and  are  inserted  each  on  the  medial  side  of  the  base 
of  the  first  phalanx  of  the  corresponding  toe.  In  the  hand  the  axis  about  which 
the  interosseous  muscles  are  arranged  passes  through  the  middle  finger,  in  the  foot 
through  the  second  toe.     The  nerve-supply  is  from  the  lateral  plantar  nerve. 

The  interossei  dorsales. — Each  of  the  three  lateral  dorsal  interosseous  muscles  arises  from 
— (1)  the  sides  of  the  shaft  and  the  plantar  surface  of  the  bases  of  the  metatarsal  bones  bounding 
the  space  in  which  it  lies;  (2)  from  the  fascia  covering  it  dorsally;  and  (3)  from  fibrous  prolonga- 
tions from  the  long  plantar  hgament.  The  first  has  a  similar  origin  except  that  it  is  attached 
medially  to  the  base  of  the  first  metatarsal  and  to  a  fibrous  arch  extending  from  the  base  to  the 
head. 

Structure. — The  component  fibre-bundles  of  each  muscle  are  inserted  bipinnately  on  a  ten- 
don which  begins  high  in  the  muscle  and  becomes  free  near  the  metatarso-phalangeal  joint. 

Insertion. — The  first  and  second  on  each  side  of  the  base  of  the  first  phalanx  of  the  second 
toe.  The  third  and  fourth  on  the  lateral  side  of  the  bases  of  the  proximal  phalanges  of  the  third 
and  fourth  toes.  Each  tendon  is  adherent  to  the  capsule  of  the  neighbouring  joint.  They 
send  no  well  marked  processes  to  the  extensor  tendons,  as  do  those  of  the  hand. 

The  interossei  plantares. — Each  plantar  interosseus  arises — (1)  from  the  proximal  third 
of  the  medial  plantar  surface  of  the  shaft  and  from  the  base  of  the  metatarsal  on  which  it  Ues; 
and  (2)  from  expansions  of  the  long  plantar  hgament. 

Structure  and  insertion. — The  obliquely  placed  fibre-bundles  are  longer  than  those  of  the 
dorsal  interossei,  and  are  inserted  in  a  tendon  which  hes  near  the  medial  border  of  the  muscle, 
becomes  free  near  the  metatarso-phalangeal  joint,  and  is  inserted  into  a  tubercle  on  the  medial 
side  of  the  base  of  the  first  phalanx  of  the  digit  to  which  it  goes. 

Nerve-supply. — From  the  deep  branch  of  the  lateral  plantar  nerve  several  rami  are  given 
ofi  for  the  interossei.  The  nerve  of  each  muscle  enters  the  plantar  surface  in  the  proximal 
third.  The  interosseous  muscles  of  the  foiirth  interspace,  however,  are  usually  supplied  by  a 
branch  from  the  superficial  ramus  of  the  lateral  plantar  nerve. 


500 


THE  MUSCULATURE 


Relations. — -The  interosseous  muscles  are  covered  on  the  plantar  surface  by  a  thin  fascia 
on  which  the  deep  branches  of  the  lateral  plantar  nerve  and  vessels  run.  The  first  dorsal  inter- 
osseous adjoins  mediaOy  the  flexor  hallucis  brevis  and  laterally  on  the  plantar  surface  of  the 
second  metatarsal,  adjoins  the  second  dorsal  interosseous.  Dorsal  and  plantar  interossei  then 
alternate  across  the  plantar  surface  of  the  foot  until  the  fifth  metatarsal  is  reached.  Here  the 
third  plantar  interosseous  adjoins  the  flexor  brevis  of  the  little  toe. 

Fig.  422. — Fourth  Layer  op  the  Muscles  op  the  Sole. 


Peroneus  longus 


Plantar  interossei 


Dorsal  interossei 


Action. — The  chief  axis  of  the  foot  may  be  taken  to  extend  through  the  second  toe.  The 
dorsal  interosseous  muscles  abduct — pull  the  digits  to  which  they  are  attached  away  from  this 
axis;  the  plantar  interosseous  muscles  adduct — pull  the  digits  toward  the  axis.  The  interossei 
all  flex  the  first  row  of  phalanges. 

Variations. — The  second  dorsal  interosseous  may  have  no  attachment  to  the  third 
metatarsal. 

BURS^ 

B.  intermetatarsophalangeae. — Four  bursse  between  the  neighbouring  sides  of  the  heads  of 
the  metatarsal  bones  and  dorsal  to  the  transverse  capitular  ligaments.  B.  mm.  lumbricalium. 
— Between  the  ends  of  the  tendons  of  the  lumbrioal  muscles  and  the  transverse  capitular  hga- 
ments.     The  three  medial  are  more  constant  than  the  lateral. 

For  other  bursas  in  the  foot,  see  pp.  483  and  491. 


MUSCLES  GROUPED  ACCORDING  TO-  FUNCTION 

The  exact  functions  of  many  of  the  muscles  have  not  yet  been  decisively  determined. 
Anatomical  studies,  the  construction  of  mechanical  models,  the  electrical  stimulation  of  the 
musculature,  and  observation  of  the  muscular  activities  of  normal  individuals  and  of  individuals 
in  whom  given  muscles  or  sets  of  muscles  are  absent  or  paralysed,  have  all  proved  valuable 
methods  of  investigation,  but  each  method  has  its  drawbacks,  and  knowledge  of  the  part  actu- 
ally played  by  individual  muscles  in  the  normal  activities  of  the  body  is  as  yet  merely  approxi- 


FUNCTIONS  OF  MUSCLES  501 

mate.  Owing  to  the  influence  of  gravity,  the  relations  of  other  muscles  to  the  skeleton,  and 
similar  factors,  a  given  muscle  may  perform  functions  which  would  not  be  deduced  from  a  simple 
study  of  the  relations  of  the  muscle  to  the  skeleton.  Thus  the  ihacus  serves  to  flex  not  only  the 
hip,  but  also  the  knee,  and  the  hamstring  muscles  may  flex  the  hip  while  flexing  the  knee.  The 
functions  ascribed  to  various  muscles  in  the  following  tables,  although  an  attempt  has  been 
made  to  base  them  upon  the  more  recent  work  on  the  action  of  the  muscles,  must  be  taken  to 
be  merely  approximately  correct.  So  far  as  possible  the  muscles  are  given  in  order  of  their 
power  in  effecting  the  various  movements.  In  this  we  have  utilized  chiefly  the  work  of  R.  Fiok: 
"Anatomie  und  Mechanik  der  Gelenke  unter  Berticksichtigung  der  bewegenden  Muskeln" 
in  von  Bardeleben's  Handbuch  der  Anatomie  des  Menschen. 

(In  this  table  have  been  included  not  only  the  voluntary  muscles,  described  in  the  preceding 
section,  but  also  several  described  in  other  parts  of  the  book. 

1.  Facial  muscles. 

These  serve  essentially  to  contract  the  various  visceral  orifices  of  the  head  or  to  retract 
the  tissue  surrounding  them. 
Ear. 

Retractors:  auricularis  anterior,  superior,  and  posterior. 
Orbit. 

(a)  Retractor:    Epicranius    (occipito-frontalis).     The    levator    palpebrse 
superioris,   innervated   by  the  third  cranial  nerve,  serves  to 
raise  the  upper  lid  of  the  eye. 
(6)   Contractors:  orbicularis  oculi,  corrugator,  and  procerus. 
Nasal  orifice. 

(o)  Dilators:  angular  head  of  the  quadratus  labii  superioris,  transverse 

portion  of  the  nasahs,  and  the  dilatores  naris. 
(6)   Contractors:  pars  alaris  of  the  nasalis  and  the  depressor  septi  nasi. 
Oral  orifice. 

(a)  Retractors: 

Upward:  zygomaticus,  quadratus  labii  superioris,  caninus. 
Lateralward:  zygomaticus,  risorius,  platysma,  triangularis,  bucci- 
nator. 
Downward:  triangularis,  quadratus  labii  inferioris,  platysma. 
(6)   Contractors:  orbicularis  oris,  compressor  labii,  incisivus  labii  inferioris 

and  superioris. 
(c)   Protractors  of  the  lips :  incisivus  labii  inferioris  and  superioris,  mentalis. 

2.  Muscles  acting  on  the  eyeball  (see  Section  on  Eye). 

To  adduct  the  pupil:  rectus  medialis. 
To  abduct  the  pupil:  rectus  lateralis. 
To  direct  the  pupil  upward:  rectus  superior,  in  association  with  the  obhquus 

inferior. 
To  direct  the  pupil  downward:  rectus  inferior,  in  association  with  the  obliquus 

superior. 

3.  Muscles  acting  on  the  lower  jaw. 

(a)  To  raise  it:  masseter,  temporal,  internal  pterygoid. 

(6)  To  lower  it:  external  pterygoid,  digastric,  mylo-hyoid,  genio-hyoid,  and  the 

infrahyoid  muscles.     The  weight  of  the  jaw  also  plays  a  part  in 

this  movement. 

(c)  To  protract  it:  external  pterygoid,  internal  pterygoid,  masseter  and  the  ante- 

rior part  of  the  temporal. 

(d)  To  retract  it:  the  inferior  dorsal  portion  of  the  temporal  and  the  digastric. 

(e)  To  produce  lateral  movements:  the  external  pterygoid  acting  on  one  side 

rotates  the  chin  and  carries  the  jaw  toward  the  opposite  side. 
The  rotation  may  be  aided  by  the  digastric  of  the  opposite 
side.  The  masseter  draws  it  slightly  toward  the  side  on  which 
the  muscle  lies.  This  action  of  the  masseter  is  counterbalanced 
by  the  internal  pterygoid  (Riegner). 

4.  Muscles  acting  on  the  hyoid  bone. 

(a)  To  elevate  it:  digastric,  stylo-hyoid,  stylo-glossus,  mylo-hyoid,  genio-hyoid, 
genio-glossus,  hyo-glossus,  and  the  middle  constrictor  of  the 
pharynx. 

(6)   To  depress  it:  thyreo-hyoid,  sterno-hyoid,  omohyoid,  sterno-thyreoid. 

(c)  To  protract  it:  genio-glossus  (inferior  portion),  genio-hyoid,  anterior  belly  of 

digastric,  and  the  mylo-hyoid. 

(d)  To  retract  it:  posterior  belly  of  digastric,  stylo-hyoid,  and  the  middle  con- 

strictor of  the  pharynx. 

5.  Muscles  acting  on  the  larynx  (see  Section  IX). 

(o)  To  elevate  it:  thyreo-hyoid,  stylo-pharyngeus,  pharyngo-palatinus,  the  in- 
ferior constrictor  of  the  pharynx,  and  the  elevators  of  the  hj'oid 
bone. 

(6)  To  depress  it:  sterno-thyreoid,  sterno-hyoid,  and  omo-hyoid. 

(c)  To    approximate    the    vocal    cords:  crico-arytenoideus    lateralis;    vocalis; 

thjTeo-arytenoideus,  arytenoideus  transversus. 

(d)  To  make  the  vocal  cord  tense:  crico-thj'reoideus. 

(e)  To  widen  the  rima  glottidis:  crico-arytenoideus  posterior. 

(/)  To  shorten  and  thicken  the  vocal  cords:  thyreo-arytenoideus  (externus), 
vocalis. 


502  THE  MUSCULATURE 

(g)  To    constrict   the    aditus    and   vestibule    of    the   larynx:    aryepiglotticus, 

thyreo-arytenoideus. 
(h)  To   widen  the   aditus   and   vestibule   of   the   larynx:    thyreo-epiglottideus 

6.  IMuscles  acting  on  the  tongue  (see  Section  IX). 

(o)  To  elevate  it:  stylo-glossus  (especially  along  the  sides),  glosso-palatinus, 

glosso-pharyngeus,  and  the  elevators  of  the  hyoid  bone. 
(6)  To  depress  it:   genio-glossus    (in   the   centre),   hyogiossus    (at   the  sides), 

chondroglossus,  and  the  depressors  of  the  hyoid  bone. 

(c)  To  protrude  it:  geniq-glossus  (middle  and  inferior  portions). 

(d)  To    retract  it:    genio-glossus    (anterior    portion),   stylo-glossus,    chondro- 


(e)   To  shorten  it   and   make  it  bulge  upwards:   longitudinalis  superior  and 

inferior. 
(/)    To  narrow  it  and  make  it  bulge  upwards:  transversus  Unguse. 
(g)   To  flatten  it:  verticalis  linguse. 
When  the  muscles  work  symmetrically,  these  movements  are  symmetrical;  when  they 

do  not  work  symmetrically,  the  tongue  is  moved  from  side  to 

side,  rotated,  etc. 

7.  Muscles  acting  on  the  palate  and  pharynx  (see  Section  IX). 

(a)  To  narrow  the  pharyngeal  opening  of  the  tuba  auditiva  (Eustachian  tube) : 

levator  veli  palatini. 
(6)  To  widen  the  isthmus  of  the  tuba:  levator  veli  palatini. 

(c)  To  open  the  tube:  tensor  veli  palatini,  pharyngo-palatinus. 

(d)  To  raise  and  shorten  the  uvula:  m.  uvulae. 

(e)  To  depress  the  soft  palate:  glosso-palatinus,  pharyngo-palatinus. 

(f)  To  make  tense  the  soft  palate:  tensor  veli  palatini. 

(g)  To  lift  the  soft  palate:  levator  veli  palatini. 

(h)  To  approximate  the  glosso-palatine  arches  (anterior  pillars  of  the  fauces): 

glosso-palatinus. 
(i)    To    approximate  the  pharyngo-palatine    arches    (posterior    pillars   of  the 

fauces):  pharyngo-palatinus,     superior     constrictor     of     the 

pharynx. 
{j)   To  constrict  the  pharynx:  superior,  middle,  and  inferior  constrictors. 
(k)  To  widen  the  pharynx:  stjdo-pharyngeus   and  the  muscles  which  protract 

the  hyoid  bone. 
(I)    To  elevate  the  pharynx:  stylo-pharyngeus,  pharyngo-palatinus. 

8.  Muscles  acting  on  the  head. 

(a)  To  flex  it:  the  supra-  and  infrahyoid  muscles,  rectus  capitis  anterior,  longus 
capitis,  rectus  capitis  lateralis. 

(6)  To  extend  it:  sterno-cleido-mastoid,  trapezius,  splenius  capitis,  longissimus 
capitis,  semispinalis  capitis,  obliquus  capitis  superior,  rectus 
capitis  posterior  major  and  minor.  When  the  hyoid  bone  and 
lower  jaw  are  fixed  by  contraction  of  the  hyomandibular  and 
infrahyoid  muscles,  the  posterior  beUy  of  the  digastric  aids  the 
extensors  of  the  head  in  opening  the  mouth. 

(c)  To  bend  it  laterally:  sterno-cleido-mastoid,  rectus  capitis  lateralis,  splenius 

capitis,  longissimus  capitis,  semispinalis  capitis,  obliquus 
capitis  superior. 

(d)  To  rotate  it:  sterno-cleido-mastoid,  trapezius,  splenius  capitis,  longissimus 

capitis,  semispinalis  capitis,  obhquus  capitis  superior  and  in- 
ferior, rectus  capitis  posterior  major. 

9.  Muscles  acting  on  the  spinal  column. 

(o)  To  flex  it:  sterno-cleido-mastoid,  longus  colli,  longus  capitis,  psoas  major 
and  minor,  scaleni,  rectus  abdominis,  obhquus  abdominis 
externus  and  internus,  the  crura  of  the  diaphragm,  levator  ani, 
and  the  coccj'geus.  . 

(6)  To  extend  it:  splenius  capitis,  splenius  cervicis,  spinahs,  sacro-spinaHs, 
semispinalis  dorsi,  cervicis  and  capitis,  multifidus,  rotatores, 
interspinales,  intertransversarii,  levatores  costarum,  quadratus 
lumborum. 

(c)  To  bent  it  laterally  and  extend  it:  quadratus  lumborvim,  splenius,  iliocostalis, 

longissimus  dorsi,  cervicis  and  capitis,  semispinales,  multi- 
fidus,   rotatores,    levatores   costarum,    intertransversarii. 

(d)  To  bend  it  laterally  and  flex  it:  scalene,   sterno-cleido-mastoid,   obliquus 

abdominis  externus  and  internus,  intercostales,  psoas  major 
and  minor. 

When  the  arm  and  shoulder  girdle  are  fixed  the  trapezius, 
levator  scapulae,  latissimus  dorsi  and  rhomboids  aid  abduction. 

(e)  To  rotate  it  to  the  right:  r.  internal  oblique,  1.  external  oblique,  r.  splenius, 

1.  sterno-cleido-mastoid,  r.  longissimus  capitis,  r.  ilio-costalis, 
1.  semispinahs,  1.  multifidus,  1.  rotatores  (except  the  lumbar) , 
longus  colli  (r.  above,  1.  below),  1.  serratus  anterior  and  rhom- 
boids, r.  levatores  costarum. 


FUNCTIONS  OF  MUSCLES  503 

10.  Muscles  of  respiration. 

Quiet  inspiration:  the  external  intercostals,  interoartilaginous  parts  of  internal 
interoostals,  diaphragm. 

Enforced  inspiration:  in  addition  to  the  muscles  mentioned  above,  the  scaleni, 
sterno-cleido-mastoid,  serratus  posterior  superior  and  inferior, 
rhomboids,  serratus  anterior,  latissimus  dorsi,  subclavius, 
pectoralis  major  and  minor,  and  the  extensors  of  the  spinal 
column,  the  trapezius  and  the  levator  scapuli. 

Quiet  expiration:  interosseous  pai'ts  of  internal  intercostals,  subcostales,  and 
transversus  thoracis. 

Enforced  expu-ation:  in  addition  to  the  muscles  mentioned  above,  the  abdominal 
muscles,  ilio-costalis  lumborum  and  dorsi,  longissimus  dorsi, 
and  the  quadratus  lumborum. 

The  chief  muscles  of  respiration  are  the  intercostals;  the  diaphragm  plays  a  minor 
part  (Fick). 

11.  Muscles  acting  on  the  abdomen. 

(a)  Constriction  of  the  abdominal  cavity:  obliquus  abdominis  externus  and 
internus,  the  transversus  and  rectus  abdominis,  and  the  dia- 
phragm, levator  ani,  and  coccygeus. 

(6)  Reduction  of  pressure  in  the  abdominal  cavity:  the  muscles  of  inspiration, 
with  the  exception  of  the  diaphragm,  serve  to  lessen  the  com- 
pression of  the  abdominal  viscera. 

12.  Action  of  the  muscles  of  the  perineal  region. 

(a)  To  close  anal  canal:  sphincter  ani  externus. 

(&)  To  constrict  the  anal  portion  of  the  rectum:  levator  ani  (pubo-coccygeal 
portion). 

(c)  To  constrict  the  bulbus  urethrae  and  the  corpus  cavernosum  urethrse  (corpus 

spongiosum) :  bulbo-cavernosus. 

(d)  To  elevate  the  prostate  gland:  levator  ani. 

(e)  To  constrict  the  vagina:  bulbo-cavernosus,  levator  ani  (pubo-coccygeal  por- 

tion), constrictor  vaginse. 

(f)  To  cause  erection  of  penis  and  clitoris:  ischio-cavernosus,  bulbo-cavernosus, 

and  sphincter  urethrae  membranaceaj. 

(g)  To  compress  the  urethra  and  the  bulbo-urethral  (Cowper's)  or  the  great  ves- 

tibular (Bartholin's)  gland:  sphincter  urethrae  membranaceae 
and  the  transversus  perinei  profundus. 
(h)  To  support  and  Uft  the  pelvic  floor :  levator  ani,  coccygeus,  transversus  perinei 
profundus  and  superficialis. 

13.  Muscles  acting  on  the  shoulder-girdle. 

The  two  joints  acted  upon  are  the  sterno-clavicular  and  the  acromio-clavicular. 
The  movements  produced  consist  in  lifting  and  lowering  the 
scapula,  carrying  it  forward  and  backward  and  rotating  it. 

(o)  Elevation:  trapezius  (upper  portion),  levator  scapulae,  sterno-cleido-mastoid, 
rhomboidei,  pectoralis  major  (upper  sternal  part),  serratus 
anterior  (middle  portion),  omo-hyoid. 

(6)  Depression:  trapezius  (lower  portion),  pectoralis  major  (lower  portion), 
pectoralis  minor,  subclavius,  latissimus  dorsi,  serratus  anterior 
(lower  part).     The  weight  of  the  limb  is  likewise  a  factor. 

(c)  Forward  movement:  serratus  anterior,  pectorales  major  and  minor. 

(d)  Backward  movement:  trapezius,  rhomboidei,  latissimus  dorsi. 

(e)  Rotation: 

Associated  with  abduction  of   the  arm :   serratus  anterior"  (inferior 

portion),  trapezius. 
Associated  with  adduction  of  the  arm:  rhomboidei,  pectoralis  major 

(pectoral  portion),  latissimus  dorsi,  pectoralis  minor,  levator 

scapulae. 

14.  Muscles  acting  on  the  arm  at  the  shoulder-joint. 

(o)  To  flex  it, 

When  the  arm  is  at  the  side:  pectoralis  major  (upper  part),  deltoid  (anterior 

part),    short   head   of   biceps,    coracobrachialis,  infraspinatus, 

long  head  of  biceps,  teres  minor,  subscapularis  (upper  part), 

supraspinatus. 
When  the  arm  is  abducted  60°:  pectoralis  major,  deltoid,  subscapularis, 

short  head  of  biceps,  coracobrachialis,  long  head  of  biceps, 

infraspinatus,  supraspinatus. 
The  movement  is  aided  by  the  trapezius  and  the  serratus  anterior. 
(6)  To  extend  it, 

When  the  arm  is  at  the  side:  latissimus  dorsi,  deltoid  (posterior  part),  teres 

major,  subscapularis  (lower  part),  triceps. 
When  the  arm  is  abducted  60°:  latissimus  dorsi,  deltoid,  teres  major,  triceps, 

teres  minor. 
The  upper  and  middle  portions  of  the  trapezius  and  the  levator  scapulae  play 

an  important  part  in  extension  of  the  arm. 
(c)   To  abduct  it, 

When  the  arm  is  at  the  side:  deltoid,  supraspinatus,  long  head  of  biceps, 

subscapularis,  infraspinatus  (upper  part). 
When  the  arm  is  abducted  60°:  deltoid,  supraspinatus,  infraspinatus  (upper 

part),  long  head  of  biceps,  short  head  of  biceps. 


504  THE  MUSCULATURE 

The  siibscapularis  is  an  adductor  when  the  arm  is  abducted.  The  inferior 
part  of  the  serratus  anterior  and  the  trapezius  are  important 
in  abduction  of  the  arm. 

(d)  To  adduct  it, 

When  the  arm  is  at  the  side:  pectoralis  major,  latissimus  dorsi,  deltoid  (pos- 
terior and  anterior  parts),  teres  major,  triceps,  coraoobrachialis, 
short  head  of  biceps,  teres  minor,  infraspinatus. 

When  the  arm  is  abducted:  pectoralis  major,  latissimus  dorsi,  teres  major, 
triceps,  subscapularis,  deltoid  (dorsal  and  ventral  parts), 
coracobrachialis. 

(e)  To  rotate  it  lateral  ward  (supinate). 

When  the  arm  is  at  the  side:  infraspinatus  (upper  part),  the  dorsal  part  of 

the  deltoid,  teres  minor,  supraspinatus. 
When  the  arm  is  abducted  60°:  teres  minor,  infraspinatus,  deltoid  (dorsal 

part),  coracobrachialis. 
(/)    To  rotate  it  medialwai-d  (pronate). 

With  the  arm  at  the  side:  latissimus  dorsi,  pectoralis  major,  subscapularis, 

deltoid  (ventral  part),  long  head  of  biceps,  teres  major,  short 

head  of  biceps. 
With  the  arm  abducted  60°:  latissimus  dorsi,  pectoralis  major,  subscapularis, 

teres  major,  deltoid  (ventral  part). 
When  the  arms  are  raised  high  the  power  of  rotation  at  the  shoulder  becomes 

slight. 

15.  Muscles  acting  on  the  forearm  at  the  elbow-joint  (arranged  according  to  R.  Fick). 

(a)  Fle-xion  at  elbow. 

Forearm  supinated:  brachialis,  long  head  of  biceps,  short  head  of  biceps, 
brachio-radialis,  pronator  teres,  extensor  carpi  radiahs  longus, 
flexor  carpi  radialis,  extensor  carpi  radialis  brevis,  palmaris 
longus. 

Forearm  in  mid-position  or  pronated:  brachiaUs,  long  head  of  biceps,  short 
head  of  biceps,  brachio-radialis,  extensor  carpi  radialis  longus, 
pronator  teres,   flexor  carpi  radialis,   extensor  carpi  radialis 
brevis,  palmaris  longus. 
(6)   Extension  at  elbow:  triceps  (lateral,  medial,  and  long  heads),  anconeus. 
(c)   Pronation  of  forearm. 

Forearm  extended:  flexor  carpi  radiahs,  pronator  teres,  pronator  quadratus, 
palmaris  longus. 

Forearm  at  right  angles:  pronator  teres,  flexor  carpi  radiahs,  brachio-radialis, 
pronator  quadratus,  extensor  carpi  radialis  longus,  palmaris 
longus. 

Forearm  flexed:  pronator  teres,  brachio-radiahs,  flexor  carpi  radialis,  pro- 
nator   quadratus,    extensor    carpi    radiahs    longus,    palmaris 
longus. 
{d)  Supination. 

Forearm  extended:  short  head  of  biceps,  supinator,  long  head  of  biceps, 
brachio-radiahs,  extensor  carpi  radialis  longus,  abductor 
poUicis  longus,  extensor  pollicis  brevis,  extensor  pollicis  longus, 
extensor  indicis  proprius. 

Forearm  at  right  angles:  short  head  of  biceps,  long  head  of  biceps,  supina- 
tor, abductor  poUicis  longus,  extensor  polhcis  brevis,  brachio- 
radialis  (in  pronation),  extensor  pollicis  longus,  extensor 
indicis  proprius. 

Forearm  flexed:  short  head  of  biceps,  long  head  of  biceps,  supinator,  ab- 
ductor pollicis  longus,  extensor  polhcis  brevis,  extensor  pollicis 
longus,  extensor  indicis  proprius. 

16.  Muscles  acting  on  the  hand  at  the  wrist  (arranged  according  to  R.  Fick). 

(o)  To  flex  it:  flexor  digitorum  sublimis,  flexor  digitorum  profundus,  flexor 
carpi  ulnaris,  flexor  pollicis  longus,  flexor  carpi  radialis,  ab- 
ductor pollicis  longus,  palmaris  longus. 

(6)  To  extend  it:  extensor  digitorum  communis,  extensor  carpi  ulnaris,  extensor 
carpi  radialis  longus  and  brevis,  extensor  indicis  proprius, 
extensor  pollicis  longus. 

(c)  Radial  abduction:  extensor   carpi   radialis  longus,   extensor   carpi  radialis 

brevis,  abductor  pollicis  longus,  flexor  carpi  radialis,  extensor 
indicis  proprius,  extensor  pollicis  longus,  extensor  polhcis  brevis. 

(d)  Ulnar  abduction:  extensor  carpi  ulnaris,  flexor  carpi  ulnaris. 

17.  Muscles  acting  on  the  palm : 

(a)  To_flex  the  ulnar  side:  opponens,  long  and  short  flexors  of  the  little  finger. 
(h)  To  extend  the  ulnar  side:  extensor  carpi  ulnaris,  extensor  digiti  quinti. 
(c)   To  adduct  the  ulnar  side:  third  volar  interosseous. 
{d)  To  abduct  the  ulnar  side:  abductor  digiti  quinti. 

For  action  on  the  radial  side  see  "  muscles  adting  on  the  thumb."  Move- 
ments of  the  second,  third  and  fourth  metacarpals  are  produced 
by  the  long  flexors  and  the  dorsal  interosseous  muscles. 

18.  Muscles  acting  on  the  thumb. 

(a)  To  oppose  the  thumb:  adductor,  opponens,  flexor  brevis,  flexor  longus,  ad- 
ductor brevis. 
(6)  To  repose  the  thumb:  long  abductor,  short  extensor. 


FUNCTIONS  OF  MUSCLES  505 

(c)  To  flex  all  joints:  flexor  poUicis  longus;  the  carpo-metacarpal  and  metacarpo- 

phalangeal joints;  flexor  brevis,  the  adductors,  abductor  brevis; 
thecarpo-metacarpaljoints:  opponens  poUicis,  abductor  longus. 

(d)  To  extend:  all  joints,  extensor  pollicis  longus;  the  carpo-metacarpal  and 

metacarpo-phalangeal  joints,  extensor  poUicis  brevis;  the  inter- 
phalangeal  joint,  abductor  brevis,  flexor  brevis. 

(e)  To  adduct:  the  adductor,  flexor  brevis,  opponens,  first  dorsal  interosseous, 

extensor  longus. 
(/)    To  abduct:  the  long  and  short  abductors. 

19.  Muscles  acting  on  the  fingers. 

(a)  To  flex:  all  the  joints,  flexor  digitorum  profundus;  all  but  the  last,  flexor  digito- 
rum  subhmis;  the  metacarpo-phalangeal  joint  only,  flexor 
digiti  quinti  brevis,  the  lumbrieales,  and  interossei. 

(6)  To  extend  the  fingers:  extensor  digitorum  communis,  extensor  indicis  pro- 
prius,  extensor  digiti  quinti  proprius;  to  extend  the  two  inter- 
phalangeal  joints:  the  lumbrieales,  interossei,  and  frequently  the 
flexor  digiti  quinti  brevis. 

(c)  To  abduct  from  the  axis  passing  through  the  centre  of  the  middle  finger: 

dorsal  interossei,  first  two  lumbrieales,  abductor  digiti  quinti, 
the  long  extensor  of  the  fingers. 

(d)  To  adduct  toward  this  axis :  volar  interossei,  last  two  lumbrieales,  opponens 

and  flexor  digiti  quinti  brevis. 

20.  Muscles  acting  on  the  pelvis. 

(o)  To  flex  it:  rectus  abdominis,  obliquus  abdominis  externus  and  internus, 
psoas  major  and  minor. 

(6)  To  extend  it:  sacro-spinalis,  multifidus,  latissimus  dorsi  and  quadratus 
lumborum. 

(c)  To  bend  it  laterally  and  rotate  it:  abdominal  muscles,  quadratus  lumbo- 
rum, psoas  muscles,  and  latissimus  dorsi  acting  on  one  side. 

21.  Muscles  acting  on  the  thigh  at  the  hip-joint  (arranged  according  to  R.  Fiok). 

(a)  To  flex  it:  ilio-psoas,  rectus  femoris,  adductor  longus,  adductor  brevis, 
obturator  externus,  tensor  fasciae  latae,  pectineus,  sartorius, 
gluteus  minimus,  adductor  magnus  (upper  part),  gracilis, 
quadratus  femoris. 

(6)  To  extend  it:  gluteus  maximus,  adductor  magnus  (posterior  lower  part), 
biceps,  semitendinosus,  semimembranosus,  gluteus  medius, 
piriformis,  obturator  internus. 

(c)  To  adduct  it:  adductor  magnus,  gluteus  maximus,  adductor  brevis,  adductor 

longus,  quadratus  femoris,  obturator  externus,  gracilis,  ad- 
ductor magnus  (upper  part),  pectineus,  biceps,  semitendinosus, 
obturator  internus  and  gemelU,  semimembranosus. 

(d)  To  abduct  it:  gluteus  medius  and  minimus,  the  piriformis,  rectus  femoris, 

tensor  fasciiB  latte,  sartorius;  and  when  the  hip  is  flexed,  the 
gluteus  maximus,  obturator  internus,  and  gemeUi. 

(e)  To  rotate  it  medialward:  gluteus  medius  (anterior  portion),  gluteus  minimus, 

ilio-psoas,  adductor  magnus  (upper  part),  pectineus,  adductor 
longus,  semitendinosus,  semimembranosus,  tensor  fasciae 
latae. 
(/)  To  rotate  it  lateralward:  gluteus  maximus,  quadratus  femoris,  obturator 
internus,  piriformis,  rectus  femoris,  adductor  brevis,  adductor 
magnus  (lower  part),  biceps,  sartorius,  obturator  externus 
gracilis,  gluteus  medius  (posterior  part). 

22.  Muscles  acting  on  the  leg  at  the  knee-joint  (arranged  according  to  R.  Fick). 

(o)  To  flex  it:  semimembranosus,  semitendinosus,  biceps,  gastrocnemius, 
gracilis,  sartorius,  popHteus. 

(6)  To  extend  it:  quadriceps  femoris  (the  tensor  fasciae  latae  and  gluteus  maxi- 
mus through  the  ilio-tibial  band  keep  the  extended  leg  fixed). 

(c)  To  rotate  it  medialward  (when  flexed):  semimembranosus,  semitendinosus, 

sartorius,  popliteus,  gracilis. 

(d)  To  rotate  it  lateralward  (when  flexed) :  biceps,  tensor  fasciae  latae. 

23.  Muscles  acting  on  the  foot  at  the  ankle-joint  (arranged  according  to  R.  Fick). 

(a)  To  flex  it:  tibialis  anterior,  extensor  digitorum  longus,  peroneus  tertius, 

extensor  hallucis  longus. 
(6)  To  extend  it:  gastrocnemius,  soleus,  flexor  hallucis  longus,  peroneus  longus, 

tibialis  posterior,  flexor  digitorum  longus,  peroneus  brevis. 

(c)  To  Invert  the  foot  at  the  inferior  articulation  of  the  talus  (art.  talo-calcanea 

and  talo-calcaneo-navicularis) :  gastrocnemius,  soleus,  tibialis 
posterior,  flexor  hallucis  longus,  flexor  digitorum  longus,  tibialis 
anterior. 

(d)  To  evert  the  foot  at  the  inferior  articulation  of  the  talus :  peroneus  longus, 

peroneus  brevis,  extensor  digitorum  longus,  peroneus  tertius, 
extensor  hallucis  longus,  tibialis  anterior. 

(e)  To   invert   the    foot    at    Chopart's    (talo-navicular-calcaneo-cuboid)    joint: 

tibialis   anterior,    tibiaUs   posterior,    flexor   digitorvmi   longus, 
flexor  hallucis  longus,  extensor  hallucis  longus. 
(J)    To  evert  the  foot  at  Chopart's  joint:  peroneus  longus,   peroneus  brevis, 
extensor  digitorum  longus,  peroneus  tertius. 


506  THE  MUSCULATURE 

24.  Muscles  acting  on  the  toes  (arranged  according  to  R.  Fick). 

(a)  To  flex:  all  the  joints,  flexor  hallucis  longus,  quadrat  us  plantse,  and  flexor 
digitorum  longus;  the  first  interphalangeal  and  the  metatarso- 
phalangeal joints  of  the  four  lateral  toes,  flexor  digitorum 
brevis;  the  metacarpo-phalangeal  joints,  the  lumbricales, 
interossei,  abductor  hallucis,  adductor  hallucis  (oblique  head), 
flexor  hallucis  brevis,  abductor  digiti  quinti,  flexor  digiti 
quinti  brevis. 

(6)  To  extend;  all  joints,  extensor  digitorum  longus,  extensor  hallucis  longus, 
extensor  digitorum  brevis;  the  interphalangeal  joints,  the 
lumbricales,  and  the  adductors  and  abductors  of  the  big  and 
little  toes. 

(c)  To  abduct  from  an  axis  passing  through  the  second  toe;  abductor  hallucis, 

dorsal  interossei,  abductor  digiti  quinti,  first  lumbrical. 

(d)  To  adduot  toward  this  axis :  adductores  hallucis,  plantar  interossei,  three  more 

lateral  lumbricals. 

(e)  To  draw  together  the  ends  of  the  metatarsals :  the  transverse  head  of  the  ad- 

ductor of  the  big  toe. 

References. — For  development  of  the  muscular  system,  consult  the  list  given  by 
W.  H.  Lewis,  Development  of  the  Muscular  System,  in  Keibel  and  Mall's  Human 
Embryology;  for  variations:  Le  Double,  Traite  cles  variations  du  systeme 
musculaire  de  I'homme;  for  action  of  muscles:  R.  Fick,  Handbuch  der  Anatomic 
und  Mechanik  der  Gelenke  unter  Berticksichtigung  der  bewegenden  Muskeln, 
in  von  Bardeleben's  Handbuch,  and  H.  Strasser,  Lehrbuch  der  Muskel  und 
Gelenkmechanik;  for  the  extremities:  Frohse  und  Frankel,  Die  Muskeln  des 
menschlichen  Armes  und  Beines,  in  von  Bardeleben's  Handbuch;  for  the  head 
and  trunk:  Eisler,  Die  Muskeln  des  Stammes,  in  von  Bardeleben's  Handbuch; 
for  the  pelvis:  Holl,  Die  Muskeln  und  Fascien  des  Beckenausganges.  Further 
references  to  the  literature  upon  the  muscular  system  may  be  found  in  Poirier- 
Charpy's  Traite  d'anatomie  humaine. 


SECTION  V 

THE  BLOOD- VASCULAR  SYSTEM 

Revised  for  the  Fifth  Edition 
By  H.  D.  senior,  M.B.,  F.R.C.S. 

PROFESSOR   OF   ANATOMY,    NEW   YORK   UNIVERSITY 

THE  organs  of  circulation  consist  of  a  system  of  tubes  or  vessels  which  during 
life  are  filled  with  fluid  constantly  moving  in  one  direction.  The  major 
portion  of  the  system  is  concerned  with  the  continuous  distribution  of  blood 
throughout  the  body  and  is  called  the  haemal  or  blood-vascular  system.  A 
circumscribed  part  of  the  hismal  circulation  is  differentiated  into  a  rhythmically 
contracting  propulsory  organ  called  the  heart.  The  minor  portion  of  the  system 
is  called  the  lymphatic  system.  The  lymphatic  vessels  convey  fluid,  the  lymph, 
from  the  tissues  to  the  haemal  system. 

The  essential  functions  of  the  blood-vascular  system  are  performed  by  the 
smallest  of  all  the  blood-vessels,  the  capillaries  [vasa  capillaria],  which  form  a 
network  pervading  practically  all  the  tissues  of  the  body.  Blood  is  carried  to  and 
from  the  capillaries  by  larger  vessels  called  the  arteries  and  veins  respectively. 
The  heart  receives  blood  from  the  veins  and  propels  it,  in  turn,  into  the  arteries. 

One  of  the  primary  functions  of  the  blood  is  the  transmission  of  oxygen  from  the  atmosphere 
to  the  tissues.  In  order  to  do  this  the  blood  must  of  necessity  pass  through  the  respiratory 
organ  before  being  deUvered  to  the  body  at  large.  In  gill-breathing  vertebrates,  the  blood, 
having  received  oxygen  in  its  passage  through  the  giUs,  passes  on  directly  to  the  tissues._  The 
entire  circuit  is  here  accomplished  by  a  single  continuous  chain  of  vessels  in  which  capillaries 
occur  twice,  once  in  the  gills  and  again  in  the  organs  and  tissues  in  general.  In  man,  as  in  other 
higher  vertebrates,  lungs  assume  the  function  of  the  gills.  Having  received  oxygen  in  the  lungs 
the  blood  is  returned  again  to  the  heart  before  being  redistributed  throughout  the  body. 
There  are  thus  in  man  two  separate  circuits  or  systems  of  blood-vessels,  one  traversing  the  lungs 
and  a  second  ramifying  throughout  the  body.  The  former  is  known  as  the  pulmonary  circula- 
tion; the  latter  as  the  systemic.  Each  has  its  own  arteries,  capillaries  and  veins;  the  heart  is 
common  to  both.  From  the  time  of  birth  the  heart  is  longitudinally  divided  into  right  and  left 
halves,  each  of  which  contains  its  own  independent  stream  of  blood.  The  blood  entering  the 
left  side  of  the  heart  has  issued  from  the  pulmonary  circulation  and  is  driven  into  the  systemic; 
that  in  the  right  side,  having  traversed  the  systemic  circuit,  is  returned  again  to  the  lungs. 

The  heart  and  blood-vessels  have  a  continuous  lining  of  flattened  cells  called  endothelium ; 
the  hsemal  system  is,  therefore,  a  closed  circuit.*  The  main  thickness  of  the  heart,_  arteries 
and  veins  consists  of  additional  tissue  developed  around  the  endothelial  lining.  It  is  due  to 
this  tissue  that  the  blood  is  continuously  delivered  to  and  withdrawn  from  the  capillaries  under 
suitable  pressure  and  velocity.  The  heart  is  mainly  composed  of  rhythmically  contracting 
muscle  and  its  valves  are  so  arranged  that  the  contained  blood  is  driven  intermittently  in  one 
direction  only.  The  walls  of  the  largest  arteries  are  formed  to  a  great  extent  of  elastic  tissue, 
and,  being  constantly  under  tension  from  within,  are  instrumental  in  converting  the  stream, 
intermittently  received  from  the  heart,  into  a  continuous  flow.  The  walls  of  the  medium  sized 
to  smallest  arteries  are  mainly  muscular.  The  smallest  arteries  are  microscopic  in  size  and 
known  as  arterioles  [arteriote].  The  muscular  arteries  are  capable  of  general  or  local  alterations 
of  calibre  regulated  by  the  nervous  system;  they  are  thus  largely  concerned  in  the  maintenance 
of  the  blood  pressure  and  in  the  regulation  of  the  volume  of  blood  entering  given  localities 
under  varying  conditions.  The  veins  have  much  thinner  walls  than  the  arteries;  the  blood  in 
them  is  under  low  tension  upon  which  they  e.xercise  little  or  no  control. 

When  an  artery  divides,  the  combined  calibre  of  its  branches  is  greater  than  that  of  the 
vessel  itself.  Since  the  arteries  divide  repeatedly  the  bed  of  the  blood-stream  increases  in 
proportion  as  the  vessels  diminish  in  size.  The  rate  of  increase,  slow  at  first,  becomes  enormous 
in  the  arterioles.  Conversely,  the  bed  of  flow  undergoes  contraction  as  the  heart  is  approached 
from  the  venous  side.     The  velocity  of  flow  in  the  capillaries  must  necessarily  be  much  lower 

*  In  the  spleen  and  bone  marrow  the  blood-channels  intermediate  between  the  arteries  and 
veins  are  possible  exceptions  to  this  statement,  but  the  essential  conditions  here  are  still  imper- 
fectly understood. 

507 


508  THE  BLOOD-VASCULAR  SYSTEM 

than  in  the  great  arteries  and  veins.  From  the  relative  slowness  of  the  blood  flow  in  the  sys- 
temic capillaries,  it  has  been  estimated  that  then-  total  bed  is  eight  hundred  times  greater  than 
the  bed  of  the  main  arterial  stem. 

Variations  in  the  course  and  arrangement  of  the  adult  arteries  and  veins,  originally  studied 
by  the  surgeon  for  utihtarian  purposes  only,  now  furnish  one  of  the  most  stimulating  fields  for 
anatomical  research.  Text-books  can  provide,  at  best,  catalogues  of  the  arrangement  commonly 
found  in  the  adult  body  and  of  the  most  ordinary  variations.  That  no  text-book  description 
can  fit  any  individual  case  in  all  particulars,  and  that  unusual  distribution  of  vessels  does  not 
necessarily  shorten  hfe  are  among  the  earhest  lessons  learned  in  the  anatomical  laboratory. 
The  adult  vascular  pattern  is  derived  from  a  symmetrical  arrangement  in  the  early  embryo 
of  which  scarcely  a  trace  remains.  The  intervening  changes  are  so  numerous  and  profound  that 
the  general  uniformity  of  vascular  distribution  Ln  different  individuals  is  more  remarkable 
than  the  occurrence  of  occasional  wide  variations  from  the  usual  type. 

In  early  stages  of  development  all  vessels  have  a  similar  structure ;  they  consist,  in  fact,  of 
a  single  layer  of  endothehum.  Some  vessels,  however,  are  larger  than  others;  these  act  as 
arteries  or  veins  (according  to  the  direction  of  flow)  while  the  smaller  channels  perform  the  office 
of  capillaries.  The  early  principal  vessels  do  not  necessarily  persist,  for  many  of  these  dwindle 
or  are  lost.  New  channels  are  meanwhile  in  continuous  process  of  formation  and  some  of  these 
may,  in  turn,  become  main  channels.  It  thus  follows  that  the  main  vessels  of  the  adult  must 
be  looked  upon  rather  as  selected  channels  through  a  plexus  of  possible  pathways,  than  as  sepa- 
rate entities  which  must  necessarily  conform  to  given  rules  of  distribution  and  branching. 

In  time,  no  doubt,  most  of  the  commoner  variations  from  the  usual  adult  type  wUl  receive 
a  rational  explanation;  at  present  enough  has  been  done  to  indicate  the  value  of  the  embryo- 
logical  method.  The  Ust  of  v.ariations  in  the  arteries  and  veins  respectively  is  preceded  by  a 
brief  account  of  the  morphogenesis  of  these  vessels. 

In  the  case  of  the  heart  anomalies  frequently  result  in  early  death,  so  that  subjects  of  devel- 
opmental irregularities  are  seldom  seen  in  the  anatomical  laboratory.  The  anomahes  usually 
consist  in  improper  development  of  the  septa  which  normally  divide  the  heart  and  main  ar- 
terial trunk  into  their  pulmonary  and  systemic  halves.  A  short  account  of  the  morphogenesis 
of  the  heart  is  appended  to  the  description  of  the  adult  organ. 

In  the  following  section  the  heart  and  pericardium  will  first  be  considered 
followed  by  the  arteries  and  veins. 


A.  THE  HEART  AND  PERICARDIUM 

1.  THE  HEART 

The  heart  [cor]  is  a  hollow  organ  principally  composed  of  muscle,  the  myo- 
cardium. It  is  lined  internally  by  endocardium  which  is  continuous  with  the 
intima  of  the  blood-vessels.  Externally,  it  is  covered  by  the  epicardium,  a  serous 
membrane  continuous  with  the  serous  Hning  of  the  pericardium.  The  form  of 
the  heart,  when  removed  from  the  body  without  previous  hardening,  is  that  of  a 
fairly  regular  truncated  cone.  The  base  [basis  cordis]  is  poorly  circumscribed 
but  corresponds,  in  a  general  way,  to  the  area  occupied  by  the  roots  of  the  great 
vessels  and  the  portion  of  the  heart-wall  between  them.  The  base  of  the  heart 
is  held  in  position*  chiefly  by  the  great  vessels,  which  are  attached  to  the  peri- 
cardium; the  remainder  of  the  organ  is  capable  of  free  movement  within  the 
pericardial  cavity. 

The  interior  of  the  heart  is  longitudinally  divided,  into  right  and  left  cavities, 
by  a  septum  passing  from  base  to  apex.  Each  cavity  is  subdivided  into  an 
atrium  [atrium  cordis]  and  a  ventricle  [ventriculus  cordis],  the  former  receiving 
the  ultimate  venous  trunks  and  the  latter  giving  rise  to  the  main  arteries.  Thus 
the  left  atrium  receives  the  four  pulmonary  veins,  and  the  right  atrium  the 
superior  and  inferior  vena  cava  and  the  coronary  sinus;  the  aorta  issues  from  the 
left  ventricle  and  the  pulmonary  artery  from  the  right.  The  ventricles,  which 
constitute  the  major  portion  of  the  heart,  may  be  recognised  by  their  very  thick 
walls.  The  atria  have  thinner  walls  and  are  less  capacious  than  the  ventricles; 
projecting  from  each  is  a  diverticulum  or  auricle  [auricula  cordis].  The  auricles 
(which  receive  their  name  from  their  resemblance  to  dog's  ears)  partially  embrace 
the  roots  of  the  pulmonary  artery  and  aorta. 

Orientation  of  the  heart. — The  apex  of  the  heart  [apex  cordis]  points  forward, 
to  the  left  and  downward.  The  base  is  directed  backward,  to  the  right  and  up- 
ward. The  longitudinal  axis  of  the  heart  forms  an  angle  of  about  40°  with  the 
horizontal  plane  and  also  with  the  median  sagittal  plane  of  the  body. 

*  Not  necessarily  fixed,  for  during  systole  the  base  performs  a  greater  excursion  than  does 
the  apex. 


EXTERIOR  OF  THE  HEART 


509 


The  long  axis  of  the  heart  is  therefore  slightly  more  horizontal  than  vertical,  and  slightly- 
more  antero-posterior  than  transverse.  The  atria  are  posterior  to  rather  than  above  the  ven- 
tricles. To  arrive  approximately  at  the  longitudinal  axis,  it  is  necessary  to  select  the  central 
point  of  the  base.  By  cutting  the  vessels  short  in  several  hearts,  hardened  by  formalin  before 
removal,  a  point  immediately  to  the  left  of  the  left  lower  pulmonary  vein  was  selected  in  deter- 
mining the  data  above  given.  A  steel  pin  was  passed  through  this  point  to  the  apex  cordis,  and 
the  angles  controlled  by  frontal  and  transverse  sections  of  the  thorax.  Mention  of  angular 
measurements  of  the  axis  of  the  heart  could  be  found  only  in  the  text-books  of  Testut  and 
Luschka;  the  former  gives  40°  to  the  horizontal  plane,  the  latter  60°  to  the  mid-sagittal. 
Luschka's  angle  appear  to  be  too  large;  but  further  investigation  in  this  direction  is  desirable. 

Fig.  423. — Steeno-costal  Surface  op  the  Heart. 


Left  subclavian  artery 
Left  inferior  thyreoid  vein 

Left  innominate  vein 


Left  superior  intercostal  vein 
Vestige  of  left  common  cardinal 
Left  pulmonary  artery 


Vena  cava  superior 


Conus  arteriosus 


Margo  obtusus 


Left  ventricle 


Incisura  apicis  cordis 


Size  and  weight. — In  the  adult  the  heart  measures  about  12.5  cm.  (5  in.)  from  base  to  apex, 
8.7  cm.  (31  in.)  across  where  it  is  broadest,  and  6.2  cm.  (24  in.)  at  its  thickest  portion.  In  the 
male  its  weight  averages  about  312  gm.  (eleven  ounces),  and  in  the  female  about  255  gm. 
(nine  ounces).  It  increases  both  in  size  and  weight  up  to  advanced  life,  the  increase  being  most 
marked  up  to  the  age  of  twenty-nine  years.  The  proportion  of  heart-weight  to  body-weight 
is  about  1:205  in  the  adult. 


EXTERIOR  OF  THE  HEART 

In  hearts  which  have  been  hardened  by  injection  before  removal  from  the 
bod}^,  the  regularity  of  the  heart-cone  is  disturbed  by  a  well-marked  triangular 
facet,  imparted  by  contact  with  the  diaphragm.  This  facet  is  the  diaphragmatic 
surface  [facies  diaphragmatica],  which  is  directed  downward  and  slightlj-  back- 
ward (fig.  424).     It  ends  abruptly  along  a  sharp  margin  extending  from  the  apex 


510 


THE  BLOOD-VASCULAR  SYSTEM 


toward  the  right.  This  margin  is  the  margo  acutus  (fig.  423) ;  it  separates  the 
diaphragmatic  surface  from  the  sternocostal  surface.  The  other  margin  of  the 
diaphragmatic  surface  is  more  rounded  and  shades  gradually  into  the  very  wide 
margo  obtusus  (fig.  423),  which  passes  almost  insensibly  into  the  sternocostal 
surface.  The  convex  sternocostal  surface  [facies  sternocostalis]  (fig.  423), 
directed  forward  and  somewhat  upward  and  to  the  right,  is  triangular  and  bounded 
below  by  the  margo  acutus.  To  the  left  it  goes  over  into  the  margo  obtusus 
along  a  line  extending  from  the  apex  of  the  heart  to  the  root  of  the  pulmonary 
artery.  The  margo  obtusus  corresponds  to  the  rounded  left  side  of  the  left 
ventricle. 

The  interventricular  sulcus  is  a  slightly  marked  groove  indicating  the  separa- 
tion of  the  ventricles  upon  the  exterior  of  the  heart.  It  lodges  coronary  blood- 
vessels and  a  moderate  quantity  of  fat  which  can  be  seen  through  the  epicardium. 


Fig.  424. — Base  and  Diaphragmatic  Surface  op  the  Heart.     (After  His.) 


Left  pulmonary  ^ 
artery 


Left  superior  pul- 
monary vein 


Left  inferior  pul- 
monary vein 


^Reflexion 
of  pericardium 


Coronary  sinus 


■  Aorta 
.  Superior 

vena  cava 
.  Right  pulmonary 
artery 


Margo  obtusus 


^ 


The  anterior  part  of  this  groove,  sulcus  longitudinalis  anterior,  beginning  poste- 
riorly, runs  obliquely  over  the  upper  part  of  the  margo  obtusus  on  to  the  sterno- 
costal surface.  Crossing  the  margo  acutus  to  the  right  of  the  apex,  it  is  continuous 
with  the  sulcus  longitudinalis  posterior  upon  the  diaphragmatic  surface.  The 
diaphragmatic  surface  is  formed  about  equally  by  the  right  and  left  ventricles, 
and  the  sterno-costal  surface  mainly  by  the  right.  Where  the  longitudinal 
sulcus  crosses  the  margo  acutus  it  produces  a  slight  notch,  the  incisura  (apicis) 
cordis. 

The  atria  are  separated  externally  from  the  ventricles  by  the  sulcus  coronarius. 
This  is  a  horseshoe-shaped  groove  well  marked  below  and  laterally,  and  inter- 
rupted above  by  the  roots  of  the  pulmonary  artery  and  aorta.  It  lodges  the 
coronary  sinus,  smaller  coronary  vessels  and  fat. 


ATRIAL  PORTION 


511 


ATRIAL  PORTION 

The  atrial  portion  of  the  heart  is  situated  behind,  and  shghtly  to  the  right  of 
and  above,  the  ventricular  portion.  The  separation  between  the  right  and  left 
atrium  is  not  indicated  behind  except  in  distended  hearts  (such  as  that  shown  in 
fig.  424) ;  in  these  it  is  marked  by  a  slight  groove  connecting  the  left  sides  of  the 
superior  and  inferior  venae  cavse.  In  front,  the  auricles  are  separated  by  the  deep 
notch  which  lodges  the  aorta  and  pulmonary  artery.  A  slight  groove  on  the 
back  of  the  right  atrium  which  connects  the  right  sides  of  the  superior  and 
inferior  vense  cavse,  is  the  sulcus  terminalis  (figs.  424,  425) .  This  represents  the 
right  limit  of  what  was,  in  the  embryo,  the  sinus  venosus.  It  also  indicates  that 
the  embryonic  sinus  venosus  has  become  an  integral  part  of  the  adult  right 
atrium.  The  superior  and  inferior  cavae  have  each  a  nearly  vertical  direction 
and  join  the  posterior  part  of  the  right  atrium  above  and  below,  respectively. 
The  coronary  sinus  runs  downward,  backward  and  to  the  right  to  join  the  lower 
part  of  the  right  atrium  anterior  to  the  inferior  vena  cava.  The  four  pulmonary 
veins  run  nearly  transversely  and  somewhat  forward  into  the  right  and  left  sides 
of  the  left  atrium. 


Fig.  425. — Atria  Opened  Posteriorly  to  show  the  Septum  Atriorum. 


Pulmonary  artery 
Aorta 


Vena  cava  superior 


Crista  terminalis 


I  ^ ^^ Sulcus 

terminalis 


Limbus  fossae 
ovalis 
(.section) 


Vena  cava  inferior 


Facies  diaphragmatica 


The  interior  of  the  atrial  portion  of  the  heart  is  divided  into  right  and  left 
cavities  by  the  septum  atriorum.  This  septum  is  a  composite  structure,  having 
been  developed  (see  morphogenesis  of  the  heart)  in  two  independent  parts,  each 
forming  an  incomplete  septum  in  itself.  The  two  incomplete  septa,  however, 
partly  overlap  one  another  so  that,  by  the  lateral  fusion  at  the  time  of  birth,  they 
together  produce  the  impervious  structure  of  the  adult  heart  (fig.  425).  Of 
these  septa,  the  first  to  be  formed  is  the  membranous  septum  [pars  membranacea 
septi  atriorum].  Later  there  is  formed  to  the  right  of  this  the  muscular  septum, 
the  margin  of  which  forms,  in  the  adult  atrium,  the  greater  part  of  the  limbus 
fossae  ovalis.     The  margin  of  the  membranous  septum  is  recognizable  as  a  fold 


512 


THE  BLOOD-VASCULAR  SYSTEM 


of  endocardium  on  the  septal  wall  of  the  left  atrium;  it  is  called  the  valvula 
foraminis  ovjilis. 

Posteriorly  into  the  right  atrium  [atrium  dextrum  (fig.  425)],  above  and  below, 
respectively,  open  the  superior  and  the  inferior  vena  cava.  Upon  the  septal 
wall,  immediately  above  the  inferior  cava  is  the  fossa  ovalis,  a  depression  of 


Fig.  426. — Section  op  the  Ventricles  in  Systole  and  Diastole.     (After  Krehl.) 


> 


which  the  floor  is  formed  by  the  membranous  septum.  Surrounding  the  fossa 
ovalis  except  below  (indeed  producing  the  fossa)  is  the  limbus  fossae  ovalis 
which  is  continuous  anteriorly  and  below  with  the  valvula  venae  cavae  (inferioris 
Eustachii).  Just  anterior  to  the  fossa  ovalis  is  the  orifice  of  the  coronary  sinus 
guarded  by  the  valvula  sinus  coronarii  (Thebesii)  (fig.  428).     Leading  from  the 


ATRIAL  PORTION 


513 


front  of  the  atrium  forward  and  slightly  downward  and  to  the  left  is  the  ostium 
venosum  (right  atrio-ventricular  orifice)  guarded  by  the  tricuspid  valve.  Above 
and  behind  this  is  the  auricle,  the  exterior  of  which  is  in  contact  medially  with  the 
root  of  the  aorta.  To  the  right  of  the  superior  and  inferior  caval  orifices  there  is  a 
vertical  ridge,  the  crista  terminalis,  which  corresponds  to  the  sulcus  terminalis  on 
the  exterior  (figs.  425,  428). 

The  portion  of  the  atrium  medial  to  the  crista  is  smooth  and  is  called  the  sinus  venarum; 
in  the  embryo  it  is  separated  from  the  atrial  cavity  proper  by  the  right  and  left  sinus  valves. 
The  crista  terminalis  marks  the  original  line  of  attachment  of  the  right  sinus  valve.  The 
valve  itself  has  disappeared,  except  at  the  lower  part  where  it  persists  as  the  caval  and  coronary 
valves.  These  valves  vary  in  size  considerably  in  different  specimens,  and  are  frequently 
nethke  from  numerous  perforations. 

The  conversion  of  a  portion  of  a  single  valve  into  two  separate  valves,  which  meet  at  an 
acute  angle,  is  brought  about  by  an  attachment  between  the  sinus  valve  and  an  embryonic 
structure  called  the  sinus-septum.  This  septum  is  a  ridge  dividing  the  right  horn  of  the  sinus 
venosus  from  the  transverse  portion  of  the  sinus  (the  coronary  of  the  adult) ;  it  probably  con- 

FiG.  427. — The  Interiok  op  the  Ventricles,  Anteriok  Half.     (After  His.) 


ilmonary  artery 


Aortic  semilunar 
valves 


Anterior  papillary 
of  left  vent. 


Muscular  ventricu- 
lar seplum 


'Opening  into  ventricle 


'Conus  arteriosus 

Membranous    ven- 
■     tricular  septum, 
'Crista  supra ven- 
\  tricularis 

■Papillary  of  conus 


-Right  ventricle 


Anterior  papillary 
muscle 


tributes  somewhat  to  the  formation  of  both  the  coronary  and  caval  valves.  The  left  sinus 
valve  usually  disappeai's  by  blending  with  the  septum  atriorum  on  which  it  unites  with  the 
limbus  fossae  ovalis;  it  ooeasionaUy  remains  partially  separate  in  the  adult. 

The  interior  of  the  right  auricle  and  of  the  portion  of  the  atrium  lateral  to  the 
crista  terminalis  is  thrown  into  ridges  (musculi  pectinati)  by  prominent  bands  of 
the  atrial  myocardium.  The  musculi  pectinati  end  abruptly  by  joining  the 
crista.  The  orifice  of  the  superior  cava  has  no  valve  and  is  directed  downward 
and  somewhat  forward;  below  it,  on  the  posterior  wall  of  the  atrium,  there  has 
been  described  a  tubercle  or  ridge,  the  tuberculum  intervenostun  (Loweri). 


Apart  from  the  posterior  circumference  of  the  superior  cava  itself  and  the  limbus  fossae 
ovalis,  the  hiunan  heart  appears  to  contain  nothing  in  this  region  that  could  be  described  as  a 
tubercle.  With  regard  to  the  segregation  of  the  streams  entering  the  foetal  right  atrium  from 
the  superior  and  inferior  cavae,  respectively,  in  which  the  tubercle  of  Lower  has  been  supposed 
to  participate,  it  is  to  be  noted  that  the  fossa  ovalis  is  just  above  (almost  within)  the  inferior 


514 


THE  BLOOD-VASCULAR  SYSTEM 


caval  orifice.  Also  that  the  caval  opening  and  the  fossal  ovalis  (containing  the  foetal  foramen 
ovale)  are,  in  hearts  well  hardened  before  removal,  situated  in  a  distinct  diverticulum  to  the 
left  of  the  remainder  of  the  atrium.  Between  this  diverticulum  and  the  atrium  proper,  the 
caval  valve  and  the  limbus  fossa?  ovalis  form  a  prominent  flange,  better  marked  in  the  foetus 
than  the  adult.  Opening  into  the  right  atrium,  particularly  upon  the  septal  and  right  lateral 
walls,  are  numerous /orowiraa  venarum  minimarum  (Thebesii). 

The  left  atrium  [a.  sinistrum]  (fig.  425)  is  to  the  left  and  somewhat  posterior 
to  the  right.     It  is  behind  the  root  of  the  aorta  and  its  auricle  is  to  the  left  of  the 

Fig.  428. — Interior  of  the  Right  Atrium  and  Ventricle. 
The  atrio-ventricvdar  bundle  is  dissected  out. 


•  Left  common  carotid  artery 


-  Innominate  artery 


Vena  cava  superior 


Reflexion  'of  pericardium 
Pulmonary  artery 


Ascending  aorta 


Left  pulmonary  valve 


Conus  arteriosus 


Vena  cava  inferior 


Part  of  posterior  tricuspid  cusp       Posterior  papillary 


pulmonary  root.  Opening  into  it  posteriorly  on  the  right  and  left  sides,  re- 
spectively, are  the  right  and  left  upper  and  lower  pulmonary  veins.  The  valvula 
foraminis  ovalis  forms  a  more  or  less  distinct  crescentic  ridge  on  the  septal  wall 
(fig.  425).  This  may  not  be  attached  to  the  limbus  fossas  ovalis,  in  which  case 
there  is  a  communication  between  the  two  atria.  Absence  of  lateral  adhesion 
between  the  two  septa  atriorum  does  not  necessarily  lead  to  admixture  of  arterial 
and  venous  blood  during  life.     The  left  ostium  venosum  (atrio-ventricular  orifice) 


ATRIO-VENTRICULAR  VALVES 


515 


guarded  by  the  mitral  valve  leads  from  the  anterior  part  of  the  atrium  forward  and 
shghtly  downward  and  to  the  left.  The  interior  of  the  left  atrium  is  smooth  ex- 
cept in  the  auricle,  in  which  musculi  pectinati  are  well  marked. 

Fig.  429. — Left  Ventricle  and  Part  op  the  Atrium. 

The  aorta  is  opened  through  the  anterior  cusp  of  the  mitral  valve.     The  plainly  visible  left 

limb  of  the  atrio-ventricular  bundle  has  been  accentuated. 

Aorta 


Pulmonary  artery 


Apex  of  the  left  ventricle 


ATRIO-VENTRICULAR  VALVES 

The  atrio-ventricular  valves  (figs.  427,  428,  429,  431)  are  attached  around  the 
venous  ostia  of  the  ventricles  in  such  a  way  as  to  open  freely  into  the  ventricles, 
but  to  prevent  regurgitation  of  the  blood  into  the  atria  during  ventricular  systole. 
Each  valve  is  continuous  along  its  line  of  attachment,  but  its  free  edge  is  notched 
so  as  to  produce  an  irregular  margin;  some  of  the  notches  are  so  deep  as  to 
partially  divide  the  valve  into  cusps.  The  right  atrio-ventricular  valve  is 
commonly  divided  by  three  deep  notches  into  three  cusps;  this  valve  is  therefore 
called  the  tricuspid  [valvula  tricuspidalis].  The  left  is  similarly  divided  into  two 
cusps  and  is  called  the  bicuspid  [v.  bicuspidalis]  or  mitral.  The  depth  of  the 
notches,  however,  is  very  variable  and  there  may  be  an  increase  or  (more  rarely) 
a  diminution  in  the  number  of  cusps;  the  addition  of  small  subsidiary  cusps  is 
quite  common.  Each  valve  cusp  is  tied  down  to  the  papillary  muscles  [mm. 
papillares]  of  the  ventricle  by  chordae  tendinese.  The  latter  are  fibrous  cords, 
generally  branched,  of  varying  thickness.  The  thinnest  cords  are  attached  to  the 
free  margin  of  the  cusp;  those  of  intermediate  thickness  to  the  ventricular  surface 
a  few  millimetres  from  the  margin,  and  the  thickest  to  the  ventricular  surface 


516  THE  BLOOD-VASCULAR  SYSTEM 

near  the  attached  margin.  The  valves  are  smooth  and  glistening  on  the  atrial 
aspect,  but  rough  and  fasciculated,  from  the  attachment  of  the  chordae,  on  the 
ventricular.  The  cusps  of  the  mitral  valve  are  called  anterior  and  posterior;  those 
of  the  tricuspid,  anterior,  posterior  and  medial.  Each  cusp  receives  chorda  from 
more  than  one  papillary  muscle  and  each  papillary  muscle  sends  chordse  to  more 
than  one  cusp.  The  chordse  tendinese  of  the  mitral  valve  are  thicker  than  those 
of  the  tricuspid  (figs.  428,  429). 

VENTRICULAR  PORTION 

The  ventricles  form  the  greater  portion  of  the  heart.  In  the  adult  the  relation 
of  the  ventricles  to  one  another  is  as  follows.  The  left  [ventriculus  sinister] 
has  the  form  of  a  narrow  cone,  the  apex  of  which  is  the  apex  of  the  heart.  The 
right  ventricle  [ventriculus  dexter]  is  crescentic  in  section  and  appears  to  be 
partially  wrapped  around  the  right  or  lower  wall  of  the  left  ventricle  which  forms 
the  septum  ventriculorum  (fig.  426).  The  left  ventricle  forms  the  margo  ob- 
tusus  of  the  heart,  about  half  the  diaphragmatic  surface,  and  a  shght  part  of  the 
sterno-costal  surface.  The  right  ventricle  forms  about  half  the  diaphragmatic 
surface  and  the  major  part  of  the  sterno-costal  surface;  it  takes  no  share  in  the 
formation  of  the  apex  of  the  heart. 

The  interventricular  septum  [septum  ventriculorum]  is  thick  and  muscular 
except  for  a  small  area  near  the  root  of  the  aorta  which  is  membranous  [septum 
membranaceum  ventriculorum].  The  latter  can  be  seen  from  the  left  ventricle  in 
the  angle  between  the  attached  edges  of  the  right  and  posterior  aortic  valves 
(fig.  429).  The  membranous  septum  is  partly  concealed  from  the  right  heart  by 
the  medial  cusp  of  the  tricuspid  valve  which  is  attached  to  it  near  its  upper  part. 
The  portion  of  the  membranous  septum  above  the  medial  tricuspid  cusp  is 
therefore  atrio-ventricular,  i.  e.,  between  the  right  atrium  and  left  ventricle. 

The  membranous  septum  is  the  extreme  lower  part  of  the  independent  septum  (s.  aorticum) 
which  divides  the  aortic  root  from  the  pulmonary  artery  and  conus  arteriosus  (and  partially 
subdivides,  also,  the  right  ventricle  by  separating  the  conus  arteriosus  from  the  remainder  of 
the  ventricle).  The  relation  of  the  part  of  the  aortic  septum  between  the  conus  arteriosus  and 
aortic  root  to  the  septum  ventriculorum  is  beautifully  shown  by  His,  in  fig.  427. 

The  greater  part  of  the  interior  of  the  ventricles  is  thrown  into  ridges  by  myocardial 
bundles  of  large  size.  These  fasciculi  [trabeculae  cordis]  either  stand  out  in  rehef  only,  or,  by 
being  undermined,  form  bands  covered  except  at  either  end  by  endotheUum.  A  careful  exam- 
ination of  the  endocardium  of  fresh  hearts  will  reveal  a  plexiform  network  of  Purkinje  fibres. 
These  fibres,  belonging  to  the  atrio-ventricular  conducting  system,  become  very  obvious  when 
the  endocardium  has  been  exposed  to  the  air  long  enough  to  become  partially  dry. 

The  wall  of  the  right  ventricle  [ventriculus  dexter]  (figs.  427,  428)  is  much 
thicker  than  that  of  the  atria,  but  less  so  than  that  of  the  left  ventricle.  The 
upper  and  anterior  part  of  the  right  ventricle  is  in  relation  posteriorly  with  the  root 
of  the  aorta.  This  portion  of  the  ventricle  is  called  the  conus  arteriosus  and  is 
separated  from  the  remainder  of  the  right  ventricle  by  a  muscular  spur  which 
extends  from  the  back  of  the  conus  to  the  right  venous  ostium.  The  spur  is  the 
crista  supraventricularis ;  its  relation  to  the  partition  between  the  conus  and 
aorta,  and  to  the  septum  membranaceum,  shows  that  it  is  the  free  edge  of  the 
embryonic  aortic  septum  (see  morphogenesis  of  the  heart). 

Two  papillary  muscles  in  the  right  ventricle  are  constant  in  position,  the 
large  anterior  papillary  muscle,  and  the  small  papillary  muscle  of  the  conus 
(Luschka).  The  anterior  papillary  is  situated  on  the  sterno-costal  wall,  near  the 
junction  of  this  with  the  septal  wall.  The  papillary  of  the  conus  is  placed  just 
below  the  septal  end  of  the  crista  supraventricularis.  The  posterior  papillary 
muscles  form  an  irregular  group  springing  from  the  diaphragmatic  wall.  Some 
chordae  tendinese  stretch  directly  from  the  septal  wall  (with  or  without  small 
muscular  elevations  at  their  bases)  to  the  medial  cusp  of  the  tricuspid  valve.  The 
chordae  tendinese  from  the  anterior  papillary  go  to  the  anterior  and  posterior 
cusps;  those  from  the  conus  papillary  to  the  medial  and  anterior,  and  those  from 
the  posterior  papillary  muscles  to  the  medial  and  posterior  cusps  of  the  tricuspid 
valve,  respectively. 

There  is  frequently  a  band  of  myocardium  extending  from  the  septal  wall  of  the  right  ven- 
tricle to  the  anterior  papillary  muscle  near  its  middle.  This  is  the  moderator  band,  which 
contains  a  part  of  the  right  limb  of  the  atrio-ventricular  bundle.     If  the  moderator  band  joins 


SEMILUNAR  VALVES 


517 


the  anterior  papUlary  near  its  base,  as  it  frequently  does,  it  is  difficult  to  distinguish  it  from  the 
ordinary  trabeoulae  in  this  situation. 

The  term  moderator  band  was  originally  applied  to  this  bridge  or  band  of  muscle  under  the 
impression  that  it  prevented  overdistention  of  the  ventricle.  Subsequent  discovery  of  the 
conducting  system  of  the  heart  makes  it  plain  that  there  is  always  a  band  conducting  the  right 
limb  of  the  atrio- ventricular  bundle  from  the  septum  to  the  anterior  papillary  muscle.  Whether 
the  band  is  isolated  from  the  other  trabecules,  and  therefore  readily  recognizable,  appears 
to  depend  somewhat  upon  the  relation  of  the  base  of  the  papillary  muscle  to  the  septum 
ventriculorum. 

The  wall  of  the  left  ventricle  [veiitriculus  sinister]  (figs.  427,  429)  is  very 
thick  except  at  the  extreme  apex,  and  at  the  membranous  septum.  In  the  left 
ventricle  are  two  large  papillary  muscles,  generally  known  as  anterior  and  posterior; 
both  send  chordae  tendineae  to  each  cusp  of  the  mitral  valve.  On  the  septal  wall 
of  the  ventricle  the  left  limb  of  the  atrio-ventricular  bundle  can  usually  be  seen 
as  a  broad,  flattened  band  beneath  the  endocardium.  The  band  appears  just 
below  the  septum  membranaceum  and  divides  into  strands  which  go  to  the  two 
papillary  muscles.  The  strands  in  many  places  bridge  across  part  of  the  ventricle 
to  reach  the  papillary  muscles  covered  only  by  tubes  of  endocardium. 

These  bridging  strands  connecting  the  papillary  muscles  with  the  septum  ventriculorum, 
which  were  formerly  called  "false  chordas  tendinese,"  are  exactly  comparable  to  the  moderator 
band  of  the  right  ventricle  which  occasionally  consists  of  atrio-ventricular  bundle  and  endo- 
cardium only. 

SEMILUNAR  VALVES 

The  semilunar  valves  [valvulse  semilunares]  guard  the  arterial  ostia  of  the 
ventricles.  The  aortic  ostium  is  directed  upward  and  slightly  forward  and  to  the 
right;  the  pulmonary  backward  and  slightly  upward  and  to  the  left.  Each  valve, 
of  which  there  are  three  to  each  ostium,  is  a  pocket-like  fold  of  endocardium 
strengthened  by  fibrous  tissue  (fig.  430) .  The  free  edge  of  each  valve  is  directed 
away  from  the  ventricle,  so  that  excess  of  pressure  within  the  great  vessels  brings 


Fig.  430. — Intbrigh  View  of  the  Aortic  Semilunar  Valves. 


Aortic  sinus 


Section  of  fibrous  ring 


Free  edge  of  valve        i 


Nodulus  Arantii 
Lunula 


the  three  valves  of  either  ostium  into  mutual  apposition.  In  the  middle  of  the 
free  edge  of  each  valve  there  is  a  small  fibro-cartilaginous  nodule;  radiating  from 
this  toward  the  entire  fundus,  and  along  the  extreme  free  edge  of  the  valve,  are 
fibrous  thickenings.  On  either  side  of  the  nodule,  between  the  thicker  margin 
and  fundus,  the  valve  is  thin  over  a  crescentic  area  called  the  lunula. 

The  aortic  valves  are  called  the  right,  left,  and  posterior;  the  pulmonary  valves, 
the  right,  left,  and  anterior.*  The  aortic  semilunar  valves  are  stronger  than  the 
pulmonary;  opposite  them  there  are  three  dilatations  in  the  aortic  wall,  the  aortic 

*  The  BNA  names  of  the  aortic  and  pulmonary  valves  are  not  based  upon  their  relative 
positions  in  the  body.  From  transverse  sections  through  the  thorax  (see  any  good  atlas)  it 
may  be  seen  that  one  aortic  valve  is  anterior,  one  pulmonary  valve  posterior,  and  the  other 
aortic  and  pulmonary  valves  are  right  and  left.  If  the  removed  heart  is  held  so  that  the  ven- 
tricles are  on  the  right  and  left  of  the  septum,  respectively,  the  valves  take  the  positions  indi- 
cated by  the  BNA.  The  names  given  by  the  BNA  to  the  valves,  although  conventional  (Uke 
many  other  terms  of  orientation  applied  to  parts  of  the  heart),  are  convenient,  particularly  from 
a  developmental  standpoint. 


518 


THE  BLOOD-VASCULAR  SYSTEM 


sinuses  [sinus  aortae]  or  sinuses  of  Valsalva.     From  the  right  and  left  sinuses  the 
right  and  left  coronary  arteries,  respectively,  arise. 

After  ventricular  systole  the  increased  pressure  in  the  great  vessels  distends  the  valves  with 
blood.  The  noduli  meet  in  the  centre  and  the  lunulas,  coming  into  mutual  contact,  produce  a 
tri-radiate  line  of  contact  between  the  valves. 

ARCHITECTURE  OF  THE  MYOCARDIUM 

In  the  adult  heart  the  myocardium  of  the  atria  is  separate  from  that  of  the  ventricles. 
There  is,  between  the  atria  and  ventricles,  a  fibrous  partition,  the  upper  and  lower  surfaces  ol 
which  give  attachment  to  the  muscle  fibres  of  these  cavities,  respectively. 

The  fibrous  partition  (fig.  431)  is  thickest  in  the  triangle  formed  by  the  meeting  of  the  aortic, 
and  right  and  left  atrio-ventricular  ostia.  This  interval  is  filled  by  a  mass  of  fibrous  tissue, 
which  in  the  angles  between  the  aortic  and  the  left  atrio-ventricular  ostium  forms  two  thickened 
triangular  masses,  the  trigona  fibrosa.  The  fibrous  mass  is  continued  to  the  pulmonary  ostium 
as  the  tendon  of  the  conus.  Below  the  point  of  junction  of  the  trigona  and  the  tendon  of  the 
conus  these  structures  blend  with  the  septum  membranaceum  ventriculorum.  The  septum 
membranaceum,  tendon  of  the  conus,  and  part  of  the  trigona  are  derived  from  the  aortic  septum 
(pp.  516,  527).  The  trigona  give  off  laterally,  on  either  side,  atrio-ventricular  rings  which  en- 
circle the  venous  ostia  and  give  attachment  to  the  atrio-ventricular  valves.     There  are  also  weak 

Fig.  431. — Base  op  a  Well  Developed  Heart  showing  the  Coubse  op  the  Superficial 

Muscle  Fibres. 

From  X  to  jX'  around  the  front  of  the  aorta  indicates  the  course  of  the  aortic  septum. 

(Mall,  I  nat.  size.) 


rings  surrounding  the  pulmonary  and  aortic  orifices;  the  aortic  and  left  atrio-ventricular  rings 
being  partly  confluent.  The  rings  surrounding  the  arterial  and  venous  ostia  axe  the  annuli 
fibrosi. 

The  atrial  musculature  is  attached  to  the  trigona  and  atrio-ventricular  rings  only.  The 
superficial  fibres  are  attached  to  both  rings  and  either  encircle  both  atria  in  one  loop,  or  enter  the 
septum  and  form  a  figure  8.  The  deeper  fibres  are  attached  to  one  ring  and  encircle  one  atrium 
only;  some  fibres  encircle  only  the  auricle. 

The  ventricular  musculature  is  very  complex  and  consists  of  numerous  superimposed  layers 
distinguished  from  one  another  by  the  direction  taken  by  the  muscle  fibres.  In  a  general  way, 
the  fibres  of  the  deepest  layer  have  a  direction  crossing  those  upon  the  surface  of  the  same  area 
at  a  right  angle.     The  intervening  layers  of  fibres  pass  through  all  stages  of  obhquity. 

Recent  work  upon  the  origin  and  distribution  of  the  ventricular  fibres  has  resulted  in  the 
recognition  of  a  certain  uniformity  of  behavior,  thus: — 

1.  AH  fibres  arise  from,  and  are  inserted  into,  the  fibrous  partition  at  the  base.  The  at- 
tachment may  be  directly  to  the  trigona  or  annuli,  or  indirectly  to  them  by  means  of  the  chordse 
tendineae  and  atrio-ventricular  valves. 

2.  The  more  superficial  fibres  (fig.  432)  tend  to  encircle  the  entire  heart,  passing  over  the 
longitudinal  sulci.  If  they  enter  the  septum  they  do  so  by  passing  into  the  vorte.x  or  whorl 
at  the  apex  of  the  left  ventricle.  These  fibres  have  always  a  definite  direction  upon  the  sur- 
face, i.  e.,  from  right  to  left  upon  the  sterno-costal  surface  and  from  left  to  right  on  the  dia- 
phragmatic (fig.  431). 

3.  The  deeper  fibres  all  enter  the  septum  in  a  direction  oblique  or  perpendicular  to  its 
longitudinal  axis.  In  addition  they  completely  encircle  one  or  both  ventricles  forming,  in  the 
latter  case,  double  loops  (fig.  433). 


VESSELS  AND  NERVES  OF  THE  HEART 


519 


During  systole,  as  a  result  of  this  arrangement: — (1)  The  papillary  muscles  and  the  longi- 
tudinal and  antero-posterior  axes  of  the  ventricles  are  simultaneously  shortened.  (2)  There  is 
a  movement  of  torsion  or  "wringing"  which  I'educes  the  ventricular  cavities  to  their  minimum 
dimensions. 

Conducting  system. — Although  the  ordinary  myocardium  of  the  atria  is  distinct  from  that 
of  the  ventricles  there  is,  at  one  place,  a  connection  between  them.  This  connection  is  by  means 
of  a  small  band  of  muscle  which  differs  histologically  from  ordinary  heart  muscle.  It  is  known 
as  the  atrio-ventricular  bundle,  and  serves  to  transmit  the  atrial  rhythm  of  contraction  to  the 
ventricles. 

The  atrio-ventricular  bundle  begins  in  the  septal  wall  of  the  atrium  a  short  distance  in 
front  of  the  coronary  orifices  (fig.  428).  It  has  an  e.xpanded  free  end,  the  atrio-ventricular  node, 
from  which  branches  pass  to  be  quickl}'  lost  in  the  atrial  myocardium.  The  bundle  passes 
forward  covered  by  endocardium  and  by  one  or  two  millimetres  of  mj'ocardium,  and  passes 
beneath  the  medial  cusp  of  the  tricuspid  valve.  In  passing  from  the  atrium  to  the  ventricle, 
the  bundle  skirts  the  lower  margin  of  the  septum  membranaceum.  Immediately  in  front  of  the 
septum  membranaceum  it  divides  into  a  left  and  right  limb,  of  which  the  former  pierces  the 
muscular  interventricular  septum .  The  right  limb  now  passes  beneath  the  crista  supra ventricul- 
aris  and  above  the  papillary  muscle  of  the  conus,  giving  off  branches  to  the  latter  and  to  other 
small  papillaries  on  the  septum  (fig.  428).  Bending  somewhat  toward  the  apex,  it  enters  the 
moderator  band  which  conducts  it  to  the  large  anterior  papillary  muscle.  From  here  it  passes 
along  one  of  the  trabeculae  connected  with  the  sterno-oostal  wall  of  the  ventricle,  or  in  the  wall 
itself,  to  reach  the  posterior  papillary  muscle  or  muscles.  The  right  limb  is  compact  and 
rounded  and  in  the  intact  heart  is  usually  invisible  except,  sometimes  near  the  root  of  the 
moderator  band  or  in  the  band  itself. 

The  left  limb  of  the  bundle  appears  in  the  left  ventricle  a  little  below  the  septum  mem- 
branaceum.    It  is  a  wide  band  immediately  beneath  the  endocardium,  which  cannot  usually  be 


Fig.  432. — Diagram  of  one  Anterior 
AND  ONE  Posterior  Superficial  Bundle 
OP  Cardiac  Muscle  Fibres  seen  from 
Behind.     (After  MacCallum.) 


Fig.  433. — Diagram  of  a  Deeper 
Bundle  of  Muscle  Fibres.  (After 
MacCallum.) 


Conus  arteriosus 

Tendon  of  the  conus 
V  ""^r^  «\  Right  atrio-ven- 
•^^   -3  '    ■■' x       tncular  ring 


stripped  off  without  injuring  the  bundle  (fig.  429).  It  passes  along  the  septal  wall  toward  the 
apex  and  divides  into  two  parts,  which  again  subdivide  to  be  distributed  to  the  anterior  and  the 
posterior  papillary  muscles.  The  branches  for  the  papillary  muscles  may  reach  them  through 
thick  trabecula;,  or  they  may  form  thin  strands  which,  covered  only  by  endocardium,  bridge 
from  septum  to  papillary  muscle. 

In  addition  to  the  comparatively  distinct  branches  to  the  papillary  muscles  of  both  ventricles, 
the  bundle  gives  off  finer  fibres  which  form  a  sub-endocardial  plexus.  This  plexus,  visible  to  the 
naked  eye  (p.  516)  is  made  up  of  fibres  having  a  structure  similar  to  those  of  the  ventricular 
portion  of  the  bundle.  The  fibres  were  described  by  Purkinje  as  long  ago  as  1845,*  but  it  was 
not  until  1906,  thirteen  years  after  the  discovery  of  the  bundle  by  W.  His,  Jr.,  that  Tawaraf 
recognised  their  significance. 

There  is  another  node  of  muscle  having  characters  similar  to  that  of  the  conducting  system, 
although  not  connected  with  it  except  by  myocardium  of  the  ordinary  character.  This  is  the 
sinus-node  which  is  situated  at  the  upper  end  of  the  crista  terminaUs  of  the  right  atrium.  Una- 
nimity is  still  lacking  with  regard  to  the  physiological  significance  of  this  structure. 

Vessels  and  Nerves  of  the  Heart 


The  arteries. — The  two  coronary  arteries  arise  from  the  right  and  left  sinuses  of  the  aorta. 

The  right  coronary  artery  [a.  coronaria  dextraj  passes  forward  between  the  pulmonary 
artery  and  the  right  atrium,  and  then  follows  the  right  coronary  sulcus  to  the  diaphragmatic 
surface  of  the  heart  (fig.  435),  to  anastomose  with  the  left  coronary  artery.  The  posterior 
descending  branch  [ramus  descendens  posterior]  arises  at  the  posterior  longitudinal  sulcus.     It 

*  Arch.  f.  Anat.,  Physiol,  u.  wissenschafthche  Medizin. 

t  Das  Reitungssystem  des  Saiigertierherzens,  Fischer,  Jena,  1906. 


520 


THE  BLOOD-VASCULAR  SYSTEM 


E asses  in  the  furrow  between  the  ventricles  toward  the  apex,  near  which  it  anastomoses  with 
ranches  derived  from  the  left  coronary  artery.  In  this  course  the  right  coronary  artery 
supplies  branches  to  the  right  atrium  and  roots  of  the  pulmonary  artery  and  aorta,  as  well  as 
one  that  descends  near  the  margo  acutus  (right  marginal),  and  a  second  (preventricular)  to  the 
anterior  wall  of  the  right  ventricle.     It  supplies  both  ventricles  and  the  septum. 

The  left  coronary  artery  [a.  coronarius  sinistra]  passes  for  a  short  distance  forward,  between 
the  pulmonary  artery  and  the  left  auricle,  and  then  divides  into  two  principal  branches,  one  of 
which  runs  in  the  anterior  longitudinal  sulcus  to  the  apex  of  the  heart,  the  anterior  descending 
branch  [r.  descendens  anterior],  around  which  it  sends  branches  to  anastomose  with  the  right 
coronary;  whilst  the  other,  the  circumflex  [ramus  circumflexus],  winds  to  the  diaphragmatic 
surface  in  the  coronary  groove,  to  anastomose  with  the  corresponding  twigs  of  the  right  artery. 
In  this  course  it  gives  off  a  branch  which  follows  the  margo  obtusus  (left  marginal)  as  well  as 
smaller  branches  to  the  left  atrium,  both  ventricles,  and  the  commencement  of  the  aorta  and 
pulmonary  vessels. 


Fig.  434. — Stebno-costal  Surface  of  the  Heart,  showing  its  Arteries  and  Veins. 
(After  Spalteholz.) 
Innominate  artery 


Left  subclavian  artery 


Superior  vena  cava 


Left  common  carotid  artery 


_  Pulmonary  artery 

Conus  arteriosus 
-  Left  auricle 


Rightcoronary. 
artery 


Right  ventricle 


The  cardiac  or  coronary  veins  accompany  the  coruuary  arteries  and  return  the  blood  from 
the  walls  of  the  heart. 

The  great  cardiac  vein  [v.  cordis  magna],  (fig.  434)  runs  in  the  anterior  longitudinal  sulcus, 
passing  round  the  left  side  of  the  heart  in  the  coronary  sulcus  to  terminate  in  the  commence- 
ment of  the  coronary  sinus.  Its  mouth  is  usually  guarded  by  two  valves,  and  it  receives  in  its 
course  the  posterior  vein  of  the  left  ventricle,  with  other  smaller  veins  from  the  left  atrium  and 
ventricle,  all  of  which  are  guarded  by  valves. 

The  middle  cardiac  vein  (v.  cordis  media],  sometimes  the  larger  of  the  two  chief  veins,  com- 
municates with  the  foregoing  at  its  commencement  above  the  heart's  apex.  It  ascends  in  the 
posterior  longitudinal  groove,  receiving  blood  from  the  ventricular  walls,  and  joins  the  coronary 
sinus  through  an  orifice  guarded  by  a  single  valve,  close  to  its  termination. 


VESSELS  AND  NERVES  OF  THE  HEART 


521 


The  posterior  vein  of  the  left  ventricle  [v.  post,  ventriculi  sinistri],  lies  upon  the  posterior 
surface  of  the  ventricle  and,  receiving  branches  from  it,  passes  upward  to  terminate  directly 
in  the  coronary  sinus. 

The  anterior  cardiac  veins  [vv.  cordis  anteriores]  consist  of  several  small  branches  from  the 
front  of  the  right  ventricle,  which  vary  in  number  and  either  open  separately  into  the  right 
atrium  or  join  the  lesser  cardiac  vein  (fig.  434). 

The  small  cardiac  vein  [v.  cordis  parva]  is  a  small  vessel  which  receives  branches  from  both 
the  right  atrium  and  ventricle,  and  winds  around  the  right  side  of  the  heart,  in  the  coronary 
sulcus,  to  terminate  in  the  coronary  sinus. 

The  coronary  sinus  [sinus  coronarius]  (fig.  435)  may  be  regarded  as  a  much  dilated  terminal 
portion  of  the  great  cardiac  vein.  It  is  about  2.5  cm.  (1  in.)  in  length,  is  covered  by  muscular 
fibres  from  the  atrium,  and  hes  in  the  coronary  sulcus  below  the  base  of  the  heart.  Its  cardiac 
orifice,  with  the  coronary  (Thebesian)  valve,  has  already  been  described.  Besides  the  tributary 
veins  already  named,  a  small  oblique  vein  [v.  obUqua  atrii  sinistri]  of  the  left  atrium  may  some- 

FiG.  435. — Base  and'  Diaphragmatic  Surface  op  the  Heart,  showing  its  Arteries  and 
Veins.     (After  Spalteholz.) 

Kigtit  pulmonary  artery 


Left  pulmouary  artery 
Left  atrium 


Great  cardiac 

vein 
Posterior 
'vein  of  tlie 

left    ven- 

tricle 


Right  pulmonary  veins 


Left  ventricle- 


Middle  cardiac  vein 


. Posterior  descending 

branch  of  the  right 
coronary  artery 


Posterior  longitudinal  sulcus 


times  be  traced,  on  the  back  of  the  left  atrium,  from  the  ligament  of  the  left  vena  cava  (Marshall) 
to  the  sinus.  This  httle  vein,  which  is  not  always  pervious  or  easy  of  demonstration,  never 
possesses  a  valve  at  its  orifice,  and,  Uke  the  coronary  sinus,  formed  a  part  of  the  left  superior 
vena  cava  of  earlyfoetal  life. 

The  smallest  cardiac  veins  [vv.  cordis  minima;]  drain  blood  from  septum  and  lateral  walls 
of  the  atria,  particularly  the  right;  also  from  the  conus  arteriosus.  They  open  directly  into  the 
right  atrium. 

Although  anastomoses  occur  between  the  two  coronary  arteries,  these  are  by  no  means 
extensive,  and  are  not  sufficient  to  allow  of  the  estabhshment  of  a  satisfactory  collateral  cir- 
culation in  the  case  of  the  blocking  of  one  coronary  artery.  Consequently  such  interference 
with  the  cardiac  circulation  produces  rapid  pathological  changes  in  the  heart  musculature, 
provided  it  is  sudden  in  occurrence.  If  the  obhteration  of  the  artery  take  place  gradually, 
however,  some  rehef  may  be  afforded  by  the  estabhshment  of  a  collateral  circulation  through 
the  vense  minimse,  which  open  out  from  both  the  atrial  and  ventricular  cavities  and  communicate 


522 


THE  BLOOD-VASCULAR  SYSTEM 


with  the  finer  branches  of  the  cardiac  veins,  and  also  with  the  general  capillary  network  in  the 
heart's  walls. 

The  lymphatic  vessels  of  the  heart  pass  chiefly  through  the  anterior  mediastinal  lymph- 
nodes  into  the  broncho-mediastinal  trunk.     (See  Section  VI.) 

The  cardiac  nerves,  derived  from  the  vagus  and  the  cervical  sympathetic,  descend  into  the 
superior  mediastinum,  passing  in  front  of  and  behind  the  arch  of  the  aorta;  they  unite  in  the 
formation  of  the  superficial  and  deep  cardiac  plexuses.  The  superficial  plexus  lies  above  the 
right  pulmonary  artery  as  the  latter  passes  beneath  the  aortic  arch.  The  deep  plexus  lies  be- 
tween the  trachea  and  the  arch  of  the  aorta,  above  the  bifurcation  of  the  pulmonary  trunk. 
For  the  connections  of  the  plexuses  see  section  on  Nervous  System. 

2.  THE  PERICARDIUM 

The  pericardium  is  a  cone-shaped,  fibro-serous  sac  which  surrounds  the  heart 
and  contains  a  small  amount  of  fluid  [liquor  pericardii].  Its  apex  is  above  at  the 
root  of  the  great  vessels,  and  its  base  below,  adherent  to  the  diaphragm.  Its 
connection  with  the  diaphragm  is  in  part  to  the  central  tendon  and  in  part  to  the 
muscle,  especially  on  the  left  side.  It  consists  of  an  outer  fibrous  layer  and  an 
inner  serous  layer.  The  virtual  space  between  the  serous  pericardium  and  the 
epicardium  is  commonly  called  the  pericardial  cavity. 

Fia.  436. — ^Lept  Posteriok  View  of  the  Heart  to  show  the  Reflections  of  the  Peri- 
cardium. 


Pulmonary  artery 


Left  pulm.  artery 


Ligament  of  left 
superior  cava 


Morgo  obtusus 


Coronary  sinus 


Vena  cava  inferior 


The  fibrous  layer  is  strong  and  inelastic,  made  of  interlacing  fibres.  Its  connection  with 
the  central  tendon  of  the  diaphragm  is  intimate,  particularly  in  the  region  of  the  caval  opening, 
but  elsewhere  it  is  attached  loosely  by  means  of  areolar  tissue.  Above,  it  is  lost  on  the  sheaths 
of  the  great  vessels,  all  of  which  receive  distinct  investments,  with  the  single  exception  of  the 
inferior  vena  cava,  which  pierces  it  from  below.  The  aorta,  superior  vena  cava,  the  pulmonary 
artery,  and  the  four  pulmonary  veins,  are  all  ensheathed  in  this  manner.  The  pericardium  is 
connected  above  with  the  deep  cervical  fascia.  Two  variable  bands  of  fibrous  tissue,  the 
sterno-pericardial  ligaments  [ligg.  sterno-pericardiaca],  connect  the  front  of  the  pericardium, 
above  and  below,  with  the  posterior  surface  of  the  sternum. 


RELATIONS  OF  HEART  AND  PERICARDIUM  523 

The  serous  layer  is  smooth  and  ghstening  and  consists  of  connective  tissue,  rich  in  elastic 
fibres,  covered  by  endotheUum.  It  lines  the  interior  of  the  fibrous  layer  and  is  continuous  with 
the  epicardium  or  serous  covering  of  the  heart.  The  reflexion  of  the  serous  layer  from  the  heart 
to  the  fibrous  layer  of  the  pericardium  occurs  at  both  the  arterial  and  venous  attachments  of  the 
heart.  At  the  arterial  attachment  a  simple  tube  of  epicardium  is  reflected  along  the  pul- 
monary artery  and  aorta.  At  the  venous  attachment  the  serous  layer  is  reflected  from  the  front 
of  the  pulmonary  veins  on  the  left,  and  from  the  front  of  these  and  from  the  roots  of  the  venae 
cavae  on  the  right.  This  reflexion  is  separated  above  from  that  around  the  aorta  and  pulmon- 
ary artery  (figs.  424,  436).  Around  the  lower  margin  of  the  left  lower  pulmonary  vein  (fig.  436) 
and  the  root  of  the  inferior  vena  cava,  this  reflexion  is  continuous  with  an  arched  refle.xion  from 
the  back  of  the  atria  (figs.  424,  436).  The  latter  reflexion  forms  a  pocket  posterior  to  the  atria 
which  is  sometimes  called  the  oblique  sinus  of  the  pericardium. 

Between  the  reflexions  of  the  epicardium  at  the  arterial  and  venous  attachments  of  the  heart 
there  is  a  dorsal  communication  between  the  right  and  left  sides  of  the  pericardial  cavity.  This 
is  the  transverse  sinus  of  the  pericardium  [s.  transversus  pericardii];  it  passes  behind  the  aorta 
and  pulmonary  artery  and  in  front  of  the  superior  cava  and  left  atrium. 

During  early  embryonic  life  the  sinus  transversus  is  closed  by  the  dorsal  mesocardium 
(see  p.  527).  The  primitive  ventral  mesocardium,  which  divides  the  right  and  left  sides  of  the 
pericardial  cavity  ventrally,  is  lost  very  early. 

The  ligament  of  the  left  superior  cava  [lig.  vense  cavae  sinistrse]  (figs.  423,  436) 
is  a  doubling  of  the  serous  layer  which  passes  between  the  left  pulmonary  artery 
above  and  the  left  superior  pulmonary  vein  below.  It  contains,  besides  some 
fatty  and  areolar  tissue,  the  shrunken  remains  of  the  left  superior  vena  cava. 
It  is  usually  connected  above  with  the  left  superior  intercostal  vein  by  means  of  a 
small  tributary  of  the  latter.  Passing  from  its  lower  end  to  the  left  end  of  the 
coronary  sinus  is  the  small  vena  obliqua  atrii  sinistri  (oblique  vein  of  Marshall). 
The  root  of  the  left  superior  intercostal  (and  the  adjacent  part  of  the  left  innom- 
inate) vein;  the  vein  passing  from  the  super  or  intercostal  to  the  lig.  venae 
cavae  sinistrse;  the  obhque  vein  of  the  left  atrium,  and  the  coronary  sinus  all 
represent  parts  of  the  embryonic  left  vena  cava  superior. 

Relations. — In  front  of  the  pericardium  are  found  the  thymus  gland  or  its  remains,  areolar 
tissue,  the  sterno-pericardial  ligaments,  the  left  transversus  thoracis  muscle,  the  internal 
mammary  vessels,  the  anterior  margins  of  the  pleural  sac  and' lungs,  and  the  sternum.  Later- 
ally, it  is  overlapped  by  the  lungs  with  their  pleural  sacs,  and  it  is  in  contact  with  the  phrenic 
nerves  and  their  accompanying  vessels.  Posteriorly,  it  is  in  relation  with  the  cesophagus  and 
vagus  nerves,  the  descending  aorta,  the  thoracic  duct  and  vena  azygos,  and  the  roots  of  the  lungs. 
Below  it  is  separated  by  the  diaphragm  from  the  stomach  and  the  left  lobe  of  the  fiver. 

Vessels. — The  arteries  of  the  pericardium  are  derived  from  the  pericardiac,  oesophageal, 
and  bronchial  branches  of  the  thoracic  aorta  and  from  the  internal  mammary  and  phrenic 
arteries. 

RELATIONS   OF  THE   HEART  AND   PERICARDIUM   TO   THE 
THORACIC   WALL 

Heart  (fig.  437  A  and  B). — The  base  of  the  heart  corresponds  posteriorly  to  the  fifth, 
to  the  ninth  thoracic  vertebra.  Anteriorly  the  apex  is  in  the  fifth  intercostal  space,  7.5  to 
S  cm.  (3  to  3i  in.)  from  the  medan  line.  The  base  (above)  corresponds  to  a  line  (A)  drawn 
from  a  point  1  cm.  (=  in.)  below  the  second  left  chondro-costal  articulation, and  3  cm  (Ij  in. 
from  the  median  line,  to  another  point  (the  same  distance  from  the  median  line)  1  cm.  above 
the  right  third  ehondro-sternal  articulation.  The  marge  acutus,  or  lower  border  corresponds 
to  a  line  (B)  drawn  from  the  apex  through  the  xiphi-sternal  articulation,  to  a  point  on 
the  sixth  costal  cartilage  2  cm.  to  the  right  of  the  median  line.  The  right  border  of  the  heart 
may  be  indicated  approximately  by  a  fine  (shghtly  convex  to  the  right)  joining  the  right  ends 
of  A  and  B.  The  left  border  corresponds  to  a  fine  (slightly  convex  to  the  left)  joining  the  left 
end  of  A  to  the  apex. 

If  a  line  be  drawn  from  the  upper  margin  of  the  left  third  ehondro-sternal  articulation  to  the 
right  edge  of  the  sternum  in  the  fifth  intercostal  space,  the  upper  end  of  the  line  wiU  he  over  the 
centre  of  the  pulmonary  ostium,  and  the  lower  two-thirds  of  it  (approximateljO  will  overlie 
the  main  axis  of  the  tricuspid  ostium.  The  aortic  ostium  is  immediately  to  the  left  of  the  above 
line  with  its  centre  at  the  left  edge  of  the  sternum  opposite  the  third  space.  The  mitral  ostium 
is  very  largely  behind  the  third  left  interspace;  its  upper  end  is  behind  the  third  cartilage,  its 
lower  behind  the  left  margin  of  the  sternum  opposite  the  fourth  cartilage  and  space. 

Of  the  ostia  of  the  heart,  the  pulmonary  is  nearest  the  anterior  thoracic  wall,  the  aortic  is 
slightly  in  advance  of  the  mitral,  and  the  tricuspid  is  the  deepest  of  all. 

The  pericardium  follows  the  heart  closely.  The  upper  end  (apex)  in  the  subject  used  in 
preparing  fig.  437  extended  up,  behind  the  sternum,  to  the  lower  margin  of  the  first  costal 
cartilage  on  the  right  and  the  upper  margin  of  the  second  on  the  left. 

MORPHOGENESIS  OF  THE  HEART  AND  PERICARDIUM 

The  heart  is  formed  by  the  blending  in  the  median  fine  of  two  longitudinal  endothehal 
tubes  lying  ventral  to  the  fore-gut  of  the  early  embryo.  Each  tube  is  partially  surrounded 
laterally  by  the  splanchnic  mesoderm  which  forms  a  septum  between  the  right  and  left  sides  of 


524 


THE  BLOOD-VASCULAR  SYSTEM 


Fig.  437. — A,  Telebobntgenogham  of  a  Formalin  Preparation  or  the  Anterior 
Thoracic  Wall  with  the  Heart,  Pericardium  and  Diaphragm  in  situ.  (Le  Wald, 
X  i).  B,  Explanatory  Outline  Drawing,  Traced  from  the  Negative  and  Con- 
trolled BY  Stereoscopic  Views. 

The  ostia  have  been  accurately  fitted  with  wire  rings.     P,  pulmonary  ostium;  M,  mitral; 
T,  tricuspid;  aortic  ostium  is  unlabelled;  I- VII,  right  costal  cartilages. 


I 


MORPHOGENESIS  OF  THE  HEART  AND  PERICARDIUM 


525 


the  ccelomic  cavity.  The  blended  endothehal  tubes  form  the  endocardium.  The  splanchnic 
mesoderm  in  relation  to  the  endocardium  becomes  the  myoepicardium,  and  the  double  layer 
connecting  the  heart  dorsally  and  ventrally  with  the  somatic  mesoderm  becomes  the  (temporary) 
dorsal  and  ventral  mesocardia.  The  somatic  mesoderm  of  the  heart  region  becomes  the  peri- 
cardium. 

The  originally  straight  heart-tube  grows  rapidly  and  becomes  tortuous  on  account  of  its 
increasing  length  between  the  hmits  assigned  by  its  fixed  arterial  and  venous  ends.  Its  arterial 
end  is  continued  into  the  truncus  arteriosus,  which  is  later  divided  into  the  pulmonary  artery 
and  the  ascending  aorta.  Its  venous  end  receives  the  vitehine  and  umbihcal  veins,  and,  later 
on,  the  common  cardinals  also.  By  the  formation  of  a  series  of  alternate  bulgings  and  constric- 
tions the  heart  becomes  differentiated  into  the  sinus  venosus,  atrium,  ventricle  and  conus  arte- 
riosus, counting  from  the  venous  to  the  arterial  end.  These  parts,  after  going  through  a  process 
of  progressive  differentiation  and  shifting  (fig.  438)  take  up  relative  positions  somewhat  ap- 
proaching those  of  the  adult. 


Fig.  438. — Models  showing  the  Development  of  the  Heart.     (After  His.) 
Conus  arteriosus  Conus  arteriosus 


The  sinus  venosus  hes  on  the  dorsal  wall  of  the  atrium,  and  is  composed  of  right  and  left 
horns  united  by  a  transverse  portion.  The  sinus  is  separated  from  the  atrium  by  a  sagitaUy 
directed  sHt-Uke  opening,  guarded  by  right  and  left  lateral  valves  which  project  into  the  atrium. 
The  atrium  is  wide,  being  prolonged  into  a  ventrally  projecting  pouch  on  either  side,  the  future 
right  and  left  auricles.  The  ventricle  is  situated  caudal  and  somewhat  ventral  to  the  atrium. 
The  right  Umb  of  the  common  ventricle,  which  leads  into  the  conus  arteriosus,  is  the  future 
right  ventricle;  the  left  limb,  connected  with  the  atrium,  is  the  future  left  ventricle.     The 


Fig.  439. — Sagittal  Section  throtjgh  a  Reconstrttction  of  the  Heart  of  a  9  mm.  Human 
Embryo  seen  FROir  the  Left  Side.     (Tandler,    X   75.) 

Septum 
=«''""1'"° Foramen  ovale 


Conus  arteriosus- 


Septum  prinum 


Sinus  venosus 


communication  between  the  atrium  and  the  ventricle,  known  as  the  atrial  canal,  is  indicated 
on  the  exterior  by  a  constriction;  its  interior  consists  of  a  transversely  placed  slit.  The  conus 
arteriosus  is  continued  from  the  ventricle  without  obvious  constriction  and  passes  over  into  the 
truncus  arteriosus. 

The  sinus  venosus  early  loses  its  bilateral  symmetry  owing  to  the  rapid  enlargement  of  the 
right  horn.  This  horn  soon  receives,  through  the  proximal  portion  of  the  right  vitelline  vein 
{inferior  vena  cayo),  all  the  blood  coming  from  the  left  vitelline  and  both  umbihcal  veins.  The 
right  common  cardinal  also  gains  ascendency  over  the  left  and  becomes  the  superior  vena  cava. 


526 


THE  BLOOD-VASCULAR  SYSTEM 


The  left  horn  and  transverse  part,  now  only  draining  the  dwindling  left  common  cardinal,  (left 
superior  cava)  and  the  coronary  veins,  become  the  coronary  sinus.  The  right  horn  gradually 
becomes  absorbed  into  the  right  end  of  the  atrial  cavity  until  the  superior  and  inferior  cava; 
and  the  coronary  sinus  acquire  separate  openings  into  that  chamber.  Between  the  opening 
of  the  coronary  sinus  and  that  of  the  inferior  cava  there  is  a  ridge,  the  sinus-septum  (between 
the  right  horn  and  transverse  parts  of  the  sinus),  which  becomes  attached  to  the  lower  part 
of  the  right  sinus  valve. 

In  the  atrium  a  septum  begins  early  to  grow  from  the  ventro-cephaUc  wall  of  the  atrium, 
toward  the  atrial  canal.  As  the  interatrial  communication  around  the  edge  of  the  septum 
(ostium  primum)  is  becoming  narrow,  a  perforation  occurs  near  the  attached  margin  of  the 
septum  (ostium  secundum).  This  fii-st  septum  (septum  primum)  is  incomplete  because  when 
its  edge  reaches  the  atrial  canal  the  atria  stiU  communicate  through  ostium  secundum.  To  the 
right  of  the  septum  primum  another  septum  (s.  secundum)  is  formed  later;  this  never  stretches 
completely  across  the  atrium  and  is  rather  a  crescentic  ridge  than  a  true  septum.  Until  the 
free  edges  of  the  two  septa  overlap  one  another  there  is  a  direct  passage  leading  from  one  side 
of  the  atrium  to  the  other;  eventually  they  do  overlap  and  the  communication  becomes 
oblique  but  persists  until  birth.  (For  adult  relations  of  septa,  see  p.  511.)  The  cavities 
resulting  from  the  division  of  the  common  atrium  are  the  right  and  left  atria  of  the  adult. 
The  obUque  channel  connecting  the  atria  (foramen  ovale)  is  bounded  on  the  right  side  by  the 
s.  secundum  the  free  edge  of  whicli  forms  the  limbus  fossae  ovalis.  The  channel  is  bounded 
on  the  left  by  the  s.  primum  which  slants  into  the  left  atrium.  The  free  edge  of  the  s. 
primum  becomes  the  valvula  foraminis  ovalis;  the  remainder,  the  membranous  atrial  septum  of 
the  adult.' 

Fig.  440. — Reconstkuction  op  the  Heart  of  an  11  mm.  Human  Embryo  viewed  from 
Below.  (Mall,  50.) 
The  lower  part  of  the  ventricular  portion  has  been  cut  off.  Connective  tissue  septa  colored 
yellow.  Ao,  aorta;  Ap,  anterior  papillary  muscle;  La,  left  atrium;  Lo,  left  venous  ostium;  Lp, 
large  (anterior)  papillary  muscle  of  right  ventricle;  Mpm,  medial  papillary  muscle;  PP,  pos- 
terior papillary  muscle;  P,  pulmonary  artery;  RA,  right  atrium. 


i 


The  portion  of  the  dorsal  wall  of  the  right  atrium  immediately  adjoining  the  septa  is  derived 
from  the  sinus  venosus.  Tliis  part  of  the  atrium  (the  sinus  venarum)  receives  the  great  venous 
openings.  The  left  side  of  the  left  sinus-valve  is  attached  to  both  septa  and  assists  the  septum 
secundum  in  the  formation  of  the  limbus  foraminis  ovalis.  The  cephalic  part  of  the  right  sinus- 
valve  disappears  along  the  line  of  the  (adult)  crista  ierminalis,  which  therefore  hmits  the  right 
portion  of  the  right  atrium  derived  from  the  sinus  venosus.  The  caudal  portion  of  this  valve 
persists  as  the  inferior  caval  and  coronary  valves.  These  are  drawn  out  of  their  original  ahgn- 
ment  by  the  adhesion  between  the  caudal  part  of  the  right  sinus-valve  and  the  sinus-septum. 

The  left  atrium  receives,  through  the  dorsal  mesocardium,  the  originally  single  pulmonary 
vein.  This  common  stem  is  absorbed  into  the  atrial  wall;  later,  the  primitive  right  and  left 
tributaries  are  absorbed  in  a  similar  way,  leaving  the  four  pulmonary  veins  of  the  adult  open- 
ing separately  into  the  left  atrium.  The  area  of  the  left  atrium  adjacent  to  the  pulinonary 
veins,  therefore,  is  not  part  of  the  original  atrial  waU. 

The  ventricles  are  divided  by  a  septum  (s.  musculare  ventriculorum)  growing  from  the  caudal 
wall  of  the  common  ventricular  cavity  toward  the  atrial  canal.  The  canal  moves  to  the  right, 
and  the  dorsal  part  of  the  septum  blends  with  the  dorsal  lip  of  the  canal.  The  free  ventral 
edge  of  the  interventricular  septum  helps  to  bound  the  foramen  through  which  blood  from  the  left 
ventricle  must  enter  the  right  on  its  way  to  the  conus  arteriosus.  The  foramen  persists  until 
(the  free  margin  of  the  interventricular  septum  having  been  joined  by  the  aortic  septum)  it 
becomes  the  circumference  of  the  aortic  ostium. 


THE  ARTERIES  AND  VEINS  527 

The  aortic  septum  is  a  composite  structure  formed  partly  by  a  septum  growing  between  tlie 
fourth  and  sixth  pairs  of  aortic  arches,  and  partly  by  sweUings  growing  in  the  interior  of  the  conus 
and  truncus  arteriosus.  When  fully  formed  it  extends  spirally  along  the  truncus  and  conus, 
and  enters  the  right  half  of  the  common  ventricular  cavity,  where  it  joins  the  right  side  of  the 
free  edge  of  the  interventricular  septum.  The  septum  is  arranged  in  such  a  way  that  the  blood 
from  the  left  ventricle  passes  no  longer  through  the  right  ventricle  but  along  its  own  channel 
{the  aorta)  through  the  conus  and  truncus  to  the  first  four  pairs  of  aortic  arches.  The  blood 
from  the  right  ventricle  passes  through  the  pulmonary  division  of  the  conus  and  truncus  arterio- 
sus, anterior  and  to  the  left  of  the  aorta,  into  the  sixth  arches.  Further  differentiation  brings 
about  the  external  separation  of  the  aorta  from  the  pulmonary  artery,  but  their  common  cover- 
ing of  epicardium  persists  as  such  in  the  adult.  The  lower  end  of  the  aortic  septum  persists 
in  the  adult  as  the  septum  membranaceum  ventriculorum  and  the  crista  supraventricularis,  the 
relations  of  which  to  the  septum  musculare  are  well  shown  in  fig.  428.  During  the  formation 
of  the  aortic  septum  four  endocardial  swelhngs  appear  at  the  distal  part  of  the  interior  of  the 
conus.  These  are  arranged  as  smaller  and  larger  opposite  pairs;  the  smaller  and  larger  swellings, 
therefore,  alternating  around  the  lumen.  The  larger  pair  of  swellings  assists  (by  partial 
blending)  in  the  formation  of  the  aortic  septum.  When  the  septum  is  complete,  half  of  each 
of  the  larger  sweUings  is  contained  in  the  aorta  and  half  of  each  in  the  pulmonary  artery.  One 
of  the  smaller  swelhngs  remains  in  the  aorta  and  one  in  the  pulmonary  artery,  so  that  there  are 
now  three  sweUings  in  each  vessel.  Each  of  the  six  swellings  becomes  undermined  to  form 
a  semilunar  valve  of  the  adult. 

The  atrio-ventricular  valves. — The  interior  of  the  ventricular  cavity,  which  is  at  first 
smooth,  becomes  undermined  in  an  irregular  way,  to  form  a  system  of  myocardial  trabeculse. 
The  Ups  of  the  transversely  directed  atrial  canal  become  thickened  into  prominent  anterior  and 
posterior  endocardial  cushions;  these  project  into  the  ventricular  cavity  and  become  involved 
in  its  myocardial  trabecular  system.  The  atrial  canal,  which  has  now  moved  to  the  right,  be- 
comes divided  sagittaUy,  into  right  and  left  venous  osiia,  by  the  septum  primum.  The  inter- 
ventricular septum  joins  the  ventricular  side  of  the  posterior  endocardial  cushion.  The  anterior 
and  posterior  endocardial  cushions,  where  they  blend  with  one  another  and  with  the  septum 
primum  on  the  medial  side  of  each  venous  ostium,  form  an  atrio-ventricular  valve-cusp  on 
either  side,  viz.,  the  anterior  cusp  of  the  mitral  in  the  left  ostium,  and  the  medial  cusp  of  the 
tricuspid  in  the  right.  The  posterior  cusp  of  the  mitral  and  the  anterior  and  posterior  of  the 
tricuspid  are  formed  later,  partly,  by  lateral  tubercles  developing  in  either  ostium,  and  partly 
by  undermining  of  the  ostia  from  the  ventricular  side.  The  atrial  musculature  extends  into  the 
atrio-ventricular  valves  and,  until  a  late  stage,  is  continuous  with  the  trabecular  system  of  the 
ventricles.  GraduaUy,  however,  this  connection  between  atrial  and  ventricular  musculature 
is  lost,  leaving  only  the  chordae  tendinese  connecting  the  papillary  muscles  with  the  valves 
Muscle  is  found  at  the  basal  region  of  the  valve-cusps  in  the  adult,  and  occasionally  persists  in 
the  chordae  tendinese. 

The  connection  between  the  atrial  and  ventricular  musculature  is  not  confined  to  that 
occurring  by  means  of  the  valves  and  trabecular  system.  The  original  myocardial  connection 
between  the  atrial  and  ventricular  portions  of  the  heart  remains  complete  until  the  embryo 
has  reached  the  length  of  about  11  mm.  From  that  time  on  the  epicardium  begins  to  blend 
with  the  fibrous  annuh  of  the  venous  ostia.  MeanwhUe  the  atrial  musculature  rapidly  loses  its 
connection  with  that  of  the  ventricles  until  they  are  connected  in  one  place  only,  i.  e.,  the  site 
of  the  atrio-vetitricular  bundle. 

The  pericardial  cavity  is  the  original  cephalic  end  of  the  intraembryonic  ccelom.  The 
somatic  mesoderm  of  the  pericardial  region  forms  the  adult  pericardium.  The  splanchnic 
mesoderm  persists  only  in  the  part  which  furnishes  the  myo-epicardium.  The  ventral  and  dorsal 
mesocardia,  both  of  which  are  formed  by  the  splanchnic  mesoderm,  are,  in  the  main,  transitory. 
The  early  disappearance  of  the  ventral  mesocardium  unites  the  right  and  left  sides  of  the  peri- 
cardial ccelom  ventral  to  the  heart.  The  dorsal  mesocardium  persists  at  the  arterial  and  venous 
ends  of  the  heart  only.  The  loss  of  the  dorsal  mesocardium  between  the  latter  points  gives 
rise  to  the  sinus  transversus  pericardii  of  the  adult. 

During  development,  the  heart  and  pericardium  migrate  from  a  point  opposite  the  cephahc 
end  of  the  pharynx  to  one  opposite  the  caudal  end  of  the  oesophagus;  in  fact,  from  the  neck  well 
into  the  thorax.  In  the  adult,  instead  of  being  at  the  cephahc  end  of  the  ccelom,  the  heart 
and  pericardium  are  contained  between  the  right  and  left  layers  of  the  ventral  mesentery  of  the 
oesophagus;  the  pericardial  pleura  of  the  adult. 

The  cranio-caudal  migration  is  evidenced  in  the  adult  by  the  course  of  the  recurrent  and  of 
the  cardiac  nerves,  and  also  by  the  apparent  migration  of  the  vessels  derived  from  some  of 
the  dorsal  segmental  arteries. 

B.  THE  ARTERIES  AND  VEINS 

The  arteries  [arteriae],  proportionately  to  their  size,  have  much  thicker  walls 
than  the  veins.  After  death  they  retain  their  natural  form,  but  are  contracted 
and  contain  usually  a  small  amount  of  pale  clot.  In  a  very  general  way  the 
thickness  of  wall  is  proportional  to  cahbre.  Some  arteries,  however,  are  con- 
stantly thicker  or  thinner  than  could  be  predicted  from  size  alone. 

The  larger  arteries  usually  take  a  direct  course  and  branch  dichotomously.  In  descriptive 
anatomy  if  dichotomous  branches  are  of  nearly  equal  size  it  is  common  for  each  to  take  another 
name;  if  one  branch  preponderates  in  size,  it  is  apt  to  retain  the  name  of  the  parent  trunk 
while  the  smaller  is  regarded  as  a  collateral  branch  [vas  coUaterale] .     There  are  numerous 


528  THE  BLOOD-VASCULAR  SYSTEM 

exceptions  to  dichotomous  branching;  branches  may  run  perpendicularly  or  recurrently  to  the 
vessel  from  which  they  arise;  or  several  branches  may  arise  simultaneously. 

There  is  less  tendency  to  anastomosis  between  large  or  medium  sized  arteries  than  in  veins 
of  corresponding  magnitude.  Anastomoses  do  occur,  however,  particularly  in  the  form  of 
arches,  such  as  the  palpebral,  plantar  and  volar  arches,  or  the  arches  between  the  intestinal 
arteries.  This  form  of  anastomosis  is  sometimes  called  inosculation.  Between  smaller  arteries 
anastomosis  is  usually  free  as  in  the  case,  for  instance,  of  the  articular  retia.  In  some  organs 
anastomosis  (excepting  capillary)  between  neighbouring  arteries  can  scarcely  be  said  to  exist 
at  all;  the  a.  centralis  retinae  affords  a  good  example  of  this,  as  do  the  arteries  of  the  brain,  spleen, 
and  kidney;  such  arteries  are  called  terminal. 

The  larger  arteries  are  supplied  by  vasa  vasorum,  frequently  arising  from  their  own  recurrent 
branches. 

The  veins  [venae]  have  thin  walls,  and  after  death  are  either  collapsed  or 
filled  with  clot  or  stained  serum.  They  are  characterized  by  the  presence  of 
valves  and  frequent  anastomoses. 

Frequent  anastomoses  occur  between  veins  of  all  sizes;  plexuses  are  common,  such,  for 
instance,  those  of  the  pelvis.  Venm  comitantes  are  veins  which,  usually  in  pairs,  accompany 
many  arteries;  they  communicate  with  one  another,  around  the  artery,  very  freely.  Veins 
do  not  primitively  accompany  arteries.  In  the  case  of  the  extremities  the  primitive  veins  are 
superficial.  The  deep  veins  of  the  hmbs  are  of  later  formation  and  to  them  the  superficial 
veins  subsequently  become  tributary. 

The  veins  from  the  stomach,  spleen,  pancreas  and  intestine  are  collected  into  a  large  trunk, 
the  portal  vein.  This  does  not  open  into  the  inferior  vena  cava  directly,  but  breaks  up  into 
numerous  smaller  vessels  in  the  Hver.  From  these  the  blood  is  returned,  through  the  hepatic 
veins,  to  the  inferior  cava. 

Many  veins  are  provided  with  valves,  the  free  borders  of  which  are  directed  toward  the  heart. 
In  the  small  veins  the  valves  are  single;  in  the  larger  veins  they  are  usually  double,  rarely  treble. 
Valves  are  much  more  numerous  in  the  veins  of  infants  than  those  of  the  adult,  they  seem  to 
disappear  progressively  with  advancing  age.  The  venous  valves  are  most  numerous  in  the 
superficial  veins,  and  in  the  deep  veins  of  the  extremities;  in  many  veins  of  the  head  and  neck 
they  occur  only  at  their  point  of  termination  in  a  larger  trunk. 

The  cranial  venous  sinuses  are  modified  veins,  consisting  of  intima  only  which  lines  channels 
in  the  fibrous  dura  mater.  The  venous  spaces  in  cavernous  tissue,  such  as  the  corpora  cavernosa, 
may  be  looked  upon  as  specially  modified  veins. 

The  larger  veins,  hke  the  arteries,  have  vasa  vasorum. 

The  arteries  and  veins  will  be  considered  in  the  following  order:  1,  pulmonary 
artery  and  veins;  2,  the  systemic  arteries;  and,  3,  the  systemic  veins.  At  the 
ends  of  the  second  and  third  divisions,  the  development  and  variations  are 
considered. 

1.  THE  PULMONARY  ARTERY  AND  VEINS 

The  pulmonary  artery  [a.  pulmonahs]  (fig.  441)  passes  from  the  right  ventricle 
to  the  lungs.  It  differs  from  all  other  arteries  in  the  body  in  that  it  contains 
venous  blood.  It  arises  as  a  short,  thick  trunk  from  the  conus  arteriosus  of 
the  right  ventricle,  and,  after  a  course  of  about  5  cm.  (2  in.)  within  the  pericar- 
dium, divides  into  a  right  and  a  left  branch.  These  branches  pass  to  the,  right 
and  the  left  lung  respectively. 

The  trunk  of  the  pulmonary  artery  at  its  origin  is  on  a  plane  anterior  to  the 
ascending  aorta,  and  slightly  overlaps  that  vessel.  Thence  it  passes  upward, 
backward,  and  to  the  left,  forming  a  slight  curve  around  the  front  and  left  side  of 
the  ascending  portion  of  the  aorta;  and,  having  reached  the  concavity  of  the 
aortic  arch,  on  a  plane  posterior  to  the  ascending  aorta,  it  divides  into  its  right 
and  left  branches,  which  diverge  from  each  other  at  an  angle  of  about  130°. 
The  division  of  the  pulmonary  artery  occurs  immediately  to  the  left  of  the  second 
left  chondrosternal  articulation. 

In  the  foetus,  the  pulmonary  artery  continues  its  course  upward,  backward,  and  to  the  left 
under  the  name  of  the  ductus  arteriosus  (Botalli),  and  opens  into  the  descending  aorta  just 
below  the  origin  of  the  left  subclavian  artery.  After  birth,  that  portion  of  the  pulmonary 
artery  which  extends  to  the  aorta  becomes  obhterated,  and  remains  merely  as  a  fibrous  cord, 
the  ligamentum  arteriosum  (fig.  436). 

Relations. — In  front,  the  trunk  of  the  pulmonary  artery  is  covered  by  the  remains  of  the 
thymus  gland,  and  the  pericardium.  The  artery  Ues,  at  its  commencement,  behind  the  upper 
margin  of  the  third  left  chondro-sternal  articulation.  The  right  margin  of  the  artery  is  behind 
the  second  piece  of  sternum  but  the  greater  part  of  the  vessel  is  behind  the  medial  end  of  the 
second  intercostal  space. 

Behind,  it  lies  successively  upon  the  ascending  aorta  and  the  left  atrium. 

To  the  right  are  the  ascending  aorta,  the  right  atrium,  the  right  coronary  artery,  and  the 
cardiac  nerves. 


THE  SYSTEMIC  ARTERIES  529 

To  the  left  are  the  pericardium,  the  left  pleura  and  lung,  the  left  auricle,  the  left  coronary 
artery,  and  the  cardiac  nerves. 

The  right  pulmonary  artery  [ramus  dexter]  longer  than  the  left,  passes  almost 
horizontally  under  the  arch  of  the  aorta  to  the  root  of  the  right  lung,  where  it 
divides,  either  directly  or  after  repeated  division,  into  three  branches,  one  for 
each  lobe.  These  branches  follow  the  course  of  the  bronchi,  dividing  and  sub- 
dividing for  the  supply  of  the  lobules  of  the  lung.  The  terminal  branches  do 
not  anastomose  with  each  other. 

Relations. — In  its  course  to  the  lung  it  has  in  front  of  it  the  ascending  aorta,  the  superior 
vena  cava,  the  phrenic  nerve,  the  anterior  pulmonary  plexus,  and  the  reflexion  of  the  pleura. 
Behind  are  the  right  bronchus  and  the  termination  of  the  azygos  vein.  Above  is  the  arch  of 
the  aorta,  and  below  are  the  left  atrium  and  the  upper  right  pulmonary  vein. 

At  the  root  of  the  lung  it  has  the  right  bronchus  above  and  behind  it;  the  pulmonary  veins 
below  and  in  front.  Crossing  in  front  of  it  and  the  other  structures  forming  the  root  of  the  lung 
are  the  phrenic  nerve  and  the  anterior  pulmonary  plexus;  behind  are  the  azygos  vein,  the  vagus 
nerve,  and  the  posterior  pulmonary  plexus. 

The  left  pulmonary  artery,  shorter  and  slightly  smaller  than  the  right,  passes 
in  front  of  the  descending  aorta  to  the  root  of  the  left  lung,  where  it  divides  into 
two  branches  for  the  supply  of  the  upper  and  lower  lobes  respectively.  These 
divide  and  subdivide  as  on  the  right  side. 

Relations. — At  the  root  of  the  lung  it  has  the  left  bronchus  behind  and  also  below  it,  in 
consequence  of  the  more  vertical  direction  taken  by  the  left  bronchus  than  by  the  right.  Below 
and  in  front  are  the  pulmonary  veins,  while  passing  from  the  artery  and  the  upper  left  pulmonary 
vein  is  the  hgament  of  the  left  superior  cava.  Crossing  in  front  of  it  and  the  other  structures 
forming  the  root  of.the  lung  are  the  phrenic  nerve,  the  anterior  pulmonary  plexus,  and  the  reflex- 
ion of  the  left  pleura;  crossing  behind,  are  the  descending  aorta,  the  left  vagus  nerve,  and  the 
posterior  pulmonary  plexus. 

The  pulmonary  veins  [vv.  pulmonales]  (figs.  424,  441)  return  the  aerated 
blood  from  the  lungs  to  the  heart.  They  are  usually  four  in  number,  superior 
and  inferior,  of  the  right  and  left  sides.  Occasionally,  however,  there  are  three 
pulmonary  veins  on  the  right  side,  the  result  of  the  vein  from  the  middle  lobe 
of  the  right  lung  opening  separately  into  the  left  atrium  instead  of  joining  as  usual 
the  upper  of  the  two  right  pulmonary  veins.  The  relations  of  the  pulmonary  veins 
to  the  pulmonary  arteries  and  bronchi  in  the  lungs-  are  given  with  the  anatomy 
of  the  lungs  (Section  X). 

The  pulmonary  veins  are  about  15  mm.  in  length.  In  the  pericardium  the 
right  pulmonary  veins  [vv.  pulmonales  dextrse]  both  pass  behind  the  superior 
vena  cava.  The  superior  vein  receives  the  vein  from  the  right  middle  lobe  and 
runs  below  and  in  front  of  the  right  pulmonary  artery. 

The  left  pulmonary  veins  [vv.  pulmonales  sinistrse]  enter  the  left  atrium  about 
3  cm.  in  front  of  the  veins  of  the  right  side.  The  superior  vein  is  below  the  left 
pulmonary  artery. 

2.  THE  SYSTEMIC  ARTERIES 

THE  AORTA 

The  aorta  (fig.  442)  is  the  main  systemic  arterial  trunk,  and  from  it  all  the 
systemic  arteries  are  derived.  It  begins  at  the  left  ventricle  of  the  heart,  and 
ascends  near  the  anterior  thoracic  wall  as  high  as  the  second  right  chondro-sternal 
articulation  [aorta  ascendens].  It  then  turns  backward  and  to  the  left  forming 
an  arch  [arcus  aortas]  which  reaches  the  posterior  thoracic  wall  at  the  left  side  of 
the  fourth  thoracic  vertebra.  From  here  it  runs  downward  along  the  vertebral 
column  [aorta  descendens]  through  the  thorax  and  abdomen  and  ends  by  dividing, 
opposite  the  fourth  lumbar  vertebra,  into  the  right  and  left  common  iliac  arteries. 
From  the  point  of  bifurcation  a  small  vessel,  the  middle  sacral,  is  continued  down 
the  middle  line  in. front  of  the  sacrum  and  coccyx.  The  midclle  sacral  represents 
the  sacral  and  coccygeal  aorta. 

The  Ascending  Aorta 

The  ascending  aorta  [aorta  ascendens]  (fig.  442)  begins  at  the  upper  part  of 
the  left  ventricle,  on  a  level  with  the  third  intercostal  space,  and  ascends  behind 


I 


530 


THE  BLOOD-VASCULAR  SYSTEM 


the  sternum  to  the  upper  border  of  the  right  second  chondrosternal  articulation. 
It  measures  about  5  to  5.5  cm.  (2  to  2i  in.),  forming,  as  it  ascends,  a  gentle  curve 
with  its  convexity  to  the  right.  It  is  enclosed  for  the  greater  part  of  its  length  in 
the  pericardium,  being  invested,  together  with  the  pulmonary  artery,  in  a  com- 
mon sheath  formed  by  the  serous  layer  of  that  membrane.  A  dilatation  known 
as  the  bulbus  aortse  occurs  immediately  above  the  heart  upon  which  are  three 
locaHzed  bulgings,  known  as  the  aortic  sinuses  (sinuses  of  Valsalva);  they  are 
placed,  one  to  the  right,  one  to  the  left,  and  one  posteriorly.  From  the  right  and 
eft  are  derived  the  coronary  arteries  of  the  heart.     (See  Heart.) 


Fig.  441. — The  Gkeat 

(Modified  from  a  dissection  in  St, 

Internal  jugular  vein 


Transverse  cervical 

artery 

Transverse  scapular 

artery 


Vessels  of  the  Thorax. 
Bartholomew's  Hospital  Museum.) 


Inferior  thyreoid  ■ 


Right   inferior   laryn- 


Right  common  carotid 

artery 


Subclavian  vein' 


Innominate  artery 

Left  innominate  vem 

Phrenic  nerve 

Superior  vena  cava 

Arch  of  aorta 

Right  bronchus 

Branch   of   right   pul- 
monary artery 

Branch   of   right  pul- 
monary vein 

Right  pulmonary 
artery 
Branch  of   right   pul- 
monary artery 

Branch  of  right  pul- 
monary vein 


Right  coronary  artery 
Thoracic  vertebra 

Azygos  vein 

Intercostal  veins 

Intercostal  arteries 


--Thyreoid  gland 

Left  internal  jugular 
vein 
, Vagus  nerve 

Left  common  carotid 

artery 
Left  inferior  laryngeal 

nerve 
-Left  subclavian  artery 

Left  subclavian  vein 
Left  internal  mammary 

vein 
Left  superior  inter- 
costal vein 

Phrenic  nerve 

Vagus  nerve 
Recurrent  nerve 

Ligamentum  arteri- 
osum 

Left  pulmonary  artery 
Left  pulmonary  vein 

Left  bronchus 
Branch  of  left  pulmon- 
ary artery 
Pulmonary  artery 

Left  pulmonary  vein 
Left  coronary  arteiy 
Conus  arteriosus 


Thoracic  duct 
Thoracic  aorta 


Relations. — In  front,  it  is  overlapped  at  its  commen-cement  by  the  right  auricle,  conut 
arteriosus  and  pulmonary  artery.  Higher  up,  as  the  pulmonary  artery  and  auricle  diverge,  is 
is  separated  from  the  manubrium  by  the  pericardium,  the  remains  of  the  thymus  gland,  and  by 
the  loose  tissue  and  fat  in  the  superior  mediastinum,  and  is  here  shghtly  overlapped  by  the  right 
pleura  and  by  the  edge  of  the  right  lung  in  full  inspiration.  The  root  of  the  right  coronary 
artery  is  also  in  front. 

Behind  are  the  left  atrium  of  the  heart,  the  right  pulmonary  artery,  the  right  bronchus, 
and  the  anterior  right  deep  cardiac  nerves. 

On  the  right  side  it  is  in  contact,  below  with  the  right  atrium,  and  above  with  the  superior 
vena  cava. 

On  the  left  side  are  the  pulmonary  artery  and  the  branches  of  the  right  superficial  cardiac 
nerves. 

Branches. — The  right  and  left  coronary  arteries  have  already  been  described  (p.  519). 

The  Arch  of  the  Aorta 

The  arch  of  the  aorta  [arcus  aortse]  (figs.  441,  442),  extends  in  a  gentle  curve 
upward,  backward,  and  to  the  left,  from  the  level  of  the  upper  border  of  the 


THE  ARCH  OF  THE  AORTA 


531 


second  right  costal  cartilage  to  the  lower  border  of  the  fourth  thoracic  vertebra. 
Attached  to  the  concavity  of  the  arch,  just  beyond  the  origin  of  the  left  sub- 
clavian artery,  is  the  ligamentum  arteriosum  (vestige  of  the  dorsal  part  of  the 
left  sixth  arch).  Between  the  left  subclavian  artery  and  the  ligamentum  arterio- 
sum there  is  sometimes  a  definite  constriction  of  the  arch  (isthmus  aortse)  situated 
opposite  the  third  thoracic  vertebra.  When  the  isthmus  is  well  marked,  it  is 
succeeded  by  a  dilatation  (aortic  spindle)  which  begins  in  the  neighbourhood  of 
the  ligamentum  arteriosum  and  passes  over  into  the  descending  aorta.  Passing 
under  the  arch  are  the  left  bronchus,  the  right  pulmonary  artery,  and  the  left 
recurrent  (inferior  laryngeal)  nerve.     It  measures  about  4.5  cm.  (14-  in.). 


Fig  442 — ^The  Thoracic  and  Abdominal  Aorta. 


Right  common  carotid 

artery 
Right  internal  jugular 

vein 


Right  lymphatic  duct 

Innominate  artery 

Right  vagus  nerve 

Right  innominate  vein 

Internal  mammary  vein 

Trunk  of  the  pericardiac 

and  thymic  veins 

Superior  vena  cava 


Hemiazygos  vein^  cross- 
ing spine  to  enter  vena 
azygos 


Inferior  vena  cava 


Right  inferior  phrenic 
artery 

Cceliac  artery 
Right  middle  suprarenal 
artery 


Right  internal  spermatic 

artery 

Right  spermatic  vein 


Left  common  carotid 

artery 
Left  vagus  nerve 

Thoracic  duct 
Left  innominate  vein 
Left  subclavian  artery 
Left  superior  intercostal 

Recurrent  (laryngeal) 


Accessory  hemiazygos 

vein 
(Esophagus 

Left  upper  azygos  vein 

(Esophageal  branches 

from  aorta 

Hemiazygos  vein 


Thoracic  duct 


Left  inferior  phrenic 

artery 

Left  middle  suprarenal 

artery 
Receptaculum  chyli 

Superior  mesenteric 
artery 


Left  ascending  lumbar 


Left  internal  spermatic 
artery 


Inferior  mesenteric 
artery 


Relations. — In  front  and  to  the  left,  it  is  slightly  overlapped  by  the  right  pleura  and  lung, 

and  to  a  greater  extent  by  the  left  pleiu-a  and  lung.  It  is  crossed  in  the  following  order  from 
right  to  left,  by  the  left  phrenic  nerve,  by  the  cardiac  branches  of  the  vagus  nerve,  the  cardiac 
braUches  of  the  sympathetic  nerve,  by  the  left  vagus  nerve,  and  by  the  left  superior  intercostal 
vein  as  it  passes  up  to  the  left  innominate  vein. 

Behind  and  to  the  right  are  the  trachea,  the  oesophagus,  the  thoracic  duct,  the  deep  cardiac 
plexus  which  is  situated  on  the  trachea  just  above  its  bif.urcation,  and  the  left  recurrent  (inferior 
laryngeal)  nerve. 

Above  it  are  the  three  chief  branches  for  the  head,  neck,  and  upper  extremities,  namely,  the 
innominate,  the  left  carotid,  and  the  left  subclavian  arteries,  and  the  left  innominate  vein. 


532 


THE  BLOOD-VASCULAR  SYSTEM 


Below  it — that  is,  in  its  concavity — are  the  bifurcation  of  the  pulmonary  artery,  the  left 
bronchus,  the  left  recurrent  (inferior  laryngeal)  nerve,  the  ligamentum  arteriosum,  the  super- 
ficial cardiac  plexus,  two  or  more  bronchial  lymphatic  glands,  and  the  reflexion  of  the 
pericardium. 

The  branches  of  the  aortic  arch  are: — the  inDominate,  the  left  common  caro- 
tid, and  the  left  subclavian  arteries.  The  innominate  and  left  carotid  arise  close 
together — indeed,  so  close  that,  when  seen  from  the  interior  of  the  aorta,  the 
orifices  appear  merely  separated  by  a  thin  septum.  The  left  subclavian  arises  a 
little  less  close  to  the  left  carotid. 


THE  INNOMINATE  ARTERY 

The  innominate  [a.  anonyma]  or  brachio-cephalic  artery  (fig.  441),  the  largest 
branch  of  the  arch  of  the  aorta,  extends  from  near  its  commencement  upward 
and  a  little  forward  and  to  the  right,  as  high  as  the  upper  limit  of  the  right 
sterno-clavicular  joint  where  it  bifurcates  into  the  right  common  carotid  and  right 
subclavian  arteries.  It  lies  obliquely  in  front  of  the  trachea,  and  measures  from 
-3.7  to  5  cm.  (1|  to  2  in.). 

Fig.  443. — -The  Thykeoidea  Ima.     (After  Henle.) 


fiight  carotid  artery 
Sight  subclavian  artery 


Innominate  artery 


Superior  vena  cava 


Left  carotid  artery 


Left  subclavian  ai'tery 


Pulmonary  artery 


Relations. — In  front  of  the  artery  are  the  manubrium,  the  origins  of  the  sterno-hyoid  and 
sterno-thyreoid  muscles,  the  right  sterno-clavicular  joint,  and  the  remains  of  the  thymus  gland. 
The  left  innominate  vein  crosses  the  root  of  the  vessel,  and  the  inferior  thyreoid  and  thyreoidea 
ima  veins  descend  obliquely  over  it  to  end  in  the  left  innominate  vein.  The  inferior  cervical 
cardiac  branches  of  the  right  vagus  nerve  pass  in  front  of  it  on  their  way  to  the  deep  cardiac 
plexus. 

Behind,  it  hes  on  the  trachea,  crossing  that  tube  obhquely  from  left  to  right,  and  coming 
into  contact  above  with  the  right  pleura. 

To  the  right  side  are  the  right  innominate  vein,  the  right  vagus,  and  the  pleura. 

To  the  left  side  are  the  left  common  carotid,  the  remains  of  the  thymus  gland,  the  right 
inferior  thyreoid  vein;  and,  higher,  the  trachea. 

The  branches  of  the  innominate  artery  are: — (1)  The  right  common  carotid; 
and  (2)  the  right  subclavian.  These  are  terminal  branches.  There  are  usually 
no  collateral  branches  from  this  vessel,  but  at  times  the  thyreoidea  ima  may  arise 
from  it. 


THE  COMMON  CAROTID  ARTERY  533 

The  thyreoida  ima  artery,  which  occurs  in  about  10  per  cent,  of  subjects,  ascends  on  the 
front  of  the  trachea  to  the  thyreoid  gland.  It  may  be  large  in  which  case  it  might  complicate 
the  low  operation  of  tracheotomy.  It  does  not  always  arise  from  the  innominate,  but  occa- 
sionally from  the  arch  of  the  aorta  (fig.  443)  or  from  the  right  common  carotid. 

THE  COMMON  CAROTID  ARTERIES 

The  common  carotid  arteries  [aa.  carotides  communes]  pass  up  deeply  from 
the  thorax  on  either  side  of  the  neck  to  about  the  level  of  the  upper  border  of  the 
thyreoid  cartilage,  where  they  divide  into  the  external  and  internal  carotid 
arteries.  The  external  carotid  supplies  the  structures  at  the  upper  part  of  the 
front  and  side  of  the  neck,  the  larynx,  pharynx,  tongue,  face,  the  upper  part  of 
the  back  of  the  neck,  the  structures  in  the  pterygoid  region,  the  scalp,  and  in 
chief  part  the  membranes  of  the  brain.  The  internal  carotid  gives  off  no  branch 
in  the  neck,  but  enters  the  cranium  and  supplies  the  greater  part  of  the  brain,  the 
structures  contained  in  the  orbit,  and  portions  of  the  membranes  of  the  brain. 

The  common  carotid  artery  on  the  right  side  arises  from  the  bifurcation  of  the 
innominate  at  the  upper  limit  of  the  sterno-clavicular  joint;  on  the  left  side  from 
the  arch  of  the  aorta  a  little  to  the  left  of  the  innominate  artery,  and  on  a  plane 
somewhat  posterior  to  that  vessel  (fig.  441).  The  portion  of  the  left  common 
carotid  artery  which  extends  from  the  arch  of  the  aorta  to  the  upper  limit  of  the 
sterno-clavicular  articulation  lies  deeply  in  the  chest,  and  requires  a  separate 
description;  but  above  the  level  of  the  sterno-clavicular  joint  the  relations  of  the 
right  and  left  carotids  are  practically  the  same,  and  are  given  under  the  account 
of  the  right  common  carotid. 

THORACIC  PORTION  OF  THE  LEFT  COMMON  CAROTID  ARTERY 

Within  the  thorax  the  left  common  carotid  is  deeply  placed  behind  the 
manubrium  of  the  sternum,  and  is  overlapped  by  the  left  lung  and  pleura.  It 
arises  from  the  middle  of  the  aortic  arch,  close  to  the  left  side  of  the  innominate 
artery,  and  a  little  posterior  to  that  vessel,  and  ascends  obliquely  in  front  of  the 
trachea  to  the  left  sterno-clavicular  articulation,  above  which  its  relations  are 
similar  to  those  of  the  right  common  carotid  (fig.  442). 

Relations. — In  front,  but  at  some  httle  distance,  are  the  manubrium  and  the  origins  of  the 
left  sterno-hyoid  and  sterno-thyreoid  muscles,  whilst  in  contact  with  it  are  the  remains  of  the 
thymus  gland,  and  the  loose  connective  tissue  and  fat  of  the  superior  mediastinum.  Crossing 
its  root  is  the  left  innominate  vein. 

Behind,  it  lies  successively  upon  the  trachea  the  left  recurrent  (inferior  laryngeal)  nerve,  the 
oesophagus  (which  here  inclines  a  little  to  the  left),  and  the  thoracic  duct. 

To  its  right  side  is  the  root  of  the  innominate  artery,  and  higher  up  are  the  trachea  and  the 
inferior  thyreoid  veins. 

To  its  left  side,  but  on  a  posterior  plane,  are  the  left  subclavian  artery  and  the  left  vagus 
nerve;  and,  shghtly  overlapping  it,  the  edge  of  the  left  pleura  and  lung. 

THE  COMMON  CAROTID  ARTERY  IN  THE  NECK 

The  common  carotid  artery  in  the  neck  extends  from  the  sterno-clavicular 
articulation  to  the  upper  border  of  the  thyreoid  cartilage  on  a  level  with  the  fourth 
cervical  vertebra,  where  it  divides  into  the  external  and  internal  carotid  arteries. 
A  line  drawn  from  the  sterno-clavicular  joint  to  the  interval  between  the  mastoid 
process  and  the  angle  of  the  jaw  would  indicate  its  course.  The  artery  is  at  first 
deeply  placed  beneath  the  sterno-mastoid,  sterno-hyoid,  and  sterno-thyreoid 
muscles,  and  at  the  level  of  the  top  of  the  sternum  is  only  2  cm.  (f  in.)  distant 
from  its  fellow  of  the  opposite  side,  and  merely  separated  from  it  by  the  trachea. 
As  the  carotid  arteries  run  up  the  neck,  however,  they  diverge  in  the  form  of  a  V 
and  become  more  superficial,  though  on  a  plane  posterior  to  that  in  which  they  lie 
at  the  root  of  the  neck,  and  are  separated  from  each  other  by  the  larynx  and 
pharynx.  At  their  bifurcation  they  are  about  6  cm.  (2j  in.)  apart.  The  com- 
mon carotid  is  contained  in  a  sheath  of  fascia  common  to  it  and  the  internal 
jugular  vein  and  vagus  nerve.  The  artery,  vein,  and  nerve,  however,  are  not  in 
contact,  but  separated  from  one  another  by  fibrous  septa,  which  divide  the  com- 
mon sheath  into  three  compartments:  one  for  the  artery,  one  for  the  vein,  and  one 


534 


THE  BLOOD-VASCULAR  SYSTEM 


for  the  nerve.  The  vein,  which  is  larger  than  the  artery,  lies  to  the  lateral  side, 
and  somewhat  overlaps  it.  The  vagus  nerve  lies  behind  and  between  the  two 
vessels.  The  artery  on  the  right  side  measures  about  9.5  cm.  (3f  in.) ;  on  the  left 
side,  about  12  cm.  (4J  in.)  in  length. 


Fig.  444. — The  Collateral  Circulation  after  Ligature  op  the  Common  Carotid  and 

Subclavian  Arteries. 
(A  ligature  is  placed  on  the  common  carotid  and  on  the  third  portion  of  the  subclavian  artery.) 

Right  anterior  cerebral - 


Internal  carotid - 
Right  posterior  cerebral  - 


Occipital 
Descending  branch  of  occipital 


External  carotid  — ^■ 

Superficial  branch  of  descending 
occipital 

Deep  branch 


Transverse  cervical 
Descending  branch 

Acromial  branch. 
Subscapular  branch 


Anterior  circumflex 

tnfraspinous  branch 

Posterior  circum 

flex 
Lateral  thorucli 

Subscapular 

Circumflex  scapulai 
Infrascapul: 
Subscapular 


Left  anterior  cerebral 
Anterior  communicating 


Posterior  communicating 
Left  posterior  cerebral 


Anterior  spinal 

Vertebral 
External  maxillary 
Lingual 

Superior  thyreoid 


.Inferior  thyreoid 

Common  carotid 


Thyreo- cervical  trunk 
Costo-cervical  trunk 


Innominate 

Superior  intercostal 

^■T Left  common  carotid 

-j Left  subclavian 

7  Superior  thoracic 

Internal  mammary 


Anterior  intercostal 

First  aortic  inter- 
costal 
Second  aortic  inter- 
costal 


■Anterior  intercostal 


Relations. — In  front  the  artery  is  covered  by  the  skin,  superficial  fascia,  platysma,  and 
deep  fascia,  and  is  more  or  less  overlapped  by  the  sterno-mastoid  muscle.  At  the  lower  part 
of  the  neck  it  is  covered  in  addition  by  the  sterno-hyoid  and  sterno-thyreoid  muscles,  and  is 
crossed  by  the  anterior  jugular  vein,  and  is  often  overlapped  by  the  thyreoid  gland.  _  Opposite 
the  cricoid  cartilage  it  is  crossed  obliquely  by  the  onio-hyoid  muscle,  and,  above  this  spot,  by 
the  superior  thyreoid  vein,  and  the  sterno-mastoid  artery.  Along  the  anterior  border  of  the 
sterno-mastoid  there  is  a  communicating  vein  between  the  facial  and  anterior  jugular  veins, 
which,  as  it  crosses  the  line  of  the  carotid  artery,  is  in  danger  of  being  wounded  in  the  operation 


THE  COMMON  CAROTID  ARTERY 


535 


of  tying  the  carotid.  The  ramus  descendens  n.  hypoglossi  generally  descends  in  front  of  the 
carotid  sheath,  being  there  joined  by  one  or  two  communicating  branches  from  the  second  and 
third  cervical  nerves.  At  times  this  nerve  runs  within  the  sheath.  There  are  usually  two 
lymphatic  glands  about  the  bifurcation  of  the  artery.  These  are  often  found  enlarged  and 
infiltrated  in  cancer  of  the  lip  and  tongue. 

Behind,  the  common  carotid  lies  on  the  longus  colli  and  scalenus  anterior  below,  and  longus 
capitis  (rectus  capitis  anterior  major)  above.  Posterior  to  the  artery,  but  in  the  same  sheath, 
is  the  vagus  nerve;  and  posterior  to  the  sheath,  the  cervical  sympathetic  and  the  cervical 

Fig.  445. — Artebies  or  the  Head  and  Neck.     (After  Toldt,  "Atlas  of  Human  Anatomy," 
Rebman,  London  and  New  York.) 
Transverse  facial  artery  Supraorbital  artery 

^   -•^^'"'t^^^'^S^^^^^  /'  Frontal  artery 

/  0<=iS^r*^i^         /  Dorsal  nasal  artery 
Superficial  temporal  artery      ^  ~^^-^T^S^   '      Infraorbital 


—  Angular  artery 

Superior  labial  artery 

-^  At —  Inferior  labial  artery 

J 
y        Mental  artery 

-  Submental  artery 

Glandular  branches 

External  maxillary  artery 
Lingual  artery 


Auricular  branch 


Stylomastoid  arterj 

Posterior  auricular  artery  ^      y 
Descending  branch  of  occipital  artery 
Splenius  capitis  muscle 
Internal  carotid  artery 

Transverse  cervical  artery 


Trapezius  muscle"" 

Ascending  branch    — 

Descending  branch  — 
Axillary  artery 


Acromial  branch  -^ 


Superior 


Hyoid  branch 
Anterior  branch  I  Vh/re'crd 
Posteriorbranch     artery 
Thyreoid  gland 
Common  carotid  artery 
Inferior  thyreoid  artery 
Ascending  cervical  artery 
Superficial  cervical  artery 
Th3n:eocervical  trunk 

V  Subclavian  artery 

^^      'm^"   Pleura 

Internal  mam- 

""   mary  artery 

"-Transverse  scap- 
ular artery 


Deltoid  branch 


I  Pectoral  branches 

Thoracoacromial  artery 


cardiac  branches  of  the  sympathetic  and  vagus  nerves.  At  the  lower  part  of  the  neck  the  inferior 
thyreoid  artery  courses  obliquely  behind  the  carotid,  as  does  Hkewise  the  inferior  (recurrent) 
laryngeal  nerve. 

Medially,  from  below  upward,  are  the  trachea  and  oesophagus,  with  the  inferior  (recurrent) 
laryngeal  nerve  in  the  groove  between  them,  and  the  terminal  branches  of  the  inferior  thyreoid 
artery,  the  lateral  lobe  of  the  thyreoid  gland,  the  cricoid  cartilage,  the  thyreoid  cartilage,  and 
the  lower  part  of  the  pharynx.  At  the  angle  of  bifurcation  is  the  carotid  gland  [glomus  caro- 
ticumj. 

Laterally  are  the  internal  jugular  vein  and  the  vagus  nerve.  On  the  right  side,  at  the 
root  of  the  neck,  the  vein  diverges  somewhat  from  the  artery,  leaving  a  space  in  which  the  vagus 


) 


536  THE  BLOOD-VASCULAR  SYSTEM 

nerve  and  vertebral  artery  are  exposed.     On  the  left  side  the  vein  approaches  and  somewhat 
overlaps  the  artery,  thus  leaving  no  interval  corresponding  to  that  on  the  right  side. 

The  cricoid  cartilage  is,  as  a  rule,  taken  as  the  centre  of  the  incision  in  the  operation  for 
ligature  of  the  common  carotid  artery.  The  incision  is  made  in  the  line  of  the  vessel  parallel 
to  the  anterior  margin  of  the  sterno-mastoid  muscle.  The  omo-hyoid  forms  one  of  the  chief 
rallying  points  in  the  course  of  the  operation  for  ligature  of  the  artery  above  that  muscle,  the 
usual  situation.  The  artery  is  found  beating  at  the  angle  formed  by  the  omo-hyoid  with  the 
sterno-mastoid. 

Branches. — (1)  External  and  (2)  internal  carotid  arteries.  The  common 
carotid  gives  off  no  lateral  branch,  and  consequently  does  not  diminish  in  size  as  it 
runs  up  the  neck.  It  is  often  a  little  swollen  just  below  its  bifurcation,  a  condition 
that  should  not  be  mistaken  for  an  aneurismal  dilation. 

The  collateral  circulation  (fig.  444),  after  Hgature  of  the  common  carotid,  is  carried  on 
chiefly  by  the  anastomosis  of  the  internal  carotid  with  the  internal  carotid  of  the  opposite  side 
through  the  circle  of  Willis;  by  the  vertebral  with  the  opposite  vertebral;  by  the  inferior  thy- 
reoid with  the  superior  thyreoid;  by  the  deep  cervical  branch  of  the  costo-cervical  trunk  (superior 
intercostal)  with  the  descending  branch  of  the  occipital;  by  the  superior  thyreoid,  hngual, 
external  maxillary  (facial),  occipital,  and  temporal,  with  the  corresponding  arteries  of  the  oppo- 
site side,  and  by  the  ophthalmic  with  the  angular.  The  anastomosis  between  the  deep  cervical 
branch  of  the  costo-cervical  trunk  with  the  descending  branch  of  the  occipital  is  an  important 
one;  it  is  situated  deeply  at  the  back  of  the  neck,  and  is  to  be  found  lying  between  the  semi- 
spinaUs  capitis  (complexus)  and  cervicis  muscles. 

THE  EXTERNAL  CAROTID  ARTERY 

The  external  carotid  artery  [a.  carotis  externa]  (fig.  445),  the  smaller  of  the 
two  branches  into  which  the  common  carotid  divides  at  the  upper  border  of  the 
thyreoid  cartilage,  is  distributed  to  the  anterior  part  of  the  neck,  the  face,  and 
the  cranial  region,  including  the  skin,  the  bones,  and  the  dura  mater.  It  is 
at  first  situated  medial  to  the  internal  carotid;  but  as  it  ascends  in  the  neck  it 
forms  a  gentle  curve,  with  its  convexity  forward,  and,  running  slightly  backward 
as  well  as  upward,  terminates  opposite  the  neck  of  the  mandible  just  below  the 
condyle,  by  dividing  into  the  internal  maxillary  and  superficial  temporal  arteries. 
It  here  lies  superficial  to  the  internal  carotid,  from  which  it  is  separated  by  a 
portion  of  the  parotid  gland.  At  its  origin  it  is  overlapped  by  the  anterior  margin 
of  the  sterno-mastoid,  and  is  covered  by  the  superficial  fascia,  platysma,  and  deep 
fascia.  Higher  up  the  neck  it  is  deeply  placed,  passing  beneath  the  stylo-hyoid 
muscle,  the  posterior  belly  of  the  digastric  muscle,  and  the  hypoglossal  nerve; 
and  finally  becomes  embedded  in  the  parotid  gland,  where  it  divides  into  its 
terminal  branches.  It  is  separated  from  the  internal  carotid  artery  posteriorly 
by  the  stylo-pharyngeus  and  stylo-glossus  muscles,  the  glosso-pharyngeal  nerve, 
the  pharyngeal  branch  of  the  vagus  nerve,  a  portion  of  the  parotid  gland,  and  the 
stylo-hyoid  ligament;  or,  if  the  styloid  process  is  abnormaUy  long,  by  that 
process  itself.     It  measures  about  6.5  cm.  (2|  in.). 

Relations. — In  front,  in  addition  to  the  skin,  superficial  fascia,  platysma,  and  deep  fascia, 
it  has  the  hypoglossal  nerve,  the  hngual,  common  facial  and  posterior  facial  veins,  the  posterior 
belly  of  the  digastric  and  stylo-hyoid  muscles,  the  superior  cervical  lymphatic  glands,  branches  of 
the  facial  nerve,  and  the  parotid  gland.  The  sterno-mastoid  also  overlaps  it  in  the  natural 
state  of  the  parts. 

Behind,  it  is  in  relation  with  the  internal  carotid,  from  which  it  is  separated  by  the  stylo- 
glossus and  stylo-pharyngeus  muscles,  the  glosso-pharyngeal  nerve,  the  pharyngeal  branch  of 
the  vagus  nerve,  the  stylo-hyoid  hgament,  and  the  parotid  gland.  The  superior  laryngeal  nerve 
crosses  behind  both  the  external  and  internal  carotid  arteries. 

Medially,  it  is  in  relation  with  the  hyoid  bone,  the  pharyngeal  wall,  the  ramus  of  the 
mandible,  the  stylo-mandibular  ligament  which  separates  it  from  the  submaxillary  gland,  and 
the  parotid  gland. 

Laterally,  in  the  first  part  of  its  course,  it  is  in  contact  with  the  internal  carotid  artery. 

The  branches  of  the  external  carotid  are  usually  given  off  in  the  following 
order,  from  below  upward: — 

1.  Ascending  pharyngeal. 

2.  Superior  thyreoid. 

3.  Lingual. 

4.  External  maxillary  (facial). 

5.  Sternocleidomastoid. 

6.  Occipital. 

7.  Posterior  auricular. 

8.  Superficial  temporal. 

9.  Internal  maxillary. 


THE  ASCENDING  PHARYNGEAL  ARTERY 


537 


1.  THE  ASCENDING  PHARYNGEAL  ARTERY 

The  ascending  pharyngeal  artery  [a.  pharyngea  ascendens]  (fig.  446)  is  usually 
the  first  or  second  branch  of  the  external  carotid.  Occasionally  it  comes  off  at 
the  bifurcation  of  the  common  carotid  from  the  common  carotid  itself.  It  is  a 
long  slender  vessel  which  runs  deeply  seated  up  the  neck  to  the  base  of  the  skull, 
having  the  walls  of  the  pharynx  and  the  tonsil  medially,  the  internal  carotid 
artery  laterally,  and  the  vertebral  column,  the  longus  capitis  (rectus  capitis 
anterior  major),  and  the  sympathetic  nerve  posteriorly.  In  front  it  is  crossed  by 
the  stylo-glossus  (fig.  446)  and  the  stylo-pharyngeus  muscles  and  the  glosso- 
pharyngeal nerve. 

Branches  of  the  Ascending  Pharyngeal  Artery 

The  branches  of  the  ascending  pharyngeal  artery  are  small  and  variable. 
They  supply  the  longus  and  rectus  capitis  muscles,  the  upper  cervical  sympathetic 
ganglion  and  adjacent  lymph-nodes,  as  well  as  the  pharynx,  soft  palate,  ear, 
cranial  nerves,  and  meninges. 

The  pharyngeal  branches  [rami  pharyngei]  supply  the  superior  and  middle  constrictor 
muscles  and  the  mucous  membrane  lining  them.     These  vessels  anastomose  with  branches 


Fig.  446. — Scheme  op  Right  Ascending  Pharyngeal  Abteey. 
The  internal  carotid  artery  is  hooked  aside. 

Meningeal    branch    passing 

through  lacerated  foramen 

Inferior  tympanic  branch 

Meningeal    branch    passing 

through  jugular  foramen 

Meningeal   branch    passing 

through  hypoglossal  canal 


(Walsham.) 


Stylo-pharyngeus 
Glosso-pharyngeal  nerve 


Occipital  artery 

Longus  capitis 

Ascending  pharyngeal 

artery 

Middle  constrictor  of 

pharynx 

Sympathetic  nerve 

Internal  carotid  artery 

External  carotid  artery 


Levator  veli  palatini 
Palatine  branch 


Buccinator  muscle 
Superior  constrictor  of 

pharynx 
Pterygo-mandibular 

raphe 
Stylo-glossus 


Ascending   palatine 
branch   of    ext. 
maxillary  artery 
Tonsillar  branch  of  ext.  maxil- 
lary artery 


xillary  artery 


Lingual  artery 


Superior  thyreoid  artery 


Common  carotid  artery 


of  the  superior  thyreoid.  One  branch  (the  palatine)  passes  over  the  upper  edge  of  the  superior 
constrictor  to  the  soft  palate  and  its  muscles.  This  branch  follows  a  course  similar  to  that  taken 
by  the  ascending  palatine  artery,  and  when  the  latter  is  small  may  take  its  place.  It  generally 
gives  off  small  twigs  to  the  Eustachian  tube  and  tonsil.  The  inferior  tympanic  artery  [a. 
tympanica  inferior]  accompanies  the  tympanic  branch  of  the  glosso-pharj'ngeal  nerve  through 
the  tympanic  canaliculus  into  the  tympanum,  and  anastomoses  with  the  other  tympanic  arteries. 
The  posterior  meningeal  artery  [a.  meningea  posterior]  is  distributed  to  the  membranes  of  the 
brain.  Some  twigs  pass  with  the  jugular  vein  through  the  jugular  foramen  into  the  cranium, 
and  supply  the  dura  mater  in  the  posterior  fossa  of  the  skull.  Others  occasionally  reach  the 
same  fossa  through  the  hypoglossal  (anterior  condyloid)  canal  in  company  with  the  hji^oglossal 
nerve;  while  others  pass  through  the  cartilage  of  the  lacerated  foramen  and  supply  the  middle 
fossa  of  the  skull. 


538 


THE  BLOOD-VASCULAR  SYSTEM 


2.  THE  SUPERIOR  THYREOID  ARTERY 

The  superior  thyreoid  artery  [a.  thyreoidea  superior]  (figs.  445,  447)  arises 
from  the  front  of  the  external  carotid  a  little  above  the  origin  of  that  vessel,  and, 
coursing  forward,  medially,  and  then  downward,  in  a  tortuous  manner,  supplies 
the  depressor  muscles  of  the  hyoid  bone,  the  larynx,  the  thyreoid  gland,  and  the 
lower  part  of  the  pharynx.  The  arterj'  at  first  runs  forward  and  a  little  upward, 
just  beneath  the  greater  cornu  of  the  hyoid  bone.  In  this  part  of  its  course  it 
lies  in  the  superior  carotid  triangle,  and  is  quite  superficial,  being  covered  only 
with  the  integument,  fascia,  and  platysma.  It  next  turns  downward,  and  passes 
beneath  the  omo-hyoid,  sterno-hyoid,  and  sterno-thyreoid  muscles,  and  ends  at 
the  upper  part  of  the  thyreoid  gland  by  breaking  up  into  terminal  glandular 
branches.  The  superior  thyreoid  vein  passes  beneath  the  artery  on  its  way  to  the 
internal  jugular  vein.  The  superior  thyreoid  is  the  artery  most  commonly 
divided  in  cases  of  suicidal  wounds  of  the  throat. 

Branches  of  the  Superior  Thyreoid  Artery 

The  named  branches  of  the  superior  thyreoid  artery  are: — (1)  The  hyoid; 
(2)  the  sterno-mastoid;  (3)  the  superior  laryngeal;  (4)  the  crico-thyreoid;  (5) 
anterior;  (6)  posterior;  and  (7)  glandular. 


Fig.  447. — Scheme  of  Left  Superior  Thyreoid  Artery.     (Walsham.) 

External  maxillary  artery 


Hyoid  branch  of  lingual 


Superior  laryngeal  branch j- — 


Crico-thyreoid  branch 


External  carotid  artery 
Ascending  pharyngeal  artery 


Internal  carotid  artery 


Sterno-mastoid  branch 


Superior  thyreoid  artery 


Common  carotid  artery 


Inferior  thyreoid  artery 


(1)  The  hyoid  [ramus  hyoideus]  is  usually  a  small  twig  which  passes  along  the  lower  border 
of  the  hyoid  bone,  lying  on  the  thyreo-hyoid  membrane  under  cover  of  the  thyreo-hyoid  and 
sterno-hyoid  muscles.  It  supplies  the  infra-hyoid  bursa  and  the  thjo-eo-hyoid  muscle,  and 
anastomoses  with  its  fellow  of  the  opposite  side,  and  with  the  hyoid  branch  of  the  lingual. 
When  the  latter  artery  is  small,  the  hyoid  branch  of  the  superior  thyreoid  is  usually  com- 
paratively large,  and  vice  versa. 

(2)  The  sterno-mastoid  [ramus  sternocleidomastoideus]  (fig.  447)  courses  downward  and 
backward  across  the  carotid  sheath,  and  entering  the  sterno-mastoid  supphes  the  middle  portion 
of  that  muscle.  It  gives  off  slender  twigs  to  the  thyreo-hyoid,  sterno-hyoid,  and  omo-hyoid 
muscles,  and  the  platysma  and  integuments  covering  it.  At  times  the  vessel  arises  directly 
from  the  external  carotid.  It  hes  usually  somewhere  in  the  upper  part  of  the  incision  for  tying 
the  common  carotid  above  the  omo-hyoid  muscle. 

(3)  The  superior  laryngeal  [a.  laryngea  superior]  (fig.  447)  passes  medially  beneath  the 


BRANCHES  OF  THE  LINGUAL  ARTERY  539 

thyreo-hyoid  muscle,  and,  perforating  the  thyreo-hyoid  membrane  along  with  the  internal 
branch  of  the  superior  laryngeal  nerve,  suppUes  the  intrinsic  muscles  and  mucous  lining  of  the 
larynx.  Its  further  distribution  within  the  larynx  is  given  with  the  description  of  that  organ. 
This  branch  sometimes  arises  from  the  external  carotid  direct.  It  may  enter  the  larynx  by 
passing  through  a  foramen  in  the  thyreoid  cartUage. 

(4)  The  crico -thyreoid  [ramus  cricothyreoideus]  passes  across  the  crico-thyreoid  membrane 
immediately  beneath  the  lower  border  of  the  thyreoid  cartilage.  It  anastomoses  with  its 
fellow  of  the  opposite  side,  and  usually  sends  a  small  branch  through  the  membrane  into  the 
interior  of  the  larynx.  Occasionally  a  considerable  twig  descends  over  the  cricoid  cartilage 
to  enter  the  isthmus  of  the  thyreoid  gland.  The  crico-thyreoid  has,  however,  frequently  been 
seen  of  comparatively  large  size — once  as  large  as  the  radial,  and  crossing  the  membrane 
obliquely.  In  order  to  avoid  injuring  the  crico-thyreoid  artery  in  the  operation  of  laryngot- 
omy,  it  is  usual,  if  the  operation  has  to  be  done  in  a  hurry,  to  make  the  incision  through  the 
crico-thyreoid  membrane  in  a  transverse  direction,  and  as  near  to  the  cricoid  cartilage  as  possible. 

(5)  The  anterior  branch  [ramus  anterior]  is  the  terminal  branch  supplying  the  isthmus  and 
the  neighbouring  part  of  the  lateral  lobe  of  the  thyreoid  gland. 

(6)  The  posterior  branch  [ramus  posterior],  the  other  terminal,  supplies  the  posterior  part 
of  the  lateral  lobe,  and  sends  branches  to  the  inferior  constrictor  of  the  pharynx  and  to  the 
oesophagus.     It  anastomoses  with  the  ascending  branches  of  the  inferior  thyreoid  artery. 

(7)  The  glandular  branches  [rami  glandulares]  are  the  ultimate  twigs,  arising  from  the  ante- 
rior and  posterior  terminal  branches,  for  the  supply  of  the  thyreoid  gland. 

3.  THE  LINGUAL  ARTERY 

The  lingual  artery  [a.  lingualis]  (fig.  448)  arises  from  tiie  front  of  the  external 
carotid,  between  the  superior  thyreoid  and  external  maxillary  (facial)  arteries, 
often  as  a  common  trunk  with  the  latter  vessel,  and  nearly  opposite  or  a  little 
below  the  greater  cornu  of  the  hyoid  bone.  It  may,  for  purposes  of  description, 
be  divided  into  three  portions:  the  first,  or  oblique,  extends  from  its  origin  to  the 
posterior  edge  of  the  hyo-glossus  muscle;  the  second,  or  horizontal,  lies  beneath 
the  hyo-glossus;  the  third,  or  ascending,  beneath  the  tongue.  The  first  or 
oblique  portion  is  situated  in  the  superior  carotid  triangle,  and  is  superficial,  being 
covered  merely  by  the  integument,  platysma,  and  deep  fascia.  Here  it  lies  on 
the  middle  constrictor  muscle  and  superior  laryngeal  nerve.  After  ascending  a 
short  distance,  it  curves  downward  and  forward  beneath  the  hypoglossal  nerve, 
and,  in  the  second  part  of  its  course,  runs  horizontally  along  the  upper  border  of 
the  hyoid  bone,  beneath  the  hyo-glossus,  by  which  it  is  separated  from  the 
hypoglossal  nerve  and  its  vena  comitans,  and  the  posterior  belly  of  the  digastric 
and  the  stylo-hyoid  muscles.  In  this  part  of  its  course  it  lies  successively  on  the 
middle  constrictor  of  the  pharj^nx  and  the  genio-glossus  muscle,  and  crosses  a 
small  triangular  space  known  as  'Lesser's  triangle,'  the  sides  of  which  are  formed 
by  the  tendons  of  the  digastric,  the  base  by  the  hypoglossal  nerve,  and  the  floor 
by  the  hyo-glossus  muscle,  in  which  situation  it  is  usually  tied.  In  the  third 
part  of  its  course  it  ascends  tortuously,  usually  beneath  the  anterior  margin  of  the 
hyo-glossus,  to  the  under  surface  of  the  tongue,  and  is  thence  continued  to  the 
tip  of  that  structure  lying  between  the  lingualis  and  the  genio-glossus  muscles. 
From  the  anterior  edge  of  the  hyo-glossus  to  its  termination  it  is  only  covered  by 
the  mucous  membrane  of  the  under  surface  of  the  tongue.  This  part  of  the 
vessel  is  sometimes  called  the  ranine  artery.  The  lingual  artery  is  accompanied 
by  small  vense  comitantes. 

Branches  op  the  Lingital  Artery 

The  named  branches  of  the  lingual  artery  are: — (1)  The  hyoid;  (2)  the  dorsal 
lingual;  (3)  the  sublingual;  and  (4)  the  deep  lingual  (ranine). 

(1)  The  hyoid  branch  [ramus  hyoideus]  (fig.  448)  is  a  small  vessel  which  arises  from  the  first 
part  of  the  lingual,  and  courses  along  the  upper  border  of  the  hyoid  bone,  superficial  to  the  hyo- 
glossus,  but  beneath  the  insertion  of  the  posterior  belly  of  the  digastric  and  the  stylo-hyoid. 
It  anastomoses  with  its  fellow  of  the  opposite  side,  and  with  the  hyoid  branch  of  the  superior 
thyreoid  artery,  and  supphes  the  contiguous  muscles. 

(2)  The  dorsalis  linguse  (fig.  448)  arises  from  the  second  portion  of  the  Ungual  artery, 
usually  under  cover  of  the  posterior  edge  of  the  h}'o-glossus  muscle.  It  ascends  to  the  back  of 
the  dorsum  of  the  tongue,  and,  dividing  into  branches,  supplies  the  mucous  membrane  on  each 
side  of  the  V  formed  by  the  vallate  papillae.  It  also  supplies  the  pillars  of  the  fauces  and  the 
tonsil,  where  it  anastomoses  with  the  other  faucial  and  tonsillar  arteries.  Instead  of  a  single 
artery,  as  above  described,  there  may  be  several  small  vessels  running  directly  to  the  parts 
mentioned.     The  artery  anastomoses  in  the  mucous  membrane  by  very  small  branches  with  the 


540 


THE  BLOOD   VASCULAR-SYSTEM 


vessel  of  the  opposite  side;  but  the  anastomosis  is  so  minute  that  when  one  Hngual  artery  is 
injected  the  injection  merely  passes  across  to  the  opposite  side  at  the  tip  of  the  tongue;  and  when 
the  tongue  is  divided  accurately  in  the  middle  line,  as  in  the  removal  of  one-half  of  that  organ, 
practically  no  haemorrhage  occurs. 

(3)  The  sublingual  artery  [a.  sublingualis]  (fig.  448)  usually  comes  off  from  the  lingual  at  the 
anterior  margin  of  the  hyo-glossus.  It  passes  beneath  the  mylo-hyoid  to  the  subhngual  gland, 
which  it  supplies,  and  finally  it  usually  anastomoses  with  the  submental  artery,  a  branch  of 
the  external  maxillary  (facial).  It  also  supplies  branches  to  the  side  of  the  tongue,  and  gives 
off  a  terminal  twig,  which  anastomoses  beneath  the  mucous  membrane  of  the  floor  of  the  mouth 
(to  which  it  also  gives  twigs)  with  the  artery  of  the  opposite  side.  The  artery  of  the  frgenum 
is  usually  derived  from  this  vessel  (fig.  448). 

(4)  The  deep  lingual  [a.  profunda  hnguai],  the  termination  of  the  hngual,  courses  forward 
beneath  the  mucous  membrane,  on  the  under  surface  of  the  tongue,  to  the  tip.  It  lies  lateral 
to  the  genio-glossus,  between  that  muscle  and  the  inferior  lingualis,  and  is  accompanied  by  the 
lingual  vein  and  terminal  branch  of  the  lingual  nerve.  It  follows  a  very  tortuous  course,  so 
that  it  is  not  stretched  when  the  tongue  is  protruded.  Branches  are  given  off  from  it  to  the 
contiguous  muscles  and  mucous  membrane.  Near  the  tip  of  the  tongue  it  communicates  with 
its  fellow  of  the  opposite  side,  as  shown  by  the  fact  that  when  the  lingual  artery  of  one  side  is 
injected,  the  injection  fluid  passes  into  the  branches  of  the  artery  of  the  other  side. 


Fig.  448. — Scheme  of  the  Right  Lingual  Artery. 

Glosso-palatinus 

Descending   palatine 
artery 
Pharyngo  -palatinus 
Palatine  tonsil 
Ascending  palatine 
branch  of  external 
maxillary 
Tonsillar  branch,  of 
dorsal  lingual 
Tonsillar    branch    of 
external  maxillary 
Stylo -glossus 

Dorsal  lingual  artery 
Middle  constrictor 
Hypoglossal  nerve 
External  maxillary 
artery 
Posteriorbelly  of  digas- 
tric and  stylohyoid 
Hyoid  branch  of  lingual 
Sup.  laryngeal  n 
Hyoid  branch  of  sup 
thyreoid 
Internal  carotid  artery 


Common  carotid 


(Walsh  am.) 


Deep  lingual  artery 


Artery  of  frsenulum 
Hyo-glossus 
Subungual  artery 
Genio -hyoid 
Anterior  belly  of 

digastric 
Submental  artery 


Superior  thyreoid  artery 


4.  THE  EXTERNAL  MAXILLARY  (FACIAL)  ARTERY 

The  external  maxillary  or  facial  artery  [a.  maxillaris  externa]  (fig.  449)  arises 
immediately  above  the  lingual  from- the  fore  part  of  the  external  carotid,  at  times 
as  a  common  trunk  with  the  lingual.  It  courses  forward  and  upward  in  a  tortuous 
manner  to  the  mandible,  and,  passing  over  the  body  of  this  bone  at  the  anterior 
edge  of  the  masseter  muscle,  winds  obliquely  upward  and  forward  over  the  face 
to  the  medial  angle  of  the  eye,  where  it  anastomoses,  under  the  name  of  the 
angular  artery,  with  the  dorsal  nasal  branch  of  the  ophthalmic.  It  is  usually 
divided  into  two  portions — the  cervical  and  the  facial. 

The  cervical  portion  (fig.  449)  ascends  tortuously  from  its  origin  from  the 
external  carotid  upward  and  forward  beneath  the  posterior  belly  of  the  digastric 
and  stylo-hyoid  muscles,  and  usualty  also  beneath  the  hypoglossal  nerve,  and  then, 
making  a  turn,  runs  horizontally  forward  for  a  short  way  beneath  the  jaw,  either 
imbedded  in  or  lying  under  the  submaxillary  gland.  It  has  here  the  mylo-hyoid 
and  stylo-glossus  beneath  it.  On  leaving  the  cover  of  the  gland  it  forms  a  loop 
passing  first  downward  and  then  upward  over  the  lower  border  of  the  jaw  imme- 
diately in  front  of  the  masseter  muscle,  where  it  is  superficial,  being  merely  cov- 
ered by  the  integument  and  platysma.  Here  it  can  be  felt  beating,  and  can  be 
readily  compressed.  In  the  above  course  it  lies  in  the  posterior  part  of  the  sub- 
maxillary triangle,  and,  in  addition  to  the  structures  already  mentioned  as  cross- 
ing it,  is  covered  by  the  skin,  superficial  fascia,  and  platysma,  and  by  one  or  two 
submaxillary  lymphatic  nodes.     The  vein  is  separated  from  the  artery  by  the 


BRANCHES  OF  THE  EXTERNAL  MAXILLARY  ARTERY  541 

submaxillary  gland,  the  posterior  belly  of  the  diagastric  muscle,  the  stylo-hyoid 
muscle,  and  the  hypoglossal  nerve. 

The  facial  portion  (fig.  449)  of  the  external  maxillary  artery  ascends  tortuously 
forward  toward  the  angle  of  the  mouth,  passing  under  the  platysma  (risorius), 
the  zygomatic  muscle,  the  zygomatic  head  of  the  quadratus  labii  superioris 
(zygomaticus  minor),  and  the  zygomatic  and  buccal  branches  of  the  facial  nerve. 
It  here  lies  upon  the  jaw  and  the  buccinator  muscle.  Thence  it  courses  upward  by 
the  side  of  the  nose  toward  the  medial  angle  of  the  eye,  passing  over  or  under  the 
infraorbital  and  angular  heads  of  the  quadratus  labii  superioris,  and  under  the 
infraorbital  branches  of  the  facial  nerve.  It  lies  on  the  caninus  (levator  anguli 
oris)  and  the  infraorbital  branches  of  the  fifth  nerve.  The  anterior  facial  vein 
takes  a  straighter  course  than  the  external  maxillary  artery,  is  separated  from  it  by 
the  zygomatic  muscle,  and  lies  lateral  to  it. 

Branches  of  the  External  Maxillary  Artery  of  the  Neck 

The  branches  of  the  external  maxillary  artery  in  the  neck  are: — (1)  The 
ascending  palatine;  (2)  the  tonsillar;  (3)  the  glandular;  (4)  the  submental. 

(1)  The  ascending  palatine  [a.  palatina  ascendens]  (figs.  448,  449) — the  first  branch  of  the 
external  maxillary,  but  often  a  distinct  branch  of  the  external  carotid — ascends  between  the 
internal  and  external  carotids,  and  then  between  the  stylo-glossus  and  stylo-pharyngeus  mus- 
cles, and  on  reaching  the  wall  of  the  pharynx  is  continued  upward  between  the  superior  constrictor 
and  internal  pterygoid  muscles  toward  the  base  of  the  skull  as  high  as  the  levator  veli  palatini, 
where  it  divides  into  two  branches,  a  palatine  and  a  tonsillar.  One  of  these  branches,  the  pala- 
tine, passes  with  the  levator  veU  palatini  over  the  curved  upper  margin  of  the  superior  constrictor 
to  the  soft  palate,  where  it  is  distributed  to  the  tissues  constituting  that  structure,  and  anasto- 
moses with  its  fellow  of  the  opposite  side  and  with  the  descending  palatine  branch  of  the  internal 
maxillary,  and  the  ascending  pharyngeal,  which  vessel  often  to  a  great  extent  supplies  the  place 
of  this  artery.  The  other  branch,  the  tonsillar,  supplies  the  tonsil  and  the  Eustachian  tube, 
anastomosing  with  the  tonsillar  branch  of  the  external  maxillary  (facial)  and  ascending  pharyn- 
geal arteries.  The  ascending  palatine  artery  supphes  the  muscles  between  which  it  runs  on  its 
way  to  the  palate. 

(2)  The  tonsillar  branch  [ramus  tonsillaris]  (fig.  449)  ascends  between  the  stylo-glossus  and 
internal  pterygoid  muscles  to  the  level  of  the  tonsil,  where  it  perforates  the  superior  constrictor 
muscle  of  the  pharynx,  and  ends  in  the  tonsil,  anastomosing  with  the  tonsillar  branch  of  the 
ascending  palatine  and  with  the  other  tonsillar  arteries  (fig.  448).  It  gives  branches  also  to  the 
root  of  the  tongue. 

(3)  The  glandular  branches  [rami  glandulares]  are  distributed  to  the  submaxillary  gland 
as  the  artery  is  passing  through  or  beneath  that  structure.  A  small  twig  from  one  of  these 
branches  usually  supplies  the  submaxillary  (Wharton's)  duct. 

(4)  The  submental  artery  [a.  submentahs]  (fig.  449)  comes  off  from  the  external  maxillary 
as  the  latter  vessel  lies  under  cover  of  the  submaxillary  gland,  and,  passing  forward  on  the 
mylo-hyoid  muscle  between  the  base  of  the  jaw  and  the  anterior  belly  of  the  digastricus,  supphes 
these  structures  and  the  overlying  platysma  and  integuments.  It  anastomoses  with  the  sub- 
lingual artery.     The  external  maxillary  also  supphes  the  adjacent  muscles  of  the  neck. 

Branches  of  the  External  Maxillary  Artery  on  the  Face 

From  the  lateral  or  concave  side  of  the  artery  are  given  off  branches  which 
supply  the  masseter  muscle  and  anastomose  with  the  masseteric  and  buccinator 
branches  of  the  internal  maxillary  artery,  the  transverse  facial  artery,  and  the 
infraorbital  arteries. 

From  the  medial  or  convex  side  the  following  larger  and  named  vessels  are 
given  off : — (1)  The  inferior  labial;  (2)  the  superior  labial;  and  (3)  the  angular. 

(1)  The  inferior  labial  artery  [a  labiahs  inferior]  arises  at  the  angle  of  the  mouth  and  runs  in 
the  under  Up  within  the  substance  of  the  orbicularis  oris,  close  to  the  mucous  membrane.  It 
anastomoses  with  the  artery  of  the  other  side.  Frequently  an  additional  branch  passes  from 
the  external  maxillary  to  the  lower  lip. 

(2)  The  superior  labial  artery  [a.  labialis  superior]  arising  from  the  facial  a  httle  higher 
than  the  inferior,  passes  forward  beneath  the  zygomaticus,  and  then,  hke  the  inferior  labial, 
courses  tortuously  along  the  lower  margin  of  the  upper  hp  between  the  orbicularis  oris  and  the 
mucous  membrane,  about  1.2  cm.  (i  in.)  from  the  junction  of  the  mucous  membrane  and  the 
skin.  It  is  usually  larger  than  the  inferior  labial.  It  anastomoses  with  its  fellow  of  the  opposite 
side,  and  gives  off  a  small  artery  to  the  septum — arteria  septi  nasi.  Compression  of  this  vessel 
will  sometimes  control  hiemorrhage  from  the  nose. 

(3)  The  angular  artery  [a.  angularis]  (fig.  449)  is  the  terminal  branch  of  the  external  max- 
illary. It  supplies  the  nose  and  anastomoses  at  the  medial  angle  of  the  eye  with  the  dorsal  nasal 
branch  of  the  ophthalmic.     It  is  accompanied  by  the  anterior  descending  vein  from  the  scalp. 


542 


THE  BLOOD-VASCULAR  SYSTEM- 


It  lies  to  the  medial  side  of  the  lacrimal  sac  and  supphes  that  structure  and  the  lower  part  of 
the  orbicularis  oculi,  beneath  which  a  branch  anastomoses  with  the  infraorbital  artery.  The 
situation  of  the  artery  to  the  medial  side  of  the  lacrimal  sac  should  be  borne  in  mind  in  opening 
a  lacrimal  abscess. 


Fig.  449. — Scheme  of  the  Right  External   Maxillary  Artery.     (Walsham.) 


Orbicularis  oculi  muscle 


Transverse  facial  artery 

Quad,  labii  sup., 

zygomatic  head 

Zygomaticus  muscle 

Buccinator  muscle 

Masseteric  branch 

Masseter  muscle 

Stylo-pharyngeus 
muscle 
Stylo-glossus  muscle 
Ascending  palatine 
branch 
Tonsillar  branch 

External  maxillary 

artery 

External  carotid 

artery 

Posterior  belly  of 

digastric  muscle 


Lingual  artery 


Frontal  branch  of  ophthal- 
mic artery 
■Dorsal  nasal  branch  of  ophthal- 
mic artery 


Angular  artery 
Quad,  labii  sup., 

angular  head 
Infraorbital  artery 
Quad,  labii  sup., 
infraorbital  head 
i-at.  nasal  artery 
Caninus  muscle 
.Artery  of  septum 
Superior  labial 
artery 


Risorius  muscle 


Inferior  labial  artery 

Mental  branch  of  inferior 

alveolar  artery 
Quadratus  labii  inferioris 

muscle 
-Inferior  labial  artery 
.Triangularis  muscle 

■Submental  artery 
.Branches  to  submaxillary 
gland 
Anterior  belly  of  digastric  muscle 


Mylo-hyoid  muscle 
■Hyo  glossus  muscle 

'Hypoglossal  nerve 


5.  THE  STERNOCLEIDOMASTOID 

The  sternocleidomastoid  artery  [a.  sternocleidomastoidea]  arises  from  the 
posterior  side  of  the  external  carotid  at  the  point  where  the  carotid  is  crossed  by 
the  digastric  muscle.  It  is  distributed  to  the  sternocleidomastoid  muscle,  and  is 
frequently  represented  by  one  of  the  muscular  branches  of  the  occipital  artery. 


6.  THE  OCCIPITAL  ARTERY 

The  occipital  artery  [a.  occipitalis]  (fig.  450)  is  usually  a  vessel  of  considerable 
size.  It  comes  off  from  the  posterior  part  of  the  external  carotid  opposite  the 
external  maxillary  (facial),  or  else  a  little  higher  than  that  vessel.     It  then  winds 


THE  POSTERIOR  AURICULAR  ARTERY  543 

upward  and  backward  to  the  interval  between  the  mastoid  process  of  the  temporal 
bone  and  transverse  process  of  the  atlas,  and,  after  running  horizontally  backward 
in  a  groove  on  the  mastoid  portion  of  the  temporal  bone,  again  turns  upward,  and 
ends  by  ramifying  in  the  scalp  over  the  back  of  the  skull,  extending  as  far  forward 
as  the  vertex. 

The  vessel  may  be  divided  into  three  parts — viz.,  that  anterior  to  the  sterno- 
mastoid  muscle;  that  beneath  the  sterno-mastoid;  and  that  posterior  to  the 
sterno-mastoid. 

In  the  first  part  of  its  course  the  occipital  artery  is  covered  by  the  integuments  and  fascia, 
and  is  more  or  less  overlapped  by  the  posterior  belly  of  the  digastric  muscle,  the  parotid  gland, 
and  posterior  facial  (temporo-maxillary)  vein.  It  is  crossed  by  the  hypoglossal  nerve  as  the 
latter  winds  forward  over  the  carotid  vessels  to  reach  the  tongue.  It  successively  crosses  in 
front  of  the  internal  carotid  artery,  the  hypoglossal  nerve,  the  vagus  nerve,  the  internal  jugular 
vein,  and  tlie  spinal  accessory  nerve. 

In  the  second  part  of  its  course  it  sinks  deeply  beneath  the  digastric  muscle  into  the  interval 
between  the  mastoid  process  of  the  temporal  bone  and  the  transverse  process  of  the  atlas.  It 
is  here  covered  by  the  sterno-mastoid,  splenius  capitis,  and  longissimus  capitis  muscles  and  by 
the  origin  of  the  digastric;  and  lies,  first  on  the  rectus  capitis  laterahs,  which  separates  it  from 
the  vertebral  artery,  then  in  a  groove,  the  occipital  groove,  on  the  mastoid  portion  of  the  tem- 
poral bone,  and  then  on  the  insertion  of  the  superior  oblique  muscle. 

In  the  third  part  of  its  course  it  enters  the  triangular  interval  formed  by  the  diverging  borders 
of  the  splenius  capitis  and  the  superior  nuchal  line  of  the  occipital  bone.  Here  it  lies  beneath 
the  integuments  and  the  aponeurosis  uniting  the  occipital  attachments  of  the  sterno-mastoid 
and  trapezius,  and  rests  upon  the  semi-spinalis  capitis  (complexus)  just  before  tlie  insertion  of 
that  muscle  into  the  occipital  bone.  In  company  with  the  greater  occipital  nerve,  it  perforates 
either  this  aponeurosis,  or  less  often  the  posterior  belly  of  the  epicranius  (occipito-frontaHs), 
and  follows  roughly,  but  in  a  tortuous  course,  the  line  of  the  lamboid  suture,  lying  between  the 
integument  and  the  cranial  aponeurosis.  In  the  scalp  it  divides  into  several  large  branches, 
which  ramify  over  the  back  of  the  skull  and  reach  as  far  forward  as  the  vertex.  They  anasto- 
mose with  the  corresponding  branches  of  the  opposite  side,  and  with  the  posterior  auricular 
and  the  superficial  temporal  arteries. 

Branches  of  the  Occipital  Arteey  (Fig.  450) 

The  branches  of  the  occipital  artery  are : — (1)  The  muscular;  (2)  the  menin- 
geal; (3)  the  auricular;  C4)  the  mastoid;  (5)  the  descending;  (6)  the  occipital. 

(1)  The  muscular  branches  [rami  musculares]  (fig.  450)  supply  the  sternocleidomastoid  and 
adjacent  muscles.  One  of  these  branches  may  take  the  place  of  the  sterno-mastoid  branch  of 
the  external  carotid.  The  hypoglossal  nerve  then,  as  a  rule,  loops  round  it  instead  of  round  the 
occipital. 

(2)  The  meningeal  branches  [rami  meningei]  (fig.  450),  one  or  more  in  number,  are  long 
slender  vessels  which  leave  the  occipital  artery  as  it  crosses  the  internal  jugular  vein  and,  ascend- 
ing along  the  vessel,  pass  with  it  through  the  jugular  or  hypoglossal  foramen,  and  are  distributed 
to  the  dura  mater  lining  the  posterior  fossa  of  the  skull. 

(3)  The  auricular  branch  [ramus  auricularis]  ascends  over  the  mastoid  process  to  the  back 
of  the  ear,  and  supphes  the  pinna  and  concha.  It  sometimes  takes  the  place  of  the  posterior 
auricular  artery  (fig.  450). 

(4)  The  mastoid  branch  [ramus  mastoideus]  is  a  small  twig  that  passes  into  the  skull  through 
the  mastoid  foramen,  supplying  the  dura  mater,  the  diploe,  the  walls  of  the  transverse  sinus, 
and  the  mastoid  cells. 

(5)  The  descending  or  princeps  cervicis  [ramus  descendens]  (fig.  450),  the  largest  of  the 
branches  of  the  occipital,  arises  from  that  artery  just  before  it  emerges  from  beneath  the  splenius, 
and,  descending  for  a  short  distance  between  the  splenius  and  semi-spinalis  capitis  (complexus), 
divides  into  a  superficial  and  a  deep  branch.  The  superficial  branch  perforates  the  splenius, 
supplies  branches  to  the  trapezius,  and  anastomoses  with  the  ascending  branch  of  the  transverse 
cervical  artery.  The  deep  branch  passes  downward  between  the  semi-spinahs  capitis  (com- 
plexus) and  colli,  and  anastomoses  with  the  deep  cervical  branch  of  the  costo-cervical  trunk 
and  with  branches  of  the  vertebral.  The  anastomoses  between  the  above-mentioned  arteries 
form  important  collateral  channels  after  hgature  of  the  common  carotid  and  subclavian  arteries 
(fig.  444). 

(6)  The  occipital  or  terminal  branches  [rami  occipitales]  (fig.  450),  usually  two  in  number, 
named  from  their  position  medial  and  lateral,  ramify  over  the  scalp,  and  have  already  been 
described.  The  medial  branch  generally  gives  off  a  twig  which  enters  the  parietal  foramen 
(parietal  artery)  and  is  distributed  to  the  dura  mater.  The  occipital  artery  may  also  give  off 
the  stylo-mastoid,  the  posterior  auricular,  or  the  ascending  pharyngeal  arteries. 

7.  THE  POSTERIOR  AURICULAR  ARTERY 

The  posterior  auricular  artery  [a.  auricularis  posterior]  (fig.  450)  arises  from 
the  posterior  part  of  the  external  carotid  artery,  usually  immediately  above  the 


544 


THE  BLOOD-VASCULAR  SYSTEM 


posterior  belly  of  the  digastric,  about  the  level  of  the  tip  of  the  styloid  process. 
Occasionally  it  arises  under  cover  of  the  digastric,  quite  close  to,  or  as  a  common 
trunk  with,  or  as  a  branch  of,  the  occipital.  It  courses  upward  and  backward  in 
the  parotid  gland  to  the  notch  between  the  margin  of  the  external  auditory  meatus 
and  the  mastoid  process,  where  it  divides  into  branches.  In  this  course  it  rests 
on  the  styloid  process,  crosses  the  spinal  accessory  nerve,  and  is  crossed  by  the 
facial  nerve. 


Fig.  450. — Scheme  of  Left  Occipital  and  Posterior  Auricular  Arteries.     (Walsham.) 


Occipital  branch  of  pos- 
terior auricular 

Parotid  gland 
Sterno -mastoid,  cut 

Auricular  branch  of 
occipital 
Post,  auricular  artery 
Rectus  capitis  lateralis 

Spinal  accessory 

Occipital  artery 
Internal  jugular  vein 

Ext.  maxillary  artery ^ 

Hypoglossal  n 

Lingual  artery 

Vagus  nerve 

Superior  thyreoid 

Common  carotid 


^^  \IM/''^_ 


Lateral  branch  of 
occipital 

'"         Medial  branch  of 
occipital 

■Semi-spinalis  capitis 
Descending  branch  of 

occipital 
■Superior  oblique 
Longissimus  capitis,  cut 
Splenius  capitis,  cut 
Meningeal  branches 
Sternocleidomastoid  branch 
of   occipital 


-Internal  carotid 

-  Sterno-mastoid 

-  External  carotid 

-  Trapezius 


Branches  of  the  Posterior  Auricular  Artery 

The  branches  of  the  posterior  auricular  artery  are: — (1)  the  stylo-mastoid;  (2) 
the  auricular;  (3)  the  occipital  ffig.  450). 

The  posterior  auricular  also  gives  branches  to  the  parotid  gland  and  the  adjacent  muscles, 
namely,  the  posterior  belly  of  the  digastric,  the  stylo-hyoid,  and  auricularis  posterior  (retrahens 
aurem) . 

(1)  The  stylo-mastoid  artery  [a.  stylomastoidea]  comes  off  from  the  posterior  auricular 
artery  just  before  it  reaches  the  notch  between  the  margin  of  the  external  auditory  meatus 
and  the  mastoid  process,  and,  following  the  facial  nerve  upward,  enters  the  stylo-mastoid  fora- 
men in  the  temporal  bone.  In  the  facial  canal  (aqueduct  of  Fallopius)  it  gives  off  the  following 
named  twigs: — (a)  meatal,  to  the  external  auditory  meatus;  (6)  mastoid  [rami  mastoidei],  to 
the  mastoid  cells  and  tympanic  antrum;  (c)  stapedic  [ramus  stapedius],  which  runs  forward  to 
the  stapedius  muscle;  (d)  posterior  tympanic  [a.  tympanica  posterior],  which  anastomoses  with 
the  anterior  tympanic  branch  of  the  internal  maxillary,  forming  with  it  in  the  foetus  a  vascular 
circle  around  the  membrana  tympani;  (e)  vestibular,  to  the  vestibule  and  semicircular  canals; 
and  (J)  terminal,  a  small  twig  which  leaves  the  facial  canal  (by  the  hiatus)  with  the  great  super- 
ficial petrosal  nerve,  and  anastomoses  with  the  superior  petrosal  branch  of  the  middle  meningeal 
artery. 

(2)  The  auricular  branch  [ramus  auricularis]  passes  upward  behind  the  ear  and  beneath  the 
auricularis  posterior  (retrahens  aurem),  supplying  the  medial  surface  of  the  pinna  and  adjacent 


THE  INTERNAL  MAXILLARY  ARTERY  545 

skin.  It  anastomoses  with  the  posterior  branch  of  the  superficial  temporal  artery.  The 
branches  to  the  pinna  not  only  supply  the  back  of  that  structure,  but  some  perforate  the 
cartilage,  and  others  turn  over  its  free  margin  to  supply  the  lateral  surface;  there  they  anasto- 
mose with  the  anterior  auricular  branches  from  the  temporal. 

(3)  The  occipital  branch  [ramus  ooeipitahs]  passes  upward  and  backward,  crossing  the 
aponeurotic  insertion  of  the  sterno-mastoid  muscle.  It  gives  a  branch  to  the  posterior  belly 
of  the  epioranius  (occipito-frontaHs),  and  anastomoses  with  the  occipital  artery. 

8.  THE  SUPERFICIAL  TEMPORAL  ARTERY 

The  superficial  temporal  artery  [a.  temporalis  superficialis]  (fig.  445),  is  the 
smaller  of  the  two  terminal  divisions  of  the  external  carotid,  though  apparently 
the  direct  continuation  of  that  vessel.  It  arises  opposite  the  neck  of  the  man- 
dible and,  under  cover  of  the  parotid  gland,  passes  upward  in  the  interval  be- 
tween the  condyle  and  the  external  auditory  meatus  to  the  zygoma,  lying  on  the 
capsule  of  the  temporo-mandibular  joint.  Thence  it  ascends  over  the  posterior 
zygomatic  root  and  the  temporal  aponeurosis  for  about  4  or  5  cm.  (1|  or  2  in.),  and 
there  divides  into  frontal  and  parietal  branches.  It  is  surrounded  by  a  dense 
plexus  of  sympathetic  nerves,  and  is  accompanied  by  the  auriculo-temporal  nerve, 
which  lies  beneath  and  generally  a  little  behind  it.  It  is  crossed  by  the  temporal 
and  zygomatic  branches  of  the  facial  nerve,  and  by  the  auricularis  anterior  (attra- 
hens  aurem)  muscle.  As  it  crosses  the  zygoma  it  can  be  readily  felt  pulsating 
immediately  in  front  of  the  ear,  and  in  this  situation  can  be  compressed  against  the 
bone.  It  is  here  quite  superficial,  being  merely  covered  by  the  integuments  and  a 
delicate  prolongation  from  the  cervical  fascia  (fig.  445) . 

Branches  of  the  Superficial  Temporal  Artery 

The  branches  of  the  superficial  temporal  artery  are: — (1)  The  parotid;  (2) 
the  transverse  facial;  (3)  the  anterior  auricular;  (4)  the  zygomatico-orbital; 
(5)  the  middle  temporal;  (6)  the  frontal;  (7)  the  parietal. 

(1)  The  parotid  branches  [rami  parotidei]  are  small  twigs  given  off  in  the  substance  of  the 
parotid  gland. 

(2)  The  transverse  facial  [a.  transversa  faciei]  is  the  largest  branch  of  the  temporal.  It 
sometimes  arises  from  the  external  carotid  as  a  common  trunk  with  the  temporal.  It  is  at 
first  deeply  seated  in  the  substance  of  the  parotid  gland,  but  soon  emerging  from  the  upper  part 
of  the  anterior  border  of  the  gland  known,  courses  transversely  across  the  masseter  muscle 
about  a  finger's  breadth  below  the  zygoma.  The  parotid  duct  runs  below  it,  and  the  zygomatic 
(infraorbital)  branches  of  the  facial  nerve  above  it.  It  supphes  the  parotid  gland,  the  masseter 
muscle,  and  the  skin  of  the  face,  and  anastomoses  with  the  infraorbital,  the  buccal,  and  the  ex- 
ternal maxillary  (facial)  arteries. 

(3)  The  anterior  auricular  branches  [rami  auriculares  anteriores]  are  three  or  four  in  number 
and  supply  the  tragus,  the  pinna,  and  the  lobule  of  the  ear,  and  to  some  extent  the  external 
auditory  meatus. 

(4)  The  zygomatico-orbital  artery  [a.  zygomaticoorbitahs]  (fig.  445),  at  times  a  branch  of 
the  deep  temporal,  passes  forward  along  the  upper  border  of  the  zygoma,  in  the  fat  between 
the  superficial  and  deep  layers  of  the  temporal  aponeurosis,  and,  after  giving  branches  to  the 
orbicularis  oculi,  sends  one  or  more  twigs  into  the  orbit  through  foramina  in  the  zygomatic 
(malar)  bone  to  anastomose  with  the  lacrimal  and  palpebral  branches  of  the  ophthalmic. 

(5)  The  middle  temporal  artery  [a.  temporahs  media]  (fig.  453),  arises  just  above  the 
zygoma,  and,  perforating  the  temporal  aponeurosis  and  temporal  muscle,  ascends  on  the  squa- 
mous portion  of  the  temporal  bone,  and  anastomoses  with  the  posterior  deep  temporal  artery. 

(6)  The  frontal  or  anterior  terminal  branch  [ramus  frontalis]  ramifies  tortuously  in  an  up- 
ward and  forward  direction  over  the  front  part  of  the  skull.  It  hes  first  between  the  skin  and 
temporal  fascia  and  then  between  the  skin  and  epicranial  aponeurosis.  It  supphes  the  anterior 
belly  of  the  epicranius  (occipito-frontahs)  and  the  orbicularis  ocuh  muscles,  and  anastomoses 
with  the  supraorbital  and  frontal  branches  of  the  ophthalmic,  and  with  the  corresponding 
artery  of  the  opposite  side.  The  secondary  branches  given  off  from  this  vessel  to  the  scalp 
run  from  before  backward. 

(7)  The  parietal  or  posterior  terminal  branch  [ramus  parietahs]  ramifies  on  the  side  of  the 
head  between  the  skin  and  temporal  fascia.  Its  branches  anastomose,  in  front  with  the  anterior 
terminal  branch;  behind,  with  the  posterior  auricular  and  occipital  arteries;  and  above,  across 
the  vertex  of  the  skull,  with  the  corresponding  artery  of  the  opposite  side. 

9.  THE  INTERNAL  MAXILLARY  ARTERY 

The  internal  maxillary  artery  [a.  maxillaris  interna]  (fig.  451)  is  the  larger  of 
the  two  terminal  divisions  of  the  external  carotid.  It  arises  opposite  the  neck  of 
the  mandible  in  the  substance  of  the  parotid  gland,  and,  passing  first  between  the 
mandible  and  the  spheno-mandibular  ligament  and  then  between  the  external 


546 


THE  BLOOD-VASCULAR  SYSTEM 


and  internal  pterygoid  muscles,  sinks  deeply  into  the  pterygo-palatine  (spheno- 
maxillary) fossa,  and  there  breaks  up  into  its  terminal  branches.  It  is  divided  into 
three  portions:  a  mandibular,  a  pterygoid,  and  a  pterygo-palatine. 

(1)  In  the  first  part  of  its  coixrse  (the  mandibular  portion)  the  artery  lies 
between  the  neck  of  the  mandible  and  the  spheno-mandibular  ligament,  taking  a 
horizontal  course  forward,  nearly  parallel  to  and  a  httle  below  the  auriculo- 
temporal nerve  and  the  external  pterygoid  muscle.  It  is  here  embedded  in  the 
parotid  gland,  and  usually  crosses  in  front  of  the  inferior  alveolar  (dental)  nerve. 

(2)  In  the  second  part  of  its  course  (the  pterygoid  portion)  the  artery  may  be 
placed  superficial  or  deep  to  the  external  pterygoid  muscle.  In  the  first  case  it 
passes  between  the  two  pterygoid  muscles  and  the  ramus  of  the  jaw,  and  then 
turns  upward  over  the  lateral  surface  of  the  external  pterygoid,  medial  to  the  tem- 
poral muscle  to  gain  the  two  heads  of  the  external  pterygoid,  between  which  it 

Fig.  451.' — Scheme  of  Left  Internal  Maxillary.     (Walsham.) 


Infraorbital  artery  and  nerve 


Spheno-palatine  branch 
Descending  palatine  branch 
Naso-palatine  branch 

Artery  of  the  pterygoid  canal  (Vidian) 

Anterior  deep  temporal  artery 
External  pterygoid  branch 


Orbital  branch 


Nasal  branch--^ 
Anterior  alveolar-/- 
branch 
Labial  branch- 
Posterior  alve-, 
olar  branch 


Alveolar  branch- 


Mental  branch 


Submental  branch 


Posterior  deep  temporal  artery 
Small  meningeal 
artery 

Middle  meningeal 
artery 

Temporal  artery 
Anterior  tympanic 
Deep  auricular 

branch 
Auriculo-temporal 

Masseteric  branch 

External  carotid 
artery 


\Spheno-mandibu- 
lar  ligament 

.Inferior     alveolar 
artery  and  nerve 


Internal  pterygoid  branch 


Mylo-hyoidean  branch 


sinks  into  the  pterygo-palatine  fossa.  In  the  second  case  it  passes  medial  to  the 
external  pterygoid,  and  is  covered  by  that  muscle  till  it  reaches  the  interval  be- 
tween its  two  heads,  where  it  then  often  forms  a  projecting  loop  as  it  turns  into  the 
pterygo-palatine  fossa. 

(3)  In  the  third  part  of  its  course  (the  pterygo-palatine  portion)  the  artery 
lies  in  the  pterygo-palatine  fossa  beneath  the  maxillary  division  of  the  fifth  nerve 
and  in  close  relationship  with  the  spheno-palatine  (Meckel's)  ganglion,  and  there 
breaks  up  into  its  terminal  branches. 


Bhanches  of  the  Internal  Maxillary  Artery 

The  branches  of  the  internal  maxillary  artery  are: — 

(A)  From  the  first  part : — (1)  The  deep  auricular;  (2)  the  anterior  tympanic; 
(3)  the  middle  meningeal;  (4)  the  inferior  alveolar  (dental);  (5)  the  accessory 
meningeal  (sometimes).  All  these  vessels  pass  through  bony  or  cartilaginous 
canals. 


FIRST  PART  OF  THE  INTERNAL  MAXILLARY  ARTERY      547 

(B)  From  the  second  part : — fl)  The  masseteric;  (2)  the  posterior  deep  tem- 
poral; (3)  the  pterygoid;  (4)  the  buccal;  and  (5)  the  anterior  deep  temporal. 
All  these  branches  supply  muscles. 

(C)  From  the  third  part: — (1)  The  posterior  superior  alveolar  (dental);  (2) 
the  infra-orbital;  (3)  the  descending  palatine;  (4)  the  a.  canalis  pterygoidei  or 
Vidian;  and  (5)  the  spheno-palatine.  All  these  branches  pass  through  bony 
canals. 


Branches  of  the  First  Part  of  the  Internal 
Maxillary  Artery 

(1)  The  deep  auricular  artery  [a.  auricularis  profunda]  (fig.  451)  passes  upward  in  the  sub- 
stance of  the  parotid  gland  behind  the  capsule  of  the  temporo-mandibular  joint,  and,  perforating 
the  bony  or  cartilaginous  wall  of  the  external  auditory  meatus,  supplies  the  skin  of  that  passage 
and  the  membrana  tympani.  It  at  times  gives  a  branch  to  the  joint  as  it  passes  behind  the 
temporo-mandibular  articular  capsule. 


Fig.  452. — The  Middle  Meningeal  Arteet  within  the  Skull. 
Middle  meningeal  artery 


Anterior  meningeal  artery 


(After  Spalteholtz.) 


Anterior    etIi-_ V 

moidal  artery  ,        ^^j^^ 

Posterior  eth- /     _>^*^w 

moidal  artery 


'  ■  ..  ■  ■    Mastoid  branch 

.- ^^     of  occipital  artery 

!r_^=;^        —  Occipital  artery 
,  •  Internal  jugular  vein 

,  ^  Posterior  auricular  artery 
\  Superficial  temporal  artery 
,  .  Deep  auricular  artery 
\  \  Anterior  tympanic  artery 
Middle  meningeal  artery 
Internal  maxillary  artery 
Accessory  meningeal  branch 


External  pterygoid  branch 
Inferior  alveolar  artery 
I  Artery  of  the  pterygoid  canal  (Vidian) 
Posterior  lateral  '    Mylohyoid  branch 

nasal  arteries  ,    , 

Major  palatine  artery    '  Spheno-palatine  artery 
Major  and  minor  palatine  arteries 

(2)  The  anterior  tympanic  artery  [a.  tympanica  anterior]  is  a  long  slender  vessel,  which  runs 
upward  behind  the  condyle  of  the  jaw  to  the  petro-tympanic  (Glaserian)  fissure,  through  which 
it  passes  to  the  interior  of  the  tympanum.  Here  it  supphes  the  fining  membrane  of  that  cavity 
and  anastomoses  with  the  other  tympanic  arteries,  forming  with  the  posterior  tympanic  branch 
of  the  stylo-mastoid  artery  a  vascular  circle  around  the  membrana  tympani.  This  circle  is 
more  distinct  in  the  foetus  than  in  the  adult. 

(3)  The  middle  meningeal  artery  [a.  meningea  media]  is  the  largest  branch  of  the  internal 
ma.xillary  artery.  It  comes  off  from  the  vessel  as  it  hes  between  the  spheno-mandibular  liga- 
ment and  the  ramus  of  the  jaw,  and  under  cover  of  the  external  pterygoid  passes  directly  up- 
ward to  the  foramen  spinosum,  through  which  it  enters  the  interior  of  the  cranium.  In  this 
part  of  its  course  it  is  crossed  by  the  chorda  tympani  nerve;  and  just  before  it  enters  the  foramen 
is  embraced  by  the  two  heads  of  origin  of  the  auriculo-temporal  nerve  (fig.  451). 

The  trunk  of  the  mandibular  division  of  the  fifth  nerve,  as  it  emerges  from  the  foramen 
ovale,  lies  in  front  of  the  artery.  As  the  artery  passes  upward  it  is  surrounded  b3'  filaments  of 
the  sympathetic  nerve,  and  is  accompanied  by  two  veins.  On  entering  the  skull  it  ramifies 
between  the  bone  and  dura  mater,  supplying  both  structures.     It  at  first  ascends  for  a  short 


548  THE  BLOOD-VASCULAR  SYSTEM 

distance  in  a  groove  on  the  greater  wing  of  the  sphenoid,  and  then  divides  into  two  branches,  an 
anterior  and  a  posterior. 

The  anterior  branch  passes  upward,  in  the  groove  on  the  greater  wing  of  the  sphenoid,  on 
to  the  parietal  bone  at  its  anterior  and  inferior  angle;  at  this  spot  the  groove  becomes  deepened 
and  often  bridged  over  by  a  thin  plate  of  bone,  being  converted  for  6  to  12  mm.  (j  to  I  in.)  or 
more  into  a  distinct  canal.  The  situation  of  the  artery  is  here  indicated  on  the  exterior  of  the 
skull  by  a  spot  3.7  cm.  (Ij  in.)  behind,  and  about  2.5  cm.  (1  in.)  above,  the  zygomatic  process 
of  the  frontal  bone.  The  anterior  branch  is  continued  along  the  anterior  border  of  the  parietal 
bone  nearly  as  far  as  the  superior  sagittal  sinus,  and  gives  off  in  its  course,  but  especially  poste- 
riorly, large  branches  which  ramify  in  an  upward  and  backward  direction  in  grooves  on  the  pari- 
etal bone  (fig.  452). 

The  posterior  branch  passes  backward  over  the  squamous  portion  of  the  temporal  bone; 
and  thence  on  to  the  parietal  bone,  behind  the  anterior  branch.  This  branch  and  its  collaterals 
extend  upward  as  far  as  the  sagittal  sinus,  and  backward  as  far  as  the  transverse  (lateral) 
sinus. 

In  addition  to  its  terminal  anterior,  and  terminal  posterior  branches,  the  middle  meningeal 
gives  off: — (a)  Ganglionic  branhecs  to  the  semOunar  (Gasserian)  gangUon  and  its  sheath  of 
dura  mater,  (b)  A  superficial  petrosal  branch  [ramus  petrosus  superficiahs],  which  enters 
the  hiatus  of  the  facial  canal  in  company  with  the  large  superficial  petrosal  nerve  and  anasto- 
moses with  the  terminal  branch  of  the  stylo-mastoid  artery,  (c)  A  superior  tympanic  artery 
[a.  tympanica  superior],  which  enters  the  canal  for  the  tensor  tympani,  and  supplies  that  muscle. 
(d)  An  orbital  or  lacrimal  branch,  which  enters  the  orbit  at  the  outermost  part  of  the  superior 
orbital  (sphenoidal)  fissure,  or  sometimes  through  a  minute  foramen,  just  lateral  to  that 
fissure,  and  anastomoses  with  the  lacrimal  branch  of  the  ophthalmic,  (e)  Anastomotic  or 
perforating  branches  which  pierce  the  greater  wing  of  the  sphenoid  bone,  and  anastomose  with 
the  deep  temporal  arteries. 

(4)  The  inferior  alveolar  artery  [a.  alveolaris  inferior]  (fig.  451),  arising  from  the  internal 
maxillary  as  it  lies  between  the  spheno-mandibular  hgament  and  neck  of  the  jaw,  courses 
downward  to  the  mandibular  foramen,  which  it  enters  in  company  with,  and  a  little  behind 
and  lateral  to,  the  inferior  alveolar  nerve.  It  then  passes  along  the  canal  in  the  interior  of  the 
bone,  giving  off  branches  to  the  molar,  premolar,  and  canine  teeth.  On  reaching  the  mental 
foramen  it  divides  into  two  branches,  the  incisive  and  the  mental.  The  incisive  continues  its 
course  in  the  bone,  supplies  branches  to  the  incisor  teeth,  and  anastomoses  with  the  artery  of 
the  opposite  side.  The  mental  branch  [ramus  mentahs]  passes  through  the  mental  foramen  in 
company  with  the  mental  branch  of  the  inferior  alveolar  (dental)  nerve,  and  emerges  on  the  chin 
under  cover  of  the  quadratus  labii  inferioris.  It  anastomoses  above  with  the  inferior  labial 
(coronary),  and  below  with  the  submental,  and  also  with  the  inferior  labial.  Near  its  origin 
the  artery  gives  off  (a)  a  lingual  or  gustatory  branch,  which  accompanies  and  supplies  the  lingual 
nerve,  and  ends  in  the  mucous  membrane  of  the  mouth;  and,  just  before  it  enters  the  man- 
dibular (dental)  foramen  in  the  lower  jaw,  (6)  a  mylo-hyoidean  branch  [ramus  mylohyoideus], 
which  accompanies  the  nerve  of  that  name  along  the  groove  in  the  lower  jaw,  and,  after  supply- 
ing the  mylo-hyoid  muscle,  anastomoses  with  the  subhngual  and  submental  arteries. 

(5)  The  accessory  or  small  meningeal  branch  [ramus  meningeus  aocessoria]  arises  either 
from  the  internal  maxillary  a  little  in  front  of  the  middle  meningeal,  or  as  a  branch  of  the  latter 
vessel.  It  passes  upward  along  the  com'se  of  the  mandibular  division  of  the  fifth  nerve,  and, 
entering  the  skull  through  the  foramen  ovale,  is  distributed  to  the  semilunar  (Gasserian) 
ganglion,  and  to  the  waUs  of  the  cavernous  sinus  and  the  dura  mater  in  the  neighbourhood. 

Branches  op  the  Second  Part  of  the  Internal  IMaxillary  Artery 

The  branches  of  the  second  portion  of  the  internal  maxillary  all  supply  muscles.  They 
are: — (1)  The  masseteric;  (2)  the  posterior  deep  temporal;  (3)  the  pterygoid;  (4)  the  buccal; 
and  (5)  the  anterior  deep  temporal. 

(1)  The  masseteric  artery  [a.  masseterica]  comes  off  from  the  internal  maxillary  as  the  latter 
is  passing  from  between  the  neck  of  the  jaw  and  the  spheno-mandibular  ligament.  It  passes, 
with  the  masseteric  nerve  tln-ough  the  mandibular  (sigmoid)  notch  in  the  mandible  and  supplies 
the  masseter  muscle.  Some  filaments  perforate  the  muscle  and  anastomose  with  the  transverse 
facial  and  with  the  masseteric  branches  of  the  external  maxillary  (facial). 

(2)  The  posterior  deep  temporal  artery  [a.  temporalis  profunda  posterior]  arises,  as  a  rule, 
from  the  internal  maxillary  in  common  with  the  masseteric  for  a  little  be3'ond  that  branch. 
It  passes  upward  beneath  the  temporal  muscle  in  a  slight  groove  on  the  anterior  margin  of 
the  squamous  portion  of  the  temporal  bone,  supplying  the  temporal  muscle,  the  pericranium 
and  the  external  layer  of  the  bone.     It  anastomoses  with  the  other  temporal  arteries. 

(3)  The  pterygoid  branches  [rami  pterygoidei]  are  short  trunks  which  pass  into  and  supply 
the  internal  and  external  pterygoid  muscles. 

(4)  The  buccal  artery  [a.  buccinatoria]  (fig.  451)  courses  forward  and  downward  with  the 
buccal  nerve  to  the  buccinator  muscle,  lying  in  close  contact  with  the  medial  side  and  anterior 
margin  of  the  tendon  of  the  temporal  muscle  and  coronoid  process  of  the  lower  jaw.  It  supplies 
the  buccinator  muscle  and  mucous  membrane  of  the  mouth,  and  anastomoses  with  the  external 
maxillary  (facial),  transverse  facial,  and  infraorbital  arteries. 

(5)  The  anterior  deep  temporal  artery  [a.  temporalis  profunda  anterior]  ascends  beneath  the 
temporal  muscle  in  a  slight  groove  on  the  greater  wing  of  the  sphenoid  bone.  It  supplies  the 
muscle,  pericranium,  and  subjacent  bone,  and  gives  off  small  branches  which  pass  through 
minute  foramina  in  the  zygomatic  (malar)  bone.  Some  of  these  last  branches  enter  the  orbit 
and  anastomose  with  the  lacrimal  artery;  others  emerge  on  the  face  and  anastomose  with  the 
transverse  facial  artery. 


THE  INTERNAL  CAROTID  ARTERY  549 

Branches  of  the  Third  Part  of  the  Internal  Maxillary  Artery 

The  branches  of  the  third  part  of  the  internal  maxillary  artery,  like  those  of  the  first  part, 
all  pass  through  bony  canals.  They  are  the  following: — (1)  The  posterior  superior  alveolar 
(dental);  (2)  the  infraorbital;  (3)  the  descending  palatine;  (4)  the  artery  of  the  pterygoid  canal 
(Vidian);  and  (5)  the  sphenopalatine. 

(1)  The  posterior  superior  alveolar  (dental)  artery  [a.  alveolaris  superior  posterior]  arises 
from  the  internal  maxiUary  as  the  latter  is  passing  into  tlie  pterygo-palatine  (spheno-maxillary) 
fossa,  and  descends  in  a  tortuous  manner  in  a  gi'oove  on  the  back  of  the  body  of  the  maxilla. 
It  gives  off  branches  to  the  maxillary  sinus,  to  the  molar  and  premolar  teeth,  the  gums,  and  to 
the  buccinator  muscle. 

(2)  The  infraorbital  artery  [a.  infraorbitalis]  arises  from  the  internal  maxillary,  generally 
as  a  common  trunk  with  the  posterior  alveolar  (dental).  It  passes  forward  and  a  little  upward 
through  the  pterygo-palatine  (spheno-maxillary)  fossa;  then  forward  in  company  with  the 
infraorbital  branch  of  the  fifth  nerve,  first  along  the  groove,  and  then  tlirough  the  canal  in  the 
orbital  plate  of  the  maxilla;  and  finally,  emerging  on  the  face  at  the  infraorbital  foramen, 
under  cover  of  the  quadratus  labii  superioris,  is  distributed  to  the  structures  forming  the  upper 
Up,  the  lower  eyeUd,  the  lacrimal  sac,  and  the  side  of  the  nose.  It  anastomoses  with  the 
superior  labial  (coronary)  and  angular  branches  of  the  external  maxillary  (facial),  with  the 
nasal  and  lacrimal  branches  of  the  ophthalmic,  and  with  the  transverse  facial.  It  gives  off 
small  branches  supplying  the  fat  of  the  orbit  and  the  inferior  rectus  and  inferior  oblique  muscles. 
The  anterior  superior  alveolar  branch  [a.  alveolaris  superior  anterior]  passes  downward  through 
a  groove  in  the  anterior  wall  of  the  maxilla,  together  with  the  anterior  alveolar  branch  of  the 
infraorbital  nerve,  and  supplies  branches  to  the  incisor  and  canine  teeth  and  the  mucous 
membrane  of  the  maxillary  sinus.  It  has  also  nasal  branches  which  pass  through  the  foramina 
in  the  nasal  process  of  the  maxiUa. 

(3)  The  descending  palatine  artery  [a.  palatina  descendens]  descends  in  the  pterygo- 
palatine canal  with  the  anterior  palatine  branch  of  the  spheno-palatine  ganglion.  On  emerging 
on  the  palate  at  the  greater  (posterior)  palatine  foramen,  it  divides  into  the  following  branches; 
— (a)  The  major  palatine  artery  [a.  palatina  major],  which  courses  forward  in  the  muco-perios- 
teum  at  the  junction  of  the  hard  palate  with  the  alveolar  process  as  far  as  the  incisive  (anterior 
palatine)  foramen,  where  it  anastomoses  with  the  spheno-palatine  artery;  and  (b)  minor 
palatine  arteries  [aa.  palatina;  minores],  which  pass  backward  and  downward  into  the  soft 
palate,  contributing  to  the  supply  of  that  structure,  and  anastomosing  with  the  ascending 
palatine  artery.  After  the  operation  for  cleft  palate,  serious  heemorrhage  occasionally  occurs 
from  the  descending  palatine  artery.  The  foramen  is  situated  a  little  behind,  and  medial 
to,  the  last  molar  tooth,  and  almost  immediately  in  front  of  the  hamular  process  (fig.  452). 

(4)  The  arteria  canalis  pterygoidei  or  Vidian  artery  is  a  long  slender  branch  which  passes 
backward  through  the  pterygoid  (Vidian)  canal  in  company  with  the  nerve  of  tlie  same  name 
into  the  cartilage  of  the  lacerated  foramen.  It  gives  off  branches  which  supply  the  roof  of  the 
pharynx,  and  anastomose  with  the  ascending  pharyngeal  and  spheno-palatine  arteries;  also  a 
branch  which  is  distributed  to  the  Eustachian  tube;  and  one  which  enters  the  tympanum,  and 
anatomoses  with  the  other  tympanic  arteries. 

(.5)  The  spheno-palatine  [a.  sphenopalatina],  the  terminal  branch  of  the  internal  maxillary, 
passes  with  the  naso-palatine  branch  of  the  spheno-palatine  ganglion  from  the  pterygo-palatine 
(spheno-maxillary)  fossa  into  the  nose  through  the  spheno-palatine  foramen.  Crossing  the 
roof  of  the  nose  in  the  muco-periosteum,  it  passes  on  to  the  septum,  and  then  runs  forward  and 
downward  in  a  groove  on  the  vomer  toward  the  incisive  (anterior  palatine)  foramen,  where  it 
anastomoses  with  the  anterior  palatine  artery,  which  enters  the  nose  through  the  lateral  com- 
partment of  that  foramen  (the  canal  of  Stenson).  In  this  course  it  gives  off  branches  to  the  roof 
and  contiguous  portions  of  the  pharynx,  and  to  the  sphenoidal  cells.  It  has  also  posterior 
lateral  nasal  branches  [aa.  nasales  post,  laterales],  which  ramify  over  the  nasal  conchse  (tur- 
binate bones)  and  lateral  walls  of  the  nose,  and  give  twigs  to  the  ethmoidal  and  frontal  sinuses 
and  the  Uning  membrane  of  the  maxillary  sinus;  and  posterior  septal  branches  [aa.  nasales 
post,  septi],  which  run  upward  and  forward,  giving  small  twigs  to  the  mucous  membrane  cover- 
ing the  upper  part  of  the  septum,  and  which  pass  through  the  cribriform  plate  of  the  ethmoid, 
and  anastomose  with  the  ethmoidal  arteries  (perforating  or  meningeal  branches). 

THE  INTERNAL  CAROTID  ARTERY 

The  internal  carotid  artery  [a.  carotis  interna]  (figs.  453  and  454)  arises  with 
the  external  carotid  at  the  bifurcation  of  the  common  carotid,  opposite  the  upper 
border  of  the  thyreoid  cartilage,  on  a  level  with  the  fourth  cervical  vertebra.  It 
is  at  first  placed  a  little  lateral  to  the  external  carotid,  but  as  it  ascends  in  the  neck 
the  external  carotid  becomes  more  superficial  and  in  front  of  the  internal.  The 
internal  carotid  passes  up  the  neck,  in  front  of  the  transverse  processes  of  the  upper 
cervical  vertebrae,  lying  upon  the  longus  capitis  (rectus  capitis  ant.  major),  to  the 
carotid  foramen,  thence  through  the  carotid  canal  in  the  petrous  portion  of  the 
temporal  bone,  making  at  first  a  forward  and  medial  turn  and  then  a  second  turn 
upward,  and  enters  the  cranium  through  the  foramen  lacerum.  It  makes  a  sig- 
moid curve  on  the  side  of  the  body  of  the  sphenoid  bone,  and  terminates,  after 
perforating  the  dura  mater,  by  dividing  opposite  the  anterior  clinoid  processes 


{ 


550 


THE  BLOOD-VASCULAR  SYSTEM 


in  the  lateral  fissure  (fissure  of  Sylvius) j  into  the  anterior  and  middle  cerebral 
arteries. 

In  its  course  up  the  neck  it  often  forms  one  or  more  curves,  especially  in  old 
people.  Between  the  internal  and  the  external  carotids,  at  their  angle  of  diver- 
gence, is  situated  the  carotid  body  or  gland  [glomus  caroticum]. 

The  internal  carotid  is  the  continuation  upward  of  the  primitive  dorsal  aorta, 
and  supplies  the  greater  part  of  the  brain,  the  contents  of  the  orbit,  and  parts  of 
the  internal  ear,  forehead,  and  nose.  It  is  divided  into  three  portions: — (1)  a 
cervical;  (2)  a  petrosal;  and  (3)  an  intracranial. 

1.  The  Cervical  Portion 

Relations. — In  the  neck  (fig.  453)  the  artery  is  at  first  comparatively  superficial,  having 
in  front  of  it,  as  it  lies  in  the  superior  carotid  triangle,  the  skin,  superficial  fascia,  platysma  and 

Fig.  453. — The  Carotid  Arteries.     (After  Toldt,  ''Atlas  of  Human  Anatomy,"  Rebman  Lon- 
don and  New  York.) 
Anterior  deep  temporal  artery 
Lacrimal  gland 
Posterior  deep  temporal  artery  Lateral  palpebral  arteries 

Temporal  muscle    \  \  *,       \ 


Supraorbital  artery 

Frontal  artery 

Dorsal  nasal  artery 


Masseteric 
artery 
External 
pterygoid 
muscle 
Middle  tem- 
poral artery 
Middle  men 
ingeal  artery  "^-.^V 
Superficial  tern-        \^ 


poral  artery 
Internal  maxil-        , 

lary  artery       -     \ 
Inferior  alveolar 

artery 
Spheno-mandibular 

ligament 
Stylomastoid  artery 
Inferior  alveolar 

Posterior  auricular 
artery 
Mylohyoid  branch. 

Posterior  belly  of 
digastric  muscle 

Internal  pterygoid  muscle 
Lingual  nerve 
Buccinator  artery 
Occipital  artery    '' 
External  carotid  artery 
External  maxillary  artery 
Sternocleidomastoid  artery  ,' 

Lingual  artery  ''  /'' 
Hyoglossus  muscle''     ^ 
Hyothyreoid  membrane   '  / 
Superior  thyreoid  artery   '  / 
Internal  carotid  artery 
Posterior  branch 

Anterior  branch 
Common  carotid  artery 

Thyreohyoid  muscle 


Infraorbital  artery 


Superior  pos- 
terior alve- 
olar artery 


Inferior  labial 
artery 


~~^  Mylohyoid  muscle 
■-^External  maxillary 
artery 
Submental  artery 


^  ThiiTreohyoid  muscle 

.^      Hyoid  branch  of  the  lingual  artery 

Superior  laryngeal  artery 

Crico-thyreoid  branch 
Middle  crico-thyreoid  ligament 


deep  fascia,  and  the  overlapping  edge  of  the  sterno-mastoid  muscle.  Higher  up,  as  it  sinksHDe- 
neath  the  parotid  gland,  it  becomes  deeply  placed,  and  is  crossed  by  the  posterior  belly  of  the 
digastric  and  stylo-hyoid  muscles,  the  hypoglossal  nerve,  and  the  occipital  and  posterior  auricu- 
lar arteries;  whilst  still  higher  it  is  separated  from  the  external  carotid  artery,  which  here  gets 


THE  INTRACRANIAL  PORTION 


551 


in  front  of  it,  by  the  stylo-glossus  and  stylo-pharyngeus  muscles,  the  glosso-pharyngeal  nerve, 
the  pharyngeal  branch  of  the  vagus  nerve,  and  by  the  stylo-hyoid  ligament. 

Behind,  it  hes  upon  the  longus  capitis  (rectus  capitis  anticus  major),  which  separates  it 
from  the  transverse  processes  of  the  three  upper  cervical  vertebrae,  on  the  superior  cervical 
ganglion  of  the  sympathetic  nerve,  and  on  the  vagus  nerve.  Near  the  base  of  the  skull,  the 
hypofilossal,  vasus,  glosso-pharyngeal,  and  spinal  accessory  nerves  cross  obhquely  behind  it, 
separating  it  here  from  the  internal  jugular  vein,  which,  as  the  artery  is  about  to 
enter  the  carotid  canal,  also  forms  one  of  its  posterior  relations. 

On  its  lateral  side  are  the  internal  jugular  vein  and  vagus  nerve. 

On  its  medial  side  it  is  in  relation  with  the  pharynx,  the  superior  constrictor  muscle  separat- 
ing it  from  the  tonsil.  The  ascending  pharyngeal  and  ascending  palatine  arteries,  and  at  the  base 
of  the  skull  the  Eustachian  tube  and  levator  palati  muscles,  are  also  medial  to  it. 

2.  Thf  Petrosal  Portion 

The  petrosal  portion  (fig.  454)  is  situated  in  the  carotid  canal  in  the  petrous  portion  of  the 
temporal  bone.  It  is  here  separated  from  the  walls  of  the  canal  by  a  prolongation  downward 
of  the  dura  mater.  In  this  part  of  its  course  it  first  ascends  in  front  of  the  tympanum  and 
cochlea  of  the  internal  ear;  it  then  turns  forward  and  medially,  lying  a  little  medial  to  and 
behind  the  Eustachian  tube,  and  enters  the  cranial  cavity  by  turning  upward  through  the  fora- 


FiG.  454. — The  Internal  Carotid  Artert  in  the  Canal. 


Superficial  petrosal  branch 


(After  Spalteholz.) 

Superior  ophthalmic  vein 
Cavernous  sinus 


Superior 
tympanic  artery 


Anterior  tympanic 
artery 


_«  Jugular  fossa 
— -Longus  capitis  muscle 
Inferior  tympanic  artery 
.^Internal  carotid  artery 


Ascending  pharyngeal 
artery 


men  lacerum,  lying  upon  the  Ungula  of  the  sphenoid  bone.  In  this  part  of  its  course  it  is  accom- 
panied by  the  ascending  branches  from  the  superior  cervical  ganghon  of  the  sympathetic. 
These  form  a  plexus  about  the  artery,  but  are  situated  chiefly  on  its  lateral  side.  It  is  also 
surrounded  by  a  number  of  small  veins,  which  receive  tributaries  from  the  tympanum  and  open 
into  the  cavernous  sinus  and  internal  jugular  vein. 


3.  The  Intracranial  Portion 

On  entering  the  cranium  through  the  foramen  lacerum,  the  internal  carotid  first  ascends 
to  reach  the  lateral  part  of  the  body  of  the  sphenoid  medial  to  the  hngula.  It  then  follows 
the  carotid  sulcus  forward  and  slightly  downward  along  the  medial  waU  of  the  cavernous  smus 
(fig.  454).  Here  it  has  the  sixth  nerve  immediately  lateral  to  it,  and  is  covered  by  the  hning 
membrane  of  the  sinus.  Again  turning  upward,  it  pierces  the  dura  mater  on  the  medial  side 
of  the  anterior  clinoid  process,  and,  passes  between  the  second  and  third  nerves  to  the  anterior 
perforated  substance.  At  the  medial  end  of  the  lateral  (Sylvian)  fissure  it  pierces  the  arachnoid 
and  divides  into  its  two  terminal  branches,  the  anterior  and  middle  cerebral.     As  it  hes  in  the 


552  THE  BLOOD-VASCULAR  SYSTEM 

foramen  laoerum  the  artery  is  crossed  on  its  lateral  side  by  the  great  superficial  petrosal  nerve 
as  the  latter  goes  to  join  the  great  deep  petrosal  from  the  carotid  plexus  to  form  the  nerve  of 
the  pterygoid,  canal  (Vidian). 

Branches  of  the  Internal  Carotid  Artery 

The  cervical  portion  gives  off  no  branch.  The  petrosal  portion  gives  off  the 
caroticotympanic.  The  branches  of  the  intracranial  portion  are : — (2)  ophthalmic ; 
(3)  posterior  communicating;  (4)  chorioid;  (5)  anterior  cerebral;  (6)  middle 
erebral. 

As  the  internal  carotid  artery  lies  on  the  medial  side  of  the  cavernois  sinus,  it  also  gives  off 
the  following  small  branches — branches  to  the  walls  of  the  cavernous  inus;  to  the  pituitary  body; 
to  the  semilunar  (Gasserian)  ganglion;  to  the  dura  mater.  These  anastomose  with  anterior 
branches  of  the  middle  meningeal. 

1.  THE  CAROTICOTYMPANIC  ARTERY 

The  caroticotympanic  enters  the  tympanum  through  a  small  foramen  in  the 
posterior  wall  of  the  carotid  canal,  and  contributes  its  quota  to  the  blood-supply  of 
that  cavity.  It  anastomoses  with  the  tympanic  branches  of  the  stylo-mastoid, 
internal  maxillary,  and  middle  meningeal  arteries. 

2.  THE  OPHTHALMIC  ARTERY 

The  ophthalmic  artery  (fig.  455)  comes  off  from  the  internal  carotid  immedi- 
ately below  the  anterior  clinoid  process  just  as  the  latter  vessel  is  passing  through 
the  dura  matter.  Entering  the  orbit  through  the  optic  foramen  below  and  lateral 
to  theo  ptic  nerve,  it  at  once  perforates  the  sheath  of  dura  mater  which  is  prolonged 
through  the  optic  foramen  on  both  artery  and  nerve.  It  then  runs  in  a  gentle 
curve  with  a  lateral  convexity  below  the  optic  nerve  and  lateral  rectus,  being  here 
crossed  by  the  naso-ciliary  (nasal)  nerve.  Turning  forward  and  upward,  it 
passes  over  the  optic  nerve,  to  its  medial  side.  Thence  it  runs  obHquely  beneath 
the  superior  rectus  in  front  of  the  naso-ciliary  (nasal)  nerve  under  the  lower  border 
of  the  superior  oblique,  but  above  the  medial  rectus,  and  continues  its  course  under 
the  pulley  for  the  superior  oblique  and  reflected  tendon  of  that  muscle  to  the 
medial  palpebral  region,  where  it  divides  into  the  frontal  and  nasal  branches. 

Branches  of  the  Ophthalmic  Artery 

The  branches  of  the  ophthalmic  artery  are: — (1)  the  lacrimal;  (2)  the  supra- 
orbital; (3)  the  central  artery  of  the  retina;  (4)  the  muscular;  (5)  the  ciliary; 
(6)  the  posterior  ethmoidal;  (7)  the  anterior  ethmoidal;  (8)  the  medial  palpe- 
bral; (9)  the  frontal;  and  (10)  the  dorsal  nasal. 

(1)  The  lacrimal  artery  [a.  laorimalis],  is  usually  the  first  and  often  the  largest  branch  9f 
the  ophthalmic.  It  arises  between  the  superior  and  lateral  rectus  on  the  lateral  side  of  the  optic 
nerve  from  the  ophthalmic,  soon  after  that  vessel  has  entered  the  orbit.  At  times  it  is  given 
off  from  the  ophthalmic  outside  the  orbit,  and  then  usually  passes  into  that  cavity  through  the 
superior  orbital  (sphenoidal)  fissure.  It  runs  forward  along  the  lateral  waO  of  the  orbit  with 
the  lacrimal  nerve,  above  the  upper  border  of  the  lateral  rectus,  to  the  lacrimal  gland,  which 
it  supplies.  In  this  course  it  furnishes  the  following  branches: — (a)  Recurrent,  one  or  more 
branches  which  pass  backward  through  the  superior  orbital  (sphenoidal)  fissure,  and  anasto- 
mose with  the  lacrimal  branch  of  the  middle  meningeal  artery.  The  anastomosis  is  sometimes 
of  large  size,  and  then  takes  the  chief  share  in  the  formation  of  the  lacrimal  artery,  (b)  Mus- 
cular branches,  distributed  chiefly  to  the  lateral  rectus,  (c)  Zygomatic  branches — small  twigs, 
which  pass  through  the  zygomatico-orbital  (malar)  canals,  and  anastomose  with  the  orbital 
branch  of  the  middle  temporal,  and  with  the  transverse  facial  on  the  cheek,  (d)  Lateral 
palpebral  arteries  [aa.  palpebrales  laterales]  which  are  distributed  to  the  upper-  and  lower 
eyelids  and  to  the  conjunctiva,     (e)  Ciliary.     See  Ciliary  Arteries,  page  553. 

(2)  The  supraorbital  artery  [a.  supraorbitaHs]  usually  arises  from  the  ophthalmic  as  the  latter 
vessel  is  about  to  cross  over  the  optic  nerve.  Passing  upward  to  the  medial  side  of  the  superior 
rectus  and  levator  palpebrse,  it  runs  along  the  upper  surface  of  the  latter  muscle  with  the 
frontal  nerve  in  the  orbital  fat,  but  beneath  the  periosteum,  to  the  supraorbital  notch.  On 
emerging  on  the  forehead  beneath  the  orbicularis  ocuU,  it  divides  into  a  superficial  and  deep 
branch,  the  former  ramifies  between  the  skin  and  epicranius  (occipito-frontahs),  the  latter 


BRANCHES  OF  THE  OPHTHALMIC  ARTERY 


553 


between  the  epicranius  and  the  pericranium.  Both  branches  anastomose  with  the  anterior 
branches  of  the  superficial  temporal,  the  angular  branch  of  the  external  maxillary  (facial), 
and  the  transverse  facial  artery.  The  branches  of  the  supraorbital  are: — (o)  periosteal,  to 
the  periosteum  of  the  roof  of  the  orbit;  (6)  muscular,  to  the  levator  palpebra;  and  superior  rectus; 

(c)  diploic,  given  off  as  the  artery  is  passing  through  the  supraorbital  notch  and,  entering  a 
minute  foramen  at  the  bottom  of  the  notch,  is  distributed  to  the  diploe  and  frontal  sinuses; 

(d)  trochlear,  to  the  pulley  of  the  superior  obhque;  (e)  palpebral,  to  the  upper  eyehd. 

(3)  The  arteria  centralis  retinae,  a  small  but  constant  branch,  comes  off  from  the  oph- 
thalmic close  to  the  optic  foramen,  and,  perforating  the  optic  nerve  about  6  mm.  (\  in.)  behind 
the  globe,  runs  forward  in  (the  substance  of  the  nerve)  to  the  eyeball,  supplying  the  retina. 
Its  further  description  is  given  in  the  section  on  the  Eye. 

(4)  The  muscular  branches  [rami  musculares]  are  very  variable  in  their  origin  and  distri- 
bution. They  may  be  roughly  divided  into  superior  and  inferior  sets.  The  superior  or  smaller 
set  supply  the  superior  oblique,  the  levator  palpebra3,  and  superior  rectus.  The  inferior  pass 
forward,  between  the  optic  nerve  and  the  inferior  rectus,  supplying  that  muscle,  the  medial 
rectus,  and  the  inferior  oblique.  From  the  muscular  branches  are  given  off  the  anterior  ciliary 
arteries.     (See  Ciliary  Arteries.) 

(5)  The  ciliary  arteries  are  divided  into  three  sets: — The  short  posterior,  the  long  posterior, 
and  the  anterior,  (i)  The  short  posterior  [aa.  oiliares  posteriores  breves],  five  or  six  in  number, 
come  off  chiefly  from  the  ophthalmic  as  it  is  crossing  the  optic  nerve.     They  run  forward  about 


Fig.  45.5. — The  Left  Ophtii.'vlmic  Artery  and  Vein. 


Supraorbital  artery 
Lacrimal  gland 
Superior  rectus,  cut — pr; 
Eyeball 


Lateral  rectus 

Lacrimal  artery 

Superior  rectus,  cut 
Inferior  ophthalmic 
Superior  ophthalmic 

Optic  nerve 

Superior  ophthalmic 


Commencement   of  superior 
ophthalmic  vein 


Reflected  tendon  of  superior  oblique 
Ophthalmic  artery 


Anterior  ethmoidal  artery 


Posterior  ethmoidal  artery 

Ciliary  arteries 

Levator  palpebrse,  cut 
Annulus  communis  (of  Zinn) 
Ophthalmic  artery 

Optic  commissure 


Internal  carotid  artery 

the  nerve,  dividing  into  twelve  or  fifteen  smaU  vessels,  which  perforate  the  sclerotic  around 
the  entrance  of  the  optic  nerve,  and  are  distributed  to  the  chorioid  coat,  (ii)  The  long  posterior 
ciUary  arteries  [aa.  ciliares  posteriores  longte],  usually  two,  sometimes  three,  in  number,  come  off 
from  the  ophthalmic  on  either  side  of  the  optic  nerve,  and  run  forward  with  the  short  ciliary  to 
the  sclerotic.  On  piercing  the  sclerotic,  they  course  forward,  one  on  either  side  of  the  eyeball 
between  the  sclerotic  and  the  chorioid  to  the  ciliary  processes  and  iris.  Their  further  distribu- 
tion is  given  under  the  anatomy  of  the  Eye.  (iii)  The  anterior  ciliary  arteries  [aa.  ciliares  an- 
teriores]  are  derived  from  the  muscular  branches  and  from  the  lacrimal.  They  run  to  the  globe 
along  the  tendons  of  the  recti,  forming  a  zone  of  radiating  vessels  beneath  the  conjunctiva. 
Some  of  them,  the  episcleral  arteries  [aa.  episclerales] ;  perforate  the  sclerotic  about  6  mm. 
(-f  in.)  behind  the  cornea,  and  supply  the  iris  and  ciUary  processes.  It  is  these  vessels  that  are 
enlarged  and  congested  in  iritis,  forming  the  circumcorneal  zone  of  redness  so  characteristic  of 
that  disease.  They  then  differ  from  the  tortuous  vessels  of  the  conjunctiva  in  that  they  are 
straight  and  parallel.  The  remainder  constitute  the  anterior  conjunctival  arteries  [aa.  oon- 
junctivales  anteriores]. 

(6)  The  posterior  ethmoidal  artery  [a.  ethmoidalis  posterior]  (fig.  455)  runs  medially  be- 
tween the  superior  oblique  and  medial  rectus,  and,  leaving  the  orbit  by  the  posterior  ethmoidal 
canal,  together  with  the  posterior  ethmoidal  branch  of  the  naso-ciliary  (nasal)  nerve,  enters 
the  posterior  ethmoidal  cells,  whence  it  passes  through  a  transverse  slit-hke  aperture  between 
the  sphenoid  bone  and  cribriform  plate  of  the  ethmoid  bone  into  the  cranium.  It  gives  off  (a) 
ethmoidal  branches  to  the  posterior  ethmoidal  cells;  (6)  meningeal  branches  to  the  dura  mater 
lining  the  cribriform  plate;  and  (c)  nasal  branches,  which  pass  through  the  cribriform  plate  to 


( 


\ 


554  THE  BLOOD-VASCULAR  SYSTEM 

the  superior  meatus  and  upper  spongy  bones  of  the  nose,  and  anastomose  with  the  nasal  branches 
of  the  spheno-palatine  artery  (fig.  452). 

(7)  The  anterior  ethmoidal  artery  [a.  ethmoidahs  anterior]  (fig.  452),  a  larger  branch 
than  the  posterior  ethmoidal,  arises  in  front  of  the  latter,  passes  medially  between  the  superior 
obhque  and  medial  rectus,  and,  leaving  the  orbit  through  the  anterior  ethmoidal  canal,  in  com- 
pany with  the  anterior  ethmoidal  nerve,  enters  the  cranial  cavity.  After  running  a  short  dis- 
tance beneath  the  dura  mater  on  the  cribriform  plate  of  the  ethmoidal  bone,  it  passes  into  the 
nose  through  the  horizontal  slit-hke  aperture  by  the  side  of  the  crista  gaUi.  Its  terminal 
branch  passes  along  the  groove  on  the  under  surface  of  the  nasal  bone,  and  emerges  on  the  nose 
between  the  bone  and  lateral  cartilage,  terminating  in  the  skin  of  that  organ.  It  gives  off  the 
following  branches  in  its  course: — (i)  Ethmoidal,  to  the  anterior  ethmoidal  cells;  (ii)  anterior 
meningeal  artery,  [a.  meningea  anterior]  to  the  dura  mater  of  the  anterior  fossa;  (iii)  nasal, 
to  the  middle  meatus  and  anterior  part  of  the  nose;  (iv)  frontal,  to  the  frontal  sinuses;  (v) 
cutaneous,  or  terminal,  to  the  skin  of  the  nose. 

(8)  The  medial  palpebral  arteries  [aa.  palpebrales  mediales]  arise  either  separately  or  by  a 
common  trunk  from  the  ophthalmic  artery  opposite  the  pulley  for  the  superior  obhque,  just 
as  the  latter  vessel  is  about  to  divide  into  its  terminal  branches.  They  pass,  one  above  and 
one  below,  the  medial  palpebral  hgament  and  then  skirt  along  the  upper  and  lower  eyelids 
respectively,  near  the  free  margin  between  the  palpebral  tarsi  and  the  orbicularis  muscle, 
and  form  a  superior  and  an  inferior  tarsal  arch  [arcus  tarsus  superior  et  inferior]  by  anastomosing 
with  the  lateral  palpebral  branches  of  the  lacrimal.  The  upper  also  anastomoses  with  the  supra- 
orbital artery  and  orbital  branch  of  the  temporal  artery;  the  lower  with  the  infraorbital,  the 
angular  branch  of  the  external  maxillary  (facial),  and  the  transverse  facial  arteries.  A  branch 
from  the  lower  palpebral  passes  with  the  ductus  nasolacrimalis  as  far  as  the  inferior  meatus. 
Small  twigs,  the  posterior  conjunctival  arteries  [aa.  conjunctivales  posteriores],  are  also  given 
to  the  caruncula  lacrimahs  and  conjunctiva. 

(9)  The  frontal  artery  [a.  frontalis],  the  upper  of  the  terminal  branches  of  the  ophthalmic, 
pierces  the  superior  tarsus  at  the  medial  angle  of  the  orbit,  passes  upward  over  the  frontal  bone 

.beneath  the  orbicularis  ocuh,  supphes  the  structures  in  its  neighbourhood,  and  anastomoses 
with  its  feUow  of  the  opposite  side,  with  the  supraorbital,  and  with  the  anterior  division  of  the 
superficial  temporal  artery. 

(10)  The  dorsal  nasal  [a.  dorsahs  nasi],  the  lower  of  the  terminal  branches  of  the  ophthalmic, 
leaves  the  orbit  at  the  medial  angle  by  perforating  the  tarsus  above  the  medial  palpebral  liga- 
ment. It  then  descends  along  the  dorsum  of  the  nose,  beneath  the  integuments,  and  anasto- 
moses with  the  angular  and  lateral  nasal  branches  of  the  external  maxillary  (facial).  It  gives 
off  a  lacrimal  branch  as  it  crosses  the  lacrimal  sac,  and  a  transverse  nasal  branch  as  it  crosses 
the  root  of  the  nose;  the  latter  vessel  anastomoses  with  its  fellow  of  the  opposite  side. 

3.  THE  POSTERIOR  COMMUNICATING  ARTERY 

The  posterior  communicating  artery  [a.  communicans  posterior]  (fig.  456)  is 
given  off  from  the  internal  carotid  just  before  the  division  of  that  vessel  into  the 
anterior  and  middle  cerebral  arteries;  occasionally  it  arises  from  the  middle  cere- 
bral itself. 

It  is  as  a  rule  a  slender  vessel  which  runs  backward  over  the  optic  tract  and  pedunculus 
cerebri  along  the  side  of  the  hippocampal  gyrus  to  join  the  posterior  cerebral.  At  times,  how- 
ever, it  is  of  considerable  size,  and  contributes  chiefly  to  form  the  posterior  cerebral,  the  portion 
of  the  latter  vessel  between  the  basilar  and  posterior  communicating  being  then  as  a  rule  reduced 
to  a  mere  rudiment.  It  gives  off  the  following  branches: — (a)  the  hippocampal,  to  the  gyrus 
of  that  name;  and  (6)  the  middle  thalamic,  to  the  optic  thalamus. 

4.  THE  CHORIOID  ARTERY 

The  chorioid  artery  [a.  chorioidea]  is  a  small  but  constant  vessel  which  arises 
as  a  rule  from  the  back  part  of  the  internal  carotid  just  lateral  to  the  origin  of  the 
posterior  communicating. 

It  passes  backward  on  the  optic  tract  and  the  pedunculus  cerebri,  at  first  lying  parallel  and 
lateral  to  the  posterior  communicating  artery.  It  then  dips  under  the  edge  of  the  uncinate 
gyrus  and,  entering  the  chorioid  fissure  at  the  lower  end  of  the  inferior  cornu  of  the  lateral 
ventricle,  ends  in  the  chorioid  plexus  and  supplies  the  hippocampus  and  fimbria. 

5.  THE  ANTERIOR  CEREBRAL  ARTERY 

The  anterior  cerebral  artery  [a.  cerebri  anterior]  (figs.  456,  459),  one  of  the 
terminal  branches  into  which  the  internal  carotid  divides  in  the  lateral  fissure 
(fissure  of  Sylvius),  supplies  a  part  of  the  cortex  of  the  frontal  and  parietal  lobes 
of  the  brain  and  a  small  part  of  the  basal  ganglia.  It  passes  at  first  anteriorly  and 
medially  across  the  anterior  perforated  substance  between  the  olfactory  and  optic 
nerves  to  the  longitudinal  fissure  where  it  approaches  its  fellow  of  the  opposite  side 


CIRCULUS  ARTERIOSUS 


555 


and  communicates  with  it  by  a  short  transverse  trunk,  about  five  mm.  long,  known 
as  the  anterior  communicating  artery  [a.  communicans  anterior]  (fig.  456).  On- 
ward from  this  point  it  runs  side  by  side  with  its  fellow  in  the  longitudinal  fissure 
round  the  genu  of  the  corpus  callosum;  then,  turning  backward,  it  continues  along 
the  upper  surface  of  that  commissure,  and,  after  giving  off  large  branches  to  the 
frontal  and  parietal  lobules,  anastomoses  with  the  posterior  cerebral  artery. 

6.  THE  MIDDLE  CEREBRAL  ARTERY 

The  middle  cerebral  artery  [a.  cerebri  media]  (figs.  456,  460),  the  larger  of  the 
terminal  divisions  of  the  internal  carotid,  supplies  the  basal  ganglia  and  a  part  of 
the  cortex  of  the  frontal  and  parietal  lobes.  It  passes  obliquely  upward  and 
lateralward  into  the  lateral  (Sylvian)  fissure,  and  opposite  the  insula  divides  into 
cortical  branches. 


CiEcuLus  Arteriosus 

The  four  arteries  which  supply  the  brain,  namely,  the  two  internal  carotid 
arteries  and  the  two  vertebrals  (which  unite  to  form  the  basilar),  form  a  remark- 

FiG.  456. — -The  Arteries  of  the  Brain. 
(The  cerebellum  has  been  out  away  on  the  left  side  to  show  the  posterior  part  of  the  cere- 
brum.    From  a  preparation  in  the  Museum  of  St.  Bartholomew's  Hospital.) 


Anterior  cerebral, 
artery 


Middle  cerebral 

artery 
Internal  carotid. 

artery 
Postero-median 

perforating 
Posterior  cere- 
bral artery 
Superior  cerebel- 
lar artery 
Anterior  inferior 
cerebellar  artery 


Vertebral  artery 


Anterior  commu- 
nicating artery 
Antero-lateral 

perforating 
Chorioid 

Posterior  com- 
municating artery 

Posterior  chorioid 

Basilar  artery 

Hum,  cut 


Anterior  spinal 
artery 


able  anastomosis  at  the  base  of  the  brain  known  as  the  circle  of  Willis  [circulus 
arteriosus  (WilHsi)].  This  so-called  circle,  which  has  really  the  form  of  a  heptagon, 
is  formed,  in  front,  by  the  anterior  communicating  artery  uniting  the  anterior 
cerebral  arteries  of  opposite  sides;  laterally,  by  the  internal  carotids  and  the 
posterior  communicating  arteries  stretching  between  these  and  the  posterior 
cerebrals;  behind,  by  the  two  posterior  cerebrals  diverging  from  the  bifurcation  of 
the  basilar  artery  (fig.  456). 

This  free  anastomosis  between  the  two  internal  carotid  and  the  two  vertebral  arteries 
serves  to  ecjuaUse  the  flow  of  blood  to  the  various  portions  of  the  brain;  and,  should  one  or  more 
of  the  arteries  entering  into  the  formation  of  the  circle  be  temporarily  or  permanently  obstructed, 
it  ensures  a  flow  of  blood  to  the  otherwise  deprived  part  through  some  of  the  collateral  arteries. 
Thus,  if  one  carotid  or  one  vertebral  is  obstructed,  the  parts  suppHed  by  that  vessel  receive 
their  blood  through  the  circle  from  the  remaining  pervious  vessels.  Indeed,  one  vertebral 
artery  alone  has  been  found  equal  to  the  task  of  carrying  sufBcient  blood  for  the  supply  of  the 


> 


556  THE  BLOOD-VASCULAR  SYSTEM 

brain  after  ligature  of  both  the  carotids  and  the  other  vertebral  artery.  Further,  the  circle  of 
Willis  is  the  only  medium  of  communication  between  the  ganglionic  or  central  and  the  peripheral 
or  cortical  branches  of  the  cerebral  arteries,  and  between  the  various  ganglionic  branches  them- 
selves. The  ganglionic  and  the  cortical  branches  form  separate  and  distinct  systems,  and  do 
not  anastomose  with  each  other;  and  the  ganglionic,  moreover,  are  so-called  end-vessels,  and  do 
not  anastomose  with  the  neighbouring  ganglionic  branches.  The  three  cerebral  arteries, 
anterior,  middle,  and  posterior  may  be  regarded  as  branches  of  the  circle  of  Willis.  (For  details 
concerning  the  distribution  of  the  cerebral  arteries  see  p.  562.) 

THE  SUBCLAVIAN  ARTERY 

The  subclavian  artery  on  the  right  side  [a.  subclavia  dextra]  arises  at  the  bifur- 
cation of  the  innominate  opposite  the  upper  limit  of  the  right  sterno-clavicular 
articulation.  On  the  left  side  it  arises  from  the  arch  of  the  aorta,  and,  as  far  as  the 
medial  border  of  the  scalenus  anterior,  is  situated  deeply  in  the  chest.  The  first 
portion  of  the  left  subclavian  artery  is  described  separately. 

Beyond  the  medial  border  of  the  scalenus  anterior  the  artery  has  the  same  rela- 
tions on  both  sides.  It  courses  from  this  point  beneath  the  clavicle  in  a  slight 
curve  across  the  root  of  the  neck  to  the  lateral  border  of  the  first  rib,  there  to  end 
in  the  axillary  artery.  Thus  the  course  of  the  artery  in  the  neck  will  be  indicated 
by  a  line  drawn  from  the  sterno-clavicular  joint  in  a  curve  with  its  convexity 
upward  to  the  middle  of  the  clavicle.  The  height  to  which  the  artery  rises  in  the 
neck  varies.  It  is  perhaps  most  commonly  about  1.2  cm.  (|  in.)  above  the  clavicle. 
If  the  cm-ved  line  above  mentioned  is  drawn  to  represent  part  of  the  circumference 
of  a  circle  having  its  center  at  a  point  on  the  lower  margin  of  the  clavicle  3.7  cm. 
d^  in.)  from  the  sternal  end  of  that  bone,  the  line  of  the  artery  will  be  sufficiently 
well  indicated  for  all  practical  purposes.  In  its  course  the  artery  arches  over  the 
dome  of  the  pleura  and  gains  the  groove  on  the  upper  surface  of  the  first  rib  by 
passing  between  the  scalenus  anterior  and  medius  muscles.  The  artery  is  accom- 
panied by  the  subclavian  vein,  the  latter  vessel  lying  in  front  of  the  scalenus 
anterior,  anterior  to  the  artery,  and  on  a  slightly  lower  plane. 

The  subclavian  artery  is  divided  into  three  portions — as  it  lies  medial  to,  pos- 
terior to,  or  lateral  to,  the  scalenus  anterior  muscle. 

THE  FIRST  OR  THORACIC  PORTION  OF  THE  LEFT 
SUBCLAVIAN  ARTERY 

The  left  subclavian  artery  [a.  subclavia  sinistra]  (fig.  457)  arises  from  the  left 
end  of  the  arch  of  the  aorta.  The  first  part  of  the  left  subclavian  is  consequently 
longer  than  the  first  part  of  the  right,  which  arises  at  the  bifurcation  of  the 
innominate  artery.  The  artery  at  its  origin  is  situated  deeply  in  the  thorax, 
and  as  it  arises  from  the  aorta  is  on  a  plane  posterior  to  and  a  little  to  the  left  of 
the  thoracic  portion  of  the  left  common  carotid.  It  first  ascends  almost  vertically 
out  of  the  chest,  and  at  the  root  of  the  neck  curves  laterally  over  the  apex  of  the 
left  plem-a  and  lung  to  the  interval  between  the  anterior  and  middle  scalene  mus- 
cles. Beyond  the  medial  border  of  the  scalenus  anterior — that  is,  in  the  second 
and  third  portions  of  its  course — its  relations  are  similar  to  those  of  the  right  sub- 
clavian artery. 

Relations. — In  front  it  is  covered  by  the  left  pleura  and  lung,  whilst  more  superficial  are 
the  sterno-thyreoid,  sterno-hyoid,  and  sterno-mastoid  muscles.  It  is  crossed  a  Uttle  above  its 
origin  by  the  left  innominate  vein,  and  higher  in  the  neck  near  the  scalenus  anterior  by  the 
internal  jugular,  vertebral,  and  subclavian  veins.  The  phrenic  nerve  crosses  the  artery  imme- 
diately medial  to  the  scalenus  anterior,  and  then  descends  parallel  to  it,  but  on  an  anterior  plane, 
to  cross  the  arch  of  the  aorta.  The  vagus  nerve  descends  parallel  to  the  artery  between  it  and 
the  left  common  carotid,  coming  into  contact  with  its  anterior  surface  just  before  crossing  the 
arch  of  the  aorta.  The  left  cervical  cardiac  nerves  of  the  sympathetic  also  descend  in  front  of 
it  on  their  way  to  the  cardiac  plexus.  The  left  ansa  subclavia  also  loops  in  front  of  the  subclavian 
artery.  The  left  common  carotid  is  situated  anteriorly  and  to  its  right.  The  thoracic  duct 
arches  over  the  artery  just  medial  to  the  scalenus  anterior,  to  empty  its  contents  into  the 
confluence  of  the  internal  jugular  and  subclavian  veins  (fig.  442). 

Behind  and  somewhat  medial  to  it  are  the  oesophagus,  thoracic  duct,  inferior  cervical  gang- 
lion of  the  sympathetic,  longus  coUi  muscle,  and  vertebral  column.  To  some  extent  it  is  over- 
lapped posteriorly  by  the  left  pleura  and  lung. 

On  its  right  side  are  the  trachea  and  the  inferior  laryngeal  nerve,  and,  higher  up,  the  oesopha- 
gus and  thoracic  duct. 

On  its  left  side  are  the  left  pleura  and  lung. 


THE  FIRST  PORTION  OF  THE  RIGHT  SUBCLAVIAN  ARTERY    557 

Branches. — The  vertebral,  internal  mammary^   and  thyreo-cervical  trunk 
(thyreoid  axis)  usually  arise  from  the  first  portion  on  the  left  side.     (See  p.  559.) 


THE  FIRST  PORTION  OF  THE  RIGHT  SUBCLAVIAN  ARTERY 

The  first  portion  of  the  right  subclavian  artery  (fig.  457)  extends  from  its  origin 
at  the  bifurcation  of  the  innominate,  behind  the  ui3per  margin  of  the  right  sterno- 

FiG.  457. — The  Subclavian  Artery.     (After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman, 
London  and  New  York.) 


Medial  palpebral  arteries 
Tarsal 


.  /  Superior  .     /, 
*^i  Inferior   s/yl/ 


Lateral  palpebral  arteries 

Infra -orbital  artery 

Superior  labial  artery 
Anterior  auricular  brancbes  -^ 


Perforating   branches   of    the 
posterior  auricular  artery 


Supra-orbital  artery 

Frontal  artery 
,Dorsal  nasal  artery 


Zygomatico-orbital  artery 
Left  naris 

..^Frontal  branch  )  of  the  superficial 
Parietal  branch  J  temporal  artery 

Zygomatic  muscle 

Transverse  facial  artery 

.. — "Superficial  temporal  artery 


of  the  superior 
thyreoid  artery 


Inferior  labial  artery 

Mental  artery  -- 
Submental  artery 


,-.      t  J      i.       [  Internal 
Carotid  artery  I  j.^j^^^^, 

Superior  th3Teoid  artery — 
Levator  scapulee  muscle 
Common  cartoid  artery      A^^s  '^f 

Inferior  thyreoid  artery //^m^  ,«   -^ 

Phrenic  nerve 
Vertebral  artery 
Transverse  scapular 
artery 
Subclavian  artery 
Serratus  anterior 
muscle 
Internal    mammary    _ 
artery  ( 

Innominate  artery"" 
Pericardico-phrenic — 

artery  _ 

vena  dSerrT^M?*  V-^^ 

Thymus-  j:^m^' 

Intercostal        £ 
branches    "^T^bm**-  -« 
Costal  pleura  -~-^  /  S^^, 
Perforating 
branches 

Anterior  medi 
astinal  artery 
Superior 
phrenic  , 
artery 
Superio; 
epigastric 
artery 
Musculo 
phrenic 
artery 


clavicular  joint,  upward  and  laterally  in  a  gentle  curve  over  the  apex  of  the  right 
lung  and  pleura  to  the  medial  border  of  the  scalenus  anterior.  It  measures  about 
3  cm,  {\\  in.).  In  this  course  it  ascends  in  the  neck  a  variable  distance  above  the 
clavicle,  but  is  so  deeply  placed,  so  surrounded  by  important  structures,  and  gives 


> 


558  THE  BLOOD-VASCULAR  SYSTEM 

off  so  many  large  branches,  that  it  is  now  seldom  or  never  selected  for  the  applica- 
tion of  a  ligature. 

Relations. — In  front  it  is  covered  by  the  integuments,  the  superficial  fascia,  the  platysma, 
the  anterior  layer  of  the  deep  fascia,  the  clavicular  origin  of  the  sterno-mastoid,  the  sterno-hyoid 
and  sterno-thyreoid  muscles,  and  the  deep  cervical  fascia.  It  is  crossed  by  the  commencement 
of  the  innominate,  by  the  internal  jugular,  and  by  the  vertebral  veins;  and,  in  a  medio-lateral 
direction,  by  the  vagus  and  phrenic  nerves,  and  the  superior  cardiac  branches  of  the  sympathetic 
nerve.  A  loop  of  the  sympathetic  nerve  itself  also  crosses  the  artery,  and  forms  with  the  trunk 
of  the  S3'mpathetic  a  ring  around  the  vessel  known  as  the  ansa  subclavia  (annulus  of  Vieussens). 

Behind,  but  separated  from  the  artery  by  a  cellular  interval,  are  the  longus  coUi  muscle, 
the  transverse  process  of  the  seventh  cervical  or  first  thoracic  vertebra,  the  main  chain  of  the 
sympathetic  nerve,  the  inferior  cardiac  nerves,  the  recurrent  laryngeal  nerve,  and  the  apex  of  the 
right  lung  and  pleura. 

Below,  it  is  in  contact  with  the  pleura  and  lung  and  the  loop  of  the  recurrent  laryngeal 
nerve,  which  winds  round  the  artery  from  the  vagus  and  ascends  behind  it  to  the  larynx.  The 
subclavian  vein  is  below  the  artery  and  on  an  anterior  plane. 

Branches. — The  vertebral,  internal  mammary,  superficial  cervical,  and  thyreo- 
cervical  trunk  (thyreoid  axis)  arise  from  this  part  of  the  vessel  on  the  right  side. 
(See  p.  559.)  Not  uncommonly  a  small  aberrant  artery  also  takes  origin  from  this 
portion  of  the  artery  and  descends  to  the  left  behind  the  oesophagus  to  join  a 
branch  of  the  aorta  opposite  the  third  or  fourth  thoracic  vertebra.  This  vessel  is 
probably  the  remains  of  the  right  dorsal  aorta. 

THE  SECOND  PORTION  OF  THE  SUBCLAVIAN  ARTERY 

The  second  portion  of  the  subclavian  artery  lies  behind  the  scalenus  anterior 
muscle.  It  measures  about  2  cm.  ff  in.)  in  length  and  here  reaches  highest  in  the 
neck.  The  subclavian  vein  is  separated  from  the  artery  by  the  scalenus  anterior, 
and  lies  on  a  lower  and  anterior  plane  (fig.  463) . 

Relations. — In  front  it  is  covered  by  the  skin,  superficial  fascia,  platysma,  anterior  layer 
of  deep  fascia,  the  clavicular  origin  of  the  sterno-mastoid,  posterior  layer  of  deep  fascia,  and  by 
the  scalenus  anterior.  The  phrenic  nerve — which,  in  consequence  of  its  oblique  course  medially 
downward,  crosses  a  portion  of  both  the  first  and  second  part  of  the  subclavian — is  separated 
from  the  second  portion  by  the  scalenus  anterior  muscle,  as  is  also  the  subclavian  vein  which 
courses  on  a  somewhat  lower  plane. 

Behind  the  artery  are  the  apex  of  the  pleura  and  lung,  and  a  portion  of  the  scalenus  medius; 
also  the  scalenus  minimus  (partially  or  entirely  fibrous,  known  as  Sibson's  fascia,  see  p.  355). 

Above  is  the  brachial  plexus. 

Below  are  the  pleura  and  lung. 

One  branch  only — the  costo-cervical  trunk  (superior  intercostal) — is,  as  a 
rule,  given  off  from  this  portion  of  the  subclavian;  occasionally  the  transverse 
cervical  or  the  descending  branch  of  the  transverse  cervical  (posterior  scapular 
artery)  arises  from  it. 

THE  THIRD  PORTION  OF  THE  SUBCLAVIAN  ARTERY 

The  third  portion  of  the  subclavian  artery  extends  from  the  lateral  margin  of 
the  scalenus  anterior  muscle  to  the  lateral  border  of  the  first  rib.  It  is  more  super- 
ficial than  either  the  first  or  second  portions;  it  is  in  relation  with  less  important 
structures,  and  as  a  rule  gives  off  no  branch,  and  for  these  reasons  is  the  part 
selected  when  practicable  for  the  application  of  a  ligature.  It  is  the  longest  of 
the  three  portions  of  the  subclavian  artery,  and  lies  in  a  triangle — the  subclavian 
triangle — bounded  by  the  sterno-mastoid,  the  omo-hyoid,  and  the  clavicle  (fig. 
445). 

Relations. — In  front  it  is  covered  by  skin,  superficial  fascia,  platysma,  supra-clavicular 
nerves  (descending  superficial  branches)  of  the  cervical  plexus;  the  anterior  layer  of  deep 
fascia  which  descends  from  the  omo-hyoid  to  the  clavicle;  and  the  posterior  layer  of  deep  fascia 
which  descends  from  the  omo-hyoid  to  the  fu'st  rib  and  passes  over  the  scalenus  anterior  and 
phrenic  nerve.  Between  the  two  layers  of  fascia  is  a  variable  amount  of  cellular  tissue  and  fat, 
and  running  in  this  is  the  transverse  scapular  (supra-scapular)  artery.  The  subclavian  is  crossed 
by  this  artery  unless  the  arm  is  drawn  well  downward.  Close  to  the  lateral  margin  of  the 
sterno-mastoid,  the  external  jugular  vein  pierces  the  fascia,  and  crosses  the  subclavian  artery 
to  open  into  the  subclavian  vein.  As  this  vein  hes  between  the  two  layers  of  fascia,  it  receives 
on  its  lateral  side  the  transverse  scapular  (supra-scapular),  transverse  cervical,  and  other  veins 
of  the  neck,  which  together  form  a  plexus  of  large  veins  in  front  of  the  arterj'.  The  nerve  to 
the  subclavius,  and,  when  present,  the  accessory  branch  from  this  nerve  to  the  phrenic,  also 


THE  VERTEBRAL  ARTERY  559 

here  cross  in  front  of  the  artery.  In  very  muscular  subjects  the  clavicular  head  of  the  sterno- 
mastoid  may  be  larger  than  usual,  and  in  such  a  case  wiU  form  one  of  the  coverings  of  the  artery. 

Behind,  the  artery  is  in  contact  with  the  scalenus  medius,  and  with  the  lower  trunk  of  the 
brachial  plexus. 

Below,  the  artery  rests  in  the  posterior  of  the  two  grooves  on  the  upper  surface  of  the  first 
rib. 

Above  is  the  brachial  plexus  of  nerves  and  the  posterior  beUy  of  the  omo-hyoid  muscle. 
The  trunk  formed  by  the  fifth  and  sixth  cervical  nerves  is  also  above  the  artery,  but  on  a  some- 
what anterior  plane.  It  is  close  to  the  vessel,  and  has  been  mistaken  for  the  artery  in  the  appU- 
cation  of  a  Kgature. 

As  a  rule  there  is  no  branch  given  off  from  the  third  portion  of  the  subclavian. 
At  times,  however,  the  transverse  cervical  or  the  descending  branch  of  the 
transverse  cervical  (posterior  scapular  artery)  may  arise  from  the  third  portion  of 
the  subclavian  instead  of  from  the  thyreo-cervical  trunk  (thyreoid  axis)  and  from 
the  transverse  cervical  respectively,  as  here  described. 

There  is  considerable  variation  in  the  branches  of  the  subclavian  artery  and 
Bean  (Am.  Jour.  Anat.,  Vol.  4,  p.  303)  has  shown  that  the  branches  are  arranged 
in  a  different  way  on  the  two  sides  of  the  body.  The  usual  form  on  the  right  side 
is  for  the  vertebral,  internal  mammary,  the  superficial  cervical  and  the  common 
trunk  of  the  inferior  thjTeoid  and  transverse  scapular  arteries  to  arise  from  the 
first  part  of  the  subclavian.  In  this  case  the  ascending  cervical  is  a  branch  of 
the  inferior  thyreoid,  while  the  transverse  cervical  and  costo-cervical  arise  from 
the  second  portion.  There  are  no  branches  from  the  third  portion.  On  the  left 
side  the  usual  form  is  for  the  vertebral  and  internal  mammary,  and  thyreo-cer- 
vical trunk,  to  arise  from  the  first  part.  The  thyreo-cervical  trunk  divides  into 
inferior  thyreoid,  transverse  scapular,  and  transverse  cervical  arteries;  the  super- 
ficial cervical  is  absent,  and  the  costo-cervical  trunk  arises  from  the  first  part. 

There  are  three  more  types  of  origin  of  the  branches;  in  one,  the  vertebral, 
internal  mammary,  costo-cervical,  and  inferior  thyreoid  come  from  the  first  part, 
while  the  transverse  cervical  arises  from  the  second  part,  and  the  transverse 
scapular  comes  either  from  the  third  part  or  the  axillary  artery;  in  the  second, 
the  inferior  thyreoid,  transverse  scapular  and  transverse  cervical  arise  in  a  com- 
mon stem  from  the  first  part;  while  in  the  third,  which  is  the  rarest  form,  the  in- 
ferior thyreoid  and  superficial  cervical  arteries  come  by  a  common  trunk  from 
the  first  part,  while  the  transverse  scapular  artery  arises  from  the  internal 
mammary. 

1.  THE  VERTEBRAL  ARTERY 

The  vertebral  artery  [a.  vertebralis]  (fig.  458)  the  first,  largest,  and  most  con- 
stant branch,  arises  from  the  upper  and  posterior  part  of  the  first  portion  of  the 
subclavian,  on  the  right  side,  about  2  cm.  (f  in.)  from  the  origin  of  the  latter  ves- 
sel from  the  innominate,  on  the  left  side,  from  the  most  prominent  part  of  the 
arch  of  the  subclavian,  close  to  the  medial  edge  of  the  scalenus  anterior  muscle.  It 
first  ascends  vertically  to  the  foramen  transversarium  of  the  sixth  cervical 
vertebra,  and,  having  passed  through  that  foramen  and  those  of  the  next  succeed- 
ing cervical  vertebrae  as  high  as  the  epistropheus  (axis),  it  tmns  laterally  and 
then  ascends  to  reach  the  foramen  in  the  transverse  process  of  the  atlas;  after 
passing  through  that  foramen  it  turns  backward  behind  the  articular  process, 
lying  in  the  groove  on  the  posterior  arch  of  the  atlas.  It  next  pierces  the  posterior 
occipito-atlantoid  membrane  and  the  dura  mater,  and  enters  the  cranium  through 
the  foramen  magnum.  Here  it  passes  upward,  at  first  lying  by  the  side  of  the 
medulla,  then  in  front  of  that  structure,  and  terminates  at  the  lower  portion  of  the 
pons  by  anastomosing  with  the  vertebral  of  the  opposite  side  to  form  the  basilar. 

The  vertebral  artery  may  be  divided  for  purposes  of  description  into  four  parts: 
the  first,  or  cervical,  extending  from  its  origin  to  the  transverse  process  of  the 
sixth  cervical  vertebra;  the  second,  or  vertebral,  situated  in  the  foramina  trans- 
versaria;  the  third,  or  occipital,  contained  in  the  suboccipital  triangle;  and  the 
fourth,  or  intracranial,  within  the  cranium. 

The  first  or  cervical  portion. — The  artery  here  lies  between  the  scalenus  anterior  and  longus 
colli  muscles.  In  front  it  is  covered  by  the  vertebral  and  internal  jugular  veins,  and  is  crossed 
by  the  inferior  thyreoid  artery,  and  on  the  left  side,  in  addition,  by  the  thoracic  duct,  which  runs 
over  it  medio-laterally.  Behind,  the  artery  hes  on  the  transverse  process  of  the  seventh  cervical 
vertebra  and  the  sympathetic  nerve.     To  its  medial  side  is  the  longus  coUi.     To  its  lateral 


i 


560 


THE  BLOOD-VASCULAR  SYSTEM 


side  is  the  scalenus  anterior.  It  gives  off  as  a  rule  no  branch  in  this  part  of  its  course.  Occa- 
sionally, however,  a  small  branch  passes  into  the  foramen  tranversarium  of  the  seventh  cervical 
vertebra. 

The  second  or  vertebral  portion. — As  the  artery  passes  through  the  foramina  transversaria, 
it  is  surriunded  by  a  plexus  of  veins  and  by  branches  of  the  sympathetic  nerve.  The  cervical 
nerves  lie  behind  it.  Between  the  transverse  processes  it  is  in  contact  with  the  intertransverse 
muscles. 

The  third  or  occipital  portion. — The  artery  here  hes  in  the  suboccipital  triangle,  bounded 
by  the  superior  oblique,  inferior  oblique,  and  rectus  capitis  posterior  major  muscles.  As  it 
winds  round  the  groove  on  the  atlas,  it  has  the  rectus  capitis  laterahs,  the  articular  process, 
and  the  posterior  ocoipito-atlantoid  membrane  in  front  of  it;  the  superior  oblique,  the  rectus 
capitis  posterior  major,  and  the  semispinalis  capitis  (complexus)  behind  it.  Separating  it 
from  the  arch  of  the  atlas,  is  the  first  cervical  or  suboccipital  nerve. 

The  fourth  or  intracranial  portion  extends  from  the  aperture  in  the  dura  mater  to  the 
lower  border  of  the  pons,  where  it  pierces  the  arachnoid  and  unites  with  its  fellow  to  form  the 
basilar  artery.     It  here  winds  round  from  the  side  to  the  front  of  the  medulla,  lying  in  the 


Fig.  458. — Scheme  op  the  Left  Veetebeal  Aeteey.     (Walsham.) 
The  internal  jugular  and  vertebral  veins  are  hooked  aside  to  expose  the  artery. 

Risht  posterior  cerebral 
artery 
Left  posterior  cerebral " 
artery 
Basilar  artery  " 


Basilar  part,  occipital 


Intracranial  portion  of  verte 
bral  artery 
Rectus  capitis  lateralis  muscl 


Second  cervical  nerve 

Vertebral  plexus  of  veins 
Third  cervical 

Vertebral  portion  of  vertebral 
artery 
Fourth  cervical  nerve 

Vertebral  plexus  of  veins 

Fifth  cervical  nerve 


Sixth  cervical 

Inferior  thyreoid  artery 

Longus  colli  muscle 

Cervical  portion  of  vertebral 

artery 

Internal  jugular  vein,  hooked  a 

little  aside 

Vertebral  vein,  cut 
Subclavian  artery 


:ipital  bone 


Occipital  portion  of  vertebral  artery 


Descending  branch  of  occipital  artery 


Semispinalis  colli  muscle 


Deep  cervical  artery 


Scalenus  anterior  muscle,  cut 


Subclavian  vein 


vertebral  groove  on  the  basilar  part  of  the  occipital  bone.  In  this  course  it  passes  beneath 
the  first  process  of  the  hgamentum  denticulatum,  and  between  the  hypoglossal  nerve  in  front, 
and  the  anterior  roots  of  the  suboccipital  nerve  behind. 


Branches  of  the  Vertebral  Artery 

The  first  part  of  the  vertebral  artery  gives  no  branches.  The  second  and  third 
parts  give  off  muscular  branches  to  the  semispinalis  and  posterior  recti  and  oblique 
muscles.  The  second  part  also  gives  off  five  or  six,  (1)  Spinal  branches.  The 
fourth  part  gives  off  the  following:  (2)  Posterior  meningeal;  (3)  posterior  spinal; 
(4)  anterior  spinal;  and  (5)  posterior  inferior  cerebellar. 

(1)  The  spinal  branches  [rami  spinales]  run  through  the  intervertebral  foramina  into  the 
vertebral  canal,  and  there  divide  into  two  branches:  one  of  which  ramifies  on  the  ba,cks  of 
the  bodies  of  the  cervical  vertebra;;  while  the  other  runs  along  the  spinal  nerves,  supphes  the 
cord  and  its  membranes,  and  anastomoses  with  the  arteries  above  and  below. 

(2)  The  meningeal  [ramus  meningeus]  is  a  small  branch  given  off  as  the  vertebral  artery 
pierces  the  dura  mater  to  enter  the  cranium.  It  supplies  the  bone  and  dura  mater  of  the 
posterior  fossa  of  the  skull,  and  anastomoses  with  the  posterior  meningeal  branches  derived 
from  the  occipital  and  ascending  pharyngeal  arteries.     It  gives  branches  to  the  falx  cerebelli. 


THE  BASILAR  ARTERY  561 

(3)  The  posterior  spinal  artery  [a.  spinalis  posterior]  runs  downward  obliquely  along  the 
side  of  the  medulla  to  the  back  of  the  cord,  down  which  it  passes  behind  the  roots  of  the  spinal 
nerves,  being  reinforced  by  spinal  branches  accompanying  these  nerves,  in  the  neck,  the  thoracic, 
and  in  the  lumbar  region.     It  can  be  traced  as  low  as  the  end  of  the  spinal  cord. 

(4)  The  anterior  spinal  artery  [a.  spinalis  anterior]  comes  off  from  the  vertebral  a  little 
below  its  termination  in  the  basilar  artery.  Descending  with  a  medial  slant  in  front  of  the 
medulla,  it  unites  on  a  level  with  the  foramen  magnum  with  its  fellow  of  the  opposite  side. 
The  single  vessel  thus  formed  runs  downward  in  front  of  the  spinal  cord  beneath  the  pia  mater 
as  far  as  the  termination  of  the  cord,  being  reinforced  by  the  spinal  branches  on  the  way  down. 
The  spinal  arteiies  are  described  in  detail  with  the  anatomy  of  the  spinal  cord. 

(5)  The  posterior  inferior  cerebellar  [a.  cerebeUi  inferior  posterior]  (fig.  456) — the  largest 
branch  of  the  vertebral — arises  from  that  vessel  just  before  it  joins  its  fellow  to  form  the  basilar 
artery.  At  times  it  may  come  off  from  the  basilar  itself.  It  runs,  at  first  laterally  across 
the  restiform  body  between  the  origin  of  the  vagus  and  hypoglossal  nerves,  and,  descending 
toward  the  vallecula,  there  divides  into  two  branches,  medial  and  lateral,  (a)  The  medial 
branch  runs  backward  between  the  vermis  and  the  lateral  hemisphere  of  the  cerebellum.  It 
supplies  the  vermis,  and  anastomoses  with  the  artery  of  the  opposite  side,  and  with  the  superior 
vermian  of  the  superior  cerebellar.  (6)  The  lateral  branch  runs  laterally  and,  ramifying  over 
the  under  surface  of  the  cerebellar  hemisphere,  supplies  its  cortex  and  anastomoses  along  its 
lateral  margin  with  the  superior  cerebellar  arteries. 

From  the  undivided  trunk  of  the  posterior  inferior  cerebellar  artery  branches  are  given 
to  the  medulla  oblongata,  supplying  the  chorioid  plexus  and  the  fourth  ventricle. 

THE  BASILAR  ARTERY 

The  basilar  artery  [a.  basilaris]  is  formed  by  the  confluence  of  the  right  and 
left  vertebral  arteries,  which  meet  at  an  acute  angle  at  the  lower  border  of  the 
pons.  It  runs  forward  and  upward  in  a  slight  groove  in  the  middle  line  of  the 
pons,  and  divides  at  the  upper  border  of  that  structure  at  the  level  of  the  tentorial 
notch  into  the  two  posterior  cerebral  arteries,  which  take  part  in  the  formation  of 
the  circle  of  Willis  (fig.  456) . 

Branches  of  the  Basilar  Artery 

The  branches  of  the  basilar  artery  are: — 1.  Pontine;  2.  internal  auditory; 
3.  anterior  inferior  cerebellar;  4.  superior  cerebellar;  5.  posterior  cerebral. 

(1)  The  pontine  branches  [rami  ad  pontem]  are  numerous  small  vessels  which  come  off  at 
right  angles  on  either  side  of  the  basilar  artery,  and,  passing  laterally  over  the  pons,  supply  that 
structure  and  adjacent  parts  of  the  brain. 

(2)  The  internal  auditory  artery  [a.  auditiva  interna],  a  long  slender  vessel,  accompanies 
the  auditory  nerve  into  the  internal  auditory  meatus  (fig  514).  It  here  lies  between  the 
facial  and  auditory  nerves,  and  at  the  bottom  of  the  meatus  passes  into  the  internal  ear,  and 
anastomoses  with  the  other  auditory  arteries.     (See  Internal  Ear.) 

(3)  The  anterior  inferior  cerebellar  [a.  cerebelU  inferior  anterior]  arises  from  the  basilar 
soon  after  its  origin,  passes  laterally  and  backward  across  the  pons,  and  then  over  the  brachium 
pontis  to  the  front  part  of  the  under  surface  of  the  cerebellum.  It  anastomoses  with  the 
posterior  inferior  cerebellar  artery  (fig.  456). 

(4)  The  superior  cerebellar  [a.  cerebelli  superior]  comes  off  from  the  basilar  immediately 
behind  its  bifurcation  into  the  posterior  cerebral  arteries.  It  courses  laterally  and  backward 
over  the  pons,  in  a  curve  roughly  corresponding  to  that  of  the  posterior  cerebral  artery,  from 
which  it  is  separated  by  the  third  cranial  nerve;  but,  soon  sinking  into  the  groove  between  the 
pons  and  the  pedunculus  cerebri,  it  curves  round  the  latter  onto  the  upper  surface  of  the 
cerebellum,  lying  nearly  parallel  to  the  fourth  nerve.  Here  it  divides  into  two  branches 
medial  and  lateral,  (o)  The  medial  branch  courses  backward  along  the  superior  vermis,  anas- 
tomosing with  its  fellow  of  the  opposite  side,  and,  at  the  posterior  notch  of  the  cerebellum,  with 
the  inferior  vermian  branch  of  the  posterior  inferior  cerebellar  artery.  (6)  The  lateral  runs 
to  the  circumference  of  the  cerebellum,  anastomosing  with  the  lateral  branch  of  the  inferior 
posterior  cerebellar  artery. 

Branches  are  given  off  from  the  main  trunk  of  the  superior  cerebellar  artery,  or  from  its 
medial  branch  to  the  anterior  velum  (valve  of  Vieussens),  the  corpora  quadrigemina,  the  pineal 
body,  and  the  chorioid  plexus. 

(5).  The  posterior  cerebral  arteries  [aa.  cerebri  posteriores]  are  the  two  terminal  branches 
into  which  the  basilar  bifurcates  at  the  upper  border  of  the  pons,  immediately  behind  the 
posterior  perforated  substance.  Each  artery  runs  at  fii'st  laterally  and  a  little  forward  across 
the  pedunculus  cerebri  immediately  in  front  of  the  third  nerve,  which  separates  it  from  the 
superior  cerelsellar  artery.  After  receiving  the  posterior  communicating  artery,  which  runs 
backward  from  the  internal  carotid,  the  posterior  cerebral  turns  backward  onto  the  under  surface 
of  the  cerebral  hemisphre,  where  it  breaks  up  into  branches  for  the  supply  of  the  temporal  and 
occipital  lobes. 

The  branches  of  the  posterior  cerebral  artery  are  described  below  in  connection  with  those 
of  the  other  cerebral  arteries. 


562 


THE  BLOOD-VASCULAR  SYSTEM 


Distribution  of  the  Cerebral  Arteries 

Although  the  brain  receives  its  blood  supply  from  two  distinct  sources,  namely,  from 
the  internal  carotids  and  from  the  vertebrals,  it  is  convenient  to  consider  together  the  dis- 
tribution of  the  various  cerebral  branches  derived  from  these  stems.  The  formation  of  the  circulus 
arteriosus  (circle  of  Willis)  and  the  origin  of  the  anterior,  middle  and  posterior  cerebral  arteries 
has  already  been  described  (pp.  554,  561).  The  detailed  distribution  of  these  vessels  will  now 
be  considered.  In  general,  their  branches  may  be  divided  into  central  or  ganglionic  and  per- 
ipheral or  cortical. 

The  anterior  cerebral  artery  has  but  a  hmited  central  distribution.  It  gives  off  a  few 
inconstant  branches  which  enter  the  anterior  perforated  substance  and  supply  the  anterior  end 
of  the  caudate  nucleus.  One  or  two  of  these  run  to  the  corpus  callosum  and  septum  peUucidum. 
The  anterior  communicating  branch  is  a  transverse  trunk  which  connects  the  two  arteries  and 
thereby  completes  the  circulus  arteriosus  in  front.  It  hes  in  front  of  the  optic  chiasm,  and 
varies  considerably  in  length  and  size.  It  may  give  off  some  of  the  branches  to  the  anterior 
perforated  substance.  The  cortical  branches  supply  the  gyrus  rectus,  the  olfactory  lobe  and  a 
part  of  the  orbital  gyri  on  the  ventral  surface.  On  the  medial  surface  branches  supply  the 
cortex  as  far  back  as  the  parieto-occipital  fissure.     These  branches  are  given  off  as  the  artery 


Fig.  459. — The  Arteries  or  the  Mesial  Surface  op  the  Brain.     (After  Spalteholz.) 

Sulcus  cinguli  Corpus  callosum 


Anterior  cerebral 
artery 


Anterior  communicating  artery    ' 
Internal  carotid  artery 


I  Posterior  cerebral  artery 

Posterior  communicating  artery 


curves  around  the  corpus  callosum  and  some  of  them  curve  over  onto  the  lateral  surface  and 
supply  the  superior  and  middle  temporal  convolutions.  Branches  from  the  anterior  cerebral 
artery  also  supply  the  corpus  callosum  (fig.  459). 

The  middle  cerebral  artery  gives  off  most  of  the  branches  to  the  basal  gangha  and  supplies 
the  greater  part  of  the  lateral  surface  of  the  brain.  It  runs  through  the  lateral  fissure  (fissure 
of  Sylvius)  (fig.  460).     The  branches  of  the  middle  cerebral  include  the  following: 

The  central  branches  are: — (i)  The  caudate,  two  or  three  small  branches,  which  arise  from 
the  medial  aspect  of  the  artery  and  pass  through  the  medial  part  of  the  floor  of  the  lateral  fissure 
(fissure  of  Sylvius)  to  the  head  of  the  caudate  nucleus,  (ii)  The  antero -lateral  are  numerous 
small  arteries  which  pass  through  the  anterior  perforated  substance  and  supply  the  caudate 
nucleus  (except  its  head),  the  internal  capsule,  and  part  of  the  optic  thalamus,  (iii)  The 
lenticulostriate,  a  larger  branch  of  the  antero-latera!  set,  passes  through  a  separate  aperture  in 
the  lateral  part  of  the  anterior  perforated  substance,  runs  upward  between  the  lenticular  nucleus, 
which  it  supplies,  and  the  external  capsule,  perforates  the  internal  capsule,  and  terminates  in  the 
caudate  nucleus.  It  has  been  so  frequently  found  ruptured  in  apoplexy  that  it  is  called  by 
Charcot  the  'artery  of  cerebral  haemorrhages.'  (iv)  Sometimes  a  more  or  less  distinct  branch, 
called  lenticulo-optic,  is  distributed  to  the  lateral  and  hinder  portion  of  the  lenticular  nucleus 
and  the  lateral  portion  of  the  optic  thalamus. 

The  cortical  branches  come  off  opposite  the  insula.  They  supply  the  insula,  the  inferior 
frontal  gyri,  the  central  gyri  (anterior  and  posterior),  the  parietal  lobules,  superior  and  in- 
ferior, the  supra-marginal,  angular,  and  superior  temporal  g}T:i. 

The  posterior  cerebral  give  off  both  central  and  cortical  branches.  The  central  branches 
are   the  postero-median,   posterior   chorioid,   and   the   postero-lateral.     The  postero-median 


THE  CEREBRAL  ARTERIES 


563 


enter  the  posterior  perforated  substance  and  supply  the  medial  portion  of  the  optic  thalamus, 
and  the  walls  of  the  third  ventricle;  the  posterior  chorioid  pass  through  the  transverse  fissure 
to  the  tela  chorioidea  (velum  interpositum)  and  chorioid  plexus;  the  postero-lateral  run  to 
the  posterior  part  of  the  optic  thalamus  and  give  branches  to  the  cerebral  peduncles  and  the 
corpora  quadrigemina. 

The  cortical  branches  of  the  posterior  cerebral  supply  the  entire  occipital  lobe  and  all  of  the 
temporal  lobe  except  the  superior  temporal  gj'rus  (fig.  459). 

In  regard  to  the  cerebral  arteries  in  general  it  may  be  said  that  there  is  no  anastomosis 
between  the  cortical  and  central  branches,  the  two  forming  distinct  and  separate  systems. 
The  cortical  may  or  may  not  anastomose  with  each  other,  but  the  communication  between  the 
neighbouring  cortical  branches  is  seldom  sufficient  to  maintain  the  nutrition  of  an  area  when 
the  vessel  that  normally  supphes  it  is  obstructed.  The  central  branches  are  so-called  end- 
vessels  and  do  not  anastomose  with  each  other.  Hence  obstruction  of  the  middle  cerebral 
artery  leads  to  softening  of  the  area  suppUed  by  its  central  branches,  but  not  always  to  softening 
of  the  region  suppHed  by  its  cortical  branches.  Indeed,  the  cortical  region  may  escape  com- 
pletely, although  the  central  area  is  irreparably  disorganised.  The  gross  anastomosis  of  the 
posterior  cerebral  with  the  anterior  cerebral  arteries  through  the  circulus  arteriosus  has  already 
been  described.  To  sum  up  the  distribution  of  the  cerebral  arteries,  the  branches  of  each  are 
divided  into  the  central,  or  ganglionic  and  the  peripheral  or  cortical.  The  central  branches 
arise  at  the  commencement  of  the  cerebral  arteries  about  the  cireulus  arteriosus  whilst  the 
cortical  are  derived  chiefly  from  the  termination  of  these  vessels. 


Fig.  460. — The  Arteries  of  the  Lateral  Surface  of  the  Brahst.     (After  Toldt, 
Human  Anatomy,"  Rebman,  London  and  New  York.) 
Central  sulcus  (Rolandi) 


'  Atlas  of 


Branches  of  the  anterior  cerebral  artery 


Branches  of  the  posterior 
cerebral  artery 


Branches  of  the  anterior  cere 
bral  artery 

Optic  nerve 


Branch  of  the  posterior  cerebral 
artery 


Middle  cerebral  artery 


(A)  The  central  branches  are  divided  into  four  sets — two  median  and  two  lateral.  1. 
The  two  median  are — (1)  The  antero-median,  which  arise  from  the  anterior  cerebral  and  the 
anterior  communicating,  and  supply  the  fore  end  of  the  caudate  nucleus,  and  (2)  the  postero- 
median, which  arise  from  the  posterior  cerebral  and  supply  the  medial  part  of  the  optic  thalamus 
and  neighbouring  wall  of  the  third  ventricle.  2.  The  two  lateral  are: — (1)  The  antero -lateral 
arise  from  the  middle  cerebral,  and,  passing  through  the  anterior  perforated  substance,  supply 
the  lenticular  nucleus,  the  posterior  part  of  the  caudate  nucleus,  the  internal  and  external 
capsules,  and  the  lateral  part  of  the  optic  thalamus.  (2)  The  postero-lateral  arise  from  the 
posterior  cerebral,  and  supply  the  hinder  part  of  the  optic  thalamus,  the  pedunculus  cerebri,  and 
the  corpora  quadrigemina. 

(B)  The  cortical  branches  ramify  in  the  pia  mater,  giving  off  branches  to  the  cortical 
substance,  some  of  which  extend  through  it  to  the  underlying  white  substance. 

It  will  be  seen  that  the  middle  cerebral  supphes  the  somaesthetic  area  of  the  cortex.  It 
also  supphes  the  cortical  auditory  centre,  and,  in  part,  the  higher  visual  centre.  The  anterior 
cerebral  supphes  only  a  small  part  of  the  somtesthetic  area,  namely,  the  part  of  the  leg  centre 
that  occupies  the  paracentral  lobule  and  the  highest  part  of  the  anterior  central  gyrus.  The 
posterior  cerebral  supphes  the  visual  path  from  the  middle  of  the  tract  backward,  and  the  half 
vision  centre  in  the  occipital  lobe.  It  supphes  also  the  corpora  quadrigemina  and  the  sensory 
part  of  the  internal  capsule. 

The  branches  which  supply  the  cerebellum  and  brain  stem  are  given  in  connection  with 
the  vertebrals  on  page  561. 


564  THE  BLOOD-VASCULAR  SYSTEM 

2.  THE  THYREOCERVICAL  TRUNK 

The  thyreocervical  trunk  [truncus  thyreocervicalis]  or  thyreoid  axis  arises  from 
the  upper  and  front  part  of  the  subclavian  artery,  usually  opposite  the  internal 
mammary,  and  slightly  medial  to  the  scalenus  anterior.  It  is  a  short  thick  trunk, 
and  divides  almost  immecUately  into  three  radiating  branches — namely,  the 
inferior  thyreoid,  the  transverse  scapular,  and  the  transverse  cervical  (figs.  444, 
457).  This  is  the  usual  form  only  on  the  left  side  (see  page  559).  It  may  give  off 
also  the  ascending  cervical. 

THE  INFERIOR  THYREOID  ARTERY 

The  inferior  thyreoid  artery  [a.  thyreoidea  inferior]  is  the  largest  of  the  three 
branches  into  which  the  thyreocervical  trunk  (thyreoid  axis)  divides,  and  may 
arise  in  a  common  trunk  with  the  transverse  scapular,  or  as  a  branch  of  the  sub- 
clavian. It  ascends  tortuously  passing  medially  in  front  of  the  vertebral  artery, 
the  inferior  laryngeal  nerve  and  the  longus  colU  muscle,  and  behind  the  common 
carotid  and  the  sympathetic  nerve  or  its  middle  cervical  ganglion,  to  the  thyreoid 
gland,  where  it  anastomoses  with  the  superior  thyreoid  artery  and  the  artery  of  the 
opposite  side. 

The  branches  of  the  inferior  thyreoid  artery  are : — (1)  Muscular;  (2)  oesophageal 
and  pharyngeal;  (3)  tracheal;  (4)  inferior  laryngeal;  (5)  glandular;  and  (6)  as- 
cending cervical. 

(1)  The  muscular  branches  supply  the  scalenus  anterior,  longus  coUi,  sternohyoid,  sterno- 
thyreoid,  and  omo-hyoid  muscles,  and  the  inferior  constrictor  muscle  of  the  pharynx. 

(2)  The  oesophageal  and  pharyngeal  branches  [rami  oesophagei  et  pharyngei]  of  the  inferior 
thyreoid  artery  supply  the  oesophagus  and  pharynx  and  anastomose  with  the  other  arteries 
supplying  those  structures. 

(3)  The  tracheal  branches  [rami  tracheales]  ramify  on  the  trachea,  where  they  anastomose 
with  the  tracheal  branches  of  the  superior  thyreoid  and  bronchial  arteries. 

(4)  The  inferior  laryngeal  artery  [a.  laryngea  inferior]  passes  along  the  trachea  to  the  back 
of  the  cricoid  cartilage  in  company  with  the  inferior  laryngeal  nerve.  It  enters  the  larynx 
beneath  the  inferior  constrictor.  Its  further  distribution  in  that  organ  is  described  under 
Larynx. 

(5)  The  glandular  branches  [rami  glandulares]  supply  the  thsrreoid  gland. 

(6)  The  ascending  cervical  artery  [a  cervicalis  ascendens]  (figs.  444,  457)  is  given  off  from 
the  thyreocervical  trunk  or  from  the  inferior  thyreoid  as  that  vessel  is  passing  beneath  the 
carotid  sheath.  It  ascends  between  the  scalenus  anterior  and  the  longus  capitis  (rectus  capitis 
anterior  major),  lying  parallel  and  medial  to  the  phrenic  nerve  and  behind  the  internal  jugular 
vein.  It  anastomoses  with  the  vertebral,  ascending  pharyngeal,  and  occipital  arteries,  and 
supphes  branches  to  the  deep  muscles  of  the  neck  [rami  musculares],  to  the  spinal  canal  [rami 
spiuales],  and  to  the  phrenic  nerve.  Two  veins  accompany  the  ascending  cervical  artery  and 
end  in  the  innominate  vein. 

THE  TRANSVERSE  SCAPULAR  ARTERY 

The  transverse  scapular  or  suprascapular  [a.  transversa  scapulae]  artery  passes 
laterally  across  the  root  of  the  neck,  lying  first  beneath  the  sterno-mastoid,  and 
then  in  the  subclavian  triangle  behind  the  clavicle  and  subcalvius  muscle.  At 
the  lateral  angle  of  this  space  it  is  joined  by  the  suprascapular  nerve,  sinks 
beneath  the  posterior  belly  of  the  omo-hyoid,  and  passes  over  the  hgament  bridg- 
ing the  scapular  notch,  the  nerve  passing  through  the  notch  (fig.  461).  It  then 
ramifies  in  the  supraspinous  fossa  of  the  scapula,  and,  winding  downward  round 
the  base  of  the  spine  over  the  neck  of  the  scapula,  enters  the  infraspinous  fossa, 
and  terminates  by  anastomosing  with  the  circumflex  (dorsal)  scapular  artery, 
and  the  descending  branch  of  the  transverse  cervical  (posterior  scapular)  artery. 

As  it  lies  under  cover  of  the  sterno-mastoid  muscle,  it  crosses  the  phrenic  nerve  and  the 
scalenus  anterior;  and  as  it  courses  through  the  subclavian  triangle,  it  is  separated  by  the 
cervical  fascia  which  descends  from  the  omo-hyoid  to  the  first  rib,  from  the  subclavian  artery 
and  brachial  plexus  of  nerves.  If  this  artery  is  seen  in  tying  the  subclavian  it  should  not  be 
injured,  as  it  is  one  of  the  chief  vessels  by  which  the  collateral  circulation  is  carried  on  after 
ligature  of  the  subclavian  in  the  third  part  of  its  course.  At  the  lateral  part  of  the  subclavian 
triangle  it  is  covered  by  the  trapezius,  and  after  passing  over  the  transverse  scapular  Mgament 
it  pierces  the  supraspinous  fascia  and  passes  beneath  the  supra-spinatus  muscle,  ramifying 
between  it  and  the  bone.  In  the  infraspinous  fossa  it  hes  between  the  infra-spinatus  and 
the  bone.     The  artery  is  accompanied  by  two  veins. 


THE  TRANSVERSE  CERVICAL  ARTERY 


565 


The  branches  of  the  transverse  scapular  are: — (1)  the  nutrient,  to  the  clavicle;  (2)  the 
acromial  [ramus  acromialis]  to  the  arterial  rete  or  plexus  on  the  acromial  process,  to  reach 
which  it  pierces  the  trapezius;  (3)  the  articular,  to  the  acromio-clavicular  joint  and  shoulder- 
joint;  (4)  the  subscapular,  given  off  as  the  artery  is  passing  over  the  transverse  scapular  liga- 
ment, descends  to  the  subscapular  fossa  between  the  subscapularis  and  the  bone,  and  anas- 
tomoses with  the  infrascapular  branch  of  the  circumflex  (dorsal)  scapular  artery,  and  with 
the  subscapular  and  transverse  cervical  arteries;  (5)  the  supraspinous  branches,  which  ramify 
in  the  supraspinous  fossa,  and  supply  the  supra-spinatus  muscle  and  the  periosteum,  and  the 
nutrient  artery  to  the  bone;  (6)  the  infraspinous  branches,  which  ramify  in  a  similar  way  in 
the  infraspinous  fossa,  giving  off  twigs  to  the  infra-spinatus  muscle,  the  periosteum,  and  the 
bone. 


Fig.  461. — Scheme  of  Anastomoses  of  the  Right  Scapular  Arteries.     (Walsham.) 


Subscapular  branch  of  transverse  scapular  artery 
Supraspinous  branch  of  transverse  scapular  artery 


Descending  branch 

of  transverse  cer^ 
vical  artery 


Branch    of   inter 
costal  artery 


Branch  of  inter- 
costal artery 
Continuation  of  de- 
scending branch 
of  transverse  cer- 
vical artery 


Transverse  scapular  artery 

-.    ^^y7  Acromial  branch  of 

;^/ A      thora  CO -acromial 

-Acromial  rete 


Subscapular    branch    of 

transverse  scapular 

artery 
Infraspinous  branch  of 

transverse  scapular 

artery 
Subscapular  branch  of 
axillary  artery 


Circumflex  scapular  artery 


branch  of  cir 
apular  artery 


Dorsal  thoracic  branch  o£ 
subscapular  artery 


THE  TRANSVERSE  CERVICAL  ARTERY 

The  tranverse  cervical  artery  [a.  transversa  colli],  somewhat  larger  than  the 
transverse  scapular  (suprascapular),  runs  like  the  latter  vessel  laterally  across  the 
root  of  the  neck,  but  on  a  slightly  higher  transverse  plane,  and  a  little  above  the 
clavicle.  At  its  origin  from  the  thyreo-cervical  trunk  (thyreoid  axis)  it  lies  under 
the  sterno-mastoid;  on  leaving  the  cover  of  this  muscle,  it  crosses  the  upper  part 
of  the  subclavian  triangle,  lying  here  only  beneath  the  platysma  and  cervical 
fascia;  further  laterally,  it  passes  beneath  the  anterior  margin  of  the  trapezius  and 
omo-hyoid  muscle,  and  at  the  lateral  margin  of  the  levator  scapulse  divides  into  a 
descending  (posterior  scapular)  and  an  ascending  (superficial  cervical)  branch. 
In  this  course  it  crosses  the  phrenic  nerve,  the  scalenus  anterior,  the  brachial 
plexus,  and  the  scalenus  medius.  Sometimes  it  passes  between  the  cords  of  the 
brachial  plexus. 

The  branches  of  the  transverse  cervical  artery  are: — (1)  a  descending 
(posterior  scapular) ;  and  (2)  an  ascending  (or  superficial)  cervical.  The  descend- 
ing branch  occasionally  arises  from  the  third  portion  of  the  subclavian  artery. 

(1)  The  descending  branch,  or  posterior  scapular  [ramus  descendens]  the  apparent  continua- 
tion of  the  transverse  cervical  artery,  begins  at  the  lateral  border  of  the  levator  scapula;,  and, 
continuing  its  course  beneath  this  muscle  to  the  upper  and  posterior  angle  of  the  scapula,  turns 
downward  and  skirts  along  the  posterior  border  of  the  scapula,  between  the  serratus  anterior 


566 


THE  BLOOD-VASCULAR  SYSTEM 


(magnus)  in  front  and  the  levator  seapulEe  and  rhomboideus  minor  and  major  behind,  to  the 
inferior  angle,  where  it  anastomoses  with  the  subscapular  artery.  It  gives  off  the  following 
branches: — (a)  Supraspinous,  which  ramifies  between  the  supraspinous  muscle  and  the  trapezius, 
and  sends  branches  through  the  muscle  into  the  fossa,  to  anastomose  with  the  transverse 
scapular  artery.  (6)  Infraspinous  branches,  one  or  more  of  which  enter  the  infraspinous 
fossa,  and  anastomose  with  the  circumflex  (dorsal)  scapular,  (c)  Subscapular  branches,  which 
enter  the  subscapular  fossa,  and  anstomose  with  the  branches  of  the  transverse  scapular  and 
subscapular  arteries,  (d)  Muscular  branches,  to  the  muscles  between  which  it  runs  and  to 
the  latissimus  dorsi.  These  branches  anastomose  with  the  posterior  divisions  of  the  intercostal 
arteries. 

(2)  The  ascending  branch  or  superficial  cervical  artery  [r.  asoendens],  smaller  than  the 
descending  branch,  ascends  under  the  anterior  margin  of  the  trapezius,  lying  upon  the  levator 
scapulae  and  splenius  muscles.  It  supplies  branches  to  the  trapezius,  levator  scapulae,  and 
splenius  muscles,  and  the  posterior  chain  of  lymphatic  glands.  It  anastomoses  with  the 
superficial  branch  of  the  descending  branch  of  the  occipital  between  the  splenius  and  semi- 
spinahs  capitis  (complexus) .  It  is  accompanied  by  two  veins.  This  artery  may  arise  directly 
from  the  thyreoid  axis,  or  from  the  third  part  of  the  subclavian  artery. 

3.  THE  INTERNAL  MAMMARY  ARTERY 

The  internal  mammary  artery  [a.  mammaria  interna]  (figs.  457,  462)  comes  off 
from  the  lower  part  of  the  first  portion  of  the  subclavian,  usually  opposite  the 

Fig.    462. — Scheme  of  the  Right  Internal  Mammary  Artery.     (Walsham.) 

_^  Common  carotid  artery 


Phremc  nerve 

Subclavian  artery 

Subclavian  vein,  cut 


Anterior  intercostal  branch 


■  intercostal  branch 


Musculo-phrenic  artery 


Deep  circumflex  iliac  artery 


Internal  jugular  vein 
Subclavian  vein,  cut 
Scalenus  anterior  muscle 

Sternum 

Transversus  thoracis  muscle 
Perforating  branch 


Superior  epigastric  artery 


-Inferior  epigastric  artery 


thyreo-cervical  trunk  (thyreoid  axis),  close  to  the  medial  edge  of  the  scalenus 
anterior,  occasionally  opposite  the  vertebral,  or  at  a  spot  between  these  two  ves- 
sels. It  descends  with  a  slight  inclination  forward  and  medialward,  under  cover 
of  the  clavicle,  and  enters  the  thorax  behind  the  cartilage  of  the  first  rib,  and 
thence  passes  down  behind  the  cartilages  of  the  next  succeeding  ribs,  about  1.2  cm. 
(I  in.  )  from  the  lateral  margin  of  the  sternum,  to  the  sixth  interspace,  where  it 
divides  into  the  superior  epigastric  and  musculo-phrenic.  It  is  accompanied  by 
two  veins,  which  unite  into  one  trunk  behind  the  first  intercostal  muscle;  this 


THE  INTERNAL  MAMMARY  ARTERY  567 

passes  to  the  medial  side  of  the  artery  into  the  corresponding  vena  innominata, 
or  occasionally  on  the  right  side  into  the  vena  cava  superior  direct.  The  artery 
may  be  divided  into  two  portions,  the  cervical  and  the  thoracic. 

The  cervical  portion  is  covered  by  the  sterno-mastoid  muscle,  subclavian  vein,  and  internal 
jugular  vein,  and  is  crossed  obliquely,  in  the  latero-medial  direction,  by  the  phrenic  nerve. 
It  rests  upon  the  pleura  and  courses  around  the  upper  part  of  the  innominate  vein.  There 
is  no  branch  from  this  part  of  the  artery. 

The  thoracic  portion  lies  behind  the  cartilages  of  the  six  upper  ribs,  and  in  the  interspace 
between  the  ribs  has  in  front  of  it  the  pectoralis  major  and  the  internal  intercostal  muscles 
and  external  intercostal  hgaments.  Behind,  it  is  in  contact  above  with  the  pleura,  but  it  is 
separated  from  it  lower  down  by  shps  of  the  transversus  thoracis  (triangularis  sterni).  On 
the  left  side,  the  artery  between  the  fourth  and  sixth  ribs  may  be  said  to  be  in  the  anterior 
mediastinum,  the  pleura  here  forming  a  notch  for  the  heart.  In  the  first,  second,  and  third 
spaces  the  artery,  if  wounded,  can  be  easily  tied;  but  in  the  fourth  space  the  operation  is  at- 
tended with  more  difficulty.  The  remaining  spaces  are  so  narrow  that  a  portion  of  the  cartilage 
would  have  to  be  removed  to  expose  the  vessel. 

The  branches  of  the  internal  mammary  artery  are: — (l)  The  pericardio- 
phrenic; (2)  the  anterior  mediastinal  and  thymic;  (3)  the  bronchial;  (4)  the  peri- 
cardiac; (5)  the  sternal;  (6)  the  anterior  intercostals;  (7)  the  perforating;  (8)  the 
lateral  costal;  (9)  the  superior  epigastric;  and  (10)  the  musculo-phrenic. 

(1)  The  pericardio-phrenic  artery  [a.  pericaridiophrenica],  is  a  long  slender  vessel  which 
comes  off  from  the  internal  mammary  just  after  it  has  entered  the  chest,  and  descends  with 
the  phrenic  nerve,  at  first  between  the  pleura  and  innominate  vein;  then  (on  the  right  side) 
between  the  pleura  and  the  vena  cava  superior ;  and  lastly,  between  the  pleura  and  the  pericardium 
to  the  diaphragm,  where  it  anastomoses  with  the  other  diaphragmatic  arteries.  It  gives 
branches  both  to  the  pleura  and  pericardium. 

(2)  The  anterior  mediastinal  and  thymic  arteries  [aa.  mediastinales  anteriores  et  thymicae] 
come  off  irregularly  from  the  internal  mammary.  They  are  of  small  size,  and  supply  the  con- 
nective tissue,  fat,  and  lymphatics  in  the  superior  and  anterior  mediastina  and  the  remains  of 
the  thymus  gland. 

(3)  The  bronchial  branches  [rami  bronchiales]  are  often  wanting.  When  present  they  are 
supphed  to  the  bronchi  and  the  lower  part  of  the  trachea. 

(4)  The  pericardiac  branches  are  distributed  to  the  anterior  surface  of  the  pericardium. 

(5)  The  sternal  branches  [rami  sternales]  enter  the  nutrient  foramina  in  the  sternum,  and 
also  supply  the  transversus  thoracis  (triangularis  sterni). 

(6)  The  anterior  intercostal  branches  [rami  intercostales]  (figs.  463,  478) — two  in  each  of 
the  five  or  six  upper  intercostal  spaces — run  laterally  from  the  internal  mammary  artery, 
along  the  lower  border  of  the  rib  above  and  the  upper  border  of  the  rib  below,  and  anastomose 
with  the  corresponding  anterior  and  collateral  branches  of  the  aortic  intercostals.  Each  pair 
of  branches  sometimes  arises  by  a  common  trunk  from  the  internal  mammary,  which  in  this  case 
soon  divides  into  an  upper  and  a  lower  branch,  as  above  described.  They  lie  at  first  between 
the  internal  intercostal  muscles  and  the  pleura;  afterward  between  the  external  and  internal 
intercostal  muscles.     They  supply  the  contiguous  muscles,  the  pectoralis  major,  and  the  ribs. 

(7)  The  perforating  or  anterior  perforating  branches  [rami  perforantes] — five  or  six  in 
number,  one  corresponding  to  each  of  the  five  or  six  upper  spaces — come  off  from  the  front  of 
the  internal  mammary,  between  the  superior  and  inferior  anterior  intercostals,  and,  perforating 
the  internal  intercostal  muscles,  pass  forward  between  the  costal  cartilages  to  the  pectoralis 
major,  which  they  supply  [rami  musculares].  The  terminal  twigs  perforate  that  muscle  close 
to  ttie  sternum,  and  are  distributed  to  the  integument  [rami  cutanei].  The  second,  third,  and 
fourth  perforating  supply  the  inner  and  deep  surface  of  the  mammary  gland,  and  become 
greatly  enlarged  during  lactation  [rami  mammaria].  They  frequently  require  ligation  in 
excision  of  the  breast. 

(8)  The  lateral  costal  branch  [ramus  costales  lateralis]  is  given  off  close  to  the  first  rib,  and 
descends  behind  the  ribs  just  external  to  the  costal  cartilages.  It  anastomoses  with  the  upper 
intercostal  arteries.     This  vessel  is  often  of  insignificant  size,  or  absent. 

(9)  The  superior  epigastric  artery  [a.  epigastrica  superior]  (fig.  462),  or  medial  terminal 
branch  of  the  internal  mammary  artery,  leaves  the  thorax  behind  the  seventh  costal  cartilage 
by  passing  through  the  costo-xiphoid  space  in  the  diaphragm.  It  is  the  direct  prolongation  of 
the  internal  mammary  downward.  In  the  abdomen  it  descends  behind  the  rectus  muscle, 
between  its  posterior  surface  and  its  sheath,  and,  lower,  entering  the  substance  of  the  muscle, 
anastomoses  with  the  inferior  epigastric,  a  branch  of  the  external  iliac.  It  gives  off  the  following 
small  branches: — (o)  The  phrenic,  to  the  diaphragm;  (b)  the  xiphoid,  which  crosses  in  front  of 
the  xiphoid  cartilage,  and  anastomoses  with  the  artery  of  the  opposite  side;  (c)  the  cutaneous, 
which  perforate  the  anterior  layer  of  the  sheath  of  the  rectus  and  supply  the  integuments; 
(d)  the  muscular,  to  the  rectus  muscle,  some  of  which  perforate  the  rectus  sheath  laterally,  and 
are  distributed  to  the  obhque  muscles;  (e)  the  hepatic  (on  the  right  side  only),  which  pass  along 
the  falciform  ligament  to  the  liver,  and  anastomose  with  the  hepatic  artery;  (/)  the  peritoneal, 
which  perforate  the  posterior  layer  of  the  sheath  of  the  rectus,  and  ramify  on  the  peritoneum. 

(10)  The  musculo-phrenic  artery  [a.  musculophrenica],  or  lateral  terminal  branch  of  the 
internal  mammary  artery,  skirts  laterally  and  downward  behind  the  costal  cartilages  of  the 
false  ribs  along  the  costal  attachments  of  the  diaphragm,  which  it  perforates  opposite  the  ninth 
rib.  It  terminates,  much  reduced  in  size,  at  the  tenth  or  eleventh  intercostal  space  by  anasto- 
mosing with  the  ascending  branch  of  the  deep  circumflex  iUac  artery.  It  gives  off  in  its  course 
the  following  small  branches: — (a)  The  phrenic  for  the  supply  of  the  diaphragm;  (b)  the  an- 
terior intercostals,  two  in  number  for  each  of  the  lower  five  or  six  intercostal  spaces,  are  dis- 


568 


THE  BLOOD-VASCULAR  SYSTEM 


tributed  like  those  to  the  upper  spaces,  aheady  described,  and  anastomose  like  them  with  the 
corresponding  anterior  branches  of  the  lower  aortic  intercostals;  (c)  the  muscular  for  the  supply 
of  the  oblique  muscles  of  the  abdomen. 

4.  THE  COSTO-CERVICAL  TRUNK 

The  costo-cervical  trunk  [truncus  costocervicalis]  (figs.  444,  463)  is  a  short 
stem  which  arises  usually  from  the  back  part  of  the  second  portion  of  the  sub- 
clavian artery,  behind  the  scalenus  anterior  on  the  right  side,  but  commonly 
just  medial  to  that  muscle  on  the  left  side.  Its  course  is  upward  and  backward 
above  the  dome  of  the  pleura  and  then  downward  toward  the  thorax,  before 
entering  which  it  divides  into  its  two  terminal  branches. 

The  branches  of  the  costo-cervical  trunk  are : — (1)  the  superior  intercostal  and 
(2)  the  deep  cervical. 

(1)  The  superior  intercostal  [a.  intercostahs  suprema]  (fig.  463)  continues  the  direction  of 
the  costo-cervical  trunk,  passing  downward  into  the  thorax  in  front  of  the  neck  of  the  first  rib. 
It  sometimes  terminates  opposite  the  first  intercostal  space  by  becoming  the  first  intercostal 
artery.  Usually,  however,  it  is  prolonged  downward  over  the  neck  of  the  second  rib  and  supplies 
the  second  intercostal  space  in  addition.  It  communicates  with  the  highest  aortic  intercostal 
artery.  As  it  crosses  the  neck  of  the  first  rib  the  superior  intercostal  lies  anterior  (ventral) 
to  the  first  intercostal  nerve  and  lateral  to  the  superior  thoracic  ganghon  of  the  sympathetic. 

Fig.  463. — Scheme  of  the  Right  Costo-cervical  Trunk.     (Walsham.) 


Scalenus  anterior  muscle 

Deep  cervical  branchi 

First  thoracic  nerve 

First  intercostal  nerve. 
Subclavian  artery. 

Second  intercostal  nerve 


Anterior  intercostal 
artery 
Third  intercostal^ 
nerve 


Anterior  intercostal 

artery 

Internal  mammary 

artery 

Intercostal  vessels  of, 
third  space 


Sympathetic  nerve 


Costo-cervical  trunk 


Arteria  aberrans 


Arteria  aberrans 


Intercostal  vessels  of  fourth  space 


The  branches  to  the  first  and  second  intercostal  spaces  resemble  in  course  and  distribution 
the  succeeding  intercostals  derived  from  the  thoracic  aorta  (see  p.  588).  Like  the  aortic  inter- 
costals they  give  off  dorsal  [rr.  dorsales]  and  spinal  branches  [rr.  spinalesj.  An  arteria  aberrans, 
when  present,  arises  from  the  medial  side  of  the  right  superior  intercostal,  or  occasionally  from 
the  right  subclavian  itself.  It  descends  as  a  slender  vessel  into  the  thorax,  passing  downward 
and  medially  behind  the  oesophagus  as  far  as  the  third  or  fourth  thoracic  vertebra,  where  in 
some  cases  it  anastomoses  with  a  similar  slender  branch  arising  from  the  aorta  below  the  hga- 
mentum  arteriosum.  This  anastomosis  represents  the  remains  of  the  embryonic  right 
dorsal  aortic  arch,  and  it  is  by  its  occasional  enlargement  that  the  anomaly  of  the  right  sub- 
clavian artery  rising  from  the  descending  portion  of  the  aortic  arch  occurs  (see  p.  637). 

(2)  The  deep  cervical  artery  [a.  cervicahs  profunda]  passes  directly  backward,  first  between 
the  seventh  and  eighth  cervical  nerves,  and  then  between  the  transverse  process  of  the  seventh 
cervical  vertebra  and  the  neck  of  the  first  rib,  having  the  body  of  the  seventh  cervical  vertebra 
to  its  medial  side,  and  the  intertransverse  muscle  to  its  lateral  side.  It  then  tm'ns  upward 
in  the  groove  between  the  transverse  and  spinous  processes  of  the  cervical  vertebrae  lying  upon 
the  semispinaUs  colh.  It  is  covered  by  the  semispinahs  capitis  (complexus).  Between  these 
muscles  it  anastomoses  with  the  deep  branch  of  the  descending  branch  (princeps  cervicis)  of 
the  occipital  artery.  It  gives  off  a  spinal  branch  which  enters  the  vertebral  canal  through 
the  intervertebral  foramen  with  the  eighth  cervical  nerve. 


THE  AXILLARY  ARTERY 


569 


THE  AXILLARY  ARTERY 


The  term  axillary  is  applied  to  that  portion  of  the  maia  arterial  stem  of  the 
upper  limb  that  passes  through  the  axillary  fossa.  The  axillary  artery  [a.  axillaris] 
(fig.  464)  therefore  is  continuous  -with  the  subclavian  above  and  with  the  brachial 
below.  It  extends  from  the  lateral  border  of  the  first  rib  to  the  lower  edge  of  the 
teres  major  muscle,  and  has  the  shoulder-joint  and  the  neck  of  the  humerus  to 
its  lateral  side.  When  the  arm  is  placed  close  to  the  side  of  the  body,  the  artery 
forms  a  gentle  curve  with  its  convexity  upward;  but  when  the  arm  is  carried  out 
from  the  side  at  right  angles  to  the  trunk  in  the  ordinary  dissecting  position,  the 
vessel  takes  a  nearly  straight  course,  which  will  then  be  indicated  by  a  Hne  drawn 
from  the  middle  of  the  clavicle  to  the  groove  on  the  medial  side  of  the  coraco- 
brachialis  and  biceps  muscles.  The  axillary  artery  is  at  first  deeply  placed 
beneath  the  pectoral  muscles,  but  in  its  lower  third  it  is  superficial,  being  covered 

Fig.  464. — The  Axillary  Artery.     (After  Spalteholz.) 

Axillary  artery 

Thoraco-acromial  artery      I  . 

I      Axillary  vein 
Acromial  branch  I  ,  J 

Deltoid  branch 
Musculo-cutaneous  j 
Circumflex  humeral  artery 
Coraco  brachial  muscle 

Deltoid  muscle 
Pectorahs 
major  muscle 


(       '     Deltoid  branch^  . 

Median     !  Ulnar  nerve     /      /  / 

nerve        I     Brachial    cutaneous/       '  / 
Brachial  vein        and  medial  anti-       /  / 
brachial  nerves  / 

Axillary  nerve  / 
Subscapular  artery 
Latissimus  dorsi  muscle ' 


Pectoralis  minor  muscle 


'■<       y^^    Pectoral  branches 


umflex  scapular  artery 


Lateral  thoracic  artery 
sal  thoracic  artery 


only  by  the  skin  and  the  superficial  fascia  and  deep  fascia.  It  is  divided  into 
three  parts,  first,  second,  and  third,  according  as  it  lies  respectively  above, 
beneath,  or  below  the  pectoralis  minor. 

The  First  Part  of  the  Axillary  Artery 

The  first  part  of  the  axillary  artery  extends  from  the  lateral  border  of  the  first 
rib  to  the  upper  border  of  the  pectorahs  minor.  It  measures  about  2.5  cm.  (1  in.) 
in  length. 

Relations. — In  front  it  is  covered  by  the  skin,  superficial  fascia,  lower  part  of  the  platysma, 
the  deep  fascia,  the  pectorahs  major,  the  coraco-clavioular  (costo-ooracoid)  fascia,  the  sub- 
clavius  muscle  and  the  clavicle  when  the  arm  hangs  down  by  the  side.  The  cephalic  and 
thoraco-acromial  veins,  the  external  anterior  thoracic  nerve,  and  the  axillary  lymphatic  trunk, 
cross  over  it.  A  layer  of  the  deep  cervical  fascia  which  has  passed  under  the  clavicle  also 
descends  in  front  of  it. 


570  THE  BLOOD-VASCULAR  SYSTEM 

Behind,  it  rests  upon  the  first  intercostal  space  and  first  intercostal  muscle,  the  first  digita- 
tion  and  sometimes  a  portion  of  the  second  digitation  of  the  serratus  anterior  (magnus)  muscle, 
and  a  part  of  the  second  rib.  The  long  thoracic  nerve,  on  its  way  to  the  serratus  anterior 
muscle,  passes  behind  it. 

To  its  lateral  side,  and  somewhat  on  a  higher  plane,  are  the  cords  of  the  brachial  plexus. 

To  its  medial  side,  and  on  a  slightly  anterior  plane,  is  the  axillary  vein.  The  internal 
anterior  thoracic  nerve  courses  between  the  vein  and  the  artery. 

The  Second  Part  of  the  Axillary  Artery 

The  second  part  of  the  axillary  artery  (fig.  464)  lies  beneath  the  pectoralis 
minor  deep  in  the  axilla.     It  measures  3  cm.  (a  little  more  than  1  in.)  in  length. 

Relations. — In  front,  in  addition  to  the  pectorahs  minor,  it  is  covered  by  the  pectoralis 
major  and  the  integuments. 

Behind,  it  is  separated  by  a  considerable  interval,  containing  loose  connective  tissue  and 
fat,  from  the  subscapularis  muscle;  whilst  behind,  and  in  contact  with  it,  is  the  posterior  cord 
of  the  brachial  plexus. 

To  the  medial  side,  but  separated  from  the  artery  by  the  medial  cord  of  the  brachial 
plexus,  is  the  axillary  vein. 

To  the  lateral  side  is  the  lateral  cord  of  the  brachial  plexus,  and  at  some  little  distance 
the  coracoid  process. 

It  is  thus  seen  that  the  second  portion  of  the  auxiliary  artery  is  surrounded  on  three  sides 
by  the  cords  of  the  brachial  plexus — one  behind,  one  medial,  and  one  lateral. 

The  Third  Part  of  the  Axillary  Artery 

The  third  part  of  the  axillary  artery  (fig.  464)  extends  from  the  lower  border 
of  the  pectoralis  minor  to  the  lower  border  of  the  teres  major.  Its  upper  half  lies 
deeply  placed  within  the  axilla,  beneath  the  lower  edge  of  the  pectoralis  major 
muscle,  but  its  lower  half  is  in  the  arm  external  to  the  axilla,  and  is  uncovered  by 
muscle.     It  measures  about  7.5  cm.  (3  in.)  in  length. 

Relations. — In  front  it  has,  in  addition  to  the  skin  and  superficial  fascia,  the  pectorahs 
major  above,  and  lower  down  the  deep  fascia  of  the  arm.  It  is  crossed  obhquely  by  the  medial 
root  of  the  median  nerve  and  by  the  lateral  brachial  vena  comitans. 

Behind,  it  lies  successively  upon  the  subscapularis,  the  latissimus  dorsi,  and  teres  major 
muscles.  From  the  first-named  muscle  it  is  separated  at  first  by  a  considerable  mass  of  fat 
and  cellular  tissue.  The  radial  (musculo-spiral)  and  axillary  (circumflex)  nerves  intervene 
between  the  artery  and  the  muscles. 

On  its  lateral  side  it  is  separated  from  the  bone  by  the  coraco-brachialis,  by  which  it  is 
partly  overlapped,  this  muscle  and  the  short  head  of  the  biceps  serving  as  a  guide  to  the  artery 
in  hgature.  For  a  part  of  its  course  it  has  also  the  musculo-cutaneous  nerve  and  the  lateral 
root  of  the  median  nerve  to  its  lateral  side. 

To  its  medial  side  it  has  the  axillary  vein,  the  ulnar  nerve,  the  medial  antibrachial  (internal) 
and  brachial  (lesser  internal)  cutaneous  nerves,  and  the  medial  root  of  the  median  nerve. 
The  ulnar  nerve  is  between  the  artery  and  the  vein.  The  medial  antibrachial  (internal) 
cutaneous  nerve  is  a  httle  in  front  of  the  artery  as  well  as  medial  to  it. 

Branches  of  the  Axillary  Artery 

The  branches  of  the  axillary  artery  are  exceedingly  variable.  In  fig.  465  is 
shown  what  Hitzrot  has  found  the  usual  type,  in  which  the  second  portion  of 
the  artery  has  no  named  branches.  The  figure  brings  out  the  segmental  relation 
of  the  branches  of  the  axillary  artery  to  the  chest  wall  and  suggests  how  one  of  the 
branches  may  supply  the  place  of  another.  If  the  lateral  thoracic  arises  directly 
from  the  axillary,  it  is  generally  from  the  second  part  as  described  below.  In 
addition  to  the  larger  branches  of  the  artery  small  twigs  are  supplied  to  the  ser- 
ratus anterior,  coraco-brachialis,  and  subscapularis;  also  to  the  axillary  lymph- 
nodes. 

The  first  part  gives  off. — ^(1)  The  superior  thoracic;  and  (2)  the  thoraco- 
acromial. 

The  second  part  gives  off: — (3)  The  lateral  thoracic. 

The  third  part  gives  off: — (4)  The  subscapular;  (5)  the  anterior  humeral 
circumflex;  and  (6)  the  posterior  humeral  circumflex. 

Branches  of  the  Axillary  Artery 

1.  The  superior  thoracic  [a.  thoracalis  suprema]  is  variously  given  off  from  the 
axillary  artery,  usually  either  as  a  common  trunk'  with  the  next  branch,  the 


THE  AXILLARY  ARTERY 


571 


thoraco-acromial,  or  a  little  above.  It  passes  behind  the  axillary  vein  across  the 
first  intercostal  space,  supplying  the  intercostal  muscles  and  the  upper  portion 
of  the  serratus  anterior,  and  anastomoses  with  the  intercostal  arteries.  At 
times  it  sends  a  branch  between  the  pectoralis  major  and  minor,  which  then,  as  a 
rule,  more  or  less  takes  the  place  of  the  pectoral  branch  of  the  thoraco-acromial 
(figs.  464  and  465). 

2.  The  thoraco-acromial  or  acromio-thoracic  axis  [a.  thoracoacromialis] 
arises  from  the  front  part  of  the  axillary  just  above  the  upper  border  of  the 
pectoralis  minor.  It  is  a  short  trunk,  and,  coming  off  from  the  front  of  the 
artery,  pierces  the  coraco-clavicular  fascia,  and  then  divides  into  three  or  four  small 
branches,  named  from  their  direction: — (a)  the  acromial;  (b)  the  deltoid;  (c)  the 
pectoral,  and  {d)  the  clavicular. 

Fig.  46.5. — The  Branches  of  the  Axillary  Artery.     (After  Hitzrot.) 
The  numbers  1-5  indicate  the  intercostal  spaces. 


Thoraco-acromial 
Superior  thoracic  Clavicular  branch 


/M/,:^ 


Acromial  branch 

Pectoral  branch 

Deltoid  branch 


Anterior  circumflex 

humeral 
Posterior  circumflex 
humeral 


Branch  to  teres  major 


Branches  to  latissimus  do 


Branch  to  serratus  anterior 


(a)  The  acromial  branch  [r.  acromiaUs]  or  branches  pass  laterally  across  the  coracoid 
process,  frequently  through  the  deltoid  muscle,  which  they  in  part  supply,  to  the  acromion, 
where  they  form,  by  anastomosing  with  the  anterior  and  posterior  circumflex  and  transverse 
scapular  (suprascapular)  arteries,  the  so-called  acromial  rete,  or  plexus  of  vessels  on  the  surface 
of  that  process. 

(6)  The  deltoid  branch  [r.  deltoideus]  runs  downward  with  the  cephalic  vein  in  the  interval 
between  the  pectorahs  major  and  the  deltoid,  and,  supplying  lateral  ofTsets  to  these  muscles 
and  the  adjacent  integument,  anastomoses  with  the  anterior  and  posterior  circumflex  humeral 
arteries. 

(c)  The  pectoral  branch  [r.  pectorahs]  passes  between  the  pectorahs  major  and  minor 
muscles,  both  of  which  it  supplies.  In  the  female,  one  or  more  branches  which  perforate  the 
pectoralis  major  are  often  of  large  size,  and  supply  the  superimposed  mammary  gland. 

(d)  The  clavicular  branch  passes  upward  beneath  the  clavicle,  supphes  the  subclavius 
muscle,  and  anastomoses  with  the  transverse  scapular  artery. 

3.  The  lateral  thoracic  artery  [a.  thoracalis  lateralis]  descends  along  the  lower 
border  of  the  pectoralis  minor,  under  cover  of  the  pectoralis  major,  to  the  chest 
wall.  It  supplies  both  pectoral  muscles  and  the  serratus  anterior  fmagnus), 
sends  branches  around  the  lower  border  of  the  pectoralis  major  to  the  mammary 
gland,  and  terminates  in  the  intercostal  muscles  by  anastomosing  with  the  aortic 
intercostals  and  the  internal  mammary.  It  also  furnishes  branches  to  the 
lymph-nodes  of  the  axillary  fossa.  The  branches  to  the  mammary  gland  in  the 
female  are  often  of  large  size. 

4.  The  subscapular  artery  [a.  subscapularis]  is  the  largest  branch  of  the 
axillary.     It  arises  opposite  the  lower  border  of  the  subscapularis,  and  runs  in  a 


572 


THE  BLOOD-VASCULAR  SYSTEM 


downward  and  medial  direction  along  the  anterior  border  of  that  muscle  under 
cover  of  the  latissimus  dorsi.  It  supplies  the  subscapularis,  teres  major,  latissimus 
dorsi,  and  serratus  anterior  (magnus)  muscles,  and  gives  branches  to  the  nodes 
in  the  axillary  fossa.  The  course  of  this  large  vessel  along  the  posterior  border 
of  the  axillary  fossa  should  be  remembered  in  opening  abscesses  in  the  fossa,  and 
in  removing  enlarged  nodes  from  it.  It  is  accompanied  by  two  veins,  which 
usually  unite  and  then  receive  the  circumflex  (dorsal)  scapular  vein,  and  open  as 
a  single  vein  of  large  size  either  into  the  axillary  or  at  the  confluence  of  the  medial 
brachial  vena  comitans  with  the  basilic  vein. 

About  2.5  or  3.7  cm.  (1  or  1|  in.)  from  its  origin,  the  subscapular  artery  divides 
into  two  end  branches,  (1)  the  circumflex  (dorsal)  scapular,  and  (2)  the  dorsal 
thoracic. 

Fig.  466. — The  Anastomoses  about  the  Scapula. 
Subscapular  branch  of  transverse  scapular  artery 
Supraspinous  branch  of  transverse  scapular  artery 


Descending  branch 
of  transverse  cer- 
vical artery 


Transverse  scapular  artery 


Acromial  branch  of 

thoraco-acromial 
Acromial  rete 


Subscapular    branch    of 

transverse  scapular 

artery 
Infraspinous  branch  of 

transverse  scapular 

artery 
Subscapular  branch  of 
axillary  artery 


Circumflex  scapular  artery 


Infrascapular  branch  of  cir- 
cumflex scapular  artery 


Branch    of    inter 
costal  artery 


Branch  of  inter- 
costal artery 
Continuation  of  de- 
scending branch 
of  transverse  cer- 
vical artery 


(1)  The  circumflex  scapular  artery  [a.  circumflexa  scapulae],  or  dorsal  scapular,  arising 
from  the  subscapular,  usually  at  the  point  above  mentioned,  passes  backward  through  the  trian- 
gular space  bounded  by  the  subscapularis  above,  the  teres  major  below,  and  the  long  head  of 
the  triceps  laterally,  and  then  between  the  teres  minor  and  the  axiUary  border  of  the  scapula, 
which  it  commonly  grooves.  It  thus  reaches  the  infraspinous  fossa,  where,  under  cover  of 
the  infra-spinatus,  it  anastomoses  with  the  transverse  scapular  (suprascapular)  artery  and  the 
descending  branch  of  the  transverse  cervical  (posterior  scapular)  (fig.  466).  As  it  passes  through 
the  triangular  space,  it  gives  off  a  ventral  branch  which  ramifies  between  the  subscapularis 
and  the  bone,  supplying  branches  to  the  subscapularis,  to  the  scapula,  and  to  the  shoulder- 
joint.  A  second  branch  is  often  given  off  near  the  triangular  space  and  passes  downward 
between  the  teres  major  and  teres  minor,  supplying  both  muscles  (fig.  467). 

(2)  The  dorsal  thoracic  artery  [a.  thoracodorsahs]  continues  in  the  course  of  the  subscapular 
as  far  as  the  angle  of  the  scapula,  where  it  anastomoses  with  the  circumflex  scapular,  the 
descending  branch  of  the  transverse  cervical  (posterior  scapular),  the  lateral  thoracic,  and 
intercostal  arteries. 

5.  The  anterior  circumflex  humeral  artery  [a.  circumflexa  humeri  anterior], 
usually  quite  a  small  vessel,  comes  off  from  the  lateral  side  of  the  axillary  artery, 
generally  opposite  the  posterior  circumflex.  It  passes  beneath  the  coraco- 
brachialis  and  short  and  long  heads  of  the  biceps,  winding  transversely  round  the 
front  of  the  surgical  neck  of  the  humerus,  across  the  intertubercular  (bicipital) 
groove,  and  anastomoses  ^vith  the  posterior  circumflex  and  thoraco-acromial 
arteries.     It  gives  off  the  following  small  branches: 


THE  BRACHIAL  ARTERY 


573 


(o)  The  bicipital  or  ascending,  which  runs  up  the  intertubercular  groove  to  supply  the  long 
tendon  of  the  biceps  and  the  shoulder-joint;  and  (h)  a  pectoral  or  descending  branch,  which 
runs  downward  along  the  insertion  of  the  pectorahs  major,  and  supplies  the  tendon  of  that 
muscle.  The  anterior  circumflex  artery,  in  consequence  of  its  being  close  to  the  bone,  is 
sometimes  difficult  to  secure  in  the  operation  for  excision  of  the  shoulder-joint. 

6.  The  posterior  circumflex  humeral  artery  [a.  circumflexa  humeri  posterior] 
(fig.  467)  arises  from  the  posterior  aspect  of  the  axillary,  just  below  the  lower 
border  of  the  subscapularis  muscle.  It  passes  through  the  quadrilateral  space, 
bounded  by  the  teres  minor  above,  the  latissimus  dorsi  and  teres  major  below,  the 
humerus  laterally,  and  the  long  head  of  the  triceps  medially,  and,  winding  round 
the  back  of  the  humerus  beneath  the  deltoid,  breaks  up  under  cover  of  that  muscle 
into  a  leash  of  branches,  which  for  the  most  part  enter  its  substance.  The  axillary 
(circumflex)  nerve  and  two  vense  comitantes  run  with  it.  It  anastomoses  with 
the  anterior  circumflex,  the  arteries  on  the  acromion,  and  the  profunda  artery. 

Fig.  467. — The  Arteries  of  the  SHOtiLDER.     (After  Spalteholz.) 
Transverse  cervical  artery 

Ascending  branch    1     Superior  transverse  scapular  Ugament 
Descending  branch    !  '  '  Transverse  scapular  artery 

—Acromion 
^^_^  «„_^     -Acromial  branch 

/A '__'__ __  ;  _'^.       _  ^^ 

■Deltoid  muscle 


Infraspinatus  muscle 


CIrcumSex 
scapular  artery 
Teres  minor  muscle   i 
Posterior  circumflex 
Teres  major         humeral  artery 
muscle 


Triceps  muscle  (lateral  head) 
Triceps  muscle  (long  head) 


In  addition  to  the  leash  of  vessels  to  the  deltoid,  it  gives  off  the  following  small  branches: 
— (a)  nutrient,  to  the  greater  tuberosity  of  the  humerus;  (b)  articular,  to  the  back  of  the  shoulder- 
joint;  (c)  acromial,  to  the  plexus  on  the  acromion;  and  [d)  muscular,  to  the  teres  minor  and  long 
and  short  heads  of  the  triceps.  One  or  more  of  these  branches  to  the  triceps  descend  either 
between  the  lateral  and  long  head  or  in  the  substance  of  that  muscle,  to  anastomose  with  an 
ascending  branch  from  the  profunda  artery.  It  is  by  means  of  this  anastomosis  that  the 
collateral  circulation  is  chiefly  carried  on  when  the  axillary  or  the  brachial  artery  is  tied  between 
the  origins  of  the  posterior  circumflex  and  profunda  arteries. 


THE  BRACHIAL  ARTERY 

The  brachial  artery  [a.  brachialis]  (fig.  468),  the  continuation  of  the  axillary, 
extends  from  the  lower  border  of  the  teres  major  to  a  little  below  the  centre  of  the 
crease  at  the  bend  of  the  elbow,  where  it  divides,  opposite  the  junction  of  the 
head  with  the  neck  of  the  radius,  into  the  radial  and  ulnar  arteries.  The  artery 
is  situated  at  first  medial  to  the  humerus;  but  as  it  passes  down  the  arm  it  gradually 
gets  in  front  of  the  bone,  and  at  the  bend  of  the  elbow  lies  midway  between  the 
two  epicondyles.  Hence,  in  controlling  hiemorrhage,  the  artery  should  be  com- 
pressed laterally  against  the  bone  in  its  upper  third,  laterally  and  backward  in  its 
middle  third,  and  directly  backward  in  its  lower  third.  Throughout  the  greater 
part  of  its  course  the  artery  is  superficial,  being  merely  overlapped  slightly  on 


574 


THE  BLOOD^VASCULAR  SYSTEM 


its  lateral  side  by  the  coraco-brachialis  and  biceps  muscles;  but  at  the  bend  of 
the  elbow  it  sinks  deeply  beneath  the  lacertus  fibrosus  of  the  biceps  into  the 
triangular  interval  (antecubital  space)  bounded  on  either  side  by  the  brachio- 

FiG.  468. — The  Brachial  Artery.     (After  Toldt,  "Atlas  of  Human   Anatomy"  Rebman, 
London  and  New  York.) 

Subscapular  artery 


Deltoid  pectoral  triangle 

Thoraco-  f  Acromial  branch 
acromial  ] 
artery      [  Deltoid  branch 


Axillary  lymph-nodes 
''y-  Dorsal  thoracic  artery 


Circumflex  scapular 
artery 


Cutaneous  branch—  V 

Coraco-brachiahs 
Brachial  artery  - 


Deltoid  muscle  — t 


Lateral  antibrachial  cutaneous  nerve f™"-^' 

/    ^ 

Brachial  artery 
Lacertus  fibrosus 
Brachio-radialis  muscle- — ' 

Radial  recurrent  artery-^ 


Cutaneous  branches  v. 


|"~ Antibrachial  fascia 


radialis  and  pronator  teres,  and  at  its  bifurcation  is  more  or  less  under  cover 
of  these  muscles  (fig.  469).  The  sheath  of  the  brachial  artery  is  closely  incor- 
porated with  the  fascia  covering  the  biceps  muscle,  and  it  is  for  this  reason  that 
in  the  operation  for  hgaturing  the  vessel  is  apt  to  be  retracted  with  the  muscle. 


THE  BRACHIAL  ARTERY 


575 


A  line  drawn  from  the  groove  medial  to  the  coraco-brachialis  and  biceps  muscles 
to  midway  between  the  epicondyles  of  the  humerus  will  indicate  its  course.  It 
is  accompanied  by  two  veins  which  frequently  communicate  across  the  artery. 
In  addition  to  the  branches  named  below  the  iDrachial  artery  gives  off  numerous 
muscular  branches  and,  occasionally,  the  nutrient  artery  to  the  humerus.  The 
muscular  branches  usualty  come  off  from  the  lateral  side  of  the  artery;  one  in 
particular,  which  supplies  the  biceps  muscle,  is  frequently  of  large  size. 

Relations. — In  front,  the  artery  is  covered  by  the  integument  and  superficial  and  deep 
fasciae,  and  at  the  bend  of  the  elbow  by  the  lacertus  fibrosus  of  the  biceps,  and  in  muscular 
subjects  by  the  overlapping  margins  of  the  brachio-radialis  and  pronator  teres.  In  the  middle 
third  of  the  arm  it  is  crossed  obliquely  from  the  lateral  to  the  medial  side  by  the  median  nerve, 
and  at  the  bend  of  the  elbow  by  the  median  cubital  vein,  the  bicipital  fascia  intervening  (fig. 475). 

Behind,  it  lies  successively  on  the  long  head  of  the  triceps  (from  which  it  is  separated  by 
the  radial  (musculo-spiral)  nerve  and  profunda  artery),  on  the  medial  head  of  the  triceps, 
on  the  insertion  of  the  ooraco-braohialis,  and  thence  to  its  bifurcation  on  the  brachiahs  muscle. 

Fig.  469. — The  Brachial  Ahteey  at  the  Bend  of  the  Elbow,  Left  Side,  Front  View. 
(From  a  mounted  specimen  in  the  Anatomical  Department  of  Trinity  College,  Dublin.) 


Posterior   branch  of   medial 

antibracliial    cutaneous 

nerve 
Anterior    branch    of    medial 

antibrachial    cutaneous 

nerve 

Brachial  artery 


Branch  to  pronator  teres 
Lacertus  fibrosus,  cut 

Pronator  teres  muscle 

Median  nerve 

Ulnar  artery 


Superficial  radial  nerve 

Radial  recurrent  artery  and 
deep  radial  nerve 

Tendon  of  biceps 

Musculo-cutaneous  nerve 

Brachio-radialis  muscle 


* —  Radial  artery 


Lateral  to  the  artery  is  the  coraco-brachialis  above,  and  the  muscular  belly  of  the  biceps 
below,  both  of  which  shghtly  overlap  the  vessel,  and  at  the  bend  of  the  elbow  the  tendon  of 
the  biceps.  The  lateral  vena  comitans  is  also  to  its  lateral  side.  The  median  nerve  is  in  close 
contact  with  the  lateral  side  of  the  artery  in  the  upper  third  of  its  course,  but  in  the  middle  third 
crosses  the  artery  obliquely  to  gain  the  medial  side. 

Medial  to  the  artery  in  the  upper  part  of  its  course  are  the  medial  antibrachial  (internal) 
cutaneous  and  the  ulnar  nerves;  the  latter  nerve,  however,  leaves  the  artery  about  the  origin 
of  the  ulnar  collateral  (inferior  profunda)  branch,  to  make,  with  that  vessel,  for  the  medial 
epicondyle.  Lower  down,  the  medial  antibrachial  cutaneous  nerve  also  leaves  the  artery, 
by  piercing  the  deep  fascia.  The  median  nerve  is  in  close  contact  with  the  medial  side  of  the 
artery  in  its  lower  third  and  at  the  bend  of  the  elbow.  The  basilic  vein  is  superficial  to  it, 
and  a  Uttle  to  its  medial  side  in  the  greater  part  of  its  course,  but  separated  from  it  by  the  deep 
fascia.     The  medial  vena  comitans  runs  along  its  medial  side. 

Branches  of  the  Brachial  Artery 

The  branches  of  the  brachial  artery  are: — (1)  The  profunda  brachii;  (2)  the 
superior  ulnar  collateral  (inferior  profunda);   (3)   the  inferior  ulnar  collateral 


576  THE  BLOOD-VASCULAR  SYSTEM 

(anastomotica  magna);  and  (4)  the  terminal  branches — the  radial  and  ulnar 
arteries. 

(1)  The  Profunda  Artery 

The  profunda  brachii  (superior  profunda)  is  the  largest  branch  of  the  brachial. 
It  arises  from  the  medial  and  hinder  aspect  of  that  artery,  a  Httle  below  the  in- 
ferior border  of  the  tendon  of  the  teres  major.  It  at  first  lies  to  the  medial  side 
of  the  brachial,  but  soon  passes  behind  that  vessel,  and,  sinking  between  the 
medial  and  long  heads  of  the  triceps  with  the  radial  (musculo-spiral)  nerve,  curves 
around  the  humerus  in  the  groove  for  the  nerve,  lying  in  contact  with  the  bone 
between  the  medial  and  lateral  heads  of  the  triceps.  On  reaching  the  lateral 
supracondyloid  ridge  of  the  humerus  it  perforates  the  lateral  intermuscular 
septum,  and,  continuing  forward  between  the  brachio-radialis  and  brachialis  to 
the  front  of  the  lateral  epicondyle,  ends  by  anastomosing  with  the  radial  re- 
current artery  (figs.  468  and  474). 

It  gives  off  the  following  branches: — 

(a)  The  deltoid  branch  [r.  deltoideus]  which  may  also  arise  from  the  brachial  itself  or  from 
the  superior  ulnar  collateral.  It  runs  across  the  anterior  surface  of  the  humerus,  under  cover 
of  the  coraco-brachialis  and  biceps,  and  suppUes  the  brachiahs  and  deltoid. 

(6)  The  middle  collateral  artery  [a.  coUaterahs  media]  runs  in  the  substance  of  the  middle 
head  of  the  triceps  as  far  as  the  elbow,  where  it  terminates  in  the  articular  rete. 

(c)  The  radial  collateral  artery  [a.  collateralis  radialis]  arises  about  the  middle  of  the  upper 
arm,  and  runs  behind  the  lateral  intermuscular  septum  to  the  rete  at  the  elbow-joint. 

(d)  A  nutrient  humeral  artery  [a.  nutritia  humeri],  which  may  come  from  the  brachial 
itself  or  from  a  muscular  branch,  enters  a  canal  in  the  humerus. 

(2)  The  Superior  Ulnar  Collateral  Artery 

The  superior  ulnar  collateral  artery  [a.  collateralis  ulnaris  superior]  (inferior 
profunda)  arises  from  the  medial  side  of  the  brachial,  usually  about  the  level  of 
the  insertion  of  the  coraco-brachialis,  at  times  as  a  common  trunk  with  the 
profunda.  It  passes  with  the  ulnar  nerve  medially  and  downward  through  the 
medial  intermuscular  septum,  and  then  along  the  medial  head  of  the  triceps  to  the 
back  of  the  medial  epicondyle,  where,  under  cover  of  the  deep  fascia  and  the 
origin  of  the  flexor  carpi  ulnaris  from  the  olecranon  and  medial  epicondyle,  it 
enters  into  the  anastomoses  around  the  elbow-joint.  It  frequently  supplies  the 
nutrient  artery  to  the  humerus.  It  gives  branches  to  the  triceps,  to  the  elbow- 
joint,  and  a  branch  which  passes  in  front  of  the  medial  epicondyle  to  anastomose 
with  the  anterior  ulnar  recurrent. 

(3)  The  Inferior  Ulnar  Collateral  Artery 

The  inferior  ulnar  collateral  artery  [a.  collateralis  ulnaris  inferior]  or  anasto- 
motica magna  arises  from  the  medial  side  of  the  brachial,  about  5  cm.  (2  in.)  above 
its  bifurcation  into  the  radial  and  ulnar  arteries,  and,  running  medially  and  down- 
ward across  the  brachialis,  divides  into  two  branches,  a  posterior  and  an  anterior. 
The  posterior  pierces  the  medial  intermuscular  septum,  winds  round  the  medial 
condyloid  ridge  of  the  humerus,  and  pierces  the  triceps,  between  which  and  the 
bone  it  anastomoses  with  the  articular  branch  of  the  profunda  artery,  and  to  a 
lesser  extent  with  the  interosseous  recurrent,  forming  an  arterial  arch  or  rete 
around  the  upper  border  of  the  olecranon  fossa.  The  anterior  branch  passes 
medially  and  downward  between  the  brachialis  and  pronator  teres,  and  anas- 
tomoses in  front  of  the  medial  epicondyle,  but  beneath  the  pronator  teres,  with 
the  anterior  ulnar  recurrent.  From  this  branch  a  small  vessel  passes  down  behind 
the  medial  epicondyle  to  anastomose  with  the  posterior  ulnar  recurrent  and 
superior  ulnar  collateral  arteries  (fig.  474). 

THE  ULNAR  ARTERY 

The  ulnar  artery  [a.  ulnaris]  (fig.  470)  the  larger  of  the  two  terminal  branches 
of  the  brachial,  begins  opposite  the  lower  border  of  the  head  of  the  radiusin  the 
middle  fine  of  the  forearm.     Thence  through  the  upper  half  of  the  forearm  it  runs 


THE  ULNAR  ARTERY  677 

beneath  the  pronator  teres  and  superficial  flexor  muscles,  and,  having  reached  the 
ulnar  side  of  the  arm  about  midway  between  the  elbow  and  the  wrist,  it  passes 
directly  downward,  being  merely  overlapped  by  the  flexor  carpi  ulnaris.  Crossing 
the  transverse  carpal  (anterior  annular)  ligament  immediately  to  the  radial  side 
of  the  pisiform  bone,  it  enters  the  palm,  where  it  divides  into  two  branches,  which 
enter  respectively  into  the  formation  of  the  superficial  and  deep  volar  arches. 
The  artery  is  accompanied  by  two  veins,  which  anastomose  with  each  other  by 
frequent  cross  branches,  and  usually  terminate  in  the  brachial  venae  comitantes. 
The  ulnar  nerve  is  at  first  some  distance  from  the  artery,  but  approaches  the 
vessel  at  the  junction  of  its  upper  and  middle  thirds,  and  then  lies  close  to  its 
medial  or  ulnar  side.  The  course  of  the  artery  in  the  lower  two-thirds  of  the 
forearm  is  indicated  by  a  line  drawn  from  the  front  of  the  medial  epicondyle  to 
the  radial  side  of  the  pisiform  bone;  and  in  the  upper  third  of  the  forearm  by  a 
line  drawn  in  a  gentle  curve  with  its  convexity  to  the  medial  side  from  2.5  cm. 
(1  in.)  below  the  centre  of  the  bend  of  the  elbow  to  a  point  in  the  former  line  at 
the  junction  of  its  upper  with  its  middle  third.  The  artery  throughout  its  course 
is  best  reached  through  the  interval  between  the  flexor  carpi  ulnaris  and  the 
flexor  digitorum  sublimis. 

The  relations  of  the  artery  will  be  given  in  detail  in  the  forearm,  and  in  the  palm  of  the 
hand. 

The  relations  in  the  forearm  are: — 

In  front. — In  the  upper  half  of  the  forearm  the  ulnar  artery  is  deeply  placed  beneath  the 
pronator  teres,  the  flexor  carpi  radialis,  the  palmaris  longus,  and  the  flexor  digitorum  sublimis. 
In  the  lower  half  it  is  comparatively  superficial,  being  merely  overlapped  above  by  the  tendon 
of  the  flexor  carpi  ulnaris,  whilst  the  last  inch  or  so  of  the  vessel  is  only  covered  as  a  rule  by 
the  skin  and  superficial  and  deep  fasciae.  As  the  artery  hes  beneath  the  pronator  teres,  it  is 
crossed  from  the  medial  to  the  lateral  side  by  the  median  nerve,  the  deep  head  of  origin  of  the 
muscle  usually  separating  the  nerve  from  the  artery.  The  lower  part  of  the  artery  is  crossed 
by  the  palmar  cutaneous  branch  of  the  ulnar  nerve. 

Behind. — For  about  2.5  cm.  (1  in.)  of  its  course  the  artery  lies  upon  the  brachialis;  but 
thence,  as  far  as  the  transverse  carpal  (anterior  annular)  ligament,  upon  the  flexor  digitorum 
profundus,  which  separates  it  above  from  the  interosseous  membrane  and  bone,  and  at  the 
wrist  from  the  pronator  quadratus.  The  artery  is  bound  down  to  the  flexor  digitorum  pro- 
fundus by  bands  of  fasciae. 

To  the  lateral  side  in  the  lower  two-thirds  of  its  course  is  the  flexor  digitorum  subMmis. 

To  the  medial  side  in  the  lower  two-thirds  is  the  flexor  carpi  ulnaris,  the  guide  to  the 
vessel.  The  ulnar  nerve,  as  it  enters  the  forearm  from  behind  the  medial  epicondyle,  is  at  first 
some  distance  from  the  artery,  being  separated  from  it  in  its  upper  third  by  the  flexor  digitorum 
subhmis,  but  in  its  lower  two-thirds  is  in  close  contact  with  the  vessel  and  on  its  ulnar  side. 

The  branches  of  the  ulnar  artery  in  the  forearm  are: — 1.  The  ulnar  recurrent 
arteries.  2.  The  common  interosseous.  3.  Muscular.  4.  Dorsal  ulnar  carpal. 
5.  Volar  ulnar  carpal. 

1.  The  ulnar  recurrent  arteries  [aa.  recurrentes  ulnares]  are  two,  the  volar,  and  dorsal. 
The  volar  is  a  small  branch  which  arises  from  the  medial  side  of  the  ulnar  artery,  or  the  dorsal 
ulnar  recurrent,  and,  running  between  the  lateral  edge  of  the  pronator  teres  and  the  brachiahs. 
anastomoses  in  front  of  the  medial  epicondyle  with  the  inferior  and  superior  ulnar  collaterals. 
It  supphes  branches  to  the  muscles  between  which  it  runs,  and  to  the  skin.  The  dorsal,  larger 
than  the  volar,  comes'off  from  the  medial  side  of  the  ulnar  artery,  either  a  little  below  the  latter 
branch,  or  else  as  a  common  trunk  with  it,  and,  passing  between  the  flexores  digitorum  subhmis 
and  profundus,  turns  upward  to  the  back  of  the  medial  epicondyle,  where  it  Ues  with  the  ulnar 
nerve  between  the  two  heads  of  origin  of  the  flexor  carpi  ulnaris.  It  supplies  the  contiguous 
muscles — the  flexor  carpi  ulnaris,  the  palmaris  longus,  and  the  flexores  digitorum  sublimis  and 
profundus — the  elbow-joint,  and  the  ulnar  nerve,  and  anastomoses  with  the  inferior  and  superior 
ulnar  collaterals,  and  with  the  interosseous  recurrent  forming  the  so-called  rete  olecrani. 

2.  The  common  interosseous  artery  [a.  interossea  communis]  is  a  short  thick 
trunk  1.2  cm.  (|  in.)  or  so  in  length,  which  comes  off  from  the  lateral  and  back 
part  of  the  ulnar  artery  about  2.5  cm.  (  1  in.)  from  its  origin,  and  just  before 
that  artery  is  crossed  by  the  median  nerve.  It  passes  backward  and  downward 
between  the  flexor  pollicis  longus  and  the  flexor  digitorum  profundus,  toward  the 
triaagular  interval  bounded  by  the  upper  border  of  the  interosseous  membrane, 
the  oblique  hgament,  and  the  lateral  border  of  the  ulna,  where  it  divides  into  the 
volar  and  dorsal  interosseous  arteries. 

(a)  The  volar  interosseous  artery  [a.  interossea  volaris],  smaller  than  the  dorsal,  but 

apparently  the  direct  continuation  of  the  common  trunk,  courses  downward  in  front  of  the 

.  interosseous  membrane.     It  lies  under  cover  of  the  overlapping  edges  of  the  flexor  digitorum 

profundus  and  flexor  poUicis  longus,  to  both  of  which  muscles  it  supphes  branches.    At  the 


578 


THE  BLOOD-VASCULAR  SYSTEM 


upper  border  of  the  pronator  quadratus  it  divides  into  two  branches,  an  anterior  terminal 
and  a  posterior  terminal  (fig.  473). 

The  volar  interosseous  artery  is  accompanied  by  two  veins  and  by  the  deep  branch  of  the 
median  nerve  which  hes  to  its  radial  side.  The  artery  is  bound  down  to  the  interosseous 
membrane  by  aponeurotic  fibres. 

Fig.  470. — The  Volar  Arteries  of  the    Forearm  and  Hand.     (After  Toldt,   "Atlas  of 
Human  Anatomy/'  Rebman,  London  and  New  York.) 


Biceps  brachii  — 

Inferior  ulnar  collateral  artery — 

Brachial  artery — 
Tendon  of  the  biceps  brachn  — 

Brachio-radiah: 

Radial  recurrent  artery 

Ulnar  recurrent  artery 
Supinator 


interosseous  artery 
f  longus 
Extensor  carpi  radialis  ] 

[  brevis 


Flexor  digitorum  sublimis^- 


Brachio -radialis 


Flexor  digitorum  profundus 1 

Median  nerve 

Pronator  quadratus ^-. 

Flexor  carpi  radiahs        '  Ir-  _ 
Radial  artery  —    -vflfll 
Superficial  volar  branch  — 
Transverse  carpal  ligament 
Abductor  brevis  pollicis 

Flexor  brevis  pollicis 

Common  volar  digital  arteries  .e^^^- 

Adductor  pollicis — tj—/-' 
First  dorsal  interosseii '      ^'j, 

LumbricaIes-^--r. 


Superior  ulnar  collateral  artery 
Medial  intermuscular  septum 


Bracbialis 
Median  nerve 


Pronator  teres 
Flexor  carpi  radialis 
Palmaris  longus 


Ulnar  artery 
Flexor  carpi  ulnaris 

Flexor  profundus  digitorun 


Deep  volar  branches  of  ulnar  artery 
Superficial  volar  arch 

Flexor  digiti  V  brevis 
Abductor  digiti  V 

Proper  volar  digital  arteries 


The  branches  of  the  volar  interosseous  artery  are: — (i)  The  median  artery  [a.  mediana] 
is  a  long  slender  vessel  which  arises  from  the  volar  interosseous  immediately  after  the  latter  is 
given  off  from  the  common  trunk.  It  passes  forward  between  the  flexor  digitorum  profundus 
and  the  flexor  pollicis  longus  to  the  median  nerve,  with  which  it  descends  beneath  the  transverse 
carpal  (anterior  annular)  ligament  into  the  palm,  and  when  of  large  size  sometimes  enters  into 
the  formation  of  the  superficial  palmar  arch.     At  times  the  artery  arises  from  the  common 


THE  ULNAR  ARTERY 


579 


interosseous  before  its  division,  (ii)  The  nutrient  arteries  of  the  radius  and  uhia  are  usually 
derived  from  this  vessel,  (iii)  The  volar  terminal  division  of  the  volar  interosseous  artery  passes 
either  in  front  of  or  behind  the  pronator  quadratus,  but  in  either  case  in  front  of  the  interos- 
seous membrane,  and  anastomoses  with  the  volar  carpal  branches  of  the  radial  and  ulnar 
arteries,  and  with  the  recurrent  branches  from  the  deep  volar  arch,  forming  the  so-called 
volar  carpal  rete.  (iv)  The  dorsal  terminal,  the  larger  division,  pierces  the  interosseous  mem- 
brane, and  continues  its  course  downward  behind  the  interosseous  membrane,  under  cover  of 
the  extensor  muscles,  to  the  back  of  the  wrist,  where  it  ends  by  anastomosing  with  the  dorsal 


Fig.  471. — The  Back  of  the  Left  Forearm,   with  the   Dorsal  Interosseous  Artery 

AND  Branches  of  the  Radial  at  the  Back  of  the  Wrist. 

(From  a  dissection  in  the  Hunterian  Museum.) 


Articular  branch  of  the  profunda 

Brachialis 

Brachio-radialis,  cut 


Common  extensor  tendon 


Supinator 
Dorsal  interosseous  artery 


Abductor  pollicis  longus 

Brachio-radialis,  cut 

Extensor  pollicis  brevis 


Dorsal  carpal  ligament 

Extensor  carpi  radialis  longus 

Radial  artery 

First  dorsal  metacarpal  artery 

Extensor  pollicis  longus 

First  dorsal  interosseous  muscle 

First  dorsal  metacarpal  artery 

Princeps  pollicis  artery 


Dorsal  digital  artery 


Rete  over  olecranon 
Interosseous  recurrent  artery 
Anconeus,  cut 


Extensor  carpi  ulnaris 
Flexor  carpi  ulnaris 

Origin  of  extensor  pollicis  longus  and 
indicis  proprius 

Dorsal    branch    of    volar    interosseous 

artery 
Interosseous  membrane 


Dorsal  ulnar  carpal  artery 
Extensor  carpi  radialis  brevis 
Dorsal  radial  carpal  artery 

Fourth  dorsal  metacarpal  artery 
Third  dorsal  metacarpal  artery 
Second  dorsal  metacarpal  artery 


carpal  branches  of  the  radial  and  ulnar  arteries,  forming  the  so-called  dorsal  carpal  rete. 
This  branch  anastomoses,  as  soon  as  it  pierces  the  interosseous  membrane,  with  the  dorsal 
interosseous  artery. 

(6)  The  dorsal  interosseous  artery  [a.  interossea  dorsalis],  the  larger  division  of  the  com- 
mon interosseous,  turns  backward  through  the  triangular  interval  bounded  by  the  interosseous 
membrane  below,  the  oblique  hgament  above,  and  the  ulna  on  the  medial  side,  and  emerging 
at  the  back  of  the  forearm  between  the  abductor  pollicis  longus  and  the  supinator,  under  cover 
of  the  superficial  extensors  of  the  forearm,  descends  between  the  superficial  and  the  deep  muscles, 
crossing  in  this  course  the  abductor  polhcis  longus,  the  extensor  pollicis  brevis,  the  extensor 
pollicis  longus,  and  the  extensor  indicis  proprius  (fig.  471).     It  anastomoses  at  the  lower  border 


580 


THE  BLOOD-VASCULAR  SYSTEM 


of  this  muscle  and  just  above  the  wrist  joint,  with  the  dorsal  branch  of  the  volar  interosseous 
which  here,  as  above  described,  has  perforated  the  interosseous  membrane.  It  is  separated 
from  the  deep  radial  nerve  at  first  by  the  radius  and  supinator,  and  on  the  back  of  the  forearm 
by  the  extensores  polUcis  longus  and  indicis  proprius. 

The  chief  branch  of  the  dorsal  interosseous  artery,  the  interosseous  recurrent  artery  [a. 
interossea  recurrens]  arises  from  the  dorsal  interosseous  as  the  latter  emerges  from  beneath 
the  supinator.  It  runs  upward  between  the  anconeus  and  supinator,  usually  under  cover 
of  the  former,  to  the  interval  between  the  lateral  epicondyle  and  the  olecranon,  where  it  anas- 
tomoses with  the  profunda,  inferior  ulnar  collateral,  radial  recurrent,  and  dorsal  ulnar  recurrent 
arteries,  and  gives  branches  to  the  retiform  plexus  over  the  olecranon — the  rete  olecrani. 


Fig.  472. — Anastomoses  and  Distribution  of  the  Arteries  of  the  Hand, 

Volar  interosseous - 
Radial  artery  - 


Volar  radial  carpal 
Superficial  volar 


Dorsal  radial  carpal 
Radial  artery  at  wrist 


First  dorsal 
metacarpal 
Second  dorsal 
metacarpal 

Princeps  polUcis 
First    dorsal    meta- 
carpal   (branch  to 
index) 

Radialis  indicis 


Dorsal  digital 

Volar  digital 

First  dorsal  branch  of  volar  digital 


Second  dorsal  branch  of  volar  digital 


Anastomosis  of  volar  digital  arteries 
about  matrix  of  nail  and  pulp  of 
finger 


Ulnar  artery 

Volar  ulnar 

carpal 

Dorsal  ulnar 
carpal 


Deep  ulnar 

Superficial  arch 

Carpal  re- 
current 

Dorsal  per- 
forating 


Volar  meta- 
carpals 

Common    volar 
digitals 

Dorsal    meta- 
carpals 
Common    volar 
digital 


3.  The  muscular  branches  [rami  musculares]  are  numerous.  *  They  supply 
the  deep  and  superficial  flexors  of  the  fingers,  the  flexor  carpi  radialis  and  ulnaris, 
and  the  pronator  radii  teres. 

4.  The  dorsal  ulnar  carpal  [ramus  carpeus  dorsafis]  comes  off  from  the  ulnar 
artery  a  little  above  the  transverse  carpal  (anterior  annular)  ligament,  and, 
winding  medially  round  the  end  of  the  ulna  or  the  ulnar  collateral  ligament  of  the 
wrist,  beneath  the  flexor  carpi  ulnaris,  ramifies  on  the  back  of  the  carpus  beneath 
the  extensor  tendons.  It  forms  by  its  anastomosis  with  the  dorsal  radial  carpal, 
with  the  dorsal  terminal  branch  of  the  volar  interosseous  and  with  the  dorsal 
interosseous  arteries  a  plexus  or  rete,  the  so-called  dorsal  carpal  rete.  The 
branches  given  off  from  this  plexus  or  arch  are  described  with  the  dorsal  carpal 
branch  of  the  radial  artery. 


THE  ULNAR  ARTERY 


581 


5.  The  volar  ulnar  carpal  [ramus  carpeus  volaris]  is  a  small  branch  given  off 
from  the  ulnar  artery  opposite  the  carpus.  It  passes  beneath  the  flexor  digitoruro 
profundus  to  anastomose  with  the  volar  radial  carpal,  with  terminal  twigs  of  the 
volar  branch  of  the  volar  interosseous,  and  with  recurrent  branches  from  the 
deep  volar  arch,  forming  an  anastomotic  arch  across  the  front  of  the  carpus — the 
volar  carpal  arch  or  rete. 

Fig.  473. — The  Arteries  op  the  Right  Forearm  and  the  Deep  Volar  Arch. 


-Superior  ulnar  collateral 
-Inferior  ulnar  collateral 


Brachial  artery  - 
Radial  recurrent  artery. 


Brachio-radialis  - 


Flexor  pollicis  longus  muscle - 


-Brachialis  muscle 
-  Volar  ulnar  recurrent 
-Dorsal  ulnar  recurrent 


-Volar  interosseous  artery 
-Flexor  carpi  ulnaris 

-Flexor  digitorum  profundus  muscle 
-Volar  interosseous  artery 


Transverse  carpal  ligament,  cut- 


"Volar  branch  of  ulnar  artery,  cut 
"Deep  volar  arch 


'H\  fe^^Vc— 


Volar  metacarpal  arteries 

Volar  digital  artery,  cut  short 


Volar  digital  artery" 


The  Ulnar  Artery  at  the  Wrist 

The  ulnar  artery  at  the  wrist  may  be  said  to  extend  from  the  upper  to  the 
lower  border  of  the  transverse  carpal  (anterior  annular)  ligament  upon  which 
it  rests.  It  here  lies  immediately  to  the  radial  side  of  the  pisiform  bone,  and 
to  the  ulnar  side  of  the  hook  of  the  hamate  (unciform),  the  two  bones  forming 
for  the  vessel  a  protecting  channel,  which  is  further  converted  into  a  short  canal 
by  the  expansion  of  the  flexor  carpi  ulnaris  passing  from  the  pisiform  to  the  hook 
of  the  hamate  (unciform).  The  ulnar  nerve  in  this  situation  is  immediately  to 
the  ulnar  side  of  the  artery. 


582  THE  BLOOD-VASCULAR  SYSTEM 

The  Ulnae  Artery  in  the  Palm     (Superficial  Volar  Arch) 

The  ulnar  artery,  on  entering  the  palm,  divides  into  two  branches,  the  super- 
ficial and  deep. 

The  superficial  branch  (fig.  472) ,  the  direct  continuation  of  the  vessel,  anasto- 
moses with  the  superficial  volar,  a  branch  of  the  radial,  forming  what  is  then 
known  as  the  superficial  volar  arch.  After  descending  a  short  distance  toward  the 
cleft  between  the  fourth  and  fifth  fingers,  it  turns  toward  the  thumb,  forming  a 
curve  with  its  convexity  toward  the  fingers  and  its  concavity  toward  the  muscles 
of  the  thumb,  and  anastomoses  opposite  the  cleft  between  the  index  and  middle 
fingers,  at  the  junction  of  the  upper  with  the  middle  third  of  the  palm,  with  the 
superficial  volar  branch  of  the  radial  artery  to  complete  the  arch.  A  line  drawn 
transversely  across  the  palm  on  a  level  with  the  metacarpo-phalangeal  joint  of  the 
thumb  will  roughly  indicate  the  situation  of  the  arch. 

Relations. — In  front:  in  addition  to  the  skin  and  superficial  fascia,  the  vessel  is  crossed 
successively,  by  the  palmaris  bevis,  the  palmar  branch  of  the  ulnar  nerve,  the  palmar  aponeuro- 
sis and  the  palmar  branch  of  the  median  nerve. 

Behind,  it  rests  successively  upon  the  short  muscles  of  the  little  finger,  the  digital  branches 
of  the  ulnar  nerve,  the  flexor  tendons,  and    the  digital  branches  of  the  median  nerve. 

The  branches  of  the  superficial  volar  arch.  In  addition  to  small  muscular 
and  cutaneous  branches  the  superficial  volar  supplies: — 

The  common  digital  arteries  [aa.  digitales  volares  communes].  These,  usually  four  in 
number,  arise  from  the  conve.xity  of  the  superficial  arch  and,  running  downward  through  the 
palm,  give  off  the  digital  arteries  proper  to  both  sides  of  the  httle,  ring,  and  middle  fingers, 
and  the  ulnar  side  of  the  index  finger.  The  radial  side  of  the  index  finger  and  the  thumb  are 
supplied  by  the  first  volar  metacarpal  branch"  of  the  radial  artery. 

The  most  ulnar  of  the  common  digital  arteries  passes  distally  over  the  muscles  in  the  ulnar 
border  of  the  palm,  and  thence  along  the  ulnar  bordet  of  the  httle  finger.  The  remaining 
arteries  pass  distaUy  in  the  three  ulnar  intermetacarpal  spaces  to  within  about  6  mm.  (j  in.)  of 
the  clefts  between  the  fingers,  where  they  divide  into  branches,  the  digital  arteries  proper 
[aa.  digitales  volares  proprise],  which  supply  the  sides  of  contiguous  fingers. 

As  the  common  digital  arteries  pass  through  the  palm,  they  lie  between  the  flexor  tendons, 
on  the  digital  nerves  and  lumbrical  muscles,  and  beneath  the  palmar  aponeurosis.  Just  before 
bifurcating  they  pass  under  the  transverse  fasciculi,  and  are  joined  b}^  the  volar  metacarpal 
branches  from  the  deep  volar  arch  (fig.  472).  At  this  spot  they  also  receive  the  volar  perforating 
branches  from  the  dorsal  metacarpal  vessels.  On  the  sides  of  the  fingers  the  proper  digital 
arteries  lie  between  the  palmar  and  dorsal  digital  nerves.  They  anastomose  by  small  branches, 
forming  an  arch  across  the  front  of  the  bones  on  the  proximal  side  of  each  interphalangeal  joint. 
They  supply  the  flexor  tendons  and  the  integuments,  and  terminate  in  a  plexiform  manner 
beneath  the  pulp  of  the  finger  and  around  the  matrix  of  the  nail.  A  dorsal  digital  branch  is 
given  off  to  the  back  of  the  fingers  about  the  level  of  the  middle  of  the  first  phalanx,  and  a 
second  but  smaller  dorsal  digital  branch  about  the  level  of  the  middle  of  the  second  phalanx. 

The  deep  branch  of  the  ulnar  artery,  also  called  the  communicating  artery, 
sinks  deeply  into  the  palm  between  the  abductor  and  flexor  quinti  digiti  brevis, 
and  joins  the  radial  to  form  the  deep  volar  arch.     (See  The  Radial  Artery.) 

THE  RADIAL  ARTERY 

The  radial  artery — the  smaller  of  the  two  arteries  into  which  the  brachial 
divides  at  the  bend  of  the  elbow — appears  as  the  direct  continuation  of  the 
brachial.  It  runs,  at  first  curving  laterally,  along  the  radial  side  of  the  forearm 
as  far  as  the  styloid  process,  then,  coiling  over  the  radial  collateral  ligament  and 
the  lateral  and  back  part  of  the  wrist,  enters  the  palm  of  the  hand  from  behind  be- 
tween the  first  and  second  metacarpal  bones,  and  ends  by  anastomosing  with  the 
deep  branch  of  the  ulnar  to  form  the  deep  volar  arch.  Hence  the  artery  is  divisible 
into  three  parts:  that  in  the  forearm,  that  at  the  wrist,  and  that  in  the  palm  of  the 
hand.  The  course  of  the  artery  is  indicated  by  a  line  drawn  from  a  point  2.5 
cm.  (1  in.)  below  the  centre  of  the  elbow  to  a  point  situated  just  medial  to  the 
styloid  process  of  the  radius. 

I.  The  Radial  Artery  in  the  Forearm 

In  its  course  through  the  forearm  (fig.  470)  the  radial  artery  is  found  in  the 
most  lateral  of  the  intermuscular  spaces,  and  it  is  only  necessary  to  divide  the. 


THE  RADIAL  ARTERY 


583 


skin,  superficial  and  deep  fascia,  to  expose  the  vessel,  and  in  addition  in  the  upper 
third  to  separate  the  brachio-radialis  from  the  pronator  teres. 

Relations. — In  front,  the  artery  is  at  first  overlapped  by  the  brachio-radialis,  but  for  the 
rest  of  its  course  it  is  merely  covered  by  the  slcin,  superficial  and  deep  fascise,  by  some  cutaneous 
veins,  and  by  cutaneous  branches  of  the  musculo-cutaneous  nerve. 

Behind,  it  lies  successively  from  above  downward  on  the  tendon  of  the  biceps,  the  supinator, 
from  which  it  is  separated  by  a  layer  of  fat,  the  insertion  of  the  pronator  teres,  the  radial  origin 
of  the  flexor  digitorum  sublimis,  the  flexor  poUicis  longus,  the  pronator  quadratus,  and  the 
volar  surface  of  the  lower  end  of  the  radius.  It  is  in  this  last  situation,  where  the  artery  Ues 
upon  the  bone  and  can  therefore  be  easily  pressed  against  it,  that  the  pulse  is  usually  felt. 

Fig.  474. — Diagram  of  the  Relation  of  the  Arteries  of  the  Left  Forearm  to 
THE  Bones.     (Walsham.) 


Superior  ulnar  collateral  artery 
Brachial  artery 


Inferior  ulnar  collateral  artery 

Volar  ulnar  recurrent 
Dorsal  ulnar  recurrent  - 

Ulnar  artery 
interosseous  artery 


Volar  interbsseous  artery 


Volar  ulnar  carpal 


Superficial  branch  of  ulnar  artery 
(superficial  volar  arch) 


L  volar  digital  artery 


Profunda  artery 


Lateral  epicondyle 

Articular  branch  of  profunda  artery 
Radial  recurrent  artery 
Interosseous  recurrent  artery 

Radial  artery 
Oblique  ligament 


Interosseous  membrane 
Dorsal  interosseous  artery 


Volar  radial  carpal 
Radial  artery  of  wrist 
Superficial  volar  branch  of  radial 
artery 


Deep  volar  arch 


On  its  lateral  side  it  has,  throughout  the  whole  of  its  course,  the  braohio-radiahs  muscle, 
the  guide  to  the  artery  in  ligature,  and  the  lateral  vena  comitans;  in  its  middle  third,  the 
superflcial  radial  nerve  as  well.  In  its  lower  third  the  superficial  radial  nerve  is  to  its  lateral 
side,  but  separated  from  it  by  the  brachio-radialis  and  fascia. 

On  its  medial  side,  in  the  upper  third  is  the  pronator  teres,  in  the  lower  third  the  tendon 
of  the  flexor  carpi  radialis,  and  throughout  the  whole  of  its  course  the  medial  vena  comitans. 

The  branches  of  the  radial  artery  in  the  forearm  are: — (1)  The  radial  re- 
current; (2)  the  muscular;  (3)  the  volar  radial  carpal;  (4)  the  superficial  volar. 

(1)  The  radial  recurrent  [a.  recurrens  radialis]  usually  arises  from  the  lateral  side  of  the 
radial  just  below  its  origin  from  the  brachial.  It  at  first  runs  laterally  on  the  supinator  and  then 
divides  into  three  chief  branches  (fig.  475).  One  of  these  continues  laterally  through  the  fibres 
of  the  radial  (musculo-spiral)  nerve,  or  between  the  superficial  (radial)  and  deep  radial  (posterior 
interosseous)  nerves  when  the  radial  (musculo-spiral)  divides  higher  than  usual,  into  the  brachio- 
radiaUs  and  extensor  carpi  radiahs  longus  and  brevis,  and  anastomoses  with  the  interosseous 
recurrent.     A  second  ascends  between  the  brachiahs  and  braehio-radiahs,   with  the  radial 


584 


THE  BLOOD-VASCULAR  SYSTEM 


(musculo-spiral)  nerve,  and  anastomoses  with  the  profunda  artery.  A  third  descends  with  the 
superficial  radial  nerve  under  cover  of  the  brachio-radialis,  supplying  that  muscle.  The 
radial  recurrent  also  gives  off  branches  to  the  elbow-joint. 

(2)  The  muscular  branches  [rami  musculares]  come  off  irregularly  to  supply  the  contiguous 
muscles  on  the  lateral  side  of  the  forearm. 

(3)  The  volar  radial  carpal  branch  [ramus  carpeus  volaris]  arises  from  the  rnedial  side  of  the 
radial  artery  about  the  level  of  the  lower  border  of  the  pronator  quadratus.  It  crosses  the  front 
of  the  radius  beneath  the  flexor  muscles,  and  anastomoses  with  the  volar  carpal  branch  of  the 
ulnar,  forming  the  volar  carpal  rete.  This  plexus  is  joined  above  by  terminal  twigs  from  the 
volar  interosseous  artery,  and  below  by  recurrent  branches  from  the  deep  volar  arch.  It  sup- 
plies branches  to  the  lower  end  of  the  radius,  and  to  the  wrist  and  carpal  joints. 

(4)  The  superficial  volar  branch  [ramus  volaris  superficialis]  leaves  the  radial  artery  as  the  lat- 
ter vessel  is  about  to  turn  over  the  radial  collateral  ligament  to  the  back  of  the  wrist.  It  courses 
forward  over  the  short  muscles  of  the  ball  of  the  thumb,  and  anastomoses  with  the  superficial. 


Fig.  475. — The  Bend  op  the  Elbow,  Left  Side. 
(From  a  dissection  by  Dr.  Alder  Smith  in  the  Museum  of  St.  Bartholomew's  Hospital.) 


Median  nerve 
Posterior  branch  of  in- 
ferior ulnar  collateral 
Branches  of   medial 
a  nti -brachial 
cutaneous  nerve 

Basilic  vein 


Brachialis 
Volar  branch  of  inferiori 
ulnar  collateral 
Median  antibrachial  vein 

Median  cubital  vein 


Tendon  of  biceps 
Lacertus  fibrosus 


Deep  median  vein 
Ulnar  artery 


Pronator  teres 


Vena  comitans  of 
brachial  artery 
Basilic  vein 

Brachialis 

Cephalic  vein 

Brachial  artery 

Dorsal  anti- 
brachial cuta- 
neous nerve 

Radial  n.  and  as- 
cending branch 
of  radial  recur- 
rent artery 

'Accessory  ceph- 
-~        alio  vein 

Cephalic  vein 

Ascending  br.  of 
radial  recurrent 

Deep    radial 
nerve 

Radial  recurrent 
artery 

Brachio-radialis 


Superficial 
radial 
nerve 


branch  of  the  ulnar  artery  to  complete  the  superficial  volar  arch.  It  supplies  small  branches 
to  the  muscles  of  the  ball  of  the  thumb,  and  frequently  terminates  in  these  muscles  without 
ioining  the  arch.     Occasionally  it  passes  beneath  the  abductor  poUicis  brevis. 

II.  The  Eadial  Artery  at  the  Wrist 

The  radial  artery  at  the  wrist  winds  over  the  radial  side  of  the  carpus,  under 
the  extensor  tendons  of  the  thumb,  from  a  spot  a  little  below  and  medial  to  the 
styloid  process  of  the  radius  to  the  base  of  the  first  interosseous  space,  where  it 
sinks  between  the  two  heads  of  the  first  dorsal  interosseous  muscle  into  the  palm, 
to  form,  by  anastomosing  with  the  deep  branch  of  the  ulnar  artery,  the  deep  volar 
arch.  A  line  drawn  from  1.2  cm.  (|  in.)  medial  to  the  styloid  process  to  the 
base  of  the  first  interosseous  space,  which  can  be  distinctly  felt  on  the  back  of 
the  hand,  will  roughly  indicate  the  course  of  the  artery  (fig.  476). 


THE  RADIAL  ARTERY 


585 


Relations. — The  artery  is  covered  successively  by  the  abductor  poUicis  longus  and  extensor 
pollicis  brevis,  by  branches  of  the  superficial  radial  nerve  and  veins,  and,  just  before  it  sinks 
between  the  two  heads  of  the  interosseous  muscle,  by  the  tendon  of  the  extensor  pollicis  longus. 
The  branches  of  the  superficial  radial  nerve  to  the  thumb  and  index  finger  cross  it.  It  is  at 
first  somewhat  deeply  placed  beneath  the  first-mentioned  extensor  muscles  of  the  thumb; 
but  subsequently  it  lies  quite  superficial,  and  can  be  felt  pulsating  in  a  fittle  triangular  depression 
bounded  on  either  side  by  the  extensores  pollicis  longus  and  brevis,  and  above  by  the  lower 
end  of  the  radius.  The  artery  lies  successively  on  the  radial  collateral  ligament  of  the  wrist,  on 
the  navicular  (scaphoid),  the  greater  multangular  (trapezium),  the  base  of  the  first  meta- 
carpjal  bone,  and  on  the  dorsal  ligaments  uniting  these  bones.  It  has  usually  with  it  two  com- 
panion veins,  and  a  few  branches  of  the  musculo-cutaneous  nerve. 

Fig.  476. — The  Radial  Artery  at  the  Wrist,  Left  Forearm. 
(From  a  dissectionjn  the  Hunterian^Museum.) 


Articular  branch  of  the  profunda 

Brachialis 

Brachio-radialis,  cut 


Common  extensor  tendon 


Supinator 
Dorsal  interosseous  artery 


Abductor  pollicis  longus 

Brachio-radialis,  cut 

Extensor  pollicis  brevis 


Borsal  carpal  ligament 

Extensor  carpi  radialis  longus 

Radial  artery 

First  dorsal  metacarpal  artery 

Extensor  pollicis  longus 

First  dorsal  interosseous  muscle 

First  dorsal  metacarpal  artery 

Princeps  pollicis  artery 

Dorsal  digital  artery 


Triceps 

Rete  over  olecranon 
Interosseous  recurrent  artery 
Anconeus,  cut 


Extensor  carpi  ulnaris 

Flexor  carpi  ulnaris 

Origin  of  extensor   pollicis  longus  and 
indicis  proprius 

Dorsal    branch    of    volar    interosseous 

artery 
Interosseous  membrane 


Dorsal  ulnar  carpal  artery 
Extensor  carpi  radialis  brevis 
Dorsal  radial  carpal  artery 

Fourth  dorsal  metacarpal  artery 
Third  dorsal  metacarpal  artery 
■^^^ — '  Second  dorsal  metacarpal  artery 


-(1)  The  dorsal  radial 


The  branches  of  the  radial  artery  at  the  wrist  are: 
carpal;  (2)  the  first  dorsal  metacarpal, 

(1)  The  dorsal  radial  carpal  branch  [ramus  carpeus  dorsaUs]  arises  from  the  radial  as  the 
latter  vessel  passes  under  the  abductor  pollicis  longus,  and  runs  medially  beneath  the  ex- 
tensor carpi  radiahs  longus  and  brevis,  and  the  extensor  pollicis  longus,  across  the  dorsal  surface 
of  the  carpus,  to  anastomose  with  the  dorsal  ulnar  carpal  and  with  the  terminal  twigs  of  the 
posterior  branch  of  the  volar  interosseous  artery.     This  anastomosis  is  called  the  dorsal  carpal 


586  THE  BLOOD-VASCULAR  SYSTEM 

rete  [rete  carpi  dorsale].  From  this  rete  are  given  oif  the  second,  third,  and  fourth  dorsal 
metacarpal  arteries  to  the  second,  third,  and  fourth  intermetacarpal  spaces  respectively.  These 
vessels  run  downward  on  the  dorsal  interosseous  muscles  as  far  as  the  flexure  of  the  fingers,  and 
there  divide  into  two  branches  (dorsal  digital),  which  run  along  the  sides  of  the  contiguous 
fingers  on  their  dorsal  aspect.  Near  their  proximal  ends  they  anastomose  with  the  dorsal 
perforating  branches  of  the  deep  volar  arch.  Distally  they  are  connected  by  volar  perforating 
branches  with  the  digital  arteries  or  the  corresponding  spaces.  The  branches  which  run  along 
the  backs  of  the  fingers  anastomose  with  the  dorsal  branches  of  the  first  dorsal  digital  arteries 
derived  from  the  volar  common  digital  vessels  (fig.  476). 

(2)  The  first  dorsal  metacarpal  (figs.  472,  476)  is  given  off  by  the  radial  shortly  before  it 
passes  between  the  two  heads  of  the  first  dorsal  interosseous  muscle.  It  quickly  divides  into 
two  branches  which  supply  the  dorsal  surface  of  the  thumb  and  the  radial  side  of  the  index- 
finger  toward  its  dorsal  surface. 

III.  The  Radial  Artery  in  the  Palm  (Deep  Volar  Arch) 

The  radial  artery  enters  the  palm  between  the  first  and  second  metacarpal 
bones  at  the  base  of  the  first  interosseous  space,  by  passing  between  the  two 
heads  of  the  first  dorsal  interosseous  muscle.  It  then  runs  medially  between  the 
transverse  and  oblique  heads  of  the  adductor  pollicis  muscle  and  continuing  its 
course  in  a  slight  curve  with  the  convexity  forward,  across  the  base  of  the  meta- 
carpal bones  and  interosseous  muscles,  it  anastomoses  with  the  deep  branch 
of  the  ulnar,  forming  the  deep  volar  arch  [arcus  volaris  profundus].  The  arch 
may  be  said  to  extend  from  the  first  interosseous  space  to  the  base  of  the  meta- 
carpal bone  of  the  little  finger,  and  is  a  finger's  breadth  nearer  the  wrist  than  the 
superficial  arch.  It  is  covered  by  the  superficial  and  deep  fiexor  tendons,  by  the 
superficial  head  of  the  flexor  pollicis  brevis,  and  by  part  of  the  flexor  quinti 
digiti  brevis.  It  is  accompanied  by  the  deep  branch  of  the  ulnar  nerve,  and  two 
small  venae  comitantes  (figs.  472,  473). 

The  branches  of  the  deep  volar  arch  are: — (1)  The  princeps  pollicis;  (2)  the 
radialis  indicis;  (5)  the  volar  metacarpals  (three  in  number);  (4)  the  recurrent 
carpal;  (3)  the  dorsal  perforating.  The  first  two  are  usually  spoken  of  as  coming 
off  from  the  radial  artery  in  the  palm;  the  last  three  from  the  deep  volar  arch. 

(1)  The  arteria  princeps  pollicis  arises  from  the  radial  artery  as  it  enters  the  palm  between 
the  two  heads  of  the  first  dorsal  interosseous  muscle.  It  passes  downward  between  the  adductor 
pollicis  transversus  and  the  first  dorsal  interosseous  muscle,  parallel  to  the  metacarpal  bone, 
and  between  the  two  portions  of  the  flexor  polhcis  brevis  under  cover  of  the  flexor  polUcis 
longus.  Opposite  the  metacarpo-phalangeal  joint  it  usually  divides  into  two  branches,  one 
of  which  is  distributed  to  each  side  of  the  thumb  on  its  volar  aspect.  These  vessels  anasto- 
mose with  each  other  at  the  end  of  the  thumb,  like  the  other  digital  arteries. 

(2)  The  arteria  radialis  indicis  comes  off  from  the  radial  artery  a  little  lower  than  the  former 
vessel,  or  as  a  common  trunk  with  it,  and  passes  forward  between  the  first  dorsal  interosseous 
and  adductor  pollicis  transversus,  parallel  to  the  radial  side  of  the  second  metacarpal  bone. 
After  emerging  from  beneath  the  adductor  poUicis  transversus  it  continues  its  course  along  the 
radial  side  of  the  index-finger,  on  its  volar  aspect,  as  far  as  the  tip,  anastomosing  in  this  course 
with  the  digital  artery  on  the  opposite  side  of  the  finger  in  a  way  similar  to  that  of  the  other 
digital  arteries.  It  frequently  communicates,  at  the  lower  border  of  the  adductor  pollicis, 
with  the  superficial  volar  arch  and  princeps  pollicis.  It  gives  off  a  dorsal  branch,  which  anasto- 
moses with  the  branch  fron  the  fu-st  dorsal  metacarpal  to  the  index  finger. 

(3)  The  volar  metacarpal  arteries  [aa.  metacarpex  volares],  three  in  number,  come  off  from 
the  convexity  of  the  deep  arch,  and,  coursing  downward  in  the  centre  of  the  second,  third,  and 
fourth  interosseous  spaces  on  the  interosseous  muscles,  terminate  near  the  cleft  of  the  fingers 
by  anastomosing  with  the  digital  arteries  from  the  superficial  arch.  These  vessels  supply  the 
interosseous  muscles  and  the  bones,  and  the  second,  third,  and  fourth  lumbricales. 

(4)  The  recurrent  branches  come  off  from  the  concavity  of  the  arch,  and  consist  of  two  or 
three  small  vessels  which  run  upward  toward  the  wrist,  and  anastomose  with  the  volar  branch 
of  the  volar  interosseous,  and  the  volar  radial  and  ulnar  carpal  arteries. 

(5)  The  dorsal  perforating  brandies  (rr.  perforantes),  which  are  usnally  three  in  number, 
pass  from  the  arch  directly  through  the  second,  third,  and  fourth  interosseous  spaces  between 
the  two  heads  of  the  corresponding  dorsal  interosseous  muscle,  and  join  the  proximal  ends  of 
the  first  dorsal  interosseous,  and  the  second,  third,  and  fourth  dorsal  metacarpal  arteries  re- 
spectively. 

THE  THORACIC  AORTA 

The  thoracic  aorta  [aorta  thoracalis]  (fig.  477)  is  the  thoracic  portion  of  the 
aorta  descendens.  It  extends  from  the  termination  of  the  aortic  arch  at  the 
lower  border  of  the  body  of  the  fourth  thoracic  vertebra  to  the  lower  border  of 
the  body  of  the  twelfth  thoracic  vertebra,  where  it  passes  between  the  medial 


THE  THORACIC  AORTA 


587 


crura  of  the  diaphragm,  and  is  thence  continued  under  the  name  of  the  abdominal 
aorta.  It  is  at  first  situated  a  little  to  the  left  of  the  vertebral  column,  but  as  it 
descends,  approaches  the  front  of  the  column,  at  the  same  time  following  the  back- 
ward curve  of  the  spine,  and  at  the  diaphragm  is  almost  in  the  middle  line.  It 
lies  in  the  posterior  mediastinum,  having  the  oesophagus  at  first  a  little  to  the 
right  of  it,  then  in  front  of  it,  and  just  above  the  tenth  thoracic  vertebra,  where 
this  tube  pierces  the  diaphragm,  a  little  to  its  left  side. 

Fig.  477. — The  Arch  of  the  Aorta,  the  Thoracic  Aorta,  and  the  Abdominal  Aorta, 
WITH  THE  Superior  and  Inferior  Vena  Cava  and  the  Innominate  and  Azygos  Veins. 


Right  common  carotid 

artery 
Right  internal  jugular 


Right  lymphatic  duct 

Innominate  artery 

Right  vagus  nerve 

Right  innominate  vein 

Internal  mammary  vein 

Trunk  of  the  pericardiac 
and  thymic  veins 

Superior  vena  cava 
Azygos  vein 


Hemiazygos  vein,  cross- 
ing spine  to  enter  vena 
azygos 


Inferior  vena  cava 


Coeliac  artery 
Right  middle  suprarenal 
artery 


Right  internal  spermatic 
artery 
Right  spermatic  vein 


Left  common  carotid 

artery 
Left  vagus  nerve 

Thoracic  duct 
Left  innominate  vein 
Left  subclavian  artery 
Left  superior  intercostal 

Recurrent  (laryngeal; 
nerve 

Accessory  hemiazygos 

vein 
(Esophagus 

Left  upper  azygos  vein 

(Esophageal  branches 

from  aorta 

_^  Hemiazygos  vein 


Thoracic  duct 


Left  inferior  phrenic 

artery 
Left  middle  suprarenal 

artery 
Receptaculum  chyH 

Superior  mesenteric 
artery 

Left  ascending  lumbar 

Left  internal  spermatic 
vessels 


Relations. — In  front  it  is  crossed  from  above  downward  by  the  root  of  the  left  lung,  by  the 
oesophagus,  which  separates  it  from  the  pericardium  and  heart,  and  by  the  diaphragm. 

Behind,  it  hes  upon  the  lower  seven  thoracic  vertebrae,  and  is  crossed  obhquely  opposite 
the  seventh  or  eighth  thoracic  vertebra  by  the  the  vena  hemiazygos  (azygos  minor)  and  op- 
posite the  fifth  or  sixth  vertebra  by  the  accessory  hemiazygos  vein,  or  by  one  or  more  of  the 
intercostal  veins. 

On  the  right  side  it  has,  above,  the  oesophagus  and  vertebral  column;  lower  down  the 
right  pleura  and  lung.  The  vena  azygos  and  thoracic  duct  also  lie  to  the  right,  but  on  a  some- 
what posterior  plane. 

On  the  left  side  it  has  the  left  lung  and  pleura  above,  and  the  oesophagus  below.  The  vena 
hemiazygos  and  the  accessory  hemiazygos  vein  are  also  to  the  left,  but  on  a  posterior  plane. 


588  THE  BLOOD-VASCULAR  SYSTEM 

Branches  of  the  Thoracic  Aorta 

The  branches  of  the  thoracic  aorta  may  be  divided  into  the  visceral  and  the 
parietal.  The  visceral  are: — (1)  The  pericardiac;  (2)  the  bronchial;  and  (3)  the 
oesophageal.  The  parietal  are: — (1)  The  intercostal;  (2)  the  superior  phrenic; 
and  (3)  the  arteria  aberrans. 

A.  Visceral  Branches 

(1)  The  pericardiac  branches  [rami  pericardiaci] — two  or  three  small  branches, 
irregular  in  their  origin,  course,  and  distribution — pass  to  the  posterior  surface  of 
the  pericardium  to  supply  that  structure,  and  anastomose  with  the  other  peri- 
cardiac branches.     They  give  small  twigs  to  the  posterior  mediastinal  glands. 

(2)  The  bronchial  arteries  [aa.  bronchiales]  supply  the  bronchi  and  the  lung 
substance.  They  vary  considerably  in  their  origin,  course,  and  distribution; 
they  are  usually  three  in  number — one  on  the  right  side,  and  two  on  the  left. 

(a)  The  right  bronchial  generally  arises  either  from  the  first  right  aortic  intercostal,  or  else 
as  a  common  trunk  witli  the  left  upper  bronchial  from  the  front  of  the  aorta  just  below  the  level 
of  the  bifurcation  of  the  trachea.  It  passes  laterally  on  the  back  of  the  right  bronchus,  and  is 
distributed  to  the  bronchi  and  lung  substance,  (b)  The  left  upper  bronchial  arises  from  the  front 
of  the  aorta  just  below  the  bifurcation  of  the  trachea,  or  as  a  common  trunk  with  the  right 
bronchial,  (c)  The  left  lower  bronchial  arises  from  the  front  of  the  aorta  just  below  the  level  of 
the  left  bronchus.  Like  the  corresponding  artery  on  the  right  side,  the  left  bronchial  arteries 
run  laterally  on  the  left  bronchus,  and,  after  dividing  and  subdividing  on  the  back  of  the  bronchi, 
supply  the  bronchi  themselves  and  the  lung  substance.  Small  twigs  are  given  off  from  the 
bronchial  arteries  to  the  bronchial  glands  and  to  the  oesophagus. 

(3)  The  oesophageal  arteries  [aa.  oesophageae],  four  or  sometimes  five  in 
number,  arise  at  intervals  from  the  front  of  the  descending  thoracic  aorta,  the 
first  coming  off  just  below  the  left  lower  bronchial.  They  usually  increase  in 
size  from  above  downward,  the  upper  coming  off  more  toward  the  right  side  of 
the  aorta,  the  lower  more  toward  the  left  side.  They  pass  forward  to  the 
oesophagus,  supplying  that  tube  and  anastomosing  with  each  other  and  with  the 
descending  oesophageal  branches  of  the  inferior  thyreoid  above,  and  with  the 
ascending  oesophageal  branches  of  the  phrenic  and  gastric  arteries  below,  thus 
forming  a  chain  of  anastomoses  along  the  whole  length  of  the  tube. 

B.  Parietal  Branches 

(1)  The  intercostal  arteries  [aa.  intercostal es],  usually  ten  in  number  on  each 
side,  supply  the  lower  intercostal  spaces,  the  two  upper  spaces  (occasionally  the 
first  only)  being  supplied  from  the  costo-cervical  trunk  of  the  subclavian  artery. 
The  lowest  artery  accompanies  the  twelfth  thoracic  nerve  below  the  last  rib  and 
is  therefore  called  the  subcostal  artery.  Its  distribution  is  similar  to  that  of  the 
lumbar  arteries  (p.  593)  except  that  it  commonly  crosses  the  anterior  surface, 
rather  than  the  posterior,  of  the  quadratus  lumborum. 

The  intercostals  arise  in  pairs  from  the  back  part  of  the  aorta,  and  at  once 
turning,  the  one  to  the  right,  the  other  to  the  left,  wind  backward  over  the 
front  and  sides  of  the  vertebral  bodies  to  reach  the  intercostal  spaces.  In  foetal  life 
these  arteries  run  almost  transversely  backward,  or  even  with  a  slight  inclination 
downward,  to  the  intercostal  spaces;  but  after  the  first  year,  in  consequence  of 
the  disproportionate  growth  of  the  aorta  and  vertebral  column,  the  upper  int-er- 
costals  have  to  ascend  to  reach  their  respective  spaces. 

The  arteries  in  their  course  around  the  vertebrae  differ  on  the  two  sides  of  the 
body.  On  the  right  side  the  arteries — and  especially  the  upper,  in  consequence 
of  the  aorta  lying  a  little  to  the  left  side  of  the  spine  in  the  upper  part  of  its 
course — are  longer  than  the  left.  They  wind  over  the  front  and  right  side  of  the 
vertebrae,  being  crossed  by  the  thoracic  duct  and  vena  azygos  (major),  and  covered 
by  the  right  pleura  and  lung.  The  upper  are  also  crossed  by  the  oesophagus. 
They  give  off  small  branches  to  the  bodies  of  the  vertebrae  and  anterior  longi- 
tudinal Hgament.  On  the  left  side,  as  the  intercostals  wind  around  the  sides  of 
the  bodies  of  the  vertebrae,  the  lower  are  crossed  by  the  vena  hemiaz3rgos  (azygos 
minor),  the  two  upper  by  the  left  superior  intercostal  vein,  and  the  two  next  by 


THE  THORACIC  AORTA 


589 


the  accessory  hemiazygos  vein  when  this  is  present.     They  are  all  covered  by 
the  left  pleura  and  lung  (fig.  478). 

The  branches  of  the  intercostal  arteries  are: — (a)  anterior,  (b)  posterior. 

(a)  The  anterior  branches  [rami  anteriores]  at  first  cross  the  intercostal  space  obliquely,  in 
consequence  of  the  downward  direction  of  the  ribs,  toward  the  angle  of  the  rib  above,  and 
thence  are  continued  forward  in  the  costal  groove,  and  anastomose  with  the  superior  branches 
of  the  anterior  intercostals  from  the  internal  mammary  in  the  upper  spaces,  and  from  the 
musculo-phrenic  in  the  lower  spaces.  They  he  at  first  on  the  external  intercostal  muscles, 
being  covered  in  front  by  the  pleura  and  lung,  the  endothoracic  fascia,  and  the  subcostal 
muscles.  Opposite  the  heads  of  the  ribs  they  are  crossed  by  the  sympathetic  nerve.  At  the 
angle  of  the  ribs  they  pass  under  cover  of  the  internal  intercostal  muscles,  and  thence  to  their 
termination  he  between  the  two  intercostal  muscles.  Their  situation  in  the  midspace  as  far 
as  the  angle  of  the  rib  should  be  remembered  in  performing  paracentesis  thoracis.  To  avoid 
the  risk  of  injuring  the  vessels,  the  puncture  should  not  be  made  further  back  than  the  angle 
of  the  ribs.  They  are  accompanied  by  a  nerve  and  vein,  the  vein  lying  above  and  the  nerve 
below,  except  in  the  upper  spaces,  where  the  artery,  having  to  ascend  to  reach  the  space,  at 
first  Mes  below  the  nerve  which  runs  more  horizontally.  The  uppermost  branch  anastomoses 
with  the  costo-oervical  artery  from  the  subclavian,  and  at  times  supplies  almost  entirely  the 
second  intercostal  space.     The  arteries  to  the  tenth  and  eleventh  spaces  on  reaching  the  end 

Fig.  478. — Scheme  op  Intercostal  Abtebt.     (Walsham.) 
Longissimus  dorsi 


Medial  cutaneous  branch 
Semlspinalis  dorsi  and  multifidus  spinse 


Prelaminar  branch 

Neural  branch 

Postcentral  branch 

Spinal  cord 

Anterior  spinal  artery 


Lateral  cutaneous  branch 
llio-costalls 


Intercostal  artery 


Vena  hemiazygos 

Vena  azygos 
Thoracic  duct 

(Esophagus 


Anterior  intercostal 

Internal  mammary  artery 
Anterior  cutaneous  branch' 


Posterior  branch 
Sympathetic 

Collateral  branch 


Medial  mammary 
branch 
^  Upper  or  main  branch 
of  anterior  intercostal 


of  their  respective  ribs  pass  between  the  abdominal  muscles,  and  anastomose  with  the  inf. 
epigastric  artery  from  the  external  ihac,  and  with  the  lumbar  arteries  from  the  abdominal 
aorta.  The  artery  beneath  the  twelfth  rib  anastomoses  with  the  lumbar  arteries  and  with 
the  external  circumflex  ihac. 

Each  anterior  branch  gives  off  the  following: — (i)  The  collateral  branch  which  comes  off 
near  the  angle  of  the  rib  and  runs  forward,  between  the  external  and  internal  intercostals, 
along  the  upper  border  of  the  lower  rib  enclosing  the  space.  It  is  smaller  than  the  main  anterior 
branch  and  anastomoses  with  tlie  lower  anterior  intercostal  in  each  space,  (ii)  Muscular 
branches  [rami  nmsculares]  supply  the  intercostal,  pectoral  and  abdominal  muscles,  (iii) 
The  lateral  cutaneous  branches  [rami  cutanei  laterales],  both  pectoral  and  abdominal,  run  with 
the  corresponding  branches  of  the  intercostal  nerves  through  the  external  intercostal  and  ser- 
ratus  anterior  muscles.  They  then  divide  into  anterior  and  -posterior  branches  which  turn  for- 
ward and  backward,  respectively,  to  supply  the  integument.  The  anterior  branches  from  the 
third,  fourth  and  fifth  spaces  supply  lateral  mammary  branches  [rr.  mammarii  laterales]  to  the 
lateral  region  of  the  breast,  (iv)  Anterior  cutaneous  branches  [rami  cutanei  anteriores] 
pierce  the  external  intercostal  ligament  and  the  pectorahs  major  just  lateral  to  the  sternum. 


590  THE  BLOOD-VASCULAR  SYSTEM 

They  are  distributed  to  the  skin  and  give  medial  mammary  branches  [rr.  mammarii  mediales] 
to  the  medial  region  of  the  breast. 

(b)  The  posterior  branches  [rami  posteriores]. — These  large  branches  are  given  oil  from  the 
intercostals  opposite  the  quadrilateral  space  bounded  by  the  transverse  process  of  the  vertebra 
above,  the  neck  of  the  rib  below,  the  body  of  the  vertebra  medially,  and  the  anterior  costo- 
transverse ligament  laterally.  Passing  backward  toward  this  space  with  the  dorsal  branch 
of  the  corresponding  intercostal  nerve,  they  divide  opposite  the  intervertebral  foramen  into  a 
muscular  and  a  spinal  branch,  (i)  The  muscular  branch  [r.  muscularis]  passes  backward 
through  the  quadrilateral  space,  and  soon  subdivides  into  a  medial  and  a  lateral  branch.  The 
former  passes  between  the  longissimus  dorsi  and  iUo-costaUs,  and,  after  supplying  these  muscles, 
gives  off  medial  cutaneous  branches  [rr.  cutanei  mediales].  The  latter  branch  pierces  the  multi- 
fidus  spinas,  and,  emerging  between  the  longissimus  dorsi  and  semispinahs  dorsi  near  the  spinous 
processes,  gives  off  lateral  cutaneous  branches  [rr.  cutanei  laterales].  It  suppHes  the  muscles  ■ 
in  its  course. 

(ii)  The  spinal  branch  [r.  spinalis]  enters  the  intervertebral  foramen  with  the  spinal  nerve 
of  the  corresponding  segment.  The  disposition  of  the  spinal  branch  is  similar  to_  that  of  the 
spinal  branches  entering  the  canalis  vertebralis  in  other  regions  and  may  be  described  here: — 

ARTERIES  OF  THE  VERTEBRAL  CANAL 

Spinal  arteries  are  derived  from  the  vertebral,  ascending  cervical  and  costo-cervical  arteries, 
from  the  dorsal  rami  of  the  intercostal  (fig.  478)  and  lumbar  arteries,  and  from  the  ilio-lumbar 
and  lateral  sacral  arteries.  The  spinal  branch  in  each  case  divides  into  three  branches,  post- 
central, prelaminar  and  neural. 

Each  post-central  branch  divides  on  the  lateral  part  of  the  posterior  longitudinal  ligament 
into  an  ascending  and  a  descending  branch  by  which  means  a  bilateral  series  of  anastomosing 
arches  are  formed  throughout  the  length  of  the  canal.  From  the  concavities  of  the  opposite 
arches  transverse  connecting  stems  are  formed  which  are  again  connected  by  a  median  longitu- 
dinal channel. 

The  pre-laminar  branches  also  divide  and  form  an  anastomosis  in  front  of  the  laminse 
and  ligamenta  flava.     This  is  similar  in  character  to  the  post-central,  but  much  less  regular. 

The  neural  branches  enter  the  dura  mater  and  are  usually  small  and  end  by  supplying  the 
nerve  roots.  A  variable  number  of  these  (5-10  on  a  side)  are  larger  than  the  others  and  rein- 
force the  longitudinal  anterior  and  posterior  spinal  arteries  given  off  from  the  vertebrals  within 
the  cranium.     (For  arteries  of  the  spinal  cord,  see  Section  VII.) 

(2)  The  superior  phrenic  arteries  [aa.  phrenicse  superiores],  are  small  twigs 
coming  off  from  the  thoracic  aorta  immediately  above  the  diaphragm.  They  are 
distributed  to  the  vertebral  portion  of  the  diaphragm  on  its  upper  surface. 

(3)  The  arteria  aberrans  is  a  small  twig  which,  arising  from  the  thoracic 
aorta  near  the  right  bronchial  artery,  passes  upward  and  to  the  right  behind  the 
oesophagus  and  trachea,  and  is  occasionally  found  to  anastomose  on  the  oesophagus 
with  the  arteria  aberrans  of  the  superior  intercostal  artery  (see  p.  568).  It  is 
regarded  as  the  remains  of  the  right  aortic  dorsal  stem  (fig.  506). 

(4)  The  mediastinal  branches  [rami  mediastinales],  numerous,  but  small,  are 
distributed  to  the  pleura,  and  the  vessels,  nerves  and  lymph-nodes  of  the  posterior 
mediastinum. 

THE  ABDOMINAL  AORTA 

The  abdominal  aorta  [aorta  abdominalis]  (fig.  479),  the  abdominal  portion  of 
the  descending  aorta,  begins  at  the  aortic  opening  in  the  diaphragm  opposite  the 
lower  broder  of  the  twelfth  thoracic  vertebra,  and  ends  usually  opposite  the  middle 
of  the  body  of  the  fourth  lumbar  vertebra  by  dividing  into  the  right  and  left 
common  iliac  arteries.  It  is  at  first  centrally  placed  between  the  medial  crura 
of  the  diaphragm,  but  as  it  descends  in  front  of  the  lumbar  vertebrse  it  leaves  the 
middle  line,  and,  at  its  bifurcation,  lies  a  little  to  the  left  side  of  the  spine. 

The  place  at  which  the  aorta  bifurcates  may  be  somewhat  roughly  indicated  on  the  surface 
of  the  abdomen  by  a  point  about  2.5  cm.  (1  in.)  below  and  a  little  to  the  left  of  the  umbilicus. 
The  level  of  its  bifurcation  may  be  more  accurately  determined  by  drawing  a  straight  line 
across  the  front  of  the  abdomen  joining  the  highest  points  of  the  iliac  crests. 

The  inferior  vena  cava,  which  accompanies  the  abdominal  aorta,  lies  to  its 
right  side.  Below,  the  vein  is  in  contact  with  the  artery  and  on  a  somewhat 
posterior  plane;  but  above,  it  is  separated  from  the  aorta  by  the  right  medial  crus 
of  the  diaphragm,  and,  in  consequence  of  the  caval  opening  in  the  diaphragm 
being  placed  further  forward  than  the  opening  for  the  aorta,  is  on  an  anterior 
plane. 


THE  ABDOMINAL  AORTA 


591 


Relations. — In  front,  the  aorta  is  successively  crossed  from  above  downward  by  the  right 
lobe  of  the  liver,  the  cceHac  (solar)  plexus,  the  lesser  omentum,  the  termination  of  the  oesophagus 
in  the  stomach,  the  ascending  layer  of  the  transverse  meso-colon,  the  splenic  vein  or  commence- 
ment of  the  portal  vein,  the  pancreas,  the  left  renal  vein,  the  third  portion  of  the  duodenum, 
the  mesentery,  the  aortic  plexus  of  the  sympathetic  nerve,  the  internal  spermatic  or  ovarian 
arteries,  the  inferior  mesenteric  artery,  the  median  lumbar  lymphatic  nodes  and  lymphatic 
vessels,  and  the  small  intestines. 

Of  these  structures  the  cceliac  (solar)  plexus,  the  aortic  plexus,  the  splenic  vein  or  the 
commencement  of  the  portal  vein,  the  pancreas,  the  left  renal  vein,  the  duodenum,  the  lym- 
phatics, the  spermatic  or  ovarian  arteries,  and  the  peritoneal  reflexions  are  in  contact  with  the 
aorta. 

Behind,  the  aorta  hes  upon  the  bodies  of  the  lumbar  vertebrae  and  intervening  intervertebral 
cartilages,  the  anterior  longitudinal  ligament,  the  origin  of  the  left  medial  crus  of  the  diaphragm, 
and  the  left  lumbar  veins. 


Fig.  479. — The  Abdominal  Aorta  and  its  Branches,  with  the  Inferior  Vena  Cava  and 

ITS  Tributaries. 


Cystic  arterj 

Hepatic  duct  — 

Cystic  duct 
Commoa  duct 
Portal  vem_ 
Gastro-duodenal  br  __ 
Right  gastric  artery_ 
Hepatic  artery^ 
Right  suprarenal  vein 

Inferior  suprarenal 
artery 

Renal  artery 
Renal  vein 

Vena  cava  inferior 

Kidney 


Right  spermatic  \ 

Right  internal  spermatic 

artery 

Quadratus  lumborum 

muscle 

Right     lumbar    artery 

and  left  lumbar  vein 

Ureteric      branch     of — 

spermatic  artery 


Middle  sacral  vessels. 


Left  lobe  of  liver 


(Esophagus 

Left  inferior  phrenic 

artery 
Right  inferior  phrenic 

artery 
Superior  suprarenal 
Left  gastric  artery 
Inferior  suprarenal 
Splenic  artery 

— — •  Left  phrenic  vein 
— —  Left  suprarenal  vein 
,. .  \—  Superior  mesenteric 

ir^.,    ^''"^ 

Kidney 

Ureteric  branch  of  renal 
Left  spermatic  vein 


Left  internal  spermatic 
artery 


Inferior  mesenteric 

artery 

Ureteric  branch  of 

spermatic 


Ureteric  branch  of 

common  iliac 
Common  iliac  artery 

External  iliac  artery 
Hypogastric  artery 


On  the  right  side  from  above  downward  are  the  right  medial  crus  of  the  diaphragm,  the 
great  splanchnic  nerve,  the  caudate  lobe  of  the  liver,  tlie  receptaculum  chyU  and  beginning 
of  the  thoracic  duct  (the  two  latter  structures  are  on  a  posterior  plane),  the  right  coeHac  (semi- 
lunar) gangUon,  and  the  inferior  vena  cava. 

On  the  left  side  are  the  left  medial  crus  of  the  diaphragm,  the  left  splanchnic  nerve,  and 
the  left  cocliac  (semilunar)  ganghon.  The  pancreas  is  also  in  contact  with  the  aorta  on  the 
left  side,  and  the  small  intestines  are  separated  from  it  only  by  peritoneum. 

Branches  of  the  Abdominal  Aorta 


The  branches  of  the  abdominal  aorta  usually  arise  in  the  following  order  from 
above  downward  (figs.  479,  480) : — ■ 

(1)  Right  and  left  inferior  phrenic;  (2)  coeliac;  (3)  right  and  left  middle 
suprarenal;  (4)  right  and  left  first  lumbar;  (5)  superior  mesenteric;  (6)  right  and 


592 


THE  BLOOD-VASCULAR  SYSTEM 


left  renal;  (7)  right  and  left  internal  spermatic;  (8)  right  and  left  second  lumbar; 
(9)  inferior  mesenteric;  (10)  right  and  left  third  lumbar;  (11)  right  and  left  fourth 
lumbar;  (12)  right  and  left  common  iliac;  (13)  middle  sacral. 

The  above  branches  may  be  divided  into  the  parietal,  the  visceral,  and  the 
terminal. 

The  parietal  branches  are  distributed  to  the  abdominal  walls.  They  are  the 
right  and  left  phrenics,  and  the  four  right  and  left  lumbars. 

The  visceral  branches  supply  the  viscera.  Three  of  these  are  given  off  singly 
from  the  front  of  the  aorta,  namely,  the  cceliac,  the  superior  mesenteric,  and  the 
inferior  mesenteric;  and  three  are  given  off  in  pairs,  namely,  the  two  suprarenals, 
the  two  renals,  and  the  two  spermatics. 

The  terminal  branches  are  the  middle  sacral  and  the  right  and  left  common 
iliac  arteries. 


Fig.  480. — Scheme  of  the  Abdominal  Aorta.     (Walsham.) 


Lesser  nmpntnm^        *'*^ 


Pancreas 

Left  renal  vein 
Superior  mesenteric 
artery 
Transverse  meso-colon 
Inferior  part  of 
duodenum 

Transverse  colon 

Mesentery 


Small  intestines 
Great  omentum' 


Inferior  mesenteric 
artery 


Thoracic  duct 
Cceliac  artery 


First  lumbar  vein 
Cisterna  chyli 


Second  lumbar  vein 


Peritoneum 
Third  lumbar  vein 


Fourth  lumbar  vein 


A.  The  Parietal  Branches  of  the  Abdominal  Aorta 

1.  THE  INFERIOR  PHRENIC  ARTERIES 

The  inferior  phrenic  artery  [a.  phrenica  inferior]  usually  arises  from  the  aorta 
as  it  passes  between  the  medial  crura  of  the  diaphragm.  At  times  it  comes  off 
from  the  cceliac  artery;  or  when  it  arises  as  two  separate  vessels,  either  the  right 
or  left  vessel  may  come  from  this  artery,  or  from  other  of  the  upper  branches  of 
the  abdominal  aorta. 

The  right  phrenic  passes  (fig.  480)  over  the  right  medial  crus  of  the  diaphragm  behind 
the  vena  cava,  and  then  upward  and  to  the  right  between  the  central  and  right  leaflets  of  the 
central  tendon  of  the  muscle,  where  it  divides  into  an  anterior  and  a  posterior  branch.  The 
former  courses  anteriorly  and  medially  and  anastomoses  with  the  anterior  branch  of  the  left 
phrenic,  with  the  musculo-phrenio  branches  of  the  internal  mammary,  and  with  the  pericardio- 
phrenic arteries;  the  latter  passes  posteriorly  and  laterally  toward  the  ribs,  and  anastomoses 
with  the  intercostal  arteries.  Besides  the  two  terminal  branches  and  branches  for  the  supply 
of  the  diaphragm  itself  the  right  phrenic  gives  off  the  right  superior  suprarenal  [ramus  supra- 
renaUs  superior],  to  the  right  suprarenal  gland,  as  well  as  branches  to  the  vena  cava,-  to  the 
hver,  and  to  the  pericardium. 

The  left  phrenic  crosses  the  left  medial  crus  of  the  diaphragm  behind  the  CESophagus, 
and,  like  the  right  artery,  divides  into  an  anterior  and  posterior  branch  and  gives  off  a  left 
suprarenal  branch.     The  distribution  and  anastamoses  are  similar  on  the  two  sides. 


THE  LUMBAR  ARTERIES  593 

2.  THE  LUMBAR  ARTERIES 

The  lumbar  arteries  [aa.  lumbales]  (fig.  479),  usually  eight  in  number,  four  on 
each  side,  come  off  in  pairs  from  the  posterior  aspect  of  the  abdominal  aorta, 
opposite  the  bodies  of  the  four  upper  lumbar  vertebrae.  A  fifth  pair  of  lumbar 
arteries,  generally  of  small  size,  frequently  arises  from  the  middle  sacral  artery 
opposite  the  fifth  lumbar  vertebra.  The  lumbar  arteries,  which  are  rather  longer 
on  the  right  than  on  the  left  side,  in  consequence  of  the  aorta  lying  a  little  to  the 
left  of  the  median  line,  wind  more  or  less  transversely  around  the  bodies  of  the 
vertebrae  to  the  space  between  the  transverse  processes,  where  they  give  off  each  a 
dorsal  branch,  and  then,  coursing  forward  between  the  abdominal  muscles,  termi- 
nate, by  anastomosing  with  the  other  arteries  of  the  abdominal  wall. 

Relations. — As  they  wind  around  tlie  bodies  of  the  vertebra  they  pass  beneath  the  chain  of 
the  sympathetic  nerve  trunk,  and  the  upper  two  beneath  the  crura  of  the  diaphragm.  The 
right  arteries  also  pass  beneath  the  vena  cava  inferior,  and  the  two  upper  on  that  side  beneath 
the  receptaculum  chyli.  The  arteries  on  both  sides  then  dip  beneath  the  tendinous  arch  thrown 
across  the  sides  of  the  bodies  of  tlie  vertebrae  by  the  psoas,  and  continue  beneath  this  muscle 
until  they  arrive  at  the  interval  between  the  transverse  processes  of  the  vertebrae  and  the 
medial  edge  of  the  quadratus  lumborum.  While  under  cover  of  the  psoas  they  are  accompanied 
by  two  slender  filaments  of  the  sympathetic  nerve  and  by  the  lumbar  veins.  A  httle  anterior 
to  the  transverse  processes  they  are  crossed  by  branches  of  the  lumbar  plexus,  and  here  usually 
cross  in  front  of  the  ascending  lumbar  vein.  They  now  pass  behind  the  quadratus  lumborum, 
with  the  exception  sometimes  of  the  last,  which  ma}'  pass  in  front  of  the  muscle.  At  the  lateral 
edge  of  the  quadratus  they  run  between  the  transversus  and  the  internal  oblique,  and  then,  after 
perforating  the  internal  oblique  between  the  internal  and  external  oblique.  Finally,  much 
diminished  in  size,  they  enter  the  rectus,  and  give  off  one  or  more  anterior  cutaneous  branches, 
which  accompany  the  last  thoracic  and  the  ilio-hypogastric  nerves  to  the  skin.  They 
anastomose  with  the  lower  intercostals,  ilio-lumbar,  deep  ckcumflex  iliac,  and  inf.  epigastric 
arteries. 

The  branches  of  the  lumbar  arteries  are ; — 

(a)  Vertebral  branches  which  supply  the  bodies  of  the  vertebrae  and  their  connecting 
ligaments. 

(6)  Muscular  branches  to  the  psoas,  quadratus  lumborum,  and  obUque  muscles  of  the 
abdomen. 

(c)  The  dorsal  branch  [r.  dorsahs].  This  is  of  large  size,  and  passes  backward  in  company 
with  the  dorsal  nerve  between  the  transverse  processes  above  and  below,  the  intertransversalis 
medially  and  the  quadratus  lumborum  laterally,  to  the  muscles  of  the  back.  On  reaching  the 
interval  between  the  longissimus  dorsi  and  multifidus  spinae,  it  divides  into  a  lateral  and  a 
medial  branch.  The  former  ends  in  the  multifidus,  the  latter  and  larger  supphes  the  sacro- 
spinalis,  and  gives  branches  which  accompany  the  termination  of  the  dorsal  nerves  to  the  skin. 
Just  before  the  artery  passes  between  the  transverse  processes  it  gives  off  a  spinal  branch  fr. 
spinalis],  which  accompanies  the  lumbar  nerve  through  the  intervertebral  foramen  into  the 
vertebral  canal  (see  p.  590). 

(d)  Renal  branches  of  small  size  pass  forward  in  front  of  the  quadratus  lumborum  to  the 
capsule  of  the  kidney.  They  anastomose  with  the  renal  artery.  A  communication  is  thus 
established  between  the  renal  arteries  and  the  arteries  supplying  the  lumbar  region. 

B.  The  Visceral  Branches  of  the  Abdominal  Aorta 
THE  CCELIAC  ARTERY 

The  coeliac  artery  [a.  coeliaca] — or  coeliac  axis,  as  it  is  commonly  called, 
because  it  breaks  up  simultaneously  into  three  branches  which  radiate  from  it 
like  the  spokes  of  a  wheel  from  the  axle — is  a  short  thick  trunk  given  off  from 
the  front  of  the  aorta  between  the  medial  crura  of  the  diaphragm  a  little  below 
the  aortic  opening.  It  passes  horizontally  forward  above  the  upper  margin 
of  the  pancreas  for  about  half  an  inch,  and  then  breaks  up  into  three  branches 
for  the  supply  of  the  stomach,  duodenum,  spleen,  pancreas,  liver,  and  gall- 
bladder (fig.  481). 

Relations. — In  front  is  the  lesser  omentum;  behind,  the  aorta;  above,  the  right  lobe  of  the 
liver;  below,  the  pancreas;  to  the  right,  the  right  coeliac  (semilunar)  ganghon  and  caudate  lobe 
of  the  liver;  to  the  left,  the  left  cceliac  (semilunar)  ganglion  and  the  cardiac  end  of  the  stomach. 
It  is  closely  surrounded  by  the  dense  coeliac  (solar)  ple.xus  of  sympathetic  nerves. 

Branches  of  the  coeliac  artery. — The  ccehac  artery  divides  into  the  left 
gastric,  the  hepatic,  and  the  splenic  arteries. 

1.  The  Left  Gastric  Artery 

The  left  gastric  [a.  gastrica  sinistra]  (fig.  481),  the  smallest  of  the  three 
branches  into  which  the  coeliac  artery  divides,  courses  at  first  upward  and  to  the 


594 


THE  BLOOD-VASCULAR  SYSTEl 


left  toward  the  cardiac  end  of  the  stomach,  where  it  turns  sharply  round,  and  then, 
following  the  lesser  curvature  of  the  stomach,  descends  from  left  to  right  toward 
the  pylorus.  It  anastomoses  with  the  right  gastric  branch  of  the  hepatic  artery, 
which  has  proceeded  from  the  opposite  direction,  the  two  branches  thus  forming  a 
continuous  arterial  arch  corresponding  to  the  lesser  curvature  of  the  stomach. 

The  artery  at  first  lies  behind  the  posterior  layer  of  the  omental  bursa  of  peritoneum 
(fig.  480),  but  on  reaching  the  cardiac  end  of  the  stomach  it  passes,  between  the  layers  of 
peritoneum  reflected  from  the  diaphragm  onto  the  oesophagus,  into  the  lesser  omentum  in  which 
it  then  runs  to  its  terminal  anastomosis  with  the  pyloric.  It  is  surrounded  by  a  plexus  of 
sympathetic  nerves. 

It  supplies  both  surfaces  of  the  stomach  around  the  lesser  curvature  and  gives  off  email 
CBSophageal  branches  [rami  oesophagei]  which  anastomose  with  the  oesophageal  branches 
from  the  thoracic  aorta. 

Fig.  481. — -The  Cceliac  Artery  and  its  Branches. 


Abdominal  aorta 


Right  medial  crus  of  diaphragm 


Cystic  artery 

Right  inferior 
phrenic  artery 

Hepatic  duct 

Cystic  duct 

Splenic  artery 

Common  bile 

duct 
Right  gastric  v 

artery  "^ 

Gastro-duod- 
enal  artery 
Superior    pan- 
creatico  -  du- 
odenal artery 

Head    of    ^ 
pancreas 
Inferior  pan- 
creatico  -  du- 


Left  crus  of  diaphragm 

(Esophageal  branch 


Coeliac  artery 
Left  gastnc 
artery  Vasa  brevia 


odenal  artery    _^ 
Right   gastro- 
epiploic artery 


2.  The  Hepatic  Artery 


Left  gastro-epiploic  artery 


The  hepatic  artery  [a.  hepatica],  the  largest  branch  of  the  coeliac  artery  in  the 
foetus,  but  intermediate  in  the  adult  between  the  left  gastric  and  the  splenic, 
comes  off  on  the  right  side  of  the  coeliac  artery,  and,  winding  upward  and  to  the 
right  to  the  porta  (portal  fissure)  of  the  liver,  there  breaks  up  into  two  chief 
branches  for  the  supply  of  the  right  and  left  lobes  of  that  organ.  It  at  first  courses 
forward  and  to  the  right  along  the  upper  border  of  the  head  of  the  pancreas,  behind 
the  posterior  layer  of  the  peritoneal  omental  bursa,  to  the  upper  margin  of  the 
duodenum,  where  it  passes  forward  beneath  the  layer  of  peritoneum  forming 
the  floor  of  the  epiploic  foramen  (of  Winslow).  It  thus  runs  between  the  two 
layers  of  the  lesser  omentum,  and  ascends  along  with  the  hepatic  duct  which  lies 
to  its  right,  and  with  the  portal  vein  which  lies  behind  it  (figs.  480,  481). 

The  branches  of  the  hepatic  artery  are: — (1)  The  right  gastric;  (2)  thegastro- 
duodenal;  (3)  the  hepatic  proper. 

(1)  The  right  gastric  artery  [a.  gastrica  dextra]  comes  off  from  the  hepatic  just 
as  the  latter  vessel  enters  the  lesser  omentum,  and,  descending  between  the  two 
layers  of  that  fold  of  peritoneum  to  the  pylorus,  there  turns  to  the  left,  and, 
ascending  from  right  to  left,  anastomoses  along  the  lesser  curvature  of  the 
stomach,  as  already  mentioned,  with  the  left  gastric  artery,  which  descends 
from  the  opposite  direction. 

(2)  The  gastro-duodenal  artery  [a.  gastroduodenalis]  arises  from  the  hepatic 


THE  SPLENIC  ARTERY  595 

a  little  beyond  the  pyloric.  It  descends  behind  the  superior  portion  of  the 
duodenum  to  the  lower  border  of  the  pylorus,  where  it  divides  into  the  right 
gastro -epiploic  and  the  superior  pancreatico-duodenal.  It  varies  from  1.2  to 
2.5  cm.  (I  to  1  in.)  in  length. 

(a)  The  right  gastro-epiploic  artery  [a.  gastroepiploica  dextra]  passes  from  right  to  left 
along  the  greater  curvature  of  the  stomach  between  the  laj;ers  of  the  great  omentum,  and 
anastomoses  with  the  left  gastro-epiploic  branch  of  the  splenic.  From  this  anastomotic  arch 
are  given  oS: — (i)  Ascending  or  gastric  branches,  which  supply  the  anterior  and  posterior 
surfaces  of  the  stomach,  and  anastomose  with  the  descending  gastric  branches  of  the  arteries 
along  the  lesser  curvature,  (ii)  Epiploic  [rami  epiploici]  or  omental  branches — long  slender 
vessels  which  descend  between  the  two  anterior  layers  of  the  great  omentum,  and  then,  looping 
upward,  anastomose  with  similar  slender  branches  given  off  from  the  middle  and  left  colic, 
and  passing  down  in  Uke  manner  between  the  two  posterior  layers  of  the  great  omentum. 

(6)  The  superior  pancreatico-duodenal  [a.  pancreaticoduodenaUs  superior] — the  smaller 
division  of  the  gastro-duodenal — arises  from  that  vessel  as  it  passes  behind  the  first  portion  of 
the  duodenum,  and  courses  downward  behind  the  peritoneum,  in  the  anterior  groove  between 
the  second  portion  of  the  duodenum  and  the  pancreas,  to  anastomose  with  the  inferior  pan- 
creatico-duodenal, a  branch  of  the  superior  mesenteric.  Both  the  inferior  and  superior  pan- 
creatico-duodenal give  off  duodenal  [rami  duodenales]  and  pancreatic  branches  [rami  pancreatici] 
to  supply  these  organs. 

(3)  The  hepatic  artery  proper  [a.  hepatica  propria]  is  the  continuation  of  the 
hepatic  after  the  gastro-duodenal  has  arisen.  It  ascends  between  the  layers  of 
the  lesser  omentum,  preserving  the  relations  of  the  main  artery  to  the  portal  vein 
and  common  bile  (and  hepatic)  duct,  and  divides,  near  the  porta  hepatis,  into 
right  and  left  branches. 

(a)  The  right  branch  [r.  dexter],  given  off  at  the  porta  (portal  fissure)  of  the  liver,  runs  to  the 
right  either  behind  the  hepatic  and  cystic  ducts,  or  between  these  strucures.  At  the  right  end 
of  the  porta  it  divides  into  or  more  branches,  which  again  subdivided  as  they  enter  the  hver  sub- 
stance for  the  supply  of  the  right  lobe.  As  it  crosses  the  cystic  duct  it  gives  off  the  cystic  artery. 
The  cystic  artery  [a.  cystica]  courses  forward  and  downward  through  the  angle  formed 
by  the  union  of  the  hepatic  and  cystic  ducts,  and  just  before  it  reaches  the  gall-bladder  divides 
into  a  superficial  and  deep  branch.  The  former  breaks  up  into  a  number  of  small  vessels,  which 
ramify  over  the  free  surface  of  the  gall-bladder  beneath  the  peritoneal  covering,  and  furnish 
branches  to  the  muscular  and  mucous  coats.  The  deep  branch  ramifies  between  the  gall- 
bladder and  the  liver^ubstance,  supplying  each,  and  anastomosing  with  the  superficial  branch. 

(b)  The  left  branch  [r.  sinister],  the  smaller  division  of  the  hepatic  artery,  runs  medialward 
toward  the  left  end  of  the  porta  hepatis,  and,  after  giving  off  a  distinct  branch  to  the  caudate 
(Spigelian)  lobe,  enters  the  left  lobe  of  the  liver. 

3.  The  Splenic  Artery 

The  splenic  artery  [a.  lienalis] — the  largest  branch  of  the  cceliac  artery — 
arises  from  the  left  side  of  the  termination  of  that  vessel  below  the  left  gastric, 
and  passes  along  the  upper  border  of  the  pancreas  in  a  tortuous  manner  to  the 
spleen.  It  at  first  lies  behind  the  ascending  layer  of  the  transverse  meso-colon, 
but  on  nearing  the  spleen  enters  the  lieno-renal  ligament,  and  there  breaks  up 
into  numerous  branches,  which  enter  the  hilus  and  supply  the  organ.  In  this 
course  it  crosses  in  front  of  the  left  medial  crus  of  the  diaphragm  and  the  upper 
end  of  the  left  kidney  and  is  placed  above  the  splenic  vein. 

The  branches  of  the  splenic  artery  are: — (1)  The  pancreatic;  (2)  the  left 
gastro-epiploic;  (3)  the  vasa  brevia;  and  (4)  the  terminal. 

(1)  The  pancreatic  branches  (rami  pancreatici)  come  off  from  the  splenic  at  varying  intervals 
as  that  vessel  courses  along  the  upper  margin  of  the  pancreas.  They  enter  and  supply  the 
organ.  One  larger  branch  usually  arises  from  the  splenic  about  the  junction  of  its  middle 
with  its  left  third.  Entering  the  pancreas  obUquely,  it  runs  from  left  to  right,  commonly  above, 
and  a  httle  behtad,  the  pancreatic  duct,  whidh  it  supplies  together  with  the  substance  of  the 
organ. 

(2)  The  left  gastro-epiploic  [a.  gastroepiploica  sinistra]  arises  from  the  splenic  near  the 
greater  curvature  and  below  the  fundus  of  the  stomach,  and,  passing  between  the  anterior 
layers  of  the  great  omentum,  descends  along  the  greater  curvature  of  the  stomach  from  left 
to  right,  and  anastomoses  with  the  right  gastro-epiploic.  Like  that  vessel,  it  gives  off  ascend- 
ing or  gastric  branches  to  the  anterior  and  posterior  surfaces  of  the  stomach  respectively,  and 
long  slender  descending  epiploic  or  omental  branches  to  the  great  omentum  which  anastomose 
with  like  branches  from  the  right  and  left  colic  arteries. 

(3)  The  vasa  brevia  [aa.  gastrics  breves]  come  off  from  the  splenic  just  before  it  divides  into 
its  terminal  branches,  oftentimes  from  some  of  these  terminal  branches  themselves.  Passing 
from  between  the  folds  of  the  Ueno-renal  ligament  into  those  of  the  gastro-henal,  they  thus 
reach  the  fundus  of  the  stomach,  where,  ramifying  over  both  its  anterior  and  posterior  surfaces, 
they  anastomose  with  the  left  gastric  and  left  gastro-epiploic  arteries. 


596 


THE  BLOOD-VASCULAR  SYSTEM 


(4)  The  splenic  or  terminal  branches,  five  to  eight  or  more  in  number,  are  given  off  from  the 
splenic  as  it  lies  in  the  lieno-renal  ligament,  and,  entering  the  spleen  at  the  hilum,  are  distributed 
in  the  way  mentioned  in  the  description  of  that  organ. 


THE  SUPERIOR  MESENTERIC  ARTERY 

The  superior  mesenteric  artery  [a.  mesenterica  superior]  is  given  off  from  the 
front  of  the  aorta  a  little  below  the  cojliac,  which  it  nearly  equals  in  size;  some- 
times it  forms  a  common  trunk  with  the  coehac.  Lying  at  first  behind  the  pan- 
creas and  splenic  vein,  it  soon  passes  forward  between  the  lower  border  of  that 
gland  and  the  upper  border  of  the  inferior  portion  of  the  duodenum,  and,  crossing 
in  front  of  the  duodenum,  enters  the  mesentery,  in  which  it  runs  from  left  to' right, 
in  the  form  of  a  curve  with  its  convexity  to  the  left,  to  the  caecum,  where  it 
anastomoses  with  its  ileo-colic  branch.     Its  vein  Hes  to  its  right  side  above,  having 

Fig.  482. — The  Supekior  Mesbntekic  Artery  and  Vein. 
(The  colon  is  turned  up,  and  the  small  intestines  are  drawn  over  to  the  left  side.) 


Middle  colic 

artery 

Inferior   pancre 

atico-duodenal         ^ 


artery 


Right  colic 

artery  \ 


Ileo-colic  artery 


Left  colic  artery 
Superior   mes- 
enteric artery 


previously  crossed  obhquely  in  front  of  the  artery  from  left  to  right.  It  is  sur- 
rounded by  the  mesenteric  plexus  of  nerves.  The  accessory  portion  of  the  head 
of  the  pancreas  dips  in  behind  the  vessel. 

The  branches  of  the  superior  mesenteric  are,  in  their  primitive  order: — 
(1)  the  inferior  pancreatico-duodenal;  (2)  the  intestinal  arteries;  (3)  the  ileo- 
colic; (4)  the  right  colic;  and  (5)  the  middle  colic. 

(1)  The  inferior  pancreatico-duodenal  [a.  pancreatico  duodenaUs  inferior]  arises  either  from 
the  superior  mesenteric  as  that  vessel  emerges  from  the  contiguous  margins  of  the  pancreas 
and  inferior  part  of  the  duodenum  or  from  its  first  intestinal  branch.  Crossing  behind  the 
superior  mesenteric  vein,  it  courses  upward  and  to  the  right  between  the  head  of  the  pancreas 
and  the  duodenum,  and  beneath  the  ascending  layer  of  the  transverse  meso-colon,  to  anas- 
tomose with  the  superior  pancreatico-duodenal. 

(2)  The  intestinal  arteries  [aa.  intestinales]  arise  from  the  convex  side  of  the  superior 
mesenteric,  and,  varying  from  twelve  to  sixteen  in  number,  radiate  in  the  mesentery,  where 


THE  SUPERIOR  MESENTERIC  ARTERY 


597 


Fig.  483. — The  Blood-vessels  of  the  Ileo-c^cal  Region.  (From  Kelly.) 
(Arteries  red,  veins  blue.)  The  peritoneal  covering  is  removed  so  as  to  show  the  vessels  more 
clearly.  Above  and  to  the  right  are  seen  the  cut  ends  of  the  ileo-cohc  artery  and  vein.  This 
artery  gives  off  a  branch  to  the  ascending  colon  and  a  posterior  and  anterior  ctecal  artery, 
the  latter  descending  through  the  ileo-colic  fold.  A  short  anastomosis  connects  the  ileo- 
cohc  with  the  mesenteric.  The  artery  of  the  vermiform  process  (appendix)  is  seen  to 
arise  from  the  posterior  cfecal  artery,  2  cm.  above  the  ileum.  It  passes  behind  the  ileum 
in  the  free  border  of  the  mesappendix  and  gives  off  five  branches  (long  appendices  have 
8-12,  short  appendices,  2-3),  which  traverse  the  mesappendix  at  fairly  regular  intervals 
in  the  direction  of  the  hilus  of  the  appendix,  where  they  divide  into  anterior  and  posterior 
branches.  The  branches  in  the  me.sappendix  are  sometimes  seen  to  anastomose,  forming 
loops  of  varying  size.  The  terminal  branch  curves  around  the  tip.  The  CEeco-appendicular 
junction  is  supplied  by  a  separate  branch  arising  likewise  from  the  posterior  ileo-caecal  trunk. 
This  branch  may  or  may  not  anastomose  with  the  proximal  appendicular  twig  and  while 
in  some  cases  it  supplies  only  the  caecum,  in  others,  as  in  the  present  case,  it  sends  a  few 
dehcate  branches  into  the  appendix.  At  the  place  where  this  caeco-appendicular  artery 
crosses  the  ileo-caecal  fold  it  is  seen  to  give  off  a  dehcate  recurrent  twig  to  this  structure. 
Throughout  their  entire  course  the  arteries  are  accompanied  by  veins. 


598  THE  BLOOD-VASCULAR  SYSTEM 

each  divides  into  two  branches,  which  inosculate  with  similar  branches  given  oS  from  the 
branch  above  and  below.  From  the  primary  loops  thus  formed,  secondary  loops  are  derived 
in  Hke  manner,  and  from  these  tertiary,  and  at  times  quaternary,  or  even  quinary  loops.  From 
the  ultimate  loops  terminal  jejunal  and  iliac  branches  [aa.  jejunales  et  iliea;]  pass  on  to  the  muscu- 
lar coat  of  the  gut.  These  terminal  vessels  bifurcate,  the  two  branches  encircling  the  intestine, 
and  thus  forming  with  those  above  and  below  a  series  of  vascular  rings  surrounding  the  small 
intestine  throughout  its  whole  length.  The  first  intestial  artery  anastomoses  with  the  pancre- 
atico-duodenal  arteries,  and  the  last  (the  continuation  of  the  main  artery)  with  the  Ueo-coUc. 
These  branches  of  the  superior  mesenteric  in  their  course  to  the  intestine  also  supply  the 
mesentery  and  the  mesenteric  glands. 

(3)  The  ileo-colic  [a.  ileocolica]  descends  behind  the  peritoneum  toward  the  caecum,  where 
it  divides  into  a  cohc  branch  which  tracks  upward  beneath  the  peritoneum  to  anastomose  with 
the  descending  branch  of  the  right  cohc;  and  into  an  ihac  branch  which  passes  between  the 
layers  of  the  mesentery  and  anastomoses  with  the  termination  of  the  superior  mesenteric 
artery.  Near  the  site  of  division  the  ileo-colic  gives  off  anterior  and  posterior  csecal  branches. 
From  the  latter  of  these  arises  a  caeco-appendicular  artery,  to  the  caecum  and  root  of  the  vermi- 
form process,  and  a  main  appendicular  artery  [a.  appendicularis]  (fig.  483). 

(4)  The  right  colic  [a.  colica  dextra] — sometimes  given  off  as  a  common  trunk  either  with 
the  middle  colic  or  with  the  ileo-colic — passes  to  the  right  behind  the  peritoneum  to  the  back 
of  the  ascending  colon,  where  it  divides  into  an  ascending  branch,  which  anastomoses  with  the 
descending  branch  of  the  middle  cohc,  and  a  descending  branch  which  anastomoses  with  the 
ascending  or  colic  branch  of  the  ileo-cohc. 

(5)  The  middle  colic  [a.  colica  media],  arising  from  the  concavity  of  the  superior  mesenteric 
a  little  below  the  pancreas,  enters  the  transverse  meso-colon,  and  divides  into  two  branches — 
one  of  which  passes  to  the  left  and  anastomoses  with  the  ascending  branch  of  the  left  colic; 
the  other,  winding  downward  and  to  the  right,  anastomoses  with  the  ascending  branch  of  the 
right  colic. 

THE  RENAL  ARTERIES 

The  renal  arteries  [aa.  renales]  come  off  one  on  each  side  of  the  abdominal 
aorta,  a  little  below  the  superior  mesenteric  and  first  lumbar  arteries,  on  a  level 
with  the  first  lumbar  vertebra.  They  pass  laterally  across  the  crura  of  the 
diaphragm  to  the  kidneys,  the  right  being  on  a  slightly  lower  plane  and  somewhat 
longer  than  the  left,  and  passing  behind  the  inferior  vena  cava.  In  front  of  each 
is  the  corresponding  renal  vein,  and  behind,  at  the  hilus  of  the  kidney,  is  the  com- 
mencement of  the  ureter.  Each  artery  as  it  enters  the  hilus  usually  divides  into 
three  main  stems,  one  of  which  passes  toward  the  upper  part  of  the  pelvis,  a  second 
to  its  middle  portion,  and  a  third  to  its  lower.  Each  of  these  primary  stems  then 
divides  so  that  there  result  from  seven  to  nine  secondary  branches,  the  majority 
of  which  pass  anterior  to  the  pelvis,  while  the  remainder  are  posterior  to  it  (fig. 
484).  No  anastomoses  take  place  between  the  branches  of  the  anterior  and 
posterior  secondary  stems  and  hence  a  longitudinal  incision  into  the  kidney  along 
its  curved  border,  half  way  between  the  anterior  and  posterior  calices,  will  cut 
only  terminal  arteries. 

The  branches  of  the  renal  arteries  are : — 

(1)  The  inferior  suprarenal  [a.  suprarenahs  inferior]  which  ascends  to  the  suprarenal  body. 

(2)  The  capsular  or  peri-renal  branches  to  the  capsule  of  the  kidney  and  peri-renal  fat. 

(3)  The  ureteral  branch  to  the  upper  end  of  the  ureter. 

THE  MIDDLE  SUPRARENAL  ARTERIES 

The  middle  suprarenal  artery  [a.  suprarenahs  media]  comes  off,  one  on  each 
side  from  the  aorta,  just  above  the  first  lumbar  artery,  and  passes  laterally  to  the 
suprarenal  body,  across  the  medial  crura  of  the  diaphragm  a  little  above  the  renal 
arteries.  In  the  foetus  they  equal  the  renals  in  size.  In  the  adult  they  are  much 
smaller. 

They  anastomose  with  the  superior  and  inferior  suprarenal  arteries  from  the 
inferior  phrenic  and  renal  arteries  respectively.  For  the  distribution  of  the 
suprarenal  vessels  within  the  suprarenal  bodies,  see  Section  XII. 

THE  INTERNAL  SPERIVIATIC  ARTERIES 

The  internal  spermatic  arteries  [a.  spermatica  interna],  (fig.  479),  right  and 
left,  come  off  from  the  front  of  the  abdominal  aorta.  They  diverge  from  each 
other  as  they  descend  over  the  aorta  and  psoas  muscle  to  the  abdominal  inguinal 
(internal  abdominal)  ring,  where  they  are  joined  by  the  ductus  deferens,  and,  pass- 


THE  INTERNAL  SPERMATIC  ARTERIES 


599 


ing  with  it  through  the  inguinal  canal  and  out  of  the  subcutaneous  inguinal  (ex- 
ternal abdominal)  ring,  run  downward  into  the  scrotum  in  a  tortuous  course  to  the 
testes.  They  terminate  in  branches  to  the  epididymis  and  body  of  those  organs. 
Within  the  abdomen  they  lie  beneath  the  peritoneum,  and  cross  in  their  descent 
over  the  ureters  and  distal  ends  of  the  external  iliac  arteries;  the  right  being  super- 

FiG.  484. — A.  The  Renal  Artery  and  the  Distribution  of  its  Branches  in  Relation 
TO  THE  Pelvis.  B.  Transverse  Section  through  the  Middle  op  the  Same  Kidney. 
(After  Brodel,  Johns  Hopkins  Hospital  Bulletin.) 

o,  renal  artery;  a'  and  a",  its  anteiior  and  pubtenor  branches,  6,  branches  to  pyramids;  c,  line 
of  division  between  anterior  and  po&tenoi  pyi  imids  The  arrow  and  dotted  Una  indicate 
the  line  of  separation  between  tin   fi  lunn  iK  ot  the  anterior  and  posterior  branches. 


ficial  to  the  vena  cava,  and  behind  the  termination  of  the  ileum;  and  the  left 
beneath  the  sigmoid  colon.  In  the  inguinal  canal  and  in  the  scrotum  the  sper- 
matic veins  lie  in  front  of  the  artery,  and  the  ductus  deferens  lies  behind  it. 

In  the  foetus  these  vessels  pass  in  a  transversely  lateral  direction  to  the  testis, 
which  in  early  foetal  life  lies  in  the  loin  in  front  of  the  kidney;  but  as  the  testes 


600  THE  BLOOD-VASCULAR  SYSTEM 

Fig.  485. — The  Vascular  Trunks  of  iiii:  Li>wi:k  Ahimi.mf.x.     (From  l\f'lly,  by  Brodel.) 


THE  INTERNAL  SPERMATIC  ARTERIES 


601 


descend  to  the  scrotum,  the  vessels  become  elongated,  and  are  drawn  with  the 
testis  into  the  scrotum. 

The  branches  of  the  internal  spermatic  artery  are: — (1)  Ureteral;  (2)  cre- 
masteric; (3)  epididymal;  and  (4)  testicular. 

(1)  The  ureteral  are  small  branches  given  off  to  the  ureter  as  the  spermatic  artery  crosses 
it.  They  anastomose  with  the  other  ureteral  branches  derived  from  the  renal,  common  ihac, 
and  vesical  arteries. 

(2)  The  cremasteric  are  small  branches  given  off  to  the  cremaster  muscle;  they  anastomose 
with  the  cremasteric  branch  of  the  inf.  epigastric. 

Fig.  486. — The  Ovakian  Vessels.     (After  Clark.) 


1 


(3)  The  epididynal  are  distributed  to  the  epididymic,  and  anastomose  with  the  deferential 
artery. 

(4)  The  testicular  arteries  [aa.  testiculares]  are  the  terminal  branches  of  the  spermatic; 
they  perforate  the  tunica  albuginea  posteriorly,  and  are  distributed  to  the  body  of  the  organ  in 
the  way  mentioned  in  the  section  on  the  Testis. 

The  e.xternal  spermatic  artery  is  a  branch  of  the  inferior  epigastric  artery  (p.  614). 


602 


THE  BLOOD-VASCULAR  SYSTEM 


THE  OVARIAN  ARTERIES 

The  ovarian  arteries  [aa.  ovaricse],  are  the  homologues  of  the  internal  sper- 
matic arteries  in  the  male,  and  correspond  in  their  relations  in  the  upper  part  of 
their  course.  They  diverge  somewhat  less,  however,  and,  on  reaching  the  level 
of  the  common  iliac  artery,  turn  medialward  over  that  vessel  and  descend  tor- 
tuously into  the  pelvis  between  the  folds  of  the  broad  ligament  to  the  ovaries. 
In  the  broad  hgament  the  ovarian  artery  lies  below  the  Fallopian  tube,  and  on 
reaching  the  ovary  turns  backward  and  supplies  that  organ.  In  fig.  486  is  shown 
how  the  artery  enters  the  hilus  of  the  ovary  and  breaks  up  into_branches  which 
determine  the  lobules  of  the  organ. 

The  branches  of  the  ovarian  arteries  are: — (1)  Ureteral;  (2)  tubal;  (3)  uterine; 
and  (4)  ligamentous. 

(1)  The  ureteral  is  distributed,  as  in  the  male,  to  the  ureter. 

F(2)  The  tubal  suppKes  the  isthmus  and  ampulla  of  the  tuba  uterina  (Fallopian  tube)  and 
its  fimbriated  extremity. 

(3)  The  uterine  runs  beneath  the  tuba  uterina  (Fallopian  tube)  to  the  uterus,  supplying 
the  upper  part  of  the  fundus,  and  anastomosing  with  the  uterine  arteries  from  the  hypogastric. 

(4)  The  ligamentous  is  distributed  to  the  round  ligament,  passing  with  that  structure  through 
the  inguinal  canal,  and  anastomosing  with  the  superficial  external  pudendal  artery. 

Like  the  spermatic,  the  ovarian  arteries  in  the  foetus  come  off  at  right  angles  to  the  aorta, 
and  pass  transversely  lateralward  to  the  ovaries,  which  are  formed,  as  are  the  testes,  in  the 
right  and  left  loin  in  front  of  the  kidneys.  They  elongate  as  the  ovaries  descend  into  the  pelvis. 
During  pregnancy  these  arteries  undergo  great  enlargement. 

THE  INFERIOR  MESENTERIC  ARTERY 

The  inferior  mesenteric  artery  [a.  mesenterica  inferior],  smaller  than  the 
superior,  arises  from  the  front  of  the  abdominal  aorta  about  3.7  cm.  (1|  in.) 


Fig.  487. — The  Inferiob  Missenteeic  Artery  and  Vein. 
(The  colon  is  turned  up,  and  the  small  intestines  me  drawn  to  the  right  side.) 


Middle  colic  artery 


Inferior  pancreatico- 
duodenal artery 
Superior  mesenteric 
artery 

Right  colic  artery 


Abdominal  aorta 
Vena  cava  inferior 


Right  common  iliac 

artery 

Middle  sacral  artery 

and  vein 


Left  colic  artery 


teric  artery 
Left  colic  artery 
Inferior  mesen- 
teric artery 


Sigmoid  artery 


Superior  haemor- 
rhoidal  artery 


above  the  bifurcation  of  that  vessel.  It  runs  obliquely  downward  and  to  the 
left,  behind  the  peritoneum,  across  the  lower  part  of  the  abdominal  aorta  a,nd  then 
over  the  left  psoas  muscle  and  left  common  iliac  artery.     It  descends  into  the 


THE  COMMON  ILIAC  ARTERIES  603 

pelvis  between  the  layers  of  the  sigmoid  meso-colon,  and  terminates  on  the  rectum 
in  the  superior  hsemorrhoidal  artery.  It  supplies  the  lower  half  of  the  large  in- 
testine. Its  vein  lies  at  first  close  to  the  left  side,  but  soon  passes  upward  on  the 
psoas,  away  from  the  artery,  to  end  in  the  splenic  vein  (fig.  487). 

The  branches  of  the  inferior  mesenteric  are: — (1)  The  left  colic;  (2)  the 
sigmoid;  and  (3)  the  superior  haemorrhoidal. 

(1)  The  left  colic  artery  [a.  colica  sinistra]  runs  transversely  to  the  left,  beneath  the  peri- 
toneum, and  divides  into  two  branches,  one  of  which,  entering  the  transverse  meso-colon,  as- 
cends upward  and  to  the  right,  to  anastomose  with  the  middle  colic.  The  other  descends,  and, 
entering  the  sigmoid  meso-coion  anastomoses  with  tlie  ascending  branch  of  the  sigmoid  artery. 

The  distribution  of  this  artery,  and  of  the  next,  to  the  colon  is  similar  to  that  of  the  cofie 
branches  of  the  superior  mesenteric,  and  does  not  require  a  separate  description.  (See  pp. 
597,  598.) 

(2)  The  sigmoid  artery  [a.  sigmoidea]  runs  downward  and  to  the  left  over  the  psoas  mus- 
cle and,  entering  the  sigmoid  meso-colon,  divides  into  two  branches;  the  upper  anastomosing 
with  the  left  cohc,  the  lower  with  the  superior  hemorrhoidal. 

(3)  The  superior  haemorrhoidal  artery  [a.  hasmorrhoidaUs  superior]  is  the  continued  trunk  of 
the  inferior  mesenteric.  It  descends  into  the  pelvis,  behind  the  rectum,  between  the  layers  of  the 
sigmoid  meso-colon.  On  reaching  the  wall  of  the  bowel  it  bifurcates,  one  branch  proceeding  on 
either  side  of  the  gut,  to  within  10  or  12  cm.  (4  or  5  in.)  of  the  anus.  Here  each  again  divides, 
and  the  branches,  piercing  the  muscular  coat,  descend  between  that  coat  and  the  mucous  mem- 
brane, forming  with  each  other,  and  with  the  middle  haemorrhoidal  arteries — derived  from  the 
hypogastric  (internal  ihac) — a  series  of  small  vessels,  running  longitudinally  to  the  rectum,  and 
parallel  to  each  other  as  far  as  the  level  of  the  internal  sphincter,  where,  by  their  anastomosis, 
they  form  a  series  of  loops  around  the  lower  part  of  the  rectum. 

C.  The  Terminal  Branches  of  the  Abdominal  Aorta 
THE  MIDDLE  SACRAL  ARTERY 

The  middle  sacral  artery  [a.  sacralis  media],  is,  anatomically,  the  continuation 
of  the  aorta.  The  coccygeal  glomerulus  [glomus  coccygeum],  in  which  it  ter- 
minates, is  believed  to  contain  the  rudiments  of  the  caudal  aorta.  The  artery 
extends  from  the  bifurcation  of  the  aorta  to  the  tip  of  the  coccyx.  As  it  passes 
downward  into  the  pelvis,  it  runs  behind  the  left  common  iliac  vein,  the  hypo- 
gastric plexus  of  the  sympathetic  nerve,  and  the  peritoneum.  It  lies  successively 
upon  the  intervertebral  disc  between  the  fourth  and  fifth  lumbar  vertebrse,  the 
fifth  lumbar  vertebra,  the  intervertebral  disc  between  that  vertebra  and  the 
sacrum,  and  lower  down  upon  the  anterior  surface  of  the  sacrum  and  coccyx. 

Branches. — The  branches  of  the  middle  sacral  artery  are : — 

(1)  The  lowest  lumbar  artery  [a.  lumbahs  ima],  which,  when  present,  usually  comes  off  from 
the  middle  sacral  artery.  Each  vessel  of  this  pair  runs  laterally  beneath  the  common  ihac  artery 
and  vein;  and,  after  giving  off  a  dorsal  branch,  ramifies  over  the  lateral  part  of  the  sacrum,  and 
ends  in  the  iliacus  muscle  by  anastomosing  with  the  circumflex  Oiac  artery.  The  dorsal  branch 
passes  to  the  back  between  the  last  lumbar  vertebra  and  the  sacrum  and  ramifies  in  the  gluteus 
maxiraus,  anastomosing  with  the  lumbar  arteries  above,  and  the  superior  gluteal  artery  below. 

(2)  Lateral  sacral  branches,  are  usually  four  in  number.  They  are  serially  homologous  with 
the  intercostal  and  lumbar  arteries  given  off  by  the  aorta.  They  run  laterally,  and  anastomose 
with  the  lateral  sacral  branches  of  the  hypogastric  (internal  iliac)  artery.  They  give  off  small 
spinal  branches,  which  pass  through  the  sacral  foramina,  and  supply  the  sacral  canal  and  back 
of  the  sacrum. 

(3)  Rectal  or  haemorrhoidal  branches  pass  forward  beneath  the  peritoneum  or  in  the  sig- 
moid meso-colon  to  the  rectum,  which  they  help  to  supply,  and  anastomose  with  the  other 
haemorrhoidal  or  rectal  arteries. 

THE  COMMON  ILIAC  ARTERIES 

The  common  iliac  arteries  [aa.  iliacse  communes]  arise  opposite  the  left  side 
of  the  middle  of  the  body  of  the  fourth  lumbar  vertebra,  at  the  bifurcation  of  the 
abdominal  aorta,  and,  diverging  from  each  other  in  the  male  at  about  an  angle 
of  60°,  and  in  the  female  at  an  angle  of  68°,  terminate  opposite  the  lumbo-sacral 
articulation  by  bifurcating  into  the  external  iliac,  which  is  continued  along  the 
brim  of  the  pelvis  to  the  lower  hmb,  and  into  the  hypogastric  (internal  iliac), 
which  passes  through  the  superior  aperture  of  the  pelvis  and  descends  into  that 
cavity  (fig.  488). 

The  relations  differ  slightly  on  the  two  sides,  and  maj^  be  considered  separately. 


604 


■THE  BLOOD-VASCULAR  SYSTEM 


Fig.  488. — The  Relations  of  the  Common 
Anatomy,"  Rebman, 

Internal  jugular  vein 
Thyreoidea  ima  vein 
Subclavian  vein 
Right  innominate  vein 

Thymic  veins     //j/^ 

Superior  vena  cava 


Iliac  Arteries.     (Alter  Toldt,  "Atlas  of  Human 
London  and  New  York.) 

Thyreoid  gland 
.,  Left  innominate  vein 


Internal  mammary  artery  and 


Suprarenal  gland  ^__  /"/ 

Superior 

teric  artery 


Inferior  vena  cava 


Spermati 
Internal  spermatic 

artery 


Common     iliai 
artery  and  vein  ^ 

Anterior  sacral, /         ■" 

plexus  '"'       1^ 

Deep  circumflex 
iliac  artery  and , 

vein  I 

Inferior  epigas-  /      N^' 

trie  artery  and /         \ 

vein  ' 

External  sper- 
matic artery 

Femoral  artery 

Femoral  vein' 

\ 
I 
External  puden-  '" 
dal  veins  '' 

Anterior  scrotal  veins 
Common  tunica  vaginali 


THE  HYPOGASTRIC  ARTERY  605 

The  Right  Common  Iliac  Artery 

The  right  common  iliac  measures  about  5  cm.  (2  in.)  in  length,  and  is  rather 
longer  than  the  left,  in  consequence  of  the  aorta  bifurcating  a  little  to  the  left  of 
the  median  line. 

Relations. — In  front  it  is  covered  by  the  peritoneum,  and  is  crossed  by  the  right  ureter  a 
little  before  its  bifurcation,  by  the  ovarian  artery  in  the  female,  by  the  termination  of  the  ileum, 
by  .the  terminal  branches  of  the  superior  mesenteric  artery,  and  by  branches  of  the  sympathetic 
nerve  descending  to  the  hypogastric  plexus. 

Behind,  it  hes  on  the  right  common  iliac  vein,  the  end  of  the  left  common  ihac  vein,  and  the 
commencement  of  the  inferior  vena  cava,  which  separate  it  from  the  fourth  and  fifth  lumbar 
vertebrae  and  their  intervening  disc,  the  psoas  muscle,  and  the  sympathetic  nerve;  whilst  still 
deeper  in  the  groove  between  the  fifth  vertebra  and  the  psoas  are  the  lumbo-sacral  trunk, 
the  obturator  nerve,  and  the  ilio-lumbar  artery. 

To  the  right  side  are  the  beginning  of  the  inferior  vena  cava,  the  end  of  the  right  common 
iliac  vein,  and  the  psoas  muscle,  which,  however,  is  separated  from  the  artery  by  the  vena  cava 
inferior  at  its  upper  part. 

To  the  left  side  are  the  right  common  iliac  vein,  the  termination  of  the  left  common  Uiac  vein, 
and  the  hypogastric  plexus. 

The  Left  Common  Iliac  Artery 

The  left  common  iliac  artery,  4  cm.  (14  in.)  in  length,  is  a  little  shorter  and 
thicker  than  the  right. 

Relations. — In  front  it  is  covered  by  the  peritoneum,  which  separates  it  from  the  intestines, 
and  is  crossed  by  the  ureter,  the  ovarian  artery  in  the  female,  branches  of  the  sympathetic  nerve 
descending  to  the  hypogastric  plexus,  the  termination  of  the  inferior  mesenteric  artery,  the 
sigmoid  colon,  and  the  sigmoid  mesocolon. 

Behind  are  the  lower  border  of  the  body  of  the  fourth  lumbar  vertebra,  the  disc  between  the 
fourth  and  fifth  lumbar  vertebra,  the  body  of  the  fifth  lumbar  vertebra,  and  the  disc  between  it 
and  the  sacrum.  Crossing  deeply  behind  the  artery  between  the  fifth  lumbar  vertebra  and  the 
psoas,  is  the  obturator  nerve,  the  lumbo-sacral  trunk,  and  the  ilio-lumbar  artery. 

To  the  left  side  is  the  psoas  muscle. 

To  the  right  side  are  the  left  common  ihac  vein,  the  hypogastric  plexus,  and  the  middle 
sacral  artery. 

Collateral  Circulation 

The  collateral  circulation  after  obstruction  or  ligature  of  the  common  ihac  artery  is  carried 
on  chiefly  (fig.  497)  by  the  anastomosis  of  the  middle  sacral  with  the  lateral  sacral;  the  internal 
mammary  with  the  epigastric;  the  lumbar  arteries  of  the  aorta  with  the  iho-lumbar  and  deep 
circumflex  iliac;  the  pubic  branch  of  the  epigastric  with  the  pubic  branch  of  the  obturator;  the 
posterior  branches  of  the  sacral  arteries  with  the  superior  gluteal  (gluteal) ;  the  superior  hem- 
orrhoidal from  the  inferior  mesenteric,  with  the  hfemorrhoidal  branches  of  the  hypogastric  (in- 
ternal iliac)  and  pudic;  the  ovarian  arteries  from  the  aorta  with  the  uterine  branches  of  the  hy- 
pogastric (internal  iliac) ;  and  by  the  anastomosis  across  the  middle  line  of  the  pubic  branch  of 
the  obturator  with  the  like  vessel  of  the  opposite  side;  the  lateral  sacral  with  the  opposite 
lateral  sacral;  and  the  vesical,  hemorrhoidal,  uterine,  and  vaginal  branches  of  the  hypogastric 
with  the  corresponding  branches  of  the  opposite  hypogastric  (internal  iliac). 

Branches  of  the  Common  Iliac  Artery 

The  branches  of  the  common  iliac  artery  are: — (1)  The  hypogastric  (internal 
iliac);  and  (2)  external  iliac. 

There  are  a  few  small,  unimportant  branches  distributed  to  the  peritoneum  and  subperi- 
toneal fat.  They  anastomose  with  vessels  given  off  from  the  lumbar,  inferior  phrenic,  and  renal 
arteries,  forming  a  subperitoneal  arterial  anastomosis.  The  ureter  receives  small  insignificant 
twigs  as  it  crosses  the  artery.  They  anastomose  with  the  ureteral  arteries  given  off  from  the 
internal  spermatic  above,  and  with  those  derived  from  the  vesical  arteries  below. 

THE  HYPOGASTRIC  ARTERY 

The  hypogastric  or  internal  iliac  artery  [a.  hypogastrica],  arises  at  the  bifur- 
cation of  the  common  iliac  opposite  the  lumbo-sacral  articulation.  It  descends 
into  the  pelvis  for  about  3  cm.  (1|  in.)  and  then  divides,  opposite  the  upper 
margin  of  the  great  sciatic  foramen,  into  an  anterior  and  a  posterior  division. 
The  anterior  divisio?i  commonly  gives  off  the  obturator,  inferior  gluteal,  umbilical, 


606 


THE  BLOOD-VASCULAR  SYSTEM 


inferior  vesical,  deferential,  middle  hsemorrhoidal,  uterine  fin  the  female),  and 
internal  pudendal  arteries.  From  the  posterior  division  the  ilio-lumbar,  lateral 
sacral,  and  superior  gluteal  arteries  arise.  These  vessels  are  classified,  for 
description,  as  parietal  and  visceral. 

In  the  adult  the  hypogastric  is  smaller  than  the  external  ihac;  in  the  foetus  it  is  much  larger 
and  through  it  the  foetal  blood  is  returned  to  the  placenta.  The  adult  hypogastric  and  common 
ihac  arteries  of  either  side  represent  the  proximal  portion  of  each  of  the  embryonic  umbilical 
arteries.  The  remainder  of  the  umbUical  artery  within  the  body  is  represented  by  the  umbiMcal 
branch  of  the  hypogastric  which  runs  to  the  navel.  At  birth,  when  the  circulation  in  the  um- 
bihcal  cord  ceases,  the  lumen  of  the  umbihcal  branch  of  the  hypogastric  becomes  obhterated 
except  a  small  channel  which  remains  pervious  as  the  superior  vesical  of  tlie  adult. 

Relations. — Behind,  the  hypogastric  artery  rests  on  the  termination  of  the  external  iliac 
vein,  the  hypogastric  vein,  the  medial  margin  of  the  psoas  muscle,  the  lumbo-sacral  trunk,  the 
obturator  nerve,  and  the  sacrum. 

In  front,  it  is  covered  by  the  peritoneum,  and  is  crossed  by  the  ureter. 

Fig.  489. — The  Htpogastbic  Artery.     (After  Henle.) 


ExternI  iliac  artery 


Hypogastric  artery 


Deep  circumflex, 
iliac  artery 


Ilio-lumbar  artery 


Lateral  sacral  artery 


Inferior  epigastric, 
artery 


Ascending  branch 


^Internal  pudic 
artery 


Internal  ves- 
ical artery 


Hsemorrhoidal 
artery 


Coccygeus  muscle 


Bladder 
Internal  obturator  muscle 


The  branches  of  the  hypogastric  artery  may  be  divided  into  parietal  and 
visceral  sets.  The  parietal  branches  are: — -(1)  The  ilio-lumbar;  (2)  the  lateral 
sacral;  (3)  the  obturator;  and  (4)  the  gluteal  arteries. 

The  visceral  branches  are: — (1)  The  umbilical;  (2)  the  inferior  vesical;  (3) 
the  middle  haemorrhoidal;  (4)  the  uterine;  and  (5)  the  internal  pudendal. 


Parietal  Branches  of  the  Hypogastric  Artery 
1.  THE  ILIO-LUMBAR  ARTERY 

The  ilio-lumbar  artery  [a.  iliolumbalis] — a  short  vessel  coming  off  from  the 
posterior  part  of  the  hypogastric  artery — -runs  upward  and  laterally  beneath  the , 
common  iliac  artery,  first  between  the  lumbo-sacral  trunk  and  obturator  nerve, 


THE  LATERAL  SACRAL  ARTERIES 


607 


and  then  between  the  psoas  muscles  and  the  vertebral  column.  On  reaching  the 
superior  aperture  of  the  pelvis  it  divides  into  two  branches,  an  iliac  and  a  lumbar 
(fig-  489). 

The  iliac  branch  [ramus  iliaous]  passes  laterally  beneath  the  psoas  and  the  femoral  (anterior 
crural)  nerve  and,  perforating  the  iUacus,  ramifies  in  the  iliac  fossa  between  that  muscle  and  the 
bone.  It  supphes  a  nutrient  artery  to  the  bone,  and  then  breaks  up  into  several  branches  which 
radiate  from  the  parent  trunk,  upward  toward  the  sacro-iUac  synchondrosis,  laterally  toward 
the  crest  of  the  Uium,  downward  toward  the  anterior  superior  spine,  and  medially  toward  the 
pelvic  cavity.  The  first  anastomoses  witli  the  last  lumbar;  the  second  with  the  external  circum- 
flex and  gluteal;  the  third  with  the  deep  circumflex  iUac  from  the  external  ihac;  the  fourth  with 
the  Uiac  branch  of  the  obturator.  The  lumbar  branch  [ramus  lumbalis]  ascends  beneath  the 
psoas,  and,  supplying  that  muscle  and  the  quadratus  lumborum,  anastomoses  with  the  last  lum- 
bar artery.  It  sends  a  spinal  branch  (ramus  spinalis)  into  the  vertebral  canal  through  the  inter- 
vertebral foramen  between  the  last  lumbar  vertebra  and  the  sacrum;  this  branch  anastomoses 
with  the  other  spinal  arteries.  The  Qio-lumbar  artery  is  serially  homologous  with  the  lumbar 
arteries.     Hence  the  similarity  in  its  course  and  distribution. 

2.  THE  LATERAL  SACRAL  ARTERIES 

The  lateral  sacral  artery  [a.  sacralis  lateralis],  commonly  arises  as  two  vessels 
from  the  posterior  division  of  the  hypogastric.     The  superior  artery,  when  two 

Fig.  490. — The  Gluteal  Artehies.     (After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman, 
London  and  New  York.) 


^  Glutaeus  medius  muscle 


Inferior  branch  - 


Superior  brancli- 
Superior  gluteal  artery - 


Piriformis  muscle- 
Inferior  gluteal  artery  — 
Internal  pudendal  artery, 

A.  comitans  nervi 
ischiadici 
Obturator  fascia 

Inferior  h£e 
rhoidal  artery  / 

Sacro-tuberous      ,' 
ligament        ~^ 

Perineal  artery 


Hedial  circumflex 
femoral  artery 
(deep  branch) 


■  Glutseus  minimus  muscle 
^  Obturator  internus  muscle 


/\ 


Biceps  femoris  muscle  • 
(long  head) 


Attachment  of  the  ilio- 
psoas muscle  to  the 
trochanter  minor 


Adductor  minimus  muscle 


First  perforating  artery 
Adductor  magnus  muscle 


Second  perforating  artery 


are  present,  runs  downward  and  medially  to  the  first  anterior  sacral  foramen, 
through  which  it  passes;  and,  after  supplying  the  spinal  membranes  and  anas- 
tomosing with  the  other  spinal  arteries,  passes  through  the  first  posterior  sacral 


08  THE  BLOOD-VASCULAR  SYSTEM 

foramen,  and  is  distributed  to  the  skin  over  the  back  of  the  sacrum,  there  anas- 
tomosing with  branches  of  the  superior  and  inferior  gluteal  arteries.  The  inferior 
lateral  sacral  descends  on  the  side  of  the  sacrum,  lateral  to  the  sacral  chain  of  the 
sympathetic,  and  medial  to  the  anterior  sacral  foramina,  crossing  in  its  course  the 
slips  of  origin  of  the  piriformis  muscle  and  the  first  anterior  sacral  nerve.  On 
reaching  the  coccyx  it  anastomoses  in  front  of  that  bone  with  the  middle  sacral 
artery,  and  with  the  inferior  lateral  sacral  of  the  opposite  side  (fig.  489). 

In  this  course  it  gives  off: — Spinal  branches  [rami  spinales],  which  enter  the  second,  third 
and  fourth  anterior  sacral  foramina,  and,  after  supplying  the  spinal  membranes  and  anastomos- 
ing with  each  other,  leave  the  spinal  canal  by  the  corresponding  posterior  sacral  foramina,  and 
are  distributed  to  the  muscle  and  skin  over  the  back  of  the  sacrum;  and  rectal  branches  which 
run  forward  to  the  rectum. 

At  times  the  lateral  sacral  arteries  are  exceedingly  small,  the  spinal  branches  then  coming 
chiefly  from  the  middle  sacral.  The  anastomosing  branches  between  the  lateral  sacral  and 
middle  sacral  are  usually  regarded  as  sacral  arteries  diminished  in  size,  and  serially  homologous 
with  the  lumbar  and  intercostal  arteries. 

3.  THE  OBTURATOR  ARTERY 

•  The  obturator  artery  [a.  obturatoria],  usually  arises  from  the  anterior  division 
of  the  hypogastric.  It  runs  forward  and  downward  a  Httle  below  the  brim  of  the 
pelvis,  having  the  obturator  nerve  above  and  the  obturator  vein  below.  It  here 
lies  between  the  peritoneum  and  the  endo-pelvic  fascia,  but  later  it  passes  through 
the  obturator  canal,  the  aperture  in  the  upper  part  of  the  obturator  membrane. 
In  this  course  it  is  crossed  by  the  ductus  deferens.  On  emerging  from  the  obturator 
canal  the  artery  divides  into  two  branches,  anterior  and  posterior,  which  wind 
around  the  margin  of  the  obturator  foramen  beneath  the  obturator  externus 
muscle. 

The  branches  of  the  obturator  artery  are: — (1)  The  iliac  or  nutrient  branch; 
(2)  a  vesical  branch;  (3)  the  pubic  branch;  (4)  the  anterior,  and  (5)  posterior 
terminal  branches. 

(1)  The  iliac  or  nutrient  branch  ascends  to  the  iliac  fossa,  passing  between  the  iUacus 
muscle  and  the  bone.  It  suppUes  a  nutrient  vessel  to  the  ihum,  and  anastomoses  with  the 
medial  branch  of  the  iliac  division  of  the  ilio-lumbar  artery. 

(2)  The  vesical  branch  or  branches  are  smaU  vessels  which  run  in  the  lateral  false  ligament 
of  the  bladder  to  that  organ,  where  they  anastomose  with  the  other  vesical  arteries. 

(3)  The  pubic  branch  [ramus  pubicus]  comes  off  from  the  obturator  as  that  vessel  is  leaving 
the  pelvis  by  the  obturator  canal.  It  runs  upward  and  medially  behind  the  pubis,  anastomosing 
with  its  feUow  of  the  opposite  side  of  the  body,  and  with  the  pubic  branch  of  the  inferior  epi- 
gastric artery.  One  of  the  anastomosing  channels  between  the  pubic  branch  of  the  obturator 
and  pubic  branch  of  the  inferior  epigastric  arteries  is  sometimes  of  large  size,  a  fact  of  surgical 
interest  in  that  the  enlarged  vessel  may  then  run  around  the  medial  side  of  the  femoral  ring 
(pp.  615  and  636). 

(4)  The  anterior  branch  [ramus  anterior]  runs  around  the  medial  margin  of  the  obturator 
foramen,  and  anastomoses  with  the  posterior  branch  and  with  the  medial  circumflex  artery.  It 
supplies  branches  to  the  obturator  and  adductor  muscles. 

(5)  The  posterior  branch  [ramus  posterior]  skirts  the  lateral  margin  of  the  obturator  fora- 
men, lying  between  the  obturator  externus  and  the  obturator  membrane.  At  the  lower  margin 
of  the  foramen  it  divides  into  two  branches.  One  branch  continues  its  course  around  the  lower 
margin  of  the  foramen,  and  anastomoses  with  the  anterior  branch  of  the  obturator  and  with 
the  medial  circumflex.  The  other  branch  turns  laterally  below  the  acetabulum,  and  ends  in  the 
muscles  arising  from  the  tuberosity  of  the  ischium.  It  anastomoses  with  the  inferior  gluteal 
artery.  This  branch  gives  off  a  small  twig,  the  acetabular  artery  [a.  acetabuli],  which  passes 
under  the  transverse  Ugament  into  the  hip-joint,  where  it  suppUes  the  synovial  membrane, 
the  hgamentum  teres,  and  the  fat  in  the  fossa  at  the  bottom  of  the  acetabulum. 

4.  THE  GLUTEAL  ARTERIES 

There  are  two  gluteal  arteries,  the  superior  and  inferior.     The  superior 

gluteal  artery  [a.  glutea  superior],  the  largest  branch  of  the  posterior  division  of 
the  hypogastric  comes  off  as  a  short,  thick  trunk  from  the  lateral  and  back  part 
of  that  vessel,  of  which  indeed  it  may  be  regarded  as  the  continuation.  Passing 
backward  between  the  first  sacral  nerve  and  the  lumbo-sacral  trunk  through  an 
osseo-tendinous  arch  formed  by  the  margin  of  the  bone  and  the  upper  edge  of  the 
endo-pelvic  fascia,  it  leaves  the  pelvis  through  the  great  sciatic  foramen  above 
the  piriformis  muscle  in  company  with  its  vein  and  the  superior  gluteal  nerve.  At 
its  exit  posteriorly  from  the  great  sciatic  foramen  it  lies  under  cover  of  the  gluteus 


THE  INFERIOR  VESICAL  ARTERY  609 

maximus  and  beneath  the  superior  gluteal  vein,  and  in  front  of  the  superior 
gluteal  nerve.  It  here  breaks  up  into  two  chief  branches,  a  superficial  and  a 
deep.  Its  emergence  from  the  pelvis  is  indicated  on  the  surface  by  a  point 
situated  at  the  junction  of  the  posterior  with  the  middle  third  of  a  line  drawn 
from  the  anterior  superior  to  the  posterior  superior  spine  of  the  ilium. 

The  branches  of  the  superior  gluteal  artery  are : — 

(o)  Within  the  pelvis,  branches  are  distributed  to  the  obturator  internus,  the 
piriformis,  the  levator  ani,  the  coccygeus,  and  the  pelvic  bones. 

(h)  External  to  the  pelvis,  the  artery  divides  into  a  superior  and  an  inferior 
branch. 

(i)  The  superior  branch  [ramus  superior]  breaks  up  into  a  number  of  large  vessels  for  the 
supply  of  the  upper  portion  of  the  gluteus  maximus,  some  of  them  piercing  the  muscle  and  supply- 
ing the  skin  over  it,  and  anastomosing  with  the  posterior  branches  of  the  lateral  sacral  arteries; 
whilst  one  of  larger  size,  emerging  from  the  muscle  near  the  ihao  crest,  anastomoses  with  the 
deep  circumflex  iliac  artery.  The  lower  branches  to  the  muscle  anastomose  with  branches  of 
the  inferior  gluteal  (sciatic). 

(ii)  The  inferior  branch  [ramus  inferior]  subdivides  into  two  branches — One  skirts  along 
the  lane  of  origin  of  the  gluteus  minimus  (fig.  490),  between  the  gluteus  medius  and  the  bone, 
and,  emerging  in  front  from  beneath  these  muscles  under  cover  of  the  tensor  fascite  lata:,  anas- 
tomoses with  the  ascending  branch  of  the  lateral  circumflex  and  the  deep  circumflex  iliac  arter- 
ies. The  other  passes  forward  between  the  gluteus  medius  and  minimus,  accompanied  by  the 
branch  to  the  tensor  fasciae  lata;  of  the  inferior  division  of  the  superior  gluteal  nerve,  toward  the 
greater  trochanter,  where  it  anastomoses  with  the  ascending  branch  of  the  lateral  circumflex. 
It  supphes  branches  to  the  contiguous  muscles  and  to  the  hip-joint.  The  inferior  branch  before 
its  division  gives  off  the  external  nutrient  artery  of  the  ilium. 

The  inferior  gluteal  [a.  glutea  inferior],  is  one  of  the  terminal  branches 
of  the  anterior  division  of  the  hypogastric  artery.  It  leaves  the  pelvis  below  the 
piriformis  muscle,  and  immediately  breaks  up  into  a  number  of  diverging  branches. 
The  largest  enter  the  gluteus  maximus  muscle,  where  they  anastomose  with  the 
superior  gluteal  branches.  Others  pass  to  the  hip-joint  and  the  deep  muscles 
around  it;  a  third  group  passes  downward  to  the  hamstring  muscles  and  anas- 
tomoses with  the  medial  and  lateral  circumflex  and  first  perforating;  a  fourth 
slender  branch,  the  sciatic  artery  [a.  comitans  n.  ischiadici],  accompanies  the 
sciatic  nerve  (fig.  490). 

Visceral  Branches  of  the  Hypogastric  Artery 

1.  THE  UMBILICAL  ARTERY 

The  umbilical  artery  in  the  fcetus  is  the  continuation  of  the  hypogastric. 
Passing  forward  along  the  side  of  the  pelvis,  it  runs  beneath  the  lateral  reflexion  of 
peritoneum  from  the  bladder,  where,  after  giving  off  one  or  more  vesical  branches, 
it  ceases  to  be  pervious  and  passes  on  to  the  side  and  upper  part  of  the  bladder. 
Thence  it  ascends  in  the  lateral  umbilical  fold,  as  a  fibrous  cord  [ligamentum 
umbilicale  laterale],  to  the  umbilicus,  where  it  is  joined  by  its  fellow  of  the 
opposite  side.     As  it  lies  lateral  to  the  bladder  it  is  crossed  by  the  ductus  deferens. 

The  branches  of  the  umbilical  artery  are: — (1)  Superior  vesical  arteries,  the 
lowest  of  which  is  sometimes  called  (2)  the  middle  vesical  artery  (fig.  489). 

The  superior  vesical  arteries  [aa.  vesicales  superiores]  ramify  over  the  upper  surface  of  the 
bladder,  anastomosing  with  the  artery  of  the  opposite  side  and  with  the  middle  and  inferior 
vesical  below.  They  give  off  the  following  branches: — (a)  The  urachal  branches  which  pass 
upward  along  the  urachus.  (h)  The  ureteric  branches  pass  to  the  lower  end  of  the  ureter, 
and  anastomose  with  the  other  ureteric  arteries,  (c)  The  middle  vesical  may  come  off  from 
one  of  the  superior  vesicals  or  from  the  umbilical.  It  is  distributed  to  the  sides  and  base  of  the 
bladder,  and  anastomoses  with  the  other  vesical  arteries. 

2.  THE  INFERIOR  VESICAL  ARTERY 

The  inferior  vesical  artery  [a.  vesicahs  inferior]  arises  from  the  anterior 
division  of  the  hypogastric,  frequently  in  common  with  the  middle  haemorrhoidal, 
and  passes  downward  and  medially  to  the  fundus  of  the  bladder,  where  it  breaks 
up  into  branches  which  ramify  over  the  lower  part  of  the  viscus.  It  gives  off 
branches  to  the  prostate,  which  supply  that  organ  and  anastomose  with  the 
arteries  of  the  opposite  side  by  means  of  descending  arteries  which  pass  through 


610  THE  BLOOD-VASCULAR  SYSTEM 

the  prostatic  plexus  of  veins,  but  outside  the  capsule  of  the  prostate,  and  with  the 
inferior  hsemorrhoidal  branches  of  the  internal  pudic.  At  times  one  of  these 
prostatic  branches  is  of  large  size,  and  supplies  certain  of  the  parts  normally 
supplied  by  the  int.  pudendal.  It  is  then  known  as  the  accessory  pudendal  and 
most  commonly  terminates  as  the  dorsal  artery  of  the  penis. 

The  inferior  vesical  usually  gives  off  the  deferential,  or  artery  of  the  ductus  deferens  [a. 
deferentialis].  This  vessel,  which  may  come  off  from  the  superior  vesical,  divides,  on  the  ductus 
deferens,  into  an  ascending  and  a  descending  branch.  The  ascending  branch  follows  the  ductus 
through  the  inguinal  canal  to  the  testis,  where  it  anastomoses  with  the  internal  spermatic  artery. 
The_  descending  branch  passes  downward  to  the  dilated  portion  of  the  ductus  and  vesiculse 
seminales. 

3.  THE  MIDDLE  HEMORRHOIDAL  ARTERY 

The  middle  hsemorrhoidal  artery  [a.  hsemorrhoidals  media],  variable  in  origin, 
perhaps  most  commonly  arises  from  the  anterior  division  of  the  hypogastric 
along  with  the  inferior  vesical.  It  runs  medially  to  the  side  of  the  middle  portion 
of  the  rectum,  dividing  into  branches  which  anastomose  above  with  the  superior 
hsemorrhoidal  derived  from  the  inferior  mesenteric,  and  below  with  the  inferior 
hsemorrhoidal  derived  from  branches  of  the  internal  pudendal.  Its  corre- 
sponding vein  terminates  in  the  inferior  mesenteric  vein.  In  the  female  it  also 
sends  branches  to  the  vagina. 

4.  THE  UTERINE  ARTERY 

The  uterine  artery  [a.  uterina],  arises  from  the  anterior  division  of  the  hypo- 
gastric close  to  or  in  conj  unction  with  the  middle  hsemorrhoidal  or  inferior  vesical. 
It  runs  downward  and  medially  through  the  pelvic  connective  tissue,  crossing  the 
ureter  about  12  mm.  (|  in.)  from  the  cervix  uteri.  It  then  turns  upward  and 
ascends  in  the  parametrium  between  the  layers  of  the  broad  ligament  at  the 
side  of  the  uterus  in  a  coiled  and  tortuous  manner,  and,  after  giving  off  a  number  of 
tortuous  branches  which  ramify  horizontally  over  the  front  and  back  of  the  uterus, 
supplying  its  substance,  anastomoses  with  the  uterine  branch  of  the  ovarian 
artery. 

In  addition  to  the  branches  to  the  uterus  the  branches  of  the  uterine  artery  are: — (1) 
Cervical. — This  branch  comes  off  from  the  uterine  as  the  latter  artery  crosses  the  ureter  to  turn 
upward  on  to  the  uterus.  It  is  directed  medially,  and  divides  into  three  or  four  branches  which 
pass  on  to  the  cervix  at  right  angles  to  it;  one  branch  anastomosing  with  its  fellow  of  the  opposite 
side  in  front  and  behind  the  neck,  forming  the  so-caUed  coronary  artery  of  the  cervix.  (2) 
Tubal  [ramus  tubarius]. — Tliis  courses  along  the  lower  surface  of  the  tuba  uterina  (FaUopian 
tube)  as  far  as  its  fimbriated  extremity,  and  may  also  send  a  brancli  to  the  ligamentum  teres. 
(3)  Ovarian  [ramus  ovarii]. — This  runs  along  the  attached  border  of  the  ovary,  sending  branches 
to  that  structure,  and  terminates  by  anastomosing  widely  with  the  ovarian  artery.  Usually 
the  vaginal  artery  also  arises  from  tlie  uterine.  (4)  The  vaginal  artery  [a.  vaginaUs]  corresponds 
to  the  inferior  vesical  artery  of  the  male,  and  may  arise  directly  from  the  hypogastric  artery, 
close  to  the  origin  of  the  uterine,  or  from  the  superior  vesical.  It  passes  medially,  behind  the 
ureter,  to  the  upper  part  of  the  vagina,  and  sends  numerous  branches  to  that  structure  and  also 
some  iio  the  posterior  part  of  the  fundus  of  the  bladder. 

The  branches  to  the  vagina  tend  to  anastomose  with  one  another  and  with  the  cervical 
branch  of  the  uterine,  to  form  a  more  or  less  perfect  vertical  stem  in  the  median  Une  of  the  vagina, 
both  back  and  front.  This  stem  is  sometimes  termed  the  azygos  artery  of  the  vagina.  Branches 
also  pass  to  the  vagina  from  the  middle  hsemorrhoidal  artery. 

5.  THE  INTERNAL  PUDENDAL  ARTERY 

The  internal  pudendal  (pudic)  artery  [a.  pudenda  interna]  (figs.  492,  493,  494) 
is  one  of  the  terminal  branches  of  the  anterior  division  of  the  hypogastric  artery 
(the  inferior  gluteal  being  the  other) .  It  arises  opposite  the  piriformis  muscle  and 
accompanies  the  inferior  gluteal  downward  to  the  lower  border  of  the  great 
sciatic  foramen.  It  leaves  the  pelvis  between  the  piriformis  and  coccygeus  and 
winds  over  the  ischial  spine  to  enter  the  ischio-rectal  fossa  through  the  small 
sciatic  foramen.  Running  forward  in  the  ischio-rectal  fossa  medial  to  the  lower 
part  of  the  obturator  internus  it  ends  by  dividing  into  the  perineal  artery  and  the 
artery  of  the  penis  (or  clitoris). 


INTERNAL  PUDENDAL  ARTERY 


611 


Relations. — Within  the  -pelvis,  the  artery  is  anterior  to  the  piriformis  muscle  and  the  sacral 
plexus  of  nerves,  and  lateral  to  the  inferior  gluteal  artery.  It  passes  between  the  piriformis 
and  coccygeus,  with  the  gluteal  artery  and  pudendal  nerve  medial  to  it,  and  the  nerve  to  the  ob- 
turator internus  lateral.  The  sciatic  and  posterior  femoral  cutaneous  (lesser  sciatic)  nerves 
are  still  more  lateral.  On,  the  ischial  spine  the  artery  retains  its  relations  to  the  pudendal  nerve 
(which  often  divides  in  this  situation  into  its  two  terminal  branches)  and  the  nerve  to  the  ob- 
turator internus.     It  is  accompanied  by  venae  comitantes  and  covered  by  the  gluteus  maximus 


muscle.  In  the  ischio-rectal  fossa  the  artery  is  placed  on  the  lateral  wall  about  3.5  cm.  (IJ  in.) 
above  the  tuberosity  of  the  ischium.  It  is  accompanied  in  a  canal  in  the  obtm-ator  fascia 
(Alcock's  canal)  by  the  dorsal  nerve  of  the  penis  and  the  perineal  nerve,  which  are  respectively 
above  and  below  the  artery. 

The  branches  of  the  internal  pudendal  artery  are: — (1)  Small  branches  to  the 
gluteal  region;  (2)  the  inferior  hsemorrhoidal  arteries;  and  the  terminal  branches 
(3)  perineal;  and  (4)  artery  to  the  penis  or  clitoris. 


612 


THE  BLOOD-VASCULAR  SYSTEM 
Fig.  492. — The  Internal  Pudendal  Artery.     (From  Kelly,  by  Brodel.) 


Dorsal  artery  of  clitoris 


Inferior  hasmorrhoidal  artery 

Internal  pudic  artery 

Sacro-spinous  ligament 

Fig.  493. — The   Perineal   and   Hemorrhoidal  Branches  of  the   Internal   Pudendal 

Arteries.     (From  Kelly,  by  Brodel.) 


INTERNAL  PUDENDAL  ARTERY 


613 


(1)  The  branches  of  the  gluteal  region  are:  (a)  twigs  to  the  gluteus  maximus;  (6)  branches 
accompanying  the  nerve  to  the  obturator  internus;  (c)  a  sacral  branch  which  pierces  the  sacro- 
tuberous  ligament,  and  anastomoses  with  the  inferior  gluteal  artery. 

(2)  The  inferior  hemorrhoidal  artery  (a.  haemorrhoidalis  inferior]  (figs,  493,  494)  arises  at 
the  posterior  part  of  the  ischio-rectal  fossa  and,  perforating  the  obturator  fascia,  at  once  breaks 
up  into  several  branches.  These,  rumiing  medially  toward  the  anus,  traverse  the  ischio-rectal 
fat  and  supply  the  fascia,  skin  and  the  levator  ani  and  external  sphincter  muscles.  The  in- 
ferior hEemorrhoidal  branches  anastomose  with  those  from  the  middle  and  superior  hemor- 
rhoidal, and  from  the  gluteal  and  perineal  arteries. 

(3)  The  perineal  artery  [a.  perinei]  (figs.  493,  494),  one  of  the  terminal  arieries  of  the  in- 
ternal pudendal,  arises  at  the  anterior  part  of  the  ischio-rectal  fossa.  It  pierces  the  base  of  the 
urogenital  diaphragm  (triangular  hgament)  anterior  or  posterior  to  the  superficial  transverse 
perineal  muscle,  and  enters  the  space  deep  to  CoUes's  fascia.  Here  it  runs  forward  between  the 
ischio-  and  bulbo-cavernosus  muscles  to  the  scrotum  or  labium  majus  and  divides  into  numer- 
ous terminal  branches.  Immediately  after  piercing  the  diaphragm,  the  perineal  artery  gives 
off  a  constant  transverse  perineal  branch  which  runs  toward  the  median  Une  along  the  super- 
ficial transverse  perineal  muscle.  The  terminal  branches  of  the  perineal  are  the  posterior 
scrotal  or  labial  arteries  [aa.  scrotales,  or  labiales  posteriores]  which  ramify  on  the  scrotum  or 
labia  majora  (according  to  sex)  and  anastomose  with  external  pudendal  arteries. 

(4)  The  artery  of  the  penis,  or  clitoris  [a.  penis  or  clitoridis]  (figs.  493,  494)  pierces  the  free 
border  of  the  urogenital  diaphragm  and  runs  forward  between  the  layers  of  the  diaphragm 
with  the  dorsal  nerve  of  the  penis  along  the  inferior  ramus  of  the  pubis.  It  traverses  the  fibres 
of  the  deep  transverse  perineal  muscle  and  of  the  sphincter  of  the  membranous  urethra  and 


Fig.  494. — The  Arteries  op  the  Male  PERiN.ffi;uM. 

On  the  right  side  CoUes's  fascia  has  been  turned  back  to  show  the  perineal  artery.  On  the 
left  side  the  perineal  vessels  have  been  cut  away  with  the  inferior  layer  of  the  urogenital  dia- 
phragm to  show  the  artery  of  the  penis. 


Posterior  sacral  artery 


Bulbo-cavernosus 


CoUes's  fascia,  turned  back 


Dorsal  artery  of  penis 
Deep  artery  of  penis 


Ischio-cavernosus 

Transverse  perineal  vessels 

Cut  edge  of  urogenital 

diaphragm 

Perineal  nerve  giving  oB 

transverse  branch 

Internal  pudendal  artery 

Inferior  hemorrhoidal 
artery 


Artery  of  bulb 
Bulbo-urethral  gland 
Artery  of  the  penis 

Sacro-tuberous  ligament 
—  Levator  ani 

External  sphincter  ani 

Gluteus  maximus 


ends  by  dividing  into  deep  and  dorsal  arteries  of  the  penis,  or  clitoris,  according  to  sex. 

The  branches  of  the  artery  of  the  penis  (or  clitoris)  are:  (a)  The  artery  to  the  bulb;  (b) 
the  uretliral  artery;  and  (c)  the  terminal,  deep  artery  of  the  penis  or  clitoris. 

(a)  The  artery  of  the  bulb  [a.  bullii  urethras  or  vestibuli  vaginas]  takes  a  medial  direction 
through  the  fibres  of  the  m.  transversus  perinei  profundus.  It  then  pierces  the  inferior  fascia 
of  the  urogenital  diaphragm  to  reach  the  bulb,  the  erectile  tissue  of  which  it  supplies,  in  either 
sex.  This  vessel  also  suppUes  branches  to  the  bulbo-urethral  gland  (Cowperi)  or  the  gland  of 
the  vestibule  (Bartholini). 

The  situation  of  the  artery  to  the  bulb  should  be  remembered  in  performing  the  operation 
of  lateral  lithotomy,  particularly  as  it  may  arise  far  back.  When  the  artery  arises,  as  it  occa- 
sionally does,  from  the  accessory  pudendal  it  pierces  the  urogenital  diaphragm  further  forward 
and  is  out  of  danger  in  the  ordinary  low  operation. 

(6)  The  urethral  artery  [a.  urethralisj.is  a  small  branch  which  passes  into  the  corpus  spongi- 
osum and  anastomoses  with  branches  from  the  artery  of  the  bulb. 


614  THE  BLOOD-VASCULAR  SYSTEM 

(c)  The  deep  artery  of  the  penis  or  clitoris  [a.  profunda  penis  or  clitoridis],  larger  in  the  male 
sex,  pierces  the  inferior  layer  of  the  urogenital  diaphragm  near  the  inferior  ramus  of  the  pubis. 
It  enters  the  crus  of  the  penis  (fig.  494)  or  clitoris,  and  is  distributed  in  the  corpus  cavernosum 
urethrae. 

(d)  The  dorsal  artery  of  the  penis  or  clitoris  [a.  dorsalis  penis  or  clitoridis]  (figs.  492,  494), 
perforates  the  inferior  fascia  of  the  urogenital  diaphragm  near  its  apex.  The  dorsal  nerve  is 
lateral  to  the  artery  and  both  join  the  dorsal  vein  (which  hes  between  the  arteries  of  either  side) 
on  the  dorsum  of  the  penis  or  clitoris.  The  artei-y  is  much  larger  in  the  male  than  the  female; 
in  either  sex  it  supphes  the  glans,  corona,  and  prepuce  and  anastomoses  with  the  external 
pudendal  artery. 

THE  EXTERNAL  ILIAC  ARTERY 

The  external  iliac  artery  [a.  iliaca  externa] — the  larger  in  the  adult  of  the  two 
vessels  into  which  the  common  iliac  divides  opposite  the  lumbo-sacral  articulation 
— extends  along  the  superior  aperture  of  the  pelvis,  lying  upon  the  medial  border 
of  the  psoas  muscle,  to  the  lower  margin  of  the  inguinal  ligament,  where,  midway 
between  the  anterior  superior  spine  of  the  ilium  and  the  symphysis  pubis,  it  passes 
into  the  thigh,  and  takes  the  name  of  the  femoral. 

It  measures  8.5  to  10  cm.  (3|  to  4  in.)  in  length.  The  course  of  the  vessel  is 
indicated  by  a  line  drawn  from  2.5  cm.  (1  in.)  below  and  a  little  to  the  left  of  the 
umbilicus  to  a  spot  midway  between  the  symphysis  pubis  and  the  anterior 
superior  spine  of  the  ilium.  If  this  line  is  divided  into  thirds,  the  lower  two-thirds 
indicate  the  situation  of  the  external  iliac,  the  upper  third  the  common  iliac.  The 
external  iliac  vein,  the  continuation  upward  of  the  femoral  vein  from  the  thigh, 
lies  to  the  medial  side  of  the  artery,  but  on  a  slightly  lower  plane,  and,  just  before 
its  termination,  gets  a  little  behind  the  artery  on  the  right  side. 

Relations. — In  front,  the  artery  together  with  the  vein  is  covered  by  the  parietal  per- 
itoneum descending  from  the  abdomen  into  the  pelvis,  and  by  a  layer  of  condensed  subperitoneal 
tissue  (Abernethy's  fascia).  It  is  crossed  by  the  termination  of  the  ileum  on  the  right  side,  and 
by  the  sigmoid  colon  on  the  left.  The  external  spermatic  (genital)  branch  of  the  genito- 
femoral (genito-crural)  nerve  runs  obhquely  over  its  lower  third,  and  just  before  its  termination 
it  is  crossed  transversely  by  the  deep  circumflex  iliac  vein.  The  internal  spermatic  or  ovarian 
vessels  lie  for  a  short  distance  on  the  lower  part  of  the  artery,  and  the  ductus  deferens  in  the  male 
curves  over  it  to  descend  to  the  pelvis.  It  is  sometimes  crossed  at  its  origin  by  the  ureter.  The 
external  iliac  lymphatic  nodes  lie  along  the  course  of  the  artery.  The  commencement  of  its 
inferior  epigastric  branch  is  also  in  front. 

Behind. — At  first  the  artery  lies  partly  upon  its  own  vein;  lower  down  upon  the  medial 
border  of  the  psoas;  and  just  before  it  passes  through  the  lacuna  vasorum,  beneath  Poupart's 
ligament,  upon  the  tendon  of  the  psoas.  The  continuation  of  the  ihac  into  the  endo-pelvic  fascia 
is  also  below  it. 

To  its  medial  side  is  the  external  iliac  vein,  the  peritoneum,  and  the  ductus  deferens  in  the 
male,  or  the  ovarian  vessels  in  the  female. 

To  its  lateral  side  is  the  psoas  muscle  and  the  iliac  fascia. 

The  collateral  circulation  is  carried  on  (fig.  497)  when  the  external  ihac  is  tied,  by  the  anas- 
tomosis of  the  iUo-lumbar  and  lumbar  arteries  with  the  circumflex  ihac;  the  internal  mammary 
with  the  inferior  epigastric;  the  obturator  with  the  medial  circumflex;  the  inferior  gluteal  with 
the  medial  circumflex  and  superior  perforating;  the  gluteal  with  the  lateral  circumflex;  the 
arteria  comitans  nervi  ischiadici  from  the  inferior  gluteal,  with  the  perforating  branches  of  the 
profunda;  the  external  pudenal  with  the  internal  pudendal;  the  pubic  branch  of  the  obturator 
with  the  pubic  branch  of  the  epigastric. 

The  branches  of  the  external  iliac  artery  are: — (1)  The  inferior  epigastric;  (2) 
the  deep  circumflex  iliac;  and  (3)  several  small  and  insignificant  twigs  to  the 
neighbouring  psoas  muscles  and  lymphatic  gland. 

(1)  The  Inferior  Epigastric  Artery 

The  inferior  or  deep  epigastric  artery  [a.  epigastrica  inferior]  (fig.  495)  usually 
comes  off  from  the  external  iliac  just  above  the  inguinal  (Poupart's)  ligament. 
Immediately  after  its  origin,  the  ductus  deferens  in  the  male,  and  the  round 
ligament  in  the  female,  loop  around  it  on  their  way  to  the  pelvis.  It  here  lies 
medial  to  the  abdominal  inguinal  (internal  abdominal)  ring,  behind  the  inguinal 
canal,  and  a  little  above  and  lateral  tc  the  femoral  ring.  Thence  it  ascends  with 
a  slightly  medial  direction  passing  above  and  to  the  lateral  side  of  the  subcu- 
taneous inguinal  (external  abdominal)  ring,  lying  between  the  fascia  transversalis 
and  the  peritoneum.     Having  pierced  the  fascia  transversalis  at  this  point,  it 


THE  INFERIOR  EPIGASTRIC  ARTERY 


615 


passes  in  front  of  the  linea  semicircularis  (Douglas'  fold)  and  turns  upward  be- 
tween the  rectus  and  its  sheath.  Higher,  it  enters  the  substance  of  the  muscle, 
and  anastomoses  with  the  superior  epigastric,  descending  in  the  rectus  from  the 
internal  mammary. 

The  situation  of  the  artery  between  the  two  inguinal  rings  should  be  borne  in 
mind  in  the  operation  for  strangulated  inguinal  hernia,  and  its  near  proximity  to 
the  upper  and  lateral  side  of  the  femoral  ring  should  not  be  forgotten  in  the 
operation  for  femoral  hernia.  The  arter3r  is  accompanied  by  two  veins  which 
end  in  a  single  trunk  before  opening  into  the  external  iliac  vein. 

The  branches  of  the  inferior  epigastric  are  small  and  include: — (a)  The  external  spermatic 
[a.  spermatica  externa],  which  runs  with  the  ductus  through  the  inguinal  canal,  supplies  the 
cremaster  muscle,  and  anastomoses  with  the  internal  spermatic,  external  pudendal,  and  perineal 
arteries.     In  the  female  a  corresponding  artery  [a.  hg.  teretis  uteri]  accompanies  the  round  liga- 

FiG.  495. — The  Inferior  (Deep)  Epigastric  Artery.     (From  Kelly,  by  Brodel). 


l^ectus  A 


"  Ovarian  vessels 

External  iliac 

artery 

^External  iliac 


ment  of  the  uterus  through  the  inguinal  canal  and  anastomoses  in  a  similar  manner.  (6)  The 
pubic  [ramus  pubicus],  which  passes  below,  or  sometimes  above,  the  femoral  ring  to  the  back 
of  the  pubis,  where  it  anastomoses  with  the  pubic  branch  of  the  obturator.  This  branch, 
though  usually  small,  is  occasionally  considerably  enlarged,  when  its  exact  course  becomes  of 
great  interest  to  the  surgeon.  Thus  it  may  descend  immediatelj'  medial  to  the  vein,  and  there- 
fore lateral  to  the  femoral  ring,  or  it  may  course  medially  in  front  of  the  femoral  ring  and  turn 
downward  either  behind  the  os  pubis  or  immediately  behind  the  free  edge  of  the  lacunar  (Gim- 
bernat's)  ligament,  in  which  situation  it  would  be  exposed  to  injury  in  the  operation  for  the  re- 
lief of  a  strangulated  femoral  hernia.  In  such  cases  the  obturator  may  lose  its  connection  with 
the  hypogastric  and  actually  arise  from  the  inferior  epigastric.  Very  rarely  the  inferior  epi- 
gastric loses  its  connection  with  the  external  iUac  and  arises  from  the  obturator.  This  abnormal 
origin  of  the  obturator  is  said  to  occur  once  in  every  three  subjects  and  a  half;  but  the  abnormal 


616  THE  BLOOD-VASCULAR  SYSTEM 

artery  only  courses  around  the  medial  side  of  the  ring — in  which  situation  it  is  liable  to  injury 
in  the  operation  for  femoral  hernia — in  exceptional  cases.  According  to  Langton  (Holden's 
'Anatomy'),  the  chances  are  about  seventy  to  one  against  this  occurring.  But  even  when  it 
takes  the  abnormal  course,  it  lies  3  mm.  or  so  from  the  margin  of  the  ring,  and  will  probably 
escape  injury  in  the  division  of  the  stricture  if  several  short  notches  are  made  in  place  of  a  single 
and  longer  incision. 

(2)  The  Deep  Circumflex  Iliac  Artery 

The  deep  circumflex  iliac  artery  [a.  circumflexa  ilium  profunda],  arises  from 
the  lateral  side  of  the  external  iliac  artery  either  opposite  the  epigastric  or  a  little 
below  the  origin  of  that  vessel.  It  courses  laterally  just  above  the  lower  margin 
of  Poupart's  ligament,  lying  between  the  fascia  transversahs  and  the  peritoneum, 
or  at  times  in  a  fibrous  canal  formed  by  the  union  of  the  fascia  transversahs  with 
the  iliac  fascia.  Near  the  anterior  superior  spine  of  the  ihum,  it  perforates  the 
transversus,  and  then  courses  between  that  muscle  and  the  internal  oblique, 
along  and  a  little  above  the  crest  of  the  ilium.  It  finally  gives  off  an  ascending 
branch,  which  anastomoses  with  the  lumbar  and  lower  intercostal  arteries,,  and 
runs  backward  to  anastomose  with  the  ilio-lumbar  artery.  It  is  accompanied  by 
two  veins.  These  unite  into  one  trunk,  which  then  crosses  the  external  iliac  artery 
to  join  the  external  iliac  vein. 

The  branches  of  the  deep  circumflex  iliac  artery  are  as  follows: — (a)  Muscular  branches 
which  supply  the  psoas,  iliacus,  sartorius,  tensor  fasciae  latse,  and  the  oblique  and  transverse 
muscles  of  the  abdomen.  One  of  these  branches,  larger  than  the  rest,  usually  arises  about 
2.5  cm.  (1  in.)  behind  the  anterior  superior  spine  of  the  ilium  and  ascends  perpendicularly  be- 
tween the  transversus  muscle  and  the  internal  oblique.  It  has  received  no  name  but  is  impor- 
tant to  the  surgeon,  as  it  indicates  the  intermuscular  plane  between  the  two  muscles.  (6) 
Cutaneous  branches,  which  supply  the  skin  over  the  course  of  the  vessel,  and  anastomose 
with  the  superficial  circumflex  ihac,  the  superior  gluteal,  and  the  ascending  branch  of  the  lateral 
circumflex. 

THE  FEMORAL  ARTERY 

The  femoral  artery  (fig.  496)  is  the  continuation  of  the  external  iliac,  and 
extends  from  the  lower  border  of  Poupart's  ligament,  down  the  anterior  and 
medial  aspect  of  the  thigh,  to  the  tendinous  opening  in  the  adductor  magnus, 
through  which  it  passes  into  the  popliteal  space,  and  is  then  known  as  the  pop- 
liteal. The  femoral  artery  is  at  first  quite  superficial,  being  merely  covered  by  the 
skin,  and  superficial  and  deep  fascia;  but,  after  thus  passing  abo.ut  13  cm.  (5  in.) 
downward  through  the  space  known  as  the  femoral  trigone  (Scarpa's  triangle), 
it  sinks  at  the  apex  of  that  triangle  beneath  the  sartorius  muscle,  and  thence 
to  its  termination  continues  beneath  the  sartorius,  coursing  deeply  between  the 
vastus  medialis  and  adductor  muscles  in  the  space  known  as  the  adductor 
(Hunter's)  canal.  It  at  first  rests  upon  the  brim  of  the  pelvis  and  head  of  the 
thigh  bone,  from  which  it  is  merely  separated  by  the  capsule  of  the  hip-joint  and 
the  tendon  of  the  psoas.  Here  it  can  be  readily  compressed.  Owing  to  the 
obliquity  of  the  neck  of  the  femin-  and  the  direct  course  taken  by  the  artery,  it 
lies  lower  down  on  muscles  only,  at  some  little  distance  from  the  bone.  At  its 
termination,  in  consequence  of  the  shaft  of  the  femur  inclining  toward  the  middle 
line  of  the  body,  the  artery  lies  close  to  the  bone,  but  to  the  mechal  side.  The 
course  of  the  vessel  when  the  thigh  is  slightly  flexed  and  abducted — the  position 
in  which  the  Hmb  is  placed  when  the  vessel  is  hgatured — is  indicated  by  a  line 
drawn  from  a  spot  midway  between  the  anterior  superior  spine  of  the  ilium  and 
the  symphysis  pubis  to  the  adductor  tubercle.  When  the  thigh  is  in  the  extended 
position  and  parallel  to  its  fellow,  the  course  of  the  artery  will  correspond  to  a  hne 
drawn  from  the  spot  above  mentioned  to  the  medial  border  of  the  patella. 

About  4-5  cm.  (li-2  in.)  below  the  inguinal  ligament  the  femoral  artery  gives 
off  a  large  branch  called  the  profunda  femoris.  The  portion  of  the  artery  proximal 
to  the  origin  of  the  profunda  is  sometimes  called  the  common  femoral,  and  the 
continuation  of  the  vessel  the  superficial  femoral. 

The  superficial  femoral  varies  in  length  according  to  the  distance  that  the  profunda  is  given 
off  from  the  common  femoral  below  Poupart's  ligament.  As  a  rule,  it  measures  9  cm.  (Ss  in.), 
the  common  4  cm.  (IJ  in.).  But  the  profunda  may  come  off  5  cm.  (2  in.)  or  more  below  Pou- 
part's ligament,  in  which  case  the  superficial  femoral  will  be  shorter  to  this  extent;  or  it  may 


THE  FEMORAL  ARTERY 


617 


come  off  less  than  3.7  cm.  (IJ  in.)  below  Poupart's  Ugament,  or  even  from  the  external  ibac  above 
Poupart's  ligament,  when  the  superficial  will  be  longer  than  normal.  The  practical  point  to 
remember  is  that  it  is  more  usual  to  meet  with  a  short  than  with  a  long  common  femoral  and 
that  if  the  superficial  femoral  is  tied  at  the  apex  of  the  femoral  trigone— i.  e.,  the  spot  where 
the  sartorius  comes  into  contact  with  the  adductor  longus— there  is  nearly  always  a  sufficient 

Fig.  496.— The  Femoral  Artert.     (After  Toldt,   "Atlas  of  Human   Anatomy,"  Rebman 
London  and  New  York.) 


Superficial  epigastric  artery- 
Tensor  of  fascia  lata 
Femoral  nerve. 
Femoral  artery. 
Femoral  vein 
Sartonus. 

Deep  femoral  artery- 

(Ascending  , 
branch 
Descending, 
branch 
Fascia  lata 

First  perforating  artery- 
Deep  femoral  artery 
Vastus  medialis 


Femoral  i 
Saphenous  nerve-  t  B.i 

Femoral  artery  " 

Rectus  femons 


Articular  rate  of  the  knee- 


External  spermatic  artery 

—  Medial  circumflex  artery 
Superficial  branch 

—  Adductor  brevis 

Adductor  longus 

Gracilis 

Ventral  wall  of  adductor  canal 


Muscular  branch 

Saphenous  nerve 

Sartorius 

Genu  suprema  artery 


-  Superior  medial  articular  artery 
Articular  branch 


Saphenous  branch 


length  of  that  vessel  above  the  ligature  to  ensm-e  a  firm  internal  clot  and  consequently,  as  far 
as  this  point  is  concerned,  a  successful  result. 

The  relations  of  the  femoral  artery  in  the  femoral  trigone.— In  front,  the  femoral  artery 
(fig.  496)  is  covered  by  the  skin,  the  superficial  fascia,  the  iUac  portion  of  the  fascia  lata,  and  the 
lumbo-inguinal  (crural)  branch  of  the  genito-femoral  nerve.  The  superficial  cu-cumflex  ihao 
vein,  and  sometimes  the  superficial  epigastric  vem,  descend  over  the  artery  from  the  medial  to 


618  THE  BLOOD-VASCULAR  SYSTEM 

the  lateral  side.  Just  above  the  sartorius,  the  artery  is  crossed  by  the  most  medial  of  the  anterior 
cutaneous  branches  of  the  femoral  nerve.  The  fascia  transversahs,  which  is  continued  down- 
ward into  the  thigh  beneath  the  inguinal  ligament,  is  also  in  anterior  relation,  but  it  soons  be- 
comes indistinguishable  from  the  sheath  of  the  vessel. 

Behind,  the  artery  rests  from  above  upon  the  tendon  of  the  psoas  muscle,  which  separates 
it  from  the  brim  of  the  pelvis  and  capsule  of  the  hip-joint;  the  pectineus,  and  adductor  longus. 
The  artery  is  partially  separated  from  the  pectineus  by  the  femoral  vein  and  the  profunda  vein 
and  artery,  and  from  the  adductor  longus  by  the  femoral  vein  which  is  almost  directly  behind 
the  artery  near  the  apex  of  the  femoral  trigone.  The  small  nerve  to  the  pectineus  crosses 
behind  the  artery  to  reach  its  medial  side. 

A  similar  prolongation  to  that  derived  from  the  fascia  transversaUs  in  front,  descends  be- 
hind the  vessel  from  the  iliac  fascia;  but  this,  lil^e  the  anterior  prolongation  or  fascia,  soon  blends 
with  the  sheath  of  the  vessels. 

To  the  medial  side  is  the  femoral  vein.  This  is  separated  above  from  the  artery,  where 
the  two  vessels  he  in  the  femoral  sheath,  by  a  thin  fascial  septum.  Below,  the  vein  is  some- 
what behind  the  artery. 

To  the  lateral  side. — Above,  the  common  stem  of  the  femoral  (anterior  crural)  nerve  ia 
about  1  cm.  (J  in.)  lateral  to  the  artery.  When  the  femoral  nerve  gives  off  its  branches,  the 
saphenous  nerve  and  the  nerve  to  the  vastus  mediaUs  accompany  the  artery  on  the  lateral 
side. 

The  adductor  canal  is  the  somewhat  triangularly  shaped  space  bounded  by  the  vastus 
medialis  on  the  lateral  side,  the  adductors  longus  and  magnus  posteriorly,  and  by  an  aponeurosis 
thrown  across  from  the  adductors  to  the  vastus  medially  and  in  front.  Below,  the  canal 
terminates  at  the  tendinous  opening  in  the  adductor  magnus;  above,  its  Umit  is  less  well  defined, 
as  here  the  aponeurosis  between  the  muscles  becomes  less  tendinous,  and  gradually  fades  away 
into  the  perimuscular  fascia.  The  transverse  direction  of  the  fibres  of  the  aponeurotic  covering 
at  the  lower  two-thirds  of  the  canal  is  characteristic,  and  serves  as  a  raUying-point  in  tying  the 
artery  in  this  part  of  its  course.  Lying  superficial  to  the  aponeurosis  is  the  sartorius  muscle. 
The  femoral  artery,  in  the  adductor  (Hunter's)  canal,  has  the  following  relations  :■ — 

In  front,  in  addition  to  the  skin,  superficial  and  deep  fascia,  are  the  sartorius  muscle  and  the 
aponeurotic  fibres  of  the  canal.  The  saphenous  nerve  crosses  in  front  of  the  artery  from  the 
lateral  to  the  medial  side,  lying  in  the  wall  of  the  canal. 

Behind,  the  artery  is  in  contact  with  the  adductor  longus,  and  just  above  the  opening  in 
the  adductor  magnus,  usually  with  the  latter  muscle. 

The  femoral  vein  lies  behind  the  artery,  but  gets  a  httle  lateral  to  it  at  the  lower  part  of 
the  canal.  It  is  here  very  firmly  and  closely  attached  to  the  artery,  embracing  it  as  it  were  on 
its  posterior  and  lateral  aspect.  Hence  it  is  very  hable  to  be  punctured  on  ligaturing  the  artery 
in  this  part  of  its  course.  Such  an  accident  is  best  avoided  by  opening  the  sheath  of  the  vessels 
well  to  the  medial  side  of  the  front  of  the  artery,  and  by  keeping  the  point  of  the  aneurysm  needle 
closely  applied  to  the  vessel  in  passing  it  between  the  vein  and  the  artery.  There  are  some- 
times two  veins,  which  then  more  or  less  surround  the  artery. 

To  the  lateral  side  are  the  vastus  mediaUs,  the  nerve  to  the  vastus  medialis,  and  at  the  lower 
part  of  the  canal,  the  femoral  vein. 

Branches  of  the  Femoral  Artery 

The  branches  of  the  femoral  artery  are: — 

(1)  The  superficial  epigastric;  (2)  the  superficial  circumflex  iUac;  (3)  the 
external  pudendal;  (4)  the  inguinal;  (5)  the  profunda;  (6)  muscular  branches; 
and  (7)  the  suprema  genu  (anastomotica  magna). 

(1)  the  superficial  epigastric  artery  [a.  epigastrica  superficialis],  comes_  off 
from  the  femoral  about  1.2  cm.  (|  in.)  below  the  inguinal  ligament.  At  its  origin 
it  is  beneath  the  fascia  lata,  but  almost  at  once  passes  through  this  fascia,  or  else 
through  the  fossa  ovalis,  and  courses  in  an  upward  and  slightly  medial  direction 
in  front  of  the  external  oblique  muscle  almost  as  far  as  the  umbilicus. 

It  ends  in  numerous  small  twigs,  which  anastomose  with  the  cutaneous  branches  from  the 
inferior  epigastric  and  internal  mammary.  In  its  course  it  gives  off  small  branches  to  the  in- 
guinal glands  and  to  the  sldn  and  superficial  f  ascifs.  Running  with  it  is  the  superficial  epigastric 
irein,  which  ends  in  the  great  saphenous  just  before  the  latter  passes  through  the  fossa  ovalis 
(saphenous  opening). 

(2)  The  superficial  circumflex  iliac  artery  [a.  circumflexa  ilium  superficialis], 
(fig.  496),  usually  smaller  than  the  superficial  epigastric,  arises  either  in  common 
with  that  vessel,  or  else  as  a  separate  branch  from  the  femoral.  It  passes  laterally 
over  the  ihacus,  and,  soon  perforating  the  fascia  lata  a  Httle  to  the  lateral  side  of 
the  fossa  ovalis,  runs  more  or  less  parallel  to  the  inguinal  ligament  about  as  far 
as  the  crest  of  the  ihum,  where  it  ends  in  branches  which  anastomose  with  the 
deep  circumflex  iliac  artery. 

In  its  course  it  gives  off  branches  to  the  iliacus  and  sartorius  muscles,  to  the  inguinal  glands, 
and  to  the  fascia  and  skin.  Its  companion  vein  ends  in  the  great  saphenous  vein  just  before  the 
latter  passes  through  the  fossa  ovaUs  (saphenous  opening). 


BRANCHES  OF  THE  FEMORAL  ARTERY 


619 


(3)  the  external  pudendal  arteries  [aa.  pudendae  externse],   arise  from  the 
medial  side  of  the  femoral.     Some  of  them  pass  either  through  the  fascia  lata,  or 

Fig.  497. — To  show  the  Anastomoses  of  the  Arteries  of  the  Lower  Extremity. 
(After  Smith  and  Walsham.) 


Inferior  epigastric  artery 

Ilio-lumbar  artery 

Deep  circumflex  iliac  artery 

Superior  gluteal  artery 

Common  femoral  artery 

Profunda  artery 

Lateral  circumflex  artery 

Crucial  anastomosis  ' 


Popliteal  artery 


Superior  lateral  articular 


Anterior  tibial  artery 


Inferior  lateral  articular  - 

Fibular  collateral  ligament  ^ U^" 

Tibial  recurrent - 


Peroneal  artery  - 


Lateral  anterior  malleolar  artery  . 

Perforating  peroneal  artery  - 

Posterior  peroneal  artery - 

Lateral  plantar  artery 


Abdominal  aorta 

Common  iliac  artery 
Middle  sacral  artery 

Hypogastric  artery 
External  iliac  artery 
Obturator  artery 
Inferior  gluteal  artery 
Internal  pudendal  artery 
Medial  circumflex  artery 

Superficial  femoral  artery 


Perforating  branches  of  profunda 


Genu  suprema 

Terminal  branch  of  profunda  anasto- 
mosing with  popliteal 


Superior  medial  Eirticular 


Tibial  collateral  ligament 
Inferior  medial  articular 
Posterior  tibial  artery 


Anterior  msdial  malleolar  artery 


lateral  tarsal  artery 
Dorsalis  pedis  artery 
Arcuate  artery 


through  the  fascia  covering  the  fossa  ovalis  (saphenous  opening)  and  cross  the 
spermatic  cord  in  the  malCj  or  round  ligament  in  the  female,  to  reach  and  supply 
the  integument  above  the  pubes.     One  branch  descends  along  the  penis  lateral 


620  THE  BLOOD-VASCULAR  SYSTEM 

to  the  dorsal  artery,  with  which,  and  with  the  corresponding  artery  of  the  opposite 
side,  it  anastomoses  at  the  corona.  In  the  female,  this  branch  terminates  in  the 
preputium  clitoridis,  anastomosing  with  the  dorsal  artery  of  the  clitoris. 

Other  branches  run  medially  beneath  the  deep  fascia,  across  the  pectineus  and  adductor 
longus  muscles,  and,  perforating  the  fascia  close  to  the  ramus  of  the  pubis,  supply  the  skin  of  the 
scrotum  or  the  labium  majus,  in  the  female  [aa.  scrotales  or  labiales  anteriores]  anastomosing 
with  the  posterior  scrotal  or  labial  branches  of  the  perineal  artery.  The  external  pudendal 
supplies  small  twigs  to  the  pectineus  and  adductor  muscles.  Its  companion  veins  terminate  as  a 
single  trunk  in  the  great  saphenous. 

(4)  The  inguinal  branches  [rami  inguinales],  a  series  of  five  or  six  small 
branches  arise  a  short  distance  below  the  inguinal  Hgament.  They  supply  the 
subinguinal  lymph-nodes,  and  the  skin  and  muscles  in  this  region. 

(5)  The  profunda  artery  [a.  profunda  femoris]  (figs.  496,  497),  is  the  chief 
nutrient  vessel  of  the  thigh.  It  is  usually  given  off  from  the  back  and  lateral 
part  of  the  common  femoral,  about  4  cm.  (1|  in.)  below  the  inguinal  fPoupart's) 
ligament.  At  first  it  is  a  little  lateral  to  the  femoral,  but  as  it  runs  downward  and 
backward  it  gets  behind  that  artery  and  closer  to  the  bone.  On  reaching  the  upper 
border  of  the  adductor  longus  muscle,  it  leaves  the  femoral,  and,  passing  beneath 
the  muscle,  pierces  the  adductor  magnus.  Finally,  much  reduced  in  size,  it  ends 
in  the  hamstraing  muscles,  anastomosing  with  the  third  perforating  and  muscular 
and  articular  branches  of  the  popliteal. 

Jlelations. — Behind,  the  artery  Hes  successively  upon  the  iKacus,  the  pectineus,  the  adduc- 
tor brevis,  and  adductor  magnus  muscles.  In  front,  at  first  it  is  superficial,  being  merely  covered 
by  the  skin,  superficial  and  deep  fascise,  and  branches  of  the  femoral  (anterior  crural)  nerve;  but 
as  it  sinks  behind  the  femoral  artery,  it  has  in  front  of  it  both  the  femoral  and  the  profunda  veins 
and  lower  down  the  adductor  longus  muscle.  Laterally  is  the  femur  at  the  angle  of  union  of  the 
adductors  longus  and  brevis.     Medially  is  the  pectineus  at  the  upper  part  of  its  course. 

Branches  of  the  profunda. — The  profunda  gives  off  the  following  branches: — 
(a)  The  lateral  circumflex;  (h)  the  medial  circumflex;  and  (c)  the  three  per- 
forating. The  termination  of  the  artery  is  sometimes  called  the  fourth  perforating 
branch. 

(a)  The  lateral-  circumflex  [a  circumflexa  femoris  laterahs]  a  short  trunk,  but  the  largest  in 
diameter  of  the  branches  of  the  artery,  arises  from  the  lateral  side  of  the  profunda  as  it  hes  on  the 
iUacus  muscle,  about  2  cm.  (f  in.)  below  the  origin  of  that  vessel  from  the  femoral.  It  passes 
in  a  transversely  lateral  direction  over  the  iliacus,  under  the  sartorius  and  rectus,  and  between  the 
branches  of  the  femoral  (anterior  crural)  nerve.  In  this  course  it  gives  off  branches  to  the  rectus 
and  vastus  intermedins  (crureus),  and  then  divides  into  two  chief  sets  of  branches — ascending 
and  descending. 

The  ascending  branch  [ramus  ascendeus]  either  breaks  up  at  once  into  numerous  branches 
or  it  may  arise  as  several  vessels  some  of  which  are  apt  to  come  from  the  profunda  itself  or  even 
from  the  femoral.  These  run  upward  under  the  sartorius  and  tensor  facise  latse  or  laterally 
under  the  rectus  femoris.  The  highest  branches  reach  the  gluteus  medius  and  minimus  and 
anastomose  with  the  gluteal  and  deep  circumflex  ihac  arteries;  one  branch  runs  beneath  the 
rectus  femoris  to  the  hip-joint,  and  the  others  cross  the  vastus  intermedins  and  pierce  the  vastus 
lateralis  to  anastomose  with  the  first  perforating  and  the  medial  circumflex. 

The  descending  branches  [rami  descendentes]  run  directly  downward  along  with  the  nerve 
to  the  vastus  laterahs  muscle.  They  lie  beneath  the  rectus  muscle  and  on  the  vastus  intermedins 
(crureus)  or  vastus  laterahs,  some  of  them  being  j  ust  under  cover  of  the  anterior  edge  of  the  latter 
muscle.  They  are  distributed  to  the  vastus  lateralis,  vastus  intermedins,  and  rectus,  one  branch 
usually  running  along  the  anterior  border  of  the  vastus  laterahs  as  far  as  the  knee-joint,  where  it 
anastomoses  with  the  superior  lateral  articular  branch  of  the  pophteal  (fig.  499);  another,  enter- 
ing the  vastus  intermedius,  anastomoses  with  the  termination  of  the  profunda  and  with  the  genu 
suprema  (anastomotica  magna). 

(6)  The  medial  circumflex  artery  [a.  circumflexa  femoris  medialis]  comes  off  from  the  back 
and  medial  aspect  of  the  profunda  artery  on  about  the  same  level  as  the  lateral  circumflex; 
sometimes  as  a  common  trunk  with  that  vessel.  As  it  winds  around  the  medial  side  of  the  femur 
to  reach  the  region  of  the  trochanters,  it  lies  successively,  flrst,  between  the  psoas  and  pectineus, 
then  between  the  obturator  externus  and  adductor  brevis;  finaUy,  between  the  adductor  mag- 
nus and  quadratus  femoris,  where  it  anastomoses  with  the  lateral  circumflex,  with  the  inferior 
gluteal  (sciatic),  and  with  the  superior  perforating,  forming  the  so-called  crucial  anastomosis. 
While  still  in  the  femoral  trgione  it  gives  off  a  superficial  branch  [r.  superfioialis]  which  runs  in  a 
transversely  medial  direction  to  supply  the  pectineus  adductor  longus  and  brevis,  and  the 
gracilis.  The  remainder  of  the  artery  is  designated  as  the  deep  branch  [r.  profundus].  An 
acetabular  branch  (r.  acetabuli]  courses  upward  beneath  the  tendon  of  the  psoas,  and  enters  the 
hip-joint  beneath  the  transverse  ligament,  and,  together  with  the  articular  branch  of  the  obtura- 
tor, supplies  the  fatty  tissue  in  the  acetabulum,  and  sends  branches  to  the  synovial  membrane. 
The  medial  circumflex  veins  join  the  profunda  vein. 

(c)  The  perforating  arteries  of  the  profunda  are  so  called  because  they  perforate,  in  a  more  or 
less  regular  manner  from  above  downward,  certain  of  the  adductor  muscles.     They  form  a  series 


THE  POPLITEAL  ARTERY  621 

of  loops  by  anastomosing  with  one  another  (fig.  497),  and  with  the  superior  gluteal,  medial  cir- 
cumflex, and  inferior  gluteal  arteries  above,  and  with  the  muscular  and  articular  branches  of  the 
popliteal  below.  They  are  distributed  chiefly  to  the  hamstring  muscles,  but  send  twigs  along 
the  lateral  intermuscular  septum  to  supply  the  integuments  at  the  back  and  lateral  parts  of  the 
thigh.  Other  branches  perforate  the  lateral  intermuscular  septum  and  the  short  head  of  the 
biceps,  and,  entering  the  vastus  intermedins  (crureus)  and  vastus  laterahs,  anastomose  with  the 
descending' branch  of  the  lateral  circumflex.  All  the  perforating  arteries,  moreover,  contribute 
to  reinforce  the  artery  of  the  sciatic  nerve,  a  branch  of  the  inferior  gluteal  (sciatic)  artery.  They 
are  each  accompanied  by  two  veins  which  terminate  in  the  profunda. 

The  first  perforating  artery  [a.  perforans  prima]  is  given  off  from  the  profunda  as  that  vessel 
sinks  beneath  the  adductor  longus.  It  either  pierces  the  adductor  brevis,  or  else  runs  between 
the  pectineus  and  adductor  brevis,  and  then  passes  through  a  small  aponeurotic  opening  in  the 
adductor  magnus  close  to  the  medial  lip  of  the  hnea  aspera.  In  this  course  it  supphes  branches 
to  the  adductors,  and,  after  perforating  the  adductor  magnus,  is  distributed  to  the  lower  part  of 
the  gluteus  maximus  and  the  hamstring  muscles,  one  branch  commonly  running  upward  beneath 
the  gluteus  maximus  to  anastomose  with  the  lateral  circumflex,  medial  circumflex,  and  inferior 
gluteal  (sciatic)  arteries,  forming  the  crucial  anastomosis  at  the  junction  of  the  neck  of  the  femur 
with  the  great  trochanter  (flg.  497).  A  second  branch  descends  to  anastomose  with  the  ascend- 
ing branch  of  the  second  perforating. 

The  second  perforating  artery  [a.  perforans  secunda]  which  is  given  off  from  the  profunda  as 
it  lies  behind  the  adductor  longus,  pierces  the  adductor  brevis,  and  then  passes  through  a  second 
aponeurotic  opening  in  the  adductor  magnus  a  httle  below  that  for  the  first  perforating  artery, 
and  also  close  to  the  linea  aspera.  It  supplies  the  hamstring  muscles,  sends  a  branch  upward  to 
anastomose  with  the  descending  branch  of  the  first  perforating,  and  another  downward  to  anas- 
tomose in  hke  manner  with  the  ascending  branch  of  the  third  perforating. 

The  third  perforating  artery  [a.  perforans  tertia]  also  arises  from  the  profunda  as  it  hes  under 
the  adductor  longus,  usually  about  the  level  of  the  lower  border  of  the  adductor  brevis.  It  turns 
beneath  this  border,  and  then,  like  the  first  and  second  perforating,  passes  through  an  aponeu- 
rotic opening  in  the  adductor  magnus  close  to  the  linea  aspera.  It  also  supplies  the  hamstring 
muscles,  and  divides  into  two  branches,  which  anastomose  above  with  the  second  perforating, 
and  below  with  the  termination  of  the  profunda. 

Two  nutrient  arteries  to  the  femur  [aa.  nutritiae  femoris  superior  et  inferior]  arise  from  the 
perforating  arteries.  The  superior  generally  arises  from  the  first  perforating,  the  inferior 
usually  from  the  third. 

(6)  The  muscular  branches  [rami  musculares],  of  the  femoral  artery  supply 
the  sartorius,  the  rectus,  the  vastus  medialis,  the  vastus  intermedius  (crureus), 
and  the  adductor  muscles. 

(7)  The  genu  suprema  (or  anastomotica  magna)  arises  from  the  front  and 
medial  side  of  the  femoral  just  before  the  latter  perforates  the  adductor  magnus 
muscle,  and  almost  immediately  divides  into  branches,  (a)  saphenous,  {h)  muscu- 
lar, and  (c)  articular.  These  branches  may  sometimes  come  off  separately  from 
the  femoral. 

(a)  The  saphenous  branch  [a.  saphena]  pierces  the  aponeurotic  covering  of  the  adductor 
canal,  passes  between  the  sartorius  and  gracilis  muscles  along  with  the  saphenous  nerve,  and, 
perforating  the  deep  fascia,  suppUes  the  skin  of  the  upper  and  medial  side  of  the  leg  and  anasto- 
moses with  the  inferior  medial  articular  branch  of  the  popUteal  and  the  other  vessels  forming  the 
plexus  or  rete  at  the  medial  side  of  the  knee.  In  its  course  it  gives  twigs  to  the  lower  part  of  the 
sartorius  and  gracihs  muscles. 

(6)  The  muscular  branches  [rr.  musculares]  run  downward  in  front  of  the  adductor  magnus 
tendon,  burrowing  amongst  the  fibres  of  the  vastus  mediahs  as  far  as  the  medial  condyle.  They 
break  up  into  numerous  twigs  which  supply  the  lower  ends  of  the  vasti  muscles  and  adductor 
magnus.  One  branch  runs  laterally  across  the  lower  end  of  the  femur  to  end  in  the  vastus 
laterahs. 

(c)  The  articular  branches  [rr.  articulares]  come  off  from  the  saphenous  and  muscular 
branches  and  enter  the  arterial  rete  on  the  medial  and  lateral  sides  of  the  knee.  They  anas- 
tamose  with  the  medial  and  lateral  superior  articular  branches  of  the  popHteal  and  the  ante- 
rior tibial  recurrent  and,  Uke  other  vessels  of  the  rete,  supply  branches  to  the  joint. 

THE  POPLITEAL  ARTERY 

The  popliteal  artery  [a.  poplitea]  (fig.  498)  runs  through  the  pophteal  space  or 
ham.  It  is  a  continuation  of  the  femoral,  and  extends  from  the  aponeurotic 
opening  in  the  adductor  magnus  at  the  junction  of  the  middle  with  the  lower 
third  of  the  thigh  to  the  lower  border  of  the  popliteus  muscle,  where  it  terminates 
by  dividing  into  the  anterior  and  posterior  tibial  arteries.  This  division  is  on  a 
level  with  the  lower  border  of  the  tuberosity  of  the  tibia.  As  the  artery  passes 
through  the  opening  in  the  adductor  magnus,  it  is  accompanied  by  the  pophteal 
vein,  and  at  times  by  the  branch  of  the  obturator  nerve  to  the  knee-joint.  The 
vein  throughout  is  behind  the  artery,  at  first  lying  a  little  lateral  to  it,  but  as  the 
vessels  pass  through  the  popliteal  space  the  vein  crosses  obliquely  over  the  artery. 


622  THE  BLOOD-VASCULAR  SYSTEM 

and  at  the  termination  of  the  artery  lies  a  little  to  its  medial  side.  The  tibial 
(internal  popliteal)  nerve  is  superficial  to  both  artery  and  vein.  As  it  enters  the 
space  it  is  well  to  the  lateral  side  of  the  vessels,  but  as  it  descends  it  gradually 
approaches  them,  crosses  behind  them,  and  at  the  lower  part  of  the  space  lies  to 
their  medial  side.  The  artery  in  the  whole  of  its  course  is  deeply  placed  and 
covered  by  a  considerable  amount  of  fat  and  cellular  tissue. 

Relations  (fig.  498). — In  front,  the  artery  lies  successively  on  the  pophteal  surface  of  the 
femur  (from  which  it  is  separated  by  a  httle  fat  and  sometimes  one  or  two  small  glands);  on  the 
posterior  ligament  of  the  knee;  on  the  hinder  edge  of  the  articular  surface  of  the  head  of  the  tibia; 
and  on  the  pophteus  muscle.  From  the  latter  muscle  it  is  separated  by  the  expansion  from  the 
semi-membranosus  which  covers  the  muscle,  and  is  attached  to  the  popUteal  line  on  the  tibia. 

Behind,  the  artery  is  covered,  above  by  the  semi-membranosus;  in  the  centre  of  the  space  by 
the  skin,  superficial  and  deep  fascia;  and  below,  by  the  medial  head  of  the  gastrocnemius.     The 

Eopliteal  vein  is  behind  it  in  the  whole  of  its  course.  The  tibial  (internal  popliteal)  nerve  crosses 
ehind  it  obUquely,  from  the  lateral  to  the  medial  side,  about  the  centre  of  the  space.  As  the 
artery  divides  into  the  anterior  and  posterior  tibial,  it  is  crossed  by  the  aponeurotic  arch  of  the 
soleus  which  stretches  between  the  tibial  and  fibular  origins  of  that  muscle. 

To  the  medial  side  are  the  semi-membranosus  above,  and  the  medial  head  of  the  gastrocne- 
mius and  the  tibial  (internal  pophteal)  nerve  below. 

To  the  lateral  side  are  the  biceps  and  the  tibial  (internal  popliteal)  nerve  above,  and  the 
lateral  head  of  the  gastrocnemius  and  the  plantaris  below. 

Branches  of  the  Popliteal  Artery 

The  branches  of  the  popliteal  include  the  following: — (1)  the  sural;  (2)  the 
articular;  and  (3)  the  terminal. 

(1)  The  sural  arteries  [aa.  surales]  arise  irregularly  from  the  popliteal  and 
supply  the  muscles  of  the  calf,  sending  branches  upward  to  the  muscles  bound- 
ing the  upper  part  of  the  popliteal  space.  From  the  sural  arteries  also  arise 
the  superficial  sural  or  cutaneous  branches  which  pass  downward  between  the 
two  heads  of  the  gastrocnemius,  and,  perforating  the  deep  fascia,  supply  the  skin 
and  fascia  of  the  calf.  A  branch,  usually  of  moderate  size,  accompanies  the  small 
saphenous  vein,  and  is  sometimes  called  the  posterior  saphenous  artery. 

(2)  The  articular,  five  in  number,  are  divided  into  two  superior  (medial  and 
lateral),  two  inferior  (medial  and  lateral),  and  the  middle  or  azygos.  The 
superior  and  inferior  come  off  transversely  in  pairs  from  either  side  of  the  popliteal, 
the  superior  above,  the  inferior  below  the  joint.  Winding  round  the  bones  to 
the  front  of  the  knee,  they  form — by  anastomosing  with  each  other  and  with  the 
genu  suprema  (anastomotica  magna) ,  the  termination  of  the  profunda,  the  descend- 
ing branch  of  the  lateral  circumflex,  and  the  anterior  tibial  recurrent — a  super- 
ficial and  deep  arterial  rete  (fig.  499).  The  superficial  anastomosis  or  rete  lies 
between  the  skin  and  fascia  round  about  the  patella  (patellar  rete),  which  it 
supplies,  the  larger  branches  entering  it  from  above.  The  deep  anastomosis  or 
articular  rete  [rete  articularis  genu]  lies  on  the  surface  of  the  bones  around  the 
articular  surfaces  of  the  femur  and  tibia,  supplying  branches  to  the  contiguous 
bones  and  to  the  joints.  The  middle  articular  is  a  single  short  trunk  coming 
off  from  the  deep  surface  of  the  popliteal  artery.  It  at  once  passes  through  the 
posterior  ligament  into  the  joint. 

(o)  The  superior  lateral  articular  artery  [a.  genu  superior  lateralis],  the  larger  of  the  two 
superior  articular  branches,  runs  in  a  lateral  direction  above  the  lateral  head  of  the  gastrocne- 
mius, and,  passing  beneath  the  biceps  and  through  the  lateral  intermuscular  septum  and  vastus 
lateralis,  enters  the  substance  of  the  vastus  intermedins  (erureus),  and  anastomoses,  above  with 
the  descending  branch  of  the  lateral  circumflex,  below  with  the  inferior  lateral  articular,  and 
across  the  front  of  the  femur  with  the  superior  medial  articular,  the  genu  suprema  (anastomot- 
ica magna),  and  termination  of  the  profunda,  forming  with  them,  as  already  described,  the 
deep  articular  rete.  Branches  are  given  off  to  the  patella,  to  the  upper  and  lateral  part  of  the 
joint,  to  the  bone,  and  to  the  contiguous  muscles. 

(6)  The  superior  medial  articular  artery  [a.  genu  superior  mediaUs]  (fig.  499)  runs  medially 
just  above  the  medial  head  of  the  gastrocnemius,  beneath  the  semi-membranosus,  and,  after 
perforating  the  tendon  of  the  adductor  magnus,  enters  the  substance  of  the  vastus  medialis. 
Here  it  anastomoses  with  the  deep  branch  of  the  genu  suprema  (anastomotica  magna)  and  ter- 
mination of  the  profunda  above,  with  the  inferior  medial  articular  below,  and  with  the  superior 
lateral  articular  across  the  front  of  the  femur.  It  supphes  small  branches  to  the  contiguous 
muscles,  to  the  femur,  to  the  patella,  and  to  the  joint. 

(c)  The  inferior  medial  articular  artery  [a.  genu  inferior  mediaUs],  the  larger  of  the  two  in- 
ferior articular  arteries,  passes  in  an  obliquely  medial  direction  across  the  pophteus,  below  the 
medial  condyle  (tuberosity)  of  the  tibia  and  beneath  the  tibial  collateral  ligament  to  the  front  and 


POPLITEAL  ARTERY 


623 


medial  side  of  the  knee-joint.  Here  it  anastomoses  (fig.  499),  above  witli  the  superior  medial 
articular  and  the  superficial  branch  of  the  genu  suprema  (anastomotica  magna),  and  across  the 
front  of  the  tibia  with  the  inferior  lateral  articular.  It  supphes  branches  to  the  lower  and  medial 
part  of  the  joint. 

(d)  The  inferior  lateral  articular  artery  [a.  genu  inferior  lateralis]  passes  laterally  above  the 
head  of  the  fibula,  along  the  tendon  of  the  popliteus  muscle,  beneath  the  lateral  head  of  the  gas- 
trocnemius, and  then  under  the  tendon  of  the  biceps,  and  between  the  long  and  short  fibular 


Fig.  498. — Relations  of  the  Popliteal  Artery  to  Bones  and  Muscles,  Left  Side. 


Superior  lateral  articular  artery  - 


Fibular  lateral  ligament llj 

IK 

Inferior  lateral  articular  artery {i- 

Popliteus 


Muscular  branch  to  soleus 

Soleus 

Anterior  tibial  artery 


Peroneus  longus  ■ 
Peroneal  artery  ■ 


Flexor  hallucis  longus 


Cutaneous  branch  of  peroneal  artery 


Peroneus  brevis  . 
Continuation  of  peroneal  artery 


Superior  medial  articular  artery 
Popliteal  artery 

Posterior  ligament  of  knee 


■  Azygos  articular  artery 
—    14 Semi-membranosus 


Inferior  medial  articular  artery 
Muscular  branch 


.  Tibialis  posterior 
■  Tibial  nerve 


Flexor  digitorum  longus 


Posterior  tibial  artery 


Tibialis  posterior 


Communicating  brauch 
Laciniate  ligament 


Internal  calcaneal  artery 


collaterallligaments.  Then  winding  to  the  front  of  the  joint,  it  anastomoses  above  with  the 
superior  lateral  articular,  below  with  the  anterior  tibial  recurrent,  and  across  the  front  of  the 
tibia  with  the  inferior  medial  articular.  It  also  supplies  branches  to  the  lateral  and  lower  part 
of  the  joint. 

(e)  The  middle  or  azygos  articular  artery  [a.  genu  media]  arises  from  the  deep  surface  of  the 
popliteal  artery,  and  passes,  with  the  articular  branch  of  the  obtiu*ator  nerve,  through  the 


624 


THE  BLOOD-VASCULAR  SYSTEM 


popliteal  ligament,  directly  into  the  knee-joint,  where  it  supplies  the  crucial  ligaments,  and  the 
patellar  synovial  and  alar  folds.  It  anastomoses  with  the  intrinsic  branches  of  the  other  articu- 
lar arteries. 

(3)  The  terminal  branches  of  the  popliteal  are  the  posterior  and  the  anterior 
tibial  arteries. 


Fig.  499. — The  Anastomosis  about  the  Left  Knee-joint.     (Walsham.) 
(Semi-diagrammatic. ) 


Deep  branch  of  genu  suprema 
Superficial  branch  of  genusuprema  . . 


Adductor  magnus 


Superior  medial  articular  artery 
piercing  tendon  of  adductor 
magnus 


Tibial  collateral  ligament 


Inferior  medial  articular  artery 
passing  under  tibial  collateral 
ligament 


Posterior  tibial  artery 


Descending    branch    of    lateral 
circum,flex  artery 


Superior  lateral  articular  artery 
passing  through  external  inter- 
muscular septum 


Lateral  epicondyle 


Fibular  collateral  ligament 


Inferior  lateral  articular  artery 
passing  under  fibular  collateral 
ligament 


Anterior  tibial  recurrent  artery 


■~  Anterior  tibial  artery 


THE  POSTERIOR  TIBIAL  ARTERY 

The  posterior  tibial  artery  [a.  tibialis  posterior]  (fig.  500) ,  the  larger  of  the 
two  branches  into  which  the  popliteal  divides  at  the  lower  border  of  the  popliteus 
muscle,  runs  downward  on  the  flexor  aspect  of  the  leg  between  the  superficial 
and  deep  muscles  to  the  back  of  the  medial  malleolus.  Midway  between  the  tip 
of  the  malleolus  and  the  calcaneus,  and  under  cover  of  the  origin  of  the  abductor 
hallucis  as  it  arises  from  the  laciniate  (internal  annular)  ligament,  it  divides  into 
the  medial  and  lateral  plantar  arteries. 

The  artery  is  first  situated  midway  between  the  tibia  and  fibula,  and  is  deeply 
placed  beneath  the  muscles  of  the  calf.  As  it  passes  downward  it  inclines  to  the 
medial  side  and  at  the  lower  third  of  the  leg  is  superficial,  being  only  covered  by 
the  skin  and  fasciae.  At  the  ankle  it  lies  beneath  the  laciniate  ligament,  and  at  its 
bifurcation  also  beneath  the  abductor  hallucis.  A  line  drawn  from  the  centre  of 
the  popliteal  space  to  a  spot  midway  between  the  medial  malleolus  and  point  of 
the  heel  will  indicate  its  course.  In  addition  to  the  branches  named  below  it 
supplies  the  muscles  between  which  it  passes,  and  the  integument  of  the  lower 
medial  region  of  the  leg. 

Relations. — Anteriorly,  from  above  downward,  it  lies  successively  on  the  tibialis  posterior, 
the  flexor  digitorum  longus,  the  posterior  surface'  of  the  tibia,  and  the  deltoid  ligament  of  the 
ankle-joint. 

Posteriorly,  it  is  covered  by  the  skin  and  fascia,  the  gastrocnemius  and  soleus,  and  the  deep 
or  intermuscular  fascia  of  the  leg,  by  which  it  is  tightly  bound  down  to  the  underlying  muscles. 
It  is  crossed  by  the  tibial  nerve  about  4  cm.  (If  in.)  below  its  origin,  after  it  has  given  off  its 


POSTERIOR  TIBIAL  ARTERY 


625 


peroneal  branch;  the  nerve  first  lies  on  the  medial,  and  for  the  rest  of  its  course  on  the  lateral 
side  of  the  vessel.  It  is  accompanied  by  two  veins,  which  send  numerous  anastomosing  branches 
across  it.  In  the  lower  third  of  the  leg  the  artery  is  superficial,  being  covered  only  by  the  skin 
and^by  the  superficial  and  deep  fascia?. 


Fig.  500. — The  Popliteal,  the  Posterior  Tibial,  and  the  Peroneal  Arteries. 
(After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 


Adductor  magnus  - 
;nu  suprema  artery- 


Vastus  medialis  -^  z: 
Superior  medial  articular  artery  — 


-  Superior  lateral  articular  artery 
a  Popliteal  artery 


Middle  articular  artery  '^  , 

Semimembranosus  —     i 

Inferior  medial  articular  artery      ~ 

Popliteal  artery  — 


-  Sural  arteries 

Collateral  fibular  ligament 

Inferior  lateral  articular  artery 

Fibular  branch 

Anterior  tibial  artery 

_,-Interosseous  membrane 
.^Tibial  nutrient  artery 


Posterior  tibial  artery  - 


Flexor  longus  digitorum- 


Flesor  hallucis  longus  b 


» Peroneal  artery 


-^ — ■  Fibtilar  nutrient  artery 


>  Flexor  hallucis  longus 


Communicating  branches  ,   ~^, 

I 

Posterior  tibial  muscle'- ^«3( 

Posterior  medial  malleolar  artery-       v^^nm^j 
Flexor  longus  hallucis- 
Communicating  branches- 
Tendo  Achllli; 

Medial  calcanean  branches   tt/V^ 


aPeroneus  brevis 

-  Perforating  branch 
^  Peroneus  longus 


-  Posterior  lateral  malleolar  artery 


— Lateral  calcanean  branche 
■•Calcanean  rete 


At  the  medial  malleolus  it  lies  beneath  the  laciniate  (internal  annular)  ligament  and  abduc- 
tor hallucis  upon  the  deltoid  ligament  of  the  ankle-joint.  Here  it  has  the  tibialis  posterior 
and  flexor  digitorum  longus  in  front  of  it,  and  the  tibial  nerve  and  the  flexor  haUucis  longus  be- 
hind and  to  its  lateral  side. 

At  times  the  tibial  nerve  divides  higher  than  usual,  when  one  branch  lies  on  the  medial  side 
of  the  artery  and  the  other  branch  on  the  lateral  side. 


626  THE  BLOOD-VASCULAR  SYSTEM 

The  branches  of  the  posterior  tibial  artery  are: — (1)  The  fibular;  (2)  the 
peroneal;  (3)  the  tibial  nutrient;  (4)  the  communicating;  (5)  the  posterior  medial 
malleolar;  (6)  the  medial  calcanean,  and  (7)  the  terminal,  medial  and  lateral 
plantar. 

(1)  The  fibular  or  superior  fibular  branch  [ramus  fibularis],  which  frequently  arises  from  the 
beginning  of  the  anterior  tibial,  runs  upward  and  laterally  toward  the  head  of  the  fibula.  It  is 
small  and  gives  twigs  to  the  soleus,  peroneus  longus,  and  extensor  digitorum  longus,  and  anasto- 
moses with  the  inferior  lateral  articular  and  the  lateral  sural  arteries. 

(2)  The  peroneal  artery  [a.  peronea]  is  a  large  vessel  which  (figs.  498,  500), 
arises  from  the  posterior  tibial  about  2.5  cm.  (1  in.)  below  the  lower  border  of  the 
popliteus  muscle.  At  first  forming  a  gentle  curve  convex  laterally,  it  approaches 
the  fibula,  and  continues  its  course  downward  close  to  that  bone  as  far  as  the  lower 
end  of  the  interosseous  membrane,  where  it  gives  off  a  large  branch,  the  perforating 
(anterior  peroneal),  and  then,  passing  over  the  back  of  the  inferior  tibio-fibular 
joint,  terminates  by  breaking  up  into  a  network,  which  is  distributed  over  the 
back  of  the  lateral  malleolus  and  lateral  surface  of  the  calcaneus  (figs.  500,  504). 
It  is  accompanied  b}^  two  vense  comitantes.  Besides  the  named  branches  it 
supplies  twigs  to  the  flexor  hallucis  longus,  tibialis  posterior,  tibialis  anterior, 
peronei  and  soleus;  also  to  the  integument  on  the  lateral  side  of  the  leg. 

Relations. — At  its  upper  part  it  is  deeply  placed  between  the  tibialis  posterior  and  soleus 
muscles,  and  beneath  the  deep  or  intermuscular  fascia.  For  the  rest  of  its  course  to  the  ankle 
it  Ues  beneath,  or  sometimes  in  the  substance  of,  the  flexor  hallucis  longus  in  the  angle  between 
the  fibula  and  interosseous  membrane.  After  giving  off  the  perforating  branch,  it  is  only  cov- 
ered, as  it  lies  behind  the  tibio-fibular  articulation,  by  the  integuments  and  deep  fascia,  and  in 
this  part  of  its  course  is  sometimes  called  the  posterior  peroneal. 

The  branches  of  the  peroneal  artery  are: — (a)  The  perforating  (anterior 
peroneal) ;  (b)  the  fibular  nutrient;  (c)  the  communicating;  (d)  the  lateral  malleolar; 
(e)  the  lateral  calcanean;  and  (/)  the  terminal. 

(o)  The  perforating  (or  anterior  peroneal)  branch  [ramus  perforans]  arises  from  the  front 
of  the  peroneal  artery  at  the  lower  part  of  the  interosseous  space,  and,  passing  through  the 
interosseous  membrane,  runs  downward  over  the  front  of  the  inferior  tibio-fibular  joint,  beneath 
the  peroneus  tertius,  and  supplies  this  muscle  and  the  inferior  tibio-fibular  joint.  It  anasto- 
moses with  the  tarsal,  arcuate  (metatarsal)  and  lateral  malleolar  branches  of  the  anterior  tibial 
artery,  and  with  the  lateral  plantar  artery  on  the  lateral  side  of  the  foot,  forming  a  plexus  over 
the  ankle  (fig.  503). 

(b)  The  fibular  nutrient  [a.  nutritia  fibula;]  enters  the  nutrient  foramen  of  the  fibula. 

(cj  The  communicating  branch  [ramus  communicans]  passes  medially  in  front  of  the  tendo 
Achillis  to  anastomose  with  the  communicating  branch  of  the  posterior  tibial.  The  usual 
situation  of  this  communication  is  from  2.5  to  5  cm.  (1  to  2  in.)  above  the  ankle-joint. 

(d)  The  lateral  posterior  malleolar  artery  [a.  malleol.aris  poster,  lateralis]  anastomoses  on 
the  lateral  malleolus  with  the  anterior  lateral  malleolar  of  the  anterior  tibial  artery  to  form  the 
lateral  malleolar  rete. 

(e)  The  lateral  calcaneal  branches  [rami  calcanei  laterales]  come  off  from  the  peroneal  below 
the  point  at  which  the  perforating  is  given  off,  and  are  distributed  over  the  lateral  surface  of  the 
calcaneus. 

(/)  The  terminal  branch  or  posterior  peroneal,  the  continuation  of  the  peroneal  artery, 
anastomoses  with  the  other  arteries  distributed  to  the  lateral  malleolus  and  heel. 

(3)  The  tibial  nutrient  artery  [a.  nutritia  tibiae],  a  vessel  of  large  size,  leaves  the  posterior 
tibial  at  its  upper  part,  pierces  the  tibialis  posterior,  and  enters  the  nutrient  foramen  in  the 
upper  third  of  the  posterior  surface  of  the  tibia.  In  the  interior  of  the  bone  it  divides  into  two 
branches:  an  ascending  or  smaller,  which  runs  upward  toward  the  head  of  the  bone;  and  a  de- 
scending or  larger,  which  courses  downward  toward  the  lower  end.  It  gives  off  two  or  three 
muscular  twigs  to  the  tibialis  posterior  before  it  enters  the  foramen.  The  nutrient  artery  of  the 
tibia  is  the  largest  nutrient  artery  of  bone  in  the  body,  and  is  accompanied  by  a  nerve  given  off 
by  the  nerve  to  the  popliteus. 

(4)  The  communicating  branch  [ramus  communicans]  arises  from  the  posterior  tibial  about 
5  cm.  (2  in.)  above  the  medial  malleolus,  and,  passing  transversely  across  the  tibia  beneath 
the  flexor  hallucis  longus  and  tendo  Achillis,  anastomoses  with  the  communicating  branch  of 
the  peroneal. 

Frequently  an  inferior  communicating  branch  between  the  posterior  tibial  and  peroneal 
arteries  is  hkewise  present  in  the  loose  connective  tissue  beneath  or  behind  the  tendo  Achillis. 

(5)  The  posterior  medial  malleolar  branch  [ramus  maUeolaris  posterior  medialis]  divides 
for  distribution  over  the  medial  malleolus,  anastomosing  with  the  other  arteries  entering  into 
the  medial  malleolar  rete  [rete  m.iUeolare  mediale]  which  is  formed  over  the  portion  of  bone. 
In  its  course  to  the  malleolus  it  runs  beneath  the  flexor  digitorum  longus  and  tibiaUs  posterior 
muscles. 

(6)  The  medial  calcanean  branches  [rami  calcanei  mediales]  are  distributed  to  the  soft 
parts  over  the  medial  side  of  the  calcaneus.  These  branches  come  off  from  the  posterior  tibial 
just  before  its  bifurcation,  and  anastomose  with  the  medial  malleolar  and  pei'oneal  arteries. 

(7)  The  terminal  branches  are  the  lateral  and  medial  plantar  arteries. 


ANTERIOR  TIBIAL  ARTERY 


627 


THE  LATERAL  PLANTAR  ARTERY 

The  lateral  plantar  artery  [a.  plantaris  lateralis]  (figs.  501,  502) — the  larger  of 
the  two  branches  into  which  the  posterior  tibial  divides  beneath  the  laciniate 
(internal  annular)  ligament — passes  at  first  laterally  and  forward  across  the  sole 
of  the  foot  to  the  base  of  the  fifth  metatarsal  bone,  where  it  bends  medially,  and 
still  running  forward  sinks  deeply  into  the  foot  and  terminates  at  the  proximal  end 
of  the  first  interosseous  space  by  anastomosing  with  the  deep  plantar  (com- 
municating) branch  of  the  dorsal  artery  of  the  foot.  In  its  course  to  the  fifth 
metatarsal  bone  the  artery  runs  in  a  more  or  less  straight  line  obliquely  across  the 
foot ;  whilst  its  deep  portion,  extending  from  thefif th  metatarsal  bone  to  the  proximal 

Fig.  501. — The  Plantar  Arteries,  Left  Foot. 
(From  a  dissection  in  the  Museum  of  St.  Bartholomew's  Hospital.) 


Lateral  calcanean  branch 


Anastomosing  branch  of  lateral 
plantar 


Abductor  digiti  quinti 


—  Medial  calcane 


Cutaneous    branch   of    medial 
plantar 

Plantar  aponeurosis,  cut 


Abductor  hallucis 


Anastomotic  branch 

Lateral  plantar  artery 


Digital  to  lateral  side  of  little  toe 

Lumbrical  muscle 
Fourth  metatarsal 

Third  metatarsal 
Second  metatarsal 


Anastomosis  about  interpha- 
langeal  joint 


Dorsal  branch  of  plantar  digital 


Anastomosis  of  plantar  digital  arteries 
around  matrix  of  nail  and  pulp  of  toe 


Medial  plantar  artery 
Flexor  digitorum  brevis 


Superior  branch  of  medial  plantar 
Flexor  hallucis  brevis 


First  plantar  metatarsal  artery 


Plantar  digital  branch  of  first  meta- 
tarsal to  toe 

Plantar  digital  branch  of  first  meta- 
tarsal to  medial  side  of  great  toe 

Plantar  digital  branch  of  first  meta- 
tarsal to  lateral  side  of  great  toe 


end  of  the  first  interosseous  space,  forms  a  slight  curve  with  the  convexity  forward, 
and  is  known  as  the  plantar  arch.  The  plantar  arch  is  comparable  to  the  deep 
volar  arch  formed  by  the  deep  branch  of  the  ulnar  anastomosing  with  the  radial 
through  the  first  interosseous  space.  This  homology  is  at  times  more  complete 
in  that  the  deep  plantar  (communicating)  branch  of  the  dorsalis  pedis,  the 
homologue  of  the  radial  in  the  upper  limb,  takes  the  chief  share  in  forming  the 
arch.  The  lateral  plantar  artery  is  accompanied  by  two  veins.  The  course  of 
the  artery  is  indicated  by  a  line  drawn  across  the  sole  of  the  foot  from  a  point 
midway  between  the  tip  of  the  medial  malleolus  and  the  medial  tubercle  of  the 
calcaneus  to  the  base  of  the  fifth  metatarsal  bone,  and  thence  to  the  lateral  side 
of  the  base  of  the  first  metatarsal. 

The  lateral  plantar  artery,  besides  the  branches  named  below  gives  twigs  to 
supply  the  muscles  between  which  it  passes,  and  the  tarsal  joints.     It  also  gives 


628 


THE  BLOOD-VASCULAR  SYSTEM 


branches  to  the  integument  of  the  lateral  side  of  the  sole,  some  of  which  anasto- 
mose with  arteries  on  tlie  lateral  side  of  the  dorsum. 

Relations. — In  the  first  part  of  its  course  from  the  medial  malleolus  to  the  base  of  the  fifth 
metatarsal  bone,  the  artery  is  covered  successively  by  the  abductor  hallucis  and  the  flexor 
digitorum  brevis,  by  which  it  is  separated  from  the  plantar  aponeurosis,  and  may  be  slightly 
overlapped  in  muscular  subjects  by  the  abductor  quinti  digiti.  As  it  approches  the  base  of  the 
fifth  metatarsal  bone  it  Ues,  as  it  turns  medially  before  sinking  into  the  foot,  in  the  interspace 
between  the  flexor  digitorum  brevis  and  the  abductor  quinti  digiti,  and  is  here  covered  only  by  the 
skin  and  superficial  fascia  and  the  plantar  aponeurosis.  It  hes  upon  the  calcaneus,  the  quadratus 
plantse  (flexor  accessorius),  and  the  flexor  digiti  quinti  brevis.  It  is  accompanied  by  the  lateral 
plantar  nerve,  the  smaller  of  the  two  divisions  into  which  the  tibial  nerve  divides.  In  this  part 
of  its  course  it  gives  off  small  branches  to  the  contiguous  muscles  and  to  the  heel. 

Fig.  502. — Plantae  Arteries  (Deep).     (After  Henle.) 


Anterior  perforating  branch 

First  dorsal  interosseous  muscle 
Metatarsal  artery 
Deep  plantar  b"°'=h\J^>«MMi  ]l||,  I  m\miiii^-\^^^^''^  metatarsal  artery 

Plantar  metatarsal  artery 
Perforating  branch 


Branch  of  the  medial  plantar  artery 


Abductor  hallucis  muscl 


Tendon  of  the  posterior  tibial 
muscle 
Medial  plantar  artery 


Tendons  of  the  flexor 

digitorum  longus 
Quadratus  plant£e 


Abductor  of  the  fifth  digit 
Lateral  plantar  artery 


tibial  artery 


In  the  second  part  of  its  course  the  artery,  which  is  here  known  as  the  plantar  arch  [arcus 
plantaris],  sinks  into  the  sole,  and  is  covered,  in  addition  to  the  skin,  superficial  fascia,  plantar 
aponeurosis,  and  flexor  digitorum  brevis  by  the  tendons  of  the  flexor  digitorum  longus,  the 
lumbricales,  branches  of  the  medial  plantar  nerve,  and  the  adductor  hallucis.  It  lies  upon  the 
proximal  ends  of  the  second,  third,  and  fourth  metatarsal  bones  and  the  corresponding  interos- 
seous muscles. 

The  branches  of  the  lateral  plantar  artery  are: — (1)  Perforating;  and  (2) 
plantar  metatarsal  (digital). 

(1)  The  perforating  branches  [rr.  perforantes],  three  in  numbers,  ascend  through  the 
proximal  end  of  the  second,  third,  and  fourth  spaces,  between  the  two  heads  of  the  correspond- 
ingly named  dorsal  interosseous  muscles,  and  communicate  with  the  proximal  ends  of  the 
first,  second,  and  third  dorsal  metatarsal  (interosseous)  arteries  (fig.  502). 

(2)  The  plantar  metatarsal  arteries  [aa.  metatarsete  plantares]  are  usually  four  in  number, 
and  pass  forward  in  the  four  intermetatarsal  spaces,  which  are  numbered  from  the  medial  side. 
They  rest  upon  the  interosseous  muscles  of  their  spaces,  and  are  at  first  under  cover  of  the  lum- 
bricals,  but  as  they  approach  the  clefts  of  the  toes  each  divides  into  two  branches,  the  plantar 
digital  arteries  [aa.  digitales  plantares],  which  supply  the  contiguous  sides  of  the  toes.  The 
plantar  digital  branch  for  the  medial  side  of  the  great  toe  is  usually  given  off  by  the  first  plantar 
metatarsal;  that  for  the  lateral  side  of  the  Uttle  toe  is  usually  a  separate  branch  from  the  lateral 
end  of  the  plantar  arch. 


ANTERIOR  TIBIAL  ARTERY  629 

The  plantar  metatarsal  arteries,  immediately  before  they  bifurcate,  send  to  the  dorsum  of 
the  foot  a  perforating  branch  each  to  the  corresponding  dorsal  metatarsal  arteries.  They 
anastomose  by  many  small  twigs  with  the  dorsal  metatarsal  arteries,  which  also  run  along  the 
sides  of  the  metatarsal  bones,  but  more  toward  the  dorsal  aspect.  Immediately  above  each 
phalangeal  joint  the  plantar  digital  vessels  communicate  by  cross  branches,  forming  a  rete  for 
the  supply  of  the  articular  end  of  the  phalanges  and  the  contiguous  joints.  At  the  distal  end 
of  the  toes  they  also  freely  anastomose  with  each  other,  forming  a  rete  beneath  the  pulp  and 
around  the  matrix  of  the  nail.  The  metatarsal  and  digital  arteries  are  each  accompanied  by 
two  small  veins. 

THE  MEDIAL  PLANTAR  ARTERY 

The  medial  plantar  artery  [a.  plantaris  medialis]  (figs.  501,  502) — much  the 
smaller  of  the  two  divisions  into  which  the  posterior  tibial  divides,  passes  forward 
along  the  medial  side  of  the  sole  of  the  foot  usually  to  the  first  interosseous  space. 
Here  it  ends  by  anastomosing  either  with  the  first  plantar  metatarsal  artery 
derived  from  the  plantar  arch,  or  with  the  branch  given  off  by  the  first  plantar 
metatarsal  to  the  medial  side  of  the  great  toe. 

Relations. — The  artery  is  at  first  under  cover  of  the  abductor  hallucis,  but  afterward  Ues 
in  the  interval  between  that  muscle  and  the  flexor  digitorum  brevis.  It  is  covered  by  the  skin 
and  superficial  fascia,  but  not  by  the  plantar  aponeurosis,  since  it  lies  between  the  central  and 
medial  portions  of  that  structure. 

The  branches  of  the  medial  plantar  are: — (1)  The  deep  and  (2)  the  superficial 
branches. 

(1)  The  deep  branch  [ramus  profundus],  which  at  once  divides — or  it  may  come  off  as 
several  branches — to  supply  the  muscles,  articulations,and  integument  of  the  medial  side  of  the 
sole.  Some  of  these  branches  form  an  anastomosis  aroundthe  medial  margin  of  the  foot,  with 
branches  of  the  dorsahs  pedis. 

(2)  The  superficial  branch  [ramus  superficialis]  breaks  up  into  very  small  twigs  which  ac- 
company the  digital  branches  of  the  medial  plantar  nerves,  and  anastomose  with  the  plantar 
metatarsal  arteries  in  the  first,  second,  and  third  spaces.  At  times  a  twig  from  one  of  these 
branches  joins  the  lateral  plantar  artery  to  form  a  superficial  plantar  arch. 

THE  ANTERIOR  TIBIAL  ARTERY 

The  anterior  tibial  artery  [a.  tibialis  anterior]  fig.  503 — the  smaller  of  the 
two  branches  into  which  the  popliteal  artery  divides  at  the  lower  border  of  the 
popliteus  muscle — at  first  courses  forward  between  the  two  heads  of  origin  of  the 
tibialis  posterior,  and,  after  passing  between  the  tibia  and  fibula  above  the  upper 
part  of  the  interosseous  membrane,  runs  downward  on  the  front  and  lateral  aspect 
of  the  leg,  between  the  anterior  muscles,  as  far  as  the  front  of  the  ankle-joint. 
Below  the  joint  it  is  known  as  the  dorsalis  pedis.  The  course  of  the  vessel  is 
indicated  by  a  line  drawn  from  the  front  of  the  head  of  the  fibula  to  a  point  mid- 
way between  the  two  malleoli. 

The  artery  is  accompanied  by  two  veins  which  communicate  with  each  other 
at  frequent  intervals  across  it.  It  is  also  accompanied  in  the  lower  three-fourths 
of  its  course  by  the  deep  pei'oneal  nerve.  The  nerve,  which  winds  round  the  head 
of  the  fibula,  and  pierces  the  extensor  digitorum  longus,  first  comes  into  contact 
with  the  lateral  side  of  the  artery  about  the  upper  third  of  the  leg;  in  the  middle 
third  it  is  a  little  in  front  of  the  artery,  and  in  the  lower  third  again  lies  to  its 
lateral  side.  In  addition  to  the  named  branches  the  anterior  tibial  artery  supplies 
muscular  twigs  to  the  extensors  of  the  toes  and  the  tibiahs  anterior. 

Relations. — The  artery  at  first  Ues  in  the  triangle  formed  by  the  two  heads  of  the  tibiahs 
posterior  and  the  popliteus  muscle;  and,  as  it  passes  above  the  interosseous  membrane,  it  has 
the  tibia  on  one  side  and  the  fibula  on  the  other.  It  is  separated  from  the  deep  peroneal  (ante- 
rior tibial)  nerve  at  its  commencement  by  the  neck  of  the  fibula  and  the  extensor  digitorum 
longus.  This  arrangement  is  homologous  with  that  met  with  in  the  forearm  in  the  case  of  the 
posterior  interosseous  artery  and  deep  radial  (posterior  interosseous)  nerve. 

Posteriorly  in  its  course  down  the  leg  it  lies  in  its  upper  two-thirds  upon  the  interosseous 
membrane,  to  which  it  is  closely  bound  by  fibrous  bands;  and  in  its  lower  tliird  upon  the  front 
of  the  tibia  and  the  ankle-joint. 

To  its  medial  side  along  its  upper  two-thirds  is  the  tibialis  anterior  muscle;  but  at  the  lower 
third  it  is  crossed  by  the  tendon  of  the  extensor  hallucis  longus  and  then  for  the  rest  of  its 
course  has  this  tendon  overlapping  it  or  to  its  medial  side. 

On  its  lateral  side  it  is  in  contact  in  its  upper  third  with  the  extensor  digitorum  longus 
muscle;  in  its  middle  third  with  the  extensor  hallucis  longus;  but,  as  this  muscle  crosses  to 
the  medial  side  of  the  artery,  the  vessel  usually  for  a  very  short  part  of  its  course  comes  again 


630 


THE  BLOOD-VASCULAR  SYSTEM 


into  contact  with  the  extensor  digitorum  longus.  At  the  upper  and  lower  thirds  of  its  course 
on  the  front  of  the  leg  the  artery  has  the  deep  peroneal  (anterior  tibial)  nerve  to  its  lateral  side. 
In  front  the  artery  is  covered  by  the  skin,  superficial  and  deep  fascia.  In  its  upper  two- 
thirds  it  is  deeply  placed  in  the  cellular  interval  between  the  tibiahs  anterior  on  the  medial 
side  and  the  extensor  digitorum  longus  and  extensor  hallucis  longus  on  its  lateral  side;  and 
in  .its  lower  third  it  is  crossed  in  the  latero-medial  direction  by  the  tendon  of  the  extensor 

Fig.  503. — The  Anterior  Tibial  Artery,  Dorsal  Artery  op  the  Foot,  and  Perforatinq 
(Anterior)  Peroneal  Artery,  and  their  Branches,  Left  Side. 


Superior  medial  articular  artery 


Inferior  medial  articular  artery 


Anterior  tibial  recurrent  artery 


Anterior  tibial  artery 


Tibialis  anterior  muscle 


Extensor  hallucis  longus' 


Medial  malleolar  artery 


Crucial  ligament- 
Dorsalis  pedis  artery. 

Most  medial  tendon  of  extensor  digi 
torum  brevis 

Deep  plantar  branch' 
First  dorsal  metatarsal  artery 


Superior  lateral  articular  artery 


— -Inferior  lateral  articular  artery 


^Extensor  digitorum  longus 


Peroneus  tertius 


^  Perforating  peroneal  artery 
Lateral  malleolar  artery 

Peroneus  brevis  muscle 

—  Extensor  digitorum  brevis,  cut 

—  Lateral  tarsal  artery 
Arcuate  artery 
Dorsal  metatarsal  artery 


hallucis  longus,  and  lies  beneath  the  cruciate  (anterior  annular)  ligament  of  the  ankle-joint 
The  deep  peroneal  nerve  is  usually  in  front  of  the  artery  in  the  middle  third  of  the  leg. 

The  branches  of  the  anterior  tibial  artery  are: — (1)  The  posterior  tibial  recur- 
rent: (2)  the  anterior  tibial  recurrent;  (3)  the  medial  malleolar;  and  (4)  the 


DORSALIS  PEDIS  ARTERY 


631 


Fig.  504.^Scheme  of  the  Distribution  and  Anastomoses  op  the  Arteries  of  the  Right 

Foot.     (Walsham.) 

(The  plantar  arteries  are  shown  in  dotted  outHne;  the  dorsal  in  solid  red.) 


Peroneal  artery 


Perforating  peroneal  branch 
Lateral  malleolar  branch 


Posterior  peroneal  artery 


Dor  sails  pedis  artery 
Lateral  plantar  artery 


Lateral  tarsal  branch 


Lateral  plantar  artery 

forming  plantar  arch    r  -| 

Posterior  perforating    \\,  |"^' 

branches  "^^^^5^^_    I  "^ 

Plantar  digital  artery  to 
lateral  side  of  Uttle  toe 


Second,  third,  and  fourth 
dorsal  metatarsal  ar- 
teries given  off  from 
arcuate  artery 

Second,  third,  and  fourth 
plantar  metatarsal  ar- 
teries 


Branch  of  third  dorsal 
metatarsal  artery  to 
lateral  side  of  little  toe 


Anterior  tibial  artery 


Medial  malleolar  branch 


Malleolar  branch  of  pos- 
terior tibial  artery 

Communicating  branch 
between  posterior 
tibial  and  peroneal 
arteries 


Medial  plantar  artery 


Medial  tarsal  branch 


■Arcuate  artery 


■Deep  plantar  artery 


First  dorsal  metatarsal 


First  plantar  metatarsal 
artery 


Dorsal  digital  branch  of 
first  dorsal  metatarsal 
to  medial  side  of  great 


632  THE  BLOOD-VASCULAR  SYSTEM 

lateral  malleolar.     In  addition,  ten  or  twelve  muscular  branches  are  given  off 
irregularly  to  the  adjacent  muscles  along  the  artery. 

(1)  The  posterior  tibial  recurrent  artery  [a.  recurrens  tibialis  posterior]  is  occasionally  absent. 
It  ascends  between  the  popliteus  muscle  and  the  popliteal  ligament  of  the  knee-joint,  supplying 
these  structures  and  the  superior  tibio-fibular  joint.  It  anastomoses  with  the  inferior  lateral 
articular  branch  of  the  pophteal,  and  to  a  less  extent  with  the  inferior  medial  articular  branch. 

(2)  The  anterior  tibial  recurrent  [a.  recurrens  tibiahs  anterior]  is  given  off  from  the  anterior 
tibial  artery  immediately  after  that  vessel  has  passed  above  the  interosseous  membrane.  It 
winds  tortuously  through  the  substance  of  the  tibialis  anterior  muscle,  over  the  lateral  condyle 
(tuberosity)  of  the  tibia  close  to  the  bone;  and,  perforating  the  deep  fascia,  ramifies  on  the  lower 
and  lateral  part  of  the  capsule  of  the  knee-joint.  It  anastomoses  with  the  inferior  and  superior 
lateral  articular  branches  of  the  pophteal,  with  the  descending  branch  of  the  lateral  circumflex, 
and  somewhat  less  freely  with  the  medial  articular  branches  of  the  pophteal  and  with  the  genu 
suprema  (anastomotica  magna).  It  gives  off  small  branches  to  the  tibialis  anterior,  the  extensor 
digitorum  longus,  the  knee-joint,  and  the  contiguous  fascia  and  skin.  It  forms  one  of  the  col- 
lateral cliannels  by  which  the  blood  is  carried  to  the  hmb  below  in  obstruction  of  the  pophteal 
artery  (fig.  503). 

(3)  The  medial  malleolar  [a.  maUeolaris  anterior  medialisj,  the  smaller  of  the  two  malleolar 
branches,  arises  from  the  lower  part  of  the  anterior  tibial  artery  a  httle  higher  than  the  lateral, 
usually  about  the  spot  where  the  tendon  of  the  extensor  haUucis  longus  crosses  the  anterior 
tibial  artery.  It  winds  over  the  medial  malleolus,  passing  beneath  the  tibiaUs  anterior,  and 
joins  the  medial  malleolar  rete  anastomosing  with  branches  from  the  posterior  tibial  artery. 

(4)  The  lateral  malleolar  artery  [a.  maUeolaris  anterior  lateralis],  larger  than  the  medial, 
arises  from  the  lateral  side  of  the  anterior  tibial  artery,  usually  on  a  lower  level  than  the  medial 
malleolar.  It  winds  downward  and  laterally  round  the  lateral  malleolus,  passing  beneath  the 
extensor  digitorum  longus  and  peroneus  tertius,  and  joins  the  lateral  malleolar  rete  by  anas- 
tomosing with  the  perforating  peroneal,  the  termination  of  the  peroneal,  and  the  lateral  tarsal 
branch  of  the  dorsahs  pedis  (fig.  503). 

The  anastomosis  between  the  lateral  malleolar  and  perforating  peroneal  is  sometimes  of 
considerable  size,  supplying  the  blood  to  the  dorsal  artery  of  the  foot;  the  anterior  tibial,  then 
much  reduced  in  size,  usually  ends  at  the  place  of  origin  of  the  lateral  malleolar. 

THE  DORSALIS  PEDIS  ARTERY 

The  dorsalis  pedis  artery  [a.  dorsalis  pedis]  (fig.  503)  is  a  continuation  of  the 
anterior  tibial.  It  extends  from  the  front  of  the  ankle-joint  to  the  proximal  end 
of  the  first  interosseous  space,  where  it  ends,  as  the  deep  plantar  branch,  by  joining 
the  lateral  plantar  artery  to  complete  the  plantar  arch.  It  is  accompanied  by 
two  venae  comitantes.  The  course  of  the  artery  is  indicated  by  a  fine  drawn  from 
a  point  midway  between  the  two  malleoli  to  the  proximal  end  of  the  first  metatar- 
sal space. 

Relations. — Behind,  the  artery  from  above  downward  Ues  successively  on  the  talus  (astrag- 
alus), navicular,  second  cuneiform,  and  the  base  of  the  second  metatarsal  bones,  and  the  hga- 
ments  uniting  these  bones.  At  times  its  course  is  a  little  more  lateral,  lying  either  partly  on 
the  second  cuneiform  bone,  or  on  the  dorsal  ligaments  uniting  the  second  cuneiform  to  the  first 
cuneiform.  It  is  more  or  less  bound  down  to  the  bones  by  aponeurotic  fibres  derived  from  the 
deep  fascia. 

In  front,  the  artery  is  covered  by  the  crucial  (anterior  annular)  hgament,  sometimes  by  the 
extensor  hallucis  longus,  by  the  skin,  the  superficial  and  deep  fascia,  and,  just  before  its  termi- 
nation, by  the  tendon  of  the  extensor  hallucis  brevis.  The  angle  formed  by  this  tendon  with  the 
extensor  hallucis  longus  is  the  best  guide  to  finding  the  artery  in  the  process  of  Ugature  (fig.  503). 

To  its  lateral  side  is  the  most  medial  tendon  of  the  extensor  digitorum  longus,  and  lower 
down  the  tendon  of  the  extensor  hallucis  brevis.  The  deep  peroneal  (anterior  tibial)  nerve  is 
also  to  its  lateral  side. 

To  its  medial  side  is  the  extensor  hallucis  longus,  except  at  times  for  about  half  an  inch  below, 
where  the  tendon  of  the  extensor  haUucis  brevis,  having  crossed  the  artery,  may  he  between  it 
and  this  tendon. 

The  branches  of  the  dorsalis  pedis  artery  are: — (1)  The  tarsal;  (2)  the  arcu- 
ate; and  (3)  the  deep  plantar. 

(1)  The  tarsal  branches  may  be  divided  into  (a)  the  lateral  and  (6)  the  medial,  (a)  The 
lateral  tarsal  artery  [a.  tarsea  lateraUs]  runs  laterally  over  the  navicular  and  cuboid  bones  beneath 
the  extensor  digitorum  brevis.  It  supplies  branches  to  that  muscle,  and  to  the  bones  and  the 
articulations  between  them,  and  anastomoses  above  with  the  lateral  malleolar  and  perforating 
(anterior)  peroneal,  below  with  the  arcuate  (metatarsal)  and,  over  the  lateral  border  of  the  foot, 
with  the  anastomotic  branches  of  the  lateral  plantar  artery.  (6)  The  medial  tarsal  arteries 
[aa.  tarseai  raediales]  consists  of  a  few  small  branches  which  run  over  the  medial  side  of  the  foot, 
supplying  the  skin  and  articulations,  and  anastomose  with  the  medial  malleolar. 

(2)  The  arcuate  (metatarsal)  artery  Ja.  arcuata]  (figs.  503,  504)  runs  laterally  across  the 
foot,  in  a  shght  curve  with  the  convexity  forward,  over  the  bases  of  the  metatarsal  bones,  and 
beneath  the  e.xtensor  tendons  and  the  extensor  digitorum  brevis.  At  the  lateral  border  of  the 
foot  it  anastomoses,  with  the  lateral  tarsal,  and  with  branches  of  the  lateral  plantar. 


MORPHOGENESIS  OF  THE  ARTERIES  633 

lYom  the  oonvexity  of  the  arch  it  gives  off  four  dorsal  metatarsal  (interosseous)  arteries, 
which  run  forward  on  the  dorsal  interosseous  muscles  in  the  centre  of  the  four  interosseous  spaces 
to  the  cleft  of  the  toes,  where  they  bifurcate  for  the  supply  of  the  contiguous  sides  of  the  toes. 
The  artery  to  the  first  space  is  large,  and  gives  off  the  digital  artery  to  the  medial  side  of  the  great 
toe.  This  vessel  continues  the  direction  of  the  dorsalis  pedis  and  is  commonly  known  as  the 
dorsalis  hallucis  artery.  The  most  lateral  of  the  interosseous  branches  gives  off  a  small  vessel 
for  the  supply  of  the  lateral  side  of  the  little  toe.  At  the  proximal  end  of  the  second,  third,  and 
fourth  interosseous  spaces  each  artery  receives  a  perforating  branch  from  the  lateral  plantar 
artery,  and  immediately  before  they  bifurcate  a  second  perforating  artery  through  the  distal 
end  of  the  interosseous  space  from  the  corresponding  digital. 

The  dorsal  digital  arteries  [aa.  digitales  dorsales],  into  which  the  dorsal  metatarsal  arteries 
divide  at  the  cleft  of  the  toes,  run  along  the  side  of  each  toe  toward  the  dorsal  aspect,  anas- 
tomosing with  each  other  across  the  dorsum  of  the  toes  and  by  frequent  branches  with  the 
digital  branches  of  the  plantar  metatarsal  arteries,  which  also  run  along  the  sides  of  the  toes, 
but  nearer  the  plantar  surface.  At  the  end  of  the  toes  they  anastomose  with  each  other  around 
the  quick  of  the  nail. 

(3)  The  deep  plantar  branch  [ramus  plantaris  profundus]  comes  off  from  the  dorsaUs  pedis 
with  the  first  dorsal  metatarsal  (into  which  arteries  indeed  the  dorsalis  pedis  may  be  said  to 
divide).  At  the  back  of  the  first  interosseous  space  it  dips  into  the  sole  between  the  two  heads 
of  the  first  dorsal  interosseous  muscle,  and  communicates  with  the  termination  of  the  lateral 
plantar  artery,  completing  the  plantar  arch,  in  a  manner  similar  to  that  in  which  the  radial 
artery,  passing  through  the  first  dorsal  interosseous  muscle  in  the  hand,  completes  by  anastomos- 
ing with  the  ulnar  the  deep  palmar  arch. 

MORPHOGENESIS  AND  VARIATIONS  OF  THE  ARTERIES 
A.    ARTERIES  OF  THE  HEAD  AND  TRUNK 

1.  MORPHOGENESIS 

In  conformity  with  the  branchiomeric  and  metameric  development  of  the  head 
and  trunk  (see  p.  15)  the  arteries  are  developed  in  two  sets,  the  branchiomeric 
(aortic  arches)  and  metameric  (segmental  arteries). 

Fig.  505. — Model  of  the  Pharynx  and  Aortic  Arches  op  a  Human  Embryo  5  mm.  Long. 

(Tandler,  X75.) 

Second  aortic  arch 

Dorsal  aorta 


Third  aortic  arch 


Sixth  aortic  arch 


(1)  The  system  of  aortic  arches  consists  of  five  pairs  of  arteries  which  spring  from  the  ven- 
tral aorta,  or  aortoe,  and  pass  around  the  pharynx  in  the  branchial  arches  to  join  the  paired 
dorsal  aorta;.  Some  of  the  arches  are  veiy  transitory,  but  all  those  that  give  rise  to  permanent 
vessels  are  present  in  embryos  about  five  miUimetres  in  length.  Fig.  505  shows  their  distri- 
bution and  rlations  to  the  pharyngeal  pouches  at  this  stage;  the  arches  which  appear  fifth  in 
order  are  regarded  as  the  sixth  because  (like  the  sixth  arches  in  lung-fish  and  amphibia)  they  give 


634 


THE  BLOOD-VASCULAR  SYSTEM 


off  the  pulmonary  arteries.  The  true  fifth  arches  are  probably  not  always  developed,  but  when 
they  occur  they  are  later  in  development,  imperfect,  and  very  transitory.  The  dorsal  aortEe, 
originally  paired,  are  now  united  to  form  a  single  vessel  as  far  forward  as  a  place  slightly  caudal 
to  the  sixth  arches. 

During  the  separation  of  the  heart  into  right  and  left  halves  (p  526.),  the  primitive  ventral 
aorta  is  divided  by  the  aortic  septum  into  two  vessels,  the  main  pulmonary  artery  and  the  as- 
cending aorta  of  the  adult.  The  pulmonary  trunk  becomes  connected  with  the  sixth  pair  of 
arches  only;  the  other  arches  then  communicate,  by  means  of  the  aorta,  with  the  left  ventricle. 
The  further  changes  which  occur  in  the  arches  to  bring  about  the  conditions  found  in  the  adult 
are  shown  diagrammatioally  in  fig.  506.  The  right  and  left  pulmonary  arteries  arise  from  the 
corresponding  sixth  arches.  The  portion  of  the  sixth  arch  dorsal  to  the  pulmonary  artery  dis- 
appears on  the  right,  on  the  left  it  persists  until  birth  as  the  ductus  arteriosus  (lig.  arteriosum  of 
the  adult).  The  fourth  arch,  including  the  short  ventral  stem  between  the  fourth  and  sixth 
arch,  becomes  the  permanent  aortic  arch  on  the  left  side,  and  the  innominate  and  proximal  por- 
tion of  the  subclavian  upon  the  right.  The  dorsal  longitudinal  stem  disappears  on  both  sides 
between  the  third  and  fourth  arches,  and  on  the  right  side  from  the  sixth  arch  back  to  the  un- 
paired dorsal  aorta.  A  trace  of  the  latter  portion  of  the  right  dorsal  stem  frequently  persists  in 
the  adult  as  a  small  vessel  (a.  aberrans)  connecting  the  dorsal  aorta,  directly  or  indirectly,  with 
the  right  subclavian  artery  (p.  590).  The  ventral  stems  between  the  fourth  and  third  arches 
form  the  common  carotids;  those  between  the  third  and  first  become  the  external  carotids.  The 
internal  carotids  are  formed  by  the  third  arches  and  tlie  dorsal  stems  between  the  third  and  first 
arches.  The  first  and  second  arches  disappear  early,  contributing  somewhat  to  the  formation 
of  the  branches  of  the  internal  and  external  carotids. 

Fig.   506. — -Diageams  showing  the   Method   of  Normal  Development  op  the  Aoetic 
(Arches,  and  Indicating  the   Mechanism  op  Some  Variations.) 

The  primitive  aortic  arches  (1-6),  and  some  of  the  cervical  dorsal  segmentals  (V-VIII)  are 
shown  in  all  the  diagrams  but  numbered  in  Y  only.  X.,  abnormal:  the  aortic  arch  is  on  the 
right;  the  left  subclavian  takes  the  dorsal  course;  the  right  vertebral  arises  direct  from  the 
aortic  arch.  Y.,  normal;  Z.,  abnormal:  the  right  subclavian  arises  from  the  sixth  cervical 
dorsal  segmental;  the  left  from  the  sixth  and  seventh.  A,  ascending  aorta;  AA,  aortic 
arch;  AD,  dorsal 'aorta ;  CC,  common  carotid;  CE,  external  carotid;  CI,  internal  carotid; 
D,  ductus  arteriosus;  IN,  innominate;  S,  subclavian;  T,  costo-cervical;  V,  vertebral. 


X 


In  early  development  the  segmental  arteries  are  caudally  placed  with  regard  to  the  aortic 
arch  vessels.  As  the  latter,  however,  become  shifted  following  the  migration  of  the  heart  from 
the  neck  into  the  thorax,  the  persistent  seventh  dorsal  cervical  segmental  (subclavian)  reaches 
the  neighbourhood  of  the  sixth  aortic  arch. 

Little  is  known  of  the  share  taken  by  the  first  and  second  aortic  arches  in  the  formation  of  the 
branches  of  the  internal  and  external  carotid  arteries.  It  has  been  shown  by  Tandler  that  the 
internal  maxillary  is  prirnarily  a  branch  of  the  internal  carotid,  (the  first  and  second  arches  tak- 
ing a  share  in  its  formation).  The  primitive  vessel  is  known  as  the  stapedial  since  it  passes  be- 
tween the  crura  of  the  developing  stapes.  It  gives  off  supraorbital,  infraorbital,  and  mandibular 
branches;  the  latter  two  arising  from  the  main  artery  by  a  common  trunk.  The  common  trunk 
is  later  joined  by  a  branch  from  the  external  carotid  and,  together  with  the  supraorbital,  becomes 
the  middle  meningeal.  An  anastomosis  between  the  supraorbital  and  the  ophthalmic  persists 
80  that  in  the  adult  the  anterior  branch  of  the  meningeal  frequently  takes  a  considerable  share  in 
the  blood-supply  of  the  orbit.  The  stapedial  trunk  undergoes  retrogression  and  is  represented 
in  the  adult  by  the  carotico-tympanic  of  the  internal  carotid  and  by  the  superior  tympanic  of  the 
middle  meningeal.  The  infraorbital  branch  of  the  stapedial  becomes  the  second  and  third  parts 
of  the  internal  maxillary  and  gives  off  branches  accordingly.  The  mandibular  branch  becomes 
the  inferior  alveolar  of  the  adult. 

(2)  The  segmental  system  (fig.  507)  consists  of  arteries  primarily  arising  from  the  aorta  in 
three  longitudinal  series,  dorsal,  lateral,  and  ventral  on  either  side.  The  segmental  arrange- 
ment is  much  less  perfect  in  the  ventral  and  lateral  groups  than  in  the  dorsal.  So  much  so,  in 
fact,   that  the  term  segmental  is  used  for  the  ventral  and  lateral  groups  rather  as  a  matter 


MORPHOGENESIS  OF  THE  ARTERIES 


635 


of  convenience  than  as  indicating  a  strict  numerical  correspondence  between  segments  and 


The  dorsal  segmental  arteries  primarily  supply  the  central  nervous  system  but  later  give 
off  two  sets  of  vessels  to  the  body  wall;  these  persist  in  the  adult  as  the  anterior  and  posterior 
main  branches  of  the  intercostal  and  lumbar  arteries.  The  remainder  of  each  segmental  artery  is 
represented  in  the  adult  by  the  spinal  ramus  which  accompanies  the  corresponding  nerve  root 
through  the  intervertebral  foramen.  The  tendency  to  form  intersegmental  anastomoses 
between  these  vessels  (and  their  branches)  gives  rise  to  many  of  the  important  longitudinal  stems 
of  adult  anatomy.  Thus,  the  spinal  ramus  gives  rise  to  a  pre-  and  postneural  anastomosing 
channel  on  either  side,  the  (primarily  paired)  anterior  and  posterior  spinal  arteries.  The  anterior 
branches  have  each  a  longitudinal  precostal  anastomosis,  and,  as  they  grow  forward  with  the 
developing  body  wall,  their  ends  are  connected  to  form  the  mammary  anastomosis. 

Between  the  posterior  rami,  a  postoostal  and  a  postvertebral  anastomosis  may  be  formed. 
In  addition,  the  anterior  rami  give  off  lateral  and  anterior  perforating  branches  (fig.  507). 

Two  dorsal  segmental  arteries  have  been  recognized  in  the  occipital  region,  the  first  dis- 
appears and  the  second,  the  hypoglossus  artery,  follows  the  hypoglossal  nerve  to  the  ventral  sur- 
face of  the  brain  where  it  is  connected  with  the  termination  of  the  internal  carotid  of  its  own  side 
by  means  of  a  longitudinal  stem  the  a.  vertebralis  cerebralis.  The  hypoglossus  artery,  by  shift- 
ing forward  to  the  third  aortic  arch,  itself  acquires  a  secondary  origin  from  the  internal  carotid. 

In  the  cervical  region,  the  spinal  ramus  of  segmental  cervical  I  forms  the  third,  or  sub' 
occipital,  part  of  the  vertebral  artery.  Cervical  segmentals  I  to  VI  lose  their  connection  with 
the  aorta  and  a  postcostal  anastomosis  between  them  forms  the  second  part  of  the  same  artery. 
The  first  part  of  the  vertebral  is  formed  by  the  posterior  ramus  of  cervical  VI  and  its  precostal 
anastomosis  with  cervical  VII  (subclavian)  (fig.  508). 


Fig.  607. — Scheme  of  the  Typical  Arrangement  of  the  Branches  op  the  Aorta.     (After 

Quaim) 

Longitudinal  anastomoses:  1,  precostal;  2,  postcostal;  3  postvertebral;  4,  preneural;  5,  post- 
neural;  6,  mammary. 

,  Posterior  branch 

Anterior  branch 


Lateral  perforating  branch 


Anterior  perforating  branch 


The  anterior  ramus  of  cervical  VII  forms  the  entire  first  part  of  the  subclavian  on  the  left, 
and  the  distal  portion  of  it  upon  the  right  (see  system  of  aortic  arches).  The  second  part  of 
the  subclavian  is  formed  by  the  lateral  branch  of  the  anterior  ramus  of  cervical  VII,  while  the 
portion  of  the  anterior  ramus  ventral  to  this  becomes  the  root  of  the  internal  mammary.  The 
anterior  ramus  of  cervical  VIII  disappears,  but  the  pi'ecostal  anastomosis  connecting  it  with  the 
subclavian  (cervical  VII)  persists  to  form  the  costo-cervical  of  the  adult.  The  posterior  ramus 
of  cervical  VIII  forms  the  root  of  the  deep  cervical,  and,  by  a  postvertebral  anastomosis  with 
the  other  posterior  cervical  rami  and  with  the  occipital,  forms  the  remainder  of  the  deep  cervical 
and  the  descending  branch  of  the  occipital  artery. 

In  the  thoracic  and  lumbar  regions,  the  embryonic  conditions  very  largely  persist  (fig.  508). 
The  anterior  rami  of  thoracic  segmentals  I  and  II,  however,  lose  their  connection  with  the 
aorta  and,  by  a  precostal  anastomosis  with  cervical  VIII,  become  secondarily  connected 
(through  the  costo-cervical  trunk)  with  the  subclavian.  The  superior  intercostal  of  the  adult 
is  thus  formed.  The  fifth  lumbar  segmental  apparently  joins  the  umbihcal  artery  (of  the 
ventral  segmental  series)  to  form  the  external  ihac  which,  in  the  adult,  provides  the  chief 
arterial  supply  to  the  lower  extremity.  The  inferior  gluteal  (sciatic),  which  is  the  primitive 
artery  of  supply  for  the  lower  extremity,  if  it  is  segmental  at  all,  belongs  to  the  sacral  region. 
The  free  ends  of  the  anterior  rami  of  all  the  thoracic  and  the  upper  four  lumbar  segmentals 
become  united,  as  they  grow  out  with  the  body  wall,  to  form  the  longitudinal  mammary 
anastomosis  (fig.  508).     This  anastomosis,  by  its  connection  with  the  anterior  ramus  of  cervical 


636  THE  BLOOD-VASCULAR  SYSTEM 

yil  (subclavian)  and  with  the  anterior  ramus  of  lumbar  V  (external  iliac),  forms  the 
internal  matnmary  (with  its  superior  epigastric  branch)  and  the  inferior  {deep)  epigastric 
arteries  of  the  adult. 

In  the  sacral  region,  the  adult  shows  evidence  of  segmental  vessels  in  branches  of  the  middle 
and  lateral  sacral  arteries;  the  latter  probably  representing  a  precostal  anastomosis.  Whether 
the  parietal  branches  may  be  derived  directly  from  segmental  sources,  or  whether  they  are  vessels 
of  new  formation,  has  not  been  determined  embryologicaUy.  The  obturator  would  appear  to 
be  segmentalifor  it  contributes  a  branch  to  the  mammary  anastomosis  which  persists  in  the  adult 
(pubic  brandies  of  obturator  and  inferior  epigastric).  If  the  connecting  branch  with  the  inferior 
epigastric  is  large,  the  obturator  may  lose  its  connection  with  the  hypogastric,  in  which  case  the 
latter  is  said  to  arise  from  the  former,  or  from  the  external  iliac, 

One  of  the  most  interesting  of  the  longitudinal  anastomoses  in  connection  with  the  dorsal 
segmentals  is  the  primitively  bilateral  preneural  anastomosis  extending  ventral  to  the  spinal 
cord 'and  connected,  beyond  the  first  spinal  segment,  with  each  internal  carotid  by  means  of  the 
right  and  left  aa.  cerebrales  vertebrales.  The  hypoglossus  artery  (p.  635)  having  lost  its  con- 
nection with  the  internal  carotid,  leaves  the  spinal  ramus  of  cervical  I  (third  part  of  the 
subclavian)  to  take  over  the  major  share  of  the  cerebral  supply.     A  process  of  blending  by  anas- 

FiG.  508. — Diagram  to  Show  the  Development  of  the  Arteries  or  the  Trunk  prom  the 
Aortic  Arches  and  Segmental  Arteries. 

The  arteries  which  persist  are  black;  those  which  degenerate  are  in  outhne;  those  newly  formed 
are  shaded.     (After  Mall.) 


txternal  Cl 
Bulbus  Arteriosus'; 

fulmooaryArleij  ' 
SabclariaffArterCffs ' 


J)eep£plgastricAtterK. 
femora  t  Artery  ,^ 
Umbilical  Artery, 


tomosis  now  occurs  resulting  in  the  single  basilar  and  anterior  spinal  arteries  of  the  adult.  The 
posterior  communicating,  proximal  portions  of  the  posterior  cerebrals,  the  fourth  part  of  the  vevte- 
brals,  and  the  right  and  left  roots  in  the  anterior  spinals  of  the  adult  alone  retain  the  primitive 
arrangement  and  testify  to  the  double  nature  of  the  original  anastomosis.  Asymmetry  in  the 
vertebrals  and  other  irregularities  in  the  adult  can  usually  be  explained  on  developmental 
grounds.  The  postneural  anastomosis,  which  joins  the  preneural  at  about  the  first  cervical  seg- 
ment, retains  its  bilaterality  throughout  to  form  tlie  paired  posterior  spinal  arteries  of  the  adult. 
The  lateral  segmental  arteries  take  origin  from  the  aorta  in  series,  intermediate  in  position 
between  the  dorsal  and  ventral  segmentals.  They  reach  their  fullest  development  in  embryos 
of  about  8  mm.,  when  they  extend  from  the  seventh  cervical  to  the  twelfth  thoracic  segment  and 
supply  the  mesonephros.  At  this  stage  Broman  found  twenty  arteries  on  each  side,  many  of 
which  were  non-segmental.  As  the  suprarenals  and  gonads  develop,  they  each  receive  branches 
from  several  mesonephric  arteries.  The  latter  arteries  now  undergo  rapid  retrogression  and 
the  suprarenal  and  gonadie  branches  are  shifted  caudally  through  the  mesonephric  series  to 
newly  formed  (non-segmental)  arteries  opposite  the  upper  lumbar  segments.  Finally  there 
remain  three  suprarenal  arteries  opposite  the  twelfth  thoracic  and  first  and  second  lumbar 
segments  and  a  gonadie  artery  {ovarian  or  internal  spermatic  of  the  adult)  opposite  the  third 
lumbar  segment.  AU  of  these  vessels  now  appear  to  be  direct  branches  from  the  aorta.  Of  the 
three  suprarenal  branches,  the  upper  and  lower  each  gives  a  large  branch  to  the  diaphragm  and 
kidney  respectively  and  become  the  inferior  phrenic  and  renal  arteries  of  the  adult.  The  middle 
becomes  the  middle  suprarenal  of  the  adult.  Felix  puts  a  somewhat  different  interpretation  upon 
the  origin  of  the  vessels  persisting  in  the  lumbar  region  after  the  disappearance  of  the  thoracic 
mesonephric  arteries.  He  finds  in  an  embryo  of  18  mm.  nine  arteries  on  either  side,  extending 
from  the  ninth  thoracic  to  the  third  lumbar  segment,  all  of  which  he  looks  upon  as  mesonephric. 
These  he  classifies  into  tlxree  groups: — Cranial,  which  reach  the  mesonephros  by  passing  dorsal 
to  the  suprarenal;  caudal  which  pass  ventral  to  the  suprarenal,  and  middle  which  pass  through 
it.  Inasmuch  as  the  arteries  anastomose  in  the  mesonephros  there  is  great  liability  to  variation 
in  the  number  and  position  of  the  stems  which  persist  in  the  adult.     The  suprarenal  arteries 


VARIATIONS  OF  THE  ARTERIES  637 

are  usually  derived  from  the  caudal  group,  the  renals  from  the  caudal  or  middle  and  the  sper- 
matics  from  the  middle.  When  accessory  renals  or  spermatics  occur  in  the  adult  their  place 
of  origin  and  course  will  generally  indicate  the  group  from  which  they  are  derived. 

The  ventral  segmental  arteries  appear  very  early.  In  an  embryo  of  seven  somites  (ca.  2 
mm.)  described  by  Dandy*  there  was  a  right  and  a  left  series  of  twelve  arteries,  each  arising 
from  the  still  ununited  dorsal  aortce,  the  artery  at  the  caudal  end  of  each  series  being  the  um- 
bihcal,  and  the  remainder  vitelline  arteries.  In  an  embryo  of  4.9  mm.  (35  somites)  described 
by  IngaUst  the  originally  paired  viteUine  arteries  had  united  (as  had  the  dorsal  aortffi  in  part) 
to  form  unpaired  vessels.  There  were  unpaired  vessels  as  follows:  one  opposite  the  seventh 
cervical  segment  (co^hac);  five  opposite  the  first  four  thoracic  (omphalo-mesenterics,  united 
by  a  longitudinal  anastomosis),  and  one  vessel  of  doubtful  significance  opposite  the  fifth  and 
sixth  thoracic  segments.  The  paired  umbiUoal  arteries  were  opposite  the  first  lumbar  segment. 
No  other  ventral  arteries  were  present. 

It  has  been  found  from  more  fully  developed  stages  that  the  inferior  mesenteric  artei-y  is 
distinguishable  at  a  stage  of  8  mm.  opposite  the  second  lumbar  segment.  Also  that  the  ventral 
segmental  vessels  undergo  a  process  of  migration  until  they  reach  their  definitive  positions, 
i.  e.,  the  coeliac  opposite  the  twelfth  thoracic  segment,  the  superior  mesenteric  opposite  the  first, 
the  inferior  mesenteric  opposite  the  third,  and  the  umbilicals  opposite  the  fourth  lumbar  seg- 
ments, respectively.  The  cesophageal  arteries  of  the  adult  do  not  belong  to  this  series;  but 
seem  to  be  vessels  of  later  formation. 

The  umbilical  arteries,  by  means  of  secondary  anastomosis,  move  laterally  upon  the  aorta 
so  as  to  pass  lateral  to  the  Wolffian  ducts  instead  of  medial .  The  proximal  portion  of  each  um- 
bilical artery  becomes  the  common  iliac  of  the  adult;  its  continuation  is  represented  by  the  hypo- 
gastric and  its  umbilical  branch.  The  external  iliac  appears  to  be  derived  from  the  dorsal  seg- 
mental artery  of  the  fifth  lumbar  segment,  and  the  parietal  branches  of  the  hypogastric 
from  corresponding  sacral  segmentals  acquired  by  anastomosis.  How  such  anastomoses  be- 
tween the  umbihcals  and  the  dorsal  segmentals  come  about  has  not  been  ascertained. 

2.  VARIATIONS 

Aorta  and  pulmonary  artery. — The  variations  met  with  in  the  arch  of  the  aorta  are  usually 
to  be  explained  as  persistent  foetal  conditions,  and  are  often  associated  with  abnormahties  of 
the  heart.  Many  of  the  variations  are  due  to  different  modes  of  transformation  of  the  primitive 
system  of  aortic  arches.  Since  the  aorta  and  pulmonary  artery  develop  from  a  common  conus 
and  truncus  arteriosus,  irregular  and  imperfect  development  of  the  aortic  septum  may  also 
produce  numerous  variations. 

It  has  been  seen  that  at  one  stage  of  development  two  fourth  arches,  a  right  and  a  left,  are 
present,  and  such  a  condition  is  occasionally  persistent  in  the  adult.  In  such  cases,  owing 
to  the  portion  of  the  aorta  derived  from  the  bulbus  arteriosus  being  directed  upward  and  to 
the  right  and  the  descending  aorta  lying  in  the  left  side  of  the  vertebral  column,  the  right  arch 
passes  from  right  to  left  behind  the  oesophagus,  which  thus  seems  to  perforate  the  aortic  arch. 

Another  variation  occasionally  seen  is  the  occurrence  of  an  aortic  arch  curving  to  the  right 
instead  of  the  left.  This  may  be  due  to  a  persistence  of  the  lower  portion  of  the  right  dorsal 
longitudinal  stem  and  the  disappearance  of  the  left,  as  shown  in  fig.  506;  or  it  may  be  associated 
with  a  complete  inversion  of  all  the  viscera,  a  situs  inversus. 

If  the  lower  portion  of  the  right  dorsal  longitudinal  trunk  should  persist,  and  the  part  of  it 
which  normally  forms  the  proximal  part  of  the  right  subclavian  should  disappear,  the  right 
subclavian  would  arise  from  the  descending  portion  of  the  aortic  arch.  It  is  to  be  noted 
that  in  such  cases  the  subclavian  passes  behind  the  oesophagus  and  below  the  right 
inferior  laryngeal  nerve.  Partial  persistence  of  the  lower  portion  of  the  right  dorsal  longitu- 
dinal trunk  is  represented  in  the  arteria  aberrans  (see  p.  590). 

Another  group  of  variations  is  based  on  the  persistence  of  the  ductus  arteriosus,  which  is 
derived  from  the  sixth  aortic  arch.  With  this  group  belong  the  cases  in  which  the  pulmonary 
artery  arises  from  the  aorta;  that  is,  where  the  blood  of  the  pulmonary  arteries  passes  from  the 
aorta  through  the  ductus  arteriosus. 

Variations  in  the  number  and  the  position  of  the  vessels  arising  from  the  arch  are  extremely 
great,  and  many  of  these  conditions  are  found  normally  in  other  mammals  or  birds.  There  may 
be  from  one  to  six  branches.  The  case  of  one  branch  is  the  normal  in  the  horse.  It  involves  the 
fusion  of  the  two  aortic  stems  and  the  shortening  of  the  fourth  arch  so  that  the  left  subclavian 
joins  with  the  common  stem.  The  avian  form  with  trto  innominate  arteries  is  extremely  rare. 
A  more  common  form  is  the  one  found  in  most  apes,  in  which  the  innominate  and  left  carotid 
form  one  branch ;  in  rare  instances  the  three  branches  are  the  two  subclavians  and  a  general 
carotid  artery.  When  there  are  more  than  three  branches  the  vertebral  arteries  are  added,  or 
the  extra  branch  may  be  the  thyreoidea  ima  (fig.  443).  The  commonest  form  with  four  vessels 
is  the  one  in  which  the  left  vertebral  arises  between  the  left  carotid  and  subclavian.  A  rarer 
form  is  to  be  found  when  the  order  is  right  subclavian,  right  carotid,  left  carotid,  and  left  sub- 
clavian. Where  there  are  five  arteries,  the  extra  ones  are  the  right  subclavian  and  left  vertebral. 
The  case  of  six  branches  is  due  to  the  separate  origin  of  both  vertebrals  and  both  subclavians. 
The  manner  in  which  the  vertebral  artery  may  arise  from  the  adult  aortic  arch  is  indicated 
in  fig.  506. 

The  innominate  artery  may  be  absent,  or  may  give  off  additional  branches  (see  Aokta). 
It  may  be  longer  than  usual  and,  bending  to  the  left,  ascend  in  front  of  the  trachea  (or  more 
rarely  behind  the  trachea  and  oesophagus)  to  turn  again  to  the  right.  The  thyroidea  ima  has 
been  referred  to  (p.  532). 

Carotid  arteries. — The  common  carotid  may  be  absent  or  bifurcate  higher  or  lower  than  usual. 

*  Am.  Journ.  Anat.,  Vol.  10,  1910. 
t  Arch.  f.  mikr.  Anat.,  Bd.  70,  1907. 


638  THE  BLOOD-VASCULAR  SYSTEM 

Itjmay  not  bifurcate  at  all,  in  which  case  the  branches  usually  arising  from  the  external  car- 
otid are  derived  from  the  common.  The  ascending  pharyngeal  and  superior  thyreoid  occa- 
sionally arise  from  an  otherwise  normal  common  carotid.  Unusual  origin  ^of  the  common 
carotids  has  been  referred  to  (see  Aorta). 

Branches  of  the  carotid  arteries. — The  superior  thyreoid,  lingual  and  external  maxillary 
sometimes  have  a  common  stem  of  origin.  The  superior  thyreoid  artery  varies  in  size  inversely 
with  the  inferior.  The  external  maxillary  occasionally  terminates  in  its  submental  branch. 
In  such  cases  the  main  supply  of  the  face  is  taken  over  by  an  abnormally  large  dorsal  nasal 
branch  of  the  ophthalmic,  or  transverse  facial  branch  of  the  temporal  artery.  The  occipital 
sometimes  arises  from  the  internal  carotid  or  from  the  ascending  cervical.  The  ascending 
pharyngeal  is  very  variable  in  its  place  of  origin  from  the  external  carotid,  it  may  arise  from  the 
common  or  internal. 

Out  of  447  arteries  examined,  the  second  portion  of  the  internal  maxillary  passed  lateral  to 
the  external  pterygoid  muscle  in  55  per  cent.,  and  medial  to  it  in  45  per  cent,  of  cases.  When 
medial  to  this  muscle  the  internal  maxillary  sometimes  passes  medial  to  the  inferior  alveolar 
and  lingual  nerves  and  occasionally  between  them.  The  variability  in  the  course  of  this  artery 
appears  to  depend  on  a  tendency  to  reduplication  of  the  infraorbital  branch  of  the  stapedial 
artery  (p.  634)  in  the  neighbourhood  of  the  mandibular  nerve.  Such  a  condition  was  found 
by  Thyng  in  a  17  mm.  human  embryo.  When  the  internal  maxiUary  passes  medial  to  the  ex- 
ternal pterygoid  there  is  often  a  parallel  anastomosing  channel  between  the  posterior  deep 
temporal  and  buccal  branches. 

The  ophthalmic  artery  may  arise,  wholly  or  in  part,  from  the  middle  meningeal,  or  vice  versa. 
This  is  due  to  the  anastomosis  between  the  supraorbital  branch  of  the  stapedial  and  the  oph- 
thalmic in  the  embryo. 

Subclavian  artery. — Irregularities  of  origin  have  been  referred  to  (see  Aorta). 

The  branches  of  the  subclavian  artery  are  very  variable  in  their  place  of  origin  (p.  559). 
The  vertebral  may  arise  directly  from  the  arch  of  the  aorta  (p.  537)  or  take  an  unusual  course 
in  the  neck.  It  may  enter  the  foramen  transversarium  of  the  fourth  or  fifth  cervical  vertebra 
instead  of  the  sixth;  this  arises  from  substitution  of  an  embryonic  precostal  anastomosis  in  these 
segments  for  the  usual  postcostal.  By  a  converse  substitution  it  may  enter  the  seventh.  The 
aa.  transversa  colli  and  scapulas  vary  inversely  in  size.  The  arteria  aberrans  connecting  the  right 
subclavian  with  the  dorsal  aorta  has  been  referred  to  (p.  634). 

The  thoracic  aorta. — Transposition,  and  the  arteria  aberrans  have  been  referred  to  above. 

Branches  of  the  thoracic  aorta. — The  intercostal  arteries  are  hable  to  numerical  variation, 
evidently  owing  to  the  occurrence  of  precostal  intersegmental  anastomoses  between  the  embry- 
onic dorsal  segmentals.  A  common  longitudinal  stem  may  even  take  over  the  vessels  of  both 
sides.  The  anterior  spinal  artery  usually  shows  lack  of  median  symmetry  which  indicates  the 
bilaterality  of  its  origin  (p.  636).  The  arrangement  of  the  bronchial  arteries  is  hable  to,  much 
variation;  this  has  not  received  adequate  explanation. 

The  abdominal  aorta  sometimes  divides  as  low  as  the  fifth  lumbar  vertebra,  occasionally 
higher  than  usual,  depending  upon  the  definitive  position  taken  by  the  umbiUcal  arteries  (p. 
637).  Cases  are  on  record  of  accessoiy  pulmonary  arteries  arising  by  a  single  stem  from  the 
abdommal  aorta,  which  passes  into  the  thorax  along  the  oesophagus.  The  aorta  and  vena  cava 
inferior  may  be  transposed  either  as  a  part  of  situs  inversus  or  as  an  abnormality  of  the  venous 
system. 

Branches  of  the  abdominal  aorta. — The  lumbar  arteries  are  subject  to  the  same  type  of 
variation  as  occurs  in  the  intercostals.  There  may  be  a  loop  connecting  the  caeliac  and  superior 
mesenteric  arteries.  Any  or  all  of  the  branches  of  the  coeUac  may  arise  from  the  superior 
mesenteric  (coelio-mesenteric  in  the  latter  case)  or  directly  from  the  aorta.  The  instabiUty  of 
the  coeUac  and  superior  mesenteric  branches  is  favored  by  the  rapid  cranio-caudal  migration 
of  the  two  trunks;  intersegmental  anastomosis,  in  some  cases,  may  be  a  factor  also.  There  is 
very  great  variation  in  the  number  of  branches  given  off  by  the  superior  mesenteric  and  in  the 
details  of  their  arrangement.  This  is  a  natural  result  of  the  number  of  possible  routes  which 
may  be  taken  by  the  blood;  these  resemble,  in  their  variety,  those  of  an  embryonic  circulation. 
The  region  of  supply  of  the  inferior  mesenteric  artery  is  sometimes  taken  over  entirely  or  in  part 
(e.  g.,  middle  colic)  by  the  superior  mesenteric.  An  omphalo-mesenteric  artery,  in  rare  cases, 
arises  from  the  superior  mesenteric  or  one  of  its  branches.  It  passes  to  the  navel  and  anasto- 
moses with  inferior  epigastric  and  with  the  small  arteries  accompanying  the  round  ligament  of 
the  liver  or  the  urachus. 

Accessory  renal  arteries  are  very  common;  as  many  as  six  have  been  recorded.  These 
may  arise  from  the  aorta,  middle  sacral,  inferior  phrenic,  middle  suprarenal  or  internal  spermatic. 
According  to  Felix,  these  are  to  be  regarded  as  persistent  mesonephric  arteries.  Those  arising 
above  the  regular  renal  frequently  enter  the  kidney  dorsal  to  the  hilum.  Those  below  it  are 
more  apt  to  be  ventraUy  placed. 

Nearly  all  possible  varieties  of  origin  are  met  with  in  the  inferior  phrenic,  middle  supra- 
renal, internal  spermatic  and  accessory  renal  arteries  which  find  explanation  in  the  caudal  migra- 
tion of,  and  anastomosis  between,  the  embryonic  representatives  of  these  vessels.  The  oc- 
casional origin  of  the  inferior  phrenic  from  the  coeUac  (or  its  branches)  or  from  the  superior 
mesenteric;  of  the  internal  spermatic  or  the  middle  suprarenal  from  the  lumbar  arteries,  or 
of  an  accessory  renal  from  the  inferior  mesenteric  must  be  taken  as  indicating  embryom'c 
anastomoses  between  the  dorsal,  lateral,  or  ventral  segmental  arteries,  as  the  case  may  be. 

The  iliac  and  hypogastric  arteries. — The  length  of  the  common  iZiac  depends  upon  the  site  of 
aortic  bifurcation  (p.  590) ;  also  upon  the  site  of  division  of  the  common  iliac  into  external  iliac 
and  hypogastric.  If  these  spring  directly  from  the  aorta  (as  they  do  in  rare  cases)  the  common 
iliac  is  absent.  The  trunk  formed  by  the  common  iliac  and  hypogastric  is  the  proximal  portion 
of  the  embryonic  umbilical  artery.  The  manner  in  which  tliis  takes  over  a  dorsal  segmental 
artery  (probably  the  fifth  lumbar)  to  become  the  external  iliac  is  not  sufficiently  undersood  to 
account  for  variations  in  this  region. 


VARIATIONS  OF  THE  ARTERIES  639 

The  branches  of  the  hypogastric  artery  show  great  variation  in  their  origin,  and  there  is 
frequently  no  separation  of  the  hj'pogastrio  into  anterior  and  posterior  divisions.  Rarely 
the  branches  all  take  origin  from  the  external  iUao,  in  which  case  the  hypogastric  (as  such) 
is  absent.  The  obturator  artery  may  arise  from  the  inferior  epigastric,  or  vice  versa  (p.  615). 
The  arleria  comitans  n.  ischiadici  may  be  larger  than  usual  and  form  a  very  pronounced  anas- 
tomosis with  the  popliteal.  In  rare  cases  the  main  blood-supply  of  the  lower  limb  is  thus 
derived  from  the  inferior  gluteal  which  is  the  primitive  embryonic  condition  (p.  640).  .The 
vesical  and  vaginal  arteries  are  liable  to  variation  in  their  relative  areas  of  distribution.  The 
internal  pudendal  is  sometimes  small  and  maj'  terminate  as  the  perineal  artery,  in  these  cases 
the  urogenital  region  is  supplied  largely  by  the  accessory  pudendal  (p.  610). 

B.  ARTERIES  OF  THE  EXTREMITIES 

1.  MORPHOGENESIS 

The  arteries  of  the  adult  extremities  represent  surviving  chaimels  resulting  from  the 
selection  of  a  chosen  path  traversing  the  perineural  arterial  plexuses  of  the  early  embryonic 
limb. 

At  present  there  is  little  unanimity  of  opinion  as  to  whether  the  pattern  of  the  developing 
nerve  trunks  is  specifically  reproduced  by  the  primitive  arterial  plexuses  or  whether  the  un- 
doubted similarity  between  the  two  is  of  a  more  general  nature.  There  occurs  in  either  ex- 
tremity one  case  in  which  an  artery  of  fundamental  importance  follows  a  course  practically 
independent  of  nerve  distribution.  The  volar  interosseous,  in  the  forearm,  and  the  peroneal, 
in  the  leg,  are  accompanied  by  insignificant  nerves  (n.  to  pronator  quadratus,  and  n.  to  fie.xor 
hallucis  longus  respectively)  which,  moreover,  do  not  ex-tend  the  full  length  of  the  arteries  in 
question. 

The  blood  of  a  developing  limb,  having  traversed  the  proximal  segment  by  means  of  the 
arterial  plexus  around  a  single  nerve,  has  the  choice  of  several  possible  paths  by  which  to 
reach  the  digits.  The  selected  channel  becomes,  for  the  time,  the  principal  artery  of  the  distal 
segment.  This  presently  gives  way  to  a  second  favoured  route,  which  may  persist  or  again 
give  way  to  a  third.  Thus,  finally,  the  adult  arrangement  is  established.  This  process  of 
alternation  is  the  cause  of  many  of  the  commoner  variations  for,  if  it  does  not  proceed  to  its 
usual  termination,  a  small  vessel,  commonly  rated  as  a  branch,  may  testify  to  its  earher  im- 
portance by  appearing  as  one  of  the  chief  vessels  of  the  part. 

In  the  upper  extremity  the  blood  first  traverses  the  peri-median  plexus  (which  becomes 
later  the  axillo-brachial  trunk)  and  flows  to  the  digits  mainly  by  the  volar  interosseous  route. 
Next  the  volar  interosseous  d-nandles  in  favour  of  the  median.  The  median  afterward  relin- 
quishes its  function  to  the  radial  and  ulnar. 

In  the  lower  extremity  the  main  blood-flow  at  first  follows  the  peri-sciatic  plexus  from 
which  it  is  dehvered  to  the  digits  chiefly  by  the  peroneal  artery.  The  peroneal  artery  passes 
from  the  sole  to  the  dorsum  of  the  foot  through  the  sinus  pedis,  and  from  here  suppUes  the  digits. 
The  anterior  and  posterior  tibial  are  at  first  small,  the  latter  supplj-ing  the  plantar  digital 
arteries.  At  a  stage  of  10  millimetres  the  femoral  artery  is  represented  by  a  peri-saphenous 
plexus  which  anastomoses  with  the  peri-sciatic  plexus  near  the  knee.  The  peri-femoral  plexus 
rapidly  consoUdates  into  the  femoral  and  genu  suprema  arteries.  The  femoral  later  takes 
over  the  pophleal  as  its  direct  continuation,  and  the  origin  of  the  genu  suprema  marks  the 
boundary  between  the  femoral  and  ischiadic  zones  of  the  main  trunk.  Finally  the  peroneal 
gives  place  to  the  anterior  and  posterior  tibial  arteries.  The  portion  of  the  peroneal  perforating 
the  tarsus  disappears.  In  so  doing  it  leaves  the  original  termination  of  the  peroneal  artery 
connected  with  the  dorsalis  pedis  to  become  the  arcuate  branch  of  the  latter. 

2.  VARIATIONS 

The  variations  of  the  arteries  of  the  upper  extremity  may  be  divided  into  two  categories, 
A  certain  number  of  them,  particularly  those  occurring  in  the  forearm  and  hand,  are  directly 
traceable  to  the  unusual  persistence  of  one  or  more  of  the  embryonic  channels;  or,  when  varia- 
tion involves  magnitude  only,  to  reciprocal  variations  in  the  size  of  the  normal  vessels.  The 
commoner  and  more  important  variations  of  the  arterial  distribution,  however,  arise  in  a  manner 
much  less  susceptible  to  ready  explanation.  They  depend,  in  fact,  upon  variations  in  the  course 
taken  by  the  single  or  double  route  which,  surviving  from  the  intricacies  of  the  peri-median 
plexus,  persists  to  maturity.     These  will  be  referred  to  later. 

The  volar  interosseous  artery  maj'  be  unusually  large.  It  may  reinforce  a  deficient  radia 
or  ulnar  through  the  volar  carpal  arterj%  or  its  dorsal  carpal  branch  may  join  the  radial  at  the 
back  of  the  wrist.  In  very  rare  cases  the  volar  interosseous,  together  with  a  large  ulnar  artery, 
replaces  the  radial  altogether. 

A  large  median  artery  may  participate  in  the  palmar  supply  of  the  fingers,  either  b}' joining 
the  superficial  volar  arch  or  (the  arch  being  absent)  by  breaking  directly  into  digital 
branches.  The  median,  when  large,  occasionally  replaces  the  ulnar,  verj'  rarely  the  radial, 
and  frequently  the  superficial  volar. 

The  superficial  volar  arch  may  be  small,  with  compensation  by  the  deep,  or  absent.  In 
the  latter  case  the  digital  arteries  may  come  directly  from  the  ulnar  and  radial,  ulnar  and  median 
or  median  and  radial.  In  the  absence  of  the  superficial  volar,  which  is  ver3-  frequent,  the  super- 
ficial arch  is  completed  by  the  princeps  pollicis  or  the  volaris  radiahs  indicis. 


640  THE  BLOOD-VASCULAR  SYSTEM 

Cases  are  on  record  in  which  the  ulnar  artery,  arising  in  the  middle  of  the  arm  passes  behind 
the  medial  epicondyle  to  follow  the  nerve  in  the  forearm  as  usual.  The  ulnar  artery  here 
replaces  the  superior  ulnar  collateral  and  the  ulnar  recurrent.  This  anomaly  is  explained  in  a 
striking  way  by  the  account  given  by  de  Vriese  of  the  development  of  the  vessels  of  the  upper 
extremity. 

Several  important  variations  in  the  distribution  of  the  main  vessels  belong  to  the  second 
category.  It  is  not  uncommon  for  tioo  arteries  to  arise  from  the  primitive  peri-median  plexus 
of  the  arm.  In  such  cases  one  artery  usuaUy  takes  a  course  dorsal  to  the  median  nerve,  i.  e., 
it  is  crossed  medio-lateraUy  by  the  medial  head  of  the  nerve  and  in  the  contrary  direction  by 
the  nerve  itseh.  Its  course  corresponds  to  that  taken  by  the  ordinary  axiUo-brachial  trunk; 
it  is  known  as  the  deep  brachial  artery.  The  other  vessel  takes  a  course  ventral  to  the  median, 
nerve,  and  is  known  as  the  superficial  brachial.  The  superficial  brachial  may  join  its  com- 
panion artery,  at  or  above  the  elbow,  or  one  of  the  forearm  vessels  arising  from  it.  In  either 
case  the  superficial  brachial  is  referred  to  as  a  "vas  aberrans."  Persistence  of  the  superficial 
brachial  further  operates  as  a  frequent  cause  of  abnormality  in  the  forearm  in  that  it  is  often 
continued  directly  into  one  or  moi-e  of  the  chief  arteries  of  the  latter,  the  deep  brachial  taking 
the  remainder.  This  condition  is  classified  as  a  high  origin  of  the  radial,  ulnar,  etc.,  as  the  case 
may  be. 

There  is  another  type  of  variation  belonging  to  the  same  category.  In  this,  one  large 
artery  only  occurs  above  the  elbow  which,  instead  of  following  the  normal  course  of  the  brachial, 
passes,  entirely  or  in  part,  ventral  to  the  median  nerve.  In  the  first  case  this  vessel  represents 
the  superficial  brachial,  the  deep  being  absent.  In  the  second  it  corresponds  in  its  upper  part 
to  the  deep  brachial  and  in  its  lower  to  the  superficial,  the  two  components  varying  in  inverse 
proportion. 

E.  MiiUer*,  who  has  made  a  study  of  the  variations  belonging  to  this  category,  classifies 
the  abnormal  artery  occurring  in  cases  of  vas  aberrans,  of  high  origin  of  fore  arm- vessels,  and 
of  single  abnormal  brachial,  according  to  the  proportion  of  superficial  brachial  present  in 
any  particular  example,  as  a.  brachialis  superficialis  superior  media,  inferior,  or  ima.  In  an 
embryo  of  11.7  milhmetres  he  found  a  system  of  arterial  channels  in  relation  with  the  median 
nerve  out  of  which  any  variation  of  this  category  might  have  been  produced  during  further 
development. 

In  cases  in  which  the  superficial  brachial  alone  persists,  the  branches  of  the  axillary  (and 
sometimes  the  profunda  brachii  and  superior  ulnar  collateral)  arise  from  a  common  (deep 
brachial)  trunk  called  the  profunda  axillaris.  In  cases  in  which  the  deep  and  superficial  brachial 
co-exist  examples  of  continuation  of  the  superficial  brachial  into  the  radial  are  rather  common, 
continuation  into  the  ulnar  less  so.  Continuation  of  the  superficial  brachial  into  the  median, 
interosseous,  or  of  posterior  interosseous  arteries  occasionally  occur,  but  they  are  rare.  In  any 
case  of  high  origin  a  cross  branch  may  connect  the  high  vessel  with  the  deep  brachial  in  the 
neighbourhood  of  the  elbow.  The  ulnar  artery  when  arising  high  is  often  superficial  to  the 
forearm  flexors  (a  fact  which  has  not  been  explained  on  embryological  grounds),  the  inter- 
osseous arising  from  the  radial. 

The  variations  occurring  in  the  arteries  of  the  lower  extremity  are  usually  compensatory, 
or  due  to  persistence  of  alternative  embryonic  channels.  The  sciatic  (inferior  gluteal)  very 
rarely  persists  as  the  main  artery  of  supply.  In  such  cases  the  small  femoral  ends  as  the  genu 
suprema  which  then  appears  to  be  a  branch  of  the  profunda. 

The  profunda  is  irregular;  its  origin  may  occur  anywhere  between  the  inguinal  Ugament 
and  a  point  four  inches  below  it.  The  median  or  lateral  circumflex  may  arise  from  the  femoral. 
The  branches  of  the  latter  commonly  arise  separately  from  the  profunda,  or  from  the  femoral. 
The  popliteal  does  not  vary  much  in  its  point  of  division.  High  division  is  commoner  than  low, 
but  is  never  higher  than  the  lower  epiphyseal  fine  of  the  femur. 

The  anterior  tibial  may  be  small  and  only  reach  the  middle  or  lower  part  of  the  leg.  In 
such  cases  an  enlarged  anterior  peroneal  may  end  as  the  dorsahs  pedis,  or  the  dorsal  metatarsal 
arteries  may  be  supphed  from  the  plantar  arch.  Cases  in  which  the  anterior  peroneal  supplies 
the  dorsum  of  the  foot  do  not  represent  a  dkect  inheritance  of  the  embryonic  method  by  which 
the  peroneal  artery  performs  this  office.  The  embryonic  route  of  the  peroneal  to  the  dorsum 
of  the  foot  is  transtarsal.  The  anterior  tibial  artery  may  reach  the  extensor  surface  of  the  leg  by 
accompanying  the  peroneal  nerve.  This  case,  hke  that  of  the  ulnar  artery  passing  around  the 
medial  epicondyle,  is  interesting  in  connection  with  the  work  of  de  Vriese.      ^  .  c      ■ 

The  posterior  tibial  artery  may  be  absent  or  small,  the  peroneal  replacing  it,  or  remforcmg 
it  by  means  of  the  ramus  communicans.  Absence  of  the  peroneal  has  been  recorded  by  Otto 
and  W.  Krause,  but  these  cases  are  explained  by  Barkow  as  being  suppression  of  the  posterior 
tibial  artery  between  the  origin  of  the  peroneal  and  the  communicating  branch  (Quain). 

The  lateral  plantar  is  sometimes  very  small,  in  which  case  the  plantar  arch  may  be  supphed 
by  a  large  deep  plantar.     In  rare  cases  there  is  a  superficial  plantar  arch  as  in  the  embryo. 

3.  THE  SYSTEMIC  VEINS 

The  systemic  veins  are  naturally  divided  into  three  groups — (1)  the  veins  of 
the  heart;  (2)  the  vena  cava  superior  and  its  tributaries,  namely  the  veins  of  the 
head,  neck,  upper  extremity,  and  thorax;  and  (3)  the  vena' cava  inferior  and  its 
tributaries,  namely,  the  portal  system,  and  the  veins  of  the  abdomen,  pelvis,  and 
lower  extremity. 

*  E.  Miiller,  Anat.  Hefte,  No.  22,  1903. 


THE  INNOMINATE  VEINS  641 

I.  THE  VEINS  OF  THE  HEART 

The  veins  of  the  heart  have  already  been  described  (p.  520). 

II.  THE  VENA  CAVA  SUPERIOR  AND  ITS  TRIBUTARIES 

THE  VENA  CAVA  SUPERIOR 

The  vena  cava  superior  (fig.  509)  carries  to  the  heart  the  blood  returned  from 
the  head  and  neck  and  upper  extremities  through  the  right  and  left  innominate 
veins,  and  from  the  walls  of  the  thorax,  either  directly  through  the  azygos  vein, 
or  indirectly  through  the  innominate  veins.  It  is  formed  (fig.  509)  by  the  con- 
fluence of  the  right  and  left  innominate  veins  behind  the  first  right  sterno-chondral 
articulation.  Descending  from  its  origin  in  a  gentle  curve  with  its  convexity  to 
the  right  and  in  a  direction  slightly  backward  behind  the  sternal  end  of  the  first 
and  second  intercostal  spaces  and  second  costal  cartilage,  it  terminates  in  the 
right  atrium  of  the  heart  on  a  level  with  the  third  right  costal  cartilage  in  front  and 
the  seventh  thoracic  vertebra  behind.  It  measures  about  7  to  8  cm.  (3  in.)  in 
length.  A  little  more  than  its  lower  half  (4  cm.)  is  contained  within  the  pericar- 
dium, the  serous  layer  of  that  membrane  being  reflected  obliquely  over  it  imme- 
diately below  the  spot  where  it  is  joined  by  the  vena  azygos,  and  on  a  lower 
level  than  the  reflexion  of  the  pericardium  on  the  aorta.  The  superior  vena 
cava  contains  no  valves. 

Relations. — In  front,  in  addition  to  the  first  and  second  intercostal  spaces  and  the  second 
costal  cartilage,  it  is  covered  by  the  remains  of  the  thymus  gland,  the  intrathoracic  fascia,  and 
the  pericardium,  and  is  overlapped  by  the  right  pleura  and  lung. 

Behind  (fig.  609)  are  the  vena  azygos  (major),  the  right  bronchus,  the  right  pulmonary 
artery,  and  the  superior  right  pulmonary  vein;  and  below,  the  fibrous  layer  of  the  pericardium. 
The  serous  layer  is  reflected  over  the  front  and  sides  of  the  vessel,  but  not  over  its  posterior 
part. 

To  the  right  side  are  the  right  lung  and  pleura  and  the  phrenic  nei've. 

To  the  left  side  are  the  innominate  artery  and  the  ascending  aorta. 

Tributaries. — In  addition  to  the  right  and  left  innominate  veins  and  the  vena 
azygos  it  receives  small  veins  from  the  mediastinum  and  pericardium. 

THE  INNOMINATE  VEINS 

The  innominate  or  brachio-cephalic  veins  [vv.  anonymae]  return  the  blood 
from  the  head  and  neck  and  upper  extremity.  They  are  formed  on  each  side  by 
the  confluence  of  the  internal  jugular  and  subclavian  veins  behind  the  sternal 
end  of  the  clavicle.  They  terminate  behind  the  first  costal  cartilage  on  the  right 
side  by  uniting  to  form  the  vena  cava  superior.  The  innominate  veins  have  no 
valves. 

The  right  innominate  vein  [v.  anonyma  dextra]  (fig.  509)  measures  about  2  to 
3  cm.  (1  to  H  in-)  in  length,  and  descends  from  its  origin  behind  the  sternal  end 
of  the  clavicle,  very  slightly  forward  and  medially,  along  the  right  side  of  the  sub- 
clavian and  innominate  arteries,  to  its  junction  with  the  left  vein  behind  the  first 
costal  cartilage  close  to  the  sternum.     It  is  superficial  to  the  innominate  artery. 

Relations. — In  front  are  the  origins  of  the  sterno-hyoid  and  sterno-thyreoid  muscles, 
the  clavicle,  the  first  costal  cartilage,  and  the  remains  of  the  thymus  gland. 

Behind  are  the  pleura  and  lung. 

To  the  right  are  the  right  pleura  and  lung  and  the  phrenic  nerve. 

To  the  left  (fig.  509)  are  the  right  subclavian  artery,  the  innominate  artery,  the  right 
vagus  nerve,  and  the  trachea. 

The  left  innominate  vein  [v.  anonyma  sinistra]  (fig.  509)  measures  6  to  7.5  cm. 
(2|  to  3  in.)  in  length,  and  extends  from  its  origin  behind  the  sternal  end  of  the 
left  clavicle  obHqueljr  across  the  three  main  branches  of  the  arch  of  the  aorta,  to 
unite  with  the  right  innominate  vein  behind  the  cartilage  of  the  first  rib  close  to 
the  sternum  to  form  the  vena  cava  superior.  In  this  course  it  runs  from  left 
to  right  with  an  inclination  downward  and  slightly  backward.  A  line  drawn 
obliquely  across  the  upper  half  of  the  manubrium  of  the  sternum,  from  the  sterno- 


642 


THE  BLOOD-VASCULAR  SYSTEM 


clavicular  articulation  on  the  left  side  to  the  lower  border  of  the  first  costal  carti- 
lage at  its  junction  with  the  sternum  on  the  right  side,  will  indicate  its  course. 
The  left  innominate  vein  is  on  a  level  with  the  top  of  the  sternum  at  birth. 

Relations. — In  front,  in  addition  to  the  manubrium  of  the  sternum,  it  has  the  origins  of 
the  sterno-hyoid  and  sterno-thyreoid  muscles,  and  the  remains  of  the  thymus  gland,  the  sternal 
end  of  the  left  clavicle,  and  the  sterno-clavicular  articulation. 

Behind  are  the  three  chief  arteries  arising  from  the  arch  of  the  aorta,  the  trachea,  and  the 
left  phrenic  and  left  vagus  nerves. 

Below  it  is  the  arch  of  the  aorta. 

Above  it  are  the  cervical  fascia,  the  inferior  thyreoid,  and  thyreoidea  ima  veins. 

Tributaries. — In  addition  to  the  internal  jugular  and  subclavian  veins,  by  the 
confluence  of  which  the  innominate  veins  are  formed,  each  vein  receives  on  its 
upper  aspect  the  vertebral,  the  deep  cervical,  and  inferior  thyreoid  veins;  and 


Fig.  509. 
(Modified 
Internal  jugular  vein- 
Transverse  cervical 

Transverse  scapular 
artery 

Right  recurrent  nerve 

Right  common  carotid 
artery 

Subclavian  vein 
Vagus  nerve 

Innominate  artery  *^ 
I* 
Left  innominate  vein 

Phrenic  nerve 

Superior  vena  cava 

Arch  of  aorta 

Right  bronchus 

Branch  of  right  pul 
monary  artery 

Branch   of  right   pul 
monary  vein 

Right  pulmonary 
artery 
Branch  of  right   pul- 
monary artery 

Branch  of  right  pul 
monary  vein 


Right  coronary  artery 
Thoracic  vertebra 

Azygos  vein 

Intercostal  veins 

Intercostal  arteries 


— The  Vena  Cava  Supeeior  and  the  Innominate  Veins. 
from  a  dissection  in  St.  Bartholomew's  Hospital  Museum.) 


Inferior  thyreoid  ' 


-Thyreoid  gland 
Left  internal  jugular 

Vagus  nerve 

Lett  common  carotid 

artery 
Left  recurrent 

nerve 
Left  subclavian  artery 

Left  subclavian  vein 
Left  internal  mammary 


Phrenic  nerve 
Vagus  nerve 
Recurrent  nerve 

Ligamentum  arteri- 
osum 

Left  pulmonary  artery 

Lett  pulmonary  vein 

Left  bronchus 
Branch  of  left  pulmon- 
ary artery 
Pulmonary  artery 

Lett  pulmonary  vein 
Left  coronary  artery 
Conns  arteriosus 

CEsophagus 
Thoracic  duct 
Thoracic  aorta 


on  its  lower  aspect  the  internal  mammary  vein.  The  left  vein,  moreover,  is 
joined  by  the  thyreoidea  ima,  the  left  superior  intercostal,  and  by  the  thymic, 
tracheal,  oesophageal,  superior  phrenic,  anterior  mediastinal,  and  pericardiac  veins. 
At  the  confluence  of  the  internal  jugular  and  subclavian  veins  on  the  right  side 
the  three  lymphatic  trunks  or  the  right  lymphatic  duct  open;  on  the  left  side  the 
thoracic  duct. 

THE  VEINS  OF  THE  HEAD  AND  NECK 

The  veins  of  the  head  and  neck  may  be  divided  for  purposes  of  description  into 
the  superficial,  which  return  the  blood  from  the  external  parts  of  the  head  and 


SUPERFICIAL  VEINS  OF  HEAD  AND  NECK 


643 


neck;  and  the  deep,  which  return  the  blood  from  the  deeper  structures.  All 
the  veins,  whether  superficial  or  deep,  terminate  in  the  internal  jugular  or  sub- 
clavian, or  open  directly  into  the  innominate  veins  at  the  root  of  the  neck. 
Through  the  latter  all  the  blood  from  the  head  and  neck  ultimately  passes  on  its 
way  to  the  heart. 

THE  SUPERFICIAL  VEINS  OF  THE  HEAD  AND  NECK 

The  venous  blood  from  the  anterior  part  of  the  scalp  and  integument  of  the 
face  is  returned,  through  the  anterior  and  posterior  facial  veins,  to  the  common 
facial,  a  tributary  of  the  internal  jugular  vein.  From  the  posterior  part  of  the 
scalp  and  from  the  integument  of  the  neck  venous  blood  is  returned,  through  the 
external  jugular  and  its  tributaries,  to  the  subclavian  vein. 


A.  The  Antehior  Facial  Vein 

The  anterior  facial  vein  [v.  facialis  anterior]  (fig.  510)  begins  a  little  below  the 
medial  end  of  the  eyebrow  where  it  is  formed  by  the  union  of  the  frontal  and 


Fig.  510. — The  Supeepicial  Veins  of  the  Face  and  Scalp.     (After  Quain.) 


Superficial  tem- 
poral 


Nasal  branch  of 
igular  vein 


Posterior  facial 


Posterior    exter^ 
nal  jugular  vein" 

External  jugula: 


Communicating 
branch  with  an- 
terior jugular 

Anterior  jugtUar 
vein 


Transverse  scapular  i 


supraorbital  veins.  It  descends  near  the  medial  angle  of  the  orbit,  and  then  by  the 
side  of  the  nose  to  the  cheek,  which  it  crosses  obliquely,  to  the  anterior  edge  of  the 
massetpr  muscle.  Thence  it  passes  through  the  digastric  triangle  to  the  upper 
border  of  the  hyoid  bone,  where  it  terminates  in  the  common  facial  vein.  In  this 
course  it  is  reinforced  by  numerous  collateral  veins,  and  gradually  increases  in 
size.  It  has,  moreover,  numerous  communications  with  the  deep  veins.  The 
portion  of  this  vein  above  the  lower  margin  of  the  orbit  is  called  the  angular  [v. 


644  THE  BLOOD-VASCULAR  SYSTEM 

angularis].     In  the  remainder  of  its  course  over  the  face  and  neck  it  is  termed  the 
anterior  facial  vein. 

The  angular  vein  skirts  around  the  medial  margin  of  the  orbit,  lying  with  the  angular 
artery  on  the  frontal  (nasal)  process  of  the  maxillary  bone  slightly  medial  to  the  lacrimal 
sac.  Branches  pass  from  the  posterior  part  of  the  angular  vein  into  the  orbit  to  join  the 
ophthalmic. 

The  angular,  the  facial,  and  the  ophthalmic  veins  contain  no  valves.  The  blood,  therefore, 
can'  pass  either  forward  from  the  ophthalmic  into  the  angular,  or  backward  through  the  facial 
and  angular  into  the  ophthalmic,  and  so  on  to  the  cavernous  and  other  venous  sinuses  of  the 
cranium.  Hence  in  certain  tumours  in  the  orbit  and  cranium,  the  congestion  of  the  angular 
and  facial  veins;  and  the  danger  in  facial  carbuncle  and  anthrax  of  septic  thrombi  spreading 
backward  through  the  angular  and  ophthalmic  veins  to  the  cranial  sinuses. 

The  anterior  facial  vein  runs  in  a  more  or  less  direct  line  behind  its  corre- 
sponding artery,  the  external  maxillary  (facial),  which  itself  pursues  a  tortuous 
course.  It  usually  passes  deep  to  the  zygomatic  muscle,  the  zygomatic  head  of  the 
quadratus  labii  superioris,  and  the  risorius,  but  superficial  to  the  other  muscles. 
At  the  anterior  edge  of  the  masseter  it  meets  the  external  maxillary  artery,  lying 
immediately  posterior  to  it.  In  the  neck  it  lies  beneath  the  platysma  and  cer- 
vical fascia,  and  is  usually  separated  from  the  external  maxillary  artery  by  the 
submaxillary  gland  and  the  stylo-hyoid  and  posterior  belly  of  the  digastric  muscles, 
below  which  it  is  joined  by  the  posterior  facial,  to  form  the  common  facial  vein. 

Tributaries. — It  receives,  from  above  downward: — fa)  the  frontal  vein;  (b) 
the  supraorbital  vein;  (c)  the  superior  palpebral  veins;  (d)  the  external  nasal 
veins;  (e)  the  inferior  palpebral  veins;  (f)  the  superior  labial  vein;  (g)  the  inferior 
labial  vein;  (h)  the  masseteric  veins;  (i)  the  anterior  parotid  veins;  (j)  the  pala- 
tine vein  and  (k)  the  submental  vein. 

(a)  The  frontal  vein  [v.  frontalis]  (fig.  510)  begins  about  the  level  of  the  coronal  suture  in  a 
venous  plexus  which  communicates  with  the  anterior  division  of  the  temporal  vein.  Soon 
forming  a  single  trunk,  it  passes  vertically  downward  over  the  frontal  bone,  a  short  distance 
from  the  middle  line  and  parallel  to  its  feUow  of  the  opposite  side,  to  the  medial  end  of  the  eye- 
brow where  it  terminates  in  the  angular  vein. 

(b)  The  supraorbital  vein  [v.  supraorbitalis]  begins  over  the  frontal  eminence  by  inter- 
communication with  the  middle  temporal  vein.  It  receives  tributaries  from  the  forehead  and 
eyebrow,  and,  running  obliquely,  medially  and  downward,  opens  into  the  termination  of  the 
frontal  vein  to  form  the  angular.  It  communicates  with  the  ophthalmic  vein,  and  receives  the 
frontal  vein  of  the  diploe  as  the  latter  vein  issues  from  the  bone  at  the  bottom  of  the  supraorbital 
notch. 

(c)  The  superior  palpebral  veins  [vv.  palpebrales  superiores]  arise  in  the  upper  eyeMd  and 
open  into  the  lateral  side  of  the  angular  vein.  They  communicate  with  the  middle  temporal 
vein. 

(d)  The  external  nasal  veins  [vv.  nasales  externae]  form  three  or  four  stems  on  either  side. 
The  upper  veins  run  upward  into  the  angular  and  the  lower,  from  the  ala,  pass  more  hori- 
zontally into  the  anterior  facial  vein. 

(e)  The  inferior  palpebral  veins  [vv.  palpebrales  inferiores]  arise  in  the  lower  eyelid,  and, 
passing  medially  and  downward  over  the  cheek  from  which  they  receive  tributaries,  open  into 
the  later.ll  side  of  the  anterior  facial  vein.     They  communicate  with  the  infraorbital  vein. 

(f)  Tlie  superior  labial  vein  [v.  labialis  superior]  and  (g)  the  inferior  labial  vein  [v.  labialis 
inferior]  arise  from  venous  plexuses  in  the  upper  and  lower  lips.  They  run  laterally  to  open 
into  the  medial  side  of  the  facial  vein. 

(h)  The  masseteric  veins  [vv.  masseterioae]  and  (i)  the  anterior  parotid  veins  [vv.  parotidae 
anteriores],  of  small  size,  drain  the  cheek  over  the  masseteric  and  parotid  regions. 

(j)  The  palatine  vein  [v.  palatina]  accompanies  the  ascending  palatine  or  tonsillar  artery 
from  the  venous  plexus  about  the  tonsil  and  soft  palate,  and  joins  the  anterior  facial  vein  just 
below  the  body  of  the  mandible. 

(k)  The  submental  vein  [v.  submentalis]  lies  on  the  mylo-hyoid  muscle  superficial  to  the 
submental  artery.  Running  back  in  the  submental  triangle,  it  joins  the  anterior  facial  vein 
just  after  the  latter  has  passed  over  the  body  of  the  mandible.  It  communicates  with  the 
anterior  jugular  vein. 

Communications. — The  tributaries  of  the  anterior  facial  vein  comrnunicate  freely  with 
the  anterior  and  middle  temporal,  ophthalmic,  infraorbital  and  anterior  jugular  veins.  The 
main  trunk  has  a  large  communicating  branch  with  the  pterygoid  plexus.  This  vein,  some- 
times known  as  the  deep  facial,  opens  into  the  anterior  facial  Ijelow  the  zygomatic  bone  under 
cover  of  the  zygomaticus  muscle. 

B.  The  Posterior  Facial  Vein 

The  posterior  facial  (temporo-maxillary)  vein  [v.  facialis  posterior]  is  formed  in 
in  the  region  of  the  root  of  the  zygoma  by  the  union  of  the  superficial  and 
middle  temporal  veins.     It  passes  downward  behind  the  ramus  of  the  mandible 


POSTERIOR  FACIAL  VEIN 


645 


through  the  substance  of  the  parotid  gland— here  lying  lateral  to  the  super- 
ficial temporal  and  external  carotid  arteries.  At  the  angle  of  the  mandible  it 
runs  medially  and  somewhat  forward,  and,  passing  either  deep  or  superficial  to 
the  stylo-hyoid  and  digastric  muscles,  joins  the  anterior  facial  to  form  the 
common  facial  vein. 

The  tributaries  received  by  the  posterior  facial  vein  are: — (a)  the  superficial 


-The  Veins  of  the  Head,  Neck,  and  Axilla.  ^  (Aft^er  Toldt,  'Atlas  of  Human 
Anatomy,"  Rebman,  London  and  New  York.) 

Frontal  diploic  veins 

Supraorbital  vein 


Middle  temporal  vein 

Superficial  temporal  artery 
and  vein 

Articular  mandibular  veins  ^^^/ 


Posterior  facial  veins 


External  nasal  veins 
Angular  vein 


Anterior  facial  vein 


Submental  vein 


Occipital  artery  and 


Hypoglossal   nerve 
''^     and  venee  comitans 

Superior    thyreoid 
artery  and  vein 
\     Superior     laryngeal 
,  artery  and  vein 


Circumflex  hum-  /  Anterior  \  15, ' 
1  Posterior  \  v;' 


Circumflex  scapular 


Lateral  thoracic  artery  and  vein 


temporal  veins;  (b)  the  middle  temporal  vein;  (c)  the  transverse  facial  vein; 
(d)  the  articular  veins;  fe)  the  posterior  parotid  veins;  (f)  the  anterior  auricular 
veins;  (g)  the  stylo-mastoid  vein;  and  (h)  the  internal  maxillary  vein  through 
which  occurs  the  principal  drainage  of  the  pterygoid  plexus. 


646  THE  BLOOD-VASCULAR  SYSTEM 

_  (a)  The  superficial  temporal  vein  [v.  temporalis  superficialis]  returns  the  blood  from  the 
parietal  region  of  the  scalp.  It  is  formed  by  the  union  of  an  anterior  and  a  posterior  branch: 
theformer  communicates  with  the  supraorbital  and  frontal  veins;  the  latter  with  the  posterior 
auricular  and  occipital  veins  and  the  temporal  vein  of  the  opposite  side.  These  branches  lie 
superficial  to  the  corresponding  branches  of  the  superficial  temporal  artery,  which  they  roughly 
though  not  accurately  follow.  Like  the  artery,  they  lie  between  the  skin  and  the  cranial 
aponeurosis,  and  descend  over  the  temporal  fascia  to  unite  a  Uttle  above  the  zygoma,  and  just 
in  front  of  the  auricle  of  the  ear,  to  form  the  superficial  temporal  trunk.  The  vein  thus  formed 
continues  its  course  downward  with  the  trunk  of  the  temporal  artery,  and  opposite  the  zygoma 
is  joined  by  the  middle  temporal  vein  to  form  the  common  temporal  vein. 

(b)  The  middle  temporal  vein  [v.  temporaUs  media]  corresponds  with  the  orbital  branch 
of  the  temporal  arterj',  and  communicates  in  front  with  the  ophthalmic  vein,  the  external 
palpebral  veins,  and  the  infraorbital  veins,  and  then  runs  backward  between  the  layers  of  the 
temporal  fascia  to  join  the  superficial  temporal  vein.  The  middle  temporal  vein  communicates 
with  the  deep  temporal  veins,  and  through  them  with  the  pterygoid  venous  plexus. 

(c)  The  transverse  facial  vein  [v.  transversa  faciei]  corresponds  to  the  transverse  facial 
artery,  (d)  Articular  veins  [vv.  articulares  mandibute]  form  the  plexus  around  the  temporo- 
mandibular joint;  this  plexus  receives  the  tympanic  veins  [w.  tympanicae),  which,  together 
with  its  corresponding  artery,  passes  through  the  petrotympanic  fissure,  (e)  Posterior  parotid 
veins  [w.  parotidese  posteriores]  emerge  from  the  substance  of  the  parotid  gland,  (f)  Anterior 
auricular  veins  [w.  auriculares  anteriores],  from  the  auricle  of  the  ear.  (g)  Stylo-mastoid  vein 
[v.  stylomastoidea]  from  the  facial  canal,  (h)  The  internal  maxallary  vein  accompanies  the 
first  part  of  the  internal  maxillary  artery.  It  begins  at  the  posterior  confluence  of  the  veins 
forming  the  pterygoid  plexus,  and  passes  backward  between  the  stylo-mandibular  ligament  and 
the  neck  of  the  mandible.     It  ends  by  joining  the  posterior  facial  vein. 

The  pterygoid  plexus  [plexus  pterygoideus]  is  formed  by  the  veins  which  correspond  to  the 
branches  of  the  internal  maxillary  artery.  It  is  situated,  partly  on  the  medial  surface  of  the 
internal  pterygoid  muscle,  and  partly  around  the  external  pterygoid  muscle.  The  veins 
entering  into  this  plexus  are: — the  two  middle  meningeal  veins  [w.  meningeae  mediae],  which 
accompany  the  artery  of  that  name;  the  posterior  superior  alveolar  (dental);  the  inferior  alveolar 
(dental);  the  masseteric;  the  buccal;  the  pterygoid  veins  from  the  pterygoid  muscles;  the  deep 
temporal  veins  [vv.  temporales  profundae],  by  which  the  plexus  communicates  with  the  temporal 
plexus;  the  spheno -palatine  vein;  the  infraorbital;  the  superior  palatine;  a  branch  of  commu- 
nication with  the  lower  branch  of  the  ophthalmic  vein,  which  courses  through  the  inferior 
orbital  (spheno-maxillary)  fissure;  and  the  rete  foraminis  ovalis  and  Vesalian  vein,  through 
which  the  plexus  communicates  with  the  cavernous  sinus.  The  plexus  ends  posteriorly  in 
the  internal  maxillary  vein,  which  joins  the  posterior  facial  vein,  and  anteriorly  in  a  com- 
municating vessel  (the  deep  facial  vein),  which  passes  forward  and  downward  between  the 
buccinator  and  masseter  muscles  to  join  the  anterior  facial  vein. 

The  above-mentioned  veins,  forming  by  their  confluence  the  pterygoid  plexus,  correspond 
in  then-  course  so  nearly  with  that  of  their  companion  arteries  that  a  detaOed  description  is 
not  necessary.  Although  for  convenience  described  with  the  superficial  veins,  they  are  all 
deeply  placed. 

Near  the  angle  of  the  mandible  there  is  almost  always  a  communicating  branch  between  the 
posterior  facial  and  the  external  jugular  veins.  When  large,  this  branch  may  drain  the  greater 
part  of  the  blood  from  the  posterior  facial. 

C.  The  Common  Facial  Vein 

The  common  facial  vein  [v.  facialis  communis]  is  a  short  thick  stem  contained 
within  the  carotid  triangle.  It  is  formed,  just  below  the  angle  of  the  mandible, 
by  the  union  of  the  anterior  and  posterior  facial  veins.  It  ends  opposite  the  hyoid 
bone,  by  opening  into  the  internal  jugular  vein.  In  addition  to  the  vessels  which 
form  it,  sometimes  it  receives  the  superior  thyreoid,  the  pharyngeal,  and  the  lin- 
gual or  the  subHngual  veins. 

D.  The  External  Jugular  Vein 

The  external  jugular  vein  [v.  jugularis  externa]  (fig.  510)  is  formed  by  the  con- 
fluence of  the  posterior  auricular  and  a  short  communicating  trunlc  from  the 
posterior  facial  near  the  angle  of  the  mandible.  It  runs  obliquely  downward  and 
backward  across  the  sterno-mastoid  muscle  to  a  point  opposite  the  middle  of  the 
clavicle,  where  it  terminates  as  a  rule  in  the  subclavian  vein.  A  line  drawn  from 
a  point  midway  between  the  mastoid  process  and  angle  of  the  jaw  to  the  middle  of 
the  clavicle  will  indicate  its  course.  It  is  covered  by  the  skin,  superficial  fascia, 
and  platysma,  and  is  crossed  by  a  few  branches  of  the  cervical  plexus,  the  great 
auricular  nerve  running  parallel  to  it  at  the  upper  part  of  the  neck.  It  is  separated 
from  the  sterno-mastoid  by  the  anterior  layer  of  the  deep  cervical  fascia. 

Just  above  the  clavicle  it  perforates  the  cervical  fascia,  by  which  it  is  prevented  from  readily 
collapsing,  the  fascia  being  attached  to  its  walls.  It  then  opens  into  the  subclavian  vein,  oc- 
casionally into  the  internal  jugular,  or  into  the  confluence  of  the  subclavian  and  internal  jugular 


THE  EXTERNAL  JUGULAR  VEIN 


647 


veins.  It  contains  a  pair  of  valves  about  2.5  to  5  cm.  (1  to  2  in.)  above  the  clavicle,  and  a 
Becond'pair  where  it  enters  the  subclavian  vein.  Neither  of  these  valves  is  sufficient  to  prevent 
the  blood  from  regurgitating,  or  injections  from  passing  from  the  larger  vein  into  the  external 
jugular. 

Tributaries  and  communications. — These  include; — (a)  The  posterior  auricular 
vein;  (b)  the  occipital  vein;  (c)  a  branch  of  communication  with  the  posterior  fa- 
cial vein;  (d)  the  posterior  external  jugular  vein;  (e)  the  transverse  scapular  vein; 
and  (f)  the  anterior  jugular  vein. 

(a)  The  posterior  auricular  vein  [v.  auricularis  posterior]  begins  in  a  venous  plexus  on  the 
posterior  part  of  the  parietal  bone.  This  plexus  communicates  with  the  vein  of  the  opposite 
side  across  the  sagittal  suture,  and  with  the  posterior  branch  of  the  superficial  temporal  vein 
in  front,  and  with  the  occipital  vein  behind.  It  descends  over  the  back  part  of  the  parietal 
bone  and  the  mastoid  process  of  the  temporal  bone,  lying  with  its  artery  behind  the  ear,  and 
joins  a  branch  from  the  posterior  facial  vein  to  form  the  external  jugular. 


Fig.  512. — The  Veins  of  the  Face.     (After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman, 
London  and  New  York.) 
Deep  temporal  veins 

Infraorbital  artery  and  i 


Lateral  lacuna  of  the  superior  sagittal  sinus 
Sphenoparietal  sinus 


Middle 
temporal 

vein 
Articular  man- 
dibular veins 
Superficial 
temporal  art*  ry 
Pterygoid 
pi. 
Internal 
maxillary  arter> 
Inferior 
alveolar  nerve 
Posterior  facial  vein  ^ 
Inferior  alveolar  artery 
and  vein 

Jugular 


Common  facial  vein 


(6)  The  occipital  vein  [v.  occipitalis]  begins  at  the  back  of  the  skuU  in  a  venous  plexus 
which  anastomoses  with  the  posterior  auricular  and  the  posterior  branch  of  the  superficial 
temporal  veins.  It  passes  downward  over  the  occipital  bone,  and  usually  perforates  the 
trapezius  with  the  occipital  artery,  to  join  a  plexus  drained  by  the  deep  crevical  and  vertebral 
veins.  It  also  communicates  with  the  posterior  auricular,  and  in  many  cases  this  forms  the 
chief  path  of  drainage.  One  of  its  branches,  usually  the  most  lateral,  receives  a  mastoid  em- 
issary vein  [emissarium  mastoideum]  which  issues  through  the  mastoid  foramen  of  the  tem- 
poral bone,  and  in  this  way  forms  a  communication  with  the  transverse  sinus. 

(c)  The  branch  of  communication  with  the  posterior  facial  vein  occurs  a  short  distance  below 
the  point  at  which  the  posterior  facial  receives  the  internal  maxillary  vein.  It  is  very  constant 
and  is  placed  immediately  behind  the  angle  of  the  mandible.    Through  it  the  external  jugular 


648  THE  BLOOD-VASCULAR  SYSTEM 

usually  receives  a  considerable  proportion  of  the  blood  returning  from  the  temporal  and  ptery- 
goid regions. 

(d)  The  posterior  external  jugular  vein  (fig.  512)  descends  from  the  upper  and  back  part 
of  the  neck,  receiving  small  tributaries  from  the  superficial  structures  and  muscles.  At  times  it 
communicates  with  the  occipital,  or  may  appear  as  a  continuation  of  that  vein.  It  opens  into 
the  external  jugular  as  the  latter  vein  is  leaving  the  sterno-mastoid  muscle. 

(e)  The  transverse  scapular  vein  [v.  transversa  scapulae]  corresponds  to  the  transverse 
scapular  (suprascapular)  artery.  If  double,  these  venae  comitantes  usually  form  one  trunk 
before  they  open  into  the  external  jugular  vein.     They  contain  well-marked  valves. 

(/)  The  anterior  jugular  vein  [v.  jugularis  anterior]  begins  below  the  chin  by  communicating 
with  the  mental,  submental,  inferior  labial,  and  inferior  hyoid  veins.  It  descends  a  little 
lateral  to  the  middle  line,  receiving  branches  from  the  superficial  structures  at  the  front  and 
side  of  the  neck,  and  occasionally  a  branch  from  the  larynx  and  thyreoid  body.  Just  above 
the  clavicle  it  turns  laterally,  and,  piercing  the  fascia,  passes  beneath  the  sterno-mastoid 
muscle  and  opens  into  the  external  jugular  vein  just  before  the  latter  joins  the  subclavian;  at 
times  it  opens  into  the  subclavian  vein  itself.  In  its  course  down  the  neck  it  communicates 
with  the  external  jugular;  and,  as  it  turns  laterally  beneath  the  sterno-mastoid,  sends  a  branch 
across  the  trachea,  between  the  layers  of  cervical  fascia,  to  join  the  anterior  jugular  of  the 
opposite  side.  This  communicating  vein,  the  jugular  venous  arch  [arcus  venosus  juguli], 
may  open  directly  into  the  external  jugular  or  into  the  internal  jugular  vein;  occasionally  one 
or  both  ends  may  open  into  the  subclavian  or  innominate  vein.  It  may  be  divided  in  the 
operation  of  tracheotomy,  and  is  then  often  found  greatly  engorged  with  blood.  Another 
branch,  often  of  considerable  size,  courses  along  the  anterior  margin  of  the  sterno-mastoid  and 
joins  the  anterior  facial  vein.  When  the  anterior  jugular  vein  is  large,  the  external  jugular  is 
small,  and  vice  versa.  It  is  usually  also  of  large  size  when  the  corresponding  vein  on  the  opposite 
side  is  absent,  as  is  frequently  the  case.     It  contains  no  valves. 

THE  DEEP  VEINS  OF  THE  HEAD  AND  NECK 

The  deep  veins  of  the  head  and  neck  may  be  divided  into: — (1)  the  veins  of 
the  diploe;  (2)  the  venous  sinuses  of  the  dura  mater  encephah;  (3)  the  veins  of 
the  brain;  (4)  the  veins  of  the  nasal  cavities;  (5)  the  veins  of  the  ear;  (6)  the 
veins  of  the  orbit;  (7)  the  veins  of  the  pharynx  and  larynx;  and  (8)  the  deep  veins 
of  the  neck.  The  veins  of  the  diploe  terminate  partly  in  the  superficial  veins 
already  described,  partly  in  the  venous  sinuses  of  the  cranium,  and  partly  in  the 
deep  veins  of  the  neck.  The  venous  sinuses  open  into  the  deep  veins  of  the  neck. 
The  veins  of  the  brain  terminate  in  the  venous  sinuses.  The  veins  of  the  nasal 
cavities  terminate  partly  in  the  deep,  and  to  some  extent  in  the  superficial  veins. 
The  veins  of  the  ear  join  both  the  superficial  and  deep  veins  and  the  venous  sinuses. 
The  veins  of  the  orbit  terminate  partly  in  the  superficial  veins,  but  chiefly  in  the 
venous  sinuses.  The  veins  of  the  pharynx  and  larynx  enter  the  deep  veins  of  the 
neck. 

1.  THE  VEINS  OF  THE  DIPLOE 

The  veins  of  the  diploe  [venae  diploicse]  (fig.  513)  are  contained  in  bony  chan- 
nels in  the  cancellous  tissue  between  the  external  and  internal  laminae  of  the  skull. 
They  are  of  comparatively  large  size,  with  very  thin  and  imperfect  walls,  and  form 
numerous  irregular  communicating  channels.  They  have  no  valves.  They  ter- 
minate in  four  or  five  main  and  descending  channels,  which  open,  some  outward 
through  the  external  cranial  lamina  into  some  of  the  superficial  and  deep  veins  of 
the  head  and  face,  and  some  inward  through  the  internal  lamina  into  the  venous 
sinuses.  They  are  divided  into  the  frontal,  anterior  temporal,  posterior  temporal, 
and  occipital. 

The  frontal  diploic  veins  are  contained  in  the  anterior  part  of  the  frontal  bone.  They 
converge  anteriorly  to  a  single  vein  [v.  diploica  frontalis]  which  passes  downward,  perforates  the 
external  table  through  a  small  aperture  in  the  roof  of  the  supraorbital  notch,  and  terminates  in 
the  supraorbital  vein.     They  also  communicate  with  the  superior  sagittal  sinus. 

The  anterior  temporal  [v.  diploica  temporahs  ant.]  are  contained  in  the  posterior  part  of 
the  frontal  and  in  the  anterior  part  of  the  parietal  bone.  They  pass  downward,  and  end,  partly 
in  the  deep  temporal  veins  by  perforating  the  greater  wing  of  the  sphenoid  bone,  and  partly 
in  the  spheno-parietal  sinus. 

The  posterior  temporal  [v.  diploica  temporalis  post.]  ramifies  in  the  parietal  bone,  and, 
coursing  downward  to  the  posterior  inferior  angle  of  that  bone,  passes  either  through  a  foramen 
in  its  inner  table,  or  through  the  mastoid  foramen  into  the  transverse  sinus. 

The  occipital  [v.  diploica  occipitalis]  ramifies  chiefly  in  the  occipital  bone,  and  opens  into 
the  occipital  vein  or  into  the  transverse  sinus. 

The  diploic  veins  freely  anastomose  with  one  another  in  the  adult;  but  in  the  foetus,  before 
the  bones  have  united,  each  system  of  veins  is  distinct. 


VENOUS  SINUS  OF  THE  DURA  MATER 


649 


2.  THE  VENOUS  SINUSES  OF  THE  DURA  MATER 

The  venous  sinuses  of  the  dura  mater  [sinus  durse  matris]  are  endothelially 
lined  blood-spaces,  situated  between  the  periosteal  and  meningeal  layers  of  the 
dura  mater.  They  are  the  channels  by  which  the  blood  is  conve3red  from  the 
cerebral  veins,  and  from  some  of  the  veins  of  the  meninges  and  diploe,  into  the 
veins  of  the  neck.  The  sinuses  at  the  base  of  the  skull  also  carry  the  chief  part  of 
the  blood  from  the  orbit  and  eyeball  to  the  jugular  veins.  At  certain  spots  the 
sinuses  communicate  with  the  superficial  veins  by  small  vessels  known  as  the  emis- 
sary veins,  which  run  through  foramina  in  the  cranial  bones. 

The  venous  sinuses  are  sixteen  in  number,  six  being  median  and  unpaired,  the 
remaining  ten  consisting  of  five  lateral  pairs.  The  median  sinuses  are: — (1)  the 
superior  sagittal;  (2)  the  inferior  sagittal;  (.3)  the  straight;  (4)  the  occipital;  (5) 
the  circular;  and  (6)  the  basilar  plexus.  The  lateral  and  paired  sinuses  are: — • 
(7)  the  two  transverse;  (8)  the  two  superior  petrosal;  (9)  the  two  inferior  petro- 
sal; (10)  the  two  cavernous;  and  (11)  the  two  spheno-parietal.  Occasionally 
there  are  two  additional  sinuses,  the  two  petro-squamous. 

(1)  The  superior  sagittal  (or  longitudinal)  sinus  [sinus  sagittalis  superior]  (fig. 
515)  lies  in  the  median  groove  on  the  inner  surface  of  the  cranium  along  the 
attached  margin  of  the  falx  cerebri.     It  extends  from  the  foramen  caecum  to  the 

Fig.  513. — The  Veins  op  the  Diploe. 
(From  a  specimen  in  St.  Bartholomew's  Hospital  Museum.) 


The     occipital 

diploic  vein 

The  posterior 

temporal  diploic 


internal  occipital  protuberance.  It  grooves  from  before  backward  the  frontal 
bone,  the  contiguous  sagittal  margins  of  the  parietal  bones,  and  the  squamous  por- 
tion of  the  occipital  bone  In  the  foetus,  and  occasionally  in  the  adult,  it  commu- 
nicates (through  the  foramen  caecum)  with  the  nasal  veins.  It  communicates 
throughout  life  with  each  superficial  temporal  vein  by  means  of  a  parietal  emis- 
sary vein  [emissarium  parietale]  which  passes  through  the  parietal  fora- 
man.  It  is  triangular  on  section,  the  base  of  the  triangle  corresponding  "to  the 
bone.  Crossing  it  are  a  number  of  fibrous  bands  known  as  the  chords  of  Willis, 
and  projecting  into  it  in  places  are  the  arachnoidal  (Pacchionian)  granulations. 
The  parts  of  the  sinus  into  which  the  arachnoidal  granulations  project  are  irregu- 
lar lateral  diverticula  from  the  main  channel  known  as  the  lacimce  laterales  ffig. 
517).  In  front  the  sinus  is  quite  small,  but  it  increases  greatly  in  calibre  as  it 
runs  backward.  It  receives  at  intervals  the  superior  cortical  cerebral  veins  and 
the  veins  from  the  falx.  The  former,  for  the  most  part,  open  into  it  in  the  direc- 
tion opposite  to  that  in  which  the  blood  is  flowing  in  the  sinus.  They  pass  for 
some  distance  in  the  walls  of  the  sinus  before  opening  into  it.  Posteriorly,  at  the 
internal  occipital  protuberance,  the  superior  sagittal  sinus  usually  turns  sharply  to 


650 


THE  BLOOD-VASCULAR  SYSTEM 


the  right,  and  ends  in  the  right  transverse  (lateral)  sinus;  the  straight  sinus  then 
usually  terminates  in  the  left  transverse  (lateral)  sinus. 

Occasionally,  however,  the  superior  sagittal  sinus  ends  in  the  left  transverse  sinus,  the 
straight  then  passing  into  the  right.  At  the  angle  of  union  between  the  superior  sagittal 
sinus  and  the  transverse  sinus  into  which  it  empties  there  is  a  dilation,  the  confluens  sinuum 
or  torcular  Herophih.  At  this  point  there  is  a  communication  between  the  right  and  left  trans- 
verse sinuses.  In  some  cases  the  communication  is  so  free  that  the  blood  from  the  sagittal 
sinus  flows  almost  equally  into  each  transverse  sinus.  The  confiuens  may  communicate  with 
the  occipital  vein  through  the  occipital  emissary  vein  [emissarium  occipitale],  which,  when  present 
passes  through  a  minute  foramen  in  the  occipital  protuberance. 

(2)  The  inferior  sagittal  (or  longitudinal)  sinus  [sinus  sagittalis  inferior]  (fig. 
515)  is  situated  at  the  free  margin  of  the  falx  cerebri.  Beginning  about  the 
junction  of  the  anterior  with  the  middle  third  of  the  falx,  it  is  continued  backward 
along  the  concave  or  lower  margin  of  that  process  to  the  junction  of  the  falx  with 
the  tentorium,  where  it  ends  in  the  straight  sinus.     The  sinus  is  cylindrical  in 


Fig.  514. — The  Venous  Sinuses. 
(From  a  dissection  by  W.  J.  Walsham  in  St.  Bartholomew's  Hospital  Museum.) 


Meningeal  branch  of  pos- 
terior ethmoidal  aitery 


Middle  meningeal 
artery 
Ophthalmic  division  of 
trigeminus 

Oculomotor  nerve 

Cavernous  sinus 

Trochlear  nerve 

Auditory  &  facial  nerve! 

Superior  petrosal  sinus 

Inferior  petrosal  sinus 

Petro-squamous  sinus 

Spinal  accessory  nerve 

Sigmoid    portion   of 

transverse  sinus 

Posterior   meningeal 

branch  of  vertebral 

artery 

Left  marginal  sinus 


'\f'iV\ — Circular  sinus 


Left  transverse  sinus 
Superior  sagittal  sinus 


Carotid  artery 
-Abducens  nerve 
Basilar  artery 
Basilar  plexus  of 

veins 
Auditory  artery 
Vertebral  artery 
—  Glosso  -  pharyngeal 
—J    and  vagus  nerves 
I'  /   Anterior  spinal 
,  artery 

/_  Hypoglossal  nerve 
/       Spinal  accessory 
nerve 

Right  marginal  sinus 
Occipital  sinus 
Right  transverse  sinus 


shape  and  of  small  size,  and  receives  some  of  the  inferior  frontal  veins  of  the  brain, 
some  of  the  veins  from  the  medial  surface  of  the  brain,  and  some  of  the  veins  of  the 
falx.  . 

(3)  The  straight  sinus  [sinus  rectus]  lies  along  the  junction  of  the  falx  cerebri 
with  the  tentorium  cerebelli.  It  is  formed  by  the  union  of  the  great  cerebral  vein 
(of  Galen)  and  the  inferior  sagittal  sinus.  It  receives  in  its  course  branches  from 
the  tentorium  cerebelh  and  from  the  upper  surface  of  the  cerebellum.  _  It  runs 
downward  and  backward  to  the  internal  occipital  protuberance,  where  it  ends  in 
the  transverse  sinus  opposite  to  that  joined  by  the  superior  sagittal  sinus.  On 
section  it  is  triangular  in  shape,  with  its  apex  upward. 

(4)  The  occipital  sinus  [sinus  occipitaHs]  (fig.  514)  ascends  at  the  attached 
margin  of  the  falx  cerebelli,  along  the  lower  half  of  the  squamous  portion  of  the 
occipital  bone  from  near  the  posterior  margin  of  the  foramen  magnum  to  the 
internal  occipital  protuberance.  It  usually  begins  in  a  right  and  a  left  branch, 
known  as  the  marginal  sinuses.     These  proceed  from  the  termination  of  each 


VENOUS  SINUSES  OF  THE  DURA  MATER 


651 


transverse  sinus,  run  around  the  foramen  magnum,  where  they  communicate  with 
the  venous  vertebral  retia,  and  unite  at  a  variable  distance  from  the  internal  oc- 
cipital protuberance  to  form  the  single  occipital  sinus.  Sometimes  they  re- 
main separate  as  far  as  the  occipital  protuberance,  then  forming  two  occipital 
sinuses.  One  of  the  two  marginal  sinuses  may  be  much  smaller  than  the  other, 
or  be  entirely  absent.  At  the  point  where  the  marginal  sinuses  unite  to  form  the 
single  occipital  sinus,  there  is  a  communication  with  the  venous  vertebral  retia. 
The  occipital  sinus  ends  in  the  confluens  sinuum.  It  receives  in  its  course  veins 
from  the  tentorium  cerebelli,  and  from  the  inferior  surface  of  the  cerebellum. 
It  communicates  through  the  plexus  of  veins  which  surrounds  the  hypoglossal 
nerve  [rete  canalis  hypoglossi]  in  the  hypoglossal  (anterior  condyloid)  canal 
with  the  vertebral  vein  and  the  longitudinal  vertebral  venous  sinuses. 

(5)  The  circular  sinus  [sinus  circularis]  (fig.  516)  encircles  the  hypophysis 
cerebri.     It  consists  of  the  two  cavernous  sinuses  and  their  communications  across 


Fig.  515. — The  Venous  Sinuses.     (Longitudinal  section.) 
Abducens.  aerve  Oculomotor  nerve 


Superior  sagit- 


Vein  of  Galen 


Middle 
meningeal 
artery 
Internal 
carotid  artery 


Superior 
petrosal  sinus 
Fabr  cerebell 

Facial  and  auditory 
nerves 
Glossopharyngeal,  vagus  and 
accessory 

Hypoglosaal 


Second  cervical  nerve 

Ligamentum  denticulatum 


petrosal  sinus 


the  median  line  by  means  of  the  anterior  and  posterior  intercavernous  sinuses. 
The  intercavernous  sinuses  are  small  and  cross  the  median  line  in  front  of  and 
behind  the  hypophysis,  respectively. 

(6)  The  basilar  plexus  [plexus  basilaris]  is  a  venous  plexus  in  the  substance  of 
the  dura  mater  over  the  basilar  part  of  the  occipital  bone.  It  extends  from 
the  cavernous  sinus  to  the  margin  of  the  foramen  magnum  below.  It  communi- 
cates laterally  with  the  inferior  petrosal  sinus,  and  inferiorly  with  the  internal 
vertebral  venous  plexuses.  One  of  the  larger  of  the  irregular  venous  channels 
forming  the  plexus  passes  transversely  from  one  inferior  petrosal  sinus  to  the 
other.  This  venous  plexus  is  serially  homologous  with  the  longitudinal  vertebral 
venous  sinuses  on  the  posterior  surfaces  of  the  bodies  of  the  vertebrae. 

(7)  The  transverse  (or  lateral)  sinus  [sinus  transversus]  (figs.  514,  516) 
extends  from  the  internal  occipital  protuberance  to  the  jugular  foramen.  In 
this  course  it  lies  in  the  groove  (which  has  been  named  after  it)  along  the  squamous 
portion  of  the  occipital  bone,  the  posterior  inferior  angle  of  the  parietal  bone,  the 
mastoid  portion  of  the  temporal  bone,  and  the  jugular  process  of  the  occipital 
bone.  It  at  first  runs  laterally  and  forward  horizontally  between  the  two  layers 
of  the  tentorium  cerebelli,  following  the  curve  of  the  groove  on  the  occipital  and 
on  the  mastoid  angle  of  the  parietal  bone.     On  reaching  the  groove  in  the  mas- 


652  THE  BLOOD-VASCULAR  SYSTEM 

1.  toid  portion  of  the  temporal  bone  it  leaves  the  tentorium  and  curves  medially 

|/  and  downward  and  then  forward  over  the  jugular  process  of  the  occipital  bone, 

and  ends  in  the  posterior  compartment  of  the  jugular  fossa  in  the  superior  bulb  of 
the  internal  jugular  vein.  The  S-shaped  part  of  the  sinus  which  hes  on  the  mas- 
toid portion  of  the  temporal  and  jugular  portion  of  the  occipital  bone  is  sometimes 
known  as  the  sigmoid  sinus.  The  transverse  sinus  receives  the  internal  auditory 
veins  [vv.  auditivse  internfe]  from  the  labyrinth,  which  emerge  from  the  internal 
auditory  meatus.  It  also  receives  veins  from  the  temporal  lobe  of  the  cerebrum, 
some  of  the  superior  and  inferior  cerebellar  veins,  some  of  the  veins  of  the  medulla 
and  pons,  the  occipital,  and  the  posterior  temporal  and  occipital  veins  of  the  diploe. 
At  the  point  where  it  leaves  the  tentorium  it  drains  the  superior  petrosal  sinus 
and,  when  present,  the  petro-squamous  sinus.  It  communicates  with  the  occip- 
ital and  vertebral  veins  through  the  mastoid  and  posterior  condyloid  foramina 
by  means  of  the  mastoid  and  condyloid  emissary  veins.  As  the  transverse  sinus 
lies  between  the  layers  of  the  tentorium  it  is  on  section  prismatic  in  shape. 
The  sigmoid  portion  is  semicylindrical. 

The  right  transverse  sinus  is  usually  the  larger  and  the  direct  continuation  of  the  superior 
sagittal  sinus,  and  hence  conveys  the  chief  part  of  the  blood  from  the  cortical  surface  of  the  brain 
and  vault  of  the  skull.  The  left  transverse  sinus  is  usually  the  smaller  and  the  direct  con- 
tinuation of  the  straight  sinus,  and  hence  returns  the  chief  part  of  the  blood  from  the  central 
ganglia  of  the  brain.  The  right  and  left  sinuses  communicate  opposite  the  internal  occipital 
protuberance. 

The  relation  of  the  lateral  sinus  to  the  outside  of  the  skuU,  especially  to  the  mastoid  process 
of  the  temporal  bone,  is  of  importance  with  reference  to  the  operations  of  trephining  the 
mastoid  cells,  opening  the  tympanum,  and  exposing  the  sinus  itself,  in  septic  thrombosis,  etc. 
The  course  of  the  sinus  corresponds  to  a  hne  drawn  from  the  external  occipital  protuberance 
to  the  base  of  the  mastoid  process,  or  to  the  asterion,  and  thence  over  the  back  of  the  mastoid 
process  in  a  curved  line  toward  its  apex. 

(8)  The  superior  petrosal  sinus  [sinus  petrosus  superior]  (figs.  514,  515) 
runs  at  the  attached  margin  of  the  tentorium  cerebelli,  along  the  upper  border 
of  the  petrous  portion  of  the  temporal  bone.  It  connects  the  cavernous  with  the 
transverse  sinus.  Leaving  the  lateral  and  back  part  of  the  cavernous  sinus  just 
below  the  fourth  nerve,  it  crosses  the  fifth  nerve,  and,  after  grooving  the  petrous 
bone,  ends  in  the  transverse  sinus  as  the  latter  turns  downward  on  the  mastoid 
portion  of  the  temporal  bone.  It  receives  veins  from  the  temporal  lobe  of  the 
cerebrum,  veins  from  the  cerebellum,  veins  from  the  tympanum  through  the 
squamo-petrosal  fissure,  and  sometimes  the  anterior  temporal  veins  of  the  diploe. 

(9)  The  inferior  petrosal  sinus  [sinus  petrosus  inferior]  (figs.  514,  516)  runs 
along  the  line  of  the  petro-occipital  suture,  and  connects  the  cavernous  sinus  with 
the  commencement  of  the  internal  jugular  vein.  It  is  shorter  than  the  superior 
petrosal,  but  considerably  wider.  As  it  crosses  the  anterior  compartment  of  the 
jugular  foramen,  it  separates  the  glosso-pharyngeal  from  the  vagus  and  accessory 
nerves.  It  receives  veins  from  the  inferior  surface  of  the  cerebellum,  from  the 
medulla  and  pons,  and  from  the  internal  ear.  The  last,  the  vein  of  the  cochlear 
canaliculus  [v.  canaliculi  cochleae],  issues  through  the  canaliculus  cochleae. 

(10)  The  cavernous  sinus  [sinus  cavernosus]  (fig.  516)  is  an  irregularly  shaped 
venous  space  situated  between  the  meningeal  and  periosteal  layers  of  the  dura 
mater  on  the  side  of  the  body  of  the  sphenoid  bone.  It  extends  from  the  medial 
end  of  the  superior  orbital  (sphenoidal)  fissure  in  front  to  the  apex  of  the  petrous 
bone  behind.  Its  lateral  wall  is  the  more  distinct,  and  contains  the  third  and 
fourth  nerves,  and  the  ophthalmic  division  of  the  fifth  nerve.  The  nerves  take 
the  above-mentioned  order  from  above  downward,  and  in  the  medio-lateral  direc- 
tion. The  internal  carotid  artery  and  the  sixth  nerve  also  pass  through  the  sinus, 
being  separated  from  the  blood  by  the  endothelial  lining.  The  right  and  left 
cavernous  sinuses  communicate  across  the  middle  line  with  the  opposite  sinus  in 
front  and  behind  the  hypophysis  cerebri  as  before  mentioned. 

The  cavernous  sinus  is  traversed  by  numerous  trabeculae  or  fibrous  bands,  so  that  there  is 
no  central  space,  but  rather  a  number  of  endotheUal-lined  irregular  lacunar  cavities  commu- 
nicating one  another.  Hence  its  name  cavernous,  from  its  resemblance  to  cavernous  tissue. 
In  front  it  receives  the  ophthalmic  vein,  with  which  it  is  practically  continuous,  and  just 
above  the  third  nerve  the  spheno-parietal  sinus.  Medially  it  communicates  with  the  opposite 
sinus,  and  posteriorly  it  ends  in  the  superior  and  inferior  petrosal  sinuses.  It  also  receives 
veins  from  the  inferior  surface  of  the  frontal  lobe  of  the  brain,  and  some  of  the  middle  cerebral 
veins.     Through  the  Vesahan  vein,  which  runs  in  a  minute  foramen  in  the  spinous  process  of 


THE  VEINS  OF  THE  BRAIN 


653 


the  sphenoid  bone,  the  sinus  communicates  with  the  pterygoid  plexus  of  veins;  through  the 
venous  plexus  around  the  petrosal  portion  of  the  internal  carotid  [plexus  venosus  caroticus 
internus],  with  the  internal  jugular  vein;  and  through  a  venous  rete  which  leaves  the  cranium 
by  the  foramen  ovale  [rete  foraminis  ovalis]  and  by  small  veins  passing  through  the  foramen 
lacerum  medium,  with  the  pterygoid  and  pharyngeal  plexuses. 

(11)  The  spheno-parietal  sinus  [sinus  sphenoparietalis]  runs  in  a  slight  groove 
on  the  under  surface  of  the  lesser  wing  of  the  sphenoid  bone.  It  originates  in 
one  of  the  meningeal  veins  near  the  apex  of  the  lesser  wang,  and,  running  roedially, 
passes  through  the  sphenoidal  fold  of  dura  mater  above  the  third  nerve  into  the 
front  part  of  the  cavernous  sinus.  It  generally  receives  the  anterior  temporal 
veins  from  the  diploe. 


( 


Fig.  516. — The  Venous  Sinttses  at  the  Base  of  the  Brain.     The  dura  mater  has  not  been 
removed.     (After  Toldt,  ''Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York,) 


Position  of  crista  gall: 
Circular  sinus  \ 

Circular  sinus  \ 


Process  of  dura  in  foramen  cEecum 


Eyeball 


Ophthalmic  vein 


Connection 
the  rete  foraminis 
ovalis 

Middle    meningea: 
artery 


Internal  carotid  _ 
artery 

Superior  T>ulb  of  the  __ 
internal  jugular 
vein 

Transverse  sinus 


Mastoid  vein 
Vertebral  artery 


._-  Maxillary  nerve 


-^  V^     ~  Facial  nerve 


■"Acoustic  nerve 


Vagus  nerve 
Accessory  nerve 


Fold  of  dura  mater 


Hypoglossal  nerve 
First  spinal  nerve 


The  petro-squamous  sinus  is  occasionally  present.  It  hes  in  a  groove  along  the  junction 
of  the  petrous  and  squamous  portions  of  the  temporal  bone.  It  opens  posteriorly  into  the  trans- 
verse sinus  at  the  spot  where  the  latter  enters  on  its  sigmoid  course.  In  front  it  sometimes, 
though  very  rarely,  passes  through  a  foramen  in  the  squamous  portion  of  the  temporal  bone 
between  the  mandibular  fossa  and  the  external  auditory  meatus  into  the  temporal  vein. 


3.  THE  VEINS  OF^THE  BRAIN 

The  veins  of  the  brain  present  the  following  peculiarities: — (a)  They  do  not 
accompany  the  cerebral  arteries,  (h)  Ascending  veins  do  not,  as  in  other  situ- 
ations, run  with  descending  arteries,  but  with  ascending  arteries,  and  vice  versa. 
(c)  The  deep  veins  do  not  freely  communicate,  {d)  The  veins  have  very  thin 
walls,  no  muscular  coat,  and  no  valves,  ie)  The  veins  opening  into  the  sagittal, 
and  some  of  those  opening  into  the  transverse  (lateral)  sinus  pour  in  their  blood  in 
a  direction  opposite  to  the  current  in  the  sinuses,  so  impeding  the  flow  in  both 


654 


THE  BLOOD-VASCULAR  SYSTEM 


vein  and  sinus.     (/)  The  flow  of  blood  in  the  sinuses  is  further  retarded  by  the 

trabeculfe  stretching  across  their  lumen,  and  in  the  sagittal  sinus  by  the  blood 

having  to  ascend,  when  the  body  is  erect,  through  the  anterior  half  of  its  course. 

The  veins  of  the  brain  may  be  divided  into  the  cerebral  and  the  cerebellar. 


Fig.  517.- 


-The  Veins  of  the  Brain,  Superior  Surface.     (After  Toldt, 
Anatomy,"  Rebman,  London  and  New  York.) 


'Atlas  of  Human 


Superior  sagittal  sinus 


Lateral    protrusion 
(lacuna)    of     superior 
sagittal   sinus   Un-  \ 
jected) 


—  Superior  cerebral  veins 


Lateral  lacuna  of  su.* 
perior  sagittal  sinus 
(opened) 


Arachnoidal 
(Pacchionian) 


Lateral  lacuna  of  superior  sagit- 
(opened) 


Venous  orifice 


The  Cerebral  Veins 

The  cerebral  veins,  like  the  cerebral  arteries,  may  be  divided  into  the  cortical 
and  the  central. 

The  cortical  or  superficial  veins  ramify  on  the  surface  of  the  brain  and  return 
the  blood  from  the  cortical  substance  into  the  venous  sinuses.  The}^  lie  for  the 
most  part  in  the  sulci  between  the  gyri,  but  some  pass  over  the  gyri  from  one  sulcus 
to  another.     They  consist  of  two  sets :  a  superior  and  an  inferior. 

(1)  The  superior  cerebral  veins  [vente  cerebri  superiores]  (fig.  517),  some  eight  to  twelve  in 
number  on  each  side,  are  formed  by  the  union  of  branches  from  the  convex  and  medial  surfaces 
of  the  cerebrum.  Those  from  the  convex  surface  pass  medially  and  forward  toward  the 
longitudinal  fissure,  where  they  are  joined  by  the  branches  coming  from  the  medial  surface. 
After  receiving  a  sheath  from  the  arachnoid,  they  enter  obliquely  into  the  superior  sagittal 


THE  CEREBRAL  VEINS 


655 


sinus,  running  for  some  distance  in  its  walls.  These  veins  freely  communicate  with  each  other, 
thus  differing  from  the  cortical  arteries.  They  also  communicate  with  the  inferior  cortical 
veins.  They  may  be  roughly  divided  into  (a)  frontal;  (6)  paracentral;  (c)  central;  (d)  occipital. 
(2)  The  inferior  cerebral  veins  [venec  cerebri  inferiores]  (fig.  518),  ramify  on  the  base  of 
the  hemisphere  and  the  lower  part  of  its  lateral  surface.  Those  on  the  inferior  surface  of  the 
frontal  lobe  pass,  in  part  into  the  inferior  sagittal  sinus,  and  in  part  into  the  cavernous  sinus. 
Those  on  the  temporal  lobe  enter  in  part  into  the  superior  petrosal  sinus,  and  in  part  into  the 
transverse  sinus,  passing  into  the  latter  from  before  backward.  A  large  vein  from  the  occipital 
lobe  winds  over  the  cerebral  peduncle  and  joins  the  great  cerebral  vein  (of  Galen)  just  before 
the  latter  enters  the  straight  sinus.  One  of  the  inferior  cortical  veins  is  called  the  middle 
cerebral  vein  [v.  cerebri  media] ;  it  runs  in  the  lateral  fissure  (of  Sylvius)  and  ends  in  the  cavernous 
sinus.     This  vein  is  sometimes  called  the  superficial  Sylvian  vein.     Another,  the  great  anasto- 

FiG.  518. — The  Veins  op  t^e  Brain,  Inpehior  Sttepace.     (After  Toldt,  "Atlas  of  Human 
Anatomy,"  Rebman,  London  and  New  York.) 

Roots  of  the  superior 
cerebral  veins 


Opening  of  the  in- 
f  e  r  i  0  r  cerebral 
veins  into  the 
transverse  sinus 


Inferior  cerebellar  veins 


Opening  of  the  superior  sagittal  sinus  -" 
into  the  right  transverse  sinus 


Inferior  cere- 
^/    bral  veins 


Anterior  external 
spinal  ^ 


Opening  of  the  straight  sinus  into  the 
left  transverse  sinus 


Occipital  sinus 


mosing  vein  of  Trolard,  a  branch  of  the  middle  cerebral,  estabhshes  a  communication  between 
the  superior  sagittal  and  cavernous  sinuses  by  anastomosing  with  one  of  the  superior  cortical 
veins.  A  second  anastomotic  vein,  that  of  Labb6,  is  also  a  tributary  of  the  middle  cerebral, 
and  connects  the  veins  over  the  temporal  lobe  with  the  transverse  sinus. 

A  small  inferior  cerebral  vein,  the  ophthalmomeningeal  vein,  estabhshes  a  communication 
between  the  cerebral  veins  and  those  of  the  orbit.  It  communicates  with  the  veins  of  the  base 
and  is  usually  drained  by  the  superior  ophthalmic  vein.  It  occasionally  opens  into  the  superior 
petrosal  sinus. 

The  central  or  deep  (ganglionic)  veins  return  blood  from  the  internal  parts  of 
the  cerebrum,  and  converge  to  the  great  cerebral  vein. 


656 


THE  BLOOD-VASCULAR  SYSTEM 


Fig.  519. — The  Veins  of  the  Brain,  Lateral  Surface.     (After  Toldt,  "Atlas  of  Human 
Anatomy/'  London  and  New  York.) 
Superior  cerebral  veins     Dura  mater 

Lateral  lacuna  of  the  superior  ^ r__^        » 

sagittal  sinus  _ ^.  ^y'7^^t0'^^mK~^  J^ 

Middle  cerebral  vein 


Transverse  sinus 
Middle  temporal  vein 


External  carotid  artery 

Palatine  vein 

Internal  pterygoid  muscle 

Posterior  facial  vein 

Internal  carotid  artery 

Hypoglossal  nerve    ' 


Internal  jugular  vein 


^^^       ^f  Internal  maxillary  artery 

&g?"**5^<^     Vena  comitans  of  hypo- 
**-^       ■*  glossal  nerve 

Submaxillary  duct 
External  maxillary  artery 
;X   ''^N^     Anterior  facial  vein 
Y  \  2»B        Lingual  artery 

Superior  thyreoid  vein 


Superior  oph 
thalmic  vein 
Inferior  oph- 
thalmic vein 
Pterygoid 
plexus 

Temporal 


Fig.  520. — The  Ophthalmic  Veins.     (After  Quain.) 

Posterior  ciliary  vein 
Superior  ophthalmic  vein 


Supraorbital  vein 
communicating 
with  nasofrontal 

Frontal  vein 
Lacrimal  gland 


Maxillary  sinus 


•Anterior  facial  vein 


THE  VEINS  OF  THE  EAR  657 

(3)  The  internal  cerebral  veins  [vv.  cerebri  internee]  are  two  large  venous  trunks  (the  vense 
Galeni)  which  leave  the  brain  at  the  transverse  fissure,  that  is,  between  the  splenium  of  the 
corpus  callosum  and  the  corpora  quadrigemina.  In  this  region  they  unite  to  form  the  great 
cerebral  vein  [v.  cerebri  magna,  Galeni],  which  opens  into  the  anterior  end  of  the  straight 
sinus.  The  internal  cerebral  veins  are  formed  by  the  union  of  the  chorioid  vein  with  the  vena 
terminalis  near  the  interventricular  foramen.  From  this  spot  they  run  backward  parallel  to 
each  other,  between  the  layers  of  the  tela  chorioidea,  and  terminate  in  the  way  above  mentioned. 

Tributaries  of  the  internal  cerebral  veins. — In  addition  to  the  vena  terminalis  and  the  chori- 
oidal,  the  internal  cerebral  veins  also  receive  the  basal  vein,  the  veins  of  the  thalmus,  the 
vein  of  the  chorioid  plexus  of  the  third  ventricle,  and  veins  from  the  corpus  callosum,  the  pineal 
body,  the  corpora  quadrigemina,  and  posterior  horn  of  the  lateral  ventricle.  The  united 
trunk,  or  great  cerebral  vein,  receives  veins  from  the  upper  surface  of  the  cerebellum,  and  one  of 
the  posterior  inferior  cerebral  veins. 

The  chorioid  vein  [v.  chorioidea]  runs  with  the  chorioid  plexus.  It  begins  in  the  inferior 
cornu  of  the  lateral  ventricle,  and  ascends  on  the  lateral  side  of  the  chorioid  plexus  along  the 
margin  of  the  tela  chorioidea  to  the  interventricular  foramen,  where  it  unites  with  the  vena 
terminalis  to  form  the  internal  cerebral  vein.  It  receives  tributaries  from  the  hippocampus, 
corpus  callosum,  and  fornix. 

The  terminal  vein  (or  vein  of  the  corpus  striatum)  [v.  terminalis],  formed  by  veins  from  the 
corpus  striatum  and  thalamus,  runs  forward  in  the  groove  between  those  structures,  passing 
in  its  course  beneath  the  stria  terminalis,  and  joins  the  chorioid  (choroid)  vein  at  the  inter- 
ventricular foramen.  Tributaries. — It  receives,  in  addition  to  the  veins  from  the  corpus 
striatum,  thalamus  and  fornix,  the  vena  septi  pellucidi  which  receives  blood  from  the  septum 
peUucidum,  and  anterior  cornu  of  the  lateral  ventricle. 

The  basal  vein  [v.  basalis],  runs  backward  over  the  cerebral  peduncle,  and  enters  the 
internal  cerebral  vein  near  the  union  of  that  vessel  with  the  vein  of  the  opposite  side. 

Tributaries. — A  vein,  the  deep  Sylvian,  from  the  insula  and  surrounding  convlutions;  the 
inferior  striate  veins  from  the  corpus  striatum,  which  they  leave  through  the  anterior  perforated 
substance;  and  the  anterior  cerebral  veins  from  the  front  of  the  corpus  callosum.  It  is  also 
joined  by  interpenduncular  veins  from  the  structures  in  the  interpeduncular  space;  ventricular 
veins  from  the  inferior  cornu  of  the  lateral  ventricle;  and  by  mesencephalic  veins  from  the 
mid-brain. 

The  Cerebellar  Veins 

The  cerebellar  veins  are  divided  into  the  superior  and  inferior. 

The  superior  [vv.  cerebeDi  superiores]  ramify  on  the  upper  surface  of  the  cerebellum;  some 
of  them  run  medially  over  the  superior  vermis  to  join  the  straight  sinus  and  great  cerebral 
vein;  others  run  laterally  to  the  transverse  and  superior  petrosal  sinuses. 

The  inferior  [vv.  cerebeUi  inferiores],  larger  than  the  superior,  run,  some  forward  and 
laterally  to  the  inferior  petrosal  and  transverse  sinuses,  and  others  directly  backward  to  the 
occipital  sinus. 

The  Veins  of  the  Medulla  and  Pons 

The  veins  from  the  medulla  oblongata  and  the  pons  terminate  in  the  inferior 
petrosal  and  transverse  sinuses. 

4.  THE  VEINS  OF  THE  NASAL  CAVITIES 

The  venous  plexuses  on  the  inferior  nasal  concha  (turbinate  bone)  and  back 
of  the  septum  are  described  with  the  Nose.  The  veins  leaving  the  nasal  cavities 
follow  roughly  the  course  of  their  corresponding  arteries.  Thus  the  spheno- 
palatine veins  pass  through  the  spheno-palatine  foramen  into  the  pterygoid  plexus; 
the  anterior  and  posterior  ethmoidal  veins  join  the  ophthalmic.  Small  veins 
accompany  branches  of  the  external  maxillary  artery  through  the  nasal  bones  and 
frontal  processes  of  the  maxillary  bones,  and  end  in  the  angular  and  anterior  facial 
veins;  and  other  small  veins  pass  from  the  nose  anteriorly  into  the  superior  labial, 
and  thence  to  the  anterior  facial. 

5.  THE  VEINS  OF  THE  EAR 

The  veins  from  the  external  ear  and  external  auditory  meatus  join  the  posterior 
facial  and  posterior  auricular  veins.  The  veins  from  the  tympanum  open  into 
the  superior  petrosal  sinus  and  posterior  facial  vein.  The  blood  from  the  laby- 
rinth flows  chiefly  through  the  internal  auditory  veins  [vv.  auditivse  internse], 
which  lie  with  the  internal  auditory  artery  in  the  internal  auditory  meatus,  and 
enters  the  transverse  or  inferior  petrosal  sinus.  Some  of  the  blood  from  the  laby- 
rinth, however,  passes  through  the  vestibular  vein  which  Hes  in  the  aquseductus 


658 


THE  BLOOD-VASCULAR  SYSTEM 


vestibuli,  into  the  inferior  petrosal  sinus.  Some  also  passes  through  the  vena 
canalicuU  cochleae  which  traverses  the  canal  of  the  same  name  and  empties  into 
the  commencement  of  the  internal  jugular  vein. 

6.  THE  VEINS  OF  THE  ORBIT 

The  blood  from  the  eyeball  and  orbit  is  returned  by  the  superior  ophthalmic 
vein  into  the  cavernous  sinus.  This  vein  and  its  tributaries  have  no  valves,  and 
communicate  with  the  frontal,  supraorbital,  inferior  cerebral,  and  other  veins. 
Hence  under  certain  conditions,  as  from  pressure  on  the  cavernous  sinus,  the  blood 

Fig.  521. — The  Veins  of  the  Orbit. 


Supraorbital  artery 

Lacrimal  gland 

Superior  rectus,  cut 

Eyeball 


Lateral  rectus 
Lacrimal  artery 

Superior  rectus,  cut 
Inferior  ophthalmic  vein 
Superior  ophthalmic  vein 


Optic  nerve 
Superior  ophthalmic 


^ Commencement  of  superior 

H^l  ophthalmic  vein 

Reflected  tendon  of  superior 

obUque 
Ophthalmic  artery 


Anterior  ethmoidal  artery 

Posterior  ethmoidal  artery 
Ciliary  arteries 

Levator  palpebrae,  cut 
Annulus  communis  of  Zinn 
Ophthalmic  artery 

Optic  chiasma 


Internal  carotid  artery 

may  flow  in  the  contrary  direction  to  the  normal — i.  e.,  from  behind  forward  into 
the  frontal  and  supraorbital,  and  thence  through  the  angular  vein  into  the  anterior 
facial;  or  upward  into  the  cerebral  venous  system.  In  this  way  pressure  on  the 
retinal  veins  is  quickly  relieved,  and  little  or  no  distension  occurs  in  cases  of 
obstruction  in  the  cavernous  sinus. 

The  superior  ophthalmic  vein  [v.  ophthalmica  superior]  begins  at  the  medial 
angle  of  the  eyelid  by  a  free  communication  with  the  frontal,  supraorbital,  and 
angular  veins,  and  thence  runs  backward  and  laterally  with  the  ophthalmic 
artery  across  the  optic  nerve  to  the  medial  end  of  the  superior  orbital  (sphenoidal) 
fissure,  where  it  is  usually  joined  by  the  inferior  ophthalmic  vein.  It  then  passes 
backward  between  the  two  heads  of  the  lateral  rectus  muscle  below  the  sixth 
nerve,  leaves  the  orbit  through  the  medial  end  of  the  superior  orbital  (sphenoidal) 
fissure  and  enters  the  front  part  of  the  cavernous  sinus.  In  this  course  it  lies 
anterior  and  superficial  to  the  ophthalmic  artery. 

Tributaries. — (1)  The  naso-frontal  vein;  (2)  the  superior  muscular  veins;  (3) 
the  veins  of  the  lids  and  conjunctiva;  (4)  the  ciliary  veins;  (5)  the  anterior  and 
posterior  ethmoidal  veins;  (6)  the  lacrimal  vein;  (7)  the  central  vein  of  the 
retina;  and  (8)  the  inferior  ophthalmic  vein. 

(1)  The  naso-frontal  vein  [v.  naso-frontalis]  begins  by  a  free  communication  with  the  supra- 
orbital vein  and  enters  the  orbit  through  the  frontal  notch  or  foramen.  It  frequently  joins 
the  superior  ophthalmic  vein  quite  far  back  in  the  orbit  (see  fig.  ,520). 

(2)  The  muscular  veins  [vv.  musculares]  are  derived  from  the  levator  palpebrse,  superior 
rectus,  superior  oblique,  and  medial  rectus. 

(3)  The  palpebral  and  conjunctival  veins  [vv.  palpebrales;  vv.  conjunctivales  ant.  et  post.], 
both  anterior  and  posterior,  open  into  the  superior  ophthalmic. 

(4)  The  ciliary  veins,  the  veins  of  the  eyeball,  are  divided  into  two  sets.  An  anterior 
[vv.   cihares  ant.]    emerge   from  the   eyeball   with   the    anterior  ciliary   arteries,   and  open 


THE  INTERNAL  JUGULAR  VEIN  659 

into  the  muscular  veins  returning  the  blood  from  the  four  recti.  They  form  a  circumcorneal 
ring  of  episcleral  veins  [w.  episclerales].  The  posterior  set,  which  drain  the  venae  vorticosae, 
leave  the  globe  midway  between  the  cornea  and  the  entrance  of  the  optic  nerve.  The  latter 
veins  are  four  or  five  m  number,  the  upper  ending  in  the  superior,  the  lower  in  the  inferior 
ophthalmic  vein  (fig.  520). 

(5)  The  anterior  and  posterior  ethmoidal  veins  [w.  ethmoidales  ant.  et  post.),  correspond 
in  their  course  with  the  arteries  of  the  same  name.  They  enter  the  orbit  through  the  anterior 
and  posterior  ethmoidal  foramina,  and  join  either  the  ophthalmic  direct,  or  one  or  other  of 
the  superior  muscular  branches. 

(6)  The  lacrimal  vein  [v.  lacrimalis]  retm-ns  the  blood  from  the  lacrimal  gland,  and  corre- 
sponds in  its  course  to  the  lacrimal  artery. 

(7)  The  central  vein  of  the  retina  [v.  centrahs  retinse]  runs  with  the  central  artery  in  the 
optic  nerve.     It  joins  the  superior  ophthalmic  at  the  back  of  the  orbit. 

(8)  The  inferior  ophthalmic  vein  [v.  ophthalmica  inferior],  smaller  than  the  superior,  is 
formed  near  the  front  of  the  orbit  by  the  confluence  of  the  inferior  muscular  with  the  lower 
posterior  ciliary  veins.  It  runs  backward  below  the  optic  nerve,  along  the  floor  of  the  orbit, 
and  either  joins  the  superior  ophthalmic  vein,  or  opens  separately  into  the  cavernous  sinus. 
A  large  communicating  branch  passes  downward  through  the  inferior  orbital  (spheno-maxillary) 
fissure  to  join  the  pterygoid  plexus  of  veins.  It  receives  muscular  twigs  from  the  inferior  and 
lateral  rectus  and  from  the  interior  oblique,  and  some  posteior  ciliary  veins. 

7.  THE  VEINS  OF  THE  PHARYNX  AND  LARYNX 

The  pharyngeal  veins  [vv.  pharyngeee]  are  arranged  in  the  form  of  a  plexus, 
between  the  constrictor  muscles  and  the  pharyngeal  or  prevertebral  fascia.  The 
pharyngeal  plexus  receives  branches  from  the  mucous  membrane,  the  pterygoid 
canal  [vv.  canalis  pterygoidei]  from  the  soft  palate,  the  Eustachian  tube  and  the 
anterior  recti  and  longus  colli  muscles.  Above,  it  communicates  with  the  ptery- 
goid plexus  of  veins;  below  it  drains  into  the  internal  jugular  vein. 

The  veins  of  the  larynx  end  partly  in  the  superior  laryngeal  vein  [v.  laryngea 
superior],  which  opens  into  the  internal  jugular  vein,  and  partly  in  the  inferior 
laryngeal  vein  [v.  laryngea  inferior],  which  terminates  in  the  plexus  thyroideus 
impar.     The  laryngeal  plexus  of  veins  communicates  with  the  pharyngeal  plexus. 

8.  THE  DEEP  VEINS  OF  THE  NECK 

The  deep  veins  of  the  neck  include  the  internal  jugular,  vertebral,  deep  cervical, 
erior  thyreoid,  thyreoidea  ima,  thymic,  tracheal,  and  oesophageal  veins. 

The  Internal  Jugular  Vein 

The  internal  jugular  vein  [v.  jugularis  interna]  begins  at  the  jugular  fossa,  and 
is  the  continuation  of  the  transverse  sinus.  It  passes  down  the  neck,  in  company 
first  with  the  internal  carotid  artery  and  then  with  the  common  carotid  artery, 
to  a  point  a  little  lateral  to  the  sterno-clavicular  articulation,  where  it  joins  the 
subclavian  to  form  the  innominate  vein.  At  its  commencement  in  the  larger, 
posterior  and  lateral  part  of  the  jugular  foramen,  it  is  somewhat  dilated,  forming 
the  superior  bulb  of  the  jugular  vein  [bulbus  v.  jugularis  superior]  (fig.  522).  This 
dilated  part  of  the  internal  jugular  vein  lies  in  the  jugular  fossa  of  the  temporal 
bone  and  is  therefore  in  immediate  relation  to  the  floor  of  the  tympanum.  At 
first  the  internal  jugular  lies  in  front  of  the  rectus  capitis  lateralis,  and  behind  the 
internal  carotid  artery,  from  which  it  is  separated  by  the  hypoglossal,  glosso- 
pharyngeal, and  vagus  nerves,  and  by  the  carotid  plexus  of  the  sympathetic. 
As  it  descends  it  passes  gradually  to  the  lateral  side  of  the  internal  carotid,  and  re- 
tains this  relation  as  far  as  the  upper  border  of  the  thyreoid  cartilage.  Thence  it 
runs  to  its  termination  along  the  lateral  side  of  the  common  carotid  artery,  being 
contained  in  the  same  sheath  with  it  and  the  vagus  nerve,  but  separated  from 
these  structures  by  a  distinct  septum.  The  vein  generally  overlaps  the  artery  in 
front.  About  2.5  cm.  (1  in.)  above  its  termination  it  contains  a  pair  of  imperfect 
valves  below  which  a  second  dilation  usually  occurs  in  the  vein.  This,  the  inferior 
bulb  [bulbus  v.  jugularis  inferior],  extends  as  low  as  the  junction  of  the  internal 
jugular  with  the  subclavian.  It  not  infrequently  receives  the  termination  of  the 
external  jugular  vein. 

Tributaries. — At  the  superior  bulb  the  internal  jugular  vein  receives  the 
inferior  petrosal  sinus;  the  vein  of  the  cochlear  canaliculus,   and  a  meningeal 


660 


THE  BLOOD-VASCULAR  SYSTEM 


vein;  opposite  the  angle  of  the  jaw,  veins  from  the  pharyngeal  plexus,  and  often  a 
communicating  branch  from  the  external  jugular  vein;  opposite  the  bifurcation  of 
the  carotid  it  is  joined  by  the  common  facial,  and  a  little  lower  down  by  the 
lingual,  sternomastoid,  and  the  superior  thyreoid  veins.  At  the  level  of  the  cricoid 
cartilage  by  the  middle  thyreoid  when  this  vein  is  present. 

The  inferior  petrosal  sinus  is  described  with  the  other  sinuses  of  the  brain  (p. 
652) ;  the  pharyngeal  plexus  with  the  veins  of  the  pharynx  (see  p.  659) ;  and  the 
common  facial  vein  with  the  superficial  veins  of  the  scalp  and  face  (p.  646). 

The  lingual  vein  [v.  lingualis],  begins  near  the  tip  of  the  tongue,  where  it  accompanies  the 
arteria  profunda  linguEe.  It  lies  at  first  beneath  the  mucous  membrane  covering  the  under 
surface  of  the  tongue.  It  then  passes  backward  medial  to  the  hyo-glossus,  and  in  company 
with  the  lingual  artery.     After  receiving  the  sublingual  vein  [v.  sublingualis]  and  the  dorsal 


Fig.  522. — The  Internal  Jugular  Vein.     (After  Henle). 


Branches  of  the 
anterior  facial 
vein 


Superficial  temporal  vein 


Styloglossus  muscle 
Sublingual  gland 


Hyoglossus  muscle 


Geniohyoid  muscli 


Sternohyoid  muscle 
Thyreohyoid  muscle 


Omohyoid  muscle 


Temporal  vein 

Stylopharyngeus 

Pterygoid  plexus 

Superficial  branches 

^Styloglossus  muscle 


^Posterior  facial  vein 
Pharyngeal  vein 
Stylohyoid  muscle 
Anterior  facial  i 
Common  facial  vein 


Superior  thyreoid  vein 


Internal  jugular  vein 


lingual  veins  [w.  dorsales  linguae],  which  roughly  correspond  to  their  respective  arteries,  it  is 
joined  by  the  small  v.  comitans  nervi  hypoglossi  which  follows  the  upper  border  of  the  hypo- 
glossal nerve.  The  trunk  finally  crosses  the  common  carotid  artery  and  opens  into  the  internal 
jugular  vein.  The  lingual  vein  communicates  with  the  pharyngeal  veins  and  with  tributariesof 
the  anterior  facial.  It  occasionally  terminates  in  the  posterior  or  in  the  common  facial  vein. 
The  sternomastoid  vein  [v.  sternocleidomastoidea]  accompanies  the  artery  of  the  same  name  and 
empties  into  the  internal  jugular. 

The  superior  thyreoid  vein  [v.  thyreoidea  superior]  emerges  from  the  upper  part  of  the 
thyreoid  gland,  in  which  it  freely  anastomoses  with  the  other  thyreoid  veins.  This  anas- 
tomosis, the  plexus  thyreoideus  impar,  occurs  both  in  the  substance  of  the  organ  and  on  its 
surface  beneath  the  capsule.  The  vein  then  passes  upward  and  laterally  into  the  interna] 
jugular  vein,  crossing  the  common  carotid  artery  in  its  course.  At  times  it  forms  a  common 
trunk  with  the  common  facial  vein.  Its  tributaries  are  the  sterno-hyoid,  sterno-thyreoid, 
and  thyreo-hyoid  veins  from  the  muscles  bearing  those  names;  and  the  crico-thyreoid  and 
superior  laryngeal  veins  which  correspond  with  the  crico-thyreoid  and  superior  laryngeal  arteries 
respectively.     These  require  no  special  description. 


THYMIC,  TRACHEAL  AND  (ESOPHAGEAL  VEINS  661 

A  separate  vein  frequently  passes  out  from  the  capsule  of  the  thyreoid  gland  near  the  lower 
part  of  the  lateral  lobe,  crosses  the  common  carotid,  and  opens  into  the  main  superior  thyreoid 
vein  or  into  the  internal  jugular  vein  a  little  below  the  cricoid  cartilage.  In  the  former  case  it 
is  regarded  as  part  of  the  superior  th3Teoid  vein  system ;  in  the  latter  it  is  generally  known  as  the 
middle, thyreoid  vein. 

The  Vertebral  Vein 

The  vertebral  vein  [v.  vertebralis]  does  not  accompany  the  vertebral  artery  in 
its  fourth  stage,  that  is,  within  the  skull,  but  begins  in  the  posterior  vertebral 
venous  plexus  of  the  suboccipital  triangle.  It  then  enters  the  foramen  in  the 
transverse  process  of  the  altas,  and  passes  with  the  vertebral  artery  through  the 
foramina  in  the  transverse  processes  of  the  cervical  vertebrae,  forming  a  plexus 
around  the  artery.  On  leaving  the  transverse  process  of  the  sixth  cervical  verte- 
bra it  crosses  in  front  of  the  subclavian  artery  and  opens  into  the  innominate  vein. 
It  has  one  or  two  semilunar  valves  at  its  entrance  into  the  innominate  vein.  In 
the  suboccipital  triangle  it  communicates  with  the  internal  vertebral  venous 
plexuses,  with  the  deep  cervical,  and  occipital  veins,  and  is  joined  by  veins  from 
the  recti  and  oblique  muscles  and  the  pericranium. 

Tributaries. — -As  it  passes  down  the  neck  it  receives  (1)  intervertebral  veins,  which  issue 
along  with  the  cervical  nerves,  from  the  spinal  canal;  (2)  tributaries  from  the  anterior  and 
posterior  vertebral  venous  plexus  from  the  bodies  of  the  cervical  vertebrse  and  their  transverse 
processes;  and  (3)  tributaries  from  the  deep  cervical  muscles.  Just  before  it  terminates  in  the 
innominate  it  is  joined  by  (4)  the  anterior  vertebral  vein,  a  small  vein  which  accompanies  the 
ascending  cervical  artery,  and,  sometimes,  by  the  deep  cervical  vein. 

The  Deep  Cervical  Vein 

The  deep  cervical  vein  [v.  cervicahs  profunda],  larger  than  the  vertebral, 
passes  down  the  neck  posterior  to  the  cervical  transverse  processes.  It  corre- 
sponds to  the  deep  cervical  artery  from  which  it  is  separated  by  the  semispinalis 
eervicis  muscle. 

It  begins  in  the  posterior  vertebral  venous  plexus  and  receives  tributaries  from  the  deep 
muscles  of  the  neck.  It  communicates  with,  or  enthely  drains,  the  occipital  vein  by  a  branch 
which  perforates  the  trapezius  muscle.  The  deep  cervical  vein  then  passes  forward  beneath 
the  transverse  process  of  the  seventh  cervical  vertebra  to  open  into  the  innominate  vein  near 
the  vertebral,  or  into  the  latter  near  its  termination.     Its  orifice  is  guarded  by  a  pair  of  valves. 

The  Inferior  Thyreoid  and  Thyreoidea  Ima  Veins 

The  inferior  thyreoid  veins  [vv.  thyreoidea  inferiores]  descend  from  the  lower 
part  of  the  thyreoid  gland  obliquely  lateralward  to  the  innominate  veins.  The 
right  vein  crosses  the  innominate  arteiy  just  before  its  bifurcation,  and  ends  in 
the  right  innominate  vein  a  little  above  the  superior  vena  cava.  It  receives 
inferior  laryngeal  veins  and  veins  from  the  trachea,  and  has  valves  at  its  termina- 
tion in  the  innominate.  The  left  vein  passes  obliquely  over  the  trachea  behind 
the  sterno-thyreoid  muscle,  and  opens  into  the  left  innominate  vein.  It  also 
receives  laryngeal  and  tracheal  veins,  and  sometimes  the  thyreoidea  ima;  it  is 
guarded  by  valves  where  it  opens  into  the  innominate  trunk. 

The  thyreoidea  ima  vein  [v.  thyreoidea  ima]  is  single  and  placed  approximately 
in  the  median  line.  It  begins  in  the  thj'reoid  isthmus  from  the  plexus  thyreoideus 
impar,  runs  downward  upon  the  anterior  surface  of  the  trachea,  and  opens  into 
the  left  innominate  vein  or  into  the  left  inferior  thja-eoid. 

The  Thymic,  Tracheal  and  CEsophageal  Veins 

These  small  veins  usually  open  into  the  left  innominate  vein.  The  thymic 
veins  [vv.  thymicae],  small  in  the  adult,  open  into  the  left  innominate  or  into  the 
inferior  thyreoid  or  thyreoidea  ima  vein.  The  tracheal  veins  [vv.  tracheales] 
anastomose  with  the  laryngeal  and  bronchial  veins.  The  oesophageal  veins 
[vv.  cesophagese]  from  the  upper  part  of  the  oesophagus,  anastomose  with  the 
lower  oesophageal  veins  and  with  the  pharyngeal  plexus. 


662  THE  BLOOD-VASCULAR  SYSTEM 

THE  VEINS  OF  THE  THORAX 
THE  SUPERFICIAL  VEINS  OF  THE  THORAX 

The  superficial  veins  of  the  front  of  the  thorax  can  be  seen  in  fig.  537.  They 
form  a  plexus  over  the  entire  chest  which  the  portion  over  the  mammary  gland  is 
called  the  mammary  plexus.  The  laterally  placed  lateral  thoracic  and  costo- 
axillary  veins  drain  the  mammary  plexus  and  communicate  with  the  thoraco- 
epigastric vein.  These  three  veins  terminate  in  the  axillary  vein  (p.  671).  The 
veins  nearer  the  median  line  are  drained  by  the  internal  mammary  vein  and  its 
anterior  intercostal  and  superior  epigastric  tributaries.  The  veins  over  the  entire 
thorax  are  in  free  communication  with  the  superficial  veins  of  the  abdominal  wall 
(p.  683). 

THE  DEEP  VEINS  OF  THE  THORAX 

The  deep  veins  of  the  thorax  are: — the  pulmonary  veins,  and  the  vena  cava 
superior  and  its  innominate  and  other  tributaries.  Of  these  veins,  the  pulmonary, 
the  vena  cava  superior,  and  the  innominate  veins  have  already  been  described, 
as  have  the  tributaries  of  the  latter  arising  in  the  neck. 

The  following  veins  are  described  below: — (1)  The  azygos  and  ascending 
lumbar  veins,  which  discharge  their  blood  into  the  vena  cava  superior;  (2)  the 
veins  of  the  vertebral  column,  which  are  tributary  to  the  azygos  veins  through  the 
intercostals;  (3)  the  internal  mammary  veins,  and  (4)  the  superior  phrenic,  an- 
terior mediastinal  and  pericardiac  veins,  all  of  which  open  into  the  innominate 
veins. 

I.  THE  AZYGOS  AND  ASCENDING  LUMBAR  VEINS 

The  azygos  veins  are  longitudinal  veins,  the  remnants  of  the  posterior  cardi- 
nals, which  are  the  main  collecting  trunks  for  the  posterior  part  of  the  body  in 
the  embryo.  They  lie  along  the  sides  of  the  thoracic  vertebrae,  and  collect  the 
blood  from  the  intercostal  veins;  they  are  the  upward  continuation  of  longitudinal 
anastomotic  trunks,  the  ascending  lumbar  veins  which  take  origin  in  the  abdomen. 
The  azygos  veins  are  three  in  number,  the  azygos  (azygos  major)  on  the  right  side, 
and  the  hemiazygos  (azygos  minor)  and  accessory  hemiazygos  (azygos  tertia)  on 
the  left. 

The  azygos  vein  [v.  azygos]  begins  in  the  abdomen  as  a  continuation  .upward  of 
the  ascending  lumbar  vein.  Through  this  means  it  connects  with  the  iliac  veins 
and  it  has  also  an  anastomosis  with  the  vena  cava  inferior  which  may  become  very 
important  in  cases  of  obstruction  of  the  vena  cava.  It  runs  up  through  the  pos- 
terior mediastinum  on  the  right  side  of  the  front  of  the  bodies  of  the  thoracic 
vertebrte  as  high  as  the  fourth  thoracic  vertebra,  in  this  part  of  its  course  lying  to 
the  right  of  the  aorta  and  thoracic  duct;  it  then  curves  forward  over  the  root  of  the 
right  lung,  and  opens  into  the  vena  cava  superior  immediately  before  the  latter 
pierces  the  pericardium. 

It  usually  contains  an  imperfect  pair  of  valves  at  the  point  where  it  turns  for- 
ward from  the  fourth  thoracic  vertebra  to  arch  over  the  root  of  the  lung;  and  still 
more  imperfect  valves  are  found  at  varying  intervals  lower  down  the  vein. 

It  receives  the  intercostal  veins  of  the  right  side,  except  the  first  two  or  three. 
These  veins  (usually  excepting  the  first)  are  collected  into  a  common  trunk 
before  joining  the  azygos  vein.  It  also  receives  the  hemiazygos  and  accessory 
hemiazygos,  the  right  posterior  bronchial  vein,  and  small  oesophageal  and  pos- 
terior mediastinal  veins. 

The  hemiazygos  vein  [v.  hemiazygos]  begins  in  the  abdomen  by  communicat- 
ing, like  the  azygos  vein,  with  the  ascending  lumbar  vein  of  its  own  side.  It 
courses  up  the  posterior  mediastinum  to  the  left  of  the  bodies  of  the  lower  thoracic 
vertebrae  as  high  as  the  eighth  or  ninth,  where  it  turns  obliquely  to  the  right,  and, 
crossing  in  front  of  the  vertebral  column  behind  the  aorta  and  the  oesophagus, 
opens  into  the  vena  azygos.  In  its  course  it  crosses  over  three  or  four  of  the  lower 
left  intercostal  arteries,  and  is  covered  by  the  pleura. 


AZYGOS  AND  ASCENDING  LUMBAR  VEINS 


663 


Tributaries. — (1)  The  lower  four  or  five  left  intercostal  veins;  (2)  the  lower 
end  of  the  accessory  hemiazygos  vein  (sometimes);  (3)  small  left  mediastinal 
veins;  and  (4)  the  lower  left  oesophageal  veins. 

The  accessory  hemiazygos  [v.  azygos  accessorial  varies  considerably  in  size, 
position,  and  arrangement,  and  is  often  continuous  with,  or  drained  by,  the  left 
superior  intercostal  vein.  It  hes  in  the  posterior  mediastinum  by  the  left  side  of 
the  bodies  of  the  fifth,  sixth,  and  seventh  or  eighth  thoracic  vertebrae,  and  is  more 


Fig.  523. — The  Superior  and  Inferior  Ven^  Cav.e,  the  Innominate  Veins, 
\ND  THE  Azygos  Veins 


Right  common  carotid 
.rtery 


Right  internal  jugular  - 


Right  lymphatic  duct 

Innominate  artery 

Right  vagus  nerve 

Right  innominate  vein 

Internal  mammary  vein 

Trunk  of  the  pericardiac 

and  thymic  veins 

Vena  cava  superior 


Vena  hemiazygos,  cross- 
ing to  enter  vena  azygos 


Hepatic  veins 


Right  inferior  phrenic 
artery 

Coeliac  artery 
iddle  suprarenal 
artery 


Right 


Right  spermatic  vein 


Left  common  carotid 

artery 
Left  vagus  nerve 

Thoracic  duct 

Left  innominate  vein 

Left  subclavian  artery 


Recurrent  nerve 


Accessory  hemiazygos 
CEsophagus 

Accessory  hemiazygos 

vein 
(Esophageal  branches 
from  aorta 

Vena  hemiazygos 


Thoracic  duct 


Left  inferior  phrenic 
artery 

Left  middle  suprarenal 

artery 
Cisterna  chyli 
Superior  mesenteric 
artery 

Left  ascending  lumbar 


or  less  vertical  in  direction.  It  communicates  above  with  the  left  superior  in- 
tercostal vein,  and  below  either  joins  the  hemiazygos  or  passes  obliquely  across 
the  seventh  or  eighth  thoracic  vertebra  to  join  the  azygos  vein.  It  crosses  the 
corresponding  left  intercostal  arteries,  and  is  covered  by  the  pleura. 

Tributaries. — (1)  The  fourth,  fifth,  sixth,  seventh,  and  sometimes  the  eighth 
intercostal  veins;  and  (2)  the  left  posterior  bronchial  vein. 

The  ascending  lumbar  vein  [v.  lumbalis  ascendens]  begins,  on  either  side,  in 
the  neighbourhood  of  the  sacral  promontory.     It  is  here  in  free  communication,  by 


664  •     THE  BLOOD-VASCULAR  SYSTEM 

means  of  the  anterior  sacral  plexus,  with  the  middle  and  lateral  sacral  veins,  and 
with  the  common  iliac,  hypogastric  and  ilio-lumbar  veins.  It  ascends  in  front  of 
the  lumbar  transverse  processes  communicating  with  the  lumbar  veins,  the  vena 
cava  inferior  and,  usually,  with  the  renal  vein.  The  right  vein  enters  the 
thorax  between  the  aorta  and  the  right  medial  crus  of  the  diaphragm,  and  is 
continued  upward  as  the  vena  azygos.  The  left  vein  pierces  the  left  medial  crus 
and  becomes  the  hemiazygos. 

The  intercostal  veins  [vv.  intercostales]. — The  intercostal  veins  are  twelve  in 
number  on  each  side,  the  last  one  being  subcostal.  They  correspond  to  the  inter- 
costal arteries.  There  is  one  vein  to  each  artery,  the  vein  lying  above  the  artery 
whilst  in  the  intercostal  space.  Each  vein  receives  a  dorsal  tributary  which 
accompanies  the  posterior  ramus  of  an  intercostal  artery  between  the  transverse 
process  of  the  vertebrae  and  the  neck  of  the  rib.  These  dorsal  branches  not  only 
return  the  blood  from  the  muscles  of  the  back,  but  receive  a  spinal  branch  from 
the  vertebral  venous  plexuses.  The  intercostal  veins  also  receive  small  tributaries 
from  the  bodies  of  the  vertebrae.  The  termination  of  the  intercostal  veins  is 
different  on  the  two  sides  and  also  varies  greatly  in  different  individuals.  The 
intercostal  vein  from  the  first  space  on  either  side  may  join  the  superior  inter- 
costal vein,  but  commonly  opens  directly  into  the  innominate  or  one  of  its  tribu- 
taries, most  frequently  the  vertebral. 

On  the  right  side. — The  second  intercostal  vein  joins  with  the  third  or  with  the  third  and 
fourth  to  form  the  right  superior  intercostal  vein  [v.  intercostalis  suprema  dextra].  This  vein 
opens  into  the  azygos  vein  as  the  latter  is  arching  over  the  root  of  the  right  lung.  The  rest 
join  the  azygos  directly.  The  upper  of  these  liave  well-marked  valves  where  they  join  the 
azygos  vein;  in  the  lower  veins  these  valves  are  imperfect.  All  the  intercostal  veins  are  pro- 
vided with  valves  in  their  course  between  the  muscles. 

On  the  left  side  the  second  intercostal  vein  joins  the  third  and  fourth  to  form  a  single 
trunk,  the  left  superior  intercostal  vein  [v.  intercostalis  suprema  sinistra].  This  vein  passes 
upward  across  the  arch  of  the  aorta  and  opens  into  the  left  innominate  vein.  The  left  superior 
intercostal  frequently  communicates  at  its  lower  end  with  the  accessory  hemiazygos  vein, 
which  is  occasionally  tributary  to  it.  In  most  oases  a  small  tributary  runs  up  over  the  front 
of  the  aortic  arch  to  join  the  superior  intercostal  vein;  it  is  a  vestige  of  the  left  common  cardinal 
and  from  it  a  small  fibrous  cord  can  often  be  traced  through  the  vestigial  fold  of  the  pericardium 
to  the  oblique  vein  of  the  left  atrium  (p.  523). 

The  left  fifth,  sixth  and  seventh  intercostal  veins  commonly  open  into  the  accessory 
hemiazygos,  and  the  eighth  or  ninth  and  succeeding  veins  into  the  hemiazygos.  The  method 
of  termination  of  the  intercostal  veins  of  the  left  side  is  subject  to  such  variation  that  a  normal 
arrangement  can  scarcely  be  said  to  exist  at  all.  The  eighth  may  open  directly  into  the  azygos, 
as  may  the  seventh  and  ninth  or  even  more  of  the  veins;  the  hemiazygos  and  accessory  hemi- 
azygos being  correspondingly  reduced  in  size. 

The  posterior  bronchial  veins  [vv.  bronchiales  posteriores]  correspond  to  the  bronchial 
arteries,  but  do  not  return  the  whole  of  the  blood  carried  to  the  lungs  by  those  vessels — that 
part  which  is  distributed  to  the  smaller  bronchial  tubes  and  the  alveola;  being  brought  back  by 
the  pulmonary  veins.  The  posterior  bronchial  veins  issue  from  the  lung  substance  behind  the 
structures  forming  the  root  of  the  lung.  The  right  vein  generally  joins  the  vena  azygos  just 
before  the  latter  vein  enters  the  superior  vena  cava.  The  left  vein  opens  into  accessory  hemi- 
azygos vein.  The  bronchial  veins  at  the  root  of  the  lung  receive  smaU  tributaries  from  the 
bronchial  glands,  from  the  trachea,  and  from  the  posterior  mediastinum. 

The  oesophageal  veins  [vv.  oesophagefe]  from  the  thoracic  portion  of  the  oesophagus  end 
in  part  in  the  vena  azygos,  and  in  part  in  the  vena  hemiazygos.  They  anastomose  with  the 
upper  oesophageal  veins,  and  with  the  coronary  vein. 

The  posterior  mediastinal  veins,  small  and  numerous,  open  into  the  azygos  and  hemiazygos 
veins. 

2.     THE  VEINS  OF  THE  VERTEBRAL  COLUMN 

The  venous  plexuses  around  and  within  the  vertebral  column  extending  from 
the  cranium  to  the  coccyx  may  be  divided  into  two  categories: — (1)  the  external 
and  (2)  the  internal  vertebral  venous  plexuses.  The  external  plexuses  consist 
of  two  parts,  the  anterior  vertebral  venous  plexuses  situated  on  the  anterior  aspect 
of  the  vertebral  bodies  and  the  posterior  vertebral  venous  plexuses  ramifying  over 
the  posterior  aspect  of  the  vertebral  arches,  spines,  and  transverse  processes. 
The  internal  plexuses  consist  of  two  longitudinal  venous  sinuses  situated  between 
the  vertebrae  and  the  posterior  longitudinal  ligament,  and  of  two  vertebral  venous 
retia  placed  immediately  external  to  the  dura  mater.  The  sinuses  of  the  internal 
plexuses  communicate  freely  with  one  another  and  with  the  internal  retia  and 
external  plexuses.  They  receive  the  external  spinal  veins  and  the  basivertebral 
veins  from  the  bodies  of  the  vertebrae.     The  venous  circulation  of  the  vertebral 


VEINS  OF  THE  VERTEBRAL  COLUMN 


665 


column  is  drained  by  the  vertebral,  intercostal,  lumbar  and  sacral  veins  either 
directly  or  by  means  of  (3)  the  intervertebral  veins. 

1.  The  external  vertebral  venous  plexuses  [plexus  venosi  vertebrales  externi]  include  the 
following : 

(a)  The  anterior  vertebral  venous  plexuses  [plexus  venosi  vertebrales  anteriores]  (fig. 
524)  consist  of  small  veins  ramifying  in  front  of  the  bodies  of  the  vertebrae.  These  veins  com- 
municate with  the  basivertebral  veins  and  are  larger  in  the  cervical  region  than  elsewhere. 

(6)  The  posterior  vertebral  venous  plexuses  [plexus  venosi  vertebrales  posteriores]  (fig. 
524)  are  situated  around  the  transverse,  articular,  spinous  processes  and  laminae  of  the  vertebrae. 
Communications  take  place  between  the  plexuses  of  each  segment  and  with  the  veins  of  the 
neighbouring  muscles  and  integuments.  Branches  are  also  sent,  through  the  ligamenta  flava, 
to  the  internal  vertebral  venous  plexuses,  and,  between  the  transverse  processes,  to  the  inter- 
vertebral veins. 

2.  The  internal  vertebral  venous  plexuses  [plexus  venosi  vertebrales  interni]  (fig.  524) : — 
(a)  The  two  longitudinal  vertebral  sinuses  [sinus  vertebrales  longitudinales]  run  through- 
out the  entire  length  of  the  vertebral  canal.     They  are  situated  behind  the  bodies  of  the  vertebrae 
on  either  side,  between  the  bone  and  the  posterior  longitudinal  hgament.     The  sinuses  have 

Fig.  524. — The  Veins  op  the  Vertebral  Column. 


{ 


Mammillary  process 
Accessory 
process  or  tip 
of     the    true 
transverse 
process 

Costal  elem 
Posterior  transverse 
branch 

Ejrternal  spinal  veins 
Intervertebral  vei 
Anterior  transversi 


Lumbar  vein 


Posterior  vertebral 
plexus 


Basivertebral  veins 


ertebral  plexu 


extremely  thin  walls,  and  their  interior  is  made  irregular  by  numerous  folds  but  no  true  valves 
are  present.  The  calibre  of  the  longitudinal  sinuses  is  reduced  by  constrictions  opposite  the 
intervertebral  discs;  the  consti'ictions  alternating  with  dilatations  opposite  the  vertebral  bodies. 
At  each  dilatation  there  occurs  a  cross  communication  between  the  longitudinal  sinuses  of 
either  side,  and  each  receives  a  basivertebral  vein  from  the  corresponding  vertebral  body. 
Opposite  every  intervertebral  foramen  and  anterior  sacral  foramen  each  longitudinal  sinus 
is  joined  by  the  corresponding  intervertebral  vein.  The  longitudinal  sinuses  communicate 
very  freely  with  one  another,  and  with  the  vertebral  retia.  At  the  foramen  magnum  they 
communicate  with  the  basilar  plexus  and,  by  means  of  the  rate  canalis  hypoglossi,  with  the 
internal  jugular  vein. 

(6)  The  venous  rete  of  the  vertebrae  [retia  venosa  vertebrarum]  (fig.  524)  extend  from  the 
foramen  magnum  to  the  coccyx.  They  consist  of  two  main  retia  situated  posteriorly  and 
lateraOy  to  the  dura  between  the  latter  and  the  vertebral  arch.  They  communicate  very 
freely  with  one  another  across  the  median  line;  with  the  posterior  external  plexus  by  means 
of  twigs  perforating  the  ligamenta  flava;  and  with  the  longitudinal  vertebral  sinuses  by  means 
of  lateral  branches.     At  the  foramen  magnum  they  communicate  with  the  occipital  sinus. 

(c)  The  external  spinal  veins  consist  of  two  sets — anterior  and  posterior — which  are  drained 
by  means  of  veins  following  the  nerve  roots,  into  the  internal  vertebral  venous  plexus. 

The  anterior  external  spinal  veins  [w.  spinales  externa;  anteriores]  form  a  tortuous  anas- 
tomosing vessel  in  the  region  of  the  anterior  median  fissure. 

The  posterior  external  spinal  ^•eins  [vv.  spinales  externse  posteriores],  smaller  than  the  an- 
terior run  longitudinally  on  the  posterior  surface  of  the  cord. 

The  external  spinal  veins  form  a  wide-meshed  plexus  in  the  pia  mater  which  drains  the 
internal  spinal  veins  [vv.  spinales  internae]  (see  Spinal  Cord). 


666 


THE  BLOOD-VASCULAR  SYSTEM 


{d)  The  basivertebral  veins  [vv.  basivertebrales]  (fig.  524)  collect  the  blood  from  the 
cancellous  tissue  of  the  bodies  of  the  vertebra;,  and  consist  of  a  tunica  intima  only.  They  take 
a  radial  direction  converging  to  the  transverse  vessels  connecting  the  longitudinal  vertebral 
sinuses.     They  communicate  with  the  anterior  external  plexus  and  with  the  intercostal  veins. 

3  The  intevertebral  veins  [vv.  intervetebrales]  (fig.  524),  emerge  from  each  longitudinal 


Fig.  525. — The  Vertebral  Venotts  Plexuses.     (After  Henle.) 


Occipital  vein 


Venous  rete 
Dura  mater  spinalis 


sinus  and  pass  out  through  the  intervertebral  or  anterior  sacral  foramina.  They  open  into  the 
vertebral,  intercostal,  lumbar  or  sacral  veins  according  to  region  and  receive  numerous  tribu- 
taries from  the  anterior  and  posterior  external  vertebral  venous  plexuses.  They  are  instru- 
mental in  draining  the  venous  system  of  the  vertebral  column  and  spinal  cord. 


3.     THE  INTERNAL  MAMMARY  VEIN 


The  internal  mammary  vein  [v.  mammaria  interna]  is  formed  by  the  union  of 
the  vena3  comitantes  corresponding  to  the  superior  epigastric  and  musculo-phrenic 
arteries.  The  right  and  left  internal  mammary  veins  pass  upward,  in  company 
with  the  corresponding  arteries,  to  open  into  the  right  and  left  innominate 
respectively. 

Tributaries. — In  addition  to  the  superficial  veins  of  the  thorax,  the  internal 
mammary  veins  receive  the  anterior  intercostal,  anterior  bronchial  and  peri- 
cardiac veins. 

The  superior  epigastric  vein  [v.  epigastrica  superior]  assists  in  the  drainage  of  the  subcu- 
taneous abdominal  veins  [vv.  subcutanCEe  abdominis]. 

The  anterior  bronchial  veins  [w.  bronchiales  anteriores]  arise  in  the  bronchial  walls  and 
communicate  with  the  tracheal  and  posterior  bronchial  veins. 


THE  VEINS  OF  THE  UPPER  EXTREMITY  667 

4.     THE  SUPERIOR  PHRENIC,  ANTERIOR  MEDIASTINAL,  AND 
PERICARDIAC  VEINS 

The  superior  phrenic  [vv.  phreniese  superiores],  the  anterior  mediastinal  [w  mediastinales 
anteriores],  and  pericardiac  [w.  pericardiacae]  veins  are  small  vessels,  corresponding  to  the  ar- 
teries of  those  names.  They  pass  over  the  arch  of  the  aorta  and  open  into  the  lower  and  an- 
terior part  of  the  left  innominate. 

THE  VEINS  OF  THE  UPPER  EXTREMITY 

The  veins  of  the  upper  limb  consist  of  two  sets — a  superficial  and  a  deep. 

The  superficial  veins  ramify  in  the  subcutaneous  tissue  above  the  deep  fascia,  and 
they  do  not  accompany  arteries.  The  deep  veins  accompany  the  arteries,  and 
have  practically  the  same  relations  as  those  vessels.  The  superficial  and  deep 
veins  communicate  at  frequent  intervals  through  the  intermuscular  veins  which 
run  between  the  muscles  and  perforate  the  deep  fascia.  Both  sets  of  veins  are 
provided  with  valves,  but  the  valves  are  more  numerous  in  the  deep  than  in  the 
superficial.  There  are  usually  valves  where  the  deep  veins  join  the  superficial. 
The  superficial  veins  are  larger  than  the  deep,  and  take  the  greater  share  in 
returning  the  blood. 

I.  THE  SUPERFICIAL  VEINS  OF  THE  UPPER  EXTREMITY 

The  superficial  veins  begin  in  two  irregular  plexuses,  one  in  the  palm  and  the 
other  on  the  back  of  the  hand.  The  plexus  in  the  palm  is  much  finer,  and  com- 
municates with  the  superficial  volar  veins  of  the  fingers.  The  latter  discharge 
their  blood  into  the  dorsal  venous  rete  by  means  of  the  veins  of  the  folds  between 
the  fingers,  or  the  intercapitular  veins  [vv.  intercapitulares]   (fig.  426). 

The  veins  of  the  back  of  the  hand  begin  in  a  longitudinal  plexus  over  the 
fingers,  and  at  the  bases  of  the  fingers  the  veins  of  the  adjacent  digits  are  con- 
nected by  digital  venous  arches  [arcus  venosi  digitales],  from  which  arise  the 
dorsal  metacarpal  veins  [vv.  metacarpese  dorsales];  these  form  upon  the  back 
of  the  hand  a  dorsal  venous  rete  [rete  venosum  dorsale  manus]  (fig.  427). 

Of  the  veins  of  the  arm,  two  stand  out  prominently,  the  basilic  and  the 
cephalic.  Both  of  these  arise  from  the  veins  of  the  back  of  the  hand,  curve 
around  to  the  volar  surface  of  the  forearm,  and  pass  to  the  upper  arm  (fig.  426). 

The  basilic  vein  [v.  basilica],*  arises  on  the  back  of  the  hand  from  the  ulnar 
end  of  the  dorsal  venous  rete,  which  usually  forms  an  arch.  It  curves  around  the 
ulnar  side  of  the  forearm  to  the  volar  surface  and  passes  to  the  elbow  and  the 
upper  arm,  where  it  lies  in  the  median  bicipital  sulcus.  It  extends  up  to  about 
the  middle  third  of  the  sulcus,  and,  piercing  the  brachial  fascia,  joins  the  brachial 
vein. 

The  cephalic  vein  [v.  cephalica],*  begins  at  the  radial  end  of  the  dorsal 
venous  rete  or  arch  and  curves  around  the  radial  border  of  the  forearm  to  the 
volar  surface  not  far  above  the  thumb.  It  passes  to  the  elbow  and  the  upper 
arm,  but,  unlike  the  basilic,  it  maintains  its  superficial  course  up  to  the  shoulder, 
lying  first  in  the  lateral  bicipital  sulcus  and  then  in  the  groove  between  the  pec- 
toralis  major  and  the  deltoid.  Just  below  the  clavicle  it  turns  into  the  depth,  and 
empties  into  the  axillary  vein. 

In  the  forearm  plexus  one  or  more  longitudinal  veins  besides  these  are  usually 
distinct.  One  lateral  to  the  cephalic  is  known  as  the  accessory  cephalic  [v. 
cephalica  accessoria]  (formerly  the  radial)  vein;  one  near  the  centre  is  known 
as  the  median  antibrachial  [v.  mediana  antibrachii],  (formerly  the  anterior 
ulnar)  vein. 

At  the  elbow  there  is  usually  an  obhque  connecting  branch,  the  median 
cubital  vein  [v.  mediana  cubiti]  (formerly  termed  median  basilic)  which  extends 

*Tlie  basilic  vein  here  described  corresponds  to  tlie  posterior  ulnar  and  basilic;  the  cephalic 
corresponds  to  the  median,  median  cephalic  and  cephalic  of  the  older  terminology  employed 
in  English  text-books.  The  BNA  terminology  has  the  gi-eat  advantage  that  it  can  be  readily 
used  to  desci'ibed  any  form  of  venous  pattern.  The  English  terminology  applies  only  to  cases 
in  which  the  M-shaped  arrangement  occurs  upon  the  volar  surface  of  the  elbow.  Berry  and 
Newton  find  the  latter  arrangement  in  only  13  per  cent,  out  of  300  cases  examined. 


668 


THE  BLOOD-VASCULAR  SYSTEM 


from  the  cephalic  up  to  the  basilic.     In  some  cases  this  anastomosis  is  made  by  a 
division  of  the  median  antibrachial  into  two  branches,  a  median  cephalic  and 


Fig.  526.- 


-The  Superficial  Veins  of  the  Akm  and  Forearm.     (After  Toldt,  "Atlas  of 
Human  Anatomy,"  Rebman,  rondon  and  New  York.) 


Cephalic  / 
vein      I 


Conaecting  branches 
between  the  superfi- 
cial and  deep  veins         Brachial 
fascia 


Accessory 
median  cubital 

(var; 


Median  cubital 


— .-  Intercapitular 

veins       Cephal: 
vein 
-Proper  volar 
--^    digital    Connec- 
veins  tion 

with  deep 
veins 

Accessory 
cephalic 
Antibrachial 
fascia 


> Basilic  vein 


Note. — In  the  limb  here  represented  the  direct  venous  channel  on  the  radial  side  of  the 
forearm,  the  accessory  cephalic  (formerly  radial)  vein,  is  continued  directly  into  the  cephalic 
above  the  elbow.  The  cephalic  in  the  forearm  (formerly  median)  is  mainly  drained  by  the 
basilic  through  the  median  antecubital.  The  vein  opposite  the  bend  of  the  elbow,  which  usu- 
ally forms  the  segment  of  the  cephalic  formerly  known  as  the  median  cephalic  vein,  is  here  a 
small  channel  draining  into  an  accessory  median  cubital.  The  basilic  vein  of  the  forearm 
(formerly  posterior  ulnar)  is  represented  by  a  plexus  of  small  venous  channels. 


SUPERFICIAL  VEINS  OF  THE  ARM 


669 


median  basilic.  Occasionally  the  cephalic  in  the  upper  arm  is  reduced  to  a  small 
tributary,  which  takes  the  course  of  the  cephalic  in  the  forearm,  but  bends  ulnar- 
ward  at  the  elbow  to  form  the  basilic.  Numerous  connections  occur  between  the 
deep  and  the  superficial  veins  at  the  elbow. 

The  superficial  plexus  of  veins  in  the  upper  arm  consists  of  small  vessels  that 
pass  to  the  cephalic  vein. 

Fig.  527. — Veins  op  the  Back  op  the  Forearm.    (After  Toldt,  "Atlas  of  Human  Anatomy," 
Rebman,  London  and  New  York.) 


Cephalic  vein 
—  Accessory  median  cubital  vein 
Median  cubital  vein 


Subcutaneous  venous  / 
network  v. 


Accessory  cephalic  vein 
Basilic  vein 


Dorsal  venous  rete  . 


Digital  venous  arch 


670 


THE  BLOOD-VASCULAR  SYSTEM 


II.  THE  DEEP  VEINS  OF  THE  UPPER  EXTREMITY 

The  deep   veins   of  the   upper   extremity   accompany  their   corresponding 

arteries.     There  are  two  veins  to  each  artery  below  the  level  of  the  axilla,  known 
as  the  vense  comitantes.     The  deep  veins  all  contain  numerous  valves,  and 

Fig.  528. — Deep  Veins  of  the  Ahm  and  Axilla.     (After  Toldt,  "Atlas  of  Human  Anatomy," 
Rebman,  London  and  New  York.) 

Internal  jugular  vein 
Transverse  scapular  vein  /   Transverse  cervical  artery 

Axillary  artery  and  vein       \  m^^  /  Transverse  cervical  vein 

Anterior  circumflex  humeral  artery  and  vem    \  ^.^^^H^^^^L  *  External  jugular  vein 

Subclavian  vein 

Jugular  venous  arch 

Right  innominate  vein 


Posterior     cir<  umflex 
humeral  artery   and 

Circumflex  scapular  vem 
Biceps  muscle 


Basilic  vein 

Biceps  muscle 

Brachial  veins 

Ulnar  nerve 


Dorsal  thoracic  artery  and  vein 


^Median  cubital  vein 
L^^^^^Inferior  ulnar  collateral  artery  and  vein 


.  v^Connection  of  radial  with  superficial  veins 
-Ulnar  artery  and  veins 


Radial  artery  and  veins 


communicate  at  frequent  intervals  through  intermuscular  veins  with  the  super- 
ficial vessels. 


DEEP  VEINS  OF  THE  UPPER  EXTREMITY  671 

Beginning  at  the  fingers,  two  minute  proper  volar  digital  veins  [venae  digitales 
volares  proprise],  accompany  each  digital  artery  along  the  sides  of  the  fingers, 
and  uniting  at  the  cleft,  form  common  volar  digital  veins  [vv.  digitales  volares 
communes],  which  join  the  vense  comitantes  of  the  arteries,  forming  the  super- 
ficial palmar  arch.  In  like  manner  the  veins  accompanying  the  arteries  forming 
the  deep  arch  receive  tributaries,  the  volar  metacarpal  veins  [vv.  metacarpese 
volares],  corresponding  to  the  branches  of  that  arch.  A  superficial  and  a  deep 
volar  venous  arch  [  arcus  volaris  venosi  superficialis  et  profundus]  are  thus  formed 
accompanying  the  arterial  arches.  The  venae  comitantes  from  the  ulnar  side  of 
the  superficial  and  deep  arches  unite  at  the  spot  where  the  ulnar  artery  divides 
into  the  superficial  and  deep  branch  to  form  two  ulniar  venae  comitantes  [vv. 
ulnares] ;  whilst  those  on  the  radial  side  of  the  superficial  and  deep  arch  accompan}^ 
the  superficial  volar  artery  and  the  termination  of  the  radial  artery  respectively, 
and  unite  at  the  spot  where  the  superficial  volar  is  given  off  from  the  radial  artery, 
to  form  the  radial  venae  comitantes  [vv.  radiales].  The  ulnar  and  radial  venae 
comitantes  thus  formed  course  up  the  forearm  with  their  respective  arteries, 
receiving  numerous  tributaries  from  the  muscles  amongst  which  they  run,  and 
giving  frequent  communications  to  the  superficial  veins.  They  finally  unite  at 
the  bend  of  the  elbow  to  form  the  brachial  venas  comitantes  [vv.  brachiales]. 
The  ulnar  venae  comitantes  receive,  before  joining  the  radial,  the  companion 
veins  of  the  interosseous  arteries.  At  the  bend  of  the  elbow  the  deep  veins  are 
connected  with  the  basilic  or  with  the  median  antibrachial  vein  by  a  short,  thick 
trunk  (fig.  528). 

The  brachial  venae  comitantes  accompany  the  brachial  artery.  At  the  lower 
border  of  either  the  teres  major  or  subscapularis  muscle,  the  more  medial  vein 
receives  the  more  lateral  and  the  basilic  vein,  to  form  a  single  axillary  vein. 

The  venae  comitantes  of  the  arteries  of  the  arm  anastomose  with  one  another 
by  frequent  cross  branches. 

The  axillary  vein  [v.  axillaris],  is  formed  by  the  junction  of  the  medial  brachial 
vena  comitans  with  the  basilic  vein  at  the  lower  border  of  either  the  teres  major 
or  subscapularis  muscle.  It  is  a  vessel  of  large  size,  conveying  as  it  does  nearly 
the  whole  of  the  returned  blood  from  the  upper  extremity.  It  accompanies  the 
axillary  artery  through  the  axillary  fossa,  lying  to  its  medial  side  and,  at  the  upper 
part  of  the  space,  on  a  slightly  posterior  plane.  At  the  lateral  border  of  the  first 
rib  it  changes  its  name  to  the  subclavian.  It  has  one  or  two  axillary  lymphatic 
nodes  in  close  connection  with  it,  and  is  liable,  if  care  is  not  taken,  to  be  wounded 
in  removing  these  glands.  The  vein  contains  a  pair  of  valves,  usually  placed 
near  the  lower  border  of  the  subscapularis  muscle. 

Tributaries : — (1)  The  subscapular  veins  which  accompany  the  subscapular 
artery;  (2)  the  circumflex  veins  accompanying  the  circumflex  arteries;  (3)  the 
lateral  thoracic  vein  [v.  thoracalis  lateralis]  a  large  vein  which  accompanies 
the  lateral  thoracic  artery  and  receives  numerous  thoraco-epigastric  veins  [vv. 
thoracoepigastricse]  from  the  epigastric  and  lower  thoracic  regions;  (4)  the  costo- 
axillary  veins  [vv.  costoaxillares]  the  radicles  of  which  arise  in  the  pectoral  region 
from  the  mammary  plexus  [plexus  venosus  mamillae] ;  and  (5)  the  cephalic  vein. 

The  subclavian  vein  [v.  subclavii]  (fig.  528),  is  the  continuation  of  the  axillary. 
It  begins  at  the  lateral  border  of  the  first  rib,  and  terminates  by  joining  the 
internal  jugular  to  form  the  innominate  vein  opposite  the  lateral  end  of  the 
sterno-clavicular  articulation.  It  lies  anterior  to  the  subclavian  artery  and  on  a 
lower  plane,  and  is  separated  from  the  artery  in  the  second  part  of  its  course 
by  the  scalenus  anterior  muscle.  The  subclavian  vein,  just  before  it  is  joined  by 
the  external  jugular,  contains  a  pair  of  valves. 

Tributaries. — The  subclavian  vein  receives  the  thoracoacromial  vein  near  its 
distal  end,  and  the  external  jugular  vein  near  the  lateral  border  of  the  sterno- 
mastoid  muscle.  The  transverse  cervical  veins  terminate  in  the  subclavian  near 
the  external  jugular,  or  in  the  latter  vein,  or  in  a  plexiform  arrangement  formed 
between  the  transverse  scapular,  transverse  cervical  and  external  jugular  veins. 
The  external  jugular  vein  is  described  with  the  superficial  veins  of  the  head 
and  neck  (p.  646). 

The  thoracoacromial  vein  [v.  thoracoacromiahs],  receiving  tributaries  cor- 
responding to  the  branches  of  the  artery  of  the  same  name,  terminates  near  the 
lateral  border  of  the  first  rib. 


672  THE  BLOOD-VASCULAR  SYSTEM 

The  transverse  cervical  veins  [vv.  transversae  colli]  receive  tributaries  cor- 
responding in  distribution  to  the  branches  of  the  transverse  cervical  artery. 
They  emerge  from  beneath  the  trapezius  muscle,  cross  the  posterior  triangle,  and 
usually  terminate  in  the  subclavian  vein.  They  usually  terminate  as  a  single  vein 
the  orifice  of  which  is  guarded  by  a  pair  of  valves.  Occasionally  the  cephahc  vein, 
or  a  branch  from  the  cephalic  (the  jugulo-cephalic),  passes  over  the  clavicle  to  the 
subclavian. 

III.  THE  VENA  CAVA  INFERIOR  AND  ITS  TRIBUTARIES 

All  the  veins  of  the  abdomen,  pelvis,  and  lower  extremities,  with  the  exception 
of  the  superior  epigastric  (p.  666),  and  ascending  lumbar  vein  (p.  521),  which 
join  with  the  superior  caval  system,  enter  directly  or  indirectly  into  the  vena 
cava  inferior.  The  veins  corresponding  to  the  parietal  branches  of  the  abdominal 
aorta,  except  the  middle  sacral  vein,  open  directly  into  the  vena  cava  inferior; 
the  middle  sacral  vein  only  indirectly  through  the  left  common  iliac  vein.  Of  the 
visceral  veins  corresponding  to  the  visceral  branches  of  the  abdominal  aorta, 
those  which  return  the  blood  from  the  stomach,  intestines,  pancreas,  and  the 
spleen  end  in  a  common  trunk  called  the  portal  vein. 

The  portal  vein  [vena  portae]  enters  the  liver  and  there  breaks  up  into  a  net- 
work of  smaller  vessels  somewhat  after  the  manner  of  an  artery.  This  network 
contains  venous  blood,  and  is  moulded  upon  the  tissue-elements  of  the  organ 
itself.  The  smaller  vessels  consist,  like  capillaries  (from  which  they  differ  in 
developmental  history)  of  intima  only;  they  are  called  sinusoids.  The  venous 
blood  is  returned  from  the  sinusoidal  plexus  by  the  hepatic  veins  which  open  into 
the  vena  cava  inferior  as  that  vessel  lies  in  the  fossa  venae  ca,v£e  of  the  liver. 

Of  the  other  visceral  veins,  both  renals,  the  right  suprarenal,  and  the  right 
spermatic  or  ovarian  open  directly  into  the  vena  cava  inferior;  whilst  the  left 
suprarenal  and  left  spermatic  or  ovarian  are  drained  through  the  left  renal. 

Two  of  the  superficial  veins  of  the  lower  part  of  the  anterior  abdominal  wall, 
the  superficial  epigastric  and  superficial  circumflex  iliac,  enter  the  great  saphenous 
vein;  and  two  of  the  deep  veins  from  the  like  situation,  the  inferior  epigastric  and 
deep  circumflex  iliac,  enter  the  external  iliac  vein.  The  blood  in  these  vessels, 
however,  can  flow  upward  as  well  as  in  the  normally  downward  direction.  In 
obstruction  of  the  vena  cava  inferior  they  become  greatly  enlarged,  and  form, 
with  the  superior  epigastric  vein  and  with  other  superficial  veins  of  the  thorax 
with  which  they  anastomose,  one  of  the  chief  channels  for  the  return  of  the  blood 
from  the  lower  limbs. 

The  veins  of  the  pelvis,  which  receive  the  veins  from  the  perinseum  and  gluteal 
region,  join  the  hypogastric  vein. 

THE  VENA  CAVA  INFERIOR 

The  vena  cava  inferior  (fig.  529)  is  the  large  vessel  which  returns  the  blood 
from  the  lower  extremities  and  the  abdomen  and  pelvis.  It  is  formed  by  the  con- 
fluence of  the  right  and  left  common  iliac  veins  opposite  the  body  of  the  fifth 
lumbar  vertebra,  ascends  in  front  of  the  lumbar  vertebrae  to  the  right  of  the  ab- 
dominal aorta,  passes  through  the  caval  opening  in  the  diaphragm,  and  ends  in 
the  lower  and  back  part  of  the  right  atrium  of  the  heart  on  a  level  with  the  lower 
border  of  the  ninth  thoracic  vertebra.  At  its  origin  it  lies  behind  the  right 
common  iliac  artery  on  a  plane  posterior  to  the  aorta,  but  as  it  ascends  it  passes 
slightly  forward  and  to  the  right,  reaching  a  plane  anterior  to  the  aorta,  and 
becoming  separated  from  that  artery  by  the  right  medial  crus  of  the  diaphragm 
and  the  caudate  lobe  of  the  liver.  While  in  contact  with  the  liver  it  lies  in  a 
deep  groove  [fossa  venae  cavje]  on  the  posterior  surface  of  that  organ,  the  groove 
being  often  converted  into  a  distinct  canal  by  a  thin  portion  of  the  hepatic  sub- 
stance bridging  across  it.  As  it  passes  through  the  diaphragm  its  walls  are 
attached  to  the  tendinous  margins  of  the  caval  opening,  and  are  thus  held  apart 
when  the  muscle  contracts.  On  the  thoracic  side  of  the  diaphragm  it  Hes  for  about 
1.2  cm.  (I  in.)  within  the  pericardium,  the  serous  layer  of  that  membrane  being 
reflected  over  it. 


THE  VENA  CAVA  INFERIOR 


673 


Relations. — In  front  it  is  covered  by  the  peritoneum,  and  crossed  by  the  right  spermatic 
artery,  branches  of  the  aortic  plexus  of  the  sympathetic,  the  transverse  colon,  the  root  of  the 
mesentery,  the  duodenum,  the  head  of  the  pancreas,  the  portal  vein,  and  the  liver.  The 
median  gi'oup  of  the  lumbar  lymphatic  nodes  are  also  in  front  of  it  below,  and  at  its  com- 
mencement the  right  common  iliac  artery  rests  upon  it. 

Behind,  it  hes  on  the  lumbar  vertebrae,  the  right  lumbar  arteries,  the  right  renal  artery, 
the  right  coehao  (semilunar)  ganglion,  and  the  right  medial  crus  of  the  diaphragm. 

To  the  right  are  the  peritoneum,  liver,  and  psoas  muscle. 

To  the  left  is  the  aorta,  and  higher  up  the  right  medial  crus  of  the  diaphragm. 

Tributaries. — The  vena  cava  inferior  receives  the  following  veins: — ■(!)  the 
renal  veins;  (2)  the  right  suprarenal  vein;  (3)  the  right  spermatic  or  the  right 

Fig.  529. — The  Abdominal  Aorta  and  Vena  Cava  Inferior. 


i 


Cystic  artery 

Hepatic  duct 

Cystic  duct 

Common  bile  duct 

Portal  vein 

Gastro-duodenal  br. 

Right  gastric  arterj 

Hepatic  artery 

Right  suprarenal  vein 

Inferior  suprarenal 
artery 

Renal  artery 
Renal  vein 

Vena  cava  inferior 
Kidney 

Right     spermatic    vein 


Right  internal  sper- 
matic artery 
Quadratus  lumborum 

muscle 

Right     lumbar    artery 

and  left  lumbar  vein 

Ui  eteric       branch     of 

spermatic  artery 


Middle  sacral  vessels, 


Left  lobe  of  liver 


(Esophagus 

Left  inferior  phrenic 

artery 
Right   inferior    phrenic 

artery 
Superior  suprarenal 
Left  gastric  artery 
Inferior  suprarenal 
Splenic  artery 

Left  inferior  phrenic  vein 
Left  suprarenal  vein 
Superior  mesenteric 

artery 
Kidney 

Ureteric  branch  of  renal 
Left  spermatic  vein 


Left  internal  spermatic 
artery 


Inferior  mesenteric 

artery 

Ureteric  branch  of 

spermatic 


Ureteric  branch  of 

common  iliac 
Common  iUac  artery 


External  iliac  artery 
Hypogastric  artery 


ovarian  vein;  (4)  the  lumbar  veins;  (5)  the  inferior  phrenic  veins;  (6)  the  hepatic 
veins;  and  (7)  the  right  and  left  common  iliac  veins. 

(1)  The  renal  veins  [vv.  renales]  (fig.  529)  return  the  blood  from  the  kidneys. 
They  are  short  but  thick  trunks,  and  open  into  the  vena  cava  nearly  at  right 
angles  to  that  vessel.  The  vein  on  the  left  side,  like  the  kidney,  is  a  little  higher 
than  on  the  right,  and  is  also  longer,  in  consequence  of  its  having  to  cross  the 
aorta. 

Each  renal  vein  lies  in  front  of  its  corresponding  artery.  The  left  vein  crosses  in  front  of 
the  aorta,  just  below  the  origin  of  the  superior  mesenteric  artery.  It  is  covered  by  the  inferior 
portion  of  the  duodenum,  and  receives  the  left  spermatic,  or  the  left  ovarian  in  the  female, 
and  usually  the  left  suprarenal,  and  sometimes  the  left  phrenic.  There  are  rudiments  of  valves 
in  each  vein  where  it  joins  the  vena  cava.  Those  on  the  right  side,  however,  are  less  well 
marked. 

(2)  The  suprarenal  veins  [vv.  suprarenales]  (fig.  529). — ^There  is  usually  only  one  suprarenal 
vein  on  each  side  to  return  the  blood  brought  to  the  suprarenal  body  by  the  three  suprarenal 
arteries.  On  the  right  side  the  vein  opens  directly  into  the  vena  cava,  above  the  opening  of  the 
right  renal  vein.     On  the  left  side,  it  opens  into  the  left  renal. 


674 


THE  BLOOD-VASCULAR  SYSTEM 


(3)  The  spermatic  veins  [vv.  sperraaticaj]  (fig.  529)  retui-n  the  blood  from  the  testis.  They 
begin  by  the  confluence  of  small  branches  from  the  body  of  the  testis  and  epididymis.  As 
they  proceed  up  the  spermatic  cord,  in  front  of  the  internal  spermatic  artery  and  ductus 
deferens,  they  become  dilated  and  plexiform,  constituting  the  pampiniform  plexus  [plexus 
pampiniformis]  (fig.  541).  After  passing  through  the  subcutaneous  inguinal  ring,  the  inguinal 
canal,  and  the  abdominal  inguinal  ring,  the  plexus  communicates  with  the  inferior  epigastric 
vein  and  is  continued  as  two  veins.  Along  with  the  artery  the  veins  pass  up  beneath  the 
peritoneum,  and  on  the  left  side  also  beneath  the  sigmoid  colon,  across  the  psoas  muscle  and 
ureter.  They  receive  small  tributaries  from  the  ureter  and  peritoneum,  and  proceed  as  a  single 
trunk,  on  the  right  side  to  the  vena  cava  inferior,  and  on  the  left  side  to  the  left  renal  vein. 
There  are  commonly  a  number  of  imperfect  valves  in  the  spermatic  plexus  and  a  perfect  pair 
at  the  termination  of  each  spermatic  vein.  On  the  left  side,  however,  the  terminal  valve  may 
be  wanting. 


Fig.  530. — The  Veins  op  the  Female  Pelvis.     (After  Toldt,  "Atlas  of  Human  Anatomy," 
Rebman,  London  and  New  York.) 

Right  common  iliac  artery  and  vein 
Right  external  iliac  artery 
Left  common  iliac  artery  and  vein  Edge  of  the  suspensory  ligament  / 

Hypogastric  artery  and  vein  of  the  ovary  ,      /  / 

Ovarian  vein  /    — «^' 

,  Left  external  iliac  artery  and  vein  -^'  ^ 


Sacrotu- 
berous 
ligament 


Obturator  in- 
ternus  muscle 
Utero-vaginal  plexus 


;  behind  the  bulbus  vestibuli 


The  ovarian  veins  [vv.  ovarica3[  begin  at  the  plexus  pampiniformis  near  the  ovary, 
between  the  layers  of  the  broad  ligament.  This  plexus  is  larger  than  in  the  male  and  com- 
municates freely  with  the  utero-vaginal  plexus  of  veins,  and  with  the  plexus  of  veins  which  ex- 
tends from  the  hilus  of  the  ovary  into  the  ovarian  ligament  (fig.  486).  After  passing  from 
between  the  layers  of  the  broad  Ugament,  the  plexus  unites  to  form  at  first  two  and  then  a 
single  vessel,  which  accompanies  the  ovarian  artery,  following  a  course  similar  to  that  of  the 
spermatic  veins  in  the  male.  The  right  ovarian  veins  open  into  the  vena  cava  inferior,  the  left 
into  the  left  renal.  They  usually  contain  imperfect  valves  in  their  plexiform  part,  and  a  perfect 
valve  where  they  join  the  vena  civa  and  renal  vein  respectively. 


THE  PORTAL  VEIN  676 

(4)  The  lumbar  veins  [vv.  lumbales],  four  to  five  on  either  side  accompany  the  lumbar 
arteries  and  collect  venous  blood  from  the  muscles  of  the  back  and  abdomen.  They  terminate 
by  passing  beneath  the  tendinous  arches  of  the  psoas  major,  along  the  sides  of  the  lumbar 
vertebrae,  and  opening  into  the  vena  cava  inferior.  The  veins  of  the  left  side  are  longer  than 
those  of  the  right  and  pass  behind  the  aorta.  Each  vein  receives  a  dorsal  tributary  corre- 
sponding in  distribution  to  the  dorsal  branch  of  the  lumbar  artery.  Between  the  dorsal  tribu- 
taries and  the  posterior  vertebral  venous  plexus  there  occurs  a  free  communication.  There 
is  also  an  anastomosis  between  the  main  lumbar  veins  and  the  anterior  vertebral  venous  plexus 
around  the  bodies  and  transverse  processes  of  the  lumbar  vertebrae.  By  means  of  these 
communications  the  intervertebral  veins,  the  internal  and  external  vertebral  and  spinal  plexuses 
are  partly  drained.  In  addition  to  these  anastomoses  the  lumbar  veins  are  connected  with  one 
another  and  with  common  iliac,  hypogastric,  ilio-lumbar,  renal,  azygos  and  hemiazygos  veins 
by  means  of  the  ascending  lumbar  vein  (p.  66.3). 

(5)  The  inferior  phrenic  veins  [v.  phrenica  inferior]  follow  the  course  of  the  inferior  phrenic 
arteries;  the  right  opens  into  the  vena  cava  direct;  the  left  into  the  suprarenal,  the  left  renal,  or 
the  vena  cava. 

(6)  The  hepatic  veins  [vv.  hepaticse],  the  largest  tributaries  of  the  vena  cava,  return  the 
blood  from  the  liver.  Commencing  in  the  substance  of  the  liver  (see  Liver),  they  converge  as 
they  approach  its  posterior  surface,  and  unite  to  form  two  or  there  large  trunks,  which  open 
into  the  vena  cava  as  it  lies  in  the  fossa  vense  cavae.  Some  smaller  vessels  from  the  caudate 
lobe,  and  other  parts  of  the  liver  in  the  nighbourhood  of  the  caval  fossa,  open  directly  into  the 
vena  cava.  The  hepatic  veins  contain  no  valves,  but,  in  consequence  of  opening  obliquely 
into  the  vena  cava,  a  semilunar  fold  occurs  at  the  lower  magin  of  each  orifice. 

THE  PORTAL  VEIN 

The  veins  corresponding  to  the  inferior  mesenteric,  the  superior  mesenteric, 
and  to  some  of  the  branches  of  the  coeliac  artery,  do  not  join  the  vena  cava  in- 
ferior direct,  but  unite  to  form  a  common  trunk — the  portal  vein. 

This  vein  enters  the  liver,  and  breaks  up  in  its  substance  into  sinusoids 
from  which  the  blood  is  again  ultimately  collected  by  the  hepatic  veins,  and  carried 
by  them  into  the  vena  cava  inferior.  The  terminal  branches  of  the  hepatic  artery 
also  empty  into  the  hepatic  sinusoids,  and  their  blood  likewise  finds  its  way 
finally  into  the  hepatic  veins,  and  thence  into  the  vena  cava  inferior.  The  portal 
vein  and  its  tributaries  have  no  valves. 

The  portal  vein  [v.  portae]  (fig.  531),  is  a  thick  trunk  7  or  8  cm.  (3  in.)  in  length. 
It  is  formed  behind  the  head  of  the  pancreas,  opposite  the  right  side  of  the  body 
of  the  second  lumbar  vertebra,  by  the  union  of  the  superior  mesenteric  with  the 
splenic  veins.  It  passes  upward  and  to  the  right  behind  the  superior  part  of  the 
duodenum,  and  then  between  the  layers  of  the  lesser  omentum.  In  the  latter 
situation  it  passes  in  front  of  the  foramen  epiploicum  and  is  accompanied  by 
the  hepatic  artery  and  the  hepatic  duct.  Finally  it  enters  the  porta  of  the  liver, 
and  there  divides  into  a  right  and  a  left  branch.  In  this  course  the  hepatic  artery 
and  the  common  bile  duct  are  in  front,  the  former  to  the  left,  the  latter  to  the 
right.  It  is  surrounded  by  branches  of  the  hepatic  plexus  of  the  sympathetic 
nerve,  and  by  numerous  lymphatic  vessels  and  some  glands.  The  connective 
tissue  sheath  enclosing  these  structures  is  called  the  fibrous  capsule  of  Glisson 
[capsula  fibrosa,  Glissoni].  Just  before  it  divides  it  is  somewhat  dilated,  the 
dilated  portion  being  called  the  sinus  of  the  portal  vein.  The  division  into  right 
and  left  branches  takes  place  toward  the  right  end  of  the  porta  of  the  liver. 
The  right  branch  is  shorter  and  thicker  than  the  left,  and  supplies  the  right 
lobe  of  the  liver  and  a  branch  to  the  quadrate  lobe.  The  left  branch  is  longer  and 
smaller  than  the  right,  and  supplies  the  left  lobe,  and  gives  a  branch  to  the  caudate 
(Spigelian)  and  quadrate  lobes.  It  is  joined,  as  it  crosses  the  left  sagittal  fossa, 
by  a  fibrous  cord,  known  as  the  ligamentum  teres  hepatis  (obUterated  vena 
umbilicalis),  and  posteriorly  by  a  second  fibrous  cord,  the  ligamentum  venosum  (ob- 
lietrated  ductus  venosus).  The  position  of  the  original  course  of  the  umbilical 
vein  across  the  left  portal  is  marked,  in.  adult  life,  by  a  dilation  of  the  latter 
vein,  called  the  umbilical  recess. 

Tributaries. — ^The  pyloric,  the  coronary  (gastric),  the  cystic,  the  superior 
mesenteric,  and  the  splenic. 

The  pyloric  vein  begins  near  the  pylorus  in  the  lesser  curve  of  the  stomach,  and,  running 
from  left  to  right  with  the  right  gastric  artery,  opens  directly  into  the  lower  part  of  the  portal 
vein.     It  receives  branches  from  the  pancreas  and  duodenum. 

The  coronary  vein  [v.  coronaria  ventriculi]  (fig.  533)  runs  with  the  left  gastric  artery  at 
first  from  right  to  left,  among  the  lesser  curvature  of  the  stomach,  toward  the  cardiac  end,  and 
then,  turning  to  the  right,  passes  across  the  spine  from  left  to  right  to  end  in  the  portal  trunk  a 


676 


THE  BLOOD-VASCULAR  SYSTEM 


Fig.  531. — The  Portal  Vein.     (From  Kelly,  by  Brodel.) 


TRIBUTARIES  OF  THE  PORTAL  VEIN 


677 


little  higher  than  the  pyloric  vein.    At  the  cardiac  end  of  the  stomach  it  receives  small  branches 
from  the  oesophagus. 

The  cystic  vein  [v.  cystica]  (fig.  533)  returns  the  blood  from  the  gall-bladder.  It  usually 
opens  into  the  right  branch  of  the  portal  vein. 

The  superior  mesenteric  vein  [v.  mesenterica  superior]  (fig.  534)  begins  in 
tributaries  whichi  correspond  witli  the  branches  of  the  superior  mesenteric  artery. 
It  courses  upward  a  little  in  front  and  to  the  right  of  the  artery,  passing  with  that 
vessel  from  between  the  layers  of  the  mesentery.  It  passes  in  front  of  the 
inferior  portion  of  the  duodenum,  and  behind  the  pancreas,  where  it  joins  the 
splenic  vein  to  form  the  portal  trunk  (fig.  531). 

Tributaries. — In  addition  to  the  tributaries  corresponding  to  the  branches  of 
the  superior  mesenteric  artery — viz.  the  ileo-colica,  colica  dextra,  colica  media,  and 
vence  intestinales  (fig.  534) — it  receives  the  right  gastro-epiploic  and  the  pan- 
creatico-duodenal  veins  just  before  its  termination  in  the  portal  vein. 

The  right  gastro-epiploic  vein  [v.  gastroepiploica  dextra]  (fig.  533)  accompanies  the  artery 
of  that  name.  It  runs  from  left  to  right  along  the  greater  curvature  of  the  stomach,  receiving 
branches  from  the  anterior  and  posterior  surfaces  of  that  viscus,  and  from  the  great  omentum, 
and,  passing  behind  the  superior  portion  of  the  duodenum,  ends  in  the,  superior  mesenteric 
vein  just  before  that  vessel  joins  the  portal  trunk. 


Fig.  532. — The  Portal  Vein  within  the  Lr^ee. 

Ascending  branch 


(After  Rex.) 


Vena  cava  inferior' 


Falci- 
form 
liga- 
ment 


Right  main  branch 


Left    Round 
'  branch     lig. 
Gall-bladder    Trunk  of  por-    Umbilical 
tal  vein  recess 


The  pancreatio-duodenal  veins  [vv.  pancreatico-duodenales]  (fig.  531)  run  with  the  superior 
and  inferior  pancreatico-duodenal  arteries  between  the  head  of  the  pancreas  and  the  second 
portion  of  the  duodenum.  They  receive  pancreatic  and  duodenal  veins  [vv.  pancreaticiE  et 
duodenales]  and  are  collected  into  a  single  stem  which  follows  the  inferior  pancreatico-duodenal 
artery  and  ends  in  the  superior  mesenteric  vein  a  little  below  the  right  gastro-epiploic  vein. 

.The  splenic  vein  [v.  lienalis]  (fig.  531)  issues  as  several  large  branches  from 
the  hilus  of  the  spleen.  These  soon  unite  to  form  a  large  trunk,  which  passes 
across  the  aorta  and  spine  in  company  with  the  splenic  artery,  below  which  it  lies, 
to  join  at  nearly  a  right  angle  the  superior  mesenteric  vein.  In  this  course  it  lies 
behind  the  pancreas;  and  at  its  union  with  the  superior  mesenteric  to  form  the 
vena  portse  in  front  of  the  vena  cava  inferior. 

Tributaries. — It  receives  the  short  gastric  veins  [vv.  gastricse  breves],  from  the 
fundus  of  the  stomach,  the  left  gastro-epiploic  vein,  and  the  inferior  mesenteric 
vein.  As  it  lies  in  contact  with  the  pancreas  it  receives  some  small  pancreatic 
veins  [vv.  pancreaticse]. 

The  left  gastro-epiploic  vein  [v.  gastroepiploica  sinistra]  (fig.  533)  accompanies  the  left 
gastro-epiploic  artery.  It  runs  from  right  to  left  along  the  greater  curvature  of  the  stomach, 
receives  branches  from  the  stomach  and  omentum,  and  opens  into  the  commencement  of  the 
splenic  vein. 


678 


THE  BLOOD-VASCULAR  SYSTEM 


The  inferior  mesenteric  vein  [v.  mesenterica  inferior]  (fig.  531)  begins  at  the 
rectum  as  the  superior  hgemorrhoidal  vein.  This  emerges  from  the  hsemor- 
rhoidal  plexus  in  which  it  communicates  freely  with  the  middle  and  inferior 
haemorrholdal  veins.  It  passes  out  of  the  pelvis  with  the  inferior  mesenteric 
artery;  but,  after  receiving  the  sigmoid  and  left  colic  veins  [vv.  sigmoideee  et 
V.  colica  sinistra]  which  accompany  the  arteries  of  the  same  names,  it  leaves  the 
artery  and  runs  upward  on  the  psoas  to  the  left  of  the  aorta  and  behind  the 
peritoneum.  On  approaching  the  pancreas  it  turns  medially,  and  passes  obliquely 
behind  that  gland  to  join  the  splenic  vein  just  before  the  latter  unites  with  the 
superior  mesenteric  to  form  the  vena  portse. 


Fig.  533.- 


-The  Veins  of  the  Stomach  and  the  Portal  Vein. 
(From  a  dissection  by  W.  J.  Walsham.) 


Right    branch  of 
portal  vein 


Hepatic  artery 

Hepatic  artery 
proper 
Gastro-duodenal 
branch  of  hepatic 
artery 

Pyloric  vein 


Right  gastro- 
epiploic vein' 


Omental  veins 


Left  branch  or 
portal  ^ 


5  corres- 
ponding to  short 
gastric  arteries 


Left  gastric  artery 
Hepatic  artery 


The  adult  portal  vein  and  its  tributaries  contain  no  valves,  a  circumstance  which  adversely 
affects  the  circulation  of  blood  within  this  system.  The  liability  to  excessive  pressure  in  the 
most  dependent  part  of  the  portal  system  is  evidenced  by  the  great  frequency  of  the  condition 
known  as  piles,  due  to  dilatation  of  the  veins  of  the  internal  hsemorrhoidal  plexus.  In  earrly 
life  valves  are  present  in  the  veins  of  the  stomach  and  of  the  intestinal  wall  but  these  undergo 
retrogression. 

The  accessory  portal  veins. — Since  the  blood  returning  from  the  abdominal  portion  of  the 
digestive  tract  and  spleen  must  pass  through  the  hepatic-capillaries  before  returning  to  the  heart, 
extensive  obliteration  of  these  capillaries,  such  as  occurs  in  certain  diseases  of  the  liver,  would 
prevent  the  return  of  the  portal  blood  to  the  heart  were  it  not  for  anastomoses  between  tribu- 
taries of  the  portal  vein  and  those  of  the  caval  systems,  constituting  what  have  been  termed 
accessory  portal  veins.  Some  of  the  more  important  of  these  are — (1)  between  the  branches  of 
the  coronary  vein  of  the  stomach  and  the  oesophageal  veins  which  open  into  the  vena  azygos; 
(2)  between  the  parumbilical  veins  [vv.  parumbilicales],  which  communicate  with  the  portal 
vein  above  and  descend  upon  the  ligamentum  teres  to  the  anterior  abdominal  wall  to  anastomose 
with  the  superior  and  inferior  epigastric  and  superior  vesical  veins;  (3)  between  the  superior 
and  middle  hsemorrhoidal  veins,  the  latter  opening  into  the  hypogastric,  and  (4)  between  a 
wide-meshed  retro-peritoneal  plexus  of  veins  which  communicates  with  the  portal  vessels 
over  the  posterior  surface  of  the  liver  and  the  veins  of  the  pancreas,  duodenum  and  ascending 
and  descending  colon  on  the  portal  side,  and  with  the  phrenic  and  azygos  veins  on  the  systemic. 


THE  HYPOGASTRIC  VEIN 
THE  COMMON  ILIAC  VEINS 


679 


The  common  iliac  veins  [vv.  iliacae  communes],  (fig.  536)  are  formed  opposite 
the  sacro-iliac  articulation  by  the  confluence  of  the  external  iliac  and  hypo- 
gastric (internal  iliac)  veins.  They  converge  as  they  ascend,  and  unite  oppo- 
site the  upper  border  of  the  fifth  lumbar  vertebra  and  a  little  to  the  right  of  the 
median  line  to  form  the  vena  cava  inferior. 

Fig.  534. — The  Superior  Mesenteric  Vein. 
(The  colon  is  turned  up,  and  the  small  intestines  are  drawn  over  to  the  left  side.) 


Middle  coin 
artery 
Inferior    pancre 


Left  colic  artery 
Superior  mes- 
enteric artery 
and  vein 


Ileo-colic  artery 


Vermiform 
process 


The  right  vein,  shorter  and  more  vertical  in  direction  than  the  left,  passes  obliquely  behind 
the  right  common  iliac  artery  to  its  lateral  side,  where  it  is  joined  by  the  left  common  iliac  vein. 

The  left  vein  lies  to  the  medial  side  of  the  left  common  iliac  artery,  and,  after  crossing  in 
front  of  the  promontory  of  the  sacrum  and  the  fifth  lumbar  vertebra  below  the  bifurcation  of 
the  aorta,  passes  beneath  the  right  common  iliac  artery  to  join  the  right  vein  and  form  the 
vena  cava  inferior.     The  left  vein  may  contain  an  imperfect  valve. 

Tributary. — The  ilio-lumbar  veins  may  enter  the  lower  part  of  the  common 
iliac,  or  open  into  the  hypogastric  vein.  The  left  vein  receives  the  middle  sacral 
vein. 

The  middle  sacral  vein  [v.  sacralis  media]  opens  usually  as  a  single  trunk 
into  the  left  common  liiac  vein.  The  venae  comitantes  which  form  it  ascend  on 
either  side  of  the  middle  sacral  artery  in  front  of  the  sacrum.  They  communicate 
with  the  lateral  sacral  veins,  forming  the  anterior  sacral  plexus  [plexus  sacralis 
anterior]  which  receives  the  sacral  intervertebral  veins,  and  anastomoses  freely 
with  the  neighbouring  lumbar  and  pelvic  veins.  Below,  the  middle  sacral  veins 
communicate  with  the  hsemorrhoidal  veins. 

THE  HYPOGASTRIC  VEIN 

The  hypogastric  (internal  iliac)  vein  [v.  hypogastrica]  (fig.  536)  is  formed  by 
the  confluence  of  the  veins  (except  the  umbilical)  corresponding  to  the  branches 


680 


THE  BLOOD-VASCULAR  SYSTEM 


of  the  hypogastric  artery.  It  varies  considerably  in  length,  but  is  usually  quite 
a  short  trunk,  extending  from  the  upper  part  of  the  great  sciatic  foramen  to  the 
sacro-liac  articulation,  where  it  joins  the  external  iliac  to  form  the  common 
iliac  vein.  It  lies  behind  and  a  little  medial  to  the  hypogastric  artery.  It  con- 
tains no  valve. 

Tributaries. — The  hypogastric  vein  receives  directly  or  indirectly  the  following 
vessels;      the  superior  gluteal,   ilio-lumbar,   lateral  sacral,   obturator,   inferior 


Fig.  635. — The  Inferior  Mesenteric  Vein. 
(The  colon  is  turned  up,  and  the  small  intestines  are  drawn  to  the  right  side.) 


Middle  colic  artery  - — 


Inferior  pancreatico- 
duodenal artery 
Superior  mesenteric 
artery 

Right  coUc  artery 


Abdominal  aorta 
/ena  cava  inferior 


Right  common  iliac 

artery 

Middle  sacral  artery 

and  vein 


Left  colic  artery 


Inferior  mesen- 
teric artery 
Left  colic  artery 
Inferior  mesen- 
teric artery 


Sigmoid  artery 


Superior  hasmor- 
rhoidal  artery 


gluteal  (sciatic),  internal  pudendal,  and  (in  the  female)  the  uterine  veins;  also 
branches  from  the  pudendal,  vesical,  and  haemorrhoidal  plexuses.  The  single 
umbilical  vein-^the  vein  corresponding  to  the  right  and  left  hypogastric  arteries 
and  their  continuation,  the  umbilical  arteries — does  not  enter  the  pelvis,  but, 
leaving  the  umbihcal  arteries  at  the  navel,  passes  along  the  falciform  ligament 
to  the  liver.  After  birth  it  is  converted  into  the  hgamentum  teres  hepatis. 
(See  Portal  Vein,  p.  675.) 

The  superior  gluteal  veins  [vv.  glutete  superiores]  accompany  the  superior  gluteal  artery 
and,  passing  through  the  upper  part  of  the  great  sciatic  foramen,  open  into  the  hypogastric 
vein  near  its  termination,  either  separately  or  as  a  single  trunk. 

The  ilio-lumbar  veins  [vv.  ilio  lumbales]  open  into  the  hypogastric  a  little  higher  than  the 
superior  gluteal.     At  times  they  join  the  common  iliac  vein. 

The  lateral  sacral  veins  [vv.  sacrales  laterales]  (fig.  536)  join  the  superior  gluteal  or  the 
hypogastric  at  or  about  the  same  situation  as  the  gluteal.  They  form  with  the  middle  sacral 
veins  a  ple.xus  in  front  of  the  sacrum,  which  receives  tributaries  from  the  sacral  canal. 

The  obturator  vein  [v.  obturatoria]  (fig.  536),  which  lies  below  the  obturator  artery  as  it 
crosses  the  side  of  the  pelvis,  opens  into  the  front  of  the  hypogastric  vein  a  little  below  the  su- 
perior gluteal.     Its  branches  correspond  to  those  of  the  artery. 

The  inferior  gluteal  veins  [vv.  giuteae  inferiores]  accompany  the  inferior  gluteal  (sciatic) 
artery,  and,  as  a  rule,  unite  to  form  a  single  trunk  before  joining  the  hypogastric  a  little  below 
the  obturator  vein. 

All  the  above  veins  so  closely  follow  the  ramifications  of  their  respective  arteries  that  no 
further  special  description  of  them  is  required.     They  all  contain  valves. 


THE  DORSAL  VEIN  OF  THE  PENIS 


681 


The  internal  pudendal  vein  [v.  pudenda  interna]  (fig.  536)  begins  at  tlie  termination  of  the 
deep  veins  of  the  penis  [w.  profundae  penis]  which  issue  from  the  corijus  coavernosum  penis  with 
the  artery  of  that  body.  Tliese  veins  communicate  with  the  dorsal  vein  at  the  root  of  the  penis 
In  its  course  the  internal  pudendal  vein  runs  with  the  internal  pudendal  artery,  receiving 
tributaries  corresponding  to  the  branches  of  that  vessel.  It.  terminates  in  the  lower  part  of  the 
hypogastric  vein. 

Fig.  536. — The  Veins  of  the  Pelvis,  Male.     (After  Toldt,  "Atlas  of  Human  Anatomy," 
Rebman,  London  and  New  York.) 


Abdominal  aorta 


Ascending  lumbar  vein 


External  iliac  artery  and  vein 


Ductus  deferens 


Inferior  gluteal  vein 
Internal  pudendal  artery  and  vein 


Vems  from  pudendal  plexus 
Obturator  fascia 


Crus  of  the  perns 


L  of  the  penis 
Corpus  cavernosun 


Deep  artery  of  penis 


The  dorsal  vein  of  the  penis  [v.  dorsalis  penis]  (fig.  536)  begins  in  a  plexus  around  the  corona 
glandis,  then  runs  along  the  centre  of  the  dorsum  of  the  penis  between  the  two  dorsal  arteries. 
In  this  course  it  receives  large  tributaries  from  the  interior  of  the  organ,  which,  emerging  for 
the_  most  part  between  the  corpus  cavernosum  lu-ethrai  and  corpus  cavernosum  penis,  wind 
obliquely  over  the  lateral  surface  of  the  latter  structure  to  the  dorsum  of  the  penis  to  end  in  the 
dorsal  vein.  At  the  root  of  the  penis  the  dorsal  vein  communicates  with  the  subcutaneous  veins 
of  the  dorsum  of  the  penis  and,  leaving  the  arteries,  passes  straight  backward  between  the  two 
layers  of  the  fundiform  (suspensory)  ligament.     It  then  goes  between  the  subpubic  linament 


682 


THE  BLOOD-VASCULAR  SYSTEM 


and  the  upper  part  of  the  fascia  of  the  urogenital  diaphragm  (fig.  542).  Here  it  bifurcates, 
each  branch  passing  backward  and  downward  to  the  pudendal  plexus  of  veins.  At  times  the 
dorsal  vein  begins  as  two  branches,  which  run  between  the  dorsal  arteries  and  only  unite  to  form 
a  single  trunk  about  3.7  cm.  (Ij  in.)  from  the  symphysis.  After  dividing  into  a  right  and  a 
left  branch  within  the  pelvis,  each  vessel  generally  communicates  with  the  obturator  vein  by  a 
branch  passing  over  the  back  of  the  pubis  to  the  obturator  foramen. 

Fig.  537. — The  SuBcrrTANEOus  Arteries  and  Veins  op  the  Anterior  Body  Wall. 
(After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 

venous  net  of  the  neck 


Anterior  jugular  vein 

Edge  of  superficial  cervical  fascia 
Superficial  cervical  artery  and  vein 
Cephalic  vein  opening  into  the  deep 
vein  of  neck  (variation) 


Subcutane 


Arch  of  the  jugular  vein 
Pectoral  venous  rete 

Mammillary  venous  plexus 


Connections  with  th 
internal  mammar 
veins  and  with  tht 
perforating  branches 
of  the  internal  mam- 
mary arteries 

Connections  with  the  su- 
perior epigastric  veins 
and  chief  branches  of 
the  superior  epigastric 
arteries 


Venous  rete  of  the 
umbilicus 
Connections  with  the  infer- 
ior  epigastric  veins   and>^. 
the  chief  branches  of  the 
inferior  epigastric  ar- 
teries 


Superficial  epigastn 
artery  and  veins 


Superficial 
iUac  artery  and  vem 


Superficial  subingxii- 
nal  lymph-nodes 


Subcutaneous  dor^ 
sal  vein  of  thi 
penis 


The  pudendal  plexus  [plexus  pudendalis]  surrounds  the  prostate  and  the  neck  and  fundus 
of  the  bladder.  It  receives  in  front  the  right  and  left  divisions  of  the  dorsal  veins  of  the  penis, 
and  communicates  with  the  posterior  scrotal  veins  [vv.  scrotales  posteriores]  and  with  the  hasmor- 
rhoidal  plexus.  The  prostatic  veins  and  the  vesical  plexus  open  into  it,  and  it  also  communi- 
cates with  the  internal  pudendal  vein.  The  veins  forming  the  plexus  are  of  large  size,  especially 
in  old  men,  in  whom  they  often  become  varicose,  and  contain  phleboliths,  or  vein-stones 


VEINS  OF  THE  LOWER  EXTREMITY  683 

The  plexus  is  surrounded  by  a  kind  of  capsule  formed  by  the  superior  fascia  of  the  pelvic 
diaphragm.  It  terminates  in  a  single  stem  on  each  side  which  opens  into  the  hypogastric 
vein. 

In  the  female  the  smaller  pudendal  plexus  surrounds  the  urethra  and  receives  the  dorsal 
and  deep  veins  of  the  clitoris  [vv.  dorsales  et  profunda  clitoridis],  veins  from  the  vestibule,  and 
the  posterior  labial  veins  [w.  labiales  posteriores].  It  communicates  freely  with  the  utero- 
vaginal plexus  and  is  drained  by  the  hypogastric  veins. 

The  vesical  plexus  [plexus  vesicalis]  surrounds  the  apex,  the  sides,  and  the  anterior  and 
posterior  surfaces  of  the  bladder.  It  is  situated  between  the  muscular  coat  and  the  peritoneum, 
and  where  the  bladder  is  uncovered  by  peritoneum  external  to  the  muscular  coat  in  the  pelvic 
cellular  tissue.     It  opens  into  the  pudendal  plexus. 

The  utero-vaginal  plexus  [plexus  uterovaginalis]  connects  with  the  haemorrhoidal,  vesical, 
and  uterine  plexuses.  Its  lower  part  drains  thi'ough  the  internal  pudendal  veins  and  the 
pudendal  plexus,  and  its  upper  protion  largely  through  the  ovarian  veins,  and  partly  through 
the  uterine  veins  [vv.  uterinae]  to  the  hypogastric  (fig.  530). 

The  hEemorrhoidal  plexus  [plexus  haemorrhoidalis]  surrounds  the  rectum,  and  is  situated  at 
the  lower  part  of  that  tube.  It  consists  of  two  portions,  one  of  which,  the  internal  haemor- 
rhoidal plexus,  is  situated  between  the  muscular  and  mucous  coats,  while  the  other,  the  external 
hsemorrhoidal  plexus,  rests  upon  the  outer  sui-face  of  the  muscular  coat.  The  veins  of  this 
latter  plexus  terminate  in  the  inferior,  middle,  and  superior  hsemorrhoidal  veins.  The  inferior 
[w.  hiemorrhoidales  inferiores]  join  the  internal  pudendal;  the  middle  [v.  haemorrhoidalis 
media]  accompanies  the  middle  hsemorrhoidal  artery  and  opens  into  the  hypogastric  and 
superior  haemorrhoidal  veins;  the  superior  (p.  678)  forms  the  commencement  of  the  inferior 
mesenteric  vein,  and  through  this  the  blood  gains  the  portal  vein.  None  of  these  veins  have 
any  valves,  hence  the  enlargement  of  the  inferior  htcmorrhoidal  veins,  when  the  portal  vein  is 
obstructed,  as  in  cirrhosis  of  the  liver.  Through  the  haemorrhoidal  veins  a  free  communication 
is  established  between  the  systemic  and  portal  system  of  veins. 

THE  EXTERNAL  ILIAC  VEIN 

The  external  iliac  vein  [v.  iliaca  externa]  (fig.  536),  is  the  upward  continuation 
of  the  femoral.  Beginning  at  the  lower  border  of  the  inguinal  ligament,  it 
accompanies  the  external  iliac  artery  medially  upward  along  the  brim  of  the  mi- 
nor pelvis,  lying  at  first  on  the  superior  ramus  of  the  pubis,  and  then  on  the  psoas 
major  muscle.  It  terminates  by  joining  the  hypogastric  vein  behind  the  hypo- 
gastric artery,  opposite  the  lower  border  of  the  sacro-iliac  articulation,  to  form 
the  common  iliac  vein.  It  lies  at  first  medial  to  the  external  iliac  artery,  and  on 
the  left  side  remains  medial  to  the  artery  throughout  its  course.  On  the  right 
side,  however,  as  it  ascends,  it  gradually  gets  behind  the  artery.  It  contains  one  or 
two  valves. 

In  addition  to  the  femoral,  the  external  iliac  receives  the  inferior  epigastric 
vein  [v.  epigastrica  inferior]  (fig.  536)  and  the  deep  circumflex  iliac  vein  [v.  cir- 
cumflexa  ilium  profunda]  (fig.  541),  which  accompany  the  arteries  of  the  same 
name. 

THE  SUPERFICIAL  VEINS  OF  THE  ABDOMINAL  WALL 

The  plexus  of  superficial  veins  of  the  anterior  abdominal  wall  is  continuous 
with  that  of  the  thorax  (fig.  537).  Its  main  channels  are  the  superficial  circumflex 
ihac,  the  superficial  epigastric,  and  the  external  pudendal,  all  of  which  open  into 
the  great  saphenous  vein.  These  communicate,  by  means  of  subcutaneous 
abdominal  veins,  with  the  superior  epigastric  vein,  and,  by  means  of  the  thoraco- 
epigastric veins,  with  the  lateral  thoracic  and  costo-axillary.  The  superficial  veins 
communicate  verj'  freely  with  the  deeper  veins  of  the  abdominal  wall,  and,  by 
means  of  parumbilical  veins,  they  communicate  to  a  slighter  extent  with  the 
portal  system. 

The  superficial  veins  of  the  lumbar  region  form  an  abundant  plexus  which 
drains  through  the  dorsal  and  lateral  perforating  branches  of  the  intercostal, 
lumbar,  and  sacral  veins. 

THE  VEINS  OF  THE  LOWER  EXTREMITY 

The  veins  of  the  lower  extremity  are  divided  into  the  superficial  and  the  deep. 
The  superficial  veins  lie  in  the  subcutaneous  tissue  superficial  to  the  deep  fascia, 
through  which  they  receive  numerous  communicating  branches  from  the  deep 
veins.  They  are  collected  chiefly  into  two  main  trunks,  which,  beginning  on  the 
foot,  extend  upward,  one,  the  great  saphenous,  lying  antero-medially,  and  the 


684  THE  BLOOD-VASCULAR  SYSTEM 

other,  the  small  saphenous,  postero-laterally.  The  former  finally  joins  the 
femoral  vein  by  passing  through  the  deep  fascia  at  the  groin;  the  latter,  the  pop- 
liteal by  perforating  the  fascia  at  the  ham.  The  deep  veins,  on  the  other  hand, 
accompany  their  corresponding  arteries.  All  the  veins  of  the  lower  limb  have 
valves  which  are  more  numerous  than  in  the  veins  of  the  upper  extremity  and  in 
the  deep  than  in  the  superficial  veins. 

I.  THE  SUPERFICIAL  VEINS  OF  THE  LOWER 
EXTREMITY 

The  superficial  veins  of  the  lower  limb  begin  in  the  plexuses  of  the  foot.  The 
dorsal  digital  veins  [vv.  digitales  pedis  dorsales]  collect  blood  from  the  dorsal 
surfaces  of  the  toes  and  unite  in  pairs,  around  each  cleft,  to  form  the  dorsal 
metatarsal  veins  [vv.  metatarsese  dorsales  pedis].  The  dorsal  metatarsal  veins,  of 
which  the  first  and  fifth  are  larger  than  the  others,  join  the  dorsal  venous  arch 
[arcus  venosus  dorsalis  pedis].  This  arch  is  convex  toward  the  toes  and  crosses 
near  the  bases  of  the  metatarsal  bones.  From  the  medial  and  lateral  ends  of  the 
arch  the  great  and  small  saphenous  veins,  respectively,  take  origin.  The  area 
of  the  dorsum  of  the  foot  contained  between  the  arch  and  the  two  saphenous 
veins  is  covered  by  the  dorsal  venous  rate  [rete  venosum  dorsale  pedis]  which 
extends  as  high  as  the  ankle-joint  (fig.  539). 

On  the  plantar  surface  the  plantar  digital  veins  [w.  digitales  plantares] 
return  the  venous  blood  to  the  clefts  of  the  toes  and  unite  to  form  the  common 
digital  veins  [vv.  digitales  communes  pedis].  The  common  digital  veins  join 
freely  with  one  another  on  the  sole  to  form  the  plantar  venous  rete  [rete  venosum 
plantare].  There  are  numerous  communications  between  the  superficial  veins 
of  the  dorsum  and  sole.  These  occur  both  in  the  clefts  of  the  toes,  by  means  of 
the  intercapitular  veins  [vv.  intercapitulares],  and  around  the  margins  of  the 
foot.  Communications  between  the  superficial  and  deep  veins  of  the  foot  are 
very  free  (fig.  540). 

The  great  (or  internal)  saphenous  vein  [v.  saphena  magna]  (fig.  538)  com- 
mences as  the  medial  end  of  the  dorsal  venous  arch,  and,  after  receiving 
branches  from  the  sole  which  join  it  by  turning  over  the  medial  border  of  the 
foot,  passes  upward  in  front  of  the  medial  malleolus,  and  then  obliquely  up- 
ward and  backward  about  a  finger's  breadth  from  the  posterior  border  of  the 
tibia  in  company  with  the  saphenous  nerve,  which  becomes  superficial  just  be- 
low the  knee.  Continuing  its  course  upward,  it  passes  behind  the  medial  epi- 
condyle,  and  then  runs  upward  on  the  medial  side  of  the  front  of  the  thigh  to 
about  3.7  cm.  (li  in.)  below  the  inguinal  Hgament,  where  it  dips  through  the  fossa 
ovalis  (saphenous  opening)  in  the  fascia  lata,  and  ends  in  the  femoral  vein. 

Tributaries. — In  its  course  up  the  leg  and  thigh  it  receives  numerous  unnamed  cutaneous 
tributaries.  As  it  passes  up  the  thigh  it  often  receives  a  large  vein,  the  femoro-popliteal  which 
communicates  with  the  small  saphenous,  and  several  of  the  cutaneous  veins  on  the  lateral  part  of 
the  thigh,  and  a  second  vein,  the  accessory  saphenous  [v.  saphena  accessorial,  formed  by  the 
union  of  the  cutaneous  veins  from  the  medial  and  back  part  of  the  thigh  (fig.  538).  The  great 
saphenous  vein  contains  from  ten  to  twenty  valves. 

Immediately  before  entering  the  fossa  ovalis  the  great  saphenous  vein  receives  the  super- 
ficial epigastric,  superficial  circumflex  iliac,  and  external  pudendal  veins,  though  any  of  these 
veins — or  all  of  them — may  pierce  the  fascia  separately  and  enter  the  femoral  vein. 

The  superficial  epigastric  vein  [v.  epigastrica  superficialis]  anastomoses  with  the  superficial 
abdominal,  and  parumbUical  veins. 

The  superficial  circumflex  iliac  vein  [v.  circumflex  ilium  superficiahs]  anastomoses  with  the 
thoraco-epigastric  and  the  superficial  circumflex  iliac  veins. 

The  external  pudendal  veins  [vv.  pudenda^  externaj]  collect  venous  blood  from  the  anterior 
scrotal  or  labial  veins,  which  anastomose  with  the  posterior  scrotal  or  labial  veins,  and  from  the 
subcutaneous  veins  of  the  dorsum  of  the  penis  [vv.  dorsales  penis  subcutanese]. 

The  small  saphenous  vein  [v.  saphena  parva]  (fig.  539)  begins  at  the  lateral  end 
of  the  venous  arch  on  the  dorsum  of  the  foot.  After  receiving  branches  from  the 
sole,  which  turn  over  the  lateral  border  of  the  foot,  it  passes  behind  the  lateral 
malleolus,  and  then  upward  and,  lying  at  first  along  the  lateral  side  of  the  tendo 
Achillis,  afterward  along  the  back  of  the  calf,  in  company  with  the  sural  (short 
saphenous)  nerve,  to  about  the  lower  part  of  the  centre  of  the  popliteal  space, 
where  it  perforates  the  deep  fascia,  and,  sinking  between  the  two  heads  of  the 
gastrocnemius,  opens  into  the  popliteal  vein. 


SUPERFICIAL  VEINS  OF  THE  LOWER  LIMB 


685 


Tributaries.^As  it  passes  up  the  calf  between  the  superficial  and  deep  fascia,  it  receives 
numerous  cutaneous  veins  from  the  heel,  and  the  lateral  side  and  back  part  of  the  leg,  and 


Fig.  538. — The  Superficial  Veins  and  Lymphatics  of  the  Left  Lower  Limb. 
(Walsham.) 


Superficial  epigastric  vein 

Lymphatics  from  penis  and 
scrotum 

Femoral  vein 

Superficial  femoral  lymphatic 
glands 
External  pudendal  vein 


Superficial  lymphatics  from 
lateral  wall  of  abdomen 

Superficial  lymphatics  from 
lower  and  anterior  walls 
of  abdomen 


Accessory  saphenous  vein. 


Great  saphenous  vein' 


Femoro-popliteal  vein, 


Medial  malleolus' 
Dorsal  venous  arch 


Superficial  inguinal  lym- 
phatic glands 
Superficial  circumflex 
iliac  vein 


communicates  at  intervals,  through  transverse  or  intermuscular  branches,  with  the  deep  veins 
accompanying  the  peroneal  artery.  Just  before  perforating  the  deep  fascia,  it  receives  a  large 
descending  branch,  the  vena  femoropoplitea,  from  the  lower  and  back  part  of  the  thigh.     This 


686  THE  BLOOD-VASCULAR  SYSTEM 

communicates  with  a  plexus  of  veins  upon  the  posterior  and  lateral  regions  of  the  thigh  and 
with  the  great  saphenous.  In  many  cases  the  small  saphenous  vein  is  entirely  drained,  by  means 
of  the  femoro-popliteal,  into  the  great  saphenous.  Under  these  circumstances  the  usual  place 
of  termination  of  the  small  saphenous  is  marked  by  a  small  vein  opening  into  the  popliteal.  A 
small  offshoot  from  the  inferior  sural  branch  of  the  popliteal  artery  accompanies  this  vein  for  a 

Fig.  539. — The  Veins  op  the  Dorsum  op  the  Foot.     (After  Toldt,  "Atlas  of  Human  Anat- 
omy," Rebman,  London  and  New  York.) 


Great  saphenous  vein 


Anterior  tibial  muscle 


Dorsal  pedal  artery  and  vein 


Extensor  hallucis  longus  tendon 


Dorsal  venous  arch 


Dorsal  digital  vein  - 


Anterior  tibial  artery 


i=— Anterior  tibial  veins 


^  Dorsal  venous  rete  of  foot 


^Dorsal  metatarsal  arteries 


-Dorsal  metatarsal  vein 


Intercapitular  veins 


short  distance  down  the  back  of  the  calf.     The  small  saphenous  vein  contains  from  nine   to 
twelve  valves. 


II.  THE  DEEP  VEINS  OF  THE  LOWER  EXTREMITY 

The  deep  veins  of  the  lower  extremity  accompany  the  arteries,  and  have 
received  corresponding  names.  From  the  foot  to  the  knee  there  are  two  veins  to 
each  artery.     These  veins  run  on  either  side  of  the  corresponding  artery,  and  com- 


DEEP  VEINS  OF  THE  LOWER  LIMB 


687 


municate  at  frequent  intervals  with  each  other  across  it.  They  are  known  as  the 
venae  comitantes.  From  the  knee  upward  there  is  a  single  main  vein  to  each 
artery,  except  at  the  back  of  the  thigh  and  in  the  gluteal  region,  where  there  are 
commonly  two. 


Fig.  540.- 


-The  Veins  op  the  Sole  of  the  Foot.     (After  Toldt,  "Atlas  of  Human  Anatom}',' 
Rebman,  London  and  New  York.) 


Intercapitular  veins 


Posterior  tibial  veins 

7    / 

Posterior  tibial  muscle— -|         t 

Posterior  tibial  artery 

Great  saphenous  vein — 

Flexor  digitorum ^^ 

longus  tendon        ^^V  ^ 


-  Plantar  digital  ^ 


.-i- Plantar  venous  arch 


Lateral  plantar  artery 
and  accompanying 
veins 

Deep  branch  of  the 
medial  plantar  and 
veins 


Venous  rete  of  the  heel 


Small  saphenous  vein 


The  veins  of  the  foot  and  leg. — The  deep  veins  of  the  foot  become  separated 
from  the  superficial  where  the  plantar  metatarsal  veins  [vv.  metatarsese  plantares] 
leave  the  plantar  digital  and  intercapitular  veins  to  accompany  the  plantar  meta- 
tarsal arteries.     The  plantar  metataisal  veins  empty  into  the  plantar  venous  arch 

[arcus  venosus  plantaris]  which  accompanies  the  arterial  plantar  arch  in  the  depth 
of  the  sole.  (fig.  540) 


THE  BLOOD-VASCULAR  SYSTEM 


The  posterior  tibial  veins  [vv.  tibiales  posteriores]  drain  the  plantar  venous 
arch  and  the  superficial  rete  (fig  542). 

They  follow  the  posterior  tibial  artery  up  the  leg,  receiving  tributaries  corresponding  to 
its  branches,  the  largest  of  which  are  the  peroneal  veins  [vv.  peronefe].  They  unite  with  the 
anterior  tibial  vense  comitantes  at  the  lower  border  of  the  popliteus  muscle. 

The  anterior  tibial  veins  [vv.  tibiales  anteriores]  begin  in  the  dorsal  venous  rete 
and  accompany  the  anterior  tibial  artery  up  the  leg  receiving  tributaries  cor- 
responding to  branches  of  the  artery. 

Fig.  541. — The  Femoral  Vein.     (After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London 

and  New  York.) 


Deep  circumflex  iliac  artery  and  v 


Inferior    epi- 
gastric  ar- 
tery and  vein 


Fundiform  ligament  of  penis 


Vastus 
medialis 
Second    per- 
forating 
artery 
and 
Adductor 
longus 


Tunica  vaginalis 
propria  testis 


Deep  femoral  artery  and  vein 


They  pass  backward  between  the  interosseous  membrane  and  the  tibia  and  fibula  to  unite 
with  the  posterior  tibial  veins.  The  posterior  and  anterior  tibial  veins  unite  at  the  lower 
border  of  the  popliteus  muscle  to  form  the  popliteal  vein. 

All  these  veins  contain  numerous  valves,  and  communicate,  by  means  of  intermuscular 
branches,  with  the  superficial  veins. 

The  popliteal  vein  [v.  poplitea]  (fig.  542),  is  formed  by  the  confluence  of  the 
venae  comitantes  of  the  anterior  and  posterior  tibial  arteries  at  the  lower  border 
of  the  popliteus,  and  extends  upward  to  the  opening  in  the  adductor  magnus  at 
the  junction  of  the  middle  and  lower  third  of  the  thigh,  where  it  changes  its  name 
to  femoral. 


TEE  POPLITEAL  VEIN 


It  accompanies  the  popliteal  artery,  lying  superficial  to  it  in  the  whole  of  its  course,  and 
tightly  bound  down  to  it  by  its  fascial  sheath.  At  the  lower  part  of  the  space  it  is  a  little  medial 
to  the  artery,  but,  crossing  the  vessel  obliquely  as  it  ascends,  lies  a  little  lateral  to  it  at  the 
upper  part  of  the  space.  The  tibial  (internal  popliteal)  nerve  lies  superficial  to  the  vein, 
being  lateral  to  it  above,  then  posterior  to  it,  and  then  a  little  to  its  medial  side.  The  popliteal 
vein  contains  two  or  three  valves. 

Fig.  542. — The  Deep  Veins  of  the  Leg.     (After  Toldt,  *' Atlas  of  Human  Anatomy,"  Rebman. 
London  and  New  York.) 
Semimenibraaosus  .^ 


Semitendinosus 


Popliteal  artery 


Medial  sural  artery  and  veins 

Popliteal  veins  <->_- 

Gastrocnemius   (medial  head) 

Deep  layer  of  the  crural  fascia  - 


Flexor  digitorum  longus 
Posterior  tibial  artery  and  veins 


Flexor  hallucis  longu: 


-     Popliteal  vein 


Lateral  sural  artery  and  veins 


al  artery  and 
Flexor  digitorum  longus  -. 

Posterior  tibial 

Posterior  medial  malleolar  artery 


Medial  calcanean  branches——- 
Venous  rete  of  the  heel — 


_  Peroneal  artery  and 


Flexor  hallucis  longus 


Posterior  lateral  malleolar  artery  and  veins 


Lateral  calcanean  branches  and  veins 


The  popliteal  receives  the  small  saphenous  vein.  It  is  also  joined  on  its  lateral  and  medial 
sides  by  the  accessory  popliteal  veins  [vv.  popliteoe  accessorise]  which  form  common  trunks  of 
termination  of  the  sural  and  articular  veins  of  the  respective  sides.  The  medial  vein  receives 
in  addition,  through  a  plexus  extending  as  high  as  the  opening  in  the  adductor  magnus,  the  veins 
accompanying  the  a.  genu  suprema. 


690  THE  BLOOD-VASCULAR  SYSTEM 

The  femoral  vein  [v.  femoralis],  the  continuation  of  the  popliteal  upward, 
extends  from  the  tendinous  opening  in  the  adductor  magnus  to  the  inguinal 
ligament.  In  this  course  its  relations  are  similar  to  those  of  the  femoral  artery. 
As  the  vein  passes  through  the  adductor  canal,  it  lies  behind  and  a  little  lateral 
to  the  artery.  At  the  apex  of  the  femoral  trigone  (Scarpa's  triangle)  it  is  still 
posterior  to  the  artery,  but  gradually  passes  to  the  medial  side  as  it  ascends 
through  the  trigone  (fig.  541). 

In  the  neighbourhood  of  the  inguinal  hgament  the  femoral  vein  hes  on  the  same  plane  as 
the  artery  from  which  it  is  separated  by  a  delicate  prolongation  of  the  fascia  stretching  be- 
tween the  front  and  back  layers  of  the  femoral  sheath.  On  the  medial  side  the  vein  is  sepa- 
rated by  a  similar  septum  from  the  femoral  canal.  The  femoral  vein  contains  five  pairs  of 
valves. 

Tributaries. — The  femoral  vein  receives  (in  addition  to  the  great  saphenous 
vein,  and,  in  some  cases  the  superficial  veins  of  the  epigastrium  and  groin)  the 
profunda  veins  and  a  variable  number  of  small  femoral  vense  comitantes. 

The  profunda  femoris  veins  [vv.  profunda  femoris)  arise  from  the  vense  comitantes  corre- 
sponding to  branches  of  the  profunda  femoris  artery.  The  medial  and  lateral  circumflex  veins 
[w.  circumflex  femoris  mediales  et  laterales]  collect  blood  from  the  muscles  of  the  adductor 
and  lateral  rotator  regions.  The  perforating  veins  anastomose  with  femoro-popliteal  and  other 
veins  of  the  posterior  femoral  region,  and  with  the  circumflex  and  accessory  popUteal  veins. 
They  return  blood  from  the  femur  and  the  adductor,  hamstring  and  vasti  muscles. 

The  venae  comitantes,  much  smaller  than  the  main  femoral  vein,  accompany  the  femoral 
artery  on  either  side.  They  anastomose  with  one  another,  with  the  femoral,  and  often  with  the 
popliteal  vein.     They  terminate  in  the  femoral  a  short  distance  above  the  profunda  veins. 

MORPHOGENESIS  AND  VARIATIONS  OF  THE  VEINS 

The  veins  of  the  adult  human  body  tend  to  accompany  the  arteries;  this  tendency  is  more 
pronounced  in  the  trunk,  neck,  and  extremities  than  in  the  cranium.  Developmental  history 
shows  that  the  primitive  distribution  of  the  veins  of  the  trunk  resembles  that  of  the  arteries 
of  the  same  region  in  its  bilateral  symmetry  only.  Also  that  the  changes  which  modify  the 
primitive  bilateral  symmetry  of  the  chief  veins  are  not  only  more  extensive  but  of  a  different 
nature  from  those  producing  a  similar  effect  upon  the  arteries.  In  both  cases  the  main  body- 
vessels  begin  as  a  pan-  of  main  longitudinal  trunks  and  end  as  a  main  unpaired  channel  (or 
channels  in  the  case  of  the  venous  system)  situated  near  the  median  plane  of  the  body.  In 
the  ease  of  the  venous  system  the  change  results  from  wholesale  destruction  of  the  vessels  on 
the  left  of  the  body  accompanied  by  enlargement  of  those  upon  the  right.  In  the  arterial 
system  destruction  occurs  to  a  much  more  limited  extent;  the  definitive  channel  results  mainly 
from  blending  of  the  two  primitive  aortse. 

The  main  venous  channels  of  the  cranium  and  extremities  are  primitively  superficial; 
in  the  cranium  they  remain  so.  In  the  extremities  new  veins  are  formed  which  follow  the  main 
arteries;  to  these  the  more  primitive  channels  become  tributary. 

The  heart,  as  soon  as  it  assumes  the  simple  tubular  form  is  found  to  receive  four  veins. 
These,  the  two  vitelline  and  two  umbilical  veins,  enter  the  sinus  venosus,  a  vitelline  and  an 
umbilical  vein  on  either  side.  The  umbilical  veins  are  lateral  to  the  vitellines,  and  are  paired 
within  the  body  only;  they  arise  from  the  placenta,  and  traverse  the  belly-stalk  as  a  single 
trunk.  The  vitelline  veins  return  blood  from  the  yolk  sac,  and,  at  first,  are  independent 
throughout. 

At  a  later  period  two  other  pairs  of  veins  arise  for  the  venous  drainage  of  the  embryonic 
body.  They  are  the  pre-  and  post-cardinals  which  drain  the  cephalic  and  caudal  regions 
respectively.  The  right  pre-cardinal  vein  unites  with  the  right  post-cardinal  to  form  the  right 
common  cardinal  (duct  of  Cuvier).  The  latter  runs  in  a  medial  direction  to  join  the  sinus 
venosus  lateral  to  the  right  umbilical.  On  the  left  side  the  arrangement  matches  that  on  the 
right  to  produce  a  primitively  symmetrical  pattern. 

During  development  changes  are  brought  about  in  the  primitive  veins  which  end  in  the 
production  of  the  adult  venous  system  as  follows:  the  common  and  pre-cardinals,  together 
with  the  subclavian  veins  and  the  cephalic  ends  of  the  post-cardinals,  are  transformed  into  the 
vena  cava  superior  and  its  larger  tributaries.  The  remainder  of  the  post-cardinal  system  is 
instrumental  in  the  production  of  the  vena  cava  inferior  and  its  tributaries.  FinaUy  the 
intra-embryonic  portions  of  the  vitelline  and  umbilical  veins  participate  in  the  formation  of  the 
portal  and  hepatic  systems  of  veins  together  with  the  proximal  end  of  the  vena  cava  inferior. 

The  following  brief  account  of  morphogenesis  and  variations  is  divided  into  three  headings 
(1)  vena  cava  superior  and  its  tributaries;  (2)  vena  cava  inferior  and  its  tributaries,  and  (3) 
the  portal  system. 

A.    THE  VENA  CAVA  SUPERIOR  AND  ITS  TRIBUTARIES 

1.  MORPHOGENESIS 

The  pre-cardinal  veins  at  first  return  blood  from  the  head  only,  but  as  the  heart  recedes 
into  the  thorax  the  cardinal  veins  migrate  with  it.  In  so  doing  the  common  cardinals  lag 
somewhat  behind  and  in  consequence  their  direction,  primitively  transverse,  approaches  the  Ion- 


THE  VENA  CAVA  SUPERIOR 


691 


gitudinal.  The  pre-cardinals,  which  have  increased  in  relative  length,  now  course  symmet- 
rically along  the  neck  into  the  thorax.  At  a  stage  of  16  mm.,  the  definitive  subclavian  vein  has 
migrated  from  the  common  to  the  pre-cardinal,  which  henceforth  receives  the  main  ven- 
ous flow  from  the  upper  extremity  as  well  as  from  the  head.  The  symmetrical  arrangement  of 
the  cardinal  veins  is  disturbed  at  a  stage  of  about  18  mm.,  by  the  development  of  a  transverse 
connection  between  the  right  and  left  pre-cardinals  (fig.  544).  This  connection,  the  left  in- 
nominate vein,  arises,  probably,  by  the  development  of  cross-anastomoses  uniting  the  lateral 
veins  draining  the  developing  thymus  and  thyreoid  glands.  On  the  right  side  of  the  embryo 
the  veins  of  the  adult  are  now  recognisable  as  follows: — the  vein  (pre-  and  common  cardinal) 
extending  from  the  left  innominate  to  the  heart  becomes  the  vena  cava  superior.  The  pre- 
cardinal,  from  the  left  innominate  to  the  subclavian,  becomes  the  right  innominate.  From 
the  subclavian  to  the  cranium  it  becomes  the  internal  jugular. 

The  vessel  of  the  left  side  corresponding  to  the  vena  cava  superior  now  rapidly  diminishes 
in  size.  It  extends  from  the  left  innominate  vein  (the  extreme  left  end  of  which  corresponds  in 
its  method  of  formation  to  the  entire  right  innominate)  to  the  right  atrium.  In  so  doing  it 
passes  ventral  to  the  aortic  arch  and  the  foot  of  the  left  lung,  dorsal  to  the  left  artium,  and 
through  part  of  the  coronary  sulcus. 

Fig.  543. — Semidiagrammatic  Reconstructions  of  the  Cranial  Venous  System.  (Mall.) 
A,  4  Weeks;  B,  5th  Week;  C,  Beginning  op  3rd  Month;  D,  An  Older  Fcetus. 

A.c.v;  pre-cardinal  vein;  A.V.,  otic  vesicle;  Inf. Pet.,  inferior  petrosal  sinus;  L.,  eye;  O.V.,  superior 
ophthalmic  vein;  S.L.S.,  superior  sagittal  sinus;  S.P.S.  sphenoparietal  sinus;  S.R.,  sinus 
rectus;  S.S.,  middle  cerebral  vein;  T.H.,  confluens  sinuum;  V.,  semilunar  ganglion;  V.C.A., 
v.  cerebralis  anterior;  V.J.,  internal  jugular  vein;  V.C.L.,  v.  capitis  lateralis;  V.O.M.  or 
sup.  pet.,  v.  cerebralis  media  and  superior  petrosal  sinus;  V.C.P.  or  L.S.,  v.  cerebralis  pos- 
terior and  transverse  sinus. 


The  segmental  veins  draining  the  second,  third  and  fourth  intercostal  spaces  of  the  left  side 
open,  by  a  common  stem  formed  by  the  left  pre-cardinal,  into  the  left  innominate.  The  cor- 
responding segmental  veins  of  the  right  side  open,  by  a  common  stem,  into  the  vena  azygos.  The 
collecting  stem,  on  either  side,  is  the  vena  intercostais  suprema.  The  method  of  origin  of  the 
azygos,  hemiazygos  and  accessory  hemiazygos  veins  is  treated  with  the  inferior  caval  system. 
Below  the  superior  intercostal  tributary,  the  left  superior  cava  is  lost  to  within  a  short  distance 
of  the  sinus  venosus.  Here  its  lower  end  persists  as  the  oblique  vein  of  the  left  atrium  and  the 
left  end  of  the  coronary  sinus.  The  former  course  of  the  left  superior  cava  is  often  indicated  in 
the  adult  by  a  small  fibrous  cord,  uniting  the  extremities  of  the  persisting  veins  and  passing 
through  the  ligamentum  v.  cavoe  sinistrae  (p.  523). 

Within  the  cranium  the  pre-cardinal  veins  are  primitively  in  close  contact  with  the  brain 
and  medial  to  the  semilunar,  acustico-facial,  glossopharyngeal  and  vagus  ganglia.  The  portion 
of  each  vein  extending  from  the  semilunar  ganglion  to  the  facial  canal  (its  exit  from  the  cranium) 
early  becomes  involved  in  a  process  of  anastomosis-migration  which  eventually  places  it  lateral 
to  the  ganglia  and  to  the  otocyst.  The  new  vein  formed  in  the  latter  situation  is  called  the  vena 
capitis  laterahs  (fig.  543).  The  portion  of  the  pre-cardinal  vein  which  remains  medial  to  the 
semilunar  ganglion  persists  as  the  adult  cavernous  sinus  and  receives  a  primitive  vein  (v.  cerebralis 
anterior)  which  drains  the  orbit  and  the  mid-  and  forebrain.     The  forebrain  tributaries  of 


692 


THE  BLOOD-VASCULAR  SYSTEM 


the  right  and  left  v.  cerebralis  anterior  unite  to  from  a  median  vein,  the  definitive  superior 
sagittal  sinus,  wliicli  at  first  drains  into  the  cavernous  sinus.  There  are  two  other  primitive 
cerebral  veins;  the  v.  cerebralis  media  and  v.  cerebralis  posterior.  The  first  receives  blood 
from  the  cerebellar  region  and  drains  into  the  cavernous  sinus.  The  second,  the  v.  cerebralis 
posterior,  also  receives  blood  from  the  hind-brain  and,  leaving  the  skull  through  the  jugular  fora- 
men, joins  the  pre-cardinal  (internal  jugular)  vein  m  the  neck.  Several  changes  occur  from 
now  on  (fig.  543)  which  bring  about  the  definitive  relations  of  the  dural  sinuses  and  transfer 
the  main  venous  exit  from  the  stylomastoid  to  the  jugular  foramen.  The  right  v.  cerebralis 
posterior  joins  the  superior  sagittal  sinus  and  this  becomes  the  right  transverse  sinus.  The 
left  V.  cerebralis  posterior  communicates  with  the  junction  of  the  superior  sagittal  and  right 
transverse  sinuses  (now  the  confluens  sinuum)  and  becomes  the  left  transverse  sinus.  The 
confluens  receives  the  sinus  rectus,  which  forms  its  adult  connections  with  the  inferior  petrosal 
sinus  and  great  cerebral  vein.  The  v.  cerebralis  media  joins  the  transverse  sinus  to  become  the 
superior  petrosal  sinus.  The  latter  forms  a  new  (intracranial)  means  of  drainage  for  the  caver- 
nous sinus  and  its  tributaries.  The  original  drainage  channel  of  the  cavernous  sinus  (v. 
capitis  lateralis),  having  been  supplanted,  disappears.  The  superior  cerebral  veins  drain  into 
the  superior  sagittal  sinus.  The  remaining  portion  of  the  interrupted  v.  cerebrah's  anterior 
drains  the  middle  cerebral  vein  and  spheno-parielal  sinus.  The  inferior  petrosal  sinus  arises 
de  novo. 

In  the  upper  extremity  the  venous  drainage  is  at  first  superficial  and  opens  into  the  post- 
cardinal  and  umbilical  veins.  The  ulnar  limb  of  the  loop-like  early  venous  channel  (marginal 
vein)  becomes  the  primitive  ulnar  vein,  but  does  not  open  into  the  pre-cardinal  until  a  stage  later 
than  that  of  10  millimetres.  The  primitive  ulnar  forms  the  basilic,  part  of  the  brachial,  the 
axillary,  and  subclavian  veins.  It  receives  the  large  thoraco-epigastric  trunk.  The  cephalic 
vein,  which  at  first  joins  the  external  jugular,  is  of  secondary  formation.  The  venoe  comitantes 
are  formed  later  still. 

2.  VARIATIONS 


The  great  veins  of  the  thorax  may  present  variations  from  the  normal  as  a  result  of  absence 
of  the  left  innominate  vein.  In  this  case  there  are  two  superior  cavse,  not  necessarily  of  equal 
size,  each  of  which  receives  an  internal  jugular  and  subclavian  vein.     Persistence  of  the  left 

Fig.  544. — The  Transformation  of  the  Postcardinal  System  of  Veins,  C  representing 
THE  Adult.  The  Wolffian  Body  is  Dotted.  (Lewis.) 
a.c,  precardinal;  as.  1.,  ascending  lumbar;  az.,  azygos;  c,  caudal;  c.h.,  common  hepatic; 
c.  il.,  common  iliac;  C.S.,  coronary  sinus;  d.C,  common  cardinal;  g.,  spermatic  or  ovarian;  h., 
hepatic;  h.-az.,  hemiazygos;  h.-az.  ac,  accessory  hemiazygos  (here  draining  into  the  intercostalis 
suprema);  i.  j.,  internal  jugular;  l.c.i.,  left  common  iliac;  1.  in.,  left  innominate;  m.s.,  middle 
sacral;  p.c,  posterior  cardinal;  r.,  renal;  r.a.,  renal  anastomosis;  r.c.i.,  right  common  iliac; 
r.  in.,  right  innominate;  s.,  suprarenal;  s-c,  subcardinal;  s-cl.,  subclavian;  s.l.,  sinusoids; 
v.c.i.,  vena  cava  inferior;  v.c.s.,  vena  cava  superior. 


^i     JL 


vena  cava  superior  without  failure  of  the  left  innominate  may  occur  in  three  classes  of  cases: 
(a)  In  which  both  cavse  are  present,  equal  in  size  or  asymmetrical,  (b)  In  which  the  left  cava 
only  occurs,  associated  with  situs  inversus,  (c)  In  which  the  left  cava  only  is  present,  without 
situs  inversus.     The  left  vena  cava  superior,  when  present,  crosses  in  front  of  the  aortic  arch  and 


THE  VENA  CAVA  INFERIOR  693 

enters  the  right  atrium  by  way  of  the  coronary  sinus,  collecting  the  coronary  veins.     Cases  are    • 
on  record  of  a  left  superior  cava  terminating  in  the  left  atrium. 

The  azygos  weins.^Variations  of  these  veins  and  of  the  intercostal  veins  have  been  dealt 
with  on  pp.  663-664.     For  their  morphogenesis,  see  under  vena  cava  inferior. 

The  veins  of  the  neck,  face,  and  scalp. — These  veins  have  so  many  variations  in  detail  that 
it  is  difficult,  in  the  case  of  some  veins,  to  assign  their  normal  distribution.  The  external 
jugular,  for  instance,  is  usually  described  in  Enghsh  text-books  as  a  tributary  of  the  subclavian 
vein;  it  is  assigned  by  the  BNA  to  the  internal  jugular.  It  is  frequently  found  to  open  into  the 
angle  between  the  two,  or,  forming  a  plexus  with  its  tributaries,  drain  into  both.  The  origin 
of  the  external  jugular  vein  is  also  exceedingly  variable.  The  external  jugular  may  be  small, 
or  absent,  in  which  case  the  anterior  jugular  is  large.  The  reverse  may  be  the  case  since  the 
external  jugular  frequently  receives  the  posterior,  and  sometimes  the  common  facial.  Fortu- 
nately venous  variations  are  not  of  prime  surgical  importance. 

Veins  of  the  cranium. — The  venous  sinuses  of  the  dura  mater  are  not  subject  to  important 
variations.  Variations  in  the  relative  size  of  the  transverse  simises  have  been  referred  to  on 
p.  651.  The  petrosquamous  sinus,  occasionally  present,  is  described  on  p.  653.  The  occipital 
and  inferior  sagittal  sinuses  are  frequently  absent. 

The  cerebral  veins  are  liable  to  great  variation  in  detail:  the  great  cerebral  vein  may  be  absent, 
as  a  single  trunk,  in  which  case  the  internal  cerebral  veins  open  directly  into  the  sinus  rectus. 
The  middle  cerebral  vein  may  open  into  the  sphenoparietal,  or  superior  petrosal  sinus  or  into  the 
basilar  plexus. 

Veins  of  the  upper  extremity. — The  subclavian  vein  is  occasionally  posterior  to  the  artery, 
or  spUts  to  enclose  the  latter  and  the  anterior  scalenus.  Either  case  represents  a  partial  re- 
tention of  the  early  condition  in  which  the  vein  passes  behind  the  brachial  plexus.  Variations 
in  the  superficial  veins  have  been  referred  to  on  p.  668.  The  question  of  the  most  common 
distribution  of  these  vessels  has  lately  been  fully  reviewed  by  Berry  and  Newton.  The  cephalic 
vein  occasionally  opens  into  the  external  jugular  by  persistence  of  the  embryonic  jugulo-cephahc 
vein. 

B.  THE  VENA  CAVA  INFERIOR  AND  ITS  TRIBUTARIES 

1.  MORPHOGENESIS 

The  right  and  left  post-cardinal  veins  (fig.  544)  are  at  first  symetrical  in  size  and  position. 
Early  in  development  each  posterior  cardinal  vein  becomes  involved  in  the  growth  of  the  cor- 
responding mesonephros,  and  the  original  venous  channel  is  converted  into  a  system  of  sinusoids. 
In  the  sinusoidal  circulation  of  each  mesonephros  two  main  longitudinal  venous  channels  soon 
make  their  appearance.  One  lies  ventro-medial  to  the  mesonephros  and  is  called  the  sub-cardinal 
vein.  The  other,  which  lies  dorsal  to  the  mesonephros,  receives  the  segmental  veins  and  is 
frequently  called  the  post-cardinal.  Since  the  mesonephric  segment  of  the  post-cardinal  vein 
has  obviously  passed  out  of  existence,  the  vein  in  question  (unlabelled  in  fig.  544)  wQl  be  here 
distinguished  as  the  dorsal  trunk.  The  sub-cardinals  communicate  freely  between  themselves 
and  with  the  dorsal  trunks,  lie  ventral  to  the  mesonephric  arteries,  and  are  at  first  symmetrical. 
The  cephalic  end  of  the  right  sub-cardinal  now  acquires  a  communication  with  the  common 
hepatic  vein,  thus  providing  a  new  means  of  drainage  for  the  sub-  and  post-cardinal  systems 
(fig.  544) .  The  rapidly  enlarging  main  venous  channel  resulting  from  this  alternative  niethod  of 
drainage  follows  the  right  dorsal  trunk  as  far  as  the  level  of  the  permanent  renal  veins.  It  is 
then  transferred,  by  means  to  an  anastomosing  channel,  to  the  right  sub-cardinal  and,  through 
this,  to  the  common  hepatic  vein;  it  becomes  the  vena  cava  inferior.  From  now  on  the  portions 
of  the  sub-cardinal  veins  not  participating  in  the  formation  of  the  cava  dwindle  rapidly.  A 
cross  anastomosis  between  the  right  and  left  sub-cardinals  persists  as  the  portion  of  the  adult 
left  renal  vein  which  crosses  ventral  to  the  aorta.  By  means  of  it  the  remainder  of  the  left 
renal;  thfe  left  internal  spermatic  and  left  suprarenal  veins  are  connected  with  the  vena  cava. 
The  left  lumbar  and  left  common  ihac  veins  are  also  transferred  to  the  vena  cava,  probably  by 
direct  anastomosis  with  the  left  post-cardinal  vein.  The  vena  cava  inferior  is  at  first  lateral 
to  the  right  ureter,  its  transference  to  the  medial  side  occurs  through  anastomosis. 

The  portion  of  the  right  posterior  cardinal  vein  above  the  mesonephric  region,  together  with 
its  continuation  into  the  dorsal  trunk,  becomes  the  azygos  vein  (fig.  544).  The  corresponding 
vessel  upon  the  left  side  is  transformed  into  the  accessory  hemiazygos  and  hemiazygos  veins. 
The  hemiazygos  vein  is  drained  into  the  azygos  by  means  of  an  anastomosing  channel  which 
may  also  drain  the  accessory  hemiazygos.  The  variability  of  the  means  of  drainage  of  the 
accessory  hemiazygos  vein,  by  means  of  anastomosing  channels,  is  referred  to  onp.  663.  The 
ascending  lumbar  veins  are  anastomosing  channels  of  new  formation. 

In  the  lower  extremity,  as  in  the  upper,  the  original  superficial  plexus  is  gradually  drained 
by  a  loop-Uke  marginal  vein.  The  fibular  limb  of  this  loop,  the  primitive  fibular  vein,  becomes 
small  saphenous;  it  follows  the  sciatic  nerve  and  opens  into  the  post-cardinal.  The  next  vein  to 
be  developed  is  the  great  saphenous;  the  small  saphenous  is  transferred  to  this  by  an  anastomos- 
ing vein  which  is  usually  present  in  the  adult — the  femoropopliteal  vein.  The  deep  veins  are 
of  later  formation.  The  drainage  of  the  small  saphenous  is  usually  taken  over  by  the  popliteal 
vein. 

2.  VARIATIONS 

In  determining  the  probable  embryonic  cause  of  variations  of  the  vena  cava  inferior  the 
possibility  of  abnormal  persistence  of  the  sub-cardinal  veins  must  be  remembered.  The  posi- 
tion of  transverse  anastomoses  with  regard  to  the  aorta  is  often  the  key  to  diagnosis.     Instruc- 


694 


THE  BLOOD-VASCULAR  SYSTEM 


tive  cases  of  abnormalities  of  the  vena  cava  inferior  have  recently  been  pubhshed  by  v.  Alten 
and  by  Neubei-ger  (see  References).  Both  articles  contain  bibUographies.  The  chief  varia- 
tions are  as  follows: — 

(1)  The  inferior  vena  cava,  in  cases  of  transposition  of  the  viscera,  may  he  on  the  left  side 
of  the  aorta.  (2)  Without  transposition  it  may  also  lie  to  the  left  of  the  aorta,  crossing  to  the 
right  to  gain  the  caval  opening  immediately  below  the  diaphragm,  or  after  receiving  the  left 
renal  vein.  (3)  It  may  be  double,  the  left  cava  than  usually  passing  across  the  aorta  into  the 
right  after  receiving  the  left  renal  vein.  A  communication  between  the  right  and  left  veins  in 
the  position  of  the  normal  left  common  iliac  vein  may  or  may  not  then  exist.  (4)  The  inferior 
vena  cava  may  be  absent,  the  blood  from  the  lower  extremities  passing  by  a  large  vein  in  the 
position  of  the  ascending  lumbar  and  azygos  veins  through  the  diaphragm  to  open  into  the 
superior  vena  cava.  The  hepatic  veins  then  open  directly  into  the  right  atrium  through  the 
normal  caval  opening  in  the  diaphragm.  (5)  The  inferior  vena  cava  may  receive  the  left  sper- 
matic vein.  (6)  It  may  receive  a  left  accessory  renal  vein  passing  behind  the  aorta,  and  into 
this  the  usual  tributaries  of  the  left  renal  vein  may  open.  (7)  It  may  receive  several  accessory 
renal  veins;  as  many  as  seven  on  each  side  have  been  met  with.  (8)  The  lumbar  veius  may 
enter  it  on  one  or  both  sides  as  a  common  trunk. 

The  variations  in  the  veins  of  the  lower  extremity  are  for  the  most  part  unimportant. 
They  have  been  mentioned  in  the  description  of  the  corresponding  veins. 


3.  THE  PORTAL  SYSTEM  OF  VEINS 

The  portal  system  arises  by  transformations  in  the  vitelline  and  umbilical  veins.  The 
proximal  ends  of  the  vitelline  veins,  where  they  lie  between  the  umbilicals,  are  early  enveloped 
in,  and  invaded  by,  the  growing  liver.  The  columns  of  liver  cells,  while  not  penetrating  the 
endothelium,  subject  the  vitelline  veins  to  a  process  of  fenestration  by  which  the  original  channels 
are  subdivided  into  innumerable  smaller  vessels  or  sinusoids.  The  sinusoids  arising  from  the 
two  vitelline  veins  intercommunicate  to  form  one  continuous  network  in  which  the  vessels  are 
larger  in  the  afferent  (portal)  and  efferent  (hepatic)  areas  than  in  the  intermediate  zone. 


Fig.  545. — Sbmidiagrammatic  Reconstructions  of  the  Veins  of  the  Liver,  Ventral 
Aspect  (Mall).  A,  Embryo  of  4.5  mm.  Long;  B,  4  mm.  (more  advanced  than  A);  C,  7  mm. 
d.v.,   ductus  venosus;   I.,  intestine;  L.,  liver;  m.,  superior  mesenteric  (continued  as  portal) 

vein;  r.a.,  ramus  angularis;  r.  a'.,  right  branch  of  portal  vein;  r.h.d.,  right  hepatic  vein; 

r.h.s.,   left  hepatic  vein;  r.u.,  recessus   umbilicahs;  u.v.,  left   umbilical  vein  (the   right 

umbihcal  vein  is  not  labelled);  v.o.m.,  vitelline  veins. 


The  two  umbilical  veins  now  form  communications  with  the  portal  area  of  the  sinusoidal 
network  and  eventually  lose  their  original  connections  with  the  sinus  venosus  (fig.  545).  The 
fate  of  the  umbilical  veins  differs  on  the  two  sides;  the  right  degenerates,  from  the  sinus  venosus 
to  the  common  umbilical  vein,  and  leaves  the  left  to  receive  all  the  blood  flowing  from  the  pla- 
centa. The  left,  having  lost  its  connection  with  the  sinus  venosus,  discharges  its  blood  partly 
into  the  portal  sinusoidal  zone,  and  partly,  by  means  of  the  newly  formed  direct  channel,  the 
ductus  venosus,  into  the  right  vitelline  (fig.  545). 

The  hepatic  end  of  the  right  vitelline  vein  enlarges  considerably,  for  the  left  vitelline  loses 
its  original  connection  with  the  sinus  venosus.  It  transmits  blood  both  from  the  sinusoids 
and  from  the  ductus  venosus  to  the  sinus  venosus,  and  is  called  the  common  hepatic. 

The  vitelline  veins  are  not  only  connected  within  the  liver,  but  their  distal  ends  become 
united  upon  the  yolk-stalk  to  form  a  single  trunk.  A  third  communication  between  them  is 
effected  by  a  transverse  vessel  passing  dorsal  to  the  duodenum.  The  portion  of  the  right 
vitelline  below  the  transverse  vessel  disappears,  as  does  the  portion  of  the  left  between  it  and 
the  liver.  A  tortuous  vitelline  vein  is  thus  produced  which  enters  the  liver  by  passing  dorsal 
to  the  intestine  from  left  to  right.  This  vessel  is  joined,  to  the  left  of  the  intestine,  by  the 
superior  mesenteric  vein  and,  dorsal  to  it,  by  the  splenic.  When  the  portion  of  the  vitelline 
below  the  termination  of  the  superior  mesenteric  finally  disappears  the  vessel  extending  from 
the  splenic  vein  to  the  liver  becomes  the  portal  vein  of  the  adult. 

Important  variations  of  the  portal  system  are  rarely  found  in  the  adult.  The  mechanism 
of  anomalies  found  in  the  embryo  have  been  investigated  by  Begg  (Anier.  Jour.  Anat.,  Vol.  13). 


THE  FCETAL  CIRCULATION 


695 


FGETAL  CIRCULATION 

The  changes  which  accompany  the  transformation  of  the  foetal  type  of 
circulation  into  that  of  the  adult  are  initiated  by  the  first  inspiration.  Prior. to 
this  act  the  functions  of  external  respiration  and  digestion  are  performed  by  the 

Fig.  546.^The   Heart,   with  the   Arch   op  the  Aorta,  the  Pulmonary  Artery,  the 
Ductus  Arteriosus,  and  the  Vessels  concerned  in  the  Fcetal  Circulation. 
(From  a  preparation  of  a  fcetua  in  the  Museum  of  St.  Bartholomew's  Hospital.) 


Right  innominate  vein 

Superior  vena  cava 

Right  pulmonary  artery 


Inferior  vena 


Left  branch  of  portal  vein 
Ductus  venosus 


Arch  of  aorta 
Ductus  arteriosus 
Left  pulmonary 
artery 


Descending  aorta 


Umbilical  vein 
Portal  vein 


Right  branch  of, 
portal  vein 


Umbilical 

Umbilical  arteries 

Umbilical  -artery 


mesenteric  vein 


Inferior 
senteric  artery 


eft  common  iliac 

artery 


Hypogastric  artery 
External  iliac  artery 


mother;  the  foetal  venous  blood  passing  to  the  placenta  through  the  umbilical 
arteries  and  returning  through  the  umbilical  vein. 

At  the  time  of  birth  the  right  and  left  chambers  of  the  heart  communicate 
only  by  means  of  an  oblique  passage  between  the  overlapping  atrial  septa  (p.  511) . 
The  pulmonary  artery  and  descending  aorta  communicate  by  means  of  the 
ductus  arteriosus  (p.  508). 


696  THE  BLOOD-VASCULAR  SYSTEM 

Arterial  blood,  transmitted  from  the  placenta  through  the  umbilical  vein, 
passes  almost  entirely  by  way  of  the  ductus  venosus  to  the  vena  cava  inferior. 
From  here  it  passes  through  the  right  atrium;  then,  obliquely  between  the  atrial 
septa  into  the  left  atrium,  from  which  it  passes  through  the  left  ventricle  and 
into  the  ascending  aorta.  Escaping  largely  through  the  branches  of  the  aortic 
arch,  it  is  distributed  to  the  head  and  upper  extremities,  and  returned  to  the  vena 
cava  superior.  Having  reached  the  right  atrium  it  passes,  to  the  right  of  the 
stream  from  the  vena  cava  inferior  fp.  513),  through  the  atrio-ventricular  ostium 
into  the  right  ventricle.  The  blood  issuing  from  the  right  ventricle  into  the 
pulmonary  artery  goes  almost  entirely  (the  lungs  being  functionless)  into  the 
ductus  arteriosus  and  so  into  the  descending  aorta.  Having  performed  two 
circuits,  the  blood  returns  to  the  placenta  through  the  umbilical  branches  of  the. 
hypogastric  arteries. 

The  two  streams,  arterial  and  semi-venous,  cross  one  another  in  the  right 
atrium.  The  degree  of  intermixture,  if  any,  which  occurs  in  this  cavity  has  been 
the  subject  of  much  discussion;  for  literature  and  experimental  evidence  on  this 
point  see  Pohlmann,  A.     (Johns  Hopkins  Hosp.  Bui.,  Vol.  18,  1907.) 

When  the  lungs  assume  their  function  at  birth  the  pressure  in  the  left  atrium 
is  suddenly  raised  by  an  inrush  of  blood.  The  overlapping  atrial  septa  (primum 
and  secundum)  are  brought  into  lateral  apposition  and  thus  the  blood  entering 
the  right  atrium  finds  but  one  exit — the  atrio-ventricular  ostium.  Since  the 
vessels  of  the  expanded  lungs  now  transmit  a  greatly  increased  volume  of  blood, 
the  stream  passing  through  the  ductus  venosus  is  diminished  proportionately. 
The  blood  traversing  the  aortic  arch,  released  from  the  check  exerted  by  the  lateral 
stream  pouring  from  the  ductus  arteriosus,  passes  more  readily  into  the  descending 
aorta;  thus  the  adult  equilibrium  is  established. 

References  for  blood-vascular  system. — A.  Heart:  (Development)  Born, 
Archiv  f.  mikr.  Anat.,  Bd.  33,  1889;  His,  Anatomie  menschl.  Embryonen, 
1880-85,  Anatomie  des  menschl.  Herzens,  1886;  Tandler,  in  Keibel  and  Mall's 
Human  Embryology.  (Morphology)  MacCallum,  Johns  Hopkins  Hospital 
Reports,  vol.  9,  1900;  Mall,  Amer.  Jour.  Anat.,  vol.  11,  1911,  vol.  13,  1912; 
(Atrio-ventricular  bundle)  Keith  and  Flack,  Jour.  Anat.  and  Physiol.,  vol.  41,  1907. 
B.  Arteries.  (Development)  Evans,  in  Keibel  and  Mall's  Human  Embryology; 
(Pulmonary)  Bremer,  Anat.  Rec,  vol.  3,  1908;  (Internal  mammary)  Mall,  Johns 
Hopkins  Hospital  Bui.,  1898;  (Cephalic)  Tandler,  Morph.  Jahrb.,  Bd.  30,  1902; 
(C celiac)  Tandler,  Anat.  Hefte,  Bd.  25,  1904;  (Extremities)  Miiller,  Anat.  Hefte, 
Bd.  22,  1903;  de  Vriese,  Arch,  de  Biol.,  T.  18,  1902;  (Variations)  Goppert, 
Morph.  Jahrb.,  Bd.  40,  1909;  C.  Veins.  (Development)  Davis,  Amer.  Jour. 
Anat.,  vol.  10,  1910;  (Brain)  Mall,  Amer.  Jour.  Anat.,  vol.  4,  1904;  (Liver)  Mall, 
Amer.  Jour.  Anat.,  vol.  5,  1905;  (Cervical)  Lewis,  F.  T.,  Amer.  Jour.  Anat.,  vol. 
9,  1909;  (Upper  extremity)  Berry  and  Newton,  Anat.  Anz.,  Bd.  33,  1908;  (Vena 
cava  inferior)  Neuberger,  Anat.  Anz.,  Bd.  43,  1913;  v.  Alten  (ibid):  (Sinusoids) 
Minot,  Proc.  Boston  Soc.  Nat.  Hist.,  vol.  29,  1900. 


S  E  C  T 1  O  N  V  [ 

THE  LYMPHATIC  SYSTEM 

Revised  for  the  Fifth  Edition 
By  ELIOT  R.  CLARK,  A.B.,  M.D. 

ASSOCIATE    IN   ANATOMY,    JOHNS   HOPKINS   MEDICAL    SCHOOL 


I.     GENERAL  ANATOMY  OF  THE  LYMPHATIC  SYSTEM 

THE  blood-vascular  system  has,  as  a  part  of  its  function,  the  collection  of 
substances  from  the  various  tissues  of  the  body  which  are  to  be  conducted 
to  the  other  tissues.     In  carrying  on  this  function  it  is  assisted  by  a  second 
system  of  collecting  vessels,  the  lymphatics. 

This  second  system  resembles  the  blood-vascular  system  in  many  ways,  but  differs  markedly 
in  others.  Like  the  tslood-vascular  system,  it  is  made  up  of  minute  endothehal-Uned  capillaries, 
where  the  absorption  of  substances  occurs,  and  of  larger  conducting  vessels.  It  differs  from  the 
blood-vascular  system'  in  two  important  particulars.  While  the  blood-vascular  system  is  pro- 
vided with  a  pumping'mechanism  by  which  its  fluid  content  is  driven  through  a  complete  circuit 
from  the  heart,  through  artery,  capillary,  vein  and  back  to  the  heart,  the  lymphatics  merely 
conduct  fluid  from,  the  capillaries  to  the  larger  vessels,  which  eventually  empty  their  contents 
into  the  large  veins  of  the  neck.  The  second  important  difference  between  the  two  systems  is 
found  in  the  presence,  along  the  course  of  the  lymphatic  vessels,  of  glands  or  nodes  (fig.  553) 
[lymphoglandulee]  in  which  the  vessels  branch  out  into  lymph  capillaries.  These  are  lined,  as  are 
the  absorbing  capillaries,  with  a  single  layer  of  endothehal  cells,  thus  permitting  an  interchange 
of  substances  between  the  contents  of  the  lymph  capillaries  and  the  lymphoid  tissue  around 
them. 

Our  present  knowledge  does  not  permit  an  exact  statement  of  the  complete  extent  of  the 
lymphatic  system.  While,  in  a  general  way,  the  lymphatics  may  be  said  to  be  present  where- 
ever  blood-capillaries  occur,  there  are  certain  tissues  where  lymphatics  have  not  been  definitely 
demonstrated. 

The  general  constitution  of  the  lymphatic  system  will  be  considered  under 
three  heads — (1)  the  capillaries,  (2)  the  collecting  vessels  and  (3)  the  lymphoid 
organs. 

I.  THE  LYMPHATIC  CAPILLARIES 

The  lymphatic  capillary,  like  the  blood-capillary,  is  the  portion  of  the  lymph- 
atic system  which  is  chiefly  concerned  in  the  specific  function  of  this  system.  In 
the  blood-capillaries,  where  the  blood  is  separated  from  the  outside  tissues  by  a 
single  layer  of  flat  endothehal  cells,  there  occurs  the  interchange  of  fluid  substances 
and  of  cells,  while  the  heart,  arteries  and  veins  serve  to  transport  the  blood,  modi- 
fied in  the  capillaries,  to  other  parts  of  the  body.  Similarly  in  the  lymphatic 
system,  it  is  in  the  capillaries,  both  those  most  peripheral  and  those  in  the  lymph 
nodes,  where  the  absorption  and  interchange  of  fluid  substances  and  of  cells  takes 
place.  Consequently  it  becomes  of  prime  importance  to  obtain  a  clear  under- 
standing of  the  structure  of  the  lymphatic  capillaries,  their  relation  to  the  other 
tissues,  and  their  mode  of  functioning.  At  the  outset,  however,  it  must  be 
admitted  that  our  knowledge  on  this  subject  is  far  from  complete. 

Historical. — Previous  to  the  development  of  microscopic  anatomy,  in  the  middle  third  of  the 
19th  century,  there  was  no  accm-ate  knowledge  of  such  small  structures  as  the  lymphatic  capil- 
lary. In  order  to  explain  the  absorption  of  substances  by  the  lymphatics,  as  well  as  the  passage 
of  substances  from  the  blood-vessels  through  the  tissues,  various  theories  were  invented.  Promi- 
nent among  such  theories  was  that  of  the  "vasa  serosa,"  of  H.  Boerhaave  and  other  18th  century 
anatomists  and  physiologists,  which  was  perhaps  most  elaborately  developed  by  Bichat,  1801-03. 
According  to  this  theory  there  are  two  sets  of  minute  vessels,  too  small  for  the  passage  of  cellu- 
lar elements.  The  one  set  leads  from  the  blood-capillaries  onto  the  various  surfaces  of  the  body 
and  into  the  loose  spaces  in  the  tissues — the  "exhalants. "  The  other  set  leads  from  the  body 
surfaces  (including  the  serous  cavities)  and  the  loose  spaces  in  the  tissues  to  the  lymphatics — 
the  "inhalants"  or  " absorbants, "  which  take  in  fluids  by  a  sucking  action. 

697 


698  THE  LYMPHATIC  SYSTEM 

This  theory  was  somewhat  shaken  by  the  discovery  of  Magendie,  in  the  first  decade  of  the 
19th  century,  that  absorption  may  take  place  by  the  veins,  as  well  as  the  lymphatics,  and  by  the 
criticism  of  early  19th  centmy  anatomists  who  developed  the  teohnio  of  injection  of  lymphatics 
to  a  high  point. 

Our  present  conception  of  the  lymphatic  capilJaries  may  be  said  to  have  started  with 
KoUiker  who,  in  1846,  saw,  with  the  aid  of  the  microscope,  the  lymphatic  capillaries  in  the  trans- 
parent tails  of  living  frog  larvae.  He  found  them  to  be  definite  structures  made  up  of  a  thin 
wall,  from  which  projected  fine-pointed  processes,  and  in  which  were  nuclei.  Like  Schwann 
who,  in  1837,  had  studied  the  blood-capillaries  in  the  tail  of  the  frog  larva,  he  erroneously  sup- 
posed that  the  fine  processes  of  the  lymphatic  capillaries  were  continuous  with  similar  proc- 
esses of  the  surrounding  connective-tissue  cells.  Since,  according  to  the  conception  current  at 
the  time,  cells  were  thought  to  be  hollow  structures,  with  a  membranous  wall  and  fluid  content, 
it  was  concluded  that  the  mode  of  transmission  of  fluid  from  blood  to  lymphatic  capillary  took 
place  through  canaliculi  inside  these  cells.  This  conception  was  elaborated  by  Virchow,  in  his 
CeUular-Pathologie. 

In  1862  von  Recklinghausen  by  means  of  the  silver  nitrate  staining  method  discovered  that 
the  lymphatic  vessels  are  lined  with  an  endothelium  made  up  of  flattened  cells  whose  outlines 
show  as  fine  dark  Knes  after  this  treatment.  Again,  however,  as  a  result  of  the  eagerness  to  find 
open  passages  through  the  tissues  from  blood  to  lymphatic  capillary,  an  erroneous  interpretation 
was  made,  von  Recklinghausen  held  that  the  unstained  parts  outside  the  lymph  vessels  rep- 
resent a  system  ofj  irregularly  shaped  lymph-canaliculi  ("Saftkanalchen")  which  are  in  open 
communication  on  the  one  hand  with  the  blood-capiUaries,  and  on  the  other  with  the  lymphatics 
This  conclusion  has  since  been  disproved  by  numerous  investigators. 

In  a  second  series  of  observations,  von  Recklinghausen  brought  evidence  in  favor  of  open 
communications  between  the  lymphatics  and  the  peritoneal  cavity.  He  watched,  under  the 
microscope,  the  passage  into  lymphatics,  through  minute  openings,  of  milk,  placed  on  a  portion  of 
the  central  tendon  of  the  diaphragm.  These  minute  openings  he  termed  "stomata. "  Cohn- 
heim  described  similar  though  smaller  openings  in  blood-capillaries,  and  His  described  them  in 
other  lymphatic  capillaries.  Arnold  termed  the  openings  in  the  vessels  "stigmata,"  as  dis- 
tinguished from  the  openings  into  the  peritoneal  cavity,  or  "stomata." 

With  the  advent  into  microscopical  technic  of  the  various  dyes  for  staining  cell-nuclei  and 
protoplasm,  and  the  more  precise  methods  for  making  histological  studies,  the  endothelial  wall 
of  the  lymphatic  capillary  has  been  definitely  established,  although  much  remains  to  be  learned 
concerning  the  differences  between  the  lymphatics  of  the  various  tissues. 

Moreover,  recent  investigators  have  failed  to  find  open  connections  between  the  lumen  of 
the  lymphatic  vessel  and  the  tissue  outside.  Kolossow  failed  to  find  the  "stomata"  of  von 
Recklinghausen  and  the  "stigmata"  of  Cohnheim,  His  and  Arnold.  The  "stomata"  have  been 
carefully  studied  by  a  number  of  other  recent  investigators.  All  agree  in  finding  a  complete 
endothelial  lining  for  the  lymphatic  capillaries  lying  underneath  the  peritoneum  and  pleura, 
with  no  openings  or  "stomata."  Careful  studies  of  the  lymphatic  capillaries  in  the  transparent 
tails  of  living  frog  larvae,  which  may  be  clearly  seen  with  the  higher  magnifications  of  the  micro- 
scope, show  that  the  endothelial  lining  of  these  capillaries  is  complete,  with  no  trace  of  an  open- 
ing into  the  spaces  in  the  tissue  outside  (E.  R.  Clark). 

Form. — The  shape  of  the  lymphatic  capillaries  has  been  found  to  vary  enormously  in  the 
different  parts  of  the  body,  where  they  have  been  studied.  In  general  they  form  richly  anas- 
tomosing plexuses,  from  which  may  extend  cul-de-sacs,  which  end  bUndly.  Such  cul-de-sacs 
are  especially  noticeable  in  the  dermal  papillae,  in  the  filiform  papillse  of  the  tongue,  and  in  the 
intestmal  villi.  The  plexuses  are  often  present  in  two  layers — a  superficial  and  a  deep.  The 
vessels  of  the  superficial  plexus  are  of  smaller  calibre  than  those  of  the  deep.  These  two  sets 
of  plexuses  are  particularly  well  seen  in  the  skin  and  the  gastro-intestinal  tract.  In  relation 
to  the  blood-capiUaries,  the  lymphatic  capillaries  are  generally  the  more  deeply  placed. 

In  cahbre,  unlike  the  comparatively  uniform  diameter  of  blood-capillaries,  the  lymphatics 
vary  enormously.  In  the  same  capillary  a  very  narrow  part  may  be  succeeded  by  a  very  wide 
one  (figs.  547,  548).  Teichmann  found  lymphatic  capillaries  varying  in  diameter  from  a  few 
thousandths  of  a  millimetre  to  one  millimetre.  In  the  capsule  of  the  spleen  of  the  cow  some  meas- 
ured more  than  1.5  mm.!     The  capillaries  are  without  valves. 

Activity. — That  the  lymphatic  endothelium  is  not  exclusively  a  passive  membrane  has  been 
shown  by  Clark  in  studies  on  the  lymphatics  in  the  transparent  tails  of  living  frog  larvae.  The 
lymphatics  here  are  seen  to  send  out  protoplasmic  processes  which,  somewhat  like  an  amoeba, 
actively  take  into  the  interior  of  the  lymphatic  red  blood-cells  accidentally  forced  from  the 
blood-capiUaries  into  the  tissue-spaces. 

The  mode  of  passage  of  leucocytes  into  or  out  of  the  lymphatics  offers  no  such  difiiculties 
as  that  of  the  fluids,  for  they  are  able,  through  their  power  of  amoeboid  movement,  to  pass 
independently  through  the  endothelium — a  process  first  directly  observed  by  Cohnheim. 

1.  The  Extent  and  Chabacter  of  Lymphatic  Capillaries 

The  skin  over  the  entire  surface  of  the  body  is  richly  provided  with  lymphatic  capiUariea. 
They  form  two  sets  of  plexuses  in  the  dermis,  a  superficial  and  a  deep.  The  superficial  set  sends 
out  bhnd  cul-de-sacs  into  the  dermal  papillae.  The  richest  skin  plexuses  are  found  in  the 
scrotum,  the  palms  of  the  hand  and  palmar  side  of  the  fingers  and  in  the  soles  of  the  feet  and 
plantar  side  of  the  toes.  In  the  loose  subcutaneous  fascia,  according  to  Teichmann,  there  are 
present  only  the  larger  collecting  vessels,  with  no  lymphatic  capillaries.  Lymphatic  capillaries 
of  the  scrotum  are  shown  in  Fig.  547. 

The  conjuntiva,  both  the  sclerotic  and  corneal,  is  supplied  with  a  rich  plexus  of  capillaries, 
which  are  narrower  in  the  corneal  than  in  the  sclerotic  portion.     At  the  corneal  border  the 


LYMPHATIC  CAPILLARIES  699 

capillaries  form  a  fairly  regular  ring  which  has  been  called  by  Teichmann  a  ciroulus  lymphaticus. 

At  the  various  orifices  of  the  body,  the  skin  plexuses  go  over  into  the  mucous  plexuses, 
forming  anastomoses  with  them.  Tiiroughout  the  entire  alimentary  tract,  including  the  nasal 
cavities,  the  lymphatic  capillaries  form  extensive  plexuses  which  are  in  many  places  divided 
into  a  superficial  plexus  in  the  mucosa  and  a  deeper  plexus  in  the  submucosa.  In  portions  pro- 
vided with  a  peritoneal  covering,  there  is  a  third  rich  subserous  plexus.  In  the  tongue  and  the 
small  intestine  the  plexus  in  the  mucosa  sends  out  blind  cul-de-sacs;  in  the  tongue  into  the 
filiform  papilla?;  in  the  small  intestine  into  the  villi.  Where  muscle  is  present  along  the  ali- 
mentary tract,  the  lymphatics  pass  between  the  muscle  bundles,  but  form  no  plexuses  around 
them. 

The  lining  of  the  tracheal  and  bronchial  passages  is  supplied  with  a  double  plexus  of  lym- 
phatic capillaries,  a  mucous  and  a  submucous  set,  which  vary  in  richness  according  to  the  loose- 
ness of  the  tissue.  In  the  smaller  bronchi  but  a  single  layer  of  capillaries  is  present,  and,  ac- 
cording to  Miller,  no  capillaries  are  present  around  the  air  cells.     Plexuses  surround  the  pul- 

FiG.  547. — The  Lymphatics  of  the  Scrotum.     (After  Teichmann.)     Showing  the  transition 
of  the  capillaries  to  the  vessels  with  valves  (o,  a,  a). 


monary  arteries  and  veins.  Under  the  pleura  lie  rich  plexuses  which  connect  with  the  deeper 
lymphatics  around  the  veins  only  in  places  where  the  veins  reach  the  surface  of  the  lung. 

Concerning  the  arrangement  of  the  lymphatic  capillaries  in  the  glands  derived  from  the 
alimentary  tract  much  remains  to  be  learned. 

The  salivary  glands  have  been  recently  studied  anew  by  Aagaard,  who  has  found  lymphatic 
capillaries  accompanying  the  blood-vessels  into  the  interior  of  the  lobules,  and  forming  here 
irregular  plexuses. 

The  thyreoid  gland  contains  lymphatic  plexuses  which  lie  in  relation  to  the  colloid-con- 
taining alveoli.  Direct  connection  between  the  lymphatics  and  the  alveoli  has  lately  been 
described  by  Matzunaga,  but  this  observation  needs  verification.  The  lymphatics  are  apparently 
concerned  in  the  absorption  of  the  colloidal  secretion,  for  traces  of  it  have  been  found  in  the 
lymphatics  draining  the  gland. 

Concerning  the  lymphatics  of  the  parathyreoids  nothing  is  known. 

The  course  of  the  lymphatics  draining  the  thymus  has  been  recently  described,  but  the 
nature  of  the  capillaries  in  this  gland  is  unknown. 

The  lymphatic  capillaries  of  the  liver  are  of  great  importance,  for  the  lymph  which  flows 
from  this  organ  forms  a  very  considerable  part  of  the  total  lymph  which  is  collected  into  the 
thoracic  duct.  And  yet  very  little  is  definitely  knowm  about  the  natm'e  and  distribution  of  the 
lymphatic  capillaries  in  the  interior  of  the  organ.  In  the  capsule  there  is  a  rich  plexus,  lying 
under  the  peritoneum,  in  which  very  large  widenings  have  been  described  (called  bj^  Teichmann 
"Lymphbehalter").  In  the  interior  rich  plexuses  surround  the  branches  of  the  hepatic  artery 
and  portal  vein  (fig.  549),  and  plexuses  have  been  described  accompanying  the  branches  of  the 
portal  vein  into  the  lobules. 

The  linings  of  the  large  bile-ducts  and  the  gall-bladder  are  provided  with  a  submucous  network 
of  lymphatics  (Sudler  and  Clermont).     The  gall-bladder  has  also  a  rich  subserous  plexus. 

Concerning  the  lymphatic  capillaries  of  the  pancreas  Bartels  notes  briefly  that  they  form 
richly  branched  plexuses  in  the  interlobular  connective  tissues,  which  surround  larger  or  smaller 
parts  of  whole  lobules,  not  the  single  gland  elements. 

The   mucous  lining  of  the  genito-urinary  tract,  wherever-  it  has  been  carefully  studied 


700 


THE  LYMPHATIC  SYSTEM 


has  been  found  provided  with  plexuses  of  lymphatics.  In  the  bladder  they  form  a  rich  plexus  of 
irregular  capillaries  which  lie  immediately  under  the  almost  intraepithelial  blood-capiUaries. 
They  connect,  through  the  muscular  layer,  with  a  subserous  plexus.  The  lymphatic  plexus  of  the 
urethra  anastomoses  \vith  the  capillaries  of  the  base  of  the  bladder,  and  in  the  male  with  those  of 
the  glans  penis.  The  lymphatic  capillaries  of  the  ductus  deferens  and  of  the  seminal  vesicles  have 
not  been  studied.  In  the  prostate  (Camineti)  the  lymphatics  form  rich  plexuses  surrounding  the 
glands,  which  connect  with  a  very  wide  meshed  subcapsular  plexus,  surrounding  the  entire 
gland. 

In  the  testis  there  is  a  rich  superficial  plexus,  lying  directly  beneath  the  tunica  albuginea. 
Concerning  the  deep  lymphatics  of  the  testis  there  has  been  much  dispute.     Ludwig  and  Thomsa 

Fig.  548. — Surface  View  and  Section  of  Lymph-nodes  op  the  Intestine.     A.  Solitary 
folhcle.     B.  Pej'er's  patch.     (After  Teiohmann.) 


found  the  lymphatic  capillaries  going  over  into  lacunse,  without  endothelium.  This  has  been 
disputed  by  Tommasi  and  Gerster,  who  find,  in  the  septa,  capillaries  with  endothelial  wall, 
which  they  consider  the  beginnings  of  the  lymphatics. 

In  the  female,  lymphatic  plexuses  have  been  found  in  the  mucosa  of  vagina  and  hymen, 
anastomosing  with  those  of  the  vulva.  In  the  uterus,  capillaries  in  the  mucosa  are  very  difficult 
to  demonstrate.  Definite  lymphatics,  however,  have  been  found  passing  through  the  mus- 
cularis,  and  under  the  peritoneum  a  rich  subserous  plexus  of  capillaries  is  present.  In  the  preg- 
nant uterus  these  subserous  capillaries  are  much  distended  (Schick).  The  Fallopian  tubes  are 
provided  v?itb  lymphatics,  but  they  have  not  been  carefully  described. 


LYMPHATIC  CAPILLARIES 


701 


The  ovary  has  a  rich  superficial  lymphatic  plexus.  In  the  iaterior  of  the  gland,  according 
to  His,  the  capUlaries  form  networks  in  the  connective- tissue  framework.  In  the  tunica  externa 
of  the  follicles  there  is  a  rich  plexus. 

The  kidney  has  two  sets  of  lymphatics,  a  superficial,  capsular  set,  and  a  deep  set.  The  cap- 
sular set  is  divided  into  two  layers,  one  lying  directly  beneath  the  peritoneum  made  up  of  a  wide 
meshed  plexus,  and  the  other  in  the  fibrous  capsule  of  the  kidney,  with  finer  capillaries  and 
narrower  meshes,  which  anastomose  with  the  deeper  capillaries.  The  lymphatic  capillaries  of 
the  kidney  parenchyma  have  recently  been  described  by  Kumita.  He  found  rich  plexuses  in 
both  cortex  and  medulla,  surrounding  the  straight  and  convoluted  tubules,  the  loops  of  Henle 
and  the  collecting  tubules.  He  also  found  a  plexus  surrounding  and  accompanying  the  blood- 
vessels into  the  interior  of  the  glomeruli. 

The  lymphatic  capillaries  of  the  adrenal  have  also  been  described  recently  by  Kumita. 
His  results  agree  with  those  of  Stilling,  who  studied  the  lymphatics  of  the  adrenal  of  horse,  cow 
and  calf.     Like  the  kidney,  the  adrenal  possesses  a  superficial  and  a  deep  set.     The  superficial  set 

Fig.  549. — ^Lymphatic  Plexus  ahound  the  PortaljVein  in"' an  Adult  Man.     (After  Teich- 
mann.)     Showing  the  supporting  relation  of  the  vein. 


is  in  two  layers,  as  in  the  kidney,  the  outer  lying  in  the  looser  tissue  around  the  adrenal  and  the 
inner  lying  within  and  just  under  the  capsule.  The  latter  is  made  up  of  a  rich  lymphatic  plexus, 
which  anastomoses  with  the  capillaries  of  the  parenchyma.  The  parenchymatous  lymphatics 
are  present  in  the  form  of  plexuses  which  surround  the  groups  of  cells. 

In  spite  of  numerous  investigations,  endothelial-lined  lymphatics  have  not  been  definitely 
found  in  the  central  nervous  system,  or  in  the  peripheral  nerves.  The  subarachnoid  and  similar 
spaces,  including  the  perineural  spaces,  do  not  form  parts  of  the  lymphatic  system. 

Rich  plexuses  of  lymphatic  capillaries  are  present  in  the  tendons  of  muscles  (Schweigger- 
Seidel  and  Ludwig).  In  muscles,  themselves,  the  question  of  the  presence  of  lymphatics  has 
long  been  disputed,  sometimes  answered  in  the  affirmative,  more  often  in  the  negative.  A  re- 
cent study  by  Aagaard,  however,  would  seem  to  place  beyond  doubt  the  presence  of  lymphatic 
capillaries  in  striated  muscles.  By  long  continued  injection,  he  was  able  to  find  Ij'mphatics  in  the 
intramuscular  portions  of  the  tendons,  which  extended  out  among  the  muscle  fibres  themselves. 
He  also  found  capillaries  in  the  tongue  musculature. 

The  heart  is  provided  with  a  subpericardial  plexus  of  lymphatic  capillaries.  A  subendocardial 
plexus  has  also  been  described  (Sappey,  Rainer).  Bock  has  recently  found  that  there  is  an  ex- 
tremely rich  lymphatic  network  throughout  the  substance  of  the  heart.  According  to  his  de- 
scription, the  lymphatic  capillaries  are  more  numerous  than  the  blood-capillaries. 
*~,  kThe  periosteum  of  bones  is  provided  with  a  rich  plexus  of  lymphatic  capillaries.  They  are 
present  in 'several  layers,  of  which  the  outermost  form  the  richest  plexus.     Lymphatic  capillaries 


702  THE  LYMPHATIC  SYSTEM 

have  also  been  described  accompanying  the  blood-vessels  in  the  Haversian  canals  in  bones 
(Rauber,  Schwalbe,  Budge).  Nothing  is  known  concerning  the  lymphatics  of  the  bone  marrow. 
Cartilage  lacks  both  blood  and  lymphatic  capillaries. 

The  capsular  membranes  of  joints  are  richly  provided  with  lymphatic  capillaries  (Tillmanns) . 
They  are  arranged  in  two  layers — an  inner  layer  made  up  of  a  rich  plexus  of  wide  capillaries, 
lying  just  outside  the  subendothelial  blood-capillaries,  and  an  outer  layer,  consisting  of  a  rich 
plexus  in  the  subsynovial  tissue.  The  lymphatic  capillaries  have  no  open  connection  with  the 
joint  cavity. 

The  membranes  suiTounding  the  pleural,  pericardial  and  peritoneal  cavities  are  richly  sup- 
plied with  lymphatic  capillaries,  which  form  here  thick  plexuses  outside  the  endotheUum.  These 
plexuses  are  usually  described  with  the  underlying  organ,  as  the  subserous  lymphatic  capillaries 
of  the  intestine,  etc.  In  the  central  tendon  of  the  diaphragm  the  subperitoneal  lymphatics  are 
extremely  rich.  They  widen  out  here  to  form  very  large  endotheUal-lined  cavities  which,  in  the 
spaces  between  the  connective-tissue  bundles,  lie  directly  in  contact  with  the  peritoneal 
epithelium.  The  existence  of  open  connections  between  these  capillaries  and  the  peritoneal  and 
pleural  surfaces  (the  "stomata"  of  von  Recklinghausen)  has  recently  been  disproven.  The 
capillaries  on  the  two  surfaces  of  the  central  tendon  communicate  freely  with  one  another. 

2.  THE  LYMPHATIC  VESSELS 

The  lymph  which  enters  the  lymphatic  capillaries  passes  over  into  collecting 
vessels  (ducts),  which  carry  it  through  the  lymph-glands  (nodes)  to  the  large  veins 
at  the  base  of  the  neck.  The  lymph-vessels  course  in  the  loose  subcutaneous 
tissues,  in  the  connective  tissues  between  muscles  and  organs,  often  accompanying 
the  arteries  and  veins,  sometimes  forming  networks  around  them.  An  idea  of 
their  arrangement  can  be  best  obtained  by  glancing  at  the  illustrations  of  the 
lymphatics  of  special  regions.  In  general  they  are  made  up  of  numerous  long, 
narrow  vessels,  rarely  more  than  half  or  three-fourths  of  a  millimetre  in  diameter, 
which  occasionally  communicate  with  one  another,  and  which  radiate  toward 
groups  of  lymph-glands  placed  in  certain  definite  regions.  In  the  lymph-glands 
the  afferent  lymph-vessels  break  up  into  capillaries,  which  again  collect  into 
efferent  vessels.  Several  of  these  efferents  from  each  lymph-gland  may  pass  to  a 
second  lymph-gland,  where  they  undergo  a  second  widening  into  capillaries.  In 
this  way  the  lymph,  passing  through  one,  two,  three  or  more  lymph-nodes  in 
succession,  eventually  reaches  the  thoracic  duct,  or  one  of  the  short  ducts,  all  of 
which  empty  into  the  large  veins  at  the  base  of  the  neck.  The  thoracic  duct, 
which  receives,  at  its  lower  end,  the  lymph  from  the  lower  half  of  the  body,  is  the 
only  lymphatic  vessel  which  attains  any  considerable  size  (four  to  six  millimetres 
in  diameter)  and  is  usually  the  only  one  large  enough  to  be  seen  readily  without 
injection. 

In  structure  the  lymphatic  vessels  much  resemble  the  veins.  They  possess  an  intima,  a 
media  and  an  adventitia,  although  the  line  of  demarcation  between  the  different  layers  is  not 
sharp.  In  the  thoracic  duct,  the  endothelium  of  the  intima  is  succeeded  by  a  delicate  layer  of 
fibres,  mainly  elastic;  outside  of  this  is  the  media,  made  up  mainly  of  circular  smooth  muscle- 
cells,  interspersed  with  elastic  and  connective-tissue  fibres;  then  follows  a  layer  of  coarse  elastic 
and  connective-tissue  fibres,  which  is  succeeded  by  the  adventitia,  containing  longitudinal  and 
transverse  bundles  of  smooth  muscle-ceUs,  as  well  as  blood-vessels  and  nerves.  The  other  lym- 
phatic vessels  possess  the  three  layers,  which,  however,  toward  the  capillaries,  grow  thinner,  and 
eventually  reach  a  stage  in  which,  outside  the  endothehum,  there  are  found  only  single  musole- 
ceUs,  or  muscle-ceUs  in  groups  of  two  or  three. 

The  lymphatic  vessels  are  characterised  by  their  great  richness  in  valves,  which  are  present 
throughout  their  entire  course,  from  their  beginnings  in  the  capillary  region  to  their  openings 
into  the  veins  of  the  neck.  The  valves  are  bi-  or  tri-cuspid,  and  are  always  arranged  so  as  to 
prevent  the  flow  of  lymph  back  to  the  capillaries.  They  thus  aid  indirectly  in  the  movement  of 
the  lymph,  in  that  any  external  pressure  on  the  vessels  must  always  force  the  lymph  onward. 

Nerves  of  lymphatic  vessels. — That  the  thoracic  duct  and  the  smaller  lymphatic  vessels  are 
provided  with  nerves  has  been  shown  by  several  observers.  According  to  Kytmanoff  (in  dogs) 
the  nerves  to  the  lymphatics  are  mainly  non-medullated,  and  are  both  motor  and  sensory 
They  form  four  sets  of  plexuses — adventitial,  supramuscular,  intermuscular  and  subendotheUal. 
Sensory  nerve-endings  (fig.  550)  are  found  in  adventitia  and  media,  in  the  form  of  free-ending 
threads,  and  bush-like  endings.  Motor  endings  are  present  in  connection  with  the  smooth 
muscle  cells  of  the  media.  In  the  intima  there  is  a  plexus  of  extremely  fine  varicose  threads. 
The  physiological  action  of  the  nerves  supplying  the  receptaculum  chyli  has  been  tested  by 
Camus  and  Gley  who  found  in  dogs  a  dilatation  of  the  receptaculum  as  the  result  of  electrical 
stimulation  of  the  splanchnic  nerve. 

Movement  of  the  lymph. — It  has  been  estimated  (Ludwig)  that  the  amount  of  lymph  which 
passes  through  the  lymphatic  ducts  of  a  dog  aggregates,  during  the  twenty-four  hours,  one-third 
the  body-weight.  In  the  thoracic  duct  the  lymph  is  under  a  sufficient  pressure  to  burst  the  duct 
behind  a  ligature.  In  the  absence  of  any  especial  propulsive  organ,  such  as  the  heart  for  the 
blood-circulation,  what  are  the  forces  which  move  the  lymph?  There  must  be  recognised  pri- 
mary and  accessory  forces.     As  accessory  forces  there  are  the  movement  of  the  muscles  and  the 


LYMPHATIC  VESSELS 


703 


general  pressure  of  the  organs  on  the  lymph-ducts.  Since  these  are  provided  with  valves,  all 
preventing  the  lymph  from  flowing  backward,  any  such  pressure  causes  the  lymph  to  move  on- 
ward. As  accessory  agents  must  also  be  reckoned  the  smooth  muscle  and  elastic  tissue  which  is 
present  in  the  walls  of  the  lymph-vessels  and  in  the  lymph-gland.  That  these  forces,  however, 
are  not  primary  is  shown  by  numerous  facts.     There  is  an  active  circulation  in  the  lymphatics  of 

Fig.  650. — A.  The  Adventitial  and  SuPKA-MusctrLAR  Nerve  Plexuses,  together  with 
Sensory  Endings  in  the  Thoracic  Duct  of  a  Dog.  (Methylene-blue  method.)  B. 
Nerve-fibres  on  the  Endothelium  op  a  Lymphatic  Capillary  of  a  Dog.  (After 
Kytmanoff.) 


U^:^^^^  ^^^'\r^i*.I^  ~'^"'*J^ 


iXiatmrft'^-:^: 


^■S53*K*^?.>S5„W^'^- 


^ 


■/' 


embryos  long  before  valves  develop.  In  many  lower  animals  no  valves  develop  save  at  the 
entrance  of  the  lymphatics  to  the  veins.  That  neither  valves  nor  muscular  movements  are  es- 
sential is  shown  by  the  fact  that,  in  the  tails  of  frog  larvae,  where  no  valves  are  present  and 
where  the  muscle  movements  have  been  completely  paralysed  by  an  anesthetic,  the  circular- 
tion  of  lymph  continues  unchecked. 

The  primary  cause,  therefore,  for  the  movement  of  lymph  is  to  be  sought  in  the  capillary 
region,  in  the  force  produced  by  the  passage  of  lymph  through  the  endothelial  wall,  whether  this 


704 


THE  LYMPHATIC  SYSTEM 


process  be  a  filtration  and  diffusion — -in  which  case  the  causes  would  he  in  the  pressure  and  mo- 
lecular condition  of  the  tissue  fluid  outside  the  lymphatic — or  whether  it  be  an  active  secretion 
by  the  endothelium — in  which  case  the  driving  force  would  be  this  secretory  power  of  the 
endothelium. 

3.  THE  LYMPHOID  ORGANS 

Closely  associated  with  the  lymphatic  capillaries  and  vessels  is  a  group  of 
glandular  structures  known  as  lymphoid  organs.  They  consist,  essentially,  of 
groups  of  round  lymphoid  cells,  lying  in  a  meshwork  of  reticulum  fibres,  and  hav- 
ing often  a  definite  relationship  to  the  blood  or  lymph  vessels. 

The  group  of  lymphoid  organs  includes,  in  addition  to  the  lymph-glands 
[lymphoglandulse]  or  lymph-nodes,  which  are  particularly  related  to  the  lymphatic 
vessels,  the  spleen,  thymus  and  bone-marrow,  which  are  also  largely  made  up  of 
lymphoid  tissue.  The  spleen  and  thymus,  however,  are  considered  separately 
with  the  Ductless  Glands. 


Fig.  551. 


-Diagram  op  a  Ltmph-nodb.     (After  Toldt,  "Atlas  of  Human  Anatomy,  "Rebman, 
London  and  New  York.) 
Capsule 


Medullary  cords 


Deep  lymph  vessels 


Anastomosis  between  afiferent  and  efferent  vessel 


-^  Superficial 
y  lymph-paths 


In  their  most  simple  form,  the  lymphoid  organs  form  mere  irregular  accumulations  or  patches 
of  lymphoid  cells,  whioh^iave  been  termed  lymphoid  infiltrations.  Such  patches  are  frequent 
in  mucous  membranes  especially  along  the  intestinal  tract  (fig.  549)  and  the  air-passages  in  the 
lungs. 

Larger  accumulations  of  lymphoid  cells  produce  definite  round  nodules,  which  may  occur 
singly,  as  solitary  follicles  or  in  groups,  as  aggregated  follicles  (Peyer's  patches)  (fig.  548).  In  the 
sohtary  foLhcle  the  lymphoid  ceSs  are  arranged  concentrically,  with  a  region  in  the  centre  where 
the  cells  are  less  closely  packed  together.  This  is  called  the  germinal  centre,  and  contains 
numerous  cells  undergoing  mitotic  division.  The  sohtary  folhole  contains  blood-capiUaries. 
Lymph-capiUaries,  however,  do  not  enter  the  follicle  but  form  a  rich  plexus  about  it. 

The  lymph-glands  or  nodes  (fig.  551)  are  larger  lymphoid  structures,  which  are  developed 
along  the  course  of  the  lymph-vessels.  They  vary  much  in  size,  shape,  and  colour,  and  may  occur 
singly  or  in  small  or  large  groups.  The  size  varies  from  the  size  of  a  pin-head  to  that  of  an  oUve, 
or  larger.  In  skape'they  may  be  spherical,  oval,  or  flattened  on  one  or  more  sides,  according  to 
their  relations  to  other  organs.  Each  gland  has  an  indentation  or  hilus,  where  the  arteries 
enter,  and  where  the  veins  and  efferent  ducts  emerge.  Their  colour  depends  upon  position  and 
state  of  function.  The  glands  along  the  respiratory  tract  are  black,  due  to  the  presence  of  car- 
bon granules.  The  mesenteric  glands  are  milk-white  during  digestion,  and  other  nodes  are  pale 
and  translucent  when  their  sinuses  are  filled  with  fluid,  and  pink  or  even  red  when  red-blood 


LYMPHOID  ORGANS 


705 


cells  are  present  in  the  sinuses.     The  lymph-gland  is  made  up  of  four  distinct  elements :  lymphoid 
elements,  lymphatic  capillaries,  supporting  structures,  and  blood-vessels. 

The  lymphoid  elements  (fiji.  .551)  are  arranged  as  follicles  and  as  cell-strings.  The  follicles 
lie  around  the  circumference  of  the  gland,  and  form  the  cortex  [substantia  corticalis].  The  cell- 
strings  or  meduUary  cords  are  irregular  cords  of  cells  which  extend  from  the  follicles  through  the 
central  or  medullary  portion  [substantia  medullaris]  of  the  gland.  The  follicles  and  medullary 
cords  are  made  up,  as  are  the  solitary  follicles,  of  round  lymphoid  cells. 


Fig.  552.- 


-SuRFACE  View  and  Section  op  a  Lymph-node  showing  the  Peripheral  and  Cen- 
tral, Sinuses.     (After  Teichmann.) 


The  lymphatic  vessels  (tig.  551)  enter  the  lymph-gland  as  several  vasa  afferentia,  and  leave 
it,  at  the  hilus,  as  the  vasa  efferentia.  The  vasa  afferentia  spread  out  in  the  cortical  portion 
of  the  gland  into  an  extremely  rich  plexus  of  wide  capillaries  which  surround  the  follicles, 
forming  the  peripheral  sinus.  The  capillaries  do  not  enter  the  follicle.  This  plexus  continues, 
around  the  foUicles,  into  the  medullary  portion  where  it  forms  again  a  rich  plexus,  the  medullary 
sinus,  in  the  spaces  around  the  meduUary  cords  (fig.  552).  At  the  hilus  the  medullary  capil- 
laries collect  into  larger  vessels  and  emerge  as  the  vasa  efferentia. 

The  supporting  structures  consist  of  a  fibrous  capsule  surrounding  the  gland,  from  which 
trabecula3  or  septa  pass  in,  around  and  between  the  foUicles  and  cords.  From  the  septa,  a 
fine  reticulum  passes  into  the  foUicles  and  cords,  where  it  forms  a  rich  dense  meshwork,  in  the 
interstices  of  which  lie  the  Ij'mphoid  cells.  The  capsule  and  trabeculse  are  made  up  of  white 
fibres,  elastic  fibres  and  smooth  muscle-fibres. 


i 


706  THE  LYMPHATIC  SYSTEM 

The  blood-vessels,  which  enter  and  leave  at  the  hilus,  send  branches  into  the  follicles  and 
into  ihe  meduUary  cords. 

The  enormous  widening  of  the  lymph-stream  in  the  lymph-node  from  the  vasa  afferentia 
to  the  capillaries — like  a  brook  widening  out  into  a  pond — causes  a  very  great  diminution  in 
the  rate  of  flow  of  the  lymph.  Thus  there  is  present  in  the  gland  a  very  slowly  moving  stream 
of  lymph,  which  is  separated  from  the  lymphoid  tissue  outside  by  a  single  layer  of  flattened 
endotheh'al  cells.  There  is  thus  possible  an  easy  interchange  of  substances,  and  an  opportunity 
for  the  passage,  through  the  endothelium,  of  wandering  cells.  While  the  entire  mode  of  func- 
tioning of  the  lymph-gland  is  not  clear,  it  is  known  that  lymphocytes,  formed  here,  enter  the 
lymph-stream,  and  that  substances  such  as,  for  instance,  carbon  granules,  or  leucocytes  laden 
with  bacteria,  are  checked  in  their  course  by  the  lymph-gland. 

Arrangement. — The  lymph-glands  are  so  arranged  throughout  the  body  that 
all  the  lymph  which  enters  the  lymphatic  capillaries  must  pass  through  one  or 
more  lymph-glands  on  its  way  to  the  veins. 

It  is  possible  that  this  rule  may  have  exceptions,  although  none  have  yet  been  definitely 
proved.  Thus,  some  of  the  small  lymphatics  which  join  the  thoracic  duct  may  enter  it  without 
having  passed  through  a  gland.  Moreover,  there  is  often  found  (fig.  551)  a  direct  anastomosis 
between  an  afferent  and  an  efferent  lymphatic  vessel. 

Most  of  the  glands  are  collected  in  certain  regions,  where  they  form  centers 
toward  which  the  lymphatic  vessels  radiate.  Such  groups  are  termed  regional 
glands.  The  glands  forming  such  a  group  are  connected  with  one  another  by 
numerous  anastomoses,  which  are  termed  lymphatic  plexuses  [plexus  lymphatici]. 
In  addition  to  the  regional  glands  there  are  many  isolated  glands  which  lie  along  the 
course  of  the  lymph-vessels,  and  through  which  pass  the  vessels  draining  a  much 
more  limited  capillary  area.     Such  glands  are  termed  intercalated  glands. 

4.     THE  DEVELOPMENT  OF  THE  LYMPHATIC  SYSTEM 

Our  knowledge  of  the  lymphatic  system  has  been  very  greatly  increased  during  the  past 
ten  years  by  studies  on  its  mode  of  development.  Previous  to  1902  nothing  definite  was  known 
about  the  primary  development  or  the  mode  of  growth  of  the  lymphatic  system.  It  was 
concluded  by  some  (Budge,  GuUard  and  Saxer)  that  the  lymphatics  arise  from  undifferentiated 
mesenchyme  cells;  Ranvier  believed  that  they  arise  from  veins  by  budding  of  the  endothelium; 
while  Sala  described  them  as  arising  partly  from  the  mesenchyme  and  partly  from  venous 
endothelium. 

Regarding  the  mode  of  growth  and  spreading  of  the  lymphatics,  various  theories  were  like- 
wise held.  Kolliker,  His,  Goethe  and,  later,  Sala  held  that  growth  takes  place  by  the  suc- 
cessive addition  of  mesenchyme  cells;  Langer,  Rouget,  and  Ranvier  maintained  that  growth 
takes  place  by  sprouting  of  the  endothelium  (fig.  553).  S.  Mayer  thought  that  new  lymphatics 
are  derived  from  transformed  blood-capillaries. 

Miss  Sabin  in  1902  gave  the  first  clear  picture  of  the  mode  of  origin  and  growth  of  the 
lymphatic  system,  and  our  present  knowledge  is  largely  based  upon  her  discoveries.  She 
showed  by  injections  of  embryo  pigs  that  the  lymphatics  of  the  skin  appear  first  in  four  regions 
of  the  body — two  on  each  side  at  the  base  of  the  neck,  and  two  in  the  inguinal  region — in  the 
form  of  sacs  which  are  connected  with  the  veins.  From  these  four  regions  the  lymphatics 
spread  out  step  by  step  over  the  skin  of  the  entire  body,  in  the  form  of  a  richly  anastomosing 
capillary  plexus.  Since  the  publication  of  Miss  Sabin's  paper,  numerous  studies  have  been 
made  on  the  mode  of  development  of  lymphatics  in  many  different  animals,  including  man. 
The  results  of  these  studies  indicate  that  the  lymphatic  endothelium  first  appears  in  the  form 
of  buddings-out  from  the  veins  in  certain  well-defined  regions  of  the  embryo.  As  to  the  exact 
manner  of  this  primary  origin  views  differ.  Miss  Sabin,  in  her  first  paper,  held  that  it  arises 
by  budding  from  the  veins.  F.  T.  Lewis  held  that  it  is  formed  by  the  transformation  of  plexuses 
of  blood-capillaries.  This  view  was  accepted  by  Miss  Sabin,  and  verified  by  Huntington  and 
McClure.  Stromsten  recuiTi'd  to  Sala's  view  that  the  first  lymphatic  endothehum  arises  in 
part  from  venous  endothelium,  and  in  part  from  the  mesenchyme  cells.  Hoyer  and  his  pupila 
find  that  the  first  lymphatics  arise  as  buds  from  the  veins.  This  has  also  been  found  (1912)  by 
E.  R.  and  E.  L.  Clark  in  chick  embryos. 

Thus  far  six  regions  have  been  found,  in  which  lymphatics  develop  from  the  veins — in  the 
neck,  on  each  side,  at  the  angle  formed  by  the  internal  jugular  and  subclavian  veins;  in  the  pelvis, 
on  each  side,  along  the  iliac  veins;  and  two  unpaired  sets  in  the  region  of  the  renal  veins,  one 
ventral  to  the  aorta,  the  mesenteric,  and  one  dorsal  to  the  aorta,  retroperitoneal.  In  these 
six  regions  the  lymphatics  soon  coalesce  to  form  large  sacs,  the  jugular,  iliac,  mesenteric  and 
retroperitoneal.  The  sacs  are  later  broken  up  into  the  primary  sets  of  lymph-nodes.  The 
receptaculum  chyli  develops  in  the  region  of  the  retroperitoneal  sac. 

From  these  primary  anlages  derived  from  the  veins  the  lymphatics  spread  out  into  the 
various  organs  and  tissues  of  the  body.  The  cutaneous  lymphatics  spread  out  from  the  two 
jugular  and  two  iliac  regions  (Sabin),  the  lymphatics  of  the  intestine  from  the  mesenteric  sac 
(Heuer). 

The  method  by  which  this  extension  of  the  primary  lymphatics  occurs  is  still  in  dispute, 
but  there  seems  to  be  conclusive  evidence  that  it  takes  place  by  the  sprouting  of  the  endothehum 
(fig.  553) ;  that  the  endothehum  of  the  lymphatics,  derived  from  the  veins,  is  a  specific,  inde- 
pendent tissue,  and  that  all  new  lymphatic  endothehum  is  formed  from  lymphatic  endothehum, 


DEVELOPMENT  OF  THE  LYMPHATICS 


707 


and  not  from  blood-vessels  or  mesenchyme  cells.  This  view  is  supported  especially  by  the 
work  of  Sabin,  MacCaUum,  Hoyer  and  his  pupils  and  E.  R.  Clark. 

On  the  other  hand,  F.  T.  Lewis  has  suggested  that  the  spreading  of  lymphatics  occurs 
by  the  transformation  of  blood-vessels  into  lymphatics;  while  Huntington  and  McClure  and 
their  pupils  maintain  that  it  occurs  by  the  continued  transformation  of  mesenchyme  cells. 

The  lymphatics  growing  from  the  various  primary  centres  meet  and  anastomose  with 
one  another,  and  gradually  lose  aU  connections  with  the  veins  save  those  at  the  base  of  the  neck 
Sylvester  has  found,  however,  that  in  South  American  monkeys  the  connections  with  the  veins 
in  the  region  of  the  renal  veins  are  maintained  in  the  adult.  Valves  do  not  appear  in  the  lym- 
phatic vessels  until  quite  late,  in  human  embryos  about  5  or  6  cm.  long.  (Sabin.) 

The  lymphatic  nodes  do  not  make  their  appearance  until  the  system  of  vessels  is  well 
established.  They  are  at  first  represented  by  masses  of  lymphoid  tissue  in  the  meshes  of  a 
lymphatic  network.  Later  the  lymphoid  mass  breaks  up  into  smaller  portions,  into  which 
the  blood-vessels  and  branches  from  the  surrounding  network  penetrate;  and  each  mass,  together 

Fig.  553. — The  Speouting  of  Lymphatic  Capillaries  in  the  Pig.     (After  MacCaUum.) 
The  lymphatics  are  injected  and  the  sprouts  are  both  single  cells  and  clumps  of  cells. 


with  the  portions  of  the  network  surrounding  it,  becomes  enclosed  in  a  connective-tissue  capsule. 
The  original  lymphoid  tissue  becomes  transformed  into  the  medullary  cords  and  cortical  nodules 
of  the  node,  while  the  enclosing  lymphatic  capillaries  form  its  peripheral  lymph-sinus. 

The  earhest  nodes  appear  in  the  places  occupied  by  the  primary  Ij'mphatic  plexuses  or 
sacs  (Miss  Sabin,  F.  T.  Lewis,  JoUy),  and  have  been  termed  the  "primary  nodes"  (Miss  Sabin). 
Secondary  and  tertiary  sets  of  nodes  develop  later  at  places  of  confluence  of  many  Ivmohatics 
(cf.  A.  H.  Clark.)  •    ^     f      ^^ 

Regeneration  and  new  growth  of  lymphatic  vessels  and  glands. — While  blood-vessels 
are  known  to  possess  throughout  life  the  capacity  for  regeneration  and  new  growth,  this  process 
in  lymph-vessels  has  been  very  little  studied.  Yet  enough  has  been  learned  from  the  work  of 
Coffin  and  Evans  to  justify  the  statement  that  lymphatic  vessels  also  possess  the  capacityFfor 
new  growth.  Evans  made  the  interesting  observation  that  lymphatic  vessels  grow  into  a  tumor 
of  connective-tissue  origin  (a  round-celled  sarcoma),  while  they  fail  to  grow  into  a  tumor  of 
epithelial  origin  (an  experimentally-produced  peritoneal  carcinoma  in  mice). 


708 


THE  LYMPHATIC  SYSTEM 


The  question  as  to  whether  lymph-glands  may  form  anew  is  not  yet  entirely  settled.  The 
study  of  the  problem  is  extremely  difficult,  because  very  small  lymph-nodes  may  be  normally 
present  in  a  csrfcain  region,  yet  they  may  escape  observation  untQ  they  become  hypertrophied 
under  certain  conditions.  A.  W.  Meyer  in  a  careful  experimental  study  found  no  evidence  of 
new-formation  of  lymph  glands.  On  the  other  hand,  there  is  considerable  evidence  for  the  new- 
formation  of  lymph-glands  under  pathological  conditions. 

The  haemolymph  nodes. — In  addition  to  the  ordinary  lymph-nodes,  there 
occur  along  the  course  of  certain  veins  small  nodes  which  are  either  red  or  brown 
in  colour,  according  to  their  state  of  functional  activity.  These  have  been  termed 
haemolymph  nodes.  The  red  nodes  closely  resemble  in  structure  an  ordinary 
lymph-node,  except  that  the  sinuses  are  filled  with  blood,  while  the  brown  nodes 
show  not  blood,  but  blood  pigment,  both  free  in  the  sinuses  and  in  the  phagocytic 
cells  of  the  sinuses.  In  certain  respects  these  nodes  resemble  the  spleen,  there 
being  a  reduction  of  the  medullary  cords  and  an  increase  in  the  amount  of  the 
sinuses,  which  resemble  those  of  the  spleen-pulp  rather  than  the  more  open 
lymphatic  sinuses;  and  their  trabeculae  are  also  like  those  of  the  spleen  in  having 
numerous  smooth  muscle-cells.     Some  of  these  hsemolymph  nodes  have  lymphatic 


Fig.  554. — A  Developing  H^moltmph  Node. 


Central  blood-vessel 


vessels,  but  whether,  as  in  the  spleen,  these  are  limited  to  the  capsule,  or  whether 
they  open  into  the  blood-sinuses,  making  true  hsemolymph  nodes,  is  not  yet  clear. 

A  difficult  point  in  connection  with  the  structure  of  the  hfemolymph  nodes  is  the  relation 
of  the  blood-sinuses  to  the  blood-vessels.  The  greater  weight  of  evidence  seems  to  favour 
the  view  that  the  sinuses  are  connected  with  the  veins  rather  than  that  the  arteries  open  directly 
into  them,  although  one  observer  fails  to  find  any  connection  between  the  blood-vessels  and 
the  central  sinus  (Schumacher).  In  fig.  554  is  shown  a  hsemolymph  node  in  the  neck  of  a  pig 
24.5  cm.  long.  This  stage  marks  the  first  appearance  of  the  hsemal  node  in  the  neck,  and  shows 
the  node  in  its  simplest  form,  the  foUicle  and  its  peripheral  blood-sinus  (Miss  Sabin). 

There  are  wide  variations  in  the  distribution  and  number  of  the  haemolymph  nodes;  indeed 
sufficient  observations  have  not  yet  been  made  to  determine  their  complete  distribution. 
They  have  been  divided  into  three  groups,  the  prsevertebral,  the  renal,  and  the  splenic.  In 
one  subject,  in  which  they  were  very  numerous,  they  occurred  at  the  root  of  the  lung,  near  the 
bronchi, and  bronchial  vessels,  a  few  near  the  oesophagus,  a  continuous  praevertebral  chain  in 
the  abdomen  extending  from  the  diaphragm  to  the  upper  two  or  three  sacral  vertebra,  as  well 
as  a  few  along  the  ccefiac  axis  and  its  branches,  the  superior  mesenteric,  renal,  and  iliac  vessels 
(Lewis). 

Schumacher,  from  a  study  of  lymph-glands  and  haemolymph  glands  of  various  stages, 
concludes  that  the  haemolymph  glands  are  not  to  be  considered  as  organs  sui  generis,  but  that 
they  represent  rudimentary  forms  of  ordinary  lymph-glands,  which  have  lost  their  connections 
with  the  lymphatic  vessels.     Further  investigations  are  needed  to  clear  up  this  subject. 


NODES  OF  THE  HEAD  AND  NECK  709 

II.  SPECIAL  ANATOMY  OF  THE  LYMPHATIC  SYSTEM 

The  lymphatic  system  will  be  considered  by  regions  as  follows:  A,  head  and 
neck;  B,  upper  extremity;  C,  thorax;  D,  abdomen  and  pelvis;  E,  lower  ex- 
tremity. 

A.  THE  LYMPHATICS  OF  THE  HEAD  AND  NECK 

The  lymphatics  of  the  head  and  neck  may  be  divided  into  two  sets.  One  set  is 
superficial,  draining  the  entire  skin  sin-face,  and  has  its  nodes,  for  the  most  part, 
in  the  neck,  the  principal  group  lying  along  the  external  jugular  vein.  The  other 
set  is  deeper  and  drains  the  mucous  membrane  of  the  upper  part  of  the  digestive 
and  respiratory  tracts,  together  with  the  deep  organs,  such  as  the  thyreoid  gland 
and  the  tendons  of  the  muscles.  The  nodes  of  this  set  are  deeply  placed,  being 
situated  along  the  carotid  arteries,  with  outlying  retro-pharyngeal  nodes. 

1.  THE  SUPERFICIAL  NODES  OF  THE  HEAD  AND  NECK 

Lymph-nodes  appear  first  in  the  neck  in  the  process  of  development.  In  the 
pig  the  first  node  to  appear  develops  from  the  lymph  heart,  which  is  in  the  supra- 
clavicular triangle  behind  the  sterno-cleido-mastoid  muscle.  From  here  ducts 
grow  across  the  muscle  and  give  rise  to  a  chain  of  nodes  along  the  external  jugular 
vein.  This  chain  is  to  be  considered  as  the  main  chain  of  superficial  nodes  in  the 
neck.  From  it  lymphatic  vessels  grow  over  the  back  of  the  head,  the  side  of  the 
head,  the  face,  and  the  front  of  the  neck,  and  in  their  course  groups  of  secondary 
nodes  develop.  The  nodes  of  the  main  chain  are  known  as  the  superficial  cervical 
nodes,  and  are  from  four  to  six  in  number.  The  secondary  groups  are — (1)  the 
occipital;  (2)  the  posterior  auricular;  (3)  the  anterior  auricular;  (4)  the  parotid; 
(5)  the  submaxillary,  with  the  facial  as  a  tertiary  set,  and  (6)  the  submental. 

1.  The  occipital  nodes  [lymphoglandulse  occipitales]. — The  lymphatics  of  the 
skin  of  the  back  of  the  head  collect  into  a  few  trunks  that  either  empty  into  from 
one  to  three  small  nodes  near  the  occipital  insertion  of  the  semispinalis  capitis 
muscle,  or  pass  by  the  secondary  group  and  empty  directly  into  the  upper  nodes 
of  the  main  superficial  cervical  chain  (fig.  555). 

2.  The  posterior  auricular  nodes  [Igl.  auriculares  posteriores]. — A  portion  of 
the  temporal  part  of  the  scalp,  together  with  the  posterior  surface  of  the  ear,  except 
the  lobule,  and  the  posterior  surface  of  the  external  auditory  meatus,  drain  into 
two  small  nodes  on  the  insertion  of  the  sterno-cleido-mastoid  muscle.  The  effer- 
ent vessels  of  these  nodes  pass  to  the  upper  part  of  the  superficial  cervical  chain. 

3.  The  anterior  auricular  nodes  [Igl.  auriculares  anteriores]  are  few  innumber — 
from  one  to  three — and  are  situated  immediately  in  front  of  the  tragus  of  the  ear. 
They  receive  vessels  from  the  anterior  surface  of  the  auricle  and  the  external  audi- 
tory meatus,  from  the  integument  of  the  temporal  region  and  the  lateral  portion 
of  the  eyelids.  Their  efferents  pass  to  the  parotid  and  superior  deep  cervical 
nodes. 

4.  The  parotid  nodes. — The  parotid  group  of  nodes  is  considerably  larger  than 
the  two  preceding,  containing  from  ten  to  sixteen  nodes,  and  the  group  drains  a 
more  complex  area.  It  receives  vessels  from  the  adjacent  surface  of  the  external 
ear,  the  external  auditory  meatus,  the  skin  of  the  temporal  and  frontal  regions, 
and  the  eyelids  and  nose.  The  deeper  nodes  of  this  set  receive  vessels  from  the 
parotid  gland. 

In  the  embryo  these  nodes  He  in  the  pathway  of  the  lymph- vessels  that  grow  to  the  scalp; 
many  of  these  vessels,  however,  pass  the  parotid  group  and  empty  into  the  superficial  cervical 
chain.  The  nodes  of  the  parotid  group  lie  embedded  in  the  substance  of  the  parotid  gland, 
and  their  efferents  pass  to  the  submaxillary  and  the  superior  superficial  and  deep  cervical  nodes. 

As  "inferior  auricular  nodes"  Bartels  designates  one  or  two  small  glands  of  the  parotid 
group  which  lie  below  the  ear,  and  receive  afferent  vessels  from  the  lower  part  of  the  ear. 

5.  The  submaxillary  [Igl.  submaxillares]  and  facial  [Igl.  faciales  profundae] 
nodes. — The  submaxillary  (perhaps  better  "mandibular")  group  consists  of  a 


i 


710 


THE  LYMPHATIC  SYSTEM 


chain  of  from  three  to  six  nodes,  resting  on  the  submaxillary  (salivary)  gland, 
along  the  inferior  border  of  the  mandible.  They  lie  usually  on  the  submaxillary 
gland,  but  may  extend  from  the  insertion  of  the  anterior  belly  of  the  digastric  to 

Fig.   555. — The  Lymphatics  of  the   Head  and  Neck.     (After  Toldt,    "Atlas  of  Human 
Anatomy  "   Rebman,  London  and  New  York  ) 


Occipital  lymph-nodes 
Posterior  auricular  lymph-nodes 


Superficial  cervical  lymph-nodes  \ 


► 


Axillary  lymph-nodes 


.i.„z:^^=^ 


the  angle  of  the  jaw.  They  are  about  the  size  of  a  pea,  and  the  largest  is  near  the 
point  where  the  external  maxillary  (facial)  artery  crosses  the  mandible.  The  sub- 
maxillary nodes,  together  with  the  next  group,  the  facial,  drain  a  complex  area, 


THE  FACIAL  NODES 


711 


including  not  only  skin,  but  mucous  membrane.  They  receive  lymph-vessels 
from  the  nose,  cheek,  upper  lip,  the  external  part  of  the  lower  lip,  together  with 
almost  all  those  from  the  gums  and  teeth  and  from  the  anterior  third  of  the  lateral 
portions  of  the  tongue.  In  agreement  with  the  fact  that  these  nodes,  though  lying 
superficially  and  draining  the  skin,  drain  also  the  mucous  membrane,  their  vessels 
empty  not  only  into  the  superficial  cervical  chain,  but  also  into  the  deep  carotid 
chain. 

The  facial  nodes  are  evidently  outlying  nodes  of  the  submaxillary  group. 
They  are  in  two  main  sets — (1)  the  supra-maxillary  set,  which  consists  of  from 
one  to  thirteen  nodes,  resting  on  the  mandible  near  the  point  where  it  is  crossed 
by  the  external  maxillary  (facial)  artery.     (2)  The  buccinator  set,  lying  on  the 

Fig.  556. — Lymphatics  or  the  Outer  Nose  and  Face.     (After  Ktittner.) 


Submax- 
illary 
node 


line  connecting  the  lower  margin  of  the  ear  and  the  angle  of  the  jaw.  Of  these 
latter  nodes,  some  lie  near  the  point  where  the  parotid  duct  perforates  the  buc- 
cinator muscle;  the  others  are  farther  forward,  between  the  external  maxillary 
artery  and  the  anterior  facial  vein.  Additional  nodes  belonging  to  the  group  may 
occur  near  the  nose  and  in  the  suborbital  region.  These  facial  nodes  receive  affer- 
ents  from  the  outer  surface  of  the  nose,  the  lips,  eyelids,  cheek,  temporal  part  of 
the  face,  the  mucosa  of  the  mouth,  the  teeth  of  the  upper  jaw,  the  gums,  the  tonsils, 
and  the  parotid  gland.  Their  efferents  pass  to  the  submaxillary  and  parotid 
nodes. 

6.  The  submental  nodes  [Igl.  submentales],  usually  two  in  number,  lie  in  the 
triangle  bounded  by  the  anterior  bellies  of  the  two  digastric  muscles  and  the  hyoid 
bone  (fig.  559).  They  are  usually  near  the  median  line,  and  drain  the  skin  of  the 
chin,  the  skin  and  corresponding  mucous  membrane  of  the  central  part  of  the  lower 


712 


THE  LYMPHATIC  SYSTEM 


lip  and  jaw,  the  floor  of  the  mouth,  and  the  tip  of  the  tongue.     The  efferent 
vessels  pass  either  to  the  submaxillary  nodes  or  to  the  deep  cervical  chain. 


2.  THE  LYMPHATIC  VESSELS  OF  THE  FACE 

The  different  parts  of  the  face  and  their  lymphatic  relation  to  these  groups  of 
superficial  nodes  will  now  be  considered. 

The  lymphatics  of  the  scalp  form  a  rich  network  in  the  neighbourhood  of  the 
vertex,  from  which  vessels  pass  in  various  directions.     From  the  frontal  region  a 

Fig  557. — Lymphatic  Nodes  and  Vessels  of  the  Ear,  Eyelids,  Nose  and  Lips.  New- 
born child.  P,  parotid.  M,  submaxillary  gland.  B,  buccal  fat  ("sucking  pad").  Supero- 
lateral deep  cervical  lymph  nodes  are  not  labelled.     (After  Bartels.) 


Ant.  auricular 
lymph  nodes 


Ant.  submaxillary  /' 
lymph  nodes 

Middle  submaxillary/ 
lymph  nodes 


Inferior  submental  lymph  nodes  (var  ) 

Posterior  submaxillary  lymph  nodes 

number  of  ducts  pass  downward  and  backward  to  the  parotid  nodes;  those  from 
the  parietal  and  temporal  regions  pass  to  the  anterior  auricular,  parotid,  and  pos- 
terior auricular  nodes;  and  those  from  the  occipital  region  pass  partly  to  the  occi- 
pital nodes  and  partly  to  the  superior  deep  cervical  group,  while  a  single  large 
vessel  descends  along  the  posterior  border  of  the  sterno-mastoid  muscle  to  ter- 
minate in  one  of  the  inferior  deep  cervical  nodes. 

The  lymphatics  of  the  eyelids  and  conjunctiva. — The  capillary  plexus  of  the 
eyelids  and  the  conjunctiva  is  an  abundant  one,  and  at  the  free  border  of  the 
eyelids  becomes  extremely  close.  The  lymphatics  from  the  lateral  three-fourths 
of  the  lids  pass  to  the  anterior  auricular  and  parotid  groups  of  nodes,  while  those 
from  the  medial  one-fourth  pass  obliquely  across  the  cheek  with  the  facial  vein  to 
terminate  in  the  facial  and  submaxillary  nodes  (figs.  556,  557,  561). 

The  lymphatics  of  the  nose. — The  lymphatics  of  the  nose  (fig.  556)  form  a  net- 
work which  is  coarse  at  the  root  of  the  organ,  but  dense  over  the  alar  region. 
The  vessels  run  in  three  sets — (1)  one  set  passing  over  the  eye  to  the  parotid  nodes; 
(2)  a  set  passing  under  the  eye  to  the  same  nodes;  and  (3)  the  most  important 


LYMPH-VESSELS  OF  THE  FACE 


713 


group,  consisting  of  from  six  to  ten  trunlts,  passing  to  the  facial  and  submaxillary 
nodes.  There  are  some  anastomoses  between  the  capillaries  of  the  skin  and  those 
of  the  mucous  membrane  of  the  nose. 

Fig.  558. — The  Facial  Nodes.     (After  Buchbinder.) 


ll 


-Suborbital  nodes 
"Node  of  nasogenial  fold 


-  Supra  maxillary  ] 
'  Inframaxillary  n( 


The  lymphatics  of  theUps  (fig.  559). — -The  capillary  plexuses  of  the  skin  and 
mucous  membrane  are  continuous  at  the  free  border  of  the  lips.  The  vessels  of 
the  upper  lip,  of  which  there  are  about  four  on  each  side,  pass  to  the  submaxillary 


Fig.  559. — The    Lymphatics    op    the     Lips.       Newborn    child. 

Dorendorf.) 


(From     Bartels     after 


Superior  submental 
lymph  nodes 


Ant.  submaxillary  lymph 


Deep  cervical  lymph  node 


nodes.  From  the  lower  lip  the  trunks  from  near  the  angle  of  the  mouth  pass  to 
the  submaxillary  nodes,  while  those  from  the  centre  of  the  lip  pass  to  the 
submental  nodes. 

There  are  from  two  to  four  subcutaneous  vessels  and  from  two  to  three  submucous  vessels  on 
either  side.     The  collecting  trunks  passing  to  the  submaxillary  nodes  do  not  anastomose,  and 


714  THE  LYMPHATIC  SYSTEM 

the  same  is  true  of  the  submucous  vessels  of  the  lower  lip.  The  subcutaneous  vessels,  on  the 
other  hand,  passing  to  the  submental  nodes,  anastomose  freely,  an  important  fact  in  connection 
withthe  extension  of  cancer  of  the  lower  lip. 

The  lymphatics  of  the  auricle  and  external  auditory  meatus. — The  lymphatic 
plexus  in  the  auricle,  external  auditory  meatus,  and  the  outer  side  of  the  tympanic 
membrane  is  an  abundant  one.  An  anastomosis  has  been  described  between  a 
scanty  plexus  on  the  inner  side  of  the  tympanic  membrane  and  the  plexus  on  the 
outside.  The  collecting  vessels  pass  to  three  sets  of  nodes: — (1)  those  from  the 
external  and  internal  surface  of  the  auricle  and  the  posterior  part  of  the  external 
auditory  meatus  pass  to  the  posterior  auricular  nodes;  (2)  those  from  the  lobule, 
the  helix,  a  part  of  the  concha  and  the  outer  portion  of  the  external  auditory  mea- 
tus pass  to  the  inferior  auricular  and  superficial  cervical  chain;  some  of  the  vessels 
from  the  first  and  second  areas  also  run  to  the  deep  cervical  group;  (3)  an  anterior 
group  from  the  tragus  and  part  of  the  external  auditory  meatus  consisting  of  from 
four  to  six  trunks,  pass  to  the  anterior  auricular  nodes,  which  are  connected  with 
the  parotid  nodes. 

3.  THE  DEEP  LYMPHATIC  NODES  OF  THE  HEAD  AND  NECK 

The  deep  cervical  chain  is  the  largest  mass  of  nodes  in  the  neck.  It  consists 
of  from  fifteen  to  thirty  nodes,  which  lie  along  the  entire  course  of  the  carotid 
artery  and  internal  jugular  vein.  This  chain  receives  vessels  from  all  the  super- 
ficial nodes,  also  directly  from  the  skin,  as  well  as  from  the  entire  mucous  mem- 
brane of  the  respiratory  and  alimentary  tracts  in  the  head  and  neck.  Thus  it 
drains  both  the  superficial  and  the  deep  structures. 

For  convenience  of  description  this  long  chain,  though  usually  continuous,  is 
divided  into  two  groups — (1)  a  superior  group,  lying  above  the  level  at  which  the 
omo-hyoid  muscle  crosses  the  carotid  artery,  and  (2)  an  inferior  or  supra-clavicular 
group,  lying  below  that  level. 

(1)  The  superior  deep  cervical  nodes  [Igl.  cervicales  profundae  superiores]. — 
This  group  of  nodes  extends  from  the  tip  of  the  mastoid  process  to  the  level  at 
which  the  omo-hyoid  muscle  crosses  the  common  carotid  artery.  The  dorsal  and 
smaller  nodes  of  the  chain  lie  on  the  splenius,  levator  scapulae,  and  scalene  mus- 
cles. They  drain  the  skin  of  the  back  part  of  the  head,  both  indirectly  and 
directly,  and  receive  (1)  efferents  from  the  occipital  and  posterior  auricular  nodes, 
(2)  a  large  vessel  from  the  skin  of  the  occipital  part  of  the  scalp,  (3)  some  trunks 
from  the  auricle,  and  (4)  cutaneous  and  muscular  vessels  from  the  neck. 

The  ventral  nodes  of  the  chain  lie  on  the  internal  jugular  vein.  They  drain 
the  face  both  directly  and  indirectly,  as  well  as  the  deeper  structures  of  the  head 
and  neck.     They  show  especially  well  in  fig.  563  in  connection  with  the  tongue. 

(2)  The  inferior  deep  cervical  [Igl.  cervicales  profundse  inferiores]  or  supra- 
clavicular nodes  lie  in  the  supra-clavicular  triangle.  In  the  upper  part  of  the  tri- 
angle the  nodes  rest  on  the  splenius,  the  levator  scapulae,  and  the  scalene  muscles, 
while  at  the  base  of  the  triangle  they  are  related  to  the  subclavian  artery  and  the 
nerves  of  the  brachial  plexus.  They  drain  a  wide  area,  receiving  vessels  from  the 
head,  neck,  arm,  and  thoracic  wall.  They  are  connected  with  the  superior  deep 
cervical  chain,  and  receive  afferents  from  the  axillary  nodes,  and,  in  addition,  they 
receive  vessels  directly  from  the  back  of  the  scalp,  from  the  skin  of  the  arm,  and 
from  the  pectoral  region.  Thus  it  will  be  seen  that  a  large  part  of  the  lymph 
of  the  head  and  neck,  as  well  as  some  from  the  arm  and  thorax,  passes  through 
these  nodes.  Their  efferents  unite  to  form  the  jugular  trunk,  which  ends  at  the 
junction  of  the  internal  jugular  and  subclavian  veins. 

In  the  descriptions  of  the  deep  lymphatic  vessels  certain  additional  groups  of 
nodes  will  be  considered,  which  may  be  regarded  as  outlying  groups  from  the  deep 
cervical  chain. 

4.  THE  DEEP  LYMPHATIC  VESSELS  OF  THE  HEAD  AND  NECK 

The  lymphatics  of  the  brain. — It  is  now  recognised  that  there  are  no  lymph- 
atics in  the  brain  and  cord,  so  that  the  function  of  absorption  must  be  accom- 
phshed  by  means  of  the  veins.  There  is  an  abundant  exudation  of  lymph  around 
the  nervous  system  into  the  subdural  space,  which  is  connected  with  the  central 


LYMPHATICS  OF  THE  MOUTH 


715 


canal  of  the  nervous  system,  and  which  is  to  be  considered  as  a  zone  in  which  the 
tissue-spaces  are  especially  large.  Along  the  arteries  of  the  brain  the  adventitia  is 
loose  and  open,  possessing  tissue-spaces  which  have  received  the  confusing  name  of 
perivascular  lymphatics.  It  would  be  better  to  name  them  perivascular  tissue- 
spaces. 

The  lymphatics  of  the  eye. — No  lymphatic  vessels  have  as  yet  been  discovered 
either  in  the  eyeball  or  in  the  orbit.  In  both,  however,  there  are  abundant  tissue- 
spaces,  the  most  noteworthy  of  the  orbit  being  the  interfascial  space  (space  of 
Tenon),  which  communicates  by  a  space  between  the  optic  nerve  and  its  sheath 
with  the  subarachnoid  spaces  of  the  cranial  cavity.  In  the  eyeball  the  tissue- 
spaces  are  abundant,  even  if  the  vitreous  and  aqueous  chamber  be  omitted  from 
the  category.  Numerous  spaces  exist  in  the  chorioid  coat,  especially  in  the  lamina 
supra-chorioidea,  and  in  the  sclerotic,  both  sets  communicating  by  perivascular 
spaces  surrounding  the  venae  vorticosae  with  the  interfascial  space.  In  the  cornea 
there  are  abundant  lacunae,  united  by  their  anastomosing  canaliculi,  to  form  a 
network  of  lymph-spaces  which  come  into  close  relation  with  the  conjunctival 
lymphatics  at  the  corneal  margin. 

Fig.  560. — The  Deep  Ceevical  Chain      (After  Poirier.) 


Mastoid  node 


Internal  jugular  chain 


The  conjunctiva,  being  a  portion  of  the  integument,  does  possess  lymphatic 
vessels  ffig.  562),  arranged  in  a  double  network  whose  collecting  vessels  accompany 
those  of  the  eyelids,  and  terminate  with  them  in  the  submaxillary,  anterior 
auricular,  and  parotid  nodes. 

The  Lymphatics  of  the  Digestive  Tract  in  the  Head  and  Neck 

The  lymphatics  of  the  gums. — ^The  lymphatics  from  the  mucous  membrane 
of  the  gums  pass  to  the  submaxillary  nodes.  The  capillary  plexus  is  abundant; 
the  collecting  vessels  arise  from  it  on  the  inner  surface  of  the  gum,  and  pass 
between  the  teeth  to  reach  a  common  semicircular  collecting  vessel  on  the  outer 
surface.  Lymphatics  have  recently  been  demonstrated  in  the  pulp  of  the  tooth 
(Schweitzer). 

The  lymphatics  of  the  tongue. — -There  is  a  rich  lymphatic  plexus  throughout 
the  entire  extent  of  the  submucosa  of  the  tongue,  but  that  portion  lying  in  the 
basal  part  of  the  tongue  seems  to  be  more  or  less  independent  of  the  rest.  Accord- 
ing to  Aagaard  the  tongue  muscles  are  provided  with  lymphatics  which  are  drained 
by  the  ducts  of  the  submucosal  plexuses.  There  are  four  groups  of  collecting 
vessels — (1)    apical;  (2)  marginal;  (3)  basal;  and  (4)  central. 


(1)  The  apical  vessels  are  usually  four  in  number,  two  on  each  side.  One  pair  perforates 
the  mylo-hyoid  muscle  and  ends  in  a  supra-hyoid  median  node,  while  the  other  pair  pass  to 
the  deep  cervical  chain.  The  latter  are  long,  slender  vessels,  which  run  along  the  frenum  of 
the  tongue  to  the  surface  of  the  mylo-hyoid  muscle,  cross  the  hj'oid  bone  just  behind  the  pulley 
of  the  digastric,  and  then  run  downward  in  the  neck  to  a  node  of  the  deep  cervical  chain,  just 


716 


THE  LYMPHATIC  SYSTEM 


above  the  omo-hyoid.     It  will  be  noted  in  fig.  563  that  the  most  anterior  vessels  end  in  the 
lowest  nodes,  while  those  from  the  back  of  the  tongue  end  in  higher  nodes, 

(2)  The  marginal  vessels  are  from  eight  to  twelve  in  number.     They  all  pass  to  the  superior 


Fig.  561. — Lymphatics  of  the  Head,  Neck,  and  Axilla.     (After  Toldt,  "Atlas  of  Human 
Anatomy,"  Rebman,  London  and  New  York.) 


Lymph-vessels  of  the  breasts 


deep  cervical  nodes,  a  part  of  them  passing  external  to  the  sublingual  gland,  while  the  larger 
number  pass  internal  to  it.  There  is  one  large  and  constant  node  at  the  point  where  the  digastric 
muscle  crosses  the  jugular  vein,  to  which  a  large  number  of  the  vessels  converge. 


LYMPHATICS  OF  NASAL  CAVITIES 


111 


(3)  The  hasal  vessels  are  seven  or  eight  in  number,  and  drain  the  basal  portion  of  the  tongue. 
Some  end  in  the  large  node  just  mentioned,  while  others  run  backward  close  to  the  median 
line,  where  they  anastomose,  as  far  as  the  glosso-epiglottidean  fold,  when  they  separate  and 
join  the  tonsillar  vessels  to  pass  outward  to  the  superior  deep  cervical  nodes. 

(4)  The  central  vessels,  arising  from  the  central  portion  of  the  tongue,  pass  backward  in 
the  median  line  on  the  ventral  surface  of  the  tongue.  They  lie  upon  the  mylo-hyoid  muscle, 
cross  the  hyoid  bone,  and  end  in  the  superior  deep  cervical  chain. 

The  lymphatics  of  the  palate. — The  lymphatics  from  the  palate  pass  to  the 
deep  cervical  chain.  The  trunks  from  the  hard  palate  run  in  the  submucosa  as 
far  as  the  last  molar  tooth,  where  they  pass  in  front  of  the  anterior  pillars  of  the 
fauces  and  end  in  the  superior  deep  cervical  nodes  beneath  the  digastric  muscle. 
In  the  soft  palate  the  capillary  plexus  is  very  rich,  reaching  a  maximum  in  the 
uvula.  From  the  inferior  surface  of  the  soft  palate  and  the  pillars  of  the  fauces 
vessels  pass  directly  to  the  superior  deep  cervical  chain,  but  some  of  the  vessels 

Fig.  562. — The  Lymphatics  of  the  Conjunctiva.     (After  Teichmann.) 


from  the  upper  surface  of  the  soft  palate  run  forward  with  the  pharyngeal  vessels 
and  end  in  the  retro-pharyngeal  nodes.  It  will  be  seen  from  fig.  564  that  the  retro- 
pharyngeal nodes  are  simply  outlying  nodes  from  the  deep  cervical  chain. 

The  lymphatics  of  the  pharynx. — As  has  just  been  stated,  there  are  certain 
outlying  nodes  of  the  deep  cervical  chain  which  lie  behind  the  phaiynx.  They 
receive  some  of  the  ducts  from  the  submucosa  of  the  roof  of  the  pharynx,  but  many 
of  the  pharyngeal  vessels  pass  by  these  nodes  and  end  directly  in  the  superior  deep 
chain.  The  tonsil  is  especially  rich  in  lymphatics,  and  its  ducts,  together  with 
those  from  the  middle  and  inferior  portions  of  the  pharynx,  end  in  the  superior 
deep  cervical  chain.  The  lymphatics  of  the  Eustachian  tube  run  to  the  lateral 
retro-pharyngeal  lymph-nodes  or,  passing  these,  to  the  deep  cervical  nodes. 

The  lymphatics  of  the  nasal  cavities. — The  mucous  membrane  of  the  nose 
contains  a  rich  lymphatic  plexus  whose  main  ducts  pass  to  the  retro-pharyngeal 
nodes.  An  anterior  set,  however,  anastomoses  with  the  subcutaneous  vessels, 
and  through  these  their  lymph  is  conveyed  to  the  facial  and  submaxillary  nodes. 
The  posterior  vessels  run  either  to  the  deep  cervical  chain  or  to  the  retro-pharyn- 
geal nodes.  Key  and  Retzius  have  shown  that  an  injection  of  the  Ij^mphatics  of 
the  nose  may  be  made  by  injecting  the  subarachnoid  spaces  at  the  base  of  the 


718 


THE  LYMPHATIC  SYSTEM 


brain,  although  there  is  presumably  no  direct  connection  between  the  spaces  and 
the  lymphatic  vessels.  The  lymphatics  of  the  nasal  sinuses  end  in  the  retro- 
pharyngeal nodes. 

Fig.  563. — The  Lymphatics  of  the  Tongite.     (Poirier  and  Charpy.) 
Basal  trunks 


ir^- 


.         Marginal  collecting  trunks 

/  with  hypoglossal  nerve 

—        Marginal  trunk 


V>___         '    Submen- 
j^y'  ^l^  '""   ^  '  tal  node 

"5^^-^-  CoUecting 

~      trunks  frora 
margin  of 
—  tongue 

Node   inter- 
calated in 
these  ducts 
Vessel  from  margin  of 
tongue  ending  in  in- 
ternal jugular  chain 

_    ^""Intercalated  node 


Central  vessel    passing 
to     node    above    the 

omo-hyoid 


Inferior  node  of  m 
ternal  jugular 
chain  (above  omo 
hyoid  muscle) 


> 


]  Collecting 
f  trunks  from 
tip  of  tongue 


1  Retro-pharyngeal 
J  nodes 

Intercalated  node 


CoUecting  vessels  of 
pharynx  to  deep  ; 
cervical  chain         [ 


NODES  OF  THE  UPPER  LIMB  719 

The  lymphatics  of  the  larynx. — The  larynx  is,  for  the  most  part,  drained  by 
the  deep  cervical  nodes,  although  its  lymph  may  also  pass  through  certain  out- 
lying nodes  situated  upon  its  ventral  surface.  The  mucous  membrane  is  divided 
into  two  zones  by  the  ventricular  folds,  the  mucous  membrane  of  these  structures 
possessing  but  a  scanty  lymphatic  plexus.  The  vessels  from  the  upper  part  of  the 
lar3'nx,  four  or  five  in  number,  pass  to  the  nodes  of  the  superior  deep  cervical  chain, 
situated  near  the  digastric  muscle;  those  from  the  lower  part  pass  to  the  lower 
nodes  of  the  same  chain,  some  even  descending  as  far  as  the  supra-clavicular  nodes. 
The  lymphatics  of  the  trachea  pass,  on  each  side,  to  the  paratracheal  and  inferior 
deep  cervical  nodes. 

The  lymphatics  of  the  thyreoid  body. — The  lymphatics  of  the  thyreoid  body 
pass  either  to  the  small  nodes  situated  in  front  of  the  larynx  and  trachea,  or  to 
nodes  of  the  deep  cervical  chain,  a  part  of  them  ascending  and  a  part  descending. 

It  will  thus  have  been  seen  that  the  lymphatics  of  the  mucous  membrane  of 
the  head  and  neck  all  end  in  the  deep  cervical  chain  of  nodes  or  in  the  outlying 
nodes  from  it.  Some  of  the  vessels  pass  by  the  outlying  nodes,  but  since  the  nodes 
of  the  chain  are  so  closely  connected,  the  lymph  must  pass  through  several  nodes 
before  entering  the  veins.  The  main  tonsils,  the  numerous  lingual  and  pharyngeal 
tonsils,  together  with  small  lymph-follicles  in  the  submucosa  of  the  respiratory 
tract,  represent  lymph-nodes  in  the  capillary  zone. 

B.    THE  LYMPHATICS  OF  THE  UPPER  EXTREMITY 
1.  THE  LYMPHATIC  NODES  OF  THE  UPPER  EXTREMITY 

The  lymph-nodes  of  the  arm  lie,  for  the  most  part,  in  the  axilla,  where  thpre  is 
a  large  group  of  nodes  which  receive  almost  the  entire  drainage  of  the  arm  and 
the  thoracic  wall.  In  addition,  there  is  in  the  arm  a  set  of  outlying  superficial 
nodes,  the  superficial  cubital  (supra-trochlear) ,  while  small  isolated  nodes  are  often 
intercalated  along  the  course  of  the  deep  lymphatic  vessels  which  accompany  the 
radial,  ulnar,  anterior  interosseus  and  brachial  arteries,  the  cephalic  vein,  and  the 
deep  cubital  vessels. 

(1)  The  antibrachial  nodes  are  very  small,  pin-head  sized  nodes  which  are 
intercalated  along  the  deep  lymphatics  which  accompany  the  radial,  ulnar,  ante- 
rior and  posterior  interosseus  arteries. 

(2)  The  deep  cubital  nodes  [Igl.  cubitales  profundse]  are  also  very  small 
nodes,  one  or  two  in  number,  intercalated  along  the  ducts,  near  the  deep  vessels 
at  the  bend  of  the  elbow. 

(3)  The  superficial  cubital  node  [Igl.  cubitales  superficiales]  (or  supratrochlear) 
is  situated  three  or  four  centimetres  above  the  medial  epicondyle  of  the  humerus. 
It  lies  in  the  superficial  fascia  on  the  medial  side  of  the  basilic  vein  near  the  place 
where  it  passes  through  the  deep  fascia.  It  is  usually  single,  but  may  be  absent 
or  represented  by  a  chain  of  from  two  to  five  nodes.  Its  eflerents  follow  the 
basilic  vein. 

(4)  The  delto-pectoral  nodes  are  very  small  intercalated  nodes  from  one  to 
three  in  number,  and  are  situated  in  the  groove  between  the  deltoid  and  pectoral 
muscles.     Their  vessels  follow  the  cephalic  vein. 

(5)  The  axillary  nodes  [Igl.  axillares],  from  twelve  to  thirty-six  in  number, 
may  be  divided  into  groups  according  to  the  areas  which  they  drain  (fig.  566). 
In  addition  to  the  upper  extremity,  they  receive  lymphatic  drainage  from  the 
thoracic  walls,  including  dorsal,  lateral  and  ventral  (mammary)  regions. 

(1)  The  subclavian  group  consists  of  four  or  five  nodes,  situated  in  the  apex  of  the  axillary 
fossa.  They  receive  the  efferent  vessels  of  all  the  other  groups,  and  their  efferent  vessels  in  turn 
unite  to  form  a  single  trunk,  the  subclavian,  which  empties  into  the  thoracic  duct  on  the  left 
side  and  on  the  right  side  either  into  the  vein  directly  or  else  after  uniting  with  the  jugular 
trunk.     (See  pp.  726-728.) 

(2)  The  central  group.  A  little  lower  along  the  axillary  artery  is  a  group  of  three  to  five 
nodes,  which  makes  a  second  centre  for  the  vessels  of  the  other  groups,  and  sends  its  efferents 
to  the  subclavian  group.  It  will  be  clear  from  the  figure  that  the  separation  of  groups  1  and  2 
is  arbitrary. 

(3)  The  brachial  group. — This  consists  of  four  or  five  nodes,  and,  as  its  position  toward 
the  junction  of  the  axillary  and  brachial  arteries  indicates,  is  the  main  station  for  the  lymphatics 
of  the  arm  proper.  It  receives  almost  all  the  superficial  and  deep  lymphatics  of  the  arm,  and 
its  efferents  pass  to  the  central  and  subclavian  groups,  although  a  few  pass  directly  to  the 


720 


THE  LYMPHATIC  SYSTEM 


suprascapular   group.     Small,    outlying  nodes  of  this  group  may  be  intercalated  along  the 
vessels  following  the  brachial  artery  throughout  its  course. 

(4)  The  subscapular  group  [Igl.  subscapulares]. — In  this  group  are  six  or  seven  nodes, 
which  follow  the  subscapular  artery  and  its  branch,  the  circumflex  (dorsal)  scapular.     Belonging 


Fig.  565. — The  Lymphatics  op  the  Uppeb  Extremity.     (After  Toldt, 
Anatomy,"  Rebman,  London  and  New  York.) 


'Atlas  of  Human 


Axillary  lymph  nodes  — 


to  it  there  are  usually  two  or  three  sjnall  nodes  on  the  dorsal  surface  of  the  scapula,  in  the 
groove  which  separates  the  teres  major  and  minor.  This  group  receives  vessels  from  the  dorsal 
surface  of  the  thorax,  aa  well  as  from  the  arm,  and  its  efferents  pass  to  the  brachial  group. 

(5)  The  anterior Jpeclmal'^group  [Igl.  peotorales]. — This  group  consists  of  four  or  five  nodes 
which  lie  along  the  lower  border  of  the  peetorahs  major  and  drain  the  mammary  gland  and 
front  of  the  chest.     Their  efferent  vessels  pass  to  the  central  and  subclavian  groups. 


LYMPH-VESSELS  OF  THE  LOWER  LIMB 


721 


(6)  The  posterior  pectoral  group  [Igl.  pectorales]  consists  of  small  nodes  situated  on  the  inner 
wall  of  the  axiUa,  along  the  course  of  the  long  thoracic  artery.  They  receive  afferents  from 
the  lateraljntegument  of  the  thorax  and  drain  into  the  nodes  of  the  central  group. 


^[2.  THE  LYMPHATIC  VESSELS  OF  THE  UPPER  EXTREMITY 

The  lymphatic  vessels  of  the  upper  extremity  are  divided  into  two  sets — -a 
superficial  and  a  deep  set. 

The  superficial  vessels. — The  superficial  lymphatic  vessels  of  the  arm  course 
in  two  layers,  the  one  quite  subcutaneous,  the  other  next  the  deep  fascia,  with 
frequent  anastomoses  between  the  two  sets.  The  majority  of  these  vessels 
remain  superficial  throughout  the  arm,  but  some  of  them  pass  through  the  deep 
fascia  in  the  upper  arm  especially  where  the  basilic  vein  pierces  the  deep  fascia, 

Fig.  566. — The  Axillary  Ltmph-nodbs.     (After  Poirier  and  Cuneo.) 
Brachial  group  Central  group 


Nodes  connect- 
ing the  central 
and  subscapu- 
lar groups 
Subscapular 
group 


Subclavian 
?S^^       group 

Vessel  from  the 

mammary 
gland 


Anterior  pec- 
toral node 

Vessel  from  the 
mammary 
gland 

Collecting  trunk 
Subareolar 

plexus 
Vessel  from 

lateral 

thoracic  wall 
Vessel  passing 

to  internal 

mammary 

node 
Collecting 

vessels 
Vessel  passing 

to  internal 

mammary 

node 


to  join  the  deep  lymphatics  accompanying  the  brachial  artery.  The  general 
distribution  of  the  superficial  lymphatics  and  their  relations  with  the  lymph- 
nodes  are  shown  in  figs.  565  and  567. 

The  capillary  plexus  is  most  dense  in  the  palmar  sm-faces  of  the  fingers,  where  the  meshes 
are  so  fine  that  they  can  only  be  seen  with  a  lens.  On  the  dorsal  surface  of  the  fingers  and  hand 
the  plexus  is  less  dense.  From  the  plexus  on  the  palmar  side  of  the  fingers  vessels  come  together 
at  the  base  of  the  fingers  where  they  pass  dorsally  to  be  joined  by  the  dorsal  vessels  of  the 
finger.  They  now  follow  two  rather  distinct  curves:  (1)  those  from  the  thumb  and  index 
finger  and  a  part  of  the  middle  finger  pass  upward  along  the  radial  side  of  the  forearm,  com-se 
medially  over  the  lower  part  of  the  biceps  muscle,  and  empty  into  the  axillary  lymph-nodes. 
One  or  two  vessels  follow  the  cephalic  vein  and,  after  traversing  the  delto-peotoral  node,  pierce 
the  costo-eoracoid  membrane  to  enter  the  subclavian  nodes,  or  pass  over  the  clavicle  into  the 
inferior  deep  cervical  nodes.  (2)  Those  from  the  rest  of  the  fingers  course  for  a  short  stretch 
on  the  dorsum  of  the  forearm,  when  they  turn  toward  the  ulnar  side,  wind  around  to  the  volar 
side  and  either  continue  superficially  along  the  upper  arm  to  the  axillary  nodes,  or  pass  into 
the  superficial  cubital  node,  or,  joining  the  efferents  from  these  nodes,  pass  through  the  deep 
fascia  to  unite  with  the  deep  lymphatics.  (3)  A  set  of  vessels  from  the  palm  of  the  hand  passes 
upward  along  the  volar  side  of  the  forearm.  Anastomoses  are  frequent  between  these  groups  of 
lymphatic  vessels,  particularly  in  the  cubital  region. 

It  will  thus  be  seen  that  the  superficial  cubital  nodes  receive  lymph  from  the  ulnar  digits 
and  from  the  palm  of  the  hand,  but  not  from  the  thumb  and  forefinger. 

The  superficial  lymphatics  from  the  rest  of  the  arm  join  these  thi'ee  main  groups  at  various 
levels. 

The  deep  vessels. — ^The  deep  lymphatic  vessels  of  the  upper  extremity  drain 
the  joint  capsules,  periosteum,  tendons,  and  (if  the  recent  work  of  Aagaard  is 


722 


THE  LYMPHATIC  SYSTEM 


correct)  the  muscles.  They  collect  into  vessels  which,  in  general,  accompany  the 
arteries,  in  the  forearm,  the  radial,  ulnar,  anterior  and  posterior  interosseous,  and 
in  the  arm  the  brachial.     Above  the  elbow  they  are  joined  by  numerous  super- 

FiG.  567. — The  Lymphatics  op  the  Forearm.     (After  Toldt,  "Atlas  of  Human 
Anatomy,"  Rebman,  London  and  New  York.) 


Brachial  fabcia 


Brachial  artery  and  veins 


^Superficial  lymphatic  vessels 


Superficial  cubital  lymph-nodes 


Tendon  of  the  biceps  muscle 


■^  Deep  cubital  lymph-nodes 


Deep  lymphatic  vessels 


AntibracMal  fascia—  - 


■  Superficial  lymphatic  vessels 


Lymph-vessels 


of  the  hand     fj  /  /  i/  ^^  ^      ^ 


Lymph-vessels  of  the  thumb  *^ 


Lymph-vessels  of  the  finger 


Lymphatic  network 
---  Superficial  volar  arch 

^---  Palmar  aponeurosis 
—  Lymphatic  network 

Subcutaneous  fat  of  the  finger 


ficiall  lymphatic  vessels  including  efferents  from  the  superficial  cubital  nodes. 
Along  their  course  in  the  forearm  are  intercalated  small  nodes  (pin-head  size), 
radial,  ulnar,  anterior  and  posterior  interosseous  (Mouchet)  and  deep  cubital;  and, 
in  the  arm,  small  brachial  intercalated  nodes.  The  deep  vessels  in  the  main  enter 
the  brachial  group  of  axillary  lymph-glands  which  lie  behind  the  large  vessels 


LYMPHATICS  OF  THE  MAMMARY  GLAND  723 

and  nerves,  the  efferents  from  which  nodes  pass  either  into  the  lower  deep  cer- 
vical lymph-nodes  or  directly  into  the  subclavian  trunk. 

The  lymphatics  of  the  shoulder-joint  have  recently  been  described  by  Tananesco.  He 
finds  a  ring  of  lymphatics  in  the  joint  capsule,  whose  efferents,  in  the  main,  following  the  arteries, 
run  to  the  central  and  subclavian  groups  of  axillary  nodes. 

C.  THE  LYMPHATICS  OF  THE  THORAX 

The  lymphatics  of  the  thorax  will  be  considered  under  the  following  divisions: 
the  superficial  vessels,  the  deep  nodes,  and  the  deep  vessels. 

1.  THE  SUPERFICIAL  LYMPHATIC  VESSELS  OF  THE  THORAX 

The  superficial  lymphatics  of  the  thorax  pass  almost  exclusively  to  the  axillary 
nodes,  and  may  be  regarded  as  forming  three  sets,  a  ventral,  a  lateral,  and  a 
dorsal.  The  ventral  set  drains  the  thoracic  integument,  which  extends  form 
the  median  line  and  the  clavicle  over  to  the  lateral  border  of  the  chest,  and  includes 
the  vessels  of  the  mammary  gland,  which  will,  however,  be  described  separately. 
The  majority  of  the  vessels  from  this  area  end  in  the  anterior  pectoral  group  of 
axillary  nodes,  a  few,  which  arise  beneath  the  clavicle,  passing  to  the  supra- 
clavicular nodes,  and  a  few  perforating  the  intercostal  spaces  and  ending  in  the 
chain  of  nodes  along  the  internal  mammary  artery. 

It  has  been  shown  that  an  injection  into  the  subcutaneous  plexus  near  the  median  line 
passes  to  the  opposite  side,  and  that,  in  addition  to  the  anastomosis  between  the  networks  of 
the  two  sides  of  the  thorax  which  this  result  manifests,  there  may  also  be  a  few  collecting  trunks 
crossing  the  median  line,  and,  furthermore,  anastomoses  occur  between  the  superficial  networks 
of  the  anterior  thoracic  and  abdominal  walls.  Thus  while  the  main  channel  of  lymphatic 
drainage  is  through  the  axiUa,  there  are  minor  accessory  channels  to  (1)  the  supraclavicular 
nodes,  (2)  to  the  axilla  of  the  opposite  side,  (3)  to  the  internal  mammary  chain,  and  (4)  in  iso- 
lated cases  even  to  the  inguinal  nodes.  These  accessory  channels  may  become  more  open  in 
cases  of  obstruction  to  the  main  channel. 

The  lateral  set  of  superficial  thoracic  lymphatics  is  much  less  extensive  than 
the  anterior,  and  its  collecting  vessels  pass  upward  to  open  into  the  posterior 
pectoral  group  of  axillary  nodes. 

The  dorsal  set,  which  occupies  the  subcutaneous  tissue  of  the  dorsal  thoracic 
wall,  sends  its  vessels  to  the  subscapular  group  of  axillary  nodes. 

The  Lymphatics  of  the  Mammary  Gland  (Figs  566,  568) 

The  lymphatic  network  over  the  peripheral  portions  of  the  mammary  gland  is 
like  that  of  the  rest  of  the  thoracic  wall.  In  the  areola,  however,  the  capillaries 
are  far  more  abundant,  forming  a  double  subareolar  plexus.  The  superficial 
plexus  is  so  dense  that  its  meshes  can  be  seen  only  with  a  lens.  The  deeper  plexus 
not  only  drains  the  superficial  plexus,  but  receives  the  vessels  from  the  mammary 
gland  itself,  and  from  it  arise  two  large  trunks,  one  from  the  inferior  and  one  from 
the  superior  part  of  the  plexus.  These  two  vessels  pass  to  one  or  two  of  the  nodes 
belonging  to  the  anterior  pectoral  group  of  axillary  nodes.  In  addition  there  may 
be — (1)  one  or  two  vessels  passing  to  the  nodes  along  the  axillary  artery;  (2)  in 
rare  cases  a  vessel  passing  directly  to  the  subclavian  nodes.  There  is  also  a  defi- 
nite channel  from  the  medial  margin  of  the  gland  to  the  internal  mammary  nodes, 
the  ducts  following  the  perforating  branches  of  the  internal  mammary  vessels, 
and  it  may  be  noted  that  the  crossed  anastomosis  and  that  with  the  abdominal 
network,  mentioned  in  connection  with  the  superficial  thoracic  vessels,  may,  on 
occasions,  serve  as  channels  for  the  mammarj^  drainage. 

There  is  also  clinical  evidence  indicating  that  lymphatic  vessels  from  the 
lower  and  medial  aspect  of  the  mammary  gland  may  pass  through  the  abdom- 
inal wall  in  the  angle  between  the  xiphoid  process  and  the  costal  cartilages, 
establishing  a  communication  with  the  lymphatics  of  the  abdomen  in  the 
diaphragmatic  region. 

Lymphatics  of  the  thoracic  muscles. — The  recent  studies  of  Aagaard  make  it  probable 
that  muscles  are  provided  with  lymphatics.  Whether  his  findings  will  be  substantiated  or 
not,  however,  it  is  unquestioned  that  lymphatic  vessels  course  through  the  pectoral  muscles — 
some  passing  to  the  axillary,  others  to  the  subclavian,  and  still  others  to  the  internal  mammary 
chain  of  nodes.  This  would  suffice  to  explain  the  fact  that  cancer  of  the  breast  may  extend 
into  and  through  the  pectoral  muscles. 


724 


THE  LYMPHATIC  SYSTEM 


2.  THE  DEEP  LYMPHATIC  NODES  OF  THE  THORAX 

The  lymphatic  nodes  of  the  thoracic  cavity  may  be  divided  into  the  parietal 
and  the  visceral.  The  parietal  nodes  are  arranged  in  two  sets,  the  internal 
mammary  chain  and  the  intercostal  nodes  (fig.  570) .  Along  the  internal  mam- 
mary artery  are  from  four  to  sLx  small  nodes,  [Igl.  sternales]  which  receive  ducts 
from  the  anterior  thoracic  and  the  upper  part  of  the  abdominal  walls,  from  the 
anterior  diaphragmatic  nodes  which  drain  the  liver,  and  from  the  medial  edge  of 
the  mammary  gland.  The  efferent  vessels  usually  unite  with  the  vessels  of  the 
anterior  mediastinal  and  bronchial  nodes,  to  form  the  broncho-mediastinal  trunk, 
which  may  join  the  thoracic  duct  on  the  left  and  the  jugular  or  subclavian  trunk 
on  the  right  or  may  empty  separately  into  the  subclavian  vein  on  both  sides. 


Fig.  568.- 


-Lymphatics  of  the  Subareolar  Plexus  of  the  Breast.     (After  Sappey.) 

Vessels  from  network 


Lobuleof  gland, 
uninjected 


Subareolar 
network 
Vessel  from   ,  .     ( 
network        n   ^ 


Lobule  of  gland 
uninjected 

Superficial    *:i— 
network 


Vessels  from  network 


The  intercostal  nodes  [Igl.  intercostales]  lie  along  the  intercostal  vessels,  near 
the  heads  of  the  ribs.  There  are  usually  one  or  two  in  each  space,  and  occasiona,lly 
a  node  is  placed  where  the  perforating  lateral  artery  is  given  off.  They  receive 
afferents  from  the  deeper  part  of  the  thoracic  wall  and  costal  pleura.  Their 
efferents  enter  the  thoracic  duct,  those  from  the  nodes  of  the  lower  four  or  five 
interspaces  uniting  usually  to  form  a  common  duct  on  each  side,  but  more  marked 
on  the  left  side,  which  descends  to  the  receptaculum  chyh. 

The  efferent  lymph-vessels  from  the  upper  intercostal  nodes  often  unite  into  common 
trunks  which  drain  several  interspaces,  and  which  may  pass  through  a  large  gland  near  the 
thoracic  duct  before  emptying  into  it.  Occasionally  such  collecting  vessels  from  the  right  side 
cross  the  mid-Une  behind  the  aorta  to  reach  a  large  gland  to  the  left  of  the  aorta. 

The  visceral  nodes  of  the  thorax  are  arranged  in  three  groups : — ■ 
1.  The  anterior  mediastinal  nodes  [Igl.  mediastinales  anteriores]  are  situated, 
as  their  name  indicates,  in  the  anterior  mediastinum,  and  are  arranged  in  an  upper 
and  a  lower  set.  The  upper  set  is  situated  upon  the  anterior  surface  of  the  arch 
of  the  aorta,  and  consists  of  eight  or  ten  nodes,  which  receive  afferents  from  the 
pericardium  and  the  remains  of  the  thymus  gland.  Their  efferent  vessels  pass 
upward  to  join  the  broncho-mediastinal  trunk.     The  lower  set  consists  of  from 


LYMPH-VESSELS  OF  THE  THORAX 


725 


three  to  six  nodes,  situated  in  the  lower  part  of  the  mediastinum.  They  receive 
afferent  ducts  from  the  diaphragm,  hence  they  are  sometimes  termed  the  dia- 
phragmatic nodes,  and  also  from  the  upper  surface  of  the  liver.  Their  efferents 
pass  upward  to  open  into  the  upper  anterior  mediastinal  nodes. 

2.  The  posterior  mediastinal  nodes  [Igl.  mediastinales  posteriores]  eight  or  ten 
in  number,  are  situated  along  the  thoracic  aorta,  and  receive  vessels  from  the  medi- 
astinal tissue  and  from  the  thoracic  portion  of  the  oesophagus.  Their  efferents 
open  directly  into  the  thoracic  duct. 

3.  The  bronchial  nodes  [Igl.  bronchiales]  form  an  extensive  group  lying  along 
the  sides  of  the  lower  part  of  the  trachea,  and  along  the  bronchi  as  far  as  the  hilus 


Fig.  569. — The  Tracheal  and  Bronchial  Nodes.     (Sukiennikow.) 


Inferior  laryngeal  nerve 


—  Tracheal  nodes 


Trachea 

Inierior  laryngeal  nerve 


Tracheo-bronchial  node 


Bronchial  nodes 
Connecting  chain 


Pulmonary  nodes 


Pulmonary  nodes 


Connecting  chain 
Pulmonary  nodes 


of  each  lung,  those  lying  in  the  hilus  being  termed  the  pulmonary  nodes,  and 
others,  according  to  their  position,  lateral  tracheo-bronchial,  inferior  tracheo- 
bronchial (nodes  of  the  bifurcation)  and  tracheal  (paratracheal).  Thej''  receive 
the  drainage  of  the  lower  part  of  the  trachea,  the  bronchi,  the  lungs,  part  of  the 
oesophagus,  and,  to  a  small  extent,  the  heart.  Thek  efferent  vessels  unite  with 
those  from  the  upper  anterior  mediastinal  and  internal  mammarj^  nodes  to  form 
the  broncho-mediastinal  trunk. 


3.  THE  DEEP  LYMPHATIC  VESSELS  OF  THE  THORAX 

In  following  the  deep  lymphatics  of  the  thorax  the  course  of  development  will 
be  followed  in  describing  first  the  thoracic  duct  and  right  lymphatic  ducts, 
second  the  parietal  vessels,  and  third  the  visceral  vessels. 


726 


THE  LYMPHATIC  SYSTEM 


The  Thoracic  Duct 

The  thoracic  duct  [ductus  thoracicus]  (fig.  570),  which  is  the  main  collecting 
duct  of  the  lymphatic  system,  extends  from  the  second  lumbar  vertebra  along 
the  spinal  column  and  course  of  the  aorta  to  the  junction  of  the  left  internal  jugular 
and  subclavian  veins.  It  receives  all  the  Ij^mphatics  below  the  diaphragm,  and 
the  deep  lymphatics  from  the  dorsal  half  of  the  chest  wall;  and  also,  when  joined, 
near  its  cephalic  end,  by  the  left  broncho-mediastinal,  subclavian  and  jugular 
trunks,  from  the  remainder  of  the  left  half  of  the  body,  above  the  diaphragm. 
At  the  caudal  end  the  duct  is  formed  usually  by  the  union  of  three  collecting 
ducts,  one  from  each  of  the  lumbar  groups  of  nodes,  and  an  unpaired  intestinal 

Fig.  570. — The   Thokacic   Duct.     (After    Toldt,   "Atlas   of   Human  Anatomy,"  Rebman, 
London  and  New  York.) 

Thoracic  duct 

Internal  jugular  vein 
Jugular  trunk 
Subclavian  trunk 
Subclavian  vein 

Right  innominate  vein —  >^~.-^.n,^,  .— ,.^^^^_^  —  ^,  .. 

Axillary  lymph  -nodes 


Intercostal  lymph-nodes  ■<!_/ 


—Thoracic  duct 


Crus  of  diaphragm 

Lumbar  trunks,  right  and         

left  "JY"^' 

Lumbar  lymphatic  plexus  — 


Jf| — Hemiazygos  vein 


; Cisterna    chyli     (recepta 

%X Intestinal  trunks 


\^     i\— =Lumbar  nodes 


trunk.  At  its  origin  then  is  usu  ilh  i  dil  i1(  d  poition  known  as  the  receptaculum 
[cisterna  chyli].  This  usually  endh  opposite  the  bodj^  of  the  eleventh  thoracic 
vertebra,  and  from  here  on  the  duct  is  from  4  to  6  mm.  in  diameter,  until  near  its 
termination,  where  it  is  again  wider. 

In  its  cadual  part,  the  duct  lies  dorsal  to  the  aorta  in  the  median  line;  it  passes 
through  the  aortic  opening  in  the  diaphragm,  and  then  inclines  to  the  right  and 
passes  upward  to  about  the  fourth,  fifth,  or  sixth  thoracic  vertebra,  when  it 
bends  to  the  left  and  passes,  continuing  upward,  over  the  apex  of  the  left  lung 
and  the  left  subclavian  artery,  and  in  front  of  the  root  of  the  left  vertebral  artery 
and  vein,  and  then  curves  downward  to  open  into  the  left  subclavian  vein,  close 
to  its  junction  with  the  left  internal  jugular.  The  duct  runs  in  the  wall  of  the 
vein  a  short  distance  before  ending. 

Variations. — There  is  a  wide  range  of  variation  from  this  usual  course.  The  duct  is  fre- 
quently double  throughout  a  part  of  its  course,  the  two  branches  being  connected  by  cross 
anastomoses,  and  finally  uniting  into  a  single  trunk  before  joining  the  veins.     It  may  be 


THE  THORACIC  DUCT 


727 


multiple,  or  a  single  trunk  may  pass  in  front  of  the  aorta  instead  of  behind.  In  a  few  instances 
it  has  been  found  emptying  into  the  right  instead  of  the  left  subclavian  vein.  There  is  also  a 
wide  range  of  variation  in  the  height  to  which  the  duct  ascends  in  the  neck  before  curving  down- 
ward to  the  vein.  As  regards  the  termination  of  the  thoracic  duct,  variations  are  also  frequent; 
it  may  bifurcate  and  end  as  two  ducts.  It  often  connects  with  the  lowermost  part  of  the 
internal  jugular,  or  the  beginning  of  the  innominate.  According  to  Henle,  there  is  one  un- 
doubted case  reported  of  a  thoracic  duct  ending  in  the  azygos  vein  near  the  sixth  thoracic 
vertebra,  the  duct  being  obliterated  above  this  point.  At  the  terminal  bend  the  thoracic 
duct  receives  the  jugular  trunk  from  the  neck;  it  may  also  receive  the  subclavian  and  the  broncho- 
mediastinal trunks,  but  it  is  more  usual  for  these  last  two  to  open  either  separately  or  together 
into  the  subclavian. 

Variations  are  extremely  numerous  in  the  region  of  the  receptaculum.  Severa  lobservers 
state  that,  in  the  majority  of  cases  in  man,  no  definite  receptaculum  exists.  Bartels  found  one 
in  only  25  per  cent,  of  the  cases  studied.  Instead,  there  is  present  a  widening  of  each  of  the  two 
lumbar  trunks,  with  several  anastomoses  between  them  (55  per  cent.,  Bartels),  or  a  widening 
of  these  two  stems  without  anastomosis  (5  per  cent.),  or  a  much  elongated  widening  arising 

Pig.  571. — Abdominal  Poetion  of  the  Thoracic  Duct.     (Poirier  and  Cun6o.) 


from  the  growing  together  of  the  two  lumbar  trunks  (10  per  cent.).  In  eases  where  the  lumbar 
trunks  remain  separate,  the  intestinal  trunk  joins  the  left  one. 

Development. — While  the  exact  mode  of  its  development  is  still  in  dispute,  enough  is 
agreed  upon  by  the  various  investigators  to  explain  most  of  the  variations  in  the  thoracic  duct. 
In  brief,  it  is  known  that  the  lymphatics  start  in  the  neck  as  a  variable  number  of  outgrowths 
from  the  veins  in  the  region  of  the  junction  between  the  later  internal  jugular  and  subclavian 
veins.  A  variable  number  of  these  connections  disappear,  while  the  various  combinations  of 
one,  two,  three  or  four  which  are  retained  furnish  the  numerous  variations  in  number  and 
position  of  the  ducts  which  empty  into  the  vein  in  the  adult.  Thus  the  thoracic  duct  may 
have  one,  two  or  even  three  openings  into  the  veins,  while  the  jugular,  subclavian  and  broncho- 
mediastinal trunks  may  join  the  thoracic  duct  or  may  enter  the  veins  separately  or  in  various 
combinations. 

It  is  also  known  that  the  upper  part  of  the  thoracic  duct  is  at  first  bilateral,  being  formed 
by  outgrowths  from  the  primary  plexus,  which  meet  in  a  common  plexus  around  the  aorta. 
Normally  the  right  portion  of  these  connections  disappears,  so  that  the  thoracic  duct  empties  into 
the  left  subclavian  vein.  In  exceptional  cases,  where  it  opens  into  the  right  subclavian  vein, 
there  have  also  been  present  variations  in  the  large  right  arterial  trunk.  These  conditions 
in  all  probability  at  a  certain  stage  in  development  produced  a  greater  resistance  to  the  lymph 
stream  in  the  left  than  in  the  right  vessel  causing  it  to  become  obliterated  so  that  the  right 
instead  of  the  left  became  the  permanent  ending  of  the  duct. 


728 


THE  LYMPHATIC  SYSTEM 


Most  of  the  other  variations — the  frequent  presence  of  longer  or  shorter  doublings  of  the 
duct  with  anastomoses  between  the  two  parts,  the  numerous  variations  in  the  region  of  the 
receptaculum  chyli — are  easily  explained  by  the  fact  that  the  duct  and  receptaculum  pass 
through  a  stage  in  development  in  which  they  form  richly  anastomosing  plexuses  around  the 
aorta. 

The  Right  Tbbminal  Collecting  Ducts 

On  the  right  side  the  jugular,  subclavian,  and  broncho-mediastinal  trunks 
usually  open  separately  into  the  subclavian  vein,  the  orifices  of  the  first  two 
being  near  together.  When  the  jugular  and  subclavian  trunks  unite,  the  com- 
mon duct  is  termed  the  right  lymphatic  duct;  this  is  a  rare  form,  and  it  is  still 
more  rare  for  the  three  ducts  to  unite  to  form  a  common  stem  (fig.  572).  These 
variations  have  the  same  explanation,  embryologically,  as  was  given  for  the 
corresponding  variations  on  the  left  side. 

Fig.  572. — Tekminal  Collecting  Ducts  on  the  Right  Side.     (Poirier  and  Cun^o.) 

V) 


Jugular  trunk 
Subclavian  trunk 


Node  of  internal  mam 
mary  chain 


Right  lymphatic  duct 


Subclavian  trunk 


Right  lymphatic  duct 
Broncho-mediastinal  trunk 


Node  of  internal  mammary  chain 


The  Deep  Lymphatic  Vessels 

As  with  the  nodes,  the  deep  lymphatic  vessels  of  the  thorax  may  be  divided 
into  a  parietal  and  a  visceral  group.  To  the  former  group  may  be  assigned  the 
lymphatics  of  the  intercostal  spaces  and  those  of  the  diaphragm. 

The  intercostal  lymphatics  form  plexuses  in  each  intercostal  space,  which 
receive  lymph  from  the  periosteum  of  the  ribs  and  from  the  parietal  pleura,  and 
from  which  the  drainage  is  either  ventral  or  dorsal.  From  the  dorsal  half  of 
each  space  the  drainage  is  to  the  intercostal  nodes,  while  from  the  ventral  half  it  is 
toward  the  internal  mammary  nodes. 

The  lymphatics  of  the  diaphragm. — There  is  an  exceedingly  rich  plexus  of 
capillaries  both  on  the  pleural  and  on  the  abdominal  surface  of  the  diaphragm, 
especially  in  the  region  of  the  central  tendon,  these  plexuses  lying  in  the  subserous 
layers  and  being  freely  connected  by  vessels  which  perforate  the  muscle.  There 
is,  however,  only  slight  communication  between  the  plexuses  of  the  right  and  left 
sides  of  the  diaphragm.  The  vessels  lie  between  the  coarse  muscle  bundles, 
forming  a  very  characteristic  picture,  in  which  the  lymphatics  stream  outward 
radially,  like  the  spokes  of  a  wheel.  The  collecting  vessels  empty  into  three 
groups  of  small  nodes  on  the  convex  surface.  The  ventral  group  lies  ventral  to 
the  central  tendon.     Two  or  three  nodes  in  the  centre  of  this  group  receive 


LYMPHATICS  OF  THE  LUNGS 


729 


afferents  from  the  liver  and  none  from  the  diaphragm,  but  the  rest  receive 
vessels  from  the  ventral  sm'face  of  the  diaphragm  and  the  efferents  of  all  pass  to 
the  lower  set  of  anterior  mediastinal  nodes. 

The  middle  group  consists  of  from  three  to  six  nodes,  which  lie,  on  the  left  side, 
near  the  point  where  the  phrenic  nerve  enters  the  diaphragm;  on  the  right  side, 
near  the  vena  cava. 

The  dorsal  group  of  four  or  five  nodes  is  placed  between  the  pillars  of  the 
diaphragm.  The  vessels  from  the  lateral  and  dorsal  groups  pass  to  the  posterior 
mediastinal  nodes,  and  also  to  the  upper  coeliac  nodes,  which  likewise  receive  the 
drainage  from  the  dorsal  part  of  the  abdominal  surface  of  the  diaphragm. 


i 


Fig.  573. — The  Lymphatics  op  the  (Esophagus.     (After  Sakata.) 


Inferior  deep  cervicl  nodes 

Deep  cervical  node 


^Ilecurrent  nerve 


'Bronchial  node 


To  the  visceral  group  of  thoracic  lymphatics  belong  the  vessels  of  the  thymus, 
the  lungs,  the  heart,  and  the  oesophagus. 

The  lymphatics  of  the  thymus  drain,  according  to  Severeanu,  into  three  sets 
of  glands,  an  anterior,  a  ventral  and  a  dorsal  group.  The  anterior  set,  one  gland 
on  each  side,  lies  lateral  to  the  cephalic  end  of  the  thymus,  and  drains  into  the 
jugular  or  subclavian  trunlc.  The  ventral  set  includes  4-6  of  the  anterior  medi- 
astinal lymph-glands.  The  dorsal  set,  2  on  each  side,  is  made  up  of  anterior 
mediastinal  glands  lying  between  the  thymus  and  the  pericardium. 

The  lymphatics  of  the  lungs  are  arranged  in  two  sets.  A  deep  set  takes  its 
origin  in  plexuses  which  surround  the  terminal  bronchi  and  follows  the  course  of 
the  bronchi,  the  pulmonar.y  artery,  and  the  pulmonary  vein  to  the  pulmonary 
nodes  at  the  hilus,  whence  the  stream  passes  to  the  main  bronchial  nodes  (fig.  569), 
especially  to  those  situated  in  the  angle  formed  by  the  bifurcation  of  the  trachea, 


I 


730  THE  LYMPHATIC  SYSTEM 

and  thence  to  the  broncho-mediastinal  trunk.     A  superficial  set  arises  in  a  network 
situated  upon  the  surface  of  the  lung  beneath  the  visceral  layer  of  the  pleura. 

According  to  Miller,  who  has  studied  the  lymphatics  of  lung  and  pleura  most  carefully  in 
dog  and  man,  the  only  communications  between  the  lymphatics  of  the  pleura  and  the  deep  lym- 
phatics oociu-  around  the  veins  which  reach  the  pleural  surface.  These  vessels  are  provided 
with  valves  so  that  the  lymph  stream  passes,  in  them,  toward  the  pleural  surface.  The  collect- 
ing stems  of  the  subpleural  lymphatics  pass  independently  to  the  pulmonary  nodes. 

Lymphatics  of  the  heart. — The  superficial  (subepicardial)  tymphatics  of  the 
heart  collect  to  two  main  stems  which  accompany  the  main  coronary  vessels. 
The  right  stem  accompanies  the  right  coronary  artery  to  its  origin,  passes  on 
over  the  arch  of  the  aorta  and  empties  into  one  of  the  anterior  mediastinal  lymph- 
nodes.  The  left  stem,  formed  by  two  stems  accompanying  the  circumflex  and 
anterior  descending  branches  of  the  coronary  vein,  passes  behind  the  arch  of  the 
aorta  to  an  anterior  mediastinal  lymph-gland.  Two  small  subepicardial  inter- 
calated nodes  have  been  described  along  these  trunks. 

Subendocardial  lymphatics  have  been  described  in  animals,  which  connect 
by  vessels  passing  through  the  musculature  with  the  superficial  lymphatics. 

Parenchymatous  lymphatics  have  recently  been  demonstrated  by  Bock. 
The  course  of  their  efferent  vessels  has  not  yet  been  described. 

The  lymphatic  vessels  of  the  oesophagus,  which  will  here  be  considered 
throughout  its  entire  extent,  cervical  as  well  as  thoracic,  are  arranged  in  two 
plexuses,  one  of  which  occurs  in  the  mucosa  and  the  other  in  the  submucosa.  The 
collecting  vessels  arising  from  the  plexuses  may  be  divided  into  three  sets,  of 
which  the  uppermost  pass  to  outlying  nodes  belonging  to  the  deep  cervical  chain, 
those  from  the  thoracic  portion  of  the  tube  pass  to  the  bronchial  and  posterior 
mediastinal  nodes,  while  those  from  its  lowermost  part  pass  to  the  superior  gastric 
nodes  (fig.  573). 

D.  THE  LYMPHATICS  OF  THE  ABDOMEN  AND  PELVIS 

In  the  following  section  there  will  be  described  successively  the  lymphatic 
nodes  of  the  abdomen  and  pelvis,  the  lymphatic  vessels  of  the  abdominal  walls, 
and  the  visceral  lymphatic  vessels. 

1.  The  Lymphatic  Nodes  of  the  Abdomen  and  Pelvis 

The  lymphatics  which  connect  directly  with  the  thoracic  duct,  though 
complicated,  may  be  described  briefly  by  saying  that  they  follow  the  aorta  and  its 
branches.  In  the  abdomen  there  are  four  main  chains  along  the  aorta — (1)  the 
left  lumbar  chain;  (2)  the  right  lumbar  chain;  (3)  the  pre-aortic  chain;  and  (4) 
the  post-aortic  chain. 

The  right  and  left  lumbar  nodes  [Igl.  lumbales],  form  an  almost  continuous 
chain  along  the  abdominal  aorta,  resting  upon  the  psoas  muscles,  some  of  those 
on  the  right  side  being  ventral  and  some  dorsal  to  the  inferior  vena  cava.  They 
receive: — (1)  the  efferent  lymphatics  of  the  common  ihac  nodes,  and  hence  drain 
the  leg  and  external  genitaha;  (2)  the  efferent  lymphatics  that  follow  the  lumbar 
arteries  and  hence  drain  the  abdominal  AvaU;  (3)  the  efferents  that  follow  the 
paired  visceral  aortic  branches,  namely,  those  from  the  kidneys,  supra-renal,  and 
internal  reproductive  organs.  On  the  right  side,  the  lymphatics  from  the  re- 
productive organs  pass  to  the  nodes  ventral  to  the  vena  cava — those  of  the 
abdominal  walls  pass  to  the  dorsal  set,  while  those  from  the  kidney  pass  to  both 
sets. 

The  efferent  vessels  of  the  lower  lumbar  nodes  pass  to  higher  ones  and  so  on  up 
the  chain,  the  vessels  from  the  uppermost  nodes  uniting  to  form  a  single  lumbar 
trunk  on  each  side.  These  trunks  pass  to  the  thoracic  duct,  forming  two  of  the 
so-called  trunks  of  origin  of  that  vessel  (fig.  571). 

The  pre-aortic  nodes  [lymphoglandulte  coeliacEe]  are  arranged  in  three  groups 
at  the  root  of  each  of  the  three  unpaired  visceral  branches  of  the  aorta — the 
cceliac,  the  superior  mesenteric,  and  the  inferior  mesenteric  arteries.  The 
cceliac  nodes  are  from  one  to  three  in  number,  and  are  in  reality  parts  of  chains  of 
nodes  extending  along  the  branches  of  the  artery  and  constituting  the  hepatic, 
gastric,  and  splenic  nodes.  They  drain  the  stomach,  duodenum,  liver,  pancreas, 
and  spleen. 


LYMPHATICS  OF  ABDOMEN 


731 


The  superior  mesenteric  group  is  larger,  and  is  continuous  with  the  mesenteric 
nodes  lying  in  the  root  of  the  mesentery.  This  group  drains  the  remainder  of  the 
small  intestine,  the  CEecum  and  appendix,  the  ascending  and  transverse  colons,  and 
the  pancreas. 

The  inferior  mesenteric  group  usually  has  two  nodes,  one  on  either  side  of  the 
artery.  It  drains  the  rectum  and  descending  and  sigmoid  colons.  All  the  nodes 
in  the  mesentery  and  intestinal  walls  may  be  considered  as  outlying  nodes  of  the 
pre-aortic  group.     They  will  be  studied  in  connection  with  the  visceral  lymphatics. 

The  inferior  mesenteric  nodes  drain  into  the  neighbouring  lumbar  nodes,  and 
also  directly  upward  to  the  superior  mesenteric  nodes,  and  then  again  to  the 
cceliac  nodes.  From  the  last  a  single  stem,  the  intestinal  trunk,  arises  and  passes 
either  to  the  right  lumbar  trunk  or  directly  to  the  thoracic  duct,  forming  the 
third  of  the  so-called  trunks  of  origin  of  the  duct. 


Fig.   574. — Abdominal  Acetic  Nodes  in  the  New-bokn.     (Poirier  and  Charpy.) 

■Suprarenal  gland 

Inferior  phrenic 
artery 

esen-         /      \ \0  \f   \i\^\^ /  I  V 

;ry       ■■■■/—     s—  u^  \^^^^)_^it^    HI  \ 

Left  spermatic 


Right  aortic  node 


I,eft  aortic  nodes 


Hypogastric  artery 


The  post -aortic  nodes  are  not  true  regional  nodes,  but  receive  vessels  from  the 
lumbar  and  pre-aortic  chains. 

Below  the  bifurcation  of  the  aorta  there  are  three  large  chains,  the  common 
iliac,  the  external  iliac,  and  the  hypogastric. 

The  common  iliac  nodes  [Igl.  iliacse],  are  in  three  groups  (fig.  575).  The 
external  set  consists  of  about  two  nodes,  which  are  in  reality  a  part  of  a  continuous 
chain  extending  along  the  side  of  the  aorta,  common  iliac,  and  external  iliac 
arteries.  A  second  set  of  two  to  four  posterior  nodes  lies  behind  the  artery. 
These  two  groups  receive  the  efferent  vessels  of  the  external  iliac  and  hypogastric 
chains.  The  internal  set  usually  consists  of  two  nodes  which  rest  upon  the 
promontory  of  the  sacrum.  They  receive  vessels  from  the  sacral  nodes,  together 
with  most  of  those  from  the  pelvic  viscera,  namely,  from  the  prostate,  neck  of 
the  bladder,  neck  of  the  uterus,  the  vagina,  and  part  of  the  rectum.  The  efferent 
lymphatic  vessels  of  the  common  iliac  nodes  pass  to  the  lumbar  chain. 


732 


THE  LYMPHATIC  SYSTEM 


External  iliac  nodes. — These  are  likewise  in  three  sets — -external,  middle,  and 
internal.  The  external  chain  consists  of  three  or  four  nodes,  the  lowest  one  being 
behind  the  crural  arch.  They  receive: — (1)  some  of  the  vessels  of  the  superficial 
and  deep  inguinal  nodes;  (2)  vessels  from  the  glans  or  chtoris,  which  come  tlirough 
the  inguinal  canal;  (3)  vessels  from  the  part  of  the  abdominal  wall  supplied  by  the 
deep  epigastric  and  deep  circumflex  arteries,  along  which  there  may  be  a  few 
outlying  nodes — the  epigastric  nodes. 

The  middle  chain  consists  of  two  or  three  nodes  behind  the  artery.  When 
there  are  three,  the  lowest  is  likewise  near  the  crural  arch.  It  receives  vessels 
from  the  bladder,  prostate,  neck  of  the  uterus,  and  upper  portion  of  the  vagina. 
The  internal  chain  consists  of  three  or  four  nodes,  and  is  the  continuation  of  the 
deep  inguinal  nodes.  Its  lowest  nodes  are  likewise  near  the  femoral  ring,  while  the 
next  node  is  large  and  constant,  and  usually  lies  within  the  pelvis.     This  chain 


Fig.  575. — Ilio-pelvic  Nodes.     (Cunto  and  Marcille.) 


Left  aortic  node 


Right  aortic  node 


Node  of  the  pro-       i  ^  i  i,  .^ ,,  ,. 


Obturator  nerve 

Obturator  artery 
External  iliac  node 
Retrocrural  node 
Obturator  node 


Hypogastric  artery 


receives  many  vessels: — (1)  from  the  superficial  and  deep  inguinal  nodes;  (2) 
from  the  glans  and  clitoris  through  the  femoral  canal;  (3)  from  the  abdominal 
wall;  (4)  from  the  neighbourhood  of  the  obturator  vessels;  (5)  from  the  neck  of 
the  bladder,  the  prostate,  and  membranous  part  of  the  urethra;  (6)  from  the 
hypogastric  chain. 

Thus,  to  sum  up  the  nodes  of  the  external  iliac  chains: — they  are  a  part  of  a 
chain  which  includes  the  lumbar,  common  iliac,  external  iliac,  and  inguinal  nodes. 
It  will  be  noted  that  this  extensive  chain  stops,  for  the  most  part,  with  the  deep 
inguinal  group.  The  external  iliac  nodes  receive  the  efferents  of  the  superficial 
and  deep  inguinal  nodes;  the  middle  and  internal  groups  receive  vessels  from  the 
pelvis.     The  efferent  vessels  of  all  the  nodes  in  the  chain  pass  to  the  higher  nodes. 

The  hypogastric  nodes  [Igl.  hypogastricse]. — ^These  nodes  are  in  groups  near 
the  origin  of  the  branches  of  the  hypogastric  (internal  iliac)  artery.  Thus  they 
occur  near  the  origin  of  the  obturator,  the  uterine,  or  prostatic,  the  trunk  of  the 


LYMPHATICS  OF  ALIMENTARY  TRACT  733 

inferior  gluteal  (sciatic)  and  pudic,  the  middle  hjemorrhoidal,  and  the  lateral 
sacral  arteries.  All  the  nodes  are  beneath  the  pelvic  fascia,  and  are  connected  by- 
numerous  anastomoses.  They  receive  lymphatics  from  the  structures  supplied 
by  the  corresponding  arteries,  namely,  from  the  pelvic  viscera,  the  perineum,  and 
the  posterior  surface  of  the  thigh  and  gluteal  region.  Their  efferent  vessels  pass 
partly  to  the  middle  group  of  the  common  iliac  nodes,  and  partly  to  the  posterior 
nodes  of  the  same  chain. 

The  sacral  nodes  [Igl.  sacrales]. — These  nodes,  5  or  6  in  number,  lie  in  the 
hollow  of  the  sacrum,  in  or  near  the  mid-line.  They  receive  afferent  vessels 
from  rectum  and  prostate,  and  their  efferents  pass  to  the  hypogastric  and  lumbar 
nodes. 

2.  THE  LYMPHATIC  VESSELS  OF  THE  ABDOMINAL  WALLS 

The  lymphatic  vessels  of  the  abdominal  walls  are  arranged  in  two  sets,  one  of 
which  is  subcutaneous  and  the  other  deep  or  aponeurotic.  The  subcutaneous 
vessels  form  a  rich  network  through  all  the  subcutaneous  tissue  of  the  abdomen, 
anastomosing  above  with  the  subcutaneous  plexus  of  the  thorax.  The  collecting 
vessels  converge  toward  the  inguinal  region,  those  from  the  posterior  wall 
curving  forward  along  the  crest  of  the  ilium,  and  they  all  terminate  in  the  super- 
ficial inguinal  nodes. 

The  deep  vessels  drain  along  three  principal  lines.  (1)  A  set  of  collecting 
vessels  follows  the  line  of  the  deep  epigastric  artery  to  terminate  in  the  lower 
external  iliac  nodes;  (2)  a  second  set  follows  the  deep  circumflex  iliac  vessels  to 
the  same  nodes;  and  (3)  a  third  set  follows  the  lumbar  vessels  to  terminate  in  the 
nodes  of  the  lumbar  chain.  A  group  of  small  epigastric  nodes,  which  may  be 
regarded  as  offsets  from  the  iliac  chain,  occur  on  the  lymph-vessels  which  ac- 
company the  deep  epigastric  vessels,  not  far  from  their  termination,  and  a 
second  less  constant  group  of  usually  three  small  umbilical  nodes  occurs  in  the 
vicinity  of  the  umbilicus  in  the  network  covering  the  posterior  layer  of  the 
sheath  of  the  rectus  abdominis  muscle. 

3.  THE  VISCERAL  LYMPHATIC  VESSELS  OF  THE  ABDOMEN  AND 

PELVIS 

The  lymphatics  to  the  viscera  follow  along  the  course  of  the  arteries.  At  the 
point  where  the  artery  of  an  organ  branches  from  the  aorta  there  is  a  group  of 
nodes  which  represents  the  main  regional  group,  and  a  second  chain  of  nodes 
extends  along  the  artery.  The  final  arrangement  of  nodes  and  ducts  varies  with 
each  organ. 

Though  the  lymphatics  follow  the  blood-vessels,  the  lymphatic  capillaries  in  the  regions  where 
their  relations  are  known  are  separated  from  the  vascular  capillaries;  in  the  intestinal  villi, 
for  example,  the  lymphatic  capillaries  are  central,  while  the  vascular  capillary  plexuses  are 
peripheral.  The  relation  of  the  lymphatic  capillaries  to  the  essential  structures  of  each  organ, 
that  is  to  say,  the  arrangement  of  the  lymphatics  in  the  absorbing  area,  is  not  yet  clear  in  many 
organs,  and  this  is  a  point  which  can  be  worked  out  by  tracing  the  development  and  gradual 
invasion  of  each  organ  by  the  lymphatics.  The  old  theory  of  the  origin  of  the  lymphatics 
from  the  tissue-spaces  made  this  problem  most  difficult  of  attack. 

In  almost  all  organs  there  is  a  peripheral  or  capsular  lymphatic  plexus,  which 
anastomoses  with  the  parietal  lymphatics,  these  anastomoses  being  particularly 
well  developed  in  the  case  of  the  liver.  In  addition  there  are  one  or  two  deep 
plexuses  in  the  great  majority  of  the  organs  which  drain  partly  directly  to  their 
regional  nodes  and  partly  by  way  of  the  peripheral  plexus. 

The  Lymphatics  of  the  Alimentary  Tract 

The  lymphatics  of  the  mouth,  pharynx,  and  oesophagus  have  already  been 
described  (pp.  715,  730).  In  general,  throughout  the  abdominal  part  of  the  ali- 
mentary canal,  the  distribution  of  nodes  is  as  follows: — (1)  There  are  primary 
regional  nodes  situated  at  the  roots  of  the  arteries  as  they  leave  the  aorta,  that  is 
to  say,  aroundthe  coeliac  and  the  superior  and  inferior  mesenteric  arteries;  these 


( 


734  THE  LYMPHATIC  SYSTEM 

drain  large  segments  of  the  intestine;  (2)  groups  of  definite  and  constant  nodes 
placed  along  the  branches  of  the  arteries  in  the  root  of  the  mesentery;  these  drain  a 
definite  smaller  segment  of  the  intestine;  (3)  chains  of  nodes  along  the  anasto- 
motic loops  of  the  arteries,  close  to  the  intestinal  wall ;  these  are  of  the  type  called 
'intercalated  nodes';  (4)  solitary  or  compound  follicles,  situated  within  the 
submucosa  or  capillary  zone  of  the  lymphatics. 

What  may  be  taken  as  the  typical  arrangement  of  the  lymphatic  vessels  in  the 
intestine  may  be  seen  in  fig.  576.  There  are  three  zones  in  which  the  capillary 
plexuses  are  spread  out,  namely,  in  the  subserosa,  the  submucosa,  and  the 
mucosa.  There  is  an  abundant  plexus  of  large  capillaries  just  beneath  the  serosa; 
inthe  submucosa  the  plexus  is  also  formed  by  large  capillaries,  while  the  mucosal 
plexus  is  finer.  The  lymph-foUicles  lie  in  the  zone  of  the  mucosal  plexus,  and  it  is 
from  this  that  the  central  chyle  vessels  of  the  villi  arise.  The  collecting  vessels 
are  formed  by  the  union  of  vessels  from  the  submucous  and  subserous  plexuses. 
They  traverse  the  three  sets  of  nodes  just  described. 

The  lymphatics  of  the  stomach  (fig.  577) . — The  stomach  differs  from  the  rest  of 
the  alimentary  canal  in  its  blood-supply  in  having  a  ventral  anastomotic  loop, 
namely,  that  along  the  lesser  curvature.  Along  this  loop  is  the  superior  gastric 
chain  [Igl.  gastricse  superiores]  of  nodes,  lying  between  the  folds  of  the  lesser 
omentum,  some  of  them  being  on  the  posterior  surface  of  the  stomach.  This  is 
the  most  important  group  of  nodes  draining  the  stomach,  and  it  has  been  shown 
that  the  lymph-vessels  from  the  pylorus  run  obliquely  across  the  stomach  to  the 
main  mass  of  nodes  near  the  cardia,  an  important  point  in  the  surgery  of  the 
pylorus.  The  efferent  vessels  of  the  chain  pass  to  the  coeliac  nodes.  The  vessels 
of  the  greater  curvature  pass  to  a  group  of  inferior  gastric  nodes  [Igl.  gastricae 
inferiores],  situated  along  the  right  gastro-epiploic  artery,  while  those  of  the  fundus 
follow  the  short  gastric  and  left  gastro-epiploic  vessels  to  the  nodes  which  lie 
along  the  splenic  artery,  both  these  sets  of  nodes  also  draining  to  the  coeliac  group. 
There  is  a  zone  half-way  between  the  lesser  and  greater  curvatures,  in  which  the 
lymphatics  are  scanty.  The  lymphatics  of  the  cardia  connect  with  those  of  the 
oesophagus,  and  the  mucosal  plexus  of  the  pylorus  is  continuous  with  that  of  the 
duodenum. 

The  lymphatics  of  the  duodenum. — The  lymphatics  of  the  duodenum  depart 
somewhat  from  the  type,  owing  to  its  relations  with  the  pancreas  and  the  bile- 
ducts.  The  collecting  vessels  end: — (1)  in  nodes  ventral  to  the  pancreas,  which 
follow  the  pancreatico-duodenal  artery  to  the  hepatic  chain;  (2)  in  nodes  dorsal  to 
the  pancreas,  which  follow  the  superior  mesenteric  artery  to  the  superior  mesen- 
teric nodes.  There  are  anastomoses  between  the  lymphatics  of  the  duodenum 
and  those  of  the  pylorus,  of  the  pancreas,  and  of  the  chain  along  the  common 
bile-duct. 

The  lymphatics  of  the  jejuno-ileum  (fig.  578)  have  already  served  as  the  type 
of  the  arrangement  of  the  intestinal  lymphatics  (see  above).  The  mass  of 
mesenteric  nodes  [Igl.  mesentericse]  to  which  the  lymphatics  of  the  small  intestine 
pass  is  the  largest  and  one  of  the  most  important  in  the  body,  its  individual  nodes 
numbering  anywhere  from  130  to  150. 

The  lymphatics  of  the  ileo-caecal  region. — The  surgical  importance  of  the 
lymph-nodes  in  connection  with  the  appendix  warrants  a  detailed  description  of 
them  in  which  the  observations  of  Broclel  will  be  followed.  The  drainage  of  the 
caecum  and  appendix  is  along  the  ileo-colic  artery,  and  is  carried  on  by  three  sets 
of  collecting  vessels — (1)  an  anterior  cajcal  set,  which  generally  pass  through 
one  or  more  outlying  nodes  before  reaching  the  ileo-csecal  mesenteric  nodes;  (2)  a 
similar  posterior  set;  and  (3)  an  appendicular  set,  three  to  sLx  in  number,  which 
usually  pass  directly  to  the  ileo-csecal  nodes.  The  appendix  thus  has  an  inde- 
pendent drainage  into  one  or  two  ileo-c£ecal  nodes,  about  3  cm.  above  the  ileum. 
The  ileo-csecal  chain  drains  through  the  mesenteric  nodes  to  the  superior  mesen- 
teric group  (figs.  579,  580). 

The  lymphatics  of  the  large  intestine. — Along  the  ascending  colon  there  are 
but  few  nodes  on  the  terminal  vascular  arches,  but  the  number  increases  along 
the  transverse  colon,  especially  at  its  two  angles.  These  nodes,  together  with 
those  along  the  descending  and  sigmoid  colons,  are  termed  the  meso-colic  nodes 
[Igl.  mesocolicse],  and  they  drain  partly  to  the  superior  mesenteric  and  partly  to 
the  inferior  mesenteric  nodes,  their  efferents  following  the  corresponding  arteries. 


LYMPHATICS  OF  RECTUM  AND  ANUS 


735 


The  lymphatics  of  the  transverse  colon  connect  with  those  of  the  omentum;  those 
of  the  descending  colon  are  more  scanty. 

The  lymphatics  of  the  rectum  and  anus. — There  are  three  lymphatic  zones 
of  the  rectum  and  anus.  (1)  An  inferior  zone,  corresponding  to  the  anal  integu- 
ment, in  which  the  capillary  networks,  both  superficial  and  deep,  are  extremely 
abundant,  and  from  which  from  three  to  five  collecting  vessels  on  either  side  pass 
to  the  inguinal  region  and  end  in  the  medial  superficial  inguinal  nodes.     (2)  A 

Pig.  576. — -The  Lymphatic  Vessels  of  the  Intestine.     (After  Mall.) 


( 


middle  zone,  corresponding  with  the  transition  zone  of  epithelium — that  is,  with 
the  mucous  membrane  below  the  columns  of  Morgagni.  Here  the  network  is 
coarse,  and  has  its  meshes  arranged  vertically;  its  ducts  drain  partly  into  nodes 
situated  along  the  inferior  and  middle  hsemorrhoidal  arteries,  and  partly  pass  to 
nodes  in  the  meso-rectum,  situated  along  the  superior  hsemorrhoidal  artery  and 
known  as  the  ano-rectal  nodes.  (3)  The  superior  zone  corresponds  to  the  re- 
mainder of  the  rectal  mucous  membrane,  and  contains  a  rich  network  whose 
collecting  vessels  pass  to  the  ano-rectal  glands,  and  thence  along  the  superior 
hsemorrhoidal  arteries  to  the  inferior  mesenteric  nodes. 


736  THE  LYMPHATIC  SYSTEM 

Lymphatics  of  the  liver. — The  lymphatic  drainage  of  the  liver  is  complicated 
and  has  great  need  of  being  entirely  restudied  from  the  standpoint  of  development. 
Its  course  is  mainly  to  the  coeliac  nodes,  but  on  the  way  it  passes  through  a  sec- 
ondary group  of  three  to  six  hepatic  nodes  [Igl.  hepaticse],  situated  along  the 
hepatic  artery.  Some  of  these  nodes  are  along  the  horizontal  part  of  the  artery, 
parallel  to  the  superior  border  of  the  pancreas,  while  the  rest  follow  the  artery 
in  its  vertical  course  along  with  the  portal  vein,  and  become  continuous  at  the 
portal  fissure  with  two  distinct  chains  of  nodes,  one  of  which  follows  the  hepatic 
artery  and  portal  vein,  and  the  other  the  cystic  and  common  bile-ducts.  These 
nodes  are  variable,  but  one  constant  node  is  at  the  junction  of  the  cystic  and 
hepatic  ducts.  A  part  of  the  drainage  of  the  liver  is  also  through  the  diaphrag- 
matic nodes. 

The  superficial  collecting  lymph-vessels  of  the  liver  have  been  studied  by 
Sappey.  Those  from  the  superior  surface  include  three  sets.  From  the  dorsal 
part  vessels  pass  through  the  diaphragm  with  the  vena  cava,  and  end  in  the  adja- 
cent posterior  mediastinal  nodes.  Some  of  these  vessels  from  the  right  lobe  pass 
in  the  coronary  ligament  to  the  coeliac  nodes,  and  some  from  the  left  lobe  to  the 
superior  gastric  nodes.  The  second  set  of  vessels  from  the  superior  surface  runs 
over  the  ventral  border  to  the  hepatic  nodes  situated  in  the  portal  fissure.  The 
third  and  most  important  set  arises  near  the  falciform  ligament,  and  passes 

Fig.  577. — The  Lymphatic  Zones  of  the  Stomach.     (Cunto.) 


jgi^^^'^  ^r^^'^°  splenic  nodes 

To  superior  gastric  nodes >*^  iSi^^  y/i 


To  inferior  gastric  node 


partly  dorsalward  to  the  anterior  mediastinal  group  of  nodes  on  the  upper  surface 
of  the  diaphragm,  and  to  the  nodes  around  the  vena  cava,  and  partly  ventral- 
ward  to  the  hepatic  nodes  of  the  portal  fissure. 

The  collecting  vessels  of  the  inferior  surface  pass  to  the  nodes  situated  in  the 
portal  fissure,  either  along  the  artery  or  the  bile-ducts. 

The  lymphatics  of  the  gall-bladder  join  the  hepatic  nodes  along  the  cystic  and 
common  bile-ducts,  and  also  the  superior  pancreatic  nodes. 

Lymphatics  of  the  pancreas. — The  lymph-vessels  which  drain  the  pancreas 
fall,  according  to  Bartels,  into  four  groups:  left,  anterior  (upper),  right  and 
posterior  (lower).  (1)  The  left  group  drain  the  tail  of  the  pancreas  and  pass  to 
the  splenic  lymph-nodes,  at  the  hilus  of  the  spleen.  (2)  Anteriorly  lymphatics 
pass  to  "superior  pancreatic  lymph-nodes,"  superior  gastric  and  hepatic  nodes. 

(3)  To   the   right,  lymphatics   pass   to    "  pancreatico-duodenal   lymph-nodes." 

(4)  Posteriorly  lymphatics  pass  to  the  aortic,  mesenteric,  meso-colic,  and  inferior 
pancreatic  nodes.  The  siDlenic,  superior  pancreatic,  inferior  pancreatic,  and 
pancreatico-duodenal  nodes  are  usually  grouped  together  as  "  lymphoglandulse 
pancreatico-l'enales."  Anastomoses  exist  between  the  lymphatics  of  the  pancreas 
and  those  of  the  duodenum. 

The  lymphatics  of  the  spleen  (fig.  582)  are  found  only  in  the  form  of  a  sub- 
capsular plexus,  there  being  no  deep  network  (Mall).  They  pass  to  the  splenic 
nodes  [Igl.  pancreatico-lienales],  which  are  variable  in  number  and  are  situated 


LYMPHATICS  OF  THE  KIDNEY 


737 


along  the  course  of  the  splenic  vessels.     In  addition  to  the  spleen  they  drain  the 
fundus  of  the  stomach  and  a  part  of  the  pancreas. 

Fig.  578.— Lymphatics  op  the  Small  Intestine.     (After  Toldt,  "Atlas  of  Human  Anatomy," 
Rebman,  London  and  New  York.) 


{ 


The  Lymphatics  of  the  Excretory  Organs  and  of  the  Suprarenal 

The  lymphatics  of  the  kidney.— The  lymphatic  vessels  from  the  deep  capsular 
and  parenchymatous  lymphatics  of  the  kidney  run  to  the  nodes  of  the  lumbar 
cham  (fig.  583).     On  the  right  side,  part  of  the  nodes  concerned  lie  ventral  and 


I 


738 


THE  LYMPHATIC  SYSTEM 


part  dorsal  to  the  renal  vein;  one  of  the  nodes  lies  as  far  caudalward  as  the  bifurca- 
tion of  the  aorta;  and  one  or  two  vessels  may  pass  to  pre-aortic  nodes.  On  the 
left  side  the  vessels  end  in  four  or  five  nodes  of  the  lumbar  group.  The  efferents 
of  these  nodes  pass  through  the  diaphragm  and  end  in  the  thoracic  duct. 

The  lymphatics  of  the  Suprarenal. — The  lymphatic  vessels  coming  from  the 
capsular  and  parenchymatous  plexuses  pass,  on  the  right  side,  into  two  or  three 
anterior  para-aortic  nodes,  and  a  small  retro-venous  gland,  near  the  pillar  of  the 
diaphragm;  on  the  left  side,  into  para-aortic  nodes,  and,  in  part,  through  the 
diaphragm,   in  company  with  the  splanchnic  nerve,  to  a  posterior  mediastinal 

Fig.  579. — The  Lymphatic  Circulation  of  the  Ileo-c^cal    Region,    Anterior  View. 

(After  Kelly.) 


gland,  lying  between  the  ninth  thoracic  vertebra  and  the  aorta.  Anasto- 
moses occur  with  the  lymphatics  of  the  kidney. 

In  addition  to  the  capsular  lymphatics  proper,  Kumita  describes  a  subserous 
plexus,  which  is  present  over  both  kidney  and  adrenal,  which  anastomoses  with 
the  lymphatics  of  the  liver  and  diaphragm.  The  efferents  of  this  plexus  collect, 
on  the  right  side,  to  a  gland  placed  to  the  right  of  the  inferior  vena  cava,  anterior 
to  the  right  renal  vein,  and  on  the  left  side  to  a  gland  anterior  to  the  left  renal 
vein. 

The  lymphatics  of  the  ureter. — Sakata  has  recently  studied  the  lymphatics  of 
the  ureter.  They  fall  into  three  groups:  (1)  An  anterior  (upper)  group,  which 
run  to  the  anterior  lumbar  nodes,  or  join  the  renal  lymphatics;  (2)  a  middle 
group  which  pass  to  the  posterior  lumbar  and  interiliac  nodes;  (3)  a  posterior 
(lower)  group  which  pass  to  hypogastric  nodes  and  which  anastomose  with  lym- 
phatics of  the  bladder. 


LYMPHATICS  OF  PROSTATE 


739 


The  lymphatics  of  the  bladder. — The  collecting  vessels  from  the  lower  part  of 
the  ventral  surface  pass  to  a  node  of  the  external  iliac  group,  situated  near  the 
femoral  ring  and  the  obturator  nerve;  those  from  the  upper  part  of  the  ventral  and 
dorsal  surfaces  pass  to  the  middle  node  of  the  middle  group  of  the  external  ihac 
chain,  and  from  the  rest  of  the  dorsal  surface  they  pass  either  to  the  hypogastric 


i 


Fig.  580.- 


-The  Lymphatic  Circulation  op  the  Ileo-c^cal  Region    Posterior   View. 
(After  KeUy.) 


nodes  or  beyond  these  to  the  nodes  at  the  bifurcation  of  the  aorta  (fig.  584). 
In  this  latter  group  end  also  the  vessels  from  the  neck  of  the  bladder.  Along  some 
of  the  lymphatics  of  the  bladder  are  intercalated  lymph-nodes,  which  have  been 
termed  anterior  and  lateral  vesical  nodes. 

The  lymphatics  of  the  prostate. — The  lymphatics  of  the  prostate  have  been 
studied  in  the  dog  by  Walker  and  in  man  by  Bruhns.  The  collecting  vessels,  sbc 
to  eight  on  each  side,  pass  along  the  prostatic  artery  to  the  nodes  along  the  ex- 
ternal border  of  the  hypogastric  artery.  These  nodes  are  connected  with  those 
along  the  external  and  common  iliac  arteries,  and  it  is  possible,  from  an  injection 
of  the  prostate,  to  fill  the  entire  chain  of  nodes  as  far  as  the  renal  artery.  A 
trunk  from  the  posterior  surface  runs  up  over  the  bladder  and  curves  outward  to 


740  THE  LYMPHATIC  SYSTEM 

the  middle  node  of  the  middle  group  of  the  external  iliac  chain,  and  still  other  vessels 
from  the  posterior  surface  run  first  downward,  pass  around  the  rectum,  and  then 
ascend  to  the  lateral  sacral  nodes.  From  the  anterior  surface  a  descending  duct 
may  follow  the  deep  artery  of  the  penis,  and  the  internal  pudic  to  the  hypogastric 

Fig.   581. — The   Superficial  Lymphatic   Netwoek   of   the   Liver.     (After   Teichmann). 


Fig.  682. — Lymphatics  of  the  Periphery  of  a  Pig's  Spleen.     (After  Teichmann.) 


nodes  (fig.  585) .     The  lymphatics  of  the  prostate  anastomose  with  those  of  the 
bladder,  ductus  deferens  and  rectum. 

The  lymphatics  of  the  urethra. — 1.  In  the  Male. — The  capillary  plexus  of  the 
urethra  is  in  the  mucous  membrane.     The  collecting  vessels  from  the  mucous 


LYMPHATICS  OF  URINARY  TRACT 
Fig.  583. — Lymphatics  of  the  Kidney.     (After  Poirier  and  Cunfio.) 


741 


Suprarenal  artery- 


Pre-aorticnode 


i 


Fig.  584. — Lymphatics  of  the  Bladder.     (After  Cunco  and  Marcille.) 


External  iliac  node- 


Collecting  trunks 
of  upper  dorsal 
surface 

Collecting  trunk  of 

upper   dorsal 

surface 
Collecting  trunk  of , 

inferior  ventral 

surface 


Hypogastric  node 


Hypogastric  node 

Ureter 

Collecting  trunks 
along  inferior 
vesical  artery 

Collecting  trunks 
to  end  in  the 
node  of    the 
promontory 


742 


THE  LYMPHATIC  SYSTEM 


membrane  of  the  glans  follow  the  dorsal  vein.  Those  from  the  penile  and^mem- 
branous  portions  of  the  urethra  start  from  the  inferior  surface  and  curve  around 
the  corpora  cavernosa,  as  seen  in  fig.  586,  to  join  the  others  along  the  dorsal  vein. 
These  vessels  run  with  the  vein  to  the  symphj^sis,  where  the}'  form  a  plexus  in 
which  there  may  be  some  small  intercalated  nodes.  From  this  plexus  vessels 
pass  in  two  directions: — (1)  Three  or  four  vessels,  the  crural  trunks,  pass  to  the 
deep  inguinal  and  external  iliac  nodes,  and  (2)  one  vessel  enters  the  inguinal 
canal  and  ends  in  one  of  the  external  iliac  nodes. 

The  vessels  from  the  bulbar  and  membranous  portions  either  follow  the  internal 
pudic  arterj',  or  pass  to  the  symphj-sis  and  end  in  the  external  iliac  nodes,  or  pass 
onto  the  surface  of  the  bladder  and  thence  to  the  external  iliac  chain.     The 


Fig.  585. — The  Lymphatics  of  the  Prostate.     (After  Ciin^o  and  Marcille.) 


External  iliac  /  — 
nodes         | 


Retro  prostatic 
lymphatics 
Collecting  vessels 
from  prostate  to 


Node  of  the  pro- 
montory 


Lateral  sacral 


Collecting  vessels 
from  prostate 
to  node  of  pro- 
montory 


Middle  hamor- 
rhoidal  node 
and  trunks 


Ijinphatics  of  the  prostatic  portion  run  with  the  prostatic  ducts.     The  lymphatics 
of  the  urethra  anastomose  with  those  of  the  bladder  and  those  of  the  glans. 

2.  Inthe  female  the  Ij-mphatic  vessels  of  the  urethra  end  in  the  external  iliac 
and  hypogastric  nodes. 

Lymphatics  of  the   Rephoductive  Org.vns 
In  the  Male  (figs.  585,  586,  587) 

The  IjTQphatics  of  the  external  genitaha  will  be  first  described  and  then  those 
of  the  internal  organs  (fig.  589). 

The  lymphatics  of  the  scrotum  form  a  rich  plexus  which  has  been  pictured  by 
Teichmann  (fig.  547).  The  collecting  vessels,  ten  to  fifteen  on  either  side,  arise 
near  the  raphe  and  pass  to  the  root  of  the  penis,  where  some  curve  lateralward  to 
the  superior  medial  superficial  inguinal  nodes;  while  others,  coming  from  the 
lateral  surface  of  the  scrotum,  pass  to  the  corresponding  inferior  nodes. 


LYMPHATICS  OF  REPRODUCTIVE  ORGAXS 


743 


Fig.  586. — ^Lymphatics  of  the  Penile  axb  Membraxous  Portioxs  of  the  Urethra.    (After 
Cuneo  and  Marcille.) 


Collecting  trunk 
in  front  of        — 
symphysis 


{ 


Vessel  along  inter- 
nal mdic  artery 


Vessel  from  anterior 
—    surface  of  the 

prostate 
Collecting  trunk 

behind  the 

symphysis 


Vessel  along   inter- 
nal pudic  artery 


Fig.  5S7. — ^Ltmphatics  of  the  Glaxs  Pexis  ix  a  Xew-borx  Child.     (Cuneo  and  Marcille.) 


External  iliac 

node 

Node  in 

abdominal 

inguinal  ring 

Presymphysial' 

node 


Network  ofr^fg^"'-- 
glans  penis     '"' 


{ 


744 


THE  LYMPHATIC  SYSTEM 


The  lymphatics  of  the  penis.— (1)  The  cutaneous  lymphatics  form  a  plexus 
from  which  collecting  vessels  follow  the  dorsal  vein  and  end  in  the  superficial 
mguinal  nodes.  (2)  The  lymphatics  of  the  glans  form  an  exceedingly  rich 
plexus  from  which  vessels  follow  the  dorsal  vein  of  the  penis,  as  described  under 
the  urethra,  and  end  in  the  deep  inguinal  and  external  iliac  nodes.  (3)  The 
lymphatics  of  the  erectile  structures  are  little  known. 

The  lymphatics  of  the  testis  are  both  superficial  and  deep,  the  latter  being 
exceedmgly  hard  to  inject.  The  collecting  vessels  follow  the  spermatic  cord  and 
artery  and  end  in  the  lumbar  nodes. 

.—Lymphatics  of  the  Pemnedm.     (After  Toldt,  "Atlas  of  Human  Anatomy,"  Reb- 
man,  London  and  New  York.) 

Dorsal  lymph-vessels  of  the  clitoris 
Glans  clitoridis 


Fig.  688, 


Superficial  epigastric  vein  \ 
Superficial  inguinal  lymph-nodes 


Labium  majus 


Region  of  the  tuberosity  of  the  ischium  / 

Fat  of  ischio -rectal  fossa  Anus 

The  lymphatics  of  the  ductus  deferens  and  vesiculse  seminales. — In  the 
ductus  deferens  only  a  superficial  set  has  been  injected,  and  its  vessels  passlto 
the  external  ihac  nodes.  The  plexus  of  the  vesiculaj  seminales  is  double,  super- 
ficial and  deep,  and  its  vessels  pass  to  the  external  iliac  and  hypogastric  nodes. 

In  the  Fernale 
(Figs.  588,  589,  590) 

The  lymphatics  of  the  vulva.— Throughout  the  vulva  there  is  an  exceedingly 
rich,  superficial  lymphatic  plexus,  from  which  collecting  vessels  pass  to  the 
symphysis  and  there  turn  lateralward  to  the  medial  superficial  inguinal'  nodes. 
The  fact  that  the  capillary  plexus  is  continuous  from  side  to  side  and  that  there 
is  a  plexus  of  the  vessels  in  front  of  the  symphysis,  makes  the  nodes  of  both  sides 
liable  to  infection  from  a  unilateral  lesion. 


LYMPHATICS  OF  VAGINA 


745 


The  lymphatics  of  the  clitoris. — The  lymphatics  of  the  glans  of  the  clitoris 
form  an  abundant  network  from  which  collecting  vessels  pass  toward  the  symphy- 
sis pubis,  and  thence  principally  to  the  deeper  inguinal  nodes,  one  or  two,  however, 
passing  through  the  inguinal  canal  to  terminate  in  the  lower  external  iliac  nodes. 

The  lymphatics  of  the  ovary. — The  ovary  has  a  remarkably  rich  lymphatic 
plexus,  from  which  from  four  to  six  vessels  leave  the  hilus  and  follow  the  ovarian 
artery  to  the  lumbar  nodes.  One  vessel  may  run  in  the  broad  ligament  to  the 
internal  iliac  group. 

The  lymphatics  of  the  Fallopian  tube  form  three  capillary  networks  from 
which  collecting  vessels  run  in  part  with  those  of  the  ovary,  and  in  part  with  the 
uterine  lymph-vessels. 

The  lymphatics  of  the  uterus. — According  to  Poirier,  the  lymphatics  of  the 
uterus  arise  from  three  capillary  plexuses,  a  mucous,  a  muscular,  and  a  peritoneal. 
The  collecting  vessels  from  the  body  of  the  uterus  are  in  three  sets: — (1)  Those 
from  the  fundus,  consisting  of  four  or  five  vessels,  run  lateralward  in  the  suspen- 

FiG.  589. — Lymphatics  op  the  Internal  Genital  Organs  in  the  Female.     (After  Poirier. 

Vena  cava- 

Kidney 

Right  renal  vein' 


( 


Right  spermatic  artery 
Lumbar  node 


Lumbar  node  — 


Anterior  crural  nerve- 
Peritoneum- 
Lymphatics  in  utero-sacral 
ligament 
Cervical  lymphatics—- 

Ovary  — 
Parovarium  — 

Lymphatics  of  round  ^ 
ligament 


/ — ^Lumbar  vein 
Spermatic  artery 


Ureter 

Inferior  mesenteric  artery 

Middle  lumbar  node 


Middle  sacral  artery 
Ovarian  lymphatics 
Pelvic  colon 

—  Lymphatics  of  the  tube 
„nterine  tube  (Falloppii) 


sory  ligament  of  the  ovary  and  follow  the  ovarian  vessels  to  the  lumbar  and  pre- 
aortic nodes.  They  anastomose  with  the  lymphatics  from  the  ovary  opposite  the 
fifth  lumbar  vertebra;  (2)  some  small  vessels  from  the  fundus  follow  the  round 
ligament  of  the  uterus  and  terminate  in  the  inguinal  nodes;  and  (3)  others  from  the 
body  of  the  uterus  pass  laterally  with  the  uterine  vessels  and  terminate  in  the  iliac 
nodes. 

The  collecting  vessels  from  the  cervix,  five  to  eight  in  number,  form  a  large 
lymphatic  plexus  just  after  leaving  the  cervix.  From  this  plexus  run  three  sets  of 
vessels.  Two  or  three  vessels  pass  lateralward  with  the  uterine  artery  in  front  of 
the  ureter,  and  end  in  the  external  iliac  nodes;  a  second  set  passes  behind  the 
ureter  and  ends  in  a  node  of  the  hypogastric  group,  and  a  third  set  from  the 
posterior  surface  runs  downward  over  the  vagina  and  then  backward  and  upward 
to  end  in  the  lateral  sacral  nodes  and  node  of  the  promontory  of  the  sacrum. 

The  lymphatics  of  the  vagina  (fig.  590) . — -There  are  two  lymphatic  plexuses  in 
the  vagina,  a  superficial  and  deep — the  latter,  the  mucosal  plexus,  being  ex- 
ceedingly rich.  The  collecting  vessels  are  in  three  groups.  The  superior  set 
drains  the  upper  third  of  the  vagina  and  takes  the  same  course  as  those  from  the 
lower  cervical  portion  of  the  uterus;  the  middle  set  follows  the  vaginal  artery  to 


746  THE  LYMPHATIC  SYSTEM 

the  hypogastric  nodes;  and  the  inferior  set  runs  to  the  lateral  sacral  nodes  and  to 
those  of  the  promontory.  The  capillary  network  of  the  lower  part  of  the  vagina 
is  continuous  with  the  plexus  of  the  vulva,  which  drains  to  the  inguinal  nodes. 

Fig.  590. — ^Lymphatics  of  the  Vagina.     (After  Poirier.) 


Utero-vaginal  lymphatics 


Vaginal  lymphatics 
(middle) 


E.  THE  LYMPHATICS  OF  THE  LOWER  EXTREMITY 
1.  THE  LYMPHATIC  NODES  OF  THE  LOWER  EXTREMITY 

The  principal  group  of  nodes  of  the  lower  extremity  is  situated  in  the  in- 
guinal region,  and  hence  is  known  as  the  inguinal  group.  It  is  in  many  respects 
similar  to  the  axillary  group,  although  it  is  not  quite  equivalent  to  it  develop- 
mentally.  The  nodes  composing  it  are  divisible  into  a  superficial  and  a  deep 
group,  the  former  containing  many  more  and  larger  nodes  than  the  latter. 
Furthermore,  it  is  convenient  to  divide  each  of  these  groups  into  an  upper  and  a 
lower  set,  the  dividing  line  being  an  arbitrary  line  drawn  horizontally  through  the 
point  where  the  saphenous  vein  pierces  the  fascia  of  the  fossa  ovalis.  The  nodes 
above  this  line  are  termed  collectively  the  inguinal  nodes,  while  those  below  it 
are  known  as  the  subinguinal  nodes. 

The  superficial  inguinal  nodes  [Igl.  inguinales  superficiales]  (fig.  591),  lie 
along  the  base  of  the  femoral  trigone  immediately  below  Poupart's  ligament, 
superficial  to  the  fascia  lata.  Then  number  varies  from  ten  to  twenty.  They 
receive  the  subcutaneous  drainage  of  the  abdominal  walls,  the  gluteal  region, 
and  the  perineal  region,  and  their  efferents  descend  to  the  fossa  ovalis,  which  they 
perforate  along  with  the  saphenous  vein  and  terminate  in  the  lower  external 
iliac  nodes. 

The  superficial  subinguinal  nodes  [Igl.  subinguinales  superficiales],  occupy 
the  lower  part  of  the  femoral  trigone  and  receive  the  entire  superficial  drainage 
of  the  leg,  as  well  as  a  few  vessels  from  the  gluteal  region  and  from  the  perineum. 
Thek  efferents  pierce  the  fossa  ovalis  and  pass  partly  to  the  deep  subinguinal 
nodes  and  partly  directly  to  the  lower  external  ihac  nodes. 


LYMPH-NODES  OF  LOWER  LIMB 


747 


The  deep  nodes. — The  deep  nodes  are  small,  and  vary  from  one  to  three. 
They  lie  medial  to  the  femoral  vein,  the  highest  one  (node  of  Cloquet  or  of 
Rosenmiiller)  being  placed  in  the  femoral  ring  and  being  of  especial  surgical 


{ 


Fig.  591.- 


-The  Sttpebficial  Inguinal  Nodes.     (After  Toldt,  "Atlas  of  Human  Anatomy," 
Rebman,  London  and  New  York.) 


Inguinal     1  \ 
ligament      ft    vs 

(Poupart  s) 


Inguinal      fc\ 
lymph-nodes^^  )  /^""^ 

Femoral 
artery 
Femoral  vein 

Falciform 
margin 

Superficial  ^    '  \ 

subinguinal 
nod 


Great  saphen-    Tjj^^ 

ous  vein         lH  IH    \i 


interest  in  that,  when  enlarged,  it  may  simulate  a  strangulated  hernia.  The 
lowest  node  is  below  the  point  where  the  lesser  saphenous  joins  the  femoral  vein. 
These  deep  nodes  receive  the  deep  lymphatics  of  the  leg,  the  vessels  from  the 
glans  penis  in  the  male,  and  the  clitoris  in  the  female,  and  some  of  the  vessels 
from  the  superficial  subinguinal  nodes.  Their  efferent  vessels  enter  the  external 
iliac  nodes. 

In  addition  to  the  inguinal  group  of  nodes  there  are  some  other  nodes  in  the 
lower  limb  situated  along  the  course  of  the  deep  vessels.  Thus  there  is  a  node  in 
the  course  of  the  anterior  tibial  vessels  below  the  knee,  and  there  is  a  small 


( 


748 


THE  LYMPHATIC  SYSTEM 


group  of  popliteal  nodes  [Igl.  popliteae],  in  the  popliteal  space,  which  are  in  the 
course  of  the  lesser  saphenous  vessels,  and  receive  the  vessels  which  accompany 
the  posterior  tibial  and  peroneal  vessels  and  those  which  drain  the  knee-joint. 

Fig.  592. — The  Superficial  Lymphatics  op  the  Lowee  Extremity.     (After  Toldt,  "Atlas  of 
Human  Anatomy,"   Rebman,  London  and  New  York.) 


Superficial  epigastric  vein 


Inguinal  node: 


Superficial  subinguinal  nodes 


Great  saphenous  vein 


Accessory  saphenous  ' 


2.  THE  LYMPHATIC  VESSELS  OF  THE  LOWER  EXTREMITY 

As  in  the  upper  extremity,  the  subcutaneous  capillary  plexus  of  the  lower 
varies  greatly  in  complexity,  being  most  abundant  in  the  soles  of  the  feet.  The 
collecting  vessels  form  two  main  groups.  The  medial,  larger  group  follows  the 
saphenous  vein,  and  ends  in  the  superficial  subinguinal  nodes,  while  the  lateral 


LYMPH-VESSELS  OF  LOWER  LIMB 


749 


group  curves  around  to  join  the  medial,  partly  in  the  leg  and  partly  in  the  thigh. 
Two  or  three  vessels  from  the  heel  follow  the  lesser  saphenous  vein  to  the  popliteal 
space.  The  vessels  from  the  upper  and  dorsal  part  of  the  thigh  curve  around  on 
both  sides  to  reach  the  superficial  inguinal  nodes.     The  vessels  of  the  anus  and 

Fig.  593. — The  Lymphatics  of  the  Back  of  the  Lower  Extremity.     (After  Toldt,  "Atlas  of 
Human  Anatomy,"   Rebman,   London  and   New  York.) 


Popliteal  lymph-nodes— 


Small  saphenous 


Deep  lymphatic  vessels 


perineum,  as  well  as  those  from  the  external  genitalia,  except  from  the  glans  penis 
or  the  clitoris,  pass  to  the  medial  nodes  of  the  superficial  inguinal  group. 

The  deep  vessels  follow  the  course  of  the  arteries  of  the  leg,  those  accompany- 
ing the  dorsalis  pedis  and  anterior  tibial  arteries  coming  into  relation  with  the 


( 


750  THE  LYMPHATIC  SYSTEM 

anterior  tibial  node,  when  it  is  present,  and  then  passing  backward  to  join  the 
vessels  which  accompany  the  posterior  tibial  and  peroneal  arteries.  These 
terminate  in  the  popliteal  nodes,  from  which  efferents  follow  the  com-se  of  the 
femoral  artery  and  terminate  in  the  deep  inguinal  nodes.  The  deep  lymphatic 
vessels  accompanying  the  gluteal  and  obturator  arteries  pass  to  the  hypogastric 
nodes. 

Lymphatics  of  the  hip-joint. — According  to  Clermont,  they  accompany,  in  the  main,  the 
arteries  about  the  joint.  (1)  Satellites  of  the  anterior  circumfle.x  artery,  draining  almost  the 
entire  ventral  surface,  pass  to  the  lateral  inferior  external  iliac  node.  (2)  Satellites  of  the  pos- 
terior circumflex  artery,  draining  the  dorsal  and  medial  surfaces,  empty  into  the  medial  inferior 
external  iliac  node,  occasionally  into  one  of  the  deep  inguinal  nodes.  (3)  Satellites  of  the 
obturator  vessel,  draining  the  round  ligament,  empty  into  the  obturator  or  hypogastric  nodes. 
(4)  Satellites  of  the  inferior  gluteal  vessels,  draining  the  dorsal  surface,  empty  into  three  small 
nodes  along  the  internal  pudic  and  inferior  gluteal  arteries.  Less  important  ("accessory") 
vessels  are:  satellites  of  the  superior  gluteal  artery  leading  to  a  gluteal  node;  vessels  from  the 
dorsal  surface  which  cross  the  lateral  border  of  the  pectineus  to  reach  the  medial  inferior 
external  iliac  node;  and  vessels  from  the  ventral  surface,  crossing  parallel  to  the  cotyloid  notch, 
passing  under  the  psoas  to  the  lateral  inferior  external  Uiae  or  one  of  the  deep  inguinal  nodes. 

Lymphatics  of  the  knee-joint. — According  to  Tanasesco  the  lymphatics  draining  the  struc- 
tures around  the  knee-joint  in  the  main  follow  the  arteries  about  the  joint  and  pass  largely  to 
the  more  deeply  placed  of  the  popliteal  nodes.  Some  (superficial)  follow  the  great  saphenous 
vein  to  the  subinguinal  nodes,  and  sometimes  deep  vessels  pass  the  pophteal  nodes  and,  ac- 
companying the  femoral  artery,  run  to  the  deep  inguinal  or  inferior  external  iliac. 

References  for  lymphatic  system. — (Development) :  Sabin,  Amer.  Jour. 
Anat.,  vols.  1,  3,  4,  9,  also  in  Keibel  and  Mall's  Human  Embryology;  Lewis, 
Amer.  Join-.  Anat.,  vols.  5,  9;  Huntington  and  McClure,  Amer.  Jour.  Anat., 
vol.  10;  Clark,  E.  L.,  Anat.  Record,  vol.  6;  Clark,  E.  R.,  Amer.  Jour.  Anat., 
vol.13.  (Regeneration):  Meyer,  Johns  Hopkins  Hosp.  Bui.,  vol.  17.  (General): 
Bartels,  in  von  Bardeleben's  Handbuch  d.  Anatomic;  Sappey,  "Description 
et  Iconographie  des  Vaisseaux  Lymphatiques,"  Paris,  1885;  Teichmann,  "Das 
Saugadersystem,"  Leipzig,  1861.  (Muscle,  etc.):  Aagaard,  Anat.  Hefte,  Bd. 47. 
(Connective  tissue):  von  Recklinghausen,  "Die  Lymphgefasse u.  ihre Beziehung 
zum  Bindegewebe,"  Berhn,  1862.  (Stomata):  Walter,  Anat.  Hefte,  Bd.  46. 
(Lung):  Miller,  Anat.  Rec,  vol.  5.  (Teeth):  Schweitzer,  Arch.  f.  mikr.  Anat., 
Bd.  74.  (Hoemolyinph  glands):  von  Schumacher,  Arch.  f.  mikr.  Anat.,  Bd.  81. 
Tumors):     Evans,  Beitr.z.  klin.  Chir.,  Bd.  78. 


i 


SECTION  VII 

THE  NERVOUS  SYSTEM 

Revised  for  the  Fifth  Edition 
Bt  IRVING  HARDESTY,  A.B.,  Ph.D. 

PBOPESSOR  OP  ANATOMY,   THE  TDLANE   UNIVERBITT  OP   LOUISIANA 


THE  nervous  system  of  man,  both  anatomically  and  functionally,  is  the  most 
highly  developed  and  definitely  distributed  of  all  the  systems  of  the  body. 
It  consists  of  an  aggregation  of  peculiarly  differentiated  tissue-elements, 
so  arranged  that  through  them  stimuli  may  be  transmitted  from  and  to  all  the 
other  tissue  systems  or  functional  apparatuses.  It  is  a  mechanism  with  parts  so 
adjusted  that  stimuli  affecting  one  tissue  may  be  conveyed,  controlled,  modified, 
and  distributed  to  other  tissues  so  that  the  appropriate  reactions  result.  While 
protoplasm  will  react  without  nerves,  while  muscle  will  contract  without  the 
mediation  of  nerves,  yet  the  nervous  system  is  of  the  most  vital  importance  to 
the  higher  organisms  in  that  the  stimuli  required  for  the  functioning  of  the  organs 
are  so  distributed  throughout  their  component  elements  that  the  necessary 
harmonious  and  coordinate  activities  are  produced.  For  this  purpose  the 
nervous  sj^stem  permeates  every  organ  of  the  body;  nerve  cell-bodies,  accu- 
mulated into  groups,  receive  impulses  and  give  rise  to  the  nerves  which  ramify 
and  divide  into  smaller  and  smaller  branches  till  the  division  attains  the  individual 
nerve-fibres  of  which  the  nerves  are  composed,  and  even  the  fibres  bifurcate 
repeatedly  before  their  final  termination  upon  their  allotted  elements.  So 
intimate  and  extensive  is  the  distribution  throughout  that  could  all  the  other 
tissues  of  the  body  be  dissolved  away,  still  there  would  be  left  in  gossamer  its 
form  and  proportions — a  phantom  of  the  body  composed  entirely  of  nerves. 

The  parent  portion  or  axis  of  the  system  extends  along  the  dorsal  mid-line  of 
the  body,  surrounded  by  bone  and,  in  addition,  protected  and  supported  by  a 
series  of  especially  constructed  membranes  or  meninges,  the  outermost  of  which 
is  the  strongest.  The  cephalic  end  of  the  axis,  the  encephalon,  is  remarkably 
enlarged  in  man,  and  is  enclosed  within  the  largest  portion  of  the  bony  cavity, 
the  cranium,  while  the  remainder  of  the  central  axis,  the  spinal  cord,  continues 
through  the  foramen  magnum  and  lies  in  the  vertebral  canal. 

The  intimate  connection  of  the  axis  with  all  the  parts  of  the  body  is  attained 
by  means  of  forty-six  pairs  of  nerves,  which  are  attached  to  the  axis  at  somewhat 
regular  intervals  along  its  extent.  They  course  from  their  segments  of  attach- 
ment through  the  meninges  and  through  their  respective  foramina  in  the  bony 
cavity  to  the  periphery.  Of  these  craniospinal  nerves,  fifteen  pairs  pass 
through  the  cranium  and  are  attached  to  the  encephalon,  and  thirty-one  pairs 
to  the  spinal  cord.  Some  of  the  cranial  nerves  and  all  of  the  thirty-one  pairs  of 
spinal  nerves  contain  both  afferent  fibres,  which  convey  impulses  from  the  per- 
ipheral tissues  to  the  central  axis,  and  efferent  fibres,  which  convey  impulses  from 
the  axis  to  the  peripheral  tissues.  The  different  pans  of  nerves  possess  the  two 
types  of  fibres  in  varying  proportions. 

Upon  approaching  the  spinal  cord,  each  spinal  nerve  is  separated  into  two  roots 
■ — its  posterior  or  dorsal  root  and  its  anterior  or  ventral  root.  The  afferent  fibres 
enter  the  axis  by  way  of  the  dorsal  roots,  which  are,  therefore,  the  sensory  roots, 
and  the  efl^erent  fibres  leave  the  axis  by  way  of  the  ventral  or  motor  roots. 

As  usually  studied,  the  nervous  sj'stem  is  referred  to  in  two  main  divisions : — 

(1)  The  central  nervous  system,  composed  of — (a)  The  spinal  cord,  or  medulla 
spinalis,  and  (6)  the  brain  or  encephalon. 

751 


752 


THE  NERVOUS  SYSTEM 


Fig.  594. — Showing  the  Ventral  Aspect  of  the  Central  Nervous  System,  with  the  Proxi- 
mal Portions  of  the  Cranio-spinal  Nerves  attached  and  the  Relation  op  the 
Proximal  Portion  (Gancliated  Cord)  of  the  Sympathetic  Nervous  System.  The 
Encephalon  or  Brain  is  Straightened  Dorsalward  prom  its  more  Horizontal 
Position  with  Reference  to  the  Spinal  Cord.  The  Spinal  Ganglia  and  the  Dorsal 
and  Ventral  roots  of  the  Spinal  Nerves  may  be  noted. 

(Composite  drawing  in  part  after  Allen  Thompson  from  Rauber — modified.') 


Superior  cervical  sympathetic 
ganglion 


Middle  cervical  sympathetic 
ganglion 


Inferior  cervical  sympathetic 
ganglion 


n  I  Thoracic  nerve 


Gangliated  cord 


~/-~t  Cervical  nerve 


I  Lumbar  nerve 


-]  Sacral  nerve 


VJ  Coccygeal  nerve 


Filum  terminale 


DEVELOPMENT  OF  NERVOUS  SYSTEM 


753 


Neurenteric  canal 

Primitive  groove 

Body-stalk 


754  THE  NERVOUS  SYSTEM 

(2)  The  peripheral  nervous  system,  composed  of — (a)  The  cranio-spinal 
nerves,  and  (6)  the  sympathetic  nervous  system. 

All  these  parts  are  so  intimately  connected  with  each  other  that  the  division  is 
purely  arbitrary.  The  cranio-spinal  nerves  are  anatomically  continuous  with  the 
central  system;  their  component  fibres  either  arise  within  or  terminate  within 
the  confines  of  the  central  system,  and  thus  actually  contribute  to  its  bulk.  The 
sympathetic  system,  however,  may  be  more  nearly  considered  as  having  a 
domain  of  its  own.  By  communicating  rami,  it  is  intimately  associated  with  the 
cranio-spinal  nerves  and  thus  with  the  central  system,  both  receiving  impulses 
from  the  central  system  and  transmitting  impulses  which  enter  it.  But,  while  its 
activities  are  largely  under  the  control  of  the  central  system,  it  is  possible  that 
impulses  may  arise  in  the  domain  of  the  sympathetic  system  and,  mediated  by 
its  nerves,  produce  reactions  in  the  tissues  it  supplies  without  involving  the 
central  system  at  all.  For  this  reason,  as  well  as  because  of  the  structural 
peculiarities  of  the  sympathetic  system,  the  nervous  system  is  sometimes  divided 
into — (1)  the  cranio-spinal  system,  consisting  of  (a)  the  central  system  and  (b) 
the  cranio-spinal  nerves;  (2)  the  sympathetic  nervous  system,  consisting  of  its 
various  peripheral  ganglia  and  their  outgrowths  forming  its  plexuses. 

Within  and  closely  pro.ximal  to  the  central  system  or  axis  are  grouped  the  parent  cell-bodies 
whose  processes  comprise  the  nerve  fibres  of  the  cranio-spinal  nerves.  Other  groups  of  nerve 
cell-bodies,  distributed  in  the  periphery  without  the  bounds  of  the  central  system,,  give  rise 
to  the  fibres  of  the  sympathetic  nerves  and  plexuses.  Any  group  of  such  cell-bodies  situated 
in  the  periphery,  whether  belonging  to  the  cranio-spinal  or  sympathetic  system,  is  known  as  a 
ganglion. 

THE  DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 

The  essential  elements  of  the  nervous  system,  the  nerve  cell-bodies  and  the 
essential  portion  of  all  nerve  fibres,  central,  cranio-spinal  and  sympathetic,  de- 
velop from  one  of  the  embryonic  germ  layers,  the  ectoderm,  and  all  arise  from  a 
given  region  of  that  germ  layer.  Further  a  small  portion  of  the  supporting  tissue 
of  the  nervous  system,  the  neuroglia,  is  of  the  same  origin. 

In  its  development  the  nervous  system  is  precocious.  It  is  the  first  of  the  functional 
apparatuses  to  begin  differentiation  and  is  the  first  to  acquire  its  form.  The  first  trace  of 
the  embryo  appears  on  the  developing  ovum  as  the  embryonic  area,  and  the  rapidly  proliferating 
cells  of  this  area  shortly  become  arranged  into  the  three  germinal  layers: — the  outer  layer  or 
ectoderm,  the  middle  layer  or  mesoderm,  and  the  inner  layer  or  entoderm.  Early  in  the  process 
of  this  arrangement  there  is  formed  along  the  axial  fine  of  the  embryonic  area  a  thickened  plate 
of  ectodermal  cells,  the  neural  plate.  In  the  further  proliferation  of  these  cells,  the  margins 
of  the  neural  plate,  which  he  parallel  with  the  long  axis  of  the  embryonic  area,  rise  shghtly  above 
the  general  surface,  forming  the  neural  folds,  and  the  floor  of  the  plate  between  the  folds  under- 
goes a  slight  invagination,  the  process  resulting  in  the  neural  groove  (fig.  595,  A,  A',  B  and  B^). 
As  development  proceeds  and  the  embryonic  area  assumes  the  form  of  a  distinct  embryo,  the 
neural  folds  or  lips  of  the  groove  graduaUy  converge,  and  beginning  at  the  oral  end,  finally  unite. 
Thus  the  groove  is  converted  into  the  neural  tube,  extending  along  the  dorsal  mid-hne  and  en- 
closed within  the  body  of  the  embryo  by  the  now  continuous  ectoderm  above  (fig  595,  C^, 
D  and  D'). 

For  a  time  the  neural  tube  remains  connected  with  the  inner  surface  of  the  general  ectoderm 
along  the  line  of  fusion  by  a  residual  lamina  of  ectodermal  cells.  This  lamina  is  known  as  the 
ganglion  crest  (neural  crest).  It  is  a  product  of  the  proliferation  of  the  ectoderm  during  the 
process  of  fusion,  consists  of  the  cells  which  composed  the  transition  between  the  closing  lips 
of  the  original  groove  and  the  general  ectoderm  or  skin,  and  whose  fusion  aided  in  the  closure 
of  the  tube.  The  ectoderm  soon  becomes  separated  from  the  ganghon  crest  and  the  cells  of  the 
crest  become  distinctly  differentiated  from  the  cells  of  the  neural  tube.  The  essential  elements 
of  the  entire  nervous  system  together  with  the  neuroglia  are  derived  from  the  cells  of  the  neural 
tube  and  the  cells  of  the  ganglion  crest. 

Fig.   595. — Dorsal  Surface  Views  of  Human  Embryos  and   Diagrams  of   Transverse 
Sections  Illustrating  the  Development  or  the  Neural  Tube. 

A,  dorsal  view  of  human  embryo  at  beginning  of  infolding  of  neural  plate  to  form  neural 
groove.  Amnion  partly  removed.  (Graf  Spee,  from  Keibel  and  Mall.)  A',  diagram  of 
portion  of  a  transverse  section  of  an  embryo  as  though  taken  through  A  at  the  fine  a'. 
B,  dorsal  view  of  human  embryo  of  7  somites,  neural  tube  not  yet  closed,  Mall  Collection. 
(Dandy,  from  Keibel  and  Mall.)  B',  diagram  of  portion  of  a  transverse  section  of  an  embryo 
as  though  taken  through  B  at  the  line  b'.  C'-,  diagram  of  portion  of  a  transverse  section  of 
an  embryo  as  though  taken  through  D  at  fine  c'.  D,  dorsal  view  of  human  embryo  of  8 
somites,  2.11  m.m.  long,  neural  tube  closed  except  at  caudal  end.  (KoUmann,  from 
Keibel  and  Mall.)  D',  diagram  of  a  portion  of  a  transverse  section  of  an  embryo  as  though 
taken  through  D  at^line  d^ 


DEVELOPMENT  OF  NERVOUS  SYSTEM 


755 


Before  the  caudal  extremity  of  the  tube  is  entirely  closed,  its  oral  end  undergoes  marked 
enlargement  and  becomes  distended  into  three  vesicular  dilations,  the  anterior,  middle,  and 
posterior  primary  brain  vesicles.  The  anterior  of  these  primary  vesicles  give  off  a  series  of 
secondary  vesicles  and  by  these,  followed  by  further  dilations,  flexures  of  its  axis,  and  by 
means  of  locahzed  thickenings  of  its  walls,  the  portion  of  the  tube  included  in  the  three  primary 
vesicles  develops  into  the  encephalon  or  brain  of  the  adult.  The  remainder  of  the  tube  becomes 
the  spinal  cord.  This  latter  portion  retains  the  simpler  form.  By  the  proliferation  and  migra- 
tion laterally  of  the  cells  lining  this  portion  of  the  tube,  there  results  a  comparatively  even 
bilateral  thickening  of  its  walls  so  that  the  mature  spinal  cord  retains  a  cylindrical  form  through- 
out its  length. 

The  proliferating  and  migrating  cells  of  the  wall  of  the  neural  tube  are  known  as  germinal 
cells.  The  products  of  their  division  are  apparently  indifferent  at  first,  but  later  they  become 
differentiated  into  two  varieties:  (1)  spongioblasts,  or  those  cells  which  will  develop  into  neu- 
roglia, and  (2)  neiiroblasts,  or  those  which  will  increase  in  size,  develop  processes  and  become 
nerve  cell-bodies.'  As  described  below,  the  processes  given  off  by  a  neuroblast  are  of  two  general 
characters:  (1)  a  long  process  or  axone  which  goes  to  form  nerves,  nerve  roots,  and  nerve  fasciculi, 
and  (2)  dendritic  processes  which  are  numerous,  branch  much  more  frequently  and  extend  but 
a  short  distance  from  the  cell-body.  An  adult  cell-body  with  all  its  processes  is  known  as  a 
neurone  and  the  neuroblasts  of  the  developing  system  become  transformed  into  the  neurones 


Fig.  596. — Diagrams  of  Tkansvebse  Sections  or  Embryonic  Spinal  Cords  showing  the 
Migration  of  the  Cells  op  the  Ganglion  Crest  to  form  the  Spinal  and  Sympathetic 
Ganglia  and  the  Origin  of  the  Dorsal  and  Ventral  Roots  of  the  Spinal  Nerves. 

A,  a- stage  following  D'  of  fig.  595.  B,  a  later  stage  in  which  the  ganglia  and  the  components  of 
the  nerve  are  assuming  their  form  resulting  from  the  further  migration  and  from  processes 
being  given  off  by  the  neuroblasts. 


—  Spinal  ganglion 


Sympatheti 


of  the  varying  sizes,  shapes,  and  arrangements  of  processes  characteristic  of  different  divisions 
and  localities  of  the  nervous  system.  Usually  the  fii-st  process  to  be  noted  is  that  which  will 
become  the  axone  or  nerve  fibre. 

Neurones  whose  cell-bodies  belong  to  the  peripheral  nervous  system  are  not  developed 
within  the  walls  of  the  neural  tube  or  central  nervous  system  at  all.  These,  comprising  the 
spinal  ganglion  neurones  and  those  of  the  sympathetic  system,  are  derived  from  the  cells  of  the 
ganglion  crest.  The  wedge-shaped  lamina  of  cells,  comprising  the  ganghon  crest,  through 
rapid  cell  division,  gradually  extends  outward  and  ventralward  over  the  surface  of  the  neural 
tube  along  either  side.  Soon  the  prohferation  becomes  most  active  in  regions  corresponding  to 
the  mesodermic  somites  or  primitive  body  segments  and  this,  together  with  the  stress  of  the 
growing  length  of  the  body,  results  in  the  ganghon  crest  (originally  a  lamina)  becoming  seg- 
mented also.  The  segments  or  locahsed  cell  masses  thus  formed  are  the  beginning  not  only  of 
the  spinal  ganglia,  but  also  of  the  ganglia  of  the  entu-e  sympathetic  system.  The  cells  of  the 
crest  migrate  to  assume  a  more  lateral  position,  and  then  occurs  a  separation  of  their  ranks. 
A  portion  of  them  remain  in  a  dorsolateral  position  near  the  wall  of  the  neural  tube  and  develop 
into  the  neurones  of  the  spinal  ganglia  (the  sensory  neurones  of  the  spinal  nerves),  but  others 
wander  further  out  into  the  periphery  and  become  the  neurones  of  the  sympathetic.  Certain 
of  those  of  this  more  nomadic  group  of  cells  settle  within  the  vicinity  of  the  vertebral  column  and 
by  sending  out  their  processes,  form  the  gangliated  cord  or  the  proximal  chain  of  sj^mpathetic 
ganglia;  others  migrate  further,  but  in  more  broken  rank,  and  become  the  gangha  of  the  pre- 
vertebral plexuses  (as  the  cardiac,  coeliac  and  hypogastric  plexuses),  or  the  scattered  intermediate 
chain  of  ganglia;  while  still  others  wander  into  the  very  walls  of  the  peripheral  organs  and 


756 


THE  NERVOUS  SYSTEM 


Fig.    597. — ^Diagram   Showing   the    Chief   Paths   of    Migration   of  the    Cells   from 

THE  Ganglia  of  the  Spinal  and  Cranial  Nerves  to  form  the  Adult  Sympathetic 
System  (After  Schwalbe,  modified.) 


Carotid  plexus 


Vagus 
I.  cervical  spinal 


Middle  cervica' 


Inferior  cervical 
ganglion 


Sympathetic   trunl 


I.  lumbar  spinal 
ganglion 


I.  sacral  spinal 
ganglion 


Ciliary  ganglion 
Otic  ganglion 
Spheno-palatine 


Submaxillary 


Pharyngeal  plexus 

Pulmonary  plexus 

Cardiac  plexus 

(Esophageal 
plexus 

Coronary  plexus 
Gastric  plexus 


Cceliac    (solar) 
plexus 


Submucous  and 
myenteric  plex- 
uses (Meissner 
and  Auerbach) 


Aortic  plexus 
Inferior  mesenteric 
plexus 


Pelvic  plexuses 


Coccygeal  ganglion 


DEVELOPMENT  OF  NERVOUS  SYSTEM 


757 


occur  singly  or  in  groups  in  such  plexuses  as  those  of  Auerbach  and  Meissner,  within  the  tunics 
of  the  walls  of  the  alimentary  canal.  Scattered  along  between  these  proximal,  intermediate, 
and  distal  groups  there  are  to  be  found  small  straggling  gangha,  many  of  which  contain  so  few 
cell-bodies  that  they  are  indistinguishable  with  the  unaided  eye.  All  these  sympathetic  neu- 
rones, however,  are  always   either  directly  or   indirectly  anatomically  associated  with  and 


Fig,   598. — Diagrams  of  Oral  Portion  of  Human  Neural  Tube  Showing  the  Three 

Primary  Brain  Vesicles  and  Some  of  the  Secondary  Vesicles  Derived  from  Them. 
A,  diagram  of  dorsal  view  of  early  stage.     B,  lateral  view  at  about  the  third  week.     C,  lateral 

view  at  about  the  eighth  week.     After  His,  modified,     m,  mamillary  vesicle;  i,  infundibular 

recess;  o,  oKactory  vesicle. 


Anterior  primary  veeicle 
^         optic  veeic] 


"middle  primary  vesicle 
-'Posterior  primary  vesicle 

Auditory  vesicl 


Middle  primary  vesicle  ^ 
epiphysis 


Anterior  primary 
Telencephalon^ 


spinal  cord 


-cerebellum 
^  ;*Posteriorprimary 
vesicle 
medulla 


olfactory  vesicle-  -^'•'' 

optic  vesicle"'  / 

Pontine  fltaure 

cervical  flexure 


Fig.  599. — Diagrammatic  Sagittal  Section  of  a  Vertebrate   Brain.     (After  Huxley.) 
4,  fourth  ventricle;  s,  cerebral  aqueduct;  3,  third  ventricle. 

Corpora  quadrigemina  Mid -brain  Epiphysis 


Lateral  ventricle 

Cerebral  hemisphere 
Corpus  striatum 


Pons  Varoli 
(.hind -brain  J 


Cerebral  peduncle 


Thalamus       [       Hypophysis       Foramen  of  Monro 
Hypothalamus 


Fig.  600.— Diagrammatic  Horizontal  Section  of  a  Vertebrate  Brain.     (Afte  Huxley.) 
4,  fourth  ventricle;  3,  third  ventricle. 
Metencephalon  Thalamus 


Medulla  oblongata ^^ 

Cerebellum 


—Lateral  ventricle 


Lamina  terminalis 


Corpus  striatum 


Mid-brain     Epiphysis     Foramen  of  Monro 


largely  under  the  control  of  the  neurones  of  the  central  system  through  central  visceral  eferent 
fibres  passing  to  them  by  way  of  the  rami  communicantes  or  by  way  of  the  peripheral  distri- 
bution of  the  spinal  nerves. 

The  ganglia  of  the  sensory  portions  of  all  those  cranial  nerves  attached  to  the  inferior  of 
the  main  divisions  of  the  brain  and  all  the  sympathetic  ganglia  of  the  head  have  an  origin 
similar  to  that  of  the  spinal  and  sympathetic  gangha  in  the  remainder  of  the  body. 

The  behavior  of  the  walls  of  the  three  primary  vesicles,  into  which  the  oral  end  of  the  neural 
tube  is  converted,  is  much  more  complex  than  in  case  of  the  spinal  cord.     Their  walls  do  not 


758 


THE  NERVOUS  SYSTEM 


thicken  uniformly  and,  to  give  rise  to  the  form  of  the  adult  brain,  the  anterior  and  the  posterior 
of  the  three  vesicles  give  off  secondary  vesicles. 

The  walls  of  the  posterior  primary  vesicle  give  rise  to  the  posterior  of  the  main  divisions 
of  the  brain,  the  hind  brain  or  rhombencephalon,  the  cerebellum  developing  from  the  anterior 
portion  only  of  its  dorsal  wall,  and  the  medulla  oblongata  and  pons  from  its  ventral  wall.  Its 
cavity  persists  and  enlarges  into  the  fourth  ventricle  of  the  adult,  while  the  posterior  portion 
of  its  dorsal  wall  does  not  develop  functional  nervous  tissue  at  all  but  persists  as  a  thin  membrane 
known  as  the  chorioid  tela  of  the  fourth  ventricle.  The  cells  which  form  the  ganglia  of  the  audi- 
tory and  vestibular  nerves  arise  from  the  dorsolateral  regions  of  this  vesicle. 

From  the  middle  primary  vesicle  comes  the  mid-brain  or  mesencephalon,  the  corprora  quad- 
rigemina  [colliculi]  developing  from  its  entire  dorsal  wall  and  the  cerebral  peduncles  occupying 
its  ventral  wall.  The  constriction  between  the  middle  and  posterior  vesicles  becomes  the 
isthmus  of  the  rhombencephalon. 

The  anterior  or  first  primary  vesicle  undergoes  greater  elaboration  than  either  of  the  other 
two.  At  an  early  period  it  gives  off  a  series  of  secondary  vesicles  or  diverticula.  First,  two 
ventrolateral  outpouchings  occur,  the  optic  vesicles,  which  later  become  the  optic  stalks  and 
optic  cups  of  the  embryo.  A  medial  protuberance  becomes  evident  in  its  antero-dorsal  wall 
and  from  each  side  of  this  quickly  starts  a  lateral  diverticulum.  The  two  lateral  diverticula 
thus  arising  from  the  protuberance  are  the  beginning  of  the  two  cerebral  hemispheres  or  the 
telencephalon,  and  the  vesicular  cavities  contained  persist  as  the  two  lateral  ventricles  of  the 
brain.  Soon,  each  of  these  vesicular  rudiments  of  the  hemispheres  gives  off  ventrally  from  its 
anterior  part  a  narrow  tube-like  diverticulum,  each  continuous  into  the  parent  primary  vesicle. 
These  are  the  olfactory  vesicles  which  are  transformed  into  the  olfactory  bulbs  and  olfactory 
tracts^  of  the  adult  encephalon.  (See  fig.  598,  B.  and  C.)  As  development  proceeds,  the 
cavities  of  the  olfactory  vesicles  become  occluded  in  man.     However,  in  many  of  those  animals 


Fig.  601. — Diagram  op  Mesial  Section  op  the  Human  Beain  showing  the  Segments  and 
THE  Flexures  and  the  Expansion  of  the  Cebebral  Hemispheres  over  the  Other 
Portions  op  the  Beain.     The  Thalamus  is  not  shown. 


Cerebral  hemisphere 
Corpus  callosum 
i- Septum  pellucidum 


Third  ventricle 


Fourth  ventricli 


Hypophysis 
Cerebral  peduncle 

Pons  1 

( 
Medulla  oblongata  ! 

Spinal  cord 


in  which  the  olfactory  apparatus  attains  greater  relative  development  than  in  man,  these  cavi- 
ties persist  as  the  olfactory  ventricles.  The  cavities  of  the  optic  vesicles  never  persist  as  ven- 
tricles in  the  adult.  They  form  stalks  which  represent  the  future  courses  of  the  optic  nerves, 
while  from  their  extremities  are  developed  the  retina;,  portions  of  the  ciliary  bodies  and  portions 
of  the  iris  of  the  ocular  bulbs. 

In  addition  to  that  which  forms  the  cerebral  hemispheres,  the  remaining  portion  of  the 
anterior  primary  vesicle  becomes  the  diencephalon  or  inter-brain.  The  lateral  walls  of  this  part 
thicken  to  form  the  tiialami,  the  posterior  end  of  its  dorsal  wall  gives  off  a  secondary  vesicle 
which  becomes  the  pineal  body  or  epiphysis,  and  from  its  ventral  waU  projects  the  infundibular 
recess  which  becomes  the  posterior  lobe  of  the  hypophysis  with  its  infundibulum  and  tuber 
cinereum. 

The  adult  human  brain  is  characterised  by  the  preponderant  development  of  the  cerebral 
hemispheres.  The  secondary  vesicles  forming  these  expand  till,  held  within  the  cranial  cavity, 
the  hemispheres  come  to  extend  posteriorly  completely  over  the  thalamencephalon  and  the 
mesencephalon  and  even  overlap  the  cerebellum  to  its  posterior  border.  Their  cavities,  which 
persist  from  their  origin  from  the  anterior  primary  vesicle,  are  correspondingly  large  (the  lateral 
ventricles)  and  comprise  two  of  the  four  ventricles  of  the  adult  brain.  The  third  ventricle  be- 
comes a  narrow  cavity  situated  between  the  two  thalami.  It  represents  the  original  cavity 
of  the  anterior  primary  vesicle  from  which  the  structures  above  mentioned  arose  as  secondary 
vesicles.  It  remains  continuous  with  the  lateral  ventricles  by  the  two  inter-ventricular  foramina, 
known  also  as  the /ora?«ma  of  mom'o,  one  into  each  cerebral  hemisphere.  The  fourth  ventricle 
of  the  adult  represents  the  cavity  of  the  posterior  primary  vesicle  and  comes  to  he  between 
the  cerebellum  and  medulla  oblongata,  since  the  cerebellum  likewise  extends  posteriorly  from 
its  region  of  origin.  The  cavity  of  the  middle  primary  vesicle  becomes  the  cerebral  aqueduct, 
or  aqueduct  of  Sylvius,  passing  under  the  corpora  quadrigemina  and  connecting  the  fourth  or 
posterior  ventricle  with  the  third. 

Development  of  the  nerve  fibres. — All  axones  begin  as  outgrowths  or  processes  of  the  cyto- 
plasm of  neuroblasts.  Most  of  such  processes  are  sent  out  at  a  very  early  stage  in  the  develop- 
ment of  the  nervous  system  and  extend  to  the  tissues  they  are  to  innervate  when  these  tissues 
are  as  yet  quite  near  the  neural  tube.     Then,  as  the  structures  of  the  body  elaborate  and  assume 


DEVELOPMENT  OF  NERVOUS  SYSTEM 


759 


their  final  forms  and  positions  more  remote  from  the  central  nervous  system,  the  axones  ter- 
minating in  them  must  necessarily  grow  and  be  drawn  out  with  the  structures.  At  need, 
later  axones  are  sent  out  by  neurones  developing  later  to  supply  the  growth  demands.  Such 
axones  follow  the  general  paths  made  by  those  aheady  extending  to  the  tissues  requiring  them. 
Being  processes  of  the  cytoplasm  of  the  cell-body,  the  growth  and  Ufe  of  all  axones  (and  dendrites) 
is  under  the  control  of  the  nucleus  in  the  cell-body.  They  grow  by  absorbing  nourishment, 
or  having  added  to  them  substances,  from  the  tissue  stroma  through  which  they  pass,  which 
stroma  may  be  either  ectodermal  or  mesodermal  in  origin. 

The  great  majority  of  axones  in  the  central  nervous  sytem  and  all  in  the  peripheral  system 
have  sheaths  about  them.  The  sheath  is  an  acquired  structure  and  is  not  added  till  a  rela- 
tively late  period  of  development.     These  sheaths  are  of  two  general  varieties,  sheaths  con- 


FiG.  602. — Diagram  illusteating  the  Gross  Divisions  of  the  Central  Nervous  System. 


Olivary  body— 


--,___  Mesencephalon  j 

(mid-brain)  J 


^«  Pons  (Varoli) 

Myelencephalon 
(medulla  oblongata) 

//-"•Pars  cervicalis 


-Pars  thoracalis 


-""Pars  lumbalis 


Spinal  cord 
(medulla  spinalis) 


sisting  merely  of  a  fibrous  coat  with  the  nuclei  belonging  to  it,  and  sheaths  in  which  there  has 
been  added  a  coating  of  fat  or  myeUn,  medullary  sheaths.  A  nerve  fibre  consists  of  an  axone  and 
its  sheath  whether  meduUated  or  non-medullated. 

In  the  embryo,  axones  are  given  off  from  the  developing  neurones  at  a  time  when  the 
entire  ectodermic  neural  tube  and  embryonic  ganglia  and  the  mesodermic  tissue  surrounding 
them  are  each  void  of  definite  cell  boundaries,  each  being  a  continuous  mass  of  nucleated 
protoplasm,  a  syncyiium.  From  these  syncytia  are  developed  the  fibrous  connective  tissues 
of  the  later  framework  supporting  the  nervous  system.  Of  this,  the  fibrous  tissue,  neuroglia, 
is  derived  from  the  ectodermal  syncytium,  while  the  white  and  elastic  fibrous  tissues  are  derived 
from  the  mesodermal  or  mesenchymal  syncytium.  Before  any  connective  tissue  fibrils  are 
developed  in  either  syncytium,  before  and  at  the  time  of  the  ingrowth  of  blood-vessels  into  the 
developing  gangha  and  the  neural  tube  from  the  mesenchyme  about  them,  there  occurs  an 
invasion  of  the  mesenchymal  syncytium  into  the  ectodermal  sjmcytium.  This  invasion 
occurs  both  as  independent  ingrowths  and  fusions  at  the  periphery  of  the  neural  tube  and  by 


760 


THE  NERVOUS  SYSTEM 


the  mesenchymal  tissue  being  carried  in  by  the  ingrowing  blood-vessels.  After  the  mixture  of 
the  nuclei  resulting  from  this  fusion  of  the  syncytia  from  the  two  sources,  nuclei  of  mesodermal 
origin  cannot  be  distinguished  from  those  of  ectodermal  origin.  Further,  axones  outgrowing 
from  the  embryonic  ganglia  and  neural  tube  carry  with  them  adhering  portions  of  the  ectodermal 
syncytium  into  the  surrounding  mesenchymal  (fig.  603). 

As  development  proceeds  further,  each  syncytium  becomes  resolved  into  a  reticulum  of 
granular  endoplasmic  processes,  containing  the  nuclei,  with  transparent  exoplasm  occupying 
its  meshes.  Fibrils  soon  form  in  the  exoplasm  and  from  these  develop  the  connective-tissue 
fibres,  whether  neurogha  in  the  central  nervous  system  or  mesenchymal  fibrous  tissue  both  without 
and  within  it.  Certain  of  these  fibrils  of  course  surround  the  axones  imbedded  among  them 
and  from  condensations  of  such  fibrils  are  derived  the  fibrous  sheaths  of  the  axones,  the  sheath 
nuclei  being  acquhed  from  the  adjacent  nuclei  of  the  original  syncytium.  These  sheaths 
become  more  dense  or  pronounced  as  the  axones  extend  and  the  fibrous  tissue  increases  with 
growth,  but  there  are  always  present  fine  marginal  fibrils  by  which  the  sheaths  grade  into  the 
looser  fibrous  tissue  about  them.     It  is  generally  beUeved  that  the  tissue  giving  rise  to  these 

Fig.  603. — Drawings  Illustrating  the  Origin  of  the  Axone  and  the  Development  of 
THE  Medullary  Sheaths. 

A,  ventral  portion  of  transverse  section  of  an  embryonic  spinal  cord  involving  portion  of 
periphery  of  future  ventral  horn  and  part  of  the  mesenchymal  (mesodermal)  syncytium  out- 
side the  external  limiting  membrane  of  the  cord.  B,  later  stage  of  ventral  root  (peripheral) 
axone  with  myehn  droplets  adhering  to  it  and  fibrillated  stroma  surrounding  it.  C,  stage 
in  which  myehn  droplets,  supported  by  fibrils  of  stroma,  have  increased  and  accumulated 
to  form  a  practically  continuous  myehn  or  meduUary  sheath.  D,  final  stage  with  medullary 
sheath  of  even  thickness,  showing  a  node,  and  showing  a  neurilemma,  sheath  nucleus  and 
fibrous  framework  of  the  myehn  ("neurokeratin")  derived  from  the  fibrils  of  the  original 
stroma. 


Myel'n 


-  Neurilemma 


Mesenchymal 
syncytium 


axone  sheaths  is  of  mesodermal  origin.  However,  in  amphibian  larvae,  Harrison  has  shown  that 
some  sheath  nuclei  at  least  are  derived  from  the  nuclei  of  the  ectodermal  syncytium  of  the 
ganghon  crest,  and  Neal  has  noted  in  elasmobranchs  the  fact  that  nuclei  migrate  from  the  ven- 
tral waU  of  the  neural  tube  along  with  the  axones  growing  out  to  form  the  ventral  roots  of  the 
spinal  nerves.  Whether  aU  or  any  of  these  nuclei  are  originally  ectoderrnal,  and,  if  so,  whether 
such  ectodermal  tissue  gives  rise  to  all  axone  sheaths,  especiaUy  in  the  higher  animals,  are 
questionable  contentions. 

Axones  possessing  only  fibrous  sheaths  comprise  the  non-meduUated  nerve  fibres.  The 
majority  of  the  sympathetic  fibres  are  of  this  variety,  and  Ranson  has  found  numerous  non- 
meduUated  fibres  present  in  the  spinal  nerves.  The  generally  accepted  form  of  non-medullated 
sympathetic  fibres  may  be  seen  in  fig.  609,  C. 

MeduUated  fibres  are  those  which  possess  an  investing  coat  of  fat  or  myehn  in  addition  to 
the  fibrous  sheath.  Most  of  the  fibres  in  the  central  nervous  system  and  most  of  those  belong- 
ing to  the  cranio-spinal  nerves  proper  acquire  myehn  sheaths.  Myehn  begins  to  appear  upon 
axones  shortly  after  the  beginning  development  in  the  syncytium  of  the  fibrils  of  the  fibrous 
connective  tissue,  and  thus  after  the  beginnings  of  what  will  become  the  fibrous  sheaths.  The 
fibrous  portions  of  the  sheaths  in  the  central  nervous  system  develop  less  rapidly  and  are  far 
more  scant  than  those  of  the  medullated  fibres  of  the  peripheral  nerves.  Probably  because 
of  this,  it  has  been  claimed  that  myehn  begins  to  appear  on  the  axones  of  the  central  system 
before  the  appearance  of  the  fibrous  sheath.  In  man,  the  first  appearance  of  myelin  occurs  at 
about  the  fourth  month,  but  myelinisation  is  not  completed  tiU  after  birth.  The  cranio-spinal 
nerves  contain  completely  meduUated  fibres  before  the  central  system  does. 

Myehn  first  appears  as  small  droplets  adhering  to  the  axone  at  irregular  intervals.  These 
droplets  increase  in  size  and  number  and  gradually  accumulate  to  form  a  practicaUy  continuous 
sheath  of  fat  immediately  investing  the  axone.  They  probably  result  from  the  coalescence  of 
finer  droplets  floating  in  the  surrounding  fibrillated  stroma.     However,  coUecting  upon  the  axone, 


DEVELOPMENT  OF  NERVOUS  SYSTEM 


761 


the  myelin  retains  the  form  of  an  emulsion,  and  as  it  increases  in  amount  it  incloses  the  adjacent 
fibrils  which  serve  as  a  framework  supporting  the  droplets  of  the  emulsion  in  its  meshes.  Thus 
supported,  the  increasing  myelin  does  not  inclose  the  adjacent  nuclei  and  endoplasm  of  the 
original  syncytium.  Probably  because  of  the  fibrous  support  of  the  myehn  thus  obtained, 
medullating  fibres  may  be  often  seen  presenting  the  beaded  appearance  shown  in  fig.  603,  C, 
instead  of  an  even  distribution  of  the  emulsion  after  it  has  become  continuous  along  the  axone. 
The  "beads"  probably  represent  the  uneven  beginning  of  the  accumulation  indicated  in  B 
of  this  figure.  Increasing  further,  the  myelin  becomes  a  cyhnder  of  even  thickness,  the  adjacent 
nuclei  being  pressed  away  against  its  surface  and  the  adjacent  fibrils  also  condensed  upon  it. 

There  is  good  reason  to  believe  that  the  fibrous  portion  of  the  sheath,  the  primilive  sheath 
or  neurilemma,  of  the  meduUated  axone  arises  as  a  condensation  of  the  fibrils  of  the  surrounding 
stroma  during  development,  that  the  sheath  cells  represent  certain  of  the  nearest  nuclei  in- 
corporated from  the  original  syncytium,  and  that  the  so-called  neuro-keralin  of  the  myehn 
represents  the  fibrous  framework  of  the  myehn  inclosed  by  it  during  its  accumulation  upon  the 

Fig.  604. — Showing  Some  of  the  Varieties  op  the  Cell-bodies  op  the  Neurones 
OP  the  Human  Nervous  System,  including  the  Dendrites  and  Small  Portions  op 
THE  Axones.     Axone  Sheaths  not  included. 

A.  From  spinal  ganghon.  B.  From  ventral  horn  of  spinal  cord.  C.  Pyramidal  cell  from  cere- 
bral cortex.  D.  Purkinje  cell  from  cerebellar  cortex.  E.  Golgi  cell  of  type  II  from  spinal 
cord.  E.  Fusiform  cell  from  cerebral  cortex.  G.  Sympathetic,  a,  axone;  d,  dendrites;  c, 
collateral  branches;  ad,  apical  dendrites;  hd,  basal  dendrites;  c,  central  process;  p,  peripheral 
process. 


axone.  The  theory  that  the  myehn  arises  as  a  differentiated  portion  of  the  axone  and  the  theory 
that  it  is  formed  by  the  neurilemma  have  been  advanced.  That  it  is  accumulated  from  the 
immediately  surrounding  fluid  of  the  stroma  and  adheres  to  the  axone,  added  droplets  coalescing 
there,  in  preference  to  other  tissue  elements  because  of  some  physical  or  chemical  peculiarity 
of  the  axone,  is  more  probably  correct. 

As  the  medullary  sheath  approaches  completeness,  constrictions  may  be  observed  at  more 
or  less  regular  intervals  at  which  the  myelin  emulsion  is  absent.  There  are  the  nodes  of 
Ranvier.  The  process  by  which  they  arise  is  not  clearly  understood.  While  the  fibre  is  growing 
in  length,  new  myehn  is  added  at  the  nodes.  The  internodal  segments  of  the  sheath  increase 
in  length  with  age,  and  each  segment  may  possess  from  one  to  several  sheath  nuclei. 

In  adolescence,  fibres  whose  medullary  sheaths  are  in  various  stages  of  completeness  may 
be  found  both  in  nerve  bundles  in  the  central  system  and  in  the  cranio-spinal  nerves,  and  in 
both,  the  sheaths  of  some  axones  certainly  never  acquire  mj'ehn.  Also,  in  the  adult,  fibres 
whose  medullary  sheaths  present  the  beaded  appearance  may  be  observed,  probably  repre- 
senting cases  of  arrested  accumulation  of  myelin.  According  to  Westphal  there  is  a  slight  in- 
crease in  the  thickness  of  the  sheath  with  age.  Larger  axones  acquire  thicker  sheaths  of  myeUn 
than  smaller  ones.  Some  fibres  of  the  sympathetic  system  are  meduhated  but  in  such  the 
myelin  sheath  is  relatively  thinner  than  in  the  cranio-spinal  system.  Beaded  sheaths  are 
frequent  in  sympathetic  rami,  though  non-meduUated  fibres  are  most  abundant. 


762  THE  NERVOUS  SYSTEM 

FUNDAMENTALS  OF  CONSTRUCTION 

The  functionally  mature  nervous  system  consists  of  peculiarly  differentiated 
essential  cell  elements  held  in  place  by  two  forms  of  supporting  tissue  and  supplied 
with  abundant  blood-vessels. 

The  nervous  element  is  distinguished  from  all  other  units  of  the  structure  of 
organs  in  that  its  cell-body  gives  off  outgrowths  or  processes  of  peculiarly  great 
length  and  characteristic  form.  Knowledge  of  the  possible  lengths  and  com- 
plexity of  these  processes  is  comparatively  recent  and,  to  include  them  together 
with  their  parent  cell-body,  which  has  long  been  known  as  the  7ierue  cell,  the 
term  neurone  is  used.  The  neurone,  therefore,  may  be  defined  as  the  nerve  cell- 
bodj'  with  all  its  processes,  however  numerous  and  far  reaching  they  may  be.  As 
a  class  of  tissue  elements,  all  neurones  possess  characteristics  distinguishing 
them  from  other  tissue  elements,  but  the  varieties  within  this  class  vary  greatly. 
They  vary  in  form  both  according  to  function  and  according  to  their  locality  in 
the  nervous  sj^stem.  They  vary  in  different  animals,  those  in  the  higher  animals 
being  more  complex  in  form.  Fig.  604  gives  illustrations  of  the  external  form  of 
the  cell-body  of  a  few  of  the  types  found  in  the  human  nervous  system. 

The  cell-body  of  the  neurone  gives  off  two  general  types  of  processes, 
■dendrites  and  axones: 

(1)  The  dendritic  processes  or  dendrites.  These  are  the  more  numerous,  the  shorter,  and 
the  more  frequently  branching  processes.  They  branch  dichotomously  and  with  rapid  decrease 
in  diameter  as  tliey  branch.  They  serve  to  increase  the  absorbing  surface  of  the  cell-body 
for  purposes  of  nutrition.  Nerve  impulses  transmitted  to  the  neurone  are  received  by  them  and, 
therefore,  they  also  serve  to  increase  the  recipient  surface  of  the  neurone.  They  never  acquire 
meduUary  sheaths.  Since  they  convey  impulses  toward  the  cell-body,  they  are  known  as 
cellipital  processes.  Their  absorbing  and  receptive  surfaces  are  further  increased  by  the  presence 
of  thickly  placed,  very  minute  projections  known  as  "pin-head  processes"  or  gemmules. 

(2)  The  axone  (neuraxis).  Each  neurone  possesses  properly  but  one  of  these  processes. 
It  arises  from  the  cell-body  more  abruptly  and  quickly  becomes  smaller  in  diameter  than  are 
most  dendrites  before  the  latter  decrease  by  branching.  It  is  the  longest  process,  in  most  cases 
very  much  longer  than  dendrites.  Computation  shows  that  some  axones  may  contain  nearly 
200  times  the  volume  of  the  parent  cell-body  of  the  neurone.  Occasionally  the  axone  gives  off 
a  few  small  branches  near  the  cell-body.  These  are  known  as  collaterals  and  are  given  off  at 
practically  right  angles  instead  of  dichotomously.  Regardless  of  its  branching,  the  axone 
maintains  a  practically  uniform  diameter  throughout  its  long  course.  Its  usual  nervous  func- 
tion is  to  convey  the  impulses  away  from  the  cell-body,  either  to  transmit  them  to  other  neu- 
rones by  contact  upon  their  dendrites,  etc.,  or  to  appropriate  elements  of  the  other  tissue 
systems  of  the  body.  Thus  the  axones  are  the  cellifugal  processes.  There  is  one  weU-known 
partial  exception  to  this,  namely,  a  part  of  the  axone  of  the  spinal  ganglion  type  of  neurone, 
the  peripheral  sensory  neurone.  The  axone  of  this  bifurcates  a  short  distance  from  the  cell- 
body  into  a  peripheral  and  a  central  branch.  See  fig.  604,  A,  and  fig.  610.  The  peripheral 
branch  collects  sensory  impulses  from  the  tissues  of  the  body,  the  skin,  etc.,  and,  in  conveying 
them  to  the  central  system,  must  necessarily  convey  them  toward  the  cell-body  as  far  as  the 
point  of  bifurcation.  Thence  the  impulse  goes  on  in  the  central  branch,  stiU  toward  the  central 
system  but  now,  in  conformity,  away  from  the  cell-body  of  the  neurone.  While  the  continued 
vitality  of  the  axone  is  dependent  upon  the  cell-body,  in  the  peculiar  case  of  the  spinal  ganglion 
neurone  the  impulse  does  not  necessarily  pass  through  the  ceU-body.  Experiments  with  the 
lower  animals  have  shown  that  the  impulses  pass  in  the  fibre  from  the  peripheral  tissues  to  the 
central  system  when  the  cell-bod^'  has  been  cut  away. 

Terminations  of  axones. — At  its  final  termination,  well  beyond  its  collateral  branches  and 
usually  a  considerable  length  from  its  ceU-body,  the  axone  practically  always  divides  into  two 
or  more  terminal  branches,  and  each  of  these  breaks  up,  now  dichotomously,  into  numerous 
terminal  twigs.  These  terminal  twigs  are  known  as  telodendria.  Telodendria  vary  in  number 
and  characterof  form  according  to  the  tissues  in  and  upon  which  they  terminate.  Functionally, 
they  are  of  three  classes:  Those  terminating  upon  and  in  the  other  (peripheral)  tissues  of  the 
body  are  either  (1)  sensory  or  (2)  motor.  In  order  to  transmit  impulses  from  one  neurone  to 
another,  telodendria  of  the  axone  of  one  neurone  are  placed  in  contact  with  the  dendrites  or 
cell-body  of  another  neurone  forming  (3)  synapses.  Upon  approaching  its  termination,  every 
axone  loses  its  sheath,  its  telodendria  being  necessarily  bare. 

Sensory  or  afferent  axones,  receiving  impulses  from  the  skin  or  other  epithelial  surfaces, 
break  up  into  very  numerous  telodendria  each  of  which  terminates  directly  upon  the  surface 
of  the  epitheUal  cell,  such  as  the  cells  of  the  germinative  (Malpigin)  layer  of  the  skin  or 
those  of  its  basal  or  columnar  layer.  Such  telodendria  are  known  as  free  terminations.  Free 
terminations  are  also  to  be  found  in  the  connective  tissues  of  the  body.  A  second  varietj'  of 
peripheral  termination  of  afferent  axones  is  the  encapsulated  for jn.  These  are  known  as  'end 
organs'  and  'corpuscles'  and  are  named  according  to  their  complexity  and  position.  Three 
of  the  different  forms  of  them  are  shown  in  fig.  605,  B,  C,  and  D.  These  are  always  situated 
in  fibrous  connective  tissue  from  which  their  capsules  are  derived.  Their  most  elaborate  form 
is  the  lamellated  or  Pacinian  corpuscle.  Besides  the  motor  axones  terminating  upon  the 
fibres  of  voluntary  or  skeletal  muscle,  sensory  impulses  are  carried  from  this  tissue  and  one  of 
the  forms  of  telodendria  for  this  purpose  terminates  upon  the  muscle  fibre.     This  is  known  as 


PERIPHERAL  TERMINATIONS  OF  AXONES 


763 


Fig.  605.— Showing  Some  Varieties  op  Pekipheeal  Terminations  of  Axones. 
'Free  termination'  in  epithelium  (after  Retzius).  B.  Krause's  corpuscle  from  conjunctiva 
(after  Dogiel).  C.  Meissner's  corpuscle  from  skin  (after  Dogiel).  D.  Pacinian  corpuscle 
(after  Dogiel).  E.  Termination  upon  tendon  sheath  (Huber  and  DeWitt).  F.  Neuro- mus- 
cular spindle  (after  Ruffini).  G.  Motor  termination  upon  smooth  muscle-cell.  H.  Motor 
'end-plate'  on  skeletal  muscle  fibre  (after  Bohmandvon  Davidoff).     a,  axone;  t,  telodendria. 

a      yf:._ 


764 


THE  NERVOUS  SYSTEM 


the  'neuromuscular  spindle.'  In  it,  the  axone  penetrates  the  sarcolemma  and  breaks  into 
telodendria  which  coil  spirally  about  the  muscle  fibre.  The  most  extensive  and  elaborate  form 
of  sensory  telodendria  are  those  which  spread  out  in  plate-form  upon  tendons  sheaths. 

Fig.  606. — Schemes  showing  Two  Forms  of  Synapses  or  the  Termination  of  Axones  upon 

Cell-bodies  of  other  Neurones. 

A.  In  ventral  horn  of  spinal  cord.     B.  In  spinal  ganglia. 


Fig.   607. — Drawings  Illustrating  two  General  Types  of  Arrangement  op  Neuro- 

FIBRILL^  IN   the  CeLL-BODIES   OF   NeURONES. 

A,  cell-body  of  spinal-ganglion  neurone.     B,  selected  "giant  pyramidal  cell"  from  cerebral 
cortex,  human,    a,  axone. 


Motor  peripheral  axones  terminate  upon  muscle  and  upon  the  secretory  cell  of  glands 
(secretory  axones).  The  motor  cranio-spinal  axones  terminate  upon  skeletal  (voluntary)  muscle 
fibres  and  upon  the  cell-bodies  of  sympathetic  neurones,  the  axones  of  which  latter  termmate 
upon  cardiac  muscle,  smooth  muscle  fibres,  and  (secretory)  in  glands.  Upon  skeletal  muscle, 
the  terminal  branch  of  the  axone  loses  its  sheath  and  breaks  up  into  numerous  telodendria  which 
themselves  branch  and  show  very  evident,  irregular  varicosities,  the  whole  of  which  spread  out 


STRUCTURE  OF  THE  NEURONE 


765 


in  plate-form,  and  lie  in  contact  with  the  substance  of  the  muscle  fibre.  In  man  and  all  mammals, 
the  area  covered  is  usually  somewhat  oval  and  is  marked  by  a  granular  differentiation  of  the 
muscle  substance.  This  with  the  telodendria  is  known  as  a  motor  end-plate.  The  telodendria 
of  sympathetic  axones  ending  upon  cardiac  and  smooth  muscle  fibres  are  fewer  and  simpler  than 
those  of  cranio-spinal  axones  upon  skeletal  muscle.  They  consist  of  a  few  fine  fibrils,  with  very 
small  varicosities  along  them  and  at  their  ultimate  terminations,  which  run  longitudinally  along 
the  muscle  fibre  in  close  relation  with  its  substance.  Those  upon  gland  cells  are  similar  in 
character  except  that  they  often  form  a  loose  pericellular  plexus  about  and  upon  the  cell.  The 
varicosities  of  telodendria  are  sometimes  called  end-feet  and  closer  study  of  them  has  shown  that 
they  themselves  consist  of  fine  plexuses  of  the  neuro-fibrils  described  below  as  contained  in  the 
cell-body  of  the  neurone  and  extending  throughout  all  its  processes.  Quite  recently  Boek  has 
found  that  a  sympathetic  axone  may  sometimes  accompany  a  cranio-spinal  axone  to  an  end 
plate  on  a  skeletal  muscle  fibre. 

^Synapses. — Every  functionally  complete  nerve  pathway  consists  of  two  or  more  neurones 
arranged  in  series.  Very  often,  the  series  consists  of  many  more  than  two,  the  impulses  being 
transmitted  from  neurone  to  neurone.  The  axone,  bearing  the  impulse  away  from  the  cell-body 
of  one  neurone,  gives  off  terminal  branches,  each  of  which  loses  its  sheath  and  breaks  up  into 
telodendria  which  twine  themselves  upon  the  dendrites  or  cell-body  of  another  neurone.  The 
mpulse  is  transferred  from  one  neurone  to  another  by  means  of  contact  rather  than  by  direct 
anatomical  continuity  of  the  parts  of  the  two  neurones.  Such  terminations  of  axones  are  known 
as  synapses. 


Fig.  608. — Drawings  Illustrating  the  Abundance  and  General  Arrangement  op  the 

Tigroid  Masses  in  Cell-bodies  of  Neurones  in  Resting  Condition. 

A,  cell-body  from  spinal  ganglion.     B,  large  cell-body  from  ventral  horn  of  spinal  cord,     a, 

axone.     d,  dendrites. 

Capsule 


'd 


a- 


B 


In  the  terminal  arrangement  of  the  telodendria,  synapses  assume  forms  varying  from  com- 
pact "pericellular  basketa"  and  "climbing  fibres"  to  the  more  open  arborisations  composed  of 
fewer  twigs  in  simpler  arrangements,  "end-brushes."  In  case  of  the  spinal  ganghon  type  of 
neurone,  the  cell-body  of  the  majority  of  which  has  no  dendritic  processes,  the  telodendria  of  the 
visiting  axone  form  an  anastomosing  pericellular  plexus  inclosing  the  entire  cell-body.  This  and 
the  simple  end-brush  form  of  synapses  are  illustrated  in  fig.  606.  It  should  be  mentioned  that, 
contrary  to  the  general  belief  that  impulses  are  transmitted  by  simple  contact  of  the  neurones  in 
the  series,  it  has  been  claimed  that  the  ultimate  twigs  of  the  telodendria  frequently  penetrate  the 
substance  of  the  receiving  cell-body  and  are  fused  in  continuity.  If  during  the  processes  of 
growth  this  becomes  true,  instead  of  being  an  appearance  produced  by  the  technique  employed, 
it  is  better  considered  as  merely  an  exception  to  the  general  rule. 

Internal  structure  of  the  neurone. — The  ceU-body  of  the  neurone  consists  of  a  large,  spherical, 
vesicular  nucleus  and  a  cytoplasm  continuous  into  its  axone  and  dendritic  outgrowths.  Its 
nucleus  is  further  characterized  by  having  most  usually  but  one  nucleolus,  large,  spherical  and 
densely  staining,  situated  in  a  karyoplasm  containing  otherwise  a  remarkably  small  amount  of 
chromatin.  Of  the  cytoplasm,  the  two  most  interesting  structures  are  its  fibrillar  and  its  gran- 
ular components. 

The  fibrillar  structure,  known  as  the  neuro-fibrillce,  represents  a  growth  and  elaboration  of 
the  spongioplasniic  reticulum  of  the  original,  embryonal  cell.  The  filaments  increase  in  thick- 
ness during  the  development  of  the  neurone,  and,  in  the  sending  out  of  its  processes,  the  meshes 
of  the  original  reticulum  become  so  drawn  out  in  the  processes  as  to  give  the  appearance  of  a  more 
or  less  parallel  arrangement  of  threads.  The  reticular  or  net-like  arrangement  is  usuallj-  more 
nearly  retained  in  the  cytoplasm  immediately  about  the  nucleus,  since  here  the  stress  of  the  out- 
growing processes  is  less  directly  applied.  In  the  cell-body  of  the  spinal  ganglion  type  of  neu- 
rone, when  no  dendrites  are  given  off,  the  net-like  arrangement  is  apparent  tlu-oughout  the  cyto- 
plasm except  in  that  region  giving  rise  to  the  axone.  On  the  other  hand,  in  the  typical  so-called 
"pyramidal  cell"  of  the  cerebral  cortex,  from  which  two  chief  processes,  the  axone  and  the  apical 


766 


THE  NERVOUS  SYSTEM 


dendrite,  are  given  off  from  opposite  poles,  the  more  reticular  arrangement  about  the  nucleus  is 
often  practically  obliterated  by  the  opposing  growth  stress. 

So  manifest  does  the  parallel  appearance  of  the  neuro-fibrillfe  in  the  processes  often  become 
that  it  has  been  interpreted  as  a  series  of  individual  and  independent  fibrils.  In  the  application 
of  gold  chloride  and  similar  methods  to  the  neurones  of  lower  forms,  the  reduced  reagent  is  often 
precipitated  upon  the  fibrils  in  parallel,  seemingly  independent  lines.  And,  assuming  the  ex- 
istence of  independent  fibrils,  it  has  been  contended  that  the  neurone  is  not  the  functional  unit 
of  the  nervous  system  but  is  itself  composed  of  numerous  functional  units,  individual  fibrils, 
each  for  the  conduction  of  nerve  impulses.  More  recent  and  trustworthy  methods,  however, 
show  that  the  neuro-fibrillaj  retain  their  original  reticular  form,  the  threads  anastomosing  in 
all  planes,  and  that  the  meshes  of  the  net  may,  in  the  processes,  be  so  drawn  in  one  direction 
that  a  parallel  appearance  predominates.  Further,  it  is  now  held  that  the  neuroplasm,  or  the 
more  fluid  substance  in  which  the  fibrils  lie  throughout,  is  capable,  and  probably  fully  as  cap- 
able, of  conducting  impulses  as  the  fibrils. 

Of  the  granules  in  the  cytoplasm,  the  most  interesting  are  those  first  described  in  detail  by 
Nissl.  These  are  the  most  abundant  of  those  in  the  cell-body  and  are  known  as  tigroid  masses 
or  Nissl  bodies.  They  consist  of  numerous  basophilic  granules  collected  into  clumps  or  masses  of 
varying  size.  They  are  known  to  disappear  during  fatigue  of  the  nervous  system  and  they  are 
more  abundant  in  animals  after  a  period  of  rest.  They  are  distributed  throughout  the  cyto- 
plasm of  the  cell-body  with  the  interesting  exception  that  they  are  not  found  in  the  axone  nor  in 
the  immediate  vicinity  of  its  place  of  origin  from  the  cytoplasm,  leaving  a  free  region  known  as 
the  axone  hillock.     As  accumulated  masses,  they  show  characteristic  shapes  and  arrangement 

Fig.  609. — Showing  Pieces  of  Axones. 

A.  From  a  cranio-spinal  nerve.  B.  From  the  spinal  cord.  C.  From  the  sympathetic,  a, 
axones;  m,  medullary  sheath;  w,  nodeof  Ranvier;s,  neurilemma  or  sheath  of  Schwann  with 
occasional  sheath-nuclei. 


which  are  interpreted  as  signifying  the  shapes  and  arrangement  of  the  spaces  or  meshes  they 
occupy  in  the  reticulum  of  the  neuro-fibriUai.  In  cell-bodies  of  the  varieties  found  in  the  ventral 
horns  of  the  spinal  cord  or  in  the  cerebral  and  cerebellar  cortex,  for  example,  the  masses  situated 
immediately  about  the  nucleus  are  smaller,  more  numerous  and  of  irregular  shape.  Nearer  and 
in  the  beginnings  of  the  dendrites,  they  are  larger  and  mostly  of  fusiform  or  diamond  shape. 
Farther  out  in  the  dendrites,  they  become  more  and  more  thin  and  attenuated;  and  in  the  dis- 
tant reaches  of  the  dendrites  they  are  invisible  or  absent.  In  the  cell-body  of  the  spinal  ganglion 
they  are  of  irregular  shape,  smaller  and  more  numerous  throughout  the  cytoplasm,  being  slightly 
smaller  and  more  thickly  placed  in  the  immediate  vicinity  of  the  nucleus.  In  all  neurones 
several  hours  post-mortem,  they  appear  in  fewer  and  larger  masses  and  it  was  in  this  condition 
that  Nissl  originally  described  them  in  man.  Closely  examined,  the  masses  of  all  sizes  are  found 
to  be  accumulations  of  finer  granules.  Functionally  they  are  supposed  to  be  of  nutritive  signi- 
ficance, substances  in  unstable  chemical  equiblibrium,  energy  stored  in  the  cytoplasm,  capable 
at  need  of  being  split  into  simpler  forms  usable  in  the  activities  of  the  neurone.  The  fact  that 
tigroid  masses  are  absent  from  the  axone  hillock,  the  axone,  and  the  distant  reaches  of  the  den- 
drites may  signify  that  the  substance  is  chiefly  present  here  only  in  the  spUt  and  usable  form. 
Also,  in  the  axone  especially,  the  neurofibrilla?  are  so  closely  arranged  that  the  meshes  of  their 
net  here  are  too  small  to  contain  masses  of  appreciable  size.  Close  examination  of  the  axone 
hillock  and  longitudinal  sections  of  the  axone  in  deeply  stained  preparations  usually  show  a  few 
very  minute  basophilic  granules. 

Sheaths  of  the  axone. — The  great  majority  of  axones  acquire  sheaths  about  them  which 
isolate  and  protect  them  in  their  course  through  other  tissues  or  in  company  with  other  axones. 
A  nerve  fibre  is  an  axone  together  with  its  sheath.     In  transverse  sections,  the  axone  comprises 


CONNECTIVE  TISSUE  OF  NERVOUS  SYSTEM 


767 


the  central  portion  of  the  nerve  fibre  or  its  so-called  "axis-cylinder."  It  is  of  course  the  essen- 
tial portion  of  the  fibre.  As  noted  above  in  describing  their  development,  nerve  fibres  are  classified 
according  to  the  character  of  the  sheaths.  Those  which  possess  sheaths  of  myehn,  a  peculiar 
form  of  fat,  are  known  as  medullaled  fibres,  and  those  in  which  the  sheaths  are  merely  mem- 
branes of  condensed  fibrous  tissue,  void  of  myelin,  are  non-medullated  fibres.  A  medullated 
fibre  also  possesses  a  fibrous  membrane  outside  its  myeUn  sheath,  known  as  the  neurilemma  or 
sheath  of  Schwann.  The  neurilemma  is  of  the  same  origin  and  general  structure  as  the  sheath 
of  the  non-medullated  fibre,  and  both  possess  nuclei  scattered  along  thern.  Medullated  fibres, 
at  more  or  less  regular  intervals,  show  constrictions  at  which  the  myelin  sheath  ceases,  but 
over  which  the  neurilemma  continues.  These  constrictions  are  the  7iodes  of  Ranvier.  The  mye- 
lin is  in  the  form  of  an  emulsion,  whose  fat  droplets  are  supported  in  a  fine  fibrous  reticulum 
(neurokeratin),  while  the  neurilemma  without  serves  to  hold  it  in  place.  The  neurilemma  pos- 
sesses from  one  to  three  or  four  sheath  nuclei  between  adjacent  nodes  of  Ranvier. 

There  is  no  sharp  line  of  separation  between  medullated  and  non-medullated  fibres,  for  in 
any  locality  there  may  be  found  axones  in  all  degrees  of  medullation.     Most  of  the  fibres 

Fig.  610. — Diagram  op  Transverse  Section  op  Spinal  Cord  with  Roots  of  Spinal  Nerve 
AND  Neighbouring  Ganglia  Attached,  Illustrating  Simplest  Forms  op  Neurone 
Chains. 

Fasciculus  cuneatus 


Cephalic  branch  of  spinal  ganglion  neurone 


belonging  to  the  sympathetic  system  (processes  of  sympathetic  neurones)  are  non-medullated, 
but  both  partially  medullated  and  completely  medullated  sympathetic  fibres  may  be  found. 
(See  fig.  609.)  The  myehn  sheaths  of  completely  medullated  sympathetic  fibres  are  always 
thinner  and  less  well  developed  than  those  of  meduUated  cranio-spinal  fibres.  Most  of  the 
fibres  belonging  to  the  cranio-spinal  nerves  and  to  the  central  nervous  system  are  medullated, 
but  among  the  fibres  belonging  to  either  there  are  to  be  found  numerous  non-medullated  fibres. 
As  indicated  in  fig.  609,  nodes  of  Ranvier  are  absent  in  the  medullated  fibres  of  the  central 
system. 

In  all  the  higher  vertebrates,  the  myehn  sheath  always  begins  on  the  axone  a  short  distance 
from  its  parent  cell-body.  The  neurilemma  of  the  medullated  and  the  fibrous  membrane  of 
the  non-medullated  fibre  are  each  faintly  continuous  with  the  fibrous  connective  tissue  sur- 
rounding it,  and,  in  the  cranio-spinal  and  sympathetic  ganglia,  in  which  each  cell-body  of  the 
neurone  has  a  fibrous  capsule  about  it,  the  fibrous  membrane  or  the  neurilemma,  as  the  case 
may  be,  is  directly  continuous  into  the  capsule  of  the  ceU-body.  Upon  approaching  its  final 
termination,  in  other  tissues  or  upon  the  dendrites  or  cell-body  of  other  neurones,  the  nerve 
fibre  always  loses  its  sheath,  the  telodendria  of  the  axone  always  being  bare  when  placed  in 
contact  with  the  other  element.  In  losing  the  sheath,  the  myelin  sheath,  if  present,  always 
ceases  and  the  fibrous  membrane  becomes  continuous  with  the  tissue  investing  the  receiving 
element,  whether  the  capsule  of  the  ganglion  cell,  the  sarcolemma  of  the  skeletal  muscle  fibre, 
the  corium  of  the  skin,  or  the  connective-tissue  capsule  of  the  encapsulated  terminal  corpuscle, 

The  connective  tissue  of  the  nervous  system  is  of  two  main  varieties — while  fibrous  connec- 
tive tissue  and  neuroglia.  White  fibrous  tissue  alone  supports  and  binds  together  the  peripheral 
system,  and  it  is  the  chief  supporting  tissue  of  the  central  system.  As  connective  tissues,  these 
two  varieties  are  quite  similar  in  structure,  each  consisting  of  fine  fibriUiE,  either  dispersed  or  in 
bundles,  among  which  are  distributed  the  nuclei  of  the  parent  syncytium.  In  both  tissues 
nuclei  are  frequently  found  possessing  varying  amounts  of  cytoplasm  which  has  not  yet  been 
transformed  into  the  essential  fibrils. 

In  addition  to  its  enveloping  membranes,  the  three  meninges,  which  are  of  white  fibrous 
tissue,  the  white  fibrous  tissue  supporting  the  central  system  within  is  quite  abundant.     It  is  aU 


768  THE  NERVOUS  SYSTEM 

sent  in  from  without,  either  as  ingrowths  of  the  developing  pia  mater,  the  most  proximal  of  the 
membranes,  or  is  carried  in  with  the  blood-vessels,  of  the  walls  of  which  it  is  an  abundant 
component.  Practically,  the  neuroglia  as  a  connective  tissue  proper  differs  from  white  fibrous 
tissue  only  in  origin  and  in  its  chemical  or  staining  properties.  Based  upon  the  latter,  there  are 
methods  of  technique  by  which  the  two  may  be  distinguished.  White  fibrous  tissue  is  derived 
from  the  middle  germ  layer  or  the  mesoderm,  while  neurogha  comes  from  the  ectoderm.  The 
epithelium  lining  the  central  canal  of  the  spinal  cord  and  the  ventricles  of  the  encephalon,  with 
which  the  canal  is  continuous,  is  the  remains  of  the  mother  tissue  of  the  neuroglia,  and  in  the 
adult  is  the  only  vestige  representing  its  origin.  The  cells  of  this  epithelium  are  known  as 
ependymal  cells,  and  they  are  usually  classed  as  a  variety  of  neuroglia. 

Axones,  with  their  meduUated  or  non-meduUated  sheaths  (nerve  fibres) 
comprise  all  nerves  in  the  periphery  and  all  nerve  tracts  in  the  central  system. 

White  substance  [substantia  alba]  ("white  matter")  consists  of  a  portion  of 
nervous  tissue  in  which  medullated  fibres  predominate.  The  myelin  sheaths, 
being  in  the  form  of  a  fat  emulsion,  reflect  the  entire  spectrum  and  thus  appear 
white. 

Grey  substance  [substantia  grisea]  ("grey  matter")  is  a  portion  of  nervous 
tissue  in  which  medullated  axones  do  not  predominate.  Thus  sympathetic 
ganglia  and  sympathetic  nerves  may  be  grey,  though  the  term  is  usually  applied 
to  grey  portions  of  the  central  system,  such  as  the  cerebral  cortex,  the  central 
grey  column  of  the  spinal  cord,  etc.  Such  grey  regions  contain  more  cell-bodies 
of  neurones  than  other  regions,  though  at  least  half  of  their  volume  may  consist 
of  neuroglia,  white  fibrous  connective  tissue,  blood-vessels,  and  axones  of  both 
varieties. 

Neurone  chains. — As  noted  above,  the  numerous  neurones  comprising  the  nervous  system 
are  functionally  and  anatomically  related  to  aU  the  other  tissues  of  the  body  and  to  each  other. 
A  functionally  complete  nerve  pathway  extends  from  the  tissue  in  which  the  nerve  impulse  is 
aroused  to  the  tissue  in  which  a  resultant  reaction  occurs.  It  is  known  that  the  simplest 
possible  of  such  paths  necessarily  comprises  at  least  two  neurones.  The  great  majority  involve 
a  greater  number.  The  axone  of  one  neurone  bearing  impulses  from  the  peripheral  tissue 
transfers  the  impulses  to  the  dendrites  or  cell-body  of  another  by  synapsis,  and  the  axone  of  this, 
in  the  same  way,  transfers  them  to  another  and  so  on  till  the  final  neurone  receives  the  impulses 
and  the  telodendria  of  its  axone  transfer  the  impulse  to  the  tissue  element  which  reacts  in  re- 
sponse to  the  stimulus  brought.  Neurones  are  thus  linked  together  in  chains.  A  neurone 
chain  may  be  defined,  therefore,  as  a  number  of  neurones  associated  with  each  other  in  series 
to  form  a  functionally  complete  nerve  pathway.  Examples  of  the  simplest  forms  of  neurone 
chains  as  contained  in  the  spinal  cord  are  illustrated  in  fig.  610.  An  impulse  aroused  in  the  skin 
is  borne  by  the  spinal  ganglion  neurone  to  the  spinal  cord  where,  in  the  left  half  of  the  figure, 
telodendria  of  one  of  the  terminal  branches  of  its  axone  form  synapses  with  a  neurone  in  the 
ventral  horn,  and  the  axone  of  this  bears  the  impulse  out  of  the  spinal  cord  to  transmit  it  proba- 
bly direct  to  skeletal  muscle.  This  arrangement  involves  but  two  neurones  and  is  supposed 
to  be  relatively  rare.  In  the  right  half  of  the  figure,  a  third  neurone  is  seen  interposed.  This  is 
a  neurone,  numerous  in  grey  substance  everywhere,  whose  axone  is  relatively  short  and  branches 
frequently,  making  possible  several  synapses  in  the  near  neighbourhood  of  its  parent  cell-body. 
Its  type  is  referred  to  as  the  Golgi  neurone  of  type  II.  This  interposed,  gives  a  chain  of  three 
neurones  between  the  origin  of  the  impulse  in  the  periphery  and  the  contraction  of  muscle  in 
response.  Simple  chains  like  these  can  result  only  in  reflex  activities  and  such  chains  are  often 
called  reflex  arcs.  Another  chain  is  indicated  in  the  figure  in  which  the  reflex  action  involves 
involuntary  or  smooth  muscle.  This  must  involve  at  least  one  sympathetic  neurone,  and,  should 
the  Golgi  neurone  of  type  II  form  synapses  with  the  ventral  horn  neurone  involved,  a  chain 
composed  of  four  neurones  results.  In  the  more  extensive  and  complex  neurone  chains,  such 
as  those  in  which  the  impulse  from  the  skin,  as  above,  ascends  to  the  cerebral  cortex  and  the 
resultant  muscular  contraction  is  thrown  under  cerebral  control,  each  of  the  several  neurones  or 
links  in  the  series  is  not  only  referred  to  by  name  according  to  the  position  of  its  cell-body,  but 
each  is  often  called  according  to  its  order  in  the  series,  as  "neurone  of  first  order,"  "second 
order,"  "third  order,"  etc. 

A  given  axone  may  break  into  a  considerable  number  of  branches  each  of  which  forms 
synapses  with  a  different  second  neurone,  or,  if  peripheral,  the  telodendria  of  each  branch  may 
terminate  upon  a  separate  peripheral  tissue  element.  Thus,  a  given  impulse  aroused  in  a 
peripheral  tissue  element  may  be  transmitted  to  an  ever  increasing  number  of  neurones, 
and  the  initial  neurone  may  comprise  the  first  link  in  a  number  of  neurone  chains.  Such  is 
quite  general  in  the  structural  plan  of  the  nervous  system  throughout.  It  is  thought  possible 
to  consider  each  neurone  interposed  in  a  chain  as  a  separate  source  of  energy,  a  sort  of  relay 
in  the  nerve  path;  that  the  impulse  passing  through  the  axone  is  gradually  weakened  in  over- 
coming resistance,  but,  when  transferred  to  another  neurone,  it  incites  a  splitting  into  usable 
form  of  the  substance  represented  by  the  tigroid  masses  and  thus  a  liberation  of  energy  or  a 
reinforcement  of  the  impulse.  Further,  thus  is  made  possible  the  economy  of  one  neurone 
serving  as  a  hnk  in  a  number  of  nem-one  chains. 

The  axones  (nerve  fibres)  taking  part  in  the  various  neurone  chains  course  in  bundles  of 
varying  size,  the  larger  of  which  have  names.  And  there  is  a  general  tendency  with  axones  of 
the  same  function  and  the  same  origin  to  course  in  company  with  each  other.  A  fibre  bearing 
impulses  from  the  peripheral  tissues  to  the  central  system  is  an  afferent  fibre  or  sensory  fibre.  A 
fibre  bearing  impulses  out  of  the  central  system  to  peripheral  tissues  is  an  efferent  fibre  or  motor 


RELATIONS  OF  NEURONES 


769 


fibre.  Efferent  fibres  which  bear  impulses  to  skeletal  muscle  are  known  as  somatic  ejferent 
fibres,  while  those  which  terminate  upon  the  cell-bodies  of  sympathetic  neurones  and  thus  bear 
impulses  destined  for  smooth  muscle,  cardiac  muscle  and  glands  (secretory)  are  visceral  or 
splanchnic  efferent  fibres. 

A  nerve  is  a  closely  associated  aggregation  of  parallel  nerve  fibres  coursing  in  the  periphery. 
It  may  be  spinal,  cranial  or  sympathetic  according  to  its  attachment  or  according  to  the  origin 
of  the  majority  of  its  fibres.  It  may  contain  several  functional  and  structural  varieties  of  fibres. 
The  spinal  nerves  contain  all  structural  varieties.  Nerve  roots  are  those  bundles  of  fibres  which 
join  to  form  a  nerve.  Most  of  the  cranial  nerves  have  but  one  root  of  origin.  Nerve  roots,  in 
their  turn,  are  formed  by  the  junction  of  smaller  root-filaments.  Nerve  branches  result  from 
the  division  of  the  nerve,  the  separation  of  its  component  fibres  into  separate  bundles.  Some 
branches  are  of  sufficient  size  and  significance  to  be  called  nerves  and  given  separate  names. 
The  smaller  branches  are  called  rami,  twigs,  etc. 

In  the  central  system,  a  given  bundle  of  fibres  is  called  a  fasciculus,  while  two  or  more  adja- 

FiG.  611. — Diagram  of.Transveese  Section  op  Medulla  Oblongata,  Illustrating  Nuclei 
OF  Termination  and  Nuclei  or  Origin. 


cent  fasciculi  com'sing  parallel  to  each  other  comprise  a  funiculus,  a  bundle  of  bundles.  The. 
central  nervous  system  is  bilaterally  symmetrical  throughout  its  length.  A  bundle  of  fibres 
arising  from  cell-bodies  situated  on  one  side  and  crossing  the  mid-line  transversely  to  terminate 
in  the  opposite  side  is  a  commissure.  The  commissures  vary  greatly  in  size  and  contain  fibres 
crossing  in  both  directions.  Scattered  fibres  which  cross  the  mid-line  are  commissural  fibres. 
Fibres  of  varying  lengtli,  arising  from  cell-bodies  situated  in  one  locality  of  the  central  sj-stem, 
which  do  not  cross  the  mid-Une,  but  terminate  in  other  localities  of  the  same  side,  above  and 
below  the  level  of  their  origin  or  in  a  different  region  of  the  same  level,  form  association  fasciculi. 
The  shortest  association  fasciculi,  not  extending  bejj^ond  the  bounds  of  a  given  division  of  the 
central  sj-stem,  are  known  as  fasciculi  proprii.  When  bundles  of  the  same  origin,  functional 
direction  and  significance,  running  one  on  either  side  of  the  mid-line,  cross  the  mid-line  they 
are  said  to  decussate  and  the  crossing  is  known  as  a  decussation.  In  the  decussations,  the  direc- 
tion of  the  crossing  is  oblique  rather  than  transverse. 

The  cell-bodies  of  neurones  whose  axones  go  to  form  certain  nerve  roots,  fasciculi  and  certain 
commissures  show  a  tendency  to  accumulation  in  localized  masses.  In  the  peripheral  system, 
such  an  accumulation  of  cell-bodies  is  known  as  a  ganglion;  in  the  central  system  such  is  distin- 
guished as  a  nucleus.  Thus,  there  are  the  sympathetic  ganglia  which  give  rise  to  sympathetic 
nerves  and  sympathetic  roots  of  nerves;  and  on  the  beginning  of  each  spinal  nerve  there  is  a 
spinal  ganglion  which  gives  rise  to  the  afferent  fibres  of  its  dorsal  root  and  in  its  nerve  trunk. 
There  are  ganglia  on  the  cranial  nerves  which  give  rise  to  the  afferent  or  sensory  axones  in  them 
and  which  are  of  the  same  significance  as  the  spinal  ganglia.     Every  ganglion,  therefore,  has 


770  THE  NERVOUS  SYSTEM 

connected  with  it  bundles  of  nerve  fibres.  Some  of  these  fibres  bear  impulses  from  neighboring 
ganglia  or  from  the  tissues  of  the  neighboring  organs  and  transmit  them  to  the  cell-bodies  of  the 
ganglion ;  others  arise  from  the  cell-bodies  in  the  ganglion  and  bear  impulses  to  the  central  system 
or,  in  case  of  the  sympathetic,  to  other  ganglia  or  to  the  tissues  of  the  peripheral  organs.  Nec- 
essarily, the  larger  the  ganglion,  the  larger  will  be  the  bundles  of  fibres  connected  with  it. 

Nuclei  may  be  considered  in  two  general  classes:  (1)  Recipient  nuclei  or  nuclei  of  termina- 
tion, and  (2)  Nuclei  of  origin. 

A  nucleus  of  termination  is  an  accumulation  of  cell-bodies  in  which  the  axones  of  a  given 
fasciculus  or  of  a  nerve  root  terminate,  that  is,  ceU-bodies  which,  by  synapses,  receive  the  im- 
pulses borne  by  the  terminating  axones.  In  most  cases  the  impulses  transferred  to  a  nucleus  so 
named  are  sensory  in  character.  The  nucleus  may  be  considered  as  a  defined  region  in  which 
neurones  of  the  next  order  are  interpolated  in  a  given  nerve  pathway  or  system  of  neurone 
chains.  Fasciculi  in  the  spinal  cord  which  bear  impulses  to  the  cerebrum  have  their  nuclei 
of  termination  in  the  meduUa  oblongata,  and  the  sensory  or  afferent  axones  of  the  cranial 
nerves  find  their  nuclei  of  termination  upon  entering  the  central  system. 

A  nucleus  of  origin  is  an  accumulation  of  ceU-bodies  of  neurones  which  give  origin  to  the 
axones  going  to  form  a  given  nerve  root  or  a  fasciculus.  Strictly  speaking,  a  nucleus  of  ter- 
mination for  one  nerve  tract  is  the  nucleus  of  origin  for  another,  the  next  link  in  the  neurone 
chain.  However,  the  term  is  commonly  used  to  distinguish  a  group  of  cell-bodies  giving  rise  to  a 
motor  nerve  tract.  Thus  each  motor  cranial  nerve  has  its  nucleus  of  origin  within  the  central 
system.  The  central  grey  substance  of  the  spinal  cord  is  in  the  form  of  a  column  continuous 
throughout  the  length  of  the  cord  and  so  the  cell-bodies  in  the  ventral  horns  of  this  column  which 
give  rise  to  the  motor  or  afferent  roots  of  the  spinal  nerves  are  not  considered  as  grouped  into 
nuclei  of  origin,  one  for  each  of  the  motor  roots. 

The  dorsal  root  of  each  spinal  nerve  is  afferent  or  sensory  in  function  and  its  axones  arise  as 
processes  of  cell-bodies  comprising  the  spinal  ganglion  of  the  nerve.  The  afferent  or  sensory 
fibres  of  the  cranial  nerves  arise  as  processes  of  ceU-bodies  comprising  the  gangha  of  the  cranial 
nerves,  which  ganglia  are,  in  development  and  character,  exactly  homologous  to  the  spinal 
ganglia. 

The  ventral  root  of  each  spinal  nerve  is  efferent  or  motor  in  function  and  its  fibres  arise  as 
processes  of  cell-bodies  situated  in  the  ventral  horn  of  the  grey  substance  of  the  spinal  cord. 
The  efferent  or  motor  fibres  of  the'cranial  nerves  arise  as  processes  of  ceU-bodies  accumulated  as 
nuclei  of  origin  in  the  grey  substance  of  the  encephalon,  and  homologous  with  those  cell-bodies 
of  the  ventral  horns  of  the  spinal  cord  which  give  origin  to  the  ventral-root  fibres. 

The  general  relation  of  the  cerebrum  (which  includes  the  mesencephalon)  to  the  remainder 
of  the  nevous  system  is  a  crossed  relation.  Neurone  chains  from  the  general  body  to  the  cere- 
brum, via  the  spinal  nerves  and  cord  and  via  the  cranial  nerves  and  medulla  oblongata  and  pons 
of  one  side,  cross  the  mid-line  to  terminate  in  the  opposite  side  of  the  cerebrum.  Axones,  and 
neurone  chains,  arising  in  response  in  one  side  of  the  cerebrum,  likewise  usually  decussate  in 
descending  to  terminate  in  the  respective  regions  of  the  opposite  side. 

Many  of  the  names  given  nervous  structures,  prior  to  1850  especially,  instead  of  suggesting 
something  of  their  functional  or  anatomical  significance,  indicate  nothing  more  than  active 
imaginations  for  accidental  resemblances  between  the  various  structures  of  the  nervous  system 
and  objects  in  ordinary  domestic  environment.  Also,  quite  often  the  name  given  a  structure  is 
merely  the  name  of  some  anatomist  associated  with  it.  The  much  needed  elimination  of  these 
old  non-descriptive  names  is  proving  a  very  slow  process.  Attempts  have  often  increased  the 
difficulty  by  making  necessary  the  use  of  several  names  for  a  given  structure  instead  of  one.  The 
most  recent  and  concerted  attempt,  the  nomenclature  known  as  the  BNA  (anatomical  names 
chosen  by  a  commission  appointed  for  the  purpose  which  convened  in  Basle  in  189.5),  has  been 
adopted  by  modern  text-books.  It  is  here  used  in  the  form  of  the  English  equivalents  of  the 
Latin  terms,  except  in  cases  of  those  Latin  terms  which  have  become  so  commonly  used  as  to  be 
considered  words  incorporated  into  the  English  language.  The  BNA  has  retained  manj'  of  the 
old  names  and,  since  a  name  should  indicate  something  of  the  locality  and  significance  of  the 
structure  to  which  it  is  applied,  it  is  not  yet  wholly  satisfactory  throughout.  In  applying  the 
names  of  a  few  fasciculi,  the  BNA  in  the  following  pages  is  slightly  modified  by  so  compounding 
the  name  that  the  first  word  in  the  compound  indicates  the  locality  of  origin  of  the  fasciculus  and 
the  second,  the  locahty  of  its  termination.  Thus,  "Dorsal  spino-cerebellar  fasciculus"  indicates 
the  more  dorsally  coursing  of  the  fasciculi  which  arise  from  cell-bodies  in  the  spinal  cord  and 
terminate  in  the  cerebellum.  This  principle  appUes  to  many  of  the  BNA  names  without  change, 
as  "lateral  cerebrospinal  fasciculus." 

THE  CENTRAL  NERVOUS  SYSTEM 

The  central  nervous  system  [systema  nervorum  centrale]  or  organ  is  an 
aggregation  of  nuclei,  fasciculi  and  commissures — a  large  axis  of  grey  and  white 
substance  situated  in  the  dorsal  mid-line  of  the  body — and  the  bundles  of  fibres 
connecting  it  with  the  tissues  of  other  systems  and  with  the  peripheral  ganglia  are 
of  necessity  correspondingly  large.  So  numerous  are  the  axones  connecting  it 
and  so  intimately  are  its  neurones  associated  that  a  disturbance  affecting  any  one 
part  of  the  system  may  extend  to  influence  all  other  parts.  The  enlarged 
cephalic  extremity  of  this  central  axis,  the  brain  or  encephalon,  is  a  special  ag- 
gregation of  nuclei  and  masses  of  grey  substance,  many  of  which  are  much  larger 
than  any  found  in  the  periphery. 


MORPHOLOGY  OF  SPINAL  CORD  771 

In  the  study  of  the  central  nervous  system  its  enveloping  membranes  or 
meninges  are  met  with  first,  and  logically  should  be  considered  first,  but  since  a 
comprehensive  description  of  these  membranes  involves  a  foreknowledge  of  the 
various  structures  with  which  they  are  related,  it  is  more  expedient  to  consider 
them  after  making  a  closer  study  of  the  entire  system  they  envelop. 

For  convenience  of  study,  the  central  nervous  system  is  separated  into  the 
gross  divisions,  spinal  cord  and  brain  (encephalon)  as  illustrated  in  fig.  602. 
Each  of  these  divisions  will  be  subdivided  and  considered  with  especial  reference 
to  its  anatomical  and  functional  relations  to  the  other  divisions  and  the  inter- 
relations of  its  component  parts. 

I.  THE  SPINAL  CORD 

The  spinal  cord  [medulla  spinalis]  is  the  lower  (caudal)  and  most  attenuated 
portion  of  the  central  nervous  system.  It  is  approximately  cylindrical  in  form 
and  terminates  conically.  Its  average  length  in  the  adult  is  45  cm.  (18  in.)  in  the 
male  and  42  cm.  in  the  female.  It  weighs  from  26  to  28  grams  or  about  2  per 
cent,  of  the  entire  cerebro-spinal  axis. 

After  birth  it  grows  more  rapidly  and  for  a  longer  period  than  the  encephalon,  increasing 
in  weight  more  than  sevenfold,  while  the  brain  increases  less  than  half  that  amount.  Its  specific 
gravity  is  given  as  1.038. 

The  Line  of  division  between  the  spinal  cord  and  the  medulla  oblongata  is  arbitrary.  The 
outer  border  of  the  foramen  magnum  is  commonly  given,  or,  better,  a  transverse  line  just  below 
the  decussation  of  the  pyramids.  Lying  in  the  vertebral  canal,  the  adult  cord  usually  extends 
to  the  upper  border  of  the  body  of  the  second  lumbar  vertebra.  However,  cases  may  be  found 
among  taller  individuals  in  which  it  extends^'no  farther  than  the  last  thoracic  vertebra.  With 
increase  in  stature,  its  actual  length  increases,  but  the  extent  to  which  it  may  descend  the  verte- 
bral canal  decreases.  Up  to  the  third  month  of  intra-uterine  life  it  occupies  the  entire  length 
of  the  vertebral  canal,  but  owing  to  the  fact  that  the  vertebral  column  lengthens  more  rapidly 
and  for  a  longer  period  than  does  the  spinal  cord,  the  latter,  being  attached  to  the  brain  above, 
soon  ceases  to  occupy  the  entire  canal.  At  birth  its  average  extent  is  to  the  body  of  the  third 
lumbar  vertebra. 

External  Morphology  of  the  Spinal  Cord 

In  position  in  the  body,  the  spinal  cord  conforms  to  the  curvatures  of  the 
canal  in  which  it  lies.  In  addition  to  the  bony  wall  of  the  vertebral  canal,  it  is 
enveloped  and  protected  by  its  three  membranes  or  meninges,  which  are  con- 
tinuous with  the  like  membranes  of  the  encephalon:  first,  the  pia  mater,  which 
closely  invests  the  cord  and  sends  ingrowths  into  its  substance,  contributing  to  its 
support;  second,  the  arachnoid,  a,  loosely  constructed,  thin  membrane,  separated 
from  the  pia  mater  by  a  considerable  subarachnoid  space ;  thnd,  the  dura  niater, 
the  outermost  and  thickest  of  the  membranes,  separated  from  the  arachnoid  by 
merely  a  sHt-hke  space,  the  subdural  space. 

The  intimate  association  of  the  central  system  with  all  the  peripheral  organs  is 
attained  chiefly  through  the  spinal  cord,  and  this  is  accomplished  by  means  of 
thirty-one  pairs  of  spinal  nerves,  which  are  attached  along  its  lateral  aspects.  The 
nerves  of  each  pair  are  attached  opposite  each  other  at  more  or  less  equal  intervals 
along  its  entire  length,  and  in  passing  to  the  periphery  they  penetrate  the  men- 
inges, which  contribute  to  and  are  continuous  with  the  connective-tissue  sheaths 
investing  them.  Each  nerve  is  attached  by  two  roots,  an  afferent  or  dorsal  root, 
which  enters  the  cord  along  its  postero-lateral  sulcus,  and  an  efferent  or  ventral 
root,  which  makes  its  exit  along  the  ventro-lateral  aspect. 

With  its  inequahties  in  thickness  and  its  conical  termination  the  spinal  cord  is 
subdivided  into  four  parts  or  regions: — (1)  The  cervical  portion,  with  eight  pairs 
of  cervical  nerves;  (2)  the  thoracic  portion,  with  twelve  pairs  of  thoracic  nerves; 
(3)  the  lumbar  portion,  with  five  pairs  of  lumbar  nerves;  and  (4)  the  conus 
meduUaris,  or  sacral  portion,  with  five  pairs  of  sacral  and  one  pair  of  coccygeal 
nerves.  From  the  termination  of  the  conus  meduUaris,  the  pia  mater  continues 
below  in  the  subarachnoid  space  into  the  portion  of  the  vertebral  canal  not 
occupied  by  the  spinal  cord,  and  forms  the  non-nervous,  slender,  thread-like 
terminus,  the  filu7n  terminale.  This  becomes  continuous  with  the  dura  mater  at 
its  lower  extremity. 


772 


THE  NERVOUS  SYSTEM 


In  the  early  fetus  the  spinal  nerves  pass  from  their  attachment  to  the  spinal 
cord  outward  through  the  intervertebral  foramina  at  right  angles  to  the  long  axis 
of  the  cord,  but,  owing  to  the  fact  that  the  vertebral  column  increases  consider- 
ably in  length  after  the  spinal  cord  has  practically  ceased  growing,  the  nerve-roots 
become  drawn  caudad  from  their  points  of  attachment,  and,  as  is  necessarily 
the  case,  their  respective  foramina  are  displaced  progressively  downward  as  the 
termination  of  the  cord  is  approached,  until  finally  the  roots  of  the  lumbar  and 
sacral  nerves  extend  downward  as  a  brush  of  parallel  bundles  considerably 
below  the  levels  at  which  they  are  attached.  This  brush  of  nerve-roots  is  the 
Cauda  equina.  The  dura  mater,  being  more  closely  related  to  the  bony  wall  of  the 
canal  than  to  the  spinal  cord,  extends  with  the  vertebral  column  and  thus  en- 
velops the  Cauda  equina,  undergoing  a  slightly  bulbous,  conical  dilation  which 
decreases  rapidly  and  terminates  in  the  attenuated  canal  of  the  coccyx  as  the 
coccygeal  ligament. 

The  enlargements. — Wherever  there  is  a  greater  mass  of  tissue  to  be  in- 
nervated, the  region  of  the  nervous  system  supplying  such  must  of  necessity 
possess  a  greater  number  of  neurones.  Therefore,  the  regions  of  the  spinal  cord 
associated  with  the  skin  and  musculature  of  the  regions  of  the  superior  and 

Fig.  612.— Dorsal  View  of  Portion  of  Spinal  Cord  in  Position  in  Vertebral  Canal 

Dura  mater  spinalis — -^fe^V{?/ "^T^felf^'"  ■^^"^chnoidea  spinalis 

■  --■*  Lower  cervical  region 


^  Spinal  nerve 


Thoracic  region 


inferior  limbs  are  thicker  than  the  regions  from  which  the  neck  or  trunk  alone  are 
innervated.  Thus  in  the  lower  cervical  region  the  spinal  cord  becomes  broadened 
into  the  cervical  enlargement,  and  likewise  in  the  lumbar  region  occurs  the  Imnbar 
enlargement.  The  spinal  nerves  attached  to  these  regions  are  of  greater  size 
than  in  other  regions. 

The  cervical  enlargement  [intumescentia  cervicalis]  begins  with  the  third 
cervical  vertebra,  acquires  its  greatest  breadth  (12  to  14  mm.)  opposite  the  lower 
part  of  the  fifth  cervical  vertebra  (origin  of  the  sixth  cervical  nerves),  and  extends 
to  opposite  the  second  thoracic  vertebra.  Unlike  the  lumbar  enlargement,  its 
lateral  is  noticeably  greater  than  its  dorso-ventral  diameter. 

The  lumbar  enlargement  [intumescentia  lumbalis]  begins  gradually  with  the 
ninth  or  tenth  thoracic  vertebra,  is  most  marked  at  the  twelfth  thoracic  vertebra 
(origin  of  the  fourth  lumbar  nerves),  and  rapidly  diminishes  into  the  conus 
medullaris. 

Both  the  lumbar  and  thoracic  regions  are  practically  circular  in  transverse  section.  Neither 
diameter  of  the  lumbar  is  ever  so  great  as  the  lateral  diameter  of  the  cervical  enlargement. 
The  thoracic  part  attains  its  smallest  diameter  opposite  the  fifth  and  si.xth  thoracic  vertebrae 
(attachment  of  the  seventh  and  eighth  thoracic  nerves.) 

The  enlargements  occur  with  the  development  of  the  upper  and  lower  limbs.  In  the  embyro 
they  are  not  evident  until  the  limbs  are  formed.  In  the  orang-utan  and  gorilla  the  cervical 
enlargement  is  greatly  developed;  the  ostrich  and  emu  have  practically  none  at  all. 

Surface  of  the  spinal  cord. — The  cord  is  separated  into  nearly  symmetrical 
right  and  left  halves  by  the  broad  anterior  median  fissure  into  which  the  pia  mater 
is  duplicated,  and  opposite  this,  on  the  dorsal  surface,  by  the  posterior  median 
sulcus.     Along  the  lower  two-thirds  of  the  cord  this  sulcus  is  shallowed  to  little 


SURFACE  OF  SPINAL  CORD 


773 


more  than  a  line  which  marks  the  position  of  the  posterior  median  septum;  in 
the  medulla  oblongata  it  opens  up  and  attains  the  character  of  a  fissure.  Each 
of  the  two  lateral  halves  of  the  cord  is  marked  off  into  a  posterior,  lateral,  and 
anterior  division  by  two  other  longitudinal  sulci.  Of  these,  the  postero-lateral 
sulcus  occurs  as  a  shght  groove  2  to  3|  mm.  lateral  from  the  posterior  median 
sulcus,  and  is  the  groove  in  which  the  root  filaments  of  the  dorsal  roots  enter  the 
cord  in  regular  linear  series.     The  ventral  division  is  separated  from  the  lateral 

Fig.  613. — Drawing  prom  Specimen  showing  Cauda  Equina,  the  Roots  op  Certain  of 
THE  Spinal  Nerves  which  form  it,  and  its  Accompanying  Dura  Mater.     (Dorsal  aspect.) 

V  /      -Dura  mater  spinalis 

I  Lumbar  enlargement 


Conus  meduUaris 


Filum  terminale 


Coccygeal  ligament  (filum 
matris  spinalis) 


by  the  antero -lateral  sulcus.  This  is  rather  an  irregular,  linear  area  than  a 
sulcus.  It  is  from  1  to  2  mm.  broad,  and  represents  the  area  along  which  the 
efferent  fibres  make  their  exit  from  the  cord  to  be  assembled  into  the  respective 
ventral  roots.  This  area  varies  in  width  according  to  the  size  of  the  nerve-roots, 
and,  like  the  postero-lateral  sulcus,  its  distance  from  the  mid-line  varies  according 
to  locality,  being  greatest  on  the  enlargements  of  the  cord.  In  the  cervical  region, 
and  along  a  part  of  the  thoracic,  the  posterior  division  is  subdivided  by  a  delicate 
longitudinal  groove,  the  postero-intermediate  sulcus,  which  becomes  more  evident 


774 


THE  NERVOUS  SYSTEM 


towardjthe  medulla  oblongata  and  represents  the  line  of  demarcation  between  the 
fasciculus  gracihs  and  the  fasciculus  cuneatus.  Occasionally  in  the  upper  cervical 
region  a  similar  line  may  be  seen  along  the  ventral  aspect  close  to  the  anterior 

Fig.  614. — Posterior  and  Anterior  Views  of  the  Spinal  Cord.     (Modified  from  Quain.) 


Clava  ^, 
Funiculus  cuneatus' 

Postero -median  sulcus  f 


Postero-Iateral  sulcus 


Postero-lateral  sulcus-  - 


Postero-median  sulcus    ^l}-i 


Cervical 
enlargement 


I/Umbar 

enlargement 


Olivary  body 
Lateral  funiculus 
Decussation  of  pyramids 

I- ^U Anterior  median  fissure 


Antero-Iateral  sulcus 
(Line  of  ventral  nerve- 
roots) 


Anterior  median  fissure 


median  fissure.     This  is  the  antero-intermediate  sulcus,   forming  the  lateral 
boundary  of  the  ventral  cerebro-spinal  fasciculus. 

Collectively,  the  entire  space  between  the  posterior  median  sulcus  and  the  line 
of  attachment  of  the  dorsal  roots  is  occupied  by  the  posterior  funiculus;  the 
lateral  space  between  the  line  of  attachment  of  the  dorsal  and  that  of  the  ventral 


GREY  SUBSTANCE  OF  SPINAL  CORD 


775 


roots,  by  the  lateral  funiculus;  and  the  space  between  the  ventral  roots  and  the 
anterior  median  fissure,  by  the  anterior  funiculus.  Each  of  these  funiculi  is 
subdivided  within  into  its  component  fasciculi. 

The  dorsal  and  ventral  nerve-roots  are  not  attached  to  the  cord  as  such,  but  are 
first  frayed  out  into  numerous  thread-like  bundles  of  axones  which  are  distributed 
along  their  lines  of  entrance  and  exit.  These  bundles  are  the  root  filaments 
[fila  radicularia]  of  the  respective  roots.  The  fila  of  the  larger  spinal  nerves  are 
fanned  out  to  the  extent  of  forming  almost  continuous  lines  of  attachment,  while 
in  the  thoracic  nerves  there  are  appreciable  intervals  between  those  of  adjacent 
roots.  Throughout,  the  intervals  are  less  between  the  fila  of  the  ventral  than 
between  those  of  the  dorsal  roots. 


Internal  Structure  of  the  Spinal  Cord 

By  reflected  light  masses  of  medullated  axones  appear  white  in  the  fresh,  and 
such  masses  are  known  as  white  substance.  The  spinaal  cord  consists  of  a 
continuous,  centrally  placed  column  of  grey  substance  surrounded  by  a  variously 
thickened  tunic  of  white  substance.     The  closely  investing  pia  mater  sends 


Fig.  615.- 


-A,   Ventral,  and  B,   Dorsal,   Views  op  Portion  op  Spinal  Cord  showing 
Modes  op  Attachment  op  Dorsal  and  Ventral  Roots. 


Antero-Iateral  sulcus  (line  of  ventral  roots) 
/'^Anterior  median  fissure 


Posteriormedian  sulcus 
/  Posterior  in- 


numerous  ingrowths  into  the  cord,  bearing  blood-vessels  and  contributing  to  its 
internal  supporting  tissue.  The  volume  of  white  and  of  grey  substance  varies 
both  absolutely  and  relatively  at  different  levels  of  the  cord.  The  absolute 
amount  of  grey  substance  increases  with  the  enlargements.  The  absolute 
amount  of  white  substance  also  increases  with  the  enlargements  coincident  with 
the  greater  amount  of  grey  substance  in  those  regions.  The  relative  amount  of 
white  substance  increases  in  passing  from  the  conus  medullaris  to  the  medulla 
oblongata,  due  to  the  fact  that  the  ascending  and  descending  axones  associating 
the  cord  with  the  encephalon  are  the  one  contributed  to  the  cord  and  the  other 
gradually  terminating  in  it  at  different  levels  along  its  entire  descent. 

The  grey  substance. — In  the  embryo  all  the  nerve-cells  of  the  grey  substance 
are  derived  from  the  cells  lining  the  neural  tube,  and  in  the  adult  the  column  of 
grey  substance,  though  greatly  modified  in  shape,  still  retains  its  position  about 
the  central  canal.  In  transverse  section  the  column  appears  as  a  grey  figure  of 
two  laterally  developed  halves,  connected  across  the  mid-line  by  a  more  attenu- 
ated portion,  the  whole  roughly  resembling  the  letter  H.  The  cross-bar  of  the  H 
is  known  as  the  grey  commissure.  Naturally,  it  contains  the  central  canal,  which  is 
quite  small  and  is  either  rounded  or  laterally  or  ventrally  oval  in  section,  according 
to  the  level  of  the  cord  in  which  it  is  examined.  The  canal  continues  upward,  and 
in  the  medulla  oblongata  opens  out  into  the  fourth  ventricle.  Downward,  in  the 
extremity  of  the  conus  medullaris,  it  widens  slightly  and  forms  the  rhomboidal 
sinus  or  terminal  ventricle,  then  is  suddenly  constricted  into  an  extremely  small 


776  THE  NERVOUS  SYSTEM 

canal  extending  a  short  distance  into  the  filum  terminale,  and  there  ends  blindly. 
The  grey  commissure  always  lies  somewhat  nearer  the  ventral  than  the  dorsal 
surface  of  the  cord,  and  itself  contains  a  few  medullated  axones  which  vary  in 
amount  in  the  different  regions  of  the  cord.  The  medullated  axones  crossing  the 
mid-line  on  the  ventral  side  of  the  central  canal  form  the  ventral  or  anterior  white 
commissure ;  those,  usually  much  fewer  in  number,  crossing  on  the  dorsal  side  of 
the  central  canal,  form  the  dorsal  or  posterior  white  commissure.  These  two 
commissures  comprise  fibres  crossing  in  the  grey  substance  as  distinguished  from 
others  which  cross  in  the  white  substance  dorsal  and  ventral  to  them.  The  axones 
of  these  commissures  serve  in  functionally  associating  the  two  lateral  halves  of  the 
grey,  column. 

Each  lateral  half  of  the  grey  column  presents  a  somewhat  crescentic  or  comma- 
shaped  appearance  in  transverse  section,  which  also  varies  at  the  different  levels 
of  the  cord.  At  all  levels  each  half  presents  two  vertical,  well-defined  horns, 
themselves  spoken  of  as  columns  of  grey  substance.  The  dorsal  horn  [columna 
posterior]  extends  posteriorly  and  somewhat  laterally  toward  the  surface  of  the 
cord  along  the  line  of  the  postero-lateral  sulcus.  It  is  composed  of  an  apex  and  a 
neck  [cervix  columnse  posterioris]. 

In  structure  the  apex  is  peculiar.  The  greater  portion  of  it  consists  of  a  mass  of  small 
nerve-cells  and  neurogha  tissue,  among  which  a  gelatinous  substance  of  questionable  origin 
predominates,  giving  the  horn  a  semi-translucent  appearance.  This  is  termed  the  gelatinous 
substance  of  Rolando,  to  distinguish  it  from  a  similar  appearance  immediate^  about  the  central 
canal,  the  central  gelatinous  substance.  The  apex  of  the  dorsal  horn  is  widest  in  the  regions 
of  the  enlargements,  especially  the  lumbar,  and  the  gelatinous  substance  of  Rolando  is  most 
marked  in  the  cervical  region.  In  these  regions  the  cervix  consists  of  a  slight  constriction  of 
the  dorsal  horn  between  the  apex  and  the  line  of  the  grey  commissure.  In  the  thoracic  region, 
however,  the  base  of  the  cervix  is  the  thiclcest  part  of  the  dorsal  horn.  This  thickness  is  due  to 
the  presence  there  of  the  nucleus  dorsalis,  or  Clarke's  column — a  column  of  grey  substance 
containing  numerous  nerve-cells  of  larger  size  than  elsewhere  in  the  dorsal  horn,  and  extending 
between  the  seventh  cervical  and  third  lumbar  segments  of  the  cord.  Tapering  finelj'  at  its 
ends,  this  nucleus  attains  its  height  in  the  lower  thoracic  or  first  lumbar  segment.  About  the 
ventro-lateral  periphery  of  the  nucleus  dorsalis  are  scattered  nerve-cells  of  the  same  type  as 
contained  in  it.  These  cells  ai'e  sometimes  distinguished  as  Stilling's  nucleus,  though  Clarke's 
column  was  also  described  by  Stilling.  They  are  more  numerous  about  the  lower  extremity 
of  the  nucleus  dorsalis,  and  they  continue  to  appear  below  its  termination  in  the  lumbar  region. 

The  ventral  horn  [columna  anterior]  of  each  lateral  half  of  the  grey  figure  is 
directed  ventrally  toward  the  surface  of  the  spinal  cord,  pointing  toward  the 
antero-lateral  sulcus.  It  contains  the  cell-bodies  which  give  origin  to  the  efferent 
or  ventral  root  axones,  and  these  axones  make  their  emergence  from  the  spinal 
cord  along  the  antero-lateral  sulcus.  The  ventral  horns  vary  markedly  in  shape 
in  the  different  regions.  In  certain  segments  each  ventral  horn  is  thickened  later- 
ally and  thus  presents  its  two  component  columns  of  grey  substance :  the  lateral 
horn  [columna  laterahs],  a  triangular  projection  of  grey  substance  into  the 
surrounding  white  substance,  in  line  with  or  a  little  ventral  to  the  line  of  the  grey 
commissure;  and  the  ventral  horn  proper  [columna  anterior],  projecting  ventrally. 
In  the  mid-thoracic  region  the  lateral  horn  is  relatively  insignificant,  and  the 
anterior  horn  is  quite  slender;  in  the  cervical  and  lumbar  enlargements  both  horns 
are  considerably  enlarged. 

The  grey  substance  is  not  sharply  demarcated  from  the  white.  In  the 
blending  of  the  two  there  are  often  small  fasciculi  of  white  substance  embedded 
in  the  grey,  and  likewise  the  grey  substance  sends  fine  processes  among  the  axones 
composing  the  white  substance.  Such  processes  or  grey  trabeculse  are  most 
marked  along  the  lateral  aspects  of  the  grey  figure  and  present  there  the  appear- 
ance known  as  the  reticular  formation.  The  reticular  formation  of  the  spinal 
cord  is  most  evident  in  the  cervical  region  (fig.  616). 

Minute  structure. — The  large  cell-bodies  of  the  ventral  horn  as  a  whole  are  divisible  into 
four  groups,  only  three  of  which  are  to  be  distinguished  in  the  mid-thoracic  region  of  the  spinal 
cord: — (1)  A  ventral  group  of  cells,  sometimes  separated  into  a  ventro-lateral  and  a  ventro- 
medial portion  (see  figs.  616,  619),  occupies  the  ventral  horn  proper,  is  constant  throughout 
the  entire  length  of  the  cord,  and  contributes  axones  to  the  ventral  root,  most  of  which  probably 
supply  the  muscles  adjacent  to  the  vertebral  column;  (2)  a  dorso-medial  group  of  cells,  situated 
in  the  medial  part  of  the  ventral  horn,  just  below  the  level  of  the  central  canal,  gives  origin  to 
axones  some  of  which  go  to  the  ventral  root  of  the  same  side,  but  most  of  which  cross  the  mid- 
line vi&  the  anterior  white  commissure,  either  to  pass  out  in  the  ventral  root  of  the  opposite 
side  or  to  enter  the  white  substance  of  that  side  and  course  upward  or  downward,  associating 
with  other  levels  of  the  cord.     Some  of  its  axones  terminate  among  the  cells  of  the  ventral  horn 


WHITE  SUBSTANCE  OF  SPINAL  CORD  111 

in  the  same  level  of  the  opposite  side;  (3)  a  lalEral  group  of  cells,  sometimes  separated  into  a  dorso- 
lateral and  a  ventro-lateral  portion,  occupies  the  lateral  column  or  horn,  and  is  best  differentiated 
in  the  cervical  and  lumbar  enlargements.  Most  of  the  axones  arising  from  its  larger  cells  are 
contributed  to  the  ventral  root  of  the  same  side,  and  such  axones  probably  supply  the  muscles 
of  the  extremities.  Some  of  those  from  its  ventral  portion  are  distributed  to  the  muscles  of 
the  body-wall;  the  dorso-lateral  portion  is  that  part  of  the  lateral  column  \vhich  persists 
throughout  the  cord,  and  is  considered  as  supplying  the  visceral  efferent  fibres  in  the  ventral 
roots.  (4)  an  intermediate  group,  occupying  the  mid-dorsal  portion  of  the  ventral  horn. 
Axones  arising  from  its  cells  are  probably  seldom  contributed  to  the  ventral  root,  but  instead 
course  wholly  within  the  central  nervous  system.  Some  pass  to  the  opposite  side  of  the  cord, 
chiefly  via  the  anterior  and  possibly  the  posterior  white  commissure,  to  terminate  either  in  the 
same  or  different  levels  of  the  grey  column.  Others  of  longer  course  pass  to  the  periphery  of 
the  cord,  join  one  of  the  spino-cerebellar  fasoicuh,  and  pass  upward  to  the  cerebellum. 

Furthermore,  there  are  scattered  throughout  the  grey  substance  many  smaller  cell-bodies 
of  neurones.  These  give  rise  to  axones  of  shorter  course,  either  commissural  or  associational 
proper.  Of  such  axones  many  are  quite  short,  coursing  practically  in  the  same  level  as  that  in 
which  their  cells  of  origin  are  located,  and  serve  to  associate  the  different  parts  of  the  grey  sub- 
stance of  that  level.  Others  course  varying  distances  upward  and  downward  for  the  association 
of  different  levels  of  the  grey  column. 

It  is  evident  from  the  above  that  in  addition  to  the  various  nerve-ceUs  it  contains,  there  is 
also  to  be  found  a  felt-work  of  axones  in  the  grey  substance.  Many  of  these  axones  are 
meduUated,  though  not  in  sufficient  abundance  to  destroy  the  grey  character  of  the  substance. 
The  felt-work  is  composed  of  three  general  varieties  of  fibres: — (1)  The  terminal  branches  of 
axones  entering  from  the  fasciculi  of  the  white  substance  and  forming  end-brushes  about  the 
various  cell-bodies  in  the  grey  substance  (partly  meduUated) ;  (2)  axones  given  off  from  the  cells 
of  the  grey  substance  and  which  pass  into  the  surrounding  white  substance  either  to  enter  the 
ventral-roots  or  to  join  the  ascending  and  descending  fasciculi  within  the  spinal  cord  (partly 
meduUated);  (3)  axones  of  Golgi  neurones  of  type  11,  which  do  not  pass  outside  the  confines 
of  the  grey  substance  (non-meduUated).  Some  axones  of  any  of  these  varieties  may 
cross  the  mid-line  and  thus  become  commissural.  In  general  all  fibres  of  long  course  acquire 
medullary  sheaths  a  short  distance  from  then-  cells  of  origin,  and  lose  them  again  just  before 
termination. 

The  white  substance  of  the  spinal  cord. — The  great  mass  of  the  axones  of  the 
spinal  cord  course  longitudinally  and  form  the  thick  mantle  surrounding  the 
column  of  grey  substance.  This  mantle  is  divided  into  right  and  left  homo- 
lateral halves  by  the  anterior  median  fissure  along  its  ventral  aspect,  and  along 
its  dorsal  aspect  by  the  posterior  median  septum,  which  is  for  the  most  part  a 
connective-tissue  partition  derived  from  the  pia  mater  along  the  line  of  the 
posterior  median  sulcus.  The  mantle  is  supported  internally  by  interwoven 
neuroglia  and  white  fibrous  connective  tissue,  the  latter,  derived  chiefly  from  the 
pia  mater,  closely  investing  it  without. 

The  axones  of  the  white  substance  belong  to  three  general  neurone  systems: — 
(1)  The  spino-cerebral  and  cerebrospinal  system,  which  consists  of  axones  of  long 
course,  one  set  ascending  and  another  descending,  forming  links  in  the  neurone 
chains  between  the  cerebrum  and  the  peripheral  organs.  The  ascending  axones 
of  this  system  collect  the  general  bodily  sensations  which  are  conve.yed 
to  the  cerebrum,  the  cells  of  which  in  response  contribute  axones  which  descend 
the  cord,  conveying  efferent  or  motor  impulses.  (2)  The  spino-cerebellar  and 
cerebellospinal  system  consists  of  conduction  paths,  one  set  ascending  and  another 
descending,  which  are  connections  between  cerebellar  structures  and  the  grey 
substance  of  the  spinal  cord.  (3)  The  spinal  association  and  commissural  system 
of  axones  which  serve  to  associate  the  different  levels  and  the  two  sides  of  the  spinal 
cord  and  which  are  proper  to  the  spinal  cord,  i.  e.,  they  do  not  pass  outside  its 
confines. 

Both  the  first  and  second  systems  increase  in  bulk  as  the  cord  is  ascended. 
The  ascending  axones  of  each  system  are  contributed  to  the  white  substance  of  the 
cord  along  its  length,  and  therefore  accumulate  upward;  the  axones  descending 
from  the  encephalon  are  distributed  to  the  different  levels  of  the  cord  along  its 
length,  and  therefore  diminish  downward. 

The  mass  of  the  third  system  of  axones  varies  according  to  locality.  Wherever 
there  is  a  greater  mass  of  neurones  to  be  associated,  as  there  is  in  the  enlargements 
of  the  cord,  a  greater  number  of  these  axones  is  required.  Their  cells  of  origin, 
being  in  the  grey  substance  of  the  cord,  contribute  to  its  bulk  and  thus  both  the 
cells  and  the  axones  of  this  S3^stem  serve  to  make  the  enlargements  more  marked. 
In  the  lumbar  and  sacral  regions  the  greater  mass  of  the  entire  white  substance 
consists  of  axones  belonging  to  this  system.  It  forms  a  dense  felt-work  about 
the  grey  column  throughout  the  cord.  Necessarily  this  system  contains  axones 
of  various  lengths.     Some  merely  associate  different  levels  within  a  single  segment 


778 


THE  NERVOUS  SYSTEM 


Fig.  616. — Transverse  Sections  prom  Different  Segments  of  the  Spinal  Cord,  show- 
ing Shape  and  Relative  Proportions  of  Grey  and  White  Substance  in  the  Various 
Regions. 

Posterior  funiculus 


Fasciculus  cuneatus 


Anterior  funiculus 
Cervical  I 


Fasciculus 
gracilis        Posterior  septum 


^  Dorsal  (posterior)  root 

D  erior)  horn 


Thoracic  \  III 


CONDUCTION  PATHS 


779 


of  the  cord;  others  associate  the  different  segments  with  each  other.  Axones 
which  associate  the  structures  of  the  spinal  cord  with  those  of  the  medulla 
■  oblongata  may  be  included  in  this  system.  Many  of  these  axones  cross  the  mid- 
line both  in  the  grey  and  in  the  white  substance  to  associate  the  neurones  of  the 
two  sides  of  the  grey  column.  For  purposes  of  distinction,  such  as  cross  the  mid- 
line are  called  commissural  fibres,  while  those  which  course  upward  and  down- 

FiG.  QilG— Continued. 


Sacral  IV 


Coccygeal 

ward  on  the  same  side  are  association  fibres.  Coursing  in  longitudinal  bundles 
about  the  grey  figure,  the  latter  compose  the  fasciculi  proprii  or  '  ground  bundles ' 
of  the  spinal  cord. 

METHODS  BY  WHICH  THE  CONDUCTION  PATHS  HAVE  BEEN 
DETERMINED 

A  purely  anatomical  examination  of  a  normal  adult  cord,  prepared  by  whatever  means, 
gives  no  indication  of  the  fact  that  the  mass  of  longitudinally  coursing  fibres  of  the  white  sub- 


780  THE  NERVOUS  SYSTEM 

stance  is  composed  of  more  or  less  definite  bundles  or  fasciculi,  each  having  a  definite  course, 
and  whose  axones  form  links  (conduction  paths)  in  a  definite  system  of  neurone  chains. 

Present  information  as  to  the  size,  position,  and  connections  of  the  various  fascicuH  is  based  , 
upon  evidence  obtained  by  three  different  lines  of  investigation: — 

(1)  Physiological  investigation. — (a)  Direct  stimulation  of  definite  bundles  or  areas  in 
section  and  carefully  noting  the  resulting  reactions  which  indicate  the  function  and  course  of 
the  axones  stimulated,  (b)  'WaUerian  degeneration'  and  the  application  of  such  methods  as 
that  of  Marchi.  When  an  axone  is  severed,  that  portion  of  it  which  is  separated  from  its  parent 
cell-body  degenerates.  Likewise  a  bundle  of  axones  severed  from  their  cells  of  origin,  whether 
by  accident  or  design,  will  degenerate  from  the  point  of  the  lesion  on  to  the  locality  of  their 
termination  in  whichever  direction  thisimay  be.  This  phenomenon  was  noted  by  Waller  in 
1852  and  is  known  as  WaUerian  degeneration.  By  the  application  of  a  staining  technique 
which  is  differential  for  degenerated  or  degenerating  axones  and  a  study  of  serial  sections  con- 
taining the  axones  in  question,  their  course  and  distribution  may  be  determined.  The  locality 
of  their  cells  of  origin,  if  unknown,  may  be  determined  by  repeated  experiment  till  a  point  of 
lesion  is  found  not  followed  by  degeneration  of  the  axones  under  investigation,  (c)  The  axonic 
reaction  or  'reaction  from  a  distance.'  Cell-bodies  whose  axones  have  been  severed  undergo 
chemical  change  and  stain  differently  from  those  whose  axones  are  intact.  Thus  cell-bodies 
giving  origin  to  a  bundle  of  severed  axones  may  be  located  in  correctly  stained  sections  of  the 
region  containing  them. 

(2)  Embryological  evidence. — In  the  first  stages  of  their  development  axones  of  the  cere- 
bro-spinal  nervous  system  are  non-medullated.  They  acquire  their  sheaths  of  myelin  later. 
Axone  pathways  forming  different  chains  become  medullated  at  different  periods.  Based 
upon  this  fact  a  method  of  investigation  originated  by  Flechsig  is  employed,  by  which  the  posi- 
tion and  course  of  various  pathways  may  be  determined.  A  staining  method  differential  for 
medullated  axones  alone  is  apphed  to  the  nervous  systems  of  foetuses  of  different  ages,  and  path- 
ways meduUated  at  given  stages  may  be  followed  from  the  locality  of  their  origin  to  their 
termination.  In  the  later  stages,  when  most  of  the  pathways  are  medullated  and  therefore 
stain  alike,  the  less  precocious  pathways  may  be  followed  by  their  absence  of  meduUation. 

(3)  Direct  anatomical  evidence. — (a)  Stains  differential  for  axones  alone  are  applied  to  a 
given  locality  to  determine  the  fact  that  the  axones  of  a  given  bundle  actually  arise  from  the 
cell-bodies  there,  or  that  axones  traced  to  a  given  locality  actually  terminate  about  the  cell- 
bodies  of  that  looahty.  For  example,  it  may  be  proved  anatomically  that  the  axones  of  a  dorsal 
root  arise  from  the  cells  of  the  corresponding  spinal  ganglion,  and  then  these  axones  may  be 
traced  into  the  spinal  cord  and  their  terminations  noted  either  by  collateral  or  terminal  twigs, 
or  the  fasciculus  they  join  in  their  cephalic  course  may  be  determined.  (6)  The  staining  prop- 
erties and  the  size  and  distribution  of  the  tigroid  masses  in  the  cell-bodies  of  sensory  neurones 
differ  from  those  in  the  motor  neurones,  and  recently  Malone  has  claimed  that,  in  the  central 
system,  the  cell-bodies  in  the  nuclei  of  sensory  neurone  chains,  those  ascending  toward  the  cere- 
bral cortex,  may  be  distinguished  from  the  cell-bodies  of  the  motor  or  descending  chains  by  the 
arrangement  and  size  of  their  tigroid  masses.  He  claims  further  that  in  the  same  way,  the  cell- 
bodies  of  the  somatic  efferent  neurones  may  be  distinguished  from  those  of  the  visceral 
efferent  neurones.  In  this  way  the  locaUty  of  origin  of  certain  physiologically  known  paths 
may  be  determined. 

(4)  The  so-called  paihologico-anatomical  method  is  based  upon  the  same  general  principles 
as  is  the  physiological  (or  experimental)  method.  A  pathological  lesion,  a  local  infection  or  a 
tumor  for  example,  may  destroy  a  nucleus  of  cell-bodies  or  sever  a  bundle  of  axones,  and  the 
resulting  degeneration  of  the  axones  may  be  followed  through  serial  sections  suitably  prepared. 
The  locahty  of  the  lesion  known,  the  path  may  be  followed  to  determine  the  locality  of  its  ter- 
mination; its  locality  of  termination  known  from  the  symptoms  resulting,  the  path  may  be  fol- 
lowed to  its  cells  of  origin,  or  to  determine  whatever  be  the  locality  of  the  lesion. 

Funiculi. — In  order  that  the  various  fasciculi  may  be  referred  to  with 
greater  ease,  the  white  substance  of  the  spinal  cord  in  section  is  divided  into  three 
areas  known  as  funiculi  or  columns  and  which  correspond  to  the  funiculi  already 
mentioned  as  evident  upon  the  surface  of  the  cord  when  intact.  The  funiculi  are 
outlined  wholly  upon  the  basis  of  their  position  in  the  cord  and  with  reference  to 
the  median  line  and  the  contour  of  the  column  of  grey  substance;  their  component 
fascicuh  are  defined  upon  the  basis  of  function.  (1)  The  'posterior  funiculus  or 
column  is  bounded  by  the  posterior  median  septum  and  the  line  of  the  dorsal  horn; 
(2)  the  lateral  funiculus  or  column  is  bounded  by  the  lateral  concavity  of  the  grey 
column  and  the  lines  of  entrance  and  exit  of  the  dorsal  and  ventral  roots;  (3)  the 
ventral  funiculus  or  column  is  bounded  by  the  Hne  of  exit  of  the  ventral  roots, 
and  by  the  anterior  median  fissure. 

The  posterior  funiculus  or  column  [funiculus  posterior]. — This  funiculus  is 
composed  of  two  general  varieties  of  axones  arranged  in  five  fasciculi.  First,  and 
constituting  the  predominant  type  in  all  the  higher  segments  of  the  cord,  are  the 
afi'erent  or  general  sensory  axones,  which  arise  in  the  spinal  ganglia,  enter  the  cord 
by  the  dorsal  roots,  assume  their  clistribution  to  the  neurones  of  the  cord,  and  then 
take  their  ascending  course  toward  the  encephalon.  The  axone  of  the  spinal 
ganglion  neurone  undergoes  a  T-shaped  division  a  short  distance  from  the  cell- 
body,  one  limb  of  this  division  terminating  in  the  peripheral  organs  and  the  other 
going  to  form  the  dorsal  root.     Upon  entering  the  cord  the  dorsal  root  axones 


POSTERIOR  FUNICULUS 


781 


undergo  a  Y-shaped  bifurcation  in  the  neighbourhood  of  the  dorsal  horn,  one 
branch  ascending  and  the  other  descending.  Their  ascending  branches  form  the 
fasciculus  gracilis  (Goll's  column)  and  the  fasciculus  cuneatus(Burdach's  column). 
These  fasciculi  are  the  chief  ascending  or  sensory  spino-cerebral  connections,  the 
direct  sensory  path  to  the  brain.  The  neurones  represented  in  them  con- 
stitute the  first  link  in  the  nem-one  chain  between  the  periphery  of  the  bodj'-  and 
the  cerebral  cortex. 

Fig.  617. — Showing  Disposition  or  the  Dorsal  Root  Fibres  Upon  Entering  the  Spinal 
Coed.     (From  Edinger,  after  Cajal.) 

A,  shows  dorsal  root  axones  DR,  entering  the  spinal  cord,  bifurcating  at  B,  and  giving  off  collat- 
erals C  to  the  neurones  of  the  cord.  B  shows  the  telodendria  of  these  axones  or  of  their 
collaterals  displayed  upon  cell-bodies  of  the  grey  substance  of  the  cord. 


In  threading  their  way  toward  the  brain,  these  sensory  axones  tend  to  work  toward  the  mid- 
line. Therefore  tliose  of  longer  course  are  to  be  found  nearer  the  posterior  septum,  in  the  upper 
segments  of  tlie  cord,  than  those  axones  which  enter  the  cord  by  the  dorsal  roots  of  the  upper 
segments.  Thus  it  is  that  the  fasciculus  gracilis,  the  medial  of  the  two  fasciculi,  contains  the 
axones  which  arise  in  the  spinal  ganglia  of  the  sacral  and  lumbar  segments.  In  other  words,  it  ia 
the  fasciculus  bearing  sensory  impulses  from  the  lower  limbs  to  the  brain,  while  the  fasciculus 
cuneatus,  the  lateral  of  the  two,  is  the  corresponding  pathway  for  the  higher  levels.  Naturally, 
there  is  no  fasciculus  cuneatus  as  such  in  the  lower  segments  of  the  spinal  cord.  The  axones 
being  mucli  blended  at  first,  it  is  only  in  the  upper  thoracic  and  cervical  region  that  there  is 
any  anatomical  demarcation  between  the  two  fasciculi.  In  this  region  the  two  become  so  dis- 
tinct that  there  is  in  some  cases  an  apparent  connective-tissue  septum  between  them,  continuing 
inward  from  the  postero-intermediate  sulcus — the  surface  indication  of  the  hne  of  their  junction 
(fig.  616). 

Upon  reaching  the  medulla  oblongata  the  fibres  of  the  fasciculus  gracilis  and  the  fasciculus 
cuneatus  terminate  about  cells  grouped  to  form  the  nuclei  of  these  fasciculi.  The  nucleus  of  the 
fasciculus  gracilis  is  situated  medially  and  begins  just  below  the  point  at  which  the  central  canal 
opens  into  the  fourth  ventricle;  the  nucleus  of  the  fasciculus  cuneatus  is  placed  laterally  and  ex- 
tends somewhat  higher  than  the  other  nucleus.     The  neurones  whose  cell-bodies  compose  these 


782  THE  NERVOUS  SYSTEM 

nuclei  constitute  the  second  links  in  the  neurone  chains  conveying  sensory  impulses  from  the 
periphery  to  the  cerebral  cortex. 

The  descending  or  caudal  branches  of  the  dorsal  root  axones  are  concerned 
wholly  with  the  neurones  of  the  spinal  cord.  They  descend  varying  distances, 
some  of  them  as  much  as  four  segments  of  the  cord,  and  give  off  numerous  col- 
laterals on  their  way  to  the  cells  of  the  grey  column.  Those  terminating  about 
cell-bodies  of  the  ventral  horn  which  give  rise  to  the  ventral  or  motor  root-fibres, 
are  responsible  for  certain  of  the  so-called  'reflex  activities'  and  thus  contribute 
to  the  simplest  of  the  reflex  arcs.  In  descending  they  serve  to  associate  different 
levels  of  the  grey  substance  of  the  cord  with  impulses  entering  by  way  of  a  single 
dorsal  root.  Some  of  their  collaterals  cross  the  mid-line  in  the  posterior  white 
commissure,  and  thus  become  connected  with  neurones  of  the  opposite  side.  The 
caudal  branches  of  longer  course  are  scattered  throughout  the  ventral  portion  of 
the  fasciculus  cuneatus  {middle  root  zone) ,  and  the  longest  show  a  tendency  to 
collect  along  the  border-line  between  the  fasciculus  cuneatus  and  the  fasciculus 
gracilis,  and  thus  contribute  largely  to  the  comma-shaped  fasciculus.  Also  some 
of  the  longest  of  them  in  the  lower  levels  course  in  the  oval  bundle  or  septo- 
marginal root  zone. 

The  ascending  branches  of  the  dorsal  root  axones  also  give  off  collaterals  to  the  grey  sub- 
stance of  the  cord,  thus  extending  the  area  of  distribution  of  a  given  dorsal  nerve-root  to  levels  of 
the  cord  above  the  region  at  which  the  root  enters. 

The  greater  number  of  the  terminations  of  dorsal  root  axones  within  the  spinal 
cord  are  concerned  first  with  neurones  other  than  those  contributing  ventral  root- 
fibres.  The  greater  mass  of  the  neurones  concerned  are  those  of  the  Golgi  type  II 
and  those  contributing  the  fasciculi  proprii  or  ground  bundles  of  the  spinal  cord, 
or  the  second  variety  of  axones  composing  the  posterior  funiculus.  The  latter 
fasciculi  arise  from  the  smaller  cells  of  the  grey  column. 

These  axones  pass  from  the  grey  substance  to  enter  the  surrounding  white  substance,  bifurcate 
into  ascending  and  descending  branches,  which  in  their  turn  give  off  numerous  collaterals  to  the 
cells  of  the  grey  substance  of  the  levels  through  which  they  pass.  The  cell-bodies  giving  origin 
to  such  axones  are  so  numerous  that  the  entire  column  of  grey  substance  is  surrounded  by  a 
continuous  felt-work  of  axones  of  this  variety. 

The  dorsal  fasciculus  proprius  (anterior  root  zone  of  posterior  column)  arises  chiefly  from 
cells  situated  in  the  dorsal  horn  (slraium  zonale).  Coincident  with  the  ingrowth  and  arrange- 
ment of  the  fasciculi  gracilis  and  cuneatus  many  fibres  of  the  dorsal  fasciculus  proprius  go  to  form 
both  the  oval  bundle  and  the  comma-shaped  fasciculus.  Thus  these  two  bundles  are  mixed, 
being  fasciculi  proprii  which  contain  caudal  branches  of  dorsal  root  axones.  The  association 
fibres  in  the  oval  bundle  are  the  longest  of  any  belonging  to  the  dorsal  fasciculus  proprius.  The 
cephalic  and  caudal  branches  combined  of  some  are  said  to  extend  more  than  half  the  length  of 
the  cord  and  it  has  been  claimed  that  some  even  associate  the  cervical  region  with  the  conus 
meduUaris.  Based  upon  this  claim,  Obersteiner  has  called  the  oval  bundle,  the  "dorso-medial 
sacral  field"  and  Edinger  has  referred  to  the  most  dorsal  part  of  it  as  the  "tractus  cervico-lum- 
balis  dorsalis."  The  'median  triangle'  is  formed  by  the  continuation  of  the  dorsal  fasciculi  proprii 
with  the  oval  or  septo-marginal  fasciculus.  Some  of  the  axones  of  the  dorsal  fasciculus  proprius 
cross  the  midline  to  distribute  impulses  to  the  neurones  of  the  opposite  side.  These  commissural 
axones,  together  with  certain  collaterals  of  the  dorsal  root  axones,  which  cross  the  mid-line  out- 
side the  dorsal  white  commissure,  compose  the  so-called  cornu-commissural  tract  at  the  base  of 
the  posterior  septum. 

The  lateral  funiculus  or  column  [funiculus  lateralis]. — Not  all  the  axones  of 
the  posterior  or  dorsal  nerve-roots  extend  to  the  encephalon.  Estimation  shows 
that  the  sum  of  all  the  dorsal  roots  is  greatly  in  excess  of  the  sum  contained  in  the 
fasciculi  cuneatus  and  gracilis  just  before  these  enter  their  nuclei  of  termination. 
Therefore  many  of  the  ascending  dorsal  root  axones  are  concerned  with  spinal- 
cord  relations  wholly. 

The  marginal  zone  of  Lissauer,  situated  along  the  lateral  margin  of  the  postero-lateral  sulcus. 
is  composed  largely  of  dorsal  root  axones.  Many  of  these  finally  work  across  the  line  of  the 
sulcus  into  the  posterior  funiculus.  Many  of  the  dorsal  root-fibres  which  do  not  reach  the  brain 
occur  in  Lissauer's  zone.  Many  others  of  course  occur  throughout  the  posterior  column. 
Lissauer's  zone  also  contains  some  fibres  arising  from  the  small  cells  of  the  dorsal  horn,  and  to 
this  extent  corresponds  to  a  fasciculus  proprius.  Ranson  has  found  that  large  numbers  of  the 
non-meduUated  dorsal  root  axones  which  enter  the  cord  are  contributed  to  Lissauer's  zone. 

The  lateral  fasciculus  proprius  (lateral  ground  bundle,  lateral  limiting  layer) 
is  situated  in  the  lateral  concavity  of  the  grey  column  and  is  continuous  with  the 
other  fasciculi  proprii  both  dorsal  and  ventral.     Beyond  that  it  probably  contains 


LATERAL  CEREBROSPINAL  FASCICULUS 


783 


fewer  commissural  axones,  it  is  of  the  same  general  significance  as  the  others. 
It  is  frequently  divided  into  small  bundles  by  the  reticular  formation  (see  fig.  616). 
The  lateral  cerebro-spinal  fasciculus  (crossed  p.yramidal  tract).  In  contrast 
to  the  sensory  fibres  passing  through  the  spinal  cord  conveying  impulses  destined 
to  reach  the  cerebral  cortex,  axones  are  given  off  from  the  pyramidal  cells  of  the 

Fig.  618. — Diageam  Illustrating  the  Formation  of  the  Fasciculi  Proprii  (association 
fasciculi)  and  the  Commissural  Fibres  of  the  Spinal  Cord,  and  the  General  Archi- 
tecture OF  THE  Cord  as  a  Mechanism  for  Reflex  Activities. 

The  ventral  fasciculus  proprius  is  omitted  and  the  lateral  is  shown  on  one  side  only.  The  lower 
spinal  ganglion  neurone  shown  illustrates  the  type  whose  ascending  branch  is  of  much  longer 
extent  than  that  of  the  upper  one. 


-*  Dorsal  fasciculus  proprius 


Commissural 
neurone  in 
ventral  fas-  *— - 
ciculus 
proprius 

Lateral 
fasciculus  'i^ 
proprius 


cortex,  which  descend  to  terminate  about  the  cells  of  the  grey  substance  of  the 
spinal  cord,  chiefly  the  cells  which  give  origin  to  the  ventral  root-fibers. 

Upon  reaching  the  medulla  oblongata  in  their  descent,  these  axones  are  accumulated  into 
two  well-defined,  ventrally  placed  bundles,  the  pyramids,  one  from  each  cerebral  hemisphere. 
In  passing  through  the  brain  stem  the  pyramids  contribute  many  fibres  which  cross  the  mid-line 
to  terminate  in  the  motor  nuclei  of  the  cranial  nerves  of  the  opposite  side,  and  thus  decrease 
appreciably  in  bulk.  According  to  the  estimate  of  Thompson,  only  about  160,000  of  the 
pyramidal  fibres  are  destined  to  enter  the  spinal  cord. 

Upon  reaching  the  lower  part  of  the  medulla,  the  greater  mass  of  the  fibres  of  each  pyramid, 
which  are  destined  to  enter  the  cord,  suddenly  cross  the  mid-line  in  the  'decussation  of  the 


784  THE  NERVOUS  SYSTEM 

pyramids.'  The  remainder  retain  their  ventral  position  in  their  descent  decussating  gradually 
in  the  cord  itself.  The  pyramidal  fibres  which  cross  in  the  medulla  course  in  the  lateral  column 
ventral  to  Lissauer'sjzone,  and  lateral  to  the  lateral  fasciculus  proprius,  and  form  the  lateral 
cerebrospinal  fasciculus  (crossed  pyramidal  tract).  It  is  a  large  fasciculus,  oval  shaped  in 
transection,  and  since  its  axones  terminate  in  the  grey  column  of  the  cord  all  along  its  length,  it 
decreases  in  bulk  as  the  cord  is  descended. 

In  addition  to  the  three  dispositions  of  the  dorsal  root  axones  given  above, 
certain  of  them,  either  by  collaterals  or  terminal  twigs,  form  telodendria  about  the 
cells  of  the  dorsal  nucleus  (Clarke's  column),  which  nucleus  extends  from  about 
the  seventh  cervical  to  the  third  lumbar  segment  of  the  cord.  The  axones  given 
off  by  these  cells  pass  to  the  dorso-lateral  periphery  of  the  lateral  funiculus,  and 
there  collect  to  form  the  dorsal  spino-cerebellar  fasciculus  (direct  cerebellar 
tract  of  Flechsig).  As  such  they  ascend  without  interruption,  and  in  the 
upper  level  of  the  medulla  oblongata  pass  into  the  cerebellum  by  way  of  the 
inferior  cerebellar  peduncle  or  restiform  body.  Necessarily,  this  fasciculus  is  not 
evident  in  levels  below  the  extent  of  the  nucleus  dorsalis. 

Also  situated  superficially  in  the  lateral  funiculus  is  another  ascending  con- 
duction path,  and,  like  the  dorsal  spino-cerebellar  fasciculus,  to  which  it  is  ad- 
jacent, it  is  also  in  part  at  least  a  cerebellar  connection.  Its  position  suggests  its 
name,  superficial  ventro-lateral  spino-cerebellar  fasciculus  (Gowers'  tract). 

This  tract  at'present'does  not  include  as  great  an  area  in  transverse  section  as  when  originally 
described.  The  more  internal  portion  of  the  original  Gowers'  tract  is  now  given  a  separate  sig- 
nificance, and  will  be  considered  separately.  While  the  exact  location  in  the  grey  column  of  all 
the  cell-bodies  giving  origin  to  the  superficial  ventro-lateral  spino-cerebellar  fasciculus  is  un- 
certain, it  is  known  that  certain  ventral  horn  cells  contribute  their  axones  to  it.  Many  of  its 
cells  of  origin  are  scattered  in  the  area  immediately  ventral  to  the  nucleus  dorsalis,  others  in  the 
intermediate  and  mesial  portion  of  the  lateral  group  of  ventral  horn  cells.  In  the  lumbar  region 
these  cells  are  quite  numerous,  and,  therefore,  the  fasciculus  begins  at  a  lower  level  in  the  spinal 
cord  than  does  the  direct  cerebellar  tract.  In  degenerations  it  becomes  visible  in  the  upper  seg- 
ments of  the  lumbar  region,  and  has  been  proved  to  increase  notably  in  volume  as  the  cord  is 
ascended.  Its  axones  arise  for  the  most  part  directly  from  cell-bodies  of  the  same  side  of  the 
cord,  though  it  has  been  shown  by  several  investigators  that  many  of  its  axones  come  from  the 
grey  substance  of  the  opposite  side  by  way  of  the  ventral  white  commissure.  Terminal  twigs  and 
collaterals  of  the  dorsal  root-fibres,  mostly  of  the  same  side,  but  occasionally  from  the  opposite 
side,  terminate  about  its  cells  of  origin.  At  one  time  Gowers'  tract  was  considered  an  entity,  but 
now,  even  in  the  more  Umited  area  it  occupies,  it  must  be  considered  a  mixture  of  axones  of  several 
terminal  destinations  or  distinct  neurone  systems.  The  destination  of  some  of  its  axones  has 
not  been  determined  with  certainty.  A  portion,  the  spino-cerebellar  fasciculus  proper,  go  to 
the  cerebellum,  and  there  have  been  traced  to  the  cortex  of  the  superior  vermis.  Most  of  these 
reach  the  cerebellum  not  by  way  of  the  restiform  body,  as  does  the  dorsal  spino-cerebellar  tract, 
but  pass  on  in  the  brain-stem  to  the  level  of  the  inferior  corpora  quadrigemina,  and  there  turn 
back£to  join  the  brachiumjconjunctivum  or  superior  cerebellar  peduncle.  (Auerbach,  Mott, 
Hoche.)  Only  a  few  of  its_ axones  leave  the  fasciculus  lower  down  in  the  medulla,  to  enter  the 
cerebellum  by  way  of  the  restiform  body,  in  company  with  the  dorsal  spino-cerebellar  tract. 
(Rossolimo,  Tschermak.)  Another  portion  of  its  axones  are  thought  to  reach  the  cerebrum, 
probably  the  nucleus  lentiformis,  though  it  has  not  been  positively  traced  further  than  the 
superior  corpora  quadrigemina.  Many  axones  in  Gowers'  tract  of  the  cord  correspond  to 
those  of  the  fasciculi  proprii,  and  merely  run  varying  distances  in  the  cord,  to  turn  again  into 
its  grey  substance.  Schaeffer  followed  some  of  these  from  the  lumbar  region  up  to  the  level 
of  the  second  cervical  nerve. 

In  the  ventro-mesial  border  of  Gowers'  tract  and  immediately  upon  the 
periphery,  near  the  antero-lateral  sulcus  (exit  of  ventral  nerve-roots),  there  is 
found  in  the  higher  segments  of  the  cord  a  small  oval  bundle,  the  spino-olivary 
fasciculus  or  Helweg's  (Bechterew's)  bundle.  The  functional  direction  of  its 
fibres  has  not  been  settled. 

It  is  asserted  to  arise  from  cell-bodies  of  the  ohve  in  the  medulla  oblongata,  and  in  the  cord 
is  beheved  to  be  associated  with  the  cells  of  the  ventral  column  of  grey  substance,  probably 
those  of  the  lateral;  horn.  More  recent  claims  assert  that  it  arises  fron  cell  bodies  inithe  cord 
and  thus  is  spino-olivary.  By  some  observers  it  has  been  traced  as  far  down  as  the  mid-thoracic 
region;  by  others,  however,  only  as  far  as  the  third  cervicalfsegment.  The  olives  being  nuclei 
largely  concerned  with  cerebellar  connections,  Helweg's  fasciculus  is  probably  an  indirect 
cerebellar  association  with  the  spinal  cord  neurones.  It  is  composed  of  axones  of  relatively  very 
small  diameter,  andjt  is  one  of  the  last  fasciculi  of  the  spinal  cord  to  become  meduUated. 

Situated  between  the  superficial  ventro-lateral  spino-cerebellar  fasciculus  and 
the  lateral  fasciculus  proprius  is  an  area  which,  in  transverse  sections,  may  be,  by 
position,  referred  to  collectively  as  the  intermediate  fasciculus.  So  intermingled 
are  the  axones  comprising  it  that  it  has  been  called  the  mixed  lateral  zone.  It 
contains  fibres  of  at  least  five  functional  varieties: 


FASCICULI  OF  SPINAL  CORD 


785 


786  THE  NERVOUS  SYSTEM 

(1)  Fibres  belonging  to  the  lateral  fasciculus  proprius  which  are  of  longer  extent  gradually 
course  farther  away  from  the  grey  substance  of  the  cord  and  such  mix  into  the  intermediate 
fasciculus. 

(2)  It  is  said  to  contain  fibres  descending  from  the  cerebellum  to  associate  with  the  neurones 
of  spinal  cord,  probably  directly  with  the  ventral  root  or  motor  neurones. 

(3)  The  rubro-spinal  fasciculus. — This  arises  from  cell-bodies  in  the  red  nucleus  of  the 
tegmentum  (in  the  mesencephalon)  and  is  a  crossed  fasciculus.  Axones  arising  from  the  red 
nucleus  of  one  side  cross  the  mid-Une  while  yet  in  the  mesencephalon  and  descend  in  the  lateral 
funiculus  of  the  cord  to  terminate  gradually  about  ceU-bodies  of  the  ventral  horn,  both  those 
which  give  rise  of  ventral  root  fibres  and  those  which  contribute  to  the  fascicuU  proprii.  Its 
fibres  are  more  thickly  bundled  in  a  crescentic  area  fitting  onto  the  ventral  side  of  the  lateral 
cerebro-spinal  fasciculus,  and  some  are  said  to  mix  into  the  area  of  this  latter. 

(4)  The  vestibulo-spinal  fasciculus. — This  is  sometimes  called  the  lateral  vestibulo-spinal 
fasciculus  from  the  fact  that  there  is  a  tract  of  similar  significance  in  the  ventral  funiculus  of 
the  cord.  It  arises  from  some  of  the  ceU-bodies  comprising  Deiter's  nucleus,  the  lateral  nucleus 
of  termination  of  the  vestibular  nerve,  and  from  some  of  those  of  the  spinal  nucleus  (nucleus 
of  the  descending  root)  of  this  nerve,  all  of  which  is  in  the  medulla.  _  It  descends  the  cord,  un- 
crossed, to  terminate  gradually  about  ventral  horn  cells,  thus  comprising  a  part  of  the  apparatus 
for  the  equilibration  of  the  body.  .  Its  fibres  are  thought  to  be  more  closely  collected  in  the  area 
immediately  ventral  to  the  rubro-spinal  fasciculus,  but  of  course  commingle  with  the  latter. 

(5)  The  corpora-quadrigemina-thalamus  path.  The  most  lateral  portion  of  the  intermediate 
fasciculus,  a  small  area  once  included  in  Gower's  tract,  contains  fibres  both  ascending  and  de- 
scending, connecting  the  spinal  cord  with  the  thalamus  (diencephalon)  and  the  quadrigeminate 
bodies  of  the  mesencephalon.  These  are  crossed  paths.  The  ascending  fibres  arise  from  ceU- 
bodies  in  the  ventral  horn  of  one  side,  cross  in  the  ventral  white  commissure  (commissural 
neurones)  and  course  upward  in  the  intermediate  fasciculus  to  their  termination  in  the  opposite 
side.  Those  terminating  about  cell-bodies  in  the  thalamus  form  what  is  known  as  the  spino- 
thalamic tract,  while  those  terminating  in  the  nuclei  of  the  quadrigeminate  bodies  are  called 
the  spino-mesencephalic  or  spino-tectal  tract  (Iradus  spino-tectalis) .  It  is  not  known  in  which 
region  of  the  cord  most  of  these  fibres  arise  but  it  is  quite  probably  the  cervical  region.  The 
fibres  which  arise  from  cell-bodies  of  the  thalamus  and  nuclei  of  the  quadrigeminate  bodies  cross 
the  mid-line  in  the  mesencephalon  and  descend  the  cord  to  terminate  graduaDy  about  cell- 
iDodies  in  the  ventral  horn  ol  the  opposite  side.  Those  from  the  thalamus  are  known  as  the 
thalamo-spinal  tract  and  those  from  the  quadrigemina,  as  the  mesencephalo-  or  tecto-spinal 
tract.     The  latter  is  thought  to  be  the  larger. 

By  the  fibres  of  the  above  tracts  general  sensory  impulses  from  the  body  (skin,  etc.)  are 
carried  to  the  central  portion  of  the  optic  apparatus,  and  the  descending  fibres  give  a  simple 
anatomical  possibility  for  the  movements  of  the  body  in  response  to  visual  and  auditory  im- 
pulses. The  descending  fibres  are  thought  to  terminate  chiefly  in  contact  with  association 
neurones  of  the  fasciculi  proprii,  these  transferring  the  impulses  to  the  neurones  giving  origin 
to  the  ventral  or  motor  root  fibres,  but  some  are  thought  to  terminate  directly  about  the  cell- 
bodies  of  ventral-root  neurones.  A  portion  of  the  intermediate  fasciculus,  most  adjacent  to 
Gower's  tract,  has  been  designated  as  Loewenthal's  tract. 

The  anterior  funiculus  or  column  [funiculus  anterior]. — The  intermediate 
fasciculus  is  continued  ventrally  and  mesially  across  the  line  of  exit  of  the  ventral 
root  axones,  and  thus  into  the  anterior  funiculus.  This  portion  is  also  mixed,  but 
its  axones  of  long  course  associate  somewhat  different  portions  of  the  nerve  axis 
from  those  connected  by  the  more  lateral  portion. 

According  to  the  studies  of  Flechsig,  von  Bechterew,  and  Held,  this  mesial  portion  contains 
fibres,  both  ascending  and  descending,  which  associate  the  various  levels  of  the  grey  substance 
of  the  spinal  cord  with  the  neurones  in  the  reticular  formation  of  the  medulla  oblongata. 
The  levels  to  which  they  have  been  traced  comprise  the  olivary  nuclei,  which  are  largely 
concerned  in  cerebellar  connections,  and  the  nuclei  of  the  vagus,  glosso-pharyngeal,  auditory, 
facial  and  the  spinal  tract  of  the  trigeminus.  Also  some  of  the  ascending  fibres  are  probably 
associated  with  the  nuclei  of  the  eye-moving  nerves.  This  portion  of  the  intermediate 
fasciculus  also  grades  into  and  is  mixed  with  the  axones  of  the  ventral  fasciculus  proprius,  as  is 
its  lateral  portion  with  the  lateral  fasciculus  proprius.  In  other  words,  the  fasciculi  proprii 
proper,  the  axones  nearest  the  grey  substance,  serve  for  the  intersegmental  association  of  the 
different  levels  ol  the  grey  substance  of  the  cord,  while  the  intermediate  fasciculus  contains 
axones  of  longer  course  which  serve  to  associate  more  distant  levels  of  the  grey  substance 
of  the  nerve  axis — that  of  the  spinal  cord  with  its  upward  continuation  into  the  medulla 
oblongata,  pons  and  mesencephalon. 

The  anterior  marginal  fasciculus,  ventral  vestibulo-spinal  tract  (Loewenthal's 
tract)  forms  the  superficial  boundary  of  the  mesial  portion  of  the  intermediate 
fasciculus.  It  is  a  narrow  band,  parallel  with  the  surface  of  the  cord,  and  extends 
mesially  from  the  mesial  extremity  of  Gowers'  tract  (from  Helweg's  bundle)  to 
the  beginning  of  the  anterior  median  fissure. 

The  axones  belonging  to  it  proper  are  descending  from  the  recipient  nuclei  of  the  vestibular 
nerve.  Of  these  nuclei  it  has  been  held  by  some  investigators  that  only  Deiters'  nucleus  (the 
lateral  nucleus  of  termination  in  the  upper  extremity  of  the  medulla  oblongata)  gives  origin 
to  the  axones  of  the  anterior  marginal  fasciculus.  Others  agree  with  Tschermak  that  the  superior 
and  more  laterally  situated  Bechterew's  nucleus  of  the  vestibular  nerve  also  contributes  axones 


ANTERIOR  MARGINAL  FASCICULUS 


787 


to  it,  and  quite  probably  the  nucleus  of  the  spinal  root  of  the  vestibular  adds  further  axones. 
Still  other  investigations  have  shown  that  a  part  at  least  of  the  fasciculus  comes  from  the 
nucleus  fastigius  (roof  nucleus)  of  the  cerebellum.  Since  many  axones  from  both  Deiters' 
and  Beehterew's  nucleus  terminate  in  the  nucleus  fastigius,  the  ventral  vestibulo-spinal  fasciculus 


Fig.  620.— Diagram  of  Spinal  Cord  Illustrating  the  Two  Chief  Varieties  of  Spino- 
CEREBRAL  AND  Cerebro-spinal  Neurone  Chains.  The  Ventral  tecto-spinal  (sulco- 
marginal) fasciculus,  fibres  descending  from  the  superior  quadrigeminate  bodies,  is  not 
filled  in. 


Soni£esthetic  i 


Optic  thalamus 


.  of  cerebral  cortex 


Tecto-spinal  tract 


Decussation  of 
1  emnisci 

Decussation  of 
pyramids 


Cervical  region  of 
spinal  cord 


Superior  quadrigeminate  body 


1 1       ,-.  Inferior  quadrigeminate  body 


'i. Nucleus  of  fasciculus  cuneatus 


TT- Nucleus  of  fasciculus  gracilis 

!  j       ^>  Spino -thalamic  and  spino-mesencephalic  paths 


~__  Fasciculus  cuneatus 
Posterior  (dorsal)  root 

Spinal  ganglion 


Lumbar  region  of 
spinal  cord 


IS,  in  any  case,  a  conduction  path  from  the  nerve  connections  for  equilibration  to  the  grey  sub- 
stance of  the  spinal  cord.  The  fasciculus  is  said  to  extend  as  far  as  the  sacral  region  of  the 
cord,  its  axones  terminating  about  the  cells  of  the  ventral  horns.  The  term  "ventral"  is 
added  to  its  name  to  distinguish  it  from  the  vestibulo-spinal  tract  described  above  as  coursing 
in  the  lateral  funiculus.    It  is  considered  an  uncrossed  pathway. 


788  THE  NERVOUS  SYSTEM 

The  ventral  cerebro-spinal  fasciculus  (anterior  or  direct  pyramidal  tract), 
as  stated  above,  is  the  uucrossed  portion  of  the  descending  cerebro-spinal  system  of 
nem-ones.  It  is  a  small,  oblong  bundle,  situated  mesially  in  the  anterior  funiculus, 
parallel  with  the  anterior  median  fissure.  Like  the  lateral  cerebro-spinal  fasci- 
culus (crossed  pyramidal  tract),  its  axones  arise  from  the  large  pyramidal  cells 
of  the  motor  area  of  the  cerebral  cortex,  and  transmit  their  impulses  to  the  neu- 
rones of  the  ventral  horns  of  the  grey  substance  of  the  spinal  cord,  and  almost 
entirely  to  those  ne.urones  which  give  origin  to  the  ventral  or  motor  root  fibres. 

It  represents  merely  a  delayed  decussation  of  the  pyramidal  fibres,  for  instead  of  crossing 
to  the  opposite  side  in  the  lower  portion  of  the  medulla  oblongata,  as  do  the  fibres  of  the  lateral 
fasciculus,  its  fibres  decussate  all  along  its  course,  crossing  in  the  ventral  white  commissure  and 
in  the  commissural  bundle  of  the  cord  to  terminate  about  the  ventral  horn  cells  of  the  opposite 
side.  Hoohe,  employing  Marchi's  method,  found  that  a  few  of  its  fibres  terminate  in  the  ven- 
tral horn  of  the  same  side.  This  conforms  to  the  pathological  and  experimental  evidence  that 
there  are  homolateral  or  uncrossed  fibres  in  the  crossed  pyramidal  tracts  also.  Like  the  crossed 
tract,  the  ventral  pyramidal  tract  diminishes  rapidly  in  volume  as  it  descends  the  cord.  Its 
loss  is  greatest  in  the  cervical  enlargement,  and  it  is  entirely  exhausted  in  the  thoracic  cord. 
With  the  exception  of  the  anthropoid  apes  and  certain  monkeys,  none  of  the  mammalia  below 
man,  which  have  been  investigated,  possess  this  ventral  pyramidal  tract 

Lying  between  the  ventral  cerebro-spinal  fasciculus  and  the  pia  mater  of  the 
anterior  median  fissure  is  a  thin  tract  of  descending  axones  continuous  ventrally 
with  the  anterior  marginal  fasciculus.  From  its  position  it  is  known  as  the  sulco- 
marginal fasciculus;  functionally  it  is  the  ventral  mesencephalo-spinal  (tecto- 
spinal) tract. 

The  extent  of  its  course  in  the  spinal  cord  is  uncertain.  It  arises  from  the  cells  of  the  grey 
substance  of  the  superior  pair  of  the  quadrigeminate  bodies,  and  there,  in  largest  part  at 
least,  it  crosses  the  mid-line,  and  in  the  so-called  'optic  acoustic  reflex  path'  descends  through 
the  medulla  oblongata  into  the  spinal  cord  of  the  opposite  side.  The  superior  quadrigeminate 
bodies  having  to  do  with  sight,  this  tract  forms  a  second  path  conveying  visual  impulses  to  the 
neurones  of  the  spinal  cord. 

The  commissural  bundle  is  situated  about  the  floor  of  the  anterior  median 
fissm-e,  and  is  the  most  dorsal  tract  of  the  anterior  funiculus.  It  contains  decus- 
sating or  commissural  axones  of  three  varieties. 

(1)  It  contains  the  decussating  axones  of  the  ventral  cerebro-spinal  fasciculus  throughout 
the  extent  of  that  fasciculus;  (2)  it  is  chiefly  composed  of  the  axones  of  the  ventral  fasciculus 
proprius  which  arise  in  the  grey  substance  (ventral  horn)  of  one  side,  cross  the  mid-line  as  com- 
missural fibres,  and  course  both  upward  and  downward  to  be  distributed  to  the  neurones  of 
different  levels  of  the  grey  substance  of  the  opposite  side;  (3)  it  contains  decussating  axones  which 
arise  from  cell-bodies  in  the  grey  substance  of  one  side  and  cross  the  mid-line  to  terminate 
about  cell-bodies  in  practically  the  same  level  of  the  opposite  side.  The  latter  are  merely 
axones  belonging  to  the  ventral  white  commissiu-e  which  course  without  the  confines  of  the  grey 
figure.  The  commissural  bundle  is  present  throughout  the  length  of  the  spinal  cord,  and  is 
largest  in  the  enlargements,  i.  e.,  where  the  association  and  commissural  neurones  occur  in 
greater  number  generally.  In  its  two  last-mentioned  varieties  of  axones  it  corresponds  to  the 
commissural  portion  of  the  dorsal  fasciculus  proprius  (the  cornu-commissural  bundle). 

The  ventral  fasciculus  proprius  is  but  a  continuation  of  the  lateral  fasciculus  proprius,  and 
is  composed  of  ascending  and  descending  association  fibres  of  the  same  general  significance. 

SUMMARY  OF  THE  SPINAL  CORD 

The  spinal  cord  contains  two  general  classes  of  axones  arranged  into  three 
general  systems.  It  contains  axones  which — (a)  enter  it  from  cell-bodies  situated 
outside  its  boundaries,  i.  e.,  in  the  spinal  ganglia  and  in  the  encephalon,  and  (b) 
axones  which  arise  from  cell-bodies  situated  within  its  own  grey  substance,  some 
of  which  axones  pass  outside  its  boundaries  both  to  the  periphery  and  into  the 
encephalon;  some  of  which  remain  wholly  within  it.  Its  axones  comprise — (1) 
a  system  for  the  intersegmental  association  of  its  grey  substance,  both  ascending 
and  descending,  association  proper  and  commissural;  (2)  a  spino-cerebral  and 
cerebro-spinal  system,  ascending  and  descending;  and  (3)  a  spino-cerebellar  and 
cerebello-spinal  system,  ascending  and  descending. 

For  these  relations  the  grey  substance  of  the  cord  contains  three  general  classes 
of  nerve-cells: — those  which  give  rise  to  the  peripheral  efferent  or  motor  axones 
of  the  ventral  roots;  those  which  give  rise  to  central  axones  of  long  course,  going 
to  the  encephalon;  and  those  which  supply  its  central  axones  of  shorter  course, 
the  association  and  commissural  systems. 


SUMMARY  OF  SPINAL  CORD  789 

The  three  systems :  (1)  Association  and  commissural. — Axones  of  spinal  ganglion  (afferent) 
neurones  bifurcate  within  the  cord  into  cephalic  and  caudal  branches  which  extend  varying 
distances  upward  and  downward  and  terminate,  (a)  about  cell-bodies  whose  axones  are  short 
and  terminate  within  the  grey  substance  of  the  same  side  and  in  the  same  level  as  their  cell- 
bodies  {Golgi  neurones  of  type  II);  (b)  about  ceO-bodies  whose  axones  pass  without  the  grey  sub- 
stance, bifurcate  into  cephalic  and  caudal  branches  to  terminate  in  the  grey  substance  of  the 
same  side  but  in  various  levels  above  and  below  (association  fibres  in  the  dorsal,  lateral  and  ven- 
tral fasciculi  proprii);  (c)  about  cell-bodies  whose  axones  cross  the  mid-line  to  terminate  either 
in  the  same  level  of  the  grey  substance  of  the  opposite  side,  or  bifurcate  and  the  cephalic  and 
caudal  branches  pass  in  the  fasciculi  proprii  to  terminate  in  various  levels  of  the  grey  substance 
of  the  opposite  side.  The  longer  cephalic  branches  of  (b)  and  (c)  may  terminate  in  the  meduUa 
oblongata.  All,  associated  with  ventral  root  (efferent)  neurones,  belong  to  the  neurone  chains 
for  the  so-oaOed  reflex  activities. 

(2)  The  cerebral  system. — (a)  The  cephalic  branches  of  certain  spinal  ganglion  neurones 
ascend  beyond  the  bounds  of  the  spinal  cord  to  terminate  within  the  medulla.  Those  ascend- 
ing from  the  spinal  ganglia  of  lower  thoracic  and  lumbo-sacral  segments  accumulate  mesiaUy 
to  form  the  fasciculus  gracilis  which  terminates  in  the  nucleus  of  this  fasciculus;  those  arising 
from  the  upper  thoracic  and  cervical  segments  accumulate  more  laterally  in  the  posterior  funi- 
culus to  form  the  fasciculus  cuneatus  which  terminates  in  the  nucleus  of  the  fasciculus  cuneatus. 
(6)  The  impulses  transferred  to  the  neurones  of  these  nuclei  are  borne  across  the  mid-line  and 
finall}'  reach  the  sensory-motor  area  of  the  cerebral  cortex,  and  cell-bodies  here  give  rise  to  axones 
which  descend,  some  decussating  in  the  medulla  to  form  the  lateral  cerebrospinal  fasciculus, 
others  form  the  uncrossed  ventral  cerebrospinal  fasciculus  which  crosses  the  mid-line  as  it  de- 
scends the  cord.  Both  of  these  fasciculi  transfer  their  impulses  either  directly  to  efferent  ven- 
tral horn  neurones,  or  to  association  neurones  and  these  to  the  efferent  neurones,  (c)  The 
cephalic  and  caudal  branches  of  spinal  ganglion  neurones  terminate  about  cell-bodies  in  the  grey 
substance  of  the  cord  whose  axones  cross  the  mid-line  and  ascend  laterally  to  terminate  either 
in  the  quadrigeminate  bodies  {spino-mesencephalic  tract),  or  in  the  thalamus  (spino-thalamic 
trad),  (d)  Cell-bodies  in  thalamus  and  superior  quadrigeminate  bodies  (receiving  optic  im- 
pulses) and  in  the  inferior  quadrigeminate  bodies  (probably  mediating  auditory  impulses), 
give  axones  which  cross  the  mid-line  in  the  mesencephalon  and  descend,  forming  the  thalamo- 
spinal  and  mesencephalospinal  tracts,  to  terminate  in  contact  with  the  efferent  neurones  of  the 
cord.  Axones  from  both  sources  descend  in  the  lateral  funiculus,  while  from  the  superior 
quadrigeminate  body,  a  separate  bundle  descends  in  the  ventral  funiculus  as  the  sulco-marginal 
{ventral  mesencephalospinal)  fasciculus,  (e)  The  rubrospinal  tract  arises  from  cell-bodies  in 
the  red  nucleus  (in  the  mesencephalon),  crosses  the  mid-line  and  descends  in  the  lateral  funiculus 
to  transfer  (probably  cerebellar)  impulses  to  the  efferent  neurones  of  the  spinal  cord. 

(.3)  The  cerebellar  system. — (a)  The  cephalic  and  caudal  branches  of  spinal  ganglion 
neurones  give  telodendria  about  the  cell-bodies  forming  the  dorsal  nucleus  of  the  cord  (Clarke's 
column)  and  about  cell-bodies  situated  in  grey  substances  ventral  to  the  dorsal  nucleus  ("Still- 
ing's  nucleus")  and  in  the  lateral  horn.  Axones  arising  from  the  cells  of  the  dorsal  nucleus 
pass  laterally  to  form  the  dorsal  spino-cerebellar  fasciculus  which  ascends  into  the  cerebellum  by 
way  of  its  inferior  peduncle  of  the  same  side  and  terminates  about  cell-bodies  of  its  cortex. 
Axones  arising  from  Stilling's  nucleus  and  the  lateral  horn  cells,  of  both  the  same  and  opposite 
sides  of  the  cord,  accumulate  to  form  the  superficial  venlro-lateral  spino-cerebellar  fasciculus, 
which  ascends  to  enter  the  cerebellum  by  way  of  its  superior  peduncle  and  terminate  about  the 
cells  of  the  cerebellar  cortex,  (b)  A  few  axones  arising  in  the  roof  nucleus  of  the  cerebellum 
probably  descent?  in  the  animor  marginal  fasciculus  in  company  with  the  ventral  vestibulospinal 
tract  to  terminate  upon  the  efferent  neurones  of  the  cord,  (c)  The  inferior  olivary  nucleus,  in  the 
medulla,  is  a  cerebellar  relay  and  its  cell-bodies  are  associated  with  the  neurones  of  the  upper  por- 
tion of  the  same  side  of  the  spinal  cord.  Whether  the  axones  arise  in  the  olivary  nucleus  or 
in  the  grey  substance  of  the  cord  is  uncertain,  but  the  more  usual  supposition  favours  the  cord 
and  thus  the  name,  spino-olivary  fasciculus  is  given  them,  (rf)  Among  its  other  functions, 
the  cerebellum  is  concerned  with  equilibration.  The  vestibular  nerve  is  the  afferent  nerve  of 
equilibration  and  a  large  mass  of  the  axones  arising  from  its  nuclei  of  termination  terminate 
in  the  cerebellum,  in  the  roof  nuclei  especially.  Axones  arising  from  cell-bodies  in  Deiters' 
nucleus  (its  lateral  nucleus  of  termination)  and  in  the  nucleus  of  its  descending  root  descend 
the  cord  in  the  lateral  funiculus  to  form  the  (lateral)  vestibulospinal  tract,  and  also  in  the  anterior 
marginal  fasciculus  to  form  ventral  vestibulospinal  tract.  Impulses  borne  by  these  axones  reach 
the  efferent  or  motor  root  neurones.  The  rubro-spinal  fasciculus,  mentioned  above  also  may 
be  possibly  considered  as  belonging  to  the  cerebellar  system. 

Sympathetic  relations. — The  cell-bodies  of  the  efferent  neurones  in  the  ventral  horns  are 
of  two  general  varieties:  (a)  those  whose  axones  terminate  upon  skeletal  muscle  (somatic 
efferent),  and  (6)  those  whose  axones  terminate  in  contact  with  cell-bodies  of  sympathetic 
neurones,  the  splanchnic  or  visceral  efferent  neurones.  The  axones  of  the  sympathetic  neurones, 
in  their  turn,  terminate  upon  cardiac  and  smooth  muscle  (motor)  and  in  glands  (secretory). 
Like  the  somatic,  the  visceral  efferent  neurones  receive  impulses  within  the  ventral  horns 
(a)  from  the  cephalic  and  caudal  branches  of  spinal  ganglion  neurones,  (b)  the  descending  cere- 
bro-spinal  fasciculi,  and  (c)  from  either,  by  way  of  the  fasciculi  proprii  and  Golgi  neurones  of 
type  II.  Their  cell-bodies  are  situated  for  the  most  part  in  the  dorsal  portion  of  the  lateral 
horn  (dorso-lateral  group  of  cells),  which  is  the  only  portion  of  the  lateral  horn  present  in  the 
thoracic  region  of  the  cord.  Many  of  the  visceral  efferent  fibres  leave  the  spinal  nerves  distal 
to  the  spinal  ganglia  and  make  the  white  communicating  rami,  thus  going  to  the  nearest  sym- 
pathetic ganglia;  others  pass  on  in  the  spinal  nerve  and  its  branches  to  terminate  in  more  distal 
sympathetic  ganglia.  Dogiel  has  described  axones  which  arise  in  sympathetic  ganglia  and  termi- 
nate upon  the  ceU-bodies  of  the  spinal  ganglia.  Such  convey  sensory  impulses  which,  however, 
enter  the  spinal  cord  by  way  of  the  dorsal  root  branch  of  the  spinal  ganglion  neurone.  Such 
afferent  sympathetic  neurones  are  relatively  rare,  the  peripheral  distribution  of  the  ordinary 


790 


THE  NERVOUS  SYSTEM 


Fig.  621. — Schematic  Representation  op  the  More  Important  Architectural  Relations 

OF  Neurones  in  the  Spinal  Cord,  Omitting  those  Involving  the  Mesencephalon 

AND  Thalamus. 

a,  afferent  (spinal  ganglion)  axone  of  spino-oerebral  chain  with  bifui'cation  and  caudal  branch; 

b,  afferent  axone  coursing  in  Lissauer's  zone  and  distributed  wholly  within  the  cord; 

c,  collaterals  of  a  and  b  disposed  in  three  ways;  p,  pyramidal  axone  in  lateral  (crossed) 
cerebro-spinal  fasciculus  distributed  to  levels  of  grey  substance;  pa,  axone  in  ventral  cerebro- 
spinal fasciculus  decussating  before  termination;  v,  ventral  root  or  motor  neurones;  n, 
nucleus  dorsalis  giving  axone  to  dorsal  spino-oerebellar  fasciculus;  g,  ascending  neurones 
of  Gowers'  tract;  d,  descending  axone  from  cerebellum  (probable);  fp,  neurones  of  fasciculi 
proprii,  association  proper;  h,  commissural  neurones;  e,  Golgi  cell  of  type  II. 


ORDER  OF  MEDULLATION 


791 


spinal  ganglion  neurone  in  the  domain  of  the  sympathetic  supplying  the  needs  for  sensory 
axones. 

In  transverse  sections  of  the  spinal  cord,  the  relative  area  of  white  substance 
as  compared  with  that  of  grey  increases  as  the  cord  is  ascended.  The  absolute 
area  of  each  varies  with  the  localitj^,  both  being  greatest  in  the  enlargements.  The 
grey  substance  predominates  in  the  conus  medullaris  and  lower  lumbar  segments. 
The  white  substance  begins  to  predominate  in  the  upper  lumbar  segments,  not 
because  of  the  increased  presence  of  ascending  and  descending  cerebral  and  cere- 
bellar axones,  but  because  of  the  increased  volume  of  the  fasciculi  proprii  coinci- 
dent with  the  greater  mass  of  grey  substance  to  be  intersegmentally  associated  in 
this  region.     In  the  thoracic  region  the  greatly  predominating  white  substance 


Fig.  622. — Graphic  Representation  of  the  Varying  Amounts  of  Grey  and  White  Sub- 
stance AND  OF  THE  VARIATIONS  IN  AbEA  OF  ENTIRE  SECTIONS  OP  THE  DIFFERENT  SEGMENTS 

OF  THE  Spinal  Cord.     (From  Donaldson  and  Davis.) 

(Based  upon  measurements  from  several  adult  human  spinal  cords.) 

Curves  showinO  area  of  cross  seel  ion  of  human  spinnl  cord. 


-Whife  ma\ter 


Grey  matter. 


-Entire  section. 


In  ra  IF  ¥  w  Mnn  I   n  m   w    v     yj    yh    yjii    ix     x     xi   xii    i    ii  m  ivyi  iiiiiivn 
CERVICAL  THORACIC  LUMBAR   SACRAL 


is  composed  mostly  of  the  axones  of  long  course.  The  greatly  increased  absolute 
amount  of  white  substance  in  the  cervical  region  is  due  both  to  the  greater  ac- 
cumulation of  cerebral  and  cerebellar  axones  in  this  region  and  to  the  increased 
volume  of  the  fasciculi  proprii  of  the  cervical  enlargement. 


ORDER  OF  MEDULLATION  OF  THE  FASCICULI  OF  THE  CORD 

The  axones  of  the  spinal  cord  begin  to  acquire  their  myehn  sheaths  during  the  fifth  month  of 
intra-uterine  hfe  and  myehnization  is  not  fuUy  completed  till  between  the  fifteenth  and  twentieth 
years.  In  general,  axones  which  have  the  same  origin  and  the  same  locality  of  termination — ■ 
the  same  function — acquire  their  sheaths  at  the  same  time.  While  it  has  been  proved  that  the 
medullary  sheath  does  not  necessarily  precede  the  functioning  of  an  axone,  it  may  be  said  that 
those  fasciculi  which  first  attain  complete  and  definite  functional  ability  are  the  first  to  become 
medullated.  At  birth  all  the  fascicuh  of  the  spinal  cord  are  meduUated  except  Helweg's  fasci- 
culus, and  occasionally  the  lateral  and  ventral  cerebro-spinal  tracts.  The  latter  tracts  vary 
considerably  and  in  general  may  be  said  to  become  medullated  between  the  ninth  month  (before 
birth)  and  the  second  year.  As  indicated  by  their  meduUation,  those  axones  by  which  the  cord 
is  enabled  to  function  as  an  organ  per  se,  that  is,  the  axones  making  possible  the  simpler  reflex 
activities,  complete  their  development  before  those  axones  which  involve  the  brain  with  the 
activities  of  the  cord. 

According  to  Flechsig  and  van  Gehuohten,  and  investigators  succeeding  them,  the  following 
is  the  order  in  which  the  axones  of  the  cord  become  medullated: — 

(1)  The  afferent  and  efferent  nerve-roots  and  commissural  fibres  of  the  grey  substance. 

(2)  The  fasciculi  proprii,  first  the  ventral,  then  the  lateral,  and  last  the  dorsal,  fasciculus 
proprius. 

(3)  The  fasciculus  cuneatus  (Burdach's  column)  and  Lissauer's  zone — the  area  of  tho.se 
ascending  spino-cerebral  fibres  which  run  the  shorter  course  and  which  convey  impulses  from 
the  upper  limbs,  thorax  and  neck. 

(4)  Fasciculus  gracilis  (GoU's  column). 

(5)  The  dorsal  spino-cerebeUar  fasciculus  (direct  cerebellar  tract). 

(6)  The  superficial  antero-lateral  spino-cerebeUar  fasciculus  (Gowers'  tract). 

1(7)  The  lateral  cerebro-spinal  fasciculus  (crossed  pyramidal)  and  the  ventral  cerebro- 
spinal fasciculus  (direct  pyramidal  tract). 

(8)  The  spino-olivary  or  Helweg's  (Beohterew's)  fasciculus. 


792 


THE  NERVOUS  SYSTEM 


The  axones  descending  from  the  cerebellum  and  the  brain-stem  are  so  mixed  with  other 
axones  that  it  is  difficult  to  determine  the  sequence  of  their  medullation.  The  fasciculi  contaia- 
ing  them  also  contain  axones  of  the  variety  in  the  fasciculi  proprii  and  so  show  medullation  early. 
It  is  probable  that  the  ascending,  spino-cerebellar,  fibres  acquire  their  myeUn  earlier  than  the 
descending,  if  descending  exist. 


Blood  Supply  of  the  Spinal  Cord 

The  spinal  rami  of  the  sacral,  lumbar,  intercostal,  or  vertebral  arteries,  as  the  case  may  be, 
accompany  the  spinal  nerves  through  the  intervertebral  foramina,  traverse  the  dura  mater 
and  arachnoid,  and  each  divides  into  a  dorsal  and  a  ventral  radicular  artery.  These  accompany 
the  nerve-roots  to  the  surface  of  the  cord,  and  there  break  up  into  an  anastomosing  plexus  in 
the  pia  mater.  From  this  plexus  are  derived  three  tortuously  coursing  longitudinal  arteries 
and! numerous  independent  central  branches,  which  latter  penetrate  the  cord  direct.  Of  the 
longitudinal  arteries,  the  anterior  spinal  artery  zigzags  along  the  anterior  median  fissure  and 
gives  off  the  anterior  central  branches,  which  pass  into  the  fissure  and  penetrate  the  cord.  These 
branches  give  ofT  a  few  twigs  to  the  white  substance  in  passing,  but  their  most  partial  distribu- 
tion is  to  the  ventral  portion  of  the  grey  substance.  The  two  posterior  spinal  arteries,  one  on 
each  side,  course  near  the  hnes  of  entrance  of  the  dorsal  root-fibres.  They  each  branch  and 
anastomose,  so  that  often  two  or  more  posterior  arteries  may  appear  in  section  upon  either  side 

Fig.  623. — Semi-diagrammatic  Representation  of  the  Blood  Supply  op  the  Spinal  Cobd, 

Posterior  external  spinal  veins 

Posterior  radicular  vein  ,'~  '  " .  ..^^^     Posterior  central  artery  and  vein 

Posterior  spinal  artery 


/PeripKeral  arterial  plexus 


Posterior  radicular  artery 


Intercostal  artery 


Anterior  radicu-     Spinal  ramus 
\       "x  lar  artery 

V  Internal  spinal  vein 
i       Anterior  central  artery 
Anterior  spinal  artery 
Anterior  central  vein 

of  the  dorsal  root.  These  give  off  transverse  or  central  twigs  to  the  white  substance,  but  espe- 
cially to  the  grey  substance  of  the  dorsal  horns.  Of  the  remaining  central  branches  many  enter 
the  cord  along  the  efferent  fibres  of  the  ventral  roots,  and  are  distributed  chiefly  to  the  grey 
substance;  others  from  the  peripheral  plexus  throughout  penetrate  the  cord  and  break  up  into 
capillaries  within  the  white  substance.  Some  of  the  terminal  twigs  of  these  also  enter  the  grey 
substance.  The  blood  supply  of  the  grey  substance  is  so  much  more  abundant  than  that  of 
the  white  substance  that  in. injected  preparations  the  outline  of  the  grey  figure  may  be  easily 
distinguished  by  its  abundance  of  capillaries  alone.  The  central  branches  are  of  the  terminal 
variety.  In  the  white  substance  the  capillaries  run  for  the  most  part  longitudinally,  or 
parallel  with  the  axones. 

The  venous  system  is  quite  similar  to  the  arterial.  The  blood  of  the  central  arteries  is  col- 
lected into  corresponding  central  venous  branches  which  converge  into  a  superficial  venous 
plexus  in  which  are  six  main  longitudinal  channels,  one  along  the  posterior  median  sulcus,  one 
along  the  anterior  median  fissure,  and  one  along  each  of  the  four  lines  of  the  nerve-roots. 
These  comprise  the  posterior  and  anterior  external  spinal  veins  (fig.  623). 

The  internal  spinal  veins  course  along  the  ventral  surface  of  the  grey  commissure,  and  arise 
from  the  convergence  of  certain  of  the  twigs  of  the  anterior  central  vein.  The  posterior  central 
vein  courses  along  the  posterior  median  septum  in  company  with  the  posterior  central  artery, 
and  empties  into  the  median  dorsal  vein.  The  venous  system  communicates  with  the  coarser 
extra-dural  or  internal  vertebral  plexus  chiefly  by  way  of  the  radicular  veins. 

II.  THE  BRAIN  OR  ENCEPHALON 

The  brain  is  that  greatly  modified  and  enlarged  portion  of  the  central  nervous 
system  which  is  enclosed  within  the  cranial  cavity.  It  is  surrounded  and  sup- 
ported by  the  same  three  membranes  (meninges)  that  envelop  the  spinal  cord. 


GENERAL  TOPOGRAPHY 


793 


While  there  is  a  considerable  subarachnoid  space,  the  brain  more  nearly  fills  its 
cavity  than  does  the  spinal  cord. 

The  average  length  of  the  brain  is  about  165  mm.  and  its  greatest  transverEe  diameter 
about  140  mm.  It  averages  longer  in  the  male  than  in  the  female.  Exclusive  of  its  dura  mater, 
the  normal  brain  weighs  from  1100  to  1700  gm.  (40-60  oz.),  varying  in  weight  with  the  stature 
of  the  individual  or  with  the  bulk  of  the  tissues  to  be  innervated.  Its  average  weight  is  1360 
gm.  (48  oz.)  in  males  and  1260  gm.  (44  oz.)  in  females.  It  averages  about  fifty  times  heavier 
than  the  spinal  cord,  or  about  98  per  cent,  of  the  entire  cerebro-spinal  axis.  In  its  precocious 
growth  it  is  at  birth  relatively  much  larger  than  at  maturity.  At  birth  it  comprises  about  13 
per  cent,  of  the  total  body-weight,  while  at  maturity  it  averages  only  about  2  per  cent  of 
the  weight  of  the  body.  Its  specific  gravity  averages  1.036.  In  proportion  to  the  body- 
weight  the  brain-weight  averages  somewhat  higher  in  smaller  men  and  women.  Some  very 
small  dogs  and  monkeys  and  some  mice  have  brains  heavier  in  proportion  to  body-weight 
than  man. 

The  minimal  weight  of  the  adult  brain  compatible  with  human  intelligence  may  be  placed 
at  from  950  to  1000  grams.  Above  the  minimal,  there  is  only  a  general  relation  between  the 
degree  of  intelligence  and  the  weight  of  the  brain,  owing  to  the  fact  that  several  factors  may  be 
coincident  with  large  brains.  It  may  be  said  in  general,  however,  that  the  average  brain  weight 
of  eminent  men  is  above  the  general  average.  Some  men  judged  eminent  have  had  brains  weigh- 
ing less  than  the  general  average.     Of  the  records  generally  accepted,  the  greatest  brain  weight 

Fig.  624. — Mesial  Section  of  the  Head  of  a  Female  Thirty-five  Yeaks  Old  . 


Corpus  callosuiu 


Septum 
pellucidum 
Thalamus 

Vein  of  Galen  -  - 

Epiphysis 
Posterior  cere- 
bral artery 

Corpora ^ 

quadrigemina 

Third  nerve  "     ^V 
Straight  sinus 
Cerebellum 
Occipital  sinus 


Fourth  ventricle 


Sulcus  cinguli 
Fornix 


Crista  galli 
Anterior  cere- 
bral artery 
Optic  chiasma 
Sphenoidal 


Pons 
Medulla  ob- 


for  eminent  men  is  2012  grams,  recorded  for  the  poet  and  noveUst,  Ivan  Tourgenieff.  The  trust- 
worthiness of  this  weighing  is  doubted  by  some  authorities.  From  the  undisputed  records  the 
following  may  be  taken:  Cuvier,  1830  grams;  John  Abercrombie,  1786  grams;  Thackery,  1658 
grams;  Kant,  1600  grams;  Spurzheim,  1559  grams;  Daniel  Webster,  1518  grams;  Louis  Agassiz, 
1495  grams;  Dante,  1420  grams;  Helmholtz,  1440  grams;  Goltz,  1395  grams;  Liebig,  1352  grams; 
Walt  Whitman,  1282  grams;  Gall,  1198  grams.  In  the  average  brain  weights  for  the  races  that 
for  the  Caucasian  stands  highest,  the  Chinese  standing  next,  then  the  Malay,  followed  by  the 
Negro,  with  the  AustraUan  lowest. 

The  differences  between  the  meninges  of  the  brain  and  those  of  the  spinal  cord  occur  chiefly 
in  the  dura  mater.  (1)  The  dura  maler  is  about  double  the  thickness  of  that  of  the  spinal  cord, 
and  consists  of  two  closely  adhering  layers,  the  outermost  of  which  serves  as  the  internal  peri- 
osteum of  the  cranial  bones,  while  that  of  the  cord  is  entirely  separate  from  the  periosteum 
lining  the  vertebral  canal.  (2)  The  inner  layer  is  duplicated  in  places  into  strong  partitions 
which  extend  between  the  great  natural  divisions  of  the  encephalon.  Of  these,  the  sickle- 
shaped  ialx  cerebri  extends  between  the  hemispheres  of  the  cerebrum,  the  crescentic  tentorium 
cerebelli  extends  between  the  cerebellum  and  the  overlapping  posterior  portion  of  the  cerebrum, 
and  the  smaller  falx  cerebelli  occupies  the  notch  between  the  hemispheres  of  the  cerebellum. 
Contained  within  these  partitions  of  the  dura  mater  are  the  great  collecting  venous  sinuses  of 
the  brain.     These  will  be  considered  in  the  more  detailed  description  of  the  cranial  meninges. 

General  topography. — In  its  superior  aspect  or  convex  surface  the  encephalon 
is  oval  in  contour,  with  its  frontal  pole  usually  narrower  than  its  occipital  pole. 


794  THE  NERVOUS  SYSTEM 

Viewed  from  above,  the  cerebrum  comprises  almost  the  entire  dorsal  aspect,  the 
occipital  lobes  overlapping  the  cerebellum  to  such  an  extent  that  only  the  lateral 
and  lower  margins  of  the  cerebellar  hemispheres  are  visible.  The  great  longitu- 
dinal fissure  of  the  cerebrum  separates  the  cerebral  hemispheres. 

Laterally  the  temporal  lobes,  with  their  rounded  anterior  extremities,  the  tem- 
poral poles,  are  each  separated  from  the  frontal  and  parietal  lobes  above  by  the 
lateral  cerebral  fissure  (fissme  of  Sylvius) .  In  the  depths  of  this  fissure  and  over- 
lapped by  the  temporal  lobe  is  situated  the  insula,  or  island  of  Reil  (central  lobe). 

The  surface  of  each  cerebral  hemisphere  is  thrown  into  numerous  folds  or 
curved  elevations,  the  gyri  cerebri  or  convolutions,  which  are  separated  from  each 
other  by  slit-like  fissures,  the  sulci  cerebri.  The  gyri  (and  sulci)  vary  greatly  in 
length,  in  depth,  and  in  their  degrees  of  curvature.  The  larger  and  deeper  of  them 
are  similar  in  the  two  hemispheres;  most  of  them  are  individually  variable,  but 
each  gyrus  of  one  hemisphere  is  homologous  with  that  of  the  like  region  of  the 
other  hemisphere.  By  gently  pressing  open  the  great  longitudinal  fissure,  the 
corpus  callosum,  the  chief  commissural  pathway  between  the  cerebral  hemi- 
spheres, may  be  seen.  The  occipital  margin  of  this  large  transverse  band  of  white 
substance  is  rounded  and  thickened  into  the  splenium  of  the  corpus  callosum, 
while  its  frontal  margin  is  curved  ventrally  into  its  genu  and  rostrum. 

The  base  of  the  encephalon  (fig.  625)  is  more  irregular  than  the  convex  surface, 
and  consists  of  a  greater  variety  of  structures.  In  the  mid-line  between  the  frontal 
lobes  appears  the  anterior  and  inferior  extension  of  the  great  longitudinal  fissure. 
When  the  margins  of  this  are  separated,  the  outer  aspect  of  the  rostrum  of  the 
corpus  callosum,  the  downward  continuation  of  the  curve  of  the  genu,  is  exposed. 

The  inferior  surface  of  each  frontal  lobe  is  concave,  due  to  its  compression  upon 
the  superior  wall  of  the  orbit.  The  orbital  gyri  with  their  respective  orbital  sulci 
occupy  this  concave  area. 

The  cranial  nerves  [nervi  cerebrales]. — Along  the  mesial  border  of  each  orbital 
area,  and  parallel  with  the  great  longitudinal  fissure,  lie  the  olfactory  bulbs  con- 
tinued into  the  olfactory  tracts.  Each  olfactory  bulb  is  the  first  central  connection 
or  the  '  nucleus  of  reception'  of  the  olfactory  nerve,  the  first  of  the  cranial  nerves. 
A  few  fine  filaments  of  this  nerve  may  often  be  discerned  penetrating  the  ventral 
surface  of  the  bulb.  The  olfactory  bulb  and  tract  lies  in  the  olfactory  sulcus, 
which  forms  the  lateral  boundary  of  the  gyrus  rectus,  the  most  mesial  gyrus  of  the 
inferior  surface  of  the  frontal  lobe.  Upon  reaching  the  area  of  Broca  (area  parol- 
factoria),  or  the  region  about  the  medial  extremity  of  the  gyrus  rectus,  each 
olfactory  tract  undergoes  a  slight  expansion,  the  olfactory  tubercle,  and  then 
divides  into  tliree  roots  or  olfactory  striae — a  medial,  an  intermediate,  and  a  lateral, 
which  comprise  the  olfactory  trigone.  The  striae  begin  their  respective  courses 
upon  the  anterior  perforated  substance,  an  area  which  contains  numerous  small 
foramina  through  which  the  antero-lateral  group  of  central  cerebral  arteries  enters 
the  brain.  This  region  forms  the  anterior  boundary  of  that  area  of  the  base  of 
the  encephalon  in  which  the  substance  of  the  brain  becomes  continuous  across  the 
mid-line. 

At  the  medial  boundary  of  the  anterior  perforated  substance  the  optic  nerves 
come  together  and  fuse  to  form  the  optic  chiasma.  Thence  the  optic  tracts  dis- 
appear under  the  poles  of  the  temporal  lobes  in  their  backward  course  to  the  thai- 
ami  and  the  geniculate  bodies  or  metathalami. 

Immediately  behind  the  optic  chiasma  occurs  that  diverticulum  from  the  floor 
of  the  third  ventricle  known  as  the  tuber  cinereum.  It  is  connected  by  its  tubular 
stalk,  the  infundibulum,  with  the  hypophysis  or  pituitary  body,  which  occupies 
its  special  depression  (sella  turcica)  in  the  floor  of  the  cranium  and  is  usually  torn 
from  the  encephalon  in  the  process  of  its  removal.  Behind  the  tuber  cinereum 
are  the  two  mammillary  bodies  (corpora  albicantia),  each  of  which  is  connected 
with  the  fornix,  one  of  the  larger  association  fasciculi  of  the  cerebrum.  The 
peduncles  of  the  cerebrum  (crura  cerebri)  are  the  two  great  funiculi  which  asso- 
ciate the  cerebral  hemispheres  with  all  the  structm-es  below  them.  They  diverge 
from  the  anterior  border  of  the  pons  (Varoli)  and,  one  for  each  hemisphere,  dis- 
appear under  the  poles  of  the  temporal  lobes.  The  pons  (brachium  pontis  or 
middle  cerebellar  peduncle)  is  chiefly  a  bridge  of  white  substance  or  a  commissure 
between  the  cerebellar  hemispheres. 


CRANIAL  NERVES 


795 


The  oculomotor  or  third  pair  of  cranial  nerves  make  their  exit  from  the  poste- 
rior perforated  substance  in  the  interpeduncular  fossa  just  behind  the  corpora 
mammillaria. 

Tlie  trochlear  nerves  emerge  around  the  lateral  aspects  of  the  pedunculi 
cerebri  along  the  anterior  border  of  the  pons.  The  trochlear  is  the  smallest  of  the 
cranial  nerves,  and  the  only  pair  arising  from  the  dorsal  aspect  of  the  brain. 

The  trigeminus,  or  fifth  cranial  nerve,  is  the  largest.  It  penetrates  the  pons  to 
find  its  recipient  nuclei  in  the  depths  of  the  brain-stem.  It  is  a  purely  sensory 
nerve,  but  it  is  accompanied  by  the  much  smaller  masticator  nerve  which  is  motor 
and  is  usually  referred  to  as  the  motor  root  of  the  trigeminus. 

Fig.  625. — View  of  the  Base  op  the  Beain.     (After  Beaunis.) 


Gyri  orbitales 


Anterior  perfor- 
ated substance 
Hypophysis 
tuber 


Inferior  vermis 


Five  pairs  of  cranial  nerves  are  attached  to  the  brain-stem  along  the  inferior 
border  of  the  pons: — the  abducens  nerve,  which  is  motor,  emerges  near  the 
mid-line;  the  facial,  motor,  emerges  from  the  more  lateral  aspect  of  the  brain- 
stem ;  the  glosso-palatine  or  the  intermediate  nerve  of  Wrisberg,  largely  sensory, 
is  attached  in  company  with  the  facial;  and,  entering  the  extreme  lateral  aspect 
of  the  stem  are  the  cochlear  and  vestibular  nerves.  These  latter  two,  when  taken 
together  as  one,  are  known  as  the  acoustic  (auditory)  or  eighth  cranial  nerve. 
They  are  both  purely  sensory.  The  cochlear  courses  for  the  most  part  laterally 
and  dorsally  around  the  inferior  cerebellar  -peduncle,  giving  it  the  appearance 
from  which  it  derives  its  name,  'restiform  body.' 

The  remaining  four  pairs  of  the  cranial  nerves  are  attached  directly  to  the 
medulla  oblongata.  This  comprises  that  portion  of  the  brain-stem  beginning  at 
the  inferior  border  of  the  pons  above,  and  continuous  with  the  first  segment  of 
the  spinal  cord  below.  On  its  ventral  surface  the  pyramids  and  the  olives  (olivary 
bodies)  are  the  two  most  prominent  structures.  The  pyramids,  which  are  con- 
tinuous below  into  the  pyramidal  (cerebro-spinal)  tracts  of  the  spinal  cord,  form 
the  two  tapering  prominences  along  either  side  of  the  anterior  median  fissure;  the 
olives  are  the  oblong  oval  elevations  situated  between  the  pyramids  and  the  resti- 


796  THE  NERVOUS  SYSTEM 

form  bodies,  and  each  is  the  superficial  indication  of  the  inferior 'olivary  nucleus. 

The  glosso-pharyngeal,  the  vagus  (pneumogastric),  and  the  spinal  accessory 
cranial  nerves  are  attached  along  the  lateral  aspect  of  the  medulla  oblongata  in 
line  with  the  facial  nerve  and  between  the  olive  and  the  restiform  body.  The 
spinal  accessory,  purely  motor,  is  assembled  from  a  series  of  rootlets  which 
emerge  from  the  lateral  aspect  of  the  first  three  or  four  cervical  segments  of  the 
spinal  cord,  as  well  as  from  the  medulla.  It  becomes  fully  formed  before  reaching 
the  level  of  the  olive,  and  passes  lateralward  in  company  with  the  vagus  and  fur- 
ther on  joins  the  latter  in  part.  The  root  filaments  of  the  vagus  and  glosso- 
pharyngeal are  arranged  in  a  continuous  series,  and,  if  severed  near  the  surface  of 
the  medulla,  those  belonging  to  the  one  nerve  are  difficult  to  distinguish  from 
those  belonging  to  the  other.     Both  of  these  are  mixed  motor  and  sensory. 

The  hypoglossal,  purely  motor,  emerges  as  a  series  of  rootlets  between  the 
pyramid  and  the  olive.  Thus  it  arises  nearer  the  mid-line,  and  in  line  with  the 
abducens,  trochlear,  and  oculomotor. 

If  the  occipital  lobes  be  lifted  from  the  superior  surface  of  the  cerebellum  and 
the  tentorium  cerebelli  removed,  the  quadrigeminate  bodies  of  the  mid-brain  or 
mesencephalon  may  be  observed.  These  are  situated  above  the  cerebral  pedun- 
cles, in  the  region  of  the  ventral  appearance  of  the  oculomotor  and  trochlear 
nerves.  Resting  upon  the  superior  pair  of  the  quadrigeminate  bodies  [colliculi 
superiores]  is  the  epiphysis  or  pineal  body,  and  just  anterior  to  this  is  the  cavity  of 
the  third  ventricle,  bounded  laterally  by  the  thalami  and  roofed  over  by  the  tela 
chorioidea  of  the  third  ventricle  (velum  interpositum) . 

By  separating  the  inferior  margin  of  the  cerebellum  from  the  dorsal  surface  of 
the  medulla  oblongata  the  lower  portion  of  the  fourth  ventricle  (rhomboid  fossa) 
may  be  seen.  The  cisterna  cerebello-meduUaris,  the  subarachnoid  space  in  this 
region,  is  occupied  in  part  by  a  thickening  of  the  arachnoid.  This  is  continuous 
with  the  tela  chorioidea  (ligula)  and  chorioid  plexus  of  the  fourth  ventricle.  The 
former  roofs  over  the  lower  portion  of  the  fourth  ventricle,  and,  passing  through  it 
in  the  medial  fine,  is  the  lymph  passage,  the  foramen  of  Magendie,  by  which  the 
cavity  of  the  fourth  ventricle  communicates  with  the  subarachnoid  space.  The 
fourth  ventricle,  as  it  becomes  continuous  with  the  central  canal  of  the  spinal  cord, 
terminates  in  a  point,  the  calamus  scriptorius.  From  the  inferior  surface,  the 
cerebellar  hemispheres  are  more  definitely  demarcated,  and  between  them  is  the 
vermis  or  central  lobe  of  the  cerebellum. 

Divisions  of  the  encephalon. — The  encephalon  as  a  whole  is  developed  from  a 
series  of  expansions,  flexures,  and  thickenings  of  the  wall  of  the  cephalic  portion  of 
the  primitive  neural  tube,  the  three  primary  brain  vesicles.  Being  continuous 
with  the  spinal  cord,  it  is  arbitrarily  considered  as  beginning  just  below  the 
level  of  the  decussation  of  the  pyramids,  or  at  a  line  drawn  transversely  between 
the  decussation  of  the  pyramids  and  the  level  of  the  first  pair  of  cervical  nerves. 

In  its  general  conformation  four  natural  divisions  of  the  brain  are  apparent: 
the  two  most  enlarged  portions — (1)  the  cerebral  hemispheres  and  (2)  the  cere- 
bellum; (3)  the  mid-brain  (mesencephalon)  between  the  cerebral  hemispheres  and 
the  cerebellum,  and  (4)  the  medulla  oblongata,  the  portion  below  the  pons  and 
above  the  spinal  cord  (fig.  602).  However,  the  most  logical  and  advantageous 
arrangement  of  the  divisions  and  subdivisions  of  the  encephalon  is  on  the  basis  of 
their  development  from  the  walls  of  the  embryonic  brain  vesicles.  (See  fig.  598.) 
On  this  basis,  for  example,  both  the  medulla  oblongata  and  the  cerebellum 
with  its  pons  are  derived  from  the  posterior  of  the  primary  vesicles,  and  are, 
therefore,  included  in  a  single  gross  division  of  the  encephalon,  viz.,  the  rhomben- 
cephalon. In  the  following  outline  the  anatomical  components  of  the  enceph- 
alon are  arranged  with  reference  to  the  three  primary  vesicles  from  the  walls 
of  which  they  are  derived,  and  the  primary  flexures  and  thickenings  of  the  walls 
of  which  they  are  elaborations. 

During  the  early  growth  of  the  neural  tube  its  basal  or  ventral  portion  and  the  lateral  por- 
tions acquire  a  greater  thickness  than  the  roof  of  the  tube,  and  thus  the  tutpe  is  longitudinally 
divided  into  a  basal  or  ventral  zone  and  an  alar  or  dorsal  zone.  This  is  especially  marked  in  the 
brain  vesicles.  Structures  arising  from  the  dorsal  zone  begin  as  localised  thickenings  of  the 
roof.  For  example,  in  the  rhombencephalon  the  greater  part  of  the  medulla  oblongata  and  of 
the  pons  region  is  derived  from  the  ventral  zone,  while  the  cerebellum  is  derived  from  the  dorsal 
zone.  The  first  of  the  flexures  occurs  in  the  region  of  the  future  mesencephalon,  and  is  known 
as  the  cephalic  flexure;  next  occurs  the  cervical  flexure,  at  the  junction  with  the  spinal  cord; 


DIVISIONS  OF  THE  ENCEPHALON 


797 


O 

O 

W 
H 

O 

CO 

O 

h-l 

02 

I— I 
> 


i=<  d 


gs 


798 


THE  NERVOUS  SYSTEM 


Fig.  626.— Median  Sagittal  Section  theough  Embryonic  Human  Bbain  at  End  of  Fiest 
Month.     (After  His.) 

(Showing  the  locahties  of  origin  of  the  derivatives  of  the  three  primary  vesicles  named  in  outline 

on  p.  797.) 


Hypophysis  (anterior  sii 

Ventral  zone 
Dorsal  zone 


Fig.  627. — Sagittal  Section  op  Brain  of  Human  Embryo  of  the  Third  Month.     (After  His) 

(Reference  numerals  correspond  with  those  of  fig.  626  and  those  after  names  of  parts  in  outline 

on  p.  797.) 


MEDULLA  OBLONGATA 


799 


third,  the  pontine  flexure,  in  the  region  of  the  future  fourth  ventricle.  Both  the  cervical  and 
pontine  flexures,  while  having  a  significance  in  the  growth  processes,  are  almost  entirely  ob- 
literated in  the  later  growth  of  the  encephalon. 

The  location  of  the  development  of  the  various  parts  of  the  encephalon  may  be 
determined,  and  their  elaboration  and  changes  in  shape  and  positionmay  be  traced 
by  comparing  the  accompanying  figs.  626,  627,  628.     The  reference  numbers  in 

Fig.  628. — Median  Sagittal  Section  op  Adult  Human  Brain.     (Drawing  of  model  by  His.) 
(Reference  numerals  same  as  in  figs.  626  and  627.) 


Olfactory  bulb 

Optic  chiasma 

Infundibulum 


the  last  three  figures  correspond  with  the  like  numerals  after  the  names  of  the 
parts  on  p.  797  in  the  outline  of  the  divisions  of  the  encephalon.  The  more 
detailed  subdivisions  of  the  parts  will  be  met  with  in  their  individual  descriptions. 

THE  RHOMBENCEPHALON 


1.  THE  MEDULLA  OBLONGATA 

The  medulla  oblongata  [myelencephalon]  is  the  upward  continuation  of  the 
spinal  cord.  It  is  only  about  25  mm.  long,  extending  from  just  above  the  first 
cervical  nerve  (beginning  of  the  first  cervical  segment  of  the  spinal  cord)  to  the 
inferior  border  of  the  pons.  It  lies  almost  wholly  within  the  cranial  cavity,  resting 
upon  the  superior  surface  of  the  basal  portion  of  the  occipital  bone,  with  its  lower 
extremity  in  the  foramen  magnum.  Its  weight  is  from  6  to  7  gm.  or  about  one- 
half  of  one  per  cent  of  the  whole  cerebro-spinal  axis.  It  is  a  continuation  of  the 
spinal  cord,  and  more.  It  contains  structures  continuous  with  and  homologous 
to  the  structures  of  the  spinal  cord,  and  in  addition  it  contains  structures  which 
have  no  homologues  in  the  spinal  cord.  Due  in  part  to  these  additional  struc- 
tures, the  medulla,  as  it  approaches  the  pons,  rapidly  expands  in  both  its  dorso- 
ventral  and  especially  in  its  lateral  diameters.  With  it  are  associated  nine  of  the 
pairs  of  cranial  nerves. 

On  its  anterior  or  ventral  aspect  the  anterior  median  fissure  of  the  spinal  cord 
becomes  broader  and  deeper  because  of  the  great  height  attained  by  the  pyramids. 
At  the  level  at  which  the  pyramids  emerge  from  the  pons,  the  region  in  which  they 
are  largest,  the  fissure  terminates  in  a  triangular  recess  so  deep  as  to  merit  the 
name  foramen  caecum.  The  pyramids  are  the  great  descending  cerebral  or  motor 
funiculi.  In  the  medulla  oblongata  they  decrease  in  bulk  in  passing  toward  the 
spinal  cord,  for  the  reason  that  many  of  the  pyramidal  axones  are  contributed  to 
structm-es  of  the  medulla,  chieflj^  after  crossing  the  mid-line.  At  the  lower  end  of 
the  medulla  occurs  the  decussation  of  the  pyramids,  by  which  the  anterior  median 
fissure  is  almost  obliterated  for  about  6  mm.,  and  which,  upon  removal  of  the  pia 
mater,  may  be  easily  observed  as  bundles  of  fibres  interdigitating  obliquely  across 
the  mid-line. 

Not  aU  the  p)Tamidal  fibres  cross  to  the  opposite  side  at  this  level  in  man,  but  a  portion 
of  those  coursing  in  the  lateral  portion  of  the  pyramid  maintain  their  ventro-mesial  position 


800 


THE  NERVOUS  SYSTEM 


and  continue  directly  into  the  spinal  cord,  to  form  there  the  ventral  cerebro-spinal  fasciculus  or 
direct  pyramidal  tract.  However,  most  of  such  fibres  finally  cross  the  mid-line  during  their 
course  in  the  spinal  cord.  The  exact  proportion  of  the  direct  fibres  is  variable,  but  always  the 
greater  mass  of  each  pjrramid  crosses  to  the  opposite  side  at  the  level  of  the  decussation  of  the 
pyramids,  and  descends  the  cord  as  the  lateral  cerebro-spinal  fasciculus  or  crossed  pyramidal 
tract.  Both  of  these  pjnramidal  tracts  are  described  in  the  discussion  of  the  fascicuU  of  the 
cord. 

Fig.  629. — Semi-diagbammatic  Representation  of  the  Ventral  Aspect  of  the  Rhomben- 
cephalon AND  Adjacent  Portions  of  the  Cerebrum.  _  (Modified  from  Quain.) 
Insula 

Olfactory  tract 

Hypophysis 


—  Optic  nerve 
Optic  tract 


Mammillary  bodies 


Cerebral  peduncle 


Semilunar  (Gasser 
ian)  ganglion 


Oblique  fasciculus 
of  pons 


Tuber  cinereum 

Oculomotor  nerve 
,--  (in) 

Lateral  geniculate 
body 

-  Trochlear  nerve  (IV) 

/         ~~-  Trigeminus  (V) 
.  Abducens  (VI) 

—  Brachlum  of  pons 
Facial  nerve  (Vn) 

~      Glosso-palatine  nerve 
(intermediate  part  of 
X  facial) 

Cochlear  and   vestibular 
\    nerves  (Acoustic  or  VIII) 

\    Glosso-pharyngeal  nerve  (IX) 
Vagus  nerve  (XJ 


\  Accessory  nerve  (XI) 
(spmal  accessory) 


Decussation  of  pyramids 


Each  pyramid  is  bounded  laterally  by  the  antero-lateral  sulcus,  also  continu- 
ous with  that  of  the  same  name  in  the  spinal  cord.  Toward  the  pons  this  sulcus 
separates  the  pyramid  from  the  olive  [oliva]  (inferior  olivary  nucleus),  and  in  the 
region  of  the  olive  there  emerge  along  this  sulcus  the  root  filaments  of  the  hypo- 
glossal nerve.  These  are  in  line  with  the  filaments  of  the  ventral  roots  of  the  spinal 
nerves.  The  olives,  as  their  name  implies,  are  oblong  oval  eminences  about  1.2 
cm.  in  length.  They  extend  to  the  border  of  the  pons,  and  are  somewhat  thicker 
at  their  upper  ends.  Their  surfaces  are  usually  smooth,  except  at  their  lower  ends, 
where  they  frequently  appear  ribbed,  owing  to  bundles  of  the  external  arcuate 
fibres  passing  across  them  to  and  from  the  restiform  body,  which  occupies  the 
extreme  lateral  portion  of  the  medulla.  Along  the  line  between  the  restiform  body 
and  the  olive  are  attached  .the  root  filaments  of  the  vagus,  glosso-'pharyngeal, 
and  spinal  accessory  nerves.  Both  the  abducens  and  the  facial  nerve  emerge  along 
the  inferior  border  of  the  pons,  the  facial  in  line  with  the  glosso-pharyngeal,  but 
the  abducens  in  line  with  the  hypoglossus. 

Dorsal  aspect. — The  increased  lateral  diameter  of  the  medulla  oblongata  is 
contributed  to  a  great  extent  by  the  restiform  bodies.     These  are  the  inferior  cere- 


MEDULLA  OBLONGATA 


801 


bellar  peduncles  (crura  cerebelli  ad  medullam  oblongatam)  and  contain  the  major- 
ity of  the  ascending  fibres,  which  associate  the  cerebellum  with  the  structures 
below  it. 

In  toto,  the  restiform  bodies  are  much  larger  than  could  be  formed  by  the  combined  cere- 
bellar fasciculi  of  the  spinal  cord,  their  great  size  being  due  to  their  receiving  numerous  axones 
coursing  in  both  directions,  which  connect  the  cerebellum  with  structures  contained  in  the 
medulla  oblongata  alone,  so  that  in  the  medulla  they  increase  as  they  approach  the  cerebellum. 
Their  mesial  borders  form  the  lateral  boundaries  of  the  fourth  ventricle.  Their  name  (resliform, 
meaning  rope-hlie)  was  suggested  from  the  appearance  frequently  given  them  by  the  fibres 
of  the  cochlear  (acoustic  division  of  the  eighth)  nerve,  which  course  around  their  lateral  per- 
iphery to  become  the  strice  medullares   in  the  floor  of  the  fourth  ventricle. 

Fia.  630. — Diagram  Showing  the  DBctrssATioN  op  the  Pyramids. 
The  uppermost  level  represented  is  near  the  inferior  border  of  the  pons. 

Chorioid  tela  of  fourth  ventricle 
Solitary  tract 

--Nucleus  of  vestibular  nerve 

y--' Restiform  body 

.  Spinal  tract  of  trigeminus 
•Nucleus  of  cochlear  nerve 

-Vagus  nerve 


Hypoglossal  nerve 
Pyramid 


Spinal  tract  of  trigeminus 

Decussation  of  pyramids 


Lateral  cerebro-spinal  fasciculus 
^crossed  pyramidal  tract) 


Ventral  cerebro-spinal  fasciculus 
(direct  pyramidal  tract) 


Upon  removal  of  the  cerebellum  it  may  be  seen  that  below  the  calamus  scrip- 
torius  (inferior  terminus  of  the  fourth  ventricle)  the  structures  manifest  in  the  dor- 
sal surface  of  the  medulla  are  directly  continuous  with  those  of  the  spinal  cord. 
The  fasciculus  gracilis  (Goll's  column)  of  the  spinal  cord  acquires  a  greater  height 
and  volume  and  becomes  the  funiculus  gracilis  of  the  medulla,  and  because  of  this 
increased  height  the  posterior  median  sulcus  of  the  cord  becomes  deepened  into  the 
posterior  median  fissure.  The  posterior  intermediate  sulcus  is  also  accentuated 
by  the  fasciculus  cuneatus  (Burdach's  column)  likewise  now  enlarged  into  the 
funiculus  cuneatus  of  the  medulla.  The  lateral  funiculus  of  the  medulla,  of 
course,  does  not  contain  the  lateral  or  crossed  pyramidal  tract  present  in  the  spi- 
nal cord. 

At  the  border  of  the  calamus  scriptorius  the  funiculus  gracilis  terminates  in  a 
slight  elevation,  the  clava,  which  is  the  superficial  indication  of  the  nucleus  of  the 
fasciculus  gracilis.  Beginning  somewhat  more  anteriorly,  and  having  a  somewhat 
greater  length,  is  a  similar  enlargement  of  the  funiculus  cuneatus,  the  tuberculum 
cuneatum  or  nucleus  of  the  fasciculus  cuneatus. 


802 


THE  NERVOUS  SYSTEM 


These  nuclei  are  the  groups  of  nerve  cell-bodies  about  which  the  ascending  or  sensory 
axones  of  the  respective  fasciculi  terminate  or  where  the  sensory  impulses  are  transferred  to  a 
second  neurone  in  their  course  to  the  structui-es  of  the  encephalon.  These  cell-bodies  in  their 
turn  give  off  axones  which  immediately  cross  the  mid-line  and  assume  a  more  ventral  position, 
contributing  largely  to  the  lemniscus  or  fillet  of  the  opposite  side,  and  thus  such  axones  are  the 
encephalic  continuation  of  the  central  sensory  pathway  conveying  impulses  from  the  periphery 
of  one  side  of  the  body  to  the  opposite  side  of  the  cerebrum.  The  crossing  of  these  axonesjis 
known  as  the  decussation  of  the  lemnisci. 

Fig.  631. — Dohsal  Aspect  op  Medulla  Oblongata  and  Mesencephalon,  Showing  the 
Floor  of  the   Fourth  Ventricle   (Rhomboid  Fossa).     (Modified  from  Spalteholz.) 

aedullaiis  of  thalamus  \  r  ^         .  , 

Internal  capsule 


Habenular  commisbur 

\ 

Trigonum  habenuls  v  /  \ 

Epiphysis 


Brachium    of    infErior 
quadrigeminate  todv 


Cerebral  pi  dund 
Anterior  medullary  velu 
Brachium  conjunctiva  m 


Brachium  of  pons  " 


Restiformbodj 


""-y 


Calamus  scriptorms 


Funiculus  gracilis 


Funiculus  cuneatus 


Lateral  funiculus 


~ Caudate  nucleus 

.^j^— Taenia  chorioidea 

Stria     terminalis 

~        ~      of  thalamus 


^1£4.S.l  i^'  tnaiamus 

Quadrigeminate  bodies 

Trochlear  nerve 

^~  Lingula  cerebelli 


Trigonum  of  vagus  (ala  cinerea) 
"--    Nucleus  of  fasciculus  cuneatus 
-    Obex 


Nucleus  of  fasciculus  gracilis  (clava) 


■Posterior  median  fis 


•Posterior  intermediate  sulcus^ 


With  the  termination  of  the  dorsal  funiculi  and  the  ventral  course  of  the  fibres 
of  the  lemnisci  in  their  decussation,  the  central  canal  of  the  spinal  cord  loses  its 
roof  of  nervous  tissue  in  the  medulla  and  comes  to  the  surface  as  the  fourth  ven- 
tricle. The  floor  of  the  fourth  ventricle,  which  corresponds  to  the  floor  of  the 
central  canal,  is  considerably  widened  into  two  lateral  recesses  opposite  the  junc- 
tion of  the  inferior  and  middle  cerebellar  peduncles  of  either  side,  and,  being 
pointed  at  both  its  superior  and  inferior  extremities,  it  is  rhomboidal  in  shape  and 
thus  is  the  rhomboid  fossa.  The  pia  mater  of  the  spinal  cord  is  maintained  across 
the  tip  of  the  calamus  scriptorius  to  form  the  obex,  a  small,  semilunar  lamina 
roofing  over  the  immediate  opening  of  the  central  canal.  The  obex  carries  a  few 
medullated  commissural  fibres.  .    ' 


MEDULLA  OBLONGATA 


803 


Fia.  632. — Diagram  of  the  Spino-cerebellar  FAscicuiii  and  the  Origin  and  Decussa- 
tion OF  the  Lemnisci. 


Nucleus  of  spinal 
tract  of  trigeminus^ 
Spinal  tract  o£  \ 
trigeminus       \ 


Root  filaments  of  glosso- 
pharyngeal ] 


Nucleus  of  ala  cinerea 


804  THE  NERVOUS  SYSTEM. 

2.  THE  PONS 

The  pons  (Varoli)  is,  for  the  most  part,-  a  great  commissure  or  'bridge'  of 
white  substance  coursing  about  the  ventral  aspect  of  the  brain-stem,  and  connect- 
ing the  cerebellar  hemisphere  of  one  side  with  that  of  the  other.  In  addition  it 
contains  fibres  passing  both  to  and  from  the  structures  of  the  brain-stem  and  the 
grey  substance  of  the  cerebellum,  and  fibres  descending  from  the  cerebral  cortex. 
Each  of  its  lateral  halves  forms  the  middle  of  the  three  cerebellar  peduncles,  the 
hrachium  pontis  of  either  side. 

In  size  it  naturally  varies  directly  with  the  development  of  the  cerebellum,  both 
in  a  given  animal  and  relatively  throughout  the  animal  series.  In  man  it  attains 
its  greatest  relative  size,  and  possesses  a  median  or  basilar  sulcus  in  which  lies 
the  basilar  artery.  Its  sagittal  dimension  varies  from  25  to  30  mm.,  while  its 
transverse  dimension  (longitudinal  with  the  course  of  its  fibres)  is  somewhat 
greater.  It  is  a  rounded  white  prominence  interposed  between  the  visible  portion 
of  the  cerebral  peduncles  (crura)  above  and  the  medulla  oblongata  below.  Its 
inferior  margin  is  rounded  to  form  the  inferior  pontine  sulcus,  which,  between  the 
points  of  the  emergence  of  the  pyramids,  is  continuous  with  and  transverse  to 
the  foramen  cjecum.  Its  superior  margin  is  thicker  and  is  rounded  to  form  the 
superior  pontine  sulcus,  which,  between  the  cerebral  peduncles,  is  continuous  with 
and  transverse  to  the  interpeduncular  fossa.  (See  fig.  629.)  It  is  bilaterally  sym- 
metrical. The  ventro-lateral  bulgings  of  its  sides  (and,  therefore,  the  basilar 
sulcus)  are  produced  by  the  passage  through  it  of  the  fibres  of  the  cerebral  pedun- 
cles from  above,  to  reappear  as  the  pyramids  below.  Its  ventral  surface  rests 
upon  the  basilar  process  of  the  occipital  bone  and  the  dorsum  sellse  of  the  sphenoid, 
while  its  lateral  surfaces  are  adjacent  to  the  posterior  parts  of  the  petrous  portions 
of  the  temporal  bones. 

The  fibres  of  the  thicker  superior  portion  of  the  pons  (Jasciculus  superior  pontis)  course 
obliquely  downward  to  their  entrance  into  the  brachium  of  the  pons  and  the  cerebellar  hemis- 
phere; those  of  the  lower  and  mid-portions  (Jasciculus  medius  pontis)  course  more  transversely, 
naturally  converging  upon  approaching  the  cerebellum.  Certain  fibres  of  the  upper  mid- 
portion  course  at  first  transversely  and  then  turn  abruptly  downward  across  the  fibres  above 
them,  to  join  the  inferior  portion  of  the  brachium  pontis.  This  bundle  is  termed  the  oblique 
fasciculus  (fig.  629).  The  trigeminus  or  fifth  cranial  nerve  penetrates  the  superior  lateral  por- 
tion of  each  brachium  pontis  near  the  point  of  the  downward  turn  of  the  obhque  fasciculus;  its 
large  afferent  root  and  the  masticator  nerve  (its  small  efferent  root)  accompany  each  other  quite 
closely.  On  either  side  of  the  basal  surface  of  the  pons  usually  may  be  seen  a  small  bundle 
of  fibres  which  begins  in  the  interpeduncular  fossa,  near  or  in  the  sulcus  of  the  oculomotor 
nerve.  It  passes  laterally  along  or  under  the  superior  border  of  the  pons,  loses  some  of  its  fibres 
in  the  lateral  sulcus  of  the  mesencephalon,  then  runs  inferiorly  between  the  superior  cerebellar 
peduncle  and  the  brachium  of  the  pons  to  disappear  in  the  junction  of  these.  Being  sometimes 
double,  it  is  known  as  the  lateral  filaments  of  the  pons  {fila  lateralia  pontis  or  Icenia  pontis). 
The  location  of  the  cell-bodies  giving  origin  to  it  is  uncertain. 

That  portion  of  the  rhombencephalon  overlying  the  pons  and  forming  the  floor  of  the 
fourth  ventricle  is  not  really  a  part  of  the  pons  at  aU.  It  is  merely  a  continuation  of  the  brain- 
stem from  the  meduOa  below  to  the  structures  above.  Therefore  on  the  dorsal  surface  there  is 
no  line  of  demarcation  between  the  pons  and  medulla  below  or  between  the  pons  and  isthmus 
above.  The  fibres  of  the  trigeminus  and  masticator  nerve  pass  through  the  pontine  fibres  to 
and  from  their  nuclei  in  the  brain-stem. 

3.  THE  CEREBELLUM 

The  cerebellum  or  hind  brain  is  the  largest  portion  of  the  rhombencephalon. 
It  lies  in  the  posterior  or  cerebellar  fossa  of  the  cranium,  and  dorsal  to  the  pons  and 
medulla  oblongata,  overhanging  the  latter.  It  fits  under  the  occipital  lobes  of  the 
cerebral  hemispheres,  from  which  it  is  separated  by  a  strong  dupUcation  of  the 
inner  layer  of  the  dura  mater,  the  tentorium  cerebelli. 

Its  greatest  diameter  Ues  transversely,  and  its  average  weight,  exclusive  of  the  dura  mater, 
is  about  140  gm.,  or  about  10  per  cent,  of  the  entire  encephalon.  It  varies  in  development 
with  the  cerebrum,  and,  like  it,  averages  larger  in  the  male.  It  is  relatively  larger  in  adults 
than  in  children.  Its  development  begins  as  a  thickening  of  the  anterior  portion  of  the  roof 
(dorsal  zone)  of  the  posterior  of  the  three  primary  brain  vesicles.  Resting  upon  the  brain- 
stem, it  roofs  over  the  fourth  ventricle  and  is  connected  with  the  structures  anterior,  below, 
and  posterior  to  it  by  its  three  pairs  of  peduncles. 

The  surface  of  the  cerebellum  is  thrown  into  numerous  narrow  folia  or  gyri, 
which  in  the  given  locaHties  run  more  or  less  parallel  with  each  other.     They  are 


THE  CEREBELLUM 


805 


separated  by  narrow  but  relatively  deep  sulci.  Unlike  the  spinal  cord  and 
medulla,  in  which  the  grey  substance  is  centrally  placed  and  surrounded  by  a 
mantle  of  white  substance,  the  surface  of  the  cerebellum  is  itself  a  cortex  of  grey 
substance,  the  cortical  substance  [substantia  corticalis],  enclosing  a  core  of  white 
substance,  the  medullary  body  [corpus  medullare].  However,  within  this  central 
core  of  white  substance  are  situated  definite  grey  masses,  the  nuclei  of  the 
ere  bellum. 

The  gross  divisions  of  the  cerebellum  are  three:  the  two  larger  lateral  portions, 
the  hemispheres,  and  between  these  the  smaller  central  portion,  the  vermis. 
The  demarcation  between  these  gross  divisions  is  not  very  evident  from  the  dorsal 
surface,  because  the  hemispheres  in  their  extraordinary  development  in  man 
encroach  upon  the  vermis,  and,  being  pressed  under  the  overlapping  occipital 
ends  of  the  cerebral  hemispheres,  they  become  partially  fused  upon  the  vermis 

Fig.  633. — Section  of  Head  Passing  Through  the  Mastoid  Processhs  op  the  Temporal 
Bones  and  Behind  the  Medulla  Oblongata.    Showing  the  Position  op  the  Cere- 
bellum. 
(From  a  mounted  specimen  in  the  Anatomical  Department  of  Trinity  College,  Dublin.) 


Corpus  callosum 

Chorioid  pli 

Veins  of  Galen 

Tentoriun 
cerebel] 

Transverse  sinus 

Dentate  nucleus 


Caudate  nucleus 
Lateral  ventricle 


Superior  petrosal 
Mastoid  antrum 

Transverse  sinus 
Mastoid  process 


along  the  dorsal  mid-line.  Though  differentiated  simultaneously  with  the  cere- 
bellar hemispheres  in  the  human  fcetus,  in  most  of  the  mammalia  the  vermis  is 
the  largest  and  most  evident  of  the  parts,  and  it  is  practically  the  only  part  which 
exists  in  the  fishes,  reptiles,  and  birds.  In  man,  owing  to  the  fact  that  the  vermis 
does  not  keep  pace  in  development  with  the  hemispheres,  there  results  a  very 
decided  notch  between  the  two  hemispheres  along  the  line  of  the  entire  ventral  and 
inferior  aspect  of  the  cerebellum,  the  floor  of  this  notch  being  the  surface  of  the 
vermis.  The  inferior  portion  of  the  notch  is  the  posterior  cerebellar  notch 
(incisura  marsupialis) ;  its  prolongation  above  is  wider  than  below,  and  is  termed 
the  superior  cerebellar  notch.  It  is  occupied  by  a  fold  of  the  diu'a  mater,  the 
falx  cerebelli.  With  the  variations  in  contour  of  the  cerebellum,  certain  of  its 
sulci  are  broader  and  deeper,  and  merit  the  name  fissures.  These  are  more  or  less 
definitely  placed,  and  subdivide  the  hemispheres  into  lobes'and  the  vermis  (the 
median  lobe)  into  lobules. 

Superior  surface. — The  superior  surface  is  bounded  from  the  inferior  sm-face 
by  the  horizontal  fissure  (fig.  635)  which  extends  ventrolaterally,  to  the  entrance  of 
the  brachium  of  the  pons.  Between  this  and  the  extreme  anterior  border  of  the 
dorsal  surface  are  two  other  fissures,  the  posterior  and  anterior  semilunar  fissures. 
These,  Hke  the  horizontal  fissure,  may  be  traced,  with  slight  interruptions,  across 
the  mid-line,  and  consequently  mark  off  not  onl}^  the  two  hemispheres  but  also  the 
vermis  into  corresponding  divisions. 


806 


THE  NERVOUS  SYSTEM 


The  superior  semilunar  lobe  [lobulus  semilunaris  superior]  (postero-superior 
lobe)  of  each  hemisphere  lies  between  the  horizontal  and  the  posterior  semilunar 
fissm-es.  It  largely  composes  the  outer  border  of  the  cerebellum,  and,  therefore, 
is  the  longest  of  the  lobes. 

The  adjacent  surface  of  the  hemispheres,  because  of  the  frequently  less  com- 
plete development  of  the  anterior  semilunar  fissure,  is  sometimes  referred  to  as  the 
quadrangular  lobe,  with  its  posterior  and  its  anterior  portions.  On  the  other 
hand,  especially  when  the  anterior  semilunar  fissure  is  well  marked,  this  area  may 
be  divided  into — (1)  the  posterior  semilunar  lobe,  between  the  posterior  and 
anterior  semilunar  fissures,  and  (2)  the  anterior  seynilunar  lobe,  anterior  to  the 
anterior  semilunar  fissure  (fig.  635). 

Anterior  to  the  quadrangular  lobe  on  each  hemisphere  is  the  ala  of  the 
central  lobule,  bounded  by  the  postcentral  and  the  precentral  sulcus.  Anterior 
to  this,  on  the  anterior  margin  of  the  hemisphere,  is  the  vinculum  lingulae, 
a  slender  process  continuous  with  the  lingula  of  the  vermis  (fig.  658). 

Fig.  634. — Median  Section  Through  Cerebellum  and  Brain-stem.     (Allen  Thompson, 
after  Reiohert.) 
1.  culmen  monticuli;  2,  superior  semilunar  lobe;  3,  inferior  semilunar  lobe;  4,  slender  lobe; 
5,  biventral  lobe;  6,  tonsil. 


Cerebral  peduncle 


Massa  intermedia 

Thalamus 

Epiphysis  (pineal  body) 

Corpora  quadrigemina 

Derive r-<ry^r^l 


Uvula  of. 
vermis 
Pyramid- 


stria  medullaris  thalami 
Third  ventricle 
Column  of  fornix 
Anterior  commissure 
Lamina  terminalis 

Z7  Tuber  cinereum 
Recessus  infun- 
dibuli 

Hypophysis  (pit- 
uitary body) 
AquiEductus  cerebri  (Sylvii) 

Pons 

■Fourth  ventricle 

-Tela  chorioidea  of  fourth  ventricle 


Medulla  oblongata 


The  superior  aspect  of  the  vermis,  the  superior  vermis,  because  of  the  fusion  of 
the  hemispheres,  is,  for  the  most  part,  a  slight  ridge,  the  monticulus  (fig.  635), 
instead  of  a  depression.  However,  in  the  posterior  portion  of  the  dorsal  surfacethe 
depression  of  the  posterior  notch  begins,  and  here  the  horizontal  and  the  posterior 
semilunar  fissures  approach  each  other  so  closely  that  the  corresponding  sub- 
division of  the  vermis  is  seldom  more  than  a  single  folium,  the  folium  vermis 
(cacuminis) .  > 

The  monticulus  proper  is  divided  into  an  inferior  lobule,  the  declive,  and  a 
superior  lobule,  the  culmen.  These  appear  as  continuations  across  the  mid- 
line of  the  posterior  and  anterior  semilunar  lobes  of  the  hemispheres,  and  are 
separated  by  the  corresponding  fissures  (fig.  635). 

At  the  extreme  anterior  part  of  the  superior  surface  and  in  the  bottom  of  the 
anterior  cerebellar  notch  lies  a  more  definitely  defined  portion  of  the  vermis. 
This  is  the  central  lobule  (fig.  635).  It  is  broadened  laterally  into  two  pointed 
wings,  the  alee  of  the  central  lobule,  the  folia  of  which,  if  present,  are  parallel  with 
those  of  the  anterior  semilunar  lobes  and  separated  from  them  by  the  post- 
central sulcus. 

If  the  anterior  margin  of  the  central  lobule  be  lifted,  the  lingula  cerebelli 


THE  CEREBELLUM 


807 


{lingula  vermis)  will  appear  separated  from  the  central  lobule  by  the  pre-central 
sulcus.  It  is  a  thin,  tongue-like  anterior  projection  of  the  cortical  substance 
comprising  four  to  eight  folia  adhering  upon  the  anterior  medullary  velwm,  the  roof 
of  the  superior  portion  of  the  fourth  ventricle. 

Inferior  surface. — ^The  three  cerebellar  peduncles  of  each  side  join  to  form  a 
single  mass  of  white  substance,  and  enter  the  ventral  aspect  of  each  hemisphere  at 
the  medial  and  ventral  extremity  of  the  horizontal  fissure.  The  inferior  surface 
of  the  cerebellum  is  less  convex  than  the  superior  surface.  The  hemispheres  are 
decidedly  separated  by  a  continuation  of  the  posterior  cerebellar  notch,  which 
becomes  broader,  the  vallecula  of  the  cerebellum,  which  contains  the  inferior 
portion  of  the  vermis,  vermis  inferior,  and  whose  margins  embrace  the  medulla 
oblongata.  The  inferior  surfaces  of  the  hemispheres  are  each  divided  by  the 
intervening  fissures  into  four  lobes  (fig.  636). 


Fig.   635.— Diagram   op  the   Superior  Surface   of   the    Cerebellum. 


Tegmentum 
Frenulum  veil 


Ala  of  central  lobuli 


Cerebral  peduncle 
Substantia  nigra 


Inferior  quadrigemmate  body 


Central  lobule 


/f"X^,        Culmen  of 


Posterior  cerebellar  notcb 


Declive  of  monticulus 
Folium  of  vermis 


Below,  the  inferior  semilunar  lobe  (postero-inferior  lobe)  is  separated  from  the 
superior  semilunar  lobe  of  the  superior  surface  by  the  horizontal  fissure.  It  is  the 
largest  of  the  inferior  lobes,  and  is  broader  at  its  medial  extremity.  Frequently 
two  and  sometimes  three  of  its  curved  sulci  appear  deeper  than  others,  and  sep- 
arate it  into  two  or  three  slender  lobules  [lobuli  graciles].  More  commonly  there 
are  two  of  these,  the  lobulus  gracilis  posterior  and  lobulus  gracilis  anterior,  separated 
by  the  postero-inferior  sulcus. 

The  biventral  lobe  is  smaller  and  more  curved  than  the  inferior  semilunar  lobe, 
from  the  anterior  margin  of  which  it  is  separated  by  the  curved  antero -inferior 
sulcus.  Its  medial  extremity  is  pointed  and  does  not  extend  to  the  vermis;  its 
lateral  extremity  is  broader  and  curves  anteriorly  to  the  ventral  extremity  of  the 
horizontal  fissure — the  line  of  outer  termination  of  the  inferior  semilunar  lobe. 

The  tonsil  [tonsilla  cerebelli]  (amygdala)  is  a  rounded,  triangular  mass,  placed 
mesially  within  the  inner  curvature  of  the  biventral  lobe,  and  separated  from  it 
by  the  retrotonsillar  fissure.  Its  inferior  mesial  border  slightly  overlaps  the 
vermis. 

The  smallest  of  the  lobes  is  the  flocculus.  It  lies  adjacent  to  the  inferior  and 
lateral  surface  of  the  mass  of  white  substance  produced  by  the  confluence  of  the 
three  cerebellar  peduncles,  and  extends  into  the  mesial  extremity  of  the  horizon- 
tal fissure.  It  is  so  flattened  that  its  short  folia  give  it  the  appearance  suggesting 
its  name.  Occasionally  there  is  added  a  second,  less  perfectly  formed  portion, 
the  secondary  flocculus.  From  each  floccular  lobe  there  passes  toward  the  mid- 
line a  thin  band  of  white  substance,  the  peduncle  of  the  flocculus ;  these  extend 


808  THE  NERVOUS  SYSTEM 

to  meet  each  other  at  the  most  anterior  portion  of  the  inferior  vermis,  and  thus 
form  the  narrow  posterior  medullary  velum. 

The  inferior  vermis  (figs.  634,  636)  is  more  definitely  demarcated  than  the 
superior.  Lying  in  the  floor  of  the  vallecula  cerebelli,  it  is  separated  on  each  side 
from  the  adjacent  lobes  of  the  hemispheres  by  a  well-marked  sulcus  about  it, 
the  nidus  avis.  By  contour  and  by  deeper  transverse  fissures  (sulci)  occurring 
at  intervals  across  it,  four  divisions  or  lobules  of  the  inferior  vermis  are  recognised. 
These  lobules,  like  those  of  the  superior  vermis,  are  each  in  intimate  relation  with 
the  pair  of  lobes  of  the  hemispheres  adjacent  to  it  on  either  side. 

1.  The  tuber  vermis  is  adjacent  to  the  folium  vermis  of  the  superior  aspect,  and 
thus  is  the  most  inferior  lobule  of  the  inferior  vermis.  It  is  a  short,  somewhat 
pyramidal-shaped  division,  whose  four  or  five  transversely  arranged  folia  are  con- 
tinuous with  the  folia  of  the  inferior  semilunar  lobes  on  either  side. 

2.  The  pyramid  is  separated  from  the  tuber  vermis  by  the  post-pyramidal 
sulcus.  Its  several  folia  cross  the  vallecula  cerebelli  and  curve  to  connect  with 
the  biventral  lobes  on  either  side. 

3.  The  uvulva  is  separated  from  the  pyramid  by  the  prepyramidal  sulcus. 
It  is  triangular  in  shape.  Its  base  or  broader  inferior  portion  appears  as  two 
laterally  projecting  ridges  of  grey  substance,  the  furrowed  bands  or  alee  uvulce, 
which  extend  across  the  floor  of  the  nidus  avis  and  under  the  mesial  margins  of  the 
tonsils  on  either  side.  In  these  bands  its  folia  curve  and  become  continuous  with 
the  tonsils.  The  uvula  and  the  two  tonsils  are  sometimes  referred  to  collectively 
as  the  uvular  lobe. 

4.  The  nodule  is  the  smallest  and  most  anterior  division  of  the  inferior  vermis. 
It  is  separated  from  the  uvula  by  the  post-nodular  sulcus,  and  is  closely  associated 
anteriorly  with  the  posterior  medullary  velum,  the  transverse  continuation  of  the 
peduncles  of  the  floccular  lobes. 

StTMMAET  OF  EXTERNAL  FEATURES  OP  CEREBELLUM 

Superior  Surface. 

Hemisphere  Vermis 

Anterior  border — Anterior  medullary  velum — Anterior  border 

Vinculum  of  Lingula Lingula 

Precentral  sulcus 

Ala  of  central  lobule Central  lobule 

Post-central  sulcus 

C  Anterior  semilunar  lobule Culmen 

Quadran-       I       Anterior  semilunar  fissure  [  Monticulus 

gular  lobe     ]  Posterior  semilunar  lobule Declive 

[      Posterior  semilunar  fissiire 

Superior  semilunar  lobe Folium. 

Horizontal  Fissure 

Inferior  Surface 

Horizontal  Fissure 

Inferior  f  Posterior  slender  lobule 1 

semilunar    -j      Posterior-inferior  sulcus [  Tuber 

lobe  [  Anterior  slender  lobule J 

Anterior-inferior  sulcus Post-pyramidal  sulcus 

Biventral  lobe Pyramid 

Retro-tonsillar  fissure Prepyramidal  sulcus 

Tonsil Uvula 

Horizontal  Fissure Post^nodular  sulcus 

Flocculus Nodule 

Posterior  medullary  velum 

Internal  structure  of  the  cerebellum  (fig.  637). — The  white  substance  of  the 
cerebellum  is  continuous  with  its  peduncles  and  forms  a  compact  central  mass. 
Over  the  surface  of  this  the  grey  substance  or  cortex  is  spread  in  a  thin  but  uniform 
and  much  folded  layer.  Upon  section  of  the  cerebellum  certain  of  the  sulci  as 
well  as  the  fissures  are  shown  to  be  much  deeper  than  is  apparent  from  the  surface. 
The  deeper  sulci  separate  the  lobes  into  divisions,  the  medullary  laminae,  each  of 
which  is  composed  of  a  number  of  folia  and  each  of  which  has  its  own  core  of  white 
substance.  The  folia  of  the  laminae  line  the  sulci  (and  fissures),  and  also  comprise 
their  surface  aspect,  and  are  separated  by  the  shallow,  secondary  sulci.     The  larger 


NUCLEI  OF  THE  CEREBELLUM 


809 


laminae  are  subdivided  into  from  two  to  four  secondary  laminae  of  varying  size. 
Such  subdivision  is  especially  marked  in  the  vermis.  Here  each  lamina  comprises 
a  lobule  and  is,  therefore,  separated  by  a  fissure,  and  each  lobule  is  usually  sub- 
divided with  the  exception  of  the  nodule,  the  folium,  and  the  lingula.  In  sagittal 
sections,  or  sections  transverse  to  the  general  direction  of  the  sulci,  this  arrange- 
ment of  the  laminae  gives  a  foliate  appearance,  which,  especially  in  sagittal  sec- 
tions of  the  vermis,  is  termed  the  arbor  vitae  (see  fig.  634). 

IThe  cerebellar  cortex  consists  of  three  layers  and  contains  four  general  types  of  cell-bodies 
of_neurones,  aD  of  which  possess  features  pecuHar  to  the  cerebellum. 

The  outermost  or  molecular  layer  contains  small  stellate  cells,  "basket  cells,"  with  rel- 
atively long  dendrites.  These  serve  to  associate  the  different  portions  of  a  given  fohum. 
The  axones  of  the  largest  of  them  give  off  branches  which  form  pericellular  baskets  about  the 
bodies  of  the  cells  of  Purkinje,  each  axone  contributing  to  several  baskets.  The  layer  of  Pur- 
kinje  cells,  or  the  middle  layer,  is  quite  thin.  The  bodies  of  the  cells  of  Purkinje  are  arranged 
in  a  single  layer,  and  their  elaborate  systems  of  dendrites  extend  throughout  and  largely  compose 
the  molecular  layer.  The  dendrites  of  these,  the  most  essential  cells  of  the  cortex,  are  displayed 
in  the  form  of  arborescent  fans  (see  fig.  604),  arranged  parallel  with  each  other  and  transverse 


Fig.  636. — Diagram  of  the  Inperioe  Surface  op  the  Cerebellum  after  the  Removal 
OF  the  Medulla  Oblongata,  Pons,  and  Mesencephalon. 
The  tonsil  of  the  right  side  is  omitted  in  order  to  display  the  connection  of  the  pyramid 
with  the  biventral  lobe,  the  furrowed  band  of  the  uvula,  and  more  fuUy  the  posterior  meduUary 
velum.     The  anterior  notch  is  less  evident  than  in  the  actual  specimen. 


Superior  cerebellar  peduncle 
Posterior  medullary  velum 
Middle  cerebellar  peduncle 
(brachium  of  pons) 

Flocculus 


Biventral  lobe 
Anterior  slender 
lobule 
Posterior  _J 
slender       \ ,    , 
lobule        \\\ 
Inferior  semilu-  . — ^ 
nar  lobe 


Anterior 
Fourth  medullary 
ventricle      velum  Lingula 


Tuber  vermis     1       Pyramid 

Posterior  cerebellar  notch 


to  the  long  axis  of  the  folium  containing  them.  Their  axones  are  given  off  from  the  base  of  the 
ceU-body  and  acquire  their  medullary  sheaths  quite  close  to  the  ceU-body,  and,  after  giving  off 
several  collaterals  in  the  inner  layer,  pass  into  the  general  white  substance  and  thence  to  other 
laminae  or  lobes.  Certain  of  them  go  to  structures  outside  the  cerebellum.  The  inner  layer 
is  the  granular  layer.  It  contains  numerous  small  nerve-cells  or  "  granule-ceUs "  which  pos- 
sess from  two  to  five  radiating  dendrites,  unbranched  except  at  their  termination,  which  occurs 
suddenly  in  the  form  of  three  to  six  claw-hke  twigs.  Thek  axones  are  given  off  either  from  the 
ceU-body  direct  or  more  often  from  the  base  of  one  of  the  dendrites,  and  pass  outward  into 
the  molecular  layer,  where  they  bifurcate  and  course  in  both  directions  parallel  to  the  long  axis 
of  the  folium,  to  become  associated  with  the  dendrites  of  the  cells  of  Purkinje.  In  the  layer 
of  the  cells  of  Purkinje  there  is  situated  at  intervals  a  neurone  of  the  Golgi  type  II  (see  fig. 
604).  The  short,  elaborately  branched  a.xone  of  this  neurone  is  distributed  among  the  cells 
of  the  granular  layer.  Axones  conveying  impulses  to  the  cerebellar  cortex  terminate  in  the 
granular  layer  as  'moss  fibres,'  or  directly  upon  the  cells  of  Purkinje  as  'climbing  fibres,'  and 
probably  upon  the  cells  of  the  Golgi  type  II. 

Thus  the  neurones  which  receive  impulses  coming  to  the  cortex  are  the  cells  of  Purkinje, 
probably  the  Golgi  cells  of  type  II,  and  the  granule-cells;  those  which  distribute  these  impulses 
to  other  neurones  of  the  folium  are  the  Golgi  cells  of  type  II,  the  granule-ceUs,  and  the  basket- 
cells  (association  neurones),  and  the  collaterals  of  the  cells  of  Purkinje.  Impulses  are  conveyed 
from  the  cortex  of  a  folium  to  that  of  other  folia,  lamina,  lobules  or  lobes,  or  to  the  nuclei  of 
the  cerebellum,  or  to  structures  outside  the  cerebellum  by  the  axones  of  the  cells  of  Purkinje. 

The  nuclei  of  the  cerebellum  (fig.  637)  are  in  its  central  core  of  white  substance. 
They  are  four  in  number,  and  all  are  paired,  those  of  each  pair  being  situated 
opposite  each  other  on  either  side  of  the  mid-line. 


810 


THE  NERVOUS  SYSTEM 


1.  The  largest  of  them  is  the  dentate  nucleus.  This  is  an  isolated  mass  of 
grey  substance  situated  in  the  core  of  white  substance  of  each  hemisphere.  It  is 
in  the  form  of  a  folded  or  corrugated  cup-shaped  lamina,  with  the  opening  of  the 
cup  (hilus)  directed  anteriorly  and  obliquely  toward  the  mid-line.  It  contains  a 
mass  of  white  substance  and  possesses  a  capsule.  Its  cell-bodies  give  rise  to  most 
of  the  fibres  forming  the  superior  cerebellar  peduncles. 

2.  The  nucleus  emboliformis  is  an  oblong  and  much  smaller  mass  of  grey 
substance,  which  lies  immediately  medial  to  the  hilus  of  the  dentate  nucleus.  It 
is  probably  of  the  same  significance  as  the  dentate  nucleus,  being  merely  a  portion 
separated  from  it. 

3.  The  nucleus  globosus,  the  smallest  of  the  cerebellar  nuclei,  is  an  irregular 
horizontal  mass  of  grey  substance  with  its  larger  end  placed  in  front.  It  lies 
close  to  the  medial  side  of  the  nucleus  emboliformis,  and  often  appears  separated 
into  two  or  more  rounded  or  globular  masses. 

4.  The  roof  nucleus  [nucleus  fastigii]  is  the  second  largest  of  the  cerebellar 
nuclei,  and  is  the  most  mesially  placed.     The  pair  is  situated  in  the  roof  of  the 


Fig.  637. — Section  op  Cerebellum  and  Brain-stem  Passing  Obliquely  Through  Inferior 
Portion  of  Cerebellum  to  Superior  Margin  op  Pons.  (After  Toldt,  "Atlas  of  Human 
Anatomy,"  Rebman,  London  and  New  York.) 

Posterior  cerebellar  notch 


Medullary  lami 
Cortical  substance 

Corpus  medullare 


Vermis  (superior) 


Nucleus 
globosus 


Capsule  of  dei 
tate  nucleus 

Dentate  nucleus 

Core  of  the  dentate  nucleus 
Hilus  of  dentate  nucleus 
Brachium  conjunctivum 

Fourth  ventricl 
Fossa  rhomboidea  (pars  superior) 

Stratum  nucleare 
Decussation  of  brachium 
conjunctivum 


Roof  nucleus 
Nucleus  emboliformis 
Lingula  cerebelli 
Anterior  medullary  velum 
Substantia  ferruginea 
Lateral  lemniscus 
Medial  longitudinal  fasciculus 
Raphe  of  medulla  oblongata 


Cerebral  peduncle 
Interpeduncular  fossa 


fourth  ventricle,  and  so  near  the  mid-line  that  both  nuclei  are  in  the  white  sub- 
stance of  the  vermis.  They  are  ovoid  in  shape,  and  the  nucleus  of  one  side  receives 
axones  from  the  nucleus  of  the  vestibular  nerve  chiefly  of  the  opposite  side,  the 
decussation  of  these  axones  taking  place  in  the  vermis.  Its  cells  are  larger  than 
those  of  the  two  first-mentioned  nuclei. 

The  peduncles  of  the  cerebellum. — The  peduncles  consist  of  three  pairs — the 
inferior,  middle,  and  superior.  The  three  peduncles  of  each  side  come  together  at 
the  level  of  the  lower  border  of  the  pons,  and  the  entering  and  emerging  fibres  of 
which  they  are  composed  become  continuous  with  the  central  core  of  white  sub- 
stance of  the  cerebellar  hemispheres.     (Fig.  631,  638,  639.) 

The  restiform  body  of  the  medulla  oblongata  is  the  inferior  peduncle.  It 
forms  the  lateral  boundary  of  the  inferior  portion  of  the  fourth  ventricle,  and  upon 
reaching  the  level  of  the  pons  turns  sharply  backward  into  the  cerebellum.  In 
the  region  of  the  turn  it  is  encircled  externally  by  fibres  of  the  cochlear  nerve.  It 
contains  fibres,  both  ascending  and  descending,  between  the  cerebellar  cortex  and 
the  structures  below  the  cerebellum. 

Its  fibres  include:  (1)  fibres  from  the  spinal  cord  including  the  dorsal  spino-cerebellar 
fasciculus  (direct  cerebellar  tract)  and  probably  a  small  proportion  of  the  ascending  fibres  of 
the  superficial  ventro-lateral  spino-cerebeUar  fasciculus  (Cowers'  tract);  (2)  fibres  from  the 


PEDUNCLES  OF  THE  CEREBELLUM 


811 


olive  of  the  same  and  opposite  side  of  the  medulla  oblongata;  (3)  fibres  from  the  nuclei  of  the 
funiculus  gracilis  and  cuneatus  of  the  same  and  opposite  sides;  (4)  fibres  to  and  from  the 
olive  of  the  opposite  side;  (5)  fibres  to  the  nuclei  of  the  motor  cranial  nerves;  (6)  fibres 
descending  to  the  ventral  horn  cells  of  the  spinal  cord.  The  ascending  or  afferent  fibres  of  the 
spino-cerebellar  and  cerebeUo-olivary  fasciculi  are  the  principal  components  of  the  inferior  ped- 
uncle; the  existence  of  fibres  (5)  and  (6)  is  not  weU  estabhshed.  Of  these,  the  fibres  of  the  direct 
cerebellar  tract  terminate  in  the  cortex  of  the  superior  vermis  of  both  sides  of  the  mid-hne,  but, 
for  the  most  part,  in  that  of  the  same  side.  The  olivary  fibres  end  in  the  cortex  of  both  the  su- 
perior vermis  and  the  adjacent  cortex  of  the  hemispheres,  and  some  of  them  terminate  in  the 
nucleus  dentatus. 

The  brachium  pontis'or  the  middle  peduncle  is  the  largest  of  the  three  cere- 
bellar peduncles.  In  it  the  pons  fibres  pass  slightly  downward  and  into  the  cere- 
bellar hemisphere,  between  the  lips  of  the  anterior  part  of  the  horizontal  fissure, 
entering  lateral  to  the  inferior  peduncle. 


Fig.  638. — Transparency  Drawing  Showing  the  Origin,  Course,  and  Connections  op  the 
Sttperior  Cerebellar  Peduncles  (Brachia  Conjunctiva)  in  the  Formation  op 
'Stilling's  Scissors.' 


Thalamus 
-\-  -  Internal  capsule 


*  Bundle  from  red  nucleus  to 

internal  capsule 
"*   Red  nucleus 

Decussation  of  brachia  conjunctiva 
Brachium  conjunctivum 
(supenor  peduncle) 


Inferior  peduncle 
(restiform  body) 
Bundle  to  cerebellar 
cortex 
Dentate  nucleus 


Medulla  oblongata 


It  consists  of  the  transverse  fibres  of  the  pons,  and  within  the  cerebellum  its  fibres  are  dis- 
tributed in  two  main  groups — the  upper  transverse  fibres  of  the  pons  apparently  pass  downward 
to  radiate  in  the  lower  portion  of  the  hemisphere,  whUe  the  lower  transverse  fibres  pass  upward 
and  medialward  to  radiate  in  the  superior  part  of  the  hemisphere  and  vermis.  For  the  most 
part  the  fibres  of  the  middle  peduncle  may  be  considered  as  commissural  fibres,  passing  from 
one  side  of  the  cerebellum  to  the  other.  Each  peduncle  contains  fibres  coursing  in  opposite 
directions.  Many  of  these  fibres  are  interrupted  in  their  course  to  the  opposite  side  by  cells 
scattered  throughout  the  pons,  nuclei  of  the  pons,  and,  therefore,  in  each  brachium  pontis  some 
of  the  fibres  are  processes  of  the  cells  of  the  cerebellum  and  course  toward  the  opposite  side, 
while  others  are  processes  of  the  cells  of  the  pontine  nuclei  and  course  to  the  cerebellar  hemis- 
phere of  the  same  side.  Many  cell-bodies  of  the  nuclei  of  the  pons  whose  axones  terminate 
in  the  cerebellum  receive  impulses  from  fibres  descending  from  the  cerebral  cortex  of  the  opposite 
side — coriico-pontine  fibres.  Furthermore,  there  are  evidences  after  degeneration  that  the 
brachium  pontis  also  contains  a  few  fibres  from  the  cerebellum  to  the  structures  of  the  brain- 
stem and  spinal  cord. 


812  THE  NERVOUS  SYSTEM 

The  brachium  conjunctivum  or  superior  cerebellar  peduncle  emerges  from  the 
cerebellum  on  the  medial  side  of  the  brachium  pontis  and  also  on  the  superior  and 
medial  side  of  the  course  of  the  restiform  body.  It  forms  the  lateral  boundary  of 
the  superior  portion  of  the  fourth  ventricle  and  is  the  cerebello-cerebral  peduncle. 
Its  transverse  sectioii  appears  semilunar  in  shape,  with  the  concave  side  next  to  the 
cavity  of  the  ventricle.  The  medial  border,  which  inclines  toward  the  mid-line, 
is  connected  with  that  of  the  corresponding  peduncle  of  the  opposite  side  by  the 
anterior  medullary  velum,  which  thus  roofs  over  the  superior  part  of  the  fourth 
ventricle.  The  lateral  border  is  distinguished  from  the  pons  by  an  open  furrow 
or  lateral  sulcus. 

The  superior  cerebellar  peduncles  are  almost  entirely  efferent  pathways  as  to  the  cerebellum 
and  form  the  chief  connections  between  the  cerebellum  and  the  cerebrum.  They  arise  almost 
wholly  from  the  dentate  nuclei.  As  they  course  forward  they  slightly  converge  and  disappear 
under  the  inferior  quadrigeminate  bodies.  Here,  in  the  tegmentum  of  the  mesencephalon, 
they  undergo  an  almost  total  decussation,  and  then  the  majority  of  the  fibres  of  each  peduncle, 
having  thus  crossed  the  mid-line,  terminate  in  the  red  nucleus  of  the  opposite  side.  The  red, 
nucleus  lies  in  the  tegmentum  of  the  mesencephalon,  below  the  superior  quadrigeminate  bodies, 
and  therefore  quite  close  to  the  decussation.  The  cells  of  the  red  nucleus,  about  which  the 
fibres  of  the  peduncle  terminate^  in  their  turn  send  processes  (axones)  into  (1)  the  rubro-spinal 
tract  of  the  spinal  cord  and  (2)  mto  the  prosencephalon,  most  of  which  latter  terminate  in  the 
thalamus  whose  ceU-bodies  give  fibres  to  the  cerebral  cortex  by  way  of  the  internal  capsule; 
but  some  pass  from  the  red  nucleus  under  the  thalamus  to  join  the  internal  capsule. 

In  addition  to  the  fibres  having  the  origin  and  course  described  above,  and  which  constitute 
the  greater  mass  of  the  superior  cerebellar  peduncle,  each  peduncle  is  said  to  contain  fibres 
which — (1)  arise  in  the  cerebellar  cortex  of  the  same  and  opposite  sides  of  the  mid-line,  instead 
of  from  the  dentate  nucleus,  and  which  join  the  peduncle  at  the  side  of  the  dentate  nucleus, 
between  it  and  the  restiform  body;  (2)  fibres  which  do  not  cross  the  mid-line  in  the  decussation, 
but  terminate  in  the  red  nucleus  of  the  same  side;  (3)  some  fibres  are  not  interrupted  in  the  red 
nucleus,  but  pass  directly  into  the  thalamus;  (4)  a  small  proportion  of  fibres  afferent  as  to  the 
cerebellum,  which  arise  in  the  structures  of  the  cerebrum  and  pass  in  to  the  cerebellum;  and 
(5)  the  greater  part,  if  not  all,  of  the  ascending  fibres  of  the  superficial  ventro-lateral  spino- 
cerebellar fasciculus  (Gowers'  tract)  of  the  spinal  cord.  The  latter,  instead  of  entering 
the  cerebellum  by  way  of  the  restiform  body,  are  deflected  in  the  upper  medulla  and  pass 
in  the  lateral  tegmentum  of  the  pons  to  the  anterior  medullary  velum,  where  they  turn  back- 
ward to  enter  the  cerebellum  in  its  superior  peduncle  and  pass  to  its  cortex,  probably  from  the 
lateral  side  of  the  dentate  nucleus  (see  fig.  656). 

The  anatomy  of  the  fourth  ventricle. — The  fourth  ventricle  is  rhomboidal  in 
shape,  being  considerably  widened  at  the  level  of  the  brachia  pontis  and  pointed  at 
each  end.  Its  floor  consists  of  a  slight  depression  in  the  brain-stem,  the  fossa 
rhomboidea,  and  corresponds  to  the  floor  of  the  central  canal.  Its  pointed  inferior 
end,  the  calamus  scriptorius,  is  directly  continuous  with  the  central  canal,  and  its 
narrowed  superior  end  is  continued  into  the  aquseductus  cerebri  (Sylvii)  of  the 
mesencephalon,  which  is  nothing  more  than  a  resumption  of  the  tubular  form  of 
the  canal. 

The  entire  cavity  of  the  ventricle  is  lined  with  an  epithelium  which  is  continuous  with  the 
epithehum,  or  ependyma,  of  the  central  canal  below  and  the  aqueduct  above.  The  entire 
ventricle  involves  the  isthmus  of  the  rhombencephalon,  the  metencephalon  and  a  portion  of  the 
medulla  oblongata.  It  is  divided  for  study  into  an  inferior,  an  intermediate  and  a  superior 
part. 

The  roof  of  the  superior  portion  of  the  fourth  ventricle  is  nervous,  consisting  of  a 
thin  lamina  of  white  substance,  the  anterior  (superior)  inedullary  velum,  thickened 
at  the  sides  by  the  brachia  conjunctiva.  At  its  extreme  mesencephalic  end  (in  the 
isthmus  of  the  rhombencephalon)  the  anterior  medullary  velum  is  slightly  thick- 
ened by  a  continuation  of  the  white  substance  of  the  inferior  quadrigeminate 
bodies,  forming  the  frenulum  veil.  The  inferior  portion  of  the  velum  is  contin- 
uous with  the  white  substance  of  the  cerebellum,  and  is  covered  by  the  lingula 
cerebelli,  an  extension  of  the  cortical  substance  of  the  superior  vermis  (fig.  631). 

The  roof  of  the  intermediate  portion  of  the  fourth  ventricle  is  formed  by  the 
cerebellum  proper,  the  vermis  and  the  mesial  portions  of  the  hemispheres.  The 
nervous  portion  of  the  roof  terminates  with  the  posterior  (inferior)  medullary 
velum,  a  thin,  narrow  band  of  white  substance  which  is  the  continuation  of  the 
peduncles  of  the  fioccular  lobes,  and  which  connects  them  at  the  mid-line  with  the 
nodule  of  the  inferior  vermis. 

The  roof  of  the  inferior  portion  of  the  fourth  ventricle  is  non-nervous.  It  is 
the  chorioid  tela  of  the  fourth  ventricle,  a  semilunar  lamina  consisting  of  the  epi- 
thelial lining  of  the  ventricle,  reinforced  by  a  continuation  of  the  connective  tissue 
of  the  pia  mater  and  the  adjacent  portion  of  the  arachnoid.     Along  the  line  of  its 


THE  FOURTH  VENTRICLE 


813 


attachment  to  the  surface  of  the  medulla  it  is  thickened,  and  in  sections  this  por- 
tion bears  the  name  ligula  {toRiiia  ventriculi  quarti).  The  thickest  portion  spans 
the  tip  of  the  calamus  scriptorius  and  is  termed  the  obex.  The  width  of  the  ven- 
tricular cavity  is  extended  laterally  from  its  widest  part  into  the  lateral  recesses. 
narrow  pockets  on  each  side  and  around  the  upper  parts  of  the  restiform  bodies. 
In  the  mid-Hne  of  the  lower  part  of  the  chorioid  tela  there  is  a  more  or  less  well- 
marked  opening,  the  foramen  of  Magendie  (medial  aperture  of  the  fourth  ventricle), 
which  is  a  lymph-channel  connecting  the  cavity  of  the  ventricle  with  the  subarach- 
noid space.  There  is  a  similar  opening  from  each  lateral  recess  {lateral  apertures 
of  Key  and  Retzius). 

The  chorioid  plexuses  of  the  fourth  ventricle  consist  of  highly  vascular,  lobular, 
villus-like  processes  of  the  ventricular  lining  (and  pia-mater)  of  the  chorioid  tela. 
They  are  reddish  in  the  fresh  specimen,  and  the  epithelial  lining  of  the  ventricle  is 
closely  adapted  to  the  unevennesses  of  their  surfaces.     From  below  they  run  as 

Fig.  639. — Diagram  of  the  Roop  and  Lateral  Boundaries  of  the  Fourth  Ventricle. 
The  trochlear  nerve  should  be  shown  emerging  from  the  lateral  boundary  of  the  frenulum  veli. 


Ii.ferior  quadrigeminate  body 
Trochlear  nerve 


Axilerior  medullary  velum 
Biachium  coniunctivum 
Brachlum  of  pOQS 


Restiform  body 

Ligula  teenia 
Chorioid  tela  of 
fourth  ventricle 

Cuneate  tubercle 

Clava 

Tubercle  of  Rolando 


Frenulum  veli 
Lateral  lemniscus 

Lingula  of  vernis 


Fourth  ventricle 


Posterior  medullary  velum 
Chorioid  plexus 

Foramen  of  Magendie 


two  parallel  masses  on  either  side  of  the  mid-line,  which  become  united  above, 
and  then  are  separated  again  into  two  lateral  processes  which  bend  at  right  angles 
and  project  into  the  lateral  recesses.  Portions  frequently  protrude  through  the 
three  openings  of  the  ventricle  into  the  subarachnoid  space. 

The  floor  of  the  fourth  ventricle  [fossa  rhomboidea]  (fig.  640). — This  is  thrown 
into  eminences  and  depressions  indicative  of  the  internal  structures  of  the 
brain-stem  subjacent  to  it.  Its  inferior  portion  is  the  dorsal  surface  of  the  upper 
portion  of  the  medulla  oblongata;  its  intermediate  portion  is  the  dorsal  surface 
of  the  pons  region,  while  its  superior  portion  belongs  to  the  isthmus  of  the 
rhombencephalon.  Its  triangular  lower  e.xtremity  terminates  as  the  opening  of 
the  central  canal  of  the  spinal  cord.  This  portion  is  deepened  at  the  obex  and 
shows  furrows  which  point  downward  and  converge  medialward,  giving  the 
appearance  known  as  the  calamus  scriptorius.  The  mid-line  of  the  floor  is  sharply 
distinguished  by  the  well-marked  median  sulcus,  which  becomes  shallower  above 
than  below.  In  the  tip  of  the  calamus  scriptorius,  immediately  anterior  to  the 
obex,  the  median  sulcus  deepens  to  become  continuous  into  the  central  canal. 
This  terminal  depression  is  known  as  the  ventricle  of  Arantius.  Throughout  the 
length  of  the  floor  on  either  side  of  the  median  sulcus  is  a  continuous  ridge,  the 
medial  eminence,  which  is  bounded  laterally  by  the  limiting  sulcus.  Underlying 
the  floor  of  the  ventricle  is  a  layer  of  grey  substance  of  varying  thickness,  which  is 
continuous  with  that  surrounding  the  central  canal  of  the  cord.  The  medial 
eminence  is  subdivided  into  portions  of  unequal  width  and  elevation,  and  the 
limiting  sulcus  accordingly  shows  fovesE  of  different  depths. 


814 


THE  NERVOUS  SYSTEM 


Beginning  at  the  calamus  soriptorius,  the  following  areas  of  the  floor  of  the  fourth  ventricle 
are  usually  distinguished  (fig.  640) : — 

The  area  postrema  of  Retzius  is  a  superficial  vascular  structure  bounded  inferiorly  by  the 
tEenia  and  overlying  the  terminal  portion  of  the  nucleus  of  the  fasciculus  gracilis  (clava)  and  a 
portion  of  the  nucleus  of  termination  of  the  vagus  nerve.  The  funiculus  separans,  a  short 
oblique  fold  of  the  floor,  composed  chiefly  of  neurogUa,  separates  the  area  postrema  from  the 
ala  cinerea  (irigonum  vagi),  which  is  an  oblique,  grey-coloured,  wing-shaped  eminence  indicating 
the  middle  third  of  the  nucleus  of  termination  (recipient  nucleus)  of  the  vagus  and  glosso- 
pharyngeal nerves.  At  the  superior  extremity  of  the  ala  cinerea  is  a  well-marked  triangular 
depression  of  the  limiting  sulcus  known  as  the  inferior  fovea.  Mesial  to  and  extending  above 
the  ala  cinerea  is  a  narrow  triangular  eminence  lying  close  to  the  median  sulcus,  which  represents 
the  nucleus  of  origin  of  the  hypoglossal  nerve,  the  hypoglossal  eminence  [trigonum  n.  hypoglossi]. 
The  lateral  field  of  this  eminence  shows  small  oblique  rugse,  giving  it  a  "feathery"  appearance, 
the  area  plumiformis  of  Retzius.  The  nucleus  intercalatus  of  Van  Gehuchten  is  a  wedge- 
shaped  portion  very  slightly  demarcated  from  the  hypoglossal  eminence,  and  intercalated 
between  it  and  the  inferior  fovea.     This  nucleus  is  considered  by  some  observers  as  an  inferior 

Fig.  640. — Dohsal  Surface  of  the  Brain-stem  Showing  the  Anatomy  of  the  Flock  op  the 
Fourth  Ventricle.     (Modified  from  Spalteholz.) 


Median  sulcus 


Limiting  sulcus  ^ 


Aqueduct  of  cerebrum 


Nucleus  incertus 


^^  Locus    cffiruleus 


Medial  eminence  ^■'^^ 


Acoustic  medullary  striae  ■ 


Inferior  fovea  - ' 

Nucleus  of  fasciculus  cuneatus  — ' 

Taenia  of  fourth  ventricle  ^' 

Area  postrema^' 

Nucleus  of  fasciculus  gracilis  (clava) 

Posterior  median  fissure. 


Nucleus  of    coch- 
*'^^^    ^    learis  (tuberculum 

''  ^  '  acusticum) 

Acustic  area    (nucleus 
vestibularis) 


^  Nucleus  intercalatus 
"~  Hypoglossal  eminence  (trigone) 
^^  Irigonum  vagi  (ala  cinerea) 

^    Funiculus  separans 
Obex 


medial  extension  of  the  nucleus  of  termination  of  the  vestibular  nerve  (area  acustica),  but 
Streeter,  who  has  made  a  detailed  study  of  the  floor  of  the  fourth  ventricle  by  means  of  serial 
sections,  doubts  that  it  is  a  part  of  this  nucleus.  It  is  much  more  probable  that  it  supplies 
visceral  efferent  flbres  to  the  vagus  and  is  thus  a  continuation  of  the  dorsal  efferent  nucleus  of 
the  vagus. 

Superior  to  the  inferior  fovea,  and  crossing  each  half  of  the  floor  of  the  fourth  ventricle, 
are  the  acoustic  striae.  These  are  bundles  of  axones  arising  in  the  dorsal  nuclei  of  termination 
of  the  cochlear  or  auditory  nerve,  which  are  situated  in  the  lateral  periphery  of  each  restiform 
body.  The  bundles  course  around  the  dorsal  periphery  of  the  upper  portion  of  the  restiform 
body,  then  across  each  half  of  the  floor  of  the  ventricle  to  the  median  sulcus,  in  which  they 
suddenly  turn  ventrally  into  the  substance  of  the  medulla  oblongata,  and  in  doing  so  they  cross 
the  mid-line  to  enter  the  substance  of  the  opposite  side.  The  striie  vary  greatly  in  different 
individuals,  both  in  the  degree  of  their  prominence  and  their  direction.  Sometimes  no  striae 
are  visible  from  the  surface.  Frequently  a  bundle  may  be  discerned  which  courses  obliquely 
upward  and  lateralward  from  the  median  sulcus  to  disappear  in  the  floor  further  away  from 
the  mid-Une  and  again,  a  bundle  may  depart  from  the  transverse  course  before  reaching  the 
median  sulcus.  Such  a  bundle  ascending  is  sometimes  called  conductor  sonorus.  The  acoustic 
striae  cross  the  acoustic  area.  This  is  the  flattened  elevation  which  occupies  the  whole  lateral 
portion  of  the  intermediate  portion  of  the  floor  of  the  ventricle,  lateral  to  the  limiting  sulcus, 
and  extends  into  the  inferior  portion  lateral  to  the  inferior  fovea.     It  represents  the  subjacent 


STRUCTURE  OF  MEDULLA  OBLONGATA  815 

nucleus  of  termination  of  the  vestibular  nerve.  The  dorsal  and  ventral  nuclei  of  the  cochlear 
nerve  {iuberculum  acusticum)  are  indicated  by  the  ventro-lateral  fullness  in  the  contour  of 
the  restiform  body.     In  many  of  the  mammals  they  produce  a  well-marked  protuberance. 

In  its  superior  portion  the  medial  eminence  occupies  the  greater  part  of  the  floor  of  the 
fourth  ventricle,  and  in  the  upper  part  of  the  intermediate  portion  of  the  floor  it  presents  a 
broader,  well-marked,  elongated  elevation,  the  eminence  of  the  facial  and  abducens  or  the 
colliculus  facialis.  This  represents  the  mesiaOy  placed  nucleus  of  origin  of  the  abducens  and 
the  genu  of  the  root  of  the  facial  nerve,  which  root  courses  around  and  above  the  nucleus  of  the 
abducens.  The  nucleus  of  the  facial  is  too  deeply  situated  to  produce  an  eminence.  Lateral 
to  this  eminence  is  a  depression  of  the  limiting  sulcus,  which  overUes  the  mesial  part  of  the  region 
of  the  larger  portion  of  the  nucleus  of  termination  of  the  trigeminus,  and  is  the  fovea  trigemini 
or  superior  fovea.  The  strip  of  the  floor  above  the  superior  fovea  and  lateral  to  the  medial 
eminence  often  appears  greyish  blue  or  dark  brown,  owing  to  pigmented  cells  subjacent  to  it, 
and  is  known  as  the  locus  caeruleus.  It  also  represents  a  portion  of  the  nucleus  of  the  trigem- 
inus. The  most  superior  portion  of  the  medial  eminence  becomes  narrow  and  lies  close  to 
the  mid-line.  The  function  of  the  underlying  grey  substance  producing  it  is  uncertain,  and 
for  this  reason  Streeter  has  named  the  elevation  nucleus  incertus,  noting  that  by  position  it  is 
closely  related  to  the  upper  portion  of  the  nucleus  of  the  trigeminus. 

Internal  Structure  of  the  Medulla  Oblongata  and  Pons 

The  finer  detail  of  the  internal  structure  lies  within  the  scope  of  microscopic  rather  than 
of  gross  anatomy.  However,  the  significance  and  relations  of  certain  of  the  more  important 
and  larger  of  the  internal  structures  of  the  meduUa  and  pons  as  observed  in  sections  may  be 
considered. 

The  entire  brain-stem  may  be  regarded  as  an  upward  continuation  of  the  spinal  cord,  to 
which  structures  are  added  giving  each  part  its  peculiar  character  and  conformation,  and  in 
which  the  structures  characteristic  of  the  spinal  cord  are  modified  in  varying  degrees. 

The  pyramids,  the  great  descending  or  motor  cerebro-spinal  fasciculi,  are  directly  con- 
tinuous into  the  pyramidal  fasciculi  of  the  spinal  cord.  They  form  the  extreme  ventro-medial 
portion  of  the  medulla,  and  from  the  fact  that  they  contribute  numerous  fibres  to  the  efferent 
nuclei  (nuclei  of  origin)  of  the  cranial  nerves  and  to  other  portions  of  the  grey  substance  of 
the  brain-stem,  they  decrease  appreciably  in  bulk  in  descending  toward  the  spinal  cord. 
Most  of  the  fibres  contributed  to  the  medulla,  as  well  as  to  other  divisions  of  the  brain-stem, 
decussate  as  they  leave  the  pyramids,  and  terminate  in  the  grey  substance  of  the  opposite 
side.  However,  the  chief  decussation  of  the  pyramids  occurs  in  the  lower  end  of  the  medulla. 
Here  usually  about  three-fourths  of  the  fibres  then  comprising  the  pyramids  cross  the  mid- 
line to  form  the  lateral  cerebro-spinal  fasciculus  (crossed  pyramidal  tract)  of  the  spinal  cord 
immediately  below.  The  remaining  fourth,  comprising  the  more  lateral  fibres  or  those  furthest 
away  from  the  mid-line,  continues  uncrossed  into  the  spinal  cord  as  the  ventral  cerebro-spinal 
fasciculus  or  direct  pyramidal  tract.  The  majority  of  the  latter  fibres  decussate  gradually 
in  the  commissural  bundle  and  in  the  ventral  white  commissure  of  the  cord  as  they  approach 
the  levels  of  their  termination.  In  practically  all  vertebrates  except  man  and  the  apes  there 
are  no  ventral  pyramidal  fasciculi,  the  decussation  in  the  medulla  being  a  total  one.  In  man, 
the  proportion  of  fibres  crossing  in  the  chief  decussation  varies.  Cases  have  been  noted  in 
which  apparently  the  entire  pjTamids  decussate  at  this  level.  In  other  cases  the  direct  or 
ventral  pyramidal  tract  may  be  much  larger  than  usual,  at  the  expense  of  the  lateral.  The 
decussation  usuaUy  appears  to  be  symmetrical  and  it  occurs  so  suddenly  that  the  fibres,  in 
coursing  from  the  ventral  to  the  lateral  positions,  detach  the  tips  of  the  ventral  horns  of  the 
spinal  cord  from  the  remainder  of  the  grey  figure,  and  these  appear  as  isolated,  irregularly 
shaped  masses  of  grey  substance  in  transverse  sections  of  the  medulla.  From  this  level  upward 
the  outline  of  the  grey  figure  of  the  cord  is  lost,  and  the  cell-columns  of  the  ventral  horns  occur 
in  more  or  less  detached  groups  as  the  motor  nuclei  of  the  cranial  nerves. 

The  origin  and  decussation  of  the  lemnisci  (fillet)  begins  immediately  above  the  decussa- 
tion of  the  pyramids,  and  here  the  arrangements  characteristic  of  the  spinal  cord  are  further 
modified.  The  dorsal  portion  of  the  grey  figure  of  the  cord  is  manifest  up  to  this  level,  but 
here,  after  a  considerable  increase  in  its  thickness,  the  grey  commissure  gives  rise  to  two  thick 
dorsal  outgrowths  on  each  side  of  the  mid-hne.  These  dorsal  projections  of  grey  substance 
comprise  the  nuclei  of  termination  (relays)  of  the  chief  ascending  or  sensory  spino-cerebral 
fasciculi  of  the  spinal  cord.  The  nucleus  of  the  fasciculus  gracilis  (nucleus  of  GoU's  column) 
arises  a  little  before  the  nucleus  of  the  fasciculus  cuneatus  (nucleus  of  Burdach's  column). 
The  former  extends  slightly  downward  from  its  point  of  origin,  so  that  its  inferior  extremity  is 
included  in  sections  through  the  decussation  of  the  pyramids  (fig.  6il).  It  produces  a  slight 
bulbous  enlargement  (the  clava)  of  the  end  of  the  funiculus  gracihs,  while  the  nucleus  of  the 
fasciculus  cuneatus  corresponds  to  the  cuneate  tubercle  of  the  external  contour  of  the  meduUa 
(figs.  632,  640).  From  the  cells  of  these  nuclei  arise  the  lemniscus — the  cephalic  continuation 
of  the  spino-cerebral  pathway  which  conveys  the  general  bodily  sensations  to  the  cerebrum. 
In  passing  out  of  the  nuclei  the  fibres  of  the  lemniscus  course  in  a  ventro-medial  direction. 
Curving  around  the  region  of  the  central  canal,  they  contribute  largely  to  the  internal  arcuate 
fibres,  then,  sweeping  across  the  mid-line,  they  convert  it  into  the  raphe,  and  immediately  after 
crossing  (decussating)  they  turn  cephalad  and  collect  to  form  the  bundle  known  as  the  lemniscus. 

In  the  medulla,  the  lemnisci  are  two  thin  bands  of  fibres  spread  vertically  on  each  side  of 
the  raphe,  with  their  lower  or  ventral  edges  thicker  than  their  dorsal  edges.  In  their  course 
toward  the  cerebrum  they  increase  in  bulk,  owing  chiefly  to  fibres  being  added  to  them  from 
the  nuclei  of  termination  of  the  aiferent  roots  of  the  cranial  nerves,  which  fibres  likewise  cross 
the  mid-line  as  internal  arcuate  fibres  to  join  the  lemniscus  of  the  opposite  side.     In  passing 


816 


THE  NERVOUS  SYSTEM 


through  the  pons,  the  lemnisci  gradually  become  spread  horizontally,  and  beyond  the  pons 
their  then  more  lateral  portions  are  further  displaced  and  come  to  course  in  the  lateral  borders 
of  the  isthmus  rhombencephali  and  mesencephalon,  while  the  medial  portions  remain  nearer 
the  mid-line.  This  lateral  spreading  of  each  lemniscus  produces  the  lateral  lemniscus  and  the 
medial  lemniscus,  distinguished  in  transverse  sections  of  the  superior  pons  and  mesencephahc 

Fia.  641. — Transverse  Section  of  Medulla  Oblongata  at  the  Level  of  the  Decussation 

OF  THE  Pyramids. 


Central  grey  substance 


Nucleus  of  fasciculus  gracilis 
Funiculus  cuneatus 


j^^^-Substantia  gelatinosa  (Rolandi) 
Spinal  tract  of  trigeminus 


if'  '  Gowers'  tract 


»        Lateral  cerebro-spinal  fasciculus 
V  '^  Ventral  horn 

\  Decussation  of  pyramids 

Pyramid 


regions  of  the  brain  stem  (fig.  660).     The  lateral  lemniscus  is  contributed  very  largely  by  the 
cell-bodies  of  the  nuclei  of  termination  of  the  cochlear  nerve  of  the  opposite  side. 

The  reticular  formation  of  the  medulla  and  pons  region  is  considerably  more  abundant 
than  in  the  spinal  cord.  As  in  the  spinal  cord,  it  consists  of  grey  substance  through  which 
nerve-fibres,  singly  and  in  small  bundles,  course  in  all  directions,  and  more  sparsely  than  in 
other  regions.     In  the  medulla  it  is  traversed  by  the  internal  arcuate  fibres.     It  may  be  con- 


FiQ.  642. — Transverse  Section  of  Medulla  Oblongata  at  Level  of  the  Decussation  of 

THE  Lemnisci, 


Posterior  median  fissure 
Central  grey  substance 
Nucleus  of  hypogl 


Internal  arcuate  fibers 


Root  filum  of  hypoglossus 
Nucleus  of  inferior  olivi 


Medial  accessory  olivary  nucleu 


Nucleus  of  fasciculus  gracilis 

*  Commissural  nucleus  of  ala  i 

'  /  Nucleus  of  fasciculus  cuneatus 


Dorsal  external  arcuate  fibres 


is  of  spinal  tract  of 
trigemi-nus 


--  Spinal  tract  of  trigi 


Raphe' 


'--  -'  Restiform  body 
■Nucleus  lateralis 


V      Substantia  reticularis 
Ventra.1  external  arcuate  fibres 
Decussation  of  lemnisci 


sidered  an  enlarged  continuation  of  the  middle  portion  of  the  grey  column  of  the  cord,  dispersed 
by  numerous  fibres,  giving  it  the  reticulated  appearance  which  suggests  its  name.  Its  numer- 
ous nerve-cells  belong,  for  the  most  part,  to  the  association  and  commissural  systems  of  the  brain 
stem,  and,  therefore,  the  fibres  arising  in  it  correspond  largely  to  the  fasciculi  proprii  of  the 
spinal  cord.  As  in  the  cord,  most  of  the  fibres  are  of  short  course,  serving  to  associate  different 
portions  of  the  same  level  and  adjacent  levels  with  each  other.  Those  of  long  course  show  a 
tendency  to  collect  into  a  small,  well-marked  bundle  which  courses  one  on  each  side  close_  to 
the  mid-line,  ventral  to  the  central  canal  in  the  closed  part  of  the  medulla,  and  near  the  median 
sulcus  of  the  floor  of  the  fourth  ventricle,  in  the  open  part.  In  the  mesencephalon  this  bundle  is 
again  situated  closely  ventral  to  the  aquaeductus  cerebri. 


STRUCTURE  OF  MEDULLA  OBLONGATA 


817 


This  bundle  is  known  as  the  medial  longitudinal  fasciculus  (posterior  longitudinal  bundle). 
It  corresponds  more  nearly  to  the  ventral  fasciculus  proprius  of  the  spinal  cord  than  to  others 
of  the  fasciculi  proprii.  In  the  medulla  it  appears  as  the  dorsal  edge  of  the  lemniscus,  but  in 
the  shifting  of  the  position  of  the  lemniscus  in  the  pons  region,  it  retains  its  medial  position  and 
thus  becomes  isolated.  By  position  it  is  especially  adapted  for  the  association  of  the  nuclei 
of  the  cranial  nerves.  Evidence  has  been  found  that  those  fibres  which  arise  in  the  corpora 
quadrigemina  and  descend  the  spinal  cord  in  its  sulco-marginal  or  ventral  mesencephalo-spinal 
fasciculus,  pass  through  the  medulla  in  the  medial  longitudinal  fasciculus.  The  nuclei  of 
termination  of  the  vestibular  nerve  are  said  also  to  contribute  many  fibres  to  it. 

The  inferior  olivary  nucleus  is  an  added  structui-e  in  the  medulla  oblongata,  i.  e.,  it  has 
no  homologue  in  the  spinal  cord.  The  two  of  them  occupy  the  olivary  prominences,  the  olives 
of  the  exterior,  and  constitute  the  most  conspicuous  and  striking  isolated  masses  of  grey  sub- 
stance in  sections  of  the  medulla.  They  appear  as  crenated  laminae  of  grey  substance  folded 
so  as  to  encup  a  dense  mass  of  white  substance,  and  in  actual  shape  the  entire  nucleus  has 
the  form  of  an  irregular  corrugated  cup  with  the  opening  or  hilus  on  the  side  toward  the  mid- 
line. The  mass  is  so  crumpled  that  the  diameter  of  the  hilus  is  appreciably  less  than  the  length 
of  the  nucleus,  and  thus  transverse  sections  of  either  extremity  of  it  appear  as  closed  capsules. 

Fig.  643. — Transverse  Section  op  Medulla  Oblongata  Through  Nuclei  of  Vagus  and 

HyPOGLOSSUS   AND   THROUGH   THE    MlDDLE    OP  THE    OlIVES. 
Medial  longitudinal  fasciculus 
Chorioid  tela  of  fourth  ventricle 


Nucleus  of  hypoglossus 
Medial  nucleus  of  vestibular  nerve  "** 
Descending  (spinal)  nucleus 
of  vestibular  nerve 


Nucleus  ambiguus 


Dorsal  accessory 
olivary  nucleus 


Root  filum  of  hypo 
glossus 


Nucleus  of  ala  cinerea  (trigonum  vagi) 
/  Dorsal  efferent  nucleus  of  vagus 
'      '  Solitary  tract 

Nucleus  of  solitary  tract 
__  / 

'^j^J/'  /^"s^       ' —  Nucleus  of  fasciculus 

^"^'^         ''< -^         ^^'  cunatus 

■^  ^        ^^^*^    ^  Nucleus  of  spinal  tract 
^  ""^    \     ./Jal^^r  °^  trigeminus 


Restiform  body 

Spinal  tract  of 

trigeminus 
Cerebello-olivary 

fibres 
Root  filum  of  vagus 
—  Nucleus  lateralis 


Thalamo-olivary  tract 


'       ''     Pyramid 
Lemniscus     Raphe 


There  are  several  small  detached  portions  of  the  olivary  nucleus  known  as  the  accessory 
olivary  nuclei.  These  are  named  according  to  their  position  with  reference  to  the  chief  portion 
or  olive  proper.  They  are  plates  less  corrugated  than  the  chief  nucleus,  and  appear  rod-like 
in  sections.  The  largest  is  the  dorsal  accessory  olivary  nucleus.  The  medial  accessory  olivary 
nucleus  is  widest  at  its  inferior  end,  which  extends  a  little  below  the  inferior  extremity  of  the 
chief  nucleus.  The  lateral  accessory  olivary  nucleus  is  the  smallest.  In  serial  sections  the 
accessory  nuclei  are  found  to  be  plates  of  grey  substance  usually  continuous  with  one  another. 

The  oUvary  nuclei  are  mainly  cerebellar  connections.  By  both  ascending  and  descending 
fibres  each  cerebellar  hemisphere  is  connected  with  the  olivary  nucleus  of  the  same  and  opposite 
sides.  Serial  sections  of  a  human  brain  with  congenital  absence  of  one  cerebellar  hemisphere, 
described  by  Strong,  show  that  the  chief  connection  of  a  hemisphere  is  with  the  olive  of  the  oppo- 
site side.  These  fibres  necessarily  pass  between  the  cerebellum  and  the  olives  by  way  of  the 
restiform  body,  and,  in  so  doing,  form  an  obliquely  coursing  bundle  in  the  lateral  border  of 
the  medulla  known  as  the  cerebello-olivary  fibres  (fig.  643).  The  olivary  nuclei  also  comprise  a 
secondary  relay  between  the  spinal  cord  and  the  cerebellum  by  way  of  the  spino-olivary  fas- 
ciculus of  the  cervical  cord,  and  it  will  be  noted  that  they  receive  fibres  from  the  thalami.  The 
latter  fibres,  the  thalamo-olivary  tract,  approach  the  olive  at  its  lateral  periphery,  while  upward 
through  the  brain-stem  the  tract  courses  in  a  more  medial  position.  This  tract  comprises  one  of 
the  cerebro-cerebellar  paths.  Arising  in  the  thalamus  and  terminating  in  the  olive,  its  impulses 
reach  the  opposite  cerebellar  hemisphere  by  way  of  the  cerebeUo-ohvary  fibres. 

The  arcuate  fibres  are  referred  to  as  internal  and  external,  according  as  they  course  dorsal 
or  ventral  to  the  inferior  ohvary  nucleus. 

The  internal  arcuate  fibres  comprise  fibres  destined  for  both  the  cerebellum  and  cerebrum, 
and  also  for  the  association  of  the  tegmental  grey  substance  of  the  two  sides  in  which  they  course. 
Certain  of  the  fibres  passing  between  one  restiform  body  (cerebellar  hemisphere)  and  the 
olive  of  the  opposite  side  course  internal  to  the  olive  of  the  same  side,  and  thus  form  the  ventral 
portion  of  the  internal  arcuate  fibres.     As  noted  above,  the  internal  arcuate  fibres  consist  in 


818  THE  NERVOUS  SYSTEM 

greatest  part  of  fibres  being  contributed  to  the  lemnisci,  arising  from  the  cells  of  the  nucleus  of 
the  fasciculus  gracOis  and  fasciculus  cuneatus  and  sweeping  downward  and  decussating  to  form 
the  lemniscus  of  the  opposite  side.  However,  all  the  fibres  arising  in  these  nuclei  do  not  enter 
the  lemniscus.  A  few  of  them  cross  the  mid-line  with  the  internal  arcuates,  but  pass  on  to 
enter  the  restiform  body  (cerebellar  hemisphere)  of  the  opposite  side.  Some  of  these  course 
ventraUy  and,  upon  approaching  the  olive  of  the  opposite  side,  are  deflected  around  the  ventral 
side  of  both  the  olive  and  the  pyramid,  and  thus  pass  to  the  restiform  body  as  external  arcuate 
fibres  also.  Certain  of  the  internal  arcuate  fibres  arise  from  the  cells  of  the  nuclei  of  termina- 
tion of  the  cranial  nerves  and  from  small  cells  situated  in  the  grey  substance  of  the  reticular 
formation.  These,  in  crossing  the  mid-line,  correspond  to  the  white  commissures  of  the  spinal 
cord.  Some  of  them  terminate  in  the  meduUa;  others,  especially  those  from  the  nuclei  of 
termination  of  the  cranial  nerves,  join  the  lemniscus  and  pass  toward  the  cerebrum;  others 
reach  the  cerebellar  hemisphere  of  the  opposite  side. 

The  external  arcuate  fibres,  in  addition  to  those  mentioned  above,  comprise  certain  fibres 
which  arise  in  the  nuclei  of  the  fasciculus  gracilis  and  cuneatus  and  pursue  a  dorso-lateral  course 
to  enter  the  restiform  body  (cerebellar  hemisphere)  ol  the  same  side.  These  form  the  dorsal 
segment  of  the  external  arcuates.  The  greater  mass  of  the  external  arcuates  are  cerebello- 
oHvary  fibres.  Certain  of  those  passing  from  one  olive  to  the  restiform  body  of  the  opposite 
side  are  deflected  at  the  raphe,  and  course  on  the  ventral  side  of  both  the  other  olive  and  the 
pyramid  in  order  to  reach  the  opposite  cerebeUo-ohvary  bundle.  Likewise,  those  passing 
from  the  restiform  body  to  the  opposite  olive  are  deflected  by  the  olive  of  the  same  side 
and  pursue  a  similar  course  to  the  raphe.  While  out  of  the  hilus  of  each  olive  streams  a 
dense  mass  of  white  substance,  yet  many  of  the  fibres  concerned  with  the  olive  pierce  its  walls 
from  all  sides. 

Many  of  the  external  arcuate  fibres  are  said  to  be  interrupted  in  the  nucleus  arcuatus. 
This  is  a  thin  sheet  of  grey  substance,  variable  in  amount,  which  lies  on  the  ventral  aspect  of 

Fig.  644. — Reconstruction  of  the  Inferior  Olivary  Nucleus,  Dorso-lateral  Surface. 

(After  Sabin.) 


each  pyramid,  and,  though  it  decreases  inferiorly,  it  may  be  evident  down  to  the  decussation 
of  the  pjTamids.  The  nucleus  receives  its  name  from  the  fact  that  its  larger  portion  is  inter- 
polated in  the  course  of  the  external  arcuates.  It  is  continuous  anteriorly  with  the  grey 
substance  or  nuclei  of  the  pons. 

The  external  arcuate  fibres  of  longer  course,  like  the  olives  with  which  they  are  largely 
concerned,  have  no  homologues  in  the  spinal  cord. 

The  central  canal  of  the  closed  portion  of  the  meduUa  is  surrounded  by  a  greater  amount 
of  central  grey  substance,  substantia  grisea  centralis,  than  is  the  canal  in  the  spinal  cord. 
This  is  largely  gelatinous  substance,  the  central  gelatinous  substance,  and  the  nerve-fibres  in 
coursing  through  the  grey  substance  are  partially  deflected  by  it,  leaving  it  as  a  cyhndrical, 
more  evident  area  of  grey  substance  than  in  other  regions.  In  the  open  portion  of  the  meduUa 
the  central  grey  substance  naturally  forms  a  more  transparent  lamina  just  under  the  floor 
of  the  fourth  ventricle.  In  the  mesencephalon  it  again  surrounds  the  reformed  canal  or  aque- 
duct of  the  cerebrum. 

The  central  connections  of  the  cranial  nerves  are  most  easily  homologised 
with  spinal-cord  structures.  Functionally  the  cranial  nerves  are  of  three  varie- 
ties:— (1)  the  motor  or  efferent  nerves,  comprising  the  oculomotor,  the  trochlear, 
masticator,  the  abducens,  the  facial,  the  spinal  accessory,  and  the  hypoglossus; 
(2)  the  sensory  or  afferent,  comprising  the  olfactory,  the  optic,  the  trigeminus,  the 
vestibular,  and  the  cochlear  and  (3)  the  mixed,  motor  and  sensory  nerves, 
comprising  the  glosso-palatine,  the  glosso-pharyngeal,  and  the  vagus.  The 
nuclei  of  origin  of  the  motor  or  efferent  cranial  nerves  and  the  efferent  portions  of 
the  mixed  nerves  are  directly  continuous  with  the  cell  columns  of  the  ventral 
horns  of  the  spinal  cord,  while  the  emerging  root  filaments  and  roots  of  these 
nerves  correspond  to  the  ventral  roots  of  the  spinal  nerves.     The  nuclei  of  ter- 


STRUCTURE  OF  MEDULLA  OBLONGATA 


819 


mination  of  the  afferent  or  sensory  cranial  nerves  and  of  the  sensory  portions  of  the 
mixed  nerves  correspond  directly  to  the  nuclei  of  the  fasciculus  gracilis  and 
fasciculus  cuneatus,  and  to  the  cell-bodies  of  association  and  commissural  neu- 
rones of  the  medulla  and  cord  and,  functionally,  are  merely  anterior  continua- 
tions of  these. 

The  nuclei  of  the  efferent  or  motor  cranial  nerves  lie  in  two  parallel  lines,  one 
near  the  mid-line  arid  the  other  more  laterally  placed.  The  nuclei  giving  origin 
to  the  oculomotor,  the  trochlear,  the  abducens,  and  the  hypoglossus  are  near  the 
mid-line,  and  correspond  to  the  ventro-medial  and  dorso-medial  cell  groups  of  the 
ventral  horns  of  the  spinal  cord;  the  nuclei  of  origin  of  the  masticator  (motor 


Figs.  645  and  646. — Diagrams  showing  the  Composition  op  the  Cerebellar  Portions 
OF  the  Internal  and  External  Arcuate  Fibres. 


Nucleus  of     Commissural  nucleus 
fasciculus       of  ala  cinerea 
gracilis 


Spinal  tract  of  trigemi] 


Dorsal  external  arcuate  fibres 


-Restiform  body 


Ventral  external  arcuate  fibers 


Nucleus  of  tractus  solitarius 
Nucleus  of  ala  cinerea  ;  Medial  nucleus  and  descending  root  ot 
vestibular  nerve 

Nucleus  of  fasciculus 
cuneatus 
^Nucleus  ambiguus 

-\ —  Restiform  body 


Root  filum  of  vagus 
Cerebello-olivary  fibres 


Ventral  external  arcuate  fibres 


root  of  the  trigeminus)  of  the  facial,  and  the  nucleus  ambiguus:  giving  origin  to 
the  motor  portions  of  the  glosso-pharyngeal  and  vagus  nerves,  together  with  the 
nucleus  of  the  spinal  accessory,  correspond  to  the  ventro-lateral  and  dorso-lateral 
cell-groups  of  the  ventral  horns  of  the  spinal  cord.  The  nerve-roots  having  medial 
nuclei  of  origin  are  those  which  make  their  exit  from  the  brain-stem  along  tlie  more 
media,l  superficial  line,  while  those  having  the  more  lateral  nuclei  comprise  the 
more  lateral  hne  of  roots  apparent  on  the  surface  of  the  stem.  Some  of  the  effer- 
ent fibres  of  the  vagus,  supposedly  visceral  efferent,  arise  from  a  small  nucleus 
dorso-medial  to  the  nucleus  ambiguus,  the  dorsal  efferent  nucleus  of  the  vagus. 
i  he  first  two  pau-s  of  cranial  nerves,  the  olfactory  and  optic,  are  attached  to  the 


820  THE  NERVOUS  SYSTEM 

prosencephalon.  These  are  purely  sensory,  and  make  their  entrance  near  the 
mid-line  of  the  brain,  both  having  superficially  placed  nuclei  of  termination.  Of 
the  other  nerves,  all  having  sensory  or  afferent  functions  enter  the  brain  along  the 
lateral  or  more  dorsal  line,  and  the  ganglia  giving  origin  to  their  afferent  axones 
correspond  directly  to  the  spinal  ganglia  of  the  dorsal  or  afferent  roots  of  the 
spinal  nerves. 

Commissural  and  associational  neurones  are  much  more  numerous  in  the 
brain-stem  than  in  the  spinal  cord.  Their  axones  serve  to  connect  the  struc- 
tures on  the  two  sides  of  the  mid-line  and  to  associate  the  different  levels  of  the 
same  side.  Just  as  in  the  spinal  cord,  those  of  longer  com-se  correspond  to  the 
fasciculi  proprii.     Many  of  their  axones  descend  into  the  spinal  cord. 

Of  the  fifteen  pairs  of  cranial  nerves,  eleven  pairs  are  attached  to  the  medulla 
oblongata  and  pons,  viz.,  the  trigeminus,  the  masticator,  abducens,  facial, 
glosso-palatine,  vestibular,  cochlear,  glosso-pharyngeal,  vagus,  spinal  accessory, 
and  hypoglossus. 

The  hypoglossus,  the  motor  nerve  of  the  tongue,  has  its  nucleus  of  origin  beginning 
in  the  lower  portion  of  the  floor  of  the  fourth  ventricle  at  the  level  of  the  acustic  striae.  It  ' 
is  a  long  nucleus,  lying  close  to  the  mid-line  and  just  under  the  floor  of  the  ventricle  (hypoglossal 
eminence)  and  extending  down  to  the  region  of  the  funiculus  separans.  Here  it  curves  ventrally 
to  a  slight  degree,  and  below  the  obex  assumes  a  position  ventro-lateral  to  the  central  canal, 
and  thus  extends  a  short  distance  below  the  level  of  the  inferior  tip  of  the  olive.  The  nerve 
arises  as  a  series  of  rootlets  which  traverse  the  entii-e  thickness  of  the  medulla  (fig.  643),  to 
emerge  in  line  in  the  furrow  between  the  olive  and  the  pyramid  and  fuse  to  form  the  trunk  of 
the  nerve.  The  lowermost  of  the  rootlets  usually  emerge  below  the  ohve.  The  nucleus 
receives  impulses — (1)  from  the  cerebrum  by  way  of  divergent  fibres  from  the  pyramid  of  the 
opposite  side  (voluntary);  (2)  impulses  brought  in  by  the  sensory  fibres  of  the  cranial  nerves 
(reflex);  and  (3)  by  axones  from  other  levels  of  the  medulla  (associational).  None  of  its  axones 
are  supposed  to  decussate,  though  numerous  commissural  fibres  are  known  to  pass  between 
the  nuclei  of  the  two  sides. 

The  spinal  accessory  is  likewise  a  purely  motor  nerve,  and  has  a  laterally  placed,  long,  and 
much  attenuated  nucleus  of  origin.  Above,  its  nucleus  is  in  line  with  and  practically  continu- 
ous with  the  nucleus  giving  motor  fibres  to  the  vagus  and  glosso-pharyngeus  (nucleus  ambiguus). 
Below,  it  consists  of  the  lateral  and  dorso-lateral  groups  of  cells  of  the  ventral  horn  of  the  first 
five  or  six  segments  of  the  spinal  cord.  The  nerve  arises  as  a  series  of  rootlets  which  emerge 
laterally  and  join  a  common  trunk,  which  passes  upward  between  the  dorsal  and  ventral  roots 
of  the  upper  cervical  nerves  and  parallel  with  the  meduOa  to  turn  lateralward  in  company 
with  the  vagus.  (See  fig.  629).  The  upper  rootlets  arise  from  that  part  of  the  nucleus  con- 
tiguous to  the  inferior  end  of  the  nucleus  ambiguus,  and  are  described  as  comprising  the  medullary 
or  accessory  part  of  the  nerve;  those  which  arise  from  the  ventral  horn  cells  below  are  described 
as  the  spinal  part.  The  trunk  of  the  spinal  accessory  fuses  with  the  vagus  in  the  region  be- 
tween its  two  ganglia,  and,  before  separation,  contributes  fibres  (the  accessory  part)  to  the 
trunk  of  the  vagus.  Some  of  the  accessory  fibres  are  distributed  as  motor  fibres  to  the  muscles 
of  the  larynx  and  some  of  them  are  visceral  efferent  fibres.  The  latter  probably  terminate 
chiefly  in  sympathetic  ganglia  which  send  axones  to  the  heart.  The  spinal  part  is  distributed  to 
the  sterno-mastoid  and  trapezius  muscles.  The  nucleus  of  the  spinal  accessory  receives  termi- 
nal twigs  of  pyramidal  fibres  from  the  opposite  side  and  is  otherwise  subjected  to  influences 
similar  to  those  afi'ecting  the  cells  giving  origin  to  the  motor  roots  of  the  spinal  nerves. 

The  vagus  or  pneumogastric  and  the  glosso-pharyngeus,  though  they  have  widely  different 
peripheral  distributions,  are  so  similar  in  origin  and  central  connections  that  they  may  be 
described  together.  Both  contain  efferent  fibres,  though  both  are  in  greater  part  sensory. 
They  are  similar  as  to  the  origin  of  both  their  efferent  and  afferent  components.  The  afferent 
fibres  of  the  vagus  arise  in  its  jugular  gangUon  and  its  nodosal  ganghon  (ganglion  of  the  trunk); 
the  afferent  fibres  of  the  glosso-pharyngeus  arise  in  its  superior  ganghon  and  its  petrosal  ganghon. 
In  both  nerves  these  fibres  enter  the  lateral  aspect  of  the  medulla  and  bifurcate  into  ascending 
and  descending  branches,  similar  to  those  of  the  dorsal  root-fibres  in  the  spinal  cord.  Some 
of  these  branches  terminate  in  practically  the  same  level  of  the  medulla  about  cell-bodies 
situated  on  the  same  and  the  opposite  sides.  Such  branches  end  chiefly  in  the  nuclei  of  the 
hypoglossal  and  spinal  accessorj^,  and  about  the  cells  giving  origin  to  the  efferent  components 
of  the  vagus  and  glosso-pharyngeus  themselves — short  reflex  arcs.  However,  most  of  the 
afferent  fibres  terminate  in  the  nucleus  of  termination  of  the  vagus  and  glosso-pharyngeus: — (1) 
the  nucleus  of  the  ala  cinerea,  the  middle  portion  of  which  is  indicated  in  the  floor  of  the  fourth 
ventricle  by  the  ala  cinerea;  (2)  in  the  closed  portion  of  the  medulla,  the  lower  end  of  the 
nucleus  of  the  ala  cinerea  comes  to  lie  in  the  dorso-lateral  proximity  of  the  central  canal,  and 
this  portion  is  known  as  the  commissural  nucleus  of  the  ala  cinera  (figs.  642  and  645)  from  the 
fact  that  fibres  may  be  seen  which  pass  directly  from  it  across  the  mid-line;  (3)  the  longer  of 
the  descending  branches  of  the  bifurcated  fibres  collect  to  form  the  solitary  tract,  a  compact 
bundle  situated  dorsaUy  just  ventro-lateral  to  the  nucleus  of  the  ala  cinerea  and  quite  con- 
spicuous in  sections  of  the  medulla.  The  fibres  of  this  bundle  terminate  in  the  nucleus  of  the 
solitary  trad,  which  is  but  a  ventro-lateral  and  downward  continuation  of  the  nucleus  of  the 
ala  cinerea  enclosing  the  bundles  forming  the  tract.  It  is  most  probable  that  the  fibres  of  the 
solitary  tract  are  chiefly  from  the  vagus  (pneumogastric),  though  Bruce  has  found  evidence 
that  the  glosso-pharyngeal  contributes  to  it  appreciably.  It  decreases  rapidly  in  descending 
the  medulla,  owing  to  the  rapid  termination  of  its  fibres  about  the  cells  of  its  nucleus.    It, 


NUCLEI  OF  CRANIAL  NERVES 


821 


with  the  axones  given  by  the  cells  of  its  nucleus,  is  believed  to  extend  as  far  downward  as  the 
level  of  the  fourth  cervical  segment  of  the  spinal  cord.  This  being  in  the  level  of  origin  of 
the  phrenic  nerve,  the  tract  forms  a  link  in  the  respiratory  apparatus  which  aids  in  the  co- 
ordinated respiratory  movements.  The  axones  given  off  by  the  cells  of  the  nucleus  of  the 
ala  cinerea  (terminal  nuclei  of  the  vagus  and  glosso-pharyngeus)  course  on  both  sides  of  the 

Fig.  647. — Scheme  showing  the  Relative  Size  and  Position  op  the  Nttclei  of  Origin 
(Red)  of  the  Motor  and  the  Nuclei  op  Termination  (Blue)  op  the  Sensory 
Cranial  Nerves. 


Nucleus  of  olfactory  nerve 


Nucleus  of  oculomotor  nerve  " 

Nucleus  of  trochlear  nerve 

Nucleus  of  mesencephalic  root  of 

masticator 

Chief  motor  nucleus  of 

masticator 


Nucleus  of  facial' 

Nucleus  of  abducens*' 

Nucleus  ambiguus  (vagus  and 
glosso-pharyngeus) 


Nuclei  of  optic 


Nucleus  of  hypoglossus  " 


Nucleus  of  spinal  accessory  nerve 


^       Pulvinar  o 
\       thalamus 
Lateral  genic- 
ulate body         I  nerve 
Nucleus  of  supe- 
rior colliculus     I 
-  Sensory  nucleus  of  trigeminus 

,  Nucleus  of  vestibular  nerve 


~  Dorsal  nucleus  of  cochlear  nerve 


Nucleus  alSE  cinerege  (vagus  and 
glosso-pharyngeus) 


Solitary  tract  (vagus  and  glo 
pharyngeus) 


--Nucleus  of  spinal  tract  of  trigeminus 


mid-line,  associating  nuclei  of  other  cranial  nerves  with  vagus  and  glosso-pharyngeal  impulses, 
many  decussating  to  be  distributed  to  the  structures  of  the  opposite  side.  Many  join  the  lemnis- 
cus of  the  opposite  side  and  pass  into  the  cerebrum;  others  are  distributed  to  the  motor  neu- 
rones of  the  cervical  cord  of  the  same  and  opposite  sides  (reflex  axones),  and  no  doubt 
others  form  central  connections  with  the  cells  of  the  reticular  formation  of  the  medulla, 
though  their  precise  relations  have  not  been  determined.  ' ' 


822 


THE  NERVOUS  SYSTEM 


Cell-bodies  in  the  nucleus  of  the  ala  cinerea,  the  nucleus  of  the  solitary  tract  and  in  the 
commissural  nucleus  of  the  ala  cinerea  comprise  the  so-called  respiratory  and  vaso-motor 
nuclei  ("centres")  of  the  medulla.  Some  of  the  caudal  branches  of  the  axones  given  off  by 
the  cells  of  these  nuclei  descend  the  spinal  cord,  not  only  to  the  segments  giving  origin  to 
the  phrenic  nerve,  but  also  to  those  supplying  the  intercostal  and  levatores  costarum  muscles. 
Some  of  these  augment  the  solitary  tract;  most  of  them  descend  in  the  reticular  formation  of 
the  meduUa  and  cord.  Further,  axones  given  off  by  these  cells  convey  vaso-motor  impulses 
which  are  distributed  to  visceral  efferent  neurones  throughout  the  cord. 


Fig.  648. — Diagbam  illustrating  Principal  Central  Relations  op  the  Vagus  Nerve, 

EXCLUSIVE    OF   RELATIONS  TO   DESCENDING   CeREBBAL   OR   PYRAMIDAL  FIBRES. 


Medial  lemniscus 


Dorsal  efferent  nucli 
of  vagus 


Nucleus  of  hypogli 


,  Nucleus  of  ala  cinerea 


Nucleus  anbiguus 
—  p#  Ganglia  of  vagus 


Solitary  tract  and  nucleus 
of  solitary  tract 


The  nuclei  of  origin  of  the  motor  fibres  of  the  vagus  and  glosso-pharyngeus  are  the  dorsal 
efferent  nucleus  of  the  vagus  and  the  nucleus  ambiguus.  The  cells  of  the  dorsal  nucleus 
of  the  vagus  lie  somewhat  clustered  in  the  ventro-mesial  side  of  the  nucleus  of  the  ala  cinerea 
and  lateral  to  the  nucleus  of  the  hypoglossus.  Their  axones  pass  outward  among  the  entering  or 
afferent  vagus  fibres,  and  it  is  suggested  that  most  of  them  are  visceral  efferent  fibres  of  the 
vagus,  i.  e.,  they  terminate  about  sympathetic  neurones.  The  nucleus  ambiguus  or  ventral 
efferent  nucleus  of  both  nerves  hes  in  the  lateral  half  of  the  reticular  formation,  about  mid-way 
between  the  olive  and  the  line  traversed  by  the  rootlets  of  the  two  nerves.  Its  upper  end  is 
larger.  Its  cells  are  considerably  dispersed  by  the  fibres  of  the  reticular  formation.  The 
axones  arising  from  its  cells  course  at  first  dorsalward  and  then  turn  abruptly  outward  to  join 


NUCLEI  OF  VESTIBULAR  NERVE 


823 


the  rootlets  of  the  vagus  or  glosso-pharyngeus,  as  the  case  may  be.  The  vagus  is  thought  to 
receive  more  efferent  fibres  from  the  nucleus  ambiguus  than  does  the  glosso-pharyngeus,  and 
Cunningham  notes  that  it  may  be  questioned  whether  the  latter  nerve  contains  any  motor 
fibres  at  all,  there  being  paths  by  which  the  fibres  of  its  motor  branch  (to  the  stylo-pharyngeus 
muscle)  might  enter  it  other  than  direct  from  motor  nuclei. 

The  oesiibtdar  and  cochlear  nerves  are  usually  considered  as  one  nerve  and  together  are 
designated  as  the  acoustic  or  eighth  cranial  nerve.  While  both  are  purely  sensory,  are  similar 
in  development  and  course  together,  they  are  distinct  as  to  function  and  their  nuclei  of  termina- 
tion differ.  They  are  here  described  as  separate  cranial  nerves.  The  two  nerves  approach  the 
brain  stem  together  and  enter  it  at  the  lateral  aspect  of  the  junction  of  medulla  oblongata  and 
pons. 

The  vestibular  nerve  arises  as  the  central  processes  of  the  bipolar  cells  of  the  vestibular 
ganglion,  and  passes  into  the  brain-stem  on  the  ventro-mesial  side  of  the  restiform  body  to  find 
its  nucleus  of  termination  (nucleus  vestibularis)  in  the  floor  of  the  fourth  ventricle.  This 
nucleus  occupies  a  triangular  area  of  considerable  extent  (area  acustica,  fig.  640),  and  is  usually 
subdivided  into  a  lateral  nucleus  (Deiters'),  a  medial  7iucleus  (Schwalbe's),  a  superior  nucleus 
(Bechterew's),  and  an  inferior  nucleus  (nucleus  spinaUs).  The  latter  is  a  downward  pro- 
longation of  the  general  nucleus  vestibularis  which  accompanies  the  descending  or  spinal  root 
of  the  nerve. 

Fig.  649. — Transverse  Section  of  Medulla  at  Inferior  Border  of  Pons. 

Medial  longitudinal  fasciculus 
Nucleus  of  medial 
^  eminence 

Acoustic  medullary 
^      \  stria 


Descending  root  of  i 
fibular  I 
^Dorsal  root  of  coch- 

■^  Restiform  body 

Dorsal  nucleus 
of  cochlear 
nerve 


^  Cochlear  nerve 
'Vestibular  nerve 
Root  filum  of  glosso  pharyngeus 

Cerebello-olivary  fibres 

Thalamo-oUvary  tract 

Nucleus  of  inferior  olive 


'^  External  arcuate  fibres 


Nucleus  arcuatas 


From  the  cells  of  the  lateral  and  inferior  nuclei  axones  are  given  off  which  form  paths  to 
the  lateral  funiculus  of  the  spinal  cord  (vestibulo-spinal  fasciculus,  fig.  619)  and  to  its  anterior 
marginal  fasciculus  (ventral  vestibulo-spinal  tract).  From  both  the  lateral  nucleus  and  the 
superior  nucleus  a  special  path  is  given  off  which  passes  upward  and  terminates  in  the  roof 
nucleus  of  the  cerebellum  (nucleus  fastigii)  of  the  opposite  side  and  in  the  nucleus  dentatus  and 
the  cortex  of  the  vermis.  Also,  fibres  arising  in  the  nuclei  fastigii  are  said  to  terminate  in  the 
lateral  (Deiters')  nucleus  in  addition  to  those  which  probably  descend  into  the  anterior 
marginal  fasciculus  of  the  spinal  cord.  From  the  medial  and  also  from  the  superior  nucleus 
fibres  pass  to  the  medial  longitudinal  fasciculus  of  both  sides,  and  are  distributed  to  the 
nucleus  of  the  abducens  of  the  same  side  and  to  the  nuclei  of  the  trochlear  and  oculo- 
motor nerves  of  the  opposite  side  and  of  the  masticator  nerve  of  the  same  and  opposite  sides. 
From  the  lateral  and  medial  nuclei,  and  probably  from  aU,  fibres  arise  which  cross  the  mid- 
line to  enter  the  lemniscus  and  ascend  to  the  cerebrum  (lateral  portion  of  the  thalamus)  on 
the  opposite  side.  The  lateral  (Deiters')  nucleus  is  said  to  contribute  more  fibres  to  the 
medial  longitudinal  fasciculus  than  does  a  nucleus  of  any  other  cranial  nerve.  If  any  of  these 
fibres  descend  the  cord,  they  must  do  so  in  its  anterior  marginal  fasciculus. 

The  inferior  nucleus  is  accompanied  by  the  descending  or  spinal  root  of  the  vestibular  nerve, 
which  begins  to  assemble  in  the  nuclei  above.  This  root  is  composed  of  both  caudal  branches 
of'  the  entering  fibres  of  the  nerve  and  chiefly  of  fibres  arising  from  the  cells  of  its  nuclei. 
Thus  for  the  vestibular  nerve  it  corresponds  in  every  way  to  the  solitary  tract  for  the  vagus, 
and  to  the  spinal  tract  of  the  trigeminus.  Such  of  its  fibres  as  descend  into  the  spinal  cord 
most  probably  do  so  in  the  lateral  vestibulo-spinal  fasciculus. 

Many  of  the  anatomical  details  of  the  central  connections  of  the  vestibular  nerve  have  not 
yet  been  determined  with  exactness.     In  addition  to  whatever  other  functions  it  may  have, 


824 


THE  NERVOUS  SYSTEM 


it  is  considered  to  be  the  nerve  of  equilibration,  and  the  connections  noted  above  may  be 
considered  the  pathways  by  which  it  exercises  this  function.  The  fibres  of  the  apparatus  which 
are  represented  in  the  spinal  cord  are  supposed  to  convey  impulses  to  the  ventral  horn  (motor) 
cells  of  the  cord  as  far  down  as  the  lumbar  region. 

The  cochlear  nerve,  the  auditory  nerve  proper,  arises  as  the  central  processes  of  the  bipolar 
cells  of  the  spiral  ganglion  of  the  cochlea.  In  the  lateral  periphery  of  the  restiform  body,  just 
before  the  latter  enters  the  cerebellum,  the  nerve  finds  its  two  nuclei  of  termination,  the  ventral 
nucleus  and  the  dorsal  nucleus  (tuberculum  acusticum,  fig.  640). 

From  the  dorsal  nucleus  arise  the  acoustic  medullary  strice.  These  bundles  pass  around  the 
dorsal  aspect  of  the  restiform  body  and  course  just  under  the  ependyma  of  the  floor  of  the  fourth 
ventricle  to  the  mid-line,  where  they  suddenly  turn  downward  into  the  substance  of  the  medullsa 
and  in  doing  so,  cross  to  the  opposite  side  and  join  the  lemniscus.  As  the  lemniscus  becomes 
separated  higher  up  into  a  medial  and  lateral  portion,  these  fibres  course  in  the  lateral  lemniscul 
and  are  distributed  chiefly  to  the  grey  substance  of  the  inferior  quadrigeminate  and  media, 


Fig.  650. — Scheme  showing  Some  of  the  Central  Connections  op  the  Acoustic  Nerve. 
(In  part  after  Edinger.) 


Medial  geniculate  body 


Inferior  quadrigeminate  body 
Nucleus  of  trochlear  nerve 


Nucleus  fastigii 

Nucleus  emboUforniis 


,'  Dentate  nucleus 


Lateral  nucleus  of 
vestibular  nerve 
Restiform  body 
Dorsal  nucleus  of 

cochlear  nerve 
Ventral  nucleus  of 
cochlear  nerve 
Cochlear  nerve 


Peduncle  of  superior  olivei 


^      Vestibular  nerve 
Superior  olivary  nucleus 
Trapezoid  body 


geniculate  body  of  that  side.  At  the  mid-line  some  of  their  fibres  join  the  median  longitudinal 
fasciculus  and  by  way  of  it  are  distributed  to  the  nuclei  of  origin  of  other  cranial  nerves.  In 
frequent  cases,  the  acoustic  striae  course  so  deeply  beneath  the  ependyma  as  not  to  be  super- 
ficially visible  in  the  floor  of  the  fourth  ventricle. 

From  the  ventral  nucleus  of  termination  fibres  arise  which  terminate  about  the  cells  of  the 
superior  olivary  nucleus  of  the  same  and  opposite  sides.  The  superior  olive  is  a  small  accumu- 
lation of  grey  substance  which  lies  in  the  level  of  the  inferior  portion  of  the  pons,  and  in  line 
with  the  much  larger  inferior  ohvary  nucleus  of  the  medulla.  However,  it  is  not  analogous 
to  the  latter  in  any  sense.  The  two  superior  olives  form  links  in  the  central  acoustic  chain. 
From  cells  of  the  superior  ohvary  nucleus  of  the  same  and  opposite  sides,  fibres  arise  which  pass 
by  way  of  the  lateral  lemniscus  and  terminate  in  the  grey  substance  of  the  inferior  quadri- 
geminate body  and  in  the  medial  geniculate  body,  thus  associating  these  bodies  with  the  ventral 
nucleus  of  cochlear  termination  of  the  opposite  side.  From  the  medial  geniculate  body  fibres 
arise  which  pass  to  the  cortex  of  the  superior  temporal  gyrus.  This  path  is  supplemented  by 
fibres  arising  in  the  inferior  quadrigeminate  body,  which  likewise  go  to  the  temporal  lobe.  In 
the  lateral  lemniscus  some  of  the  acoustic  fibres  are  interrupted  by  cells  of  the  nucleus  of  the 
lateral  lemniscus.  In  crossing  the  mid-line,  between  the  superior  olives,  the  fibres  from  the  two 
sources  form  a  more  or  less  compact  bundle,  the  corpus  trapezoideum  (trapezium).  To  this 
are  added  fibres  crossing  between  the  nuclei  trapeozidei,  smaller  masses  of  grey  substance 
just  ventral  to  the  superior  olives  and  probably  of  the  same  significance. 

Also,  some  fibres  arising  in  the  nuclei  of  termination  of  the  cochlear  nerve  pass  to  the  in- 
ferior quadrigeminate  body  of  the  same  side.     On  the  other  hand,  the  connection  with  the  medial 


NUCLEI  OF  CRANIAL  NERVES 


825 


geniculate  body  is  thought  to  be  wholly  a  crossed  one.  Further,  some  fibres  are  described  aa 
terminating  in  the  superior  quadrigeminale  body  of  both  the  same  and  the  opposite  side.  These, 
forming  the  stratum  lemnisci  of  this  body,  are  especially  suggestive  of  associating  auditory 
impulses  with  eye  movements. 

All  the  fibres  arising  in  the  superior  ohvary  nucleus  do  not  enter  the  corpus  trapezoideum 
and  the  lateral  lemniscus.  A  small  bundle,  the  peduncle  of  the  superior  olive,  arises  in  each 
nucleus  and  courses  dorsally  to  the  region  of  the  nucleus  of  the  abducens.  Here  certain  of  its 
fibres  terminate  about  the  cells  of  the  nucleus  of  the  abducens,  while  others  enter  the  medial 
longitudinal  fasciculus  and  pass  to  the  nuclei  of  the  trochlear  and  oculomotor  nerves,  thus 
further  establishing  connections  between  auditory  impulses  and  eye  movements. 

The  facial  nerve  is  commonly  described  as  consisting  of  the  "facial  proper"  and  its  so-called 
sensory  root  or  pars  intermedia,  the  two  together  being  designated  as  the  seventh  cranial  nerve. 
However,  the  pars  intermedia  neither  serves  as  a  sensory  root  for  the  facial  nor  is  it  purely 
sensory.  Many  years  ago  Sapolini  considered  it  a  separate  nerve  and  later  it  was  called  the 
intermediate  nerve  of  Wrisberg.  More  recent  investigations  of  its  development  and  distribution, 
especially  those  of  Streeter  and  Sheldon,  further  indicate  that  it  merits  a  separate  description 


Fig.  651. — Transverse   Section  through  Inferior  Border  op  Pons  and   Portion   of 
Overlying  Cerebellum      (From  ViUiger.) 


Nucleus  of  roof 


Nucleus  globosus 


Nucleus  emboliformis- 


Dentate  nucleus 


Superior  nucleus 
of  vestibular 
(Becht 
Lateral  nucleus  of 
vestibular 
(Deiters') 
Spinal  tract  of 
trigeminus     '  \\ 


Nucleus  of  facial 


M|fw^»~~  K  estif orm  body 


Superior  olive 

Thalamo-ohvans  tract 


and  a  separate  name,  and,  indicative  of  its  distribution,  it  is  here  described  as  the  glosso-palatine 
nerve.  The  facial,  the  glosso-palatine  and  the  abducens  all  have  their  nuclei  within  the  level 
of  the  pons  though  the  roots  of  all  appear  from  under  its  inferior  border. 

The  facial  [nervus  faciahs]  has  its  nucleus  (of  origin)  in  the  ventro-lateral  region  of  the 
reticular  formation,  superior  to  and  in  line  with  the  nucleus  ambiguus.  The  axones  given  off 
by  the  cell-bodies  of  the  nucleus  collect  into  a  bundle  which,  instead  of  passing  ventrally  and 
directly  to  the  exterior  of  the  pons,  courses  at  first  dorso-mesially  to  the  mesial  side  of  the  nucleus 
of  the  abducens  (ascending  root  of  the  facial) ;  then  it  turns  and  courses  superiorly  for  a  few  milli- 
metres, parallel  with  the  nucleus  of  the  abducens  and  immediately  beneath  the  floor  of  the  fourth 
ventricle  {genu  internum);  then  it  turns  abruptly  and  pursues  a  ventro-lateral  and  inferior 
direction  to  its  point  of  exit  at  the  inferior  border  of  the  pons,  just  lateral  to  the  olive  and 
mesial  to  the  entrance  of  the  vestibular  nerve.  Its  exit  usually  involves  a  few  pons  fibres. 
In  transverse  sections  through  the  middle  of  the  nucleus  of  the  abducens  the  genu  of  the  facial 
appears  as  a  compact  transversely  cut  bundle  at  the  dorso-medial  side  of  this  nucleus. 

The  nucleus  of  the  facial  is  described  as  consisting  of  two  chief  groups  of  cells,  an  anterior 
and  a  posterior  group  which  give  rise  respectively  to  the  axones  of  the  superior  and  inferior 
branches  of  the  facial  nerve.  It  receives  cortical  impulses  from  the  lower  portion  of  the  anteiior 
central  gjTus  of  the  cerebral  cortex,  from  the  root  fibres  of  the  trigeminus  of  the  same  side,  which 
serves  as  its  sensory  root,  and  (chiefly)  fibres  arising  from  the  nuclei  of  termination  of  the 
trigeminus.  The  nuclei  of  termination  of  the  optic  and  the  auditory  nerves  of  the  same  and 
opposite  sides  give  rise  to  fibres  which  terminate  about  its  cells.  The  fibres  from  the  cerebral 
cortex  descend  in  the  pyramidal  fasciculi  and  cross  by  way  of  the  raphe  and  arcuate  fibres  to 
terminate  in  the  nucleus  of  the  opposite  side.  The  anterior  group  of  the  cells  of  the  facial 
nucleus  must  receive  cortical  fibres  not  only  from  the  cerebral  hemisphere  of  the  opposite  but 
also  from  that  of  the  same  side,  evidenced  by  the  fact  that  the  superior  branch  of  the  nerve  is 
but  little  affected  in  facial  paralysis  resulting  from  a  lesion  in  the  cerebral  cortex  of  one  side. 
A  lesion  destroying  the  root  of  the  nerve  or  its  nucleus  of  origin  will  of  course  give  total  facial 
paralysis  in  the  side  of  the  lesion. 


826 


THE  NERVOUS  SYSTEM 


The  glosso-palatine  nerve  {nervus  intermedius,  sensory  root  of  facial,  etc.)  is  a  mixed  nerve 
but  largely  sensory.  It  accompanies  the  facial  from  a  short  distance  beyond  the  geniculum  (genu 
externum)  of  the  facial  to  its  attachment  to  the  brain  stem.  Its  sensory  fibres  arise  as  T-fibres  of 
the  cells  of  the  geniculate  ganglion  (at  the  geniculum  of  the  facial) .  The  peripheral  processes  go  aa 
the  chorda  tympani  to  supply  the  epitheUum  of  the  anterior  part  of  the  tongue  and  that  of  the 
palate,  especially  of  the  palatine  arches.  The  central  processes  enter  the  brain  stem,  bifurcate 
into  caudal  and  cephahc  branches,  and  find  their  nucleus  of  termination  in  a  superior  extension 
of  the  nucleus  of  the  solitary  tract  (the  ventral  portion  of  the  nucleus  of  the  ala  cinerea).  The 
geniculate  ganghon  contains  some  ceU-bodies  of  sympathetic  neurones,  left  over  in  it  during 
the  period  of  migration  form  its  homologue  of  the  ganglion  crest. 

The  efferent  fibres  of  the  glosso-palatine  arise  from  ceU-bodies  lying  dorso-medial  to  the 
nucleus  of  the  facial  and  in  the  level  between  this  and  the  nucleus  of  the  masticator  nerve 
superior  to  it.  Its  cells  are  usually  scattered  in  the  reticular  formation  in  Mne  with  the  dorsal 
efferent  nucleus  of  the  vagus.  Since  most  of  its  fibres,  at  least,  are  concerned  with  sympathetic 
neurones  (terminate  in  sympathetic  gangha)  and  convey  secretory  impulses  destined  for  the 
salivary  glands,  it  has  been  called  the  nucleus  salivatorius. 

Fig.  652. — Transverse  Section  through  Pons  and  Portion  of  CEREBELLtrM  at  Level 
OP  Nuclei  and  Root  Filaments  of  Abducens  and  Facial  Nerves.     (From  Villiger.) 
Nucleus  globosus 


Nucleus  emboliformis 
Brachium  conjunctivum 

Restiform  body 


Tractus  thalamo-olivaris 
Corpus  trapezoideum  and  medial 


Fourth  ventricle 
Brachium  conjunctivum 


Genu  of  facial  nerve  (pars 
ascendens  n.  facialis) 

Tractus  nucleo-cerebellaris 


Nucleus  of  abducens 


Nuclei  and  root  of 
~       trigeminus 


Brachium  pontis 

Nucleus  reticularis 
tegmenti 


Beep  stratum  of  pons 


Superficial  stratum  of  pons 


Pyramid 
Medial  stratum  of  pons 


The  abducens  is  a  smaU,  purely  motor  nerve,  which  suppUes  the  lateral  rectus  muscle 
of  the  eye.  Its  nucleus  of  origin  Hes  close  to  the  mid-line  in  the  medial  eminence  of  the  floor 
of  the  fourth  ventricle,  and  in  line  with  that  of  the  hypoglossus.  Its  root-fibres,  uncrossed,  pursue 
a  ventral  course,  inclining  a  Httle  laterally  and  curving  inferiorly  to  emerge  from  under  the 
inferior  border  of  the  pons.  They  pass  lateral  to  the  pyramid,  and  often  between  some  of  its 
fascicuh.  The  nucleus  receives  cortical  or  voluntary  impulses  by  way  of  the  pyramidal 
fascicuU  chiefly  of  the  opposite  side.  Its  connection  with  the  auditory  apparatus  and  the 
medial  longitudinal  fasciculus  has  already  been  noted.  It  probably  receives  afferent  impulses 
through  the  fibres  of  the  trigeminus  as  well  as  by  fibres  descending  from  the  nuclei  of  termi- 
nation of  the  optic  nerve.  It  is  also  associated,  by  way  of  the  medial  longitudinal  fasciculus, 
with  the  nucleus  of  the  oculomotor  nerve  of  the  same  and  opposite  sides. 

The  trigeminus  is  considerably  larger  than  any  of  the  nerves  inferior  to  it,  and  has  the  most 
extensive  central  connections  of  any  of  the  cranial  nerves.  It  is  a  purely  sensory  nerve  which 
enters  through  the  brachium  pontis  in  line  with  the  facial  nerve.  It  serves  as  the  nerve  of 
general  sensibility  for  the  face  from  the  vertex  of  the  scalp  downward,  and  thus  it  corresponds 
to  the  afferent  fibres  (dorsal  root)  for  all  the  nerves  giving  motor  supply  to  structures  underlying 
its  domain.  Its  fibres  arise  from  its  large,  trilobed,  semilunar  (Gasserian)  ganglion,  situated 
outside  the  brain.  This  corresponds  to  the  dorsal  root  ganglion  of  a  spinal  nerve,  and  its  cells 
give  off  the  characteristic  T-fibres  with  peripheral  and  central  branches.  The  central  or 
afferent  branches  upon  entering  the  brain-stem  bifurcate  into  ascending  and  descending  divi- 
sions, just  as  the  entering  dorsal  root-fibres  of  the  spinal  nerves,  and  find  their  nucleus  of  ter- 
mination in  a  dorso-lateral  column  of  grey  substance,  lying  deeply  and  extending  longitudinally 
through  the  brain  stem,  and  consisting  of  the  upward  continuation  of  the  gelatinous  substance 
of  Rolando  of  the  spinal  cord.  Opposite  the  entrance  of  the  nerve  is  a  considerably  thickened 
portion  of  this  column  of  grey  substance,  known  as  the  sensory  nucleus  of  the  trigeminus,  and 
the  remainder  below  is  called  the  nucleus  of  the  spinal  tract  (fig.  647).  Both  parts  are  equally 
"sensory."  After  bifurcation  the  branches  of  the  entering  fibres  of  the  trigeminus  terminate 
about  the  cells  of  these  nuclei.     The  descending  branches  are  much  longer  than  the  ascending, 


NUCLEI  OF  CRANIAL  NERVES 


827 


Fig.  653. — Dkawing  of  Model  of  Bbain-stem  showing  the  Nuclei  of  Origin  of  the 
Motor  Cranial  Nerves.     (After  Sabin.) 


828 


THE  NERVOUS  SYSTEM 


and  in  passing  downward  form  the  spinal  tract  of  the  trigeminus,  weU  marked  in  aU  transverse 
sections  of  the  meduDa  oblongata  figs.  641,  642,  643,  649).  The  spinal  tract  decreases  Snfdfv 
m  descendmg  the  medulla,  owing  to  the  rapid  termination  of  its  fibr1L"n  the  nucleus  ofthetmct^^ 

^'^■fi^'^^''*'^'''^'^  Illustrating  the  Principal  Central  Connections  of  the  Trigeminus 

orP™lMIDAL°FlBRET''''    ^""^^^'^^    °^   ^HEIR   RELATIONS   TO   DESCENDING   CeR^rIl 


Mesencephalic 
nucleus  and 
root  of  masti- 
cator nerve 
Medial  lem- 
niscus 


Medial  longi- 
tudinal 
fasciculus 


\  Masticator  nerve 

\ 
Semilunar  ganglion 


■Fasciculus  proprius 


It  has  been  traced  as  far  down  as  the  second  cervical  segment  of  the  spinal  cord.  The  ascending 
Pvt.n«i^n  ^^^  f^'^l'  T'*  °^  *^^'^,  terminate  in  the  'sensory  nucleus,'  and,  therefore,  the 
extension  upward  into  the  mesencephalon  of  the  nucleus  of  termination  of  the  trigeminus  is 
both  shorter  and  more  scant  than  the  spinal  extension. 

Axones  from  the  nucleus  of  termination  of  the  trigeminus  are  distributed— (1)  to  the  nuclei 
01  masticator  nerve  of  the  same  and  opposite  sides  (short  or  simple  reflex  fibres);  (2)  to  the 


INTERNAL  STRUCTURE  OF  THE  PONS 


829 


nuclei  of  the  other  motor  cranial  nerves,  especially  of  the  facial;  (3)  to  the  thalamus  of  the  same 
and  chiefly  the  opposite  side,  and  thus,  through  interpolation  of  thalamic  neurones,  their 
impulses  reach  the  somaisthetio  area  of  the  cerebral  cortex.  These  fibres  ascend  in  the  recticular 
formation  of  the  opposite  side,  most  of  them  finally  coursing  strictly  withia  the  medial  lemniscus. 
In  crossing  the  mid-line  they  contribute  to  the  internal  arcuates.  (4)  Some  fibres  of  both 
the  trigeminus  direct  and  from  its  nucleus  pass  laterally  into  the  cerebellum.  The  longer  of 
the  reflex  or  association  axones  arising  in  the  nucleus  of  termination  may  contribute  to  the 
medial  longitudinal  fasciculus;  many  of  them  descend  to  terminate  in  the  grey  substance  of  the 
spinal  cord  below  the  levels  in  which  the  fibres  of  the  spinal  tract  proper  terminate.  The 
nucleus  of  termination  is  directly  homologous  to  the  nuclei  of  the  fasciculus  graciUs  and  fasci- 
culus cuneatus,  and,  like  the  nuclei  of  termination  of  all  sensory  cranial  nerves,  it  contains 
cell-bodies  homologous  to  those  which  give  rise  to  the  fasciculi  proprii  and  commissural  fibres 
of  the  spinal  cord. 

The  masticator  nerve  [porlio  minor  n.  irigemini]  is  a  purely  motor  nerve,  usually  called  the 
motor  root  of  the  trigeminus  from  the  fact  only  that  it  makes  its  exit  from  the  pons  by  the  side 
of  the  entering  fibres  of  the  trigeminus,  passes  outward  over  the  ventro-mesial  side  of  the 
semilunar  ganglion  and  accompanies  the  inferior  maxiUary  division  (mandibular  nerve)  of  the 
trigeminus  till  it  divides  totally  into  its  branches  for  the  motor  supply  of  the  muscles  of  mastica- 
tion.    It  serves,  therefore,  as  but  a  relatively  small  part  of  the  "motor  root"  of  the  trigeminus. 

The  nucleus  of  origin  of  the  masticator  nerve  is  attenuated  into  two  parts:  (1)  The  chief 
nucleus  (nucleus  princeps)  lies  on  the  dorso-medial  side  of  the  larger  portion  (sensory  nucleus) 
of  the  nucleus  of  termination  of  the  trigeminus.  It  is  the  larger  of  the  two  parts  and  gives 
origin  to  much  the  greater  part  of  the  masticator.     (2)  Scattered  anteriorly  and  continuous 

Fig.  655. — Transverse    Section  Through  i  Upper  Part  of  Pons  at  the  Level  of  the 
Entrance  op  the  Trigeminus.     (From  Villiger.) 
Anterior  medullary  velum 


Gowers'  tract- 
Fourth  ventricle 


Fasc.  long,  dorsalis 
(Schiitz) 
Medial  longitudinal 
fasciculus 


Corpus  trapez. 
and  medial 
lemniscus 


Deep  stratum  of 
pons 


Brachium  conjunctivum 


Sensory  nucleus  of 

trigeminus 
Chief  nucleus  of  ma 
ticator  nerve 
Thalamo- 
olivary  tract 
Lateral 
aJ      lemniscus 
JS^      Brachium 
pontis 


Superficial  stratum  of  pons 


with  the  chief  nucleus,  in  line  with  the  locus  coci'uleus,  are  the  cell-bodies  usually  described  as 
the  nucleus  of  the  mesencephalic  (descending)  root.  These  cells  lie  in  decreasing  linear  distribu- 
tion, through  the  mesencephalon,  as  far  anterior  as  the  posterior  commissure  of  the  cerebrum, 
and  the  mesencephalic  root  of  the  nerve  accumulates  as  it  descends  to  join  the  exit  of  the 
fibres  arising  from  the  chief  nucleus.  The  average  diameter  of  its  cells  is  somewhat  less  than 
for  the  chief  nucleus. 

It  is  not  clearly  settled  that  the  fibres  arising  from  the  mesencephahc  nucleus  of  the  masti- 
cator nerve  go  to  the  muscles  of  mastication.  As  suggested  by  KoUiker,  some  of  these  may 
supply  the  tensor  veli  palatini  and  tensor  tympani  muscles.  Recent  investigations  of  lower  ani- 
mals by  Johnston  and  Willems  indicate  that  the  mesencephalic  root  may  contain  no  motor 
fibres  at  all,  representing  instead  a  portion  of  the  sensory  trigeminus  fibres.  It  is  claimed  that 
some  fibres  in  descendtug  give  off  collaterals  which  terminate  about  cells  in  the  chief  nucleus, 
and  thus  an  impulse  descending  by  them  is  given  a  wider  distribution  and  also  reinforced  by 
the  interpolation  of  another  neurone.  Such  fibres,  however,  maj'  be  the  sensory  fibres  just 
mentioned  terminating  upon  the  cells  of  the  nucleus  to  form  simple  reflex  arcs. 

It  is  claimed  that  each  masticator  nerve  receives  a  few  fibres  arising  from  the  cells  of  the 
nucleus  of  that  of  the  opposite  side. 

Both  parts  of  the  nucleus  of  the  masticator  receive  afferent  impulses  brought  in  by  the 
trigeminus  of  the  same  (chiefly)  and  of  the  opposite  side,  and  both  receive  cortical  impulses 
by  fibres  from  the  inferior  portion  of  the  precentral  gyrus  which  descend  in  the  cerebral  ped- 
uncles and  cross  to  terminate  in  the  nucleus  of  the  opposite  side. 

The  internal  structure  of  the  pons. — The  nuclei  and  roots  of  the  trigeminus,  masticator, 
abducens,  facial,  glosso-palatine,  cochlear  and  vestibular  nerves  are  extended  within  the  level 


830 


THE  NERVOUS  SYSTEM 


of  the  pons,  and  their  position  and  course  have  been  described  above.  The  pons  proper 
(the  bridge)  consists  of  a  mass  of  transversely  running  fibres  continuous  on  either  side  into 
the  brachia  pontis  or  middle  cerebellar  peduncles.  In  the  animal  series  the  relative  amount 
of  these  fibres  varies  with  the  size  of  the  cerebellum  upon  which  they  are  dependent.  They 
are  relatively  more  abundant  in  man  than  in  other  animals. 

In  transverse  sections  the  pons  fibres  are  seen  to  course  ventrally  about  the  main  axis  of 
the  brain-stem,  making  it  possible  to  divide  the  section  into  a  basilar  or  ventral  part  and  a  dorsal 
part  {tegmentum).  The  fibres  in  their  transverse  and  ventral  course  around  the  medulla  oblon- 
gata involve  the  pyramids.  At  the  inferior  border  of  the  pons  the  fibres  little  more  than  separate 
the  pyramids  as  such  from  the  main  axis  of  the  brain-stem,  but  more  superiorly  the  pons  fibres 
pass  through  the  pyramids,  splitting  them  into  the  pyramidal  fasciculi.  These  pyramidal  or 
chief  longitudinal  fibres  of  the  pons  are  the  continuation  of  the  basal  portion  of  the  cerebral 
peduncles  through  the  pons,  to  emerge  as  the  pyramids  proper  at  its  inferior  border.  They 
occupy  an  intermediate  or  central  area  among  the  pons  fibres  of  either  side,  leaving  the  periphery 
of  the  pons  uninvaded.  The  superficial  pons  fibres  form  the  solid  bundle  of  its  ventral  and  lateral 
periphery  and  the  deep  pons  fibres  form  similar  bundles  dorsaUy  enclosing  the  area  of  pyramidal 
fasciculi  (fig.  655). 

In  transverse  sections  through  the  inferior  portion  of  the  pons,  the  dorsal  or  tegmental  part 
consists  of  structures  continuous  with  and  analogous  to  the  structures  of  the  meduUa  oblongata 
immediately  below,  exclusive  of  the  pyramids.  In  addition,  this  region  contains  the  superior 
ohvary  nucleus  and  the  corpus  trapezoideum.  The  significance  of  these  structures  and  their 
relation  to  the  nucleus  of  termination  of  the  cochlear  nerve  is  shown  in  figs.  650,  651  and  652.  In 
this  region  the  lemniscus  (fillet)    changes   from  the  sagittal   to  the  coronal  plane,  and  its 


Fig.  656.- 


-DiAGBAM  SHOWING  THE   RhOMBENCEPHALIC  CoUBSE  OP  GOWEBS'   TrACT  AND  THE 

Direct  Cerebellar  Tract. 


Brachium  conjunctivum 


Dorsal  spino-cerebellar  fasciculus 
(direct  cerebellar  tract) 


Superficial  antero-lateral  spino-cerebellar 
fasciculus  (Gowers'  tract) 


lateral  edges  are  becoming  drawn  outward  and  carry  the  lateral  lemniscus  of  the  regions 
superior  to  this.  The  medial  longitudinal  fasciculus,  left  alone  by  the  change  in  the  arrangement 
of  the  leminscus,  maintains  its  dorsal  position  throughout  the  pons  and  into  the  mesencephalon 
above.  The  thalamo-olivary  tract  appears  loosely  collected  in  the  dorsal  part  of  the  pons, 
dorso-medial  to  the  nucleus  of  the  superior  olive. 

The  restiform  body  acquires  in  this  inferior  region  a  more  dorso-lateral  position  than  in  the 
medulla  below.  Its  fibres  are  beginning  to  turn  upward  in  their  course  to  the  cerebellum  mesial 
to  the  brachium  pontis.  Here  the  restiform  body  is  nearing  completion,  and  the  fibres  now 
contained  in  it  may  be  summarised  as  foUows: — 

(1)  The  fibres  of  the  dorsal  spino-cerebellar  fasciculus  (direct  cerebellar  tract)  of  the  same 
side. 

(2)  Fibres  from  the  nuclei  of  the  fasciculus  gracilis  and  fasciculus  cuneatus  of  the  same  and 
opposite  side  (external  arcuate  fibres). 

(3)  Fibres  to  and  from  the  inferior  olives  of  the  same  and  (chiefly)  the  opposite  side  (cere- 
bello-olivary  fibres). 

(4)  Sensory  cerebellar  fibres  from  the  nuclei  of  termination  of  the  vagus,  glosso-pharyngeus, 
vestibular  and  trigeminus,  vestibular  especially,  and  from  the  cells  of  the  reticular  formation. 

(5)  Descending  fibres  to  the  motor  nuclei  of  the  vagus  and  glosso-pharyngeal,  and  fibres 
descending  into  the  anterior  marginal  fasciculus  of  the  spinal  cord,  the  latter,  however,  being 
in  large  part  interrupted  by  cells  in  the  nuclei  of  the  vestibular  nerve. 

(6)  A  few  fibres  arising  from  the  arcuate  nuclei.  These  nuclei  are  continuous  superiorly 
with  the  nuclei  of  the  pons  and  some  of  their  fibres  are  described  as  entering  the  cerebellum  by 
way  of  the  restiform  body  instead  of  by  way  of  the  brachium  of  the  pons  as  in  the  levels  above. 

The  ascending  fibres  of  the  restiform  body  are  distributed  to  the  cortex  of  the  vermis,  the 

nucleus  of  the  roof  (fastigii),  the  nucleus  dentatus,  nucleus  emboliformis,  and  nucleus  globosus. 

Very  few  if  any  of  the  fibres  ascending  the  cord  in  Gowers'  tract  enter  the  cerebellum  by  way 

of  the  restiform  body.     This  tract  (the  superficial  antero-lateral  spino-cerebellar  fasciculus) 


GREY  SUBSTANCE  OF  THE  PONS 


831 


ascends  the  medulla,  dispersed  in  the  reticular  formation,  and  therefore  in  a  more  ventral  posi- 
tion than  that  of  the  direct  cerebellar  tract.  In  this  position  it  becomes  enclosed  by  the 
fibres  of  the  pons,  and  so  it  passes  upward,  beyond  the  pons,  around  the  lateral  lemniscus  to 
the  brachium  conjunctivum,  and  there  turns  back  to  enter  the  cerebellum  by  way  of  its  supe- 
rior peduncle.  Certain  clinical  phenomena,  probably  purely  psychological,  have  been  alleged  to 
indicate  that  some  of  the  fibres  of  Gowers'  tract  pass  on  to  the  cerebrum  instead  of  turning  in 
the  medullary  velum  to  enter  the  cerebellum. 

The  dorsal  part  of  a  transverse  section  through  the  upper  part  of  the  pons  contains  the 
superior  cerebellar  peduncles  [brachia  conjunctiva]  instead  of  the  restiform  bodies  or  inferior 
peduncles.  Instead  of  the  cerebellum  forming  the  roof  of  the  fourth  ventricle,  in  this  region 
the  roof  is  formed  by  the  anterior  medullary  velum  bridging  the  space  between  the  two  brachia 
conjunctiva.  Adhering  upon  the  meduUary  velum  is  the  lingula  cerebelli — the  superior  and 
ventral  extremity  of  the  superior  vermis.  This  is  the  only  portion  of  the  cerebellum  attached 
to  this  region. 

The  lemniscus  (fUlet)  is  found  more  lateral  than  at  the  inferior  border  of  the  pons,  and  is 
divided  into  the  medial  lemniscus  and  lateral  lemniscus  proper.  The  lateral  lemniscus  has  shifted 
dorsally  until  in  this  region  it  courses  in  the  dorso-lateral  margin  of  the  section  external  to  the 
brachium  conjunctivum.     The  mesencephalic  root  of  the  masticatornerve  occurs  in  the  dorso- 

FiG.  657. — Diagram  showing  Connections  op  the  Fibres  of  the  Pons. 
The  plane  of  the  section  is  obliquely  transverse  or  parallel  with  the  direction  of  the  brachia  pontis 


J]^  —— Restiform  body 


Medial  descending 
cerebro-pontile  path 


•^Medial  lemniscus 


Longitudinal  (pyramidal)  fasciculi 


lateral  margin  of  transverse  sections  through  this  region,  and  this  and  the  trigeminus  are  the 
only  cranial  nerves  represented  here. 

The  transverse  fibres  of  the  ventral  part  of  the  section  (pons  proper),  and  therefore  the 
brachia  pontis,  consist  of  fibres  coursing  in  opposite  directions.  Many  are  fibres  which  are  out- 
growths of  the  Purkinje  cells  of  the  cortex  of  the  cerebellar  hemispheres,  and  pass  either  directly 
to  the  cerebellar  hemisphere  of  the  opposite  side  or  turn  dorsalward  in  the  raphe  to  course 
longitudinally  in  the  brain-stem  both  toward  the  spinal  cord  and  toward  the  mesencephalon. 
Others  terminate  in  the  grey  substance  (nuclei)  of  the  pons.  Others  are  fibres  which  arise  in 
the  grey  substance  of  the  pons  and  pass  to  the  cerebellar  hemispheres,  and  still  others  are 
the  cerebro-pontile  fibres,  from  the  temporal,  occipital  and  frontal  lobes. 

The  grey  substance  of  the  pons  [nuclei  pontis  1  occurs  quite  abundantly.  At  the  inferior 
border  of  the  pons  it  is  found  concentrated  about  the  then  more  accumulated  bundles  of  the 
emerging  pyramids,  and  serial  sections  show  it  to  be  a  direct  upward  continuation  of  the  arcuate 
nuclei  of  the  medulla  oblongata  below.  Higher  up  it  is  dispersed  throughout  the  central  area 
in  the  interspaces  between  the  transverse  pontile  and  longitudinal  pyramidal  fasciculi.  A 
large  portion  of  the  nerve-fibres  passing  through  it  are  thought  to  iDe  interrupted  by  its  cells, 
which  thus  serve  as  links  in  some  of  the  neurone  chains  represented  by  the  fibres  of  the  pons. 
Of  the  more  important  of  such  relations,  the  following  are  said  to  exist: — 

(1)  Fibres  which  arise  in  the  cortex  of  one  cerebellar  hemisphere  and  terminate  about  cells 
of  the  nucleus  pontis  of  the  same  and  opposite  side  of  the  mid-line.  These  cells  give  off  axones 
which  pass  to  the  other  cerebellar  hemisphere.  In  this  relation  the  nuclei  of  the  pons  are 
analogous  to  the  arcuate  nuclei,  save  that  the  cerebellar  fibres  interrupted  in  the  former  are 
connected  with  the  cerebellum  by  way  of  the  brachia  pontis  instead  of  the  restiform  bodies. 


832  THE  NERVOUS  SYSTEM 

(2)  Certain  of  the  descending  oerebro-pontile  fibres  terminate  about  cells  of  the  nuclei  of 
the  pons.  Such  cells  give  off  fibres  which  probably,  for  the  most  part,  pass  to  the  cerebellar 
hemispheres,  the  impulses  from  the  cerebral  hemisphere  of  one  side  being  conveyed  to  the 
opposite  cerebellar  hemisphere.  Most  of  the  descending  cerebro-pontile  fibres  are  thought  to 
cross  the  mid-line  to  terminate  about  cells  of  the  nuclei  of  the  pons  of  the  opposite  side,  a  rela- 
tion not  sufficiently  emphasised  in  the  accompanying  diagram  (fig.  657). 

Of  the  cerebro-pontile  paths,  the  frontal  pontile  path  (Ai-nold's  bundle)  is  described  as 
arising  in  the  cortex  of  the  frontal  lobe  (frontal  operculum)  passing  in  the  anterior  portion  of 
the  internal  capsule  down  into  the  medial  part  of  the  base  of  the  cerebral  peduncle,  and  terminat- 
ing in  the  grey  substance  of  the  pons.  The  descending  temporal  pontile  path,  sometimes 
caOed  Turk's  bundle,  arises  in  the  cortex  of  the  temporal  lobe,  traverses  the  posterior  portion 
of  the  internal  capsule,  lies  lateral  in  the  pyramidal  portion  of  the  cerebral  peduncle,  and  termi- 
nates in  the  grey  substance  of  the  pons.  In  the  posterior  part  of  the  internal  capsule,  the  tem- 
poral pontile  path  is  joined  by  a  small  bundle  arising  in  the  occipital  lobe  and  going  to  the 
pons  nuclei.     This,  supposedly  smaller  than  the  other  two,  adds  an  occipito-pontile  path. 

The  total  area  in  cross  section  of  the  pyramidal  fasciculi  as  they  enter  the  pons  above  is 
considerably  greater  than  that  which  they  possess  as  they  emerge  as  the  pyramids  of  the  medulla 
below.  The  difference  is  considered  very  appreciably  greater  than  can  be  explained  as  due 
to  the  loss  of  pyramidal  fibres  supplied  to  the  nuclei  of  origin  of  the  cranial  nerves  lying  within 
the  level  of  the  pons,  and  the  additional  difference  is  explained  as  due  to  the  termination 
within  the  pons  of  the  oerebro-pontile  paths. 

THE  ISTHMUS  OF  THE  RHOMBENCEPHALON 

The  isthmus  of  the  rhombencephalon  is  nothing  more  than  the  transition  of 
the  metencephalon  into  the  mesencephalon  above.  It  is  quite  short  and  com- 
prised of  only  the  structures  which  run  through  it,  namely,  the  brachia  conjunc- 
tiva (superior  peduncles  of  the  cerebellum),  the  anterior  medullary  velum,  the 
lateral  sulcus  of  the  mesencephalon,  the  cerebral  peduncles,  and  the  inferior  end  of 
the  interpeduncular  fossa.  It  surrounds  the  superior  extremity  of  the  fourth 
ventricle.  The  lateral  and  medial  lemnisci,  the  superior  extension  of  the  nucleus 
of  the  trigeminus,  the  mesencephalic  nucleus  and  root  of  the  masticator  nerve  and 
Gowers'  tract  extend  through  it.  At  the  mid-line,  just  inferior  to  the  inferior 
quadrigeminate  bodies  is  the  frenulum  of  the  anterior  medullary  velum  and  the 
trochlear  nerves,  emerging  at  the  sides  of  this,  course  ventrally  around  the  sides 
of  the  isthmus.  In  the  lateral  sulcus,  the  isthmus  shows  usually  a  small  triangular 
elevation  known  as  the  trigonum  lemnisci  from  the  fact  that  the  lateral  lemniscus 
tends  toward  the  surface  in  this  region. 

Functions  of  the  cerebellum. — From  the  above  descriptions  involving  the  structures  of  the 
metencephalon,  it  may  be  noted  (1)  that  a  given  side  of  the  cerebellum  is  associated  chiefly 
with  the  same  side  of  the  general  body  and  with  the  opposite  side  of  the  cerebrum.  (2)  That 
it  receives  afferent  impulses  from  the  spinal  cord  (brought  into  the  cord  by  the  dorsal  roots  of 
the  spinal  nerves)  by  way  of  the  direct  cerebellar  fasciculus  of  the  same  side,  and  by  Gowers' 
tract  and  from  the  nuclei  of  the  fasciculus  gracilis  and  cimeatus  of  the  same  and  opposite  sides. 
It  further  receives  afferent  impulses  from  the  nuclei  of  termination  of  the  trigeminus,  glosso- 
pharyngeal and  vagus  of  the  same  side  chiefly,  and  especially  does  it  receive  afferent  impulses 
from  the  nuclei  of  the  vestibular  nerve  of  the  opposite  and  same  side.  (3)  That  the  cerebellum 
sends  impulses  to  the  red  nucleus,  the  thalamus  and  the  cerebral  cortex  of  the  opposite  side, 
and  some  of  its  fibres  terminate  in  the  nuclei  of  termination  of  the  vestibular  nerve  and  probably 
some  fibres  arising  in  its  roof  nuclei  descend  into  the  spinal  cord  direct.  (4)  That  the  cerebel- 
lum receives  impulses  from  the  thalamus  of  the  opposite  side  by  way  of  the  thalamo-olivary 
tract  and  the  inferior  olive,  and  especially  from  the  cerebral  cortex  of  the  opposite  side  by  way 
of  the  frontal,  temporal  and  occipital  pontile  paths  and  the  nuclei  of  the  pons.  Further, 
fibres  from  the  general  pyramidal  fascicuh  are  described  as  terminating  about  ceUs  of  the  nuclei 
of  the  pons. 

Taking  into  consideration  these  known  associations  of  the  cerebellum,  the  anatomically 
possible  paths  which  in  part  may  distribute  cerebellar  impulses  to  the  grey  substance  sending 
efferent  fibres  to  the  peripheral  tissues  are  (1)  the  general  pyramidal  fasciculi  whose  cortex 
of  origin  may  receive  impulses  by  fibroi  proprioe  from  the  cortical  areas  receiving  impulses  from 
the  cerebellum.  The  pyramidal  fasciculi,  decussating,  distribute  impulses  to  the  grey  substance 
of i the  medulla  and  cord  of  the  same  side  as  that  from  which  the  cerebeUo-cerebral  impulses 
passed  to  the  cortex.  (2)  The  lateral  vestibulo-spinal  and  the  anterior  marginal  fasciculi  to 
the  ventral  horn  of  the  spinal  cord  of  the  same  side,  probably  carrying  impulses  descending 
from  the  cerebellum  as  well  as  impulses  brought  in  by  the  vestibular  nerve  and  descending 
direct  from  its  nuclei  of  termination  into  the  spinal  cord.  (3)  The  rubro-spinal  tract  of  the 
cord  and  probably  some  of  the  thalamo-spinal  fibres  (corpora-quadrigemina-thalamus  path), 
the  red  nuclei  and  thalami  being  associated  abundantly  with  the  cerebellum.  These  tracts 
Hkewise  decussate  in  descending  but  likewise  do  the  cerebellar  impulses  ascending  to  their  cells 
of  origin. 

Whatever  other  functions  it  may  possess,  developmental  defects  and  pathologic  lesions 
show  that  the  cerebellum  has  to  do  with  the  equilibration  of  the  body  and  the  finer  coordinations, 
adjustive  control  of  the  contractions  of  functionally  correlated  groups  of  muscles.     Making  this 


THE  MESENCEPHALON  833 

possible,  in  part  at  least,  it  is  seen  above  that  is  it  associated  (1)  directly  with  the  special  nerve 
of  equihbration,  the  vestibular;  (2)  with  the  optic  apparatus  by  way  of  the  thalamus,  and  (3) 
with  the  afferent  impulses  from  the  general  body,  by  way  of  the  direct  cerebellar  and  Gowers' 
tracts,  by  way  of  the  nuclei  of  the  fasciculus  gracilis  and  cuneatus,  and  the  nuclei  of  termination 
of  the  trigeminus,  glosso-pharyngeal  and  vagus.  It  has  been  suggested  that  by  way  of  these 
latter  paths  the  cerebellum  deals  especially  with  those  general  afferent  impulses  which  arise 
within  the  muscles  of  the  body  (neuro-musoular  spindles,  etc.)  and  which  are  grouped  under  the 
name  "muscular  sense."  The  cerebellum  can  be  considered  as  an  enlarged  and  modified  por- 
tion of  the  grey  substance  of  the  spinal  cord,  receiving  a  greater  number  and  variety  of  afferent 
impulses  and  with  them  mediating  more  comprehensive  and  complicated  reflex  activities  than 
is  possible  with  the  less  abundant  grey  substance  of  a  given  portion  of  the  cord  proper. 

SUMMARY  OF  PRINCIPAL  STRUCTURES  IN  RHOMBENCEPHALON 

A.  Gross  Exterior. 

1.  Medulla  Oblongata  (Myelencephalon). 

f  Cerebellum  I  Hemispheres — lobes  and  lobules. 
I  I  Vermis — lobules  and  lingula. 

2.  Metencephalon  \   Pons  {  Dorsal  part  (preoblongata). 
^  y  Ventral  part  (pons  proper). 

I  superior — brachium  conjunctivum. 
[  Cerebellar  peduncles  \  middle — brachium  of  pons. 
[  inferior — restiform  body. 

3.  Isthmus  of  Rhombencephalon. 

4.  Fourth  Ventricle  and  its  Chorioid  tela. 

5.  Anterior  and  Posterior  Medullary  Vela. 

B.  Grey  and  White  Substance. 

1.  Funiculus  gracilis,  nucleus  of  fasciculus  gracihs,  funiculus  cuneatus,  nucleus  of  fasciculus 
cuneatus. 

2.  Internal  and  external  arcuate  fibres,  decussation  of  lemnisci,  lemniscus,  medial  lemniscus, 
lateral  lemniscus. 

3.  Cerebral  peduncles,  pyramidal  fasciculi,  pyramids,  decussation  of  pyramids,  arcuate 
nuclei. 

4.  Superficial  and  deep  strata  of  pons,  nuclei  of  pons,  branchia  of  pons. 

5.  Inferior  olivary  nuclei,  cerebello-olivary  fibres,  thalamo-olivary  tract,  spino-olivary  tract. 

6.  Nuclei  emboliformis,  globosus  and  fastigii  (of  the  roof),  and  nucleus  dentatus  with  bra- 
chium conjunctivum  of  cerebellum. 

7.  Central  gelatinous  substance  and  gelatinous  substance  of  Rolando. 

8.  Reticular  formation. 

9.  Hypoglossal  nerve  and  nucleus  of  hypoglossal. 

10.  Spinal  accessory  nerve  and  lateral  nucleus. 

11.  Vagus  and  glossopharyngeal  nerves,  nucleus  of  ala  cinerea,  solitary  tract  and  nucleus 
of  solitary  tract,  commissural  nucleus  of  ala  cinerea,  nucleus  ambiguus,  dorsal  efferent  nucleus 
of  vagus. 

12.  Vestibular  nerve — its  superior  nucleus  (Bechterew),  its  medial  nucleus  (Schwalbe), 
its  lateral  nucleus  (Deiters),  and  the  nucleus  of  its  descending  (spinal)  root. 

13.  Cochlear  nerve,  dorsal  nucleus  and  ventral  nucleus  of  cochlear,  acoustic  medullary  striae, 
nucleus  of  superior  olive,  trapezoid  body,  nucleus  trapezoidei,  lateral  lemniscus,  nucleus  of 
lateral  lemniscus. 

14.  Facial  nerve  and  nucleus  of  facial  nerve. 

15.  Glosso-palatine  nerve,  nucleus  of  glosso-palatine  and  nucleus  salivatorius. 

16.  Abducens  and  nucleus  of  abducens. 

17.  Trigeminus,  "sensory  nucleus"  of  trigeminus,  spinal  tract  and  nucleus  of  spinal  tract 
of  trigeminus. 

18.  Masticator  nerve,  chief  nucleus  and  (so-called)  mesencephaUc  nucleus  and  root  of 
masticator. 

19.  Medial  longitudinal  fasciculus. 

20.  Nucleus  intercalatus,  nucleus  of  median  eminence,  nucleus  incertus. 

THE  CEREBRUM 

1.  THE  MESENCEPHALON 

The  mesencephalon  or  mid-brain  is  that  small  portion  of  the  encephalon  which 
is  situated  between  and  connects  the  rhombencephalon  below  with  the  prosen- 
cephalon above.  It  is  continuous  with  the  isthmus  rhombencephali,  and  occupies 
the  tentorial  notch,  the  aperture  of  the  dm-a  mater  which  connects  the  meningeal 
cavity  containing  the  cerebellum  with  that  occupied  by  the  prosencephalon. 
Its  greatest  length  is  about  18  mm.,  and  it  is  broader  ventrally  than  dorsally. 
Its  dorsal  surface  is  hidden  by  the  overlapping  occipital  lobes  of  the  cerebral  hemis- 
pheres. It  consists  of — (1)  the  lamina  quadrigemina,  a  plate  of  mixed  grey 
and  white  substance  which  goes  over  lateralward  and  below  into  (2),  the  cerebral 


834 


THE  NERVOUS  SYSTEM 


peduncles  (crura)  and  their  tegmental  structures,  and  it  contains  (3),  the  nuclei 
of  origin  of  the  trochlear  and  oculomotor  nerves.  It  arises  from  thickenings  of  the 
walls  of  the  middle  cerebral  vesicle  of  the  embryo,  the  lamina  quadrigemina 
arising  from  the  dorsal  or  alar  lamina  of  this  portion  of  the  neural  tube,  while  the 
basal  lamina  thickens  to  form  the  nuclei  of  the  nerves,  the  substantia  nigra,  etc., 
and  by  the  ingrowing  of  the  cerebral  peduncles.  By  means  of  the  lamina  quad- 
rigemina roofing  it  over,  the  neural  canal  throughout  the  mesencephalon  retains 
its  tubular  form  and  is  known  as  the  aquaeductus  cerebri  (Sylvii) ,  connecting  the 
cavity  of  tlie  fourth  ventricle  below  with  that  of  the  third  ventricle  above. 

External  features. — Dorsal  surface. — The  lamina  quadrigemina  shows  four 
well-rounded  elevations,  the  quadrigeminate  bodies  [corpora  quadrigemina], 
divided  by  a  flat  median  groove  crossed  at  right  angles  by  a  transverse  groove. 
The  anterior  pair  of  these,  the  superior  quadrigeminate  bodies  [colliculi],  are 

Fig.  668. — Dorsal  Surface  op  Mesencephalon  and  Adjacent  Parts.     (After  Spalteholz.) 


Epiphysis  (lifted) 


Taenia  cliorioidea 
■Camina  affiza 


Supi 

Brachium  quadn 
geminum  superiu 
Bracliium  quadn 
geminum  Infenus  ^ 


Medial  genicu 
late  body 

lateral  genicu- 
late body 


Cerebral  peduncle 

Inferior  colhculus 

Frenulum  of  anterior  med 

ullary  velum 

Trigone  of  lemniscus 

Trochlear  nerve 

Brachium  conjunctivum 
Lateral  filaments  of  pons- 


"  Trigeminus 

—  Lingula  of  vermis 
Vinculum  of  lingula 
Brachium  of  pons 


Cerebellum  (cut) 


larger  though  less  prominent  than  the  inferior  pair  or  inferior  colliculi.  Each 
colliculus  is  continued  laterally  and  upward  into  its  arm  or  brachium.  The 
inferior  brachium  proceeds  from  the  inferior  colliculus,  disappears  beneath  and  is 
continuous  into  the  medial  geniculate  body,  and  enters  the  thalamus.  The  supe- 
rior brachium  proceeds  from  the  superior  colliculus,  disappears  between  the  medial 
geniculate  body  and  the  overlapping  pulvinar  of  the  thalamus,  and  becomes  con- 
tinuous with  the  lateral  geniculate  body  and  thus  with  the  lateral  root  of  the  optic 
tract. 

The  geniculate  bodies  are  rounded  elevations  of  grey  substance  which  arise  as  detached 
portions  of  the  thalami,  and  therefore  belong  to  the  thalamencephalon  rather  than  to  the 
mesencephalon.  The  superior  quadrigeminate  body  or  superior  colliculus  and  the  lateral  gen- 
iculate body  are  a  part  of  the  optic  apparatus,  while  the  inferior  colliculus  and  the  medial  genicu- 
late body  belong  chiefly  to  the  auditory  apparatus  (see  Central  Connections  of  Cochlear 
Nerve).  Just  as  the  terminal  cochlear  nuclei  are  connected  by  a  few  fibres  with  the  superior 
colliculus,  so  do  some  fibres  from  the  optic  tract  pass  mto  the  inferior  colliculus.  Also  some 
fibres  form  the  optic  tract  (mesial  root)  are  said  to  terminate  in  the  medial  geniculate  body. 
Resting  in  the  broadened  medial  groove  between  the  superior  quadrigeminate  bodies  lies 
the  non-nervous  epiphysis  or  pineal  body.  This  also  belongs  to  the  thalamencephalon. 
Under  the  stem  of  the  epiphysis  is  a  strong  transverse  band  of  white  substance  crossing  the 


THE  MESENCEPHALON 


835 


mid-line  as  a  bridge  over  the  opening  of  the  cerebral  aqueduct  into  the  third  ventricle.  This  is 
the  posterior  commissure  of  the  cerebrum,  and  contains  commissural  fibres  arising  in  both  the 
thalamencephalon  and  mesencephalon.  The  triangular  area  bounded  by  the  stem  of  the  epi- 
physis, the  thalamus,  and  the  superior  coUiculus  with  its  brachium,  is  known  as  the  habenular 
trigone. 

Inferiorly,  the  lamina  quadrigemina  is  continuous  with  the  isthmus  of  the 
rhombencephalon  by  way  of  the  brachia  conjunctiva  or  superior  cerebellar  pedun- 
cles, and  the  anterior  medullary  velum  which  bridges  between  the  mesial  margins 
of  these  peduncles.  The  narrowed  upper  end  of  the  velum,  the  part  directly  below 
the  inferior  quadrigeminate  bodies,  is  thickened  into  a  well-defined  white  band 
known  as  the  frenulum  veil.  From  the  lateral  margins  of  this  band  on  each  side 
and  just  below  the  inferior  quadrigeminate  bodies  emerge  the  trochlear  nerves 
(the  fourth  pair  of  cranial  nerves),  and  the  increased  thickness  of  the  band  is 
largely  due  to  the  decussation  of  this  pair  of  nerves  taking  place  within  it. 

The  brachium  conjunctivum,  together  with  the  inferior  and  superior  colliculi 
of  each  side,  form  a  marked  ridge  which  results  in  the  lateral  sulcus  of  the  mesen- 
cephalon, a  lateral  depression  between  the  base  of  this  ridge  and  the  cerebral 
peduncle  below  and  continuous  into  the  transverse  sulcus  at  the  superior  border 

Fig.  659. — Diagram  op  Lateral  View  of  Mesencephalon  and  Adjacent  STRtrcTURES. 
(After  Gegenbaur,  modified.) 


Pulvinar  of  thalamus 


Lateral  geniculate  body 
Cerebral  peduncle 


Epiphysis 

Medial  geniculate  body 


Quadrigeminate  bodies 
iuJ ^  Lateral  lemniscus 


Superior  cerebellar  peduncle 
Middle  cerebellar  peduncle 
Inferior  cerebellar  peduncle 


of  the  pons.  The  ridge  is  thickened  laterally  by  the  lateral  lemniscus,  which  is 
disposed  as  a  band  of  white  substance  passing  obhquely  upward  from  under  the 
brachium  pontis,  applied  to  the  lateral  surface  of  the  brachium  conjunctivum  and 
which  enters  the  lateral  margin  of  the  mesencephalon.  The  region  at  which  the 
lateral  lemniscus  approaches  nearest  the  surface  and  in  which  the  largest  portion 
of  its  nucleus  lies  is  the  slightly  elevated  trigone  of  the  lemniscus. 

The  ventral  surface  of  the  mesencephalon  is  formed  by  the  cerebral  peduncles 
(crura),  two  large  bundles  of  white  substance  which  are  close  to  one  another  at  the 
superior  margin  of  the  pons,  but  immediately  diverge  somewhat,  producing 
the  interpeduncular  fossa,  and  in  so  doing  pass  upward  and  lateralward  to  disap- 
pear beneath  the  optic  tracts  (fig.  629) .  The  posterior  recess  of  the  interpeduncu- 
lar fossa  extends  slightly  under  the  superior  margin  of  the  pons,  while  its  anterior 
recess  is  occupied  by  the  corpora  mammillaria  of  the  prosencephalon.  The  tri- 
angular floor  of  the  fossa  is  the  posterior  perforated  substance,  a  greyish  area 
presenting  numerous  openings  for  the  passage  of  blood-vessels.  It  is  divided  by 
a  shallow  median  groove  and  is  marked  off  from  the  medial  surface  of  each  peduncle 
by  the  oculomotor  sulcus,  out  of  which  emerge  the  roots  of  the  oculomotor  nerves. 
The  ventral  surface  of  each  peduncle  is  rounded  and  has  a  somewhat  twisted 
appearance,  indicating  that  its  fibres  curve  from  above  medialward  and  downward. 
Sometimes  two  small,  more  or  less  transverse  bands  of  fibres  may  be  noted  crossing 
the  peduncle — an  inferior,  the  tcenia  pontis,  and  a  superior,  the  transverse  pedun- 


836 


THE  NERVOUS  SYSTEM 


cular  tract.  The  inferior  represents  detached  fibres  of  the  pons;  the  superior, 
running  from  the  brachium  of  the  inferior  quadrigeminate  body  and  disappearing 
in  the  oculomotor  sulcus,  appears  to  be  derived  from  the  quadrigeminate  bodies. 
Since  it  is  well  developed  in  the  cat,  dog,  sheep,  and  rabbit,  but  is  absent  or  little 
marked  in  the  mole,  it  is  supposed  to  be  concerned  with  the  optic  apparatus. 

Internal  structure. — Transverse  sections  of  the  mesencephalon  throughout 
are  composed  of — (1)  a  dorsal  -part,  consisting  of  the  lamina  quadrigemina  or  the 
grey  sulDstance  of  the  corpora  quadrigemina,  with  the  strata  and  bundles  of 
nerve-fibres  connected  with  them,  and  the  abundant  central  grey  .substance 
sm-rounding  the  aqueduct;  (2)  a  tegmental  part,  consisting  of  the  upward  con- 
tinuation of  the  reticular  formation  of  the  medulla  oblongata  and  that  of  the 

Fig.  660. — Transverse  Section  Through  the  Inpekior  Quadrigeminate  Bodies. 

Central  grey  substance 


Stratum  zonaIe-~, 


Aqueduct  of-^     & 
cerebrum  /  ~  - 
Nucleus   of    mesen- 
cephalic    (descend- , 

ing)  root  of    masti-  y't^  ^ 

cater  ■'^  »■ 

Nucleus  of  trochlear  - 
nerve 


of  lateral  lemniscus 

Lateral  lemniscus  (acoustic) 


Thalamo-olivary  tract 


Medial  lemniscus 


Decussation  of 
brachia  conjunctiva 


Posterior  recess  of  in^ 
terpeduncular  fossa 


Substantia  nigra 


Basis  of  cerebral  peduncle 
Superficial  stratum  of  pons 

dorsal  (tegmental)  portion  of  the  pons  region,  to  which  are  added  the  superior 
cerebellar  peduncles  and  the  red  nuclei  of  the  tegmentum  in  which  these  peduncles 
terminate;  (3)  a  paired  ventral  part,  the  cerebral  peduncles,  each  of  which  consists 
of  a  thick,  pigmented  stratum  of  grey  substance,  the  substantia  nigra,  spread 
upon  the  large,  superficial,  and  somewhat  crescentic  tract  of  white  substance 
known  as  the  basis  of  the  peduncle.  The  cerebral  peduncles  correspond  to  the 
longitudinal  or  pyramidal  fasciculi  of  the  pons  and  medulla.  Likewise  the 
lemniscus  and  the  medial  longitudinal  fasciculus  of  the  medulla  and  pons  continue 
through  all  sections  of  the  mesencephalon. 

The  central  grey  substance  is  a  continuation  of  the  central  gelatinous 
substance  of  the  spinal  cord  and  the  similar  stratum  of  the  medulla  and  that 
which  immediately  underlies  the  ependyma  of  the  fourth  ventricle.  As  in  the 
spinal  cord  and  medulla,  it  is  largely  composed  of  gelatinous  substance.  It  is 
much  more  abundant  in  the  mesencephalon,  and  in  sections  appears  as  a  cir- 
cumscribed area  comparatively  void  of  nerve-fibres. 

The  nucleus  of  the  mesencephalic  root  of  the  masticator  nerve  may  likewise  be  traced  through- 
out the  mesencephalon.     It  consists  of  a  few  small  bundles  of  fibres  surrounding  a  thin  strand 


THE  MESENCEPHALON  837 

of  nerve-cells  which  give  origin  to  its  fibres.  It  courses  caudalward  close  to  the  lateral  margin 
of  the  central  grey  substance,  and  is  quite  small  at  its  beginning  in  the  extreme  superior  part  of 
the  mesencephalon,  but  as  it  descends  toward  the  exit  of  its  fibres  from  the  pons,  it  increases 
slightly  in  size,  due  to  the  progressive  addition  of  fibres.  Its  nucleus  also  increases  sUghtly 
in  bulk  in  approaching  the  region  of  the  chief  motor  nucleus  of  the  nerve.  As  mentioned 
above,  the  investigations  of  Johnston  and  Willems  in  lower  animals  suggest  that  the  cells  of 
the  mesencephalic  nucleus  may  be  sensory  instead  of  motor  in  character.  The  sensory 
nucleus  (nucleus  of  termination)  of  the  trigeminus  tapers  rapidly  and  probably  does  not 
extend  throughout  the  mesencephalon. 

The  nuclei  of  the  trochlear  and  oculomotor  nerves  form  a  practically  continuous 
column  of  nerve-cells  extending  close  to  the  mid-line  and  ventral  to  the  aqueduct 
of  the  cerebrum.  They  are  in  hne  with  the  nuclei  of  origin  of  the  abducens  and 
hypoglossus,  and,  like  them,  may  be  regarded  as  an  upward  continuation  of  the 
ventral  group  of  the  cells  of  the  ventral  horn  of  the  spinal  cord.  The  portion  of 
the  column  giving  origin  to  the  oculomotor  nerve  is  considerably  larger  than  that 
for  the  trochlear. 

Fig.  661 . — Diagrams  showing  the  Course  op  Origin  of  the  Trochlear  Nerves.     (Stilling. 
The  upper  figure  shows  roughly  the  entire  central  course  of  the  trochlear  nerves;  the  lower  rep- 
resents their  region  of  exit  in  transverse  section. 


Aquasductus  cerebri 


of  trochlear,  nerve TT'^A 

(^■' 

Decussation  of  trochlear  nerves 

\ 

,  Trochlear  nerve 

^- — - — ' 

i-i       —     — 

-V Aquaeductus  cerebri 

r  w. 'X  —  Mesencephalic  root 
\  \\  \           of  masticator 
"'  ^'-  ■■ Brachium  conjunctivum 


Lateral  lemniscus 


A  transverse  section  through  the  inferior  quadrigeminate  bodies  involves  a 
portion  of  the  decussation  of  the  brachia  conjunctiva  and  the  nuclei  of  origin  of 
the  trochlear  nerves,  while  a  transverse  section  through  the  superior  quadri- 
geminate bodies  passes  through  the  red  nuclei  of  the  tegmentum  and  the  nuclei 
of  origin  of  the  oculomotor  nerves.  The  latter  section  will  also  involve  the 
brachia  of  the  inferior  quadrigeminate  bodies  and  the  medial  geniculate  bodies 
connected  with  them,  and,  if  slanting  slightly  forward  it  will  involve  the  pul- 
vinars  of  the  thalami  and  the  lateral  geniculate  bodies. 

The  trochlear  or  fourth  nerve  is  the  smallest  of  the  cranial  nerves,  and  is  the 
only  one  which  makes  its  exit  from  the  dorsal  surface  of  the  brain,  as  well  as  the 
only  one  whose  fibres  undergo  a  total  decussation. 

Its  nucleus  of  origin  is  situated  beneath  the  inferior  quadrigeminate  bodies  in  the  ventral 
margin  of  the  central  grey  substance,  quite  close  to  the  mid-line  and  to  its  fellow  nucleus  of 
the  opposite  side,  and  it  is  closely  associated  with  the  dorso-mesial  margin  of  the  medial  longi- 
tudinal fasciculus.  Its  root-fibres  pass  lateralward  and  dorsalward,  curving  around  the  margin 
of  the  central  grey  substance,  mesial  to  the  mesencephalic  root  of  the  masticator  nerve.  As 
the  root  curves  toward  the  mid-line  in  the  dorsal  region  just  beneath  the  inferior  quadrigeminate 
bodies,  it  turns  sharply  and  courses  inferiorly  to  approach  the  surface  in  the  superior  portion 
of  the  anterior  medullary  velum,  the  frenulum  veli.  In  this  it  meets  and  undergoes  a  total 
decussation  with  the  root  of  its  fellow  nerve,  and  then  emerges  at  the  medial  margin  of  the  supe- 
rior cerebellar  peduncle  of  the  opposite  side.  Having  emerged,  it  then  passes  ventraUy 
around  the  cerebral  peduncle,  and  thence  pursues  its  course  to  the  superior  obhque  muscle  of 
the  eye.  It  receives  optic  impulses  from  the  superior  quadrigeminate  bodies  and  impulses 
from  the  cerebral  cortex  of  chiefly  the  same  side,  and  it  is  associated  with  the  nuclei  of  other 
cranial  nerves  by  way  of  the  medial  longitudinal  fasciculus. 


838 


THE  NERVOUS  SYSTEM 


The  oculomotor  or  third  nerve,  like  the  trochlear,  is  purely  motor.  It  is  the 
largest  of  the  eye-muscle  nerves.  It  supplies  in  all  seven  muscles  of  the  optic 
apparatus: — two  intrinsic,  the  sphincter  iridis  and  the  ciliary  muscle,  and  five 
extrinsic.  Of  the  latter,  the  levator  palpebrse  superioris  is  of  the  upper  eyelid, 
while  the  remaining  four,  the  superior,  medial,  and  inferior  recti  and  the  obliquus 
inferior,  are  attached  to  the  bulb  of  the  eye.  As  is  to  be  expected,  its  nucleus  of 
origin  is  larger  and  much  more  complicated  than  that  of  the  trochlear  nerve. 

Practically  continuous  with  that  of  the  trochlear  below,  the  nucleus  is  5  or  6  mm.  in  length 
and  extends  anteriorly  a  short  distance  beyond  the  bounds  of  the  mesencephalon  into  the  grey 
substance  by  the  side  of  the  third  ventricle.  It  hes  in  the  ventral  part  of  the  central  grey 
substance,  and  is  very  intimately  associated  with  the  medial  longitudinal  fasciculus.     Its  thickest 


Fig.  662. — Transverse  Section  Through  Level  op  Superior  Quadrigbminate  Bodies. 
Stratum  zonale  of  thalamus 

N  Stratum  zonale 

/       Nucleus  of  superior  colliculus 

Epiphysis  (pineal 
^'—'^—•"  bodyj 

^^ Central  grey 

^^^Va         -  "^    ~ "     substance 


Optic-acoustic 
reflex  path 


f  —  ^  Aquasductus 
cerebri 
Nucleus  of  mes- 
—    encephalic   (de- 
scending) root  of 
masticator 
nerve 
Nucleus  of 
^    oculo-motor 


Fila  of  oculomotor  nerve 


Substantia  nigra 


portion  is  beneath  the  summit  of  the  superior  quadrigeminate  body.  The  root-fibres  leave  the 
nucleus  from  its  ventral  side  and  collect  into  bundles  which  pass  through  the  medial  longitudinal 
fasciculus  and  course  ventrally  to  the  mesial  portion  of  the  substantia  nigra,  where  they  emerge 
in  from  six  to  fifteen  rootlets  which  blend  to  form  the  trunk  of  the  nerve  in  the  oculomotor 
sulcus  of  the  cerebral  peduncles.  Those  bundles  which  arise  from  the  more  lateral  portion  of 
the  nucleus  course  in  a  series  of  curves  through  and  around  the  substance  of  the  red  nucleus 
below  and,  in  the  substantia  nigra,  join  those  which  pursue  the  more  direct  course.  The  trunk 
thus  assembled  passes  lateralward  around  the  mesial  border  of  the  cerebral  peduncle. 

A  portion  of  the  fibres  of  the  oculomotor  nerve  upon  leaving  the  nucleus  decussate  in  the 
tegmentum  immediately  below  and  pass  into  the  nerve  of  the  opposite  side,  in  which  they  are 
beUeved  to  be  distributed  to  the  opposite  medial  rectus  muscle.  The  ceUs  of  the  nucleus  have 
been  variously  grouped  and  subdivided  with  reference  to  the  difTerent  muscles  supphed  by  the 
nerve.  Perlia  has  divided  them  into  eight  cell-groups.  The  nucleus  may  be  more  easily  con- 
sidered as  composed  of  an  inferior  and  a  superior  medial  group.  The  inferior  group  consists  of 
a  long  lateral  portion  continuous  with  the  nucleus  of  the  trochlear  nerve  below,  and  a  smaller 
medial  portion,  situated  in  the  medial  plane  and  continuous  across  the  mid-line  with  its  fellow 
of  the  opposite  side.  The  superior  medial  group  consists  of  cells  of  smaller  size  than  the 
inferior,  and  is  known  as  the  nucleus  of  Edinger  and  Weslphal.     It  is  believed  to  give  origin  to 


THE  LEMNISCUS 


839 


the  fibres  (visceral  efferent  fibres)  which  terminate  in  the  ciliary  ganglion,  axones  from  which 
supply  the  two  intrinsic  muscles  concerned,  viz.,  the  ciliary  muscle  and  the  sphincter  iridis. 

The  nucleus  of  the  oculomotor  is  associated  with  the  remainder  of  the  optic  apparatus — (1) 
by  way  of  the  neurones  of  the  superior  quadrigemtnate  body  with  the  optic  tract  (retina)  and 
it  receives  impulses  from  the  occipital  part  of  the  cerebral  cortex  of  the  same  and  the  opposite 
sides,  and  probably  from  the  motor  cortex  of  the  frontal  lobe;  (2)  by  way  of  the  medial  longitudi- 
nal fasciculus  with  the  nuclei  of  the  trochlear  and  abducens  (the  latter  making  possible  the  co- 
ordinate action  of  the  lateral  and  medial  recti  for  the  conjugate  eye  movements  produced  by 
these  muscles),  and  with  the  nucleus  of  the  facial  (associating  the  innervation  of  the  levator 
palpebrifi  with  that  of  the  orbicularis  oculi);  (3)  with  the  nuclei  of  termination  of  the  sensory 
nerves,  especially  the  auditory,  by  way  of  the  lateral  lemniscus  and  medial  longitudinal 
fasciculus.  It  is  probably  connected  with  the  cerebellum  by  way  of  the  brachia  conjunctiva 
and  red  nuclei. 

Fig.  663. — Diagram  of  Longitudinal  Section  of  NtrcLEus  of  Oculomotoe  Neeve. 
(After  Edinger.) 


Nucleus  of  posterior  com- 
missure and  med.  longit. 
fasc. 

Medial  longitudinal 
fasciculus 

Ciliary  muscles  (a)  and 
sphincter  of  iris  (b) 

Levator  palpebrse 


Superior  rectus 
Medial    rectus 

Inferior  oblique 
Inferior  rectus 


Superior  group(nucleus 
of  Edinger  and  West- 
phal) 


.--Inferior  group 


The  eminence  representing  the  inferior  quadrigeminate  body  proper  consists 
of  an  oval  mass  of  grey  substance,  the  nucleus  of  the  inferior  coUiculus,  containing 
numerous  nerve-cells,  most  of  which  are  of  small  size.  A  thin  superficial  lamina 
of  white  substance,  the  stratum  zonale,  forms  its  outermost  boundary,  and 
fibres  from  the  lateral  lemniscus  enter  it  laterally  and  from  below  {stratum 
lemnisci).  Near  the  lateral  margin  of  the  central  grey  substance  occurs  the 
beginning  of  the  inferior  brachium,  a  bundle  containing  fibres  to  and  from  the 
medial  geniculate  body  and  the  inferior  quadrigeminate  body. 

The  lemniscus  in  the  mesencephalon  is  considered  in  two  parts.  The  more 
lateral  portion  of  the  lemniscal  plate  occuring  in  the  pons  has  here  spread 
dorso-latorally,  and  occupies  a  position  in  the  lateral  margin  of  the  section,  and  is 
known  as  the  lateral  lemniscus,  while  the  medial  portion  which  remains  practically 
unchanged  in  the  tegmentum  is  distinguished  as  the  medial  lemniscus.  (See 
fig.  660).  In  the  upper  portion  of  the  lateral  lemniscus  occurs  a  small,  scattered 
mass  of  grey  substance,  the  nucleus  of  the  lateral  lemniscus,  in  which  manj'  of  its 
fibres  are  interrupted. 

The  upper  and  greater  portion  of  the  lateral  lemniscus  with  its  nucleus  belongs  to  the 
auditory  apparatus,  being  connected  with  the  nucleus  of  termination  of  the  cochlear  nerve, 
chiefly  of  the  opposite  side.  (See  fig.  650.)  A  large  part  of  the  fibres  of  this  portion  terminate 
in  the  inferior  quadrigeminate  bodies.     Many  of  the  latter  enter  at  once  the  nucleus  of  the  body 


840  THE  NERVOUS  SYSTEM 

(nucleus  of  inferior  colliculus)  of  the  same  side,  and  disappear  among  its  cells;  others  cross  the 
mid-line  to  the  quadrigeminate  body  of  the  opposite  side.  In  crossing,  some  pass  superficially 
and  thus  contribute  to  the  stratum  zonale,  while  others  pass  either  through  the  nucleus  or  below 
it  and  cross  beneath  the  floor  of  the  mecUan  groove  between  the  stratum  zonale  and  the  dorsal 
surface  of  the  central  grey  substance,  forming  there  an  evident  decussation  with  similar  fibres 
crossing  from  the  opposite  side.  Most  of  the  fibres  arising  from  the  cells  of  the  nucleus  of  the 
inferior  quadrigeminate  body  pass  by  way  of  the  inferior  brachium  to  the  medial  geniculate 
body  and  the  thalamus;  some  pass  ventrally  to  terminate  in  the  nucleus  of  origin  of  the  trochlear 
nerve  and  some  pass  forward  and  laterally  to  terminate  in  the  cortex  of  the  superior  gyrus  of 
the  temporal  lobe,  the  cortical  area  of  hearing.  Another  portion  of  the  lateral  lemniscus  passes 
obliquely  forward  in  company  with  the  inferior  brachium,  and  terminates  in  the  medial  gen- 
iculate body.  Thus  a  large  portion  of  the  lateral  lemniscus,  the  inferior  quadrigeminate  bodies 
with  their  brachia  and  the  medial  geniculate  bodies  are  concerned  with  the  sense  of  hearing. 
The  nucleus  of  the  inferior  quadrigeminate  body  receives  fibres  which  arise  in  the  cortex  of  the 
superior  temporal  gyrus  of  chiefly  the  same  side. 

Practically  all  the  remainder  of  the  lateral  lemniscus  terminates  in  the  nucleus,  or  stratum 
cinereum,  of  the  superior  quadrigeminate  body  of  the  same  and  opposite  sides.  They  approach 
the  nucleus  from  below,  and  contribute  to  the  well-marked  band  of  fibres  coursing  on  the  dorso- 
lateral margin  of  the  central  grey  substance,  and  known  as  the  'optic-acoustic  reflex  path'  or 
stratum  lemnisci  (fig.  662). 

The  medial  lemniscus  arises  in  the  medulla  oblongata  from  the  nuclei  (of  termination)  of 
the  funiculus  gracilis  and  funiculus  cimeatus  of  the  opposite  side,  and  likewise  from  the  nuclei 
of  termination  of  the  sensory  roots  of  the  cranial  nerves  of  the  opposite  side.  It  is,  therefore, 
a  continuation  of  the  central  sensory  pathway  conveying  the  general  bodily  (including  the 
head)  sensations  into  the  prosencephalon.  CoursLag  still  more  laterally  than  in  the  pons  below, 
it  passes  into  the  hypothalamic  grey  substance,  in  the  lateral  portion  of  which  most  of  its  fibres 
terminate.  By  axones  given  off  from  the  cells  of  the  hypothalamic  nucleus  the  impulses  borne 
thither  by  the  lemniscus  are  conveyed  by  way  of  the  internal  capsule  and  corona  radiata  to  the 
gyri  of  the  somsesthetic  area  of  the  cerebral  cortex. 

The  basis  (pes)  pedunculi  comprises  the  great  descending  pathway  from  the 
cerebral  cortex,  and  thus  is  continuous  with  the  internal  capsule  of  the  telen- 
cephalon. 

The  principal  components  of  each  basis  pedunculi  are  as  follows: — (1)  The  pyramidal  fibres, 
which  occupy  the  middle  portion  of  the  peduncle  and  comprise  three-fifths  of  its  bulk,  and  which 
are  outgrowths  of  the  giant  pyramidal  cells  of  the  somaesthetic  area  of  the  cerebral  cortex, 
chiefly  the  anterior  central  gyi'us.  These  supply  '  voluntary '  impulses  to  the  motor  nuclei  of 
the  cranial  nerves  on  the  opposite  side,  form  the  pyramids  of  the  medulla,  and  are  distributed 
to  the  ventral  horn  cells  of  the  spinal  cord  of  the  opposite  side.  (2)  The  frontal  pontile  fibres, 
which  course  in  the  mesial  part  of  the  peduncle  from  the  cortex  of  the  frontal  lobe  to  their 
termination  in  the  grey  substance  of  the  pons.  (3)  The  occipital  and  temporal  pontile  fibres. 
which  run  in  the  ventral  and  lateral  portion  of  the  peduncle  from  their  origin  in  the  occipital 
and  temporal  lobes  to  their  termination  in  the  grey  substance  of  the  pons. 

The  substantia  nigra  is  continuous  with  the  grey  substance  of  the  pons  and 
that  of  the  reticular  formation  below,  and  with  that  of  the  hypothalamic  region 
above.  Its  remarkable  abundance  begins  at  the  superior  border  of  the  pons,  and 
it  conforms  to  the  crescentic  inner  contour  of  the  cerebral  peduncle,  sending 
numerous  processes  which  occupy  the  inter-fascicular  spaces  of  the  latter.  It 
contains  numerous  deeply  pigmented  nerve-cells,  which  in  the  fresh  specimen 
give  the  appearance  suggesting  its  name. 

Its  anatomical  significance  is  not  well  understood.  It  is  known  that  some  fibres  of  the 
medial  lemniscus  terminate  about  its  ceUs  instead  of  in  the  hypothalamus  higher  up,  and  Melius 
has  found  in  the  monkey  that  a  large  portion  of  the  pyramidal  fibres  arising  in  the  thumb  area 
of  the  cerebral  cortex  are  interrupted  in  the  substantia  nigra.  It  is  probable  that  other  fibres 
of  the  peduncle  also  terminate  here. 

The  brachia  conjunctiva  or  superior  cerebellar  peduncles,  in  passing  from  their 
origin  in  the  dentate  nuclei,  lose  their  flattened  form  and  enter  the  mesencephalon 
as  rounded  bundles.  In  the  tegmentum,  under  the  inferior  colliculi,  the  two 
brachia  come  together  and  undergo  a  sudden  and  complete  decussation.  Through 
this  decussation  the  fibres  of  the  brachium  of  one  side  pass  forward  to  terminate, 
most  of  them,  in  the  red  nucleus  [nucleus  ruber]  of  the  tegmentum  of  the  opposite 
side  (fig.  589).  Some  fibres  are  said  to  pass  the  red  nucleus  and  terminate  in  the 
ventrolateral  part  of  the  thalamus. 

The  red  nuclei  are  two  large,  globular  masses  of  nerve-cells  situated  in  the 
tegmentum  under  the  superior  quadrigeminate  bodies.  At  all  levels  they  are 
considerably  mixed  with  the  entering  bundles  of  the  brachia  conjunctiva,  and 
they  contain  a  pigment  which  in  the  fresh  condition  gives  them  a  reddish  colour, 
suggesting  their  name. 

They  receive  in  addition  descending  fibres  from  the  cerebral  cortex  (frontal  operculum) 
and  from  the  nuclei  of  the  corpus  striatum.     From  the  cells  of  each  red  nucleus  arise  fibres 


THE  MESENCEPHALON 


841 


which  pass — (1)  into  the  thalamus  and  to  the  telencephalon  (prosencephalic  continuation  of  the 
cerebellar  path),  and  (2)  fibres  which  descend  into  the  spinal  cord,  the  'rubro-spinal  tract,' 
in  the  lateral  funiculus  (fig.  619).  The  latter  cross  from  the  red  nucleus  of  the  opposite 
side  and  descend  in  the  tegmentum.  The  red  nuclei  are  also  in  relation  with  the  fasciculus 
relroflexus  of  Meynert,  which  belongs  to  the  inter-brain. 

Fig.  664. — Scheme  to  Illustrate  the  Principal  or  Crossed  Relations  op  the  Descend- 
ing Cortical  (Pyramidal)  Fibrbs  to  the  Nuclei  op  Origin  op  the  Cranial  Nerves. 


'^  Motor  gyri  of  cerebral  cortex 


Corona  radiata 


^Internal  capsule 


^  -Cerebral  peduncle 

^  -Nucleus  of  oculomotor  nerve 


.-■Nucleus  of  trochlear  nerve 

Nucleus  of  mesencephalic 
'  "  root  of  masticator  nerve 


Nucleus  of  facial  nerve 
Nucleus  of  glosso-palatine 

:  of  abducens 
^  _. Nucleus  ambiguus 

.Dorsal  efferent  nucleus 
of  vagus 

^Nucleus  of  hypoglossal  nerve 
-Nucleus  of  accessory  nerve 
_  --Decussation  of  the  pyramids 


The  thalamo -olivary  tract  courses  in  the  mesencephalon  more  dorsally  than  in  the  pons 
region.  It  runs  in  the  ventro-lateral  boundary  of  central  grey  substance  just  lateral  to  the 
nuclei  of  the  trochlear  and  oculomotor  nerves. 

A  small  guadrigemino-pontile  strand  of  fibres  has  been  described  as  arising  in  the  quadri- 
gemina,  especially  the  inferior  pair,  and  terminating  in  the  nuclei  of  the  pons.  Impulses  carried 
by  these  fibres  are  probably  destined  for  the  cerebellar  hemisphere  of  the  opposite  side. 

The  superior  quadrigeminate  bodies  (superior  colliculi)  are  phylogenetically 
more  important  than  the  inferior.     In  certain  of  the  lower  vertebrates  they  are 


842  THE  NERVOUS  SYSTEM 

enormously  developed  and  in  most  of  the  mammals  they  are  relatively  larger  and 
appear  more  complicated  in  structure  than  in  man.  They  are  concerned  almost 
wholly  with  the  visual  apparatus,  mediating  most  of  the  reflexes  with  which  it 
is  concerned. 

The  nucleus  of  the  superior  colliculus  is  of  somewhat  greater  bulk  than  that  of  the  inferior. 
It  is  capped  by  a  strong  stratum  zonale  (fig.  662),  which  has  been  described  as  composed  chiefly 
of  retinal  fibres,  passing  to  it  from  the  optic  tract  by  way  of  the  superior  brachium,  but,  since 
Cajal  found  in  the  rabbit  that  extirpation  of  the  eye  is  followed  by  very  slight  degeneration  of 
the  stratum  zonale,  it  is  probable  that  it  is  composed  of  other  than  retinal  fibres — possibly 
fibres  from  the  occipital  cortex  and  fibres  arising  within  the  nucleus  itself.  The  nucleus  is 
separated  from  the  central  grey  substance  by  a  weU-marked  band  of  fibres,  the  stratum  album 
profundum.  This  contains  fibres  from  two  sources: — (1)  fibres  from  the  lateral  lemniscus 
which  approach  the  nucleus  from  the  under  side,  some  to  terminate  within  it,  others  to  cross 
to  the  nucleus  of  the  opposite  side;  (2)  fibres  which  arise  within  the  nucleus  and  course  ventrally 
around  the  central  grey  substance,  both  to  terminate  in  the  nucleus  of  the  oculomotor  nerve  and 
to  join  the  medial  longitudinal  fasciculus  and  pass  probably  to  the  nuclei  of  the  trochlear  and 
abducens.  The  lemniscus  fibres  often  course  less  deeply  than  (2)  and  give  the  stratum  lemnisci. 
The  optic  fibres  proper  approach  the  nucleus  by  way  of  the  superior  brachium,  and  are  dispersed 
directly  among  its  cells;  only  a  small  proportion  of  them  cross  over  to  terminate  in  the  nucleus 
of  the  opposite  side.  They  consist  of  two  varieties: — (1)  retinal  fibres  which  arise  in  the  gang- 
lion-cell layer  of  the  retina  and  enter  the  superior  brachium  at  its  junction  with  the  lateral  root 
of  the  optic  tract,  and  (2)  fibres  from  the  visual  area  of  the  occipital  lobe  of  the  cerebral  hemi- 
sphere. Sometimes  the  optic  fibres  in  their  course  within  the  nucleus  of  the  superior  coUiculus 
form  a  more  or  less  evident  stratum  near  the  stratum  album  profundum.  This  is  known  as  the 
stratum  oplicum  (stratum  album  medium).  The  portion  of  the  nucleus  between  this  stratum 
and  the  stratum  zonale  is  called  the  stratum  cinereum. 

The  fibres  entering  the  nucleus  from  the  lateral  lemniscus  probably  all  represent  auditory 
connections.  The  stratum  album  profundum,  composed  of  the  lemniscus  fibres  and  fibres 
from  cells  of  the  nucleus,  and  the  stratum  opticum  together,  form  the  so-caOed  'optic-acoustic 
reflex  path'  (fig.  662). 

The  mesencephalo-spinal  amd  the  spine -mesencephalic  (spino-tectal)  paths  course  together 
ventro-lateral  to  the  nuclei  of  the  coUiculi.  In  the  superior  quadrigeminate  bodies  they  course 
in  the  dorsal  edge  of  the  median  lemniscus,  between  the  stratum  opticum  and  stratum  album 
profundum. 

From  the  various  studies  that  have  been  made  it  appears  that  the  superior  coUiculus  of  the 
corpora  quadrigemina  is  merely  the  central  reflex  organ  concerned  in  the  control  of  the  eye 
muscles — eye  muscle  refle.xes  which  result  from  retinal  and  cochlear  stimulation,  and  from  some 
general  body  sensations  by  way  of  the  spinal  cord.  Fibres  from  its  nucleus  to  the  visual  area 
of  the  occipital  cortex  have  been  claimed  for  certain  mammals,  but  in  man  the  superior  colliculus 
may  be  entirely  destroyed  without  disturbance  of  the  perception  of  light  or  color  and  flbres 
arising  from  its  nucleus  to  terminate  in  the  cerebral  cortex  are  denied. 

In  the  level  of  the  anterior  part  of  the  superior  colliculus  the  fibres  which  arise  from  the  cells 
of  its  nucleus  and  course  ventrally  in  the  stratum  album  profundum  ooUect  into  a  strong  bundle. 
This  bundle  passes  ventral  to  the  medial  longitudinal  fasciculus  and,  in  the  space  between  the 
two  red  nuclei,  it  forms  a  dense  decussation  with  the  similar  bundle  from  the  opposite  side.  In 
decussating  the  fibres  turn  in  spray-like  curves  downward  and  soon  join  the  medial  longitudinal 
fasciculus.  This  is  the  'fountain  decussation'  of  Forel.  It  is  said  to  be  augmented  by  decus- 
sating fibres  from  the  two  red  nuclei. 

There  is  abundant  evidence  that  fibres  arising  in  the  corpora  quadrigemina  descend  into 
the  spinal  cord.  Various  studies  make  it  appear  that  at  least  part  of  these  are  fibres  from  the 
fountain  decussation,  and  that  these  course  through  the  medulla  oblongata  in  the  ventral  part 
of  the  medial  longitudinal  fasciculus,  and  thence  descend  into  the  cord  in  the  'quadrigemino- 
thalamus  path'  (lateral  mesencephalo-spinal  tract)  (fig.  619).  The  medial  longitudinal  fasci- 
culus is  continuous  with  the  ventral  fasciculus  proprius  of  the  spinal  cord  and  most  of  these 
fibres  arising  in  the  superior  quadrigeminate  bodies  retain  their  ventral  position  in  the  cord 
as  the  sulco-marginal  fasciculus  of  the  opposite  side.  Their  termination  about  those  ventral 
horn  cells  of  the  cervical  cord  which  send  fibres  through  the  rami  communicantes  probably 
establishes  the  pathway  by  which  the  superior  quadrigeminate  bodies  are  connected  with  the 
cervical  sympathetic  ganglia,  and  by  which  may  be  explained  the  disturbances  in  pupillary 
contraction  induced  by  lesions  of  the  lower  cervical  cord. 

The  medial  geniculate  body  and  the  medial  root  of  the  optic  tract,  which  runs  into  the 
former,  probably  have  nothing  to  do  with  the  functions  of  the  optic  apparatus.  Both  remain 
intact  after  extirpation  of  the  eyes.  The  medial  root  of  the  optic  tract  is  apparently  nothing 
more  than  the  beginning  of  the  inferior  cerebral  (Gudden's)  commissure,  a  bundle  passing  by 
way  of  the  optic  tract,  connecting  the  medial  geniculate  body  of  one  side  with  that  of  the  other 
side,  and  probably  with  the  inferior  colliculus. 

The  medial  longitudinal  fasciculus  (posterior  longitudinal  fasciculus),  con- 
tinuous into  the  ventral  fasciculus  proprius  and  the  sulco-marginal  fasciculus  of 
the  spinal  cord,  extends  throughout  tlae  rhombencephalon  and  mesencephalon, 
and  is  represented  in  the  hypothalamic  region  of  the  prosencephalon.  Deserted 
by  the  lemniscus  at  the  inferior  border  of  the  pons,  it  maintains  its  closely  medial 
position  and  courses  throughout  in  the  immediate  ventral  margin  of  the  central 
grey  substance  of  the  medulla  and  floor  of  the  fourth  ventricle,  and  likewise 
in  the  ventral  margin  of  the  central  grey  substance  of  the  mesencephalon. 


THE  PROSENCEPHALON  843 

The  two  fasciculi  constitute  the  principal  association  pathways  of  the  brain-stem,  and,  true 
to  their  nature  as  such,  they  are  among  the  first  of  its  pathways  to  acquire  medullation.  In  the 
mesencephalon  they  become  two  of  its  most  conspicuous  tracts,  and  their  course,  in  most  inti- 
mate association  with  the  nuclei  of  origin  of  the  nerves  supplying  the  eye  muscles,  suggests 
what  is  probably  one  of  their  most  important  functions,  viz.,  that  of  associating  these  nuclei 
with  each  other  and  of  bearing  to  them  fibres  from  the  nuclei  of  the  other  cranial  nerves  neces- 
sary for  the  co-ordinate  action  of  the  muscles  of  the  optic  apparatus  associated  with  the  functions 
of  these  other  nerves. 

Fibres  from  each  medial  longitudinal  fasciculus  terminate  either  by  collaterals  or  terminal 
arborisations  about  the  cells  of  the  motor  nuclei  of  aU  the  cranial  nerves,  and  each  nucleus  prob- 
ably contributes  fibres  to  it.  It  also  receives  fibres  from  the  nuclei  of  termination  of  the  sensory 
nerves  especially  the  vestibular.  Thus  it  contains  fibres  coursing  in  both  directions,  and, 
while  it  is  continually  losing  fibres  by  termination,  it  is  being  continually  recruited  and  so 
maintains  a  practically  uniform  bulk.  Thus,  a  given  lesion  never  results  iu  its  total  degenera- 
tion. Many  of  the  fibres  coursing  in  it  arise  from  the  opposite  side  of  the  mid-line.  A  special 
contribution  of  fibres  of  this  kind  is  received  by  way  of  the  fovmtain  decussation  from  the 
nucleus  of  the  superior  coUiculus  of  the  opposite  side.  As  noted  above,  it  is  in  part  continu- 
ous into  the  spinal  cord  as  the  ventral  fasciculus  proprius.  It  receives  some  fibres  by  way  of 
the  posterior  commissure  of  the  prosencephalon  from  a  small  nucleus  common  to  it  and  the 
posterior  commissure  situated  in  the  superior  extension  of  the  central  grey  substance  of  the 
mesencephalon.  Van  Gehuchten  and  Edinger  describe  for  it  a  special  nucleus  of  the  medial 
longitudinal  fasciculus  situated  beyond  this  commissure  in  the  hypothalamic  rsgion.  This 
nucleus  may  be  explained  as  an  accumulation  of  the  gray  substance  of  the  reticular  forma- 
tion below  and  as  receiving  impulses  from  the  structures  of  the  prosencephalon  which  are  dis- 
tributed by  its  axones  to  the  structures  below  by  way  of  the  medial  longitudinal  fasciculus. 

Scattered  in  the  posterior  part  of  the  posterior  perforated  substance,  near  the  superior 
border  of  the  pons,  is  a  small  group  of  ceU-bodies  forming  the  inter -peduncular  nucleus  (inter- 
peduncular gangUon  of  von  Gudden).  Fibres  arising  in  the  habenular  nucleus  of  the  diencepha- 
lon  curve  posteriorly,  forming  the  fasciculus  retroflexus  of  Meynert,  and  terminate  about  its 
cells.  Fibres  arising  from  its  cells  course  dorsalward  and  terminate  about  association  neurones 
in  the  ventral  periphery  of  the  central  grey  substance.     It  is  concerned  with  olfactory  impulses. 

SUMMARY  OF  THE  MESENCEPHALON 

1.  Quadrigeminate  bodies: 

(a)  Inferior  coUicuU,  their  nuclei  and  brachia. 
(6)   Superior  colhculi,  their  nuclei  and  brachia. 

2.  Pedimcles  of  the  cerebrum 

3.  Aqueduct  of  the  cerebrum. 

4.  Central  grey  substance. 

5.  Substantia  nigra. 

6.  Decussation  of  superior  cerebellar  peduncles  and  the  red  nuclei. 

7.  Medial  lemniscus,  lateral  lemniscus  and  nucleus  of  lateral  lemniscus. 

8.  Mesencephalic  nucleus  and  root  of  masticator  nerve. 

9.  Trochlear  nerve  and  its  nucleus. 

10.  Oculomotor  nerve  and  its  nucleus. 

11.  Mesencephalo-spinal  and  rubro-spinal  tracts. 

12.  Medial  longitudinal  fasciculus,  its  nucleus,  the  nucleus  of  the  posterior  commissure. 

13.  The  fountain  decussation. 

14.  Interpeduncular  nucleus. 

As  frequently  reaUzed  in  the  above,  the  structures  of  the  mesencephalon  are  both  overlapped 
by,  and  are  of  necessity  functionally  continuous  with,  the  structures  of  the  next  and  most  ante- 
rior division  of  the  encephalon,  the  prosencephalon. 

2.  THE  PROSENCEPHALON 

The  prosencephalon  or  fore-brain  includes  those  portions  of  the  encephalon 
derived  from  the  walls  of  the  anterior  of  the  three  embryonic  brain-vesicles.  In 
its  adult  architecture  it  consists  of — (1)  the  diencephalon  (interbrain),  comprising 
the  thalamencephalon  or  the  thalami  and  the  structm-es  derived  from  and 
immediately  adjacent  to  them,  and,  in  addition,  the  mammillary  portion  of  the 
hypothalamic  region;  (2)  the  telencephalon  (end -brain),  comprising  the  optic 
portion  of  the  hypothalamic  region  and  the  cerebral  hemispheres  proper.  The 
last  mentioned  consist  of  the  entire  cerebral  cortex  or  superficial  mantle  of  grey 
substance,  including  the  rhinencephalon,  and  also  the  basal  ganglia  or  buried 
nuclei  (corpus  striatum),  together  with  the  tracts  of  white  substance  connecting 
and  associating  the  different  regions  of  the  hemispheres  with  each  other  and  with 
the  structures  of  the  other  divisions  of  the  central  nervous  system. 

EXTERNAL  FEATURES  OF  THE  PROSENCEPHALON 

A.  THE  DIENCEPHALON. — The  basal  surface  of  this  division  of  the  brain 
consists  of  only  the  mammillary  portion  of  the  hypothalamic  region  (fig.  668). 


844 


THE  NERVOUS  SYSTEM 


This  comprises — (1)  the  mammillary  bodies  [corpora  mammillaria]  (albicantia) , 
the  two  rounded  projections  situated  in  the  anterior  part  of  the  interpeduncular 
fossa,  and  (2)  the  anterior  portion  of  the  posterior  perforated  substance  or  the 
small  triangle  of  grey  substance  forming  the  floor  of  the  posterior  part  of  the 
third  ventricle,  and  which  represents  numerous  openings  for  the  passage  of 
branches  of  the  posterior  cerebral  arteries  (fig.  668) .  The  hypothalamic  portions 
of  the  cerebral  peduncles  might  be  included.  The  structures  of  the  optic  or  re- 
maining portion  of  the  hypothalamus  belong  to  the  telencephalon. 

The  upper  or  dorsal  surface  of  the  diencephalon  is  completely  overlapped  and 
hidden  by  the  telencephalon,  and  covered  by  the  intervening  ingrowth  of  the 


Fig.  665. — Doesal  Surface  of  Diencephalon  with  Adjacent  Structukes. 
(After  Obersteiner.) 


Coipus  callosum 


Fifth  ventricle 
Septum  pellucidum 


Caudate    nucleus 


Lateral  sul 

encephalon 


Eminence  of  hypoglossal 

Restifcrm  body 

Clava 

Posterior  fissure 

Postero-intermediate  sulcus 

Postero-lateral  sulcus 


Habenular  commissure 
Epiphysis 

Sulcus  cor] 
media 

Inferior  coUiculus 
Frenulum  veli 
Lingula  cerebelli 


Acoustic  area 
vagi 


Tuberculum  cuneatum 
Funiculus  gracilis 
Funiculus  cuneatus 
Lateral  funiculus 


cerebral  meninges,  the  tela  chorioidea  of  the  third  ventricle  (velum  interpositum). 
These  removed  (fig.  665),  it  is  seen  that  the  thalami  on  either  side  are  by  far  the 
most  conspicuous  objects  of  the  diencephalon.  They,  together  with  the  parts 
developed  in  connection  with  them,  are  distinguished  as  the  thalamencpehalon. 
The  thalamencephalon  consists  of — (1)  the  thalami;  (2)  the  metathalamus  or 
geniculate  bodies;  and  (3)  the  epithalanius,  comprising  the  epiphysis  with  the 
posterior  commissure  below  it  and  the  habenular  trigone  on  either  side. 

The  thalami  are  two  ovoid,  couch-like  masses  of  grey  substance  which  form 
the  lateral  walls  of  the  third  ventricle.  The  cavity  of  the  ventricle  is  narrow,  and 
quite  frequently  the  thalami  are  continuous  through  it  across  the  mid-hne  by  a 
small  but  variable  neck  of  grey  substance,  the  massa  intermedia  ("middle  com- 
missure"). The  upper  surfaces  of  the  thalami  are  free.  The  edges  of  the  tela 
chorioidea  of  the  third  ventricle  are  attached  to  the  lateral  part  of  the  surface  of 
each  thalamus,  and,  when  removed,  leave  the  taenia  chorioidea  lying  in  the  chori- 


THE  DIENCEPHALON 


845 


oidal  sulcus.  Each  thalamus  is  separated  laterally  from  the  caudate  nucleus  of 
the  telencephalon,  by  a  linear  continuation  of  the  white  substance  below,  known 
as  the  stria  terminalis  thalami  (taenia  semicircularis).  Like  the  quadrigemina, 
each  thalamus  is  covered  by  a  thin  capsule  of  white  substance,  the  stratum 
zonale.  The  average  length  of  the  thalamus  is  about  38  mm.,  and  its  width  about 
14  mm.;  its  inferior  extremity  is  directed  obliquely  lateralward.  The  dorsal 
surface  usually  shows  four  eminences,  indicating  the  position  of  the  so-called 
nuclei  of  the  thalamus  within.  These  are  the  anterior  nucleus  or  anterior  tubercle, 
the  medial  nucleus  or  tubercle,  the  lateral  nucleus,  and  the  pulvinar,  the  tubercle  of 
the  posterior  extremity.  The  pulvinar  of  the  human  brain  is  peculiar  in  the  fact 
that  it  is  so  developed  as  to  project  inferiorly  and  slightly  overhang  the  level  of 
the  quadrigeminate  bodies.  The  projecting  portion  assumes  relations  with  the 
optic  tract  and  the  metathalamus. 


Fig.  666.- 


-DissECTioN  OF  Brain  showing  Metathalamus  and  Pulvinar  with  Adjacent 
Structures. 


Caudate  nucleus 

Stria  terminalis  of  thalamus 

Pulvinar 


Optic  tract 


Inferior  quadrigemi 
nate  body 

Medial  geniculate  body 
Lateral  geniculate  body 

Mammillary  body 
Optic  tract 


Olfactory  buib 


Insula  (central  lobe) 
Tail  of  caudate  nuclei 


Both  the  structures  of  the  metathalamus,  the  lateral  and  medial  geniculate 
bodies,  are  connected  with  the  optic  tract,  but  it  is  thought  that  actual  visual 
axones  terminate  only  in  the  lateral  genticulate  body.  As  the  optic  tract  curves 
around  the  cerebral  peduncle  it  divides  into  two  main  roots.  The  lateral  gen- 
iculate body  receives  a  small  portion  of  the  fibres  of  the  lateral  root  of  the  optic 
tract;  the  remainder  pass  under  this  body  and  enter  the  pulvinar  of  the  thalamus. 
The  medial  geniculate  body  is  connected  with  the  medial  root  of  the  optic  tract, 
which  root  consists  largely,  not  of  retinal  fibres,  as  does  the  lateral  root,  but  of  the 
fibres  forming  Gudden's  commissure  (the  inferior  cerebral  commissure).  The 
retinal  fibres  contained  in  the  medial  root  pass  to  terminate  in  the  superior 
quadrigeminate  bodies. 

Of  the  epithalamus,  the  epiphysis  (pineal  body,  conarium)  is  the  most  con- 
spicuous external  feature.  This  is  an  unpaired,  cone-shaped  structure,  about  7 
mm.  long  and  4  mm.  broad,  which  also  projects  upon  the  mesencephalon  so  that 
its  body  rests  in  the  groove  between  the  superior  quadrigeminate  bodies.  Its 
stem  is  attached  in  the  mid-line  at  the  posterior  extremity  of  the  third  ventricle, 
and  therefore  just  above  the  posterior  commissure  of  the  cerebrum  (fig.  658). 
It  is  covered  by  pia  mater,  and  is  involved  in  a  continuation  of  the  tela  chorioidea 


846 


THE  NERVOUS  SYSTEM 


of  the  third  ventricle.  Though  it  develops  as  a  diverticulum  of  that  portion  of 
the  anterior  primary  vesicle  which  gives  origin  to  the  thalamencephalon,  it  is 
wholly  a  non-nervous  structure,  other  than  the  sympathetic  fibres  which  enter  it 
for  the  supply  of  its  blood-vessels. 

It  consists  of  a  dense  capsule  of  fibrous  tissue  (pia  mater)  from  which  numerous  septa  pass 
inward,  dividing  tlie  interior  into  a  number  of  intercommunicating  compartments  filled  with 
epithelial  (ependymal)  cells  of  the  same  origin  as  the  ependyma  lining  the  ventricles  and  aque- 
duct below.  Among  these  cells  are  frequently  found  small  accretions  (brain-sand,  acervulus 
cerebri),  consisting  of  mixed  phosphates  of  lime,  magnesia,  and  ammonia  and  carbonates  of 
lime.  The  compartments  form  a  closed  system.  In  function  the  epiphysis  ranks  as  one  of  the 
glands  of  internal  secretion  of  the  body,  and  it  is  often  referred  to  as  the  'pineal  gland.'  How- 
ever, it  is  perhaps  funotionless  in  man. 

Fig.  667. — Mesial  Section  of  Entire  Brain,  showing  Mesial  Surface  of  Diencephalon 
_^'7' ;  AND  Telencephalon.     (After  Henle.) 

Massa 
Hypothalamic  sulcus      intermedia         Interventricular  foramen  (Monroi) 
Posterior  commissure  \  i  . 

/  Sulcus  of  corpus  callosum 


Epiphys 


Splemum  of  corpus 

callos 
Lamina 
quadrigemina 


Anterior  commissure 
Sub-callosal 
gyrus 


Aqueduct  of 
cerebrum  (Sylvii) 
Anterior  medullary 
velum 


Genu  of  corpus 
V  callosum 

Rostrum  of  corpus 

callosum 
Lamina  terminalis 


Cerebellum 

Fourth  ventricle 


Hypo-  \  Optic  1 

Medulla    /         /         I       Physis        Qptic  chiasma 
Pons  Mammil-    Tuber 
lary  body  cinereum 


Apparently  arising  from  the  base  of  the  epiphysis,  but  having  practically 
nothing  to  do  with  it,  are  the  striae  meduUares  of  the  thalamus  (striae  pineales, 
pedunculi  conarii,  taenia  thalami,  habenulse) .  These  are  two  thin  bands  of  white 
substance  which  extend  from  under  the  epiphysis  anteriorly  upon  the  thalamus, 
along  the  superior  border  of  each  lateral  wall  of  the  third  ventricle,  and  thus  form 
the  boundaries  between  the  superior  and  mesial  surfaces  of  each  thalamus. 

They  have  been  called  the  habenulce,  from  their  relation  to  the  habenular  nucleus,  situated 
in  the  mesial  grey  substance  at  their  inferior  ends.  They  are  continuous  across  the  mid-line 
in  the  habenular  commissure,  just  below  the  neck  of  the  epiphysis,  and  between  it  and  the  pos- 
terior cerebral  commissure,  or,  rather  the  superior  part  of  the  latter  (figs.  631,  665).  It  will  be 
seen  below  that  each  habenula  contains  olfactory  fibers  from  the  fornix,  the  anterior  perfor- 
ated substance  and  the  septum  pellucidum,  as  well  as  fibres  out  of  the  thalamus,  and  that  most 
of  its  fibres  terminate  in  the  habenular  nucleus. 

The  ventro-lateral  surface  of  the  thalamencephalon  is  continuous  into  the 
hypothalamic  tegmental  region,  the  upward  continuation  of  the  tegmental  grey 
substance  of  the  mesencephalon.  It  is  also  adjacent  to  a  portion  of  the  internal 
capsule.  Both  these  relationships,  as  well  as  the  fibre  connections  of  the  dien- 
cephalon with  the  structures  above  and  below  it,  are  deferred  until  the  discussion 
of  the  internal  structure  of  the  prosencephalon. 

The  mesial  surface  of  the  diencephalon  (fig.  667),  allows  a  better  view  of  the 
shape  and  relations  of  the  third  ventricle.  Below  the  line  of  the  massa  inter- 
media the  ventricle  is  usually  somewhat  wider  than  it  is  along  the  upper  margins  of 


THE  TELENCEPHALON 


847 


the  thalami.  This  greater  width  is  occasioned  by  a  groove  in  the  ventromesial 
surface  of  each  thalamus,  known  as  the  hjrpothalamic  sulcus  (sulcus  of  Monro). 
It  is  along  the  line  of  this  sulcus  that  the  third  ventricle  is  continuous  with  the 
aqueduct  of  the  cerebrum,  and  thus  with  the  fourth  ventricle  below,  and,  likewise, 
with  the  two  lateral  ventricles  of  the  cerebral  hemispheres  at  its  anterior  end. 
The  latter  junction  occurs  through  a  small  oblique  aperture,  the  interventricular 
foramen  (foramen  of  Monro),  one  into  each  lateral  ventricle.  The  dorsal  or 
upper  portion  of  the  third  ventricle  extends  posteriorly  beneath  its  chorioid  tela 

Fig.  668. — Ventral  Aspect  of  Brain-stem  Including  Mammillaht  and  Optic  Portions 
OF  THE  Hypothalamus. 
Insula 


Anterior  perforated 
substance ^^| 


nillary  bodies, 


Cerebral  peduncle 


Semilunar  (Gasser 
ian)  ganglion 


Oblique  fascicul 
of  pons 


Hypophysis 
1         TN 


Optic  nerve 
Optic  tract 


Oculomotor  nerve 


Hypoglossal  nerve 


Decussation  of  pyramids 


_-- Cervical  II 


(velum  interpositum)  to  form  a  small  postfiiur  n^ccss  about  the  epiphysis.  This  is 
known  as  the  supra-pineal  recess.  The  anterior  and  ventral  extremity  of  the 
third  ventricle  involves  the  pars  optica  hypothalami,  which  belongs  to  the 
telencephalon. 

B.  THE  TELENCEPHALON. — External  features. — The  optic  portion  of  the 
hypothalamus  consists  of  that  small  central  area  of  the  basal  surface  of  the  telen- 
cephalon which  includes  and  surrounds  the  optic  chiasma,  and  comprises  the 
structures  of  the  floor  of  the  anterior  and  ventral  portion  of  the  third  ventricle. 
The  area  extends  anteriorly  from  the  mammillary  bodies  in  the  interpeduncular 
fossa,  and  includes  the  tuber  cinereum  and  hypophysis  behind  the  optic  chiasma, 
and  some  of  the  anterior  perforated  substance  in  front  of  it. 

The  most  anterior  portion  of  the  third  ventricle  is  in  the  form  of  a  ventral  ex- 
tension. The  wall  of  this  portion  is  almost  wholly  non-nervous  and  quite  thin, 
and  thus  the  cavity  of  the  ventricle  is  but  thinly  separated  from  the  exterior  of 


848  THE  NERVOUS  SYSTEM 

the  brain.  The  front  portion  of  this  wall  is  the  lamina  terminalis  and  in  the  ven- 
tricular side  of  the  upper  part  of  this  lamina  the  anterior  commissure  of  the 
cerebrum  is  apparent. 

The  optic  chiasma  lies  across  and  presses  into  the  lower  portion  of  the  lamina 
terminalis,  and  in  so  doing  produces  an  anterior  recess  in  the  cavity  of  the  ventri- 
cle known  as  the  optic  recess.  Behind  the  optic  chiasma  the  floor  of  the  third 
ventricle  bulges  slightly,  giving  the  outward  appearance  known  as  the  tuber 
cinereum,  and  the  cavity  bounded  by  this  terminates  in  the  infundibular  recess. 

The  tuber  cinereum  then  is  a  hollow,  conical  projection  of  the  floor  of  the 
third  ventricle,  between  the  corpora  mammillaria  and  the  optic  chiasma.  Its  wall 
is  continuous  anteriorly  with  the  lamina  terminalis  and  laterally  with  the  anterior 
perforated  substance. 

The  infundibulum  is  but  the  attenuated  apex  of  the  conical  tuber  cinereum, 
and  forms  the  neck  connecting  it  with  the  hypophysis.  It  is  so  drawn  out  that  it 
is  referred  to  as  the  stalk  of  the  hypophysis.  The  cavity  of  the  tuber  cinereum 
(infundibular  recess)  is  sometimes  maintained  throughout  the  greater  part  of  the 
length  of  the  infundibulum,  giving  it  the  form  of  a  long-necked  funnel.  Near  the 
hypophysis  the  cavity  is  always  occluded. 

Fig.  669. — Diagrams  op  the  Hypophysis  Cerebri.     (After  Testut.) 
A,  posterior  surface;  B.  transverse  section;  C,  sagittal  section;  1,  anterior  lobe;  2,  posterior 
lobe;  3,  infundibulum;  4,  optic  chiasma;  5,  infundibular  recess;  6,  optic  recess.     In  C  the 
infundibulum  is  relatively  much  shorter  than  in  the  actual  specimen. 


The  hypophysis  cerebri  (pituitary  body  or  gland)  is  an  ovoid  mass  terminating 
the  infundibulum.  It  lies  in  the  sella  turcica  of  the  sphenoid  bone,  where  it  is  held 
down  and  roofed  in  by  the  diaphragma  selloe,  a  spheroid  pocket  of  the  dura  mater. 
It  consists  of  two  lobes,  a  large  anterior  lobe,  the  glandular  or  buccal  lobe,  and  a 
smaller  posterior  or  cerebral  lobe.  The  posterior  lobe  is  usually  enclasped  in  a 
concavity  of  the  anterior  lobe. 

Development. — The  posterior  or  cerebral  lobe  alone  is  originally  continuous  with  and  a  part 
of  the  infundibulum.  It  alone  represents  the  termination  of  the  hollow  diverticulum  which, 
in  the  embryo,  grows  downward  from  that  part  of  the  anterior  cerebral  vesicle  which  later 
becomes  the  third  ventricle.  The  driginal  cavity  afterward  becomes  obliterated  except  in  the 
upper  part  of  the  infundibulum.  It  is,  therefore,  of  cerebral  origin.  The  anterior  or  buccal 
lobe  arises  quite  differently.  It  is  developed  from  an  upward  tubular  diverticulum  (Rathke's 
pouch)  of  the  primitive  buccal  cavity.  In  the  higher  vertebrates,  including  man,  its  connection 
with  the  buccal  cavity  becomes  obliterated  as  the  cartilaginous  base  of  the  cranium  is  consoli- 
dated, but  in  the  myxinoid  fishes  the  connection  remains  patent  in  the  adult.  Cut  off  within 
the  cranial  cavity,  the  embryonic  buccal  lobe  assumes  its  intimate  association  with  the  cerebral 
lobe.  In  about  the  second  month  of  fetal  life  it  begins  to  develop  numerous  secondary  diverti- 
cula which  become  the  epithelial  structures  evident  in  the  adult  human  subject. 

Structure. — The  posterior  or  cerebral  lobe  retains  no  organized  structure.  It  may  be  said 
to  consist  of  a  mass  of  neuroglia  and  other  fibrous  connective  tissue  with  the  cells  belonging  to 
these  and  a  moderate  suppl}'  of  blood-vessels,  with  some  sympathetic  cell-bodies  and  fibres  for 
the  blood-vessels.  The  anterior  or  glandular  lobe  is  probably  the  functional  part  of  the  organ. 
In  addition  to  its  abundant  supporting  tissue,  it  consists  of  compartments  lined  with  two  kinds  of 
ouboidal  cells — cells  of  different  size  and  different  staining  properties.  The  principal  or  more 
numerous  cells  are  smaller,  with  thicldy  granular  cytoplasm.  In  mi.xtures  containing  orange  G 
and  fuchsin  these  cells  stain  orange,  while  the  chromophile  cells,  the  larger  and  less  numerous 
variety,  take  the  fuchsin  deeply.  The  compartments  have  an  abundant  blood  supply.  Near 
the  interlobar  septum,  the  cells  frequently  are  arranged  to  form  small  vesicles  which  contain 
colloid  substance,  resembling  the  typical  structure  of  the  thyreoid  body. 

Like  the  epiphysis,  the  hypophysis  must  be  regarded  as  glandular — a  gland  with  internal 
secretion.  In  the  case  of  giants  and  in  acromegaly  it  is  usually  greatly  enlarged.  The  principal 
cells  increase  greatly  in  number  after  removal  of  the  thyreoid  body. 

The  fundaments  of  the  optic  nerve  are  derived  from  this  portion  of  the  telen- 
cephalon, though  the  nuclei  of  termination  of  its  fibres  are  located  in  the  thalam- 


THE  OPTIC  TRACTS 


849 


encephalon  and  mesencephalon.  The  optic  apparatus  consists  of  the  retinae 
and  optic  nerves,  the  optic  chiasma,  the  optic  tracts,  the  superior  quadrigeminate 
bodies  with  their  relations  with  the  nuclei  of  the  eye-moving  nerves,  the  meta- 
thalamus,  the  pulvinar  of  the  thalamus,  and  the  visual  area  of  the  cerebral  cortex 
of  the  occipital  lobe.  The  fibres  of  the  optic  nerves  arise  from  the  cells  of  the 
ganglion-cell  layer  of  the  retinae.  The  fibres  which  arise  in  the  mesial  or  nasal 
halves  of  each  retina  cross  the  mid-line  to  find  their  nuclei  of  termination  in  the 
central  grey  substance  of  the  opposite  side,  while  those  from  the  outer  or  lateral 
halves  terminate  on  the  same  side  (fig.  670.) 

The  optic  chiasma  (optic  commissure)  is  functionally  independent  of  the  struc- 
tures of  the  optic  portion  of  the  hypothalamus  adjacent  to  it.     It  is  formed  by  the 

Fig.  670. — Diagram   of  the   Principal  Components   op  the   Optic  Apparatus.     (After 

Cunningham.) 


approach  and  fusion  of  the  two  optic  nerves,  and  is  knit  together  by  the  decussat- 
ing fibres  from  the  nasal  halves  of  each  retina,  and,  in  addition,  by  the  fibres  of 
Gudden's  commissure  which  is  contained  in  it. 

Beyond  the  chiasma  the  optic  fibres  continue  as  the  optic  tracts  which  course 
posteriorly  around  the  cerebral  peduncles  to  attain  their  entrance  into  the  thalam- 
enchephalon  and  mesencephalon.  Upon  reaching  the  pulvinar  of  the  thalamus 
each  optic  tract  divides  into  two  roots,  a  lateral  and  mesial. 

The  lateral  root  contains  practically  all  of  the  true  visual  fibres — fibres  arising  from  the  latera 
half  of  the  retina  of  the  same  side  and  the  nasal  half  of  the  retina  of  the  opposite  side.  These 
fibres  are  distributed  to  three  localities: — (1)  part  of  them  terminate  in  the  lateral  geniculate 
body;  (2)  the  greater  portion  pass  over  and  around  the  lateral  geniculate  body  and  enter  the 
pulvinar;  (3)  a  considerable  portion  enter  the  superior  quadrigeminal  brachium  and  course  in 
it  to  terminate  in  the  nucleus  of  the  superior  quadrigeminate  body.  The  most  evident  function 
of  this  latter  portion  is  to  bear  impulses  which,  by  way  of  the  neurones  of  the  quadrigeminate 
body,  are  distributed  to  the  nuclei  of  the  oculomotor,  trochlear,  and  abducent  nerves,  and  thus 
mediate  eye-moving  refiexes.  The  cells  of  the  lateral  geniculate  body  and  the  pulvinar,  about 
which  the  retinal  fibres  terminate,  give  off  a.xones  which  terminate  in  the  cortex  of  the  visual 
area,  chiefly  the  gyri  about  the  calcarine  fissure  of  the  occipital  lobe.  In  reaching  this  area  they 
curve  upward  and  backward,  coursing  in  a  compact  band  of  white  substance  known  as  the  optic 


850  THE  NERVOUS  SYSTEM 

radiation  (radiatio  oocipito-thalamica,  fig.  699).  Whetlier  any  fibres  of  the  optic  radiation  arise 
in  tlie  superor  quadrigeminate  body  is  doubtful.  It  also  is  in  large  part  composed  of  fibres 
arising  from  the  cells  of  the  visual  area,  which  pass  from  the  cortex  to  the  pulvinar,  superior 
quadrigeminate  bodies,  and  possibly  some  to  the  medulla  oblongata  and  spinal  cord. 

The  mesial  root  of  the  optic  tract  contains  few  true  visual  fibres.  It  runs  into  the  medial 
geniculate  body,  and  neither  it  nor  this  body  are  appreciably  affected  after  extirpation  of  both 
eyes.  It  may  be  considered  as  largely  representing  the  fibres  of  Gudden's  commissure  (infe- 
rior cerebral  commissure).  This  commissure  consists  of  fibres  which  connect  the  medial  genicu- 
late bodies  of  the  two  sides  with  each  other,  and  which,  instead  of  crossing  the  mid-line  through 
the  mesencephalon,  course  in  the  optic  tracts  and  cross  by  way  of  the  posterior  portion  of  the 
optic  chiasma.  It  consists  of  fibres  which  both  arise  and  terminate  in  each  of  the  bodies,  and, 
therefore,  of  fibres  coursing  in  both  directions.  It  is  also  claimed  that  the  fibres  of  Gudden's 
commissure  connect  the  medial  geniculate  body  of  each  side  with  the  inferior  colliculus  of  the 
opposite  side. 

THE  CEREBEAL  HEMISPHERES 

The  cerebral  hemispheres  in  man  form  by  far  the  largest  part  of  the  central 
nervous  system.  Together,  when  viewed  from  above,  they  present  an  ovoid 
surface,  markedly  convex  upward,  which  corresponds  to  the  inner  surface  of  the 
vault  of  the  cranium.  The  greater  transverse  diameter  of  this  surface'  lies 
posteriorly  in  the  vicinity  of  the  parietal  eminences  of  the  cranium.  The  outline 
of  the  superior  aspect  varies  according  to  the  form  of  the  cranium,  being  more 
spheroidal  in  the  brachycephalic  and  more  ellipsoidal  in  the  dolichocephalic 
forms.  The  hemispheres  are  separated  from  each  other  superiorly  by  a  deep 
median  slit,  the  longitudinal  fissure,  into  which  fits  a  duplication  of  the  inner  layer 
of  the  dura  mater  known  as  the  falx  cerebri.  The  posterior  or  occipital  extrem- 
ities of  the  hemispheres  overlap  the  cerebellum,  and  thus  entirely  conceal  the 
mesencephalon  and  thalamencephalon.  They  are  separated  from  the  superior 
surface  of  the  cerebellum  and  the  corpora  quadrigemina  by  the  deep  transverse 
fissure.  This  is  occupied  by  the  tentorium  cerebelli,  which  is  similar  to  and  con- 
tinuous with  the  falx  cerebri  and  is  connected  with  the  tela  chorioidea  of  the  third 
ventricle  below. 

Each  of  the  hemispheres  is  usually  described  as  having  three  poles  or  projecting 
extremities,  and  three  surfaces  bounded  by  intervening  borders.  The  most 
anterior  projection  is  the  frontal  pole.  This  is  near  the  mid-line,  and  with  its 
fellow  of  the  other  hemisphere,  forms  the  frontal  end  of  the  ovoid  contour  of  the 
cerebrum.  The  occipital  pole  is  the  most  projecting  portion  of  the  posterior  and 
inferior  end,  and  is  more  pointed  than  the  frontal  pole.  The  infero-lateral  por- 
tion of  the  hemisphere  is  separated  anteriorly  by  the  deep  lateral  fissure  (fissure 
of  Sylvius)  into  a  distinct  division,  the  temporal  lobe,  and  the  anterior  portion 
of  this  lobe  projects  prominently  forward  and  is  known  as  the  temporal  pole. 

The  surfaces  of  the  hemisphere  are — (1)  the  lateral  or  convex  surface;  (2)  the 
medial  surface;  and  (3)  the  hasal  surface.  The  convex  surface  comprises  the 
entire  rounded  aspect  of  the  hemisphere  visible  previous  to  manipulation  or 
dissection,  and  is  the  surface  subjacent  to  the  vault  of  the  cranium.  The  mesial 
surface  is  perpendicular,  flat,  and  parallel  with  that  of  the  other  hemisphere,  the 
two  bounding  the  longitudinal  fissure  and  for  the  most  part  in  contact  with  the 
falx  cerebri.  The  superomesial  border  intervenes  between  the  convex  and  medial 
surfaces,  and  is  thus  convex  and  extends  from  the  frontal  to  the  occipital  pole. 

The  more  complex  hasal  surface  fits  into  the  anterior  and  middle  cranial 
fossae,  and  posteriorly  rests  upon  the  tentorium  cerebelh.  Thus  it  is  subdivided 
into — (a)  an  orbital  area,  which  is  slightly  concave,  since  it  is  adapted  to  the 
orbital  plate  of  the  frontal  bone,  and  is  separated  from  the  convex  surface  by  the 
necessarily  arched  superciliary  border  and  from  the  mesial  surface  by  the  medial 
orbital  border,  the  latter  being  straight  and  extending  from  the  frontal  pole 
mesial  to  the  olfactory  bulb  and  tract;  (fo)  a  tentorial  area  or  surface,  which  is  arched 
in  conformity  with  the  dorsal  surface  of  the  cerebellum.  This  is  separated  from 
the  convex  surface  by  the  infero-lateral  border,  which  runs  from  the  occipital  to 
the  temporal  pole;  and  from  the  mesial  surface  by  the  medial  occipital  border, 
which  is  a  more  or  less  rounded  ridge  extending  from  the  occipital  pole  obliquely 
upward  in  the  angle  formed  by  the  junction  of  the  perpendicular  falx  cerebri  and 
the  horizontal  tentorium  cerebeUi.  This  border  is  best  seen  in  brains  which  have 
been  hardened  with  the  membranes  in  situ.  The  remainder  of  the  basal  surface 
includes  the  ojDtic  portion  of  the  hypothalamus  already  considered,  and  the  small 


THE  CORPUS  CALLOSUM 


851 


depressed  and  punctate  area,  the  anterior  perforated  substance,  which  is  pene- 
trated by  the  antero-lateral  group  of  the  central  branches  of  the  anterior  and 
middle  cerebral  arteries  and  into  which  the  striae  of  the  olfactory  trigone  disappear. 
In  addition  to  the  orbital  area  the  basal  surface  of  the  hemisphere  shows  signs  of 
the  impress  of  the  petrous  portion  of  the  temporal  bone  and  of  the  great  wing  of 
the  sphenoid. 

The  corpus  callosum. — In  their  early  development  as  lateral  dilations  of  the 
anterior  primary  brain-vesicles,  the  hemispheres  are  connected  with  each  other 
only  at  the  anterior  end  of  the  thalamencephalon,  where  they  are  both  continuous 
with  the  lamina  terminalis.  As  development  proceeds  and  the  hemispheres 
extend  upward,  backward,  forward,  and  laterally  to  completely  conceal  the  base,, 
and  as  the  palhum,  or  cortex,  thickens  and  its  folds  begin  to  appear,  the  two  hemi- 
spheres become  united  across  the  mid-hne  above  the  thalamencephalon  and  the 
third  ventricle  by  the  inter-growth  of  the  great  cerebral  commissure,  the  corpus 
callosum.     After  removal  of  the  falx  cerebri  from  the  longitudinal  fissure,  the 


Fig.  671. — Mesial  and  Tentorial  Surfaces  op  Right  Cerebral  Hemisphere,  Viewed  from 
THE  Left.    (After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 

Sulcus  oi  corpus  callosum 
Body  of  fornix    J 
Body  of  corpus  callosum         '       '      Thalamus 
Interventricular  foramen  \^,.-»— -«-s..^--''^-w/  Crus  of  fonux 

Cut  surface  of  cerebral  peduncle 


Genu  of  corpus  callosum 


of  corpus  callo 


Columns  of  formx 
Anterior  comnussure/ 
Optic  chiasma 
Columns  of  formx' 
Corpus  mammillare 


'^'  Isthmus  of  gyrus  fornicatus 

^        *  Chorioid  fissure 
,    \  Fimbria 

I         *       Hippocampal  fissure 
1        I      Impressure  for  petrous  bone 
Mammillo-thalamic  fasciculus       Dentate  fascia 


dorsal  surface  of  the  corpus  callosum  'may  be  exposed  by  drawing  apart  the 
contiguous  mesial  surfaces  of  the  hemispheres.  It  consists  of  a  dense  mass  of 
pure  white  substance  coursing  transversely,  and  arises  as  out-growths  from  the 
cortical  cells  of  both  hemispheres.  Thus  it  is  the  great  pathway  which  associates 
the  cortex  of  the  two  sides  of  the  telencephalon.  Only  the  smaller  medial 
portion  of  the  body  lies  free  in  the  floor  of  the  longitudinal  fissure,  by  far  the  greater 
part  being  concealed  in  the  substance  of  the  hemispheres,  where  its  fibres  radiate 
to  and  from  different  localities  of  the  pallium,  forming  the  radiation  of  the  corpus 
callosum.  Its  surface  shows  numerous  transverse  markings,  the  transverse  strice, 
which  indicate  the  course  of  its  component  bundles  of  fibres.  In  addition  there 
may  be  seen  two  delicate,  variable  longitudinal  bands  running  over  its  surface 
on  each  side  of  the  mid-line.  The  medial  longitudinal  stria  {stria  Lancisii) 
runs  close  to  the  median  plane,  around  the  anterior  end  from  the  gyrus  subcallosus 
(fig.  672),  and  over  the  posterior  end  downward  and  lateralward  to  disaiipcai'  in 
the  hippocampal  gyrus  of  the  base  of  the  telencephalon.  The  lateral  longitudinal 
stria  is  more  delicate  than  the  mesial  stria,  courses  lateral  to  the  medial  stria,  and 
can  be  seen  only  within  the  sulcus  of  the  corpus  callosum  (fig.  672).  Both 
striae  are  composed  largely  of  axones  having  to  do  with  the  olfactory  apparatus. 

When  severed  along  the  median  plane,  it  may  be  seen  that  the  anterior  margin 
of  the  corpus  callosum  is  turned  abruptly  downward,  forming  the  genu,  and  that 
this  turn  continues,  so  that  the  tapering  edge  of  the  body  points  posteriorly  and 


852 


THE  NERVOUS  SYSTEM 


constitutes  the  rostrum  (figs.  667,  671).  The  rostrum  is  in  contact  with  the 
lamina  terminalis  of  the  third  ventricle  below  by  a  short,  thin,  dorso-frontal 
continuation  of  this  lamina,  linown  as  the  rostral  lamina.  The  rostral  lamina  may 
be  considered  as  beginning  at  the  anterior  cerebral  commissure  with  the  anterior 
aspect  of  which  it  is  in  contact,  and  extending  to  the  rostrum.  Beginning  with  the 
rostrum  and  genu,  the  corpus  callosum  arches  backward  as  the  body  of  the  corpus 
callosum,  and  ends  over  the  quadrigeminate  region  in  its  rounded,  thickened 
posterior  margin,  the  splenium.  It  is  bounded  above  by  the  sulcus  of  the  corpus 
callosum,  and,  attached  to  its  concave  inferior  surface,  are  the  chorioid  tela  of  the 
third  ventricle,  the  fornix,  the  septum  pellucidum,  and  the  medial  walls  of  the 
lateral  ventricles. 

Each  cerebral  hemisphere  includes — -(1)  a  superficial  and  much  folded  mantle 
or  pallium,  divided  into  lobes  and  gyri,  and  consisting  of  grey  substance,  the 
cortex,  covering  an  abundant  mass  of  white  substance;  (2)  a  modified  portion,  the 


Fig.  672. — Diagram  of  Convex  Surface  of  Right  Ceeebral  Hemisphere  and  Part  of 
Upper  Surface  of  Corpus  Callosum. 
Paramesial  sulcus 

Superior  frontal  sulcus 


M  iddle  frontal  sulcus 
Inferior  frontal  sulcus 
Precentral  sulcus 


Lateral  longitudinal  stria 

Medial  longitudinal  stria 

Corpus  callosum 


Central  sulcus  (Rolandi) 
Postcentral  sulcus 
Lateral  fissure  (Sylvii) 

Intraparietal  sulcus 
.Lateraroccipital  sulcus 
Transverse  occipital  sulcus 


rhinencephalon,  having  especially  to  do  with  the  impulses  brought  in  by  the  olfac- 
tory nerve;  (3)  a  cavity  ,  the  lateral  ventricle;  and  (4)  a  buried  mass  of  grey  sub- 
stance, the  caudate  and  lenticular  nuclei,  which  together  with  the  internal  capsule 
of  white  substance,  are  known  as  the  corpus  striatum. 

Gyri,  fissures,  and  sulci. — The  cerebral  pallium  is  thrown  into  numerous  and 
variable  folds  or  gyri  (convolutions).  These  are  separated  from  each  other  by 
corresponding  furrows,  tlie  deeper  and  most  constant  of  which  are  called  fissures; 
the  remainder,  sulci.  All  the  fissures  and  the  main  sulci  are  named.  There  are, 
however,  numerous  small  and  shallow  sulci  to  which  names  are  seldom  given. 
These  occur  as  short  branches  of  main  sulci  or  as  short,  isolated  furrows  bounding 
small  gyri  which  connect  adjacent  gyri.  These  small  gyri  are  likewise  seldom 
given  individual  names.  They  are  very  variable  both  in  different  specimens  and 
in  the  two  hemispheres  of  the  same  specimen.  Collectively,  they  are  the  so-called 
transitory  gyri  (gyri  transitivi).  Certain  groups  of  them  are  named  according  to 
their  locahty,  such  as  orbital  gyri  and  lateral  occipital  gyri.  Even  the  main  gyri 
[gyri  profundi]  (and  sulci)  are  very  irregular  in  detail.  Some  of  the  main  and 
deeper  fissures  are  considerably  deeper  than  others.  Some  are  infoldings  of  the 
grey  cortex  so  deep  that  a  portion  of  their  course  may  be  indicated  as  slight  bulgings 
in  the  walls  of  the  lateral  ventricles,  e.  g.,  the  hippocampal  and  collateral  fissures. 
While  the  general  surface  pattern  is  similar  for  all  normal  human  brains,  yet  when 
a  detailed  comparison  is  made,  the  given  gyri  of  different  specimens  are  found  to 


LOBES  OF  THE  TELENCEPHALON  853 

vary  greatly.  The  main  gyii  of  the  two  hemispheres  of  the  same  brain,  how- 
ever, are  nearly  alike. 

Origin  of  the  gyri. — The  gjrri  (and  sulci)  are  the  result  of  processes  of  unequal  growth — 
folds  necessarily  resulting  from  the  surface  portion  of  the  hemispheres  increasing  mucli  more 
rapidly  than  the  central  core.  In  the  early  periods  of  fetal  life  the  surfaces  of  the  hemispheres 
are  quite  smooth.  In  many  of  the  smaller  mammals  this  condition  is  retained  throughout  life, 
but  in  the  larger  mammals,  including  man,  as  development  proceeds  the  cerebral  cortex  becomes 
thrown  into  folds.  The  absolute  amount  of  the  grey  substance  of  the  hemispheres  varies  with 
the  bulk  of  the  animal,  and  apparently  with  its  mental  capabihties.  This  is  especially  true  of 
the  cortex,  for  in  the  larger  brains,  and  that  of  man  especially,  by  far  the  greater  amount  of  the 
cerebral  grey  substance  lies  on  the  surface.  Therefore,  in  either  the  growth  or  evolution  of  a 
smaU  animal  into  a  large  one  the  amount  of  cerebral  grey  substance  is  increased,  and  in  this 
increase  the  surface  area  of  the  brain  is  necessarily  enlarged.  It  is  a  geometrical  law  that  in  the 
growth  of  a  body  the  surface  increases  with  the  square,  while  the  volume  increases  with  the 
cube  of  the  diameter.  The  cerebral  hemisphere  is  a  mass  the  increase  of  whose  volume  does  not 
keep  the  required  pace  with  the  increase  of  its  surface  area  or  cortical  layer.  The  white  sub- 
stance which  forms  the  palUum  arises  in  large  measure  as  outgrowths  from  the  cells  of  the 
cortical  layer,  and  thus  it  can  only  increase  in  a  certain  proportion  to  the  grey  substance. 
Therefore,  the  surface  mantle  of  grey  substance  of  a  hemisphere,  enlarged  in  accordance  with  an 
increased  bulk  of  body,  is  greater  than  is  necessary  to  cover  the  surface  of  the  geometrical  figure 
formed  by  the  combined  white  and  grey  substance.  Consequently,  in  order  to  possess  the 
preponderant  amount  of  grey  substance,  the  surface  of  the  hemisphere  is  of  necessity  thrown 
into  folds.  It  follows  also  that  the  thinner  the  cortical  layer  in  proportion  to  the  volume  of 
the  hemisphere,  the  greater  and  more  folded  will  be  the  surface  area.  In  accordance  with  this 
theory  small  animals  have  smooth  or  relatively  smooth  hemispheres,  and  that  independently  of 
their  position  in  the  animal  scale  or  the  amount  of  their  inteUigence,  while  large  animals  have 
convoluted  brains. 

The  sulci  in  general  begin  to  appear  with  the  fifth  month  of  fetal  life,  the  larger  of  them, 
the  fissures,  appearing  first  and  in  a  more  or  less  regular  order.  Up  to  the  fifth  month  the  en- 
cephalon,  due  to  its  rapid  growth,  closely  occupies  the  cranial  capsule.  During  the  fifth  month 
the  cranium  begins  to  grow  more  rapidly  than  the  encephalon,  and  a  space  is  formed  between 
the  cerebrum  and  the  inner  surface  of  the  cranium.  This  space  allows  further  expansion  of  the 
palUura,  and  at  the  time  the  space  is  relatively  greatest  (during  the  sixth  month)  the  form  and 
direction  of  the  principal  gyri  and  sulci  begin  to  be  indicated.  As  growth  proceeds  the  unre- 
stricted expansion  of  the  pallium  results  in  the  gyri  again  approaching  the  wall  of  the  cranium, 
and  during  the  eighth  month  of  fetal  life  they  again  come  in  contact  with  it.  Finally,  the  later 
relative  growth  of  the  cranium  results  in  the  space  found  between  it  and  the  cortex  in  the  adult. 
It  is  obvious  that  the  relation  of  the  cranium  may  be  a  factor  in  the  causation  of  the  gyri,  for 
the  increase  of  surface  area  necessitated  by  the  increased  amount  of  cortical  grey  substance 
might  be  limited  by  a  cranial  cavity  of  small  size.  It  is  probable  that  the  second  contact  of  the 
cortex  with  the  cranium  (during  the  eighth  month)  may  at  least  cause  a  deepening  and  accentua- 
tion of  the  gyri  already  begun.  Evidently  the  form  of  the  cranium  modifies  the  gyri,  and  to  a 
certain  extent  probably  determines  their  direction,  for  in  long,  dolichocephahe  crania  the  an- 
tero-posterior  gyri  are  most  accentuated,  and  in  the  wide,  brachycephalic  crania  the  transverse 
gyri  are  most  marked.  At  birth  all  the  main  fissures  and  sulci  are  present,  but  some  of  the 
smaller  sulci  appear  later.  In  the  growing  pallium  both  the  bottoms  of  the  sulci  as  well  as  the 
summits  of  the  gyri  move  away  from  the  geometrical  center  of  the  hemisphere,  the  summits  more 
rapidly,  and  hence  the  sulci  or  fissures  first  formed  grow  gradually  deeper  as  long  as  growth 
continues. 

The  mechanical  factors  in  the  growth  processes  which  result  in  the  more  or  less  regular 
arrangement  of  the  gyri  of  the  hemispheres  of  a  given  group  of  animals  have  not  been  satis- 
factorily determined.  It  has  been  suggested  that  the  differences  in  arrangement  of  the  gyri  in 
different  groups  of  animals  may  be  in  part  dependent  upon  the  functional  importance  of  the 
various  regions — the  amount  of  grey  substance  of  a  region  varying  with  the  functional  impor- 
tance, and  the  consequent  local  increases  being  accompanied  by  resultant  local  foldings.  This 
idea  is  supported  by  the  fact  that  while  the  soma^sthetic  (sensory-motor)  area  of  the  cortex 
varies  with  the  bullc  of  the  body,  the  frontal  gyri,  so  much  developed  in  man  and  which  are 
one  of  the  chief  regions  of  the  assooiational  phenomena,  are  relatively  independent  of  and  do 
not  vary  with  the  weight  of  either  the  body  or  the  brain. 

Surface  area. — The  total  surface  area  of  the  adult  human  telencephalon  is  about  2300  sq. 
cm.  Of  this  area  almost  exactly  one-third  is  contained  on  the  outer  or  exposed  surfaces  of  the 
gyri,  while  the  other  two-thirds  is  found  in  the  walls  of  the  sulci  and  fissures. 

Lobes  of  the  Telencephalon  and  the  Gyri  and  Sulci 

The  folded  pallium  of  each  hemisphere  is  arbitrarily  divided  into  lobes,  partly 
by  the  use  of  certain  of  the  main  fissures  and  sulci  as  boundaries  and  partly  by  the 
use  of  imaginary  Hues  (figs.  672,  673).  These  divisions  are  sbc  in  number,  them- 
selves subdivided  into  their  component  gyri: — 

(1)  Temporal  lobe. 

(2)  Insula  (Central  lobe  or  Island  of  Reil). 

(3)  Frontal  lobe. 

(4)  Parietal  lobe. 

(5)  Occipital  lobe. 


854 


THE  NERVOUS  SYSTEM 


(6)  Olfactory  brain  or  rhinencephalon  (including  structures  comprised  in  the 
other  lobes  and  often  grouped  under  the  two  names  olfactory  lobe  and  limbic 
lobe) . 

This  division  of  the  cortex  of  the  hemisphere  is  largely  a  merely  topographical 
one.  With  the  exception  of  the  temporal  lobe  and  the  rhinencephalon,  it  has 
little  of  either  morphological  or  functional  value.  The  occipital  lobe  contains  the 
recognised  visual  area  of  the  cortex,  but  this  area,  as  such,  does  not  involve  all  of 
the  lobe.  In  their  functional  significance,  the  frontal  and  parietal  lobes,  especi- 
ally,  overlap  each  other. 

The  temporal  lobe. — This  is  the  first  lobe  whose  demarciition  is  indicated. 
During  the  second  month  of  intra-uterine  life  there  appears  a  slight  depression  on 
the  lateral  aspect  of  the  then  smooth  hemisphere.  As  the  pallium  further  grows, 
this  depression  deepens  into  a  well-marked  fossa  with  a  relatively  broad  floor. 
This  fossa  marks  the  beginning  of  the  lateral  cerebral  fissure  or  fissure  of  Sylvius, 
and  is,  therefore,  known  as  the  Sylvian  fossa.  As  the  pallium  continues  to  project 
outward,  the  folds  which  form  the  margins  of  the  Sylvian  fossa  increase  in  size 
and  height  and  begin  to  overlap  and  conceal  its  broad  floor,  which  is  the  beginning 

Fig.  673. — Diagram  of  the  Convex  Surface  of  the  Left  Cerebral  Hemisphere  showing 

THE  Five  Principal  Lobes  op  the  Pallium. 
The  opercular  regions  of  the  frontal,  parietal,  and  temporal  lobes  are  removed  to  show  the  cen- 
tral lobe  or  island  of  Reil. 
Central  sulcus  (Roland!) 


Parietal  lobe 


Central  lobe  (insula) 


Central  sulcus  of  insula 


of  the  insula.  The  overlapping  folds  thus  become  the  opercula,  and  as  their  lips 
approach  each  other,  there  results  the  deep  fissure  of  Sylvius,  which  marks  off 
anteriorly  an  infero-lateral  limb  of  the  pallium,  termed  by  position  the  temporal 
lobe.  As  growth  proceeds  further,  the  temporal  lobe  thickens,  the  temporal  pole 
extends  further  forward  and  becomes  a  free  projection,  thus  lengthening  the 
fissure  of  Sylvius  and  resulting  in  the  inferior  extension  or  stem  of  this  fissure, 
which  runs  between  the  temporal  pole  and  the  frontal  lobe  and  curves  under  so  as 
to  appear  on  the  basal  surface  of  the  hemisphere.  Finally  the  cortex  of  the  lobe 
itself  is  thrown  into  folds  or  gyri.  Its  posterior  end  is  never  marked  off  from  the 
lobes  above  and  behind,  except  by  arbitrary  fines  which  will  be  mentioned  in  con- 
nection with  those  lobes. 

The  temporal  lobe  forms  part  of  the  lateral  convex  and  tentorial  surfaces  of  the 
hemisphere,  and  its  anterior  portion  is  adapted  to  the  surface  of  the  middle 
cranial  fossa.  It  thus  has  a  superior  and  lateral  surface  and  a  basal  and  tentorial 
surface.  In  these  surfaces  are  the  following  gyri  with  their  intervening  and 
bounding  sulci  (fig.  674) : — 

The  superior  temporal  gyrus  is  bounded  by  the  posterior  ramus  of  the  lateral 
fissure,  and  extends  from  the  temporal  pole  backward  into  the  supra-marginal 
region  of  the  parietal  lobe  above.  The  upper  margin  of  this  gyrus  constitutes  the 
temporal  operculum,  in  that  it  aids  in  overlapping  and  enclosing  the  insula  in  the 
floor  of  the  lateral  fissure.     This  margin  is  for  the  most  part  smooth,  being 


THE  TEMPORAL  LOBE 


855 


occasionally  interrupted  by  a  few  weak  twigs  of  the  lateral  fissure.  It  is  separated 
from  the  gyrus  below  by  the  superior  temporal  sulcus,  which  is  parallel  with  the 
posterior  ramus  of  the  lateral  fissure  and  is  frequently  called  the  parallel  sulcus. 
The  posterior  extremity  of  this  sulcus  divides  the  angular  gyrus  of  the  parietal 
lobe,  and  its  anterior  end  disappears  in  the  temporal  pole,  sometimes  as  a  continu- 
ous groove,  sometimes  in  isolated  pieces. 

The  middle  temporal  gyrus  likewise  begins  in  the  temporal  pole  and  is  con- 
tinuous backward  into  the  angular  gyrus  of  the  parietal  lobe. 

The  inferior  temporal  gyrus  forms  the  infero-lateral  border  of  the  temporal 
lobe,  and  is  usually  more  broken  up  than  the  two  gyri  above  it.  It  begins 
continuous  with  them  in  the  frontal  pole,  and  extends  horizontally  backward  into 
the  lateral  gyri  of  the  occipital  lobe.  It  is  separated  from  the  middle  gyrus  by  the 
middle  temporal  sulcus,  which  likewise  is  never  so  continuous  a  furrow  as  the 
superior  temporal  sulcus.  Frequently  this  sulcus  occurs  in  detached  portions 
and  often  terminates  within  the  temporal  lobe. 


Fig.  674. — Outline  Dkawing  of  Convex  Surface  of  Left  Cerebral  Hemisphere. 

(After  Toldt,  "Atlas  of  Human  .^atomy,"  Rebman,  London  and  New  York.) 

Precentral  sulcus       Central  sulcus  (RolandiJ 

Inferior 
frontal  sulcus\ 

y^  ^  \/^      ^  f  vj? . ^    >      ,^,^ 

Horizontal  ramus " 
of  interparietal 
sulcus 


Superior  ex- 
tremity of 
parieto-occi- 
pital  tissure 


Gyri, 

LpitalesI  Transverse 


Inferior 
frontal 
gyrus 


The  fusiform  gyrus  is  in  the  basal  and  tentorial  surface  of  the  temporal  lobe 
(fig.  676).  Its  usual  somewhat  spindle  shape  suggests  its  name,  and  it  is  con- 
tinuous backward  into  the  occipital  gyri,  or  its  posterior  end  may  be  completely 
isolated  by  a  union  of  the  inferior  temporal  sulcus  and  the  collateral  fissure, 
which  two  furrows  separate  it  from  its  neighbours  on  either  side.  Anteriorly  the 
fusiform  gyrus  runs  into  the  common  substance  of  the  other  three  gyri  at  the 
temporal  pole. 

The  lingual  gyrus  is  usually  included  in  the  tentorial  surface  of  the  temporal 
lobe,  though  in  some  texts  it  is  regarded  as  a  part  of  the  occipital  lobe.  Its  larger, 
posterior  portion  lies  within  the  boundaries  of  the  occipital  lobe.  Bounded 
laterally  by  the  collateral  fissure,  it  is  continuous  anteriorly  into  the  hippocampai 
gyrus  of  the  rhinencephalon  (fig.  676). 

All  of  the  sulci  give  off  occasional  lateral  twigs  {transverse  temporal  sulci)  which 
themselves  may  or  may  not  branch,  and  which  tend  to  divide  the  main  gyri  into 
transverse  temporal  gyri. 

The  lateral  fissure  (fissure  of  Sylvius). — -As  promised  in  its  origin  by  the  over- 
lapping and  enclosing  of  the  broad  floor  of  the  Sylvian  fossa  by  the  adjacent  folds 
of  the  pallium,  the  lateral  fissure  is  the  deepest  and  most  conspicuous  fissure  of 
the  cerebral  hemisphere.  Its  main  divisions  are  a  short  stem  and  three  main 
branches.     The  stem  lies  in  the  basal  surface  of  the  hemisphere,  where  it  begins 


856 


THE  NERVOUS  SYSTEM 


in  a  depression  in  the  anterior  perforated  substance,  the  vallecula  Sylvii,  and  passes 
forward  and  upward  between  and  separating  the  temporal  pole  and  the  super- 
ciliary border  of  the  frontal  lobe.  It  corresponds  in  direction  with  the  posterior 
border  of  the  lesser  wing  of  the  sphenoid  bone,  which  projects  backward  into  it, 
and  it  contains  the  middle  cerebral  artery,  the  Sylvian  vein,  and  the  sinus  alse 
parvse.  It  appears  on  the  upper  surface  at  a  point  known  in  cranial  topography 
as  the  Sylvian  point,  where  it  divides  into  its  three  main  branches : — 

(1)  The  posterior  ramus  is  the  linear  continuation  of  the  fissure,  and  runs 
horizontally  backward  and  upward  to  terminate  in  the  supra-marginal  gyrus  of 
the  parietal  lobe. 

(2)  The  anterior  ascending  ramus  passes  upward  for  about  10  mm.,  sub- 
dividing the  inferior  gyrus  of  the  frontal  lobe. 

(3)  The  anterior  horizontal  ramus  passes  forward  from  the  stem  of  the  fissure 
about  10  mm.,  and  likewise  into  the' inferior  frontal  gyrus,  but  parallel  with  the 
superciliary  border. 


Fig.  675. — The  Insula  with  its  Gtki  and  StrLCi.    (Shown  by  widely  separating  the  opercula.) 

Gyri  breves  ) 

Operculum  '  I  „  t  of  insula 

C^yrus  longus  J 


Circular  sulcus 


Transverse 
-W  — J>    temporal 
"         gyri 


Central  sulcus  of 


Superior  temporal  gyrus 


These  branches,  together  with  certain  smaller  collateral  twigs,  divide  the  over- 
lapping or  opercular  portions  of  the  adjacent  pallium  into  (a)  the  tem-poral  opercu- 
lum, which  lies  below  the  posterior  ramus;  {h)  the  fronto-parietal  operculum,  or 
operculum  proper,  which  lies  above  and  behind  the  anterior  ascending  ramus;  (c) 
the  frontal  operculum,,  between  the  latter  and  the  anterior  horizontal  ramus;  {d) 
and  the  orbital  operculum,  below  the  anterior  horizontal  ramus.  Collectively  the 
opercula  are  known  as  the  opercula  of  the  insula. 

The  insula  (central  lobe). — The  insula  or  island  of  Reil  is  a  triangular  area  of 
the  cerebral  cortex  lying  in  the  floor  of  the  lateral  fissure,  and  concealed  by  the 
opercula.  Of  these,  the  temporal  operculum  overlaps  the  insula  to  a  greater 
extent  than  either  the  frontal  or  parietal.  More  than  half  of  it  may,  therefore, 
be  exposed,  by  gently  pressing  away  the  temporal  lobe.  The  insula  corresponds 
to  the  broad  floor  of  the  Sylvian  fossa  of  the  embryonic  brain.  In  the  developed 
condition  its  surface  is  convex  lateralward  and  is  itself  folded  into  gyri.  The  apex 
of  the  triangle  appears  upon  the  basal  surface  of  the  hemisphere,  and  is  the  only 
portion  which  may  be  seen  without  disturbing  the  specimen.  The  apex  appears 
as  the  end  of  a  small  gyrus  under  the  temporal  pole,  and  in  close  relation  with  the 


THE  FRONTAL  LOBE 


857 


anterior  perforated  substance  and  the  vallecula  Sylvii,  and  is  known  as  the 
limen  of  the  insula.  In  the  folding  process  by  which  the  opercula  accomplish 
the  overlapping  and  enclosing  of  the  island,  there  results  a  deep  sulcus  which  sur- 
rounds its  entire  area  except  at  the  limen  insulse.  This  is  known  as  the  circular 
sulcus,  or  limiting  sulcus  of  Reil.  The  gyri  (and  sulci)  of  the  insula  radiate  from 
the  apex  of  the  triangle.  The  central  sulcus  of  the  insula  is  the  deepest.  It  runs 
from  below  backward  and  upward,  parallel  with  the  central  sulcus  of  Rolando 
above  and  divides  the  insula  into  a  larger  anterior  and  a  smaller  posterior  portion. 
The  anterior  portion  consists  of  from  three  to  five  short  irregular  gyri  breves  or 
precentral  gyri,  separated  by  sulci  brevis ;  the  posterior  portion  consists  of  a  single, 
slightly  furrowed  gyrus,  which  is  long  and  arched  and  extends  from  the  apex  to 
the  base  of  tlTe  triangle,  the  gyrus  longus. 

In  a  recent  study  of  the  insula  of  more  than  200  human  brains,  including  a  few  of  idiots 
and  paralytics  and  a  series  of  young  fcetuses,  Nelidoff  finds  that  the  left  island  is  more  deeply 
marked  by  sulci  and  averages  11  mm.  longer  than  the  right;  that,  of  the  sulci  in  the  island,  the 
central  sulcus  is  the  first  to  appear,  is  the  most  persistent  sulcus  in  defective  brains,  though 
occasionally  absent  in  microcephalic  idiots,  and  that  in  the  average  it  is  more  pronounced 
in  males  than  in  females. 

The  frontal  lobe. — This  is  the  most  anterior  of  the  lobes  of  the  hemisphere, 
and  hke  the  two  lobes  behind,  it  has  a  convex  or  lateral,  a  basal,  and  a  mesial 
surface.  The  convex  surface  begins  with  the  frontal  pole,  and  is  bounded 
posteriorly  by  the  central  sulcus  {Rolandi).  The  basal  surface  extends  backward 
to  the  stem  of  the  lateral  fissure,  covered  by  the  frontal  pole.  The  mesial  surface 
is  separated  from  the  gyrus  cinguli  of  the  rhinencephalon  (limbic  lobe)  by  the  sub- 
frontal  part  of  the  sulcus  cinguli  (calloso-marginal  fissure),  and  from  the  parietal 
lobe  by  a  line  drawn  perpendicularly  from  the  upper  extremity  of  the  central 
sulcus  (Rolandi)  to  the  sulcus  cinguli.  These  surfaces  include  the  following  gyri 
and  sulci: — • 


Convex 
surface 


Basal 
surface 


Mesial 
surface 


Gyri. 

Anterior  central  gyrus. 
Superior  frontal  gyrus. 

Middle  frontal  gyrus  < 
Inferior  frontal  gyrus  \ 


Sulci. 


Precentral  sulcus 


Superior  portion. 
Inferior  portion. 
Opercular  portion. 
Triangular  portion. 
Orbital  portion. 


Orbital  gyri 


Lateral. 

Anterior. 

Posterior. 

Medial. 
Gyrus  rectus. 
Superior  frontal  gyrus. 
Marginal  gyrus. 
Paracentral  lobule  (anterior  part). 


Superior. 
Inferior. 
Superior  frontal  sulcus. 
Middle  frontal  sulcus. 
Inferior  frontal  sulcus. 
Anterior  ascending  ramus  of  lateral 

fissure. 
Anterior  horizontal  ramus  of  lat- 
eral fissure. 

Lateral. 
Orbital  sulci  \   Medial. 

Transverse. 

Olfactory  sulcus. 


Rostral  sulci. 

Many  of  the  sulci,  especially  the  superior  frontal  and  the  rostral  sulci,  often 
give  off  twigs  or  are  broken  up  into  short  furrows  which  give  rise  to  small  folds 
[gyri  transitivi],  too  inconstant  to  be  given  special  names. 

The  anterior  central  gyrus  (ascending  frontal  convolution)  is  the  only  gyrus 
of  the  frontal  lobe  having  a  vertical  direction.  It  lies  parallel  to  the  central  sulcus 
(Rolandi),  and  thus  extends  obliquely  across  the  convex  surface  from  the  posterior 
ramus  of  the  lateral  fissure  (frontal  operculum)  to  the  supero-mesial  border,  and  is 
continuous  on  the  mesial  surface  with  the  anterior  portion  of  the  para-central 
lobule.  It  comprises  the  larger  part  of  the  motor  portion  of  the  somsesthetic 
(sensory-motor)  area  of  the  cerebral  cortex.  It  is  separated  from  the  horizontal 
frontal  gyri  in  front  of  it  by  the  precentral  sulcus. 

This  sulcus  is  developed  in  three  parts,  but  the  upper  and  middle  parts  in  the  foetal  brain 
usually  fuse  together,  so  that  in  the  later  condition  it  consists  of  a  superior  and  an  inferior 
segment.  The  superior  cuts  the  supero-mesial  border  of  the  hemisphere  and  appears  on  the 
mesial  surface  in  the  paracentral  lobule.  On  the  convex  surface  it  is  usually  cormected  with  the 
posterior  end  of  the  superior  frontal  sulcus  (fig.  674). 

The  superior  frontal  gyrus  is  a  relatively  broad,  uneven  convolution,  com- 
prising the  anterior  portion  of  the  supero-mesial  border  of  the  hemisphere,  and 
therefore  extends  horizontally  from  the  precentral  sulcus  to  the  frontal  pole.  It 
is  sometimes  inperfectly  divided  into  a  superior  and  an  inferior  part  by  a  series  of 


858  THE  NERVOUS  SYSTEM 

detached,  irregular  furrows,  spoken  of  collectively  as  the  para-medial  sulcus. 
The  resulting  transitory  gyri  are  of  considerable  interest  in  that  they  are  peculiar 
to  the  human  brain,  and  are  said  to  be  more  marked  in  the  higher  than  in  the 
lower  types. 

The  middle  frontal  gyrus  is  likewise  a  broad  strip  of  pallium  extending  from 
the  precentral  sulcus  to  the  temporal  pole.  It  is  separated  from  the  superior 
frontal  gyrus  by  the  superior  frontal  sulcus,  which  is  usually  continuous  into  the 
superior  section  of  the  precentral  sulcus  and  thence  extends  horizontally  to  the 
frontal  pole.  The  middle  frontal  gyrus  is  in  most  cases  subdivided  anteriorly 
into  a  superior  and  an  inferior  portioii  by  a  middle  frontal  sulcus.  This  sulcus  begins 
above  and  runs  into  the  frontal  pole,  where,  upon  reaching  the  superciliary  border, 
it  frequently  bifurcates  into  a  transverse  furrow,  known  as  the  Jronto-marginal 
sulcus. 

The  inferior  frontal  gyrus  forms  the  superior  wall  of  the  lateral  fissure,  and  is 
separated  from  the  middle  frontal  gyrus  by  the  inferior  frontal  sulcus.  This 
sulcus  usually  begins  continuous  with  the  inferior  section  of  the  precentral  sulcus, 
and  extends,  very  irregularly  and  frequently  interrupted,  toward  the  frontal  pole. 
The  gyrus  abuts  upon  the  anterior  central  gyrus,  and  its  posterior  portion  is 
divided  into  three  parts  (the  frontal  opercula)  by  the  anterior  ascending  and 
horizontal  rami  of  the  lateral  fissure.  The  part  behind  the  anterior  ascending 
ramus  is  the  opercular  portion  (a  part  of  the  fronto-parietal  operculum  or  opercu- 
lum proper),  sometimes  referred  to  as  the  basilar  portion.  In  most  brains  this 
part  is  traversed  by  a  short  oblique  furrow,  the  diagonal  sulcus.  The  part  be- 
tween the  two  anterior  rami  of  the  lateral  fissure  is  the  cap-shaped  triangular 
portion.  This  portion  frequently  involves  one  and  sometimes  two  descending 
twigs  of  the  inferior  frontal  sulcus.  The  part  below  the  anterior  horizontal  ramus 
is  by  position  the  orbital  portion. 

It  is  seen  that  the  inferior  frontal  gyrus  gives  rise  to  the  whole  of  the  frontal  operculum  and 
the  antei'ior  half  of  the  fronto-parietal  operculum.  The  opercular  portion  is  of  special  interest 
in  that  in  the  left  hemisphere  it  constitutes  the  celebrated  convolution  of  Broca,  the  motor  area 
for  the  function  of  speech.  The  area  controlling  speech,  however,  involves  that  part  of  the 
triangular  portion  bounding  the  anterior  ascending  ramus  of  the  lateral  fissure  as  well,  and 
both  these  parts  often  appear  more  developed  on  the  left  hemisphere.  The  development  of 
the  opercula  of  the  inferior  frontal  gyrus  is  a  distinctive  characteristic  of  the  human  brain. 
This  gyrus  does  not  develop  opercula  even  in  the  highest  varieties  of  apes.  The  development  of 
the  function  of  speech  in  man  no  doubt  influences  the  development  of  the  frontal  opercula. 

On  the  basal  surface  (fig.  676)  of  the  frontal  lobe  is  the  orbital  area  and  the 
gyrus  rectus.  The  more  pronounced  of  the  orbital  sulci  are  often  so  joined  with 
each  other  as  to  form  an  H-shaped  figure  standing  parallel  to  the  mesial  plane, 
and  thus  they  comprise  a  medial,  a  lateral  and  a  transverse  orbtial  sulcus. 
This  figure  naturally  divides  the  orbital  area  into  four  gyri: — (1)  The  lateral 
orbital  gyrus  is  tlie  basal  continuation  of  the  inferior  frontal  gyrus,  and  is  thus 
related  to  the  orbital  portion  of  the  frontal  operculum;  (2)  the  anterior  orbital 
gyrus  is  continuous  at  the  pole  with  the  middle  frontal  gyrus;  (3)  the  posterior 
orbital  gyrus  is  closely  related  to  the  limen  insulse  and  the  stem  of  the  lateral 
fissure,  and  its  outer  part  is  in  relation  with  the  orbital  portion  of  the  operculum ; 
(4)  the  medial  orbital  gyrus  is  continuous  over  the  superciliarj^  border  with  the 
superior  frontal  gyrus.  It  frequently  contains  one  or  two  short,  isolated  sulci. 
Its  mesial  boundary  is  the  straight  olfactory  sulcus,  in  which  lies  the  olfactory 
bulb  and  tract  of  the  rhinencephalon.  This  sulcus  marks  off  a  narrow  straight 
strip  of  cortex  between  it  and  the  mesial  border  of  the  lobe  known  as  the  gyrus 
rectus.  The  posterior  portion  of  the  gyrus  rectus  comprises  a  part  of  the  parol- 
factory area  or  Broca's  area,  which  functionally  belongs  to  the  rhinencephalon. 
As  an  area  or  field,  this  appears  mesially  lying  between  the  anterior  and  posterior 
parolfactory  sulci. 

On  the  mesial  surface  (fig.  679),  of  the  frontal  lobe  the  superior  frontal  gyrus  is 
separated  from  the  gyrus  cinguli  of  the  rhinencephalon  (limbic  lobe)  by  the  well- 
marked  sulcus  cinguli.  Anteriorly  the  superior  frontal  gyrus  is  subdivided  by  the 
main  stem  of  the  rostral  sulci  into  a  marginal  gyrus,  and  what  may  be  termed  a 
sub'marginal  gyrus.  The  marginal  gyrus  is  usually  broken  into  smaller  parts  by 
twifi's  of  the  rostral  sulci,  most  of  which  are  perpendicular  to  the  main  stem,  while 
the  submargJnal  gyrus  is  less  frequently  interrupted.  Posteriorly  the  superior 
frontal  gyrus  constitutes  the  anterior  portion  of  the  paracentral  lobide,  a  part  of 


THE  CENTRAL  SULCUS 


859 


the  somsesthetic  area  of  the  mesial  surface  of  the  hemisphere.     This  lobule  is 
usually  marked  off  anteriorly  by  a  vertical  twig  from  the  sulcus  cinguli. 

The  sulcus  cinguli  (calloso-marginal  fissure)  is  the  longest  and  one  of  the  most 
prominent  sulci  on  the  mesial  surface  of  the  hemisphere.  It  divides  the  anterior 
portion  of  the  mesial  surface  into  a  marginal  part  above  and  a  callosal  part  below 
— in  other  words,  it  separates  the  superior  frontal  gyrus  from  the  gyrus  cinguli. 
Its  subfrontal  portion  begins  below  the  rostrum  of  the  corpus  callosum  and  curves 
forward  and  upward  around  the  genu,  and  then  turns  backward  above  the  body 
of  the  corpus  callosum.  Before  it  reaches  the  level  of  the  splenium,  it  turns  up- 
ward and  cuts  and  terminates  in  the  supero-mesial  border  of  the  hemisphere,  as 
the  next  sulcus  behind  the  upper  termination  of  the  central  sulcus.     This  upward 

Fig.  676. — Basal  Surface  of  the  Cehebbal  Hemisphebes.     (After  Toldt,  "Atlas  of  Human 
Anatomy,"  Rebman,  London  and  New  York.) 
Longitudinal  fissure 


Frontal  pol 
Olfactory  sulcus 
Orbital  sulci 


Olfactory  bulb 

Olfactory  tract 


Medial,  intermediate,  and 
lateral  olfactory  strige 


Temporal  pole 
Olfactory  trigone^  I    ^ 

Optic  chiasma  ~4-A^ 
Chorioid  fissure     -^[ 
Collateral  fissure 


Isthmus  of  gyrus  fornicatus 


Substantia  nigra 


Tegmentum  of 
mesencephalon 


Gyrus  fornicatus 


Occipital  pole 


Aquseductus  cerebri 
(Sylvu) 


Lamina  quadrigemina 
of  corpus  callosum 


Longitudinal  fissure 


turn  is  the  marginal  portion  of  the  sulcus  cinguli.  It  is  sometimes  an  abrupt 
curve  and  sometimes  curves  gradually,  but  its  marginal  relation  to  the  upper  end 
of  the  central  sulcus  is  so  constant  that  it  serves  as  a  means  by  which  either  of  the 
sulci  may  be  identified.  The  marginal  portion  separates  the  paracentral  lobule 
from  the  precuneus  (quadrate  lobule),  and  is  wholly  within  the  parietal  lobe. 
One  of  the  most  constant  twigs  of  the  sulcus  cinguli  is  that  which  marks  off  the 
paracentral  lobule  from  the  superior  frontal  gyrus.  Another  sometimes  divides 
the  paracentral  lobule  into  its  frontal  and  parietal  portions. 

The  sulcus  cinguli  is  developed  from  two  and  sometimes  three  (anterior,  middle,  and  pos- 
terior) separate  furrows,  which  later  extend  and  fuse  into  continuity.  This  metliod  of  its 
development  may  explain  the  irregularities  frequently  met  with  and  the  fact  that  sometimes 
in  the  adult  the  sulcus  occurs  in  separate  pieces. 

The  central  sulcus  (fissure  of  Rolando)  (figs.  674, 678)  is  one  of  the  principal  land- 
marks of  the  convex  surface  of  the  hemisphere.  It  separates  the  frontal  from  the 
parietal  lobe,  and  likewise  divides  the  somsesthetic  area  of  the  palUum.     Its 


860  THE  NERVOUS  SYSTEM 

upper  end  terminates  in  and  usually  cuts  the  supero-mesial  border  of  the  hemis- 
phere immediately  in  front  of  the  termination  of  the  marginal  portion  of  the  sulcus 
cinguli.  Thence  it  pursues  an  oblique  though  sinuous  course  forward  across  the 
convex  surface  of  the  hemisphere,  forming  on  the  average  an  angle  of  about  72° 
with  the  supero-mesial  border  (Rolandic  angle),  and  terminates  in  the  fronto- 
parietal operculum  immediately  above  the  posterior  ramus,  and  about  2.5  cm.  be- 
hind the  point  of  origin  of  the  anterior  rami  of  the  lateral  fissure.  It  rarely  cuts 
through  the  fronto-parietal  operculum.  In  its  sinuous  course,  varying  from  the 
line  of  its  supero-mesial  end,  two  bends  are  marked  (fig.  677) : — (1)  The  superior 
genu  occurs  at  about  the  junction  of  the  upper  and  middle  thirds  of  the  sulcus  and 
is  concave  forward.  It  accommodates  the  greater  part  of  that  portion  of  the  cor- 
tex which  is  the  motor  area  for  the  muscles  of  the  leg  and  trunk,  and  the  develop- 
ment of  this  area  in  man  probably  aids  in  producing  it.  (2)  The  inferior  genu 
occurs  below,  is  concave  forward  and  is  commonly  a  little  more  marked  than  the 
superior  genu.  It  is  probably  in  part  a  result  of  the  superior  genu — the  turn  of  the 
sulcus  in  resuming  its  general  course,  but  it  may  further  result  from  the  develop- 
ment of  the  shoulder  and  arm  area  of  the  cortex  which  occupies  its  concavity. 

Fig.  677. — Diagram  Representing  the  Most  Common  Form  of  the  Central  Sulcus  and 
Indicating  the  Regions  of  Junction  upon  it  of  the  Areas  of  the  Peecenteal  Gyrus 
Devoted  to  the  Dipfeeent  Regions  of  the  Body,  as  Estimated  by  Symington  and 
Crymble. 

Superior-mesial  border  of   hemisphere '         ^''''  ^^ 


Regionof  junctionof  legand  trunk  areas 

Region  of  junction  of  trunli  and 


Lateral  end  of  sulcus  , 
Operculum 


The  central  sulcus  (Rolandi)  appears  in  the  pallium  of  the  fcetus  during  the  latter  part  of 
the  fifth  month.  It  then  consists  of  a  lower  longer  and  an  upper  shorter  part.  Usually  these 
two  parts  become  continuous  before  birth;  very  rarely  do  they  remain  separate  in  the  adult. 
The  point  of  their  fusion  is  sometimes  manifest  within  the  depth  of  the  sulcus.  If  the  lips  of 
the  sulcus  be  pressed  widely  apart  at  about  the  region  of  the  junction  of  its  middle  and  upper 
thirds,  it  will  be  found  that  the  opposing  walls  give  off  a  number  of  protuberances  or  lateral  gyri, 
which  dovetail  into  each  other  when  the  sulcus  is  closed.  Sometimes  two  of  these  lateral  gyri 
appear  fused  across  the  floor  of  the  sulcus,  so  as  to  form  a  bridge  of  grey  substance  known  as  the 
deep  annectant  gyrus.  This  interruption  of  the  continuity  of  the  sulcus,  when  present,  repre- 
sents the  point  at  which  the  two  parts  of  the  sulcus  in  the  fcctal  brain  joined  each  other  without 
the  continuity  becoming  wholly  completed  in  the  adult.  The  genua  of  the  adult  sulcus  may 
often  be  due  to  the  precedent  parts  not  being  ia  hne  at  the  time  of  their  fusion. 

From  a  special  study  of  the  central  sulcus  of  237  normal  adult  hemispheres,  Symington 
and  Crymble  (1913)  give  the  following  details:  (1)  that  the  most  common  course  of  the  sulcus 
is  that  illustrated  in  fig.  677,  above;  (2)  that  it  varies  in  depth  both  in  a  given  specimen  and  in 
different  specimens — the  greatest  variations  in  depth  reported  for  a  given  sulcus  being  from 
22  to  12  millimeters,  the  shallowest  part  being  in  the  region  of  the  deep  annectant  gyrus;  (3) 
that  the  average  length  from  the  supero-mesial  border  of  the  hemisphere  to  the  opercular 
end  of  the  sulcus  is  about  9  cm.  in  direct  line  and  10.4  cm.  following  the  curves  of  the  sulcus. 
The  average  length  of  the  curved  floor  is  7.9  cm.  (4)  From  the  supro-meisal  end  of  the  sulcus 
to  the  points  of  junction  of  the  general  areas  of  the  precentral  gyrus,  direct  line  measurements 
give  averages,  (a)  to  the  junction  of  leg  and  trunk  areas,  3.5  cm.;  (b)  to  junction  of  trunk  and 
arm  areas,  4.5  cm.;  (c)  to  junction  of  arm  and  face  areas,  7.5  cm. 

The  parietal  lobe. — The  parietal  lobe  occupies  a  somewhat  smaller  area  of 
the  human  telencephalon  than  either  the  frontal  or  the  temporal  lobe.  It  has  a 
convex  and  a  mesial  surface,  but  no  basal  surface.  It  is  separated  from  the 
frontal  lobe  in  front  by  the  central  sulcus;  from  the  occipital  lobe  behind,  on  the 
mesial  surface  by  the  parieto-occi-pital  fissure  (fig.  650),  and,  on  the  convex  surface, 


THE  PARIETAL  LOBE 


861 


by  an  arbitrary  line  drawn  transversely  around  the  convex  surface  of  the  hemi- 
sphere from  the  superior  extremity  of  this  fissure  to  the  infero-lateral  border; 
and  it  is  separated  from  the  temporal  lobe  below  by  the  horizontal  part  of  the 
posterior  ramus  of  the  lateral  fissure,  and  by  a  line  drawn  in  continuity  with  this 
horizontal  part  to  intersect  the  transverse  line  drawn  to  limit  it  from  the  occipital 
lobe. 

.  The  preoccipital  notch. — In  situ,  the  infero-lateral  border  of  the  posterior  portion  of  the 
hemisphere  rests  over  a  small  portion  of  the  parieto-mastoid  suture  of  the  cranium,  and  upon 
this  structure  occurs  a  fold  or  vertical  thickening  of  the  dura  mater,  which  slightly  indents  the 
infero-lateral  border.  This  indentation  occurs  about  4  cm.  from  the  occipital  pole,  and  is  con- 
sidered one  of  the  points  of  hmitation  of  the  parietal  from  the  occipital  lobe,  and  is  therefore 
called  the  preoccipital  notch.  While  during  late  foetal  Ufe  and  early  childhood  it  is  well  marked, 
it  is  usually  very  shght  in  the  adult  bram,  and  is,  as  a  rule,  evident  only  in  brains  hardened 

Fig.  678. — Convex  Surface  of  the  Cerebral  Hemispheres  as  Viewed  prom  Above. 
(After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 

Frontal  pole 


Supero-mesial  border 


^5^-   Longitudinal  fissure 


Precentral  sulcus 


Central  sulcus 


Interparietal  sulc 


Superior  occipital  sulci 


,^  Occipital  pole 


in  situ.  When  it  is  visible,  the  arbitrary  transverse  line  from  the  superior  extremity  of  the 
parieto-occipital  fissure,  used  as  a  boundary,  between  the  convex  surfaces  of  the  parietal  and 
occipital  lobes,  should  be  so  drawn  as  to  bisect  the  preoccipital  notch. 

The  convex  surface  of  the  parietal  lobe  comprises  the  following  gyri  and  sulci : — 
The  posterior  central  gyrus  (ascending  parietal)  extends  obliquely  across  the 
hemisphere  parallel  with  the  anterior  central  gyrus  of  the  frontal  lobe,  from  which 
it  is  separated  by  the  central  sulcus.  Its  inferior  end  is  bounded  by  the  posterior 
ramus  of  the  lateral  fissure,  and  constitutes  the  posterior  or  parietal  portion  of  the 
fronto-parietal  operculum.  Its  upper  end  takes  part  in  the  supero-mesial 
border  of  the  hemisphere,  and  is  bounded  posteriorly  by  the  tip  end  of  the 
marginal  portion  of  the  sulcus  cinguli.  Its  postero-lateral  boundary  consists 
of  the  two  more  or  less  vertical  rami  or  factors  of  the  interparietal  sulcus,  viz.,  the 
inferior  and  superior  portions  of  the  postcentral  sulcus,  either  continuous  -nith  each 
other  or  detached. 

The  interparietal  sulcus  (intraparietal)  is  often  the  most  complicated  sulcus 
of  the  pallium.  Its  development  usually  begins  as  four  different  furrows  in  the 
foetal  brain,  and  the  difficulty  with  which  it  is  traced  in  the  adult  brain  depends 


862 


THE  NERVOUS  SYSTEM 


upon  the  extent  to  which  these  four  factors  become  continuous  in  the  later  de- 
velopment. When  continuity  of  the  furrows  is  well  established,  the  entire  sulcus 
may  be  described  as  consisting  of  a  convex  horizontal  ramus,  which  gives  off  a  few 
short  collateral  twigs  and  wliose  either  end  is  in  the  form  of  an  irregular,  reclining 
-\ .  The  transverse  bar  of  the  anterior  end  arises  fron  two  of  the  four  factors  of 
the  entire  sulcus: — (1)  an  inferior  furrow,  the  inferior  postcentral  sulcus,  commenc- 
ing above  the  posterior  ramus  of  the  lateral  fissure  and  ascending  as  the  boundary 
of  the  lower  half  of  the  posterior  central  gyrus,  and  (2)  a  superior  furrow,  the 
superior  postcentral  sulcus,  lying  behind  the  upper  portion  of  the  posterior  central 
gyrus,  and  which,  upon  approaching  the  supero-mesial  border,  may  turn  back- 
ward a  short  distance  parallel  with  the  horizontal  ramus,  as  in  fig.  674.  When 
confluent,  these  two  factors  form  together  a  continuous  postcentral  sulcus. 
In  the  adult  the  inferior  of  the  two  is  always  continuous  with  the  horizontal 
ramus;  when  confluent,  the  two  figures  join  so  as  to  form  the  transverse  bar  of 
the  anterior  end  of  this  ramus.     The  horizontal  ramus,  which  represents  the 

Fig.  679. — Outline  Drawing  op  Mesial  Surface  of  Left  Cerebral  Hemisphere. 
(After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 


Sulcus  cinguli  (marginal  portion) 


Parieto-occipital  fissun 
Calcarine  fissure 


Sulcus  cinguli  (subfrontal  portion) 


Sulcus  corporis  callosi 


'.  Genu  of  corpus  callosum 

\    \       \      Rostum  of  corpus  callosum 
,    v^   \    Anterior  parolfactory  sulcus 
\  \  Parolfactory  area  (Broca's  area) 
\  Posterior  parolfactory  sulcus 
Sub-callosal  gyrus  (peduncle  of 
/  corpus  callosum) 

Tuber  cinereum  Infundibulum 

third  of  the  primary  furrows,  is  continued  backward  past  the  superior  extremity 
of  the  parieto-occipital  fissure  into  the  occipital  lobe,  where  it  usually  joins  the 
occipital  ramus,  the  fourth  of  the  primary  furrows.  This  ramus  divides  shortly 
into  two  branches  which  run  at  right  angles  to  the  stem,  forming  the  transverse 
occipital  sulcus,  and  thus  arises  the  transverse  bar  of  the  posterior  end  of  the  inter- 
parietal sulcus.  The  occipital  ramus  may,  however,  consist  of  little  more  than 
the  transverse  bar,  which  may  or  may  not  be  joined  by  the  horizontal  ramus. 
The  occipital  ram.us  is  more  frequently  separate  from  the  horizontal  than  is  the 
postcentral  sulcus.  In  their  development  the  inferior  postcentral  sulcus  appears 
first  (during  the  latter  part  of  the  sixth  month),  the  occipital  ramus  second,  the 
horizontal  ramus  third,  and  last,  the  superior  postcentral  sulcus. 

The  superior  parietal  lobule  (gyrus)  is  the  area  of  the  supero-mesial  border 
of  the  parietal  lobe.  It  is  limited  in  front  by  the  superior  postcentral  sulcus, 
below  by  the  horizontal  ramus  of  the  interparietal  sulcus,  and  posteriorly  it  is 
continuous  around  the  superior  end  of  the  parieto-occipital  fissure  into  the  cortex 
of  the  occipital  lobe.  It  is  a  relatively  wide  area  (lobule),' always  invaded  by 
collateral  twigs  of  its  limiting  sulci,  and  usually  contains  a  few  short,  isolated 
furrows.  When  the  parieto-occipital  fissure  is  considerably  prolonged  over  the 
supero-mesial  border  (external  parieto-occipital  fissure),  the  continuation  of  the 


THE  OCCIPITAL  LOBE  863 

lobule  about  the  end  of  this  fissure  presents  the  appearance  described  as  the 
parieto-occipital  arch. 

The  inferior  parietal  lobule  is  limited  in  front  by  the  inferior  postcentral 
sulcus,  and  above  by  the  horizontal  ramus  of  the  interparietal  sulcus.  It  is  con- 
tinuous with  the  cortex  of  the  temporal  lobe  below,  and  with  that  of  the  occipital 
lobe  behind,  and  is  therefore  invaded  by  the  ends  of  the  sulci  belonging  to  these 
lobes.  Its  anterior  portion  is  separated  from  the  temporal  lobe  by  the  horizontal 
portion  of  the  posterior  ramus  of  the  lateral  fissure.  The  upturned  end  of  this 
ramus  invades  the  anterior  portion  of  the  lobule  and  the  broad  fold,  arched  around 
this  end  and  continuous  behind  it  into  the  superior  temporal  gyrus,  is  known  as 
the  supramarginal  gryus — the  area  to  which  auditory  word-  and  tone-images  are 
attributed.  The  angular  gyrus  is  the  portion  which  embraces  the  posterior  end 
of  the  superior  temporal  sulcus,  and  is  continuous  behind  this  into  the  middle 
temporal  gyrus  and  in  front  with  the  superior  temporal  gyrus.  It  is  the  area  for 
visual  word  images.  Its  shape  is  usually  such  as  to  suggest  its  name.  The  most 
posterior  part  of  the  inferior  parietal  lobule,  when  arching  in  a  similar  way  about 
the  end  of  the  middle  temporal  sulcus  and  continuous  with  the  temporal  gyri 
on  its  either  side,  is  known  as  the  post -parietal  gyrus.  This  is  a  smaller  area  than 
either  of  the  other  two,  and,  owing  to  the  variability  of  the  end  of  the  middle  tem- 
poral sulcus,  is  not  always  evident. 

The  mesial  surface  of  the  parietal  lobe  is  divided  into  two  parts  by  the  marginal 
portion  of  the  sulcus  cinguli.  The  anterior  and  smaller  part  is  the  mesial  con- 
tinuation of  the  posterior  central  gyrus,  and  comprises  the  posterior  portion  of 
the  paracentral  lobule.  It  is  limited  from  the  part  of  this  lobule  belonging  to  the 
frontal  lobe  by  a  vertical  line  drawn  from  the  marginal  extremity  of  the  central 
sulcus.  The  praecuneus  {quadrate  lobule)  is  the  posterior  and  larger  part  of  the 
mesial  surface  of  the  parietal  lobe.  It  is  separatd  from  the  cuneus  of  the  occipital 
lobe  by  the  parieto-occipital  fissure,  and  is  imperfectly  separated  from  the  gyrus 
cinguli  (limbic  lobe)  below  by  the  sub-parietal  sulcus  (postlimbic  fissure),  branches 
of  which  invade  it  extensively. 

The  occipital  lobe. — This  is  a  relatively  small,  trifacial,  pyramidal  segment, 
comprising  the  posterior  extremity  of  the  hemisphere,  its  apex  being  the  occipital 
pole.  Though  one  of  the  natural  divisions  of  the  cerebral  hemisphere,  it  is  very 
indefinitely  marked  off  from  the  lobes  anterior  to  it.  Though  it  contains  the 
cortical  area  of  the  visual  apparatus,  only  in  the  brains  of  man  and  the  apes  does 
it  occur  as  a  well-defined  posterior  projection.  In  most  of  the  mammalia  it  is 
not  differentiated  at  all.  Its  three  surfaces  comprise  a  convex,  a  mesial,  and  a 
tentorial  surface. 

Its  convex  surface  is  separated  from  that  of  the  parietal  and  temporal  lobes  by 
the  superior  and  external  extremity  of  the  parieto-occipital  fissure,  and  by  an 
arbitrary  line  drawn  transversely  from  this  extremity  to  the  infero-lateral  border 
of  the  hemisphere,  or  so  drawn  as  to  bisect  the  pre-occipital  notch  when  this  is 
evident.  The  sulci  which  occur  on  the  convex  surface  may  be  described  as  two, 
though  both  of  these  are  very  variable  in  their  e.xtent  and  shape,  and  their 
branches  are  inconstant  both  as  to  number  and  length.  (1)  the  transverse  oc- 
cipital sulcus  is  the  most  constant  in  shape.  It  extends  a  variable  distance 
transversely  across  the  superior  portion  of  the  lobe,  and,  as  noted  above,  it  is 
frequently  continuous  with  the  interparietal  sulcus  through  its  occipital  ramus, 
and  when  so,  it  appears  as  the  posterior  terminal  bifurcation  of  this  sulcus 
(fig.  674).  When  detached,  it  often  occurs  merely  as  a  definite  furrow  with  few 
rami,  and  sometimes  the  ramus  by  which  it  otherwise  would  join  the  inter- 
parietal sulcus  is  entirely  absent.  (2)  The  lateral  occipital  sulcus  is  always 
short,  and  has  its  deepest  portion  below  the  transverse  sulcus.  It  usually  has  a 
somewhat  oblique  course  toward  the  supero-mesial  border.  Sometimes  it  occurs 
in  several  detached  pieces,  then  known  collectively  as  the  lateral  occipital  sulci. 

Therefore,  the  gyri  of  the  convex  surface  of  the  lobe  are  also  variable.  They  are  not 
sufficiently  constant  to  merit  individual  names.  The  lateral  occipital  sulcus  or  sulci  roughly 
divide  them  into  an  inferior  and  lateral  area,  known  as  the  lateral  occipital  gyri,  and  into  a 
uperior  larea,  the  superior  occipital  gyri.  The  lateral  area  is  continuous  into  the  gyri  of  the 
temporal  lobe,  while  the  superior  area  is  continuous  into  the  gyri  of  the  parietal  lobe. 

The  mesial  surface  of  the  occipital  lobe  is  separated  from  that  of  the  parietal 
lobe   (precuneus)    and  from  the  gyrus  cinguh  of  the  limbic  lobe  by  the  well- 


864  THE  NERVOUS  SYSTEM 

marked  parieto-occipital  fissure.  It  comprises  the  constantly  defined,  wedge- 
shaped  lobule  known  as  the  cuneus,  and  the  posterior  and  mesial  extremitj'-  of  the 
lingual  gyrus.  Since  the  greater  portion  of  the  length  of  the  lingual  gyrus  is 
involved  in  the  basal  surface  of  the  temporal  lobe,  this  gyrus  as  a  whole  has  been 
considered  as  belonging  to  the  temporal  lobe  (see  figs.  671,  676).  The  cuneus 
is  separated  from  the  hngual  gyrus  by  the  posterior  portion  of  the  calcarine 
fissure,  which  always  terminates  in  a  bifurcation,  one  limb  of  which  invades  the 
cuneus  near  the  superomesial  border.  In  addition  the  cuneus  may  contain 
other  twigs  from  both  the  fissures  bounding  it,  and  also,  when  wide,  may  contain 
one  or  more  short,  detached  sulci  cunei. 

The  calcarine  fissure  and  the  parieto-occipital  fissure  are  almost  invariably  joined  in  the 
human  brain,  forming  a  Y-shaped  figure,  the  prongs  of  which  give  the  cuneus  its  shape.  The 
calcarine  fissure  begins  on  the  tentorial  surface  in  the  posterior  portion  of  the  hippocampal 
gyrus  of  the  Umbic  lobe,  below  the  splenium  of  the  corpus  callosum,  and  extends  backward 
across  the  internal  occipital  border  of  the  hemisphere.  It  then  bends  downward  and  proceeds 
to  its  terminal  bifurcation  in  the  polar  portion  of  the  occipital  lobe.  The  stem  or  hippocampal 
portion  of  the  fissure  is  deeper  than  the  posterior  or  occipital  portion.  It  produces  a  well- 
marked  eminence  in  the  medial  wall  of  the  posterior  cornu  of  the  lateral  ventricle,  known  a^  the 
calcar  avis  or  hippocampus  minor.  It  is  developed  separately  from  the  posterior  portion,  which 
itself  first  appears  as  two  grooves.  All  three  parts  are  usually  continuous  with  each  other  before 
birth. 

The  parieto-occipital  fissure  usually  appears  from  the  first  as  a  continuous  groove.  It 
begins  in  the  supero-mesial  border  of  the  hemisphere,  rarely  extending  into  the  convex  surface 
more  than  10  mm.  (external  parieto-occipital  fissure),  thence  it  extends  vertically  downward 
across  the  mesial  surface  (internal  parieto-occipital  fissure),  and  terminates  by  joining  the  cal- 
carine fissure  at  the  region  of  the  downward  bend  of  the  latter,  or  at  about  the  junction  of  its 
anterior  and  middle  thirds.  In  certain  of  the  lower  apes  and  in  the  brain  of  the  chimpanzee 
there  is  no  junction  between  the  two  fissures,  they  being  kept  apart  by  a  narrow  neck  of  cortex, 
the  gyrus  cunei.  Neither  are  they  joined  in  the  human  foetus.  If  in  the  adult  human  brain 
the  region  of  their'junction  be  opened  widely,  there  will  be  found  a  submerged  transitory  gyrus 
(deep  annectant  gyrus),  which  is  the  gyrus  cunei,  superficial  in  the  fcetus.  In  the  higher  apes 
and  in  micro-cephalic  idiots  this  gyrus  may  be  on  the  surface  or  partially  submerged.  Two 
other  transitory  gyri  (annectant  gyxi)  are  to  be  found  by  pressing  open  the  calcarine  fissure, 
and  they  mark  the  points  at  which  its  three  original  grooves  became  continuous  during  its 
development  into  a  boundary  between  the  cuneus  and  the  lingual  gyi'us.  Of  these,  the  anterior 
cuneo-lingual  gyrus  crosses  the  floor  of  the  calcarine  fissure  on  the  posterior  side  of  its  junction 
with  the  parieto-occipital  fissure,  and  therefore  near  the  gyrus  cunei.  The  posterior  cuneo- 
lingual  gyrus  occurs  near  the  region  of  the  terminal  bifurcation  of  the  fissure. 

The  tentorial  surface  of  the  occipital  lobe  is  blended  intimately  with  that  of 
the  temporal  lobe,  from  which  it  is  separated  only  by  an  arbitrary  line  drawn  to 
join  the  line  of  demarcation  for  the  convex  surface,  at  the  region  of  the  pre- 
occipital notch,  and  thence  to  the  isthmus  of  the  gyrus  fornicatus — the  narrow 
neck  of  cortex  connecting  the  gyrus  cinguh  with  the  hippocampal  gyrus,  just  below 
the  splenium  of  the  corpus  callosum  (see  fig.  671).  The  gyri  blending  the  occip- 
ital and  temporal  lobes  across  this  fine  are  the  lingual  gyrus,  already  mentioned, 
and  the  fusiform  gyrus  (occipito-temporal  convolution).  In  fact,  the  tentorial 
surface  of  the  lobe  may  be  considered  as  nothing  more  than  the  posterior  ex- 
tremity of  the  fusiform  gyrus,  and  the  inferior  portion  of  the  same  extremity  of  the 
lingual  gyrus.  The  former  is  often  somewhat  broken  up  and  is  then  continuous 
into  the  lateral  occipital  gyri.  The  two  gyri  are  separated  by  the  collateral  fissure 
the  posterior  end  of  which  extends  into  the  occipital  lobe.  The  fusiform  gyrus  is 
bounded  laterally  by  the  inferior  temporal  sulcus,  which  sometimes  is  continuous 
by  a  lateral  twig,  across  the  posterior  end  of  this  gyrus,  with  the  collateral  fissure. 

The  Rhinencephalon 

The  rhinencephalon  or  olfactory  brain  includes  those  portions  of  the  cerebral 
hemisphere  which  are  chiefly  concerned  as  the  central  components  of  thie  olfactory 
apparatus.  Owing  to  the  preponderant  development  of  the  other  divisions  of  the 
hemisphere,  the  parts  comprising  this  division  appear  relatively  but  feebly  de- 
veloped in  the  human  brain.  In  most  of  the  mammals  the  sense  of  smell  is 
relatively  much  more  highly  developed,  and  in  many  of  the  larger  mammals 
the  parts  comprising  the  rhinencephalon  are  of  greater  absolute  size  than  in  man, 
though  their  cerebral  hemispheres  may  be  considerably  smaller.  In  the  human 
foetus  the  parts  of  the  rhinencephalon  are  relatively  much  more  prominent  than 
after  the  completed  differentiations  into  the  adult  condition.     In  the  broader 


THE  RHINENCEPHALON 


865 


sense  of  the  term  the  rhinencephalon  includes  those  parts  of  the  hemisphere 
usually  classed  as  comprising  two  lobes,  viz.,  the  olfactory  lobe  and  the  limbic 
lobe.  Neither  of  these  is  a  'lobe'  in  the  sense  of  comprising  a  definite  segment 
of  the  hemisphere,  as  do  the  other  lobes,  and  therefore  the  rhinencephalon 
cannot  be  called  a  distinct  lobe.  It  is  so  strung  out  that  by  one  or  the  other  of 
its  parts  it  is  either  in  contact  or  continuity  with  each  of  the  other  lobes  of 
the  hemisphere. 

Morphologically,  the  rhinencephalon  may  be  divided  into  an  anterior  and  a 
posterior  division. 

The  anterior  division. — the  olfactory  lobe  proper,  belongs  almost  wholly  to 
the  base  of  the  encephalon,  and  consists  of  the  following  parts: — 

(1)  The  olfactory  bulb  is  an  elongated,  oval  enlargement  of  grey  substance 
which  lies  upon  the  lamina  cribrosa  of  the  ethmoid  bone,  and,  practically  free,  it 
presses  under  the  anterior  end  of  the  olfactory  sulcus  in  the  basal  surface  of  the 
frontal  lobe.  The  numerous  thin  filaments  of  nonmeduUated  axones  of  the 
olfactory  nerve  enter  the  cranium  through  the  foramina  of  the  lamina  cribrosa  and 
pass  into  the  ventral  surface  of  the  bulb. 

Fig.  680. — Brain  of  Human  Fcbtus  of  22.5  Cm.  (Beginning  of  Fifth  Month),  showing 
THE  Parts  of  the  Developing  Rhinencephalon  Apparent  on  the  Basal  Surface. 
(After  Retzius.) 


dial  olfactory  gyrus  (stria) 


Lateral  olfactory  gyrus  (stria) 

Posterior  parolfactory  sulcus 

Uncus  (hippocampal  gyrus) 


Limen  insulae 

■Anterior  perforated  substance 


Hippocampal  gyrus 


(2)  The  olfactory  tract  is  a  triangular  band  of  white  substance  which  arises  in 
the  olfactory  bulb,  and  continues  backward  about  20  mm.  to  the  region  of  the 
anterior  perforated  substance.  It  appears  triangular  in  transverse  section  from 
the  fact  that  its  upper  side  fits  into  the  olfactory  sulcus.  It  becomes  somewhat 
broader  at  its  posterior  end. 

(3)  The  olfactory  trigone  {olfactory  tubercle)  is  the  small  triangular  ridge,  the 
posterior  continuation  of  the  olfactory  tract  joining  the  anterior  perforated  sub- 
stance. In  it  the  olfactory  tract  breaks  up  into  three  roots,  the  lateral,  in- 
termediate, and  medial  olfactory  strice  {gyri).  The  lateral  olfactory  stria  em- 
phasizes the  lateral  portion  of  the  trigone  into  the  lateral  olfactory  gyrus,  a  portion 
of  which  is  directly  continuous  into  the  lijnen  insulce  (figs.  676,  680). 

While  a  few  of  the  fibres  of  the  lateral  stria  penetrate  this  region,  the  greater  mass  of  them 
pass  obhquely  lateralward  over  it  and  gradually  disappear  in  the  antero-lateral  portion  of  the 
anterior  perforated  substance,  in  which  some  of  them  terminate,  but  through  which  most  of 
them  pass  to  curve  into  the  anterior  end  of  the  hippocampal  gyrus  and  terminate  there,  chiefly 
in  the  uncus.  In  most  of  the  mammals  the  lateral  stria  is  so  strong  that  it  appears  as  a  super- 
ficial white  band  passing  directly  into  the  uncus.  In  the  early  foetus  it  is  seen  to  enter  the 
uncus  in  two  branches,  forming  the  medial  semilunar  gyms  and  the  lateral  gyrus  ambiens  upon 
the  uncus.     A  portion  of  the  limen  insulce  belongs  to  the  rhinencephalon. 

(4)  The  parolfactory  area  (Broca's  area)  involves  the  mesial  extension  of  the 
olfactory  trigone,  and  is  concerned  with  the  medial  olfactory  stria.  On  the  basal 
surface  of  the  hemisphere  this  area  involves  the  posterior  extremity  of  the  gyrus 
rectus — a  portion  of  which  is  sometimes  separated  from  the  remainder  of  the  gyrus 
by  a  ventral  prolongation  of  the  anterior  parolfactory  sulcus  of  the  medial  surface 
(see  figs.  679,  706).  This  prolongation  when  present  has  been  called  the 
fissura  serotina.     On   the  medial  surface  the  parolfactory  area  appears  as  a 


866  THE  NERVOUS  SYSTEM 

definite  gyrus.  In  front  this  is  separated  from  the  superior  frontal  gyrus  by  the 
anterior  -parolfactory  sulcus,  and  from  the  subcallosal  gyrus  behind  by  the  deeper 
posterior  parolfactory  sulcus  (fig.  679) .  It  is  continuous  above  into  the  gyrus  cin- 
guli  of  the  limbic  lobe,  a  portion  of  the  posterior  part  of  the  rhinencephalon. 

A  large  portion  of  the  fibres  of  the  medial  stria  are  lost  in  the  parolfactory  area,  and  are 
known  to  terminate  about  the  cells  there.  This  stria  or  root  of  the  olfactory  tract  forms  a 
slight  ridge  on  the  ventral  surface  of  the  area,  which  is  frequently  pi-ominent  enough  to  retain 
the  name  medial  olfactory  gyrus  appUed  to  it  in  the  foetal  brain  (fig.  680). 

(5)  The  subcallosal  gyrus  (peduncle  of  the  corpus  callosum)  is  the  narrow  fold 
of  the  pallium  which  lies  between  the  posterior  parolfactory  sulcus  and  the  rostral 
lamina  and  the  ventral  continuation  of  the  latter  into  the  lamina  terminalis.  It 
begins  above,  in  part  fused  to  the  rostrum  of  the  corpus  callosum,  and  in  part 
continuous  with  the  gyrus  cinguli,  and  ventrally  it  goes  over  lateral  ward  and 
posteriorly  into  that  portion  of  the  anterior  perforated  substance  known  as  the 
diagonal  band  of  Broca,  and  in  this  way  it  extends  into  the  uncus.  Mesially,  it 
approaches  its  fellow  of  the  opposite  side  so  closely  that  the  groove  separating 
the  two  is  known  as  the  median  subcallosal  sulcus  of  Retzius.  Some  fibres  of  the 
medial  olfactory  stria  disappear  in  the  substance  of  the  subcallosal  gyrus. 

(6)  The  anterior  perforated  substance  must  be  considered  with  the  rhinen- 
cephalon, but,  like  the  limen  insulae,  it  can  only  be  considered  as  belonging  in  part 
to  this  division  of  the  brain.  It  comprises  the  basal  region  between  the  optic 
chiasma  and  tract  and  the  olfactory  trigone.  Usually  the  posterior  parolfactory 
sulcus  (fissura  jmnia  of  the  embryo)  is  sufficiently  evident  to  more  or  less 
distinctly  separate  it  from  the  latter.  Its  postero-lateral  area  is  occupied  by  the 
diagonal  band  of  Broca.  A  few  fibres  from  the  medial  stria  are  known  to  dis- 
appear within  its  depths,  and,  as  mentioned  above,  many  fibres  from  the  lateral 
stria  also  pass  into  it.  The  intermediate  olfactory  stria  is  always  much  the  weakest 
of  the  three  striae,  and  in  many  specimens  is  apparently  absent.  The  fibres  of  this 
stria  run  almost  straight  backward  and  plunge  directly  into  the  anterior  area  of 
the  anterior  perforated  substance,  where  some  of  them  are  known  to  terminate, 
while  others  continue  into  the  uncus. 

On  embryological  grounds,  the  subcallosal  gyrus  and  the  anterior  perforated  substance  are 
classed  with  the  posterior  division  of  the  'olfactory'  lobe  or  anterior  division  of  the  rhinen- 
cephalon. 

The  olfactory  bulb  and  tract  arise  as  a  hollow  outgrowth  from  the  lower  and  anterior  part 
of  the  anterior  of  the  three  primary  vesicles.  It  is  a  tubular  structure  at  first,  and  in  many  of 
the  mammals  the  cavity  maintains  throughout  hfe  as  the  olfactory  ventricle.  In  man  the  cavity 
becomes  occluded  and  the  ependyma  and  gelatinous  substance  which  surround  it  become 
the  grey  core  of  the  bulb  and  tract  of  the  adult. 

The  grey  substance  persists  and  develops  chiefly  in  the  bulb,  and  in  fact  produces  it  as  such. 
It  is  much  thicker  on  the  inferior  surface  of  the  bulb  than  on  the  superior  surface,  and  in  section 
shows  definite  layers.  From  within  outward,  the  principal  of  these  layers  are — (1)  the  layer  of 
large  cells  whose  shape  suggests  their  name,  mitral  cells;  (2)  large  dendrites  of  the  mitral  cells 
project  toward  the  inferior  surface  of  the  bulb  and  there  break  up  into  numerous  telodendria 
which  copiously  form  synapses  with  like  telodendria  of  the  entering  fibres  of  the  olfactory  nerve, 
thus  forming  rounded,  much  tangled  glomeruli  and  the  layer  containing  these,  the  glomerular 
layer;  (3)  the  superficial  layer,  or  olfactory  layer,  consists  of  the  fibres  of  the  olfactory  nerve 
which  form  a  dense  interlacement  with  each  other  on  the  inferior  surface  of  the  bulb  before  they 
pass  into  its  interior.  The  superior  surface  of  the  bulb  becomes  formed  almost  wholly  of  the 
fibres  which  arise  as  axones  of  the  mitral  cells  and  pass  backward  to  form  the  olfactory  tract,  and 
thence  to  their  localities  of  termination,  chiefly  by  way  of  the  three  striiE.  Along  the  dorsal, 
covered,  aspect  of  the  olfactory  tract  the  gelatinous  substance  of  the  core  may  show  through  as 
a  grey  ridge. 

The  posterior  division  of  the  rhinencephalon  or  the  so-called  limbic  lobe  (a 

name  introduced  by  Broca  in  1878)  takes  part  in  both  the  medial  and  tentorial 
surfaces  of  the  hemisphere  (fig.  681).  Seen  from  the  medial  surface,  it  forms  an 
irregular  eUiptical  figure  which  encloses  the  corpus  callosum  and  the  extremities 
of  which  approach  each  other  at  the  anterior  perforated  substance,  where  they 
are  continuous  with  the  structures  of  the  anterior  division  of  the  rhinencephalon. 
The  figure  is  bounded  externally  by  the  sulcus  cinguU  above,  by  the  subparietal 
sulcus  (postlimbic  sulcus)  and  the  anterior  limb  of  the  calcarine  fissure  behind, 
and  by  the  collateral  fissure  below.  These  respectively  separate  it  from  the 
frontal,  parietal,  occipital,    and   temporal   lobes.     It    comprises   the   following 


THE  RHINENCEPHALON 


867 


structures  which  are  either  wholly  or  in  part  devoted  to  the  functions  of  the 
olfactory  apparatus: — 

Part  of  gyrus  cinguli  and  cingulum. 

Isthmus  of  the  gj^rus  fornicatus. 

1.  Gyrus  fornicatus  i  f  hippocampal  gyrus. 

TT-  uncus. 

Hippocampus       ^^^^^^^  ^^^^^  ^^^^^.^^ 

[  fimbria. 

2.  The  medial  and  lateral  longitudinal  strise  upon  the  corpus  callosum. 

3.  The  fornix. 

4.  The  mammillary  body,  the  mammillo-thalamic  fasciculus  to  the  anterior 

nucleus  of  the  thalamus  and  the  mammillo-peduncular  fasciculus. 

5.  Part  of  anterior  cerebral  commissure. 

6.  Part  of  septum  pellucidum. 

7.  Most  of  medullary  stria  of  thalamus. 

8.  Most  of  habenular  nucleus. 

The  gyrus  fornicatus  comprises  the  greater  mass  of  the  limbic  lobe.     As  seen 
above,  it  is  a  term  used  to  collectively  represent  a  number  of  conjoined  structures. 

Fig.  681. — Diagram  showing  Position  of  Structures  Comprising  the  Limbic  Lobe  as 
Seen  from  the  Mesial  Aspect  of  the  Cerebral  Hemisphere. 


Fasciola  cinerea 


Mammillo-thalamic  fasciculus 
(Vicq  d'azyri) 


^V  ^ Gyrus  cinguli 

X  \         Medial  and  lateral 

.'     \ V —  longitudinal  striae  of 

\             \       corpus  callosum 
Septum  pellucidum 


Subcallosal  gyrus 
Olfactory  bulb 


Medial  olfactory  stria 


Mammillary  body 


Lateral  olfactory  stria 


Dentate  fascia  or  gyrus 


Being  an  incomplete  ellipse  in  form,  its  two  ends  are  united  to  form  a  closed  ring 
by  means  of  the  connection  of  the  parolfactory  area  with  the  gyrus  cinguli  and 
the  connection  of  the  anterior  perforated  substance  with  the  uncus  of  the  hippo- 
campal gyrus.  It  is  best  described  in  terms  of  its  three  component  parts  indi- 
cated above: 

The  gyrus  cinguli  begins  in  junction  with  the  area  parolfactoria  below  the 
anterior  end  of  the  corpus  callosum,  and  curves  above  so  as  to  entirely  embrace 
the  upper  surface  of  the  latter.  It  is  separated  from  the  frontal  lobe  by  the  sulcus 
cinguli  (calloso-marginal  fissure),  from  the  parietal  lobe  by  the  subparietal  sulcus, 
and  from  the  corpus  callosum  below  by  the  sulcus  of  the  corpus  callosum.  By  the 
latter  it  is  separated  from  the  longitudinal  strite  of  the  upper  surface  of  the  corpus 
callosum. 

The  gyrus  cinguli  covers  over,  and  its  cells  are  closely  associated  with,  the  cingulum,  a  well- 
marked  arcuate  band  of  white  substance,  which  follows  the  gyrus  in  its  bend  around  the  rostrum 
and  backward  to  turn  around  the  splenium  of  the  corpus  callosum  in  the  isthmus  of  the  gjTus 
fornicatus,  and  then  to  course  forward  into  the  hippocampal  gyrus  and  the  uncus.  The  cingulum 
is  largely  an  association  fasciculus  between  the  gjTi  of  the  temporal  lobe  and  those  gyri  on  the 
mesial  surface  of  the  cerebral  hemisphere,  its  fibres  for  the  most  part  running  short  courses,  being 
continually  added  to  it  and  continually  leaving  it.  However,  it  contains  olfactory  axones 
running  in  two  directions:  (1)  fibres  from  the  medial  olfactory  stria  and  fibres  arising  in  the 
parolfactory  area,  the  gyrus  subcaDosus  and  the  anterior  perforated  substance  which  course 
posteriorly  for  distribution  in  the  cortex  of  the  gjTUs  cinguli  and  hippocampal  gyrus;  (2) fibres 
arising  in  the  hippocampal  gyrus,  especially  the  uncus,  to  course  dorsalward  through  the  isthmus 
and  then  forward  as  association  fibres.  Some  fibres  arising  from  the  cortical  cells  of  the  g3TUS 
cinguli  pass  inferiorly  through  the  cingulum,  through  the  corpus  callosum  and,  anteriorly, 
through  the  septum  pellucidum  to  join  the  fornix  below  {perforating  fibres  of  Ike  fornix). 

The  isthmus  of  the  gyrus  fornicatus  is  the  constricted  portion  connecting  the 
posterior  end  of  the  gja-us  cinguli  with  that  of  the  hippocampal  gyrus  (fig.  619 


868  THE  NERVOUS  SYSTEM 

and  671).     It  is  bounded  externally  by  the  anterior  end  of  the  calcarine  fissure, 
and  incloses  the  posterior  turn  of  the  cingulum. 

The  hippocampus  is  the  name  applied  to  the  curved  appearances  produced  in 
the  floor  of  the  lateral  ventricle  by  the  peculiar  foldings  of  this  part  of  the  cerebral 
cortex.  The  hippocanipal  gyi'us  (gyrus  of  the  hippocampus)  is  the  main  gyrus  of 
the  tentorial  surface  of  the  hmbic  lobe.  Externally  it  is  separated  from  the  fusi- 
form gyrus  by  the  collateral  fissure,  and  it  is  bounded  internally  by  the  hippo- 
campal  or,  more  inclusive,  the  chorioid  fissure.  Posteriorly  it  is  partially  divided 
by  the  calcarine  fissme  into  the  lingual  gyrus  (of  the  temporal  lobe)  and  the 
isthmus  of  the  gyrus  fornicatus.  Its  anterior  extremity  is  hooked  backward  and 
is  known  as  the  uncus  {gyrus  uncinatus) .  This  is  almost  entirely  separated  from 
the  temporal  lobe  by  a  groove,  the  temporal  notch.  If  the  hippocampal  fissure 
be  opened  up,  the  dentate  gyrus  or  fascia  and  the  fimbria  will  be  seen.  These  lie 
side  by  side,  separated  by  the  shallow  fimbrio -dentate  sulcus  (fig.  690.) 

The  free  edge  of  the  dentate  gyrus  presents  a  peculiarly  notched  appearance,  produced  by 
numerous  parallel  grooves  cutting  it  transversely.  Its  posterior  end,  sometimes  called  the 
fasciola  cinerea,  continues  backward  over  the  splenium  of  the  corpus  callosum,  and  upon  the 
upper  surface  of  the  corpus  callosum  appears  as  a  thin  strip  of  grey  substance  which  contains 
embedded  in  it  the  medial  and  lateral  longitudinal  strice.  This  thin  strip  is  sometimes  called  the 
supracallosal  gyrus  (gyrus  epicallosus,  induseum  griseum),  and  is  thought  to  represent  a  ves- 
tigial part  of  the  hippocampal  gyrus.  Closely  beneath  the  splenium  of  the  corpus  caUosum,  on 
the  supero-mesial  side  of  the  hippocampal  gyrus  and  mesial  to  the  dentate  gyrus,  there  sometimes 
occur  suggestions  of  round  or  oval  elevations  of  the  grey  substance  which  have  been  called 
the  "callosal  convolutions"  or  gyri  Andrece  Retzii.  Rarely  are  they  strongly  developed,  but  when 
so  they  often  produce  a  spiral  appearance. 

The  fimbria  is  but  the  fimbriated,  free  border  of  the  posterior  end  or  origin 
of  the  fornix,  so  folded  as  to  project  into  the  hippocampal  fissure,  parallel  with  the 
dentate  gyrus  (fig.  690).  It  is  a  conspicuous  iDand  composed  almost  entirely  of 
white  substance,  continuous  laterally  with  the  thick  stratum  covering  the  ven- 
tricular surface  of  the  hippocampus.  It  begins  anteriorly  in  the  hook  or  recurved 
extremity  of  the  uncus.  Traced  backward,  it  is  seen  so  curve  upward,  and  within 
the  ventricle  it  becomes  part  of  the  general  accumulation  of  the  white  substance 
(alveus)  of  the  surface  of  the  hippocampus,  which  accumulation  is  the  beginning 
of  the  fornix.  The  free  border  of  the  fimbria  (seen  in  section)  is  known  as  the 
tcenia  fimhrim.  The  fimbria  is  separated  from  the  cerebral  peduncles  by  the 
chorioid  fissure,  the  thin,  non-nervous  floor  of  which  alone  intervenes  between  the 
exterior  of  the  brain  and  the  cavity  of  the  lateral  ventricle  within. 

The  hippocampal  fissure  attains  its  greatest  depth  between  the  dentate  gyrus 
and  the  hippocampal  gyrus,  and  the  resulting  eminence  produced  in  the  floor  of 
the  lateral  ventricle  is  known  as  the  hippocampus  major,  as  distinguished  from 
the  lesser  eminence  produced  posteriorly  by  the  end  of  the  calcarine  fissme  and 
known  as  the  hippocampus  minor  [calcar  avis].  The  collateral  fissure  may  like- 
wise produce  a  bulging  in  the  wall  of  the  ventricle,  the  collateral  eminence.  In 
transverse  sections  of  the  hippocampus  major,  the  layers  of  grey  and  white  sub- 
stance present  a  coiled  appearance  known  as  the  cornu  ammonis.  Externally 
the  medial  surface  of  the  hippocampal  gyrus  adjoining  the  dentate  gyrus  has 
reflected  over  it  a  delicate  reticular  layer  of  white  substance  known  as  the  sub- 
stantia reticularis  alba  (Arnoldi). 

The  fornix  is  the  great  association  pathway  of  the  limbic  lobe,  and  appears  to 
be  wholly  concerned  in  the  apparatus  of  the  rhinencephalon.  It  is  a  bilateral 
structure  arched  beneath  the  corpus  callosum,  with  which  it  is  connected  ante- 
riorly by  the  septum  pellucidum.  Posteriorly  it  passes  in  contact  with  the 
splenium.  It  consists  of  two  prominent  strips  of  white  substance,  one  for  each 
hemisphere,  the  ends  of  which  are  separate  from  each  other,  while  their  inter- 
mediate parts  are  fused  across  the  mid-line.  These  run  above  the  chorioid  tela  of 
the  third  ventricle,  and  their  lateral  edges  (tcenice  fornicis)  rest,  on  each  side,  along 
the  line  of  the  taenia  chorioidea.  The  posterior,  separate  ends  are  known  as  the 
posterior  pillars  or  crura  of  the  fornix;  the  fused,  intermediate  portion  is  the  body, 
and  the  separate,  anterior  ends  are  the  anterior  pillars  or  columns  of  the  fornix. 

The  posterior  pillars  [crura]  of  the  fornix. — When  seen  from  the  medial 
aspect  of  the  hemisphere,  the  fused  portion  of  the  fornix,  in  the  separation  of  the 
hemispheres,  is  split  along  the  mid-line  (fig.  671).     The  half  under  examination 


THE  FORNIX 


869 


may  be  seen  to  course  obliquely  lateralward  under  the  splenium  of  the  corpus  cal- 
losum,  and  then,  continuous  into  the  fimbria,  to  curve  forward  and  ventralward 
toward  the  uncus.  The  greater  mass  of  the  fibres  coursing  in  the  fornix  arise  as 
outgrowths  of  the  cells  of  the  uncus,  hippocampal  gyrus,  and  dentate  gyrus.  They 
accumulate  as  a  dense  stratum  on  the  ventricular  surface  of  these  gyri,  termed  the 
alveus,  which  crops  outward  as  the  fimbria  and  which  passes  backward  and  up- 
ward; upon  reaching  the  region  of  the  splenium  it  turns  obliquely  forward  under 

Fig.  682. — Diagram  Showing  Fornix  and  its  Connections  as  seen  from  Above. 

olfactory  bulb  - 

Medial  olfactory  stria 
Subcallosal  gyrus 
Column  (anterior  pillar) 


Fimbria 

Mammillo-thalamic  fasciculus 
Stria  terminalis  of  thalamus 

Stria  meduUaris  of  thalamus 
Crus  (posterior  pillai) 

Epiphysis  (below) 


Amygdaloid  nucleus 


Hippocampus  major 


Hippocampal  commissure  (lyra) 

it  and  approa(3hes  the  mid-line,  to  fuse  with  the  hke  bundle  from  the  gyri  of  the 
hippocampus  of  the  opposite  side.  The  bundles  thus  arising  from  the  two  sides 
are  the  pillars  or  crura  of  the  fornix.  They  appear  as  two  flattened  bands  of  white 
substance  which  come  in  close  contact  with  and  even  adhere  to  the  splenium. 

The  angle  formed  by  the  mutual  approach  of  the  posterior  pillars  of  the  fornix  is  crossed 
by  a  lamina  of  commissural  fibres  connecting  the  hippocampal  gyri  of  the  two  hemispheres 
(fig.  684).  This  lamina  is  the  hippocampal  commissure  or  transverse  fornix.  Like  those  of  the 
fornix,  its  fibres  arise  from  the  cortex  of  the  hippocampal  gyri,  but  they  serve  as  commissural 
fibres  between  the  hippocampal  gyri  of  the  two  hemispheres.  Being  of  a  different  functional 
direction,  it  should  not  be  considered  a  part  of  the  fornix.     The  angle  formed  by  the  two  pos- 

FiG.  683. — Diagram  Illttsteating  the  Origin  and  Course  of  Forndc  as  viewed  from  the 

Side. 


Gyrus  cinguli  - 
Cinguli 


Longitudinal  stris-- 
Fornix 


Perforating  fibres 


Thalamic  medullary  stria 
Habenular  nucleus 


Olfactory  bulb  and  tract 


Anterior  perforated  substanci 
Uncus - 


---Longitudinal  strise 
Calcarine  fissure 


^Fimbria 
Hippocampal  gyrus 

Mammillary  body 


terior  pillars  of  the  fornix  as  traversed  by  the  hippocampal  commissure  gives  a  picture  named  the 
psalterium  or  lyra.  Usually  the  hippocampal  commissure  and  the  posterior  pillars  (crura)  are 
in  close  contact  with  the  under  surface  of  the  splenium.  When  occasionally  they  do  not  adhere, 
the  space  between  is  known  as  Verga's  ventricle.  According  to  recent  studies  of  brains  with 
degenerated  corpus  callosum,  further  commissural  fibres  between  the  limbic  lobes  course  in  the 
posterior  angle  of  the  septum  pellucidum,  and  all  along,  transverse  to  the  body  of  the  fornix. 

The  body  of  the  fornix  appears  as  a  triangular  plate  of  white  substance 
produced  by  the  fusion  of  the  pillars.  Its  base  or  widest  portion  is  behind.  It 
is  not  always  bilaterally  symmetrical.     Its  upper  surface  is  attached  by  the  septum 


870 


THE  NERVOUS  SYSTEM 


pellucidum  to  the  lower  surface  of  the  corpus  callosum.  Below,  it  lies  over  the 
chorioid  tela  of  the  third  ventricle,  which  separates  it  mesially  from  the  cavity 
of  the  third  ventricle  and  laterally  from  the  upper  surfaces  of  the  thalami.  Its 
sharp  lateral  edge  or  margin  (taenia  fornicis)  projects  into  the  lateral  ventricle 
of  either  side  in  relation  with  the  chorioid  plexus  of  that  ventricle,  and  thus  the 
lateral  portion  of  its  upper  surface  forms  part  of  the  floor  of  the  lateral  ventricle — 
an  arrangement  to  be  expected,  since  the  posterior  pillars  arise  from  the  floor  of 

Fig.  684. — Horizontal  Section  of  Telencephalon  showing  Bodt  of  Fornix  and  Hippo- 
CAMPAL  Commissure  as  seen  from  Below  and  the  Anterior  Commissure  in  Section. 
(After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 

Genu  of  corpus  callosum 
Parolfactory  area  (Broc^)  ^  ^^^         ^„:,.-^    ^/  ^^^^^^^  „f  ^^^^^^  ^^^^^^^ 

Triangular  recess       /f^  if  \\\  TVX.      ^^^^  ^^  caudate  nucleus 

Putamen  of  lenticular  nucleus 


Temporal  lobe  ^ 

Lateral  cerebral  fissure 
(Sylvii) 

Claustrum 
External  capsule 


Internal  capsule  — 


Interventricular  fora- 
men  (MonroiJ 


Crus  of  fornix 


Gyrus  cinguU  ' 


Parieto-occipital  fissure 


Globus  pallidus 


Habenular  nucleus 

fTail  of  caudate 
nucleus 

^ —  Inferior  cornu  of  lat- 
eral ventricle 


Longitudinal  fissure 


Medial  surface  of  hemisphere 


Cuneus 
Calcarine  fissure 

the  ventricle,  viz.,  the  hippocampus.     The  ventricular  portion  is  covered  by  a 
layer  of  ependyma  in  common  with  that  lining  the  rest  of  the  ventricle. 

Along  its  body  the  fornix  receives  fibres  arising  from  the  cells  of  the  cortex  of  the  gjTus 
cinguli  and  fibres  from  the  longitudinal  striaj  upon  the  dorsal  surface  of  the  corpus  callosum. 
These  are  known  as  the  perforating  fibres  of  the  fornix.  In  their  ventral  course,  they  pass  ob- 
liquely forward  through  the  corpus  callosum  and,  anteriorly,  through  the  posterior  angle  of  the 
septum  pellucidum  to  join  the  fornix  and  course  in  its  functional  direction.  Tlie  fibres  arising 
in  the  cortex  of  the  gyrus  cinguli  may  course  short  distances  in  the  cingulum  before  perforating 
the  corpus  callosum. 

The  columns  or  anterior  pillars  of  the  fornix  [coluranse  fornicis],  are  two  separ- 
ate, cyhndrical  bundles  which  pass  forward  from  the  apex  of  the  body  of  the  fornix 
and  then  turn  sharply  downward  along  the  anterior  boundary  of  the  third  ven- 
tricle, just  behind  the  anterior  cerebral  commissure.  A  part  of  each  column,  the 
/ree  portion  [pars  libera],  forms  the  anterior  boundary  of  the  interventricular 
foramen  (Monroi).     Thence  the  covered  portion  [pars  tecta]  sinks  into  the  grey 


ANTERIOR  CEREBRAL  COMMISSURE  871 

substance  of  the  lateral  wall  of  the  third  ventricle,  and  passes  downward  to  the 
base  of  the  brain,  where  it  appears  on  the  exterior  as  the  mammillary  body 
[corpus  mammillare]  (fig.  671). 

Some  of  its  fibres  are  interrupted  in  the  nuclei  of  the  mammillary  body,  chiefly  in  its  lateral 
nucleus;  probably  most  of  them  merely  double  back,  forming  a  genu.  From  the  mammUlary 
body  the  fibres  are  disposed  in  at  least  three  ways: — (1)  The  greater  part  perhaps  pass  directly 
upward  and  are  lost  in  the  anterior  nucleus  of  the  thalamus,  where  they  ramify  freely  and  term- 
inate about  its  cells.  These  fibres  form  the  bundle  known  as  the  mammillo-thalamic  fasciculus, 
or  bundle  of  Vicq  d'Azyr;  (2)  A  portion  of  the  fibres  go  to  form  a  mammillo-mesencephalic  fas- 
ciculus (tegmento-mammiilary  fasciculus,  mammillo-peduncular  fasciculus.  This  begins  in  the 
mammillary  body  and  passes  caudalward  into  the  mesencephalon  to  terminate  about  cell-bodies  in 
or  in  the  region  of,  the  so-called  nucleus  of  the  medial  longitudinal  fasciculus  and  posterior  com- 
missure. Fibres  given  by  these  cell-bodies  may  convey  impulses  by  way  of  the  medial  longi- 
tudinal fasciculus  or  the  general  reticular  formation  to  the  nuclei  in  the  mesencephalon,  rhomb- 
encephalon and  perhaps  into  the  spinal  cord.  Some  of  this  portion  of  the  fibres  from  the  mam- 
millary body  are  said  to  pass  caudalward  through  the  mesencephalon  without  interruption 
there.  (3)  A  portion  of  the  fibres  decussate  in  the  superior  parts  of  the  mamillary  bodies 
and  are  distributed  to  both  the  thalamus  and  the  mesencephalon  of  the  opposite  side.  This 
decussation  is  the  supraraamillary  commissure. 

As  seen  above,  the  fornix  as  a  whole  is  composed  of  longitudinally  directed  fibres,  some  of 
which,  however,  cross  the  mid-line  in  the  region  of  its  body  and  course  in  the  columns  of  the 
opposite  side.  For  the  greater  part,  its  fibres  rise  from  the  cells  of  the  hippocampal  gyri,  but 
it  is  known  to  contain  some  fibres  which  arise  in  the  anterior  perforated  substance  and  sub- 
callosal gyrus  and  course  through  the  fornix  to  the  hippocampal  gyri. 

The  medial  and  lateral  longitudinal  striae  upon  the  corpus  callosum  consist  of  olfactory 
fibres  coursing  in  both  directions:  (1)  fibres  arising  in  the  parolfactory  area,  the  subcallosal 
gyrus  and  the  anterior  perforated  substance  (diagonal  band  of  Broca)  course  posteriorly  and 
then  inferiorly  in  them  to  the  grey  substance  of  the  gryi  of  the  hippocampus;  (2)  and  chiefly, 
fibres  from  the  hippocampal  gyri  course  in  them  anteriorly  and  inferiorly  around  the  rostrum 
of  the  corpus  callosum,  through  the  ventral  part  of  the  septum  pelluoidum,  to  join  the  fornix. 
It  is  suggested  that  the  strise,  especially  the  medial,  may  be  considered  as  a  part  of  the  fornix 
detached  upon  the  dorsal  surface  of  the  corpus  callosum  during  the  projection  of  the  latter 
between  the  cerebral  hemispheres.     The  medial  stria  is  often  called  the  stria  Lancisii. 

The  anterior  cerebral  commissure  is  only  in  part  concerned  in  the  rhinenceph- 
alon;  it  consists  in  greater  part  of  commissural  fibres  connecting  the  two  temporal 
lobes.  It  forms  one  of  the  four  commissures  of  the  telencephalon,  the  other  three 
being  the  corpus  callosum,  the  hippocampal  commissure  and  the  inferior  cerebral 
commissure.  It  is  a  bundle  of  white  substance  with  a  slightly  twisted  appearance, 
which  crosses  the  mid-line  in  the  anterior  boundary  of  the  third  ventricle  be- 
tween the  lamina  terminalis  and  the  columns  of  the  fornix  (figs.  671  and  684), 
just  below  the  interventricular  foramen  (foramen  of  Monro).  In  each  hemis- 
phere its  main  or  temporal  portion  passes  lateralward  and  slightly  backward 
beneath  the  head  of  the  caudate  nucleus  and  through  the  anterior  end  of  the 
lenticular  nucleus,  and  thence  is  dispersed  to  the  grey  substance  of  the  temporal 
lobe. 

It  contains  fibres  both  to  and  from  the  temporal  lobe  of  each  side.  In  addition  to  these 
fibres  the  anterior  commissure  carries  in  its  frontal  side  two  sets  of  fibres  belonging  to  the  ol- 
factory apparatus: — (1)  fibres  arising  in  the  olfactory  bulb  of  one  side,  which  pass  by  way  of  the 
medial  olfactory  striae  through  it  to  the  olfactory  bulb  of  the  opposite  side;  (2)  fibres  which  pass 
through  it  from  the  medial  stria  (olfactory  bulb)  of  one  side  to  the  uncus  of  the  opposite  side. 

The  anterior  commissure  is  a  more  primitive  commissure  than  the  corpus  callosum,  in  that 
it  is  present  in  the  lower  forms  when  the  latter  is  absent,  and  diminishes  in  relative  size  and 
importance  as  the  corpus  callosum  appears  and  increases  in  size.  In  man  the  appearance  of  the 
anterior  commissure  precedes  but  little  that  of  the  corpus  callosum.  During  the  fifth  month 
the  lamina  terminalis,  which  then  alone  unites  the  anterior  ends  of  the  two  hemispheres,  develops 
a  thickening  of  its  dorsal  portion.  In  a  part  of  this  thickening,  transverse  fibres  begin  to  appear 
and  their  increase  in  number  results  in  the  partial  separation  posteriorly  of  the  part  containing 
them  from  the  rest  of  the  lamina,  and  then  follows  the  differentiation  of  this  part  into  the  anterior 
commissure.  The  remainder  of  the  thickening  of  the  lamina  continues  to  increase  in  size  with 
the  increase  of  the  hemispheres;  its  upper  edge  is  directed  posteriorly,  and  fibres  begin  to  appear 
in  it  which  arise  in  the  cortex  of  one  side  and  cross  over  to  that  of  the  other  side.  These  fibres 
form  the  corpus  callosum. 

The  corpus  callosum,  a  development  of  fibres  in  the  upper,  expanded  portion  of  the  lamina 
terminalis,  thus  bridges  over  a  portion  of  the  longitudinal  fissure  between  the  hemispheres.  In 
the  mean  time,  the /ornts  arises  as  two  bundles  of  fibres,  one  from  the  hippocampus  of  each  side. 
In  the  complex  mechanics  of  the  development  of  the  cerebrum  these  two  bundles  approach  each 
other  under  the  corpus  callosum,  fuse  for  a  certain  distance,  and  together  arch  the  cavity  of 
the  third  ventricle  and  come  to  acquire  their  adult  position.  There  results  from  these  processes 
of  growth  a  completely  enclosed  space,  a  portion  of  the  longitudinal  fissure,  the  roof  of  which 
is  the  corpus  callosum,  its  floor,  the  body  of  the  fornix,  and  its  lateral  walls,  portions  of  the 
mesial  surfaces  of  the  two  cerebral  hemispheres.     The  lateral  walls  of  this  space  do  not  thicken 


872 


THE  NERVOUS  SYSTEM 


as  do  the  other  regions  of  the  pallium,  but  remain  thin  and  constitute  the  septum  pellucidum  of 
the  adult,  the  space  itself  being  the  so-called  fifth  ventricle  or  cavity  of  the  septum  pellucidum. 

The  septum  pellucidum  is  a  thin,  approximately  triangular,  vertically  placed 
partition  which  separates  the  anterior  portions  of  the  two  lateral  ventricles  from 
each  other.  Its  widest  portion  lies  in  front,  bounded  by  the  genu  and  rostrum 
of  the  corpus  callosum,  the  rostral  lamina,  and  the  anterior  pillars  of  the 
fornix,  to  all  of  which  it  is  attached.  Prolonged  backward  under  the  body  of  the 
corpus  callosum,  it  narrows  rapidly  and  terminates  at  the  line  of  adherence  be- 
tween the  posterior  portion  of  the  fornix  and  the  splenium  of  the  corpus  callosum. 
It  consists  of  two  thin  layers,  the  laminae  of  the  septum  pellucidum,  arrested 
developments  of  portions  of  the  pallium  of  the  hemispheres.  The  laminae 
enclose  a  narrow  median  cavity  known  as  the  fifth  ventricle  [cavum  septi  pellucidi]. 
This  cavity  is  of  very  variable  size,  is  completely  closed,  and  does  not  merit  the 
term  '  ventricle, '  as  apphed  to  the  other  cavities  of  the  brain,  in  that  it  has  no 
communication  with  the  ventricular  system  and  has  a  different  lining  from  the 
other  ventricles. 

Fig.  685. — Diagram  showing  Some  of  the  Pkincipal  Tracts  and  Synapses  of  the  Ol- 
factory Apparatus. 


Perforating  fibre 


Fornix 
Anterior  commissure         '. 


Medullary  stria  of  thalamus 


Subcallosal  gyrus 
Parolfactory  are 


^  Longitudinal  strise 
on  corpus  callosum 

Hippocampal  com- 

(Lyre) 


*"  Habenular  nucleus 


,  Habenulo-pedun- 
cular  tract  (fasci- 
culus retroflexus) 


^*  Mammillo-mesen- 
^"^0^^  cephalic  fasciculus 

^  ,---"^^  Penduculo-tegmental 
'"^^  tract 

Interpeduncular  nucleus 


Uncinat' 
fasciculus        ' 
Uncus 


\       Fimbria  hippocampi 
Mammillary  body 
Anterior  perforated  substance 


Olfactory  epithelium 

Each  lamina  of  the  septum  pellucidum  consists  of  a  layer  of  degenerated  grey  substance  next 
to  the  fifth  ventricle  and  a  layer  of  white  substance  next  to  the  lateral  ventricle,  the  latter  covered 
by  a  layer  of  ependyma  common  to  that  ventricle.  The  white  substance  consists  in  part  of 
fibres  belonging  to  the  general  association  systems  of  the  hemispheres,  and  in  part  of  four  varie- 
ties of  fibres  concerned  with  the  rhinencephalon: — (1)  fibres  from  each  medial  olfactory  stria 
are  known  to  reach  the  septum  pellucidum  and  thence  go  by  way  of  the  fornix  to  the  hippo- 
campus major;  (2)  fibres  are  thought  to  be  contributed  by  the  fornix  to  the  septum  pellucidum, 
and  through  it  reach  the  subcallosal  gyrus  and  perhaps  the  parolfactory  area  and  even  the  ol- 
factory bulb ;  (3)  the  posterior  angle  of  the  septum  pellucidum  is  preforated  by  some  commissural 
fibres  passing  from  the  body  of  the  fornix  and  by  some  perforating  fibres  of  the  fornix,  passing 
from  above  through  it  to  the  fornix  below;  (4)  anteriorly,  some  fibres  from  the  longitudinal 
strife  upon  the  corpus  callosum  pass  tlirough  its  inferior  portion  to  join  the  fornix. 

The  medullary  stria  of  the  thalamus  [stria  meduUaris  thalami]  {striai  pinealis,  lamia  thalami), 
already  described  as  to  position,  receives  fibres  from  three  sources,  the  majority  at  least  of 
which  belong  to  the  rhinencephalon:  (1)  fibres  from  the  fornix  near-by  and  thus  from  the  cor- 
tex of  hippocampal  gyrus  and  gryus  cinguli  (a  cortico-habenular  tract) ;  (2)  fibres  from  the  parol- 
factory area  and  the  anterior  perforated  substance,  through  the  septum  pellucidum  and  lamina 
terminahs  (a  more  direct  olfaoto-habenular  tract) ;  (3)  fibres  arising  from  the  cell-bodies  in  the 
thalamus,  supposedly  chiefly  from  its  anterior  (olfactory)  nucleus.  These  latter  fibres  make  a 
thalamo-habenular  tract. 

The  majority  of  the  fibres  of  the  medullary  striae  terminate  in  the  habenular  nuclei,  situated 
at  the  two  sides  of  the  stalk  of  the  epiphysis.  Most  terminate  in  the  habenular  nucleus  of  the 
same  side.  Some  cross  in  the  habenular  commissure  (dorsal  part  of  the  posterior  cerebral  com- 
missure) and  terminate  in  the  nucleus  of  the  opposite  side.  A  few  are  claimed  to  pass  to  the 
nuclei  of  the  quadrigeminate  bodies  and  a  few  others  to  join  the  association  tracts  of  the  mesen- 
cephalon. Axones  given  off  by  the  cells  of  the  habenular  nucleus  curve  anteriorly,  inferiorly, 
and  then  course  posteriorly  (fasciculus  retroflexus)  to  terminate  in  the  interpeduncular  nucleus 


THE  LATERAh  VENTRICLES  873 

(a  hahenulo-peduncular  tract),  and  fibres  arising  in  this  latter  nucleus  pass  to  the  cells  about  the 
central  grey  substance  of  the  mesenecphalon  (an  inter-pedunculo-tegmental  tract).  The  two 
mesencephalic  paths  here  noted  and  the  mammillo-mesencephalic  fasciculus  noted  above  give 
three  anatomical  possibilities  for  olfactory  reflex  activities,  visceral  (or  sympathetic)  and 
somatic,  involving  the  motor  cranial  nerves  and  possibly  the  spinal  nerves.  Fibres  arising  in  the 
cortex  of  the  hippocampal  gyrus,  uncus  especiaDy,  may  pass  by  way  of  the  cingulum  and  thence 
by  any  suitable  association  fasciculus  of  the  cerebral  hemisphere  to  the  motor  area  of  the  cere- 
bral cortex;  also  fibres  may  arise  from  the  anterior  nucleus  of  the  thalamus  and  pass  to  the  motor 
cortex  by  way  of  the  internal  capsule.  From  the  motor  cortex,  the  descending  pyramidal 
fibres  give  the  possibihties  for  any  higher  cortical  activities  induced  by  smell. 

A  more  direct  mesencephahc  path  has  been  suggested  by  Wallenberg,  namely,  that  cells 
in  the  olfactory  trigone  and  anterior  perforated  substance,  about  which  terminates  fibres  of 
the  olfactory  tract,  send  axones  directly  postei-iorly,  ai'ound  the  tuber  cinereum,  to  terminate 
in  the  mammiUary  body  and  thence  the  impulses  may  go  to  the  mesencephalon.  Such  fibres, 
if  they  exist,  would  form  an  olfacto-mammillary  tract.  A  path  is  described  in  the  hedge-hog 
which  arises  from  cells  in  the  olfactory  trigone  and  passes  directly  posteriorly  to  terminate  in 
the  grey  substance  of  the  mesencephalon — an  olfacto-mesencephalic  tract. 

To  the  complicated  central  connections  of  the  sense  of  smell,  Dejerine  adds  yet  another  path, 
namely,  a  portion  at  least  of  the  terminal  stria  [stria  terminalis]  of  the  thalamus  (taenia  semi- 
circularis).  This  contains  fibres  arising  from  cells  in  the  anterior  perforated  substance  and  in 
the  septum  pellucidum  and  fibres  from  the  opposite  side  by  way  of  the  anterior  commissure.  It 
runs  a  crescentic  course  posteriorly,  bounding  the  thalamus  from  the  caudate  nucleus,  turning 
downward  and  then  anteriorly  in  the  wall  of  the  inferior  cornu  of  the  lateral  ventricle  to  termi- 
nate in  the  amygdaloid  nucleus,  which  latter  is  a  more  or  less  detached  bit  of  the  cortex  of  the 
extreme  anterior  portion  of  the  hippocampal  gyrus  (uncus).  The  stria  is  said  also  to  contain 
fibres  which  arise  in  the  amygdaloid  nucleus  and  course  in  it  forward  to  be  given  off  to  the  thala- 
mus and  probably  to  the  internal  capsule  and  thence  to  the  cerebral  cortex  above. 

SUMMARY  OF  THE  OLFACTORY  APPARATUS 

I.  Peripheral  part. 

(1)  Olfactory  area  of  nasal  epithelium  containing  the  cell-bodies  and  peripheral  processes 
of  olfactory  neurones  (olfactory  ganglion). 

(2)  Non-meduIIated  central  processes  of  olfactory  neurones,  the  olfactory  nerve,  passing  as 
numerous  filaments  through  the  cribriform  plate  of  the  ethmoid,  to  terminate  in  contact  with 
the  dendrites  of  the  "mitral  cells"  (stratum  glomerulosum)  in  the  olfactory  bulb. 

II.  The  Rhinencephalon. 

A.  The  anterior  division. 

(1)  Olfactory  bulb,  olfactory  tract,  olfactory  trigone  (tubercle),  lateral  olfactory  stria 
(gyrus),  medial  and  intermediate  olfactory  stria;. 

(2)  The  parolfactory  area,  subcallosal  gyi'us,  anterior  perforated  substance  including  the 
diagonal  band  of  Broca. 

B.  The  posterior  division. 

(1)  Part  of  anterior  commissure,  septum  pellucidum,  uncinate  fasciculus,  hippocampal 
gyrus  (uncus  especially),  dentate  g3Tus,  gyrus  cinguU  and  cingulum. 

(2)  Fimbria,  hippocampal  commissure,  fornix,  longitudinal  strise  upon  corpus  callosum, 
mammiUary  body,  mammillo-thalamic  fasciculus,  mammiUo-mesencephahc  fasciculus. 

(3)  The  anterior  nucleus  of  the  thalamus. 

(4)  The  medullary  stria  of  the  thalamus,  habenular  nucleus,  fasciculus  retroflexus,  inter- 
peduncular nucleus,  and  Lnterpedunculo-tegmental  tract. 

(5)  Probably  an  olfacto-mammillary  and  an  olfacto-mesencephalic  tract,  and  a  part  of  the 
terminal  stria  of  the  thalamus  with  the  amygdaloid  nucleus. 

THE  LATERAL  VENTRICLES 

Two  of  the  four  cavities  of  the  ventricular  system  of  the  brain  are  in  the  telen- 
cephalon. From  their  position,  one  in  each  cerebral  hemisphere,  they  are  known 
as  the  lateral  ventricles.  They  arise  as  lateral  dilations  of  the  cavity  of  the  anter- 
ior of  the  prhnary  vesicles,  and,  just  as  the  fourth  ventricle  remains  in  communi- 
cation with  the  third  by  way  of  the  aqueduct  of  the  cerebrum,  so  the  lateral  are 
connected  with  the  third  by  the  two  interventricular  foramina  (Monroi).  The 
whole  ventricular  system,  including  the  central  canal  of  the  spinal  cord,  is  Hned 
by  a  continuous  layer  of  ependyma  and  contains  a  small  quantity  of  liquid  known 
as  the  cerebro-spinal  fluid. 

Each  lateral  ventricle  is  of  an  irregular,  horseshoe  shape.  It  consists  of  a 
central  portion  or  body  and  three  cornua,  which  correspond  to  the  three  poles  of 
the  hemisphere.  The  portion  projecting  into  the  frontal  lobe  is  known  as  the 
anterior  cornu,  that  projecting  into  the  occipital  lobe  is  the  posterior  cornu,  and 
the  portion  which  sweeps  anteriorly  downward  into  the  temporal  lobe  is  the 
inferior  cornu.  The  ventricles  of  different  individuals  vary  considerably  in  capac- 
ity, and  the  cavity  of  a  given  ventricle  is  not  uniform  throughout.    In  some 


874 


THE  NERVOUS  SYSTEM 


localities  the  space  may  be  quite  appreciable,  while  in  other  places  the  walls  may 
be  approximate  or  even  in  apposition.  Each  lateral  ventricle  is  a  completely 
closed  cavity  except  at  the  interventricular  foramen.  However,  a  strip  of  the 
floor  of  the  inferior  cornu  is  separated  from  the  exterior  of  the  brain  by  only  the 
thin,  non-nervous  lamina  forming  the  floor  of  the  chorioid  fissure. 

The  interventricular  foramen  (foramen  of  Monro),  by  which  the  lateral  ven- 
tricle is  continuous  with  the  cavity  of  the  third  ventricle,  is  a  small,  roundish  chan- 


FiG.  686. — A  Cast  of  the  Four  Ventricles  of  the  Encephalon.     (After  Weloker.) 

Anterior  cornu  of  lateral  ventricle  " 

Interventricular  foramen  (Monro!) 

Third  ventricle 

Inferior  cornu  of  lateral  ventricle 

Aqueduct  of  cerebrum 

Fourth  ventricle 

Posterior  cornu  of  lateral  ventricle' 


nel,  2 to 4  mm.  wide,  which  opens  into  the  mesial  side  of  the  posterior  end  of  the 
anterior  cornu.  It  is  bounded  in  front  by  the  free  portion  of  the  anterior  pillars 
of  the  fornix,  and  behind  by  the  anterior  tubercle  of  the  thalamus.  That  the  greater 
part  of  the  lateral  ventricle  is  posterior  to  it  is  due  to  the  backward  extension  of 


Fig.  687. — Di.4.gram  of  Sagittal  Section  through  Lateral  Part  of  Right  Hemisphbke 
SHOWING  Lateral  Ventricle  from  the  Mesial  Side  of  the  Section. 


Chorioid  plexus 


Septum  pellucidum 

Fornix 

Caudate  nucleus 


Interventricular  foramen 
Caudate  nucleus 


Hippocampus  major 
Chorioid  plexus  of  inferior  cornu 


Internal  capsule 
Lenticular  nucleus 
Anterior  commissure 


the  hemispheres  during  their  growth  and  elaboration.  Through  the  two  foramina 
indirectly,  the  cavities  of  the  two  lateral  ventricles  are  in  communication  with 
each  other. 

The  walls  of  the  lateral  ventricle. — The  anterior  cornu  is  a  bowl-like  cavity, 
convex  forward  and  extending  downward  and  medial  ward  into  the  frontal  lobe. 
Above  and  anteriorly  it  is  bounded  by  the  under  surface  of  the  corpus  callosum  and 
the  radiations  of  its  genu  into  the  substance  of  the  frontal  lobe.  Its  median  bound- 
ary is  the  septum  pellucidum;  the  head  of  the  caudate  nucleus  (part  of  the  corpus 
striatum)  gives  it  a  bulging,  infero-lateral  wall,  and  the  balance  of  its  floor  is 
formed  by  the  white  substance  of  the  orbital  part  of  the  frontal  lobe. 


THE  LATERAL  VENTRICLES 


875 


The  central  portion  or  body  is  more  nearly  horizontal.  It  lies  within  the 
parietal  lobe  and  extends  from  the  interventricular  foramen  to  the  level  of  the 
splenium  of  the  corpus  callosum.  Its  roof  is  formed  by  the  inferior  surface  of  the 
body  of  the  corpus  callosum,  and  its  mesial  wall  consists  of  the  posterior  part  of 
the  septum  pellucidum,  attaching  the  fornix  to  the  under  surface  of  the  corpus 
callosum.  Like  the  anterior  horn,  it  is  given  an  oblique,  infero-lateral  wall  by 
the  narrower,  middle  part  of  the  caudate  nucleus.  Several  structures  contribute 
to  its  floor: — (1)  the  stria  terminalis  of  the  thalamus,  a  hne  of  white  substance 
conforming  to  the  genu  of  the  internal  capsule  without,  and  constituting  the 

Fig.  688. — Horizontal  Dissection  of  the  Cerebral  Hemispheres. 
The  fornix  has  been  removed  to  show  the  relation  of  the  tela  chorioidea  of  the  third  ventricle  to 
the  chorioid  plexus  of  the  lateral  ventricles.     (From  a  mounted  specimen  in  the  Anatomical 
Department  of  Trmity  College   Dulilin  ) 


Corpus 
callosum 
(dissected) 


Veins  of  Galen 


Crus  of  fornix 


Straight  sinus. 


boundary  between  the  caudate  nucleus  and  the  thalamus,  and  containing  (2)  the 
vena  terminalis  (vein  of  the  corpus  striatum);  (3)  the  lamina  affixa,  a  mesial 
continuation  of  the  stria  terminalis  upon  the  surface  of  (4)  the  lateral  part  of  the 
thalamus;  (5)  the  medial  edge  of  the  lamina  affixa,  the  tsenia  chorioidea,  and  the 
chorioid  plexus  continuing  under  (6)  the  edge  (taenia)  of  the  body  and  the  begin- 
ning crura  (posterior  pillars)  of  the  fornix  (fig.  688). 

The  chorioid  plexus  of  the  lateral  ventricle  is  continuous  with  that  of  the  third 
ventricle.  The  chorioid  tela  of  the  third  ventricle  (velum  interpositum)  con- 
tinues under  the  taenia  of  the  fornix  into  the  lateral  ventricle,  and  there,  along  the 
line  of  the  taenia  chorioidea,  becomes  elaborated  into  a  varicose,  convoluted, 
villus-like  fringe,  rich  in  venous  capillaries  and  lymphatics.  This  fringe  is  the 
chorioid  plexus.  It  is  continuous  anteriorly,  at  the  interventricular  foramen,  with 
the  corresponding  plexus  of  the  opposite  lateral  ventricle  and  with  the  chorioid 
plexus  of  the  third  ventricle.  The  latter  consists  of  two  similar  but  smaller 
fringes,  which  project  close  together  into  the  cavity  of  the  third  ventricle  from  the 
median  portion  of  the  ventral  surface  of  the  chorioid  tela.     Behind,  the  chorioid 


876 


THE  NERVOUS  SYSTEM 


plexus  of  the  lateral  ventricle  curves  posteriorly  and  inferiorly  into  the  inferior 
cornu,  being  especially  well  developed  at  the  region  of  its  entrance  into  the  latter, 
into  what  is  called  the  chorioid  glomus. 

Though  apparently  lying  free  in  the  ventricle,  the  chorioid  plexus  is  invested  throughout 
by  a  layer  of  epithelium,  the  epithelial  chorioid  lamina,  which  is  adapted  to  all  its  unevennesses 
of  surface  and  which  is  a  continuation  of  the  ependymal  lining  of  the  remainder  of  the  ventricle 
— continuous,  on  the  one  hand,  with  that  of  the  lamina  affixa  and  thalamus,  and,  on  the  other, 
with  the  epithehal  covering  upon  the  upper  surface  of  the  tania  of  the  fornix  and  fimbria. 

The  posterior  cornu  of  the  lateral  ventricle  is  a  crescentic  cleft  of  variable  length, 
convex  lateralward,  which  is  carried  backward  from  the  posterior  end  of  the  body 
of  the  ventricle  and,  curving  medialward,  comes  to  a  point  in  the  occipital  lobe. 
Its  roof  and  lateral  wall  are  formed  by  a  portion  of  the  posterior  radiation  of  the 
corpus  callosum,  which  forms  a  layer,  from  its  appearance  known  as  the  tapetum. 
In  transverse  sections  of  the  occipital  lobe  (fig.  699)  the  tapetum  appears  as  a 

Fig.  689. — Diagrammatic  Transverse  Section  op  Prosencephalon  through  Bodies  of 
Lateral  Ventricles  and  Middle  op  Thalamencephalon. 
Fifth  ventricle  .  Fornix 


Caudate 

nucleus 

Lamina  affixa 

Vena  ter- 

minalis 

Stria  ter- 

minalisof         /         /«i\  \  "^       T    "^1^ <    !  //      \ -Chorioid  tela 

thalamus  «v.smwa  \    \    \        #  ^     i-ii»i«t-^ 

f  Puta-       /^#%*^\    \  \      /  VlliH  ^      I  /  I  i  _\ 'Thalamus 

§»       men  /*'  ^       \\    W    /  ili  Oii   \m  \    //  //  \ Third 


Globus 
pallidus 


Caudate 

nucleus 

Chorioid 

plexus 

Inferior  cornu 

of  lateral 

ventricle 

Fimbria 


Mammillo- 
thalamic 
fasciculus 


Internal 
capsule 


thin  lamina  of  obliquely  cut  white  substance  immediately  bounding  the  cavity, 
while  outside  the  tapetum  occurs  a  thicker  layer  of  more  transversely  cut  fibres, 
the  occipito-thalamic  radiation.  In  the  medial  or  inner  wall  of  the  posterior  horn 
run  two  variable  longitudinal  eminences: — (1)  The  superior  of  these  is  the  bulb  of 
the  posterior  cornu,  and  is  formed  by  the  occipital  portion  of  the  radiation  of  the 
corpus  callosum  (splenium),  which  bends  around  the  impression  of  the  deep  pa- 
rieto-occipital  fissure,  and,  hook-like,  sweeps  into  the  occipital  lobe.  In  horizontal 
sections  these  fibres,  together  with  the  splenium  and  the  similar  fibres  into  the 
opposite  occipital  lobe,  form  the  figure  known  as  the  forceps  major.  (2)  The 
inferior  and  thicker  of  the  eminences  is  the  hippocampus  minor  [calcar  avis] 
(cock's  spur),  and  is  due  to  the  anterior  part  of  the  calcarine  fissure,  by  which  the 
wall  of  the  hemisphere  is  projected  into  the  ventricle.  The  posterior  horn,  like 
the  anterior,  is  not  entered  by  the  chorioid  plexu  i. 

The  inferior  cornu. — In  its  inferior  and  slightly  lateral  origin  from  the  region 
of  junction  between  the  body  of  the  ventricle  and  the  posterior  cornu,  the  inferior 
horn  aids  in  producing  a  somewhat  triangular  dilation  of  the  cavity  known  as  the 
collateral  trigone.  Beginning  as  a  part  of  the  trigone,  the  cavity  of  this  horn  at 
first  passes  posteriorly  and  lateralward,  but  then  suddenly  curves  anteriorly  and 


THE  CAUDATE  NUCLEUS 


877 


inferiorly  into  the  medial  part  of  the  temporal  lobe  nearly  parallel  wdth  the  supe- 
rior temporal  sulcus.  Above,  it  follows  the  curved  crura  (posterior  pillars)  of  the 
fornix  and  fimbria;  below,  it  does  not  extend  to  the  temporal  pole  by  from  2  to  3 
cm.  The  roof  and  lateral  wall  are,  for  the  most  part,  like  those  of  the  posterior 
horn,  being  formed  by  the  tapetum,  but  medialward  a  strip  of  the  roof  is  formed  by 
the  attenuated,  inferior  prolongation,  or  tail,  of  the  caudate  nucleus,  together 
with  the  inferior  extension  of  the  stria  terminalis  of  the  thalamus.  At  the  end  of 
the  inferior  horn  the  roof  shows  a  bulging,  the  amygdaloid  tubercle,  situated  at 
the  termination  of  the  tail  of  the  caudate  nucleus.  This  bulging  is  produced  by 
the  amygdaloid  nucleus,  an  accumulation  of  grey  substance  continuous  with 
that  of  the  cortex  of  the  hippocampal  gyrus,  and  which  gives  origin  to  part  of  the 
longitudinal  fibres  coursing  in  the  stria  terminalis  of  the  thalamus. 

In  the  medial  wall  and  floor  of  the  inferior  horn  the  follo'ning  structures  are 
shown: — (1)  In  the  posterior  or  trigonal  part  of  the  floor  is  the  longitudinal 
collateral  eminence,  a  bulging,  very  variable  in  development  in  different  speci- 
mens, produced  by  the  collateral  fissure.  This  is  often  pronouncedly  in  two  parts, 
a  posterior  prominence  corresponding  to  the  middle  portion  of  the  collateral  fissure 
and  an  anterior  prominence  (less  frequent)  produced  by  the  anterior  part  of  the 

Fig.  690. — Dissection  of  Right  Temporal  Lobe  showing  the  Medial  Wall  op  the  End 
OP  the  Inperior  Horn  op  the  Lateral  Ventricle.     (From  Spalteholz.) 


Digitations  of 
hippocampus 


Fimbria  of 
hippocampus 


Hippocampal  fissure 
Dentate  gyrus  or  fascia  ^  ^ 


Substantia  reticularis  i 

alba   (Arnoldi)  I 


Hippocampal  gyrus 


■■ Hippocampus 


Collateral  eminence 


Tffinia  fimbriae  j 

Collateral  fissure 


fissure.  (2)  Medial  to  this  eminence  lies  the  inferior  extension  of  the  chorioid 
plexus,  usually  more  voluminous  than  the  part  in  the  bodj^  of  the  ventricle.  (3) 
Partly  covered  by  the  chorioid  plexus  is  the  hippocampus  major,  a  prominent, 
sickle-like  ridge  corresponding  to  the  indentation  of  the  hippocampal  fissure.  It 
begins  as  a  narrow  ridge  posteriorly,  at  the  end  of  the  body  of  the  ventricle,  as  the 
extension  of  the  posterior  pillar  of  the  fornbc,  and  expands  anteriorly  as  the  ven- 
tricular surface  of  the  uncus.  Its  surface  is  not  regular,  but  shows  a  concave 
medial  margin  as  distinguished  from  a  wider,  convex,  lateral  sm'face.  Its  ter- 
mination in  front  (pes  hippocampi)  is  divided  by  two  or  three  flat,  radial  grooves 
into  a  corresponding  number  of  short  elevations  known  as  the  hippocampal  dig- 
itations. It  is  covered  by  a  thick  stratum  of  white  substance,  the  alveus,  arising 
from  its  depths  and  continued  mesially  into  the  fimbria.  (4)  The  fimbria  is  so 
folded  that  its  margin,  ta:nia  fimhrice,  lies  in  the  cavity  of  the  inferior  horn  attached 
to  the  chorioid  plexus  and  the  thin,  non-nervous  floor  of  the  chorioid  fissure. 

The  caudate  nucleus  (fig.  691). — As  realised  in  the  study  of  the  lateral  ven- 
tricle, the  caudate  nucleus  is  a  comma-shaped  mass  of  grey  substance  with  a 
long,  much-curved,  and  attenuated  tail.  Its  head  forms  the  bulging  lateral  wall 
of  the  anterior  horn;  thence  it  proceeds  posteriorly  in  the  lateral  wall  of  the  body 
of  the  ventricle  and,  at  the  collateral  trigone,  curves  downward  and  its  tail  becomes 


878 


THE  NERVOUS  SYSTEM 


a  medial  portion  of  the  roof  of  the  inferior  horn.  It  is  separated  from  the  thala- 
mus adjacent  to  it  by  the  stria  terminalis  of  the  thalamus  (taenia  semicircularis). 
The  end  of  its  tail  extends  anteriorly  below  to  the  level  of  the  anterior  horn  of  the 
ventricle  above.  Owing  to  its  much  curved  shape,  both  horizontal  and  vertical 
sections  of  the  hemisphere  passing  through  the  inferior  horn  may  contain  the 
nucleus  cut  at  two  places  (see  figs.  694  and  698.) 

The  caudate  nucleus  is  the  intraventricular  of  the  two  masses  of  grey  substance 
which  together  are  sometimes  referred  to  as  the  basal  ganglia.  The  extraventri- 
cular  of  these  masses  is  the  lenticular  nucleus,  which  is  bmied  in  the  substance  of 
the  hemisphere,  laterally  and  inferior  to  the  caudate  nucleus.     The  two  masses 


Fig.  691. — Diageams  of  Lateral  View  and  Sections  op  the  NtrcLEi  of  the  Corpus  Stria- 
tum WITH  THE  Internal  Capsule  Omitted. 
A  and  B  below  represent  horizontal  sections  along  the  lines  A  and  B  in  the  figure  above.     The 
figure  also  shows  the  relative  position  of  the  thalamus  and  the  amygdaloid  nucleus. 


date  nucleus 


Lenticular  nucleus 
Amygdaloid  nucleus 
Caudate  nucleus 


^^^7 Thalamus 


Tail  of  caudate 


Internal  capsule 
Lenticular  nucleus 


Caudate  nucleus 


Tail  of  caudate  nucleus 
Internal  capsule 


are  separated  by  the  internal  capsule,  a  thick  band  of  nerve-fibres  continuous  into 
the  cerebral  peduncles,  and  connecting  the  grey  cortex  of  the  hemisphere  with  the 
structures  inferior  to  it.  Anteriorly  and  below,  the  two  nuclei  become  continuous 
and  the  white  substance  of  the  internal  capsule,  in  separating  them  posteriorly, 
contributes  to  the  striated  appearance  in  sections,  known  collectively  as  the  corpus 
striatum  (figs.  692,  695) .     The  corpus  striatum  as  such  is  described  below. 

INTERNAL  STRUCTURE  OF  THE  PROSENCEPHALON 

From  the  above  examinations  of  their  external  and  ventricular  sinfaces,  it  is 
apparent  that  the  cerebral  hemispheres  consist  of  a  folded,  external  mantle  of 
grey  substance,  the  cortex  cerebri,  spread  more  or  less  evenly  over  an  internal  mass 


THE  LENTICULAR  NUCLEUS  879 

of  white  substance  which  contains  embedded  within  it  certain  masses  of  grey  sub- 
stance, the  chief  of  which  are  known  as  the  caudate  and  lenticular  nuclei  of  the 
corpus  striatum.  In  addition,  the  hemispheres  of  the  telencephalon  overlie  and 
are  in  functional  connection  with  the  structures  of  the  diencephalon  below,  the 
chief  of  which  are  the  thalamencephalon  and  the  bases  of  the  cerebral  peduncles. 

The  grey  substance  of  the  telencephalon. — The  grey  substance  is  in  intimate 
relation  with  the  white  substance,  and  in  fact  its  cells  give  origin  to  the  greater 
part  of  the  fibres  composing  the  white  substance.  The  accumulations  of  grey 
substance  to  be  considered  are  the  cerebral  cortex,  with  its  variations  in  thickness 
and  arrangement,  the  corpus  striatum,  the  claustrum,  and  the  amygdaloid  nucleus. 

The  cerebral  cortex  [substantia  corticalis]  is  distributed  over  the  entire  surface 
of  each  hemisphere  except  the  peduncular  region  of  the  base  and  the  region  of  the 
corpus  callosum  and  fornix  of  the  medial  surface.  Numerous  measmrements 
have  been  made  to  determine  its  average  thickness.  These  have  shown  that  the 
mantle  is  not  uniformly  distributed: — (1)  that  it  is  thicker  on  the  convex  surface 
than  on  the  basal  and  medial  surfaces;  (2)  that  on  the  convex  smrface  it  is  thicker 
on  the  central  region  of  the  hemisphere,  somsesthetic  area,  than  at  the  poles;  (3) 
that  in  the  average  normal  specimen  it  averages  somewhat  thicker  on  the  left  than 
on  the  right  hemisphere;  (4)  that  its  average  thickness  varies  greatly  in  different 
individuals,  and  that  the  thickness  decreases  with  old  age;  (5)  that  it  is  probably 
somewhat  thicker  in  males  than  in  females,  and  (6)  that  in  a  given  specimen  it 
averages  thicker  on  the  summits  of  the  gyri  than  in  the  floor  of  the  corresponding 
sulci.  In  the  normal  adult  conditions  it  averages  about  4  mm.  thick  on  the  ante- 
rior and  posterior  central  gyri,  in  the  somsesthetic  area,  while  it  attains  its  mimi- 
mum  thickness  of  about  2.5  mm.  on  the  basal  surface  of  the  occipital  and  frontal 
lobes.  Its  total  average  thickness  is  about  2.9  mm.  The  practically  non- 
nervous  floor  of  the  third  ventricle  and  that  of  the  chorioid  fissure  are  very  much 
thinner  but  are  not  considered  in  these  measurements. 

The  cerebral  cortex  consists  of  layers  of  the  cell-bodies  of  neurones,  chiefly  of  the  pyramidal 
type  (fig.  604),  which  receive  impulses  from  the  structures  below  and  from  other  regions  of  the 
cortex  by  way  of  fibres  reaching  them  through  the  internal  mass  of  white  substance,  and  which 
in  turn  contribute  fibres  to  the  white  substance.  Certain  fibres  of  shorter  course  and  numerous 
collateral  branches  of  fibres  passing  out  of  the  cortex  are  devoted  to  the  association  of  the  region 
of  their  origin  with  the  cortex  of  the  immediate  vicinity  of  their  origin,  and  most  of  these  course 
within  the  grey  cortex  itself.  In  certain  gyri,  such  as  the  anterior  central  gyri  and  those  of  the 
medial  surface  of  the  occipital  lobe,  these  short  association  fibres  accumulate  into  strata,  and 
in  vertical  sections  give  the  cortex  a  stratified  appearance.  Two  such  strata  of  white  substance 
may  be  noted  in  the  above  localities,  one  lying  about  midway  in  the  thickness  of  the  cortex  and 
one  slightly  internal  to  this.  They  are  known  as  the  inner  and  outer  stripes  of  Baillarger.  In 
addition,  a  thin,  superficial  or  tangential  layer  of  fibres  may  often  be  distinguished  lying  in  the 
surface  of  the  cortex.  Transverse  sections  through  the  anterior  end  of  the  hippocampus  show 
a  coiled  arrangement  of  the  layers  of  white  substance,  to  which  has  been  given  the  name  cornu 
ammonis.  The  peculiar  structure  and  appearance  of  the  olfactory  bulb  and  tract,  parts  of 
the  cortex,  have  already  been  mentioned. 

The  corpus  striatum  is  so  called  on  account  of  the  appearance  in  section  of 
its  component  parts,  the  caudate  and  lenticular  nuclei  (basal  ganglia)  and  the 
internal  capsule  between  them.  The  two  nuclei  are  directly  continuous  with 
each  other  at  their  anterior  ends  (fig.  691),  and  in  addition  they  are  connected  by 
numerous  small  bands  of  grey  substance  which  pass  from  one  to  the  other  through 
the  internal  capsule,  especially  its  anterior  part.  Also  each  nucleus  contributes 
numerous  fibres  to,  and  receives  fibres  from,  the  internal  capsule.  These  bundles 
of  fibres  both  arising  and  terminating  within  the  nuclei,  together  with  the  grey 
substance  among  the  fibres  of  the  capsule,  produce  the  ribbed  and  striped  appear- 
ance suggesting  the  name,  corpus  striatum.  The  caudate  nucleus — the  intra- 
ventricular part  of  the  corpus  striatum — hes  with  its  thicker  anterior  part  (head) 
closely  related  to  the  internal  capsule,  but  its  tail  passes  posteriorly  around  the 
posterior  border  of  the  capsule  and  curves  downward  and  anteriorly  into  the  roof 
of  the  inferior  cornu  of  the  lateral  ventricle. 

The  lenticular  nucleus  [nucleus  lentiformis] — the  extraventricular  part  of 
the  corpus  striatum — is  embedded  in  the  white  substance  of  the  cerebral  hemi- 
sphere. It  is  somewhat  pyriform  in  shape,  not  being  so  long  as  the  caudate 
nucleus,  and  neither  having  a  tail  nor  extending  so  far  anteriorly.  Its  lower  sur- 
face is  separated  from  the  inferior  cornu  of  the  lateral  ventricle  by  the  white  sub- 
stance of  the  roof  of  that  cornu,  and  by  the  tail  of  the  caudate  nucleus,  and,  fur- 


880  THE  NERVOUS  SYSTEM 

ther  forward,  the  anterior  commissure  passes  through  its  base.  Its  lateral  sur- 
face is  rounded  and  conforms  both  in  extent  and  curvature  with  the  surface  of  the 
insula,  from  which  it  is  separated  by  the  fibres  of  the  external  capsule  and  the 
intervening  claustrum.  Its  oblique  superior  and  mesial  surface  is  adapted  to  the 
lateral  surface  of  the  internal  capsule,  and  it  comes  to  a  rounded  apex  in  the  angle 
formed  by  the  internal  capsule  and  a  plane  parallel  with  the  base  of  the  hemi- 
sphere. In  both  horizontal  and  coronal  (transverse)  sections  through  its  middle 
it  resembles  a  compound  biconvex  lens.  Internally  this  appearance  is  produced 
by  two  vertically  curving  laminae  of  white  substance,  an  external  and  an  internal 
medullary  lamina,  which  divide  its  substance  into  three  zones: — the  two  medial 
zones  together  form  an  area,  triangular  in  section,  known  as  the  globus  pallidus ; 
the  lateral,  larger  and  more  grey,  concavo-convex  zone  is  the  putamen.  Radiat- 
ing fibres  from  the  medullary  laminae  extend  into  the  zones,  especially  those  of  the 
globus  pallidus.     These  zones  disappear  in  transverse  sections  of  the  anterior 


Fig.  692. — Coronal  Section  of  Telencephalon  Passing  Through  Fbontal  Lobes  and 

Anterior  Portion  of  Corpus  Striatum. 

(From  mounted  specimen  in  the  Anatnmiral  Department  of  Trinity  College,  Dublin.) 


Longi- 
tudin 
fissure 


Olfactory  tract' 


portion  of  the  lenticular  nucleus  (fig.  692),  due  to  the  fact  that  the  larger  putamen 
alone  comprises  this  portion  and  alone  becomes  continuous  with  the  caudate 
nucleus.     (See  figs.  691,  696.) 

Connections. — Both  nuclei  of  the  corpus  striatum  become  continuous  with  the  cortex  in 
the  region  of  the  anterior  perforated  substance,  and  the  putamen  of  the  lenticular  nucleus  may 
blend  with  the  anterior  part  of  the  base  of  the  claustrum.  The  following  are  the  principal  fibre 
connections: — (1)  Fibres  arising  in  the  nuclei  which  join  the  internal  capsule  to  reach  the 
cerebral  cortex,  and  fibres  arising  in  the  cortex  which  descend  by  the  same  course  to  the  cells 
of  the  nuclei.  (2)  Fibres  which  pass  in  both  directions  between  the  thalamus  and  the  corpus 
striatum  (caudate  nucleus  especially).  These  are  more  abundant  anteriorly,  and  necessarily 
pass  through  the  internal  capsule.  (3)  The  ansa  lenticularis,  or  strio-subthalamio  radiation, 
a  usually  distinct  lamina,  composed  largely  of  fibres  passing  inferiorly  between  the  thalamus 
and  lenticular  nucleus.  It  passes  from  the  basal  aspect  of  the  anterior  tubercle  of  the  thalamus 
and  curves  below  through  the  internal  capsule  to  the  basal  surface  of  the  lenticular  nucleus, 
and  there  its  fibres  are  distributed  upward  through  its  medullary  lamina  to  the  globus  pallidus 
and  putamen.  Some  enter  the  internal  capsule  and  reach  the  cortex,  chiefly  that  of  the  tem- 
poral lobe.  The  ansa  lenticularis  also  contains  fibres  from  the  cortex  of  the  temporal  lobe  to 
terminate  in  the  inferior  and  mesial  parts  of  the  thalamus.  The  fibres  associating  the  thalamus 
with  the  temporal  lobe  belong  to  the  so-called  inferior  peduncle  of  the  thalamus.  (4)  Fibres 
connecting  both  nuclei  (chiefly  the  caudate)  with  the  red  nucleus  and  substantia  nigra  of  the 
mesencephalon.  These  pass  through  the  hypothalamic  region  and  along  the  cerebral  peduncle. 
No  definitely  localised  functions  have  been  with  certainty  ascribed  to  either  nucleus.  They 
serve  as  1-elays  in  the  pathways  associating  the  cortical  grey  substance  with  the  structures  below 
and  in  them  the  neurones  concerned  in  these  pathways  are  greatly  increased. 

The  claustrum  is  a  triangular  plate  of  grey  substance  which  is  embedded  in 
the  white  substance  between  the  lenticular  nucleus  and  the  insula.     Its  medial 


THE  THALAMUS 


881 


surface  is  concave,  conforming  to  the  convexity  of  the  putamen.  The  sheet  of 
white  substance  intervening  between  it  and  the  putamen  is  known  as  the  external 
capsule.  Its  lateral  surface  shows  ridges  or  projections  in  section  which  conform 
to  the  neighbouring  gyri  of  the  insula,  and  it  is  spread  through  an  area  which  quite 
closely  coincides  with  that  of  the  inusla.  Below  and  anteriorly  it  becomes  con- 
tinuous with  the  cortex  of  the  anterior  perforated  substance  and  with  the  lenticu- 
lar nucleus  at  the  region  of  the  junction  of  these.  Above  and  posteriorly  it  gradu- 
ally becomes  thinner,  and  finally  disappears  in  the  white  substance  about  it. 
In  origin  it  is  thought  to  be  a  detached  portion  of  the  cortical  grey  substance  of 
the  insula. 

The  amygdaloid  nucleus  [nucleus  amygdalae]  is  represented  by  the  amygda- 
loid tubercle,  which  has  already  been  described  in  the  extremity  of  the  inferior 
cornu  of  the  lateral  ventricle  (figs.  666  and  691).  It  is  an  almond-shaped  mass  of 
cells  joined  to  the  tail  of  the  caudate  nucleus,  continuous  above  with  the  putamen 
and  anteriorly  continuous  with  the  cortex  of  the  hippocampal  gyrus. 

Fig.  693. — Coronal  Section  op  Telencephalon  through  the   Anterior  Commissure, 
Optic  Chiasma,  and  Trunk  op  Corpus  Callosum.     (After  Toldt,   "Atlas  of   Human 
Anatomy,"  Rebman,  London  and  New  York.) 
Caudate  nucleus 


(head) 


Internal  capsule 
(frontal  portion 


^,'  Longitudinal  fissure 
Corpus  callosum 


Anterior  cornu 
of  lateral  ven- 
tricle 

Chorioid  plexus 
of  lateral  i 


The  chief  connections  of  the  amygdaloid  nucleus  by  way  of  the  stria  tertjiinalis  of  the 
thalamus  are  noted  above  under  the  description  of  the  posterior  division  of  the  rhinencephalon. 
The  amygdaloid  nucleus,  like  the  claustrum,  is  thought  to  represent  a  detached  portion  of  the 
cortex,  it  being  detached  from  the  uncus.  Considering  this  and  its  chief  connections,  it,  with 
the  stria  terminahs  of  the  thalamus,  are  concerned  in  the  central  portion  of  the  olfactory 
apparatus. 

The  thalamus  and  hypothalamus. — The  external  features  of  these  portions  of 
the  prosencephalon  have  been  described  in  their  natural  place,  but  inasmuch  as 
they  contain  the  chief  relays  between  the  telencephalon  and  the  divisions  of  the 
nervous  system  caudal  to  the  prosencephalon,  the  consideration  of  their  internal 
structure  has  been  deferred  till  now.  The  principal  grey  masses  to  be  considered 
are  the  thalamus  and  the  hypothalamic  nucleus.  The  structures  comprising  the 
metathalamus  and  epithalamus  have  already  been  mentioned  in  their  relations 
with  the  mesencephalon  and  the  optic  and  auditory  apparatus. 

The  thalamus  has  upon  its  upper  surface,  under  its  ependyma,  a  thin  stratum 
zonale  of  white  substance,  derived  in  part  from  the  incoming  fibres  and  in  part 
from  its  own  cells.  Its  oblique  lateral  surface  conforms  to  the  medial  surface  of  the 
internal  capsule;  its  vertical  medial  surface  forms  the  lateral  wall  of  the  third 
ventricle,  and  below  it  is  continuous  into  the  hypothalamic  (tegmental)  region. 


882 


THE  NERVOUS  SYSTEM 


Its  upper  surface  shows  a  middle,  an  anterior,  and  a  posterior  prominence  or  tuber- 
cle. The  anterior  tubercle  (nucleus)  forms  the  posterior  boundary  of  the  inter- 
ventricular foramen;  the  posterior  tubercle  is  the  cushion-like  pulvinar  which 
projects  backward  over  the  lateral  geniculate  body  and  the  brachium  of  the 
superior  quadrigeminate  body. 

A  horizontal  section  through  the  supero-medial  edge,  spHtting  the  stria  medul- 
laris  of  the  thalamus  and  thus  passing  above  the  massa  intermedia,  shows  the  grey 
mass  of  the  thalamus  divided  into  segments  or  nuclei  by  a  more  or  less  distinct 
internal  medullary  lamina.  This  extends  the  whole  length  of  the  thalamus, 
dividing  its  middle  and  posterior  portion  into  the  medial  and  the  lateral  nucleus. 

Fia.  694. — HoKizoNTAii  Dissection  showing  the  Grey  and  White  Substance  op  the 
Telencephalon  Below  the  Corpus  Callosum  and  the  Relative  Position  of  the 
Thalamencephalon.     (After  Landois  and  Stirling.) 


Gyrus  cinguU 


Genu  of  corpus  callosum 


Anterior  cornu 


Caudate  nucleus 

Internal  capsule 
(Frontal  portion) 

External  capsule 

_      ^     .         f   Putamen 

Lenticular  Globus. 

nucleus      |     palUdus 

Claustrum 

Internal  capsule  (occr 

pital  portion) 


Medial  geniculate 
body 
Tail  of  caudate 
nucleus 
Hippocampus  major' 

Hippocampus  minor' 


Septum  pellucidum 


Corpus  striatum 
Column  of  fornix 


Clava 

Funiculus  cuneatus 

Funiculus  gracilis 

Anteriorly  the  lamina  bifurcates  into  a  medial  limb,  extending  to  the  medial  sur- 
face of  the  thalamus,  and  a  lateral  limb,  extending  forward  to  join  the  genu  of  the 
internal  capsule  (figs.  695,  700).  This  bifurcation  results  in  a  cup-like  sheet  of 
white  substance  which  encloses  the  anterior  nucleus.  On  the  lateral  surface  of 
the  section,  next  to  the  internal  capsule,  there  may  usually  be  distinguished  an 
external  medullary  lamina,  separated  from  the  white  substance  of  the  capsule 
by  a  reticular  layer  of  mixed  white  and  grey  substance. 

The  anterior  nucleus,  lying  partially  encapsulated  in  the  bifurcation  of  the 
internal  medullary  lamina,  is  somewhat  wedge-shaped  and  points  backward  be- 
tween the  anterior  portions  of  the  lateral  and  medial  nuclei. 

It  is  composed  chiefly  of  large  cells,  and  constitutes  the  anterior  tubercle  of  the  superior 
aspect.  Its  principal  connection  from  below  is  with  the  nuclei  of  the  mammillary  body  of  the 
same  and  opposite  sides,  and  with  uninterrupted  fibres  derived  from  the  columns  of  the  forni.x. 


THE  THALAMUS 


883 


The  fibres  from  both  sources  enter  it  by  way  of  the  mammillo-thalamic  fasciculus  (figs.  671  and 
695).     The  significance  of  this  connection  is  mentioned  in  the  description  of  the  limbic  lobe. 

The  lateral  nucleus,  lying  between  the  external  and  internal  medullary  lam- 
inae, extends  posteriorly  to  include  the  entire  pulvinar. 

The  pulvinar,  as  already  noted,  together  with  the  lateral  geniculate  body,  constitutes  the 
prosencephalic  nucleus  of  termination  of  the  optic  tract,  and  the  stratum  zonale  upon  the  surface 
of  this  nucleus  might  be  called  the  stratum  opticum.  The  anterior  portion  of  the  lateral 
nucleus  receives  fibres  inferiorly  from  the  red  nucleus,  from  the  brachium  conjunctivum 
(cerebellum  direct),  and  some  fibres  of  the  medial  lemniscus  terminate  about  its  cells. 

The  medial  nucleus  lies  medial  to  the  internal  medullary  lamina  and  forms  the 
posterior  portion  of  the  lateral  wall  of  the  third  ventricle.  It  is  shorter  than  the 
lateral  nucleus,  and  is  less  extensively  pervaded  by  fibres. 

Fig.  695. — Coronal  Section  of  Prosencephalon  through  Thalamencephalon  at  Region 
OP  Corpora  Mammillaria.  (Seen  from  in  front.)  (After  Toldt,  "Atlas  of  Human 
Anatomy,"  Rebman,  London  and  New  York.) 

Lateral  ventricle  ^  __.._-^  ,  ^  ,  . ,  ,  ,  Corpus  callosum 

(central  portion) 
Chorioid  plexus 
of  lateral  ven- 
tricle 
Caudate  nucleus  ^ 

Massa   inter-  ~,- 
media 
Internal  capsule 

Lenti-  [  (Puta 
cular     !      men 

nu-       I  Globus 

cleus     I  pallidus 

External  capsule 

Claustrum 
Ansa   peduncu- 
laris 
Optic  tract 

Inferior  peduncle  ^ 

of  thalamus 
Inferior  cornu  of 
lateral  ventricle 
Hippocampal  ^ 
digitations 

Oculomotor  nerve 


Fornix 


It  is  thought  to  receive  fibres  from  the  red  nucleus,  and  perhaps  some  from  the  lemniscus, 
and  is  usually  continuous  across  the  third  ventricle  with  the  opposite  medial  nucleus  by  the 
massa  intermedia. 

In  comparative  anatomy,  the  nuclei  of  the  thalamus  have  been  variously  subdivided  by 
the  different  investigators.  All  the  nuclei  are  connected  with  the  lenticular  nucleus  by  fibres 
passing  between  the  two  through  the  internal  capsule  directly,  and  by  fibres  curving  from  below, 
chiefly  from  the  anterior,  lateral  and  medial  nuclei,  and  passing  in  the  ansa  lenticularis. 

The  cortical  connections  of  the  thalamus  are  abundant.  They  consist  of  fibres 
both  to  and  from  the  cortex  of  the  different  lobes  of  the  hemisphere,  the  greater 
part  arising  in  the  thalamus  and  terminating  in  the  cortex.  These  fibres  collect 
in  the  internal  and  external  medullary  laminae  and  the  stratum  zonale;  most  of 
them  enter  the  internal  capsule  and  thence  radiate  to  the  different  parts  of  the 
cortex. 

They  form  the  so-called  peduncles  of  the  thalamus,  which  have  been  distinguished  both  by 
the  Flechsig  method  of  investigation  and  by  the  degeneration  method.  The  anterior  or  frontal 
peduncle  passes  from  the  lateral  and  anterior  part  of  the  thalamus  through  the  frontal  portion 
of  the  internal  capsule,  and  radiates  to  the  cortex  of  the  frontal  lobe.  (See  fig.  700.)  The 
middle  or  parietal  peduncle  passes  from  the  lateral  surface  of  the  thalamus  through  the  inter- 
mediate part  of  the  internal  capsule,  and  upward  to  the  cortex  of  the  parietal  lobe.  The  pos- 
terior or  occipital  peduncle  passes  chiefly  from  the  pulvinar,  through  the  occipital  portion  of  the 
internal  capsule,  and  radiates  backward  to  the  occipital  lobe  by  way  of  the  occipito-thalamic 
(optic)  radiation  (fig.  699).  The  inferior  peduncle  passes  from  the  medial  and  basal  surface 
of  the  thalamus  (from  the  anterior  and  medial  nuclei  chiefly),  turns  outward  to  course  beneath 
the  lenticular  nucleus,  and  radiates  to  the  cortex  of  the  temporal  lobe  and  insula.  The  fibres 
of  this  peduncle  course  chiefly  in  the  ansa  lenticularis  (fig.  695).  Some  turn  upward  in  the 
external  capsule  to  reach  the  cortex  above  the  insula;  others  pass  upward  through  the  medullary 
laminae  of  the  lenticular  nucleus. 


884  THE  NERVOUS  SYSTEM 

The  h3rpothalamic  nuclues  (fig.  698) ,  or  body  of  Luys,  is  the  principal  nucleus  of 
termination  of  the  medial  lemniscus,  the  great  sensory  spino-cerebral  pathwayl 
It  is  a  biconvex  plate  of  grey  substance  situated  on  the  basal  aspect  of  the  latera. 
and  anterior  nuclei  of  the  thalamus,  and  between  these  and  the  basis  of  the  cerebral 


Fig.  696. — Horizontal  Sections  of  the  Peosencephalon  through  the  Thalamus  and 

Corpus  Striatum. 
The  plane  of  the  section  of  the  left  hemisphere  splits  the  medullary  stria  of  the  thalamus  and 

is  about  15  millimeters  superior  to  the  plane  through  which  the  right  hemisphere  is  cut. 

(After  Toldt.) 


Trunk  of  corpus  caliosum 
Septum  pellucidum 


Genu  of  corpus  caliosum 

Anterior  cornu  of  lateral  ventricle 
Head  of  caudate  nucleus 
Column  of  fornix 
Internal  capsule 


Island  of  Reil 
(insula) 


Chorioid  glomu: 


Occipito- 
thalamic 
radiation 


Splenium  of  corpus  caliosum 


Calcarine  fissure 

peduncle,  or  rather  the  substantia  nigra,  which  is  spread  upon  the  dorsal  surface 
of  the  peduncle,  and  which,  though  greatly  diminished,  extends  into  the  hypo- 
thalamic region.  The  hypothalamic  nucleus  presents  a  brownish-pink  colour 
in  fresh  material,  due  to  pigment  in  its  cells  and  to  its  abundant  blood  capillaries. 

It  contains  the  cell-bodies  of  the  neurones  of  the  third  order  in  this  pathway,  those  of  the 
first  order  being  situated  in  the  spinal  ganglia,  and  those  of  the  second  order  in  the  nuclei  of  the 
fasciculus  gracilis  and  fasciculus  cimeatus.  It  is  enclosed  by  a  thin  capsule  of  white  substance, 
some  of  the  fibres  of  which  seem  to  decussate  with  those  of  the  opposite  side  in  the  floor  of  the 
third  ventricle,  above  and  just  behind  the  region  of  the  corpora  mammiUaria.  By  far  the  greater 
part  of  the  fibres  arising  from  the  nucleus  join  the  internal  capsule,  and  through  it  ascend  to 


WHITE  SUBSTANCE  OF  TELENCEPHALON  885 

radiate  to  the  cortex  of  the  pre-  and  post-central  gyri,  the  sensory-motor  or  somsesthetic  area 
of  the  hemisphere.     The  majority  terminate  in  the  post-central  gyrus. 

All  the  fibres  connecting  the  cerebral  cortex  with  both  the  thalamus  and  the  hypothalamic 
nucleus  belong  to  the  so-called  projection  fibres  of  the  cerebral  hemisphere. 

The  habenular  nucleus  and  the  fasciculus  relroflexus  of  Meynert  have  been  noted  in  the  de- 
scription of  the  rhinencephalon.  The  habenular  nucleus,  a  part  of  the  epithalainus,  is  a  small 
group  of  nerve  cells  situated  in  the  habenular  trigone  just  infero-lateral  to  the  epiphysis.  The 
fibres  of  the  medullary  stria  of  the  thalamus  (habenula)  terminate  about  its  cells.  A  small 
bundle  of  fibres  crossing  the  mid-hne  under  the  epiphysis  in  the  superior  aspect  of  the  posterior 
cerebral  commissure  is  called  the  commissure  of  the  habenuloe,  from  the  fact  that  it  connects  the 
habenular  nuclei  of  the  two  sides. 


Fig.  BOy.' — Oblique  Feontal  Section  through  the  Brain  in  the  Direction  of  the 
Cerebral  Peduncles  and  the  Pyramids.  (Seen  from  in  front.)  (After  Toldt,  "Atlas 
of  Human  Anatomy,"  Rebman,  London  and  New  York.) 


Longitudinal  fissure 
Radiation  of  corpus  callosum 


Septum  pE  llucidum 


Superior  frontal  gyrus 

Body  of  corpus  callosum 


Anterior  horn  of  lateral  ventricle 
Head  of  caudate  nucleus 


Corona  radiata 


Column  of  formz 


Internal  capsule 


Thalamus  ~ 
Third  ventricle  - 


Cerebral  peduncle 


Brachium  pontis 


Longitudinal  pyramidal 
fasciculi  of  pons 


Superficial  fibres  of  pons        /' 
Pyramid 


External  capsule 


Globus  pallldus 
Optic  tract 
Mammillary  body 
Oculo-motor  nerve 

Trigeminal  nerve 
Facial  and  cochlear 


Glosso-pharyngeal  nerve 

Vagus  nerve 
Inferior  ohvary  nucle 
Decussation  of  pyramids 


The  fasciculus  retroflexus  (Meynerti)  is  a  relatively  strong  bundle  of  medullated  fibres 
which  runs  downward  and  then  turns  caudalward  from  the  habenular  nucleus  toward  the  inferior 
portion  of  the  interpeduncular  fossa.  It  has  been  shown  that  many,  at  least,  of  the  fibres  of 
this  bundle  arise  from  the  cells  of  the  habenular  nucleus.  In  its  slightly  caudad  course,  the 
bundle  passes  obliquely  through  the  red  nucleus,  entering  the  medial  superior  aspect  and  making 
its  exit  from  the  ventro-mesial  side  of  the  inferior  extremity  of  this  nucleus.  In  the  animals  in 
which  it  has  been  studied,  the  bundle  ends  in  the  interpeduncular  nucleus  (ganglion),  a  group  of 
nerve  cells  lying  in  the  floor  of  the  interpeduncular  fossa  at  the  level  of  the  inferior  quadrigemina. 
In  man,  the  interpeduncular  nucleus  is  not  definitely  assembled  and  the  bundle  seems  to  dis- 
appear in  the  posterior  perforated  substance.  However,  the  microscope  shows  cells  dispersed 
among  the  fibres  of  the  bundle  and  these  cells  probably  represent  the  nucleus. 

The  white  substance  of  the  telencephalon. — A  horizontal  section  through  the 
upper  part  of  the  trunk  of  the  corpus  callosum  will  pass  above  the  basal  grey 
substance  of  the  corpus  striatum,  and,  aided  by  the  corpus  callosum,  each  hemi- 
sphere in  such  a  section  will  appear  as  if  consisting  of  a  solid,  half-oval  mass  of 
white  substance,  bounded  without  by  the  grey  layer  of  the  cortex  (fig.  672).    As 


886 


THE  NERVOUS  SYSTEM 


seen  at  this  level,  the  white  substance  of  each  hemisphere  is  known  as  the  centrum 
semiovale.  Horizontal  sections  passing  below  the  body  of  the  corpus  callosum 
involve  the  corpus  striatum  and  thalamus,  and  the  appearance  of  the  white  sub- 
stance is  modified  accordingly  (fig.  694). 

In  the  white  substance  of  the  cerebral  hemispheres  as  a  whole  three  main  sys- 
tems of  fibres  are  recognised: — projection  fibres,  commissural  fibres,  and  associa- 
tion fibres.  The  projection  fibres  are  those  of  a  more  or  less  vertical  course,  which 
pass  to  and  from  the  cortex  of  the  hemisphere,  associating  it  with  the  structures 
below  the  confines  of  the  hemisphere.  The  commissural  fibres  are  those  of  a 
transverse  or  horizontal  course,  which  cross  the  mid-line  and  functionally  connect 
the  two  hemispheres  with  each  other.  The  association  fibres  are  those  which 
neither  cross  the  mid-line  nor  pass  beyond  the  bounds  of  the  hemisphere  in  which 
they  arise,  but  instead  associate  the  different  parts  of  the  same  hemisphere — lobes 
with  lobes  and  gyri  with  gyri.     The  fibres  which  associate  the  cortex  with  the 

Fig.  698. — Coronal  Section  op  Brain  Passing  Through  the  Pulvinah  of  the  Thalamus 
AND  the  Uncus  of  the  Hippocampal  Gyrus.     (After  Toldt.) 

Chorioid  tela  of  ■ 
third  ventricle 

\  \  I       r'n/n "'/'/"  ~'»*ip''/^>'  '^ 

Chorioid  plexus 
of  third  ven- 
tricle 


Internal   capsult 


Habenular 
nucleus 
Tail  of  caudate 
nucleus 
Optic  tract 

Fimbria  of 
hippocampus 


Peduncle  of 
cerebrum 
Post,  recess  of 
interpeduncular 


Red  nucleus 


nuclei  of  the  corpus  striatum  must  also  be  classed  as  association  fibres,  since  these 
masses  of  grey  substance  are  a  part  of  the  telencephalon,  while  by  definition  those 
which  associate  the  thalamus  and  hypothalamus  with  the  cortex  belong  to  the 
projection  system.  Some  of  the  fibre  bundles  of  the  above  systems  have  already 
been  described  in  connection  with  the  parts  with  which  they  are  concerned. 

The  projection  fibres  of  the  hemisphere  comprise  both  ascending  and  descend- 
ing fibres  between  the  cerebral  cortex  and  structures  below  the  bounds  of  the  hemi- 
sphere, i.e.,  some  arise  in  the  structures  below  and  terminate  in  the  cortex;  others 
arise  from  the  cortical  cells  and  terminate  in  the  structures  below,  including  the 
grey  substance  of  the  thalamencephalon,  mesencephalon,  rhombencephalon,  and 
spinal  cord.  The  projection  fibres  are  given  different  names  in  the  hemisphere 
according  to  their  arrangement  and  the  appearances  to  which  they  contribute 
in  the  dissections.  Beginning  with  the  pyramidal  fasciculi  and  the  basis  of  the 
peduncle,  they  contribute — (1)  to  the  internal  capsule  and  some  to  the  external 
capsule  and  (2)  to  the  corona  radiata. 

The  internal  capsule  [capsula  interna]  is  a  band  of  white  substance,  consisting 
of  the  ascending  fibres  from  the  nuclei  of  the  thalamus,  hypothalamus,  and  corpus 
striatum,  reinforced  by  the  descending  fibres  from  the  cortex  to  these  nuclei  and 
by  those  descending  in  the  cerebral  peduncle  to  terminate  in  the  mesencephalon, 
rhombencephalon  and  spinal  cord.  It  is  a  broad,  fan-like  mass  of  fibres,  which 
increases  in  width  from  the  base  of  the  hemisphere  upward,  and  which  is  spread 
between  the  lenticular  nucleus  on  its  lateral  aspect  and  the  caudate  nucleus  and 


THE  CORONA  RADIATA 


887 


thalamus  on  its  medial  side.  To  reach  the  cortex  above,  the  course  of  its  fibres 
necessarily  intersects  that  of  the  radiations  of  the  corpus  callosum,  and  thus, 
together  with  the  corpus  callosum,  the  fan-like  bands  of  the  two  hemispheres  form 
a  capsule  containing  the  thalami,  the  third  ventricle,  the  caudate  nuclei,  and  the 
anterior  and  central  portions  of  the  lateral  ventricles.  In  horizontal  sections, 
each  internal  capsule  appears  bent  at  an  angle,  the  genu,  which  approaches  the 
cavity  of  the  lateral  ventricle  along  the  line  of  the  boundary  between  the  thalamus 
and  the  caudate  nucleus.  Along  the  genu  runs  the  stria  terminalis  of  the  thala- 
mus, and  through  the  genu  the  capsule  receives  fibres  from  the  internal  medullary 
lamina  of  the  thalamus,  from  the  stratum  zonale  of  the  thalamus  and  from  that 
of  the  caudate  nucleus.  At  the  genu  each  capsule  is  separable  into  two  parts: — 
(1)  the  anterior  (frontal)  portion,  spreading  between  the  caudate  and  lenticular 
nuclei;  (2)  the  posterior  (occipital)  portion,  between  the  lenticular  nucleus  and  the 
thalamus  (fig.  700.) 

Fig.  699. — Coeonal  Section  THROtroH  the  Splenium  op  the  Corpus  Callosum  and  the 
Posterior  Cornua  op  the  Lateral  Ventricles.  (Viewed  from  behind.)  (After  Toldt, 
"Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 


Radiation  of,  corpus  callosum 
Bulb  of  posterioi 


Splen 


Corpora  quadri- 
gemina 


L  of  corpus  callosum 


Tela  chorioidea 
of  third  ven- 
tricle 


Medial  longitu. L 

dinal  fasciculus 

Cerebellum 
Brachium  pontis 

Flocculus 


Epiphysis 


Posterior  cornu 
^  ^  ^  of  lateral  ven- 

tiicle 
^      Glomus  chori- 
^     ^       oideum 

Tapetum 

_  Occipito-thalamic 
radiation 
Collateral  emin- 
en:e 


Collateral  fissure 

Lateral  Lemniscus 

Brachium  con- 

junctivum 
Central  grey 
substance 

Medial  lemniscus 


Pyramid 


FunctionaOy,  the  internal  capsule  may  be  divided  into  a  frontal,  a  fronto-parietal  and  an 
occipital  part.  The  frontal  part  consists  of  (1)  an  anterior  segment,  carrying  chiefly  fibres 
coursing  in  both  directions  between  the  thalamus  and  the  cortex  of  the  frontal  lobe,  and  (2) 
a  posterior  segment  carrying  the  frontol-pontUe  tract. 

The  fronto-parietal  part  may  be  considered  in  four  segments; — (1)  An  anterior  segment, 
the  genu,  carrying  fibres  from  the  cortex  to  the  nuclei  of  the  motor  cranial  nerves;  (2)  posterior 
to  this  is  the  corticospinal  segment  for  the  arm  and  thorax,  descending  cortical  fibres  to  the  regions 
of  the  spinal  cord  supplying  these;  (3)  next  is  the  corticospinal  segment  }or  the  lower  extremity; 
(4)  a  posterior  segment  carrying  the  general  sensory  path  ascending  from  the  hypothalamic 
nucleus,  the  infero-lateral  part  of  the  thalamus  and  the  red  nucleus  to  the  cortex.  All  the 
segments  of  the  fronto-parietal  part  carry  in  addition,  fibres  in  both  directions  between  the 
cortex  above  and  the  thalamus  and  the  nuclei  of  the  striate  body. 

The  occipital  part  consists  (1)  of  an  anterior  segment  which  carries  the  temporal  and  occipital 
pontile  paths,  and  (2)  a  posterior  segment  carrying  the  visual  fibres  between  the  occipital  cortex 
and  the  nuclei  of  termination  of  the  optic  nerve.  This  segment  also  carries  the  auditory  fibres 
passing  between  the  cortex  of  the  superior  temporal  gyrus  and  the  regions  of  termination  of  the 
lateral  lemniscus.     Thus  it  carries  a  visual  and  an  auditory  path. 

The  corona  radiata. — Above  the  corpus  callosum  and  laterally  joining  its 
radiations,  the  fibres  of  the  internal  capsule  are  dispersed  in  all  directions.  The 
appearance  known  in  coronal  sections  of  the  hemispheres  as  the  corona  radiata  is 
produced  by  the  ascending  and  descending  fibres  of  the  internal  capsule  combined 
with  the  radiations  of  the  corpus  callosum.     The  radiations  related  to  the  internal 


THE  NERVOUS  SYSTEM 


capsule  may  be  divided  into  a  frontal,  a  parietal  and  an  occipital  part,  corres- 
ponding to  the  frontal,  parietal  and  occipital  peduncles  of  the  thalamus,  or  to  the 
parts  of  the  internal  capsule. 

The  radiation  derived  from  the  posterior  segment  of  the  occipital  part  of  the 
internal  capsule,  the  visual  path,  accumulates  into  a  well-defined  band  of  fibres 
which  passes  posteriorly  into  the  occipital  lobe,  spreading  in  the  lateral  wall  of  the 
posterior  cornu  of  the  lateral  ventricle  immediately  lateral  to  the  tapetum.  This 
band  consists  for  the  most  part  of  fibres  arising  in  the  pulvinar  of  the  thalamus  and 


Fig.  700.- 


-DiAGBAM  TO  Indicate  the  Relative  positions  of  the  Projection  Fibees  in 
THE  Intehnal  Capsule.     (In  part  after  VilEger.) 


yy4     y  Stria  terminalis  of 

'/^j  /  thalamus 


«?■,////'/  ••  Fronto-pon- 


-™  Cortico-spinal 
path  (arm) 

~~  ^  Cortico-spinal 
path  (leg) 

"^  General  sen- 
sory path 

■  ^  Temporal        1 
and    occipital 
pontile  path    I 

■^    visual  and 
auditory  path  J 


Fronto- 
parietal 
part 


in  the  lateral  geniculate  body  and  going  to  the  visual  area  of  the  occipital  cortex, 
and  of  fibres  arising  in  this  cortex  to  terminate  in  the  thalamus  and  mesenceph- 
alon. Being  thus  concerned  with  the  optic  apparatus,  it  is  known  as  the  occipito- 
thalamic  radiation  or  optic  radiation  (fig.  699). 

The  external  capsule  is,  as  already  noted,  a  thin  sheet  of  white  substance 
spread  between  the  claustrum  and  the  lenticular  nucleus. 

It  owes  its  appearance  as  such  to  the  presence  of  the  claustrum.  It  joins  the  internal  cap- 
sule at  the  upper,  posterior,  and  anterior  borders  of  the  putamen,  and  below  the  claustrum  it 
is  continuous  with  the  general  white  substance  of  the  temporal  lobe.  Thus  it  contributes  to 
an  encapsulation  of  the  lenticular  nucleus  by  white  substance.  Most  of  the  fibres  contained 
in  it  belong  to  the  association  system.  Its  projection  fibres  consist  of  those  of  the  inferior 
peduncle  of  the  thalamus,  which  pass  from  the  basal  surface  of  the  thalamus  and,  instead  of 
continuing  below  to  the  cortex  of  the  temporal  lobe  and  insula,  turn  upward,  around  the  lenticu- 
lar nucleus  to  the  cortex  above  the  insula.  Some  of  these  thalamus  fibres  are  known  to  pass 
upward  through  the  lamina;  of  the  lenticular  nucleus  instead  of  through  the  external  capsule. 


DESCENDING  PROJECTION  FIBERS  889 

The  ascending  projection  fibres  arise  mostly  from  the  cells  of  the  nuclei  of  the 
thalamus  and  hypothalamic  nucleus;  some  arise  from  nuclei  in  the  mesencephalon 
and  from  the  red  nucleus. 

They  may  be  summarised  as  follows: — 

(1)  The  terminal  part  of  the  general  sensory  pathway  of  the  body.  The  portion  of  the  medial 
lemniscus  which  arises  in  the  nuclei  of  the  fasciculus  gracilis  and  cuneatus,  of  the  opposite  side, 
terminates  in  the  hypothalamic  nucleus  and  the  inferior  portion  of  the  lateral  nucleus  of  the 
thalamus.  The  projection  fibres  given  off  by  the  latter  nuclei  pass  chiefly  through  the  posterior 
segment  of  the  fronto-parietal  part  of  the  internal  capsule  and  radiate  to  and  terminate  in  the 
somaesthetic  area  of  the  cortex,  chiefly  in  the  posterior  central  gyrus.  Some  few  pass  outside 
around  the  lenticular  nucleus,  and  ascend  by  way  of  the  external  capsule. 

(2)  The  terminal  part  of  the  general  sensory  pathway  of  the  head  and  neck.  The  nuclei  of 
termination  of  the  sensory  portions  of  the  cranial  nerves  of  the  rhombencephalon  (except  the 
nuclei  of  the  cochlear  nerve)  give  fibres  which  course  upward  in  the  medial  lemniscus  (fillet) 
and  reticular  substance  of  the  opposite  side  and  terminate  in  the  infero-lateral  portions  of  the 
thalamus  and  in  the  h3rpothalamic  nucleus.  Thence  arise  projection  fibres  which  ascend  to 
the  somaesthetic  area  by  practically  the  same  route  as  those  of  the  general  sensory  system  for 
the  body. 

'  (3)  The  terminal  part  of  the  auditory  pathway.  The  ventral  and  dorsal  nuclei  of  termina- 
tion of  the  cochlear  nerve  send  impulses  which,  by  way  of  the  lateral  lemniscus,  are  distributed 
to  the  inferior  quadrigeminate  body,  the  medial  geniculate  body,  and  the  nucleus  of  the  lateral 
lemniscus  of  the  opposite  side.  These  nuclei  send  projection  fibres  through  the  posterior 
segment  of  the  fronto-parietal  part  of  the  internal  capsule,  and  thence  by  the  temporal  portion 
of  the  corona  radiata  to  the  cortex  of  the  superior  temporal  gjrrus  (auditory  area).  Probably 
some  of  these  fibres  pass  by  way  of  the  inferior  peduncle  of  the  thalamus.  Some  of  the  fibres 
arising  in  the  nuclei  of  termination  of  the  vestibular  nerve  convey  impulses  which  reach  the 
somaesthetic  area,  but  the  origin  of  the  terminal  portion  of  this  system  is  uncertain. 

(4)  The  terminal  part  of  the  visual  pathway.  The  cells  of  the  pulvinar  and  the  lateral 
geniculate  body,  serving  as  nuclei  of  termination  of  the  optic  tract,  give  off  projection  fibres 
which  pass  by  way  of  the  posterior  segment  of  the  occipital  portion  of  the  internal  capsule 
and  the  occipito-thalamic  radiation  to  the  cortex  of  the  occipital  lobe,  chiefly  the  region  about 
the  posterior  end  of  the  calcarine  fissure — the  visual  area. 

(5)  The  terminal  ascending  cerebellar  pathway.  The  fibres  of  the  brachium  conjunctivum, 
after  decussating,  terminate  both  in  the  red  nucleus  and  in  the  lateral  nucleus  of  the  thalamus. 
Some  fibres  from  the  red  nucleus  become  projection  fibres  direct,  others  terminate  in  the 
medial  and  anterior  portion  of  the  lateral  nucleus  of  the  thalamus.  From  the  thalamus  the 
projection  fibres  of  this  system  pass  in  the  parietal  peduncle  of  the  thalamus  to  the  somaesthetic 
area. 

The  descending  projection  fibres  arise  as  outgrowths  of  the  pyramidal  cells 
of  the  cerebral  cortex.  Practically  all  of  them  cross  to  the  opposite  side  in  their 
descent  to  the  structures  of  the  brain  stem  and  spinal  cord.  The  majority  of  them 
arise  near  and  within  the  gyri  in  which  the  respective  ascending  fibres  terminate. 
Those  transmitting  cortical  impulses  to  the  cells  giving  origin  to  the  motor  fibres 
of  the  cranial  and  spinal  nerves  arise  chiefly  from  the  giant  pyramidal  cells  of  the 
precentral  (anterior  central)  gyrus,  the  paracentral  lobule  and  the  posterior  ends 
of  the  superior,  middle,  and  inferior  frontal  gyri.  These  latter  occupy  nearly 
three-fourths  (the  anterior  three  segments)  of  the  fronto-parietal  part  of  the  inter- 
nal capsule  and  the  middle  three-fifths  of  the  basis  of  the  cerebral  peduncle,  and 
are  usually  called  'pyramidal  fibres  (fig.  700). 

The  principal  descending  projection  fibres  may  be  grouped  as  follows: 

(1)  The  pyramidal  fibres  to  the  spinal  cord  (cortico-spinal  or  pyramidal  fascicuh  proper). 
These  arise  from  the  giant  pyramidal  cells  of  the  upper  two-thirds  of  the  precentral  gyrus, 
the  anterior  portion  of  the  paracentral  lobule  and  the  posterior  third  of  the  superior  frontal 
gyrus.  Those  for  the  lumbo-sacral  region  of  the  spinal  cord  arise  nearest  the  supero-mesial 
border  of  the  cerebral  hemisphere.  The  tract  descends  through  the  two  middle  segments  of 
the  fronto-parietal  part  of  the  internal  capsule.  Those  carrying  cortical  impulses  for  the 
muscles  of  the  arm  and  shoulder  course  in  the  segment  anterior  to  the  course  of  those  for  the 
muscles  of  the  leg.  Both  continue  through  the  cerebral  peduncles  and  the  pons  and  through 
the  pyramids  of  the  medulla,  and  then  decussate,  passing  down  the  spinal  cord  to  terminate 
about  the  ventral  horn  ccUs  (the  origin  of  the  motor  nerve  roots)  of  the  opposite  side. 

(2)  The  pyramidal  fibres  to  the  nuclei  of  origin  of  the  motor  cranial  nerves  arise  from 
the  pyramidal  cells  in  the  inferior  third  of  the  precentral  gyrus,  the  posterior  end  of  the  inferior 
frontal  gyrus,  the  opercular  margin  of  the  posterior  central  gyrus,  and  probably  some  (for  eye 
movements)  in  the  posterior  end  of  the  middle  frontal  gyrus.  The  locality  of  the  origin  of 
the  pyramidal  fibres  terminating  in  the  nuclei  of  the  facial  and  hypoglossal  nerves  only  has  been 
determined  with  certainty.  The  general  tract  passes  in  the  genu  of  the  internal  capsule, 
through  the  cerebral  peduncle,  and,  gradually  decussating  along  the  brain  stem,  terminates  in 
the  nuclei  of  the  motor  cranial  nerves  of  the  opposite  side. 

(3)  The  frontal  pontile  path  (Arnold's  bundle)  arises  in  the  cortex  of  the  frontal  lobe, 
anterior  to  the  precentral  gyrus,  descends  through  the  frontal  part  of  the  corona  radiata  and 
posterior  segment  of  the  frontal  portion  of  the  internal  capsule  into  the  fronto-mesial  portion  of 
the  cerebral  peduncle,  and  terminates  in  the  nuclei  of  the  pons. 


890  THE  NERVOUS  SYSTEM 

(4)  The  temporal  pontile  path  (Turk's  bundle)  arises  in  the  cortex  of  the  superior  and  middle 
temporal  gyri,  passes  through  the  posterior  segment  of  the  occipital  part  of  the  internal  capsule, 
enters  the  cerebral  peduncle  postero-lateral  to  its  pyramidal  portion,  and  terminates  in  the 
nuclei  of  the  pons.  An  occipito-pontile  path  is  described  as  arising  in  the  occipital  cortex  and 
joining  the  temporal  pontile  path  in  the  internal  capsule  to  pass  to  the  nuclei  of  the  pons. 

(5)  The  occipito-mesencephalic  path  (Flechsig's  secondary  optic  radiation)  arises  in  the 
cortex  of  the  visual  area  of  the  occipital  lobe  (cuneus  and  about  the  calcarine  fissure),  passes 
forward  through  the  occipito-thalamic  radiation,  downward  in  the  posterior  segment  of  the 
occipital  portion  of  the  internal  capsule,  and  terminates  in  the  nucleus  of  the  superior  quadri- 
geminate  body  and  the  lateral  geniculate  body.  It  is  probable  that  some  of  its  fibres  terminate 
directly  in  the  nuclei  of  the  eye-moving  nerves. 

(6)  Those  fibres  of  the  fornix  which  arise  in  the  hippocampus  and  terminate  in  the  corpus 
mammiUare  or  pass  through  it  to  the  anterior  nucleus  of  the  thalamus  of  the  same  and  opposite 
side  (mammiUo-thalamic  fasciculus)  or  pass  into  the  mescencephalon  and  probably  to  structures 
lower  down. 

The  commissural  system  of  fibres. — ^The  commisstiral  fibres  of  the  telenceph- 
alon serve  to  connect  or  associate  the  functional  activities  of  one  hemisphere 
with  those  of  the  other.  They  consist  of  three  groups: — The  corpus  callosum, 
the  anterior  commissure  and  the  hippocampal  commissure. 

(1)  The  corpus  callosum,  the  great  commissure  of  the  brain.  A  general  description  of 
this  with  the  medial  and  lateral  striae  running  over  it  has  aheady  been  given.  It  is  a  thick  band 
of  white  substance,  about  10  cm.  wide,  which  crosses  between  the  two  hemispheres  at  the  bottom 
of  the  longitudinal  fissure.  Its  shape  is  such  that  in  its  medial  transverse  section  its  parts  are 
given  the  names  splenium,  body,  genu,  and  rostrum  (figs.  667  and  679).  Its  lower  surface  is 
medially  joined  to  the  fornix,  in  part  by  the  septum  peUucidum  and  in  part  directly.  Laterally 
it  is  the  tapetum  of  the  roof  of  the  lateral  ventricle  of  either  side.  The  majority  of  its  fibres 
arise  from  the  cortical  cells  of  the  two  hemispheres,  and  terminate  in  the  cortex  of  the  side 
opposite  that  of  their  origin.  In  dissections,  its  fibres  are  seen  to  radiate  toward  all  parts  of 
the  cortex — the  radiation  of  the  corpus  callosum.  These  radiations  may  be  divided  into 
frontal,  parietal,  temporal  and  occipital  parts.  The  occipital  parts  curve  posteriorly  in  two 
strong  bands  from  the  splenium  into  the  occipital  lobes,  producing  the  figure  known  as  the 
forceps  major.  Anteriorly,  the  frontal  parts  are  two  similar  but  lesser  bands  which  curve 
from  the  genu  forward  into  the  frontal  lobe,  producing  the  forceps  minor. 

(2)  The  anterior  commissure  has  been  described  in  connection  with  the  rhinencephalon. 
In  addition  to  the  ohactory  fibres  coursing  through  it  from  the  olfactory  bulb  and  parolfactory 
area  of  one  hemisphere  to  the  uncus  of  the  opposite  hemisphere,  its  greater  part  consists  of 
fibres  which  arise  in  the  cortex  of  the  temporal  lobe,  the  uncus  chiefly,  of  one  side  and  terminate 
in  that  of  the  opposite  side.  It  crosses  in  the  substance  of  the  anterior  boundary  of  the  third 
ventricle,  and  through  the  inferior  portions  of  the  lenticular  nuclei,  and  can  be  seen  only  in 
dissections  (figs.  684,  693).  It  is  a  relatively  small,  round  bundle,  and  its  mid-portion 
between  its  terminal  radiations  presents  a  somewhat  twisted  appearance. 

(3)  The  hippocampal  commissure  (transverse  fornix)  belongs  wholly  to  the  limbic  lobe 
(rhinencephalon),  and  has  been  described  there.  It  connects  the  hippocampal  gyri  of  the 
two  sides,  and  crosses  the  mid-Mne  under  and  usually  adhering  to  the  under  surface  of  the 
splenium  of  the  corpus  callosum.  Crossing  the  body  of  the  fornix,  it  thins  anteriorly  and  ceases 
in  the  posterior  angle  of  the  septum  peUucidum. 

With  these  three  commissures  of  the  telencephalon,  the  three  other  commissures  of  the 
prosencephalon  should  be  called  to  mind.  The  inferior  cerebral  commissure  (Gudden's 
commissure),  while  occurring  in  the  optic  chiasma  and  allotted  by  position  to  the  telencephalon, 
really  belongs  to  the  diencephalon  since  it  connects  with  each  other  the  medial  geniculate 
bodies  of  the  two  sides.  The  supra-mammillary  commissure,  connecting  the  nuclei  of  the  mam- 
miUary  bodies  of  the  two  sides,  is  allotted  to  the  diencephalon.  The  posterior  cerebral  com- 
missure, situated  just  below  the  stalk  of  the  epiphysis,  belongs  to  both  the  diencephalon  and 
mesencephalon.  Its  superior  part,  the  habenular  commissure,  connecting  the  two  nuclei  of  the 
habenulae,  belongs  wholly  to  the  diencephalon.  In  its  inferior  part,  the  fibres  arising  in  the 
thalamus  of  one  side  and  terminating  in  that  of  the  other  side  belong  likewise  to  the  diencephalon, 
but  those  passing  between  the  superior  quadrigeminate  bodies  of  the  two  sides  and  between 
the  so-called  nuclei  of  the  medial  longitudinal  fasciculi  belong  to  the  mesencephalon. 

The  association  system  of  the  hemisphere. — The  possibilities  for  association 
bundles  connecting  the  different  parts  of  the  same  hemisphere  with  each  other  are 
innumerable,  and  a  large  number  are  recognised.  They  serve  for  the  distribution 
or  diffusion  of  impulses  brought  in  from  the  exterior  by  the  ascending  projection 
system,  and  it  is  by  means  of  them  that  the  different  areas  of  the  cortex  may 
function  in  harmony  and  coordination.  Most  of  the  association  bundles  are 
supposed  to  contain  fibres  coursing  in  both  directions.  Several  of  them  have 
already  been  described  in  company  with  the  grey  masses  with  which  they  are 
concerned.     They  may  be  summarised  as  follows  (see  figs.  683,  701  and  702) : — ■ 

(1)  Those  of  short  course,  the  fibrse  propriae,  which  associate  contiguous  gyri  with  each 
other.  These  arise  from  the  ceUs  of  a  gyrus  and  loop  around  the  bottoms  of  the  sulci,  continu- 
ally receiving  and  losing  fibres  in  the  cortex  they  associate.  The  stripes  of  BaiUarger  within 
the  cortical  layer  might  be  included  among  the  short  association  bundles. 

(2)  The  cingulum   (girdle)   lies  in  the  gyrus  cinguli  and  is  shaped  correspondingly.     It 


ASSOCIATION  FIBRES 


891 


extends  from  the  anterior  perforated  substance  and  the  subcallosal  gyrus  around  the  genu  of  the 
corpus  callosum,  then,  under  cover  of  the  gyrus  cinguU  and  around  the  splenium,  and  thence 
downward  and  forward  in  the  hippocampal  gyrus  to  the  uncus.  It  is  chiefly  an  aggregation  of 
fibres  of  short  course — fibres  which  associate  neighbouring  portions  of  the  cortical  substance 

Fig.  701. — Photogeaph   of  "Torn  Preparation "   op  Cerebral  Hemisphere   showing 
SOME  OP  THE  Association  Fasciculi.     (After  R.  B.  Bean.) 

Central  sulcus 


External  capsule 


Superior  and  inferior  longitudinal  fasciculi 
and  temporal  pontile  path 


External  capsule,  posterior  part 


Fig.  702. — Schematic  Representation  op  Certain  op  the  Association  Pathways  of  the 
Cerebral  Hemisphere. 

Fibrse  proprise 
Superior  longitudinal  ,'j 

fasciculus  ^ '    ■, 

Stria  terminalis  \  ^'  '; 

of  thalamus  \         ^— *w^ "y-^  "^       ,''  ';  Cingulum 


Uncinate  fasciculus 


Inferior  longitudinal  fasciculus 


beneath  which  they  course,  and  which,  by  continually  overlapping  each  other,  form  the  bundle. 
(3)  The  uncinate  fasciculus  is  a  hook-shaped  bundle  which  associates  the  uncus  and  anterior 
portion  of  the  temporal  lobe  with  the  olfactory  bulb,  parolfactory  area  and  anterior  perforated 
substance  and  perhaps  the  frontal  pole  with  the  orbital  gyri.  Its  shape  is  due  to  its  having  to 
curve  medialward  around  the  stem  of  the  lateral  cerebral  fissure. 


892 


THE  NERVOUS  SYSTEM 


(4)  The  superior  longitudinal  fasciculus  is  the  longest  of  the  association  paths,  and  asso- 
ciates the  frontal,  occipital,  and  temporal  lobes.  From  the  frontal  lobe  it  passes  laterally  in 
the  frontal  and  parietal  operculum,  transverse  to  the  radiations  of  the  corpus  callosum  and  the 
lower  part  of  the  corona  radiata,  and  above  the  insula  to  the  region  of  the  posterior  end  of  the 
lateral  fissure,  and  thence  it  curves  downward  and  forward  to  the  cortex  of  the  temporal  lobe. 
Some  of  its  fibres  extend  to  the  cortex  of  the  temporal  pole.  The  occipital  portion  consists 
of  a  loose  bundle  given  off  from  the  region  of  the  downward  curve,  which  radiates  thence  to 
the  occipital  cortex. 

(5)  The  inferior  longitudinal  fasciculus  associates  the  temporal  and  occipital  lobes  and 
extends  along  the  whole  length  of  these  lobes  parallel  with  their  tentorial  surfaces.  Posteriorly 
it  courses  lateral  to  the  lower  part  of  the  oceipito-thalamic  radiation,  from  which  it  differs  by 

Fig.  703. — Diagrams  Suggesting  the  General  Motor,  General  and  Special  Sensory 
AND  THE  Association  Areas  of  the  Convex  and  Mesial  Surfaces  of  the  Cerebral 
Hemisphere. 


Parietal 
*'  association 
area 


Temporo-occlpifal 
association  area 


Frontal 

-association 

area 


Temporo-  occipital 
association  area 


the  fact  that  its  fibres  are  less  compactly  arranged.     It  associates  the  lingual  and  fusiform  gyri 
and  the  cuneus  with  the  temporal  pole. 

(6)  The  medial  and  lateral  longitudinal  striae  of  the  upper  surface  of  the  corpus  caUosum 
may  be  considered  among  the  association  pathways,  since  most  of  their  fibres  associate  the  grey 
substance  of  the  hippocampal  gyrus  with  the  subcallosal  gyrus  and  the  anterior  perforated 
substance  of  the  same  hemisphere.  Their  significance  as  parts  of  the  rhinencephalon  has  already 
been  given. 

(7)  Likewise  the  longitudinal  fibres  in  the  stria  terminalis  of  the  thalamus  (taenia  semi- 
circularis)  may  be  considered  among  the  association  pathways,  since  these  connect  the  amyg- 
daloid nucleus  with  the  anterior  perforated  substance. 

(8)  The  numerous  fibres  passing  in  both  directions  between  the  cerebral  cortex  and  the 
nuclei  of  the  corpus  striatum  belong  to  the  association  system.  These  do  not  form  a  definite 
bundle,  but,  instead,  contribute  appreciably  to  the  corona  radiata.  However,  a  pathway 
described  as  the  occipito-frontal  fasciculus  probably  consists  largely  of  the  more  sagittally 
running  fibres  of  this  nature.  The  existence  of  this  fasciculus  has  been  noted  in  degenerations 
and  in  cases  of  arrested  development  of  the  corpus  callosum.  Its  fibres  are  described  as  con- 
tributing greatly  to  the  tapetum,  and  as  coursing  beneath  the  corpus  callosum  immediately 


FUNCTIONAL  AREAS  OF  CORTEX  893 

next  to  the  ependyma  of  the  lateral  ventricle.  As  a  mass,  they  appear  in  intimate  connection 
with  the  caudate  nucleus,  and  are  spread  toward  both  the  frontal  and  the  occipital  lobes  (chiefly 
the  latter),  in  the  mesial  part  of  the  corona  radiata  of  those  lobes.  It  is  described  as  also  con- 
taining fibres  in  both  directions  associating  the  occipital  with  the  temporal  lobe.  Vertical 
association  fibres  pass  through  the  caudate  and  lenticular  nuclei  between  the  cortex  above  and 
that  of  the  temporal  lobe  below. 

(9)  Since  the  olfactory  bulb  is  a  part  of  the  hemisphere  proper,  the  olfactory  tract  may  be 
considered  an  association  pathway  connecting  the  olfactory  bulb  with  the  parolfactory  area, 
the  subcallosal  gyrus,  the  anterior  perforated  substance,  and  the  uncus.  As  already  shown, 
a  portion  of  the  fibres  of  the  tract  belongs  to  the  commissural  system. 

THE   FUNCTIONAL   AREAS    OF   THE   CEREBRAL    CORTEX 

The  definitely  known  areas  of  specific  function  of  the  human  cerebral  cortex  are  relatively 
small.  They  comprise  but  little  more  than  a  third  of  the  area  of  the  entire  hemisphere.  They 
are — (1)  the  general  sensory-motor  or  somaisthetic  area,  and  (2)  the  areas  for  the  organs  of 
special  sense.  They  represent  portions  of  the  cortex  in  which  terminate  sensory  or  ascending 
projection  fibres  bearing  impulses  from  the  given  peripheral  structures,  and  in  which  arise  motor 
or  descending  projection  fibres  bearing  impulses  in  response. 

Knowledge  of  the  location  of  the  areas  has  been  obtained — (1)  by  the  Flechsig  method  of 
investigation,  and  to  a  considerable  extent  by  Flechsig  himself;  (2)  from  clinico-pathological 
observations,  largely  studies  of  the  phenomena  resulting  from  brain  tumors  and  traumatic 
lesions;  (3)  by  experimental  excitation  of  the  cortex  of  monkeys  and  apes,  the  resulting  phe- 
nomena being  correlated  with  the  anatomical  findings  and  compared  with  the  observations  upon 
the  human  brain.  The  remaining  larger  and  less  known  areas  of  the  cortex  are  referred  to  as 
'association  centres'  or  areas  of  the  'higher  psychic  activities.' 

In  development,  the  sensory  fibres  to  the  specific  areas  acquire  their  medullary  sheaths 
first,  before  birth,  and  then  the  respective  motor  fibres  from  each  become  medullated.  It  ia 
not  till  a  month  after  birth  that  the  association  centres  show  medullation  and  therefore  acquire 
active  functional  connection  with  the  specific  areas. 

In  defining  an  area  it  is  not  claimed  that  all  the  fibres  bearing  a  given  type  of  impulse 
terminate  in  that  area,  nor  that  all  the  motor  fibres  leading  to  the  given  reaction  originate  in 
the  area.  It  can  only  be  said  that  of  the  fibres  concerned  in  a  given  group  of  reactions,  more 
terminate  and  arise  in  the  areas  cited  than  in  any  other  areas  of  the  cortex.  The  corresponding 
motor  fibres  arise  both  in  the  region  of  the  termination  of  the  sensory  fibres  (sensory  area) 
and  also  in  a  zone  (motor  area)  either  partially  surrounding  or  bordering  upon  a  part  of  the 
region  of  termination. 

The  different  areas  are  as  follows: — 

(1)  The  somaesthetic  (sensory-motor)  area,  the  area  of  general  sensibility,  and  the  area  in 
which  arise  the  larger  part  of  the  cerebral  motor  or  pyramidal  fibres  for  the  cortical  control 
of  the  general  muscular  system.  As  is  to  be  expected,  it  is  the  largest  of  the  specific  areas.  It 
includes  the  anterior  central  gyrus,  posterior  central  gyrus,  the  posterior  ends  of  the  superior, 
middle,  and  inferior  frontal  gyri,  the  paracentral  lobules,  and  the  immediately  adjacent  part  of 
the  gyrus  cinguli.  The  ascending  or  sensory  fibres  are  found  to  terminate  most  abundantly 
in  the  part  posterior  to  the  central  sulcus  (Rolandi),  the  posterior  central  gyrus  being  the  special 
area  of  cutaneous  sensibility,  and  the  adjacent  anterior  ends  of  the  horizontal  parietal  gyri  have 
been  designated  as  the  area  of  'muscular  sense.'  Both  these  areas  are  carried  over  upon  the 
medial  surface  to  involve  the  lower  part  of  the  paracentral  lobule  and  a  part  of  the  gyrus  cinguli. 
The  anterior  central  gyrus  gives  origin  to  relatively  more  motor  fibres  than  the  other  portions  of 
the  somffisthetic  area.  In  distribution,  the  muscles  furthest  away  from  the  cortex  are  innervated 
from  the  most  superior  part  of  the  area,  the  leg  area  being  in  the  supero-mesial  border  of  the 
hemisphere,  while  that  from  the  head  is  in  the  anterior  and  inferior  part  of  the  area  (fig.  703). 
The  muscles  of  mastication  and  the  laryngeal  muscles  are  controlled  from  the  fronto-parietal 
operculum.  Broca's  convolution,  the  opercular  portion  and  part  of  the  triangular  portion 
of  the  inferior  frontal  gyrus,  of  the  left  hemisphere,  constitutes  the  especial  motor  area  of  speech, 
and  Mills  has  extended  this  area  to  include  the  supero-anterior  portion  of  the  insula  below. 
The  various  authorities  differ  considerably  as  to  the  exact  locations  of  many  of  the  areas  for 
the  cortical  control  of  given  sets  of  muscles.  Further  observations  must  be  skillfully  made 
tor  localisation  of  areas  of  the  human  cortex  in  detail  and  further  correlations  must  be  deter- 
mined between  the  experiments  upon  the  cortex  of  anthropoid  apes  and  the  functions  of  that 
of  man.  The  accompanying  diagrams  are  compiled  from  several  of  the  diagrams  more  usually 
given  and  must  be  considered  as  only  approximately  correct. 

(2)  The  visual  area. — The  especial  sensory  portion  of  this  area  is  that  immediately  border- 
ing upon  either  side  of  the  posterior  part  of  the  calcarine  fissure.  The  entire  area,  motor  and 
sensory  overlapping  each  other,  includes  the  whole  of  the  cuneus.  The  motor  visual  area  proper 
is  described  as  the  more  peripheral  portion  of  the  entire  area.  In  addition,  an  area  producing 
eye  movements  is  described  as  situated  in  the  posterior  end  of  the  middle  frontal  gyrus. 

(3)  The  auditory  (cochlear)  area  comprises  the  middle  third  of  the  superior  temporal  gyrus 
and  the  transverse  temporal  gyri  of  the  temporal  operculum.  The  motor  portion  of  this  area 
hes  in  its  inferior  border.  The  fibres  arising  in  the  area  course  downward  ia  the  temporal 
pontile  path  to  the  motor  nuclei  of  the  medulla. 

(4)  The  olfactory  area  consists  of  the  olfactory  trigone,  the  parolfactory  area,  the  sub- 
callosal gyrus,  part  of  the  anterior  perforated  substance,  the  hippocampal  gyrus  (especiaUj'  the 
uncus),  and  the  callosal  half  of  the  gyrus  cinguli.  Its  motor  or  efferent  area  lies  chiefly  in  the 
hippocampal  g3T.'us,  the  fibres  from  which  pass  out  from  the  telencephalon  by  way  of  the  fornix 
and  cingulum. 


894 


THE  NERVOUS  SYSTEM 


(5)  The  gustatory  area  is  supposed  to  comprise  the  anterior  portion  of  the  fusiform  gyrus 
and  the  zone  (motor  portion)  about  the  anterior  extremity  of  the  inferior  temporal  sulcus. 

(6)  The  assocaition  areas. — The  relatively  large  areas  allotted  at  present  to  the  so-called 
higher  psychic  activities  are  indicated  in  fig.  703.  The  great  relative  extent  of  these  is  one  of 
the  characteristics  of  the  human  brain.  They  probably  merely  represent  the  portions  of  the 
cortex  of  which  httle  is  known,  and  may  eventually  be  subdivided  into  more  specific  areas. 
They  are  considered  to  be  connected  with  the  structures  below  by  fewer  projection  fibres  than 
are  the  recognised  areas  named  above,  while,  on  the  other  hand,  they  are  rich  in  association 
fibres.  By  means  of  the  latter  they  are  in  intimate  connection  with  the  specific  areas  and  have 
abundant  means  of  correlating  and  exercising  a  controlhng  influence  upon  the  functions  of  these 
areas.  According  to  Flechsig,  they  consist  of — (1)  a  parietal  association  area,  comprising  that 
part  of  the  parietal  cortex  between  the  somaesthetic  area  and  the  visual  area;  (2)  an  occipito- 
temporal association  area,  including  the  unspecified  portions  of  the  temporal  lobe  and  the  ad- 
joining portion  of  the  occipital  lobe  not  included  in  the  visual  area;  (3)  a  frontal  association 
area,  including  all  the  frontal  lobe  anterior  to  the  somesthetic  and  olfactory  area.  In  the 
folds  of  the  inferior  parietal  lobule  of  the  parietal  association  area  such  intellectual  activities 
as  the  optic  discrimination  of  words,  letters,  numbers,  and  objects  generally  are  supposed  to 

Fig.  704. — Convex  Surface  op  left  Cebebral  Hemisphere  with  Diagrammatic  Presenta- 
tion OF  the  Areas  Suggested  as  Concerned  with  Speech. 

Area  for  coordination  of  muscles  producing  speech 
f  (Broca's  convolution) 

I  Motor  area  for  hand  (graphic) 


Motor  area  for  mouth  and  larynx 


^  Auditory    word 
images 


Visual  word 
'      images 


Auditory  area 


Word  understanding 


take  place,  while  the  superior  parietal  lobule  continued  into  the  posterior  part  of  the  praecxmeus 
is  the  general  region  for  the  perception  of  form  and  solidity  of  objects — the  stereognostic  centre. 

The  insula  is  suggested  as  the  area  in  which  auditory,  olfactory  and  gustatory  impulses 
are  associated  with  the  motor  areas  beginning  in  the  operculum  dorso-laterally  adjacent  to  it. 

Observations  of  symptoms  and  the  position  of  lesions  accompanying  them  have  made  it 
possible  to  arrive  at  some  trustworthy  conclusions  regarding  the  cortical  areas  controlling 
speech.  Broca  announced  in  1861  that  the  inferior  frontal  gjTus  of  the  left  hemisphere  was 
peculiarly  concerned  with  speech.  This  area  was  later  confined  to  the  posterior  end  or  opercular 
portion  of  this  gyrus  and  the  name  "Broca's  Convolution"  was  given  it.  It  is  now  known  that 
Broca's  convolution  and  the  adjacent  portion  of  the  triangular  part  of  the  inferior  frontal  gyrus 
as  well  comprise  the  motor  area  or  emissive  speech  area — the  area  especially  devoted  to  the 
control  of  that  coordinated  action  of  the  muscles  concerned  which  makes  possible  articulate 
speech.  Patients  in  whom  this  area  is  impaired  are  unable  to  give  utterance  to  words  though 
they  may  understand  them  both  written  and  spoken,  and  though  they  may  give  utterance  to 
sound.  This  inability  is  known  as  motor  aphasia.  Results  of  observed  lesions  have  further 
shown  that  the  area  in  which  the  auditory  images  of  words  are  retained  (word  memories)  com- 
prises the  posterior  end  of  the  superior  temporal  gyrus  and  the  adjoining  portion  of  the  supra- 
marginal  gyrus.  Injury  to  this  area  is  accompanied  by  inability  to  recognise  spoken  words 
although  the  patient  hears  them  and  may  recognise  and  understand  written  words,  a  phe- 
nomenon known  as  "word-deafness"  or  sensory  aphasia.  This  area  may  be  considered  as 
continuous  with  the  superior  portion  of  the  posterior  end  of  the  middle  temporal  gyrus  which 
has  been  suggested  as  the  area  of  "word-understanding,"  or  "lalognosis."  On  the  other 
hand,  the  area  in  which  visual  images  of  words  are  retained  is  located  as  the  angular  gyrus. 
Injury  to  this  results  in  an  inability  to  recognise  printed  or  written  words  although  the  patient 


CONDUCTION  PATHS  895 

may  hear,  understand  and  speak  them.  This  is  called  "word-Uindness."  This  area  is  nearest 
the  special  area  of  vision  on  the  one  hand  and  on  the  other  hand,  is  continuous  into  the  area  to 
which  word-understanding  is  attributed.  For  purposes  of  writing,  it  must  be  associated  with 
the  motor  area  for  the  muscles  of  the  hand  in  the  precentral  gyrus. 

While  the  motor  area  for  speech  is  most  functional  in  the  left  hemisphere,  the  remaining 
areas  concerned  are  probably  equally  developed  in  the  two  hemispheres. 

III.  GENERAL  SUMMARY  OF  SOME  OF  THE  PRINCIPAL 
CONDUCTION  PATHS  OF  THE  NERVOUS  SYSTEM 

In  the  following  summary  the  arabic  numerals  indicate  paragraphs  in  which  are  mentioned 
the  nuclei  or  ganglia  containing  the  cell-bodies  of  the  neurones  interposed  in  the  chains;  the 
small  letters  indicate  the  different  names  given  to  the  different  levels  of  the  pathways  through 
which  their  fibres  run.  For  detailed  descriptions  of  either  nuclei  or  pathways  see  pages  de- 
scribing them.     Only  the  more  common  neurone  chains  are  followed  here. 

I.  The  Spino-cbrebhal  and  Cerebro-spinal  Path 

A.  The  ascending  system  of  neurones,  (fig.  706) 

1.  Spinal  ganglion — neurone  of  first  order. 

(a)     Terminal  corpuscles  and  peripheral  process  of  T-fibre. 
(6)     Dorsal  or  afferent  root  of  spinal  nerve. 

(c)     Ascending  branch  of  bifurcation  of  dorsal  root  fibre  in  fasciculus  gracihs,  or 
fasciculus  cuneatus  of  spinal  cord. 

2.  Nucleus  of  fasciculus  gracilis  or  nucleus  of  fasciculus  cuneatus  in  meduUa  oblongata — 

neurone  of  second  order, 
(a)     Internal  arcuate  fibres. 
(6)     Decussation  of  lemniscus. 

(c)  Interolivary  stratum  of  lemniscus  of  opposite  side. 

(d)  Medial  lemniscus. 

3.  Hypothalamic  nucleus  and  lateral  nucleus  of  thalamus — neurone  of  third  order. 

(a)     Internal  capsule,  posterior  segment  of  fronto-parietal  portion. 

(6)     Corona  radiata,  fronto-parietal  part. 

(c)     Posterior  central  gyrus  of  somsesthetic  area  of  cerebral  cortex. 

B.  Descending  system  of  neurones  (fig.  706). 

1.  Giant  pyramidal  cells  of  precentral  g}TUS  of  somaesthetic  area. 

(o)  Corona  radiata,  fronto-parietal  part. 

(6)  Internal  capsule,  middle  segments  of  fronto-parietal  portion. 

(c)  Basis  of  the  cerebral  peduncle  and  the  peduncle. 

(d)  Pyramid  of  medulla  oblongata. 
(el)  Decussation  of  pyramids. 

(/')    Lateral  cerebro-spinal  fasciculus  (crossed  pyramidal  tract), 
(e^)    Ventral  cerebro-spinal  fasciculus  (direct  or  uncrossed  pyramidal  tract). 
(P)    Gradual  decussation  of  latter  in  cervical  and  upper  thoracic  regions  of  spinal 
cord. 

2.  Cells  of  ventral  horn  of  spinal  cord  of  opposite  side, 
(o)     Ventral  or  efferent  roots  of  spinal  nerves. 

(6)     Peripheral  nerve-trunks  directly  to  skeletal  muscles  or  indirectly  to  smooth 
muscle  or  glands  by  way  of  sympathetic  neurones. 

II.  Short  'Reflex'  Paths  of  Spinal  Cord 

1.  Spinal  gangha. 

(o)  Terminal  corpuscles  and  peripheral  process  of  T-fibres. 

(6)  Dorsal  root  of  spinal  nerve. 

(c)  Collaterals  and  descending  branches  of  bifurcation  of  dorsal  root  fibres  in  spinal  cord 

(d)  Directly  to  ventral  horn  cells  of  same  level  of  spinal  cord. 

(e)  Or,  more  commonly,  to  same  through  intermediation  of  Golgi  cell  of  type  II. 

(/)    Or  to  neurones  of  fasciculi  proprii  to  ventral  horn  cells  of  other  levels  of  spinal  cord. 

2.  Ventral  horn  cells  of  same  (chiefly)  and  opposite  side  and  thence  by  way  of  ventral  roots 

and  peripheral  nerve  trunks  directly  to  muscles. 

3.  Dorso-lateral  group  of  ventral   horn  cells  of  same   (chiefly)  and    opposite  sides  and 

thence  by  ventral  root  fibres  to  cell-bodies  in  sympathetic  gangha. 

4.  Sympathetic  axones  to  smooth  muscle  or  glands. 

III.  Cerebral  Path  for  the  Cranial  Nerves,  ExcLusrvE  of  Those  of  Special  Sense 
A.  Ascending  system  of  neurones. 

1,  Ganglia  of  origin  of  sensory  components  of  vagus,  glossopharyngeus,  glosso-palatine 

and  trigeminus. 
(a)  Peripheral  arborisations  and  afferent  peripheral  branches  of  T-fibres  of  same. 
(6)  Central  branches  of  T-fibres  of  same  (sensory  nerve  roots). 

2.  Nuclei  of  termination  of  central  branches  (bifurcated  and  imbifurcated)  in  meduUa 

oblongata, 
(a)  Reticular  formation,  internal  arcuate  fibres  and  medial  lemniscus  of  the  opposite 
side. 


896 


THE  NERVOUS  SYSTEM 


3.  Hypothalamic  nucleus  and  lateral  nucleus  of  thalamus. 

(a)  Internal  capsule,  posterior  segment  of  fronto-parietal  portion. 

(6)   Corona  radiata,  fronto-parietal  part. 

(c)   Cerebral  cortex — chiefly  lower  third  of  posterior  central  gyrus. 

Fig.  705. — Scheme  of  Ascending  or  Spino-cerebeal  Conduction  Pathways. 


-Fibrse  propriEe 
P3Tamidal  fibre 


Corona  radiata 


■Internal  capsule 
-Hypothalamic  nucleus 


.Nuclei  of  termination  of 
sensory  cranial  ] 


Ganglia  of  sensory  cranial  nerves 


Nucleus  of  spinal  tract  of  trigeminus 


.Nucleus  of  fasciculus 

cuneatus 
■Nucleus  of  fasciculus 
gracilis 


^N.  Posterior  root 
'  Spinal 
ganglion 


'Fasciculus  cuneatus 


•Fasciculus  gracilis 


B.  Descending  system  of  neurones. 

1.  Pyramidal  cells  of  opercular  region  of  soma^sthetic  area. 

(a)  Corona  radiata,  fronto-parietal. 

(b)  Internal  capsule,  genu  chiefly. 

(c)  Basis  of  cerebral  peduncle  and  peduncle. 

(d)  Decussation  in  brain  stem. 


CONDUCTION  PATHS 


897 


2.  Nuclei  of  origin  of  motor  cranial  nerves  and  motor  components  of  mixed  cranial 
nerves,  of  opposite  side  chiefly  and  thence  by  way  of  these  nerves  to  the  respective 
muscles  supplied. 
Notes:  (1)  Most  of  the  descending  cortical  fibres  to  the  nucleus  of  origin  of  the  trochlear 

Fig.  706. — Scheme  of  Descending  Ceeebeo-spinal  Conduction  Pathways. 


Caoidate  nucleus' 


Internal  capsule 


Cerebral 

peduncle 

Trochlear  nerv 


Medulla  oblongati 


Ventral  roots  of 
spinal  nerves 

Ventral  white 
commissure 


nerve  and  that  portion  of  the  nucleus  of  the  oculomotor  which  supplies  the  internal  rectus 
muscle  apparently  do  not  decussate  but  terminate  in  the  nuclei  of  the  same  side. 

(2)  The  efferent  nucleus  of  the  glosso-palatine  (salivatory  nucleus)  and  the  dorsal  efferent 
nucleus  of  the  vagus  give  rise  to  visceral  efferent  fibres,  i.e.,  carry  impulses  destined  for  smooth 
muscle  and  glands  by  way  of  sympathetic  neurones.  The  same  is  true  for  the  supero-median 
part  of  the  nucleus  of  the  oculomotor. 


898  THE  NERVOUS  SYSTEM 

(3)  The  nuclei  of  termination  of  the  cranial  nerves,  especially  those  of  the  vestibular  and 
trigeminus,  send  fibres  also  into  the  cerebellum. 

IV.  The  Short  'Reflex'  Paths  of  the  Cranial  Nehves 

These  consist  of  the  central  branches  of  their  afferent  or  sensory  fibres,  bearing  impulses  to 
the  nuclei  of  origin  of  both  their  own  motor  components  and  to  the  nuclei  of  origin  of  other 


Fig.  707. — Scheme  of  Principal  Ascending  Cerebellar  Conduction  Paths. 


-*•  Corona  radiata 

Thalamus 

Lateral  nucleus  of 

thalamus 
-  Internal  capsule 


Red  nucleus 

Decussation  of  brachia  conjunctiva 
Nucleus  fastigii 

Dentate  nucleus 


3        v^eicuciiuut 

(displaced) 


--._  Ganglia  of  afferent  cranial  nerves 
--''  (vestibular  chiefly) 


—  •  Nucleus  of  funiculus  cuneatus 
'  Nucleus  of  funiculus  gracilis 


>  Spinal  ganglia 


motor  nerves.  Fibres  to  the  more  distant  nuclei  pass  to  them  by  way  of  the  medial  longi- 
tudinal fasciculus.  Instead  of  terminating  in  the  motor  nuclei  directly,  the  sensory  fibres  are 
usually  interrupted  by  a  third  or  intermediate  neurone  interposed  in  the  chain.  The  vagus  and 
glosso-pharyngcus  are  connected  by  way  of  the  solitary  fasciculus  and  its  nucleus  with  the 
structures  below  their  level  of  entrance,  even  with  the  ventral  horn  cells  of  the  upper  segments 
of  the  cervical  cord,  and  through  these  with  the  muscles  of  respiration. 


CONDUCTION  PATHS  899 

V.  Conduction  Paths  Involving  the  Cerebellum 

A.  Ascending  cerebellar  pathways. 
1.  Spinal  ganglia. 

(a)  Dorsal  roots  of  spinal  nerves. 

(6)   Collaterals  and  descendiag  branches  of  bifurcation  of  dorsal  root  fibres  in  spinal 
cord,  chiefly  those  conveying  impulses  of  muscle-sense. 
2x.  Dorsal  nucleus  (Clarke's  column). 

(o)  Dorsal  spino-cerebellar  fasciculus  (direct  cerebellar  tract). 
(6)   Restiform  body  (inferior  cerebellar  peduncle) — 

(c)  Joined  in  meduUa  by  external  arcuate  fibres  (crossed  and  uncrossed  fibres  arising 
in  nuclei  of  funiculus  gracilis  and  cuneatus) ; 

(d)  Joined  in  medulla  by  fibres  arising  in  nuclei  of  termination  of  afferent  vagus, 
glosso-pharyngeal,  vestibular,  and  trigeminal  nerves; 

(e)  Joined  by  fibres  both  to  and  from  (ascending  and  descending)  the  inferior  olivary 
nucleus  of  the  same  and  opposite  sides  (cerebello-olivary  fibres). 

2y.  Nerve-cells  in  base  of  ventral  horn  of  same  and  opposite  side. 

(a)  Superficial  antero-lateral  spino-cerebellar  fasciculus  (Gowers'  tract),  ascending 

through  spinal  cord  and  reticular  formation'  of  medulla  and  pons. 
(6)   Anterior  meduUary  velum  and  brachium  conjunctivum  to   cerebellar  cortex 
(vermis). 

3.  Cerebellar  cortex  (vermis),  dentate  nucleus,  nucleus  fastigii,  nucleus  emboliformis, 

and  nucleus  globosus. 
(a)  White  substance  (corpus  medullars)  of  cerebellum,  associating  various  regions 

of  its  cortex  and  its  nuclei  with  each  other. 
(6)   Brachium   conjunctivum    (superior   cerebellar  peduncle)    arising   chiefly   from 

dentate  nucleus, 
(c)    Decussation  of  brachium  conjunctivum. 

4.  Red  nucleus  and  ventral  portion  of  lateral  nucleus  of  thalamus.     Most  fibres  of  the 

brachium  conjunctivum  terminate  in  the  red  nucleus;  many  merely  give  off 
collaterals  to  it  in  passing  to  their  termination  in  the  thalamus.  Most  of  the 
ascending  fibres  arising  in  the  red  nucleus  also  terminate  in  the  ventral  part 
of  the  thalamus;  some  ascend  to  the  cerebral  cortex  direct. 

(a)  Internal  capsule,  middle  third,  and  fronto-parietal  part  of  corona  radiata. 

(6)   Somsesthetic  area  of  cerebral  cortex  and  cortex  of  frontal  lobe  anterior  to  it. 

(c)    Inferior  peduncle  of  thalamus  to  cortex  of  temporal  lobe. 

B.  Descending  cerebrocerebellar  paths. 

1.  Pyramdial  cells  of  somsesthetic  area  send  fibres  through  corona  radiata,  internal 

capsule,  and  cerebral  peduncle  to  nuclei  of  pons  and  arcuate  nucleus  of  same  and 
opposite  side. 

2.  Gelt  of  cortex  of  posterior  part  of  frontal  lobe  give  fibres  to  form  frontal  pontile 

path  through  frontal  parts  of  corona  radiata  and  internal  capsule  and  through  medial 
part  of  cerebral  peduncle  to  nuclei  of  pons  of  opposite  side. 

3.  Cells  of  cortex  of  temporal  lobe  (superior  and  middle  gyri)  give  fibres  to  form  temporal 

pontile  path  which  passes  under  the  lenticular  nucleus  into  anterior  segment  of 
occipital  portion  of  internal  capsule  and  lateral  part  of  cerebral  peduncle  to  nuclei  of 
pons  of  opposite  side.  This  path  is  joined  in  the  internal  capsule  by  a  small  occipito- 
pontile  path. 

4.  Cells  of  nuclei  of  pons  send  fibres  by  way  of  brachium  pontis  (middle  cerebeOar 
peduncle)  to  cortex  of  cerebellar  hemisphere,  of  side  opposite  to  that  of  the  origin 
of  the  cei-ebral  fibres  making  synapses  with  the  cells  of  the  pons. 

C.  Descending  cerebellospinal  paths. 

1.  From  cells  of  nucleus  fastigii  of  same  and  opposite  sides  and  probably  from  other  nuclei 
of  cerebellum  arise  fibres  which  terminate  in  the  nuclei  of  termination  of  the  vestib- 
ular nerve  and  these  send  fibres  into  the  intermediate  and  anterior  marginal  fasciculi 
of  spinal  cord  (fig.  619),  and  thence  to  the  cells  of  the  anterior  horn. 

2.  Probably  connected  with  the  cerebellum  is  the  pathway  arising  in  the  red  nucleus 
of  the  opposite  side  and  descending  in  the  rubro-spinal  tract  of  the  lateral  funiculus 
of  the  spinal  cord  (fig.  619).  The  rubro-spinal  tract  decussates  in  the  ventral  portion 
of  the  tegmentum  of  the  mesencephalon  and  is  said  to  pass  through  the  medulla  oblon- 
gata in  the  medial  longitudinal  fasciculus.  It  must  be  noted  here  that  some  fibres 
arising  in  the  cortex  of  the  frontal  lobe  terminate  in  the  red  nucleus. 

VI.  The  Vestibular  Conduction  Paths  (Equilibration) 

1.  Vestibular  ganglion  gives  origin  to  the  peripheral  utricular  and  three  ampullar 
branches  and  to  the  combined  and  centrally  directed  vestibular  nerve. 

2.  Lateral  vestibular  nucleus  (Deiters'),  medial  nucleus,  superior  nucleus,  and  nucleus 

of  descending  or  spinal  root  (nuclei  of  termination)  give  origin  to  fibres  as  follows: — 
(a)  From  lateral  and  superior  nuclei  to  nucleus  fastigii  of  opposite   side  and  to 

cortex  of  vermis  and  to  dentate  nucleus  (cerebellar  connection). 
(6)  From  medial  and  superior  nuclei  to  nuclei  of  origin  of  eye-muscle   nerves  of 

same  and  opposite  sides,  by  way  of  medial  longitudinal  fascicuh. 
(c)   From  lateral  nucleus  and  nucleus  of  descending  root  through  reticular  formation 

into_lateral  and  ventral  vestibulo-spinal  tracts  of  spinal  cord. 


900 


THE  NERVOUS  SYSTEM 


(d)  The  nuclei  receive  fibres  from  the  grey  substance  of  the  vermis.  It  is  probable 
that  all  the  nuclei  of  termination  give  off  fibres  bearing  ascending  impulses  which 
ultimately  reach  the  somresthetic  area,  but  the  course  pursued  and  neurones 
involved  in  such  a  chain  are  uncertain. 

VII.  The  Auditory  Conduction  Path  (Cochlear  Nerve) 

1.  Spiral  ganglion  of  the  cochlea  gives  origin  to  short  peripheral  fibres  to  organ  of 

Corti,  and  to  the  centrally  directed  cochlear  nerve. 

2.  Dorsal  and  ventral  nuclei  of  the  cochlear  nerve  (nuclei  of  termination). 

(o)  Striae  medullares  arise  from  dorsal  nucleus  and  pass  around  outer  side  of  resti- 
form  body  (acoustic  tubercle),  then  medianward  under  ependyma  of  floor 
of  fourth  ventricle  to  mid-line,  then  ventralward  into  tegmentum,  where 
they  decussate  and  join  trapezoid  body  and  lateral  lemniscus  of  opposite  side. 

Fig.  708. — -Diagram  Showing  Some  op  the  Connections  op  the  Vbstibxjlar  and  Cochlear 

Nerves. 


Medial  geniculate  body 


Nucleus  of  lateral  lemmscus 

Medial  longitudinal  fasciculus 

Lateral  lemniscus. 

Peduncle  of  superior  olive. 


^Inferior  quadngeminate  body 


Nucleus  of  trochlear  nerve 


Nucleus  fastigii 

Nucleus  emboliformis 


Dentate  nucleus 


^  Lateral  nucleus  of 
"■'   vestibular  nerve 
_^Restiform  body 

Dorsal   nucleus   of 
^'^    cochlear  nerve 
^^Ventral  nucleus  of 
''      cochlear  nerve 
.Cochlear  nerve 


Superior  olivary  nucleus 


Trapezoid  body 

(6)  Fibres  arising  in  ventral  nucleus  pass  ventraDy  medianward  and  some  termi- 
nate in  the  superior  ohvary  nucleus  of  same  side;  others  pass  by  way  of  trapezoid 
body  and  lateral  lemniscus  to  terminate  in  superior  olivary  nucleus,  nucleus 
of  lateral  lemniscus,  medial  geniculate  body  and  nucleus  of  inferior  quadri- 
geminate  body  of  the  opposite  side. 

3.  Nuclei  of  superior  olives  of  both  sides  and  nucleus  of  lateral  lemniscus  send  fibres 
by  way  of  lateral  lemniscus  to  inferior  quadrigeminate  body  and  through  inferior 
brachium  to  medial  geniculate  body,  and  some  may  pass  uninterrupted  to  the 
cortex  of  the  temporal  lobe. 

4.  Fibres  from  medial  geniculate  body  and  probably  from  nucleus  of  inferior  quadri- 
geminate body  pass  into  internal  capsule  and  through  temporal  part  of  corona  radiata 
to  middle  third  of  superior  temporal  gyrus  and  adjacent  portions  (auditory  area). 

6.  From  strife  medullares  and  from  superior  ohvary  nucleus  (peduncle  of  superior  olive) 
arise  fibres  which  terminate  in  nucleus  of  abducens  or  pass  by  way  of  the  medial 
longitudinal  fasciculus  to  other  motor  nuclei  of  cranial  nerves.  It  is  probable  that 
fibres  from  the  auditory  area  of  the  cerebral  cortex  are  also  distributed  to  nuclei  of 
the  cranial  nerves. 

VIII.  Conduction  Paths  op  the  Optic  Apparatus 
.  Oplic  impulses. 
1.  'Bipolar'  cells  of  retina  with  short  (peripheral)  processes  to  layer  of  rods  and  cones 
(neuro-epithehum)   and  short   centrally  directed  processes  to  ganglion-cell  layer 
of  retina  (nucleus  of  termination). 


CONDUCTION  PATHS 


901 


2.  Ganglion-cells  of  retina  give  origin  to — 

(o)  Optic  stratum  of  retina. 
(6)   Optic  nerve. 

(c)  Optic  chiasma;  fibres  from  nasal  side  of  retina  cross  in  chiasma  to  opposite  side; 

fibres  from  lateral  side  of  retina  continue  on  same  side  in— 

(d)  Optic  tract  to — 

3.  Pulvinar  of  thalamus,  lateral  geniculate  body,  and  nucleus  of  superior  quadrigeminate 
body. 

(o)  Fibres  from  nucleus  of  superior  quadrigeminate  body  pass  ventrally,  to  nuclei  of 
origin  of  oculomotor  and  trochlear  nerves  and  to  medial  longitudinal  fasciculus 
of  same  and  opposite  sides,  and  from  it  are  distributed  to  nucleus  of  origin,  of 
abducens. 

(6)  Fibres  from  lateral  geniculate  body  and  pulvinar  pass  through  occipitafportion 
of  internal  capsule  and  oocipito- thalamic  radiation  (optic  radiation)  to  cortex  of 
occipital  lobe  (visual  area). 

Fig.  709. — Diagram  of  Principal  Pathways  of  Optic  Apparatus.     (After  Cunningham,) 


CORP.  GEN. M 


4.  Cells  of  visual  area  of  cortex  send  fibres  through  occipito-thalamic  radiation  and 
occipital  portion  of  internal  capsule  to  nucleus  of  superior  quadrigeminate  body 
(oocipito-mesencephalic  fasciculus),  and  thence,  probably  interrupted  by  cells  of 
this  nucleus,  to  nuclei  of  eye-muscle  nerves. 

5.  Cells  of  nucleus  of  superior  quadrigeminate  body  and  pulvinar  send  fibres  by  way  of 
medial  longitudinal  iasciculus  into  lateral  and  ventral  funicuU  of  spinal  cord  (see 
fig.  619),  chiefly  of  the  opposite  side.  Fibres  from  the  quadrigeminate  body  cross 
mid-line  chiefly  in  decussation  of  'optic-acoustic  reflex  path'  (fig.  662). 

6.  The  smaller  cells  of  the  supero-mesial  group  of  the  nucleus  of  the  oculomotor  nerve 

(nucleus  of  Edinger  and  Westphal)  send  axones,  by  way  of  the  trunk  of  the  nerve 
and  the  short  root  of  the  ciliary  ganglion,  which  terminate  about  cells  in — 

7.  The  ciliary  gangUon,  whose   cells  send  axones  to  enter  the  ocular  bulb  and  termi- 

nate upon  the  smooth  muscle  fibres  of  the  cihary  body  and  iris. 

B.  Skin-pupillary  reflexes. 

1.  Peripheral  processes  of  spinal  gangUon  cells  terminating  in  the  skin  and  central 
processes  of  same  entering  by  way  of  dorsal  roots  of  cervical  nerves  to  bifurcate  in 
spinal  cord  and  give  terminal  twigs  about — • 

2.  Cells  of  the  dorso-lateral  group  of  the  ventral  horn  of  the  same  and  opposite  sides. 
These  cells  send  (visceral  efferent)  axones  to  terminate  about  cells  in — 


902 


THE  NERVOUS  SYSTEM 


3.  The  superior  cervical  sympathetic  ganglion,  which  cells  send  axones  chiefly  by  way 
of  the  carotid  plexus  and  the  sympathetic  roots  of  the  ciUary  ganglion  to  terminat 
about  cells  in — 

4.  The  ciliary  ganglion.  Such  cells  send  axones  into  the  ocular  bulb  to  terminate  in 
the  ciliary  body  and  radial  muscle  fibres  of  the  iris,  producing  dilation  of  the  pupil. 

C.  Auditory-eye  reflexes. 

1.  Cells  of  the  nuclei  of  termination  of  the  cochlear  nerve  and  superior  olive  send  fibres 
by  way  of  the  medial  longitudinal  fasciculus  (some  to  this  by  way  of  the  peduncle 
of  the  superior  olive)  to  the  nuclei  of  origin  of  the  eye-moving  nerves. 

2.  The  same  nuclei  of  the  cochlear  nerve  send  axones  by  way  of  the  lateral  lemniscus 
to  terminate  in  the  superior  quadrigeminate  body  and  thence  may  be  sent  impulses 
which  are  distributed  to  the  nuclei  of  the  eye-moving  nerves. 

IX.  Principal  Conduction  Paths  op  Olfactoky  Apparatus 

1.  Bipolar  cells  of  olfactory  region  of  nasal  epithelium  send  short  (peripheral)  processes 
toward  surface  of  nasal  cavity  and  centrally  directed  processes,  the  olfactory  nerve, 
through  lamina  cribrosa  of  ethmoid  bone  into  olfactory  bulb  (glomerular  layer). 

2.  'Mitral  cells'  of  olfactory  bulb  give  fibres  which  form — 
(a)  The  olfactory  tract  which  divides  into — ■ 


Fig.  710.- 


-Diagram  SHcmNG  Some  of  the  Principal  Tracts  and  Synapses  op  the  Olpac- 
TORY  Apparatus. 


Anterior 
Subcallosal  gyrus 
Parolfactory  area 


Gyrus  rectus  ^ 


Olfactory  tract 
Olfactory  bulb 


Perforating  fibres 

\  Medullary  stria  of  thalamus 


^  Longitudinal  striae 
on  corpus  callosum 

Hippocampal  com- 

(Lyre) 


~*  Habenular nucleus 

_ .  Habenulo-pedun- 
cular  tract  (fasci- 
culus retroflexus) 


Mammillo-mesen- 
o  cephalic  fasciculus 

■  ^x  Penduculo-tegmental 

tract 
Interpeduncular  nucleus 


Fimbria  hippocampi 

Uary  body 

Anterior  perforated  substance 


Olfactory  epithelium 


(6)  Medial  olfactory  stria  through  which  fibres  pass — (1)  into  parolfactory  area  (Broca's 
area);  (2)  into  subcallosal  gyrus;  and  (3)  by  way  of  anterior  cerebral  commissure 
to  olfactory  bulb  and  uncus  of  hippocampal  gyrus  of  opposite  side. 

(c)  Intermediate  olfactory  stria  to  anterior  perforated  substance. 

(d)  Lateral  olfactory  stria,  which  terminates  to  some  extent  in  anterior  perforated 

substance,  but  chiefly  in  uncus,  hippocampal  gyrus,  and  gyrus  cinguU   (olfactory 
area)  of  same  side. 

3.  Cells  of  uncus  and  hippocampal  gyrus  give  fibres  which  form — 

(a)  The  cingulum  (in  part),  by  which  they  are  associated  with  the  cortex  of  the  gyrus 
cinguli  and  other  areas  of  the  cerebral  cortex. 

(b)  The  hippocampal  commissure  (in  part),  by  which  they  are  connected  with  the  grey 
substance  of  the  opposite  side. 

(c)  The  fornix,  which,  interrupted  in  part  in  the  nuclei  of  the  corpus  mammUlare, 
conveys  impulses — (1)  to  the  anterior  nucleus  of  thalamus  of  the  same  (chiefly) 
and  opposite  sides  (mammillo-thalamic  fasciculus),  and  (2)  into  the  mesencephalon 
and  substantia  nigra  (mammillo-mesencephalic  fasciculus),  and  by  way  of  this 
tract  probably  to  the  nuclei  of  the  mesencephalon  and  medulla  oblongata. 

4.  The  parolfactory  area,  anterior  perforated  substance,  anterior  portion  of  thalamus  and 
fornix  give  fibres  which  form  the  medullary  stria  of  the  thalamus  and  which  terminate 
in  the  habenular  nucleus. 

5.  Habenular  nucleus  sends  fibres  in  fasciculus  retroflexus  to  terminate  in  interpeduncular 
nucleus. 

6.  Interpeduncular  nucleus  sends  fibres  to  nuclei  of  mesencephalon  and  probably  to 
structures  below  it. 


RELATIONS  OF  BRAIN  AND  CRANIUM 


903 


The  Relations  of  the  Brain  to  the  Walls  of  the  Ceanial  Cavity 

The  precise  methods  by  which  the  exact  positions  of  the  most  important  fissures,  sulci, 
gyri,  and  areas  can  be  ascertained  and  mapped  out  on  the  surface  of  the  head  in  the  living  subject 
are  fully  described  in  Section  XIII.  Here,  only  a  very  general  survey  of  the  relations  of  the 
brain  to  the  cranial  bones  is  given  and  from  a  purely  anatomical  standpoint. 

The  parts  of  the  brain  which  lie  in  closest  relation  with  the  walls  of  the  cranial  cavity  are 
the  olfactory  bulb  and  tract,  the  basal  and  lateral  surfaces  of  the  cerebral  hemispheres,  the 
inferior  surfaces  of  the  lateral  lobes  of  the  cerebellum,  the  ventral  surfaces  of  the  medulla  and 
pons,  and  the  hypophysis. 

Certain  of  these  portions  of  the  brain  lie  in  relation  with  the  basi-cranial  axis,  that  is,  with 
the  basi-oGcipital,  the  basi-sphenoid,  and  the  ethmoid  bones,  while  others  are  associated  with  the 
sides  and  vault  of  the  cranial  cavity.  Considering  the  former  portions  first,  the  ventral  surface 
of  the  medulla  oblongata,  which  is  formed  by  the  pyramids,  lies  upon  the  upper  surface  of 
the  basi-occipital  bone.     More  superiorly  the  ventral  surface  of  the  pons  rests  upon  the  basi- 

Fig.  711. — Drawing  of  a  Cast  of  the  Head  op  an  Adttlt  Male. 
(Prepared  by  Professor  CuiininKliam  to  illustrate  cranio-cerebral  topography.) 


Position  of 
frontal 
eminence 


Transverse 
(lateral) 
sinus 


sphenoid,  from  which  it  is  partly  separated  by  the  basilar  artery  and  the  pair  of  abducens 
nerves.  In  front  of  the  dorsum  sella3  the  hypophysis  (pituitary  body)  is  lodged  in  the  hypophyseal 
fossa.  Still  further  forward  the  olfactory  tracts  he  in  grooves  on  the  upper  surface  of  the  pre- 
sphenoid  section  of  the  sphenoid  bone;  and  in  front  of  the  sphenoid  the  olfactory  bulbs  rest  upon 
the  cribriform  plates  of  the  ethmoid. 

Posterior  and  lateral  to  the  posterior  part  of  the  foramen  magnum  the  lateral  lobes  of  the 
cerebellum  are  in  relation  with  the  cranial  wall,  resting  upon  the  lower  parts  of  the  supra- 
occipital  and  the  posterior  parts  of  the  ex-occipital  portions  of  the  occipital  bone,  while  anteriorly 
each  lobe  is  in  relation  with  the  inner  surface  of  the  mastoid  process  and  the  posterior  surface 
of  the  petrous  portion  of  the  temporal  bone.  The  area  of  the  skull  wall  which  is  in  close  re- 
lationship with  the  cerebellar  hemispheres  may  be  indicated,  on  the  external  surface  of  the  skull, 
by  a  line  which  commences  at  the  inferior  part  of  the  external  occipital  protuberance  and  thence 
runs  upward  and  lateralward.  It  crosses  the  superior  nuchal  line  a  httle  beyond  its  centre,  and, 
continuing  in  the  same  direction,  crosses  the  inferior  part  of  the  lambdoid  suture  and  reaches  a 

Eoint  directly  above  the  asterion  (the  meeting-point  of  the  occipital,  temporal,  and  parietal 
ones) ;  thence  it  descends,  just  in  front  of  the  occipito-mastoid  suture,  to  the  tip  of  the  mastoid 
process,  and  there  turns  medialward  to  its  termination  at  the  margin  of  the  foramen  magnum, 
immediately  behind  the  posterior  end  of  the  oociptal  condyle. 

The  basal  surface  of  each  cerebral  hemisphere  may  be  said  to  consist  of  two  parts,  an  anterior 
and  a  posterior,  separated  by  the  stem  of  the  lateral  cerebral  fissure.     The  anterior  part,  formed 


904 


THE  NERVOUS  SYSTEM 


by  the  orbital  surface  of  the  frontal  lobe,  rests  upon  the  upper  surfaces  of  the  orbital  plate  of 
the  frontal  bone  and  the  lesser  wing  of  the  sphenoid.  It  is,  therefore,  in  close  relation  with  the 
upper  wall  of  the  orbital  cavity.  The  posterior  part,  behind  the  stem  of  the  lateral  fissure, 
begins  with  the  anterior  portion  of  the  temporal  lobe,  including  its  pole.  The  pole  itself 
projects  against  the  orbital  plate  of  the  great  wing  of  the  sphenoid  bone,  and  it  is  in  relationship 
with  the  posterior  part  of  the  lateral  wall  of  the  orbit.  The  basal  surface  of  the  hemisphere, 
behind  the  pole  of  the  temporal  lobe  is  in  contact  with  the  upper  surfaces  of  the  great  wing  of 
the  sphenoid  and  the  petrous  part  of  the  temporal  bone. 

The  convex  surfaces  of  the  cerebral  hemispheres  have  the  most  extensive  relationships  with 
the  cranial  wall,  and  it  is  more  especially  to  these  surfaces  that  the  surgeon  turns  his  attention. 
The  general  area  in  which  the  convex  surface  of  each  cerebral  hemisphere  is  in  relation  with  the 
skuU  bones  is  readily  indicated  by  a  series  of  lines  which  correspond  with  the  positions  of  its 
superciliary,  infero-lateral,  and  supero-mesial  borders. 

The  line  marking  the  superciliary  margin  of  the  hemisphere  commences  at  the  nasion  (the 
mid-point  of  the  fronto-nasal  suture) ;  it  passes  lateralward  above  the  superciliary  ridge,  crosses 
the  temporal  ridge,  then,  turning  posteriorly  in  the  temporal  fossa,  it  reaches  the  parieto- 
sphenoidal  suture,  and  continues  backward  along  it  to  its  posterior  extremity. 


Fig.  712. — Drawing  op  a  Cast  of  the  Head  of  a  Newly  Born  Male  Infant. 
(Prepared  by  Professor  Cunningham  to  illustrate  cranio-cerebral  topography.) 


Interparietal 
sulcus 
External  part  of 
parieto-occip- 
ital  fissure 


Position  of 
frontal  eminence 
Lateral  fissure 


The  line  marking  out  the  infero-lateral  border  commences  at  the  posterior  end  of  the  parieto- 
sphenoidal  suture,  whence  it  passes  downward,  in  front  of  the  spheno-squamous  suture,  to  the 
infra-temporal  ci-est  (pterygoid  ridge) ;  there  it  turns  posteriorly  and,  running  parallel  with  and 
mesial  to  the  zygomatic  arch,  it  crosses  the  root  of  the  zygoma,  and,  ascending  slightly,  it  passes 
above  the  external  auditory  meatus.  Continuing  backward  with  an  incliriation  upward  it 
reaches  a  point  immediately  above  the  asterion;  thence  it  descends,  and,  crossing  the  inferior 
part  of  the  lambdoid  suture  and  the  superior  nuchal  line,  it  passes  medialward  to  the  inferior 
part  of  the  external  occipital  protuberance. 

The  supero-mesial  border  of  the  hemisphere  is  defined  by  a  line  which  runs  from  the  nasion 
to  the  inion.  This  line  should  be  drawn  about  5  mm.  lateral  to  the  sagittal  suture,  because 
the  mesial  area  is  occupied  by  the  superior  sagittal  sinus,  and  it  should  be  further  away  from 
the  middle  line  on  the  right  than  on  the  left  side,  because  the  sinus  tends  to  he  more  to  the 
right  side. 

The  area  of  the  skull  wall  enclosed  by  the  three  lines  which  mark  the  positions  of  the  super- 
ciliary, infero-lateral,  and  the  supero-mesial  borders  of  the  cerebral  hemisphere  is  formed  by  the 
vertical  plate  of  the  frontal  bone,  the  parietal  bone,  the  great  wing  of  the  sphenoid,  the  squamous 
part  of  the  temporal,  and  the  upper  section  of  the  supra-occipital  segment  of  the  occipital  bone. 
It  covers  the  outer  surfaces  of  the  frontal,  parietal,  temporal,  and  occipital  lobes  of  the  cerebrum 
and  the  fissures  and  sulci  which  bound  and  mark  them. 

In  every  consideration  of  the  topographical  relations  of  the  cerebral  g3Ti  to  the  walls  of  the 
cranial  cavity  it  must  be  borne  in  mind  that  the  conditions  are  not  constant,  and  that,  therefore, 
the  relations  are  variable.  The  three  main  factors  upon  which  this  variability  depends  are  age, 
sex,  and  the  shape  of  the  skull.  As  examples  of  the  variations  which  occur  it  may  be  mentioned 
that  the  lateral  cerebral  fissure  is  relatively  higher  in  the  child  than  in  the  adult  (compare 
figs.  711  and  712).  The  supero-mesial  end  of  the  central  sulcus  is  further  away  from  the  coronal 
suture  in  the  female  and  in  the  child  than  in  the  adult  male,  and  in  dolichocephalic  than  in 


BLOOD-SUPPLY  OF  BRAIN  905 

braohycephalic  heads.  The  angle  formed  between  the  Hne  of  the  central  fissure  and  the  mid- 
sagittal  plane,  which  averages  about  68°  in  the  adult,  is  more  acute  in  dolichocephalic  heads, 
and  the  external  part  of  the  parieto-occipital  fissure  is  further  forward  in  the  child,  and  possibly 
in  the  female,  than  it  is  in  the  adult  male. 

The  position  of  the  posterior  horizontal  limb  of  the  lateral  fissure  varies  even  in  the  adult. 
Its  posterior  part  is  always  under  cover  of  the  parietal  bone,  and  it  terminates  either  in  front  of 
or  inferior  to  the  parietal  eminence,  but  the  anterior  part  may  be  above,  parallel  with,  or  inferior 
to  the  squamo-parietal  suture.  In  the  adult  the  anterior  part  of  the  fissure  runs  upward  and 
backward  from  the  posterior  end  of  the  spheno-parietal  suture  along  the  anterior  part  of  the 
squamo-parietal  suture  to  its  highest  point;  thence  it  continues  in  the  same  direction  beneath  the 
parietal  bone  toward  the  lambda,  terminating  either  in  front  of  or  below  the  parietal  eminence. 
In  the  child,  however,  the  fissure  is  considerably  above  the  hne  of  the  squamo-parietal  suture 
(fig.  712),  which  it  gradually  approaches,  attaining  its  adult  position  about  the  ninth  year. 
This  change  of  position,  which  occurs  during  the  first  nine  years,  is  due  partly  to  the  ascent  of 
the  sutural  hne  and  partly  to  the  descent  of  the  fissure  on  the  surface  of  the  brain. 

The  frontal  bone  always  covers  the  superior,  middle,  and  inferior  frontal  gyri,  except  their 
posterior  extremities,  which  are  beneath  the  parietal  bone  (fig.  711).  The  ascending  limb  (ramus 
anterior  ascendens)  of  the  lateral  fissure,  which  cuts  into  the  posterior  part  of  the  inferior  frontal 
gyrus,  runs  parallel  with  and  under  cover  of  the  lower  part  of  the  coronal  suture,  or  immediately 
in  front  of  it,  and  the  anterior  horizontal  hmb  is  parallel  with  and  beneath  the  upper  margin  of 
the  great  wing  of  the  sphenoid. 

The  parietal  bone  is  in  relation  with  the  convex  surfaces  of  four  lobes  of  the  brain.  Speaking 
very  generally,  it  may  be  said  that  the  anterior  third  covers  the  posterior  part  of  the  frontal 
lobe,  including  the  anterior  central  gyrus,  and  the  posterior  ends  of  the  superior,  middle,  and  in- 
ferior frontal  gyri  and  the  precentral  sulcus.  The  posterior  two-thirds  of  the  bone  are  superficial 
to  the  perietal  lobe,  the  posterior  part  of  the  temporal  lobe,  the  anterior  part  of  the  occipital  lobe, 
the  posterior  part  of  the  horizontal  limb  of  the  lateral  fissure,  the  superior  and  inferior  parts  of 
the  post-central  sulcus,  the  interparietal  sulcus,  the  posterior  sections  of  the  superior  and  middle 
temporal  sulci,  and  the  external  part  of  the  parieto-occipital  fissure.  The  central  sulcus  is 
beneath  the  parietal  bone  at  the  junction  of  its  middle  and  anterior  thirds  (fig.  711). 

In  the  adult,  the  upper  end  of  the  central  sulcus  is  situated  at  about  55  per  cent,  of  the  whole 
length  of  the  naso-inionic  hne  posterior  to  the  nasion.  It  is  about  4  or  5  cm.  from  the  coronal 
suture.  The  inferior  end  of  the  sulcus,  which  extends  to  near  the  posterior  horizontal  limb 
of  the  lateral  fissure,  lies  beneath  the  point  of  intersection  of  the  auriculo-bregmatic  line  with 
a  hne  drawn  from  the  stephanion  (the  point  where  the  temporal  ridge  cuts  the  coronal  suture) 
to  the  asterion.  This  point  is  about  46  per  cent,  of  the  horizontal  arc  measured  from  the 
glabella  to  the  inion. 

The  superior  end  of  the  parieto-occipital  fissure  usually  lies  about  6  mm.  in  front  of  the 
lambda,  and  the  course  of  the  fissure  may  be  indicated  by  a  line  drawn  from  5  mm.  in  front  of 
the  lambda  to  a  point  immediately  above  the  asterion,  and,  as  the  latter  point  corresponds  with 
the  pre-occipital  notch  on  the  infero-lateral  border  of  the  hemisphere,  the  line  in  question  will 
indicate  the  adjacent  margins  of  the  parietal,  temporal,  and  occipital  lobes. 

The  occipital  bone  is  in  close  relation  with  the  cerebellum,  as  already  pointed  out,  but  it 
also  covers  the  posterior  part  of  the  lateral  surface  of  the  occipital  lobe  of  the  cerebral  hemisphere. 
The  great  wing  of  the  sphenoid  covers  the  outer  surface  of  the  pole  of  the  temporal  lobe,  and 
the  squamous  part  of  the  temporal  bone  covers  the  anterior  parts  of  the  superior,  middle,  and 
inferior  temporal  gyri  and  the  sulci  which  separate  them. 

The  Blood  Supply  of  the  Encephalon 

The  double  origin  of  the  continuous  arterial  system  of  the  brain  given  by  the  confluence  of 
the  two  vertebral  arteries  and  the  two  internal  carotid  arteries,  together  with  the  description 
of  the  general  distribution  of  the  different  cerebral,  mesencephalic,  and  cerebellar  arteries  into 
which  the  system  is  divided,  and  the  origin  and  course  of  the  corresponding  veins,  are  fuUy  dealt 
with  in  Section  V.  Here  attention  may  be  called  briefly  to  the  abundant  and  systematic 
internal  distribution  of  the  terminal  branches  of  the  system  and  their  intimate  arrangement  for 
the  actual  nourishment  of  the  nervous  tissues  within. 

The  general  plan  of  the  blood  supply  for  the  entire  encephalon  may  be  summarised  as  fol- 
lows:— (1)  At  their  origin  the  different  arteries  are  so  connected,  directly  or  indirectly,  on  the 
base  of  the  encephalon,  that  the  blood  approaching  the  brain  by  way  of  the  vertebral  and 
internal  carotid  arteries  is  practically  a  common  supply  for  all  the  arteries  of  the  encephalon, 
and  a  given  part  of  it  may  possibly  pass  mto  any  one  of  them.  (2)  In  the  pia  mater  of  each 
gross  division  of  the  encephalon  the  different  arteries  again  become  coimected  with  each 
other  in  a  superficial,  freely  anastomosing  plexus,  contmuous  thi'oughout.  (3)  From  this 
plexus  of  the  surface,  naturally  composed  in  part  of  the  trunks  of  the  different  arteries 
themselves,  arise  branches  which  enter  directly  into  the  nervous  substance  and  which  break 
up  into  twigs  that  are  terminal;  i.  e.,  twigs  that  do  not  anastomose  with  each  other.  (4)  The 
arterial  capillary  system  arising  from  the  terminal  twigs  passes  over  into  venous  capillaries 
which  converge  to  form  corresponding  venous  twigs  which  in  their  turn  pass  to  the  sm-face 
and  join  in  forming  a  peripheral,  anastomosing  venous  plexus  superimposed  upon  the  similar 
arterial  plexus.  (5)  From  this  venous  plexus  arise  the  different  veins  of  the  encephalon  which 
may  or  may  not  accompany  the  arteries  for  a  short  distance,  and  which  finaUy  empty  into  the 
sinuses  in  the  cranial  dura  mater.  These,  likewise  confluent,  empty  into  the  internal  jugular 
veins.  The  chorioid  plexuses  of  the  ventricles  of  the  brain  are  modifications  of  the  general 
anastomosing  peripheral  plexuses.  The  chorioid  plexuses  of  the  lateral  and  third  ventricles 
are  derived  largely  from  branches  of  the  chorioid  arteries,  which  arises  separately  from  the 
internal  carotid  artery. 


906 


THE  NERVOUS  SYSTEM 


The  blood  supply  of  the  cerebrum  may  best  be  taken  as  an  illustration  of  the  general  plan 
of  the  blood-vascular  system  of  the  encephalon.  The  terminal  or  internal  branches  of  the 
surface  plexus,  derived  from  the  posterior,  middle,  and  anterior  cerebral  arteries,  are  arranged 
into  two  groups,  a  central  or  ganglionic  and  a  cortical  group.  The  central  branches  themselves 
form  four  groups  in  each  hemisphere: — 

(1)  The  antero-mesial  group  consists  of  terminal  branches  from  the  plexus  of  the  domain 
of  the  anterior  cerebral  artery,  which  pass  through  the  medial  part  of  the  anterior  perforated 
substance  and  supply  the  head  of  the  caudate  nucleus,  the  septum  peUucidum,  the  columns 
of  the  fornix,  and  the  lamina  terminaUs. 

(2)  The  antero-lateral  group  consists  of  terminal  branches  from  the  domain  of  the  middle 
cerebral  artery.  These  pierce  the  anterior  perforated  substance  in  two  sub-groups — (a)  the 
internal  and  (6)  the  external  striate  arteries  (fig.  713).  The  internal  striate  arteries  pass 
thi'ough  the  segments  of  the  globus  paUidus  of  the  lenticular  nucleus  and  through  the  internal 
capsule,  to  both  of  which  they  give  branches,  and  they  terminate  in  the  caudate  nucleus  and 
thalamus.  The  external  striate  arteries  are  larger  and  more  numerous.  They  pass  upward 
between  the  external  capsule  and  the  putameu,  and  then  through  or  around  the  upper  part 
of  the  putamen  into  the  internal  capsule,  where  they  form  two  groups,  the  lenticulo-lhalamic 
and  the  lenticulo-caudate  groups.  The  former  terminate  in  the  thalamus  and  the  latter  in  the 
caudate  nucleus.  On  account  of  its  larger  size  at  its  origin  and  its  direct  linear  continuation 
with  the  internal  carotid,  emboU  {thrombi)  pass  more  frequently  into  the  middle  cerebral  artery 


Fig.  713. — Diagram  Showing  the  Manner  of  Distribution  of  the  Cortical  and  Central 
Branches  of  the  Cerebral  Arteries. 


Cortical  arteries. 


External  striate  arteries- 
Middle  cerebral  artery 


Caudate  nucleus 
Thalamus 


Tuber  cinereum 


Internal  striate  arteries 


than  into  the  anterior  cerebral  artery.  One  of  the  lenticulo-caudate  arteries  which  is  larger 
and  longer  than  the  others  and  which  is  a  direct  branch  from  the  middle  cerebral  artery  has  been 
called  the  'artery  of  cerebral  hemorrhage'  (Charcot),  on  account  of  the  greater  frequency 
with  which  it  is  ruptured. 

(3)  The  postero-medial  central  arteries  are  terminal  branches  of  the  posterior  cerebral 
artery.  They  also  enter  the  anterior  perforated  substance,  but  supply  the  floor  of  the  third 
ventricle,  the  posterior  part  of  the  thalamus,  and  the  hypothalamic  region. 

(4)  The  postero-lateral  group  are  also  terminal  branches  of  the  posterior  cerebral  artery. 
They  supply  the  posterior  part  of  the  internal  capsule,  the  pulvinar  of  the  thalamus,  the  gen- 
iculate bodies,  the  corpora  quadrigemina  and  their  brachia,  the  epiphysis,  and  the  cerebral 
pedunces. 

The  cortical  group  of  the  cerebral  arteries  arise  from  the  anastomosing  plexus  in  the  pia 
mater  of  the  cortical  surfaces  of  the  hemisphere.  They  pass  into  the  cortical  substance  both 
from  the  summits  of  the  gyri  and  from  the  walls  of  the  sulci.  They  consist  of  short,  medium, 
and  long  branches,  and  pass  at  right  angles  into  the  gyri.  The  short  branches  terminate  in  the 
cortical  substance;  the  medium  branches  supply  the  more  adjacent  white  substance,  and  the 
longer  branches  pass  more  deeply  into  the  general  medullary  centre  of  the  hemisphere. 

All  of  both  the  central  or  ganglionic  and  the  cortical  arteries  are  terminal  in  the  sense  that 
they  do  not  anastomose  in  the  substance  of  the  cerebrum. 

The  blood-vascular  system  of  the  other  divisions  of  the  encephalon  is  in  accordance  with 
the  same  general  plan  of  that  of  the  cerebrum.  Slight  individual  modifications  of  the  general 
plan  are  to  be  expected. 


BLOOD-VESSELS  OF  CEREBELLUM 


907 


The  blood-vessels  of  the  mesencephalon,  in  addition  to  the  supply  derived  from  the  postero- 
lateral group  of  central  arteries,  include  the  vessels  of  the  quadrigeminate  bodies  and  those  of  the 
cerebral  peduncles.  The  arteries  of  the  quadrigeminate  bodies  are  usually  six  in  number, 
three  for  each  side — the  superior,  middle,  and  inferior  quadrigeminate  arteries.  The  superior 
and  middle  are  branches  of  the  posterior  cerebral  arteries,  and  the  inferior  are  branches  of  the 
superior  cerebellar  arteries.  The  superior  supply  the  superior  quadrigeminate  bodies  and  the 
epiphysis;  the  middle  supply  both  the  superior  and  inferior  quadrigeminate  bodies,  and  the 
inferior  the  inferior  quadrigeminate  bodies.  They  all  anastomose  in  the  pia  on  the  surface  of  the 
stratum  zouale,  forming  a  fine-meshed  plexus,  and  from  this  superficial  plexus  the  terminal 
branches  pass  into  the  substance  of  the  bodies.  The  veins  terminate  in  the  vein  of  Galen  (v. 
cerebri  magna.) 

The  arteries  of  the  cerebral  peduncles  form  two  groups,  mesial  and  lateral.  The  mesial 
peduncular  arteries  are  branches  of  the  basilar  and  the  posterior  cerebral  arteries.  They  pass 
to  the  medial  sides  of  the  pendunoles  and  supply  the  superior  and  medial  part  of  the  tegmentum. 
The  vessels  of  this  group  which  accompany  the  fibres  of  the  oculomotor  nerves  are  known  as  the 
radicular  arteries;  they  supply  the  root-fibres  and  the  nuclei  of  the  nerves,  which  receive  no 
other  branches.     The  lateral  peduncular  arteries  are  branches  of  the  posterior  cerebral  and 


Fig.  714.- 


-Showing  the   Capillary  Supplt  op  the  Cerebellar  Cortex. 
"Journal  of  Comparative  Neurology,"  Vol.  IX.) 


(After  Aby, 


Capillaries 
of   molecu- 
lar layer 


Line  of  the 

Purkinje 

cells 

Recurrent 

capillaries 

to  granular 

layer 

Arteriole 


through 

cortex  to 

medulla 

Recurrent 

capillaries 

to  granular 

layer 

Line  of  the 

Purkinje 

cells 

Arteriole 

passing 

through 

cortex  to 

medulla 


Recurrent 

capillary  to 

granular 

layer 

Recurrent 
capillaries 
to  molecu- 
lar layer 
Junction  of 
cortex  and 
meduUa 
Capillaries 
of  molecu- 
lar layer 


Junction  of 
cortex  and 
medulla 


Arteriole 

passing 
through 
cortex  to 
medulla 


superior  cerebellar  arteries.  They  supply  the  lateral  portions  of  the  peduncles  and  the  lateral 
part  of  the  tegmentum.  The  veins  of  the  mid-brain  terminate  in  the  basilar  veins  and  the  vein 
of  Galen. 

The  blood-vessels  of  the  cerebellum. — Six  arteries  supply  the  cerebellum;  two,  the 
posterior  inferior  cerebellar,  are  derived  from  the  vertebral  arteries,  and  the  remaining  four, 
two  anterior  inferior  and  two  superior  cerebellar,  from  the  basilar  artery.  The  course  and 
general  distribution  of  the  arteries  are  described  m  Section  V,  but  here  it  must  be  noted  that  the 
branches  of  these  six  vessels  form  a  rich  network  in  the  pia  mater  on  the  surfaces  of  the  cerebellar 
lobes,  and  that  extensions  of  the  plexus  pass  with  the  folds  of  the  pia  mater  into  the  sulci  and 
fissures.  From  the  superficial  plexus  terminal  branches  pass  mto  the  interior  of  the  cerebellum 
and  their  collaterals  form  capillary  plexuses  in  the  white  and  grey  substance.  The  extensions 
of  the  surface  plexus  are  of  three  lengths: — (1)  a  longer  set,  which  pass  through  the  cortex  of  the 
cerebellum  and  supply  the  white  substance  of  the  corpus  meduUare;  (2)  a  set  of  shorter  arterioles 
which  pass  through  the  molecular  layer  of  the  cortex  and  break  up  in  its  granular  layer;  (3)  the 
shortest  set  pass  into  the  cortex  and  immediately  break  up  in  its  molecular  layer.  The  meshes 
of  the  capillary  plexuses  in  the  grey  susbtance  are  ovoidal  and  their  axes  run  radially.  The 
meshes  of  the  plexuses  in  the  white  substance  are  parallel  with  the  nerve-fibres.  In  addition  to 
the  vessels  mentioned,  a  distinct  branch  is  distributed  to  each  dentate  nucleus.  This  springs 
either  from  the  superior  cerebellar  or  from  the  anterior  inferior  cerebellar  artery  of  the  corre- 
sponding side. 


908  THE  NERVOUS  SYSTEM 

The  efferent  veins  of  the  cerebellum  do  not  accompany  the  arteries;  they  spring  from  a 
plexus  in  the  pia  mater  which  receives  tributaries  from  the  interior,  and  they  form  three  groups 
on  each  cerebellar  surface,  the  vermian  veins  and  the  lateral  veins.  The  superior  vermian  vein 
runs  forward  on  the  superior  surface  of  the  vermis  and  terminates  in  the  vein  of  Galen.  The 
inferior  vermian  vein  runs  posteriorly  and  ends  in  one  of  the  transverse  sinuses.  The  superior 
lateral  veins  open  into  the  superior  petrosal  or  transverse  sinuses,  and  the  inferior  lateral  veins 
into  the  inferior  petrosal  and  transverse  sinuses.  The  vein  from  the  dentate  nucleus  usuaDy 
joins  the  inferior  lateral  veins. 

The  blood-vessels  of  the  pons. — The  arteries  to  the  pons  are  branches  of  the  basilar  artery, 
and  of  its  anterior  inferior  and  superior  cerebellar  branches.  The  plexus  in  the  pia  mater 
is  comparatively  unimportant,  and  the  branches  which  enter  the  substance  of  the  pons  form 
two  main  groups,  the  central  and  the  peripheral.  The  central  arteries  spring  directly  from  the 
basilar.  They  pass  backward  along  the  raphe,  giving  branches  to  the  adjacent  parts,  and  they 
terminate  in  the  nuclei  of  the  pons  and  those  in  the  floor  of  the  fourth  ventricle.  The  peripheral 
arteries  are  radicular  and  intermediate.  The  radicular  branches  spring  from  the  peripheral 
plexus  and  from  the  anterior  inferior  cerebellar  arteries;  they  accompany  the  roots  of  the 
trigeminus,  abducens,  facial,  vestibular,  and  cochlear  nerves,  supply  their  fibres  and  the  adjacent 
parts,  and  they  end  in  the  grey  nuclei  with  which  the  nerve-fibres  are  connected.  The  inter- 
mediate  arteries  enter  the  surfaces  of  the  pons  irregularly  and  break  up  into  capillaries  in  its 
substance.  The  veins  form  a  plexus  on  the  surface.  The  dorsal  and  lateral  part  of  this  plexu- 
is  drained  into  the  basilar  vein  on  each  side,  and  the  inferior  part  is  connected  by  efferent 
channels  with  the  inferior  petrosal  sinus  and  the  cerebellar  veins. 

The  blood-vessels  of  the  medulla  oblongata. — The  arteries  of  the  medulla  are  derived 
directly  from  the  vertebral  arteries,  from  their  anterior  and  posterior  spinal  and  posterior  inferior 
cerebellar  branches,  and  from  the  basilar  artery.  The  branches  of  these  vessels  form  a  plexus  in 
the  pia  mater  from  which,  and  from  the  arteries  themselves,  three  main  groups  of  vessels  pass 
into  the  medulla — the  chorioidal,  the  central,  and  the  peripheral.  The  chorioidal  arteries  are 
derived  chiefly  from  the  posterior  inferior  cerebellar  arteries.  They  supply  the  chorioid  plexus 
of  the  fourth  ventricle.  The  anterior  central  arteries  rise  from  the  anterior  spinal  artery,  from 
the  basilar  artery,  and  from  the  peripheral  plexus;  they  pass  caudalward  along  the  raphe, 
supplying  the  adjacent  parts  of  the  ventral  funicuh  and  the  olivary  bodies,  and  they  break  up 
into  fine  terminals  in  the  grey  substance  of  the  floor  of  the  fourth  ventricle  around  the  nuclei 
of  the  cranial  nerves.  The  posterior  central  arteries  spring  from  the  posterior  spinal  arteries; 
they  pass  down  the  median  septum  of  the  inferior  part  of  the  medulla  and  supply  the  adjacent 
nervous  substance.  The  peripheral  arteries,  like  those  of  the  spinal  cord,  are  separable  into 
radicular  and  intermediate  groups.  The  radicular  arteries  pass  from  the  anterior  and  posterior 
spinal  branches  and  from  the  trunks  of  the  vertebral  arteries  and  accompany  the  fibres  of  the 
last  six  cranial  nerves  into  the  substance  of  the  medulla.  They  supply  the  nerve-roots  and 
adjacent  white  substance  and  they  terminate  in  capillaries  in  the  grey  substance  of  the  lateral 
part  of  the  floor  of  the  ventricle.  The  intermediate  peripheral  arteries  spring  from  the  arteries 
previously  named  and  from  the  peripheral  plexus,  and  they  pass  directly  into  the  funiculi  of 
the  meduUa,  where  they  terminate  in  a  capillary  plexus  which  supplies  the  white  substance  and 
the  grey  nuclei;  some  of  these  arteries,  more  especially  those  derived  from  the  posterior  inferior 
cerebellar  and  the  posterior  spinal  arteries,  extend  inward  to  the  lateral  part  of  the  floor  of  the 
fourth  ventricle. 

The  veins  which  issue  from  the  medulla  form  a  peripheral  plexus  in  the  pia  mater  in  which 
there  are  two  main  longitudinal  channels,  an  anterior  median  and  a  posterior  median  vein. 
The  former  communicates  posteriorly  with  the  anterior  median  vein  of  the  cord,  and  anteriorly 
with  the  veins  of  the  pons  and  with  the  veins  which  accompany  the  hypoglossal  nerves.  The 
latter  veins  empty  into  the  internal  jugular  veins.  The  posterior  median  vein  is  continuous 
caudally  with  the  corresponding  vein  of  the  cord,  and  anteriorly,  in  the  region  of  the  calamus 
scriptorius,  it  divides  into  branches  which  join  the  radicular  veins.  The  blood  is  carried 
away  from  the  peripheral  plexus  mainly  by  the  radicular  veins,  which  pass  along  the  roots  of 
the  last  six  cranial  nerves.  Those  which  accompany  the  hypoglossal  nerves  have  already 
been  referred  to.  The  others  end  in  the  terminal  parts  of  the  transverse  sinuses,  the  inferior 
petrosal  sinuses,  or  the  inferior  part  of  the  occipital  sinuses. 

The  nerve  supply  of  the  blood-vessels  of  the  brain  consists  of  a  perivascular  plexus  of  sympa- 
thetic nerve-fibres  upon  the  walls  of  the  vessels  and  meduUated  fibres  which  accompany  the 
vessels  and  apparently  terminate,  for  the  most  part,  in  the  connective  tissue  about  them.  The 
former  are  thought  to  be  vaso-motor  in  function;  the  latter  probably  sensory  fibres  of  the 
cranio-spinal  type.     Nerves  have  been  described  only  for  the  larger  vessels. 

IV.  THE  MENINGES 

Three  membranes,  collectively  called  the  meninges,  envelope  the  entire  cen- 
tral nervous  system,  separate  it  from  the  walls  of  the  bony  cavities  in  which  it  lies, 
and  aid  in  its  protection  and  support.  They  consist  of  feltworks  in  which  white 
fibrous  connective  tissue  predominates,  and  through  them  pass  the  blood-vessels 
which  supply  the  central  nerve-axis  and  the  nerves  by  which  the  axis  is  connected 
with  the  periphery.  Though  there  are  definite  spaces  or  cavities  between  them, 
the  membranes  are  not  wholly  separated  from  each  other,  and  they  are  both 
continuous  with  and  contribute  to  the  walls  of  the  blood-vessels  and  the  sheaths 
(epineurium)  of  the  nerves  passing  through  them.  Beginning  with  the  outermost, 
they  are — (1)  the  dura  mater,  the  thickest,  most  dense  and  resistant  of  the  mem- 


THE  DURA  MATER 


909 


Fia.  715. — Showing  the  Spinal  Dura  Mater  Exposed  in  situ.     (Dorsal  aspect.)     (After 
Toldt,   "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 

Foramen  magnum 


Vertebral   artery  , 


Transverse  process  of  atlas" 


■  Cervical  nerve  I 


Spinal  dura  mater^^ 


Epidural  cavity,^  f-j 


^^?]^ii-)  Thoracic  nerve  I 


^Spinal  ganglion 


^Anterior  ramus 
^Posterior  ramus 


Posterior  costotransverse  ligament**' 


Costal  process  of  lumbar  vertebrae*. 


.  Lumbar  nerve  I 


Sacrum  (dorsal  surface) 


Anterior  sacral  foramina^: 


-  Sacral  nerve  I 
Posterior  ramus  of  sacral  nerve  I 


Filum  of  dura  mater 
(coccygeal  ligament) 


Sacral   canal- 


,  Continuation    of    spinal    dura    mater 
upon  the  roots  of  the  sacral  nerves. 


'  Coccygeal  nerve 


910 


THE  NERVOUS  SYSTEM 


branes;  (2)  the  arachnoid,  the  much  less  dense,  web-hke  middle  membrane; 
and  (3)  the  pia  mater,  a  thin,  compact  membrane,  closely  adapted  to  the  sm-face 
of  the  central  system,  into  which  it  sends  numerous  connective-tissue  processes. 
It  is  highly  vascular  in  that  it  contains  the  rich  superficial  plexuses  of  blood- 
vessels from  which  the  intrinsic  blood  supply  of  the  central  system  is  derived. 
The  space  between  the  dura  mater  and  the  arachnoid  is  known  as  the  sub-dural 

Fig.  716. — Dorsal  Aspect  of  the  Medulla  Oblongata  and  Spinal  Cord  with  the  Dura 
Mater  Partially  Removed.     (Hirschfeld  and  Leveill6.) 
A  B 


Superior  peduncle 
of  the  cerebellum 
Median  sulcus  ot 

4tli  ventricle 
Glosso-pharyngeus 
Vagus 

Spinal  accessory 


A  ventral  root 
A  dorsal  root 


lllfnrrfc^^-^-^^   Fiium 

terminale 
surround- 
ed by 
Cauda 
equina 


ni.— (.^1 


IV.-.r^  1 


-Spinal 
ganglion 


cavity,  and  that  between  the  arachnoid  and  the  pia  mater  is  the  sub-arachnoid 
cavity. 

The  Duea  Mater 

In  the  fresh  condition  the  dura  mater  appears  as  a  bluish-white,  exceedingly 
resistant  membrane,  forming  the  outermost  envelope  of  the  entire  central  nervous 
system.  Its  external  surface  or  that  next  to  the  bony  wall  is  rough,  while  its 
internal  surface  appears  smooth,  due  to  the  fact  that  the  subdural  cavity  partakes 
of  the  nature  and  has  the  hning  of  a  lymph-space.  The  cranial  dura  mater 
consists  of  two  distinct,  closely  associated  layers,  the  outermost  of  which  serves 
as  the  internal  periosteum  of  the  cranial  bones.  The  spinal  dura  mater  is 
described  as  consisting  of  but  one  layer.     The  internal  periosteum  of  the  spinal 


SPINAL  DURA  MATER 


911 


canal,  though  continuous  at  the  foramen  magnum  with  the  outer  layer  of  the 
cranial  dura  mater,  is  not  considered  a  part  of  the  spinal  dura  mater,  from  the 
fact  that  it  is  so  widely  separated  from  the  layer  actually  investing  the  spinal 
cord.  Thus,  since  the  cranial  and  spinal  portions  of  the  dura  mater  differ,  they 
are  described  separately. 

The  spinal  dura  mater  is  a  fibrous  tube  with  funnel-shaped  caudal  end  which 
encloses  and  forms  the  outermost  support  of  the  spinal  cord.  It  consists  of  but 
one  layer  and  this  corresponds  to  the  inner  layer  of  the  cranial  dura  mater.  It 
begins  at  the  foramen  magnum  and  terminates  in  the  spinal  canal  at  about  the 
level  of  the  second  piece  of  the  os  sacrum.  It  is  firmly  attached  to  the  periosteum  of 
the  surrounding  bones  only  in  certain  localities: — 

(1)  The  upper  end  of  the  tube  blends  intimately  with  the  periosteum  of  the  margin  of  the 
foramen  magnum,  and  thus  in  this  locality  it  becomes  continuous  with  the  outer  layer  of  the 
cranial  dura  mater.  Also  in  this  locahty  it  is  attached  firmly,  though  less  intimately,  to  the 
periosteum  of  the  posterior  surfaces  of  the  second  and  third  cervical  vertebrae.  This  locahty 
may  be  considered  the  upper  fixation-point  of  the  spinal  dura  mater.  (2)  It  extends  laterally 
and  contributes  to  the  connective  tissue  investments  of  each  pair  of  spinal  nerves,  and  as  such 
it  passes  into  the  intervertebral  foramina  and  becomes  continuous  with  the  periosteum 
lining  each.     (3)  Along  its  ventral  aspect  the  spinal  dura  mater  is  attached  by  numerous  proc- 

FiG.  717. — View  of  Membranes  op  Spinal  Cord  from  Ventral  Aspect.     (EUis.) 


Spinal  dura  mater' 


Spinal  arachnoid 

Dorsal  root 

Ventral  root 

Ligamentum  denticulatum 


esses  to  the  posterior  longitudinal  ligament  of  the  vertebral  canal.  These  attachments  are 
more  or  less  delicate,  loose,  and  irregular,  and  are  easily  torn  or  cut  in  removing  the  speci- 
men. They  are  stronger  and  more  numerous  in  the  cervical  and  lumbar  regions  than  in  the 
thoracic.  (4)  In  the  space  between  the  dura  and  the  walls  of  the  vertebral  canal  (epidural 
cavity)  lies  the  rich  internal  vertebral  venous  plexus,  and  along  the  lateral  aspect  the  dura  is 
occasionally  connected  with  the  periosteum  through  the  tissue  of  the  walls  of  the  vessels  of  this 
plexus,  especially  in  case  of  the  vessels  which  penetrate  the  dura.  Along  its  dorsal  aspect  the 
spinal  dura  mater  is  practically  free  from  the  wall  of  the  vertebral  canal.  (5)  At  its  lower 
and  funnel-shaped  extremity,  opposite  the  second  sacral  vertebra,  the  tube  suddenly  contracts 
into  a  filament  extending  into  the  coccyx  and  breaking  up  into  a  number  of  processes  which 
become  continuous  with  the  periosteum  of  the  dorsal  surface  of  the  coccyx.  This  filament 
is  the  coccygeal  ligament  or  filum  of  the  dura  mater,  and  its  attachment  may  be  considered 
the  lower  fixation-point  of  the  spinal  dura  mater.  (See  figs.  613  and  715).  The  extent  of  the 
tube  is  maintained  chiefly  by  means  of  the  two  fixation-points,  for  all  the  other_ attachments 
are  sufficiently  loose  to  permit  of  the  movements  of  the  vertebral  column. 

The  inner  surface  of  the  spinal  dura  mater  appears  smooth,  but  upon  closer 
examination  it  is  found  to  be  connected  with  the  arachnoid  by  a  few  delicate  sub- 
dural trabeculse — occasional  fine  strands  of  connective  tissue  bridging  the  sub- 
dural space  (fig.  725).  Along  its  lateral  aspects  the  inner  sm-face  is  at  intervals 
quite  firmly  attached  to  the  pia  mater  by  the  dentations  of  the  ligamenta  dentic- 
ulata,  which  are  prolonged  through  the  arachnoid. 


912 


THE  NERVOUS  SYSTEM 


Further,  it  is  continuous  at  intervals  with  both  the  pia  mater  and  arachnoid  by  way  of  the 
connective-tissue  sheaths  of  the  nerve-roots  which  are  prolonged  from  the  pia  and  blend  with 
the  dura  mater  in  the  passage  of  the  nerve-roots  through  it.  The  dura  is  also  pierced  by  the 
spinal  rami  of  the  vertebral  arteries,  and  the  connective  tissue  of  the  outer  walls  of  these  vessels 
blends  with  aU  three  of  the  meninges.  The  filum  terminate  of  the  pia  mater  extends  below  the 
termination  of  the  spinal  cord  into  the  point  of  the  funnel-shaped  end  of  the  dura  mater,  and 
there  blends  with  it  in  line  with  the  coccygeal  ligament  of  the  outer  surface. 

The  tube  of  the  spinal  dura  mater  varies  in  calibre  with  the  variations  in  the 
diameter  of  the  spinal  cord.  However,  the  termination  of  its  cavity  occurs  about 
seven  segments  below  the  termination  of  the  spinal  cord.  This  extension  con- 
tains the  long  intra-dural  nerve-roots  forming  the  cauda  equina,  and  the  calibre 
of  this  part,  before  its  sudden  contraction,  is  about  as  great  as  that  found  in  any 


Fig.  718. — The  Dura  Mater  Encephali  of  the  Base  op  the  CRANitrM. 
(After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 
Position  of  crista  galli  Process  of  dura  in  foramen  csecum 

Circular  sinus 


Circular  sinus 

\ 


Olfactory  bulb 


Eyeball 


Ophthalmic  vein 


Cavernous  sinus 


Connection  with 
the  rete  f  oraminis 
ovalis 


Internal  carotid 
artery 

Bulb  of  the  internal 
jugular  vein 


Transverse  sinuS' 


Vertebral  artery  "" 

Fold  of  dura  mater^ 


Vrt«^  Maxillary  nerve 

\ 

i «    Mandibular 
i  Jl-»"    nerve 


Abducens  nerve 


Acoustic  nerve 

jlossophar; 
nerve 

Vagus  nerve 

Accessory  nerve 

Hypoglossal  nerve 
First  spinal  nerve 


/ 
Dura  mater 

other  region.  As  each  pair  of  nerve-roots  of  the  cauda  equina  passes  outward, 
they  lie  free  for  a  variable  distance  in  a  tubular  extension  of  the  dura  before  the 
latter  blends  with  and  contributes  to  the  thickness  of  their  sheath. 

The  subdural  cavity,  the  space  between  the  dura  mater  and  the  arachnoid,  is 
the  thinnest  of  the  meningeal  spaces.  Along  the  ventral  aspect  especially,  the 
spinal  arachnoid  is  quite  closely  applied  to  the  inner  surface  of  the  dura  mater.  It 
contains  a  small  amount  of  cerebro-spinal  fluid  (lymph)  which  prevents  friction 
between  the  opposing  surfaces,  and  is  continuous  with  the  fluid  in  the  like  space 
of  the  cranial  meninges. 

The  space  communicates  with  the  venous  sinuses  of  the  cranium  in  the  region  of  the 
Pacchionian  bodies,  and  its  fluid  is  likewise  in  contact  with  the  blood-vessels  passing  through  it. 
It  is  probably  continuous  with  the  lymph-spaces  of  the  nerve-roots  passing  through  it,  for 
colored  fluids  injected  into  it  pass  into  the  nerve-roots.  The  arachnoid  is  so  thin  and  gauze- 
Uke  that  a  ready  interchange  of  fiuids  between  this  space  and  the  subarachnoid  space  is  possible 
by  simple  filtration. 


CRANIAL  DURA  MATER 


913 


The  cranial  dura  mater  [dura  mater  encephali]. — The  dura  mater  investing  the 
brain  performs  a  double  function — it  serves  as  an  internal  periosteum  for  the 
cranial  bones  and  gives  support  and  protection  to  the  brain.  In  conformity  with 
its  double  function  it  consists  of  two  layers,  easily  separable  in  the  child,  but 
closely  adhering  to  each  other  in  the  adult,  except  in  occasional  localities,  where 
there  exist  small  clefts  lined  with  endothelium.  The  large  blood  sinuses  and  ven- 
ous lacunse,  corresponding  to  the  internal  vertebral  venous  plexus  of  the  vertebral 
canal,  are  placed  between  the  two  layers  and  the  semilunar  ganglia  of  the  trigem- 
ini  also  lie  between  them.  The  cranial  dura  begins  with  the  adhesion  of  the 
spinal  dura  mater  to  the  periosteum  at  the  foramen  magnum,  and  it  forms  a  sac- 
like envelope  about  the  entire  encephalon.  Consisting  of  two  layers,  it  is  a  much 
thicker  membrane  than  that  of  the  spinal  cord. 

The  outer  surface  of  the  cranial  dura  mater  when  torn  away  from  the  cranial 
bones  appears  very  uneven,  and  when  placed  in  water  presents  a  flocculent 
appearance. 


G.  719. — CoBONAL  Section  of  the  Head,  Passing  through  the  Posterior  Horns  of 

THE  Lateral  VENTRicLEb 
From  a  mounted  specimen  m  the  Anatomical  Department  of  Trinity  College,  Dublin. 


Inferior  long 
itudinal  fas 
ciculus 


Transverse  sinus 


Dentate  nucleus       Tentorium  cerebelli 


This  is  due  to  the  many  fine  bundles  of  connective  tissue  and  the  blood-vessels  which  pass 
between  the  dura  and  the  cranial  bones  and  which  are  partially  pulled  out  of  their  openings  in 
the  latter  in  the  process  of  separation.  The  abundance  of  these  connections,  and,  therefore, 
the  degree  of  adhesion  to  the  bones,  varies  in  different  localities.  The  separation  is  much  less 
difficult  from  the  inner  table  of  the  bones  of  the  vault  of  the  cranium  than  from  the  bones  of 
the  base  of  the  cavity.  The  adhesions  to  the  vault  of  the  cranium  are  most  firm  along  the  lines 
of  the  sutures.  This  is  due  to  the  fact  that  during  the  period  before  the  sutures  are  closed  the 
outer  layer  of  the  dura  mater  is  directly  continuous  with  the  external  periosteum,  and,  in 
consequence  of  this  condition  during  development,  the  connective-tissue  connection  is  more 
abundant  along  these  lines  and  some  is  even  caught  in  the  closure  of  the  sutures.  Along  the 
vault  there  are  occasionally  noticed  small  lymph-spaces  between  the  bone  and  the  dura  mater. 
The  stronger  adherence  to  the  base  of  the  cranial  cavity  is  due  to  the  numerous  foramina  in  the 
floor,  through  which  all  the  larger  cranial  blood-vessels  and  the  cranial  nerves  pass,  and  the 
dura  mater  is  continuous  with  the  connective-tissue  investments  of  these  as  well  as  with  the 
periosteum  lining  the  foramina.  Also  the  floor  of  the  cavitj'  is  more  uneven  than  the  vault,  and 
the  projections  of  the  bones  here  tend  to  increase  the  firmness  of  attachment.  The  weight  of 
the  brain  upon  the  floor  probably  contributes  to  the  result. 

The  inner  surface  of  the  inner  layer  of  the  cranial  dura  mater  forms  the  outer 
boundary  of  the  subdural  cavity.  Except  for  the  occasional  delicate  subdural 
trabeculse  and  the  passage  of  blood-vessels  and  nerve-roots,  this  surface  appears 


914 


THE  NERVOUS  SYSTEM 


smooth  and  glistening,  being  lined  by  a  layer  of  endothelium  and  containing  a 
small  amount  of  the  cerebro-spinal  lymph. 

The  subdural  cavity  of  the  base  of  the  brain  is  prolonged  a  short  distance  outward  along 
the  roots  of  the  various  cranial  nerves  before  it  is  obUterated  by  the  blending  of  the  dura 
mater  with  the  sheaths  of  the  nerves.  This  outward  extension  of  the  space  is  most  marked 
about  tlie  optic  and  auditory  nerves.  In  the  optic  especially,  the  dura  mater  remains  separate 
from  the  nerve  throughout  its  length,  only  fusing  with  its  sheath  upon  the  posterior  surface  of 
the  ocular  bulb  (fig.  718). 

One  of  the  most  striking  differences  between  the  cranial  dura  mater  and  that  of 
the  spinal  cord  is  that  the  inner  layer  of  the  former  undergoes  striking  septa-like 
duplications  or  folds,  forming  exceedingly  strong  partitions  which  project  between 
the  larger  subdivisions  of  the  encephalon.  These  are  four  in  number,  two  large 
and  two  small — the  falx  cerebri  and  the  tentorium  cerebelli;  the  falx  cerebelli 
and  the  diaphragma  sellse.  The  larger  enclose  within  their  folds  the  great  venous 
sinuses,  into  which  most  of  the  spent  blood  of  the  encephalon  collects  to  pass  out- 
ward by  way  of  the  internal  jugular  veins  (figs.  720,  721). 

Fig.  720. — The  Cranium  with  Encephalon  Removed  to  show  the  Falx  Cerebri,  the 
Tentorium  Cerebelli,  and  the  Places  where  the  Cranial  Nerves  pierce  the  Dura 
Mater.     (Sappey.) 

Trochlear  nerve  Oculomotor  nerve 

Falx  cerebri 


Superior  sagit- 
tal sinus 

Inferior  sagit- 
tal sinus 

Vein  of  Galen 


artery 

Internal 
carotid  artery 


Falx  cerebelli 

Facial  and 
auditory  nerves 
Glassopharyngeal,  vag:us 
and  accessory  nerves 

Hypoglossal  nerve 


Second  cervical  nerve 


First    Inferior   Abducens    Trigeminus 
cervical    petrosal      nerve  nerve 


Ligamentum  denticulatum      nerve       sinus 

The  falx  cerebri  is  the  most  striking  of  these  partitions.  It  is  a  sickle-shaped 
fold  which  projects  vertically  from  the  vault  into  the  longitudinal  fissure  between 
the  cerebral  hemispheres.  It  begins  attached  to  the  crista  galli  in  front,  and 
arches  to  terminate  by  blending  with  the  superior  surface  of  the  hirozontally 
placed  tentorium  cerebelli.  Its  convex,  superior  border  joins  the  outer  layer  of  the 
dura  along  the  medial  plane  of  the  vault,  and  encloses  the  superior  sagittal  sinus. 
Its  concave  border  is  free  and  contains  in  its  posterior  two-thirds  the  smaller 
inferior  sagittal  sinus.  The  anterior  and  narrower  end  is  often  perforated  and 
occasionally  so  much  so  as  to  appear  as  a  coarse,  fibrous  reticulum.  The  pos- 
terior part  of  the  concave  border  touches  the  upper  surface  of  the  corpus  callosum, 
but  the  anterior  part,  which  does  not  descend  so  low,  is  separated  from  the  corpus 
callosum  by  a  part  of  the  subarachnoid  space.  The  base  of  the  fold  which  slopes 
downward  and  blends  with  the  upper  surface  of  the  tentorium  cerebelli,  contains 
the  straight  sinus  running  along  the  line  of  junction. 

The  tentorium  cerebelli  is  a  large  transverse,  semilunar  fold,  concave  forward. 
It  descends  from  its  central  part  which  is  elevated,  and  consequently  it  forms  a 


i 


THE  DURA  MATER 


915 


tent-shaped  covering.  Its  superior  surface  is  in  relation  with  the  tentorial  surfaces 
of  the  hemispheres,  and  its  inferior  surface  conforms  accurately  to  the  superior 
surface  of  the  cerebellum.  The  outer  or  convex  border  of  the  fold  is  attached 
on  each  side  to  the  posterior  clinoid  process,  the  superior  border  of  the  petrous 
portion  of  the  temporal  bone,  the  mastoid  portion  of  the  temporal  bone,  the  pos- 
terior inferior  angle  of  the  parietal  bone,  and  the  horizontal  ridge  of  the  occipital 
bone.  The  transverse  sinus  lies  in  this  border.  From  the  internal  occipital  pro- 
tuberance to  the  mastoid  portion  of  the  temporal  bone  and  along  the  petrous  part 
of  the  temporal  bone  it  encloses  the  superior  petrosal  sinus. 

The  greater  part  of  the  inner  or  anterior  border  of  the  tentorium  is  free,  and  it 
forms  the  superior  and  lateral  boundaries  of  an  arched  cavity,  the  tentorial  notch 
or  foramen  ovale  of  Pacchioni,  which  encloses  the  mesencephalon,  and  through 
which  ascend  the  cerebral  peduncles  and  the  posterior  cerebral  arteries.  The 
anterior  extremities  of  the  inner  border  cross  the  outer  border,  and  they  are 
attached  to  the  anterior  clinoid  processes.     A  depressed  angle  is  formed  between 

Fig.  721.— Showing  the  Upper  Surface  op  the  Tentorium  Cbrebelli  and  the  Tentorial 
Notch  through  which  the  Mid-bkain  and  Posterior  Cerebral  Arteries  enter  the 
Middle  Fossa  of  the  Cranium. 

Infundibulum  _ 

Crista  galli 
Optic  nerve 


Middle  cerebral 

artery 
Arterior  cerebral 

artery 
Posterior  commu- 
nicating artery 
Cavernous  sinus 
Superior   cerebel- 
lar artery 
Posterior  cerebral 

artery 
Superior   petrosal 

sinus 
Free     border     of 
tentorium  bound- 
ing tentorial  notcb 


Optic  tract 

Oculomotor  nerve 

Cerebral 

peduncle 

Aqueduct  of 

cerebrum 

Mesencepbalon 

Falx  cerebri 


Transverse  sinus 


Superior  sagittal  sinus 


the  inner  and  outer  borders  of  the  tentorium  in  the  middle  fossa  of  the  skull  at 
the  lateral  portion  of  the  posterior  clinoid  process,  and  in  this  angle  the  root  of  the 
oculo-motor  nerve  pierces  the  inner  layer  of  the  dura  mater. 

The  falx  cerebelli  is  a  small,  sickle-shaped,  triangular  fold  which  projects 
forward  into  the  small  groove  {-posterior  cerebellar  notch),  between  the  hemispheres 
of  the  cerebellum.  Its  base  is  attached  to  the  tentorium;  its  postero-inferior 
border,  along  which  runs  the  occipital  sinus,  is  attached  to  the  internal  occipital 
crest.  Its  anterior  border  is  free,  and  its  apex,  which  lies  immediately  above  the 
foramen  magnum,  usually  bifurcates  as  it  disappears  anteriorly,  grasping  the 
foramen  magnum  from  behind.  Bifurcation  is  always  the  case  when  the  internal 
occipital  crest  splits  below  to  enclose  a  vermiform  fossa. 

The  diaphragma  sellae  is  a  small  circular  fold,  deficient  in  the  centre,  which 
projects  horizontally  from  the  margins  of  the  hypophyseal  fossa  or  sella  turcica. 
Its  lateral  border  is  attached  to  the  clinoid  processes  and  the  limbus  of  the  sphe- 


916 


THE  NERVOUS  SYSTEM 


noid,  and  its  medial  border  forms  the  boundary  of  the  foramen  of  the  diaphragma 
sellce  and  surrounds  the  infundibulum.  Its  superior  surface  is  in  relation  with  the 
base  of  the  brain,  and  its  inferior  surface  is  in  relation  with  the  hypophysis,  which 
it  binds  down  in  the  hypophyseal  fossa. 

The  spaces  which  lie  between  the  layers  of  the  cranial  dura  mater  are  Meckel's 
caves,  the  spaces  which  lodge  the  endolymphatic  sacs,  and  the  blood  sinuses  and 
lacunae. 

Meckel's  caves  are  two  cleft-like  spaces  or  niches  which  lie,  one  on  each  side, 
in  the  trigeminal  impression  on  the  apex  of  the  petrous  portion  of  the  temporal 
bone.  Each  space  lodges  the  semilunar  (Gasserian)  ganglion  and  the  trigeminus 
and  masticator  nerves  of  the  corresponding  side,  and  it  communicates  with  the 
subdm-al  space  in  the  posterior  fossa  of  the  cranium  by  an  oval  opening,  which  lies 
above  the  superior  border  of  the  petrous  portion  of  the  temporal  bone  and  inferior 
to  the  superior  petrosal  sinus. 


Fig.  722. — Showing  Blood-vessels  of  Cranial  Dura  Mater  and  Cranial  Nerves  in  the 
Base  op  the  Skull. 
(On  the  left  side  the  dura  mater  has  been  removed  from  the  middle  fossa.) 


Meningeal  branch  of  an- 
terior etlunoidal  artery 


Meningeal  branch  of  pos 
terior  ethmoidal   artery 


Middle  meningeal 
artery 
Ophthalmic  division  of 
trigeminus 

Oculomotor  nerve 

Cavernous  sinus. 

Trochlear  nerve 

Auditory  and  facial 

nerves 

Superior  petrosal  sinus 

Inferior  petrosal  sinus 

Petro-squamous  sinus 

Spinal  accessory  nerve 

Sigmoid  sinus 

Posterior  meningeal 
branch  of  vertebral 
artery 

Left  marginal  sinus 


Left  transverse  sinus 
Superior  sagittal  sinus 


Circular  sinus 
Carotid  artery 
Abducens 
^....ilar  artery 
Basilar  plexus  of 
veins 
-^  —j- Auditory  artery 
—L  Vertebral  artery 
— j-Glosso  -pharyngeal 
,  and  vagus  nerves 
^Anterior  spinal 
py         artery 
'    ^Hypoglossal  nerve 
Spinal  accessory 

Right  marginal  sinus 


Right  transverse  sinus 


The  space  which  contains  the  endolymphatic  sac  on  each  side  hes  behind  the 
petrous  portion  of  the  temporal  bone  and  communicates  with  the  aquseductus 
vestibuli. 

The  venous  sinuses  and  lacunae. — The  cranial  blood  sinuses  have  already  been  fully 
described  in  the  account  of  the  vascular  system,  and  it  is  sufficient  to  note  here  that  they  are 
continuous,  on  the  one  hand,  with  the  meningeal  veins,  and,  on'the  other,  with  the  veins  outside 
the  cranial  waDs.  The  vessels  which  establish  communication  between  the  blood  sinuses  and 
the  extracranial  veins  are  referred  to  collectively  as  emissary  veins.  They  possibly  help  to 
maintain  the  regularity  of  the  cranial  circulation,  and  they  have  therefore  a  certain  amount  of 
practical  importance. 

The  sinuses  which  are  connected  with  the  extracranial^veins  by  emissary  veins  are  the 
superior  sagittal,  the  transverse  (lateral),  and  the  cavernous.  Three  or  four  emissary  veins 
pass  from  the  superior  sagittal  sinus; — one  passes  through  the  foramen  caecum  and  communicates 
with  the  veins  of  the  roof  of  the  nose,  or,  through  the  nasal  bones,  with  the  angular  veins. 
Two  pass  through  the  parietal  foramina  and  establish  communications  with  the  occipital 
veins,  and  a  fourth,  which  is  very  inconstant,  pierces  the  occipital  protuberance  and  joins  the 
tributaries  of  the  occipital  veins.     Connecting  each  lateral  sinus  with  the  extracranial  veins 


THE  ARACHNOID  917 

there  are,  as  a  rule,  two  emissary  veins: —  one,  the  mastoid  emissary  vein,  which  passes  through 
the  mastoid  foramen  to  the  occipital  or  posterior  auricular  vein;  and  the  other,  the  post-condy- 
loid  vein,  which  traverses  the  condyloid  (posterior  condyloid)  foramen  and  joins  the  suboccipital 
plexus.  The  cavernous  sinus  is  in  communication  anteriorly  with  the  superior  ophthalmic 
vein,  and  through  the  latter  with  the  angular  vein;  it  is  connected  with  the  pterygoid  plexus 
by  emissary  veins  which  pass  either  through  the  foramen  ovale  or  the  foramen  Vesalii,  and 
with  the  pharyngeal  plexus  by  small  venous  channels  which  accompany  the  internal  carotid 
artery  through  the  carotid  canal. 

The  venous  lacunae  or  spaces  are  small  clefts  lined  by  endotheUum  which  communicate 
with  the  meningeal  veins  and  with  the  blood  sinuses.  They  also  have  communications  with 
the  emissary  veins  and  the  diploic  veins.  They  lie  between  the  outer  and  inner  layers  of  the 
dura  mater,  the  majority  of  them  at  the  sides  of  the  superior  sagittal  sinus,  but  others  are  found 
in  the  tentorium  associated  with  the  transverse  sinuses  and  the  straight  sinus. 

Blood-vessels. — The  blood  supply  of  the  cranial  dura  mater  is  derived  from  the  meningeal 
arteries,  which  ramify  in  its  outer  layer.  The  more  important  of  these  arteries  have  already 
been  described  in  the  account  of  the  vascular  system,  and  it  is  only  necessary  here  to  recall 
the  fact  that  the  greater  part  of  the  dura  mater  above  the  tentorium  cerebelli  is  supplied  by 
branches  of  the  middle  meningeal  arteries.  These  are  reinforced — (1)  at  the  vertex  by  branches 
of  the  occipital  arteries  which  enter  through  the  parietal  foramina;  (2)  in  the  middle  fossa  by 
the  small  meningeal  arteries'  and  by  meningeal  branches  of  the  internal  carotid,  lacrimal, 
and  ascending  pharyngeal  arteries;  and  (3)  in  the  anterior  fossa  by  meningeal  branches  of  the 
anterior  and  posterior  ethmoidal  arteries. 

The  dura  mater  in  the  posterior  fossa  of  the  skull,  below  the  tentorium  cerebelU,  also  re- 
ceives branches  from  the  middle  meningeal  arteries,  but  its  blood  supply  is  derived  mainly — (1) 
from  the  meningeal  branches  of  the  vertebral  arteries  which  enter- the  fossa  through  the  foramen 
magnum,  (2)  from  meningeal  branches  of  the  occipital  arteries  which  enter  through  the  mastoid 
and  hypoglossal  foramina,  and  (3)  from  meningeal  branches  of  the  occipital  and  ascending 
pharyngeal  arteries  which  enter  through  the  jugular  and  hypoglossal  (anterior  condyloid) 
foramina. 

The  meningeal  veins  accompany  the  arteries  as  vena  comitantes,  usually  one  vein  with  each 
artery.  The  middle  meningeal  artery  usually  has  two  venae  comitantes.  The  meningeal  veins 
communicate  with  the  venous  sinuses  and  with  the  diploic  veins,  and,  unlike  ordinary  veins, 
they  do  not  increase  much  in  calibre  as  they  approach  their  terminations. 

The  nerves  of  the  dura  mater  are  partly  derived  from  the  sympathetic  filaments  which 
accompany  the  arteries  and  partly  from  the  cranial  nerves.  The  nerves,  other  than  sympathetic 
filaments,  which  supply  the  cranial  dura  mater  are  sensory  fibres  derived  from  the  trigeminus 
and  vagus  nerves,  and  possibly  from  the  first  cervical  nerves.  The  branches  from  the  trigeminus 
are  derived  from  the  three  divisions  of  that  nerve  on  each  side,  and  it  has  been  stated  that 
branches  are  given  from  the  nasal  branch  of  the  ophthalmic  division  to  the  dura  mater  in  the 
anterior  fossa. 

The  meningeal  branch  of  the  ophthalmic  division  of  the  trigeminus  supplies  the  tentorium ; 
that  from  the  maxillary  division  accompanies  the  branches  of  the  middle  meningeal  artery. 
The  meningeal  branch  of  the  mandibular  division  (nervus  spinosus)  passes  into  the  skull  through 
the  foramen  spinosum  and  is  distributed  to  the  dura  mater  over  the  great  wing  of  the  sphenoid 
and  to  the  mastoid  ceOs.  The  "recurrent  branch  of  the  hypoglossal  nerve"  passes  to  the  dura 
mater  of  the  posterior  fossa  of  the  cranium.  This  recurrent  or  meningeal  branch  of  the  hypo- 
glossal nerve  really  consists  of  fibres  derived  from  the  superior  cervical  ganglion  of  the  sympa- 
thetic, and  contains  sensorj'  fibres  from  the  first  and  second  cervical  nerves.  The  meningeal 
branch  of  the  vagus  springs  from  the  ganglion  of  the  root  of  that  nerve,  and  is  distributed  in  the 
posterior  cranial  fossa.  The  sympathetic  filaments  are  distributed  to  the  smooth  muscle  of  the 
walls  of  the  blood-vessels. 

The  cranial  subdiiral  cavity  is  not  of  uniform  thickness  throughout,  being 
thinner  along  the  basal  aspect  of  the  encephalon.  The  lymph  contained  in  it  is 
usually  but  little  more  than  is  sufficient  to  keep  moist  its  bounding  surfaces.  It 
is  continuous  with  the  lymph  capillaries  of  the  nerves  and  those  of  all  the  tissues 
it  bathes,  and  it  is  continuous  with  the  similar  cavity  of  the  spinal  canal.  Its 
lymph  is  in  free  contact  with  the  blood-vessels  passing  through  it  and  with 
those  in  the  tissues  it  bathes,  and  it  is  replenished  by  filtration  through  their 
walls.  Though  extensive,  the  subdural  space  is  thin  at  best,  for  the  dura  mater  is 
quite  closely  applied  to  the  second  of  the  three  meninges. 

The  Arachnoid 

The  arachnoid  or  '  serous '  membrane  is  the  middle  of  the  three  meninges  of  the 
central  nervous  system.  As  in  the  case  of  the  other  two,  an  attempt  is  made  to 
give  this  membrane  a  name  descriptive  of  its  texture.  It  is  a  gauzy  reticulum  of 
almost  web-like  delicacy,  which  in  reality  pervades  the  space  it  occupies. 

Its  outer  surface,  or  that  closely  related  to  the  dura  mater  and  bounding  the  subdural  cavity 
alone  shows  a  sufficiently  organized  structure  to  merit  the  name  of  membrane.  This  surface 
is  covered  by  a  layer  of  endothehum  which  is  identical  with  that  lining  the  inner  surface  of  the 
dura  mater  and  is  continuous  with  it  by  way  of  the  endothehal  cells  covering  the  blood-vessels, 


918 


THE  NERVOUS  SYSTEM 


the  nerve-roots,  the  ligamenta  dentioulata  of  the  spinal  cord,  and  the  occasional  delicate  tra- 
beculae  passing  between  the  dura  mater  and  the  arachnoid.  Immediately  under  the  endothehum, 
the  connective-tissue  fibres  of  the  arachnoid  are  woven  into  a  very  thin,  more  or  less  compact 
web.  This,  however,  quickly  grades  into  a  loose,  spongy  reticulum  which  pervades  the  thick 
subarachnoid  cavity  throughout,  and  the  strands  of  which  are  directly  continuous  into  the 
more  compact  tissue  of  the  pia  mater.  Thus  an  inner  surface  can  hardly  be  claimed.  This 
loose,  sponge-like  arachnoid  tissue  holds  the  cerebro-spinal  fluid  of  the  subarachnoid  cavity, 
the  meshes  of  the  sponge  constituting  a  reticular  web  of  intercommunicating  spaces  hned  by 
endothehoidal  cells  covering  the  strands  of  the  web.  The  cranial  subarachnoid  cavity  is  larger, 
and  the  strands  of  the  web  are  relatively  more  abundant  than  in  that  of  the  spinal  canal.  In 
addition,  the  cavity  is  traversed  by  the  spinal  and  cranial  nerves,  by  the  blood-vessels  passing 
to]  and  from  the  pia,  and,  in  the  spinal  canal  distinctively,  it  is  traversed  by  the  ligamenta 
denticulata  and  the  filum  terminale.  Through  these  the  arachnoid  is  further  continuous  with 
the  pia  mater. 

The  cranial  arachnoid  is  directly  continuous  into  that  of  the  spinal  cord,  and 
in  the  two  localities  does  not  differ  as  much  as  does  the  dura  mater.  Within  the 
cranium,  the  arachnoid  does  not  closely  follow  the  surface  of  the  encephalon.  It 
is  folded  in  between  the  cerebellum  and  cerebral  hemispheres,  following  the  con- 
tour of  the  tentorium  cerebelli,  but  it  does  not  dip  into  the  fissures  and  sulci  except 
the  anterior  part  of  the  longitudinal  fissure  and  slightly  into  the  lateral  (Sylvian) 
fissure.  Otherwise  it  fills  in  the  inequalities  of  surface  of  the  encephalon,  its  outer 
surface  forming  a  sheet  enveloping  the  whole  and  bridging  over  the  sulci  and  the 
deeper  grooves  between  the  gross  divisions.  Upon  the  summits  of  the  gyri  it  is 
more  closely  applied  to  the  pia  mater,  and  there  its  reticulum  becomes  so  dense 


Fig.  723. — Diagram  showing  the  Relations  op  the  Pia  Mater,  the  Arachnoid,  and  the 
Stibarachnoid  Cavity  to  the  Brain. 
Pia  mater     Subarachnoid  cavity 


Third  ventricle 
Infundibulum 


Clsterna  basalis 
Cisterna  pontis 


Fourth  ventricle 
Cisterna  cerebello- 

medullaris 
Foramen  of 
Magendie 


that  the  two  membranes  almost  appear  as  one.  The  sulci,  occupied  by  looser 
reticulum,  form  a  continuous  system  of  channels  filled  more  abundantly  by  the 
cerebro-spinal  fluid. 

The  arachnoid  folds  in  between  the  cerebellum  and  medulla  oblongata,  and 
at  the  base  of  the  brain  it  ensheathes  the  olfactory  bulbs  and  tracts,  and  its  outer 
surface  forms  a  continuous  sheet  stretching  from  one  temporal  lobe  to  the  other 
and  bridging  over  the  interpeduncular  fossa  and  the  inequahties  of  surface  in  the 
region  of  the  optic  chiasma  and  the  stems  of  the  lateral  fissures.  Obviously, 
therefore,  the  subarachnoid  cavity  between  its  outer  surface  and  the  pia  mater  is  of 
considerable  depth  in  certain  localities.  These  localities  comprise  the  subarach- 
noid cisternoe.  These  occur  where  the  cavity  at  the  base  of  the  brain  is  especially 
large,  and  make  possible  a  'water-bed'  which  serves  to  protect  the  brain  from 
injurious  contact  with  the  bones. 

The  foUowing  cisternae  are  distinguished  (fig.  723) : — 

(1)  The  cisterna  basalis  lies  at  the  base  of  the  cerebrum  and  is  divided  by  the  optic  chiasma 
into  two  parts — (a)  the  cisterna  chiasmatis  and  (b)  the  cisterna  interpeduncularis. 

(2)  The  cisterna  pontis  is  situated  about  the  pons,  especially  in  its  basilar  sulcus  and  the 


THE  SPINAL  ARACHNOID 


919 


transverse  fissures  of  either  border,  and  is  continuous  anteriorly  with  the  cisterna  basalis  and 
posteriorly  with  the  subarachnoid  cavity  about  the  medulla. 

(3)  The  cisterna  superior  Ues  in  the  angle  between  the  splenium  of  the  corpus  callosum 
and  the  superior  surfaces  of  the  cerebellum  and  the  mesencephalon,  and  is  connected  ventrally, 
around  the  cerebral  peduncles,  with  the  cisterna  basalis. 

(4)  The  cisterna  cerebello-medullaris  (cisterna  magna)  is  the  cavity  between  the  inferior 
surface  of  the  cerebellum  and  the  dorsal  surface  of  the  medulla  oblongata.  It  is  continuous 
below  into  the  spinal  subarachnoid  space.  The  fluid  in  this  cavity  is  directly  continuous  with 
that  in  the  fourth  ventricle  by  way  of  the  foramen  of  Magendie  (median  aperture  of  the  fourth 
ventricle). 

Pacchionian  bodies  [granulationes  arachnoideales]  (fig.  724.) — In  certain  situ- 
ations, more  particularly  along  the  margins  of  the  longitudinal  fissure,  particu- 
larly in  the  frontal  region,  and  to  a  much  less  extent  upon  the  superior  surface  of 
the  vermis  of  the  cerebellum,  the  subarachnoid  tissue  elaborates  numerous  small, 
ovoid  or  spherical  nodules,  the  Pacchionian  bodies.  Each  body  or  arachnoid 
villus  consists  of  a  retiform  network  of  subarachnoid  substance  and  its  meshes  are 
filled  with  cerebro-spinal  fluid.  The  Pacchionian  bodies  on  the  vertex  of  the  brain 
project  through  the  inner  layer  of  the  dura  mater,  both  into  the  superior  sagittal 
sinus  and  into  the  venous  spaces  or  parasinoidal  sinuses  which  lie  at  the  sides  of 
that  sinus,  and,  as  they  become  larger,  they  press  against  the  outer  layer  of  the 
dura  mater  and  produce  ovoid  depressions  in  the  inner  plate  of  the  cranium. 

Fig.  724. — Coronal  Section  transverse  to  the  Great  Longitudinal  Fissure,  Showing 
THE  Meninges.     (Key    and    Retzius.) 
Subarachnoid  space  Superior  sagittal  sinus  Pacchionian  body 


-Corpus  callosum 


They  probably  facihtate  the  passage  of  lymph  from  the  subarachnoid  cavity  into  the 
blood  sinuses,  and  thus  may  aid  in  relieving  pressure  within.  On  the  other  hand,  through  them 
the  cerebro-spinal  fluid  is  replenished  at  need  from  the  blood  plasma.  They  are  not  present 
at  birth,  but  they  appear  at  the  tenth  year  and  increase  in  number  and  size  with  advancing  age. 
They  are  less  marked  in  the  female  than  in  the  male. 

The  spinal  arachnoid  (figs.  725,  726)  is  a  loose,  reticular  sac  which  is  most 
capacious  about  the  lumbar  enlargement  of  the  spinal  cord  and  about  the  Cauda 
equina.  Like  that  of  the  encephalon,  the  portion  next  to  the  dura  mater  alone 
resembles  a  membrane,  being  a  loosely  organized  feltwork,  covered  on  the  side  of 
the  subdural  cavity  by  a  layer  of  endothelium  common  to  that  cavity.  Through- 
out its  length  the  spinal  subarachnoid  cavity  is  relatively  wide,  and,  as  in  the 
cranium,  contains  a  fine,  spongy,  web-like  reticulum,  numerous  threads  of  which 
are  continuous  with  the  pia  mater.  This  spongy  tissue  is  the  inner  modification 
of  the  arachnoid,  and  its  meshes  are  occupied  by  the  cerebro-spinal  fluid.  It  is 
not  so  abundant  as  in  the  cranial  subarachnoid  cavity. 

In  addition  to  the  delicate  threads,  the  arachnoid  is  more  firmly  attached  to  the  pia  mater 
by  three  incomplete  partitions.  The  most  continuous  of  these  is  arranged  along  the  dorsal 
mid-line  and  is  known  as  the  septum  posticum  of  Schwalbe  (subarachnoid  septum).  This  may 
be  described  as  a  linear  accumulation  of  the  spongy  tissue  which  pervades  the  subarachnoid 
space.  It  is  most  incomplete  in  the  upper  cervical  region,  where  it  becomes  merely  a  line  of 
threads  connecting  with  the  pia.  It  is  most  complete  as  a  septum  in  the  lower  cervical  and  in 
the  thoracic  region,  but  at  best  it  maintains  a  spongy  character.     The  other  two  partitions  are 


920 


THE  NERVOUS  SYSTEM 


formed  by  the  denticulate  ligaments,  which  extend  laterally  from  either  side  of  the  spinal  cord, 
connecting  the  pia  and  dura  mater  and  involving  the  arachnoid  in  passing  through  it.  Within 
the  subarachnoid  cavity  these  form  more  or  less  complete  septa,  though  outside  the  arachnoid 
they  are  attached  to  the  dura  only  at  the  intervals  of  their  pointed  dentations.  They  belong 
to  the  pia  mater  and  will  be  described  with  it.  The  arachnoid  is  further  continuous  with 
the  pia  by  way  of  the  connective-tissue  sheaths  of  the  roots  of  the  spinal  nerves  and  the  blood- 
vessels passing  through  the  subarachnoid  cavity. 

Vessels  and  nerves. — The  arachnoid  has  no  special  blood  supply  and  probably  no  special 
nerves  other  than  those  supplying  the  walls  of  the  blood-vessels  passing  through  it. 

The  cerebro-spinal  fluid. — The  subarachnoid  cavity  is  the  great  lymph-space  of  the  central 
nervous  system.  That  of  the  spinal  region  is  directly  continuous  into  that  of  the  cranium,  and 
the  fluid  contained  communicates  freely  with  that  in  the  ventricles  of  the  brain  and  the  central 
canal  of  the  meduUa  and  spinal  cord  by  way  of  the  foramen  of  Magendie  or  medial  aperture 
into  the  fourth  ventricle.  In  addition,  there  are  the  lateral  apertures  into  the  fourth  ventricle 
and  there  is  possible  an  interchange  of  fluid  between  the  lateral  ventricle  and  the  subarachnoid 
cavity  of  the  base  of  the  brain  by  diffusion  through  the  thin  floor  of  the  chorioid  fissure.  The 
arachnoid  throughout  is  not  a  membrane  sufficiently  compact  to  seriously  oppose  diffusion 
between  the  fluid  contained  in  its  cavity  and  that  contained  in  the  subdural  cavity,  and  the 
endotheUum  covering  it  probably  even  facilitates  such  activities.  The  cerebro-spinal  fluid 
occupying  the  cavities  is  a  transparent  fluid  of  a  slight  yellow  tinge,  characteristic  of  the 

Fig.  725. — Diagram  op  Transverse  Section  op  Upper  Thoracic  Region  of  the  Spinal 
Cord  showing  the  Relations  op  the  Spinal  Meninges  and  their  Cavities. 
Dura  mater 


Arachnoidea 
(      Pia  mater 


Septum  posticum 

Subdural  trabeculee 
Subdural  space 


Fila  of  dorsal  root 
^^Subarachnoid  cavity 

Denticulate  ligament 


§*1 =*  Fila  of  ventral  root 


^  *  ^  *  Linea  splendens  with  anterior 

^  "-  ^  \  spinal  artery 

Epidural  trabecule  to  periosteum 

lymph  in  other  lymph-spaces  of  the  body.  It  is  not  very  great  in  amount,  probably  never 
exceeding  200  c.c.  in  normal  conditions.  It  is  greatest  in  amount  in  old  age,  when  the  cavities 
are  larger,  due  to  atrophy  and  shrinkage  of  the  nervous  tissues.  It  collects  from  the  lymph 
spaces  in  the  meninges,  and  from  exudation  through  the  walls  of  the  vascular  chorioid  plexuses 
and  sinuses  of  the  system  it  bathes.  Its  amount  may  be  temporarily  increased  by  a  period 
of  increased  blood-pressure  in  the  cranial  vessels.  Pressure  due  to  its  abundance  may  be 
relieved  by  diffusion  through  the  membranes  containing  it,  and  especially  through  the  viUi 
of  the  Pacchionian  bodies  into  the  venous  sinuses  and  lacunae  and  thence  into  the  venous  system 
through  the  internal  jugular  veins. 


The  Pia  Mater 

The  pia  mater,  the  third  of  the  meninges,  is  a  thin  membrane  which  envelopes 
and  closely  adheres  to  the  entire  central  nervous  system  and  sends  numerous  proc- 
esses into  its  substance.  It  likewise  contributes  the  most  proximal  and  compact 
portion  of  the  sheaths  worn  by  the  nerve-roots  in  their  passage  through  the  menin- 
geal spaces.     It  is  very  vascular  in  that  the  superficial  plexuses  of  blood-vessels  of 


THE  PI  A  MATER 


921 


both  the  brain  and  spinal  cord  ramify  in  it  as  they  give  off  the  central  branches 
into  the  nervous  substance.  The  structure  and  arrangement  of  the  membrane 
vary  somewhat  in  the  cranial  and  spinal  regions. 

The  spinal  pia  mater  consists  of  two  layers,  an  inner  and  an  outer.  It  is 
thicker  and  more  compact  than  that  of  the  encephalon,  due  to  the  extra  develop- 
ment of  its  outer  layer,  which  is  in  the  form  of  a  strong,  fibrous  layer  with  the 
fibres  arranged  for  the  most  part  longitudinally. 

The  spinal  pia  mater  also  appears  less  vascular  than  the  cranial  from  the  fact  that  the 
blood-vessels  composing  the  plexus  lying  in  it  are  obviously  much  smaller  than  those  of  the 
encephalon.  Its  inner  layer  is  a  thin  feltworlt  of  fibres  which  is  closely  adherent  to  the  surface 
of  the  spinal  cord  throughout,  sending  numerous  connective-tissue  processes  into  it  which 
contributes  to  the  support  of  the  nervous  tissues.  The  larger  of  these  processes  carry  with  them 
the  numerous  intrinsic  blood-vessels  from  the  superficial  plexus.  The  two  layers  are  closely 
connected  with  each  other,  and  are  distinguished  by  the  difference  in  the  arrangement  of  their 
fibres. 

The  membrane  dips  into  the  anterior  median  fissure  and  bridges  it  over  by  forming  an 
extra  thickening  along  it.  This  thickening  appears  as  a  band  along  the  mid-line  of  the  ventral 
surface  of  the  cord,  the  linea  splendens  (fig.  717).  It  carries,  or  ensheathes,  the  anterior  spinal 
artery,  the  largest  of  the  arterial  trunks  of  the  superficial  ple.xus  (fig.  725). 


Fig.  726. — Diagram  showing  Rel.ations  op  Meninges  to  Spinal  Nekve-hoots. 
Denticulate  ligament 


Body  of  vertebra 
Periosteum 

Bura  mater 
Subdural  cavity 
Arachnoid 

Subarachnoid  cavity 
Pia  mater 


Intervertebral  foramen- 


The  pia  mater  contributes  the  innermost  and  most  compact  portion  of  the  epineurium  of 
each  of  the  nerve-roots,  and  thus,  upon  the  roots,  it  is  prolonged  laterally  into  the  intervertebral 
foramina,  where  the  dura  mater  blends  with  it  in  producing  the  increased  thickness  of  the 
epineurium. 

From  each  side  of  the  cord  the  pia  mater  gives  off  a  leaf-like  fold,  the  den- 
ticulate ligament,  which  spreads  laterally  toward  the  dura  mater  midway  between 
the  lines  of  attachment  of  the  dorsal  and  ventral  nerve-roots.  The  outer  border  of 
this  fold  is  dentate  or  scalloped  into  about  twenty-one  pointed  processes,  which 
extend  through  the  arachnoid  and  are  attached  to  the  inner  surface  of  the  dura 
mater.  The  dentations  are  usually  inserted  between  the  levels  of  exit  of  the  roots 
of  the  spinal  nerves,  the  uppermost  one  a  little  cephalad  to  the  first  cervical  nerve 
and  the  region  where  the  vertebral  artery  perforates  the  dura  mater;  the  most 
caudal  one  between  the  last  thoracic  and  first  lumbar  nerves,  or,  between  the  last 
two  thoracic  nerves.  The  ligaments,  aided  slightly  by  the  septum  posticum, 
serve  to  hold  the  spinal  cord  more  or  less  suspended  in  the  subarachnoid  cavity. 

Below,  at  the  sudden,  conical  termination  of  the  spinal  cord  in  the  lumbar 
portion  of  the  spinal  canal,  the  pia  mater  is  spun  out  into  a  thin,  tubular  filament, 
the  filum  terminale,  which  continues  caudalward  into  the  sac  formed  by  the  dura 
mater  about  the  cauda  equina,  and  at  the  end  fuses  with  the  dura  mater  in  line 
with  the  filum  of  the  spinal  dura  mater  (coccygeal  ligament)  of  the  outside  (figs. 
613,  715). 


922 


THE  NERVOUS  SYSTEM 


The  cranial  pia  mater  is  closely  applied  to  the  external  surface  of  the  brain, 
dipping  into  all  the  fissures,  furrows,  and  sulci.  It  is  connected  with  the  arach- 
noid by  numerous  filaments  of  the  spongy  subarachnoid  tissue  and  by  the  blood- 
vessels traversing  the  subarachnoid  cavity.  It  is  also  pierced  by  the  cranial 
nerves,  and  furnishes  them  their  sheaths,  which  become  continuous  with  the 
arachnoid  and  dura  mater. 

Its  outer  surface  bounds  the  subarachnoid  cavity.  It  is  with  difficulty  separable  into  two 
layers  of  mixed  white  fibrous  and  elastic  connective  tissue,  with  slightly  pigmented  con- 
nective-tissue cells  enmeshed  between  them.  Its  inner  surface  sends  a  large  number  of  fibrous 
processes  into  the  nervous  substance,  which  blend  with  the  neuroglia  and  aid  in  the  support 
of  the  nervous  elements.  The  larger  of  these  processes  accompany  the  central  arterial  and 
venous  branches  of  the  rich  superficial  plexuses  of  blood-vessels  contained  in  the  pia  on  the 
surface  of  the  brain.  Pieces  of  the  pia  when  pulled  off  and  placed  in  water  present  a  flocculent 
appearance  as  to  their  inner  surfaces,  due  to  these  processes  having  been  pulled  out. 

The  cranial  pia  mater  sends  strong,  vascular  duplications  into  two  of  the  great 
fissures  of  the  encephalon;  viz.,  the  transverse  cerebellar  fissure,  between  the  cere- 
bellum and  the  medulla  oblongata,  and  the  transverse  cerebral  fissure,  between  the 
cerebellum,  mesencephalon,  and  thalamencephalon,  and  the  overhanging  cerebral 
hemispheres.  These  duplications  are  spread  over  the  cavities  of  the  fourth  and 
third  ventricles,  and  are  known  as  the  chorioid  telce  of  these  ventricles  respectively. 

Fig.  727. — Diagram  showing  Chorioid  Tela  of  Fourth  Ventricle  after  Removal  of 

Cerebellum. 
(The  trochlear  nerve  should  be  shown  emerging  from  the  frenulum  veli.) 


Inferior  quadrigeminate  body 
Trochlear  nerve 


Superior  medullary  velum 
Brachium  conjunctivuMl 
Brachium  of  pons 


Restiform  body 

Ligula  (taenia) 
Chorioid  tela  of 
fourth  ventricle 
Cuneate  tubercle 
Clava 
Tubercle  of  Rolando 


Frenulum  veil 
Lateral  lemniscus 

Lingula  of  cerebellum 


Fourth  ventricle 


VeBsels  to  chorioid  plexus 


Inferior  medullary  velum 
Chorioid  plexus 


The  tela  chorioidea  of  the  fourth  ventricle  lies  in  the  transverse  cerebellar 
fissure,  between  the  inferior  surface  of  the  cerebellum  (vermis  chiefly)  and  the 
dorsal  surface  of  the  medulla  (fourth  ventricle).  The  two  layers  of  this  fold  of 
the  pia  remain  separate  and  a  portion  of  the  cisterna  posterior  of  the  subarachnoid 
cavity  lies  between  them.  The  inferior  of  the  layers  is  the  tela  chorioidea 
(fig.  727.)  It  is  triangular  in  shape,  with  its  base  cephalad  at  the  nodule  of  the 
vermis  and  its  apex  below  at  the  level  of  the  tuber  vermis.  The  superior  layer  of 
the  fold  is  the  pia  mater  of  the  vermis.  The  tela  chorioidea  is  strengthened  by  the 
epithelial  roof  (ependyma)  of  the  fourth  ventricle  and  is  continuous  with  the  pia 
mater  of  the  medulla  oblongata  and  spinal  cord.  In  roofing  over  the  fourth 
ventricle  the  tela  chorioidea  of  the  fourth  ventricle  constitutes  the  ligula  and 
the  obex.  A  little  above  the  calamus  scriptorius  it  is  pierced  by  the  foramen  of 
Magendie  and  the  two  lateral  apertures  into  the  fourth  ventricle. 

In  front  of  the  foramen  of  Magendie  the  vessels  of  the  chorioid  tela,  which  are 
derived  from  the  posterior  inferior  cerebellar  arteries,  form  two  longitudinal, 
lobulated  strands  which  invaginate  the  epithelial  roof  of  the  ventricle,  one  on 
either  side  of  the  mid-hne,  and  project  into  its  cavity.     These  form  the  chorioid 


THE  CHORIOID  TELA 


923 


plexus  of  the  fourth  ventricle.  At  the  base  of  the  tela  the  two  chorioid  plex- 
uses join  each  other  and  then  turn  transversely  lateral  ward  into  the  lateral  re- 
cesses of  the  ventricle,  where  they  pass  behind  the  restiform  bodies  and  form  the 
'  cornucopicB.' 

The  chorioid  tela  of  the  third  ventricle,  or  velum  interpositum,  is  a  triangular 
duplication  of  the  pia  mater  which  extends  between  the  fornix  above  and  the  thai- 
ami  and  third  ventricle  below,  and  in  front  fuses  with  the  brain  substance  at  the 
interventricular  foramina. 

In  the  transverse  cerebral  fissure  the  layers  of  pia  forming  this  tela  are  separate,  the  upper 
being  the  pia  of  the  under  surface  of  the  corpus  caUosum  and  continuous  with  that  of  the  ten- 
torial surfaces  of  the  occipital  lobes;  the  lower  being  continuous  into  the  pia  enfolding  the 
epiphysis,  and  covering  the  mesencephalon,  anterior  medullary  velum,  and  cerebellum.     The 


Fig.  728. — Hokizontal  Dissection  op  the  Cerebrum  showing  the  Tela  Chorioidea  of 

THE  Third  Ventricle. 

(From  a  mounted  specimen  in  the  Anatomical  Department  of  Trinity  College,  DubUn.) 

The  fornix  has  been  removed  to  show  the  chorioid  tela  of  the  third  ventricle. 


Corpus 
caUosum 
(dissected) 


Veins  ofGalei 


Crura  of  fornix. 


Septum 
pellucidum 


Thalamus 

Chorioid  tela 
(velum  inter- 
positum) 

Chorioid 
plexus 

Fimbria 

Hippocampus 
major 

Collateral 

eminence 


layers  forming  the  portion  of  the  dupUcation  which  roofs  over  the  third  ventricle  are  loosely 
adherent  to  each  other  and  form  the  tela  chorioidea  proper  of  that  ventricle.  The  upper  surface 
of  this  portion  is  in  relation  with  the  fornix  and  its  lower  surface,  covered  by  the  epithelial 
chorioid  lamina,  lies  laterally  over  the  superior  surfaces  of  both  thalami,  and  mesiaUy  forms  the 
roof  of  the  third  ventricle  between  them.  The  epitheUum  or  ependyma  is  continuous  with  that 
covering  the  thalami  and  lining  the  ventricles.  Between  the  two  layers  of  this  portion,  and 
embedded  in  a  small  amount  of  the  spongy  subarachnoid  tissue  retained  between  them,  are 
the  two  veins  of  Galen,  the  internal  cerebral  veins.  Posteriorly  these  veins  unite  in  the  region 
of  the  epiphysis  to  form  the  single  great  cerebral  vein  (vena  cerebri  magna)  which  empties  into 
the  straight  sinus.  Anteriorly  the  veins  of  Galen  receive  the  veins  of  the  septum  pellucidum 
from  each  lamina  of  the  septum  pellucidum  above,  and  also  the  terminal  vein  (vein  of  corpus 
striatum),  lying  in  the  stria  terminahs  of  the  thalamus,  empties  into  them  from  each  side. 

The  chorioid  tela  of  the  third  ventricle  or  velum  interpositum  extends  laterally 
between  the  fornix  and  fimbria  above  and  the  stria  terminalis  of  the  thalamus  be- 


924 


THE  NERVOUS  SYSTEM 


low  into  each  lateral  ventricle.  The  blood-vessels  of  the  border  proj  ecting  into  the 
lateral  ventricle  are  amplified  into  a  plexus  which  appears  as  a  strip  of  reddish, 
lobulated,  villus-like  processes  known  as  the  chorioid  plexus  of  the  lateral  ven- 
tricle. The  plexus,  being  in  the  border  of  the  tela,  begins  at  the  interventricular 
foramen,  extends  through  the  body  or  central  portion  of  the  ventricle,  and  down- 
ward into  its  inferior  cornu.  It  is  most  developed  at  the  junction  of  the  body  with 
the  inferior  cornu,  and  is  there  known  as  the  glomus  chorioideum. 

From  the  under  surface  of  the  chorioid  tela  of  the  third  ventricle,  hanging 
down  on  either  side  of  the  mid-line  into  the  cavity  of  the  ventricle,  are  two  other 
longitudinal,  lobulated  strands  of  blood-vessels  which  are  the  chorioid  plexuses  of 
the  third  ventricle.  At  the  anterior  end  of  the  third  ventricle  these  two  plexuses 
join  with  each  other  and  also  with  the  plexus  of  the  lateral  ventricle  of  each  side 
through  the  interventricular  foramina. 

The  chorioid  plexuses  of  both  the  ventricles  are  covered  by  a  layer  of  ependyma,  epithelial 
chorioid  lamina,  which  is  but  a  reflexion  of  the  ependyma  lining  the  cavities  throughout  and 
represents  the  remains  of  the  germinal  layer  of  the  embryonic  brain  vesicles.     The  blood-vessels 

Fig.  729. — Diagram  op  Coronal  Section  of   Cerebrum  through  Middle  of  Thalamen- 

CEPHALON  SHOWING   RELATIONS    OF   PlA    MaTER   EnCEPHALI   AND    ChORIOID   PlEXUSES   OP 

Third  and  Lateral  Ventricles. 

Fifth  ventricle  Fornix 


of  the  chorioid  plexus  of  the  lateral  ventricle  receive  blood  by  the  chorioid  artery  (a  direct  branch 
of  the  internal  carotid),  which  enters  the  plex-us  through  the  chorioid  fissure  immediately  mesial 
to  the  uncus,  and  also  by  the  chorioidal  branches  of  the  posterior  cerebral  artery,  which  supply 
the  plexus  of  the  body  of  the  ventricle.  The  chorioid  plexuses  of  the  third  ventricle  receive  blood 
chiefly  by  branches  from  the  superior  cerebellar  arteries.  The  greater  part  of  the  blood  of  both 
plexuses  passes  out  by  way  of  the  tortuous  chorioid  veins,  which,  at  the  interventricular  foramen, 
empty  into  the  vense  terminates  (veins  of  the  corpus  striatum),  which,  in  their  turn,  go  to  form 
the  greater  part  of  the  veins  of  Galen.  Thence  the  blood  passes  by  way  of  the  vena  cerebri 
magna  into  the  straight  sinus.  It  is  probable  that  a  large  part  of  the  oerebro-spinal  fluid  of  the 
third  and  lateral  ventricles  is  derived  by  diffusion  through  the  walls  of  the  vessels  of  the  chorioid 
plexuses. 

THE  PERIPHERAL  NERVOUS  SYSTEM 


The  intimate  connection  and  consequent  control  exercised  by  the  central 
nervous  system  over  all  the  tissues  and  organs  of  the  body  is  attained  through  the 


THE  PERIPHERAL  NERVOUS  SYSTEM 


925 


Fig.  730. — Showing  the  Relation  between  the  Central  and  the  Peripheral  Nervous 

Systems. 
(Combination  drawing,  spinal  part  after  Allen  Thompson,  from  Rauber.) 


-/"  -  I  Cervical  nerve 


Gangliated  cord 


vi  Coccygeal  nerve 


Filum  terminale 


926  THE  NERVOUS  SYSTEM 

peripheral  nervous  system.  This  system,  abundantly  attached  to  the  central 
system,  consists  of  numerous  bundles  of  nerve-fibres  which  divide  and  ramify 
throughout  the  body,  anastomosing  with  each  other  and  forming  various  plexuses, 
large  and  small.  The  terminal  rami  divide  and  subdivide  until  the  divisions  attain 
the  individual  nerve-fibres  of  which  they  are  composed,  and  finally  the  nerve- 
fibres  themselves  divide  and  terminate  in  relations  with  their  allotted  peripheral 
elements.  It  is  by  means  of  this  system  that  stimuli  arising  in  the  peripheral 
tissues  are  conveyed  to  the  central  system,  and  that  impulses  in  response  are  borne 
from  the  central  system  to  the  peripheral  organs.  For  pm-poses  of  description,  as 
well  as  upon  the  basis  of  certain  differences  in  structm-e,  arrangement,  and  dis- 
tribution, the  peripheral  nervous  system  is  separated  into  two  main  divisions: — 
(1)  the  cranio-spinal  and  (2)  the  sympathetic  system. 

Both  of  these  divisions  include  numerous  ganglia  or  peripheral  groups  of  nerve- 
cells  from  which  arise  a  considerable  proportion  of  the  fibres  forming  their  nerve- 
trunks,  but  neither  of  the  divisions  may  be  considered  wholly  apart  from  the 
central  system  nor  are  they  independent  or  separate  from  each  other.  The  sen- 
sory or  afferent  fibres  of  the  cranio-spinal  nerves  pass  by  way  of  the  afferent  nerve- 
roots  into  the  central  system  and  contribute  appreciably  to  its  bulk,  and  the  motor 
or  efferent  fibres  of  these  nerves  have  their  cells  of  origin  (nuclei)  situated  within 
the  confines  of  the  central  system.  The  sympathetic  system  is  intimately  asso- 
ciated with  the  cranio-spinal,  and  consequently  with  the  central  system — (1) 
by  means  of  fibres  which  enter  and  terminate  in  the  cranio-spinal  gangha  and 
transfer  impulses  which  enter  the  central  system;  (2)  by  efferent  fibres  of  central 
origin  which  com'se  in  the  nerve-trunks  and  terminate  in  the  ganglia  of  the  sym- 
pathetic system;  (3)  also,  the  sympathetic  trunks  usually  contain  numerous 
afferent  cranio-spinal  fibres  which  thus  course  to  their  peripheral  termination, 
usually  in  the  so-called  'splanchnic  area,'  or  domain  of  the  sympathetic,  in 
company  with  the  sympathetic  fibres.  Likewise  the  peripheral  branches  of 
the  cranio-spinal  nerves  often  carry  for  varying  distances  numerous  sympathetic 
fibres  which  are  on  their  way  to  terminate  either  in  other  sympathetic  ganglia  or 
upon  their  allotted  peripheral  tissue-elements. 

The  following  differences  between  the  cranio-spinal  and  sympathetic  systems  of  nerves  may 
be  cited: — (1)  The  cranio-spinal  nerves  are  anatomically  continuous  with  the  brain  and  spinal- 
cord;  probably  no  fibres  arising  in  the  sympathetic  gangha  actually  enter  the  central  system 
other  than  for  the  innervation  of  its  blood-vessels,  (2)  The  gangha  of  the  cranio-spinal 
nerves  all  lie  quite  near  the  central  axis,  in  hne  on  either  side  of  it,  and  at  more  or  less  regular 
intervals;  the  sympathetic  gangha  are  scattered  throughout  the  body  tissues,  are  far  more 
numerous  and  more  variable  in  size,  and  probably  only  the  larger  of  them  are  symmetrical 
for  the  two  sides  of  the  body.  (3)  The  cranio-spinal  nerves  are  paired  throughout,  and  the 
nerves  of  each  pair  are  symmetrical  as  to  their  origin  and  also,  with  certain  exceptions  (notably 
the  vagus),  in  their  course  and  distribution;  most  of  the  larger  and  more  proximal  of  the  sym- 
pathetic nerve-trunks  are  symmetrical  for  the  two  sides  of  the  body;  many  of  them  are  not, 
and  many  of  the  smaller  and  most  of  the  more  peripheral  nerves  and  gangha,  large  and  srnall, 
are  not  paired  at  all.  (4)  Even  in  their  finer  twigs,  the  cranio-spinal  nerves  of  the  two  sides 
probably  do  not  anastomose  with  each  other  across  the  mid-hne  of  the  body;  the  sympathetic 
nerves  do  so  abundantly,  especially  within  the  body  cavity.  (5)  The  cranio-spinal  nerve;  are 
distributed  to  the  ordinary  sensory  surfaces  of  the  body  and  the  organs  of  special  sense  and  to 
the  somatic,  striated  or  'voluntary'  muscles  of  the  body;  the  sympathetic  fibres  are  devoted 
chiefly  to  the  supply  of  the  so-caUed  involuntary  muscles  of  the  body,  including  the  smooth 
muscle  in  the  walls  of  the  viscera  and  in  the  walls  of  the  blood  and  lymph  vascular-systems, 
while  others  serve  as  secretory  fibres  to  the  glands.  (6)  Cranio-spinal  nerve-fibres  are  char- 
acterized in  general  by  well-developed  medullary  sheaths,  making  the  nerves  appear  as  white 
strands;  most  of  the  sympathetic  fibres  are  non-medullated,  some  are  completely  and  some 
partially  medullated,  but  none  possess  as  thick  medullary  sheaths  as  those  of  the  cranio-spinal 
nerves.     Thus  sympathetic  nerves  appear  as  grey  strands. 

The  cranio-spinal  nerves.^ — There  are  forty-six  pairs  of  cranio-spinal  nerves, 
of  which  thirty-one  pairs  are  attached  to  the  spinal  cord  (spinal  nerves)  and  fifteen 
pairs  to  the  encephalon  (cranial  nerves) .  The  spinal  nerves  are  the  more  primi- 
tive and  retain  the  typical  character,  i.  e.,  each  is  attached  to  the  spinal  cord  by  two 
roots,  a  dorsal  or  sensory  ganglionated  root,  and  a  ventral,  which  is  motor,  and 
thus  not  ganglionated.  Most  of  the  cranial  nerves  have  only  one  root,  which  in 
come  cases  corresponds  to  a  dorsal  root  and  therefore  has  a  ganglion,  and  in  other 
cases  corresponds,  physiologically  at  least,  to  a  ventral  root  of  a  spinal  nerve. 
Among  other  differences,  the  fibres  of  the  first  cranial  nerve,  for  example,  do  not 
collect  to  form  a  distinct  nerve-trunk. 


THE  CRANIAL  NERVES  927 

I.  THE  CRANIAL  NERVES 

Customarily,  the  cranial  nerves  are  described  as  comprising  twelve  pairs  and 
each  is  referred  to  by  number.  However,  present  knowledge  of  their  origin, 
central  connections  and  peripheral  distribution  suggests  that  those  enumerated  as 
the  fifth,  seventh,  and  eighth  pairs  under  the  old  nomenclature  are  better  each 
separated  into  its  two  component  nerves,  each  of  which  merits  a  separate  descrip- 
tion and  a  separate  name.  None  of  the  cranial  nerves  corresponds  closely  to 
a  typical  spinal  nerve  with  its  motor  and  sensory  root.  The  so-called  motor  por- 
tion of  the  fifth  is  no  more  its  motor  root  than  is  the  seventh  nerve.  The  sensory 
portion  of  the  seventh  is  not  wholly  sensory  and  rather  resembles  the  ninth  pair  in 
distribution,  and  it  has  long  been  commonly  referred  to  as  a  separate  nerve.  The 
two  parts  of  the  eighth  nerve,  both  sensory,  are  known  to  be  wholly  different  in 
functional  character  and  are  so  named.  Further,  the  names  of  the  nerves,  descrip- 
tive of  their  function,  are  pedagogically  much  more  eflacient  than  the  use  of  num- 
bers in  referring  to  them. 

Separating  the  three  pairs  mentioned,  each  into  its  two  nerves,  gives  fifteen 
pairs  instead  of  twelve.  Their  names  and  functional  nature  are  given  in  the  fol- 
lowing table.  The  Roman  numerals  given  in  parentheses  correspond  to  the  serial 
numbers  given  when  twelve  pairs  only  are  considered.  It  is  also  customary  to 
enumerate  the  cranial  nerves  from  in  front  backward  and  caudalward,  and  this 
custom  is  followed  here,  but  again  it  would  be  pedagogically  better  to  take  them 
in  the  reverse  order.  Then  each  in  its  turn  could  be  directly  considered  as  in 
continuous  series  with  the  spinal  nerves  below  and  the  similarities  to  and  progres- 
sive modifications  from  the  spinal  type  could  be  better  realized.  It  will  be  remem- 
bered that  somatic  motor  or  efferent  fibres  are  those  which  terminate  directly  upon 
the  fibres  of  skeletal  muscle  while  visceral  motor  fibres  transfer  their  impulses  to 
sympathetic  neurones,  and  the  axones  of  the  latter  terminate  upon  gland  cells  and 
upon  the  fibres  of  cardiac  and  smooth  muscle. 

Name  Nature  General  Distribution 

Olfactory  (I) Sensory Olfactory  region,  nasal  epithelium. 

Optic  (II) Sensory Retina. 

Oculomotor  (III) Motor  {  |-^- ;  ;  ■  ;  ;  ;  ;   if.tr/bt/y.Tif "' 

Trochlear  (IV) Motor-somatic Eye-moving  muscles. 

Abducens  (VI) Motor-somatic Eye-moving  muscles. 

Trigeminus  (V) Sensory Face,  mouth,  and  scalp. 

Masticator    (minor  part   or  Motor-somatic Muscles  of  mastication. 

motor  root  of  trigeminus). 

T?„„;„i  /^7TT^  A/r„i„>  /  Somatic Facial  muscles. 

Facial  (VII) Motor  '^  visceral  (?) Sahvary  glands,  vessels(?). 

Glossopalatine.     (Intermedi-    ( Sensory Tongue,  palate. 

ate  pari  of  facial).  \  Motor- visceral Sahvary  glands. 

Cochlear  (auditory)  (VIII)..   Sensory Internal  ear. 

Vestibular    (equilibrator)         Sensory Semicircular    canals,    utriculus,    sac- 

(VIII).  cuius. 

i  Sensory Tongue,  palate,  pharynx. 
,;,„.„,/  Somatic Pharynx. 
Motor|  yjgj.gj.^j Glands  and  vessels. 
Sensory Alimentary  canal,  lung,  heart. 
Motor  I  Somatic Larynx,  pharynx. 
\  Visceral Alimentary  canal,  heart,  larjmx,  tra- 
chea, lung. 

Hypoglossal  (XII) Motor-somatic Tongue-moving  muscles. 

Q„;„„i  „„„„„ cvTN  A/i«t„.  /Somatic Neck  and  shoulder  muscles. 

Spmal  acessory  (XI) Motor  |  visceral Pharynx,  larynx,  heart. 

The  cranial  nerves,  like  the  spinal  nerves,  are  developed  from  cells  of  the  primi- 
tive neural  tube  and,  beginning  with  the  fifth  pair  downward,  all  the  sensory 
nerves  are  developed  from  the  cells  corresponding  to  those  of  the  ganglion  crest 
which  give  origin  to  the  spinal  ganglia  with  the  sensory  components  or  dorsal  roots 
of  the  spinal  nerves.  Otherwise  between  the  cranial  nerves  and  the  spinal  nerves 
there  are  many  important  differences.  Each  spinal  nerve  has  a  dorsal  or  sensory 
root,  which  springs  from  the  cells  of  a  spinal  ganglion;  a  ventral  or  motor  root, 
whose  fibres  are  processes  of  the  nerve-cells  which  are  situated  in  the  walls  of  the 
central  system,  and  at  their  attachment  to  the  surface  of  the  cord  the  two  roots  are 
some  distance  apart.     Only  one  of  the  (usually  considered)  twelve  pairs  of  cranial 


928 


THE  NERVOUS  SYSTEM 


nerves  corresponds  at  all  closely  with  typical  spinal  nerves.  This  one  is  the 
trigeminus  which  possesses  a  sensory  ganglionated  root  and  near  its  attachment 
is  accompanied  by  a  small  motor  nerve,  the  masticator,  which  serves  in  very 
small  part  as  a  corresponding  motor  root  of  the  trigeminus.  But  even  in  this  case 
where  the  similarity  between  the  cranial  and  spinal  nerves  is  greatest,  there  are 
still  points  of  anatomical  difference,  which  if  not  essential  are  very  obvious,  for 
the  so-called  motor  root  joins  not  the  whole  but  only  with  one  branch  of  the  sen- 
sory portion.  The  two  are  only  slightly  separated  from  each  other  at  their  attach- 
ment to  the  surface  of  the  brain.  All  the  other  cranial  nerves  differ  in  a  still  more 
marked  manner  from  typical  spinal  nerves.  The  first  nerve  is  an  afferent  nerve 
whose  cells  of  origin  (olfactory  ganglion)  are  scattered  in  the  mucous  membrane 


Fig.  731. — -Subface  Attachment  op  the  Cranial  Nerves. 
(After  Allen  Thomson,  modified.) 
Insula 
/  Olfactory  tract 

Hypophysis 


Anterior  perforated 

substance"^^^^J 


Corpora  mammillai 


N.  opticus  (II) 
Optic  tract 


Cerebral  peduncl 


Oblique  fasciculus 


—  Tuber  cinereum 


N.  oculomotorius 
(m) 


--  N.  trochlearis  (IV) 

\        "N.  masticatorius 

"^  N.  trigeminus  (V) 

,___..  N  abducens  (VI) 

,'  Brachium  pontis 

N.  facialis  (VH) 

N.  glossopalatinus 

^  N.   cochlearis      and    N, 
vestibularis  (VM) 

N-  glosso-pbaryngeus  (IX) 
N.  vagus  (X) 


N.  accesfeorius  (XI) 
(spinal  accessory) 


N.  Hypoglossus  (XU) 


Pyramid 


Decussation  of  pyramids' 


_  Cervical  II 


of  the  nose,  an  organ  of  special  sense,  and  its  fibres  are  not  collected  together  into  a 
nerve-trunk,  but  pass,  as  a  number  of  small  bundles,  through  the  lamina  cribrosa 
of  the  ethmoid  bone  directly  into  the  olfactory  bulb.  The  optic  nerve  is  also  a 
nerve  of  special  sense.  Its  fibres  form  a  very  distinct  bundle,  similar  in  appear- 
ance to  an  ordinary  nerve,  from  which,  however,  it  differs  essentially,  both  with 
regard  to  structure  and  development;  for,  unlike  an  ordinary  nerve,  its  connective 
tissue  consists  to  a  large  extent  of  neurogha  instead  of  ordinary  connective  tissue, 
and  its  component  nerve-fibres  are  of  much  smaller  calibre  than  those  of  an  ordi- 
nary nerve.  It  represents  the  location  of  the  original  optic  stalk,  a  diverticulum 
from  the  neural  tube  and  it  associates  the  retina  (optic  cup) ,  a  bit  of  modified  cor- 


THE  TERMINAL  NERVE  929 

tex,  with  the  encephalon.  The  optic  nerve,  therefore,  corresponds  more  closely 
with  an  association  tract  of  the  central  system  than  with  an  ordinary  nerve. 

The  oculomotor,  trochlear,  abducens  and  hypoglossal  nerves  are  purely  motor 
nerves,  and  thus  correspond  only  with  the  ventral  roots  of  spinal  nerves.  The 
spinal  accessory  is  also  purely  motor.  Its  fibres  arise  from  the  cells  of  the  anterior 
horn  of  the  spinal  cord  and  from  a  nucleus  of  the  medulla  which  represents  a  dis- 
placed portion  of  that  horn,  but  they  do  not  leave  the  surface  of  the  spinal  cord  and 
brain  in  the  usual  situation  of  ventral  roots.  On  the  contrary,  they  emerge  in  a 
series  of  rootlets  from  the  lateral  funiculus  of  the  cord  on  the  dorsal  side  of  the 
ligamentum  denticulatum,  and  from  the  upward  prolongation  of  this  funiculus. 

The  cochlear  and  vestibular  are  nerves  of  special  sense,  and  in  some  respects 
both  correspond  closely  with  the  dorsal  root  of  a  typical  spinal  nerve,  and  the  gan- 
glia of  both  represent  spinal  ganglia,  but  their  distribution  is  limited  to  the  mem- 
branous labyrinth. 

The  vagus  and  glosso-pharyngeal  nerves  contain  both  motor  and  sensory  fibres, 
but  they  differ  from  typical  spinal  nerves  in  that  the  motor  fibres,  in  company 
with  the  sensory,  issue  from  the  postero-lateral  sulcus  of  the  medulla,  and  they  are 
intimately  intermingled,  from  their  origin,  with  the  sensory  fibres,  which  latter 
arise  from  ganglia  interposed  in  the  trunks  of  the  nerves  and  otherwise  correspond 
with  the  fibres  of  the  dorsal  root  of  a  typical  spinal  nerve. 

Superficial  attachments  and  origins. — It  is  customary  to  speak  of  the  area 
where  the  nerve-fibres  leave  or  enter  the  brain  substance  as  the  superficial 
attachments  of  the  cranial  nerves,  and  the  groups  of  cells  from  which  the  fibres 
spring,  and  about  which  they  terminate,  as  their  nuclei  of  origin  or  termination, 
respectively. 

THE  OLFACTORY  NERVES 

The  olfactory  nerve-fibres  are  the  central  processes  of  the  bipolar  olfactory 
nerve  cell-bodies  situated  in  the  olfactory  region  of  the  nasal  mucous  membrane. 
In  man,  the  olfactory  region  comprises  the  epithelium  upon  the  superior  third  of 
the  nasal  septum  and  that  upon  practically  the  whole  of  the  superior  nasal  concha. 
The  area  is  relatively  small  as  compared  with  that  of  other  mammals  and,  as  in 
other  mammals,  is  characterized  by  an  increased  thickness  of  the  epithelium  and  a 
yellowish  brown  colour  in  the  fresh.  The  peripheral  processes  of  the  olfactory 
cell-bodies  (the  olfactory  gangUon)  are  short  and  extend  only  to  the  surface  of  the 
olfactory  epithehum.  As  the  central  processes  pass  upward  from  their  cells  of 
origin  they  form  plexuses  in  the  mucous  membrane,  and  from  the  upper  parts  of 
these  plexuses,  immediately  below  the  lamiiia  cribrosa  of  the  ethmoid,  about 
twenty  filaments  issue  on  each  side.  These  filaments  comprise  the  olfactory 
nerve.  They  are  non-medullated.  They  pass  upward,  through  the  foramina  in 
the  lamina  cribrosa,  into  the  anterior  fossa  of  the  cranium  in  two  rows,  and  after 
piercing  the  dura  mater,  the  arachnoid,  and  the  pia  mater,  they  enter  the  inferior 
surface  of  the  olfactory  bulb.  They  contribute  to  the  superficial  stratum  of  nerve- 
fibres  on  the  inferior  surface  of  the  olfactory  bulb  and  end  in  the  glomeruli,  which 
are  formed  by  the  terminal  ramifications  of  the  olfactory  nerve-fibres  intermingled 
with  the  similar  ramifications  of  the  main  dendrites  of  the  large  mitral  cells  which 
lie  in  the  deeper  part  of  the  grey  substance  of  the  olfactory  bulb. 

The  olfactory  nerve-fibres  are  grey  fibres,  since  they  do  not  possess  medullary  sheaths, 
and  they  are  bound  together  into  nerves  by  connective-tissue  sheaths  derived  from  the  pia 
mater,  from  the  subarachnoid  tissue,  and  from  the  dura  mater.  Prolongations  of  the  subarach- 
noid space  pass  outward  along  the  nerves  for  a  short  distance. 

Central  connections. — The  olfactory  impulses  are  transmitted  by  way  of  the  peripheral  proc- 
esses of  the  olfactory  neurones  through  the  cell-bodies  and  the  olfactory  nerve-fibres  and 
through  the  glomeruli  to  the  mitral  cells.  Thence  they  are  carried  by  the  central  processes 
(axones)  of  the  mitral  cells,  which  pass  backward  along  each  olfactorj'  tract  and  its  three  olfac- 
tory strise  (see  Rhinencephalon,  p.  864). 

THE  TERMINAL  NERVE  (Nervus  Terminalis) 

In  lower  vertebrates  and  recently  in  those  mammals  whose  sense  of  smell  is  relatively  much 
more  developed  than  in  man,  three  nerves  have  been  found  concerned  with  the  olfactorj'  appara- 
tus:— ■(!)  The  olfactory  nerve  proper  whose  fibres,  as  noted  above,  are  the  central  processes  of 


930  THE  NERVOUS  SYSTEM 

the  nerve  cell-bodies  situated  in  the  epithelium  of  the  olfactory  region  of  the  nasal  mucosa,  and 
which  terminate  in  the  olfactory  bulb;  (2)  The  vomero-nasal  nerve,  whose  fibres  are  the  central 
processes  of  nerve  cell-bodies  situated  in  the  epithelium  of  the  vomero-nasal  (Jacobson's)  organ 
and  which  pass  caudalward  in  the  submucosa  and  upward  to  join  the  filaments  of  the  olfactory 
nerve  proper  and  which,  in  the  dog,  cat,  rabbit,  rat,  etc.,  terminate  in  the  accessory  olfactory 
bulb — a  small  protuberance  possessed  by  these  animals  on  the  postero-median  aspect  of  the 
olfactory  bulb  proper;  (3)  The  terminal  nerve,  a  small  plexiform  nerve,  which  unlike  the  other 
two,  is  ganglionated. 

In  man,  the  vomero-nasal  (Jacobson's)  organ  is  rudimentary  after  birth  and,  therefore,  the 
vomero-nasal  nerve  is  not  present,  the  only  fibres  for  the  vomero-nasal  region  being  those  of  gen- 
eral sensibility  from  the  trigeminus  and  sympathetic  fibres  common  to  the  epithelium  of  the 
entire  nasal  fossa. 

The  terminal  nerve  has  been  recently  described  as  present  in  the  human  foetus  and  it  is  men- 
tioned here  because  of  the  expressed  belief  that  it  is  present  in  the  adult.  From  the  observations 
recorded  for  human  and  rabbit  foetuses  and  the  adult  dog  and  cat,  the  following  description  may 
be  given:  It  is  variably  plexiform  throughout  its  course.  Its  peripheral  twigs  are  distributed 
to  the  mucosa  of  the  nasal  septum,  some  to  the  mucosa  joining  the  olfactory  region  while  other 
and  larger  twigs  extend  further  forward  and  are  distributed  to  mucosa  of  the  vomero-nasal  organ, 
accompanying  and  sharing  in  the  distribution  of  the  vomero-nasal  nerve  when  this  is  present. 
Its  central  connections  are  in  the  form  of  two  or  three  small  roots  which  pass  through  the  cribri- 
form plate  of  the  ethmoid  bone  in  company  with  and  mesial  to  the  vomero-nasal  nerve  and  then, 
still  plexiform,  extend  caudalward  over  the  infero-mesial  aspect  of  the  olfactory  bulb  and  upon 
the  olfactory  peduncle  or  stalk  (olfactory  tract)  beyond,  a  root  often  extending  to  near_the 
lamina  terminalis  and  optic  chiasma.  The  roots  disappear  in  the  mesial  and  infero-mesial 
aspect  of  the  frontal  portion  of  the  brain  at  different  localities  caudal  to  the  olfactory  bulb  and 
usually  near  the  olfactory  peduncle,  but  often  one  may  disappear  in  the  region  corresponding  to 
the  anterior  perforated  substance  of  the  adult  human  brain. 

Numerous  small  groups  of  ganglion  cells  are  found  interposed  along  both  the  peripheral  and 
intracranial  course  of  the  terminal  nerve.  A  group,  larger  in  size  than  the  others  and  situated  in 
the  intracranial  course  of  the  nerve,  is  called  the  ganglion  ierminale.  The  fibres  of  the  nerve  are 
non-medullated.  Both  the  ganglion  cells  and  the  fibres  of  the  nerve  are  described  as  having 
more  the  appearances  characteristic  of  sympathetic  neurones  than  of  cranio-spinal.  On  the 
other  hand,  our  conceptions  of  sympathetic  neurones  do  not  permit  of  their  terminating  within 
the  central  system  except  for  the  innervation  of  its  bloodvessels.  It  may  result  that,  instead  of 
being  an  independent  nerve  as  now  claimed,  the  nervus  terminalis  is  a  part  of  the  forward  exten- 
sion of  the  cephalic  sympathetic,  the  larger  ganglia  and  plexuses  of  which  latter  are  well  known, 
and  that  its  neurones  receive  and  convey  impulses  to  the  gland  cells  of  the  nasal  mucosa  and  to 
the  muscle  of  the  blood-vessels  of  the  mucosa  and  those  supplying  the  infero-mesial  part  of  the 
frontal  end  of  the  cerebrum. 

THE  OPTIC  NERVES 

The  fibres  of  the  optic  nerve  are  the  central  processes  of  the  ganglion  cells  of  the 
retina.  Within  the  ocular  bulb  they  converge  to  the  optic  papilla,  where  they 
are  accumulated  into  a  rounded  bundle,  the  optic  nerve.  The  nerve  thus  formed 
pierces  the  chorioid  and  the  sclerotic  coats,  and,  at  the  back  of  the  bulb,  enters  the 
orbital  fat,  in  which  it  passes  backward  and  medialward  to  the  optic  foramen. 
After  traversing  the  foramen  it  enters  the  middle  fossa  of  the  cranium,  and  anas- 
tomoses with  its  fellow  from  the  opposite  side,  forming  the  optic  chiasma.  It 
may,  therefore,  for  descriptive  purposes,  be  divided  into  four  portions — the 
intra-ocular,  the  intra-orbital,  the  intra-osseous,  and  the  intra-cranial.  The 
total  length  of  the  nerve  varies  from  forty-five  to  fifty  millimetres. 

The  intra-ocular  part  is  rather  less  than  one  millimetre  in  length.  It  passes 
backward  from  the  optic  papilla  through  the  chorioid  and  through  the  sclerotic 
coats  of  the  bulb.  As  it  passes  through  the  latter  coat  of  the  bulb  in  many  sep- 
arate bundles,  the  area  it  traverses  has  a  cribriform  appearance  when  the  nerve 
is  removed,  and  consequently  is  known  as  the  lamina  cribrosa  sclerce. 

The  intra-orbital  part  of  the  nerve  emerges  from  the  sclerotic  about  three  milli- 
metres below  and  to  the  median  side  of  the  posterior  pole  of  the  bulbus,  and  it  is 
about  thirty  millimetres  long.  It  passes  backward  and  medialward,  surrounded 
by  the  posterior  part  of  the  fascia  bulbi  (Tenon's  capsule)  and  by  the  orbital  fat, 
to  the  optic  foramen. 

As  it  runs  backward  in  the  orbit  it  is  in  relation  above  with  the  naso-ciliary  (nasal)  nerve  and 
the  ophthalmic  artery  which  pass  obliquely  from  behind  and  laterally,  forward  and  medialward 
across  the  junction  of  its  posterior  and  middle  thirds,  and  also  in  relation  with  the  superior  oph- 
thalmic vein,  the  superior  rectus  muscle,  and  the  upper  branch  of  the  oculo-motor  nerve.  Below 
it  are  the  inferior  rectus  muscle,  and  the  inferior  division  of  the  oculo-motor  nerve.  To  its  lateral 
side,  near  the  posterior  part  of  the  orbit,  are  the  ophthalmic  artery,  the  ciliary  ganglion,  the 
abducens  nerve,, and  the  external  rectus  muscle.  The  anterior  two-thirds  of  this  portion  of  the 
optic  nerve  are  surrounded  by  the  ciliary  arteries  and  the  ciliary  nerves  and  it  is  penetrated  on  its 


THE  OCULO-MOTOR  NERVES 


931 


medial  and  lower  aspect  by  the  central  artery  of  the  retina.  As  it  enters  the  optic  foramen  to 
become  continuous  with  the  intra-osseous  part,  it  is  in  close  relation  with  the  ligaments  of  Lock- 
wood  and  Zinn  (annulus  tendineus  communis)  and  with  the  four  recti  muscles  which  arise  from 
them. 

The  intra-osseous  portion  is  from  six  to  seven  millimetres  long.  It  lies  be- 
tween the  roots  of  the  small  wing  of  the  sphenoid  and  the  body  of  that  bone,  and  it 
is  in  relation  below  and  laterally  with  the  ophthalmic  artery. 

The  intra-cranial  portion,  which  is  from  ten  to  twelve  millimetres  long,  runs 
backward  and  medialward,  beneath  the  posterior  end  of  the  olfactory  tract,  and 
above  the  ophthalmic  artery,  the  medial  border  of  the  internal  carotid  artery 
and  the  diaphragma  sellse  to  the  chiasma.  From  the  chiasma  to  the  central 
connections  of  the  nerve,  the  path  is  known  as  the  optic  tract. 

Central  connections. — The  central  connections  of  the  fibres  of  the  optic  nerve  have  been 
considered  with  the  optic  chiasma  and  the  optic  tract  (see  p.  849). 

Fig.  732. — Nerves  op  the  Nasal  Cavitt. 

Nasal  branch 
^       ^  ,    .        "'  ethmoidal     Olfactory 
^"' *       "  nerve  plexus 


Superior  nasal  co: 
Sphenoidal  sinus 


Spheno-palatine 
ganglion 
Palatine  nerves 


—  Nasal  branches 

Posterior  palatine 
Anterior  palatine 
Middle  palatine 


The  sheaths  of  the  optic  nerve. — The  optic  nerve  receives  a  sheath  from 
each  of  the  membranes  of  the  brain,  and  prolongations  of  the  subdural  and  sub- 
arachnoid cavities  also  pass  outward  along  it  to  the  posterior  part  of  the  sclera. 

THE  OCULO-MOTOR  NERVES 


The  oculo-motor  or  third  cranial  nerve  is  a  purely  motor  nerve.  Each  sup- 
plies seven  muscles  connected  with  the  eye,  two  of  which,  the  sphincter  of  the  iris 
and  cihary  muscle,  are  within  the  ocular  bulb.  The  remaining  five  are  in  the  orbi- 
tal cavity,  and  four  of  them — the  superior,  inferior,  and  medial  recti  and  the 
inferior  oblique — are  attached  to  the  bulb,  while  the  fifth,  the  levator  palpebrje 
superioris,  is  inserted  into  the  upper  eyelid. 

The  fibres  of  the  oculo-motor  nerve  spring  from  their  nucleus  of  origin  situated  in  the  grey 
substance  of  the  floor  of  the  cerebral  aquteduct  in  the  region  of  the  superior  quadrigeminate 
body  (fig.  662).  The  cells  of  tliis  nucleus  are  divided  into  two  main  groups,  a  superior  and  an 
inferior  (fig.  663).  The  superior  group  includes  two  nuclei,  a  medial  and  a  lateral.  The  latter, 
besides  being  lateral,  is  also  somewhat  dorsal  to  the  former.  The  inferior  group  has  been 
divided  into  five  secondary  nuclei,  according  to  the  eye-muscles  the  cells  of  each  group  innervate. 
Three  of  the  five  lie  lateral  to  the  others  and  somewhat  dorsally,  and  of  the  remaining  two, 
which  are  placed  more  medially,  one  encroaches  upon  the  mid-line  (nucleits  mediaiis)  and  is  con- 


932 


THE  NERVOUS  SYSTEM 


tinuous  with  the  corresponding  group  of  the  opposite  side  and  is  common  to  the  oculo-motor 
nerves  of  both  sides. 

It  has  been  foimd,  by  the  study  of  diseased  conditions  and  by  experiments  with  animals, 
that  the  centres  of  innervation  of  the  eye-muscles  suppUed  by  the  nerve  correspond  to  the  above 
divisions  of  both  the  superior  and  inferior  group  of  cells  into  a  medial  and  lateral  series.  The 
relative  position  of  the  divisions  of  each  group  and  the  muscles  they  are  thought  to  innervate 
are  shown  in  the  following  diagram  devised  by  Starr: — 


Mesial  Plane. 


StrPBRIOR 

Grotip. 


Inferior 
Group. 


Sphincter 
of  Iris. 

Ciliary 
Muscle. 

Ciliary 
Muscle. 

Sphincter 
of  Iris. 

Levator 
Palpcbrae 
Superioris. 

Medial 
Rectus. 

Medial 
Rectus. 

Levator 
Palpebrse 
Superioris. 

1 
Superior 
Rectus. 

Inferior 
Rectus. 

Inferior 
Rectus. 

Superior 
Rectus. 

Inferior 
Oblique. 

Inferior 
Oblique. 

As  they  leave  their  nucleus  of  origin  in  the  mid-brain,  the  fibres  of  the  oculo- 
motor nerve  form  a  series  of  fasciculi,  which  curve  ventrally  around  and  through 
the  red  nucleus  and  the  medial  part  of  the  substantia  nigra,  to  the  oculo-motor 
sulcus  on  the  medial  surface  of  the  cerebral  peduncle,  where  they  emerge  in  from 
six  to  fifteen  small  bundles  which  pierce  the  pia  mater  and  collect  into  the  trunk 
of  the  nerve.  Immediately  after  its  formation  along  the  oculo-motor  sulcus,  the 
trunk  of  the  nerve  passes  between  the  posterior  cerebral  and  the  superior  cere- 
bellar arteries,  and,  running  downward,  forward,  and  laterally  in  the  posterior 
part  of  the  cisterna  basalis,  it  crosses  the  anterior  part  of  the  attached  border  of  the 
tentorium  cerebelli  at  the  side  of  the  dorsum  sellse,  and,  piercing  the  arachnoid 
and  the  inner  layer  of  the  dura  mater,  it  enters  the  wall  of  the  cavernous  sinus 
about  midway  between  the  anterior  and  posterior  clinoid  processes.  Immediately 
after  its  entry  into  the  wall  of  the  sinus  it  lies  at  a  higher  level  than  the  trochlear 
nerve,  but  the  latter  soon  crosses  on  its  lateral  side  and  gets  above  it,  and  directly 
afterward  the  oculo-motor  nerve  divides  into  a  smaller  superior  and  a  larger 
inferior  branch  (fig.  734).  Before  its  division  communications  join  it  from  the 
cavernous  plexus  of  the  sympathetic  about  the  internal  carotid  artery,  and  from 
the  ophthalmic  division  of  the  trigeminus.  Both  branches  proceed  forward,  and 
the  nasal  branch  of  the  trigeminus,  which  has  passed  upward,  on  the  lateral  side  of 
the  inferior  branch  of  the  oculomotor  lies  between  them.  At  the  anterior  end  of 
the  cavernous  sinus  the  two  branches  pass  through  the  superior  orbital  (sphe- 
noidal) fissure,  between  the  heads  of  the  lateral  rectus  muscle,  and  enter  the  or- 
bital cavity.  In  the  orbit,  the  superior  branch  hes  between  the  superior  rectus  and 
the  optic  nerve;  it  supplies  the  superior  rectus  and  then  turns  round  the  medial 
border  of  that  muscle  and  terminates  in  the  levator  palpebrse  superioris.  The 
inferior  branch  runs  forward,  beneath  the  optic  nerve,  and  divides  into  three 
branches  which  supply  the  inferior  and  medial  recti  and  the  inferior  oblique. 

The  branch  to  the  inferior  oblique  muscle  is  connected  with  the  ciliary  ganglion 
by  a  short  thick  offset,  the  short  root  of  the  ciliary  ganglion,  by  mediation  of  the 
sympathetic  neurones  of  which  the  oculo-motor  nerve  sends  impulses  to  the  ciliary 
muscle  and  the  sphincter  muscle  of  the  iris.  The  inferior  branch  also  gives  some 
small  twigs  to  the  inferior  rectus.  The  branches  of  the  oculo-motor  nerve,  which 
supply  the  recti  muscles,  enter  the  muscles  on  their  ocular  surfaces,  but  the  branch 
to  the  inferior  oblique  muscle  enters  the  posterior  border  of  that  muscle. 


THE  TROCHLEAR  NERVES 


933 


Some  of  the  fibres  which  spring  from  the  medial  portion  of  the  oculo-motor  nucleus  do  not 
pass  into  the  nerve  of  the  same  side,  but  into  that  of  the  opposite  side,  and  it  is  beheved  that 
they  are  distributed  to  the  opposite  medial  rectus  muscle.  Other  fibres  which  arise  from  the 
nucleus  descend  in  the  medial  longitudinal  fasciculus  and  either  terminate  about  the  cells  of 
the  nucleus  of  the  facial  or  join  the  facial  nerve,  in  which  they  pass  to  the  upper  part  of  the 
orbicularis  palpebrarum.  The  eye  is  opened  by  the  oculo-motor  and  closed  by  the  facial  nerve. 
Central  connections. — The  nucleus  of  the  oculo-motor  is  associated  with  the  middle  portion  of 
the  anterior  central  gyrus,  the  posterior  end  of  the  middle  frontal  gyrus  and  with  the  cortex  about 
the  visual  area  of  the  occipital  lobe  of  the  opposite  side  of  the  brain  by  the  pyramidal  fibres.  It  is 
probably  associated  with  the  cerebellum  by  the  fibres  in  the  superior  cerebellar  peduncles,  with 
the  superior  calliculus,  and  with  the  sensory  nuclei  of  the  other  cranial  nerves  by  the  medial 
longitudinal  fasciculus.  To  produce  the  coordinated  activities  of  the  eye-moving  muscles,  it 
must  be  associated  with  the  nuclei  of  the  trochlear  and  abducens. 

THE  TROCHLEAR  NERVES 

The  fibres  of  each  trochlear  or  fourth  nerve  (or  patheticus)  spring  from  the 
cells  of  a  nucleus  which  lies  in  the  grey  substance  of  the  floor  of  the  cerebral  aquse- 
duct  in  hne  with  the  oculo-motor  nucleus,  but  in  the  region  of  the  inferior  quadri- 
geminate  bodies.  As  the  fibres  pass  from  their  origins  they  rim  ventrally  and  lat- 
erally in  the  substance  of  the  tegmentum  for  a  short  distance,  then  they  curve 
medianward  and  dorsalward,  and,  in  passing  through  the  anterior  end  of  the  supe- 
rior medullary  velum  they  decussate  totally  with  the  fibres  of  the  trochlear  nerve 


Fig.  733. — Diagrams  op  Sections  through  the  Origin  op  the  Trochlear  Nerve.     (Still- 
ing.) (The  upper  figure  is  an  obUque  section,  the  lower  is  a  coronal  section.) 


Cerebral  aqueduct- 


Nucleus  of  trochlear  nerve 


Trochlear  nerve 


Trochleai  nerve 


■Cerebral  aqueduct 
Nucleus  of  masticator 

Brachium  conjunctivum 


•Lateral  lemniscus 


of  the  opposite  side.  After  the  decussation  the  fibres  emerge  from  the  surface  of 
the  superior  medullary  velum,  at  the  side  of  the  frenulum  veli,  usually  in  two  small 
bundles,  which  pierce  the  pia  mater  and  join  together  to  form  the  slender  trunk  of 
the  nerve.  This  trunk  curves  forward  and  ventralward  to  the  base  of  the  brain 
around  the  sides  of  the  superior  peduncle  of  the  cerebellum  and  cerebral  peduncle 
of  the  side  opposite  to  that  in  which  the  nerve  originates,  running  parallel  with  and 
between  the  superior  cerebellar  and  posterior  cerebral  arteries.  As  it  reaches  the 
base  of  the  brain  behind  the  optic  tract  the  nerve  enters  the  cisterna  basalis,  in 
which  it  runs  forward,  immediately  beneath  or  piercing  the  free  border  of  the  ten- 
torium cerebelli,  to  the  superior  border  of  the  petrous  portion  of  the  temporal 
bone,  where  it  pierces  the  arachnoid  and  the  dura  mater  and  enters  the  posterior 
end  of  the  lateral  wall  of  the  cavernous  sinus.  In  the  wall  of  the  cavernous  sinus 
it  receives  communications  from  the  cavernous  plexus  of  the  sympathetic  and  bj' 
a  small  filament  from  the  ophthalmic  division  of  the  trigeminus.  It  gradually 
ascends,  as  it  passes  forward  in  the  lateral  wall  of  the  sinus,  and,  beyond  the 
middle  of  the  sinus,  it  crosses  the  lateral  side  of  the  trunk  of  the  oculo-motor 
nerve  and  gains  a  higher  position.     At  the  anterior  end  of  the  sinus  the  nerve 


934  THE  NERVOUS  SYSTEM 

enters  the  orbit  above  the  lateral  rectus  and  immediately  turns  medialward 
between  the  periosteum  of  the  roof  of  the  orbit  and  the  levator  palpebrae  superioris. 
At  the  medial  border  of  the  roof  it  turns  forward  to  its  termination,  and  enters 
the  orbital  or  superior  surface  of  the  superior  oblique  muscle  to  which  its  fibres 
are  distributed. 

The  central  connections  of  the  nucleus  of  the  trochlear  nerve  are  similar  to  those  of  the 
oculo-motor  save  that  its  cells  probably  do  not  send  fibres  which  connect  with  the  facial  nerve. 

The  trochlear  is  peculiar  in  that — (1)  it  is  the  smallest  of  the  cranial  nerves;  (2)  it  is  the 
only  nerve  having  its  superficial  attachment  upon  the  dorsal  aspect  of  the  euoephalon;  (3)  it 
is  the  only  cranial  nerve  whose  fibres  undergo  a  total  decussation,  and  (4)  in  that  it  terminates 
in  a  muscle  of  the  side  of  the  body  opposite  that  in  which  it  has  its  origin.  GaskeU  has  suggested 
that  this  latter  condition  has  probably  been  brought  about,  phylogenetically,  by  the  trans- 
ference of  the  muscles  which  have  carried  their  nerves  with  them.  It  should  be  remembered 
that  most  of  the  fibres  arising  from  the  medial  group  of  the  cells  of  the  nucleus  of  the  oculo-motor, 
cross  the  opposite  side.  This  is  thought  to  be  especially  true  for  those  supplying  the  medial 
rectus  muscle. 

THE  ABDUCENS 

The  abducens  (or  sixth  nerve)  on  each  side  arises  from  the  cells  of  a  nucleus 
which  lies  in  the  grey  substance  of  the  floor  of  the  fourth  ventricle  in  the  region  of 
the  inferior  part  of  the  pons.  The  nucleus  is  situated  close  to  the  middle  line, 
ventral  to  the  acoustic  medullary  strise  and  beneath  the  colliculus  facialis  and 
it  is  in  direct  linear  series  with  the  nuclei  of  the  oculo-motor,  trochlear  and  hypo- 
glossal nerves.  It  is  the  third  of  the  eye-moving  nerves.  The  fibres  which  pass 
from  the  nucleus  into  the  nerve  run  inferiorly  and  ventralward  through  the  ret- 
icular formation,  the  trapezium,  and  the  pyramidal  fasciculi,  and  they  emerge 
from  the  ventral  surface  of  the  medulla  in  the  sulcus  at  the  inferior  border  of  the 
pons  and  the  upper  end  of  the  pyramid  of  the  medulla.  From  this  superficial 
attachment  the  nerve  runs  upward  and  forward  in  the  subarachnoid  space  between 
the  pons  and  the  basisphenoid  and  at  the  side  of  the  basilar  artery.  A  little  below 
the  level  of  the  upper  border  of  the  petrous  portion  of  the  temporal  bone  it  pierces 
the  dura  mater,  passes  beneath  the  petro-sphenoidal  hgament,  at  the  side  of  the 
dorsum  sellte,  and  enters  the  cavernous  sinus,  in  which  it  runs  forward  along  the 
lateral  side  of  the  internal  carotid  artery.  At  the  anterior  end  of  the  sinus  it 
passes  through  the  superior  orbital  (sphenoidal)  fissure  between  the  heads  of 
the  rectus  lateralis,  below  the  inferior  branch  of  the  oculo-motor  nerve,  and  above 
the  ophthalmic  vein.  In  the  orbit  it  runs  forward  on  the  inner  or  ocular  surface 
of  the  rectus  lateralis,  and  finally  it  pierces  this  muscle  and  terminates  upon  its 
fibres. 

While  it  is  in  the  cavernous  sinus  it  receives  communications  from  the  carotid 
plexus  of  the  sympathetic  and  from  the  ophthalmic  nerve. 

All  the  fibres  arising  in  the  nucleus  of  the  sixth  nerve  do  not  pass  into  the  sixth  nerve.  Some 
of  them  ascend  in  the  medial  longitudinal  fasciculus  of  the  same  and  opposite  sides,  and  ter- 
minate about  cells  of  the  medial  group  of  the  nucleus  of  the  oculo-motor  nerve,  by  which  the 
impulses  are  conveyed  to  the  opposite  medial  rectus  muscle.  Thus  impulses  reaching  the  abdu- 
cens nucleus  can  throw  into  simultaneous  action  the  lateral  rectus  of  the  same  side  and  the 
medial  rectus  of  the  opposite  side,  and  thus  turn  both  ej'es  in  the  same  direction. 

Central  connections. — The  nucleus  of  the  abducens  receives  impulses  from  the  anterior 
central  gyrus  of  the  opposite  side  by  the  pj'ramidal  fibres,  and  it  is  associated  with  the  sensory 
nuclei  of  other  nerves  by  way  of  the  medial  longitudinal  fasciculus,  and  that  of  the  trigemiuus 
especially  through  the  reticular  formation. 

THE  TRIGEMINUS 

The  trigeminus  is  the  largest  of  the  cranial  nerves  with  the  exception  of  the 
optic.  It  is  usually  described  as  the  fifth  cranial  nerve  and  as  possessing  both  a 
sensory  and  a  motor  root.  For  reasons  already  given,  the  "motor  root"  is  here 
described  separately  and  given  the  separate  name,  masticator  nerve.  The 
fibres  of  the  trigeminus,  which  are  all  sensory,  spring  from  the  cells  of  the  semi- 
lunar (Gasserian)  ganglion,  which  corresponds  with  the  ganglion  of  the  dorsal 
root  of  a  spinal  nerve,  and  they  enter  the  brain  stem  through  the  side  of  the 
anterior  third  of  the  pons. 


BRANCHES  OF  THE  TRIGEMINUS  935 

The  semilunar  (Gasserian)  ganglion  is  a  semilunar  mass  which  lies  in 
Meckel's  cave,  a  cleft  in  the  dura  mater  above  a  depression  in  the  medial  part  of 
the  upper  surface  of  the  petrous  portion  of  the  temporal  bone.  The  convexity  of 
the  ganglion  is  turned  forward,  and  from  it  three  large  nerves,  the  ophthalmic, 
the  maxillary,  and  the  mandibular,  are  given  off.  From  the  concavity,  which  is 
directed  backward,  springs  the  root  of  the  nerve.  The  medial  end  of  the  ganglion 
is  in  close  relation  with  the  cavernous  sinus  and  the  internal  carotid  artery  at  the 
foramen  lacerum,  and  the  lateral  end  lies  to  the  medial  side  of  the  foramen  ovale. 
The  surfaces  of  the  ganglion  are  striated,  due  to  bundles  of  fibres  traversing  them. 
The  upper  surface  is  separated  by  the  dura  mater  from  the  temporal  lobe  of  the 
brain,  and  the  lower  rests  upon  the  masticator  nerve  and  the  outer  layer  of  dura 
mater  upon  the  petrous  portion  of  the  temporal  bone. 

The  fibres  of  the  trigeminus  root  as  they  leave  the  semilunar  (Gasserian)  ganglion,  form  from 
thirty  to  forty  fasciculi  which  are  bound  together  into  a  flat  band,  from  six  to  seven  millimetres 
broad,  which  passes  backward  over  the  upper  border  of  the  petrous  portion  of  the  temporal 
bone  and  below  the  superior  petrosal  sinus  into  the  posterior  fossa  of  the  cranium.  In  the 
posterior  fossa  it  runs  backward,  medialward,  and  downward,  and  passes  into  the  pons  through 
its  continuation  into  the  middle  peduncle  of  the  cerebellum.  In  the  tegmentum  of  the  pons 
region,  the  fibres  bifurcate  into  ascending  and  descending  branches  which  terminate  about 
the  cells  of  the  nucleus  of  termination  of  the  trigeminus.  This  nucleus,  large  at  the  level  of 
the  entrance  of  the  root,  has  tapering  superior  and  inferior  e.xtremities.  The  inferior  ex- 
tremity of  the  nucleus,  which  is  much  the  longer,  descends  as  low  as  the  upper  portion  of  the 
spinal  cord  and  the  fibres  of  the  root  terminating  about  the  cells  of  this  extremity  are  known 
as  the  spinal  tract  of  the  trigeminus. 

Central  connections. — The  nuclei  of  termination  of  the  trigeminus  send  impulses  to  the 
somaesthetic  area  of  the  cortex  of  the  opposite  side  by  the  fibres  of  the  medial  lemniscus  (fillet) 
and,  for  reflex  actions,  to  the  motor  nuclei  of  other  cranial  nerves  by  the  medial  longitudinal 
fasciculus  and  by  fascicuU  propri  in  the  reticular  formation  of  the  same,  and  opposite  sides. 

THE  BRANCHES  OF  THE  TRIGEMINUS 

The  main  branches  of  the  trigeminus,  given  off  by  the  front  side  of  the  semi- 
lunar ganglion,  are  three  in  number  (ophthalmic,  maxillary,  and  mandibular) , 
each  of  which  is  referred  to  as  a  nerve  and  each  of  which  is  purely  sensory,  though 
the  third  branch,  or  mandibular  nerve,  is  joined  by  the  fibres  of  the  masticator 
nerve  which  is  motor. 


(1)  The  Ophthalmic  Nerve  or  First  Division 

The  ophthalmic  nerve,  the  first  division  of  the  trigeminus,  is  the  smallest  of  the 
three  branches  which  arise  from  the  semilunar  (Gasserian)  ganglion.  It  springs 
from  the  medial  part  of  the  front  of  the  ganglion  and  passes  forward,  in  the  lateral 
wall  of  the  cavernous  sinus,  where  it  lies  below  the  trochlear  nerve  and  lateral  to 
the  abducens  nerve  and  the  internal  carotid  artery  (fig.  734).  A  short  distance 
behind  the  superior  orbital  (sphenoidal)  fissure  the  nerve  divides  into  three  ter- 
minal branches — the  frontal,  lacrimal,  and  naso-ciliary  (nasal)  nerves.  They 
pierce  the  dura  mater,  which  closes  the  fissure,  and  pass  forward  into  the  orbit. 
Before  its  division  the  ophthalmic  nerve  receives  filaments  from  the  cavernous 
plexus  of  the  sympathetic  and  it  gives  off,  soon  after  its  origin,  a  tentorial  (recur- 
rent meningeal)  branch  which  runs  backward,  in  close  association  with  the  troch- 
lear nerve,  and  ramifies  between  the  layers  of  the  tentorium  cerebelli.  Further 
forward  three  branches  spring  from  the  ophthalmic  nerve  which  contribute  sen- 
sory fibres  to  the  oculo-motor,  trochlear,  and  abducens  nerves. 

The  terminal  branches. — (a)  The  frontal  nerve  is  the  largest  terminal 
branch.  It  pierces  the  dura  mater  and  passes  into  the  orbit  through  the  superior 
orbital  (sphenoidal)  fissure,  above  the  rectus  lateralis  and  a  little  below  and  to 
the  lateral  side  of  the  trochlear  nerve.  In  the  orbit  it  runs  forward,  between  the 
levator  palpebrse  superioris  and  the  periosteum,  and  breaks  up  into  three  branches, 
the  supra-orbital,  frontal  proper,  and  supratrochlear. 

The  supra-orbital  nerve,  the  largest  of  the  three  branches,  leaves  the  orbit  at  the  supra- 
orbital notch  (fig.  734).  As  it  passes  thi-ough  the  notch  it  gives  off  a  small  branch  which  enters 
the  bone  and  supphes  the  diploe  and  the  mucous  membrane  of  the  frontal  sinus.  Its  terminal 
branches  give  twigs  to  the  pericranium  and  to  the  skin  of  the  scalp,  the  upper  ej-eUd,  the  frontal 


936 


THE  NERVOUS  SYSTEM 


region,  and  the  parietal  region  almost  as  far  as  the  lambdoid  suture  (fig.  740).  One  branch 
running  at  the  upper  margin  of  the  orbital  cavity  unites  with  a  branch  of  the  facial  nerve. 

The  frontal  branch,  given  off  at  a  variable  point,  lies  medial  to  the  supra-orbital,  passes 
through  the  frontal  foramen,  and  is  distributed  to  the  skin  of  the  forehead  and  upper  eyehd 
(fig.  734). 

The  supratrochlear  branch  runs  forward  and  medialward  toward  the  upper  and  medial 
angle  of  the  orbit,  where  it  passes  above  the  pulley  of  the  superior  obhque  muscle,  pierces  the 
palpebral  fascia,  and  ascends  to  the  lower  and  middle  part  of  the  forehead,  accompanied  by 
the  frontal  artery  (fig.  734).  Before  it  leaves  the  orbit  it  sends  a  branch  downward  behind  or 
in  front  of  the  pulley  of  the  obliquus  superior  which  joins  with  the  infratrochlear  nerve,  and  as 
it  leaves  the  orbit  it  gives  off  filaments  to  supply  the  skin  and  conjunctiva  of  the  medial  third 
of  the  upper  eyelid.  Its  terminal  branches  pierce  the  orbicularis  and  frontalis,  and,  as  they  pass 
to  the  skin  of  the  forehead,  they  communicate  with  branches  of  the  facial  nerve. 

(b)  The  lacrimal  nerve  [n.  lacrimalis]  is  the  smallest  of  the  three  branches  of  the 
ophthalmic  division.  It  passes  through  the  superior  orbital  (sphenoidal)  fissure 
lateral  to  and  slightly  below  the  frontal  nerve,  and  is  directed  forward  and  lateral- 


FiG.  734. — Nerves  op  the  Orbit  from  Above  and  Behind.     (Schematic.) 

Infratrochlear 
1  Supratrochlear 
I  1       Frontal  branch  of  frontal 
,       Supraorbital 


Superior  ob-^ 
lique  muscle"" 


Trochlear 
Naso-ciliary 
(nasal)    " 
Annular  com- 
mon tendon 
of  Zinn 
Optic  nerve  - 


Internal  car- 
otid artery 


Abducens ^-r 


Semilunar        ^ 
(Gasserian) "^  j    ^ 


Levator  palpebrse 

superioris 
Superior  rectus 
Lacrimal  gland 
Frontal 

Short  ciliary  nerves 
Anastomosing  branch 

with  zygomatic 
Lacrimal 

Long  ciliary  nerves 
Inferior  rectus 
Branch  to  internal 

oblique 
Lateral  rectus 
Ciliary  ganghon 
Sympathetic  ]  Roots  of 
Short  }    ciliary 

Long  J  ganghon 

Abducens 
Inferior  branch  of 

oculo-motor 
Superior  branch  of 

oculo-motor 
Lateral  rectus  (lat. 

head) 
Ophthalmic 
Maxillary 


Mandibular 
A' — Foramen  spinosum 


ward,  along  the  upper  border  of  the  rectus  lateralis  to  the  lacrimal  gland  (fig.  734) . 
On  the  lateral  wall  of  the  orbit  it  receives  a  small  branch  from  the  zygomatic 
nerve  (the  orbital  branch  of  the  maxillary  nerve).  This  branch  brings  to  the 
lacrimal  nerve  secretory  fibres  for  the  lacrimal  gland.  A  small  twig  passes  beyond 
the  gland,  pierces  the  palpebral  fascia,  supplies  filaments  to  the  conjunctiva,  and 
is  then  distributed  to  the  integument  at  the  lateral  angle  of  the  eye  and  to  the  skin 
over  the  zygomatic  process  of  the  frontal  bone. 

(c)  The  naso-ciliary  (nasal)  nerve  enters  the  orbit  between  the  two  heads  of  the 
rectus  lateralis  and  between  the  superior  and  inferior  branches  of  the  oculo-motor 
nerve.  In  the  orbit  it  lies  at  first  lateral  to  the  optic  nerve,  but,  as  it  runs  obliquely 
forward  and  medialward  to  the  medial  wall  of  the  orbital  cavity,  it  crosses  above 
the  optic  nerve  and  between  it  and  the  rectus  superior,  and  near  the  border  of  the 
rectus  medialis  it  divides  into  its  terminal  branches,  the  chief  of  which  are  the 
infratrochlear  and  anterior  ethmoidal  nerves  (fig.  734).  In  addition  to  those 
received  from  the  cavernous  plexus  before  the  division  of  the  ophthalmic  nerve , 


THE  MAXILLARY  NERVE  937 

the  naso-ciliary  nei've  itself  receives  numerous  sympathetic  (secretory  and  vaso- 
motor) fibres. 

Its  several  branches  are:  (i)  The  long  root  of  the  ciliary  ganglion  which  is  given  off  at  the 
superior  orbital  (sphenoidal)  fissure.  It  is  a  slender  filament  which  runs  forward  on  the  lateral 
side  of  the  optic  nerve  to  the  superior  and  posterior  part  of  the  ciliary  ganglion  (fig.  734). 

(ii)  The  long  ciliary  nerves,  usually  two  in  number,  which  arise  from  the  naso-cihary  nerve 
as  the  latter  is  crossing  above  the  optic  nerve.  They  run  forward,  on  the  medial  side  of  the  optic 
nerve,  pierce  the  sclerotic,  and  are  distributed  with  the  lower  set  of  short  ciliary  nerves  (fig.  734). 
The  long  root  of  the  cihary  ganglion  and  the  long  ciUary  nerves  carry  sensory  fibres  which 
belong  to  the  naso-ciliary  nerve  proper,  most  of  which  merely  pass  through  the  ganglion,  and 
it  carries  sympathetic  fibres,  added  to  it,  most  of  which  may  terminate  about  the  cell-bodies  of 
the  ganglion. 

(iii)  The  posterior  ethmoidal  (spheno-ethmoidal)  branch  springs  from  the  posterior  border 
of  the  naso-ciUary  nerve  near  the  upper  border  of  the  rectus  medialis.  It  passes  through  the 
posterior  ethmoidal  canal  and  is  distributed  to  the  mucous  membrane  of  the  posterior  ethmoidal 
cells  and  the  sphenoidal  sinus. 

(iv)  The  infratrochlear  nerve  passes  forward  between  the  obhquus  superior  and  the  rectus 
medialis,  and  under  the  pulley  of  the  former  muscle  divides  into  two  branches: — The  superior 
palpebral  branch  helps  to  supply  the  eyehds  with  sensory  fibres  and  usually  anastomoses  with 
the  supratrochlear  nerve.  The  inferior  palpebral  branch  is  distributed  to  the  lacrimal  sac, 
the  conjunctiva  and  skin  of  the  medial  part  of  the  upper  eyehd,  the  caruncle,  and  the  skin  of 
the  upper  part  of  the  side  of  the  nose. 

(v)  The  anterior  ethmoidal  (distal  part  of  the  nasal)  nerve,  passing  forward  and  medial- 
ward  between  the  obhquus  superior  and  the  rectus  medialis,  leaves  the  orbit  through  the  anterior 
ethmoidal  foramen,  accompanied  by  the  anterior  ethmoidal  vessels,  and  enters  into  the  anterior 
fossa  of  the  cranium  (fig.  734).  It  then  crosses  the  lamina  cribrosa  of  the  ethmoid,  lying  outside 
the  dura  mater,  which  separates  it  from  the  olfactory  bulb,  and  descends  into  the  nasal  fossa 
through  the  ethmoidal  fissure,  a  slit-like  aperture  at  the  side  of  the  crista  galli.  In  the  sub- 
mucosa  of  the  nasal  fossa  it  terminates  by  dividing  into  two  sets  of  anterior  nasal  branches: 
the  internal  nasal  branches  and  the  external  nasal  branch  (fig.  732). 

The  internal  nasal  branches  divide  into  the  medial  nasal  branches  (the  septal  branches  of 
the  nasal  nerve),  which  run  downward  and  forward  on  the  upper  and  front  part  of  the  septum, 
and  the  lateral  nasal  branches  (the  external  terminal  branch  of  the  nasal  nerve),  which  give 
twigs  to  the  anterior  extremities  of  the  superior  and  middle  nasal  conchae  (turbinated  bones), 
and  to  the  mucous  membrane  of  the  lateral  wall  of  the  nose  (fig.  732). 

The  external  nasal  branch  (the  anterior  terminal  branch  of  the  nasal  nerve)  runs  downward 
in  a  groove  on  the  inner  surface  of  the  nasal  bone.  It  pierces  the  wall  of  the  nose  between  the 
nasal  bone  and  the  upper  lateral  cartilage,  and  supphes  the  integument  of  the  lower  part  of 
the  dorsum  of  the  nose  as  far  as  the  tip. 


(2)  The  Maxillary  Nerve  or  Second  Division  of  the   Trigeminus 

The  maxillary  nerve  is  entirely  sensory  in  function  and  it  is  intermediate  in 
size  between  the  ophthalmic  and  mandibular  nerves. 

It  springs  from  the  middle  of  the  anterior  border  of  the  semilunar  (Gasserian) 
ganglion  and  runs  forward  in  the  lower  and  outer  part  of  the  lateral  wall  of  the 
cavernous  sinus  (fig.  735).  Leaving  the  middle  fossa  of  the  cranium,  by  passing 
through  the  foramen  rotundum,  it  enters  the  pterygo-palatine  (spheno-maxillary) 
fossa  (fig.  734),  where  it  is  joined  by  twigs  with  the  spheno-palatine  ganglion; 
then,  changing  its  name,  it  passes  forward,  as  the  infra-orbital  nerve,  through  the 
inferior  orbital  (spheno-maxillary)  fissure  into  the  infra-orbital  sulcus  in  the  floor 
of  the  orbit;  continuing  forward  it  traverses  the  infra-orbital  canal  accompanied 
by  the  infra-orbital  artery,  and  appears  in  the  face,  beneath  the  levator  labii 
superioris  (quadratus)  and  above  the  levator  anguli  oris  (caninus)  where  it  divides 
into  four  sets  of  terminal  branches  which  anastomose  more  or  less  freely  with 
branches  of  the  facial  nerve  to  form  the  infra-orbital  plexus. 

Branches. — The  branches  of  the  maxillary  nerve  are — (a)  branches  given  off 
in  the  middle  fossa  of  the  cranium;  (6)  branches  given  off  in  the  pterygo-palatine 
(spheno-maxillary)  fossa;  (c)  branches  given  off  in  the  infra-orbital  sulcus  and 
canal;  and  (d)  terminal  branches. 

(a)  The  middle  (recurrent)  meningeal  branch,  given  off  in  the  middle  fossa 
of  the  cranium,  breaks  up  into  numerous  branches  which  supply  the  dura  mater 
with  sensory  fibres,  reinforce  the  sympathetic  plexus  on  the  middle  meningeal 
artery,  and  anastomose  with  the  spinous  nerve  (the  recurrent  branch  of  the  man- 
dibular nerve). 

(b)  The  branches  given  off  in  the  pterygo-palatine  (spheno-maxillar}^  fossa 
are  the  spheno-palatine  nerves,  the  zygomatic  branch  of  the  maxillary  nerve,  and 
the  posterior  superior  alveolar  nerves. 


938 


THE  NERVOUS  SYSTEM 


The  spheno -palatine  nerve  has  two  or  three  branches  which  descend  in  the  pterygo- 
palatine fossa  and  give  a  small  part  of  their  fibres  to  the  spheno-palatine  (Meckel's)  ganghon 
(fig.  735),  the  larger  part  of  their  fibres  passing  tlirough  the  ganghon  into  its  orbital,  nasal, 
and  palatine  branches.     (See  Spheno-p.\l.\tine  Ganglion,  p.  962.) 

The  zygomatic  (orbital  or  temporo-malar)  branch,  given  off  from  the  upper  surface  of  the 
maxiUary  nerve,  passes  forward  and  lateralward,  and,  at  the  end  of  the  inferior  orbital  (spheno- 
maxillary) fissure,  passes  through  it  into  the  orbit  and  divides  into  two  branches,  facial  and 
temporal. 

The  zygomatico -facial  (malar)  branch  runs  forward,  passes  through  a  zygomatico-orbital 
foramen,  then  thi-ough  the  zygomatico-facial  (malar)  foramen,  pierces  the  orbicularis  palpe- 
brarum, communicates  with  the  zygomatic  (malar)  branch  of  the  facial  nerve,  and  supplies 
the  skin  of  the  prominence  of  the  cheek.  The  zygomatico -temporal  (temporal)  branch  runs 
upward  in  a  groove  in  the  lateral  wall  of  the  orbit,  passes  through  a  zygomatico-orbital  foramen, 
then  through  the  zygomatico-temporal  (spheno-malar)  foramen,  and  enters  the  temporal  fossa. 
It  turns  around  the  anterior  border  of  the  temporal  muscle,  pierces  the  deep  layer  of  the  temporal 
fascia,  and  runs  backward  for  a  short  distance  in  the  fat  between  the  superficial  and  deep  lam- 
ellae, then,  turning  lateralward,  it  pierces  the  superficial  lamellae  about  an  inch  above  the  zygoma, 
anastomoses  with  the  temporal  branch  of  the  facial  nerve,  and  supphes  the  skin  of  the  anterior 
part  of  the  temporal  region. 

The  infra-orbital  nerve,  that  part  of  the  maxiUary  nerve  lying  distal  to  the  spheno- 
palatine ganghon,  enters  the  orbit  through  the  inferior  orbital  (spheno-maxiUary)  fissure, 
accompanied  by  the  infra-orbital  artery,  and  with  it  passes  through  the  infra-orbital  canal 
(fig.  735)  to  the  face,  where  it  divides  into  four  sets  of  terminal  branches,  some  of  which,  by 
anastomoses  with  the  branches  of  the  facial  nerve,  form  the  infra-orbital  plexus. 

Three  sets  of  superior  alveolar  nerves  arise  from  the  maxillary  and  the  infra-orbital  nerves, 
namely,  the  posterior  superior  alveolar  branches,  the  middle  superior  alveolar  branch,  and  the 
anterior  superior  alveolar  branches. 

Fig.  735. — Lateral  View  of  the  Maxillary  Nerve. 

Mandibular  Ophthalmic       MaxiUary  Zygomatic 

lunar-  \  <• 
(Gasser-      V,, 
ian)    r  ^ 
ganglion    ^  • 


y  Anterior 
\^,'        superior 
v*s^         alveolar 
branches 


Vidian 
Spheno-palatine  ganglion 

Spheno-palatine  nerves/ 


Posterior  inferior  nasal 
Posterior  superior  alveolar  branches 


Middle  superior  alveolar  branch 


The  posterior  superior  alveolar  (dental)  nerves  are  usually  two  in  number,  but  sometimes 
arise  by  a  single  trunk.  They  pass  downward  and  lateralward  through  the  pterygo-maxillary 
fissure  into  the  zygomatic  fossa,  where  they  give  branches  to  the  mucous  membrane  of  the  gums 
and  the  posterior  part  of  the  mouth;  then  they  enter  the  posterior  alveolar  (dental)  canals  and 
unite  with  the  other  alveolar  branches  to  form  the  superior  dental  plexus,  through  which  they 
give  branches  to  the  roots  and  pulp  cavities  of  the  molar  teeth  and  to  the  mucous  membrane 
of  the  maxillary  sinus  (fig.  735). 

(c)  The  branches  given  off  in  the  infra-orbital  sulcus  and  canal  are  the  middle 
and  anterior  superior  alveolar  (dental)  nerves. 

(i)  The  middle  superior  alveolar  (dental)  nerve  leaves  the  infra-orbital  nerve  in  the  pos- 
terior part  of  the  inlVa-orliital  sulcus,  and,  pa.ssing  downward  and  forward  in  a  canal  in  the  max- 
illa, it  divides  into  terminal  branches  that  anastomose  with  the  other  alveolar  branches  to  form 
the  superior  dental  plexus.  Through  the  plexus  it  supplies  the  bicuspid  teeth  and  gives  branches 
to  the  mucous  membrane  of  the  maxillary  sinus  and  also  to  the  gums  (fig.  735). 


THE  MANDIBULAR  NERVE  939 

(ii)  The  anterior  superior  alveolar  (dental)  nerve  is  the  largest  of  the  superior  alveolar 
nerves.  It  is  given  off  by  the  infra-orbital  nerve  in  the  anterior  part  of  the  infra-orbital  canal, 
and  passes  downward  in  a  bony  canal  in  the  anterior  wall  of  the  maxilla.  After  uniting  with 
the  other  alveolar  nerves  to  form  the  superior  dental  ple.xus,  it  supplies  the  canines  and  the 
incisors  and  gives  branches  to  the  mucous  membrane  of  the  maxillary  sinus  and  the  gums  (fig. 
735).  It  also  gives  off  a  nasal  branch  which  enters  the  nasal  fossa  through  a  small  foramen,  and 
supphes  the  mucous  membrane  of  the  anterior  part  of  the  inferior  meatus  and  the  adjacent 
part  of  the  floor  of  the  nasal  cavity. 

(iii)  The  superior  dental  plexus  is  formed  in  the  bony  alveolar  canals  by  the  three  superior 
alveolar  nerves.  It  is  convex  downward  and  anastomoses  across  the  mid-line  with  the  corre- 
sponding plexus  of  the  other  side  (fig.  735).  From  it  arise  the  superior  dental  branches  supply- 
ing the  superior  canines  and  incisors,  superior  gingival  branches  supplying  the  gums,  and  also 
branches  to  the  mucous  membrane  of  the  maxiUary  sinus  and  to  the  bone.  On  the  plexus  are 
two  gangliform  enlargements,  one,  called  the  ganglion  of  Valentine,  situated  at  the  junction  of 
the  middle  and  the  posterior  branches,  and  the  other,  called  the  ganglion  of  Bochdalek,  at  the 
junction  of  the  middle  and  anterior  branches. 

(d)  The  terminal  branches  of  the  maxillary  nerve  are  the  inferior  palpebral, 
the  external  and  internal  nasal  (nasal),  and  the  superior  labial. 

The  inferior  palpebral  branches,  usually  two,  pass  upward  and  supply  sensory  fibres  to  all 
the  skin  and  conjunctiva  of  the  lower  eyelid  (fig.  740). 

The  external  nasal  branches  pass  medialward  under  cover  of  the  levator  labii  superioris 
(quadratus),  and  supply  the  skin  of  the  posterior  part  of  the  lateral  aspect  of  the  nose. 

The  internal  nasal  branches  pass  downward  and  medialward  under  the  lateral  wall  of  the 
aose,  and  then  turn  ujnvard  to  supply  the  skin  of  the  vestibule  of  the  nose. 

The  superior  labial  branches,  three  or  four  in  number,  as  a  rule  are  larger  than  the  palpebral 
and  nasal  branches.  They  pass  downward  to  supply  the  skin  and  mucous  membrane  of  the 
upper  Up  and  the  neighbouring  part  of  the  cheek. 

(3)  The  Mandtbular  Nerve  or  Third  Division  of  the  Trigeminus 

The  mandibular  division  is  the  largest  of  the  three  divisions  of  the  trigeminus 
(figs.  736  and  740).  As  a  nerve,  it  is  usually  described  as  formed  by  the  union  of 
two  distinct  nerves,  namely,  the  entire  masticator  nerve  and  the  large  bundle 
of  sensory  fibres  derived  from  the  semilunar  (Gasserian)  ganglion  which  pass 
peripherally  as  the  third  division  of  the  trigeminus.  These  two  nerves  remain 
separate  until  they  pass  through  the  foramen  ovale  and  then  unite  immediately 
outside  the  skull  to  form  a  large  trunk  which  almost  directly  after  its  formation 
divides  into  a  small  anterior  and  a  larger  posterior  portion.  The  trunk  is  situated 
between  the  pterygoideus  externus,  laterally,  and  the  otic  ganglion  and  the 
tensor  palati  medially.  In  front  of  it  is  the  posterior  border  of  the  pterygoideus 
internus,  and  behind  it,  the  middle  meningeal  artery.  Two  branches  arise  from 
the  trunk  of  the  nerve  before  its  division,  namely,  the  spinous  (recurrent)  nerve 
and  the  nerve  to  the  pterygoideus  internus. 

The  spinous  (recurrent)  nerve,  after  receiving  a  vasomotor  filament  from  the  otic  ganglion, 
enters  the  cranium  through  the  foramen  spinosum,  accompanying  the  middle  meningeal  artery, 
and  divides  into  an  anterior  and  a  posterior  branch.  The  anterior  branch  communicates  with 
the  meningeal  branch  of  the  maxillary  division  of  the  trigeminus,  furnishes  filaments  to  the 
dura  mater,  and  ends  in  the  osseous  substance  of  the  great  wing  of  the  sphenoid.  The  posterior 
branch  traverses  the  petrosquamous  suture  and  ends  in  the  Uning  membrane  of  the  mastoid 
ceUs. 

The  fibres  going  to  form  the  neriie  to  the  internal  pterygoid  muscle  are  almost  wholly  motor 
fibres  and  therefore  comprise  a  branch  of  the  masticator  nerve  and  are  described  as  such  under 
the  description  of  the  masticator  (fig.  737). 

The  anterior  portion  of  the  mendibular  nerve  is  smaller  than  the  posterior  and 
is  chiefly  composed  of  motor  fibres  which  form  branches  of  the  masticator  nerve 
and  supply  the  muscles  of  mastication,  the  temporalis,  masseter,  and  pteryg- 
oideus externus.  Practically  all  of  the  sensory  fibres  of  the  anterior  portion  (fibres 
of  the  mandibular  nerve  proper)  form  the  buccinator  (long  buccal)  nerve.  The 
latter  is  accompanied,  in  the  first  part  of  its  course,  by  a  small  strand  of  motor  or 
masticator  fibres  which  leaves  it  to  end  in  the  anterior  part  of  the  temporal 
muscle. 

The  buccinator  (long  buccal)  nerve,  entirely  sensory,  passes  between  the  two  heads  of  the 
external  pterygoid  muscle  and  runs  do\\Tiward  and  forward  under  cover  of  or  through  the  ante- 
rior fibres  of  the  temporahs  to  the  cheek  (fig.  736).  As  it  passes  forward  it  emerges  from  under 
cover  of  the  anterior  border  of  the  masseter  and  lies  on  the  superficial  surface  of  the  buccinator, 
where  it  interlaces  with  the  buccal  branches  of  the  facial  nerve  and  gives  off  filaments  to  supply 
the  superjacent  skin;  finally  it  pierces  the  buccinator  and  supphes  the  mucous  membrane  on  its 


940 


THE  NERVOUS  SYSTEM 


inner  surface  as  far  forward  as  the  angle  of  the  mouth.  The  fibres  of  the  anterior  deep  temporal 
nerve,  a  branch  of  the  masticator,  are  frequently  associated  with  the  buccinator  until  the  latter 
has  passed  between  the  heads  of  the  external  pterygoid;  then  the  anterior  deep  temporal  nerve 
separates  from  the  buccinator  and  passes  upward  on  the  lateral  surface  of  the  upper  head  of  the 
external  pterygoid. 

The  posterior  portion  of  the  mandibular  nerve  divides  into  three  large  branches. 
Two  of  these,  the  lingual  and  the  auriculo-temporal  nerves,  are  exclusively- 
sensory;  the  third,  the  inferior  alveolar  (dental)  nerve,  contains  a  strand  of  motor 
fibres,  the  mylo-hj^oid  nerve,  which  comprise  a  branch  of  the  masticator  nerve. 

The  lingual  nerve  is  the  most  anterior  branch  of  the  mandibular  nerve  (figs. 
736,  743) .  It  lies  in  front  and  to  the  medial  side  of  the  inferior  alveolar  (dental) 
nerve  and  descends  at  first  on  the  medial  side  of  the  pterygoideus  externus,  then 
between  the  pterygoideus  internus  and  the  ramus  of  the  mandible  to  the  posterior 
part  of  the  mylohyoid  ridge,  where  it  passes  off  the  anterior  border  of  the  ptery- 
goideus internus;  at  this  point  it  is  situated  a  short  distance  behind  the  last 

Fig.  736. — DisTRiBTrTioN  of  the  Mandibular  Division  op  the  Trigeminus  combined  with 
Branches  op  the  Masticator  Nerve.     (Henle.) 


Auriculo-temporal 

nerve 
Posterior  deep 
temporal  nerve 


Nerve  to  masseter 


Mylo-hyoid  ne 
Lingual  nerve 


molar  tooth  and  is  covered  in  front  by  the  mucous  membrane  of  the  posterior 
part  of  the  mouth  cavity.  After  leaving  the  pterygoideus  internus  it  crosses  the 
fibres  of  the  superior  constrictor,  which  are  attached  to  the  mandible,  and  turns 
forward  toward  the  tip  of  the  tongue,  crossing  the  lateral  surfaces  of  the  stylo- 
glossus, hyoglossus,  and  genioglossus.  In  its  com-se  across  the  hyoglossus  it 
lies  first  above,  then  to  the  lateral  side  of,  and  finally  below  Wharton's  duct,  and 
as  it  ascends  on  the  genioglossus  it  lies  on  the  medial  side  of  the  duct. 

Communications  and  branches. — While  it  is  on  the  medial  side  of  the  pterygoideus  externus 
the  lingual  nerve  is  joined,  at  an  acute  angle,  by  the  chorda  tympani  (figs.  736,  743),  a  branch 
of  the  glosso-palatine  nerve,  and  as  it  hes  between  the  ramus  of  the  mandible  and  the  pterygoid- 
eus internus  it  is  connected  by  a  branch  with  the  inferior  alveolar  (dental)  nerve,  and  gives  off 
one  or  two  small  branches,  the  rami  isthmi  faucium,  which  are  ditributed  as  sensory  fibres  to 
the  tonsil  and  the  mucous  membrane  of  the  posterior  part  of  the  mouth  (fig.  743). 

While  it  is  above  the  duct  it  gives  a  branch,  which  contains  many  sensory  and  visceral 
motor  chorda  tympani  fibres,  to  the  submaxillary  ganghon  (.seep.  963),  and  it  receives  branches, 
chiefly  sympathetic,  from  that  ganglion.  A  little  further  forward  it  is  connected  by  one  or  two 
branches,  which  run  along  the  anterior  border  of  the  hyoglossus,  with  the  hypoglossal   nerve 


THE  MANDIBULAR  NERVE  941 

(fig.  743).  It  then  gives  off  the  sublingual  nerve,  which  runs  forward  to  supply  the  subHngual 
gland  and  the  neighbouring  mucous  membrane  (fig.  74.3).  Its  terminal  (lingual)  branches  are 
derived  chiefly  from  the  glosso-palatine  nerve.  They  pierce  the  muscular  substance  of  the 
tongue  and  are  distributed  to  the  mucous  membrane  of  its  anterior  two-thu-ds.  They  interlace 
with  similar  branches  of  the  other  side  and  with  branches  of  the  glosso-pharyngeal  nerve. 

The  inferior  alveolar  (dental)  nerve  is  the  largest  branch  of  the  posterior 
portion  of  the  mandibular  nerve.  It  commences  on  the  medial  side  of  the  ex- 
ternal pterygoid  muscle  and  descends  to  the  interval  between  the  spheno-man- 
dibular  ligament  and  the  ramus  of  the  mandible,  where  it  receives  one  or  two 
communicating  branches  from  the  lingual  nerve.  Opposite  the  middle  of  the 
medial  surface  of  the  ramus  it  enters  the  mandibular  (inferior  dental)  canal,  ac- 
companied by  the  inferior  alveolar  (dental)  artery,  which  lies  in  front  of  the  nerve, 
and  it  runs  downward  and  forward  through  the  ramus  and  the  body  of  the 
mandible  (fig.  736).  At  the  mental  foramen  it  divides  into  two  parts,  one  of 
which,  the  mental  nerve,  passes  out  through  the  mental  foramen,  the  other,  com- 
monly called  the  incisive  branch,  continues  forward  in  the  canal,  and  supplies, 
through  the  inferior  dental  plexus,  the  inferior  canine  and  incisor  teeth  and  the 
corresponding  regions  of  the  gums. 

Branches. — ^The  branches  of  the  inferior  alveolar  (dental)  nerve  are  branches 
forming  the  inferior  dental  plexus,  and  the  mental  branch.  A  bundle  of  motor 
fibres,  the  mylohyoid  nerve,  a  branch  of  the  masticator  nerve,  is  given  off  just 
before  the  inferior  alevolar  nerve  enters  the  mandibular  canal. 

The  inferior  dental  plexus  is  formed  by  a  series  of  branches  which  communicate  with  one 
another  within  the  bone,  giving  rise  to  a  fine  network.  From  this  plexus  two  sets  of  branches 
are  given  off: — the  inferior  dental  branches,  corresponding  in  number  to  the  roots  of  the  teeth, 
enter  the  minute  foramina  of  the  apices  of  the  roots  and  end  in  the  pulp;  the  second  set,  the 
inferior  gingival  branches,  supply  the  gums. 

The  mental  nerve  is  a  nerve  of  considerable  size  which  emerges  through  the  mental  foramen 
(fig.  736).  It  communicates,  near  its  exit  from  the  bone,  with  branches  of  the  facial  nerve,  and 
then  divides  into  three  branches.  The  smallest  branch,  turning  downward,  divides  into  several 
twigs,  the  menial  branches,  which  supply  the  integument  of  the  chin.  _  The  other  two,  inferior 
labial  branches,  pass  upward,  diverging  as  they  ascend,  and  divide  into  a  number  of  twigs. 
The  stoutest  twigs  ramify  to  the  mucous  membrane  which  lines  the  lower  hp.  Other  twigs 
are  distributed  to  the  integument  and  fascia  of  the  hp  and  chin. 

The  auriculo -temporal  nerve  usually  arises  from  the  posterior  portion  of  the 
mandibular  nerve  by  two  roots  which  embrace  the  middle  meningeal  artery  and 
unite  behind  it  to  form  the  trunk  of  the  nerve.  The  trunk  passes  backward  on 
the  medial  aspect  of  the  pterygoideus  externus,  and  between  the  spheno-man- 
dibular  ligament  and  the  temporo-mandibular  articulation,  lying  in  close  relation 
with  the  capsule  of  the  joint.  Behind  the  joint  it  enters  the  upper  part  of  the 
parotid  gland,  through  which  it  turns  upward  and  lateralward.  It  emerges  from 
the  upper  end  of  the  gland,  crosses  the  root  of  the  zygoma  close  to  the  posterior 
border  of  the  superficial  temporal  artery,  and  divides  into  auricular  and  temporal 
terminal  branches  at  the  level  of  the  tragus  of  the  pinna  (fig.  736) . 

Communications. — (a)  Each  of  the  two  roots  of  the  nerve  receives  a  communication  from 
the  otic  ganglion  containing  fibres  derived  from  the  glosso-pharyngeal  nerve.  These  fibres 
have  passed  from  the  glosso-pharyngeal  through  the  tympanic  plex-us  and  the  smaU  superficial 
petrosal  nerve  and  through  the  otic  ganglion. 

(b)  Sensory  filaments  pass  from  the  auriculo-temporal  nerve  to  the  temporo-facial  branch 
of  the  facial  nerve. 

(c)  Filaments  of  connection  with  the  sympathetic  plexus  on  the  internal  maxiUary  artery. 

(d)  A  communication  to  the  inferior  alveolar  (dental)  nerve. 

Branches  of  the  auriculo-temporal  nerve. — (a)  An  articular  branch  to  the  temporo-man- 
dibular joint,  given  off  as  the  nerve  lies  on  the  medial  side  of  the  capsule. 

(6)  Branches  to  the  external  auditory  meatus.  Two  branches,  as  a  rule,  are  given  off  in 
the  parotid  gland.  They  enter  the  meatus  by  passing  between  the  cartilage  and  the  bone  and 
supply  the  upper  part  of  the  meatus,  the  membrana  tympani  by  a  fine  branch,  and  occasionally 
the  lower  branch  gives  twigs  to  the  skin  of  the  lobule  of  the  pinna. 

(c)  Parotid  branches  are  distributed  to  the  substance  of  the  parotid  gland.  Sensory  or 
trigeminal  fibres  for  the  gland  spring  either  directly  from  the  nerve  or  from  the  communicating 
branches  previously  given  by  it  to  the  glosso-palatine  nerve.  The  parotid  branches  also  con- 
tain filDres  derived  from  the  glosso-pharyngeal  nerve  which  pass  successively  through  its  tym- 
panic branch,  the  tympanic  plexus,  the  small  superficial  petrosal  nerve,  the  otic  ganglion,  and 
the  communicating  twigs  from  the  otic  ganglion  to  the  roots  of  the  auriculo-temporal  nerve. 
The  parotid  branches  are  later  again  mentioned  as  concerned  chiefiy  with  the  ganglialed 
cephalic  plexus. 

(d)  The  anterior  auricular  branches,  usually  two  in  number,  are  distributed  to  the  skin 
of  the  tragus  and  the  upper  and  outer  part  of  the  pinna. 


942 


THE  NERVOUS  SYSTEM 


(e)  The  superficial  temporal  branches  supply  the  integument  of  the  greater  part  of  the  tem- 
poral region,  and  anastomose  with  the  temporal  branch  of  the  facial  nerve. 


THE  MASTICATOR  NERVE  (Fig.  737) 

The  masticator  nerve  (motor  root  or  portio  minor  of  trigeminus) .  The  fibres 
of  the  masticator  nerve  spring  from  two  nuclei,  a  slender  upper  or  mesencephalic 
nucleus  and  a  clustered  lower  or  chief  nucleus.  The  fibres  arising  in  the  mesen- 
cephalic nucleus  descend  along  the  lateral  aspect  of  the  nucleus  to  the  pons  as 
the  descending  or  mesencephalic  root;*  here  they  join  the  fibres  from  the  chief  motor 
nucleus  and  issue  with  them  from  the  side  of  the  pons  in  from  six  to  ten  root 
filaments.  These  blend  to  form  the  nerve,  which  is  from  one  and  a  half  to  two 
millimetres  broad.  At  the  point  where  it  emerges  from  the  pons  the  nerve  is  in 
front  of  and  ventral  to  the  root  of  the  trigeminus  and  it  is  separated  from  the 
latter  by  a  few  of  the  transverse  fibres  of  the  pons  which  constitute  the  lingula  oj 
Wrisberg.  From  its  superficial  exit  from  the  pons,  the  masticator  nerve  passes 
upward,  lateralward,  and  forward  in  the  posterior  fossa  of  the  cranum,  and  along 
the  medial  and  anterior  aspect  of  the  trigeminus,  to  the  mouth  of  Meckel's  cave. 
In  this  cavity  it  runs  lateralward  below  the  semilunar  (Gasserian)  ganglion  to  the 
foramen  ovale,  through  which  it  passes  to  join  the  mandibular  division  of  the 

Fig.  737. — Schematic   Representation   of  the   Masticator   Nerve   and   its   Branches 
(in  Black).     Lateral  view.     Modified  from  Spalteholz. 
Gasserian  ganglion 
Masticator  nerve  /  External  pterygoid  nerve 

Auriculo-temporal  i 

1 

\ 

1 

Internal  maxillary  artery\ 


Posterior  deep 
temporal  nerve 

Anterior  deep 
temporal  nerve 

Internal   pterygoid 
nerve 

Masseter  nerve 

Buccinator  nerve 


External  carotid  artery  -■' 
Mylo-hyoid  nerve  ^  " 


trigeminus  immediately  outside  and  below  the  base  of  the  skull.  The  nerve  is 
purely  motor  and  its  fibres  are  devoted  almost  wholly  to  the  muscles  having  to  do 
with  mastication. 

Central  connections. — The  nuclei  of  origin  of  the  masticator  nerve  are  connected  with  the 
lower  part  of  the  somaesthetic  area  of  the  cerebral  cortex  of  the  opposite  side  by  the  p}Tamidal 
fibres  descending  in  the  genu  of  the  internal  capsule,  and  they  are  associated  with  the  sensory 
nuclei  of  other  cranial  nerves  through  the  reticular  formation  and  by  the  medial  longitudinal 
fasciculus. 

Branches. — Almost  immediately  after  joining  the  trunk  of  the  mandibular 
nerve,  most  of  the  fibres  of  the  masticator  leave  it  to  form  the  greater  part  of  the 
so-called  anterior  portion  of  the  mandibular.  However,  one  branch  of  masticator 
fibres,  the  nerve  to  the  internal  pterygoid  muscle,  is  given  off  from  the  mandibular 
just  before  its  division  into  anterior  and  posterior  portions.     The  masticator 

*  Recent  investigations  indicate  that  the  mesenephalic  root  is  not  wholly  motor  but  at 
least  in  part  sensory  in  character,  and  thus  belongs  partly  to  the  trigeminal  nerve.  (See 
page  829.) 


THE  FACIAL  NERVE  943 

branches  derived  from  the  anterior  portion  are  the  deep  tem-poral  nerves,  the 
masseteric  nerve,  and  the  nerve  to  the  external  -pterygoid.  One  branch,  the 
mylo-hyoid  nerve,  is  carried  in  the  posterior  portion  of  the  mandibular  and  is  given 
off  from  its  inferior  alveolar  branch. 

The  nerve  to  the  internal  pterygoid  passes  under  cover  of  a  dense  layer  of  fascia  derived 
from  an  expansion  of  the  ligamentum  pterygo-spinosum,  and  enters  the  deep  surface  of  the 
muscle.  Near  its  commencement  this  nerve  furnishes  a  visceral  motor  root  to  the  otic  ganglion, 
and  small  twigs  to  the  tensor  tympani  and  tensor  palati. 

The  deep  temporal  nerves,  usually  two  in  number,  posterior  and  anterior,  pass  between  the 
bone  and  the  upper  border  of  the  external  pterygoid  muscle,  and  turn  upward  around  the  infra- 
temporal crest  of  the  sphenoid  bone  to  end  in  the  deep  surface  of  the  temporalis  (fig.  736). 
The  posterior  of  the  two  often  arises  in  common  with  the  masseteric  nerve.  The  anterior  is 
frequently  associated  with  the  buccinator  (long  buccal)  nerve  till  the  latter  has  passed  between 
the  two  heads  of  the  pterygoideus  externus.  There  is  frequently  a  third  branch,  the  medius, 
which  passes  lateralward  above  the  pterygoideus  externus,  and  turns  upward  close  to  the  bone 
to  enter  the  deep  surface  of  that  muscle.  A  small  strand  of  masticator  fibres  accompanies  the 
buccinator  nerve  to  enter  and  end  in  the  anterior  part  of  the  temporal  muscle. 

The  masseteric  nerve,  which  frequently  arises  in  common  with  the  posterior  deep  temporal 
nerve,  passes  between  the  bone  and  the  pterygoideus  externus,  and  accompanies  the  masseteric 
artery  through  the  notch  of  the  mandible  to  be  distributed  to  the  masseter  (fig.  736).  It  is 
easily  traced  through  the  deeper  fibres  nearly  to  the  anterior  border  of  the  masseter.  As 
it  emerges  above  the  pterygoideus  externus  it  gives  off  a  twig  to  the  temporo-mandibular 
articulation. 

The  nerve  to  the  external  pterygoid,  after  a  course  of  about  3  mm.  (an  eighth  of  an  inch), 
divides  into  twigs  which  enter  the  deep  surface  of  the  two  heads  of  the  muscle.  It  is  usually 
adherent  at  its  origin  to  the  buccinator  nerve. 

The  mylo-hyoid  branch,  carried  in  the  posterior  portion  of  the  mandibular  nerve,  is  given 
off  immediately  before  the  inferior  alveolar  (dental)  nerve  enters  the  mandibular  (inferior  dental) 
canal.  It  pierces  the  lower  and  back  part  of  the  spheno-mandibular  ligament  and  runs  down- 
ward and  forward  in  the  mylo-hyoid  groove  between  the  mandible  on  the  lateral  side,  and  the 
internal  pterygoid  muscle  and  the  lateral  surface  of  the  submaxillary  gland  on  the  medial  side. 
In  the  anterior  part  of  the  digastric  triangle  it  is  continued  forward  between  the  anterior  part 
of  the  submaxillary  gland  and  the  mylo-hyoideus,  and  it  breaks  up  into  branches  which  supply 
the  mylo-hyoideus  and  the  anterior  belly  of  the  digastric  (fig.  736). 

THE  FACIAL  NERVE 

The  facial  or  seventh  nerve  is  purely  motor.  It  is  accompanied  a  short 
distance  by  a  bundle  usually  called  its  sensory  root  or  the  intermediate  nerve. 
This  latter,  however,  on  the  Ijasis  of  its  origin,  distribution,  and  mixed  instead  of 
sensory  character,  is  described  separately  below  as  the  glosso-palatine  nerve. 
It  is  smaller  than  the  facial,  is  fused  to  the  trunk  of  the  facial  and  the  ganglion 
giving  rise  to  its  sensory  fibres  is  situated  upon  the  external  genu  of  the  facial 
(figs.  738  and  741). 

The  fibres  of  the  facial  nerve  (fig.  738)  spring  from  a  nucleus  of  cells  situated 
laterally  in  the  reticular  formation  at  the  level  of  the  lower  pons,  dorsal  to  the  supe- 
rior olive,  and  between  the  root  fibres  of  the  abducens  nerve  and  the  laterally  placed 
spinal  tract  of  the  trigeminus.  From  this  nucleus  the  fibres  of  the  nerve  pass 
medially  and  dorsalward  to  the  floor  of  the  fourth  ventricle  and,  just  under  the 
floor,  they  turn  anteriorly,  passing  dorsal  to  the  nucleus  of  the  abducens  (fig.  653, 
p.  827).  At  the  anterior  end  of  this  nucleus  they  turn  sharply  ventralward  and 
lateralward,  and  at  this  point  it  is  claimed  that  fibres  descending  in  the  near-by 
medial  longitudinal  fasciculus  from  the  nucleus  of  the  oculo-motor  nerve  of  the 
same  side  become  intermingled  with  the  fibres  of  the  facial  nerve  and  pass 
outward  with  them.  This,  however,  is  uncertain.  Continuing  ventralwai'd 
through  the  reticular  formation  the  fibres  of  the  facial  emerge  from  the  brain-stem 
at  the  inferior  border  of  the  pons,  lateral  to  the  superficial  attachment  of  the 
abducens.  At  the  point  of  its  emergence,  the  facial  nerve  pierces  the  pia  mater, 
from  which  it  receives  a  sheath,  and  then  proceeds  forward  and  lateralward 
in  the  posterior  fossa  of  the  cranium  to  the  internal  auditory  meatus,  which  it 
enters  in  company  with  the  glosso-palatine  nerve  and  with  the  cochlear  and 
vestibular  nerves.  As  it  lies  in  the  meatus  it  is  situated  above  and  in  front  of 
the  latter  nerves,  from  which  it  is  separated  by  the  glosso-palatine,  and  it  is 
surrounded,  together  with  these  three  nerves,  by  sheaths  of  both  the  arachnoid 
and  the  dura  mater  and  by  prolongations  of  the  subarachnoid  and  sub-dural 
spaces.  While  it  is  still  in  the  meatus  it  blends  with  the  glosso-palatine  and  thus 
the  combined  trunk  is  formed.     At  the  outer  end  of  the  meatus  the  trunk  pierces 


944 


THE  NERVOUS  SYSTEM 


the  arachnoid  and  the  dura  mater  and  enters  the  facial  canal  (aqueduct  of  Fallo- 
pius),  in  which  it  runs  forward  and  slightly  lateralward  to  the  hiatus  Fallopii, 
where  it  makes  an  angular  bend,  the  external  genu  [geniculum],  around  the 
anterior  boundary  of  the  vestibule  of  the  inner  ear;  this  bend  is  enlarged  by  the 
adhesion  of  the  geniculate  ganglion  (of  the  glosso-palatine)  upon  its  anterior 
border.  From  the  geniculum  the  facial  nerve  runs  backward  in  the  facial  canal 
along  the  lateral  wall  of  the  vestibule  and  the  medial  wall  of  the  tympanum,  above 
the  fenestra  vestibuli  (ovalis),  to  the  junction  of  the  medial  and  posterior  walls  of 
the  tympanic  cavity;  then,  bending  downward,  it  descends  in  the  posterior  wall 
to  the  stylo-mastoid  foramen.  As  soon  as  it  emerges  from  the  stylo-mastoid 
foramen  it  turns  forward  around  the  lateral  side  of  the  base  of  the  styloid  process. 


Fig.  738.- 


Fibres  from  oc- 
ulomotor nerve 
Nucleus  of 
abducens 


Diagram  of  the  Facial  (Yellow)  and  Glosso-palatine  Nerve  (Blue). 
Facial  i 


Glosso- 
palatine 
Internal 
auditory 
meatus 
Small  superficial 
petrosal  nerve 
Fenestra  vestibuli 
Tympanic  plexus 
Chorda  tympani 

Communication  to 

auricular  branch 

of  vagus 

Fenestra  cochlese 

Posterior  auricular 

Communication  to 

glosso-pharyngeal 

Nerve  to  post,  belly 

of  diagastric 

Nerve  to  stylo- 

hyoideus 

Styloid  process 
Tympanic  branch  of  facial  nerve 


Hilary 

Spheno- 
palatine 
ganglion 
Vidian  nerve 

Great  deep 
petrosal  nerve 
Middle   memng( 

Foramen  ovale     artery 

Otic  ganglion 

Spine  of  sphenoid 
Communication  fron 

temporal 
Chorda  tympani 

Communication  from  auricular 
branch  of  glosso-pharyngeal 

Lingual  nerve 


Small  deep  petrosal  nerve 


and  plunges  into  the  substance  of  the  parotid  gland,  where  it  divides  into  its 
cervico-facial  and  temporo-facial  terminal  divisions.  Before  its  terminal  divisions, 
the  nerve  gives  off  three,  and  sometimes  four,  small  branches:  one,  the  nerve  to 
the  stapedius  muscle,  before  it  leaves  the  skull,  the  others  after  it  leaves  the  skull. 

The  nerve  to  the  stapedius  is  given  off  from  the  facial  nerve  as  it  descends  in  the  posterior 
wall  of  the  tympanum  behind  the  pyramidal  eminence.  It  is  stated  that  filaments  are  also 
given  off  from  the  facial  to  the  auditory  artery  (probably  visceral  motor  from  the  glosso-palatine) 
while  the  nerve  is  passing  through  the  internal  auditory  meatus. 

After  it  leaves  the  skull  the  facial  nerve  gives  off  two  or  three  coll  terai 
branches  and  its  two  terminal  divisions,  the  temporo-facial  and  cervico-facial. 
The  collateral  branches  are  the  posterior  auricular  nerve,  a  branch  to  the  posterior 
belly  of  the  digastric,  and  sometimes  a  lingual  branch. 

(1)  The  posterior  auricular  nerve  is  the  first  branch  of  the  extracranial  portion  of  the  facial 
nerve.  It  passes  between  the  parotid  gland  and  the  anterior  border  of  the  sterno-mastoid 
muscle  and  runs  upward  in  the  deep  interval  between  the  external  auditory  meatus  and  the 
mastoid  process.  In  this  situation  it  communicates  with  the  auricular  branch  of  the  vagus. 
It  supplies  the  auricularis  posterior,  sends  a  slender  twig  upward  to  the  am-ioularis  superior, 
and  ends  in  a  long  slender  branch,  the  occipital  branch,  which  passes  backward  to  supply  the 
occipitalis  muscle.  It  also  receives  filaments  from  the  small  occipital  and  great  auricular  nerves, 
and  supplies  the  intrinsic  muscles  of  the  auricle  (pinna). 

(2)  The  nerve  to  the  posterior  belly  of  the  digastric  arises  from  the  facial  nerve  close  to 
the  stylo-mastoid  foramen  and  enters  the  muscle  near  its  centre,  or  sometimes  near  its  origin. 
It  usually  gives  off  two  branches:  the  nerve  to  the  stylo-hyoid,  which  sometimes  arises  directly 
from  the  facial  nerve  and  passes  to  the  upper  part  of  the  muscle  that  it  supplies,  and  the  anas- 
tomotic branch,  which  joins  the  glosso-pharyngeal  nerve  below  its  petrous  ganglion. 

(3)  The  lingual  branch,  first  described  by  CruveiUiier,  is  not  commonly  present.  It  arises 
a  little  below  the  nerve  to  the  stylo-hyoideus  and  runs  downward  and  medialward  to  the  base 
of  the  tongue.     In  its  course  it  passes  to  the  medial  sides  of  the  stylo-glossus  and  stylo-pharyn- 


THE  FACIAL  NERVE 


945 


geus,  and  runs  downward  along  the  anterior  border  of  the  latter  muscle  to  the  wall  of  the 
pharynx.  It  pierces  the  superior  constrictor,  insinuates  itself  between  the  tonsil  and  the  anterior 
piUar  of  the  fauces,  and  it  is  stated  that  it  gives  filaments  to  the  base  of  the  tongue  and  to  the 
stylo-glossus  and  glosso-palatinus  (palato-glossus)  muscles. 

The  terminal  divisions. — In  the  substance  of  the  parotid  gland  the  two 
terminal  divisions  of  the  facial  nerve  he  superficial  to  the  external  carotid  artery 
and  to  the  posterior  facial  (temporo-maxillary)  vein.  The  way  in  which  these 
terminal  divisions  give  off  their  branches  varies  much  in  different  subjects  and 
often  on  the  opposite  sides  of  the  same  subject.  One  of  the  more  common  forms 
is  here  described. 

The  temporo-facial  or  upper  division  runs  upward  and  forward,  and,  after 
receiving  communicating  twigs  from  the  auriculo-temporal  nerve,  gives  off  tem- 
poral and  zygomatic  (malar)  branches.  The  cervico -facial  or  lower  division  runs 
downward  and  forward,  receives  branches  from  the  great  auricular  nerve,  and 

Fig.  739. — The  Right  Facial  Nekvb,  within  the  Skull,   and  the  Relations  op  the 

Glosso-palatine  and  Glosso-pharyngeal  Nerves  with  the  Tympanic  and 

Internal  Carotid  Plexuses.     (From  Sobotta's  Atlas,  modified.) 

Tensor  tympani  muscle      Deep  petrosal  nerve 


Auditory  (Eustachian)  tubi 
Superior  carotico-tympanic  n. 
Great  superficial  petrosal  n 

Ramus  anastomotic  with  tympanic  plexus 
Geniculate  gangli' 
Glosso-palatine  n 
Stapes        Facial  n 
Tympanic  sinus 
Stapedius  muscl 
stapedius, 
nerve 


Maxillary  nerve  (lifted) 
'  Nerve  of  pterygoid  canal 
(Vidian) 
Spheno-palatine  ganglion 


Mastoid  cells 
Chorda  tympani 
Stylo-mastoid  foramen 

Tympanic 
Petrosal  ganglion  of  glosso 

pharyngeal  ^ 

Nodosal  ganghon  of  vagus  . 
Superior  cervical  sympathetic  ganghon 


gives  off — (1)  buccal  branches,  comprising  what  have  been  called  infraorbital 
and  buccal  branches;  (2)  the  marginal  mandibular  (supra-mandibular)  branch; 
and  (3)  the  ramus  colli  (infra-mandibular  branch).  These  branches  from  the 
two  terminal  divisions  anastomose  freely  to  form  the  parotid  plexus  (pes  anserinus). 

The  temporal  branches  passing  upward  communicate  freely  with  each  other  and  with  the 
zygomatic  branches.  They  also  communicate  with  the  zygomatico-temporal  branch  of  the 
zygomatic  nerve  (the  orbital  branch  of  the  maxillary  nerve)  and  with  the  supra-orbital  nerve. 
They  supply  the  frontalis,  orbicularis  oouli,  corrugator  supercilii,  and  auricularis  anterior  and 
superior  (fig.  740). 

The  zygomatic  (malar)  branches  passing  upward  and  forward,  communicate  with  the  buccal 
branches  of  the  facial  nerve;  with  the  zygomatico-facial  branch  of  the  zygomatic  nerve  (the 
orbital  branch  of  the  maxillary  nerve) ;  with  the  supraorbital  and  lacrimal  branches  of  the  oph- 
thalmic nerve,  and  with  the  palpebral  twigs  of  the  maxillary.  They  supply  both  ej'ehds,  the 
orbicularis  oculi,  and  tlie  zygomaticus  (fig.  740). 

The  buccal  (infra-orbital  and  buccal)  branches  arise  sometimes  from  the  lower  terminal 
division  and  sometimes  from  both  the  upper  and  the  lower  terminal  divisions.  The  buccal 
branches,  passing  forward  upon  the  masseter  and  underneath  the  zygomaticus  and  quadratus 
labii  superioris,  interlace  with  the  zygomatic  and  marginal  mandibular  (supra-mandibular) 
branches  of  the  facial  nerve,  with  the  buccinator  (long  buccal)  branch  of  the  trigeminus,  and  with 
the  terminal  branches  of  the  maxillary  nerve,  forming  with  the  last-named  nerve  the  infra- 
orbital plexus.     They  supply  the  zygomaticus,  risorius,  quadratus  labii  superioris,  caninus. 


946 


THE  NERVOUS  SYSTEM 


buccinator,  inoisivi,  orbicularis  oris,  triangularis,  quadratus  labii  inferioris,  and  the  muscles 
of  the  nose  (fig.  740). 

The  marginal  mandibular  (supra-mandibular)  branch,  passing  downward  and  forward  under 
cover  of  the  risorius  and  the  depressors  of  the  lower  hp,  commimicates  with  the  buccal  branches 
and  with  the  ramus  colli  of  the  facial  nerve,  and  with  the  mental  branch  of  the  mandibular  nerve. 
It  supplies  the  quadratus  labii  inferioris  and  mentalis. 

The  ramus  colli  (infra-mandibular  branch)  runs  downward  and  forward  under  cover  of 
the  platysma,  which  muscle  it  innervates  (fig.  740).  Beneath  the  platysma  it  forms  one  or 
more  communicating  loops,  near  its  commencement,  with  the  great  auricular  nerve,  and  longer 
loops,  lower  down,  with  the  superficial  cervical  nerve. 

Central  connections. — The  nucleus  of  origin  of  the  facial  in  the  rhombencephalon  includes 
an  anterior  and  a  posterior  group  of  cells  which  give  rise  respectively  to  its  upper  and  lower  ter- 
minal divisions.  They  are  associated  with  the  somaesthetic  area  (lower  third  of  the  anterior 
central  gyrus)  by  way  of  the  pyramidal  fasciculi  of  the  opposite  and  same  sides,  and  with  the 
nuclei  of  the  other  cranial  nerves,  including  the  nucleus  of  termination  of  the  glosso-palatine,  by 
way  of  the  reticular  formation  and  the  medial  longitudinal  fasciculus. 


Fig.  740. — S"0pekpicial_ Distribution  of  the  Facial  and  other  Nerves  of  the  Head. 
(After  Hirschfield  and  Leveill(5.) 


Supra-orbital 
Palpebral  twig  of 
lacrimal 
Infratrochlear 

Temporal  braacli 
of  facial 
Zygomatic    br. 

of  facial 
Maxillary   div. 
of  trigeminus 


Posterior  auricular 


Auriculo-temporal 


Lesser  occipital 
Great  auricular 


Cervical  cutaneous 


GLOSSO-PALATINE  NERVE 

The  glosso-palatine  nerve  (sensory  root  or  pars  intermedia  of  facial,  nerve  of 
Wrisberg)  contains  both  sen.sory  and  motor  fibres.  While  it  has  a  separate 
attachment  to  the  medulla,  it  courses  in  close  company  with  the  facial  and,  in 
the  internal  auditory  meatus,  it  is  involved  in  the  same  sheath  with  the  facial, 
which  relation  is  maintained  by  its  larger  part  thence  through  the  facial  canal  till 
a  short  distance  above  the  stylo-mastoid  foramen.  Here  this  larger  part  leaves 
the  trunk  of  the  facial  as  the  chorda  tympani  nerve.  The  origin,  central  connec- 
tions and  peripheral  distribution  of  the  glosso-palatine  are  similar  to  those  of  the 


THE  GLOSSO-PALATINE  NERVE  947 

glosso-pharyngeal  nerve  and  suggest  that  it  may  be  considered  an  aberrant  portion 
of  that  nerve. 

The  sensory  portion  is  much  greater  than  the  motor.  Its  fibres  arise  from  cells 
situated  in  the  geniculate  ganglion  which  thus  corresponds  to  a  spinal  ganglion. 
The  central  processes  from  these  cells  pass  medialward  in  the  facial  canal  (aqueduct 
of  Fallopius)  enclosed  in  the  sheath  of  the  facial  nerve,  which  they  leave  in  passing 
through  the  internal  auditory  meatus,  to  turn  slightly  downward  in  the  posterior 
fossa  of  the  cranium  and  enter  the  medulla  at  the  inferior  border  of  the  pons,  be- 
tween the  attachments  of  the  facial  and  vestibular  nerves.  They  com-se  through 
the  reticular  formation  of  the  medulla,  medianward  and  dorsalward  to  terminate 
about  cells  which  comprise  a  superior  extension  of  the  nucleus  of  termination 
of  the  glosso-pharyngeal  nerve  (nucleus  of  ala  cmerea).  The  peripheral  processes 
from  the  geniculate  ganglion  are  distributed  chiefly  to  the  epithelium  covering  the 
soft  palate,  portions  of  the  glosso-palatine  arches,  and  the  anterior  two  thirds  of 
the  tongue. 

The  geniculate  ganglion  is  so  named  from  the  fact  that  it  is  embedded  upon  the 
anterior  border  of  the  external  genu  {geniculum,  great  bend)  of  the  facial  nerve, 
behind  the  hiatus  Fallopii.  It  is  somewhat  triangular  in  form.  From  its  supero- 
medial  angle  leave  the  central  processes  of  its  cells,  the  root  of  the  nerve;  from  its 
infero-lateral  angle  leave  the  fibres  which  later  leave  the  sheath  of  the  facial  as  the 
chorda  tympani,  and  its  anterior  angle  is  connected  with  the  great  superficial 
petrosal  nerve  (figs.  738  and  741).  The  geniculate  ganglion  contains  a  rel- 
atively large  number  of  cell-bodies  of  sympathetic  neurones  many  of  whose 
processes  run  in  this  latter  nerve,  a  relation  mentioned  below  with  the  gangliated 
cephalic  plexus. 

The  motor  portion  of  the  glosso-palatine  consists  for  the  most  part  of  visceral 
efferent  fibres,  chiefly  secretory.  These  arise  in  the  medulla  oblongata  from  a 
small  group  of  cells  scattered  in  the  reticular  formation  dorso-medial  to  the 
nucleus  of  the  facial  and  in  line  with  the  dorsal  efferent  nucleus  of  the  vagus 
below.  It  is  called  the  salivaiory  nucleus.  The  fibres  course  ventralward  and 
lateralward  to  their  exit,  mingle  with  the  entering  sensory  fibres  of  the  glosso- 
palatine  in  the  sheath  of  the  facial  and,  through  the  branches  of  the  glosso- 
palatine,  pass  to  terminate  in  sympathetic  ganglia  of  the  head,  large  and  small. 
These  gangfia  send  axones  which  terminate  in  the  smooth  muscle  of  vessels  and 
about  the  cells  of  the  glands  of  the  lingual  and  palatine  mucous  membrane  and  of 
the  salivary  glands  proper.  Some  of  the  motor  fibres  of  the  nerve  terminate  in 
contact  with  the  sympathetic  cells  remaining  in  the  geniculate  ganglion  and  which 
give  rise  to  sympathetic  fibres  issuing  from  it.  Most  of  the  motor  fibres  pass 
into  the  great  superficial  petrosal  nerve  and  the  chorda  tympani  to  terminate  in 
(chiefly)  or  pass  through  the  spheno-palatine  and  submaxillary  ganglia  re- 
spectivelJ^  Some  may  pass  by  the  geniculo-tympanic  branch  and  tympanic 
plexus  to  end  in  the  otic  ganghon.  Many  no  doubt  end  in  the  smafler  ganglia 
involved  in  the  various  sympathetic  plexuses.  It  is  suggested  that  the  motor 
part  carries  secretory  impulses  destined  chiefly  for  the  sub-maxillary  and  sublin- 
gual glands.  A  small  gangliated  plexus  on  the  capsule  of  the  medial  side  of  the 
parotid  gland  has  been  frequently  dissected  and  found  to  communicate  freely  with 
twigs  from  the  facial  nerve  and  twigs  concerned  with  the  trigeminus.  It  is 
possible  that  some  glosso-palatine  visceral  motor  fibres  terminate  in  these  ganglia 
for  secretory  impulses  to  the  parotid  gland  as  well. 

Central  connections. — The  nucleus  of  termination  of  tlie  glosso-palatine  nerve  (superior 
extension  of  the  nucleus  of  termination  of  the  sensory  portion  of  the  glosso-pharyngeal)  is 
associated  with  the  somffisthetic  area  of  the  cerebral  cortex  of  the  opposite  and  same  sides  by 
way  of  the  medial  lemniscus,  and  with  the  saUvatory  nucleus  and  motor  nuclei  of  other  cranial 
nerves  by  way  of  the  reticular  formation  and  medial  longitudinal  fasciculus.  The  nucleus  of 
origin  of  the  motor  portion  (sahvatory  nucleus)  may  be  associated  not  only  with  the  nucleus 
of  termination  of  the  sensory  part,  but  with  the  nuclei  of  termination  of  other  cranial  nerves, 
and  perhaps  with  the  motor  area  of  the  cortex  of  the  opposite  side  by  way  of  the  pjTamidal 
fascicuh. 

Branches  and  communications. — Aside  from  its  two  or  three  small  collateral 
twigs  of  communication,  the  fibres  of  the  glosso-palatine  course  in  two  main 
branches  or  nerves:  (1)  the  great  superficial  petrosal  nerve,  continued  through 
the  Vidian  nerve,  and  extended  through  and  beyond  the  spheno-palatine  ganglion 
as  the  palatine  portion  of  the  glosso-palatine  (palatine  nerve) ;  (2)  the  chorda  tym- 


948 


THE  NERVOUS  SYSTEM 


pani,  the  larger  branch,  which  extends  to  join  and  contribute  its  quota  of  fibres 
to  the  lingual  nerve,  a  branch  of  the  trigeminus. 

In  the  internal  auditory  meatus,  the  glosso-palatine  gives  two  delicate 
collaterals  to  the  vestibular  nerve,  and  some  filaments  (visceral  motor  probably) 
are  described  as  given  to  the  auditory  artery  and  to  the  temporal  bone. 

A  small  geniculo-tympanic  branch  is  given,  in  the  facial  canal,  from  the  geniculate  ganglion 
to  the  small  superficial  petrosal  nerve.  This  is  probably  aU  visceral  motor  and  sympathetic 
fibres  (fig.  741). 

There  may  occur  a  twig  arising  from  or  near  the  beginning  of  the  chorda  tympani  and  form- 
ing a  cormnunicatio?i  vnih  the  auricular  branch  of  the  vagus. 

A  large  part  of  the  great  superficial  petrosal  nerve  is  formed  of  glosso-palatine  fibres. 
This  nerve  is  further  described  below  in  its  relation  to  the  spheno-palatine  ganglion.  It  arises 
from  the  anterior  angle  of  the  geniculate  ganglion,  enters  the  middle  fossa  of  the  cranium  through 


Fig.  741. — Diagram  of  the  Glosso-palatine  Nekve  (Black)  and  the  Relations  op  the 
Gangliated  Cephalic  Plexus  to  otheb  Cbanial  Nebves.  (After  Bean.)  Broken  Mnes, 
motor;  continuous  hues,  S3'mpathetic;  glosso-palatine  in  solid  black.  Medial  view.  Left 
side. 


Superior  cervical 
sympathetic  gangli 


Ciliary 
ganglion 


--  Ophthalmic  nerve 


kw     "\  X Maxillary  nerve 

i\i)  -  - -V^N.^-- Mandibular  nerve 

-\V -^V^V^^^-^-v^ Great  deep 

jV    '  \    ^^M~^     petrosal  nerve 

'^\.\N^^^^~- Sphenopalatine 

'A\'\\\rl^  ganglion 

Palatine  portion  of 
glosso-palatine  nerve 

Nerve  of  pterygoid 
canal  (Vidian  nerve) 

Otic  ganglion 

Middle  meningeal 
.  ,  artery 


( Submaxillary  ganglion 


External  maxillary 
artery 


the  hiatus  FaUopii,  and  passes  beneath  the  semilunar  ganglion  into  the  foramen  lacerum,  where 
it  joins  with  the  great  deep  petrosal  nerve  to  form  the  Vidian  nerve.  Thence  the  glosso- 
palatine  portion  passes  over  or  through  the  spheno-palatine  ganglion  to  form  the  greater  part 
of  the  small  and  middle  palatine  nerves  which  are  distributed  to  the  epithelium  and  glands  of 
the  soft  palate,  some  of  the  sensory  fibres  probably  terminating  in  the  taste  organs  found  there; 
the  remainder  serving  as  fibres  of  general  sensibility.  It  is  probable  that  most  of  the  motor 
glosso-palatine  fibres  in  the  great  superficial  petrosal  nerve  terminate  in  the  spheno-palatine 
ganglion;  some  may  pass  to  the  carotid  plexus  and  to  smaU  gangUa  elsewhere. 

The  chorda  tympani  consists  to  a  very  large  extent  of  sensory  fibres  (peripheral  processes 
of  the  cells  of  the  geniculate  ganglion),  but  it  also  contains  motor  fibres  and  is  thus  also  a  mixed 
nerve.  It  leaves  the  trunk  of  the  facial  nerve  a  short  distance  above  the  stylo-mastoid  foramen, 
and  pursues  a  slightly  recurrent  course  upward  and  forward  in  the  canaliculus  chorda  tympani 
(iter  chordae  posterius),  a  minute  canal  in  the  posterior  wall  of  the  tympanic  cavity,  and  it 


THE  VESTIBULAR  NERVE 


949 


enters  that  cavity  close  to  the  posterior  border  of  the  membrana  tympani.  It  crosses  the  cavity, 
running  on  the  medial  surface  of  the  tympanic  membrane  at  the  junction  of  its  upper  and  middle 
thirds,  covered  by  the  mucous  membrane  lining  the  tympanic  cavity,  and  passes  to  the  medial 
Bide  of  the  manubi-ium  of  the  malleus  above  the  tendon  of  the  tensor  tympani.  It  leaves  the 
tympanic  cavity  and  passes  to  the  base  of  the  skull  through  a  smaU  foramen  (the  iter  chordae 
anterius)  at  the  medial  end  of  the  petro-tympanic  (Glaserian)  fissure.  At  the  base  of  the  skull 
it  inclines  downward  and  forward  on  the  medial  side  of  the  spine  of  the  sphenoid,  which  it 
frequently  grooves,  and,  on  the  medial  side  of  the  pterygoideus  externus,  it  joins  the  posterior 
border  of  the  hngual  nerve  at  an  acute  angle.  Some  of  its  fibres  (motor  chiefly)  leave  the  lingual 
nerve  and  pass  to  the  sub-maxillary  ganglion,  and  others  (sensory)  continue  forward  to  the 
tongue,  where,  in  company  with  fibres  of  the  lingual  nerve,  they  terminate  in  the  epithehum 
covering  the  anterior  two-thirds  of  the  tongue.  Some  probably  serve  to  convey  sensations  of 
taste,  most  of  them  are  fibres  of  general  sensibility.  Before  it  joins  the  lingual  nerve  the  chorda 
tympani  receives  a  communicating  twig  from  the  otic  ganglion  (figs.  738,  741). 


THE  VESTIBULAR  NERVE 

The  vestibular  nerve  is  purely  sensory.     With  the  peripheral  processes  of  its 
cells  of  origin  terminating  in  the  neuro-epithelium  of  the  semicircular  canals  and 

Fig.  742. — The  Left  Membeanoits  Labyrinth  of  a  Human  Fcetus-of  lO  Weeks  (30  mm.), 
Lateral  Aspect.  Vestibular  ganglion  and  nerve,  red;  cochlear  nerve,  yellow.  (Streeter, 
American  Journal  of  Anatomy.) 


a.  3omm.  lateral. 

the  vestibule,  and  their  central  processes  conveying  impulses  which  are  dis- 
tributed to  the  gray  substance  of  the  cerebellum  and  spinal  cord,  the  nerve  com- 
prises a  most  important  part  of  the  apparatus  for  the  equilibration  of  the  body. 
It  has  been  customary  to  describe  the  vestibular  [radix  vestibularis]  and  the  coch- 
lear [radix  cochlearis]  nerves  combined  as  the  acoustic  (auditory)  or  eighth  cranial 
nerve.  While  the  two  are  blended  in  a  common  sheath  from  near  the  medulla  to 
the  bottom  of  the  internal  auditory  meatus,  they  are  likewise  partty  enclosed  in 
the  same  sheath  with  the  facial  and  glosso-palatine  nerves  and  the  internal  audi- 
tory artery  which  accompany  them  in  this  meatus.     At  the  bottom  of  the  meatus 


950  THE  NERVOUS  SYSTEM 

the  vestibular  and  the  cochlear  are  separate;  they  are  separate  at  their  entrance 
into  the  lateral  aspect  of  the  medulla  oblongata;  and  their  central  connections, 
peripheral  distributions  and  functions  are  different. 

The  vestibular  nerve  arises  as  processes  of  the  cells  of  the  vestibular  ganglion 
(ganglion  of  Scarpa),  situated  upon  and  blended  within  the  nerve  at  the  bottom 
of  the  internal  auditory  meatus.  Unlike  the  ordinary  spinal  ganglion,  to  which 
it  corresponds,  the  cells  of  the  vestibular  ganglion  retain  an  embryonal,  "bipolar," 
form.  The  central  processes  course  v/ith  the  cochlear  nerve  in  the  internal 
auditory  meatus  medialward,  caudad  and  slightly  downward,  inferior  to  the 
accompanying' if acial  and  glosso-palatine  nerves,  and,  arching  ventrally  around 
the  restiform  body,  they  enter  the  medulla  at  the  inferior  border  of  the  pons,  lat- 
eral to  the  glosso-palatine  and  facial  and  medial  to  the  entrance  of  the  cochlear 
nerve.  They  find  their  nucleus  of  termination  spread  in  the  floor  of  the  fourth 
ventricle  and  grouped  as  the  median,  the  lateral  (Deiters'),  the  superior,  and  the 
nucleus  of  the  spinal  root  of  the  vestibular  nei've.  In  the  internal  auditory  mea- 
tus, the  vestibular  nerve  is  connected  by  two  small  filaments  of  fibres  with  the 
glosso-palatine  nerve.  These  are  either  visceral  motor  fibres  for  the  vessels  of  the 
domain  of  the  vestibular  or  are  aberrant  fibres  which  course  only  temporarily 
with  the  vestibular  and  return  to  the  glosso-palatine. 

The  peripheral  processes  of  the  cells  of  the  vestibular  ganglion  terminate  in  the 
specialised  or  neuro-epithelium  comprising  the  maculm  in  the  sacculus  and  the 
utriculus  and  the  cristce  in  the  ampullte  of  the  three  semicircular  canals.  Thus 
there  are  five  terminal  branches  of  the  nerve.  None  of  its  fibres  terminates  in  the 
cochlea.  The  vestibular  ganglion  has  a  lobar  form,  one  lobe  giving  rise  to  a 
superior  utriculo-ampuUar  division  which  divides  into  three  terminal  branches;  the 
other  giving  a  sacculo-ampuUar  division  which  gives  two  terminals. 

The  superior  or  utriculo -ampullar  branch  divides  into  the  following  terminal 
branches: — 

(1)  The  utricular  branch  passes  through  the  superior  macula  cribrosa  of  the  vestibule 
and  terminates  in  the  macula  acustica  of  the  utriculus. 

(2)  Accompanying  the  utricular  branch  through  the  superior  macula  cribrosa  is  a  branch, 
the  superior  ampuUar,  to  the  crista  acustica  of  the  ampulla  of  the  superior  semicircular  canal, 
and — 

(3)  A  similar  branch,  the  lateral  ampullar,  to  the  ampulla  of  the  lateral  semicircular  canal. 

The  inferior  or  saccule -ampullar  branch  accompanies  the  cochlear  nerve  a 
short  distance  further  than  the  superior,  and  divides  into — 

(4)  A  branch,  the  posterior  ampullar,  which  passes  through  the  foramen  singulare  and  the 
inferior  macula  cribrosa  and  tormiiiatcs  in  the  ampulla  of  the  posterior  semicircular  canal,  and — 

(5)  A  branch,  the  saccular,  which  passes  through  the  middle  macula  cribrosa  and  terminates 
in  the  macula  acustica  of  the  sacculus. 

The  central  connections  of  the  vestibular  nerve  are  described  in  detail  on  pages  823,  824. 
Its  large  nucleus  of  termination,  spread  through  the  area  acustica  in  the  floor  of  the  fourth 
ventricle,  and  divided  into  four  sub-nuclei,  is  associated  with  the  nuclei  fastigii,  globosus,  and 
emboliformis  of  the  cerebellum,  with  the  nuclei  of  the  eye-moving  nerves,  with  the  spinal  cord, 
and  probably  with  the  cerebral  corte.x. 

THE  COCHLEAR  OR  AUDITORY  NERVE 

The  fibres  of  the  cochlear  nerve  are  distributed  to  the  organ  of  Corti  in  the 
cochlea,  and  so  are  considered  as  comprising  the  auditory  nerve  proper.  They 
arise  from  the  long,  coiled  spiral  ganglion  of  the  cochlea,  the  cells  of  which,  like 
those  of  the  vestibular  ganglion,  are  bipolar.  The  peripheral  processes  of  these 
cehs  are  shorter  than  those  of  the  vestibular  ganglion.  They  terminate  about  the 
auditory  or  hair-ceUs  of  the  organ  of  Corti  and  thus  collect  impulses  aroused  by 
stimuli  affecting  these  cells.  The  central  processes  of  the  ganglion  cells  continue 
through  the  modiolar  canal  and  the  tractus  spiralis  foraminosus  of  the  cochlea, 
and  thence,  joining  the  vestibular  nerve  through  the  internal  auditory  meatus, 
accompanying  the  facial  nerve  and  internal  auditory  artery,  they  course  medial- 
ward  and  downward,  approach  and  enclasp  the  restiform  body  (fig.  665)  and 
enter  the  lateral  aspect  of  brain-stem  to  terminate  in  their  dorsal  and  ventral 
nuclei.  A  description  of  these  nuclei  and  the  further  central  connections  of  the 
cochlea  with  the  superior  olive,  the  nuclei  of  the  eye-moving  nerves,  the  inferior 
quadrigeminate  bodies,  the  medial  geniculate  bodies,  and  with  the  cerebellum 
and  temporal  lobes  of  the  cerebral  hemispheres  is  given  on  pages  824,  839. 


THE  GLOSSO-PHARYNGEAL  NERVE  951 

The  cochlear  nerve  is  separate  from  the  vestibular  at  the  bottom  of  the  internal 
auditory  meatus  and  at  its  entrance  into  the  medulla. 

THE  GLOSSO-PHARYNGEAL  NERVE 

The  glosso-pharyngeal  or  ninth  cranial  nerves  are  mixed  nerves  and  each  is 
attached  to  the  medulla  by  several  roots  which  enter  the  posterolateral  sulcus, 
dorsal  to  the  anterior  end  of  the  olivary  body  and  in  direct  line  with  the  facial 
nerve. 

The  filaments,  when  traced  lateralward,  are  seen  to  blend,  in  front  of  the 
flocculus,  into  a  trunlc  which  hes  in  front  of  the  vagus  nerve,  but  which  passes 
through  a  separate  opening  through  the  arachnoid  and  the  dura  mater  and  through 
the  jugular  foramen.  In  the  foramen  this  trunk  hes  in  front,  and  lateral  to  the 
vagus  nerve  in  a  groove  on  the  petrous  portion  of  the  temporal  bone;  and  in  this 
situation  two  ganglia  are  interposed  in  it,  a  superior  or  jugular,  and  an  inferior 
or  petrosal.  After  it  emerges  from  the  jugular  foramen  the  glosso-pharyngeal 
nerve  descends  at  first  between  the  internal  carotid  artery  and  the  internal  jugular 
vein  and  to  the  lateral  side  of  the  vagus;  then,  bending  forward  and  medialward, 
it  descends  medial  to  the  styloid  process  and  the  muscles  arising  from  it,  and 
turning  around  the  lower  border  of  the  stylo-pharyngeus  it  passes  between  the 
internal  and  the  external  carotid  arteries,  crosses  the  superficial  surface  of  the 
stylo-pharyngeus,  and  runs  forward  and  upward  medial  to  the  hyoglossus  muscle 
and  across  the  middle  constrictor  and  the  stylo-hyoid  ligament,  to  the  base  of  the 
tongue  (fig.  743). 

Ganglia. — The  superior  or  jugular  ganglion  (ganglion  of  Ehrenritter),  is  a  small, 
ovoid,  reddish-grey  body  which  lies  on  the  back  part  of  the  nerve-trunk  in  the 
upper  part  of  the  jugular  foramen.  No  branches  arise  from  it.  It  is  sometimes 
continuous  with  the  petrosal  ganglion  or  it  may  be  absent. 

The  inferior  or  petrosal  ganglion,  (ganglion  of  Andersch),  is  an  ovoid  grey 
body  which  lies  in  the  lower  part  of  the  jugular  foramen,  and  appears  to  include 
all  the  fibres  of  the  nerve. 

Branches  and  communications. — (1)  The  petrosal  ganglion  is  connected  with  the  superior 
cervical  ganglion  of  the  sympathetic  by  a  fine  filament. 

(2)  It  also  has  a  filament  of  communication  with  the  auricular  branch  of  the  vagus  which 
varies  inversely  in  size  with  the  latter  branch  and  sometimes  entirely  replaces  it.  This  filament 
may  be  absent. 

(3)  An  inconstant  communication  with  the  ganglion  of  the  root  of  the  vagus. 

(4)  A  short  distance  below  the  petrous  gangUon  the  trunk  of  the  nerve  is  connected  by  a 
twig  with  that  branch  of  the  facial  nerve  which  supplies  the  posterior  belly  of  the  digastric 
muscle.     There  is  also  a  small  twig  (probalily  sensdryl  to  the  stylo-hyoid. 

(5)  From  the  petrosal  ganglion :  The  tympanic  branch  (nerve  of  Jacobson)  arises  from  the 
petrosal  ganglion  and  passes  through  a  foramen,  which  lies  in  the  ridge  of  bone  between  the  car- 
otid canal  and  the  jugular  fossa,  into  the  tympanic  canahculus  (Jacobson's  canal),  where  it  is 
surrounded  by  a  small,  fusiform  mass  of  vascular  tissue,  the  iniumesceniia  tympanica.  After 
traversing  the  tympanic  canaliculus  it  enters  the  tympanum  at  the  junction  of  its  lower  and 
medial  walls,  and,  ascending  on  the  medial  wall,  breaks  up  into  a  number  of  branches  which  take 
part  in  the  formation  of  the  tympanic  plexus  on  the  surface  of  the  promontory  (fig.  739).  The 
continuation  of  the  nerve  emerges  from  this  plexus  as  the  small  superficial  petrosal  nerve,  which 
runs  through  a  small  canal  in  the  petrous  portion  of  the  temporal  bone,  beneath  the  canal  for  the 
tensor  tympani,  and  appears  in  the  middle  fossa  of  the  cranium  through  a  foramen  which  lies 
in  front  of  the  hiatus  Fallopii.  From  this  foramen  it  runs  forward  and  passes  through  the  fora- 
men ovale,  the  canaliculus  innominatus,  or  the  spheno-petrosal  suture,  and  enters  the  zygomatic 
fossa,  where  it  joins  the  otic  ganghon.  While  it  is  in  tlie  canal  in  the  temporal  bone  the  small 
superficial  petrosal  nerve  is  joined  by  a  geniculo-tympanic  branch  from  the  geniculate  gangUon 
of  the  glosso-palatine  nerve. 

(6)  Branches  from  the  tympanic  plexus : — (a)  The  tubal  branch  (ramus  tubae),  a  dehcate 
branch,  which  runs  forward  to  the  mucous  membrane  of  the  tuba  auditiva  (Eustachian  tube) 
and  sends  filaments  backward  to  the  region  of  the  fenestra  vestibuli  (ovahs)  and  the  fenestra 
cochleaj  (rotunda). 

(6)  The  superior  and  inferior  carotico-tympanic  (carotid)  branches  pass  medianward  to 
the  internal  carotid  plexus  (fig.  741). 

The  above  communications  carry  fibres  almost  entirely  concerned  with  the  sympathetic 
plexuses  of  the  head  and  they  will  be  again  mentioned  below  with  the  gangUated  cephalic  plexus. 

Branches  from  the  trunk  of  the  nerve : — (1)  Pharyngeal  branches,  which  may  be  two  or 
three  in  number,  arise  from  the  nerve  a  short  distance  below  the  petrosal  ganglion.  The  prin- 
cipal and  most  constant  of  these  passes  on  the  lateral  side  of  the  internal  carotid  artery,  and 
after  a  very  short  independent  course  joins  with  the  pharyngeal  branch  of  the  vagus  and  with 
branches  of  the  superior  cervical  ganglion  to  form  the  pharyngeal  plexus  (fig.  743). 


952  .  THE  NERVOUS  SYSTEM 

(2)  A  muscular  brancli  is  distributed  to  the  stylo-pharyngeus  muscle.  This  branch  re- 
ceives  a  communication  from  the  facial  nerve  (fig.  743). 

(3)  The  tonsillar  branches  are  a  number  of  small  twigs  which  arise  under  cover  of  the  hyo- 
glossus  muscle;  they  proceed  to  the  tonsil,  around  which  they  form  a  plexus,  the  circulus 
tonsillaris.  From  this  plexus  fine  twigs  proceed  to  the  glosso-palatine  arches  (pillars  of  the 
fauces)  and  to  the  soft  palate. 

(4)  The  lingual  branches  are  the  terminal  branches  of  the  nerve  and  supply  the  mucous 
membrane  of  the  posterior  half  of  the  dorsum  of  the  tongue,  where,  chiefly  as  taste-fibres,  they 
are  distributed  to  the  vallate  papillae.  Some  small  twigs  pass  backward  to  the  follicular  glands  of 
the  tongue,  and  to  the  anterior  surface  of  the  epiglottis.  Other  twigs  are  distributed  around  the 
foramen  officum,  where  they  communicate  with  the  corresponding  twigs  of  the  opposite  side. 

The  sensory  fibres. — The  sensory  fibres  of  the  glosso-pharyngeal  nerve  spring  from  the  supe- 
rior and  petrosal  ganglia  and  pass  peripherally  and  centrally.  The  peripheral  processes  of  the 
ganglion  cells  are  those  which  are  distributed  to  the  mucous  membrane  (taste-buds)  of  the  tongue 
and  pharynx,  and  the  central  processes  pass  medialward  to  the  medulla.  In  the  medulla  they 
pass  dorsalward  and  medianward  through  the  reticular  formation  and,  bifurcating  into  ascend- 
ing and  descending  branches,  they  end  in  the  nucleus  of  termination  of  the  glosso-pharyngeal 
nerve,  that  is,  in  the  superior  part  of  the  nucleus  alae  cinereae  and  in  the  nucleus  of  the  tractus 
solitarius. 

The  motor  fibres  arise  from  the  nucleus  ambiguus  in  the  lateral  funiculus  of  the  medulla, 
in  fine  with  the  nucleus  of  origin  of  the  facial  nerve.  From  this  nucleus  they  pass  at  first 
dorsalward  and  then,  turning  lateralward,  they  emerge  and  join  the  sensory  fibres  and  run  with 
them  in  the  trunk  of  the  nerve  (fig.  646). 

Van  Gehuchten's  observations  point  to  the  conclusion  that  one  motor  nucleus  of  the  glosso- 
pharyngeal nerve  is  separate  from  and  Kes  above  and  to  the  medial  side  of  the  nucleus  ambiguus, 
and  that  a  portion  of  the  nucleus  of  the  ala  cinerea  is  also  a  motor  nucleus  common  to  the 
glosso-pharyngeal  and  vagus  nerves.  It  is  quite  probable  that  the  former  motor  nucleus  is 
that  now  considered  as  the  dorsal  motor  nucleus  of  the  vagus.  An  unknown  proportion  of 
the  motor  fibres  are  visceral  motor  and  course  in  the  various  communications  of  the  glosso- 
phar3mgeal  nerve  with  cephalic  plexus. 

Central  connections. — The  nuclei  of  termination  of  the  glosso-pharyngeal  nerve  are  asso- 
ciated with  the  motor  nuclei  of  other  cranial  nerves  by  the  medial  longitudinal  fasciculus,  and 
with  the  somaesthetic  area  of  the  cortex  cerebri  of  the  opposite  side  by  the  medial  lemniscus 
(fillet).  The  motor  nucleus  of  the  nerve  is  associated  with  the  somaesthetic  area  by  the  pyra- 
midal fibres. 

THE  HYPOGLOSSAL  NERVE 

The  hypoglossal  nerves  are  exclusively  motor;  they  supply  the  genio-hyoidei 
and  the  extrinsic  and  intrinsic  muscles  of  the  tongue  except  the  glosso-palatini. 
They  are  usually  designated  as  the  twelfth  pair  of  cranial  nerves.  The  fibres  of 
each  nerve  issue  from  the  cells  of  an  elongated  nucleus  which  lies  in  the  floor 
of  the  central  canal  in  the  lower  half  of  the  medulla  and  in  the  floor  of  the  fourth 
ventricle  in  the  upper  half  beneath  the  trigonum  hypoglossi.  This  nucleus  is  the 
upward  continuation  of  the  ventro-medial  group  of  cells  of  the  ventral  horn  of  the 
spinal  cord.  From  their  origin  the  fibres  run  ventralward  and  somewhat  lateral- 
ward,  probably  joined  in  the  medulla  by  a  few  fibres  from  the  nucleus  ambiguus 
which  is  a  segment  of  the  upward  prolongation  of  the  lateral  group  of  cells  of  the 
ventral  horn.  The  conjoined  fibres  issue  from  the  medulla  in  the  sulcus  between 
the  pyramid  and  the  olivary  body,  in  a  series  of  from  ten  to  sixteen  root  filaments, 
which  pierce  the  pia  mater  and  unite  with  each  other  to  form  two  bundles  (fig. 
731).  These  bundles  pass  forward  and  lateralward  to  the  hypoglossal  (anterior 
condyloid)  foramen,  where  they  pierce  the  arachnoid  and  dura  mater.  In  the 
outer  part  of  the  foramen  the  two  bundles  unite  to  form  the  trunk  of  the  nerve. 
At  its  commencement,  at  the  base  of  the  skull,  the  trunk  of  the  hypoglossus  lies  on 
the  medial  side  of  the  vagus,  but  as  it  descends  in  the  neck  it  turns  gradually 
around  the  dorsal  and  the  lateral  side  of  the  latter  nerve,  lying  between  it  and  the 
internal  jugular  vein,  and  a  little  above  the  level  of  the  hyoid  bone  it  bends  for- 
ward, and  crosses  lateral  to  the  internal  carotid  artery,  the  root  of  origin  of  the 
occipital  artery,  the  external  carotid,  and  the  loop  formed  by  the  first  part  of  the 
lingual  artery  (fig.  743).  After  crossing  the  lingual  artery  it  proceeds  forward 
on  the  lateral  svnface  of  the  hyo-glossus,  crossing  to  the  medial  side  of  the  posterior 
belly  of  the  digastric,  and  the  stylo-hyoid  muscles.  It  disappears  in  the  anterior 
part  of  the  submaxillary  region  between  the  mylo-hyoid  and  the  hyo-glossus,  and 
divides  into  its  terminal  branches  between  the  latter  muscle  and  the  genio-glossus. 

As  it  descends  in  the  neck  the  trunk  lies  deeply  between  the  internal  jugular  vein  and 
the  internal  carotid  artery  under  cover  of  the  parotid  gland,  the  styloid  muscles,  and  the  pos- 
terior beUy  of  the  digastric,  and  it  is  crossed  superficially  by  the  posterior  auricular  and  the  occip- 
ital arteries.  As  it  turns  forward  around  the  root  of  the  occipital  artery  the  sterno-mastoid 
branch  of  that  vessel  hooks  downward  across  the  nerve,  and  as  it  turns  forward  on  the  hyo- 


THE  HYPOGLOSSAL  NERVE 


953 


glossus  muscle  it  lies  immediately  above  the  ranine  vein.  It  is  crossed  by  the  posterior  belly 
of  the  digastric  and  the  stylo-hyoid  muscle,  and  it  is  covered  superficially,  behind  the  mylo- 
hyoid, by  the  lower  part  of  the  submaxillary  gland. 

Communications. — The  hypoglossus  is  connected  with  the  first  cervical  gan- 
glion of  the  sympathetic,  with  the  ganglion  nodosum  of  the  vagus,  with  the  loop 
between  the  first  and  second  cervical  nerves,  and  with  the  lingual  nerve;  the 
latter  communication  is  established  along  the  anterior  border  of  the  hyo-glossus 
muscle  (figs.  743  and  744). 

Terminal  branches. — These  include  (1)  a  meningeal  branch;  (2)  branches  from 
the  cervical  plexus;  and  (3)  branches  from  the  hypoglossus  proper. 

(1)  A  meningeal  branch,  frequently  represented  by  two  filaments,  is  given  off  in  the  hypo- 
glossal (anterior  condyloid)  canal.  It  passes  backward  into  the  posterior  fossa  of  the  cranium 
and  is  distributed  to  the  dura  mater.  It  was  believed  at  one  time  that  the  fibres  of  the  meningeal 
branch  were  derived  from  the  lingual  nerve,  but  it  is  now  deemed  more  probable  that  they  are 
either  sensory  or  visceral  motor  fibres  from  the  cervical  nerves,  or  from  the  vagus. 


Fig.  743. — The    Hypoglossal,  Glosso-phartngeal,  and   Lingual   Nerves.     (Spalteholz.) 


Ganglion  nodosum 
Cut  surface  of  the  styloid 

process  ._- 

Internal  jugular 
vein 
Facial  nerve 
(cut  off) 
Spinal  accessory 
(external  branch ) 
Transverse  proc- 
ess of  atlas 
Anterior    branch 
of  first  cervical 


Glosso-        Internal 
pharyngeal     carotid     Semilunar 
nerve  artery       ganglion 


^ 


Pharyn- 


r  Of  vagus 
Of  glos- 

branches  |  fy^l^l{ 

Anterior    branch   of 
second  cervical  nerve 

'Stylo -pharyngeal 
branch 

Stylo-pharyngeus 

Hypoglossal  nerve 


External  carotid  artery 

Anterior  branch  of 
third  cervical  nerve 
Descendeus  cervicalis 
(hypoglossi) 
Anterior  branch  of  fourth 
cervical  nerve 
Steruo-mastoideus         i 


Ansa  cervicalis 
(hypoglossi) 


Ophthalmic 


_  Maxillary 

nerve 
'    Mandibular 

—  nerve 
Lateral    plate 

—  of   pterygoid 
process 

,, Chorda 

tympani 
^ensor  veli 
palatini 
Lingual  nerve 

Buccinator 
Branches  to 
isthmus   of 
fauces 

ff-  Stylo- 
glossus 


Vagus        i 


Lingual 
branches  of 
lingual  nerve 
Sublingual 

nerve 
Anastomotic 
"^N-.branch  to 
.,     hypoglossal 
Genio-glossus 
Lingual  branches 
\  \        of  hypoglossal 

N     Genio-liyoideus 
Hyoglossus 

Thyreo-hyoid  branch 

Lingual  artery 


Phrenic  nerve  ~ 


Superior  thyreoid  artery 
Thyreo-hyoideus 


Branch  to  the  sterno-hyoideus 
Common  carotid  artery 


(2)  Branches  which  consist  of  fibres  derived  from  the  cervical  plexus. — The  descendens 
cervicalis  (hypoglossi)  and  the  muscular  twig  to  the  thyi'eo-hyoid  muscle,  though  apparently 
arising  from  the  hypoglossal  nerve,  consists  entirely  of  fibres  which  have  passed  into  the  hypo- 
glossal nerve  from  the  loop  between  the  first  two  cervical  nerves.  Therefore,  neither  of  them 
are  branches  of  the  hypoglossus  proper.      (See  fig.  752.) 

(a)  The  descendens  cervicalis  (hypoglossi)  parts  company  with  the  hypoglossus  at  the  point 
where  the  latter  hooks  around  the  occipital  artery  (fig.  743).  It  runs  downward  and  slightly 
medialward  on  the  sheath  of  the  great  vessels  (occasionally  within  the  sheath),  and  is  joined 
at  a  variable  level  by  branches  from  the  second  and  third  cervical  nerves,  forming  with  them  a 
loop,  the  cervical  loop  [ansa  hypoglossi]  (fig.  743).  The  cervical  loop  rnay  be  placed  at  any  level 
from  a  point  immediately  below  the  occipital  artery  to  about  four  centinietres  above  the  sternum. 
From  this  loop  aU  the  muscles  attached  to  the  hyoid  bone  are  supphed.  A  twig  to  the  anterior 
belly  of  the  omo-hyoid  arises  from  the  descendens  cervicalis  in  the  upper  part  of  its  course. 
The  nerves  which  supply  the  sterno-hyoid,  sterno-thyreoid,  and  posterior  belly  of  the  omo- 
hyoid are  given  off  by  the  cervical  loop.  Twigs  from  the  first  two  nerves  pass  downward  in 
the  muscles  behind  the  manubrium  sterni  and  •in  rare  cases   communicate  with  the  phrenic 


954  THE  NERVOUS  SYSTEM 

nerve  within  the  thorax.     The  nerve  to  the  posterior  belly  of  the  omo-hyoid  runs  in  a  loop  of 
the  cervical  fascia  below  the  central  tendon  of  the  muscle. 

(b)  The  nerve  to  the  thyreo-hyoid  leaves  the  hypoglossus  near  the  tip  of  the  great  cornu  of 
the  hyoid  bone,  and  runs  obhquely  downward  and  medialward  to  reach  the  muscle.  AU  the 
fibres  in  (a)  and  (b)  are  derived  from  the  first,  second  and  third  cervical  nerves. 

(c)  The  nerve  to  the  genio-hyoid  arises  under  cover  of  the  mylo-hyoid,  where  loops  are 
formed  with  the  lingual  nerve  from  which  loops  branches  pass  into  the  muscle.  It  probably 
contains  some  true  h}fpoglossal  fibres. 

(3)  The  branches  of  the  hypoglossus  proper,  the  rami  linguales,  supply  the  stylo-glossus, 
hj'O-glossus,  genio-glossus,  and  the  intrinsic  muscular  fibres  of  the  tongue. 

The  nerve  to  the  stylo-glossus  is  given  off  near  the  posterior  border  of  the  hyo-glossus. 
It  pierces  the  st3'lo-glossus,  and  its  fibres  pursue  a  more  or  less  recurrent  course  within  the  muscle. 

The  nerves  to  the  hyo-glossus  are  several  twigs  which  are  supphed  to  the  muscle  as  the 
hypoglossal  nerve  crosses  it. 

The  nerve  to  the  genio-glossus  arises  under  cover  of  the  mylo-hyoid  in  common  with  the  ter- 
minal branches  to  the  intrinsic  muscles  of  the  tongue.  It  communicates  freely  with  branches  of 
the  lingual,  forming  long  loops  which  lie  on  the  genio-glossus.  From  these  loops  twigs  pass  into 
the  genio-glossus  and  into  the  muscular  substance  of  the  tongue. 

Central  connections. — The  nucleus  of  origin  of  the  hypoglossus  is  associated  with  the  som- 
Eesthetic  area  (operculum)  of  the  cortex  cerebri  of  the  opposite  side  by  the  pyramidal  fibres, 
and  it  is  connected  with  the  sensory  nuclei  (nuclei  of  termination)  of  other  cranial  nerves  by 
way  of  the  reticular  formation  and  the  medial  longitudinal  fasciculus. 

THE  VAGUS  OR  PNEUMOGASTRIC  NERVE 

The  vagus  or  pneumogastric  nerves  are  the  longest  of  the  cranial  nerves,  and 
they  are  remarkable  for  their  almost  vertical  course,  their  asymmetry,  and  their 
extensive  distribution,  for,  in  addition  to  supplying  the  lung  and  stomach,  as  the 
name  '  pneumo-gastric '  indicates,  each  nerve  gives  branches  to  the  external  ear, 
the  pharynx,  the  larynx,  the  trachea,  the  oesophagus,  the  heart,  and  the  abdominal 
viscera.     They  are  commonly  referred  to  as  the  tenth  pair  of  cranial  nerves. 

Each  nerve  is  attached  to  the  side  of  the  medulla,  in  the  postero-lateral  sulcus, 
dorsal  to  the  olivary  body,  by  from  twelve  to  fifteen  root  filaments  which  are  in 
linear  series  with  the  filaments  of  the  glosso-pharyngeal  nerve.  The  filaments 
contain  both  sensory  and  motor  fibres.  They  pierce  the  pia  mater,  from  which 
they  receive  sheaths,  and,  traced  outward,  they  pass  into  the  posterior  fossa  of  the 
cranium  toward  the  jugular  foramen  and  unite  to  form  the  trunk  of  the  nerve, 
which  passes  through  openings  in  the  arachnoid  and  the  dtira  mater  which  are 
common  to  it  and  to  the  spinal  accessory  nerve.  In  the  jugular  foramen  a  small 
spherical  ganglion,  the  jugular  ganglion  (ganglion  of  the  root) ,  is  interposed  in  the 
trunk  which  here  turns  at  right  angles  to  its  former  course  and  descends  through 
the  neck.  As  it  leaves  the  jugular  foramen  it  is  joined  by  the  internal  or  accessory 
portion  of  the  spinal  accessory  nerve,  and  immediately  below  this  junction  it 
enters  a  large  ovoid  ganglion,  the  ganglio7i  nodosum  or  ganglion  of  the  trimk  (fig. 
743).  As  it  descends  through  the  neck  the  nerve  passes  ventral  and  somewhat 
lateral  to  the  superior  cervical  sympathetic  ganglion,  and  in  front  of  the  longus 
capitis  and  longus  colh,  from  which  it  is  separated  by  the  prevertebral  fascia.  In 
the  upper  part  of  the  neck  it  is  placed  between  the  internal  carotid  artery  and  the 
internal  jugular  vein,  and  on  a  plane  dorsal  to  them,  the  artery  being  ventral  and 
mesial,  and  the  vein  ventral  and  lateral.  In  the  lower  part  of  the  neck  it  occupies 
a  similar  position  in  regard  to  the  common  carotid  artery  and  the  internal  jugular 
vein,  and  the  three  structures  are  enclosed  in  a  common  sheath  derived  from  the 
deep  cervical  fascia,  but  within  the  sheath  each  structure  occupies  a  separate 
compartment  (fig.  743) .  In  the  root  of  the  neck  and  in  the  thorax  the  relations  of 
the  nerves  of  the  two  sides  of  the  body  differ  somewhat,  and  they  must,  therefore, 
be  considered  separately. 

The  right  vagus  passes  in  front  of  the  first  part  of  the  right  subclavian  artery  in  the  root  of 
the  neck  and  then  descends  in  the  thorax,  passing  obliquely  downward  and  backward  on  the  right 
of  the  trachea,  and  behind  the  right  innominate  vein  and  the  superior  vena  cava,  to  the  back  of 
the  root  of  the  right  lung.  Just  before  it  reaches  the  right  bronchus  it  lies  close  to  the  medial 
side  of  the  vena  azygos  as  the  latter  hooks  forward  over  the  root  of  the  lung.  At  the  back  of  the 
right  bronchus  the  right  vagus  breaks  up  into  a  number  of  branches  which  join  with  the  branches 
of  tlie  sympathetic  to  form  the  right  posterior  pulmonary  plexus,  and  from  this  plexus  it  issues 
in'the  form  of  one  or  more  cords,  combined  .sensory,  visceral  motor  and  sympathetic,  which  de- 
scend on  the  cesophagus  and  break  up  into  branches  which  join  with  branches  of  the  left  vagus, 
forming  the  posterior  oesophageal  plexus.  At  the  lower  part  of  the  thorax  fibres  of  this  plexus 
become  again  associated  in  one  trunk  which  passes  througli  the  diaphragm  on  the  posterior 


THE  VAGUS  NERVE 


955 


surface  of  the  oesophagus,  and  is  distributed  to  the  posterior  surface  of  the  stomach  and  to  the 
coeliac  (solar)  plexus  and  its  offsets. 

The  left  vagus  descends  through  the  root  of  the  neck  between  the  carotid  and  subclavian 
arteries  and  in  front  of  the  thoracic  duct.  In  the  upper  part  of  the  superior  mediastinum  it  ia 
crossed  in  front  by  the  left  phrenic  nerve,  and  in  the  lower  part  of  the  same  region  it  crosses  in 


Fig.  744. — Diagram  of  the  Branches  of  the  Vagus  Nerves. 

Auricular  branch 
Meningeal  branch 
Ganglion  of  root 
Spinal  accessory  nerve 


'  Hypoglossal  nerve 
Loop  between  first  two  cervical 


External  carotid  artery 


Cardiac  branch  from  recurrent 
nerve 
Thoracic  cardiac  branch 
(right  vagus) 


Hepatic  plexus 
Coeliac  plexus 


front  of  the  root  of  the  subclavian  artery  and  the  arch  of  the  aorta  and  behind  the  left  superior 
intercostal  vein.  Below  the  aortic  arch  it  passes  behind  the  left  bronchus  and  divides  into 
branches  which  unite  with  twigs  of  the  sj'mpathetic  to  form  the  left  posterior  pulmonary  plexus. 
Prom  this  plexus  the  fibres  of  the  left  vagus  issue  as  one  or  more  cords  that  break  up  into  anas- 
tomosing branches  to  form  the  anterior  oesophageal  plexus.  At  the  lower  part  of  the  thorax 
this  plexus  becomes  a  single  trunk,  which  passes  through  the  diaphragm  on  the  anterior  surface 
of  the  oesophagus,  and  it  is  distributed  to_the  anterior  surface  of  the  stomach  and  tothe  liver. 


956  THE  NERVOUS  SYSTEM 

The  jugular  ganglion  (ganglion  of  the  root)  is  a  spherical  grey  mass  about 
five  miUimetres  in  diameter  which  lies  in  the  jugular  foramen  (fig.  744).  It  is 
connected  with  the  spinal  accessory  nerve  and  with  the  superior  cervical  sympa- 
thetic ganglion,  and  it  gives  off  an  auricular  branch,  by  means  of  which  it  becomes 
associated  with  the  facial  and  glosso-pharyngeal  nerves,  and  a  recurrent  meningeal 
branch. 

The  ganglion  nodosum  (ganglion  of  the  trunk)  lies  below  the  base  of  the 
skull  and  in  front  of  the  upper  part  of  the  internal  jugular  vein.  It  is  of  flattened 
ovoid  form  and  about  seventeen  miUimetres  long  and  four  millimetres  broad 
(figs.  744  and  743).  It  is  joined  by  the  accessory  part  of  the  spinal  accessory 
nerve,  and  is  associated  with  the  hypoglossal  nerve,  with  the  superior  cervical 
ganglion  of  the  sympathetic,  and  with  the  loop  between  the  first  two  cervical 
nerves,  and  it  gives  off  a  pharyngeal,  a  superior  laryngeal,  and  a  superior  cardiac 
branch.  Both  ganglia  and  especially  the  nodosal  retain  numerous  cell-bodies  of 
sympathetic  neurones  and  the  twigs  issuing  from  the  ganglia  thus  contain  sympa- 
thetic fibres.     The  greater  part  of  the  cell-bodies  are  of  sensory  neurones. 

Communications. — The  vagus  nerve  is  connected  with  the  glosso-pharyngeal, 
spinal  accessory  and  hypoglossal  nerves,  with  the  sympathetic,  and  with  the  loop 
between  the  first  and  second  cervical  nerves. 

(1)  Two  communications  exist  between  the  vagus  and  glosso-pharyngeal  nerves:  one 
between  their  trunlis,  just  below  the  base  of  the  skull,  and  one,  in  the  region  of  their  gangha, 
consisting  of  one  or  two  filaments.  When  two  filaments  are  present  one  passes  from  the  jugular 
gangUon  and  the  other  from  the  auricular  nerve  to  the  petrosal  ganghon  of  the  glosso-pharyngeal 
nerve.     Either  or  both  of  these  filaments  may  be  absent. 

(2)  Two  twigs  pass  from  the  spinal  accessory  nerve  to  the  ganglion  nodosum,  and  at  a 
lower  level  the  accessory  part  of  the  spinal  accessory  nerve  also  joins  the  same  gangUon  (fig. 
744).  The  majority  of  the  fibres  of  the  accessory  part  of  the  spinal  accessory  nerve  merely 
pass  across  the  surface  of  the  ganglion  and  are  continued  into  the  pharyngeal  and  superior 
laryngeal  branches  of  the  vagus,  but  a  certain  number  blend  with  the  trunk  of  the  vagus  and 
are  continued  into  its  recurrent  laryngeal  and  cardiac  branches. 

(3)  Two  or  three  fine  filaments  connect  the  ganghon  nodosum  with  the  hypoglossal  nerve 
as  the  latter  turns  around  the  lower  part  of  the  gangUon  (fig.  744). 

(4)  Fibres  pass  from  the  superior  cervical  ganghon  of  the  sympathetic  to  both  ganglia 
of  the  vagus  (fig.  744). 

(5)  A  twig  sometimes  passes  from  the  loop  between  the  first  two  cervical  nerves  to  the 
gangUon  nodosum  (fig.  744). 

Terminal  branches. — These  are  the  meningeal,  auricular,  pharyngeal,  superior 
laryngeal,  recurrent  (inferior  laryngeal),  cardiac,  bronchial,  pericardial,  oesopha- 
geal, and  the  abdominal  branches. 

(1)  The  meningeal  or  recurrent  branch  is  a  slender  filament  which  is  given  off  from  the 
jugular  ganglion.  It  takes  a  recurrent  course  through  the  jugular  foramen,  and  is  distributed 
to  the  dura  mater  around  the  transverse  (lateral)  sinus. 

(2)  The  auricular  branch,  or  nerve  of  Arnold,  arises  from  the  jugular  gangUon  in  the  jugular 
foramen.  It  receives  a  branch  from  the  petrosal  gangUon  of  the  glosso-pharyngeal,  enters  the 
petrous  part  of  the  temporal  bone  through  a  foramen  in  the  lateral  wall  of  the  jugular  fossa, 
and  communicates  with  the  facial  nerve  or  merely  Ues  in  contact  with  it  as  far  as  the  stylo- 
mastoid foramen.  It  usually  leaves  the  temporal  bone  by  the  stylo-mastoid  foramen,  but  it 
may  pass  through  the  tympano-mastoid  fissure,  and  it  divides,  behind  the  pinna,  into  two 
branches,  one  of  which  joins  the  posterior  auricular  branch  of  the  facial  while  the  other  suppUes 
sensory  fibres  to  the  posterior  and  inferior  part  of  the  external  auditory  meatus  and  the  back 
of  the  pinna.  It  also  suppUes  twigs  to  the  osseous  part  of  the  external  auditory  meatus  and 
to  the  lower  part  of  the  outer  surface  of  the  tympanic  membrane. 

(3)  The  pharyngeal  branches  may  be  two  or  three  in  number.  The  principal  of  these 
joins  the  pharyngeal  branch  of  the  glosso-pharyngeal  on  the  lateral  surface  of  the  internal  car- 
otid artery,  and  after  passing  with  the  latter  medial  to  the  external  carotid  artery  it  turns 
downward  and  medialward  to  reach  the  posterior  aspect  of  the  pharynx.  Here  the  two  nerves 
are  joined  by  branches  from  the  superior  cervical  ganglion  of  the  sympathetic,  with  which  they 
form  the  pharyngeal  plexus  (figs.  743,  744).  Branches  from  this  plexus  supply  sensory  fibres 
to  the  mucous  membrane  of  the  pharynx  and  motor  fibres  to  the  constrictores  pharyngis,  levator 
palatini,  uvulae,  glosso-palatinus,  and  pharyngo-palatinus. 

(4)  The  superior  laryngeal  nerve  arises  from  the  lower  part  of  the  ganghon 
nodosum,  and  passes  obliquely  downward  and  medialward  behind  and  medial  to 
both  internal  and  external  carotid  arteries  toward  the  larynx.  In  this  course  it 
describes  a  curve  with  the  convexity  downward  and  lateralward  and  divides  into 
(i)  a  larger  internal  and  (ii)  a  smaller  external  branch  (fig.  744).  Before  its 
division  it  is  joined  by  twigs  with  the  sympathetic  and  with  the  pharyngeal  plexus, 
and  it  gives  a  small  branch  to  the  internal  carotid  artery. 


THE  VAGUS  NERVE  957 

(a)  The  internal  branch  accompanies  the  superior  laryngeal  artery  to  the  interval  between 
the  upper  border  of  the  thyreoid  cartilage  and  the  great  cornu  of  the  hyoid  bone.  It  passes 
under  cover  of  the  thyreo-hyoid  muscle  and  pierces  the  hyo-thyreoid  membrane  to  gain  the 
interior  of  the  pharynx,  where  it  hes  in  the  lateral  wall  of  the  sinus  piriformis  and  divides  into 
a  number  of  diverging  branches.  The  ascending  branches  supply  the  mucous  membrane  on 
both  surfaces  of  the  epiglottis,  and  probably  that  of  a  small  part  of  the  root  of  the  tongue.  The 
descending  branches  ramify  in  the  mucous  membrane  lining  the  larjmx,  and  supply  the  mucous 
membrane  which  covers  the  back  of  the  cricoid  cartilage.  One  of  the  descending  branches 
passes  downward  on  the  internal  muscles  of  the  larynx  to  anastomose  with  the  terminal  part  of 
the  inferior  (recurrent)  laryngeal  nerve. 

(b)  The  external  branch  runs  downward  on  the  inferior  constrictor  to  the  lower  border  of 
the  th}Teoid  cartilage,  where  it  ends,  for  the  most  part,  in  the  crico-thyreoid  muscle.  A  few 
filaments  pierce  the  crico-thyreoid  membrane  and  are  distributed  to  the  membrane  lining  the 
larynx.  It  occasionally  gives  off  a  cardiac  branch  which  joins  one  of  the  cardiac  branches  of 
the  sympathetic;  it  also  furnishes  twigs  to  the  inferior  constrictor,  and  communicating  twigs 
to  the  pharyngeal  plexus,  and  it  receives  a  communication  from  the  superior  cervical  gangUon 
of  the  sympathetic. 

(5)  The  recurrent  (inferior  or  recurrent  laryngeal)  nerve  of  the  right  side 
arises  from  the  vagus  at  the  root  of  the  neck  in  front  of  the  right  subclavian 
artery.  It  hooks  around  the  artery,  passing  below  and  then  behind  that  vessel, 
and  runs  upward  and  slightly  medialward,  crossing  obliquely  behind  the  common 
carotid  artery  (fig.  744).  Having  gained  the  side  of  the  trachea,  it  runs  upward  in 
the  groove  between  the  trachea  and  the  CBsophagus,  accompanying  branches  of  the 
inferior  thja-eoid  artery,  and,  near  the  level  of  the  lower  border  of  the  cricoid  car- 
tilage, becomes  the  inferior  laryngeal  nerve. 

In  its  course  the  right  recurrent  nerve  gives  off  branches  to  the  trachea,  cesophageal  branches 
to  the  ojsophagus  and  pharynx,  and,  near  its  commencement,  one  or  more  inferior  cardiac 
branches.  It  communicates  with  the  inferior  cervical  sympathetic  ganghon  and  with  the  superior 
laryngeal  nerve. 

The  inferior  laryngeal  nerve,  the  continuation  of  the  recurrent,  ascends  between  the  trachea 
and  oesophagus,  enters  the  larynx  under  cover  of  the  inferior  constrictor  of  the  pharynx,  and 
divides  into  two  branches,  anterior  and  posterior.  The  anterior  branch  passes  upward  and  for- 
ward on  the  crico-arytajnoideus  lateralis  and  thyreo-arytajnoideus,  and  supplies  these  muscles 
and  also  the  vocalis,  arytsenoideus  obliquus,  ary-epiglotticus,  and  thyreo-epiglotticus.  The 
posterior  branch,  passing  upward,  supplies  the  crico-arytaenoideus  posterior  and  arytsenoideus 
obliquus,  and  anastomoses  with  the  medial  branch  of  the  superior  laryngeal  nerve. 

On  the  left  side  the  recurrent  nerve  arises  in  front  of  the  aortic  arch  and  winds 
around  the  concavity  of  the  arch  lateral  to  the  ligamentum  arteriosum.  It  crosses 
obliquely  behind  the  root  of  the  left  common  carotid  artery,  gains  the  angular 
interval  between  the  oesophagus  and  trachea,  and  corresponds  with  the  nerve  of 
the  right  side  in  the  remainder  of  its  course  and  distribution  (fig.  744). 

(6)  Cardiac  branches. — Of  these  branches  of  the  vagus,  there  are  two  sets,  the 
superior  and  inferior.  All  the  branches  of  both  sets  pass  to  the  deep  part  of  the 
cardiac  plexus  except  a  superior  branch  on  the  left  side  that  passes  to  the  super- 
ficial part  of  the  cardiac  plexus.  All  contain  visceral  motor,  sympathetic  and 
sensory  fibres. 

(a)  The  superior  (superior  and  inferior  cervical)  cardiac  nerves  arise  from  the  vagus  and 
its  branches  in  the  neck  (figs.  744,  786).  Some  of  these  branches  on  both  sides  join  with  the 
cardiac  branches  of  the  sympathetic  in  the  neck  and  pass  with  them  to  the  cardiac  plexus.  Some 
on  the  right  side  pass  independently  through  the  thorax  to  the  deep  part  of  the  cardiac  plexus, 
and  a  branch  on  the  left  side  passes  through  the  thorax  to  the  superficial  part  of  the  cardiac 
plexus. 

(b)  The  inferior  (thoracic)  cardiac  branches. — These  branches  on  the  right  side  arise  in 
part  from  the  recurrent  nerve  and  in  part  from  the  main  trunk  of  the  vagus,  while  on  the  left 
side  they  usually  arise  entirely  from  the  recurrent.  AU  these  branches  pass  to  the  deep  part 
of  the  cardiac  plexus  (figs.  744,  786). 

(7)  The  bronchial  (pulmonary)  branches  are  anterior  and  posterior  (fig.  744) . 

(a)  The  anterior  bronchial  (pulmonary)  branches  consist  of  a  few  small  branches  which  arise 
at  the  upper  border  of  the  root  of  the  lung.  They  pass  forward  to  gain  the  anterior  aspect  of 
the  bronchus,  where  they  communicate  with  the  sympathetic  and  form  the  anterior  pulmonary 
plexus,  from  which  fine  twigs  pass  along  the  bronchus. 

(b)  The  posterior  bronchial  (pulmonary)  branches. — Almost  the  entire  remaining  trunk 
of  the  vagus  usuallj'  divides  into  these  branches,  which  join  with  branches  from  the  second, 
third,  and  fourth  thoracic  ganglia  of  the  sympathetic  to  form  the  posterior  pulmonary  plexus 
(fig.  744).  The  plexuses  of  the  two  sides  join  freely  behind  the  bifurcation  of  the  trachea, 
and  branches  from  the  plexus  pass  along  each  bronchus  into  the  lung. 

(8)  The  pericardial  branches  pass  from  the  trunk  of  the  vagus  or  from  the  bronchial  or 
oesophageal  plexuses  to  the  anterior  and  posterior  surfaces  of  the  pericardium.  They  are 
chiefly  sensory. 


958  THE  NERVOUS  SYSTEM 

(9)  CEsophageal  branches,  given  off  by  the  trunk  of  the  nerve  above  the  bronchial  plexuses 
and  from  the  oesophageal  plexuses  lower  down,  pass  to  the  wall  of  the  oesophagus. 

(10)  Abdominal  branches. — The  terminal  part  of  the  left  vagus  divides  into  many  branches, 
some  of  which  communicate  freely  along  the  lesser  curvature  of  the  stomach  with  filaments 
from  the  gastric  plexus  of  the  sympathetic,  and  to  some  extent  with  branches  of  the  right  vagus, 
to  form  the  elongated  anterior  gastric  plexus  (fig.  744).  From  this  plexus  as  well  as  from  the 
nerve-trunk,  gastric  branches  are  given  to  the  anterior  surface  of  the  stomach.  Hepatic 
branches  from  the  trunk  or  from  this  plexus  pass  in  the  lesser  omentum  to  the  hepatic  plexus 
(fig.  744).  The  terminal  part  of  the  right  vagus  divides  into  many  branches,  and  forms  along 
the  lesser  curvature  of  the  stomach  an  elongated  posterior  gastric  plexus  by  communications 
with  branches  from  the  gastric  plexus  of  the  sympathetic  and  with  branches  from  the  right  vagus. 
Gastric  branches  are  given  off  by  the  trunk  of  the  nerve  and  from  this  plexus.  Coeliac  branches 
are  given  by  the  trunk  to  the  cceliac  (solar)  plexus,  and  splenic  and  renal  branches,  either 
directly  or  through  the  coeliac  (solar)  plexus,  are  given  to  the  splenic  and  renal  plexuses  (fig.  744) . 

Central  connections. — The  sensory  fibres  of  the  vagus  are  processes  of  the  cells  of  the  jugular 
ganglion  and  the  ganglion  nodosum.  The  peripheral  fibres  from  these  cells  bring  in  sensory 
impulses  from  the  periphery,  and  their  central  fibres  convey  the  impulses  to  the  brain.  The 
latter  fibres  enter  the  medulla  in  the  filaments  of  attachment  in  the  postero-lateral  sulcus,  and, 
in  the  reticular  formation,  they  bifurcate  into  ascending  and  descending  branches  which  end  in 
the  nuclei  of  termination  of  the  vagus,  namely,  in  the  nucleus  alae  cinerese  in  the  floor  of  the 
fourth  ventricle  and  in  the  nucleus  tractus  solitarii.  The  tractus  solitarius  consists  largely  of  the 
descending  branches.  These  and  the  axones  arising  from  the  nuclei  of  termination  of  the  vagus 
descend  the  spinal  cord  to  terminate  about  ventral  horn  cells  which  give  origin  to  the  phrenic 
nerve  and  to  motor  fibres  supplying  other  muscles  of  respiration,  and  they  also  convey  impulses 
which  are  distributed  to  visceral  motor  neurones  along  the  spinal  cord. 

The  motor  fibres  spring  from  the  nucleus  ambiguus  and  from  the  dorsal  efferent  (motor) 
nucleus  of  the  vagus,  described  on  page  820.  They  join  the  sensory  fibres  in  the  reticular 
formation.  Some  of  the  motor  fibres,  especially  those  from  the  dorsal  efferent  nucleus,  are 
visceral  motor  fibres. 

The  central  connections  of  the  vagus  are  similar  to  those  of  the  glosso-pharyngeal  nerve 
(fig.  647).  Van  Gehuchten's  observations  point  to  the  conclusion  that  the  chief  nucleus  of 
termination  of  the  vagus  nerve  is  that  of  the  tractus  solitarius. 

THE  SPINAL  ACCESSORY  NERVE 

The  spinal  accessory  nerve  [n.  accessorius]  is  exclusively  motor.  It  consists  of 
two  parts,  the  accessory  or  superior,  and  the  spinal  or  inferior  part. 

The  fibres  of  the  accessory  or  superior  portion  [ramus  internus]  ("accessory 
vagus")  spring  chiefly  from  the  inferior  continuation  of  the  nucleus  ambiguus,  in 
common  with  the  motor  fibres  of  the  vagus  above,  and  they  pass  through  the 
reticular  formation  to  the  postero-lateral  sulcus  of  the  medulla,  where  they  emerge 
as  a  series  of  filaments,  below  those  of  the  vagus.  The  filaments  pierce  the  pia 
mater  and  unite,  as  they  pass  outward  in  the  posterior  fossa  of  the  cranium,  to 
form  a  part  of  the  nerve  which  enters  the  apertm-e  in  the  dura  mater  common  to 
the  vagus  and  spinal  accessory  nerves.  In  the  aperture  this  trunk  is  joined  by  the 
spinal  portion  of  the  nerve. 

The  spinal  or  inferior  portion  [ramus  externus]  arises  from  the  ventro-lateral 
cells  of  the  ventral  horn  of  the  cord  as  low  as  the  fifth,  and  rarely  the  seventh, 
cervical  nerve.  The  fibres  pass  dorsalward  and  lateralward  from  their  origins 
through  the  lateral  part  of  the  ventral  horn  and  through  the  lateral  funiculus  of 
white  substance,  and  they  emerge  from  the  lateral  aspect  of  the  cord  behind  the 
ligamentum  denticulatum,  along  an  oblique  line,  the  lower  fibres  passing  out 
immediately  dorsal  to  the  ligament,  and  the  upper  close  to  and  sometimes  in 
association  with  the  dorsal  roots  of  the  upper  two  spinal  nerves.  As  the  spinal 
fibres  pass  out  of  the  surface  of  the  cord  they  unite  to  form  an  ascending  strand 
which  enters  the  posterior  fossa  of  the  cranium,  through  the  foramen  magnum, 
and,  turning  lateralward,  blends  more  or  less  intimately  with  the  accessory  por- 
tion. Thus  combined,  the  nerve  enters  the  jugular  foramen  in  company  with  the 
vagus,  but  here  it  is  again  separated  into  its  two  branches,  which  contain  chiefly 
the  same  fibres  as  the  original  superior  and  inferior  parts. 

The  superior  branch,  or  accessory  portion  of  the  nerve,  gives  one  or  more  filaments  to  the 
jugular  ganghon  (ganglion  of  the  root  of  the  vagus),  and  then  joins  either  the  trunk  of  the  vagus 
directly  or  its  ganglion  nodosum,  the  fibres  of  the  branch  being  contributed  to  the  pharyngeal, 
laryngeal,  and  cardiac  branches  of  the  vagus.  Fibres  corresponding  to  the  white  rami  communi- 
cantes,  absent  in  the  cervical  nerves,  probably  enter  the  cervical  sympathetic  ganglion  through 
this  ramus  of  the  spinal  accessory  nerve.  The  fibres  from  the  accessory  to  the  vagus  therefore 
probably  include  visceral  motor  and  cardio-inhibitory  fibres. 

The  inferior  branch  or  the  spinal  portion  runs  backward  and  downward  under  cover  of  the 
posterior  belly  of  the  digastric  and  the  sterno-mastoid.  It  usually  crosses  in  front  of  and  to 
the  lateral  side  of  the  internal  jugular  vein  and  between  it  and  the  occipital  artery;  then  it 


GANGLIATED  CEPHALIC  PLEXUS  959 

pierces  the  slerno-mastoid,  supplies  filaments  to  it,  and  interlaces  in  its  substance  with  branches 
of  the  Second  cervical  nerve.  It  emerges  from  the  posterior  border  of  the  sterno-mastoid 
slightly  above  the  level  of  the  upper  border  of  the  thyreoid  cartilage,  passes  obliquely  downward 
and  backward  across  the  occipital  portion  of  the  posterior  triangle,  and  disappears  beneath  the 
trapezius  about  the  junction  of  the  middle  and  lower  thirds  of  the  anterior  border  of  that  muscle 
(fig.  743).  In  the  posterior  triangle  it  receives  communications  from  the  third  and  fourth 
cervical  nerves,  and  beneath  the  trapezius  its  fibres  form  a  plexus  with  other  branches  of  the 
same  nerves.  Its  terminal  filaments  are  distributed  to  the  trapezius  and  they  can  be  traced 
almost  to  the  lower  extremity  of  that  muscle. 

Central  connections. — The  nuclei  of  origin,  like  other  motor  nuclei,  are  connected  with  the 
somsesthetic  area  of  the  cerebral  cortex  of  the  opposite  side  by  the  pyramidal  fibres,  and  they  are 
associated  with  the  sensory  nuclei  of  other  cranial  nerves  by  the  medial  longitudinal  fasciculus, 
and  with  sensations  brought  in  by  the  spinal  nerves  by  the  fibres  of  the  fasciculi  proprii. 

THE  GANGLIATED  CEPHALIC  PLEXUS 

The  Sympathetic  Ganglia  of  the  Head  and  Their  Associations  with 
THE  Cranial  Nerves 

The  sympathetic  system  of  the  head,  like  that  of  the  remainder  of  the  body 
described  below,  is  arranged  in  the  form  of  a  continuous  gangHated  plexus  subdi- 
vided into  sub-plexuses.  Unlike  the  great  unpaired  prevertebral  plexuses  in  the 
thoracic  and  abdominal  cavities,  all  the  larger  sympathetic  ganglia  of  the  head  are 
paired,  gangha  corresponding  to  each  other  being  found  on  either  side.  Thus 
they  may  be  considered  as  an  upward  extension  of  the  series  of  paired  lumbar, 
thoracic  and  cervical  ganglia  belonging  to  the  sympathetic  trunks  lying  along 
either  side  of  the  vertebral  column.  Numerous  small  ganglia,  many  of  them 
microscopic,  occur  in  the  sub-plexuses  throughout  the  head.  These  are  irregular 
in  size  and  position  and  those  in  the  region  of  the  median  line  are  no  doubt 
unpaired. 

In  origin,  the  ganglia  of  the  cephalic  plexus  consist  of  cell-bodies  which,  in  the  early  stages 
of  development,  migrated  from  the  fundaments  of  the  ganglia  of  the  vagus,  glosso-phar3mgeal 
and  glosso-palatine  nerves,  and  most  especially  from  that  of  the  semilunar  (Gasserian)  ganglion 
of  the  trigeminus — a  developmental  relation  identical  with  that  of  the  remainder  of  the  sym- 
pathetic system  to  the  ganglia  of  the  spinal  nerves.  Just  as  is  known  for  the  spina!  ganglia, 
some  cell-bodies  destined  to  develop  into  sympathetic  neurones,  instead  of  migrating,  remained 
within  the  confines  of  the  ganglia  of  the  above  nerves,  in  company  with  the  cell-bodies  of  their 
sensory  neurones.  This  is  thought  to  be  especially  true  for  the  geniculate,  the  petrosal  and  the 
jugular  ganglion.  Therefore  these  ganglia  must  be  considered  as  in  small  part  sympathetic 
ganglia. 

The  gangliated  cephalic  plexus  could  properly  be  included  as  a  division  of  the  general  sym- 
pathetic system  described  later.  However,  because  its  larger  ganglia  are  so  intimately  asso- 
ciated with  branches  of  the  oculomotor,  trigeminal,  masticator,  glosso-palatine,  glosso-pharyngeal 
and  vagus  nerves,  it  is  customary  to  describe  it  in  connexion  with  the  cranial  nerves. 

The  larger  ganglia,  one  on  either  side  of  the  head,  comprise  the  ciliary  ganglion, 
the  spheno-palatine  (Meckel's)  ganghon,  the  otic  and  the  submaxillary  ganglion. 
To  these  must  be  added  portions  of  the  geniculate,  petrosal,  jugular  and  the  gan- 
ghon nodosum,  and  a  part  of  the  superior  cervical  sympathetic  ganglion.  The 
chief  relations  of  the  gangliated  cephalic  plexus  to  the  cranial  nerves  are  shown  in 
fig.  741. 

The  so-called  roots  and  branches  of  the  ganglia  carry  three  varieties  of  fibres: 
(1)  Sensory,  (2)  Motor  (visceral  motor  or  preganglionic),  and  (3)  Sympathetic. 
Most  roots  and  branches  are  mixed,  the  name  of  a  root  being  determined  only  by 
the  variety  of  fibres  predominating  in  it. 

A  bundle  of  sensory  fibres  going  to  a  ganghon  is  called  its  sensory  root.  Such,  however, 
cannot  comprise  a  true  root  since  none  of  its  fibres  arises  in  the  ganghon  and  very  few  or  none  may 
terminate  in  it.  The  only  sensory  fibres  terminating  in  a  ganghon  are  the  few  which  may  ap- 
proach it  in  any  of  the  roots  to  terminate  in  its  capsule  or  the  capsules  of  its  cells  and  convey 
impulses  of  general  sensibility  from  the  ganghon  to  the  central  nervous  system.  Almost  all  of 
the  fibres  of  a  "sensory  root"  merely  pass  around  or  through  a  ganglion  and  into  its  branches 
beyond,  which  they  borrow  as  paths  for  reaching  their  allotted  fields  of  distribution.  In  this 
relation  it  should  be  realized  that  while  the  cihary,  spheno-palatine,  otic  and  submaxillary 
ganglia  are  customarily  described  under  the  discussion  of  the  trigeminus,  this  nerve  has  func- 
tionally less  to  do  with  them  than  any  of  the  other  cranial  nerves  with  which  they  are  associated. 
Bundles  of  trigeminal  (sensory)  fibres,  traceable  in  gross  anatomy  because  meduUated  and  of 
appreciable  size,  pass  to  the  gangha,  but  only  to  pass  through  them  as  continuations  of  the  ter- 
minal branches  of  the  trigeminus. 

The  so-called  motor  root  of  a  ganglion  may  carry  two  kinds  of  fibres:  (a)  visceral  motor 
(preganglionic)  fibres,  arising  in  the  nuclei  of  origin  in  the  central  system  and  passing  in  the  trunk 


960 


THE  NERVOUS  SYSTEM 


and  branches  of  a  cranial  nerve  (oculomotor,  masticator,  etc.)  to  enter  and  terminate  in  contact 
with  the  ceU-bodies  of  the  ganglion,  which,  in  their  turn,  give  fibres  to  the  branches  of  the  gang- 
lion; (b)  fibres  of  the  same  origin,  name  and  course  but  which  may  pass  thi-ough  the  ganglion  to 
terminate  in  contact  with  the  cells  of  a  more  distant  ganglion.  Any  root,  the  motor  especially, 
may  contain  somatic  motor  fibres,  that  is,  fibres  of  central  origin  which  pass  through  the  gang- 
lion uninterrupted  and  into  its  branches  to  terminate  upon  the  fibres  of  skeletal  (voluntary) 
muscle. 

A  sympathetic  root  likewise  may  carry  two  and  perhaps  three  varieties  of  fibres  conforming 
to  the  name:  (a)  fibres  arising  from  the  cells  of  other  sympathetic  gangha  and  terminating  in  the 
ganghon  in  question;  (b)  fibres  arising  in  other  ganglia  which  pass  through  the  gangfion  in 
question  to  enter  its  branches  and  terminate  either  in  other  ganglia  or  upon  their  allotted  mus- 
cular or  glandular  elements.  A  third  is  the  fibre  of  the  sensory  sympathetic  neurone,  probably 
quite  rare,  which  may  arise  from  a  cell-body  in  the  ganglion  and  pass  centralward  in  its  root  and 
in  the  appropi'iate  cranial  nerve  to  terminate  about  a  cell-body  of  the  dorsal-root  or  spinal  gang- 
hon type,  the  central  process  of  which  latter  conveys  this  sensory  impulse  of  sympathetic  origin 
into  the  central  system  just  as  sensory  oranio-spinal  impulses  are  conveyed. 


Fig.  745. — Diagram  to  Illtjsteate  the  Sthtjctural  Relations  op  the  Roots  and 
BsANCHES  OF  A  CEPHALIC  SYMPATHETIC  GANGLION.  Sensory  fibres,  blue;  motor,  red; 
sympathetic,  black. 


Sensory  fibre  terminating  in  capsule 
of  ganglion  and  capsule  of  its  cells 


Sensory  root 


Sympathetic  root 


Branches  of  distribution 


The  branches  of  distribution  of  the  gangha,  the  larger  of  them  often  called  nerves,  are  those 
bundles  in  which  the  fibres,  both  arising  in  or  passing  through  the  gangha,  course  toward  their 
terminations  upon  their  allotted  tissue  elements  of  the  head.  The  larger  gangha  of  the  head  are 
described  as  each  possessing  the  three  roots  above  mentioned.  In  the  branches  pass  fibres 
motor  to  the  vessels  of  the  head,  to  the  intrinsic  muscles  of  the  eye  bulb,  to  the  [lacrimal  glands, 
the  mucous  membranes  (gland  cells)  of  the  nasal  and  oral  cavities  and  the  salivary  glands,  and 
sensory  fibres  conveying  impulses  from  these  structures. 

The  plexuses  into  which  the  gangliated  cephalic  plexus  is  divided  and  which  connect  the 
ganglia  to  form  it,  are  numerous  and  vary  greatly  in  size.  They  underlie  the  mucous  membranes 
and  they  surround  all  the  vessels  and  glands.  They  are  named  according  to  their  locahty. 
The  largest  of  them  are  the  tympanic  plexus  and  the  carotid  and  cavernous  plexuses.  They 
have  been  repeatedly  referred  to  in  their  relations  to  the  branches  of  the  cranial  nerves. 

Of  the  numerous  branches  described  from  the  superior  cervical  sympathetic  ganglion,  the 
two  large  ones  which  pass  upward  associate  it  especially  with  the  gangliated  cephalic  plexus. 
That  branch  known  as  the  internal  carotid  nerve  may  be  considered  as  the  direct  continuation 
upward  of  the  gangUated  sympathetic  trunk  of  the  body.  Through  the  branches  of  this,  the 
carotico-tympanic  and  the  deep  petrosal  nerves,  and  through  the  plexuses  derived  from  it,  the 
superior  cervical  ganghon  may  be  associated  with  practically  all  the  other  sympathetic  gangha 
of  the  head  (figs.  7.39  and  741).  The  other  branch  from  the  superior  cervical  ganghon,  the 
jugular  nerve,  associates  it  with  the  ganglia  of  the  glosso-pharyngeal  and  vagus  nerves,  with  the 
petrosa  ganghon  by  a  direct  branch  and  with  the  gangha  of  the  vagus  through  the  nodosal 
plexus.     These  latter  gangha  (and  the  nerves  to  which  they  belong)  are  connected,  chiefly  by 


THE  CILIARY  GANGLION  961 

way  of  the  tympanic  nerve,  which  is  from  the  petrosal  ganghon,  with  the  tympanic  plexus  (fig. 
741). 

The  tympanic  plexus  serves  as  a  common  point  of  distribution  of  fibres  from  the  superior 
cervical  sympathetic  ganglion,  the  gangha  of  the  vagus,  the  petrosal  ganghon,  and  the  geniculate 
ganglion,  to  the  cavernous  and  carotid  plexuses  and  to  the  spheno-palatine  and  otic  gangha. 
The  superior  cervical  ganglion  is  associated  with  the  cavernous  and  carotid  plexuses  direct  by 
the  internal  carotid  nerve  and  with  the  tympanic  plexus  by  the  Inferior  and  superior  carotico- 
tympanic nerves.  The  tympanic  plexus  receives  fibres  from  the  geniculate  ganghon  by  a  small 
geniculo-tympanic  branch  and  it  is  connected  with  the  spheno-palatine  ganghon  by  a  small 
anastomotic  or  tympano-petrosal  branch  to  the  great  superficial  petrosal  nerve,  and  with  the  otic 
ganglion  by  the  small  superficial  petrosal  nerve.  It  is  not  directly  connected  with  either  the 
cihary  or  the  submaxillary  ganglion.  However,  these  ganglia,  as  well  as  the  sphenopalatine 
and  otic,  are  connected  with  the  carotid  plexus  either  directly  by  named  branches  or  indirectly 
by  way  of  plexuses  derived  from  the  carotid.  The  geniculo-tympanic  branch,  the  tympanic 
nerve  and  twigs  of  the  nodosal  plexus  may  be  considered  as  analogous  to  the  rami  oommunicantes 
of^the  spinal  nerves. 

The  parotid  branches,  described  above  as  branches  of  the  auriculo-temporal  nerve  (from  the 
trigeminus)  and  as  containing  fibres  from  the  glossopharyngeal,  should  be  mentioned  here  as 
belonging  to  the  gangliated  cephalic  plexus.  These  branches  are  sympathetic  fibres  arising 
in  the  otic  ganglion  and  passing  as  branches  of  the  ganglion  to  the  auriculo-temporal  in  which 
they  remain  till  this  nerve  enters  the  parotid  gland  and  then  they  are  distributed  to  the  gland. 
The  visceral  motor  or  preganglionic  fibres  which  terminate  about  their  cells  of  origin  in  the  otic 
ganglion  are  derived  from  the  glosso-pharyngeal  nerve  and  pass  successively  through  the  tym- 
panic nerve,  the  tympanic  plexus,  and  the  small  superficial  petrosal  nerve  to  the  otic  ganglion. 

The  tympanic  nerve  (tympanic  branch  of  the  glosso-pharyngeal,  or  nerve  of  Jacobson),  the 
branch  to  the  Eustachian  tube  (ramus  tubes),  and  the  superior  and  inferior  carotico-lympanic 
branches  are  also  described  as  branches  of  the  glosso-pharyngeal  nerve.  These  must  hkewise 
be  considered  as  belonging  to  the  gangliated  cephahc  plexus. 

For  purposes  of  dissection,  it  may  be  more  expedient  to  consider  separately, 
with  its  roots  and  branches,  each  of  the  larger  ganglia  of  the  gangliated  cephalic 
plexus.  Under  this  heading  belong  in  part  the  geniculate  ganglion  of  the  glosso- 
palatine  nerve,  and  the  ganglia  of  the  glosso-pharyngeal  and  vagus,  especially  the 
petrosal  ganglion  of  the  former  and  the  jugular  ganglion  of  the  latter,  from  the 
fact  that  these  ganglia  contain  numerous  cell-bodies  of  sympathetic  neurones  as 
well  as  those  of  the  sensory  neurones  of  their  nerves. 

These  ganglia,  however,  have  been  described  with  their  corresponding  cranial  nerves.  The 
sensory  and  motor  roots  of  their  sympathetic  portions  are  contained  in  the  roots  of  their  nerves. 
The  geniculate  probably  has  no  sympathetic  root.  The  sympathetic  roots  of  the  petrosal  and 
jugular  ganglia  are  contained  in  the  branches  of  the  jugular  nerve.  The  chief  branches  of 
distribution  of  the  geniculate  are  the  geniculo-tympanic  branch,  the  great  superficial  petrosal 
nerve,  and  the  external  superficial  petrosal  nerve.  The  branches  of  the  petrosal  ganghon  are 
the  tympanic  nerve  and  its  branches  of  the  tympanic  plexus.  The  chief  branch  of  distribution 
from  the  jugular  ganglion  is  contained  in  the  auricular  branch  of  the  vagus,  or  nerve  of  Arnold, 
supplemented  by  sympathetic  fibres  in  the  trunk  of  the  vagus  itself. 

The  principal  cephalic  sympathetic  ganglia  are  the  ciliary,  the  spheno-palatine 
(Meckel's),  the  otic  and  the  submaxillary. 

The  Ciliary  Ganglion 

The  ciliary,  lenticular,  or  ophthalmic  ganglion  lies  in  the  posterior  part  of  the 
orbital  cavity,  about  6  mm.  in  front  of  the  superior  orbital  (sphenoidal)  fissure, 
to  the  lateral  side  of  the  optic  nerve,  and  between  the  optic  nerve  and  the  external 
rectus  muscle.  It  is  a  small,  reddish,  quadrangular  body,  compressed  laterally, 
and  it  measures  about  two  millimetres  from  before  backward  (fig.  734). 

Roots. — (o)  Its  motor  or  short  root  enters  its  lower  and  posterior  angle  and  is  a  visceral 
motor  branch  derived  from  the  branch  of  the  inferior  division  of  the  oculomotor  nerve  which 
supplies  the  inferior  oblique  muscle.  The  fibres  of  the  motor  root  probably  all  terminate  in  the 
ciliary  ganglion  in  connection  with  motor  sympathetic  neurones. 

(6)  The  sensory  or  long  root  passes  through  the  upper  and  back  part  of  the  ganglion.  It 
is  a  branch  of  the  naso-oiliary  (nasal)  nerve  and  is,  therefore,  composed  of  fibres  from  the 
trigeminus  passing  through  the  ganglion. 

(c)  The  sympathetic  root  consists  of  fibres  derived  from  the  cavernous  plexus  of  the 
sympathetic;  it  passes  to  the  ganglion  with  the  long  root. 

Branches. — From  three  to  six  short  ciliary  nerves  emerge  from  the  anterior  border  of  the 
ganglion ;  they  divide  as  they  pass  forward  and  eventually  form  about  twenty  nerves  which  are 
arranged  in  aii  upper  and  a  lower  group,  and  the  latter  group  is  joined  by  the  long  ciliary 
branches  of  the  naso-ciliary  (nasal)  nerve,  now  sensory  and  sympathetic  (fig.  73-1).  When 
they  reach  the  eyeball,  the  ciliary  nerves  pierce  the  sclerotic  around  the  optic  nerve,  and  pass 
forward  in  grooves  on  the  inner  surface  of  the  sclera.  The  sympathetic  fibres  contained  are  dis- 
tributed as  motor  fibres  to  the  ciliary  muscle,  the  sphincter  of  the  iris,  and  to  the  vessels  of  these 
and  of  the  cornea. 


962  THE  NERVOUS  SYSTEM 

The  Spheno-palatine  or  Meckel's  Ganglion 

This  ganglion  is  associated  with  the  maxillary  nerve  (fig.  743).  It  is  a  small 
reddish-grey  body  of  triangular  form,  which  is  flattened  at  the  sides,  and  measiu-es 
about  five  millimetres  from  before  backward.  It  lies  deeply  in  the  pterygo- 
palatine (spheno-maxillary)  fossa  at  the  lateral  side  of  the  spheno-palatine  fora- 
men and  in  front  of  the  anterior  end  of  the  pterygoid  (Vidian)  canal.  It  is 
attached  to  the  maxillary  nerve,  from  which  it  receives  its  sensory  root,  and  it  is 
connected  with  the  Vidian  nerve,  which  furnishes  it  with  motor  and  sympathetic 
filaments  (fig.  739). 

The  exact  position  of  the  ganghon  depends  upon  the  size  and  shape  of  the  sphenoidal  air 
cells.  When  these  are  small,  or  high  and  narrow,  the  ganglion  lies  lateral  to  them;  when  they 
are  large,  or  broad  and  fiat,  the  ganglion  lies  inferior  to  them.  Sometimes  it  may  lie  anterior 
to  them  if  the  cells  are  short  from  in  front  backward.  The  ganglion  may  be  reached  with  ease 
by  chipping  away  the  bone  around  the  sphenoidal  air  cells  after  the  skull  is  divided  sagitally. 

Roots. — (a)  Its  motor  root,  consisting  of  visceral  motor  fibres  of  the  glosso-palatine  nerve, 
is  contained  in  the  great  superficial  petrosal  nerve  which  is  incorporated  in  the  Vidian  nerve. 
It  springs  from  the  anterior  angle  of  the  geniculate  ganglion  and  passes  through  the  hiatus 
of  the  facial  canal  (hiatus  Fallopii)  into  the  middle  fossa  of  the  cranium,  where  it  runs  forward 
and  medialward,  in  a  groove  on  the  upper  surface  of  the  petrous  part  of  the  temporal  bone,  to 
the  foramen  laoerum,  and  in  this  part  of  its  course  it  passes  beneath  the  semilunar  (Gasserian) 
ganghon  and  the  masticator  nerve.  In  the  foramen  lacerum  it  joins  with  the  great  deep  petrosal 
nerve  to  form  the  Vidian  nerve  (nerve  of  the  pterygoid  canal),  which  passes  forward  through  the 
pterygoid  (Vidian)  canal  and  its  motor  and  sympathetic  fibres  terminate  in  the  spheno-palatine 
ganglion  in  the  pterygo-palatine  (spheno-maxillary)  fossa.  The  great  superficial  petrosal  nerve 
contains  sensory  as  well  as  sympathetic  and  motor  fibres.  The  sensory  fibres  pass  through  the 
ganghon  and,  in  the  small  palatine  nerve,  descend  to  the  soft  palate,  where  they  terminate  in 
the  epithelium  covering  it  and  some  are  probably  concerned  with  peripheral  taste  organs 
found  there.  They  arise  from  the  cells  of  the  geniculate  ganglion  and  therefore  belong  to  the 
glosso-palatine  nerve. 

(6)  The  sympathetic  root  is  the  great  deep  petrosal  portion  of  the  Vidian  nerve.  This 
root,  which  is  of  reddish  colour  and  of  soft  texture,  springs  from  the  carotid  plexus  which  lies 
on  the  outer  side  of  the  internal  carotid  artery  in  the  carotid  canal.  It  enters  the  foramen 
lacerum  through  the  apex  of  the  petrous  portion  of  the  temporal  bone,  and  unites  with  the  great 
superficial  petrosal  branch  of  the  facial  nerve  to  form  the  Vidian  nerve.  The  great  superficial 
petrosal  nerve  also  carries  sympathetic  fibres  to  the  spheno-palatine  ganglion,  derived  from  the 
geniculate  ganglion  and  from  the  tj'mpanic  plexus. 

The  Vidian  nerve  [n.  canalis  pterygoidei]  commences  by  the  union  of  the  great  superficial 
and  deep  petrosal  nerves  in  the  foramen  lacerum,  and  runs  forward  through  the  pterygoid 
(Vidian)  canal  to  the  pterygo-palatine  (spheno-maxillary)  fossa  to  the  spheno-palatine  ganglion. 
The  Vidian  nerve  often  may  be  seen  in  a  ridge  of  bone  along  the  floor  of  the  sphenoidal  cells 
and  its  direction  there  depends  upon  the  position  of  the  spheno-palatine  ganglion.  While  it  is 
in  the  pterygoid  canal  the  Vidian  nerve  is  joined  by  a  sphenoidal  filament  from  the  otic  ganghon, 
and  it  gives  branches  to  the  upper  and  back  part  of  the  roof  and  septum  of  the  nose,  and  to  the 
lower  end  of  the  Eustachian  tube. 

(c)  The  sensory  roots  consist  of  the  sensory  fibres  mentioned  above  in  the  great  superficial 
petrosal  nerve  and  of  usually  two  spheno-palatine  branches  from  the  maxillary  nerve.  The 
majority  of  the  fibres  of  these  roots  do  not  join  the  ganghon,  but  pass  by  its  medial  side  and 
enter  the  palatine  branches. 

Branches. — The  branches  of  the  ganghon,  containing  sensory,  vaso-motor  and  secretory 
fibres,  are  orbital  or  ascending,  internal  or  nasal,  descending  or  palatine,  and  posterior  or  pharyn- 
geal. 

Ascending  branches. — The  orbital  or  ascending  branches  are  two  or  three  small  twigs 
which  enter  the  orbit  through  the  inferior  orbital  (spheno-maxillary)  fissure  and  proceed,  within 
the  periosteum,  to  the  inner  wall  of  the  orbit,  where  they  pass  through  the  posterior  ethmoidal 
foramen  and  through  the  foramina  in  the  suture  behind  that  foramen  to  be  distributed  to  the 
mucous  membrane  which  lines  the  posterior  ethmoidal  cells  and  the  sphenoidal  sinus. 

Internal  branches. — The  internal  or  nasal  branches  are  derived  in  part  from  the  medial 
side  of  the  ganglion,  but  are  also  largely  made  up  of  fibres  which  pass  from  the  spheno-palatine 
branches  of  the  maxillary  nerve  without  traversing  the  ganglionic  substance.  They  are  dis- 
posed in  two  sets,  the  lateral  and  the  medial  (septal)  posterior  superior  nasal  branches. 

The  lateral  posterior  superior  nasal  branches  are  six  or  seven  small  twigs  which  pass  through 
the  spheno-palatine  foramen,  and  are  distributed  to  the  mucous  membrane  covering  the  poster- 
ior parts  of  the  superior  and  middle  nasal  conchae  (turbinated  bones)  (fig.  732).  They  also 
furnish  twigs  to  the  lining  membrane  of  the  posterior  etlimoidal  cells. 

The  medial  posterior  superior  nasal  (septal)  branches,  two  or  three  in  number,  pass  medial- 
ward  through  the  spheno-palatine  foramen.  They  cross  the  roof  of  the  nasal  fossa  to  reach  the 
back  part  of  the  nasal  septum,  where  the  smaller  twigs  terminate.  The  largest  nerve  of  the  set, 
the  naso-palatine  nerve,  or  nerve  of  Cotunnius,  runs  downward  and  forward  in  a  groove  in  the 
vomer  between  the  periosteum  and  the  mucous  membrane  to  the  incisive  (anterior  palatine) 
canal,  where  it  communicates  with  the  nasal  branch  of  the  anterior  superior  alveolar  nerve. 
The  two  naso-palatine  nerves  then  pass  through  the  foramina  of  Scarpa  in  the  intermaxillary 
suture,  the  left  nerve  passing  through  the  anterior  of  the  two  foramina.  In  the  lower  part 
of  the  incisive  (anterior  palatine)  canal  the  two  nerves  form  a  plexiform  communication  (for- 


THE  SUBMAXILLARY  GANGLION  963 

merly  described  as  Cloquet's  ganglion)  and  they  furnisli  twigs  to  the  anterior  or  premaxillary 
part  of  the  hard  palate  behind  the  incisor  teeth.  In  this  situation  they  communicate  with  the 
anterior  palatine  nerves. 

Descending  branches. — The  descending  branches  are  the  great  or  anterior,  the  posterior, 
and  the  middle  (external)  palatine  nerves.  Like  the  internal  set  of  branches,  they  are  in  part 
derived  from  the  ganglion  and  in  part  are  directly  continuous  with  the  spheno-palatine  nerves 
(fig.  732). 

The  great  or  anterior  palatine  nerve,  its  sensory  fibres  derived  from  the  maxillary  nerve, 
arises  from  the  inferior  angle  of  Meckel's  ganglion,  and  passes  downward  through  the  pterygo- 
palatine canal,  accompanied  by  the  descending  palatine  artery.  Emerging  from  the  canal  at 
the  greater  (posterior)  palatine  foramen  it  divides  into  two  or  three  branches,  which  pass  for- 
ward in  gi-ooves  in  the  hard  palate  and  supply  the  glands  and  mucous  membrane  of  the  hard 
palate  and  the  gums  on  the  inner  aspect  of  the  alveolar  border  of  the  upper  jaw.  During  its 
cour.se  through  the  pterygo-palatine  canal  the  anterior  palatine  nerve  gives  off  the  posterior 
inferior  nasal  nerves.  These  nerves  pass  through  small  openings  in  the  perpendicular  plate 
of  the  palate  bone  to  supply  the  mucous  membrane  covering  the  posterior  part  of  the  inferior 
nasal  concha  (turbinated  bone)  and  the  adjacent  portions  of  the  middle  and  inferior  meatuses 
of  the  nose. 

The  posterior  or  small  palatine  nerve  passes  downward  through  a  lesser  palatine  foramen 
(accessory  palatine  canal),  and  enters  the  soft  palate,  distributing  branches  to  that  organ,  to 
the  uvula,  and  to  the  tonsil.  Its  sensory  fibres  are  derived  from  the  glosso-palatine  nerve, 
through  the  great  superficial  petrosal  nerve  and  through  the  spheno-palatine  ganglion.  It 
was  formerly  believed  to  convey  motor  fibres  from  the  facial  nerve  to  the  levator  palati  and 
azygos  uvulae,  but  it  is  now  beheved  that  these  muscles  are  supplied  by  the  spinal  accessory 
nerve  through  the  pharyngeal  plexus  (fig.  732). 

The  middle  (external)  palatine  nerve,  the  smallest  of  the  three,  in  part,  likewise  from  the 
glosso-palatine  nerve,  traverses  a  lesser  palatine  foramen  and  supplies  twigs  to  the  tonsil  and 
to  the  adjacent  part  of  the  soft  palate  (fig.  732). 

Posterior  branch. — The  pharyngeal  branch,  which  is  of  small  size,  passes  backward  and 
somewhat  medialward  through  the  pharyngeal  canal  accompanied  by  a  pharj'ngeal  branch 
of  the  spheno-palatine  artery.  It  is  distributed  to  the  mucous  membrane  of  the  uppermost 
part  of  the  pharynx,  to  the  upper  part  of  the  posterior  nares,  to  the  opening  of  the  Eustachian 
tube,  and  to  the  lining  of  the  sphenoidal  sinus.  Its  sensory  fibres  are  derived  from  the  maxillary 
nerve. 

The  Otic  Ganglion 

The  otic  or  Arnold's  ganglion  is  a  small  reddish-grey  body  which  is  associated 
with  the  mandibular  nerve.  It  lies  deeply  in  the  zygomatic  fossa,  immediately 
below  the  foramen  ovale,  on  the  inner  side  of  the  trunk  of  the  mandibular  nerve. 
It  is  in  relation  internally  with  the  tensor  palati,  which  separates  it  from  the  Eusta- 
chian tube.  In  front  of  it  is  the  posterior  border  of  the  pterygoideus  internus,  and 
behind  it  lie  the  middle  and  small  meningeal  arteries.  It  is  compressed  laterally, 
and  its  greatest  diameter,  which  lies  antero-posteriorly,  is  about  three  millimetres. 

Roots. — The  ganglion  is  closely  connected  with  the  nerve  to  the  pterygoideus  internus, 
through  which  it  may  receive  a  motor  root  from  the  masticator  nerve.  Through  the  small 
superficial  petrosal  nerve,  which  joins  the  upper  and  back  part  of  the  ganglion,  it  receives  a 
motor  root  from  the  glosso-palatine  nerve  and  sensory  and  motor  fibres  from  the  glosso- 
pharyngeal nerve.  It  receives  also  a  slender  sphenoidal  filament  from  the  Vidian  nerve. 
The  sympathetic  roots  are  derived  from  the  small  superficial  petrosal  nerve  and  from  the 
sympathetic  plexus  on  the  middle  meningeal  artery. 

Branches. — The  communicating  branches  which  pass  from  the  ganglion  are: — (1)  The 
filaments  to  the  chorda  tympani;  some  of  whose  fibres  probably  terminate  in  the  submaxillary 
ganglion;  (2)  filaments  to  the  auriculo-temporal  nerve;  (3)  filaments  to  the  spinous  nerve 
(the  recurrent  branch  of  the  mandibular  nerve).  The  branches  of  distribution  are  sympathetic 
to  the  vessels  and  somatic  motor  branches  to  the  tensor  tympani,  and  tensor  veli  palatini. 

The  Submaxillary  Ganglion 

The  submaxillary  ganglion  is  suspended  from  the  lingual  division  of  the  man- 
dibular nerve  by  anterior  and  posterior  branches.  It  is  a  small  reddish  body,  of 
triangular  or  fusiform  shape,  which  lies  between  the  mylo-hyoideus  and  hyo- 
glossus  and  above  the  duct  of  the  submaxillary  gland. 

Roots. — The  sensory  root  is  received  from  the  lingual  nerve.  The  motor  root  is  from  both 
the  masticator  nerve  by  way  of  the  lingual  nerve,  and  from  the  glosso-palatine  nerve  by  way  of 
the  chorda  tympani.  The  motor  fibres  pass  from  the  chorda  tympani  after  it  has  joined  the 
lingual,  and  the  sensory  fibres  come  directly  from  the  lingual  nerve.  The  sympathetic  root  is 
formed  by  filaments  from  the  sympathetic  plexus  on  the  facial  artery. 

Branches. — (a)  Five  or  six  glandular  branches  are  given  to  the  submaxillary  gland  and  to 
Wharton's  duct. 

(6)  Branches  to  the  lingual  nerve  and  the  sublingual  gland. 

(c)  To  the  mucous  membrane  of  the  floor  of  the  mouth. 


964 


THE  NERVOUS  SYSTEM 


II.  THE  SPINAL  NERVES 


The  spinal  nerves  are  arranged  in  pairs,  the  nerves  of  each  pair  being  symmet- 
rical in  their  attachment  to  either  side  of  their  respective  segment  of  the  spinal 
cord,  and,  in  general,  symmetrical  in  their  course  and  distribution.  There  are 
usually  thirty-one  pairs  of  functional  spinal  nerves.  For  purposes  of  description 
these  are  topographically  separated  into  eight  pairs  of  cervical  nerves,  twelve  pairs 
of  thoracic  nerves,  five  pairs  of  lumbar,  five  pairs  of  sacral,  and  one  pair  of  coccygeal 
nerves.  Occasionally  the  coccygeal  or  thirty-first  pair  is  practically  wanting, 
while,  on  the  other  hand,  there  may  be  frequently  found  small  filaments  represent- 
ing one  or  even  two  additional  pairs  of  coccygeal  nerves  below  the  thirty-first 
pair.  These  rudimentary  coccygeal  nerves  are  probably  not  functional.  They 
never  pass  outside  the  vertebral  canal,  and  often  even  remain  within  the  tubular 
portion  of  the  filum  terminale.  There  sometimes  occurs  an  increase  in  the  number 
of  vertebrae  in  the  vertebral  column  and  in  such  cases  there  is  always  a  correspond- 
ing increase  in  the  number  of  the  spinal  nerves. 

Origin  and  attachment. — Each  spinal  nerve  (unlike  the  cranial  nerves)  is 
attached  to  the  spinal  cord  by  two  roots: — a  sensory  or  afferent  dorsal  root  [radix 
posterior]  and  a  motor  or  efferent  ventral  root  [radix  anterior].  Each  dorsal  root 
has  interposed  in  its  course  an  ovoid  mass  of  nerve-cells,  the  spinal  ganglion,  and 
the  nerve-fibres  forming  the  root  arise  from  the  cells  of  this  ganglion  and  are  thus 
of  peripheral  origin.  The  fibres  composing  the  ventral  root,  on  the  other  hand,  are 
of  central  origin;  they  arise  from  the  large  motor  cells  of  the  ventral  horn  of  the 
grey  column  within  the  spinal  cord. 

Each  dorsal  root-fibre  upon  leaving  its  cell  of  origin  pursues  a  short  tortuous  course  within 
the  spinal  ganglion  and  ^hen  undergoes  a  T-shaped  bifurcation,  one  product  of  which  passes 
toward  the  periphery,  where  it  terminates  for  the  collection  of  sensations  and  is  known  as  the 
peripheral  branch,  or,  since  it  conveys  impulses  toward  the  cell-body,  the  dendrite  of  the  spinal 

Fig.  746. — Ventral  and  Dohsal  Views  op  Spinal  Cord  showing  Manner  of  Attachment 
OF  Dorsal  and  Ventral  Roots. 


Antero-lateral  sulcus  (line  of  ventral  i 
/"Anterior  median  fissure 


Posterior  median  sulcus 
/Posterior  in- 


ganglion  neurone.  It  is  more  correct,  however,  to  consider  the  T-fibre  as  a  bifurcated  axone. 
The  other  product  of  the  bifurcation,  the  central  branch,  passes  into  the  spinal  cord  and  in  its 
course  toward  the  cord  contributes  to  form  the  dorsal  root  proper. 

The  central  branches,  upon  emerging  from  the  spinal  ganglia,  form  a  single  compact  bundle 
at  first,  which  passes  through  the  dura  mater  of  the  spinal  cord  and  then  breaks  up  into  a  series, 
of  root-filaments  [fila  radicularia].  These  thread-like  bundles  of  fibres  spread  out  vertically 
in  a  fan-like  manner  and  enter  the  cord  in  a  direct  linear  series  along  its  postero-lateral  sulcus. 
The  fibres  of  the  ventral  root  emerge  from  the  cord  in  a  series  of  more  finely  divided  root  fila- 
ments, which,  unlike  the  entering  filaments  of  the  dorsal  root,  are  not  arranged  in  direct  linear 
series,  but  make  their  exit  over  a  strip  of  the  ventro-lateral  aspect  of  the  cord  in  some  places  as 
much  as  two  millimetres  wide. 

As  they  enter  the  spinal  cord  the  fibres  of  the  dorsal  roots  undergo  a  Y-shaped  division, 
both  products  of  which  course  in  the  cord  longitudinally,  an  ascending  and  a  descending  branch. 
The  descending  or  caudal  branches  are  shorter  than  the  ascending,  and  soon  enter  and  terminate 


THE  SPINAL  NERVES  965 

about  the  cells  within  the  grey  column  of  the  cord,  forming  either  associational,  commissural, 
or  reflex  connections,  or  about  cells  whose  fibres  form  cerebellar  connections.  The  ascending 
or  cephalic  branches  are  either  short,  intermediate,  or  long.  The  short  and  intermediate 
branches  are  similar  in  function  to  the  descending  branches,  save  that  they  become  associated 
with  the  grey  substance  of  segments  of  the  cord  above  rather  than  below  the  level  of  their  en- 
trance. The  long  branches  convey  impulses  destined  for  the  structures  of  the  brain,  and  pass 
upward  in  the  fasciculus  gracilis  or  fasciculus  cuneatus  of  the  cord,  and  terminate  in  the  nuclei 
of  these  fasciculi  in  the  meduUa  oblongata  (figs.  618  and  620). 

Aberrant  spinal  ganglia. — In  serial  sections  on  either  side  of  the  spinal  ganglion  of  a  nerve 
there  may  often  be  found  outlying  cells  either  scattered  or  in  groups  of  sufficient  size  to  be  called 
small  gangUa.  Such  are  more  often  found  in  the  dorsal  roots  of  the  lumbar  and  sacral  nerves. 
These  cells  are  nothing  more  than  spinal  ganghon-cells  displaced  in  the  growth  processes, 
and  have  the  same  nature  and  function  as  those  in  the  ganghon.  In  some  animals  occasional 
cells  very  rarely  have  been  found  in  the  outer  portion  of  the  ventral  root.  These  probably 
represent  afferent  fibres  which  enter  the  cord  by  way  of  the  ventral  root.  Likewise,  especially 
in  the  birds  and  amphibia,  it  has  been  shown  that  occasional  efferent  fibres  may  pass  from  the 
grey  substance  of  the  cord  to  the  periphery  by  way  of  the  dorsal  instead  of  the  ventral  root. 

Relative  size  of  the  roots. — The  sensory  or  dorsal  root  is  larger  than  the  ventral 
root,  indicating  that  the  sensory  area  to  be  supplied  is  greater  and  perhaps  more 
abundantly  innervated  than  the  area  requiring  motor  fibres. 

It  has  been  shown  that  in  the  entire  thirty-one  spinal  nerves  of  one  side  of  the  body  of  man 
the  dorsal  root-fibres  number  653,627,  while  all  the  corresponding  ventral  roots  contain  but 
233,700  fibres,  a  ratio  of  3.2  :  1.  (Ingbert.)  In  the  increase  in  the  size  of  the  nerves  for  the 
supply  of  the  limbs  the  gain  of  dorsal  root  or  sensory  fibres  is  far  greater  than  the  gain  of  ventral 
root-fibres.  The  first  cervical  or  the  sub-occipital  nerve  is  always  an  exception  to  the  rule; 
its  dorsal  root  is  always  smaller  than  its  ventral,  and  in  rare  cases  may  be  rudimentary  or  entirely 
absent.  The  spinal  ganghon  and,  therefore,  the  sensory  root  of  the  coccygeal  nerve,  is  also 
quite  frequently  absent. 

The  dorsal  and  ventral  root-fibres  of  each  spinal  nerve  proceed  outward  from 
their  segment  of  attachment  to  the  spinal  cord,  pierce  the  pia  mater  and  arachnoid, 
collect  to  form  their  respective  roots,  and  pass  into  their  respective  intervertebral 
foramina.  On  the  immediate  peripheral  side  of  the  spinal  ganglion  the  two  roots 
blend,  giving  origin  to  the  thus  mixed  nerve-trunk.  As  the  trunk,  the  sensory 
and  motor  fibres  make  their  exit  from  the  vertebral  canal  through  the  interverte- 
bral foramen. 

Relation  to  the  meninges. — The  root  filaments  of  each  nerve  receive  connec- 
tive-tissue support  from  the  pia  mater  and  arachnoid  in  passing  through  them.  In 
the  sub-arachnoid  cavity  they  become  assembled  into  their  respective  nerve-roots; 
and  the  roots,  closely  approaching  each  other,  pass  into  the  dura  mater,  from  which 
they  receive  separate  sheaths  at  first,  but  at  the  peripheral  side  of  the  ganglion 
these  sheaths  blend  into  one,  which,  with  the  subsequent  blending  of  the  roots, 
becomes  the  sheath  or  epineurium  of  the  nerve  trunk.  By  means  of  the  sheaths 
derived  from  the  meninges,  especially  the  dura,  the  nerve-roots  and  the  trunk  are 
attached  to  the  periosteum  of  the  margins  of  the  intervertebral  foramina  and 
thus  are  enabled  to  give  some  lateral  support  to  the  spinal  cord  in  the  upper  por- 
tion of  the  canal. 

The  majority  of  the  spinal  ganglia  lie  in  the  intervertebral  foramina,  closely  ensheathed, 
and  thus  outside  the  actual  sac  or  cavity  of  the  dura  mater.  The  gangha  of  the  last  lumbar 
and  first  four  sacral  nerves  he  inside  the  vertebral  canal,  but  since  the  sheath  derived  from  the 
dura  mater  closely  adheres  to  them,  they  are  still  outside  the  sac  of  the  dura  mater.  The  gan- 
gha of  the  last  sacral  and  of  the  coccygeal  nerves  (when  present)  lie  in  tubular  extensions  of  the 
sub-dural  cavity,  and  thus  not  only  within  the  vertebral  canal,  but  actually  within  the  sac  of 
the  dura  mater.  The  trunk  of  the  first  cervical  nerve  is  assembled  within  the  sac  of  the  dura 
mater,  and,  therefore,  the  spinal  ganghon  of  this  nerve,  when  present,  may  he  within  the  sac. 

Course  and  direction  of  emergence. — Invested  with  the  connective-tissue 
sheath  derived  from  the  meninges,  each  thoracic,  lumbar  and  sacral  nerve  emerges 
from  the  vertebral  canal  through  the  intervertebral  foramen  below  the  correspond- 
ing vertebra,  and  all  the  nerves  are  in  relation  with  the  spinal  rami  of  the  arteries 
and  veins  associated  with  the  blood  supply  of  the  given  localities  of  the  spinal  cord. 

The  first  cervical  nerve  does  not  pass  outward  in  an  intervertebral  foramen  proper,  but 
between  the  occipital  bone  and  the  posterior  arch  of  the  atlas  and  beneath  the  vertebral  artery. 
Thus  the  eighth  or  last  cervical  nerve  emerges  between  the  seventh  cervical  and  the  first  thor- 
acic vertebra. 

The  first  and  second  pairs  of  cervical  nerves  pass  out  of  the  vertebral  canal  almost  at  right 
angles  to  the  levels  of  their  attachment  to  the  spinal  cord.  During  the  early  periods  of  develop- 
ment the  level  of  exit  of  each  pair  of  spinal  nerves  is  opposite  the  level  of  its  attachment  to  the 


966 


THE  NERVOUS  SYSTEM 


cord,  but,  owing  to  the  fact  that  in  the  later  periods  the  vertebral  column  grows  more  rapidly 
than  the  cord  and  increases  considerably  in  length  after  the  cord  has  practically  ceased  growing, 
all  the  spinal  nerves,  with  the  exception  of  the  first  two,  pass  downward  as  well  as  outward. 
The  obhquity  of  their  course  from  the  level  of  attachment  to  the  level  of  exit  increases  progres- 
sively from  above  downward,  and,  as  the  cord  ends  at  the  level  of  the  first  or  second  lumbar 
vertebra,  the  roots  of  the  lower  lumbar  and  of  the  sacral  nerves  pass  at  first  vertically  downward 
within  the  dura  mater,  and  form  aroimd  the  filum  terminale  a  tapering  sheaf  of  nerve-roots, 
the  Cauda  equina  (horse's  tail)  (fig.  613,  p.  773). 

Topography  of  attachment. — The  relations  between  the  levels  of  attachment  of 
the  spinal  nerves  to  the  cord  and  the  spinous  processes  of  the  vertebrae  situated 
opposite  these  levels  have  been  investigated  by  Nuhn  and  by  Reid.  The  follow- 
ing table  compiled  by  Reid  gives  the  extreme  limits  of  attachment  as  observed  in 
six  subjects. 


Table  of  Topogkaphy  of  Attachment  of  Spinal  Nerves  to  the  Spinal  Cord.     (Reid.) 

(A)  signifies  the  highest  level  at  which  the  root  filaments  of  a  given  nerve  are  attached 
to  the  cord,  and  (B)  the  lowest  level  observed.  For  example,  the  root  filaments  of  the  sixth 
thoracic  nerve  may  be  attached  as  high  as  the  lower  border  of  the  spinous  process  of  the  second 
thoracic  vertebra,  or  some  may  be  attached  as  low  as  the  upper  border  of  the  spinous  process  of 
the  fifth  thoracic  vertebra,  but  in  a  given  subject  they  do  not  necessarily  extend  either  as  high 
or  as  low  as  either  of  the  levels  indicated. 

Nerves 
Second  cervical   (A)  A  httle  above  the  posterior  arch  of  atlas. 

(B)  Midway  between  posterior  arch  of  atlas  and  spine  of  epistropheus. 
Third  "        (A)  A  Uttle  below  posterior  arch  of  atlas. 

(B)  Junction  of  upper  two-thirds  and  lower  third  of  spine  of  epistropheus. 
Fourth         "        (A)  Just  below  upper  border  of  spine  of  epistropheus. 

(B)  Middle  of  spine  of  third  cervical  vertebra. 
Fifth  "        (A)  Just  below  lower  border  of  spine  of  epistropheus. 

(B)  Just  below  lower  border  of  spine  of  fourth  cervical  vertebra. 
Sixth  "        (A)  Lower  border  of  spine  of  third  cervical  vertebra. 

(B)  Lower  border  of  spine  of  fifth  cervical  vertebra. 
Seventh       "        (A)  Just  below  upper  border  of  spine  of  fourth  cervical  vertebra. 

(B)  Just  above  lower  border  of  spine  of  sixth  cervical  vertebra. 
Eighth         "        (A)  Upper  border  of  spine  of  fifth  cervical  vertebra. 

(B)  Upper  border  of  spine  of  seventh  cervical  vertebra. 
First  thoracic      (A)  Midway  between  spines  of  fifth  cervical  and  sixth  cervical  vertebra. 

(B)  Junction  of  upper  two-thirds  and  lower  third  of  interval  between  seventh 
cervical  and  first  thoracic  vertebra. 
Second         "        (A)  Lower  border  of  spine  of  sixth  cervical  vertebra. 

(B)  Just  above  lower  border  of  spine  of  first  thoracic  vertebra. 
Third  thoracic     (A)  Just  above  middle  of  spine  of  seventh  cervical  vertebra. 

(B)  Lower  border  of  spine  of  second  thoracic  vertebra. 
Fourth         "        (A)  Just  below  upper  border  of  spine  of  first  thoracic  vertebra. 

(B)  Junction  of  upper  third  and  lower  two-thirds  of  spine  of  third  thoracic 
vertebra. 
Fifth  "        (A)  Upper  border  of  spine  of  second  thoracic  vertebra. 

(B)  Junction  of  upper  quarter  and  lower  three-quarters  of  spine  of  fourth 
thoracic  vertebra. 
Sixth  "        (A)  Lower  border  of  spine  of  second  thoracic  vertebra. 

(B)  Just  below  upper  border  of  spine  of  fifth  thoracic  vertebra. 
Seventh       "        (A)  Junction  of  upper  third  and  lower  two-thirds  of  spine  of  fourth  thoracic 
vertebra. 

(B)  Just  above  lower  border  of  spine  of  fifth  thoracic  vertebra. 
Eighth         "        (A)  Junction  of  upper  two-thirds  and  lower  third  of  interval  between  spines 
of  fourth  thoracic  and  fifth  thoracic  vertebra. 

(B)  Junction  of  upper  quarter  and  lower  three-quarters  of  spine  of  sixth 
thoracic  vertebra. 
Ninth  "        (A)  Midway  between  spines  of  fifth  thoracic  and  sixth  thoracic  vertebra. 

(B)  Upper  border  of  spine  of  seventh  thoracic  vertebra. 
Tenth  "        (A)  Midway  between  "spines  of  sixth  thoracic  and  seventh  thoracic  vertebra. 

(B)  Middle  of  the  spine  of  eighth  thoracic  vertebra. 
Eleventh     "        (A)  Junction  of  upper  quarter  and  lower  three-quarters  of  spine  of  seventh 
thoracic   vertebra. 

(B)  Just  above  spine  of  ninth  thoracic  vertebra. 
Twelfth       "        (A)  Junction  of  upper  quarter  and  lower  three-quarters  of  spine  of  eighth 
thoracic  vertebra. 

(B)  Just  below  spine  of  ninth  thoracic  vertebra. 
First  lumbar        (A)  Midway  between  spines  of  eighth  thoracic  and  ninth  thoracic  vertebrae. 

(B)  Lower  border  of  spine  of  tenth  thoracic  vertebra. 
Second         "        (A)  Middle  of  spine  of  ninth  thoracic  vertebra. 

(B)  Junction  of  upper  third  and  lower  two-thirds  of  spine  of  eleventh  thoracic 
vertebra. 


PRIMARY  DIVISIONS  OF  SPINAL  NERVES 


967 


Nerves 


Third 
Fourth 


Fifth 


First  sacral 

Fifth 

Coccygeal 


(A)  Middle  of  spine  of  tenth  thoracic  vertebra. 

(B)  Just  below  spine  of  eleventh  thoracic  vertebra. 

(A)  Just  below  spine  of  tenth  thoracic  vertebra. 

(B)  Junction  of  upper  quarter  and  lower  three-quarters  of  spine  of  twelfth 
thoracic  vertebra. 

(A)  Junction  of  upper  third  and  lower  two-thirds  of  spine  of  eleventh  thoracic 
vertebra. 

(B)  Middle  of  spine  of  twelfth  thoracic  vertebra. 

(A)  Just  above  lower  border  of  spine  of  eleventh  thoracic  vertebra. 

(B)  Lower  border  of  spine  of  first  lumbar  vertebra. 

(A)  Lower  border  of  spine  of  first  lumbar  vertebra. 

(B)  Just  below  upper  border  of  spine  of  second  lumbar  vertebra. 

Relative  size  of  the  nerves. — The  size  of  the  different  spinal  nerves  varies 
greatly.  Just  as  the  spinal  cord  shows  marked  enlargements  in  the  cervical  and 
lumbar  regions  necessitated  by  the  greater  amount  of  innervation  required  of  these 
regions  for  the  structures  of  the  upper  and  lower  limbs,  so  the  nerves  attached  to 
these  regions  are  considerably  larger  than  elsewhere. 

The  smaller  nerves  are  found  at  the  two  extremities  of  the  cord  and  in  the  mid-thoracic 
region.  The  smallest  nerve  is  the  coccygeal,  and  the  next  in  order  of  size  are  the  lower  sacral 
and  the  first  two  or  three  cervical  nerves.  The  largest  nerves  are  those  which  contribute 
most  to  the  great  nerve  trunks  for  the  innervation  of  the  skin  and  muscles  of  the  limbs: — the 
lower  cervical  and  first  thoracic  for  the  upper  limbs  and  the  lower  lumbar  and  first  sacral  for 
the  lower  Umbs.  The  nerves  gradually  increase  in  the  series  in  passing  from  the  smaller  toward 
the  larger. 


Fig.  747. — Diagrams  Illustrating  the  Origin  and  DisTRiBtrTioN  op  a  Typical  Spinal 

Nerve. 
A,  in  thoracic  region;  B,  in  region  of  a  limb  (highly  schematic). 


Medial 
branch 
'  Lateral 
branch 
Posterior 
primary 
division 
Anterior 
primary 
division 
Lateral 
branch 


Anterior 

or  ventral 

branch 


Medial 

branch 
Lateral 

branch 

Posterior 

primary 

\     division 

Anterior 

primary 

division 

Lateral 

or  dorsal 

\      branch 


Alimentary  canal 


The  primary  divisions  of  the  nerve-trunk. — A  typical  spinal  nerve  (middle 
thoracic,  for  example),  just  as  it  emerges  from  the  intervertebral  foramen,  divides 
into  four  branches: — the  two  large  primary  divisions;  viz.,  the  posterior  primary 
division  [ramus  posterior]  and  the  anterior  primary  division  [ramus  anterior]; 
third,  the  small  ramus  communicans,  by  which  it  is  connected  with  the  sympa- 
thetic; and  fourth,  the  smaller,  ramus  meningeus  {recurrent  branch),  which  im- 
mediately turns  centralward  for  the  innervation  of  the  membranes  and  vessels  of 
the  spinal  cord. 

In  general,  the  posterior  primary  division  passes  dorsalward  between  the  arches 
or  transverse  processes  of  the  two  adjacent  vertebrae  in  relation  with  the  anterior 
costo-transverse  ligament,  and  then  divides  (with  the  exception  of  the  first  cer- 
vical, the  fourth  and  fifth  thoracic,  and  the  coccygeal  nerves)  into  a  medial  (inter- 
nal) branch  and  a  lateral  (external)  branch.  The  medial  branch  turns  toward  the 
spinous  processes  of  the  vertebrse,  and  supplies  the  bones  and  joints  and  the  mus- 
cles about  them,  and  may  or  may  not  supply  the  skin  overlying  them.  The 
lateral  branch  turns  dorsalward  and  also  supplies  the  adjacent  muscles  and  bones, 
and,  if  the  medial  branch  has  not  supplied  the  overlying  skin,  it  also  terminates 
in  cutaneous  twigs. 


968 


THE  NERVOUS  SYSTEM 


In  the  upper  half  of  the  spinal  nerves  the  medial  branches  supply  the  skin;  in  the  lower  half, 
it  is  the  lateral  branches  which  do  so.  Both  branches  of  almost  aU  the  posterior  divisions,  espe- 
cially those  of  the  lower  nerves,  show  a  tendency  to  run  caudalward  and  thus  are  distributed 
to  muscles  and  skin  below  the  levels  of  their  respective  intervertebral  foramina.  They  never 
supply  the  muscles  of  the  limbs,  though  their  cutaneous  distribution  extends  upon  the  buttock, 
the  shoulder,  and  the  skin  of  the  back  of  the  head  as  far  upward  as  the  vertex.  The  posterior 
primary  divisions,  with  the  exception  of  those  of  the  first  three  cervical  nerves,  are  much  smaller 
than  the  anterior  primary  divisions. 

As  their  mixed  function  suggests,  the  posterior  primary  divisions  contain  both  nerve-fibres 
from  the  ventral  roots  and  peripheral  processes  of  the  spinal  ganghon-cells.  If  the  nerve-trunk 
on  the  immediate  peripheral  side  of  the  spinal  ganghon  be  teased,  bimdles  of  ventral  root-fibres 
may  be  seen  crossing  the  trunk  obliquely  to  enter  the  posterior  division,  and  fibres  from  the 
spinal  ganghon  may  be  also  traced  into  it.  Also  a  few  sympathetic  fibres,  derived  chiefly  by 
way  of  the  ramus  communicans,  are  known  to  course  in  it  for  distribution  in  the  walls  of  the 
blood-vessels,  etc.,  of  the  area  it  suppUes. 

The  anterior  primary  divisions  run  lateralward  and  ventralward.  With  the 
exception  of  the  first  two  cervical  nerves,  which  contribute  the  hypoglossal  loop, 
they  are  larger  than  the  posterior  primary  divisions,  and  appear  as  direct  continu- 
ations of  the  nerve-trunks.  Only  in  case  of  most  of  the  thoracic  nerves  do  thej^ 
remain  independent  in  their  course.  In  these  they  run  lateralward  and  ventral- 
ward  in  the  body-wall.     In  general,  these  divisions  supply  the  lateral  and  ventral 


Fig.  748.- 


-DlAGBAM   IlLTJSTRATING   THE    OrIGIN    OF   THE    COMPONENT   NEEVE-FrBKES    OF   THE 

Pbimaey  Divisions  of  a  Typical  Spinal  Nerve. 


Spinal  ganglion  neurone 
to  capsule  of  ganglion 


^  Gray  ramus  communicans 
—  White  ramus  com 


Sympathetic  ganglion  \  Gangliated 
Sympathetic  trunk       j       trunk 
Sympathetic  cell  body  in  spinal 
ganglion 


Posterior  primary  division  \  Spinal 
Anterior  primary  division   J   nerve 


^>^  ^Gray  ramus  communicans 
\         ^White  ramus  communicans 

Sensory  sympathetic  neurone 
Branch  to  prevertebral  ganglion 


parts  of  the  body,  the  limbs,  and  the  perineum.  In  the  cervical,  lumbar,  and 
sacral  regions  they  lose  their  anatomical  identity  by  dividing,  subdividing,  and 
anastomosing  with  each  other  so  as  to  give  rise  to  the  three  great  spinal  plexuses  of 
the  body — the  cervical,  the  brachial,  and  the  lumbo-sacral  plexuses.  The  major- 
ity of  the  thoracic  nerves  retain  the  typical  or  primitive  character  in  both  their 
anterior  and  posterior  primary  divisions.  In  them  the  anterior  division  (inter- 
costal nerve)  divides  into  a  lateral  or  dorsal  and  an  anterior  or  ventral  branch, 
both  of  which  subdivide.  The  lateral  branch  is  chiefly  cutaneous;  it  pierces  the 
superficial  muscles  and,  in  the  subcutaneous  connective  tissue,  divides  into  a 
smaller  posterior  and  a  larger  anterior  ramus,  which  respectively  supply  the  skin 
of  the  sides  and  the  lateral  part  of  the  ventral  surface  of  the  body.  The  anterior 
branch  continues  ventralward  iii  the  body-wall,  giving  off  twigs  along  its  course  to 
the  adjacent  muscles  and  bones,  and,  as  it  approaches  the  ventral  mid-fine  of  the 
body,  it  turns  sharply  lateralward  and  sends  rami  medialward  and  lateralward  to 
supply  the  skin  of  the  ventral  aspect  of  the  bodjr.  In  the  region  of  the  limbs  the 
typical  arrangement  is  interfered  with  in  that  what  corresponds  to  the  lateral  and 
anterior  branches  of  the  division  are  carried  out  into  the  limbs  for  the  skin  and 
muscles  there,  instead  of  supplying  the  lateral  and  ventral  parts  of  the  body-wall. 


RAMI  COMMUNICANTES 


969 


Nerve-fibres  arising  in  the  spinal  ganglion  and  fibres  from  the  ventral  root  pass 
directly  from  the  nerve-trunk  into  the  anterior  primary  division  of  the  spinal 
nerve.  This  division  also  receives  sympathetic  nerve-fibres  by  way  of  the  ramus 
communicans.  These  latter  accompany  the  division  and  are  distributed  to  their 
allotted  elements  in  the  territory  it  supplies. 


Fig.  749. — Table  Giving  the  Approximate  Areas  of  Distribution  of  the  Different 
Spinal  Nerves  with  a  Diagram  showing  Their  Respective  Levels  of  Exit  from  the 
Vertebral  Column.     (Arranged  by  Dr.  Gowers.) 

MOTOR  SENSORY  REFLEX 


Sterno -mastoid 
Trapezius 


\  Serratus 
j  Shoulder 
Arm  }  muse. 


Flexors,  hip 

Extensors,  knee 


Extensors  (?■) 
Flexors,  knee  (?) 

Muscles  of  leg  m( 
ing  foot 

J  Perineal  and  anal 
muscles 


Neck  and  scalp 
1  Neck  and  shoulder 


I  Shoulder 
Arm 


[  Front  of  thorax 


Abdomen 

(.Umbilicus  10th) 


I-  Groin  and  scrotum 

I     (front)  ■  Cremasteric 

I  [  Lateral  side  !   |    | 

I  Knee-joint 


j  (  Medial  side 

'  Leg,  medial  side 
Buttock,  lower 


Back  of  thigh 

Leg    1 

and     }  except  medial 
I     [ foot    j    part 


I  Perineum  and  anus 


Foot-clonus 
Plantar 


The  rami  communicantes  are  small,  short,  thread-like  branches  by  which  the 
nerve-trunks  are  connected  with  the  nearest  ganglion  of  the  vertically  running 
gangliated  cord  of  the  sympathetic  (sympathetic  trunk).  The  trunk  or  anterior 
primary  division  of  every  spinal  nerve  has  at  least  one  of  these;  most  of  the  nerves 
have  two,  and  sometimes  there  are  three.  The  nerves  of  the  cervical  region  usu- 
ally have  but  one,  and  this  is  composed  largely  of  sympathetic  fibres  (grey 


970  THE  NERVOUS  SYSTEM 

ramus).     Where  there  are  two,  one  usually  contains  medullated  fibres,  chiefly 
from  the  ventral  root,  sufficient  to  give  it  a  whiter  appearance  (white  ramus). 

In  the  upper  cervical  and  in  the  sacral  regions  one  sympathetic  ganglion  may  be  connected 
with  two  or  more  spinal  nerves,  and  sometimes  one  nerve  is  connected  with  two  ganglia.  The 
rami  communicantes  of  the  spinal  nerves  are  equivalent  to  the  communicating  rami  connecting 
certain  of  the  cranial  nerves  with  the  sympathetic  system  (trigeminus,  glosso-pharyngeus,  vagus) . 
The  medullated  fibres  of  the  rami  and,  therefore,  the  white  rami  consist  chiefly  of  fibres  from  the 
spinal  nerves,  viz.,  fibres  from  the  spinal  ganglion-cells  which  enter  and  course  to  their  distri- 
bution through  branches  of  the  sympathetic  nerves,  visceral  afferent  fibres,  and  fibres  from 
the  ventral  roots  of  the  spinal  nerves  which  terminate  in  the  sympathetic  ganglia,  visceral 
efferent (preganghonic)  fibres.  Thus  the  white  rami  have  been  termed  the  visceral  divisions 
of  the  spinal  nerves.  The  grey  rami  consist  chiefly  of  sympathetic  fibres,  most  of  which  are 
non-meduUated  or  partially  medullated,  and  which  course  to  their  distribution  by  way  of 
the  spinal  nerves.  Some  of  the  sympathetic  fibres  terminate  in  the  spinal  ganghon,  afferent 
sympathetic  fibres  (fig.  748).  The  usual  absence  of  white  rami  communicantes  from  the  cervical 
nerves  is  explained  on  the  grounds — (1)  that  probably  relatively  few  efferent  visceral  fibres 
are  given  to  the  sympathetic  from  this  region  of  the  cord;  (2)  that  many  of  the  visceral  efferent 
fibres  which  do  arise  from  this  region  of  the  cord  probably  join  the  rootlets  of  the  spinal  accessory 
nerve  and  pass  to  the  sympathetic  system  through  the  trunk  of  this  nerve,  and  through  the  vagus 
with  which  it  anastomoses;  and  (3)  that  such  of  these  fibres  as  are  given  off  from  the  lower 
segments  of  the  cervical  region,  descend  the  cord  and  pass  out  by  way  of  the  upper  thoracic 
nerves  which  give  very  evident  white  rami  to  the  sympathetic. 

The  meningeal  or  recurrent  branch  (figs.  747,  748,  and  762)  is  very  small  and  variable, 
and  is  often  difficult  to  find  in  ordinary  dissections.  It  is  given  off  from  the  nerve-trunk  just 
before  its  anterior  and  posterior  primary  divisions  are  formed.  It  consists  of  a  few  peripheral 
branches  of  spinal  ganglion-cells  (sensory  fibres)  which  leave  the  nerve-trunk  and  re-enter  the 
vertebral  canal  for  the  sensory  innervation  of  the  meninges,  and  which  are  joined  by  a  twig 
from  the  grey  ramus  or  directly  from  the  nearest  sympathetic  ganglion  (vaso-motor  fibres). 
There  is  considerable  evidence,  both  physiological  and  anatomical,  obtained  chiefly  from  the 
animals,  which  shows  that  at  times  certain  of  the  peripheral  spinal  ganghon  or  sensory  fibres 
may  turn  backward  in  the  nerve-trunk  and  pass  to  the  meninges  within  the  ventral  root  instead 
of  contributing  to  a  recurrent  branch.  The  occurrence  of  such  fibres  in  the  ventral  root  explains 
the  physiological  phenomenon  known  as  'recurrent  sensibility.'  Likewise,  sympathetic  fibres 
entering  the  trunk  through  the  grey  ramus  may  pass  to  the  meninges  by  way  of  the  ventral 
root,  and  at  times  the  recurrent  branch  is  probably  absent  altogether,  its  place  being  taken 
entirely  by  the  meningeal  fibres  passing  in  the  ventral  root. 

Areas  of  distribution  of  the  spinal  nerves. — Both  the  posterior  and  anterior 
primary  divisions  divide  and  subdivide  repeatedly,  and  their  component  fibres  are 
distributed  to  areas  of  the  body  more  or  less  constant  for  the  nerves  of  each  pair, 
but  the  distribution  of  the  different  nerves  is  very  variable.  Corresponding  to 
their  attachment,  each  to  a  given  segment  of  the  spinal  cord,  the  nerves  have  pri- 
marily a  segmental  distribution,  but,  owing  to  the  developmental  changes  and 
displacement  of  parts  during  the  growth  of  the  body,  the  segmental  distribution 
becomes  greatly  obscured  and  in  some  nerves  practically  obliterated.  Naturally 
it  is  more  retained  by  the  nerves  supplying  the  trunk  than  by  those  contributing  to 
the  innervation  of  the  limbs  and  head,  and  the  areas  supplied  by  the  posterior 
primary  divisions  are  less  disturbed  than  those  supplied  by  the  anterior.  The 
segmental  areas  of  cutaneous  distribution  of  the  posterior  divisions  are  more  evi- 
dent than  the  areas  of  muscle  supplied  by  these  divisions,  from  the  fact  that  the 
segmental  myotomes  from  which  the  dorsal  muscles  arise  fuse  together  and  over- 
lap each  other  considerably  during  development.  No  nerve  has  a  definitely  pre- 
scribed area  of  distribution,  cutaneous  or  muscular,  for  its  area  is  always  consider- 
ably overlapped  by  the  areas  of  the  nerves  adjacent  to  it.  The  mid-thoracic 
nerves  more  nearly  supply  a  definitely  prescribed  belt  of  the  body. 


A.  POSTERIOR  PRIMARY  DIVISIONS 

The  posterior  primary  divisions  of  the  spinal  nerves  spring  from  the  trunks 
immediately  outside  the  intervertebral  foramina,  and  they  pass  dorsalward 
between  the  adjacent  transverse  processes.  With  the  exceptions  of  the  first  and 
second  cervical  nerves  they  are  smaller  than  the  corresponding  anterior  primary 
divisions,  which  in  these  nerves  is  smaller  from  the  fact  that  a  large  portion  of 
them  go  over  into  the  hypoglossal  or  cervical  loop.  The  posterior  primary  divi- 
sions, after  passing  between  the  transverse  processes  into  the  region  of  the  back, 
divide  into  medial  and  lateral  branches.  This  division,  however,  does  not  occur 
in  the  cases  of  the  first  cervical,  the  last  two  sacral,  and  the  coccygeal  nerves. 


THORACIC  NERVES  971 

1.  Cervical  Nerves 

The  posterior  primary  division  of  the  first  cervical  or  sub -occipital  nerve 
springs  from  the  trunk,  between  the  vertebral  artery  and  the  posterior  arch  of 
the  atlas,  passes  dorsalward  into  the  sub-occipital  triangle,  and  breaks  up  into 
branches  which  supply  the  superior  oblique,  the  inferior  oblique,  and  the  major 
rectus  capitis  posterior  muscles,  which  form  the  lateral  boundaries  of  the  triangle. 
It  also  gives  a  branch  across  the  posterior  surface  of  the  major  rectus  capitis  pos- 
terior to  the  minor  rectus  capitis  posterior,  and  a  branch  to  the  semispinalis 
capitis  (complexus)  in  the  roof  of  the  triangle. 

It  communicates  with  the  medial  branch  of  the  posterior  primary  division  of  the  second 
cervical  nerve,  either  through  or  over  the  inferior  obUque  muscle,  and  it  occasionally  gives  a 
cutaneous  branch  to  the  skin  of  the  upper  part  of  the  back  of  the  neck  and  the  lower  part  of 
the  scalp. 

The  posterior  primary  division  of  the  second  cervical  nerve  is  the  largest  pos- 
terior division  of  all  the  cervical  nerves.  It  divides  into  a  small  lateral  branch  and 
a  very  large  medial  branch.  The  lateral  branch  gives  a  twig  to  the  inferior  oblique 
and  terminates  in  branches  which  supply  the  splenius  and  longissimus  capitis 
(trachelo-mastoid)  muscles.  The  medial  branch  is  the  greater  occipital  nerve. 
It  turns  around  the  lower  border  of  the  inferior  oblique,  crosses  the  sub-occipital 
triangle  obliquely,  pierces  the  semispinalis  capitis  (complexus),  the  tendon  of  the 
trapezius,  and  the  deep  cervical  fascia,  passing  through  the  latter  immediately 
below  the  superior  nuchal  line  of  the  occipital  bone,  and  it  divides  into  several 
terminal  sensory  branches  which  ramify  in  the  superficial  fascia  of  the  scalp. 

It  gives  one  or  two  motor  twigs  to  the  semispinalis  capitis  (complexus),  and  its  terminal 
branches  which  are  accompanied  by  branches  of  the  occipital  artery  supply  the  skin  of  the  scalp, 
above  the  superior  nuchal  Une,  as  far  forward  as  the  vertex.  Occasionally  one  branch  reaches 
the  pinna  and  supplies  the  skin  on  the  upper  part  of  its  medial  aspect.  As  it  turns  around  the 
inferior  oblique  it  gives  branches  which  join  with  the  medial  branches  of  the  posterior  primary 
divisions  of  the  first  and  third  cervical  nerves,  and  in  this  manner  a  small  looped  plexus  is  formed 
beneath  the  semispinalis  capitis  (complexus)  muscle,  the  posterior  cervical  plexus  of  Cruveilhier. 

The  posterior  primary  branches  of  the  third,  fourth,  and  fifth  cervical  nerves 

divide  at  the  lateral  border  of  the  semispinalis  colli  into  medial  and  lateral  branches. 
The  medial  branches  of  the  third,  fourth,  and  fifth  nerves  run  backward  between 
the  semispinalis  colli  and  capitis  (complexus),  supplying  both  muscles.  Then, 
after  passing  backward  between  the  semispinalis  capitis  and  the  ligamentum 
nuchse,  they  pierce  the  origin  of  the  trapezius  and  supply  the  skin  of  the  back  of 
the  neck.  The  greater  part  of  the  medial  branch  of  the  third  nerve,  which  runs 
upward  in  the  superficial  fascia  to  the  scalp,  is  called  the  third  or  smallest  occipital 
nerve ;  it  interlaces  with  the  greater  occipital  nerve,  and  it  supplies  the  skin  of  the 
upper  part  of  the  back  of  the  neck,  near  the  middle  line,  and  the  skin  of  the 
scalp  in  the  region  of  the  external  occipital  protuberance. 

The  medial  branches  of  the  posterior  primary  divisions  of  the  sixth,  seventh, 
and  eighth  cervical  nerves  pass  to  the  median  side  of  the  semispinalis  colli,  between 
it  and  the  subjacent  multifidus  spinse,  and  they  end  in  the  neighbouring  muscles. 
The  lateral  branches  of  the  posterior  primary  divisions  of  the  last  five  cervical 
nerves  are  small  and  they  are  distributed  to  the  longissimus  capitis  (trachelo- 
mastoid),  the  ilio-costalis  cervicis  (cervicalis  ascendens),  the  longissimus  cervicis 
(transversalis  cervicis),  the  semispinalis  capitis  (complexus),  and  the  splenius 
muscles. 

2.  Thohacic  Nerves 

The  posterior  primary  divisions  of  all  the  thoracic  nerves  divide  into  medial 
and  lateral  branches  while  in  the  vertebral  groove.  The  medial  branches  of  the 
upper  six  thoracic  nerves  pass  dorsalward  between  the  semispinalis  dorsi  and  the 
multifidus  spinje;  they  supply  the  spinalis  dorsi,  the  semispinahs  dorsi,  the  multi- 
fidus spinse,  the  rotatores  spinse,  the  intertransversales,  and  the  interspinales 
muscles;  and  they  end  in  cutaneous  branches  which,  after  piercing  the  trapezius, 
turn  lateralward  in  the  superficial  fascia  of  the  back,  and  supply  the  skin  as  far  as 
the  middle  of  the  scapula.  The  cutaneous  branch  of  the  second  nerve  is  the  larg- 
est; it  can  be  traced  lateralward  as  far  as  the  acromion  process.  The  medial 
branches  of  the  lower  six  thoracic  nerves  run  dorsalward,  between  the  longissi- 


972 


THE  NERVOUS  SYSTEM 


mus  dorsi  and  the  multifidus  spinae;  they  chiefly  end  in  twigs  to  the  adjacent 

muscles,  but  not  uncommonly  they  give  small  cutaneous  twigs  which  pierce  the 

latissimus  dorsi  and  the  trapezius  and  end  in  the  skin  near  the  mid-line  of  the  back. 

The  lateral  branches  of  the  upper  six  thoracic  nerves  pass  between  the  longis- 


FlG.    750. DlSTRLBCTION    OF    THE    POSTERIOR    PRIMARY    DIVISIONS    OP    THE^SPINAL    NeRVES. 

(Henle.) 


Semispinalis  colli- 


Multifidus  spinx 


Gluteus  mazimus 


simus  dorsi  and  the  ilio-costalis  dorsi  (accessorius)  and  end  in  those  muscles,  but 
the  lateral  branches  of  the  six  lower  nerves  are  longer;  they  pass  into  the  interval 
between  the  longissimus  dorsi  and  the  ilio-costalis  dorsi  and  give  branches  to  them, 
and  then  they  pierce  the  latissimus  dorsi  and  are  distributed  to  the  skin  of  the 
lower  and  lateral  part  of  the  back. 


ANTERIOR  PRIMARY  DIVISIONS  -  973 

3.  Lumbar  Nerves 

The  medial  branches  of  the  posterior  primary  divisions  of  all  the  lumbar 
nerves  end  in  the  multifidus  spinse  and  those  of  the  three  lower  nerves  send  very 
small  branches  to  the  skin  of  the  sacral  region. 

The  lateral  branches  of  the  upper  three  nerves  pass  obliquely  lateralward, 
supplying  twigs  to  the  adjacent  muscles,  pierce  the  posterior  layer  of  the  lumbar 
aponeurosis  at  the  lateral  bord^'  of  the  sacro-spinalis  (erector  spinse)  and  enter 
the  subcutaneous  tissue.  They  are,  for  the  most  part,  cutaneous,  forming  the 
superior  clunial  nerves,  which  cross  the  crest  of  the  iUum  and  pass  downward  to 
occupy  different  planes  in  the  thick  superficial  fascia  which  covers  the  upper  part 
of  the  gluteus  medius. 

The  branch  from  the  first  lumbar  nerve  is  comparatively  small,  and  occupies  the  most  super- 
ficial plane.  The  second  occupies  an  intermediate  position.  The  lateral  branch  from  the  third 
nerve  is  the  largest  of  the  three,  and  occupies  the  lowest  position;  it  distributes  branches  over 
the  gluteus  maximus  as  far  as  the  great  trochanter.  The  three  nerves  anastomose  with  one 
another  and  also  with  the  cutaneous  branches  from  the  posterior  primary  divisions  of  the  two 
upper  sacral  nerves. 

The  lateral  branch  of  the  fourth  lumbar  nerve  is  of  small  size  and  ends  in  the 
lower  part  of  the  sacro-spinalis  (erector  spinas).  That  of  the  fifth  lumbar  is 
distributed  to  the  sacro-spinalis  and  communicates  with  the  first  sacral  nerve. 

4.  Saceal  Nerves 

The  posterior  primary  divisions  of  the  upper  four  sacral  nerves  escape  from  the 
vertebral  canal  by  passing  through  the  posterior  sacral  foramina;  those  of  the 
fifth  sacral  nerve  pass  out  through  the  hiatus  sacralis  between  the  posterior  sacro- 
coccygeal ligaments.  Those  of  the  upper  three  sacral  nerves  divide  in  the  ordi- 
nary manner  into  medial  and  lateral  branches.  Those  of  the  lower  two  sacral 
nerves  remain  undivided. 

The  medial  branches  of  the  upper  three  sacral  nerves  are  of  small  size,  and  are 
distributed  to  the  multifidus  spinse.  The  lateral  branches  anastomose  with  one 
another  and  with  the  lateral  branch  of  the  last  lumbar  nerve,  forming  loops  on 
the  posterior  surface  of  the  sacrum  from  which  branches  proceed  to  the  posterior 
surface  of  the  sacro-tuberous  (great  sacro-sciatic)  ligament,  where  they  anasto- 
mose and  form  a  second  series  of  loops,  from  which  loops  two  or  three  branches  are 
given  off.  These  branches  pierce  the  gluteus  maximus  and  come  to  the  surface 
of  that  muscle  in  a  line  between  the  posterior  superior  spine  of  the  ilium  and 
the  tip  of  the  coccyx.  Then,  as  the  middle  clunial  nerves,  they  are  distributed 
to  the  integument  over  the  medial  part  of  the  gluteus  maximus,  and  communi- 
cate, in  their  course  through  the  superficial  fascia,  with  the  posterior  branches 
of  the  lumbar  nerves. 

The  posterior  divisions  of  the  lower  two  sacral  nerves  unite  with  one  another, 
with  the  posterior  branch  of  the  third  sacral,  and  with  the  coccygeal  nerve,  form- 
ing loops  from  which  twigs  pass  to  the  integument  over  the  lower  end  of  the 
coccyx. 

The  posterior  primary  division  of  the  coccygeal  nerve  is  also  undivided.  It 
separates  from  the  anterior  division  in  the  sacral  canal  and  emerges  through  the 
hiatus  sacralis,  pierces  the  hgaments  which  close  the  lower  part  of  that  canal, 
receives  a  communication  from  the  posterior  division  of  the  last  sacral  nerve,  and 
ends  in  the  skin  over  the  dorsal  aspect  of  the  coccyx. 

B.  ANTERIOR  PRIMARY  DIVISIONS 

The  anterior  primary  divisions  of  the  spinal  nerves  are  larger  than  the  pos- 
terior primary  divisions,  and  each  is  joined  near  its  origin  bj^  a  grey  ramus  commu- 
nicans  from  the  sympathetic  gangUated  cord  (figs.  751,  752,  762).  Beginning  with 
the  first  or  second  thoracic  nerve  and  ending  with  the  second  or  third  lumber 
nerve,  each  anterior  division  sends  to  the  gangliated  cord  a  white  ramus  communi- 
cans.  The  same  is  true  of  the  second  and  third  or  of  the  third  and  fourth  sacral 
nerves.     These  white  rami  are  appropriately  designated  the  visceral  branches  of 


974  THE  NERVOUS  SYSTEM 

the  spinal  nerves.  The  anterior  primary  divisions  of  the  cervical,  lumbar,  sacral, 
and  coccygeal  nerves  unite  with  one  another  to  form  plexuses,  but  the  anterior 
primary  divisions  of  the  thoracic  nerves,  except  the  first  and  last,  remain  separate, 
pursue  independent  courses,  and  each  divides,  in  a  typical  manner,  into  a  lateral 
and  an  anterior  or  ventral  branch.  The  separation  of  the  anterior  primary  divi- 
sion into  lateral  and  anterior  branches  is  not  confined  to  the  thoracic  nerves;  it 
occurs  also  in  the  lower  cervical,  the  lumbar,  and  the  sacral  nerves,  but  such  a  divi- 
sion cannot  be  clearly  distinguished  either  in  the  upper  cervical  nerves,  or  in  the 
coccygeal  nerve. 

1.  CERVICAL  NERVES 

The  anterior  primary  divisions  of  the  upper  four  cervical  nerves  unite  to  form 
the  cervical  plexus,  and  each  receives  a  communicating  branch  from  the  superior 
cervical  sympathetic  ganglion.  The  anterior  divisions  of  the  lower  four  cervical 
nerves  are  joined  by  the  greater  part  of  the  first  thoracic  nerve  and  they  unite  to 
form  the  brachial  plexus  (figs.  751,  754,  755).  The  fifth  and  sixth  cervical  nerves 
receive  communicating  branches  from  the  middle  cervical  sympathetic  ganglion, 
and  the  seventh  and  eighth  from  the  inferior  cervical  ganglion,  while  the  first 
thoracic  nerve  is  always  connected  with  the  first  thoracic  sympathetic  gang- 
lion by  a  grey  ramus  (figs.  751,  786)  and  in  most  cases  also  by  a  white  ramus 
communicans. 

THE  CERVICAL  PLEXUS 

The  cervical  plexus  (figs.  751,  752)  is  formed  by  the  anterior  primary  divisions 
of  the  upper  fom-  cervical  nerves  which  constitute  the  roots  of  the  plexus.  It 
lies  in  the  upper  part  of  the  side  of  the  neck,  under  cover  of  the  sterno-mastoid, 
and  upon  the  levator  scapulse  and  the  scalenus  medius.  It  is  a  looped  plexus, 
consisting  of  three  loops. 

A  large  part  of  the  anterior  primary  division  of  the  first  cervical  nerve  is  given 
to  the  hypoglossal  or  cervical  loop;  the  remainder  passes  to  the  cervical  plexus  and 
in  doing  so  it  runs  lateralward  on  the  posterior  arch  of  the  atlas  beneath  the  verte- 
bral artery,  then  it  turns  forward,  between  the  vertebral  artery  and  the  outer  side 
of  the  upper  articular  process  of  the  atlas,  and  finally  it  descends,  in  front  of  the 
transverse  process  of  the  atlas,  and  unites  with  the  upper  branch  of  the  second 
nerve,  forming  with  it  the  first  loop  of  the  plexus.  It  gives  branches  to  the  rectus 
capitis  lateralis,  longus  capitis  (major  rectus  capitis  anterior),  and  to  the  rectus 
capitis  anterior  (minor).  The  division  communicates  with  the  ganglion  of  the 
trunk  of  the  vagus  and  with  the  superior  cervical  ganglion  of  the  sympathetic 
system  (fig.  752) .  From  the  first  loop  of  the  plexus,  two  branches  of  the  division 
pass  over  into  the  sheath  of  the  hypoglossal  nerve  and  descend  with  it  to  contrib- 
ute to  the  hypoglossal  loop  [ansa  hypoglossi]  or  better,  the  cervical  loop.  The 
fibres  entering  the  sheath  of  the  hypoglossus,  after  giving  a  few  twigs  to  the 
gpnio-hyoid  and  thyreo-hyoid  muscles,  leave  the  sheath  as  the  descendens  cer- 
vicalis  (hypoglossi)  and  this  latter  joins  the  communicans  cervicalis,  (the  portion 
of  the  loop  from  the  second  and  third  cervical  nerves)  and  thus  completes  the 
cervical  or  hypoglossal  loop. 

This  loop  usually  may  be  found  between  the  sheaths  of  the  sterno-mastoid  muscle  and  the 
carotid  artery,  superficial  to  the  internal  jugular  vein;  sometimes  it  may  lie  in  the  carotid 
sheath  between  the  carotid  artery  and  the  internal  jugular  vein;  rarely  it  may  lie  dorsal  to  both 
the  artery  and  vein.  Sometimes  it  is  relatively  long,  descending  toward  the  sternum  below  the 
level  of  the  thyreoid  cartilage;  again  it  is  quite  short  and  occurs  near  the  level  of  the  hyoid 
bone.  The  descendens  cervicahs  (hypoglossi)  parts  company  with  the  hypoglossal  nerve  at 
the  level  at  which  the  nerve  curves  around  the  occipital  artery.  It  runs  downward  and  shghtly 
medialward  on  the  sheaths  of  the  great  vessels  and  occasionally  within  the  sheath  of  one  of 
them. 

The  second  cervical  nerve  (anterior  primary  division)  passes  behind  the  upper 
articular  process  of  the  axis  and  the  vertebral  artery,  and  between  the  inter- 
transverse muscles  extending  from  the  first  to  the  second  cervical  vertebrse,  to 
the  interval  between  the  scalenus  medius  and  the  longus  capitis  (rectus  capitis 
anterior  major),  where  it  divides  into  two  parts.  The  upper  part  ascends  and 
unites  with  the  first  nerve  to  form  the  first  loop  of  the  plexus,  and  the  lower  branch 
passes  downward  and  dorsalward  and  joins  the  upper  branch  of  the  third  nerve  in 


CERVICAL  PLEXUS 


975 


the  second  loop  of  the  plexus  (figs.  751,  752).  This  branch  gives  off  the  small 
occipital  nerve  and  a  filament  to  the  sterno-mastoid,  which  communicates  with 
the  spinal  accessory  nerve  in  the  substance  of  the  muscle,  and  it  gives  branches 
which  assist  in  forming  the  hypoglossal  or  cervical  loop  (ansa  hypoglossi)  the  cer- 
vical cutaneous  and  the  great  auricular  nerves  (fig.  752). 

Fig.  751. — Origin  of  the  Cervical  and  Brachial  Plexus.     (After  Toldt,  "Atlas  of  Human 
Anatomy,"  Rebman,  London  and  New  York.) 


Anatomy,"  Rebman 

Muscular  branch  to  rectus  capitis  anterior  and 
lateralis  and  longus  capitis        m^  \ 


Rectus  capitis  lateralis  s^^W, 


Muscular  branch  to  longus  capitis  and  longus  colli 


eating  branch  to  descendens 
2rvicalis  (hypoglossi) 


Small  occipital 
Communicating  branch  to  spinal  accessory 
Great  auricular   -,^ 
Cervical  cutaneous 

Muscular  branch 
Supra -da  viculaiis  -v;- 

Phrenic .-i^ 

Dorsal  scapul 
Supra-scapular 

Axillary 


Internal  carotid  artery 

Rectus  capitis  anterior 


Radial 
Musculo-cutaneous  . 


Medial  ulnar 
Anti -brachial 
cutaneous 


Internal    car- 
otid nerve 
First  cervical 

nerve 
Ramus  communi- 
cans 

Second  cervical 
nerve 

Superior  cervical 
ganglion 

Third    and   fourth 

cervical  nerves 
Ramus  communi- 
cans 

Vertebral  artery 

Ganglia  ted  trunk 

^  Fifth,    sixth    and 
seventh    cer- 
vical nerves 


Middle     cervical 
ganglion 

Eighth  cervical 

nerve 
Inferior   cervical 

ganghon 


First    thoracic 
nerve 

Vertebral 
exus 


Subscapular  ^'''''' 
Long  thoracic 


Serratus  anterior 

Anterior  thoracic 


Scalenus  medius 


Subclavian 
artery 


The  third  and  fourth  cervical  nerves  pass  behind  the  vertebral  artery  (fig.  751) 
and  between  the  intertransverse  muscles  to  the  interval  between  the  scalenus 
medius  and  the  longus  capitis  (rectus  capitis  anterior  major),  where  the  third 
unites  with  the  second  and  fourth  nerves  and  completes  the  lower  two  loops  of  the 
plexus.  The  anterior  primary  divisions  of  these  nerves  are  about  double  the  size 
of  the  preceding.     The  third  gives  off  branches  to  the  hypoglossal  loop,  to  the 


976 


THE  NERVOUS  SYSTEM 


larger  part  of  the  great  auricular  and  cervical  cutaneous  nerves,  a  branch  to  the 
phrenic,  a  branch  to  the  supra-clavicular  nerves,  and  muscular  branches  to  the 
scalenus  medius,  levator  scapulse,  longus  capitis,  and  trapezius  (fig.  752).  The 
trapezius  branch  joins  the  spinal  accessory  nerve  beneath  the  muscle.  The 
fourth  nerve  gives  a  branch  to  the  phrenic,  a  branch  to  the  supra-clavicular  nerves, 
and  muscular  branches  to  the  scalenus  medius,  levator  scapulae,  longus  colli,  and 
trapezius  (fig.  752).  The  branch  to  the  trapezius  unites  with  the  one  from  the 
third  nerve  and  joins  the  spinal  accessory  nerve  beneath  the  muscle. 

The  fibres  forming  the  cervical  (hypoglossal)  loop  innervate  all  the  muscles 
of  the  infra-hyoid  group,  though  twigs  to  the  genio-hyoid  and  thyreohyoid 
seemingly  enter  these  muscles  from  the  trunk  of  the  hypoglossus  (fig.  752). 

Fig.  752. — Diagram  op  the  Cervical  Plexus. 


Ganglion  of  trunk 
of  vagus 


Sterno-mastoid 
Small  occipital 

Great  auricular 

Scalenus  medius 

Spinal  accessory 

Cervical  cutaneous 

Scalenus 

medius 

Levator  scapulae - 
Sympathetic  - 


Longus  capitis 
Rectus  capitis  anterior 
Rectus  capitis  lateralis 

Hypoglossal  nerve 


Superior  cervical 
sympathetic  ganglion 


Scalenus  anterior 
S  t  e  r  n  o  -thyreoid 


Trapezius  Posterior  Middle  _     Anterior  supraclavicular 

supraclavicular  supraclavicular 

The  nerve  to  genio-hyoid  is  given  off  from  the  trunk  under  cover  of  the  mylo-hyoid  in  com- 
mon with  the  terminal  branches  of  the  hypoglossal  proper  going  to  the  intrinsic  muscles  of  the 
tongue.  The  nerve  to  the  thyreo-hyoid  muscles  leaves  the  trunk  of  the  hypoglossal  near  the 
tip  of  the  great  cornu  of  the  hyoid  bone,  running  obUquely  downward  and  medianward  to  reach 
its  muscle.  A  twig  to  the  anterior  belly  of  the  omo-hyoid  is  given  from  the  upper  part  of  the 
descendens  cervicalis  and  the  nerves  for  the  sterno-hyoid,  the  sterno-thyreoid  and  the  pos- 
terior belly  of  the  omo-hyoid  are  supplied  from  the  turn  of  the  loop  (fig.  7.52).  The  nerves  to 
the  sterno-hyoid  and  sterno-thyreoid  send  twigs  downward  in  the  muscles  behind  the  manubrium 
sterni  and  fibres  from  these  in  rare  cases  join  the  phrenic  nerve  in  the  thorax.  The  nerve  to 
the  posterior  belly  of  the  omo-hyoid  courses  as  a  loop  in  the  cervical  fascia  below  the  central 
tendon  of  its  muscle. 

Each  root  of  the  cervical  plexus  receives  a  communicating  grey  ramus  from 
the  superior  cervical  ganglion  of  the  sympathetic,  and  from  the  roots  and  loops  of 


BRANCHES  OF  CERVICAL  PLEXUS 


977 


the  plexus  a  number  of  branches  arise  which  form  two  main  groups,  the  superficial 
and  the  deep. 

Superficial  Branches  of  the  Cervical  Plexus 

The  superficial  branches  are  described,  according  to  the  direction  in  which 
they  run,  as  ascending,  transverse,  and  descending  branches.  The  ascending 
branches  are  the  small  occipital  and  the  great  auricular  nerves.  There  is  only  one 
transverse  branch,  the  cervical  cutaneous  (transverse  cervical),  and  the  descending 
branches  are  distinguished  as  the  supraclavicular  nerves  and  the  cervical  (hypo- 
glossal) loop. 

The  ascending  branches. — (1)  The  small  occipital  nerve  (fig.  751)  arises  from 
the  second  and  third  cervical  nerves,  or  from  the  loop  between  them,  and  runs 


Fig.  753.- 


-SuPEHFiciAL  Branches  op  the  Cervical  Plexus. 
(After  Hirschfeld  and  Leveill6.) 


Posterior 
auricular 
nerve 


Auricular  br   of 

great  auricular    V* 
Cervical  brauch 
of  facial 


Cervical  cutaneous- ^ 


Branches  of  cervical  f 
cutaneous  nerve      \ 


Great  occipital 


Great  auricular 
Mastoid  br.  or  2nd 

small  occipital 
Spinal  accessory 

Twigs  from  the 
mastoid  branch 

Br.  to  levator 
scapulse 

Posterior  supra- 
clavicular 

Middle  supra- 
clavicular 


upward  and^dorsalward  to  the  posterior  border  of  the  sterno-mastoid,  where  it 
hooks  around  the  lower  border  of  the  spinal  accessory  nerve  and  then  ascends 
along  the  posterior  border  of  the  muscle  to  the  mastoid  process.  It  pierces  the 
deep  cervical  fascia  and  passes  across  the  posterior  part  of  the  insertion  of  the 
sterno-mastoid  into  the  superficial  fascia  of  the  scalp,  in  which  it  breaks  up  into 
auricular,  mastoid,  and  occipital  terminal  branches. 

(a)  The  auriculax  branch  runs  upward  and  slighly  forward  to  reach  the  integument  on  the 
upper  median  part  of  the  auricle  (pinna),  wliioh  it  supphes.  (6)  The  mastoid  branch  is  distrib- 
uted to  the  slvin  covering  the  base  of  the  mastoid  process,  (c)  The  occipital  branches  ramify 
over  the  occipitaUs  muscle  and  are  distributed  to  the  skin  of  the  scalp '  they  communicate  with 
one  another  and  with  the  great  occipital  nerve.     The  branches  of  the  small  occipital  nerve 


978  THE  NERVOUS  SYSTEM 

anastomose  with  twigs  of  the  posterior  auricular,  great  auricular,  and  great  occipital  nerves 
(fig.  753). 

(2)  The  great  atiricular  nerve  arises  from  the  second  and  third  cervical  nerves 
(figs.  751,  752).  It  accompanies  the  small  occipital  to  the  posterior  border  of 
the  sterno-mastoid,  but  at  that  point  it  diverges  from  the  small  occipital  (fig.  753) 
and  runs  upward  and  forward  across  the  sterno-mastoid  toward  the  angle  of  the 
mandible.  When  it  is  about  half-way  across  the  muscle  it  begins  to  break  up  into 
its  terminal  branches,  which  are  named,  according  to  the  area  of  their  distribution, 
mastoid,  auricular,  and  facial. 

As  the  nerve  ascends  obliquely  across  the  sterno-mastoid  it  is  embedded  in  the  deep  cervical 
fascia,  is  covered  by  superficial  fascia  and  the  platysma,  and  it  lies  parallel  with  and  slightly 
dorsal  to  the  external  jugular  vein,  (a)  The  mastoid  branch  is  small,  and  is  distributed  to  the 
integument  covering  the  mastoid  process.  It  anastomoses  with  the  posterior  auricular  and  small 
occipital  nerves.  (6)  The  auricular  branches  are  three  or  four  stout  twigs  which  interlace  with 
the  branches  of  the  posterior  auricular  nerve;  they  cross  the  superficial  surface  of  the  posterior 
auricular  branch  of  the  facial,  and  are  distributed  to  the  skin  on  the  back  of  the  auricle  with  the 
exception  of  its  uppermost  part.  One  or  two  twigs  pass  through  fissures  in  the  cartilage  of  the 
auricle,  and  are  distributed  to  the  integument  on  the  lateral  surface  of  the  lobule  and  the  lateral 
surface  of  the  lower  part  of  the  helix  and  anthelix.  (c)  The  facial  branches  pass  upward  and 
forward  among  the  superficial  lobules  of  the  parotid  gland,  and  supply  the  skin  over  that  gland 
and  immediately  in  front  of  it,  and  they  anastomose  in  the  substance  of  the  gland  with  the  cer- 
vico-facial  division  of  the  facial  nerve.  In  some  cases  fine  twigs  may  be  traced  forward  nearly 
to  the  angle  of  the  mouth. 

Transverse  branch  of  the  plexus. — The  superficial  cervical  cutaneous  nerve 

(transverse  cervical)  arises  from  the  second  and  third  cervical  nerves  (figs.  751, 
752),  and  appears  at  the  posterior  border  of  the  sterno-mastoid,  a  little  below  the 
great  auricular  nerve.  It  passes  transversely  across  the  sterno-mastoid  under 
cover  of  the  integument,  platysma,  and  external  jugular  vein,  and  divides  into  a 
number  of  twigs  which  spread  out  after  the  manner  of  a  fan,  and,  as  they  approach 
the  middle  line,  extend  from  the  chin  to  the  sternum  (fig.  753). 

The  upper  two  or  three  of  these  twigs  unite,  beneath  the  platysma,  with  the  cervical  (infra- 
mandibular)  branch  of  the  facial  and  thus  form  loops.  From  the  terminal  branches  of  the  nerve 
numerous  twigs  arise  which  pierce  the  platysma  and  end  in  the  skin  of  the  front  part  of  the  neck. 

The  descending  or  supra-clavicular  branches. — These  are  derived  from  the 
third  and  fourth  cervical  nerves  (figs.  751,  752),  and  arise  under  cover  of  the 
sterno-mastoid.  At  their  commencements  they  are  usually  united  with  the  mus- 
cular branches  destined  for  the  trapezius.  They  become  superficial  at  the  middle 
of  the  posterior  border  of  the  sterno-mastoid,  and  as  they  pass  downward  they 
pierce  the  deep  cervical  fascia.     They  include  the  following: 

(1)  The  anterior  supra-clavicular  (suprasternal)  branches  (fig.  753)  are  small,  and  cross 
over  the  clavicular  attachment  of  the  sterno-mastoid  to  reach  the  integument  over  the  upper  part 
of  the  manulDrium  sterni.  They  also  supply  the  sterno-clavicular  joint.  (2)  The  middle 
supra-clavicular  (supra-clavicular)  nerves  are  of  considerable  size.  They  cross  in  front  of  the 
middle  third  of  the  clavicle  under  cover  of  the  platysma,  and  are  distributed  to  the  skin  cover- 
ing the  upper  part  of  the  pectoralis  major  as  low  as  the  third  rib.  (3)  The  posterior  supra- 
clavicular (supra-acromial)  branches  (fig.  753)  cross  the  clavicular  insertion  of  the  trapezius 
and  the  acromion  process.  They  are  distributed  to  the  skin  which  covers  the  upper  two-thirds  of 
the  deltoid  muscle  and  they  supply  the  acromio-clavicular  joint. 

Deep  Branches  of  the  Cervical  Plexus 

The  deep  branches  of  the  plexus  pass  lateralward  and  dorsalward,  or  ventral- 
ward  and  medialward;  therefore  they  form  two  series,  the  lateral  and  the  medial. 

The  lateral  branches  of  the  deep  series  include  communicating  branches  from 
the  second,  third,  and  fourth  cervical  nerves  to  the  spinal  accessory  nerve,  and 
muscular  branches  to  the  sterno-mastoid  and  the  scalenus  medius,  levator  scap- 
ulse,  and  trapezius. 

The  communicating  branches. — The  communicating  branch  from  the  second  cervical 
nerve  is  ultimately  distributed  to  the  sterno-mastoid,  and  those  from  the  third  and  fourth  nerves 
end  in  the  trapezius. 

1.  The  nerve  to  the  sterno-mastoid  arises  from  the  second  cervical  nerve  (fig.  753).  It 
pierces  the  deep  surface  of  the  sterno-mastoid,  and  coinmunicates  within  the  muscle  with  the 
spinal  accessory  nerve. 

2.  The  nerves  to  the  scalenus  medius  (fig.  752)  are  derived  from  the  third  or  fourth 
to  the  eighth  cervical  nerves  close  to  their  exit  from  the  intervertebral  foramina. 


BRANCHES  OF  CERVICAL  PLEXUS  979 

3.  The  nerves  to  the  levator  scapulae  (fig.  752)  are  derived  from  the  third  and  fourth  cervical 
nerves,  and  occasionally  from  the  second  or  fifth.  They  pierce  the  superficial  surface  of  the 
levator  scapute,  and  supply  the  upper  three  divisions  of  that  muscle. 

4.  The  branches  to  the  trapezius  (fig.  752)  are  usually  in  the  form  of  two  stout  twigs  which 
are  given  off  by  the  third  and  fourth  cervical  nerves.  They  emerge  from  under  cover  of  the 
sterno-mastoid  at  its  posterior  border  and  cross  the  posterior  superior  triangle  of  the  neck  at  a 
lower  level  than  the  spinal  accessory  nerve  (fig.  753).  They  pass  under  cover  of  the  trapezius 
in  company  with  the  last-named  nerve,  and  communicate  with  it  to  form  the  subtrapezial 
plexus,  from  which  the  trapezius  is  supplied. 

The  medial  branches  of  the  deep  series  also  comprise  communicating  and  mus- 
cular branches. 

The  communicating  branches  (figs.  751,  752)  include  (1)  branches  which  connect  each 
of  the  first  four  cervical  nerves  with  the  superior  cervical  ganghon  of  the  sympathetic;  (2)  a 
branch  to  the  vagus;  (3)  a  branch  to  the  hypoglossal;  and  (4)  branches  which  pass  from  the 
second  and  third  cervical  nerves  to  the  descendens  cervicalis  (hypoglossi) .  The  ultimate  dis- 
tribution of  the  twigs  connected  with  the  sympathetic  and  the  vagus  nerves  is  not  known,  but 
the  fibres  which  pass  to  the  hypoglossal  nerve  pass  from  it  to  the  thyreo-hyoideus  muscle,  and 
to  the  descendens  cervicalis  and  the  latter  joins  with  the  branches  from  the  second  and  third 
cervical  nerves,  forming  with  them  the  cervical  or  hypoglossal  loop  [ansa  hypoglossi]  which 
lies  on  the  carotid  sheath.  From  this  loop  the  two  beUies  of  the  omo-hyoid  muscle  and  the 
sterno-hyoid  and  sterno-thyreoid  muscles  are  supphed  as  described  above. 

The  muscular  branches  supply  the  rectus  capitis  lateralis,  the  longus  cap'tis 
(rectus  capitis  anterior  major),  the  rectus  capitis  anterior  (minor),  the  scalenus 
anterior,  and  the  diaphragm.     The  nerve  to  the  latter  muscle  is  the  phrenic. 

1.  The  branch  to  the  rectus  capitis  lateralis  is  furnished  to  that  muscle  by  the  first  cervical 
nerve  as  it  crosses  the  deep  surface  of  the  muscle. 

2.  The  nerve  to  the  rectus  capitis  anterior  (minor)  is  given  off  by  the  first  nerve  at  the 
upper  part  of  the  loop  in  front  of  the  transverse  process  of  the  atlas. 

3.  The  longus  capitis  (rectus  capitis  anterior  major)  receives  twigs  from  the  upper  four 
cervical  nerves. 

4.  The  longus  colli  receives  branches  from  the  second,  third,  and  fourth  cervical  nerves, 
and  additional  branches  also  from  the  fifth  and  sixth  nerves. 

5.  The  phrenic  nerve  (fig.  752)  springs  chiefly  from  the  fourth  cervical  nerve, 
but  it  usually  receives  a  twig  from  the  third  and  another  from  the  fifth  cervical 
nerve,  a  small  communicating  branch  from  the  sympathetic,  and,  rarely,  a  branch 
from  the  vagus.  The  twig  from  the  fifth  cervical  nerve  is  frequently  connected 
with  the  nerve  to  the  subclavius.  After  the  union  of  its  roots  the  phrenic  nerve 
passes  downward  and  medialward  on  the  scalenus  anterior  (fig.  755).  In  this 
part  of  its  course  it  is  crossed  by  the  tendon  of  the  omo-hyoid  and  by  the  trans- 
verse cervical  and  transverse  scapular  (suprascapular)  arteries.  It  is  overlapped 
by  the  internal  jugular  vein,  and  it  is  covered  by  the  sterno-mastoid  muscle.  At 
the  root  of  the  neck  the  left  phrenic  nerve  lies  behind  the  terminal  portion  of  the 
thoracic  duct,  and  each  nerve  passes  off  the  anterior  border  of  the  scalenus  anterior 
and  descends  in  front  of  the  first  part  of  the  subclavian  artery  and  the  pleura  imme- 
diately below  that  artery;  each  nerve  passes  dorsal  to  the  terminus  of  the  sub- 
clavian vein,  crosses  either  in  front  of  or  dorsal  to  the  internal  mammary  artery  and 
gains  the  medial  surface  of  the  pleural  sac.  From  the  root  of  the  neck  the  rela- 
tions of  the  phrenic  nerves  differ.  The  right  phrenic  nerve  descends  along  the  medial 
surface  of  the  right  pleural  sac  and  crosses  in  front  of  the  root  of  the  lung.  It  is 
accompanied  by  the  pericardiaco-phrenic  artery  (comes  nervi  phrenici),  and  it  is 
in  relation  medially,  and  from  above  downward,  with  the  right  innominate  vein, 
the  superior  vena  cava,  and  the  pericardium,  the  latter  membrane  separating  it 
from  the  wall  of  the  right  atrium  (auricle) .  The  left  phrenic  nerve  descends  along 
the  medial  surface  of  the  left  pleural  sac  accompanied  by  the  pericardiaco-phrenic 
(comes  nervi  phrenici)  artery.  In  the  superior  mediastinum  it  lies  between  the 
left  common  carotid  and  the  left  subclavian  arteries,  and  it  crosses  in  front  of  the 
left  vagus,  the  left  superior  intercostal  vein,  and  the  arch  of  the  aorta.  Below 
the  arch  of  the  aorta  it  crosses  in  front  of  the  root  of  the  left  lung,  and  then  hes 
along  the  left  lateral  surface  of  the  pericardium,  which  separates  it  from  the  wall  of 
the  left  ventricle. 

Branches. — Both  phrenic  nerves  distribute  branches  to  the  pericardium  and  to  the  pleura. 
The  right  nerve  gives  off  a  branch,  pericardiac,  which  accompanies  the  superior  vena  cava  and 
supplies  the  pericardium.  Each  phrenic  nerve  divides  into  numerous  terminal  phrenico- 
abdominal  branches.  As  a  rule,  the  right  phrenic  nerve  divides  into  two  main  terminal  branches, 
an  anterior  and  a  posterior.     The  anterior  branch  runs  forward  and  one  of  its  terminal  filaments 


980 


THE  NERVOUS  SYSTEM 


anastomoses  with  the  phrenic  of  the  opposite  side  in  front  of  the  pericardium;  others  descend 
between  the  sternal  and  costal  attachments  of  the  diaphragm  into  the  abdomen,  where  some  of 
them  supply  the  diaphragm  and  others  descend  in  the  falciform  Ugament  to  the  peritoneum  on 
the  upper  surface  of  the  liver.  The  posterior  branch  passes  through  the  vena  caval  opening  and 
ramifies  upon  the  lower  surface  of  the  diaphragm,  anastomosing  with  the  diaphragmatic  plexus 
of  the  sympathetic,  and  its  terminal  branches  supply  the  muscular  fibi-es  of  the  right  half  of 
the  diaphragm,  the  inferior  vena  cava,  and  the  right  suprarenal  gland. 

The  left  phrenic  nerve  divides  into  several  branches.  One  of  the  most  anterior  branches 
anastomoses  with  the  right  phrenic  nerve;  the  others  pierce  the  diaphragm  and  ramify  on  its 
under  surface,  where  they  anastomose  with  filaments  of  the  left  diaphragmatic  plexus  of  the 
sympathetic  and  supply  the  left  half  of  the  diaphragm  and  the  left  suprarenal  gland.  The  left 
phrenic  nerve  is  considerably  longer  than  the  right  nerve,  partly  on  account  of  the  lower  level 
of  the  diaphragm  on  the  left  side,  and  partly  on  account  of  the  greater  convexity  of  the  left 
side  of  the  pericardium. 

THE  BRACHIAL  PLEXUS 

The  brachial  plexus  (figs.  751,  754,  755)  is  formed  by  the  anterior  primary 
divisions  of  the  four  lower  cervical  nerves  and  the  greater  part  of  that  of  the 


Fig.  754. — Diagbam  op  a  Common  Form  op  Bbachial  Plexus. 
The  posterior  cord  of  the  plexus  is  darkly  shaded. 
Fifth  cervical — ^j\      \( From  fourth  cervical 


Sixth  cervical 


Seventh  cervic; 


Eighth  cervical 


Long  thoracic. 

First  thoracic. 


First  intercostal 
Second  thoracic 


Second  intercostal 
Third  thoracic 


Third  intercostal 


ical^^ 


-Nerve  to  subclavius 

-  Suprascapular 


Anterior  thoracic  nerves 


Lateral  cord  of  plexus 


N.^ = — Radial  (musculo-spiral) 

—   ;_: <rX;^ — Medial  cord  of  plexus 


Thoraco-dorsal 
Median 


trinar 

Medial  antibrachial 
cutaneous 

Medial  brachial  cuta- 
neous (nerve  of 
Wrisberg) 


Intercosto-brachial         Lateral  cutaneous 


first  thoracic  nerve.     It  is  usually  joined  by  small  twigs  from  the  foxirth  cervical 
and  second  thoracic  nerves. 

The  anterior  primary  divisions  of  the  lower  four  cervical  nerves,  after  passing 
dorsal  to  the  vertebral  artery  and  between  the  anterior  and  posterior  parts  of  the 
intertransverse  muscles,  pass  into  the  posterior  triangle  in  the  interval  between 
the  adjacent  borders  of  the  anterior  and  middle  scalene  muscles,  where  the  fifth 
and  sixth  nerves  receive  a  grey  ramus  communicans  each  from  the  middle  cervical 
sympathetic  ganglion,  and  the  seventh  and  eighth  nerves  each  receive  a  grey 
ramus  from  the  inferior  cervical  sympathetic  ganglion.  The  first  thoracic  is 
connected  by  two  rami  communicantes  with  the  first  thoracic  sympathetic  gang- 
lion, and  it  divides  into  a  smaller  and  a  larger  branch.  The  smaller  branch  passes 
along  the  intercostal  space  as  the  first  intercostal  nerve,  and  the  larger  branch, 
after  being  joined  by  a  twig  from  the  second  thoracic  nerve,  passes  upward  and 
lateralward,  in  front  of  the  neck  of  the  first  rib  and  behind  the  apex  of  the  pleural 
sac,  into  the  lower  part  of  the  posterior  triangle  of  the  neck,  where  it  takes  part  in 
the  formation  of  the  plexus. 

The  anterior  primary  divisions  of  those  cervical  nerves  that  form  the  brachial 
plexus  may  be  considered  as  typically  giving  off  anterior  and  posterior  branches, 


THE  BRACHIAL  PLEXUS 


981 


except  that  the  fifth  and  sixth  nerves  often  unite  before  branching  and  give  off 
their  posterior  branches  as  a  common  trunk,  and  the  eighth  nerve  often  receives 
its  branch  from  the  first  thoracic  nerve  before  giving  off  its  posterior  branch. 

It  is  on  account  of  this  variation  in  the  point  of  union  of  the  fifth  and  sixth 
cervical  nerves  and  of  the  eighth  cervical  and  first  thoracic  nerves  that  so  many 
different  forms  of  the  plexus  have  been  pictured  and  described.  But  if  the  differ- 
ences in  primary  branching  be  borne  in  mind,  the  formation  of  the  plexus  is  always 
uniform  and  simple,  notwithstanding  its  different  appearances. 

Fig.  755. — The  Brachial  Plexus  and  its  Branches  op  the  Region  of  the  Neck  and 
Shoulder.     (After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 

Internal  jugular  vein 
Phrenic  /      "'T^ 

Branch  to  levator  scapulae  (  ' 


■  branch  of  cervical  V 


f  Dorsal  scapular 
Long  thoracic 
Supra-clavicular 
portion  of  plexus 
Subscapular 
Auxiliary  and  radial 
Twig  to  coraco-brachiahs 

Musculo-cutaneous 


__  Descendens  cer- 
vicalis  (hypoglossi) 
Sterno-tiyoideus 
^       and  sterno- 
thyreoideus 
Subclavian 
muscle  and 
nerve 
^^  Anterior 
^  .thoracic 


Muscular 

branches  of 

axillary 


Branches 

to  bicep 

brachii 


Lateral 
antibrachial  ' 
cutaneous 


/  L-one:  thoracic  to 

■'  serratus  anterior 

/  \^  Thoraco-dorsal  to 
''^  latissimus  dorsi 


\ 


Median 


Bracliial  artery 

~^  Ulnar 

Medial  antibrachi: 
cutaneous 


Three  cords  are  formed  from  these  branches  in  the  following  manner: — (1) 
The  lateral  (outer)  cord  [fasciculus  lateralis]  is  formed  by  the  anterior  branches  of 
the  fifth,  sbcth,  and  seventh  nerves;  (2)  the  medial  (inner)  cord  [fasciculus  medi- 
alis],  by  the  anterior  branches  of  the  eighth  cervical  and  first  thoracic  nerves;  and 
(3)  the  'posterior  cord  [fasciculus  posterior],  by  the  posterior  branches  of  all  of  these 
cervical  nerves. 

Relations. — The  plexus  extends  from  the  lateral  border  of  the  scalenus  anterior,  where  the 
roots  of  its  constituent  nerves  appear,  to  the  lower  border  of  the  peotoralis  minor,  where  each 


982  THE  NERVOUS  SYSTEM 

of  its  three  cords  divides  into  two  terminal  branches,  and  it  lies  in  the  posterior  triangle,  in  the 
root  of  the  neck,  and  in  the  axillary  fossa.  In  the  posterior  triangle  and  in  the  root  of  the  neck 
it  is  in  relation  liehind  with  the  scalenus  medius  (figs.  751,  755).  In  the  posterior  triangle  it  is 
covered  superficially  by  the  skin  and  superficial  fascia,  the  pJatysma,  the  supra-clavicular 
branches  of  the  cervical  plexus,  and  the  deep  fascia,  and  it  is  crossed  by  the  lower  part  of  the 
external  jugular  vein,  by  the  nerve  to  the  subclavius,  the  transverse  cervical  vein  and  the 
transverse  scapular  (supra-scapular)  vein,  the  posterior  belly  of  the  omo-hyoid  muscle,  and  by 
the  transverse  cervical  artery.  At  the  root  of  the  neck  it  lies  behind  the  clavicle  and  the  sub- 
clavius muscle,  and  the  transverse  scapular  (suprascapular)  artery  crosses  in  front  of  it.  In  the 
axillary  fossa  the  cords  are  arranged  around  the  axillary  artery,  the  lateral  (outer)  cord  lying 
lateral  to  the  artery,  the  medial  (inner)  cord  medial  to  it,  and  the  posterior  cord  dorsal  to  the 
artery.  In  this  region  the  posterior  relations  of  the  plexus  are  the  fat  in  the  upper  part  of  the 
fossa  and  the  subscapularis  muscle,  and  it  is  covered  in  front  by  the  pectoral  muscles  and  the 
coraco-clavicular  fascia.  The  lower  border  of  the  plexus  is  in  relation  in  the  posterior  triangle 
and  at  the  root  of  the  neck  with  the  pleura  and  the  first  rib,  and  it  is  overlapped  in  front  by  the 
third  part  of  the  subclavian  artery.  In  the  axillary  fossa  the  medial  cord  which  forms  the  lower 
border  of  the  plexus  is  overlapped  anteriorly  by  the  axillary  vein.  The  upper  and  lateral  border 
of  the  plexus  has  no  very  important  relations. 

In  gross,  the  brachial  plexus  may  be  formulated  as  beginning  with  five  nerves 
and  terminating  in  five  nerves,  with  its  intermediate  portions  displayed  in  sets  of 
threes.  It  begins  with  the  fifth,  sixth,  seventh  and  eighth  cervical  and  first 
thoracic  nerves;  it  terminates  as  a  plexus  with  the  formation  of  the  musculo- 
cutaneous, radial,  axillary,  median,  and  ulnar  nerves;  in  its  intermediate  portions, 
first  main  trunlcs  are  formed  and  these  divide  into  two  sets  of  threes  which,  by 
union,  give  rise  to  three  cords.  The  branches  from  the  cords  are  three  main 
lateral  branches  from  each  and  the  terminal  branches  of  the  plexus.  The  lateral 
branches,  according  as  they  are  given  off  above,  below,  and  dorsal  to  the  clavicle, 
are  grouped  as  the  supra-clavicular,  the  infra-clavicular  and  the  subscapular  por- 
tions of  the  plexus. 

The  branches  of  the  supra-clavicular  portion. — After  the  roots  of  the  plexus 
have  received  communications  from  the  sympathetic,  which  have  already  been 
referred  to,  they  give  off  a  series  of  muscular  branches,  viz. — the  posterior  thoracic 
nerves  (the  dorsal  scapular  and  the  long  thoracic  nerve),  the  suprascapular  nerve, 
a  twig  to  the  phrenic,  the  nerve  to  the  subclavius,  and  small  twigs  to  the  scalene 
muscles  and  the  longus  colli  muscle. 

The  posterior  thoracic  nerves  are  two  in  number: — (a)  the  dorsal  scapular 
(nerve  to  the  rhomboids)  arises  principally  from  the  fifth  cervical  nerve,  but  it 
frequently  receives  a  twig  from  tihe  fourth  nerve  (fig.  751). 

It  passes  downward  and  dorsalward,  across  the  middle  scalene,  parallel  with  and  below  the 
spinal  accessory  nerve  to  the  anterior  border  of  the  levator  scapulae,  under  which  it  disappears. 
It  continues  its  descent  under  cover  of  the  levator  scapulae  and  the  rhomboids  almost  to  the 
lower  angle  of  the  scapula,  lying  a  little  medial  to  the  posterior  border  of  the  bone,  and  it  supplies 
the  lower  fibres  of  the  levator  and  the  smaller  and  larger  rhomboid  muscles. 

(&)  The  long  thoracic  nerve  (external  respiratory  nerve  of  Bell)  supplies  the 
serratus  anterior. 

It  usually  arises,  by  three  roots,  from  the  fifth,  sixth,  and  seventh  cervical  nerves.  The 
last  is  sometimes  absent  (figs.  751  and  754).  The  upper  two  roots  traverse  the  substance  of 
the  scalenus  medius;  the  root  from  the  seventh  passes  in  front  of  that  muscle.  Twigs  are  fur- 
nished to  the  superior  portion  of  the  serratus  anterior  by  the  upper  two  roots;  lower  down  they 
unite  and  are  subsequently  joined  by  the  root  from  the  seventh  when  present.  The  trunk  of  the 
nerve  passes  downward  behind  the  brachial  plexus  and  the  first  stage  of  the  axillary  artery, 
and  runs  along  the  axihary  surface  of  the  serratus  anterior  (magnus),  supplying  twigs  to  each  of 
the  digitations  of  that  muscle  (fig.  755). 

The  suprascapular  nerve  (fig.  751)  supplies  the  supraspinatus  and  infraspi- 
natus muscles. 

It  receives  fibres  from  the  fifth  and  sixth  cervical  nerves,  and  occasionally  also  a  twig  from 
the  fourth  nerve.  It  is  a  nerve  of  considerable  size,  and  it  passes  downward  and  dorsalward 
parallel  with  the  dorsal  scapular  nerve,  at  first  along  the  upper  border  of  the  posterior  belly 
of  the  omo-hyoid  muscle,  then  internal  to  the  latter  muscle  and  under  cover  of  the  anterior 
border  of  the  trapezius  to  the  suprascapular  notch  (fig.  755),  where  it  comes  into  relation  with 
the  transverse  scapular  (suprascapular)  artery.  It  is  separated  from  the  artery  at  the  notch 
by  the  superior  transverse  ligament,  the  nerve  passing  through  the  notch  and  the  artery  above 
the  ligament.  After  entering  the  supraspinous  fossa  the  nerve  supplies  branches  to  the  supra- 
spinatus and  a  branch  to  the  shoulder-joint;  then  it  descends  through  the  great  scapular  notch 
between  the  bone  and  the  inferior  transverse  ligament  to  the  infraspinous  fossa,  where  it  ter- 
minates in  the  infraspinatus  muscle. 

The  twig  to  the  phrenic  (fig.  751)  arises  from  the  fifth  cervical  nerve  close  to  the  point  where 
the  latter  nerve  receives  its  twig  from  the  cervical  plexus. 


MEDIAL  BRACHIAL  CUTANEOUS  NERVE 


983 


The  nerve  to  the  subclavius  (fig.  755)  is  a  small  twig  which  arises  from  the  fifth  nerve  or 
from  the  upper  trunk  of  the  plexus,  but  occasionally  it  receives  additional  fibres  from  the 
fourth  and  sixth  nerves.  It  runs  downward  in  front  of  the  lower  part  of  the  plexus  and  the  third 
stage  of  the  subclavian  artery  and,  after  giving  off  sometimes  a  branch  to  the  phrenic,  pierces  the 
posterior  layer  of  the  coraco-clavicular  fascia,  and  enters  the  subclavius  at  its  lower  border._ 

Variety. — In  rare  cases  the  entire  phrenic  nerve  may  pass  vid  the  nerve  to  the  subclavius 
in  front  of  the  third  stage  of  the  subclavian  artery. 

The  scaleni  and  longus  colli  (figs.  751,  754)  are  supplied  by  twigs  which  arise  from  the  lower 
three  or  four  cervical  nerves  immediately  after  their  exit  from  the  intervertebral  foramina. 

The  lateral  branches  of  the  infra-clavicular  portion  of  the  brachial  plexus 
are  the  anterior  thoracic  nerves,  from  the  lateral  and  medial  cords  respectively, 
the  medial  antibrachial  (internal)  cutaneous  and  the  medial  brachial  (lesser 
internal)  cutaneous  nerves,  from  the  medial  cord,  and  the  subscapular  nerves 
and  thoraco-dorsal  from  the  posterior  cord. 

The  lateral  anterior  thoracic  nerve  joins  with  the  medial  to  form  a  loop  which 
supplies  the  pectoralis  major  and  minor. 


Fig.  756.- 


-DlSTBIBUTION  OF  CuTANEOrrS  NeRVES  ON  THE  ANTERIOR  AND  PoSTEHIOR  ASPECTS 

OF  THE  Superior  Extremity. 


Medial  anti- 
brachial 
cutaneous 


Supra-acromial 


Lateral  brachial 

cutaneous 
Intercosto- 

brachial 
Twig  of  medial 

antibrachial 

cutaneous 
Dorsal 

antibrachial 

cutaneous 


Lateral  anti- 
brachial 
cutaneous 
(musculo- 
cutaneous I 


Supraacromial 


It  arises  from  the  lateral  cord  of  the  plexus  and  contains  fibres  from  the  fifth,  sixth,  and 
seventh  cervical  nerves  (figs.  751,  754,  755).  After  joining  the  medial  anterior  thoracic  it  pierces 
the  coraco-clavicular  fascia  and  ends  in  branches  that  supply  the  pectoraUs  major  muscle. 
The  medial  anterior  thoracic  nerve  arises  from  the  medial  cord  (figs.  751,  754,  755),  contains 
fibres  from  the  eighth  cervical  and  first  thoracic  nerves,  and  passes  forward  between  the  first 
stage  of  the  axillary  artery  and  the  axillary  vein.  It  unites  with  a  branch  from  the  lateral 
anterior  thoracic,  to  form  a  loop  which  is  placed  in  front  of  the  first  stage  of  the  axillary  artery; 
it  gives  branches  to  the  pectoralis  minor,  and  branches  which  pass  through  the  latter  muscle  and 
end  in  the  pectorahs  major.  From  the  loop  additional  branches  are  furnished  to  the  pectoralis 
major. 

The  medial  brachial  (lesser  internal)  cutaneous  nerve,  or  nerve  of  Wrisberg 
(fig.  754),  arises  from  the  medial  cord  of  the  brachial  plexus  and  sometimes  con- 
tains fibres  from  the  eighth  cervical  and  first  thoracic  nerves,  but  usually  fibres 


984  THE  NERVOUS  SYSTEM 

from  the  first  thoracic  nerve  alone.  It  runs  downward  on  the  medial  side  of  the 
axillary  vein,  being  separated  by  that  vessel  from  the  ulnar  nerve,  and  it  continues 
downward  with  a  slight  inclination  dorsalward  under  cover  of  the  deep  fascia  on 
the  inner  side  of  the  arm.  At  the  middle  of  the  arm  it  pierces  the  deep  fascia, 
and  near  the  bend  of  the  elbow  it  turns  somewhat  sharply  dorsalward  to  supply 
the  integument  which  covers  the  olecranon  process  (fig.  756). 

As  it  traverses  the  axilla  the  nerve  of  Wrisberg  communicates  with  the  intercosto-braohial 
nerve,  forming  one,  or  sometimes  two  loops  (fig.  754).  In  its  course  clown  the  arm  it  gives  a 
few  fine  twigs  to  the  integument.  This  nerve  may  be  absent,  its  place  being  taken  by  the  inter- 
costo-braohial or  by  part  of  the  posterior  brachial  (.internal)  cutaneous  branch  of  the  radial 
(musculo-spu-al)  or,  rarely,  by  a  branch  from  the  fu'st  intercostal  nerve. 

The  medial  antibrachial  (internal)  cutaneous  nerve  (figs.  751  and  754)  arises 
from  the  medial  cord  in  close  relation  with  the  ulnar  nerve.  It  contains  fibres 
from  the  eighth  cervical  and  first  thoracic  nerves.  At  its  origin  it  lies  directly  on 
the  medial  side  of  the  axillary  artery  (fig.  755),  but  it  soon  becomes  more  super- 
ficial and  then  lies  in  the  groove  between  the  arterj^  and  the  vein.  In  the  upper 
two-thirds  of  the  arm  it  lies  in  front  and  to  the  medial  side  of  the  brachial  artery. 
It  divides  into  two  branches  (volar  and  ulnar)  which  supply  the  medial  aspect 
of  the  forearm. 

At  the  junction  of  the  middle  and  lower  thirds  of  the  arm  this  nerve  pierces  the  deep  fascia, 
in  company  with  the  basilic  vein,  and  divides  into  an  anterior  and  a  posterior  branch.  Previous 
to  its  division  it  gives  off  twigs  which  pierce  the  deep  fascia  and  supply  the  integument  of  the 
upper  and  medial  part  of  the  arm.  The  volar  (anterior)  branch  is  larger  than  the  ulnar  (pos- 
terior) ;  it  passes  in  front  of  or  dorsal  to  the  median  basilic  vein,  and  divides  into  several  twigs 
which  run  down  the  forearm,  supplying  the  integument  covering  its  anterior  and  medial  aspect 
as  far  as  the  wrist,  and  anastomosing  with  the  branches  of  the  ulnar  nerve.  The  ulnar  (posterior) 
branch  passes  downward  and  dorsalward  in  front  of  the  medial  condyle  of  the  humerus,  and  di- 
vides into  branches  which  supply  the  skin  on  the  postero-medial  aspect  of  the  forearm.  It 
anastomoses  with  the  dorsal  antibrachial  (inferior  external)  cutaneous  branch  of  the  radial 
(musculo-spiral)  nerve  and  the  dorsal  branch  of  the  ulnar  nerve). 

The  subscapular  nerves  are  branches  of  the  posterior  cord  (fig.  754).  They 
are  three  in  number,  are  distinguished  as  upper,  thoraco-dorsal  or  middle,  and 
lower,  and  are  distributed  to  the  subscapularis,  latissimus  dorsi,  and  teres  major 
muscles. 

The  upper  or  short  subscapular  nerve  is  derived  from  the  fifth  and  sixth  cervical  nerves. 
It  hes  in  the  upper  and  posterior  part  of  the  a.xillary  fossa,  and  it  is  distributed  exclusively  to 
the  subscapularis  muscle.     It  is  occasionally  double. 

The  thoraco-dorsal,  middle,  or  long  subscapular  nerve  consists  mainly  of  fibres  from  the 
seventh  and  eighth  cervical  nerves,  but  it  may  contain  fibres  from  the  fifth  or  the  sixth  nerve. 
It  passes  behind  the  axillary  artery,  accompanies  the  subscapular  artery  along  the  axillary  margin 
of  the  subscapularis  muscle,  and  ends  in  the  latissimus  dorsi  (fig.  755). 

The  lower  subscapular  nerve,  carrying  fibres  from  the  fifth  and  sixth  cervical  nerves, 
passes  behind  the  subscapular  artery,  below  the  circumflex  branch  (dorsahs  scapulae),  and  is 
distributed  to  the  teres  major,  and  furnishes  to  the  subscapularis  one  or  two  twigs  which  enter 
that  muscle  near  its  axillary  margin. 

The  terminal  branches  of  the  plexus  are  two  from  each  cord.  The  posterior 
cord  divides  into  the  axillary  (circumflex)  and  the  radial  (musculo-spiral)  nerves. 
The  lateral  cord  divides  into  the  musculo-cutaneous  nerve,  and  the  lateral  root  of 
the  median  nerve;  the  medial  cord  divides  into  the  ulnar  nerve,  and  the  medial 
root  of  the  median  nerve,  the  median  nerve  as  a  whole  being  one  of  the  five  ter- 
minal branches  of  the  plexus. 

The  axillary  (circumflex)  nerve  is  the  smaller  of  the  two  terminal  branches  of 
the  posterior  cord,  and  contains  fibres  from  the  fifth  and  sixth  cervical  nerves 
(figs.  751  and  754).  At  the  lower  border  of  the  subscapularis  it  passes  dorsalward 
and  accompanies  the  posterior  circumflex  artery  through  the  quadrilateral  space, 
which  is  bounded  by  the  teres  major,  long  head  of  triceps,  and  subscapularis  mus- 
cles, and  the  surgical  neck  of  the  humerus,  and  it  divides  into  a  smaller  superior 
and.  a  larger  inferior  division.  Previous  to  its  division  it  furnishes  an  articular 
twig  to  the  shoulder-joint.  This  twig  pierces  the  inferior  part  of  the  articular 
capsule. 

The  superior  division  accompanies  the  posterior  circumflex  artery  around  the 
neck  of  the  humerus,  and  gives  off  a  number  of  stout  twigs  which  enter  the  del- 
toid muscle  (fig.  755) .  A  few  fine  filaments  pierce  the  deltoid  and  end  in  the  integ- 
ument which  covers  the  middle  third  of  that  muscle. 


THE  RADIAL  NERVE  985 

The  inferior  division  divides  into  cutaneous  and  muscular  branches.  The 
cutaneous  branch  (the  lateral  brachial  cutaneous  nerve)  turns  around  the  pos- 
terior border  of  the  deltoid,  pierces  the  deep  fascia,  and  supplies  the  skin  covering 
the  lower  third  of  the  deltoid  and  a  small  area  of  integument  below  the  insertion  of 
the  muscle  (fig.  756).  One  muscular  branch  is  distributed  to  the  teres  minor;  it  ' 
swells  out  into  an  ovoid  or  fusiform,  reddish,  gangliform  enlargement  before 
entering  the  muscle.  Other  branches  supply  the  lower  and  posterior  part  of  the 
deltoid. 

The  radial  (musculo-spiral)  nerve  is  the  largest  branch  of  the  brachial  plexus. 
It  contains  fibres  from  the  sixth,  seventh,  and  eighth  cervical  and  sometimes 
from  the  fifth  cervical  and  first  thoracic  nerves  (figs.  751,  754).  It  commences 
at  the  lower  border  of  the  pectoralis  minor,  as  the  direct  continuation  of  the 
posterior  cord  of  the  brachial  plexus,  and  passes  downward  and  lateralward  in  the 
axillary  fossa  behind  the  third  part  of  the  axillary  artery  (fig.  755)  and  in  front  of 
the  subscapulars,  latissimus  dorsi,  and  teres  major  muscles.  From  the  lower 
border  of  the  axillary  fossa  it  descends  into  the  arm,  where  it  lies,  at'  first,  on  the 
medial  side  of  the  upper  third  of  the  humerus,  behind  the  brachial  artery  and  in 
front  of  the  long  head  of  the  triceps ;  then  it  runs  obliquely  downward  and  lateral- 
ward  behind  the  middle  third  of  the  humerus,  in  the  groove  for  the  radial  nerve 
(musculo-spiral  groove),  and  between  the  lateral  and  medial  heads  of  the  triceps. 
It  is  accompanied,  in  this  part  of  its  course,  by  the  profunda  artery.  At  the  junc- 
tion of  the  middle  and  lower  thirds  of  the  humerus  it  reaches  the  lateral  side  of  the 
arm,  pierces  the  external  intermuscular  septum,  and  runs  downward  and  forward 
between  the  brachio-radialis  and  extensor  carpi  radialis  longus  externally,  and 
the  brachialis  internally  (fig.  758),  and  it  terminates,  a  short  distance  above  the 
capitulum,  by  dividing  into  deep  and  superficial  terminal  branches.  In  the  last 
part  of  its  course  it  is  accompanied  by  the  anterior  terminal  branch  of  the  pro- 
funda artery. 

Branches. — The  branches  of  the  radial  or  musculo-spiral  nerve  are  cutaneous, 
muscular,  articular^  and  terminal,  but  for  practical  purposes  it  is  best  to  consider 
them  in  association  with  the  situations  of  their  origins.  While  it  is  in  the  axillary 
fossa  the  radial  (musculo-spiral)  nerve  gives  branches  to  the  medial  and  long 
heads  of  the  triceps  (fig.  758),  and  a  medial  cutaneous  branch.  The  branch  to  the 
long  head  of  the  triceps  at  once  enters  the  substance  of  the  muscle,  that  to  the 
medial  head  breaks  into  branches  which  terminate  in  the  muscle  at  different  levels, 
and  one  of  them,  the  ulnar  collateral  nerve,  accompanies  the  ulnar  nerve  to  the 
lower  part  of  the  arm.  The  posterior  brachial  (internal)  cutaneous  branch 
crosses  the  tendon  of  the  latissimus  dorsi,  passes  dorsal  to  the  intercosto-brachial 
(intercosto-humeral)  nerve,  pierces  the  deep  fascia,  and  is  distributed  to  the  skin 
of  the  middle  of  the  back  of  the  arm  below  the  deltoid. 

While  it  lies  behind  the  middle  third  of  the  humerus,  the  radial  nerve  gives 
branches  to  the  lateral  and  medial  heads  of  the  triceps  and  to  the  anconeus.  The 
latter  branch  descends  in  the  substance  of  the  median  head  of  the  triceps,  close  to 
the  bone,  and  it  is  accompanied  by  a  small  branch  of  the  profunda  artery.  The 
dorsal  antibrachial  (external)  cutaneous  branch,  passing  down  between  the 
lateral  and  median  heads  of  the  triceps,  divides  near  the  elbow  into  its  upper  and 
lower  branches  (fig.  756),  each  of  which  perforates  either  the  lateral  head  of  the 
triceps  muscle  near  its  attachment  to  the  humerus  or  the  external  intermuscular 
septum. 

The  upper  branch,  much  the  smaller,  pierces  the  deep  fascia  in  the  line  of  the  external  inter- 
muscular septum;  it  accompanies  the  lower  part  of  the  cephaUc  vein,  and  supphes  the  skin  over 
the  lower  half  of  the  lateral  and  anterior  aspect  of  the  arm.  The  lower  branch  is  of  considerable 
size.  It  pierces  the  deep  fascia  a  httle  below  the  upper  branch,  runs  behind  the  external  con- 
dyle, and  supplies  the  skin  of  the  middle  of  the  back  of  the  forearm  as  far  as  the  wrist,  an- 
astomosing with  the  medial  antibrachial  (internal)  cutaneous  and  musculo-cutaneous  nerves 
(fig.  759). 

After  the  radial  nerve  has  pierced  the  external  intermuscular  septum  it  gives 
branches  to  the  brachio-radialis,  extensor  carpi  radialis  longus,  and  to  the  lateral 
portion  of  the  brachialis  (fig.  759).  From  one  of  these  branches  an  articular 
filament  is  distributed  to  the  elbow-joint. 

The  terminal  branches  of  the  radial  nei"ve  are: — a  motor  branch,  the  deep 
radial,  to  the  supinator  and  extensor  muscles  of  the  forearm,  and  a  sensory 


THE  NERVOUS  SYSTEM 


branch,  the  superficial  radial,  which  supplies  the  dorsal  aspect  of  the  radial  half 
of  the  hand. 

The  deep  radial  [ramus  profundus]  (posterior  interosseous)  nerve  runs  down- 
ward in  the  interval  between  the  brachialis  and  extensor  carpi  radialis  longus. 
It  passes  in  front  of  the  lateral  part  of  the  elbow-joint,  and  after  giving  off  branches 
to  supply  the  extensor  carpi  radialis  brevis  and  supinator,  it  is  crossed  in  front 
by  the  radial  recurrent  artery  (fig.  759) .  It  then  runs  downward  and  dorsalward 
through  the  substance  of  the  supinator,  and  enters  the  interval  between  the 
superficial  and  deep  layers  of  muscles  at  the  back  of  the  forearm,  where  it  comes 
into  relation  with  the  posterior  interosseous  artery,  and  accompanies  it  across 

Fig.  767. — A  Dissection  or  the  Cutaneous  Nbeves  on  the  Dohsal  Aspect  of  the  Hand 

AND  Fingers.     (H.  St.  J.  B.) 

The  branches  of  the  median  nerve  are  shown  in  black. 


Dorsal  branch  of 
ulnar  nerve 


Branch  of  radial  (musculo-spiral) 


—  Superficial  radial  (radial)  nerve 


the  abductor  pollicis  longus.  At  the  lower  border  of  the  latter  muscle  it  gives  off 
a  branch  to  the  extensor  pollicis  longus,  and  another  which  crosses  this  muscle  to 
the  extensor  indicis  proprius. 

Continuing  distalward  as  the  dorsal  antibrachial  interosseous  nerve  the  deep  radial  leaves  the 
posterior  interosseous  artery,  dips  beneath  the  e.xtensor  pollicis  longus,  and  joins  the  volar  inter- 
osseous artery.  It  accompanies  this  artery  upon  the  interosseous  membrane  and  upon  the  back 
of  the  radius,  passes  through  the  groove  for  the  extensor  digitorum  communis  and  extensor 
indicis  proprius  to  the  dorsum  of  the  wrist,  and  terminates  in  a  gangliform  enlargement  which 
gives  branches  to  the  carpal  articulations.  The  muscles  supplied  by  the  deep  radial  nerve 
are  the  extensor  carpi  radialis  brevis,  brachio-radialis  (supinator  longus),  extensor  digitorum 
communis,  extensor  digiti  quinti  proprius,  extensor  carpi  ulnaris,  extensor  indicis  proprius, 
and  the  extensor  muscles  of  the  thumb.  The  supinator  (brevis)  receives  two  twigs,  one  of  which 
is  given  off  before  the  nerve  pierces  the  muscle  and  the  other  while  it  is  passmg  through  it. 


THE  ULNAR  NERVE  987 

The  superficial  radial  (radial)  nerve  [ramus  superficialis  n.  radialis]  is  some- 
what smaller  than  the  deep  radial  (posterior  interosseous),  and  is  a  purely  cuta- 
neous nerve.  It  runs  downward  under  cover  of  the  brachio-radialis,  passing  in 
front  of  the  elbow-joint,  the  radial  recurrent  artery,  and  the  supinator  (brevis). 
At  the  lower  border  of  the  supinator  it  approaches  the  radial  artery  at  an  acute 
angle,  and  runs  parallel  to  the  lateral  side  of  that  vessel  in  the  middle  third  of  the 
forearm,  across  the  pronator  teres.  At  the  lower  border  of  the  pronator  teres  it 
bends  dorsalward  on  the  deep  surface  of  the  tendon  of  the  brachio-radialis,  and 
appears  on  the  back  of  the  forearm.  It  pierces  the  deep  fascia  and  is  directed 
across  the  dorsal  carpal  (posterior  annular)  ligament  toward  the  dorsum  of  the 
wrist,  where  it  divides  into  its  terminal  branches  (fig.  759). 

The  most  lateral  of  these  branches  suppUes  the  skin  on  the  radial  part  of  the  thenar  eminence; 
the  most  medial,  designated  the  ulnar  anastomotic  branch,  communicates  with  the'dorsal  branch 
of  the  ulnar  nerve.  The  other  terminal  branches,  the  dorsal  digital  nerves,  supply  to  a  variable 
extent  the  skin  on  the  dorsum  of  the  first  digit,  both  sides  of  the  second  and  the  radial  side 
of  the  third  digit.  These  branches  usually  extend  to  the  base  of  the  nail  of  the  first  digit,  to  the 
distal  interphalangeal  joint  of  the  second,  not  quite  to  the  proximal  interphalangeal  joint  of 
the  third,  and  to  the  metacarpo-phalangeal  joint  of  the  fourth  digit. 

The  terminal  branches  of  the  lateral  cord  of  the  brachial  plexus  are  the  mus- 
culo-cutaneous  and  the  lateral  component  of  the  median  nei-ve.  The  latter  nerve 
will  be  described  with  the  medial  cord. 

The  musculo-cutaneous  nerve  is  composed  of  fibres  derived  chiefly  from  the 
anterior  divisions  of  the  fifth  and  sixth  cervical  nerves,  together  usually  with 
some  fibres  from  that  of  the  seventh  (figs.  751  and  754).  The  nerve  to  the  coraco- 
brachialis  usually  consists  of  two  or  three  twigs  given  off  from  the  nerve  close  to 
its  origin  before  it  enters  the  muscle  (fig.  755).  Sometimes,  however,  the  fibres 
from  the  seventh  cervical  nerve  pass  directly  to  this  muscle  without  joining  the 
main  trunk.  The  musculo-cutaneous  nerve  is  placed  at  first  close  to  the  lateral 
sideof  the  axillary  artery  (fig.  755),  but  soon  it  leaves  that  vessel  and,  piercing  the 
coraco-brachialis  muscle,  it  passes  obliquely  downward  and  lateralward  between 
the  biceps  and  brachialis  muscles.  Soon  after  piercing  the  coraco-brachialis  it 
gives  off  muscular  branches  to  each  head  of  the  biceps  and  to  the  brachialis  (fig. 
758).  It  also  gives  twigs  to  the  humerus,  to  the  nutrient  artery,  and  gives  the  chief 
supply  to  the  elbow-joint.  Below  the  branch  to  the  brachialis  the  cutaneous  por- 
tion of  the  nerve  forms  the  lateral  antibrachial  cutaneous  nerve  (figs.  756,  758) . 
This  portion  continues  downward  between  the  biceps  and  brachialis,  pierces  the 
deep  fascia  at  the  lateral  border  of  the  former  muscle  a  little  above  the  bend  of  the 
elbow,  receives  a  communication  from  the  upper  branch  of  the  dorsal  antibrachial 
(upper  external)  cutaneous  branch  of  the  radial  (musculo-spiral)  nerve,  passes 
dorsal  to  the  median  cephalic  vein,  and  divides  into  an  anterior  and  a  posterior 
branch. 

The  anterior  branch  runs  downward  on  the  lateral  and  anterior  part  of  the  forearm,  sup- 
plying the  integument  of  that  region,  and  it  terminates  in  the  skin  covering  the  middle  part  of 
the  thenar  eminence  (fig.  759).  A  short  distance  above  the  wrist,  after  it  has  received  a  com- 
municating twig  from  the  superficial  radial  nerve,  it  gives  off  an  articular  branch  to  the  carpal 
joints.  This  branch  pierces  the  deep  fascia  and  accompanies  the  radial  artery  to  the  dorsum 
of  the  wrist.  The  posterior  terminal  branch  is  small,  and  is  directed  downward  and  backward 
in  front  of  the  external  condyle  of  the  humerus,  to  be  distributed  to  the  skin  on  the  lateral  and 
posterior  aspect  of  the  forearm  as  low  as  the  wrist  (fig.  756).  It  anastomoses  with  the  superficial 
radial  and  with  the  lower  branch  of  the  dorsal  antibrachial  (lower  external)  cutaneous  branch 
of  the  radial  nerve. 

The  terminal  branches  of  the  medial  cord  of  the  brachial  plexus  are  the  ulnar 
nerve  and  the  medial  component  of  the  median  nerve.  Neither  of  these  gives  any 
branches  in  the  upper  arm,  and  thus  they  differ  from  the  other  terminal  branches 
of  the  plexus.  They  both  supply  the  muscles  and  joints  of  the  forearm,  and  the 
muscles,  joints,  and  integument  of  the  hand. 

The  ulnar  nerve,  which  is  the  largest  branch  of  the  medial  cord  of  the  brachial 
plexus,  contains  fibres  from  the  anterior  divisions  of  the  eighth  cervical  and  first 
thoracic  nerves  (figs.  752  and  762).  It  commences  at  the  lower  border  of  the 
pectoralis  minor  and  runs  downward  in  the  axillary  fossa  in  the  posterior  angle 
between  the  axillary  artery  and  vein.  In  the  upper  half  of  the  arm  it  lies  on  the 
medial  side  of  the  brachial  artery  (fig.  755),  but  at  the  level  of  the  insertion  of  the 


THE  NERVOUS  SYSTEM 


coraco-brachialis  it  passes  backward  at  an  acute  angle,  and,  accompanied  by  the 
superior  ulnar  collateral  (inferior  profunda)  artery,  it  pierces  the  internal  inter- 
muscular septum.  After  passing  through  the  septum  it  runs  downward,  in  a 
groove  in  the  medial  head  of  the  triceps  (fig.  758),  to  the  interval  between  the  olec- 

FiG.  758. — Nerves    op  the  Right  Upper  Arm  viewed  from  in  Front.     (Spalteholz.) 


Latissimus  dorsi 

Teres  major 
Radial  (musculo -spiral)  nerve 


Musculo-cutaneous  nerve  - 

Muscular  branch r 

Deltoid  - 
Coraco-brachialis  - 
Median  nerve 
Biceps  brachii 

Musculo-cutaneous  nerve 

Anastomosis  with  median 
(variable) 

Muscular  branch  to  biceps . 


Muscular  branches  to  long 
head  of  triceps 


Ulnar  nerve 
Brachial  artery 


Triceps  (long  head) 


..  Muscular  branch  to  medial 
head  of  triceps 


Triceps  (medial  head) 


Medial  inter-muscular  septum 


—  Median  nerve 


Radial  (musculo-spiral)  nerve 

Supinator  - 

Deep  radial 
Brachio-radialis 

Superficial  radial 
Radial  artery  — 


Pronator  teres 


Muscular  branches  to  flexor 
carpi  radialis,  palmaris 
longus,  and  flexor  digitorum 
sublimis 


Flexor  carpi  radialis 


ranon  process  and  the  medial  condyle  of  the  humerus,  and  in  this  part  of  its 
course  it  is  closely  bound  to  the  muscle  by  the  deep  fascia.  Immediately  below 
the  medial  condyle  it  passes  between  the  two  heads  of  the  flexor  carpi  ulnaris, 
along  the  medial  side  of  the  medial  collateral  ligament  of  the  elbow,  and  it  comes 
into  relation  with  the  dorsal  ulnar  recurrent  artery. 


THE  ULNAR  NERVE  989 

In  the  upper  forearm  the  ulnar  nerve  has  on  the  flexor  digitorum  profundus,  covered  by  the 
flexor  carpi  uhiaris.  Near  the  junction  of  the  upper  and  middle  thirds  of  the  forearm  it  is  joined 
by  the  ulnar  artery,  which  accompanies  it  to  its  termination,  lying  throughout  on  its  radial  side 
(fig.  759).     In  the  lower  part  of  the  forearm  it  still  rests  on  the  flexor  digitorum  profundus,  but 

Fig.  759. — Deep  Nerves  op  the  Volar  Surface  op  the  Forearm.     (After  Toldt,  "Atlas 
of  Human  Anatomy,"  Rebman,  London  and  New  York.) 


Biceps  brachu 


I 
Bracliialis*      m. 


Radial  (musculo-spiral)  nerve 
Muscular  branches 


Medial  intermuscular  septum 


Brachial  artery 


Deep  radial" 
Superficial  radial. 


Muscular  branches  ' 


Median  nerve  (drawn 
^  medialward) 


-Muscular  branches 


Common  head  for  the  super- 
AV  '  ficial  palmar  muscles 


brevis 


Ulnar  artery 


[  longus     ..■ 
Brachio-radialis  -- 


Muscular  branch 
--  Flexor  carpi  ulnaris 


Pronator  teres  -- 


Radial  artery. 


Lateral  antibrachial  cutaneous  nerve 
Flexor  pollicis  longus 


Superficial  radial 

Palmar  branch  of  median  - 
Twig  to  wrist-joiut  - 

Tendon  of  flexor  carpi  radial; 


Twig  to  wrist-joint  >■• 
Transverse  carpal  ligament  ^ 


Volar  antibrachial  interosseous 


-  Palmar  cutaneous  branch  (cut  short) 

Median  nerve 
Pisiform  bone 

_  Deep  branch  of  ulnar 
Abductor  digiti  quinti 

,  Flexor  digiti  quinti  brevis 

'*-*  Palmaris  brevis 


between  the  flexor  carpi  ulnaris  and  flexor  digitorum  sublimis,  and  is  covered  only  by  skin  and 
fascia.  At  a  variable  point  in  this  part  of  the  forearm,  usually  about  5  to  S  cm.  (2  to  3  in.) 
from  the  carpus,  the  nerve  divides  into  its  two  terminal  branches,  a  dorsal  branch  to  the  dorsal 
aspect  of  the  hand,  and  a  volar  branch  to  the  volar  aspect. 


990 


THE  NERVOUS  SYSTEM 


Branches. — ^The  ulnar  resembles  the  median  nerve  in  not  furnishing  any 
branches  to  the  upper  arm.  As  it  passes  between  the  olecranon  process  and  the 
medial  condyle  it  gives  off  two  or  three  fine  filaments  to  the  elbow-joint.  In 
the  upper  part  of  the  forearm  it  supplies  the  flexor  carpi  ulnaris  and  the  medial 
portion  of  the  flexor  digitorum  profundus,  and  in  the  lower  half  it  gives  off  the 
three  cutaneous  branches.  In  the  palm  of  the  hand  it  supplies  the  integument 
of  the  hypothenar  eminence,  the  fifth  digit,  and  half  of  the  fourth  digit,  and  part 
of  the  skin  of  the  dorsum.  It  also  supplies  the  short  intrinsic  muscles  of  the 
hand  with  the  exception  of  the  abductor  poUicis,  the  opponens,  the  lateral  head 
of  the  flexor  poUicis  brevis,  and  the  two  lateral  lumbricales. 

The  nerves  to  the  flexor  carpi  ulnaris  and  to  the  medial  two  divisions  of  the  flexor  digitorum 
profundus  arise  from  the  ulnar  nerve  in  the  upper  third  of  the  forearm. 

Cutaneous  branches. — About  the  middle  of  the  forearm  the  ulnar  nerve  gives  off  two 
cutaneous  branches: — one  pierces  the  fascia  and  anastomoses  with  the  volar  branch  of  the 
medial  antibrachial  (internal)  cutaneous  nerve,  and  the  other,  the  palmar  cutaneous  branch, 
runs  downward  in  front  of  the  ulnar  artery  (fig.  759)  and  is  conducted  by  this  vessel  into  the  palm 


Fig.  760. — Diagrams  Illustrating  a  Common  Distribution  op  Cutaneous  Nerves  op 


Ulnar  branch 

of  medial  anti- ' 

brachial 
cutaneous 


Dorsal  cutane- 
ous branch' 
of  ulnar 

Dorsal  digital 
nerves  (ulnar) 


Forearm.     A,  dorsum;  B,  volar  aspect 

Dorsal  antibrachial...//  \ 
cutaneous  (radial)     l/j  \ 
Dorsal  antibrachial  '  '    ^ 

cutaneous  (radial) 


\  Lateral  antibrachial 
'*  cutaneous  (musculo.. 
cutaneous) 

Lateral  antibrachial 
cutaneous  (musculo- 
cutaneous 


Median  nerve 
.-Superficial  radial 

Superficial  radial 
From 

lateral  anti- 
brachial Dorsal 
cutaneous         digital 
branches 
of  radial 
Dorsal  branches 
of  radial 


Dorsal  branches  of 
proper  volar  dii^tal 
Dorsal  nerves  (median)' 

-^*» branches  of  proper 
volar  digital 
nerves  (median) 


Ulnar  branches 
dial  anti- 
brachial cuta- 
neous 


Volar  branches  of 
medial  anti- 
brachial cutaneus 


-.-Volar  branch  of  ulnar 


.^Cutaneous  branches 
of  common  volar 
digital  nerves 

Proper  volar 

digital  nerves 
(ulnar) 


(fig.  756).  It  furnishes  some  filaments  to  the  vessel,  supplies  a  few  twigs  to  the  skin  of  the  hypo- 
thenar eminence,  and  ends  in  the  integument  covering  the  central  depressed  surface  of  the  palm. 

The  dorsal  or  posterior  cutaneous  branch,  usually  the  smaller  of  the  terminal  branches, 
arises  about  5  cm.  (2  in.)  above  the  wrist-joint,  and  passes  backward  under  cover  of  the  flexor 
carpi  ulnaris  to  reach  the  dorsal  aspect  of  the  wrist  (fig.  761),  where  it  gives  off  dehoate  branches 
to  anastomose  with  branches  of  the  medial  antibrachial  (internal)  cutaneous,  the  dorsal  anti- 
brachial (external)  cutaneous  branch  of  the  radial  (musculo-spiral),  the  lateral  antibrachial 
cutaneous  of  the  musculo-cutaneous  nerve,  and  with  branches  of  the  superficial  radial,  and  then 
divides  into  five  branches,  the  dorsal  digitals  (fig.  757),  which  are  distributed  to  the  ulnar 
sides  of  the  third,  fourth,  and  fifth  digits  and  the  radial  sides  of  the  fourth  and  fifth  digits. 
These  branches  usually  extend  on  the  fifth  digit  only  as  far  as  the  base  of  the  terminal  phalanx, 
and  on  the  fourth  digit  as  far  as  the  base  of  the  second  phalanx.  The  more  distal  parts  of 
these  digits  are  supplied  by  palmar  digital  branches  of  the  ulnar  nerve. 

The  volar  branch,  the  other  terminal  branch  of  the  ulnar  nerve,  continues  its  course  between 
the  flexor  carpi  ulnaris  and  flexor  digitorum  sublimis,  on  the  medial  side  of  the  ulnar  artery,  to 
the  wrist,  where,  on  the  lateral  side  of  the  pisiform  bone,  it  divides  into  a  superficial  and  a 
d£ep  branch  (figs.  759  and  761).  The  latter  accompanies  the  deep  branch  of  the  ulnar  artery 
into  the  interval  between  the  abductor  digiti  quinti  and  flexor  digiti  quinti  brevis,  and  then 


THE  MEDIAN  NERVE 


991 


passes  through  the  fibres  of  the  opponens  digiti  quinti  to  reach  the  deep  surface  of  the  flexor 
tendons  and  theu-  synovial  sheaths.  It  supphes  the  abductor  and  opponens  digiti  quinti,  the 
flexor  digiti  quinti  brevis,  the  third  and  fourth  lumbricales,  all  the  interossei,  the  adductors  of 
the  thumb,  and  the  medial  head,  and  occasionally  the  lateral  head,  of  the  flexor  poUicis  brevis. 
The  superficial  branch  gives  off  a  branch  to  supply  the  palmaris  brevis  muscle,  an  anastomosing 
branch  to  the  median  nerve,  and  then  divides  into  two  branches,  the  proper  volar  digital  branch, 
which  is  distributed  to  the  medial  side  of  the  fifth  digit  on  its  volar  aspect,  and  the  common 
volar  digital  branch,  which  passes  underneath  the  palmar  aponeurosis  and  divides  into  two 
branches,  which  supply  the  contiguous  margins  of  the  fourth  and  fifth  digits.  These  branches 
usually  supply  also  the  dorsal  surface  of  the  second  and  third  phalanges  of  the  same  digits. 

The  median  nerve  contains  fibres  of  the  sixth,  seventh,  and  eighth  cervical 
nerves  and  of  the  first  thoracic,  and  sometimes  of  the  fifth  cervical  nerve.  The 
trunk  is  formed  a  little  below  the  lower  margin  of  the  pectorahs  minor,  by  the 


Fig.  761. — Nerves  op  the  Palmar  Surface  op  the  Hand.     (Testut.) 

The  transverse  carpal  (anterior  annular)  ligament,  superficial  palmar  arch,  the  flexor  tendons 

of  the  digits,  and  the  proximal  portions  of  the  lumbrical  muscles  have  been  removed. 


Superficial  radial 
Palmar  branch  of  median 


Branches  of  superficial  radial 


Branch  to  adductor  polhi 
Proper  volar  digital  -y^ 


Deep  branch  of  ulnar 

Dorsal  branch  of  ulnar 


— Superficial  branch 
-Muscular  branch 


'almar  cutaneous  brancb 


— Branch  to  lumbrical  IV 
■Common  volar  digital 
•Proper  volar  digital 


union  of  two  components,  one  from  the  medial  and  one  from  the  lateral  cord  "of 
the  brachial  plexus  (fig.  755).  The  medial  component  passes  obliquely  across  the 
third  part  of  the  axillary  artery,  and  in  the  upper  part  of  the  trunk  the  fibres  of  the 
two  components  are  felted  together.  From  its  commencement  the  median  nerve 
runs  almost  vertically  through  the  lower  part  of  the  axillary  fossa  and  through  the 
arm  and  forearm  to  the  hand. 

In  the  fossa  it  hes  lateral  to  the  axillary  artery  and  it  is  overlapped,  on  its  lateral  side,  by 
the  cqraco-brachiahs  muscle.  In  the  upper  half  of  the  arm  it  lies  along  the  lateral  side  of  the 
brachial  artery,  and  it  is  overlapped  by  the  medial  border  of  the  biceps.  At  the  middle  of  the 
arm  it  passes  in  front  of  the  brachial  artery,  and  then  it  descends,  on  the  medial  side  of  the  artery, 
to  the  elbow.  In  the  upper  part  of  the  antecubital  fossa  it  is  still  at  the  medial  side  of  the  bra- 
chial artery,  but  separated  from  it  by  a  small  interval,  and  in  the  lower  part  of  the  fossa  it  Lies 


992  THE  NERVOUS  SYSTEM 

along  the  medial  side  of  the  ulnar  artery.  In  case  of  the  high  division  of  the  brachial  artery, 
when  the  radial  and  the  ulnar  arteries  lie  together  in  the  upper  arm,  the  median  nerve  may  pass 
between  them  and  then  one  or  the  other  of  the  arteries  will  be  superficial  to  the  nerve.  As 
it  leaves  the  antecubital  fossa  it  passes  between  the  two  heads  of  the  pronator  teres,  and  it 
crosses  in  front  of  the  ulnar  artery  (fig.  759),  from  which  it  is  separated  by  the  deep  head  of  the 
pronator.  In  the  forearm  it  passes  vertically  downward,  accompanied  by  the  median  (comes 
nervi  mediani)  artery.  In  the  upper  two-thirds  of  this  region  it  lies  deeply,  between  the  flexor 
digitorum  sublimis  and  the  flexor  digitorum  profundus,  but  in  the  lower  third  it  becomes  more 
superficial,  and  is  placed  beneath  the  deep  fascia,  between  the  flexor  carpi  radialis  on  the  radial 
side  and  the  palmaris  longus  and  flexor  digitorum  sublimis  tendons  on  the  ulnar  side.  It  crosses 
beneath  the  transverse  carpal  (anterior  annular)  ligament,  in  front  of  the  flexor  tendons,  and 
in  the  palm  at  the  lower  border  of  the  ligament  it  enlarges  and  divides  into  three  branches,  the 
common  volar  digital  nerves  (fig.  760). 

Branches. — The  median  nerve  does  not  supply  any  part  of  the  upper  arm. 
In  front  of  the  elbow-joint  it  furnishes  one  or  two  filaments  to  that  articulation. 
In  the  forearm  it  supplies  all  the  superficial  anterior  muscles  (with  the  exception 
of  the  flexor  carpi  ulnaris)  directly  from  its  trunk,  and  it  supplies  the  deep 
muscles  (with  the  exception  of  the  ulnar  half  of  the  flexor  digitorum  profundus) 
by  its  volar  (anterior)  interosseous  branch.  Thus  in  general  it  supplies  the 
pronator  and  flexor  muscles  of  the  forearm  (radial  side).  In  the  hand  it  supplies 
the  group  of  short  muscles  of  the  thumb,  which  are  placed  on  the  radial  side  of 
the  tendon  of  the  flexor  pollicis  longus, the  two  lateral  lumbricales,  the  integument 
covering  the  central,  part  of  the  palm  and  ulnar  aspect  of  the  thenar  eminence,  and 
the  palmar  aspect  of  the  first,  second,  third,  and  radial  half  of  the  fourth  digits. 
It  also  sends  twigs  to  the  dorsal  aspect  of  these  digits. 

The  nerve  to  the  pronator  teres  usually  arises  a  little  above  the  bend  of  the  elbow,  and 
pierces  the  lateral  border  of  the  muscle  (figs.  759  and  761).  It  may  arise  in  a  common  trunk 
with  the  following  nerves: — 

The  nerves  to  the  flexor  carpi  radialis,  palmaris  longus,  and  flexor  digitorum  sublimis 
arise  a  Uttle  lower  down,  and  pierce  the  pronator-flexor  mass  of  muscles  to  end  in  the  respective 
members  of  the  group  for  which  they  are  destined  (fig.  758). 

The  volar  (anterior)  interosseous  nerve  arises  from  the  median  at  the  level  of  the  bicipital 
tubercle  of  the  radius  (fig.  759),  and  runs  downward,  on  the  interosseous  membrane,  accom- 
panied by  the  volar  (anterior)  interosseous  artery.  It  passes  under  cover  of  the  pronator  quad- 
ratus,  and  pierces  the  deep  surface  of  that  muscle,  which  it  supplies.  The  volar  interosseous 
nerve  also  furnishes  a  twig  to  the  front  of  the  wrist-joint,  and  supphes  the  flexor  digitorum 
profundus  and  the  flexor  poUicis  longus.  The  nerve  to  the  former  muscle  arises  from  the  volar 
interosseous  near  its  commencement;  it  supplies  the  outer  two  divisions  of  the  muscle,  and  it 
communicates  within  the  substance  of  the  muscle  with  twigs  derived  from  the  ulnar  nerve. 

It  also  supphes  a  branch  to  the  interosseous  membrane  which  runs  downward  upon,  or  in, 
the  membrane,  supplying  it  and  giving  branches  to  the  volar  (anterior)  interosseous  and  nutrient 
arteries  and  to  the  periosteum  of  the  radius,  the  ulna,  and  the  carpus. 

The  palmar  cutaneous  branch  arises  immediately  above  the  transverse  carpal  (anterior 
annular)  ligament  and  passes  between  the  tendons  of  the  flexor  carpi  radialis  and  the  palmaris 
longus  (fig.  759).  It  then  crosses  the  superficial  surface  of  the  transverse  carpal  ligament, 
and  is  distributed  to  the  integument  and  fascia  on  the  central,  depressed  surface  of  the  palm. 
It  also  supplies  a  few  twigs  to  the  medial  border  of  the  thenar  eminence;  these  twigs  commu- 
nicate with  the  musculo-cutaneous  and  superficial  radial  nerves. 

The  three  common  volar  digital  nerves  pass  in  the  palm  of  the  hand  dorsal  to  the  superficial 
palmar  arch  and  its  digital  branches,  while  the  proper  volar  digitals,  branches  of  these  nerves, 
lie  on  the  volar  side  of  the  digital  arteries. 

The  first  of  the  common  volar  digital  nerves  gives  off  a  branch  to  supply  the  abductor 
pollicis,  the  opponens,  and  the  superficial  head  of  the  flexor  pollicis  brevis,  and  joins  by  a  delicate 
branch  with  the  deep  branch  of  the  ulnar  nerve.  It  then  divides  into  three  proper  volar  digitals 
(fig.  761).  The  lateral  of  these  passes  obhquely  across  the  long  flexor  tendon  of  the  thumb  and 
runs  along  the  radial  border  of  the  thumb  to  its  extremity.  It  gives  numerous  branches  to  the 
pulp  of  the  thumb,  and  a  strong  twig  which  passes  to  the  dorsum  to  supply  the  matrix  of  the 
nail.  The  second  of  these  proper  volar  digitals  supplies  the  medial  side  of  the  volar  aspect  of 
the  thumb  and  gives  off  a  twig  to  the  matrix  of  the  thumb  nail.  The  third  supplies  the  radial 
side  of  the  second  digit  and  gives  a  twig  to  the  flrst  lumbrical  muscle. 

The  second  common  volar  digital  sends  a  twig  to  the  second  lumbrical  muscle,  and  divides 
a  httle  above  the  metacarpo-phalangeal  articulation  into  two  proper  volar  digitals,  which 
respectively  supply  the  adjacent  sides  of  the  second  and  third  digits. 

The  third  common  volar  digital  communicates  with  the  ulnar  nerve,  often  gives  a  branch 
to  the  third  lumbrical  muscle,  and  divides  into  two  proper  volar  digitals  which  supply  the  adja- 
cent sides  of  the  third  and  fourth  digits. 

As  the  proper  volar  digitals  pass  along  the  margins  of  the  fingers  they  give  off  twigs  for 
the  innervation  of  the  skin  on  the  dorsum  of  the  second  and  third  phalanges  and  the  matrix 
of  their  nails.     Each  of  the  nerves  terminates  in  filaments  to  the  pulp  of  the  finger. 


RELATIONS  OF  NERVES 


993 


Table  Showing  Relation   op  Cervical  and  Thoracic  Nerves  to 
Branches  op  Brachial  Plexus 

Nerves  Contributing.  Nerves,  Branches  op  Plexus. 

5C f  Dorsal  scapular  (nerve  to  rhomboids) 

\  Nerve  to  subclavius 
(  Suprascapular 

5  and  6  C J  ^erve  to  subclavius 

1  Upper  subscapular 
Lower  subscapular 
*■  Axillary  (circumflex) 
5   6   and  7  C  I  ^°"S  (posterior)  thoracic 

'    '  I  Lateral  anterior  thoracic 

5,  6,  and  (7)  C Musculo-cutaneous 

(5),  6,  7,  8  C    Radial  (musculo-spiral) 

(5),  6,  7,  8  C,  and  1  T      Median 

7  and  8  C Thoraco-dorsal  (middle  or  long  subscapular) 

f  Medial  anterior  thoracic 

8  C.  andl  T \  Uhiar 

[  Medial  antibrachial  (internal)  cutaneous 
IT Medial  brachial  (lesser  internal)  cutaneous 

Table  Showing  the  Relations  op  the  Cervical  Nerves  to  the  Muscles 
OF  the  Upper  Extremity 


Nerves  Contributing. 

Accessory,  2  C 

3,  4C... 
3  and  4  C 


Muscles. 


5  and  6  C. 


6C. 


6  and  7  C. 


5,  6,  and;i;7  C. 


7C. 


7  and  8  C 

5,  6,  7,  andSC. 

8  C 


7,  8  Cand'l  T. 


8C.and  IT. 


Sterno-mastoid 

Trapezius 

Levator  scapulae 

Subclavius 

Supraspinatus 

Infraspinatus 

Subscapularis 

Teres  major 

Teres  minor 

Deltoid 

Brachiahs 
^  Biceps 

Braohioradialis 

Supinator 
■I  Pronator  teres 

Fle.xor  carpi  radialis 
I  Palmaris  longus 
I  Ext.  carpi  radialis  longus 
I  "        "  brevis 

\  Abductor  pollicis  brevis 

Opponens      " 
I  Flexor  poUicis  brevis  (superf. 
head) 

Serratus  anterior 

Coraoo-brachialis 

Ext.  digitorum  coram. 
"     digiti  quinti  proprius 
"     carpi  ulnaris 

Abductor  pollicis  longus 

Extensor  pollicis  brevis 

Extensor  pollicis  longus 

Ext.  indicus  proprius 

Latissimus  dorsi 

Triceps 

Anconeus 

Pectoralis  major 

Dorsal  inteross. 

Palmar       " 

Add.  pollicis 
"     pollicis  trans. 

Flex,  polhois  brev.  (deep) 

Pectoralis  minor 

Flex,  digit,  subl. 

Lumbricalis 

Flex,  carpi  ulnaris 
"    digit,  prof. 
"     pollicis  long. 

Pronator  quadratus 


Nerves  to  Muscles. 

Spinal  accessory 

"       ,  3  and  4  C. 
3  and  4  C. 
Nerve  to  subclavius 

!•  Suprascapular 

Upper  and  lower  subscapular 
Lower  subscapular 

Axillary  (circumfle.x) 

Musculo-cutaneous 

Radial  (musculo-spiral) 

Deep  radial  (posterior  interosseous) 

Median 


Radial  (musculo-spiral) 

Deep  radial  (posterior  interosseous) 

Median 


Long  (posterior)  thoracic 

Musculo-cutaneous 

Deep  radial  (posterior  interosseous) 


Thoraco-dorsal  (long"subscapular) 
Radial  (musculo-spiral) 

Lat.  and  med.  ant.  thoracic 
Ulnar  ■ 


Med.  ant.  thoracic 
Median 

"        and  ulnar 
Ulnar 

"      and  median 
Median 


994 


THE  NERVOUS  SYSTEM 


2.  THE  THORACIC  NERVES 

The  anterior  primary  divisions  of  the  thoracic  nerves,  with  the  exception  of 
the  first,  retain,  in  the  simplest  form,  the  characters  of  anterior  primary  divisions 
of  the  typical  spinal  nerve.  They  do  not  form  plexuses,  but  remain  distinct  from 
each  other.  Each  divides  into  an  easily  recognisable  lateral  or  dorsal  and  anterior 
or  ventral  branch  (figs.  762  and  763),  and  they  are  not  distributed  to  the  limbs. 
The  first,  second,  and  last  thoracic  nerves,  on  account  of  their  pecuUarities,  require 
separate  description.  The  remainder  are  separable  into  two  groups,  an  upper  and 
a  lower.  The  upper  group  consists  of  four  nerves,  the  third  to  the  sixth  inclusive, 
which  are  distributed  entirely  to  the  thoracic  wall.  The  lower  group  contains 
five  nerves,  the  seventh  to  the  eleventh  inclusive,  which  are  distributed  partly 


Fig.  762. — Diagram  of  the  Distribution  of  a  Typical  Thoracic  Nerve. 


Longissimus  dorsi 

Semispinalis  dorsi 

Medial  branch'    i  y 
Superior  costo-transversf~     ' 
ligament 

Dorsal  root 

Ventral  root 

Recurrent  branch' 

Sympathetic  ganglion- 

Viceral  branch 
Branch  to  aorta' 
(Esophagu 


Internal  mammary  artery 
Transverse  thoracic  muscle 


Ilio-costalisldorsi 
Lateral  branch 

Posterior  primary  division 

Anterior  primary  division 
Internal  intercostal  muscle 
External  intercostal  muscle 


■Lateral  cutaneous  bianch 


Anterior  branch 


Anterior  intercostal  membrane 


to  the  thoracic  and  partly  to  the  abdominal  wall.     The  upper  group  is  therefore 
purely  thoracic  in  distribution,  and  the  lower  thoraco-abdominal. 

The  first  thoracic  nerve  is  connected  with  the  first  thoracic  sympathetic  gang- 
lion, and  it  frequently  is  joined  by  a  small  branch  with  the  second  nerve.  It  is 
distributed  chiefly  to  the  upper  limb.  Opposite  the  superior  costo-transverse 
ligament  of  the  second  rib  it  divides  into  a  larger  and  a  smaller  branch;  the 
larger  passes  upward  and  lateralward,  between  the  apex  of  the  pleura  and  the 
neck  of  the  first  rib,  and  on  the  lateral  side  of  the  superior  intercostal  artery,  to 
the  root  of  the  neck,  where  it  joins  the  brachial  plexus.  The  smaller  branch  con- 
tinues along  the  intercostal  space,  below  the  first  rib  and  between  the  intercostal 
muscles  in  which,  as  a  rule,  all  its  fibres  terminate. 

However,  the  smaller  branch  may  give  off  a  lateral  cutaneous  branch  which  connects  with  the 
medial  brachial  (lesser  internal)  cutaneous  nerve  and  with  the  intercosto-brachial  nerve  in  the 
axillary  fossa;  and  occasionally  it  terminates  in  an  anterior  cutaneous  branch  at  the  anterior 
extremity  of  the  first  intercostal  space. 

The  second  thoracic  nerve,  as  it  lies  between  the  pleura  and  the  superior 
costo-transverse  ligament  of  the  third  rib,  gives  a  branch  to  the  first  nerve,  then 
it  pierces  the  posterior  intercostal  membrane  and  passes  between  the  external  and 
internal  intercostal  muscles  in  the  second  intercostal  space.  In  the  dorsal  part 
of  the  space  it  sends  branches  backward,  through  the  external  intercostal  muscle, 


THE  THORACIC  NERVES  995 

to  supply  the  second  levator  costse  and  the  serratus  posterior  superior,  and  then 
it  divides  into  a  lateral  and  an  anterior  branch.  The  two  branches  run  forward 
together  to  the  mid-axillary  line,  where  the  lateral  branch  pierces  the  external 
intercostal  muscle  and  passes  between  two  digitations  of  the  serratus  anterior 
(magnus)  into  the  axillary  fossa;  the  anterior  branch  enters  the  substance  of  the 
internal  intercostal  muscle. 

The  lateral  branch,  the  intercosto-brachial  (intercosto-humeral) ,  may  divide  into  a  small 
anterior  and  a  large  posterior  division,  or  the  anterior  division  may  be  absent.  In  either  case 
the  lateral  branch  anastomoses  with  the  medial  brachial  (lesser  internal)  cutaneous  nerve,  and 
usually  with  the  lateral  branch  of  the  third  intercostal  nerve;  it  also  anastomoses  with  the  lateral 
branch  of  the  first  nerve,  if  the  latter  is  present.  After  forming  these  junctions  it  passes  out 
of  the  axillary  fossa,  pierces  the  deep  fascia,  and  supplies  the  integument  in  the  upper  and  pos- 
terior half  of  the  arm.  It  also  gives  off  a  few  filaments  which  terminate  in  the  skin  over  the 
ajdllary  border  of  the  scapula.  The  size  of  the  intercosto-brachial  nerve  and  the  extent  of  its 
distribution  are  usually  in  inverse  proportion  to  the  size  of  the  other  cutaneous  nerves  of  the 
upper  arm,  especially  the  middle  brachial  (lesser  internal)  cutaneous.  When  the  latter  nerve 
is  absent,  the  intercosto-brachial  usually  takes  its  place. 

The  course  and  distribution  of  the  anterior  branch,  when  it  is  present,  being  similar  to  the 
course  and  distribution  of  the  anterior  branches  of  the  next  four  nerves,  do  not  require  a  separate 
description. 

The  thoracic  intercostal  nerves  (upper  group). — The  third,  fourth,  fifth,  and 
sixth  thoracic  nerves,  in  the  posterior  parts  of  the  intercostal  spaces,  give  muscu- 
lar branches  to  the  levatores  costarum,  the  first  to  the  fourth  also  giving  branches 
to  the  serratus  posterior  superior.  They  pass  forward  a  short  distance  between 
the  external  and  internal  intercostals,  giving  twigs  to  these  muscles,  and  divide 
into  two  branches,  lateral  and  anterior. 

The  lateral  cutaneous  branches  continue  forward  between  the  intercostal 
muscles,  and,  near  the  mid-axillary  line,  pierce  the  external  intercostals  and 
serratus  anterior  (magnus)  and  divide  into  two  branches,  posterior  and  anterior. 
The  posterior  branches  pass  backward  over  the  latissimus  dorsi  to  supply  the  skin 
in  the  lower  part  of  the  scapular  region.  The  anterior  branches,  in  the  four  nerves, 
increase  in  size  from  above  downward.  They  pass  around  the  lateral  border  of 
the  great  pectoral  muscle  and  are  distributed  to  the  integument  over  the  front 
of  the  thorax  and  m'anima,  sending  filaments,  the  lateral  mammary  branches,  into 
the  latter  organ.  The  lowest  two  nerves  also  supply  twigs  to  the  upper  digita- 
tions of  the  external  oblique  muscle. 

The  anterior  branches  run  obliquely  forward  and  medialward  through  the 
substance  of  the  internal  intercostal  muscles,  reaching  the  deep  surface  of  these 
muscles  at  the  extremity  of  the  costal  cartilages  (fig.  762).  They  continue 
forward  between  these  muscles  and  the  pleura,  pass  in  front  of  the  internal 
■  mammary  artery,  turn  abruptly  ventralward  a  short  distance  from  the  sternum, 
pierce  the  internal  intercostals,  the  anterior  intercostal  membrane,  and  the  pec- 
toralis  major,  and  give  off  three  sets  of  terminal  branches.  One  set  supplies  the 
transverse  thoracic  muscle  and  the  back  of  the  sternum.  A  second  set,  cutaneous, 
runs  mesially.  The  third  set  passes  laterally  over  the  pectoralis  major,  supplying 
the  skin  in  that  region,  and,  in  the  female,  the  mammary  gland  through  the 
medial  mammary  branches.  The  anterior  branches  in  their  course  supply  the 
intercostal  and  subcostal  muscles  and  give  filaments  that  supply  the  ribs,  the 
periosteum,  and  the  pleura. 

The  thoraco-abdominal  nerves  (lower  group). — The  relations  of  the  posterior 
portions  of  the  seventh,  eighth,  ninth,  tenth,  and  eleventh  thoracic  nei'ves  to  the 
thoracic  wall  are  similar  to  those  of  the  upper  thoracic  intercostal  nerves.  Each 
divides  in  a  similar  manner  into  a  lateral  and  an  anterior  branch,  but  these  branches 
are  distributed  partly  to  the  abdominal  and  partly  to  the  thoracic  wall,  and  the 
smaller  muscular  branches  have  also  different  distributions. 

The  lateral  branches,  lateral  cutaneous  nerves  of  the  abdomen,  pierce  the 
external  intercostal  muscles  and  pass  through  or  between  the  digitations  of  the 
external  oblique  into  the  subcutaneous  tissue,  where  they  divide  in  the  typical 
way  into  anterior  and  posterior  branches.  The  posterior  branches  pass  backward 
over  the  latissimus  dorsi.  The  anterior  branches  give  filaments  to  the  digitations 
of  the  external  oblique  and  extend  forward,  medialward  and  downward  to  the 
outer  border  of  the  sheath  of  the  rectus. 

The  anterior  branches  pass  forward  between  the  external  and  internal 
intercostal  muscles,  to  the  ends  of  the  intercostal  spaces;  there  they  insinuate 


996  THE  NERVOUS  SYSTEM 

themselves  between  the  interdigitating  slips  of  the  diaphragm  and  the  transversus 
abdominis  and  enter  the  abdominal  wall.  The  seventh,  eighth,  and  ninth  nerves, 
in  their  transit  from  the  thoracic  to  the  abdominal  wall,  pass  behind  the  upturned 
ends  of  the  eighth,  ninth,  and  tenth  rib-cartilages  respectively.  Having  entered 
the  abdominal  wall  the  nerves  run  forward  between  the  transversus  abdominis 
and  the  internal  oblique,  muscles  to  the  outer  border  of  the  rectus  abdominis, 
where  they  pierce  the  posterior  lamella  of  the  internal  oblique  aponeurosis  and 
enter  the  sheath  of  the  rectus.  In  the  sheath  they  pass  through  the  substance  of 
the  rectus.  Finally  they  turn  directly  forward,  pierce  the  anterior  part  of  the 
sheath,  and  become  anterior  cutaneous  nerves  of  the  abdomen. 

The  muscular  branches. — Muscular  branches  from  all  the  thoraco-abdominal 
nerves  are  distributed  to  the  levatores  costarum,  the  intercostal  muscles,  the 
transversus  abdominis,  the  internal  oblique,  and  to  the  rectus  abdominis,  and  the 
ninth,  tenth,  and  eleventh  nerves  gives  branches  also  to  the  serratus  posterior 
inferior.  Branches  are  also  distributed  from  a  variable  number  of  the  lower  nerves 
to  the  costal  portions  of  the  diaphragm. 

The  last  thoracic  nerve. — The  anterior  primary  division  of  the  last  thoracic 
nerve  is  distributed  to  the  wall  of  the  abdomen  and  to  the  skin  of  the  upper  and 
front  part  of  the  buttock.  It  appears  in  the  thoracic  wall  immediately  below  the 
last  rib,  where  it  communicates  with  the  sympathetic  cord  and  gives  off  a  com- 
municating branch  to  the  first  lumbar  nerve.  It  passes  from  the  thorax  into  the 
abdomen  beneath  the  lateral  lumbo-costal  arch  (external  arcuate  ligament), 
accompanied  by  the  subcostal  artery,  and  it  runs  across  the  upper  part  of  the 
quadratus  lumborum  dorsal  to  the  kidney  and  to  the  ascending  or  the  descending 
colon  according  to  the  side  considered.  At  the  lateral  border  of  the  quadratus 
lumborum  it  pierces  the  aponeurosis  of  attachment  of  the  transversus  abdominis 
muscle  and  divides,  between  the  transversus  and  the  internal  oblique  muscle,  into 
a  lateral  and  an  anterior  branch.  It  gives  branches  to  the  transversus  abdominis, 
the  quadratus  lumborum,  and  the  internal  oblique  muscles. 

The  anterior  branch  passes  forward,  between  the  internal  oblique  and  the  transversus 
abdominis,  to  which  it  suppUes  twigs.  It  enters  the  sheath  of  the  rectus,  turns  forward  through 
that  muscle,  and  terminates  in  branches  which  become  cutaneous  midway  between  the  umbilicus 
and  the  symphysis.  Before  it  becomes  cutaneous  it  supplies  twigs  to  the  transversus  abdominis, 
the  internal  oblique,  the  rectus  abdominis,  and  the  pyramidalis  muscles. 

The  lateral  branch  pierces  the  internal  obhque;  it  supplies  the  lowest  digitation  of  the 
external  obhque,  and  then  pierces  the  latter  muscle  from  2.5  to  S  cm.  (1  to  3  in.)  above  the  iliac 
crest,  and  descends  in  the  superficial  fascia  of  the  anterior  part  of  the  gluteal  region,  crossing  the 
ihac  crest  about  2.5  cm.  (1  in.)  behind  its  anterior  extremity  and  reaching  as  far  down  as  the 
level  of  the  great  trochanter.  Occasionally  this  branch  is  absent  and  its  place  is  taken  by  the 
iliac  branch  of  the  ilio-hypogastric.  In  such  oases,  however,  the  branch  from  the  last  thoracic 
to  the  first  lumbar  nerve  is  larger  than  usual. 

THE  LUMBO-SACRAL  PLEXUS 

The  lumbo-sacral  plexus  is  formed  by  the  union  of  the  anterior  primary 
divisions  of  the  lumbar,  sacral,  and  coccygeal  nerves.  In  about  50  per  cent,  of 
cases  it  receives  a  branch  from  the  twelfth  thoracic  nerve.  Its  components  are 
distributed  to  the  lower  extremity  in  a  manner  homologous  and  similar  to  the 
distribution  of  the  parts  of  the  brachial  plexus  to  the  upper  extremity;  the 
lumbar  nerves  are  distributed  similarly  to  the  nerves  formed  from  the  anterior 
(medial  and  lateral)  cords  of  the  brachial  plexus,  and  the  sacral  nerves  are 
distributed  in  a  manner  similar  to  the  distribution  of  the  nerves  from  the  posterior 
cord  of  the  brachial  plexus. 

Partly  for  convenience  of  description  and  partly  on  account  of  the  differences 
in  position  and  course  of  some  of  the  nerves  arising  from  it,  this  plexus  is  sub- 
divided into  four  parts — the  lumbar,  sacral,  pudendal,  and  coccygeal  plexuses. 
These  plexuses  overlap  so  that  there  is  no  definite  line  of  demarcation  between 
them.     However,  they  will  be  considered  separately. 

3.  THE  LUMBAR  NERVES 

The  anterior  primary  divisions  of  the  five  lumbar  nerves  increase  in  size  from 
the  first  to  the  last.     Each  lumbar  nerve  is  connected  by  one  or  two  long,  slender 


THE  LUMBAR  NERVES 


997 


rami  with  a  lumbar  sympathetic  ganglion.    The  first  three  nerves  and  the  greater 
part  of  the  fom-th  enter  into  the  formation  of  the  lumbar  plexus,  and  the  smaller 

Fig.  763. — Cutaneous  Nerves  of  the  Thorax  and  Abdomen,  viewed  prom  the  Side. 

(After  Henle.) 


PectoraliB  major 


Supraclavicular    branch    of 
cervical  plexus 


Pectoralis  minor 


Sheath  of  rectus  _- 


Ilio-hypogastric 


Brachial  plexus 


Intercosto-brachial 


part  of  the  fourth  and  the  fifth  nerve  commonly  unite  to  form  the  lumbo-sacral 
cord  which  takes  part  in  the  formation  of  the  sacral  plexus  (figs.  764,  765) .  When 
the  fourth  nerve  enters  into  the  formation  of  both  lumbar  and  sacral  plexuses, 


998  THE  NERVOUS  SYSTEM 

it  may  be  called  the  furcal  nerve,  but  this  name  is  also  applied  to  any  of  the 
nerves  that  enter  into  the  formation  of  both  plexuses,  so  there  may  be  one  or  more 
furcal  nerves. 

THE  LUMBAR  PLEXUS 

Although  the  lumbar  plexus  is  ordinarily  formed  by  the  first  three  lumbar 
nerves  and  a  part  of  the  fourth,  yet  it  is  subject  to  considerable  variation  in  the 
manner  of  its  formation. 

Owing  to  this  variation  three  general  classes  of  plexuses  may  be  found,  proximal  or  pre- 
fixed, ordinary,  and  distal  or  post-fixed.  The  basis  of  classification  is  the  relation  of  the  nerves 
of  the  limb  to  the  spinal  nerves  which  enter  into  their  formation.  The  intermediate  or  slighter 
degrees  of  variation  may  consist  only  of  changes  in  the  size  of  the  portions  contributed  by  the 
diHerent  spinal  nerves  to  a  given  peripheral  nerve,  for  a  given  nerve  may  receive  a  larger  share 
of  its  fibres  from  a  more  proximal  spinal  nerve,  and  a  smaller  share  from  a  more  distal  nerve,  or 
vice  versd.  However,  in  the  more  marked  degrees  of  variation  the  origin  of  a  given  peripheral 
nerve  may  vary  in  either  direction  to  the  extent  of  one  spinal  nerve.  The  more  extreme  types 
of  the  plexuses  are  sometimes  associated  with  abnormal  conditions  of  the  vertebral  column. 
It  has  been  suggested  that  when  the  prefixed  or  proximal  condition  occurs,  it  indicates  that  the 
lower  limb  is  placed  a  segment  more  proximal  than  in  the  ordinary  cases,  and  when  the  distal 
condition  is  present,  that  the  limb  is  arranged  a  segment  more  distal.  Three  types  each  of  the 
proximal  and  the  distal  classes  and  one  type  of  the  ordinary  class  have  been  described  by  Bar- 
deen.  His  statistics  are  made  use  of  in  the  compilation  of  the  following  tables,  in  which  are 
shown  the  range  of  variation  and  the  common  composition  of  each  class  of  plexus: — 

Composition  of  the  Nerves  of  the  Lumbar  Plexus 
Range  of  Variation 

Nerve.  Proximal.  Ordinary.  Distal. 

Lateral  (external)  cutaneous  12  T,  1,  2,  3  L.  1,  2,  3,  4  L.  1,  2,  3,  4  L. 

Femoral  (anterior  crural)  ...  12  T,  1,  2,  3,  4  L.  1,  2,  3,  4  L.  1,  2,  3,  4,  5  L. 

Obturator 1,  2,  3,  4  L.  1,  2,  3,  4  L.  2,  3,  4,  5  L. 

Furcal 3  or  3,  4  L.  4  L.  4,  5  or  5  L. 

Common  Composition 

Nerve.  Proximal.  Ordinary.  Distal. 

Lateral  (external)  cutaneous  1,  2  L.  1,  2,  3  L.  2,  3  L. 

Femoral  (anterior  crural)  . .  1,  2,  3,  4  L.  2,  3,  4  L.  2,  3,  4,  5,  L. 

Obturator 1,  2,  3,  4  L.  2,  3,  4  L.  2,  3,  4  L. 

Furcal 4  L.  4  L.  4  L. 

The  lumbar  plexus  lies  in  the  posterior  part  of  the  psoas  muscle  (fig.  765),  in 
front  of  the  transverse  processes  of  the  lumbar  vertebrae  and  the  medial  border 
of  the  quadratus  lumborum,  and  its  terminal  branches  are  distributed  to  the 
lower  part  of  the  abdominal  wall,  the  front  and  medial  part  of  the  thigh,  the 
external  genital  organs,  the  front  of  the  knee,  the  medial  side  of  the  leg,  and  the 
medial  side  of  the  foot. 

The  first  and  second  of  the  lumbar  nerves  give  collateral  muscular  branches  to 
the  quadratus  lumborum  muscle,  and  the  second  and  third  nerves  give  similar 
branches  to  the  psoas.  The  remaining  branches  of  the  plexus  are  terminal 
branches.  The  first  lumbar  nerve,  after  it  has  been  joined  by  the  branch  from  the 
last  thoracic  nerve,  divides  into  three  terminal  branches,  the  ilio-hypogastric 
nerve,  the  ilio-inguinal  nerve,  and  a  branch  which  joins  the  second  nerve.  The 
fibres  of  this  latter  branch  pass  mainly  into  the  genito-femoral  (genito-crural) 
nerve,  but  occasionally  some  of  them  enter  the  femoral  (anterior  crural)  and 
obturator  nerves.  The  remaining  nerves  divide  into  anterior  or  ventral  and 
posterior  or  dorsal  divisions.  The  anterior  divisions  form  a  portion  of  the  genito- 
femoral (genito-crural)  nerve  and  the  obturator  nerve,  and  the  posterior  divisions 
enter  the  lateral  (external)  cutaneous  and  femoral  (anterior  crural)  nerves. 

All  the  terminal  branches  of  the  plexus  are  formed  in  the  substance  of  the 
psoas  muscle;  four  of  them,  the  ilio-hypogastric,  the  ilio-inguinal,  the  lateral 
(external)  cutaneous,  and  the  femoral  (anterior  crural),  leave  the  muscle  at  its 
lateral  border.  The  genito-femoral  (genito-crural)  passes  through  its  anterior 
surface,  and  the  obturator  through  its  medial  border. 

Terminal  branches. — The  ilio-hypogastric  nerve  springs  from  the  first 
lumbar  nerve,  after  the  latter  has  been  joined  by  the  communicating  branch 


THE  LUMBAR  PLEXUS 


999 


from  the  last  thoracic  nerve,  as  it  is  in  about  50  per  cent,  of  the  cases,  and  it  thus 
contains  fibres  of  both  the  last  thoracic  and  the  iirst  lumbar  nerves.  It  pierces 
the  lateral  border  of  the  psoas  and  crosses  in  front  of  the  quadratus  lumborum 
(fig.  765),  and  behind  the  kidney  and  the  colon.  At  the  lateral  border  of  the 
quadratus  it  pierces  the  aponeurosis  of  origin  of  the  transversus  abdominis  and 
enters  the  areolar  tissue  between  the  transversus  and  the  internal  oblique,  where 
it  frequently  communicates  with  the  last  thoracic  and  with  the  ilio-inguinal 

Fig.  764. — Diagram  of  a  Common  Form  of  Lumbo-saceal  Plexus.     (Modified  from 

Paterson.) 
From  last  thoracic  nerve  •< 

-  r — First  lumbar 


Genito-femoral 

lUo-hypogastrici 

Ilio-inguinal> 

Lateral  cutaneo 

Obturator 
Accessory  obturator. 


To  superior  gluteal 

To  inferior  gluteal --- 

To  piriformis  - 

Sciatic _  ^^ 

J/ 
To  quadratus  femons 


Common 
peroneal 
section 


-  —  •Second  lumbar 


— —Third  lumbar 


Fourth  lumbar 


Fifth  lumbar 


-  Second  sacral 

-  Third  sacral  J 

•  Visceral    branches 

-  Fourth  sacral 
.  Visceral  branches 
■•  Perineal 

*  Fifth  sacral 

-  To  coccygeus 

-  To  levator  ani 


To  hamstrings 

'  Fosterior  femora]    Perforating 
t         cutaneous  cutaneous 

To  obturator  internus 

nerve,  and  it  divides  into  an  iliac  and  a  hypogastric  branch,  which  correspond, 
respectively,  with  the  lateral  and  anterior  branches  of  a  typical  spinal  nerve. 

The  anterior  cutaneous  (hypogastric)  branch  passes  forward  and  downward,  between  the 
transversus  abdominis  and  the  internal  oblique  muscles,  giving  branches  to  both;  it  communi- 
cates with  the  ilio-inguinal  nerve,  and,  near  the  anterior  superior  spine  of  the  ilium,  it  pierces 
the  internal  oblique  muscle  and  continues  forward  beneath  the  external  obhque  aponeurosis 
toward  the  middle  line.  About  2. .5  cm.  (1  in.)  above  the  subcutaneous  inguinal  ring  it  pierces 
the  aponeurosis  of  the  external  oblique,  becomes  subcutaneous,  and  supplies  the  skin  above  the 
symphysis. 

The  lateral  cutaneous  (iliac)  branch  pierces  the  internal  and  external  obhque  muscles, 
emerging  through  the  latter  above  the  iUac  crest  at  the  junction  of  its  anterior  and  middle 
thirds  (fig.  769).  It  is  distributed  to  the  integument  of  the  upper  and  lateral  part  of  the  thigh, 
in  the  neighborhood  of  the  gluteus  medius  and  tensor  fasciae  latae  muscles  (fig.  768). 


1000  THE  NERVOUS  SYSTEM 

The  ilio-inguinal  nerve  arises  principally  from  the  first  lumbar  nerve,  but  it 
frequently  contains  fibres  of  the  last  thoracic  nerve.  It  emerges  from  the  lateral 
border  of  the  psoas,  at  a  lower  level  than  the  ilio-hypogastric  nerve,  and  passes 
across  the  quadratus  lumborum  (figs.  765,  766).  As  a  rule,  it  is  below  the  level 
of  the  inferior  end  of  the  kidney,  but  it  passes  dorsal  to  the  ascending  or  the 
descending  colon  according  to  the  side  considered,  and  crosses  the  posterior  part 
of  the  inner  lip  of  the  iliac  crest;  it  then  runs  forward  on  the  upper  part  of  the 
iliacus,  pierces  the  transverus  abdominis  near  the  anterior  part  of  the  crest,  and 
communicates  with  the  anterior  cutaneous  (hypogastric)  branch  of  the  ilio- 
hypogastric nerve.  A  short  distance  below  the  anterior  superior  spine  it  passes 
through  the  internal  oblique  muscle,  and  then  descends  in  the  inguinal  canal  to 
the  subcutaneous  inguinal  (external  abdominal)  ring,  through  which  it  emerges 
into  the  thigh  on  the  lateral  side  of  the  spermatic  cord  (fig.  763).  It  is  distributed 
to  the  skin  of  the  upper  and  medial  part  of  the  thigh,  in  the  male  to  the  root  of  the 
penis  and  to  the  skin  of  the  root  of  the  scrotum  through  the  anterior  scrotal 
nerves  (fig.  768),  and  in  the  female  to  the  mons  veneris  and  labium  majus  through 
the  anterior  labial  nerves. 

Not  uncommonly  the  iho-inguinal  nerve  is  blended  with  the  iho-hypogastric  nerve  and 
separates  from  the  latter  between  the  transversus  abdominis  and  the  internal  obUque  muscles. 
It  may  be  replaced  by  branches  of  the  genito-femoral  (genito-orural)  nerve,  or  it  may  replace 
that  nerve  or  the  lateral  cutaneous  nerve. 

cs 

The  genito-femoral  (genito-crural)  nerve  is  connected  with  the  first  and 
second  lumbar  nerves,  but  the  majority  of  its  fibres  are  derived  from  the  second 
nerve.  It  passes  obliquely  forwarcl  and  downward  through  the  psoas  and  emerges 
from  the  anterior  surface  of  that  muscle,  close  to  its  medial  border,  at  the  level 
of  the  lower  border  of  the  third  lumbar  vertebra.  After  emerging  from  the  sub- 
stance of  the  psoas  it  runs  downward  on  the  anterior  surface  of  the  muscle 
(fig.  765),  to  the  lateral  side  of  the  aorta  and  the  common  iliac  artery,  passes 
behind  the  ureter  and  divides  into  two  branches,  an  external  spermatic  or  genital, 
and  a  lumbo-inguinal  or  crural  (fig.  766).  Occasionally  it  divides  in  the  substance 
of  the  psoas,  and  then  the  two  branches  issue  separately  through  the  anterior 
surface  of  the  muscle. 

The  external  spermatic  (genital)  branch  runs  downward  on  the  psoas  muscle,  external  to 
the  external  iliac  artery;  it  gives  a  branch  to  the  psoas,  and  at  Poupart's  hgament  it  turns 
around  the  inferior  epigastric  artery  and  enters  the  inguinal  canal,  accompanjdng  the  spermatic 
cord  in  the  male  or  the  round  hgament  in  the  female.  It  suppUes  the  cremaster  muscle,  and 
gives  twigs  to  the  integument  of  the  scrotum  (fig.  766)  or  the  labium  majus. 

The  lumbo-inguinal  (crural)  branch  passes  downward  along  the  external  ihac  artery  and 
beneath  Poupart's  hgament  into  the  thigh,  which  it  enters  to  the  lateral  side  of  the  femoral 
artery.  A  short  distance  below  Poupart's  ligament  it  pierces  the  fascia  lata  or  passes  through 
the  fossa  ovalis  (saphenous  opening)  and  supplies  the  skin  in  the  middle  of  the  upper  part  of  the 
thigh.  A  short  distance  below  Poupart's  hgament  it  sometimes  sends  branches  to  the  anterior 
branch  bf  the  lateral  cutaneous  nerve,  and  about  the  middle  of  the  thigh  it  often  joins  with  the 
cutaneous  branches  of  the  femoral  (anterior  crural)  nerve. 

The  lateral  cutaneous  nerve  receives  fibres  from  the  dorsal  branches  of  the 
anterior  primary  divisions  of  the  second  and  third  lumbar  nerves,  and  frequently 
some  fibres  from  the  first  lumbar  (fig.  769).  It  emerges  from  the  lateral  border 
of  the  psoas  and  passes  obliquely  across  the  iliacus  dorsal  to  the  iliac  fascia,  and 
dorsal  to  the  caecum  on  the  right  side  and  the  sigmoid  colon  on  the  left  side,  to  a 
point  immediately  below  the  anterior  superior  spine  of  the  ilium,  where  it  passes 
below  Poupart's  ligament  into  the  lateral  angle  of  the  femoral  trigone  (Scarpa's 
triangle).  Leaving  the  trigone  at  once  it  passes  through,  behind,  or  in  front  of 
the  sartorius  and  divides  into  two  branches,  anterior  and  posterior,  which  enter 
the  deep  fascia  (fig.  766). 

The  posterior  branch  of  the  lateral  cutaneous  nerve  breaks  up  into  several  secondary 
branches  which  become  subcutaneous,  and  they  supply  the  integument  of  the  lateral  part  of  the 
thigh,  from  the  great  trochanter  to  the  level  of  the  middle  of  the  femur.  The  anterior  branch 
runs  downward  in  a  canal  in  the  deep  fascia,  for  three  or  four  inches,  before  it  becomes  sub- 
cutaneous. It  usually  divides  into  two  branches,  a  lateral  and  a  medial.  The  lateral  branch 
supplies  the  skin  of  the  lower  half  of  the  lateral  side  of  the  thigh,  and  the  medial  branch  is  dis- 
tributed to  the  skin  of  the  lateral  side  of  the  front  of  the  thigh  as  far  as  the  knee  (fig.  766). 
Its  lower  filaments  frequently  unite  with  the  cutaneous  branches  of  the  femoral  (anterior 


THE  FEMORAL  NERVE 


1001 


crural),  and  with  the  patellar  branch  of  the  saphenous  nerve  in  front  of  the  patella,  forming 
with  them  the  patellar  plexus. 

The  femoral  (anterior  crural)  nerve  is  the  largest  terminal  branch  of  the  lum- 
bar plexus.  It  is  formed  chiefly  by  fibres  of  the  dorsal  branches  of  the  anterior 
primary  divisions  of  the  second,  third,  and  fourth  lunibar  nerves,  but  it  sometimes 
receives  fibres  from  the  first  nerve  also  (figs.  765  and  769).  It  emerges  from  the 
lateral  border  of  the  psoas  a  short  distance  above  Poupart's  ligament,  and  descends 
in  the  groove  between  the  psoas  and  the  iliacus,  behindPoupart's  ligment,  into 


Fig.  765. — Lumbo-sacral   Plexus.     (After  Toldt,    'Atlas  of   Human   Anatomy,'    Rebman, 
London  and  New  York.) 
Lumbar  vertebrae 


Medial  crus  of  diaphrag: 
Rib  XU 


Psoas  minor 
Intercostal  XII 


/I 

Q  jadratus  lumborum  -^  /?  I 

lUo-hypogastnCs^/^/'    '-J, ''j 

Ilio-mgumal  v.^  MMtjK') 
Psoas  major 


Transversus  v//  '^    /A 
abdominis      "  ^ 

Genito-femoral-' 


'  Lumbar  I  (anterior  bran::h) 
/Muscular  branch 
-■  Ilio -hypogastric 
'Psoas  minor 

*^  //Ifa^W ^<*|^^-=' R^mi  communicantes 

^\^j^^p^.^  Sympathetic  trunk 
Lumbar  II 

Muscular  branche 


V^     Gemto-femoral 


Obturator  fascia 
Piriformis  with  its  muscular  branch 


j^y    s.  Muscular 

branches  for 
J  iliacus 

'J>    Fe 


J   ^Obturator 
^Lumbo-sacral  trunk 

g!^^  \    \  '^^^^^  ^  Piriformis 

|_^A^/l  "    '    ^P//     \  Y*^  \Sciatic 

V7  J;  ^/Mt         \  \  \  Sacral  pie 

~^  N    ^v Posterior  cutaneo 


Ganghon  coccygeum  impar  /   /   jj 
Coccygeal '    / 


Ano-coccygeal 


Middle  h£emorrhoidal  and 
\         inferior  ve; 

Pudendal  plexus 


the  femoral  trigone  (Scarpa's  triangle),  where  it  lies  to  the  lateral  side  of  the 
femoral  artery  (fig.  767) ,  from  which  it  is  separated  by  some  of  the  fibres  of  the 
psoas.  In  this  situation  it  is  flattened  out  and  it  divides  into  two  series  of  ter- 
minal branches,  the  superficial  and  the  deep.  In  general,  they  supply  the  muscles 
and  skin  on  the  anterior  aspect  of  the  thigh. 

Branches. — The  branches  of  the  femoral  nerve  are  collateral  and  terminal. 

The  collateral  branches  are  twigs  of  supply  to  the  ihacus,  and  a  branch  to  the 
femoral  artery;  they  are  given  off  before  the  nerve  enters  the  femoral  trigone. 


1002 


THE  NERVOUS  SYSTEM 


The  terminal  branches  form  two  groups,  the  superficial  and  the  deep. 
The  superficial  terminal  branches  are  two  muscular  branches,  the  nerve  to 
the  pectineus,  and  the  nerve  to  the  sartorius,  and  two  anterior  cutaneous  branches. 

Fig.  766. — Cutaneous  Nerves  of  the  Right  Thigh,     (Spalteholz.) 
(The  iliac  fascia  has  been  removed,  the  fascia  lata  retained.) 


Ilio-hypogast: 
Ilio -inguinal 

Transversus  abdominis. 

Obliquus  internus  abdom- 
inis 

Obliquus  externus  ab-  • 
dominis 
Lateral  cutaneous  branch  •■ 
of  inter-  costal  XU 

Intercostal  XII 
Lateral  cutaneous 


Lumbo-inguinal  nerve    - 


Psoas  minor 
Genito-femoral  nerve 

_N Psoas  major 

^j Lateral  cutaneous  nerve 

' Iliacus 

...  External  iliac  artery 

.,    External  spermatic  nerve 

-^„^    ,.   Lumbo-inguinal  nerve 
.•^1^.      _   Femoral  nerve 

(       Internal  spermatic  artery  and 

—  Ductus  deferens 

--y,--  Rectus  abdominis 

Anterior   cutaneous   branch 
of  ilio-hypogastric  nerve 

Fossa  ovalis 

External  spermatic  nerve 
Anterior  scrotal  nerves 
Ixii....  Spermatic  cord 

Great  saphenous  vein 

Anterior  cutaneous  branches 
''      of  femoral  nerve 


(Anterior     cutaneous    branches 
of  femoral  nerve 


'The  nerve  to  the  pectineus  passes  medially  and  downward  behind  the  femoral  sheath  and  in 
front  of  the  psoas  to  the  anterior  surface  of  the  pectineus,  in  which  it  terminates. 

The  nerve  to  the  sartorius  accompanies  the  middle  cutaneous  nerve;  it  leaves  the  latter 
nerve  above  the  sartorius  and  ends  in  the  upper  part  of  the  muscle. 


THE  OBTURATOR  NERVE  1003 

The  anterior  (middle  and  internal)  cutaneous  nerves  are  best  described  separately.  The 
middle  cutaneous  nerve  soon  divides  into  two  branches,  medial  and  lateral.  The  lateral  branch 
pierces  the  sartorius  and  both  branches  become  cutaneous  about  the  junction  of  the  upper  and 
middle  thirds  of  the  tliigh  (figs.  766,  768).  They  descend  along  the  medial  part  of  the  front  of 
the  thigh  to  the  knee,  supplying  the  skin  in  the  lower  two-thirds  of  the  medial  part  of  the  front 
of  the  thigh,  and  their  terminal  filaments  take  part  in  the  formation  of  the  patellar  plexus. 
About  the  middle  of  the  thigh  the  middle  cutaneous  is  often  joined  by  a  twig  with  the  lumbo- 
inguinal  nerve  (crural  branch  of  the  genito-crural  nerve).  The  medial  or  internal  cutaneous 
nerve  runs  downward  and  medialward  along  the  lateral  side  of  the  femoral  artery,  to  the  apex  of 
the  femoral  trigone  (Scarpa's  triangle),  where  it  crosses  in  front  of  the  artery  and  divides  into  an 
anterior  and  a  posterior  terminal  branch.  Before  this  division  takes  place,  however,  two  or 
three  collateral  branches  are  given  off  from  the  trunk.  The  highest  of  these  passes  through  the 
fossa  ovalis  (saphenous  opening),  or  it  pierces  the  deep  fascia  immediately  below  the  opening,  and 
supplies  the  skin  as  low  as  the  middle  of  the  thigh.  The  lowest  pierces  the  deep  fascia  at  the 
middle  of  the  thigh  and  it  descends  in  the  subcutaneous  tissue,  supplying  the  skin  on  the  medial 
side  of  the  thigh  from  the  middle  of  the  thigh  to  the  knee  (figs.  768,  769).  This  nerve  frequently 
varies  in  size  inversely  with  the  cutaneous  branches  of  the  obturator  and  saphenous  nerves. 
The  anterior  branch  of  the  internal  cutaneous  nerve  passes  vertically  downward  to  the 
junction  of  the  middle  and  lower  thirds  of  the  thigh,  where  it  pierces  the  deep  fascia.  It 
still  continues  downward  for  a  short  distance,  then  it  turns  lateralward  and  passes  to  the 
front  of  the  knee,  where  it  enters  into  the  patellar  plexus. 

The  posterior  branch  descends  along  the  dorsal  border  of  the  sartorius,  and  it  gives  off  a 
branch  which  passes  beneath  that  muscle  to  unite  with  twigs  from  the  saphenous  and  from  the 
superficial  division  of  the  obturator  nerve,  forming  with  them  the  subsartorial  plexus  which 
lies  on  the  roof  of  the  adductor  (Hunter's)  canal.  At  the  medial  side  of  the  knee  the  nerve 
pierces  the  deep  fascia  and  it  descends  to  the  middle  of  the  calf  (figs.  766,  768). 

The  deep  terminal  branches  of  the  femoral  nerve  are  six  in  number,  one 
cutaneous  branch,  the  saphenous,  and  five  muscular  branches.  The  branches 
radiate  from  the  termination  of  the  trunk  of  the  femoral  nerve,  and  thej^  are 
arranged  in  the  following  order  from  medial  to  lateral: — the  saphenous  nerve, 
the  nerve  to  the  vastus  medialis,  the  nerve  to  the  articularis  genu  (subcrureus) , 
the  nerve  to  the  vastus  intermedins  (crureus),  the  nerve  to  the  vastus  lateralis, 
and  the  nerve  to  the  rectus  femoris. 

The  saphenous  nerve  passes  down  through  Scarpa's  triangle  along  the  lateral  side  of  the 
femoral  artery.  At  the  apex  of  the  triangle  it  enters  the  adductor  (Hunter's)  canal  and  descends 
through  it,  lying  first  to  the  lateral  side,  then  in  front,  and  finally  to  the  medial  side  of  the  artery 
(fig.  767).  After  emerging  from  the  lower  end  of  the  canal,  accompanied  by  the  superficial 
branch  of  the  genu  suprema  (anastomotic)  artery,  it  passes  between  the  dorsal  border  of  the 
sartorius  and  the  anterior  border  of  the  tendon  of  the  gracihs,  and,  becoming  superficial,  it 
enters  into  relationship  with  the  great  saphenous  vein  and  descends  with  it  along  the  inner  border 
of  the  upper  two-thirds  of  the  tibia  (fig.  768).  It  crosses  the  medial  surface  of  the  lower  third 
of  the  tibia,  passes  in  front  of  the  internal  malleolus,  and  runs  forward  along  the  medial  border 
of  the  foot  to  the  ball  of  the  great  toe. 

While  it  is  in  the  adductor  (Hunter's)  canal  it  gives  off  a  twig  to  the  subsartorial  plexus. 
Before  it  passes  from  under  cover  of  the  sartorius  it  gives  off  an  infra-patellar  branch,  which 

Eierces  the  sartorius  just  above  the  knee  and  passes  outward  to  the  patellar  plexus.  After  it 
ecomes  superficial  it  supphes  the  integument  on  the  medial  side  of  the  leg  and  foot,  and  it 
anastomoses,  in  the  foot,  with  the  medial  dorsal  cutaneous  branch  of  the  superficial  peroneal 
(musculo-outaneous)  nerve. 

The  nerve  to  the  vastus  medialis  accompanies  the  saphenous  nerve  in  the  femoral  trigone 
(Scarpa's  triangle),  lying  to  its  outer  side.  At  the  upper  end  of  the  adductor  canal  it  passes 
beneath  the  sartorius,  external  to  the  roof  of  the  canal,  and  enters  the  medial  surface  of  the  vas- 
tus medialis.     It  sends  a  twig  down  to  the  knee-joint. 

The  nerve  to  the  articularis  genu  (subcrureus),  usually  a  terminal  branch  of  the  femoral, 
frequently  arises  from  the  nerve  to  the  vastus  intermedins.  It  passes  between  the  vastus 
medialis  and  the  vastus  intermedins  to  the  lower  third  of  the  thigh,  where  it  supplies  the  artic- 
ularis genu  and  sends  a  branch  to  the  knee-joint. 

The  nerve  to  the  vastus  intermedins  (crureus)  is  represented  by  two  or  three  branches  which 
enter  the  upper  part  of  the  muscle.     One  of  them  frequently  sends  a  twig  to  the  knee-joint. 

The  nerve  to  the  vastus  lateralis  pas.ses  downward  behind  the  rectus  and  along  the  anterior 
border  of  the  vastus  lateralis  accompanied  by  the  descending  branch  of  the  lateral  circumfiex 
artery.     It  also  sends  a  branch  to  the  knee-joint. 

'The  nerve  to  the  rectus  femoris  (fig.  767)  enters  the  deep  surface  of  that  muscle,  having 
previously  given  off  a  twig  to  the  hip-joint  which  accompanies  the  ascending  branch  of  the 
external  circumflex  artery. 

The  obturator  nerve  contains  fibres  from  the  anterior  primary  divisions  of  the 
second,  third,  and  fourth  lumbar  nerves,  but  its  largest  root  is  derived  from  the 
third  nerve  (figs.  765,  769).  It  sometimes  receives  fibres  from  the  first  and  third 
lumbar  nerves.  It  emerges  from  the  medial  border  of  the  psoas  at  the  dorsal 
part  of  the  brim  of  the  pelvis,  where  it  lies  in  close  relation  with  the  lumbo-sacrai 
trunk  of  the  plexus,  from  which  it  is  separated  by  the  iho-lumbar  artery.  Im- 
mediately after  its  exit  from  the  psoas  it  pierces  the  pelvic  fascia,  crosses  the 


1004 


THE  NERVOUS  SYSTEM 


lateral  side  of  the  internal  iliac  vessels  and  the  ureter,  and  runs  forward  in  the 
extraperitoneal  fat,  below  the  obliterated  hypogastric  artery  and  along  the 
upper  part  of  the  medial  surface  of  the  obturator  internus  to  the  upper  part  of  the 
obturator  foramen,  where  it  passes  through  the  obturator  canal  below  the  so- 
called  horizontal  ramus  of  the  pubis  and  above  the  obturator  membrane,  into  the 
upper  part  of  the  thigh.  It  is  accompanied  in  the  pelvis  and  the  obturator  canal 
by  the  obtm-ator  arterj^,  which  lies  at  a  lower  level  than  the  nerve,  and  it  divides 


Fig.  767. — Femoral  and  Obtubator  Nerves.     (Ellis.) 
Femoral  vein  Femoral  artery 


Pectineus 
Obturator  (anterior  div.) 


Adductor  longus 


Adductor  brevis 


Adductor  magnus 
Geniculate  branch  of  obturator 

Semi-membranosus 


Tensor  fasciae  latffi 

Profunda  artery 
Pectineus 
Rectus  femoris 

Saphenous 

Nerve  to  vastus  medialis 


Adductor  longus 
Femoral  artery 


Genu  suprema  artery 
Patellar  branch  of  saphenous 


in  the  obturator  canal  into  two  branches,  an  anterior  and  a  posterior,  which 
supply  the  adductor  group  of  muscles,  the  hip  and  knee-joints,  and  the  skin  on  the 
medial  aspect  of  the  leg. 

The  anterior  branch  of  the  obturator  has  a  twig  joining  it  with  the  accessory 
obturator  nerve,  if  that  nerve  is  present,  and  then  descends  behind  the  pectineus 
and  adductor  longus  and  in  front  of  the  obturator  externus  and  adductor  magnus 
muscles  (fig.  767).     Its  branches  are: — 

1.  A  twig  to  the  accessory  obturator  nerve  if  the  latter  is  present. 

2.  An  articular  branch  to  the  hip-joint. 

3.  Muscular  branches  to  the  gracihs,  adductor  longus,  and,  usuaOy,  to  the  adductor 
brevis. 

4.  Two  terminal  branches,  of  which  one  is  distributed  to  the  femoral  artery  and  the  other 
communicates  with  the  subsartorial  plexus.     The  subsartorial  branch  is  occasionally  longer 


THE  LUMBOSACRAL  TRUNK 


1005 


than  usual,  and  it  then  descends,  along  the  dorsal  border  of  the  sartorius,  to  the  medial  side  of  the 
knee,  where  it  enters  the  subcutaneous  tissue,  and,  proceeding  downward,  supplies  the  skin 
on  the  medial  side  of  the  leg  as  far  as  the  middle  of  the  calf.     Twigs  join  it  with  the  saphenous. 

The  posterior  branch  of  the  obturator  (fig.  767)  pierces  the  upper  part  of  the 
obturator  externus  and  passes  downward  between  the  adductor  brevis  and  adduc- 
tor magnus.     Its  branches  are: — 

1.  Muscular  branches  to  the  obturator  externus,  to  the  oblique  fibres  of  the  adductor  magnua 
and  to  the  adductor  brevis  when  the  latter  is  not  entirely  suppUed  by  the  anterior  branch. 
The  branch  to  the  obturator  externus  is  given  off  in  the  obturator  canal. 

2.  An  articular  branch  to  the  knee-joint  which  appears  in  some  cases  to  be  the  continuation 
of  the  trunk  of  the  posterior  branch  (fig.  767).     It  either  pierces  the  lower  part  of  the  adductor 


Fig.  768. — Distribution  op  Cutaneous  Nerves  on  the  Postebior  and  Anterior  Aspects 
OF  the  Inferior  Extremity. 


Middle  clunial 


Infra-patellar 
branch  of 
saphenous 


Superficial 
peroneal 


Deep  peroneal 


magnus,  or  it  passes  through  the  opening  for  the  femoral  artery.  In  the  popliteal  space  it 
descends  on  the  popUteal  artery  to  the  back  of  the  joint,  where  it  pierces  the  posterior  hgament, 
and  its  terminal  filaments  are  distributed  to  the  crucial  ligaments  and  the  structures  in  their 
immediate  neighbourhood.  This  branch  is  not  uncomraoulj'  absent.  Occasionally  the  posterior 
branch  of  the  obturator  nerve  also  supples  a  twig  to  the  hip-joint. 

The  accessory  obturator  nerve  arises  from  the  third  or  fourth  or  from  the  third  and  fourth 
lumbar  nerves,  in  the  angles  between  the  roots  of  the  femoral  (anterior  crural)  and  obturator 
nerves.  It  is  present  in  about  twenty-nine  per  cent,  of  all  cases  (Eisler).  It  is  often  closely 
associated  with  the  obturator  nerve  to  the  level  of  the  brim  of  the  pelvis,  but  instead  of  passing 
through  the  obturator  foramen,  it  descends  along  the  medial  border  of  the  psoas,  crosses  the 
anterior  part  of  the  brim  of  the  pelvis,  passes  beneath  the  pectineus,  and  terminates  in  three 
main  branches.  One  of  these  branches  joins  the  anterior  division  of  the  obturator  nerve, 
another  supplies  the  pectineus,  and  the  third  is  distributed  to  the  hip-joint. 


The  Lumbo-sacral  Trunk 

The  trunk  of  the  plexus  usually  formed  by  the  union  of  the  smaller  part  of 
the  fourth  and  the  entire  fifth  lumbar  nerves  is  called  the  lumbo-sacral  trunk 


1006  THE  NERVOUS  SYSTEM 

(figs.  765,  769).  Sometimes  the  larger  part  of  the  fourth  nerve  may  help  to 
form  the  trunk.  It  may  receive  fibres  from  the  third  lumbar  nerve  or  be  formed 
entirely  from  the  fifth.  At  its  formation  it  is  situated  on  the  ala  of  the  sacrum 
under  cover  of  the  psoas.  It  descends  into  the  pelvis,  and,  as  it  crosses  the 
anterior  border  of  the  ala  of  the  sacrum,  it  emerges  from  beneath  the  psoas  at  the 
medial  side  of  the  obturator  nerve,  from  which  it  is  separated  by  the  ilio-lumbar 
artery.  It  passes  behind  the  common  iliac  vessels  and  unites  with  the  first  and 
second  sacral  nerves,  forming  with  them  the  upper  trunk  of  the  sacral  plexus. 

4.  SACRAL  NERVES 

The  anterior  primary  divisions  of  the  upper  four  sacral  nerves  enter  the  pelvis 
through  the  anterior  sacral  foramina  and  they  diminish  in  size  progressively  from 
above  downward.  The  first  sacral  is  the  largest  of  the  spinal  nerves,  the  second 
is  slightly  smaller  than  the  first,  while  the  third  and  fourth  are  relatively  small. 
The  fifth  sacral  nerve  is  still  smaller  than  the  fourth;  it  enters  the  pelvis  between 
the  sacrum  and  the  coccyx.  The  anterior  divisions  of  these  nerves  enter  into  the 
formation  of  three  parts  of  the  lumbo-sacral  plexus,  the  sacral,  pudendal,  and 
coccygeal. 

Sacral  Plexus 

The  sacral  plexus  shows  in  its  formation  variations  similar  to  those  of  the 
lumbar  plexus;  hence  there  are  also  seven  types  of  this  plexus,  three  of  them 
belonging  to  the  prefixed  or  proximal  class,  three  to  the  postfixed  or  distal  class, 
and  one  to  the  ordinary  class.  The  following  tables  show  the  range  of  variation 
and  the  common  arrangement  in  these  classes: — • 

Composition  of  the  Nerves  of  the  Sacral  Plexus 
Range  of  Variation 

Nerve.  Proximal. 

Furcal 3  or  3,  4  L. 

Common  peroneal  (exter- 
nal popliteal) 3,  4,  5  L.     1,  2  S. 

Tibial   (internal  popliteal)  3,  4,  5  L.     1,  2,  S. 

Posterior  femoral  cutane- 
ous (smaU  sciatic) 5  L.         1,  2,  3  S.  5  L.l,  2,     3,  4  S.  5  L.     1,  2,  3,  4  S. 

Common  Composition 
Nerve.  Proximal.  Ordinary.  Distal. 

Furcal 4  L.  4L.  4L. 

Common  peroneal  (exter- 
nal popliteal 4,  5  L.     1,  2  S.  4,  5  L.     1,  2  S.  4,  5  L.     1,  2  S. 

Tibial  (internal  popliteal) .  4,  5  L.     1,2  S.  4,  5  L.     1,  2,  3  S.  4,  ,  1^.    1,  2,  3,  4  S. 

Posterior  femoral  cutane- 
ous (small  sciatic) 1,  2,  3  S.  1,  2,  3  S.  2,  3  S. 

The  ordinary  type  of  sacral  plexus  is  commonly  formed  by  the  smaller  part  of 
the  anterior  division  of  the  fourth  lumbar  nerve  and  the  entire  anterior  division  of 
the  fifth  lumbar  nerve,  together  with  the  first  and  parts  of  the  second  and  third 
sacral  nerves. 

The  plexus  lies  in  the  pelvis  on  the  anterior  surface  of  the  piriformis  (fig.  765) 
and  behind  the  pelvic  fascia  and  the  branches  of  the  hypogastric  (internal  iliac) 
artery.  It  is  also  dorsal  to  the  coils  of  intestine,  the  lower  part  of  the  ilio-pelvic 
colon  lying  in  front  of  the  left  plexus,  and  the  lower  part  of  the  ileum  in  front  of  the 
right  plexus. 

The  branches  given  off  by  this  plexus  are : — visceral,  cutaneous,  and  muscular. 

Visceral  branches  are  given  off  from  the  second,  third,  and  fourth  sacral 
nerves  to  the  pelvic  viscera. 

The  visceral  branches  correspond  to  white  rami  communicantes,  through  not  joining  the 
sympathetic  trunk.    The  branches  from  the  second  and  fourth  sacral  nerves  are  inconstant. 


Ordinary. 

Distal. 

4L. 

4,  5  or  5  L. 

4,  5  L.     I,  2  S. 
4,  5,  L.     1,  2,  3  S. 

4,  5  L.     1,  2,  3  S. 
4,  5  L.     1,  2,  3,  4,  S. 

THE  SACRAL  PLEXUS  1007 

Cutaneous  branches. — (a)  The  posterior  femoral  cutaneous  (small  sciatic) 
nerve  arises  partly  from  the  anterior  and  partly  from  the  posterior  branches  of 
the  anterior  primary  divisions  of  the  first,  second,  and  third  sacral  nerves.  It 
lies  on  the  back  of  the  plexus  (figs.  765,  769),  leaves  the  pelvis  at  the  lower 
border  of  the  piriformis,  and  descends  in  the  buttock  between  the  gluteus  maxi- 
mus  and  the  posterior  surface  of  the  sciatic  nerve  (fig.  770).  At  the  lower 
border  of  the  gluteus  maximus  it  passes  behind  the  long  head  of  the  biceps  femoris, 
and  descends,  immediately  beneath  the  deep  fascia,  through  the  thigh  and  the 
upper  part  of  the  popliteal  space  (fig.  740).  At  the  lower  part  of  the  popliteal 
region  it  perforates  the  deep  fascia,  and  it  terminates  in  branches  which  are  dis- 
tributed to  the  skin  of  the  calf. 

Branches  of  the  small  sciatic. — 1.  Perineal  branches  are  distributed  in  part  to  the  skin  of 
the  upper  and  medial  sides  of  the  thigh  on  its  dorsal  aspect.  One  of  the  branches,  kno\\Ti  as  the 
long  pudendal  nerve,  runs  forward  and  medialward  in  front  of  the  tuberosity  of  the  ischium  to 
the  lateral  margin  of  the  anterior  part  of  the  perineum,  where  it  perforates  the  fascia  lata  and 
CoUes'  fascia  and  enters  the  anterior  compartment  of  the  perineum.  In  the  perineum  twigs 
join  it  with  the  superficial  perineal  nerves,  and  its  terminal  filaments  are  distributed  to  the  skin 
of  the  scrotum  in  the  male,  and  to  the  labium  majus  in  the  female. 

2.  Inferior  clunial  (gluteal)  branches,  two  or  three  in  number,  are  given  off  beneath  the 
gluteus  maximus;  they  turn  around  the  lower  border  of  this  muscle  and  are  distributed  to  the 
skin  of  the  lower  and  lateral  part  of  the  gluteal  region. 

3.  Femoral  cutaneous  branches  are  given  off  as  the  nerve  descends  through  the  thigh. 
They  perforate  the  deep  fascia  and  are  distributed  to  the  skin  of  the  back  of  the  thigh,  especially 
on  the  medial  side. 

In  case  of  the  separate  origin  of  the  tibial  (internal  popliteal)  and  common  peroneal  (external 
popliteal)  nerves,  the  posterior  femoral  cutaneous  (small  sciatic)  also  arises  from  the  sacral 
plexus  in  two  parts.  The  ventral  portion  descends  with  the  tibial  nerve  below  the  piriformis  and 
gives  off  the  perineal  branches  and  medial  femoral  branches,  while  the  dorsal  portion  passes 
through  that  muscle  with  the  common  peroneal  nerve,  and  furnishes  the  gluteal  and  lateral 
femoral  branches. 

(6)  The  inferior  medial  clunial  (perforating  cutaneous)  nerve  arises  from  the  posterior 
portion  of  the  second  and  third  sacral  nerves  (figs.  765,  769).  It  perforates  the  lower  part  of  the 
sacro-tuberous  (great  sciatic)  ligament,  turns  around  the  inferior  border  of  the  gluteus  maximus, 
and  is  distribtued  to  the  skin  over  the  lower  and  medial  part  of  that  muscle.  It  is  sometimes 
associated  at  its  origin  with  the  pudic  nerve.  It  is  not  always  present.  Its  place  is  sometirnes 
taken  by  a  small  nerve  (the  greater  coccygeal  perforating  nerve  of  Eisler),  arising  from  the  third 
and  fourth  or  fourth  and  fifth  sacral  nerves,  and  sometimes  it  is  represented  by  a  branch  of  the 
posterior  femoral  cutaneous. 

Muscular  branches  of  the  sacral  plexus. — (a)  One  or  two  small  nerves  to  the 

piriformis  pass  from  the  posterior  divisions  of  the  first  and  second  sacral  nerves. 

(b)  The  superior  gluteal  nerve  receives  fibres  from  the  posterior  branches  of 
the  fourth  and  fifth  lumbar,  and  the  first  sacral  nerves.  It  passes  out  of  the 
pelvis  through  the  great  sciatic  foramen,  above  the  upper  border  of  the  piriformis, 
and  it  is  accompanied  by  the  superior  gluteal  artery.  As  soon  as  it  enters  the 
buttock  it  divides  into  two  branches,  an  upper  and  a  lower. 

1.  The  upper  branch  is  the  smaller.  It  accompanies  the  upper  branch  of  the  deep  division 
of  the  superior  gluteal  artery  below  the  middle  curved  line  of  the  ihum,  and  it  ends  entirely 
in  the  gluteus  medius  (fig.  770). 

2.  The  lower  branch,  larger  than  the  upper,  passes  forward  across  the  middle  of  the  gluteus 
minimus,  with  the  lower  branch  of  the  gluteal  artery;  it  supphes  the  gluteus  medius  and  the 
gluteus  minimus,  and  it  ends  in  the  medial  and  posterior  part  of  the  tensor  fasoias  latse. 

(c)  The  inferior  gluteal  nerve  is  formed  by  fibres  from  the  posterior  branches 
of  the  fifth  lumbar,  and  the  first  and  second  sacral  nerves.  It  passes  through  the 
great  sciatic  foramen,  below  the  piriformis,  and  divides  into  a  number  of  branches 
which  end  in  the  gluteus  maximus  (figs.  765,  769). 

(d)  The  nerve  of  the  quadratus  femoris  is  formed  by  the  anterior  branches  of 
the  fom'th  and  fifth  lumbar  and  the  first  and  second  sacral  nerves.  It  lies  on  the 
front  of  the  plexus  and  issues  from  the  pelvis  below  the  piriformis.  In  the 
buttock  it  lies  at  first  between  the  sciatic  nerve  and  the  back  of  the  ischium,  and, 
at  a  lower  level ,  between  the  obtxu-ator  internus  with  the  gemelli  and  the  ischium . 
It  terminates  in  the  anterior  surface  of  the  quadratus  femoris,  having  previouslj^ 
given  off  a  branch  to  the  hip-joint  and  another  to  the  inferior  gemellus. 

(e)  The  nerve  of  the  obturator  internus  is  formed  by  the  anterior  branches 
of  the  fifth  lumbar,  and  the  first  and  second  sacral  nerves  (figs.  765,  769).  It 
leaves  the  pelvis  below  the  pii-iformis,  and  crosses  the  spine  of  the  ischium  on  the 


1008 


THE  NERVOUS  SYSTEM 


lateral  side  of  the  internal  pudic  artery  and  on  the  medial  side  of  the  sciatic  nerve. 
It  gives  a  branch  to  the  gemellus  superior,  and  turns  forward  through  the  small 
sciatic  foramen  into  the  perineum,  where  it  terminates  in  the  inner  surface  of  the 
obturator  internus. 

The  sciatic  nerve  [n.  ischiadicus]. — -The  sciatic  is  not  only  the  largest  nerve 
of  the  sacral  plexus,  but  it  is  also  the  largest  nerve  in  the  body.  Its  terminal 
branches  are  chiefly  muscular,  though  some  of  its  fibres  are  cutaneous.  Although 
it  is  referred  to  as  one  trunk,  it  consists  in  reality  of  peroneal  (lateral)  and  tibial 
(medial  popliteal)  portions,  which  are  bound  together  by  a  sheath  of  fibrous  tissue 
as  far  as  the  upper  end  of  the  popliteal  space.  In  about  10  per  cent,  of  the  cases 
the  two  parts  remain  separate,  and  in  such  cases  the  peroneal  (lateral  popliteal) 


Fig.  769. — A  Dissection  op  the  Lumbar  and  Saceal  Plexuses,  from  Behind. 
(The  anterior  crural  nerve  is  placed  between  the  external  cutaneous  and  obturator  nerves.) 


Dura  mater  of  cord 


Last  thoracic  nerve 


Ilio -hypogastric 


Iliac  branch  of  ilio 
hypogastric 


Gluteus  medius 
Superior  gluteal  artery 
Superior  gluteal 

Sciatic  nerve 

Inferior  gluteal  nerve 


G  eni  to -femoral 


Cauda  equina 


Filum  terminale 
Lateral  cutaneous 


Obturator 
\^  '  —  Lumbo-sacral  trunk 
-^i First  sacral  nerve 


Fifth  sacral  nerve 


Visceral  branches 
Inferior  gluteal  artery 
Sacro-spinous 

ligament 
Pudic  nerve 


Inferior  medial  clunial 
of  second  and  third 
sacral  i 


part  usually  pierces  the  piriformis.  The  peroneal  portion  of  the  nerve  consists  of 
fibres  derived  from  the  dorsal  branches  of  the  anterior  primary  divisions  of  the 
fourth  and  fifth  lumbar  and  the  first  and  second  sacral  nerves,  while  the  tibial 
part  is  formed  by  the  fibres  from  the  anterior  branches  of  the  fourth  and  fifth 
lumbar,  and  the  first,  second,  and  third  sacral  nerves  (figs.  765,  769).  ^  The  com- 
mon trunk  leaves  the  pelvis  by  passing  through  the  great  sacro-sciatic  foramen, 
usually  below  the  piriformis,  and  descends  through  the  buttock,  running  midway 
between  the  tuber  ischii  and  the  great  trochanter  (fig.  770).  Passing  down  the 
thigh,  the  trunk  terminates  at  the  upper  angle  of  the  popliteal  space  by  dividing 


THE  SCIATIC  NERVE 


1009 


into  the  common  peroneal  (external  politeal)  and  the  tibial  (internal  popliteal) 
nerves  (fig.  771). 

The  relation  of  the  trunk  to  the  piriformis  muscle  is  more  or  less  unique.  It  may  pass  either 
above  or  below  the  muscle,  it  may  spht  and  pass  around  the  muscle,  or  the  muscle  may  be  spUt 
and  surround  the  nerve.  Again,  there  may  be  a  sphtting  of  both  the  muscle  and  the  nerve,  in 
which  case  any  possible  combination  of  the  four  parts  may  occur;  a  portion  of  the  nerve  may  be 
above  and  a  portion  between  the  parts  of  the  muscle,  or  a  portion  may  be  below  and  a  portion 
between.  The  trunk  of  the  nerve  hes  deeply  in  the  thigh,  and  it  is  covered  posteriorly  by  the 
skin  and  fascia,  the  gluteus  maximus  and  the  long  head  of  the  biceps  femoris.  Anteriorly  it 
is  in  relation,  from  above  downward,  with  the  following  structures: — the  posterior  surface  of 
the  ischium  and  the  nerve  to  the  quadratus  femoris,  the  gemellus  superior,  obturator  internus, 
gemellus  inferior,  quadratus  femoris,  and  adductor  magnus  muscles. 

Muscular  branches  of  the  sciatic  are  given  off  at  the  upper  part  of  the  thigh  to 
the  semitendinosus,  to  the  long  head  of  the  biceps  femoris,  to  the  semi  membranosus, 

Fig.  770. — A  Dissection  op  the  Nerves  in  the  Gluteal  Region. 
(The  gluteus  maximus  and  gluteus  medius  have  been  divided  near  their  insertions,  and  thrown 

upward.) 

Inferior  gluteral    artery 

-Gluteus  maximus 


Inferior  gluteal  nerve 
Gluteal  artery 


Sacro-tuberous 
ligament 

Comes  nervi 

ischiadici 
Gemellus 
inferior 
Tuberosity  of 
ischium 

Long  pudendal 


\ Adductor 

^     magnus 


Sciatic  nerve 

Posterior 
cutaneous 
nerve 


Tendon  of  obturator  externus 


Vastus  externus 


Gluteus  maximus 


and  to  the  adductor  magnus,  and,  about  the  middle  of  the  thigh,  a  branch  is  fur- 
nished to  the  short  head  of  the  biceps. 

The  branch  to  the  short  head  of  the  biceps  femoris  is  derived  from  the  peroneal  (lateral 
popliteal)  portion  of  the  nerve,  while  all  the  other  muscular  branches  are  given  off  by  the  tibial 
(medial  pophteal)  part.  The  semitendinosus  receives  two  branches,  one  which  enters  it  above 
and  another  which  passes  into  it  below  its  tendinous  intersection.  The  nerve  to  the  long  head 
of  the  biceps  descends  along  the  sciatic  trunk  and  enters  the  middle  of  the  deep  surface  of  the 
muscle.  The  nerves  to  the  semimembranosus  and  adductor  magnus  arise  by  a  common  trunk 
'  which  divides  into  three  or  four  branches.  One  branch  ends  in  the  adductor,  and  the  others 
are  distributed  to  the  semimembranosus.  The  branch  to  the  adductor  magnus  supplies  only 
those  fibres  of  the  muscle  which  begin  from  the  tuberosity  of  the  ischium  and  descend  vertically 
to  the  medial  condyle  of  the  femur. 

At  the  apex  of  the  popliteal  space  the  two  component  parts  of  the  common 
trunk  of  the  sciatic  become  distinct.  The  tibial  nerve  (internal  popliteal) ,  formed 
by  fibres  from  the  anterior  branches  of  the  fourth  and  fifth  lumbar  and  first, 
second,  and  third  sacral  nerves,  passes  vertically  through  the  popliteal  space, 
descends  through  the  leg  to  a  point  midway  between  the  medial  malleolus  and 
the  most  prominent  part  of  the  medial  tubercle  of  the  os  calcis,  where  it  divides 
into  its  terminal  branches,  the  lateral  plantar  and  the  medial  plantar  nerves. 
The  part  of  the  nerve  from  the  point  of  bifurcation  to  the  lower  border  of  the 
popliteus  muscle  is  sometimes  called  the  internal  popliteal;  the  part  of  the  nerve 
in  the  dorsum  of  the  leg  being  then  designated  the  posterior  tibial  nerve. 


1010  THE  NERVOUS  SYSTEM 

In  the  upper  part  of  the  pophteal  space  the  tibial  nerve  lies  relatively  superficially,  being 
covered  dorsally  by  the  skin  and  fascia,  while  in  the  lower  part  of  the  space  it  is  overlapped  by 
the  heads  of  the  gastrocnemius  and  is  crossed  by  the  plantaris.  In  the  upper  part  of  the  space 
it  lies  in  front  of  the  posterior  femoral  cutaneous  (small  sciatic)  nerve  and  to  the  lateral  side  of 
the  vein  and  artery;  at  the  middle  of  the  space  it  is  dorsal  and  in  the  lower  part  of  the  space 
it  is  medial  to  both  of  them. 

The  branches  given  off  by  the  tibial  nerve  in  the  popliteal  space  are  articular, 
cutaneous,  and  muscular. 

The  articular  branches  are  usually  three  in  number,  a  superior  and  an  inferior 
internal  articular  and  an  azygos  articular.  They  accompany  the  corresponding 
arteries,  and,  after  piercing  the  ligaments,  are  distributed  in  the  interior  of  the 
joint.     The  superior  branch  is  often  wanting. 

The  cutaneous  branch,  the  medial  sural  cutaneous  (tibial  communicating) 
nerve,  descends  between  the  heads  of  the  gastrocnemius,  beneath  the  deep 
fascia,  to  the  middle  of  the  calf,  where  it  pierces  the  fascia  and  unites  with  the 
peroneal  anastomotic  branch  of  the  lateral  sural  cutaneous  to  form  the  sural 
(external  saphenous)  nerve,  through  which  its  fibres  are  distributed  to  the  skin 
of  the  lower  and  dorsal  part  of  the  leg  and  the  lateral  side  of  the  foot. 

The  muscular  branches  are  distributed  to  both  heads  of  the  gastrocnemius,  to 
the  plantaris,  soleus,  and  popliteus. 

The  nerve  io  the  soleus  is  relatively  large,  and  passes  between  the  lateral  head  of  the  gastroc- 
nemius and  the  plantaris  before  it  reaches  its  termination  (fig.  771).  The  nerve  to  the  popliteus 
descends  on  the  posterior  surface  of  the  muscle,  turns  around  its  lower  border,  and  is  distributed 
on  its  anterior  aspect.  In  addition  to  supplying  the  popliteus,  it  gives  articular  branches  to 
the  knee  and  superior  tibio-fibular  joints,  a  branch  to  the  tibia  which  accompanies  the  medullary 
artery,  and  a  long,  slender  twig  which  gives  filaments  to  the  anterior  and  posterior  tibial  arteries, 
and  it  descends  as  the  interosseous  crural  nerve  on  the  interosseous  membrane  to  the  inferior 
tibio-fibular  joint.  It  also  gives  branches  to  the  interosseous  membrane  and  to  the  periosteum 
of  the  lower  part  of  the  tibia. 

Relations. — In  the  upper  part  of  the  leg  the  tibial  nerve  is  placed  deeply,  under  the  gas- 
trocnemius and  soleus,  but  in  the  lower  half  it  is  merely  covered  by  the  deep  fascia,  which  is 
thickened  between  the  medial  maleolus  and  the  calcaneus  to  form  the  lacinate  (internal  annular) 
ligament,  and  the  termination  of  the  nerve  lies  either  under  cover  of  this  hgament,  or  under  the 
attachment  of  the  abductor  hallucis.  The  anterior  relations  of  the  nerve  are,  from  above  down- 
ward, the  tibialis  posterior,  the  flexor  digitorum  longus,  the  lower  part  of  the  tibia,  and  the  pos- 
terior ligament  of  the  ankle-joint.  For  a  short  distance  after  its  commencement  the  nerve  lies 
to  the  medial  side  of  the  posterior  tibial  artery;  then  it  crosses  behind  the  artery  and  runs  down- 
ward along  its  lateral  aspect. 

The  branches  of  the  lower  part  of  the  tibial  nerve  (below  the  popliteal  space) 
are  likewise  muscular,  cutaneous,  and  articular.  They  are  supplied  to  the  deep 
muscles  of  the  dorsum  of  the  leg,  to  the  fibula,  to  the  skin  of  the  heel  and  foot,  and 
to  the  ankle-joint.  Several  of  the  terminal  branches  are  important  enough  to 
receive  special  names  and  special  treatment. 

The  muscular  branches  pass  from  the  upper  part  of  the  nerve  to  the  tibiahs  posterior, 
flexor  digitorum  longus,  soleus,  and  flexor  haUuois  longus.  The  fibular  branch  arises  with  the 
nerve  to  the  flexor  hallucis  longus,  and  accompanies  the  peroneal  artery.  It  supplies  the  peri- 
osteum and  gives  filaments  which  accompany  the  medullary  artery. 

The  articular  branches  arise  from  the  lower  part  of  the  nerve,  immediately  above  its 
terminal  branches,  and  they  pass  into  the  ankle-joint  through  the  deltoid  ligament. 

The  medial  calcaneal  (calcaneo-plantar  cutaneous)  nerves  ai-ise  from  the  trunk  of  the 
tibial  nerve  in  the  lower  part  of  the  leg.  They  pierce  the  laciniate  (internal  annular)  ligament, 
and  are  distributed  to  the  integument  of  the  medial  side  and  plantar  surface  of  the  heel  and 
the  adjoining  part  of  the  sole  of  the  foot  (fig.  771). 

Terminal  branches  of  tibial  nerve. — The  medial  plantar  nerve  is  the  larger  of 
the  two  terminal  branches  of  the  tibial  nerve.  It  commences  under  cover  of  the 
lower  border  of  the  laciniate  (internal  annular)  ligament,  or  under  the  posterior 
border  of  the  abductor  hallucis,  and  passes  forward,  accompanied  by  the  small 
internal  plantar  artery,  in  the  inter-muscular  septum  between  the  abductor 
hallucis  and  the  flexor  digitorum  brevis.  At  the  middle  of  the  length  of  the  foot 
it  becomes  superficial,  in  the  interval  between  the  two  muscles,  and  divides  into 
four  sets  of  terminal  branches  (fig.  772) : — 

(a)  Muscular  branches  pass  from  the  trunk  of  the  nerve  to  the  abductor 
hallucis  and  the  flexor  digitorum  brevis. 

(6)  Articular  branches  are  distributed  to  the  talo-navicular  (astragalo- 
sacphoid)  and  the  naviculari-cuneiform'joint. 

(c)  Plantar  cutaneous  branches  are  supplied  to  the  skin  of  the  medial  part  of 
the  sole. 


THE  TIBIAL  NERVE 


1011 


{d)  The  digital  branches  are  four  in  number,  the  first,  a  proper  plantar  digital, 
the  secondj  third,  and  fourth,  the  common  plantar  digitals.     Near  the  bases  of  the 

Fig.  771. — Muscle  Nerves  of  the  Right  Leg,  viewed  from  Behind.     (Spalteholz.) 
The  semitendinosus,  semimembranosus,  biceps  femoris,  gastrocnemius,  plantaris,  soleus,  and 
flexor  hallucis  longus  have  been  wholly  or  in  part  removed. 


Sciatic  nerve  ■ 

Popliteal  vein  — 

Popliteal  artery -- 


Adductor  magnus  -- J 


Vastus  medialis  ^'-'^■r .,  ■   -- >  ;  ■  '  i 
Articular  branch  -  -  -j.-^r ;-  ^r     ^j^ ,  "1 


Tibial  nerve 

1 

Semimembranosus  — r-? 
Medial  head  of  gastrocnemius — Jf- 
Lateral  head  of  gastrocnemius  ■' 
Popliteus 


■"Biceps  f' 

—Medial  sural  cutaneous  nerve 
— Common  peroneal  nerve 
~  Articular  branch 
■-  Lateral  sural  cutaneous  nerve 

/^M^--^-"***"  Muscular  branches 

Plantar  muscle 
Head  of  fibula 
— Interosseus  cruris  nerve 

—  Popliteal  artery 


Soleus  (cut)    — - 


-Muscular  branch 


Posterior  tibial  artery  ■ 
Tibial  nerve 
Muscular  branch  * 
Flexor  digitorum  longus 

Posterior  tibisil  artery   — g 

Tibialis  posterior 


\Jd 


|--PeroneaI  artery 

—  Muscular  branch 

Flexor  hallucis  longus 

—  Peroneus  longus 

5--Peroneal  artery 


Tendo  calcaneus  (Achillis) 

Articular  branch  • 

Medial  calcaneal  nerves 

Posterior  tibial  artery ' 

Laciniate  ligament 


|---  Articular  branch 
—  Flexor  hallucis  longus  (cut) 
^---Sural  nerve 

-Lateral  calcaneal  branches 


metatarsal  bones,  the   second,  third  and  fourth  common  plantar  digital  divide 
into  proper  plantar  digital  nerves. 

The  first  proper  plantar  digital  nerve  becomes  subcutaneous  farther  back  than  the  others, 
and,  after  sending  a  branch  to  the  flexor  hallucis  brevis,  passes  to  the  medial  side  of  the  great 


1012 


THE  NERVOUS  SYSTEM 


toe.  The  second  (common  digital)  nerve  gives  a  twig  to  the  first  lumbrical  and  bifurcates 
to  supply  the  adjacent  sides  of  the  first  and  second  toes.  The  third  supplies  the  adjacent  sides 
of  the  second  and  third  toes,  and  the  fourth,  after  connecting  with  the  superficial  branch  of  the 
lateral  plantar  nerve,  divides  to  supply  the  adjacent  sides  of  the  third  and  fourth  toes.  All  the 
proper  digital  nerves  run  along  the  sides  of  the  toes  and  he  below  the  corresponding  arteries; 
they  supply  the  joints  of  the  toes,  and  each  gives  off  a  dorsal  branch  to  the  skin  over  the  second 
and  terminal  phalanges  and  to  the  bed  of  the  nail.  All  of  them  give  fibres  terminating  in 
numerous  Pacinian  corpuscles. 

The  lateral  plantar  nerve  is  the  smaller  of  the  two  terminal  branches  of  the 
tibial  nerve.     It  commences  at  the  lower  border  of  the  laciniate  (internal  annular) 


Fig.  772. — Superficial  Nerves  in  the  Sole  op  the  Foot.     (Ellis.) 


Abductor  hallucis- 

Flexor  digitorum  brevis" 
Medial  plantar 
Medial  plantar  artery. 


Proper  plantar  digital 

nerve  to  medial  side 

of  hallux 


Abductor  minimi  digit! 


Lateral  plantar  artery 
Lateral  plantar  nerve 


Proper  plantar  digital 
branches  of  the 
lateral  plantar 


.ti^- 


Proper  plantar  digital 
branches  of  the 
11  J  medial  plantar 


ligament,  or  under  cover  of  the  origin  of  the  abductor  hallucis,  and  passes  forward 
and  lateralward  to  the  base  of  the  fifth  metatarsal  bone,  where  it  divides  into  a 
superficial  and  a  deep  branch  (fig.  772).  As  it  runs  forward  and  lateralward  it 
it  is  superficial  to  the  tendon  of  the  flexor  hallucis  longus  and  to  the  quadratus 
plantse  (flexor  accessorius),  and  deep  to  the  flexor  digitorum  brevis.  At  its  ter- 
mination it  lies  in  the  interval  between  the  flexor  digitorum  brevis  and  abductor 
digiti  quinti. 

Branches. — -From  the  trunk  of  the  lateral  plantar  nerve  muscular,  superficial 
and  deep,  and  articular  branches  are  given  off. 


THE  COMMON  PERONEAL  NERVE  1013 

The  muscular  branches  arise  from  the  commencement  of  the  nerve  and  are  dis- 
tributed to  the  abductor  digiti  quinti  and  quadratus  plantse. 

The  articular  branches  supply  the  calcaneo-cuboid  joint. 

The  superficial  branch  supplies  muscular  filaments  to  the  flexor  digiti  quinti 
brevis,  the  opponens,  the  third  plantar  and  fourth  dorsal  interosseous  muscles, 
and  divides  into  two  common  plantar  digital  nerves,  each  of  which  subdivides  to 
form  proper  plantar  digital  nerves. 

The  lateral  of  the  two  common  branches  supplies  the  lateral  side  of  the  fifth  digit;  the  medial 
connects  with  the  lateral  digital  branch  of  the  medial  plantar  nerve  (fig.  772)  and  divides  into 
proper  plantar  digital  nerves  for  the  adjacent  sides  of  the  fourth  and  fifth  digits.  The  digital 
branches  of  the  superficial  division  of  the  lateral  plantar,  like  those  of  the  medial  plantar,  supply 
the  skin  of  the  toes  and  the  beds  of  the  nails,  and  their  fibres  terminate  in  numerouos  Pacinian 
corpuscles. 

The  deep  branch  passes  forward  and  medialward  into  the  deep  part  of  the 
sole  with  the  plantar  arterial  arch.  It  runs  deep  to  the  quadratus  plantse,  the  long 
flexor  tendons  and  the  lumbricals,  and  the  oblique  adductor  of  the  great  toe.  It 
lies,  therefore,  immediately  beneath  the  bases  of  the  metatarsal  bones  and  it 
supplies  the  following  muscular  and  articular  branches: — • 

Muscular  branches  to  the  lateral  three  lumbricals,  the  interossei  of  the  medial  three  inter- 
metatarsal  spaces,  and  the  transverse  and  oblique  adductor  muscles  of  the  great  toe. 

Articular  branches  to  the  intertarsal  and  to  the  tarso-metatarsal  joints  and  not  uncommonly 
to  the  metatarso-phalangeal  joints  also.  Filaments  from  the  deep  branch  frequently  pass 
through  the  interosseous  spaces  and  join  with  the  interosseous  branches  of  the  deep  peroneal 
(anterior  tibial)  nerve. 

The  common  peroneal  (external  popliteal)  nerve. — ^At  the  apex  of  the  pop- 
liteal space,  where  the  two  component  parts  of  the  sciatic  trunk  usually  become 
distinct,  the  lateral  portion  receives  the  name  common  peroneal  nerve.  It  de- 
scends along  the  posterior  border  of  the  biceps  femoris,  which  forms  the  upper  part 
of  the  lateral  boundary  of  the  space  (fig.  771).  It  leaves  the  space  at  the  lateral 
angle,  crosses  the  plantaris,  the  lateral  head  of  the  gastrocnemius,  the  pop- 
liteus,  and  the  inferior  external  artery,  and  descends  behind  the  upper  part  of  the 
soleus,  to  the  neck  of  the  fibula,  where  it  turns  forward  between  the  peroneus 
longus  and  the  bone,  and  breaks  up  into  its  three  terminal  branches,  the  recurrent 
articular,  the  superficial  peroneal  (musculo-cutaneous),  and  the  deep  peroneal 
(anterior  tibial)  nerves  (fig.  773). 

Upper  branches. — While  it  is  in  the  popliteal  space  the  common  peroneal 
(external  popliteal)  nerve  gives  off  two  articular  branches  and  a  cutaneous  branch. 

The  superior  articular  branch  accompanies  the  superior  external  articular  artery.  The 
lateral  head  of  the  gastrocnemius,  and  it  joins  the  inferior  external  articular  artery  behind  the 
tendon  of  the  biceps  femoris.  Both  the  upper  and  lower  articular  branches  pierce  the  ligaments 
and  are  distributed  in  the  interior  of  the  knee  joint. 

The  cutaneous  branch  {communicans  fibularis) ,  lateral  sural  cutaneous,  is  extremely  variable 
both  as  to  the  number  of  its  branches  and  as  to  the  place  of  its  anastomosis  with  the  medial 
sural  cutaneous.  Leaving  the  common  peroneal  (external  popliteal)  in  the  popliteal  space,  it 
descends  between  the  deep  fascia  and  the  lateral  head  of  the  gastrocnemius  to  the  middle  of 
the  calf,  where  it  pierces  the  fascia  and  unites  with  the  medial  sural  cutaneous  to  form  the 
sural  (external  saphenous)  nerve.  In  its  course  it  may  give  off  no  branches;  or  it  may  give  off 
several,  some  of  which  supply  the  skin  of  the  dorsum  of  the  leg,  while  one  of  them,  the  peroneal 
anastomotic  branch,  unites  with  the  medial  sural  cutaneous  to  form  the  sural  (short  saphenous) 
nerve.  The  junction  of  the  peroneal  anastomotic  branch  with  the  medial  sural  cutaneous  may 
take  place  at  any  point  between  the  popliteal  space  and  the  lower  third  of  the  leg. 

The  sural  (external  or  short  saphenous)  nerve  is  formed  by  the  union  of  the 
lateral  sural  cutaneous  nerve  either  directly,  or  tlu-ough  a  connecting  branch, 
the  peroneal  anastomotic,  with  the  medial  sural  cutaneous  (fig.  771).  It  descends 
along  the  lateral  border  of  the  tendo  Achillis,  giving  branches  to  the  lower  and 
lateral  part  of  the  leg,  and  lateral  calcaneal  branches  to  the  lateral  side  of  the  heel. 
It  passes  dorsal  to  the  lateral  malleolus,  turns  forward  across  the  lateral  surface  of 
the  cruciate  (external  annular)  ligament,  and  becomes  the  lateral  dorsal  cutaneous 
nerve.  Continuing  along  the  lateral  side  of  the  foot  it  divides  into  two  branches, 
the  dorsal  digitals,  one  of  which  supplies  the  lateral  side  of  the  fifth  digit,  while  the 
other  anastomoses  with  or  takes  the  place  of  a  branch  of  the  superficial  peroneal 
(musculo-cutaneous)  nerve,  which  is  distributed  to  the  adjacent  sides  of  the  fourth 
and  fifth  digits  (fig.  773). 

The  terminal  branches  of  the  common  peroneal. — (1)  The  recurrent  articular 
nerve  passes  medialward,  around  the  neck  of  the  fibula,  and  through  the  upper 


1014 


THE  NERVOUS  SYSTEM 


part  of  the  attachment  of  the  extensor  digitorum  longus.  At  the  medial  border 
of  the  fibula  it  becomes  associated  with  the  anterior  tibial  recmrent  artery,  with 
which  it  ascends  through  the  upper  part  of  the  tibialis  anterior  to  the  head  of  the 


Fig.  773. — Distrebtjtion  of  the  Superficial  and  Deep  Peroneal  Nerves  on  the  Ante- 
rior Aspect  of  the  Leg  and  on  the  Dorsum  of  the  Foot.     (Hirschfeld  and  Leveill^.) 


Common  peroneal  nerve- 
Recurrent  articular' 


Superficial  peroneal 
Branch  to  peroneus  longus' 


Branch  to  external 
digitorum  longus 


Branch  to  peroneus  brevis' 


Superficial  peroneal' 


Intermediate  dorsal  cutaneous- 


Lateral  dorsal  cutaneous' 


Deep  peroneal  nerve 


■Anterior  tibial  artery 


Tibialis  anterior 


'Deep  peroneal  nerve 
Medial  dorsal  cutaneous 


Deep  peroneal  (lateral  division) 


Deep  peroneal  (medial  division) 


tibia  and  the  knee-joint.     It  supplies  the  tibialis  anterior,  the  superior  tibio- 
fibular joint,  and  the  knee-joint. 

(2)  The  superficial  peroneal  (musculo-cutaneous)  nerve  arises  from  the  com- 
mon peroneal  between  the  peroneus  longus  and  the  neck  of  the  fibula  and  de- 
scends in  the  intermuscular  septum  between  the  long  and  short  peronei  on  the 


I 


THE  DEEP  PERONEAL  NERVE  1015 

lateral  side,  and  the  extensor  digitorum  longus  on  the  medial  side.  It  gives  off 
muscular  and  cutaneous  branches  in  its  descent,  and  at  the  junction  of  the  middle 
and  lower  thii-ds  of  the  leg  it  pierces  the  deep  fascia  and  divides  into  a  medial 
and  a  lateral  branch  (fig.  773). 

Muscular  branches  are  given  off  from  the  superficial  peroneal  to  the  peroneus 
longus  and  peroneus  brevis  before  the  nerve  pierces  the  deep  fascia. 

Cutaneous  branches  pass  from  the  trunk  of  the  superficial  peroneal  to  the 
skin  of  the  lower  part  of  the  front  of  the  leg. 

The  medial  dorsal  cutaneous  (internal  cruciate  branch  of  the  superficial 
peroneal),  passes  downward  and  medialward  across  the  transverse  and  the  cru- 
ciate (anterior  annular)  ligament  of  the  ankle  and  subdivides  into  two  branches. 
The  medial  branch  passes  to  the  medial  side  of  the  great  toe;  it  also  supplies  twigs 
to  the  skin  of  the  medial  side  of  the  foot,  and  it  anastomoses  with  the  deep  saphen- 
ous nerve  and  with  the  medial  terminal  branch  of  the  deep  peroneal  (anterior 
tibial)  nerve.  The  lateral  branch  passes  to  the  base  of  the  cleft  between  the  second 
and  third  toes  and  divides  into  two  dorsal  digital  branches  which  supply  the 
adjacent  sides  of  the  cleft. 

The  lateral  branch  (intermediate  dorsal  cutaneous)  of  the  superficial  peroneal, 
in  separating  from  the  medial,  crosses  in  front  of  the  cruciate  ligament  and  divides 
into  two  dorsal  digital  branches,  which  pass  beneath  the  dorsal  venous  arch. 
The  medial  of  these  branches  supplies  the  adjacent  sides  of  the  third  and  fourth 
toes  (fig.  773).  The  lateral  branch  communicates  with  the  sural  (external  saphen- 
ous) nerve  and  is  distributed  to  the  adjacent  sides  of  the  fourth  and  fifth  toes. 
This  latter  branch  is  frequently  replaced  by  the  sural  nei-ve. 

(3)  The  deep  peroneal  (anterior  tibial)  nerve  springs  from  the  end  of  the 
common  peroneal  (external  popliteal)  nerve  between  the  peroneus  longus  muscle 
and  the  neck  of  the  fibula.  It  passes  forward  and  medialward  through  the  upper 
part  of  the  origin  of  the  extensor  digitorum  longus,  to  the  interval  between  that 
muscle  and  the  tibialis  anterior;  then  it  descends,  in  the  anterior  compartment  of 
the  leg,  to  the  ankle,  where  it  divides  into  a  medial  and  a  lateral  terminal 
branch  (fig.  773). 

In  the  upper  part  of  the  leg  the  deep  peroneal  nerve  lies  between  the  extensor  digitorum  lon- 
gus and  tibialis  anterior  and  lateral  to  the  anterior  tibial  artery.  In  the  middle  of  the  leg  it  is  in 
front  of  the  artery  and  between  the  extensor  hallucis  longus  and  tibiaMs  anterior;  then  it  crosses 
beneath  the  extensor  hallucis,  and  in  the  lower  third  of  the  leg  it  is  again  to  the  lateral  side  of 
the  artery,  but  between  the  extensor  hallucis  longus  and  the  extensor  digitorum  longus. 

Branches  furnished  from  the  trunk  of  the  deep  peroneal  are  muscular,  articu- 
lar, and  terminal. 

The  muscular  branches  supply  the  tibialis  anterior,  extensor  digitorum 
longus,  extensor  hallucis  longus,  and  peroneus  tertius. 

Articular  filaments  are  given  to  the  ankle-joint  and  the  inferior  tibio-fibular 
articulation. 

Terminal  branches. — The  medial  terminal  branch  passes  downward  along 
the  side  of  the  dorsalis  pedis  artery  and  divides  into  two  dorsal  digital  branches 
which  supply  the  adjacent  sides  of  the  first  and  second  toes.  It  also  gives  fila- 
ments to  the  periosteum  of  the  adjacent  bones,  to  the  metatarso-phalangeal  and 
interphalangeal  articulations,  a  twig  to  the  dorsal  interosseous  muscle  of  the 
first  space,  and  a  perforating  twig  which  connects  with  the  lateral  plantar  nerve. 
The  lateral  terminal  branch  passes  lateralward,  beneath  the  extensor  digitorum 
brevis,  and  it  ends  in  a  gangliform  enlargement  from  which  branches  are  dis- 
tributed to  the  extensor  digitorum  brevis,  the  tarsal  joints,  and  to  the  three  lateral 
intermetatarsal  spaces.  The  latter  branches  supply  the  neighbouring  bones, 
periosteum,  and  joints.  They  give  off  perforating  twigs,  which  pass  through  the 
spaces  and  anastomose  with  branches  of  the  lateral  plantar  nerve,  and  the 
most  medial  also  gives  a  twig  to  the  second  dorsal  interosseous  muscle. 


1016 


THE  NERVOUS  SYSTEM 


Table  Showing  Ordinary  Relations  op  Lumbar  and  Sackal  Nerves  to 
Branches  op  the  Lumbar  and  Sacral  Plexuses  and  to  the  Pudic  Nerve 


Neeves  Contributing. 


Nerves. 


Nerves. 
Femoral 


Obturator 


1  L, /  Ilio-hypogastric 

\  Ilio-inguinal 
1  and  2  L Genito-femoral 

1,  2,  and  3  L Lateral  cutaneous 

2,  3,  and  4  L (  Femoral 

1  Ubturator 
4,  5  L.,  and  1  S /  Superior  gluteal 

(  JNerve  to  quadratus  lemons 

4,  5  L.,  1  and  2  S Sciatic  (peroneal  part) 

4,  5  L.,  1,  2,  and  3  S Sciatic  (tibial  part) 

5  L.,  1  and  2  S  . .  I  Inferior  gluteal 

1  Nerve  to  obturator  internus 

1  and  2  S Nerve  to  piriformis 

2  and  3  S Medial  inferior  clunial 

1,  2,  and  3  S Posterior  femoral  cutaneous 

2,  3,  and  4  S Pudic 

Table  Showing  Relations  op  Muscles  op  Lower  Extremity  to  Nerves  op 
Lumbar  and  Sacral  Plexuses 

Nerves  Contributing.  Muscles. 

Illio-psoas 
Sartorius 
rectineus 
Adductor  longus 

2,  3,  and  4  L 19^"'^'!     u      ■ 

I  Adductor  brevis 

3  and  4  L  <  Quadriceps  femoris 

\  Obturator  externus 

3,  4,  and  5  L _  Adductor  magnus 

'  Gluteus  medius 

"     minimus 

Tensor  fasc.  latae 

Semimembranosus 

Plantaris 

Popliteus 

Quadratus  femoris 

Inferior  gemellus 
'  Flex,  digit,  long. 

Tibialis  posterior 

Flexor  digit,  brev. 
"     haUucis  brev. 

Abductor  hallucis 

First  lumbrical 

Superior  gemellus 

Obturator  internus 

Gluteus  maximus 

Semitendinosus 

Soleus 
I  Flex,  hallucis  long. 
I  Piriformis 
I  Gastrocnemius 
I  Flexor  quadratus  plantse 

1  and  2  S  ]  ^*"^-  1^?^*^  '^^^iti 

I  Plantar  interossei 

I  Dorsal  " 

I  Add.  haUucis  trans. 

l      "  "     obliq. 

1,  2,  and  3  S Long  head  of  biceps  femoris 

f  Ext.  haU.  long. 
"    digit.    " 
"    digit,  brev. 
4,  5  L.,  and  IS \  Tibialis  anterior 


4,  5L.,  and  1  S. 


5L.,  and  1  S. 


5L.,  1  and2S. 


Peroneus  tertius 
longus 
brevis 

THE  PUDENDAL  PLEXUS 


Femoral 
Obturator 

Obturator  and  sciatic 
Superior  gluteal 


Sciatic 
Tibial 

Nerve  to  quad.  fern. 

Tibial 

Posterior  medial 
Plantar 


Nerve  to  obt.  int. 

Inferior  gluteal 

Sciatic 

Tibial 


Tibial 
Lateral  plantar 


Sciatic 

Deep  peroneal 


Superficial  peroneal 
"  peroneal 


The  pudendal  plexus,  like  the  parts  of  the  lumbo-sacral  plexus  ah-eady 
described,  varies  in  its  formation.     The  accompanying  tables  show  the  extreme 


THE  PUDENDAL  PLEXUS  1017 

range  of  variation  and  the  common  method  of  formation  of  the  large  nerve  of  this 
plexus  in  each  of  the  three  classes. 

COMPOSITION  OF  THE  NERVES  OF  THE  PUDENDAL  PLEXUS 
Range  of  Variation 
Nerve.  Proximal.  Ordinary.  Distal. 

Pudic  nerve 1,2,3,4,5  8.         1,2,3,4  8.  2,3,4,5  8. 

Common  Composition 
Nerve.  Proximal.  Ordinary.  Distal. 

Pudic  nerve 2,3  8.  2,3,4  8.  3,  4  S. 

The  pudendal  plexus  is  commonly  formed  by  parts  of  the  anterior  divisions  of 
the  second,  third,  and  fourth  sacral  nerves.  It  lies  in  the  lower  part  of  the  back 
of  the  pelvis,  and  gives  off  visceral,  muscular,  and  terminal  branches. 

Visceral  branches  (pelvic  splanchnics)  arise  from  the  third  and  fourth  sacral 
nerves  especially,  and  enter  branches  of  the  sympathetic  plexus.  They  are 
distributed  both  directly  (their  afferent  or  sensory  fibres  terminating  in  the  pelvic 
viscera)  and  by  their  visceral  efferent  fibres  terminating  in  the  ganglia  of  the 
sympathetic  plexus  to  the  pelvic  viscera  (figs.  765,  791).  The  middle  hsemor- 
rhoidal  nerves  pass  to  the  rectum,  the  inferior  vesical  nerves  to  the  bladder,  and, 
in  the  female,  the  vaginal  nerves  to  the  vagina  fsee  Sympathetic  System). 

Muscular  branches  are  given  by  the  fourth  sacral  nerve  to  the  coccygeus, 
levator  ani,  and  sphincter  ani  externus  (fig.  765). 

The  nerves  to  the  two  former  muscles  pass  into  the  pelvic  surfaces  of  the  muscles,  but  that 
to  the  last-named  muscle,  called  the  perineal  branch,  passes  backward  between  the  levator 
ani  and  the  coccygeus,  or  through  the  posterior  fibres  of  the  latter  muscle,  into  the  posterior 
part  of  the  ischio-rectal  fossa,  and,  in  addition  to  supplying  the  sphincter  ani,  it  gives  cutaneous 
filaments  to  the  skin  between  the  anus  and  the  coccyx. 

Terminal  branches. — The  pudic  nerve  [n.  pudendus]  rises  usually  from  the 
anterior  primary  divisions  of  the  second,  third,  and  fourth  sacral  nerves  (fig.  765). 
It  emerges  from  the  pelvis  below  the  piriformis,  crosses  the  spine  of  the  ischium, 
lying  to  the  medial  side  of  the  internal  pudic  artery  (fig.  769),  and  accompanies 
the  artery,  through  the  small  sciatic  foramen,  into  Alcock's  canal  in  the  ob- 
turator fascia  on  the  lateral  wall  of  the  ischio-rectal  fossa,  where  it  terminates  by 
dividing  into  three  branches,  the  inferior  hsemorrhoidal,  the  perineal,  and  the 
dorsal  nerve  of  the  penis. 

The  inferior  haemorrhoidal  nerves  frequently  arise  independently  from  the 
third  and  fourth  sacral  nerves,  pierce  the  medial  wall  of  Alcock's  canal,  and  pass 
forward  and  medialward  through  the  ischio-rectal  fat  to  supply  the  sphincter  ani 
externus  and  adjacent  skin.  They  anastomose  with  branches  of  the  perineal 
nerve. 

The  perineal  nerve  runs  forward  for  a  short  distance  in  Alcock's  canal  and 
divides  into  a  deep  and  a  superficial  branch.  The  deep  branch  breaks  up  into 
filaments,  one  or  two  of  which  pierce  the  medial  wall  of  the  canal  and  pass 
medialward  to  the  anterior  fibres  of  the  sphincter  and  levator  ani.  The  re- 
maining part  of  the  nerve  pierces  the  base  of  the  m-o-genital  trigone  (triangular 
ligament),  and  enters  the  superficial  pouch  of  the  urethral  triangle,  where  it  is 
distributed  to  the  bulb  of  the  urethra,  and  to  the  transversus  perinei,  bulbocaver- 
nosus,  and  ischiocavernosus.  It  also  sends  some  sensory  filaments  to  the  mucous 
membrane  of  the  urethra.  The  superficial  branch  almost  at  once  divides  into 
medial  and  lateral  branches,  the  posterior  scrotal  (labial)  nerves. 

Both  branches  pass  through  the  wall  of  Alcock's  canal  into  the  anterior  part  of  the  ischio- 
rectal fossa,  then  they  pierce  the  base  of  the  uro-genital  trigone,  and  enter  the  superficial  pouch 
of  the  urethral  triangle.  The  lateral  branch  usually  passes  below  the  transversus  perinei, 
and  the  medial  branch  above  the  muscle  or  through  its  fibres.  The  lateral  branch  connects 
with  the  long  pudendal  nerve,  and  with  the  inferior  hsemorrhoidal  nerve,  and  both  branches 
end  in  terminal  filaments  which  anastomose  and  which  are  distributed  to  the  skin  of  the  scrotum 
and  the  anterior  part  of  the  perineum  in  the  male,  and  to  the  labium  majus  in  the  female. 


1018  THE  NERVOUS  SYSTEM 

The  dorsal  nerve  of  the  penis  runs  forward  in  Alcock's  canal  above  the 
internal  pudic  artery.  It  pierces  the  base  of  the  uro-genital  trigone,  continues 
forward  between  the  layers  of  the  trigone,  embedded  in  the  fibres  of  the  con- 
strictor urethrse,  and  it  gradually  passes  to  the  lateral  side  of  the  internal  pudic 
artery.  A  short  distance  below  the  pudic  arch  it  pierces  the  anterior  layer  of  the 
uro-genital  trigone,  gives  a  branch  to  the  corpus  cavernosum  penis,  passes 
forward  between  that  structure  and  the  bone,  and  turns  downward  on  the  dorsum 
of  the  penis,  passing  between  the  layers  of  the  fundiform  (suspensory)  ligament 
and  along  the  outer  side  of  the  dorsal  artery  of  the  penis.  It  supplies  the  skin 
of  the  dorsum  of  the  penis,  and,  having  given  branches  to  the  prepuce,  it  breaks 
up  into  terminal  filaments  which  are  distributed  to  the  glans  penis. 

The  dorsal  nerve  of  the  clitoris  is  much  smaller  than  the  dorsal  nerve  of  the 
penis  to  which  it  corresponds.     Is  is  distributed  to  the  clitories. 

THE  COCCYGEAL  PLEXUS 

This  plexus  is  frequently,  and  with  some  reason,  considered  as  a  subdivision  of 
the  pudendal  plexus,  and  sometimes  it  is  described  with  the  coccygeal  nerves. 
It  is  formed  chiefly  by  the  anterior  division  of  the  fifth  sacral  nerve  and  the 
coccygeal  nerve,  but  it  receives  a  small  filament  from  the  anterior  division  of  the 
fourth  sacral  nerve  (figs.  765,  769).  These  constituents  unite  to  form  plexiform 
cords  lying  on  either  side  of  the  coccyx.  From  these  cords  arise  the  ano-coccygeal 
nerves,  which  pierce  the  sacro-tuberous  (great  sacro-sciatic)  ligament  and  supply 
the  skin  in  the  neighbourhood  of  the  coccyx. 

III.  THE  DISTRIBUTION  OF  THE  CUTANEOUS  BRANCHES 

OF  THE  SENSORY  AND  MIXED  CRANIAL 

AND  SPINAL  NERVES 

The  cutaneous  filaments  of  the  sensory  and  mixed  nerves  are  distributed  to 
definite  regions  of  the  surface  of  the  body  which  are  known  as  'cutaneous  areas.' 
Each  cutaneous  area  has  one  special  nerve  of  supply  and  the  central  part  of  the 
area  receives  that  nerve  alone,  but  wherever  the  borders  of  two  areas  meet  they 
reciprocally  overlap,  therefore  each  margin  of  every  cutaneous  area  has  two 
nerves  of  supply,  its  own  nerve  and  that  of  an  adjacent  area,  and  of  these,  some- 
times one  and  sometimes  the  other  preponderates. 

The  Cutaneous  Areas  of  the  Scalp 

The  limits  of  the  cutaneous  areas  in  the  scalp  region  are  indicated  in  figs.  774,  776,  but 
in  general  terms  it  may  be  said  that  the  skin  of  the  scalp  in  front  of  the  pinna  is  supphed  by 
four  cutaneous  nerves,  viz. ,  the  mesial  part  by  the  supratrochlear  and  the  supra-orbital  branches 
of  the  ophthalmic  division  of  the  trigeminus,  and  the  lateral  part  by  the  temporal  branch  of  the 
maxillary  division,  and  the  auriculo-temporal  branch  of  the  mandibular  division  of  the  same 
nerve. 

The  portion  of  the  scalp  behind  the  pinna  also  receives  four  cutaneous  nerves;  laterally  it 
is  supplied  by  the  great  auricular  and  small  occipital  branches  of  the  cervical  plexus  which 
contain  filaments  from  the  second  and  third  cervical  nerves,  and  medially  it  receives  the  great 
and  smallest  occipital  nerves  which  are  derived  from  the  internal  branches  of  the  posterior 
primary  divisions  of  the  second  and  third  cervical  nerves  respectively. 

The  Cutaneous  Areas  of  the  Face 

With  the  exception  of  the  skin  over  the  posterior  part  of  the  masseter  muscle,  the  whole 
of  the  skin  of  the  face  is  supplied  by  the  branches  of  the  trigeminus.  The  nose  is  supplied 
medially  by  the  supratrochlear,  the  infratrochlear,  and  the  nasal  branches  of  the  ophthalmic 
division,  and  laterally  by  the  infra-orbital  branch  of  the  maxillary  division.  The  upper  eyelid 
is  supplied  by  the  supratrochlear,  the  supra-orbital,  and  the  lacrimal  branches  of  the  ophthal- 
mic division;  the  lower  eyelid  by  the  infratrochlear  branch  of  the  ophthalmic  division  and 
by  the  infra-orbital  and  the  zygomatico-facial  (malar)  branches  of  the  maxillary  division. 
The  skin  over  the  upper  jaw  and  the  zygomatic  (malar)  bone  is  supplied  by  the  infra-orbital 
and  zygomatico-facial  branches  of  the  maxillary  division,  that  over  the  buccinator  by  the  buccal 
branch  of  the  mandibular  division,  and  that  over  the  lower  jaw,  fiom  in  front  backward,  by 
the  mental,  buccal,  and  auriculo-temporal  branches  of  the  mandibular  division,  except  a  small 
part  near  the  posterior  border  which  receives  its  supply  from  the  great  auricular  nerve. 


CUTANEOUS  AREAS  OF  THE  NECK 
The  Cutaneous  Areas  of  the  Auricle  (Pinna) 


1019 


The  upper  two-thirds  of  the  outer  surface  of  the  pinna  are  suppUed  by  the  auriculo-temporal 
branch  of  the  mandibular  division  of  the  trigeminus,  and  the  lower  third  by  twigs  of  the  great 

Fig    774— Diageam  of  the  Cutaneous  Nerve  Areas  of  the  Head  and  Neck. 
Red— ophthalmic  division  of  trigeminus.  White-maxillary  division  of  trigemmus. 

Blue— mandibular  division  of  trigemmus. 
Dotted  shading— Posterior  primary  divisions  of  cervical  nerves.  . 

Obhque  shading— Ascending  and  transverse  superficial  branches  of  cervical  plexus. 
Transverse  shadmg— Descending  superficial  branches  of  cervical  plexus. 
It  i^ult  be  remembered  that  the  boundaries  of  each  area  are  not  distmct;  wherever  two 
areas  meet  they  overlap. 


Supra-trochlear 

Lacrimal 
Infra -trochlear 


Smallest  occipital ^\-*V/.' 


auricular  nerve.  The  lower  three-fourths  of  the  cranial  surface  of  the  pinna  are  supphed  by 
the  great  auricular  nerve,  and  the  upper  fourth  by  the  small  occipital  nerve.  The  posterior 
surffce  of  the  external  auditory  meatus  receives  filaments  from  the  auricular  branch  of  the 
vagus. 

The  Cutaneous  Areas  of  the  Neck 

The  skin  over  the  anterior  part  of  the  neck  is  supplied  by  the  superficial  cervical  branch 
of  the  cervical  plexus,  which  contains  fibres  from  the  second  and  third  cervical  nerves  and 
in  the  lower  part  of  its  extent,  by  the  anterior  supra-clavicular  nerves  (suprasternal  branches). 


1020 


THE  NERVOUS  SYSTEM 


which  convey  twigs  of  the  third  and  fourth  cervical  nerves  (fig.  774).  The  lateral  part  of  the 
neck  receives  filaments  from  the  second,  third,  and  fourth  cervical  nerves  by  way  of  the  great 
auricular,  small  occipital,  and  middle  supraclavicular  (supra-clavicular)  branches  of  the  cervical 
plexus,  and  posteriorly  the  skin  of  the  neck  is  suppUed  by  the  small  occipital  nerve  and  by  the 
medial  branches  of  the  posterior  primary  divisions  of  the  cervical  nerves  from  the  second  to 
the  sixth  inclusive  (fig.  776). 

The  Cutaneous  Areas  of  the  Trunk 

The  skin  over  the  ventral  aspect  of  the  trunk  as  far  down  as  the  third  rib  is  supphed  by 
the  anterior  supra-clavicular  (suprasternal)  and  middle  supra-olavicular  (supra-clavicular) 
branches  of  the  cervical  plexus,  which  contain  filaments  from  the  third  and  fourth  cervical 
nerves  (fig:  776).  From  the  third  rib  to  tlie  lower  part  of  the  abdominal  wall  the  skin  receives 
the  anterior  cutaneous  branches,  and  the  anterior  divisions  of  the  lateral  cutaneous  branches  of 

Fig.  775. — Diagram  of  the  Cutanbotts  Areas  of  the  Side  of  the  Body  and  Part  of  the 
Limb.     (After  Head.) 


the  thoracic  nerves  except  the  first,  second,  and  twelfth  (fig.  776).  The  skin  over  the  lower 
and  anterior  part  of  the  abdominal  wall  is  supplied  by  the  iho-hypogastric  branch  of  the  first 
lumbar  nerve. 

The  cutaneous  supply  of  the  lateral  aspects  of  the  body  is  derived  from  the  lateral  branches 
of  the  anterior  primary  divisions  of  the  thoracic  nerves  from  the  second  to  the  eleventh,  and 
the  skin  over  the  dorsal  aspect  of  the  body  is  supplied  laterally  by  the  posterior  divisions  of 
the  lateral  branches  of  the  thoracic  nerves  from  the  third  to  the  eleventh,  and  medially  by  the 
posterior  primary  divisions  of  the  thoracic  nerves,  in  the  upper  half  by  their  medial  branches 
and  in  the  lower  half  principally  by  their  lateral  branches. 


THE  CUTANEOUS  AREAS  OF  THE  LIMBS 

The  areas  of  skin  of  the  upper  and  lower  limbs  which  are  supplied  by  the  branches  of  the 
brachial,  lumbar,  and  sacral  plexuses  are  indicated  in  fig.  776,  and  the  spinal  nerves  which  con- 
tribute to  each  nerve  area  are  noted.  The  question  of  the  skin  areas  supplied  by  any  given  spinal 
nerve  is  one  of  great  chnical  importance,  in  connection  with  the  diagnosis  of  injuries  of  nerves 
and  of  pathological  conditions  affecting  them.  Therefore,  considerable  attention  has  been 
directed  to  the  matter  and  it  has  been  found  that  the  areas  which  become  hypersensitive 
when  certain  spinal  nerve-roots  are  irritated,  or  anaesthetic  when  the  roots  are  destroyed,  do 


CUTANEOUS  AREAS  OF  THE  BODY 


1021 


Fig.  776. — Diagram  showing  Areas  op  Distriution  of  Cutaneous  Nerves. 

Head  : — 

Red — Ophthalmic  division  of  trigeminus.  White — maxillary  division  of  trigeminus. 
Blue — mandibular  division  of  trigeminus.  Dotted  area — Posterior  primary  divisions 
of  cervical  nerves.     Oblique  and  transverse  shading — Branches  of  cervical  plexus. 

Body  and  Limbs  : — 

Red — Anterior  branches  of  anterior  primary  divisions..  Blue — Posterior  branches  of 
anterior  primary  divisions.  Two  colours  in  one  area  indicate  that  the  area  is  supplied 
by  two  sets  of  nerves,  and  it  should  be  remembered  that  wherever  two  nerve  areas 
approach  each  other  they  overlap.  The  dotted  blue  area  of  the  posterior  femoral 
cutaneous  (small  sciatic)  indicates  that  the  nerve  comes  from  the  posterior  as  well  as 
from  the  anterior  parts  of  the  anterior  primary  divisions  of  the  sacral  nerves,  but  it 
supplies  a  flexor  area.  The  area  of  the  inferior  medial  cluneal  nerve  is  left  uncoloured, 
because  its  true  nature  is  uncertain.  Dotted  shading — posterior  primary  divisions. 
The  numbers  and  initial  letters  refer  to  the  respective  spinal  nerves  from  which  the 
nerves  are  derived. 


Ophthalmic  division  of  trigeminus  - - 


Mandibular  division  of  trigeminus 
Maxillary  division  of  trigeminus 


Supraorbital 


Great  auricular  - 
Cutaneous  colli,  3,  3  C  -. 


Supra  -clavi  cular 


Axillary 
Lateral  cutaneous  nerves 

Anterior  cutaneous  nerves 


Medial  brachial  cutaneous 

and  intercosto- 

brachial,  1,2  T 

Posterior  brachial, 

cutaneous 

Medial  antibrachial 
cutaneous 
Musculo-cutaneous 
(Lateral  antibrachialj 


Lateral  femoral  cutaneous 


Geni  to -femoral 

Superficial 

radial,  6  C 

Ilio-inguinial,  i  L 

Median,  6,7,  C.  i  T 

Ulnar,  i  T 


Supra-clavicular,  3,  4  C 


Axillary,  5,  6  C 

Lateral  branches  of 

thoracic  nerves 
Posterior  brachial 

cutaneous 

Medial  and  intercosto- 
brachial  cutaneous 
Medial  antibrachial 

cutaneous 
Dorsal  antibrachial 

cutaneous,  6,  7,  8  C 
Medial  antibrachial 

cutaneous 
Superior  clunial 
Lateral  cutaneous  of 

ilio-hypogastric 
Musculo-cutaneous,  5,  6  C 
Middle  clunial 

Inferior  medial 
clunial  2,  3  S 


Ulnar,  8  C 
Superficial 

radial,  6,  7  C 
Area  supplied  by 

superficial    radial 

and  ulnar 
Median,  6,7,  8  C,  i  T 


Common  peroneal  — 
Saphenous  — 


Superficial  peroneal 


Deep  peroneal 

Medial  plantar 


Lateral  femoral  cutaneous 
Posterior  femoral  cutaneous 


Common  peroneal,  5  L,  i,  2  S 
Saphenous,  3,  4  L 


Medial  calcaneal  of  tibial,  i,  2  S 
■  J'-ii Lateral  plantar,  i,  2  S 

V... 

Medial  plantar,  4,  5  L, 


1022 


THE  NERVOUS  SYSTEM 


not  correspond  exactly  with  the  regions  to  which  the  fibres  of  the  roots  can  apparently  be 
traced  by  dissection.  Moreover,  it  has  been  discovered,  partly  by  clinical  observations  on  the 
human  subject  and  partly  by  experiment  on  monkeys,  that  the  nerves  of  the  hmbs  have  a 
more  or  less  definite  segmental  distribution.  To  understand  clearly  this  segmental  arrange- 
ment the  reader  must  remember  that  in  the  embryonic  stage  when  no  limbs  are  present  the 
body  is  formed  of  a  series  of  similar  segments,  each  of  which  is  provided  with  its  own  nerve. 
At  a  later  stage  when  the  limbs  grow  outward,  each  limb  is  formed  by  portions  of  a  definite 
number  of  segments  which  fuse  together  into  a  common  mass  of  somewhat  wedge-hke  outline. 
Each  rudimentary  limb  possesses  a  dorsal  and  a  ventral  surface.  The  dorsal  surfaces  of  both 
the  upper  and  the  lower  limbs  are  originally  the  extensor  surfaces,  and  the  ventral  surfaces  the 
flexor  surfaces,  but,  as  the  upper  limb  rotates  lateralward  and  the  lower  limb  rotates  median- 
ward  as  development  proceeds,  in  the  adult,  the  extensor  surface  of  the  upper  Umb  becomes  the 
posterior  surface,  and  the  extensor  surface  of  the  lower  limb,  the  anterior  surface.  The  preaxial 
border  of  the  upper  limb  is  the  radial  or  thumb  border,  and  the  postaxial  border,  the  ulnar  or 
little  finger  border.  The  preaxial  border  of  the  lower  hmb  is  the  tibial  or  great  toe  border, 
and  the  postaxial  border,  the  fibular  or  little  toe  border.  As  projections  of  the  segments  of  the 
body  grow  out  to  form  the  limb-buds  and  limbs  each  projection  carries  with  it  the  whole  or 
part  of  the  nerve  of  the  segment  to  which  it  belongs,  and  therefore  the  number  of  body  segments 
which  take  part  in  a  hmb  is  indicated  by  the  number  of  spinal  nerves  which  pass  into  it.  If 
these  facts  are  remembered  it  will  naturally  be  expected  (1)  that  the  highest  spinal  nerves 
passing  into  a  hmb  will  be  associated  with  its  preaxial  portion  and  the  lowest  with  its  post- 

FiG.  777. — Diagrams  A,  B,  and  C,  Illustrating  Stages  in  the  Projection  op  the  Limb- 

BDDS  FOR  THE  IJPPER  EXTREMITY,  AND  THE  DRAWING  OUT  OF  THE  NeRVBS  OF  THE  CORKESPOND- 

ing  Body  SegmentsfoetheCutanbous  Areas  of  the  Preaxial  and  Postaxial  Border  of 
THE  Limb. 

Postaxial  border  shaded. 


axial  portion;  (2)  that  only  the  nerves  of  those  segments  forming  middle  or  central  portions  of 
the  limbs  will  extend  to  the  tips  of  the  hmbs;  (3)  that  the  highest  and  lowest  segments  in  each 
hmb  area  wiU  take  a  smaller  part  in  the  formation  of  the  limb  that  the -middle  segments;  and 
(4)  that,  consequently,  the  highest  and  lowest  nerves  wiU  pass  outward  into  the  limb  for  a 
shorter  distance  than  the  middle  nerves.  Observers  are  not  yet  in  perfect  agreement  as  to  the 
exact  distribution  of  each  nerve,  but  the  diagrams  in  figs.  775  to  781  show  the  embryonic 
derivation  of  the  cutaneous  areas  and  the  adult  dorso-ventral  segmental  arrangement  in  the 
projected  portions  of  both  the  upper  and  lower  limbs  as  assumed  from  clinical  observations. 
In  the  upper  parts  of  the  lower  limbs,  the  original  segmental  distributuion  appears  to  be  masked. 
This  may  be  due  (1)  partly  to  the  fact  that  the  areas  recognisable  by  clinical  phenomena  do 
not  correspond  exactly  with  the  areas  to  which  definite  dorsal  root-fibres  are  distributed,  but 
rather  to  definite  segments  of  the  grey  substance  of  the  spinal  cord  with  which  the  root-fibres 
are  connected;  (2)  partly  to  the  overlapping  of  segments  and  the  acquired  preponderance  of  one 
nerve  over  another  in  the  overlapping  areas,  and  (3)  partly  to  the  fact  that  in  the  lower  hmb 
there  has  been  a  greater  amount  of  shifting  of  parts  to  result  in  the  fixed  fiat  position  of  the 
sole  of  the  foot;  (4)  and  partly  to  the  incompleteness  of  the  data  which  are  at  our  disposal  in 
the  case  of  the  human  subject.  Sherrington  has  proved  that  in  the  monkey  the  sensory  areas 
of  the  limbs  are  arranged  in  serial  correspondence  with  the  spinal  nerves,  the  middle  nerves 
of  each  limb  series  passing  to  the  distal  extremity  while  the  higher  and  lower  nerves  are 
limited  to  the  proximal  regions.  Thorburn's  observations,  which  differ  from  Head's,  are, 
especially  as  regards  the  upper  limb,  in  close  conformity  with  the  results  obtained  by  Sherring- 
ton's experiments  on  monkeys. 

Each  limb  may  be  divided  into  its  preaxial  and  postaxial  borders  by  a  line  drawn  longi- 
tudinally along  the  middle  of  both  its  anterior  and  posterior  surfaces  (compare  figs.  777  and  779) 
The  cutaneous  nerves  to  the  preaxial  border  are  from  the  cephalic  portion  of  the  hmb  plexus, 
and  those  to  the  postaxial  are  from  the  caudal  components  of  the  plexus.  Thus  the  thumb 
and  index  finger  are  cephalad. 


The  Cutaneous  Areas  of  the  Upper  Limb 

A  line  passing  along  the  middle  of  both  the  anterior  and  posterior  surfaces  of  the  upper  ex- 
tremity to  the  tip  of  the  middle  finger  (fig.  779)  separates  the  preaxial  from  the  postaxial 
border  and  passes  longitudinally  along  the  area  of  the  cutaneous  fibres  derived  from  the  seventh 
cervical  nerve. 


CUTANEOUS  AREAS  OF  THE  LIMBS 


1023 


The  skin  over  the  upper  third  of  the  deltoid  muscle  is  supplied  by  the  posterior  supra- 
clavicular (supra-acromial)  and  middle  supra-clavicular  (supra-clavicular)  nerves,  which  are 
branches  of  the  cervical  plexus  containing  fibres  of  the  third  and  fourth  cervical  nerves,  and 
that  over  the  lower  two-thirds  by  the  axillary  (circumflex)  nerve  which  conveys  fibres  of  the 
fifth  and  sixth  cervical  nerves  (fig.  776). 

The  skin  over  the  lateral  surface  of  the  upper  arm  is  supphed  externally  by  the  axillary 
(circumflex)  nerve  above,  and  below  by  the  superior  branch  of  the  dorsal  antibrachial  cutaneous, 

Fig.  778. — Diagram  of  the  Cutaneous  Areas  op  the  Upper  Extremity. 
(Modified  from  Head.) 


the  external  cutaneous  branch  of  the  radial  (musculo-spiral)  nerve.  The  former  contains 
filaments  of  both  the  fifth  and  sixth  cervical  nerves,  and  the  latter  filaments  of  the  sixth  alone. 
The  skin  of  the  medial  side  of  the  upper  arm  is  supplied  by  the  medial  antibrachial  cutaneous 
(internal  cutaneous)  nerve  with  fibres  of  the  eighth  cervical  and  first  thoracic  nerves,  and  by 
the  medial  brachial  cutaneous  (lesser  internal  cutaneous)  and  intercosto-brachial  (intercosto- 
humeral)  nerves  which  are  derived  from  the  first  and  second  thoracic  nerves.  The  dorsal  side 
of  the  upper  arm  is  supphed,  laterally,  by  the  fifth  and  sixth  cervical  nerves  through  the  axillary 


Fig.  779. — Diagram  of  the  Cutaneous  Areas  op  the  Upper  EIxtremitt. 
The  solid  middle  lines  are  drawn  to  separate  preaxial  (radial)  borders  from  postaxial  borders. 
(After  Thorburn,  modified.) 


(circumflex)  nerve  and  by  the  dorsal  antibrachial  cutaneous;  the  middle  portion,  by  the  seventh 
cervical  nerve  through  the  posterior  brachial  cutaneous,  the  internal  cutaneous  branch  of  the 
radial  (musculo-spiral)  nerve;  and  the  medial  portion  by  the  first  and  second  thoracic  nerves 
through  the  medial  brachial  cutaneous  (lesser  internal  cutaneous)  nerve,  and  the  intercosto- 
brachial  (intercosto-humeral)  nerve  (fig.  776). 

The  front  of  the  forearm  is  divided  into  three  areas,  a  lateral  which  is  supphed  by  the  fifth, 
sixth,  and  possibly  the  seventh  cervical  nerves,  through  the  musculo-cutaneous  branch  of  the 


1024 


THE  NERVOUS  SYSTEM 


brachial  plexus;  a  middle  which  is  supplied  by  the  seventh  cervical  nerve  as  above,  and  a  medial 
area  supplied  by  the  eighth  cervical  and  first  thoracic  nerve  through  the  medial  antibrachial 
cutaneous  (internal  cutaneous)  nerve.  On  the  dorsal  side  of  the  forearm  there  are  three  areas: 
— (1)  a  lateral  suppUed  by  fibres  of  the  fifth  and  sixth  cervical  nerves  through  the  musculo- 
cutaneous nerve;  (2)  a  middle,  which  receives  fibres  of  the  seventh,  and  probably  some  from  the 
sixth  and  eighth  cervical  nerves  through  the  lower  branch  of  the  dorsal  antibrachial  cutaneous 
of  the  radial  (inferior  external  cutaneous  branch  of  the  musculo-spiral  nerve),  and  (3)  a  medial 
which  receives  the  eighth  cervical  and  first  thoracic  nerves  through  the  medial  antibrachial 
cutaneous  (figs.  776,  779). 

The  palm  of  the  hand  is  supplied  by  the  sixth,  seventh,  and  eighth  cervical  nerves  through 
the  superficial  radial  (radial)  nerve,  and  through  the  median  and  ulnar  nerves.  The  super- 
ficial radial  supplies  the  radial  side  of  the  thumb  by  its  palmar  cutaneous  branch.  The  re- 
mainder of  the  palm  and  the  palmar  aspects  of  the  fingers  are  supplied  by  the  median  and 
ulnar  nerves  through  their  palmar  cutaneous  and  digital  branches,  the  median  supplying 
three  and  a  half  digits  and  the  ulnar  the  remaining  one  and  a  half  (figs.  776  and  779). 

The  dorsal  aspect  of  the  hand  is  suppUed  by  the  sixth,  seventh,  and  eighth  cervical  nerves, 
which  reach  it  through  the  superficial  radial(  radial)  and  through  the  median  and  ulnar  nerves. 
The  superficial  radial  supplies  the  lateral  part  of  the  dorsum  and  the  lateral  three  and  a  half 
digits,  except  the  lower  portions  of  the  second,  third,  and  half  of  the  fourth  digits,  which 
■receive  twigs  from  the  median  nerve;  the  ulnar  nerve  supplies  the  ulnar  half  of  the  dorsum  of 

Fia.  780.— Diagram  op  the  Cutaneotts  Areas  op  the  Lower  Extremity.     (After  Head.) 


the  hand,  including  the  medial  one  and  a  half  digits.  The  areas  supplied  by  definite  spinal 
nerves,  according  to  the  observations  of  Head  and  Thorburn,  are  shown  in  figures  778  and  779 
respectively. 

The  Cutaneous  Areas  of  the  Lower  Extremity 

The  segmental  arrangement  of  the  cutaneous  areas  of  the  lower  extremity  is  not  so  well 
retained  as  in  the  upper,  due  largely  to  a  greater  amount  of  developmental  shifting  of  the  parts. 
Both  of  the  lines  separating  the  areas  of  the  lumbar  (cephalic)  and  the  sacral  (caudal)  parts 
of  the  lumbo-sacral  plexus  he  on  the  dorsal  aspect  of  the  limb.  The  nerves  from  the  lumbar 
part  of  the  plexus  are  distributed  to  the  entire  anterior  and  the  medial  and  lateral  surfaces  of 
the  hmb  and  to  the  muscles  of  the  anterior  and  medial  portions  of  the  thigh  and  the  anterior 
portion  of  the  leg,  whereas  the  cutaneous  nerves  from  the  sacral  part  of  the  plexus  are  con- 
fined to  a  narrow  strip  along  the  dorsal  aspect  of  the  limb  (fig.  781).  However,  the  muscular 
distribution  of  the  sacral  part  is  as  much  expanded  as  its  cutaneous  area  is  contracted;  it  supplies 
the  muscles  in  the  dorsal  portions  of  the  hip,  thigh  and  knee,  the  whole  of  the  dorsal  part  of 
the  leg  and  ankle  and  the  plantar  muscles  of  the  foot. 

There  are  six  cutaneous  areas  in  the  region  of  the  buttock,  three  upper  and  three  lower. 
Of  the  upper  areas  the  lateral  is  supplied  by  the  anterior  primary  divisions  of  the  last  thoracic 
and  first  lumbar  nerves  through  the  iliac  branches  of  the  last  thoracic  and  the  iho-hypogastric 
nerves;  the  middle  upper  area  receives  the  lateral  divisions  of  the  posterior  primary  branches 
of  the  upper  three  lumbar  nerves,  and  the  medial  upper  area  is  supplied  by  twigs  from  the  lateral 
branches  of  the  posterior  primary  divisions  of  the  upper  two  or  three  sacral  nerves  (figs.  776, 
780). 


CUTANEOUS  AREAS  OF  THE  LIMBS 


1025 


Of  the  lower  three  areas,  the  lateral  receives  filaments  from  the  second  and  third  lumbar 
nerves  through  the  lateral  femoral  cutaneous  (external  cutaneous)  branch  of  the  lumbar  plexus; 
the  middle  area  is  supplied  by  the  first,  second,  and  third  sacral  nerves  through  the  posterior 
femoral  cutaneous  (small  sciatic)  nerve;  and  the  medial  area  by  the  second  and  third  sacral 
nerves  through  the  medial  inferior  clunial  (perforating  cutaneous)  branch  of  the  sacral  plexus 
(fig.  776). 

On  the  back  of  the  thigh  there  are  three  areas.  According  to  Head,  the  medial  and  lateral 
areas  are  supphed  by  the  second  and  third  lumbar  nerves,  the  former  through  the  lateral 
femoral  cutaneous  (external  cutaneous)  branch  of  the  lumbar  plexus,  and  the  latter  through 
the  anterior  cutaneous  branches  of  the  femoral  (internal  cutaneous  branch  of  the  anterior  crural) 
nerve.  The  middle  area  receives  twigs  from  the  first,  second,  and  third  sacral  nerves  through 
the  posterior  femoral  cutaneous  (small  sciatic),  a  branch  of  the  sacral  plexus. 

The  front  of  the  thigh  is  supplied  by  the  first,  second,  and  third  lumbar  nerves,  and, 
according  to  Head,  there  are  five  cutaneous  areas.  The  lateral  area  receives  twigs  of  the 
second  and  third  lumbar  nerves  through  the  lateral  (external)  cutaneous  nerves.  There  are 
two  medial  areas,  an  upper  and  a  lower.  The  former  is  supplied  by  the  lumbo-tnguinal  (crural) 
branch  of  the  genito-femoral  (genito-  crural), which  conveys  twigs  of  the  first  and  second  lumbar 
nerves;  the  latter  receives  fibres  of  the  second  and  third  lumbar  nerves  through  one  of  the  an- 


FiG.  781. 


-Diagram  op  the  Cutaneous  Areas  of  the  Lower  Extremity 
(After  Thorburn,  modified.) 


t'W 


terior  (middle)  cutaneous  branches  of  the  femoral  (anterior  crural)  nerve.  The  small  upper 
and  medial  area  is  supplied  by  the  first  lumbar  nerve  through  the  iUo-inguinal,  and  the  lower 
medial  area  receives  twigs  of  the  second  and  third  lumbar  nerves  through  one  of  the  anterior 
cutaneous  branches  (internal  cutaneous)  of  the  femoral  (anterior  crural)  nerve  (fig.  776). 

The  front  of  the  knee  is  supplied  by  the  second,  third,  and  fourth  lumbar  nerves  through 
the  anterior  (middle  and  internal)  cutaneous  and  saphenous  (long  saphenous)  branches  of  the 
femoral  (fig.  776). 

Of  the  skin  over  the  region  of  the  popliteal  space,  the  medial  portion  receives  fibres  from  the 
second,  third,  and  fourth  lumbar  nerves  through  the  anterior  (internal)  cutaneous  branch  of 
the  femoral  (anterior  crural)  nerve  and  through  the  superficial  division  of  the  obturator  nerve; 
the  middle  and  lateral  portion  receives  twigs  of  the  first  three  sacral  nerves  through  the  pos- 
terior cutaneous  (small  sciatic)  nerve  (fig.  776). 

The  skin  over  the  front  and  medial  side  of  the  leg  is  supplied  by  the  fourth  lumbar  nerve 
through  the  saphenous  nerve,  and  the  skin  of  the  front  and  lateral  side  receives  nerve-fibres  from 
the  fifth  lumbar  nerves  through  the  sural  cutaneous  (fibular  communicating)  branch  of  the 
common  peroneal  (external  popliteal)  nerve. 

In  the  skin  of  the  back  of  the  leg  four  areas  can  be  distinguished,  a  medial,  two  middle, 
upper  and  lower,  and  a  lateral  area.  The  medial  area  is  supphed  by  the  fourth  lumbar  nerves 
through  an  anterior  cutaneous  branch  (internal  cutaneous)  of  the  femoral  (anterior  crural) 


1026 


THE  NERVOUS  SYSTEM 


nerve  and  the  superficial  branch  of  the  obturator  nerve.  The  upper  middle  area  is  supplied 
by  the  second,  and  third  sacral  nerves  through  the  posterior  femoral  cutaneous  (small  sciatic) 
nerve,  and  the  lower  middle  area  by  the  first  sacral  nerve  through  the  sural  (external  saphenous) 
nerve.  The  lateral  area  is  supphed  by  the  fifth  lumbar  nerve  through  the  lateral  sural  cutaneous 
(fibular  communicating)  branch  of  the  common  peroneal  (external  popliteal)  nerve  (fig.  776,  780, 
781). 

The  skin  of  the  dorsum  of  the  foot  is  supplied  principally  by  the  fifth  lumbar  and  by  the 
first  sacral  nerves,"  the  majority  of  the  nerve-fibres  travel  by  the  superficial  peroneal  (musculo- 
cutaneous) nerve,  but  the  adjacent  sides  of  the  first  and  second  toes  are  supplied  by  the  femoral 
(anterior  crural)  nerve  and  the  side  of  the  dorsum  of  the  httle  toe  is  supplied  through  the 
sural  (external  saphenous). 

The  skin  of  the  region  of  the  heel  is  supplied  by  the  first  sacral  nerve,  the  medial  surface 
and  medial  part  of  the  under  surface  by  the  medial  calcaneal  branches  of  the  tibial  (calcaneo- 
plantar)  nerve  and  the  posterior,  external,  and  lower  aspects  by  the  sural  (external  saphenous) 
nerve  (fig.  776). 

The  sole  of  the  foot  in  front  of  the  heel  receives  cutaneous  fibres  from  the  fifth  lumbar 
and  the  first  sacral  nerves;  the  medial  area,  which  includes  the  medial  three  and  a  half  digits, 
being  supplied  by  the  medial  plantar  nerve  which  conveys  fibres  of  the  fifth  lumbar  and  the  first 
sacral  nerves;  and  the  lateral  area  by  the  fifth  lumbar  nerve  through  the  lateral  plantar  nerve. 

The  medial  side  of  the  foot  is  supphed  by  the  first  sacral  and  fourth  lumbar  nerves  through 
the  saphenous  nerve  and  the  lateral  side  by  the  fifth  lumbar  nerve  through  the  sural  (external 
saphenous)  nerve. 

The  skin  of  the  scrotum  and  penis  is  supphed  by  the  first  lumbar  nerve  through  the  iho- 
inguinal  nerves,  and  by  the  second  and  third  sacral  nerves  through  the  perineal  and  dorsal  penile 
branches  of  the  pudendal  (pudic)  nerve. 

The  cutaneous  areas  of  the  lower  extremity  which  have  been  demarcated  by  Head  and 
Thorburn  are  shown  in  fig.  780.  These  do  not  conform  wholly  with  each  other  nor  with  the 
areas  given  in  more  detail  in  fig.  776,  due  probably  to  individual  differences  in  subject  and 
observer  and  to  the  difficulties  coincident  with  the  overlapping  of  the  areas.  Fig.  781  is  more 
general  in  character  and  is  considered  more  approximately  correct. 

The  homology  of  the  parts  of  the  plexuses  of  the  upper  and  lower  extremities  is  not  well 
carried  out  in  the  distribution  of  the  nerves.  The  radial  and  great  sciatic  nerves  are  similar 
to  the  extent  that  the  one  arises  from  the  posterior  cord  of  the  brachial  plexus  and  the  other 
from  the  sacral  ple.xus,  and  that  the  one  is  distributed  to  the  dorsal  aspect  of  the  arm  and  the 
other  to  the  dorsal  surface  of  the  lower  extremity,  but  the  great  sciatic  supplies  the  sole  of  the 
foot,  and  the  plantar  muscles,  whereas  the  radial  does  not  supply  the  palm  of  the  hand  and  the 
palmar  muscles. 

THE  SYMPATHETIC  SYSTEM 

The  so-called  sympathetic  system  is  that  portion  of  the  peripheral  nervous 
system  which  is  especially  concerned  in  the  distribution  of  impulses  to  the 

Fig.  782. — Diagram  showing  two  stages  of  the  Migration  op  the  Primitive  Ganglia 
PROM  THE  Ganglion  Crest;  A.  the  Division  of  the  Primitive  Ganglia  into  Spinal 
AND  Sympathetic  Portions,  and  B.  the  Formation  op  the  Nerves. 


~-^  Ectoderm 


ganglion 


glandular  tissues,  to  the  muscle  of  the  heart  and  blood-vessels,  and  to  the  non- 
striated  muscular  tissue  of  the  body  wherever  found.     Since  these  tissues  are  most 


THE  SYMPATHETIC  SYSTEM 


1027 


Fig.  783. — Diagram  Showing  the  Chief  Paths  of  Migration  op  the  Cells  from 
THE  Ganglia  of  the  Spinal  and  Cranial  Nerves  to  form  the  Adult  Sympathetic 
System  (After  Schwalbe,  modified.) 


Carotid  plexus 
Closso-pharyngeal 

Vagus  nerve 

I.  cervical  spinal 
ganglion 

Superior  cervical 
ganglion 


Inf. 


Middle  cervical 
ganglion 
Tior  cervical 
ganglion 


I.  thoracic  spinal 
ganglion 


Sympathetic   trunk 


I,  lumbar  spinal 
ganglion 


I.  sacral  spinal 
ganglion 


Pharyngeal  plexus 


Coccygeal  spinal 
ganglion 


Aortic  plexus 
Inferior  mesenteric 

plexus 


Pelvic  plexuses 


Coccygeal  ganglion 


1028 


THE  NERVOUS  SYSTEM 


abundant  in  and  largely  comprise  the  viscera  or  splanchnic  organs  of  the  body, 
the  largest  and  most  evident  of  the  structures  comprising  the  sympathetic  system 
are  found  either  in  or  near  the  cavities  containing  the  viscera.     However,  the 

Fig.  784. — Scheme  showing  General  Plan  of  the  Coarser  Portions  op  the  Sympa- 
thetic Nervous  System  and  its  Principal  Communications  with  the  Cbrebro-spinal 
System.     (After  Flower,  modified.) 


Intgrfta! CttToUd pU 

J^ami  communicantes 
Jittuieen  ^anffUated  cord  and 

Jniular  G(imlion  of  vafju-f  *' 

To  Petrosal  ganglion  o/^_ 

glossopharyngeal 

Cervical  nerve  J 

JI- 

m 


"  Ciliary  ganafien 
^ .  &7jjy/imM)doium^.Vayi^ '  Spfieno-palatine^eckl'syanaiion . 


mpocAsmic  piekus 

Ga/iff//on  Cocci/ffeum  impar 

finer  divisions  of  the  system  ramify  throughout  the  whole  body,  supplying  vaso- 
motor fibres  to  the  blood-vessels  throughout  their  course,  controlling  the  glands 
of  the  skin,  and  supplying  pilo-motor  fibres  for  the  hairs,  forming  intrinsic 
plexuses  within  the  walls  of  the  viscera,  and  it  is  claimed  that  a  few  of  its  neurones 


THE  SYMPATHETIC  SYSTEM 


1029 


convey  inpulses  toward  the  central  system  (sensory  sympathetic  neurones). 
While  it  is  very  probable  that  certain  of  the  simpler  reflexes  of  the  splanchnic 
organs  may  be  mediated  by  the  sympathetic  system  alone,  yet  the  sympathetic 
is  by  no  means  independent  of  the  cranio-spinal  system,  but  is  rather,  both  ana- 
tomically and  functionally  merely  a  part  of  one  continuous  whole.  Throughout, 
it  shares  its  domain  of  termination  with  cranio-spinal  fibres,  chiefly  of  the  sensory 
variety,  and  most  of  its  rami  and  terminal  branches  carry  a  few  cranio-spinal 
fibres  toward  their  areas  of  distribution.  Likewise  the  cranio-spina,l  nerves  carry 
numerous  sympathetic  fibres  gained  by  way  of  rami  connecting  the  two  systems. 

Like  the  cranio-spinal  system,  the  sympathetic  consists  of  cell-bodies,  each  of  which  gives 
off  one  axone.  In  addition,  the  cell-bodies  give  off  numerous  dichotomously  branched  den- 
drites by  which  their  receptive  surfaces  are  increased,  and  they  are  accumulated  into  ganglia, 
large  and  small.  The  larger  ganglia  have  more  or  less  constant  positions,  shapes,  and  arrange- 
ments, while  the  smaller,  some  of  which  are  microscopic,  are  scattered  throughout  the  body  in 
a  seemingly  more  indefinite  manner.  The  axones  or  fibres  arising  in  these  gangha  are  given  off 
in  trunks  and  rami  which  associate  the  ganglia  with  each  other  or  with  the  cranio-spinal  system, 
or  which  pass  from  the  ganglia  to  be  distributed  directly  upon  their  allotted  elements. 

The  sympathetic  fibres  arising  from  the  ganglia  are,  for  the  most  part,  either  totally  non- 
medullated  or  partially  medullated.  Some  fibres  are  completely  medullated  near  their  cells 
of  origin,  but  lose  their  meduUary  sheaths  before  reaching  their  terminations.  Some  of  them 
possess  complete  medullary  sheaths  throughout,  but  in  no  cases  are  the  sheaths  as  thick  or 
well  developed  as  is  the  rule  with  the  cranio-spinal  fibres.  Thus,  nerve-trunks  and  rami  in 
which  sympathetic  fibres  predominate  appear  greyish  in  colour  and  more  indefinite,  as  dis- 
tinguished from  those  of  the  cranio-spinal  nerves,  which  always  appear  a  glistening  white,  due 
to  hght  being  reflected  from  the  emulsified  myelin  of  the  sheaths  of  their  fibres. 

Origin  of  the  S3rmpathetic  system. — Not  only  must  the  cranio-spinal  and  sympathetic 
systems  be  considered  anatomically  continuous  and  dependent,  but  ako  the  neurones  of  the 
two  systems  have  a  common  origin,  namely,  the  ectoderm  of  the  dorsal  mid-line  of  the  embryo. 
The  cells  of  the  ganglion  crest  (see  p.  754)  become  arranged  in  segmental  groups  and  soon 
separate  into  two  varieties: — those  which  will  remain  near  the  spinal  cord  and  develop  into 
the  spinal  ganglia,  and  those  which,  during  the  growth  processes,  migrate  and  become  displaced 
further  into  the  periphery  and  form  the  sympathetic  gangha. 


Fig.  785. — Scheme  showing  the  Connection  between  the  Sympathetic  and  the  Cranio- 
spinal  AND   Central   Nbrvous   Systems. 


Spinal  ganglion  neurone 
to  capsule  of  ganglion 


Meningeal  ramus 
Dorso-Iateral  group  of      ' 
ventral  horn  ceUs         Ventral 
root 


/  J Gray  ramus  communicans 

~yt^y     White  ramus  co  mmunicans 


Sympathetic  ganglion  1  Gangliated 
^  Sympathetic  trunk       /       trunk 
'  Sympathetic  cell  body  in  spinal 
ganglion 


Posterior  primary  division  1  Spinal 
Anterior  primary  division  J  nerve 


^^^  ^Gray  ramus  communicans 
\         ^White  ramus  communicans 

Sensory  sympathetic  neurone 
Branch  to  prevertebral  ganglion 


In  the  development  of  the  sympathetic  system  the  migration  from  the 
vicinity  of  the  central  system  occurs  to  varying  extents,  so  that  in  the  adult  the 
cells  comprise  three  general  groups  of  ganglia  situated  different  distances  away 
from  the  central  nerve  axis. — (1)  A  large  portion  of  the  cells  remain  near  the 
central  system  and  form  a  linear  series  of  ganglia  which,  with  the  trunks  con- 
necting them,  become  two  gangliated  nerve  trunks  extending  along  each  side, 
proximal  to  and  parallel  with  the  vertebral  column;  (2)  a  still  larger  portion  of  the 
cells  migrate  further  toward  the  periphery  and  are  accumulated  into  ganglia 
which  assume  an  intermediate  position  and  which,  with  the  rami  associating  them 
with  each  other  and  with  other  structures,  form  a  series  of  great  prevertebral 


1030  THE  NERVOUS  SYSTEM 

plexuses;  (3)  still  other  cells  wander  even  further  away  from  the  locality  of  their 
origin  and  invade  the  very  walls  of  the  organs  innervated  by  the  sympathetic 
system.  The  latter  cells  occur  as  numerous  small  terminal  ganglia,  most  of  which 
are  microscopic  and  which,  with  the  twigs  connecting  them,  form  the  most 
peripheral  of  the  sympathetic  plexuses.  Examples  of  these  are  the  intrinsic 
ganglia  of  the  heart  and  pancreas  and  the  plexuses  of  Auerbach  and  Meissner 
in  the  walls  of  the  digestive  canal.  Small,  straggling  ganglia  may  be  found 
scattered  between  these  three  general  groups.  In  the  head,  the  gangliated  trunks 
and  great  prevertebral  plexuses  are  represented  by  the  ciliary,  sphenopalatine,  otic 
and  submaxillary  ganglia  and  the  plexuses  associated  with  these.  The  supporting 
tissue  of  the  sympathetic  system  accumulates  early  and  is  probably  all  of  meso- 
dermic  origin. 

Construction  of  the  sympathetic  system. — The  sympathetic  ganglia  may  be 
considered  as  relays  in  the  pathways  for  the  transmission  of  impulses  from  the 
region  in  which  they  arise  to  the  tissues  in  which  they  are  distributed;  the  cells 
composing  the  ganglia  are  the  cell-bodies  of  the  neurones  interposed  in  the 
various  neurone  chains  performing  this  function.  A  fibre  arising  from  a  cell-body 
in  a  given  ganglion  may  pass  out  of  the  ganglion  and  proceed  directly  to  its 
termination  upon  a  smooth  muscle-fibre  or  gland-cell,  or  it  may  pass  through  a 
connecting  trunk  to  another  ganglion  and  there  terminate  about  and  thus  trans- 
mit the  impulse  to  another  cell,  which,  in  its  turn,  may  give  off  the  fibre  which 
bears  the  impulse  to  the  appropriate  tissue-element.  Fibres  arising  in  given 
ganglia  may  pass  uninterrupted  through  other  ganglia  and  proceed  to  their  re- 
spective destinations.  On  the  other  hand,  several  neurones  may  be  involved  in 
the  transmission  of  a  given  impulse  when  sent  from  a  region  distant  from  the  tissue 
to  which  it  is  distributed. 

Communication  between  the  central  nervous  system  and  the  sympathetic  is 
established  through  both  efferent  and  afferent  fibres.  In  the  region  of  the 
spinal  cord  both  varieties  of  fibres  pass  from  one  system  to  the  other  by  way  of  the 
rami  communicantes,  delicate  bundles  of  fibres  connecting  the  nearby  sympa- 
thetic trunk  with  the  respective  spinal  nerves  (fig.  785). 

The  efferent  fibres  of  the  rami  arise  in  the  ventral  horn  (dorso-lateral  cell-group  chiefly)  of 
the  spinal  cord,  emerge  through  the  ventral  roots,  enter  the  rami,  and  terminate  chiefly  about 
the  cells  of  the  nearest  sympathetic  ganglion;  some,  however,  may  pass  through  or  over  the 
ganglion  of  the  sympathetic  cord  and  terminate  about  cells  in  more  distant  ganglia.  Since 
these  fibres  transmit  impulses  from  the  central  to  the  sympathetic  system,  they  are  known  as 
visceral  efferent  fibres.  They  are  of  smaller  size  than  is  the  average  for  the  cranio-spinal  effer- 
ent or  motor  fibres  of  the  ventral  root.  The  visceral  afferent  fibres  are  of  two  varieties: — (1) 
Peripheral  processes  of  the  spinal  ganglion-cells  which  run  outward  in  the  nerve-trunk,  enter 
the  rami  communicantes,  pass  through  the  various  connecting  trunks  and  terminal  rami  of  the 
sympathetic  and  terminate  in  the  tissues  supplied  by  these  rami.  .  Such  are  merely  sensory  fibres 
of  the  cranio-spinal  type  which  collect  impulses  in  the  domain  of  the  sympathetic  and  convey 
them  to  the  central  system  by  way  of  the  sympathetic  nerves  and  the  dorsal  roots  of  the  spinal 
nerves.  (2)  Afferent  sympathetic  fibres  proper.  The  actual  existence  of  these  has  not  been 
long  established,  and  their  relative  abundance  is  as  yet  uncertain.  They  consist  of  fibres  arising 
in  the  sympathetic  ganglia  which  enter  the  spinal  ganglia  by  way  of  the  rami  commnicantes 
and  the  cranio-spinal  nerve-trunk  and  terminate  in  arborisations  about  the  spinal  ganglion-cells 
(fig.  785).  The  afferent  impulses  transmitted  by  these  sympathetic  fibres  are  borne  into  the 
spinal  cord  or  brain  by  way  of  the  cranio-spinal  fibres  of  the  dorsal  roots.  These  sensory 
sympathetic  fibres  must  necessarily  either  receive  the  impulses  they  bear  from  sympathetic 
neurones  having  both  peripheral  and  central  processes  or  they  themselves  must  be  axones  or 
central  processes  of  neurones  having  also  processes  terminating  in  the  peripheral  tissues. 
Doubtless  the  variety  of  visceral  afferent  fibres  first  mentioned  greatly  predominates. 

The  thoracic  and  the  lumbar  spinal  nerves  are  connected  with  the  sympathetic 
trunk  (gangliated  cord)  by  two  rami  communicantes.  Most  of  both  the  visceral 
efferent  and  also  the  visceral  afferent  fibres  (which  arise  in  the  spinal  ganglia) 
pass  by  way  of  a  separate  ramus.  Both  these  varieties  being  of  the  cranio-spinal 
type,  and,  therefore,  medullated,  they  give  the  ramus  a  white  appearance  meriting 
the  name  white  ramus  communicans.  Fibres  of  the  sympathetic  type  predomi- 
nate in  the  second  ramus  and  thus  it  is  the  grey  ramus  communicans.  The  latter 
consists  of: — (1)  afferent  sympathetic  fibres  and  (2)  of  sympathetic  fibres  which 
join  the  primary  divisions  of  the  spinal  nerves  and  course  in  them  to  their  allotted 
tissues  (fig.  785). 

In  the  sacral  region,  most  of  the  visceral  efferent  fibres  pass  over  the  ganglia  of  the  sympa- 
thetic trunk  and  terminate  in  the  more  peripheral  ganglia  of  the  plexuses  of  this  region.     This  is 


THE  SYMPATHETIC  SYSTEM 


1031 


especially  true  for  the  fibres  passing  from  the  second,  third,  and  fourth  sacral  nerves.  In  the  cer- 
vical region  white  rami  are  not  in  evidence,  a  fact  probably  exphcable  as  due  to  an  arrangement 
by  which  at  least  most  of  the  visceral  efferent  fibres  arising  in  the  cervical  segments  of  the  spinal 
cord  pass  downward  in  these  segments  and  join  the  sympathetic  tlirough  the  white  rami  of  the 
upper  thoracic  nerves;  others  may  enter  the  cervical  portion  of  the  gangliated  cord  through  the 
spinal  accessory  or  eleventh  cranial  nerve,  rather  than  through  individual  white  rami,  while 
others  pass  into  the  nerves  of  the  brachial  plexus  to  terminate  in  the  minute  ganglia  of  the  plex- 
uses upon  the  blood-vessels  of  the  limb.  All  the  spinal  nerves  are  joined  by  grey  rami  communi- 
cantes  from  the  sympathetic  trunk. 

Vaso-motor  fibres  to  the  meninges  and  intrinsic  blood-vessels  of  the  spinal 
cord  pass  to  the  spinal  nerves  by  way  of  the  grey  rami.  Thence  they  may  reach 
the  meninges  by  one  of  three  ways: — (1)  through  the  delicate  recurrent  or 
meningeal  branch  of  the  spinal  nerve  (fig.  785) ;  (2)  through  the  trunk  and  ventral 


Fig.  786. — Diagram  suggesting  the  Origin,  Course  and  Connections  of 
Sympathetic  Nerve-fibres. 


Spinal  ganglion  •- 


Sympathetic  trunk 


SympatliQtic  ganglion 


Grey  ramus  communicans 

White  ramus  communicans 


White  ramus  communicans 
Grey 


Sympathetic  trunk 


communicans  ^ 


root  of  the  spinal  nerve;  (3)  probably  more  rarely,  through  the  trunk  and  dorsal 
root  of  the  spinal  nerve  (fig.  786). 

Corresponding  communications  exist  between  the  cranial  nerves  and  the  sympathetic, 
but  the  corresponding  rami  usually  extend  further  toward  the  periphery  and  in  not  so  regular  a 
manner  as  the  communications  between  the  spinal  nerves  and  the  sympathetic  system.  The 
mesencephalon,  for  example,  is  chiefly  connected  with  the  ciUary  ganglion  of  the  sympathetic 
by_  fibres  which  are  sent  through  the  oculo-motor  nerve  and  which  enter  this  ganghon  by  way 
of  its  short  root  and  terminate  about  its  cells.  Visceral  efferent  fibres  from  the  rhombencephalon 
pass  outward  to  the  sympathetic  in  the  roots  of  the  facial,  glosso-palatine,  glosso-pharyngeal. 


1032  THE  NERVOUS  SYSTEM 

vagus,  and  spinal  accessory  nerves,  all  of  which  have  more  or  less  irregularly  disposed  com- 
municating rami.  The  ganglia  of  origin  of  the  vagus,  more  than  perhaps  any  other  nerve,  both 
receive  impulses  from  visceral  efferent  fibres  and  give  origin  to  sympathetic  fibres.  Likewise 
twigs  of  other  cranial  nerves,  especially  of  the  trigeminus,  connect  with  (pass  through)  the  small 
sympathetic  ganglia  of  the  head.  The  meningeal  branches  given  by  certain  of  the  cranial  nerves 
contain  vaso-motor  fibres,  and  these  correspond  to  the  sympathetic  fibres  in  the  recurrent 
branches  and  in  the  roots  of  the  spinal  nerves. 

It  is  known  that  spinal  ganglia  and  certain  of  the  ganglia  of  the  cranial  nerves 
contain  cell-bodies  of  sympathetic  neurones — cell-bodies  which,  during  the  period 
of  the  migration  peripheralward,  remained  within  the  confines  of  these  ganglia 
(fig.  785).  These  cell  bodies  receive  efferent  impulses  from  ventral  root  fibres 
and  send  their  axones  further  into  the  periphery  just  as  if  in  the  sympathetic 
ganglion.  Their  relative  abundance  is  not  known.  It  is  supposed  that  the  ganglia 
of  the  vagus,  glosso-pharyngeus,  trigeminus  and  the  geniculate  ganglion  contain 
a  considerable  proportion  of  such  sympathetic  cell-bodies. 

From  the  above  it  may  be  seen  that  the  ganglia  and  connecting  trunks  and  rami 
of  the  sympathetic  system  may  be  divided  as  follows: — (1)  The  two  sympathetic 
gangliated  trunks  lying  proximal  to  and  parallel  with  the  vertebral  column;  (2)  the 
great  prevertebral  plexuses,  of  which  there  are  roughly  four,  one  in  the  head,  one 
in  the  thorax,  one  in  the  abdomen,  and  one  in  the  pelvic  cavity  (fig.  784),  each  of 
which  is  subdivided;  (3)  the  numerous  terminal  ganglia  and  plexuses  situated 
either  within  or  close  to  the  walls  of  the  various  organs;  (4)  the  trunks  and  rami 
associating  the  ganglia  with  each  other  and  thus  contributing  to  the  plexuses,  or 
connecting  the  ganglia  with  other  nerves  or  with  the  organs  with  whose  innerva- 
tion they  are  concerned.  The  trunks  and  rami  may  be  divided  into — (a)  the 
rami  communicantes,  or  central  branches,  connecting  the  sympathetic  with  the 
cranio-spinal  and  central  systems;  (Ja)  associative  trunks,  best  considered  as  those 
which  associate  sympathetic  ganglia  situated  on  the  same  side  of  the  body;  (c) 
commissural  branches,  or  those  which  associate  ganglia  situated  on  opposite  sides 
of  the  mid-line  of  the  body,  such  as  the  transverse  connecting  branches  between 
the  sympathetic  trunk  in  the  lumbo-sacral  region  (fig.  787) ,  or  all  the  associating 
trunks  between  the  ganglia  of  plexuses  occupying  the  mid-region  of  the  body; 
{d)  terminal  or  peripheral  branches,  or  those  which  pass  from  the  ganglia  to  their 
final  distribution  apparently  uninterrupted  by  other  ganglia. 

THE  SYMPATHETIC  TRUNKS 

The  sympathetic  gangliated  trunks,  or  gangliated  cords,  of  the  sympathetic 
system  are  two  symmetrical  trunks  with  ganglia  interposed  in  them  at  intervals 
of  varying  regularity,  and  extending  vertically,  one  on  each  side  of  the  ventral 
aspect  of  the  vertebral  column,  from  the  second  cervical  vertebra  to  the  first 
piece  of  the  coccyx.  Upon  the  coccyx  the  two  trunks  unite  and  terminate  in  a 
single  medial  ganglion,  the  ganglion  coccygeum  impar.  The  various  ganglia  are 
connected  with  the  cranio-spinal  nerves  by  the  rami  communicantes.  Mor- 
phologically, each  trunk  might  be  expected  to  possess  thirty-one  ganglia,  one  for 
each  spinal  nerve,  but,  owing  to  the  fusion  of  adjacent  ganglia  in  certain  regions, 
especially  in  the  cervical,  there  are  in  the  adult  only  twenty-one  or  twenty-two 
ganglia  in  each  trunk.  These  occur  as  three  cervical  ganglia,  ten  or  eleven  thoracic 
ganglia,  four  lumbar  and  four  sacral  ganglia,  and  the  ganglia  n  coccygeum  impar, 
which  is  common  to  both  trunks. 

In  the  cervical  region  the  sympathetic  trunks  lie  in  front  of  the  transverse  processes  of  the 
vertebra3,  from  which  they  are  separated  by  the  longus  capitis  (rectus  capitis  anticus  major) 
and  longus  colli;  in  the  thoracic  region  they  he  at  the  sides  of  the  bodies  of  the  vertebrae  and  on 
the  heads  of  the  ribs;  in  the  lumbar  region  they  are  placed  more  ventraUy  with  reference  to 
the  spinal  nerves  and  more  in  front  of  the  bodies  of  the  vertebrte  and  along  the  anterior  borders 
of  the  psoas  muscles;  in  the  pelvis  the  ganglia  lie  between  and  ventral  to  the  openings  of  the 
sacral  foramina.  In  the  lower  lumbar  and  sacral  region  one  gangUon  may  send  rami  commu- 
nicantes to  two  spinal  nerves  and  one  spinal  nerve  may  be  connected  with  two  gangha.  The 
ganglia  of  the  trunks  throughout  give  off  associative  branches  to  the  gangha  of  the  prevertebral 
plexuses  and  branches  to  the  nearby  viscera  and  blood-vessels.  These  branches  may  appear 
either  white  or  grey  according  to  the  predominance  of  meduUated  or  non-medullated  fibres  in 
them.  In  the  lumbo-sacral  region  commissural  or  transverse  branches  between  the  gangha 
of  the  two  trunks  are  especially  abundant.  In  trunks  having  a  whiter  appearance,  the  greater 
part  of  the  meduUated  fibres  producing  it  are  sensory  and  visceral  motor  fibres  from  the  spinal 
nerves  which  have  passed  through  the  sympathetic  ganglia  without  termination.  The  nerve 
trunks  connecting  the  ganglia  of  the  sympathetic  trunks  all  contain  three  varieties  of  fibres: — (1) 


THE  SYMPATHETIC  TRUNK  1033 

visceral  motor  fibres  which  have  entered  them  in  the  white  rami  communicantes  from  the  spinal 
nerves  of  higher  or  lower  levels,  and  which  are  coursing  in  them  to  terminate  in  other  gangUa, 
either  in  the  trunks  above  or  below  or  in  ganglia  not  belonging  to  the  trunks;  (2)  fibres  arising  in 
sympathetic  ganglia  of  a  higher  or  lower  level  and  passing  upward  or  downward  to  terminate 
in  other  ganglia  of  the  trunk  or  to  issue  from  the  trunk  and  proceed  to  more  peripheral  ganglia  or 
to  ganglia  of  the  opposite  trunk  (both  associative  and  commissural  fibres);  (3)  afferent  fibres 
or  sensory  fibres  arising  either  in  the  spinal  ganglia,  or  sensory  sympathetic  fibres  arising  in 
sympathetic  ganglia  and  coursing  in  the  trunk  to  pass  into  spinal  ganglia  above  or  below  by  way 
of  the  grey  rami  communicantes. 

THE  CEPHALIC  AND  CERVICAL  PORTIONS  OF  THE  SYMPATHETIC 

TRUNK 

The  cephalic  portion  of  the  sympathetic  system  consists  of  numerous  small 
ganglia  and  of  numerous  plexuses  connected  with  the  internal  carotid  nerve,  the 
ascending  branch  given  off  by  the  superior  cervical  sympathetic  ganglion.  The 
cephalic  ganglia  are  all  relatively  small.  There  are  four  considered  in  the 
ordinary  macroscopic  dissections,  namely,  the  ciliary  or  ophthalmic,  the  spheno- 
palatine or  Meckel's  ganglion,  the  otic,  and  the  submaxillary.  To  these  may  be 
added  a  portion  of  the  superior  cervical  sympathetic  ganglion,  the  sympathetic 
portions  of  the  nodosal,  petrous,  geniculate  and  semilunar  ganglia,  and  the  var- 
ious small  ganglia  dispersed  in  the  plexuses.  These  ganglia  with  their  roots  or 
communicating  branches  have  been  described  in  their  relations  with  the  divisions 
of  the  trigeminus  and  with  the  oculo-motor,  glosso-palatine,  vagus  and  facial 
nerves. 

The  internal  carotid  nerve,  the  ascending  branch  from  the  superior  cervical 
sympathetic  ganglion,  may  be  regarded  as  an  upward  prolongation  of  the  primi- 
tive sympathetic  trunk. 

It  arises  from  the  upper  end  of  the  superior  cervical  ganglion  and  passes  through  the  carotid 
canal  into  the  cranial  cavity.  It  divides  into  two  branches  which  subdivide  to  form  a  coarse 
plexus,  the  internal  carotid  plexus,  which  partly  surrounds  the  internal  carotid  artery  before 
the  latter  enters  the  cavernous  sinus  (fig.  787  and  788).  It  passes  with  the  artery  to  the  caver- 
nous sinus,  where  it  forms  the  finer  meshed  cavernous  plexus. 

The  internal  carotid  plexus  supplies  offsets  to  the  artery  and  receives  branches 
from  the  tympanic  plexus  through  the  inferior  carotico-tympanic  nerve  and 
from  the  spheno-palatine  ganglion  through  the  great  deep  petrosal  nerve.  It  also 
communicates  by  fine  branches  with  the  semilunar  (Gasserian)  ganglion  and 
with  the  abducens  nerve. 

The  cavernous  plexus  gives  branches  of  communication  to  the  oculo-motor 
and  trochlear  nerves  and  to  the  opthalmic  division  of  the  trigeminus.  According 
to  Toldt  and  Spalteholz,  it  communicates  with  the  tympanic  plexus  through  the 
superior  carotico-tympanic  (small  deep  petrosal)  nerve.  It  also  communicates 
with  the  ciliary  ganglion  through  the  long  root  of  the  ciliary  ganglion  and  usually 
through  a  separate  sympathetic  root  of  this  ganglion.  These  branches  may  pass 
through  the  superior  orbital  (sphenoidal)  fissure  either  separately  or  with  the  naso- 
ciliary (nasal)  nerve. 

The  cavernous  plexus  also  gives  branches  to  the  carotid  artery  and  filaments  of  the  plexus 
accompany  small  branches  of  the  artery  to  the  hypophysis  (pituitary  body)  and  to  the  dura 
mater  on  the  sphenoid  bone. 

The  terminal  branches  of  the  cavernous  plexus  consist  of  delicate  filaments  that  anastomose 
freely,  forming  fine  plexuses,  and  pass  from  the  cavernous  plexus  along  the  terminal  divisions 
of  the  internal  carotid  artery  and  their  branches.  These  fine  plexuses  take  the  name  of  the 
artery  on  which  they  lie.  The  four  larger  of  them  are  the  plexuses  of  the  anterior  and  middle 
cerebral  arteries,  the  plexus  of  the  chorioid  artery,  and  the  ophthalmic  plexus. 

The  cervical  portion  of  the  sympathetic  cord  extends  upward  along  the  great 
vessels  of  the  neck.  No  white  rami  communicantes  connect  it  directly  with  the 
spinal  cord,  but  instead  it  receives  visceral  efferent  fibres  from  the  upper  thoracic 
spinal  nerves  through  the  sympathetic  trunk,  and  probably  also  from  the  cervical 
spinal  cord  through  the  spinal  acessory  nerve  and  the  connections  with  the  vagus. 
It  sends  grey  rami  communicantes  to  each  of  the  cervical  nerves.  It  extends 
from  the  subclavian  artery  to  the  base  of  the  skull,  lying  dorsal  to  the  sheath  of 
the  great  vessels  and  in  front  of  the  longus  capitis  and  longus  colli,  which  separate 
is  from  the  transverse  processes  of  the  cervical  vertebrae  (fig.  787).     It  usually 


1034 


THE  NERVOUS  SYSTEM 


Fig.  787. — Showing  the  Sympathetic  Trunks  in  their  Relation  to  the  Vertebral 
Column,  to  the  Spinal  Nerves,  and  to  each  Other.  (Modified  from^Toldt,  "Atlas  of 
Human  Anatomy,"  Rebman,  London  and  New  York.) 

Cavernous  plexus 
Internal  carotid  plexi 

Internal  carotid  nerve 
Jugular  nerve 

Vagus 
Superior  cervical  ganglion  - 
rical  plexus 

Cervical  portion  of  sympathetic  trunk 
Superior  cardiac  nerve' 
Rami  communicantes 

Middle  cervical  ganglion 

Brachial  plexus 

Inferior  cervical  ganghon 

.First  thora.,ic  ganghon' 

Ansa  subclavia  (Vieussenii) 

Inferior  cardiac 

or  and  middle  c 
nerves 

Pulmonary  branches 
Twigs  to  aortic  plexus 
Splanchnic  gangUons. 

Last  thoracic  ganghon^ 

Splanchnic  minor  nerve 
Medial  part  of  lumbo 
costal  arch 
Lateral  part  of  lumbo-costal  arch 
Psoas  major- 
Second  lumbar  nerve 

Twelfth  intercostal  nerve 
Lumbar  plexus 


Li  Glossopharyngeus 
..-  Jugular  nerve 


--—Pharyngeal  plexus 
■"-»  Pharyngeal  branches 
**Vagus 

External  carotid  nerves 

ylnfenor  thyreoid  plexus 
Vertebral  plexus 


Subclavian  plexus 


Rami  communicantes 


Thoracic  portion  of 
sympathetic  trunk 

Thoracic  ganglia 
.-.Intercostal  nerves 

—  Greater  splanchnic  nerve 


/^„-  Lesser  splanchnic  nerve 

>-^ /^    I -Thoracic  aortic  plexus 

splanchnic  nerve 


Greater  splanchnic  nerve 
Branches  to  phrenic  plexus 
..•Branches  to  coeliac  ganglia 
**Rami  communicantes 


Rami  communicantes 


Lumbo-sacral  trunk 


Rami   communicantes 


Branches  to  abdominal 
aortic  plexus 

Branches  to  hypogastric 
plexus 

^. Fifth  lumbar  ganglion 

._  Commissural  branches 
■First  sacral  ganglion 


U  V  '"-^^Rami  communicantes 
Ganghon  coccygeum  impar 


SUPERIOR  CERVICAL  GANGLION 


1035 


has  but  three  ganglia,  one  at  each  end,  the  superior  and  inferior,  and  one  between 
these  two,  called  the  middle  ganglion.  The  latter  varies  somewhat  in  position  and 
is  sometimes  absent. 

1.  Superior  Cervical  Ganglion 

The  superior  cervical  ganglion  is  usually  fusiform  in  shape  and  is  sometimes 
marked  by  one  or  more  constrictions.  There  is  ground  for  the  belief  that  it  is 
formed  by  the  coalescence  of  four  ganglia  corresponding  to  the  first  four  cervical 
nerves.  It  varies  from  an  inch  to  one  and  one-half  inches  (2.5  to  3.7  cm.)  in 
length,  lying  dorsal  to  the  upper  part  of  the  sheath  of  the  great  vessels  of  the  neck 
and  in  front  of  the  transverse  processes  of  the  second  and  third  cervical  vertebrae. 

Fig.  788. — Diagram  op  the  Glosso-palatine  Nerve  and  the  Relations  op  the  Gangli- 
ATED  Cephalic  Plexus  to  other  Cranial  Nerves.     (After  Bean.) 
Broken  lines,  motor;  continuous  lines,  sympathetic;  glosso-palatine  .in  solid  black.    Medial 
view.    Left  side. 

£  >    en  d 

S  a  «  3 


Glosso-palatine  ."  g  «  S  "  a  °  3 -g     p,      '    '      ' 


Carotid 
_  ^  artery       Oculomotor  nerve 


Chorda  tympani 


Ciliary 
ganglion 

—  Ophthalniic  nerve 

.1       i  V ^ Maxillary  nerve 

4^i)--\-TX— Mandibular  nerve 

jV/^wSj^^^::^;^^ Great  deep 

\\    »  \     » "'^"^yi^     petrosal  nerve 

W'W^^^^""' Sphenopalatine 

'A ^ ^  \r\^  ganglion 

Palatine  portion  of 
glosso-palatine  nerve 

Nerve  of  pterygoid 
canal  (Vidian  nerve) 

Otic  ganglion 

•  Middle  meningeal 
([l\  artery 

\ 

i^ r  Submaxillary  ganglion 

)nr\rr 

External  ma^llaiy 
artery 


It  occasionally  extends  upward  as  high  as  the  transverse  process  of  the  first 
vertebra  (fig.  787).  It  is  connected  with  the  middle  cervical  ganglion  by  the 
intervening  trunk,  and  it  gives  off  a  large  number  of  communicating  branches. 
Rarely,  the  ganglion  may  be  double  or  split  with  a  ventral  portion  lying  superfi- 
cial to  the  carotid  sheath  and  a  dorsal  portion  dorsal  to  the  sheath,  connected  by 
sympathetic  filaments  near  the  superior  and  inferior  extremities  of  the  ganglion. 

Communications: — (1)  Four  grey  rami  communicantes  associate  the  ganglion  with  the 
anterior  primary  divisions  of  the  first  four  cervical  nerves. 

(2)  Communicating  branches  to  the  cranial  nerves. — An  iiTegular  number  of  small  twigs 
pass  between  the  superior  cervical  gangUon  and  the  hypoglossal  nerve  and  to  the  ganghon  nodo- 
sum of  the  vagus.  A  named  branch,  the  jugular  nerve,  runs  upward  to  the  base  of  the  skull 
and  divides  into  two  branches,  one  of  which  enters  the  jugular  foramen  and  terminates  in  the 
jugular  ganghon  of  the  vagus,  and  the  other  ends  in  the  petrous  ganghon  of  the  glosso- 
pharyngeus.    (See  fig.  788). 


1036  THE  NERVOUS  SYSTEM 

(3)  Four  or  five  laryngo -pharyngeal  branches  come  from  the  superior  ganglion  and  the 
plexus  extending  downward  from  it,  and  pass  forward  and  medialward,  lateral  to  the  carotid 
vessels,  to  the  wall  of  the  pharynx,  where  they  unite  on  the  middle  constrictor  with  the  pharyn- 
geal branches  of  the  glosso-pharyngeus  and  vagus,  forming  with  them  the  pharyngeal  plexus, 
from  which  branches  are  distributed  to  the  walls  of  the  pharynx  and  to  the  superior  and 
external  laryngeal  nerves  (fig.  787). 

(4)  The  superior  cervical  cardiac  nerve  springs  from  the  lower  part  of  the  ganglion  or  from 
the  trunk  immediately  below  it.  It  passes  downward  behind  the  carotid  sheath,  either  in  front 
of  or  dorsal  to  the  inferior  thyreoid  artery,  and  in  front  of  the  longus  colli,  and  establishes 
communications  with  the  upper  cervical  cardiac  branch  of  the  vagus,  the  middle  cervical  cardiac 
branch  of  the  sympathetic,  and  with  the  inferior  and  external  laryngeal  nerves.  At  the  root 
of  the  neck  the  nerve  of  the  right  side  passes  in  front  of  or  behind  the  first  part  of  the  right  sub- 
clavian artery,  and  is  continued  along  the  innominate  artery  to  the  front  of  the  bifurcation  of 
the  trachea,  where  it  ends  in  the  deep  part  of  the  cardiac  plexus.  The  left  nerve  passes  into  the 
thorax  along  the  front  of  the  left  common  carotid  artery,  crosses  the  front  of  the  arch  of  the  aorta 
immediately  anterior  to  the  vagus,  and  terminates  in  the  superficial  part  of  the  cardiac  plexus 
(fig.  789).     Filaments  from  both  the  right  and  left  nerves  pass  to  the  inferior  thyreoid  plexus. 

(5)  The  external  carotid  nerves  (fig.  787)  pass  forward  from  the  .superior  cervical  ganglion 
to  the  external  carotid  arlcry,  where  they  divide  into  branches  which  anastomose  freely  to  form 
around  the  artery  the  external  carotid  plexus.  This  plexus  extends  to  the  beginning  of  the 
artery,  and  is  continued  upon  the  common  carotid  artery  as  the  common  carotid  plexus.  From 
the  external  carotid  plexus,  filaments  pass  to  form  secondary  plexuses  around  each  of  the 
branches  of  the  external  carotid  artery.  These  plexuses  take  the  names  of  the  arteries  which 
they  follow,  namely,  the  superior  thyreoid  plexus,  lingual  plexus,  etc.  Filaments  pass  from 
the  external  carotid  plexus  to  the  glomus  caroticum  (the  carotid  gland),  and  from  the  superior 
thyreoid  plexus  to  the  thyreoid  gland. 

From  the  external  maxillary  (facial)  plexus  passes  the  sympathetic  root  of  the  submaxillary 

glion. 

A  part  of  the  internal  maxillary  plexus  is  continued  upon  the  middle  meningeal  artery  as 
the  meningeal  plexus.  From  this  plexus  filaments  pass  to  the  otic  ganglion,  and  sometimes 
a  branch,  called  by  English  anatomists  the  external  superficial  petrossal  nerve,  passes  to  the 
geniculate  ganglion. 

(6)  Small  branches  to  the  ligaments  and  bones  of  the  upper  part  of  the  vertebral  column. 

(7)  The  internal  carotid  nerve  (ascending  branch)  and  plexus  have  been  described  with 
the  cephalic  portion  of  the  sympathetic  system. 

2.  The  Middle  Cervical  Ganglion 

The  middle  cervical  ganglion  is  small  and  somewhat  triangular  in  outline.  It 
is  sometimes  absent.  Its  position  is  variable,  but  it  commonly  lies  about  the 
level  of  the  cricoid  cartilage,  in  front  of  the  bend  of  the  inferior  thyreoid  artery 
(fig.  787),  and  it  is  associated  with  the  superior  cervical  ganglion  and  with  the 
inferior  cervical  ganglion  by  the  trunk  of  the  gangliated  cord.  From  the  lower 
part  of  the  middle  ganglion  some  filaments  pass  dorsal  to  the  subclavian  artery, 
while  others  pass  in  front  of  and  beneath  that  artery  and  anastomose  with  the 
first-mentioned  filaments  to  form  a  loop,  the  ansa  subclavia  {ansa  Vieussenii) 
(figs.  751,  787).  Filaments  from  this  loop  to  the  inferior  cervical  ganglion  thus 
form  another  communication  between  the  middle  and  inferior  cervical  ganglia. 

Connections. — The  middle  cervical  ganghon  gives  off  four  or  more  rami. 

Two  (a  and  h)  are  grey  rami  communicantes  which  connect  the  middle  ganglion  with  the 
anterior  primary  iDranches  of  the  fifth  and  sixth  cervical  nerves. 

(c)  One  or  more  peripheral  branches  pass  along  the  inferior  thyreoid  artery  and  anastomose 
with  branches  from  the  superior  and  middle  cardiac  nerves  and  from  the  inferior  cervical 
ganghon,  thus  taking  part  in  the  formation  of  the  inferior  thyreoid  plexus,  from  which  branches 
pass  to  the  thyreoid  gland. 

{d)  The  middle  cardiac  nerve  arises  by  one  or  more  branches  from  the  ganghon,  or  from 
the  trunk  of  the  cord,  and  passes  downward  dorsal  to  the  common  carotid  artery  and,  on  the 
right  side,  either  in  front  of  or  dorsal  to  the  subclavian  artery,  and  then  along  the  innominate 
artery  to  the  deep  part  of  the  cardiac  plexus  (figs.  787  and  789).  It  is  frequently  larger  than 
the  superior  cardiac  nerve.  On  the  left  side  the  nerve  runs  between  the  subclavian  and  common 
carotid  arteries.  On  both  sides  the  nerve  communicates  with  the  inferior  laryngeal  nerve  and 
external  laryngeal  nerve. 

The  middle  cervical  ganglion  also  gives  branches  to  the  common  carotid  plexus. 

3.  The  Inferior  Cervical  Ganglion 

The  inferior  cervical  ganglion  is  irregular  in  form.  It  is  larger  than  the 
middle  cervical  ganglion,  and  it  lies  deeply  in  the  root  of  the  neck  dorsal  to  the 
vertebral  artery  or  the  first  part  of  the  subclavian  artery,  and  ventral  to  the 
interval  between  the  transverse  processes  of  the  last  cervical  and  the  first  thoracic 
vertebrse  (figs.  759,  761).     It  is  connected  with  the  middle  cervical  ganglion  by 


THE  SYMPATHETIC  TRUNK  1037 

the  sympathetic  trunk,  and  by  filaments  passing  to  the  ansa  subclavia  (Vieussenii), 
and  it  is  either  blended  directly  with  the  first  thoracic  ganglion  or  connected  with 
it  by  a  short  stout  portion  of  the  trunk.  It  gives  rami  to  the  last  two  cervical 
nerves  and  peripheral  branches  to  the  vertebral  and  internal  mammary  arteries, 
to  the  heart,  and  to  the  inferior  thyreoid  plexus. 

Connections. — (1)  The  rami  to  the  seventh  and  eighth  cervical  nerves  are  grey  rami 
communicantes. 

(2)  The  branches  to  the  vertebral  artery  are  large  and  they  unite  with  similar  branches 
from  the  first  thoracic  ganglion  to  form  a  plexus,  the  vertebral  plexus  (fig.  787),  which  accom- 
panies the  artery  into  the  posterior  fossa  of  the  cranium,  where  it  is  continued  on  the  basilar 
artery.  The  plexus  communicates  in  the  neck  by  delicate  threads  with  the  cervical  spinal 
nerves.     These  are  probably  meningeal  rami. 

(3)  The  branches  to  the  internal  mammary  artery  form  the  internal  mammary  plexus. 

(4)  The  inferior  cardiac  nerve  may  arise  from  the  inferior  cervical  ganglion,  from  the  first 
thoracic  ganglion,  or  by  filaments  from  both  these  ganglia  (figs.  787  and  789).  It  communicates 
with  the  recurrent  laryngeal  nerve  and  with  the  middle  cardiac  nerve,  and  passes  to  the  deep 
part  of  the  cardiac  plexus.  On  the  left  side  it  frequently  joins  the  middle  cardiac  nerve  to 
form  a  common  trunk. 

Construction  of  the  cervical  portion  of  the  sympathetic  trunk. — This  portion  of  the  trunk 
contains  both  meduUated  and  non-medullated  fibres,  and  a  large  part  of  the  former  are  of 
cranio-spinal  origin.  In  the  absence  of  white  rami  communicantes  to  this  portion  of  the  sym- 
pathetic trunk,  it  is  evident  that  few  if  any  of  the  cranio-spinal  or  efferent  visceral  fibres  are 
contributed  to  it  below  the  superior  ganglion  by  the  cervical  region  of  the  spinal  cord.  Instead, 
such  fibres  are  known  to  enter  by  way  of  the  white  rami  from  the  upper  thoracic  nerves,  and 
to  ascend  to  this  portion  of  the  sympathetic  trunk.  Most  of  these  fibres  terminate  about  the 
cells  of  the  superior,  middle,  and  inferior  cervical  ganglia,  and  these  cells  in  their  turn  give  off 
sympathetic  fibres  which  pass  by  way  of  the  branches  mentioned  above  for  the  cephalic  and 
cervical  portions,  to  their  distribution  in  the  structures  of  the  head,  neck,  and  thorax.  The 
efferent  visceral  fibres  which  terminate  in  the  superior  ganghon  especially  are  among  those 
which  mediate — (1)  vaso-motor  impulses  for  the  head;  (2)  secretory  impulses  for  the  submaxil- 
lary gland;  (3)  pilo-motor  impulses  for  the  hairs  of  the  face  and  neck;  (4)  motor  impulses  for  the 
smooth  muscle  of  the  eyelids  and  orbit,  and  (5)  dilator  impulses  for  the  pupil.  The  sympathetic 
or  grey  fibres  in  the  cervical  portion  of  the  sympathetic  trunk  arise  from  the  cells  of  the  upper 
thoracic  and  the  cervical  ganglia,  and  are  passing  either  to  connect  the  ganglia  with  each  other 
or  to  enter  the  peripheral  branches  and  proceed  to  their  terminal  distribution. 

THE  THORACIC  PORTION  OF  THE  SYMPATHETIC  TRUNK 

The  thoracic  part  of  the  gangliated  trunk  runs  downward  on  the  heads  of  the 
ribs  from  the  first  to  the  tenth,  and  then  passes  a  little  ventralward  on  the  sides 
of  the  bodies  of  the  lower  two  thoracic  vertebrse.  Above  it  is  continuous  with  the 
cervical  portion  at  the  root  of  the  neck,  dorsal  to  the  vertebral  artery.  Below  it 
leaves  the  thorax  dorsal  to  the  medial  lumbo-costal  arch  (arcuate  ligament),  or 
sometimes  dorsal  to  the  lateral  lumbo-costal  arch,  and  continues  into  the  lumbar 
portion  of  the  trunk.  It  lies  behind  the  costal  pleura  and  crosses  over  the  aortic 
intercostal  arteries. 

The  number  of  ganglia  in  this  part  of  the  trunk  is  variable.  There  are 
usually  ten  or  eleven,  but  the  first  is  sometimes  fused  with  the  inferior  cervical 
ganglion  and  occasionally  other  ganglia  fuse.  The  ganglia  are  irregularly 
angular  or  fusiform  in  shape,  and  lie  on  the  head  of  the  ribs,  on  the  costo-vertebral 
articulations,  or  on  the  bodies  of  the  vertebrae.  The  portions  of  the  trunk 
connecting  the  ganglia  usually  are  single,  but  sometimes  they  are  composed  of 
two  or  three  small  cords  in  juxtaposition.  Each  ganglion,  with  the  possible 
exception  of  the  first,  receives  a  white  ramus  comnmnicans  from  a  thoracic  nerve 
and  all  give  off  grey  rami  communicantes  to  these  nerves. 

The  white  rami  communicantes,  as  they  approach  the  sympathetic  trunk, 
quite  often  appear  double,  due  to  the  separation  of  a  large  portion  of  their  fibres 
into  two  main  streams,  one  passing  upward  in  the  sympathetic  trunk,  and  one 
passing  downward.  Of  the  white  rami  from  the  upper  five  thoracic  nerves,  the 
upward  stream  of  fibres  is  much  larger  than  the  downward,  due  to  the  fact  that  a 
greater  part  of  the  efferent  visceral  fibers  from  these  nerves  are  distributed  through 
the  cervical  portion  of  the  sympathetic  trunk,  as  noted  above  in  the  construction 
of  that  portion.  Usually  the  white  rami  from  the  spinal  nerves  pass  directly  to 
the  corresponding  ganglia  of  the  trunk,  and  thus  lie  in  company  with  the  corre- 
sponding grey  rami.  Sometimes,  however,  they  may  join  the  intermediate  por- 
tions of  the  trunk,  and  in  the  lower  thoracic  region  especially,  a  ramus  may  pass 
from  a  nerve  to  the  ganglion  corresponding  to  the  nerve  above  or  below.     The 


1038  THE  NERVOUS  SYSTEM 

fibres  of  the  white  rami  from  the  lower  thoracic  nerves  are  in  greater  part  directed 
downward  in  the  sympathetic  trunk,  and  also  downward  in  its  peripheral 
branches,  to  be  distributed  to  the  abdominal  viscera.  In  all  cases,  however,  some 
of  the  fibres  of  the  thoracic  white  rami  terminate  in  the  ganglia  nearest  their 
junction  with  the  trunk,  while  others  pass  into  the  nearest  peripheral  branches. 
In  this  way  the  white  rami  from  all  the  thoracic  spinal  nerves,  especially  those 
of  the  mid-region,  are  directly  concerned  in  the  innervation  of  the  thoracic 
viscera,  lungs,  oesophagus,  aorta,  etc. 

The  first  thoracic  ganglion  is  larger  than  the  other  ganglia  of  this  region  and  is 
irregular  in  form.  It  may  be  narrowly  ovoid  or  semilunar.  It  lies  in  front  of  the 
neck  of  the  first  rib,  behind  the  pleura,  and  on  the  medial  side  of  the  costo- 
cervical  trunk  (superior  intercostal  artery),  which  vessel  separates  it  from  the 
prolongation  of  the  portion  of  the  first  thoracic  nerve  which  passes  to  the  brachial 
plexus.  It  sometimes  fuses  with  the  inferior  cervical  ganglion,  and,  on  the  other 
hand,  sometimes  extends  to  the  upper  part  of  the  second  rib  to  fuse  with  the 
second  thoracic  ganglion.  The  result  of  the  latter  fusion  resembles  the  stellate 
ganglion  of  the  carnivora,  and  when  it  occurs,  is  sometimes  referred  to  as  the 
ganglion  stellatimn.  When  well  developed,  the  first  ganglion  sends  a  branch  to  the 
cardiac  plexus,  forming  the  fourth  cardiac  nerve  of  Valentin.  ^ 

The  second  thoracic  ganglion,  triangular  in  shape  and  almost  as  large  as  the 
preceding,  is  sometimes  placed  on  the  costo-vertebral  articulation,  and  is  some- 
times partly  concealed  by  the  first  rib. 

The  third  to  the  ninth  thoracic  ganglia  are  usually  placed  opposite  the  heads  of 
the  corresponding  ribs,  but  the  tenth  and  eleventh  may  lie  on  the  bodies  of  the 
vertebrae. 

The  fibres  passing  from  the  ganglia  form  two  groups  of  branches,  the  central 
and  the  peripheral. 

The  central  branches  are  the  grey  rami  communicantes,  which  pass  from  the 
ganglia  to  the  corresponding  spinal  nerves.  After  they  have  joined  with  the 
anterior  primary  divisions  of  the  nerves,  the  fibres  of  these  rami  divide  into  four 
groups: — (1)  Fibres  which  pass  medialward  along  the  roots  of  the  nerves  to  supply 
vessels  of  the  membranes  of  the  spinal  cord,  or  enter  a  meningeal  or  recurrent 
branch  for  the  same  purpose;  (2)  fibres  which  enter  the  spinal  ganglion  and 
terminate  there  (sensory  sympathetic  fibres) ;  (3)  fibres  which  pass  dorsalward 
into  the  posterior  primary  divisions  of  the  nerves;  (4)  fibres  which  pass  lateral- 
ward  in  the  anterior  primary  divisions  of  the  nerves.  The  last  two  groups  of 
fibres  are  distributed  to  the  muscle  of  the  blood-vessels  of  the  body-walls,  to  the 
skin-glands,  and  to  the  muscles  of  the  hairs  of  the  body. 

The  peripheral  branches  of  the  ganglia  form  two  series,  an  upper  and  a 
lower. 

Those  of  the  upper' series  pass  from  the  upper  four  or  five  ganglia  ventralward 
to  be  distributed  as  follows: — 

(1)  Pulmonary  branches  which  accompany  the  intercostal  arteries  toward  their  aortic 
origin  without  forming  plexuses  around  them,  and  pass  to  the  posterior  pulmonary  plexus 
(fig.  789). 

(2)  Aortic  branches,  some  of  which  arise  directly  from  the  gangha  and  some  from  the 
pulmonary  branches,  and  unite  with  branches  from  the  cardiac  plexus  and  from  the  splanchnic 
nerves  to  surround  the  aorta  as  the  thoracic  aortic  plexus  (fig.  789).  This  plexus  accompanies 
the  aorta  into  the  abdomen  and  there  joins  with  the  coehac  (solar)  plexus. 

(3)  (Esophageal  branches  join  with  the  oesophageal  plexus  of  the  vagus. 

(4)  Vertebral  branches,  some  of  which  pass  with  the  nutrient  arteries  into  the  bodies  of 
the  vertebra;  and  some  of  which  pass  to  the  median  line  and  there  anastomose  with  similar 
branches  from  the  opposite  side  (commissural  branches). 

The  peripheral  ganglionic  branches  forming  the  lower  series  consist  largely  of 
efferent  and  afferent  fibres  from  the  spinal  nerves,  which  pass  through  the  gangha 
and  reinforce  the  sympathetic  filaments  proper.  Thus  composed,  these  branches 
run  ventralward  and  medialward  on  the  sides  of  the  bodies  of  the  vertebrae  and 
unite  to  form  the  splanchnic  nerves  which  supply  the  abdominal  organs,  the 
afferent  fibres  serving  to  collect  sensory  impulses  in  this  domain  of  the  sym- 
pathetic. 

(1)  The  great  splanchnic  nerve  may  be  formed  by  branches  from  all  the  thoracic  ganglia 
from  the  fifth  to  the  tenth  inclusive,  or  it  may  receive  fibres  from  only  two  or  three  of  these 


THE  SYMPATHETIC  TRUNK  1039 

ganglia  (fig.  787).  It  is  usually  formed  by  branches  from  the  fifth  to  the  tenth.  The  superior 
branch,  usually  the  largest,  receives  smaller  inferior  branches  from  the  lower  ganglia  as  it  passes 
downward  on  the  sides  of  the  bodies  of  the  vertebrae  in  the  posterior  mediastinum.  The  nerve 
enters  the  abdominal  cavity  bypassing  through  the  crus  of  the  diaphragm,  and  joins  the  upper 
end  of  the  coeliac  (semilunar)  ganglion  of  the  coeliac  (solar)  plexus.  Near  the  disk  between  the 
eleventh  and  the  twelfth  thoracic  vertebra  there  is  formed  on  the  nerve  the  splanchnic  ganglion. 
Filaments  from  the  nerve  and  from  this  ganglion  pass  along  the  intercostal  arteries  to  the  aorta, 
oesophagus,  and  the  thoracic  duct,  and  some  fibres  from  the  right  side  pass  to  the  vena  azygos 
(major).  Sometimes  this  nerve  divides  into  two  cords,  giving  off  numerous  branches  which 
anastomose  with  each  other  and  with  the  lesser  splanchnic  nerve  to  form  a  plexus,  in  the  meshes 
of  which  are  found  some  small  ganglia. 

(2)  The  lesser  splanchnic  nerve  receives  fibres  from  the  ninth  and  tenth  gangha.  Its 
course  is  similar  to  that  of  the  great  splanchnic  nerve  (fig.  787),  but  on  a  more  dorsal  plane,  and 
it  terminates  in  the  cceliac  (solar)  and  renal  plexuses. 

(3)  The  least  splanchnic  nerve,  not  always  present,  arises  from  the  last  thoracic  ganghon 
or  sometimes  from  the  small  splanchnic  nerve.  It  passes  through  the  crus  of  the  diaphragm 
and  ends  in  the  renal  plexus. 

Construction  of  the  thoracic  portion  of  the  cord. — The  majority  of  the  visceral  efferent 
fibres  which  pass  from  the  central  nervous  system  enter  the  thoracic  portion  of  the  sympathetic 
trunk;  some  end  there  in  ramifications  around  the  cells  of  its  ganglia,  while  others  merely  pass 
through  on  their  way  to  more  distant  terminations.  With  regard  to  those  which  terminate 
in  the  gangha,  it  has  been  shown  that  in  the  dog  and  cat  many  end  in  the  ganglion  stellatum 
which  corresponds  with  the  last  cervical  and  the  upper  three  or  four  thoracic  ganglia  in  man. 
Among  these  are  the  fibres  conveying  secretory  impulses  to  the  sweat-glands  of  the  upper  hmb, 
which  emerge  from  the  spinal  cord  in  the  thoracic  nerves  from  the  sixth  to  the  ninth,  and,  in 
the  dog,  those  which  convey  and  transfer  vaso-constrictor  impulses  to  the  sympathetic  neurones 
supplying  the  pulmonary  blood-vessels.  These  visceral  efferent  fibres  leave  the  spinal  cord 
in  the  second  to  the  seventh  thoracic  nerves.  Other  fibres  which  terminate  around  the  thoracic 
sympathetic  ganglion-cells  in  the  dog  and  cat  are  the  vaso-constrictor  fibres  for  the  upper  limbs 
and  some  of  the  vaso-constrictor  fibres  for  the  lower  limbs. 

Of  the  fibres  which  traverse  the  thoracic  portion  of  the  sympathetic  trunk  to  gain  more 
distant  terminations,  some  ascend  to  the  cervical  region  (p.  1033),  others  descend  to  the  lumbar 
region,  and  many  pass  by  the  immediate  peripheral  branches  to  the  splanchnic  nerves. 

Among  those  which  descend  to  the  lumbar  region  are  pilo-motor  fibres,  vaso-motor  fibres, 
and  secretory  fibres  to  the  lower  limb,  some  vaso-constrictor  fibres  to  the  abdominal  blood- 
vessels, motor  fibres  to  the  circular,  and  inhibitory  fibres  to  the  longitudinal  muscle  of  the 
rectum.  The  latter  enter  the  sympathetic  trunk  by  the  lower  thoracic  nerves  and  pass  in  the 
lumbar  peripheral  branches  to  the  aortic  plexus,  and  terminate  around  the  cells  of  the  inferior 
mesenteric  ganglion. 

The  visceral  efferent  fibres  which  pass  through  the  thoracic  ganglia  to  the  splanchnic  nerves 
are  mainly  vaso-motor  fibres  to  the  abdominal  blood-vessels;  the  majority  of  them  probably 
terminate  around  the  cells  of  the  ganglia  in  the  coelio  (solar)  plexus,  but  those  for  the  renal  blood- 
vessels no  doubt  end  in  the  renal  ganglia.  In  addition  to  all  the  above-mentioned  fibres  there 
are  in  the  thoracic  part  of  the  sympathetic  trunk  afferent  fibres  of  both  sympathetic  and  cere- 
bro-spinal  type,  passing  toward  the  spinal  ganglia  and  the  latter,  greatly  predominating,  pass 
into  the  dorsal  roots  of  the  thoracic  spinal  nerves. 


THE  LUMBAR  PORTION  OF  THE  SYMPATHETIC  TRUNK 

The  lumbar  portion  of  each  trunk  lies  on  the  fronts  of  the  bodies  of  the  verte- 
brae along  the  anterior  border  of  the  psoas  muscle,  and  nearer  to  the  median  line 
than  the  thoracic  portion.  It  is  connected  with  the  thoracic  portion  of  the 
sympathetic  trunk  by  a  slender  intermediate  portion  of  the  trunk  that  may  pass 
through  the  diaphragm  or  dorsal  to  it  (fig.  787).  The  continuation  of  the 
lumbar  into  the  sacral  portion  is  also  slender,  and  descends  dorsal  to  the  common 
iliac  artery.  The  right  trunk  is  partly  covered  by  the  vena  cava  inferior  and  the 
left  by  the  aorta. 

The  ganglia,  which  are  small  and  oval,  vary  in  number  from  three  to  eight,  but 
are  usually  four.     Rarely  they  are  so  fused  as  to  form  one  continuous  ganglion. 

White  rami  communicantes  pass  to  the  ganglia  from  the  first  two  or  three 
lumbar  nerves  only.  This  portion  of  the  sympathetic  trunk  also  receives  visceral 
efferent  and  afferent  fibres  which  are  derived  from  the  white  rami  communicantes 
of  the  lower  thoracic  nerves  and  continue  downward  in  the  trunk. 

Branches. — As  in  the  thoracic  region,  the  branches  from  the  gangha  are  central  and  per- 
ipheral. The  central  are  grey  rami  communicantes.  There  may  be  two  branches  to  a  nerve 
or  one  ramus  may  divide  so  as  to  join  two  adjacent  spinal  nerves.  Sometimes  a  spinal  nerve 
may  receive  as  many  as  five  grey  rami  from  the  sympathetic  trunk. 

The  peripheral  branches  include; — (a)  Branches  passing  to  the  aorta  and  taking  part  in 
the  formation  of  the  aortic  plexus;  (6)  branches  which  descend  in  front  of  the  common  ihac 
artery  to  the  hypogastric  plexus;  and  (c)  branches  to  the  vertebrse  and  ligaments. 


1040  THE  NERVOUS  SYSTEM 

THE  SACRAL  PORTION  OF  THE  SYMPATHETIC  TRUNK 

The  sacral  part  of  each  truak  passes  downward  in  front  of  the  sacrum,  imme- 
diately lateral  to  the  medial  borders  of  the  anterior  sacral  foramina.  It  is 
continuous  above  with  the  lumbar  portion  of  the  trunk,  and  below  it  anastomoses 
freely  in  front  of  the  coccyx  with  the  trunk  of  the  other  side  to  form  a  plexus 
in  the  terminus  of  which  is  the  coccygeal  ganglion  {ganglion  coccygeum  impar) 
(fig.  787).  Like  the  cervical  and  lower  lumbar  portions  of  the  sympathetic 
trunk,  the  sacral  part  receives  no  white  rami  communicantes  from  the  spinal 
nerves. 

The  sacral  ganglia  are  small  in  size,  and  usually  four  in  number.  The  varia- 
tion both  in  size  and  number  is  more  marked  in  this  portion  of  the  trunk  than  in 
the  two  parts  above. 

Branches. — The  branches  of  the  sacral  gangha  include: — 

(1)  Grey  rami  communicantes  to  the  sacral  nerves. 

(2)  Branches  to  the  front  of  the  sacrum  which  anastomose  with  their  fellows  of  the  opposite 
side  (commissural  branches). 

(3)  Branches  which  enter  into  the  formation  of  the  plexus  on  the  middle  sacral  artery. 

(4)  Branches  which  join  the  pelvic  plexuses. 

(5)  Branches  given  off  by  the  ganglion  coccygeum  impar  to  the  coccyx  and  its  ligaments 
and  to  the  glomus  coccygeum  (coccygeal  gland). 

Construction  of  the  lumbar  and  sacral  portions  of  the  gangliated  trunk. — The  ganglia 
of  both  these  portions  of  the  trunk  are  very  variable  in  shape,  size,  position,  and  number.  There 
are  usually  four  gangha  belonging  to  each  portion,  but  sometimes  as  many  as  eight  may  be 
distinguished  in  the  lumbar  and  at  other  times  there  may  be  as  many  as  six  in  the  sacral  portion. 
In  the  majority  of  cases,  especially  in  the  sacral  region,  these  masses  of  cells  are  so  fused  that 
their  number  is  less  than  the  number  of  the  spinal  nerves  with  which  they  are  associated.  As 
noted  above,  only  the  first  two  or  three  lumbar  spinal  nerves  send  white  rami  which  enter  these 
ganglia  directly  as  such.  However,  visceral  efferent  fibres  descend  this  entire  stretch  of  the 
trunk,  through  both  the  lumbar  and  sacral  portions,  from  the  white  rami  of  the  lower  thoracic 
and  the  upper  lumbar  nerves  above.  These  fibres  either  terminate  in  the  various  gangha  or 
pass  uninterrupted  to  the  more  distant  sympathetic  cell-bodies  which  are  concerned  in  impulses 
that  are  vaso-motor  to  the  genital  organs,  motor  for  the  uterus,  the  vas  deferens,  and  the  mus- 
cular coats  (circular  coat  especially)  of  the  bladder.  Also,  some  of  them  convey  secretory,  pilo- 
motor, and  vaso-motor  impulses  for  the  glands,  skin,  and  vessels  of  the  lower  extremity  in 
addition  to  the  similar  impulses  conveyed  in  the  peripheral  branches  from  the  lower  part  of 
the  thoracic  portion  of  the  sympathetic  trunk.  The  motor  impulses  for  the  uterus  or  vas 
deferens  and  for  the  bladder  pass,  in  most  part  probably,  by  way  of  the  peripheral  branches 
from  the  lumbar  portion  of  the  cord,  through  the  aortic  plexus  to  the  inferior  mesenteric  gang- 
lion; others,  the  vaso-motor  impulses  to  the  genital  organs  especially,  pass  by  way  of  the  sacral 
ganglia  and  the  peripheral  branches  from  them  to  the  hypogastric  or  pelvic  plexus  and  the  appro- 
priate subplexuses  of  this  region.  Of  the  vaso-motor  fibres  for  the  penis,  some  of  the  constrictor 
fibres  pass  down  the  sacral  portion  of  the  sympathetic  trunk  and  terminate  about  the  cells  of 
the  sacral  ganglia,  and  these  cells  send  out  sympathetic  fibres  which  join  and  course  in  the  pudic 
nerve  (n.  pudendus). 

All  of  both  the  lumbar  and  sacral  spinal  nerves  receive  grey  rami  from  the  gangliated  trunk. 
These,  just  as  those  from  the  other  portions  of  the  trunk,  consist  of — (1)  vaso-motor  fibres  to 
vessels  of  the  meninges  and  the  vertebral  canal;  (2)  sympathetic  fibres  which  join  the  divisions 
of  the  spinal  nerves  and  course  in  them  to  their  distribution,  and  (3)  afferent  sympathetic 
fibres  terminating  in  the  spinal  ganglia. 

In  addition  to  the  visceral  efferent  fibres,  the  branches  of  the  lumbo-sacral  portion  of  the 
sympathetic  trunk  carry  cerebro-spinal  fibres  of  general  sensibility — sensory  fibres  arising  in 
the  spinal  gangha  of  this  and  the  lower  thoracic  region. 

There  are  no  white  rami  proper  passing  from  the  sacral  spinal  nerves  to  course  or  terminate 
in  the  sympathetic  trunk.  Visceral  efferent  fibres  are  given  off  by  these  nerves  in  abundance, 
but,  instead  of  entering  the  trunk  and  its  ganglia,  they  form  bundles  which  pass  over  the  trunk 
and  directly  into  its  peripheral  branches  and  to  the  more  distant  ganglia.  The  bundles  passing 
from  the  second,  third,  and  fourth  sacral  nerves  are  large  and  especially  definite.  While 
homologous  to  white  rami,  such  bundles  are  better  known  as  the  visceral  branches  of  the  sacral 
nerves  or  the  plevic  splanchnics.  They  contain  some  spinal  sensory  fibres,  but  consist  for  the 
most  part  of  visceral  efferent,  conveying  impulses,  vaso-motor  (vaso-dilator,  chiefly)  to  the  gen- 
ital organs,  both  motor  and  inhibitory  for  the  rectum,  uterus,  and  bladder  (longitudinal  coat 
especially),  and  secretory  for  the  prostate  gland.  These  fibres  contribute  to  the  hypogastric 
plexus  and  are  interrupted  in  the  small  gangUa  of  its  sub-plexuses,  named  according  to  the 
various  urino-genital  organs  concerned. 

THE  GREAT  PREVERTEBRAL  PLEXUSES 

The  great  prevertebral  plexuses,  in  the  body  cavities,  are  three  in  number — 
the  cardiac,  the  coeliac  (solar  or  epigastric),  and  the  hypogastric  or  pelvic.  The 
cardiac  plexus  lies  behind  and  below  the  arch  of  the  aorta,  and  the  coeliac  and 


THE  CARDIAC  PLEXUS  1041 

hypogastric  plexuses  are  situated  in  front  of  the  lumbar  vertebrae.  Each  plexus 
receives  not  only  sympathetic  fibres  which  have  passed  from  or  through  the 
ganglia  of  the  sympathetic  trunks  of  either  side,  but  also  both  afferent  and  efferent 
cranio-spinal  nerve-fibres  derived  directly  from  the  cranio-spinal  nerves.  In 
addition  the  cardiac  and  coeliac  plexuses  receive  both  efferent  visceral  and  cranio- 
spinal sensory  or  afferent  visceral  fibres  from  both  vagus  nerves.  It  should  be 
clearly  understood  that  the  branches  which  run  from  the  sympathetic  gangliated 
trunks  to  the  prevertebral  plexuses  contain  meduUated  fibres  which  are  passing, 
like  the  fibres  from  the  sacral  nei'ves,  directly  from  the  spinal  cord  to  terminate 
about  the  cells  of  the  plexuses. 

1.  The  Cardiac  Plexus 

The  cardiac  plexus  is  formed  by  the  cardiac  branches  from  both  vagus  nerves 
and  from  both  sympathetic  trunks.  It  lies  beneath  and  dorsal  to  the  arch  of  the 
aorta,  in  front  of  the  bifurcation  of  the  trachea,  and  extends  a  short  distance 
upward  on  the  sides  of  the  trachea.  It  is  composed  of  a  superficial  and  a  deep 
part  (fig.  789). 

The  superficial  part  of  the  cardiac  plexus  is  much  smaller  than  the  deep  part, 
and  lies  beneath  the  arch  of  the  aorta  in  front  of  the  right  pulmonary  artery.  It 
is  formed  chiefiy  by  the  cardiac  branches  of  the  left  vagus  and  by  the  left  superior 
cardiac  nerve,  but  sometimes  receives  filaments  from  the  deep  cardiac  plexus. 
The  cardiac  ganglion  (ganglion  of  Wrisberg,)  usually  found  connected  with  this 
plexus,  lies  on  the  right  side  of  the  ligamentum  arteriosum. 

Branches. — From  this  plexus  some  branches  pass  to  the  left  half  of  the  deep  cardiac  plexus, 
and  others  accompany  the  left  pulmonary  artery  to  the  left  anterior  pulmonary  plexus.  It  also 
sends  branches  to  the  right  anterior  coronary  plexus.  , 

The  deep  portion  of  the  cardiac  plexus  lies  dorsal  to  the  arch  of  the  aorta  at  the 
sides  of  the  lower  part  of  the  trachea  and  in  front  of  its  bifurcation.  It  consists  of 
two  lateral  parts,  more  or  less  distinct,  connected  by  numerous  branches,  which 
pass  around  the  lower  part  of  the  trachea.  It  is  formed  by  the  superior,  middle, 
and  inferior  cervical  cardiac  branches  from  the  right  sympathetic  trunk,  the  mid- 
dle and  inferior  cervical  cardiac  branches  from  the  left  trunk,  and  all  the  cervical 
and  thoracic  cardiac  branches  of  the  vagus  except  the  superior  cervical  cardiac 
branch  of  the  left  vagus.  It  also  receives  branches  from  the  superficial  cardiac 
plexus. 

The  left  part  of  the  deep  cardiac  plexus  gives  branches  to  the  left  atrium  (auricle)  of  the  heart, 
to  the  left  anterior  pulmonary  plexus,  to  the  left  coronary  plexus,  and  sometimes  to  the  super- 
ficial part  of  the  cardiac  plexus. 

The  right  part  of  the  deep  cardiac  plexus  gives  branches  to  the  right  atrium,  to  the  right  an- 
terior pulmonary  plexus,  and  to  the  right  and  the  left  coronary  plexuses  (fig.  789).  The  branches 
to  the  left  coronary  plexus  pass  behind  the  pulmonary  artery.  Some  of  those  to  the  right  coro- 
nary plexus  pass  anterior  and  some  posterior  to  the  right  pulmonary  artery. 

The  coronary  plexuses  are  formed  by  branches  given  off  by  the  cardiac  plexus. 
They  accompany  the  coronary  arteries  and  are  right  and  left. 

The  right  {anterior)  coronary  -plexus  receives  filaments  from  the  superficial  part 
of  the  cardiac  plexus,  but  is  formed  chiefiy  by  filaments  from  the  right  portion  of 
the  deep  cardiac  plexus  (fig.  789).  Its  distribution  to  the  heart  follows  that  of 
the  right  coronary  artery. 

The  left  {posterior)  coronary  plexus  is  larger  than  the  right  plexus,  and  is  formed 
for  the  most  part  by  filaments  from  the  left  portion  of  the  deep  cardiac  plexus,  but 
it  receives  some  filaments  from  the  right  portion  of  the  deep  cardiac  plexus 
(fig.  789).     Its  distribution  to  the  heart  follows  that  of  the  left  coronary  artery. 

The  cardiac  plexus  and  the  network  of  nervous  structures  in  the  walls  of  the  atria  are  the 
remains  of  the  primitive  plexuses  found  in  the  embryo,  which  are  called  the  bulbarj  the  inter- 
mediate, and  the  atrial  plexuses,  terms  which  sufficiently  indicate  their  relative  positions.  The 
bulbar  plexus  gives  off  the  coronary  nerves  and  is  transformed  into  the  superficial  part  of  the 
deep  cardiac  plexus;  the  remainder  of  the  deep  cardiac  plexus  is  formed  by  the  intermediate 
plexus,  and  the  atrial  plexus  becomes  the  network  of  the  atrium. 

The  fibres  which  pass  to  the  cardiac  plexus  are  meduUated  and  non-meduUated;  the  former 


1042 


THE  NERVOUS  SYSTEM 


Fig.  789.  Caediac,  Pulmonary,  and  Coronary  Plexuses.     (Schematic.) 
(Modified  from  Cunningham.) 


Superior  cardiac  nerve- 


Middle  cardiac  nerve' 


Cervical  cardiac  branches 
of  vagus 


Inferior  cardiac  nerve- 
Recurrent  nerve^ 


Thoracic  cardiac  branches, 
of  vagus 


Right  coronary  plexus—  — 


Middle  cervical 

ganglion 


_  Inferior  cervical 
ganglion 


Deep  cardiac  plexus 
Superficial  cardiac  plexus 


NLeft  posterior  pulmonary 
plexus 


-  Left  coronary  pie: 


THE  C (ELI AC  PLEXUS  1043 

are  the  so-called  inhibitory,  the  latter  motor.  The  inhibitory  impulses  leave  the  central 
nervous  system  by  the  spinal  accessory  and  vagus  nerves.  The  motor  iibres  leave  the  spinal 
cord  by  the  ventral  roots  and  white  rami  communicantes  of  the  thoracic  nerves  and  terminate 
about  the  cells  of  the  intervening  sympathetic  ganglia.  From  the  cells  of  these  gangha  arise 
the  non-meduUated  (grey)  fibres  of  the  plexus.  These  fibres  terminate  directly  upon  the  fibres 
of  cardiac  muscle  or  about  the  cells  of  the  minute  intrinsic  cardiac  ganglia  which  in  their  turn 
give  axones  to  the  muscle. 

2.  The  Pulmonary  Plexuses 

The  pulmonary  plexuses  are  a  continuation  of  the  cardiac  plexuses.  The 
two  are  so  intimately  joined  that  it  is  difficult  to  distinguish  them  as  separate 
plexuses.  The  pulmonary  are  formed  by  fibres  from  both  the  vagus  and  sympa- 
thetic nerves.  The  anterior  and  posterior  pulmonary  branches  of  the  vagus 
unite,  dorsal  to  the  bifurcation  of  the  trachea,  with  fibres  from  the  second,  third 
and  fourth  ganglia  of  the  thoracic  portion  of  the  sympathetic  trunk  to  form  the 
anterior  and  posterior  pulmonary  plexuses  that  lie  ventral  and  dorsal  to  the 
bifurcation  of  the  trachea.  Here  the  pulmonary  plexuses  of  both  sides  connect 
with  each  other  freely.  Leaving  the  trachea,  the  plexuses  pass  into  the  lungs 
along  the  pulmonary  arteries  (figs.  744,  789) .  The  parts  of  the  plexus  of  each  side 
are  named  according  to  their  position  anterior  or  posterior  to  the  right  and  left 
pulmonary  arteries;  thus,  there  is  a  right  anterior  and  a  right  posterior,  a  left 
anterior  and  a  left  posterior  pulmonary  plexus. 

3.  The  C  celiac  Plexus 

The  coeliac  (solar  or  epigastric)  plexus  is  the  largest  of  the  prevertebral 
plexuses.  It  is  unpaired,  and  is  continuous  above  with  the  aortic  plexus  of  the 
thorax  and  below  with  the  abdominal  aortic  and  superior  mesenteric  plexuses. 
It  lies  in  the  epigastric  region  of  the  abdomen  behind  the  bursa  omentalis  (lesser 
sac  of  the  peritoneum)  and  the  pancreas,  upon  the  crura  of  the  diaphragm  and  over 
the  abdominal  aorta,  and  around  the  origin  of  the  coeliac  and  the  superior  mesen- 
teric arteries.  It  occupies  the  interval  between  the  suprarenal  bodies  and  extends 
downward  as  far  as  the  renal  arteries.  It  is  formed  by  the  great  and  the  lesser 
splanchnic  nerves  of  both  sides,  by  coeliac  branches  of  the  right  vagus,  and  by 
filaments  from  the  upper  lumbar  ganglia  of  the  sympathetic  trunlc.  It  sometimes 
receives  coeliac  branches  from  the  left  vagus.  It  contains  two  large  ganglia,  the 
right  and  left  coeliac  (semilunar)  ganglia  (fig.  790). 

The  coeliac  (semilunar)  ganglia  are  two  large,  flat,  irregularly  shaped  masses, 
separable  into  a  varying  number  of  ganglia.  These  two  masses,  or  rather  the 
smaller  ganglia  which  compose  them,  are  associated  by  a  varying  number  of  com- 
municating branches.  Each  mass,  right  and  left,  lies  upon  the  corresponding  crus 
of  the  diaphragm,  at  the  medial  border  of  the  corresponding  suprarenal  body, 
being  sometimes  overlapped  by  this  body.  The  right  mass  lies  behind  the  inferior 
vena  cava.  Each  coeliac  ganglion  receives  at  its  upper  border  the  greater 
splanchnic  nerve,  and,  near  its  lower  border,  lying  over  the  origin  of  the  renal 
artery,  is  a  more  or  less  detached  part,  known  as  the  aortico-renal  ganglion. 
This  ganglion  receives  the  lesser  splanchnic  nerve  and  may  seemingly  give  origin 
to  the  greater  part  of  the  renal  plexus.  Another  part  of  the  cceliac  ganglion,  often 
found  dorsal  to  the  origin  of  the  superior  mesenteric  artery,  is  known  as  the 
superior  mesenteric  ganglion  (fig.  790) . 

From  the  coeliac  plexus  and  its  ganglia  subordinate  plexuses  are  continued 
upon  the  aorta  and  its  branches.  These  comprise  both  paired  and  unpaired 
plexuses.  The  paired  plexuses  are  the  phrenic,  suprarenal  and  renal,  the  sper- 
matic in  the  male,  and,  in  the  female,  the  ovarian  plexuses.  The  unpaired  plex- 
uses are  the  aortic,  hepatic,  splenic,  superior  gastric,  inferior  gastric,  superior  mesen- 
teric, and  inferior  mesenteric. 

That  part  of  the  coeliac  plexus  surrounding  the  coeliac  artery  was  formerly 
described  as  the  coeliac  plexus.  It  is  better  considered  as  an  unnamed  part  of  the 
larger  coeliac  (solar)  plexus.  This  part  of  the  plexus  receives  fibres  from  both 
vagus  nerves,  and  gives  filaments  that  form  plexuses  around  the  branches  of  the 
cceliac  artery  and  their  ramifications. 


1044 


THE  NERVOUS  SYSTEM 


The  paired  subordinate  plexuses  of  the  coeliac. — (1)  The  phrenic  (diaphragmatic)  plexuses 

consist  of  fibres  from  the  upper  part  of  the  cceliac  ganglia,  which  follow  the  inferior  phrenic 
arteries  and  their  branches  on  the  under  surface  of  the  diaphragm  (fig.  790).  Filaments  are 
given  off  by  the  roots  of  the  plexuses  to  the  suprarenal  bodies,  and  others  unite  with  the  ter- 
minal branches  of  the  phrenic  nerves.  The  point  of  junction  with  the  right  phrenic  nerve  is 
marked  by  the  phrenic  ganglion,  from  which  branches  are  distributed  to  the  inferior  vena  cava, 
to  the  right  suprarenal  body,  and  to  the  hepatic  plexus. 

(2)   The  suprarenal  plexuses  are  comparatively  large  plexuses,  formed  mainly  by  branches 
from  the  cceliac  (semilunar)  ganglia.     However,  fibres  come  to  them  from  the  coeliac  plexus 

Fig,  790. — Abdominal  Plexuses  of  the  Sympathetic.     (After  Toldt,   "Atlas  of  Human 
Anatomy,"  Rebman,  London  and  New  York.) 
Coeliac  plexus  Left  vagus  nerve 


Phrenic  pie 


..-,<i^r^* 


Right  vagus  nerve 


Superior  gastric  plexus 

X  Phrenic  plexus 

'  Suprarenal  plexus 

\ 

_3~Splenic  plexus 


along  the  suprarenal  arteries,  from  the  phrenic  plexus  along  the  inferior  phrenic  arteries,  and 
from  the  renal  plexus  along  the  inferior  suprarenal  arteries.  They  are  distributed  to  the- 
substance  of  the  suprarenal  bodies.  Cell-bodies  of  sympathetic  neurones  are  enclosed  within 
the  suprarenal  bodies  forming  intrinsic  ganglia.  The  medulla  of  the  suprarenal  is  of  ecto- 
dermal origin  and  considered  as  derived  from  undeveloped  components  of  the  sympathetic 
nervous  system. 

(3)  The  renal  plexuses  receive  fibres  from  the  lower  part  of  the  coeliac  ganglia  and  from 
the  coeliac  and  aortic  plexuses.  They  also  receive  filaments  from  the  least  splanchnic  nerves, 
when  these  nerves  are  present,  and  sometimes  filaments  from  the  small  splanchnic  nerves  and 
from  the  first  lumbar  ganghon  of  the  sympathetic  trunk.  These  plexuses  pass  along  the  renal 
arteries  into  the  substance  of  the  kidneys.  Most  of  the  fibres  of  each  renal  plexus  are  grey  fibres, 
and  as  they  pass  to  the  kidneys  small  renal  ganglia  are  present  upon  them.  Both  renal 
plexuses  give  branches  to  the  corresponding  spermatic  plexuses  and  to  the  ureter,  and  the 
right  renal  plexus  gives  filaments  also  to  the  inferior  vena  cava. 


THE  HYPOGASTRIC  PLEXUS  1045 

(4a)  The  spermatic  plexuses  (fig.  790)  are  formed  by  fibres  from  the  renal  and  aortic 
plexuses.  They  accompany  the  spermatic  arteries  and  are  joined  at  the  abdominal  inguinal 
(internal  abdominal)  ring  by  fibres  that  have  passed  along  the  vas  deferens  from  the  pelvic 
plexuses.     Their  terminal  filaments  are  distributed  to  the  testis  and  the  epididymis. 

(4b)  The  ovarian  plexuses  are  formed  in  the  female  like  the  spermatic  plexuses  in  the 
male.  They  accompany  the  ovarian  arteries  and,  in  the  broad  ligament,  receive  fibres  from 
the  utero-vaginal  plexus.  They  supply  the  ovaries,  the  broad  ligaments,  and  the  Fallopian 
tubes,  and  send  some  fibres  to  the  fundus  of  the  uterus,  where  they  become  continuous  with 
the  utero-vaginal  plexus. 

The  unpaired  subordinate  plexuses: — (I)  The  abdominal  aortic  plexus  is  formed  by 
two  strands  of  fibres  which  descend  along  the  sides  of  the  aorta  and  communicate  with  each 
other  across  its  ventral  aspect.  It  is  connected  above  with  the  renal  plexuses,  and  it  receives 
peripheral  branches  from  some  of  the  lumbar  ganglia  of  the  sympathetic  trunk  on  each  side.  It 
often  contains  a  number  of  ganglia,  which  are  situated  at  the  points  where  the  peripheral 
branches  join  the  plexus,  and  it  terminates  below,  chiefly  by  anastomoses  with  the  hypogastric 
plexus  (figs.  790  and  791).  Besides  giving  filaments  to  the  inferior  vena  cava,  it  also  gives 
fibres  that  form  plexuses  along  each  of  the  branches  of  the  aorta.  The  fibres  tnat  pass  from 
the  lower  end  of  the  aortic  plexus  upon  the  common  ihac  artery  form  the  iliac  plexus,  which 
is  continued  along  the  femoral  artery  as  the  femoral  plexus,  and  still  further  along  the  popliteal 
artery  as  the  popliteal  plexus. 

(2)  The  superior  gastric  (coronary)  plexus,  receiving  filaments  from  the  coeliac  plexus, 
accompanies  the  left  gastric  (coronary)  artery  along  the  lesser  curvature  of  the  stomach. 
Its  filaments  anastomose  with  filaments  of  the  vagus  nerves  and  with  the  plexus  that  accom- 
panies the  right  gastric  (pyloric)  artery  (fig.  790),  and  it  gives  fibres  to  the  walls  of  the  stomach 
which  terminate  within  the  walls,  about  the  cell  bodies  of  the  delicate  gangliated  plexus  myen- 
tericus  and  plexus  submucosus  (plexuses  of  Auerbach  and  Meissner).  The  axones  of  these 
supply'  the  smooth  muscle  of  the  stomach  walls  and  its  vessels. 

(.3)  The  inferior  gastric  plexus  receives  from  the  splenic  plexus  filaments  that  accompany 
the  left  gastro-epiploic  artery.  It  gives  filaments  to  the  walls  of  the  stomach,  which  terminate 
as  in  the  superior  gastric  plexus,  and  it  receives  filaments  from  the  vagus  nerves  and  from 
the  plexus  that  accompanies  the  right  gastro-epiploic  artery. 

(4)  The  hepatic  plexus  receives  filaments  from  the  cceUac  plexus  and  from  the  left  vagus. 
It  accompanies  the  hepatic  artery  and  gives  fibres  that  form  plexuses  on  the  branches  of  the 
artery  and  on  their  ramifications  within  the  liver  and  gives  secretory  fibres  to  the  liver  cells. 
It  also  gives  filaments  to  the  portal  vein  (fig.  790). 

The  splenic  or  lienal  plexus  is  formed  by  filaments  from  the  coeliac  plexus,  the  left  cceliac 
(semilunar)  ganglion,  and  from  the  right  vagus.  It  accompanies  the  splenic  artery  and  gives 
filaments  which  form  plexuses  on  the  branches  of  this  artery,  and  which  pass  with  the  branches 
to  supply  fibres  to  the  stomach  and  the  pancreas  (fig.  790). 

(5)  The  superior  mesenteric  plexus  is  formed  chiefly  by  filaments  from  the  lower  part 
of  the  coeliac  plexus,  but  it  also  receives  fibres  from  the  right  vagus  and  fibres  direct  from  the 
coeliac  (semilunar)  gangUa.  At  the  origin  of  this  plexus,  dorsal  to  the  superior  mesenteric 
artery,  lies  the  superior  mesenteric  ganglion  (fig.  790).  The  filaments  of  the  plexus,  which  are 
white  and  firm,  accompany  the  superior  mesenteric  artery  and,  following  its  branches  and  their 
ramifications,  are  distributed  to  the  walls  of  the  small  intestine,  the  caecum,  and  the  ascending 
and  transverse  colon.  From  the  secondary  plexuses  that  accompany  the  branches  of  the  artery 
fibres  pass  to  form  still  other  plexuses  that  lie  near  the  wall  of  the  intestine,  between  the  branches 
of  the  artery  and  between  the  layers  of  the  mesentery.  Filaments  pass  with  the  branches  of 
the  arteries  and  from  plexuses  between  them  into  the  intestinal  wall,  and  there  form  between 
the  longitudinal  and  circular  muscle  layers  of  the  intestine  the  fine  ganghated  plexus  myen- 
tericus  (plexus  of  Auerbach),  and  filaments  from  this  plexus  form  in  the  submucosa  the  deUcate 
plexus  submucosus  or  plexus  of  Meissner.  From  these  latter  plexuses  fibres  arise  which  ter- 
minate upon  the  gland  cells  and  smooth  muscle  fibres  of  the  intestinal  wall  and  its  vessels. 
The  white  appearance  of  the  filaments  of  the  superior  mesenteric  plexus  is  due  to  the  large 
number  of  cranio-spinal  sensory  and  visceral  motor  fibres  (vagus  especially)  in  it. 

(6)  The  inferior  mesenteric  plexus  is  derived  chiefly  from  the  left  side  of  the  aortic  plexus. 
It  descends  upon  the  inferior  mesenteric  artery  and  gives  off  filaments  which  accompany  the 
branches  of  the  artery  and  are  distributed  to  the  descendiog  colon  and  to  the  iho-pelvic  colon 
(figs.  790  and  791).  The  filaments  which  accompany  the  left  colic  brunch  of  the  inferior  mesen- 
teric artery  anastomose  with  the  filaments  of  the  superior  mesenteric  plexus  which  accompany 
the  middle  coHc  artery.  The  filaments  which  accompany  the  superior  hasmorrhoidal  artery 
form  the  superior  hsemorrhoidal  plexus.  This  plexus  gives  off  the  superior  hcemorrhoidal 
nerves  (fig.  791)  which  supply  the  upper  part  of  the  rectum  and  anastomose  with  the  middle 
hcemorrhoidal  plexus. 

4.  The  Hypogastric  Plexus 

The  hypogastric  plexus  Ues  partly  in  the  abdominal  cavity  and  partly  in  the 
pelvic  cavity.  It  is  formed  chiefly  by  filaments  continued  downward  from  the 
aortic  plexus,  and  by  the  pelvic  splanchnics  and  peripheral  branches  from  the 
lumbo-sacral  nerves  and  sympathetic  trunk  (fig.  784).  The  abdominal  part  of 
this  plexus  consists  of  plexiform  bundles  of  fibres  descending  between  the  common 
iliac  arteries  and  interlacing  in  front  of  the  fifth  lumbar  vertebra  to  form  a  broad, 
flattened,  plexiform  mass.  In  its  extent  it  receives  branches  from  the  lumbar 
ganglia  of  the  sympathetic  trunk.     This  plexiform  mass  then  divides  into  two 


1046 


THE  NERVOUS  SYSTEM 


parts,  right  and  left,  which  descend  into  the  pelvic  cavity  and  which,  by  English 
authors,  are  frequently  designated  as  the  pelvic  plexuses. 

The  pelvic  parts  of  the  hypogastric  plexus  (pelvic  plexuses)  lie  at  the  sides  of  the 
rectum  in  the  male,  and  at  the  sides  of  the  rectum  and  the  vagina  in  the  female. 
They  receive  peripheral  branches  from  the  sacral  ganglia  of  the  sympathetic  trunk 
and  visceral  efferent  fibres  by  way  of  the  pelvic  splanchnics  from  the  second  and 

Fig.  791. — The  Hypogastric  and  Sub-plexuses  of  the  Pelvic  Cavity.     (After  Spalteholz.) 

Abdominal  aortic  plexus -^'^'^^"^  ^      ^      Sympathetic  ganghated  trunk 

b-\y  J,-'  ^"^~x.-'     Lumbar  ganglion 


—  Iliac  plexus 

*-J-    Transverse  process  of  fourth 
lumbar  vertebra 

Hypogastric  plexus 

Anterior  prii 
"     fifth  lumbi 

Inferior  mesenteric  plexus 


1^\  \  ^^__Lef  t  branch  of  the 

\  ^  K»»  ""*">      X"*    hypogastric  plexus 

*^       *»t,^  V — Sympathetic  trunk 

'^"■f^-^^X        Superior 
~      *'^^^     -^K--^ —     h£emorrhoidal 


Sacral 
plexus 
Visceral  branches  of 
pudendal  plexus 

-  Middle  hsEmorrhoidal  plexus 
"-  Pudic  nerve 
"Ureter 
Vesicula  seminalis 

Prostatic  plexus 
Rectum 
Levator  am 

Cavernous  plexus  of  penis 
Great  cavernous  nerve 

third  or  third  and  fourth  sacral  spinal  nerves.  Each  pelvic  part  of  the  plexus 
accompanies  the  corresponding  hypogastric  (internal  ihac)  artery,  and  gives  off 
secondary  plexuses  that  continue  on  the  branches  of  the  artery  to  the  pelvic 
viscera.  Of  these  secondary  plexuses,  the  middle  hsemorrhoidal  and  the  vesical 
plexus  are  common  to  both  sexes  and  are  paired. 

The  middle  hsemorrhoidal  plexus  passes  on  each  side  along  the  middle  hsemorrhoidal  artery 
to  the  rectum,  where  it  receives  the  superior  hsemorrhoidal  nerves  and  sends  filaments  into  the 
wall  of  the  rectum  (fig.  791). 


REFERENCES  FOR  NERVOUS  SYSTEM  1047 

The  vesical  plexus  receives  some  branches  from  the  pelvic  parts  of  the  hypogastric  plexus, 
but  is  largely  reinforced  by  way  of  the  pelvic  splanchnios,  from  the  third  and  fourth  sacral 
nerves.  Each  part  passes  along  the  corresponding  vesical  arteries  to  the  bladder,  and  gives 
off  two  sets  of  branches,  namely,  the  superior  vesical  nerves  (fig.  791),  which  supply  the  upper 
part  of  the  bladder-waU  and  send  some  branches  to  the  ureter,  and  the  inferior  vesical  nerves, 
which  supply  the  lower  part  of  the  bladder  and,  in  the  male,  give  secondary  deferential  plexuses 
to  the  vas  deferens.  These  plexuses  surround  the  vasa  deferentia  and  the  vesiculse  seminales 
and  anastomose  with  the  spermatic  plexuses. 

The  prostatic  plexus,  found  only  in  the  male,  is  formed  in  two  parts  by  nerves  of  con- 
siderable size,  and  lies  chiefly  on  the  sides  of  the  prostate  gland  between  it  and  the  levator  ani 
(fig.  791).  Each  of  the.se  parts  supplies  the  gland  and  the  prostatic  part  of  the  urethra^  and 
sends  offsets  to  the  neck  of  the  bladder  and  the  vesioute  seminales.  This  plexus  is  contmued 
forward  on  either  side  to  form  the  cavernous  plexus  of  the  penis  (fig.  791),  which  anastomoses 
with  branches  of  the  dorsal  nerve  of  the  penis,  gives  off  branches  to  the  membranous  part  of 
the  urethra,  and  also  gives  origin  to  two  sets  of  nerves,  namely,  the  large  and  the  small  cavernous 
nerves  of  the  penis. 

The  large  cavernous  nerve,  one  on  each  side,  runs  forward  to  the  middle  of  the  dorsum  of 
the  penis,  where  it  anastomoses  with  the  dorsal  nerve  of  the  penis  on  the  corresponding  side, 
and  ends  in  twigs  which  are  distributed  chiefly  to  the  walls  of  the  sinuses  of  the  corpus  caver- 
nosum  penis,  but  some  of  the  terminal  filaments  supply  the  corpus  cavernosum  urethrte  (corpus 
spongiosum)  (fig.  791). 

The  small  cavernous  nerves  are  small  filaments  which  pierce  the  uro-genital  trigone  (tri- 
angular ligament)  and  the  compressor  urethra;,  and  enter  the  posterior  part  of  the  corpus 
cavernosum. 

The  utero-vaginal  plexus,  found  in  the  female,  is  formed  in  its  upper  part  on  each  side 
largely  by  fibres  clerived  from  the  pelvic  part  of  the  hypogastric  plexus,  but  it  receives  some 
fibres  from  the  pelvic  splanchnics  of  the  third  and  fourth  sacral  nerves.  The  nerves  from  this 
part  of  the  plexus  accompany  the  uterine  arteries  as  they  pass  between  the  layers  of  the  broad 
ligament.  Some  accompany  each  uterine  artery  and  its  branches  to  their  termination,  but  a 
considerable  number  of  fibres  leave  the  artery  and  pass  into  the  body  of  the  uterus  to  supply 
its  lower  part  and  cervix.  Between  the  layers  of  the  broad  ligament  this  plexus  anastomoses 
with  the  ovarian  plexus  and  sends  some  filaments  to  the  uterine  tube  (Fallopian  tube).  The 
lower  part  of  the  plexus  ulero-vaginalis  receives  some  fibres  on  each  side  from  the  pelvic  part  of 
the  hypogastric  plexus,  but  it  is  formed  chiefly  by  efferent  visceral  fibres  from  the  second,  third, 
and  fourth  sacral  nerves.  These  fibres  terminate  in  contact  with  intrinsic  cell-bodies  whose 
axones  supply  the  wall  and  mucous  membrane  of  the  vagina  and  urethra.  From  the  plexus  on 
the  anterior  surface  of  the  vagina  fibres  pass  to  form  the  cavernous  plexus  of  the  clitoris,  which 
gives  off  the  great  and  lesser  cavernous  nerves  of  the  clitoris  for  the  supply  of  the  clitoris.  The 
utero-vaginal  plexus  of  the  female  corresponds  to  the  prostatic  plexus  of  the  male. 

References  for  the  Nervous  System.  A.  General.  Barker,  Nervous 
System,  1899;  Edinger,  Vorlesungen,  1908;  Johnston,  Nervous  System,  1906; 
(phylogeny)  Parker,  Anat.  Eec,  vol.  4;  {develo-pment)  Streeter,  in  Keibel  and 
Mall's  Human  Embryology.  B.  Brain  and  Spinal  Cord.  Bechterew,  Funktio- 
nen  der  Nervencentra,  3  vols.,  1908;  {cell-structure)  Malone,  Anat.  Rec,  vol.  7; 
{axone-sheaths)  Hardesty,  Amer.  Jom*.  Anat.,  vol.  4;  (cortical  localization) 
Donaldson,  Jour.  Nerv.  and  Mental  Dis.,  vol.  13;  Smith,  Jour.  Anat.  and 
Physiol.,  vol.  41;  Israelsohn  Ai'b.  Wien.  neurol.  Inst.,  vol.  20;  (central  fissure) 
Symington  and  Crymble,  Jour.  Anat.  and  Physiol.,  vol.  47;  (brain-weight)  Pearl, 
Jour.  Comp.  Neurol.,  vol.  25;  Spitzka,  Phila.  Med.  Jour.,  1903;  (ventricles 
Harvey,  Anat.  Rec,  vol.  4;  (mid-brain  and  medulla)  Sabin,  Atlas,  1901;  (tri- 
geminal nuclei)  Willems,  Nevraxe,  T.  12;  (spinal  cord,  cornparative)  BuUard, 
Amer.  Jour.  Anat.,  vol.  14.  C.  Peripheral.  (Histogenesis)  Bardeen,  Amer. 
Jour.  Anat.,  vol.  2;  (experimental)  Harrison,  Amer.  Jour.  Anat.,  vol.  5;  Jour. 
Exper.  ZooL,  vol.  9;  (phylogeny  of  facial)  Sheldon,  Anat.  Rec,  vol.  3;  (trigeminus) 
Symington,  Jour.  Anat.  and  Physiol.,  vol.  45;  (nervus  termnialis)  Johnston,  Anat. 
Rec,  vol.  8.  (afferent  spinal  neurones)  Ranson,  Jour.  Comp.  Neurol.,  vol.  18; 
(structure)  Ranson,  Anat.  Rec,  vol.  3;  (brachial  plexus)  Todd,  Anat.  Anz.,  Bd.  42; 
(abdominal,  statistical)  Bardeen,  Amer.  Jour.  Anat.,  vol.  1  (sympathetic  termina- 
tions) Boeke,  Anat.  Anz.,  vol.  44. 


SECTION  YIII 

SPECIAL  SENSE  OEGANS 


Revised  for  the  Fifth  Edition 
By  DAVID  WATERSTON,  M.A.,M.D.,  F.R.C.S.E.,  King's  College,  London 

PROFESSOR    OF   ANATOMY    IN   THE    UNrVERSITT    OF    LONDON 

GENERAL   CONSIDERATIONS 

THE  term  "special  sense  organs"  indicates  those  structures  situated  on  or 
near  the  surface  of  the  body  which  receive  the  impressions  of  sound,  light 
taste  and  smell,  and  transmit  them  to  the  brain  in  the  form  of  nerve 
impulses. 

The  essential  difference  between  what  is  termed  general  sensibility  and  the 
special  senses  lies  in  the  fact  that  the  organs  of  special  sense  are  each  sensitive  to 
a  specific  stimulus  which  does  not  affect  the  general  sensory  apparatus  of  the 
body  surface  to  an  appreciable  degree. 

Thus,  the  waves  of  light  or  of  sound,  flavoured  substances  which  have  a  taste,  and  the 
minute  particles  which  stimulate  the  sensory  organ  for  smell — all  these  varied  stimuli  create 
no  impression  when  they  come  into  contact  with  the  sensitive  general  surface  of  the  body. 

The  vibration  of  sound  waves  present  in  an  organ  pipe  may  indeed  be  felt  by  the  hand,  but 
the  sensation  is  that  of  vibration  and  not  of  sound. 

This  difference  in  function  between  the  ordinary  and  the  special  senses 
as  well  as  the  difference  between  the  individual  organs  of  special  sense,  is  as- 
sociated with  a  difference  in  structure;  for  each  special  sense  organ  has  a  charac- 
teristic receptive  mechanism  of  cells  highly  specialised  in  form  and  structure, 
which  receive  the  stimuli  coming  from  without,  and  transmit  them  to  the  brain  in 
the  form  of  a  nerve-current.  These  cells  may  be  derived  by  the  specialisation  of 
certain  cells  coming  directly  from  the  surface  of  the  body,  or  they  may  be  cells 
derived  from  the  central  nervous  system — as  in  the  case  of  the  eye.  In  this  case, 
the  cells  are  placed  in  close  relation  to  the  terminals  of  a  special  cranial  nerve. 

Many  of  the  sense  organs,  and  especially  the  eye  and  ear,  are  highly  com- 
plex in  structure.  The  complexity  is  due  largely  to  the  elaborate  mechanical 
arrangement  for  receiving  the  external  stimulus,  and  for  conveying  it  to,  or 
focussing  it  upon,  the  sensory  cells  proper. 

It  must  always  be  borne  in  mind  that  sensation  itself  is  a  function  of  the  brain — it  is  the 
response  in  consciousness  to  the  afferent  impressions  transmitted  to  the  brain  by  the  sensory 
nerves.  Further,  the  quality  of  the  sensation  does  not  arise  in  the  sense  organ,  but  in  the  brain 
itself.  Thus,  stimulation  of  the  trunk  of  the  optic  nerve  by  mechanical  means  produces 
sensations  of  light,  apart  from  stimulation  of  the  retina. 

In  the  following  account,  the  organs  of  smell,  taste,  vision  and  hearing  will  be 
successively  considered. 

I.  THE  OLFACTORY  ORGAN 

The  olfactory  apparatus  [organon  olfactus]  in  man  does  not  reach  the  high 
development  which  is  found  in  many  of  the  lower  animals.  In  them,  not  only  is 
the  sensory  apparatus  found  distributed  over  a  large  area  of  the  nasal  mucous 
membrane,  but  the  central  connections  of  the  olfactory  nerves  make  up  a 
considerable  portion  of  the  brain,  including  all  those  structures  known  under  the 
name  of  rhinencephalon.  In  man,  sensibility  to  smell  is  localised  to  a  compara- 
tively limited  area  in  the  upper  part  of  the  nasal  cavity,  known  as  the  olfactory 
area. 

The  structure  of  the  nose  in  all  its  parts  has  been  fully  dealt  with  in  the 

1049 


1050 


SPECIAL  SENSE  ORGANS 


section  on  the  Respiratory  System — and  hence  it  is  not  necessary  to  describe 
the  whole  nasal  cavity. 

The  olfactory  area  of  the  nose  includes  the  uppermost  part  of  the  nasal  fossae 
on  the  lateral  wall  above  the  superior  concha,  and  a  slightly  larger  area  of  the 
septum. 

Fig.  792  shows  the  size  of  this  area,  and  it  will  be  noticed  that  the  area  on  the 
lateral  wall  of  the  nose  does  not  coincide  with  the  area  of  the  superior  concha,  but 
is  rather  smaller.  It  should  be  added  that  the  olfactory  nerves  can  be  traced 
to  a  somewhat  larger  area  of  the  mucous  membrane,  to  the  middle  concha; 
it  is,  therefore,  possible  that  the  area  indicated  is  too  small. 

The  mucous  membrane  in  the  olfactory  area  has  special  characters,  both  naked 
eye  and  microscopic,  which  distinguish  it  from  the  rest  of  the  nasal  mucous 

Fig.  792. — Diagram  op  the  Distribution  op  the  Nerves  in  the  Nasal  Cavity.     (Poirier 
and  Charpy.)     The  olfactory  area  is  represented  by  dots.    A,  septum.     B,  lateral  wall. 

Posterior  su- 
,        ,  ,  t     .       A     Afiterior     perior  nasal 

Posterior  superior  nasal     /  [  r  \     •    \  ethmoid 

-  ,    ^ —  "^'W 


membrane.  It  is  usually  of  a  yellowish  colour,  and  is  soft  and  pulpy  in  consistence 
It  is  covered  by  a  columnar  ciliated  epithelium  and  contains  numerous  glands 
(glands  of  Bowman) . 

The  olfactory  apparatus  within  it  consists  of  the  olfactory  cells.  These  cells  are  elongated 
spindle-shaped  structures,  lying  between  the  deeper  parts  of  the  investing  columnar  cells. 
From  each  a  slender  process  passes  to  the  surface  of  the  mucosa,  and  terminates  in  a  group  of 
short  hair-like  processes,  the  olfactory  hairs  (v.  Bumm),  while  from  the  deep  portion  of  the  cell 
a  long  slender  process  passes  deeply  into  the  mucosa.  These  processes  resemble  nerve  filaments, 
with  no  medullary  sheath,  and  they  pass  in  the  olfactory  nerves  to  the  olfactory  bulb,  in  which 
they  terminate  in  arborisation  around  the  dendritic  enlargements  of  the  mitral  cells  of  the 
olfactory  bulb  (see  fig.  795;  also  Olfactory  Nerve,  p.  929). 

Fig.  793. — Section  Showing  the  Development  op  the  Olpactort  Pit. 


The  connections  of  the  olfactory  bundle  and  tract  with  the  brain  are  fully 
dealt  with  in  the  section  on  the  Nervous  System. 

The  development  of  the  olfactory  organ  is  connected  with  the  development  of  the  nose, 
which  represents  at  first  only  the  olfactory  portion.  About  the  third  week,  a  localised  thicken- 
ing of  the  surface  epithelium  occurs  on  the  antero-ventral  aspect  of  the  head  in  the  region  of  the 
fore-brain,  forming  on  each  side  an  olfactory  plate.  These  plates  become  depressed  from  the  sur- 
face by  the  growth  of  the  margins,  giving  rise  to  the  olfactory  pits.     The  further  changes  are 


THE  EYE 


1051 


associated  with  the  formation  of  the  face  and  nose  (see  Morphogenesis).  The  cells  of  the  sur- 
face epithelium  on  the  olfactory  pits  in  part  form  olfactory  cells,  and  send  processes  inward  which 
pass  to  the  olfactory  lobe  of  the  brain,  and  form  the  olfactory  nerve. 

The  organ  of  Jacobson  is  a  small  rudimentary  structure  in  man.  It  is  represented  by  a 
minute  canal,  2  to  9  mm.  long,  placed  on  each  side  in  the  lower  portion  of  the  nasal  septum, 
opening  on  the  surface  slightly  above  the  orifice  of  the  naso-palatine  canal.  Below  it  lies  a 
small  piece  of  cartilage,  lying  below  the  cartilage  of  the  septum,  and  known  as  Jacobson's  carti- 
lage. The  canal  is  lined  by  epithelium,  but  contains  no  olfactory  cells.  It  is  developed  from 
a  small  portion  of  the  olfactory  plate  which  becomes  separated  from  the  area  which  gives  rise 
to  epithelium  of  the  olf actor j'  region. 


II.  ORGAN  OF  TASTE 

The  taste  organs  [organon  gustus]  consist  of  minute  epithelial  structures,  the 
taste  buds  [calyculi  gustatorii],  situated  mainly  in  the  epithelial  covering  of  the 
tongue  and  also  in  the  epiglottis. 

In  the  tongue,  the  taste  buds  are  found  mainly  on  the  walls  of  the  vallate 
papillse  (see  p.  1106),  but  they  are  found  to  a  slight  extent  scattered  over  the 
whole  area  of  distribution  of  the  glosso-pharyngeal  nerve,  on  the  surface  of  the 
foliate  and  fungiform  papillse,  and  on  the  plicse  fimbriatse  on  the  lower  surface  of  the 
tongue. 

Tigs.  794  and  795. — Diagrams  Illustrating  the  Structure  of  the  Taste  Buds 
AND  the  Olfactory  Mucosa. 


In  the  foetus,  the  distribution  is  even  wider,  and  they  have  been  described  as  occurring  on 
the  soft  palate,  palatine  arches,  uvula,  and  in  the  mucous  membrane  covering  the  medial  surfaces 
of  the  arytenoid  cartilages.  It  is  possible  that  such  structures,  though  found  in  these  regions 
in  the  foetus,  usually  disappear  in  the  adult. 

Each  taste  bud  is  a  hollow  conical  or  oval  structure,  measuring  .07-.08  mm. 
in  length.  At  one  end  it  opens  by  a  small  channel,  termed  the  pore  canal,  which 
passes  to  the  surface  between  adjacent  epithelial  cells.  The  surface  opening  is 
termed  the  outer  -pore  and  the  opening  at  the  taste  bud  the  inner  taste  pore. 

The  taste  bud  consists  of  epitheUal  supporting,  of  gustatory  and  of  basal  cells,  arranged  as 
seen  in  figure  794.  The  gustatory  cells  are  long  slender  fusiform  cells.  The  free  end  of 
each  passes  to  the  inner  taste  pore,  and  terminates  in  stiff  hair-like  processes,  which  project 
toward  the  pore  canal.  The  deep  end  of  each  is  connected  with  a  basal  cell.  Terminal  branches 
of  the  glosso-pharyngeal  nerve  ramify  around  the  gustatory  cells,  and  convey  to  the  brain  the 
impulses  generated  by  contact  of  the  ends  of  these  cells  with  sapid  particles.  The  epithelial 
supporting  cells  line  the  taste  buds,  and  also  project  into  the  interior  between  the  olfactory  cells. 

Development. — The  taste  buds  appear  comparatively  late  in  embryonic  life — about  the 
third  month.  They  arise  mainly  from  the  entodermal  portion  of  the  tongue,  b}'  differentiation 
of  the  deeper  cells  of  the  epithelial  covering  over  localised  areas.  Around  these  cells  terminations 
of  the  glosso-pharyngeal  nerve  are  found.  These  cells  assume  the  characteristic  shape  and 
arrangement  of  the  adult  to  form  a  taste  bud.  At  first  the  opening  of  the  bud  lies  upon  the 
surface,  but  as  the  surrounding  epithelial  cells  increase  in  size  and  thickness,  the  pore-canal  is 
formed  as  a  space  between  adjacent  epithelial  cells  on  the  summit  of  the  bud. 


III.  THE  EYE 

The  sensory  portion  of  the  eye  is  the  retina,  a  cup-shaped  membrane,  which 
lines  the  posterior  half  of  the  eyeball.     It  is  formed  of  layers  of  nerve  cells,  from 


1052 


SPECIAL  SENSE  ORGANS 


which  processes  pass  to  the  brain  in  the  optic  nerve.  The  eyeball  is  a  hollow  spher- 
ical structure,  whose  wall  is  formed  externally  by  a  fibrous  tunic  including  the 
sclera  (the  white  of  the  eye),  and  the  cornea  (the  transparent  area  in  the  anterior 
aspect  of  the  eyeball).  Internal  to  the  tunic  formed  by  these  membranes  is  a 
pigmented  vascular  membrane,  the  chorioidal  membrane,  of  which  the  anterior 
part  forms  the  iris,  or  the  coloured  part  of  the  eye. 

Within  these  tunics  is  formed  a  cavity,  in  which  lies  the  crystalline  lens  of  the 
eye.  In  front  and  behind  the  lens  are  two  chambers;  that  in  front  of  the  lens 
contains  the  aqueous  humour  and  that  behind  it  the  vitreous. 

The  study  of  the  eye  is  best  undertaken  by  examining  the  eye  in  the  living,  and 
subsequently  by  the  dissection  of  specimens,  and  that  order  is  followed  in  this 
account. 

General  Surface  View 

The  two  eyes  are  situated  nearly  in  the  line  where  the  upper  and  middle  thirds  of  the  face 
meet;  they  lie  right  and  left  of  the  root  of  the  nose,  the  most  prominent  part  of  the  front  of  each 
globe  being  about  3  cm.  (1 J  in.)  from  the  mid-line  of  the  face.  Each  eye  is  overshadowed  by 
the  corresponding  eyebrow,  and  is  capable  of  being  concealed  by  its  eyehds,  upper  and  lower. 

The  orbital  margin  may  be  traced  all  round  with  the  finger.  At  the  junction  of  the  medial 
and  intermediate  thirds  of  the  upper  margin  the  supraorbital  notch  (incisura  supraorbitalis) 
can  usually  be  felt,  and  the  supraorbital  nerve  passing  through  it  can  sometimes  be  made  to 
roll  from  side  to  side  under  the  finger.  The  medial  margin  is  the  most  difficult  to  trace  in  this 
way,  partly  because  it  is  more  rounded  ofi'  than  the  others,  partly  because  it  is  bridged  over  by 
a  firm  band  (medial  palpebral  ligament),  passing  medially  from  the  medial  angle  of  the  eyelids; 
below  this  band,  however,  a  sharp  bony  crest  is  felt,  which  lies  anterior  to  the  lacrimal  sac. 
Note  how  the  eye  is  protectedby  the  rim  of  the  orbit,  above  and  below;  if  we  lay  a  hard  flat 

Fig.  796. — View  of  the  Eye  with  Eyelids  Open. 
Palpebra  superior  (pars  tarsalis) 
Cilia  I  Sulcus  orbitopalpebralis  superior 
Sclera    r      '       I  Angulus  oculi  medialis 

'  Medial  palpebral  commissure 


Ins  I 


^  Pupil     Caruncula  lacrimalis 


Palpebra  inferior 


body  over  the  orbital  opening,  it  will  rest  upon  the  upper  and  lower  bony  prominences,  and  will 
not  touch  the  surface  of  the  globe.  Medially,  the  eye  is  protected  from  injury  mainly  by  the 
bridge  of  the  nose;  laterally  it  is  most  readily  vulnerable,  as  here  the  orbital  rim  is  comparatively 
low.  With  one  finger  placed  over  the  closed  upper  lid,  press  the  eyeball  gently  backward  into 
the  orbit,  and  observe  the  elastic  resistance  met  with,  due  to  the  fact  that  the  globe  rests  pos- 
teriorly on  a  pad  of  fat. 

The  space  between  the  free  edges  of  the  upper  and  lower  lids  is  known  as  the  palpebral 
aperture  [rima  palpebrarum]:  it  is  a  mere  slit  when  the  lids  are  closed;  but  when  they  are  open 
its  shape  is,  roughly,  that  of  an  almond  lying  with  its  long  axis  horizontal,  and  about  thirty 
millimetres  in  length. 

When  the  eyes  are  directed  to  an  object  straight  in  front  of  them,  this  aperture  is  about 
twelve  millimetres  wide,  but  its  width  varies  with  upward  and  downward  movements  of  the 
eyeball,  being  greatest  on  looking  strongly  upward,  diminishing  gradually  as  the  eye  looks 
progi'essively  lower.  The  angles  formed  by  the  meeting  of  the  lids  at  each  end  of  the  palpebral 
aperture  are  named  respectively  the  lateral  and  medial  angles  (or  canthi)  [angulus  oculi  later- 
alis, medialis],  of  which  the  lateral  is  sharp,  while  the  medial  is  rounded  off.  On  a  closer  in- 
spection, it  will  be  found  that,  for  the  last  five  millimetres  or  so  before  reaching  the  medial  angle 
the  edges  of  the  lids  run  an  almost  parallel  course,  and  are  here  devoid  of  lashes.  Through  the 
open  palpebral  aperture  the  front  of  the  eyeball  comes  into  view,  extending  quHe  to  the  lateral, 
but  not  reaching  as  far  as  the  medial,  angle;  just  within  the  latter  we  find  a  small  reddish  promi- 
nence, the  lacrimal  caruncle  [caruncula  lacrimalis] ;   and  between  this  and  the  eyeball  a  fold  of 


SURFACE  VIEW  OF  THE  EYE 


1053 


conjunctiva  known  as  the  plica  semilunaris.  While  the  eye  is  open,  press  one  finger  on  the  skin, 
a  little  beyond  the  lateral  angle,  and  draw  it  firmly  away  from  the  middle  line;  observe  that  the 
upper  lid  then  falls  over  the  eyeball,  and  that  the  outline  of  a  firm  band  already  referred  to 
(the  medial  palpebral  ligament)  becomes  evident,  passing  between  the  medial  angle  and  the 
nose.  The  falling  of  the  lid  is  caused  by  our  dragging  upon  a  ligament  (the  lateral  palpebral 
raph6)  to  which  the  lateral  end  of  its  tarsus  is  attached,  and  so  putting  the  lid  itself  upon  the 
stretch.  If,  while  the  eyeball  is  directed  downward,  we  place  one  finger  on  the  lateral  end  of  the 
upper  eyelid  and  draw  it  forcibly  upward  and  laterally,  we  can  usually  cause  the  lower  division 
of  the  lacrimal  gland  to  present  just  above  the  lateral  angle. 

Fig.  797. — View  op  the  Eye  with  Eyelids  Closed. 
Sulcus  orbitopalpebralis  superior        Angulus  oculi  medialis 


Cilia    Palpebra        Medial  palpebral  commissure 
inferior 

The  upper  eyelid  [palpebra  superior]  is  much  broader  than  the  lower,  extending  upward 
as  far  as  the  eyebrow.  The  skin  covering  it  is  loosely  attached  to  the  subjacent  tissues  above, 
but  more  firmly  below,  nearer  the  free  margin,  where  it  overlies  a  firm  fibrous  tissue  called  the 
tarsus  superior.  When  the  eye  is  open,  a  fold  is  present  at  the  upper  border  of  this  lower  more 
tightly  applied  portion  of  skin,  called  the  superior  palpebral  fold,  and  by  it  the  lid  is  marked  off 
into  an  upper  or  orbital,  and  a  lower  or  tarsal,  division.  The  presence  of  the  tarsus  can  be 
readily  appreciated  on  our  pinching  horizontally  the  entire  thicloiess  of  the  eyelid  below  the 
palpebral  fold.  The  lower  eyelid  [palpebra  inferior]  is  similarly  divided  anatomically  into  a 
tarsal  and  an  orbital  part,  but  the  demarcation  is  sometimes  unrecognisable  on  the  surface, 


Fig.  798. — View  of  Medial  Region  op  the  Eye,  with  the  Eyelids  Widely  Separated 
AND  THE  Eyeball  Turned  Laterally. 

Edge  of 
palpebra  superior 


Tarsal  (Meibomian)  glands 


though  a  fold  or  groove  (the  inferior  palpebral)  is  usually  visible  when  the  eye  is  widely  opened. 
There  is  no  precise  limit  of  this  lid  below,  but  it  maybe  regarded  ase.xtending  to  the  level  of  the 
lower  margin  of  the  orbit.  Numerous  very  fine  short  hairs  are  seen  on  the  anterior  surface  of 
both  eyelids.  Each  eyelid  presents  an  anterior  and  a  posterior  surface,  separated  by  a  free 
margin  with  two  edges: — (a)  An  anterior,  rounded  edge  [limbus  palpebralis  anterior]  along 
which  the  stiff  cilia,  or  eyelashes,  are  closely  placed  in  a  triple  row;  and  (b)  a  sharp  posterior 
edge  [limbus  palpetjralis  posterior]  which  is  applied  to  the  surface  of  the  globe  (see  fig.  813). 
The  cilia  of  both  eyeUds  have  their  points  turned  away  from  the  palpebral  aperture,  so  that 
the  upper  ones  curve  upward,  and  the  lower  downward;  the  oiha  of  the  upper  lid  are  the  stronger, 


1054  SPECIAL  SENSE  ORGANS 

and  those  in  the  middle  of  each  row  are  longer  than  those  at  each  end.  Between  the  two  edges 
just  described,  the  Ud-margin  has  a  smooth  surface,  on  which  is  a  single  row  of  minute  apertures, 
the  openings  of  large  modified  sebaceous  glands,  the  tarsal  or  Meibomian  glands.  It  is  by  these 
glistening,  weU-lubricated  surfaces  that  the  opposite  lids  come  into  apposition  when  they  are 
closed.  The  secretion  of  these  glands  is  known  as  the  sebum  palpebrale.  The  sharp  posterior 
edge  of  the  lid-margin  marks  the  situation  of  the  transition  of  skin  into  mucous  membrane. 
Near  the  medial  end  of  the  margin  of  the  lids  we  find  a  prominence,  the  lacrimal  papilla,  on  the 
summit  of  which  is  a  small  hole  [punctum  lacrimale],  the  opening  of  the  lacrimal  duct  (ductus 
lacrimaUs)  for  the  passage  of  tears  into  the  lacrimal  sac.  The  lower  punctum  is  rather  larger 
than  the  upper,  and  is  placed  further  from  the  medial  angle  of  the  eye. 

If  we  now  examine  the  posterior  surface  of  the  eyelids — e.  g.,  of  the  lower — we  observe 
that  it  is  lined  by  a  soft  mucous  membrane,  the  palpebral  conjunctiva  [tunica  conjunctiva 
palpebrarum].  Over  the  tarsal  part  of  the  lid  the  conjunctiva  is  closely  adherent,  but  beyond 
this  it  is  freely  movable  along  with  the  loose  submucous  tissue  here  present.  On  tracing  it 
backward,  we  find  that  it  covers  the  whole  posterior  surface  of  the  hds,  and  is  then  continued 
forward  over  the  front  of  the  eyeball,  forming  the  conjunctival  tunic  of  the  globe  [tunica  con- 
junctiva bulbi].  The  bend  it  makes  as  it  changes  its  direction  here  is  called  the  conjunctival 
fornix  [fornix  oonjuuotivEe  superior  or  inferior].  Numerous  underlying  blood-vessels  are  visible 
through  the  palpebral  conjunctiva,  and  under  cover  of  its  tarsal  part  we  can  see  a  series  of  nearly 
straight,  parallel,  light  yellow  lines,  arranged  perpendicularly  to  the  free  margin  of  the  hd — 
the  tarsal  glands.  The  conjunctiva  over  the  medial  and  lateral  fourths  of  each  lid  is  not  quite 
so  smooth  as  elsewhere,  and  is  normally  of  a  deeper  red  colour;  we  shall  find  later  that  there  are 
glands  well  developed  in  these  positions. 

When  the  eyelids  are  opened  naturally,  we  see  through  the  palpebral  aperture  the  following: 
the  greater  part  of  the  transparent  cornea,  and  behind  it  the  coloured  iris  with  the  pupil  in  its 
centre;  white  sclera  to  the  medial  and  lateral  sides  of  the  cornea;  the  semilunar  fold  and  lacrimal 
caruncle  at  the  medial  angle.  The  extent  of  the  eyeball  visible  in  this  way  varies  according  to 
its  position.  Thus,  with  the  eyes  looking  straight  forward,  the  lower  margin  of  the  upper  Ud 
is  nearly  opposite  to  the  top  of  the  cornea,  or,  more  strictly,  to  a  line  midway  between  the  top 
of  the  cornea  and  the  upper  border  of  the  pupil,  while  the  lower  lid  corresponds  with  the  lower 
margin  of  the  cornea.  When  the  eyes  are  directed  strongly  upward,  the  upper  lid  is  relatively 
on  a  slightly  higher  level,  as  it  is  simultaneously  raised,  but  the  lower  lid  now  leaves  a  strip  of 
sclera  exposed  below  the  cornea.  On  looking  downward  the  upper  lid  covers  the  upper  part 
of  the  cornea  as  low  down  as  the  level  of  the  top  of  the  pupil,  while  the  lower  hd  is  about  mid- 
way between  the  pupil  and  the  lower  margin  of  the  cornea. 

If  we  draw  the  eyelids  forcibly  apart,  we  expose  the  whole  cornea,  and  a  zone  of  sclera 
about  eight  and  a  half  milhmetres  in  breadth  above  and  below,  and  ten  milHmetres  in  breadth 
to  the  lateral  and  medial  sides — altogether  about  one-third  of  the  globe;  all  the  eyeball  thus 
exposed  is  covered  by  the  ocular  conjunctiva  [tunica  conjunctiva  bulbi].  Over  the  sclera  the 
conjunctiva  is  freely  movable,  and  through  it  we  see  superficial  blood-vessels  that  can  be  made 
to  slip  from  side  to  side  along  with  it  (episcleral  vessels).  Occasionally  other  deeper  vessels 
may  also  be  seen  which  do  not  move  with  the  conjunctiva,  but  are  attached  to  the  sclera  (an- 
terior ciliary  arteries  and  veins).  Near  the  corneal  border  the  conjunctiva  ceases  to  be  fieely 
movable,  and  it  is  closely  adherent  to  the  whole  anterior  surface  of  the  cornea,  giving  the  latter 
its  characteristic  bright,  reflecting  appearance;  no  blood-vessels  are  visible  through  it  here  in 
health.  When  the  lids  are  shut,  the  space  enclosed  between  their  posterior  surfaces  and  the 
front  of  the  eyeball  is  thus  everywhere  lined  by  conjunctiva,  and  is  known  as  the  con- 
junctival sac. 

Not  unfrequently  the  tendinous  insertions  of  some  or  aU  of  the  recti  muscles  into  the  sclera 
may  be  seen  through  the  conjunctiva,  each  insertion  appearing  as  a  series  of  whitish  parallel 
lines  running  toward,  but  terminating  about  seven  mUhmetres  from,  the  corresponding  corneal 
border. 

The  cornea  appears  as  a  transparent  dome,  having  a  curvature  greater  than  that  of  the 
sclera;  the  junction  of  the  two  unequally  curved  surfaces  is  marked  by  a  shallow  depression 
running  around  the  cornea,  known  as  the  scleral  sulcus  [sulcus  sclerse].  In  outline  the  cornea  is 
nearly  circular,  but  its  horizontal  diameter  is  slightly  greater  than  its  vertical.  Between  it 
and  the  iris  a  space  exists,  whose  depth  we  can  estimate  roughly  by  looking  at  the  eye  from  one 
side;  this  space,  or  anterior  chamber  [camera  ocuh  anterior]  is  occupied  by  a  clear  fluid,  the 
aqueous  humour.  Almost  the  whole  anterior  surface  of  the  iris  is  visible,  its  extreme  periphery 
only  being  concealed  by  sclera. 

In  colour  the  iris  varies  greatly  in  diiferent  individuals.  Near  its  centre  (really  a  little  up 
and  in)  a  round  hole  exists  in  the  iris,  the  black  pupil  [pupUla],  whose  size  varies  considerably 
in  different  eyes,  and  in  the  same  eye  according  to  temporary  conditions,  such  as  exposure  to 
light,  etc. 

On  the  surface  of  the  iris  we  see  a  number  of  ridges  [plicae  iridis]  running  more  or  less  radially ; 
adjoining  ones  occasionaUy  unite  and  interlace  to  some  extent,  so  as  to  leave  large  depressed 
meshes  at  intervals.  These  are  the  crypts  of  the  iris.  The  radial  ridges  coming  from  the  edge 
of  the  pupil,  and  those  coming  from  the  more  peripheral  part  of  the  iris,  meet  in  a  zigzag  ele- 
vated ridge  concentric  with  the  pupil,  called  the  corona  iridis,  and  by  this  ridge  the  iris  is 
roughly  marked  off  into  two  unequal  zones — an  outer,  the  greater  [annulus  U'idis  major]  and 
an  inner,  the  lesser  [annulus  iridis  minor].  The  border  next  the  pupil  [margo  pupillaris] 
is  edged  with  small,  roundish,  bead-like  prominences  of  a  dark  brown  colour,  separated 
from  one  another  by  depressions,  so  that  it  presents  a  finely  notched  contour.  Not  infrequently, 
in  a  light-coloured  iris,  we  may  see  the  sphincter  muscle  through  the  anterior  layers,  in  the  form 
of  a  ring  about  one  millimetre  in  breadth  around  the  pupil.  The  annulus  iridis  major  may  be 
described  as  consisting  of  three  parts: — (a)  A  comparatively  smooth  zone  next  the  zigzag 
ridge;  (6)  a  middle  area,  showing  concentric  but  incompletely  circular  furrows;  (c)  a  small  per- 
ipheral darker  part,  presenting  a  sieve-like  appearance.     On  the  floor  of  the  large  depressed 


THE  EYEBALL 


1055 


meshes,  or  crypts,  parallel  radial  vessels  can  be  traced,  belonging  to  the  iris-stroma.  The  zig- 
zag line  mentioned  above  corresponds  to  the  position  of  the  circulus  arteriosus  minor.  Occa- 
sionally, especially  in  a  hght  iris,  superficial  pigment  spots  of  a  rusty  brown  colour  occur. 

(In  examining  the  living  eye,  the  ophthalmoscope  may  now  be  used,  so  as  to  gain  a  view 
of  the  fundus,  and  to  study  the  termination  of  the  optic  nerve,  the  distribution  of  the  larger 
retinal  vessels,  etc.) 

The  general  red  reflex  obtained  from  the  fundus  is  due  to  the  blood  in  a  capillary  network 
(chorio-capillaris)  situated  in  the  inner  part  of  the  chorioid.  To  the  nasal  side  of  the  centre  of 
the  fundus  is  a  paler  area  of  a  disc  shape  corresponding  to  the  intraocular  end  of  the  optic  nerve, 
and  known  as  the  papilla  of  the  optic  nerve  [papilla  n.  optici].  This  papilla  (or  'optic  disc') 
is  nearly  circular,  but  usually  slightly  oval  vertically;  it  is  of  a  light  orange-pink  colour,  with  a 
characteristic  superficial  translucency;  its  lateral  third  segment  is  paler  than  the  rest  as  nerve- 
fibres  and  capillaries  here  are  fewer  in  number.  About  its  centre  we  often  observe  a  weU- 
marked  whitish  depression  [excavatio  papillae  n.  optici],  formed  by  the  dispersion  of  the  nerve- 
fibres  as  they  spread  out  over  the  fundus;  at  the  bottom  of  this  depression  a  sieve-like  appearance 
may  be  seen,  due  to  the  presence  of  the  lamina  cribrosa  sclerae,  which  consists  of  a  white  fibrous 
tissue  framework,  with  small,  roundish,  light-grey  meshes  in  it,  through  which  the  nerve-fibre 
bundles  pass.  Also  near  the  centre  of  the  papiUa,  the  retinal  blood-vessels  first  come  into  view, 
the  arteries  narrower  in  size  and  lighter  in  colour  than  the  veins;  they  divide  dichotomously 
as  they  are  distributed  over  the  fundus.  The  retina  proper  is  so  transparent  as  to  be  ophthal- 
moscopically  invisible,  but  its  pigment-epithelium  gives  a  very  finely  granular  or  darkly  stippled 
appearance  to  the  general  red  reflex.  In  the  centre  of  the  fundus,  and  therefore  to  the  lateral 
side  of  the  papilla,  the  ophthalmoscope  often  shows  a  shifting  halo  of  light  playing  round  a 

Fig.  799. — The  Normal  Fundus  op  the  Eyeball.     (Parsons.) 


horizontally  oval,  comparatively  dark  enclosed  area;  this  latter  corresponds  to  the  yellow 
spot  [macula  lutea]  region,  and  about  its  centre  a  small  pale  spot  usuafly  marks  the  position  of 
the  fovea  centralis. 

Two  structures  visible  at  the  nasal  end  of  the  palpebral  aperture  have  been  previously 
mentioned,  and  should  now  be  examined  more  narrowly.  The  lacrimal  caruncle  is  an  island 
of  modified  skin,  and  fine  hairs  can  commonly  be  detected  on  its  surface,  and  it  contains  sebaceous 
and  sweat  glands.  Lateral  to  it  and  separated  from  it  by  a  narrow  groove,  is  the  semilunar 
fold  of  conjunctiva;  it  rests  on  the  eyeball,  and  is  a  rudiment  of  the  third  eyelid  or  nictitating 
membrane,  present  in  birds  and  well  represented  in  many  other  vertebrates. 


Examination  of  the  Eyeball 

(In  the  following  account,  the  structure  of  the  eyeball  is  described  as  it  would 
appear  upon  dissection.) 

The  eyeball  [bulbus  oculi]  is  almost  spherical,  but  not  perfectly  so,  mainly  be- 
cause its  anterior,  clear,  or  corneal  segment  has  a  greater  curvature  than  the  rest  of 
the  eye.  Considering  it  as  a  globe,  it  has  an  anterior  pole  [polus  anterior]  and 
a  posterior  pole  [polus  posterior];  the  former  corresponding  to  the  centre  of  the 
front  of  the  cornea,  the  latter  to  the  center  of  the  posterior  curvature.  An  imag- 
inary straight  line  joining  the  two  poles  is  called  the  axis  of  the  eyeball.  The 
equator  of  the  eye  is  that  part  of  its  surface  which  lies  midway  between  the  two 
poles.  The  various  meridians  are  circles  which  intersect  the  poles.  The  sagittal 
axis  of  the  globe  is  the  greatest  (about  24 . 5  mm.),  the  vertical  equatorial  the  least 


1056 


SPECIAL  SENSE  ORGANS 


(about  23.5  mm.),  and  the  transverse  equatorial  axis  is  intermediate  in  length 
(about  23 . 9),  so  that  the  eyeball  is  in  reality  an  ellipsoid,  flattened  slightly  from 
above  downward.  These  figures  refer  to  the  adult  male;  in  the  female  the  eyeball 
is  .  5  mm.  smaller  in  aU  axes.  Again,  if  the  globe  is  divided  in  its  mid-sagittal 
plane,  the  nasal  division  will  be  found  to  be  slightly  smaller  than  the  temporal. 
The  optic  nerve  joins  the  globe  three  or  four  millimetres  to  the  nasal  side  of  the 
posterior  pole. 

The  shape  of  the  eye  depends  on,  and  is  preserved  by,  the  outermost  tunic, 
formed  conjointly  by  the  cornea  and  sclera,  the  entire  outer  surfaces  of  which  are 
now  in  view.  The  anterior  or  corneal  part  has  already  been  examined.  All  around 
the  cornea  there  remains  a  little  adherent  conjunctiva;  elsewhere,  the  sclerals 
directly  exposed,  except  for  some  loose  connective  tissue  which  adheres  to  it, 
especially  around  the  optic  nerve  entrance.  In  front  of  the  equator  we  see  the 
tendinous  insertions  of  the  four  recti  muscles.  Behind  the  equator  are  the  inser- 
tions of  the  two  oblique  muscles — that  of  the  superior  oblique  tendinous,  and 
further  forward;  that  of  the  inferior  more  fleshy,  and  placed  between  the  optic 
nerve  and  the  lateral  rectus. 


Fig.  800. — Diagrammatic  View  of  the  Insertions  of  the  Ocular  Muscles. 

Superior  rectus 


Lareral  rectus 


Inferior  rectus 


It  is  difficult  to  recognise  the  different  recti  muscles  by  their  insertions  if  we  do  not  know 
whether  the  eye  examined  is  a  right  or  a  left  one.  To  determine  this  we  should  hold  the  globe 
with  the  optic  nerve  toward  us,  and  in  the  natural  position  with  the  superior  oblique  tendon 
uppermost.  The  inferior  oblique  tendon  will  now  point  to  the  side  to  which  the  eye  belongs, 
and  we  can  consequently  determine  the  difTerent  recti  muscles. 

The  medial  [m.  rectus  medialis]  rectus  is  inserted  nearest  (5.5  to  7  mm.  from)  the  corneal 
border;  the  superior  [m.  rectus  superior]  rectus  commonly,  sometimes  the  lateral  [m.  rectus 
laterahs],  is  inserted  furthest  from  it  (7.7  to  8  mm.).  All  the  recti  tendons  are  broad  and  thin, 
but  that  of  the  medial  is  the  broadest  (8  to  10.3  mm.);  those  of  the  lateral  and  inferior  the 
narrowest  (6  to  9.2,  or  9.8  mm.,  respectively).  The  greatest  interval  between  two  neighbouring 
tendons  is  that  between  the  superior  and  medial  recti  (about  12  mm.);  the  least  is  between 
the  superior  and  lateral  (7  mm.).  The  form  of  the  lines  of  insertion  of  the  different  tendons 
varies  considerably,  the  inferior  being  almost  straight,  the  superior  and  lateral  convex  forward, 
the  medial  further  removed  from  the  corneal  border  below  than  above. 

The  insertions  of  the  oblique  muscles  [mm.  obliqui]  are  at  more  than  double  the  average 
distance  of  the  insertions  of  the  recti  from  the  corneal  border.  That  of  the  superior  oblique  is 
found  on  the  superior  surface  of  the  sclera,  about  sixteen  millimetres  from  the  corneal  edge, 
in  the  form  of  a  line  10.7  mm.  long  sloping  from  before  backward  and  medially.  The  inferior 
oblique  has  a  long  fleshy  insertion  lying  between  the  lateral  rectus  and  the  optic  nerve  entrance; 
the  posterior  end  of  the  insertion,  which  is  also  the  higher,  is  only  about  five  to  six  millipietres 
from  the  optic  nerve,  and  from  this  point  it  slopes  forward,  laterally,  and  slightly  downward. 

Several  small  nerves  and  two  arteries  may  be  seen  running  forward  and  ulti- 
mately perforating  the  sclera  not  far  from  the  entrance  of  the  optic  nerve.  The 
two  arteries  are  the  long  posterior  ciliary  [aa.  ciliares  posteriores  longi] ;  they  both 
perforate  the  globe  in  the  horizontal  meridian,  3.5  mm.  from  the  optic  nerve,  one 
on  the  lateral,  the  other  on  the  medial,  side.     The  short  ciliary  arteries  [aa.  ciliares 


THE  EYEBALL  1057 

posteriores  breves]  are  too  small  to  be  seen  in  an  ordinary  examination.  The 
nerves  are  the  long  and  short  ciUary  [nn.  ciliareslongi,  breves].  Nearer  the  equator 
large  venous  trunks  emerge;  they  can  be  traced  for  some  distance  in  front  of  their 
exit  as  dark  lines,  running  antero-posteriorly  internal  to  the  sclera.  The  optic 
nerve  is  seen  in  section,  surrounded  loosely  by  a  thick  outer  sheath;  in  the  centre  of 
the  nerve-section  a  small  red  spot  indicates  the  position  of  the  central  retinal 
blood-vessels  [a.  et  v.  centralis  retinae]. 

(The  following  structures  appear  in  an  eyeball  divided  into  fore  and  hind  halves  by  cutting 
through  it  in  the  equatorial  plane.) 

1.  Posterior  hemisphere  seen  from  in  front. — This  is  much  the  same  view  that  the  ophthal- 
moscope affords  us.  Unless  the  eye  be  very  fresh,  however,  the  retina  will  have  lost  its  trans- 
parency, and  will  now  present  the  appearance  of  a  thin  whitish  membrane,  detached  in  folds 
from  the  external  coats,  but  still  adherent  at  the  optic  papilla.  The  vitreous  jelly  lying  within 
the  retinal  cup  may  be  torn  away.  In  the  human  eye  the  retina  next  the  posterior  pole  is  stained 
yellow  [macula  lutea].  On  turning  the  retina  over,  a  little  pigment  may  be  seen  adhering  to 
its  outer  surface  here  and  there.  Cut  through  the  retina  close  to  the  optic  disc  all  around  and 
remove  it:  note  how  easily  it  is  torn.  We  now  see  a  dark  brown  surface,  consisting  of  the 
retinal  pigment  layer  [stratum  pigmenti  retinas]  adherent  to  the  inner  surface  of  the  chorioid. 
Brush  off  the  retinal  pigment  under  water.  The  chorioid  thus  exposed  can  for  the  most  part 
be  fairly  easily  torn  away  from  the  thick  sclera,  as  a  lymph-space  exists  between  them,  but  the 
attachment  is  firm  around  the  optic  nerve  entrance,  and  also  where  the  arteries  and  nerves  join 
the  chorioid  after  penetrating  the  sclera.  The  chorioid  is  darkly  pigmented,  of  a  brown  colour, 
with  markings  on  its  surfaces  corresponding  to  the  distribution  of  its  large  veins.     The  inner 

Fig.  801. — Anteeiob  Hemisphere  of  Eyeball,  Viewed  from  Behind. 
Pupil 

Ciliary  processes 


surface  of  the  sclera  is  of  a  light  brownish  colour,  mainly  from  the  presence  of  a  delicate  pig- 
mented layer,  the  lamina  suprachorioidea,  which  adheres  partly  to  it,  partly  to  the  chorioid, 
giving  to  their  adjacent  surfaces  a  flocculent  appearance  when  examined  under  water. 

2.  Anterior  hemisphere  viewed  from  behind. — The  round  opening  of  the  pupil  is  visible  in 
the  middle,  in  front  of  the  large  clear  crystalline  lens.  The  retina  proper  extends  forward  a 
little  way  from  the  line  of  section,  and  then  ends  abruptly  in  a  wavy  line  called  the  era  serrata, 
beyond  which  it  is  only  represented  by  a  very  thin  membrane  [pars  ciliaris  retinae].  Outside 
the  periphery  of  the  lens  are  a  number  of  ciliary  processes  arranged  closely  together  in  a  circle 
concentric  with  the  pupil,  and  each  radially  elongated;  posteriorly  they  are  continuous  with 
n  umerous  fine  folds,  also  radial,  which  soon  get  very  indistinct  as  they  pass  backward,  but 
reach  almost  to  the  ora  serrata  [plicae  ciliares].  Between  the  front  of  the  ciliary  processes  and 
the  edge  of  the  pupU  lies  the  iris.  On  removal  of  the  retina  the  inner  surface  of  all  this  region 
is  seen  to  be  darkly  pigmented,  but  especially  dark  in  front  of  the  position  of  the  ora  serrata. 
Vitreous  probably  still  adheres  to  the  back  of  the  lens,  and  by  pulhng  upon  it  the  lens  can  be 
removed  along  with  its  capsule  and  suspensory  ligament;  some  pigment  will  now  be  found 
adhering  to  the  front  of  the  vitreous,  torn  from  the  ciliary  processes,  which  are  consequently 
now  lighter  in  colour  than  before.  The  lens-capsule  is  transparent,  and  has  a  smooth  glistening 
outer  surface;  through  it  a  greyish,  star-shaped  figure  may  be  observed  on  the  anterior  and 
posterior  surfaces  of  the  lens.  The  suspensory  ligament  is  a  transparent  membrane  attached  to 
the  capsule  of  the  lens  about  its  equator,  and  is  best  seen  by  floating  the  lens  in  water  in  a  glass 
vessel  placed  on  a  dark  ground.  On  opening  the  capsule  we  expose  the  lens  itself,  which  is 
superficially  soft  and  glutinous  to  the  touch,  but  becomes  firmer  as  we  rub  off  its  outer  laj-ers  and 
approach  its  centre.  Carefully  tear  the  chorioid  and  iris  from  the  sclerotic  as  far  as  possible; 
a  firm  adhesion  exists  just  behind  the  corneal  periphery.  The  outer  surface  of  the  chorioid 
thus  exposed  is  found  to  be  also  rather  darkly  pigmented,  taut  it  shows  a  white  ring  corresponding 
to  the  adhesion  just  mentioned,  and  a  pale  area  behind  this  ring  indicates  the  position  of 
the  ciliary  muscle  [m.  ciharis].     On  this  surface  numerous  white  nerve-cords  are  visible  running 


1058 


SPECIAL  SENSE  ORGANS 


forward.  Observe  that  the  iris,  the  ciliary  processes,  etc.,  and  the  chorioid  are  all  different 
parts  of  the  same  ocular  tunic — mere  local  modifications  of  it.  Similarly  the  sclera  and  cornea 
are  seen  to  blend  together  to  form  one  outer  coat. 

An  eyeball  should  now  be  placed  for  half  an  hour  in  a  freezing  mixture  of  crushed  ice  and 
salt.  It  will  thus  become  quite  hard,  and  should  at  once  be  divided  into  two  parts  by  cutting 
it  antero-posteriorly  through  the  centre  of  the  cornea  and  the  optic  nerve.  We  thus  gain  another 
view  of  the  relations  of  parts,  the  position  of  the  lens  between  the  aqueous  and  vitreous  chambers, 
etc.  On  removing  the  lens,  vitreous,  and  retina,  and  brushing  off  its  pigment,  the  light  markings 
corresponding  to  the  chorioidal  veins  (venae  vorticosse)  should  be  noted,  and  their  distribution 
studied.     Usually  four  vortices  or  fountain-like  markings  are  found  in  the  whole  chorioid, 

Fig.  802. — Horizontal  Section  of  the  Eyeball.   X  4. 

Anterior  surface  of  lens 


Optic  axil 
Corneal  epithelium 
Posterior  surface  of  cornea     '^^ 
Cornea 


Crystalline  lens 


Zonula  ciliaris 


Posterior 
surface  of 
lens 


Sulcus  sclerse 
/  Lig.  pectinatum  iridis 
I  Posterior  chamber 
/  /Sinus  venosus  scle___ 
/  yScleral  conjunctiva 

^Anterior  chambe 
^^^^_-  Angulus  indis 


Ciliary  body 
Ciliary  processes 
-  Zonular  fibres 


Papilla  of  optic  nerve 

Lamina  cribrosa  scleras 

A.  Centralis  retinse 


Retina 
dea 
Macula  latea  and  fovea  centralis 
Sclera 


their  points  of  junction  situated  at  approximately  equal  distances  from  one  another  at  about 
the  hne  where  the  posterior  and  middle  thii-ds  of  the  globe  meet.  These  sections  should  be  kept 
for  reference  while  following  the  further  description  of  the  ocular  tunics. 

The  coats  of  the  eyeball. — 1.  The  outer,  fibrous  coat  of  the  eye  [tunica 
fibrosa  oculi]  is  formed  by  the  sclera  and  cornea,  which  pass  into  one  another 
at  the  scleral  sulcus.  It  consists  throughout  mainly  of  fine  connective-tissue 
fibres,  arranged  in  interlacing  bundles,  with  small  lymph-spaces  at  intervals 
between  them.  The  naked-eye  appearance  of  the  two  divisions  of  this  fibrous 
coat  is,  however,  quite  different,  the  cornea  being  transparent,  while  the  sclera 
is  white  and  opaque. 

The  sclera  encloses  the  posterior  five-sixths  or  so  of  the  eyeball.     It  is  perfo- 


THE  CORNEA 


1059 


rated  bj''  the  entrance  of  the  optic  nerve,  and  the  opening  in  the  sclera,  only 
partially  bridged  across  by  fibres  from  the  inner  layers,  forms  the  lamina 
cribrosa. 

The  fibre-bundles  composing  the  solera  are  arranged  more  irregularly  than  in  the  cornea, 
and  run  mainly  in  two  directions,  viz.,  antero-posteriorly  and  circularly;  the  circular  fibres 
are  particularly  well  developed  just  behind  the  sulcus.  It  is  thickest  (about  1  mm.)  posteriorly, 
where  it  is  strengthened  chiefly  by  the  outer  sheath  of  the  optic  nerve,  and  partly  also  by  the 
tissue  surrounding  the  ciliary  vessels  and  nerves.  It  becomes  gradually  thinner  as  it  passes 
forward,  up  to  the  line  of  insertion  of  the  I'ecti  muscles,  where  it  is  .3  mm.  thick.  In  front  of 
that  line  it  is  again  reinforced  by  their  tendinous  fibres  becoming  incorporated  with  it  and  its 
thickness  increases  to  .6  mm.  In  children  the  sclera  is  often  so  thin  as  to  allow  the  underlying 
chorioidal  pigment  to  show  through,  its  colour  then  appearing  bluish  white.  In  the  aged,  again, 
it  is  sometimes  yellowish.  It  always  contains  a  few  pigment  cells,  but  these  are  in  the  deep 
layer  termed  the  lamina  fusca,  and  only  become  visible  externally  where  the  sclera  is  pierced 
by  vessels  and  nerves  going  to  the  chorioid.  It  is  almost  non-vascidar,  but  quite  at  its  anterior 
end  a  large  venous  sinus  [sinus  venosus  sclerse;  canalis  Schlemmi  (Lauthi)],  (canal  of  Schlemm) 
runs  in  its  deeper  layers  circularly  around  the  cornea.  Just  in  front  of  this  sinus,  at  the  corneal 
limbus,  the  sclera  merges  into  the  cornea,  its  inner  layers  changing  first,  and  finally  the  outer 
ones. 


Fig.  803.— Portion  op  Fig.  802,  Enlarged. 
Anterior  surface  of  lens 
Crystalline  lens 


Iris 

/ 


Sulcus  sclerEQ 

t  Lig,  pectinatum  iridis 
I       ^Posterior  chamber 

;  venosus  sclerae 
/  Scleral  conjunctiva 

Anterior  chamber 


Angulus  iridis 
;.'*Circulus  arteriosus  majo 
Ciliary  muscle 


Ciliary  muscle,  circular  fibres 
Ciliary  processes 
.  Zonular  fibres 


Ora  serrata 


Insertion  of 
tendon  of 
rectus  lateralis 


The  cornea  forms  the  anterior  sixth  of  the  eyeball.  It  is  thickest  ,'at 
its  periphery  (1.1  mm.)  and  becomes  gradually  thinner  toward  its  centre 
(0.8  mm.);  the  curvature  of  its  posterior  is  consequently  greater  than  that  of  its 
anterior  surface,  but  even  the  latter  is  more  curved  than  the  surface  of  the  sclera. 

In  the  cornea  proper,  fibre-bundles  are  arranged  so  as  to  form  a  series  of  superposed  lameUse, 
each  of  which  is  connected  here  and  there  to  the  adjacent  ones  by  fibres  passing  from  one  to  the 
other,  so  that  they  can  only  be  torn  apart  with  difficulty.  The  corneal  lymph-spaces  communi- 
cate with  one  another  by  very  fine  canals,  and  thus  not  only  is  a  thorough  lymph-circulation 
provided  for,  but  the  protoplasm  with  which  these  spaces  are  partially  occupied  may  be  also 
regarded  as  continuous  throughout.  It  contains  no  blood-vessels,  with  the  exception  of  a  rich 
plexus  at  its  extreme  periphery,  on  which  its  nutrition  is  ultimately  dependent.  The  sinus 
venosus  o}  Schlemm  is  an  important  channel  for  the  return  of  blood  and  also  of  fluid  which 
transudes  into  it  from  the  anterior  chamber.  It  consists  of  a  network  of  venous  spaces,  formed 
of  a  principal  vessel  accompanied  by  several  smaller  ones,  which  unite  with  it  and  with  one 
another  in  a  plexiform  manner.  -They  commence  indirectly  with  the  spaces  of  the  angle  of  the 
iris  and  they  are  in  direct  communication  with  the  anterior  ciliary  veins. 


1060  SPECIAL  SENSE  ORGANS 

The  outer  surface  of  the  cornea  is  covered  by  an  extension  of  the  ocular  conjunctiva,  in 
the  form  of  an  epitheUum  several  layers  deep.  The  most  external  part  of  the  true  cornea  appears 
homogeneous,  even  when  highly  magnified  and  constitutes  the  anterior  elastic  lamina,  Bow- 
man's membrane,  though  there  is  reason  to  believe  that  its  structure  only  differs  from  that 
already  described  in  the  closeness  of  its  fibrous  texture;  the  two  parts  are  certainly  connected  by 
fine  fibres.  Posteriorly,  the  cornea  is  lined  by  a  fu-m,  thin,  glass-hke  layer  (posterior  elastic 
lamina,  membrane  of  Descemet),  distinct  from  the  corneal  tissue  both  anatomically  and  chem- 
ically. At  the  periphery  this  membrane  breaks  up  into  a  number  of  fibres,  which  mainly  arch 
over  to  join  the  base  of  the  iris  and  form  part  of  the  ligamentum  pectinatum  iridis.  The  pectin- 
ate ligament  is  an  open  network  of  interlacing  fibres,  directly  continuous  with  the  circular 
and  longitudinal  bundles  of  sclera  surrounding  the  venous  sinus  of  Schlemm  (Henderson). 
The  interstices  between  these  fibres  constitute  spaces  (spaces  of  Fontana)  [spatia  anguli  iridis 
(Fontanse)]  freely  communicating  with  the  aqueous  chamber  on  the  one  hand,  and  indirectly 
with  the  venous  sinus  of  the  sclera  on  the  other.  The  posterior  elastic  lamina  is  in  turn  lined 
by  a  single  layer  of  flat  cells,  which  are  continuous  peripherally  with  cells  lining  the  spaces  of  the 
angle  and  the  anterior  surface  of  the  iris  which  form  the  endothelium  of  the  anterior  chamber. 
The  cornea  is  richly  supplied  with  nerves,  particularly  in  its  most  superficial  layers. 

2.  The  dark,  middle,  or  vascular  coat  of  the  eye  [tunica  vasculosa  oculi]  i? 
formed  by  the  iris,  ciliary  body,  and  chorioid.  It  is  closely  applied  to  the  sclera, 
but  actually  joins  it  only  at  the  anterior  and  posterior  limits  of  their  course  to- 
gether, viz.,  at  the  scleral  sulcus,  and  around  the  optic  nerve  entrance.  It  is 
separated  from  the  sclera  between  these  two  points  by  a  narrow  slit-like  lymp- 
space  [spatium  perichorioideale].  In  front  of  the  sulcus,  the  middle  coat  is  sepa- 
rated from  the  outer  (i.  e.,  the  iris  from  the  cornea)  by  a  considerable  space  filled 
with  fluid,  caUed  the  anterior  aqueous  chamber.  The  vascular  coat  has  two  open- 
ings in  it;  a  larger  one  in  front,  the  pupil,  and  a  smaller  one  behind,  for  the  passage 
of  the  optic  nerve.  Its  structure  is  that  of  a  pigmented  connective  tissue,  support- 
ing numerous  blood-vessels  and  containing  many  nerves  and  three  deposits  of 
smooth  muscle-fibres. 

The  chorioid  [chorioidea]  forms  the  posterior  part  of  the  vascular  coat,  and  extends,  with 
slowly  diminishing  thickness,  forward  as  far  as  the  ora  serrata.  Its  outer  and  inner  surfaces 
are  botli  formed  by  non-vascular  layers;  that  covering  the  outer,  the  lamina  suprachorioidea, 
is  pigmented,  arranged  in  several  fine  loose  lamelte;  that  covering  the  inner  surface  is  a  thin, 
transparent,  homogeneous  membrane,  called  the  basal  lamina  of  the  chorioid.  The  inter- 
vening chorioidal  stroma  is  very  rich  in  blood-vessels,  which  are  of  largest  size  next  its  outer 
surface  constituting  the  lamina  vasculosa.  These  become  progressively  smaller  toward  the 
basal  lamina,  next  to  which  is  a  layer  of  closely  placed  wide  capillaries,  called  the  lamina  chorio- 
capillaris.  The  pigment  becomes  less  in  amount  as  we  pass  inward,  and  finally  ceases,  being 
absent  entirely  from  the  choriocapillary  and  basal  laminae. 

In  front  of  the  ora  serrata  the  vascular  coat  becomes  considerably  modified' 
and  the  part  reaching  from  the  ora  serrata  of  the  retina  to  the  iris  is  termed  the 
ciliary  region  of  the  tract,  or  ciliary  body  [corpus  ciliare].  Its  superficial  aspects 
have  been  already  briefly  described.  In  front,  the  cihary  processes,  about  seventy 
in  number,  project  toward  the  interior  of  the  eye,  forming  the  corona  ciliaris.  Be- 
hind this  part  lies  the  orbiculus  ciliaris,  whose  inner  surface  is  almost  smooth, 
faint  radial  folds  [plic£e  ciliares]  only  being  present,  three  or  four  of  which  join  each 
ciliary  process. 

The  more  minute  structure  of  this  ciliary  region  resembles  closely  that  of  the  chorioid,  except 
that  the  chorio-capillaris  is  no  longer  present,  that  the  stroma  is  thicker  and  richer  in  blood- 
vessels, and  that  a  muscular  element  (ciliary  muscle)  exists  between  the  vascular  layer  and  the 
lamina  suprachorioidea.  On  antero-posterior  section  the  ciliary  body  is  triangular;  the  shortest 
side  looks  forward,  and  from  about  its  middle  the  iris  arises;  the  two  long  sides  look  respectively 
inward  and  outward,  the  inner  having  the  ciliary  processes  upon  it,  while  the  outer  is  formed  by 
the  ciliary  muscle.  This  muscle  possesses  smooth  fibres  and  consists  of  an  outer  [fibrfe  me- 
ridionales  (Brueckei)]  and  an  inner  division  [fibra;  circulares  (Muelleri)].  The  meridional  fibres 
take  origin  from  the  outer  fibrous  coat  of  the  eye  at  the  sclero-corneal  junction  in  front,  and  pass- 
ing backward  to  join  the  outer  layers  of  the  orbiculus  ciliaris  and  chorioid;  the  circular  fibres 
are  situated  next  to  the  ciliary  processes.  The  entire  muscle  is  destitute  of  pigment,  and  there- 
fore is  recognisable  in  the  section  by  its  light  colour.  The  whole  thickening  of  the  vascular 
tunic  in  this  region,  muscle  and  folds  and  processes  together,  is  named  the  ciliary  body.  It 
includes  the  corona  ciliaris,  formed  of  the  ciliary  processes  and  folds,  and  the  orbicularis  ciliaris 
containing  the  ciliary  muscle. 

The  iris  projects  into  the  interior  of  the  front  half  of  the  eye  in  the  form  of  a 
circular  disc  perforated  in  the  middle.  The  appearance  of  its  anterior  surface  has 
already  been  described.  The  anterior  surface  is  covered  with  a  layer  of  endothe- 
lium except  at  the  crypts  near  the  cihary  border.  Thus  the  lymph  spaces  between 
the  stroma  cells  communicate  directly  with  the  anterior  chamber.     Its  posterior 


THE  RETINA 


1061 


surface  exhibits  numerous  radial  folds  running  from  the  ciliary  processes  to  near 
the  pupillary  margin;  a  thick  layer  of  black  pigment  covers  it  and  curls  around  this 
edge,  so  as  to  come  into  view  all  around  the  pupil  as  seen  from  in  front.  The 
ciliary  border  of  the  iris  is  continuous  with  the  front  of  the  ciliary  body,  and  there 
it  also  receives  fibres  from  the  ligamentum  pectinatum  iridis;  in  other  respects  the 
iris  is  quite  free,  merely  resting  on  the  front  of  the  lens-capsule  near  the  pupil. 

Its  stroma  [stroma  iridis]  is  spongy  in  character,  being  made  up  of  vessels  covered  by  a  thick 
adventitia,  running  from  the  periphery  to  the  pupillary  border,  with  interspaces  filled  by  branch- 
ing pigment  cells,  which  are  particularly  abundant  near  the  front  surface.  Deep  in  the  stroma, 
running  around  near  the  pupillary  border,  we  find  a  broad  flat  band  of  smooth  muscle-fibres, 
constituting  the  m.  sphincter  pupillse.  Immediately  behind  the  vascular  tissue  hes  a  thin 
membrane,  consisting  of  fine,  straight  fibres  running  radially  from  the  ciliary  border  to  the 
stroma  behind  the  sphincter.  The  nature  of  these  fibres  was  long  in  dispute,  but  they  are  now 
accepted  as  being  undoubtedly  smooth  muscular — and  comprise  the  m.  dilatator  pupillae. 


Fig.  804. — Diagrammatic  Horizontal  Section  of  Eyeball  and  Orbit. 
(After  Fuchs,  much  modified.) 
Periorbita  green;  muscle-fascia  red;  Tenon's  capsule  yellow. 
Lower  lacrimal  punctum 

Cornea  \   .     Caruncle 


Opening  of  Meibo: 


Anterior  chamber 

Iris 
Corona  ciliaris 

Orbiculus  cili 


Outer  check  ligament 

Fovea  centralis  retina 

Muscle-fascia 

Orbital  blood-vessel. 

Central  retinal  vessels 
optic  nerve 

External  rectus  muscle_ 


Inner  palpebral  ligament 


Nasal    process    of 

upper  jaw 
Anterior     limb    of 
inner      palpebral 
ligament 
Lacrimal  sac 
Posterior  limb  of  inner 
palpebral  ligament 
with  Horner's  muscle 
springing  from  it 
Lacrimal  bone 
Process  of  muscle-fas- 
cia to  under  surface  of 
conjunctiva 
Ora  serrata 
Tendon  of  insertion  of 

internal  rectus 
Inner  check  ligament 
Periorbita 
Orbital  plate  of  ethmoid 

bone 
Posterior  lamina  of 
muscle-fascia  lined 
by  Tenon's  capsule 


Internal  rectus  muscle 


The  m.  sphincter  pupiUos  and  the  ciliary  muscle  are  supplied  indirectly  by  the  oculomotor 
nerve  through  the  ciliary  ganglion.  The  dilatator  pupillae  is  supplied  by  sympathetic  fibres ,  which 
have  their  origin  from  the  cells  of  the  superior  cervical  ganghon.  Thence  they  ascend  in  the 
carotid  and  cavernous  plexuses,  and  join  the  ophthalmic  division  of  the  trigeminal  nerve,  passing 
to  the  eyeball  by  way  of  the  long  ciliary  nerves.  The  pre-ganglionic  sympathetic  fibres  leave  the 
spinal  cord  by  the  motor  roots  of  the  first  two  or  three  thoracic  nerves,  and  ascend  the  sympa- 
thetic trunlv  to  the  superior  cervical  ganglion  without  interruption. 

The  posterior  surface  of  the  iris  is  lined  by  pigment  already  mentioned,  consisting  of  two 
layers  of  pigmented  cells,  each  layer  representing  the  extension  forward  of  one  subdivision  of 
the  retina.  The  anterior  surface  of  the  iris  is  covered  by  a  delicate  epithehal  layer,  continuous 
with  the  ceils  of  the  posterior  elastic  lamina  of  the  cornea.  The  colour  of  the  iris  in 
different  individuals  depends  upon  the  amount  of  stromal  pigment. 

3.  The  retina. — The  inner  surface  of  the  vascular  coat  is  everywhere  lined  by  a 
layer  of  pigment  of  corresponding  extent,  which  usually  adheres  to  it  closely  on 
dissection. 


1062  SPECIAL  SENSE  ORGANS 

Developmentally  this  general  pigment  lining  is  quite  distinct  from  the  vascular  coat,  and 
represents  the  outer  wall  of  the  secondary  optic  vesicle  or  embryonic  retina;  it  consists  of  a  single 
layer  of  pigmented  epithelial  cells.  It  is  known  as  the  slratum  pigmenti.  The  amount  of 
pigment  is  greatest  anteriorly,  over  the  ciliary  region  and  iris,  and  there  is  again  a  small  local 
increase  posteriorly,  corresponding  to  the  macula  lutea  and  to  the  edge  of  the  optic  nerve  en- 
trance. In  the  ciliary  region  these  cells  have  recently  been  described  as  Uning  numerous  nar- 
row tubular  depressions  in  the  inner  part  of  the  vascular  tract,  and  they  are  said  to  have  here  a 
special  function,  viz.,  that  of  secreting  the  intraocular  fluid. 

From  the  manner  in  which  the  secondary  optic  vesicle,  or  optic  cup,  is  formed, 
its  two  walls  are  necessarily  continuous  in  front,  at  what  may  be  termed  the  lip  of 
the  cup;  we  have  just  observed  that  the  outer  wall  lines  the  vascular  coat  every- 
where and  corresponds  in  extent;  consequently,  the  lip  must  be  looked  for  at  the 
edge  of  the  pupil,  i.  e.,  at  the  termination  of  this  coat  anterorly.  The  inner  wall  of 
the  cup,  consequently,  reaches  from  the  lip,  or  pupillary  edge,  in  front  to  the  optic 
stalk  or  nerve  behind,  and  is  in  close  apposition  to  the  pigment-epithelium;  unlike 
the  outer,  however,  this  wall  is  represented  in  the  developed  eye  by  tissues  very 
dissimilar  in  structure  in  different  parts  of  its  extent.  Tracing  it  backward  from 
the  pupillary  edge,  we  find  that  over  the  whole  posterior  surface  of  the  iris  it  exists 
as  a  single  layer  of  pigmented  epithelium,  the  two  layers  of  the  cup  having  here 
produced  a  double  layer  of  pigment  cells.  At  the  root  of  the  iris  the  single  inner 
layer  of  cells  still  exists;  but  now  they  become  destitute  of  pigment,  and  this  con- 
dition obtains  over  the  entire  ciliary  region,  constituting  what  is  known  as  the  pars 
ciliaris  retinae.  At  the  l^ne  of  the  ora  serrata  the  tissue  derived  from  the  inner 
wall  abruptly  increases  in  thickness,  and  rapidly  acquires  that  complexity  of 
structure  characteristic  of  the  retina  proper,  which  extends  from  here  to  the  optic 
nerve  and  is  termed  the  pars  optica  retinas.  It  consists  of  several  layers — nerve- 
fibres,  nerve-cells,  and  nerve-epithelium — held  together  by  a  supporting  frame- 
work of  delicate  connective  tissue. 

The  nerve-epithelium  is  on  the  outer  surface,  immediately  applied  to  the  pigment-epithe- 
lium; at  the  posterior  pole  of  the  eye  a  small  spot  [fovea  centralis]  exists,  where  this  is  the  only 
retinal  layer  represented,  and  where  consequently  the  retina  is  extremely  thin.  The  nerve- 
fibres  run  on  the  inner  surface  of  the  retina  and  are  continuous  with  those  of  the  optic  nerve; 
they  constitute  the  only  retinal  layer  that  is  continued  into  the  intraocular  end  of  the  nerve. 
The  nerve-cells  are  found  between  these  surface  layers.  The  larger  blood-vessels  of  the  retina 
run  in  the  inner  layers,  and  none  encroach  on  the  layer  of  nerve-epithelium. 


Fig.  805. — The  Lens.     (Side  view;  enlarged.) 


Within  the  coats  mentioned,  the  interior  of  the  eyeball  is  fully  occupied  by  con- 
cents, which  are  divided  into  three  parts,  which  are  named  according  to  their 
consistence  and  anatomical  form.  They  are  all  transparent,  as  through  them  the 
light  has  to  pass  so  as  to  gain  the  retina.  Of  these,  the  only  one  that  is  sharply  and 
independently  outlined  is  the  lens,  which  is  situated  in  the  anterior  half  of  the  globe 
at  the  level  of  the  ciliary  processes,  where  it  is  suspended  between  the  other  con- 
tents, which  fill  respectively  the  space  in  front  of  it  and  the  space  behind  it.  The 
space  in  front  of  the  lens  called  the  aqueous  chamber;  that  behind  the  lens  is  the 
vitreous  chamber. 

The  lens  [lens  crystallina]  is  a  biconvex  disc,  with  its  surfaces  directed  ante- 
riorly and  posteriorly;  these  surfaces  meet  at  its  rounded-off  edge  or  equator 
[sequator  lentis]  which  is  near  (but  does  not  touch)  the  adjacent  ciliary  processes. 
The  posterior  is  considerably  more  convex  than  the  anterior  surface;  the  central 
part  of  each  surface  is  called  its  pole  [polus  anterior;  polus  posterior].  The  lens 
is  closely  encased  in  a  hyaline  elastic  capsule  [capsula  lentis]  thicker  over  the  an- 
terior than  over  the  posterior  surface.  Thus  enclosed,  it  is  held  in  position  in  the 
globe  by  a  suspensory  ligament,  attached  to  the  lens  capsule  near  the  equator  of 
the  eye,  and  swung  from  the  ciliary  region.     Posteriorly,  the  lens  rests  in  a  cup 


THE  LENS 


1063 


formed  by  the  front  part  of  the  vitreous,  while  its  anterior  capsule  is  in  contact 
with  the  aqueous  fluid  and  lies  close  against  the  back  of  the  pupillary  margin  of 
the  iris.  When  in  position  the  lens  measures  nine  millimetres  across,  and  about 
four  millimetres  between  its  poles. 

On  each  surface  a  series  of  fine,  sinuous,  grey  lines  can  be  seen  radiating  from  the  pole  to- 
ward the  equator,  called  respectively  the  anterior  and  posterior  stellate  figures.  The  liiies 
observable  on  the  posterior  are  always  so  placed  as  to  be  intermediate  with  those  on  the  anterior 
surface,  so  that  on  viewing  them  through  the  lens  they  occupy  a  position  corresponding  to  the 

Fig.  806. — Diagrammatic  Representation  op  the  Blood-vessels  of  the  Eyeball. 

(Parsons,  after  Leber.) 

Arteries  red;  veins  blue. 

s.p.,  Short  posterior  ciliary   arteries,     l.p.c,  Long  posterior  ciliary  artery,     a.c,  Anterior 

ciliary  vessels.     C  of  S.,  Canal  of  Schlemm.     c.a.i.ma.,  Circulus  arteriosus  iridis  rnajor.     v.v,. 

Venae  vorticosEe.     a.  conj.,  Anterior  conjunctival  vessels,     p.  conj.,  Posterior  conjunctival  vessels. 


intervals  between  the  lines  on  the  anterior  surface.  The  lens-capsule  is  comparatively  brittle, 
and  can  be  readily  cut  through  when  scraped  with  a  sharp-pointed  instrument;  on  doing  so  the 
divided  edges  curl  outward,  away  from  the  lenticular  substance.  When  removed  from  its 
capsule,  the  outer  portion  of  the  lens  is  found  to  be  soft  and  glutinous,  but  its  substance  gets 
progressively  firmer  as  we  approach  the  centre.  This  harder  central  part  is  known  as  the 
nucleus  [nucleus  lentis],  and  the  surrounding  softer  matter  as  cortex  [substantia  corticahsj. 
The  cortical  part  shows  a  tendency  to  peel  off  in  successive  layers.  It  consists  of  long  fibres, 
the  ends  of  which  meet  in  front  and  behind  at  the  anterior  and  posterior  stellate  figures. 


1064 


SPECIAL  SENSE  ORGANS 


Histologically  the  capsule  is  not  in  immediate  contact  with  the  cortex  over  the  front  surface 
of  the  lens,  a  single  layer  of  cells  intervening,  called  the  epithelium  lentis. 

The  zonula  ciliaris  or  suspensory  ligament  of  the  lens  is  formed  by  a  number  of 
fine  zonular  fibres  [fibrse  zonulares]  passing  from  the  ciliary  body.  They  are 
attached  to  the  lens-capsule  a  little  in  front  of  and  behind  the  equator,  and  the 
spaces  included  between  the  fibres  of  the  ligament  are  termed  the  zonular 
spaces  [spatia  zonularia].  A  continuous  space,  which  can.be  injected  after 
death,  round  the  margin  of  the  lens  is  known  as  the  canal  of  Petit.  It  is  probably 
an  artefact.  This  space  is  bridged  across  by  fine  intermediate  suspensory 
fibres,  and  is  occupied  by  fluid. 

The  vitreous  body  [corpus  vitreum]  is  a  transparent,  colourless,  jelly-like  mass, 
the  vitreous  humour,  enclosed  in  a  delicate,  clear,  structureless  membrane,  called 
the  hyaloid  membrane.  This  latter  is  closely  applied  to  the  back  of  the  posterior 
lens-capsule  and  of  the  suppensorj^  ligament,  and  to  the  inner  surface  of  the  pars 
ciliaris  retinse,  retina  proper,  and  optic  papilla.  Although  possessing  some  degree 
of  firmness,  the  vitreous  humour  contains  quite  98  per  cent,  of  water,  and  has  no 
definite  structure. 


Fig.  807. — Blood-vessels  of  the  Eyeball,  Lateral  View. 

Cornea 

Anterior  chamber 


Sclero-corneal  junction 


g  Anterior  ciliary  artery 


Long  posterior 
"*  ciliary  artery 


4 J'7~ """■■•  V.  Vorticosa 


Optic  nerve  ---- 


Arteria  centralis  retinse 


Membranes  have  been  described  in  it,  but  these  are  really  artificial  products.  In  certain 
situations  spaces  e.xist  in  the  vitreous  mass,  the  most  determinate  of  which  runs  in  the  form  of  a 
canal  from  the  optic  papilla  to  the  posterior  pole  of  the  lens,  corresponding  to  the  position  of 
the  foetal  hyaloid  artery  (hyaloid  canal  or  canalis  hyaloidea).  Other  very  fine  spaces  are  de- 
scribed running  circularly  in  the  peripheral  part  of  the  vitreous  concentric  with  its  outer  sur- 
face. Microscopically,  wandering  cells  are  found  in  the  vitreous,  which  often  here  assume 
pecuhar  forms  which  the  observer  can,  not  infrequently,  study  subjectively. 

The  aqueous  humour  is  a  clear,  watery  fluid,  occupying  the  space  between  the 
cornea  on  the  one  hand,  and  the  ciliary  body,  zonula  ciliaris,  and  lens  on  the  other. 
The  iris,  projecting  into  this  space,  has  both  its  surfaces  liathed  in  the  aqueous; 
but,  as  its  inner  part  rests  on  the  lens,  it  is  regarded  as  <liviiling  the  sjiace  into  two 
parts,  an  anterior  larger,  and  a  posterior  smaller,  aqueous  chamber  [camera  oculi 
anterior;  posterior],  which  communicate  freely  through  the  pupil. 

Ciliary  nerves  of  the  eyeball. — The  long  and  short  ciliary  nerves,  after  per- 
forating the  sclera  run  forward  between  it  and  the  chorioid  to  the  ciliary  region. 


LYMPHATIC  SYSTEM  OF  EYEBALL  1065 

where  they  form  a  plexus,  from  which  proceed  branches  for  the  ciUary  muscle,  the 
iris,  and  the  cornea. 

The  nerves  of  the  iris  enter  it  at  its  ciliary  border,  and  run  toward  its  pupillary  edge,  losing 
their  medullary  sheath  sooner  or  later,  and  supplying  especially  the  sphincter  muscle.  The 
corneal  nerves  form  an  annular  plexus  near  the  limbus,  from  which  a  few  twigs  proceed  to  the 
sclera  and  conjunctiva,  while  most  of  the  offsets  enter  and  run  radially  in  the  corneal  stroma, 
branching  and  anastomosing  so  as  to  form  a  plexus.  The  nerves  entering  the  cornea  are  about 
sixty  in  number,  each  containing  from  two  to  twelve  non-medullated  nerve-fibres. 

Blood-vessels  of  the  eyeball. — The  eyeball  receives  blood  from  two  sets  of 
vessels,  viz.,  the  retinal  and  the  ciliary  arteries,  as  described  in  the  section  on 
the  Blood-vascular  System. 

1.  The  arteria  centralis  retinae  either  comes  direct  from  the  ophthalmic  artery,  or  from  one 
of  its  branches  near  the  apex  of  the  orbit.  Entering  the  optic  nerve  twenty  miUimetres  or  less 
behind  the  globe,  it  runs  forward  in  its  axis  to  the  end  of  the  nerve-trunk,  and  then  divides  into 
branches  which  run  in  the  inner  layers  of  the  retina,  and  divide  dichotomously  as  they  radiate 
toward  the  equator.  The  smaller  branches  lie  more  deeply  in  the  retina,  but  none  penetrate  into 
the  nerve-epithelium,  so  that  the  fovea  centralis  is  non-vascular.  In  the  retina,  the  branches 
of  the  central  artery  do  not  communicate  with  any  other  arteries,  but  while  still  in  the  optic 
nerve  fine  communications  take  place  between  this  artery  and  neighbouring  vessels.  Thus 
(a)  minute  twigs  from  it,  which  help  to  nourish  the  axial  pai-t  of  the  nerve,  communicate  with 
those  running  in  the  septa  derived  from  the  pial  sheath.  Again,  as  the  nerve  passes  through 
the  sclera,  it  is  surrounded  by  a  vascular  ring  [circulus  vasculosus  n.  optici  (Halleri)],  formed 
of  fine  branches  derived  from  the  short  posterior  cihary  arteries;  fine  twigs  passing  inward 
from  this  ring  to  the  optic  nerve  join  the  vessels  of  the  pial  sheath,  and  (b)  an  indirect  communi- 
cation is  thus  brought  about  between  the  retinal  and  ciliary  vessels.  Finally,  as  the  nerve  passes 
through  the  chorioid,  there  is  (c)  a  direct  connection  between  these  two  sets  of  vessels,  the  cap- 
illary network  of  the  optic  nerve  being  here  continuous  with  the  chorio-capillaris.  Not  infre- 
quently, a  branch  from  a  short  posterior  ciliary  artery  pierces  the  optic  papilla,  and  then  courses 
over  the  adjoining  retina  (a  cilio-retinal  artery),  supplying  the  latter  in  part  in  place  of  the  cen- 
tral artery. 

The  branches  of  the  a.  centralis  retina  in  the  retina  are:  arteriola  temporalis  retinae  supe- 
rior, arteriola  temporalis  retinse  inferior,  arteriola  nasalis  retinae  superior,  arteriola  nasalis 
retinte  inferior,  arteriola  macularis  superior,  arteriola  macularis  inferior,  arteriola  retinae 
medialis. 

The  vena  centralis  retinae  returns  the  blood  of  the  corresponding  artery  and  has  branches 
corresponding  to  those  of  the  artery. 

2.  The  ciliary  system  of  blood-vessels  (see  Blood- Vascular  Sj'stem). — There  are  three  sets 
of  arteries  belonging  to  this  system,  all  derived  directly  or  indirectly  from  the  ophthalmic 
artery. 

(1)  Short  posterior  ciliary  arteries  twelve  to  twenty  in  number,  pierce  the  sclera  round  the 
optic  nerve  entrance,  and  are  distributed  in  the  chorioid.  Before  entering  the  eyeball,  small 
twigs  are  given  off  to  the  adjoining  sclera  and  to  the  dural  sheath  of  the  optic  nerve. 

(2)  Two  long  posterior  ciliary  arteries,  medial  and  lateral,  piercing  the  sclera  further  from 
the  nerve  than  the  short  ciharies,  run  horizontally  forward  between  the  sclera  and  chorioid, 
one  on  each  side  of  the  globe.  On  arriving  at  the  ciliary  body,  they  join  with  the  anterior  ciliary 
arteries,  forming  the  circulus  arteriosus  major,  which  sends  off  branches  to  the  ciliary  processes 
and  the  iris.  The  long  ciliaries  also  give  twigs  to  the  cihary  muscle,  and  small  recurrent  branches 
run  backward  to  anastomose  with  the  short  ciliary  arteries.  The  arteries  of  the  iris  run  radially 
toward  the  pupillary  border,  anastomosing  with  one  another  opposite  the  outer  border  of  the 
sphincter  and  forming  there  the  circulus  arteriosus  minor. 

(3)  The  anterior  ciliary  arteries  come  from  the  arteries  of  the  four  recti  muscles,  one  or 
two  from  each;  they  run  forward,  branching  as  they  go,  and  finally  pierce  the  sclera  near  the 
corneal  border.  Externally  to  the  globe  they  send  twigs  to  the  adjoining  sclera,  to  the  conjunc- 
tiva, and  to  the  border  of  the  cornea.  After  passing  through  the  sclera  the  arteries  enter  the 
ciliary  muscle,  where  they  end  in  twigs  to  the  muscle  and  to  the  circulus  arteriosus  major,  and 
in  recurrent  branches  to  the  chorioid. 

Veins. — The  venous  blood  from  almost  the  whole  middle  coat  (chorioid,  ciliary  processes 
and  iris,  and  part  of  the  ciliary  muscle)  ultimately  leaves  the  eyeball  by — (1)  the  venae  vorticosae, 
which  have  been  already  noticed  in  describing  an  antero-posterior  section  through  the  globe. 
One  large  vein  passes  backward  from  each  vortex,  piercing  the  sclera  obliquelj';  it  is  joined  by 
small  episcleral  veins  when  outside  the  globe. 

(2)  The  anterior  ciliary  veins  commence  by  the  junction  of  a  few  small  veins  of  the  ciliary 
muscle;  they  pass  outward  through  the  sclera  near  the  corneal  border,  receiving  blood  from  the 
veins  in  connection  with  the  sinus  venosus  of  the  sclera,  and  afterward  from  episcleral  and  con- 
junctival veins,  and  from  the  marginal  corneal  plexus.  Finally  they  join  the  veins  running 
in  the  recti  muscles. 

Lymphatic  system  of  the  eyeball. — Apart  from  those  in  the  conjunctiva  there 
are  no  Ij^mphatic  vessels  in  the  eyeball,  but  the  fluid  is  contained  in  spaces  of  vari- 
ous sizes.     These  are  usually  divided  into  an  anterior  and  a  posterior  set. 

1.  Anteriorly,  we  have  the  anterior  and  posterior  aqueous  chambers  (together 
composing  the  aqueous  chamber  of  the  ej^e),  which  communicate  freelj'  through  the 
pupil.     The  aqueous  humour  is  formed  in  the  posterior  of  these  chambers  by 


1066 


SPECIAL  SENSE  ORGANS 


transudation  from  the  vessels  of  the  ciliary  body  and  posterior  surface  of  the  iris 
(see  also  page  1076).  The  stream  passes  mainly  forward  through  the  pupil  into 
the  anterior  aqueous  chamber,  whence  it  escapes  slowly  by  passing  through  the 
spaces  of  the  angle  of  the  iris  into  the  venous  sinus  of  the  sclera,  and  thence  into 
the  anterior  ciliary  veins.  Part  of  the  lymph-stream  passes  from  the  posterior 
aqueous  chamber  backward  into  the  zonular  spaces,  out  of  which  fluid  can  pass 
into  the  lens  substance,  or  diffuse  itself  into  the  front  of  the  vitreous  body. 

In  the  cornea  the  lymph  travels  in  the  spaces  already  mentioned  as  existing 
between  the  fibre-bundles,  and  in  the  nerve-chaiinels  and  at  the  periphery  of  the 
cornea  it  flows  off  into  the  lymphatic  vessels  of  the  conjunctiva. 

In  the  iris  there  is  a  system  of  lymphatic  spaces  opening  anteriorly  into  the 
crypts  of  the  surface,  and  communicating  peripherally  with  the  spaces  of  the  angle 
of  the  iris. 


Fig.  808.- 


-Lymphatic  Spaces  of  the  Eyeball  (in  green). 
Anterior  chamber 


Filtration  angl 
Zonular  space 


V.  Ciliaris  anterior 

Sinus  venosus  sclerse 
Corpus  ciliare 


Spatium  interfasciale  (Tenoni) 


Supravaginal  space 
Intervaginal  space 


2.  Posteriorly,  we  have  (a)  the  hyaloid  canal,  between  the  posterior  pole  of  the 
lens  and  the  optic  nerve  entrance,  and  (6)  the  perivascular  canals  of  the  retina; 
the  lymph  from  both  of  these  situations  flows  into  the  spaces  of  the  optic  nerve, 
which  communicate  with  the  intervaginal  spaces  of  the  nerve,  and  thus  with  the 
great  intracranial  spaces.  Further,  between  chorioid  and  sclera  we  have  (c)  the 
perichorioidal  space,  which  gets  the  lymph  from  the  chorioid,  and  communicates 
with  the  interf ascial  space  (of  Tenon)  outside  the  sclera  by  perforations  correspond- 
ing to  the  vasa  vorticosa  and  posterior  cihary  arteries,  and  with  the  intervaginal 
spaces  around  the  optic  nerve  entrance.  The  interfascial  space  of  Tenon,  again, 
is  continuous  with  the  supravaginal  space  around  the  optic  nerve,  which  conamuni- 
cates  both  with  the  intervaginal  spaces,  with  the  lymph-spaces  of  the  orbit,  and 
directly  with  the  intracranial  spaces  at  the  apex  of  the  orbit. 

CAVITY  OF  THE  ORBIT 

General  Arrangement  of  its  Contents 

The  anterior  wider  half  of  the  cavity  is  mainly  occupied  by  the  eyeball,  which 

lies  almost  axially,  but  is  rather  nearer  to  the  upper  and  lateral  than  it  is  to  the 

other  walls.     The  posterior  two-thirds  of  the  globe  are  in  relation  with  soft  parts, 


MUSCLES  OF  THE  ORBIT 


1067 


chiefly  muscles  and  fat,  and  its  posterior  pole  is  situated  midway  between  the  base 
(or  opening)  and  the  apex  of  the  orbital  cavity.  The  anterior  third  of  the  eye- 
ball is  naturally  free,  except  for  a  thin  covering  of  the  conjunctiva,  and  projects 
slightly  beyond  the  opening  of  the  orbit,  the  degree  of  prominence  varying  with 
the  amount  of  orbital  fat,  and  also  to  some  extent  with  the  length  of  the  globe.  A 
straight  line  joining  the  medial  and  lateral  orbital  margins  usually  cuts  the  eye 
behind  the  cornea — laterally  behind  the  ora  serrata,  medially  further  forward,  at 
the  junction  of  the  ciliary  body  and  iris.  The  globe  is  held  in  position  by  numer- 
ous bands  of  connective  tissue.  The  lacrimal  gland  lies  under  the  lateral  part  of 
the  roof  of  the  orbit  anteriorly.  The  orbital  fat  occupies  the  spaces  between  the 
orbital  muscles,  and  is  in  greatest  amount  immediately  behind  the  eyeball;  it  also 
exists  between  the  muscles  and  the  orbital  walls  in  the  anterior  half  of  the  cavity. 
Six  muscles,  viz.,  the  four  recti,  the  superior  oblique,  and  the  levator  palpebrae 
superioris,  arise  at  the  apex  of  the  orbit,  and  diverge  as  they  pass  forward.  The 
recti  muscles — superior,  inferior,  lateral,  and  medial — rim  each  near  the  corre- 


FiQ.  809.- 


-Horizontal  Section  op  the  Oebital  Region,  Viewed  From  Above. 

Nasal  septum 

Nasal  fossa 
/  Infundibulum 

Ethmoidal  cells 
'  Medial  wall  of  orbit 

Palpebra  superior 
Cornea 

■^?*- Ciliary  processes 

1^' 


Lateral  v/all  of  orbit 


spending  orbital  wall,  but  the  superior  is  overlapped  in  part  by  the  levator  pal- 
pebrae. The  superior  oblique  lies  about  midway  between  the  superior  and  medial 
recti.  A  seventh  muscle,  the  inferior  oblique,  has  a  short  course  entirely  in  the 
anterior  part  of  the  orbit,  coming  from  its  medial  wall  and  passing  below  the  globe 
between  the  termination  of  the  inferior  rectus  and  the  orbital  floor.  The  optic 
nerve  with  its  sheaths  passes  from  the  optic  foramen  to  the  back  of  the  eyeball, 
surrounded  ^by  the  orbital  fat,  and  more  immediately  by  a  loose  connective  tis- 
sue. Among  the  contents  of  the  cavity  are  also  to  be  enumerated  many  vessels 
and  nerves  and  fibrous  tissue  septa,  while  its  walls  are  clothed  by  periosteum 
(periorbita) . 

The  muscles  of  the  orbit  are  seven  in  number,  of  which  six  are  ocular,  i.  e.,  are  inserted  into 
the  eyeball  and  rotate  it  in  different  directions.  These  ocular  muscles  are  arranged  in  opponent 
pairs,  viz.,  superior  and  inferior  recti,  superior  and  inferior  obliques,  lateral  and  medial  recti. 
With  the  exception  of  the  short  inferior  oblique,  they  all  arise  from  the  back  of  the  orbit  along 
with  the  seventh  orbital  muscle,  the  levator  palpebrse  superioris.  All  these  long  muscles  take 
their  origin  from  the  periosteum  in  the  vicinity  of  the  optic  foramen.  The  four  recti  muscles 
arise  from  a  fibrous  ring,  the  annulus  tendineus  communis,  which  arches  close  over  the  upper 


1068 


SPECIAL  SENSE  ORGANS 


and  medial  edge  of  the  foramen,  and  extends  down  and  out  so  as  to  embrace  part  of  the  opening 
of  the  superior  orbital  fissure.  Their  origins  may  be  said  at  first  to  form  a  short,  common, 
tendinous  tube,  from  which  the  individual  muscles  soon  separate,  taking  the  positions  indicated 
by  their  respective  names.  The  lateral  rectus  has  two  origins  from  bone,  one  on  either  side  of 
the  superior  orbital  fissure.  But  in  the  fresh  state  the  fissure  is  here  bridged  across  by  fibrous 
tissue,  from  which  this  rectus  also  springs,  so  that  its  origin  is  in  reality  continuous.  The  part 
of  this  fibrous  ring  nearest  the  foramen  (corresponding  to  the  origins  of  the  superior  and  medial 
recti)  is  closely  connected  with  the  outer  sheath  of  the  optic  nerve.  The  remaining  two  long 
muscles  arise  just  outside  the  upper  and  medial  part  of  the  above-mentioned  ring,  and  are  often 
partially  united;  the  levator  palpebrEB  tendon  is  in  close  relation  to  the  origin  of  the  superior 
rectus,  while  the  superior  oblique  arises  from  the  periosteum  of  the  body  of  the  sphenoid  bone 
one  or  two  millimetres  in  front  of  the  origin  of  the  medial  rectus. 

The  four  recti  muscles  lie  rather  close  to  the  coi-responding  orbital  walls  for  the  first  half  of 
their  course,  the  superior  rectus,  however,  being  overlapped  in  part  by  the  levator  palpebrse; 
they  then  tm-n  toward  the  eyeball,  running  obliquely  through  the  orbital  fat,  and  are  finally 
inserted  by  broad,  thin  tendons  into  the  sclera  in  front  of  the  equator.  From  their  respective 
positions  in  the  orbit,  the  axis  of  this  cone  of  muscles  is  obHque  to  the  antero-posterior  axis  of 
the  eyeball.     The  thickest  of  these  muscles  is  the  medial  rectus,  next  the  lateral,  then  the  infe- 


FiG.  810. — Dissection  op  the  Left  Orbit  fkom  in  Front. 
Levator  palpebrse  superioris 
Sclera 


Tendon  of  superior  oblique 


I  Superior  rectus 


Lacrimal  gland 


•y  -^'  Lateral  rectus 


~       Inferior  rectus 
-  Orbital  adipose 


Medial  rectus 


Inferior  oblique 


rior,  and  the  superior  rectus  is  the  thinnest.  As  regards  length,  the  muscular  belly  of  the  superior 
rectus  has  the  longest  course,  and  the  others  diminish  in  the  order — medial,  lateral,  and  inferior 
rectus.  The  lateral  rectus  is  supplied  by  the  abduoens  nerve.  The  other  three  recti  muscles 
are  aU  supplied  by  the  oculomotor  nerve. 

The  levator  palpebras  superioris  courses  along  the  roof  of  the  orbit  close  to  the  periosteum 
for  the  greater  part  of  its  course,  partially  overlapping  the  superior  rectus;  it  finally  descends 
through  the  orbital  fat,  and  widens  out  to  be  inserted  into  the  root  of  the  upper  hd.  It  may  be 
briefly  described  as  being  inserted  in  two  distinct  layers  separated  by  a  horizontal  interval. 
The  upper  or  anterior  layer  of  insertion  is  fibrous,  and  passes  in  front  of  the  tarsus)  where  it  comes 
into  relation  with  fibres  of  the  orbicularis.  The  lower  layer  consists  of  smooth  muscle  (Miiller's 
superior  tarsal  muscle),  and  is  inserted  along  the  upper  border  of  the  tarsus.  The  levator  has 
also,  connections  with  the  sheath  of  the  superior  rectus.  These  different  insertions  of  the  muscle 
will  be  referred  to  later  along  with  the  description  of  the  orbital  fasciae  and  of  the  upper  eyelid. 
It  gets  its  nerve  supply  from  the  oculomotor  nerve,  but  the  smooth  muscle  developed  in  its  lower 
layer  of  insertion  is  supplied  by  the  sympathetic  nervous  system.  As  its  name  expresses,  its 
action  is  to  raise  the  upper  lid  and  to  support  it  while  the  ej'e  is  open. 

The  superior  oblique  runs  forward  close  to  the  medial  part  of  the  orbital  roof  until  it  reaches 
the  fovea  trochlearis  near  the  medial  angular  process,  where  it  becomes  tendinous  and  passes 
through  a  fibro-cartilaginous  pulley  attached  to  the  fovea  just  named.  On  passing  through 
this  pulley,  or  trochlea,  the  tendon  bends  at  an  angle  of  50°,  running  posteriorly  and  laterally 
under  the  superior  rectus  to  its  insertion  into  the  sclera.     It  is  supplied  by  the  trochlear  nerve. 

The  inferior  oblique  arises  from  the  front  of  the  orbit,  about  the  junction  of  its  medial  and 
inferior  walls,  just  lateral  to  the  lower  end  of  the  lacrimal  gi-oove.  It  runs,  in  a  sloping  direction, 
laterally  and  posteriorly,  lying  at  first  between  the  inferior  rectus  and  the  orbital  floor,  then 
between  the  lateral  rectus  and  the  globe;  finally  it  ascends  slightly,  to  be  inserted  by  a  short 


MUSCLES  OF  THE  ORBIT 


1069 


tendon  into  the  sclera  at  the  back  of  the  eye.  Its  nervous  supply  is  derived  from  the  oculomotor 
nerve.  The  precise  manner  of  insertion  of  the  different  ocular  muscles  has  been  described 
above  (p.  1056).     For  muscles  of  the  eyehds  and  eyebrows,  see  pp.  1077  and  1078. 

Action  of  the  ocular  muscles. — While  rotating  the  globe  so  that  the  cornea  is  turned  in 
different  directions,  the  ocular  muscles  do  not  alter  the  position  of  the  eyeball  in  the  orbit  either 


Fig.  811. — Section  through  Contents  of  Right  Orbit  8-11  mm.  behind  the   Eyeball, 
VIEWED  FROM  Behind.     (After  Lange.) 


Supraorbital  nerve 

Supraorbital  artery 

Levator  palpeb: 

supenons  muscle 


Lacrimal   nerve 


Optic  nerve 

Ciliary  artery 
Central  retinal        v"'./ 
artery  ^^-^ 

Ciliary  artery 


j — Ciliary  artery 


Oculomotor  nerve 
(branch  to  inferior 
oblique  muscle) 


Fig.  812. — Diagram  Representing  the  Origin  of  the  Muscles  at  the  Apex 
OF  the  Right  Orbit. 

Lacrimal     Frontal    Trochlear    Levator  palpebree 
nerve  superioris 


Superior  oblique 


-- — 1^    Optic  nerve  and 

ophthalmic  artery 


Medial  rectus 


Lateral  Naso-  Abducens 
rectus    ciliary 
nerve 


Inferior  rectus 


Oculomotor  nerve 


laterally,  vertically,  or  antero-post^riorly.  In  speaking,  therefore,  of  the  eye  being  moved 
upward  or  laterally^  etc.,  it  is  the  altered  position  of  the  cornea  or  front  of  the  eye  that  we  mean 
to  express;  it  is  manifest  that,  if  the  cornea  moves  up,  the  back  of  the  eyeball  must  simultane- 
ously be  depressed.,  and  similarly  with  other  movements.     All  the  movements  of  the  globe  take 


1070 


SPECIAL  SENSE  ORGANS 


place  by  rotation,  on  axes  passing  through  the  centre.  Though  the  possible  axes  are  numerous 
in  combined  muscular  action,  there  are  three  principal  axes  of  rotation  of  the  eyeball,  and  in 
reference  to  these  the  action  of  individual  muscles  must  be  described.  Two  of  these  axes  are 
horizontal  and  one  vertical;  they  all  pass  through  the  centre  of  rotation  at  right  angles  to  one 
another.  By  rotation  of  the  eye  on  its  vertical  axis  the  cornea  is  moved  laterally  (toward  the 
temple)  and  medially  (toward  the  nose) :  movements  called  respectively  abduction  and  adduc- 

FiG.  813. — Dissection  of  the  Muscles  of  the  Right  Orbit,  Lateral  View, 

Frontal  sinus 

N.  frontalis 

Frontal  sinus 

Superior  oblique        \ 

Levator  palpebrae  superioris 
Rectus  superior      ^ 

Rectus  medialis        \  ^ 

Optic  nerve 
Annulus  tendineus  com-    > 
mums  (Zinni)  ^ 

Lesser  wing  of  sphenoid     \ 


Sheath  of  optic  nerve 


Rectus  inferior 


Lateral  rectus 
Inferior  oblique 


tion.  In  upward  and  downward  movements  of  the  cornea  the  eye  rotates  on  its  horizontal 
equatorial  axis.  The  other  principal  axis  of  rotation  is  the  sagittal,  which  we  have  previously 
described  as  corresponding  to  the  line  joining  the  anterior  and  posterior  poles  of  the  globe 
(page  1055).  In  rotation  of  the  eye  on  its  sagittal  axis,  therefore,  the  cornea  may  be  said  to 
move  as  a  wheel  on  its  axle,  for  its  centre  now  corresponds  to  one  end  of  the  axis;  in  other  words, 
this  is  a  rotation  of  the  cornea.  Such  movements  may,  consequently,  be  expressed  with  refer- 
ence to  their  effect  on  an  imaginary  spoke  of  the  corneal  wheel — e.  g.,  one- running  vertically 

Fig.  814. — Dissection  of  the  Mttsclbs  of  the  Left  Okbit,  From  Above. 


Lateral  rectus 
Inferior  oblique     J 


Rectus  medialis 


Rectus  superior 
,     Tendon  of  superior  oblique  ' 
!       ;     Trochlea  of   superior  oblique 

Levator  palpebrae  superioris 


Levator  palpebrae  superioris 
Periorbita 


upward  from  the  corneal  centre.     Thus  we  may  say  'rotation  of  the  cornea  laterally'  when  this 
part  of  the  wheel  moves  toward  the  lateral  angle,  or  'medially'  when  toward  the  nose. 

The  only  two  muscles  that  rotate  the  eyeball  merely  on  one  axis  are  the  lateral  rectus  and 
the  medial  rectus ;  the  former  abducting,  and  the  latter  adducting,  the  cornea.  The  action  of 
the  superior  and  inferior  recti  is  complicated  by  the  obliquity  of  the  axes  of  muscles  and  globe 
previously  mentioned. 


ORBITAL  FASCIM 


1071 


The  chief  action  of  the  superior  rectus  is  to  draw  the  cornea  upward,  but  at  the  same  time 
it  adducts  and  rotates  the  cornea  medially. 

The  inferior  rectus  mainly  draws  the  cornea  downward,  also  adducting  it  and  rotating  it 
laterally. 

The  chief  action  of  the  superior  oblique  is  to  rotate  the  cornea  medially,  also  drawing  it 
downward  and  slightly  abducting  it. 

The  inferior  oblique  mainly  rotates  the  cornea  laterally,  also  drawing  it  upward  and  slightly 
abducting  it. 

The  fasciae  of  the  orbit  [fascise  orbitales]. — The  orbital  contents  are  bound  to- 
gether and  supported  by  fibrous  tissues,  which  are  connected  with  each  other,  but 
which  may  conveniently  be  regarded  as  belonging  to  tliree  systems.  These  are : — • 
(1)  Those  lining  the  bony  walls;  (2)  those  ensheathing  the  muscles;  and  (3)  the 
tissue  which  partially  encapsules  the  eyeball. 

1.  The  orbital  periosteum  [periorbita],  is  closely  applied  to  the  bones  forming 
the  walls  of  the  cavity,  but  may  be  stripped  off  with  comparative  ease.  It  pre- 
sents openings  for  the  passage  of  vessels  and  nerves  entering  and  leaving  the  orbit. 


Periorbita 


Fig.  815. — Diagram  Representing  the  Orbital  Fasciss  in  Vertical  Section. 
black;  muscular  sheaths  violet;  Tenon's  capsule  green. 
Tbicularis  oculi 

'  Periorbita  and  septum  orbitale 

'  Anterior  insertion  of  levator  palpebrae 

Process  from  periorbita  to  slieatli  of  lacrimal  gland 
Sheath  of  levator  palpebrse 

Periorbita 

.  levator  palpebrse  superioris 
.  rectus  superior 

Space  filled  by  orbital  fat 
Fascial  sheath  of  optic 
ic  nerve 


M.  rectus  inferior 


M.  obliquus  inferior 


Posteriorly  this  tissue  is  very  firm,  being  joined  by  processes  of  the  dura  mater  at  the  optic 
foramen  and  superior  orbital  fissure;  at  the  optic  foramen  it  is  also  connected  with  the  dm'a 
sheath  of  the  optic  nerve.  As  it  covers  the  inferior  orbital  (spheno-maxillary)  fissure  its  fibres 
are  interwoven  with  smooth  muscle,  forming  the  orbital  muscle  of  MtiUer.  From  its  inner  sur- 
face processes  run  into  the  orbital  cavity,  separating  the  fat  lobules.  One  important  process 
comes  from  the  periorbita  about  midway  along  the  roof  of  the  orbit,  runs  forward  to  the  back  of 
the  upper  division  of  the  lacrimal  gland,  and  there  spUts,  helping  to  form  the  gland-capsule: 
this  capsule  is  joined  at  its  medial  border  by  other  periorbital  bands  coming  off  near  the  upper 
orbital  rim,  and  forming  the  suspensory  ligament  of  the  gland.  On  the  side  of  the  orbit  the  peri- 
orbita sends  fibrous  processes  to  the  trochlea  of  the  superior  obUque,  which  keep  it  in  position. 
On  arriving  at  the  lacrimal  groove  the  periorbita  divides  into  two  layers,  a  thin  posterior  one 
continuing  to  line  the  bone  forming  the  floor  of  the  groove,  whilst  the  thicker  anterior  layer 
bridges  over  the  groove  and  the  sac  which  lies  in  it,  forming  the  limbs  of  the  medial  palpebral 
ligament  (p.  1052). 

Quite  anteriorly,  at  the  rim  of  the  orbit,  the  periorbita  sends  off  a  membranous  process  which 
aids  in  forming  the  fibrous  tissue  of  the  eyelids  (orbito -tarsal  ligament,  or  palpebral  fascia), 
and  is  itself  continuous  with  the  periosteum  of  the  bones  outside  the  orbital  margin. 

2.  The  orbital  muscles  are  connected  by  a  common  fascia,  which  splits  at  their 
borders  and  furnishes  a  sheath  to  each.  Processes  of  this  fascia  give  membranous 
investments  for  the  vessels  and  nerves  (including  the  optic  nerve),  splitting  simi- 


1072 


SPECIAL  SENSE  ORGANS 


larly  to  enclose  them;  these  membranous  processes  also  assist  in  separating  the 
fat  lobules. 

Posteriorly,  this  fascia  is  thin  and  loose,  and  blends  with  the  periorbita  at  the  origin  of  the 
muscles.  Anteriorly,  it  becomes  thicker  and  firmer,  accompanies  the  muscles  to  near  the  equa- 
tor of  the  eyeball,  and  there  divides  into  two  laminte,  an  anterior  and  a  posterior;  the  former 
continues  a  forward  course,  forming  a  complete  funnel-shaped  investment  all  around,  passing 
ultimately  to  the  eyelids  and  orbital  margin — whilst  the  latter  turns  backward,  covering  the 
hinder  third  of  the  globe. 

The  anterior  lamina  is  a  well-marked  membrane  everywhere,  but  in  certain  situations  it 
presents  special  bands  of  thickening,  corresponding  to  the  direct  continuation  forward  of  the 
sheath  of  each  rectus  muscle.  Above  and  below,  this  lamina  spreads  out  in  the  form  of  two 
large  membranes,  which  are  finally  applied  to  the  deep  surface  of  the  palpebral  fascia;  the  lower 
membrane  constitutes  what  has  been  described  as  the  suspensory  hgament  of  the  eyeball.' 
The  upper  membrane  requires  a  fuller  description,  as  its  distribution  is  modified  by  the  presence 
of  the  levator  palpebrae  muscle. 

Fig.  816. — Hokizontal  Section  Through  Left  Orbit,  viewed  prom  above. 
(After  von  Gerlach.     To  show  check  ligaments,  etc.) 


Conjunctival  fornix 
Lacrimal  gland 

Palpebral  raphe 
Lateral  check  ligament- 
Lateral  orbital  wall 


Lateral  rectus 
Orbital  fat 


Space    occupied    by 
subconjunctival  tis- 
^_^_^  sue,  and  by  fascia 
YhH         bulbi  further  back 

' Upper  part  of  Horner's 

muscle 
Palpebral  fascia 

Medial  check  ligament 


Medial  wall  of  orbit 


Medial  rectus 


Ethmoidal  cells 


The  upper  part  of  the  sheath  of  the  superior  rectus  (along  with  the  adjoining  membrane  on 
each  side  of  it)  passes  to  the  deep  surface  of  the  levator,  to  which  it  closely  adheres,  and  com- 
pletely ensheaths  this  tendon  by  extending  round  its  borders  to  its  upper  surface.  The  lower 
part  of  this  levator  sheath  is  applied  to  the  inferior  surface  of  the  deeper  of  the  two  divisions  of 
the  levator  muscle,  superior  tarsal  muscle,  and  is  attached  to  the  upper  border  of  the  tarsus  of 
the  upper  lid,  reaching  on  each  side  to  the  lateral  and  medial  angles  of  the  orbit.  The  upper 
part  of  the  sheath  of  the  superior  tarsal  muscle  reaches  to  the  middle  of  the  palpebral  fascia,  and 
is  mainly  continued  forward  between  the  muscle  and  the  fascia  to  the  anterior  surface  of  the 
tarsus. 

The  lower  membrane  (suspensory  ligament  of  the  eyeball),  joined  by  the  sheath  of  the 
inferior  rectus,  reaches  forward  to  the  attached  (posterior)  border  of  the  tarsus  of  the  lower  lid, 
where  it  is  mainly  attached,  while  a  part  of  it  extends  to  the  lower  palpebral  fascia. 

To  understand  the  special  bands  of  the  anterior  lamina  mentioned  above,  we  must  follow 
the  sheath  of  each  rectus  muscle  forward,  when  we  find  that,  while  it  is  rather  loosely  applied 
to  the  muscular  belly  in  its  posterior  two-thirds,  it  then  suddenly  becomes  thicker,  and  is 
firmly  attached  to  the  muscle  for  some  distance  before  finally  leaving  it,  and  is  thereafter  often 
accompanied  by  some  muscle-fibres.  The  best  developed  of  these  bands,  the  lateral  check 
ligament,  passes  anteriorly  and  laterally  to  the  lateral  angle  of  the  orbit,  helping  to  support  the 
lacrimal  gland  on  its  way,  and  is  inserted  near  the  orbital  edge  immediately  behind  the 
lateral  palpebral  raphe.  The  medial  band,  or  medial  check  ligament,  is  larger  than  the  lateral, 
but  not  so  thick;  it  passes  forward  and  medially  to  be  inserted  into  the  upper  part  of  the  lacrimal 
crest  and  just  behind  it.     These  two  bands,  lateral  and  medial,  come  from  the  sheaths  of  the 


THE  OPTIC  NERVE  1073 

corresponding  recti  muscles.  From  the  sheath  of  the  superior  rectus  come  two  thin  bands,  one 
from  each  border.  The  medial  joins  the  sheath  of  the  tendon  of  the  superior  obhque;  the 
lateral  goes  to  the  lateral  angle  of  the  orbit,  assisting  in  the  support  of  part  of  the  lacrimal 
gland.  The  sheath  of  the  inferior  rectus  is  thickened  in  front,  and,  on  leaving  the  muscle,  goes 
to  the  middle  of  the  inferior  oblique,  splitting  to  enclose  it;  it  then  passes  to  be  inserted  into  the 
lower  medial  angle  of  the  orbit  close  behind  its  margin,  about  midway  between  the  medial  check 
ligament  and  the  orbital  attachment  of  the  inferior  obhque. 

3.  In  addition  to  its  partial  investment  by  the  muscle-fascia,  the  eyeball  has  a 
special  membrane  enclosing  its  hinder  two-thirds,  the  fascia  bulbi  ("Tenon's 
capsule"). 

This  is  a  thin,  transparent  tissue,  situated  immediately  internal  to  the  posterior  lamina  of 
the  muscle-fascia.  It  follows  the  curve  of  the  solera  from  the  insertion  of  the  recti  to  about  3 
mm.  from  the  optic  nerve  entrance.  There  it  leaves  the  eyeball  and  blends  with  the  posterior 
lamina  of  the  muscle-fascia;  the  combined  membrane  may  be  traced  backward,  enveloping  the 
optic  nerve-sheath  loosely,  approaching  it  as  it  nears  the  optic  foramen,  but  never  actually 
joining  it.  The  interval  between  it  and  the  nerve-sheath  is  called  the  supravaginal  lymph-space. 
The  fascia  bulbi  first  comes  into  relation  with  the  muscles  at  the  point  where  they  are  left  by 
their  proper  sheaths;  it  there  invests  their  tendons,  forms  a  small  serous  bursa  on  the  anterior 
surface  of  each,  and  adheres  to  the  sclera  along  a  line  running  around  the  globe,  just  anterior 
to  the  insertions  of  the  four -recti  muscles.  Between  this  line  and  the  corneal  border,  the  con- 
junctiva is  separated  from  the  sclei'a  by  the  subconjunctival  tissue,  strengthened  by  a  fine 
expansion  of  the  muscle-fascia. 

The  inner  surface  of  the  fascia  is  smooth,  and  is  onlj^  connected  with  the  sclera 
by  a  loose,  wide-meshed  areolar  tissue.  This  interval  between  the  sclera  and 
fascia,  known  as  the  interfascial  (Tenon's)  space,  is  a  Ij^mph  cavitJ^  and  permits 
free  movements  of  the  eyeball  within  the  capsule. 

Relation  of  the  Fascia  Bulbi  to  the  Oblique  Muscles. — The  fascia  surrounds  the  posterior  third 
of  the  inferior  oblique  and  its  tendon,  running  along  its  ocular  sm'face  till  it  meets  the  fascial 
band  coming  from  the  inferior  rectus  (see  above),  and  forming  a  serous  bursa  on  the  superficial 
surface  of  the  oblique  near  its  insertion.  The  tendon  of  the  superior  oblique  for  about  its  last 
five  milhmetres  is  invested  solely  by  the  fascia  bulbi;  in  front  of  this,  as  far  as  the  trochlea,  the 
tendon  lies  in  a  membranous  tube  derived  from  the  muscle  fascia,  the  inner  lining  of  which  is 
smooth,  and  may  be  considered  as  a  prolongation  of  the  fascia  bulbi. 

The  Optic  Nerve 

The  part  of  this  nerve  with  which  we  have  here  to  do  lies  within  the  orbit,  ex- 
tending from  the  optic  foramen  to  the  eyeball  (fig.  813).  The  length  of  this 
portion  of  the  nerve  is  from  20  to  30  mm.  and  its  diameter  about  5  mm.  Its  course 
is  somewhat  S-shaped;  thus,  on  entering  the  orbit,  it  describes  a  curve,  with  its 
convexity  down  and  laterally,  and  then  a  second  slighter  curve,  convex  medially. 
Finally,  it  runs  straight  forward  to  the  globe,  which  it  enters  3  to  4  mm.  to  the 
medial  side  of  its  posterior  pole. 

In  its  passage  through  the  optic  foramen  the  nerve  is  surrounded  by  a  prolongation  of  the 
meninges.  The  dura  mater  splits  at  the  optic  foramen,  part  of  it  joining  the  periorbita,  while 
the  remainder  continues  to  surround  the  nerve  loosely  as  its  outer  or  dural  sheath.  The  nerve 
is  closely  enveloped  by  a  vascular  covering  derived  from  the  pia  mater,  named  accordingly  the 
pial  sheath.  The  space  between  these  two  sheaths  is  subdivided  by  a  fine  prolongation  of  the 
arachnoid  (the  arachnoidal  sheath)  into  two  parts,  termed  the  intervaginal  spaces  [spatia  inter- 
vaginalia],  viz.,  an  outer,  narrow,  subdural,  and  an  inner,  wider,  subarachnoid  space,  communi- 
cating with  the  coiTesponding  intracranial  spaces.  The  arachnoidal  sheath  is  connected  with 
the  sheath  on  each  side  of  it  by  numerous  fine  processes  which  bridge  across  the  intervening 
spaces.  The  pial  sheath  sends  processes  inward,  which  form  a  framework  separating  the  bundles 
of  nerve-fibres;  between  the  enclosed  nerve-fibres  and  each  mesh  of  this  framework  there  is  a 
narrow  interval  occupied  by  lymph.  The  nerve-fibres  are  medullated,  but  have  no  primitive 
sheath.  About  fifteen  or  twenty  millimetres  behind  the  globe  the  central  vessels  enter,  piercing 
obliquely  the  lower  lateral  quadrant  of  the  nerve,  and  then  run  forward  in  its  axis.  They  are 
accompanied  throughout  by  a  special  process  of  the  pial  sheath,  which  forms  a  fibrous  cord  in 
the  centre  of  the  nerve. 

On  reaching  the  eyeball,  the  dural  sheath  is  joined  by  the  arachnoid,  and  turns  away  from 
the  nerve  to  be  continued  into  the  outer  two-thirds  of  the  sclera.  Similarly  the  pial  sheath  also 
here  leaves  the  nerve,  its  greater  part  running  into  the  inner  third  of  the  sclera,  while  a  few  of  its 
fibres  join  the  chorioid;  the  intervaginal  spaces  consequently  end  abruptlj'  in  the  sclera  around 
the  nerve-entrance.  In  this  locality  the  connective-tissue  framework  of  the  nerve  becomes 
thicker  and  closer  in  its  meshwork,  and  has  been  already  alluded  to  as  the  lamina  cribrosa 
sclerae.  It  is  formed  by  processes  passing  out  from  the  central  fibrous  cord  at  its  termination 
and  by  processes  passing  inward  from  the  pial  sheath,  sclera,  and  chorioid.  It  does  not  pass 
straight  across  the  nerve,  but  follows  the  curve  of  the  surrounding  sclera,  being  therefore  slightly 
convex  backward.     The  nerve-trunk  here  quickly  becomes  reduced  to  one-half  its  former  diam- 


1074 


SPECIAL  SENSE  ORGANS 


eter,  the  fibres  losing  their  medullary  sheath,  and  being  continued  henceforward  as  mere  axis- 
cylinders.  Apart  from  the  consequent  loss  of  bulk,  this  histological  change  may  be  readUy 
recognised  macroscopicaUy  in  a  longitudinal  section  of  the  nerve,  its  aspect  here  changing 
from  opaque  white  to  semi-translucent  grey.  The  part  of  the  nerve  within  the  lamina 
cribrosa  has  aheady  been  noted  in  the  ophthalinoscopic  examination  of  the  Uving  eye  (p.  1055). 
The  optic  nerve  is  mainly  nourished  by  fine  vessels  derived  from  those  of  the  pial  sheath, 
which  run  into  the  substance  of  the  nerve  in  the  processes  above  mentioned.  In  front  of  the 
entrance  of  the  central  retinal  artery  this  vessel  aids  to  some  extent  in  the  blood-supply  of  the 
axial  part  of  the  nerve. 


Fig.  817. — Tkansvehse  Section  through  Optic  Nerve,  showing  the  Relations  of  its 
Sheaths  and  Connective-tissue  Framework. 


Dural  sheath 
Arachnoidal  sheath 


Suharachnoid  space 


Subdural  space  -; 


Central  retinal  artery 
Central  retinal  vein 


Connective-tissue  frame- 
work, with  meshes  in 
which  the  nerve-fibre 
bundles  lie 


Fig.  818. — ^Longitudinal  Section  through  Termination  of  Optic  Nerve. 

"Pit  in  optic  papilla 
Chorioid ~;;^^5!i3?i,-__r""^^^^S?r^^S>k  /a0^^-^    s.— ^m, ""^^i Retina 


Short  posterior^ 
ciUary  artery 


Central  retinal 

vessels 
Dural  sheath 


Arachnoidal  sheath 


Optic  nerve  with 
connective-tiss 
framework 


Pigment  epithelium 
Suprachorioidal 

space 
Lamina  cribrosa 

Sclera 


The  Blood-vessels  and  Nerves  of  the  Orbit 

As  these  structures  will  be  more  particularly  described  in  other  sections  of  this 
work,  a  very  short  general  account  will  suffice  here. 

Arteries. — The  main  blood-supply  is  afforded  by  the  ophthalmic  artery,  a  branch  of  the 
internal  carotid,  which  gains  the  orbit  through  the  optic  foramen,  where  it  lies  below  and  lateral 
to  the  nerve.  On  entering  the  orbit  it  ascends,  and  passes  obliquely  over  the  optic  nerve  to 
the  medial  wall  of  the  orbit;  in  this  early  part  of  its  course  it  gives  off  most  of  its  branches,  which 
vary  much  in  their  manner  of  origin  and  also  in  their  course.  The  arteries  of  the  orbit  are 
remarkable  for  their  tortuous  course,  for  their  delicate  walls,  and  for  their  loose  attachment  to 
the  surrounding  tissues.  The  ophthalmic  artery  gives  off  special  branches  in  the  orbit  to  the 
lacrimal  gland,  the  muscles,  the  retina  (through  the  optic  nerve),  and  the  eyeball,  as  well  as 
to  the  meninges,  the  ethmoidal  cells,  and  the  nasal  mucous  membrane.  Twigs  from  all  the 
different  branches  go  to  supply  the  fat,  fasciae,  and  ordinary  nerves  of  the  orbit.  Branches 
which  leave  the  orbit  anteriorly  ramify  on  the  forehead  and  nose,  and  also  go  to  the  supply  of 


ORBITAL  VESSELS  AND  NERVES 


1075 


the  eyelids  and  the  tear-passages.  The  ophthalmic  artery  has  many  anastomoses  with  branches 
of  the  external  carotid.  The  contents  of  the  orbit  are  also  supplied  in  part  by  the  Infraorbital 
artery,  a  branch  of  the  internal  maxillary;  in  particular  this  artery  supplies  part  of  the  inferior 
rectus  and  inferior  oblique  muscles  in  the  cavity,  and  also  gives  a  branch  to  the  lower  eyelid. 

Veins. — Branches,  corresponding  generally  to  those  of  the  artery,  unite  to  form  the  superior 
and  inferior  ophthalmic  veins,  which  ultimately,  either  separately  or  united  into  one  trunk, 
pass  through  the  superior  orbital  fissure  and  empty  into  the  cavernous  sinus.  The  inferior  vein 
is  connected  with  the  pterygoid  plexus  by  a  branch  which  leaves  the  orbit  by  the  inferior  orbital 
fissure. 

Nerves  of  the  orbit. — These  are  (A)  motor,  (B)  sensory,  and  (C)  sympathetic,  and  aU 
enter  the  orbit  by  the  superior  orbital  fissure,  with  the  exception  of  one  small  sensory  branch 
passing  through  the  inferior  orbital  fissure.  (The  optic  nerve  has  been  already  described,  and 
is  not  included  in  this  account.) 

A.  The  motor  nerves  are  the  oculomotor,  trochlear,  and  abducens. 

1.  The  oculomotor  nerve  enters  the  orbit  in  two  parts,  an  upper  smaller,  and  a  lower 
larger,  division.  The  upper  division  [ramus  superior]  gives  off  two  branches:  one  suppHes  the 
superior  rectus,  entering  its  lower  surface  far  back;  the  other  branch  goes  to  the  levator  pal- 
pebra?,  entering  its  lower  surface  in  its  posterior  third.  The  lower  division  [ramus  inferior] 
divides  into  three  branches,  of  which  one  supplies  the  inferior  rectus,  entering  its  upper  surface 

Fig.  819. — The  Blood-vessels  of  the  Left  Orbit,  viewed  from  above. 


Supraorbital  artery- 

Lacrimal  gland' 

Superior  rectus,  cut' 

Eyeball 


Lateral  rectus 
Lacrimal  artery 

Superior  rectus,  cut 
Inferior  ophthalmic  vein 
Superior  ophthalmic  vem 


Opt] 
Superior  ophthalmic  vein 


Commencement  of  superior 
ophthalmic  vein 

Reflected  tendon  of  superior 

oblique 
Ophthalmic  artery 


7]      Anterior  ethmoidal  artery 


Posterior  ethmoidal  artery* 
Ciliary  arteries 

Levator  palpebr^e,  cut 

Common  tendon  ring 

(of  Zinn) 

Ophthalmic  artery 
Optic  chiasma 


Internal  carotid  artery 

far  back,  and  another  supplies  the  medial  rectus,  entering  its  medial  surface  a  little  behind 
its  middle.  The  third  branch  of  the  lower  division  gives  (1)  the  short  root  to  the  cihary  ganglion, 
and  (2)  one  or  more  twigs  to  the  inferior  rectus,  and  the  remainder  of  this  branch  then  enters 
the  lower  surface  of  the  inferior  oblique  muscle  about  its  middle. 

2.  The  trochlear  nerve  supplies  the  superior  oblique  muscle,  entering  its  upper  surface 
about  midway  in  its  course. 

3.  The  abducens  nerve  supplies  the  lateral  rectus,  entering  its  medial  surface  about  the 
junction  of  the  posterior  and  middle  thirds  of  the  muscle. 

As  regards  the  manner  of  termination  of  these  motor  nerves,  it  is  found  that  in  aU  the  ocular 
muscles  the  nerve  on  its  entrance  breaks  up  into  numerous  bundles  of  fibres,  which  form  first 
coarse  and  then  fine  plexuses,  the  latter  ultimately  sending  off  fine  twigs  supplying  the  muscle 
throughout  with  nerve-endings.  The  posterior  third  of  these  muscles  is,  however,  comparatively 
poorly  supplied  with  both  kinds  of  plexuses  and  with  nerve-endings. 

B.  The  sensory  nerves  are  supplied  by  the  ophthalmic  and  maxillary  divisions  of  the 
trigeminal  cranial  nerve.  The  ophthalmic  division  is  chiefly  orbital;  while  the  maxillary 
sends  only  a  small  branch  to  the  orbit. 

1.  The  ophthalmic  division  of  the  trigeminal  nerve  enters  the  orbit  in  three  divisions, 
namely: — 

(1)  Frontal,  spUtting  subsequently  into  supratrochlear  and  supraorbital,  both  passing  out 
of  the  orbit.  It  is  distributed  to  the  corresponding  upper  eyehd,  and  the  skin  over  the  root  of 
the  nose,  the  forehead,  and  the  hairy  scalp  as  far  back  as  the  coronal  suture  on  the  same  side. 
It  also  gives  branches  to  the  periosteum  in  this  region,  and  to  the  frontal  sinus. 

(2)  Lacrimal,  supplying  the  lacrimal  gland,  anastomosing  with  a  branch  of  the  maxillary 


1076 


SPECIAL  SENSE  ORGANS 


in  the  orbit,  and  finally  piercing  the  upper  eyelid.  Outside  the  orbit  it  is  distributed  to  the 
lateral  part  of  the  upper  lid,  the  conjunctiva  at  the  lateral  angle,  and  the  skin  between  this  and 
the  temporal  region. 

(3)  Naso-ciliary  [n.  naso-ciUaris]  giving  off — (a)  a  branch  to  the  ciliary  gangUon,  constituting 
its  long  root ;  (6)  two  or  three  long  ciliary  nerves;  and  (c)  the  injratrochlear,  passing  out  of  the  orbit. 
The  nerve  then  leaves  the  orbit  as  the  anterior  ethmoidal  nerve  [n.  ethnioidaUs  anterior],  re- 
entering the  cranial  cavity  before  being  finally  distributed  to  the  nose.  The  infratroohlear  branch 
[n.  infratrochlearis],  supplies  the  eyehds  and  skin  of  the  side  of  the  nose  near  the  medial  angle  of 
the  eye,  the  lacrimal  sac,  caruncle,  and  plica  semilunaris.  The  anterior  ethmoidal  nerve,  after 
its  course  in  the  cranial  cavity,  passes  through  an  aperture  in  the  front  of  the  lamina  cribrosa 
of  the  ethmoid  bone,  and  is  ultimately  distributed  to  the  nasal  mucous  membrane,  and  to  the 
skin  of  the  side  and  ridge  of  the  nose  near  its  tip. 

2.  The  maxillary  division  of  the  fifth  nerve  gives  a  branch,  called  the  zygomatic  nerve, 
which  passes  into  the  orbit  through  the  inferior  orbital  fissure,  anastomoses  with  the  lacrimal, 
and  leaves  the  orbit  in  two  divisions.  These  are  distributed  to  the  skin  of  the  temple  and  of  the 
prominent  part  of  the  cheek. 

A  few  minute  twigs  from  the  spheno-palatine  ganghon,  and  sometimes  from  the  maxillary 
division  of  the  fifth  nerve,  also  pass  through  the  inferior  orbital  fissure  to  supply  the  periorbita 
in  this  neighbourhood. 

C.  The  sympathetic  nerves  of  the  orbit  are  mainly  derived  from  the  plexus  on  the  internal 
carotid  arterj'.  With  the  exception  of  branches  accompanying  the  ophthalmic  artery,  and  of 
the  distinct  sympathetic  root  of  the  ciUary  ganghon,  they  enter  the  orbit  in  the  substance  of 

Fig.  820. — Section  through  Contents  op  Right  Orbit,  1-2  mm.  in  front  of  the  Optic 
Foramen,  viewed  from  behind.     (After  Lange.) 


Trochlear  nerve 

Superior  rectus  and  levator  palpe-. 

bras  superioris  muscles 


■  oblique  musclC' 


Ophthalmic  vein 

ve  (frontal, 
liary,  and  lacrimal 
branches) 


Medial  rectus  muscle— -^^      \ 


Inferior  rectus  muscle 


''      \m — "'^'^  Ophthalmic  vein 

117. 


Ophthalmic  artery 
Abducens  nerve 
Oculomotor  nerve 
Lateral  rectus  muscle 


the  other  nerve-cords.  The  connections  between  the  ocular  nerves  and  the  carotid  plexus  are 
recognisable  as  fibres  going  to  the  oculomotor,  abducens,  and  ophthalmic  nerves;  as  a  rule,  the 
comparatively  large  twigs  going  to  the  abducens  join  it  furthest  back,  and  those  to  the  oculo- 
motor furthest  forward.  Sympathetic  connections  with  the  trochlear  nerve  are  very  doubt- 
ful. The  special  courses  of  the  motor  fibres  to  the  dilatator  pupillae  muscle  have  already  been 
described. 

The  ciliary  ganglion  is  situated  between  the  optic  nerve  and  lateral  rectus  far  back  in  the 
orbit.  Its  three  roots — motor,  sensory,  and  sympathetic — have  been  already  mentioned. 
Anteriorly,  it  gives  off  three  to  six  smaU  trunks,  which  subdivide  to  form  the  short  ciliary  nerves 
[nn.  cihares  breves]  about  twenty  in  number,  piercing  the  sclera  around  the  optic  nerve 
entrance. 

The  lymphatic  system  of  the  orbit. — Although  there  are  no  lymphatic  vessels 
or  glands  in  the  orbit,  the  passage  of  lymph  is  nevertheless  well  provided  for.  We 
have  already  observed  the  lymph  channels  within,  between,  and  outside  the 
sheaths  of  the  optic  nerve,  and  have  seen  how  these  communicate  anteriorly  with 
the  lymph  channels  of  the  eyeball,  and  posteriorly  with  the  intracranial  meningeal 
spaces.  In  addition,  there  are  lymph-spaces  around  the  blood-vessels,  situated 
between  the  outer  coat  and  the  loose  investment  furnished  by  the  muscle  fascia. 
The  nerves  of  the  orbit  (apart  from  the  optic)  are  probably  similarly  surrounded 
by  lymph-spaces.  In  the  absence  of  lymphatic  vessels  it  is  difficult  to  trace  the 
circulation  thoroughly;  much  of  the  lymph  from  the  orbital  cavity  is  said  to  pass 
into  the  parotid  nodes. 

The  Eyelids 

The  cutaneous  and  conjunctival  surfaces  of  the  eyelids  [palpebras]  have  al- 
ready been  examined  (p.  1053),  and  the  position  of  the  tarsus  has  been  indicated. 
We  have  now  to  ascertain  the  nature  and  relations  of  the  tarsus,  and  describe  the 
other  tissues  entering  into  the  formation  of  the  eyelids  (fig.  821). 


THE  EYELIDS 


1077 


The  skin  here  is  thin,  bearing  fine  hairs,  and  having  small  sebaceous  and  nu- 
merous small  sweat-glands.  Immediately  beneath  it  is  a  loose  subcutaneous 
tissue,  destitute  of  fat,  separating  the  skin  from  the  palpebral  part  of  the  orbicu- 
laris muscle.  The  lid-fibres  of  this  muscle  arise  from  the  medial  palpebral  liga- 
ment, and  course  over  the  whole  upper  and  lower  eyelids  in  a  succession  of  arches, 
so  as  to  meet  again  beyond  the  lateral  angle;  there  they  in  part  join  one  another, 
in  part  are  inserted  into  the  lateral  palpebral  raphe.  The  muscular  fibres  are 
arranged  in  loose  bundles,  with  spaces  between  them  occupied  by  connective 
tissue;  in  the  upper  lid  these  connective-tissue  fibres  may  be  traced  upward  and 
backward  into  the  fibrous  expansion  of  the  tendon  of  the  levator  palpebree  supe- 


FiG.  821. — Sagittal  Section  op  the  Upper  Eyelid.     (After  Waldeyer  and  Fuohs.) 


Orbicularis  oculi  - 
Sweat  gland  ■ 


-!:• 


Sebaceous  gland  — 


Cross  section  of 
orbicularis  oculi 


^^Sltt/ 


Ciliary  gland  (of  Moll) 
Ciha 


^  :i 


Anterior  insertion  of  leva- 
tor palpebree  superioris 

Superior  tarsal  muscle 
of  MuUer 
-  Fibres  from  levator  to  skin 


7' 


^  Mucous  glands  (Krause) 


Conjunctival  papillse  over 
attached  border  of  tarsus 


Mucous  glands  (of  Krause) 


^_       Tarsal  (Meibomian)  glands 
M.  ciliaris  (Riolani) 

Posterior  edge  of  lid-margin 


Opening  of  duct  of  tarsal  gland 


rioris.  One  strong  bundle  of  orbicularis  fibres,  called  the  musculus  ciliaris  Riolani, 
is  found  near  the  edge  of  the  lid,  in  front  of  and  behind  the  efferent  ducts  of  the 
tarsal  glands  (fig.  821). 

A  central  connective  tissue  separates  the  orbicularis  muscle  from  the  tarsus  in  the  tarsal 
division  of  the  lids.  In  the  upper  Ud  this  is  to  be  regarded  as  mainly  the  anterior  or  fibrous 
expansion  of  the  tendon  of  the  levator  palpebrse,  which  sends  connective-tissue  septa  between  the 
bundles  of  the  overlying  orbicularis  (as  just  mentioned)  going  to  the  skin.  In  the  orbital  part 
of  this  hd  the  central  connective  tissue  includes  also  the  palpebral  fascia,  lying  here  immediately 
beneath  the  orbicularis  muscle;  but  this  soon  thins  off  and  fades  into  the  more  deeply  placed 
levator  expansion.  This  latter  is  strengthened  by  an  extension  of  the  sheath  of  the  superior 
rectus,  by  which  this  muscle  is  enabled  to  influence  the  elevation  of  the  Ud  indirectl.y.  In  the 
lower  lid  the  central  connective  tissue  similarly  consists  of  palpebral  fascia,  blended  with  a  thin 
fibrous  extension  of  the  sheath  of  the  inferior  rectus.  Immediately  in  front  of  each  tarsus  is 
a  little  loose  connective  tissue,  which  contains  the  large  blood-vessels  and  nerves  of  the  hds. 

The  tarsus  of  each  lid  is  a  stiff  plate  of  close  connective  tissue,  with  its  sur- 
faces directed  anteriorly  and  posterior^;  in  its  substance  the  tarsal  glands  are 


1078  SPECIAL  SENSE  ORGANS 

embedded.  One  tarsal  border  is  free,  viz.,  toward  the  edge  of  the  lid,  the  other 
is  attached;  the  former  is  straight,  while  the  latter  is  convex,  especially  in  the 
upper  lid. 

The  length  of  each  tarsus  is  about  twenty  millimetres.  Its  breadth  is  greatest  in  the  middle 
of  the  hd,  and  becomes  gradually  smaller  toward  'each  angle,  where  the  tarsi  are  joined  to  the 
lateral  raphe  and  medial  palpebral  ligament.  The  breadth  of  the  upper  tarsus  (10  mm.)  is 
about  twice  that  of  the  lower.  The  thickness  of  each  is  greatest,  and  its  texture  closest,  at  the 
middle  of  its  length,  thinning  off  toward  the  angles  of  the  eye  and  toward  both  borders.  Into 
the  superior  anterior  border  of  the  upper  tarsus  the  lower  layer  of  the  levator  expansion  is 
attached,  consisting  of  smooth  muscle-fibres  constituting  the  superior  tarsal  muscle  of  Mtiller. 
In  like  manner,  at  the  inferior  border  of  the  lower  tarsus,  bundles  of  smooth  muscle-fibre  are 
inserted  (the  inferior  tarsal  muscle  of  Miiller),  developed  in  what  has  been  regarded  as  part 
of  the  extension  of  the  sheath  of  the  inferior  rectus. 

The  palpebral  conjunctiva  is  firmly  adherent  to  the  posterior  aspect  of  the 
tarsus;  but  in  the  orbital  part  of  the  lid  loose  subconjunctival  tissue  intervenes 
between  it  and  Miiller's  tarsal  muscle.  Lymphoid  tissue  occurs  in  the  substance 
of  the  conjunctiva,  especially  in  its  orbital  division.  Near  the  upper  fornix,  the 
conjunctiva  receives  expansions  of  the  tendon  of  the  levator  palpebrse  and  of  the 
sheath  of  the  superior  rectus,  and,  at  the  lower  fornix,  of  the  sheath  of  the  inferior 
rectus.  The  surface  of  the  tarsal  conjunctiva  shows  small  elevations  or  papillae 
everywhere;  but  these  are  particularly  well  marked  over  the  attached  border  of 
the  tarsus. 

Glands  of  the  eyelids. — From  its  manner  of  formation  the  eyelid  may  be 
regarded  as  consisting  of  two  thicknesses  of  skin,  the  posterior  having  been 
doubled  back  upon  the  anterior  at  the  edge  of  the  lid;  thus  the  epidermis  and 
corium  of  the  skin  proper  are  represented  respectively  by  the  conjunctiva  (epi- 
thelium) and  tarsus  of  the  inner  thickness.  At  the  free  border  of  the  lid,  accord- 
ingly, we  find  glands  corresponding  to  the  sebaceous  and  sweat-glands  of  the  skin, 
viz.,  large  sebaceous  glands  of  the  cilia  (Zeiss's  glands)  and  the  ciliary  glands  of 
Moll,  which  are  modified  sweat-glands.  Again,  in  the  inner  skin-thickness  of 
the  lid,  the  tarsal  (Meibomian)  glands  are  sebaceous. 

Acino-tubular  mucous  glands  occur  at  the  attached  border  of  the  tarsus  (Krause's  or 
Waldeyer's  glands),  and  similar  glands  also  occur  at  the  fornix,  and  are  especially  abundant 
near  the  outer  angle  of  the  upper  lid,  close  to  the  efferent  ducts  of  the  lacrimal  gland;  from  their 
structure  and  the  character  of  their  secretion,  these  acinous  or  acino-tubular  glands  have  been 
termed  by  Henle  'accessory  lacrimal  glands.'  Other  simple  tubular  glands  (Henle),  formed 
merely  by  the  depressions  between  the  papiUae,  are  best  developed  in  the  medial  and  lateral 
fourths  of  the  tarsal  conjunctiva  of  both  hds. 

Blood-vessels. — The  arteries  run  in  the  central  connective  tissue  of  the  lids,  mainly  in 
the  form  of  arches  near  the  borders  of  the  tarsus,  from  which  twigs  go  to  the  different  pal- 
pebral tissues.  They  are  supplied  by  the  lacrimal  and  palpebral  branches  of  the  ophthalmic, 
and  by  small  branches  derived  from  the  temporal  artery.  The  veins  are  more  numerous  and 
larger  than  the  arteries,  and  form  a  close  plexus  beneath  each  fornix.  They  empty  themselves 
into  the  veins  of  the  face  at  the  medial,  and  into  the  orbital  veins  at  the  lateral  angle  of  the  eye. 

The  lymphatic  vessels  of  the  lids  are  numerous,  and  are  principally  situated  in  the  con- 
junctiva. Lymph-spaces  also  surround  the  follicles  of  the  tarsal  glands.  The  palpebral 
lymphatic  vessels  from  the  lateral  three-fourths  of  the  lid  pass  through  the  anterior  auricular 
and  parotid  nodes;  those  from  the  medial  fourth  of  the  lower  lid  go  to  the  facial  and  submaxil- 
lary lymphatic  nodes. 

Nerves. — (a)  Sensory.  The  upper  lid  is  chiefly  supplied  by  branches  of  the  supraorbital 
and  supratrochlear  nerves,  the  lower  Ud  by  one  or  two  branches  of  the  infraoibital.  At  the 
medial  angle  the  infratrochlear  nerve  also  aids  in  the  supply,  and,  at  the  lateral  angle,  the 
lacrimal,  (b)  Motor.  The  palpebral  part  of  the  orbicularis  is  suppKed  by  branches  of  the 
facial  nerve,  which  mainly  enter  it  near  the  lateral  angle.  The  tarsal  muscles  are  suppUed 
by  the  sympathetic  nervous  system. 

The  medial  palpebral  ligament  has  been  referred  to  previously.  Arising  from 
the  frontal  process  of  the  maxilla,  it  extends  laterally  over  the  front  wall  of  the 
lacrimal  sac,  bends  round  the  lateral  wall  of  the  sac,  and  then  passes  backward  to 
the  posterior  crest  on  the  lacrimal  bone.  It  is  thus  U-shaped,  having  its  limbs 
anterior  and  posterior,  embracing  the  lacrimal  sac;  the  anterior  limb  lies  immedi- 
ately beneath  the  skin,  and  is  visible  in  the  living.  The  palpebral  fibres  of  the 
orbicularis  are  inserted  into  the  anterior  surface  of  both  limbs,  those  attached  to 
the  posterior  limb  constituting  the  pars  lacrimalis  of  the  orbicularis  palpebrarum 
(Horner's  muscle).  The  lateral  palpebral  raphe  is  merely  a  stronger  development 
of  connective  tissue  in  the  orbicularis.  Both  ligaments  are  connected  with  the 
tarsi  as  already  mentioned. 


LACRIMAL  APPARATUS 


1079 


The  Lacrimal  Apparatus 

The  tears  are  secreted  by  an  acinous  gland,  and  flow  through  fine  ducts  to  the 
upper  lateral  part  of  the  conjunctival  sac,  whence  they  pass  over  the  cornea  and 
are  drained  off  through  the  puncta,  pass  along  the  canaliculi  into  the  lacrimal  sac, 
and  ultimately  down  the  naso-lacrimal  duet  to  the  inferior  meatus  of  the  nose. 

The  lacrimal  gland  is  situated  near  the  front  of  the  lateral  part  of  the  roof  of 
the  orbit,  lying  in  a  depression  in  the  orbital  plate  of  the  frontal  bone.  It  consists 
of  two  very  unequal  parts,  one  placed  above  and  the  other  beneath  the  tendinous 
expansion  of  the  levator  palpebree  superioris,  but  small  gaps  in  the  expansion  per- 
mit of  connections  between  these  two  parts  of  the  gland.  The  upper  and  larger 
subdivision  (superior  lacrimal  gland)  is  a  firm  elongated  body,  about  the  size  of 
a  small  almond;  it  has  a  greyish-red  colour,  and  is  made  up  of  closely  aggregated 
lobules.  The  upper  surface  (next  the  orbital  roof)  is  convex,  and  its  lower  surface 
is  slightly  concave. 

Anteriorly,  the  gland  almost  reaches  the  upper  orbital  margin,  and  it  extends  backward 
for  approximately  one-fourth  the  depth  of  the  orbit,  measuring  about  twelve  mUlimetres  in 
this  direction.  The  lateral  border  of  the  gland  descends  to  near  the  insertion  of  the  fascial 
expansion  of  the  lateral  rectus,  while  its  medial  border  almost  reaches  the  lateral  edge  of  the 
superior  rectus;  its  transverse  measurement  is  about  twenty  millimetres.  It  is  enveloped  in  a 
capsule,  which  is  slung  by  strong  fibrous  bands  passing  to  its  medial  border  from  the  orbital 
margin  (suspensory  hgament  of  the  gland). 

Fig.  822. — Dissection  of  the  Eye  to  Show  the  Lacrimal  Appakatus,  Anterior  View. 


Inferior  lacrimal  gland 
Excretory  ducts/ 
Superior  lacrimal  gland  i    I 


Palpebra  superior 


Tendon  of  superior  oblique 
}  Superior  lacrimal  duct 


^  Lacus  lacrimalis 

y  Medial  palpebral  commissure 

-  Fornix  of  lacrimal  sac 

-  Junction  of  lacrimal  ducts 

-  Inferior  lacrimal  duct 

-  Nasolacrimal  duct 


^        I--        i'  Lacrimal  papilla  and  punctum 

Inferior  oblique 
Palpebra  inferior 

The  lower  subdivision  of  the  gland  (^inferior  lacrimal  gland)  is  composed  of 
loosely  applied  lobules,  and  lies  immediately  over  the  lateral  third  of  the  upper 
conjunctival  fornix,  reaching  lateralward  as  far  as  the  lateral  angle. 

Each  subdivision  of  the  gland  possesses  several  excretory  ducts,  which  all  open 
on  the  lateral  part  of  the  upper  fornix  conjunctivae,  about  four  millimetres  above 
the  upper  border  of  the  tarsus.  Those  of  the  superior  gland,  three  or  four  in 
number,  pass  betweefi  the  lobules  of  the  lower  gland;  the  most  lateral  duct  is  the 
largest,  and  opens  at  the  level  of  the  lateral  angle  of  the  eye.  The  ducts  of  the 
inferior  gland  in  part  discharge  themselves  into  those  of  the  upper,  but  there  are 
also  several  fine  ducts  from  this  subdivision  that  run  an  independent  course. 

Near  the  medial  angle  are  the  two  puncta  lacrimalia,  upper  and  lower,  each 
situated  at  the  summit  of  its  papilla.  The  top  of  each  papilla  curves  backward 
toward  the  conjunctival  sac,  so  that  the  puncta  are  well  adapted  for  their  function 
of  draining  off  any  fluid  collecting  there. 

The  ductus  (canaliculi)  lacrimales  extend  from  the  puncta  to  the  lacrimal  sac. 
The  lumen  at  the  pmrctum  is  horizontally  oval,  from  its  lips  being  slightly  com- 
pressed antero-posteriorly;  the  lumen  of  the  lower  punctum  is  somewhat  larger 
than  that  of  the  upper.  As  the  lower  papilla  is  a  little  further  from  the  medial 
angle  of  the  eye  than  the  upper,  the  corresponding  canaliculus  is  longer. 

On  tracing  either  ductus  from  its  origin,  we  flnd  that  at  first  it  runs  nearly 
vertically  for  a  short  distance,  then  bends  sharply  toward  the  nose,  and  finally 


1080  SPECIAL  SENSE  ORGANS 

courses  more  or  less  horizontally,  converging  slightly  toward  its  fellow,  and  not 
infrequently  joining  it  before  opening  into  the  sac.  The  calibre  varies  consider- 
ably in  this  course,  being  narrowest  a  short  distance  from  the  punctum,  and  widest 
at  the  bend,  from  which  point  it  again  narrows  very  gradually  as  it  nears  the  sac. 

The  wall  of  the  ductus  consists  mainly  of  elastic  and  white  fibrous  tissue,  lined  internally 
by  epitheUum,  and  covered  externally  by  striated  muscle  (part  of  the  orbicularis).  The  muscle- 
fibres  run  parallel  to  the  ductus  in  the  horizontal  part  of  its  course;  but  they  are  placed,  some 
in  front  and  some  behind,  around  the  vertical  part,  acting  here  as  a  kind  of  sphincter.  Just 
before  their  termination,  the  ducts  pierce  the  periosteal  thickening  that  constitutes  the  posterior 
limb  of  the  medial  palpebral  ligament. 

The  lacrimal  sac  [saccus  lacrimalis]  lies  in  a  depression  in  the  bone  at  the  medial 
angle  of  the  orbit  (the  lacrimal  fossa).  It  is  vertically  elongated,  and  narrows  at 
its  upper  and  lower  ends;  the  upper  extremity  or  fundus  is  closed,  while  the  lower 
is  continuous  with  the  naso-lacrimal  duct.  Laterally,  the  sac  is  somewhat  com- 
pressed, so  that  its  antero-posterior  is  greater  than  its  transverse  diameter.  The 
ducts,  either  separately  or  by  a  short  common  tube,  open  into  a  bulging  on  the 
lateral  surface  of  the  sac  near  the  fundus. 

As  has  previously  been  mentioned,  the  sac  is  surrounded  by  periosteum,  but  between  this 
and  the  mucous  membrane  forming  the  true  sac-wall  there  is  a  loose  connective  tissue,  so  that 
the  cavity  is  capable  of  considerable  distention.  The  relations  of  the  medial  palpebral  Ligament 
have  already  been  described;  it  is  to  be  noted  that  the  fundus  of  the  sac  extends  above  this 
ligament. 

The  naso-lacrimal  duct  [ductus  naso-lacrimalis]  reaches  from  the  lower  end  of 
the  sac  to  the  top  of  the  inferior  meatus  of  the  nose,  opening  into  the  latter  just 
beneath  the  adherent  border  of  the  inferior  nasal  concha.  Traced  from  above, 
its  main  direction  is  downward,  but  it  has  also  a  slight  inclination  backward  and 
laterally.  It  lies  in  a  bony  canal,  whose  periosteum  forms  its  outer  covering. 
Between  this  and  the  mucous  membrane  of  the  duct  there  is  a  little  intermediate 
tissue,  in  which  run  veins  of  considerable  size  connected  with  the  plexus  of  the 
inferior  concha.  The  duct  does  not  usually  open  directly  into  the  nasal  cavity 
at  the  lower  end  of  the  bony  canal,  but  pierces  the  nasal  mucous  membrane  very 
obliquely,  so  that  a  flap  [plica  lacrimalis  (Hasneri)]  of  mucous  membrane  covers 
the  lower  border  of  the  opening  in  the  bone,  upon  which  flap  the  tears  first  trickle 
after  escaping  from  the  duct  proper. 

The  sac  and  naso-lacrimal  duct  together  constitute  the  lacrimal  canal,  lined  throughout  by 
a  continuous  mucous  membrane.  This  membrane  presents  folds  in  some  situations,  especially 
near  the  opening  of  the  canaliculi,  at  the  junction  of  the  sac  and  duct,  and  at  the  lower  end  of 
the  duct.  That  at  the  top  of  the  duct  is  the  most  important,  as  it  sometimes  interferes  with  the 
proper  flow  of  tears  out  of  the  sac.  The  total  length  of  the  lacrimal  canal  is  roughly  twenty-four 
millimetres,  half  of  this  being  sac,  and  half  naso-lacrimal  duct.  If,  however,  we  reckon  as  duct 
the  obUque  passage  through  the  nasal  mucous  membrane,  this  measurement  may  occasionally 
be  increased  by  eight  or  ten  millimetres.  The  lacrimal  sac,  when  distended,  measures  about 
six  millimetres  from  before  backward,  by  four  millimetres  transversely.  The  naso-lacrimal  duct 
is  practically  circular,  and  has  a  diameter  of  about  three  millimetres,  rather  less  at  its  junction 
with  the  sac,  where  we  find  the  narrowest  part  of  the  whole  lacrimal  canal. 

Development  of  the  ■  Eye 

The  eye  is  developed  from  the  three  sources  involving  two  fundamental  embryonic  layers — 
the  retina  from  a  portion  of  the  ectodermal  wall  of  the  forebrain  on  each  side;  the  lens  from  the 
ectodermal  surface  epithelium;  and  the  sclera,  cornea  (except  epithelium)  and  chorioidal 
coat  from  the  mesoderm  which  surrounds  the  former  structures. 

The  process  of  development  is,  briefly,  as  follows: — The  site  of  the  eye  is  marked  by  a  sUght 
depression  on  the  surface  of  the  forebrain  on  either  side.  There  later  an  outgrowth  occurs 
from  the  ventro-lateral  aspect  on  each  side  of  the  forebrain,  in  the  form  of  a  hoUow  vesicle, 
whose  cavity  is  continuous  with  that  of  the  forebrain.  This  outgrowth  is  termed  the  •primary 
optic  vesicle  [vesicula  ophthalmicaj.  The  lateral  surface  of  the  vesicle  comes  into  contact  with 
the  surface  epithelium  of  the  head  and  this  epithelium  becomes  thickened  at  the  area  of  contact. 
The  superficial  portion  of  the  vesicle  expands,  while  its  connection  with  the  brain  remains 
slender;  becoming  depressed  on  the  surface,  it  forms  a  cup-shaped  hollow,  the  secondary  optic 
vesicle  or  optic  cup  [caliculus  ophthalmicus]  whose  wall  is  formed  of  two  layers,  an  outer  investing 
layer  and  an  inner  inverted  one. 

The  chorioidal  fissure  is  present  almost  from  the  first  stages,  as  a  cleft  on  the  ventral  aspect 
of  both  the  distal  portion  of  the  vesicle,  or  cup,  and  of  the  stalk;  and  it  is  formed  by  an  infolding 
of  the  surface  into  the  cavity  of  the  vesicle  along  a  narrow  linear  area. 

In  this  cleft  are  found  vessels  which  pass  to  the  hollow  of  the  optic  cup.  The  margins  of 
the  cleft  meet  and  fuse,  and  enclose  the  vessels  in  the  interior — hence  the  enclosure  of  the 
a.  centralis  retina  within  the  optic  nerve,  and  of  the  hyaloid  artery  in  the  interior  of  the  vitreous. 
Should  the  margins  of  the  cleft  remain  separate,  the. condition  of  coloboma  results. 


DEVELOPMENT  OF  THE  EYE 


1081 


From  the  optic  cup  is  formed  the  whole  of  the  retinal  or  nervous  tunic.  It  will  be  noticed 
that  this  tunic  is  composed  of  two  layers,  with  a  narrow  sUt-like  interval  between  them,  but  that 
the  layers  are  continuous  with  one  another  at  the  margin  of  the  cup.  This  margin  is  afterward 
found,  in  the  fully  developed  eye,  at  the  pupillary  margin  of  the  iris.  The  outer  investing  layer 
forms  the  pigment  layer,  and  the  inner  inverted  layer  gives  rise  to  the  other  parts  of  the  retina, 
viz.,  the  pars  optica,  over  the  bottom  of  the  cup,  the  pars  ciliaris,  in  the  ciliary  region,  and  the 
pars  iridica,  near  the  margin  of  the  original  cup,  including  the  dilatator  and  sphincter  pupillae 
muscles  of  the  iris. 

The  lens  is  formed  as  a  hollow  invagination  from  the  surface  epitheKum,  which  sinks  into 
the  hoUow  of  the  optic  cup.  The  margins  meet  and  fuse,  enclosing  a  cavity,  and  the  lens  mass 
sinking  more  deeply  in,  loses  its  connection  with  the  surface,  and  a  layer  of  mesoderm  passes 
in  between  them. 

The  anlages  of  the  lens  and  the  primitive  retina  are  at  first  in  contact  with  one  another. 
They  graduaUy  draw  apart,  and  the  intervening  space  is  filled  by  the  vitreous  humour.  The 
origin  of  the  vitreous  humour  is  not  yet  fully  understood,  but  it  appears  to  be  developed  from  the 
adjacent  ectoderm  of  the  optic  cup,  and  in  part  from  the  surrounding  mesoderm. 

Figs.  823,  824,  825  and  826. — Sections  Representing  Four  Successive  Stages  in  the 
Origin  op  the  Optic^ Vesicle  and  the  Development  op  the  Eyeball. 


■W 


The  optic  cup  and  the  lens  are  surrounded  by  mesoderm  and  from  it  are  formed  the  struc- 
tures of  the  tunica  vasculosa  (middle  coat)  in  its  different  parts,  viz.,  chorioid,  ciliary  body 
and  ins,  and  also  the  sclera  and  cornea  (fibrous  portion). 

Bii  I^^-  f"  n®''J5'"  <'lia'»ber  is  formed  by  cleavage  of  the  mesoderm,  a  space  appearing  in  it, 
hUed  with  fluid.  The  mesoderm  surrounding  this  space  forms  the  endothehum  Hning  the 
anterior  chamber.  The  mesoderm  also  forms  a  vascular  covering  for  the  front  of  the  lens, 
termed  the  capsula  vasculosa  leniis,  or  pupillary  membrane,  which  disappears  from  the  sur- 
face of  the  lens  in  the  later  months  of  development. 

The  eyehds  and  conjunctiva  are  formed  from  the  integumentary  covering  of  the  eye. 
1  he  former  are  mostly  skin  folds,  which,  at  first  separate,  meet  and  fuse  with  one  another  along 
their  margin.  Subsequently  they  become  undermined  by  the  ingrowth  of  epithelium  from  a 
central  horizontal  sht,  the  rima  palpebrarum ;  the  central  part  of  the  invading  epithehum  breaks 
down,  and  the  free  folds  are  formed. 

The  lacrimal  gland  is  developed  from  a  series  of  tubular  outgrowths  from  the  conjunctival  sac. 


1082  SPECIAL  SENSE  ORGANS 

The  lacrimal  canals  and  naso-lacrimal  duct  are  formed  by  the  growth  of  an  epithelial 
band  which  passes  through  the  mesoderm  to  the  nasal  cavity  along  the  naso-lacrimal  groove. 
This  band  loses  its  primitive  connection  with  the  groove,  and  is  reunited  to  the  lid  margins 
by  secondary  epithelial  bands  which  grow  from  the  naso-lacrimal  duct  to  the  lid  margin.  Simi- 
larly a  secondary  connection  is  later  made  with  the  nasal  cavity  at  the  lower  end  of  the  duct. 
The  position  of  the  naso-lacrimal  duct  corresponds  to  the  line  of  union  of  the  nasal  and  maxillary 
processes;  but  the  duct  does  not  represent  a  portion  of  the  cleft  between  these  processes,  and 
is  formed  secondarily  between  them. 

IV.  THE  EAR 

Under  the  name  of  the  ear  [organon  auditus]  there  is  included  a  number  of 
structures  of  which  some,  the  ear  proper,  constitute  the  auditory  mechanism — 
that  is,  an  apparatus  for  the  collection,  transmission  and  reception  of  the  waves  of 
sound;  while  others — the  semicircular  ducts  and  associated  structures — are 
concerned  in  receiving  and  transmitting  impressions  produced  by  movements  of  the 
head.  These  impressions  constitute  the  basis  of  what  may  be  termed  the  static  or 
equilibratory  sense,  and  afford  data  employed  in  estimating  movements  of  the 
body  in  relation  to  surrounding  objects. 

The  former  of  these,  the  ear  proper,  consists  of  three  main  parts,  each  possess- 
ing distinct  structural  and  functional  characters.  The  first  portion,  often  known  as 
the  external  ear,  consists  of  a  receptive  organ  placed  upon  the  surface  of  the  head, 
the  auricle  or  pinna,  and  of  a  short  tube,  the  external  auditory  meatus,  which 
leads  into  the  interior,  and  is  closed  at  its  deep  end  by  the  tympanic  membrane. 

The  second  portion,  known  as  the  middle  ear,  consists  of  the  tympanic  cavity, 
a  small  air-containing  chamber  in  the  petrous  portion  of  the  temporal  bone,  con- 
nected with  the  nasal  part  of  the  pharynx  by  a  tube,  the  auditory  (or  Eustachian) 
tube.  From  the  tympanic  chamber  a  recess  passes  posteriorly  and  leads  to  a  cavity 
in  the  mastoid  portion  of  the  temporal  bone,  the  mastoid  or  tympanic  antrum. 
A  chain  of  three  small  bones  transmits  the  sounds  across  the  middle  ear. 

The  third  part,  or  internal  ear  which  contains  the  essential  sensory  apparatus, 
lies  within  the  complex  cavities  in  the  interior  of  the  petrous  temporal  bone  known 
as  the  osseous  labyrinth.  It  consists  of  (1)  the  utricle  and  saccule,  two  small  ves- 
icular structures  lying  in  the  bony  vestibule,  and  (2)  the  membranous  semicir- 
cular ducts  and  (3)  the  membranous  cochlea,  which  lie  within  the  corresponding 
bony  canals. 

These  structures  are  filled  with  fluid,  the  endolymph,  and  communicate  with  one 
another.  They  are  largelj'  separated  from  the  bony  walls  by  fluid,  perilymph,  and 
they  are  lined  by  sensory  epithelium.  Closely  related  to  the  epithelial  sensory 
cells  are  found  the  terminal  branches  of  the  cochlear  and  vestibular  nerves. 

The  description  of  the  three  divisions  of  the  ear  is  taken  up  in  order  from  the 
surface  inward. 

1.  THE  EXTERNAL  EAR 

The  external  ear  consists  of  the  auricle  attached  to  the  side  of  the  head,  and 
the  external  auditory  meatus  leading  from  it  to  the  middle  ear  (flg.  829). 

THE  AURICLE 

The  auricle,  or  pinna,  is  an  irregular  oval  plate-like  structure  which  lies  upon 
the  lateral  surface  of  the  head.  It  presents  a  lateral  and  a  medial  surface.  The 
lateral  surface  is  irregularly  concave  (fig.  827).  The  deepest  part  of  its  concavity 
situated  near  the  centre,  is  termed  the  concha,  and  it  is  partially  divided  by 
a  prominent  oblique  ridge,  the  crus  of  the  helix,  into  a  superior  part,  the  cymba 
conchae,  and  a  large  inferior  part,  the  cavum  conchae.  The  cavum  conchse  leads 
into  the  external  auditory  meatus,  and  is  bounded  ventrally  by  a  prominent  proc- 
ess, the  tragus,  which  projects  posteriorly  over  the  entrance  to  the  meatus.  The 
tragus,  is  separated  from  the  crus  of  the  helix  by  a  well-marked  depression,  the 
anterior  incisure  and  has  a  small  tubercle  on  it  superiorly,  the  supratragic  tuber- 
cle. Bounding  the  cavum  conchte  posteriorly  and  inferiorly  is  a  projection,  the 
antitragus,  lying  opposite,  but  inferior,  to  the  tragus,  and  between  the  two  is  a 
deep  notch,  the intertragic notch  [incisura  intertragica].     A  prominent  semicircular 


THE  AURICLE 


1083 


ridge,  the  anthelix,  bounds  the  concha  posteriorly  and  superiorly.  Inferiorly  it 
is  separated  from  the  antitragus  by  a  slight  depression,  the  posterior  auricular 
sulcus.  Superiorly  the  anthelix  divides  into  two  ridges,  the  crura  of  the  anthelix, 
and  between  these  is  a  shallow  depression,  the  triangular  fossa.  The  superior  and 
dorsal  margin  of  the  auricle  is  inverted  and  forms  a  prominent  rim,  the  helix,  which 

Fig.  827 — ^Lateral  Surface  or  the  Left  Auriole. 


Crura  of  anthelix 


Crus  of  tne  helix- 
Anterior  incisure- 

Supratragic  tubercle 

Tragu; 

Intertragic  incisure- 


HeUx 

Auricular  tubercle 

Triangular  fossa 
Scapha 


Cavum  J 
Anthelix 
Posterior  auricular  sulcus 


is  continued  anteriorly  into  the  crus  of  the  helix,  and  inferiorly  into  the  lobule. 
An  elongated  depression,  partly  overlapped  by  the  helix,  termed  the  scapha 
(scaphoid  fossa)  separates  the  helix  and  the  anthelix.  Superiorly  and  dorsally 
the  free  margin  of  the  helix  frequently  presents  a  slight  projection,  the  auricular, 
tubercle  (tubercle  of  Darwin). 


Fig.  828. — Lateral  and  Medial  Surface  of  the  Cartilage  of  the  Right  Auricle  and  its 

Muscles,  etc. 
Helicis  major  Obliquus  Transversus 


Helicis  minor' 


Ebrous  band 
pleting  fore  part  of 
meatus 


l.yy  Antitrago-helicin 


Terminal  fissure 
Isthn 


Antitragicus         ,        Tragicus    Spine  of      Fissure  of  Santorini 
Lamina  tragi  helix    Cartilage  of  meatus 


Upon  the  medial  surface  of  the  auricle  the  depressions  of  the  lateral  surface  are 
represented  by  elevations,  viz.,  the  eminence  of  the  concha,  the  eminence  of  the 
scapha,  and  the  eminence  of  the  triangular  fossa,  respectively;  and  the  elevations 
by  depressed  areas,  viz.,  the  fossa  of  the  anthelix,  transverse  sulcus  of  the  anthelix. 


1084  SPECIAL  SENSE  ORGANS 

and  the  sulcus  of  the  crus  of  the  helix.  The  attachment  of  approximately  one- 
third  of  the  medial  surface  covers  up  the  two  latter  depressions.  The  cephalo-au- 
ricular  angle,  between  the  dorsal  free  part  of  the  auricle  and  the  side  of  the 
head,  averages  20  to  30  degrees. 

Structure  of  the  Auricle 

The  features  of  the  auricle  just  described  are  mainly  produced  by  a  plate  of  yellow  elastic 
cartilage,  the  auricular  cartilage.  In  addition  to  the  elevations  and  depressions  already 
noted,  it  presents  the  following  additional  features.  Projecting  anteriorly  from  the  helix, 
near  the  crus  is  a  small  tubercle,  spine  of  the  helix  (fig  828) ;  while  the  posterior  margin  of  the 
helix  terminates  in  a  pointed  tail-like  process,  the  cauda  helicis  which  is  separated  inf eriorly 
from  the  antitragus  by  the  deep  antitrago-helicine  fissure.  Another  deep  fissure,  the  terminal 
notch  [incisura  terminalis  auris],  separates  the  cartilage  of  the  auricle  from  that  of  the  meatus, 
leaving  only  a  narrow  strip,  the  isthmus,  connecting  the  two.  The  cartilage  of  the  tragus, 
the  lamina  tragi,  is  separated  from  that  of  the  auricle  and  is  attached  to  the  lateral  margin  of 
the  cartilage  of  the  meatus. 

The  auricle  is  covered  on  both  its  medial  and  lateral  aspects  by  skin  which 
closely  follows  the  irregularities  of  the  cartilage.  Thus  it  is  tightly  bound  to  the 
perichondrium  of  the  lateral  surface  by  the  subcutaneous  areolar  tissue,  but  much 
more  loosely  attached  to  the  medial  surface,  and  in  the  subcutaneous  tissue  there 
is  little  fat  except  in  the  lobule,  which  is  made  up  almost  entirely  of  fat  and  tough 
fibrous  tissue.  Hairs  are  abundant  but  rudimentary,  except  in  the  region  of  the 
tragus  and  antitragus,  where  they  may  be  large  and  long,  particularly  in  males  and 
in  the  aged.  Sebaceous  glands  are  found  on  both  surfaces,  and  are  especially  well 
developed  in  the  concha  and  triangular  fossa,  but  sudoriferous  glands  are  few  and 
scattered. 

Ligaments  and  muscles. — The  auricle  is  attached  to  the  side  of  the  head  by  the  skin,  by 
the  continuity  of  its  cartilage  with  that  of  the  acoustic  meatus,  and  by  certain  extrinsic  ligamente 
and  muscles.  Three  ligaments  may  be  distinguished  in  the  connective  tissue: — The  anterior 
ligament,  stretching  from  the  zygoma  to  the  helix  and  tragus;  the  superior  ligament,  from  the 
superior  margin  of  the  bony  external  acoustic  meatus  to  the  spine  of  the  helix;  and  the  posterior 
ligament,  from  the  mastoid  process  to  the  eminence  of  the  concha.  There  are  also  three  ex- 
trinsic muscles,  the  anterior,  superior,  and  posterior  auricular  (see  p.  337,  fig.  341).  Six  intrinsic 
muscles  are  distinguished.  These  are  poorly  marked  in  man  and  vary  much  in  development. 
Upon  the  lateral  surface  (fig.  828)  the  helicis  major  stretches  from  the  spine  of  the  helix  to 
the  ventral  superior  margin  of  the  helix;  the  helicis  minor  overlies  the  crus  helicis;  the  tragicus 
runs  vertically  upon  the  tragus;  and  the  antitragicus  stretches  from  the  antitragus  to  the  cauda 
helicis.  Upon  the  medial  surface  (fig.  828)  the  transversus  auriculae  stretches  between  the 
eminences  of  concha  and  scapha,  and  the  obliquus  between  the  eminences  of  the  concha  and  the 
triangular  fossa.  Two  small  muscles  occasionally  present  are  the  m.  pyramidalis  auriculse 
(Jungi)  and  the  m.  incisurse  heUcis  (Santorini). 

Vessels  and  Nerves  of  the  Auricle 

The  arteries  are  the  auricular  branch  of  the  posterior  auricular  and  the  anterior  auricular 
branches  of  the  superficial  temporal  arteries.  The  veins  are  the  anterior  auricular  vein 
of  the  posterior  facial  (temporal)  and  the  auricular  branches  of  the  posterior  auricular  veins. 
The  latter  vessels  sometimes  join  the  transverse  (lateral)  sinus  through  the  mastoid  emissary 
vein.  The  lymphatics  empty  into  the  anterior,  posterior  and  inferior  auricular  lymph-nodes. 
The  sensory  nerves  of  the  auricle  are  the  branches  of  the  great  auricular,  small  occipital  (p.  977, 
fig.  753),  and  auriculo-temporal  (p.  941,  fig.  740).  The  muscles  are  suppUed  by  the  posterior 
auricular  branch  of  the  facial  (p.  944,  fig.  740). 

Variations 

There  are  many  variations  in  the  size,  shape,  and  conformation  of  the  auricle  and  in  the 
cephalo-auricular  angle.  These  are  associated  not  only  with  differences  in  sex,  age,  and  race, 
but  are  also  found  in  individuals  of  the  same  family. 

THE  EXTERNAL  AUDITORY  MEATUS 

The  external  auditory  (acoustic)  meatus  [meatus  acusticus  externus]  extends 
medially  and  somewhat  anteriorly  and  inf  eriorly  from  the  concha  to  the  tympanic 
membrane  (fig.  829).  It  is  about  twenty-five  mm.  (1  in.)  long,  and,  owing  to  the 
obliquity  of  the  tympanic  membrane,  its  anterior  and  inferior  wall  is  5-6  mm. 


EXTERNAL  AUDITORY  MEATUS 


1085 


longer  than  the  posterior  and  superior.  It  consists  of  a  lateral  cartilaginous  and 
a  medial  osseous  portion.  The  canal  describes  an  S-shaped  curve  in  both  hori- 
zontal and  vertical  directions.  Near  the  auricular  end  it  is  convex  anteriorly  and 
inferiorly,  while  at  the  tympanic  end  the  curve  is  reversed,  and  is  concave  in  the 
same  direction.  The  lumen  is  irregularly  elliptical  in  outhne,  the  longer  axis 
being  vertical  at  the  auricular,  but  nearly  horizontal  at  its  tympanic  end.  The 
meatus  is  constricted  at  about  its  centre,  and  also  near  the  tympanum. 

Fig.  829. — -Vertical  Section  of  the  Middle  and  External  Ear. 


Semi  circular  Glands  in  oq 
canals  (ducts)  secus  meatus 
Tympanic  membrane  ^ 

Cochlea     \  \ 

Cavity  of  tympanum  \         f   '' 


Cartilaginous  tuba  auditiva 


Cartilagp 


—  Osseous 
meatus 
Cartilage  of 
external 
meatus 
Parotid  gland 


Styloid  process 


Osseous  tuba  auditiva 


Relations. — The  anterior  loall  is  in  relation  with  the  condyle  of  the  mandible  medially,  and 
with  the  parotid  gland  laterally;  the  inferior  wall  is  closely  bound  to  the  parotid  gland;  and 
the  'posterior  tuall  of  the  bony  part  is  separated  by  only  a  thin  plate  of  bone  from  the  mastoid 
cells.  The  superior  loall  is  separated  at  its  medial  end  by  a  thin  plate  of  bone  from  the  epi- 
tympanic  recess,  and  laterallj'  a  thicker  layer  of  bone  separates  it  from  the  cranial  cavity. 

Structure  of  the  meatus. — The  walls  of  the  meatus  are  formed  laterally  of 
fibro-cartilage  and  medially  of  bone,  lined  internally  by  skin.  The  cartilage  is 
folded  upon  itself  to  form  a  groove,  deficient  in  its  dorsal  part,  where  the  edges 
of  the  cartilage  are  united  by  dense  connective  tissue.  The  cartilaginous  groove 
is  thus  converted  into  a  canal.  Medially,  the  cartilage  forms  about  one-third  of 
the  circumference;  laterally,  two-thirds.  Two  fissures  (incisures  of  Santbrini) 
usually  occur  in  its  anterior  wall  (fig.  828).  Laterally  the  cartilage  is  directly 
continuous  with  the  cartilage  of  the  auricle  and  medially  it  is  firmly  connected 
with  the  lateral  lip  of  the  osseous  portion.  The  osseous  portion,  which  forms 
slightly  more  than  half  the  canal,  is  formed  by  the  tympanic  portion  of  the 
temporal  bone;  it  is  described  in  connection  with  that  bone. 

The  skin  of  the  meatus  forms  a  continuous  covering  for  the  canal  and  tympanic 
membrane.  It  is  thick  in  the  cartilaginous,  but  very  thin  in  the  bony,  part  of  the 
meatus,  especially  near  the  tympanic  end,  where  it  is  tightly  bound  to  the  perios- 
teum .  In  the  cartilaginous  meatus  it  contains  numerous  fine  hairs  and  sebaceous 
glands,  but  neither  hairs  nor  sebaceous  glands  are  found  in  the  bony  meatus. 
Tubular  ceruminous  glands,  which  secrete  the  cerumen  (ear  wax) ,  form  a  nearly 
continuous  layer  throughout  the  cartilaginous,  but  occur  on  onlj-  a  small  part  of 
the  posterior  and  superior  wall  of  the  bonj',  meatus.  The  openings  of  their  ducts 
appear  as  dark  points  to  the  naked  eye  (fig.  829). 


1086 


SPECIAL  SENSE  ORGANS 


The  arteries  are  branches  from  the  posterior  auricular,  superficial  temporal,  and  deep 
auricular  arteries  (q.v.)-  The  veins  and  lymphatics  connect  with  those  of  the  auricle  and 
empty  similarly.  The  nerves  are  branches  from  the  auriculo-temporal  and  the  auricular 
ramus  of  the  vagus. 

2.    THE  MIDDLE  EAR 

Under  the  term  middle  ear  there  are  included  the  tympanic  cavity  (tym- 
panum), the  tympanic  antrum  and  the  auditory  (Eustachian)  tube.  These  form 
a  continuous  irregular  passage,  filled  with  air,  and  located  within  and  upon  the 
surface  of  the  temporal  bone.     The  tympanum  is  shut  off  from  the  external  ear 

Fig.  830. — Frozen  Coronal  Section  op  the  Right  Ear.     (Somewhat  Enlarged.) 

Chorda  tympani 

Manubrium  mallei    /  Capitulum  maUei 

j  Tympanic  cavity 


Stapes    / 


Facial  nerve 

Tympani  membrane 
Promontorium   1 
Lamina  spiralis 

Modiolus  ' 

\  I 

Tempoial  bone  \ 


I  Dura  mater 


/  Temporal  bone 


Temporal  muscle 


Cochlea 
Internal  carotid 


Internal  jugular  vein 

Internal  carotid  artery 


Cartilage  of  meatus 
'     External  auditory  meatus  (cartilaginous) 
Parotid  gland 


by  the  tympanic  membrane;  and  from  the  chamber  which  forms  the  internal  ear 
by  the  structures  which  fill  in  the  cochlear  and  vestibular  fenestra.  It  commu- 
nicates with  the  pharynx  by  the  auditory  (Eustachian)  tube.  _  The  structures  of 
the  middle  ear  are  of  importance,  and  the  study  is  somewhat  difficult,  on  account 
of  the  small  size  of  the  structures,  the  depth  at  which  they  lie,  and  the  hard  charac- 
ter of  the  surrounding  bone. 

The  illustrations  (figs.  829,  830,  831,  833,  834)  will  help  to  explain  the  text  and  should 
be  constantly  referred  to.  Figs.  830  and  831  are  taken  from  frozen  sections  traversing  the 
right  ear  in  the  coronal  planes;  while  figs.  833,  834  represent  dissections. 

The  parts  to  be  considered  in  order  are  the  tympanic  rnembrane,  the  tympanic 
cavity,  the  tympanic  antrum  and  the  auditory  (Eustachian)  tube. 

The  Tympanic  Membrane 
The  tympanic  membrane  [membrana  tympani]  (fig.  835)  is  elliptical  in  shape, 
its  long  axis  nearly  vertical,  measuring  9  to  10  mm.,  its  short  axis,  8  to  9  mm. 
It  slopes  medially  from  the  superior  and  posterior  to  the  inferior  and  anterior 


THE  TYMPANIC  MEMBRANE 


1087 


wall  of  the  meatus,  forming,  as  a  rule,  with  the  superior  wall,  an  angle  of  140 
degrees.  It  varies,  however,  greatly  in  form,  size,  and  obliquity.  Viewed  from 
the  meatus,  it  appears  as  a  semitransparent  membrane,  which  sometimes  has  a 
reddish  tinge.  It  is  drawn  medially  and  made  funnel-shape  by  the  manubrium  of 
the  malleus,  but  the  walls  of  the  funnel  bulge  toward  the  meatus  (fig.  834) .  The 
most  depressed  point  at  its  centre,  the  umbo,  is  slightly  inferior  and  posterior  to 
the  centre  of  the  membrane,  and  corresponds  to  the  tip  of  the  manubrium  (fig. 
832).  From  it  a  whitish  streak,  the  malleolar  stria,  caused  by  the  manubrium 
shining  through,  passes  superiorly  toward  the  circumference.  At  the  superior 
end  of  the  stria  is  a  slight  projection,  the  malleolar  prominence,  formed  by  the 
lateral  process  of  the  malleus.  From  it  two  folds,  the  anterior  and  posterior 
Fig.  831. — Frozen  Coronal  Section  op  the  Right  Ear.     (Somewhat  Enlarged.) 

Prominence  of  facial  canal 


Medial  tympanic  wall 

Tegmen  tympani 
Recessus  epitympanicus         \ 


Stapes 

I 
Facial  nerve 


^  Fenestra  vestibuli 

;  Cochlea 

,  Facial,  and  cochlear 
vestibular  nerves 


Cavum  conchse 


Internal  carotid  artery 


Cartilage  of  meatus  j 

Parotid  gland 

plicffi,  stretch  to  the  extremities  of  the  tympanic  sulcus  (fig.  832).  The  small 
triangular  area  of  the  membrane  bounded  by  the  plicae,  is  termed  the  pars  flaccida 
(Shrapnell's  membrane).  It  is  thin  and  flaccid,  and  is  attached  directly  to  the 
petrous  bone  in  the  tympanic  notch  (notch  of  Rivinus).  The  larger  part  of  the 
tympanic  membrane,  the  pars  tensa,  is  inferior  to  the  plicae  and  is  tightly  stretched. 
Its  thickened  margin,  the  limbus,  is  attached  by  a  fibro -cartilaginous  annulus 
to  the  tympanic  sulcus,  and  at  the  spines  of  the  tympanic  ring  is  continuous  with 
the  plicae. 

Structure  of  the  tympanic  membrane. — The  tympanic  membrane  is  about  .1  mm.  thick, 
and  consists  of  four  layers.  The  lateral  cutaneous  layer,  relatively  thick,  is  a  continuation 
of  the  skin  lining  the  external  auditory  meatus.  Next  to  it  is  a  radiate  fibrous  layer,  composed 
of  connective  tissue,  the  fibres  of  which  are  attached  to  the  manubrium  of  the  malleus  and  radiate 
from  it.  Medial  to  it  is  the  circular  fibrous  layer,  which  has  its  fibres  arranged  concentrically 
and  is  esijecially  thick  at  the  cncumference.  It  is  closely  bound  to  the  rachate  layer.  The 
mucous  layer,  which  is  a  continuation  of  the  mucosa  of  the  tympanic  cavity,  covers  the  medial 
surface  of  the  membrane  smoothl}',  except  where  the  manubrium  of  the  malleus  causes  a  pro- 
jection. The  fibrous  layers  are  attached  to  the  fibro-cartilaginous  ring  and  are  not  present 
in  the  pars  flaccida. 


1088 


SPECIAL  SENSE  ORGANS 


The  Tympanic  Cavity 

The  tympanic  cavity  [cavum  tympani],  as  has  been  stated,  is  an  air-space, 
lined  with  mucous  membrane,  situated  between  the  external  and  the  internal  ear. 
It  is  of  irregular  outline,  but,  roughty,  it  is  a  slit-like  cavity,  lying  in  an  oblique 
antero-posterior  plane.  Its  transverse  diameter  measures  only  from  2-4  mm., 
while  the  vertical  and  antero-posterior  diameters  measure  about  15  mm.  (fig.  834). 

It  is  narrowest  at  the  centre,  and  wider  superiorly  than  inferiorly.  The  bony 
walls  have  already  been  partly  described  with  the  temporal  bone,  and  hence  the 
description  given  here  will  refer  to  the  appearance  found  in  the  fresh,  or  un- 
macerated  condition. 

It  will  be  noticed  (see  fig.  829)  that  the  floor  of  the  space  is  on  very  much 
the  same  horizontal  plane  as  the  floor  of  the  external  meatus,  and  the  lower 
margin  of  the  tympanic  membrane.     The  roof,  on  the  other  hand,  lies  at  a  much 


Fig.  832. — ^Lateral  Surface  op  the  Left  Membhana  Tympani.     (Enlarged  from  life.) 
Pars  flaccida  or  Shrapnell's  membrane       Posterior  plica 


Malleolar  prominence  caused  by' 
lateral  process  of  malleus 


Long  process  of  incus 


Malleolar  stria 


7    Pars  tensa  of  tympanic  membrane 


higher  level  than  the  upper  margin  of  that  membrane.  Hence  the  cavity  may 
be  divided  into  two  regions,  a  loiver  part,  corresponding  in  extent  to  the  tym- 
panic membrane,  and  an  upper,  above  the  upper  border  of  the  membrane,  known 
as  the  epitympanic  recess.  This  division  forms  a  definite  chamber,  and  con- 
tains the  head  of  the  malleus  and  the  body  and  short  process  of  the  incus. 
It  is  on  the  posterior  part  of  this  chamber  that  the  communication  with  the 
tympanic  antrum  is  found  (fig.  835). 

As  the  shape  of  the  tympanum  is  irregular,  its  walls  are  not  everywhere 
clearly  marked  off  from  one  another,  but  there  may  be  recognized  (figs.  829 
and  835)  a  roof,  or  tegmental  wall,  a  floor,  or  jugular  wall,  a  medial  or  labyrin- 
thine wall  and  a  lateral  or  membranous  wall,  an  anterior  or  carotid,  and  a  pos- 
terior or  mastoid  boundary  or  wall. 

The  roof,  or  tegmental  wall,  is  formed  by  a  portion  of  the  tegmen  tympani,  a  thin  plate 
of  bone  which  is  continued  backward  to  form  the  roof  of  the  tympanic  antrum.  This  plate  is 
formed  by  the  petrous  part  of  the  temporal  bone,  and  at  its  lateral  margin  is  the  petro-squamous 
suture,  where  a  slight  deficiency  in  the  roof  may  occur. 

The  floor,  or  jugular  wall  is  very  narrow  transversely,  and  is  in  intimate  relation  to  the 
internal  jugular  vein  (fig.  831).  As  shown  in  fig.  833,  the  surface  is  frequently  very  irregular 
from  stalactite-lilve  projections  between  which  are  the  tympanic  cellulas  (air  cells),  while  near 
the  back  there  is  occasionally  a  marked  projection  corresponding  externally  to  the  root  of  the 
styloid  process. 

The  posterior  or  mastoid  wall  presents  at  its  lower  part,  many  additional  tympanic  ceUulse, 
and  higher  up,  an  elevation,  the  pyramidal  eminence,  on  whose  apex  is  an  aperture  transmitting 
the  tendon  of  the  stapedius  muscle.  The  fleshy  beUy  of  that  muscle  is  contained  in  a  cavity 
in, the  interior  of  the  bony  pyramid  of  the  posterior  wall.  Lateral  to  this  is  an  aperture,  the 
aperiura  tympanica  canaliculm  chorda,  through  which  the  chorda  tympani  nerve  enters  the  tym- 
panum, covered  by  a  reflexion  of  the  mucous  membrane.  Between  this  opening  and  the  pyra- 
mid is  a  slight  elevation;  and  above  it  is  a  fossa,  termed  the  sinus  posterior.  Above  this  again 
is  a  recess,  where  the  posterior  ligament  of  the  incus  is  attached,  known  as  the  fossa  incudis. 
This  portion  of  the  posterior  wall  forms  the  boundary  of  the  epitympanic  recess.  Here  the 
■cavity  of  the  tympanum  is  continued  with  that  of  the  antrum  tympanicum,  or  mastoid  antrum, 


THE  TYMPANIC  CAVITY 


1089 


a  large  irregular  space  into  which  open  the  mastoid  cells  (see  p.  1092).  The  boundaries  of  the 
orifice  are  formed  above  by  the  tegmen  tympani,  medially  by  the  prominences  of  the  lateral 
semicircular  canal  and  facial  nerve,  and  laterally  by  a  plate  of  bone  termed  the  scutum. 

The  carotid  (anterior)  wall  presents  superiorly  the  tensor  tympani  muscle  in  its  canal, 
and  at  a  lower  level  the  opening  of  the  tuba  audiliva  (Eustachian  tube)  (fig.  835).  Inferiorly, 
a  thin,  bony  wall,  covered  with  tympanic  cellulse  and  pierced  by  the  carotico-tympanic  nerves, 
separates  the  tympanic  cavity  from  the  carotid  canal. 

The  membranous  (lateral)  wall  is  formed  mainly  by  the  tympanic  membrane,  with  the 
small  rim  of  bone  to  which  it  is  attached,  but  superiorly  the  lateral  wall  of  the  epitympanic 
recess  is  formed  by  a  plate  of  bone  termed  the  scutum. 

The  labyrinth  (medial)  wall  (fig.  833)  presents  inferiorly  the  promontory,  produced  by  the 
first  turn  of  the  cochlea  with  the  tympanic  plexus  (Jacobson's  nerve)  lodged  in  grooves  upon  its 
surface.     Inferior  and  posterior  to  the  promontory  is  a  depression  or  fossula  at  the  bottom  of 


Fig.  833.- 


-The  Labyrinth  (Medial)  Wall  op  the  Right  Tympanum  with  the  Tympanic 
Ossicles  in  Position. 


Short  process  of  incu: 


Long  process  of  incus 

Chorda  tympani 

Facial  nerve 

Pyramidal 

eminence 

Tendon  of 

stapedius 

Stapes 


Cochlear  fossula  — 


Torn  edge  of  mucosa 
of    superior    liga- 
ment of  incus 

Body  of  incus 


Neck  of  malleus 

Anterior  malleolar 

ligament 
Lateral  process  of 

malleus 
Chorda  tympani 


j""  Tympanic  pies 
Promontory 


Tympanic  cellulae 


which  is  the  cochlear  fenestra  (fenestra  rotunda),  closed  by  the  secondary  tympanic  membrane, 
and  posterior  to  the  promontory  is  a  smooth  projection,  the  subiculum  of  the  promontory,  which 
forms  the  inferior  border  of  a  rather  deep  depression  known  as  the  tympanic  sinus.  Anteriorly 
and  superiorly  is  the  cochleariform  process,  and  superiorly  and  posteriorly  are  a  depression  or 
fossula  leading  to  the  vestibular  fenestra  (fenestra  ovalis),  which  is  closed  by  the  base  of  the  stapes, 
the  prominence  of  the  facial  (Fallopian)  canal,  and  the  prominence  of  the  lateral  semicii'oular 
canal,  the  two  latter  being  formed  in  the  medial  wall  of  the  entrance  to  the  mastoid  antrum. 


The  tympanic  mucous  membrane  forms  a  complete  covering  for  the  walls  and 
contents  of  the  tympanic  cavity.  It  is  continuous  anteriorly  with  the  mucosa  of 
the  tuba  auditiva  (Eustachian  tube)  and  posteriorly  with  that  of  the  tympanic 
(mastoid)  antrum  and  mastoid  cells.  It  is  a  thin,  transparent,  vascular  membrane 
intimately  united  to  the  periosteum.  As  it  passes  from  the  walls  to  the  contents  of 
the  tympanic  cavity,  besides  covering  the  ligaments  of  the  malleus  and  the  incus 
and  the  tendons  of  the  tensor  tympani  and  stapedius  muscles,  it  forms  a  number  of 
special  folds  and  pouches. 

The  anterior  malleolar  fold  is  reflected  from  the  tympanic  membrane  over  the  anterior 
process  and  ligament  of  the  malleus  and  the  adjacent  part  of  the  chorda  tympani,  and  the 
posterior  malleolar  fold  stretching  between  the  manubrium  and  the  posterior  tympanic  wall, 
surrounds  the  lateral  ligament  of  the  malleus  and  the  posterior  part  of  the  chorda  tympani. 
Each  of  these  folds  presents  inferiorly  a  concave  free  border,  and  between  them  and  the  tym- 
panic membrane  are  two  blind  pouches,  the  anterior  and  posterior  malleolar  recesses  or  pouches 


1090 


SPECIAL  SENSE  ORGANS 


of  Troltsch.  Connected  with  the  posterior  recess  is  a  third  cul-de-sac,  the  superior  recess  of 
the  tympanic  membrane,  or  pouch  of  Prussak,  situated  between  the  pars  flaccida  of  the  tym- 
panic membrane  and  the  neck  of  the  malleus.  The  floor  of  this  recess  is  formed  by  the  lateral 
process  of  the  malleus,  and  is  lower  than  its  outlet;  therefore,  the  recess  may  serve  as  a  pocket 
in  which  pus  or  other  fluid  may  accumulate.  A  somewhat  variable  fold  of  mucosa,  the  plica 
incudis,  passes  from  the  roof  of  the  tympanic  cavity  to  the  body  and  short  process  of  the  incus. 
The  body  and  short  process  of  the  incus,  the  head  of  the  malleus,  and  this  fold  incompletelj 
separate  off  a  lateral  cupular  portion  of  the  epitympanic  recess,  and  a  stapedial  fold  stretches 
from  the  posterior  wall  of  the  tympanic  cavity  and  surrounds  the  stapes,  including  the  oburator 
membrane,  which  stretches  between  its  crura.  Other  inconstant  folds  have  been  described. 
The  mucosa  of  the  typanic  cavity,  except  over  the  tympanic  membrane,  promontory,  and 
ossicles,  is  covered  by  a  columnar  ciliated  epithelium. 


Fig.  834. — The  Tympanic  Cavity,  Antehiob  Wall  Removed, 


Epitympanic  recess 


Lateral  malleolar 

ligament 

Pars  flaccida 

Superior  recess 

Lateral  process  of 

Anterior  malleolar 

ligament 

Insertion  of  tensor 

tampani 

Manubrium  of 
malleus 
External  acoustic 
meatus 


Umbo  and  tip  of 
manubrium  of 
malleus 


Tympanic  cellula 


Head  of  malleus 

Neck  of  malleus 

Facial  nerve 
Long  process  of 

incus 
Pyramidal 
eminence 
Tendon  of 
stapedius 


Bones. — The  tympanic  cavity  contains  three  small  movable  bones,  joined  to- 
gether and  to  the  walls  of  the  cavity,  and  having  attached  to  them  special  muscles 
and  ligaments.  These  auditory  ossicles  form  a  chain  across  the  tympanic  cavity 
connecting  the  tympanic  membrane  and  the  vestibular  (oval)  fenestra.  They  are 
the  malleus,  the  incus,  and  the  stapes,  and  are  described  in  the  section  on  Oste- 
ology on  p.  79. 

Articulations  of  the  ossicles. — The  manubrium  and  lateral  process  of  the  maUeus  are  im- 
oedded  in  the  tympanic  membrane.  The  margin  of  the  irregularly  elliptical  articular  surface 
bn  the  posterior  side  of  the  head  of  the  malleus  is  bound  to  the  body  of  the  incus  by  a  thin 
capsular  ligament,  forming  a  diarthrodial  joint,  the  incudo-malleolar  articulation.  From  the 
inner  surface  of  the  capsular  ligament,  a  wedge-shaped  rim  projects  into  the  joint  cavity  and 
incompletely  divides  it.  The  long  crus  of  the  incus  lies  parallel  to  the  manubrium  of  the 
malleus  and  on  its  superior  and  medial  aspect  (figs.  833  and  835).  It  ends  in  the  lenticular 
process.  The  convex  extremity  of  this  fits  into  the  concavity  on  the  head  of  the  stapes,  to 
form  a  diarthrodial  joint,  the  incudo-stapedial  articulation.  From  its  articulation  with  the 
incus,  the  stapes  passes  almost  horizontally  across  the  tympanic  cavity  to  its  junction  with 
the  medial  wall.  The  cartilage-covered  edge  of  the  base  is  bound  to  the  cartilage-covered  rim 
of  the  vestibular  (oval)  fenestra  by  the  annular  ligament  of  the  base  of  the  stapes,  thus  forming 
the  tympano-stapedial  syndesmosis. 

Ligaments  of  the  ossicles. — In  addition  to  the  attachment  of  the  manubrium 
of  the  malleus  and  the  base  of  the  stapes  to  the  walls  of  the  tympanic  cavity,  the 
bones  have  additional  ligamentous  attachments.     The  superior  malleolar  liga- 


THE  TYMPANIC  CAVITY 


1091 


ment  runs  almost  vertically  from  the  superior  wall  of  the  epitympanic  recess  to  the 
head  of  the  malleus  (fig.  834) .  The  anterior  malleolar  ligament  extends  from  the 
angular  spine  of  the  sphenoid  bone  through  the  petro-tympanic  (Glaserian)  fissure 
to  the  anterior  or  long  process  of  the  malleus,  which  it  surrounds,  and  is  inserted 
with  it  into  the  neck  of  the  malleus.  The  lateral  malleolar  ligament  is  short  and 
thick,  and  runs  from  the  margins  of  the  tympanic  notch  (notch  of  Rivinus)  to  the 
neck  of  the  malleus  (fig.  834) .  The  posterior  ligament  of  the  incus  passes  from  the 
fossa  on  the  posterior  tympanic  wall  to  the  crus  brevis  of  the  incus  (fig.  835) .  The 
superior  ligament  of  the  incus  is  little  more  than  mucous  membrane;  it  runs  from 
the  tympanic  roof  to  the  body  of  the  incus. 

Muscles  of  the  ossicles. — Each  of  the  muscles  of  the  ossicles  is  contained  in  a 
bony  canal.  The  tensor  tympani  is  a  pinniform  muscle  about  2  cm.  long.  It 
arises  from  the  cartilaginous  part  of  the  tuba  auditiva  (Eustachian  tube),  from  the 


Fig.  835. — Medial  Surface  op  Right  Membrana  Tympani.     (Enlarged.) 
Superior  malleolar  ligament       Incus 


Head  of  malleus 

Chorda  tympani  nerve 
Tendon  of  tensor  tympani 

Manubrium  of  malleus 

Tensor  tympani  muscle 

Tuba  auditiva 


Posterior  ligament  of  incus 


Posterior  portion  of 
epitympanic  recess 


■Base  of  stapes 


'Lenticular  process  of  incus 


Posterior  portion  of 
membrana  tympani 


adjacent  part  of  the  great  wing  of  the  sphenoid,  and  from  the  bony  walls  of  the 
semicanal  which  encloses  it.  It  ends  in  a  round  tendon  which  turns  almost  at  right 
angles  over  the  cochleariform  process  and  passes  laterally  across  the  tympanic 
cavity  to  be  attached  to  the  manubrium  of  the  malleus  near  the  neck.  It  draws 
the  manubrium  medially  and  tightens  the  tympanic  membrane,  and  is  supplied  by 
the  motor  division  of  the  trigeminal  cranial  nerve,  through  the  tensor  tympani 
branch  from  the  otic  ganglion.  The  stapedius  arises  in  the  interior  of  the  hollow 
pyramidal  eminence.  The  tendon  escapes  through  the  openings  at  the  apex  and 
then  turns  inferiorly  and  is  inserted  on  the  posterior  surface  of  the  neck  of 
the  stapes.  It  draws  laterally  the  ventral  border  of  the  base  of  the  stapes  and  is 
supplied  by  the  facial  nerve. 


Vessels  and  nerves. — The  arteries  of  the  tympanic  cavity  are  the  anterior  tympanic  from 
the  internal  maxillary  artery  (fig.  451),  the  stylo-mastoid  from  the  posterior  auricular  artery, 
the  superficial  petrosal  from  the  middle  meningeal  artery,  the  inferior-tympanic  from  the 
ascending  pharyngeal  (fig.  446),  and  the  carotio-tympanic  branch  from  the  internal  carotid. 
The  veins  empty  into  the  superior  petrosal  sinus  and  into  the  posterior  facial  (temporo- 
maxillary  vein).  The  nerves  are  the  tympanic  plexus  formed  by  the  tympanic  branch  of  the 
glosso-pharyngeal  (p.  951),  and  the  inferior  and  superior  carotico-tympanic  nerves  which  join 
the  internal  carotid  plexus  of  the  sympathetic  (p.  960).  The  small  superficial  petrosal  nerve 
takes  its  origin  from  the  tympanic  plexus,  and  the  chorda  tympani  crosses  the  t)"mpanic 
cavity  from  the  posterior  to  the  anterior  wall  (p.  948,  figs,  738  and  835). 


1092  SPECIAL  SENSE  ORGANS 

The  Antrum  Tympanicum 

The  aperture  {aditus)  in  the  upper  part  of  the  posterior  wall  of  the  tympanum 
leads  into  the  chamber  termed  the  antrum  tympanicum.  This  is  a  comparatively 
large  cavity,  of  irregular  form,  lying  mainly  behind  but  also  somewhat  above  and 
lateral  to  the  tympanum,  and  extends  to  the  medial  end  of  the  external  auditory 
meatus.  It  is  lined  by  mucous  membrane,  continuous  with  that  of  the  tympanic 
cavity,  and  into  it  open  the  mastoid  cells  (cellulse  mastoidese).  These  cells  are 
small,  irregular  cavities  in  the  interior  of  the  mastoid  process  and  they  com- 
municate with  one  another  freely.  They  vary  exceedingly  in  their  size  and 
asrangement. 

The  antrum  tympanicum  has  a  roof,  formed  by  the  tegmen  tympani,  a  posterior  wall, 
separating  it  from  the  bend  of  the  transverse  sinus,  a  lateral  wall,  lying  about  10  mm.  from  the 
surface  of  the  head,  a  inedial  wall,  and  an  anterior  wall  (see  also  p.  78). 

The  Auditory  (Eustachian)  Tube 

The  auditory  tube  [tuba  auditiva]  (Eustachian  tube)  (fig.  829)  extends  from 
the  carotid  (anterior)  wall  of  the  tympanic  cavity  inferiorly,  medially,  and 
anteriorly  to  the  pharynx.  It  is  about  37  mm.  (1.5  in.)  long.  In  the  lateral 
one-third  of  its  length  it  has  a  bony  wall,  while  in  the  medial  two-thirds 
this  wall  is  cartilaginous.  The  osseous  part  (see  p.  74)  begins  at  the  tympanic 
ostium  on  the  anterior  wall  of  the  tympanic  cavity.  It  is  in  relation  medially 
and  inferiorly  with  the  carotid  canal,  and  gradually  contracts  to  its  irregular 
medial  extremity,  which  is  the  narrowest  point  in  the  tube,  and  is  termed  the 
isthmus.  The  cartilaginous  part  is  firmly  attached  to  the  osseous  and  hes  in  a 
sulcus  at  the  base  of  the  angular  spine  of  the  sphenoid  bone.  It  gradually  dilates 
in  its  passage  to  the  lateral  wall  of  the  pharynx,  where  its  opening,  pharyngeal 
sotium,  is  just  posterior  to  the  inferior  nasal  concha  (turbinated  bone).  The 
walls  of  the  cartilaginous  part  are  formed  by  a  cartilaginous  plate  which  is  folded 
so  as  to  form  a  trough-like  structure,  consisting  of  a  medial  and  a  lateral  lamina, 
completed  inferiorly  by  a  membranous  lamina  formed  of  connective  tissue. 

A  small  portion  of  the  lumen  in  the  superior  part  of  the  cartilaginous  tube  remains  per- 
manently open;  elsewhere  the  walls  are  in  contact,  except  during  deglutition,  when  they  are 
opened  by  the  tensor  veli  palatini  muscles.  The  mucosa  of  the  osseous  part  is  thin,  and  firmly 
attached  to  the  bony  wall,  but  in  the  cartilaginous  part  it  becomes  thicker,  looser,  and  folded, 
and  contains  mucous  glands,  especially  near  the  pharynx,  where  there  is  also  some  adenoid 
tissue. 

3.     THE  INTERNAL  EAR 

The  internal  ear  [auris  interna]  is  the  essential  part  of  the  organ  of  hearing. 
It  consists  of  a  cavity,  the  osseous  labyrinth,  contained  within  the  petrous  portion 
of  the  temporal  bone,  and  enclosing  a  membranous  labyrinth.  The  osseous 
labyrinth  is  divided  into  cochlea,  vestibule,  and  semicircular  canals  (seep.  80), 
and  the  accompanying  figures  (338-838  )show  their  position  and  relations. 

It  will  be  noticed  that  the  vestibule  forms  a  central  chamber,  from  which  the  semicircular 
canals  and  the  cochlea  branch  off;  the  former  from  the  superior  and  dorsal  portion,  and  the  latter 
from  the  ventral  and  inferior. 

It  will  further  be  noticed  that  the  bony  wall  of  this  vestibule  shows  depressions  and  ridges  on 
its  interior,  which  are  associated  with  parts  of  the  membranous  labyrinth,  viz.,  an  upper  recess 
for  the  utricle  (fovea  hemielliptica)  and  a  lower  recess  for  the  saccule  (foyea  hemispherica). 
There  are  openings  in  the  bony  wall  for  the  entrance  of  nerves  to  the  different  parts  of  the 
membranous  labyrinth,  and  for  the  transmission  of  the  ductus  endolymphaticus,  as  well 
as  the  small  openings  of  the  semicircular  canals  (ducts)  and  the  opening  of  the  cochlear  canal 
(or  duct). 

The  membranous  labyrinth,  in  which  the  auditory  (acoustic)  nerves  (cochlear 
and  vestibular)  end,  lies  within  the  osseous  labyrinth,  the  form  of  which  it  more 
or  less  closely  resembles.  Thus  the  membranous  semicircular  ducts  lie  within 
the  bony  semicircular  canals,  the  membranous  cochlear  duct  within  the  bony 
cochlea;  while  the  vestibule  contains  two  small  membranous  sacs,  the  utricle 
and  saccule,  with  their  connections.  The  membranous  structures  are  much 
smaller  in  diameter  than  the  osseous,  and  are  partially  separated  from  the  bone 
by  an  endothelial-Hned  space  which  is  filled  with  a  fluid,  the  perilymph.     The 


THE  MEMBRANOUS  LABYRINTH 


1093 


membranes  are  in  contact,  however,  with  the  bony  wall  along  their  convex  margin, 
and  the  utricle,  saccule  and  cochlear  canals  are  in  contact  with  the  bony  walls 
over  the  areas  where  the  nerves  enter  them.  The  fluid  which  fills  the  mem- 
branous labyrinth  is  termed  the  endolymph. 

Fig.  836. — The  Osseous  Labyrinth  of  the  Right  Side. 
(Modified  from  Soemmerring.     Enlarged.) 
Superior  semicircular  caiial< 


Posterior  semicircular  canal 

Lateral  semicircular  canal 

Vestibule  and  fenestra  ovahs' 


Second  turn  of  cochlea 

Cupula  of  cocMea 


Ampulla 
Fenestra  cochleari: 

Commencement  of  first  turn   of   the  cochlea 


The  utricle  is  an  oval  tubular  sac,  whose  rounded  end  lies  in  the  superior  and 
dorsal  portion  of  the  vestibule.  It  is  here  tightly  bound  to  the  elliptic  recess 
(fovea  hemielliptica)  by  connective  tissue  and  by  the  entrance  of  the  filaments 
of  the  utricular  division  of  the  vestibular  nerve  as  they  pass  from  the  superior 


837. — Interior  of  the  Osseous  Labyrinth  of  the  Left  Side. 
(Modified  from  Soemmerring.     Enlarged.) 

-Superior  semicircular  canal 


Elliptic  recess  (fovea 
hemielliptica) 

Superficial  recess  (fo 
hemispherica 


Lamina  spirali 
Scaia  tympani  of  cochlea. 


•Posterior  semicircular  canal 

Lateral  semicircular  canal 
.Opening  common  to  superior  and 


posterior  semicircular  canal 
Internal  aperture  of  vestibular 
aquseduct 

■Internal  aperture  of  cochlear 
canaliculus 


macula  cribrosa  to  the  wall  of  the  utricle.  In  the  anterior  part  of  the  interior  of 
the  utricle,  an  oval,  whitish,  thickened  area,  macula  acustica  utriculi,  marks  the 
terminal  distribution  of  the  nerve,  and  posteriorly  the  utricle  is  joined  by  the 
orifices  of  the  semicircular  ducts. 


Fig.  838. — Interior  of  the  Osseous  Cochlea.     (Enlarged.) 


Lamina  spiralis 

Modiolus 


The  saccule  is  a  flattened,  oval  sac,  smaller  than  the  utricle,  and  situated  in 
the  anterior  and  inferior  part  of  the  vestibule.  It  is  bound  to  the  spherical  recess 
(fovea  hemisphserica)  by  connective  tissue  and  by  the  saccular  division  of  the 


1094 


SPECIAL  SENSE  ORGANS 


vestibular  nerve,  filaments  of  which  extend  from  the  middle  macula  cribrosa  to 
the  anterior  and  medial  wall  of  the  saccule,  to  be  distributed  over  a  thickened 
area,  macula  acustica  sacculi.  Anteriorly  and  inferiorly  the  saccule  gradually 
passes  into  a  short  canal,  the  ductus  reuniens,  which  connects  it  with  the  cochlear 
duct,  and  posteriorly  the  very  small  endolymphatic  duct  is  attached  (fig.  839). 


Fig.  839. — Diagram  of  the  Left  Membranous  Labyrinth.     (Deaver.) 
Superior  and  lateral  membranous  ampullje 


Superior  semicircular 
duct 


Cupular  CEecum 


Cochlear  duct 


Dtricle 


Lateral  semicircular  duct 
Posterior  membranous  ampulla 
Ductus  endolymphaticus 


This  extends  through  the  aquseductus  vestibuli  to  the  posterior  surface  of  the 
petrous  portion  of  the  temporal  bone,  where  it  ends  in  a  dilated  blind  pouch, 
the  endolymphatic  sac,  situated  just  beneath  the  dura.  Just  beyond  the  saccule, 
the  endolymphatic  duct  is  joined  at  an  acute  angle  by  a  short  canal  of  minute 
calibre,  the  utriculo-saccular  duct,  which  opens  into  the  utricle  through  its  anterior 
medial  wall  and,  with  the  endolymphatic  duct,  connects  it  with  the  saccule. 

Fig.  840. — Right  Membranous  Labyrinth  of  a  Newborn  Child.  Exposed  by  Partial 
Removal  OF  THE  Bony  Labyrinth.  Dorsal  view.  (Toldt,  "Atlas  of  Human  Anatomy," 
Rebman,  London  and  New  York.) 


Facial  nerve 


Osseous  lamina 
spiralis 

Lamina  basilans 
(membranous  *• 
lamina  spiralis) 


Scala  tympani 


Supenor  semicircular  duct 


Common  crus 


Saccule  i    Posterior  membranous  ampulla 
Posterior  ampuUary  nerve 


The  semicircular  ducts  (membranous  semicircular  canals)  are  situated  within 
the  osseous  semicircular  canals  and  are,  therefore,  known  as  the  lateral,  superior, 
and  posterior  semicircular  ducts.  They  connect  with  the  utricle  by  five  openings, 
the  posterior  and  superior  ducts  uniting  to  form  a  common  crus  before  their 


THE  MEMBRANOUS  LABYRINTH 


1095 


termination.  Each  duct  is  less  than  a  third  of  the  diameter  of  the  bony  canal, 
from  which  it  is  separated  by  a  large  perilymphatic  space,  except  along  the 
greater  cm*vature,  where  it  is  attached.     The  ducts  are  dilated  in  the  bony 

Fig.  841. — Schematic  Representation  of  the  Right  Membranotjs  Labyrinth  and  the 
Divisions  of  the  Acoustic  Nerve.  Dorsal  view.  (Toldt,  "Atlas  of  Human  Anatomy," 
Rebman,  London  and  New  York.) 

Utriculo-saccular  duct 
Macula  acustica  of  utricle 


Macula  acustica  of  saccule 

Vestibular  ganglion 

Vestibular  nerve 
Saccular  nerve         \ 


Cochlear  nerve.^^ 


Cochlear  duct " 


Saccule 
Ductus  reuniens  (of  Hensen) 


Posterior  ampullary  nerve 


--Superior  semicircular  duct 

Ampullary  cristae  of  the 

superior  and  lateral 

semi-circular  ducts 


— ,  Endolymphatic 
duct 
Posterior    semicir- 
cular duct 

Ampullary  crista  of 
the  posterior  semi- 
circular duct 


-"  Endolymphatic  ; 


ampullse,  producing  the  lateral,  superior,  and  posterior  membranous  ampullae, 
and  on  the  attached  surface  of  each  of  these  there  is  a  transverse  groove,  the 
ampullary  sulcus,  for  the  ampullary  division  of  the  vestibular  nerve,  and  corre- 
sponding to  the  sulcus  a  ridge,  the  ampullary  crista,  projects  into  the  interior. 


Fig.  842. — Axial  Section  Through  the  Decalcified  Cochlea  of  a  Newborn  Child 
(Toldt,  '*  Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 


Hamulus  of  lamina  spirahs^ 
Apical  spiral'^;;; 


Helicotrema 

Modiolus 

Scala  vestibuli 
Cochlear  duct 


Lamina  basilans 
(membranous  lamina' 
spiralis) 


Osseous  lamina  spirabs 

Spiral  ganglion  of  cochlea 

Base  of  modiolus 


Cochlear  nerve 
Internal  acoustic  meatus 

Acoustic  nerve  (cochlear  division) 


rl^V^  Spiral  ligament  of  cochlea 
jj;^v^ScaIa  tympan 

f 

Macula  acustica  sacculi 

Wall  of  saccule 
Saccular  nerve 

:tibular  ganglion 

Acoustic  nerve  (vestib- 
ular division) 


The  cristse  in  the  ampullee  of  the  membranous  semicircular  ducts  and  the  maculae 
in  the  saccule  and  utricle  are  superficially  covered  with  fine  crystals  of  calcium 
carbonate,  otoconia  (otohths). 


1096 


SPECIAL  SENSE  ORGANS 


The  cochlear  duct  (membranous  cochlea  or  scala  media)  begins  within  the 
cochlear  recess  of  the  vestibule  in  a  blind  pouch,  the  vestibular  caecum,  and 
traversing  the  spiral  canal  of  the  cochlea,  ends  just  beyond  the  hamulus  of  the 
lamina  spiralis  in  a  second  blind  pouch,  the  cupular  caecum.  Close  to  the  ves- 
tibular caecum  it  is  joined  to  the  saccule  by  the  ductus  reuniens.  It  is  lined 
throughout  by  epithelium  and  is  somewhat  triangular  in  cross-section.  Its 
floor  is  formed  by  thickened  periosteum  over  part  of  the  osseous  lamina  spiralis 
and  by  a  fibrous  membrane,  the  lamina  basilaris,  which  stretches  from  the  free 
border  of  the  lamina  spiralis  to  a  thickening  of  the  periosteum,  the  spiral  ligament 
of  the  cochlea,  on  the  peripheral  wall. 

The  epithelium  of  this  floor  is  greatly  modified,  forming  the  spiral  organ  (organ  of  Corti) 
in  which  the  fibres  of  the  cochlear  nerve  terminate.  The  periplieral  wall  is  formed  by  the 
thickened  periosteum  upon  the  peripheral  wall  of  the  cochlear  canal,  while  the  third  waU  is 


Figs.  843  and  844. — Sections  Showing   Early  Stages  in  the  Development  op  the  Otic 

Vesicle. 


fomed  by  a  thin  vestibular  membrane  (membrane  of  Reissner)  which  passes  from  the  periphera 
wall  to  the  osseous  lamina  spiralis  near  its  free  margin,  forming  with  the  lamina  spiralis  an  angle 
Ff  45  degrees.  The  cochlear  duct  and  the  osseous  spiral  lamina  divide  the  cochlear  spiral 
canal  into  two  parts,  one  next  to  the  basilar  membrane,  the  scala  tympani,  and  one  next  to 
the  vestibular  membrane,  the  scala  vestibuli.  The  scala  tympani  unites  with  the  scala  vestibuli 
at  the  helicotrema,  and  from  the  scala  tympani  a  minute  canal,  the  perilymphatic  duct,  passes 
through  the  cochlear  canaliculus  and  connects  with  the  subarachnoid  space.  A  thin  fibrous 
layer,  the  secondary  tympanic  membrane,  closes  the  cochlear  fenestra  (fenestra  rotunda) 
and  thus  separates  the  scala  tympani  from  the  tympanic  cavity,  and  the  vestibular  perilym- 
phatic space  (scala  vestibuli)  is  separated  from  the  tympanic  cavity  by  the  base  of  the  stapes 
in  the  vestibular  fenestra  (fenestra  ovalis). 

Vessels  and  nerves. — The  internal  auditory  artery  ,  fig.  514),  a  branch  of  the  basilar  artery, 
accompanies  the  cochlear  and  vestibular  nerve.  It  supplies  the  vestibule,  semicircular  canals, 
and  cochlea,  and  their  membranous  contents.  The  blood  is  returned  by  the  internal  auditory 
vein  into  the  inferior  petrosal  sinus,  and  by  small  veins  which  pass  through  the  cochlear  and 
vestibular  aqueducts  to  the  inferior  and  superior  petrosal  sinuses.  The  acoustic  nerve  (p.  949, 
figs.  841  and  842)  consists  of  a  vestibular  and  a  cochlear  division.  The  membranous  ampuUse  of 
the  semicircular  ducts  and  the  acoustic  maculae  of  the  utricle  and  saccule  are  supplied  by 
the  vestibular  nerve.  The  spiral  organ  (organ  of  Corti)  in  the  cochlear  duct  is  supphed  by 
the  cochlear  nerve. 

Development  of  the  Ear 


The  external  and  middle  ears  have  a  common  origin  quite  distinct  frorn  that  which  gives 
rise  to  the  internal  ears,  and  are  to  be  regarded  as  portions  of  the  branchial  arch  apparatus 
secondarily  adapted  to  auditory  purposes. 

The  sensory  epithelium  lining  the  internal  ear  is  derived  from  the  otic  vesicle,  a  structure 
formed  from  the  surface  epithelium  of  the  head,  while  the  membrane  and  bones  surrounding 
it  are  formed  from  the  mesoderm  which  surrounds  the  vesicle. 


DEVELOPMENT  OF  THE  EAR 


1097 


Internal  ear. — The  process  of  development  is  as  follows  (fig.  843-845) : — 
By  invagination  from  the  surface,  an  epithelial-lined  vesicle,  termed  the  primitive  otocyst 
or  otic  vesicle,  is  formed  dorsal  to  the  extremity  of  the  second  branchial  cleft.  It  is  at  first 
merely  a  pit  on  the  surface,  but  eventually  it  loses  its  connection  with  the  surface  epithe- 
lium and  sinks  into  the  interior.  It  then  undergoes  the  alterations  in  shape  and  form  shown 
in  the  accompanying  fig.  845.  The  vesicle  is  at  first  somewhat  oval,  and  a  small  hollow 
stalk  arises  from  it,  the  recess  of  the  labyrinth,  which  forms  the  ductus  endolymphaticus  in 
the  adult.  The  ventral  and  dorsal  portions  of  the  cyst  become  enlarged.  From  the  former  two 
hoUow  plate-like  projections  arise,  one  placed  vertically,  the  other  horizontally,  and  along  the 
free  margins  of  these  plates  are  formed  the  semicircular  ducts,  the  superior  and  posterior  from 
the  vertical,  and  the  lateral  duct  from  the  horizontal  one.  The  central  part  of  each  plate  be- 
comes peforated,  and  the  periphery  is  thus  altered  to  the  characteristic  loop  form  of  the  adult 
semicircular  ducts.  The  portion  of  the  vesicle  lying  between  the  dorsal  and  ventral  enlarge- 
ments forms  the  primitive  atrium.  It  becomes  divided  into  two  chambers,  an  upper  dorsal 
connected  with  the  semicircular  ducts,  forming  the  utricle,  and  an  inferior  ventral,  the  saccule, 
which  is  connected  with  that  portion  of  the  ventral  expansion  from  which  the  cochlea  is  formed. 
The  recess  of  the  labyrinth  retains  its  connection  with  the  cavity  of  the  vesicle  at  the  narrow 
stalk  connecting  utricle  and  saccule,  (fig.  845).  The  cochlea  is  formed  by  an  outgrowth  from 
the  saccule,  at  first  straight,  and  later  coiled  in  the  fashion  formed  in  the  adult. 

Fig.  845. — Diageams  Illustrating  Successive  Stages  in  the  Development  of  the 
Membranous  Ear. 

Semicircular  canals  Ductus  endolym- 

Semicircnlar        Ductus  endo-       •i^^HSBmiiN.    I 
canal  lymphaticus 


Vestibular  pouch 
Recessus 


Cochlear  pouch 


Ductus  reuniens 
Saccule 
Utricle 


Ductus  reuniens 


Cochlea 


External  and  middle  ear. — The  external  auditory  meatus  is  formed  from  the  dorsal  part 
of  the  first  (external  branchial)  pouch,  and  the  tympanic  membrane  from  the  membrane 
which  forms  the  floor  of  that  pocket  and  separates  it  from  the  corresponding  pharyngeal 
(internal)  pouch.  Its  outer  surface  is  thus  formed  from  ectoderm  and  the  inner  from  endoderm. 
The  internal  (pharyngeal)  groove  gives  origin  to  the  tympanic  cavity  and  tuba  auditiva, 
the  margins  of  the  groove  uniting. 

The  auricle  is  formed  from  nodular  thickening  of  the  tissue  bounding  the  outer  end  of  the 
first  branchial  cleft.  Three  nodules  are  formed  on  the  first  (mandibular)  and  three  on  the  second 
(hyoid)  arch.  Behind  the  latter,  the  free  margin  of  the  auricle  is  formed  by  a  folding  off  of  the 
integument.  Later  an  additional  tubercle  is  formed  dorsally  between  the  two  sets  of  nodules. 
From  the  mandibular  nodules  are  formed  mainly  the  tragus  and  the  crus  of  the  helix — from 
the  hyoid  tubercles  the  scaphoid  fossa,  antitragus  and  the  crus  of  the  anthchx. 

The  auditory  ossicles,  and  their  muscles  are  formed  from  the  neighbouring  arches,  the  malleus 
and  incus,  together  with  the  tensor  tympani,  being  derived  from  the  first  arch,  while  the  stapes 
and  stapedius  probably  are  derived  from  the  second  arch. 

The  tympanic  cavity  is  at  first  quite  small,  but  later  increases  greatly,  partly  by  the  con- 
densation bf  the  loose  areolar  tissue  which  underlies  its  mucous  membrane,  the  auditory  ossicles 
and  their  muscles  being  thus  apparently  brought  within  the  cavity,  and  partty  by  the  absorption 
of  the  neighbouring  bone.  By  this  latter  process  the  antrum  and  the  tympanic  and  mastoid 
cells  are  formed,  all  these  depressions  or  cavities  being  lined  by  mucous  membrane  continuous 
with  that  of  the  tj'mpanic  cavit}'. 

The  Ear  in  the  Child. — The  ear  in  the  newborn  child  shows  several  marked  differences 
from  the  adult  ear. 

Among  the  principal  differences  are  the  following: — 

1.  The  external  auditory  meatus  is  very  short,  since  the  bony  portion  is  undeveloped, 
and  is  represented  only  by  the  tympanic  ring.  As  a  result  of  this,  the  tympanic  membrane  is 
placed  on  a  level  with  the  surface  of  the  head,  and  looks  very  much  downward. 

2.  The  mastoid  or  tympanic  antrum  is  relatively  very  large,  and  lies  above  and  behind  the 
tympanum.     Its  lateral  wall  is  only  about  1  mm.  in  thickness. 

3.  The  mastoid  process  is  not  developed,  and  hence  the  stylomastoid  foramen  opens  on 
the  surface  behind  the  lower  part  of  the  tympanic  ring.  The  exit  of  the  facial  nerve  is  therefore 
much  more  upon  the  surface,  and  higher  up  than  in  the  adult. 

4.  The  auditory  (Eustachian)  tube  is  nearly  horizontal  in  direction. 

5.  The  ossicles  are  of  nearly  the] same  size  as  in  the  adult. 


1098  SPECIAL  SENSE  ORGANS 

References  for  the  Special  Sense  Organs. — For  the  development  of  the  various 
sense  organs,  see  article  by  Keibel  in  Keibel  and  Mall's  Human  Embryology, 
vol.  2.  A.  Visual.  Graefe-Saemisch,  Handbuch  d.  ges.  Augenheilkunde; 
Salzmann,  Anat.  u.  Histol.  d.  Augapfels,  1912;  various  papers  in  Archiv  f.  Oph- 
thalmologic; (Anterior  chamber,  etc.)  Henderson,  Ophthalmic  Review,  1910-11; 
{Optic  disc)  Johnson,  Phil.  Trans.  Royal  Soc.  B.  vol.  194;  B.  Auditory.  Gray, 
Labyrinth  of  Mammals,  1910;  (Tectorial  membrane,  etc.)  Hardesty,  Amer.  Jour. 
Anat.,  vol.  8;  (Auditory  nerve,  comparative)  Holmes,  Trans.  Royal  Irish  Acad., 
vol.  32,  ser.  B;  (Experimental  embryology)  Lewis,  Amer.  Jour.  Anat.,  vols.  3,  7; 
C.  Olfactory.  Read,  Amer.  Jour.  Anat.,  vol.  8.  D.  Taste.  Von  Ebner,  in  Koel- 
liker's  Handbuch  d.  Gewebelehre;  Graberg,  Anat.  Hefte,  Bd.  12. 


SECTION  IX 

DIGESTIVE  SYSTEM 


Revised  for  the  Fifth  Edition 
By  C.  M.  JACKSON,  M.S.,  M.D., 

PROFESSOR   OF   ANATOMY  IN   THE    UNIVERSITY    OF   MINNESOTA 

IN  order  to  furnish  the  living  protoplasm  with  the  materials  necessary  for 
energy,  growth  and  repair,  a  constant  supply  of  food  must  be  provided. 
Most  foods  must  be  rendered  soluble,  and  must  undergo  certain  preliminary 
chemical  changes,  in  order  to  render  them  suitable  for  absorption  and  assimilation 
by  the  cells  of  the  body.  For  this  preparation  of  the  food-supply,  the  digestive 
system  [apparatus  digestorius]  is  provided,  which  includes  the  alimentary  canal 
and  certain  accessory  glands  (salivary  glands,  liver  and  pancreas) .  The  alimen- 
tary canal  is  divided  into  a  number  of  successive  segments,  varying  in  size  and 
structure  according  to  their  function.  These  segments  (fig.  846)  include  the 
mouth,  pharynx,  oesophagus,  stomach,  small  and  large  intestines. 

Typical  structure. — The  most  important  layer  of  the  tubular  alimentary  canal  is  the  inner 
mucous  memhrane  [tunica  mucosa].  From  its  epithelial  lining,  the  various  digestive  glands  are 
derived,  and  through  it  the  process  of  absorption  takes  place.  The  epithelium  is  supported 
by  a  fibrous  tunic  [lamina  propria  mucosa;]  beneath  which  is  a  thin  layer  of  smooth  muscle 
[lamina  muscularis  mucosae].  The  layer  next  in  importance  is  the  muscular  coat  [tunica  muscu- 
laris]  which  propels  the  contents  along  the  canal.  It  is  typically  composed  of  two  layers  of 
smooth  (involuntary)  muscle,  the  inner  circular  and  the  outer  longitudinal  in  arrangement. 
Between  the  mucosa  and  the  muscularis  is  a  loose,  fibrous  submucous  layer  [tela  submucosal, 
which  allows  the  folds  in  the  mucosa  to  spread  out  when  the  canal  is  distended.  Finally,  there 
is  an  outer  fibrous  coat  [tunica  fibrosa],  which  in  the  abdominal  cavity  becomes  the  smooth 
serous  coat  [tunica  serosa],  or  visceral  layer  of  the  peritoneum,  which  eliminates  friction  during 
movements.  The  variations  in  the  structure  of  the  aUmentary  canal  in  different  regions  are 
due  chiefly  to  differences  in  the  mucosa. 

Glands. — Since  the  glands  form  an  important  part  of  the  digestive  system,  the  classifica- 
tion of  glands  in  general  will  be  discussed  briefiy.  A  gland  may  be  somewhat  loosely  defined 
as  an  organ  which  elaborates  a  definite  substance  which  is  either  a  waste  product  to  be  eliminated 
(excreted),  or  a  secretion  to  be  further  utilized  by  the  organism.  Glands  may  be  divided  into 
(a)  ductless  glands  (e.  g.,  spleen,  thyreoid  gland),  which  pour  their  secretions  directly  into  the 
blood  or  lymph;  and  (b)  glands  with  ducts,  which  open  upon  an  epithelial  surface.  Some  organs, 
however,  belong  in  both  classes  (e.  g.,  liver,  pancreas). 

The  glands  with  ducts  (the  so-called  true'  glands)  are  always  derived  from  an  epithelial 
surface  and  may  be  further  subdivided  upon  the  basis  of  either  (1)  form  or  (2)  cell-structure. 
According  to  form,  glands  are  classified  as  either  <?<iwtor  or  saccular  (alveolar,  acinous).  Each 
of  these  may  be  either  simple  or  compound  (branched).  The  compound  saccular  form  is  often 
called  racemose.     Moreover,  intermediate  forms  (tubulo-racemose)  occur. 

According  to  cell-structure  and  character  of  secretion,  glands  are  divided  into  mucous 
and  serous  types.  In  the  mucous  type,  the  ceUs  appear  larger  and  fighter  (fig.  867)  when  swollen 
with  mucus  which  is  secreted  for  purposes  of  lubrication.  The  goblet^ceUs  of  the  intestine 
represent  imicellular  glands  of  this  type.  In  the  serous  (or  albuminous)  type  of  glands,  the 
cells  usually  appear  somewhat  smaller  and  more  deeply  stained,  with  numerous  zymogen 
granules  (fig.  867).  The  secretion  is  a  watery,  albuminous  fluid,  which  contains  the  digestive 
enzymes.  There  occurs  also  a  mixed  type,  with  separate  mucous  and  serous  saccules,  or  both 
types  of  cells  may  occur  in  the  same  saccule  (the  serous  cells  as  'demilunes'  or  'crescents' 
(fig.  867).  In  aU  cases,  the  epithelial  gland  ceUs  are  supported  by  a  fibrous  connective-tissue 
stroma,  which  provides  a  rich  vascular  and  nerve-supply. 

Morphology. — The  alimentary  canal  in  comparative  anatomy  is  divided  into  the  head-gut 
(mouth  and  pharynx),  fore-gut  (cesophagus  and  stomach),  mid-gut  (smaU  intestine),  and  hind- 
gut  (large  intestine).  Embryologically,  the  mid-gut  corresponds  roughly  to  the  portion  of  the 
archenteron  attached  to  the  yolk-sac,  the  portions  of  the  archenteron  anterior  and  posterior  to 
the  yolk-sac  being  designated  as  fore-gut  and  hind-gut  respectively.  (See  Section  I,  Morpho- 
genesis.) The  lining  epithelium  of  the  alimentarj'  tract  is  endodermal,  excepting  the  anal  canal 
and  the  mouth  cavity,  which  are  lined  by  invaginations  of  the  ectoderm. 

In  the  region  of  the  mouth  and  pharynx,  the  digestive  and  respiratory  systems  are  closely 
related  in  position,  structure,  function  and  origin.  Morphologically,  the  head-gut  represents 
a  primitive  aUmentary-respiratory  apparatus. 

1099 


1100 


DIGESTIVE  SYSTEM 


THE  MOUTH 

The  oral  cavity  [cavum  oris]  represents  the  first  segment  of  the  alimentary 
canal.  Its  walls  are  exceedingly  specialised  in  structm-e,  corresponding  to  its 
manifold  functions  (mastication,  insalivation,  taste,  speech,  etc.). 

Boundaries. — The  oral  cavity  communicates  anteriorly  with  the  exterior 
through  the  transverse  oral  fissure  [rima  oris],  and  posteriorly  with  the  pharynx 
through  the  isthmus  of  the  fauces  [isthmus  faucium].  The  anterolateral  walls 
are  formed  by  the  flexible  lips  and  cheeks.     The  roof  is  chiefly  immovable  and  is 


Fig.  846. — Di.^gram  op  the  Alimentary  Canal. 


NASAL  CAVITY 

PALATE 
MOnTH  CAVITY'  /,' 

TONGUE 


NASAL  PHARY1«C 


formed  by  the  upper  jaw  with  the  hard  and  soft  palate.     The  movable  floor  is 
formed  by  the  lower  jaw  and  the  tongue. 

Subdivisions. — The  oral  cavity  is  subdivided  by  the  alveolar  and  dental 
arches  into  an  inner  cavity,  the  oral  cavity  proper  [cavum  oris  proprium],  and  an 
outer  vestibule  [veigtibulum  oris]  adjacent  to  the  lips  and  cheeks  (fig.  848).  When 
the  upper  and  the  lower  teeth  are  in  apposition,  the  vestibule  communicates 


THE  MOUTH 


1101 


with  the  oral  cavity  proper  (aside  from  the  small  interdental  spaces)  only  through 
a  space  behind  the  last  molar  teeth  on  each  side.  Opening  into  the  oral  cavity  are 
certain  accessory  glands,  the  salivary  glands. 

Fig.  847. — Coronal  Section  thhotjgh  Oral  Region. 
Maxillary  sinus  Nasal  cavity 

/  / 


Lingual  art 
Platysma 


Genio-glossus^' 

Genio-hyoid 


Sublingual 
gland 
—  Exte 

Uary  art. 
^Submaxillary  gland 

"^Sublingual  art.  and 
Ungual  n. 


NMylohyoid 


^^  Digastric 


Structure. — Of  the  typical  layers  of  the  alimentary  canal,  only  the  mucous  membrane  can 
be  recognised  as  a  continuous  layer  in  the  mouth  cavity.  Even  this  is  greatly  modified  and  in 
structure  somewhat  resembles  the  skin,  from  which  it  is  derived  and  with  which  it  is  continuous 


Fig.  848. — Mid-sagittal  Section  of  the  Head,  through  Oral  and  Nasal  Regions. 
(Rauber-Kopsch.) 


Cribriform  plate 
Spheno-ethmoidal 
Hypophysis  recess 

\ 


Dorsum  sellas 


Choanal  arch 
Nasopharyngeal 
meatus 
Pharyngeal  recess 

Torus  lubanus 

Levator  cushion 

Anterior  hp 

Salpingopharyn 

geal  fold 

Uvula 

Foramen  caecum 
lingUEe 
Palatopharyngeal  fold 


Hyoid  bone 


Mental  spine 


cisive  canal 
Upper  lip 

Vestibulum  oris 
Oral  cavity  proper 
Lower  Up 


at  the  rima  oris.  The  submucosa  is  a  strong  fibrous  layer  connecting  the  mucosa  with  adjacent 
structures,  and  lodging  numerous  racemose  mucous  glands.  The  muscles  in  the  walls  of  the 
mouth  cavity  are  not  homologous  with  the  typical  muscularis  of  the  alimentary  canal.  The 
outer  fibrous  tunic  is  also  wanting. 


1102 


DIGESTIVE  SYSTEM 


The  development  of  the  oral  cavity. — As  stated  in  the  section  on  Morphogenesis,  the  oral 
cavity  has  its  origin  in  a  depression,  the  oral  fossa,  situated  between  the  ventrally  bent,  devel- 
oping head  and  the  region  occupied  by  the  developing  heart.  This  fossa  is  bounded  anteriorly 
by  the  fronto-nasal  process,  and  laterally  by  the  maxillary  and  mandibular  processes,  portions 
of  the  first  branchial  arches.  The  fossa  is  lined  by  ectoderm.  Its  floor  is  in  apposition  with 
the  cephalic  end  of  the  archenteron,  lined  by  entoderm,  the  ectoderm  of  the  oral  fossa  and  the 
entoderm  of  the  archenteron  being  in  immediate  contact  and  forming  the  pharyngeal  mem- 
brane. The  oral  fossa  deepens  with  further  development,  and  becomes  the  oral  sinus.  The 
pharjmgeal  membrane  becomes  perforated  in  embryos  about  2  mm.  in  length  and  disappears, 
leaving  a  free  communication  between  the  oral  sinus  and  archenteron.  On  each  side  of  the 
developing  head  and  in  a  latero-ventral  position  there  is  early  developed  an  area  of  thickened 
ectoderm,  known  as  the  nasal  area.  These  areas  soon  develop  into  depressions,  the  nasal  fossae, 
and  assume  a  position,  one  on  either  side  of  the  fronto-nasal  process;  on  each  side  of  the  fronto- 
nasal process  there  is  developed  a  prominent  protuberance,  the  globular  process,  each  process 
forming  the  median  wall  of  a  nasal  fossa.  The  lateral  wall  of  each  nasal  fossa  also  thickens 
to  form  the  lateral  nasal  process.  With  the  further  development,  the  ventral  portion  of  each 
lateral  nasal  process  fuses  with  the  corresponding  globular  process,  the  maxillary  processes  also 
uniting  with  the  globular  processes,  in  this  way  separating  the  nasal  fossae  from  the  oral  sinus. 
With  the  further  growth  toward  the  median  hne  of  the  maxiUary  processes  the  fronto-nasal 
process  becomes  narrower,  ultimately  forming  the  nasal  septum  and  a  small  median  portion 
of  the  upper  jaw,  the  remainder  of  the  upper  jaw  being  formed  by  the  maxillary  processes,  and 
the  lower  jaw  having  its  origin  in  the  mandibular  processes. 


Fig.  849. — Sagittal  Section  of  the  Lower  Lip.     (Lewis  and  Stohr.) 

Sebaceous  gland 

Tall  papillffi— -/JJ' 


Oblique  sec-  / 

tion  of  palpillae 


Labial  gland 


Hair  shafts  and 
sebaceous  glands 


Sebaceous  gland 
Hair  shaft 


Artery 

Bulb  of  a  hair 


Submucosa    Orbicular     Mimetic         Conum       Epidermis 
muscle       muscle 


Variations. — The  mouth  is  rarely  absent,  due  to  failure  of  the  stomatodeal  invagination, 
or  imperforate,  due  to  atresia  of  the  pharyngeal  membrane.  Other  variations  wiU  be  mentioned 
in  connection  with  the  various  mouth  organs. 

Comparative. — The  phylogenetic  origin  of  the  mouth  cavity  from  the  integument  is  indi- 
cated not  only  by  the  ectodermal  origin  of  its  lining  epithelium,  but  by  its  general  structure 
and  its  appendages.  Among  the  latter  may  be  noted  the  teeth  (representing  modified  dermal 
papillae),  sebaceous  glands,  and  (in  some  rodents)  even  hairs  in  the  mucosa  lining  pouches  in 
the  cheeks. 


THE  LIPS  AND  CHEEKS 

The  lips  [labia  oris]  form  the  anterior  wall  of  the  mouth  cavity.  The  lower 
Up  [labium  inferius]  is  marked  off  from  the  chin  by  the  sulcus  mentolabialis. 
The  upper  lip  [labium  superius]  extends  upward  to  the  nose  medially  and  the  sul- 
cus nasolabialis  laterally.  The  philtruni  is  a  median  groove  on  the  upper  lip 
extending  from  the  septum  of  the  nose  above  to  the  labial  tubercle  [tuberculum 
labii  superioris]  below,  at  the  middle  of  the  rima  oris.  On  each  side  of  the  rima 
oris  the  upper  and  the  lower  lips  are  continuous  at  the  angle  of  the  mouth  [angulus 
oris],  which  is  usually  opposite  the  first  premolar  teeth.     Laterally,  the  lips  are 


THE  LIPS  AND  CHEEKS 


1103 


continuous  with  the  cheeks  [buccse],  which  form  the  lateral  walls  of  the  mouth 
cavity. 

In  structure,  the  lips  (fig.  849)  consist  essentially  in  a  middle  layer  of  cross-striated  muscle 
(orbicularis  oris)  covered  externally  by  skin  which  is  continuous  through  the  rima  oris  with  the 
mucosa  forming  the  inner  layer  of  the  hps.  The  mucosa  lines  the  vestibulum  oris  and  is  reflected 
upon  the  gums  above  and  below.  In  the  median  line  above  and  below,  there  extends  fi-om  the 
lip  to  the  gum  a  small  fold  of  the  mucosa  [frenulum  labii  superioris  vel  inferioris].  The  structure 
of  the  cheeks  (figs.  847,  864)  is  similar  to  that  of  the  lips  but  somewhat  more  complicated. 


Fig.  850. — ^Labial  and  Buccal  Glands  Exposed  by  Dissection  of  the  Skin  feom  in  Front. 
(From  Toldt's  Atlas.) 
Labial  glands       ^PP^r  Up 
Tunica  mucosa  oris  (tela  submucosa) 

Buccal  glands 


Labial  glands 


Lower  Up 


Buccinator 


The  muscular  basis  of  the  cheek  is  the  buccinator  muscle.  External  to  this  is  a  thick  layer 
of  fat  [corpus  adiposum  buccae]  covered  partly  by  the  dermal  muscles  (platysma,  zygomaticus, 
etc.)  and  lastly  the  skin.  Internally  the  cheek  is  lined  by  the  mucosa,  continuous  with  that 
of  the  cheeks.  The  parotid  duct  opens  into  the  vestibule  opposite  the  second  upper  molar 
tooth. 

Glands. — The  skin  of  the  lips  and  cheeks  is  well  supplied  with  the  usual  sudoriparous  and 
sebaceous  glands.  The  mucosa  likewise  presents  two  kinds  of  glands,  the  sebaceous  and  the 
mucous  glands.  The  sebaceous  glands  are  relatively  few  in  number  and  variable,  being  present 
in  about  30  per  cent,  of  cases  in  the  adult  (Stieda).     They  are  similar  in  structure  to  those  of 


Fig.  851. — Section  of  Labial  Mtcos-i   Snr-mMj  C  lwd';      X  16      (From  Toldt's  Atlas.) 
Epithelium  —  H^^^^^^^^S^IT^li  ^S^W^^ilW-     ~  Epithelium 

Duct 
-  Accessory  gland 


Lan 


Tela  submucosa 


M.  orbicularis  oris 


Mucous  gland 


the  skin  (though  not  associated  with  hair  foUicles),  and  when  present  are  visible  as  small  yellow- 
ish bodies  in  the  mucosa.  They  occur  chiefly  near  the  free  margins  of  the  lips  and  along  the 
cheek  opposite  the  teeth. 

The  mucous  glands  are  much  more  numerous  and  constantly  present  (figs.  850,  851).  They 
are  all  of  the  racemose  type.  They  are  variable  but  small  in  size,  and  closely  packed  together 
in  the  submucosa  of  the  lips  [glandulte  labiales],  where  they  may  easily  be  felt.  Those  of  the 
cheeks  [gl.  buccales]  are  less  numerous.     A  few  of  them  especially  in  the  region  of  the  molar 


1104  DIGESTIVE  SYSTEM 

teeth  [gl.  molares],  are  placed  outside  the  buccinator.  The  ducts  of  the  molar  glands  pierce 
this  muscle  near  the  parotid  duct  to  open  on  the  surface  of  the  mucosa. 

Vessels  and  nerves. — The  mucosa  of  the  lips  and  cheeks  has  a  characteristic  reddish  hue,  on 
account  of  the  numerous  blood-vessels  which  are  visible  through  the  thick  but  transparent 
stratified  squamous  epithelium  (figs.  849,  851)  The  numerous  papillae  of  the  lamina  propria 
are  highly  vascular.  The  hlood-supply  of  the  lips  and  cheeks  is  derived  chiefly  from  the  labial 
(coronary)  and  buccal  arteries.  The  rich  nerve-supply  (sensory)  is  from  the  infra-orbital, 
mental  and  buccal  branches  of  the  fifth.     The  lips  are  especially  sensitive  near  the  rima  oris. 

Development. — During  the  second  month  in  the  human  embryo,  ledges  of  epithelium 
grow  into  the  substance  of  the  mandibular  and  the  fused  fronto-nasal  and  maxillary  processes. 
These  ledges  develop  into  grooves  which  separate  the  upper  and  the  lower  lips  from  the  upper 
and  the  lower  jaws,  the  grooves  forming  the  oral  vestibule. 

The  philtrum  and  labial  tubercle  are  said  to  correspond  to  the  lower  part  of  the  fronto- 
nasal process.  A  failure  of  union  between  the  globular  and  the  maxillary  processes  presents  an 
arrest  of  development  resulting  in  the  malformation  known  as  "hare-lip."  ■ 

In  the  late  fcetus  and  newborn,  the  red  portion  of  the  lips  consists  of  an  external  smooth 
pars  glabra,  and  an  inner  zone,  pars  villosa,  which  is  covered  with  numerous  villus-like  pro- 
jections. The  largest  of  these  reach  a  length  of  1  mm.  They  also  extend  backward  in  an  irregu- 
lar band  along  the  mucosa  of  the  cheek.  They  disappear  during  the  first  few  weeks  of  post- 
natal life. 

In  the  infant,  the  corpus  adiposum  is  especially  well  developed.  On  account  of  its  supposed 
aid  as  a  support  for  the  buccinator  in  sucking,  it  has  been  called  the  "sucking  pad." 

The  sebaceous  glands  of  the  mucosa  are  said  not  to  appear  until  about  the  age  of  puberty. 

Variations. — As  is  well  known,  the  lips  and  cheeks  are  exceedingly  variable  in  shape,  size 
and  structure  in  different  individuals.  There  are  also  characteristic  differences  according  to 
race  and  sex  in  the  form  and  structure  of  the  lips,  rima  oris,  beard,  etc.  The  "harcrlip" 
malformation  was  mentioned  above. 

Comparative. — Typical  lips  are  found  only  in  mammals,  and  are  probably  organs  phylo- 
genetically  developed  in  connection  with  the  process  of  suckling. 

THE  PALATE 

The  palate  forms  the  roof  of  the  mouth  cavity  proper,  and  consists  of  two  por- 
tions, the  anterior  or  hard  palate  and  the  posterior  or  soft  palate. 

The  hard  palate  [palatum  durum]  (figs.  848,  852)  is  continuous  in  front  and 
laterally  with  the  alveolar  processes  of  the  upper  jaw,  and  gives  attachment 
posteriorly  to  the  soft  palate.  It  separates  the  mouth  from  the  nasal  cavity.  It 
is  supported  by  the  palatine  process  of  the  maxilla  and  the  horizontal  part  of  the 
palate  bone.  The  oral  surface  is  concave  from  side  to  side,  and  also  from  before 
backward.  It  is  covered  by  a  thick,  somewhat  pale  mucosa,  which  is  firmly 
adherent  to  the  periosteum  through  the  submucosa.  The  submucosa  contains 
numerous  mucous  glands  [gl.  palatinse]  (fig.  852),  similar  to  those  of  the  lips. 

In  the  median  line  of  the  hard  palate  is  a  line  or  ridge,  the  raphe  (fig.  852) 
terminating  anteriorly  in  the  small  incisive  papilla,  which  corresponds  in  position 
to  the  bony  incisive  foramen.  Anteriorly  there  occur  four  to  six  more  or  less 
distinct  transverse  ridges  [plicae  palatinse  transversse].  Near  the  posterior  margin 
of  the  hard  palate  there  is  on  each  side  of  the  raphe  a  small  pit  (fig.  852),  the 
foveola  palatina,  which  is  variable  and  inconstant. 

The  soft  palate  [palatum  moUe]  (figs.  848,  892)  separates  the  posterior  portion 
of  the  mouth  cavity  from  the  nasal  part  of  the  pharynx.  It  is  attached  to  the 
hard  palate  anteriorly  and  to  the  pharyngeal  wall  laterally.  The  posterior  por- 
tion or  velum  projects  backward  and  downward  into  the  pharynx.  Its  free  mar- 
gin presents  a  median  conical  projection,  the  uvula,  and  splits  laterally  on  each 
side  to  form  two  folds,  the  palatine  arches,  between  which  is  located  the  palatine 
tonsil  (fig.  852).  The  palatine  arches  and  tonsil  will  be  described  later  in  con- 
nection with  the  pharynx. 

Structure. — The  soft  palate  is  a  fold  of  mucous  membrane  enclosing  a  fibrous  aponeurosis, 
muscles,  vessels,  and  nerves.  It  is  marked  in  the  middle  line  by  a  raphe  indicating  the  hue  of 
junction  of  the  two  halves  from  which  it  was  formed. 

The  posterior  layer  of  the  mucous  fold  which  is  directed  toward  the  cavity  of  the  pharynx 
is  continuous  with  the  na.sal  mucous  membrane;  the  anterior  layer  lies  in  the  posterior  boundary 
of  the  mouth  and  is  continuous  with  the  mucous  membrane  of  the  hard  palate.  The  structure 
of  the  mucosa  is  very  similar  to  that  of  the  lips  (fig.  849).  Mucous  glands  are  numerous  in  both 
layers,  but  more  especially  in  the  anterior,  and  make  up  a  large  portion  of  the  mucosa  and  sub- 
mucosa (figs.  851,  852). 

The  aponeurosis  is  attached  above  to  the  posterior  margin  of  the  hard  palate;  laterally  it 
is  continuous  with  the  aponem-otic  layer  of  the  pharyngeal  wall;  below,  toward  the  lower 
margin  of  the  velum,  it  gradually  disappears.  It  gives  attachment  to  fibres  of  the  levator  veli 
palatini  and  the  jjharyngo-palatinus  (palato-pharyngeus)  and  to  the  tendon  of  the  tensor  veli 
palatini. 


THE  PALATE 


1105 


Muscles. — The  muscles  of  the  soft  palate  are  described  later  (p.  1134)  with  those  of  the 
pharynx,  with  which  they  are  closely  associated. 

Vessels  and  nerves. — The  arterial  supply  of  the  hard  palate  is  derived  chiefly  from  the 
major  palatine  branches  of  the  internal  maxillary.     The  arteries  of  the  sojt  palate  include: 


Fig.  852. — Roof  op  Mouth,  Showing  Haed  and  Soft  Palate  Dissected  on  One  Side. 
(Rauber-Kopsch.) 

Papilla  incisiva 


Foveola 
palatina 


Arcus  pharyngopalatinus 


M.  glosspalatiaus 
Palatine  tonsil 
M.  pharyngopalatinus 


(1)  Ascending  palatine  of  external  maxillary  (facial);  (2)  pharyngeal  branches  of  ascending 
pharyngeal;  (3)  twigs  from  descending  palatine  of  internal  maxillary,  which  enter  the  smaller 
palatine  canals,  are  distributed  to  the  soft  palate  and  tonsils,  and  communicate  with  the 
ascending  palatine  of  the  external  maxillary  (facial)  artery;  (4)  lingual  artery,  by  twigs  from 
the  dorsal  branch. 

Fig.  853. — Developing  Palatine  Shelves,  Viewed  from  Below.     (McMurrich,  from  His.) 


The  sensory  nerves  to  the'palate  are  derived  chiefly  from  the  fifth' through  che  sphenopalatine 
ganglion.  The  hard  palate  is  supplied  by  the  nasopalatine  and  anterior  palatine  branches; 
the  soft  palate  chiefly  by  the  median  and  posterior  palatine  branches.  The  motor  nerves 
will  be  mentioned  later  in  connection  witli  the  muscles. 


1106  DIGESTIVE  SYSTEM 

The  development  of  the  palate. — The  hard  and  soft  palates  arise  (fig.  853)  in  two  ridges 
of  tissue,  designated  the  palate  shelves,  which  develop  on  the  inner  surfaces  of  the  maxillary 
processes.  These  shelves  grow  toward  the  median  line,  and  at  the  beginning  of  the  third 
month  of  fcetal  life  meet  beneath  the  nasal  septum,  uniting  with  each  other  and  with  the  nasal 
septum,  the  union  taking  place  from  before  backward.  The  incisive  foramen  indicates  the 
place  of  meeting  of  the  premaxillary  and  palate  shelves,  which  closes  the  primitive  communi- 
cation between  the  oral  and  the  nasal  cavity.  A  want  of  union  of  the  palate  shelves  presents 
an  arrest  of  development  known  as  cleft-palate.  The  uvula  is  similarly  formed  by  the  union  of 
the  posterior  ends  of  the  lateral  palate  anlages,  and  a  failure  to  unite  may  produce  a  bifid  uvula. 
The  transverse  palatine  ridges  are  better  developed  in  the  infant  than  in  the  adult,  and  may 
assist  in  holding  the  nipple  in  sucking. 

Variations. — Cleft-palate  and  bifid  uvula  were  mentioned  above.  The  transverse  palatine 
ridges  are  quite  variable  in  number  and  prominence.  On  each  side  of  the  incisive  papilla 
there  is  often  found  a  small  pit  or  shallow  tube,  a  vestige  of  the  embryonal  incisive  canal  (Mer- 
kel).  Sometimes  there  is  instead  a  single  median  pit,  representing  the  lower  end  of  the  incisive 
(Stenson's)  canal.  These  pits  are  remnants  of  the  primitive  embryonic  communication  between 
mouth  and  nasal  cavities. 

Comparative. — The  palate  is  absent  in  fishes  and  amphibia,  the  ohoanse  opening  directly 
into  the  primitive  mouth  cavity.  In  some  birds,  the  palate  shelves  fail  to  unite,  leaving  a  normal 
cleft-palate.  The  incisive  (Stenson's)  canal  remains  open  permanently  in  some  mammals 
(e.  g.,  ruminants),  bifurcating  above  and  thus  placing  the  mouth  cavity  in  communication 
with  the  nasal  cavity  on  each  side  in  the  vicinity  of  Jacobson's  organ.  The  transverse  palatine 
ridges  are  much  better  developed  among  many  mammals,  especially  the  carnivora. 

THE  TONGUE 

The  tongue  [lingua]  is  a  muscular  organ  covered  with  mucous  membrane  and 
located  in  the  floor  of  the  mouth.  It  is  an  important  organ  of  mastication,  deglu- 
tition, taste  and  speech.  Upon  its  upper  surface  (figs.  854,  864)  is  a  V-shaped 
groove  (sulcus  terminalis)  indicating  the  division  of  the  tongue  into  two  parts. 
The  larger  anterior  part,  or  body  [corpus  linguae]  belongs  to  the  floor  of  the  mouth, 
while  the  smaller  posterior  part,  or  root  [radix  linguae],  forms  the  anterior  wall  of 
the  oral  pharynx.  The  inferior  surface  (facies  inferior)  of  the  tongue  is  chiefly 
attached  to  the  muscles  of  the  floor  of  the  mouth,  from  the  hyoid  bone  to  the  man- 
dible (fig.  858).  Anteriorly  and  laterally,  however,  the  inferior  surface  of  the 
body  is  free  and  covered  with  mucosa.  The  superior  surface  of  the  body  is  called 
the  dorsum.  It  is  separated  from  the  inferior  surface  by  the  lateral  margins, 
which  meet  anteriorly  at  the  tip  [apex  linguae]. 

The  dorsum  of  the  tongue  usually  presents  a  slight  median  groove  [sulcus  medi- 
anus  linguae].  Its  posterior  end  corresponds  to  a  small  pit  of  variable  depth,  the 
foramen  ccecum,  which  is  placed  at  the  apex  of  the  V-shaped  terminal  sulcus, 
The  dorsum  of  the  body  has  a  characteristic  rough  appearance  due  to  numerous 
small  projections,  the  lingual  papillce. 

Lingual  papillae. — Five  or  six  varieties  of  papilte  are  distinguished,  between  which  inter- 
mediate forms  occur.  The  conical  [papillse  conices]  and  thread-like  [papillae  filiformes]  are 
most  numerous,  and  are  arranged  more  or  less  distinctly  in  rows  parallel  with  the  terminal 
sulcus  (fig.  856).  They  are  best  developed  toward  the  mid-line  of  the  dorsum  in  its  posterior 
part.  As  shown  in  vertical  section  (fig.  856),  each  papilla  consists  of  an  axial  core  of  vascular 
fibrous  tissue  (from  the  lamina  propria)  often  beset  with  smaller  secondary  papillse.  The 
stratified  squamous  epithelial  covering  often  presents  numerous  thread-like  prolongations  from 
the  apex  of  the  papilla.     The  papillse  vary  from  1  to  3  mm.  in  length. 

The  fungiform  ("toad-stool  shaped")  papillae  are  somewhat  similar  to  the  conical  in  struc- 
ture, but  larger  and  more  prominent,  with  an  expanded  free  portion  and  a  slightly  constricted 
stalk  of  attachment.  They  are  relatively  few  in  number  and  are  scattered  irregularly  over 
the  dorsum,  being  most  numerous  near  the  margins  (fig.  864).  They  are  easily  distinguished 
in  hfe  by  their  larger  size  and  reddish  colour.  A  smaller,  flattened  variety  of  the  fungiform  is 
sometimes  called  the  lenticular  ('lens-shaped')  papillse.  (This  term,  however,  is  apphed  by 
Toldt  to  certain  small  rounded- elevations  with  underlying  lymphatic  nodules  in  the  mucosa  of 
the  root  of  the  tongue.) 

The  vallate  (circumvallate)  papillfe,  usually  seven  to  eleven  in  number,  are  conspicuous 
and  arranged  in  a  V-shaped  line  parallel  with  and  slightly  anterior  to  the  sulcus  terminalis, 
(figs.  854,  857).  They  are,  as  a  rule,  shaped  hke  short  cyhnders,  1  to  2  mm.  in  width,  and 
somewhat  less  in  height.  As  is  shown  in  section  (fig.  857),  each  is  surrounded  by  a  trench  or 
fossa,  into  the  bottom  of  which  open  ducts  of  the  serous  glands  of  von  Ebner.  On  the  sides  of 
the  fossaj  are  the  taste-buds,  as  described  in  the  section  on  Sense  Organs. 

The  foliate  papillie  are  represented  by  a  few  (five  to  eight)  parallel  transverse  or  vertical 
folds  of  mucosa,  along  the  margins  of  the  tongue  just  anterior  to  the  glosso-palatine  arch  on 
each  side  (fig.  864).  They  are  variable  in  size  and  sometimes  rudimentary.  In  structure  they 
somewhat  resemble  the  vallate  papillse  (though  of  different  form),  their  walls  being  studded 
with  taste-buds. 


THE  TONGUE 


1107 


The  free  inferior  surface  of  the  tongue  (fig.  858)  is  covered  by  a  thin  smooth 
mucosa.  In  the  median  line  is  a  prominent  fold,  the  frenulum,  which  connects 
the  tongue  with  the  mandible  and  the  floor  of  the  mouth.  On  each  side  of  the 
inferior  surface,  an  irregular,  variable,  fringed  fold,  the  plica  fimbriata,  extends 
from  near  the  apex  backward  approximately  parallel  with  the  lateral  margin  of 
the  tongue  (fig.  858).  Between  the  frenulum  and  the  plicae  fimbriatse,  the  lingual 
(ranine)  veins  are  visible  on  each  side  beneath  the  mucosa. 

The  root  (or  base)  of  the  tongue  [radix  linguae]  belongs  to  the  pharynx,  but  is 
here  included  with  the  mouth  for  convenience  of  description.  Its  free  surface  is 
directed  posteriorly,  and  represents  the  continuation  of  the  dorsum  linguae  (fig. 
854).    Laterally  it  is  continuous  with  the  region  of  the  palatine  tonsils.      Infe- 


FiG.  854. — Dorsum  and  Root  of  the  Tongue.     (Papillae  diagrammatic.) 
Ventricular  fold      Lower  part  of  pharynx 


Extremity  of  __. 

hyoid  bone 

Superior  cornu  of 

thyreoid  cartilage 


Lateral  glosso- 
epiglottidean  told 


Anterior  wall  of  the 

pharynx 
Cornicular  tubercle 

Cuneiform  tubercle 
Recessus  piriformis 

Vocal  fold  (true  vocal 
cord) 


Median  glosso- 
epiglottidean  fold 


Pharyngopalatine  arch 

Glossopalatine  arch 

Vallate  (circumvallate)  papiU 


Fungiform  papillee 


riorly  it  extends  to  the  epiglottis,  with  which  it  is  connected  by  a  median  and  two 
lateral  folds,  between  which  are  the  depressions  known  as  the  valleculce.  The 
mucosa  over  the  root  of  the  tongue  is  irregular  and  warty  in  appearance  due  to 
the  projections  of  the  underlying  nodular  masses  of  lymphoid  tissue,  the  lingual 
follicles.  A  crypt  or  tubular  pocket  of  surface  epithelium  usually  dips  down  into 
each  of  these  follicles,  as  seen  in  surface  view  (fig.  854),  and  shown  in  section  (fig. 
859) .  The  follicles  vary  from  34  to  102  in  number,  the  average  being  66  (Ostman) j 
and  are  somewhat  irregular  in  size  and  form.  They  are  often  arranged  in  more  or 
less  distinct  longitudinal  rows,  with  corresponding  folds  of  the  mucosa  (Jurisch). 
The  lingual  follicles  are  collectively  designated  as  the  lingual  tonsil  [tonsilla 
linguae].  Between  the  lingual  follicles  and  around  the  periphery  of  the  lingual 
tonsil  there  are  found  smaller  ordinary  nodules  (without  crypts)  and  indefinite 


1108 


DIGESTIVE  SYSTEM 


masses  of  lymphoid  tissue.  The  sulcus  terminalis  forms  a  fairly  sharp  boundary 
between  the  lymphoid  mucosa  of  the  root  and  the  papillated  mucosa  of  the  body 
of  the  tongue  (fig.  854). 

Fig.  865. — Left  Side  of  the  Tongue,  with  its  Muscles,  etc. 

Stylo-glossus 
Dorsum  of  tongue 


Genio-hyoid 


Genio-glossus 

\ 


Styloid  process 
Stylo-hyoid 
Root  of  tongue 


Stylo-pharyngeus 


Epiglottis  (indicated  by  dotted  lines) 


Crxeater  comu  of  hyoid  bone 


Cartilago  triticea 


Thyreoid  cartilage 


Median  portion  o£ 
crico-thyreoid 
membrane 

Cricoid  cartilage 


Glands. — The  glands  of  the  tongue  are  of  three  types — mucous,  serous  and  mixed — and 
are  distributed  as  shown  in  fig.  860.     The  most  numerous  are  those  of  the  mucous  type,  which 


Fig.  856. — Section  of  Lingual  Papilla.     X  20.     (From  Toldt's  Atlas.) 

Stratified  epithelium 

Secondary  papilla 

,Cl    '  ^  '     ISWllfe      \     PV\  Conical  papilla 

fM  %mm  mA 

Filiform  papillse 
Capillary  vessels 


Artery 
Vein 

Lamina  propria 
Fascia  linguae 

Tongue  muscle 


are  typical  for  the  mouth  cavity  in  general  and  resemble  those  already  described  in  the  lips, 
cheeks  and  palate.     They  are  spread  over  the  entire  surface  of  the  root  of  the  tongue,  in  the 


THE  TONGUE 


1109 


spaces  between  the  lingual  foUioles,  usually  opening  upon  the  surface  but  in  many  cases  into 
the  crypts.     Anteriorly,  they  extend  a  short  distance  along  the  posterior  portion  of  the  lateral 

Fig.  857. — Vertical  Section  of  a  Human  Vallate  Papilla  With  Lingual  Glands. 
X  25.     (Lewis  and  Stbhr.) 
Secondary  papillee       Taste  bud 

Orifice 
of  a 
serous 
Tuicapiopria  \      XS?i  jSH^"   W^"'fS^  /       e''*"* 


Vallate  papilla 
Groove 


Small 
papilla 


Inferior  surface 
Lateral  margin 
Plica  fimbriata 


Sublingual  fold 
Sublingual  caruncle 


margm  of  the  tongue,  and  also  occupy  small  areas  in  and  near  the  mid-hne  in  front  of  the  vallate 
papillae. 

In  the  immediate  region  of  the  vallate  papiUse,  and  in  the  small  lateral  areas  corresponding 


1110 


DIGESTIVE  SYSTEM 


to  the  foliate  papiUse  (i.  e.,  in  the  regions  of  the  taste-buds),  the  mucous  glands  are  displaced  by 
the  serous  glands  (of  von  Ebner),  which  have  a  watery  secretion  (fig.  860).  Finally,  on  the 
inferior  surface  of  the  tongue,  on  either  side  of  the  frenulum  near  the  apex,  are  the  anterior 
lingual  glands  (glands  of  Nuhn  or  Blandin).  Each  is  about  15  mm.  in  length,  and  is  composed 
of  a  group  of  racemose  glands  with  three  or  four  very  small  ducts  opening  on  the  surface  of  the 
tongue  near  the  plica  fimbriata.  The  anterior  lingual  glands  are  deeply  placed  and  are  covered 
not  only  by  the  mucosa,  but  also  by  some  of  the  longitudinal  muscle  fibres  (inferior  longitudinal 
and  styloglossus).     This  gland  is  of  the  mixed  type,  though  chiefly  mucous. 

Fig.  859. — From  a  Section  of  the  Lingual  Tonsil  op  an  Adult  Man.  X  20.  1.  Pit 
containing  leucocytes  which  have  infiltrated  its  epithelium  on  the  left  side ;  that  on  the  right  is 
almost  intact.     (Lewis  and  Stohr.) 


Median  section  of  a  nodule 


BiSuse  lumphoid  tissue 


Lymph  nodules 


Duct  of  a  mucous  gland' 


J'J'3«^_/-rj:ji 


Periphery  of  a  nodule 


Tunica  propria 
Fibrous  capsule 


Blood  vessel 


Muscles  of  the  tongue. — A  layer  of  fibrous  connective  tissue,  the  lingual  septum,  separates 
the  halves  of  the  tongue,  extending  in  the  median  plane  from  the  apex  to  the  root,  where  it  is 
attached  below  to  the  hyoid  bone.  The  muscles  of  the  tongue  are  classified  as  extrinsic  and 
intrinsic.  The  extrinsic  muscles  (fig.  855)  extend  into  the  tongue  from  without.  They  are 
the  hyoglossus,  chondroglossus,  genioglossus,  styloglossus,  and  glossopalatinus  (palatoglossus), 
all  of  which  are  described  elsewhere  (see  Section  IV.) 

Fig.  860. — Diagram  op  the  Distribution  of  the  Lingual  Glands.  Horizontal  lines 
indicate  the  mucous  type;  cross-hatched,  the  mixed  type;  and  dotted  areas,  the  serous  type. 
(After  Oppel.) 


The  intrinsic  muscles. — The  longitudinalis  superior  (fig.  861)  is  a  superficial  longitudinal 
stratum  extending  from  the  base  to  the  apex  of  the  tongue,  immediately  beneath  the  mucosa 
of  the  dorsum,  to  which  many  of  its  fibres  are  attached.  The  longitudinalis  inferior  (fig.  861) 
is  composed  of  two  muscle-bands  extending  from  base  to  apex  on  the  inferior  surface  of  the 
tongue,  and  ia  situated  between  the  hyoglossus  and  the  genioglossus,  some  of  its  fibres  near 
the  apex  mixing  with  the  styloglossus,  while  dorsaUy  some  are  attached  to  the  hyoid  bone.  The 
transversus  linguae  (fig.  861)  consists  of  fibres  which  pass  transversely,  and  is  situated  between 


THE  TONGUE 


nil 


the  superior  and  inferior  longitudinal  muscles.  The  fibres  arise  from,  or  pass  through,  the  sep- 
tum linguae,  and  are  attached  to  the  mucosa  of  the  dorsum  and  lateral  margins  of  the  tongue. 
The  verticalis  linguae  (fig.  861)  is  composed  of  fibres  which  pass  from  the  mucosa  of  the  dorsum 
to  the  mucosa  of  the  inferior  surface  of  the  tongue,  interlacing  "with  those  of  the  other  intrinsic 
and  extrinsic  muscles. 

Fig.  861. — Teansversb  Section  through  the  Left  Half  op  the  Tongue.     (Magnified.) 

(From  a  preparation  by  Mr.  J.  Pollard,  Middlesex  Hospital  Museum.) 

Transversus  linguffi 


Lateral  margin  of 
tongue 


Verticalis  linguae 


Vessels  and  nerves. — The  lingual  arteries  furnish  the  principal  blood-supply.  The  lingual 
veins  carry  the  blood  from  the  tongue  to  the  internal  jugular.  The  lymphatics  form  a  network 
in  the  lamina  propria,  connected  with  a  deeper  network  in  the  submucosa.  The  latter  forms 
plexuses  around  the  lingual  follicles.  The  efferent  lymph-vessels  from  the  tongue  empty  chiefly 
into  the  superior  deep  cervical  lymph-nodes.  (For  details  concerning  the  blood-  and  lymph- 
vessels,  see  Sections  V  and  VI.)     The  nerves  are  motor  and  sensory.     The  hypoglossal  nerve 


Fig.  862. — Schematic  Representation  of  the  Distribution  op  tee  Sensory  Nerves 
in'the  Mucous  Membrane  op  the  Tongue.  (Areas  of  distribution  according  to  R.  Zander. 
White  dotted  area  indicates  vagus;  oblique  lines,  glosso-pharyngeal;  horizontal  lines  lingual 
nerves.) 


Right  vagus  nerve- 


Right  glosso- 
pharyngeal 
nerve 


Left  vagus  nerve 


eft  glosso-phar- 
yngeal nerve 


Right  lingual  nerve 


Left  lingual  nerve 


supplies  the  intrinsic  and  all  the  extrinsic  muscles  of  the  tongue  except  the  glossopalatinus 
(palato-glossus),  which  is  supplied  from  the  pliar}'ngeal  plexus.  The  sensory  nerves  (fig.  862) 
are: — the  lingual  nerve,  a  branch  of  the  mandibular  division  of  the  fifth,  which,  after  joining  with 
the'chorc'.a  tympani  from  the  seventh,  is  distril^uted  to  the  anterior  two-thirds  of  the  tongue  and 
represents  the  nerve  of  touch;  the  Ungual  branches  of  the  glossopharyngeal,  which  are  distrib- 


1112 


DIGESTIVE  SYSTEM 


uted  to  the  root  of  the  tongue,  including  also  the  vallate  and  foliate  papillae  (nerve  of  taste) ; 
and  the  superior  laryngeal  branch  of  the  vagus,  which  supplies  a  small  area  near  the  epiglottis. 

Development. — The  development  of  the  tongue  is  quite  complicated.  In  general,  the  body 
of  the  tongue  is  derived  from  the  region  corresponding  to  the  ventral  portion  of  the  first  arch, 
just  behind  the  mandible.  It  does  not  develop  from  the  tuberculum  impar,  however,  which  is 
a  transitory  structure  (Hammar).  The  epithelium  of  the  body  of  the  tongue  is  probably  of 
ectodermal  origin.  The  root  of  the  tongue  develops  from  the  corresponding  lower  portion  of  the 
second  or  hyoid  arch,  and  its  epithelium  is  endodermal  in  origin.  The  transverse  groove  be- 
tween the  two  arches  later  becomes  the  sulcus  tenninaUs.  At  the  middle  of  this  groove  there 
is  an  ingrowth  of  the  epithelium  to  form  the  anlage  of  the  thyreoid  gland.  The  foramen  ccecum 
and  the  occasional  ductus  linguaHs  represent  persistent  portions  of  the  thyreoid  duct.  The  third 
arch  does  not  appear  to  enter  into  the  formation  of  the  tongue,  but  forms  the  epiglottis 
(Hammar). 

The  musculature  of  the  tongue  appears  to  develop  from  the  mesenchyme  in  situ  although 
its  innervation  from  the  hypoglossal  would  indicate  a  derivation  from  the  occipital  myotomes. 
A  pair  of  premuscle  masses  appears  in  the  9  mm,  embryo,  the  individual  extrinsic  muscles  being 
distinguishable  at  14  mm.,  and  the  intrinsic  at  20  mm.  (W.  H.  Lewis).  The  glands  appear 
in  the  fourth  fcetal  month  as  solid  epithelial  downgrowths  which  later  acquire  a  lumen.  The 
mucous  glands  appear  first,  the  serous  slightly  later.     Longitudinal  folds  in  the  mucosa  of  the 


The  Salivary  Gi/ANDb 


Accessory  parotid 


Duct  of  accessory 
parotid 


Duct  of  parotid 


Frenulum  linguas 


Sublingual  gland 

Duct  of  submaxil 
lary  gland 

Mylo-hyoid  muscle 

Anterior  belly  of 
digastric  muscle 


Parotid  gland 


Masseter  muscle 


Posterior  belly  of 
digastric  muscle 

Lingual  nerve 

Submaxillary 
gland, 
drawn  backward 


Deep  portion  of  submaxillary  gland 


radix  appear  in  the  third  or  fourth  fcetal  month  (Jurisch).  The  lymphoid  tissue  appears  some- 
what later  as  aggregations  in  the  lamina  propria,  chiefly  around  the  gland-ducts.  From  the 
beginning,  the  lymphoid  structures  are  subject  to  marked  individual  variations.  Character- 
istic, well-developed  lingual  follicles  do  not  appear  until  some  time  after  birth,  however  (Jurisch). 
Of  the  lingual  papilloe,  the  fungiform  appear  at  the  end  of  the  third  foetal  month,  followed 
shortly  by  the  fihform  and  vallate.  The  formation  of  the  papillae  is  not  completed  at  birth, 
however,  since  they  later  undergo  changes  in  number,  form,  size  and  arrangement.  The 
foliate  papillae  appear  about  the  fifth  foetal  month.  They  are  best  developed  in  infants,  under- 
going retrogressive  changes  in  the  adult  (Stahr).     The  same  is  true  of  the  plicae  fimbriatae. 

Variations. — Of  the  manifold  variations  in  the  structure  of  the  tongue,  some  have  already 
been  mentioned.  Additional  mucous  glands  sometimes  occur  along  the  margin  of  the  tongue 
(completing  Oppel's  "glandular  ring").  In  "tongue-tied"  individuals,  the  frenulum  is  ab- 
normally short.  A  forked  tongue  (normal  in  some  animals)  is  a  rare  congenital  anomaly. 
Another  rare  variation  is  the  so-called  "hairy"  tongue,  due  to  hypertrophy  of  the  filiform 
papillae.  While  the  V-shaped  arrangement  of  the  vallate  papillae  is  typical,  the  Y-form  (two 
to  four  papillae  in  the  median  line  forming  the  stem  of  the  Y)  is  nearly  as  frequent.  Indeed, 
in  some  of  the  coloured  races  the  latter  type  seems  to  predominate.  The  sulcus  terminalis 
and  foramen  caecum  are  often  indistinct  and  sometimes  absent. 

Comparative. — The  tongue  of  fishes  and  lower  amphibia  contains  neither  glar.ds  nor  in- 
trinsic musculature.  Among  higher  vertebrates,  the  tongue  varies  exceedingly  in  form  and 
structure,  but  always  contains  intrinsic  musculature  and  mucous  glands.  The  latter  primi- 
tively form  a  ring  around  the  margin  and  root  of  the  tongue  (Oppel).  The  serous  glands  occur 
only  in  mammals,  and  are  associated  closely  with  the  papillae  bearing  taste-buds.         ' 


THE  PAROTID  GLAND 


1113 


The  plica  fimbriata  in  man  is  homologous  with  the  'sublingua'  of  lower  mammals.  Ac- 
cording to  Gegenbaur,  the  'sublingua'  represents  the  entire  primitive  vertebrate  tongue, 
but  this  view  is  opposed  by  Oppel.  Among  various  mammals,  the  number  of  vallate  papilte 
varies  from  one  to  thirty,  but  the  V-  or  Y-arrangement  is  typical.  The  region  of  the  foliate 
papillae  ('marginal  organ')  is  typical  for  mammals,  and  is  much  better  developed  in  some 
(e.  g.,  rabbit)  than  in  man.  The  mucosa  of  the  root  of  the  tongue  is  always  different  from  that 
of  the  body.     The  lingual  papillae  are  especially  developed  in  the  tongue  of  carnivora. 

THE  SALIVARY  GLANDS 

Numerous  glands — labial,  buccal,  palatine  and  lingual — have  already  been 
mentioned,  which  pour  their  secretions  into  the  mouth  cavity.  In  addition  to 
these,  there  are  three  larger  pairs,  the  salivary  glands  proper.  They  include  the 
parotid,  the  submaxillary,  and  the  sublingual  (the  latter  really  a  group  of  glands). 

THE  PAROTID  GLAND 

The  parotid  gland  [gl.  parotis]  is  the  largest  of  the  salivary  glands,  varying 
from  15  to  30  gm.  in  weight.     It  is  located  below  and  in  front  of  the  ear  in  the 

Fig.  864. — Horizontal  Section  throttgh  Head  at  Level  of  Rima  Oris.     (After  Henle, 

modified.) 

v.  jugularis  int. 

Eigastric    ,      n,  hypoglossus 
Sternomastoid 


Stylo-hyoid  V 
v.  jugularis  est.  ».^ 


A.  carotis  int. 
I     I     N.  vagus 

I     j      I    N.  sympath.         Dens, 
\    \     I    /A.pharyng.         /  Atlas 

:-  \     ',    I    j    ^^'^'  I  I        Longus  colli 

Longus  capiti; 


V.  facialis  post, 

Stylo-glossus—  i-v 
Ramus  of  t    I 

mandible     f  t 
Asc.  palatine  art.- 


Int.  pterygoi 
Masseter 


Lingual  tonsil " 
Sulcus  terminalis  -■ 


Foliate  papillse  - 


Fungiform  papilla 

External  maxillary  art 
Vestibule  of  mouth 


nt 


Retropharyngeal 
lymph  node 


_-- —   Superior  constr. 


Pharyngo- 
palatine  i 


Fungiform  papillEE  "■         ""        \ '^S, 
Angle  of  mouth  --> 


retromandibular  fossa  (fig.  863),  extending  from  the  zygomatic  arch  above  to  the 
angle  of  the  mandible  below. 

Form  and  relations. — The  parotid  is  somewhat  prismatic  or  wedge-shaped 
(figs.  863,  864),  with  three  surfaces  and  three  borders  or  angles.  The  lateral  sur- 
face is  covered  by  skin  and  superficial  fascia,  and  in  its  lower  part  by  the  platysma. 
The  anterior  surface  overlaps  the  masseter  and  extends  medialward  in  contact 


1114 


DIGESTIVE  SYSTEM 


with  the  posterior  border  of  the  mandibular  ramus  and  with  the  posterior  aspect 
of  the  internal  pterygoid  muscle.  An  irregular  "pterygoid  lobe"  may  extend 
between  the  internal  and  the  external  pterygoid  muscles.  The  posterior  surface 
is  in  contact  with  the  sternomastoid  muscle  laterally,  and  with  the  styloid  process 
and  associated  muscles  medially.  Between  the  sternomastoid  and  styloid  process 
it  touches  the  posterior  belly  of  the  digastric,  and  is  in  relation  with  the  internal 
carotid  and  jugular  vessels.  The  various  structures  in  contact  with  the  parotid 
gland  often  make  more  or  less  distinct  grooves  upon  its  posterior  and  anterior 
surfaces. 

Borders. — -The  anterior  border  usually  extends  from  below  obliquely  upward 
and  forward  so  as  to  give  the  whole  superficial  surface  a  triangular  appearance. 
Near  the  upper  end  of  the  anterior  border,  the  parotid  duct  leaves  the  gland,  and 
just  above  this  there  is  usually  a  small  separate  accessory  lobe  [gl.  parotis  acces- 
soria],  of  variable  form  and  size.  The  branches  of  the  facial  nerve  also  emerge 
from  the  anterior  border.  The  posterior  border  extends  along  the  anterior  aspect 
of  the  sterno-mastoid  muscle  up  to  the  mastoid  process.  The  medial  border 
is  deeply  placed  (at  the  junction  of  the  anterior  and  posterior  surfaces),  and 
approaches  the  wall  of  the  pharynx. 

The  upper  extremity  of  the  parotid  sends  a  process  into  the  posterior  part  of 
the  manibular  fossa,  behind  the  condyle  of  the  mandible,  and  is  related  with  the 

Fig.  865. — Diagram  op  Horizontal  Section  Showing  the  Parotid  Compartment  and 
Relations.     Arrow  indicates  opening  in  sheath.     (Modified  from  Woolsey  after  Testut.) 


EXTERNUi 
CAROTI9 
ARTERY 
l»HAHYN- 
FACIAL  .         -,  ,  —»,, 

NER\ 
PAROTID 
APONEU- 
ROSIS _ 
SUPERFIC    t       M             ■      LAYER         ^  ^^=>,  \STYLOII 
'LAYER             1           I             '              \yif^    ^~S!K)      ^PROCESS 

AND    ITS 
MUSCLES 


external  auditory  meatus.  From  the  upper  extremity  emerge  the  superficial  tem- 
poral vessels  and  the  auriculo-temporal  nerve.  The  lower  extremity  is  separated  by 
the  stylo-mandibular  ligament  from  the  posterior  end  of  the  submaxillary  gland. 

Fascia. — As  shown  in  fig.  865,  the  parotid  gland  is  enclosed  in  a  sheath  (called  the  parotid 
fascia  or  aponeurosis)  derived  from  the  deep  fascia  of  the  neighbourhood.  The  superficial 
layer  of  the  sheath  covers  the  lateral  surface  of  the  gland,  while  the  deep  layers  correspond  to 
the  anterior  and  posterior  surfaces  of  the  gland.  The  sheath  is  very  feeble  or  deficient  at  the 
medial  angle.  The  superficial  and  deep  layers  of  the  parotid  sheath  unite  below  to  form  a  thick 
fascial  band  extending  from  the  angle  of  the  mandible  to  the  sterno-mastoid  muscle. 

Contents. — Within  the  sheath,  the  parotid  gland  is  in  intimate  relation  with  numerous 
important  structures.  Extending  along  the  medial  border,  and  partly  embedded  in  the  gland, 
is  the  external  carotid  artery,  dividing  above  into  the  superficial  temporal  and  internal  maxillary 
(including  the  origins  of  the  deep  auricular  and  transverse  facial);  and  the  posterior  facial 
(temporo-maxillary)  vein  and  branches.  The  auriculo-temporal  nerve  passes  through  the  upper 
part  of  the  gland,  while  the  facial  nerve  passes  somewhat  horizontally  through  it,  dividing 
into  its  temporo-facial  and  oervico-facial  divisions.  Finally,  there  are  embedded  m  the  gland 
two  or  three  deep  lymphatic  nodes,  which  receive  lymphatic  vessels  from  the  external  auditory 
meatus,  the  soft  palate  and  the  posterior  part  of  the  nasal  fossa;  and  several  superficial_ nodes, 
which  receive  lymphatic  vessels  from  the  temple,  eyebrows  and  eyelids,  cheek  and  auricle. 

Structure. — The  parotid  is  a  racemose  gland  of  the  serous  type. 


THE  SUBMAXILLARY  GLAND 


1115 


Duct,  vessels  and  nerves. — The  duct  of  the  parotid  (Stenson's)  issues  from  tlie  anterior  bor- 
der of  the  gland,  crosses  the  masseter  a  finger's  breadth  below  the  zygoma,  and  turns  abruptly 
medialward  round  its  anterior  border.  It  penetrates  the  fat  of  the  cheek  and  the  fibres  of 
the  buccinator  muscle,  between  which  and  the  mucous  membrane  it  runs  for  a  short  distance 
before  it  terminates,  sometimes  on  the  summit  of  a  little  papilla,  by  a  minute  orifice.  This 
opening  is  placed  opposite  the  crown  of  the  second  upper  molar  tooth.  The  duct  commences 
by  numerous  branches,  which  converge  toward  the  anterior  border  of  the  gland,  and  receives 
in  its  passage  across  the  masseter  the  duct  of  the  accessory  parotid  gland.  The  canal  is  about 
the  size  of  a  crow-quill,  length  about  35  to  40  mm.,  diameter  3  mm.  Its  mucous  membrane 
is  covered  for  a  short  distance,  beginning  with  its  oral  termination,  by  stratified  pavement 
epitheUum,  for  the  remainder  of  the  distance  by  columnar  epithelium.  The  coat  of  the  duct 
is  thick  and  tough,  and  consists  of  fibrous  tissue  intermixed  with  nonstriated  muscle-fibres. 

The  arteries  are  derived  from  those  lying  in  the  gland  substance  and  from  the  posterior 
auricular  artery. 

The  veins  terminate  in  the  posterior  facial  (temporo-maxillary)  trunk. 

The  nerves. — The  parotid  gland  receives  its  secretory  fibres  from  the  otic  ganglion,  con- 
veying impulses  from  the  glosso-pharyngeal  via  the  lesser  petrosal  and  the  auriculo-temporal; 
its  sensory  supply  through  branches  of  the  fifth  nerve;  and  its  sympathetic  supply  from  the 
carotid  plexus.  The  lymphatics  from  the  parotid  gland  terminate  in  the  superficial  and  deep 
cervical  glands,  especially  in  the  deeper  group  of  parotid  nodes  embedded  in  the  substance  of 
the  gland. 

Variations. — The  parotid  is  quite  variable  in  size  and  in  the  form  of  its  various  processes, 
especially  of  the  accessory  lobe,  as  already  mentioned.  The  lobulations  are  less  distinct  in 
infancy.  Rarely  the  parotid  is  confined  to  the  masseteric  region,  the  retro-mandibular  fossa 
being  filled  with  a  fatty  tissue  enclosing  the  vessels  and  nerves  normally  found  with  the  gland. 

THE  SUBMAXILLARY  GLAND 

The  submaxillary  gland  [gl.  submaxillaris]  weighs  7  to  10  grams,  and  is  of 
about  the  form  and  size  of  a  flattened  walnut.  It  consists  of  a  chief  or  superficial 
part,  and  a  smaller  deep  process.  The  chief  portion  is  located  in  the  digastric 
triangle,  and  presents  three  surfaces — superficial,  deep  and  lateral  (figs.  847,  866). 


Fig.  866. — Medial  View  of  the    Submaxillary  and    Sublingual    Glands.     (Sobotta — 
McMurrich's  Atlas.) 


Sublingual  caruncle       Ductus  sublingualis  major 


Orbicularis 
Labial  glands 


Minor  sublingual  ducts 

^Submaxillary  ducts 


---Lingual  nerve 
,Deep  process  of 
^       submaxillary 


/  'A 


Genio-glossus 


Gemo-hyoideus 


Mylo-byoideus 


Submaxillar; 
gland 


Surfaces. — The  superficial  or  latero-inferior  surface  is  covered  by  skin,  super- 
ficial fascia,  platysma  and  deep  fascia  (which  forms  an  incomplete  capsule  around 
the  gland).  It  is  crossed  by  the  facial  vein  and  by  cervical  branches  of  the  facial 
nerve.  Several  lymphatic  glands,  which  receive  vessels  from  the  anterior  facial 
region,  lie  upon  or  embedded  in  this  surface. 

The  lateral  surface  is  the  smallest  of  the  three.  It  is  in  contact  with  the  sub- 
maxillary fossa  of  the  medial  surface  of  the  mandible,  and  with  the  lower  part  of 
the  internal  pterygoid  muscle.  The  posterior  aspect  of  the  gland  is  deeply 
grooved  by  the  external  maxillary  (facial)  artery  and  is  separated  from  the  parotid 
gland  by  the  stylo-mandibular  ligament.  The  deep  or  medio-superior  surface  is 
in  contact  with  the  lower  surface  of  the  mylohyoid,  and  behind  this  with  thehyo- 


1116 


DIGESTIVE  SYSTEM 


glossus,  stylohyoid  and  posterior  belly  of  the  digastric.  Between  this  surface 
and  the  mylohyoid  muscle  are  the  mylohyoid  nerve  and  artery  and  the  sub- 
mental artery. 

The  deep  portion  is  a  tongue-like  process  which  passes  from  the  deep  surface 
of  the  submaxillary  gland  around  the  posterior  border  of  the  mylohyoid  muscle, 
and  extends  forward  in  company  with  the  duct,  under  cover  of  (above)  the  mylo- 
hyoid, and  in  relation  with  the  hyoglossus  and  genioglossus  muscles.  At  its 
commencement,  the  deep  process  lies  just  below  the  submaxillary  ganglion  and 
■  anteriorly  it  gives  off  the  submaxillary  duct  as  it  approaches  the  sublingual  gland. 

Structure. — The  submaxillary  is  a  racemose  gland  belonging  to  the  mixed  type,  some  of 
the  acini  being  serous,  others  mucous  (fig.  867). 

The  submaxillary  (Wharton's)  duct  springs  from  the  deep  surface  of  the  superficial  part 
of  the  gland;  it  passes  forward  and  inward,  along  the  medial  surface  of  the  deep  lobe,  and  opens 
by  a  small  orifice  on  the  summit  of  a  papilla  [caruncula  sublinguahs]  by  the  side  of  the  frenulum 
of  the  tongue.     It  is  crossed  superficially  by  the  lingual  nerve.     It  hes  at  first  between  the  mylo- 


FiQ.  867. — Section  op  the  Submaxillary  Gland  op  an  Adult  Man.      X  252.     (Lewis  and 

Stohr.) 


Mucous  gland  cells 


Connective  tissue 


Secretory  duct 


hyoid  and  hyoglossus;  next,  between  the  mylohyoid  and  genioglossus;  and  lastly,  under  cover 
of  the  mucous  membrane  of  the  mouth,  between  the  genioglossus  and  the  sublingual  gland. 
The  duct  is  about  5  cm.  in  length,  and  has  comparatively  thin  walls.  It  is  lined  by  columnar 
epithelium. 

Vessels  and  nerves. — The  arteries  to  the  gland  are  derived  from  the  external  maxillary 
(facial)  and  lingual,  and  they  are  accompanied  by  corresponding  veins. 

The  nerves. — The  submaxillary  gland  receives  its  secretory  fibres  from  numerous  small 
sympathetic  ganglia  situated  on  the  submaxillary  duct  and  in  the  hilus  of  the  gland,  these 
conveying  impulses  from  the  chorda  tympani;  its  sensory  branches  probably  come  from  the 
geniculate  ganglion,  and  its  sympathetic  branches  from  the  cervical  sympathetic. 

Variations. — Absence  of  the  gland  is  a  rare  anomaly.  A  case  is  recorded  (Turner)  where 
the  submaxillary  was  placed  entirely  under  cover  of  the  mylohyoid,  being  closely  associated 
with  the  sublingual  gland. 

THE  SUBLINGUAL  GLAND 

The  sublingual  gland  [gl.  sublingualis] — the  smallest  of  the  salivary  glands 
(2  to  3  gm.)  is  in  reality  a  group  of  glands  forming  an  elongated  mass  in  the  floor 
of  the  mouth  under  the  tongue  (fig.  847) .  Above,  it  forms  a  distinct  ridge,  covered 
by  a  fold  of  mucosa  (plica  sublingualis)  upon  which  its  ducts  open  (fig.  866).  It  is 
flattened  from  side  to  side,  its  loioer  border  resting  upon  the  upper  surface  of  the 
mylohyoid,  its  lateral  surface  in  contact  with  the  sublingual  fossa  of  the  mandible, 
and  its  medial  surface  with  the  geniohyoid,  geniohyoglossus,  lingual  nerve,  deep 
lingual  artery  and  submaxillary  duct  (fig.  863).  Anteriorly  it  touches  its  fellow  of 
the  opposite  side,  while  'posteriorly  it  is  often  related  with  the  deep  process  of  the 


THE  TEETH  1117 

submaxillary  gland.  It  has  no  distinct  capsule,  thus  differing  from  the  submaxil- 
lary and  parotid  glands.  In  structure,  it  is  a  racemose  mixed  gland,  but  predomi- 
inantly  mucous. 

Ducts. — The  minor  sublingual  duels  [ductus  sublinguales  minores],  ducts  of  Rivinus,  vary 
from  five  to  fifteen  or  more  in  number,  and  open  on  minute  papillae  along  the  crest  of  the  plica 
sublingualis  (fig.  858).  The  anterior  portion  of  the  gland  often  forms  a  larger  [Bartholin' s) 
duel  [ductus  sublingualis  major]  which  opens  alongside  the  submaxillary  duct  on  the  caruncula 
sublingualis  (figs.  858,  866). 

Vessels  and  nerves. — The  arteries  are  derived  from  the  sublingual  and  submental,  with 
corresponding  vci^is.     The  lymphatics  are  tributaries  of  the  superior  deep  cervical  nodes. 

Nerves. — The  sublingual  glands  receive  their  secretory  fibres  from  the  subma.xillary  and 
associated  sympathetic  ganglia,  conveying  impulses  from  the  chorda  tympani;  sympathetic, 
branches  come  from  the  cervical  sympathetic  and  sensory  fibres  probably  from  the  geniculate 
ganglion,  although  this  question  needs  further  investigation. 

Development  of  the  salivary  glands. — The  salivary  glands  appear  early  as  buds  from  the 
ectodermal  epithelium  extending  into  the  adjacent  mesenchyme  of  the  mouth  cavity.  The 
parotid  appears  first  on  the  side  of  the  mouth  cavity  in  an  embryo  of  8  mm.,  as  a  groove  which 
becomes  tubular  and  pushes  back  over  the  masseter  to  the  ear  region,  developing  branches  (at 
first  solid).  Around  the  gland  and  between  the  branches  is  mesenchyme  which  becomes 
condensed  to  form  the  peripheral  capsule.  The  submaxillary  gland  appears  in  the  13  mm. 
embryo  as  a  ridge  in  the  epithelium  of  the  alveolo-lingual  groove.  The  solid  cord  (lumen 
appearing  later)  grows  forward  to  the  region  of  its  adult  orifice.  Its  posterior  end  extends 
backward  and  gives  off  solid  branches  which  later  form  the  acini  and  duct  system  of  the  mature 
gland.  The  sublingual  glands  appear  somewhat  later  (24  mm.  embryo)  as  a  series  of  separate 
anlages  of  variable  number,  budding  off  in  the  positions  where  the  adult  ducts  empty.  The 
major  sublingual  gland,  if  present,  appears  fii'st.  The  histogenetic  development  of  the  salivary 
glands  is  not  completed  until  some  time  after  birth,  probably  about  the  time  of  weaning. 
However,  mucin  cells  appear  in  the  sublingual  glands  in  the  foetus  of  four  months  and  serous 
cells  in  the  parotid  of  five  months. 

Variations. — The  duct  of  Bartholin  is  present  in  about  half  of  the  cases,  and  the  corre- 
sponding anterior  part  of  the  gland  may  be  more  or  less  separate  [gl.  sublingualis  major].  The 
number  of  ducts  may  reach  thirty  (TiUaux).  Rarely  processes  from  the  gland  may  penetrate 
the  mylohyoid,  appearing  on  its  lower  surface  in  one  or  more  places  (Moustin).  Most  of  the 
variations  in  this  and  the  other  salivary  glands  are  due  to  developmental  irregularities. 

Comparative. — Oral  glands  are  not  found  in  the  lower  aquatic  vertebrates.  Mucous 
glands  occur  in  all  terrestrial  vertebrates,  but  true  sahvary  (digestive)  glands  appear  only  in 
mammals.  Although  great  variations  occur  in  the  different  species  of  mammals,  those  in  man 
(excepting  the  anterior  lingual)  are  typical  for  the  order.  The  sublingual  gland,  however, 
often  occurs  as  two  separate  glands,  corresponding  to  the  sublinguaUs  major  and  minor.  The 
parotid  gland  apparently  has  no  representative  in  forms  below  mammals.  In  some  mammals 
(e.  g.,  monkey)  it  has  two  main  lobes — a  larger  superficial  and  a  smaller  deeper  lobe  between 
which  lies  the  facial  nerve  (Gregoire).  Other  oral  glands  (e.  g.,  orbital,  zygomatic)  appear  in 
some  mammals. 

THE  TEETH 

The  teeth  [dentes]  are  highly  specialized  structures  developed  in  the  oral 
mucosa  as  organs  of  mastication  and  also  (in  man)  of  speech.  The  adult  indi- 
vidual with  perfect  dentition  has  thirty-two  teeth,  arranged  arch-like  in  the  sock- 
ets (alveoli)  of  the  maxilla  and  the  mandible.  Sixteen  belong  to  the  upper  or 
maxillary  arch;  and  sixteen  to  the  lower  or  mandibular.  The  four  central  teeth 
in  each  dental  arch  are  the  incisors;  the  tooth  next  to  these  on  each  side  is  the 
canine;  behind  these  are  the  two  premolars  (bicuspids) ;  and  lastly  the  three 
molars.     This  relation  of  teeth  is  expressed  by  the  following  dental  formula: 

.21  2       3     „„ 

i2,Cj-,pm2,m3  =  32. 

Form. — Each  tooth  [dens]  has  a  crown  [corona  dentis],  the  portion  exposed 
beyond  the  gum,  and  covered  with  enamel  (figs.  871,  872).  The  root  [radix  den- 
tis] is  the  portion  covered  with  cementura  and  embedded  in  the  bony  socket.  At 
the  line  of  union  of  crown  and  root  is  the  slightly  constricted  neck  [coUum  dentis]. 
The  surface  of  the  tooth  directed  toward  the  lip  (or  cheek)  is  termed  the  labial 
(or  buccal)  surface  [facies  labialis;  f.  buccalis];  while  that  toward  the  tongue  is 
the  lingual  surface  [f.  lingualis].  The  crowns  of  the  opposite  arches  meet  at  the 
masticating  surface  [f.  masticatoria].  The  surfaces  in  contact  with  the  adjacent 
teeth  of  the  same  arch  [facies  contactus]  are,  for  the  incisors  and  canines,  termed 
medial  and  lateral,  while  those  for  the  premolars  and  molars  are  termed  anterior 
and  posterior. 


1118 


DIGESTIVE  SYSTEM 


Structure. — As  shown  in  longitudinal  section  (fig.  873),  each  tooth  has  a  central  cavity 
[cavum  dentis]  or  pulp  cavity,  which  is  filled  with  pulp  [pulpa  dentis].  The  pulp  is  a  soft  fibrous 
tissue  richly  supplied  with  vessels  and  sensory  nerves  which  enter  the  root  canal  through  the 
apical /orame?i  [foramen  apicis  dentis].  The  body  of  the  tooth,  both  crown  and  root,  is  composed 
of  a  dense  modified  variety  of  bone  called  dentine  [substantia  eburnea].  It  is  yellowish  in 
colour.     The  striated  appearance  of  the  dentine  is  due  to  numerous  fine  canals,  the  dentinal 

; '  ':■     Fig.  868. — Teeth  of  an  Adult,  Exteknal  View. 
Incisors  Canine  Premolar  Molars  Wisdom  tooth 


Fig.  869. — Teeth  of    Adult,    Lingual        Fig.  870. — Teeth  of  Adult,  Labial  and 
Surfaces.     (Broomell  and  Fischelis.)       Buccal  Surfaces.     (Broomell  and  Fische- 

lis.) 


Fig.  871. — Canine  Tooth,  Lingual  Surface.  Fig.  872. — A  Molar  Tooth  in  Section. 

n* Root 

Cusp fP^^^^) 

~  -Pulp  cavity 

Neck 
Cingulum 


tubules.  These  contain  'Tomes'  fibrils,'  which  are  long  protoplasmic  branches  of  the  odonto- 
blasts, a  layer  of  cells  on  the  surface  of  the  pulp.  At  the  outer  surface  of  the  dentine  are  numer- 
ous small,  irregular  interglobular  spaces,  corresponduig  in  the  root  to  Tomes'  'granular  sheath' 
(fig.  873).  The  dentine  of  the  crown  is  covered  with  a  layer  of  white  enamel  [substantia 
adamantina],  which  is  the  hardest  substance  in  the  body.     It  is  composed  of  numerous  mmute 


THE  TEETH 


1119 


hexagonal  -prisms  [prismata  adamantina]  which  are  arranged  perpendicular  to  the  surface  and 
are  of  epithelial  origin.  In  adult  teeth,  the  enamel  is  often  worn  through  in  places,  exposing 
the  yellowish  dentine.  The  dentine  of  the  root  is  covered  by  a  thin  layer  of  cementum  [sub- 
stantia ossea],  a  layer  of  bone  which  is  very  thin  at  the  neck,  but  becomes  thicker  toward  the 
root  apex  (fig.  873).  Surrounding  the  root  is  the  aUeolar  periosteum,  a  fibrous  membrane 
connecting  the  cementum  firmly  with  the  bony  lining  of  the  socket.  For  further  details  of 
the  minute  structure  of  teeth,  works  on  histology  may  be  consulted. 

Gums. — Covering  the  alveolar  portions  of  the  maxilla  and  mandible  are  the 
gums  [gingivae].     They  are  continuous  with  the  mucosa  of  the  vestibule  exter- 


FiG.  873. — Vertical  Section  op  an  Inferior  Canine  Tooth,  in  Situ. 
Toldt's  Atlas.) 


X  4.     (From 


Transition  from  mandibular  to 
i^\       ^  alveolar  periosteum 


Pulp  capillaries 


Alveolar  periosteum 
Cementum 


Compact  bone  of  mandible 


Marrow  spaces  of  mandible 


nally  and  of  the  palate  or  floor  of  the  mouth  internally.  Like  the  mucosa  of  the 
mouth  elsewhere,  they  are  covered  with  stratified  squamous  epithelium.  The 
lamina  propria  is  especially  thick  and  strong,  and  is  firmly  attached  to  the  sub- 
jacent bone.  Around  the  neck  of  each  tooth,  the  epithelium  of  the  gum  forms  an 
overlapping  collar  and  the  lamina  propria  is  continuous  with  the  alveolar  perios- 
teum (fig.  873). 

The  incisors.— (Figs.  868,  869,  870,  874.)     The  incisor  teeth  [dentes  incisivi] 
are  so  named  on  account  of  then:  function  in  cutting  the  food.     The  crown  has  a 


1120 


DIGESTIVE  SYSTEM 


characteristic  chisel  shape.  The  masticating  surface  is  narrow  and  chisel-edged. 
In  recently  erupted  teeth,  the  cutting  edge  is  elevated  into  three  small  cusps, 
which  soon  wear  down,  leaving  a  straight  edge.  These  cusps  correspond  to  three 
indistinct  ridges  on  the  labial  surfaces.  The  lateral  angle  of  the  crown  is  usually 
more  rounded  than  the  medial.     The  labial  surfaces  are  slightly  convex,  the  lin- 

FiG.  874. — Cross-Section  of  the  Medi  ^i.  Upper  Incisor,  in  Situ.     X  4.     (From  Toldt's 

\tl    IS     1 


Dentine  of  root  of  tooth 


Root  canal  of  tooth' 


Alveolar  periosteum 


Wall  of  dental  alveolus 


gual  slightly  concave.  The  contact  surfaces  are  somewhat  triangular.  The  roots 
of  the  incisors  are  single,  though  often  longitudinally  grooved,  indicating  traces  of 
a  division.  They  are  somewhat  conical,  but  flattened  from  side  to  side,  expecially 
the  lower  set,  and  are  slightly  curved  lateralward. 

The  upper  or  maxillary  incisors  are  much  larger  than  the  lower.  They  are  lodged  in  the 
premaxilla,  and  are  inclined  downward  and  forward.  They  overlap  the  lower  incisors  in  masti- 
cation, hence  the  masticating  surface  is  worn  off  and  rounded  at  its  posterior  edge,  while  the 
anterior  edge  becomes  sharp  and  chisel-hke.  The  lingual  surfaces  of  the  crowns  terminate 
near  the  gum  in  a  low,  inverted  V-shaped  ridge,  the  basal  ridge  or  cingulum.     At  the  apex  of 

Fig.  875. — Variations  in  the  Form  of  the  Upper  Third  Molar.     (BroomellandFischelis.) 


the  V,  near  the  gum,  there  is  often  (especially  on  the  lateral  incisor)  a  smaU  lingual  cusp.     The 
medial  upper  incisor  is  distinguished  from  the  lateral  by  its  much  larger  size. 

The  lower  or  mandibular  incisors  are  smaller  than  the  upper,  the  cutting  edges  being  only 
about  half  as  wide.  Being  overlapped  by  the  upper  set,  the  lower  incisors  have  the  masti- 
cating surface  worn  ofT  anteriorly,  leaving  a  sharp  cutting  edge  posteriorly.  The  lower  mcisors 
are  vertically  placed,  and  the  crown  becomes  narrower  toward  the  neck.  A  cingulum  is  rarely 
visible.     The  medial  lower  incisor,  unlike  the  upper,  is  slightly  smaller  than  the  lateral. 

The  canines.— (Figs.  868,  869,  870,  871.)  The  canine  teeth  [dentes  canini] 
so-called  from  their  prominence  in  the  dog-tribe,  are  the  longest  of  all  the  teeth 
(fig.  868).  The  crown  is  thicker  and  more  conical  than  in  the  mcisors.  The  mas- 
ticating surface  forms  a  median  angular  poi  nt,  on  either  side  of  which  the  cutting 


THE  TEETH 


1121 


edge  slopes  to  the  lateral  angle.  The  medial  limb  of  the  cutting  edge  is  usually 
somewhat  shorter  than  the  lateral,  rendering  the  crown  asymmetrical.  The 
labial  surface  is  convex,  the  lingual  somewhat  concave.  The  root  is  single,  long, 
flattened  from  side  to  side  and  grooved  on  the  sides  as  in  the  incisors.  The  canine 
root  is  usually  slightly  curved  lateralward.  The  bony  alveolar  protuberances 
[juga  alveolaria]  are  more  prominent  than  those  of  any  other  teeth. 

The  upper  canine  slants  forward  and  overlaps  the  lower,  as  in  the  incisors.  The  upper 
canine  also  presents  a  well-marked  cingulum,  and  usually  a  distinct  lingual  cusp  (fig.  871) 
below  which  a  slight  median  ridge  extends  along  the  lingual  surface.  On  the  lower  canine, 
these  structures  are  poorly  marked  or  absent.  The  lower  canine  is  somewhat  smaller  than  the 
upper,  and  its  root  is  occasionally  bifid. 

The  premolars.— (Figs.  868,  869,  870,  876,  877.)  The  premolars  [dentes 
premolares]  are  so  named  on  account  of  their  position  in  front  of  the  molars.     The 


Fig. 


876. — Dissection  Showing  the   Roots  op  the  Teeth.     Teeth  in   Occlusion.     X  1 
(From  Toldt's  Atlas.) 


Buccal  surface 


Wisdom  tooth 


Premolar  teeth 


Mental  foramen 


crown  presents  on  the  masticating  surface  two  prominent  cusps,  on  account  of 
which  the  premolars  are  often  called  'bicuspids.'  The  buccal  and  lingual  sur- 
faces are  convex  especially  from  side  to  side,  so  that  the  crown  is  somewhat 
cylindrical  in  form,  with  flattened,  quadrilateral  anterior  and  posterior  contact 
surfaces.  The  root  is  (usually)  single  and  more  or  less  flattened  antero-posteriorly, 
and  usually  somewhat  curved  backward. 

The  upper  premolars  are  distinguished  from  the  lower  by  a  greater  antero-posterior  flatten- 
ing of  the  crown  and  by  a  deep  groove  separating  the  cusps  (excepting  at  their  anterior  and 
posterior  margins)  on  the  masticating  surface.  In  the  first  upper  premolar  the  lingual  cusp 
and  surface  are  decidedly  smaller  than  the  buccal;  and  the  root  is  frequently  bifid  or  double 
(occasionally  even  triple).  In  the  second  upper  premolar  the  lingual  cusp  and  surface  are  as 
large  as  the  buccal;  and  the  root,  though  deeply  grooved,  is  rarely  bifid. 

In  the  lower  premolars,  the  crowns  are  more  cylindrical  in  form,  and  the  cusps  are  united 
by  a  median  ridge  so  that  the  masticating  surface  presents  two  small  pits.  The  roots  are  more 
rounded  and  tapering,  and  rarely  grooved.  In  the  first  lower  premolar  (like  the  corresponding 
upper)  the  lingual  cusp  and  surface  are  much  smaller  than  the  buccal,  the  lingual  cusp  some- 
times being  rudimentary;  while  in  the  second  they  are  more  nearly  equal.  The  second  lower 
premolar  is  often  slightly  larger  than  the  first,  while  in  the  upper  premolars  the  converse  is  true. 
It  should  be  noted,  however,  that  the  premolars  are  quite  variable  in  all  respects,  and  it  is 
therefore  often  difficult  to  identify  the  individual  isolated  teeth. 

The  molars.— (Figs.  868,  869,  870,  872,  875,  876.)  The  molars  [dentes  mol- 
ares]  or  'grinders'  are  characterized  by  their  large  size,  and  by  the  presence  of 


1122 


DIGESTIVE  SYSTEM 


three  to  five  masticating  cusps  (hence  sometimes  called  'multicuspids')-  The 
crowns  are  massive,  somewhat  resembling  rounded  cubes,  and  the  lingual  and  buc- 
cal surfaces  present  vertical  grooves  continuous  with  the  fissures  separating  the 
cusps.  The  pulp  cavity  (fig.  872)  has  slight  extensions  corresponding  to  the  cusps, 
and  also  communicates  with  the  canals  of  the  roots,  which  are  usually  two  or  three 
in  number,  and  more  or  less  curved. 

Fig.  877. — Diagram  Showing  the  Articulation  of  the  Teeth.     (Poirier-Charpy.) 


labial-!/,  WcalA 

Vlmgual 


^"8"^^  buoci 


-lingual 


The  upper  molars  are  most  easily  distinguished  from  the  lower  by  the  presence  of  a  triple 
root.  The  masticating  surface  is  nearly  square  with  rounded  angles.  They  each  have  typically 
four  cusps,  separated  by  grooves  resembling  a  diagonally  placed  H  (fig.  852).  The  crowns  of 
the  upper  molars  are  obliquely  placed  so  as  to  slant  downward  and   slightly  lateralward. 

Each  upper  molar  has  three  roots,  two  buccal  and  one  Ungual  or  palatal.  They  are  aU 
(especially  the  buccal)  in  more  or  less  close  relation  with  the  floor  of  the  maxillary  antrum  (of 
Highmore)  (fig.  876).  The  buccal  roots  are  flattened  antero-posteriorly,  and  longitudinally 
grooved,  and  bent  backward.  The  palatal  root  is  more  rounded,  with  a  groove  on  the  hngual 
surface,  and  usually  bent  medialward.  Either  of  the  buccal  roots  may  fuse  with  the  palatal, 
or  there  may  be  an  extra  fourth  root. 

As  to  the  individual  upper  molars,  the  first  has  almost  invariably  four  typical  cusps  (rarely 
only  three,  or  with  an  additional  fifth  rudimentary).  The  second  upper  molar  has  only  three 
cusps  in  about  half  of  the  cases  (in  Europeans),  and  four  in  the  remainder.  The  third,  or  wisdom 
tooth  [dens  serotinus]  is  exceedingly  variable  in  size  and  form  (fig.  875).  It  has  three  cusps 
much  more  frequently  than  four,  and  its  three  roots  are  often  more  or  less  fused  into  a  conical 
mass.  It  is  usually  much  smaller  than  the  other  molars,  and  is  absent  in  nearly  one-fifth  of  all 
cases. 


Fig.  878. — Diagrams  Showing  the  Early  Development  or  Three  Teeth,  One  of  which 
IS  Shown  in  Vertical  Section.     (Lewis  and  Stohr.) 

Epithelium  of  the  margin  Enamel         Dental 

of  the  jaw  organs        groove 


Dental  ridge  Z^-'''^ 

Papillae 

A  B 


Enamel  organs       Necks  of  enamel  organs 

C  D 


The  lower  molars  have  usually  four  or  five  cusps  (two  lingual,  and  two  or  three  buccal) 
the  fissures  separating  them  being  cross-shaped  or  stellate  (fig.  864).  The  crowns  incUne 
upward  and  slightly  medialward.  They  have  each  two  roots,  anterior  and  posterior,  flattened 
antero-posteriorly,  and  usually  somewhat  curved  backward.  The  roots,  especially  the  anterior, 
may  be  longitudinally  grooved.  The  anterior  has  two  root-canals,  the  posterior  usually  only 
one.  The  apices  of  the  roots  of  the  lower  molars,  especially  of  the  third,  approach  the  man- 
dibular (inferior  dental)  canal  (fig.  876). 

Of  the  individual  lower  molars,  the  first  is  usually  slightly  the  largest,  and  has  five  cusps 
in  the  great  majority  of  cases  (variously  estimated  at  from  60  to  95  per  cent.),  otherwise  four. 
The  four  main  cusps  (two  buccal  and  two  lingual)  are  separated  by  a  cruciform  fissure,  which 
bifurcates  posteriorly  to  embrace  the  small  fifth  cusp  (which  is  placed  shghtly  to  the  buccal 


THE  TEETH 


1123 


side)  when  present.  The  second  lower  molar  has  usually  four  cusps  (75  to  85  per  cent,  of  cases) , 
otherwise  five,  the  fifth  usually  small  or  rudimentary.  The  roots  are  sometimes  confluent. 
The  lower  third  or  wisdom  tooth,  like  the  upper,  is  usually  small  and  exceedingly  variable 
(fig.  875).     It  has  usually  four  or  five  cusps;  but  the  number  may  be  increased  to  six  or  seven, 

Fig.  879.^Modei,  of  Ectoderm  op  Jaw  of  Hitman  Embryo  40  mm.  Long,  Showing 
Dental  Ridge  with  Enamel  Organs  for  the  First  Teeth.     (Kingsley,  after  Rose.) , 


or  reduced  to  three,  two,  or  one.     The  roots  are  often  short  and  fused  into  a  conical  mass 
in  which  sometimes  only  a  single  canal  is  present. 

The  dental  arches. — On  comparing  the  upper  and  the  lower  dental  arches,  it  is  seen  that 
the  upper  (fig.  852)  forms  an  elliptical  curve,  while  the  lower  (fig.  864)  resembles  a  parabola. 

Fig.  880. — Section  Showing  Later  Stages  op  Tooth  Development.     (Szymonowicz.) 


^^ 


^ .Epithelium  of  oral  cavity 


Enamel  - 
pulp 


Inner  _ 

enamel'" 

cells 


Neck  of 
enamel  organ 


Dental  ridge 
of  permanent 
tooth 


,  Bone  trabecu- 
l3s  of  lower  jaw 


The  upper  arch  is  slightly  larger  (due  chiefly  to  the  slant  of  the  teeth,  as  previously  explained) 
so  that  it  shghtly  overlaps  the  lower  when  the  teeth  are  in  occlusion.  Thus,  as  showli  in  fig. 
876,  the  upper  incisors  (and  canines)  overlap  the  lower.  The  buccal  cusps  of  the  lower  pre- 
molars and  molars  fit  into  the  groove  between  the  upper  buccal  and  lingual  cusps;  while  the 
upper  lingual  cusps  correspond  to  the  groove  between  lower  buccal  and  lingual  cusps.  This 
arrangement  favors  a  more  perfect  mastication  (see  fig.  877). 

Moreover,  when  viewed  from  the  side  (fig.  876),  it  is  seen  that  in  general,  the  corresponding 
teeth  of  the  upper  and  the  lower  arches  are  not  opposite,  but  alternate  with  each  other.     This  is 


1124 


DIGESTIVE  SYSTEM 


due  chiefly  to  the  great  width  of  the  upper  central  incisor.  The  lower  molars,  however,  es- 
pecially the  third,  are  wider  (antero-posteriorly)  than  the  upper,  so  that  the  two  arches  are 
nearly  equal  in  length.  The  interdental  line  between  the  two  arches  is  not  straight,  but  shghtly 
convex  downward  (fig.  876).  In  both  arches,  the  crowns  of  the  incisors  and  canines  are  taller 
than  those  of  the  premolars  and  molars. 

Vessels  and  nerves. — The  vessels  and  nerves  of  the  teeth  are  distributed  partly  to  the 
pulp  and  partly  to  the  surrounding  alveolar  periosteum.  The  arteries  are  all  derived  from  the 
internal  maxillary.  Those  for  the  upper  teeth  are  the  posterior  superior  alveolar  and  the 
anterior  superior  alveolar  (from  the  infraorbital).  Similar  branches  to  the  lower  jaw  are  given 
off  by  the  inferior  alveolar.     They  give  off  twigs  to  the  gums  (rami  gingivales),  the  alveolar 

Fig.  881. — Hard  Palate  op  a  Child  of  Five  Years,  Showing  Decidtjous  Teeth. 


Gubernacular  canal 


_  Palate  process  of  maxilla 


Greater  palatine  foramen 
palatine  foramea 


periosteum  (rr.  alveolares),  and  the  pulp  cavities  (rr.  dentales).  A  dental  branch  enters  each 
root  canal  through  the  apical  foramen,  and  breaks  up  into  a  rich  peripheral  capillary  plexus 
under  the  odontoblast  layer.  From  this  plex-us,  the  corresponding  veins  arise.  There  is  a  plex-us 
of  peridental  lymphatics,  which  anastomose  with  those  of  the  surrounding  gums,  and  drain 
chiefly  into  the  submaxillary  nodes.  Lymphatics  have  also  recently  been  demonstrated  in  the 
pulp  of  the  tooth  (Schweitzer). 

The  nerves  are  sensory  branches  derived  from  the  trigeminus.  Those  for  the  upper  teeth 
are  from  the  anterior,  middle,  and  posterior  superior  alveolar  (fig.  735);  while  those  for  the 
lower  teeth  are  from  the  inferior  alveolar  (fig.  736).     These  nerves  give  numerous  branches  to 


Fig.  882. — The  Deciduous  Teeth,  External  View. 
Incisors  Canine        Deciduous  molars 


Maxillary  or  upper  set 


Mandibular  or  lower  set 


the  gums,  alveolar  periosteum,  and  pulp  cavities.  The  latter  enter  with  the  corresponding 
vessels,  and  their  distribution  within  the  tooth  is  a  subject  of  controversy.  They  may  be 
followed  easily  to  a  plexus  under  the  odontoblasts;  but  whether  they  end  freely,  or  in  connection 
with  the  odontoblasts  (which  by  some  are  considered  as  peripheral  sensory  cells),  or  send  fine 
terminal  branches  out  into  the  dentinal  canals  is  still  uncertain. 

Development  of  the  teeth. — The  teeth  represent  calcified  papillae  of  the  oral  mucosa,  the 
enamel  being  a  derivative  of  the  ectodermal  epithehum,  and  the  remainder  of  the  tooth  coming 
from  the  underlying  mesenchyme.  The  first  trace  of  the  teeth  appears  in  the  human  embryo 
of  about  11  mm.,  in  the  form  of  an  epithelial  shelf,  the  dental  ridge,  extending  into  the  mesen- 
chyme corresponding  to  the  future  alveolar  portions  of  the  jaws  (figs.  878,  879).  From  the 
dental  ridge  there  is  later  produced  a  series  of  cup-shaped  enlargements,  the  enamel  organs, 
which  become  constricted  off  except  for  a  slender  neck  attaching  each  to  the  common  ridge. 
By  the  end  of  the  third  foetal  month,  the  twenty  enamel  organs  of  the  temporary  or  deciduous 
teeth  are  formed.  The  concavity  of  each  enamel  organ  is  filled  by  the  dental  papilla  of  mesen- 
chyme. 


THE  TEETH 


1125 


A  somewhat  later  stage  in  the  organogenesis  of  a  tooth  is  shown  in  fig.  880.  The  mesen- 
chymal cells  on  the  surface  of  the  dental  papilla,  next  to  the  enamel  organ,  form  a  single  layer 
of  columnar  cells,  the  odontoblasts.  These  cells  form  the  dentine  upon  their  outer  surfaces, 
gradually  retreating  toward  the  center  of  the  tooth  as  the  dentine  increases  in  thickness.  The 
first  dentine  formed  is  irregular,  enclosing  the  spatia  interglobularia.  The  odontoblasts  re- 
main through  life  just  beneath  the  dentine  on  the  surface  of  the  pulp,  sending  slender  processes, 
up  into  the  dentinal  tubules  as  previously  noted  in  the  structure  of  the  adult  tooth.  The  re- 
mainder of  the  dental  papilla  becomes  the  pulp,  receiving  its  vascular  and  nerve  supply  at  the 
point  opposite  the  enamel  organ,  corresponding  to  the  future  root. 

The  enamel  organ  (fig.  880)  is  differentiated  into  three  layers:  a  thin  outer  layer  attached  by 
the  neck  to  the  dental  ridge;  a  thick  middle  layer  (forming  the  spongy  "enamel  pulp");  and  a 
single  inner  layer  of  cylindrical  enamel  cells,  the  adamantoblasts.  The  latter  form  the 
prisms,  which  are  deposited  gradually  upon  the  outer  surface  of  the  dentine. 


Fig.  883. — Dissection  Showing  the  Teeth  at  about  Six  Years. 
Fischelis.) 


(Broomell  and 


4^;,,>.^/,tijf|. 


Surrounding  the  entire  developing  tooth  there  is  formed  a  strong,  fibrous  connective- 
tissue  membrane,  the  tooth-sac.  The  deeper  part  of  this  sac  later  becomes  the  alveolar  periosteum 
around  which  the  bony  alveoli  are  formed.  This  bone  may  entirely  surround  the  tooth-sac, 
excepting  at  the  summit,  where  a  foramen  persists  through  which  a  process  of  connective 
tissue  {gubernanilnm  dentis)  connects  the  tooth-sac  with  the  overlying  gum  (see  figs.  114,  881). 
Upon  the  inner  surface  of  the  tooth-sac,  next  to  the  root,  the  bony  cemenlum  is  deposited  upon 
the  dentine.  The  root  gradually  elongates,  and  is  usually  not  completed  until  long  after  the 
eruption.  The  remaining  superficial  portion  of  the  tooth-sac  undergoes  pressure  atrophy  and 
absorption.  The  remnants  of  the  enamel  organ,  however,  persist  and  form  a  thin  tough 
cuticle  [cuticula  dentis],  Nasmyth's  membrane,  which  is  soon  worn  off  when  the  crown  is  exposed 
at  the  surface. 

From  the  remainder  of  the  dental  ridge,  which  lies  on  the  lingual  side  of  the  deciduous 
teeth  (fig.  878),  the  permanent  teeth  are  later  derived  in  a  very  similar  manner.  (Rudimentary 
indications  of  a  prelacteal  dental  ridge  have  also  been  described.)  The  anlages  of  the  per- 
manent teeth  therefore  lie  to  the  lingual  side  of  the  deciduous  (fig.  883).  From  the  posterior 
end  of  the  dental  ridge  a  process  extends  into  the  jaw  behind  the  deciduous  teeth,  and  from 
this  process  the  permanent  molars  (which  have  no  deciduous  predecessors)  are  formed.  At 
birth,  although  no  teeth  have  yet  been  cut,  there  are  present  in  the  gums  the  anlages  of  not 
only  all  of  the  deciduous  teeth,  but  also  all  of  the  permanent  teeth,  with  two  exceptions.  Those 
of  the  second  molars  do  not  appear  until  six  weeks  after  birth,  and  of  the  third  molars  not  until 
the  fifth  year.  The  remnants  of  the  dental  ridges  become  broken  up  into  small  masses  of 
epithehal  cells,  which  persist  for  a  variable  time. 


1126 


DIGESTIVE  SYSTEM 


The  deciduous  teeth. — The  deciduous  [dentes  decidui],  temporary  or  milk 
teeth  are  twenty  in  number,  corresponding  to  the  following  formula: 

di|,  dc[,  dm|  =  20. 

The  deciduous  teeth  (figs.  882,  883)  are  much  smaller  in  size  than  the  perma- 
nent teeth,  and  their  necks  are  more  constricted.  The  enamel  of  the  crown  cap  is 
thicker.     In  general,  their  form  and  structure  otherwise  is  very  similar  to  that 

Fia.  884. — Pulp-cavity  op  the  Upper  First  Molar,  From  the  Fifth  to  the  Ninth  Year 
(Broomell  and  Fischelis.) 


already  described  in  the  case  of  the  permanent  incisors  and  canines.  The  molars, 
however,  are  different.  Their  cusps  on  the  masticating  surface  are  very  sharp  and 
irregular.  There  are  usually  three  'cusps  on  the  first  upper  molar  and  four  on  the 
second;  four  cusps  on  the  first  lower  molar  and  five  on  the  second.     The  roots 

Fig.  885. — Showing  the  Extent  of  Calcification  op  Deciduous  Teeth.     (Peirce.) 


40weeks(newli.} 
30weel(S(foe<ai> 
18weeks(foetslX 
17wee]i5(&etal> 

correspond  to  those  of  the  permanent  molars  (three  above  and  two  below),  but 
they  are  much  more  divergent,  to  allow  room  for  the  development  of  the  corre- 
sponding subjacent  permanent  premolar  teeth.  The  first  molar  is  always  con- 
siderably smaller  than  the  second. 

Fig."  886. — Showing  the  Extent  op  Calcification  op  the  Permanent  Teeth.    (Peirce.) 


Calcification  in  the  dentine  and  enamel  of  the  teeth  does  not  begin  until  the  anlages  of 
the  crowns  are  well  formed.  The  process  of  calcification  follows  that  of  the  development  of 
the  tooth  in  general,  beginning  in  the  superficial  portion  of  the  crown  and  gradually  spreading 
toward  the  root.  Calcification  in  the  deciduous  teeth  begins  during  the  fifth  foetal  month,  and 
at  birth  the  crowns  are  nearly  completed  (fig.  885).  Of  the  permanent  set  of  teeth,  only  the 
first  molar  has  begun  to  calcify  at  birth  (fig.  886).  Calcification  of  the  other  permanent  teeth 
begins  during  the  second  year;  excepting  the  second  molar,  which  begins  during  the  fifth,  and 
the  third  molar,  which  begins  about  the  eighth  year.     There  are,  however,  great  variations 


THE  TEETH  1127 

in  the  time  at  which  the  caloificatioa  of  the  various  teeth  begins.  As  a  rule,  the  calcification 
of  the  roots  is  not  completed  at  the  apices  until  some  time  after  the  crowns  are  exposed  in 
eruption. 

Eruption  of  the  teeth. — -Oa  account  of  pressure  due  to  growth  and  expansion  at  the  root  of 
the  tooth  (and  probably  other  obscure  factors),  the  crowns  are  pushed  toward  the  surface.  The 
overlying  portion  of  the  tooth-sac,  together  with  corresponding  portions  of  the  temporary 
alveolar  bone,  are  absorbed,  and  the  crown  is  "cut,"  i.  e.,  breaks  through  the  surface  of  the  gum 
in  eruption.  In  the  case  of  the  permanent  teeth,  this  is  normally  preceded  by  a  shedding  of 
the  deciduous  teeth.  The  latter  have  been  loosened  by  the  absorption  of  their  roots,  which  is 
perhaps  due  largely  to  the  activity  of  certain  odontoclasts  (like  the  osteoclasts  of  bone)  which 
are  found  in  the  region  of  absorption. 

Time  and  order  of  eruption. — The  time  of  the  eruption  of  the  various  teeth  is  subject  to 
great  variation,  so  that  no  two  investigators  agree  upon  it.  Aside  from  the  wisdom  teeth,  the 
time  of  eruption  is  most  variable  in  the  canines  and  premolars,  and  least  variable  in  the  first 
permanent  molars  (Rose).  The  eruption  averages  four  and  one-half  months  earliei  in  the 
male,  and  is  also  earlier  in  well-to-do  and  city  children  (Rose).  The  order  in  which  the  teeth 
appear  is  less  variable.  The  average  time  at  which  the  various  deciduous  and  permanent 
teeth  appear  is  indicated  approximately  in  the  following  table. 

A.  Deciduous  Teeth 

Months  after  Birth 
(Average) 

Lower  central  incisors 7  (6-8) 

Upper  central  incisors 8-9 

Upper  lateral  incisors 9-10 

Lower  lateral  incisors 12-14 

First  molars 14 

Canines 18 

Second  molars 22-24 

B.  Permanent  Teeth 

The  average  time  at  which  the  teeth  in  the  lower  jaw  undergo  eruption  is  shown  in  the  table 
below.     The  corresponding  teeth  in  the  upper  jaw  appear  a  little  later : — 

Years 

First  molars 6-7 

Central  incisors 7 

Lateral  incisors 8 

First  premolars 9-10 

Second  premolars 9-10 

Canines 11 

Second  molars 12 

Third  molars  (wisdom  teeth) 17-25 

Variations. — The  great  variabihty  of  the  teeth  has  already  been  emphasized,  and  numerous 
variations  described  in  connection  with  the  various  individual  teeth  and  their  development. 
In  number,  the  teeth  may  be  reduced,  due  to  absence  (oftenest  of  the  third  molar)  or  incom- 
plete development  with  failure  of  eruption.  An  increase  in  the  normal  number  is  less  common' 
It  may  be  only  apparent,  due  to  the  retention  of  a  deciduous  tooth.  There  may  rarely,  however, 
be  a  true  extra  third  incisor  or  premolar,  or  a  fourth  molar.  Aberrant  teeth  may  occur  either  on 
the  labial  or  palatal  side  of  the  dental  arch.  A  third  dentition  appears  rarely  in  old  age.  In 
form,  there  is  much  greater  variation  as  before  mentioned.  All  intermediate  forms  between 
rudimentary  and  fully  developed  teeth  may  occur.  Fusion  between  neighbouring  teeth  is 
sometimes  found,  and  deformities  in  the  dental  arches  necessarily  accompany  palatal  defects 
involving  the  alveolar  arches. 

Comparative. — As  the  oral  mucosa  represents  an  invagination  of  the  integument,  so  the 
teeth  are  morphologically  equivalent  to  dermal  papilliE.  The  close  relationship  between  the 
teeth  and  the  dermal  appendages  is  clearly  shown  among  many  of  the  lower  vertebrates,  but 
most  clearly  in  the  Selachians  (which  include  sharks  and  allied  forms).  In  fig.  887,  which 
illustrates  a  sagittal  section  through  the  lower  jaw  of  a  young  dogfish,  it  is  clearly  evident  that 
the  external  placoid  scales  or  'dermal  teeth'  are  continuous  with  the  equivalent  oral  teeth 
at  the  oral  margin  of  the  jaw.  Both  the  dermal  teeth  and  the  oral  teeth  are  composed  of  dentine 
which  presents  an  enlarged  base  and  a  somewhat  conical  apex.  The  base  is  embedded  in  the 
fibrous  lamina  propria  (often  in  bony  plates)  while  the  apex  projects  through  the  epithehum 
and  is  covered  with  a  thin  cuticular  layer  the  "enamel  membrane."  True  enamel  is  usually 
rudimentary  or  absent  in  the  primitive  teeth  of  lower  vertebrates,  and  represents  a  secondary 
acquisition.  The  dentine  is  in  aU  cases  derived  from  the  connective  tissue,  and  the  enamel 
from  the  epithelium . 

The  process  of  development  of  the  primitive  oral  teeth  is  also  iDustrated  in  fig.  887.  Just 
within  the  oral  margin  there  is  a  shelf-like  downgrowth  of  the  ectodermal  epithelium,  forming 
a  primitive  germinal  ridge.  Along  this  ridge  may  be  seen  the  anlages  of  several  rows  of  teeth 
in  various  stages  of  development.  As  fast  as  the  mature  teeth  at  the  oral  margin  are  worn  off, 
new  teeth  pass  up  from  below  to  replace  them.  Thus  the  primitive  form  of  dentition  is  polij- 
■phyodont,  with  many  sets  of  teeth  developed  successively  thi'oughout  hfe.  As  we  pass  up  the 
vertebrate  scale  there  is  a  tendency  to  a  reduction  in  the  number  of  sets,  although  there  is  a 


1128 


DIGESTIVE  SYSTEM 


wide  variation  among  the  various  forms.  In  most  mammals,  as  in  man,  the  number  of  sets  of 
teeth  has  been  reduced  to  two,  or  diphyodojit  dentition,  with  only  traces  of  an  earher  (pre- 
lacteal)  and  also  a  later  (post-permanent)  set.  In  some  mammals  (monotremes,  oetacea) 
the  dentition  has  been  reduced  to  a  single  set,  jnonophyodont,  while  in  birds  all  except  rudi- 
mentary traces  of  dentition  have  been  lost. 

pAs  may  be  further  observed  in  fig.  887,  the  primitive  teeth  are  of  a  recurved  conical  form, 
and  serve  primarily  for  grasping  and  holding  the  food.  The  speciahzation  of  the  teeth  for 
purposes  of  mastication  is  in  general  a  secondary  acquisition  amongst  higher  vertebrates. 

It  is  also  noteworthy  that  the  primitive  teeth,  as  found  among  nearly  all  forms  below  the 
mammals,  are  practicaOy  alike  in  form,  i.  e.,  homodont.  Among  mammals,  however,  there  is 
a  marked  speciahzation  of  the  teeth,  or  helerodont  dentition.  The  mammalian  teeth  are  usually 
differentiated  into  four  distinct  classes,  incisors,  canines,  premolars  and  molars,  similar  to  those 
found  in  man. 

The  typical  or  complete  mammalian  dentition,  however,  contains  a  larger  number  of  teeth 
than  found  in  man,  and  is  represented  by  the  formula 

•  31  43 

1—,  c -,  pm-,  m-=44 
3'      1'  ^     4'      3     **• 

Thus  it  is  evident  that  there  has  been  a  reduction  in  the  incisors  and  premolars  in  the  human 
species,  and  there  has  been  considerable  discussion  of  the  question  as  to  which  teeth  of  the 


Fig.  887. — Section  through  Lower  Jaw  op  Dog-fish,  Showing  the  Development  of  the 
Oral  Teeth,  and  the  Transition  to  Dermal  Teeth.     M,  mandible.     (After  Gegenbaur.) 

Intermediary  forms — *-  - 


^,'  Developing  tooth 


Skin  of  lower  jaw 


Dermal  tooth  ^ 


„ Dental  epithelial  ridge 


...  Epithelium  of  oral  mucosa 


«.  Anlage  of  tooth 


primitive  series  have  been  lost.  This  reduction  in  the  number  of  teeth  is  probably  correlated 
with  the  general  reduction  in  the  jaws,  which  are  relatively  much  larger  and  stronger  in  the 
savage  races  and  lower  animals.  The  third  molar,  or  wisdom  tooth,  is  probably  now  on  the 
road  to  extinction,  due  to  a  continuation  of  the  same  evolutionary  process. 

Another  interesting  problem,  concerning  which  there  has  been  much  speculation,  is  the 
origin  of  the  multicuspidate  mammalian  molar.  It  has  clearly  been  derived  from  the  primitive 
conical  type  of  the  homodont  dentition,  but  as  to  the  method  of  evolution  there  is  a  difference 
of  opinion.  According  to  one  view  (the  'concrescence'  theory),  the  molar  has  been  derived 
by  a  process  of  fusion,  each  cusp  representing  a  primitive  conical  tooth.  Another  view  (the 
'differentiation'  theory)  is  that  the  molar  represents  a  single  primitive  tooth,  upon  the  crown 
of  which  the  various  cusps  have  been  differentiated.  According  to  a  third  view,  which  is  a 
compromise,  the  tritubercular  (tricuspid)  form  of  tooth,  which  is  that  found  in  the  earliest 
fossil  mammals,  was  derived  by  a  process  of  concrescence  of  three  primitive  teeth,  while  from 
this  tricuspid  form  the  multicuspidate  molar  has  been  derived  by  a  process  of  differentiation. 

THE  PHARYNX 

The  pharynx  is  a  vertical,  tubular  passage,  flattened  antero-posteriorly,  and 
extending  from  the  base  of  the  cranium  above  to  the  beginning  of  the  oesophagus 
below.  Posteriorly,  it  is  in  contact  with  the  bodies  of  the  upper  six  cervical  verte- 
brae.   Laterally,  it  is  in  relation  with  the  internal  and  common  carotid  arteries, 


THE  PHARYNX 


1129 


the  internal  jugular  vein,  the  sympathetic  and  the  last  four  cranial  nerves. 
Anteriorly,  it  communicates  above  with  the  nasal  cavity,  beneath  this  with  the 
oral  cavity,  and  below  with  the  laryngeal  cavity.  The  pharynx  is  correspondingly 
divided  into  three  parts:  the  nasal  -pharynx  [pars  nasalis],  which  is  exclusively 
respiratory  in  function;  the  oral  pharynx  [pars  oralis],  which  is  both  respiratory 
and  alimentary;  and  the  laryngeal  pharynx  [pars  laryngea],  which  is  almost 
entirely  alimentary. 

Size   and  form. — The  average  length  of  the  pharynx  is  about  12  cm.  (5 
inches).     It  is  widest  at  the  nasal  pharynx,  with  a  constriction  (isthmus)  connect- 

(Sobotta-McMurrioh.) 


1. — The  Interior  op  the  Pharynx,  Viewed  prom  Behind. 
Pharyngeal  tonsil    geptum 


Torus  tubarius 

L 


Pharyngeal  recess 


Glossopalatine  arch 


Styloid  process 


Styloid  muscles 
Salpingopharyngeal 
fold 
Parotid  gland 

Pharyngopalatine  arch 


Pharyngo  epiglottic  fold 
Aryepiglottic  fold 


Aditus  laryngis 

Cuneate  tubercle  "^S 

Corniculate  tubercle  ^\ 


Fold  of  laryngeal  l 


Thyreoid  gland 


ing  it  with  the  widened  oral  pharynx,  and  is  again  somewhat  narrowed  at  the  junc- 
tion of  oral  and  laryngeal  pharynx  (fig.  888) .  It  is  narrowest  at  the  point  where 
it  joins  the  oesophagus  below.  In  sagittal  section  (fig.'  848),  it  is  evident  that  the 
anterior  and  posterior  walls  are  closely  approximated  in  the  laryngeal  pharynx, 
and  have  only  a  small  space  between  them  in  the  oral  pharynx.  The  nasal 
pharynx,  however,  has  a  considerable  antero-posterior  depth,  and  by  its  bony 
walls  is  always  kept  open  for  respiratory  purposes. 

Structure. — The  pharynx  approaches  the  typical  structure  of  the  alimentary  canal,  yet 
differs  from  it  in  several  important  respects.  The  lining  mucosa  is  continuous  with  that  of  the 
various  cavities  which  open  into  the  pharynx.  Above,  it  is  closely  adherent  to  the  base  of  the 
cranium,  where  it  is  thick  and  dark  in  colour.  It  becomes  thinner  where  it  approaches  the  open- 
ings of  the  auditory  tubes  and  choana;;  and  below  it  is  paler  and  thrown  into  longitudinal  folds. 
The  epithehum  of  the  greater  part  of  the  nasal  pharynx  (from  the  orifice  of  the  auditory  tube 
upward)  is  stratified  cihated  columnar,  while  that  of  the  remainder  of  the  pharynx  is  stratified 
squamous. 


1130  DIGESTIVE  SYSTEM 

External  to  the  mucosa,  there  is  a  characteristic  fibrous  membrane,  the  pharyngeal  apo- 
neurosis [fascia  pharyngobasilaris],  which  is  well  marked  above,  but  below  it  loses  its  density 
and  gradually  disappears  as  a  definite  structure.  Above,  it  is  attached  to  the  basilar  portion 
of  the  occipital  bone  in  front  of  the  pharyngeal  tubercle.  Its  attachment  may  be  traced  to 
the  apex  of  the  petrous  portion  of  the  temporal  bone,  and  thence  to  the  auditory  (Eustachian) 
tube  and  medial  lamina  of  the  pterygoid  process.  It  descends  along  the  pterygo-mandibular 
ligament  to  the  posterior  end  of  the  mylohyoid  ridge  of  the  lower  jaw,  and  passes  thence  along 
the  side  of  the  tongue  to  the  stylohyoid  ligament,  the  hyoid  bone,  and  thyreoid  cartilage. 

External  to  the  pharyngeal  aponeurosis  is  a  thick  muscular  layer,  made  up  of  various  cross- 
striated  muscles,  as  will  be  described  later.  Outside  of  the  muscular  layer  is  a  thin  fibrous 
tunica  adventitia,  connected  with  the  adjacent  prevertebral  fascia  by  a  loose,  areolar  tissue. 
This  loose  tissue  allows  movement  of  the  pharynx,  and  also  favours  the  spreading  of  post- 
pharyngeal abscesses. 

The  nasal  pharynx  (figs.  848,  888)  belongs,  strictly  speaking,  with  the  nasal 
fossa  as  a  part  of  the  respiratory  rather  than  the  digestive  system.  Its  anterior 
wall  is  occupied  by  the  two  choance  (posterior  nares),  with  the  nasal  septum 
between  them.  The  floor  is  formed  by  the  upper  surface  of  the  soft  palate  and  in 
a  direct  posterior  continuation  of  the  floor  of  the  nasal  fossae.  Posteriorly,  how- 
ever, the  floor  presents  a  more  or  less  narrowed  opening,  the  pharyngeal  isthmus, 
which  communicates  with  the  oral  pharynx  below.  The  isthmus  is  formed  ante- 
riorly by  the  uvula,  laterally  by  the  posterior  (pharyngo-palatine)  arches.  These 
slope  backward  and  downward  to  the  posterior  wall  of  the  pharynx,  which  forms 
the  posterior  boundary  of  the  isthmus.  The  floor  and  isthmus  change  their  form 
and  position  greatly  during  the  action  of  the  palatal  muscles,  as  will  be  mentioned 
later. 

The  lateral  wall  of  the  nasal  pharynx  presents  above  and  behind,  correspond- 
ing to  its  widest  point,  a  wide,  slit-like  lateral  extension,  the  pharyngeal  recess 
[recessus  pharyngeus]  or  fossa  of  Rosenmueller  (fig.  888).  Below  and  in  front  of 
this  recess,  the  greater  part  of  the  lateral  wall  is  occupied  by  the  aperture  of  the 
auditory  (Eustachian)  tube  [ostium  pharyngeum  tubse].  This  is  a  somewhat 
triangular,  funnel-shaped  opening,  with  an  inconspicuous  anterior  lip  [labium 
anterius],  a  more  distinct  posterior  lip  [labium  posterius],  which  presents  poste- 
riorly a  rounded  prominence  (due  to  the  projecting  cartilage  of  the  auditory  tube), 
called  the  torus  tubarius.  The  prominence  of  the  posterior  lip  facilitates  the  intro- 
duction of  the  Eustachian  catheter,  in  connection  with  which  the  location  of  the 
aperture  in  the  mid-lateral  wall  just  above  the  level  of  the  floor  of  the  nasal  fossa 
should  be  carefully  noted.  On  the  lower  aspect  of  the  triangular  apertm-e  is  a 
slightly  rounded  fold,  the  levator  cushion,  which  is  a  prominence  caused  by  the 
levator  palati  muscle.  A  fold  of  mucosa  descending  from  the  posterior  lip  of  the 
aperture  to  the  lateral  pharyngeal  wall  is  the  plica  salpingo-pharyngea  (due  to 
the  m.  salpingo-pharyngeus).  An  inconspicuous  plica  salpingo-palatina  descends 
from  the  anterior  lip  to  the  soft  palate. 

The  posterior  wall  (fig.  848)  of  the  nasal  pharynx  slopes  from  below  upward 
and  forward,  passing  (at  the  level  of  the  anterior  arch  of  the  atlas)  into  the  roof 
[fornix  pharyngis].  The  roof  is  attached  chiefly  to  the  basi-occipital  and  basi- 
sphenoid  bones,  extending  laterally  to  the  carotid  canal  of  the  pyramid,  and  ante- 
riorly to  the  base  of  the  nasal  septum.  In  the  posterior  wall  of  the  nasal  pharynx 
there  is  found  in  the  mucosa  a  variable  and  inconstant  blind  sac,  the  pharyngeal 
bursa. 

The  mucosa  of  the  roof,  and  to  a  certain  extent  also  of  the  posterior  wall, 
especially  in  children,  is  thrown  into  numerous  folds,  which  may  be  irregular  or 
radiate  from  the  neighbourhood  of  the  bursa.  There  is  often  a  median  longitu- 
dinal groove  (or  sometimes  ridge)  at  the  posterior  (inferior)  end  of  which  is  the 
bursa.  These  folds  of  the  mucosa  contain  much  lymphoid  tissue,  both  diffuse 
and  in  the  form  of  numerous  characteristic  lymphoid  nodules,  with  crypt-like 
invaginations  of  the  surface  epithelium.  This  area  constitutes  the  pharyngeal 
tonsil  [tonsilla  pharyngea]  (fig.  890),  which  is  well-developed  in  children  (often 
abnormally  enlarged,  producing  'adenoids'),  but  usually,  though  not  always, 
atrophied  in  the  adult.  According  to  Symington,  the  involution  of  the  pharyn- 
geal tonsils  begins  at  6  or  7  years,  and  is  usually  completed  at  10  years.  In  the 
region  of  the  pharyngeal  tonsil  and  elsewhere,  the  mucosa  presents  numerous 
small  racemose  mucous  glands,  especially  thick  in  the  palatal  floor  of  the  nasal 
pharynx  and  similar  to  those  of  the  oral  cavity. 

The  oral  pharynx  (figs.  848,  864,  888)  is  continuous  above  through  the  pharyn- 


THE  PHARYNX 


1131 


geal  isthmus  with  the  nasal  pharynx  and  below  with  the  laryngeal  pharynx.  Its 
posterior  wall  presents  no  special  features.  The  anterior  wall  is  deficient  above, 
where  there  is  a  communication  with  the  mouth  cavity  through  the  isthmus 

Fig.  889. — Vertical  Section  op  a  Human  Palatine  Tonsil,  a,  Stratified  epithelium; 
b,  basement  membrane;  c,  tunica  propria;  d,  trabeculse;  e,  diffuse  lymphoid  tissue;  /,  nodules; 
h,  capsule;  i,  mucous  glands;  k,  striated  muscle;  I,  blood  vessel;  q,  pits.     (From  Radasch.) 


faucium.  The  faucial  isthmus  is  bounded  above  by  the  uvula,  laterally  by  the 
anterior  (glosso-palatine)  arches,  and  below  by  the  dorsum  of  the  tongue  in  the 
region  of  the  sulcus  terminalis.     Below  the  faucial  isthmus,  the  anterior  wall  of 


Fig.  890. — Portion  op  a  Cobonal  Section  through  the  Pharyngeal  Region,  Showing 
Waldbyer's  Tonsillar  Ring.     (Palatine  tonsils  hypertrophied. ) 


Temporal  lobe 


External  pterygoid  - 
Tensor  veli  palatinJ 

Levator  veli  palatini  ^  ^.^  ^    yr  - 

Internal     {[  V-i-Z^ 

maxillary  art      ,^  f  "^^t^^^^ 
Neck.of  mandible 

Internal  pterygoid 
Superior  constrictor 
and  capsule  of  tonsil 

Styloglossus 

Stylohyoid 

Lymph  node 
Hypoglossal  nerve 

Lingual  artery   -^ 


Epiglottis 
Cavity  of  larynx 


V_^3 — J — ^ 


Palatine  tonsil 

(hypertrophied) 
Angle  of  mandible 
External  maxillary 
j~      artery 
\      Lingual  tonsil 
"*  M.  hyoglossus 

—  Vallecula 

->  .  Platysma 


the  oral  pharynx  is  formed  by  the  root  of  the  tongue,  which  has  been  described 
previously.  The  lateral  wall  of  the  oral  pharynx  on  each  side  presents  the  pala- 
tine tonsil,  enclosed  in  a  somewhat  triangular  tonsillar  fossa   [sinus  tonsillaris] 


1132  DIGESTIVE  SYSTEM 

limited  anteriorly  and  posteriorly  by  the  anterior  and  posterior  palatine  arches, 
and  below  by  the  root  of  the  tongue. 

The  palatine  arches  are  folds  of  the  mucosa  formed  at  the  sides  of  the  free 
posterior  border  of  the  soft  palate,  as  already  mentioned  in  connection  with  that 
organ.  The  anterior  arch  (or  pillar)  [arcus  glossopalatinus]  extends  from  the 
soft  palate  downward  and  forward  to  the  lateral  margin  of  the  tongue,  just  behind 
the  papillfe  foliatse.  It  is  a  fold  of  mucosa  due  to  the  underlying  glosso-palatine 
muscle,  and  inconspicuous  except  when  this  muscle  is  in  action,  or  when  the 
tongue  is  depressed.  It  forms  the  lateral  boundary  of  the  faucial  isthmus.  The 
posterior  arch  [arcus  pharyngopalatinus]  is  a  more  prominent  fold  which  extends 
from  the  soft  palate  in  the  region  of  the  uvula  downward  and  backward  to  join 
the  postero-lateral  aspect  of  the  pharyngeal  wall.  It  forms  the  lateral  boundary  of 
the  pharyngeal  isthmus,  and  encloses  the  pharyngo-palatine  muscle,  whose  actior 
will  be  explained  later. 

The  palatine  tonsil  [tonsilla  palatina]  (figs.  864,  889,  890,  891)  is  a  flattened 
ovoidal  body,  usually  visible  through  the  mouth  cavity  and  faucial  isthmus,  and 
located  on  each  side  of  the  oral  pharynx.  The  tonsil  is  extremely  variable  in 
size,  but  in  the  young  adult  averages  about  20  mm.  in  height,  15  mm.  in  width 
(antero-posteriorly)  and  12  mm.  in  thickness. 

The  lateral  or  attached  surface  of  the  tonsil  is  covered  by  a  thin  but  firm 
fibrous  capsule,  which  is  continuous  with  the  pharyngeal  aponeurosis,  and  in 
contact  with  the  middle  constrictor  muscle  of  the  pharynx  (fig.  864).  Just  out- 
side the  constrictor,  the  tonsil  is  in  relation  with  the  ascending  pharyngeal  and 
ascending  palatine  arteries,  but  is  separated  by  a  considerable  space  from  the 
external  and  internal  carotids.  Rarely,  however,  the  lingual  or  external  maxil- 
lary may  extend  up  higher  than  usual,  so  as  to  be  in  close  relation  with  the  lower 
aspect  of  the  tonsil.  Further  lateralward,  the  palatine  tonsil  is  in  relation  with 
the  internal  pterygoid  muscle,  and  on  the  surface  corresponds  to  a  point  somewhat 
above  and  in  front  of  the  angle  of  the  mandible.  The  posterior  border  of  the 
tonsil  is  thicker  than  the  anterior,  and  forms  a  somewhat  flattened  surface  in  con- 
tact with  the  pharyngo-palatine  muscle  (fig.  891). 

The  medial  or  free  surface  of  the  tonsil  is  covered  with  mucosa  and  presents  a 
variable  number  (12  to  30)  small  pits  which  are  the  openings  into  the  tubular  or 
slit-like  crypts  [fossulse  tonsillares].  These  crypts  are  somewhat  more  numerous 
in  the  upper  part  of  the  tonsil,  and  are  sometimes  branched  or  irregular  in  form. 
Usually  they  end  blindly  in  the  substance  of  the  tonsil,  surrounded  by  lymphoid 
tissue  in  characteristic  nodular  masses  (fig.  889).  The  lymphocytes  normally 
migrate  through  the  stratified  squamous  epithelium  lining  the  crypts  (occasion- 
ally eroding  passages  of  considerable  size),  and  escape  into  the  pharyngeal  and 
mouth  cavities,  where  they  form  the  so-called  salivary  corpuscles.  Around  the 
periphery  of  the  palatine  tonsil,  within  the  capsule,  are  many  mucous  glands  (fig. 
889),  similar  to  those  described  in  connection  with  the  lingual  and  pharyngeal 
tonsils.  The  ducts  of  the  mucous  glands  sometimes  enter  the  crypts,  but  usually 
pass  to  the  surface  chiefly  around  the  margins  of  the  palatine  tonsil. 

Tonsillar  plicae  and  fossae. — Connected  with  the  tonsil  are  certain  important 
folds  and  fossse.  The  plica  triangularis  (fig.  891)  is  a  fold  of  variable  extent  and 
appearance,  placed  just  behind  the  anterior  arch,  wider  below  and  narrower 
above.  According  to  Fetterolf,  it  is  a  prolongation  of  the  tonsillar  capsule,  cov- 
ered with  mucosa.  It  may  be  adherent  to  the  anterior  part  of  the  medial  surface 
of  the  tonsil,  or  it  may  be  free,  in  which  case  it  covers  a  recess  called  the  anterior 
tonsillar  fossa.  Occasionally  there  is  a  similar  plica  and  fossa  at  the  posterior 
border  of  the  tonsil.  Above  the  tonsil  there  is  similarly  a  supratonsillar  fossa 
[fossa  supratonsillaris],  which  is  also  inconstant  and  exceedingly  variable  in  size 
and  shape.     Killian  found  a  supratonsillar  fossa  or  canal  in  41  of  105  cadavers. 

Tonsillar  vessels. — The  arteries  to  the  tonsil  include  the  anterior  tonsillar  (from  the  dorsalis 
linguEe);  the  inferior  tonsillar  (from  the  external  maxillary);  the  -posterior  tonsillar  (from  the 
ascending  pharyngeal)  and  the  superior  tonsillar  (from  the  descending  palatine).  These 
pierce  the  capsule  and  supply  the  gland.  The  veins  form  a  plexus  around  the  capsule  and  empty 
into  the  lingual  vein  and  the  pharyngeal  plexus.  The  lymphatic  relations  of  the  palatine 
tonsil  are  important.  Afferent  vessels  are  received  from  adjacent  areas  of  the  mucosa  in  the 
pharynx,  mouth  and  lower  part  of  the  nasal  cavity  (v.  Lenart).  These  are  connected  with  an 
extensive  lymphatic  plexus  around  the  lymph  follicles  within  the  tonsil.  Efferent  lymphatic 
vessels  pass  chiefly  to  the  upper  deep  cervical  lymphatic  nodes.  One  of  these,  located  just 
behind  the  angle  of  the  mandible,  is  so  closely  connected  with  the  tonsil,  and  so  constantly 


THE  PALATINE  TONSIL 


1133 


enlarged  following  tonsillar  infection,  that  it  has  been  called  the  tonsillar  lymph  gland  (Wood). 
There  are  also  communications  with  the  submaxillary  and  superficial  cervical  lymphatic  nodes. 
The  tonsillar  lymphatic  vessels  connect  also  with  those  of  the  lingual  tonsil  in  the  root  of  the 
tongue. 

The  tonsillar  ring. — The  two  palatine  tonsils,  together  with  the  lingual  tonsil  below  and  the 
pharyngeal  tonsil  above,  form  an  almost  complete  ring  of  characteristic  tonsillar  tissue  sur- 
rounding the  pharynx  and  known  as  Waldeyer's  'tonsillar  ring'  (fig.  890).  It  is  a  highly 
specialized  development  of  the  diffuse  lymphoid  tissue  which  is  found  everywhere  in  the  mucosa 
of  the  alimentary  and  respiratory  tracts.  It  may  be  noted  that  the  'tonsillar  ring'  corre- 
sponds to  the  anterior  limit  of  the  embryonic  foregut,  hence  the  epithehum  is  of  endodermic 
origin.  The  arrangement  of  the  tonsils,  together  with  their  lymphatic  connections,  has  sug- 
gested the  widely  accepted  view  that  they  are  to  be  considered  as  protective  mechanisms 
whose  function  is  to  intercept  infectious  material  which  has  entered  the  mouth  or  nasal  cavities. 
This  theory  is  supported  by  the  experiments  of  v.  Lenart,  who  found  that  substances  injected 
into  the  nasal  mucosa  are  intercepted  partly  in  the  tonsils,  and  partly  in  the  cervical  lymph 

Fig.  891. — The  Left  Palatine  Tonsil,  Showing  the  Arterial  Supply. 
1,  Mesial  aspect.  2,  Postero-lateral  aspect.  E,  lateral  surface.  B,  posterior  surface. 
T,  medial  surface.  G,  groove  for  pharyngo-palatine  muscle.  C,  capsule.  PT,  plica  triangu- 
laris. Arteries:  AA,  anterior  tonsillar  (from  dorsal  lingual);  PA,  posterior  tonsillar  (from 
ascending  pharyngeal) ;  SA,  superior  tonsillar  (from  descending  palatine) ;  lA,  inferior  tonsil- 
lar (anterior  from  dorsal  lingual;  posterior  from  tonsillar  branch  of  internal  maxillary).  (Fet- 
terolf :  Amer.  J.  Med.  Sc,  1912.) 


nodes.  Oppel,  however,  opposes  this  view,  holding  that  the  function  of  the  tonsils,  as  of  lym- 
phoid tissue  elsewhere,  is  merely  the  production  of  lymphocytes. 

Development  of  the  tonsil. — According  to  Hammar,  the  palatine  fossa  (sinus  tonsillaris) 
is  a  derivative  of  the  second  inner  branchial  groove  and  is  visible  in  the  human  embryo  of  17 
mm.  There  appears  in  the  floor  of  the  fossa  a  tubercle  (tuberculum  tonsillare)  which  later 
becomes  atrophied,  excepting  a  portion  which  is  converted  into  the  plica  triangularis.  The 
primitive  tonsil  becomes  divided  into  two  lobes,  upper  and  lower,  by  a  fold  (plica  intratonsillaris) 
which  later  usually  disappears.  In  the  fojtus  of  about  100  mm.  (crown-rump  length)  the 
epithelium  of  the  floor  grows  into  the  subjacent  mesenchyme  in  the  form  of  somewhat  irregular 
solid  sprouts  of  epithelium.  These  later  become  hollow  and  form  the  crypts.  Ai'ound  them, 
in  about  the  sixth  fa-tal  month,  the  lymphoid  tissue  begins  to  accumulate,  at  first  diffusely, 
later  forming  characteristic  follicles.  The  lymphocytes  arise  in  situ  from  the  connective- 
tissue  cells  (Hammar)  or  by  immigration  from  the  blood-vessels  (Stohr).  Retterer's  claim 
that  the  tonsillar  lymphoid  cells  are  derived  from  the  epithelial  cells  has  not  been  confirmed. 

The  later  fcetal  development  of  the  tonsil  is  subject  to  considerable  individual  variation. 
The  supratonsillar  fossa  is  a  remnant  of  the  upper  part  of  the  primitive  sinus  tonsillaris,  which 
may  be  transformed  into  a  canal  by  growth  of  adenoid  tissue  around  it.  It  is  inconstant  and 
quite  variable  in  size  and  extent.  A  portion  of  the  sinus  may  likewise  persist  anteriorly  (an- 
terior tonsillar  fossa)  between  the  tonsil  and  the  plica  triangularis,  but  this  portion  is  usually 
obliterated  by  fusion  of  the  plica  with  the  tonsil.  The  occasional  retro-tonsillar  fold  and  fossa 
are  said  to  arise  secondarily  (Hammar). 

Variations  in  the  tonsil. — The  palatine  tonsil,  like  the  lingual  and  pharyngeal  tonsils,  is  an 
exceedingly  variable  organ.  Many  of  the  variations  are  developmental  in  origin,  as  above 
indicated,  and  ai-e  therefore  congenital.  Furthermore,  the  tonsils,  hke  all  lymphoid  structures, 
are  subject  to  marked  age  variations.  Though  fairly  well  formed  at  birth,  they  are  yet  some- 
what undeveloped.     They  rapidly  increase  in  relative  size  and  complexity,  however,  being 


1134 


DIGESTIVE  SYSTEM 


best  developed  in  childhood.  After  the  age  of  puberty,  they  usually  undergo  certain  retro- 
gressive changes,  become  smaller  in  size,  and  in  old  age  become  almost  entirely  atrophied  and 
lost.  They  are  also  markedly  subject  to  inflammatory  hypertrophy,  especially  in  children. 
Variations  in  the  relations  of  the  blood-vessels  were  mentioned  above. 

The  laryngeal  pharynx  (fig.  848)  is  the  lower  portion  leading  from  the  oral 
pharynx  above  into  the  oesophagus  below  (at  the  level  of  the  lower  border  of  the 
cricoid  cartilage,  usually  opposite  the  sixth  cervical  centrum).     It  is  wide  above 


Fig.  892. — The  Muscles  of  the  Soft  Palate  and  the  Palatal  Arches  as  Seen  fbom  in 
Front.     (After  Toldt,  "Atlas  of  Human  Anatomy,"  Rebman,  London  and  New  York.) 

Incisive  papilla 


Upper  bp 


Second  molar 


Maxillary  tuberosity 


Hamulus  of  internal 
pterygoid  plate 


Transverse  palatine  ridges 
^  Angle  of  mouth 

-  X^^^v.         So^*  parts  of  cheek  (cut) 

Oral  vestibule 
Palatine  glands 


Palatine  foramen  with 

anterior  palatine  nerve 
-Posterior  nasal  spine 
'^^j^m/'^    Buccinator 

X— .  Pterygo-mandibular  raphe 
Levator  veli  palatini 

Constrictor  pharyngis 
superior 

Pharyngo-palatinus 
Glosso-palatinus 
Bucco-pharyngeal  fascia 
Palatine  tonsil 
''^W'W-^^   Stylo-glossus 

fa  ~^^^  Isthmus  of  the  fauces 


Dorsum  of  tongue 


and  narrow  below  (fig.  888) .  Its  posterior  walls  are  continuous  with  those  of  the 
oral  pharynx  and  in  relation  with  the  vertebral  centra.  Its  lateral  walls  are 
attached  to  the  hyoid  bone  and  the  posterior  part  of  the  medial  surface  of  the 
thyreoid  cartilage.  Anteriorly  it  is  in  relation  with  the  larynx.  In  the  median 
line  above  is  the  epiglottis,  below  which  is  the  superior  aperture  of  the  larynx. 
Still  lower  is  the  posterior  wall  of  the  larynx,  containing  the  arytenoid  and  lamina 
of  the  cricoid  cartilage.  Laterally,  are  the  pharyngo-epiglottic  folds,  and  below 
these  on  each  side  a  deep,  elongated  fossa,  the  recessus  piriformis,  bounded 
laterally  by  the  medial  surface  of  the  thyreoid  cartilage.  The  mucosa  of  the  laryn- 
geal pharynx  is  similar  to  that  of  the  oral  pharynx,  and  contains  racemose  mucous 
glands,  which  are  especially  numerous  in  its  anterior  wall. 

Muscles  of  the  pharynx  and  soft  palate. — These  muscles  (figs.  892,  893,  894), 
which  are  here  grouped  together  for  convenience  of  description,  are  chiefly 
sphincter-hke  constrictors  in  function.  They  include  the  constrictors  of  the 
faucial  isthmus  (mm.  glossopalatini),  the  constrictors  of  the  pharyngeal  isthmus 


MUSCLES  OF  PHARYNX  AND  PALATE 


1135 


(mm.  pharyngopalatini) ,  the  three  pharyngeal  constrictors,  and  also  the  levator 
and  the  tensor  veil  palatini,  the  m.  uvulae  and  the  stylo-pharyngeus.  The  stylo- 
pharyngeus  and  pharyngo-palatine  muscles  form  an  incomplete  longitudinal  layer 
within  the  more  circularly  arranged  constrictors  of  the  pharynx. 


Fig.  893. — View  of  Muscles  of  Soft  Palate,  as  Seen  feom  Behind,  Within  the  Pharynx. 
(Modified  from  Bourgery.) 


PharyngeaT  "''       \ll 

aponeurosis  — ^ 


M.  uvulae 
Hamular  process 


Pharyngo-palatinus 


Constrictor  pharyngis 
superior 


Crico-arytaenoideus 
posterior 


Thyreoid  cartilage 
Cncoid  cartilage 


The  muscles  are  arranged  in  layers  either  behind  or  in  front  of  the  aponeurosis, 
and  in  a  horizontal  section  of  the  soft  palate  the  following  layers  are  met  with  from 
behind  forward:  (1)  The  mucous  membrane  on  the  pharyngeal  surface;  (2)  the 
posterior  layer  of  the  pharyngo-palatinus  (palato-pharyngeus) ;  (3)  the  m.  uvulae; 
(4)  the  levator  veli  palatini;  (5)  the  anterior  layer  of  the  pharyngo-palatinus;  (6) 
the  palatal  aponeurosis  with  the  tensor  veli  palatini;  (7)  the  glosso-palatinus 
palato-glossus) ;  and  (8)  the  mucous  membrane  on  the  oral  aspect. 

The  glosso-palatinus  (palato-glossus)  is  a  cylindrical  muscle  extending  between  the  soft 
palate  and  the  lateral  border  of  the  tongue.  Origin. — From  the  oral  surface  of  the  palatal  apo- 
neurosis. Insertion. — (1)  The  superficial  layer  of  muscles  which  covers  the  side  and  adjacent 
part  of  the  under  surface  of  the  tongue;  (2)  the  transversus  linguae.  Structure. — At  its  origin 
the  muscle  forms  a  thin  sheet,  but  the  fibres,  passing  lateralward,  quiclcly  concentrate  to  form 
a  cylindrical  bundle,  which  passes  downward  beneath  the  mucous  membrane  of  the  pharynx 


1136 


DIGESTIVE  SYSTEM 


and  in  front  of  the  tonsil,  forming  the  glosso-palatine  arch  of  the  fauces.  It  reaches  the  side 
of  the  tongue  at  the  junction  of  its  middle  and  posterior  thirds,  and  some  of  its  fibres  continue 
forward  to  join  with  those  of  the  stylo-glossus  and  hyo-glossus,  while  the  majority  pass  medially 
to  become  continuous  with  the  transversus  linguse.  Nerve-supply. — From  the  pharjmgeal 
branches  (plexus)  of  the  vagus.  Action. — (1)  To  draw  the  sides  of  the  soft  palate  downward; 
(2)  to  draw  the  sides  of  the  tongue  upward  and  backward.  The  combination  of  these  actions 
tends  to  constrict  the  faucial  isthmus.  (The  origin  and  insertion  of  the  glosso-palatinus  as 
given  above  are  often  described  as  reversed.) 

The  pharyngo-palatinus  (palato-pharyngeus) — named  from  its  attachments — is  a  thin 
sheet.  Origin. — (1)  From  the  aponeurosis  of  the  soft  palate  by  two  heads  which  are  separated 
by  the  insertion  of  the  levator  veli  palatini;  (2)  by  one  or  two  narrow  bundles  from  the  lower 
part  of  the  cartilage  of  the  auditory  (Eustachian)  tube  (salpingo-pharyngeus) .  Insertion. — (1) 
By  a  narrow  fasciculus  into  the  posterior  border  of  the  thyreoid  cartilage  near  the  base  of  the 
superior  cornu ;  (2)  by  a  broad  expansion  into  the  fibrous  layer  of  the  pharynx  at  its  lower  part . 


Fto.  894. — Thk  Musrir=i  op  the  Pharynx,  Lateral  View. 


Medial  lamina  of 

pterygoid  process 

Constrictor  pharyngis 

superior 

Pterygo-mandibular  raphe 

Stylo-hyoid  ligament 


Stylo-pharyngeus 


Crico-thyreoideus 
Cricoid  cartilage 


Structure. — The  upper  head  of  the  muscle  consists  of  scattered  fibres  which  blend  with  the  oppo- 
site muscle  across  the  middle  line;  the  lower  head  is  thicker,  and  foUows  the  curve  of  the  posterior 
border  of  the  palate.  The  two  heads  with  the  fasciculus  from  the  auditory  (Eustachian)  tube 
form  a  compact  muscular  band  in  the  posterior  palatine  arch;  the  fibres  mingle  with  those  of 
the  stylo-pharyngeus,  at  the  lower  border  of  the  superior  constrictor,  and  then  expand  upon  the 
lower  part  of  the  pharynx.  Nerve-supply. — From  the  pharyngeal  branch  (plexus)  of  the  vagus. 
Action. — (1)  Approximates  the  posterior  arches  of  the  fauces;  (2)  depresses  the  soft  palate; 
(3)  elevates  the  pharynx  and  larynx.  (The  origin  and  insertion  above  given  are  often  described 
as  reversed.) 

The  inferior  constrictor  is  thick  and  strong.  It  arises  from  the  thyreoid  cartilage  im- 
mediately behind  the  oblique  hne  and  superior  tubercle  (thyreo-pharyngeus),  and  from  a 
tendinous  arch  extending  between  the  inferior  tubercle  of  the  thyreoid  and  the  cricoid  cartilage 
and  also  from  the  lateral  surface  of  the  cricoid  cartilage  (cricopharyngeus)  (fig.  894).  The 
fibres  spread  backward  and  medialward,  the  lowest  horizontally,  whilst  those  above  ascend 
more  and  more  obUquely,  and  are  inserted  into  the  fibrous  raph6  of  the  pharynx.     Some  of 


MUSCLES  OF  PHARYNX  AND  PALATE  1137 

the  lowest  fibres  are  continuous  with  the  muscular  fibres  of  the  oesophagus,  and  the  upper  over- 
lap the  middle  constrictor  (fig.  894).  The  nerve-supply  of  all  three  constrictors  is  from  the 
pharyngeal  nerve. 

Near  the  upper  border  the  superior  laryngeal  nerve  and  artery  pierce  the  thyreo-hyoid 
membrane  to  reach  the  larynx.  The  inferior  laryngeal  nerve  ascends  beneath  the  lower  border 
immediately  behind  the  crico-thyreoid  articulation. 

The  middle  constrictor  is  a  fan-shaped  muscle  which  arises  from  the  lesser  cornu  of  the 
hyoid  bone  and  from  the  stylo-hyoid  Ugament  (chondro-pharyngeus),  and  from  the  whole 
length  of  the  greater  cornu  (cerato-pharyngeus).  The  diverging  fibres  are  inserted  into  the 
median  raphe,  and  blend  with  those  of  the  opposite  side.  The  lower  fibres  of  the  muscle  descend, 
beneath  the  inferior  constrictor,  to  the  lower  part  of  the  pharynx;  the  upper  overlap  the  superior 
constrictor,  and  reach  the  basilar  process  of  the  occipital  bone,  whilst  the  middle  fibres  run 
transversely  (fig.  894). 

The  glosso-pharyngeal  nerve  passes  downward  above  its  upper  border,  the  stylo-pharyngeus 
passes  between  it  and  the  superior  constrictor,  and  near  its  origin  it  is  overlapped  by  the  hyo- 
glossus  and  crossed  by  the  lingual  artery. 

The  superior  constrictor  is  quadrilateral  in  shape,  pale,  and  thin  (fig.  894).  It  arises 
from  the  lower  third  of  the  hinder  edge  of  the  median  lamina  of  the  pterygoid  process  and  its 
hamular  process  (pterygo-pharyngeus),  from  the  pterygo-mandibular  ligament  (buoco-pharyn- 
geus),  from  the  posterior  fifth  of  the  mylo-hyoid  ridge  of  the  mandible  (mylo-pharyngeus), 
and  from  the  side  of  the  root  of  the  tongue  (glosso-pharyngeus) .  The  fibres  pass  backward  to 
be  inserted  into  the  median  raphd,  the  highest  reaching  the  pharyngeal  tubercle.  The  Eu- 
stachian tube  and  the  levator  veli  palatini  are  placed  above  the  superior  arched  border,  and  the 
space  {sinus  of  Morgagni)  between  this  and  the  basilar  process,  devoid  of  muscular  fibres,  is 
strengthened  by  the  pharjmgeal  aponeurosis,  this  portion  of  it  being  semilunar  in  shape. 

The  stylo-pharyngeus  arises  from  the  base  of  the  styloid  process  internally.  It  passes  down- 
ward and  medialward  to  reach  the  pharynx  between  the  superior  and  middle  constrictors. 
Its  fibres  spread  out  as  it  descends  beneath  the  mucous  membrane.  At  the  lower  border  of 
the  superior  constrictor  some  of  its  fibres  join  fibres  of  the  pharyngo-palatinus  (palato-pharyn- 
geus),  and  are  inserted  mto  the  posterior  border  of  the  thyreoid  cartilage  (fig.  894);  the  rest 
blend  with  the  constrictors.  The  nerve-supply  of  the  stylo-pharyngeus  is  from  the  glosso-phar- 
yngeal nerve. 

The  levator  veli  palatini — named  from  its  action  on  the  velum  of  the  soft  palate — is  some- 
what rounded  in  its  upper,  but  flattened  in  its  lower,  half.  Origin. — (1)  The  inferior  surface 
of  the  petrous  portion  of  the  temporal,  anterior  to  the  orifice  of  the  carotid  canal;  (2)  the  lower 
margin  of  the  cartilage  of  the  auditory  (Eustachian)  tube.  Insertion. — The  aponeurosis  of 
the  soft  palate;  the  terminal  fibres  of  the  muscles  of  each  side  meet  in  the  middle  line  in  front 
of  the  m.  uvulae.  Structure. — Its  origin  is  by  a  short  tendon;  the  muscle  then  becomes  fleshy, 
and  continues  so  to  its  insertion.  Nerve-supply. — From  a  pharyngeal  branch  (plexus)  of  the 
vagus.  Action. — (1)  To  raise  up  the  velum  of  the  soft  palate,  and  bring  it  in  contact  with  the 
posterior  wall  of  the  pharynx;  (2)  to  narrow  the  pharyngeal  opening  and  to  widen  the  isthmus  of 
the  auditory  (Eustachian)  tube.  (According  to  Cleland,  it  closes  the  pharyngeal  opening  of  this 
tube.) 

The  tensor  veli  palatini — named  from  its  action  on  the  velum  of  the  soft  palate — is  a  thin, 
flat,  and  narrow  sheet.  Origin. — (1)  The  scaphoid  fossa  of  the  sphenoid;  (2)  the  angular  spine 
of  the  sphenoid;  (3)  the  lateral  side  of  the  membranous  and  cartilaginous  wall  of  the  auditory 
(Eustachian)  tube.  Insertion. — (1)  Into  the  transverse  ridge  on  the  under  surface  of  the  hori- 
zontal plate  of  the  palate  bone;  (2)  the  aponeurosis  of  the  soft  palate. 

Structure. — Its  belly  as  it  descends  between  the  pterygoideus  internus  and  the  internal 
pterygoid  plate  is  muscular.  On  approaching  the  hamular  process  it  becomes  tendinous,  and 
continues  so  to  its  insertion.  A  bursa  is  interposed  between  the  hamular  process  and  the  tendon. 
The  belly  of  the  muscle  is  at  nearly  a  right  angle  with  its  tendon.  Nerve-supply. — From  the 
mandibular  division  of  the  trigeminus  through  the  tensor  palati  branch  of  the  otic  ganglion. 
Actions. — (1)  Tightens  the  soft  palate;  (2)  opens  the  auditory  (Eustachian)  tube  during  deglu- 
tition. 

The  m.  uvulse. — so  named  by  reason  of  its  position  in  the  uvula.  Origin. — (1)  From  the 
aponeurosis  of  the  soft  palate  and  tendinous  expansions  of  the  two  tensores  veli  palatini.  In- 
sertion.— Into  the  uvula.  Structure. — The  muscle  consists  of  two  narrow  parallel  strips  lying 
on  each  side  of  the  middle  Une  of  the  palate.  Nerve-supply. — From  the  pharyngeal  branch  of 
the  vagus.     Action. — To  draw  up  the  uvula. 

Origin  of  the  muscles. — According  to  W.  H.  Lewis,  the  tensor  palati  is  a  derivative  of  the 
mandibular  arch  (probably  split  off  from  the  pterygoid  mass) ;  the  levator  palati  and  m.  uvulae 
come  with  the  facial  musculature  from  the  hyoid  arch;  the  glosso-palatine,  stylo-pharyngeus 
and  pharyngeal  constrictors  probably  from  the  third  visceral  arch,  in  a  pre-muscle  mass  visible 
in  a  9  mm.  embryo.  The  adult  innervation  of  the  pharyngeal  muscles  does  not  agree  entirely 
with  this,  however.  The  pharyngeal  muscles  (as  above  stated)  are  innervated  chiefly  from  the 
vagus,  whereas  if  derived  from  the  third  arch  their  innervation  from  the  glosso-pharyngeus 
would  be  expected. 

Process  of  swallowing. — In  the  act  of  swallowing,  practically  aU  of  the  muscles  of  the  mouth, 
tongue,  palate  and  pharynx  are  involved.  By  compression  of  the  hps  and  cheeks,  together 
with  elevation  of  the  tongue,  the  food  is  forced  backward  through  the  faucial  isthmus  into  the 
oral  pharynx.  Constriction  of  the  faucial  isthmus  by  the  glosso-palatine  muscles  assists  in 
preventing  a  return  to  the  mouth.  By  the  action  of  the  levator  palati,  tensor  palati,  and 
pharyngo-palatine  muscles,  the  soft  palate  is  retracted  and  tightened,  with  constriction  of  the 
pharyngeal  isthmus,  so  as  to  prevent  the  passage  of  the  food  upward  into  the  nasal  pharynx. 
The  pharynx  is  dra-nm  upward  by  the  stylo-pharyngeus,  and  the  pressure  produced  by  the 
pharyngeal  constrictors  (the  contraction  beginning  above  and  extending  downward)  forces 
the  food  dowTiward  through  the  laryngeal  pharynx  and  into  the  oesophagus.  Passage  of  the 
food  into  the  larynx  is  prevented  by  constriction  of  the  superior  aperture  of  the  larynx. 


1138  DIGESTIVE  SYSTEM 

Vessels  and  nerves. — The  vessels  of  the  tonsil  and  the  motor  nerves  of  the  various  muscles 
have  aheady  been  mentioned.  In  general,  the  arteries  to  the  pharynx  are  derived  chiefly  from 
the  ascending  pharyngeal,  the  ascending  palatine  branch  of  the  external  maxillary,  and  the 
descending  palatine  and  pterygo-palatine  branches  of  the  internal  maxillary.  The  veins 
form  a  venous  plexus  between  the  pharyngeal  constrictors  and  the  pharyngeal  aponeurosis, 
and  also  an  external  plexus,  communicating  with  the  pterygoid  plexus  above  and  with  the 
posterior  facial  or  internal  jugular  vein  below.  The  lymphatic  vessels  pass  chiefly  to  the 
deep  cervical  nodes,  those  from  the  upper  portion  (including  the  pharyngeal  tonsil)  ending 
partly  in  the  retro-pharyngeal  glands.  The  nerves  of  the  pharynx,  both  motor  and  sensory,  are 
derived  chiefly  from  the  glosso-pharyngeal  and  vagus,  by  way  of  the  pharyngeal  plexus. 

The  development  of  the  pharynx. — The  pharynx  is  developed  chiefly  (if  not  entirely)  from 
the  anterior  end  of  the  archenteron.  In  this  portion  of  the  archenteron,  with  the  develop- 
ment of  the  branchial  arches,  there  are  formed  on  each  side  four  entodermal  pouches  or  grooves 
(with  a  rudimentary  fifth),  the  branchial  clefts  (see  p.  17).  With  further  development  the  first 
pair  of  branchial  clefts  form  the  tympanic  cavities  and  the  auditory  or  Eustachian  tubes;  the 
lower  portion  of  each  second  branchial  cleft  persists  as  a  fossa  in  which  a  palatine  tonsil  is 
developed ;  the  remains  of  the  third  and  fourth  pairs  are  found  on  each  side  in  the  vaUecula 
and  piriform  sinus  of  the  larynx.  The  origin  of  the  pharyngeal  tonsil  may  be  observed  in  the 
■third  month  of  foetal  life  in  the  form  of  small  folds  of  mucous  membrane  which,  during  the 
sixth  month,  become  infiltrated  with  diffuse  adenoid  tissue,  lymph-nodules  differentiating  in  this 
toward  the  end  of  foetal  life.  The  pharyngeal  bursa,  which  is  not  a  constant  structure  (Kilr 
lian),  may  be  observed  as  a  small  diverticulum  of  the  pharyngeal  waU,  closely  connected  with 
the  anterior  extremity  of  the  notochord.  The  diverticulum  develops  independently  of  Rathke's 
pouch  (which  gives  rise  to  the  anterior  portion  of  the  hypophysis),  and  is  also  apparently  distinct 
from  Seesel's  pocket. 

The  entire  pharynx,  like  the  associated  facial  region,  is  relatively  small  and  undeveloped 
in  the  foetus  and  newborn,  but  develops  rapidly  during  infancy.  The  development  of  the 
muscles  and  of  the  palatine  tonsils  has  already  been  considered. 

Variations. — Variations  in  the  palatine  and  pharyngeal  tonsils  and  in  the  pharyngeal  bursa 
have  already  been  mentioned.  Remnants  of  the  visceral  clefts  may  persist  as  aberrant  diver- 
-ticula  or  as  'branchial  fistulae'  connected  with  the  pharynx.  Many  additional  muscles  have  been 
described,  chiefly  longitudinal  muscles  arising  from  the  base  of  the  cranium  either  by  spUt- 
•ting  of  those  normally  present,  or  as  separate  slips.  A  detailed  description  of  these  may  be 
found  in  Poirier-Charpy's  work.  Abnormally  extensive  fusion  of  the  posterior  arches  of  the 
■palate  with  the  walls  of  the  pharynx  may  produce  a  congenital  stenosis  of  the  pharyngeal  isthmusi 

Comparative. — The  pharynx  is  not  distinctly  separated  from  the  mouth  cavity  in  the 
.lower  vertebrates.  It  is  the  region  containing  the  branchial  or  visceral  clefts  and  is  thus  both 
.respiratory  and  aUmentary  in  function.  The  nasal  pharynx,  including  the  apertures  of  the 
•auditory  tubes,  becomes  distinct  along  with  the  nasal  cavity  when  the  palate  is  formed  (from 
the  reptiles  upward).  In  the  air-breathing  vertebrates,  the  laryngeal  aperture  appears  in 
the  ventral  wall  of  the  pharynx  just  anterior  to  the  beginning  of  the  cesophagus.  Of  the  tonsils, 
the  pharyngeal  are  the  most  primitive,  being  present  in  the  roof  of  the  pharynx  in  amphibia, 
weU-developed  in  reptiles,  birds,  and  mammals  (Killian).  The  palatine  tonsils,  on  the  other 
hand,  are  characteristic  of  mammals,  being  rarely  absent,  however  (e.  g.,  rat,  guinea  pig). 
From  the  embryological  point  of  view,  Hammar  has  classified  the  palatine  ^tonsils  in  the 
various  mammals  under  (1)  the  primary  type  (including  rabbit,  cat,  and  dog),  in  which  the 
tonsil  is  formed  from  the  embryonic  tonsillar  tubercle  (described  above  under  development 
of  tonsil);  and  (2)  the  secondary  type  (including  pig,  ox,  sheep  and  man),  in  which  the  tonsilt 
lar  tubercle  disappears  and  the  tonsil  is  developed  from  the  wall  of  the  surrounding  tonsillar 
sinus.  Typical  epithelial  crypts  (highly  branched  in  the  ox)  are  found  only  in  the  secondary 
•type.  The  tonsil  may  form  a  single  (lymphoid)  lobe  (cat,  pig,  rabbit)  or  may  develop  typi- 
cally two  lobes  (ox,  sheep,  man),  separated  by  the  intratonsillar  fold.  There  are  great  varia- 
tions among  difl'erent  species  as  to  relative  size,  number  and  character  of  folds,  crypts, 
«tc.  The  intimate  relation  of  the  epithelium  with  the  underlying  lymphoid  tissue  is  charac- 
teristic and  constant. 

THE  (ESOPHAGUS 

The  cesophagus  (figs.  895,  896)  is  that  portion  of  the  alimentary  tract  which! 
extends  between  the  pharynx  and  the  stomach.  It  is  more  constricted  than  the 
rest  of  the  canal,  being  narrowest  at  its  commencement  opposite  the  lower 
border  of  the  cricoid  cartilage.  It  is  again  somewhat  contracted  behind  the  left 
bronchus,  and  at  its  passage  through  the  diaphragm,  which  is  opposite  the  tenth 
or  eleventh  thoracic  vertebra.  It  has  an  average  length  of  25  cm.  (varying  from 
20  to  35  cm.).  The  average  distance  from  the  rima  oris  to  the  beginning  of  the 
cesophagus  is  about  15  cm.  In  its  course  downward  the  oesophagus  follows  the 
curves  of  the  vertebral  column  until  it  finally  passes  forward  in  front  of,  and 
slightly  to  the  left  of,  the  aorta  to  gain  the  oesophageal  opening  in  the  diaphragm. 
In  addition  to  these  curves  it  presents  two  lateral  curvatures,  one  convex  toward 
the  left  side  at  the  root  of  the  neck  and  in  the  upper  part  of  the  thorax,  and  the 
other  concave  toward  the  left  in  the  lower  part  of  the  thorax  where  it  leaves  the 
vertebral  column.  It  lies  in  the  middle  line  at  its  commencement  (usually 
opposite  the  sixth  cervical  vertebra),  and  again,  at  a  lower  level,  opposite  the  fifth 
thoracic  vertebra. 


THE  (ESOPHAGUS 


1139 


After  death  the  oesophagus  is  somewhat  flattened  from  before  backward,  but 
it  is  more  rounded  during  life.     It  is  closed  except  during  the  passage  of  food,  etc. 

The  -peristaltic  movements  of  the  oesophagus  can  readily  be  observed  by  means  of  the  Roent- 
gen-rays. Solids  often  lodge  a  short  time  at  the  level  of  the  arch  of  the  aorta,  but  pass  quickly 
through  the  cardiac  orifice.  A  swallow  of  liquid,  on  the  other  hand,  is  usually  detained  at  the 
lower  end  of  the  oesophagus  (probably  by  sphincteric  action  of  the  cardia)  for  about  seven 
seconds  before  passing  into  the  stomach  (Pfahler). 

Fig.  895. — The  CEsophagus  and  Stomach.     (Testut.) 


Thyreoid  cartilage' 
Trachea 


Left  flexure  of  cesophagus 
Aortic  arch 


Right  flexure  of  oesophagus 


Descending  aorta 


Hiatus  (Esophagus 
(Esophagus,  pars  abd 

Lesser  curvature 

Pars  pylorica 

Descending  duodenum 

Inferior  duodenu: 


Fundus  of  stomach 


—  Greater  curvature 


Bifurcation  of  aorta 


The  oesophagus  is  divided  into  three  parts:  cervical,  thoracic  and  abdominal. 

Cervical  portion. — The  oesophagus  has  anteriorly  the  trachea,  the  posterior 
portion  of  the  left  lateral  lobe  of  the  thyreoid  gland,  and  the  left  recurrent  nerve, 
branches  of  the  inferior  thyreoid  artery,  and  the  carotid  sheath.  Posteriorly, 
it  rests  upon  the  vertebral  column,  the  longus  colli  muscles,  and  prevertebral 
fascia.  On  its  right  side  are  placed  the  right  carotid  and  right  recurrent  nerve; 
and  on  the  left  side  the  left  inferior  thyreoid  vessels,  left  carotid  artery,  left  sub- 
clavian, and  the  thoracic  duct.  The  recurrent  nerves  pass  upward  on  each  side 
to  gain  the  interval  between  the  trachea  and  oesophagus.  The  left  nerve,  as 
already  described,  lies  in  front  of  the  tube,  and  the  right  along  its  right  border. 

Thoracic  portion. — The  oesophagus  descends  in  the  thorax  through  the  super- 
ior and  the  posterior  mediastina.  In  the  superior  mediastinum  its  anterior  rela- 
tions are  the  trachea,  with  the  deep  cardiac  plexus  in  front  of  its  bifurcation,  the 
left  subclavian  and  carotid  arteries  crossing  its  left  border  obliquely,  the  left 
recurrent  nerve,  and  the  arch  of  the  aorta.  To  the  left  are  the  left  carotid- and 
subclavian  arteries,  the  end  of  the  arch  of  the  aorta,  and  the  left  pleural  sac.  To 
the  right  it  is  in  relation  with  the  right  vagus  nerve  and  the  right  pleural  sac. 
Posteriorly,  it  rests  upon  the  vertebral  column,  the  left  longus  colli  muscle,  and  it 
overlaps  the  thoracic  duct.  As  it  enters  the  posterior  mediastinum,  it  passes  behind 
the  left  bronchus  (or  bifurcation  of  the  trachea)  and  the  right  pulmonary  artery, 
resting  posteriorly  on  the  vertebral  column  and  thoracic  duct.     In  the  posterior 


1140 


DIGESTIVE  SYSTEM 


mediastinum  it  has  anteriorly  the  pericardium,  which  separates  it  from  the  left 
atrium  and  a  portion  of  the  diaphragm;  posteriorly  it  rests  upon  the  vertebral 
column,  accessory  hemiazygos  and  hemiazygos  veins,  the  right  aortic  intercostal 
arteries,  the  thoracic  duct,  and  the  descending  aorta.  To  the  right  is  the  right 
pleural  sac,  the  vena  azygos,  which  it  partly  overlaps,  and  below,  the  thoracic 
duct.  To  the  left  in  the  upper  part  is  the  descending  thoracic  aorta,  and, 
below,  the  left  pleural  sac  is  separated  from  it  by  a  little  loose  areolar  tissue. 
It  is  surrounded  by  the  oesophageal  ple.xus  formed  by  the  vagi  nerves,  and,  as 
they  emerge  from  the  lower  part  of  the  plexus,  the  left  vagus  lies  in  front  of  the 
oesophagus  and  the  right  vagus  behind. 

Fig.  896. — Cross-sections  Illustrating  the  Relations  of  the  CEsoPHAGtrs  at  Various 

Levels. 


Abdominal  portion. — The  oesophagus  lies  in  the  epigastric  region  of  the  abdo- 
men. Anteriorly  is  the  left  lobe  of  the  liver.  To  the  left  the  left  lobe  of  the  liver 
and  the  fundus  of  the  stomach.  To  the  right  the  caudate  (Spigelian)  lobe  of  the 
liver,  and  posteriorly  the  decussating  fibres  of  the  crura  of  the  diaphragm  and  the 
left  inferior  phrenic  artery.  The  abdominal  portion  is  very  short,  usuallj^  not 
more  than  2  cm.  (4/5  inch)  in  length  (see  figs.  896  D,  907). 

Structure. — The  thick-walled  oesophagus  presents  the  four  typical  tunics  of  the  alimentary 
canal  (fig.  897).  The  mucosa  and  the  muscularis  are  the  most  important,  the  submucosa  and 
the  external  adventitia  being  accessory  layers.  The  mucosa  (fig.  897)  is  thick  and  strong,  of 
reddish  colour  in  its  upper  portion  and  more  greyish  below.  It  presents  deep  longitudinal  folds 
to  allow  for  distention,  and  when  empty  the  lumen  is  therefore  stellate  in  cross  sections.  The 
hning  epithelium  is  stratified  squamous.  The  lamina  propria  presents  numerous  papiUse, 
and  is  limited  externally  by  a  muscularis  mucosm.  This  is  a  comparatively  thick  layer  (except 
at  the  upper  end)  and  is  composed  of  smooth  muscle  fibres,  longitudinally  arranged. 


THE  (ESOPHAGUS 


1141 


The  submucosa  (fig.  897)  is  a  thick,  very  loose  fibrous  layer  connecting  the  mucosa  with  the 
muscularis.  It  contains  numerous  vessels  and  nerves,  and  mucous  glands.  The  latter  [gl. 
oesophageae]  are  of  the  racemose  type,  Uke  those  of  the  mouth,  and  are  variable  in  number. 
There  are  also  two  sets  of  superficial  glands,  confined  to  the  lamina  propria,  and  resembling 
the  fundus  glands  of  the  stomach.  The  upper  set  (Rtidinger-Sohaffer  glands)  are  found  in  70 
per  cent,  of  oases,  occurring  above  the  level  of  the  fifth  tracheal  ring.  The  lower  set  (ojsophageal 
cardiac  glands)  form  a  ring  around  the  ccsophagus  just  above  the  cardiac  aperture.  A  few  small 
lymph  nodes  also  occur  in  the  submucosa,  often  around  the  ducts  of  the  mucous  glands. 

The  muscularis  (fig.  897)  is  a  thick  reddish  tunic  with  two  distinct  layers,  approximately 
equal  in  thickness.  The  fibres  of  the  inner  layer  are  arranged  circularly  and  are  continuous 
with  the  inferior  constrictor  above  and  with  the  obhque  fibres  of  the  stomach  below.  The 
fibres  of  the  outer  layer  are  longitudinal  and  commence  above  as  three  flattened  bands:  a  strong 
anterior  band  arising  from  the  ridge  on  the  back  of  the  cricoid  cartilage,  and  two  lateral  bands 
blending  with  the  fibres  of  the  stylo-pharyngeus  and  the  pharyngo-palatine.  These  all  unite 
into  a  continuous  layer  which  below  passes  into  the  muscular  coat  of  the  stomach.  The  upper 
third  or  fourth  of  the  oesophagus  contains  e.xclusively  cross-striated  muscle  fibres,  like  those 
of  the  pharynx.  Below  this,  there  is  a  zone  of  intermingled  smooth  and  cross-striated  fibres. 
The  lower  half  of  the  cesophagus  muscle  is  usually  composed  exclusively  of  smooth  fibres. 

Around  the  muscular  coat  is  a  thin  loose  fibrous  layer  [tunica  adventitial  connecting  the 
oesophagus  with  neighbouring  structures. 

Vessels  and  nerves. — The  arterial  supply  of  the  oesophagus  is  derived  from  the  inferior 
thyreoid,  the  oesophageal  branches  of  the  aorta,  the  intercostals,  the  inferior  phrenic  and  the 


Fig.  897.- 


-Transveesb  Section  of  the  Uppee  Third  of  the  Human  CEsophagus. 
(Lewis  and  Stohr.) 


Stratified  epithelium 


X5. 


Group  of  fat-cells'^^JI 


*^^\       Circular  muscles       |  Muscu- 
■^''''^       Longitudinal  muscles   J     laris 


Lymph  nodule 


'  "'^A  Tunica  adventitia 

Mucous  gland 


left  gastric  arteries.  Branches  pierce  the  wall  and  supply  the  various  coats.  The  veins 
accompany  the  arteries.  They  form  on  the  outer  surface  of  the  ccsophagus  a  venous  plexus 
opening  into  the  gastric  coronary  vein  below  and  the  azygos  and  thyreoid  veins  above  (thus 
estabUshing  a  communication  between  portal  and  systemic  veins).  There  are  also  numerous 
lymphatics  in  the  cesophagus  arising  chiefly  in  the  mucosa  and  draining  into  the  lower  deep 
cervical,  posterior  mediastinal  and  superior  gastric  nodes.  The  nerves  form  two  sympathetic 
plexuses,  the  submucous  and  the  myenteric,  from  which  the  walls  are  supphed  as  will  be  de- 
scribed later  for  the  stomach  and  intestine.  Branches  are  received  from  the  sympathetics,  and 
from  the  vagus,  including  the  recurrent  nerve. 

Development. — The  embryonic  oesophagus  is  at  first  relatively  very  short,  but  lengthens 
rapidly  in  connection  with  the  descent  of  the  stomach.  The  upper  end  is  still  high  in  children, 
corresponding  to  the  higher  vertebral  level  of  the  larynx.  The  lining  epithehal  cells  are  primi- 
tively cylindrical  in  form,  and  irregular  ciliated  areas  are  found  from  the  third  foetal  month  up 
to  birth  (F.  T.Lewis).  In  the  embryo  of  about  20  mm.,  there  is  a  proHferation  of  the  epithelium, 
associated  with  the  formation  of  vacuoles,  but  the  lumen  does  not  appear  to  be  normally  oc- 
cluded. The  primary  longitudinal  folds  of  the  mucosa  appear  early  (third  month)  and  at  the 
lower  end  seem  to  participate  in  the  rotation  of  the  stomach  (F.  P.  Johnson).  The  superficial 
oesophageal  glands  appear  about  the  fourth  month  (78  mm.),  the  deep  glands  at  240  mm. 
(Johnson).  Of  the  muscular  layers,  the  circular  appears  first  (at  about  10  mm.)  the  longi- 
tudinal shghtly  later  (17  mm.). 

Variations. — Usually  a  bundle  of  smooth  muscle  connects  the  oesophagus  with  the  left 
bronchus  [m.  broncho-oesophageus],  and  another  similarly  with  the  left  mediastinal  pleura  [m. 
pleuro-oesophageus].     More  rarely  there  are  similar  bands  connecting  with  the  trachea,  peri- 


1142 


DIGESTIVE  SYSTEM 


cardium,  etc.  Pouch-like  dilatations  of  the  oesophagus  may  occur,  especially  in  the  upper 
part  of  its  posterior  wall  or  at  the  lower  end.  According  to  C.  R.  Robinson,  the  latter  include 
(1)  ampulla  phrenica,  just  above  the  diaphragm,  and  (2)  antrum  cardiacum,  in  the  abdominal 
portion  of  the  oesophagus.  Diverticula  also  occur,  some  of  which  may  be  derived  from  the 
embryonic  vacuolization  of  the  epithehum  previously  described,  as  may  likewise  the  occasional 
congenital  atresia.  Abnormal  strictures  of  the  ccsophagus  may  occur,  oftenest  at  the  upper 
end,  at  the  left  bronchus,  and  near  the  lower  end.  Finally,  the  oesophagus  may  be  in  part 
either  double  or  absent,  and  may  communicate  by  fistula  with  the  trachea. 

Comparative. — The  length  of  the  oesophagus  varies  with  the  length  of  the  neck,  being 
shortest  in  fishes  and  amphibia  where  the  cesophagus  is  not  well  marked  off  from  the  stomach. 
The  lining  epithelium  is  stratified  squamous  in  mammals  and  birds,  but  often  ciliated  in  lower 
forms.  Mucous  glands  are  absent  in  fishes,  but  occur  typically  m  all  higher  forms.  They 
are  found  best  developed  toward  the  lower  end  of  the  cesophagus,  except  in  mammals,  where 
they  are  usually  more  numerous  at  the  upper  end.  Dilatations  may  occur  normally,  as  in 
the  crop  of  birds,  which  is  richly  supphed  with  glands.  The  musculature  of  the  oesophagus  is 
primitively  entirely  smooth  (Oppel)  as  found  in  amphibia,  reptiles  and  birds.  A  secondary 
replacement  by  cross-striated  muscle  is  found  to  a  variable  extent  in  the  majority  of  mammals 
and  fishes. 

THE  ABDOMEN 

The  abdomen  properly  consists  of  that  part  of  the  body  situated  between  the 
thorax  and  the  pelvis.  It  is  bounded  above  by  the  diaphragm;  below,  by  the  brim 
of  the  true  pelvis;  behind,  by  the  vertebral  column,  diaphragm,  quadratus  lum- 
borum  and  psoas  muscles,  and  by  the  posterior  portions  of  the  ilia.  At  the  sides 
it  is  limited  by  the  anterior  parts  of  the  ilia  and  the  hinder  segments  of  the  muscles 
which  compose  the  anterior  abdominal  wall,  viz.,  the  transversus,  internal  oblique. 


Fig.  898. — Diagram  of  the  Abdominal  Regions. 


Joint  between  meso-sternum 
and  ensiform  cartilage 

Tip  of  ensiform  cartilage 
Costal  border 


■TJpper  horizontal  plane 


Lower  horizontal  plane  A,  at 
"level  of  tubercles  of  iliac  crest 
Lower  horizontal  plane  B,  at 
'  level  of  anterior  iliac  spines 


Vertical  plane  A,  from  middle 
of  inguinal  ligament 


.Vertical  plane  B,  at  lateral  bor- 
der of  rectus  (semilunar  line) 
Summit  of  symphysis  pubis 


and  external  oblique.  In  front,  besides  these  muscles,  there  are  the  two  recti  and 
pyramidales  muscles.  External  to  the  peritoneum  the  abdomen  is  hned  by  a 
special  layer  of  fascia. 

It  is  customary  for  anatomists  and  physicians  to  divide,  for  purposes  of  descrip- 
tion, the  ventral  surface  of  the  abdomen,  by  means  of  two  horizontal  and  two  ver- 
tical lines,  into  nine  regions  (fig.  898).  A  complete  uniformity  in  the  use  of  the 
boundary  hues  marking  these  regional  subdivisions  has  not  as  yet  been  attained, 
although  the  variations  in  the  schemes  used  are  not  marked  as  concerns  the  main 
features.  It  should  be  borne  in  mind  that  it  is  necessary  that  the  boundary  lines 
used  should  be  converted  into  planes  carried  through  the  whole  depth  of  the  abdo- 
men and  defined  on  the  dorsal  as  well  as  the  ventral  surface,  and  that  the  relations 
defined  can  only  be  approximate,  owing  to  the  wide  range  of  the  physiological 
variation  in  the  position  of  the  abdominal  contents.  The  nine  regions  or  subdivi- 
sions may  be  outhned  as  follows: — The  upper  horizontal  line  or  plane  passes 
through  the  lowest  point  of  the  tenth  costal  cartilages,  about  5  cm.  above  the  um- 
bihcus,  and  dorsally  through  the  second  or  third  lumbar  vertebra.     The  lower 


THE  ABDOMEN 


1143 


horizontal  line  and  plane  passes  through  the  level  of  the  anterior  superior  iliac 
spines,  and  dorsally  about  2.5  cm.  below  the  promontory  of  the  sacrum.  Cun- 
ningham has  proposed  that  this  hne  be  passed  through  the  tuberculum  cristse, 
therefore  in  a  plane  slightly  higher  than  the  interspinous  plane.  For  the  longitu- 
dinal hnes  and  planes  it  has  been  customary  to  run  vertical  hnes  parallel  with  the 
mid-body  line  or  mid-sagittal  plane,  and  from  the  middle  of  the  inguinal  Ugaments. 
The  outer  border  of  each  rectus  would  seem,  however,  preferable  as  a  guide  for 
these  longitudinal  lines  and  planes,  which  may  be  easily  locahsed  above  by  the 
lateral  infra-costal  furrow  and  below  by  the  pubic  spines,  leaving  thus  on  each  side 
an  inguinal  region  which  includes  the  whole  of  the  inguinal  canal.  The  boundary 
lines  here  indicated  may  be  made  intelligible  by  a  reference  to  fig.  898.  The 
regions  thus  outhned  are  known  as  the  right  and  left  hypochondriac  and  epigas- 
tric regions,  found  above  the  upper  horizontal  line;  the  right  and  left  lumbar  and 
the  umbiUcal  regions,  found  between  the  two  horizontal  lines;  the  right  and  left 

Fig.  899. — The  Adbominal  Visceea  in  Situ,  after  Removal  of  the  Anterior  Abdom- 
inal Wall      (After  Sarazm  ) 


Transverse  colon 


Great  omentum 


Small  intestine 


Sigmoid  coloDJ 


inguinal  or  iliac  and  the  hypogastric  regions,  found  below  the  lower  horizontal  lines. 
(According  to  the  BNA,  the  lumbar  regions  are  termed  'lateral  abdominal'.) 

On  freely  laying  open  an  abdomen  from  the  front,  the  general  form  of  the  space 
is  seen  to  be  an  irregular  hexagon,  the  sides  of  which  are  formed  as  follows: — The 
upper  two  by  the  margins  of  the  costal  cartilages  with  the  ensiform  cartilage 
between;  the  two  lateral  sides  by  the  edges  of  the  lateral  boundary;  and  the  two 
lower  by  the  two  inguinal  ligaments  which  meet  at  the  pubes. 

In  this  irregular  hexagon  the  following  organs  can  be  observed  without  dis- 
arranging their  normal  position  (fig.  899).  Above,  on  the  right  side,  under  the 
costal  cartilages,  can  be  seen  the  liver,  which  extends  from  the  right  across  the 
median  line  to  a  point  below  the  left  costal  cartilages.  Below  the  liver,  and  lying 
to  the  left  side,  can  be  seen  the  anterior  surface  of  the  stomach;  from  the  lower 
border  of  the  stomach  the  omentum  extends  downward,  and  shining  through  it 
can  be  seen  the  middle  part  of  the  transverse  colon.     On  each  side  and  below  the 


1144 


DIGESTIVE  SYSTEM 


irregularly  folded  omentum  are  exposed  the  coils  of  the  small  intestine;  in  the  right 
iliac  fossa  a  part  of  the  csecum  appears;-  and  in  the  left  iliac  fossa  the  lower  (iliac) 
part  of  the  descending  colon  and  the  beginning  of  the  sigmoid  colon. 

To  the  left  of  the  stomach  and  under  cover  of  the  lower  ribs  of  the  left  side  the 
edge  of  the  spleen  may  possibly  be  observed;  and  just  below  the  edge  of  the  liver, 
and  about  the  level  of  the  tip  of  the  ninth  rib,  the  gall-bladder  may  be  seen.  The 
dome  of  the  urinary  bladder  may  be  noticed  just  behind  the  symphysis  pubis  and 
in  the  median  line.     The  disposition  of  the  viscera  in  the  foetus  is  shown  in  fig.  953. 

General  morphology — Before  taking  up  the  various  individual  organs  included  in  the 
abdominal  and  pelvic  portions  of  the  alimentary  canal,  a  brief  consideration  of  their  general 
morphology  is  desirable.     The  primitive  canal,  as  already  described  in  the  embryo  (in  the 


Fig.  900. — Digeammatic  Representation  of  an   Early  Stage  in  the  Development  of 
THE  Alimentary  Canal  and  the  PERiTONEtrM.     (After  Sobotta-McMurrich.) 
Lesser  curvature  CEsophagus 

Ventral  mesogastrium  "v  y^       Stomach 

(lesser  omentum)  \        _^.?^=:S^r-_  /         Greater  curvature 


Ventral  mesogas- 
trium (falciform 
lig.) 


Falciform  lig. 


Umbilical  vein 


Omphalo-mesenteric  duct 
Umbilical 


Dorsal  meso- 
/      gastrium 


Sup.  mesenteric  art. 


Left  colic  flexure 


Inf.  mesenteric  art. 


Distal  limb  of  intestinal  loop 


section  on  Morphogenesis),  and  as  found  in  the  lower  vertebrates  is  a  comparatively  straight, 
simple  tube  extending  ventral  to  the  body  axis  from  mouth  to  anus.  In  the  abdominal  region 
(and  primitively  throughout  the  whole  trunk),  the  canal  lies  within  the  body  cavity,  which  is 
lined  by  parietal  peritoneum.  The  visceral  peritoneum  is  reflected  from  the  mid-dorsal  line 
as  a  double  layer,  the  ■primiiive  dorsal  mesentery,  within  which  the  vessels  and  nerves  pass  to 
the  walls  of  the  canal.  Within  the  dorsal  mesentery  are  also  the  spleen  and  pancreas.  In 
the  anterior  (upper)  region  of  the  abdomen  there  is  also  a  similar  primitive  ventral  mesentery, 
which  contains  the  liver. 

The  relations  above  mentioned  are  indicated  diagrammatically  in  fig.  900,  which  represents 
a  comparatively  early  stage  in  the  development  of  the  intestinal  canal.  The  hver  is  already 
almost  completely  separated  from  the  diaphragm  (with  which  it  was  intimately  associated  in 
the  earher  septum  transversum).     The  ventral  mesentery  persists  in  the  form  of  (1)  the  gastro- 


THE  PERITONEUM  1145 

hepatic  or  lesser  omentum,  connecting  the  stomach  with  the  hver;  and  (2)  the  falciform  ligament, 
connecting  the  hver  with  the  ventral  body  wall. 

The  stomach  undergoes  a  rotation  on  its  longitudinal  axis  so  that  its  anterior  border 
(lesser  curvature)  is  turned  to  the  right,  and  its  posterior  border  (greater  curvature)  to  the  left 
(fig.  901).  Thus  the  posterior  mesentery  of  the  stomach  [mesogastrium],  bulges  to  the  left  and 
forward,  carrying  with  it  the  spleen  and  pancreas.  The  portion  of  the  mesentery  corresponding 
to  the  pancreas,  and  that  from  the  spleen  to  the  root  of  the  mesentery,  become  fused  with  the 
posterior  body  wall.  The  portion  of  the  primitive  mesogastrium  between  the  stomach  and 
spleen  persists  as  the  gastro-splenic  omentum  (or  ligament),  while  the  lower  portion  arches 
forward  and  downward  as  an  extensive  fold,  the  great  omentum.  The  portion  of  the  peritoneal 
cavity  left  behind  the  stomach  is  termed  the  bursa  omentalis,  or  lesser  sac,  the  remainder  of 
the  peritoneal  cavity  being  the  greater  sac. 

Along  with  the  pancreas,  the  duodenum  becomes  adherent  to  the  posterior  wall.  The 
remainder  of  the  intestine  forms  a  loop  (fig.  901),  the  upper  portion  of  which  forms  the  jejuno- 
ileum,  the  lower  portion  the  large  intestine.  The  intestinal  loop  rotates  counter-clockwise, 
so  that  the  csecum  and  ascending  colon  are  carried  over  to  the  right  side  of  the  body  cavity, 
where  (with  the  corresponding  portion  of  the  primitive  mesentery)  they  become  adherent  to 
the  posterior  body  wall  (fig.  901).  The  mesentery  of  the  transverse  colon  persists  (though 
fused  partly  with  the  great  omentum,  as  explained  later  under  development).  The  descending 
colon  becomes  displaced  to  the  left  side,  and  (together  with  its  mesentery)  becomes  adherent 
to  the  posterior  wall  of  the  abdomen.  The  mesentery  of  the  sigmoid  colon  usually  persists 
(in  part),  whUe  that  of  the  rectum  is  obhterated.     Through  these  modifications  of  the  peri- 

FiG.  901. — Diagrams  Illustrating  the  Development  of  the  Great  Omentum,  Mesentery, 
ETC.  A,  Earlier  Stage;  B,  Later  Stage. 
bid,  caecum;  dd,  small  intestine;  dg,  yolli-stallc;  di,  colon;  du,  duodenum;  gc,  greater 
curvature  of  the  stomach;  gg,  bile  duct;  gn,  mesogastrium;  k,  point  where  the  loops  of  the 
intestine  cross;  mo,  mesocolon;  md,  rectum;  mes,  mesentery;  wf,  vermiform  appendix. 
(McMurrich  after  Hertwig.) 


mS 


toneum,  and  through  unequal  growth  in  the  different  regions,  the  simple  primitive  intestinal 
tube  is  transformed  into  the  complicated  adult  canal.  The  details  of  the  transformation  will 
be  more  fuUy  discussed  later. 

Under  certain  rare  conditions,  the  developmental  process  is  modified  so  as  to  produce  a 
situs  inversus,  which  may  be  partial  or  complete,  involving  both  thoracic  and  abdominal 
viscera.  Under  these  circumstances,  the  viscera  are  transposed,  the  right  and  left  sides  being 
reversed. 

THE  PERITONEUM 

The  peritoneum,  as  has  been  shown,  is  a  serous  membrane  which  lines  the  cav- 
ity of  the  abdomen  from  the  diaphragm  to  the  pelvic  floor,  and  invests  or  covers  to 
a  varying  extent  the  viscera  which  that  cavity  contains.  Viewed  in  its  very  sim- 
plest condition,  it  may  be  regarded  as  a  closed  sac,  the  inner  surface  of  which  is 
smooth,  while  the  outer  surface  is  rough  and  is  attached  to  the  tissues  which  sur- 
round it. 

In  the  male  subject  the  peritoneum  forms  actually  a  closed  sac;  but  in  the 
female  its  wall  exhibits  two  minute  punctures,  which  correspond  to  the  openings 
of  the  Fallopian  tubes.  That  part  which  lines  the  walls  of  the  abdomen  is  termed 
the  parietal  peritoneum;  that  which  is  reflected  on  to  the  viscera  is  the  visceral 
peritoneum.     The  disposition  of  the  peritoneum  may  first  be  studied  by  noting 


1146 


DIGESTIVE  SYSTEM 


its  arrangement  as  made  evident  in  transverse  sections  of  the  abdomen  at  certain 
levels. 

The  first  section  to  be  described  shows  the  peritoneum  in  its  simplest  condition. 
This  is  a  transverse  section  through  the  body,  at  about  the  level  of  the  upper  sur- 
face of  the  fourth  lumbar  vertebra,  and  therefore  about  the  site  of  the  umbilicus 
(fig.  902). 

Starting  on  the  inner  surface  of  the  anterior  abdominal  wall,  the  peritoneum  is  seen  to 
cover  the  transversalis  fascia,  and  indirectly  the  anterior  abdominal  muscles;  then,  passing 

Fig.  902. — Diagram  of  Cross-section  of  the  Abdomen,  Showing  the  Peritoneal 
Belations  AT  THE  Level  OF  THE  Umbilicus.  A 0,  Aorta.  AS.  COL.,  Ascending  colon.  DES. 
COL.,  Descending  colon.  MES.,  Mesentery.  M.  COL.,  Descending  mesocolon.  »S/,  Small 
intestine.     V.C.,  Vena  cava  inferior. 


to  the  left,  it  lines  the  side  of  the  abdomen,  until  it  reaches  the  descending  colon.  This  it  covers, 
as  a  rule,  in  front  and  on  the  sides,  though  occasionally  it  forms  a  mesocolon.  Then  it  passes 
over  the  bodies  of  the  vertebrae  with  the  large  vessels  upon  them,  and  leaves  the  back  of  the  abdo- 
men to  run  forward  and  enclose  the  small  intestine,  returnuig  again  to  the  spine.  The  two 
layers  thus  form  the  mesentery,  having  between  them  a  middle  layer  [lamina  mesenterii  propria] 
containing  the  terminal  branches  of  the  superior  mesenteric  vessels.  It  then  passes  over  the 
right  half  of  the  posterior  abdominal  wall,  covering  the  ascending  colon  in  front  and  at  the 
sides  only  (unless  there  be  a  mesocolon),  and  then  passes  on  to  the  side  and  front  of  the  abdomen 
to  the  point  from  which  it  was  first  traced. 

Fig.  903. — Diagram  of  Cross-section  of  the  Abdomen,  Showing  the  Peritoneal  Rela- 
tions AT  THE  Level  of  the  Foramen  op  Winslow.     (P.  of  W.) 

Gastro-hepatic  omeatum 


In  tracing  the  peritoneum  in  a  section  of  the  body  opposite  the  stomach  (fig. 
903),  on  a  level  with  the  first  lumbar  vertebra,  its  course  becomes  more  com- 
plicated and  difficult  to  follow. 

In  the  section  already  given  the  peritoneum  as  a  simple  closed  sac  can  be  readily  con- 
ceived; but  at  the  level  now  exposed  the  serous  membrane  has  been  so  introverted  that  there 
appear  to  be  two  sacs,  one  leading  from  the  other,  and  known  respectively  as  the  greater  and 
the  lesser  sac  of  the  peritoneum.  They  communicate  through  the  epiploic  foramen  (of  Winslow) . 
The  le.sser  sac  [bursa  omentahs]  is  situated  behind  the  stomach,  so  that  on  first  opening  the 
abdomen  no  trace  of  it  is  to  be  seen.  It  extends  downward  [recessus  inferior]  between  the  layers 
of  the  great  omentum  (though  this  part  of  the  lesser  sac  is  largely  obliterated  by  adhesion 


THE  PERITONEUM 


1147 


in  the  adult).  It  extends  upward  [recessus  superior]  beiiind  tlie  caudate  lobe  of  the  liver. 
The  vestibule  [vestibulum  bur.sse  omentalis]  is  the  portion  which  lies  just  behind  the  lesser 
omentum,  and  communicates  with  the  greater  sac  through  the  epiploic  foramen.  In  general, 
the  lesser  sac  is  Umited  anteriorly  by  the  liver,  stomach,  and  omenta;  posteriorii/ by  the  posterior 
abdominal  wall,  and  below,  behind  the  great  omentum,  by  the  transverse  meso-colon.  Its 
disposition  on  vertical  section  is  shown  in  fig.  904. 

The  epiploic  foramen  (foramen  of  Winslow)  (figs.  903,  906)  is  situated  just 
below  the  liver;  it  looks  toward  the  right,  and  will  readily  admit  one  or  two  fin- 
gers. It  is  bounded  superiorly  by  the  caudate  lobe  of  the  liver;  inferiorly, 
by  the  duodenum  (pars  superior);  posteriorly,  by  the  vena  cava;  and  anteriorly 
by  the  right  margin  of  the  gastro-hepatic  or  lesser  omentum,  containing  the  struc- 
tures passing  to  and  from  the  hver.  Starting  at  the  epiploic  foramen,  the  lesser 
sac  will  be  found  to  turn  to  the  left. 


Fig. 


904. — DiAGEAM  OP  A  Sagittal  Section  of  the  Trunk,  Showing  the  Relations  op  the 
Peritoneum.     (Allen  Thompson.) 


Gastro-hepatic  omentum 
Stomach 

Transverse  colon 

Mesentery 

Smairintestine 

Uterus 


Epiploic  foramen 
Pancreas 

Duodenum 

■Transverse  meso-colon 
Aorta 


If,  now,  the  peritoneum  be  viewed  in  a  transverse  section  of  the  body  at  the  level  named, 
viz.,  through  the  first  lumbar  vertebra,  it  will  be  found  that  the  section  has  probably  passed 
through  the  epiploic  foramen  (fig.  903).  Starting  at  the  front  of  the  abdomen  and- going  to 
theright,  the  peritoneum  is  seen  to  line  the  anterior  abdominal  wall,  to  pass  over  the  side  of 
the  abdomen,  and  to  cover  the  front  of  the  right  kidney;  it  then  extends  on  to  the  vena  cava, 
when  it  becomes  a  part  of  the  lesser  sac;  then  along  the  back  of  the  lesser  sac,  over  the  aorta  and 
pancreas,  which  separate  it  from  the  vertebral  column ;  next  it  reaches  the  anterior  of  the  two 
internal  surfaces  of  the  spleen  internal  to  the  hilus.  Here  it  meets  with  another  layer  of  peri- 
toneum, and  helps  to  form  the  gastro-splenic  ligament  [lig.  gastrolienale].  Leaving  the  spleen,  it 
changes  its  direction  forward  and  to  the  right,  and  runs  to  the  stomach,  forming  the  posterior, 
layer  of  the  gastro-splenic  hgament;  it  covers  the  posterior  surface  of  the  stomach,  and  leaves 
its  mesial  border  (lesser  curvature)  to  form  the  posterior  layer  of  the  lesser  omentum,  and 
then  passes  upward  and  to  the  right  to  the  liver.  In  this  transverse  section  it  is  only  seen 
passing  on  the  right  margin  of  the  lesser  omentum,  where  it  forms  the  anterior  boundary  of  the 
epiploic  foramen.  Here  it  bends  sharply  around  the  omental  margin  enclosing  the  hepatic  vessels 
continuing  to  the  left  as  the  anterior  layer  of  the  lesser  omentum;  and  then  passing  to  the  left 
reaches  the  stomach,  which  it  covers  in  front.     It  then  forms  the  anterior  layer  of  the  gastro- 


1148  DIGESTIVE  SYSTEM 

splenic  ligament,  and  once  more  reaches  the  spleen.  It  passes  right  around  the  spleen  to 
the  back  of  the  hilus,  where  it  is  reflected  on  to  the  left  kidney  as  the  lieno-renal  hgament 
(fig.  903).  Hence  the  peritoneum  passes  along  the  side  and  front  of  the  abdomen  to  the  point 
from  which  it  started.  In  this  section  the  liver  is  so  divided  as  to  appear  separated  from  all 
connection  with  the  other  viscera  and  the  abdominal  wall,  and  to  be  surrounded  by  peritoneum. 

The  course  of  the  peritoneum  in  a  longitudinal  section  of  the  body  will  now 
be  considered  (fig.  904).  Starting  at  the  umbilicus  and  passing  downward,  the 
peritoneum  is  seen  to  line  the  anterior  abdominal  wall.  Before  reaching  the  pelvis 
it  covers  also  the  urachus,  the  deep  epigastric  arteries,  and  obliterated  hypogastric 
arteries,  which  form  ridges  beneath  it.  For  some  little  way  above  the  os  pubis 
the  peritoneum  is  loosely  connected  with  the  abdominal  wall,  a  circumstance 
which  is  made  use  of  in  supra-pubic  cystotomy.  Moreover,  as  the  distended  blad- 
der rises  from  the  pelvis  it  can  detach  the  serous  membrane  to  some  extent  from 
the  anterior  abdominal  wall.  In  extreme  distension  of  the  bladder  the  peritoneum 
may  be  lifted  up  for  some  5  cm.  vertically  above  the  symphysis.  On  reaching  the 
OS  pubis  it  is  reflected  on  to  the  upper  part  of  the  bladder,  covering  it  as  far  back 
as  the  base  of  the  trigone;  thence  it  is  reflected  on  to  the  rectum,  wihch  it  covers 
in  front  and  at  the  sides  on  its  upper  part,  rarely  forming  a  distinct  mesorectum. 
Between  the  bladder  and  rectum  it  forms  in  the  male  the  recto-vesical  pouch. 
The  mouth  of  this  pouch  is  bounded  on  either  side  by  a  crescentic  fold,  the  plica 
semilunaris.  In  the  female  the  peritoneum  is  reflected  from  the  bladder  on  to  the 
uterus,  which  it  covers;  it  then  extends  so  far  down  in  the  pelvis  as  to  pass  over 
the  upper  part  of  the  vagina  behind;  thence  it  extends  to  the  rectum.  The  peri- 
toneum which  invests  the  uterus  is  reflected  laterally  to  form  the  broad  ligaments. 
The  fold  between  the  vagina  and  rectum  forms  the  recto-vaginal  pouch,  or  pouch 
of  Douglas.     The  membrane  has  now  been  traced  back  to  the  spine. 

Following  it  upward,  the  sigmoid  colon  wifl  be  found  to  be  completely  covered 
by  peritoneum,  a  mesocolon  attaching  the  gut  to  the  abdominal  wall  (shown 
in  fig.  905).  A  little  higher  up  in  the  median  line  the  peritoneum  passes  forward, 
to  enclose  the  small  intestine,  and,  returning  to  the  spine,  forms  the  mesentery 
(fig.  904).  It  now  passes  over  the  third  part  of  the  duodenum  to  the  pancreas, 
from  which  point  it  again  passes  forward  to  form  the  lower  layer  of  the  transverse 
mesocolon.  It  invests  the  transverse  colon  below  and  partly  in  front,  and  then 
leaves  it  to  pass  downward  to  take  part  in  the  great  omentum.  Running  down- 
ward some  distance,  it  returns  and  forms  the  anterior  layer  of  the  omentum.  On 
reaching  the  stomach  it  goes  over  the  anterior  surface,  and  at  the  upper  border 
forms  the  anterior  layer  of  the  lesser  or  gastro-hepatic  omentum,  which  extends 
between  the  stomach  and  the  liver.  It  invests  the  inferior  surface  of  the  liver  in 
front  of  the  transverse  fissure,  and,  turning  over  its  anterior  border,  covers  the 
upper  surface.  At  the  posterior  limit  of  the  upper  surface  it  leaves  the  liver  and 
goes  to  the  diaphragm,  forming  the  superior  layer  of  the  coronary  ligament.  It 
covers  the  anterior  part  of  the  dome  of  the  diaphragm,  and,  once  more  reaching 
the  anterior  abdominal  wall,  can  be  followed  to  the  umbilicus,  where  it  was  first 
described.  This  completes  the  boundary  of  the  greater  sac.  On  reference  to  the 
diagram  (fig.  904)  the  student  might  be  led  to  suppose  that  the  two  sacs  are  quite 
separate.  This,  of  course,  is  not  the  case;  but  in  a  longitudinal  section  of  the 
body  made  anywhere  to  the  left  of  the  epiploic  foramen  (foramen  of  Winslow), 
it  is  impossible  to  show  the  direct  connection  between  the  two  sacs.     (See  fig.  905.) 

The  peritoneum  has  only  been  traced  in  this  longitudinal  section  so  far  as  it 
concerns  the  greater  sac.  It  now  remains  to  follow  upon  the  same  section  (fig. 
904)  such  part  of  the  membrane  as  forms  the  lesser  sac.  The  peritoneum  here 
will  be  seen  to  cover  the  posterior  surface  of  the  stomach;  thence  from  the  lesser 
curvature  it  runs  upward  to  the  liver,  forming  the  posterior  layer  of  the  lesser  or 
gastro-hepatic  omentum.  It  reaches  the  liver  behind  the  transverse  fissure.  It 
covers  only  a  part  of  its  posterior  surface  (caudate  lobe),  and  is  reflected  on  to  the 
diaphragm,  forming  the  lower  layer  of  the  coronary  ligament.  It  now  goes  down- 
ward over  the  posterior  part  of  the  dome  of  the  diaphragm  to  the  spine,  separated 
from  the  latter  by  the  great  vessels.  On  reaching  the  anterior  border  of  the  pan- 
creas it  passes  forward,  and  forms  the  upper  layer  of  the  transverse  meso-colon. 
It  then  covers  the  upper  half  of  the  transverse  colon,  and,  descending,  forms  the 
innermost  layer  of  the  great  omentum.  (The  inner  layers  of  the  great  omentum 
are  usually  fused  in  the  adult,  however,  thus  obliterating  this  portion  of  the  lesser 
sac.)     It  now  ascends,  and,  arriving  at  the  greater  curvature  of  the  stomach, 


THE  PERITONEUM 


1149 


passes  on  to  its  posterior  wall.  At  this  point  its  description  was  commenced. 
The  general  relations  of  the  greater  and  the  lesser  sac  are  also  evident  in  fig.  905 
showing  the  hnes  along  which  the  parietal  peritoneum  is  reflected  from  the  pos- 
terior abdominal  wall  as  the  visceral  peritoneum,  forming  the  various  mesenteries 
and  covering  the  various  abdominal  organs. 

Fig.  905. — Reflections  of  the  Peritoneum  on  the  Posterior  Abdominal  Wall. 
(From  Rauber-Kopsch,  modified.) 

T..     .       „        Falciform  lig. 

Recessus  superior  omentalis 
;  Lig.  triangulare  sinistrum 


Opening  of  hepatic 

veins  into  V.  cava 

inferior 


Lig.  coronarium 
Epiploic  foramen 
(of  Winslowj 
Hepato -duodenal 
lig.  and  root  struc- 
tures of  livei 
Duodenum,  parb 
sup 


Duodenum, 
pars  faoriz, 


Radix  mesenterii 


Uncovered  area 
for  ascending 
colon 


Plica  gastro- 

pancreatica 
.,—  Gastro-lienal 
lig. 

Bursa  omen- 
—  talis,  recessus 

lienalis 
Phreno-colic 

lig. 

Duodeno- 
jejunal flexure 


Uncovered  area 
for  descending 
colon 


The  precise  manner  in  which  certain  organs — such  as  the  hver,  the  caecum,  the  duodenum, 
and  the  kidneys — are  invested  by  peritoneum  is  described  in  the  accounts  of  those  viscera. 
To  such  accounts  the  reader  is  referred  for  a  description  of  the  many  'ligaments'  (such  as 
those  of  the  bladder  and  liver)  which  are  formed  by  the  peritoneum. 

The  great  omentum. — As  is  evident  from  its  development,  the  great  omentum 
[omentum  majus]  is  formed  of  four  layers  of  peritoneum,  though  this  is  quite 
impossible  to  demonstrate  in  an  adult,  the  individual  layers  having  become 
adherent. 

The  great  omentum  acts  as  an  apron,  protecting  the  intestines  and  providing 


1150 


DIGESTIVE  SYSTEM 


them  with  a  heat-economising  covering  of  fat.  It  is  nearly  quadrilateral  in  shape, 
and  is  variable  in  extent.  In  fig.  904  the  great  omentum  is  shown  to  be  connected 
with  the  greater  curvature  of  the  stomach,  on  the  one  hand,  and  the  transverse 
colon,  on  the  other.  Originally  it  extended  backward  above  the  transverse  colon 
and  mesocolon  to  the  posterior  abdominal  wall.  The  line  along  which  it  fuses  with 
the  transverse  colon  and  mesocolon  during  development  is  shown  in  fig.  904. 

Mr.  Lockwood  has  made  some  investigations  on  the  lengths  of  the  transverse  meso-colon 
and  great  omentum  in  thirty-three  cases.  In  twenty,  under  the  age  of  forty-five,  only  one  sub- 
ject had  a  great  omentum  long  enough  to  be  drawn  beyond  the  pubic  spine;  in  five,  the  omentum 
reached  as  far  as  the  pubes.  In  the  cases  beyond  forty-five  years  it  was  the  exception  rather 
than  the  rule  to  find  an  omentum  which  could  not  be  puUed  beyond  the  lower  Umits  of  the 
abdomen. 

The  lesser  omentum  [omentum  minus]  consists  of  a  double  layer  of  peritoneum 
extending  between  the  stomach  and  the  liver.  If  the  two  anterior  layers  of  the 
great  omentum  are  traced  upward,  they  are  seen  to  enclose  the  stomach,  and  then 


Fig.  906. — Abdominal  Visceka,  Anterior  View,  after  Removal  of  a  Part  of  the  Liver 
AND  Intestines.     (Rauber-Kopsch.) 


Right  lung 
lesser  jOas|-:^epa 

t"™      [      denallig.  

Foramen  epiploicum mm.!  "t 

Fundus  of  gall  bladder SHSSu. 


Right  colic  flexure 

Duodenum 

Right  kidney 

Radix  mesenteni 

Appendices  epiploicee 

Ileo-colic  fold  and  fossa 


Processus  vermiformis 


Phreno- 

r^f~  ""'"^- 

Duodeno- 
/     jejunal  flexure 
Superior 
II  J  mesenteric 

\^  vessels 

■ r~f1       Left  kidney 

\_M Abdominal 


'M  aorta 

J^       Inf  mesenteric 


join  together  again  at  the  lesser  curvature  to  form  the  lesser  omentum  (fig.  904). 
It  is  connected  above  with  the  portal  (transverse)  fissure  and  the  fissure  for  the 
ductus  venosus;  below,  with  the  lesser  curvature  of  the  stomach;  the  left  extrem- 
ity encloses  the  oesophagus;  the  right  border  contains  the  hepatic  vessels  and  is 
free,  forming  the  anterior  boundary  of  the  epiploic  foramen  (see  fig.  906). 

The  lesser  omentum  is  divided  into  two  parts.  The  portion  connecting  the  portal  fissure 
of  the  hver  with  the  first  part  of  the  duodenum,  and  enclosing  the  root  structures  of  the  liver, 
is  called  the  hepalo-duodenal  ligament  [fig.  hepatoduodenale].  The  portion  of  the  lesser  omentum 
connecting  the  lesser  curvature  of  the  stomach  with  the  fissure  of  the  ductus  venosus  is  the 
gastro-hepatic  hgament  [lig.  hepatogastricum]. 

The  gastro-splenic  ligament  [fig.  gastrolienale]  connects  the  left  extremity  of 
the  stomach  with  the  spleen,  continuing  the  layers  of  peritoneum  which  enclose 
the  stomach  (fig.  903). 

The  gastro-phrenic  and  phreno-colic  ligaments. — As  the  peritoneum  passes 
from  the  diaphragm  to  the  stomach  it  forms  a  small  fold  just  to  the  left  of  the 


THE  STOMACH  1151 

oesophagus.  This  is  the  gastr  o-phrenic  ligament.  A  strong  fold  of  the  membrane 
also  extends  from  the  diaphragm  (opposite  the  tenth  and  eleventh  ribs)  to  the 
splenic  flexure  of  the  colon,  and  is  knoM'n  as  the  phreno-colic  (costo-colic)  hgament 
[lig.  phrenicolienale].     (See  figs.  905,  906.) 

Minute  anatomy. — The  peritoneum,  like  all  serous  membranes,  consists  of  two  layers;  a 
lining  layer  composed  of  simple  squamous  epithelium  (mesothelium),  and  an  underlying 
layer  of  fibrous  connective  tissue.  The  latter  is  highly  elastic,  and  denser  in  the  parietal  than 
in  the  visceral  layer.  It  often  contains  fat.  In  mesenteries  and  similar  structures,  the  con- 
nective tissue  is  usually  very  scanty,  except  surrounding  the  vessels  and  nerves.  Ruptures 
often  occur  in  the  omenta,  which  thus  become  fenestrated  in  structure.  The  visceral  peritoneum 
is  usually  closely  attached  to  the  organs  for  which  it  forms  the  outer  serous  tunic,  but  the  pa- 
rietal peritoneum  is  often  loosely  attached  to  the  adjacent  wall  by  a  fatty  subserous  layer  [tela 
subserosa].     Smooth  muscle  occurs  frequently  in  the  various  peritoneal  folds. 

The  peritoneal  cavity  contains  normally  a  very  sUght  amount  of  watery  fluid,  which 
serves  to  lubricate  the  smooth  peritoneal  surface  and  thus  to  ehminate  friction  between 
adjacent  surfaces  during  the  movements  of  the  alimentary  canal. 

Vessels  and  nerves. — The  peritoneum  is  in  general  somewhat  sparsely  supphed  with  blood- 
vessels from  various  adjacent  trunks.  Lymph-vessels  also  occur,  but  they  probably  do  not 
connect  directly  with  the  peritoneal  cavity  by  stomata  (as  is  found  in  the  frog  and  as  claimed  by 
some  to  occur  in  man).  They  communicate  with  the  lymphatics  of  neighbouring  i-egions. 
The  nerves  are  also  comparatively  scarce.  They  are  partly  of  sympathetic  origin  (vasomotor), 
and  partly  sensory  nerves  from  the  intercostal  (7th  to  12th),  and  lumbar  nerves.  The  sensory 
nerves  are  more  frequent  in  the  parietal  peritoneum  and  end  in  the  connective  tissue,  either 
freely  or  in  special  end-organs  (varying  from  simple  end-bulbs  to  Pacinian  corpuscles). 

Development. — The  principal  features  in  the  development  of  the  peritoneum  have  already 
been  mentioned  in  the  section  on  Morphogenesis  and  in  the  remarks  on  the  general  morphology 
of  the  intestinal  canal  (p.  19).  Further  details  will  be  included  later  under  the  development  of 
the  intestine,  etc. 

Variations. — Variations  in  the  form  and  relations  of  the  peritoneum  are  exceedingly 
common,  and  are  most  commonly  of  developmental  origin.  Variations  in  the  form  and  re- 
lations of  the  various  abdominal  organs  necessarily  involve  corresponding  modifications  in 
the  peritoneum.  The  diaphragm  may  be  incomplete!}'  formed,  leaving  the  peritoneal  cavity 
in  communication  with  the  pleural,  or  more  rarely  the  pericardial  cavity.  The  primitive 
dorsal  mesentery  of  the  intestine  [mesenterium  commune]  may  persist  unmodified  (in  about 
2  per  cent,  of  adults),  or  the  various  secondary  changes  may  be  inhibited  at  any  stage.  Thus 
the'stomach  or  the  intestinal  loop  may  fail,  either  wholly  or  partly,  to  undergo  their  character- 
istic rotations.  The  adhesions  of  the  various  mesenteries  may  be  incomplete,  or  they  may  be 
more  extensive  than  usual.  For  example,  the  sigmoid  mesocolon  may  be  more  or  less  com- 
pletely obliterated  by  adhesion,  and  numerous  unusual  peritoneal  pockets  or  hgamentous  bands 
may  be  formed  in  this  way  in  various  localities.  Variations  thus  due  to  extensions  of  the  normal 
developmental  process  are  sometimes  difficult  to  distinguish  from  pathological  adhesions 
caused  by  peritonitis. 

Comparative. — As  previously  mentioned,  the  primitive  body  cavity  in  vertebrates  extends 
throughout  the  trunk  region.  In  the  oyclostomata,  this  primitive  relation  persists,  the  peri- 
cardial cavity  remaining  in  communication  with  the  general  body  cavity.  In  all  higher  forms, 
however,  the  pericardial  cavity  becomes  entirely  separated.  In  amphibia  the  lungs  he  in  the 
general  (pleuroperitoneal)  body  cavity;  in  the  reptiles  and  birds,  they  are  partially  separated; 
but  a  complete  separation  of  the  pleural  cavities  occurs  only  with  the  formation  of  the  definite 
diaphragm  in  mammals. 

The  formation  in  the  peritoneal  cavity  of  a  complete  dorsal  mesentery,  and  an  incomplete 
ventral  mesentery  (in  the  hepatic  region)  is  typical  for  all  classes  of  vertebrates.  Slight 
modifications  in  the  form  of  the  mesenteries  depend  chiefly  upon  the  diiJerent  degrees  of  com- 
ple.xity  in  the  development  of  the  various  parts  of  the  intestinal  tract.  The  marked  changes 
associated  with  extensive  secondary  adhesions  of  the  primitive  peritoneal  structures  are  found 
only  among  the  higher  mammaha,  especially  in  man. 

THE  STOMACH 

The  stomach  [ventriculus ;  gaster]  is  a  dilation  of  the  alimentary  canal  suc- 
ceeding the  oesophagus.  In  the  stomach  the  food  is  mixed  with  the  gastric  juice 
and  reduced  to  a  viscid,  pulpy  liquid,  the  chyme  [chymus],  which  undergoes  a 
certain  amount  of  digestion  and  absorption  before  passing  into  the  duodenum. 

The  stomach  (figs.  906,  907)  is  a  somewhat  pear-shaped  organ  located  in  the 
upper,  left  side  of  the  abdominal  cavity.  It  presents  a  body  [corpus  ventricuh], 
with  an  enlarged  upper  end  or  fimdus,  on  the  right  side  of  which  is  the  cardia, 
the  aperture  communicating  with  the  oesophagus.  The  body  of  the  stomach  is 
extremely  variable  in  form,  as  will  be  explained  later,  but  is  in  general  divisible 
into  a  more  expanded  upper  two-thirds,  the  cardiac  portion  [pars  cardiaca], 
which  is  nearly  vertical,  and  a  more  constricted  lower  third,  the  pyloric  portion 
[pars  pylorica],  which  tm-ns  horizontally  toward  the  right.  The  pyloric  portion 
often  presents  toward  its  lower  end  a  slight,  variable  dilation,  the  antrum  pylori, 


1152 


DIGESTIVE  SYSTEM 


succeeded  by  a  short  constricted  pyloric  canal  (Jonnesco) .  At  the  lower  end  of  this 
canal  the  pylorus  forms  the  aperture  leading  into  the  duodenum,  and  contains  a 
thick  sphincter  derived  from  the  circular  fibres  of  the  muscular  layer.  The  stom- 
ach has  two  borders  and  two  surfaces.  The  medial  (or  upper)  border  forms  the 
lesser  curvature  [curvatura  ventriculi  minor],  which  is  concave  (except  near  the 
pylorus)  and  gives  attachment  to  the  lesser  omentum.  The  lateral  (or  lower) 
border  forms  the  greater  curvature  [curvatura  ventriculi  major],  which  is  convex, 
and  gives  attachment  to  the  great  omentum.  The  curvatures  separate  the 
anterior  surface  [paries  anterior],  which  faces  forward  and  upward,  from  the 
posterior  surface  [paries  posterior],  which  is  placed  backward  and  downward. 

Dimensions. — The  dimensions  of  the  stomach  are  subject  to  great  variation 
and  therefore  only  a  gross  approximation  can  be  given.  The  length  of  the  lesser 
curvature  averages  about  10  cm.  (7.5  cm.  to  15  cm.),  and  that  of  the  greater 

Fig.  907. — ^Longitudinal  Section  op  Stomach,  Showing  the  Interior  of  the  Posterior 
Half.     (Rauber-Kopsoh.) 

Fundus  of  stomach. 


<Esophagus  (pars  abdominalis)  — ^  ■*  ^'^tc/ 


Pars  cardiaca 


L-   Tunica  mucosa 
—  Tela  submucosa 


Tunica  serosa 
PiiCEE  mucosse 


Sphincter  pylori 
Pyloric  valve 


Duodenum 
(pars  superior) 


curvature  is  three  or  four  times  as  great.  The  diameter  varies  exceedingly  accord- 
ing to  the  amount  of  contents.  When  nearly  empty,  it  presents,  especially  in 
the  pyloric  portion,  a  narrow  tubular  form,  with  a  diameter  of  about  4  cm.  or  5 
cm.  (fig.  1108,  Section  XIII).  The  diameter  of  the  pylorus,  which  is  the  narrow- 
est point  in  the  alimentary  canal  when  constricted  is  only  about  1.5  cm.  It  is 
distensible,  however,  as  hard  bodies  with  diameters  of  2  cm.  or  more  may  readily 
pass  through. 

The  average  capacity  of  the  stomach  is  between  one  and  two  litres,  being  sub- 
ject to  extreme  individual  variations.  In  the  newborn,  it  averages  about  30  cc. 
(25  to  35  cc),  increasing  very  rapidly  in  the  early  postnatal  months  and  reaching 
an  average  of  270  cc.  at  one  year  (Lissenko).  The  average  weight  of  the  adult 
stomach  is  about  135  gm. 

Position  and  relations  of  the  stomach. — The  position  and  relations  of  the  stom- 
ach, like  its  form  and  structure,  are  subject  to  many  variations  in  different  indi- 


THE  STOMACH 


1153 


viduals,  and  in  the  same  individual  according  to  changes  in  physiological  condition, 
posture,  etc.     It  is  therefore  difficult  to  give  a  concise  and  accurate  description. 

The  normal  position  of  the  stomach  has  long  been  disputed.  It  is  generally 
recognised  that  the  long  axis  is  oblique,  extending  from  above  downward,  forward 
and  to  the  right.  Some,  however,  especially  among  the  older  anatomists,  have 
maintained  that  the  gastric  axis  normally  approaches  more  nearly  to  the  horizon- 
tal type,  with  the  pylorus  but  little  below  the  cardia  (approximately  the  position 
shown  in  figs.  915,  916).  Others,  especially  among  the  more  recent  anatomists, 
have  maintained  that  the  axis  of  the  stomach  is  normally  more  nearly  vertical  in 
position  (see  fig.  1125,  Section  XIII).  The  results  of  an  extended  and  careful 
study,  both  in  formalin-hardened  bodies  and  by  means  of  the  Roentgen-rays  in  the 
living  body,  demonstrate  that  there  is  much  variability  in  the  position  of  the  stom- 
ach. Both  the  horizontal  and  the  vertical  types  may  occur  as  the  extremes  of 
normal  variation,  but  the  more  usual  type  is  the  intermediate  oblique  position. 
The  gastric  axis,  however,  is  not  straight,  but  somewhat  curved  and  bent  in  a 
reverse  L-shape.  The  larger  cardiac  portion  is  approximately  vertical  (especially 
when  the  trunk  is  in  the  upright  posture)  the  smaller  pyloric  portion  more  nearly 
horizontal  (figs.  895,  906,  918,  919).  In  the  empty  stomach,  the  pylorus  opens 
into  the  duodenum  from  left  to  right.  In  distention,  however,  the  pylorus  is 
carried  in  front  of  the  duodenum.  In  extreme  distention,  it  is  carried  to  the 
right  and  downward  so  as  to  open  upward  and  to  the  left. 

Fig.  908. — Longitudinal  Section  op  the  Ptloeic  Portion  op  the.  Stomach.     (Cunning- 
ham, Trans.  Royal  Soc.  Edinb.,  vol.  45.) 


Sphinctenc  cylinder 
Duodeno-pyloric  constriction    \ 


Pyloric  canal         Sulcus  intermedius 


In  surface  relation  (fig.  914),  the  stomach  lies  within  the  left  hypochondriac 
and  the  epigastric  regions.  Often,  however,  especially  when  distended,  it  extends 
into  the  umbilical  and  even  the  right  hypochondriac  region.  When  empty,  it 
usually  lies  almost  entirely  in  the  left  half  of  the  body,  with  the  pjdorus  not  more 
than  1  cm.  or  2  cm.  to  the  right  of  the  mid-sagittal  plane.  When  distended,  the 
long  axis  of  the  stomach  is  lengthened  and  the  pylorus  is  displaced  5  cm.  or  more 
to  the  right  and  downward.  In  distention,  the  stomach  expands  in  all  directions 
(except  posteriorly) ,  and  does  not  appear  to  rotate  as  is  sometimes  stated.  The 
position  of  the  stomach,  especially  when  distended,  also  varies  appreciably  accord- 
ing to  the  posture  of  the  body.  It  sags  downward  when  the  body  is  in  the  upright 
position,  and  to  the  right  or  left  when  the  body  is  placed  on  the  corresponding 
side.  The  cardia  hes  on  the  left  side  of  the  10th  or  11th  thoracic  vertebra,  and 
corresponds  to  a  surface  point  behind  the  left  7th  costal  cartilage  about  2.5  cm. 
from  its  sternal  end.  The  pylorus  usually  lies  opposite  the  right  side  of  the 
1st  lumbar  vertebra,  about  midway  between  ensiform  cartilage  and  umbilicus, 
or  in  Addison's  '  transpyloric  line,'  midwaj'  between  the  suprasternal  notch 
and  the  symphysis  pubis,  when  the  body  is  recumbent;  but  descends  to  the  2d 
or  lower  in  upright  posture.     The  Jwndus  corresponds  to  the  left  dome  of  the 


1154  DIGESTIVE  SYSTEM 

diaphragm  (which  separates  it  from  the  lung  and  heart) ,  opposite  the  sixth  sterno- 
costal junction.  The  fundus  of  course  rises  and  falls  with  respiratory  movements 
of  the  diaphragm,  the  excursion  being  from  2  to  6  cm. 

The  relations  of  the  stomach  with  surrounding  organs  are  indicated  diagram- 
matically  in  figs.  915  and  916.  The  anterior  surface  is  in  contact  on  the  right  with 
the  left  lobe  of  the  liver,  the  pylorus  reaching  the  quadrate  lobe;  on  the  left  it 
is  in  contact  with  the  diaphragm  (separating  it  from  the  heart  and  left  lung) ; 
and  below  with  the  anterior  body  wall  by  a  triangular  area  of  variable  size. 
The  posterior  surface  is  in  relation  (separated  by  the  lesser  sac)  with  the  pancreas, 
above  which  are  areas  of  contact  with  the  diaphragm,  spleen,  left  kidney  and 
suprarenal  body;  below  the  pancreas,  the  stomach  is  in  contact  with  the  trans- 
verse mesocolon,  and  through  this  with  the  transverse  colon  and  coils  of  small 
intestine.  The  relation  with  the  duodeno-jejunal  angle  is  indicated  in  fig.  895. 
Further  details  concerning  topography  of  the  stomach  are  given  in  section  XIII 
on  Clinical  and  Topographical  Anatomy. 

Peritoneal  relations. — The  stomach  is  covered  by  peritoneum  in  its  whole 
extent,  except  immediately  along  the  curvatures  and  upon  a  small  triangular 
space  at  the  back  of  the  cardiac  orifice,  where  the  viscus  lies  in  direct  contact  with 
the  diaphragm  and  possibly  with  the  upper  part  of  the  left  suprarenal  gland. 
It  is  enclosed  between  two  layers.  These  two  layers  at  its  lesser  curvature 
come  together  to  form  the  gastro-hepatic  portion  of  the  lesser  omentum,  and  at 
the  greater  curvature  extend  downward  to  form  the  great  omentum  (figs.  903, 
904).     At  the  left  of  the  oesophagus  the  two  layers  pass  to  the  diaphragm,  form- 

FiG.  909. — StTHFACE  View  of  Gastric  Mucosa.      X  4.     (Sobotta-McMurrich.) 


Gastric  areas  and  foveolge 

ing  the  gastro-phrenic  ligament;  and  at  the  fundus  they  pass  on  to  the  spleen, 
forming  the  gastro-splenic  ligament. 

The  posterior  surface  of  the  stomach  is  in  relation  with  the  lesser  sac  (bursa 
omentalis),  forming  part  of  its  anterior  wall.  The  anterior  surface  of  the  stomach 
is  in  relation  with  the  greater  sac  of  the  peritoneal  cavity. 

Minute  anatomy. — The  stomach  is  composed  of  the  four  typical  layers  of  the  alimentary 
canal — mucosa,  submucosa,  muscularis  and  serosa.  The  mucosa  (figs.  907,  90S,  and  909)  is 
thrown  into  a  series  of  coarse  folds  (pUcse  mucosoe),  chiefly  longitudinal,  which  disappear  when 
the  stomach  is  distended.  Along  the  lesser  curvature,  the  ridges  are  more  regular  (corre- 
sponding to  Waldeyer's  'Magenstrasse')  and  form  a  longitudinal  grooved  channel  from  cardia 
to  pylorus.  Upon  closer  examination  (fig.  909)  the  inner  surface  of  the  mucosa  presents  a 
somewhat  warty  ('mammilated')  appearance,  due  to  numerous  small  elevated  areas  [areae 
gastricae],  varying  from  1  to  6  mm.  in  diameter.  When  examined  with  a  lens,  it  is  seen  that 
each  area  is  beset  with  numerous  small  pits  [foveolae  gastricae],  separated  by  partitions  which 
sometimes  (especially  in  the  pyloric  region)  bear  villus-hke  prolongations  [plicae  villosse]. 
The  average  number  of  foveolai  is  estimated  at  87  per  sq.  mm.,  or  more  than  6  millions  for 
the  entire  stomach  (Toldt).  Into  each  pit  or  foveola  open  3  to  5  gastric  glands.  The  entire 
surface  is  covered  with  a  simple  columnar  mucigenous  epithelium. 

The  relations  of  the  mucosa  in  section  are  shown  in  fig.  910.  The  thickness  of  the  mucosa 
varies,  being  greatest  (about  2  mm.)  in  the  pyloric  region,  decreasing  to  less  than  .5  mm.  in 
the  cardiac  region  (Kolliker).  The  lamina  propria  is  crowded  with  glands,  of  which  three 
varieties  are  distinguished.  The  cardiac  glands  are  tubulo-racemose  (chiefly  mucous)  glands 
occupying  a  narrow  zone  a  few  millimeters  in  width  adjacent  to  the  cardiac  orifice.  The 
fundic  glands  [gl.  gastricae  propriae]  occupy  the  greater  part  of  the  stomach,  and  are  simple 
(partly  branched)  tubular  glands  (fig.  910).  They  contain  three  varieties  of  cells— mucous 
cells,  peptic  cells,  and  parietal  cells.  The  parietal  cells  may  secrete  an  organic  chloride  com- 
pound, but  the  HCl  of  the  gastric  juice  is  formed  not  in  the  gland  tubules  but  at  the  surface  of 


THE  STOMACH 


1155 


the  mucosa  (Harvey  and  Bensley).  The  pyloric  glands  [gl.  pyloricae]  are  branched  tubular 
glands  occupying  the  pyloric  region.  Whether  they  are  merely  mucous  or  also  secrete  pepsin 
is  still  in  dispute. 

The  interstitial  tissue  of  the  lamina  propria  contains  diffuse  lymphoid  tissue  and  a  few 
small  lymph  nodules,  especially  in  the  pyloric  region.  The  muscularis  mucosw  is  a  thin  sheet 
of  smooth  muscle  lying  just  below  the  fundus  of  the  glands  and  is  composed  of  an  inner  circular 
and  an  outer  longitudinal  layer. 

The  tela  submucosa  (fig.  910)  is  a  very  loose  areolar,  vascular  layer  which  permits  the 
wrinkling  of  the  mucosa  according  to  the  degree  of  distention. 

The  tunica  muscularis  contains  three  layers  of  smooth  muscle  (figs.  911,  912,  and  913). 
The  outer  or  longitudinal  layer  [stratum  longitudinale]  is  thickest  along  the  lesser  curvature, 
and  is  continuous  with  the  longitudinal  fibres  of  the  oesophagus  and  the  duodenum.  On  the 
anterior  and  posterior  walls  of  the  antrum  pylori,  the  longitudinal  fibres  form  thickened  bands. 

Fig.  910. — Diagrammatic  Section  of  the  Stomach  Wall  Showing  (A.)  The  Blood 
vessels,  (B)  the  Tunics,  and  (C)  the  Lymphatics.  M,  Mucosa.  Mi,  Muscularis  mucoste.  S, 
Submucosa.     I,  Circular,  and  0,  longitudinal  muscle  layer.     (Szymonowicz,  after  Mall.) 


the  ligamenla  pylori.  The  middle  or  circular  layer  Istratum  circulare]  is  continuous  with  the 
circular  fibres  of  oesophagus  and  duodenum  and  surrounds  the  entire  stomach.  It  is  especially 
thickened  in  the  region  of  the  pyloric  canal,  at  the  lower  end  of  which  it  forms  a  thickened 
ring-like  band,  the  pyloric  sphincter  [m.  sphincter  pylori].  The  inner  or  oblique  layer  [fibrae 
obliquse]  is  composed  of  fibres  continuous  with  the  deepest  circular  fibres  of  the  oesophagus. 
They  form  an  incomplete  layer  which  encircles  the  fundus  and  passes  obliquels'  downward 
around  the  body  of  the  stomach  toward  the  greater  curvature. 

The  external  tunica  serosa  is  formed  by  the  peritoneum,  and  has  the  smooth  shiny  appear- 
ance and  the  structure  typical  for  a  serous  membrane. 

Blood-vessels. — The  stomach  receives  its  blood-supply  from  many  branches.  From  the 
coeliac  axis  there  is  the  left  gastric  artery,  which  runs  along  the  lesser  curve  from  left  to  right, 
anastomosing  with  the  right  gastric  branch  of  the  hepatic.  Along  the  greater  curve  run  the 
right  and  left  gastro-epiploic  arteries,  anastomosing  at  the  middle  of  the  border,  the  left  being 


1156 


DIGESTIVE  SYSTEM 


a  branch  of  the  splenic,  the  right  a  branch  of  the  hepatic,  through  the  gastro-duodenal  artery. 
The  stomach  also  receives  branches  from  the  splenic  (vasa  brevia)  at  the  fundus.  The  vascular 
arches  along  the  curvatures  of  the  stomach  are  comparable  to  those  in  the  intestinal  mesentery 
(MaU). 

The  blood  of  the  stomach  is  returned  into  the  portal  vein.  The  coronary  vein  and  pyloric 
vein  open  separately  into  the  portal  vein ;  the  right  gastro-epiploic  vein  opens  into  the  superior 
mesenteric,  the  left  into  the  splenic. 

The  arrangement  and  distribution  of  the  blood-vessels  within  the  stomach  wall  are  illus- 

FiG.  911. — A  Dissection  of  the  MtrscuLATURE  of  the  Stomach.  (Lewis  and  Stohr, 
after  Spalteholz.)  a  and  e,  Longitudinal  layer,  b  and  d,  Circular  layer,  c.  Oblique  layer. 
Py,  Pylorus.     S.I.,  Sulcus  intermedins. 


&I. 


trated  in  fig.  910.     The  rich  capillary  ple.xus  in  the  mucosa  supplies  the  glands  and  also  serves 
for  absorption. 

Lymphatics. — There  is  a  set  of  nodes  lying  along  the  lesser  and  the  pyloric  portion  of  the 
greater  curvature,  and  others  at  the  pyloric  and  cardiac  ends.  These  are  entered  by  lymphatic 
vessels  which,  beginning  in  the  mucous  membrane  (fig.  910),  accompany  all  the  gastric  veins, 
but  chiefly  those  of  the  lesser  curvature.  Vessels  also  accompany  the  left  gastro-epiploic  veins 
to  terminate  in  the  splenic  nodes.  On  its  wa}'  to  the  receptaculum  chyli,  the  gastric  lymph 
passes  through  groups  of  nodes  [lymphoglandulae  pancreaticoUenales]  situated  above  and 
behind  the  head  and  neck  of  the  pancreas. 

Figs.  912  and  913. — Dissections  Showing  the  MtrsctrLAB  Layers  of  the  Stomach.     X  1. 
(From  Toldt's  Atlas.) 


Circular  layer 
Longitudinal  layer 


Tela  submucose 


The  arrangement  of  the  lymphatic  plexus  within  the  stomach  wall,  beginning  with  blind 
rootlets  in  the  mucosa,  is  shown  in  fig.  910. 

Nerves. — The  nerves  of  the  stomach  are  derived  in  part  from  the  vagi  (which  form  the  motor 
fibres  of  the  stomach),  the  right  vagus  descending  on  the  posterior  wall,  and  the  left  on  the 
anterior  wall.  The  stomach  also  receives  sympathetic  branches  from  the  coeliac  plexus,  follow- 
ing the  arteries.  Small  ganglia  occur  along  both  vagus  and  sympathetic  branches  (Remak). 
The  nerves  join  the  gangliated  plexuses,  myenteric  and  submucous,  in  the  wall  of  the  stomach, 


J 


THE  STOMACH 


1157 


from  which  branches  are  distributed  to  the  muscularis  and  the  mucosa  as  for  the  intestine  in 
general. 

Development. — The  stomach  at  first  lies  in  the  mid-sagittal  plane  in  the  cervical  region. 
It  participates  in  the  general  descent  of  the  viscera  (the  cesophagus  becoming  correspondingly 
lengthened)  and  reaches  its  permanent  vertebral  level  in  the  17  mm.  embryo  (Jackson).  In 
the  meantime,  beginning  in  the  7.5  mm.  embryo  (F.  T.  Lewis),  a  rotation  of  the  stomach  has 
occurred.  The  rotation  is  around  the  long  axis,  so  that  the  anterior  border  (lesser  curvature) 
is  turned  to  the  right,  and  the  posterior  border  (greater  curvature)  to  the  left.  The  right 
surface  therefore  becomes  posterior  and  the  left  anterior.  During  the  process  of  descent,  the 
pyloric  end  is  the  first  to  become  fixed  (at  about  12  mm.).  As  the  cardiac  end  continues  to 
descend,  it  is  displaced  to  the  left,  so  the  oblique  position  of  the  stomach  is  estabUshed  early. 
The  stomach  is  at  first  spindle-shaped,  but  the  upper  end  begins  to  enlarge  at  about  10  mm. 
The  fundus  develops  somewhat  later  as  a  locahzed  outgrowth  (Keith  and  Jones). 

The  foetal  stomach  is  somewhat  crowded  to  the  left  by  the  relatively  large  liver  (fig.  953). 

Fig.  914. — Outline  Showing  the  Average  Position  op  the  Abdominal.  iVisceea  in 
40  Bodies,  on  a  Centimetre  Scale  (Reduced  to  .36  Natural  Size).  ML,  anterior  mid-hne 
EF,  horizontal  line  half-way  between  pubes  and  suprasternal  margin  ("transpyloric"  line), 
CD,  line  half  way  between  pubes  and  line  EF.     (Addison.) 


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and  its  relations  to  surrounding  organs  undergo  considerable  change.  Even  in  the  foetus  it  is 
quite  variable,  but  its  general  form  and  position  do  not  differ  essentially  from  the  adult  condition. 
Glands. — According  to  Johnson,  in  an  embryo  of  16  mm.,  the  lining  epitheUum  shows  the 
primitive  foveols  as  pit-hke  depressions  which  become  elongated,  forming  irregular  anasto- 
mosing grooves,  separated  by  vilJus-like  projections.  The  pits  multiply  and  deepen,  and  from 
their  bottoms  the  gastric  glands  bud  off  (at  120  mm.).  The  parietal  cells  appear  very  early 
in  the  gland  fundus,  but  the  differentiation  of  gland  cells  is  still  incomplete  at  birth. 


1158 


DIGESTIVE  SYSTEM 


Figs.  915  and   916. — Diagrams  of  the  Contact  Areas  of  the  Stomach,  Anterior     and 
Posterior  Views. 


cardia 


Mid- line 
of  body 

Fig.  917. — ^The    Abdominal  Viscera,  From  Behind.     (Riidinger,) 


Larynx 


Lung 

Diaphragm 

Pancreas 

Spleen 

Stomach 

Descending  colon 
Inferior  mesenteric  vein 


Superior  mesenteric 

vein 
Ascending  colon 


THE  STOMACH 


1159 


^The  circular  layer  of  muscle  is  indicated  at  16  mm.;  the  longitudinal  much  later,  about 
90  mm.,  and  not  completed  before  240  mm.  (F.  T.  Lewis). 

Variations. — The  great  variability  of  the  stomach  in  form,  position  and  relations  has 
already  been  repeatedly  emphasized.  These  variations  have  been  most  carefully  studied 
recently  by  various  observers  in  the  living  body  by  means  of  the  Roentgen-rays.  Some  of  the 
results  of  study  by  this  method  are  sho\vn  in  figs.  918,  919. 

Peristalsis. — It  would  appear  that  most  of  the  variations  in  the  form  of  the  stomach  that 
have  been  described  are  merely  various  phases  in  the  series  of  changes  undergone  by  the 
stomach  during  the  normal  process  of  physiological  digestion.  The  following  account  of  these 
changes  is  based  largely  upon  the  radiographic  observations  of  Cole.  Earlier  observations  by 
various  investigators  upon  the  Uving  stomach  of  man  and  lower  animals  (and  especially  the 
radiographic  study  of  the  cat  by  Cannon)  have  shown  that  the  cardiac  portion  of  the  stomach 
is  the  first  to  become  distended  with  food  (and  gas).  Until  a  considerable  degree  of  distention 
is  reached,  the  pyloric  portion  usually  remains  a  somewhat  narrow  contracted  canal,  along 
which  distinct  peristaltic  contractions  pass  pylorusward. 

Under  favorable  conditions,  however,  the  peristaltic  contractions  may  be  observed  to  begin 
in  the  cardiac  portion,  although  they  are  usually  most  distinct  in  the  pyloric  portion.  Each 
individual  contraction  travels  at  the  rate  of  about  2,5  cm.  (1  inch)  per  second,  so  that  it  requires 
several  seconds  for  a  contraction  to  travel  from  fundus  to  pylorus.     The  number  of  simultaneous 


Fig.  918. — Different  Forms  of  the  Stomach  as  Shown  by  The  Rcentgen  Rats.     Fundus 
not  represented.     (Cole.) 


C — "Drain-trap 


D — "Fish-hook" 


contractions  present  in  the  stomach  varies  from  1  to  6  or  7,  3  or  4  being  the  most  common. 
In  fig.  919,  a  series  of  10  successive  radiographs  show  the  progression  in  a  stomach  with  four 
simultaneous  individual  peristaltic  contractions.  The  peristaltic  movements  are  further  com- 
phcated  by  the  appearance  (simultaneously  in  all)  of  successive  periods  of  'systole,'  during 
which  the  peristaltic  contractions  become  stronger  and  deeper,  and  '  diastole,'  in  which  the 
contractions  relax  and  become  less  distinct  (Cole).  In  fig.  919,  phases  1  to  6  represent  the 
'systole,'  and  7  to  10  the  'diastole.'  A  'systole'  and  a  'diastole'  together  make  up  a 
'  gastric  cycle.'  During  the  entire  progress  of  an  individual  peristaltic  contraction  from  fundus 
to  pylorus,  the  number  of  'cycles'  appears  to  correspond  to  the  number  of  peristaltic  con- 
tractions present.  Thus  the  figure  represents  a  stomach  of  the  4-cyole  type.  The  time  required 
for  a  '  cycle '  varies  widely,  the  average  (in  the  3-  or  4-cycle  type)  being  about  2  or  3  seconds. 

In  the  earlier  stages  of  gastric  digestion  the  pylorus  usually  remains  closed,  but  after  a 
variable  time  it  relaxes  slightly  (lumen  about  3  mm.  in  diameter)  at  intervals,  allowing  the 
chyme  to  be  spurted  into  the  duodenum. 

Thus  the  various  constrictions  often  found  in  the  formalin-hardened  stomachs,  and  the 
pyloric  antrum,  appear  to  be  merely  transient  phases  of  the  digestive  process.  The  'hour- 
glass' stomach  is  in  many  cases  to  be  explained  in  this  way;  in  others,  however,  the  constriction 
is  pathological  and  permanent.  Various  forms  of  abnormal  lobulations  and  dilations  also 
rarely  occur. 


1160 


DIGESTIVE  SYSTEM 


Gastroptosis  is  a  very  common  abnormality  in  which  the  body  of  the  stomach  extends 
vertically  downward  to  the  umbilicus,  or  lower,  forming  a  sharp  bend  beyond  which  the  pyloric 
portion  turns  upward  to  reach  its  termination.  This  form  is  especially  common  in  women, 
due  to  tight  lacing. 

Fig.  919. — Serial  Radiographs  Taken  at  Short  Intervals,  Showing  Diastole 
(Phases  7-10)  and  Systole  (Phases  1-6),  and  the  Progression  toward  the  Pylorus  op  a 
Four-cyclBjType  of  Gastric  Peristalsis.     Fundus  of  the  stomach  not  shown.      (Cole.) 


Comparative. — The  primitive  stomach  is  perhaps  merely  a  receptacle  for  food,  true'digestive 
glands  being  absent  in  many  of  the  fishes.  The  vertebrate  stomach  is  a  dilated  sac  of  variable 
form,  but  is  typically  somewhat  looped,  with  cardiac  and  pyloric  segments.  In  birds,  there  is 
a  peculiar  arrangement,  correlated  with  the  absence  of  teeth.     The  stomach  is  divided  into  an 


THE  DUODENUM 


1161 


anterior  glandular  proventriculus,  and  a  posterior  muscular  gizzard  with  a  homy  lining 
serving  to  grind  the  food.  The  mammalian  stomach  is  the  most  variable  in  form  and 
structure  which  are  correlated  with  the  method  and  character  of  alimentation.  The  cardiac 
end  of  the  stomach  is  often  hned  to  a  variable  extent  with  a  prolongation  of  the  oesophageal 
stratified  squamous  epithelium.  The  three  kinds  of  glands,  cardiac,  fundic  and  pyloric,  are 
typically  present.  In  general,  the  stomach  is  larger  and  more  complicated  in  herbivora  than 
in  carnivora.  Instead  of  being  a  single  sac,  the  stomach  may  be  more  or  less  divided  into 
chambers.  An  incomplete  division  into  cardiac  and  pyloric  portions  is  so  common  that  it  may 
be  considered  typical.  The  most  extreme  specialization  is  found  in  the  ruminants.  In 
these  the  stomach  has  four  chambers,  the  first  two  of  which,  however,  are  expansions  of  the 
oesophagus. 

THE  SMALL  INTESTINE 

The  small  intestine  [intestinum  tenue]  extends  from  the  pylorus  to  the  ileo- 
csecal  orifice,  and  occupies  most  of  the  abdominal  cavity  below  the  liver  and 
stomach.  It  is  a  cylindrical  tube  whose  diameter  decreases  from  about  4  cm. 
above  to  about  2.5  cm.  at  the  lower  end.  Its  length,  when  removed  from  the 
body  and  measured  fresh,  averages  about  7  metres  (23  ft.) ;  but  when  formalin- 
hardened  in  situ,  the  length  (which  is  probably  nearer  that  during  life)  is  only 
about  4  metres.  The  length  does  not  seem  to  vary  according  to  sex,  height  or 
weight  in  the  adult,  but  it  is  said  to  be  relatively  longer  in  the  child. 

The  small  intestine  includes  two  main  divisions,  the  duodenum  and  the 
mesenteric  small  intestine,  the  latter  being  further  subdivided  into  jejunum  and 
ileum. 

THE  DUODENUM 

The  duodenum  is  the  first  part  of  the  small  intestine,  and  is  very  definite  in 
position  and  extent.  It  is  firmly  attached  to  the  posterior  abdominal  wall,  being 
almost  entirely  retroperitoneal.     It  is  the  widest  part  of  the  small  intestine,  the 

Fig.  920. — The  Duodenum  and  Pancreas,  Anterior  View. 
Superior  layer  of  transverse  meso-colon 


Inferior  layer  of  transverse  meso-colon 


Inferior  part  of  duodenum 


Superior  mesenteric  i 


average  width  being  4  cm.  or  more,  and  is  also  the  shortest  segment,  being  only 
about  25  cm.  in  length.  In  general,  it  is  somewhat  C-shaped,  the  concavity 
enclosing  the  head  of  the  pancreas  (figs.  920,  921,  922). 

Parts. — For  convenience  of  description,  the  duodenum  is  divided  into  the 
following  parts:  (1)  the  first  or  superior  portion  [pars  superior]  which  is  short 
(5  cm.  or  less),  leading  from  the  pylorus  and  forming  the  superior  flexure  [flexura 
duodenalis  superior];  (2)  the  descending  portion  [pars  descendens],  about  7  or  8 
cm.  in  length,  which  receives  the  bile  and  pancreatic  ducts  and  joins  the  inferior 
portion  at  the  inferior  flexure  [flexm-a  duodenalis  inferior];  and  (3)  the  inferior 
portion  [pars  inferior],  which  is  again  subdivided  into  (a)  transverse  portion  [pars 
horizontaHs],  about  10  cm.  long,  which  usually  ascends  slightly  and  passes 
gradually  into  (b)  the  ascending  portion  [pars  ascendens],  2  or  3  cm.  long,  ter- 
minating in  the  duodeno-jejunal  flexure  [flexura  duodenojejunalis]. 


1162 


DIGESTIVE  SYSTEM 


Position  and  relations. — As  shown  in  fig.  914,  the  duodenum  usually  lies 
chiefly  in  the  lower  part  of  the  epigastric  region,  only  the  inferior  (transverse) 
portion  extending  into  the  umbilical  region.  All  but  the  terminal  (ascending) 
portion  of  the  duodenum  lies  to  the  right  of  the  mid-line. 

The  superior  portion  usually  lies  at  the  level  of  the  first  lumbar  vertebra  (or 
the  disk  below).  It  is  covered  anteriorly,  and  to  a  variable  extent  posteriorly, 
by  a  prolongation  of  the  peritoneum  from  the  corresponding  surfaces  of  the 
stomach.  It  is  somewhat  freely  movable.  When  the  stomach  is  empty,  it 
extends  from  the  pylorus  almost  horizontally  to  the  right  and  backward.  As 
the  stomach  becomes  distended,  however,  the  pylorus  is  carried  to  the  right  and 
downward  for  a  variable  distance,  and  the  position  of  the  superior  part  of  the 
duodenum  is  correspondingly  altered. 

Superiorly  it  is  in  contact  with  the  hver  (quadrate  lobe)  and  the  neck  of  the  gall-bladder 
and  forms  the  lower  boundary  of  the  epiploic  foramen;  anteriorly,  with  the  liver  and  (often) 
the  transverse  colon;  inferiorly  and  posteriorly,  with  the  head  of  the  pancreas  below,  and  with 
the  common  bile  duct,  hepatic  vessels  and  portal  vein  above. 

The  second  or  descending  portion  of  the  duodenum  extends  along  the  right 
side  of  the  first  to  the  third  lumbar  vertebra.  It  is  covered  antero-laterally  by 
peritoneum,  excepting  (usually)  the  area  of  contact  with  the  transverse  colon 
(figs.  906,  920). 

Posteriorly  (fig.  956)  it  is  in  contact  with  the  right  kidney,  ureter  and  renal  vessels,  and  below 
with  the  psoas  muscle.  Anteriorly  (fig.  906)  it  is  crossed  by  the  transverse  colon  (the  layers  of 
the  transverse  mesocolon  usually  separated  by  an  area  of  direct  contact);  above  the  colon,  it 
may  be  in  contact  with  the  gall-bladder,  and  below  the  colon  with  coils  of  small  intestine.     The 

Fig.  921. — The  Duodenum  and  Pancbeas,  Posterior  View. 

Portal  vein 


Terminal  part  of  duodenum 


Head  of  pancreas 


left  or  medial  aspect  of  the  descending  duodenum  (figs.  920,  921,  922)  is  in  contact  with  the 
head  of  the  pancreas,  and  some  fibres  from  the  muscular  tunic  are  said  to  become  intermingled 
with  the  pancreatic  lobules.  Somewhat  posteriorly  the  common  bile  duct  descends  between 
pancreas  and  duodenum,  and  enters  the  descending  duodenum,  in  common  with  the  pancreatic 
duct,  about  10  cm.  below  the  pylorus.  The  loop  formed  by  the  pancreatico-duodenal  arteries 
also  runs  along  the  descending  duodenum. 

The  third  or  transverse  portion  of  the  duodenum  usually  crosses  the  body  of 
the  third  lumbar  vertebra,  ascending  slightly  from  the  right  to  the  left  side 
(figs.  920,  921).  It  is  covered  anteriorly  with  peritoneum,  excepting  a  small 
space  where  the  superior  mesenteric  vessels  enter  the  root  of  the  mesentery. 

Anteriorly  it  is  further  in  contact  with  coils  of  smaU  intestine;  superiorly,  with  the  head  of 
the  pancreas,  and  the  inferior  pancreatico-duodenal  vessels;  posteriorly,  with  the  vena  cava. 

The  terminal  or  ascending  portion  is  covered  anteriorly  and  laterally  by 
peritoneum,  and  is  in  contact  with  coils  of  the  ileum.  To  the  right  it  is  in  rela- 
tion with  the  head  of  the  pancreas  (processus  uncinatus)  and  the  superior  mesen- 
teric vessels;  and  posteriorly  with  the  psoas  muscle,  aorta  and  left  renal  vessels. 
The  duodeno-jejunal  flexure  usually  lies  opposite  the  second  lumbar  vertebra,  and 
is  in  contact  above  with  the  inferior  surface  of  the  body  of  the  pancreas,  and  the 
root  of  the  transverse  mesocolon. 


THE  DUODENUM 


1163 


Fig.  922. — ^Dissection  op  the  Duodenum  and  Pancreas,  Anterior  View. 
(Rauber-Kopsch.) 


1164 


DIGESTIVE  SYSTEM 


The  end  of  the  duodenum  is  firmly  fixed  in  its  place  by  the  suspensorius  duodeni.  This 
name  has  been  given  to  a  fibro-muscular  band  that  contains,  according  to  Treitz,  non-striated 
muscular  fibres,  and  descends  to  the  terminal  part  of  the  duodenum  from  the  lumbar  part 
of  the  diaphragm,  passing  to  the  left  of  the  cceliac  artery  and  behind  the  pancreas.  Lockwood 
points  out  that  this  band  is  continued  on,  after  being  inserted  into  the  duodenum,  between 
the  layers  of  the  mesentery.  He  suggests  the  name  of  the  'suspensory  muscle  of  the  duodenum 
and  mesentery,'  and  says,  'together  with  the  other  constituents  of  the  root  of  the  mesentery, 
it  forms  a  band  of  considerable  strength,  sufficient  not  only  to  support  the  weight  of  the  intestines 
and  mesentery,  but  also  to  resist  the  pressure  of  the  descent  of  the  diaphragm.' 

In  connection  with  this  fourth  portion  of  the  duodenum,  mention  may  be  made  of  certain 
peritoneal  folds  and  fosste  which  are  of  some  surgical  interest  by  reason  of  their  being  associated 
with  retro-peritoneal  hernia.  Four  such  fossEE  may  be  mentioned,  namely,  the  superior  and  in- 
ferior duodenal  fossa:,  paraduodenal  and  the  retroduodenal,;  f osste.  On  drawing  the  terminal 
portions  of  the  duodenum  to  the  right,  two  triangular  folds  of  peritoneum,  the  superior  and  in- 
ferior duodenal  folds,  which  extend  from  the  wall  of  the  duodenum  to  the  posterior  abdominal  wall 
may  be  observed.  Each  fold  has  a  free  edge.  Beneath  each  fold  is  found  a  pouch  of  peri- 
toneum, constituting  the  superior  and  inferior  duodenal  fossae.  The  former,  the  smaller, 
opens  downward  and  is  present  in  about  50  per  cent.,  while  the  latter  opens  upward  and  is 
present  in  about  75  per  cent.,  of  the  subjects  examined  (Jonnesco).  The  paraduodenal  fossa 
(fossa  of  Landzert)  is  not  often  found  in  the  adult;  when  present,  it  is  situated  to  the  left  of  the 
last  part  of  the  duodenum,  and  is  formed  by  a  fold  of  peritoneum  enclosing  the  inferior  mesen- 
teric vein.  The  retroduodenal  fossa  is  a  rare  form  extending  from  below  upward  behind  the 
transverse  portion  of  the  duodenum. 

Interior  of  the  duodenum. — -The  interior  of  the  first  part  of  the  duodenum 
is  smooth.  The  pylorus  is  often  somewhat  invaginated,  much  in  the  same  way 
that  the  uterus  projects  into  the  vagina  (fig.  908).     On  account  of  this  arrange- 

FiG.  923. — Duodenal   Foss^    and    Folds.     Paraduodenal   fossa   is   not   shown. 
(After  Cunningham.) 

Transverse  meso-colon 


Transverse  colon 


Superior  duodenal  fossa 

Inferior  duodenal  fossa 

The  mesentery 


Inferior  mesenteric  vein 
Inferior  mesenteric  artery 


ment  fwhich  renders  the  complete  emptying  of  the  cavity  somewhat  difficult) 
and  also  on  account  of  the  distensibility  of  this  portion,  it  usually  shows  up  very 
distinctly  in  radiographic  pictures  as  a  '  cap '  to  the  pyloric  end  of  the  stomach 
during  digestion.  In  the  lower  portions  of  the  duodenum,  transverse  ridges  or 
folds  of  the  mucosa  appear  (fig.  922)  which  are  also  apparent  in  radiographs 
occasionally.  On  the  medial  wall  of  the  descending  portion,  posteriorly,  about 
half-way  down,  is  a  more  or  less  distinct  longitudinal  fold  [plica  longitudinahs 
duodeni],  toward  the  lower  end  of  which  is  a  small  elevation,  the  bile  papillaj'or 
papilla  major  [papilla  duodeni],  upon  which  open  the  common  bile  duct  and  the 
pancreatic  duct,  either  separately  or  by  a  common  aperture  (fig.  922).  Above 
the  papilla  there  is  usually  a  prominent  hood-like  fold  (valvula  connivens),  and 
below  it  a  variable  fold  or  frcenum  which  forms  a  continuation  of  the  plica  longi- 
tudinahs. About  2  cm.  (.9  to  3.5  cm.,  Baldwin)  above  and  in  front  of  the  bile 
papilla  there  is  a  second,  smaller,  rounded  papilla  minor,  upon  which  the  ac- 
cessory pancreatic  duct  (of  Santorini)  ends. 

The  minute  structure,  vascular  relations,  development,  variations,  etc.,  of  the  duodenum 
will  be  considered  later,  with  those  of  the  small  intestine  as  a  whole. 


THE  JEJUNUM  AND  ILEUM 


1165 


THE  JEJUNUM  AND  ILEUM 

The  mesenteric  portion  of  the  small  intestine  is  divided  into  an  upper  half 
(or  two-fifths) ,  the  jejunum,  and  a  lower  half  (or  three-fifths) ,  the  ileum.  Although 
the  character  of  the  gut  changes  considerably  from  the  upper  end  of  the  jejunum 
to  the  lower  end  of  the  ileum,  the  transition  is  gradual,  and  there  is  no  definite 
line  of  demarcation.  In  general,  the  jejunum  is  somewhat  wider,  has  thicker  walls, 
is  more  vascular  and  has  a  more  complicated  mucosa.  The  lymphoid  organs 
(Peyer's  patches)  are,  however,  characteristic  of  the  ileum. 

The  jejunum  begins  at  the  duodeno-jejunal  flexure.  The  first  coil  is  variable 
in  direction,  being  found  (in  order  of  frequency)  as  follows:  (1)  downward,  for- 
ward and  to  the  left;  (2)  directly  forward  and  downward;  (.3)  to  the  left,  then 
downward;  (4)  forward  and  to  the  right  (Harman).  Some  further  details  as  to 
the  position  of  the  various  succeeding  coils  are  given  later  under  the  development 
of  the  intestine  (figs.  930,  931).  While  there  is  considerable  individual  variation, 
it  is  true  in  general  that  the  coils  of  jejunum  occupy  the  upper  and  left  portion  of 
the  body  cavity,  while  those  of  the  ileuyn  occupy  the  lower  and  right  side,  the  lower 
portion  lying  in  the  pelvic  cavity.  The  ileum  finally  passes  upward  over  the  pel- 
vic brim  to  the  right  iliac  fossa  where  it  terminates  in  the  ileo-csecal  orifice. 

Fig.  924. — Pohtion  of  the  Small.  Intestine,  Laid  open  to  Show  the  Plic.e  Circtj- 
LARBS.     (Brinton.) 


The  mesentery  [mesenterium]  is  a  fan-shaped  fold  extending  from  the  duodeno- 
jejunal flexure  to  the  ileo-csecal  junction.  It  is  composed  of  a  double  layer  of 
peritoneum  which  encloses  and  supports  the  jejunum  and  ileum  and  their  vessels, 
connecting  them  with  the  abdominal  wall.  The  root  of  the  mesentery  [radix 
mesenterii]  or  parietal  attachment,  is  only  about  15  cm.  long,  corresponding  to 
a  line  extending  from  the  duodeno-jejunal  flexure  obliquely  downward  and  to  the 
right,  across  the  transverse  duodenum,  the  great  vessels  and  the  vertebral  column 
to  the  ileo-csecal  junction  (fig.  905). 


The  visceral  attachment  of  the  mesentery  to  the  intestine,  corresponding  to  the  length  of 
the  jejuno-ileum,  is  nearly  7  metres  long,  and  is  thinner  than  at  the  root.  The  loidth  of  the 
mesentery,  measured  from  parietal  to  visceral  attachment,  varies  somewhat  in  different  parts 
of  the  canal,  the  average  being  18  or  20  cm.  (ranging  from  15  to  22.5  cm.).  It  is  narrow  above 
(also  at  the  lower  end),  but  reaches  its  full  width  about  30  cm.  below  its  upper  end.  Between 
the  two  peritoneal  layers  of  the  mesentery  is  a  third  layer  [lamina  mesenterii  propria]  con- 
taining the  superior  mesenteric  vessels  (arteries,  veins  and  lymphatics)  with  their  branches  and 
accompanying  nerves,  the  small  mesenteric  lymph-nodes  (50  to  100  in  number),  and  a  variable 
amount  of  fibro-adipose  connective  tissue. 

Minute  anatomy. — The  small  intestine  has  the  four  typical  layers, — mucosa,  submucosa, 
muscularis  and  serosa  (figs.  927,  928).  They  are,  in  general,  somewhat  similar  in  structure 
to  those  of  the  stomach  (fig.  910),  excepting  the  mucosa. 

The  mucosa  is  lined  with  a  simple  cyhndrical  epithehum,  underneath  which  is  a  fibrous 
lamina  propria,  limited  externally  by  a  muscularis  mucosoe,  as  in  the  stomach.  The  muscularis 
mucosae  sends  slender  muscular  bundles  upward  into  the  villi.  The  inner  surface  of  the  mucosa 
(fig.  924)  presents  numerous  coarse,  closely  set,  transverse  folds  [plicaj  circulares].  These  are 
permanent,  crescentic  folds,  involving  both  mucosa  and  submucosa,  and  usually  extending  one- 
half  to  two-thirds  of  the  way  around  the  lumen.  They  often  branch  and  anastomose,  sometimes 
forming  circles  or  spirals.   The  largest  exceed  5  cm.  in  length  and  3  mm.  in  width.    The  plicae 


1166 


DIGESTIVE  SYSTEM 


circulares  are  absent  from  the  first  part  of  the  duodenum,  but  become  well-marked  in  the  descend- 
ing portion  (fig.  922).  They  are  largest  and  best  developed  in  the  lower  duodenum  and  upper 
half  of  the  jejunum,  below  which  they  graduaUy  become  smaller  (fig.  924)  and  disappear  at  the 
lower  end  of  the  ileum. 

The  digestive  and  absorptive  surface  of  the  small  intestine  is  further  greatly  increased  by 
multitudes  of  small  processes,  the  villi  (figs.  925,  927),  which  give  the  mucosa  a  velvety  appear- 
ance. They  are  largest  (.5  to  .7  mm.  in  height)  and  most  numerous  in  the  duodenum  and 
jejunum,  where  they  are  typically  leaf-shaped,  and  gradually  become  smaller,  scattered  and 
conical  in  the  ileum.  The  villi  are  much  reduced  in  distention  of  the  intestine,  and  may  even 
be  temporarily  obliterated.  Between  the  bases  of  the  vilh  there  open  short,  simple  tubular 
glands — the  crypts  of  Lieberkuehn  [gl.  intestinales],  whose  fundus  cells  (of  Paneth)  probably 
secrete  digestive  enzymes.     In  the  duodenum  there  are  found,  in  addition,  the  larger  tubulo- 

FiG.  925. — A,  Surface  View  op  the  Hardened  Mucosa  op  the  Small  Intestine.  (After 
Kolliker.)  B,  Side  View  of  a  Wax  Reconstruction  op  the  Epithelium  in  the  Human 
Duodenum.     (Huber.)     i  g  ,  Intestmal  gland      v  ,  Villus 


racemose  glands  of  Brunner  [gl.  duodenales],  which  occupy  the  submucosa,  and  are  especially 
numerous  in  the  upper  portion  of  the  duodenum.  They  are  purely  mucous  in  character  ac- 
cording to  Bensley,  although  Oppel  describes  granular  cells,  similar  to  Paneth  cells,  which  may 
secrete  digestive  enzymes. 

Scattered  over  the  whole  of  the  mucous  membrane  of  the  small  intestine  are  numerous 
small  lymph-nodules,  the  larger  of  which  extend  into  the  submucosa;  these  are  the  so-caUed 
solitary  glands  [noduli  lymphatici  solitarii].  Aggregations  of  lymph-nodules,  known  as  Peyer's 
patches  [noduli  lymphatici  aggregati],  situated  in  the  mucosa  and  submucosa,  are  found  in 
the  ileum  especially  toward  the  lower  end  (fig.  926).  They  are  oval,  from  1.2  to  7.5  cm.  in 
length  and  about  1  to  2.5  cm.  in  breadth,  and  are  placed  in  the  long  axis  of  the  bowel  along  a 
line  most  remote  from  the  mesentery.  They  are  variable  in  number,  the  average  being  about 
20  to  30. 


Fig.  926.- 


-SuRF.\CE  View  op  the  Mucosa  op  the  Ileum,  Showing  Aggregated  Lymph 
Nodes  (Peyer's  Patch).     (From  Toldt's  Atlas.) 


Aggregated  lymph  nodes  Solitary  lymph  nodes 

(Peyer's  patch) 


The  submucosa  is  in  general  a  loose  areolar  layer  containing  vascular  and  sympathetic 
plexuses  (figs.  927,  928).  The  muscularis  is  composed  of  smooth  muscle  arranged  in  the  two 
typical  layers, — a  thinner,  outer  longitudinal  and  a  thicker,  inner  circular, — both  of  which 
become  thinner  toward  the  lower  end  of  the  ileum.  The  serosa  is  typical  in  structure,  the 
squamous  epithelial  covering  being  absent  in  the  retroperitoneal  areas  of  the  duodenum. 

Blood-supply  of  the  small  intestine. — The  small  intestine  receives  its  blood  from  the  superior 
mesenteric  artery  and  a  branch  coming  indirectly  from  the  hepatic,  the  superior  pancreatico- 
duodenal. The  superior  mesenteric  artery  runs  between  the  layers  of  the  mesentery  and  gives 
off  six  or  seven  relatively  large  branches  and  a  variable  number  of  smaller  branches.  The 
first  two  or  three  of  the  larger  branches  divide  into  an  ascending  and  a  descending  branch, 
which  join  above  and  below  with  the  corresponding  branches  of  the  continguous  arteries,  form- 
ing thus  a  single  row  of  arches.     From  about  the  beginning  of  the  second  quarter  of  the  small 


THE  JEJUNUM  AND  ILEUM 


1167 


Fig.  927. — Cross-section  op  Ileum  (contracted),  a,  b,  c,  Villi,  d,- Intestinal  gland,  e, 
Tunica  propria.  /,  /.,  Muscularis  mucosa,  g,  Blood-vessel,  h,  Submucosa.  i,  Circular 
muscle,  k,  Longitudinal  muscle.  I,  Serosa,  m,  Subserosa.  n,  Aggregated  lymph  nodules 
(Peyer's  patch).     (Radasch.) 


'^^\ 


^  ^ 

x^.^; 


) 


/I  I 


41       J 


'%— & 


/ 


V 


XJ^     t 


Fig.  928. — Diagrams  op  the  Vascular  Supply  and  Nerves  op  the  Small  Intestine. 

A,  Blood  vessels;  arteries  as  coarse  black  lines,  capillaries  as  fine  Hnes,  veins  shaded  (after.Mall). 

B,  Lymphatics  (after  Mall).  C,  Nerves,  based  on  Golgi preparations  (after  Cajal).  m,  Mucosa. 
mm.,  Muscularis  mucosae,  s.m.,  Submucosa.  cm.,  Circular  muscle,  i.e..  Intermuscular 
connective  tissue.  Z.m.,  Longitudinal  muscle,  s.  Serosa,  c.i.,  Central  lymphatic.  n.,"Nodule. 
s.pl.  Submucous  plexus,     m.pl..  Myenteric  plexus.     (Lewis  and  Stohr.) 


m.m. 
s.m. 


^^^  '■'' 


m.pl,^=Af_  >. 


1168  DIGESTIVE  SYSTEM 

intestine  a  second  tier  of  arches,  formed  in  a  similar  manner,  is  often  noted,  and  below  the  middle 
of  the  jejuno-ileum  more  than  two  tiers  of  arches  may  be  present  the  complexity  of  the  arches 
increasing,  while  the  size  of  the  vessels  diminishes.  From  the  convex  border  of  the  most  dis- 
tally  placed  arches  there  pass  to  the  intestine  straight  branches,  so-called  vasa  recta.  Near  the 
beginning  of  the  jejunum  these  are  numerous  and  large,  and  have  a  length  of  about  4  cm., 
and  are  quite  regular.  After  the  first  third  of  the  intestine  is  passed  the  vasa  recta  become 
smaller  and  shorter,  and  toward  the  lower  end  of  the  ileum  they  become  short  and  irregular 
and  are  often  less  than  1  cm.  in  length.  (Dwight.)  The  blood  is  returned  by  means  of  the 
superior  mesenteric  vein,  which,  with  the  splenic  vein,  forms  the  portal.  The  vascular  ar- 
rangement in  the  intestinal  wall  is  shown  in  fig.  928. 

The  lymphatic  vessels  form  a  continuous  series,  which  is  divided  into  two  sets — viz.,  that 
of  the  mucous  membrane  and  that  of  the  muscular  coat.  The  lymph-vessels  of  both  sets  form 
a  copious  plexus  (fig.  928).  The  efferent  lymphatic  vessels  form  the  so-called  laoteals,  which 
pass  through  the  mesenteric  lymph-nodes,  finally  reaching  the  cisterna  (receptaculum)  chyli. 

The  nerves. — The  small  intestine  is  supplied  by  means  of  the  superior  mesenteric  plexus 
which  is  continuous  with  the  lower  part  of  the  cceUac  (solar)  plexus.  The  branches  follow  the 
blood-vessels,  and  finally  form  two  plexuses:  one  (Auerbach's  or  myenteric)  which  lies  between 
the  muscular  coats;  and  another  (Meissner's)  in  the  submucous  coat.  The  nerve  fibres  are 
chiefly  from  the  sympathetic,  partly  from  the  vagus. 

Development  of  the  small  intestine. — As  the  intestine  is  being  separated  from  the  yolk- 
vesicle  it  forms  at  first  a  relatively  straight  tube,  and  as  the  tube  elongates  there  is  formed  a 
single  primary  loop,  situated  in  the  sagittal  plane  of  the  embryo,  which  loop  extends  into  the 
coelom  of  the  umbilical  cord;  to  its  summit  is  attached  the  constricted  attachment  of  the  yolk- 
vesicle,  the  yolk-stalk  (fig.  929).  This  primary  loop  of  the  intestine,  as  it  elongates,  turns  on 
an  axis,  so  that  its  caudal  portion  turns  toward  the  left  and  its  cephalic  portion  toward  the 
right.  We  may  then  speak  of  a  right  and  a  left  half  of  the  loop.  Near  the  top  of  the  left  half 
of  the  loop,  there  is  noted  an  enlargement  which  marks  the  caecum,  the  greater  part  of  the  left 

Fig.  929. — Model  of  Stomach  and   Intestine  of  Human  Embhyo   19  mm.    Long.     The 
figures  on  the  intestine  indicate  the  primary  coils  (X  16).     (Mall.) 


half  of  the  loop  forming,  therefore,  the  large  intestine,  while  the  right  half  of  the  loop  forms  the 
small  intestine.  In  the  further  growth  of  the  loop  the  right  half  elongates  more  rapidly  than 
the  left  half,  so  that  the  caecum  is  no  longer  found  in  the  middle  of  the  loop.  In  an  embryo 
of  the  fifth  week,  as  noted  by  Mall,  whose  account  is  here  followed  closely,  'the  right  half  of 
the  loop  has  a  number  of  small  bends  in  it,  which  are  of  great  importance  in  the  further  develop- 
ment of  the  intestine.'  These  small  bends  or  loops  he  has  marked  with  the  numbers  1,  2,  3,  4, 
5,  6.  (See  figs.  929,  930,  931.)  The  first  of  these  bends  is  primarily  not  clear,  appearing  as  a 
portion  of  the  pyloric  end  of  the  stomach;  however,  it  is  recognised  by  the  fact  that  the  ducts 
of  the  liver  and  pancreas  terminate  in  it,  marking  it  as  the  duodenum.  The  omphalo-mesenteric 
veins  and  arteries,  the  future  superior  mesenteric  vessels,  pass  through  the  middle  of  the 
mesentery  of  the  large  primary  loop  and  pass  over  the  sixth  bend  or  secondary  loop,  to  which 
is  also  attached  the  yolk-stalk.  With  the  elongation  of  the  intestine  these  six  bends  or  loops 
become  accentuated  and  acquire  secondary  loops  or  coils,  nearly  all  of  which  are  still  found  in 
the  ccelorn  of  the  umbihcal  cord,  but  even  with  this  more  complicated  coiling  of  the  intestine 
the  six  primary  divisions  may  be  clearly  made  out.     (See  fig.  929.) 

The  large  mtestine,  the  left  half  of  the  large  primary  loop,  lies  in  the  sagittal  plane  of  the 
embryo  and  does  not  grow  as  rapidly  as  the  small  intestine,  and  while  this  is  acquiring  the 
secondary  coils,  the  whole  mass  rotates  about  the  large  intestine  as  an  axis.  'By  this  process  the 
small  intestine  is  gradually  turned  from  the  right  to  the  left  side  of  the  body,  and  in  so  doing  is 
rolled  under  the  superior  mesenteric  artery.  This  takes  place  while  the  large  intestine  has  an 
antero-posterior  direction  and  before  there  is  a  transverse  colon.'  (Mall.)  With  the  return 
of  the  small  intestine  from  the  umbilical  coelom  to  the  peritoneal  cavity,  which  occurs  apparently 
quite  suddenly  and  during  the  middle  of  the  fourth  month,  the  caecum  comes  to  lie  in  the  right 
half  of  the  abdominal  cavity,  just  below  the  liver;  the  greater  portion  of  the  remainder  of  the 
large  intestine  then  lies  transversely  across  the  abdominal  cavity  as  the  transverse  colon.  The 
six  groups  of  loops  of  the  small  intestine  may  still  be  recognised,  the  loops  of  the  upper  part 


THE  SMALL  INTESTINE 


1169 


of  the  small  intestine  having  roOed  to  the  left  of  the  superior  mesenteric  artery,  while  the  loops 
which  were  formerly  in  the  cord  are  found  in  the  right  side  of  the  abdominal  cavity.  It  is 
not  difficult  to  trace  these  six  groups  of  loops  through  the  later  stages  of  foetal  life  to  the  new- 
born, and  thence  to  the  adult  stage.  In  the  adult,  as  also  through  the  various  stages  of  develop- 
ment, loop  1  forms  the  duodenum.  From  the  primary  groups  of  coils  marked  2  and  3  are 
developed  the  greater  part  of  the  jejunum,  arranged  in  two  distinct  groups  of  loops,  situated 
in  the  left  hypochondriac  region.  The  part  of  the  intestine  developed  from  group  4  of  the 
primary  coils  passes  across  the  umbilical  region  to  the  right  upper  part  of  the  abdomen.  That 
part  developed  from  group  5  of  the  primary  coils  recrosses  the  median  line  to  the  left  iliac  fossa, 
whUe  that  part  derived  from  group  6  of  the  primary  coils  is  found  in  the  false  pelvis  and  the 
lower  part  of  the  abdominal  cavity  between  the  psoas  muscles.  (Mall.)  Figs.  900,  901,  930 
may  serve  to  make  clear  these  statements.  They  present  what  may  be  regarded  as  the  normal 
arrangement  of  the  small  intestine,  having  been  found  21  times  in  41  cadavers  examined. 
Variations  from  this  arrangement  occur;  the  great  majority  of  such  variations  are,  however, 
not  of  sufficient  importance  to  require  special  mention. 

According  to  Johnson  (upon  whose  descriptions  the  following  account  is  based),  there  is 
in  embryos  of  13  mm.  to  23  mm.  a  formation  of  vacuoles  in  the  duodenal  epithelium,  which 


Fig.  930. — Model  Showing  Course 
OF  Intestine,  Made  phom  Same  Ca- 
daver FROM  WHICH  Fig.  931  was  Drawn. 
(MaU.) 


Fig.  931. — The  Usttal  Position  of  the 
Intestine  in  the  Abdominal  Cavity.  The 
numbers  in  the  figure  mark  the  parts  which  are 
homologous  with  the  primary  bends  and  groups 
of  coils  numbered  from  1  to  6.     (Mall.) 


leads  to  complete  temporary  occlusion  of  the  lumen.  A  persistence  of  this  condition  may  cause 
permanent  atresia.  In  the  epithelium  of  the  small  intestine  numerous  pockets  or  cysts  occur, 
which  usually  disappear,  but  may  persist  and  form  permanent  diverticula  or  accessory  pancreas. 
The  villi  begin  to  appear  at  19  mm.,  first  in  the  mucosa  of  the  upper  portion  of  the  intestine,  as 
localized  outgrowths  which  become  arranged  in  longitudinal  rows.  The  crypts  of  Lieberkuehn 
bud  off  from  the  epithehum  at  55  mm.,  and  from  those  in  the  duodenum,  the  duodenal  (Brun- 
ner's)  glands  begin  to  bud  off  at  78  mm.  The  plicte  circulares  begin  to  appear  at  the  mid- 
region  of  the  small  intestine  at  73  mm.  The  circular  muscle  layer  begins  to  appear  at  about  12 
mm.,  the  longitudinal  at  75  mm. 

Variations  in  the  small  intestine. — Although  relatively  fixed  in  position,  the  duodenum 
is  quite  variable  in  form.  The  C-shape  previously  described  is  the  most  common.  When 
the  pylorus  and  the  duodeno-jejunal  flexure  are  approximated,  the  form  is  nearly  circular. 
When  the  two  ends  are  more  widely  divergent,  it  approaches  a  U-form.  Not  infrequently, 
the  inferior  portion  ascends  abruptly  from  the  inferior  angle,  giving  a  V-form.  Finally,  the 
terminal  ascending  portion  may  be  very  small  or  absent,  in  which  case  the  duodenum  ap- 
proaches an  L-form.  Variations  in  the  position  of  the  various  coils  of  the  jejunum  and  ileum 
have  already  been  discussed.  The  lymph-nodules,  including  Feyer's  patches,  like  all  lym- 
phoid structures,  are  prominent  during  youth,  but  become  atrophied  in  old  age. 

Meckel's  diverticulum,  which  represents  a  derivation  from  the  embryonic  yolk  stalk  and 
sac,  is  found  in  about  2  per  cent,  of  all  adults.     It  is  a  blind  tube  or  diverticulum  of  variable 


1170  DIGESTIVE  SYSTEM 

size,  usually  approaching  the  intestine  in  width  and  averaging  5  cm.  in  length  (ranging  from 
1  cm.  to  13  cm.).  Its  attachment  to  the  intestine  varies  from  15  cm.  to  360  cm.  (average 
80  cm.)  above  the  caecum.  It  is  usually  attached  opposite  the  mesentery.  It  may  end  freely, 
but  is  occasionally  adherent  to  adjacent  intestinal  coils  or  connected  with  the  anterior  abdominal 
wall  by  a  cord  or  band-hke  process. 

Other  diverticula  of  variable  size  and  number  may  occur,  usually  along  the  mesenteric 
border  of  the  intestine.  They  may  be  either  congenital  (probably  from  the  embryonic  pockets 
previously  mentioned)  or  acquired.  They  occur  most  frequently  in  the  duodenum  (found  by 
Baldwin  in  15  of  105  cases)  where  they  are  usually  associated  with  the  openings  of  the  bile  and 
pancreatic  ducts. 

Comparative. — The  comparative  anatomy  of  the  small  intestine  will  be  discussed  later 
together  with  that  of  the  large  intestine. 

THE  LARGE  INTESTINE 

The  large  intestine  [intestinum  crassum]  is  that  part  of  the  alimentary  canal 
which  extends  between  the  ileum  and  the  anus.  It  is  divided  into  the  following 
parts:  Csecum,  ascending,  transverse,  descending,  and  sigmoid  colon,  and  rec- 
tum. It  is  so  arranged  as  to  surround  the  small  intestine,  making  a  circuit  around 
the  abdominal  cavity  from  right  to  left  (fig.  899).  The  caecum  lies  in  the  right 
iliac  fossa;  thence  the  colon  passes  vertically  upward  on  the  right  side  (ascending 
colon)  until  the  liver  is  reached.  Here  it  forms  a  more  or  less  rectangular  bend 
(the  right  colic  or  hepatic  flexure),  and  then  passes  transversely  across  the  belly 
(transverse  colon)  below  the  stomach.  It  then  reaches  the  spleen,  where  it  makes 
a  second  sharp  bend  (the  left  colic  or  splenic  flexure),  and,  passing  vertically  down- 
ward on  the  left  side  (descending  colon),  reaches  the  left  iliac  fossa.  At  this  point 
it  forms  the  loop  of  the  sigmoid  colon,  and  finally  passes  through  the  pelvis  as  the 
rectum  (fig.  906).  The  large  intestine  is  much  larger  in  diameter  than  the  small 
intestine,  and  is  not  so  much  convoluted.  Excepting  the  dilated  portion  of  the 
rectum,  it  is  wider  at  the  beginning  than  at  the  end.  It  varies  in  width  at  different 
parts  from  3  to  8  cm.  The  length  from  the  root  of  the  appendix  or  tip  of  the  cse- 
cum to  the  point  where  the  meso-colon  ends  is,  in  the  male,  about  140  cm.,  and 
in  the  female  about  130  cm.  The  average  total  length,  including  the  rectum,  is 
about  150  cm.  (5  ft.).     The  extremes  found  are  100  to  200  cm. 

The  large  intestine,  in  all  parts  except  the  rectum,  has  a  peculiar  arrangement 
of  its  walls,  which  gives  it  a  very  different  appearance  from  the  small  intestine. 
It  is  sacculated,  and  the  sacculations  [haustra]  are  produced  by  the  gut  having  to 
adapt  its  length  to  three  shorter  muscular  bands  which  run  the  course  of  the  intes- 
tine. These  bands,  which  are  about  12  mm.  wide  and  1  mm.  thick,  aie  really  the 
longitudinal  fibres  of  the  muscular  wall,  which  are  chiefly  collected  along  three 
lines  (fig.  935).  One  band  [taenia  mesocolica],  corresponding  to  the  attachment  of 
the  mesocolon,  is  posterior  on  the  transverse  colon,  and  postero-median  on  the 
ascending  and  descending  colons.  A  second  band  [taenia  omentalis]  is  antero- 
superior  on  the  transverse  colon,  elsewhere  postero-lateral.  The  third  band 
[taenia  libera]  is  free;  it  is  inferior  on  the  transverse  colon,  anterior  elsewhere.  All 
these  bands  start  on  the  caecum  at  the  vermiform  process,  and  spread  out  to  form 
a  uniform  layer  on  the  rectum.  Between  the  sacculations  are  semilunar  folds 
[plicae  semilunares  coli],  which  involve  the  entire  thickness  of  the  intestinal  wall, 
forming  crescentic  ridges  of  the  mucosa  which  project  into  the  lumen  (figs.  932, 
935) .  Along  the  free  surface  of  the  colon,  especially  near  the  taeniae,  are  numerous 
small  appendages  [appendices  epiploicae],  which  are  pouches  of  peritoneum  con- 
taining fat  (fig.  906). 

The  caecum. — The  caecum  [intestinum  caecum]  is  a  cul-de-sac  forming  the  first 
part  of  the  large  intestine.  It  is  defined  as  that  part  of  the  colon  which  is  situated 
below  the  entrance  of  the  ileum.  Its  breadth  is  about  7.5  cm.,  and  its  length 
about  6  cm.    (Fig.  932). 

There  is  usually  a  more  or  less  well-marked  constriction  opposite  the  ileo- 
caecal  orifice  marking  the  boundary  between  caecum  and  colon.  The  caecum  itself 
also  frequently  presents  a  constriction  dividing  it  into  two  sacculations. 

It  lies  in  the  right  iliac  fossa,  and  is  usually  situated  upon  the  iHo-psoas  muscle, 
and  so  placed  that  its  apex  or  lowest  point  is  just  projecting  beyond  the  medial 
border  of  that  muscle  (figs.  899,  906).  It  is  usually  entirely  enveloped  in  periton- 
eum, and  is  free  in  the  abdominal  cavity,  but  more  or  less  attached  in  about  10 
per  cent,  of  all  cases.     The  apex  of  the  caecum  usually  corresponds  to  a  point  a 


THE  LARGE  INTESTINE 


1171 


little  to  the  medial  side  of  the  middle  of  the  inguinal  ligament.  Less  frequently 
the  caecum  will  be  found  to  be  in  relation  with  the  iliacus  muscle  only;  or  the  bulk 
of  it  will  lie  upon  that  muscle,  while  the  apex  rests  upon  the  psoas.  In  a  number  of 
cases  the  caecum  is  entirely  clear  of  both  psoas  and  iliacus  muscles,  and  hangs  over 
the  pelvic  brim,  or  is  lodged  entirely  within  the  pelvic  cavity.  Sometimes  the 
caecum  may  pass  even  to  the  left  of  the  median  line  of  the  body. 
This  part  of  the  colon  is  liable  to  considerable  variation. 

Fig.  932. — Interior  of  the  Caecum,  Anterior  View.     (Rauber-Kopsch.) 


-.-PUcEe  semilunares  coli 


Frenulum  (siaistrum)  valvule  coli 


Frenulum 
(dextrum)  , 
valvulse 
coli 


Ostium  et  valvula  processus  vermiformis 

Its  variations  in  form  may  be  described  under  four  types: 

1.  The  foetal  type  is  conical  in  shape,  the  appendix  arising  from  the  apex,  and  forming  a 
continuation  of  the  long  axis  of  the  colon.  The  three  muscular  bands  which  meet  at  the 
appendix  are  nearly  at  equal  distances  apart  (fig.  933,  A).  When  the  cascum  is  empty  and 
contracted  it  tends  to  approach  this  type. 

2.  The  second  form  is  more  quadrilateral  in  shape  than  the  last;  the  three  bands  retain 
their  relative  positions;  the  appendix  appears  between  two  bulging  saccuU,  instead  of  at  the 
summit  of  a  cone  (fig.  933,  B). 


Fig.  933. — The  Four  Types  op  C^cum. 
A  B  C 


(Treves.) 


3.  In  the  third  type,  that  part  of  the  caecum  lying  to  the  right  side  of  the  anterior  band 
grows  out  of  proportion  to  that  part  to  the  left  of  the  band.  The  anterior  wall  becomes  more 
developed  than  the  posterior,  so  that  the  apex  is  turned  so  much  to  the  left  and  posteriorly 
that  it  nearly  meets  the  ileo-cajcal  junction.  A  false  apex  is  formed  by  the  highly  developed 
part  to  the  right  of  the  anterior  band.     This  is  the  usual  caecum  found  (fig.  933,  C). 


1172 


DIGESTIVE  SYSTEM 


4.  In  the  fourth  type,  the  development  of  the  part  to  the  right  of  the  anterior  band  is 
excessive,  while  the  segment  to  the  left  of  the  band  has  atrophied.  In  this  form  the  anterior 
band  runs  to  the  inferior  angle  of  junction  of  the  ileum  with  the  ciecum.  The  root  of  the 
appendix  is  posterior  to  that  angle.  There  is  no  trace  of  the  original  apex,  and  the  appendix 
appears  to  spring  almost  from  the  ileo-cscal  junction  (fig.  933,  D.) 

The  ileo-csecal  valve. — The  ileo-caecal  valve  [valvula  coli]  is  situated  at  the 
entrance  of  the  ileum  into  the  large  intestine  at  the  upper  border  of  the  caecum, 
on  the  posterior  aspect  and  toward  the  medial  side  (fig.  932).  The  valve  usually 
lies  nearly  opposite  the  middle  of  a  line  from  the  anterior  superior  iliac  spine  (left) 
to  the  umbilicus.  The  ileum  passes  from  below  upward  and  toward  the  right,  and 
terminates  with  a  considerable  degree  of  obliquity.  The  valve  is  formed  by  two 
lip-like  folds  projecting  into  the  large  intestine,  the  upper  [labium  superius], 
and  the  lower  [labium  inferius].  They  are  a  little  oblique.  The  opening  between 
them  takes  the  form  of  a  narrow  transverse  slit  about  1.2  cm.  in  length.  At  the 
ends  of  the  slit  the  valves  unite  and  are  prolonged  at  either  end  as  a  ridge  [frenu- 
lum valvula;  coli]  partially  surrounding  the  intestine. 

Villi  cover  that  surface  of  the  folds  looking  toward  the  ileum;  the  surface  toward  the  large 
intestine  is  free  from  villi.  In  the  formation  of  this  valve  the  longitudinal  muscular  fibres 
pass  across  from  the  ileum  to  the  large  intestine  without  dipping  down  between  the  two  layers 
of  each  fold.  The  circular  muscular  fibres,  on  the  other  hand,  are  contained  between  the 
mucous  and  submucous  layers  which  form  these  folds. 

The  efficiency  of  the  valve  in  preventing  the  return  of  faeces  is  due  largely  to  its  oblique 
position.     (Symington.) 

Fig.  934. — C^ctjm,  Vermiform  Process,  and  End  of  Ileum,  with  the  Blood-supply  and 
THE  Neighbouring  Foss.e.     (Woolsey,  after  Merkel.) 


Sup.  ileo-caec.  fossa 


Plic.  ileocsec.  ant. 

T.V  ,-         imnmim'r^^  \    \    -^£r^     \    >.<///,- 'i e-^^'^biuiimijii  •  i      Inf.  ileo-CffiC.  fossa 

Plica  csecabs HFPIIlii^^^  ^^i^^^r       \'J^,  'lif^  ^^B?/ 

iMesenteriolum 


Subcsecai  fossa 


Ileo-caecal  fossae. — About  the  caecum,  and  especially  in  the  vicinity  of  the  ileo- 
caecal  junction,  are  certain  fossae  collectively  known  as  the  ileo-caecal  fossae.  Two 
only  appear  to  be  fairly  constant,  although  a  third  is  now  and  then  present. 

The  first,  the  superior  ileo-cmcal  or  ileo-colic  fossa,  is  formed  by  the  passage  across  the 
junction  of  the  caecum  and  ileum  of  the  anterior  csecal  artery,  a  branch  of  the  ileo-cohc  artery, 
which  produces  a  fold  of  peritoneum  [plica  ileocolica]  limiting  a  pouch.  It  is  on  the  anterior 
aspect  of  the  ileo-colic  junction,  and  the  pouch  opens  downward  (figs.  906,  934).  It  is  present 
in  about  one-third  of  all  cases. 

The  second  fossa  is  not  quite  so  simple.  If  the  caecum  be  turned  upward  so  as  to  expose 
its  posterior  surface  as  it  lies  in  situ,  and  if  the  appendix  be  drawn  down  so  as  to  put  its  mesentery 
on  the  stretch,  a  peculiar  fold  will  be  found  to  join  that  mesentery  (fig.  934).  This  fold  arises 
from  the  border  of  the  ileum  opposite  the  insertion  of  its  mesentery.  It  then  passes  over  the 
ileo-caecal  jimction  on  its  inferior  aspect,  is  adherent  to  the  caecum,  and  finaUy  joins  the  surface 
of  the  mesentery  of  the  appendix.  This  fold  is  peculiar  in  the  absence  of  any  visible  vessels, 
and  is  often  known  as  the  'bloodless  fold  of  Treves.'  Between  it  and  the  appendix  there  is  an 
almost  constant  fossa,  the  inferior  ileo-eoeeal  fossa.  It  is  usually  large,  admitting  two  fingers, 
and  occurs  in  nearly  85  per  cent,  of  all  cases.  It  is  bounded  on  one  side  by  the  smaU  intestine, 
and  on  the  other  by  the  ctecum.     The  appendix  is  occasionally  found  in  the  fossa. 

The  subciecal  or  retrocolic  fossa  is  behind  the  caecum  and  is  found  in  about  ten  per  cent,  of 
aU  cases.  It  may  extend  for  some  distance  behind  the  ascending  colon.  The  appendix  may  be 
lodged  in  this  fossa. 

ParaccBcal  fossse  rarely  occur,  at  the  side  of  the  caecum. 

Variqtions. — In  addition  to  variations  already  mentioned  the  caecum  may  vary  in  its  general 


i 


THE  LARGE  INTESTINE 


1173 


development.  It  is  sometimes  small  and  insignificant;  in  other  cases  it  reaches  a  large  size. 
It  may  be  so  rotated  that  the  ileum  passes  behind  the  colon  and  opens  on  the  right  side.  The 
posterior  part  has  been  seen  much  more  developed  than  the  anterior,  so  that  the  ileum  has 
entered  from  the  front,  and  the  appendix  has  come  off  from  the  anterior  wall.  The  c^cum 
may  remain  undescended,  and  be  found  just  under  the  liver  or  in  the  vicinity  of  the  umbihcus. 
In  case  the  rotation  of  the  embryonic  intestinal  loop  fails  to  occur  (which  rarely  happens) 
the  csecum  may  remain  permanently  upon  the  right  side.  If  the  normal  process  of  adhesion 
fails  to  occur,  the  caecum  and  colon,  along  with  the  small  intestine,  may  remain  suspended  from 
the  mid-dorsal  line  by  the  primitive  mesenleriuw.  commune.  Or  any  of  the  intermediate  stages 
of  partial  adhesion  may  persist. 

The  vermiform  process. — Attached  to  what  was  originally  the  apex  of  the 
caecum  is  a  narrow,  blind  tube,  the  vermiform  process  [processus  vermiformis]  or 
appendix.  It  comes  off  at  a  variable  distance  (usually  about  2.5  cm.)  below  the 
ileo-csecal  valve  on  the  postero-medial  aspect  of  the  csecum,  though  sometimes 
from  the  lower  end  of  the  caecum,  or  elsewhere.  On  the  interior,  at  the  point 
where  it  joins  the  caecum  (fig.  932),  there  is  a  sUght  inconstant  valve  [valvula  pro- 
cessus vermiformis].     The  appendix  joins  the  caecum  at  the  point  where  the  three 

Fig.  9.35. — Cross-section  of  the  Ascending  Colon.     (Allen  Thomson.) 

Crescentic  ridge  of  mucous  mem- 
brane which  divides  the  sacculi      Longitudinal  muscle 


Tsenia  libera 
Mucous  membrane' 


Circular  muscle 


Appendix  epiploica' 


'Tsnia  mesocolica 
Mucous  membrane 


Tffinia  omeatalis        Circular 


taeniae  meet,  and  the  anterior  taenia  forms  the  best  guide  to  this  point.  In  the 
adult,  the  average  length  of  the  appendix  is  between  8  cm.  and  10  cm.,  the  extremes 
being  2  cm.  to  25  cm.  It  is  usually  much  twisted  and  coiled  upon  itself.  Its  direc- 
tion is  most  frequently  downward  toward  the  pelvic  cavity,  or  upward  and  medial- 
ward  behind  the  ileum  in  the  direction  of  the  spleen.  It  occasionally  turns  lateral- 
ward,  or  more  rarely  upward  behind  the  caecum. 

The  vermiform  process  does  not  have  a  true  mesentery,  but  usually  (in  about 
90  per  cent,  of  cases)  is  provided  with  a  falciform  fold  [mesenteriolum]  of  periton- 
eum, continuous  with  the  left  (lower)  layer  of  the  mesentery  of  the  ileum  (figs. 
906,  934). 

In  general  outline  this  fold  of  peritoneum  is  triangular.  In  the  adult  it  does  not  extend 
along  the  whole  length  of  the  tube.  It  is,  in  fact,  too  short  for  the  appendix,  and  it  is  this 
that  accounts  for  the  twisted  condition  of  this  process.  Along  the  free  margin  of  the  fold  runs 
a  branch  of  the  ileo-coUc  artery  (fig.  934). 

The  ascending  colon. — The  ascending  colon  [colon  ascendens]  (figs.  906,  914) 
extends  in  the  right  lumbar  (lateral  abdominal)  region  from  the  caecum  to  the  infe- 
rior surface  of  the  liver,  lateral  to  the  gall-bladder,  forming  there  the  right  colic 
[flexura  coli  dextra]  or  hepatic  flexure.  Its  average  length  is  about  20  cm.  (or 
somewhat  less  when  measured  in  site).  It  is  covered  by  peritoneum  in  front  and 
on  the  side  (fig.  902),  but  in  a  certain  proportion  of  cases  (26  per  cent,  according 
to  Treves)  this  part  of  the  large  intestine  is  connected  with  the  posterior  wall  of 
the  abdomen  by  a  meso-colon  (usually  very  short)  and  is  therefore  surrounded  by 
peritoneum.     Connected  with  the  ascending  colon  is  sometimes  found  a  fold  'of 


1174  DIGESTIVE  SYSTEM 

peritoneum,  extending  from  the  right  side  of  the  gut  to  the  abdominal  wall  at  a 
little  above  the  level  of  the  highest  part  of  the  iUac  crest.  It  forms  a  shelf  upon 
which  rests  the  extreme  right  margin  of  the  liver.  It  might  be  called  the  susten- 
taculum hepatis. 

The  ascending  colon  is  in  relation  behind  with  the  right  kidney,  and  the  iliacus 
and  quadratus  lumborum.  In  front  are  some  of  the  coils  of  the  ileum  (fig.  899), 
separating  it  from  the  anterior  abdominal  wall. 

The  transverse  colon. — The  transverse  colon  [colon  transversum],  smaller  in 
diameter  than  the  ascending,  extends  from  the  lower  surface  of  the  liver  to  the 
spleen.  Its  average  length  is  from  40  to  50  cm.  It  describes  an  arch  with  its 
convexity  forward  and  downward.  It  crosses  through  the  umbilical  region  from 
the  right  hypochondrium  to  the  left  hypochondrium  (figs.  899,  906,  914). 

In  the  majority  of  cases  the  superficial  part  of  the  colic  arch — as  seen  before 
the  viscera  are  disturbed — is  either  in  whole  or  in  greater  part  above  a  straight 
line  drawn  transversely  across  the  body  between  the  highest  points  of  the  iliac 
crest.  In  about  one-fourth  of  all  cases  it  lies,  in  whole  or  in  greater  part,  below 
this  line. 

Certain  remarkable  bends  are  sometimes  formed  by  this  part  of  the  bowel. 
The  bending  is  always  in  the  same  direction,  namely,  downward,  and  is  usually 
abrupt  and  angular.  The  apex  of  the  V  or  U-shaped  bend  thus  formed  may  reach 
the  pubes.  This  bend  appears  to  be  due  to  two  distinct  causes:  namely,  long- 
continued  distention,  on  the  one  hand,  and  congenital  malformation  on  the  other. 

The  transverse  colon  is  in  relation  above  with  the  liver  and  gall-bladder,  the 
stomach,  and  at  its  left  extremity  with  the  spleen.  The  second  portion  of  the 
duodenum  passes  behind  it.  Below  are  the  coils  of  the  small  intestine.  It  is 
almost  completely  surrounded  by  peritoneum,  being  connected  with  the  posterior 
abdominal  wall  (chiefly  the  anterior  border  of  the  pancreas)  by  the  transverse  mes- 
ocolon. This  is  usually  lacking  on  the  right  of  the  mid-line,  however,  where  the 
colon  crosses  the  descending  duodenum  and  the  head  of  the  pancreas  (fig.  905). 

The  descending  colon  [colon  descendens]  is  25  cm.  to  30  cm.  in  length  (less 
when  in  situ)  and  extends  from  the  spleen  to  the  pelvic  brim  (figs.  906,  914).  It 
is  more  movable  than  the  ascending  colon  and  is  also  narrower.  At  its  beginning 
it  is  usually  connected  with  the  diaphragm,  on  a  level  with  the  tenth  and  eleventh 
ribs,  by  a  fold  of  peritoneum,  the  phreno-colic  ligament  [lig.  phrenicocolicum] 
(or  sustentaculum  lienis,  from  the  fact  that  it  supports  the  spleen).  The  bend 
between  the  transverse  colon  and  descending  colon  is  called  the  left  colic  or  splenic 
flexure  [flexura  coli  sinistra].  The  descending  colon  is  situated  in  the  left  hypo- 
chondriac, lumbar  and  iliac  regions  (fig.  906).  Its  relations  to  the  peritoneum 
are  the  same  as  obtain  with  the  ascending  colon,  that  is,  it  is  covered  in  front  and 
on  the  sides.  A  mesocolon  is  met  with  oftener  on  this  side  than  on  the  light, 
occurring  in  36  per  cent,  of  all  cases  (Treves)  (see  fig.  902).  It  is  found  especially 
in  the  lower  part  of  the  descending  colon,  in  the  iliac  fossa.  This  portion,  extend- 
ing from  the  iliac  crest  to  the  brim  fsuperior  aperture)  of  the  pelvis,  is  sometimes 
described  as  a  separate  segment,  the  iliac  colon  (Jonnesco). 

The  descending  colon  is  covered  anteriorly  by  coils  of  small  intestine;  pos- 
teriorly it  is  in  contact  with  the  lower  part  of  the  left  kidney,  the  quadi  atus  lum- 
borum, iliacus  and  psoas  muscles.  It  terminates  by  crossing  medialward  over  the 
psoas  muscle  and  the  external  iliac  vessels  to  join  the  sigmoid  colon. 

The  sigmoid  colon  [colon  sigmoideum]  or  pelvic  colon,  extends  from  the 
descending  colon  to  the  rectum  (figs.  906,  914).  It  includes  what  was  formerly 
described  as  the  'sigmoid  flexure'  and  also  the  'first  portion'  of  the  rectum. 
These  together  form  a  single  loop  which  cannot  conveniently  be  divided  into  parts. 

The  loop,  the  sigmoid  colon,  begins  at  the  margin  of  the  psoas,  and  ends  where 
the  sigmoid  mesocolon  ceases,  opposite  the  second  or  third  sacral  vertebra. 

The  loop  when  unfolded  describes  a  figure  that  may  be  compared  to  the  capital 
omega.  The  average  length  of  this  sigmoid  colon  is  about  40  cm.  The  normal 
position  of  the  loop  is  not  in  the  left  iliac  fossa,  but  wholly  in  the  pelvis.  The  most 
common  disposition  of  it  may  now  be  described.  The  sigmoid  (pelvic)  colon 
begins  about  midway  between  the  lumbo-sacral  eminence  and  the  inguinal 
(Poupart's)  ligament.  It  descends  at  first  along  the  left  pelvic  wall,  and  may  at 
once  reach  the  pelvic  floor.  It  then  passes  more  or  less  horizontally  and  trans- 
versely across  the  pelvis  from  left  to  right,  and  commonly  comes  into  contact  with 
the  right  pelvic  wall.     At  this  point  it  is  bent  upon  itself,  and,  passing  once  more 


i 


THE  LARGE  INTESTINE 


1175 


toward  the  left,  reaches  the  middle  line  and  joins  the  rectum.  It  will  lie,  there- 
fore, in  more  or  less  direct  contact  with  the  bladder  (and  uterus  in  the  female), 
and  may  possibly  touch  the  caecum.  It  is  very  closely  related  with  the  coils  of 
small  intestine  that  occupy  the  pelvis,  and  by  these  coils  the  loop  is  usually  hid- 
den. In  about  90  per  cent,  of  cases,  the  sigmoid  colon  lies  entirely  within  the 
true  pelvic  cavity.  In  the  remainder,  it  loops  upward  for  a  variable  distance 
toward  the  umbilicus,  a  position  normally  found  in  infancy. 

Fig.  936. — Interior  op  the  Rectum.     (X  §•)     (From  Toldt's  Atlas.) 

Jl ■—  „,,^ 

Solitary  lymph  nodes 
Tunica  mucosa 

Tunica    f     Longitudi- 

laris  Circular 

'^"^       [ ,         layer 


Pars  analis  recti 


Rectal  sinuses 

Sphincter  ani  extemus 
Sphincter  ani  internus 


The  sigmoid  colon  is  attached  to  the  abdominal  and  pelvic  wall  by  the  sigmoid  mesocolon, 
so  that  it  is  quite  surrounded  by  peritoneum.  The  line  of  attachment  of  this  mesocolon  is 
as  follows :  It  usually  crosses  the  psoas  in  a  slight  cm've  upward  so  as  to  pass  over  the  iliac  vessels 
at  or  about  their  bifurcation.  The  curve  ends  at  a  point  either  just  to  the  medial  side  of  the 
psoas  muscle,  or  between  the  psoas  and  the  middle  line,  or,  as  is  most  frequently  the  case,  just 
over  the  bifurcation  of  the  vessels.     From  this  point  the  line  of  attachment  proceeds  vertically 


Fig.  937.- 


-MID-SAGITT.4.L  Section  of  the  Male  Pelvis. 


(Xi).     (Braune.) 


Bladder 

Symphysis  pubis. 
Urethral  bulb 


Recto-vesicaJ  pouch 
Rectum 

Transverse  fold 
Vesicula  seminalis 

■Ductus  ejaculatorius 

Prostate 

External  sphincter  ani 
^Internal  sphincter  ani 

.External  sphincter  ani 


down,  taking  at  first  a  slight  curve  to  the  right.  Its  course  is  to  the  left  of  the  middle  line, 
while  its  ending  will  be  upon  that  line,  about  the  second  or  third  sacral  vertebra.  The  sig- 
moid mesocolon  measures  from  3  to  8.7  cm.  in  width — i.  e.,  from  the  parietes  to  the  bowel, — 
at  the  widest  point. 

When  a  descending  mesocolon  exists,  it  joins  that  of  the  sigmoid  colon.  There  is  often 
no  mesocolon  over  the  psoas,  the  gut  being  adherent  to  that  muscle.  In  connection  with  the 
sigmoid  mesocolon  is  often  found  a  fossa  or  pouch  of  peritoneum,  known  as  the  intersigtnoid 
fossa  [reeessus  intersigmoideus].     This  pouch  is  formed  by  the  incomplete  adhesion  of  the 


1176 


DIGESTIVE  SYSTEM 


primitive  mesocolon  to  the  posterior  abdominal  wall.  It  is  generally  found  over  the  bifui- 
cation  of  the  iUao  vessels.  The  pouch  is  funnel-shaped,  and  the  opening  looks  downward  and 
to  the  left.     It  varies  in  depth  from  2.5  to  3.7  cm.,  and  is  rarely  the  seat  of  the  sigmoid  hernia. 

The  rectum. — The  rectum,  according  to  the  BNA  nomenclature,  is  recognised 
as  a  division  separate  from  the  large  intestine.  The  term  rectum  is  now  limited 
to  that  portion  of  the  bowel  below  the  mid-sacral  region,  where  the  mesocolon 
ceases.  It  is  divided  into  two  portions:  the  first  extends  downward  and  forward, 
in  front  of  sacrum  and  coccyx,  to  the  level  of  the  pelvic  floor ;  the  second  portion 
(the  anal  canal)  extends  from  this  point  downward  and  backward  to  the  anus 
(figs.  937,  938). 


Fig.  938. — Mid-sagittal  Section  of  the  Female  Pelvis.     (Spalteholz.) 

Hypogastric  artery 
/     Hypogastric  vein 
'  InJundibulum  of  tuba  uterina 


Suspensory  ligament  of  ovary 


External  iliac  vein 
Ovary 


Ampulla  of  tuba  uterina 
Ovarian  ligament 
Fundus  uteri       \ 

Ligamentum  teres         \ 
Transverse  fold  of      *■  ^ 

bladder  .> 

Vertex  of  bladder  ^     \        ^ 
Middle  umbilical 
ligament 


Parietal  peritoneum 

uteri 
Recto-uterine  fold 


,     Recto-uter- 
\  /  ine  (recto- 
vaginal) pouch 


TJrachus 
Symphysis  pubis 

Labium  majus 
Body  of  uterus 
Labium  minus 

External  orifice  of  urethra 

Urethra'     , 
Internal  orifie  of  urethra      / 
Orifice  of  vagina 


Rectum 
Posterior  labium 
External  os  uteri 
Anterior  labium 


Anus 
Vagina 

'  Vesico-uterine  pouch 

Vestibule 


The  upper  or  first  portion  of  the  rectum  is  about  10  cm.  long,  and  is  concave 
forward  [fiexura  sacralis]  except  at  the  lower  end  where  it  curves  backward  and 
downward  [flexura  perinealis]  to  join  the  second  portion.  The  lower  part  of  the 
first  portion  often  presents  a  dilation  [ampulla  recti],  due  to  accumulation  of 
faeces.  This  part  is  sometimes  described  as  the  infra-peritoneal  portion  of  the 
rectum  proper. 

Anteriorly,  the  rectum  is  in  contact  with  coils  of  ileum  and,  in  the  male,  with  the  trigone  of 
the  bladder,  the  vesiculse  seminales,  ductus  deferentes,  and  posterior  aspect  of  the  prostate  (fig. 
937).  In  the  female,  it  is  in  contact  anteriorly  with  the  vagina  and  the  cervix  uteri  (fig.  938). 
Posteriorly,  it  is  in  contact  with  the  sacrum,  coccyx  and  ano-coccygeal  body. 

In  the  male,  a  small  band  of  muscle  fibres,  the  recio-urethral  muscle,  extends  from  the  per- 
ineal flexure  of  the  rectum  to  the  membranous  urethra. 


THE  RECTUM  1177 

The  peritoneum  is  reflected  anteriorly  from  the  rectum  to  the  bladder  in  the 
male  (recto-vesical  pouch)  and  to  fornix  of  the  vagina  in  the  female  (recto-vaginal 
pouch).  In  the  newborn,  the  peritoneum  reaches  to  the  base  of  the  prostate 
(Symington).  On  the  posterior  surface  of  the  gut,  there  is  no  peritoneum  below 
a  point  about  12.5  cm.  from  the  anus.  Thus  the  peritoneum  at  the  upper  end  of 
the  rectum  entirely  surrounds  the  gut.  Lower  down  it  covers  only  the  sides  and 
anterior  wall,  and  lower  still  the  anterior  wall  only,  where  it  is  reflected  upon  the 
bladder  or  vagina. 

The  second  portion  of  the  rectum,  or  anal  canal  [pars  analis  recti]  is  from  2.5 
cm.  to  3.5  cm.  in  length.  From  the  lower  end  of  the  first  portion,  it  turns  at  right 
angles  downward  and  backward,  passing  through  the  pelvic  floor,  and  ending  at 
the  anus.  It  is  entirely  below  the  peritoneum,  and  is  surrounded  by  the  two 
sphincter  muscles  (figs.  936,  937). 

Anteriorly  is  the  bulb  of  the  urethra  and  the  posterior  margin  of  the  urogenital  trigone  in 
the  male  (fig.  937),  while  in  the  female  it  is  separated  from  the  vestibule  and  the  lower  part  of 
the  vagina  by  the  'perineal  body'  (fig.  938).  Posteriorly  it  is  connected  with  the  tip  of  the 
coccyx  by  the  ano-coccygeal  body.  Laterally  it  is  in  contact  with  the  margins  of  the  levatores 
ani,  which  act  as  an  acoessory_  sphincter,  and  help  to  support  the  ampulla  recti. 

The  anus. — The  anus  is  the  aperture  by  which  the  intestine  opens  externally. 
During  life  it  is  contracted  by  the  sphincters,  so  as  to  give  the  surrounding  skin 
a  wrinkled  appearance.  Around  the  lower  part  of  the  rectum  and  anus  certain 
muscles  that  are  connected  with  its  proper  function  are  situated.  They  are  the 
internal  sphincter,  the  levator  ani,  and  the  external  sphincter.  The  levator  ani 
and  external  sphincter  will  be  found  described  in  the  section  on  Musculature. 
The  internal  sphincter  is  a  thickening  of  the  circular  fibres  of  the  intestine,  situated 
around  the  second  portion  or  anal  canal.  It  forms  a  complete  muscular  ring,  2  to 
3  mm.  thick,  and  is  composed  of  non-striated  muscle. 

The  rectum  differs  from  the  rest  of  the  colon  in  having  smoother  walls  and  no 
appendices  epiploicse.  At  the  upper  end  of  the  rectum,  the  taenia  libera  and  taenia 
omentalis  join  to  form  a  broad  band  which  spreads  out,  covering  the  entire  anter- 
ior aspect  of  the  rectum.  Similarly  the  taenia  mesocolica  spreads  out  upon  the 
posterior  aspect.  Thus  the  rectum  has  a  complete  longitudinal  muscle  layer, 
which,  however,  is  thicker  anteriorly  and  posteriorly  than  laterally.  It  sends  a 
bundle  of  fibres  to  the  coccyx  [m.  recto-coccygeus].  Below,  the  longitudinal  layer 
passes  between  the  two  sphincters  and  breaks  up  into  numerous  bundles  which  are 
interwoven  with  the  external  sphincter  and  levator  ani,  some  of  them  terminating 
in  the  circumanal  skin. 

Its  mucous  membrane  is  thicker  than  that  of  the  rest  of  the  large  intestine.  Certain 
folds,  chiefly  longitudinal  in  direction,  are  seen  in  the  lax  state  of  the  tube,  which  disappear 
when  distended,  but  Houston  had  described  three  permanent  oblique  transverse  folds  [plicae 
transversales  recti]  (fig.  936),  containing  bundles  of  non-striated  muscle-cells,  which  project 
into  the  lumen  of  the  tube:  one  is  on  the  right  at  the  level  of  the  reflection  of  the  peritoneum 
from  the  rectum;  and  two  are  on  the  left,  one  above  and  one  below  the  right  fold.  That  upon 
the  right  side  is  the  largest  and  most  constant,  and  its  muscular  bundle  is  sometimes  called 
the  sphincter  tertius.  It  is  located  about  7.5  cm.  above  the  anus.  These  folds,  like  the  corre- 
sponding semilunar  folds  of  the  colon,  when  well  marked  involve  the  entire  wall. 

The  mucous  membrane  of  the  upper  portion  of  the  anal  canal  presents  a  series  of  vertical 
folds  known  as  rectal  columns  [columnae  rectales]  (columns  of  Morgagni),  containing  bundles 
of  non-striated  muscle  longitudinally  arranged.  These  columns  become  more  prominent  as 
they  extend  downward.  Just  above  the  anus  each  two  adjacent  columns  are  united  by  an 
arch-hke  fold  of  mucous  membrane,  these  folds  forming  what  are  known  as  the  anal  valves, 
while  the  small  fossse  behind  them  are  known  as  the  rectal  sinuses.  The  area  below  the  valves 
and  extending  to  the  anus  is  termed  the  annulus  hcemorrhoidalis  (fig.  936).  This  is  lined  by  a 
modified  skin,  while  the  area  above  the  valves  forms  a  transition  to  the  typical  mucosa  of  the 
rectum. 

Minute  structure  of  the  large  intestine. — In  general,  the  large  intestine  has  the  four  coats 
(fig.  939) — mucosa,  submucosa,  muscularis,  and  serosa — characteristic  of  the  alimentary 
canal.  The  mucosa  lacks  the  villi  and  plicae  circulares  characteristic  of  the  small  intestine. 
It  contains  many  solitary  lymphatic  nodules,  but  no  Peyer's  patches.  It  differs  from  the 
stomach  in  the  absence  of  foveolse,  and  in  the  presence  of  large  numbers  of  mucous  'goblet 
cells'  found  both  on  the  surface  and  along  the  numerous  crypts  of  Lieberkuehn  (which  con- 
tain no  cells  of  Paneth).  The  subrnucosa  is  much  as  in  the  small  intestine.  The  muscularis 
has  a  continuous  inner  circular  layer,  the  outer  longitudinal  fibres  being  chiefly  gathered  into 
the  three  bands,  the  teniae  coh,  as  above  mentioned.  The  serosa  is  typical,  excepting  extra- 
peritoneal areas  where  the  epithehum  is  lacking.  The  appendices  epiploicae  were  also  mentioned 
above. 

The  caecum  and  colon  present  no  special  features  worthy  of  mention,  beyond  the  typical 
structure  above  outlined. 


1178 


DIGESTIVE  SYSTEM 


The  vermiform  process,  however,  differs  in  several  important  respects  (fig.  940).  The 
walls  are  relatively  thick  and  the  lumen  small.  The  solitary  lymph  nodules  are  closely  packed 
or  confluent  (especially  in  young  people).  They  occupy  the  greater  part  of  the  sub  mucosa, 
and  somewhat  resemble  the  Payer's  patches  of  the  ileum.     They,  like  all  the  lymphoid  structures 

Fig.  939. — Cross-section  of  the  Large  Intestine,     a,  Mucosa.     6,  Submucosa.     c,  Mus- 
cularis.     d,  Serosa.     (Radasch.) 


in  general,  tend  to  become  atrophied  in  old  age.  Fat  cells  are  usually  abundant  in  the  sub- 
mucosa. The  muscularis  presents  an  inner  circular  layer  and  also  a  thin  but  complete  outer 
longitudinal  layer.  The  serosa  is  typical.  The  lumen  shows  a  progressive  tendency  to  ob- 
literation as  age  advances  (Ribbert).     This  condition  is  never  found  in  infancy  but  occurs 

Fig.  940. — Transverse  Section  of  the  Human  Vermiform  Process.  (X  20).  (Stohr 
and  Lewis,  from  Sobotta.)  Note  absence  of  villi  and  abundance  of  lymph  nodules.  F,  Clusters 
of  fat  cells  in  submucosa.     Only  the  inner  part  of  the  circular  muscle  is  shown. 


usually  only  partial)  in  over  25  per  cent,  of  adults  and  in  50  per  cent,  of  all  cases  over  50  years 
of  age.  It  is,  however,  somewhat  uncertain  whether  this  represents  a  normal  process.  In 
obliteration,  the  glands  and  lymphoid  nodules  disappear,  and  the  entire  mucosa  is  transformed 
into  an  axial  mass  of  fibrous  connective  tissue. 

The  rectum  also  presents  several  peculiarities  of  structure.     Attention  has  already  been 


/ 


THE  LARGE  INTESTINE  1179 

called  to  the  transverse  folds  (of  Houston)  and  the  rectal  columns,  sinuses  and  valves.  Just 
above  the  valves,  the  mucosa  is  transitional,  the  epithelium  being  partly  stratified,  and  the 
crypts  of  Lieberkuehn  few  and  scattering.  Below  the  valves,  the  annulus  hEemorrhoidalis  is 
lined  by  a  modified  slcin.  Hairs  and  sebaceous  and  sweat  glands  do  not  appear  until  just 
outside  the  anal  orifice.  The  thickening  of  the  circular  muscle  to  form  the  internal  sphincter, 
and  the  somewhat  uniform  disposition  of  the  longitudinal  muscle  have  already  been  mentioned, 
as  well  as  the  absence  of  a  serous  coat  in  the  lower  portions. 

Blood-vessels. — The  large  intestine  is  supplied  with  blood  by  the  branches  of  the  superior 
mesenteric  and  inferior  mesenteric  arteries,  while  it  also  receives  a  blood-supply  from  the 
internal  iliac  at  the  rectum.  The  vessels  form  a  continuous  series  of  arches  from  the  caecum, 
where  the  vasa  intestini  tenuis  anastomose  with  the  ileo-colic,  the  first  branch  of  the  superior 
mesenteric  given  to  the  large  intestine. 

The  blood-supply  of  the  rectum  is  from  the  inferior  mesenteric  by  the  superior  ha^morrhoidal, 
from  the  hypogastric  (internal  ihac)  by  the  middle  haemorrhoidal,  and  from  the  internal  pudic 
by  the  inferior  hEemorrhoidal.  The  vessels  at  the  lower  end  of  the  rectum  assume  a  longitudinal 
direction,  communicating  freely  near  the  anus,  and  less  freely  above. 

The  blood  of  the  large  intestine  is  returned  into  the  portal  vein  by  means  of  the  superior 
mesenteric  and  inferior  mesenteric  veins.  At  the  rectum  a  communication  is  set  up  between 
the  systemic  and  portal  system  of  veins,  since  some  of  the  blood  of  that  part  of  the  intestine  is 
returned  into  the  hypogastric  (internal  ihac)  veins.  In  the  lower  end  of  the  rectum  the  veins, 
like  the  arteries,  are  arranged  longitudinally.  This  arrangement  is  called  the  haemorrhoidal 
plexus. 

The  vermiform  process  is  supphed  by  a  special  branch  of  the  ileo-colic  artery  (fig.  934). 
This  branch,  the  appendicular  artery,  crosses  behind  the  terminal  portion  of  the  ileum  (where 
pressure  may  obstruct  the  circulation)  to  enter  the  mesenteriolum.  An  accessory  artery  of 
small  size  also  descends  along  the  medial  margin  of  the  colon  and  caecum,  entering  the  base  of 
the  appendix. 

The  nerves  and  lymphatics  of  the  large  intestine  differ  in  no  important  particular  from  those 
of  the  small  intestine,  so  far  as  their  relations  within  the  intestinal  wall  are  concerned. 

The  efferent  lymphatic  vessels  in  general  follow  the  blood-vessels  and  pass  through  cor- 
responding lymph  nodes  in  the  various  regions  (see  p.  734).  Those  of  the  caecum  and  vermi- 
form process  pass  through  the  appendicular  and  ileo-caecal  nodes;  those  of  the  colon  through 
mesocolic  and  mesenteric  nodes.  Those  of  the  descending  and  sigmoid  colons  connect  with 
the  inferior  mesenteric  and  lumbar  nodes.  The  superior  zone  of  the  rectum  is  drained  by 
lymphatics  passing  to  the  ano-rectal  and  inferior  mesenteric  nodes;  the  middle  zone  (region  of 
rectal  columns)  to  nodes  along  the  three  haemorrhoidal  arteries;  the  inferior  zone  (anal  in- 
tegument) chiefly  to  the  superficial  inguinal  nodes. 

Development  of  the  large  intestine. — At  an  early  stage  in  the  development  of  the  intestinal . 
canal,  when  this  presents  a  single  primary  loop  and  soon  after  this  loop  has  turned  on  its  axis, 
there  is  observed  on  the  left  half  of  the  loop,  near  its  top,  an  enlargement  which  marks  the  be- 
ginning of  the  large  intestine.  With  further  growth  this  enlargement  develops  a  lateral  out- 
growth on  the  side  opposite  to  that  to  which  the  mesentery  is  attached,  therefore  free  from  the 
mesentery.  A  conical  projection  of  the  large  intestine  or  colon  beyond  the  place  where  this  is 
joined  to  the  small  intestine  is  thus  formed.  This  conical  projection  or  pouch  of  the  large  in- 
testine, which  continues  the  colon  somewhat  beyond  the  insertion  of  the  small  intestine,  develops 
into  the  caecum  and  the  vermiform  process.  It  does  not  present,  in  its  further  growth,  a  uniform 
enlargement.  The  portion  nearest  the  colon  grows  in  size  more  rapidly  than  the  terminal  por- 
tion, this  difference  in  size  becoming  more  apparent  as  development  proceeds,  the  smaller 
terminal  portion  forming  the  vermiform  process.  On  the  return  of  the  intestine  to  the  peritoneal 
cavity  (in  embryos  of  about  40  mm.)  the  csecum  lies  on  the  right  side,  immediately  below  the 
liver.  During  the  later  fcetal  months  the  caecum  gradually  descends  into  the  right  iliac  fossa, 
and  there  is  thus  established  an  ascending  colon.  The  caecum  may,  however,  even  in  the  adult, 
retain  its  embryonic  position  on  the  right  side  immediately  beneath  the  liver,  or  may  descend 
farther  than  usual. 

The  ascending  and  descending  colons,  the  sigmoid  meso-colon  (in  part),  and  the  rectum 
with  corresponding  portions  of  the  mesorectum,  become  adherent  to  the  posterior  body  wall 
during  the  fourth  and  fifth  fcetal  months.  At  the  same  time,  the  posterior  layer  of  the  great 
omentum  becomes  fused  with  the  upper  (anterior)  surface  of  the  transverse  meso-colon.  The 
layer  of  retroperitoneal  fascia  corresponding  to  the  obliterated  mesocolon  is  shown  in  fig.  1005. 
Variations  in  the  process  of  fusion  give  rise  to  numerous  peritoneal  variations  in  the  adult. 

The  sigmoid  colon  is  relatively  long  at  birth.  On  account  of  the  relatively  small  size  of  the 
true  pelvic  cavity,  both  sigmoid  colon  and  coils  of  ileum  are  usually  excluded  from  it  in  the 
foetus  and  infant. 

In  fcetuses  of  four  to  six  months  (length  100  mm.  to  240  mm.)  transitory  viUi  appear  in 
the  mucosa  throughout  the  large  intestine,  including  the  vermiform  process.  They  appear 
in  rows,  corresponding  to  longitudinal  folds.  Their  early  obliteration  is  possibly  due  to  dis- 
tention of  the  gut  by  the  meconium.-'  The  glands  bud  off  like  those  of  the  small  intestine. 
Lymphoid  nodules  are  present  abundantly  in  the  vermiform  process  at  birth  (Johnson).  The 
circular  muscular  layer  begins  to  appear  in  the  lower  part  of  the  large  intestine  at  23  mm.; 
the  tenia  at  75  to  99  mm.     (F.  T.  Lewis). 

Development  of  the  rectum  and  anus. — The  posterior  end  of  the  primitive  intestine  or  arch- 
enteron,  designated  the  hind-gut,  presents  a  terminal  portion  which  is  somewhat  dilated  and 
known  as  the  cloaca,  into  the  lateral  and  ventral  portions  of  which  open  the  Wolffian  ducts, 
and  from  the  ventral  portion  of  which  arises  the  allantois.  The  ventral  portion  of  the  cloaca, 
which  is  an  entodermal  structure,  comes  in  contact  with  the  ectoderm  to  form  the  cloacal 
membrane,  and  this  forms  the  floor  of  a  slight  depression.  For  a  time  the  cloaca  or  hind-gut 
extends  for  some  distance  caudal  to  the  cloacal  membrane,  forming  what  is  known  as  the  post 
anal  gut;  this,  however,  soon  disappears.     Early  in  the  development  of  the  human  embryo 


1180  DIGESTIVE  SYSTEM 

when  this  has  attained  a  length  of  about  6.5  mm.,  the  fold  which  separates  the  cloaca  and  hind, 
gut  from  the  allantois  deepens,  and  folds  develop  from  the  lateral  walls  of  the  cloaca  which  meet 
and  gradually  separate  the  cloaca  into  a  dorsal  portion,  which  forms  the  rectum,  and  a  ventral 
portion  which  forms  the  uro-genital  sinus.  This  uro-rectal  septum  extends  in  its  further  growth 
until  the  cloacal  membrane  is  reached,  separating  it  into  a  ventral  portion  known  as  the  uro- 
genital membrane,  and  a  dorsal  portion  known  as  the  anal  membrane.  The  anal  membrane 
ruptures  comparatively  late  in  development,  establishing  thus  a  communication  between  the 
hind-gut  (rectum)  and  the  exterior.  The  mesoderm  develops  around  the  lower  end  of  the 
rectum,  so  that  the  ectoderm  becomes  slightly  invaginated  and  hnes  the  portion  of  the  anal 
canal  below  the  valves.  A  want  of  ruptui-e  of  the  anal  membrane  constitutes  an  arrest  of  devel- 
opment known  as  atresia  of  the  anus. 

Folds  of  the  mucosa  representing  the  rectal  columns,  valves  and  sinuses  appear  in  embryos 
during  the  third  month,  and  are  well  developed  during  the  latter  half  of  the  foetal  period 
(Johnson). 

Variations. — The  large  intestine  is  exceedingly  variable  in  its  structure  and  relations, 
especiaUy  with  reference  to  the  peritoneum — so  much  so  that  it  has  been  found  more  convenient 
to  include  a  consideration  of  the  variations  along  with  the  preceding  description  of  the  individual 
parts.  The  content  of  faeces  (and  gas)  is  as  a  rule  relatively  greatest  in  the  csecum,  decreasing 
in  ascending  and  transverse  colons.  The  descending  colon  is  usually  empty,  or  nearly  so,  the 
sigmoid  colon  and  rectum  somewhat  variable.  The  rectal  ampulla  is  usually  more  dilated  in 
women. 

Comparative. — The  morphology  of  both  small  and  large  intestines  will  be  briefly  considered 
here.  As  previously  mentioned,  the  primitive  form  of  intestine  is  a  comparatively  straight 
tube  extending  from  stomach  to  anus,  and  connected  by  a  primitive  mesentery  to  the  mid- 
dorsal  line  of  the  body  cavity.  There  is  in  many  of  the  lower  forms  no  clear  division  into  small 
and  large  intestine,  though  the  rectal  region  is  usually  more  dilated,  and  opens  into  a  cloaca. 
Diverticula  often  occur  in  the  region  between  large  and  small  intestine.  In  many  fishes, 
numerous  "caeca"  occur  just  below  the  pylorus,  and  in  others  an  extensive  spiral  valve  projects 
into  the  lumen  of  the  intestine.  The  absorptive  and  digestive  surface  of  the  mucosa  is  further 
increased  by  the  formation  of  various  kinds  of  folds,  and  (beginning  in  amphibia)  of  villi. 
Lymphoid  tissue  is  typically  present  in  the  mucosa,  often  locaUzed  in  definite  masses.  Solitary 
nodules  appear  in  amphibia,  and  Peyer's  patches  in  birds.  Tubular  mucous  glands  occur  in 
the  lower  forms,  but  Brunner's  glands  and  crypts  of  Lieberkuehn  with  Paneth  cells  apparently 
only  in  mammals.  A  cmcum  is  usually  present  from  the  reptiles  upward  (double  in  birds), 
and  often  forms  an  important  organ  of  digestion.  The  bile  and  pancreatic  ducts  open  constantly 
a  short  distance  below  the  pylorus.  The  small  intestine  is  always  longer  than  the  large,  but 
there  is  extreme  variation  in  length  among  the  various  species.  The  four  tunics — mucosa, 
submucosa,  muscularis  and  serosa — are  tjqDical  for  vertebrates,  the  muscularis  consisting  of 
inner  circular  and  outer  longitudinal  smooth  muscle  fibres. 

Among  mammals,  the  divisions  of  the  intestine  correspond  in  general  to  those  found  in 
the  human  species,  but  there  is  exceedingly  great  variation  in  the  relative  development  of  the 
various  parts.  In  general,  the  length,  size  and  complexity  of  structure  is  relatively  greatest 
in  the  herbivora  (whose  food  is  more  difficult  of  digestion),  least  in  the  carnivora,  and  intermediate 
in  the  omnivora.  Even  in  the  same  species,  the  structure  of  the  intestine  may  be  appreciably 
modified  according  to  habitual  diet.  The  large  intestine  varies,  but  is  always  shorter  and  wider 
than  the  small  intestine.  In  mammals  the  rectum  only  is  said  to  be  homologous  with  the  large 
intestine  of  lower  vertebrates.  The  cmcum  is  rarely  absent  and  is  enormously  developed  in 
herbivora.  It  often  contains  large  amounts  of  Ij'mphoid  tissue,  which,  in  pig  and  ox  forms  a 
so-called  'intestinal  tonsil. '  The  vermiform  process  (found  typically  developed  in  man  and 
higher  anthropoids)  apparently  represents  a  retrogressive  evolutionary  change  in  the  cffical 
apex,  although  this  interpretation  is  denied  by  some  (Berry),  who  interpret  the  appendix  as  a 
progressive,  functional  lymphoid  organ. 

THE  LIVER 

The  liver  [hepar]  is  tiie  largest  gland  in  the  body.  Its  secretion,  the  bile  [bills ; 
fel],  is  poured  into  the  duodenum  through  the  common  bile  duct.  In  addition  it 
has  important  functions  as  a  'ductless  gland'  in  connection  with  the  nitrogenous 
and  carbohydrate  metabolism.  In  form  it  is  a  variable  somewhat  irregular  mass, 
roughly  comparable  to  a  modified  hemisphere  occupying  the  upper  right  portion  of 
the  abdominal  cavity  (figs.  899,  914).  It  presents  a  convex,  rounded  upper  or 
parietal  aspect,  which  is  in  contact  with  the  diaphragm  and  adjacent  body  walls, 
and  a  lower,  flattened  visceral  surface,  in  contact  with  the  abdominal  viscera. 
When  viewed  from  the  front,  it  is  somewhat  triangular  in  outline,  occupying  the 
right  hypochondriac,  the  epigastric  and  (slightly)  the  left  hypochondriac  regions. 

Physical  characters. — In  weight,  the  liver  averages  about  1500  gm.  (3|  lbs.), 
but  it  is  exceedingly  variable,  commonly  ranging  from  1000  gm.  to  2000  gm.  Its 
relative  weight  is  also  variable,  averaging  about  2.5  per  cent,  of  the  body  in  the 
adult  male  (somewhat  higher  in  the  female).  Its  specific  gravity  averages  1.056, 
so  that  the  average  weight  of  1500  gm.  would  correspond  to  a  volume  of  1420  cc. 
Its  dimensions  are  also  quite  variable.  Its  greatest  depth  (antero-posterior) 
averages  about  15  cm.,  and  its  greatest  height  (vertical)  is  about  the  same.     Its 


THE  LIVER 


1181 


width  (horizontal)  is  about  20  cm.,  while  its  greatest  length  (measured  obliquely 
from  side  to  side)  averages  about  25  cm.  The  colour  of  the  liver  is  a  reddish- 
brown.     It  is  firm  in  consistency,  but  friable,  so  that  it  is  easily  ruptured. 

Surfaces  and  borders. — The  most  general  division  of  the  surface  of  the  liver, 

Fig.  941  — Superior  Surface  op  the  Liver. 


Site  of  the  caudate  (Spigelian)  lobe 


as  above  stated,  is  into  two — the  parietal  and  the  visceral.     The  parietal  surface 
is  again  subdivided,  usually  into  two  surfaces — posterior  and  superior. 

The  posterior  surface  [facies  posterior]  is  triangular  (fig.  943).     It  is  wide  on 
the  right,  where  the  right  lobe  is  in  contact  with  the  diaphragm  (corresponding 


Fig.  942. — Inferior  Surface  of  the  Liver. 

Vena  cava  inferior 


Common  bile-duct 
Portal 
Hepatic  artery 
Caudate  (Spigelian)  lobe 


Umbilical  fissure 


chiefly  to  the  'uncovered  area'  of  the  coronary  ligament),  and  narrow  on  the 
left  side,  where  the  posterior  margin  of  the  left  lobe  is  likewise  attached  to  the  dia- 
phragm. At  the  lower,  left  hand  corner  of  the  right  lobe  is  a  small  triangular  area 
of  contact  with  the  suprarenal  body  [impressio  suprarenalis].     Near  the  mid-line 


1182 


DIGESTIVE  SYSTEM 


is  the  caudate  (Spigelian)  lobe,  opposite  the  tenth  and  eleventh  thoracic  vertebral 
bodies,  from  which  it  is  separated  by  the  diaphragm  (chiefly  the  right  crus). 
On  the  right  of  the  caudate  lobe  is  the  fossa  lodging  the  vena  cava  (sometimes 
bridged  over),  while  to  the  left  is  the  fissure  of  the  ductus  venosus,  giving  attach- 
ment to  the  upper  portion  of  the  lesser  omentum  (relations  in  cross-section  shown 
in  fig.  945). 

The  superior  surface  [facies  superior]  is  in  general  convex  and  moulded  to  the 
inferior  surface  of  the  diaphragm  (fig.  941).     Tne  relations  in  cross-section  of  the 


Fig.  943.- 


-PosTEEioE  Surface  of  the  Livdr. 

Vena  cava  inferior 


Tuber  omentale 


Papillary  process  of  caudate  (Spigelian)  lobe 

Impression  for  right  kidney 


body  are  shown  in  fig.  945.  It  extends  downward  upon  the  anterior  abdominal 
wall  to  a  variable  extent  in  the  epigastric  region,  including  the  entire  area  of  the 
liver  visible  from  the  front  (fig.  941).  It  also  presents  a  broad  area  extending 
downward  on  the  right  side.  Symington  accordingly  distinguishes  three  surfaces 
corresponding  to  the  superior  surface  above  described,  viz.,  right  surface,  anterior 
surface  and  superior  surface.  The  superior  surface  is  related  above,  through  the 
diaphragm,  with  the  base  of  the  right  lung,  the  pericardium  and  heart,  and  (on 
the  extreme  left)  with  the  base  of  the  left  lung.  Where  it  rests  upon  the  liver, 
the  heart  forms  a  shallow  fossa  [impressio  cardiaca]. 

Fig.  944. — Diagram  Showing  Ligaments  on  the  Dorso-inferior  Aspect  of  the 
LrvER.  (Lewis  and  Stohr.)  c.l.,  Coronary  lig.  f.l.  Falciform  lig.  g.b.,  Gall  bladder,  l.o., 
Lesser  omentum,  l.t.l.,  Left  triangular  lig.  o.b.,  Caudate  lobe,  p.v.,  Portal  vein,  r.l.,  Lig. 
teres,     r.t.l.,  Right  triangular  lig.     v.c.i.,  Vena  cava  inf. 


.Itl 


The  inferior  or  visceral  stxrface  [facies  inferior]  (fig.  942)  faces  downward  and 
backward.  It  is  irregularly  concave,  with  impressions  due  to  contact  with  the 
underlying  viscera.  It  is  divided  into  three  lobes,  right,  left,  and  quadrate,  whose 
relations  will  be  described  later. 

Of  the  borders,  the  anterior  [margo  anterior]  is  the  best  marked.  It  forms  the 
inferior  boundary  of  the  triangular  anterior  view  of  the  liver  (figs.  899,  914,  941), 
and  separates  the  superior  from  the  inferior  surface.  Slightly  to  the  left  of  the 
mid-line,  it  often  presents  a  slight  umbilical  notch  [incisura  umbilicalis],  where  it 


THE  LIVER 


1183 


is  crossed  by  the  falciform  ligament.  The  posterior  surface  is  separated  from  the 
superior  and  inferior  surfaces  by  ill-defined  postero-superior  and  postero-inferior 
borders. 

Surface  outline. — The  average  position  of  the  hver  may  be  outlined  upon  the  anterior 
surface  of  the  body  as  follows  (fig.  914):  Locate  one  point  on  the  right  mid-clavicular  (mid- 
Poupart)  line  opposite  the  fifth  rib;  a  second  point  on  the  left  mid-clavicular  line  about  2  cm. 
lower,  in  the  fifth  interspace;  and  a  third  point  about  2  cm.  below  the  costal  arch  (10th  rib) 
on  the  right  lateral  wall.  A  line  slightly  concave  upward,  joining  the  first  and  second  points 
defines  the  uppermost  aspect  of  the  lever.  A  line,  strongly  convex  laterally,  joining  the  first 
and  third  points,  defines  the  right  side  of  the  liver.  Finally,  a  third  line,  joining  the  second  and 
third  points,  corresponds  to  the  anterior  border  and  defines  the  lowermost  portion  of  the  liver. 
This  line  is  subject  to  many  individual  variations.  In  general,  it  is  usually  slightly  convex 
downward  as  it  crosses  the  epigastric  region.  It  usually  presents  a  slight  umbilical  notch,  as 
before  mentioned,  and  frequently  a  notch  for  the  fundus  of  the  gall-bladder,  which  is  placed  near 
the  right  mammarj'  (mid-Poupart)  line.  The  lower  and  right  portion  of  the  anterior  border  of 
the  liver  runs  somewhat  parallel  with  the  infracostal  margin.  In  the  upright  position,  and  in 
livers  larger  than  usual,  it  extends  about  2  cm.  below  the  hypochondrium  into  the  right  lateral 
abdominal  (lumbar)  region  (fig.  914).  In  the  supine  position,  however,  the  liver  recedes  about 
2  cm.  toward  the  head.  The  liver  of  course  participates  also  in  the  respiratory  movements  of 
the  diaphragm. 


Fig.  945.- 


-Ceoss-section  of  Body  at  Level  op  the  Eleventh  Thoracic  Vertebra. 
(Poirier-Charpy.) 
Caudate  lobe  of  liver 
Suprarenal  gl. 
Vena  cava  inf.  1  I  Aorta 


Spleen 


Falciform  lig. 


Lobes  and  fissures. — The  superior  surface  is  divided  by  the  falciform  ligament 
into  two  areas,  corresponding  to  a  larger  right  and  a  smaller  left  lobe  (fig.  941). 
On  the  posterior  and  inferior  surfaces  of  the  liver  (figs.  942,  943),  an  H-shaped 
arrangement  of  fossae  and  fissures  completes  the  demarcation  of  lobes.  The  left 
upright  of  the  H  [fossa  sagittalis  sinistra]  corresponds  to  the  prolongation  of  the 
line  of  attachment  of  the  falciform  ligament.  It  is  made  up  of  the  umbilical 
fissure  [fossa  venae  umbilicalis],  containing  the  round  ligament,  on  the  inferior 
surface;  and  of  the  fossa  ductus  venosi,  containing  the  ligamentum  venosum 
(obliterated  ductus  venosus)  and  the  upper  part  of  the  lesser  omentum,  on  the 
posterior  surface  of  the  liver.  This  left  sagittal  fossa  separates  the  left  lobe  of  the 
liver  from  the  right  lobe  (in  the  wider  sense  of  the  term).  The  right  lobe  is  further 
subdivided  by  the  right  upright  and  cross-bar  of  the  H.  The  right  upright  [fossae 
sagittales  dextrae]  is  made  up  of  the  broad  fossa  for  the  gall-bladder  [fossa  vesicae 
felleae]  on  the  inferior  surface,  and  the  broad  fossa  vence  cavce  on  the  posterior  sur- 
face (fig.  943.  These  two  fossae  are  not  continuous,  but  are  separated  by  a  narrow 
strip  of  liver,  the  caudate  process  of  the  caudate  lobe  (fig.  942).  The  cross-bar 
of  the  H  is  formed  by  the  transverse  or  portal  fissure  [porta  hepatis],  which  encloses 
the  root  structures  of  the  liver,  within  the  lower  part  of  the  lesser  omentum  (fig. 
942).     The  area  anterior  to  the  cross-bar  of  the  H  corresponds  to  the  quadrate 


1184  DIGESTIVE  SYSTEM 

lobe  of  the  inferior  surface;  that  posterior  to  the  cross-bar  to  the  caudate  lobe  of 
the  posterior  surface;  while  the  remainder  of  the  liver,  to  the  right  of  the  H,  is 
the  right  lobe  (in  the  narrower  sense). 

The  right  lobe  [lobus  hepatis  dexter]  makes  up  the  greater  part  of  the  hver.  Its  relations 
on  the  superior  and  posterior  surfaces  have  already  been  mentioned.  On  the  inferior  or  visceral 
surface  (fig.  942),  there  appears  posteriorly  a  large  concavity  [impressio  renalis]  for  the  right 
kidney;  medially  a  faint  impression  [impressio  duodenalis]  for  the  descending  duodenum;  and 
antero-inferiorly  a  variable  area  [impressio  coHca]  of  contact  with  the  right  (hepatic)  flexure 
of  the  colon.     The  caudate  process  joins  the  right  with  the  caudate  lobe. 

The  left  lobe  [lobus  hepatis  sinister]  lies  to  the  left  of  the  left  sagittal  fissure  and  the  falci- 
form ligament.  It  is  flattened  but  variable  in  form  and  size,  and  makes  only  about  one-fifth 
of  the  entire  liver.  In  children  and  especially  in  early  foetal  life,  it  is  relatively  much  larger. 
At  the  left  extremity,  there  is  usually  found  in  the  adult  liver  a  variable  fibrous  band  [appendix 
fibrosa  hepatis]  representing  the  atrophied  remnant  of  the  more  extensive  gland  in  earlier  life. 
In  this  fibrous  appendix  (and  in  other  parts  of  the  liver)  the  bile  ducts  of  the  atrophied  liver 
substance  persist  as  vasa  aberrantia  hepatis. 

The  left  lobe  is  related  superiorly,  through  the  diaphragm,  with  the  heart  and  the  base  of 
the  left  lung.  Injeriorly  (fig.  942)  it  presents  a  large  concavity  [impressio  gastrioa]  which  is 
in  contact  with  the  anterior  surface  of  the  stomach.  Above  and  behind  the  gastric  impression 
is  the  rounded  tuber  omentale  which  is  placed  above  the  lesser  curvature  of  the  stomach  and  re- 
lated, through  the  lesser  omentum,  with  a  corresponding  tuberosity  on  the  pancreas.  To  the 
left  of  the  tuber  omentale,  and  near  the  posterior  aspect  of  the  liver,  is  a  small  inconspicuous 
groove  [impressio  cesophagea]  for  the  abdominal  part  of  the  oesophagus. 

The  quadrate  lobe  [lobus  quadratus]  lies,  as  before  mentioned,  on  the  inferior  surface  of 
the  liver  (fig.  942)  in  the  anterior  or  inferior  area  of  the  H.  It  is  in  contact  with  the  pylorus 
and  the  first  part  of  the  duodenum. 

Pig.  946. — Relation  op  STBucTtrRBs  at  and  Below  the  Teansvekse  or  Portal 
PissuHE.     Anteioe  view.     (Thane.) 


Common  bile-duct- 


The  caudate  or  Spigelian  lobe  [lobus  caudatus;  SpigeU]  was  described  on  the  posterior  sur- 
face of  the  liver  (fig.  943).  Inferiorly,  the  caudate  lobe,  behind  the  portal  fissure,  is  divided 
by  a  notch  into  two  processes.  The  left  or  papillary  process  [processus  papillaris]  is  short  and 
rounded,  and  lies  opposite  the  tuber  omentale.  In  the  fcetus  it  is  relatively  much  larger  and  ia 
in  contact  with  the  pancreas.  The  right  or  caudate  process  [processus  caudatus]  is  of  variable 
size,  and  joins  the  caudate  with  the  right  lobe  of  the  hver.  It  is  usually  small  and  inconspicuous. 
In  the  foetus,  however,  it  is  relatively  much  larger,  and  extends  downward  to  a  variable  extent 
behind  the  duodenum  and  head  of  the  pancreas.  In  the  adult,  it  forms  the  upper  boundary  of 
the  epiploic  foramen  (of  Winslow). 

Peritoneal  relations. — -The  liver  in  the  adult  is  almost  entirely  surrounded  by 
peritoneum.  Although  it  develops  together  with  the  diaphragm  in  the  common 
septum  transversum  (as  explained  previously,  see  figs.  951,952),  the  peritoneum 
soon  extends  in  between  liver  and  diaphragm,  so  that  they  remain  in  immediate 
contact  only  in  the  so-called  'uncovered  area.'  This  is  an  irregular  area  on  the 
posterior  surface  of  the  liver  (chiefly  on  the  right  lobe),  the  margins  of  which  cor- 
respond to  the  coronary  ligament  (figs.  905,  944).  The  posterior  surface  of  the 
liver  is  therefore  chiefly  retroperitoneal,  excepting  the  caudate  (Spigelian)  lobe, 
which  is  in  contact  with  the  recessus  superior  of  the  bursa  omentalis  (fig.  905). 
The  superior  and  inferior  surfaces  of  the  liver  are  entirely  covered  with  peritoneum, 
excepting  the  lines  of  attachment  of  the  various  peritoneal  ligaments,  and  the 
fossa  for  the  gall-bladder,  which  is  usually  directly  in  contact  with  the  gall  blad- 
der with  no  intervening  peritoneum. 

Ligaments. — The  liver  is  attached  by  five  peritoneal  ligaments — coronary, 
right  and  left  triangular  (lateral)  and  falciform  ligaments  and  lesser  omentum—" 
and  two  accessory  ligaments — teres  and  venosum. 

The  coronary  ligament  [lig.  coronarium  hepatis],  as  before  mentioned,  corre- 


THE  LIVER  1185 

sponds  to  the  reflections  of  peritoneum  from  the  liver  to  the  diaphragm  at  the  mar- 
gins of  the  'uncovered  area'  (fig.  944)  on  the  posterior  surface  of  the  liver. 

Within  this  uncovered  area  the  hepatic  veins  join  the  inferior  vena  cava.  The  coronary 
ligament,  though  somewhat  irregular  and  variable  in  form,  is  elongated  laterally  and  roughly 
quadrangular.  At  the  four  angles,  the  peritoneal  layers  come  together  and  are  prolonged  into 
four  ligaments — right  and  left  triangular  (lateral)  and  falciform  hgaments  and  lesser  omentum. 
There  is  often  also  a  special  prolongation  of  the  coronary  ligament  downward  upon  the  right 
kidney,  forming  the  hepato-renal  ligament  [lig.  hepatorenale].  This  lies  to  the  right  of  the  fora- 
men epiploicum. 

The  right  triangular  (or  lateral)  ligament  [hg.  triangulare  dextrum]  is  a  short  but  variable 
prolongation  of  the  coronary  ligament  to  the  right  and  downward  (figs.  905,  944) .  It  connects 
the  posterior  surface  of  the  right  lobe  of  the  liver  with  the  corresponding  portion  of  the  diaphragm. 

The  left  triangular  (lateral)  ligament  [lig.  triangulare  sinistrum]  is  a  longer,  narrower  pro- 
longation of  the  coronary  ligament  to  the  left  (figs.  905,  944).  It  connects  the  posterior  as- 
pect of  the  left  lobe  of  the  hver  with  the  corresponding  portion  of  the  diaphragm. 

The  falciform  ligament  [lig.  falciforme  hepatis]  is  a  double  layer  of  peritoneum 
representing  (as  before  mentioned)  the  ventral  portion  of  the  primitive  ventral 
mesogastrium. 

Its  upper  end  is  continuous  posteriorly  with  the  coronary  ligament.  It  passes  forward 
and  downward  over  the  superior  surface  of  the  liver.  From  its  line  of  attachment  to  the  liver 
(between  right  and  left  lobes)  it  passes  forward  and  slightly  to  the  left  to  the  attachment  on  the 
anterior  body  wall.  This  attachment  extends  downward  slightly  to  the  right  of  the  mid-line 
to  the  umbilicus.  The  lower  margin  of  the  falciform  ligament  is  free,  and  encloses  the  roimd 
ligament. 

The  round  ligament  [lig.  teres  hepatis]  is  a  fibrous  cord  representing  the  obliter- 
ated foetal  left  umbilical  vein.  It  extends  upward  from  the  umbilicus  enclosed  in 
the  lower  margin  of  the  falciform  ligament. 

At  the  anterior  margin  of  the  liver  it  passes  backward  on  the  inferior  surface,  enclosed  in  a 
slight  peritoneal  fold  at  the  bottom  of  the  fossa  vense  umbilicalis  (sometimes  bridged  over  by 
liver  tissue).     It  ends  by  joining  the  left  branch  of  the  portal  vein. 

The  ligamentum  venosum  [lig.  venosum;  Arantii]  similarly  represents  the  obliterated  fcetal 
ductus  venosus.  It  is  a  fibrous  cord  lying  in  the  fossa  ductus  venosi,  and  e.xtends  from  the  left 
branch  of  the  portal  vein  upward  to  the  left  hepatic  vein  near  its  opening  into  the  vena  cava. 
The  ligamentum  venosum  lies  within  the  hepatic  attachment  of  the  lesser  omentum. 

The  lesser  omentum  [omentum  minus]  has  already  been  discussed  in  connec- 
tion with  the  peritoneum.  It  represents  the  dorsal  part  of  the  primitive  ventral 
mesogastrium,  extending  from  the  stomach  to  the  liver.  It  includes  two  parts,  as 
shown  in  fig.  906. 

The  upper  and  larger  part  forms  the  gasiro-hepalic  ligament  [lig.  hepato-gastricum],  connect- 
ing the  liver  (fossa  ductus  venosi)  with  the  lesser  curvature  of  the  stomach.  The  upper  part 
of  this  ligament  is  somewhat  thicker,  the  lower  part  thinner  and  more  transparent.  The  rela- 
tions of  the  lesser  omentum  in  cross-section  of  the  body  are  shown  in  fig.  903.  The  lower  and 
right  portion  of  the  lesser  omentum  extends  beyond  the  pylorus  and  connects  the  portal  fissure 
with  the  duodenum,  forming  the  hepalo-duodenal  ligament  [lig.  hepatoduodenale]  (fig.  905). 
Its  right  margin  forms  the  anterior  boundary  of  the  epiploic  foramen  (of  Winslow).  Between 
its  layers  are  located  the  root  structures  of  the  hver,  as  follows:  hepatic  artery  to  the  left, 
common  bile  duct  to  the  right,  portal  vein  behind  and  between.  A  special  prolongation  of  the 
hepato-duodenal  ligament  frequently  extends  downward  to  the  transverse  colon,  forming  the 
hepato-colic  ligament  [lig.  hepatocoHcum]. 

Fixation  of  the  liver. — The  liver  is  to  a  certain  extent  fixed  in  place  by  means  of 
its  various  ligaments,  and  especially  through  the  attachment  of  the  hepatic  veins 
to  the  inferior  vena  cava.  On  account  of  the  close  apposition  of  the  liver  to  the 
diaphragm,  the  atmospheric  pressure  also  helps  in  its  support.  Finally,  the  sup- 
port of  the  liver,  as  well  as  of  the  abdominal  viscera  in  general,  is  dependent  to  a 
considerable  extent  upon  the  tonic  contraction  of  the  abdominal  muscles,  which 
exerts  a  constant  pressure  upon  the  abdominal  contents. 

Blood-vessels. — The  liver  receives  its  arterial  supply  of  blood  from  the  hepatic  artery,  a 
branch  of  the  coeliac,  which  passes  up  between  the  two  layers  of  the  lesser  omentum,  and 
dividing  into  two  branches,  one  for  each  lobe,  enters  the  liver  at  the  portal  fissure.  The  right 
branch  gives  off  a  branch  to  the  gall-bladder.  The  liver  receives  a  much  larger  supply  of  blood 
from  the  portal  vein,  which  conveys  to  the  liver  blood  from  the  stomach,  intestines,  pancreas, 
and  spleen.  It  enters  the  portal  fissure,  and  there  divides  into  two  branches.  Below  this 
fissure  the  hepatic  artery  lies  to  the  left,  the  bile-duct  to  the  right,  and  the  portal  vein  behind  and 
between  the  two  (fig.  946).  These  three  structures  ascend  to  the  liver  between  the  layers  of 
the  lesser  omentum  in  front  of  the  epiploic  foramen.  At  the  actual  fissure  the  order  of  the  three 
structures  from  before  backward  is — duct,  artery,  vein. 


1186  DIGESTIVE  SYSTEM 

The  hepatic  veins,  by  which  the  blood  of  the  hver  passes  into  the  inferior  vena  cava,  open 
usually  by  two  large  and  several  small  openings  into  that  vessel  on  the  posterior  surface  of  the 
gland  at  the  bottom  of  the  fossa  venae  cavoe. 

Lymphatics. — The  lymphatics  are  divided  into  a  deep  and  a  superficial  set.  The  deep  set 
runs  with  the  branches  of  the  portal  vein,  artery,  and  duct  through  the  liver,  leaving  at  the  portal 
fissure,  where  they  join  the  vessels  of  the  superficial  set.  The  efferent  deep  vessels  after  leaving 
the  portal  fissure  pass  down  in  the  lesser  omentum  in  front  of  the  portal  vein,  through  the  chain 
of  hepatic  lymphatic  nodes,  and  ultimately  end  in  a  group  of  nodes  at  the  upper  border  of  the 
neck  of  the  pancreas,  in  which  the  pyloric  lymphatics  also  terminate. 

The  superficial  set  begins  in  the  subperitoneal  tissue.  Those  of  the  upper  surface  consist: — 
(1)  Of  vessels  which  pass  up,  principally,  in  the  falciform  ligament  and  right  and  left  triangular 
ligaments,  through  the  diaphragm,  and  so  into  the  anterior  mediastinal  nodes,  and  finally 
into  the  right  lymphatic  duct.  Some  lymphatics  of  the  right  triangular  ligament  pass  to  the 
posterior  mediastinal  lymph-nodes  and  into  the  thoracic  duct.  (2)  Of  a  set  passing  downward 
over  the  anterior  border  of  the  liver  to  the  hepatic  nodes  in  the  portal  fissure,  and  over  the  pos- 
terior surface  to  reach  the  superior  gastric  and  coeliac  nodes.  On  the  lower  surface,  the  lym- 
phatics to  the  right  of  the  gall-bladder  enter  the  lumbar  nodes.  Those  around  the  gall-bladder 
enter  the  hepatic  nodes  of  the  lesser  omentum.  Those  to  the  left  of  the  gall-bladder  enter  the 
superior  gastric  nodes. 

Nerves. — The  nerves  of  the  liver  are  derived  from  the  vagi  (those  from  the  left  vagus 
entering  from  the  stomach  through  the  lesser  omentum),  and  from  the  coehac  plexus  of  the 
sympathetic  (including  right  vagus  branches)  through  a  plexus  accompanying  the  hepatic 
artery.  The  terminations,  so  far  as  known,  are  chiefly  to  the  walls  of  the  vessels  and  of  the  bile 
ducts. 

Structure  of  the  liver. — The  liver  is,  for  the  greater  part,  covered  by  peritoneum,  beneath 
which  is  found  the  fibro-elastio  layer  known  as  Glisson's  capsule.  At  the  portal  fissure,  Ghsson's 
capsule  passes  into  the  substance  of  the  liver,  accompanying  the  portal  vessels,  the  branches  of 
the  hepatic  artery,  and  the  bile-ducts.  The  hver  substance  is  composed  of  vascular  units 
measuring  from  1  to  2  mm.,  and  Icnown  as  hver  lobules.     These  are  in  part  (man)  separated  by 

Fig.  947. — Section  of  a  Portal  Canal.     (Quain.) 


Branch  of  porl'al  vein 


I  I  -^ Lymphatics  in  Glisson's  capsule 

Lymphatics  in  Glisson's  capsule  -r^^  I 

-Branch  of  hepatic  artery 


a  small  amount  of  interlobular  connective  tissue,  which  is  a  continuation  of  Ghsson's  capsule. 
In  this  interlobular  connective  tissue  are  found  the  terminal  branches  of  the  portal  vessels; 
the  hepatic  artery,  and  the  bile-ducts  (figs.  947,  948).  The  branches  of  the  portal  vessels  which 
encircle  the  liver  lobules  are  known  as  the  interlobular  veins.  From  these  are  given  off  hepatic 
capillaries,  which  anastomose  freely,  but  have  in  general  a  direction  toward  the  centre  of  the 
lobule,  and  unite  to  form  the  central  or  intralobular  veins,  which  in  turn  unite  to  form  the  sub- 
lobular  veins,  and  these  the  hepatic  veins.  The  intralobular  branches  of  the  hepatic  arteries 
form  capillaries  which  unite  with  the  capillaries  of  the  intralobular  portal  veins. 

The  liver  is  a  modified  compound  tubular  gland.  The  liver-cells  are  arranged  in  anas- 
tomosing cords  and  columns  occupying  the  spaces  formed  by  the  hepatic  capillaries.  The 
bile-ducts  have  their  origin  in  so-called  bile-capillaries  [ductus  biliferi],  situated  in  the  columns 
of  liver-cells;  they  anastomose  freely  and  pass  to  the  periphery  of  the  lobules  to  form  the  pri- 
mary divisions  of  the  bile-ducts,  and  these  unite  to  form  the  larger  bile-ducts.  The  branches  of 
the  portal  vessel  are  accompanied  in  their  course  through  the  liver  by  the  branches  of  the  hepatic 
artery  and  the  bile-ducts,  surrounded  by  extensions  of  Ghsson's  capsule  forming  the  so-called 
'portal  canals'  (fig.  947).  The  branches  of  the  hepatic  vein  are  solitary,  their  walls  are  thin 
and  closely  adherent  to  the  liver  substance,  whence  they  remain  wide  open  on  sectioning  the 
liver. 

While  it  is  customary  to  describe  thus  the  hver  lobules,  it  would  be  more  logical  to  con- 
sider as  the  real  lobules  what  Mall  has  described  as  the  'portal  units.'  Each  portal  unit 
includes  the  territory  supplied  by  one  interlobular  branch  of  the  portal  vein,  and  drained  by 
the  accompanying  bile-duct.  The  relations  of  the  ordinary  lobules  and  the  portal  units  are 
evident  in  fig.  948.  The  portal  unit  corresponds  more  nearly  to  the  lobule  of  other  glands, 
where  the  duct  is  in  the  centre  of  the  lobule. 


THE  LIVER 


1187 


Bile  passages. — The  bile  passages,  which  transmit  the  bile  from  the  liver  to  the 
duodenum,  include  the  gall-bladder,  the  cystic  duct,  the  hepatic  ducts,  and  the 
common  bile  duct. 

The  gall-bladder  [vesica  fellea],  which  retains  the  bile,  is  situated  between  the 
right  and  quadrate  lobes  on  the  lower  surface  of  the  liver.  It  is  pear-shaped, 
and  when  full,  is  usually  seen  projecting  beyond  the  anterior  border  of  the  liver, 
coming  in  contact  with  the  abdominal  wall  opposite  the  ninth  costal  cartilage  at 
the  lateral  margin  of  the  right  rectus  muscle  (fig.  914).  It  extends  back  as  far  as 
the  portal  fissure. 

It  measures  in  length,  from  before  backward,  7  to  10  cm.  It  is  2.5  to  3.5  cm. 
across  at  the  widest  part,  and  will  hold  about  35  cc.  (Ij  oz.).  The  broad  end  of  the 
sac  is  directed  forward,  downward,  and  to  the  right,  and  is  called  the  fundus. 
The  narrow  end,  or  neck  [collum  vesicae  fellete],  which  is  curved  first  to  the  right, 
then  to  the  left,  lies  within  the  gastro-duodenal  Ugament  at  the  portal  fissure. 
The  intervening  part  is  called  the  body  [corpus  vesicae  felleae]. 


Fig.  948.- 


-Diagram  of  the  Portal  Unit  and  Vascular  Relations  of  the  Hepatic  Lobule. 
(After  Szymonowicz.) 


PORTAL    UNIT 


PORTAL  UNIT 


Its  upper  surface  is  in  contact  with  the  liver,  lying  in  the  fossa  of  the  gall-bladder.  It  is 
attached  to  the  liver  by  connective  tissue.  The  lower  surface  is  covered  by  peritoneum,  which 
passes  over  its  sides  and  inferior  surface,  though  occasionally  it  entirely  surrounds  the  gall- 
bladder, forming  a  sort  of  mesentery  attaching  to  the  liver.  The  lower  surface  comes  into  con- 
tact with  the  first  part  of  the  duodenum  and  the  transverse  colon,  and  occasionally  with  the 
pyloric  end  of  the  stomach  or  small  intestine,  which  post  mortem  are  often  found  stained  with 
bile. 

The  neck  of  the  gall-bladder  opens  into  the  cystic  duct  [ductus  cysticus]. 
This  is  a  tube  about  3.5  cm.  long  and  3  mm.  wide,  which  unites  with  the  hepatic 
duct  to  form  the  ductus  choledochus;  it  is  directed  backward  and  to  the  left  as 
it  runs  in  the  gastro-hepatic  ligament,  the  common  hepatic  artery  being  to  the  left 
and  the  right  branch  of  the  artery  and  portal  vein  behind.  It  joins  the  hepatic 
duct  at  an  acute  angle,  and  is  kept  patent  by  a  spiral  valve  [valvula  spiralis; 
Heisteri],  formed  by  its  mucous  coat  (fig.  949). 

The  hepatic  duct  [ductus  hepaticus]  Ijegins  with  a  branch  from  each  lobe,  right 
and  left  (that  from  the  left  receiving  also  the  ducts  from  the  caudate  lobe),  in 
the  portal  fissure,  and  is  directed  downward  and  to  the  right  within  the  portal 
fissure  and  the  hepato-duodenal  ligament,  the  right  branch  of  the  hepatic  artery 
being  behind  and  the  left  branch  to  the  left.  It  is  from  3  to  5  cm.  long;  its  diame- 
ter is  about  4  mm.  Uniting  with  the  cystic  duct,  it  forms  the  common  bile-duct 
[ductus  choledochus]. 


1188 


DIGESTIVE  SYSTEM 


The  ductus  choledochus  or  common  bile-duct  is  about  7.5  cm.  in  length  and 
6  mm.  in  width.  It  passes  down  between  the  layers  of  the  lesser  omentum,  in 
front  of  the  portal  vein,  and  to  the  right  of  the  hepatic  artery  (fig.  946) ;  it  then 
passes  behind  the  first  part  of  the  duodenum,  then  between  the  second  part  and  the 
head  of  the  pancreas,  being  almost  completely  embedded  in  the  substance  of  the 
pancreas,  and  ends  a  little  below  the  middle  of  the  descending  duodenum  by  open- 
ing into  that  part  of  the  intestine  on  its  left  side  and  somewhat  behind  (figs.  921, 


Fig.  949.- 


-Intekior  of  the  Gall  Bladder  and  Ducts.     (From  Toldt's  Atlas.) 
Tunica  mucosa  of  gall  bladder 
Plicae  tunicse  mucosae 


/  Spiral  valve  (of  Heistet) 


Common  bile  duct  (ductus  choledochus) 


Biliary  mucous  glands 


922,  957).  It  pierces  the  intestinal  wall  very  obliquely,  running  between  the 
muscular  layers  for  a  distance  of  about  1  to  2  cm.  There  is  a  slight  constriction 
at  its  termination.  The  pancreatic  duct  is  generally  united  with  the  ductus 
choledochus  just  before  its  termination,  and  there  is  a  slight  papilla  at  their  place 
of  opening  on  the  mucous  surface  of  the  duodenum.  This  papilla  is  about  8  or 
10  cm.  from  the  pylorus.  After  the  pancreatic  duct  has  entered  the  bile-duct  there 
is  (in  about  half  the  cases)  a  dilatation  of  the  common  tube  called  the  ampulla  of 
Vater. 


THE  LIVER 


1189 


In  its  oblique  course  through  the  duodenal  wall,  the  common  bile  duct  is  accompanied  by 
the  pancreatic  duct,  the  two  together  usually  causing  the  pUca  longitudinalis  duodeni  (fig.  922). 
Circular  muscle  fibres  join  with  bundles  of  longitudinal  fibres  at  the  lower  part  of  the  ducts 
and  form  a  sphincter  around  each  (fig.  950).  Contraction  of  the  sphincter  probably  closes  the 
orifice  of.'the  common  bile  duct,  so  that  (except  during  digestion)  the  bile  is  backed  up  into  the 
gall-bladder. 

Structure  of  the  gall-bladder. — The  wall  of  the  gall-bladder  is  made  up  of  three  coats — 
mucosa,  fibro-muscular  and  serosa. 

Fig.  950. — Macerated  Duodenal  Portion  op  the  Common  Bile  Duct,  Showing 
Musculature.  B,  Common  bile  duct.  TT^,  Pancreatic  duct  (of  Wirsung).  iS,  Tij,  Sphincter 
fibres  of  Isile  duct.     H,  Fibres  of  pancreatic  duct.     (Hendrickson.) 


1.  The  mucosa  is  raised  into  folds  bounding  polygonal  spaces,  giving  the  interior  a  honey-* 
comb  appearance.  It  is  lined  with  columnar  epithelium,  and  contains  a  few  tubular  mucous 
glands  and  lymph-nodules,  and  is  hmited  externally  by  a  poorly  developed  muscularis  mucosae. 
At  the  neck  the  mucous  membrane  forms  valve-like  folds  which  project  into  the  interior.  This 
layer  contains  an  anastomosis  of  blood-vessels,  the  capillaries  being  most  numerous  in  the  folds 
of  the  mucosa,  and  a  fine  plexus  of  lymphatics. 

2.  The  fibro-muscular  coat  consists  of  interlacing  bundles  of  non-striated  muscle  and  fibrous 
tissue  not  definitely  arranged,  the  muscular  bundles  running  longitudinally  and  obliquely 
This  layer  contains  the  principal  blood-vessels  and  lymphatics,  and  also  a  nerve  plexus. 

Fig.  951. — Diagrams  op  the  Development  op  the  Liver.  (Lewis  and  Stbhr.) 
A,  The  condition  in  a  4.0  mm.-  human  embryo.  B,  A  12  mm.  pig.  C,  The  arrangement  of 
ducts  in  the  human  adult,  c.  d.,  Cystic  duct;  c.  p.,  cavity  of  the  peritoneum;  d.,  duodenum; 
d.c,  ductus  choledochus;  dia.,  diaphragm;  div.,  diverticulum;  /.  I.,  falciform  ligament;  g.  b., 
gall  bladder;  g.  a.,  greater  omentum;  h.  d.,  hepatic  duct;  ht.,  heart;  int.,  intestine;  li.,  liver; 
I.O.,  lesser  omentum;  to.,  mediastinum;  on.,  cesophagus;  p.  c,  pericardial  cavity;  p.  d.  pan- 
creatic duct;  ph.,  pharynx;  p.  v.,  portal  vein;  st  ,  stomach;  Ir.,  trabecula;  v.  c.  i.,  vena  cava  in- 
ferior; v.v.  vitelline  vein;  y.  s.,  yolk  sac. 


v.v.      ml.  B 


3.  The  serosa  being  formed  by  the  peritoneum,  is  only  found  on  the  lower  surface  and  part 
of  the  sides. 

The  ducts  consist  of  a  fibro-muscular  and  a  mucous  layer.  In  the  fibro-muscular  layer  are 
non-striated  muscle-cells  which  are  chiefly  circular,  together  with  white  fibrous  tissue  and  elastic 
fibres.  The  mucous  layer  is  lined  with  columnar  epithehum,  and  has  manj'  mucous  glands.  In 
the  cystic  duct  the  mucous  membrane  is  raised  into  folds,  which  are  crescentic  in  form,  and 
directed  so  obUquely  as  to  seem  to  surround  the  lumen  of  the  tube  in  a  spiral  manner. 

The  development  of  the  liver. — The  relations  which  the  liver  bears  to  the  diaphragm,  to 
its  vessels  and  more  especially  the  veins,  and  to  its  so-called  hgaments,  may  be  understood  by 
a  reference  to  its  development  (figs.  951,  952).  In  discussing  the  development  of  the  peritoneum 
and  the  mesenteries  it  was  shown  that  the  liver  has  its  origin  in  a  bud  of  entoderm,  which  grows 


1190 


DIGESTIVE  SYSTEM 


into  the  transverse  septum  in  the  region  where  this  is  attached  to  the  ventral  mesoderm  of  the 
developing  intestine;  and  that,  with  further  development,  the  transverse  septum  differentiates 
into  an  upper  thinner  portion,  inclosing  the  Cuvierian  ducts,  and  destined  to  form  the  diaphragm, 
and  a  lower  thicker  portion  in  which  the  liver  develops.  Shortly  after  the  formation  of  the 
entodermal  bud  which  forms  the  liver  this  mass  of  epithelium  taecomes  penetrated  by  out- 
growths from  the  omphalo-mesenteric  veins,  reducing  the  epithelial  mass  to  anastomosing 
trabeculae  separated  by  blood-spaces  forming  a  sinusoidal  circulation.  The  definite  hepatic 
lobules  are  not  differentiated  until  after  birth.  The  process  of  the  development  of  the  lobules 
is  very  complicated,  the  vascular  arrangement  being  shifted  repeatedly  (Mall). 

The  liver  rapidly  enlarges,  filling  the  upper  portion  of  the  abdominal  cavity,  and  extending 
along  its  ventral  wall  to  the  region  of  the  umbilicus.  During  the  enlargement  it  in  a  measure 
outgrows  the  transverse  septum,  and  there  are  developed  grooves  which  result  in  an  infolding 
of  the  peritoneum  covering  the  transverse  septum,  and  which  in  part  separate  the  developing 
liver  from  that  part  of  the  septum  destined  to  form  the  diaphragm_,  and  also  from  the  ventral 
abdominal  wall.  These  grooves  appear  at  the  sides  and  also  ventral  to  the  hver,  but  do  not 
completely  separate  the  liver  from  the  diaphragm,  nor  do  they  meet  in  the  median  line.  A 
portion  of  the  liver,  therefore,  remains  uncovered  by  peritoneum,  and  remains  attached  to  the 
diaphragm;  this  area  may  be  known  as  the  uncovered  or  phrenic  area  of  the  hver.  Around 
this  area  the  peritoneum  of  the  hver  is  reflected  on  to  the  diaphragm,  forming  the  coronary 
ligament,  with  right  and  left  extensions,  designated  as  the  right  and  left  triangular  hgaments. 
Owing  'to  the  fact  that  the  grooves  which  develop  on  the  sides  of  the  liver  do  not  meet  in  the 
median  line,  there  persists  a  fold  of  peritoneum  which  attaches  the  Hver  to  the  ventral  abdominal 

Fig.  952. — Diagram  (A) :  A  Sagittal,  Section  of  an  Embryo  showing  the  Liver  en- 
closed WITHIN  THE  Septum  Transversum;  (B)  AFbontal  Section  of  the  same;  (C)  Fron- 
tal Section  of  a  Later  Stage  when  the  Liver  has  separated  from  the  Diaphragm. 

All,  Allantois;  CI,  cloaca;  D,  diaphragm;  Li,  liver;  Ls,  falciform  ligament  of  the  liver,  M, 
mesentery;  Mg,  mesogastrium;  Pc,  pericardium;  iS,  stomach;  ST,  septum  transversum;  U, 
umbilicus.     (McMurrich.) 


wall;  this  forms  the  falciform  ligament,  which  divides  the  superior  surface  of  the  hver  into  a 
right  and  a  left  lobe.  The  region  of  the  attachment  of  the  ventral  mesentery  (mesogastrium) 
into  which  grows  the  entodermal  liver  bud,  forms  the  lesser  omentum.  The  developing  liver 
early  comes  into  intimate  relation  with  the  omphalo-mesenteric  veins,  and  a  little  later  the  um- 
bilical veins.  The  developmental  history  of  these  veins  and  their  relation  to  the  developing 
liver  is  discussed  elsewhere  (see  Development  of  the  Portal  Vein  and  Inferior  Vena 
Cava,  p.  694).  After  birth  the  left  umbilical  vein  forms  the  hepatic  ligamentum  teres,  situated 
in  the  free  edge  of  the  falciform  hgament.  The  ductus  venosus  likewise  atrophies  to  form  the 
ligamentum  venosum. 

The  gall-bladder  has  its  origin  in  a  groove  lined  by  entoderm,  which  appears  on  the  ventral 
surface  of  the  primitive  intestine  or  archenteron,  between  the  stomach  and  the  yolk-vesicle. 
From  the  cephalic  end  of  this  groove  grows  out  the  bud  destined  to  form  the  liver;  the  caudal 
end  of  the  groove  becomes  gradually  separated  from  the  developing  intestine  to  form  a  pouch, 
lined  by  entoderm,  which  forms  the  beginning  of  the  gall-bladder.  With  further  growth  the 
attachment  to  the  intestine  of  both  the  liver  and  the  gall-bladder  becomes  narrowed  to  form  the 
ductus  choledochus. 

During  development,  the  liver  undergoes  marked  changes  in  form  and  relative  size.  It 
grows  with  great  rapidity  in  the  embryo,  its  maximum  relative  size  reaching  7  to  10  per  cent,  of 
the  entire  body  about  the  third  prenatal  month.  At  this  time,  the  hver  is  globular  in  form,  the 
visceral  surface  very  small,  and  the  left  lobe  more  nearly  approaching  the  right  in  size.  During 
the  later  foetal  months  (fig.  953)  and  at  birth,  the  liver  forms  about  5  per  cent,  of  the  whole 
body.  It  stiU  remains  relatively  large  in  infancy,  but  decreases  to  about  2.5  per  cent,  in  the 
adult.  From  the  beginning,  the  relative  weight  of  the  liver  averages  slightly  higher  in  the 
female. 

Variations  of  the  liver  and  bile  passages. — Many  variations  of  the  liver  have  already 
been  mentioned.  In  size,  both  relative  and  absolute,  it  is  subject  to  marked  individual  varia- 
tions, as  well  as  according  to  age  and  sex  (previously  described).  Inform,  the  liver  is  also  quite 
variable.  There  are  two  extreme  types:  (1)  in  which  the  liver  is  very  wide,  extending  far  over 
into  the  left  hypoohondrium,  but  relatively  flattened  from  above  downward;  and  (2)  in  which  it 


THE  LIVER 


1191 


extends  but  slightly  to  the  left,  being  somewhat  flattened  from  side  to  side,  and  elongated 
vertically.  This  type  may  occur  as  a  result  of  tight  lacing,  in  which  the  liver  is  frequently 
deformed.  The  part  projecting  below  the  right  costal  margin  may  form  the  so-called  'Riedel's 
lobe.'  All  intermediate  forms  between  these  two  types  occur.  Its  position  and  relations  will 
also  vary  necessarily  according  to  differences  in  size  and  shape.  For  example,  in  the  wide  type 
and  also  in  enlarged  livers,  the  left  lobe  may  extend  over  upon  the  spleen,  a  relation  which  is 
constant  during  prenatal  life. 

There  may  be  supernumerary  fissures,  dividing  the  hver  into  additional  lobes,  as  many  as 
16  having  been  described  in  an  extreme  case  (Moser).  These  extra  fissures  often  correspond 
to  fissures  which  are  normal  in  other  mammals.  There  may  also  be  accessory  lobes,  usually 
small,  and  connected  with  the  main  gland  by  stalks.  Any  one  of  the  normal  lobes  may  be 
atrophied  or  absent.  There  may  also  be  abnormal  grooves  on  the  parietal  surface  of  the  liver. 
Of  these,  there  are  two  varieties:  (1)  costal  grooves,  due  to  impressions  of  the  overlying  ribs 
and  costa!  cartilages;  and  (2)  diaphragmatic  grooves,  due  to  wrinkles  in  the  diaphragm.     These 


Fig.  953. — The  Viscera  op  the  Fcettjs.     (Rudinger.) 


Thyreoid 


Liver 
Falciform  ligament 


Small  intestine 


Right  ventricle 


Stomach 

Part  of  transverse  colon 


Hypogastric  artery 


grooves  most  frequently  occur  in  females,  as  a  result  of  tight  lacing.  The  appendix  fibrosa 
has  already  been  mentioned.  There  are  numerous  variation  in  the  vascular  arrangements,  as 
well  as  in  the  psritoneal  relations  (particularly  in  connection  with  the  coronary  ligament). 

The  bile  passages  are  even  more  variable  than  the  liver  proper.  The  gall-bladder  is  variable 
in  size  and  capacity  (25  cc.  to  50  oc.  or  more),  as  well  as  in  its  position,  and  relations.  The 
fundus  projects  to  a  variable  extent  beyond  the  anterior  margin  of  the  liver  so  as  to  come  into 
contact  with  the  abdominal  wall  in  a  little  more  than  half  the  cases,  but  is  often  retracted.  The 
fossa  of  the  gall-bladder  is  of  variable  depth,  rarely  so  deep  that  it  reaches  the  superior  surface 
of  the  liver.  The  peritoneum  usually  covers  only  the  sides  and  inferior  surface  of  the  gall- 
bladder, but  occasionally  surrounds  it  entirely,  forming  a  short  'mesentery.'  In  rare  cases 
the  gall-bladder  is  bilid  or  double,  and  is  occasionally  absent.  There  are  numerous  variations  in 
the  bile-ducts.  Rarely  the  hepatic  ducts  may  communicate  directly  with  the  gall-bladder. 
The  point  at  which  hepatic  and  cystic  ducts  unite  is  variable,  which  affects  the  relative  lengths 
of  these  and  the  ductus  choledochus.  The  latter  may  open  into  the  duodenum  separately, 
instead  of  with  the  pancreatic  duct. 


1192 


DIGESTIVE  SYSTEM 


Comparative. — The  liver  arises  in  all  vertebrates  as  an  outgrowth  of  the  entodermic  epi- 
thelium of  the  intestine  just  beyond  the  stomach.  In  amphioxus  it  remains  a  simple  saccular 
diverticulum,  but  in  aU  higher  forms  becomes  a  compound  tubular  gland.  The  tubular  char- 
acter becomes  masked,  however  (in  amniota,  and  especially  in  mammals),  by  the  abundant 
anastomosis  between  the  tubules,  forming  what  is  called  a  'solid'  gland.  The  relations  with 
the  portal  venous  system  are  constant.  The  liver  frequently  stores  large  quantities  of  fat,  and 
may  even  undergo  a  complete  fatty  metamorphosis  (lamprey).  The  colour  of  the  liver  is  usually 
reddish-brown,  but  may  be  yellow,  purple,  green  or  even  vermillion  (due  to  bile  pigments). 
In  size,  the  liver  is  variable,  but  is  usually  relatively  larger  in  anamniota.  Among  mammals, 
there  is  great  variation  according  to  diet,  the  liver  being  relatively  larger  in  carnivora,  smaller 
in  herbivora,  and  intermediate  in  omnivora  (including  man).  It  is  also  relatively  larger  in  small 
animals  (including  young  and  foetal  stages),  probably  on  account  of  their  more  intense  metabo- 
lism. There  are  typically  two  lobes,  right  and  left,  in  the  vertebrate  hver.  These  are  frequently 
subdivided,  however,  especially  in  mammals,  which  often  present  numerous  lobes. 

The  gall-bladder  is  typically  present,  as  in  man,  but  varies  in  form,  size  and  position.  It 
may  be  completely  buried  in  the  fiver.  In  some  species  it  is  absent,  in  which  case  the  hepatic 
ducts  open  directly  into  the  duodenum  by  one  or  more  apertures.  The  hepatic  and  cystic 
ducts  typically  unite  to  form  a  common  bile-duct,  as  in  man,  but  there  are  numerous  variations 
in  the  detailed  arrangement  of  the  ducts. 


THE  PANCREAS 

The  pancreas  (figs.  922,  954,  955,  956)  is  an  elongated  gland  extending  trans- 
versely across  the  posterior  abdominal  wall  behind  the  stomach  from  the  duode- 
num to  the  spleen.  Through  the  pancreatic  duct,  opening  into  the  descending 
duodenum,  flows  its  secretion  [succus  pancreaticus],  which  is  of  importance  in 
digestion.     The  pancreas  also  has  a  very  important  internal  secretion. 

Fig.  954. — The  Duodenum  and  Pancreas,  Anterior  View. 
Superior  layer  of  transverse  meso-colon 


Duodeno-jejunal  Sesure 


Inferior  layer  of  transverse  meso-colon 

Inferior  part  of  duodenum 


Superior  mesenteric  vessels 


The  pancreas  is  greyish-pink  in  colour;  average  length  {in  situ),  12  cm.  to  15 
cm.;  average  weight  about  80  gm.  (extremes  60  gm.  to  100  gm.  or  more);  specific 
gravity,  1.047,  which  is  about  the  same  as  that  of  the  salivary  glands. 

In  position,  the  pancreas  lies  in  the  epigastric  and  left  hypochondriac  regions. 
In  form,  it  somewhat  resembles  a  pistol,  with  the  handle  placed  to  the  right  and 
the  barrel  to  the  left.  The  pancreas  is  accordingly  divided  into  a  head,  lying 
within  the  duodenal  loop;  a  body,  extending  to  the  left;  and  a  tail,  or  splenic 
extremity. 

The  head  [caput  pancreatis]  is  a  discoidal  mass  somewhat  elongated  vertically 
and  flattened  dorso-ventrally.  It  forms  the  enlarged  right  extremity  of  the  pan- 
creas and  lies  within  the  concavity  of  the  duodenum  (flgs.  922,  954,  955).  Its 
relations  are  as  follows  (figs.  954,  955,  956) :  Its  posterior  surface  is  placed  opposite 
the  second  and  third  lumbar  vertebrae,  and  is  in  contact  with  the  aorta,  the  vena 
cava,  the  renal  veins  and  right  renal  artery.  The  common  bile-duct  is  also  partly 
embedded  in  this  surface.  Its  anterior  surface  is  crossed  by  the  transverse  colon, 
above  which  is  the  pyloric  extremity  of  the  stomach,  and  below  which  are  coils  of 


THE  PANCREAS 


1193 


Fig.  955. — The  Duodenum  and  Pancreas,  Posterior  View. 

Portal  vein 


Terminal  part  of  duodenum 


Head  of  pancreas 


Fig.  956. — Outline  Showing  the  Average  Position  op  the  Deeper  Abdominal 
Viscera  in  40  Bodies,  on  a  Centimetre  Scale  (reduced  to  .36  natural  size).  AB,  anterior 
mid-line.  EF,  horizontal  line  half  way  between  pubes  and  suprasternal  margin.  CD,  line 
half  way  between  pubes  and  line  EF.     (Addison.) 


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1194  DIGESTIVE  SYSTEM 

small  intestine.  Upon  this  surface  are  also  the  pancreatico-duodenal  and  (in 
part)  the  superior  mesenteric  vessels.  The  margin  of  the  head  of  the  pancreas  is 
C-shaped,  corresponding  to  the  inner  aspect  of  the  duodenal  loop,  with  which  it 
is  closely  related.  Superiorly  the  margin  is  in  contact  with  the  pylorus  and  first 
part  of  the  duodenum;  on  the  right,  with  the  descending  duodenum  and  the  ter- 
minal portion  of  the  common  bile  duct ;  inferiorly,  with  the  horizontal,  and  on  the 
left,  with  the  terminal  ascending  portion  of  the  duodenum. 

The  lower  and  left  portion  of  the  head  of  the  pancreas  is  hooked  around  behind 
the  superior  mesenteric  vessels,  forming  the  processus  uncinatus  or  pancreas  of 
Winslow  (fig.  922).  A  groove,  the  pancreatic  notch  [incisura  pancreatis],  is  thus 
formed  for  the  vessels.  The  morphology  of  this  process  is  explained  later  under 
development  (fig.  958). 

In  the  adult  condition,  the  head  of  the  pancreas  is  largely  retroperitoneal. 
The  only  portions  covered  by  peritoneum  are  (1)  a  small  area  above  the  attach- 
ment of  the  colon,  and  in  relation  with  a  pocket-like  recess  of  the  bursa  omentalis, 
and  (2)  a  small  area  below  the  transverse  colon,  which  is  in  relation  with  coils  of 
small  intestine.  The  mesentery  of  the  small  intestine  begins  where  the  superior 
mesenteric  vessels  pass  downward  from  in  front  of  the  processus  uncinatus. 

The  junction  of  the  upper  and  left  aspect  of  the  head  with  the  body  of  the 
pancreas  is  called  the  neck.  This  is  a  somewhat  constricted  portion  grooved 
posteriorly  by  the  superior  mesenteric  vessels,  the  vein  here  joining  with  the  splenic 
to  form  the  portal  vein  (fig.  955).  Anterior  to  the  neck  is  the  pyloric  portion  of 
the  stomach.  The  upper  portion  of  the  neck  (together  with  a  variable  area  on  the 
left  end  of  the  body)  projects  above  the  lesser  curvature  of  the  stomach.  This 
projection  [tuber  omentale]  is  related,  through  the  lesser  omentum,  with  a  similar 
tuberosity  on  the  left  lobe  of  the  liver.  The  anterior  aspect  of  the  neck  is  covered 
with  peritoneum  of  the  bursa  omentalis  (lesser  sac),  and  is  continuous  with  the 
anterior  surface  of  the  body  of  the  pancreas  (fig.  922). 

The  body  [corpus  pancreatis]  is  the  triangularly  prismatic  portion  of  the  pan- 
creas extending  from  the  neck  on  the  right  to  the  tail  on  the  left.  Its  direction  is 
transversely  to  the  left  and  (usually)  somewhat  upward.  It  is  therefore  usually 
placed  at  a  somewhat  higher  level  than  the  head,  opposite  the  first  lumbar  verte- 
bra. It  presents  three  surfaces — anterior,  posterior,  and  inferior — and  three 
borders — superior,  anterior,  and  posterior. 

Of  the  surfaces,  the  anterior  [facies  anterior]  faces  forward  and  somewhat 
upward.  It  is  covered  with  the  peritoneum  of  the  posterior  wall  of  the  bursa 
omentalis  (lesser  sac),  and  forms  a  slightly  concave  area  which  is  in  contact  with 
the  posterior  surface  of  the  stomach  (figs.  904,  906).  The  posterior  surface  [f. 
posterior]  of  the  body  of  the  pancreas  is  flattened  and  retroperitoneal.  From  right 
to  left  it  crosses  the  anterior  aspect  of  aorta,  left  suprarenal  body  and  left  kidney. 
The  splenic  vessels  also  run  along  the  posterior  surface,  the  artery,  which  is  above, 
corresponding  more  nearly  with  the  superior  border.  The  inferior  surface  [f. 
inferior]  is  usually  the  narrowest  of  the  three.  It  is  covered  by  peritoneum  (con- 
tinuous with  the  lower  layer  of  the  transverse  mesocolon)  and  is  in  contact  with 
the  duodeno-jejunal  angle  medially  and  with  coils  of  jejunum  laterally. 

Of  the  borders,  the  superior  [margo  superior]  is  related  with  the  splenic  artery 
along  its  whole  length  from  its  origin  in  the  coeliac,  and  the  posterior  [margo 
posterior]  separates  posterior  and  inferior  surfaces.  The  anterior  border  [margo 
anterior]  is  sharp  and  prominent.  It  gives  attachment  to  the  transverse  meso- 
colon, whose  upper  layer  (belonging  to  the  lesser  sac)  is  continuous  with  that  on 
the  anterior  surface  of  the  pancreas,  and  whose  lower  layer  (belonging  to  the 
greater  sac)  is  continuous  with  that  on  the  inferior  surface. 

The  tail  of  the  pancreas  [cauda  pancreatis]  is  at  the  left  extremity  of  the  body. 
It  is  variable  in  form,  but  usually  somewhat  blunted  and  upturned.  It  is  almost 
invariably  in  contact  laterally  with  the  medial  aspect  of  the  spleen,  and  inferiorly 
with  the  splenic  flexure  of  the  colon.  The  splenic  vessels  often  cross  from  above 
in  front  of  the  tail  of  the  pancreas  on  their  way  to  join  the  spleen. 

Ducts. — The  pancreas  has  usually  two  ducts,  the  main  pancreatic  duct  and  the 
accessory  duct.  The  main  pancreatic  or  duct  of  Wirsung  [ductus  pancreaticus; 
Wirsungi]  begins  in  the  tail  of  the  pancreas,  and  extends  to  the  right  within  the 
body  of  the  pancreas,  about  midway  between  upper  and  posterior  borders,  but 
nearer  the  posterior  surface  (figs.  922,  957).     It  runs  a  slightly  sinuous  course 


THE  PANCREAS 


1195 


receiving  branches  all  along,  which  enter  nearly  at  right  angles.  It  is  largest  in 
the  head  of  the  pancreas  (diameter  about  3  mm.)  where  it  turns  obliquely  down- 
ward. As  it  approaches  the  duodenum,  it  is  joined  by  the  common  bile  duct,  the 
two  running  side  by  side.  They  pass  obliquely  through  the  wall  of  the  duodenum 
for  a  distance  of  about  15  mm.  (usually  causing  a  fold  of  the  mucosa,  the  plica 
longitudinalis  duodeni).  They  terminate  finally,  usually  by  a  common  aperture, 
but  sometimes  separately,  on  the  duodenal  papilla  major,  as  described  in  connec- 
tion with  the  interior  of  the  duodenum.  The  common  aperture  is  somewhat  nar- 
row, but  just  preceding  this  the  duct  is  frequently  dilated,  forming  what  is  called 
the  ampulla  of  Vater. 

The  accessory  pancreatic  duct  (duct  of  Santorini)  is  nearly  always  present 
(figs.  922,  957),  but  variable.  This  duct  is  small,  and  lies  within  the  head  of  the 
pancreas.  At  its  left  end,  it  usually  joins  the  main  duct  in  the  neck  of  the  pan- 
creas. From  here  it  extends  nearly  horizontally  across  to  the  upper  part  of  the 
descending  duodenum  and,  piercing  its  wall,  usually  ends  upon  the  small  papilla 
minor,  about  2  cm.  above  and  slightly  ventral  to  the  papilla  major.  The  relations 
of  the  ducts  are  explained  later  under  development. 


Fig.  957. — The  Pancreas  and  its  Ducts,  Dissected  from  Behind. 

Duct  of  pancreas  Accessory  duct  of  Santorini      Common  bile-duct 


Blood-vessels. — The  pancreas  receives  blood  chiefly  from  the  splenic  artery  through  its 
pancreatic  branches,  and  from  the  superior  mesenteric  and  hepatic  by  the  inferior  and  superior 
pancreatico-duodenal  arteries,  which  form  a  loop  running  around,  below,  and  to  the  right  of 
its  head. 

The  blood  is  returned  into  the  portal  vein  by  means  of  the  splenic  and  superior  mesenteric 
veins. 

Lymphatics. — ;The  lymphatics  terminate  in  numerous  glands  which  lie  near  the  root  of  the 
superior  mesenteric  artery,  above  and  below  the  neck  of  the  pancreas.  All  the  lymphatics 
drain  ultimately  into  the  cceliac  glands. 

Nerves. — These  are  branches  of  the  coeliac  plexus  which  accompany  the  arteries  entering 
the  gland.     The  main  part  of  the  coehac  plexus  lies  behind  the  gland. 

Minute  anatomy. — In  many  respects,  the  pancreas  resembles  the  salivary  glands  in  struc- 
ture, hence  its  German  name  'Bauchspeicheldrtise'  ('abdominal  sahvary  gland').  The 
gland  proper  is  racemose  (or  tubulo-racemose)  in  structure,  the  secreting  cells  characteristically 
granular  and  'serous'  in  type.  The  thin-walled  'intercalary  ducts,'  often  invaginated  to 
form  'centroacinar'  cells,  are  characteristic.  The  lobules  are  very  loosely  joined  by  areolar 
tissue,  and  there  is  no  distinct  fibrous  capsule  around  the  gland.  'The  most  important  of  the 
distinctive  characters  of  the  pancreas  is  the  presence  throughout  the  gland  of  numerous  small 
interlobular  ceU-masses  of  varied  form  and  size — the  islets  of  Langerhans  (fig.  959).  These  have 
no  ducts,  but  are  richly  supplied  with  blood-vessels.  They  are  ductless  glands  of  great  import- 
ance in  sugar  metabolism,  and  their  removal  or  disease  produces  diabetes.  While  derived 
embryologically  from  the  same  entodermal  anlage  which  gives  rise  to  the  pancreas  gland 
proper,  they  apparently  have  no  direct  connections  with  it  in  the  adult.  The  question  as  to 
the  possible  metamorphosis  of  acini  into  islets,  or  vice  versa,  under  certain  conditions  (e.  g., 
hunger)  in  the  adult  has  been  much  disputed.  Bensley,  however,  has  recently  presented  strong 
evidence  against  this  view. 

Development  of  the  pancreas. — The  pancreas  has  its  origin  in  three  entodermal  buds,  one 
of  which  (the  dorsal  anlage)  grows  from  the  dorsal  portion  of  the  duodenum,  the  other  two 
(ventral  anlages)  from  either  side  of  the  bile-duct.  Of  the  two  latter,  only  that  growing  from 
the  right  side  of  the  bile-duct  needs  further  consideration,  as  the  other  soon  disappears.  The 
dorsal  anlage  grows  at  first  more  rapidly  than  the  ventral,  which  arises  from  the  bile-duct.  In 
their  further  growth  both  the  dorsal  and  ventral  anlages  become  lobed,  these  lobes  dividing 
further  to  form  the  ducts  and  the  alveoh  of  the  gland.  By  about  the  end  of  the  second  month 
the  distal  end  of  the  ventral  portion  comes  in  contact  with  the  dorsal  portion  at  a  short  distance 


1196 


DIGESTIVE  SYSTEM 


from  the  latter's  connection  with  the  duodenum.  A  fusion  of  the  two  portions  thus  takes 
place  in  this  region,  and  at  the  same  time  there  is  estabhshed  by  anastomosis  a  connection  be- 
tween the  terminal  branches  of  the  main  duct  of  the  dorsal  portion — duct  of  Santorini — and  the 
branches  of  the  main  duct  of  the  ventral  portion — the  duct  of  Wirsung.  With  further  devel- 
opment the  duct  of  Wirsung  develops  into  the  main  pancreatic  duct,  the  duct  of  the  dorsal 


Fig.  958.- 


-DiAGEAM  Showing  the  Relations  of  the  Pancreas  to  the  Primitive  Mesen- 
tery.    (Poirier-Charpy.) 
Aorta 

Left  gastric  art. 

Dorsal  mesogastrium  (pr.rtion 
becoming  adherent) 


Tail  of  pancreas 
Splenic  art. 


Right  gastro-epiploic 

art. 

Superior  pancre- 

atico-duodenal 

art. 

Head  of  pancreas 


Mesentery  at  duodeno-jejunal  fle 
''Processus  uncinatus 


Body  of  pancreas 


Dorsal  mesogastriu 
(portion  fusing  w 
transverse  meso- 
colon) 


portion  (duct  of  Santorini)  either  losing  its  connection  with  the  duodenum  or  remaining  as  the 
accessory  pancreatic  duct. 

Thus  of  the  adult  gland,  only  the  lower  portion  of  the  head  is  derived  from  the  primitive 
ventral  anlage,  although  the  duct  of  the  latter  drains  nearly  the  entire  adult  gland.  The  upper 
part  of  the  head  of  the  pancreas,  and  all  of  the  body  and  tail  are  derived  from  the  dorsal  anlage; 
although  most  of  its  duct  joins  with  the  duct  of  Wirsung  to  form  the  main  pancreatic  duct, 
only  a  small  part  persisting  as  the  accessory  duct  of  Santorini. 


Fig.  959. — Section  op  Human  Pancreas,  Magnified,  Showing  Several  Islets  of 
Langerhans.  (Radasch.)  a,  Interlobular  connective  tissue,  containing  an  interlobular  duct, 
c,     b.  Capillary,     d,  Interlobular  duct,     e,  Alveoli.    /,  Islet  of  Langerhans. 


During  the  early  stages  in  the  development  of  the  pancreas  the  entodermal  buds  from 
which  it  forms  grow  into  the  mesoduodenum,  and  later  the  dorsal  mesogastrium.  With  the 
rotation  of  the  stomach  and  the  consequent  change  in  the  position  of  the  mesogastrium  and  its 
partial  fusion  with  the  abdominal  wall,  the  pancreas  assumes  a  retroperitoneal  position.  This 
is  illustrated  by  fig.  958.     The  head  of  the  pancreas  is  involved  in  the  rotation  of  the  primitive 


REFERENCES  FOR  DIGESTIVE  SYSTEM  1197 

intestinal  loop  counter-clockwise  around  the  superior  mesenteric  artery.  This  accounts  for 
the  position  and  the  hook-like  form  of  the  processus  uncinatus.  Following  this  rotation,  the 
duodenum  and  the  head  of  .the  pancreas  become  pressed  backward  against  the  posterior  ab- 
dominal wall,  where  they  become  adherent,  with  fusion  and  obliteration  of  the  primitive  peri- 
toneum. The  body  of  the  pancreas,  extending  mto  the  dorsal  mesogastrium  (fig.  900),  is  simi- 
larly caught  in  the  pouch-like  downgrowth  of  the  latter  to  form  the  bursa  omentahs  (lesser  sac), 
and  is  thereby  carried  over  to  the  left  side.  When  the  posterior  layer  of  the  primitive  bursa 
fold  becomes  fused  with  the  posterior  abdominal  wall,  the  enclosed  pancreas  is  likewise  fixed 
and  becomes  retroperitoneal.  Of  these  obUterated  peritoneal  layers  of  the  embryo,  only  certain 
layers  of  fascia  remain  as  their  representatives  in  the  adult.  From  the  lower  aspect  of  the  pan- 
creas downward,  the  posterior  layer  of  the  bursa  fold  becomes  fused  with  the  transverse  meso- 
colon, so  that  in  the  adult  the  latter  appears  to  arise  from  the  anterior  border  of  the  pancreas 
(fig.  904). 

Variations. — Aside  from  minor  fluctuations  in  size  and  form,  the  variations  of  the  pancreas 
are  chiefly  congenital  and  of  embryonic  origin.  Cases  of  accessory  or  supernumerary  pancreas  are 
not  rare.  They  are  usually  of  small  size  and  have  separate  ducts.  They  may  occur  along  the 
wall  of  the  duodenum,  or  even  in  the  stomach  or  jejunum.  They  are  perhaps  m  some  way  con- 
nected with  the  numerous  intestinal  diverticula  which  occur  in  the  embryo.  Divided  pancreas 
differ  from  the  accessory  in  that  a  mass  of  the  pancreas  becomes  separated  from  the  main  gland, 
connected  only  by  a  duct.  This  occurs  oftenest  in  the  region  of  the  tail  (sometimes  extending 
into  the  spleen)  or  of  the  processus  uncinatus,  forming  what  is  termed  a  'lesser  pancreas.' 
Sometimes  a  ring  of  glandular  tissue  from  the  head  of  the  pancreas  surrounds  the  descending 
duodenum,  forming  an  annular  pancreas.  Variations  in  the  direction  of  the  body  are  numerous; 
it  may  be  horizontal,  ascending  or  bent  in  various  ways.  These  are  doubtless  congenital  vari- 
ations, as  similar  types  have  been  described  in  the  foetus  (Jackson).  It  has  been  experimentally 
demonstrated  that  varying  degrees  of  distention  of  the  stomach  and  intestines  affect  profoundly 
the  form  of  the  body  of  the  pancreas.  When  the  stomach  alone  is  distended,  the  pancreas  is 
flattened  antero-posteriorly,  the  inferior  surface  being  practically  obliterated.  When  both 
stomach  and  intestines  are  distended,  the  pancreas  is  flattened  from  above  downward,  and 
e.xtends  forward  hke  a  shelf,  the  posterior  surface  being  much  reduced  (Jackson).  Numerous 
variations  in  the  ducts  are  easily  understood  from  their  complicated  development.  The  acces- 
sory duct  (of  Satorini)  is  in  the  foetus  as  large  as  the  main  duct  (of  Wirsung),  the  preponderance 
of  the  latter  being  established  later.  The  accessory  duct  in  the  adult  may  be  larger  than  usual, 
and  retain  its  primitive  drainage,  or  even  drain  the  entire  gland  in  rare  cases  where  the  duct 
of  Wirsung  is  absent.  Or  the  accessory  duct  may  be  rudimentary  or  (rarely)  absent.  Similar 
variations  occur  in  the  main  duct  of  Wirsung.  Rarely  the  pancreas  may  open  into  the  duo- 
denum by  three  ducts,  probably  representing  three  embryonic  anlages.  Abnormalities  of  the 
pancreas  are  often  associated  with  duodenal  diverticula. 

Comparative. — The  pancreas,  like  the  liver,  is  constant  throughout  the  vertebrates.  It 
always  arises  by  budding  off  from  the  endodermal  epithelium  of  the  intestine,  closely  associated 
with  the  Uver.  There  is  typically  a  triple  anlage  (rarely  multiple,  which  is  perhaps  the  ancestral 
type),  with  one  dorsal  and  two  ventral  outgrowths.  These  fuse  and  form  the  adult  pancreas 
in  a  variety  of  ways.  In  many  of  the  fishes,  the  pancreas  is  very  small,  diffuse  and  incon- 
spicuous, sometimes  embedded  in  the  liver  or  intestinal  wall.  Of  the  three  primitive  ducts, 
usually  only  two  persist  (as  in  man),  but  often  only  one,  or  all  three  (in  birds).  All  three  types 
occur  in  mammals.  The  islets  of  Langerhans  arise  from  the  epithelial  pancreas  anlage,  and  ap- 
pear to  be  constantly  present,  even  in  the  lowest  vertebrates.  Laguesse  even  considers  that 
phylogeneticaUy  they  form  the  most  primitive  part  of  the  pancreas,  but  this  is  doubtful. 

References  for  digestive  system. — General  and  Co7nparative:  Quain's  Anat- 
omy, 11th  ecL;  Poirier-Charpy,  Traits  d'anatomie;  Rauber-Kopsch,  Lehrbuch 
der  Anatomie,  9te  Aufl.;  Oppel,  Mikroskopische  Anatomie,  Bd.  1-3;  also  'Ver- 
dauungsapparat '  in  Merkel  and  Bonnet's  'Ergebnisse';  Wiedersheim,  Bau  des 
Menschen.  Topography:  (adult)  Merkel,  Topographische  Anatomie;  (develop- 
mental) Jackson,  Anat.  Rec,  vol.  3.  Development:  Keibel  and  Mall's  Manual. 
Teeth:  Tomes,  Dental  Anatomy.  Tonsils:  (lingual)  Jurisch,  Anatomische, 
Hefte,  Bd.  47;  (pharyngeal)  Symington,  Brit.  Med.  Jour.  (Oct.,  1910);  (palatine) 
Killian,  Archiv  f.  LaryngoL,  Bd.  7.  (Esophagus:  Goetsch,  Amer.  Jour.  Anat., 
vol.  10.  Stomach:  (structure),  Bensley,  Buck's  Ref.  Handb.  Med.  Sc,  vol. 
7  (1904);  (form)  Cunningham,  Trans  Royal  Soc.  Edinb.,  vol.  45;  (radiography) 
Cole,  Archives  Roentgen  Rays,  1911;  also  Journal  Amer.  Med.  Assn.,  vol.  59. 
Duodenum:  (diverticula),  Baldwin,  Anat.  Rec,  vol.  5.  Vermiform  process:  Berry 
and  Lack,  Jour.  Anat.  and  Phys.,  vol.  40.  Rectum:  Symington,  Jour.  Anat. 
and  Phys.,  vol.  46.  Liver:  Mall,  Amer.  Jour.  Anat.,  vol.  5.  Pancreas:  (islets) 
Bensley,  Amer.  Jour.  Anat.,  vol.  12;  (ducts)  Baldwin,  Anat.  Rec,  vol.  5. 


SECTION  X 


THE  RESPIRATOEY  SYSTEM 


Revised  fob  the  Fifth  Edition 
By  R.  J.  TERRY,  A.B.,  M.D., 

PHOFESSOR    OF    ANATOMY    IN    WASHINGTON    UNIVERSITr 


R 


ESPIRATION  consists  in  the  absorption  by  the  organism  of  oxygen  and 
the  discharge  of  a  waste-product,  carbon  dioxide. 


Among  unicellular  animals  the  oxygen  is  taken  up  directly  from  the  medium — water  or  air — 
in  which  they  Hve,  and  the  carbon  dioxide  given  off  into  it.  With  the  cells  which  make  up  the 
body  of  higher  animals  the  principle  is  the  same,  but  the  interchange  of  gases  is  indirect.  The 
blood  stands  as  an  intermediate  element  between  the  cells  of  the  body  and  the  medium  inhabited 

Fig.  960. — Dissection  of  a  Male  Negro,  Age  43  Years,  to  Show  the    Organs  of  Res- 
piration in  Situ. 


Frontal  sinus' 
Nasal  cavityj 


Thyreoid  gland 


Left  bronchus 


by  the  animals,  and  serves  as  a  carrier  of  the  gases  between  them.  Moreover,  special  organs 
are  provided  for  the  rapid  interchange  between  air  and  blood,  which  constitute  the  so-caUed 
respiratory  system. 

The  respiratory  system  of  air-breathing  vertebrates  consists  of  tubular  and 
cavernous  organs  constructed  so  as  to  permit  of  the  atmospheric  air  reaching  the 

1199 


1200 


THE  RESPIRATORY  SYSTEM 


blood  circulating  in  the  body.  The  essential  organs  in  the  system  are  the  paired 
lungs  located  in  the  thoracic  cavity.  Air  is  carried  to  and  from  the  lungs  by  the 
trachea  and  bronchi,  and  these  simple  transmitting  tubes  are  in  turn  put  into 
communication  with  the  exterior  by  the  mediation  of  other  organs.  The  latter 
are,  however,  specially  constructed  in  adaptation  to  other  functions  in  addition 
to  those  relating  to  respiration:  the  larynx  for  the  production  of  the  voice,  the 
pharynx  and  mouth  in  connection  with  alimentation,  the  nasal  cavity  and  external 
nose  functioning  in  the  sense  of  smell.  (For  the  description  of  the  mouth  and 
pharynx  see  Section  IX;  for  the  olfactory  organ  see  Section  VIII.) 

The  organs  of  circulation  are  always  adapted  to  the  form  of  the  respiratory  apparatus,  and 
among  all  higher  animals  a  connection  is  established  between  heart  and  lungs  by  the  pulmonary 
artery,  which  carries  venous  blood  to  the  latter,  and  by  the  pulmonary  veins,  which  convey 
arterial  blood  from  the  lungs  to  the  heart,  whence  the  aorta  takes  it  into  the  general  circulation. 

In  their  origin  and  development  the  respiratory  organs  are  closely  associated  with  or 
differentiated  from  the  beginnings  of  the  digestive  apparatus.  Thus  the  processes  of  the  early 
development  of  the  nasal  cavity  and  mouth  are  interdependent;  the  origin  of  the  greater 
part  of  the  larynx,  the  trachea  and  lungs  is  by  ventral  outgrowth  of  the  entodermal  canal. 


THE  NOSE 

The  external  nose  [nasus  externus]  (fig.  961),  shaped  like  a  triangular  pyramid, 
is  formed  of  a  bony  and  cartilaginous  framework  covered  by  muscles  and  the  in- 
tegument of  the  face  externally  and  lined  within  by  periosteal  and  perichondral 
layers  overspread  by  mucous  membrane.     At  the  forehead,  between  the  eyes,  is 

Fig.  961. — The  Left  Side  of  the  External  Nose,  showing  its  Cartilages,  etc. 


Nasal  bone 
Nasal  process  of  the  maxilla 

Lateral  nasal  cartilage 
Nasal  septal  cartilage 


Lateral  cms  of  greater  alar 
cartilage 


Medial  crus  of  greater  alar 
cartilage 


Sesamoid  cartilages 
Fibrous  tissue 
Lesser  alar  cartilages 

Cellular  tissue  forming  ala 


the  root  of  the  nose  [radix  nasi],  and  from  this,  extending  inferiorly  and  anteriorly, 
is  a  rounded  ventral  border,  the  dorsum  of  the  nose  [dorsum  nasi],  which  may  be 
either  straight,  convex,  or  concave,  and  which  ends  inferiorly  at  the  apex  of  the 
nose  [apex  nasi].  The  superior  part  of  the  dorsum  is  known  as  the  bridge.  Inferi- 
only,  overhanging  the  upper  lip,  is  the  base  of  the  nose  [basis  nasi]  which  presents 
two  orifices,  the  nares  or  nostrils,  separated  from  one  another  by  the  inferior  mov- 
able part  of  the  nasal  septum  [septum  mobile  nasi]. 

The  nostril  of  man  is  remarkable  on  account  of  its  position,  facing  as  it  does  almost  directly 
downward.  It  is  oval  in  form,  with  the  long  axis  directed  antero-posteriorly,  or  approximately 
so,  in  Europeans.  The  size  of  the  nostril  is  under  the  control  of  muscles  (see  p.  334)  and  may 
be  dilated  or  constricted  by  their  action. 

The  sides  of  the  nose  slope  from  the  dorsum  laterally  and  posteriorly,  and 


THE  NOSE 


1201 


below  ferminate  on  each  side  in  the  margin  of  the  nose  [margo  nasi];  posteriorly 
and  interiorly  the  sides  are  expanded  and  more  convex,  forming  the  alae  nasi. 
Each  of  these  is  separated  from  the  rest  of  the  lateral  surface  by  a  sulcus,  and  the 
inferior  free  margin  of  each  bounds  a  naris  laterally. 

Three  types  of  nose,  distinguished  by  differences  in  the  proportion  of  breadth  and  length  are 
recognised  by  anthropologists:  the  leptorrhine  or  long,  high  nose;  the  platyrrhine  or  short,  low 
nose;  the  mesorrhine,  a  form  intermediate  between  the  other  two.  The  leptorrhine  type 
prevails  among  white  races,  the  platyrrhine  in  the  blaeli  peoples  and  the  mesorrhine  in  the 
red  and  yellow  races. 

Fig.  962. — Anterior  View  op  the  External  Nose,  showing  its  Cartilages,  etc. 


Lacrimal  groove —  7 — 


Groove   on  anterior  border  of 
nasal  septal  cartilage 


jid  cartilages 
Lesser  alar  cartilages 

Cellular  tissue  of  ala 


Nasal  process  of  the  maxilla 


Lateral  nasal  cartilage 


Lateral  crus  of  greater 
alar  cartilage 


The  framework  of  the  external  nose  is  formed  partly  of  bone  and  partly  of  hyaline  cartilage 
The  bones,  which  form  only  the  smaller  superior  part,  are  the  two  nasal  bones  and  the  fronta 
processes  and  anterior  nasal  spines  of  the  two  maxillae  (pp.  87,  108). 

The  nasal  cartilages  [cartilagines  nasi]  are  located  about  the  piriform  aperture 
and  constitute  the  larger  part  of  the  nasal  framework.  There  are  five  principal 
cartilages:  superiorly,  the  two  lateral  nasal  cartilages,  interiorly  the  two  greater 

Fig.  963. — Inferior  View  op  the  External  Nose,  showing  its  Cartilages,  etc. 

ITasal  septal  cartilage - 


Medial  crus  of  greate: 
alar  cartilage 


Nasal  septal  cartilage 
Cellular  tissue  of  ala 


alar  cartilages,  and  the  single  median  nasal  septal  cartilage.  Beides  these  there 
are  the  lesser  alar  cartilages,  the  sesamoid  cartilages,  and  the  vomero-nasal  carti- 
lages of  Jacobson.  The  lateral  nasal  cartilages  [cartilagines  nasi  laterales]  are 
triangular  and  nearly  flat  lateral  e.xpansions  of  the  septal  cartilage,  placed  one  on 
each  side  of  the  nose  just  inferior  to  the  nasal  bone.  Each  presents  an  inner  and 
an  outer  surface  and  three  margins.  The  medial  margin  is  continuous  in  its  supe- 
rior third  with  the  anterior  margin  of  the  septal  cartilage,  and  through  this  with  its 


1202 


THE  RESPIRATORY  SYSTEM 


fellow  of  the  opposite  side,  but  it  is  separated  inferiorly  from  the  septal  cartilage 
by  a  narrow  cleft.  The  curved  supero-lateral  margin  is  firmly  attached  b}^  strong 
fibrous  tissue  to  the  nasal  bone  and  frontal  process  of  the  maxilla,  and  underlies 
these  bones  for  a  considerable  distance,  especially  near  the  septum.  The  inferior 
margin  is  connected  by  fibrous  tissue  to  the  greater  alar  cartilage.  The  greater 
alar  cartilages  [cartilagines  alares  majores],  variable  in  form,  are  situated  one  on 
each  side  of  the  apex  of  the  nose  (figs.  961,  963).  Each  is  thin,  pliant,  curved, 
and  so  folded  that  it  forms  a  medial  and  a  lateral  crus,  which  bound  and  tend  to 
hold  open  each  naris.  The  medial  crus  [crus  mediale]  is  loosely  attached  to  its 
fellow  of  the  opposite  side,  the  two  being  situated  inferior  to  the  septal  cartilage 
and  forming  the  tip  of  the  nose  and  the  inferior  part  of  the  mobile  septum.  The 
lateral  crus  [crus  laterale]  joins  the  medial  crus  at  the  apex  of  the  nose;  it  is 
somewhat  oval  in  shape,  and  curves  dorsally  in  the  superior  and  anterior  portion 
of  the  ala.  It  is  connected  posteriorly  to  the  nasal  margin  of  the  maxilla  by  a 
broad  mass  of  dense  fibrous  and  fatty  tissue,  and  helps  to  maintain  the  contour 
of  this  part  of  the  nose. 


Fig.  964. — Medial  Wall  of  the  Nasal  Cavity,  the  Mucotts  Membrane  Being  Removed. 
The  dotted  line  indicates  the  course  of  the  incisive  canal. 

Nasal  bone  Frontal  i 


Lateral  nasal 


Groove  between  septal 
and  lateral  nasal 
cartilage 


Thickened  bord' 
resting  upon  anterior 


papilla    Septal  cartilage 


Orifice  of  tuba  auditiva 
Soft  palate 


The  angle  formed  by  the  crura  (angulis  pinnahs)  varies  with  the  shape  of  the  nose;  it  aver- 
ages 30°.  The  greater  and  lesser  alar  cartilages  together  form  an  incomplete  ring  arotmd  the 
naris. 

A  variable  number  of  small  cartilages,  lesser  alar  cartilages  [cartilagines  alares  minores] 
are  found  in  the  fibrous  tissue  of  the  ala,  and  in  the  interval  between  each  greater  alar  and 
lateral  cartilage  occur  one  or  more  small  plates,  sesamoid  cartilages  [cartilagines  sesamoidese] 
(fig.  961). 

The  septal  cartilage  [cartilago  septi  nasi]  (fig.  964)  forms  the  anterior  part  of  the 
septum.  It  is  quadrilateral  in  shape  and  fits  into  the  triangular  interval  of  the 
bony  septum.  Its  antero-superior  margin  in  its  upper  part  meets  the  inter- 
nasal  suture.  Inferior  to  the  nasal  bone  it  presents  a  shallow  groove  which  gradu- 
ally narrows  toward  the  tip  of  the  nose,  and  whose  borders  are  continuous  supe- 
riorly with  the  lateral  nasal  cartilages,  but  are  separated  from  their  inferior  two- 
thirds  by  a  narrow  slit.  The  most  inferior  part  of  this  margin  of  the  septal  car- 
tilage is  placed  between  the  greater  alar  cartilages.  The  antero-inferior  margin 
extends  backward  from  the  rounded  anterior  angle  to  the  anterior  nasal  spine. 
Inferiorly  it  is  attached  to  the  medial  crus  of  the  greater  alar  cartilage  and  to  the 


THE  NASAL  CAVITY 


1203 


mobile  nasal  septum.  The  postero-superior  margin  is  attached  to  the  perpen- 
dicular plate  of  the  ethmoid,  and  the  postero-inferior  margin  joins  the  vomer  and 
the  ventral  part  of  the  nasal  crest  of  the  maxilla,  the  cartilage  broadening  out  to 
obtain  a  wide  though  lax  attachment  to  the  nasal  spine. 

The  shape  of  the  septal  cartilage  varies  with  the  extent  of  the  ossification  of  the  bony 
septum.  Even  in  the  adult  a  strip  of  cartilage  may  extend  for  a  varying  distance  postero- 
superiorly  between  the  vomer  and  perpendicular  plate  of  the  ethmoid,  sometimes  reaching  the 
body  of  the  sphenoid;  it  is  known  as  the  sphenoidal  process  of  the  septal  cartilage  [proc- 
essus sphenoidalis  septi  cartilaginei].  The  vomero-nasal  cartilage  [cartilago  vomero-nasalis 
Jacobsoni*]  is  a  narrow  strip  of  cartilage  firmly  attached  to  each  side  of  the  septal  cartilage, 
where  this  joins  the  anterior  portion  of  the  vomer. 

Muscles. — The  muscles  are  grouped  according  to  function  as  dilators  and 
contractors,  the  latter  being  comparatively  feeble  in  their  action.  They  are 
described  on  p.  334. 

The  skin  covering  the  external  nose  is  thin  and  freely  movable  upon  the  sub- 
jacent parts,  except  at  the  tip  and  over  the  cartilages,  where  it  is  much  thicker, 

Fig.  965. — Obliqite  Section  passing  through  the  Nasal  Cavity  just  in  Front  of  the 
CHOANiE.     (Seen  from  behind.) 


Crista  galli 


Front  wall  of  left     '  •>!/\ 
sphenoidal  sinub 
with  orifice  belov 
Orifice  of  righl 
sphenoidal  sinus 


Superior  nasal  concha 
Middle  nasal  concha' 


Upper  surface  of. 
soft  palate 


more  adherent,  and  furnished  with  numerous  exceptionally  large  sebaceous  glands. 
At  the  nares  it  is  reflected  into  the  nasal  cavity,  where  it  passes  into  the  mucous 
membrane.  The  hairs  on  the  skin  of  the  nose  are  very  fine,  except  in  the  nares, 
where  they  may  be  strongly  developed. 

Vessels  and  nerves. — The  arteries  of  the  external  nose  are  derived  from  the  external  maxil- 
lary (facial)  artery  (pp.  540  and  541),  the  ophthalmic  artery  (p.  554),  and  the  infra-orbital 
artery  (p.  549).  The  veins  terminate  in  the  anterior  facial  vein  and  the  ophthalmic  vein  (p. 
644).  The  lymphatics  pass  to  the  submaxillary  lymphatic  nodes  (p.  712).  The  motor  nerves 
are  branches  of  the  facial  (p.  946).  The  sensory  nerves  are  derived  from  the  trigeminal  through 
the  frontal  and  naso-cihary  branches  of  the  ophthalmic  (p.  936)  and  infra-orbital  branch  of  the 
maxiUary  (p.  939). 

The  nasal  cavity  [cavum  nasi]  is  the  ample  space  situated  between  the  floor  of 
the  cranium  and  the  roof  of  the  mouth  extending  forward  into  the  external  nose 
and  backward  to  the  nasal  part  of  the  pharynx.  With  the  exception  of  the 
inferior  part  of  the  nose  its  walls  are  of  bone  as  already  described  (pp.  110,  112). 
The  cartilages  and  membranes  of  the  nose  complete  the  boundaries  anteriorly. 
Here  the  cavity  opens  to  the  exterior  by  the  nares.     At  the  back  a  free  communi- 

*Jaeobson:  Danish  anatomist.     B.  17S3,  D.  1843. 


1204 


THE  RESPIRATORY  SYSTEM 


cation  with  the  pharynx  is  established  through  the  paired  ehoana;.  Furthermore 
accessory  nasal  cavities,  the  paranasal  sinuses,  open  into  the  cavum  nasi.  The 
walls  of  the  nasal  cavity  are  covered  with  periosteum  and  mucosa,  the  latter  pre- 
senting important  differences  in  the  respiratory  and  olfactory  regions.  The 
organ  of  smell,  included  in  the  nasal  cavity,  is  described  on  p.  1049. 

The  cavum  nasi  is  divided  into  right  and  left  symmetrical  parts,  called  the  nasal 
fossae,  by  the  septum  of  the  nose  [septum  nasi].  The  latter  is  supported  by  a 
framework  composed  of  the  osseous  septum  [septum  nasi  osseum]  posteriorly,  and 
the  cartilaginous  septum  [septum  cartilagineum]  anteriorly.  Antero-inferiorly, 
the  small  movable  part  of  the  septum  is  also  called  the  membranous  septum 
[septum    membranaceum]. 

The  nasal  septum  is  almost  always  straight  in  primitive  races  and  Caucasian 
children;  but  in  a  large  proportion  of  Caucasian  adults  it  is  deflected  to  one  side  or 
the  other. 

Fig.  966. — Sagittal  Section  through  the  Facial  Part  op  the  Head  and  the  Bodies 
OP  THE  UPPER  THREE  Cervical  Vertebrae.  The  section  lies  to  the  right  of  the  median 
plane.     The  nasal  septum  has  been  removed.     (Rauber-Kopsch.) 


Cribriform  plate 

Spheno-ethmoidal  , 

Hypophysis 


Dorsum  sellae 


Choanal  arch  .. 
Nasopharyngeal  - 
meatus 
Pharyngeal  tonsil 

Torus  tubarius 

Levator  cushion 

Anterior  lip 

of  tubal  aperture 

Salpingopharyn 

goal  fold 

Uvula 

Foramen  cgecum 
Palatopharyngeal  fold 


Incisive  canal 
Upper  lip 

Vestibulum  oris 
Mouth  cavity  proper 
Lower  lip 
Sublingual  mucosa 


Hyoid  bone 


Mental  spme 


In  the  septum,  upon  each  side,  just  superior  to  the  nasal  spines  of  the  maxillas,  there  is 
frequently  a  minute  opening  leading  superiorly  and  posteriorly  and  ending  blindly.  This  cavity 
is  closely  related  to  the  vomero-nasal  cartilage  and  is  a  rudimentary  representative  of  the  vomero- 
nasal organ  (of  Jacobson)  [organon  vomero-nasale],  which  in  some  animals  is  well  developed 
and  receives  a  branch  of  the  olfactory  nerve.  On  the  floor  of  the  nasal  cavity  about  2  cm.  from 
the  posterior  margin  of  the  naris  and  near  the  nasal  septum  a  small  depression,  the  nasopalatine 
recess,  is  often  seen.  This  is  the  mouth  of  the  incisive  duct  [ductus  incisivus]  which  leads  into 
the  incisive  canal  for  a  greater  or  less  distance  and  may  even  extend  to  the  mouth,  where  its 
termination  is  marked  by  the  incisive  papilla.  The  incisive  duct  indicates  the  position  of  a 
foramen  which  in  the  embryo  connected  the  mouth  and  nose. 

The  naris  leads  upward  into  the  vestibule  of  the  nose  [vestibulum  nasi],  the 
small  cavity  within  the  compass  of  the  greater  alar  cartilage.  Its  walls  are  lined 
with  skin  beset  with  the  large  hairs  called  vibrissas  and  containing  many  seba- 
ceous glands.  The  vibrissae  serve  to  protect  the  nasal  cavity  from  the  entrance  of 
foreign  matter.  On  the  lateral  wall,  the  vestibule  is  marked  off  from  the  rest  of 
the  nasal  cavity  by  a  cUstinct  ridge,  the  limen  nasi,  corresponding  to  the  superior 
margin  of  the  greater  alar  cartilage.  On  the  lateral  wall  of  the  cavity  within  the 
limen  nasi  are  three  antero-posterior  ridges,  the  superior,  middle,  and  inferior 


I 


THE  NASAL  MEATUSES 


1205 


conchae  (fig.  966).  These  have  a  bony  framework  (described  on  pp.  83,  110) 
and  are  covered  by  the  mucous  membrane  of  the  nose.  The  conchje  are  not 
parallel  to  one  another  but  converge  in  a  backward  direction.  The  superior  nasal 
concha  [concha  nasaUs  superior]  is  the  smallest,  projects  only  slightly  medialward 
and  downward  from  the  upper,  posterior  part  of  the  lateral  wall,  overhanging  the 
groove  called  superior  meatus  of  the  nose.  The  middle  nasal  concha  [concha 
nasalis  media]  is  extensive,  reaching  from  the  fore  part  to  the  posterior  confines  of 
the  lateral  wall.  Its  free  margin  is  nearly  vertical  in  its  anterior  one-fourth,  hori- 
zontal and  laterally  rolled  in  the  rest  of  its  extent.  Under  cover  of  this  concha 
runs  the  middle  meatus.  The  inferior  nasal  concha,  [concha  nasalis  inferior]  is  the 
longest,  has  a  lateral  attached  and  an  inferior  laterally  rolled  free  margin  running 
near  the  floor  of  the  nasal  cavity.     Beneath  it  lies  the  inferior  meatus. 

Meatuses  of  the  nose  [meatus  nasi]   (figs.  966,  968).     The  name  common 
meatus  of  the  nose  [meatus  nasi  communis]  is  given  to  that  part  of  the  nasal  cav- 

FiG.  967. — Frontal  Section  through  the  Facial  Portion  op  the  Head  of  a  White 
Man,  Age  28  Years. 


lofundibulum  - 
Ethmoidal  cell  — 

Middle  meatus 
Maxillary  sinus 
Inferior   meatus 


ity  which  lies  between  the  septum  nasi  and  the  nasal  conchas  and  stretches  from 
floor  to  roof.  The  three  meatuses  under  cover  of  the  nasal  conchae  have  been 
mentioned.  These  passages  all  communicate  freely  with  the  common  meatus, 
extend  antero- posteriorly  and  have  a  greater  capacity  in  front  than  behind. 
The  superior  meatus  [meatus  nasi  superior]  is  the  smallest  of  the  three.  Into 
it  open  the  posterior  ethmoidal  cells  by  one  or  two  small  foramina.  The  spheno- 
palatine foramen,  which  communicates  with  the  meatus  in  the  dry  skull,  is  entirely 
covered  up  bj^  mucous  membrane.  The  middle  meatus  [meatus  nasi  medius] 
is  a  much  larger  passage.  Upon  its  lateral  wall  is  a  rounded  eminence,  the 
ethmoidal  bulla,  caused  by  the  middle  ethmoidal  cells  and  perforated  by  the  open- 
ing into  them.  Inferior  to  this  is  a  deep  curved  groove,  the  hiatus  semilunaris, 
which  is  continued  superiorly  by  the  ethmoidal  infundibulum  [infundibulum  eth- 
moidale]  into  the  frontal  sinus.  It  also  receives  the  openings  of  the  anterior  eth- 
moidal cells  and  the  maxillary  sinus.  The  inferior  meatus  [meatus  nasi  inferior] 
is  the  longest  of  the  three.  Upon  its  lateral  wall,  just  inferior  to  the  attachment 
of  the  inferior  concha,  is  the  slit-like  opening  of  the  naso-lacrimal  duct  [ductus 
naso-lacrimalis],  around  the  opening  of  which  the  mucous  membrane  forms  a  valve, 
the  plica  lacrimalis  (Hasneri). 

Recent  investigation  of  the  nasal  conchae  indicates  that  two  upper  conchae  (concha  nasalis 
superior  and  concha  nasalis  suprema  [Santorini])  are  more  often  present  than  one.  Three  upper 
conchae  are  not  rare. 


1206  THE  RESPIRATORY  SYSTEM 

The  attached  margins  of  the  middle  and  inferior  conchse  are  both  arched,  the  convexities 
being  upward.  The  highest  point  of  the  convexity  is  near  the  middle  of  the  attached  margin 
in  the  inferior  concha  and  lies  about  17  mm.  above  the  floor  of  the  nose;  the  anterior  end  of  this 
concha  is  approximately  25-35  mm.  distant  from  the  apex  of  the  nose  (KaUius). 

From  the  anterior  end  of  the  middle  concha  a  slight  variable  elevation  of  the  mucous  mem- 
brane of  the  nose  extends  forward  and  downward.  This,  the  agger  nasi,  which  is  regarded  as 
of  constant  occurrence  in  the  new-born,  appears  to  be  a  rudimentary  representative  of  the  naso- 
turbinale  of  mammals  (Schwalbe). 

Below  the  agger  nasi  a  broad  depression  of  the  lateral  wall,  the  atrium  meatus  medii,  leads 
posteriorly  beneath  the  anterior  free  margin  of  the  middle  concha  to  the  middle  meatus,  while 
above  the  agger,  between  it  and  the  roof  of  the  nasal  cavity,  the  slight  olfactory  groove  [sulcus 
olfactorius]  ascends  upon  the  lateral  wall  to  the  olfactory  region.  In  this  region,  above  the 
superior  concha,  is  a  corner  of  the  nasal  cavity  of  interest  on  account  of  the  sphenoidal  sinus 
opening  into  it:  this  is  the  spheno-ethmoidal  recess  [recessus  spheno-ethmoidalis]. 

Variation  in  the  number  and  position  of  the  openings  into  the  meatuses  is  of  practical  inter- 
est. An  accessory  mouth  of  the  maxillary  sinus  is  rather  frequently  met  with,  especially  in  old 
people;  it  lies  most  commonly  behind  the  hiatus  semilunaris.  The  infundibulum  ethmoidale 
may  open  independently  of  the  hiatus  semilunaris  at  a  spot  beneath  the  anterior  end  of  the  at- 
tached margin  of  the  middle  concha.  In  the  inferior  meatus  the  mouth  of  the  naso-laorimal 
duct,  which  is  found  22-25  mm.  behind  the  posterior  margin  of  the  nares,  may  have  one  or  more 
accessory  openings  associated  with  it;  these  are  perforations  of  the  plica  lacrimalis. 

Communication  between  the  nasal  cavity  and  the  nasal  part  of  the  pharynx 
is  effected  by  means  of  the  paired  posterior  apertures  [choanse].  These  are  oval 
in  form,  their  height  greater  than  their  width.  They  are  located  at  either  side 
of  the  posterior  edge  of  the  nasal  septum  and  are  limited  above  by  the  body  of 
the  sphenoid,  below  by  the  line  of  junction  of  the  hard  and  soft  palate. 

From  the  plane  of  the  choana  forward  a  rather  constricted  portion  of  the  nasal  cavity  ex- 
tends for  a  short  distance  to  reach  the  level  of  the  posterior  ends  of  the  middle  and  inferior  con- 
chse. Into  this  region,  which  is  known  as  the  meatus  naso-pharyngeus,  open  posteriorly  the 
superior,  middle  and  inferior  meatuses.  Posterior  rhinoscopic  examination  reveals  the  choanse, 
the  naso-pharyngeal  meatus,  the  posterior  extremities  of  the  three  conchse  and  of  the  meatuses 
beneath  them. 

Dimensions  of  the  nasal  cavity. — The  length  of  the  floor  averages  approximately  40  mm., 
the  width  32  mm.,  the  height  from  floor  to  lamina  cribrosa  47  mm.  The  length  of  the  lateral 
wall  is  about  63  mm.  The  choana  measures  29.8  mm.  high  and  15.5  mm.  broad.  The  area  of 
the  two  nares  is  2  sq.  cm. 

Paranasal  sinuses  [sinus  paranasales]  (figs.  964-968). — The  location,  form  and 
relations  of  the  bony-walled  spaces  connected  with  the  nasal  cavity  have  been 
fully  described  in  the  section  on  Osteology.  The  conditions  observed  in  the 
living  subject  differ  in  certain  respects  from  those  present  in  the  macerated  skull; 
the  spaces  are  lined  by  a  mucous  membrane  which,  though  affecting  but  slightly 
the  form  of  these  chambers,  modifies  considerably  the  openings  by  which  they 
communicate  with  the  nasal  cavity.  These  openings  permit  the  entrance  and 
exit  of  air  and  to  some  extent  the  escape  of  fluids  which  may  accumulate  in  the 
sinuses.  While  the  significance  of  these  spaces  is  not  at  present  clear  it  is,  how- 
ever, certain  that  they  function  in  lightening  the  weight  of  the  skull,  and  probable 
that  indirectly  they  serve  in  connection  with  the  sense  of  smell. 

Maxillary  sinus  (of  Highmore*)  [sinus  maxillaris  Highmori]  (figs.  965, 966, 967). 

Entrance  into  the  maxillary  sinus  is  offered  through  the  middle  part  of  the  hiatus 
semilunaris,  that  is,  the  deep,  narrow  notch  between  the  ethmoidal  bulla  and  un- 
cinate process  of  the  ethmoid.  Viewed  from  within  the  sinus,  the  opening  appears 
as  an  oval  window  in  the  upper  part  of  the  medial  wall — a  position  unfavourable 
to  the  discharge  of  matter,  when  the  body  is  in  the  upright  posture.  An  accessory 
opening,  situated  behind  the  normal  ostium,  is  present  in  about  10  per  cent,  of 
cases. 

Measurements  of  90  specimens  of  the  adult  sinus  maxiUaris  gave  as  the  average  the  following 
(Schaeffer) : 

Dorsosuperior  diagonal 38     mm. 

Ventrosuperior  diagonal 38.5  mm. 

Superoinferior 33     mm. 

Ventrodorsal ". 34     mm. 

Mediolateral 23     mm. 

Increase  in  capacity  of  the  maxillary  sinus  is  sometimes  observed  as  the  result  of  more  or 
less  extensive  excavation  of  the  bony  processes  of  the  maxilla  adjacent  to  it,  viz. :  the  alveolar, 
palatal,  frontal  and  zygomatic.     On  the  other  hand  narrowing  of  the  cavity  is  encountered, 

*  Highmore,  Nathaniel:  English  physician.     B.  1613,  D.  1685. 


THE  NASAL  CAVITY 


1207 


caused  by  unusually  thick  walls  of  bone,  bulging  inward  of  the  facial  or  nasal  walls,  and  through 
retention  of  teeth.  Incomplete  division  into  two  parts  through  the  presence  of  a  septum  has 
several  times  been  observed.  Communication  with  ethmoidal  cells  and  with  the  cavity  of  the 
orbital  process  of  the  palate  bone  sometimes  exists. 

Frontal  sinus  [sinus  frontalis]  (figs.  78,  964,  968). — The  paired  frontal  sinuses, 
separated  from  each  other  by  a  bony  septum,  have  in  general  the  shape  of  a  three- 
sided  pyramid  with  the  base  below  and  the  apex  formed  above  in  the  frontal 
squama.  In  the  base  near  the  septum  is  located  the  superior  aperture  of  the 
infundibulum  which,  it  will  be  recalled,  opens  inferiorly  at  the  anterior  extremity 
of  the  hiatus  semilunaris. 

The  form  and  size  of  the  frontal  sinuses  are  exceedingly  variable.  They  may  extend  back- 
ward in  the  orbital  part  of  the  frontal  bone  as  far  as  the  suture  between  it  and  the  small  wing  of 
the  sphenoid;  laterally  into  the  zygomatic  process;  upward  toward  the  coronal  suture.  The 
capacity  of  the  sinus,  as  determined  in  a  small  number  of  cases,  varied  from  3  to  7.8  ccm. 
(Brvihl).  Asymmetry  of  the  septum  is  frequently  observed.  Absence  of  one  of  the  sinuses  is 
not  a  rare  condition;  absence  of  both  is  occasionally  encountered. 

Fig.  968. — ^Left  Nasal  Cavity.     (Rauber-Kopsch.) 


Opening  of 
sphe- 
Hypophysis        noidal  sinus 


Choanal  arch 

Pharyngeal  tonsil  — 

Torus  tubanus" 

Levator  cushion 

Anterior  lip  of 

tubal  aperture 

Salpingo- 
pharyngeal 
fold 


w     Naso-pharyngeal 
!  meatus  Sound 

Uvula  in  naso- 

lacrimal      „ 
canal  •-  S 


Ethmoidal  cells  [cellulse  ethmoidales]  (figs-  965,  968). — The  openings  of  the 
anterior  cells  into  the  semilunar  hiatus  and  infundibulum,  and  of  the  posterior 
cells  at  the  superior  meatus  have  already  been  described. 

Communications  between  the  ethmoidal  cells  and  the  sphenoidal  and  maxillary  sinuses  are 
not  rare;  the  cavity  in  the  orbital  process  of  the  palate  bone  may  open  into  the  posterior  cells. 
In  old  age,  foramina  through  the  lamina  papyracea  may  appear,  leading  to  the  introduction  of 
air  into  the  orbit. 

Sphenoidal  sinus  [sinus  sphenoidalis]  (figs.  964,  965,  966). — The  apertures  of 
the  paired  sphenoidal  sinuses  are,  on  account  of  the  mucous  membrane  covering, 
much  smaller  than  they  are  in  the  dried  skull.  They  lie  in  the  anterior  wall  near 
the  septum,  nearer  the  roof  than  the  floor,  and  open  into  the  spheno-ethmoidal 
recess. 

Extension  of  the  sphenoidal  sinuses  backward  and  also  into  neighbouring  processes,  and 
communication  with  ethmoidal  cells  and  with  the  small  cavity  of  the  orbital  process  of  the  palate 
are  not  unusual.     The  capacity  of  the  sinus  varies  between  1  and  4.2  ccm.  (Briihl). 

Functions  of  the  paranasal  sinuses. — Various  functions  have  been  attributed  to  the  sinuses 
near  the  nose,  none  of  which  is  entirely  satisfying.  Medieval  anatomists  proposed  that  these 
cavities  contributed  to  the  resonance  of  the  voice,  or  that  they  supplied  the  mucus  by  which  the 
nasal  cavity  is  kept  moist.  Lightening  the  skull,  warming  the  inspired  air  and  taking  part, 
indirectly,  in  the  sense  of  smell  are  functions  assigned  by  anatomists  of  later  times. 

The  mucous  membrane  of  the  nose  [membrana  mucosa  nasi]. — The  nasal  cav- 
ity is  completely  lined  with  mucous  membrane,  which  inferiorly,  at  the  limen  nasi 
blends  with  the  skin  covering  the  walls  of  the  vestibule  (p.  1204).  Posteriorly 
it  joins  the  mucous  membrane  of  the  pharynx  and  palate.     It  covers  some  of  the 


1208 


THE  RESPIRATORY  SYSTEM 


openings  which  are  seen  in  the  bony  walls;  those  apertures,  however,  which 
lead  into  the  paranasal-sinuses  and  into  the  naso-lacrimal  duct  remain  patent, 
although  as  already  stated  the  bony  openings  are  much  reduced  in  size. 

In  the  nasal  cavity  the  bright  rose-red  vascular  mucous  membrane  is  tightly  bound  to  the 
periosteum  and  perichondrium,  and  is  covered  with  a  cihated  columnar  epithelium.  Numerous 
large  mucous  nasal  glands  [glandules  nasales]  pour  their  more  or  less  watery  secretion  over  the 
entire  surface.  A  very  considerable  venous  plexus  is  found  in  many  parts  of  the  nasal  mucosa. 
Over  the  inferior  concha  and  to  a  less  extent  in  the  mucosa  of  the  middle  and  superior  conchEB, 
it  forms  the  cavernous  plexuses  of  the  conchse  [plexus  cavernosi  concharum]  contributing  to 
build  up  about  these  bodies  a  true  erectile  tissue.  The  thickness  which  these  glands  and  venous 
plexuses  give  to  the  mucous  membrane  of  the  conchoe  causes  the  marked  increase  in  size  of 
these  bodies  over  that  of  their  bony  supports.  The  region  covered  by  the  mucous  membrane 
just  described  forms  the  greater  part  of  the  nasal  cavity,  and  is  loiowTi  as  the  respiratory  region 
[regio  respiratoria].  The  mucous  membrane  of  a  small  area  over  the  superior  concha  and  the 
adjacent  septal  wall  (fig.  969)  has  a  somewhat  different  structure.  In  this  area  the  olfactory 
nerves  are  distributed,  whence  it  is  known  as  the  olfactory  region  [regiojolfactoria]  and  its  mucous 
membrane,  compared  with  that  of  the  respiratory  region,  is  less  vascular,  yellow  or  yellowish- 
brown  in  colour,  and  covered  by  a  non-ciliated  epitheUum.  Its  cells,  specially  modified,  some 
of  which  are  directly  connected  with  the  olfactory  nerve,  form  the  olfactory  organ  [organon 
olfactus].  Small  mucous  olfactory  glands  [glanduloe  olfactoria;]  occur  in  the  region.  The 
mucous  membrane  which  lines  the  paranasal  sinuses  throughout  is  a  continuation  of  the  nasal 
mucosa;  it  is,  however,  paler,  less  vascular,  somewhat  thinner,  and  more  loosely  attached  to 
the  bones.     Mucous  glands  are  numerous. 

The  waving  of  the  ciha  in  the  nasal  cavity  is  such  as  to  sweep  foreign  matter  toward  the 
choanje;  in  the  paranasal  sinuses,  toward  the  nasal  cavity. 


Fig.  969. — Diagram  of  the  Distribution  of  the  Nerves  in  the  Nasal  Cavity.     (Poirier 

and  Charpy.) 
The  olfactory  area  is  represented  by  dots. 


Posterior  superior  nasal 


Posterior  su- 
Anterior  perior  nasal 
ethmoid      ant  pal 


Vessels  and  nerves. — The  arteries  of  the  nasal  cavity  are  the  spheno-palatine  artery  from 
the  internal  maxillary  which,  through  its  posterior  lateral  nasal  branches,  supplies  the  middle 
and  inferior  conchfe  (p.  549),  the  anterior  and  posterior  ethmoidal  arteries  from  the  ophthalmic 
(p.  553),  the  descending  palatine  artery  from  the  internal  maxiUary  (p.  549),  and  the  superior 
labial  branch  of  the  external  ma.xiUary  to  the  vestibule.  The  venous  plexuses  of  the  mucous 
membrane  are  drained  posteriorly  by  the  spheno-palatine  to  join  the  pterygoid  plexus,  superiorlj 
by  the  anterior  and  posterior  ethmoidal  veins  to  join  the  superior  ophthalmic  vein,  and  ante- 
riorly by  small  branches  to  join  the  facial.  The  lymphatics  form  a  weU-developed  plexus  which 
is  said  to  communicate  indirectly,  through  the  lymphatics  surrounding  the  olfactory  nerves, 
with  the  subdural  and  subarachnoid  spaces.  Posteriorly  two  or  more  well-developed  trunks 
communicate  with  the  pharyngeal  lymphatics,  and  anteriorly  the  nasal  lymphatics  join  with 
the  lymphatics  of  the  face.  The  olfactory  nerves  pass  through  the  cribriform  plate  of  the 
ethmoid  bone  and  are  distributed  to  the  olfactory  area  (p.  929).  The  trigeminal  nerve  furnishes 
the  following  branches  to  the  nasal  cavity: — branches  from  the  naso-ciliary  branch  of  the  oph- 
thalmic nerve ;  the  Vidian  nerve ;  the  posterior  superior  and  posterior  inferior  nasal  and  the  ante- 
rior palatine  from  the  spheno-palatine  ganglion  (p.  962);  the  anterior  superior  alveolar  from  the 
infra-orbital  division  of  the  maxillary  nerve  (p.  938). 

The  development  of  the  nose. — The  nasal  cavity  malves  its  appearance  as  a  depression  of 
the  ectoderm  on  either  side  of  the  median  line,  immediately  in  front  of  the  oral  fossa,  with 
which  the  depressions  are  at  first  continuous.  Later,  by  the  union  of  the  maxillary  and  globular 
processes  (see  p.  18),  the  depressions  are  separated  from  the  anterior  part  of  the  oral  fossa,  and 
this  separation  is  continued  by  the  formation  of  the  palatal  processes  of  the  maxillas  and  palatine 
bones,  so  that  finally  the  nasal  cavities  communicate  posteriorly  only  with  the  pharynx. 

The  cartilage  which  forms  the  lateral  walls  of  the  nasal  fossas  is  at  first  quite  smooth,  but 
later  it  becomes  eroded  by  absorption,  whereby  the  nasal  concha;  are  formed.  The  erosion  also 
extends  into  the  ethmoid  bone,  forming  the  ethmoidal  cells,  and  into  the  neighbouring  bones 
to  form  the  frontal,  sphenoidal,  and  maxillarjf  sinuses. 


CARTILAGES  OF  THE  LARYNX 
THE  LARYNX 


1209 


The  larynx  (figs.  960,  970,  971,),  is  a  tubular  organ,  the  framework  of  which  is 
made  of  cartilages  joined  together  and  of  elastic  membranes.  Its  inner  surface 
is  covered  by  mucosa.  From  the  membranes  are  formed  a  pair  of  vocal  folds 
which,  by  the  passage  of  air  through  the  larynx,  are  thrown  into  vibration  and  so 
function  in  the  generation  of  sound.     These  folds  are  affected  in  respect  to  their 

Fig.  970. — View  of  Interior  op  Larynx  as  seen  from  above  during  Inspiration. 


"Base  of  tongue 


Median  glo 

Epiglottis 

Tubercle  of  epiglotti 

Ventricular  fold 
Ary-epiglottic  fold 
Cuneiform  tubercle 
Corniculate  tubercle 


Arytenoid  commissure 


Pharynx 


tension  and  in  their  mutual  relation  by  the  actions  of  a  system  of  laryngeal 
muscles  under  the  control  of  the  vagus  nerve  and  are  made  thereby,  on  the  one 
hand,  to  produce  those  modifications  of  the  sound  involved  in  the  voice  and  on 
the  other  hand  to  regulate  the  amount  of  air  passing  through  the  cavity  of  the 
larynx.  The  latter  communicates  above  with  the  pharynx  by  means  of  the 
opening  called  the  laryngeal  aperture,  and  below  with  the  cavity  of  the  trachea. 
Figure  970  shows  the  laiyngeal  aperture  with  its  boundaries,  the  epiglottis  and 

Fig.  971. — View  of  Interior  of  Larynx  as  seen  from  above  during  Vocalisation. 


Base  of  tongue 
Median  glosso-epiglottic  fold 


Ventricular  fold 

Vocal  fold 

Piriform  recess 

Vocal  process. 


Epiglottis 

Tubercle  of  epiglottis 


Ventricle 
Ary-epiglottic  fold 


the  aryepiglottic  folds ;  also  the  cavity  of  the  larynx  where,  on  the  walls  right 
and  left,  appear  the  ventricular  and  vocal  folds  with  the  chink  called  rima  glot- 
tidis  separating  them. 

The  position  of  the  larynx  and  some  of  its  important  parts  can  be  well  seen  in 
a  median  section  (fig.  972). 

THE  CARTILAGES  OF  THE  LARYNX 

The  number  of  cartilages  entering  into  the  framework  of  the  larj^nx  is  nine, 
three  of  which  are  single  and  the  rest  in  pairs.  Their  forms  and  positions  are 
shown  in  fig.  973. 


1210 


THE  RESPIRATORY  SYSTEM 


The  cricoid  cartilage  [cartilago  cricoidea]  (figs.  973,  974,  975,  978),  single,  has 
been  compared  in  its  shape  to  a  signet  ring.  Its  position  is  at  the  lower  end  of 
the  larynx,  where  it  is  connected  with  the  first  ring  of  the  trachea.  Posteriorly 
the  cricoid  cartilage  expands  into  a  broad  lamina  [lamina  cartilaginis  cricoidese] 
which  enters  into  the  posterior  boundary  of  the  laryngeal  cavity,  while  laterally 
and  in  front  it  forms  a  narrow  arch  [arcus  cartilaginis  cricoideae].  On  either  side 
of  the  upper  margin  of  the  lamina  is  the  elliptical  arytaenoid  articular  surface 
[facies  articularis  arytsenoidea]  its  long  axis  parallel  with  the  margin  of  the  cricoid, 
its  steeply  sloping  surface  convex  for  articulation  with  the  arytsenoid  cartilage. 
The  hinder  surface  of  the  lamina  presents  a  median  ridge  and  lateral  impressions 
for  the  attachment  of  the  posterior  crico-arytsenoid  muscles.     The  arch,  weakest 


Fig.  972.- 


-Median  Section  op  a  Man  21  Years  of  Age,  showing  the  Position  of  Larynx 
AND  Trachea.     (After  W.  Braune,  from  Poirier  and  Charpy.) 


Epiglottis — 

Hyoid  bone^ 

Laryngeal 

aperture 

Fat  mass' 

Laryngeal 

ventricle 

Thyreoid 

cartilage 

Lamina  of 

cricoid 

Arch  of  cricoid 

Trachea 

(Esophagus 

Thyreoid  body 

Sterno- 

thyreoid  m.' 

Sternum' 

Left  innominate. 

vein 

Innominate, 
artery 


Ascending  aorta 

Right  lung — 
Right  auricle — 


Pharynx 

Arytaenoid 

.  cartilage 

WW      '„  ~""  Ventricular  fold 

^  \\\' ^  Vocal  fold 

\YI  cervical 
vertebra 


in  its  middle  part,  presents  concave  upper  and  straight  lower  margins.  A  circular, 
elevated  thyreoid  articular  surface  [facies  articularis  thyreoidea]  for  articulation 
with  the  inferior  cornu  of  the  thyreoid  cartilage  is  situated  upon  the  side  of  the 
cricoid  where  arch  and  lamina  are  continuous.  The  internal  surface  is  covered  by 
the  laryngeal  mucosa. 

The  thyreoid  cartilage  [cartilago  thyreoidea]  (figs.  973,  974,  975,  977),  single 
and  the  largest  in  the  laryngeal  skeleton  is  composed  of  two  broad  laminae, 
right  and  left,  which  meet  and  are  fused  anteriorly  in  the  mid-line  in  a  right  angle, 
partly  covering  the  other  cartilages  laterally  and  in  front.  The  laminae  are  stout, 
but  their  connection  at  the  angle  is  through  a  weak  strip  of  cartilage.  The  upper 
margin  of  each  lamina  is  convex,  and  in  front  drops  abruptly  to  form  in  the  median 
line  the  superior  thyreoid  notch  [incisura  thyreoidea  superior] .     The  anterior  edges 


CARTILAGES  OF  THE  LARYNX 


1211 


meeting  in  the  angle  produce  the  laryngeal  prominence  [prominentia  laryngea] 
("Adam's  apple"),  which  is  seen  on  the  front  of  the  neck.  The  horizontal  in- 
ferior margin  presents  near  its  middle  the  inferior  thyreoid  tubercle  [tuberculum 
thyreoideum  inferius],  and  in  the  median  line  the  inferior  thyreoid  notch  [incisura 
thyreoidea  inferior].  The  thick  posterior  margin  of  each  lamina  is  continued  above 
the  superior  edge  in  the  long  superior  cornu  [cornu  superius],  and  below  the  inferior 
margin  in  the  short  inferior  cornu  [cornu  inferius].  The  former  is  directed  slightly 
backward  and  medial  ward,  and  joins  with  the  end  of  the  greater  cornu  of  the 
hyoid  by  ligament.  The  inferior  cornu,  curving  medialward  as  it  descends,  articu- 
lates by  a  flat,  circular  facet  upon  the  medial  side  of  its  extremity  with  the  thy- 
reoid articular  surface  of  the  cricoid  cartilage.  The  external  surface  of  the  lamina 
affords  attachment  for  muscles  and  presents  in  its  upper  posterior  part   the 

Fig.  973. — Caetilaqes  op  the  Labynx  seen  prom  behind  in  Their  Natural  Positions. 
The  CtTNEiFORM  Cartilage  is  Somewhat  Higher  than  Normal.     (Merkel.) 


Epiglottic  cartilage 


Corniculate  cartilage 


Arytaenoid  cartilage 


I —  Superior  cornu  of  thyreoid 


Cuneiform  cartilage 


Thyreoid  cartilage 


Inferior  cornu  of  thyreoid 


Median  crest 


superior  thyreoid  tubercle  [tuberculum  thyreoideum  superius] ;  in  its  lower  part 
the  inferior  thyreoid  tubercle.  The  internal  surface  of  the  thyreoid  cartilage  is 
smooth. 

A  thyreoid  foramen  [foramen  thyreoideum],  sometimes  seen  in  the  upper  part  of  the  lamina, 
giving  passage  to  the  superior  laryngeal  artery,  results  from  the  incomplete  union  of  the  fourth 
and  fifth  branchial  cartilages  from  which  the  lamina  are  derived.  The  oblique  line  [lines 
obUqua],  extending  between  the  thyreoid  tubercles,  is  commonly  present  and  is  regarded  by 
many  anatomists  as  a  normal  feature  of  the  external  surface  of  the  thyreoid  cartilage.  It 
marks  the  attachment  of  the  sternohyoid  and  thyreohyoid  muscles.  At  the  insertion  of  the 
vocal  ligaments  in  the  angle  of  the  laminae  a  small  perichondral  process  is  often  observed. 

The  arytaenoid  cartilages  [cartilagines  arytsenoidese]  (figs.  973,  977,  978, 
979),  paired,  surmount  the  lamina  of  the  cricoid  cartilage  and  give  attachment  to 
the  vocal  ligaments,  whose  relations  and  state  of  tension  are  altered  by  the  changes 
in  position  which  these  cartilages  are  almost  constantly  undergoing. 

Each  cartilage  is  pyramidal  in  form,  and  moulded  for  the  attachment  of  several 
muscles.  The  apex,  which  is  above,  is  bent  backward  and  medialward  and  is 
connected  with  a  corniculate  cartilage.  The  base,  somewhat  triangular  in  shape, 
presents  at  the  lateral  and  posterior  part  an  oval  or  circular  concave  articular 
surface  [facies  articularis],  directed  medialward  and  downward  to  meet  the 
aryteenoid  articular  surface  of  the  cricoid  cartilage.  The  lateral  angle  of  the  base 
is  prolonged  into  a  stout  muscular  process  [processus  muscularis]  for  the  attach- 


1212 


THE  RESPIRATORY  SYSTEM 


ment  of  the  crico-arytsenoid  muscles,  while  the  anterior  angle  is  extended  as  a 
sharp  projection,  the  vocal  process  [processus  vocalis],  which  serves  for  the 
attachment  of  the  vocal  ligament.  The  surfaces  of  the  arytsenoid  are  named 
medial,  posterior,  and  antero-lateral.  The  narrow  medial  surface,  covered  by  the 
mucosa  of  the  larynx,  is  nearly  vertical,  and  faces  the  corresponchng  side  of  the 
opposite  arytsenoid,  from  which  it  is  separated  by  a  small  space.  The  posterior 
surface  is  concave  for  muscular  attachment.  The  antero-lateral  surface  is  the 
largest,  and  presents  an  irregular  contour. 

On  this  surface  a  ridge,  the  arcuate  crest  [crista  arcuata],  extends  horizontally  between 
two  hollows — the  triangular  fovea  [fovea  triangularis]  above,  which  lodges  some  mucous 
glands,  and  a  larger  depression  below,  the  oblong  fovea  [fovea  oblonga]  for  the  vocal  muscle. 
The  colliculus  is  a  small  eminence  found  upon  the  anterior  margin  and  antero-lateral  surf  ace. 


Fig.  974. — Fkont  View  of  the  Laryngeal  Skeleton.     (Modified  from  Bourgery  and  Jacob.) 

Greater  corau  of  hyoid* 

Body  of  hyoid 

Lateral  hyo-thyreoid  ligament 

Triticeous  cartilage 

Foramina  for    superior    laryngeal 

vessels  and  internal  laryngeal  n. 

Median  hyo-thyreoid  ligament 

Superior  cornu  of  thyreoid 

Superior  thyreoid  notch 
Lamina  of  thyreoid 

Oblique  line 

Median  crico-thyreoid  ligament. 
Inferior  cornu  of  thyr 

Crico-thyreoid  joint" 
Crico-tracheal  ligament 

Tracheal  cartilagt 


The  corniculate  cartilages  (of  Santorini)  [cartilagines  corniculatse  (Santorini*)] 
(figs.  973,  977). — This  pair  of  small  conical  cartilages  is  set  upon  the  bent  apices  of 
the  arytsenoids,  continuing  their  curves  backward  and  mechalward. 

The  corniculate  cartilage  is  not  an  independent  structure  in  many  lower  animals,  and  its 
continuity  with  the  arytsenoid  is  sometimes  met  with  in  man  where  the  two  cartilages  are 
normally  developed  in  a  continuous  mass  of  tissue. 

The  epiglottic  cartilage  [cartilago  epiglottica]  (figs.  973,  977,  981,  987), 
unpaired,  invested  by  mucosa  behind  and  partly  in  front,  thin  and  leaf-shaped, 
stands  behind  the  root  of  the  tongue  and  the  body  of  the  hyoid.  It  lies  above  the 
thyreoid  cartilage,  in  front  of  the  entrance  of  the  larynx.  The  free  upper  margin 
is  convex,  or  notched;  the  lower  end  tapers  to  a  short  stalk,  the  petiole  of  the 
epiglottis  [petiolus  epiglottidis],  to  which  the  thyreo-epiglottic  ligament  is 
attached. 

The  anterior  surface  is  free  above  and  covered  by  mucosa;  in  its  lower  part 
it  is  bound  to  the  body  of  the  hyoid,  and  is  separated  by  a  mass  of  fat  from 

*  Santorini:  Venetian  anatomist.     B.  1681,  D.  1737. 


JOINTS  OF  THE  LARYNX 


1213 


the  hyo-thyreoicl  ligament.  Its  posterior  surface  above  is  saddle-shaped;  below, 
it  is  convex,  presenting  the  epiglottic  tubercle  [tuberculum  epiglotticum].  To 
the  margins  are  attached  the  ary-epiglottic  folds.  The  epiglottic  cartilage 
presents  numerous  small  holes  and  depressions  for  the  accommodation  of  glands. 
The  cuneiform  cartilages  (of  Wrisberg)  [cartilagines  cuneiformes  (Wrisbergi*)] 
(fig.  973)  lie  as  small,  rod-like  bodies  in  the  ary-epiglottic  folds  anterior  to  the 
corniculate_  cartilages.  They  are  variable  in  form  and  size  and  not  rarely  absent 
altogether. 

These  cartilages  are  parts  of  the  epiglottic  cartilage  in  some  mammals  where,  as  in  man, 
they  he  in  the  ary-epiglottic  folds.  Their  relations  to  the  arytEcnoids  are  regarded  as  secondary. 
Sutton  has  shown  that  in  the  ant-eater  a  continuous  rim  of  yellow  elastic  cartilage  extends 
from  the  sides  of  the  epiglottic  cartilage  to  the  summits  of  the  aryttenoids.  A  minute  unpaired 
inlerarylmnoid  or  procricoid  cartilage  is  rarely  present  imbedded  in  the  cricopharyngeal  ligament 
and  covered  by  the  pharyngeal  mucosa.  It  is  a  constant  structure  in  certain  mammals.  A 
pair  of  small  sesamoid  cariilages,  also  constantly  present  in  some  mammals,  is  occasionally 
found  in  man  at  the  lateral  margins  of  the  arytaenoids,  connected  with  them  and  with  the 
corniculate  cartilages  by  elastic  ligaments. 

Structure  of  the  cartilages. — The  thyreoid,  cricoid,  and  greater  part  of  the  aryta;noid  are 
composed  of  hyaline  cartilage;  the  epiglottic,  corniculate,  and  cuneiform  cartilages,  as  well  as 
the  ape.x  and  vocal  process  of  the  arytsenoid,  are  of  elastic  cartilage.  Certain  parts  of  the  laryn- 
geal skeleton  normally  undergo  calcification  and  subsequent  ossification.  Calcification  begins 
at  about  twenty  years  of  age  in  the  thyreoid  and  cricoid  cartilages,  and  later  in  the  arytenoid. 
The  process  begins  a  little  later  in  the  female  than  in  the  male,  and  does  not  extend  so  rapidly. 
The  extent  to  which  the  cartilages  are  ossified  and  the  time  occupied  in  the  process  vary  con- 
siderably.    The  elastic  elements  are  not  involved  in  the  process. 


Fig.  975.- 
FiG.  976.- 


-Cricoid  AND  Arytenoid  Cartilages  seen  prom  Before. 
-Cricoid  and  Arytenoid  Cartilages  seen  erom  the  Left. 


(Rauber-Kopsch.) 
(Rauber-Kopsch.) 


Corniculate  cart. 


Apex  of  arytjenoid 
CoUiculus 
"  Arcuate  crest 


^  Muscular 
process 
■  Vocal  process 


Ary-corniculate  synchondrosis 

Corniculate 

Colliculus..- 

g,  ^  Arcuate 

Tnangular  pit ** crest 

Oblong  pit  "■■■■/"'^W^^ft-  Muscular 
Vocal  process  .— *''^^^ait^9*'^^SS|^H     process 

-  .  ^™-|...,  Lamina  of 

.^'^  HIh     cricoid 

-Thyreoid 
A     1.    £        /  w^mobUr't'  nMMMjcffi^       artlcular 

Arch  of  ...4i^mi!,,..:      "mai       surface 


THE  JOINTS  AND  FIBROUS  MEMBRANES  OF  THE  LARYNX 
(1)  Connections  between  the  Laryngeal  Cartilages 

The  crico-thyreoid  articulation  (figs.  973,  974,  975). — The  articular  surfaces 
concerned  are  the  thyreoid  articular  surface  on  the  side  of  the  cricoid  and  the 
articular  surface  on  the  inferior  cornu  of  the  thyreoid  cartilage.  The  crico- 
thyreoid  articular  capsule  [capsula  articularis  cricothyreoidea]  attached  around 
the  margins  of  these  surfaces  and  certain  accessory  bands  serve  to  bind  the  carti- 
lages together. 

The  accessory  bands,  cerato-cricoid  ligaments  fall  into  three  groups  radiating  from  the 
inferior  cornu:  the  ligamenta  ceratocricoidea  posteriora  upward  and  medialward  to  the  superior 
margin  of  the  cricoid;  tlie  ligamenta  ceratocricoidea  lateralia  downward  at  the  side  and  back 
of  the  capsule;  the  ligarnentum  ceratocricoideum  anterius  downward  and  forward.  The 
capsule  possesses  a  synovial  layer. 

A  rotary  movement  about  a  transverse  axis  of  the  cricoid  upon  the  thyreoid 
or  vice  versa  and  a  slight  backward  and  forward  gliding  are  permitted  at  this 
joint. 

*  Wrisberg:  German  anatomist.    B.  1737,  D.  1808. 


1214 


THE  RESPIRATORY  SYSTEM 


The  crico-arytaenoid  articulation  [articulatio  cricoarytsenoidea  (figs.  973,  977, 
978). — The  articular  surface  of  the  cricoid  cartilage  and  the  articular  surface 
of  the  arytsenoid  which  enter  into  this  articulation  are  so  disposed  that  at  no  time 
do  they  meet  in  complete  apposition.     A  loose  capsule  [capsula  articularis  crico- 

FiQ.  977. — The  Laryngeal  Skeleton  seen  from  Behind.     (Poirier  and  Charpy.) 

—    ____ Epiglottic  cartilage 

— . — ^Greater  cornu  of  hyoid 
-Triticeous  cartilage 


Hyo-thyreoid  membrane——. 


Posterior  crico-arytae 
ligament 


Inferior  comu  of  thyreoid 
Lamina  of  cricoid 


Membranous  wall  of   trachea 


Body  of  hyoid 

Superior  comu  of  thyreoid 


"Thyreo-epigottic  ligament 


Corniculate  cartilage 

Corniculo-  and  crico- 

geal  ligaments 
'ArytEenoid  cartilage 


Crico-aryt£enoid  joint 

Posterior  cerato-cricoid 

ligament 
Crico-thyreoid  joint 

^Lateral  cerato-cricoid  ligament 


Fig.  978. — The  Larynx  with  its  Ligaments,  viewed  from  the  Right.     (The  right  lamina  of 
the  thyreoid  cartilage  has  been  removed.)     (Spalteholz.) 


Eoiglottis 
Ary-epiglo  tti 
fold  (section 
through  the 
mucous  mem- 
brane) 


Arytenoid  cartilage 

Muscular  process  — 

Crico-arytEenoid  joint  '^ 
Vocal  process 

Theyreoid  articular  surface''' 

Tracheal  cartilages  <^ 


epiglottic  ligament 


—Median  hyo-thyreoid  ligament 
'/'—Quadrangular  membrane 
—  Thyreoid  cartilage 

Ventricular  ligament 

'Vocal  ligament 

"Elastic  cone 
Median  crico-thyreoid  ligament 

-  Arch  of  cricoid 

—  Cnco-tracheal  ligament 

—  Annular  ligament 


arytaenoidea]  of  fibrous  and  synovial  strata  attached  around  the  edges  of  the  joint 
surfaces  unites  the  cartilages. 

Posterior  crico-arytsenoid  ligament  [Hg.  cricoarytsenoideum  posterius],  attached  above„  to 
the  medial  surface  of  the  base  and  muscular  process  of  the  arytainoid,  and  below  to  the  lamina 


MEMBRANES  OF  THE  LARYNX  1215 

of  the  cricoid,  is  important  in  helping  to  fix  the  former  cartilage  in  place  upon  the  sloping 
arytaenoid  articular  surface  of  the  cricoid  and  in  limiting  its  movements.  Motion  at  this 
articulation  is  very  free.  The  following  simple  movements  of  the  arytaenoid  are  best  under- 
stood:— (1)  gliding  of  the  arytaenoid  toward  or  away  from  its  fellow;  (2)  inclining  forward  and 
backward;  (3)  rotating  on  a  vertical  axis,  so  that  the  vocal  process  sweeps  medialward  or  lateral- 
ward  and  also  a  little  downward  or  upward. 

The  union  of  the  corniculate  cartilage  with  the  apex  of  the  arytsenoid  cartilage 
[synchondrosis  arycorniculata]  is  usually  by  connective  tissue;  rarely  is  there  a 
joint  cavity. 

The  petiole  of  the  epiglottic  cartilage  is  connected  with  the  thyreoid,  below 
and  behind  the  superior  notch,  by  a  strong,  elastic  thyreo-epiglottic  ligament 
[lig.  thyreoepiglotticum]  (fig.  977). 

(2)  The  Elastic  Membrane  of  the  Larynx 
[Membrana  elastica  laryngis] 

This  name  is  given  to  a  more  or  less  continuous  sheet  of  elastic  fibres  connected 
with  the  deeper  parts  of  the  laryngeal  mucosa.  Its  upper  part  is  known  as  the 
quadrangular  membrane,  the  lower  part  as  the  elastic  cone.  A  middle  region  of  the 
elastic  membrane  lies  opposite  the  ventricle  of  the  larynx. 

The  quadrangular  membrane  (figs.  978,  981,  988)  extends  from  the  ary-epi- 
glottic  folds  above  to  the  level  of  the  ventricular  folds  (false  vocal  cords)  below. 
The  lateral  parts  of  this  membrane  are  widely  separated  superiorly,  but  they  con- 
verge toward  the  middle  line  as  they  descend.  Anteriorly,  the  membrane  is 
fixed  in  the  angle  of  the  thyreoid  laminae  and  to  the  sides  of  the  epiglottic  car- 
tilage; posteriorly,  to  the  corniculate  cartilages  and  to  the  arytaenoids.  The 
superior  edge  on  either  side  lies  within  the  ary-epiglottic  fold,  which  it  supports; 
it  slopes  downward  and  backward  and  includes  the  cuneiform  cartilage.  The 
inferior  edge,  horizontal  and  in  a  sagittal  plane,  is  best  developed  in  front,  where 
it  is  attached  in  the  angle  of  the  thyreoid  a  little  way  from  the  middle  line ;  behind, 
it  is  fixed  to  the  medial  margin  of  the  triangular  fovea  of  the  arytsenoid.  This 
inferior  free  margin,  differentiated  as  the  ventricular  ligament  [lig.  ventriculare], 
is  enclosed  within,  and  is  the  support  for  the  ventricular  fold. 

Fia.  979. — The  Elastic  Cone  seen  from  Above.     (Modified  from  Luschka.) 
Nodule  of  elastic  tissue  ^„..^I'erichondraI  insertion  of  vocal  ligaments 


Nodule  of  elastic  tissue 
.Vocal  ligament 
Elastic  I 

tilage 


Arytaenoid  cartilage  in  transverse  section 
Posterior  crico-arytaenoid  ligament 

The  elastic  cone  [conus  elasticus]  (figs.  978,  979). — -This  part  of  the  elastic 
membrane  extends  from  the  level  of  the  vocal  folds  to  the  superior  margin  of  the 
cricoid  cartilage.  Its  component  fibres  are  attached  in  the  re-entrant  angle  and 
adjacent  lower  margin  of  the  thyreoid  cartilage,  whence  they  spread  downward 
and  backward  to  the  upper  edge  of  the  cricoid  arch  and  to  the  arytsenoid  carti- 
lages. The  strong  anterior  portion,  perforated  by  vessels,  is  the  median  crico- 
thyreoid  ligament  [fig.  cricothyreoideum  (medium)]  (figs.  974,  975).  The  lateral 
parts  (lateral  portions  of  the  crico-thyreoid  membrane)  present  superior  free 
edges,  somewhat  thickened,  which,  running  horizontally  near  the  middle  line  from 
the  thyreoid  angle  to  the  vocal  processes,  constitute  the  vocal  ligaments.  These 
are  inserted  anteriorly  into  a  perichondral  process  in  the  thyreoid  angle;  poster- 
iorly, they  have  a  wide  area  of  attachment  to  the  upper  and  medial  surfaces  of  the 
vocal  processes  of  the  arytaenoids  with  the  elastic  fibres  of  which  they  are  in  part 
continuous.     A  yellowish,  cellular  nodule  (sometimes  cartilage)  occurs  in   the 


1216 


THE  RESPIRATORY  SYSTEM 


anterior  end  of  each  ligament.     The  vocal  ligaments  enter  into  the  formation  of 
the  vocal  folds  (true  vocal  cords). 

Fig.  980. — The  Larynx  seen  from  the  Left  Side.     (Modified  from  Luschka.) 

Epiglottis  J 


Hyoid  bone 


Thyreo-hyoid  musclo— ^ 


Thyreoid  cartilage- 


Median  crico-thyreoid  ligament' 
Crico-thyreoid  muscle  (straight  part) 


Tracheal  cartilage 


Internal  laryngeal  nerve 
Hyo-thyreoid  membrane 


Superior  laryngeal  artery 
Superior  laryngeal  vein 


Cricothyreoid  muscle  (oblique  part) 
ry — Posterior  crico-arytsenoid  muscle 
Cricoid  cartilage 


Fig.  981. — The  Muscles  and  Ligaments  of  the  Larynx  seen  from  the  Side.     (The  left 
lamina  of  the  thyreoid  cartilage  has  been  removed.) 


Hyo-epiglottic  ligament- 
Body  of  hyoid. 
Fat  mas?. 
Hyo-thyreoid  membrane — 

Thyreo-epiglottic  muscle 

Quadrangular  membrane — 


Thyreoid  cartilage 

External  thyreo-arytaenoid  muscle 

Elastic  cone 

Lateral  crico-arytaenoid  muscle 

Median  crico-thyreoid  ligament 


Cricoid  cartilage 


■Ary-epiglottic  fold 
Ary-epiglottic  and  ary- 
_|  -'--•  membranosus  muscles 


Posterior  crico-arytaenoid  muscle 
-Thyreoid  articular  surface 


Lamina  of  cricoid 


Inferior  laryngeal  nerve 


The  median  crico-thyreoid  ligament  is  incised  m  the  operation  of  laryngotomy.  It  is 
crossed  by  the  anastomotic  arch  of  the  crico-thyreoid  arteries,  which,  however,  can  be  avoided 
in  the  operation  by  making  a  transverse  cut  through  the  ligament  close  to  the  superior  margm 
of  the  arch  of  the  cricoid  cartilage. 


LIGAMENTS  OF  THE  LARYNX  1217 

(3)  Connections  between  the  Larynx  and  Neighbouring  Structures 

The  hyo-thyreoid  membrane  [membrana  hyothyreoidea]  (figs.  977,  980,  981) 
is  a  loose,  fibrous,  elastic  sheet,  binding  together  the  thyreoid  cartilage  and  hyoid 
bone.     It  extends  from  the  superior  margin  of  the  former  to  the  greater  cornua  and 

Fig.  982. — Scheme  of  Rima,  showing  Action  of  Posterior  Crico-aryt^noid  Muscle, 
WHICH  DRAWS  THE  ArttjEnoid  Cartilage  PROM  I  TO  II.     (Modified  from  Stirling.) 


superior  margin  of  the  body  of  the  latter.  The  superior  laryngeal  artery  and  vein 
and  the  internal  laryngeal  nerve  pass  through  it  from  the  side.  Its  posterior  and 
lateral  edge  is  cord-like,  consisting  of  elastic  fibres  which  stretch  as  the  lateral 

Fig.  983. — Scheme  showing  Action  of  the  Transverse  Arytenoid  drawing  Arytenoid 
Cartilage  from  Neutral  Position  I  to  II.     (Modified  from  Stirling.) 


hyo-thyreoid  ligament  [lig.  hyothyreoideum  laterale]  from  the  superior  cornu  of  the 
thyreoid  to  the  greater  cornu  of  the  hyoid.  A  small  cartilago  triticea  is  sometimes 
present   in  this  band.     The  middle    part,  median  hyo-thyreoid  ligament  [hg. 

Fig.  984. — Scheme  showing  Action  of  Thyreo-arty^noid  drawing  the  Vocal  Processes 
and   the    Vocal   Ligaments   from   II   to   I.     (Modified   from   Stirling.) 


hyothyreoideum  medium]  thick  and  elastic,  extends  from  the  superior  thyreoid 
notch  upward  behind  the  body  of  the  hyoid  to  be  attached  to  its  superior  margin, 
the  hyoid  bursa  being  interposed  between  the  bone  and  the  membrane. 


1218  THE  RESPIRATORY  SYSTEM 

The  cartilage  tritioea  is  the  remains  of  a  connection  between  the  thyreoid  and  hyoid  present 
in  the  embryo.     It  persists  in  adult  hfe  in  some  lower  animals. 

The  hyo-epiglottic  ligament  [lig.  hyoepiglotticum]  (figs.  978,  981)  connects  the 
anterior  surface  of  the  epiglottic  cartilage  with  the  superior  margin  of  the  body  and 
the  greater  cornua  of  the  hyoid.  It  is  a  broad  sheet,  lying  above  a  mass  of  fat 
which  stands  between  the  median  hyo-thyreoid  membrane  and  the  epiglottis 
and  spreading  laterally  to  join  the  pharyngeal  aponeurosis  in  the  region  of  the 
piriform  recess. 

The  name  glosso-epiglottic  ligament  is  given  to  the  elastic  fibres  extending 
between  the  root  of  the  tongue  and  the  epiglottis  within  the  median  glosso-epi- 
glottic fold. 

The  corniculo -pharyngeal  ligament  (fig.  977)  extends  from  the  corniculate  cartilage  down- 
ward and  toward  the  median  hne,  attaching  to  the  mucosa  of  the  pharjoix  and  joining  its 
fellow  behind  the  arytaenoid  muscle.  From  this  point  a  single  band,  the  crico -pharyngeal  liga- 
ment [hg.  oricopharyngeum],  which  may  enclose  a  nodule  of  cartilage  (the  interarytsenoid 
or  procricoid  cartilage),  descends  in  the  middle  line,  to  be  fixed  to  the  cricoid  lamina  and  into 
the  pharyngeal  mucosa. 

The  larynx  and  trachea  are  united  by  fibrous  membrane,  the  crico-tracheal 
ligament  [lig.  cricotracheale]  (figs.  974,  978),  between  the  inferior  margin  of  the 
cricoid  cartilage  and  the  upper  margin  of  the  first  tracheal  ring.  Posteriorly 
the  ligament  is  continued  into  the  membranous  wall  of  the  trachea. 

MUSCLES  OF  THE  LARYNX 

Of  the  many  muscles  connected  with  the  larynx,  two  groups  may  be  recog- 
nised, the  members  of  one  coming  from  neighbouring  parts,  fixing  themselves  to 
the  larynx  and  acting  upon  the  organ  as  a  whole;  the  members  of  the  other 
group  confining  themselves  exclusively  to  the  larynx  and  acting  so  as  to  affect  its 
parts.  The  muscles  composing  the  first  group  are  described  elsewhere.  (See 
Section  IV.)  The  muscles  of  the  second  group  are  composed  of  striated  fibres 
and  are  supplied  by  the  vagus  nerve  through  its  laryngeal  branches.  These 
muscles  are  all  more  or  less  under  cover  of  the  thyreoid  cartilage,  with  one  ex- 
ception, the  crico-thyreoid. 

The  crico-thyreoid  muscles  [m.  cricothyreoideus]  (fig.  980)  are  placed  one  on 
either  side  of  the  outer  surface  of  the  larynx  in  its  lower  part.  Each  muscle  is 
partially  separated  into  an  anterior  straight  [pars  recta]  and  a  posterior  oblique 
portion  [pars  obliqua],  which  together  arise  from  the  arch  of  the  cricoid.  The 
fibres  of  the  straight  part  ascend  steeply  and  are  inserted  into  the  inferior  margin 
of  the  thyreoid  cartilage.  The  oblique  portion  is  inserted  into  the  inferior  cornu 
and  into  the  lower  margin  and  inner  surface  of  the  thyreoid  cartilage. 

The  straight  part  elevates  the  arch  of  the  cricoid,  causing  the  lamina,  and  with  it  the 
arytsenoid  cartilages,  to  sLuk,  while  the  obhque  part  draws  forward  the  thyreoid;  thus  the  vocal 
ligaments  are  made  tense.  The  muscle  is  supplied  by  the  external  branch  of  the  superior  larjTi- 
geal  nerve.  A  connexion  between  the  posterior  part  of  this  muscle  and  the  inferior  constrictor 
of  the  pharynx  and  their  common  nerve-supply  indicate  their  genetic  relationship. 

The  posterior  crico-arytffinoid  muscle  [m.  cricoarytasnoideus  posterior]  (figs. 
980,  981,  982),  paired,  is  situated  at  the  back  of  the  larynx,  covered  by  the  submu- 
cous coat  of  the  pharynx.  It  is  a  thick,  triangular  mass  which  takes  origin  from 
the  posterior  surface  of  the  cricoid  lamina,  the  two  muscles  being  well  separated 
by  the  median  crest  of  the  cartilage.  The  lower  fibres  ascend  and  the  upper 
ones  pass  horizontally  lateralward  and  are  inserted  into  the  muscular  process 
of  the  arytaenoid  cartilage  on  its  posterior  surface  and  tip. 

When  these  muscles  contract,  the  muscular  processes  of  the  arytsenqids  are  puUed  back- 
ward and  downward,  while  the  vocal  processes  travel  lateralward  and  a  Uttle  upward,  so  that 
the  rima  glottidis  is  widened  and  the  vocal  hgaments  made  tense  (fig.  982).  The  innervation 
is  by  the  posterior  branch  of  the  inferior  laryngeal  nerve. 

In  ether  narcosis  the  dilator  muscle  is  later  paralyzed  and  afterward  earlier  restored  than 
the  constrictors  of  the  larynx. 

At  the  lower  margin  of  this  muscle  a  small  slip,  the  cerato-cricoid  muscle  [m.  ceratocri- 
coideus],  is  sometimes  found,  extending  between  the  lamina  of  the  cricoid  and  the  inferior  cornu 
of  the  thyreoid  cartilage. 

The  constrictor  laryngis. — Whereas  the  crico-arytgenoideus  posterior  is  a  dila- 
tor of  the  larynx,  the  several  muscles  now  to  be  considered  are  in  the  main  con- 


MUSCLES  OF  THE  LARYNX 


1219 


strictors.  They  form  a  ring,  the  constrictor  laryrigis,  around  the  laryngeal  cavity, 
interrupted,  however,  by  the  cartilages.  In  the  larynx  of  amphibia  and  reptiles 
a  complete  sphincter  guards  the  entrance  to  the  air-passages. 

The  following  muscles  are  included  in  the  constrictor  group: — 
The  transverse  arytaenoid  muscle  [m.  arytaenoideus  transversus]  (figs.  981) 
983,  985)  is.  a  single  muscle  of  quadrilateral  form,  extending  across  the  middle 
line  from  the  posterior  concave  surface  of  one  arytaenoid  cartilage  to  that  of  the 
other.  Its  anterior  surface,  between  the  cartilages,  is  covered  by  the  laryngeal 
mucosa;  its  posterior  surface,  crossed  by  the  arytaenoideus  obliquus,  is  clothed  by 
the  submucous  coat  of  the  pharynx. 

The  arytaenoideus  transversus  approximates  the  arytenoid  cartilages  and  their  vocal  proc- 
esses, which  are  at  the  same  time  elevated,  and  the  vocal  Ugaments  made  tense.  It  is  supplied 
by  the  posterior  branch  of  the  inferior  laryngeal  nerve. 


Fig.  985. — -The  Nerves  of  the  Larynx  seen  from  Behind. 


Greater  cornu  of  hyoid 
Triticeous  cartilage 


Ary-epiglottic  fold 

Superior  cornu  of 
thyreoid 
orniculate  cartilage 


Anterior  branch  of  in- 
ferior laryngeal  nerve 

Posterior  branch  of  in- 
ferior laryngeal  nerve 
Posterior  crico-arytas- 
noid  muscle 

Crico-thyreoid  joint 


Base  of  the  tongue 


Epiglottis 

External  branch  of  su- 
perior laryngeal  nerve 

Internal  branch  of  su- 
perior laryngeal  nerve 

Cut  edge  of  hyo-thy- 
reoid  membrane 

Cuneiform  tubercle 

Oblique  arytagnoid 
Arytsenoid  cartilage 


Lamina  of  cricoid 


Inferior  laryngeal 


The  lateral  crico -arytaenoid  muscle  [m.  cricoarytaenoideus  lateralis]  (fig.  981) 
arises  from  the  upper  margin  and  outer  surface  of  the  cricoid  arch  and  from  the 
elastic  cone,  whence  the  fibres  extend  backward  and  upward  to  an  insertion  on 
the  anterior  surface  of  the  muscular  process  of  the  arytaenoid  cartilage.  This 
muscle  is  inseparable  from  the  thyreo-arytsenoideus  in  about  half  the  cases. 

The  lateral  oricoarytsnoids  by  their  contraction  cause  the  vocal  processes  to  move  toward 
the  median  line  and  a  little  downward,  so  that  the  vocal  Ugaments  are  approximated  and  shghtly 
stretched.  They  antagonise  the  posterior  crico-arytaenoids.  The  anterior  branch  of  the  in- 
ferior laryngeal  nerve  supphes  these  muscles. 

The  external  thyreo-arytaenoid  muscle  [m.  thyreoarytsenoideus  (externus)] 
(figs.  981,  984,  988),  variable  in  form  and  in  the  disposition  of  its  fibres,  is  closely 
connected  with  the  preceding.  It  Hes  under  cover  of  the  thyreoid  lamina  lateral 
to  the  laryngeal  saccule  (ventricular  appendix)  and  elastic  cone.  Arising  within 
the  angle  of  the  thyreoid  laminae  the  muscle  extends  upward  and  backward  to  its 
insertion  on  the  lateral  margin  of  the  arytaenoid  cartilage. 


1220  THE  RESPIRATORY  SYSTEM 

It  draws  forward  the  arytsenoid  cartilage  (and  also  tilts  the  cricoid),  and  rotates  it  so  that 
the  vocal  process  passes  medialward  and  downward,  relaxing  the  vocal  ligament.  It  is  the 
antagonist  of  the  crioo-thyreoid  (fig.  984).  Its  nerve-supply  is  the  anterior  branch  of  the  in- 
ferior laryngeal. 

The  vocal  muscle  [m.  vocalis],  (fig.  988),  prismatic  in  form,  is  tiie  inner  con- 
stant part  of  tlie  thyreo-arytasnoideus.  It  lies  in  tiie  vocal  lip  lateral  to  the  vocal 
ligament.  Its  fibres  run  from  their  origin  in  the  angle  of  the  thyreoid  laminse  to 
their  insertion  in  the  vocal  process  and  oblong  fovea  of  the  arytaenoid  cartilage. 

It  draws  forward  the  vocal  process,  relaxing  the  vocal  ligament.  Its  nerve  comes  from  the 
anterior  branch  of  the  inferior  laryngeal. 

The  insertion  of  certain  fibres  of  this  muscle  into  the  elastic  vocal  ligament  has  been  observed 
(ary-vocalis  muscle  of  Ludwig).  D.  Lewis  has  shown  that  some  of  the  elastic  fibres  in  the  vocal 
ligament  are  derived  from  the  perimysium  of  the  vocal  muscle. 

The  ventricular  muscle  [m.  ventricularis]  consists  of  a  few  fibres  derived  from  the  thyreo- 
arytffinoideus  which  reach  the  back  of  the  laryngeal  saccule  and  enter  the  ventricular  fold. 
The  small  thyreo-arytwnoideus  superior  extends  from  the  angle  of  the  thjrreoid  to  the  muscular 
process  of  the  arytaenoid  upon  the  lateral  surface  of  the  main  muscle. 

The  oblique  arytsenoid  muscle  [m.  arytsenoideus  obhquus]  is  a  slender  band 
lying  at  the  back  of  the  larynx  and  under  the  pharyngeal  submucosa.  It  arises 
from  the  muscular  process  of  the  arytsenoid  posteriorly,  and,  ascending  obliquely, 
crosses  its  fellow  in  the  median  line.  Some  fibres  are  inserted  into  the  apex  of 
the  opposite  arytsenoid  cartilage;  other  fibres  sweep  around  the  apex  and  accom- 
pany the  thyreo-arytsenoid  to  an  insertion  in  the  angle  of  the  thyreoid  cartilage, 
constituting  the  thyreo-arytcenoideus  obliquus. 

This  muscle  contracts  the  laryngeal  aperture  and  vestibule  of  the  larynx.  Its  nerve  is 
derived  from  the  anterior  branch  of  the  inferior  laryngeal. 

Closely  connected  with  the  thyreo-arytsenoideus  is  a  bundle  of  fibres  of  fairly 
regular  occurrence,  called  the  thyreo-epiglottic  muscle  [m.  thyreoepiglotticus] 
(fig.  981).  It  originates  from  the  inner  surface  of  the  thyreoid  lamina  and  pro- 
ceeds upward  and  backward  to  end  in  the  quadrangular  membrane  and  to  become 
attached  to  the  lateral  border  of  the  epiglottis. 

The  ary-membranosus  and  ary-epiglotlic  muscles  are  inconstant  fascicles  of  the  constrictor 
group  which  run  in  the  ary-epiglottic  fold  and  become  fixed  into  the  quadrangular  membrane 
and  margin  of  the  epiglottic  cartilage. 

Summary  of  the  Actions  of  the  Laryngeal  Muscles 

According  to  their  actions,  the  laryngeal  muscles  may  be  divided  into — (a)  those  which 
effect  the  tension  of  the  vocal  folds;  (b)  those  which  control  the  rima  glottidis;  (c)  those  which 
effect  the  closure  of  the  laryngeal  aperture  and  vestibule. 

(a)  The  vocal  ligaments  are  made  tense  by  the  action  of  the  crico-thyreoid,  the  lateral  and 
posterior  cricoarytsenoid  and  the  transverse  arytaenoid  muscles.  The  vocal  ligaments  are  re- 
laxed as  the  result  of  the  action  of  the  external  thyreo-arytaenoid  and  vocal  muscles. 

(6)  The  rima  glottidis  is  widened  by  the  crico-arytajnoideus  posterior  and  made  narrow 
by  the  contraction  of  the  arytaenoids.  The  crico-arytaenoideus  lateralis  also  assists  in  closing 
the  rima  glottidis  by  rotating  the  vocal  processes  medialward,  and  if  the  crico-arytsenoideus 
posterior  contracts  simultaneously,  it  aids  in  the  closure.  The  vocal  hgaments  are  approxi- 
mated also  by  the  thyreo-arytaenoideus  [externus]. 

(c)  The  laryngeal  aperture  and  vestibule  are  closed  mainly  by  the  arytsenoideus  transversus 
and  thyreo-arytsenoideus  (externus),  by  which  the  arytaenoid  cartilages  are  brought  into  apposi- 
tion and  drawn  toward  the  epiglottis.  Other  muscles  derived  from  the  constrictor  group, 
arytaenoideus  obliquus  and  ary-epiglotticus  assist  in  closing  the  laryngeal  aperture. 

CAVITY  OF  THE  LARYNX  AND  LARYNGEAL  MUCOSA 

The  cavity  of  the  larynx  [cavum  laryngis]  is  relatively  narrow  and  does  not 
correspond  in  shape  with  the  outer  surface  of  the  organ.  Its  form  is  shown  in 
fig.  986  taken  from  a  cast  of  the  laryngeal  cavity  and  the  spaces  continuous  with 
it.  Its  walls  are  covered  throughout  by  the  mucous  membrane  of  the  larynx 
(figs.  987,  988). 

The  mucosa  of  the  larynx  is  continuous  above  with  the  mucous  membrane 
of  the  pharynx,  below  with  that  of  the  trachea  (figs.  970,  971).  At  the  root  of 
the  tongue  the  pharyngeal  mucosa  is  reflected  backward  to  the  anterior  surface 
of  the  epiglottis,  presenting  the  median  and  lateral  glosso-epiglottic  folds  [plica 


CAVITY  OF  THE  LARYNX 


1221 


glosso  epiglottica  medianaet  lateralis].  From  the  sides  of  the  pharynx  it  passes 
medialward,  first  sinking  between  the  thyreoid  cartilage  laterally  and  the  aryt- 
senoid  and  cricoid  medially,  entering  into  the  walls  of  the  piriform  recess;  then 
passing  over  the  superior  margin  of  the  quadrangular  membrane  to  form  the  ary- 
epiglottic  fold. 

At  the  medial  side  of  the  piriform  recess  a  slight  fold  of  the  mucosa  [phca  nervi  laryngei) 
corresponds  to  the  superior  lar3Tigeal  nerve.  Between  the  root  of  the  tongue  and  the  epiglottis 
is  a  depression  subdivided  in  the  middle  line  and  limited  laterally  by  the  median  and  lateral 

Fig.  986. — Cast  of  the  Vestibulum  and  Cavum  Oris,  op  the  Phahtnx,  Laeynx,  op  the 
Upper  Part  op  the  Trachea  and  (Esophagus.  Seen  from  in  front  And  below.  (Rauber- 
Kopsch.) 

Rima  oris 


Alveolar  part  of  mandible 

*■       --^'tf'-ymM         Tongue 


Glosso-epiglottic  vallecula 
S      Vestibule  of  larynx 

Piriform  recess 
Laryngeal  ventricle 

Cavum  laryngis  inferius 


(Esophagus 


glosso-epiglottic  folds;  this  is  the  epiglottic  vallecula  [vallecula  epiglottica].  The  piriform 
recess  and  the  epiglottic  vallecula  are  favorite  sites  for  the  lodgment  of  foreign  bodies.  The 
ary-epiglottic  fold  [plica  aryepiglottica]  extends  from  the  side  of  the  epiglottis  to  the  apex 
of  the  aryt:rnoid  cartilage;  within  it  are  fibres  of  the  ary-epiglottic  and  thyreo-epiglottic 
muscles  and  the  cuneiform  and  corniculate  cartilages.  These  cartilages  correspond  to  two 
rounded  eminences  on  each  side  of  the  laryngeal  entrance,  the  cuneiform  and  corniculate 
tubercles  [tuberculum  cuneiforme  (Wrisbergi);  tubereulum  corniculatum  (Santorini)],  respec- 
tively. Of  these,  the  former  is  often  small  and  inconspicuous,  the  latter  usually  well  developed 
and  prominent. 

The  cavity  of  the  larynx  above  the  level  of  the  ventricular  folds  is  known  as  the 
vestibule  [vestibulum  laryngis].  This  is  wide  in  its  upper  part,  but  the  sides 
incline  toward  the  median  line  in  descending,  and  the  cavity  becomes  narrow 


1222 


THE  RESPIRATORY  SYSTEM 


transversely  in  approaching  the  region  of  the  glottis.  Here  the  cavity  has  received 
the  special  name,  superior  entrance  to  the  glottis  [aditus  glottidis  superior].  The 
parts  of  the  framework  of  the  larynx  which  enter  into  the  walls  of  the  vestibule  are : 
in  front,  the  epiglottic  and  thyreoid  cartilages  with  the  thyreo-epiglottic  hgament; 
at  the  side,  the  quadrangular  membrane,  the  cuneifoi-m  and  corniculate  cartilages, 
and  the  medial  surface  of  the  arytsenoid  cartilage;  behind,  the  anterior  surface  of 
the  transverse  arytsenoid  muscle.  The  vestibule  communicates  with  the  pharynx 
by  the  laryngeal  aperture  [aditus  laryngis]  (figs.  970,  971,  972,  987),  which 
looks  upward  and  backward.  The  form  of  the  aperture  is  oval  or  triangular, 
with  the  base  in  front;  here  it  is  bounded  by  the  epiglottis;  laterally  by  the  ary- 
epiglottic  fold  of  the  mucosa.  Posteriorly  the  laryngeal  aperture  is  prolonged  as 
a  little  notch  between  the  corniculate  cartilages  and  the  apices  of  the  arytsenoids 
[incisura  interarytsenoidea]  limited  behind  by  a  commissure  of  the  mucosa. 

The  high  anterior  waU  of  the  vestibule  presents  a  marked  convexity,  the  tubercle  of  the 
epiglottis  [tuberculum  epiglotticum],  over  the  thyreo-epiglottic  ligament.     The  lateral  walls, 

Fig.  987. — Median  Section  op  the  Larynx.     (Merkel.) 


Median  glosso-epiglottic  fold 


Cuneiform  tubercle' 
Corniculate  tubercle 


Arytaenoid  muscles' 


Lamina  of  cricoid' 


—  Epiglotti::  cartilage 


— ^Appendix  of  the  ventricle 
-/^ — Ventricular  fold 


Ventricle 
Vocal  fold 
Thyreoid  cartilage 

Median  crico-thyreoid  ligament 


Arch  of  cricoid 
Crico-tracheal  ligament 
First  tracheal  cartilage 


higher  in  front  than  behind,  show  two  slight  ridges,  separated  by  a  shallow  groove,  extending 
downward  from  the  cuneiform  and  corniculate  tubercles.  The  posterior  wall,  very  low,  corre- 
sponds to  the  commissure  connecting  the  arytsenoid  cartilages. 

On  either  side  of  the  vestibule,  toward  its  inferior  end,  is  the  sagittally  running 
ventricular  fold  [plica  ventricularis]  (false  vocal  cord)  (figs.  970,  971,  987,  988). 
This  appears  as  an  elevation  of  the  mucous  coat  of  the  lateral  wall,  prominent  in 
its  middle  and  anteriorly,  fading  away  posteriorly.  The  ventricular  fold  contains 
the  inferior  free  edge  of  the  quadrangular  membrane,  that  is,  the  ventricular  liga- 
ment, and  numerous  glands. 

Wylie's  experiments  with  the  ventricular  folds  led  him  to  conclude  that  the  closure  of  the 
glottis  in  defaecation  and  vomiting  is  mainly  effected  by  the  apposition  of  these  folds.     (Quain.) 

The  interval  between  the  right  and  left  ventricular  folds,  the  vestibular  slit 
[rima  vestibuli]  leads  downward  to  a  space  between  the  planes  of  the  ventricular 
and  vocal  folds,  which  extends  on  each  side  into  the  laryngeal  ventricle  [ventricu- 
lus  laryngis  (Morgagni*)]  (figs.  970,  971,  987,  988).  The  latter  is  a  little  antero- 
posterior pocket  of  the  mucosa  reaching  from  the  level  of  the  arytsenoid  nearly 
to  the  angle  of  the  thyreoid  cartilage,  and  undermining  the  ventricular  fold; 
it  opens  into  the  cavity  of  the  larynx  by  a  narrow  mouth  limited  above  and  below 
by  the  ventricular  and  vocal  folds.     From  its  anterior  part  a  small  diverticulum, 

*  Morgagni.  ItaUan  anatomist.     B.  1682,  D.  1771. 


THE  VOCAL  FOLDS 


1223 


the  ventricular  appendix  [appendix  ventriculi  laryngis]  extends  upward  between 
the  ventricular  fold  medially  and  the  thyreo-arytsenoid  muscle  and  thyreoid  car- 
tilage laterally.     Many  mucous  glands  open  into  it. 

The  appendix  is  occasionally  so  large  as  to  reach  the  level  of  the  upper  margin  of  the  thyreoid 
cartilage  or  even  the  great  cornu  of  the  hyoid  bone.  The  laryngeal  pouches  of  some  of  the 
apes  are  remarkably  developed  and  appear  to  serve  in  affecting  the  resonance  of  the  voice. 
In  man,  their  function,  besides  that  of  pouring  out  the  secretion  of  the  glands  located  within 
their  walls,  is  not  known. 

The  vocal  fold  [plica  vocalis]  (or  true  vocal  cord)  (figs.  970,  971,  987,  988) 
is  the  thin  edge  of  a  full,  lip-like  projection,  the  vocal  lip.  The  vocal  folds  cor- 
respond in  antero-posterior  extent  to  the  vocal  hgament,  and  stand  nearer  the 
median  line  than  the  ventricular  fold.  In  colour  the  vocal  folds  are  pearly  white, 
excepting  the  anterior  end  of  each,  where  there  is  a  yellow  spot  [macula  flava] 
produced  by  a  little  mass  of  elastic  tissue  (sometimes  cartilage)  in  the  ligament. 
The  vocal  lip  [labium  vocale]  forms  the  floor  of  the  ventricle  and  contains  the  upper 
part  of  the  elastic  cone,  whose  thickened  free  edge,  the  vocal  ligament,  lies  in  the 


Fig.  988. — Fbontal  Section  op  a  Larynx  Hardened  in  Alcohol. 
B.  Anterior  segment.     (Poirier  and  Charpy.) 


A.  Posterior  segment. 


Cunei- 
form 
tubercle 

Ventri- 
cular 
muscle 

Appen- 
dix 
Thy- 
.  reo- 
arytae- 
noid 
(ext.) 

Cricoid 
.Crico- 
thyreoid 


B. 


vocal  fold  and  along  the  vocal  muscle.  The  two  vocal  lips  with  the  vocal  folds 
and  the  intervening  space,  the  rima  glottidis,  together  constitute  the  sound- 
producing  apparatus,  the  glottis. 

Below  the  vocal  folds  and  the  medial  surfaces  of  the  arytenoid  cartilages 
is  a  slit,  the  rima  glottidis  (figs.  970,  971,  988),  the  narrowest  part  of  the  laryngeal 
cavity,  extending  from  the  arytsenoideus  transversus  muscle  posteriorly  to  the 
thyreoid  cartilage  in  front.  The  portion  of  the  rima  between  the  vocal  folds  is 
known  as  the  pars  intermembranacea ;  that  between  the  arytsenoids  the  pars 
intercartilaginea.  The  rima  glottidis  in  easy  respiration  is  narrow  and  has  the 
form  of  a  long  triangle;  in  laboured  breathing  it  is  widely  open  and  lozenge-shaped. 

Below  the  level  of  the  vocal  folds  is  the  space  called  the  inferior  entrance  to 
the  glottis  [aditus  glottidis  inferior]  (fig.  988),  which  is  narrow  from  side  to  side 
above,  wide  and  circular  in  section  below — altogether  somewhat  funnel-shaped. 
Its  walls  are  formed  by  the  elastic  cone  and  by  the  arch  and  lamina  of  the  cricoid 
cartilage.  The  lining  mucosa  is  separated  from  the  elastic  cone  by  numerous 
glands  and  loose  connective  tissue,  a  condition  favorable  to  the  development  of 
oedema;  below  it  is  continuous  with  the  mucosa  of  the  trachea. 

By  means  of  the  laryngoscope  a  more  or  less  complete  picture  of  the  laryngeal  aperture 
and  the  cavity  of  the  larynx  can  be  obtained  (figs.  970,  971).     There  appear,  highest  up,  the 


1224  THE  RESPIRATORY  SYSTEM 

root  of  the  tongue  with  the  epiglottic  valleculse  and  glosso-epiglottic  folds  leading  backward 
to  the  epiglottis;  behind  the  latter,  the  triangular  aperture  of  the  larynx,  bounded  at  the  sides 
by  the  ary-epiglottic  folds.  Further  lateralward  appear  the  piriform  recesses,  the  laryngeal 
portions  of  which  lie  as  transverse  fissures  behind  the  laryngeal  aperture.  Within  the  ary- 
epiglottic  folds  are  seen  the  prominent  corniculate  tubercles  on  either  side  of  the  inter- 
arytaenoid  commissure  and  just  anterior,  the  variable  cuneiform  tubercles.  Within  the  vesti- 
bule the  epiglottic  tubercle  rises  upon  the  anterior  wall,  while  at  the  sides  appear  the  ventricular 
folds  overhanging  the  slit-like  openings  of  the  laryngeal  ventricles.  Below  this  level  the  vocal 
folds  stand  out  on  either  side  approaching  nearer  the  median  plane  than  do  the  ventricular 
folds  and  conspicuous  by  their  pearly  whiteness.  The  form  and  extent  of  the  rima  glottidis 
and  of  its  divisions,  the  intermembranous  and  intercartilaginous  parts,  can  be  inspected.  Far 
down,  the  cricoid  cartilage  and  anterior  wall  of  the  trachea  may  appear  and  under  favourable 
conditions  a  glimpse  of  the  bifurcation  of  the  latter  can  be  obtained. 

The  mucous  coat  of  the  larynx  [tunica  mucosa  laryngis]  in  general  is  covered  by  a  ciliated 
epithelium;  the  vocal  lips,  and,  exceptionally,  small  areas  of  the  mucosa  of  the  laryngeal  surface 
of  the  epiglottis  and  the  ventricular  folds  possess  a  covering  of  flat,  non-ciliated  cells.  The 
attachment  of  the  mucosa  to  the  underlying  parts  is  very  firm  about  the  vocal  folds  and  dorsal 
side  of  the  epiglottis,  and  loose  in  the  ary-epiglottic  folds,  where  much  areolar  tissue  is  present. 
In  general  the  mucosa  is  pink  in  colour,  becoming  bright  red  over  the  epiglottic  tubercle  and 
edges  of  the  epiglottis  and  fading  over  the  vocal  folds,  which  appear  almost  white. 

Numerous  mucous  glands  [glandulse  laryngeal]  occur  about  the  larynx  and  are  aggregated 
into  groups  in  certain  places.  One  cluster  of  anterior  glands  [gl.  laryiifjoa-  nnteriores]  is  found 
in  front  of  and  on  the  posterior  side  of  the  epiglottis;  another,  the  middle  glands  [gl.  laryngeae 
media;],  is  in  the  ventricular  fold,  in  the  triangular  fovea  of  the  arytfonoid  curtilage  and  clustered 
about  the  cuneiform  cartilage,  while  a  third  set,  the  posterior  glands  [gl.  laryngea;  posteriores], 
is  disposed  about  the  transverse  arytajnoid  muscle.  Many  glands  pour  their  secretion  into  the 
appendix  of  the  laryngeal  ventricle,  but  there  are  none  on  or  about  the  vocal  folds.  Lymph- 
nodules  of  the  larynx  [noduli  lymphatici  laryngei]  occur  in  the  mucosa  of  the  ventricle  and  on 
the  posterior  surface  of  the  epiglottis. 

Position  and  relations. — The  larynx  opens  above  into  the  pharynx  by  the  aditu  and  in  thiss 
region  is  connected  with  the  hyoid  bone.  Below,  its  cavity  leads  into  the  trachea.  Its  position 
in  the  neck  is  indicated  on  the  surface  by  the  laryngeal  prominence  (Adam's  apple).  It  stands 
in  front  of  the  fourth,  fifth,  sixth,  and  seventh  cervical  vertebrae;  from  these  it  is  separated  by 
the  prevertebral  muscles  and  the  pharynx,  into  the  anterior  wall  of  which  it  enters.  The 
integument  and  cervical  fascia  cover  the  larynx  anteriorly  in  the  middle  line,  while  toward  the 
side  are  the  sterno-hyoid,  sterno-thryeoid,  and  thyreo-hyoid  muscles.  The  lateral  lobe  of  the 
thyreoid  gland  and  the  inferior  constrictor  of  the  pharynx  are  in  relation  to  it  laterally,  while 
further  removed  are  the  great  vessels  and  nerves  of  the  neck. 

Peculiarities  of  age  and  sex.  Position. — The  larynx  is  placed  high  in  the  neck  in  foetal 
and  infantile  life  and  descends  in  later  life.  In  a  six-months  foetus  the  organ  is  two  vertebra 
higher  than  in  the  adult.  (Symington.)  The  descent  of  the  larynx  has-been  attributed  to 
the  vertical  growth  of  the  facial  part  of  the  skull,  but  this  cause  is  questioned  by  Cunningham, 
who  points  out  the  high  position  of  the  larynx  in  the  anthropoid  apes,  where  the  facial  growth 
is  more  striking  than  in  man;  it  appears  also  that  the  larynx  follows  the  thoracic  viscera  in  their 
subsidence,  which,  according  to  Mehnert,  continues  until  old  age.  At  birth  the  interval  between 
the  hyoid  bone  and  thyreoid  cartilage  is  relatively  very  small  and  increases  but  little  during 
early  life. 

Growth  and  form. — The  larynx  of  the  new-born  is  relatively  large  and  in  contour  more 
rounded  than  that  of  the  adult.  The  organ  continues  to  grow  until  the  third  year,  when  a 
resting  period  begins,  lasting  until  about  twelve  years  of  age,  during  which  time  there  appears 
to  be  no  difference  between  the  larynx  of  the  male  and  that  of  the  female.  At  puberty,  while 
no  marked  change  is  observable  in  the  larynx  of  the  female,  rapid  growth  accompanied  by 
modification  of  form  of  the  larynx  is  initiated  in  the  male.  The  laryngeal  cavity  is  enlarged, 
the  antero-posterior  diameter  markedly  increased;  the  whole  framework  becomes  stronger;  the 
thyreoid  cartilage  especially  increases  greatly  in  its  dimensions,  giving  rise  to  the  laryngeal 
prominence;  the  vocal  folds  are  lengthened  and  thickened,  the  voice  changing  in  quality  and 
pitch.  These  changes  are,  for  the  most  part,  effected  in  about  two  years,  but  complete  develop- 
ment is  not  attained  before  twenty  to  twenty-five  years  of  age.  Castration  is  known  to  in- 
fluence the  development  of  the  larynx,  for  in  the  eunuch  it  has  been  found  to  resemble  that  of  a 
young  woman.     The  changes  in  the  structure  of  the  cartilages  have  already  been  described. 

Dimensions. — In  the  male  the  distance  from  the  upper  edge  of  the  epiglottis  to  the  lower 
margin  of  \\u:  cricoid  is  70  mm.;  in  the  female,  48  mm.  The  transverse  diameter  is  40  mm. 
in  the  nial(\  'Ao  mm.  in  the  female.  The  greatest  sagittal  diameter  is  40  mm.  in  the  male,  37 
mm.  in  the  female.  The  vocal  folds  in  the  male  measure  relaxed  about  15  mm.,  in  the  female, 
but  11  mm.;  when  stretched,  about  20  mm.  and  15  mm.  respectively.  ' 

The  length  of  the  rima  glottidis  in  the  quiescent  state  is  on  the  average  23  mm.  in' the  male; 
17  mm.  in  the  female.  In  the  male  the  pars  intermembranacea  measures  15.5  mm.,  the  pars 
intercartilaginea,  7.5  mm.  In  the  female  these  are  11,5  mm.  and  5.5  mm.  respectively.  The 
rima  may  be  lengthened  by  stretching  of  the  vocal  folds  to  27.5  mm.  in  the  male  and  20  mm.  in 
the  female.  (Moura.)  In  the  male  the  width  of  the  rima  glottidis  is  6-8  mm.  in  its  widest 
part,  but  may  be  increased  nearly  to  12  mm. 

Vessels  and  nerves  (figs.  980,  985), — The  arteries  supplying  the  larynx  are  the  superior 
and  inferior  laryngeal,  which  accompany  the  internal  and  inferior  laryngeal  nerves  respectively, 
and  the  crico-thyreoid  arteries  (see  pp.  538,  564). 

The  superior  and  inferior  laryngeal  veins  join  the  superior  and  inferior  thyreoid  veins  re- 
spectively. 

The  lymph  vascular  system  is  well  developed  throughout  the  larynx  generally,  but  in  the 


THE  TRACHEA  AND  BRONCHI 


1225 


vocal  folds  where  the  mucosa  is  thin  and  tightly  bound  down  the  vessels  are  scarce  and  small 
in  size  (see  p.  719). 

The  nerves  of  the  larynx  are  the  superior  and  inferior  laryngeal  branches  of  the  vagus  and 
also  certain  branches  of  the  sympathetic.  Taste-buds  occur  and  are  abundant  in  the  mucosa 
of  the  posterior  surface  of  the  epiglottis.  The  innervation  of  the  muscles  has  already  been  in- 
dicated, and  the  description  of  the  course  and  relations  of  these  nerves  will  be  found  in  the  chapter 
on  the  Peripheral  Nervous  System.  It  should  be  mentioned  here,  however,  that  the  idea 
of  sharply  limited  territories  of  innervation,  not  only  for  the  mucosa,  but  for  the  muscles  as 
well,  has  been  brought  into  question  by  the  researches  of  Semon  and  Horsley,  E.xner,  and  others, 
which  show  that  the  distribution  and  functions  of  the  laryngeal  nerves  are  e.xtremely  complex. 

The  development  of  the  larynx. — The  larynx  is  developed  partly  from  the  lower  portion 
of  the  embryonic  pharynx  and  partly  from  the  upper  portion  of  the  trachea.  The  .cricoid  carti- 
lage represents  the  uppermost  tracheal  cartilage,  while  the  thyreoid  is  formed  by  the  fusion  of 
four  cartilages  representing  the  ventral  portions  of  the  cartilages  of  the  fourth  and  fifth  branchial 
arches.  The  laryngeal  muscles  are  derived  from  the  musculature  of  these  arches  and  conse- 
quently their  nerve-supply  is  from  the  vagus.  Whether  or  not  the  arytenoid  and  epiglottic 
cartilages  are  also  derivatives  of  the  branchial  arches  is  uncertain,  although  it  seems  probable 
that  they  are. 

THE  TRACHEA  AND  BRONCHI 

The  tubular  trachea  (figs.  972,  989),  or  windpipe,  extends  from  the  larynx 
downward  through  the  neck  and  into  the  thorax  to  end  by  dividing  into  two 
branches,  the  right  and  left  bronchi  [bronchus  (dexter  et  sinister)],  which  lead  to 

Fig.  989 — Trachea  and  Bronchi  in  Their  Relations  to  the  Great  Vessels  as  seen  from 
Behind.      (After  Gegenbaur.) 


Left  subclavian  artery 
Superior  vena  cava 


Right  pulmonary  veins 


Inferior  vena  cava 


the  lungs.  These  tubes  are  simple  transmitters  of  the  respiratory  air.  Their  walls 
are,  for  the  most  part,  stiff  and  elastic,  consisting  in  large  part  of  cartilage.  While 
the_  general  form  of  these  tubes  is  cyhndrical,  a  rounded  contour  is  presented  by 
their  walls  only  in  front  and  at  the  sides,  the  posterior  surface  being  flat.  The 
inner  surface  of  the  walls  of  the  tubes  presents  a  succession  of  slight  annular  pro- 
jections caused  by  the  cartilaginous  rings  which  enter  into  their  structure.  The 
calibre  of  the  trachea  varies  at  different  levels,  a  cast  of  the  lumen  being  in  gen- 
eral spindle-shaped.  Its  sectional  area  is  less  than  the  combined  sectional  areas 
of  the  two  bronchi.  When  the  bifurcation  of  the  trachea  [bifurcatio  tracheae]  is 
viewed  by  looking  down  into  its  cavity,  a  sagitally  directed  keel,  the  carina 
tracheae  (fig.  990),  is  seen  standing  between  the  openings  which  lead  into  the 
bronchi.  Its  position  is  a  httle  to  the  left  of  the  mid-plane  of  the  trachea 
in  a  slight  majority  of  cases,  or  in  the  mid-plane  in  a  large  percentage. 


1226  THE  RESPIRATORY  SYSTEM 

Position  and  relations  (figs.  972,  989,  1000). — The  trachea  lies  in  the  median 
plane,  extending  from  the  level  of  the  sixth  cervical  vertebra  downward  and 
backward,  receding  from  the  surface  in  following  the  curve  of  the  vertebral  col- 
umn, and  deviating  a  little  to  the  right  in  approaching  the  level  of  the  fourth 
thoracic  vertebra,  where  it  divides.  Its  lower  end  is  fixed  so  that  with  elevation 
and  descent  of  the  larynx  the  tube  is  stretched  and  contracted,  ■  changes  in  length 
which  also  result  from  extension  and  flexion  of  the  head  and  neck.  The  mobility 
of  the  trachea  is  favored  by  its  loose  investment  of  connective  tissue. 

About  half  of  the  trachea  lies  in  the  neclj,  but  the  extent  varies  with  the  length  of  the  neck, 
the  position  of  the  head  and  with  age;  the  trachea  holds  a  lower  position  in  adult  life  than  in 
childhood  and  a  still  lower  one  in  old  age  when  the  bifurcation  may  be  as  low  as  the  sixth  or 
seventh  thoracic  vertebra.  In  front  and  closely  connected  with  it  is  the  isthmus  of  the  thyreoid 
gland,  covering  usually  the  second  to  fourth  cartilages;  anterior  to  this  the  cervical  fascia  and 
integuments.  The  cervical  aponeurosis  is  attached  to  the  upper  margin  of  the  sternum  in  two 
lamellae,  with  an  interspace  containing  the  venous  jugular  arch,  a  lymph  gland,  and  some  fat. 
Between  these  aponeuroses  and  the  trachea  is  another  space  containing  the  inferior  thyreoid 
veins  and  some  tracheal  lymph-glands,  and  sometimes  a  thyreoidea  ima  artery.  The  innominate 
artery  occasionally  crosses  the  trachea  obUquely  in  the  root  of  the  neck.  Behind  the  trachea, 
in  its  whole  length,  Ues  the  oesophagus,  which  in  this  part  of  its  course  inclines  to  the  left. 
On  either  side  are  the  great  vessels  and  nerves  of  the  neck,  and  the  lobes  of  the  thyreoid  gland. 
The  inferior  laryngeal  nerve  lies  in  the  angle  between  the  (Esophagus  and  trachea. 

Fig.  990. — Bifurcation  op  the  Trachea  showing  the  Tracheal  Keel.    R.  L.  Right  and 
left  bronchi.     (Heller  and  von  Schrootter,  from  Poirier  and  Charpy.) 


Within  the  thorax  the  trachea  lies  in  the  mediastinum,  enveloped  in  loose  areolar  tissue 
and  fixed  through  strong  fibrous  connections  with  the  central  tendon  of  the  diaphragm.  The 
innominate  artery  and  the  left  common  carotid  are  at  first  in  front  and  then  at  its  sides  as  they 
ascend,  while  the  left  innominate  vein  and  the  remains  of  the  thymus  are  further  forward. 
The  aortic  arch  is  in  contact  with  the  anterior  surface  of  the  trachea  near  the  bifurcation. 
On  the  right  side  are  the  vagus  nerve,  the  arch  of  the  vena  azygos,  the  superior  vena  cava,  and 
the  mediastinal  pleura;  on  the  left,  the  arch  of  the  aorta,  the  left  subclavian  artery,  and  the 
recurrent  laryngeal  nerve.  A  large  group  of  bronchial  lymph-glands  [lymphoglandulae  bron- 
chiales]  lies  below  the  angle  of  bifurcation.     The  oesophagus  is  behind  and  to  the  left. 

The  bronchi  take  an  obfique  course  to  the  hilus  of  the  lung,  where  they  branch. 
The  right  bronchus  is  nearer  to  the  vertical  in  its  course  than  is  the  left;  it  is 
also  shorter  and  broader.  These  conditions,  together  with  the  position  of  the 
tracheal  keel,  explain  the  more  frequent  entrance  of  foreign  bodies  into  the  right 
than  into  the  left  bronchus.  The  asymmetrical  course  of  the  two  bronchi  is 
probably  genetically  associated  with  the  position  of  the  heart  and  aorta. 

The  azygos  vein  arches  over  the  right  bronchus,  the  vagus  passes  behind,  and  the  right 
branch  of  the  pulmonary  artery  crosses  anteriorly  below  the  level  of  the  first  (eparterial) 
branch  of  the  bronchus.  The  aorta  arches  over  the  left  bronchus  and  gains  its  posterior  surface 
along  with  the  cesophagus;  the  left  branch  of  the  pulmonary  artery  passes  at  first  in  front  and 
then  above  the  bronchus. 

Dimensions. — On  account  of  their  elasticity  considerable  difficulty  is  met  with  in  obtaining 
accurate  measurements  of  the  air-tubes.  The  length  of  the  trachea  is  given  at  95-122  mm.; 
its  transverse  diameter  20-27  mm. ;  the  sagittal  diameter  16-20  mm.  The  right  bronchus  has 
a  length  of  25-34  mm.;  the  left,  41-47  mm.  The  transverse  diameter  of  the  right  is  18  mm.;  of 
the  left,  16  mm.  The  angle  of  bifurcation  of  the  trachea  varies  from  56°  to  90°,  the  mean 
being  70.4°  a  wide  angle  corresponding  to  the  breadth  of  the  thorax  of  man.  The  right  bronchus 
makes  an  angle  of  24.8°  with  the  median  plane;  the  left,  45.6°. 

According  to  Tillaux  the  length  of  that  portion  of  the  trachea  between  the  superior  edge  of 
the  sternum  and  the  cricoid  cartilage  varies  with  age  and  sex  as  follows: — 

Adult  male,  from  4.5  to  8.5  cm average,  6.5  cm. 

Adult  female,  "     5     to  7.5  cm "        6.4  cm. 

Boys  2|  to  10    years,     "     2.7  to  6.5  cm "        4.4  cm. 

Girls  3i  to  101      "         "     4     to  6.5  cm "        5.1  cm. 


THE  TRACHEA  AND  BRONCHI 


1227 


The  diameter  of  the  lumen  of  the  trachea  when  distended  to  a  cylindrical  form  has  been 
measured  by  S&: — 

New-born 4.12  to    5.6  mm. 

Infant  2  years 7.5    to    8     mm. 

Infant  4  to  7 8       to  10.5  mm. 

Over  20  years,  male 16       to  22.5  mm. 

Over  20  years,  female 13       to  16     mm. 

Structure  of  the  trachea  and  bronchi  (figs.  978,  988,  989,  991).— The  walls  of 
the  trachea  and  bronchi  are  composed  of  a  series  of  cartilages  having  the  form  of 
incomplete  rings,  held  together  and  enclosed  by  a  strong  and  elastic  fibrous  mem- 
brane. Posteriorly,  where  the  rings  are  deficient,  this  membrane  remains  as  the 
membranous  wall  [paries  membranacea] ;  between  the  cartilages  it  constitutes 
the  annular  ligaments  [ligg.  annularia  (trachealia)]. 


Fig.  991. — Schematic  Longitudinal  Section  of  the  Wall  op  the  Trachea.    (Gegenbaur.) 


Fibrous  membrane^ 


Annular  ligament 
Tracheal  glandS' 


Tracheal  cartilage 


A  tracheal  cartilage  [cartilago  trachealis]  comprises  a  little  more  than  two- 
thirds  of  a  circle.  Its  ends  are  rounded,  its  outer  surface  flat,  while  the  inner  sur- 
face is  convex  from  above  downward;  the  upper  and  lower  margins  are  nearly 
parallel.  The  cartilages  are  from  sixteen  to  twenty  in  number.  The  first  is 
usually  broader  than  the  type,  and  is  connected  by  the  crico-tracheal  ligament 
with  the  cricoid  cartilage.  Sometimes  these  two  cartilages  are  in  part  continuous. 
The  last  cartilage  is  adapted  to  the  bifurcation  of  the  trachea  and  presents  at 
the  middle  of  its  lower  margin  a  hook-hke  process.  This  turns  backward  between 
the  origins  of  the  bronchi,  and  in  the  majority  of  cases  gives  a  cartilaginous  basis 
to  the  tracheal  carina.  Some  of  the  tracheal  cartilages  vary  from  the  type  by 
bifurcating  at  one  end.  The  cartilages  keep  the  lumen  of  the  trachea  patent  for 
the  free  passage  of  the  air.  Calcification  occurs  as  with  the  laryngeal  cartilages, 
but  much  later  in  life. 

A  mucous  coat  [tunica  mucosa],  soft  and  pinkish-white  in  colour,  covers  the 
inner  surface  of  the  trachea;  posteriorly  it  is  thrown  into  longitudinal  folds. 
Mucous  secreting  tracheal  glands  [gl.  tracheales]  are  present  in  the  elastic  sub- 
mucous coat  [tela  submucosa]  between  the  cartilages  and  at  the  back  of  the 
trachea.  A  thin  layer  of  transversely  disposed  smooth  muscle-fibres,  stretching 
between  the  ends  of  the  cartilages  in  the  posterior  wall,  constitutes  the  muscular 


1228  THE  RESPIRATORY  SYSTEM 

coat  [tunica  muscularis].  Contraction  of  this  trachealis  muscle,  as  it  is  more  prop- 
erly named,  causes  the  ends  of  the  tracheal  cartilages  to  be  approximated  and 
the  lumen  of  the  wind-pipe  to  be  diminished. 

The  structure  of  the  walls  of  the  bronchi  is  similar  to  that  of  the  trachea.  The 
right  bronchus  possesses  six  to  eight  cartilages;  the  left,  nine  to  twelve. 

An  inconstant  broncho-asophageal  muscle  may  connect  the  back  of  the  left  bronchus  with 
the    gullet. 

Vessels  and  nerves. — The  arteries  supplying  these  air-tubes  come  from  the  inferior  thyreoid 
and  from  the  internal  mammary  by  its  anterior  mediastinal  or  broncliial  branches.  Venous 
radicles  come  together  in  the  annular  ligaments  and  join  lateral  veins  on  either  side,  which  empty 
the  blood  into  the  plexuses  of  the  neighbouring  thyreoid  veins. 

Lyinph-vessels  are  abundant,  and  are  disposed  in  two  sets,  one  in  the  mucosa,  another  in 
the  submucosa.  They  drain  into  the  tracheal,  bronchial  and  oesophageal  lymph-glands. 
Neri'es  are  provided  by  the  vagus  direct,  by  the  inferior  laryngeal,  and  by  the  sympathetic. 

THE  LUNGS 

The  lungs  [pulmones],  the  essential  organs  of  respiration,  are  constructed  in 
such  a  way  as  to  permit  the  blood  to  come  into  close  relation  with  the  air  (fig. 
992).  Their  genetic  connection  with  the  entodermal  canal  has  already  been  indi- 
cated (see  also  p.  1099).     In  plan  of  structure  the  lung  has  been  compared  with 

Fig.  992. — Schematic  Section  of  a  Lobule  of  the  Lung  showing  the  Relation  of  the 
Blood-vessels  to  the  Air-spaces.  (After  Miller,  from  the  'Reference  Handbook  of  the 
Medical  Sciences.') 

b.r.  Respiratory  bronchiole,  d.al.  Alveolar  duct;  a  second  alveolar  duct  is  shown  cut  off. 
a,a.  Atria,  s.al.  Alveolar  saccule,  a.p.  Alveolus,  art.  Pulmonary  artery  with  its  branches 
to  the  atria  and  saccules,  v.  Pulmonary  vein  with  its  tributaries  from  the  pleura  (1),  the 
alveolar  duct  (2),  and  the  place  where  the  respiratory  bronchiole  divides  into  the  two  alveolar 
ducts  (3). 

)sa/ 


a  gland,  since  it  is  composed  of  a  tree-like  system  of  tubes  terminating  in  expanded 
spaces.  Closely  associated  with  the  system  of  tubes  are  certain  blood-vessels, 
some  of  which  take  part  in  nourishing  the  organ,  others  participate  in  its  special 
mechanism. 

The  lungs  are  two  in  number,  and  lie  one  on  either  side  of  the  thoracic  cavity, 
separated  by  a  partition  known  as  the  mediastinum  (figs.  993,  997,  1000).  Serous 
membranes  covering  the  latter  right  and  left  are  parts  of  two  closed  sacs,  the 
pleurse,  each  of  which  is  reflected  about  a  lung  and  the  neighbouring  chest-wall 
after  the  manner  of  serous  membranes  in  general.  The  space  enclosed  within  the 
sac-walls  is  the  pleural  cavity,  genetically  a  subdivision  of  the  ccelom. 

Form  (figs.  994,  998). — The  lung  is  pyramidal  or  conical  in  form,  with  the  base 
[basis  pulmonis]  below  and  resting  on  the  diaphragm,  and  with  apex  [apex  pul- 
moni.s]  above,  in  the  root  of  the  neck.  Two  surfaces,  costal  and  mediastinal,  are 
described.     The  broad  convex  costal  surface  [fades  costalis]  is  directed  against 


THE  LUNGS 


1229 


the  thoracic  wall  in  front,  laterally  and  behind,  and  is  marked  by  grooves  corre- 
sponding to  the  ribs.  The  mediastinal  surface  [f  acies  mediastinalis]  is  concave  and 
presents  a  contour  adapted  to  structures  of  the  mediastinum  (fig.  994).  A  special 
concavity  on  this  surface,  known  as  the  cardiac  fossa,  corresponds  to  the  promi- 
nence of  the  heart  and  is  deeper  in  the  left  lung  than  in  the  right.  Above  and 
behind  the  cardiac  fossa  is  a  depression,  the  hilus  of  the  lung  [hilus  pulmonis], 
where  the  bronchus  and  pulmonary  vessels  and  nerves  together  constituting  the 
root  of  the  lung  [radix  pulmonis],  enter  and  leave.  Near  the  posterior  edge  of  the 
mediastinal  surface  is  a  groove,  which  ascends  and  turns  forward  over  the  hilus ; 
the  groove  of  the  left  lung  is  adapted  to  the  cylindrical  surface  of  the  aorta; 
that  of  the  right,  the  vena  azygos.     A  well-marked  subclavian  sulcus  [sulcus  sub- 

FiG.  993. — Horizontal  Section  of  the  Thorax  op  a  Man,  aged  Fifty-seven,  at  the  Level 
OP  the  Roots  of  the  Lungs,  seen  prom  Above.  (J.  S.)  (Quain.)  X  1. 
A. A.  Ascending  aorta.  A.M.  Anterior  mediastinum.  A.V.  Azygos  vein.  D.A.  Descend- 
ing aorta.  E.  Eparterial  bronchus.  I.  Superior  lobe  of  lung.  L.B.  Left  bronchus.  L.P. 
Left  phrenic.  L.P.V.  Left  pulmonary  vein.  L.V.  Left  vagus.  (Es.  CEsophagus.  P  A. 
Pulmonary  artery.  P.C.  Pericardial  cavity.  R.B.  Right  bronchus.  R.P.A.  Right 
branch  of  pulmonary  artery.  R.P.C.  Right  pleural  cavity.  R.P.N.  Right  phrenic. 
R.P.V.  Right  pulmonary  vein.  R.V.  Right  vagus.  S.  Inferior  lobe  of  lung.  Sc. 
Scapula.     T.D.  Thoracic  duct.     3,  4,  .5,  6,  7.  Corresponding  ribs. 


clavius]  extends  upward  on  this  surface  to  the  apex,  corresponding  on  the  right 
side  to  the  lower  part  of  the  trachea  and  right  subclavian  artery,  on  the  left  tothe 
left  subclavian  artery  alone.  Further  forward  is  a  groove  adapted  in  the  right 
lung  to  the  superior  cava;  in  the  left  to  the  left  innominate  vein.  The  lung  is  not 
in  actual  contact  with  these  several  structures,  but  is  separated  from  them  by  the 
mediastinal  pleura.  The  mediastinal  surface  passes  gradually  into  the  costal 
surface  posteriorly,  there  being  no  proper  posterior  edge.  Where  the  mediastinal 
and  costal  surfaces  meet  in  front,  a  sharp  anterior  margin  [margo  anterior]  exists 
(fig.  997).  In  the  right  lung  this  runs  down  in  a  gentle  curve  to  turn  lateralward 
in  the  inferior  margin.  In  the  left  lung  the  anterior  margin  is  cut  into  by  a  wide 
cardiac  notch  [incisura  cardiaca],  which  is  occupied  bj'  the  heart  in  the  pericardium 
as  it  is  pressed  toward  the  anterior  thoracic  wall.  The  cardiac  notch  is  separated 
from  the  inferior  margin  by  a  little  tongue  of  lung  substance,  the  pulmonary 
lingula  [lingula  pulmonis]. 

The  base  of  the  lung  (fig.  994)  presents  the  diaphragmatic  surface  [facies 
diaphragmatica]  concave  and  oblique  in  adaptation  to  the  dome  of  the  diaphragm. 
It  is  limited  by  a  sharp  inferior  margin  [margo  inferior],  which  follows  the  curves 
of  the  mediastinal  and  costal  surfaces,  and  fits  into  the  angle  between  the  dia- 
phragm and  thoracic  wall. 


1230 


THE  RESPIRATORY  SYSTEM 


The  apex  (figs.  994,  997,  998)  is  rounded  and  points  upward  with  an  inclination 
forward  and  medially,  accommodating  itself  to  the  structures  within  and  about 
the  superior  aperture  of  the  thorax. 

A  deep  interlobar  fissure  [incisura  interlobaris]  (figs.  994,  998),  reaching 
through  the  lung  substance  nearly  to  the  hilus,  divides  each  organ  into  a  smaller 
superior  lobe  [lobus  superior]  and  a  larger  inferior  lobe  [lobus  inferior].  The 
interlobar  fissure  runs  downward  and  forward  beginning  a  short  distance  below  the 
apex,  and  reaching  the  base  near  the  anterior  margin  in  the  left  lung,  somewhat 
further  back  in  the  right  lung.  From  the  obliquity  of  the  plane  of  the  fissure  it 
will  be  noticed  that  the  inferior  lobe  reaches  posteriorly  to  within  a  short  distance 
of  the  apex,  and  includes  the  greater  part  of  the  back  and  base  of  the  lung,  while 
the  superior  lobe  takes  in  the  anterior  margin  and  apex.  The  presence  of  a  mid- 
dle lobe  [lobus  medius]  disturbs  the  symmetry  of  the  right  lung.  This  results 
from  a  deep,  nearly  horizontal  incisure  cutting  through  the  lung  somewhat  below 
its  middle,  and  extending  between  the  anterior  margin  and  the  main  interlobar 
fissure,  which  it  reaches  at  about  the  level  of  the  axillary  line. 


Fig.  994. — Left  Lung,  viewed  pbom  the  Mediastinal  Surface. 
Apex      Subclavian  groove 
I 


(Spalteholz.) 


Costal  surface 


Hilus,  with  line  of  section 
of  the  pleura 


Interlobar  fissure —  ' 


Left  branch  of  puln 
nary  artery 


Left  bronchus- 


Mediastinal  surface 


^^Left  pulmonary  veins 


-Cardiac  fossa 


Pulmonary  ligament  — 


-Anterior  margin 


Inferior  lobc_.- 


Inferior  margin  - 


Interlobar  fissure 


Diaphragmatic  surface 


Besides  possessing  the  individual  peculiarities  mentioned,  the  two  lungs  further  differ  from 
each  other  in  general  form  and  weight,  the  right  lung  being  considerably  broader  and  heavier 
than  the  left.  The  difference  in  length  maintained  by  some  anatomists,  even  if  it  prove  constant, 
must  be  slight  and  of  httle  practical  importance.  These  difJerenoes  seem  to  foUow  the  asym- 
metry of  the  vault  of  the  diaphragm  and  the  position  of  the  heart. 

The  hilus  (fig.  994),  already  mentioned  as  situated  on  the  mediastinal  surface,  presents  in 
the  left  lung  a  raquette-shaped  outline.  Its  average  height  is  about  8.8  cm.  (Luschka);it 
extends  over  both  lobes.  The  hilu  of  the  right  lung,  rather  four-sided  in  outline  and  shorter 
than  that  of  the  left,  is  related  to  the  three  lobes.  The  entering  structures,  constituting  the 
root  of  the  lung  (figs.  989,  993,  994),  include  the  bronchus,  pulmonary  artery  and  veins,  bron- 
chial vessels,  lymphatic  vessels  and  glands,  and  pulmonary  nerves.  These  are  bound  together 
by  connective  tissue  and  invested  by  the  pleura.  The  bronchus  is  in  the  posterior  and  upper 
part  of  the  root;  the  pulmonary  vessels  he  anteriorly,  the  veins  below  the  arteries. 

The  surface  of  the  lung  is  marked  off  in  polygonal  areas  of  different  sizes  (secondary  lobules) 
by  lines  containing  pigment.  The  pigmentation  is  especially  deep  on  the  lateral  surface  along 
the  furrows  corresponding  to  the  ribs. 


THE  BRONCHIAL  TUBES 


1231 


Branching  of  the  bronchial  tubes  (fig.  995) . — Each  bronchus,  from  its  origin  at 
the  bifurcation  of  the  trachea,  takes  an  oblique  course  to  the  hilus,  and  then  con- 
tinues in  the  lung  as  a  main  tube,  extending  toward  the  posterior  part  of  the  base. 
These  stem-bronchi  are  curved,  probably  in  adaptation  to  the  heart,  the  right  hke 
the  letter  C  and  the  left  like  an  S.  Throughout  their  course  the  stem-bronchi  give 
off  in  monopodic  fashion  collateral  branches,  the  bronchial  rami  [rami  bronchiales], 
and  these,  branching  in  a  similar  way,  reach  all  parts  of  the  lung. 

The  first  bronchial  ramus  of  the  right  stem-bronchus  arises  above  the  place  where  the  latter 
is  crossed  by  the  pulmonary  artery  and  is  named  the  eparterial  bronchial  ramus  [ramus 
bronohialis  eparterialis];  it  supphes  the  superior  lobe  of  the  right  lung,  sending  a  special  branch 
to  the  apex.     All  other  bronchial  rami,  whether  in  the  right  or  left  lung,  take  origin  from  the 

Fig.  995. — Cast  of  the  Air-tubes  and  Their  Branches,  viewed  from  in  Front. 
(Spalteholz.) 


Ttachea  (also  the  position  of  tlie  median  plane) 
I 


Bifurcation  of  trachea 
/^      Left  bronchus 


Main  bronchus 

Hyparterial 

branch  to 

middle  lobe 


Hyparterial  branch 
to  superior  lobe 


Position  of  median  plane 


stem-bronchi  below  the  level  of  the  crossing  of  the  pulmonary  artery  and  are  called  hyparterial 
bronchial  rami  [rami  bronchiales  hyparterialesj.  The  second  bronchial  branch  of  the  right  lung 
goes  to  supply  the  middle  lobe,  while  several  bronchial  branches  enter  the  inferior  lobe.  On 
the  left  side,  the  first  bronchial  branch  arises  below  the  crossing  of  the  pulmonary  artery,  and 
goes  to  supply  the  supei-ior  lobe,  providing  it  with  an  apical  ramus.  The  other  branches  are 
given  to  the  inferior  lobe. 

Structure  of  the  bronchial  rami. — The  larger  bronchial  rami  contain  in  their  walls  both 
C-shaped  and  irregular  plates  of  cartilage,  the  latter  gradually  replacing  the  former  as  the 
branches  become  smaller.  The  membranous  wall  is  lost  and  plates  of  cartilage  are  disposed 
on  all  sides.  The  mucosa,  with  ciUated  epithehum,  is  thrown  into  longitudinal  folds  covering 
bundles  of  elastic  fibres  of  the  membrana  propria.  Next  to  the  latter  is  a  continuous  layer  of 
smooth  muscle-fibres  circularly  arranged.  Mucous  secreting  bronchial  glands  [gl.  bronchiales] 
are  present  as  far  as  tubes  of  1  mm.  diameter;  here  the  cartilages  also  disappear. 

To  W.  S.  IVIiller  is  due  the  credit  of  having  greatly  increased  our  knowledge  of  the  finer 
structure  of  the  lung  and  for  having  presented  the  conception  of  the  primary  lung  lobule  now 
generally  accepted  by  anatomists.     Some  of  the  chief  results  of  MiUer's  work  are  embodied  in 


1232 


THE  RESPIRATORY  SYSTEM 


the  following  descriptions  pertaining  to  the  termination  of  the  air-tubes  and  to  the  blood  and 
lymph  vascular  systems  of  the  lungs  and  pleurse. 

Through  further  branching  of  the  bronchial  rami  a  great  number  of  very  fine  bronchioles 
[bronchioli]  are  reached,  whose  walls  possess  a  weak  muscle  layer  and  are  lined  by  mucosa 
having  an  epithelium  of  flattened  non-ciliated  cells.  These,  subdividing,  give  rise  to  the 
respiratory  bronchioles  [bronchioh  respiratorii],  the  walls  of  which  are  beset  with  alveoli 
(fig.  992).  From  the  respiratory  bronchioles  arise  the  alveolar  ducts  [ductuli  alveolares],  or 
terminal  bronchi,  each  of  which  leads  to  a  group  of  air-spaces,  called  atria,  each  of  which  again 
communicates  with  a  second  series  of  air-spaces,  tlie  air-sacs  (alveolar  sacs  or  infundibula), 
whose  walls  are  pouched  out  to  form  numerous  pulmonary  alveoli  [alveoli  pulmonum]. 

A  terminal  bronchus  with  its  air-spaces  and  blood-vessels,  lymphatics  and  nerves,  together 
form  a  pulmonary  lobule  [lobulus  pulmonum],  the  unit  of  lung  structure. 

Aeby  divided  the  bronchial  branches  into  two  sets,  according  to  their  relation  to  the  pul- 
monary artery.  The  branch  arising  above  the  place  where  the  pulmonary  artery  crosses  the 
stem-bronchus  he  named  the  eparterial  bronchus,  and  those  arising  below  the  crossing  he  called 
hyparterial.  An  eparterial  bronchus  exists  only  on  the  right  side ;  all  other  branches  are  hy- 
parterial.  Since  the  eparterial  supplies  the  superior  lobe  of  the  right  lung  and  no  eparterial 
branch  is  present  on  the  left  side,  Aeby  concluded  that  the  left  lung  had  no  lobe  homologous 
with  the  superior  lobe  of  the  right  lung.  He  compared  the  middle  lobe  of  the  right  with  the 
superior  lobe  of  the  left  lung.  The  collateral  branches  of  the  stem-bronchi  arise  in  a  dorsal 
and  ventral  series  in  the  lower  mammals,  and  the  same  arrangement,  though  less  obvious, 
obtains  in  man.  According  to  the  views  of  Aeby  and  Hasse,  the  first  ventral  branch  of  the  right 
side  is  distributed  to  the  middle  lobe,  while  the  remaining  three  ventral  and  all  the  dorsal  lateral 
branches  are  given  to  the  inferior  lobe.  On  the  left  side,  the  first  ventral  branch  is  given  to  the 
superior  lobe;  the  other  ventral  branches  and  the  dorsal  branches  are  distributed  to  the  inferior 
lobe. 

Fig.  996. — Scheme  of  the  Bbonchial  Tree  According  to  Narath.     A.  Anterior  view.     B. 

Right  lateral  view.     (Poirier  and  Charpy.) 

A.  Apical  bronchus,  collateral  of  the  first  ventral  and  susceptible  of  becoming  eparterial,  Ap 

in  migrating  to  the  bronchial  trunk. 


Narath  considers  the  division  of  bronchial  branches  in  accordance  with  their  relation  to 
the  pulmonary  artery  as  of  no  great  morphological  significance.  He  attributes  the  apparent 
differences  on  the  two  sides  to  a  shifting  in  position  of  homologous  branches.  Thus,  Narath 
considers  that  the  eparterial  bronchus  of  Aebj'  has  become  the  first  dorsal  lateral  branch  by 
displacement  above  the  pulmonary  artery  and  that  it  is  homologous  with  an  apical  branch  of 
the  left  side,  which  retains  its  primitive  origin  from  the  first  ventral  branch  (fig.  996) .  Narath's 
conception  of  the  migration  of  the  bronchial  branches  is  supported  by  the  results  of  Hunting- 
ton's extensive  stiulii's  of  the  bronchial  tree  in  mammals. 

The  physical  properties  of  the  lungs. — The  average  dimensions  in  the  adult  male  are  as 
follows:  Height  of  the  lung  is  given  at  2.5-27  cm.,  the  greatest  sagittal  diameter  at  16-17  cm., 
and  the  greatest  transverse  measurement  as  10  cm.  for  the  right  and  7  cm.  for  the  left.  The 
volume  of  the  lungs  when  well  expanded  is  6500  c.c.  (Merkel.)  The  loeight  of  the  lungs  can 
be  found  only  approximately  on  account  of  the  presence  of  blood  and  mucus.  In  the  adult 
male  the  weight  of  both  lungs  is  given  as  1300  gm.;  female,  1023  gm.  The  weight  of  the  right 
lung  compared  with  the  left  is  as  11  is  to  10.  Ried  and  Hutchinson  found  the  weight  of  the 
lungs  compared  with  that  of  the  body  as  1  :37  (male),  1  :43  (female);  in  the  foetus  at  term, 
1  :  70.  After  respiration  has  been  established,  the  lung,  if  placed  in  water,  will  float.  Its 
specific  gravity  is  between  0.345  and  0.746,  (Rauber.)  The  fcetal  lung  contains  no  air  and  is 
heavier  than  water.  Its  specific  gravity  is  1.045  to  1.056.  (Ivrause.)  Lung  tissue,  free  of 
air,  with  vessels  moderately  filled,  has  likewise  a  specific  gravity  of  1.045  to  1.056.     (Vierordt). 

The  colour  of  the  lung  result  sfrom  the  presence  of  blood,  pigment,  and  the  air  in  the  alveoli. 
It  varies  therefore  as  these  constituents  are  all  or  in  part  present  and  with  differences  in  their 


TOPOGRAPHY  OF  THE  LUNGS 


1233 


proportions.  Thus  the  general  colour  is  red  in  the  fcetus,  pink,  in  the  infant,  and  grey  mottled 
with  black  in  the  adult.  The  dark  colour  is  traceable  to  the  carbonaceous  matter  carried  into 
the  lungs  from  the  atmosphere. 

In  consistence  the  lung  is  soft  and  spongy,  and  when  compressed  between  the  fingers, 
emits  a  crackling  sound.  Among  the  physical  properties  the  elasticity  of  the  lung  is  quite 
remarkable:  Under  ordinary  conditions  the  pressure  of  the  air  in  the  lung  keeps  the  alveoli 
and  the  organ  as  a  whole  distended,  but  when  the  pleura  has  been  opened  and  the  air  pressure 
equalised  without  and  within,  the  lung  collapses. 

Topography. — The  apices  of  the  lungs  extend  upward  as  high  as  the  first  thoracic  vertebra- 
a  level  considerably  higher  than  the  superior  margin  of  the  sternum  (figs.  997,  998).  The  sub, 
clavian  vein  and  artery  and  the  brachial  plexus,  together  with  the  anterior  scalene  muscle, 
control  to  a  certain  degree  the  height  reached.  There  seems  to  be  no  constant  difference  be- 
tween the  levels  attained  by  the  apices  of  the  two  lungs.  The  extent  to  which  the  apex  rises 
above  the  clavicle  is  rarely  more  than  3.5  cm.  (Merkel),  and  will,  of  course,  vary  with  individual 
differences  in  the  position  and  form  of  this  bone.     The  average  is  not  over  2.5  cm.  (1  in.). 

The  base  of  the  lung,  resting  on  the  diaphragm,  is  separated  by  that  thin  partition  from  the 
underlying  abdominal  viscera:  thus  beneath  the  base  of  the  right  lung  is  the  right  lobe  of  the 
liver,  while  under  the  left  lung  are  the  left  lobe  of  the  liver,  the  fundus  of  the  stomach,  and  the 
spleen.     The  position  of  the  apex  changes  very  little  in  respiration,  and  the  same  holds  true  for 

Fig.  997. — Position  of  the  Lungs  from  Before.     (Merkel.) 
,    The  parietal  pleura  is  shaded  and  outlined  in  black. 


the  hinder  bulky  part  of  the  lung.  The  latter  rests  against  the  side  of  the  vertebral  column  in 
the  deep  hollow  of  the  angles  of  the  ribs,  and  reaches  below  to  the  level  of  the  eleventh  costo- 
vertebral joint  (fig.  998).  The  anterior  margins  (fig.  997)  descend  in  curves  from  behind  the 
sterno-clavicular  joints,  and  run  near  together  a  little  to  the  left  of  the  median  line.  At  the 
level  of  the  sixth  costo-sternal  junction  the  anterior  margin  of  the  right  lung  turns  lateral- 
ward  to  follow  the  sixth  costal  cartilage.  The  anterior  margin  of  the  left  lung  turns  lateralward 
a,long  the  fourth  costal  cartilage  as  far  as  the  para-sternal  line,  descending  in  .a  curve  to  the 
lingula  and  thus  forming  the  cardiac  incisure.  The  positions  of  the  inferior  margins  (figs. 
997,  998)  of  the  two  lungs  are  practically  alike  in  their  positions.  Each  extends  in  a  curve  cov- 
yex  downward,  behind  the  sixth  costal  cartilage  in  its  entire  length,  crosses  the  costo-chondral 
junction  of  the  sixth  rib  to  the  superior  margin  of  the  eighth  rib  in  the  axillary  hne,  and  so  to 
the  ninth  or  tenth  rib  in  the  scapular  line,  whence  they  run  horizontally  medialward  to  the 
eleventh  costo-vertebral  joint.  * 

*  These  relations  are  the  mean  between  the  conditions  observed  in  the  cadaver  and  as  found 
by  physical  examination  of  the  hving.  In  old  age  the  inferior  margins  of  the  lungs  reach  a 
level  one  or  two  intercostal  spaces  lower  than  is  the  case  in  adult  life  (Mehnert). 


1234 


THE  RESPIRATORY  SYSTEM 


The  interlobar  fissure  (fig.  998)  begins  about  6  cm.  below  the  apex  of  the  lung  at  the  level 
of  the  head  of  the  third  rib.  With  the  arm  hanging  at  the  side,  a  hne  drawn  across  the  back 
from  the  third  thoracic  spine  to  the  root  of  the  scapular  spine  would  indicate  the  course  of 
the  upper  part  of  this  fissure.  (Merkel.)  Thence  it  passes  downward  and  around  the  chest  to 
the  end  of  the  sixth  bony  rib  in  the  mammillary  line.  Merkel  points  out  the  use  of  the  root 
of  the  scapular  spine  as  a  landmark  for  finding  the  limits  of  the  lobes  posteriorly:  with  the 
arm  hanging  at  the  side  all  above  this  spot  is  superior  lobe;  aU  below  it  the  inferior.  The  short 
fissure  of  the  right  lung  begins  at  the  main  interlobar  fissure  in  the  axillary  line,  about  the 
level  of  the  fourth  rib  or  fourth  interspace,  and  passes  nearly  horizontally  to  the  anterior  margin 
of  the  lung  at  the  level  of  the  fourth  costal  arch. 

The  roots  of  the  lungs  are  placed  opposite  the  fifth,  sixth,  and  seventh  thoracic  vertebrae. 
The  right  root  lies  behind  the  inferior  vena  cava  and  under  the  arch  of  the  azygos  vein;  the  left 
root  is  beneath  the  aortic  arch  and  in  front  of  the  thoracic  aorta.  The  phrenic  nerve  passes 
in  front  of  each  root,  the  vagus  behind.  On  the  front  and  back  are  the  pulmonary  plexuses, 
anterior  and  posterior.     The  ligament  of  the  pleura  goes  from  the  lower  edge  of  the  root. 

Vessels  and  nerves  of  the  lungs. — The  bronchial  arteries  (see  p.  588),  belonging  to  the 
systemic  system,  carry  blood  for  the  novirishment  of  the  lungs.  They  arise  from  the  aorta  or 
from  an  intercostal  artery,  two  for  the  left  lung  and  one  for  the  right,  and,  entering  at  the  hilus, 

Fig.  998. — Position  of  the  Lungs  from  Behind.     (Merkel.) 
The  pleura  is  represented  as  in  Fig.  997. 


reach  the  hinder  wall  of  the  main  bronchus.  The  bronchial  arteries  accompany  the  bronchi, 
whose  walls  they  supply,  as  far  as  the  distal  ends  of  the  alveolar  ducts,  beyond  which  they  do 
not  go.  These  vessels  also  supply  the  lymph  glands  of  the  hilus,  the  walls  of  the  large  pulmonary 
vessels,  and  the  connective-tissue  septa  of  the  lung.  Bronchial  veins  (see  p.  664),  anterior 
and  posterior,  arise  from  the  walls  of  the  first  two  or  three  divisions  of  the  bronchi  and  end  in 
the  innominate  and  the  azygos  or  in  one  of  the  intercostal  veins;  those  arising  from  the  walls 
of  the  smaller  tubes,  including  the  alveolar  ducts,  join  the  pulmonary  veins.  The  pulmonary 
artery  (see  p.  528),  entering  the  hilus  in  a  plane  anterior  to  the  bronchus,  tm-ns  to  the  posterior 
aspect  of  the  main-stem,  following  its  branches  and  their  subdivisions  to  the  lobules.  Entering 
the  lobule,  the  last  branch  of  the  vessel  gives  off  as  many  twigs  as  there  are  atria  (fig.  992), 
and  these  twigs  end  in  dense  capillary  nets  in  the  walls  of  the  alveoli.  Here  the  venous  blood 
brought  by  the  pulmonary  artery,  separated  from  the  air  in  the  alveolus  only  by  a  thin  septum, 
is  changed  to  arterial  blood  in  the  respiratory  process.  According  to  Miller,  anastomosis 
between  the  branches  of  the  pulmonary  artery  are  exceptional.  Anastomosis  between  the 
bronchial  and  pulmonary  arteries  has  been  claimed,  but  the  connection  apparently  existing 
between  these  vessels  is  through  the  radicles  of  the  bronchial  veins  which  join  the  pulmonary 
veins.  The  pulmonary  venous  radicles  begin  at  the  capillary  networks  and  drain  the  arterial 
blood  into  the  pulmonary  veins,  which  run  between  adjacent  lobules  and  which  receive  also 


THE  THORACIC  CAVITY  1235 

blood  coming  from  the  capillary  network  of  the  pulmonary  pleura  and  from  the  capillary  net- 
work of  the  bronchi  (fig.  992).  Thus  it  wiU  be  seen  that  while  the  pulmonary  vein  carries 
mainly  arterial  blood,  it  carries  also  some  venous  blood.  The  pulmonary  veins  (see  p.  529) 
follow  the  bronchial  tree  on  the  side  opposite  the  arteries  to  the  hilus,  where,  having  converged 
to  two  large  trunks  located  in  the  root  of  the  lung  below  the  plane  of  the  artery,  they  pass  to  the 
left  atrium.     The  pulmonary  veins  have  no  valves. 

Lymphatics. — Miller  has  found  the  lymphatic  vessels  forming  a  closed  tube  system  in  the 
walls  of  the  bronchi,  in  the  pleura,  and  along  the  branches  of  the  pulmonary  artery  and  veins. 
Within  the  lung  numerous  pulmonary  lymph-glands  [lymphoglandulse  pulmonales]  are  found 
chiefly  at  the  places  of  branching  of  the  larger  bronchi  [lymphoglandulae  bronchiales[.  Scat- 
tered along  the  latter,  as  well  as  associated  with  the  branches  of  the  pulmonary  artery  and 
vein,  are  found  masses  of  lymphoid  tissue.  Deposits  of  carbonaceous  matter  in  the  lymphoid 
structures  of  the  lung  are  present,  except  in  early  infancy  ;  the  amount  increases  with  age. 

Nerves. — The  vagus  and  sympathetic  contribute  to  form  the  pulmonary  plexuses  in  front 
and  behind  the  root  of  the  lung,  from  which  branches  go  to  accompany  bronchial  arteries;  a 
smaller  number  accompany  the  air-tubes  (see  p.  957). 

Variations. — Congenital  absence  of  one  or  both  lungs  has  been  observed.  Variations  in  the 
lobes  are  not  uncommon — four  for  the  right  and  three  for  the  left  lung  has  been  recorded.  An 
infracardiac  lobe,  as  found  in  certain  mammals,  sometimes  occurs;  an  infracardiac  bronchus  is, 
however,  constant  in  man.  More  or  less  complete  fusion  of  the  middle  and  upper  lobes  of  the 
right  lung  is  not  rare.  The  lungs  may  be  symmetrical,  with  two  lobes  each,  the  apical  bronchus 
of  the  right  springing  from  the  first  ventral  bronchus,  as  is  normal  for  the  left  lung  (Waldeyer, 
Narath) ;  or  the  lungs  may  have  three  lobes  each,  the  apical  bronchus  of  the  left  arising  from  the 
main  bronchus.  The  apical  bronchus  of  the  right  lung  may  arise  from  the  trachea,  an  origin 
that  is  normal  in  the  hog  and  other  artiodactyls. 

Development  of  the  lungs  and  trachea. — The  first  indication  of  the  trachea  and  lungs 
appears  in  embryos  of  about  32  mm.  as  a  trough-like  groove  in  the  ventral  wall  of  the  upper 
part  of  the  oesophagus,  communicating  above  with  the  pharynx.  Later  the  groove  becomes 
constricted  oi?  from  the  oesophagus,  the  constriction  extending  from  below  upward,  so  that  a 
tube  is  formed  which  opens  into  the  pharynx  above.  The  lower  end  of  this  tube  soon  becomes 
bilobed,  and  the  lobes,  elongating,  give  rise  to  additional  lobes,  of  which  there  are  primarily 
three  in  the  right  side  and  two  in  the  left.  The  upper  unpaired  portion  of  the  tube  becomes  the 
trachea,  while  the  lobed  lower  portion  gives  rise  to  the  bronchi  and  lungs,  the  complicated  struc- 
ture of  the  latter  being  produced  by  oft-repeated  branchings  of  the  bronchi. 


THORACIC  CAVITY 

Thoracic  cavity  [cavum  thoracis]  is  the  term  used  to  denote  the  space  included 
by  the  walls  of  the  thorax  and  occupied  by  the  thoracic  viscera.  These  are,  on 
each  side,  the  lung,  surrounded  by  the  pleural  cavity,  and  in  the  middle  the 
pericardium  and  heart,  great  vessels,  trachea  and  oesophagus,  all  closely  associated 
and  forming  a  dividing  wall,  the  mediastinal  septum,  standing  between  the  right 
and  left  sides  of  the  thoracic  space. 

The  limits  of  the  thoracic  space  are  given  by  the  skeletal  parts  of  the  thorax 
together  with  the  ligaments  involved  in  the  articulations  and  the  muscles  and 
membranes  interposed  between  the  bones.  The  arched  diaphragm  forms  the 
inferior  limit;  and  the  barrier  presented  by  the  scalene  muscles  and  the  cervical 
fascia  makes  the  superior  boundary,  which,  it  is  to  be  observed,  lies  above  the 
plane  of  the  superior  aperture  of  the  thorax  and  therefore  in  the  base  of  the  neck. 
These  boundaries  are  approached  by  the  extension  of  the  pleural  cavities;  yet 
there  intervenes  the  parietal  layer  of  the  pleural  sac  which  is  connected  with 
the  thoracic  walls  by  loose  connective  tissue,  the  endothoracic  fascia  [fascia 
endothoracica]. 

The  form  of  the  thoracic  space  departs  from  the  external  contour  of  the  thorax 
chiefly  through  the  projection  into  it  of  the  ridge  made  by  the  succession  of  centra 
of  the  thoracic  spine,  and  by  the  presence  on  either  side  of  the  latter  of  the  broad, 
deep  pulmonary  sulcus.  On  account  of  these  features  a  transverse  section  of  the 
thoracic  space  is  somewhat  heart-shaped,  but,  however,  much  compressed  antero- 
posteriorly  (fig.  993). 

The  arch  of  the  diaphragm  on  the  right  side  rises  to  the  level  of  the  spinous  process  of  the 
seventh  thoracic  vertebra;  on  the  left,  to  the  level  of  the  eighth  thoracic  spinous  process.  At 
its  circumference  the  diaphragm  is  in  contact  to  a  variable  extent  above  its  origin  with  the  inner 
surfaces  of  the  costal  arches.  In  the  lower  part  of  this  zone  a  connection  exists  between  the 
muscle  and  the  thoracic  wall  through  a  continuation  of  the  endothoracic  fascia;  in  the  upper 
part,  the  phrenico-costal  sinus  (see  p.  1237)  intervenes.  The  level  reached  by  this  deepest 
part  of  the  pleural  cavity  is  lower  than  the  summit  of  the  peritoneal  cavity,  so  they  overlap  to  a 
considerable  extent. 


1236 


THE  RESPIRATORY  SYSTEM 


THE  PLEURA 

The  pleura  (fig.  993)  is  a  closed  serous  sac,  which  invests  the  lung  (pulmonary 
pleura),  and  lines  the  inner  surface  of  the  thoracic  walls  (parietal  pleura).  The 
pleural  cavity  [cavum  pleurae]  is  the  capillary  space  enclosed  by  the  walls  of  the  sac 
containing  a  little  fluid  which  lubricates  the  apposed  surfaces  of  the  pulmonary 
and  parietal  membranes.  There  are  two  pleurae,  one  in  relation  to  each  lung, 
completely  separated  by  a  sagittal  partition,  the  mediastinum. 

FiQ.  999. — Plettral  Cavity  Opened  From  in  Front. 
1,  first  rib;  2,  manubrium  sterni;  3,  acromial  extremity  of  clavicle;  4,  xiphoid  process, 
5,  linea  alba;  6,  m.  transversus  abdominis;  7,  seventh  rib;  8,  sternocleidomastoid  m.;  9, 
anterior  scalene  m.;  10,  larynx;  11,  thyreoid  gland;  12,  deep  layer  of  cervical  fascia  in  front 
of  the  trachea;  13,  corresponds  to  upper  part  of  anterior  mediastinal  cave;  14,  pleural  cupola; 
15,  mediastinal  pleura;  16,  lower  margin  of  costal  pleura;  17,  pericardium;  18,  superior  lobe 
of  lung;  19,  middle  lobe  of  right  lung;  20,  inferior  lobe  of  lung;  21,  diaphragm.  (Rauber- 
Kopsch.) 


The  pulmonary  pleura  [pleura  pulmonalis]  forms  a  smooth  glistening  coat  over 
the  outer  surface  of  the  lung,  with  the  tissue  of  which  it  is  inseparably  connected. 
At  the  hilus  the  pulmonary  pleura  passes  from  the  mediastinal  surface  of  the  lung 
to  cover  the  root  above,  in  front,  and  behind,  and  becomes  continuous  medialward 
with  the  parietal  pleura  of  the  mediastinum.  Below  the  root  of  the  lung  the 
pleura  is  reflected  medialward  in  a  double  layer  as  the  pulmonary  ligament 
[Hg.  pulmonale]  (fig.  994). 

This  presents  anterior  and  posterior  surfaces  and  three  margins;  the  base  is  mostly  free,  and 
directed  toward  the  diaphragm,  with  which  it  is  connected  at  its  medial  end;  the  apex  is  at  the 
lung  root,  one  margin  is  next  to  the  lung,  and  the  other  joins  the  mediastinal  pleura. 


THE  PLEURA 


1237 


The  parietal  pleura  [pleura  parietalis]  is  divided,  according  to  the  regions  of  the  chest  with 
which  it  is  associated,  into  the  costal,  diaphragmatic,  and  mediastinal  pleura.  The  costal 
pleura  [pleura  costahs]  hnes  the  thoracic  wall,  to  which  it  is  bound  not  very  firmly  by  the 
endothoracic  fascia.  It  covers  incompletely  the  back  of  the  sternum  and  extends  laterally  upon 
the  ribs  and  "intercostal  muscles.  Posteriorly  beyond  the  angles  of  the  ribs  it  passes  over  the 
anterior  rami  of  the  thoracic  nerves  and  intercostal  vessels,  the  heads  of  the  ribs,  and  the 
sympathetic  trunk  to  the  vertebral  column;  here  it  becomes  continuous  with  the  mediastinal 
pleura.  Above,  the  pleura  reaches  beyond  the  superior  margin  of  the  sternum  into  the  root  of 
the  neck,  and  in  the  form  of  a  dome,  the  cupola  of  the  pleura  [cupola  pleurae],  is  adapted  to  the 
ape.x  of  the  lung.  It  is  supported  by  processes  of  the  deep  cervical  fascia,  and  by  a  fibrous 
aponeurosis  known  as  Sibson's  fascia,  coming  from  the  scalenus  minimus  muscle  and  connected 
with  the  inner  margin  of  the  first  rib.  In  relation  to  the  pleural  cupola  are  those  structures 
already  described  as  grouped  about  the  lung  apex:  the  brachial  plexus,  subclavian  artery,  ante- 
rior scalene  muscle,  and  the  subclavian  vein,  and,  on  the  left  side,  in  addition,  the  thoracic  duct. 

Below,  the  costal  pleura  is  continuous  with  the  diaphragmatic  pleura  [pleura  diaphragmatica], 
which  adheres  closely  to  the  thoracic  surface  of  the  diaphragm  and  covers  it,  excepting  the 
pericardial  area  and  where  the  diaphragm  and  thoracic  wall  are  in  contact. 

The  mediastinal  pleura  [pleura  mediastinalis]  is  reflected  from  before  backward  at  the 
right  and  left  sides  of  the  mediastinum  as  the  laminEB  mediastinales,  covering  the  pericardium 


Fig.  1000. — Right  Lateral  Surface  op  the  Mediastinum  after  Removal  op  the  Pleura. 
(Poii-ier  and  Charpy.) 


Trachea  .   — 


Phrenic  nerve 


[pleura  pericardiaca],  to  which  it  is  closely  adherent,  and  also  the  other  structures  of 
the  mediastinum,  with  which  the  two  layers  are  less  firmly  connected.  Above  the  lung  root 
the  mediastinal  pleura  stretches  directly  from  the  spine  to  the  sternum;  but  at  the  level  of  the 
root  and  below  it,  it  is  reflected  laterally  to  the  pulmonary  pleura  covering  the  root  in  front  and 
behind  and  forming  the  pulmonary  ligament. 

The  right  mediastinal  lamina  covers  (fig.  1000)  the  right  innominate  vein,  the  superior  vena 
cava,  the  vena  azygos,  the  trachea,  the  innominate  artery,  the  right  vagus  and  phrenic  nerves, 
and  the  oesophagus.  The  left  lamina  lies  against  the  left  innominate  vein,  the  arch  of  the  aorta 
the  left  subclavian  artery,  the  thoracic  aorta,  the  left  phrenic  and  vagus  nerves,  and  the  cesoph- 
agus.  About  the  base  of  the  heart-sac  are  a  number  of  adipose  folds  [plica?  adiposis)  projecting 
from  the  pleura,  the  surfaces  of  which  present  some  villous  processes,  the  pleural  villi  [villi 
pleurales] ;  the  latter  also  occur  on  the  pulmonary  pleura  along  the  inferior  margin  of  the  lung. 

The  lines  of  pleural  reflexion  are  of  practical  importance  (figs.  997,  998,  1003).  Posteriorly, 
the  costal  pleura  simply  turns  forward  in  a  gentle  curve  to  become  the  mediastinal  pleura,  but 
anteriorly  and  inferiorly  the  membrane  is  folded  upon  itself,  leaving  intervening  capiUary 
spaces,  the  sinuses  of  the  pleura  [sinus  pleurtT;].  Such  a  space  is  present  where  the  costal  pleura 
is  reflected  upon  the  diaphragm,  the  sinus  phrenicocostalis,  the  fold  of  the  pleura  occupying 
the  upper  part  of  the  angle  between  the  thoracic  wall  and  diaphragm,  the  endothoracic  fascia 


1238 


THE  RESPIRATORY  SYSTEM 


filling  the  lower  part.  The  inferior  margui  of  the  lung  enters  this  sinus  a  variable  distance  in 
iuspiration.  The  line  of  the  costo-diaphragmatio  reflexion  begins  in  front  on  the  sixth  costal 
cartilage,  which  it  follows,  descending  obliquely  to  cross  the  seventh  interspace  in  the  mam- 
millary  line.  The  greatest  depth  reached  is  at  the  tenth  rib  or  interspace  in  the  axillary  line. 
The  line  of  reflexion  then  continues  around  the  thorax  ascending  slightly  to  the  twelfth  costo- 
vertebral joint. 

The  Ime  of  reflexion  behind  is  sometimes  found  as  low  as  the  level  of  the  transverse  process 

Figs.  1001  and  1002. — Boundaeibs  op  the  Pleura  and  Lungs. 

Lines  of  pleural  reflection  red,  boundaries  of  the  lungs  and  pulmonary  lobes  black. 

1,  sixth  cervical  vertebra;  2,  first  thoracic  vetebra;  3,  twelfth  thoracic  vertebra;  4,  first 
lumbar  vertebra;  5,  manubrium  sterni;  6,  body  of  sternum;  7,  xiphoid  process;  8,  first  rib; 
9,  cartilage  of  seventh  rib;  10,  11,  12,  tenth,  eleventh  and  twelfth  ribs.     (Rauber-Kopsch.) 


of  the  first  lumbar  vertebra.  Such  a  possibility  must  be  considered  in  operating  upon  the  kidney. 
The  lines  of  reflexion  of  the  costal  pleura  backward  to  the  mediastinal  pleura  behind  the 
sternum  begin  opposite  the  sterno-clavicular  joints,  descend  obhquely  medialward  to  the  level 
of  the  second  costal  cartilage,  whence  they  run  near  together  or  in  contact,  but  to  the  left  of  the 
medianHline,  to  the  level  of  the  fourth  cartilage.  The  reflexion  on  the  right  side  continues 
from  the  sternum  as  far  as  the  sixth  rib  cartilage,  there  turning  laterally  into  the  costo-dia- 
phragmatic  reflexion.     The  line  on  the  left  side,  in  the  region  of  the  cardiac  notch  (from  the  fourth 


Fig. 


J103. — Schematic  Drawing  to  Represent  the  Maximum  op  Fluctuation  in  the 
Position  op  the  Anterior  Lines  op  Pleural  Reflexion.     (Tanja.) 


to  the  sixth  cartilages),  is  a  little  to  the  left  of  the  sternal  margin.  From  this  position  of  the 
line  of  reflexion  it  happens  that  there  is  left  uncovered  by  pleura  a  small  area  of  the  pericardium 
which  is  in  contact  immediately  with  the  chest-wall.  A  reduplication  of  the  pleura  takes 
place  along  the  anterior  line  of  reflexion,  and  into  the  sinus  costomediastinalis  so  formed  the 
thin  anterior  margin  of  the  lung  advances  in  inspiration.  That  part  of  the  left  costo-mediastinal 
sinus  which  is  in  front  of  the  pericardium  is  not  completely  filled  by  the  margin  of  the  lung. 
Although  the  positions  of  the  lines  of  reflexion  of  the  mediastinal  pleura  here  described  are  those 


THE  MEDIASTINAL  SEPTUM  1239 

usually  encountered,  it  should  be  noted  that  they  are  subject    to  variation.     The  extremes  of 
variation  of  the  anterior  lines,  as  determined  by  Tanja,  are  indicated  in  fig.  1003. 

Blood-vessels. — The  vascular  networks  of  the  pulmonary  pleura  are  derived  from  the 
bronchial  artery  and  probably  to  some  extent  from  the  pulmonary  artery  which  in  the  dog,  is 
the  only  source  of  blood  supply.  The  venous  radicles  arising  from  the  network  enter  the  lung. 
(See  radicles  of  the  pulmonary  vein  on  page  1235.)  The  parietal  pleura  is  supplied  by  arteries 
from  several  sources:  internal  mammary,  intercostals,  phrenics,  mediastinal,  and  bronchial. 
The  veins  correspond  to  the  arteries.  The  lymphatics  of  the  pulmonary  pleura  form  rich 
networks  without  definite  relations  to  the  lobules  of  the  lung.  They  accompany  the  radicles 
of  the  pulmonary  veins  and  drain  into  the  bronchial  lymph-glands.  In  the  parietal  pleura 
lymph-vessels  are  present  most  abundantly  over  the  interspaces;  they  empty  into  the  sternal 
and  intercostal  glands.  (See  p.  728.)  The  nerves  supplied  to  the  pulmonary  pleura  are 
branches  from  the  pulmonary  plexus;  to  the  parietal  pleura,  from  the  intercostals,  vagus, 
phrenic,  and  sympathetic. 

MEDIASTINAL  SEPTUM 

The  two  pleural  cavities  are  separated  from  each  other  by  the  mediastinal  sep- 
tum [septum  mediastinale]  (fig.  1000).  This  is  a  sagittal  partition  extending 
from  the  superior  aperture  of  the  thorax  to  the  diaphragm  between  the  thoracic 
vertebrae  and  the  sternum,  its  free  surfaces,  right  and  left,  formed  by  the  mediast- 
inal layers  of  the  pleurae.  It  is  composed  of  the  pericardium  and  heart  and  of 
structures  which,  for  the  most  part,  extend  in  a  longitudinal  direction  through  the 
thoracic  cavity. 

These  include  the  oesophagus  together  with  the  vagus  nerves,  the  thoracic  duct,  thoracic 
aorta  and  azygos  vein;  the  trachea,  the  pulmonary  vessels  and  the  arch  of  the  aorta  with  its 
great  branches,  the  superior  vena  cava  and  its  tributaries  and  the  phrenic  nerves;  the  thymus 
gland,  internal  mammary  vessels  and  many  lymph  glands  throughout  the  septum.  These 
structures  are  packed  together  and  supported  by  intervening  connective  tissue.  Moreover, 
the  connection  of  the  sheaths  of  the  great  vessels  with  processes  of  the  cervical  fascia  and  the 
fixation  of  the  pericardium  to  tlie  diaphragm,  give  to  the  latter  a  strong  support.  Owing  to 
the  position  of  the  heart,  the  two  sides  of  the  septum  are  not  symmetrical,  and  it  follows  from 
the  bulging  of  the  left  surface  of  the  mediastinal  septum  that  the  left  pleural  cavity  is  encroached 
upon. 

The  name  mediastinal  cavity  has  been  applied  to  the  two  regions  of  the  medi- 
astinal partition  which  find  themselves  located,  the  one  in  front,  the  other  behind 
the  plane  of  the  heart.  There  is  in  reality  no  cavity,  the  term  being  used  in  this 
connection  merely  to  donate  space.  Between  the  two  spaces  are  interposed  the 
pericardium  and  heart,  the  great  vessels,  trachea  and  bronchi.  The  anterior 
mediastinal  cavity  [cavum  mediastinale  anterius]  is  small.  Its  lateral  limits  are 
formed  by  the  mediastinal  layers  of  the  pleurse,  right  and  left,  which  are  reflected 
backward  from  the  costal  pleurae  of  the  anterior  thoracic  wall.  The  space  is 
occupied  by  loose  connective  tissue,  surrounding  the  thymus  gland,  the  internal 
mammary  vessels  and  a  number  of  lymph-glands. 

Recalling  the  lines  of  reflexion  of  the  mediastinal  pleurfe  as  above  described,  the  form, 
position  and  extent  of  this  space  as  observed  from  in  front,  will  be  understood;  it  is  widest 
behind  the  inferior  end  of  the  body  of  the  sternum  and  fifth  and  sixth  costal  cartilages  of  the 
left  side  {area  inlerpleurica  inferior) ;  narrowest  where  the  mediastinal  layers  are  approximated 
behind  the  body  of  the  sternum,  broader  again  where  the  laminae  deviate  posterior  to  the 
manubrium  sterni  {area  inlerpleurica  superior).  In  the  latter  space  lies  the  thymus  gland  and 
the  superior  portions  of  the  internal  mammary  vessels.  In  the  area  interpleurica  inferior 
the  pericardium  comes  into  immediate  contact  with  the  anterior  thoracic  wall,  and  here  the 
inferior  portions  of  the  left  internal  mammary  vessels  are  found.  The  lymphatic  vessels  and 
glands  of  the  anterior  mediastinal  space  belong  to  the  anterior  mediastinal  and  sternal  groups. 

The  posterior  mediastinal  cavity  [cavum  mediastinale  posterius]  (fig.  1000), 
hmited  behind  by  the  thoracic  vertebrae  and  laterally  by  the  mediastinal  layers  of 
the  pleurae  where  they  are  reflected  forward  from  the  costal  plem-ae  of  the  pos- 
terior thoracic  walls,  is  elongated  and  of  more  regular  form  than  the  anterior  space. 
It  includes  the  thoracic  aorta,  the  oesophagus  and  vagi,  the  thoracic  duct,  azygos 
vein  and  lymph  glands. 

Within  this  space  are  also  to  be  found  the  origins  of  the  right  intercostal  arteries,  the 
hemiazygos  and,  when  present,  the  accessory  hemiazygos  veins,  terminations  of  some  of  the 
left  intercostal  veins  and  the  greater  splanchnic  nerves.  The  lymph  glands  belong  to  the 
posterior  mediastinal  group. 

(Pigs.  993,  994). — A  subdivision  of  the  mediastinal  septum  into  anterior,  middle,  posterior, 
and  superior  mediastinal  spaces  has  long  been  customary,  and  is  useful  for  descriptive  purposes. 

The  superior  mediastinum  is  that  part  of  the  mediastinum  which  Ues  above  the  level  of 


1240  THE  RESPIRATORY  SYSTEM 

the  pericardium.  It  extends"  between  the  first  four  thoracic  vertebrse  behind  and  the  manu- 
brium sterni  in  front,  and  contains  the  arch  of  the  aorta  and  the  great  vessels  arising  from  it, 
the  innominate  veins,  and  the  upper  part  of  the  superior  vena  cava,  the  thoracic  duct,  the  lower 
portion  of  the  trachea,  and  a  portion  of  the  oesophagus,  the  phrenics,  vagi,  left  recurrent  and 
cardiac  nerves,  and  the  thymus  gland. 

From  the  superior  mediastinum  the  other  three  divisions  of  the  space  extend  downward. 
The  anterior  mediastinum  is  identical  with  that  part  of  the  anterior  mediastinal  cavity  which 
is  below  the  level  of  manubrium  sterni.  The  middle  mediastinum  lies  between  the  layers  of 
the  mediastinal  pleura?  in  front  of  the  root  of  the  lungs;  it  contains  the  heart,  enclosed  in  the 
pericardium,  and  the  phrenic  nerves.  The  posterior  mediastinum  corresponds  to  that  portion 
of  the  posterior  mediastinal  cavity  which  extends  below  the  plane  of  the  fifth  intervertebral 
fibro-cartilage. 

References  for  Respiratory  System.     A.     External   nose  and  nasal  cavity. 

Kallius,  in  von  Bardeleben's  Handbuch;  Zuckerkandl,  Normale  u.  path.  Anatomie 
d.  Nasenhohle,  Bd.  1,  Wien,  1893;  {Develo-pvient)  His,  Archiv  f.  Anat.  u.  Phys., 
1892;  Killian,  Arch.  f.  LaryngoL,  Bd.  4,  1896;  Schaeffer,  Jour.  MorphoL,  vol. 
21,  1910;  {Concha)  Peter,  Arch.  f.  mikr.  Anat.,  Bd.  60, 1902;  {Paranasal sinuses) 
Bartels,  Zeitschr.  f.  Morph.  u.  Anthrop.,  Bd.  8;  Turner,  Accessory  Sinuses  of 
the  Nose,  Edinburgh,  1901;  {Anthropology)  Hoyer,  Morph.  Arbeiten,  vol.  4, 
1894.  B.  Larynx.  Gerlach,  Anat.  Hefte,  H.  56;  {Development)  Lisser,  Amer. 
Jour.  Anat.,  vol.  12;  {Ossification)  Scheier,  Arch.  f.  mikr.  Anat.,  Bd.  59. 
C.  Lungs.  {Structure;  vascular  supply)  Miller,  Arch.  f.  Anat.  u.  Entw.,  1900; 
Amer.  Jour.  Anat.,  vol.  7;  Schultze,  Sitzb.  AkadWiss.,  Berlin,  1906;  {Develop- 
ment) Flint,  Amer.  Jour.  Anat.,  vol.6  {Topographical)  Mehnert,  Topogr.  Alters- 
veranderungen  d.  Atmungsapparatus,  Jena,  1901.  D.  Pleura.  Ruge  Morph. 
Jahrb.    Be.    41. 


SECTION  XI 

UEOGENITAL  SYSTEM 


Revised  foe  the  Fifth  Edition 
By  J.  PLAYFAIR  McMURRICH,  A.M.,  Ph.D.,  LL.D. 

PROFEasOR   OF  ANATOMY   IN  THE   UNIVERSITY  OP  TORONTO 


The  urogenital   system   [apparatus  urogenitalis]   includes   (A)   the  urinary 
organs  and  (B)  the  reproductive  organs. 

A.  THE  URINARY  ORGANS 

THE  organs  forming  the  urinary  apparatus  [organa  uropoetica]  are  the 
kidneys,  by  which  the  secretion  is  produced;  a  duct,  the  ureter,  proceeding 
from  each  kidney  and  convejdng  the  secretion  to  the  bladder,  which 
serves  as  a  reservoir  for  the  urine  and  from  which,  by  a  single  duct,  the  urethra, 
the  secretion  is  carried  to  the  exterior. 

Fig.  1004. — Postero-medial  Aspect  of  the  Right  Kidney. 


THE  KIDNEYS 

The  kidneys  [renes]  are  paired  organs  situated  in  the  abdominal  region  and 
each  is  composed  of  a  very  great  number  of  minute  tubules,  the  renal  tubules, 
enclosed  within  a  definite  and  firm  fibrous  capsule.  Each  kidney  is  somewhat 
bean-shaped  (fig.  1004)  and  is  situated  on  the  dorsal  wall  of  the  body,  behind  the 
parietal  peritoneum,  in  such  a  way  that  the  ventral  or  visceral  surface  [facies  ante- 
rior] which  is  convex,  looks  obhquely  ventrally  and  laterally,  while  the  dorsal  or 
parietal  surface  [facies  posterior],  usually  less  convex,  looks  dorsally  and  somewhat 
medially  (fig.  1005).     The  upper  extremity  {extremitas  superior]  is  usually  larger 

1241 


1242 


UROGENITAL  SYSTEM 


than  the  lower  [extremitas  inferior]  and  is  about  1  cm.  nearer  the  median  sagittal 
plane  of  the  body,  owing  to  the  long  axis  of  the  organ  being  directed  obliquely 
downward  and  laterally.  The  lateral  border  [margo  lateralis]  is  narrow  and  con- 
vex, and  the  medial  border  [margo  medialis],  which  looks  medially  and  ventrally, 
is  concave,  its  middle  third  presenting  a  slit-hke  aperture,  the  hilus.  This  opens 
into  a  cavity,  called  the  sinus  (fig.  1006),  which  is  about  2.5  cm.  in  depth  and  is 
occupied  mainly  by  the  dilated  upper  extremity  of  the  ureter,  known  as  the  renal 
pelvis,  the  interval  between  this  and  the  actual  kidney  substance  containing  adi- 
pose tissue  in  which  are  imbedded  the  renal  vessels  and  nerves. 

Size. — The  length  of  the  kidney  in  the  male  averages  10-12  cm.,  its  breadth  about  5.5  cm. 
and  its  thickness  3  cm.;  it  weighs  115-150  grams.  The  dimensions  of  the  female  kidney  are 
nearly  as  great,  but  its  weight  is  from  one-seventh  to  one-fifth  less.  In  the  child  the  organ  is 
relatively  large,  its  weight  compared  with  that  of  the  entire  body  being  about  1 :  133  at  birth; 
but  its  permanent  relation,  which  is  about  1:217,  is  usually  attained  at  the  end  of  the  tenth 
year. 


Fig.  1005. — Diagram  showing  Relation  of  Kidnet  to  Capsule.     (Gerota.) 

Aorta 


Pararenal  adipose  — 
body 


Aponeurosis  of  trans-    Fascia  of  quadratus 
versus  abdominis  lumborum 


Renal  fascia  (posterior  layer)  Fascia  of  psoas 


Investment  and  fixation. — The  surface  of  the  kidney  is  covered  by  a  thin  but 
strong  ^??roMs  capsule  [tunica  fibrosa],  which  turns  inward  at  the  hilus  to  line  the 
walls  of  the  sinus  (fig.  1006).  It  may  readily  be  peeled  off  from  a  healthy  kidney, 
except  at  the  bottom  of  the  sinus,  where  it  is  adherent  to  the  blood-vessels  entering 
the  kidney  substance  and  to  the  terminal  portions  of  the  pelvis.  External  to 
the  capsule  is  a  quantity  of  fat  tissue,  the  adipose  capsule  [capsula  adiposa], 
which  forms  a  complete  investment  for  the  organ  and  is  prolonged  through  the 
hilus  into  the  sinus. 

The  peritoneum,  which  covers  the  ventral  surface  of  the  adipose  capsule,  has 
usually  been  regarded  as  the  principal  means  of  fixation  of  the  kidney,  but  in 
reality  this  is  accompHshed  by  means  of  a  special  renal  fascia  (fig.  1005),  developed 
from  the  subperitoneal  areolar  tissue  (Gerota). 

Renal  fascia. — Lateral  to  the  kidney  there  occurs  between  the  transversalis  fascia  and  the 
peritoneum  a  subperitoneal  fascia,  which,  as  it  approaches  the  convex  border  of  the  kidney, 
divides  into  two  layers,  one  of  which  passes  in  front  of  and  the  other  behind  the  kidney,  enclos- 
ing the  adipose  capsule.     Traced  medially,  the  anterior  layer  of  the  renal  fascia  passes  in  front 


THE  KIDNEY 


1243 


of  the  renal  vessels,  and,  over  the  aorta,  becomes  continuous  with  the  corresponding  layer  of 
the  opposite  side;  upward,  it  passes  over  the  suprarenal  gland  and  at  the  upper  border  of  that 
organ  becomes  continuous  with  the  posterior  layer;  and  downward,  it  is  lost  in  the  adipose 
tissue  intervening  between  the  iliac  fascia  and  muscle.  The  posterior  layer,  which  is  the  thicker 
of  the  two,  passes  medially  behind  the  renal  vessels  and  is  lost  in  the  connective  tissue  in  front 
of  the  vertebral  column,  and  below  it  is  lost,  like  the  anterior  layer,  in  the  ihac  region.  Behind 
the  posterior  layer,  between  it  and  the  quadratus  lumborum,  is  a  mass  of  adipose  tissue,  the 
pararenal  adipose  body,  and  both  layers  are  united  to  the  fibrous  capsule  of  the  kidney  by 
trabeculae  of  connective  tissue  which  transverse  the  adipose  capsule. 

Each  kidney  is,  accordingly,  supported  by  these  trabecute  in  a  space  bounded  laterally  and 
above  by  the  layers  of  the  renal  fascia,  and  open  medially  and  below.  Should  these  trabeculse 
become  atrophied  by  wasting  disease  or  ruptured  by  the  pressure  of  the  pregnant  uterus,  by 
the  improper  use  of  corsets,  or  by  any  other  cause,  the  phenomenon  of  movable  or  wandering 
kidney  may  be  set  up  by  slight  external  violence,  the  organ  tending  to  shift  its  place  as  far  as 
the  attachment  of  its  vessels  to  the  main  trunks  and  the  arrangement  of  the  renal  fascia  will 
permit. 

Position  and  relations. — The  kidney  is  said  to  lie  in  the  lumbar  region.  It  is, 
however,  intersected  by  the  horizontal  and  vertical  planes  which  separate  the 
hypochondriac,  lumbar,  epigastric  and  umbilical  regions  from  each  other,  and 
hence  belongs  to  all  these  segments  of  the  abdominal  space.  Its  vertical  level 
may  be  said  to  correspond  to  the  last  thoracic  and  upper  two  or  three  lumbar 


Fig.  1006. — Section  of  Kidney  showing  the  Sinus.     (After  Henle.) 
Cortex- 


Vessels 
Bottom  of 


Attachment  of  calyx 
Apex  of  papilla  with  orifices  of — (  -=r^ ■ 
papillary  ducts 


Margin  of  hilus  " 


vertebrffi,  the  right  lying  in  most  cases  from  8  to  12  mm.  (|  to  \  in.)  lower  than 
the  left;  but  exceptions  to  this  rule  are  not  infrequent. 

The  posterior  surface  (figs.  1007,  1008),  with  the  corresponding  portion  of  the 
fatty  capsule  and  the  pararenal  adipose  body,  rests  against  the  posterior  ab- 
dominal wall  extending  upward  in  front  of  the  eleventh  and  twelfth  ribs,  and 
medialward  to  overlap  the  tips  of  the  transverse  processes  of  the  first  and  second 
lumbar  vertebrae;  the  left  kidney  usually  reaches  as  high  as  the  upper  border  of  the 
eleventh  rib,  the  right  only  to  its  lower  border.  The  only  visceral  relation  pos- 
teriorly is  on  the  left  side,  where  the  spleen  slightly  overlaps  the  kidney  opposite 
the  upper  half  of  its  lateral  border,  the  adjacent  surfaces  of  the  two  organs  loeing, 
however,  covered  by  peritoneum.  The  parietal  relations  (fig.  1008)  on  both 
sides  are  as  follows:  (1)  the  diaphragm,  the  left  kidney,  on  account  of  its  higher 
position,  entering  more  extensively  into  this  relation  than  the  right ;  (2)  the  por- 
tion of  the  transversalis  fascia  covering  the  ventral  surface  of  the  quadratus 
lumborum;  (3)  the  lateral  border  of  the  psoas;  and  (4)  the  last  thoracic,  ilio- 


1244 


UROGENITAL  SYSTEM 


hypogastric  and  ilio-inguinal  nerves  and  the  anterior  divisions  of  the  subcostal  and 
first  lumbar  vessels,  all  of  which  run  obhquely  downward  and  laterally  in  front 
of  the  quadratus  lumborum. 

The  upper  extremity  of  each  kidney  is  crowned  by  the  suprarenal  gland  (figs. 
1007,  1009),  which  encroaches  also  upon  its  ventral  surface  and  medial  border 
and  is  fixed  to  it  by  fibres  derived  from  the  subperitoneal  tissue. 

The  anterior  surface  of  each  kidney  was  primarily  completely  covered  by 
peritoneum  that  separated  it  from  neighboring  viscera,  but,  owing  to  secondary 
changes  whereby  the  ascending  and  descending  colons,  the  duodenum  and  the 
pancreas  become  retro-peritoneal  organs,  these  come  into  direct  relation  with  one 
or  the  other  of  the  kidneys  and  separate  portions  of  them  from  actual  contact 
with  the  peritoneum.     Thus,  in  the  case  of  the  right  kidney  (fig.  1009),  the 

Fig.  1007. — The  Abdominal  Viscera,  seen  from  Behind. 

(From  the  model  of  His.) 

The  kidneys  are  somewhat  lower  than  usual  in  their  relations  to  the  ribs. 


Caudate  lobe  of  liv 


Aorta 
Outline  of  last  nb 


^ 


Spleen 

Left  kidney,  with L 

SUprarenal  body       j      ^  ^A 

Duodenum \— 

Descending  colon 

Cut    edge    of i  %  . 

peritoneum  ^ 


Outline  of  iliac  crest 


-      -^Lung 

^eJ   1  ^^~^\^"*s^^~-.  ~  "T Suprarenal  body 

"^      S^^ymmmmd-  Outline  of  last  rib 
— r^i^irJi — Vena  cava 


Right  kidney  with 
ureter  medially 


Small  intestine 


Outline  of  iliac  crest 
Colon  ascendens 


Termination  of  colon 


Small  intestine 


•Bladder 

mpulla  of  rectum 


portion  of  the  anterior  surface  immediately  adjacent  to  the  medial  border  has  the 
descending  portion  of  the  duodenum  in  direct  contact  with  it,  and  throughout  a 
zone  extending  downward  and  laterally  from  the  middle  of  the  duodenal  area  to 
the  lateral  border  the  ascending  colon  and  right  colic  flexure.  Almost  the  entire 
upper  half,  however,  and  a  small  portion  of  the  lower  pole  are  covered  directly 
by  peritoneum,  the  upper  peritoneal  area  having  an  indirect  relation  with  the 
lower  surface  of  the  liver,  upon  which  it  produces  the  renal  impression. 

Similarly  the  anterior  surface  of  the  left  kidney  (fig.  1009)  is  in  direct  contact 
with  the  pancreas  throughout  a  broad  transverse  band  situated  a  little  above  the 
middle  of  the  organ,  and  the  splenic  artery  pursues  its  tortuous  course  along  the 
upper  border  of  this  pancreatic  area,  while  the  corresponding  vein  is  interposed 
between  the  pancreas  and  the  surface  of  the  kidney.  The  lateral  portion  of  the 
lower  extremity  is  in  direct  contact  with  the  descending  colon  and  its  splenic 


THE  KIDNEY 


1245 


flexure,  but  the  remainder  of  the  lower  extremity  and  the  whole  of  the  upper  one- 
fourth  of  the  organ  is  directly  covered  by  peritoneum,  the  upper  peritoneal  area 
having,  as  an  indirect  relation,  the  posterior  surface  of  the  stomach  medially, 
and  the  spleen  laterally  (figs.  956,  1009). 

The  medial  border  of  the  right  kidney  approaches  the  vena  cava  inferior  very 
closely,  especially  above;  that  of  the  left  is  separated  from  the  aorta  by  an  inter- 
val of  about  2.5  cm. 


Fig.  1008. — Diagram  of  Relations  of  Posterior  Suepace  of  Left  Kidney. 

1  Lower  border  of  eleventh 
j         and  twelfth  ribs 


Medial  lumbo-costal  arch 
Lateral  lumbo-costal  arch 


Variation  in  position. — The  position  of  the  kidneys  in  the  abdominal  cavity  is  subject 
to  considerable  variation.  Thus  while  the  upper  pole  of  the  right  kidney  may  be  said  to  lie 
typically  opposite  the  lower  half  of  the  eleventh  thoracic  vertebra,  it  may  be  placed  as  high  as 
the  lower  part  of  the  tenth  thoracic  or  as  low  as  the  upper  half  of  the  fii'st  lumbar.  Similarly 
while  the  upper  pole  of  the  left  kidney  is  as  a  rule  opposite  the  middle  of  the  eleventh  thoracic 
vertebra  it  may  lie  half  a  vertebra  higher  or  as  low  as  the  lower  part  of  the  second  lumbar 
vertebra.     The  lower  poles  are  distant  from  the  crests  of  the  ilia  anywhere  from  1.0  cm.-3.0 


Fig.  1009. — Diagram  showing  Anterior  Relations  of  Kidneys  and  Suprarenal  Bodies. 

Duodenal  area      Hepatic  area  Gastric  area 

(non-peritoneal)  (non-peritoneal)     Caval  area    (peritoneal) 


Duodenal  area         

(non-peritoneal)       /ul'||i]|| 


Colic  area  [^ 
(non-peritoneal 


Colic  area 
(non-peritoneal) 


Peritoneal  'ixea  wih  right  coUc  vessels 


Pentoneal  area  with  left  cohc  vessels 


cm.,  the  distance  being,  as  a  rule,  somewhat  less  in  females  than  in  males.     Occasionally  the 
lower  pole  may  even  extend  below  the  iliac  crest,  especially  on  the  right  side. 

The  lateral  border  of  each  kidney  lies  8.5-10.0  cm.  lateral  to  the  spines  of  the  lumbar 
vertebrae,  a  distance  that  brings  them  lateral  to  the  lateral  edge  of  the  sacro-spinahs  muscle 
and  even  to  the  lateral  edge  of  the  quadratus  lumborum,  so  that  this  border  may  be  readily 
approached  through  the  posterior  wall  of  the  body.  It  must  be  remembered,  however,  that 
the  upper  part  of  the  kidney  rests  upon  the  diaphragm,  so  that  in  the  event  of  the  twelfth  rib 
being  very  short  there  may  be  danger  of  the  incision  being  carried  too  far  upward,  resulting  in 
injury  to  the  diaphragm  and  pleura.     It  is  also  worthy  of  note  that  the  diaphragmatic. area  of 


1246 


UROGENITAL  SYSTEM 


the  kidney  corresponds  with  the  region  where  a  hiatus  diaphragmaticus  between  the  costal  and 
lumbar  portions  of  the  muscle  may  occur  and  if  this  be  pronounced  the  upper  part  of  the  pos- 
terior surface  of  the  kidney  may  come  into  more  or  less  direct  relations  to  the  pleura  (fig.  1008). 

Just  as  there  may  be  variation  in  the  position  of  the  kidneys,  so  too  there  may  be  con- 
siderable variation  in  the  extent  to  which  they  are  in  relation  to  the  various  structures  men- 
tioned above.  And  this  is  especially  true  as  regards  their  relations  to  the  colons;  for  if  the 
kidneys  were  lower  than  usual  they  might  lie  entirely  beneath  the  line  of  attachment  of  the 
transverse  mesocolon  and  thus  have  no  direct  relations  with  either  colon,  or  on  the  other  hand 
either  the  ascending  or  descending  colon,  or  both,  may  be  provided  with  a  mesentery,  whereby 
they  would  be  removed  from  direct  contact  with  the  kidney. 

Structure. — A  section  through  the  kidney  shows  its  substance  to  be  composed  of  an  ex- 
ternal or  cortical  [substantia  corticalis]  and  an  internal  or  medullary  portion  [substantia 
medullaris]  (fig.  1010).  The  medulla  consists  of  a  variable  number  (eight  to  eighteen)  of 
conical  segments  termed  renal  pyramids  [pyramides  renales  (Malpighii)],  the  apices  of  which 
project  into  the  bottom  of  the  sinus  (fig.  1006)  and  are  received  into  the  primary  segments 
(calyces)  of  the  pelvis,  while  their  bases  are  turned  toward  the  surface,  but  are  separated  from 
it  and  from  each  other  by  the  cortex.  The  pyramids  are  smooth  and  somewhat  glistening  in 
section  and  are  marked  with  delicate  striae  which  converge  from  the  base  to  the  apex  and  in- 
dicate the  course  of  the  renal  tubules.  The  blunted  apex,  or  papilla,  of  each  pyramid,  either 
singly  or  blended  with  one  or  even  two  of  its  fellows,  is  embraced  by  a  calyx  (fig.  1006),  and,  if 
examined  with  a  hand-lens,  will  be  seen  to  present  a  variable  number  (twelve  to  eighty)  of 
minute  apertures,  the  foramina  papillaria,  which  represent  the  terminations  of  as  many 
papillary  ducts  (of  Bellini)  through  which  the  secretion  escapes  into  the  pelvis. 

Fig.  1010. — Hohizontal  Section  of  Kidney  showing  the  Sinus. 


Pyramid  of 

Malpighi 

Column  of  Bertin 


Interlobar 

artery 


Artery 


Cortex  with  pyramids 


Branch  of  artery  Irregular  branch  of  artery 

Ureter     Portion  of 

fatty  capsule 

The  cortex  may  be  regarded  as  composed  of  two  portions,  (1)  a  peripheral  layer,  the  cor- 
tex proper,  which  is  about  12  mm.  in  thickness  and  extends  from  the  fibrous  capsule  to 
the  bases  of  the  pyramids,  and  (2)  processes  termed  renal  columns  [columnse  renales  (Bertini)] 
which  dip  inward  between  the  pyramids  to  reach  the  bottom  of  the  sinus  (fig.  1010).  In 
section  the  cortex  is  somewhat  granular  in  aspect,  and  when  examined  closely  shows  a  differen- 
tiation into  a  number  of  imperfectly  separated  portions  termed  cortical  lobules  [lobuli  oorticales]. 
Each  of  these  is  composed  of  a  convoluted  portion  [pars  convoluta],  surrounding  an  axial  radiate 
portion  (pyramid  of  Ferrein)  [pars  radiata  (processus  Ferreini)].  The  latter  consists  of  a  group 
of  tubules  which  extend  from  the  cortex  into  the  base  of  one  of  the  medullary  pyramids,  whence 
it  is  also  termed  a  medullary  ray;  and  each  medullary  pyramid  is  formed  from  the  rays  of  a 
number  of  cortical  lobules,  these  structures,  therefore,  greatly  exceeding  the  pyramids  in 
number. 

Renal  tubules  (fig.  1011). — The  structure  described  above  is  the  result  of  the  arrange- 
ment of  the  renal  tubules,  which  constitute  the  essential  units  of  the  kidney.  Each  of  these  com- 
mences in  a  spherical  glomerular  capsule  (fig.  1011),  one  wall  of  which  is  invaginated  by  a  small 
glomerulus  of  blood-vessels,  the  combination  of  glomerulus  and  capsule  forming  what  is  termed 
a  renal  (Malpighian)  corpuscle.  These  corpuscles  are  situated  in  the  convoluted  portions  of 
the  cortical  lobules,  and  from  each  of  them  there  arises  by  a  narrow  neck  a  tubule,  which  quickly 
becomes  wide  and  convoluted,  this  fiortion  being  termed  the  first  convoluted  tubule.  This 
enters  a  medullary  ray,  where  it  narrows  again  and  descends  as  a  straight  tubule,  the  de- 
scending limb  of  Henle's  loop,  into  the  subjacent  medullary  pyramid,  and,  turning  upon  itself, 
forming  the  loop  of  Henle,  ascends  to  the  cortex,  where  it  again  becomes  wide  and  contorted, 
forming  the  second  convoluted  tubule.  This  again  lies  in  the  convoluted  portion  of  the  cortical 
lobule,  and,  becoming  narrower,  opens  with  other  similar  tubules  into  a  straight  or  collecting 


THE  URETERS 


1247 


tubule,  which  occupies  the  axis  of  the  medullary  ray.  Then,  descending  into  the  subjacent 
medullary  pyramid,  it  unites  with  other  collecting  tubules,  and  finally  opens  into  the  renal  pelvis 
at  the  summit  of  a  papilla. 

The  tubules  are  hned  with  epithelium  throughout,  the  cells  being  tesselated  in  the  capsule, 
irregularly  cubical  in  the  convoluted  tubules  and  ascending  limbs,  flattened  on  the  descending 
limbs  and  loops  of  Henle,  and  columnar  in  the  cortical  collecting  tubules  and  in  the  straight 
tubules  of  the  medulla. 

Vessels  (fig.  1011). — The  kidney  is  very  vascular.  The  larger  arterial  branches,  arranged 
in  the  sinus  as  has  already  been  described,  enter  the  substance  of  the  kidney  and  pass  up  as  the 
interlobar  arteries  in  the  renal  columns.  On  reaching  the  bases  of  the  pyramids  they  bend  so  as 
to  run  horizontaUy  between  these  and  the  cortex,  forming  the  arcuate  arteries  [arterife  arciformes] 
from  which  interlobular  branches  pass  up  into  the  cortex  and  supply  afferent  branches  to  the 
Malpighian  glomeruh.     From  the  arcuate  arteries  numerous  branches,  the  arterioloe  rectces, 

Fig.  1011. — Scheme  of  Tubules  and  Vessels  op  the  Kidney. 


Renal  corpuscle 


Cortical  vein 
Arcuate  artery 

Medullary  artery 


Efferent  vessel 

forming  medullary 

plexus 


Papillary  pli 
surrounding  th 
foramina  papill; 


Renal  corpuscle 


Duct  of  Bellini  open- 
ing atthefora- 
papillare 


pass  down  into  the  pyramids,  supplying  the  tubules  of  which  these  are  composed.  Efferent 
stems  which  issue  from  the  Malpighian  glomeruli  break  up  into  capillaries  which  supply  the 
tubules  contained  in  the  cortex.  Veins  corresponding  to  the  arteriolse  rectce  and  to  the  inter- 
lobular, arcuate  and  interlobar  arteries  occur,  opening  into  the  renal  veins,  and,  at  the  surface 
of  the  kidney,  arranged  in  star-like  groups,  are  the  stellate  veins  [vense  steUatae],  which  open 
into  the  interlobular  veins  and  also  communicate  with  the  veins  of  the  adipose  capsule.  The 
renal  lymphatics  may  be  divided  into  two  sets,  capsular  and  parenchymatous.  They  terminate 
in  the  upper  lumbar  nodes. 

Nerves. — The  nerves  form  a  plexus  accompanying  the  vessels,  and  are  derived  from  the 
sympathetic  and  vagus  through  the  renal  plexuses. 

Variations. — The  kidney  of  a  foetus  differs  from  that  of  the  adult  in  being  divided  into  a 
number  of  distinct  renal  lobes,  each  of  which  corresponds  to  the  base  of  a  renal  pyramid  and 


1248  UROGENITAL  SYSTEM 

is  capped  by  a  thin  layer  of  cortex.  Such  a  condition  is  permanent  in  some  of  the  lower  animals; 
but  in  man  the  superficial  indications  of  morphological  segmentation  usually  become  obliterated 
during  the  progress  of  growth  of  the  cortical  tissue,  and  are  seldom  visible  after  the  age  of  ten. 

Development. — In  the  development  of  the  embryo,  representatives  of  three  different  sets 
of  excretory  organs  occur,  the  permanent  kidney  (metanephros)  being  the  last  to  form.  The 
two  earlier  sets  (pronephros  and  mesonephros)  have  a  common  duct,  the  Wolffian  duct,  and 
from  the  lower  end  of  this  an  outgrowth  develops,  which  extends  upward  on  the  posterior 
abdominal  wall  and  comes  into  connection  with  a  mass  of  embryonic  tissue  known  as  the 
metanephric  blastema.  The  outgrowth  gives  rise  to  the  ureter,  pelvis  and  collecting  tubules, 
while  the  remaining  portions  of  the  tubules  are  formed  from  the  blastema. 

Various  abnormalities  may  result  from  modifications  of  the  development  of  the  kidneys. 
(1)  Occasionally  the  ureteric  outgrowth  of  one  side  fails  to  develop,  the  result  being  the  occur- 
rence of  a  single  kidney.  (2)  The  blastema  may  fail  to  attain  its  normal  position,  in  which 
case  the  kidney  may  be  situated  in  the  iliac  region  or  even  in  the  pelvis;  or  the  blastema  may  be 
drawn  into  an  unusual  position,  the  kidney  resting  on  the  vertebral  column,  or  even  on  the 
opposite  side  of  the  abdomen;  (3)  or  the  two  blastemas  may  fuse  to  a  greater  or  less  extent, 
forming  a  "horse-shoe  kidney,"  extending  across  the  vertebral  column;  or,  if  the  fusion  be  more 
extensive,  an  apparently  single  kidney,  which  may  rest  upon  the  vertebral  column,  or  to  one 
side  of  it.  Such  fused  kidneys  may  be  distinguished  from  single  kidneys  by  the  fact  that  they 
possess  two  ureters  opening  normally  into  the  bladder.  (4)  In  rare  cases,  a  blastema  may  be- 
come divided,  an  accessory  kidney  of  varying  size  being  thus  produced.  (5)  Finally,  in  one  or 
more  of  the  tubules  there  may  be  a  failure  of  the  union  of  the  portion  derived  from  the  blas- 
tema with  the  collecting  tubule  derived  from  the  ureteric  upgrowth,  and  the  secretion  having 
no  means  of  escape  from  such  malformed  tubules,  they  become  greatly  dilated,  producing  a 
cystic  kidney. 

THE  URETERS 

The  ureter  (figs.  1004,  1007,  1012,  1015),  which  serves  as  the  excretory  duct 
of  the  kidney,  is  a  canal,  expanded  and  irregularly  branched  above,  but  narrow 
and  of  fairly  uniform  dimensions  throughout  the  rest  of  its  course.  At  its  origin 
in  the  renal  sinus  it  consists  of  a  number  of  short  tubes,  usually  eight  or  nine,  called 
calyces  minores  (fig.  1012),  each  of  which  embraces  a  renal  papilla,  or  occasionally 
two  papillae  may  be  connected  with  a  single  calyx.  These  calyces  minores  open 
directly  or  by  means  of  short  intermediate  tubes  (infundibula)  into  two  short 
passages,  the  superior  and  inferior  calyces  majores,  which  in  turn  unite  after  a 
longer  or  shorter  course  to  form  the  pelvis.  Occasionally  a  third  or  middle  calyx 
major  is  present. 

The  pelvis  [pelvis  renalis]  (fig.  1012)  is  usually  more  or  less  funnel-shaped, 
being  wider  above,  where  it  lies  between  the  two  lips  of  the  hilus,  and  narrower 
below,  where  it  arches  downward  and  medially  to  become  continuous  with  the 
ureter  proper.  It  is,  however,  very  variable  in  shape  and  in  some  cases  is  hardly 
larger  than  the  ureter.  Usually  it  is  flattened  dorso-ventrally  so  that  its  anterior 
and  posterior  walls  are  in  contact  and  its  cavity  represented  merely  by  a  fissure. 
The  majority  of  the  branches  of  the  renal  vein  and  artery  lie  in  front  of  it,  im- 
bedded in  fat  tissue,  and  anterior  to  these  are  the  descending  portion  of  the  duo- 
denum on  the  right  side  and  the  pancreas  on  the  left.  The  intra-renal  portions  of 
the  ducts,  including  the  pelvis,  are  considered  parts  of  the  kidney. 

The  ureter  proper  (fig.  1007)  extends  from  the  termination  of  the  pelvis  to  the 
bladder,  its  course  lying  in  the  subperitoneal  tissue.  It  is  a  tube  about  5  mm.  in 
diameter  when  distended  and  it  is  fairly  uniform  in  size,  except  that  a  slight  con- 
striction occurs  where  it  enters  the  pelvis  and  a  second  one  occurs  at  about  the 
middle  of  its  abdominal  portion.  Its  length  is  variously  stated,  but  the  average 
in  the  male  adult  may  be  taken  as  about  30  cm.,  the  right  being  usually  a  little 
the  shorter. 

Course  and  relations. — The  course  of  each  ureter  may  be  conveniently  divided 
into  three  portions,  abdominal,  pelvic,  and  vesical.  The  abdominal  portion 
[pars  abdominalis]  runs  downward  and  shghtly  medially  and  is  in  relation  pos- 
teriorly with  the  psoas  muscle  and  its  fascia;  it  crosses  the  genito-femoral  nerve 
obhquely  and  in  the  lower  part  of  its  course  passes  in  front  of  the  common  iliac 
artery  near  its  bifurcation.  Anteriorly  it  is  covered  by  peritoneum  and  is  crossed 
by  the  spermatic  or  ovarian  vessels.  Medially  it  is  in  relation  on  the  right  side 
with  the  inferior  vena  cava  and  on  the  left  with  the  aorta,  the  vein  being  almost 
in  contact  with  the  right  ureter,  while  the  artery  is  separated  from  the  left  one 
by  an  interval  that  diminishes  from  2.5  cm.  above,  to  1.5  cm.  opposite  the 
bifurcation  of  the  vessel. 

The  pelvic  portion  [pars  pelvina]  passes  in  front  of  the  sacro-ihac  articulation 


THE  URINARY  BLADDER  1249 

and  then  forward  and  downward  upon  the  obturator  internus  and  its  fascia 
behind  and  below  the  psoas,  crossing  the  obturator  vessels  and  nerve  and  having 
anterior  to  it  in  the  female  the  posterior  border  of  the  ovary.  It  thus  reaches  the 
level  of  the  floor  of  the  peritoneal  cavity,  whereupon,  at  about  the  level  of  the 
ischial  spine,  its  course  is  directed  forward  and  medially  toward  the  bladder. 
In  this  part  of  its  course  in  the  m.ale,  it  is  crossed  superiorly  and  medially  by  the 
ductus  deferens,  and  then  passes  under  cover  of  the  free  extremity  of  the  vesicula 
seminalis,  separated  from  its  fellow  by  a  distance  of  37  mm.  In  the  female  it 
runs  parallel  with,  and  8  to  12  mm.  distant  from,  the  cervix  uteri,  passes  behind 
the  uterine  artery,  through  the  uterine  plexus  of  veins,  and  beneath  the  root  of 
the  broad  ligament,  and  finally  crosses  the  upper  third  of  the  lateral  wall  of  the 
vagina  to  reach  the  vesico-vaginal  interspace  and  enter  the  substance  of  the 
bladder  at  about  the  junction  of  its  posterior,  superior  and  lateral  surfaces. 

The  vesical  portion,  about  12  mm.  in  length,  runs  obliquely  downward  and 
medialward  through  the  coats  of  the  bladder,  and  opens  on  its  mucous  surface 
about  20  to  25  mm.  from  both  its  fellow  and  the  internal  urethral  orifice. 

Structure. — The  wall  of  the  ureter  is  about  1  mm.  (jV  in.)  in  thickness,  and  consists  of  a 
mucous  membrane,  a  muscular  coat,  and  an  external  connective-tissue  investment.  The  mucous 
membrane  is  longitudinally  plicated,  and  is  lined  by  transitional  epithelium,  continuous  with 
that  of  the  papillse  above  and  with  that  of  the  bladder  below.  Mucous  follicles  of  simple  form 
have  been  found  in  the  upper  part  of  the  canal.  The  muscularis  is  about  0.5  mm.  (1/50  in.)  in 
thickness,  and  consists  of  two  layers,  an  external,  composed  of  annular  fibres,  and  an  internal, 

Fig.  1012. — Pelvis  and  Upper  Portion  op  Ureter.     (After  Henle.) 


Calyx  minor 


Infundibulum 


Superior  calyx  nxajor 


Inferior  calyx  major 


of  fibres  longitudinally  disposed.  After  the  tube  has  entered  the  bladder  the  circular  fibres  form 
a  kind  of  sphincter  around  its  vesical  orifice;  while  the  longitudinal  fibres  are  continued  onward 
through  the  wall  of  the  bladder  and  terminate  beneath  its  mucous  membrane. 

Vessels  and  nerves. — The  arteries  supplying  the  pelvis  and  upper  part  of  the  ureter  come 
from  the  renal;  the  rest  of  the  abdominal  portion  of  the  ureter  is  supplied  by  the  spermatic 
(or  ovarian),  and  its  pelvic  portion  receives  branches  from  the  middle  haemorrhoidal  and  in- 
ferior vesical;  the  veins  terminate  in  the  corresponding  trunks;  and  the  lymphatics  pass  to  the 
lumbar  and  hypogastric  nodes.  The  nerves  are  supplied  by  the  spermatic,  renal,  and  hypo- 
gastric plexuses. 

Variations. — Occasionally  the  depression  which  separates  the  two  calyces  majores  extends 
through  the  pelvis,  so  that  the  calyces  appear  to  open  directly  into  the  ureter.  The  fission  may 
also  affect  the  ureter  to  a  greater  or  less  extent,  in  extreme  cases  producing  a  duplication  of 
the  tube  throughout  its  entire  length. 

THE  URINARY  BLADDER 

The  urinary  bladder  [vesica  urinaria]  is  a  receptacle,  whose  form,  size,  and 
position  vary  with  the  amount  of  its  contents.  The  adult  organ  in  its  empty  or 
moderately  filled  condition  Hes  entirely  below  the  level  of  the  obhque  plane  of 
the  pelvic  inlet;  but  when  considerably  distended  it  rises  into  the  abdomen  and 
shows  itself  beneath  the  parietes  as  a  characteristic  mesial  projection  above  the 
symphysis,  a  projection  which  in  extreme  distention  of  the  bladder  may  extend 
nearly  to  the  level  of  the  umbilicus. 


1250 


UROGENITAL  SYSTEM 


Form. — When  distended  it  assumes  in  the  male  an  ovoid  shape  with  its 
longest  diameter  directed  from  above  downward  and  backward;  but  in  the  female 
the  transverse  diameter  is  the  greatest,  in  accordance  with  the  greater  breadth 
of  the  pelvic  cavity.  In  the  child  it  is  somewhat  pear-shaped,  the  stalk  being 
represented  by  the  urachus. 

Parts. — ^For  convenience  in  description  five  surfaces  may  be  recognized,  but 
they  are  but  indistinctly  separated  from  each  other.  One,  the  anterior  or  pubic 
surface,  is  directed  forward  and  downward;  second,  the  superior  or  intestinal 
surface,  looks  upward;  the  third,  the  posterior  surface,  looks  backward;  and  the 
other  two  are  the  lateral  surfaces.  The  anterior,  superior,  and  lateral  surfaces 
meet  at  the  vertex  of  the  bladder,  from  which  the  middle  umbilical  ligament 
(urachus)  extends  to  the  umbilicus;  the  posterior  surface,  sometimes  flat  and  some- 
times, especially  in  old  age,  convex,  forms  what  is  known  as  the  base  or  fundus 
[fundus  vesicae] ;  and  the  portion  of  the  viscus  intervening  between  the  vertex  and 

Fig    1013  — Median  Sagittal  Section  op  the  Male  Pelvis 
(From  a  prepaiation  in  the  Museum  of  St  Thomas's  Hospital ) 


Small 
intes- 
tine 


fundus  is  termed  the  body  [corpus  vesicae].  In  the  centre  of  the  line  between 
the  anterior  and  posterior  surfaces  is  the  internal  urethral  orifice  [orificium  urethrae 
internum],  by  which  the  bladder  communicates  with  the  urethra,  and  the  portion 
of  the  organ  immediately  surrounding  this  is  sometimes  spoken  of  as  the  neck. 

When  the  bladder  is  empty  and  relaxed,  the  superior  surface  sinks  down  upon 
the  anterior  and  posterior  surfaces,  thus  becoming  concave,  and  the  cavity  of  the 
organ  is  reduced  to  a  T-  or  Y-shaped  fissure.  In  the  female,  the  cavity  of  the 
empty  bladder  in  mid-sagittal  section  often  more  nearly  resembles  a  figure  7  (see 
fig.  1014). 

Relations. — The  anterior  surface  looks  downward  and  forward  toward  the 
symphysis  pubis  (figs.  1013,  1014).  It  is  uncovered  by  peritoneum,  but  is  sepa- 
rated from  the  pubic  bones  and  anterior  attachments  of  the  obturatores  interni 
and  the  levatores  ani  by  a  space  known  as  the  prevesical  space  (cavum  Retzii), 


THE  URINARY  BLADDER 


1251 


which  contains  a  variable  quantity  of  loose  fat  continuous  with  the  pelvic  and 
abdominal  subperitoneal  tissue.  Each  lateral  surface  is  covered  by  peritoneum 
down  to  the  level  at  which  it  is  crossed  obliquely  from  behind  forward  and  upward 
by  the  obUterated  hypogastric  artery.  Below  this  level  it  is  separated  from  the 
levator  ani  and  obturator  internus  by  subperitoneal  tissue,  which  usually  bears 
much  fat  in  its  meshes  and  ensheaths  the  vesical  vessels  and  nerves.  It  is  also 
crossed  by  the  ductus  deferens,  which  passes  between  the  ureter  and  the  wall 
of  the  bladder,  a  little  above  the  level  at  which  the  former  enters  the  wall  of  the 
bladder,  at  the  junction  of  its  lateral  and  posterior  surfaces  and  about  3.5'^cm. 
above  the  fundus.  The  posterior  surface  may  be  divided  into  two  portions, 
an  upper  covered  by  the  peritoneum  of  the  recto-vesical  or  vesico-uterine  pouch 
(fig.  1013),  and  a  lower  in  direct  contact  in  the  male  with  the  anterior  wall  of  the 

Fig.  1014. — Mid-sagittal  Section  of  the  Female  Pelvis.     (Spalteholz.) 

Hypogastric  artery 
^t  Hypogastric  vein 
Promontory      /      /  Infundibulum  of  tuba  uterina 


Suspensory  ligament  of  ovary 


External  ihac  vein 
Ovary 


Ampulla  of  tuba  utenua 

Ovarian  ligament 

Fundus  uteri 

\ 


,  Parietal  peritoneum 

Uterus 
k.  /     Interna!  orifice  of 
V    /  uterus 

\/   y Recto  uterine  fold 

X     ,  Recto  uterine 
\  /        muscle 


Ligamentum  teres 
Transverse  fold  of 
bladder 
Vertex  of  bladder  .      ^\ 
Middle  umbilical      \ 
ligament 


Urach 

Symphysis  pub 

Labium  majus 
Body  of  uterus 
Labium  minus 

External  orifice  of  urethra 

Urethra      /'    / 
Internal  orifice  of  urethra      / 
Orifice  of  vagina 


Coccyx 

Recto  coccy- 
\        geus  muscle 

Rectum 
Posterior  labium 
External  orifice  of  uterus 
Anterior  labium 


Vagina 
a.yuiKu.  Vesico-uterine  pouch 

Vestibule 

rectum  and  with  the  lower  part  of  the  ductus  deferentes  and  the  vesiculse  semin- 
ales.  Between  the  diverging  ductus  deferentes  there  is  a  triangular  space,  whose 
base  is  formed  by  the  line  of  reflexion  of  the  recto-vesical  pouch  of  peritoneum 
and  the  apex  by  the  meeting  of  the  ejaculatory  ducts  at  the  summit  of  the  prostate. 
It  represents  the  area  of  direct  contact  of  the  posterior  wall  of  the  bladder  withjthe 
rectum.  In  the  female  the  posterior  surface  is  adherent  in  its  lower  part  to  the 
cervix  of  the  uterus  and  the  upper  part  of  the  anterior  wall  of  the  vagina  (fig.  1014), 
but  it  is  separated  above  from  the  body  of  the  uterus  by  the  shallow  vesico- 
uterine pouch  of  peritoneum. 

The  superior  surface   is  entirely  covered   by  peritoneum.     It   looks  almost 


1252 


UROGENITAL  SYSTEM 


directly  upward  into  the  abdominal  cavity  and  has  resting  upon  it  coils  of  the 
small  intestines  and  sometimes  a  portion  of  the  sigmoid  colon  behind  these. 

Variation  in  position. — In  the  normal  condition  the  bladder  of  the  adult  lies  below  the  upper 
border  of  the  symphysis  pubis,  but  if  fully  distended  it  may  rise  above  this  level,  carrying 
with  it  the  reflexion  of  peritoneum  from  its  upper  surface  to  the  anterior  abdominal  wall. 
The  anterior  surface  of  the  bladder  is  thus  brought  into  relation  with  the  anterior  abdominal 
wall,  being  separated  from  it  only  by  the  enlarged  prevesical  space,  and  it  is  thus  possible  to 
enter  the  bladder  above  the  symphysis  pubis  without  penetrating  the  peritoneum. 

In  the  infant,  owing  to  the  smaller  extent  of  the  pelvic  cavity,  the  bladder  hes  at  a  some- 
what higher  level  than  in  the  adult  and  rises  into  the  abdominal  cavity.  Indeed  the  entire 
bladder  is  above  the  horizontal  level  of  the  pubic  crests,  the  urethral  orifice  being  behind  the 
upper  margin  of  the  symphysis  pubis.  As  the  child  learns  to  walk,  however,  this  position 
gradually  alters  and  usually  by  the  age  of  six  years  the  adult  relations  have  been  acquired. 

The  fixation  of  the  bladder. — The  reflections  of  the  peritoneum  from  the 
superior  surface  of  the  bladder  to  the  anterior  abdominal  wall  and  from  the  sides 
and  back  to  the  corresponding  walls  of  the  pelvis  are  sometimes  described  as  the 
superior,  lateral  and  posterior  false  ligaments.  Furthermore  there  extends  from 
the  apex  of  the  bladder  to  the  umbilicus  a  fibrous  cord,  the  urachus,  the  remains 
of  the  embryonic  allantois;  this  is  described  as  the  middle  umbilical  ligament  of 
the  bladder  (fig.  1014),  and  lateral  umbilical  ligaments  are  formed  by  the  obliter- 
ated hypogastric  arteries  which  carried  the  foetal  blood  to  the  placenta  and  in  the 

Fig.  1015. — The  Posterior  Wall  of  the  Bladder.     (After  Henle.) 


Ductus  deferens 


Plica  ureterica 
Vesical  aperture 


Colliculus  seminalis- 
Opening  of  ejaculatory  duct 
Prostatic  utriculu 
Prostatic 


adult  are  represented  by  fibrous  cords  passing  over  the  sides  of  the  bladder  and 
ascending  to  the  umbilicus. 

In  addition  to  these  structures  certain  thickenings  of  the  endopelvic  fascia, 
where  it  comes  into  relation  with  the  base  of  the  bladder  and  prostate  gland, 
constitute  what  are  termed  the  true  ligaments.  Two  such  thickenings  extend 
from  the  anterior  surface  of  the  capsule  of  the  prostate  gland,  or  from  the  lower 
part  of  the  anterior  surface  of  the  bladder  in  the  female,  to  the  pubic  bones  and 
constitute  what  are  known  as  the  middle  pubo-prostatic  {pubo-vesical)  ligaments, 
with  which  muscle  fibres  [m.  pubovesicahs]  are  usually  associated.  Similarly, 
thickenings  of  the  fascia  extending  from  the  sides  of  the  prostate  gland  or  from  the 
sides  of  the  base  of  the  bladder  to  the  lateral  walls  of  the  pelvis  form  the  lateral 
true  ligaments. 

Muscle  fibres  [m.  rectovesicahs]  also  occur  in  the  subperitoneal  tissue  contained  within 
the  peritoneal  folds  (posterior  false  ligaments)  extending  from  the  back  of  the  bladder  to  the 
posterior  wall  of  the  pelvis  and  bounding  the  recto-vesical  pouch  of  peritoneum  in  the  male. 
They  correspond  to  the  mm.  redouterini  of  the  female. 

The  internal  surface. — The  mucous  membrane  lining  the  internal  surface  of 
the  bladder  is  soft  and  rose-coloured  during  life,  and  in  the  empty  bladder  is 
thrown  into  irregular  folds  which  become  effaced  by  distention.  It  is  modified 
over  a  triangular  area  at  the  base  of  the  bladder,  termed  the  trigone  [trigonum 
vesicae  (Lieutaudi)]  (fig.  1015)  whose  three  angles  correspond  with  the  orifices 
of  the  urethra  and  of  the  two  ureters,  and  are  separated  from  one  another  by  a 


MALE  REPRODUCTIVE  ORGANS  1253 

distance  of  20  to  25  mm.  This  area  is  paler  in  colour  and  free  from  the  plication 
that  characterizes  the  rest  of  the  mucous  membrane;  it  is  bounded  posteriorly 
by  a  transv.erse  ridge,  the  plica  ureterica,  extending  between  the  orifices  of  the 
ureters,  and  toward  the  urethral  orifice  presents  a  median  longitudinal  elevation, 
the  uvula  vesicae,  which  is  apt  to  be  especially  prominent  in  aged  persons.  The 
internal  urethral  orifice  is  normally  situated  at  the  lowest  point  of  the  bladder,  at 
the  junction  of  the  anterior  and  posterior  surfaces.  It  is  surrounded  by  a  more 
or  less  distinct  circular  elevation,  the  urethral  annulus,  and  is  usually  on  a  level 
with  about  the  center  of  the  symphysis  pubis  and  from  2.0  to  2.5  cm.  behind  it. 

Structure. — The  general  characteristics  of  the  mucous  membrane  of  the  bladder,  which  is 
lined  by  epithelium  of  the  transitional  variety,  have  already  been  described.  It  rests  upon  a 
loose  submucous  tissue,  which  contains  numerous  elastic  fibres.  The  greater  part  of  the  thick- 
ness of  the  waU  is  formed,  however,  of  the  muscular  coal,  consisting  of  non-striped  muscle 
tissue,  the  fibres  of  which  are  arranged  in  three  more  or  less  distinct  layers.  The  outer  layer 
is  composed  mainly  of  longitudinal  fibres,  some  of  which  are  continued  forward  to  the  pubis 
from  the  neck  of  the  bladder  to  form  the  mm.  pubovesioales  and  others  backward  to  form  the 
mm.  rectovesicales.  To  this  outer  layer  the  term  m.  detrusor  uriruB  has  been  applied,  but  it 
should  be  noted  that  it  does  not  contract  independently  of  the  circular  layer.  The  middle 
ayer  is  thicker  than  the  outer  and  more  uniformly  developed.  It  consists  of  fibres  having 
for  the  most  part  a  circular  direction  and  is  well  developed  over  all  the  upper  portion  of  the 
bladder,  but  becomes  thinner  in  the  region  corresponding  to  the  trigone.  It  is  here  that  the 
inner  layer  is  chiefly  developed,  consisting  of  fibres,  which  are  situated  partly  in  the  submucous 
tissue  and  have  a  general  longitudinal  direction  throughout  the  region  of  the  trigone.  At 
the  neck  of  the  bladder,  however,  they  form  a  strong  circular  bundle,  which  is  continued  into 
the  prostatic  portion  of  the  urethra  and  forms  what  is  termed  the  internal  sphincter  of  the  bladder. 

Vessels. — The  arteries  of  the  bladder  are  usually  two  in  number,  the  superior  and  inferior 
vesical,  branches  of  the  hypogastric  artery;  the  fundus  also  receives  branches  from  the  middle 
hsemorrhoidal  and  in  the  female  twigs  are  also  sent  to  it  from  the  uterine  and  vaginal  arteries. 
The  veins  form  an  extensive  plexus  at  the  sides  of  the  bladder,  from  which  stems  pass  to  the 
hypogastric  trunk.  The  lymphatics  accompany  the  veins  and  communicate  with  the  hypo- 
gastric nodes,  some  of  those  from  the  fundus  passing  to  nodes  situated  at  the  promontory  of 
the  sacrum. 

Nerves. — -The  nerves  are  derived  partly  from  the  hypogastric  sympathetic  plexus  and  partly 
from  the  second  and  third  sacral  nerves.  The  fibres  from  the  latter  constitute  the  nervi 
erigentes,  stimulation  of  which  produces  contraction  of  the  general  musculature  and  rela.xation 
of  the  internal  sphincter.  On  each  side  of  the  bladder  there  is  formed  a  sympathetic  vesical 
plexus,  from  which  superior  and  inferior  vesical  nerves  pass  to  the  corresponding  parts  of  the 
bladder. 

Development. — In  the  earlier  stages  of  development  the  urogenital  ducts  and  the  digestive 
tract  open  below  into  a  common  cavity,  the  cloaca,  from  the  ventral  portion  of  which  a  long 
tubular  outgrowth,  the  allantois,  extends  out  to  the  placenta  through  the  umbilical  cord. 
Later  the  cloaca  becomes  divided  in  the  frontal  plane  into  a  ventral  portion  which  receives  the 
urogenital  ducts,  and  a  dorsal  portion,  which  becomes  the  lower  end  of  the  rectum.  From 
the  upper  part  of  the  ventral  portion  the  bladder  is  developed.  Since  the  cloaca  is  fined  by 
endoderm  the  mucous  membrane  of  the  bladder  is  mainly  derived  from  that  embryonic  layer, 
but  it  is  worthy  of  note  that  portions  of  the  lower  ends  of  the  ureters  are  taken  up  into  the  wall 
of  the  bladder,  giving  rise  to  the  area  of  the  trigone,  whose  mucous  membrane  is  thus  of  meso- 
dermal origin.  The  portion  of  the  allantois  within  the  body  of  the  foetus  is  transformed  after 
birth  into  a  fibrous  cord,  the  urachus. 

The  urethra  will  be  considered  later  in  connection  with  the  reproductive 
organs. 

B.  THE  REPRODUCTIVE  ORGANS 

The  reproductive  organs  include  those  of  the  male  [organa  genitalia  viriHa] 
and  those  of  the  female  [organa  genitalia  muliebria]. 

THE  MALE  REPRODUCTIVE  ORGANS 

The  reproductive  organs  of  the  male  consist  of  (1)  two  testes  in  which  the 
spermatozoa  are  formed,  (2)  their  ducts,  the  ductus  def erentes ;  enclosed  through- 
out a  portion  of  their  course  in  the  spermatic  cord;  and  the  seminal  vesicles, 
reservoirs  for  the  semen,  connected  with  the  ductus  def  erentes;  (3)  the  penis, 
the  organ  of  copulation,  which  is  traversed  by  the  urethra;  (4)  the  urethra,  a 
canal  into  which  the  ductus  deferentes  open  and  which  also  gives  exit  to  the 
contents  of  the  bladder;  (5)  the  prostate  gland,  a  musculoglandular  structure 
surrounding  the  beginning  of  the  urethra;  (6)  the  bulbo-urethral  glands  which 
open  into  the  urethra. 


{ 


1254 


UROGENITAL  SYSTEM 


1.  The  Testes  and  Their  Appendages 

The  scrotum. — The  two  testes,  together  with  the  beginning  of  the  ductus 
deferentes,  are  contained  within  a  pouch,  the  scrotum,  which  is  divided  into  two 
compartments  by  a  median  sagittal  septum,  the  edge  of  which  is  indicated  on  the 
surface  by  a  ridge-hke  thickening  of  the  integument,  termed  the  raphe. 

This  double  condition  of  the  scrotum  is  explained  by  its  origin  from  the  fusion  of  two  out- 
pouchings  of  the  lower  portion  of  the  abdominal  wall,  the  inguinal  canals  forming,  as  it  were, 
the  necks  of  the  outpouchings.  The  testes  are  primarily  retroperitoneal  abdominal  organs, 
but  later  they  descend  through  the  inguinal  canals  into  the  scrotal  outpouchings,  where  they 
lie  between  the  peritoneal  sac  which  each  of  these  contains  and  the  remaining  layers  of  the  wall, 
thus  retaining  their  retroperitoneal  position.  The  peritoneal  sacs  are  at  first  in  communication 
with  the  abdominal  cavity,  but  after  the  descent  of  the  testes  each  undergoes  degeneration  in 
its  upper  part,  the  cavity  disappearing  and  the  peritoneal  tissue  becoming  converted  into  a 
portion  of  the  connective  tissue  in  which  the  ductus  deferens  and  the  vessels  and  nerves  asso- 
ciated with  it  are  imbedded  in  their  course  through  the  spermatic  cord.  The  portion  of  the  sac 
in  relation  with  each  testis  persists,  however,  and  wrapping  itself  around  that  structure  forms 
for  it  a  serous  investment,  the  tunica  vaginalis  propria  (fig.  1016). 

The  integument  oi  the  scrotum  is  more  or  less  pigmented  and  presents  numerous 
transverse  ridges  extending  laterally  on  either  side  from  the  raphe.  It  is  furnished 
in  the  adult  with  coarse,  scattered  hairs  and  its  sebaceous  and  sudoriparous  glands 
are  well  developed.  The  deeper  layers  of  the  dermis,  have  a  pinkish  colour,  and 
form  what  is  termed  the  dartos  (fig.  1016),  the  colouration  being  due  to  the 

Fig.  1016. — Horizontal  Section  op  the  Sceotum  and  Testis.     (Diagrammatic.) 

Skin 
Dartos 

Cremasteric  fascia 
Cremaster  muscle 


Septum  scroti 


Mediastinum  testis 


Ductus  deferens 


Parietal  layer  of  tunica  vaginalis 

propria 
Tunica  vaginalis  communis 

Cavity  of  tunica  vaginalis 

Visceral  layer  of  tunica  vaginalis 

propria 
Tunica  albuginea 

Sinus  epididymidis 
Epididymis 


presence  in  it  of  numerous  non-striated  muscle  fibres,  which  are  for  the  most 
part  arranged  at  right  angles  to  the  wrinkles  of  the  surface  and  are  the  cause  of 
these.  The  more  superficial  fibres  of  the  dartos,  hke  the  rest  of  the  integument, 
form  a  common  investment  for  both  testes,  but  the  deeper  ones  of  either  side  bend 
inward  at  the  raphe  and  assist  in  the  formation  of  the  septum. 

Internal  to  the  dartos  and  closely  related  to  it  is  a  layer  of  laminated  con- 
nective tissue,  the  cremasteric  fascia.  It  is  destitute  of  fat  and  is  continuous  at 
the  subcutaneous  inguinal  ring  with  the  intercrural  fibres,  being  probably  the 
scrotal  representative  of  the  external  oblique  muscle.  It  is  succeeded  by  a 
strong  sheet  of  fascia  containing  longitudinal  bands  of  striated  muscle  tissue, 
forming  what  is  termed  the  cremaster  muscle  (figs.  389,  1016)  and  being  con- 
tinuous above  with  the  fibres  of  the  internal  oblique  muscle  of  the  abdomen. 
Internal  to  this  is  a  thin  layer  of  connective  tissue,  the  tunica  vaginalis  communis, 
which  is  continuous  with  the  transversalis  fascia  at  the  inguinal  ring,  and,  finally, 
there  is  the  tunica  vaginalis  propria,  which  forms  the  serous  investment  of  the 
testis  and,  as  has  been  stated,  is  of  peritoneal  origin.  Like  other  similar  serous 
investments  it  has  the  form  of  a  double  sac,  the  outer  or  parietal  layer  of  which  is 
closely  adherent  to  the  tunica  vaginahs  communis  and  contains  numerous  non- 
striped  muscle  fibres  forming  what  has  been  termed  the  internal  cremaster 
muscle.     The  inner  or  visceral  layer  is  thinner  and  closely  invests  the  testis  and  a 


THE  TESTIS  AND  EPIDIDYMIS 


1255 


portion  of  the  epididymis,  being  reflected  from  the  inferior  and  posterior  parts  of 
the  latter  to  be  continuous  with  the  parietal  layer.  Toward  the  upper  part  of  the 
lateral  surface  of  the  testis  it  is  folded  in  between  that  structure  and  the  epididy- 
mis, forming  a  well-marked  pocket,  the  sinus  eipididymidis  (digital  fossa)  (fig. 
1017),  whose  upper  and  lower  lips  form  what  are  termed  the  ligamentaepididymidis. 

Vessels  and  nerves. — The  skin  and  dartos  of  the  scrotum  are  supplied  partly  by  the  peri- 
neal branch  of  the  internal  pudendal  artery  and  partly  by  the  external  pudendal  branches  of 
the  femoral.  The  deeper  layers  are  supplied  by  the  spermatic  branch  of  the  inferior  epigastric. 
The  veins  accompany  the  arteries,  the  external  pudendals  opening  into  the  internal  saphenous 
vein  near  its  termination.  The  lymphatics  terminate  in  the  more  medial  inguinal  nodes. 
Several  nerves  take  part  in  the  supply  of  the  scrotum.  The  external  spermatic  branch  of  the 
genito-femoral  gives  sensory  branches  to  the  anterior  and  lateral  surfaces  and  also  supplies 
the  external  cremaster  muscle;  the  posterior  surface  is  supplied  by  the  periaeal  branch  of  the 
pudendal  nerve;  and  the  inferior  surface  by  the  perineal  branches  of  the  posterior  femoral 

Fig.  1017. — The  Left  Testis  with  Vessels  and  Duct.     (After  Sappey.) 


Internal  spermatic  artery' 


Internal  spermatic  veins- 


Branch  of  spermatic  artery 


Head  of  epididy 


Appendix  testi 


Lateral  wall  of  body  of  testi 


Ductus  deferens  with 
deferential  artery 


Vein 

Ductus  deferens 


Body  of  epididymis 
Sinus  epididymidis 

Vessels  of  epididymis 
Tail  of  epididymis 


cutaneous.  The  anterior  aspect  of  the  scrotum  is  also  supplied  by  anterior  scrotal  branches 
of  the  ilio-inguinal.  The  non-striped  musculature  is  probably  supplied  by  the  internal 
spermatic   nerve  from  the  hypogastric  plexus. 

Hernia. — The  communication  of  the  tunica  vaginaUs  propria  vrith  the  abdominal  perito- 
neum is  usually  obliterated  within  a  few  days  after  birth,  but  sometimes  the  process  of  oblitera- 
tion is  more  or  less  incomplete.  If  the  communication  remains  open  there  is  a  free  passage 
for  a  loop  of  the  intestine  to  enter  the  cavity  of  the  tunica  vaginalis,  such  a  condition  consti- 
tuting what  is  known  as  the  congenital  variety  of  inguinal  hernia.  If  the  communication  be 
interrupted  only  at  the  upper  part  of  the  original  sac,  so  that  the  cavity  of  the  tunica  vagin- 
alis propria  extends  a  considerable  distance  up  the  spermatic  cord  a  hernia,  passing  through 
the  inguinal  canal,  may  invaginate  the  upper  part  of  the  tunica  vaginalis  into  the  lower,  pro- 
ducing what  is  termed  the  encysted  variety  of  hernia.  Or  if,  finally,  the  obliteration  of  the 
communication  begins  in  the  neighbourhood  of  the  testis,  a  funnel-shaped  prolongation  of  the 
peritoneal  cavity  may  extend  downward  into  the  spermatic  cord,  and  hernia  into  this  con- 
stitutes the  variety  known  as  hernia  i^ito  the  funicular  process. 

The  testis  and  epididymis. — The  testes  (fig.  1017)  are  the  essential  male  organs 
of  reproduction  and  are  contained  within  the  scrotum.     They  are  two  in  number, 


1256 


UROGENITAL  SYSTEM 


each  being  of  a  flattened  oval  form,  with  two  surfaces,  medial  and  lateral,  two 
borders,  anterior  and  posterior,  and  two  extremities,  superior  and  inferior.  To  the 
whole  of  the  posterior  border  there  is  attached  the  epididymis,  formed  by  the 
efferent  ducts.  The  testis  is  obliquely  placed,  so  that  the  medial  surface  also  looks 
somewhat  forward  and  downward. 

The  surface  of  the  testis  is  covered  by  the  visceral  layer  of  the  tunica  vaginalis 
propria  except  where  it  is  in  contact  with  the  epididymis,  and  is  formed  by  a 
dense  white  inelastic  capsule,  the  tunica  albuginea,  beneath  which  is  a  looser  and 
more  vascular  layer  known  as  the  tunica  vascidosa.  From  the  inner  surface  of  the 
albuginea,  lamellae  of  connective  tissue,  known  as  septula,  converge  toward  the 
posterior  border  of  the  testis  and  toward  its  upper  part  unite  together  to  form  a 
network  (fig.  1018),  the  mediastinum  testis  (or  corpus  Highmori),  through  which 
blood-vessels  and  lymphatics  enter  and  leave  the  testis,  while  by  the  interspaces 
of  the  network,  known  as  the  rete  testis,  the  tubules  of  the  testis  are  placed  in  com- 
munication with  the  epididymis. 

The  septula  divide  the  substance  of  the  testis  into  a  number  of  compartments  or  lohules, 
each  of  which  is  occupied  by  a  number  of  slender,  greatly  contorted  canals,  the  seminiferous 
tubules  [tubuli  seminiferi],  from  whose  epithelial  lining  the  spermatozoa  are  formed.  The 
tubules  of  each  lobule  converge  to  form  a  single,  almost  straight  duct  and  these  tubuli  recti  pass 


Fig. 


lOlS. — Diagram  of  the  Testicular  Tubules. 

Ductus  epididymidis 
ua Lobulus  epididymidis 


Efferent  ducts 


Tunic  albuginea  receiving  attacli- 
ment  of  septula 

Tubulus  rectus 


Rete  testis  in  mediastinum  testis 
Ductus  epididymidis 


Ductulus  aberrans 
Ductus  deferens 


toward  the  mediastinum,  where  they  open  into  the  rete  testis.  In  the  lobules  the  seminif- 
erous tubules  are  imbedded  in  a  loose  connective  tissue  that  contains  certain  pecuhar  cells, 
the  interstitial  cells,  to  which  has  been  attributed  the  formation  of  an  internal  secretion. 

The  epididymis  (fig.  1017),  which  lies  along  the  posterior  border  of  the  testis, 
is  an  elongated  structure  with  a  body  [corpus  epididymidis],  enlarged  above  to  form 
the  head  [caput]  and  to  a  less  extent  below  to  form  the  tail  [cauda].  It  is  invested 
by  a  tunica  albuginea,  continuous  with,  but  much  thinner  than  that  of  the  testis, 
and  is  formed  mainly  by  the  greatly  contorted  duct  of  the  epididymis,  which 
represents  the  beginning  of  the  ductus  deferens. 

The  head  is  formed  by  12-14  tubules,  the  efferent  ducts  (fig.  1018),  which  take  their  origin 
from  the  rete  testis  as  almost  straight  tubules,  but  gradually  become  greatly  coiled,  so  that 
each  duct  has  the  form  of  an  elongated  cone,  its  coiled  portion  forming  what  is  termed  a  lobulus 
epididymidis.  At  their  coiled  ends  the  various  efferent  ducts  open  into  a  single  tube,  the 
ductus  epididymidis.  Its  diameter  is  only  about  0.4  mm.,  but  it  measures  6.0-7.0  metres  (18-21 
feet)  in  its  entire  length,  being  coiled  so  extensively  as  to  be  contained  within  the  body  and 
tail  of  the  epididymis.     In  this  latter  region  it  passes  over  into  the  ductus  deferens. 

Vessels. — The  principal  artery  supplying  the  testis  is  the  internal  spermatic,  from  which 
branches  are  also  sent  to  the  epididymis.  The  deferential  artery,  a  branch  of  the  superior 
vesical,  also  sends  branches  to  the  epididymis  and  enters  into  extensive  anastomoses  with  the 
testicular  branches  of  the  internal  spermatic,  and  anastomoses  also  occur  with  the  vessels 
supplying  the  scrotum.  The  veins  correspond  with  the  arteries.  The  lymphatics  of  the  testis 
and  epididymis  unite  to  form  four  to  six  large  stems  which  pass  upward  in  the  spermatic  cord 
to  terminate  in  the  lower  lumbar  nodes. 

Morphology. — The  testis  is  primarily  an  abdominal  organ  and  is  developed  in  close  relation- 
ship with  the  provisional  kidney  [mesonephros]  whose  duct,  indeed,  becomes  the  ductus  deferens 


DUCTUS  DEFERENS  AND  SEMINAL  VESICLE  1257 

and  some  of  whose  tubules,  becoming  the  efferent  ducts,  place  the  seminiferous  tubules  in  com- 
naunioation  with  the  ductus  deferens.  The  epididymis  may  therefore  be  said  to  be  developed 
from  the  mesonephros.  The  portions  of  this  structure  that  are  not  concerned  in  the  formation 
of  the  efferent  ducts  disappear  for  the  most  part;  a  few  of  the  tubules  persist,  however,  as 
rudimentary  organs  associated  with  the  epididymis.  Among  these  may  be  mentioned  one  or 
more  blindly  ending,  coiled  tubules,  varying  from  5-30  cm.  in  length,  which  are  connected  with 
the  ductus  epididymidis  usually  in  the  tail  of  the  epididymis.  They  are  knowTi  as  the  ducluli 
aberrantes  (fig.  1018)  and  may  be  regarded  as  persistent  excretory  mesonephric  tubules.  Another 
of  the  rudimentary  organs  is  the  paradidymis  {organ  of  Giraldes),  which  is  a  whitish  body, 
situated  immediately  above  the  head  of  the  epididymis,  and  is  composed  of  irregularly  coiled 
tubules,  which  terminate  blindly  at  both  extremities.  They  may  be  regarded  as  efferent 
ducts  that  have  failed  to  connect  with  the  testis  and  are  of  interest  in  that  they  sometimes 
develop  into  cysts  connected  with  the  epididymis. 

In  addition  there  is  frequently  attached  to  the  upper  pole  of  the  testis  a  sohd  oval  body 
composed  of  connective  tissue,  known  as  the  appendix  testis  {hydatid  of  Morgagni)  (fig.  1017). 
It  measures  from  3  to  8  mm.  in  length  and  its  significance  is  doubtful.  A  similar,  though 
smaller  structure,  the  appendix  epididymidis,  is  attached  less  frequently  to  the  head  of  the 
epididymis.  It  is  usually  provided  with  a  distinct  stalk  and  contains  a  cavity;  it  is  believed  to 
represent  the  upper  end  of  the  Miillerian  duct,  present  in  the  embryo  and  giving  rise  to  the  tuba 
uterina  in  the  female,  but  almost  completely  degenerating  in  the  male. 

The  testis  begins  its  descent  from  the  abdominal  cavity  into  the  scrotum  at  the  third  month 
of  fetal  life  and  reaches  the  abdominal  inguinal  ring  at  about  the  sixth  month,  but  it  is  not 
until  shortly  before  birth  that  it  arrives  at  its  final  location  in  the  scrotum.  The  cause  of  the 
descent  is  stiU  uncertain,  but  it  is  supposed  to  be  partly  due  to  the  failure  of  a  band  of  connective 
tissue,  which  extends  from  the  lower  pole  of  the  embryonic  testis  to  the  bottom  of  the  scrotal 
pouch,  to  keep  pace  with  the  growth  of  the  body  walls.  This  hgament,  which  is  known  as  the 
gubernac.ulum  testis,  thus  becomes  relatively  shorter  and  draws  the  testis  downward  toward  the 
point  of  its  attachment  to  the  scrotum.  There  are  various  features  in  the  descent,  however, 
that  cannot  be  explained  by  the  simple  traction  of  the  gubernaculum  and  it  must  be  regarded 
as  a  complicated  growth  process  whose  meaning  is  yet  uncertain.  The  gubernaculum  testis 
apparently  undergoes  degeneration  after  the  testis  has  reached  its  definitive  location  and  cannot 
be  recognized  in  connection  with  the  adult  testis. 

Occasionally  the  descent  of  the  testis  is  interrupted,  the  organ  remaining  either  in  the 
abdomen  or  in  the  inguinal  canal.  This  condition  of  cryptorchism  is  always  associated  with  a 
suppression  of  the  function  of  the  organ. 


2.  The  Ductus  Deferentes  and  Vesicul^  Seminales 

Each  ductus  deferens  is  the  continuation  of  a  ductus  epididymidis  and  ex- 
tends from  the  tail  of  the  epididymis  to  the  prostatic  portion  of  the  urethra.  At 
its  beginning  it  ascends  along  the  posterior  border  of  the  epididymis  (testicular 
portion)  and  is  at  first  slender  and  tortuous  (fig.  1018),  but  before  reaching  the 
level  of  the  head  of  the  epididymis  it  becomes  straighter  and  thicker  (fig.  1017), 
owing  to  the  development  in  its  walls  of  strong  layers  of  longitudinal  and  circular 
non-striated  muscle  tissue.  Thence  it  is  continued  almost  vertically  upward  as 
one  of  the  constituents  of  the  spermatic  cord  {funicular  portion)  to  the  subcu- 
taneous inguinal  ring,  and,  entering  this,  traverses  the  inguinal  canal  {inguinal 
portion),  still  forming  a  portion  of  the  cord.  At  the  abdominal  ring  it  separates 
from  the  other  constituents  of  the  cord  and,  looping  over  the  inferior  epigastric 
artery  near  its  origin,  passes  downward  and  backward  over  the  lateral  surface  of 
the  bladder  {pelvic  portion).  At  the  junction  of  the  posterior  and  lateral  surfaces 
of  the  bladder  it  passes  medially  to  the  ureter  and  is  then  continued  downward, 
forward  and  medially  upon  the  base  of  the  bladder  until  it  reaches  the  prostate 
gland  (fig.  1019),  whose  substance  it  traverses,  as  the  ductus  ejaculatorius,  to  open 
into  the  prostatic  portion  of  the  urethra  (see  p.  1263). 

Just  before  it  reaches  the  prostate  gland  each  ductus  deferens  presents  an 
irregular  spindle-shaped  enlargement,  the  ampulla  (figs.  1019,  1020),  whose  walls 
are  somewhat  sacculated.  Just  beyond  this  it  is  joined  upon  its  lateral  surface 
by  a  club-shaped  lobulated  structure,  the  vesicula  seminalis  (fig.  1019).  Each 
vesicle  measures  4.5-5.5  cm.  in  length  and  has  a  greatest  diameter  of  about  2  cm. 
It  rests  upon  the  posterior  surface  of  the  bladder,  lying  parallel  with  and  lateral 
to  the  corresponding  ductus  deferens,  and  in  its  upper  one-third  is  in  relation 
posteriorly  with  the  peritoneum  which  forms  the  anterior  wall  of  the  recto- 
vesical pouch,  while  below  it  is  in  contact  with  the  anterior  wall  of  the  lower  part 
of  the  rectum,  through  which  it  may  be  palpated.  Indeed,  the  two  vesiculee, 
together  with  the  ductus  deferentes,  form  the  lateral  boundaries  of  the  triangular 
area  at  the  base  of  the  bladder,  throughout  which  that  organ  is  in  relation  to  the 
rectum. 


1258 


UROGENITAL  SYSTEM 


Each  vesicle  is  enclosed  within  a  fine  capsule  of  connective  tissue,  which  contains  numerous 
non-striated  muscle  fibres  and  is  continuous  below  with  the  capsule  of  the  prostate  gland. 
On  removing  this  capsule  the  vesicle  will  be  found  to  consist  of  a  greatly  coiled  tube,  10-12  cm. 


Fig.  1019. — Ductus  Depeeentes  and  Vesicul^  Seminales.     (After  Sappey.) 


Ejaculatory  duct 
Prostatic  utriculus  — 


CoUiculus  seminali 
Orifice  of  ejaculatory  duct -J'- — 


Ampulla  of  ductus  deferens 


Ejaculatory  duct  entering 
prostatic  fissure 


Membranous  urethra 


Ductus  deferens 


Orifice  of  prostatic  utriculus 


Vesicula  seminalis 


Fig.  1020. — Ductus  Deferens  and  Vesicula  Seminalis  dissected.     (After  Sappey.) 


Diverticula!         '"\^     ^     p^ 


Sacculi  of  ampulla  of  ductus  deferens 


Junction  of  ductus  deferens  and  vesicula 
seminalis 


Ejaculatory  duct 


in  length,  which  ends  blindly  and  has  attached  to  it  on  either  side  a  number  of  short  diverticula 
(fig.  1020).  The  walls  of  the  tube  and  diverticula  are  formed  of  smooth  muscle  tissue,  arranged 
in  layers  similar  to  those  of  the  ductus  deferentes,  and  are  lined  by  a  much  folded  mucous 


THE  SPERMATIC  CORD 


1259 


membrane,  whose  cells  contain  considerable  quantities  of  a  yeUowish-brown  pigment,  and  also 
contribute  a  secretion  to  the  seminal  fluid.  In  addition  to  having  this  function  the  vesiculse 
also  serve  as  receptacles  for  the  spermatozoa.  They  arise  as  diverticula  from  the  embryonic 
ductus  deferens,  and  it  is  worthy  of  note  that  a  number  (4  or  5)  of  similar  but  quite  small  diver- 
ticula arise  from  the  upper  part  of  each  ductus  ejaculatorius. 

Vessels  and  nerves. — The  artery  supplying  the  ductus  deferens  is  the  a.  deferentialis,  a 
branch  of  the  superior  vesical.  It  accompanies  the  ductus  to  the  tail  of  the  epididymis  and  also 
gives  a  branch  to  the  vesicula  seminalis.  The  latter  also  receives  branches  from  the  middle 
haemorrhoidal  and  inferior  vesical  arteries.  The  deferential  vein  accompanies  the  ductus 
deferens  to  the  base  of  the  bladder  where  it  breaks  up  into  a  plexus  that  communicates  with 
the  seminal  venous  plexus  formed  by  the  veins  from  the  seminal  vesicles.  This  joins  with  the 
vesical  and  pudendal  ple.xus  and  so  communicates  with  the  hypogastric  vein.  The  lymphatics 
of  the  ductus  deferentes  and  seminal  vesicles  pass  to  the  external  iliac  and  hypogastric 
nodes.     The  nerves  of  both  structures  are  derived  from  the  hypogastric  plexus. 

The  spermatic  cord. — In  its  descent  through  the  inguinal  canal  into  the 
scrotum  the  testis  necessarily  drags  after  it  the  ductus  deferens  and  the  testicular 
vessels  and  nerves,  these  structures  coming  together  at  the  abdominal  inguinal 

Fig.  1021. — Ceoss-section  of  the  Spermatic  Cord. 


A.  spermatica  interna 
N.  spermaticus  int. 


Lympli  vessel 


Vv.  spermaticae  int. 

Fascia  cremasterica 


Lymph  vessel 


Ductus  deferens 


Vv.  spermaticse  int 


A.  et  V.  deferentialis 


V.  spermatica  ext. 


ring  to  form  what  is  termed  the  spermatic  cord  [funiculus  spermaticus].  This 
structure  extends,  therefore,  from  the  abdominal  inguinal  ring,  through  the  in- 
guinal canal  and  the  neck  of  the  scrotal  sack  to  the  testis,  and  is  enclosed  within 
the  same  investing  layers  as  the  testis. 

Thus  as  it  emerges  from  the  subcutaneous  inguinal  ring  it  receives  an  investment  of  con- 
nective tissue  continuous  with  the  intercrural  fibres  and  the  aponeurosis  of  the  external  oblique 
muscle.  This  cremasteric  fascia  has  beneath  it  bands  of  striated  muscle  tissue,  the  external 
cremaster  muscle  (fig.  1021),  especially  developed  on  the  posterior  surface  of  the  cord  and  con- 
tinuous with  the  internal  oblique  muscle  of  the  abdomen,  and  within  these  is  an  indistinct 
layer  of  connective  tissue,  the  tunica  vaginalis  communis,  which  is  received  at  the  abdominal 
inguinal  ring  where  it  is  continuous  with  the  fascia  transver.saUs. 

Within  the  sheath  thus  formed  there  is  a  matrix  of  connective  tissue,  usually 
containing  considerable  amounts  of  fat  and  strands  of  non-striated  muscle  tissue, 
which  form  what  is  termed  the  internal  cremaster  muscle  {funicular  portion), 
and  imbedded  in  this  connective  tissue  are  the  various  essential  constituents  of 
the  cord.  These  are  as  follows  (figs.  1017,  1021) :  (1)  the  ductus  deferens,  occupy- 
ing the  posterior  surface  of  the  cord  and  having  associated  with  it  the  deferential 
artery  and  veins  and  the  deferential  plexus  of  nerve  fibres;  (2)  the  internal 
spermatic  artery,  which  occupies  the  axis  of  the  cord  and  is  surrounded  by  (3)  the 
internal  spermatic  veins,  which  form  a  complicated  network,  known  as  the  pam- 


1260 


UROGENITAL  SYSTEM 


piniform  plexus;  (4)  the  testicular  lymphatics;  and  (5)  the  internal  spermatic 
plexus  of  nerves  from  the  hypogastric  plexus;  and  (6)  branches  of  the  genito- 
femoral nerve  for  the  supply  of  the  external  cremaster  muscles. 


3.  The  Penis 

The  penis  is  composed  of  three  rod-like  bodies  composed  of  erectile  tissue 
(fig.  1023),  firmly  united  together  and  invested  by  fascia  and  integument  (fig. 
1022).  When  this  erectile  tissue  becomes  engorged  with  blood  the  organ  assumes 
an  erect  position,  but  otherwise  it  is  pendulous,  hanging  downward  in  front  of  the 
scrotum  from  its  attachment  to  the  symphysis  pubis.  The  erectile  bodies  are, 
however,  prolonged  backward  beyond  the  symphysis  pubis  into  the  perineal  re- 
gion, and  it  is  customary  to  speak  of  this  perineal  portion  as  the  root  of  the  penis 
[radix  penis]  or  pars  fixa  in  contrast  to  the  body  of  the  penis  [corpus  penis]  or  pars 
libera. 

The  body  of  the  penis  in  its  flaccid  condition  is  almost  cylindrical,  but  in 
erection  it  becomes  somewhat  triangular  in  section,  what  was  the  anterior  surface 
or  dorsum  penis*  becoming  flattened,  while  the  opposite  one,  the  urethral  surface 
[facies  urethralis],  becomes  more  sharply  rounded.  At  the  free  extremity  of  the 
penis  there  is  a  blunt  conical  enlargement,  the  glans  penis  (fig.  1023),  at  the  apex 
of  which  is  the  external  orifice  of  the  methra.  The  glans  is  separated  from  the 
body  by  a  constriction,  the  ?ieck  [coUum  glandis],  and  from  this  region  a  fold  of 
integument  arises,  which  more  or  less  completely  encloses  the  glans,  forming  the 
prepuce  [prseputium]  (fig.  1024).  The  prepuce  is  quite  free  from  the  glans 
dorsally  but  in  the  ventral  mid-line  it  is  attached  to  it,  almost  to  the  urethral 

Fig.  1022. — Transverse  Section  through  the  Bodt  op  the  Penis. 

Superficial  dorsal  vein  of  penis 
Dorsal  artery  ^  |        /Deep  dorsal  vein 


Tunica  albuginea 


Tunica  albuginea- 


Skin 

Dartos 

Septum 

.Corpus  cavernosum  penis 

Fascia  penis 


Artery 

Urethra 
Corpus  cavernosum  urethrs 

orifice,  by  a  narrow  fine  of  adhesion,  the  frenulum  [frenulum  prseputii],  which 
contains  blood-vessels  of  considerable  size.  The  base  of  the  glans  has  a  well- 
marked  rounded  border,  the  corona  [corona  glandis],  and  is  deeply  concave  for  the 
reception  of  the  distal  ends  of  the  corpora  cavernosa  penis. 

The  integument  of  the  penis  is  continuous  with  that  of  the  scrotum  and  like 
it  is  pigmented  and  contains  no  fat.  Immediately  below  it  there  is  a  layer  of  non- 
striated  muscular  tissue,  the  dartos,  and  beneath  this  a  layer  of  loose  connective 
tissue,  containing  the  superficial  vessels  and  nerves  of  the  penis;  beneath  this 
again  is  a  denser,  elastic  sheet  of  connective  tissue,  the  fascia  penis  (fig.  1022), 
which  encloses  the  erectile  bodies  as  far  as  the  base  of  the  glans  and  is  continuous 
with  the  superficial  fascia  of  the  perineum  and  inguinal  region.  Where  it  passes 
beneath  the  symphysis  pubis  it  receives  from  the  anterior  surface  of  the  latter  a 
strong  band  of  fibrous  tissue,  which  forms  the  suspensory  ligament  of  the  penis 
[Hg.  suspensorium  penis]. 

Two  of  the  erectile  bodies  of  the  penis,  the  corpora  cavernosa  penis,  are  paired 
(fig.  1023).  They  are  attached  at  their  proximal  ends  to  the  base  of  the  tuberosity 
of  the  ischium,  and  in  this  part  of  their  extent  are  termed  the  c7-ura  penis,  being 

*  It  should  be  noted  that  the  terms  "dorsum"  and  "dorsal"  are  used  for  the  penis  in  a 
sense  directly  opposite  their  usual  meaning. 


THE  PENIS  1261 

composed  of  fibrotis  connective  tissue,  whicli  lias  resting  upon  it  the  m.  ischio- 
cavernosus  (see  Section  IV).  The  two  crura  are  situated  in  the  lateral  portions 
of  the  superficial  perineal  interspace  and  pass  forward  parallel  with  the  rami  of 
the  ischia  and  pubis,  gradually  becoming  transformed  into  cavernous  erectile 
tissue.  Shortly  before  they  reach  the  level  of  the  symphysis  pubis  the  two 
corpora  come  into  contact  in  the  median  hne,  their  medial  walls  fusing  to  form  a 
septum,  and  thus  united  they  extend  throughout  the  entire  length  of  the  body  of 
the  penis,  occupying  the  dorsal  portion  of  the  space  enclosed  by  the  fascia  penis 
(fig.  1022) .     They  terminate  at  the  posterior  surface  of  the  glans,  where  they  taper 

Fig.  1023. — Dissection  of  the  Perineum  Showing  the  STRtrcTTTBE  and  Relations  op  the 

Penis. 


Corona  glandis  — 


Corpus  cavernosum  xirethr^ 


Corpus  cavernosum  penis  ■ 


■  M,  ischio-cavernosus 


.  Urogenital  trigone 
(diaphragm) 


Prostate  gland  - 


somewhat  to  be  received  into  its  basal  concavity  (fig.  1024).  The  septum  in  its 
proximal  part  forms  a  complete  partition  between  the  two  bodies,  but  distally  it 
is  broken  through  by  numerous  clefts  by  which  the  blood  lacunse  of  the  two  bodies 
are  placed  in  communication. 

Each  corpus  cavernosum  penis  consists  of  a  strong  elastic  fibrous  sheath,  the  tunica  albu- 
ginea,  from  which  trabeculiB  extend  into  the  substance  of  the  organ,  dividing  it  into  a  network 
of  communicating  cavities,  into  which  open  terminal  branches  of  the  a.  profunda  penis,  which 
traverses  the  axis  of  the  corpus.  These  cavities  consequently  are  to  be  regarded  as  vascular 
lacunae,  which,  becoming  engorged  with  blood,  produce  the  enlargement  and  erection  of  the 
organ. 

The  third  erectile  organ  is  the  corpus  cavernosum  urethra  (formerly  "corpus 
spongiosum")  (fig.  1023),  so  called  because  it  is  traversed  throughout  its  entire 
length  by  the  urethra  (fig.  1024).     It  is  an  unpaired,  median  structure,  having  no 


1262 


UROGENITAL  SYSTEM 


bony  attachments  and  begins  posteriorly  in  the  superficial  perineal  interspace 
with  an  enlargement,  the  bulb  [bulbus  urethrae]  (fig.  1023),  whose  posterior  surface 
rests  on  the  superficial  fascia  of  the  urogenital  trigone  and  is  enclosed  by  the  m. 
bulbo-cavernosus.  Anteriorly  the  bulb  gradually  tapers  to  a  rather  slender 
cylindrical  portion,  the  body,  very  uniform  in  diameter,  which  extends  throughout 
the  entire  length  of  the  body  of  the  penis,  lying  in  the  median  hne  beneath  the 
fused  corpora  cavernosa  penis  (figs.  1022,  1023).  At  the  neck  of  the  penis  it 
undergoes  a  sudden  enlargement  to  form  the  glans,  the  whole  of  that  structure, 
which  has  already  been  described,  being  formed  by  the  corpus  cavernosum 
urethras.  The  structure  of  the  corpus  cavernosum  urethrae  is  essentially  the  same 
as  that  of  the  corpora  cavernosa  penis,  the  tunica  albuginea,  however,  being  much 
thinner. 

Vessels  and  nerves. — The  principal  arterial  supply  of  the  penis  is  derived  from  the  internal 
pudendal  artery  (see  p.  610),  although  the  proximal  portion  of  its  integument  is  also  supplied 
by  the  external  pudendal  branches  of  the  femoral  artery.     The  veins  from  the  integument 

Fig.  1024. — Mid-sagittal  Section  (diagrammatic)  Showing  Male  Bladder,  Ukethba,  etc. 


Symphysis  pub: 


Subpubic  lig. 

Suspensory  lig. 

Urogenital  trigone 

(diaphragm) 


Bladder 

Seminal  vesicle 
Ampulla 


Prostate  middle  lobe 
Ejaculatory  duct 
Prostatic  utriculus 
Prostate  gland 


Bulbo-iurethral 
(Cowper's)  gland 
Ductus  deferens 


Prepuce. 
Fossa  navicularis 


collect  into  one  or  more  stems,  the  superficial  dorsal  veins,  which  run  along  the  dorsal  mid-line 
and,  diverging,  open  into  the  great  saphenous  vein.  The  deep  veins  from  the  corpora  cavernosa 
open  into  a  median  deep  dorsal  vein,  which  connects  partly  with  the  internal  pudendal  veins 
and  partly  with  the  pudendal  plexus.  Both  the  superficial  and  deep  lymphatics  terminate  in 
the  superficial  inguinal  nodes.  The  lymph-vessels  from  the  glans  are  said  to  follow  those  of  the 
urethra  and  end  in  the  deep  inguinal  and  external  iliac  nodes. 

The  nerves  supplying  the  penis  are  the  anterior  scrotal  branches  of  the  ilio-inguinal  and  the 
perineal  branches  and  dorsal  nerve  of  the  penis  from  the  pudendal.  Sympathetic  fibres  also 
pass  to  the  penis  from  the  hypogastric  plexus  and  with  these  fibres  from  the  third  and  fourth 
sacral  nerves,  which  constitute  what  is  termed  the  nervus  erigens,  since  stiinulation  of  it  pro- 
duces erection  of  the  organ.  An  anatomical  provision  for  the  production  of  this  phenomenon  has 
been  found  in  the  occurrence  of  peculiar  thickenings  of  the  intima  of  the  arteries  of  the  penis, 
by  which  the  lamina  of  the  vessels  are  greatly  diminished  or  even  occluded  when  in  a  state 
of  moderate  contraction,  as  when  the  organ  is  flaccid.  When  the  arteries  are  dilated  the  intimal 
thickenings  become  reduced  in  height  and  the  blood  is  afforded  a  free  passage  into  the  lacunar 
spaces  of  the  corpora  cavernosa,  which  thus  become  engorged. 


4.  The  Male  Urethra 

The  urethra  is  the  canal  which  extends  from  the  bladder  to  the  extremity  of 
the  glans  penis  and  serves  for  the  passage  of  both  the  urine  and  the  seminal  fluid. 


THE  MALE  URETHRA 


1263 


In  its  course  (fig.  1024)  it  traverses  first  the  prostate  gland,  then  the  urogenital 
diaphgram  and  then  the  entire  length  of  the  corpus  cavernosum  urethrse,  and  may 
thus  be  regarded  as  being  composed  of  three  portions. 

The  prostatic  portion  [pars  prostatica]  (fig.  1024)  extends  almost  vertically 
downward  from  the  neck  of  the  bladder,  traversing  the  substance  of  the  prostate 
gland.  In  its  proximal  part  there  is  on  its  posterior  wall  a  median  longitudinal 
ridge,  the  crista  urethralis,  which  below  dilates  into  an  oval  enlargement,  the 
colliculus  seminalis  (figs.  1015,  1025),  to  accommodate  which  there  is  a  marked 

Fig.  1025. — The  Male  Urethra,  cleft  anteriorly  to  show  the  Mucous  Coat. 

Ureter   ,  -^r *  ^ 


Section  of  bladder 

Internal  urethral  onfice 


Openings  of  prostatic  glands' 

Prostatic  utricnlus    '^m  ©j^ 
Follicular  glands  of  dorsal  wall — VmL  ;.  ' 


Bulbo-urethral  gland 


Septum  of  penis 


Section  of  prostate 
Colliculus  seminalis 
Ejaculatory  duct 
Openings  of  prostatic  glands 


"7  Membranous  uerthra 


Section  of  corpus  cavernosum  penis 


Orifice  of  bulbo-urethral  gland 


Section  of  corpus  cavernosum  penis '^  ^  1' 


Bulbous  portion  of  urethra 


Mucous  membrane 


Fossa  navicularis 


External  urethral  orifice 


widening  of  the  lumen  of  the  urethra  in  this  part  of  its  course.  At  the  centre  of 
the  colliculus  there  is  an  elongated  opening  of  a  pouch  of  varying  depth, termed  the 
utricnlus  prostaticus  ("uterus  masculinus"),  which  corresponds  to  the  lower  part 
of  the  vagina  in  the  female  (see  p.  1279).  Situated  one  on  either  side  of  this  are 
the  much  smaller  openings  of  the  ejaculatory  ducts.  Owing  to  the  prominence 
formed  by  the  coUiculus  a  section  of  the  urethra  in  this  region  is  somewhat 
fl-shaped,  and  at  the  bottom  of  the  furrows  on  either  side  of  the  median  eleva- 


1264  UROGENITAL  SYSTEM 

tion  are  the  minute  openings  of  the  numerous  ducts  of  the  prostate  gland 
(fig.  1025).  ^  ^ 

On  its  emergence  from  the  prostate  gland  the  urethra  at  once  penetrates  the 
deep  layer  of  fascia  of  the  urogenital  trigone  and  enters  the  deep  perineal  inter- 
space, this  portion  of  its  course  being  known  as  the  membranous  portion  [pars 
membranacea].  Its  direction  is  now  downward  and  slightly  forward,  curving 
beneath  the  subpubic  ligament,  from  which  it  is  separated  by  a  plexus  of  veins  and 
by  the  fibres  of  the  sphincter  urethras  membranaceae,  which  form  an  almost 
complete  investment  for  it.  The  lumen  of  this  part  of  the  urethra  is  much 
narrower  than  that  of  the  prostatic  portion,  and  since  it  traverses  the  rather 
unyielding  fasciae  of  the  urogenital  trigone  it  is  less  dilatable  than  in  other  parts 
of  its  extent,  with  the  exception  of  the  external  orifice. 

Passing  through  the  superficial  layer  of  fascia  of  the  urogenital  trigone  the 
urethra  then  enters  the  bulb  of  the  corpus  cavernosum  urethrae  (fig.  1024)  and  is 
invested  throughout  the  remainder  of  its  extent  by  this  structure,  whence  this 
portion  is  known  as  the  cavernous  portion  [pars  cavernosa].  In  its  proximal  part 
this  hes  in  the  superficial  interspace  of  the  perineum  and  passes  almost  directly 
forward;  but  more  distally,  where  it  enters  the  body  of  the  penis,  it  accommodates 
itself  to  the  position  of  that  organ,  which  it  traverses  lengthwise,  lying  in  the  mid- 
line near  its  ventral  surface  (fig.  1022).  Thus  the  proximal  portion  of  the 
cavernous  and  the  whole  of  the  membranous  and  prostatic  portions  have  a 
fixed  position,  whence  they  are  sometimes  associated  as  the  pars  fixa  of  the  urethra, 
while  the  penial  portion  forms  the  pars  mobilis.  On  entering  the  bulb  the  lumen 
of  the  urethra  dilates  somewhat  and  in  this  region  has  opening  into  it  the  ducts  of 
the  bulbo-urethral  glands  (fig.  1025),  but  as  it  enters  the  body  of  the  corpus  caver- 
nosum it  diminishes  again  and  maintains  a  uniform  diameter  throughout  the 
extent  of  that  structure.  When  it  reaches  the  glans  penis  it  undergoes  another 
dilation,  which  is  known  as  the  fossa  navicularis  (fig.  1025),  beyond  which  it 
diminishes  to  the  slit-hke  external  orifice,  situated  at  the  extremity  of  the  glans 
and  forming  the  least  dilatable  portion  of  the  entire  urethral  canal. 

Throughout  the  greater  part  of  its  extent  the  cavernous  portion  of  the  urethra  shows  upon 
its  dorsal  wall  the  openings  of  numerous  tubular  depressions  of  the  mucous  membrane,  the 
urethral  lacunm  [lacunas  urethrales  (Morgagnii)].  One  of  these,  the  lacuna  magna,  situated 
m  the  mid-dorsal  line  of  the  proximal  part  of  the  fossa  navicularis,  has  its  orifice  guarded  by  a 
valve-hke  fold  [valvula  fossEe  navicularis]  of  the  mucous  membrane  and  is  sufficiently  large  to 
receive  the  point  of  a  small  catheter.  Numerous  minute  glands  [gl.  urethrales]  open  upon 
the  surface  of  the  urethral  mucosa.  They  are  most  abundant  in  the  anterior  wall,  but  occur 
also  on  the  sides  and  floor. 

,.„  Dimensions  of  the  urethra.— The  entire  length  of  the  urethra  is  somewhat  variable  in 
ditterent  individuals,  the  greatest  variation  being  in  the  length  of  the  pars  mobihs.  Of  the  pars 
fi^a  the  prostatic  portion  is  2.5-3.0  cm.  in  length,  the  membranous  portion  about  1.0  cm.,  and 
the  fixed  part  of  the  cavernous  portion  6.5  cm.,  the  entire  pars  fixa  having  thus  a  length  of  some- 
what over  10.0  cm.  (4  in.).  The  average  diameter  of  the  urethra  is  5.0-7.0  mm.,  but  it  will  be 
noted  that  the  canal  presents  in  its  course  three  dilatations;  namely,  (1)  at  the  fossa  navic- 
ularis, which  begins  about  0.5  cm.  from  the  external  orifice;  (2)  the  bulb  of  the  corpus  caverno- 
sum urethras;  and  (3)  in  the  prostatic  portion.  Furthermore  there  are  two  regions  in  which  it 
is  distinctly  narrowed;  namely,  at  the  external  orifice  and  in  the  memjjranous  portion.  While 
the  remaining  portions  are  capable  of  considerable  distention,  these  are  relatively  indistensible, 
the  maximum  diameter  to  which  they  may  be  dilated  being  about  10  mm.  Arranged  in  an 
ascending  order  according  to  their  capability  for  distention  the  parts  would  have  the  followmg 
order:  external  orifice,  membranous  portion,  penial  portion,  prostatic  portion,  bulbar  portion. 

5.  The  Prostate  Gland 

The  prostate  gland  [prostata]  (figs.  1013,  1019,  1024  and  1025)  is  a  mass  of 
glandular  and  muscular  tissue  surrounding  the  proximal  portion  of  the  male 
urethra,  and  may,  indeed,  be  regarded  as  a  special  development  of  the  wall  of 
this  portion  of  the  canal.  It  is  a  more  or  less  flattened  conical  structure  whose 
base  [basis  prostatse]  is  in  contact  with  the  lower  surface  of  the  bladder  and  the 
apex  [apex  prostatse]  with  the  deep  fascia  of  the  urogenital  trigone.  Its  anterior 
surface  [facies  anterior]  is  in  relation  with  the  symphysis  pubis,  from  which  it  is 
separated  by  the  pudendal  plexus  of  veins,  and  posteriorly  [facies  posterior]  it  is 
separated  from  the  lower  portion  of  the  rectum  only  by  some  loose  connective 
tissue;  laterally  it  is  in  relation  with  the  levatores  ani,  receiving  an  investment  from 
the  endopelvic  fascia  covering  these. 


i 


THE  FEMALE  REPRODUCTIVE  ORGANS  1265 

The  urethra  enters  the  base  of  the  gland  near  its  anterior  border  and  traverses 
it  almost  vertically,  so  that  the  greater  portion  of  the  gland  is  posterior  to  the 
canal.  On  the  posterior  surface  of  the  gland  is  a  more  or  less  distinct  median 
vertical  groove,  which  serves  to  separate  the  lateral  portion  as  the  lateral  lobes 
[lobus  dexter  et  sinister],  although  the  demarcation  is  merely  a  superficial  one. 
The  groove  terminates  above  in  a  well-marked  notch  on  the  posterior  border  of 
the  base,  and  immediately  in  front  of  this  there  is  a  deep  funnel-shaped  depression 
of  the  surface,  which  receives  the  ejaculatory  ducts.  Beginning  at  this  depression 
two  grooves  pass  forward  and  slightly  lateralward  across  the  surface  of  the  base, 
marking  off  a  more  or  less  pronounced  median  elevation,  which  constitutes  what 
is  termed  the  middle  lobe  [lobus  medius]  (fig.  1024);  since  this  lies  beneath  the 
trigone  of  the  bladder  behind  the  internal  orifice  of  the  urethra  its  enlargement 
may  produce  more  or  less  occlusion  of  the  latter. 

Dimensions. — The  longest  axis  of  the  prostate,  which  is  almost  vertical  in  the  erect  posture 
measures  2.5-3.0  cm.,  the  transverse  diameter  at  the  base  is  4.0-4.5  cm.  and  the  thickness  2.0-2.5 
cm.  Its  iveight  is  normally  20-25  grms.  but  in  old  age  it  may  be  double  that,  its  dimensions 
having  correspondingly  increased. 

Structure. — The  prostate  consists  of  some  15-30  branched  tubular  glands  imbedded  in 
a  matrix  of  connective  tissue,  containing  a  large  amount  of  non-striped  muscle  tissue  and  form- 
ing at  the  surface  of  the  gland  a  strong  fibro-muscular  capsule  from  which  prolongations  are 
contributed  to  the  pubo-vesical  ligaments  and  muscles.  The  glands,  which  vary  greatly  in 
their  development,  are  outgrowths  from  the  mucous  membrane  of  the  urethra,  into  which  their 
ducts  open  at  the  bottom  of  the  grooves  that  lie  lateral  to  the  colliculus  seminahs;  similarly, 
the  matrix  with  its  muscle  tissue  is  evidently  the  modified  muscular  coat  of  the  urethra.  Con- 
sequently there  is  no  distinct  demarcation  between  the  wall  of  the  urethra  and  the  substance 
of  the  gland,  and  from  the  developmental  standpoint  the  gland  is  to  be  regarded  as  the  modified 
wall  of  the  urethra. 

The  facts  that  the  prostate  shows  a  special  development  at  puberty  and  undergoes  more  or 
less  extensive  degenerative  changes  with  the  cessation  of  the  reproductive  function,  as  seen  in 
old  age  and  in  castrates,  indicate  that  it  is  associated  physiologically  with  the  reproductive 
organs.  Its  secretion  is  a  thin  alkaline  fluid,  which  may  contain  round  or  elongate,  concen- 
trically layered  bodies,  measuring  0.3-0.5  mm.  in  diameter  and  known  as  amyloid  bodies, 
although  they  are  really  albuminous  in  chemical  composition.  They  are  constantly  found  in 
adults  in  the  lumina  of  the  glands  and  may  become  calcified.  The  secretion  has  been  found  to 
have  a  stimulating  effect  upon  the  spermatozoa,  and  this  may  be  its  principal  function. 

Vessels  and  nerves. — The  arterial  supply  of  the  prostate  is  derived  from  the  inferior  vesical 
and  middle  hemorrhoidal  branches  of  the  hypogastric  artery.  The  veins  form  a  rich  prostatic 
plexus  in  the  immediate  vicinity  of  the  gland,  this  being  part  of  the  general  plexus  at  the  base 
of  the  bladder  and  communicating  posteriorly  with  the  seminal  plexus  and  anteriorly  with  the 
pudendal  plexus.  It  drains  finally  into  the  hypogastric  vein.  The  lymphatics  are  very  abun- 
dant and  form  a  network  on  the  posterior  surface  of  the  gland  -from  which  four  principal  vessels 
pass  to  the  hypogastric  nodes.     The  nerves  are  derived  from  the  hypogastric  plexus. 

6.  The  Bulbo-urethral  Gl.inds 

The  bulbo-urethral  glands  [gl.  bulbo-urethralis  (Cowperi)]  or  Cowper's  glands 
(figs.  1024,  1025)  are  two  small  tubulo-alveolar  glands  which  fie  one  on  either 
side  of  the  membranous  portion  of  the  urethra,  imbedded  among  the  fibres  of  the 
sphincter  urethrse  membranacete,  between  the  two  layers  of  fascia  of  the  uro- 
genital trigone.  Each  is  a  rounded  body  with  a  diameter  of  4.0-9.0  mm.  and  is 
drained  by  a  duct  [ductus  excretorius]  which  perforates  the  superficial  fascia  of  the 
trigone  and,  entering  the  substance  of  the  bulb  of  the  corpus  cavernosum  urethrse, 
traverses  it  to  open  on  the  floor  of  the  bulbar  portion  of  the  urethra  after  a  total 
course  of  3.0-4.0  cm.  Nothing  is  definitely  known  as  to  the  nature  of  the  secre- 
tion or  the  functions  of  the  glands. 

THE  FEMALE  REPRODUCTIVE  ORGANS 

The  organs  of  reproduction  in  the  female  consist  of  (1)  the  ovaries,  the 
essential  organs  of  reproduction;  (2)  the  tubce  uterince  (Fallopian  tubes),  which 
serve  as  ducts  for  the  conveyance  of  the  ova  to  (3)  the  uterus,  in  which  the  embryo 
normally  undergoes  its  development;  (4)  the  vagina,  a  canal  by  which  the  uterus 
is  placed  in  communication  with  the  e.xterior;  and  (5)  the  external  genitalia.  In 
addition  it  will  be  necessary  to  consider  here  the  female  urethra,  although  it  differs 
from  that  of  the  male  in  that  it  serves  merely  as  a  passage  for  the  contents  of  the 
bladder  and  does  not  transmit  the  reproductive  elements. 


i 

{ 


1266 


UROGENITAL  SYSTEM 


Fig;  1026. — The  Female  Organs  of  Generation.     (Modified  from  Sappey.) 
(Vagina  divided  and  laid  open  behind.) 


Posterior  surface  of  body  of  uterus 


Ovarian  ligament 

Ovary 


Tuba  uterina 
Mesosalpinx 


Fimbriated 
extremity  of  tube 
Fimbria  ovarica 
Mesometrium 

Supravaginal  zone  of  cervix 

External  orifice  of  uterus 
Vaginal  wall,  divided 
and  reflected 


Vagina,  anterior  wall 


iG,  1027. — Diagrammatic  Sagittal  Section  of  the  Broad  Ligament. 


Tuba  uterina 


Mesometriu: 
Posterior  surfac 


Connective  tissue  and  unstriped 
muscle  (utero-pelvic  band) 


Uterine  veins 


-Uterine  artery 


Ease  of  ligament 


THE  BROAD  LIGAMENT 


1267 


Broad  ligament. — ^The  first  three  of  these  structures  are  entirelj^  contained 
within  the  true  pelvis  and  are  associated  with  a  transverse  fold  of  peritoneum 
which  rises  from  the  floor  of  the  pelvic  cavity  between  the  bladder  and  the  rectum, 
incompletely  dividing  the  cavity  into  an  anterior  and  a  posterior  compartment. 
It  is  known  as  the  hroad  ligament  of  the  uterus  [lig.  latum  uteri]  (fig.  1026).  The 
broad  ligament  appears  to  extend  laterally  from  the  sides  of  the  uterus  to  the 
lateral  walls  and  floor  of  the  pelvis,  although  in  reality  it  extends  across  the  pelvic 
cavity  from  side  to  side  and  encloses  the  uterus  between  the  two  layers  of  which 
it  is  composed.  It  is  attached  to  the  floor  of  the  pelvis  below,  where  the  two  layers 
are  reflected,  the  one  upon  the  anterior  wall  of  the  pelvis  and  the  posterior  and 
superior  surfaces  of  the  bladder,  and  the  other  posteriorly  over  the  floor  of  the 
pelvis  to  the  posterior  pelvic  wall  and  the  rectum,  forming  the  anterior  wall  of  a 
deep  depression  between  the  rectum  and  uterus,  known  as  the  recto-uterine  pouch 
(of  Douglas)  [excavatio  rectouterina  (cavum  Douglasi)]  (fig.  1035).  Its  lower 
border  also  passes  upward  upon  the  sides  of  the  pelvis,  resting  upon  the  pelvic 
fascia,  but  its  lateral  borders  are  free,  extending  between  the  lateral  wall  of  the 
pelvis  and  the  extremity  of  the  tuba  uterina  on  each  side  and  forming  what  are 
termed  the  infundibulo-pelvic  ligaments.  The  upper  border  is  also  free  and  con- 
tains the  tuba  uterina  on  either  side,  and  the  fundus  of  the  uterus  in  the  midline 
(fig.  1027). 

Fig.  1028. — Cross-sections  of  the  Body  Illustrating  the  Development  of  the  Female 
Urogenital  system.    A,  at  Higher  Level.     B,  at  Lower  Level. 


Epodpliorou 


Attached  to  the  posterior  layer  of  the  broad  hgament  a  httle  below  its  upper 
border  and  therefore  projecting  into  the  posterior  compartment  of  the  pelvis, 
there  is  a  horizontal  shelf,  termed  the  mesovarium,  since  it  has  the  ovary  attached 
to  its  free  edge  (fig.  1027).  The  portion  of  the  broad  hgament  above  this  is  known 
as  the  mesosalpinx  (salpinx  =  tuba),  while  that  below  istermed  the  mesometrium 
(metra=  uterus).  The  remaining  structm-es  that  occur  between  the  two  layers 
of  the  broad  ligament  will  be  described  with  the  organs  with  which  they  are 
associated,  but  it  is  to  be  noted  that  the  ligament  in  its  upper  part  is  broader  than 
the  transverse  diameter  of  the  pelvic  cavity  and  its  sides  are  accordingly  folded 
back  upon  the  lateral  walls  of  the  cavity,  following  the  course  of  the  tuba  uterina. 

The  broad  ligament  is  the  adult  representative  of  the  fold  of  peritoneum  which  encloses 
the  embryonic  excretory  organ,  the  mesonephros.  This  is  for  a  time  a  voluminous  organ, 
projecting  under  cover  of  the  peritoneum  from  the  dorsal  wall  of  the  abdomen  and  bearing 
upon  its  medial  wall  a  thickening,  the  genital  ridge  (fig.  1028  A),  from  which  the  reproductive 
gland  develops.  In  the  free  edge  of  the  peritoneum  enclosing  it  two  ducts  occur,  the  Wolffian 
duct,  which  is  the  duct  of  the  excretory  organ  and  becomes  the  ductus  deferens  of  the  male, 
and  the  Miillerian  duct.  With  the  progress  of  development  the  two  MuUerian  ducts  fuse  in 
the  lower  portions  of  their  course  to  form  the  uterus  and  vagina  (prostatic  utriculus  of  the  male), 
while  in  their  upper  parts  they  remain  separate  and  form  the  tubs  uterinae.  By  this  fusion 
the  two  peritoneal  folds  are  brought  into  continuity  at  their  edges,  and  (the  mesonephros  de- 
generating on  the  formation  of  the  permanent  kidney)  constitute  the  broad  ligament  (fig. 
1028  B).  This  structure  therefore  contains  between  its  two  layers  the  uterus  and  the  remains 
of  the  mesonephros,  and  has  the  ovary  attached  to  its  posterior  surface.  In  the  male  what 
corresponds  to  the  broad  hgament  fuses  with  the  peritoneum  covering  the  posterior  surface  of 
the  bladder. 


i 

( 


1268 


UROGENITAL  SYSTEM 


1.  The  Ovaries 

Form  and  position. — The  ovarie,s  [ovaria]  are  two  whitish  organs,  situated 
one  on  either  side  of  the  pelvic  cavity.  Each  has  somewhat  the  shape  of  an 
almond  (fig.  1026).  It  is  attached  by  one  of  its  edges  [margo  mesovaricus]  to 
the  border  of  the  mesovarium,  and  since  it  is  along  this  line  of  attachment  that 
the  vascular  and  nerve  supply  enters  the  substance  of  the  organ,  this  border  is 
spoken  of  as  the  hilus  [hilus  ovarii].  The  opposite  border  is  free  [margo  liber]. 
The  larger  rounded  end  is  directed  toward  the  free  extremity  of  the  tuba  uterina 
and  hence  is  known  as  the  tubal  extremity  [extremitas  tubaria],  while  the  other, 
the  uterine  extremity  [extremitas  uterina],  is  directed  toward  the  uterus;  the  two 
surfaces,  owing  to  their  topographic  relations,  are  known  as  the  lateral  and  medial 
surfaces  [facies  mediahs  et  lateralis]. 


Fig.  1029. — The  Female  Pelvic  Organs  Viewed  from  Above.     (Spalteholz.) 

Sigmoid  colon 

'  ~  Recto-uterine  pouch 


Rectum 
Ureter  \. 


;-fflffs?r 


Recto-uterine  fold 

/ 

Parietal  peri- 
/  .  /      toneum 

/         Ureter 
'       •/ 

Suspensory 
/  ligament  of 
/     ovary 


!    Ampulla 

of  tuba 

/  uterina 


^  ^i  Isthmus 
of  tuba 
uterina 

^Ligamen- 
tum  teres 


Transverse  vesical  fold 


The  exact  position  of  the  ovary  in  the  pelvis  is  subject  to  some  variation,  but 
typically  it  hes  almost  in  a  sagittal  plane  (fig.  1029)  against  the  lateral  wall  of  the 
pelvis,  resting  in  a  distinct  depression,  the /ossa  ovarica,  lined  by  peritoneum  and 
bounded  above  by  the  external  iliac  vessels  and  behind  by  the  ureter  and  uterine 
artery,  while  beneath  its  floor  are  the  obturator  vessels  and  nerve.  The  long  axis 
of  the  ovary  is  almost  vertical  when  the  body  is  erect,  the  tubal  pole  being  upward; 
the  mesovarial  border  is  directed  forward  and  laterally,  its  free  border  dorsally 
and  medially  while  its  surfaces  look  almost  laterally  and  medially. 

Frequently,  however,  the  uterus  is  displaced  to  one  side,  dragging  the  uterine  extremity 
of  the  opposite  ovary  (by  the  attachment  of  the  ovarian  ligament)  toward  the  mid-plane.  The 
long  axis  of  the  ovary  thus  becomes  oblique,  approaching  more  or  less  the  horizontal.  The  as- 
cending portion  of  the  tuba  uterina  rests  upon  its  mesovarial  border  and  the  fimbriated  mouth 


THE  UTERINE  TUBES  1269 

of  the  tube  is  in  contact  with  its  medial  surface.  When  enlarged  the  ovary  may  be  felt  through 
lateral  wall  of  the  vagina  and,  better,  through  that  of  the  rectum;  and  its  position  with  regard 
to  the  surface  may  be  indicated  by  a  point  midway  between  the  anterior  superior  spine  of  the 
ilium  and  the  symphysis  pubis  or  the  opposite  pubic  tubercle. 

The  position  assumed  by  the  ovary  is  due  to  its  attachment  to  the  edge  of 
the  mesovarium  and  to  the  upper  portion  of  the  broad  hgament  being  broader 
than  the  diameter  of  the  pelvis,  so  that  it  is  folded  back  upon  the  lateral  walls  of 
the  cavity.  In  addition  to  its  attachment  to  the  broad  hgament  through  the 
mesovarium,  the  ovary  is  also  connected  to  the  side  of  the  uterus  by  the  ovarian 
ligament  [hg.  ovarii  proprium]  (fig.  1026),  a' band  of  connective  tissue  with  which 
numerous  non-striped  muscle  fibres  are  intermingled.  It  lies  between  the  two 
layers  of  the  broad  hgament,  on  the  boundary  line  between  the  mesosalpinx  and 
the  mesometrium,  and  extends  from  the  uterine  pole  of  the  ovary  to  the  side  of  the 
uterus.  Here  it  is  attached  just  below  the  origin  of  the  tuba  uterina  and  above 
the  point  of  attachment  of  the  round  hgament  of  the  uterus,  with  which  it  is 
primarily  continuous.  Another  Hgament,  termed  the  suspensory  ligament  of  the 
ovary  (figs.  1029,  1034),  extends  laterally  between  the  two  layers  of  the  broad 
hgament  from  the  tubal  extremity  of  the  ovary  to  the  pelvic  walls,  forming  the 
lateral  portion  of  the  lower  boundary  of  the  mesosalpinx.  It  is  formed  by  the 
vessels  and  nerves  (internal  spermatic)  passing  to  and  from  the  ovary,  and  from 
the  point  where  it  meets  the  lateral  pelvic  wall  it  may  be  traced  upward  for  some 
distance  upon  the  posterior  wall  of  the  abdomen,  behind  the  peritoneum,  which  it 
elevates  into  a  more  or  less  distinct  fold,  whose  lateral  wall  on  the  right  side 
becomes  continuous  above  with  the  peritoneum  lining  the  subccecal  fossa. 

Size. — The  size  of  the  ovary  varies  considerably,  that  of  the  right  side  being  as  a  rule 
somewhat  larger  than  that  of  the  left.  The  length  may  be  anywhere  from  2.5  cm.  to  5.0  cm.,  the 
breadth  about  half  the  length  and  the  thickness  half  the  breadth.  Its  average  weight  in  the 
adult  is  from  6.0  to  8.0  grms.,  but  in  old  age  it  may  fall  to  2.0  grms. 

Structure. — The  ovary  is  covered  by  a  layer  of  columnar  epithehum  which  is  continuous 
with  the  peritoneal  epithelium  along  the  line  of  the  attachment  of  the  mesovarium;  the  ovary 
consequently  is  not  covered  by  peritoneum,  but  is  rather  to  be  regarded  as  a  local  thickening 
of  the  peritoneum.  Its  substance  is  a  network  of  connective  tissue,  in  which  non-striped 
muscle  fibres  also  occur,  and  is  known  as  the  stroma.  The  more  central  portions  of  this  are 
largely  occupied  by  blood-vessels  but  in  the  cortical  portions  are  multitudes  of  immature  ova, 
surrounded  by  their  follicle  cells  [follicuU  oophori  primarii];  and  also  numbers  of  cavities  of 
various  sizes,  lined  with  foUicle  cells  and  filled  with  fluid,  each  containing  an  ovum  [ovulumj 
in  a  more  or  less  advanced  stage  toward  maturity.  These  are  the  Graafian  follicles  [follicuU 
oophori  vesiculosi  (Graafi)],  and  as  they  ripen  they  increase  in  diameter  and  approach  the 
surface,  upon  which  they  may  form  marked  prominences.  When  mature  the  follicles  burst, 
allowing  the  escape  of  the  ovum,  scars  being  thus  formed  upon  the  surface  of  the  ovary  that  are 
known  as  corpora  albicantia.  If,  however,  the  ovum  becomes  fertilized  and  pregnancy  results 
the  walls  of  the  follicle  undergo  a  remarkable  development,  forming  what  is  known  as  a  corpus 
luteum. 

Epoophoron  and  paroophoron. — Closely  associated  with  the  ovaries  are  two  rudimentary 
organs  situated  between  the  layers  of  the  mesosalpinx  and  representing  remains  of  the  meso- 
nephros  of  the  embryo.  The  larger  of  these  is  the  epoophoron  (fig.  1030).  It  consists  of  a  longi- 
tudinal duct  [ductus  epoophori  longitudinalis  (Gartneri)],  lying  parallel  with  the  tuba  uterina 
and  closed  at  either  extremity,  and  10-15  transverse  ducts  [ductuli  transversi],  which  open 
into  the  longitudinal  duct.  It  is  the  remains  of  the  upper  or  reproductive  portion  of  the  meso- 
nephros  and  therefore  is  the  homologue  of  the  epididymis  of  the  male.  In  addition  there  is  fre- 
quently to  be  found  in  the  neighbourhood  of  the  epoophoron  and  close  to  the  mouth  of  the  tuba 
uterina  one  or  more  stalked,  oval  cysts,  the  appendices  vesiculosi  {hydatids  of  Morgagni),  which 
may  reach  the  size  of  a  small  pea. 

The  other  organ  is  the  parobphoron;  it  is  much  smaller  than  the  epoophoron  and  usually 
disappears  before  adult  life,  but  when  present  consists  of  a  small  group  of  coiled  tubules,  more 
or  less  distinct,  representing  a  portion  of  the  excretory  portion  of  the  mesonephros.  Its  equiva- 
lent in  the  male  is  therefore  the  paradidymis. 

Vessels  and  nerves. — The  chief  artery  is  the  ovarian,  which  together  with  the  ovarian  veins 
and  lymphatics  passes  to  the  ovary  in  the  suspensory  ligament.  An  additional  blood  supply 
is  furnished  by  the  ovarian  branch  of  the  uterme  artery.  The  veins  follow  the  course  of  the 
arteries.  As  they  emerge  from  the  hilus  they  form  a  weU-developed  plexus  (pampiniform 
plexus)  between  the  laj'ers  of  the  mesovarium.  Unstriped  muscle  fibres  occur  in  the  meshes 
of  the  plexus  and  the  whole  structure  has  much  the  appearance  of  erectile  tissue.  The  lym- 
phatics accompany  the  blood-vessels  and  terminate  in  the  lumbar  nodes.  Nerves  pass  to  the 
ovary  with  the  ovarian  artery  from  the  renal  and  aortic  sympathetic  plexus. 

2.  The  Titb^  Uterine 

The  tubae  uterinse  or  Fallopian  tubes  (figs.  1026,  1030)  serve  to  convey  the 
ova  to  the  uterus.     They  are  two  trumpet-shaped  tubes,  structurally  continuous 


1270 


UROGENITAL  SYSTEM 


with  the  superior  angles  of  the  uterus  and  running  in  the  superior  border  of  the 
broad  hgament  (mesosalpinx)  to  come  into  relation  with  the  ovaries  at  their 
distal  extremities.  Each  tube  opens  proximally  into  the  uterine  cavity  and  dis- 
tally  communicates  witli  the  pelvic  portion  of  the  peritoneal  cavity  by  a  funnel- 
shaped  mouth,  the  ostium  abdominale,  which  under  normal  conditions  is  closely 
applied  to  the  surface  of  the  ovary,  so  as  to  receive  the  ova  as  they  are  expelled 
from  the  Graafian  follicles.  Each  tube  is  from  7  to  14  cm.  in  length  and  con- 
sists of  a  narrow  straight  portion,  the  isthmus,  immediately  adjoining  the  uterus, 
followed  by  a  broader,  more  or  less  flexuous  portion,  the  mnpulla,  which  terminates 
in  a  funnel-like  dilatation,  the  infundibulum.  The  margins  of  the  infundibulum 
are  fringed  by  numerous  diverging  processes,  the  fimbria,  one  of  which,  the 
fimbria  ovarica,  is  much  longer  than  the  rest  and  extends  along  the  free  border  of 
the  mesosalpinx  (the  infundibulo-pelvic  ligament)  to  reach  the  tubal  pole  of  the 
ovary. 

The  course  of  each  tube  is  at  first  almost  horizontally  laterally  and  backward 
from  its  attachment  to  the  uterus,  until  it  reaches  the  lateral  wall  of  the  pelvis 
and  there  comes  into  relation  with  the  uterine  extremity  of  the  ovary  (figs. 
1029,  1034).     It  then  bends  at  right  angles  and  passes  almost  vertically  upward 


1030. — The   Broad  Ligament  and  its   Contents,   seen  prom  the  Front. 
(After  Sappey.) 
EpoCphoron 


Ampulla  of  Fallopian  tube 


Tuba  uterina 

External  angle  of  uterus 


Fimbriated  extremity  of  tube 

Fimbria  ovarica 


Round  ligament 
Ovarian  ligament 


Anterior  peritoneal  lamina 


along  the  mesovarial  border  of  the  ovary  until  it  reaches  its  tubal  extremity, 
where  it  curves  downward  and  backward  so  that  the  mouth  of  the  infundibulum 
and  the  fimbriae  rest  upon  the  medial  surface  of  the  ovary. 

Structure. — The  tubas  occupy  the  upper  free  edge  of  the  mesosalpinx  and  are  therefore 
enclosed  within  a  peritoneal  covering  [tunica  serosa]  except  a  small  strip  along  their  lower  surface 
(fig.  1027),  and  hence  a  rupture  of  one  of  them  may  lead  to  the  escape  of  its  contents  either 
into  the  peritoneal  cavity  or  into  the  subserous  areolar  tissue  between  the  two  laj'ers  of  the  broad 
ligament.  At  the  margins  of  the  infundibulum  and  the  borders  of  its  fimbrite  the  peritoneal 
epithelium  becomes  directly  continuous  with  the  mucous  membrane  lining  the  interior  of 
the  tube.  The  subserous  areolar  tissue  [tunica  adventitial  in  the  immediate  vicinity  of  the  tube 
is  lax  and  contains  the  blood-vessels  and  nerves  by  which  the  tube  is  supplied;  it  forms  a  loose 
connection  between  the  peritoneum  and  the  muscular  wall  [timica  muscularis]  of  the  tube.  This 
consists  of  two  layers  of  non-striped  muscle  fibres,  an  outer  longitudinal  and  an  inner  circular 
one,  and  reaches  its  greatest  development  toward  the  uterine  end  of  the  tube.  The  inner 
layer  [tunica  mucosa]  of  the  tube  is  hned  by  a  columnar  cihated  epithelium  which  is  raised  into 
numerous  folds,  simple  in  the  region  of  the  isthmus,  but  becoming  higher  and  more  complex 
in  the  ampulla,  where,  in  transverse  sections,  the  lumen  seems  to  have  a  lab3Tinthine  form. 
The  beat  of  the  cilia  is  toward  the  uterus. 

Vessels  and  nerves. — The  arteries  of  the  tubaj  are  derived  from  the  ovarian  and  uterine, 
each  of  which  gives  off  a  tubal  branch,  which  pass  between  the  two  layers  of  the  mesosalpinx, 
the  one  medially  and  the  other  laterally,  and  anastomose  to  form  a  single  stem.  The  veins 
accompany  the  arteries.  The  lymphatics  accompany  those  from  the  ovary  and  fundus  uteri  and 
terminate  chiefly  in  the  lumbar  nodes.  The  nerves  of  the  ampuUa  are  given  off  from  the 
branches  passing  to  the  ovary,  while  those  of  the  isthmus  come  from  the  uterine  branches. 


THE  UTERUS 


1271 


3.  The  Uterus 

The  uterus  (fig.  1031)  is  an  unpaired  organ,  situated  between  the  two  layers  of 
the  broad  ligament  and  communicating  above  with  the  tubse  uterinse  and  below 
with  the  vagina.  It  is  pyriform  in  outhne,  although  flattened  antero-posteriorly 
(fig.  1032)  and  it  is  divided  into  two  main  portions,  the  body  [corpus  uteri]  and  the 
cervix  by  a  transverse  constriction,  the  isthmus. 

The  body  is  the  portion  above  the  isthmus  and  in  adults,  especially  in  women 

Fig.   1031. — The  Posterior  Surface  of  the  Uterus.     (After  Sappey.) 

---.__  — Tuba  uterina 


Supra-vaginal  cervix 


External  orifice 
Vaginal  wall 


\  \     ^Edge  of  peritoneum 


Cervical  attaciiment  of  vagina 


who  have  borne  children,  is  much  larger  than  the  cervix,  although  the  reverse  is 
the  case  in  children.  In  young  girls  the  two  parts  are  about  equal  in  size.  The 
anterior  or  vesical  surface  [fades  vesicalis]  is  almost  flat  (fig.  1032),  while  the  pos- 
terior or  intestinal  surface  [facies  intestinalis]  is  distinctly  convex,  the  two 
surfaces  meeting  in  well-marked  rounded  borders,  at  the  upper  extremities  of 
which  the  tubas  uterinse  are  attached.  The  superior  border  which  extends  be- 
tween the  points  of  attachment  of  the  two  tubse  is  thick  and  rounded  and  forms 

Fig.   1032. — -Sagittal  Section  op  the  Virgin  Uterus.     (After  Sappey.) 

'A 


Internal  orifice 


Canal  of  cervix 

Posterior  fornix 

Posterior  lip 


Reflection  of  peritoneun 


Anterior  lip 
Anterior  forni: 


External  orifice 


what  is  termed  the  fundus  uteri.  The  cavity  [cavum  uteri]  of  the  body  is  reduced 
to  a  fissure  by  the  antero-posterior  flattening  of  the  walls  and  has  a  triangular  form 
(fig.  1033),  broad  above  where  it  communicates  on  either  side  with  the  cavity  of  a 
tuba  uterina  and  narrow  below  where  it  communicates  with  the  cavity  of  the 
cervix,  this  communication,  which  corresponds  in  position  with  the  isthmus,  form- 
ing what  is  known  as  the  internal  orifice  [orificium  internum]  (internal  os  uteri). 
The  cervix  is  more  cj'lindrical  in  form,  though  slightly  expanded  in  the  middle 


1272 


UROGENITAL  SYSTEM 


of  its  length,  and  is  divided  into  a  suTpravaginal  [portio  supravaginalis]  and  a 
vaginal  -portion  [portio  vaginalis]  by  the  attachment  to  it  of  the  vagina  (fig.  1031). 
The  line  of  this  attachment  is  obhque,  about  one-third  of  the  anterior  surface  of 
the  cervix  and  about  one-half  of  the  posterior  surface  belonging  to  the  vaginal 
portion.  At  the  lower  extremity  of  the  cervix  is  the  external  orifice  [orificium 
externum]  (external  os  uteri),  which  is  round  or  oval  before  parturition  has  taken 
place  and  is  bounded  by  two  prominent  labia,  anterior  and  posterior,  the  anterior 
one  [labium  anterius]  being  shorter  and  thicker  than  the  posterior  [labium  pos- 
terius]  and  reaching  a  lower  level  (fig.  1032).  In  women  who  have  borne  children 
the  external  orifice  assumes  a  more  slit-like  form  and  the  labia  become  notched 
and  irregular.  The  cavity  of  the  cervix,  known  as  the  canal  of  the  cervix  [canaHs 
cervicis],  is  fusiform  in  shape,  and  extends  from  the  internal  to  the  external 
orifice.  On  its  anterior  and  posterior  walls  are  folds  known  as  the  plicce  palmatce 
(fig.  1033),  consisting  of  a  median  longitudinal  ridge  from  which  shorter  elevations 
extend  laterally  and  slightly  upward;  these  are  most  distinct  in  young  individuals 
and  are  apt  to  become  obliterated  by  parturition. 


Fig.   1033. — Frontal  Section  of  the  Vihgin  Uterus.     (After  Sappey.) 


Uterine  wall 
Cavity  of  body 


Internal  orifice 


Uterine  wall 
:  with  plicEe  palmatse 


External  orifice 
Vaginal  wall 


Position  and  relations. — The  direction  of  the  axis  of  the  uterus  is  apparently 
variable  within  considerable  limits,  not  only  in  different  individuals,  but  also  in 
any  one  individual  in  correspondence  with  the  degree  of  distention  of  the  bladder 
anteriorly  and  the  rectum  posteriorly.  In  what  may  be  regarded  as  the  typical 
condition  (fig.  1034)  the  external  orifice  lies  at  about  the  level  of  the  upper  border 
of  the  symphysis  pubis  and  in  the  plane  of  the  spines  of  the  ischia.  From  this 
point  the  axis  of  the  cervix  is  directed  upward  and  slightly  forward,  the  lower 
level  of  the  anterior  labium  being  thus  brought  about.  The  entire  uterus  is, 
accordingly,  anteverted,  and,  furthermore,  the  body  is  bent  forward  (anteflexed) 
upon  the  cervix  at  the  isthmus,  the  axis  of  the  two  portions  making  an  angle, 
open  anteriorly,  of  from  70°  to  100°.  Frequently,  also,  the  body  is  sHghtly  in- 
clined either  to  the  right  or  to  the  left. 

The  anterior  surface  of  the  uterus  rests  upon  the  upper  and  posterior  surfaces  of  the  bladder 
(fig.  1029),  from  which  the  body  is  separated  by  the  utero-vesical  pouch  of  peritoneum.  The 
anterior  layer  of  the  broad  ligament  as  it  passes  over  the  anterior  surface  of  the  uterus  forms 
the  posterior  wall  of  this  pouch  and  is  reflected  forward  to  the  superior  surface  of  the  bladder 
at  about  the  level  of  the  isthmus  (fig.  1034),  so  that  the  whole  of  the  anterior  wall  of  the  cervix 
is  below  the  floor  of  the  pouch  and  is  separated  from  the  posterior  surface  of  the  bladder  only 
by  connective  tissue.  Posteriorly,  however,  the  peritoneal  covering  of  the  uterus,  which  here 
forms  the  anterior  wall  of  the  recto-uterine  pouch,  e.xtends  down  as  far  as  the  uppermost 
portion  of  the  vagina  and  consequently  invests  the  entire  surface  of  the  uterus,  whose  convex 
posterior  wall  is  thus  separated  from  the  rectum  by  the  recto-uterine  pouch  (figs.  1029,  1035). 
Coils  of  the  small  intestine  rest  upon  the  posterior  surface  of  the  body  and  may  also  be  inter- 
posed between  the  cervix  and  the  rectum.  An  important  relation  is  that  of  the  ureters  to  the 
cervix,  these  ducts,  as  they  pass  to  the  bladder,  running  parallel  with  the  cervix  at  a  distance 
of  from  8  to  12  mm.  from  it. 

Ligaments. — The  broad  ligament  between  whose  layers  the  uterus  is  situated 
has  already  been  described  (p.  1267).     In  addition  there  is  attached  to  each  border 


THE  UTERUS 


1273 


Fig.  1034 — Mid-sagittal  Section  of  the  Female  Pelvis     (Spalteholz.) 

Hypogastric  artery 
,  Hypogastric  vein 
Promontory       /      /  Infundibulum  of  tuba  uterina 
Ureter 


Parietal  pentoneum 


Suspensory  ligament  of  ovary 

External  iliac  vein 
Ovary 


Ampulla  of  tuba  utenna 
Ovarian  ligament 
Fundus  uteri       \ 

Ligamentum  teres  \ 

Transverse  fold  of      \        \ 
bladder  >.        \ 

Vertex  of  bladder  v       \       \ 
Middle  umbilical      \      \ 
ligament 


Recto-uterine  fold 


Urach 
Symphysis  pubis 

Labium  maju 
Body  of  uterus 
Labium  minus 


External  orifice  of  urethra    / 
Urethra 
Internal  orifice  of  urethra 

Orifice  of  vagina 


Rectum 
Posterior  labii 
External  orifice  of  uterus 
Anterior  labium 


Hymen 


Anus 
Vagina 
Vesico-uterine  pouch 
Vestibule 
Fig.   1035. — Section  of  the  Pelvis  showing  the  Ligaments  of  the  Uterus. 


Symphysis 
Prevesical  fat 
Bladder-waU 


Obturator  inter nus 
Obturator  fascia 

Subperitoneal  tissue 
Broad  ligament 

Peritoneum 

Sacro-tuberous 
ligament 


Utero-sacral  ligament 
running  forward  into 
recto-uterine  Ugament 


Vesical  cavity 


Peritoneum  of  utero- 

vesical  pouch 
Utero-vesical  ligament 


Broad  ligament 


Recto-uterine  pouch 
of  Douglas 


'^^5o     ]  ^^^^®^® 


1274  UROGENITAL  SYSTEM 

of  the  uterus,  immediately  below  the  point  of  attachment  of  the  ovarian  ligament, 
the  ligamentum  teres  (round  ligament)  (fig.  1030),  which  is  a  fibrous  cord  con- 
taioing  non-striped  muscle  tissue.  It  extends  downward,  laterally  and  forward 
between  the  two  layers  of  the  mesometrium  toward  the  abdominal  inguinal  ring, 
and,  traversing  this  and  the  inguinal  canal,  it  terminates  in  the  labium  majus  by 
becoming  continuous  with  its  connective  tissue. 

It  is  accompanied  by  a  funicular  branch  of  the  ovarian  artery  and  a  branch  from  the  ovarian 
venous  plexus,  and  in  the  lower  part  of  its  course  by  a  branch  from  the  inferior  epigastric  artery, 
over  which  it  passes  as  it  enters  the  abdominal  ring.  In  its  course  through  the  inguinal  canal 
it  is  accompanied  by  the  iho-inguinal  nerve  and  the  external  spermatic  branch  of  the  genito- 
femoral. 

The  utero-sacral  ligaments  are  flat  fibro-muscular  bands  which  extend,  one  on 
each  side,  from  the  upper  part  of  the  cervix  uteri  to  the  sides  of  the  sacrum  op- 
posite the  lower  border  of  the  sacro-iliac  articulation.  They  produce  the  recto- 
uterine folds  (fig.  1029)  of  peritoneum,  which  form  the  lateral  boundaries  of  the 
mouth  of  the  recto-uterine  pouch  (of  Douglas)  and  their  muscle  fibres  [m.  rec- 
touterinus]  are  continuous  at  one  extremity  with  the  muscular  tissue  of  the 
uterus  and  at  the  other  with  that  of  the  rectum. 

Structure. — The  portion  of  the  broad  ligament  that  invests  the  uterus  forms  the  serous 
covering  [tunica  serosa]  of  the  organ  and  is  sometimes  termed  the  perimetrium.  Over  the  fundus 
and  the  greater  portion  of  the  body  it  is  thin  and  firmly  adherent  to  the  subjacent  muscular 
substance  of  the  uterus,  so  that  it  cannot  readily  be  separated  from  it.  Over  the  posterior 
surface  of  the  cervix  and  the  lower  part  of  the  anterior  surface  of  the  body,  however,  it  is  thicker, 
and  is  separated  from  the  muscular  substance  by  a  layer  of  loose  connective  tissue,  the  para- 
metrium, which  also  extends  upward  along  the  sides  of  the  uterus  between  the  two  layers  of  the 
broad  hgament,  with  whose  subserous  areolar  tissue  it  is  continuous.  Owing  to  this  disposition 
of  the  parametrium  the  whole  of  the  cervix  may  be  amputated  without  encroaching  upon  the 
peritoneal  cavity. 

The  main  mass  of  the  uterus  is  formed  by  the  muscle  tissue  [tunica  muscularis]  or  myome- 
trium, whose  fibres  have  a  very  complicated  arrangement.  Two  principal  layers  may  be 
distinguished,  an  outer,  wealv  one,  composed  partly  of  longitudinal  fibres  continuous  with  those 
of  the  tub®  uterinje,  and  of  the  round  and  utero-sacral  hgaments,  and  a  much  stronger  inner 
one,  whose  fibres  run  in  various  du-ections  and  have  intermingled  with  them  in  the  body  of  the 
uterus  large  venous  plexuses.  The  inner  surface  of  the  myometrium  is  hned  by  a  mucous 
membrane  [tunica  mucosa]  or  endometrium,  which  has  a  thickness  of  from  0.5  to  1.0  mm.  and 
is  composed  of  tissue  resembling  embryonic  connective  tissue,  bearing  upon  its  free  surface  a 
single  layer  of  cihated  columnar  epithelium.  On  account  of  its  structure  the  tissue  is  rather 
delicate  and  friable,  and  numerous  simple  tubular  glands,  which  open  into  the  cavity  of  the 
uterus,  traverse  its  entire  thickness.  In  the  cervix  the  mouths  of  some  of  the  glands  may 
become  occluded,  produci^g  retention  cysts,  which  appear  as  minute  vesicles  projecting  from 
the  surface  between  the  plicse  palmatae;  they  are  known  as  ovula  Nabothi,  after  the  anatomist 
who  first  described  them. 

Vessels  and  nerves. — The  principal  artery  of  the  uterus  is  the  uterine,  whose  terminal 
portion  ascends  along  the  lateral  border  of  the  uterus  in  a  tortuous  course  through  the  para- 
metrium, giving  off  as  it  goes  lateral  branches  to  both  surfaces  of  the  uterus.  Above,  it  anasto- 
moses with  the  ovarian  artery,  which  thus  forms  an  accessory  source  of  blood  supply  during 
pregnancy.  The  veins  form  a  plexus  that  is  drained  by  the  ovarian  and  uterine  veins,  a  com- 
munication with  the  inferior  epigastric  being  also  made  by  way  of  the  vein  accompanying  the 
round  ligament.  The  lymphatics  from  the  greater  portion  of  the  body  pass  to  the  iliac 
nodes:  those  of  the  fundus  accompany  the  ovarian  vessels  to  the  lumbar  nodes.  A  vessel  also 
accompanies  the  round  hgament  to  terminate  in  one  of  the  superficial  inguinal  nodes.  The 
lymph-vessels  from  the  cervix  terminate  in  the  external  iliac,  hypogastric  and  lateral 
sacral  nodes. 

The  nerves  of  the  uterus  pass  to  it  from  two  sympathetic  gangha,  situated  one  on  either 
side  of  the  cervix,  whence  they  are  termed  the  cervical  gangha,  and  forming  part  of  the  plexus 
utero-vaginalis.  Branches  pass  to  the  ganglia  from  the  hypogastric  plexus  and  also  from  the 
second,  third  and  fourth  sacral  nerves. 

4.  The  Vagina 

The  vagina  (fig.  1034)  is  a  muscular,  highly  dilatable  canal  lined  by  mucous 
membrane,  and  extends  from  the  uterus  to  the  external  genitaUa,  where  it  opens 
to  the  exterior.  Its  long  axis  is  practically  parallel  with  that  of  the  lower  part 
of  the  sacrum  and  it  therefore  meets  the  cervix  uteri  at  a  wide  angle  which  is 
open  anteriorly.  Its  anterior  wall  is,  accordingly,  somewhat  shorter  than  the 
posterior,  measuring  6.0-7.0  cm.,  while  the  posterior  one  is  about  1.5  cm.  longer. 
It  becomes  continuous  with  the  cervix  uteri  some  distance  above  the  lower 
extremity  of  that  structure,  which  thus  projects  into  the  lumen  of  the  vagina,  and 
there  is  so  formed  a  narrow  circular  space  between  the  wall  of  the  vagina  and 


THE  VAGINA 


1275 


the  vaginal  portion  of  the  cervix  uteri.  The  roof  of  the  space  is  formed  by  the 
reflection  of  the  vagina  upon  the  cervix  and  is  termed  the  fornix.  Owing  to  the 
greater  length  of  the  posterior  wall  of  the  vagina  the  portion  of  the  circular  space 
below  the  posterior  fornix  is  considerably  deeper  than  that  below  the  anterior. 

In  its  ordinary  condition  the  lumen  of  the  vaginal  canal  is  a  fissure,  which  in 
transverse  section  resembles  the  form  of  the  letter  H  with  a  rather  long  trans- 
verse bar  (fig.  1036).  On  both  the  anterior  and  the  posterior  wall  there  is  in  the 
median  line  a  well-marked  longitudinal  ridge,  the  columna  rugarum,  which  is 
especially  distinct  in  the  lower  part  of  the  anterior  wall,  where  it  lies  immediately 
beneath  the  urethra  and  forms  what  is  known  as  the  urethral  carina.  From  both 
columnse  other  ridges  pass  laterally  and  upward  on  either  side,  forming  the 
rugw  vaginales.  Both  these  and  the  columnee  diminish  in  distinctness  with  ad- 
vance in  age  and  with  successive  parturitions.  Toward  its  lower  end  the  vagina 
traverses  the  urogenital  trigone,  being  much  less  dilatable  in  this  region  than 
elsewhere,  and  it  opens  below  into  the  vestibule  of  the  external  genitalia.  Its 
orifice  is  partially  closed  by  a  fold  of  connective  tissue,  rich  in  blood-vessels,  and 
lined  on  both  surfaces  by  mucous  membrane.     This  membrane,  known  as  the 

Fig.  1036. — Horizontal   Section  of  Vagina  and  adjacent  Structures.     (After  Henle.) 


hymen,  has  usually  a  somewhat  semilunar  form,  surrounding  the  posterior  border 
of  the  orifice,  but  it  may  take  the  form  of  a  circular  curtain  pierced  by  one  or  several 
apertures. 

It  varies  greatly  in  strength  and  development  and  although  it  is  nearly  always  ruptured 
by  the  first  act  of  sexual  congress,  it  may  remain  unbroken  until  parturition.  Rarely  it  takes 
the  form  of  a  complete  imperforate  curtain  and  may  necessitate  a  surgical  operation  at  the 
commencement  of  the  menstrual  periods.  After  rupture  the  remains  of  the  hymen  persist  as 
small  lobed  or  wart-like  structures,  the  carunculoe  hymenales,  around  the  vaginal  orifice. 

Relations. — The  uppermost  part  of  the  posterior  wall  of  the  vagina  is  in 
relation  with  the  peritoneum  forming  the  floor  of  the  recto-uterine  pouch  (of 
Douglas),  but  elsewhere  the  canal  is  entirely  below  the  floor  of  the  peritoneal 
cavity.  Posteriorly  it  rests  almost  directly  upon  the  rectum  (flg.  1036),  and  the 
contents  of  that  viscus  may  be  readily  felt  through  its  walls.  Anteriorly  it  is  in 
intimate  relation  with  the  urethra  and  the  posterior  wall  of  the  bladder  (figs. 
1034,  1036),  while  laterally  it  is  crossed  obliquely  in  its  upper  third  by  the  ureters 
as  they  pass  to  the  base  of  the  bladder,  and  in  its  lower  two-thirds  by  the  edges  of 
the  anterior  portion  of  the  levatores  ani.  The  duct  of  Gartner,  the  remains  of  the 
lower  portion  of  the  Wolffian  duct,  may  occasionally  be  found  at  the  side  of  the 


1276 


UROGENITAL  SYSTEM 


upper  half  of  the  vagina  as  a  minute  tube  or  fibrous  cord.  The  external  orifice 
is  surrounded  by  the  fibres  of  the  bulbo-cavernosus  muscle,  which  may  be  re- 
garded as  forming  a  sphincter  {s-phinder  vagince) . 

Structure. — The  wall  of  the  vagina  is  formed  mainly  of  non-striped  muscle  tissue,  whose 
fibres  are  indistinctly  arranged  in  two  layers,  an  outer  longitudinal  and  a  less  distinct  inner 
circular  one.  Above,  this  tissue  is  continuous  with  that  of  the  cervix  uteri,  as  is  also  the  mucous 
membrane  which  lines  the  lumen.  This  differs  from  that  of  the  cervix  in  having  a  stratified 
squamous  epithelium  and  in  being  destitute  of  glands. 

Vessels  and  nerves. — The  arteries  of  the  upper  part  of  the  vagina  are  derived  from  the 
vaginal  branch  of  the  uterine;  its  middle  portion  is  supplied  by  a  vaginal  branch  from  the 
inferior  vesical  and  its  lower  part  by  the  middle  hssmorrhoidal  and  internal  pudendal.  The 
veins  form  a  rich  plexus  on  the  surface  and  drain  into  the  hypogastric  vein.  The  lymphalics 
are  very  numerous  and  drain  for  the  most  part  to  the  hypogastric  and  lateral  sacral  nodes;  some 
of  those  from  the  lower  portion  of  the  canal  joining  with  those  from  the  external  genitalia  to  pass 
to  the  inguinal  nodes.  The  nerves  passing  to  the  vagina  are  derived  from  the  utero-vaginal  and 
vesical  plexuses. 

5.  The  Female  External  Genitalia  and  Urethra 

The  female  external  genitalia  [pudendum  muliebre]  (vulva)  present  an  elon- 
gated depression,  occupying  the  entire  perineal  region  and  bounded  laterally  by 


Fig.  1037. — The  External  Genitals  op  the  Female. 


Corpus  clitoridis 


Labium  majus 
Labium  minus 


Fossa  navicularis 

— ~  Frenulum  labiorum  pudendi 


Posterior  commissure 


two  folds  of  integument,  the  labia  majora  (fig.  1037).  These  anteriorly  are 
continued  into  the  mojis  pubis,  an  eminence  of  the  integument  over  the  symphysis 
pubis  due  to  a  development  of  adipose  tissue.  The  medial  surfaces  of  the  two 
labia  are  normally  iii  contact,  the  fissure  between  them  being  termed  the  rinia 
pudendi,  and  where  they  meet  anteriorly  and  posteriorly  they  form  the  anterior 
and  posterior  commissures  [commissura  labiorum  anterior  et  posterior].  Just 
anterior  to  the  latter  is  an  inconstant  transverse  fold,  the  frenuhim  labiorum 
pudendi  ("fourchette")  (fig.  1037).  The  mons  and  the  outer  sm-faces  of  the 
labia  are  covered  by  short  crisp  hairs,  but  tlie  medial  surfaces  of  the  labia  are 
smooth,  possessing  only  rudimentary  hairs,  but  beset  with  large  sebaceous  and 
sudoriparous  glands.  The  interior  of  the  labia  is  occupied  by  a  mass  of  fat  tissue 
in  which  the  distal  extremity  of  the  round  ligament  of  the  uterus  breaks  up. 


FEMALE  EXTERNAL  GENITALIA 


1277 


Within  the  depression  bounded  by  the  labia  majora  is  a  second  pair  of  integu- 
mental  folds,  the  labia  yninora  (fig,  1037),  which  difTer  from  the  labia  majora  in 
being  destitute  of  hairs  and  fat.  They  are  usually  concealed  by  the  labia  majora, 
but  are  sometimes  largely  developed  and  may  then  project  through  tlie  rima 
pudendi,  assuming  a  dried  and  pigmented  appearance. 

The  labia  minora  divide  and  unite  anteriorly  over  the  distal  extremity  of  the  clitoris,  form- 
ing the  prcepuiiuni  cliioridis  in  front  of  the  clitoris,  and  the  frenulum  diloridis  behind  it.  Pos- 
terior to  this  they  diverge  and  reach  their  greatest  height,  gradually  diminishing  as  they  pass 
backward  to  terminate  in  a  slight,  inconstant,  transverse  fold,  the  frenulum  labiorum  pudendi, 
situated  just  anterior  to  the  posterior  commissure  of  the  labia  majora.  Anterior  to  the  frenu- 
lum is  the  fossa  navicularis  of  the  vestibule. 

The  vestibule. — The  space  between  the  two  labia  minora  is  termed  the 
vestibule,  and  into  its  most  anterior  portion  there  projects  the  extremity  of  an 
erectile  organ,  the  clitoris  (fig.  1037),  which  is  comparable  to  the  penis  of  the  male. 
It  is,  however,  relatively  small  and  is  not  perforated  by  the  urethra,  which  lies 
below  it.  It  is  composed  of  two  masses  of  erectile  tissue,  the  corpora  cavernosa 
clitoridis,  which  differ  from  the  corresponding  structures  of  the  penis  only  in  size. 
They  are  attached  posteriorl3^  to  the  rami  of  the  pubis  by  the  cr^ira  clitoridis 
(fig.  1038),  and  as  they  pass  forward  they  converge  and  meet  together  to  form  the 
body  of  the  organ,  which,  beneath  the  symphysis  pubis,  bends  sharply  upon  itself 

Fig.  1038. — Diagrammatic  Repkesentation  of  the  Pehin^al  Structures  in  the  Female. 


Glans    clitoridis 

Pars  intermedialls 
Mucous  membrane  of 
vestibule 

Urethral  orifice 


Ischio-pubic  arch 


Bulbo-cave 
covering  bulb' 
vestibuU 


Inferior  layer  of  uro 
genital  trigone 


Bulbus  vestibuli 


Greater  vestibular 
(Bartholin's)  gland 


External  sphincter  < 


and  passes  posteriorly  beneath  the  anterior  commissure  of  the  labia  majora. 
Distally  the  corpora  cavernosa  abut  upon  another  mass  of  erectile  tissue,  which 
fits  hke  a  cap  over  their  extremities;  it  is  formed  by  an  anterior  prolongation  of  the 
bulbi  vestibuli  and  is  termed  the  glans  clitoridis,  being  comparable  to  the  glans 
penis,  from  which  it  differs  only  in  not  being  perforated  by  the  urethra. 

A  short  distance  posterior  to  the  glans  chtoridis  is  the  opening  of  the  urethra 
[orificium  urethrse  externum],  situated  upon  the  summit  of  a  slight  papilla-like 
elevation.  Lateral  to  this  orifice  are  sometimes  found  the  openings,  one  on 
either  side,  of  two  elongated  slender  ducts,  the  'paraurethral  ducts  (ducts  of  Skene). 
Still  more  posteriorly  is  the  external  orifice  of  the  vagina  [orificium  vaginae], 
partially  closed  in  the  virgin  bj^  the  hymen.  Lateral  to  this,  in  the  angles  between 
the  hymen  and  the  labium  minus  on  either  side,  is  the  opening  of  the  greater 
vestibular  gland,  while  the  lesser  glands  open  at  various  points  on  the  floor  of  the 
vestibule,  sometimes  at  the  bottom  of  more  or  less  distinct  depressions. 

Beneath  the  floor  of  the  vestibule  and  resting  upon  the  superficial  layer  of  the 
urogenital  trigone  are  two  oval  masses  of  erectile  tissue,  the  hidbi  vestibuli  (fig. 
1038),  homologous  with  the  corpus  cavernosum  urethriE  of  the  male.  They  con- 
sist principally  of  a  dense  network  of  anastomosing  blood-vessels,  enclosed  within 


1278  UROGENITAL  SYSTEM 

a  thin  investment  of  connective  tissue.  From  the  main  mass  of  each  bulbus  a 
slender  prolongation,  the  pars  intermedia,  extends  anteriorly  past  the  side  of  the 
urethra,  to  form  the  glans  clitoridis. 

The  greater  vestibular  glands  [gl.  vestibularis  major  (Bartholini)]  or  glands  of 
Bartholin  (fig.  1038)  represent  the  bulbo-urethral  glands  of  the  male.  They  are 
two  small,  compound  tubular  glands,  situated  one  on  either  side  immediately 
posterior  to  the  bulbi  vestibuli. 

The  single  duct  of  each  gland  opens  on  the  floor  of  the  vestibule  in  the  angle  between  the 
hymen  and  the  orifice  of  the  vagina  and  a  httle  posterior  to  the  mid-transverse  line  of  the  latter. 
Numerous  small  tubular  glands  occur  in  the  integument  forming  the  floor  of  the  vestibule; 
they  are  termed  the  lesser  vestibular  glands  and  are  especially  developed  in  the  interval  between 
the  urethral  and  vaginal  orifices. 

The  muscles  of  the  female  external  genitalia  (fig.  1038)  correspond  to  the 
perineal  muscles  of  the  male  (see  Section  IV).  There  are  two  transverse  perineal 
muscles,  which  have  the  same  relations  as  in  the  male,  and  two  ischio-cavernosi, 
which  are  related  to  the  crura  clitoridis  just  as  those  of  the  male  are  to  the  crura 
penis.  The  bulbo-cavernosi,  however,  present  somewhat  different  relations,  each 
being  band-like  in  form,  arising  from  the  central  point  of  the  perineum  and  ex- 
tending forward  past  the  orifice  of  the  vagina,  over  the  greater  vestibular  gland 
and  the  bulbus,  to  form  with  its  fellow  of  the  other  side  a  tendinous  investment  of 
the  body  of  the  clitoris.  The  two  muscles  act  as  a  sphincter  to  the  vagina  and 
are  sometimes  termed  the  sphincter  vagince. 

The  urethra. — The  urethra  of  the  female  [urethra  muKebris]  (figs.  1034,  1036) 
corresponds  only  to  the  prostatic  and  membranous  portions  of  the  male  and  is  a 
relatively  short  canal,  measuring  from  3.0  to  4.0  cm.  in  length.  At  its  origin  from 
the  bladder  it  lies  about  opposite  the  middle  of  the  symphysis  pubis  and  thence 
extends  downward  and  slightly  forward  to  open  into  the  vestibule  between  the 
glans  clitoridis  and  the  orifice  of  the  vagina.  Its  posterior  wall  is  closely  united 
with  the  anterior  wall  of  the  vagina,  especially  in  the  lower  part  of  its  course  where 
it  forms  the  urethral  carina  of  the  vaginal  wall;  laterally  and  anteriorly  it  is  sur- 
rounded by  the  pudendal  plexus  of  veins. 

Structure. — Its  walls  are  very  distensible,  and  are  lined  by  a  mucous  membrane  with 
numerous  longitudinal  folds,  one  of  which  on  the  posterior  side  is  more  prominent  and  is 
termed  the  crista  urethralis.  The  mucosa  contains  numerous  small  glands  [gl.  urethrales], 
a  group  of  which  on  each  side  is  drained  by  the  inconstant  ductus  paraurethrahs.  External 
to  the  loose  submucosa  is  a  sheet  of  smooth  muscle,  whose  fibres  are  arranged  in  an  outer 
circular  and  an  inner  longitudinal  layer,  a  rich  plexus  of  veins  lying  between  the  two  and 
giving  the  entire  sheet  a  somewhat  spongy  appearance.  The  circular  fibres  are  especially 
developed  at  the  vesical  end  of  the  canal,  forming  there  a  strong  sphincter,  and  striped  muscle 
fibres,  derived  from  the  bulbo-cavernosus,  form  a  sphincter  around  its  vestibular  orifice.  The 
female  urethra  differs  from  that  of  the  male  in  not  being  enclosed  within  a  prostate  gland;  but 
what  are  probably  rudiments  of  this  structure  are  to  be  found  in  the  groups  of  urethral  glands 
drained  by  the  paraurethral  ducts. 

Vessels  and  nerves. — The  arteries  supplying  the  external  female  genitalia  are  the  internal 
and  external  pudendals,  and  the  veins  terminate  in  corresponding  trunks.  The  lymphatics, 
which  are  very  richly  developed,  drain  for  the  most  part  to  the  inguinal  nodes;  those  from  the 
urethra  pass  to  the  iliac  nodes.  The  nerves  are  partly  sympathetic  and  partly  spinal;  the  former 
are  derived  from  the  hypogastric  plexus,  the  latter  principally  from  the  pudendal,  the  anterior 
portions  of  the  labia  majora  being  supplied  by  the  iUo-inguinal  and  the  external  spermatic 
branch  of  the  genito-femoral. 

DEVELOPMENT  OF  THE  REPRODUCTIVE  ORGANS 

It  has  already  been  pointed  out  (p.  1267)  that  during  development  a  transitory  excretory 
organ,  the  mesonephros  or  WolfEan  body,  reaches  a  high  degree  of  development,  and  its  duct, 
the  Wolffian  duct,  opens  into  a  cloaca  or  common  outlet  for  the  intestinal  and  urinary  passages. 
The  mesonephros  forms  a  strong  projection  from  the  posterior  wall  of  the  abdomen  into  the 
body  cavity,  and  on  the  medial  surface  of  the  peritoneum  which  covers  it  a  thickening  appears 
which  is  termed  the  genital  ridge.  The  upper  part  of  this  ridge  becomes  the  ovary  or  testis, 
as  the  case  may  be,  while  the  remainder  of  it  becomes  the  ovarian  and  round  ligaments  in  the 
female  and  the  gubernaculum  testis  in  the  male. 

As  the  ovary  or  testis  develops  the  tubules  of  the  upper  part  of  the  Wolffian  body  enter 
into  relation  with  it,  forming,  indeed,  in  the  case  of  the  testis,  a  direct  union  with  the  semin- 
ferous  tubules.  The  Wolffian  body  then  becomes  divisible  into  a  reproductive  and  an  excretory 
portion,  and,  when  the  metanephros  or  permanent  kidney  develops,  the  latter  portion  degene- 
rates, leaving  only  a  few  rudiments,  such  as  the  paroophoron  in  the  female  (p.  1269)  and  the  vas 
aberrans  and  paradidymis  (p.  1257)  in  the  male.  The  reproductive  portion  also  becomes  much 
reduced  in  the  female,  persisting  as  the  tubules  of  the  epoophoron  (p.  1269),  but  in  the  male  it 


DEVELOPMENT  OF  THE  REPRODUCTIVE  ORGANS 


1279 


forms  the  lobules  of  the  epididymis  and  serves  to  transmit  the  spermatozoa  to  the  Wolffian 
duct. 

In  addition  to  the  Wolffian  duct,  a  second  duct,  the  Miillerian,  occurs  in  connection  with 
the  genito-urinary  apparatus,  and,  like  the  Wolffian  duct,  it  opens  below  into  the  cloaca.  The 
history  of  the  two  ducts  is  very  different  in  the  two  sexes.  In  the  male  the  Wolffian  duct 
persists  to  form  the  vas  deferens,  of  which  the  seminal  vesicle  is  an  outgrowth  and  the  ejaculatory 
duct  the  continuation,  while  the  MilUerian  duct  degenerates,  its  lower  end  persisting  as  the 
prostatic  utriculus  and  its  upper  end  as  the  appendix  of  the  epididymis.  In  the  female,  on 
the  contrary,  it  is  the  Miillerian  duct  which  persists,  its  lower  portion  fusing  with  the  duct  of 
the  opposite  side  to  form  the  vagina  and  uterus,  while  its  upper  portion  forms  the  tuba 
uterina.  Inhibition  of  the  fusion  of  the  lower  ends  of  the  two  Miillerian  ducts  gives  rise  to  the 
bihorned  or  divided  uteri,  or  the  bilocular  uteri  and  vaginse  which  occasionally  occur.  The 
Wolffian  duct  in  the  female  almost  completely  disappears,  persisting  only  as  the  longitudinal 
tube  of  the  epoophoron  and  as  the  rudimentary  canal  of  Gartner  (p.  1275) .  With  the  degenera- 
tion of  the  mesonephros  the  peritoneum  which  covered  it  becomes  a  thin  fold,  having  in  its 
free  edge  the  Miillerian  duct  and,  on  the  fusion  of  the  lower  ends  of  the  ducts,  the  two  folds  also 
fuse  and  so  give  rise  to  the  broad  hgament. 

Fig.  1039. — Development  of  the  Reproductive  Organs. 
Epoophoron  Wolffian  body  Epididymis 


SinuB 
pocu- 
laris 


INDIFFERENT 


The  developmental  relations  of  the  male  and  female  organs  may  be  seen  from  figure  1039 
and  also  from  the  following  table: — 

Female 

Ovary 
f  Ovarian  ligament 
,  Round  ligament 

Epoophoron 

Paroophoron 

Longitudinal  tubule  of  epoophoron 
Canal  of  Gartner 

Uterine  (Fallopian)  tube 

Uterus 

Vagina 


Genital  ridge 
Wolffian  body 
Wolffian  duct 
Miillerian  duct 


Testis 

Gubernaculum  testis 

Head  of  epididymis 
-j  Paradidymis  1 
I  Vas  aberrans  / 
j  Body  and  tail  of  epididymis 
i  Ductus  deferens 
!  Ejaculatory  duct 
f  Appendix  of  epididymis  (?) 

Prostatic  utriculus 


The  development  of  the  external  organs  of  generation  in  the  two  sexes  presents  a  similar 
differentiation  from  a  common  condition.  The  division  of  the  cloaca  to  form  a  urogenital 
sinus  and  the  terminal  part  of  the  rectum  has  already  been  noted  (p.  1253).  In  the  floor  of  the 
sinus,  to  the  sides  of  and  above  the  urethral  orifice,  erectile  tissue  develops,  forming  a  genital 
tubercle.  An  outpouching  of  that  portion  of  the  anterior  abdominal  wall  to  which  the  round 
ligament  of  the  uterus  or  the  gubernaculum  was  attached  occurs  to  form  the  genital  swellings. 


1280  UROGENITAL  SYSTEM 

lying  one  on  either  side  of  the  sinua,  and  medial  to  these  a  pair  of  folds  develop  at  the  borders 
of  the  sinus,  enclosing  the  genital  tubercle  above  and  forming  the  genital  folds. 

This  condition  practically  represents  the  arrangement  which  persists  to  adult  life  in  the 
female.  The  genital  tubercle  becomes  the  clitoris,  the  genital  swellings  the  labia  raajora,  the 
genital  folds  the  labia  minora,  and  the  urogenital  sinus,  into  which  the  urethra  and  Miillerian 
ducts  (vagina)  open,  is  the  vestibule.  In  the  male  tlie  development  proceeds  farther.  The 
genital  tubercle  elongates  to  form  the  penis,  and  the  free  edges  of  the  genital  folds  meet  together 
and  fuse,  closing  in  the  urogenital  sinus  and  transforming  it  into  the  cavernous  portion  of  the 
urethra,  thus  bringing  it  about  that  the  male  urethra  subserves  both  reproductive  and  urinary 
functions.  The  genital  swellings  also  meet  and  fuse  together  below  the  root  of  the  penis,  form- 
ing the  scrotum. 

The  homologies  of  the  parts  in  the  two  sexes  may  be  seen  from  the  following  table: — 

Male  Female 

Urogenital  sinus         Cavernous  portion  of  urethra  Vestibule 

Genital  tubercle  Penis  Chtoris 

Genital  folds  Integument  and  prepuce  of  penis  Prepuce  of  clitoris  and  labia  minora 

Genital  swellings        Scrotum  Labia  majora 

Inhibition  of  the  development  of  the  parts  in  the  male  or  their  over-development  in  the 
female  will  produce  a  condition  resembling  superficially  the  normal  condition  of  the  opposite 
sex,  and  constituting  what  is  termed  pseudo-hermaproditism;  or  a  failure  of  the  genital  ridges 
to  fuse  may  result  in  what  is  known  as  hypospadias,  the  cavernous  portion  of  the  urethra  being 
merely  a  groove  in  the  under  surface  of  the  otherwise  normal  penis. 

References  for  the  Urogenital  System.  A.  Urinary  tract.  {General,  incl. 
literature  to  1900)  Disse,  in  von  Bardeleben's  Handbuch;  {Renal  blood-vessels) 
Brodel,  Proc.  Ass'n  Amer.  Anatomists,  1901;  {Renal  tubules)  Huber,  Amer. 
Jour.  Anat.,  vol.  4;  Peter,  Die  Nierenkanalchen,  etc.,  Jena,  1909;  {Topog- 
raphy of  female  ureter)  Tandler  u.  Halban,  Monatschr.  Geburtsh.  u.  Gynak., 
Bd.  15.  B.  Male  reproductive  tract.  {General,  incl.  literature  to  1903)  Eberth, 
in  von  Bardeleben's  Handbuch;  {Histology  and  development)  von  Lichtenberg, 
Anat.  Hefte,  Bd.  31;  Hill,  Amer.  Jour.  Anat.,  vol.  9;  {Prostate)  Bruhns 
{lymphatics)  Arch.  f.  Anat.  u.  Entw.,  1904;  Ferguson  {Stroma)  Anat.  Rec,  vol. 
5;  Thompson  (topography)  Jour.  Anat.  and  Physiol.,  vol.  47;  {External 
genitals)  Forster,  Zeitschr.  f.  Morph.  u.  Anthrop.,  Bd.  6.  C.  Female  repro- 
ductive tract.  {General,  incl.  literature  to  1896)  Nagel,  in  von  Bardeleben's 
Handbuch;  Waldeyer,  Das  Becken,  Bonn,  1899;  {Lymphatics)  Bruhns,  Arch, 
f.  Anat.  u.  Entw.,  1898;  Polano  {ovary)  Monatschr.  Geburtsh.  u.  Gynak., 
Bd.  17;  {Nerves)  Roith,  Arch.  f.  Gynak.,  Bd.  81;  {Histology,  ovary)  von 
Winiwarter,  Anat.  Anz.,  Bd.  33;  {Develop?/ient,  uterus)  Hegar,  Beitr.  z.  Geburtsh. 
u.  Gynak.,  Bd.  13;  Stratz,  Zeitschr.  Geburtsh.  u.  Gynak.,  Bd.  72;  {Lig. 
eres)  Sellheim,  Beitr.  z.  Geburtsh.  u.  Gynak.,  Bd.  4,  1901. 


SECTION  XII 

THE   SKIN,   MAMMAEY   GLANDS 
AND  DUCTLESS  GLANDS 


Rewritten  for  the  Fifth  Edition 
By  ABRAM  T.  KERR,  B.S.,  M.D. 


PBOPESSOK    OP   ANATOMY   IN   THE 


UNIVERSITT    MEDICAL'    COLLEGE 


THE  SKIN 


THE  covering  which  envelops  the  whole  external  surface  of  the  body  is 
known  as  the  common  integument  [integumentum  commune].  This  con- 
sists of  the  cutis  or  skin  proper  and  of  appendages,  the  hair,  nails,  and  skin 
glands.  The  cutis  is  composed  of  a  superficial  epithelial  layer,  the  epidermis, 
derived  from  the  ectoderm,  and  a  deep  connective  tissue  layer  developed  from  the 
mesoderm  and  divided  into  a  superficial  part,  the  corium,  and  a  deeper  part  the 
tela  subcutanea  (figs.  1040,  1041).  The  subcutaneous  tela  is  not  usually  con- 
sidered as  a  part  of  the  skin  in  a  restricted  sense,  but  as  a  superficial  fascia,  which 
name  is  often  applied  to  it. 

Fig.  1040. — Magnified  Section  of  the  Thickened  Skin  of  the  Palm  op  the  Hand.      X  6 


Corpus  papillare  , l!^,_^ 


Retinaculum 


Tela  Subcutanea 


The  skin  forms  an  encasement  for  the  entire  body  broken  only  in  the  regions  where  it  merges 
with  the  mucous  membranes.  It  serves  not  only  as  a  direct  physical  protection  to  the  under- 
lying structures,  but  also,  through  its  function  as  an  organ  of  touch  and  of  general  sensibility, 
it  indirectly  protects  the  body  by  the  action  of  the  special  end  organs  and  peripheral  termina- 
tions of  the  sensory  nerves  which  thus  bring  the  body  into  relations  with  its  surroundings. 
Through  the  radiation  and  conduction  of  heat  to  and  from  the  blood  circulating  in  it,  through 
the  amount  of  secretion  of  its  glands  and  the  evaporation  from  its  surface,  the  skin  forms  the 
principal  organ  for  the  regulation  of  the  bodily  heat.  By  means  of  the  action  of  its  sweat  and 
sebaceous  glands  it  possesses  an  important  secretory  function.  It  has  also  a  minor  role  as  an 
organ  of  respiration  and  absorption. 

The  surface  area  of  the  skin  corresponds  approximately  to  the  surface  of  the 
body  and  naturally  varies  with  the  size  of  the  individual.     It  has  been  variously 
estimated  at  from  10,500  to  18,700  sq.  cm.  for  a  medium-sized  adult  male. 
81  1281 


1282    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

The  aperturae  cutis  are  holes  through  the  skm  where  it  joins  with  the  mucous  membrane, 
usually  without  sharp  line  of  demarcation,  at  the  nares,  the  rima  oris,  the  anus,  and  the  external 
urethra  in  the  male,  and  at  the  vaginal  vestibule  in  the  female. 

Owing  to  the  fact  that  the  skin  extends  beyond  the  surface  at  the  aperaturse  cutis,  and 
covers  the  major  and  minor  pudendal  labia,  and  the  prepuce  and  extends  into  the  external 
acoustic  canal,  the  surface  area  is  slightly  greater  than  the  surface  of  the  body. 

The  thickness  of  the  skin  varies  in  different  regions  of  the  body  and  also  in 
different  individuals.  The  mean  thickness  is  between  1  and  2  mm.,  the  extremes 
ranging  from  .3  to  4.0  mm.  or  more.  This  is  exclusive  of  the  subcutaneous  tela. 
The  thickness  appears  to  be  in  direct  proportion  to  the  amount  of  friction  and 
pressure  to  which  the  part  is  subjected.  Thus  it  is  thicker  on  the  dorsal  than  on 
the  ventral  surface  of  the  trunk  and  neck,  and  on  the  flexor  than  on  the  extensor 
surfaces  of  the  hands  and  feet.  Otherwise  it  is  thicker  upon  the  extensor  than  on 
the  flexor  surface  of  the  extremities. 


1041. — ^Vertical  Section  prom  the  Sole  of  the  Foot  of  an  Adult. 

Str.lir.) 


X  25.     (Lewis  and 


Duct  of  a  sweat  gland  — 


stratum  corneum 
,^  Stratum  lucidum 


Stratum  granulosura 
stratum  germinativum 


Coil  of  a  sweat  gland  - 


[  Corpus 
I  papillare 


■  Tela  subcutanea 


Fat  tissue  ■ — fe^rj^  '^ 


^^^^fe.b:^i:. 


The  thickness  of  the  skin  is  least  upon  the  tympanum  and  it  is  also  thin  upon  the  eyehds 
and  penis.  It  obtains  a  thickness  of  3  mm.  on  the  volar  surface  of  hands  and  plantar  surface  of 
the  feet  and  gains  a  thicliness  of  about  4  mm.  on  the  cephalic  part  of  the  back  and  dorsal  surface 
of  the  neck.  It  is  thinner  in  the  aged  than  in  the  adult,  thicker  in  men  than  in  women,  and 
in  the  same  sex  is  subject  to  much  individual  variation  depending  upon  exercise,  occupation, 
etc.     The  vascularity  of  the  skin  also  influences  its  thickness. 

Over  most  of  the  surface  of  the  body  the  skin  is  elastic  and  so  loosely  attached 
that  it  may  be  stretched  to  a  greater  or  less  extent.  The  elasticity  varies  in 
different  individuals.  Closely  associated  with  the  elasticity  is  the  manner  of 
attachment  of  the  skin  to  underlying  structures.  This  varies  somewhat  according 
to  the  tissues  which  are  covered  but  the  great  motility  is  due  in  the  main  to  the 
very  oblique  arrangement  of  the  connective  tissue  and  elastic  fibres  of  the  deeper 
layers  of  the  skin;  the  fixity  to  the  more  vertical  arrangement  of  these  fibres.  An 
understanding  of  the  looseness  and  elasticity  of  the  skan  is  of  much  practical  im- 
portance to  the  surgeon  in  certain  operations. 

When  the  [traction  is  slow  as  over  a  slow-growing  tumour,  or  over  the  abdomen  and  breasts  in 
pregnancy,  the  skin  may  be  stretched  to  a  very  considerable  degree.  In  these  cases  there  are 
often  produced  short  parallel  reddish  streaks  which  when  the  stretching  is  reheved  are  re- 


THE  SKIN 


1283 


placed  by  whitish,  silvery  lines,  striae  or  lineae  albicantes,  due  to  atrophy  of  the  tissues.  In 
spite  of  this  the  skin  usually  retains  enough  elasticity  to  contract  gradually  to  its  former 
extent  as  it  does  immediately  after  moderate  stretching. 

In  most  parts  of  the  body  the  attachment  is  loose  so  that  the  skin  is  movable  and  may  be 
pinched  up  into  folds.  In  some  places  the  attachment  of  the  skin  is  firm  and  there  is  no  slip- 
ping of  the  skin  over  underlying  parts,  as  on  the  glans  penis.  In  some  other  parts  the  motion 
is  very  limited  as  in  the  scalp  and  the  volar  surface  of  the  hands  and  the  plantar  surface  of  the 
feet. 

•     Fig.  1042. — Finger  Print  (Natural  Size)  Showing  Crist*  and  Sulci. 


The  colour  of  the  skin  varies  greatly.  It  may  be  white,  yellow,  black,  red,  or 
any  of  the  shades  of  these  colours,  and,  according  to  the  colour,  the  races  of  man- 
Idnd  have  been  roughly  divided.  The  colouration  is  due  partly  to  pigment  and 
partly  to  the  blood  within  the  cutaneous  vessels.  The  amount  of  pigment  varies 
with  race,  age,  sex,  and  with  exposure  to  the  sun  and  air.  In  the  white  races  the 
skin  of  the  child  is  a  pinkish  white,  tending  to  become  dead  white  in  the  adult 
and  yellowish  in  the  aged,  and  it  is  normally  more  pigmented  in  certain  regions, 
such  as  the  axillary  region,  the  scrotum,  the  vulva,  and  the  mammary  areola. 

Fig.  1043. — Diagram  Showing  the  Arrangement  of  the  Principal  Crist.®  of  the  Thumb 


The  colour  of  the  white,  yellow,  red,  and  black  races  is  not  produced  by  the  climate,  as  we 
find  different  races  existing  under  the  same  climatic  conditions  and  the  same  coloured  race  under 
different  conditions  of  climate.  Each  race  presents  several  variations  of  colour;  for  example, 
in  the  white  race  we  distinguish  a  blonde,  a  brimette,  and  an  intermediate  tj'pe.  Anthropolo- 
gists distinguish  twenty  to  thirty  different  shades  of  colour  in  the  skin.  In  blondes  of  the  white 
race  under  the  action  of  strong  sun  light  the  skin  passes  from  a  rose  white  to  a  brick  red  or 
becomes  pigmented  in  spots,  freckles.  In  the  first  case  the  pigment  in  the  skin  is  not  increased 
to  any  great  extent  but  the  skin  is  affected  by  a  superficial  inflammation,  erythema,  associated 
with  exfoliation  and  often  with  the  formation  of  blisters.  In  brunettes  of  the  white  race  the  sun 
burns  the  skin  a  dark  yellowish  or  reddish  brown,  the  degree  of  pigmentation  here  being  increased 
and  is  spoken  of  as  tan.  The  colouration  is  onlj'  temporary  and  diminishes  on  withdrawal  from 
exposure.  The  sun  darkens  the  skin  in  the  yellow  races  also.  In  the  newborn  of  the  black 
races  the  skin  is  of  a  reddish  colour,  since  the  pigment  although  developed  to  some  extent  is  at 
birth  obscured  by  overlying  opaque  cells  which  later  become  transparent.  The  newborn  of  the 
yellow  races  are  also  hghter  than  their  parents.  In  white  races  the  shade  of  the  skin  is  clearer  on 
the  ventral  surface  of  the  trimk  and  on  the  flexor  surface  of  the  extremities.  In  the  black  races 
the  volar  surface  of  the  hands  and  the  plantar  surface  of  the  feet  as  well  as  the  sides  of  the  digits 
are  less  deeply  pigmented  than  the  rest  of  the  body.  The  colour  of  the  skin  is  greatly  influenced 
by  the  blood  in  its  deeper  layers  which  during  life  gives  it  a  more  or  less  distinctly  reddish  tinge, 
varying  directly  with  the  vascularity  and  inversely  with  the  thickness  of  the  epidermis.    Absence 


i 


1284   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

of  the  normal  pigment  is  a  not  uncommon  congenital  anomaly  producing  albinism  or  leuko- 
derma.    It  may  affect  all  the  skin  structures  or  it  may  be  partial. 

The  skin  presents  certain  elevations  and  depressions  due  to  the  fact  that  it 
follows  more  or  less  closely  the  contour  of  the  underlying  structures,  but  in  addi- 
tion to  this  it  possesses  certain  elevations  and  depressions  peculiarly  its  own. 
They  are  found  on  the  skin  in  various  parts  of  the  body.  Some  are  permanent, 
others  only  temporary.  Large  permanent  folds  which  include  all  the  layers  of 
the  skin  are  seen,  as  the  prepuce  of  the  penis  and  the  pudendal  labia.  The  most 
marked  depression  is  the  umbilical  fovea.  Other  conspicuous  folds  and  furrows 
are  seen  in  the  neighbourhood  of  the  lips  and  eyelids.  Certain  other  less  permanent 
folds  and  furrows  are  produced  by  the  action  of  the  joints,  joint-furrows,  and  of 
the  muscles  of  expression  of  the  skin,*'wrinkles." 


Fig.  1044.- 


-From  a  Photograph  op  the  Superficial  Fubhows  on  the  Back  of  the  Hand. 
(X  1.) 


Other  minute  folds  and  furrows  which  affect  only  the  epidermis  and  the  super- 
ficial layer  of  the  corium  are  seen  in  various  places.  These  are  represented  by  the 
numerous  fine  superficial  creases,  unassociated  with  elevations,  forming  rhom- 
boidal  and  triangular  figures  over  almost  the  whole  of  the  surface  of  the  skin 
(figs.  1042,  1043).  They  are  especially  numerous  on  the  dorsal  surface  of  the 
hands  (fig.  1044).  The  fine  curvilinear  ridges  [cristse  cutis]  with  intervening 
furrows  [sulci  cutis]  arranged  in  parallel  lines  in  groups  on  the  flexor  surface  of 
the  hands  and  feet  are  also  of  this  type.  They  form  patterns  characteristic  for 
each  individual  and  permanent  throughout  life. 

Fig.  1045. — From  a  Photograph  op  the  Skin  Ridges  and  Papillae  op  the  Palm  op  the 
Hand.     Epithelium  Completely  Removed  Above;  Partly  Removed  Below.     (X  5.) 


--^—  Corpus  papillare  corii 


";^  Sulci  cutis 


Among  the  projections  are  the  large  permanent  folds  of  skin  such  as  the  labia  pudendi,  the 
preputium  penis,  the  frenula  preputii,  clitoridis,  and  labiorum  pudendi,  and  less  marked  ridges 
as  the  median  raphe  of  the  perineum,  scrotum  and  penis,  and  the  tuberculum  labii  superioris. 
Of  a  somewhat  different  sort  are  the  touch  pads  (toruli  tactiles]  of  the  hands  and  feet.  Among 
the  larger  depressions  in  addition  to  the  umbilical  fovea,  is  the  coccygeal  foveola,  and  a  consider- 
able num))er  of  well-marked  permanent  furrows  found  in  various  places,  such  as  the  nasolabial 
and  mentolabial  sulci,  the  philtrum  labii  superioris,  the  infraorbital  sulcus,  and  the  infra-  and 
supraorbitial  palpebral  sulci.  There  are  numerous  articular  furrows  on  both  the  flexor  and 
extensor  surfaces  produced  by  the  action  of  the  joints,  and  associated  with  intervening  folds 
of  skin,  particularly  on  the  dorsal  surface.  They  are  especially  noticeable  on  the  hands.  Varia- 
tions of  the  palmar  joint  sulci  are  due  to  variations  in  opposition  of  the  thumb  and  the  use  of 
the  fingers  and  the  relative  arrangement  of  the  thumb  and  fingers  and  joints.     They  are  of 


THE  EPIDERMIS  1285 

especial  medical  and  surgical  importance  as  indicating  topographically  the  position  of  the  joints, 
their  relation  to  which  has  been  recently  made  clearer  by  means  of  the  X-ray. 

The  folds  and  furrows  brought  about  through  the  action  of  the  skin  muscles  run  at  right 
angles  to  the  muscle  fibres  and  are  more  or  less  transitory  at  first  but  become  more  permanent 
through  repeated  or  long-continued  action.  They  are  represented  by  the  wrinkles  of  the  fore- 
head, the  lines  of  expression  of  the  face,  the  transverse  wrinkles  of  the  scrotum  and  the  radiating 
folds  around  the  anus.  The  more  superficial  cristae  cutis  and  sulci  cutis  are  arranged  in  groups 
within  and  around  the  touch  pads,  on  the  volar  surface  of  the  hands  and  the  plantar  surface  of 
the  feet  (figs.  1042,  1043).  The  crista;  of  each  group  are  parallel.  They  correspond  to  the  rows 
of  papillfe  of  the  corium. 

Because  the  patterns  of  the  crista;  and  sulci  are  characteristic  for  the  individual,  and  per- 
manent from  youth  to  old  age,  they  have  been  classified  in  a  number  of  types  and  are  important 
medioolegally  as  a  means  of  identification.  The  various  systems  of  classification  are  based 
upon  the  arrangement  over  the  distal  phalanges  of  the  fingers  and  make  use  of  (1)  a  transverse 
ridge  which  is  parallel  with  the  articular  plicae  (2)  a  curved  ridge  with  its  convexity  distally 
and  more  or  less  closely  meeting  the  first,  medially  and  laterally,  and  (3)  the  curved  and  concen- 
tric ridges  between  these  two  (fig.  1043). 

There  are  also  a  great  number  of  minute  depressions  which  mark  the  points  where  the  hairs 
pierce  the  surface  and  where  the  glands  open.     These  are  popularly  known  as  pores.     Under 

Fig.  1046. — PAPii.i,.ffi:  of  the  Cohium  after  Maceration.     From  Retouched  Photograph. 
Epithelium  Removed  by  Maceration.     ( X  25.) 


^>-Papinee  corii 


the  influence  of  cold  and  emotion  the  hair  muscles  contract  and  cause  a  slight  elevation  of  the 
skin  at  the  point  where  the  hair  emerges.  This  roughened  appearance  of  the  skin  is  popularly 
known  as  "goose-flesh." 

A  complex  wrinkling  of  the  skin  appears  in  old  age,  or  in  the  course  of  exhausting  diseases/as 
a  result  of  loss  of  elasticity  and  from  absorption  of  the  cutaneous  and  subcutaneous  fat.  Rounded 
depressions  called  dimples  are  produced  by  the  attachment  of  muscle-fibres  to  the  deep  surface 
of  the  skin,  as  on  the  chin  and  cheek,  and  are  made  more  evident  by  the  contraction  of  these 
fibres.  Others  are  produced  by  the  attachment  of  the  skin  by  fibrous  bands  to  bony  eminences, 
as  the  elbow,  shoulder,  vertebrse,  and  posterior  iliac  spines.  They  are  best  seen  when  the  sub- 
cutaneous adipose  tissue  is  well  developed. 

The  cutis  is  made  up  of  two  layers  which  are  structurally  and  developmentally 
markedly  different.  The  superficial  ectodermic  portion,  epidermis,  is  made  up 
almost  entirely  of  closely  packed  epithelial  cells,  the  deeper  mesodermic  part, 
corium,  is  formed  largely  of  connective-tissue  fibres. 

The  epidermis  (cuticle,  scarf-skin)  is  a  cellular  non-vascular  membrane  which 
forms  the  whole  of  the  superficial  layer  of  the  skin  and  at  the  great  openings 
through  the  skin,  as  the  mouth  and  anus,  blends  gradually  with  the  mucous  mem- 
brane. It  represents  from  one-tenth  to  over  half  the  thickness  of  the  skin,  in 
different  parts  of  the  body,  the  usual  thickness  being  .05  to  .2  mm.,  ranging  from 
.03  mm,  to  nearly  3  mm.  The  thickness  varies  also  in  different  individuals. 
Its  deep  surface  is  molded  exactly  to  the  underlying  corium  but  its  superficial 
surface  fails  to  reproduce  all  of  the  irregularities  of  the  latter.  In  spite  of  this 
close  association,  blood-vessels  never  enter  the  epidermis. 

Structure  of  the  epidermis. — The  cells  of  the  epidermis  are  packed  together  in  many  irregu- 
lar layers.     The  deepest  cells  are  soft  protoplasmic,  somewhat  elongated,  perpendicular  to 


i 


1286    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

the  surface  of  the  corium  and  joined  together  by  fine  fibrils;  more  superficially  they  become 
round  or  polyhedral.  These  cells  together  with  several  more  superficial  layers  form  a  stratum 
from  which  the  other  cells  of  the  epidermis  are  developed  and  which  therefore  are  laiown  as  the 
stratum  germinativum  (Malpighii).  The  cells  in  the  superficial  part  of  this  stratum,  in  some 
situations,  have  a  granular  appearance  forming  a  layer  which  is  called  the  stratum  granulosum. 
Superficial  to  this  there  is,  also  only  in  some  places,  a  layer  in  which  the  cells  are  somewhat 
indistinct  and  transparent,  and  therefore  known  as  the  stratum  lucidum.  This  is  a  transition 
between  the  softer  and  more  opaque  stratum  germinativum  and  the  firmer  and  more  transparent 
superficial  layer  formed  of  large,  flattened,  dry,  horny  cells,  known  as  stratum  corneum. 

In  general  the  stratum  germinativum  is  thicker  than  the  stratum  corneum.  In  certain 
parts  as  the  face,  the  back,  the  back  of  the  hands  and  feet,  the  two  layers  are  equal  in  thicloiess. 
In  other  regions,  as  in  the  volar  surface  of  the  hands  and  plantar  surface  of  the  feet,  the  stratum 
corneum  is  much  thicker  than  the  stratum  germinativum  varying  from  two  to  three  or  even  five 
times  as  thick.  This  increased  thickness  of  the  stratum  corneum  is  not  due  to  pressure  alone 
as  it  is  well  marked  in  the  foetus,  but  it  is  not  improbable  that  pressure  may  stimulate  the 
further  growth  of  the  cells. 

Where  the  papilte  of  the  corium  are  arranged  in  rows  as  on  the  volar  surface  of  the  hands 
and  the  plantar  surface  of  the  feet,  the  epidermis  is  molded  to  these  so  as  to  appear  as  ridges 
on  the  surface,  already  described  as  cristse.  In  most  other  places  the  irregularities  of  the  papillae 
of  the  corium  do  not  show  on  the  sm-face.  At  short  and  regular  intervals  on  the  cristse  are 
notches  and  transverse  furrows  which  mark  the  openings  of  the  sweat  glands. 

The  separation  of  the  epidermis  from  the  corium  by  the  accumulation  of  serous  fluid  between 
the  layers  is  known  as  a  bUster.  Sometimes  it  is  only  the  separation  of  the  superficial  layers 
from  the  deeper  layers  of  the  epidermis. 

The  skin  is  regenerated  after  a  blister  or  a  wound  by  growth  of  the  cells  of  the  stratum  ger- 
minativum. It  is  probable  that  cells  of  the  superficial  layers  take  no  part  in  this.  Therefore  in 
skin  grafting  the  surgeon  in  order  to  transplant  the  cells  of  the  stratum  germinativum  usually 
includes  all  the  layers  of  the  epidermis  and  the  extreme  tips  of  the  papillae  of  the  corium  as  shown 
by  the  minute  bleeding  points  left  on  the  surface  from  which  the  graft  has  been  cut. 

The  pigment  which  gives  the  main  colour  to  the  skin  is  caused  by  the  accumulation  of  pig- 
ment granules,  melanin,  in  the  deepest  cells  of  the  stratum  germinativum.  It  does  not  occur 
until  after  the  sixth  month  of  foetal  life  and  develops  chiefly  after  birth.  The  blackness  of  the 
skin  of  the  negro  depends  almost  entirely  upon  this  pigment.  Pigment  granules  are  also  found 
to  a  less  extent  in  more  superficial  cells  and  sometimes  in  the  corium. 

Development  of  the  epidermis. — The  epidermis  is  derived  from  the  ectoderm,  in  early 
embryos  appearing  as  a  double  stratum  of  cells,  the  superficial  layer  of  which  is  known  as  the 
epitrichium  or  periderm,  the  deep  layer  becomes  the  stratum  germinativum.  By  multiplica- 
tion of  the  deep  cells  a  number  of  layers  are  produced  and  the  more  superficial  cells  tend  to 
assume  the  adult  characteristics.  At  about  the  sixth  month  of  foetal  hfe  the  epitrichial  layer 
finally  disappears.  The  surface  layers  are  cast  off  and  mixing  with  the  secretion  of  the  cutaneous 
glands  form  a  yellowish  layer  over  the  surface  of  the  skin  of  the  foetus,  the  vernix  caseosa. 

Growth  continues  throughout  life.  New  cells  are  formed  in  the  deeper  layers  pushing  the 
older  cells  toward  the  surface.  The  character  of  the  cells  changes  as  they  approach  the  surface, 
the  change  being  quite  abrupt  at  the  level  of  the  stratum  lucidum.  As  the  form  of  the  cells 
changes,  chemical  and  physical  alterations  of  their  contents  occur.  In  most  places  the  super- 
ficial cells  are  represented  by  thin  scales  but  in  the  palms  and  soles  the  cells  are  somewhat  swol- 
len.    The  superficial  cells  are  being  constantly  thrown  off  and  replaced  by  deeper  ones. 

The  corium  (cutis,  cutis  vera,  derma)  is  a  fibrous  vascular  sh.eath  composed 
of  interwoven  bundles  of  connective-tissue  fibres  intermixed  with  elastic  fibres, 
connective-tissue  cells,  fat,  and  scattered  unstriped  muscle-fibres.  It  is  traversed 
by  rich  plexuses  of  blood-vessels,  lymph-vessels,  and  nerves,  and  encloses  hair- 
bulbs  and  sebaceous  and  sudoriferous  glands.  It  varies  in  thickness  from  .3 
mm.  to  3.0  mm.  or  more,  usually  ranging  from  .5  to  1.5  mm.  It  is  to  this  layer 
that  the  strength  and  elasticity  of  the  skin  are  due  and  it  is  also  only  this  layer 
which  when  properly  cured  we  know  as  leather. 

The  superficial  layer  of  the  corium  is  of  finer,  closer  texture,  free  from  fat,  and 
forms  a  multitude  of  eminences  called  papillae  corii  (figs.  1040,  1045,  1046)  which 
project  into  corresponding  depressions  on  the  deep  surface  of  the  epidermis. 
For  this  reason  this  part  of  the  corium  although  but  indistinctly  separated  from 
the  deeper  layer  is  called  the  corpus  papillare. 

Some  of  the  papillae  contain  vessels,  others  nerves,  hence  they  are  known  as  vascular  or 
tactile  papillse.  They  are  very  closely  set,  varying  considerably  in  number  in  different  parts  of 
the  body  from  .36  to  130  to  a  square  millimetre,  and  it  has  been  estimated  that  there  are  about 
150  million  papilloe  on.  the  whole  surface.  They  also  vary  greatly  in  size  not  only  in  different 
regions  but  in  the  same  region,  being  from  .03  to  .2  mm.  or  more  in  height. 

The  deeper  layer  of  the  corium,  the  tunica  propria  (stratum  reticulare),  is 
composed  of  coarser  and  less  compact  bands  of  fibrous  tissue  intermingled  with 
small  fat  lobules.  The  fibrous  and  elastic  tissue  is  arranged  for  the  most  part  in 
intercrossing  bundles  nearly  parallel  to  the  surface  of  the  skin. 

The  bundles  running  in  some  directions  are  usually  more  strongly  developed  and  more 
numerous  than  those  in  others  but  the  direction  of  the  strongly  developed  bundles  varies  in 


THE  TELA  SUBCUTANEA 


1287 


different  parts  of  the  body.  In  general  those  are  best  developed  which  have  a  direction  parallel 
with  the  usual  lines  of  tension  of  the  slcin,  hence  it  results  that  wounds  of  the  skin  tend  to  gape 
most  at  right  angles  to  these  lines.  The  bundles  take  a  direction  nearly  at  right  angles  to  the 
long  axis  of  the  hmbs,  and  on  the  trunk  run  obhquely,  caudally,  and  laterally  from  the  spine 
(figs.  1047,  1048).  On  the  scalp,  forehead,  chin,  and  epigastrium,  equally  strong  bundles  cross 
in  all  directions,  and  a  round  wound,  instead  of  being  linear  as  elsewhere,  appears  as  a  ragged  or 
triangular  hole.  The  arrangement  of  the  connective-tissue  bundles  influences  the  arrangement 
of  the  blood-vessels  of  the  skin. 

The  tela  subcutanea  or  superficial  fascia  is  also  a  fibrous  vascular  layer  which 
passes  as  a  gradual  transition  without  definite  line  of  demarcation  from  the  deep 
surface  of  the  tunica  propria  of  the  corium  to  connect  it  with  the  underlying 
structures. 

Like  the  tunica  propria  it  is  composed  of  bundles  of  connective  tissue  containing  elastic 
fibres  and  fat,  but  the  bundles  are  larger  and  more  loosely  arranged,  and  form  more  distinct 
cormeotive-tissue  septa,  which  divide  the  fat,  when  present,  into  smaller  and  larger  lobules. 
Where  these  connecting  strands  are  especially  large  and  well  defined,  they  are  known  as  re- 
tinacula.     Over  almost  the  whole  surface  of  the  body  the  connective-tissue  strands  of  the  tela 


Figs.  1047  and  1048. — Diagrams  Showing  the  Arbangembnt  op  the  Connective 
Tissue  Bundles  of  the  Skin  on  the  Anterior  and  Posterior  Surfaces  of  the  Body. 
(After  Langer.) 


are  arranged  nearly  parallel  with  the  surface,  and  bind  the  skin  so  loosely  to  the  parts  beneath 
that  it  may  stretch  and  move  freely  over  the  deeper  parts.  In  some  situations  the  connective- 
tissue  bundles  of  the  tela  subcutanea  run  almost  at  right  angles  to  the  surface  and  bind  the  skin 
firmly  to  the  deep  fascia,  as  in  the  flexor  surface  of  the  hands  and  feet  and  in  the  scalp  and  face. 

The  quantity  of  subcutaneous  fat  varies  considerably  in  different  parts  of  the 
body.  It  is,  for  instance,  entirely  absent  in  the  penis,  scrotum,  and  eyeUds.  When 
it  is  abundant,  the  subcutaneous  layer  is  known  as  the  panniculus  adiposus. 

In  some  situations,  as  in  the  caudal  portion  of  the  abdomen  and  in  the  perineum,  the 
connective  tissue  is  so  arranged  that  the  panniculus  may  be  divided  into  layers,  so  that  a 
superficial  and  a  deep  layer  of  the  superficial  fascia  may  be  recognised.  The  fat  is  well  de- 
veloped over  the  nates,  volar  surface  of  the  hands  and  plantar  surface  of  the  feet,  where  it 
serves  as  pads  or  cushions;  in  the  scalp  it  appears  as  a  single  uniform  lobulated  layer  between  the 
corium  and  the  aponeurosis  of  the  epicranial  muscle;  and  on  other  parts  of  the  surface  it  is  some- 
what unequally  distributed  and  shows  a  tendency  to  accumulate  in  apparent  disproportion  in 
some  localities,  as  on  the  abdomen,  over  the  symphysis  pubis,  about  the  mammse  in  females, 
etc.  Everywhere  except  on  the  scalp  it  may  undergo  rapid  and  visible  increase  or  decrease 
under  the  influence  of  change  of  nutrition. 


1288   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

The  amount  of  elastic  tissue  mixed  with  the  white  fibrous  connective  tissue  of  which  the 
corium  and  subcutaneous  tela  mainly  consist  varies  in  the  different  parts  of  the  body.  It  is 
especially  abundant  in  the  deeper  layer  of  the  tela  over  the  caudal  part  of  the  ventral  ab- 
dominal wall  where  it  forms  almost  a  continuous  sheet.  Many  elastic  fibres  also  accompany  the 
blood-vessels  and  are  mingled  with  the  connective-tissue  sheaths  around  the  hairs,  the  sweat 
glands,  and  their  ducts. 

The  papillce  corii  are  usually  simple  cones  but  some  are  bulbous  at  their  ends  and  others 
have  duplicated  apices.  They  may  be  perpendicular  to  the  surface  or  oblique,  in  some  places 
overlapping.  Those  on  the  flexor  surfaces  of  the  hands  and  feet  are  best  developed  and  are 
arranged  in  rows  so  as  to  form  long  parallel  curvilinear  ridges,  two  of  which  are  grouped  together 
and  correspond  to  one  crista  on  the  surface  of  the  epidermis  (figs.  1045,  1046).  When  there  are 
no  papillary  ridges  the  papilte  are  irregularly  scattered,  shorter,  and  may  disappear  in  places 
or  be  replaced  by  ridges.  The  papilliE  serve  to  give  a  greater  surface  area  to  the  corium  so  as 
to  bring  a  greater  number  of  blood-vessels  and  nerves  into  closer  relation  with  the  epidermis  and 
thus  with  the  surface  of  the  body.  They  are  best  developed  where  the  epidermis  is  thickest. 
Thus  they  are  the  largest  on  the  flexor  surface  of  the  hands  and  feet  and  beneath  the  nails  and 
are  smallest  on  the  face,  scrotum,  and  mammEe. 

The  skin,  as  removed  in  the  dissecting  room,  usually  includes  the  epidermis  and  more  or 
less  of  the  corium  and  subcutaneous  tela.  The  cut  surface  is  formed  of  connective  tissue  which 
has  a  shining  bluish-white  appearance  with  minute  pits  closely  scattered  over  the  surface. 
These  pits  are  usually  more  or  less  completely  filled  with  small  yellow  fat  lobules. 

Skin  muscles. — In  the  subcutaneous  tela  and  the  corium  muscle  fibres  are 
found  in  large  and  small  groups.  These  are  of  two  kinds,  striated  muscle  and 
unstriated  muscle. 

Subcutaneous  planes  of  striated  muscle  are  relatively  scanty  in  man  when  compared  with  the 
great  panniculus  carnosus  of  the  lower  mammalia.  This  is  mainly  represented  by  the  platysma 
in  the  neck  which  has  both  its  origin  and  part  of  its  insertion  in  the  skin.  Closely  associated 
with  this  are  the  muscles  of  expression  of  the  face  and  the  palmaris  brevis  muscle  which  have 
one  end  terminating  in  the  deep  surface  of  the  skin.  The  epicranial  muscle  is  also  considered  by 
some  to  belong  to  this  group. 

Unstriated  muscle  fibres  are  scattered  through  the  corium  collected  into  bundles  in  the 
neighbourhood  of  the  sebaceous  glands  and  the  hairs.  They  are  described  in  connection  with 
these  latter  (p.  1293).  In  addition  to  these  unstriated  muscles  are  found  in  the  scrotum  as  the 
dartos,  in  the  perineum,  around  the  anus,  and  beneath  the  papilla  and  areola  of  the  mammary 
gland. 

Burssa  mucosae  subcutanea. — In  some  situations  where  the  integument  is 
exposed  to  repeated  friction  over  subjacent  bones  or  other  hard  structures  its 
movements  are  facilitated  by  the  development  of  sac-like  interspaces  in  the  sub- 
cutaneous tissue,  the  subcutaneous  mucous  bursse.  They  are  similar  to  the  more 
deeply  placed  bursse  which  are  found  in  relation  with  muscle  tendons.  Their 
occurrence  is  quite  variable.  In  some  individuals  they  are  numerous,  in  others 
very  few.  They  have  a  considerable  practical  importance  from  the  fact  that  they 
may  become  greatly  swollen. 

The  most  constant  subcutaneous  mucous  bursae  are  the  following: 

Bursa  anguli  mandibulae;  B.  subcutanea  prementalis,  between  the  periosteum  and  soft  parts 
over  the  tip  of  the  chin;  B.  subcutanea  prominentise  laryngese  over  the  ventral  prominence  of 
the  thyreoid  cartilage  of  the  larynx  (often  found  in  the  male;  B.  subcutanea  acromialis,  between 
the  acromion  and  the  skin;  B.  subcutanea  olecrani,  beneath  the  skin  on  the  dorsal  surface  of 
the  olecranon;  B.  subcutanea  epicondyli  humeri  lateralis,  found  beneath  the  skin  over  the 
lateral  epioondyle  of  the  humerus  (occasional);  B.  subcutanea  epicondyli  humeri  medialis, 
between  the  skin  and  the  medial  epicondyle  of  the  humerus  (more  frequent);  B.  subcutanea 
metacarpophalangea  dorsalis,  between  the  sldn  and  the  dorsal  side  of  the  metacarpophalangeal 
joints  (occasional,  especially  the  fifth);  B.  subcutanea  digitorum  dorsalis,  beneath  the  skin  over 
the  proximal  finger-joints;  and  rarely  over  the  distal  finger-joints;  B.  subcutanea  trochanterica, 
between  the  skin  and  the  great  trochanter  of  the  femur;  B.  subcutanea  praepatellaris,  beneath 
the  skin  covering  the  caudal  half  of  the  patella;  B.  subcutanea  infrapatellaris,  between  the  skin 
and  the  cephahc  end  of  the  ligamentum  patella;;  B.  subcutanea  tuberositatis  tibiae  ventral  to 
the  tibial  tuberosity,  covered  by  skin  or  by  skin  and  crural  fascia;  B.  subcutanea  malleoli 
lateralis,  between  the  skin  and  the  point  of  the  lateral  malleolus;  B.  subcutanea  malleoli  me- 
dialis, between  the  skin  and  medial  malleolus;  B.  subcutanea  calcanea,  in  the  sole  of  the  foot 
between  the  skin  and  the  plantar  surface  of  the  calcaneum;  B.  subcutanea  sacralis,  beneath 
the  skin  which  covers  the  lumbodorsal  fascia  and  the  region  between  the  sacrum  and  coccyx. 

Blood-vessels  of  the  skin. — Both  the  corium  and  the  subcutaneous  tela  are  very  vascular, 
but  the  size  and  number  of  vessels  varies  in  different  situations.  Although  the  origin  of  the 
cutaneous  arteries  from  the  deep  arteries  and  the  positions  where  the  subcutaneous  arteries 
pierce  the  muscles  vary  greatly,  the  areas  supplied  by  certain  groups  of  arteries  and  the  direc- 
tion in  which  the  arteries  of  the  skin  run  show  much  regularity.  Moreover  the  metameric 
arrangement  of  the  arteries  in  the  skin  is  clearly  seen,  especially  upon  the  trunk.  We  can  recog- 
nise two  groups  of  skin  arteries.  One  group  is  represented  by  a  small  number  of  rather  large 
branches  which  are  distributed  throughout  or  principally  in  the  subcutaneous  tela  and  corium, 
as  the  inferior  superficial  epigastric  artery,  the  arteries  of  the  scalp,  etc.     These  arteries  tend  to 


NERVES  OF  THE  SKIN 


1289 


disturb  the  metameric  arrangement.  In  the  other  group  the  arteries  are  intrinsically  for  the 
supply  of  other  organs  but  give  off  small  end  twigs  to  the  skin,  e.  g.,  the  arteries  to  the  superficial 
muscles. 

The  arteries  enter  the  corium  from  the  subcutaneous  tela,  break  up  into  smaller  branches 
anastomose  freely  and  in  the  deepest  layer  of  the  corium  form  a  network,  the  cutaneous  rate 
(subcutaneous  plexus),  rete  arteriosum  cutaneum,  from  which  small  branches  are  given  off  to 
supply  the  fat  and  sweat  glands  and  also  to  the  papillary  layer  of  the  corium.  Here  another 
network  of  arteries  is  formed,  the  subpapillary  rete,  rete  arteriosum  subpapillare.  From  the 
subpapillary  plexus,  minute  twigs  pass  to  the  papilla;,  to  the  hair  follicles,  and  to  the  sebaceous 
and  sudoriferous  glands. 

The  cutaneous  veins  like  the  arteries  may  be  divided  into  three  groups:  (1)  small  radicals 
which  accompany  the  corresponding  arteries  and  go  to  make  up  veins  whose  main  function  is  to 
collect  the  blood  from  the  muscles;  (2)  larger  branches  accompanying  the  arteries  whose  main 
course  is  in  the  subcutaneous  tela  as  the  inferior  superficial  epigastric  vein;  (3)  large  veins  which 
run  in  the  subcutaneous  tela  but  have  a  course  independent  of  the  arteries  such  as  those  seen 
through  the  slcin  on  the  hands  and  arms.  These  large  vessels  will  be  found  described  in  con- 
nection with  the  general  description  of  the  veins  (Section  V). 

Minute  venules  arise  from  the  capillaries  of  the  papilla,  accompany  the  arteries  and  form 
parallel  with  the  surface  of  the  skin  a  series  of  closely  connected  plexuses.     Four  such  plexuses, 


Fig.  1049. — Cutaneous  Nerves  of  the  Middle  Finger  and  Lamellotts  (Pacinian)  Cor- 

n  s,  MS       ,ri(.iii  T,.!,irs   \ths) 


Twig  from  n.  digitalis 
Volaris  proprius 


LamellousCPacinian'^ 
puscles  with  nerves 


■  Interdigital  fold 


Cut  edge  of  skin  along 
mid-line  of  dorsal  sur- 
face of  finger 


Mid-line  of  volar  surface  of  finger 


more  distinct  than  the  arterial,  may  be  recognised  in  some  situations.  Of  these  retia  venosa 
one  is  situated  just  beneath  the  papilla;,  and  another  at  the  junction  of  the  corium  and  subcu- 
taneous tela.  They  receive  branches  from  the  fat,  hair  folhcles,  and  glands,  and  empty  into  the 
large  veins  of  the  sldn  situated  in  the  subcutaneous  tissue. 

Lymphatics  of  the  skin. — The  cutaneous  lymphatic  vessels  are  found  in  the  skin  of  all  parts 
of  the  body  but  are  more  abundant  in  certain  places.  The  lymph-vessels  of  the  skin  are 
developmentally  among  the  first  lymph-vessels  to  appear.  The  larger  vessels  and  glands  of  the 
subcutaneous  tela  will  be  found  described  in  connection  with  the  general  lymphatic  system 
Section  VI).  In  the  corium  the  lymphatics  from  the  papillae  form  a  subpapillary  network 
which  opens  into  a  subcutaneous  plexus  connected  with  the  larger  lymph-vessels  of  the  subcu- 
taneous tela.  There  are  no  lymph-vessels  in  the  epidermis,  but  this  is  supposed  to  be  nourished 
by  the  lymph  in  the  tissue  spaces  between  the  cells  and  these  spaces  connect  indirectly  with  the 
lymph-vessels. 

The  nerves. — The  skin  has  one  of  the  richest  nerve  supplies  of  the  body.  The  nerves  are  in 
greater  proportion  in  those  parts  which  are  most  sensitive.  The  various  skin  areas  are  supplied 
by  specific  (segmental)  nerves  with  much  greater  regularity  than  in  the  case  of  the  arteries.  The 
nerves  supplying  adjoining  areas  overlap  so  that  there  is  an  intermediate  space  supphed  by  both. 
The  variations  consist  in  an  extension  of  one  area  and  a  corresponding  contraction  of  an  adjoin- 
ing area.  The  distribution  of  the  nerves  in  the  skin  shows,  especially  on  the  trunk  and  neck,  a 
marked  metameric  arrangement.     The  arrangement  of  these  nerves  in  the  subcutaneous  tela 


1290    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

and  their  areas  of  distribution  will  be  found  described  in  detail  in  the  section  on  the  Nervous 
System. 

With  the  exception  of  the  nerves  to  the  sudoriferous  and  sebaceous  glands,  the  skin-muscles 
and  blood-vessels,  all  the  cutaneous  nerves  are  sensory.  They  have  diverse  modes  of  termina- 
tion. Some  end  in  the  subcutaneous  tela;  others,  the  greater  number,  terminate  in  the  corium; 
still  others  extend  to  the  epidermis. 

Toward  their  termination  the  nerves  branch  and  rebranch,  and  just  beneath  the  surface  they 
form  a  great  number  of  small  twigs  from  which  the  terminal  fibres  arise.  These  may  be  divided 
into  two  groups,  those  that  end  freely  and  those  whose  termination  is  surrounded  by  a  capsule. 
The  free  ends  are  slightly  enlarged  and  terminate  in  the  epidermis  and  in  certain  regions  in  the 
corium.  The  encapsulated  terminations  form  special  end  organs  and  are  found  in  the  corium  as 
the  bulbous  corpuscles  (end-bulbs  of  Krause)  [corpuscula  bulboidea,  Krauserii];  the  tactile 
corpuscles  (corpuscles  of  Meissner  or  Wagner)  [corpuscula  tactus,  MeissneriJ;  and  the  genital 
corpuscles  [corpuscula  nervorum  genitalia[.  In  the  subcutaneous  tela  the  end-bulbs  are  seen  as 
the  lamellous  corpuscles  (corpuscles  of  Vater:  Pacinian  corpuscles),  [corpuscula  lamellosa; 
Vateri,  Pacini[  shown  in  fig.  1049;  the  Golgi-Mazzoni  corpuscles  and  the  Rufflni  corpuscles. 
All  the  terminations  except  the  lamellous  corpuscles  are  microscopic,  not  exceeding  0.2  mm.  in 
length.  The  lamellous  corpuscles,  which  are  readily  seen  in  reflecting  the  skin  from  the  fingers 
and  toes,  may  be  as  much  as  2  mm.  long  and  half  as  thick  (fig.  1049).  The  exact  function  of 
each  of  the  various  endings  is  not  known.  They  are  undoubtedly  sensory  fibres  except  those  to 
the  glands,  muscles,  and  blood-vessels. 

Development  of  the  corium  and  subcutaneous  tela. — The  corium  is  developed  from  the 
superficial  part  of  the  myotome  or  dermo-muscular  plate  of  mesoderm.  At  first  it  is  very  largely 
cellular  but  later  fibres  are  produced.  In  the  earlier  stages  the  corium  and  tela  subcutanea  are  not 
distinguishable  and  only  in  the  later  embryonic  period  may  the  corium  be  separated  into  the 
papillary  stratum  and  the  tunica  propria. 

THE  APPENDAGES  OF  THE  SKIN 

The  appendages  of  the  skin  include:  (A)  the  hairs;  (B)  the  nails;  (C)  the 
cutaneous  glands;  and  (D)  the  mammary  glands. 

A.  THE  HAIRS 

The  hairs  [pili]  are  less  developed  in  man  than  in  any  other  primate.  Where 
well  developed  they  in  themselves  serve  as  a  protective  organ  and  moreover 
through  their  connection  with  the  nervous  system  they  become  in  a  measure 
organs  of  special  sense.  They  are  strong,  flexible,  somewhat  elastic,  and  poor 
conductors  of  heat.  They  cover  the  entire  surface  of  the  body  with  the  following 
exceptions:  The  flexor  surfaces  of  the  hands  and  feet;  the  dorsal  bends  and  sides 
of  the  fingers  and  toes;  the  dorsal  surfaces  of  the  distal  phalanges  of  the  fingers 
and  toes;  the  red  borders  of  the  lips;  the  glands  and  inner  surface  of  the  prepuce 
of  the  penis  and  clitoris;  the  inner  surface  of  the  labia  majora;  the  labia  minora 
and  the  papilla  mammae. 

The  size  and  length  of  hairs  varies  greatly  not  only  in  different  parts  of  the 
body  but  also  in  different  individuals  and  races.  In  certain  situations  the  hairs 
are  especially  long  and  large  and  are  designated  by  special  names. 

Thus  upon  the  scalp,  capilli,  in  the  axillary  region,  hirci,  and  after  puberty  upon  the  face  in 
the  male,  the  beard,  barba,  and  in  the  pubic  region  in  both  sexes,  pubes.  The  pubic  hairs  extend 
upon  the  external  genital  organs  and  upon  the  ventral  abdominal  wall  toward  the  umbilicus. 
All  of  the  hairs  of  these  regions  are  not  long  and  large  but  short  and  finer  hairs  are  mixed 
with  them  in  varying  numbers.  Strong,  well-developed  short  hairs  are  found  in  connection  with 
the  organs  of  sense  forming  the  eyebrows,  supercilia,  the  eyelashes,  cilia,  at  the  entrance  to  the 
external  acoustic  meatus,  tragi,  and  at  the  nares,  vibrissse.  Upon  the  extensor  surfaces  of  the 
extremities,  upon  the  chest,  and  in  other  situations  in  some  individuals,  especially  in  adult 
males,  the  hairs  are  also  longer  and  stronger  than  upon  the  rest  of  the  body,  where  they  are,  as  a 
rule,  short,  fine  and  downy.  The  first  hairs  appearing  in  the  foetus  are  very  fine,  and  are  called 
lanugo.  The  long  hairs  of  the  adult  scalp  may  attain  a  length  of  ISO  cm.  or  more;  the  short 
hairs  average  from  .5  to  1.3  cm.  in  length,  while  the  lanugo  does  not  exceed  1.4  cm. 

Excess  of  long  hairs,  hypertrichosis,  may  involve  the  whole  hairy  surface  of  the  body.  It  is 
usually  inherited  and  affects  several  individuals  in  the  same  family.  Local  areas  of  long  hairs 
also  occur  as  over  naevi  and  upon  the  sacrum.  Local  congestion  due  to  inflammation,  irritation, 
or  pressure  may  cause  hypertrichosis.  In  women,  hair  upon  the  upper  lip  or  other  parts  of  the 
face  may  be  an  inherited  peculiarity  or  due  to  some  abnormahty  of  the  sexual  organs.  It  is  also 
not  uncommon  after  the  menopause. 

In  diameter  the  hairs  vary  from  .005  mm.  for  the  finest  lanugo  to  .203  mm. 
for  the  coarsest  hair  of  the  beard ;  but  they  usually  taper  toward  the  tip  and  also 
are  narrower  toward  the  base.  As  a  general  rule,  blonde  hairs  are  the  finest  and 
black  hairs  the  coarsest. 


THE  HAIRS 


1291 


In  colour  the  hairs  may  be  either  blonde,  brown,  black,  red,  or  some  gradation 
of  these  colours.  The  colour  varies  with  the  race,  and  also  with  the  individual, 
and  according  to  age.  It  is  due  to  pigment  in  the  cells  of  the  hair  but  is  also 
influenced  by  the  amount  of  air  between  the  cells. 

Greying  and  whitening  of  the  hair  is  due  not  only  to  a  decrease  of  pigment  but  also  to  an 
increase  in  the  amount  of  air  between  the  cells.  Sudden  blanching  of  the  hair  is  thought  to  be 
due  almost  entirely  to  an  increase  in  the  quantity  of  this  contained  air.  Whitening  of  the  hair  is 
physiological  in  old  age  and  not  infrequent  in  younger  persons.  This  may  be  an  inherited  pecul- 
iarity or  may  follow  mental  overwork,  nervous  shock,  or  prolonged  disease.  Local  blanching  is 
also  seen  as  the  result  of  disease. 

The  hair  may  be  straight,  waved,  curled,  or  frizzled  in  varying  degree.  Here  also  there  is 
not  only  an  individual  but  also  a  racial  variation,  as  instanced  in  the  curled  or  crinkled  hair  of 
the  African  negro  and  the  straight  hair  of  the  American  Indian.  The  curliness  is  caused  by  the 
form  and  the  manner  of  implantation  in  the  skin.     Straight  hairs  are  round  or  oval  in  transection 


Fig. 


1050. — Longitudinal  Section  of  a  Growing  Hair  of  the  Head. 
Toldt's  Atlas.) 


(X30.)      (From 


Epidermal 
coat  of 
follicle 


Scapus  pili  (shaft) 


Collum  foUiculi  pili- 


Inner  root  sheath 


Outer  root  sheath  ' 


Radix  pili  (root  i 


■  Substantia  corticalis 

— "  Substantia  medullaris 


Sebaceous  gland 


f 

\  Arrector  pili  muscle 


Outer   fibrous  layer  — 

Dermal  I     ,  ^.  , 

coat  of  1     I°°<='  fi''""^  '^y"  ~~  • 
follicle 

I  Hyaline  layer ; 


Bulbus  pil 
Fundus  folliculi  pil 


and  curled  hairs  are  more  flattened.  The  root  of  curled  hair  has  been  observed  in  certain 
instances,  as  in  the  negro,  to  have  a  curved  course  in  the  skin  which  may  account  in  a  measure 
for  its  curliuess. 

The  hairs  are  arranged  singly  or  in  groups  of  from  two  to  five  and,  except  those  of  the  eye- 
lashes, are  implanted  at  oblique  angles  to  the  surface  of  the  skin.  The  directions  in  which  the 
hairs  point  are  constant  throughout  life  for  the  same  individual.  They  are  arranged  in  tracts 
in  which  the  hairs  diverge  from  a  centre  in  whorls,  the  vortices  pilorum. 

These  vortices  are  found  oonstantty  in  certain  definite  regions  and  apportion  the  whole  hairy 
surface.  The  centres  of  vortices  are  found  at  the  vertex  (sometimes  double)  upon  the  face, 
around  the  external  auditory  meatus,  in  the  axilla,  in  the  inguinal  region,  and  sometimes  on  the 
lateral  surface  of  the  body.  These  are  all  paired  except  as  a  rule  the  first.  Where  adjoining 
vortices  come  together  the  hairs  are  arranged  in  lines  along  which  they  all  point  in  nearly  the 
same  direction,  only  slightly  diverging,  forming  the  hair  streams,  fiumina  pilorum.  In  other 
lines  and  places  the  hairs  point  in  converging  directions  such  as  at  the  umbihcus  and  over  the 
tip  of  the  coccyx. 


1292   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

The  number  of  hairs  to  the  square  centimetre  varies  in  different  parts  of  the  body  and  also  in 
the  same  situation  with  the  individual  and  with  differences  in  race,  colour  and  diameters. 

The  hairs  are  most  numerous  on  the  head,  ranging  from  170  to  300  to  the  square  centimetre 
at  the  vertex.  They  are  less  numerous  on  other  parts  of  the  body,  varying  from  23  to  44  (per 
square  centimetre)  on  the  chin,  and  from  24  to  80  on  the  forearm.  The  greatest  number  is 
found  with  blonde  hair,  the  next  with  brown,  then  black,  and  the  least  with  red  hair. 

The  structure  of  the  hair. — Each  hair  consists  of  a  shaft  [scapus  pili]  (fig.  1050) 
projecting  from  the  free  surface  of  the  skin  to  end  (unless  broken  or  cut)  in  a 
conical  end  [apex  pih],  and  of  a  root  [radix  pili],  imbedded  in  the  case  of  the  lanugo 
hair  in  the  corium  and  of  the  larger  hairs  at  various  depths  in  the  subcutaneous 
tela.  Surrounding  the  root  is  a  downgrowth  of  the  skin  known  as  the  follicle 
[folliculus  pili]. 


Fig.  1051. — ^Longitudinal  Section  of  a  Hair  Ready  to  Fall  out,  with  Follicle  roR  New 
Haik.     (X30)      (From  Toldt's  Atlas.) 
,  Shaft 


Orifice  of  sebace 
ous  gland 


Dermal  coat  of  hair -follicle 


iA Epidermal  coat  of  hair-follicle 


Hair-knot  (modified  hair -bulb) 


The  root  of  the  hair  at  its  deepest  parts  swells  to  from  one  and  one-half  to  three 
times  the  diameter  of  the  shaft  forming  thus  the  bulb  [bulbus  pili]  (fig.  1050). 
The  bulb  is  hollow  and  a  vascular  connective-tissue  process,  the  hair  papilla  [papilla 
pili]  (figs.  1050,  1051)  extends  from  the  deepest  part  of  the  follicle  into  the  cavity 
in  its  base.  The  follicle  consists  of  an  external  connective-tissue  portion  formed 
by  the  corium,  the  theca  folliculi  and  an  internal  epithelial  portion  belonging  to 
the  epidermis  and  divided  into  two  portions,  the  inner  and  outer  root  sheaths 
(fig.  1050). 

The  theca  of  the  follicle  is  composed  of  an  outer  loose  longitudinal  and  a  middle  circular 
layer  of  connective  tissue  and  an  inner  basement  membrane.  The  outer  root  sheath  is  directly 
connected  with  the  stratum  germinativum  of  the  epidermis.  In  its  deeper  part  it  consists  of 
several  layers  of  cells  but  of  only  one  near  the  surface.  The  inner  root  sheath  has  been  divided 
into  three  layers.  At  the  junction  of  the  outer  and  middle  thirds  of  the  follicle  of  most  of  the 
hairs,  the  ducts  of  usually  two  or  more  sebaceous  glands  connect  with  the  space  between  the  hair 


THE  NAILS 


1293 


and  its  follicle  (figs.  1050,  1051).  Immediately  beneath  this  is  the  narrowest  part  of  the  follicle 
the  neck  [collum  folhcuU  piU],  especially  important  as  the  position  of  the  nerve  ending  of  the 
hair. 

The  hair  is  formed  of  epithelial  cells  arranged  in  two  and  sometimes  three  layers;  an  outer 
single-celled  layer  of  transparent  over-lapping  cells,  the  cuticle,  an  intermediate  layer  several 
cells  thick  formed  of  irregular  fusiform  horny  cells  containing  pigment  and  arranged  in  fibrous 
strands,  the  substantia  corticalis,  and  in  some  of  the  larger  hairs  an  internal  two  or  three  celled 
layer  of  angular  cells  occupying  the  center  of  the  hair  shaft  for  only  part  of  its  length,  the 
substantia  meduUaris.  Between  both  the  cortical  and  medullary  cells  are  spaces  containing  air. 
In  the  hair  bulb,  where  the  cells  are  larger  and  softer  the  layers  are  not  distinguishable.  The 
cells  here  being  in  process  of  division  and  being  gradually  transformed  into  the  horny  cells  of 
the  shaft. 

Many  of  the  hairs  have  in  connection  with  their  follicle  round  or  flat  bundles 
of  unstriped  muscle  fibres,  the  arrectores  pilorum  (figs.  1050,  1052).  These  are 
situated  on  the  side  toward  which  the  hairs  point,  their  deep  ends  being  attached 
to  the  hair  follicle  beneath  the  sebaceous  glands  which  they  more  or  less  embrace 
and  their  superficial  ends  connected  with  the  papillary  layer  of  the  skin.  Con- 
traction of  the  arrectores  not  only  causes  the  hairs  to  become  more  erect  and  the 
skin  around  them  to  project  somewhat  causing  "goose  flesh, "  but  also  compresses 
the  sebaceous  glands  which  are  situated  between  the  follicle  and  muscle  and  helps 
to  empty  the  glands  of  their  secretion. 


Vertical  Section  of  the  Skin  fbom  Scalp. 


—  Sebaceous  gland 


Fat  and  connec 
tive  tissue 


The  blood  supply  of  the  hairs. — The  hair  follicles  arc  surrounded  by  a  capillary  network 
of  arteries  connected  with  those  of  the  corium  and  the  papill-ae  are  also  supplied  with  loops  of 
arteries. 

The  nerves  of  the  corium  supply  branches  to  the  hairs.  Some  of  these  branches  enter  the 
papillEE,  others  surround  the  follicle  at  its  neck  and  are  distributed  among  the  cells  of  the  outer 
root  sheath. 

Development. — The  hairs  are  developed  from  the  epidermis  by  thickenings  and  down- 
growths  into  the  corium  of  plugs  of  epithelium.  The  deepest  parts  of  these  plugs  become  swol- 
len to  form  bulbs  and  from  these  the  hairs  are  produced.  The  central  cells  of  the  epithehal 
downgrowths  disintegrate  producing  the  lumen  of  the  follicle.  The  hairs  continue  to  grow  from 
the  deeper  cells  and  protrude  from  their  follicles  between  the  fifth  and  seventh  foetal  months. 
Abnormally  they  may  be  scanty  at  birth  and  rarely  entirely  absent,  alopecia.  The  lanugo  hairs 
which  cover  all  the  hairy  parts  of  the  body  at  birth  are  soon  shed  and  replaced  by  new  hairs  in- 
the  old  follicles.  Throughout  lite  also  the  hairs  are  being  constantly  shed  and  replaced  by  new 
ones.  This  is  accompanied  by  cornification  of  the  bulb  and  fibrillation  of  the  deep  end  of  the 
hair  (fig.  1051).  Thinning  of  the  hair  and  baldness  occur  when  the  shed  hairs  cease  to  be 
replaced.  This  is  common  in  old  age  and  a  premature  baldness  appears  to  run  in  certain  fam- 
ilies.    The  rate  of  growth  is  normally  from  1  to  1.5  cm.  per  month,  but  is  subject  to  variation. 


B.  THE  NAILS 

The  nails  [ungues]  are  thin,  semi-transparent,  horny  epidermic  plates  upon  the 
dorsal  surfaces  of  the  distal  phalanges  of  the  fingers  and  toes.  Through  their 
hardness  they  serve  as  protective  organs  not  only  by  covering  the  nerve  endings 
and  other  delicate  structures  of  the  skin;  but  also  by  acting  as  natural  weapons. 
On  the  fingers  they  form  useful  tools.     They  are  four-sided  plates  presenting  a  dis- 


1294   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 


tal  free  border  [margo  liber],  which  overhangs  the  tips  of  the  fingers,  an  irregular, 
sharp  proximal  edge  [margo  occultus],  and  on  each  side  a  somewhat  thinned 
border  [margo  lateralis]  (fig.  1053). 


Fig.  1053.- 


-DoHSAL  Surface   of  Isolated   Finger  Nail. 
Margo  liber 


Corpus  unguis 


(XI.)     (From Toldt's   Atlas.) 


^   A  ■         |l''hl,':??W-  Lunula 

Radix  unguis  ---fj-'f'&Wjmil 


Margo  occultus 

Each  nail  is  composed  of  an  exposed  distal  part,  the  body  [corpus  unguis], 
and  a  proximal  covered  part,  the  root  [radix  unguis],  (fig.  1053),  which  ends  in 
the  margo  occultus.  The  nail  is  at  a  slightly  deeper  level  than  the  surrounding 
skin  which  overhangs  the  root  and  the  lateral  margins  in  a  fold,  the  nail  wall 

Fig.  1054. — Finger  Nail  and  Nail  Bed. 


Corpus  unguis 
Margo  lateralis 


Lunula 
Vallum  unguis 


Radix  unguis- — 


Matrix  unguis 

Cristse  matricis  unguis 

Sulci  matricis  unguis 
Margo  occultus 


[vallum  unguis]  (figs.  1054,  1055,  1056).  The  epidermis  of  the  free  edge  of  the 
nail  wall,  especially  proximally,  is  thickened  and  often  appears  as  a  ragged  edge. 
At  a  deeper  level  than  the  above  and  extending  somewhat  more  distally  is  a  vari- 
ably developed  thin  parchment-like  membrane,  the  eponychium,  closely  attached  to 

Fig.  1055. — ^Longitudinal  Section  Through  the  Tip  op  the   Middle  Finger.     ( X  2) 

(From  Toldt's  Atlas.) 

Stratum  corneum 


Stratum  germinativum 


Corpus  papiUare 


Margo  liber 


Stratum  corneum 


Stratum  germinativum 


1/  Matrix  unguis 


.  Radix  unguis 


the  superficial  surface  of  the  nail.  It  is  the  representative  of  the  superficial  layers 
of  the  embryonic  epidermis  which  do  not  take  part  in  the  formation  of  the  nail. 
The  groove  which  is  formed  between  the  vallum  and  the  underlying  nail  bed  is 
known  as  the  sulcus  matricis  unguis.     This  lodges  the  root  and  lateral  margins 


THE  NAILS 


1395 


of  the  nail  and  is  deepest  in  the  centre  of  the  root,  becomes  shallower  toward  the 
lateral  margins,  and  finally  disappears  entirely  toward  the  free  border  of  the 
nail  (figs.  1055,  1056). 

The  dorsal  free  exposed  surface  of  the  nail  is  formed  by  a  hardened,  thickened,  horny  layer  of 
epithelium  corresponding  to  the  deeper  parts  of  the  stratum  corneum  (or  the  stratum  lucidum) 
of  the  skin,  the  stratum  corneum  unguis  (fig.  1056).  It  is  convex  from  side  to  side  (especially 
on  the  fifth  finger),  and  also  in  some  cases  longitudinally.  It  presents  a  number  of  more  or  less 
well-marked  fine  longitudinal  ridges.  The  stratum  corneum  forms  the  principal  thickness  of 
the  nail.  It  is  thicker  and  more  solid  on  the  toes  than  on  the  fingers.  The  portion  of  the 
nail  which  projects  beyond  the  skin  of  the  fingers  and  toes  is  greyish-white  in  colour.  Unless 
broken  or  cut,  it  curves  ventrally  upon  the  ball  of  the  finger  or  toe  and  tends  to  become  long  and 
claw-like.     It  may  attain  a  length  of  3  or  more  centimetres. 

The  concave  volar  or  plantar  surface  of  the  nail  is  softer  and  is  formed  of  a  layer  of  epithehal 
cells  which  corresponds  to  the  stratum  germuiativum  (Malpgihii)  of  the  skin  and  is  known  as 
the  stratum  germinativum  unguis  (fig.  1056).  Because  of  the  transparency  of  both  layers  of 
the  nail  the  blood  in  the  underlying  matrix  is  seen  through  the  body  of  the  nail  and  gives  to  it  a 


Fig.  1056. — Cross-section   Through   the   Nail   and   Tip   of  the  Ring  Finger.     (X4). 
(From  Toldt's  Atlas.) 


Corpus  unguis 

Cristffi  matricis  unguis 
Vallum  unguis  ^ 


Sulcus  matricis 
unguis 


Periosteum  ^^^  "^ 

Retinacula  cutis  '^  ^^ 


CristEe  cutis 
Volar  surface  of  finger 


Stratum  corneum  unguis 
Stratum  germinativum 
Matrix  unguis 


pinkish  colour;  but  toward  the  root  of  the  nail  there  is  a  semilunar  area  convex  distally,  the 
lunula,  which  is  less  transparent  and  opaque  whitish  in  color  (fig.  1053).  The  lunula  is  vari- 
ously developed  in  different  individuals.  It  is  largest  on  the  thumb  and  is  often  abssnt  on  the 
little  finger.     It  is  also  smaller  on  the  toes  than  on  the  fingers. 

The  stratum  corneum  unguis  consist  of  thin,  flattened,  transparent,  horny  scales  with  shrunken 
nuclei.  These  cells  are  intimately  joined  together  in  thin  layers.  The  stratum  germina- 
tivum unguis  is  formed  of  cells  continuous  with  and  resembling  those  of  the  corresponding 
layer  of  the  epidermis.  Air  may  occur  between  the  cells  as  with  the  hair.  The  cells  of  the  root 
are  not  yet  cornified  or  dried  out. 

The  stratum  germinativum  unguis  rests  upon  the  corium,  which  here  forms  the  so-called 
nail  bed  [matrix  unguis].'  This  is  made  up  of  a  dense  feltwork  of  connective  tissue  fibres 
without  fat.  It  is  highly  vascular  and  sensitive  and  the  vertically  arranged  bundles  bind  the 
nails  tightly  to  the  periosteum  of  the  termmal  phalanges.  The  papillte  of  the  matrix  beneath  the 
body  of  the  nail  are  arranged  in  stronglj'  marked  longitudinal  ridges,  the  cristee  matricis  unguis. 
The  cristffi  and  papilla;  of  the  matrix  fit  into  corresponding  depressions  on  the  deep  surface  of 
the  stratum  germinativum  unguis. 

The  cristse  of  the  matrix  are  small  and  low  proximally  and  become  larger  and  fewer  distally. 
Those  toward  the  lateral  borders  are  somewhat  oblique.  The  papillae  of  the  root  are  not  in  rows 
but  are  irregularly  arranged  and  disappear  entirely  near  the  distal  border  of  the  lunula.  Toward 
the  free  border  of  the  nail  the  papilte  become  large  and  change  in  character  to  that  of  the  adja- 
cent skin. 

The  best  developed  nails  are  those  of  the  thumbs  and  great  toes,  the  least  developed,  those 
of  the  fifth  digits  which  on  the  toes  are  often  represented  only  by  a  horny  tubercle. 

Blood-supply  of  the  nails. — The  arteries  are  numerous  in  the  matrix  beneath  the  body  of  the 
nail  but  fewer  beneath  the  root.  They  pass  from  the  deep  parts  of  the  nail  bed  toward  the  sur- 
face, running  in  the  main  longitudinally  and  sending  anastomosing  branches  to  tlie  papillte. 

The  nerves  beneath  the  nail  are  abundant  and  terminate  in  free  sensorjf  endings  and  in  special 
end  organs  of  several  sorts. 

1  The  term  nail  bed  is  applied  by  some  anatomists  to  that  part  of  the  corium  beneath  the 
body  of  the  nail,  the  term  matrix  being  reserved  for  the  corium  beneath  the  lunula  and  root. 


i 


1296     THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

Development  of  the  nails. — The  nails  are  developed  from  the  epidermis.  In  early  embryos 
over  the  dorsal  surface  of  each  distal  phalanx  there  is  seen  a  smoother  and  more  adherent  area 
of  skin  which  becomes  Umited  by  folds  distally  as  well  as  proximally  and  laterally.  It  is  also 
distinguished  by  a  greater  number  of  cell  layers  which  later  become  flatter  than  the  surrounding 
cells.  The  number  of  cell  layers  still  further  increases  and  at  about  the  fifth  foetal  month  the 
nail  proper  is  formed  by  the  deeper  lying  cells  over  an  area  extending  from  the  proximal  fold 
to  the  distal  end  of  the  lunula.  The  nail  is  pushed  distally  by  constant  formation  of  new  cells 
in  the  same  way  as  it  continues  to  grow  throughout  life.  The  surface  epithelial  cells  of  the  nail 
field  cover  the  nail  for  some  time  as  a  thin  layer,  the  eponychium,  which  later  disappears  except 
a  small  fringe  near  the  root. 

Growth  of  the  Nails. — The  nail  grows  in  length  and  thickness  by  multiplication  of  those 
cells  of  the  stratum  germinativum  which  are  situated  between  the  margo  occultus  of  the  root 
and  the  distal  border  of  the  lunula.  The  older  cells  are  pushed  distally  and  toward  the  sur- 
face by  the  deeper  cells.  As  a  result  the  nail  becomes  gradually  thicker  from  the  occult  bor- 
der as  far  as  the  distal  margin  of  the  lunula.  Over  the  rest  of  the  nail  bed  no  thickening  appears 
to  take  place.  The  rate  of  growth  is  faster  on  the  fingers  than  on  the  toes  and  varies  with  age, 
season,  and  the  individual.  When  the  nail  is  torn  off,  or  detached  through  inflammation,  it 
may  be  regenerated  if  the  cells  of  the  stratum  germinativum  have  not  been  destroyed. 

Congenital  hypertrophy  of  the  nails  sometimes  occurs,  but  absence  or  imperfect  development  is 
rarely  seen.  The  white  spots  so  frequently  seen  in  the  nail  are  caused  by  air  between  the  cell 
layers  due  usually  to  injury  or  impaired  development. 

C.  THE  CUTANEOUS  GLANDS 

The  glands  of  the  skin  [glandulae  cutis]  are  of  two  kinds:  glomiform  glands, 
and  sebaceous  glands.  The  glomiform  ("skein-like")  glands  [glandulae  glomi- 
formes]  are  of  four  types:  sudoriferous  glands,  ciliary  glands,  ceruminous  glands 
and  circumanal  glands. 

Fig.  1057. — Vertical  Section  of  the  Palmar  Skin  Showing  an  Isolated 

Sudoriferous  Gland.  (Testut.) 

1,  Stratum  corneum;  2,  Malpighian  layer;  3.  corium;  4,  papilla;  5,  body  of  sudoriferous  gland; 

and  6,  7,  its  excretory  duct;  8,  orifice  of  duct  on  surface;  9,  subcutaneous  fat. 


The  sudoriferous  glands  [glandulae  sudoriferae]  or  sweat  glands  are  modified 
simple  tubular  glands  which  secrete  the  siveat  [sudor].  They  are  found  in  the 
skin  of  all  parts  of  the  body  except  that  part  of  the  terminal  phalanges  covered 
by  the  nails,  the  concave  surface  of  the  concha  of  the  ear,  the  labia  minora,  and  the 
inferior  part  of  the  labia  majora  in  the  female  and  the  surface  of  the  prepuce 
and  the  glans  penis  in  the  male.  The  number  found  in  different  parts  of  the  body 
varies  greatly.     They  are  very  few  on  the  convex  surface  of  the  concha  and  on 


THE  CERUMINOUS  GLANDS  1297 

the  eyelid.  They  are  also  rather  scanty  on  the  dorsal  surface  of  the  trunk 
and  neck,  more  numerous  on  the  ventral  surface  of  these  parts  and  on  the 
extensor  surfaces  of  the  extremities,  still  more  numerous  on  the  flexor  surfaces, 
and  most  numerous  on  the  volar  surface  of  the  hands  and  plantar  surface  of  the 
feet.  They  vary  from  less  than  57  to  more  than  370  to  the  square  centimetre. 
The  total  number  has  been  variously  estimated  at  from  two  to  fifteen  millions. 
Each  gland  (fig.  1057)  consists  of  a  secretory  portion  or  body  [corpus  gl. 
sudoriferae],  and  an  excretory  duct  [ductus  sudoriferus],  which  opens  on  the  sur- 
face of  the  skin  by  a  mouth  visible  to  the  unaided  eye,  the  so-called  'pore'  [porus 
sudoriferus].     Occasionally  the  duct  opens  into  a  hair  follicle. 

The  bodies  of  the  glands  are  irregular  or  flattened  spherical  masses,  yellowish  or  yellowish 
red  in  colour  and  somewhat  transparent.  They  vary  in  size  from  .06  to  4  mm.  or  more  with  a 
mean  diameter  of  .2  to  .4  mm.,  the  largest  being  found  in  the  axilla.  They  are  formed  of  the 
irregularly,  many  times  coiled,  terminal  part  of  the  gland  tube.  The  bodies  of  the  glands  are 
situated  in  the  deeper  part  of  the  corium  or  in  the  subcutaneous  tela. 

The  wall  of  the  rather  wide-lumened  gland  tube  is  formed  of  a  single  layer  of  cubical  or  col- 
umnar epithelium  containing  fat  and  pigment  granules  and  surrounded  externally  by  a  basement 
membrane.  Enclosing  these  is  a  more  or  less  dense  connective-tissue  sheath.  In  many  of  the 
glands,  especially  the  larger  ones,  there  is  a  layer  of  obliquely  running  unstriped  muscle  fibres, 
the  so-called  myoepithelium,  between  the  basement  membrane  and  the  cells.  In  some  cases 
the  bodies  of  the  glands  are  imbedded  in  a  more  or  less  dense  mass  of  lymphoid  tissue. 

The  ducts,  beginning  as  several  coils  bound  up  with  those  of  the  bodies,  extend  often  in  a 
straight  or  sUghtly  wavy  course  nearly  at  right  angles  to  the  surface  as  far  as  the  epidermis. 
This  they  pierce  as  spiral  canals  of  from  two  to  sixteen  turns,  more  marked  where  the  epidermis 
is  thickest  (fig.  1041),  and  opened  on  the  surface  by  somewhat  widened  funnel-shaped  mouths. 
The  ducts  pass  between  the  papilla?  of  the  corium  and  open  on  the  summits  of  the  cutaneous 
cristae  where  these  are  present.  The  diameter  of  the  ducts  is  distinctly  smaller  than  that  of 
the  secreting  part  of  the  glands,  and  this  is  true  of  the  lumen  also. 

The  ducts  are  lined  by  a  stratified  epithelium  composed  of  two,  three,  or  more  layers  of  cella 
resting  on  a  basement  membrane  without  any  intervening  layers  of  muscle-cells,  and  surrounded 
by  a  connective-tissue  sheath.  This  latter  as  well  as  the  basement  membrane  ceases  at  the 
epidermis  and  the  epithelial  cells  of  the  duct  walls  join  those  of  the  stratum  germinativum.  The 
duct  for  the  rest  of  its  course  to  the  surface  is  merely  a  canal  through  the  cells  of  the  epidermis. 

The  degree  of  development  of  the  sweat  glands  varies  with  the  situation,  the  individual,  and 
also  racially,  as  instanced  by  their  great  development  in  the  negro.  In  some  individuals  the 
perspiration  is  much  more  profuse  than  in  others.  The  glands  are  smaller  in  the  aged  than  in 
the  young.  The  odour  of  the  sweat  is  peculiar  and  more  or  less  characteristic,  varying  with  the 
individual. 

The  sudoriferous  glands  in  the  axillary  region  seem  to  be  in  some  way  connected  with  the  sex- 
ual function  for  although  a  large  number  persist  as  small  glands,  others  undergo  further  develop- 
ment beginning  about  the  ninth  year  in  the  female  and  at  puberty  in  the  male.  These  glands  in 
places  form  almost  a  continuous  layer  and  are  formed  of  large  partly  branched  tubules  with  high 
secreting  cells.  The  reddish  colour  of  the  sweat  in  the  axillary  and  some  other  regions,  especially 
in  certain  individuals,  is  probably  derived  from  the  pigment  granules  which  are  found  in  the 
glands  here.     The  oil  in  the  secretion  lubricates  the  skin  and  keeps  it  soft  and  supple. 

Blood-supply  of  the  sudoriferous  glands. — The  sudoriferous  glands  are  supplied  from  the 
deep  cutaneous  plexus  by  an  abundant  network  of  arteries  which  surround  and  penetrate 
between  the  coils  of  the  gland  tubules. 

Nerves. — There  is  an  enclosing  network  of  nerve  fibres  some  of  which  have  been  traced  to 
the  gland  cells. 

Development. — The  sudoriferous  glands  are  seen  first  in  the  fourth  or  fifth  foetal  month. 
The  anlages  resemble  closely  those  of  the  hair,  but  the  cells  are  not  so  loosely  packed.  They 
project  down  as  solid  plugs  which  become  long,  slender,  and  tortuous  rods.  In  the  seventh 
foetal  month  the  rods  begin  to  develop  a  lumen  in  the  deeper  parts,  which  also  now  begin  to  coil. 
A  lumen  soon  develops  also  in  the  superficial  parts  and  joins  that  in  the  deeper  part  of  the 
gland.  The  outer  of  the  two  layers  of  epitheUum  in  the  ducts  becomes  transformed  at  its  transi- 
tion into  the  gland  proper  into  the  myoepithelial  layer. 

The  ciliary  glands  [gl.  ciliares;  Molli]  are  modified  sudoriferous  glands  of  the 
branched  tubo-alveolar  type.  They  have  simpler  coils  but  are  larger  than  ordi- 
nary sweat  glands.  They  are  situated  in  the  eyelids  near  their  free  borders 
and  open  into  the  follicles  of  the  cilia  or  close  to  them  (see  Section  VIII). 

The  circumanal  glands  [gl.  circumanales]  are  found  in  a  circular  area  about 
1.5  cm.  wide  which  surrounds  the  anus,  a  short  distance  from  it. 

These  glands  are  several  times  the  size  of  the  ordinary  sweat  glands  and  resemble  the  glands 
found  in  the  axilla,  their  secretion  likewise  having  a  strong  odour.  They  are  branching  tubular 
glands.  The  other  kinds  of  glands  which  are  found  in  this  same  area  are  ordinary  sweat  glands, 
glands  with  straight  duets,  with  saccules  and  secondary  alveoli,  and  tubo-alveolar  glands. 

Cerumimous  glands  [gl.  ceruminosse]  are  glomiform  glands  somewhat  modi- 
fied from   the   sudoriferous   type.     They   are   branched  tubo-alveolar    glands 


( 


1298   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

with  relatively  large  lumina  in  the  coils  and  narrow  short  ducts,  and  occur  only 
in  the  external  acoustic  (auditory)  meatus. 

They  are  very  abundant  on  the  dorsal  and  superior  part  of  the  acoustic  meatus  in  the  region  of 
the  cartilaginous  part,  where  in  the  adult  most  of  them  open  on  the  surface  of  the  skin  close  to 
hairs.  Others  open  into  the  hair  follicles  as  they  all  do  in  the  foetus  and  child.  Their  secretion, 
the  cerumen,  is,  when  freshly  secreted,  a  fluid  or  semifluid  oily  material  of  a  yellowish-brown 
colour,  which  on  exposure  to  the  air  becomes  solid  like  wax. 

The  sebaceous  glands  [gl.  sebaceae]  are  simple  branched  or  unbranched 
alveolar  glands  distributed  over  nearly  the  whole  surface  of  the  body.  Nine- 
tenths  of  them  are  closely  associated  with  the  hairs,  into  the  follicles  of  which 
they  empty  (figs.  1050,  1051),  and  are  therefore  absent  from  certain  of  the  non- 
hairy  parts  of  the  body,  as  the  flexor  surfaces  of  the  hands  and  feet,  the  dorsal 
surfaces  of  the  distal  phalanges  of  the  fingers  and  toes.  On  the  other  hand,  a  few 
are  found,  usually  much  modified,  opening  independent  of  the  hair  follicles,  as 
at  the  angles  of  the  red  margins  of  the  lips,  around  the  nares,  around  the  anus, 
and  the  tarsal  (Meibomian)  glands  in  the  eyelids.  Modified  sebaceous  glands 
are  also  found  upon  the  mammary  papilla  and  areola  in  the  female,  and  in  some 
cases  upon  the  superficial  surface  of  the  glans  and  the  surface  of  the  prepuce  of 
the  penis,  here  known  as  preputial  glands ;  also  a  few  very  small  ones  may  be  found 
upon  the  labia  minora,  the  glans  and  prepuce  of  the  clitoris. 

The  glands  vary  in  size  in  different  situations  and  also  in  individuals  and  races.  They 
range  from  .2  to  2.2  mm.  long  and  nearly  as  broad.  Among  the  smallest  are  those  of  the  scalp. 
The  largest  are  found  on  the  alse  of  the  nose  and  on  the  cheeks  where  their  ducts  are  visible  to 
the  unaided  eye.  They  are  also  large  on  the  mons  pubis,  labia  majora,  scrotum,  about  the  anus 
and  on  the  mammary  areola.  Smaller  glands  are  also  found  associated  with  these  large  ones. 
The  size  of  the  glands  is  independent  of  the  size  of  the  hairs  with  which  they  are  associated  but 
the  number  of  glands  depends  upon  the  size  of  the  hair.  On  small  hairs  one  or  more  glands  are 
always  found  and  on  large  hairs  there  may  be  a  whole  wreath  of  from  four  to  six  separate  glands 
opening  into  the  hair  follicle. 

The  number  of  sebaceous  glands  has  never  been  exactly  estimated,  although,  it  is  known 
that  they  are  less  numerous  than  the  sudoriferous  glands.  This  is  very  evident  on  the  extrem- 
ities, trunk,  and  neck,  where  they  bear  a  relation  of  1  to  6  or  8.  On  the  scalp,  concha  of  the  ear, 
and  skin  of  the  face  they  are  about  equal  in  number  while  on  the  forehead,  alae  of  the  nose,  free 
borders  of  the  eyehds  and  external  genital  organs  in  the  female  the  number  of  sebaceous  glands 
is  greater  than  the  number  of  sudoriferous  glands. 

Each  sebaceous  gland  consists  of  a  secretory  portion,  the  body,  connected  with 
the  hair  follicle  or  the  surface  of  the  skin  by  a  wide  short  duct.  In  the  small 
glands,  the  body  of  the  gland  may  consist  of  a  single  alveolus  but  in  the  larger 
glands  there  are  from  four  to  twenty  of  these  connected  by  irregular  ducts  to  a 
single  excretory  duct. 

The  ducts  open  into  the  hair  follicles  near  their  necks  between  the  inner  root  sheath  and  the 
hair  or  upon  the  surface  of  the  skin.  They  are  always  very  short,  cylindrical,  or  infimdibuli- 
form,  and  their  epithelium  is  directly  connected  with  that  of  the  outer  root  sheath  of  the  hau' 
folhcle  or  with  the  epidermis  where  the  hair  is  wanting. 

The  glands  lie  in  the  superficial  layers  of  the  corium  and  where  one  or  a  few  are  connected  to 
a  single  hair,  they  usually  open  into  the  hair  follicles  on  the  side  toward  which  the  hairs  point. 
Where  there  are  several  glands  for  one  hair  they  may  completely  surround  the  hairs  like  a  rosette. 

The  cells  of  the  body  of  the  gland  and  of  the  duct  are  surrounded  by  a  basement  membrane 
outside  of  which  is  a  connective-tissue  sheath,  both  of  which  are  continuous  with  corresponding 
coverings  of  the  hair  folhcle. 

The  periphery  of  the  alveolus  is  formed  of  small  cubical  epithehal  cells,  the  central  part  of 
larger  and  more  rounded  cells.  The  cells  of  the  alveolus  show  all  stages  of  fatty  degeneration, 
the  peripheral  cells  contain  small  fatty  particles,  those  nearest  the  centre  larger  and  more  nu- 
merous fat  droplets,  some  of  them  being  completely  broken  down.  There  is  no  distinct  lumen  to 
the  alveolus  but  this  is  filled  with  degenerated  cells,  fatty  particles  and  ddbris  of  broken-down  and 
cast-off  cells.  The  deeper  cells  continue  to  multiply  and  push  the  more  superficial  cells  toward 
the  lumen  where  they  in  turn  are  cast  off.  The  secretion  thus  formed  is  known  as  the  sebum 
cutaneum.  It  is  a  whitish  or  whitish-yellow  mass  composed  of  fat  and  broken-down  cells  of  the 
consistency  of  thick  oil  which  spreads  over  the  surface  of  the  skin  and  hair  as  a  lubricant. 
Through  the  decomposition  of  its  fat  more  or  less  odour  is  produced.  When  the  gland  duct  is 
blocked  the  secretion  is  retained  and  becomes  more  solid  and  is  known  as  a  comedo.  The  active 
secretion  of  the  sebaceous  glands  does  not  begin  before  the  fifth  or  sixth  year  of  life.  It  attains 
its  maximum  in  the  adult  and  decreases  in  the  aged. 

The  relation  of  the  arreotores  pilorum  to  the  sebaceous  glands  has  been  described  in  con- 
nection with  the  relation  of  these  muscles  to  the  hairs. 

Vessels  and  nerves. — The  sebaceous  glands  are  surrounded  by  a  fine  capillary  plexus  of 
blood-vessels  closely  associated  with  those  of  the  hairs  and  skin.  Concerning  their  lymph- 
vessels  little  is  known.  The  nerves  of  the  sebaceous  glands  are  connected  with  those  of  the 
skin  and  hair  but  the  exact  manner  of  distribution  is  not  clearly  understood.] 


THE  MAMMARY  GLANDS 


1299 


Development. — The  sebaceous  glands  appear  lirst  in  the  fifth  foetal  month  as  single,  rarely 
double,  buds  on  the  anlages  of  the  hair  follicles.  The  distal  ends  of  these  enlarge  and  become 
lobulated.  In  these  solid  masses  of  cells  lumina  for  the  alveoli  and  the  ducts  later  are  formed, 
through  the  fatty  degeneration  of  the  central  cells.  The  oily  contents  of  these  cells  together 
with  the  debris  and  the  cast-off  surface  cells  of  the  epidermis  form  the  vernix  caseosa  on  the  sur- 
face of.the  foetus. 

D.  THE  MAMMARY  GLANDS 

The  mammary  glands  [mammae]  or  breasts  are  modified  cutaneous  glands. 
In  tlie  male  they  remain  rudimentary  and  functionless  throughout  life,  but  in 
the  female  they  are  functionally  closely  associated  with  the  reproductive  organs 
since  they  secrete  the  milk  for  the  nourishment  of  the  newborn  and  are  subjected 
to  marked  changes  at  puberty,  throughout  pregnancy,  during  and  after  lacta- 
tion, and  after  the  menopause. 


Fig.  1058. — The  Right  Mamma  op  a  Girl  18  Years  Old.     (Modified  from  Spalteholz.) 


Areolar 

gland' 

Papilla 

Areola 


The  two  mammffi  (fig.  1058)  are  situated  on  the  ventral  surface  of  the  thorax 
one  on  each  side  of  the  sternum.  As  examined  from  the  surface  in  a  well-developed 
nulliparous  female  they  appear  to  extend  from  the  second  or  third  rib  to  the  si.xth 
or  seventh  costal  cartilage  and  from  the  lateral  border  of  the  sternum  to  beyond 
the  ventral  folds  of  the  axillse.  Separating  the  two  mammae  there  is  a  median 
unraised  area  of  variable  size,  the  sinus  mammarum. 

In  shape  they  are  conical  or  hemispherical,  and  in  consistency  somewhat 
firm  and  elastic:  The  size  of  the  two  breasts  is  seldom  equal,  the  left,  as  a  rule 
being  slightly  the  larger.  Each  measures  from  10  to  13  cm.  in  diameter  being 
slightly  longer  in  the  direction  parallel  to  the  lateral  border  of  the  pectoralis  major 
muscle.     The  weight  of  each  gland  varies  from  140  to  200  grams,  or  more. 

Each  mamma  presents  for  examination  a  ventral  surface  and  a  dorsal  surface. 
The  ventral  surface  is  free,  covered  by  skin,  smooth  and  convex.     It  is  continuous 


i 


1300  THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 


cephalically,  without  sharp  demarcation,  with  the  ventral  surface  of  the  thorax 
but  laterally  and  caudally  it  is  usually  sharply  defined  (figs.  1058,  1060).     It  is 

Fig.  1059. — The  Female  Mamma  Dt-hing  Lactation.     (After  Luschka.) 


Adipose  loculus 


Gland  loculus 


Fig.  1060. — Sagittal  Section  of  the    Right  Mamma  of  a  Woman  Twenty-two   Years 
Old      (Testut ) 


Pectoralis  major 
Skin 


Retinaculum  cutis   /"^ 
Pyramidal  process 


„,  Pectoralis  minor 

■jfS^    -Intercostal  muscle 
Pectoral  fascia 


Connective  tissue 
Superficial  fascia 


--^(^         horizontal  plane 


Fifth  nb 


Pyramidal  process 

Rectinaculum  Fat 
cutis 


External  oblique 


most  prominent  slightly  meso-caudal  to  the  centre  and  at  this  point  there  is  a 
marked  pigmented  projection,  the  nipple  [papilla  mammse]  surrounded  by   a 


THE  MAMMARY  GLANDS 


1301 


slightly  raised  area,  also  pigmented,  the  areola  mammae.     These  two  structures 
will  be  described  separately  later. 

The  dorsal  surface  of  the  mammary  gland  (figs.  1060,  1061)  is  attached  and 
concave.  It  is  in  relation  in  its  cephalo-medial  two-thirds  with  the  fsacia  over  the 
pectoralis  major  muscle.  In  its  caudo-lateral  third  it  extends  over  the  base  of 
the  axillary  fossa,  where  it  is  in  relation  with  lymphatic  glands  and  with  the  ser- 
ratus  anterior  muscle,  and  at  its  most  caudal  part,  sometimes  with  the  external 
abdominal  oblique  muscle. 

The  usual  number  of  breasts  in  the  human  species  is  two;  rarely  is  the  number  reduced, 
much  more  often  do  we  find  an  increase  in  this  number.  Each  of  these  conditions  is  found  in 
both  sexes  and  may  be  complete  or  partial.  Complete  suppression  of  both  breasts,  amastia,  is 
one  of  the  rarest  anomaUes  and  is  usually  associated  with  other  defects.  Complete  absence  of 
one  is  less  rare.  A  more  frequent  condition  is  arrest  of  development,  micromastia,  leading  to 
rudimentary  but  functionless  organs.  Absence  of  the  nipple,  athelia,  is  much  commoner  and 
generally  affects  both  breasts.  All  grades  of  the  imperfection  from  complete  absence  to 
shghtly  imperfect  nipple  may  be  found.  When  there  is  an  increase  this  may  include  the  whole 
breast,   polymastia,   or  just  the  nipple,  polythelia.     The  supernumerary  structures  [mammae 


Fig.  1061. — Horizontal  Section  of  the  Right  Mamma  or  a  Woman  22  Years  Old. 

(Testut.) 


Pyramidal  process 


Skin 
Retinaculum  cutis 


Areola 
Duct 
-^       Retinaculum  cutis 

■^  Pyramidal  proces 
ir1?X     -Skin 


Superficial  fascia 

Connective  tissue 


'  Sixth  rib 
-IntercQstals 


accessori8e]  may  be  represented  only  bj'  a  pigmented  area  representing  an  areola;  or  by  a  nipple 
with  or  without  an  areola;  by  a  gland  with  a  more  or  less  perfect  nipple  and  areola;  or  with 
ducts  opening  without  a  nipple;  or  there  may  be  no  opening  on  the  surface.  The  extra  mamma 
is  very  rarely  perfectly  developed  and  functional.  Various  observers  have  found  the  super- 
numerary breasts  or  nipples  occurring  in  from  1  to  7  per  cent,  of  the  cases  examined  and  some- 
what oftener  in  males  than  in  females.  The  extra  organs  are  found  more  frequently  on  the  left 
side,  usually  along  a  line  extending  from  the  axilla  toward  the  genitalia.  Tliis  corresponds  to 
the  position  in  which  the  mammae  occur  m  some  other  mammals  and  also  to  the  milk  line  of  the 
embryo.  Although  they  are  occasionally  found  in  other  situations,  over  90  per  cent,  of  them 
are  encountered  upon  the  ventral  surface  of  the  thorax  along  the  above-mentioned  line  caudal 
and  medial  to  the  normal  pair  of  breasts.  They  are  frequently  hereditary.  It  is  doubtful 
whether  their  possessors  are  either  more  fertile  or  more  Uable  to  bear  twins. 

The  shape  of  the  breasts  varies  with  the  development  and  functional  activity'and  the  amount 
of  fat.  The  smooth,  somewhat  conical  breast  of  the  nullipara  becomes  hemispherical  with 
increase  in  the  amount  of  fat,  while  in  emaciation  it  may  be  reduced  to  a  flattened  disc  with  an 
irregular  surface.  After  lactation  the  breasts  tend  to  become  more  pendulous  with  marked 
sulci  between  them  and  the  thoracic  walls,  and  after  repeated  pregnancies  they  may  become  elon- 
gated so  as  to  be  almost  conical  or  even  have  pedunculated  bases. 

The  size  of  the  mammary  gland  in  girls  remains  relatively  the  same  as  in  the 
infant  up  to  puberty  when  it  suddenly  increases  considerably  and  continues  for  a 
time  to  enlarge  slightly  at  each  menstrual  period.  There  is  also  a  temporary 
enlargement  and  soreness  at  each  menstrual  period,  due  perhaps  to  the  increased 
vascular  supply.  Until  the  age  of  puberty  the  glands  measure  8  to  10  mm.  in 
diameter  but  when  they  have  attained  their  complete  adult  development  they 
have  increased  to  100  to  110  mm.  in  the  cephalo-medial,  120  to  130  mm.  in  the 
cephalo-lateral  (obliquely  from  above  downward)  direction,  and  50  to  60  mm.  in 
thickness.     During  pregnancy  the  breasts  again  increase  in  size,  more  especially 


i 


1302    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

after  the  birth  of  the  child.  When  their  full  functional  activity  is  established, 
their  volume  may  be  two  or  three  times  as  great  as  before  pregnancy.  After  lacta- 
tion they  return  again  nearly  to  their  former  size,  which  they  retain  until  another 
pregnancy.  After  the  menopause  the  useless  glands  in  some  cases  atrophy  and 
are  reduced  to  small  discoidal  masses.  In  others,  especially  in  fat  individuals, 
although  the  secreting  tissue  disappears,  it  is  replaced  by  fat  so  that  there  is  little 
or  no  reduction  in  size.  In  addition  to  the  above-mentioned  variations  in  size, 
the  breasts  are  subject  to  great  individual  differences,  the  cause  of  which  is  little 
understood.  Large  robust  women  are  sometimes  seen  with  small  mammary 
glands,  and  small  women  with  large  glands.  In  some  individuals  they  are  espe- 
cially large. 

The  weight  of  each  mamma  varies,  naturally,  with  the  volume,  increasing  from  30  to  60 
centigrams  in  the  small  gland  of  a  young  child  to  140  to  200  grams  after  puberty  and  in  nursing 
women  reaching  400  to  500  and  occasionally  800  to  900  grams. 

The  firm  and  elastic,  well-developed  breasts  of  young  nullipara  become  during  lactation 
even  more  firm  and  tense,  but  after  lactation  especially  if  there  has  been  a  long  period  of  nursing 
they  lose  their  consistency  and  after  several  pregnancies  become  soft  and  flabby. 

The  sulcus  which  defines  the  caudal  border  of  the  breast  is  but  little  marked  in  thin  nulli- 
para, more  marked  in  fat  women,  and  especially  evident  in  some  multipara.  The  relations  of 
the  dorsal  surface  of  the  gland  vary  somewhat  with  the  position.  The  level  varies  with  the 
stature;  as  a  rule,  in  tall  women  it  is  more  caudal  and  in  short  and  broad-chested  women  it  is 
more  cephalic.  The  tightness  of  the  attachment  to  the  sheath  of  the  pectoralis  major  muscle  is 
quite  variable,  but  even  when  quite  loose  there  is  some  movement  of  the  breast  when  the  arm  is 
raised.  The  glandular  tissue  of  that  part  of  the  breast  which  overhangs  the  axilla  may  be  in 
direct  contact  with  the  lymphatic  glands. 

Structure. — The  mammary  glands  are  composed  of  the  essential  epithelial 
glandular  tissue,  the  parenchyma,  the  supporting  and  enclosing  connective 
tissue  of  the  subcutaneous  tela,  the  stroma,  and  the  covering  cutaneous  layer. 

Parenchyma. — The  essential  part  of  each  mamma  is  a  flattened,  circular  mass 
of  glandular  tissue  of  a  whitish  or  reddish-white  colour,  the  corpus  mammae.  This 
is  thickest  opposite  the  nipple  and  thinner  toward  the  periphery.  The  ventral 
surface  of  this  mass  is  convex  and  made  uneven  by  numerous  irregular  pyramidal 
processes  which  project  toward  the  skin.  The  dorsal  surface,  or  base,  is  flat  or 
slightly  concave  and  much  less  irregular  than  the  ventral  surface.  Minute  proc- 
esses of  glandular  tissue  extend  from  the  corpus  mammse  into  the  retromammary 
tissue,  some  of  them  accompanying  the  septa  of  the  pectoral  fascia  between  the 
bundles  of  muscle  fibres  of  the  pectoralis  major  muscle.  The  circumference  of  the 
mamma  is  thick  and  well  defined,  more  marked  caudally  than  cephalically,  but 
it  presents  numerous  irregular  processes  which  extend  beyond  the  limits  apparent 
from  the  surface.  One  of  these  especially  large  and  well  marked  extends  cephalo- 
laterally  into  the  axillary  fossa,  and  there  are  frequently  other  large  but  less- 
marked  projections. 

The  corpus  mammae  is  not  a  single  structure  but  is  composed  of  from  fifteen  to 
twenty  separate  lobes  [lobi  mammse]  (fig.  1059).  These  are  larger  and  smaller 
irregular  flattened  pyramidal  groups  of  glandular  tissue,  with  their  apices  toward 
the  nipple  and  their  bases  radiating  toward  the  periphery  of  the  gland. 

Each  lobe  has  a  single  excretory  duct  [ductus  lactiferus]  (figs.  1059,  1060, 
1061),  which  opens  by  a  contracted  orifice  [porus  lactiferus]  in  a  depression  upon 
the  tip  of  the  nipple.  When  traced  from  the  pore  toward  the  circumference  of 
the  gland,  the  ducts  are  seen  to  run  first  directly  dorsally  through  the  nipple, 
parallel  and  close  to  one  another.  From  the  base  of  the  nipple  they  diverge. 
Each  duct  is  here  visible  to  the  unaided  eye  and  measures  from  1.5  to  2.5  mm.  in 
diameter.  Beneath  the  areola  its  diameter  increases  for  a  short  distance  to  from 
4  to  9  mm.,  forming  thus  a  reservoir,  the  ampulla  or  sinus  lactiferus,  in  which  the 
secretion  may  accumulate  for  a  time.  Beyond  this  dilation  the  duct  continues, 
gradually  decreasing  in  size  as  it  breaks  up  into  smaller  and  smaller  branches, 
There  is  no  anastomosis  between  the  ducts  during  their  course,  although  at  or 
beneath  the  pore  two  or  more  ducts  may  join  to  have  a  common  opening.  They 
possess  no  valves  but  when  empty  their  inner  surface  is  thrown  into  longitudinal 
plicse. 

The  ducts  have  an  external  coat  of  white  fibrous  connective  tissue  mixed  with  circular  and 
longitudinal  elastic  fibres.  They  are  lined  with  a  simple  cuboidal  or  columnar  epithelium, 
except  near  the  orifice,  where  it  is  stratified  squamous.     External  to  the  lining  epithelium  there 


THE  MAMMARY  GLANDS  1303 

occurs  in  the  smaller  ducts  a  second  layer  of  elongated  cells  resembling  the  myoepithelium  of  the 
sudoriparous  glands. 

Each  of  the  terminal  branches  of  a  duct  ends  in  a  tubulosaccular,  spherical  or  pyriform  alveo- 
lus. A  number  of  these  alveoli  which  open  into  a  common  branch  of  the  duct,  when  grouped 
together  and  bound  up  with  connective  tissue,  constitute  a  lobule  of  the  gland  (lobulus  mammae). 
A  lobe  is  made  up  of  all  the  lobules  whose  ducts  join  one  common  excretory  duct. 

The  alveoli  are  composed  typically  of  a  single  layer  of  epithehal  cells  enclosed  by  a  basement 
membrane.  This  layer  is  the  true  secretory  epithelium.  It  consists  in  the  more  active  gland 
of  granular  polyhedral  or  cuboidal  cells  which  may  be  so  closely  placed  as  to  leave  almost  no 
lumen  to  the  alveoh.  During  lactation  these  cells  may  be  found  in  different  stages  of  secretory 
activity,  their  central  ends  being  filled  with  minute  oil  globules  and  more  or  less  flattened  accord- 
ing to  the  degree  of  distention  of  the  alveoli.  The  alveoli  and  ductules  now  possess  considerable 
lumina  which  are  filled  with  the  above-mentioned  millc  globules  Uberated  from  the  cells  and  sus- 
pended in  a  serous  fluid  also  secreted  by  the  cells.     TMs  constitutes  the  milk  (lac  femininum). 

Stroma. — The  lobes,  lobules,  and  alveoli  are  completely  covered  by  a  connective-tissue 
sheath  too  delicate  to  constitute  a  distinct  capsule.  Outside  of  this  the  whole  gland  is  embedded 
in  the  subcutaneous  tela  which  forms  for  it  a  sheath,  capsula  adiposa  mammae.  This  is  particu- 
larly well  developed  on  the  ventral  surface  where  the  fat  fills  in  between  the  irregularities  caused 
by  the  lobes  and  lobules  and  gives  to  the  surface  of  the  gland  its  smooth  appearance.  Within 
the  corpus  mammte  there  is  little  fat  between  the  lobules  in  nulhpariB  but  much  more  fat  is  found 
here  in  the  stroma  in  multipara;.  When  the  fat  is  absorbed,  as  it  is  during  lactation  and  in 
emaciation,  the  lobules  stand  out  much  more  distinctly.  There  is  however,  no  fat  immediately 
beneath  the  areola  and  nipple.  The  connective  tissue  is  here  loosely  arranged  and  allows  free 
motility  of  the  nipple  and  also  permits  the  more  easy  distention  of  the  ducts  and  sinuses  during 
lactation.  The  connective-tissue  strands,  retinacula  mammae,  which  extend  from  the  apices 
of  the  glandular  processes  on  the  ventral  surface  of  the  mamma  are  connected  to  the  cerium  and 
correspond  to  the  retinacula  cutis  found  in  other  situations.  These  are  sometimes  particularly 
well  developed  over  the  cephaUc  part  of  the  mamma  and  have  been  called  the  suspensory  liga- 
ment of  Cooper. 

The  dorsal  surface  of  the  mamma  is  bound  to  the  pectoral  fascia  by  loose  connective  tissue 
containing,  as  a  rule,  only  a  small  amount  of  retromammary  fat  (figs.  1060, 1061).  The  attach- 
ment to  the  sheath  of  the  pectorahs  major  muscle  is  at  times  so  loose  that  the  spaces  between 
the  connective  tissue  appear  to  form  serous  sinuses,  the  sub-  or  retromammary  bursas. 

In  addition  to  the  axillary  process  or  'tail'  of  the  gland,  a  projection  is  sometimes  seen  extend- 
ing toward  the  sternum  and  another  caudolaterally;  also  processes  extending  toward  the  clavicle 
and  caudomedially  have  been  described.  Besides  these  large  projections  there  are  numerous 
branched  interlacing  processes  which  combine  into  larger  and  smaller  masses  on  the  ventral 
surface  and  exist  as  minute  extensions  on  the  dorsal  sm'face.  In  thin  women,  the  parenchyma 
at  the  apex  of  these  triangular  processes  reaches  nearly  to  the  surface. 

A  mammary  gland  may  be  made  up  of  a  larger  amount  of  stroma  and  a  smaller  amount  of 
glandular  tissue,  or  the  reverse,  and  therefore  a  small  breast  may  fiu-nish  more  milk  than  a  large 
one.  There  is  also  a  variation  in  different  parts  of  the  same  breast,  one  lobe  or  section  may  have 
well-developed  lobules  while  in  another  they  remain  almost  as  at  puberty,  merely  branching 
ducts. 

The  glandular  tissue  when  sectioned  is  whitish  with  a  greyish  or  pinkish  cast  and  is  firm  and 
resistant,  almost  cartilaginous  in  consistency.  It  is  thus  easily  distinguished  from  the  adipose 
capsule. 

Changes  due  to  age  and  functional  activity. — At  birth  the  mamma  consists  mainly  of 
fifteen  to  twenty  slightly  branched  ducts  lined  with  stratified  squamous  or  columnar  epithelium. 
In  spite  of  the  lack  of  true  glandular  tissue,  within  the  first  few  days  there  may  be  such  rapid 
cell  proliferation  that  the  ducts  become  distended  with  cells  and  detritus.  By  pressure  upon  the 
gland  a  few  drops  of  this  material  may  be  expressed  which  constitutes  the  so-called  'witches 
milk.'  From  birth  until  puberty  the  mamma  remains  rudimentary,  simply  keeping  pace  with 
the  general  body  growth,  but  in  the  female,  at  puberty,  an  abrupt  change  occurs.  The  tubules 
grow  rapidly  into  the  smTOunding  tissue  and  some  acini  (alveoli)  appear;  the  stroma  and  fat  are 
also  greatly  increased;  and  the  breast  becomes  rounded  and  well  formed  but  consists  mainly  of 
fatty  stroma  and  ducts,  with  but  a  very  small  number  (if  any)  of  true  secreting  acini.  At  this 
time  in  both  boys  and  girls  the  breast  may  become  swollen  and  tender  and  a  milk-hke  secretion 
may  be  produced  similar  to  that  at  birth.  The  great  increase  in  volume  during  pregnancy  and 
lactation  is  due  to  the  increase  in  the  size  and  number  of  the  lobules  and  acini,  and  is  accom- 
panied by  a  decrease  in  the  interlobular  and  intralobular  stroma  and  in  the  fat,  so  that  the  gland 
feels  hard  and  imeven.  The  acini  appear  first  in  the  periphery,  thence  along  the  larger  ducts 
toward  the  centre  of  the  corpus  mammte. 

The  secretion  of  the  gland  for  the  first  two  or  three  days  after  parturition  until  the  free  secre- 
tion of  milk  is  established  is  termed  the  colostrum.  It  differs  from  normal  milk  not  only  in 
chemical  composition  but  also  in  containing  larger  fat  globules  and  special  cells  known  as 
colostrum  corpuscles. 

The  decrease  of  the  gland  nearly  to  its  original  size  after  lactation  is  due  to  an  involution 
of  the  parenchyma,  the  acini  being  reduced  to  narrow  tubules,  most  of  them  completely  atrophy- 
ing. With  this  is  associated  a  development  of  fat  and  fibrous  stroma.  The  gland  does  not, 
however,  regain  its  virgin  appearance  but  its  main  mass  is  looser  and  more  irregular,  less  dis- 
tinct, and  the  peripheral  processes  larger,  while  the  stroma  contains  numerous  fat-lobules.  This 
causes  the  breast  to  be  less  smooth,  fii-m,  and  elastic,  and  it  tends  to  become  pendulous  and  form 
a  sulcus  where  it  overhangs  its  base.  With  the  end  of  sexual  activity  the  secreting  portions  of 
the  glands  gradually  atrophy,  finally  leaving  Uttle  more  than  the  ducts.  Even  these  undergo 
senile  atrophj',  and  the  main  mass  of  the  gland  is  represented  only  by  a  flattened  disc,  in  which 
the  peripheral  processes  can  scarcely  be  made  out.  In  fat  women  there  may  be  little  reduction 
in  size,  but  the  breast  is  here  transformed  almost  entirely  into  fat. 


i 


1304   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

The  skin  covering  the  ventral  surface  of  the  breast  is  very  white,  covered  with 
lanugo  hairs  associated  with  sebaceous  glands,  and  contains  many  sweat  glands  of 
the  ordinary  type.  It  is  so  thin  that  the  subjacent  veins  are  readily  seen  through 
it.  It  is  closely  adherent  to  the  subjacent  fatty  layer  but  its  flexibility,  elasticity, 
and  motility  over  the  deeper  glandular  tissue  permit  much  stretching  during  the 
enlargement  which  occurs  at  the  time  of  lactation.  In  spite  of  this,  linea  albi- 
cantes  are  often  produced  especially  when  the  breasts  have  been  unusually  large. 
Aside  from  the  above-mentioned  particulars,  it  does  not  differ  from  the  skin  of 
the  adjacent  part  of  the  thorax,  except  over  the  centre  of  the  breast  where  it 
forms  the  areola  and  nipple. 

The  areola  mammae  (figs.  1058,  1059,  1060,  1061)  is  covered  by  a  thin,  deli- 
cate, pigmented  skin.  The  colour  in  young  nulliparae  is  reddish,  the  shade  varjang 
with  the  complexion.  During  pregnancy  the  colour  darkens,  slightly  in  blondes, 
but  so  as  to  become  almost  black  in  marked  brunettes. 

This  pigmentation  serves  as  one  of  the  signs  of  gestation.  After  lactation  the  colour  fades, 
but  little  pigmentation  remaining  in  blondes,  considerable  in  brunettes.  During  pregnancy- 
there  is  sometimes  seen  extending  more  or  less  beyond  the  areola  a  less  deeply  and  less  uniformly 
pigmented  ring,  the  secondary  areola.  In  size,  the  areola  is  subject  to  considerable  individual 
variation  and  is  increased  in  pregnancy. 

The  surface  of  the  areola  is  roughened  by  a  number  of  slight  elevations  irregu- 
larly arranged.  These  are  due  to  underlying  large  sebaceous  and  rudimentary 
milk  glands  [gl.  areolares;  Montgomerii],  tubercles  of  Montgomery.  Projections 
caused  by  sebaceous  glands  are  also  found  in  the  secondary  areola.  All  of  these 
tubercles  enlarge  greatly  during  pregnancy  and  the  glands  produce  a  slight  secre- 
tion which  is  discharged  through  ducts  that  open  on  their  summits.  The  sweat 
glands  are  few  but  large,  and  in  addition  to  the  lanugo  hairs  there  are  usually 
several  well-developed  hairs. 

The  corium  of  the  areola  is  devoid  of  fat  but  contains  a  well-developed  layer  of  smooth  muscle 
fibres,  the  fascicles  of  which  intercross  in  various  directions  but  may  be  seen  to  be  mainly  of  two 
orders,  circular  and  radial.  They  are  continuous  with  those  of  the  nipple.  The  circular 
fibres  are  most  numerous  adjacent  to  the  nipple,  where  they  may  form  a  layer  nearly  2  mm.  in 
thickness. 

The  areola  varies  greatly  in  size,  measuring  from  15  to  60  mm.  in  diameter.  There  is  some 
confusion  in  regard  to  the  areolar  glands  and  the  tubercles  of  Montgomery.  Some  consider 
the  tubercles  to  be  caused  by  the  areolar  glands,  others  consider  them  caused  by  the  sebaceous 
glands.  Sebaceous  glands  undoubtedly  cause  the  projections  in  the  secondary  areola.  The 
sudoriferous  glands  of  the  areola  are  large  and  compound  tubular  glands  with  a  comphcated 
glomerulus  and  are  considered  as  transitions  between  sweat  and  mammary  glands.  The  seba- 
ceous glands  are  even  more  numerous  than  the  sudoriferous  and  are  composed  of  several  lobes. 
They  also  have  been  considered  by  some  as  intermediate  stages  in  the  formation  of  mammary 
glands,  but  this  is  improbable.  There  are  ten  to  fifteen  very  small  areolar  glands  (though  Pinard 
found  an  average  of  but  four  to  each  breast),  whose  structure  is  essentially  identical  with  that 
of  the  principal  mammary  glands.  They  have  dilations  on  their  ducts  and  they  open  on  the 
areola  at  times  in  common  with  a  sebaceous  gland. 

The  nipple  [papilla  mamma]  (figs.  1058,  1059,  1060,  1061)  in  well-developed 
nulliparae  is  situated  slightly  meso-caudal  to  the  centre  of  the  breast  and  on  a 
level  with  the  fourth  rib  or  fourth  intercostal  space  about  12  cm.  from  the  median 
line.  But  its  position  in  reference  to  the  thoracic  wall  varies  greatly  with  age, 
individual,  and  the  present  and  past  activity  of  the  gland.  The  nipple  is  usually 
somewhat  conical  or  cylindrical  with  a  rounded  fissured  tip  marked  by  fifteen  to 
twenty  minute  depressions  into  which  the  lactiferous  ducts  empty.  The  average 
length  of  the  nipple  is  10  mm.  to  12  mm.  The  skin  is  thin,  wrinkled,  and  pig- 
mented like  the  areola,  except  over  the  tip  of  the  nipple  where  there  is  no  pigment. 

The  corium  of  the  nipple  has  many  large  vascular  and  nervous  papilla;  and  there  is  no  fat  in 
it.  Hairs  and  sudoriferous  glands  are  absent  but  sebaceous  glands  are  present  in  great  numbers. 
Their  secretion  here  and  over  the  areola  serves  to  keep  the  skin  soft  and  to  protect  it  from  the 
saliva  of  the  nursing  infant.  In  the  deeper  layers  of  the  corium  smooth  muscle  fibres  form  a 
loose  stratum  continuous  with  that  of  the  areola.  This  is  made  up  principally  of  an  external 
circular  layer  and  to  a  slight  extent  by  an  internal  layer  whose  bundles  of  fibres  are  parallel  with 
the  milk  ducts.  Numerous  interlacing  muscle  fibres  connected  with  these  layers  and  mixed 
with  loose  connective  tissue,  and  elastic  fibres,  but  no  fat,  surround  the  lactiferous  ducts  as  they 
pass  through  the  axis  of  the  nipple. 

The  nipple  usually  does  not  project  from  the  surface  until  the  third  year.  It  soon  becomes 
conical  but  does  not  attain  its  full  size  until  shortly  after  puberty.  The  size  of  the  nipple  is 
variable,  ordinarily  in  proportion  to  the  size  of  the  gland,  but  large  nipples  are  sometimes  found 
on  small  breasts  and  small  nipples  on  large  breasts.     During  pregnancy  the  nipple  increases  in 


THE  MAMMARY  GLANDS  1305 

size  and  becomes  more  sensitive  and  more  easily  erectile.  The  shape  of  the  nipple  in  addition  to 
conical  or  cylindrical  may  be  hemispherical,  flattened,  discoidal,  or  slightly  pedunculated.  Its 
end  may  be  invagtnated  or  the  entire  nipple  retracted  beneath  the  surface  of  the  gland  and  pro- 
jecting only  in  response  to  stimuli. 

The  circular  muscle  fibres  of  the  nipple  act  like  those  at  its  base  in  the  areola.  By  inter- 
mittent, rhythmic  contractions  they  tend  to  empty  the  lactiferous  ducts;  by  continuous  and  tight 
contraction  they  act  as  a  sphincter.  When  contracted  they  also  narrow  the  nipple,  make  it 
harder,  erect,  and  more  projecting.  When  the  vertical  fibres  contract  they  depress  the  tip  of 
the  nipple  or  they  may  retract  the  whole  nipple  beneath  the  surface.  The  muscle  of  the  areola 
when  stimulated  puckers  the  skin  toward  the  nipple  causing  circular  concentric  folds  in  the 
skin  of  the  areola. 

The  male  mammary  gland  [mamma  virilis].  This  develops  exactly  as  with 
the  female.  From  birth  to  puberty  the  glands  in  the  two  sexes  have  a  parallel 
growth  and  development,  but  from  this  time  on  the  glands  in  the  male  grow  but 
slightly  and  reach  their  full  development  about  the  twentieth  year. 

The  corpus  mammae  in  the  adult  male  measures  from  1.5  to  2.5  cm.  in  diametei  and  .3  to 
.5  cm.  in  thickness.  It  is  whitish  in  colour,  tough,  and  stringy.  It  is  composed  of  the  same 
number  of  lobes  as  in  the  female  but  these  consist  of  little  more  than  short  ducts  with  no  true 
acini  and  may  be  reduced  to  mere  epitheUal  or  connective-tissue  strands.  The  areola  and  nipple 
are  present  and  pigmented,  but  the  nipple  averages  only  2  to  5  mm.  in  height.  The  areola  has 
a  diameter  of  2  to  3  cm.  and  is  covered  with  hairs.  The  areolar  tubercles  may  be  recognised 
and  the  areolar  muscle  is  present.  The  position  of  the  nipple  in  relation  to  the  chest-wall  is 
more  constant  than  in  the  female  as  the  breast  is  less  movable.  It  is  seldom  beyond  the  limits 
of  the  fourth  intercostal  space  or  the  two  adjacent  ribs,  and  averages  12  cm.  from  the  median 
line.     Occasionally  the  male  breast  may  hypertrophy  on  one  or  both  sides,  gynecomastia. 

Blood-supply. — The  main  arterial  supply  to  the  mammary  gland  is  from  mam- 
mary rami  of  perforating  branches  of  the  internal  mammary  artery  (p.  567). 
Usually  that  from  the  second  or  third  intercostal  space  is  especially  large.  Small 
branches,  external  mammary  rami,  are  also  supplied  to  the  caudal  and  lateral 
segments  of  the  breast  by  the  lateral  thoracic  artery  (p.  571 ).  Some  rami  from 
the  thoracoacromial  or  supreme  thoracic  arteries  (p.  571)  may  reach  the  cephalo- 
lateral  segment  of  the  breast  and  small  twigs,  lateral  mammary  rami,  from  the 
anterior  branches  of  the  lateral  cutaneous  rami  of  the  aortic  intercostal  arteries  (p. 
589)  supply  its  deep  surface. 

These  vessels  anastomose  freely  and  form  a  wide-meshed  network  in  the  stroma  of  the  ventral 
and  dorsal  surfaces  from  which  branches  proceed  around  the  lobes  and  lobules  and  finally  form  a 
close  network  of  capillaries  around  the  alveoli.  From  these,  venous  capillaries  arise  and  pass  in 
two  groups,  one  deep,  accompanying  the  arteries,  the  others  superficial.  These  latter  extend  to 
the  ventral  surface  of  the  gland  to  form  a  loose  network  beneath  the  skin.  During  lactation 
these  subcutaneous  veins  show  through  the  sldn  as  bluish  lines,  and  frequently  form  a  more  or 
less  complete  circle  around  the  nipple.  They  connect  with  the  superficial  veins  of  the  neck 
superiorly,  with  those  of  the  abdomen  inferiorly,  and  with  the  thoracoepigastric  vein  laterally. 
The  deep  veins  carry  the  blood  to  larger  vessels,  which  empty  into  the  subclavian,  the  inter- 
costal, the  internal  mammary,  and  the  axillary;  and  the  superficial  group  may  connect  with  the 
external  jugular  and  femoral  veins. 

The  lymphatics. — The  lymphatics  of  the  mammae  are  extremely  numerous, 
forming  rich  plexuses  and  free  anastomoses.  Their  exact  origin  and  distribution 
are  not  yet  fully  understood,  but  it  is  clear  that  there  is  a  rich  plexus  in  the  skin  of 
the  areola  and  nipple  which  empties  mainly  into  a  subareolar  plexus.  Deep  lym- 
phatics arise  in  the  spaces  around  the  alveoli  in  all  parts  of  the  gland,  and  most  of 
these  converge  toward  the  nipple  where  they  join  the  subareolar  plexuses.  They 
anastomose  freely  with  the  cutaneous  lymphatics  and  many  of  them  empty  into 
the  subareolar  plexus  through  large  lymph-vessels  which  run  parallel  with  the 
lacteal  ducts.  From  the  subareolar  plexus  usually  two  large  lymph-vessels  arise 
and  pass  toward  the  axilla  to  empty  into  the  axillary  lymph-glands  (p.  719). 
Other  lymphatic  vessels  of  the  mammary  gland  follow  the  course  of  the  various 
blood-vessels. 

There  is  usually  a  third  trunk  from  the  cephahc  part  of  the  breast  and  often  a  fourth  from 
the  caudal  segment  which  join  with  the  others  to  the  axillary  glands.  The  lymphatics  of  the 
mammary  gland  also  commimicate  with  the  lymphatics  of  the  skin,  the  ventral  chest-wall 
and  those  of  the  deep  fascia  over  the  pectoral  muscles,  as  well  as  the  lymphatics  of  the  opposite 
side.  They  also  empty  into  the  lymphatics  which  accompany  the  blood-vessels  of  this  region, 
and  thus  communicate  with  the  axillarj',  subclavicular,  and  supraclavicular  lymphatic  nodes 
(p.  722).  Moreover,  those  from  the  medial  portion  of  the  gland  accompany  the  branches  of 
the  internal  mammary  artery  and  empty  into  the  sternal  glands  along  the  artery  within  the 
thorax.  Since  cancer  of  the  breast  extends  and  is  disseminated  through  Ij'mphatic  channels, 
their  distribution  and  connections  are  of  great  practical  importance. 


i 


1306    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

The  nerves. — The  gland  proper  receives  its  nerves  laterally  from  the  lateral  mammary  rami 
of  the  anterior  rami  of  the  lateral  cutaneous  branches  of  the  fourth  to  sixth  intercostal  nerves 
and  medially  from  the  medial  mammary  rami  of  the  anterior  cutaneous  branches  of  the  second 
to  the  fourth  intercostal  nerves.  The  skin  over  the  breast  receives  in  addition  to  branches  from 
the  above  nerves,  branches  from  the  supraclavicular  nerves  of  the  cervical  plexus.  It  is  alto- 
gether probable  that  sympathetic  fibres  reach  the  gland  but  by  what  course  is  not  yet  clear. 
The  nerves  are  distributed  in  part  to  the  sliin,  in  part  to  the  plain  muscle  of  the  areola  and  nip- 
ple, some  to  the  blood-vessels,  and  others  to  the  glandular  tissue.  The  secretion  is,  however, 
not  entirely  controlled  by  nerves  as  it  is  influenced  also  by  hormones  from  other  organs  brought 
to  it  by  the  blood. 

Development. — In  very  early  embryos  the  epithelium  over  an  area  on  the  side  of  the  body 
extending  from  the  fore  to  the  hind  limb  (or  beyond  these  limits)  is  seen  to  be  deeper  and  more 
cubical,  the  mammary  streak.  In  this  area  there  is  produced  by  multiplication  of  cells  a  ridge, 
the  mammry  line  or  ridge.  In  spots  along  this  line,  corresponding  to  the  relative  position  of 
the  mammary  glands  in  some  mammals  and  the  supernumerary  mammse  in  man,  the  epithelium 
thickens.  The  intervening  parts  of  the  line  disappear  as  the  spots  enlarge  to  form  transient 
mammary  hillocks.  In  man  ordinarily  development  proceeds  in  but  one  of  these  hillocks  on 
each  side.  The  deep  surface  of  the  hillock  projects  into  the  corium  as  the  superficial  surface 
flattens  out  and  the  mesodermic  cells  of  the  corium  condense  around  the  ingrowth  producing 
the  nipple  zone.  Rapid  proliferation  of  the  deeper  cells  produces  a  club-shaped  stage  from  the 
deeper  surface  of  which  small  bud-like  masses  of  epithelial  cells  sprout  and  extend  as  solid  plugs 
into  the  corium.  These  are  the  anlages  of  the  true  secreting  part  of  tlie  gland  and  the  number  of 
buds  corresponds  to  the  number  of  lobes  of  the  future  gland.  The  sprouts  extend  beyond  and 
beneath  the  nipple  zone  and  are  supported  by  closely  packed  connective-tissue  cells  forming  the 
stroma  zone.  The  epithelial  buds  continue  to  grow  and  branch  and  a  lumen  is  finally  produced 
in  the  originally  solid  plugs.  The  primary  epithelial  ingrowth  degenerates  and  ultimately  dis- 
appears. A  cavity  is  produced  in  it  which  later  connects  with  the  lumina  of  the  gland  ducts. 
The  depressed  nipple  zone  becomes  elevated  above  the  surface  soon  after  birth.  Further 
development  of  the  mammary  gland  has  been  discussed  previously  under  changes  due  to  age 
and  functional  activity  (p.  1303). 

THE  DUCTLESS  GLANDS 

Under  the  term  ductless  glands  are  included  not  only  certain  glandular  struc- 
tures of  epithelial  origin  with  a  more  or  less  definitely  known  function  and  an 
internal  secretion  but  also  certain  organs  whose  function  is  not  definitely  known  or 
understood.  Of  the  organs  here  considered,  the  function  of  the  thyreoid  gland, 
the  parathyreoid  glands,  the  chromaffin  system,  the  medullary  portion  of  the 
suprarenal  glands,  and  the  aortic  paraganglia  is  somewhat  definitely  known. 
But  the  function  of  the  thymus,  the  spleen,  the  cortical  portion  of  the  superenal 
glands,  the  glomus  caroticum,  and  the  glomus  coccygeum  is  still  in  doubt; 
although  probably  some,  if  not  all  of  them,  have  an  internal  secretion  or  at  any 
rate  are  closely  associated  with  the  other  glands  of  internal  secretion.  The  hypo- 
physis and  the  pineal  body  are  not  considered  in  this  connection  but  will  be  found 
described  with  the  brain  (pp.  845,848).  The  lymph-nodes,  which  may  also 
be  considered  as  ductless  glands,  are  described  in  Section  VI.  Many  of  the 
true  glands,  such  as  the  liver,  pancreas  and  sexual  glands,  have  also  internal  secre- 
tions which  pass  directly  into  the  vascular  system  as  in  the  ductless  glands. 

THE  SPLEEN 

The  spleen  [lien]  is  a  large  blood-vascular  organ  closely  associated  with  the 
lymphatic  system.     Its  exact  function  is  still  in  doubt. 

Position. — The  spleen  is  situated  in  the  dorsal  part  of  the  left  cephalic  segment 
of  the  abdominal  cavity  so  deeply  placed  against  the  diaphragm  and  dorsal  to  the 
stomach  and  colon  as  to  be  invisible  from  the  ventral  surface  of  the  body  when  the 
abdominal  cavity  is  opened.  It  is  mainly  in  the  left  hypochondriac  region  but  its 
deepest  and  most  cephalic  part  extends  also  into  the  epigastric  region.  It  is 
obliquely  placed  with  its  long  axis  corresponding  approximately  to  the  line  of  the 
caudal  ribs.  It  tends  to  become  more  vertical  when  the  stomach  is  fully  distended 
but  when  the  stomach  is  empty  and  the  colon  distended  it  assumes  a  more  hori- 
zontal position.  Changes  in  the  attitude  of  the  body  also  cause  slight  altera- 
tions in  the  situation  of  the  spleen.  It  moves  with  the  excursions  of  the  dia- 
phragm in  expiration  and  inspiration. 

The  colour  of  the  spleen  is,  in  life,  a  dark  bluish-red  or  brownish-red,  but  after 
death  it  becomes  darker  with  a  more  bluish  or  violet  tint. 

The  size  of  the  spleen  is  perhaps  more  variable  than  that  of  any  other  large 


THE  SPLEEN 


1307 


organ  in  the  body.  Not  only  does  the  size  differ  in  different  individuals  but  it 
changes  greatly  with  the  blood  content  in  the  same  individual.  There  is  a  dis- 
tinct expansion  for  a  time  after  each  meal  and  the  spleen  contracts  and  expands 
rythmically. 

Fig.  1062. — Wedge-shaped  Spleen,  Viscebal  Surface. 
Diaphragmatic  surface      Margo  anterior 


Extremitas  superior 


Margo  posterior 


Margo  posteno. 


Lower  end  of  renal  surface 


Gastric  surface 


Extremitas  inferior 


In  the  adult  it  usually  measures  10  to  15  cm.  in  length,  7.5  to  10  cm.  in  breadth,  and  2.5  to 
4  cm.  in  thickness.  The  weight  usually  ranges  from  150  to  225  gm.  At  birth  it  represents 
from  jitg  to  jjo  of  the  total  body  weight  and  this  porportion  is  maintained  wuthout  much  varia- 
tion until  the  age  of  fifty  years,  when  (like  the  lymphoid  organs  in  general)  it  begins  to  diminish 

Fig.  1063. — Tetkahedral-shaped  Spleen,  Visceral  Surface. 

Extremitas  superior 


Renal  surface- 


Margo  posterior 


Intermediate  angle 


Posterior  extremity 


Gastric  surface 


Hilus  lienis 
Margo  anterior 


Anterior  extremity 


in  size.     This  diminution  continues  until  in  the  very  old  it  represents  but  y  J  „  of  the  body  weight- 
There  is  no  great  difference  in  relative  size  in  the  two  sexes. 

The  spleen  is  somewhat  soft  and  very  friable.     It  is  elastic,  extensible,  contractile,  and 
extremely  vascular. 

Shape. — Iia  form  the  spleen  varies  greatly.     This  is  due  largely  to  its  softness 
which  permits  considerable  modifications  by  the  pressure  of  the  distended  or  con- 


1308   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 


tracted  surrounding  hollow  viscera.  When  in  situ  with  the  stomach  distended,  its 
shape  may  be  compared  to  a  blunt  spherical  wedge  with  a  concave  apex  and 
rounded  extremities,  and  possessing  therefore  three  surfaces  (fig.  1062);  but 
when  the  stomach  is  contracted  and  the  left  flexure  of  the  colon  distended  an  addi- 
tional surface  is  produced  and  its  shape  becomes  tetrahedral  (fig.  1063).     Inter- 

FiG.  1064. — Spleen  Showing  Tttbebcle  on  the  Intermediate  Border. 

-Extremitas  superior 


Gastric  surface 


Margo  anterior 


Extremitas  inferior 


mediate  forms  between  these  extremes  are  produced  by  variations  in  the  degree 
of  distention  of  stomach  and  colon.  The  spleen  presents  two  aspects:  lateral  or 
parietal,  against  the  diaphragm;  and  medial  or  visceral,  toward  the  abdominal 
cavity.  In  its  usual  wedge  form  the  three  surfaces  of  the  spleen  are  diaphrag- 
matic, gastric,  and  renal.  There  are  three  borders,  anterior,  posterior,  and  inter- 
mediate; and  two  extremities,  superior  and  inferior. 


Fig.  1065.- 


-Cross-section  op  the  Body  at  the  Lower  Part  of  the  Epigastric  Region. 
(Rtidinger.) 

Transverse  colon        Aorta 


Stomacli 


Liver 
Gall-bladder 


Kidney 


The  diaphragmatic  surface  [facies  diaphragmatica]  is  a  smooth  convex  surface 
with  an  irregularly  oval  outline,  in  the  wedge-shaped  spleens  wider  cephalically, 
but  in  the  tetrahedral-shaped  spleens  wider  caudally.  It  looks  dorsally  toward 
the  left  and  somewhat  cephahcally. 

It  lies  against  the  diaphragm  over  an  area  opposite  the  ninth,  tenth,  and  eleventh  ribs  and 
the  intervening  intercostal  spaces,  with  its  long  axis  corresponding  in  a  general  way  to  the  course 


THE  SPLEEN 


1309 


of  the  ribs.  Although  it  is  separated  from  the  ribs  by  the  peritoneum,  the  diaphragm,  and  the 
left  pleural  cavity  (cephalically  also  by  the  left  lung)  (figs.  1065,  1066),  the  ribs  sometimes  make 
impressions  upon  it. 

The  gastric  surface  [facies  gastrica]  is  a  semilunar-shaped  surface,  concave 
cephalo-caudally  and  from  side  to  side,  wiiich  looks  ventrally  to  the  right  and 
somewhat  caudally  (figs.  1062,  1065,  1066).  Nearly  parallel  with  the  dorsal 
boundary  of  this  surface  is  a  narrow  depression  usually  formed  by  a  series  of  pits, 
as  a  rule  six  or  eight,  which  together  form  the  hilus  of  the  spleen  [hilus  lienis]. 
In  this  situation  the  vessels  and  nerves  enter  and  leave  the  spleen,  the  vein  being 
dorsal. 

When  the  stomach  is  distended  it  is  in  contact  with  the  major  part  of  the  gastric  surface; 
the  left  flexure  of  the  colon  forming  an  impression  upon  a  small  area  near  the  caudal  extremity 
and  the  taU  of  the  pancreas,  as  a  rule,  resting  against  a  narrow  area  dorsal  to  the  hilus  or  just 

Fig.  1066. — Sagittal  Section  through  the  Left  Side  op  the  Body,  Showing  the 
Relations  of  the  Spleen.  IX,  X,  XI,  XII,  corresponding  ribs.  1,  Left  kidney;  2,  spleen;  3, 
pancreas;  4,  splenic  vessels;  5,  transverse  colon;  6,  stomach;  7,  left  lobe  of  liver;  12,  lung;  14,  heart; 
16,  diaphragm.     (Testut  and  Jacob.) 


L'  '  vnr 


cephalic  to  the  colon.  When  the  stomach  is  empty  and  contracted  and  the  colon  distended  the 
size  of  the  gastric  area  is  considerably  decreased  and  the  relative  size  of  the  coUc  impression 
greatly  increased  so  as  to  form  upon  the  spleen  in  this  situation  a  colic  or  basal  surface  (fig. 
1063).     The  stomach  is,  however,  at  all  times  in  contact  with  some  part  of  the  spleen. 

The  renal  surface  [facies  renalis]  the  smallest  of  the  three  surfaces,  shorter  as 
well  as  narrower  than  the  gastric  surface,  is  an  oblong,  flat  or  slightly  concave 
area,  which  faces  dorsally,  to  the  right  and  slightly  caudally.  It  is  in  relation 
with  the  anterior  surface  of  the  left  kidney  (fig.  1066). 

In  some  cases  the  cephalic  third  of  the  renal  surface  is  also  in  relation  with  the  anterior  sur- 
face of  the  suprarenal  gland.  It  is  separated  from  these  latter  structures,  however,  by  the  renal 
adipose  capsule  as  well  as  by  the  peritoneum.  The  tail  of  the  pancreas  in  some  cases  is  in  con- 
tact with  a  small  area  on  the  ventral  part  of  this  surface.  In  fat  individuals  these  relations  are 
not  as  intimate  as  the  relations  with  other  organs  because  of  the  large  amount  of  suprarenal 
fat. 

The  anterior  border  [margo  anterior]  is  clearly  defined,  thin,  sharp,  and  more  or 
less  convex.  It  is  marked  in  over  90  per  cent,  of  the  cases  by  one  or  more  trans- 
verse or  oblique  notches,  especially  in  its  cephalic  part.     It  is  placed  between  the 


1310    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

diaphragm  and  the  stomach  and  separates  the  diaphragmatic  from  the  gastric 
surface  (figs.  1062-1065). 

The  posterior  border  [margo  posterior]  is  rounded,  shorter,  and  straighter  than 
the  anterior  border  and  is  notched  in  less  than  a  third  of  the  cases.  It  separates 
the  diaphragmatic  from  the  renal  surface  and  is  lodged  in  the  angle  between  the 
left  kidney  and  the  diaphragm  (figs.  1062-1065). 

The  intermediate  border  is  a  blunt  ridge  dorsal  to  the  hilus,  separating  the 
gastric  from  the  renal  surface. 

It  may  be  clearly  defined  or  more  or  less  obscure  and  often  shows  a  marked  tubercle  (fig. 
1064).  When  the  stomach  is  contracted  and  the  colon  distended  this  border  divides  caudally 
into  ventral  and  dorsal  limbs  both  of  which  may  be  well  marked  or  either  may  be  deficient 
depending  on  the  direction  and  degree  of  pressure  of  surrounding  organs.  When  well  marked 
there  is  produced  at  the  point  where  the  two  limbs  diverge  a  more  or  less  marked  projection,  the 
intermediate  extremity  or  angle  (fig.  1063). 

The  superior  extremity  [extremitas  superior],  usually  larger  than  the  inferior 
extremity  in  the  wedge-shaped  spleens  but  smaller  in  the  tetrahedral  form,  is 
rounded  and  bent  medially.  It  extends  as  high  as  the  tenth  thoracic  vertebra  and 
lies  1  to  2  cm.  from  the  vertebral  column. 

The  inferior  extremity  [extremitas  inferior],  also  somewhat  rounded,  is  directed 
toward  the  left  and  caudally.     It  is  in  relation  with  the  phrenicocolic  ligament. 

When  the  stomach  is  contracted  and  the  colon  distended  the  inferior  extremity  becomes  much 
broader,  in  extreme  cases  forming  a  distinct  inferior  border  ending  ventrally  in  the  anterior 
margin  as  an  anterior  extremity  and  dorsally  in  the  posterior  margin  as  the  posterior  extremity 
(fig.  1063). 

In  the  tetrahedral-shaped  spleen  the  additional  surface  produced  by  the  pres- 
sure of  the  colon  is  known  as  the  basal  or  colic  surface  (fig.  1063).  This  varies  in 
size  reciprocally  with  the  degree  of  pressure  of  colon  and  stomach. 

When  well  developed  the  cohc  surface  is  concave  and  is  separated  from  the  renal  and  gastric 
surfaces  by  the  more  or  less  sliarply  defined  dorsal  and  ventral  limbs  of  the  intermediate  border 
and  separated  from  the  diaphragmatic  surface  by  an  inferior  margin  produced  from  the  broadened 
inferior  extremity.  The  left  flexure  of  the  colon  is  in  contact  with  the  greater  part  of  this  sur- 
face, but  the  pancreas  also  usually  hes  against  it  in  its  cephahc  part  (fig.  1063). 

Peritoneal  relations. — The  surface  of  the  spleen  is  completely  covered,  except 
for  a  small  area  at  the  hilus,  by  a  peritoneal  coat,  the  tunica  serosa.  Ventral  to 
the  hilus  a  double  layer  of  peritoneum  is  prolonged  from  the  spleen  to  the  left 
side  of  the  greater  curvature  of  the  stomach  and  the  left  edge  of  the  ventral  layer 
of  the  great  omentum,  forming  the  gastrolienal  ligament  which  contains  the  short 
gastric  arteries  and  veins.  Dorsally  a  second  double  layer  of  peritoneum  extends 
from  the  hilus  to  the  ventral  surface  of  the  kidney  and  the  caudal  surface  of  the 
diaphragm  forming  the  phrenicolienal  (lienorenal)  ligament.  This  ligament 
encloses  the  splenic  artery  and  veins  as  they  pass  to  and  from  the  spleen.  It  is 
also  between  the  two  layers  of  peritoneum  of  this  ligament  that  the  tail  of  the  pan- 
creas reaches  the  spleen  (fig.  1065).  Except  by  these  two  Hgaments  the  spleen 
has  normally  no  attachment  to  the  abdominal  wall  or  to  any  of  the  surrounding 
viscera.  The  gastroHenal,  and  more  especially  the  phrenicohenal  ligament,  serve 
in  a  measure  to  anchor  the  spleen  in  its  place  in  the  abdominal  cavity  but  in  addi- 
tion to  these  the  spleen  is  supported  by  a  fold  of  peritoneum  which  e.xtends  from 
the  left  cohc  flexure  to  the  parietal  peritoneum  over  the  diaphragm,  the  phrenico- 
colic ligament.  This  serves  as  a  shng  in  which  the  inferior  extremity  of  the  spleen 
rests.  The  spleen,  however,  is  held  in  position  in  the  abdominal  cavity  mainly  by 
the  intraabdominal  pressure. 

Topography. — The  superior  extremity  of  an  average-sized  spleen  is  located  between  the  angle 
and  tubercle  of  the  tenth  rib  on  the  left  side  and  about  3  to  4  cm.  from  the  median  line  on  a  level 
with  the  spinous  process  of  the  ninth  thoracic  vertebra.  In  the  majority  of  cases,  it  does  not 
extend  more  than  2  cm.  either  cephalic  or  caudal  to  a  transverse  plane  at  the  level  of  the  infra- 
sternal  notch.  The  inferior  extremity  reaches  nearly  to  the  midaxillary  lioe  in  the  tenth  inter- 
costal space  and  10  to  15  cm.  from  the  superior  extremity.  The  long  axis  therefore  corresponds 
nearly  to  the  shaft  of  the  tenth  rib.  The  posterior  border  lies  beneath  the  cephalic  border  of 
the  eleventh  rib.  The  whole  spleen  (unless  enlarged)  lies  dorsal  to  a  plane  passed  through  the 
midaxillary  lines  and  is  lateral  to  a  line  from  the  left  sternoclavicular  joint  to  the  tip  of  the 
left  eleventh  rib.  In  deep  inspiration  the  spleen  is  greatly  depressed  and  if  enlarged  may  be 
felt  beneath  the  ribs. 

Variations. — From  the  mean  weight  between  150  and  200  gm.  there  are  wide  variations.  It 
is  not  rare  to  find  spleens  weighing  80  to  100  gin.  and  they  are  recorded  as  light  as  10  and 


THE  SPLEEN 


1311 


20  gm.  On  the  other  hand,  spleens  weighing  3000  to  4000  gm.  are  sometimes  foimd.  These  are 
usually,  however,  associated  with  an  acute  infectious  disease,  such  as  malaria  or  typhoid  fever, 
or  a  progressive  metamorphosis,  such  as  leukemia. 

Congenital  absence  of  the  spleen  is  one  of  the  rarest  anomaUes.  The  presence  of  more  than 
one  spleen  is  the  commonest  anomaly  of  the  spleen.  Adami  has  found  accessory  spleens  to 
occur  in  11  per  cent,  of  all  autopsies.  They  are  round  or  oblong  and  vary  in  size  from  a  pea,  or 
smaller,  to  a  walnut.  There  are  most  often  one  or  two  but  there  may  be  twenty  or  more. 
They  are  found  near  the  hilus  on  the  dorsal  side  of  the  gastroUenal  ligament,  less  often,  in  the 
great  omentum,  in  the  mesentery,  on  the  wall  of  the  intestine,  or  in  the  tail  of  the  pancreas. 

In  certain  cases  the  left  lobe  of  the  liver  is  very  long  and  prolonged  far  to  the  left  and  sepa- 
rates the  spleen  from  the  diaphragm.  This  is  the  rule  in  the  foetus  and  is  often  found  in  the 
infant  but  is  exceptional  in  the  adult. 

Exceptionally  the  spleen  may  be  placed  far  caudal  to  the  normal  situation  extending  into 
the  iliac  region  and  even  into  the  pelvis.  This  is  due  in  part  to  congenital  laxness  of  the  supports, 
also  to  increase  in  weight.  The  spleen  has  been  found  in  almost  every  part  of  the  abdominal 
cavity  and  in  transposition  of  the  viscera  it  is  upon  the  right  side. 

One  or  more  notches  on  the  anterior  border  are  present  according  to  Parsons  in  93  per  cent, 
of  the  oases,  two  or  more  in  66  per  cent.,  but  five,  six,  or  seven  much  more  rarely.  On  the  pos- 
terior border  notches  are  found  in  32  per  cent,  of  the  cases,  and  on  the  inferior  border  in  8  per 
cent.  In  20  per  cent,  of  the  cases  a  marked  fissure,  occasionally  more  than  one,  is  found  on  the 
diaphragmatic  surface.  Most  frequently  it  begins  at  one  of  the  notches  in  the  posterior  border 
and  passes  for  a  distance  across  the  surface,  rarely  reaching  the  anterior  border.  Occasionally 
such  a  fissure  starts  from  the  anterior  border  and  rarely  there  is  such  a  fissure  connecting  with 
neither  border. 


Fig.  1067. — Portion  op  Section  op  the  Spleen  of  an  Adult  Man. 
(Lewis  and  Stohr.) 


X15. 


'(  1  f 


Splenic  pulp 


Spindle-shaped  nodule 


Trabeculse  lienis 


Central  arteries  in 
splenic  nodules 


Structure. — The  peritoneal  covering  of  tlie  spleen,  tunica  serosa,  is  intimately 
bound  to  the  underlying,  whitish,  highly  elastic  fibrous  capsule,  the  tunica  albu- 
ginea  (fig.  1067).  This  is  composed  mainly  of  white  fibrous  connective  tissue  but 
contains  numerous  fine  elastic  fibers,  and  a  few  smooth  muscle  fibres.  It  is  much 
thicker  than  the  serous  covering  and  completely  invests  the  spleen.  From  its 
dee])  s\irt':ice  the  tunica  albuginea  gives  off  into  the  interior  numerous  trabecule, 
trabeculae  lienis,  which  join  with  one  another  and  form  a  framework  in  which 
course  the  blood-vessels,  more  especially  the  veins.  It  is  through  the  contraction 
of  the  smooth  muscle  fibres  in  the  tunica  albuginea  and  trabeculae,  that  the  regular 
periodic  contraction  and  expansion  of  the  spleen  is  produced. 

In  the  meshes  of  the  trabecular  network,  lymphoid  tissue  which  forms  the 
proper  splenic  tissue,  the  pulpa  lienis,  is  located.  This  is  soft,  friable,  and  dark 
brownish  or  bluish-red  in  colour.  In  this,  in  a  fresh  spleen,  are  seen  small  round 
whitish  or  greyish  masses  from  .25  to  1.5  mm.  in  diameter,  the  Malpighian  cor- 
puscles [noduli  lymphatici  lienales;  Malpighii]. 

The  trabecula3  are  in  connection  with  a  reticular  network  which  permeates  the  spleen  sub- 
stance or  spleen-pulp.     Mall  has  shown  that  the  trabeculse  and  vascular  system  together  out- 


1312    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

line  masses  of  spleen-pulp  about  1  mm.  in  diameter,  known  as  splenic  lobules.  Each  lobule  is 
bounded  by  three  main  trabeculae,  from  each  of  which  secondary  trabeculoB  pass  into  the  sub- 
stance of  the  lobule  incompletely  subdividing  it  into  compartments,  filled  with  splenic  pulp, 
arranged  in  the  form  of  anastomosing  columns  or  cords  and  designated  as  pulp-cords.  The 
branches  of  the  splenic  artery,  after  coursing  for  a  short  distance  in  the  main  trabeculae,  leave 
these,  and,  after  further  division,  become  surrounded  with  a  layer  of  adenoid  tissue,  which  layer 
presents  here  and  there  irregular  thickenings  forming  the  Malpighian  corpuscles.  An  arterial 
branch,  surrounded  with  adenoid  tissue,  enters  the  apex  of  a  splenic  lobule,  constituting  its 
intralobular  vessel,  which,  soon  after  entering  the  lobule,  loses  its  adenoid  sheath  and  then 
sends  a  branch  to  each  of  the  above-mentioned  compartments.  These  branches  do  not  anas- 
tomose. They  give  off  terminal  branches  which  course  in  the  pulp-cords,  form  dilations, 
ampuUse,  and  terminate  directly  or  indirectly  in  the  large  venous  spaces  found  between  the  pulp- 
cords.  From  the  latter  the  blood  passes,  by  means  of  small  intralobular  veins,  to  interlobular 
veins  situated  in  the  trabeculae  bounding  the  lobules.  Some  of  the  ampullae  are  connected  with 
one  another  by  capillary  branches. 

Blood-supply. — The  spleen  receives  its  blood  from  the  splenic  artery,  which  is  very  large  in 
proportion  to  the  size  of  the  organ  it  supplies.  It  divides  in  the  phrenicolienal  ligament  into 
from  three  to  six  or  eight  branches,  rami  lienales  (fig.  1062),  which  enter  the  spleen  at  the  hilus. 
After  entering  the  spleen  the  arteries  divide  and  subdivide  and  run  to  their  termination  in  the 
ampullae  without  anastomosing.  They  form  what  are  known  as  terminal  arteries.  The  main 
splenic  artery  is  very  tortuous.  The  vein,  vena  lienalis,  leaves  the  spleen  usually  by  the  same 
number  of  branches  as  the  entering  artery.  These  imite  in  the  phrenicohenal  ligament  to  form 
a  large  trunk  which  is  straighter  than  the  splenic  artery  and  hes  caudal  to  it. 

The  lymphatics. — A  superficial  and  a  deep  set  of  lymphatics  have  been  described  in  the 
spleen.  The  former  is  said  to  form  a  plexus  beneath  the  peritoneum  and  the  latter  to  be  derived 
from  the  fine  perivascular  spaces  in  the  adenoid  tissue  around  the  vessels.  From  these  several 
trunks  arise  and  joining  at  the  hilus  pass  between  the  layers  of  the  phrenicolienal  hgament  to 
empty  into  the  lymph-glands  dorsal  to  and  around  the  cephalic  border  of  the  tail  of  the  pancreas. 
The  presence  of  both  superficial  and  deep  sets  of  lymphatics  in  the  human  spleen  has  been  denied 
by  some  investigators.     According  to  Mall,  there  is  no  deep  set. 

The  nerves. — The  nerves  are  derived  from  the  right  vagus  and  from  the  coeliac  plexus. 
They  enter  the  spleen  at  the  hilus,  accompanying  the  branches  of  the  lienal  artery.  They  are 
composed  mostly  of  non-medullated  fibres  which  form  a  rich  plexus  around  the  arteries  supply- 
ing the  muscular  fibres  in  the  media  while  a  second  group  has  been  traced  to  the  muscular  fibres 
of  the  trabecule. 

Development  of  the  spleen. — The  first  anlage  of  the  spleen  is  seen  in  the  fifth  week  of  foetal 
life  as  a  swelling  on  the  dorsal  (left)  surface  of  the  mesogastrium.  This  is  due  to  an  increase  in 
the  mesenchymal  cells  as  well  as  to  a  thickening  of  the  coelomic  epithelium.  This  latter  becomes 
stratified,  and  indistinctly  differentiated  from  the  underlying  embryonic  connective  tissue 
through  the  transformation  of  the  deepest  of  the  epithelial  cells  into  mesenchymal  cells.  As 
development  proceeds  the  thickened  mass  becomes  entirely  isolated  and  the  ccelomic  epithelium 
covers  it  as  a  single  layer. 

The  arteries  are  seen  first  as  a  capillary  network  throughout  the  organ  which  considerably 
later  become  arranged  as  tufts  of  widened  capillaries,  the  anlage, of  the  vascular  structural  unit. 
These  spherical  groups  of  arterial  capillaries  leading  by  wide  openings  into  a  wide  meshed  venous 
plexus  are  boimded  by  trabecule  from  the  capsule.  The  number  of  structural  units  in  the 
spleen  seems  to  be  fixed  fairly  early  but  the  size  and  complexity  changes  greatly.  The  spherical 
mass  with  a  single  central  artery  changes  to  the  adult  condition  where  the  central  artery  gives 
off  side  branches,  each  of  which  has  a  spherical  mass  of  capillaries,  and  the  pulp  intervenes 
between  the  artery  and  the  vein  so  that  the  capillary  circulation  of  the  early  embryo  becomes 
the  cavernous  circulation  of  the  adult.  The  lienal  lymphatic  nodules  of  Malpighi  and  the  splenic 
pulp  appear  only  in  the  latter  half  of  embryonic  life. 

THYREOID  GLAND 

The  thyreoid  gland  [glandula  thyreoiclea]  is  an  extremely  vascular,  ductless 
gland,  whose  internal  secretion,  acting  as  a  stimulus  to  the  tissues,  has  a  profound 
influence  on  the  nutrition  of  the  body  and  on  the  nervous  system.  It  is  a  single 
organ  composed  of  two  lateral,  frequently  unsymmetrical,  masses,  joined  to- 
gether by  a  transverse  median  band.  The  median  transverse  band  or  isthmus 
[isthmus  gl.  thyreoidese]  is  thin  and  narrow,  and  often  has  a  long  slender  process, 
'  the  pyramidal  lobe  [lobus  pyramidalis],  extending  from  it  cephalically.  The  lat- 
eral parts  or  lobes  [lobi,  dexter  et  sinister]  form  the  principal  mass  of  the  gland. 

It  is  situated  in  the  ventral  portion  of  the  middle  third  of  the  neck  on  both 
sides  of  the  larynx  and  the  cephalic  end  of  the  trachea,  dorsal  to  the  infrahyoid 
group  of  muscles. 

The  consistency  of  the  thyreoid  gland  is  uniformly  soft  and  compressible.  The 
colour  is  reddish,  with  a  brownish  or  yellowish  cast,  but  becoming  more  bluish  or 
reddish  with  changes  in  its  blood  content. 

The  size  is  subject  to  considerable  individual  variation  and  is  slightly  greater 
in  women  than  in  men.  The  normal  thyreoid  gland  measures  from  4  to  6  cm. 
in  width  at  its  widest  part.     The  lateral  lobes  measure  from  5  to  8  cm.  in  length. 


THE  THYREOID  GLAND 


1313 


about  2  cm.  in  width,  and  from  1.5  to  2.5  cm.  in  thickness.  The  right  is  usually  a 
little  longer  than  the  left.  The  isthmus  averages  from  .6  to  .8  cm.  in  thickness 
and  from  .5  to  1.5  cm.  in  height. 

The  weight  of  the  normal  gland  averages  about  30  grams;  but  many  specimens  are  found  as 
light  as  20  grams,  and  others  weigh  as  much  as  60  grams. 

When  hyperemio  or  congested  the  size  of  the  gland  may  be  markedly  augumented.  This 
occurs  normally  in  most  women  at  puberty  and  dm-ing  menstruation  and  pregnancy.  In 
various  abnormal  conditions  of  the  gland  there  is  an  increase  in  size,  sometimes  to  a  marked 
degree.  These  enlargements  are  ordinarily  grouped  under  the  term  struma  or  goitre,  and  may 
be  associated  with  either  a  hyper-  or  hyposecretion  of  the  gland.  Decrease  in  size  is  common  in 
old  age  and  may  appear  prematurely  in  certain  diseases. 

The  shape  of  the  gland  as  viewed  from  the  ventral  surface  is  that  of  a  capital 
U  with  the  concavity  directed  cephahcally  (fig.  1068).  The  sides  of  the  U  are 
formed  of  the  more  or  less  elongated  lobes  connected  slightly  cephahc  to  their 

Fig.  1068. — Ventral  View  op  the  Thyreoid  Gland. 

t  of  hyoid  bo 

-Body  of  hyoid  bone 


Hyo-tbyreoid  ligament  — 


Thyreoid  cartilage 


Thyreoid  isthmus 


Hyo-thyreoid  membrane 


Thyreo-hyoid  muscle 
Inferior  constrictor 


Sterno-thyreoid  muscle 


Median  portion  of  crico- 
thyreoid  membrane 


Crico-thyreoid  muscle 


Lateral  lobe  of  thyreoid  gland 


thickened  caudal  ends  by  the  thin  transverse  isthmus.  In  transverse  sections 
through  the  isthmus  the  gland  is  also  U-shaped  with  the  concavity  directed  dor- 
sally,  the  lobes  being  on  each  side  and  the  isthmus  ventral  to  the  trachea  (fig. 
1068).     The  surface  of  the  gland  is  somewhat  unevenly  roughened. 

The  isthmus  glandulae  thyreoidae  usually  becomes  wider  laterally  where  it  is 
attached  by  its  two  extremities  to  the  lateral  lobes  (figs.  1068,  1069).  Its  ventral 
surface  which  is  flat  or  somewhat  convex  is  covered  superficially  by  the  sub- 
cutaneous tela  and  skin  and  beneath  these  by  the  superficial  and  middle  layers  of 
the  cervical  fascia.  Between  the  layers  of  cervical  fascia  and  close  to  the  median 
line  is  the  sterno-hyoid  muscle  and  more  laterally  and  deeper  the  sterno-thyreoid 
muscle.  The  dorsal  surface  is  concave  and  is  in  relation  with  the  first  two  to  four 
rings  of  the  trachea  and  sometimes  with  the  cricoid  cartilage. 

The  size  and  form  of  the  isthmus  is  subject  to  considerable  variation.  It  may  be  very  short. 
Rarely  it  is  wanting  entirely  or  connects  with  but  one  lateral  lobe.  Its  superior  border  is,  as  a 
rule,  concave  and  is  connected  in  many  cases  with  the  pyramidal  lobe.  The  caudal  border, 
although  usually  on  the  third  ring  of  the  trachea  and  2.5  to  3  cm.  from  the  jugular  notch  of  the 
sternum,  may  be  especially  developed  so  that  it  extends  caudally  beyond  the  lateral  lobes  and 
produces  a  process  which  is  known  as  the  medial  lobe. 


i 


1314    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 


The  pyramidal  lobe  is  usually  a  narrow  elongated  flattened  somewhat  conical 
process  of  thyreoid  tissue  representing  the  persistent  portion  of  the  median  embry- 
onic thyreoid  (fig.  1069).     Its  base  is  attached  ordinarily  to  the  left  side  of  the 

Fig.  1069. — Thyreoid  Gland,  with  Pthamidal  Lobe  and  Levator  Muscle. 


Sterno-hyoid  ligament 

Sterno-hyoid  muscle 

Omo-hyoid 

Thyreo-hyoid 


Body  of  hyoid  bone 
F/— Hyo-thyreoid  ligament 
•llljl 

Hyo-thyreoid  membrane 


Levator  glandules  thyreoidese 
Thyreoid  cartilage 


Pyramidal  lobe  of  thyreoid  gland 


Left  lateral  lobe 


superior  border  of  the  isthmus  and  its  apex  which  extends  cephalically  a  variable 
distance,  often  to  the  superior  border  of  the  thyreoid  cartilage,  is  attached  by  a 
fibrous  cord,  the  thyreoid  ligament. 

The  pyramidal  lobe  is  not  always  present.     Some  investigators  have  fomid  it  present  in 
only  40  per  cent  of  all  cases ;  others  in  as  high  as  90  per  cent.     The  average  is  somewhere  between 

Fig.  1070. — Cross-section  op  Neck  Showing  Relations  op  the  Thyreoid  Gland. 
(After  Braune,  from  Porier  and  Charpy.) 
Sterno-hyoid 

--Sterno-thyroid 

•  Trachea 
Omohyoid 

'ni//|/ffl^ffll^^^^'^>^^.^^^      Platysma 

laV>Cl'^'^  ^    Sterno-mastoid 

■/  \               \    ■  t      /'/ij'i.MlJL         --         ^-J    LateraMobe  of 

4i'  \    ^     -^ ^^1    r.^f?^Kl^X        il     '^y'-idsland 

^^>#i"'^'-A      ^*>tenD«rf!>"'    )|\v. "> ;;*^ 'SfflH»^^^l&.>^    A    carotiscom. 
^  ^^  p^=^_=^r^#;— .t-;^__—  ^  l^r      ^  -     N.  vagus 

K%'''Vp'^eh"8fCSf^PfW^W^  T^  ^^'' *•   ttyreoidea  sup. 

t^^->^,'ii'^'^*i.^M^W  ^      ^^- Sympathetic  trunk 

^t^J^^i^MmVTi^'l  ^ A.  thyreoideainf. 

A.  vertebralis 

these  extremes.  It  is  closely  adherent  to  the  subjacent  structures,  usually  at  one  side  of 
the  median  line,  more  often  the  left.  The  superficial  relations  of  the  pyramidal  lobe  are 
similar  to  those  of  the  isthmus.  Its  deep  surface  is  in  relation  also  with  the  cricoid  and  thyreoid 
cartilages,  the  crico-thyreoid  muscle  and  the  hyo-thyreoid  ligament. 


THE  THYREOID  GLAND  1315 

The  pyramidal  lobe,  though  usually  single,  may  be  double  or  bifid  at  its  caudal  end,  one 
process  joining  each  lateral  lobe.  It  may  be  attached  in  the  angle  between  the  isthmus  and 
one  of  the  lateral  lobes,  or  to  the  lateral  lobe  itself.  It  may  be  cylindrical,  band-hke,  or  swollen 
at  its  centre  or  cephaho  end  and  is  occasionally  entirely  separate  from  the  rest  of  the  th}Teoid 
or  divided  into  separate  detached  parts,  thus  forming  accessory  th}Teoids.  The  apex  in  some 
cases  extends  to  the  middle  of  the  thyreohyoid  membrane  or  rarely  to  or  beyond  the  hyoid 
bone  or  the  process  may  be  quite  short.  In  the  thyreoid  ligament,  attached  to  the  apex, 
muscle  fibres  are  sometimes  found,  aberrant  parts  of  the  infrahyoid  muscles,  the  levator  of  the 
thyreoid  gland. 

The  thyreoid  lobes,  right  and  left,  are  placed  on  each  side  of  the  trachea  and 
larynx  (figs.  1068,  1069,  1070).  Each  lobe  is  somewhat  pyramidal  in  shape  and 
presents  for  examination  a  base,  an  apex,  a  medial,  a  ventro-lateral,  and  a  dorsal 
surface. 

The  base  is  roughly  convex  or  pointed,  rarely  flattened,  usually  at  the  level  of 
the  fifth  or  sixth  ring  of  the  trachea  (figs.  1068,  1069). 

It  is  separated  from  the  jugular  notch  of  the  sternum  by  a  distance  of  1.5  to  2  cm.  but  when 
the  head  is  extended  the  distance  is  greatly  increased.  It  is  in  relation  with  the  inferior  thy- 
reoid artery  and  numerous  veins,  mostly  tributaries  of  the  inferior  thyreoid  vein. 

The  apex  is  pointed  or  rounded  (figs.  1068,  1069).  It  is  directed  cephalo- 
dorsally  and  is  situated  at  the  dorsal  border  of  the  lateral  lamina  of  the  thyreoid 
cartilage  at  the  level  of  its  caudal,  or  rarely  its  middle,  third.  ' 

It  is  covered  by  the  sterno-thyreoid  muscle  beneath  which  the  superior  thyreoid  artery 
accompanied  by  the  corresponding  vein  crosses  the  apex  to  reach  the  gland.  It  is  also  crossed 
in  this  situation  by  the  external  ramus  of  the  superior  laryngeal  nerve  as  it  passes  to  the  crico- 
thyreoid  muscle. 

The  medial  surface  of  the  lateral  lobe  is  concave  and  intimately  bound  to  the 
trachea  and  cricoid  cartilage  (fig.  1070).  Toward  the  apex  it  becomes  more 
flattened  where  it  comes  into  contact  with  the  lateral  lamina  of  the  thyreoid 
cartilage. 

At  the  border  where  this  surface  joins  with  the  dorsal  surface  it  is  in  relation  with  the 
oesophagus  and  pharynx,  and  in  the  angle  between  these  structures  and  the  trachea  and  larynx 
it  is  close  to  the  recurrent  laryngeal  nerve. 

The  dorsal  surface  (fig.  1070)  is  broad  and  rounded  caudally,  but  toward  the 
apex  is  reduced  to  a  mere  border.  It  lies  upon  the  fascial  sheath  containing  the 
common  carotid  artery,  the  jugular  vein,  and  vagus  nerve,  most  intimately 
related  to  the  common  carotid  artery  which  usually  produces  a  groove  in  it. 

The  inferior  thyreoid  artery  sends  large  branches  over  this  surface.  The  inferior  thyreoid 
veins  also  have  large  branches  here.  Imbedded  in  the  connective  tissue  in  relation  with  this 
surface  the  parathyreoid  bodies  are  found,  and  in  some  cases  the  recurrent  nerves  are  placed  so 
far  laterally  that  they  also  touch  this  siu-face.  In  many  cases  the  sympathetic  trunk  and  the 
middle  cervical  ganglia  of  the  sympathetic  with  the  cardiac  branches  are  closely  related  to  the 
dorsal  surface  of  the  gland. 

The  ventro-lateral  surface  is  convex  and  is  separated  by  loose  connective  tis- 
sue from  the  overlapping  sterno-thyreoid,  sterno-hyoid,  and  omo-hyoid  muscles. 

More  superficial  on  its  lateral  aspect  is  the  sterno-cleido-mastoid  muscle.  The  above 
muscles  are  enclosed  by  the  superficial  and  middle  sheets  of  the  cervical  fascia.  In  the  subcu- 
taneous tela  the  platysma  muscle  spreads  over  the  gland.  This  surface  of  the  gland  is 
covered  by  a  plexus  of  veins  and  by  branches  of  the  superior  thyreoid  artery. 

Accessory  thyreoid  glands  are  small  masses  of  glandular  tissue  one  or  more  of  which  may 
be  found  situated  in  the  median  line  or  at  one  side  of  it  anywhere  between  the  isthmus  and  the 
root  of  the  tongue.  They  vary  considerably  in  size  and  represent  parts  of  the  pyramidal  lobe 
or  isthmus  which  have  become  completely  separated  from  the  rest  of  the  gland.  In  structure 
they  are  composed  of  the  same  tissue  as  the  rest  of  the  gland. 

Fixation. — In  addition  to  the  connective  tissue  which  binds  the  thyreoid  gland 
to  the  trachea,  it  is  attached  by  the  connection  of  its  capsule  with  the  cervical 
fascia  and  by  the  fibrous  prolongations  from  the  capsule. 

These  prolongations  are  found  medially  attaching  the  isthmus  and  adjoining  portions  of 
the  lateral  lobes  to  the  ventral  surface  of  the  cricoid  cartilage,  the  caudal  border  of  the  thyreoid 
cartilage,  and  the  sheath  of  the  crico-thyreoid  muscles,  and  laterally  attaching  the  lateral  lobes 
to  the  trachea  and  lateral  surface  of  the  cricoid  cartilage.  In  addition  to  these  the  connection 
of  the  vessels  and  nerves  to  the  gland  helps  to  fix  it  in  position. 

Structure. — The  thyreoid  gland  like  other  glands  is  composed  of  a  connective- 
tissue  stroma  supporting  an  epithelial  secreting  parenchyma. 


1316    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

The  connective  tissue  which  covers  the  surface  of  the  gland  forming  for  it  a 
capsule,  may  be  divided  into  two  layers,  superficial  and  deep. 

The  superficial  layer  intimately  connected  with  and  derived  from  the  fascia  colli  as  pointed 
out  above  has  an  important  fimotion  in  supporting  and  fixing  the  gland.  This  layer  is  in  some 
cases  thin  and  transparent;  in  other  cases  it  is  very  tough  and  thick.  It  is  connected  by  loose 
areolar  tissue  with  the  thin  deep  layer  of  the  capsule.  Between  these  two  layers  the  larger 
vessels  run  for  a  space  before  entering  the  gland  and  the  veins,  particularly,  form  here  con- 
siderable plexuses. 

From  the  deeper  layer  of  the  capsule  numerous  trabeculse  and  septa  carrying 
blood-vessels,  lymphatics,  and  nerves  pass  into  the  gland  and  imperfectly  separate 
its  parenchyma  into  irregular  masses  of  variable  size,  the  lobules  [lobuli].  Each 
lobule  is  composed  of  a  number  of  closed,  non-communicating,  irregular,  spherical, 
ovoid,  or  sometimes  branched  alveoli,  acini  or  vesicles,  varying  in  size  from  .045 
to  .22  mm.  in  diameter  and  separated  and  bound  together  by  a  vascular  connect- 
ive tissue  continuous  with  that  surrounding  the  lobules  and  with  that  of  the  cap- 

FiQ.  1071. — Arteries  of  the  Thyreoid  Gland,  Anterior  View.  1.  Lateral  lobe;  1' 
pyramidal  lobe;  2,  trachea;  3,  thjrreoid  cartilage;  4,  crico-thyreoid  membrane;  5,  hyo-thyreoid 
membrane;  6,  7,  8,  9,  inferior  thyreoid  artery  and  branches;  10,  11,  12,  13,  14,  15,  superior; 
thyreoid  artery  and  branches;  16,  thyreoidea  ima.     (Testut  and  Jacob.) 


—    I'l    4i 


sale.     The  vesicles  are  filled  with  a  yellowish  viscous  fluid,  known  as  coUoid, 
the  secretion  of  the  epithelial  cells. 

The  vesicles  are  lined  with  a  single  layer  of  epithelial  cells  of  a  fairly  uniform  cuboidal  or 
columnar  shape,  becoming  flattened  in  distended  vesicles  and  ia  old  age.  The  cells  are  not 
supported  by  a  basement  membrane  but  are  in  close  relation  with  connective  tissue  and 
capillary  blood-vessels.  An  extremely  rich  lymphatic  network  surrounds  the  vesicles  and  the 
lymph-vessels  come  into  intimate  relation  with  the  cells.  Through  these  vessels  the  secretion 
is  conveyed  from  the  gland  to  the  general  circulation. 

Blood-vessels. — The  thyreoid  gland  has  an  extremely  abundant  blood- 
supply.  The  arteries  are  usually  four  in  number  but  occasionally  five  (figs. 
1071-1073). 

The  superior  thyreoid  arteries  divide  into  two,  three,  or  more  main  branches  which  reach  the 
gland  near  the  apex  of  the  lateral  lobes  and  supply  mainly  the  ventral  and  medial  surfaces  of  the 
cephahc  portion  of  the  lobes  (fig.  1071).  There  is  usually  also  a  dorsal  branch,  which  anasto- 
moses with  a  branch  from  the  inferior  thyreoid.  One  of  the  ventral  branches  frequently  con- 
nects along  the  cephalic  border  of  the  isthmus  with  its  fellow  of  the  opposite  side.  The  inferior 
thyreoid  arteries  break  up  into  two  or  three  main  branches,  occasionally  into  many  fine  twigs, 
which  reach  the  dorsal  surface  of  the  lateral  lobes  near  the  eaudolateral  borders  and  supply 


THE  THYREOID  GLAND 


1317 


mainly  the  dorsal  and  lateral  surfaces  of  the  caudal  part  of  the  gland  (fig.  1071).  There  is 
usually  a  well-marked  branch  which  passes  cephalioally  to  anastomose  with  a  good-sized 
branch  from  the  superior  thyreoid.  Small  branches  are  distributed  to  the  ventral  surface  of  the 
caudal  portion  of  the  lobes  and  isthmus.  The  small  fifth  artery,  the  thyreoid  ima  artery, 
occasionally  present,  ascends  on  the  ventral  surface  of  the  trachea  and  reaches  the  gland  at  the 
caudal  border  of  the  isthmus  or  of  either  lobe.  It  anastomoses  with  the  other  arteries  which 
may  be  correspondingly  reduced  in  size.  The  above-mentioned  arteries  branch  freely  and  are 
distributed  over  the  surface  of  the  gland  between  the  two  layers  of  the  capsule  where  they 
anastomose  extensively  with  one  another  and  with  the  arteries  of  the  opposite  side.  From  the 
surface  plexus  branches  pass  with  the  septa  and  trabeculse  through  the  gland  to  break  up  into 
the  capillary  plexuses  around  the  vesicles. 

The  relation  of  the  inferior  thyreoid  artery  to  the  recurrent  nerve  is  important  from  a 
surgical  point  of  view  but  unfortunately  is  not  constant.  In  some  cases  the  nerve  is  ventral 
to  the  artery,  more  often  on  the  right,  in  other  cases  it  is  dorsal  and  often  the  nerve  passes  be- 
tween the  branches  of  the  artery.     Their  relation  is  most  intimate  close  to  the  trachea  Fig.  1073. 

Fig.  1072. — Vessels  of  the  Thyreoid  Gland,  Anterior  View.  1, 2, 3,  Lateral  lobes  and 
isthmus;  4,  pyramidal  lobe;  5,  hyoid  bone;  6,  thyreoid  cartilage;  7,  trachea;  8,  common  carotid;. 
9,  internal  jugular;  10,  thyreo-linguo-facial  vein;  11,  superior  thyreoid  artery;  12,  inferior  laryn- 
geal vessels;  13,  middle  thyreoid  vein;  14,  subclavian  artery;  15,  inferior  thyreoid  artery;  16^ 
inferior  lateral  thyreoid  veins;  17,  inferior  medial  thyreoid  veins;  18,  left  innominate  vein;  Ift 
aortic  arch;  20,  vagus  nerve.     (Testut.) 


The  veins  (fig.  1072)  issue  from  the  substance  of  the  gland  along  the  septa 
which  penetrate  from  its  capsule.  Between  the  two  layers  of  the  capsule  they 
form  a  rich  plexus  of  large  vessels  from  which  three  large  branches  issue  on  each 
side. 

The  superior  thyreoid  veins  leave  the  capsule  of  the  ventral  surfaces  of  the  lateral  lobes 
near  their  apices  and  pass  cephalo-laterally  to  empty  into  the  internal  jugular  veins,  sometimes 
with  the  facial  veins.  The  middle  thyreoid  veins  are  sometimes  absent,  when  present  they^are 
often  very  small  and  pass  from  the  lateral  border  of  the  lateral  lobes  laterally  to  empty  in  to' the 
internal  jugular  vein.  The  inferior  thyreoid  veins  arise  from  the  caudal  and  lateral  part  of 
the  dorsal  surfaces  of  the  lateral  lobes  and  pass  caudolaterally  to  open  into  the  innominate 
veins.  Ventral  to  tlie  trachea,  caudal  to  the  isthmus,  the  two  inferior  thyreoid  veins  are 
connected  by  numerous  cross  anastomoses  and  occasionally  they  open  by  a  single  trunk  which 
joins  the  left  innominate  vein.     A  thyreoidea  ima  vein  is  sometimes  present. 

The  lymphatics  of  the  thjTeoid  gland  begin  as  abundant  plexuses  arovmd  the  vesicles  of  the 
gland  lobules.  These  connect  with  the  interlobular  branches  which  empty  into  radicles 
accompanying  the  blood-vessels  through  the  septa  to  the  surface  of  the  gland  where  they 
join  a  considerable  plexus  placed  between  the  two  layers  of  the  capsule.  From  the  cephalic 
portion  of  the  isthmus  and  lobes  efferent  vessels  extend  cephalo-medially  to  one  or  two  small 


i 


1318   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

pre-laryngeal  glands  and  cephalo-laterally  along  with  the  superior  thyreoid  artery  to  the  deep 
cervical  glands.  From  the  caudal  part  of  the  lateral  lobes  and  isthmus  efferent  vessels  pass 
caudally  to  some  small  pre-tracheal  glands  and  caudolaterally  to  the  deep  cervical  glands. 

The  nerves  of  the  thyreoid  gland  are  probablj'  all  derived  from  the  sympathetic  and  arise 
from  the  middle  and  inferior  cervical  ganglia  and  accompany  the  arteries  to  the  gland. 

Development. — The  thyreoid  gland  is  first  seen  in  very  young  embryos  as  a  prominence  on 
the  ventral  wall  of  the  pharynx.  This  becomes  a  stalked  vesicle  and  divides  into  lateral  lobes. 
The  stalk  elongates  forming  the  thyreoglossal  duct  of  His.  Later  the  lumen  is  obliterated  and 
the  duct  is  then  represented  by  an  epithehal  cord  which  soon  loses  its  connection  with  the 
pharynx.  It  opens  at  first  cephalic  to  the  regular  second  branchial  arch  on  the  summit  of  the 
tuberculum  impar  but  later  shifts  to  its  caudal  boundary  (Grosser).  It  is  represented  in  the 
adult  only  by  a  short  blind  pouch,  the  foramen  csecum  but  very  rarely  a  considerable  duct  may 
be  present.  The  bilobed  mass  appears  to  shift  caudally,  increasing  m  size  and  spreading 
laterally  and  dorsally.  The  median  cord  of  cells  formed  from  the  stalk  becomes  the  isthmus 
and  the  p3rramidal  lobe,  when  this  is  present,  the  lateral  portions  form  the  lateral  lobes.  The 
gland  is  now  composed  of  irregular,  in  general  transversely  disposed  cords  of  cells.  More  rapid 
growth  later  occurs  in  the  centres  of  the  lateral  lobes  and  the  cell  cords  become  closely  packed 
with,Jittle  connective  tissue  between.  Lumina  appear  in  different  places  in  the  cell  cords  and 
the  cell  cords  are  broken  up  into  groups  of  cells;  in  these  the  lumina  continue  to  appear  even 
up  into  early  childhood.  On  each  side,  diverticula  from  the  more  caudal  pharyngeal  pouches, 
the  ultimobranchial  bodies,  come  into  contact  with  the  dorsal  and  lateral  parts  of  the  anlage 
of  the  thyreoid  gland  and  become  partly  enclosed  in  the  neighbourhood  of  the  transversely 
running  cell  cords.  This  core  of  cells  becomes  either  a  compact  body  or  an  irregular  group  of 
cells  and  is  probably  not  transformed  into  thyreoid  tissue. 

THE  PARATHYREOID  GLANDS 

The  parathyreoid  glands  are  small  masses  of  epithelial  cells  found  in  the  neigh- 
bourhood of  the  dorsal  surface  of  the  thyreoid  gland  but  quite  distinct  from  it  and 

Fig.  1073. — Parathteeoid  Glands,  Viewed  Fkom  Behind  (Natural  Size). 

H — Pharynz 

Common  carotid  ort. 

i_  Branch  of  sup. 
thyreoid  art. 

I — Internal  jugular  V. 

Superior  parathyreoid 
p- Vagus  nerve 
— Lateral  lobe  of  thyreoid 

— Inferior  parathyreoid 

i 
I 
' — Inferior  thyreoid  art. 

Recurrent  (inferior 
'laryngeal)  nerve 

I — Trachea 
^(Esophagus 

of  different  structure.  They  are  ductless  glands  and  although  very  small  they  are 
essential  to  life. 

The  usual  number  is  four,  two  on  each  side,  in  relation  with  the  lateral  lobes 
of  the  thyreoid  gland  (fig.  1073) .  In  colour  they  are  yellowish  with  more  or  less  of 
a  reddish  or  brownish  tint  but  lighter  than  the  thyreoid  gland.  Their  consistency 
varies  somewhat  but  usually  it  is  softer  than  that  of  the  thyreoid  gland.  The 
shape  of  the  majority  of  the  glands  is  a  flattened  ovoid,  sometimes  tapering  at  one 
or  both  ends,  rarely  a  flattened  circular  disc.  At  some  place  on  the  surface  there 
is  usually  a  depressed  hilum  where  the  artery  enters  and  the  vein  leaves.  The 
average  size  of  the  glands  is  6  to  7  mm.  in  length;  3  to  4  mm.  in  width  and  1  to  2 
mm.  in  thickness.     Occasionally  they  may  be  found  15  mm.  in  length.     They 


THE  THYMUS  1319 

weigh  from  .01  to  .1  gm.  with  an  average  of  .035  gm.  From  their  situation  they 
have  been  divided  into  a  superior,  or  internal,  derived  from  the  fourth  branchial 
pouch,  and  an  inferior,  or  external,  derived  from  the  third  branchial  pouch. 

The  superior  parathyreoid  glands  (fig.  1073)  are  found,  as  a  rule,  on  the  dorsal  surfaces  of 
the  lateral  lobes  of  the  thyreoid  gland  at  about  the  junction  of  the  cephalic  and  middle  thirds 
Occasionally  they  may  be  situated  in  the  areolar  tissue  at  the  level  of  the  apex  of  the  thyreoid 
gland  or  cephalic  to  it.  They  may  be  ventral  to  the  prevertebral  layer  of  the  cervical  fascia,  on 
the  dorsal  wall  of  the  oesophagus  or  pharynx  and  close  to  the  dorsomedial  margin  of  the  thy- 
reoid gland.  They  may  also  be  placed  at  the  level  of  the  caudal  border  of  the  cricoid  cartilagel 
rarely  as  high  as  the  inferior  cornu  of  the  thyreoid  cartilage  or  as  low  as  the  sixth  trachea, 
ring.  Sometimes  they  are  imbedded  completely  in  the  thyreoid  gland.  As  a  rule,  they  are 
tightly  attached  to  the  capsule  of  the  thyreoid  gland  or  situated  between  its  layers. 

The  inferior  parathyreoid  glands  (fig.  1073)  are  less  constant  in  their  situation  than  the 
superior.  They  usually  are  found  in  relation  with  the  dorsal  surface  of  the  lateral  lobes  of  the 
thyreoid  glands,  not  far  from  their  bases.  They  may  be  quite  outside  the  region  of  the  thy- 
reoid gland  along  the  carotid  arteries  or  tlie  sides  of  the  trachea,  or  they  may  be  placed  more 
cephalically  than  usual  or  extend  caudal  to  the  gland  as  far  as  the  tenth  tracheal  ring,  even  into 
the  thorax.  They  are  imbedded,  when  caudally  placed,  in  fatty  areolar  tissue  in  relation  with 
the  apex  of  the  thymus  gland  and  the  inferior  thyreoid  veins  or  applied  against  the  oesophagus. 

The  parathyreoids  are  intimately  related  to  branches  of  the  inferior  thyreoid  artery,  a 
separate  branch  of  which  supplies  each  of  them.  When  there  is  a  large  branch  of  the  inferior 
thyreoid  artery  anastomosing  with  the  superior  they  are  more  or  less  in  line  with  this. 

Each  parathyreoid  gland  is  surrounded  by  a  fibrous  capsule  from  which  extremely  vascular 
septa  and  trabecula;  penetrate  into  the  gland  separating  and  binding  together  the  masses  of 
polyhedral  cells  which  are  arranged  in  solid  groups  or  intercommunicating  cords  of  varying 
sizes  and  shapes. 

The  cell  cords,  as  a  rule,  are  not  arranged  like  the  thyreoid  vesicles.  At  times  the  secretion 
may  accumulate  and  produce  a  vesicular  appearance  and  the  secretion  then  closely  resembles 
colloid.  Two  kinds  of  cells,  oxyphile  and  principal  cells,  have  been  described;  but  the  inter- 
mediate forms  suggest  that  these  are  the  same  sort  of  cells  in  different  stages  of  functional 
activity.  The  blood-vessels  are  distributed  m  the  connective  tissue  of  the  trabeculae  and  thus 
their  sinusoids  are  brought  into  close  connection  with  the  cells  of  the  gland.  The  nerves  are 
also  distributed  along  the  septa.  In  the  highly  vascular  connective  tissue  ^between  the  cell 
cords  fat  cells  are  found  separate  or  in  groups. 

The  number  of  parathyreoid  glands  found  by  different  investigators  varies.  The  average 
number  in  a  series  of  cases  is  less  than  four.  Whether  this  is  due  to  a  real  absence  of  the 
glands  or  to  failure  to  find  them  due  to  their  aberrant  location,  their  inclusion  in  the  thyreoid 
gland,  or  the  fusion  of  two  glands,  is  not  clear.  In  some  cases  it  is  the  superior  glands,  in 
other  cases  the  inferior  glands,  which  appear  to  be  missing.  On  the  other  hand  various  com- 
petent observers  have  reported  finding  more  than  four  parathyreoid  glands.  Five  or  six  are 
occasionally  found;  as  many  as  eight  have  been  recorded  in  one  instance.  In  these  cases  the 
number  on  a  side  may  not  be  symmetrical.  The  increased  number  may  be  due  to  the  separation 
of  buds  in  the  course  of  development.  The  parathyreoid  glands  are  liable  to  be  associated  with 
accessory  thymus  masses,  with  small  lymphatic  glands,  and  with  fat  lobules;  and  as  they  may 
somewhat  resemble  each  of  these,  they  may  be  mistaken  unless  a  microscopic  examination  is 
made. 

Blood-supply. — Each  parath3Teoid  gland  is  supplied  by  a  single  separate  artery  derived,  as 
a  rule,  from  one  of  the  glandular,  muscular,  or  oesophageal  branches  of  the  inferior  thyreoid 
artery  or  from  the  anastomosing  branch  between  the  superior  and  inferior  thyreoid  arteries. 
When  the  glands  are  in  aberrant  positions  their  arteries  may  be  derived  from  the  nearest  source. 
The  arteries  are  distributed  along  the  trabeculae  and  septa.  The  veins  returnmg  the  blood 
either  follow  the  arteries  or  they  pass  to  the  surface  of  the  gland  where  they  break  up  into  a 
plexus  of  thin-walled  vessels.  Upon  leaving  the  gland  the  veins  empty  into  some  one  of  the 
branches  of  the  thyreoid  veins. 

Development. — The  parathyreoids  (epithelial  bodies)  begin  as  proliferations  of  the  epi- 
thelium on  the  oral  and  lateral  walls  of  the  dorsal  diverticulum  of  the  third  and  fourth  pharyn- 
geal pouches.  The  cells  show  early  a  histological  differentiation  with  vacuolated  and 
reticulated  plasma.  The  common  pharyngo-branchial  ducts  diminish  in  size  and  become 
constricted  off  and  separated  from  the  pharynx.  The  parathyreoid  glands  later  become 
independent  and  separated  from  the  thymus  anlages.  The  epithelial  cells  grow  out  in  the 
form  of  cords  separated  by  connective  tissue  and  in  intimate  relation  to  the  blood-vessels. 
Different  kinds  of  cells  are  not  distinguishable  until  postfcetal  life  when  evidence  of  secretion 
begins. 

THYMUS 

The  thymus  is  a  transitory  organ  of  epithelial  origin,  but  in  structure  resem- 
bling the  lymphoid  tissue.  Its  function  is  not  clearly  understood  but  it  seems  to  be 
intimately  associated  with  the  growth  and  nutrition  of  the  individual,  and  it  is 
classed  with  the  ductless  glands  of  internal  secretion. 

It  is  situated  in  the  ventro-cephalic  part  of  the  thorax  and  extends  into  the 
caudal  part  of  the  neck  (fig.  1074).  It  lies  between  the  two  pleural  sacs  ventral  to 
the  heart  and  great  vessels,  dorsal  to  the  sternum  and  the  sterno-thyreoid  and 
sterno-cleido-mastoid  muscles. 


1320   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

Although  arising  from  the  branchial  clefts  one  on  each  side  of  the  neck,  the 
two  portions  become  so  closely  associated  that  they  are  usually  spoken  of  as  one. 
Each  of  these  parts  is  ordinarily  regarded  as  a  lobe  of  the  thymus  [lobus,  dexter 
et  sinister]. 

In  colour  the  thymus  is  pinkish  or  reddish  grey  in  the  foetus  and  newborn, 
becoming  greyish  white  in  the  adult  or  yellowish  as  it  undergoes  involution.  It 
is  composed  of  soft,  yielding  tissue  more  friable  than  the  thyreoid  or  spleen. 

In  size  the  thymus  varies  greatly.  Under  normal  conditions  it  appears  to 
attain  its  maximum  size  at  about  the  age  of  puberty,  and  to  continue  large  as 
long  as  the  body  continues  to  grow  and  then  to  undergo  a  gradual  involution. 

Fig.  1074. — Thymus  Gland  in  a  Child  at  Birth. 


Thyreoid  cartilage./^ 


Sterno  -  thyre  oi  d  e  u  s 

Crico-thyreoid 

membrane 

Crico-thyreoid  muscle 

Thyreoid  gland 


Right  common  carotid 
artery 

Right  vagus 

Right  internal  jugu- 
lar vein 
Level  of  sternum 

Section  of  clavicle 
Section  of  first  rib 


Section  of  sternum 


Thyreo-hyoideus 


-hyoideus 


Cricoid  cartilage 
First  ring  of  trachea 


Trachea 

Left  suspensory 

ligament 
Left  recurrent  nerve 
(Esophagus 
Left  innominate  vein 

Left  lobe  of  thymus 

Left  internal  mam- 
mary artery 

Left  lung 


Section  of  fifth  rib 
cartilage 


Xiphoid  process 


It  is,  however,  very  sensitive  to  any  nutritive  changes  of  the  individual  and  becomes  very 
small,  even  in  the  infant,  under  the  influence  of  wasting  diseases.  It  not  infrequently  exists  in 
the  adult  only  as  a  vestige  but  in  some  cases  it  may  remain  large  until  middle  age  or  later.  At 
birth  it  is  usually  from  50  to  60  mm.  long  cephalo-caudally  and  about  half  as  broad. 

The  weight  varies  with  the  size.  It  is  given  by  Hammar  as  over  13  gm.  at  birth,  increasing 
to  double  this  between  the  sixth  and  the  tenth  years  and  gaining  its  maximum  of  between  37 
and  38  gm.  between  the  eleventh  and  fifteenth  years.  From  this  time  the  weight  decreases 
until  between  the  ages  of  fifty-six  and  sixty-five  it  weighs  between  25  and  26  gm.  and  at  seventy- 
five  years  may  be  as  light  as  6  gm.  The  involution  of  the  gland  is  not  accompanied  by  a  cor- 
responding reduction  in  size  and  weight  as  the  thymic  tissue  is  gradually  invaded  by  fatty  tissue 
which  maintains  to  some  extent  the  form  of  the  organ. 

In  shape  the  thymus  is  an  elongated,  spindle-shaped  mass  consisting  of  the 
central  portion  or  body  and  two  extremities  (figs.  1074,  1075).     The  body  is  the 


THE  THYMUS 


1321 


widest  and  largest  part  of  the  organ  and  has  no  distinct  separation  from  the 
extremities.  The  inferior  extremity  is  also  broad  and  is  known  as  the  base.  It 
rests  on  the  pericardium,  ordinarily  extending  as  far  caudal  at  birth  as  the  atrio- 
ventricular furrow  but  rarely  it  may  extend  as  far  as  the  diaphragm.  The 
superior  extremity  is  much  elongated  and  extends  into  the  neck.  It  is  represented 
by  two  horns  nearly  always  unequal  in  size  the  left  being  usually  the  larger. 
It  extends  nearly  to  the  thyreoid  gland,  in  some  cases  reaching  it. 

Relations. — Topographically  the  thymus  when  well  developed  is  divided  into 
cervical  and  thoracic  parts. 

The  cervical  portion  presents  for  examination  an  anterior  surface  and  a  posterior  surface. 
The  anterior  surface  is  convex  and  is  in  relation  with  the  sterno-thyreoid  and  sterno-cleido- 
mastoid  muscle.  The  posterior  surface  is  concave  and  rests  medially  upon  the  anterior  surface 
of  the  trachea,  laterally  upon  the  common  carotid  artery  and  sometimes  on  the  left  side  upon  the 
oesophagus. 

The  thoracic  portion  of  the  thymus  is  much  more  important  representing  four-fifths  of  the 
organ  (fig.  1075).  It  presents  for  examination  an  anterior,  a  posterior,  and  two  lateral  surfaces. 
The  anterior  surface  is  dorsal  to  the  sternum  from  which  it  is  separated  cephalically  by  the 
origin  of  the  sterno-thyreoid  muscle.  To  a  less  extent  it  is  in  relation  with  the  sterno-clavicular 
articulation  and  comes  into  contact  laterally  with  three  or  four  of  the  cephalic  sterno-costal 
articulations  and  lateral  to  this  with  the  internal  mammary  artery.  The  posterior  surface  is 
largely  concave  and  is  in  relation  caudally  with  the  pericardium  which  separates  it  from   the 


Fig.  1075.- — Thymus  in  an  Adult 


Superior  mediastinum" 


Cupula  pleurae... 


Right  lung,  __  I 
superior  lobe      ") 


(From  Toldt's  Atlas.) 


A^l^'^^ 


U  ^'K\ —  sternal  end  of  clavicle 


Mediastinal 
■     pleura 


Mediastinal. 

pleura 


-—  Left  lung 


Pleural 

cavity 


•vmsi.'\\.,^-:-\.k'l,t::   iiaiitiKv.s.'. 


^Asi 


Anterior 
*  mediastinal 
space 


right  atrium  and  ventricular  portion  of  the  aorta  and  pulmonary  artery.  The  middle  part  is  in 
relation  with  the  aorta  and  to  the  right  of  this  with  the  superior  vena  cava.  The  cephaUc  part 
is  in  relation  with  the  branches  of  the  aorta  and  superior  vena  cava.  The  lateral  surfaces  are 
somewhat  flattened  and  are  separated  from  the  lungs  by  the  mediastinal  pleura.  The  phrenic 
nerve  on  the  right  side  runs  in  the  pleura  near  the  dorsal  border  of  this  surface,  on  the  left  it  is, 
as  a  rule,  not  in  direct  contact  with  the  thymus. 

Structure. — The  two  lateral  lobes  of  which  the  thymus  is  composed  are  rarely  of  the  same 
size;  the  right  is  usually  the  more  strongly  developed.  They  are  joined  at  an  oblique  plane  so 
that  the  ventral  surface  of  the  right  is  narrow  and  its  dorsal  surface  broader  and  the  reverse 
condition  is  found  in  the  left  lobe.  The  two  lobes  are  separated  from  one  another  by  connective 
tissue.  Rarely  the  two  are  joined  by  a  medial  portion,  isthmus,  near  the  middle  or  toward  the 
caudal  end  (fig.  1076). 

Each  lobe  of  the  thymus  is  completely  surrounded  by  a  thin  dehcate  connective-tissue 
capsule  from  which  numerous  septa  extend  through  the  gland  accompanied  by  the  blood-vessels 
and  nerves.  The  capsule  is  composed  mainly  of  white  fibrous  connective  tissue  with  some 
elastic  fibres.  It  rarely  contains  much  fat  in  the  newborn  but  the  amount  of  fat  increases  as 
development  and  involution  proceed.  Fibrous  prolongations  from  the  capsule  may  extend 
from  the  apices  of  the  lobes  to  be  attached  to  the  cervical  fascia  in  the  region  of  the  lateral 
lobes  of  the  thyreoid  gland,  acting  as  suspensory  ligaments  for  the  gland. 

The  lobes  of  thymus  are  divided  into  numerous  small  lobules  [lobuli  thymi]  4  to  11  mm.  in 
diameter.  These  are  of  roundish  or  polyhedral  shape  with  bases  toward  the  surface  where  they 
show  as  polygonal  areas.  The  lobules  are  separated  and  also  bound  together  by  the  loose 
fibrous  tissue  septa  which  extend  from  the  capsule. 

Each  of  the  primary  lobules  of  the  thymus  is  divided  into  a  number  of  secondary  lobules  or 
follicles  1  to  2  mm.  in  diameter.  These  lymphoid-like  masses  of  tissue  are  composed  of  a 
reticulum  containing  in  its  meshes  lymphocytes  or  thymus  corpuscles.  The  tissue  is  denser 
near  the  surface,  forming  a  cortex  and  passes  gradually  into  a  tissue  with  looser  meshed  reticulum 
near  the  centre,  medulla.  In  the  medulla  there  are  nests  of  concentrically  arranged  de- 
generated epitheKal  cells  enclosing  a  central  mass  of  granular  cells  containing  colloid.     These 


1322   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

nests  are  termed  the  concentric  corpuscles  of  Hassall.     The  cortex  is  subdivided  by  secondary 
connective-tissue  septa  extending  in  from  the  septa  between  the  lobules. 

t,The  arteries  of  the  thymus  are  somewhat  varied  in  their  origin,  usually  derived  from  the 
internal  mammary  and  inferior  thyreoid  of  each  side;  branches  are  sometimes  received  from  the 
innominate,  subclavian,  and  superior  thyreoid  arteries.  They  reach  the  gland  in  various  places 
and  spreading  out  in  the  capsule  pass  with  the  trabeculae  through  the  gland  to  form  a  plexus 
around  each  small  lobule.  From  this  capillaries  pass  through  the  cortex  to  the  medulla. 
The  veins  issue  from  the  thj'mus  in  various  places  and  are  seen  as  numerous  branches  on  its 
surface.  The  efferent  vessels  drain  into  various  veins,  mostly  into  the  left  innominate  vein, 
also  smaller  branches  into  the  internal  mammary  and  inferior  thyreoid  veins. 

The  lymphatics  arise  around  the  small  lobules  and  pass  through  the  interlobular  septa  to 
the  sm-face  from  which  they  are  drained  into  small  lymph  nodes  near  the  cephalic  extremity, 
into  glands  ventrally  between  the  thymus  and  the  sternum,  and  into  other  glands  dorsally  be- 
tween the  thymus  and  the  pericardium. 

The  nerves  of  the  thymus  are  very  minute.  They  are  derived  from  the  cervical  sympa- 
thetic and  from  the  vagus  and  reach  the  thymus  for  the  most  part  along  with  the  blood- 
vessels which  they  accompany  through  the  septa. 


Fig.  1076. — Thymus  in  a  Child  of  Two  Years. 


Thyreoid  cartilage 


Seventh  ring  of  trachea 
Right  carotid  artery 


Right  subclavian  artery j]. 

Right  innominate  vein 


Thymus 
Vena  cava  superior 

Arch  of  aorta 


Central  portion  of  crico-thyreoid 

membrane 
Crico-thyreoideus 
First  ring  of  trachea 

Thyreoid  gland 


Ligament  connecting  thyreoid  and 
thymus  gland 


Left  carotid  artery 


Left  subclavian  artery 


Arch  of  aorta 


Development. — The  thymus  arises  from  the  endodermal  portion  of  the  third  pharyngeal 
pouch  on  each  side,  as  a  thickening  due  to  an  increase  in  the  epitheUal  cells,  followed  by  the 
production  of  a  diverticulum.  At  about  the  sixth  week  the  connections  of  the  pouches  with  the 
branchial  clefts  are  cut  off  but  a  strand  of  tissue  may  persist  to  represent  the  stalk.  These 
thick-walled  cylinders  become  sohd  cords,  elongate  so  as  to  extend  caudally  into  the  thorax, 
and  enlarge  by  a  series  of  secondary  buddings.  The  glands  of  the  two  sides  come  into  contact 
and  become  intimately  associated.  The  cephahc  portion,  as  a  rule,  later  atrophies  and  disap- 
pears. Occasionally  a  small  part  of  it  remains  near  the  thyreoid  cut  off  from  the  rest  of  the 
gland  as  an  accessory  thymus.  From  the  fourth  pharyngeal  pouch  rarely  a  thymus  bud  may 
be  developed  which  produces  in  the  adult  also  an  accessory  thymus.  The  epithelial  character 
of  the  cells  remains  plainly  evident  for  a  time,  then  the  characteristic  differentiation  into 
lymphoid  structure,  cortex  and  medulla  appears.  The  reticulum  and  concentric  corpuscles 
are  undoubtedly  of  epithelial  origin;  but  the  thymus  lymphocytes  are  considered  by  Hammar 
and  others  as  leucocytes  which  have  migrated  to  the  thymus,  while  they  are  regarded   by 


THE  SUPRARENAL  GLANDS 


1323 


Stohr  and  his  followers  as  modified  epithelial  elements,  not  true  blood  cells.     Maurer,  Bruant, 
and  Bell  regard  them  as  modified  epithelial  cells  which  become  true  functional  leucocytes. 


THE  CHROMAFFIN  SYSTEM 

It  has  recently  been  shown  that  in  connection  with  the  ganglia  of  the  sympa- 
thetic nervous  system,  special  cells,  other  than  the  nerve  cells,  are  found.  These 
differ  from  the  nerve  cells  in  that  when  subjected  to  the  action  of  chromic  acid 
salts  there  can  be  demonstrated  in  their  protoplasm  small  granules  which  take  on 
a  darker  stain.  These  cells  are  therefore  known  as  chromaffin  cells.  They,  with 
the  cells  of  the  sympathetic  system,  are  derived  from  the  ectoderm.  They  ap- 
pear first  as  indifferent  cells,  the  sympatho-chromaffin  cells.  Some  of  these  later 
develop  into  sympathetic  ganglion  cells,  others  into  chromaffin  cells.  Some  of 
these  latter  cells  remain,  isolated  or  in  groups,  permanently  associated  with  the 
sympathetic  ganglia,  the  paraganglia;  others  become  separated  and  form  the 
medullary  portion  of  the  suprarenal  glands,  the  aortic  paraganglia,  and  the 
glomus  caroticum. 

THE  SUPRARENAL  GLANDS 

The  suprarenal  glands  [glandulae  suprarenales]  or  adrenal  glands  are  small 
irregularly  shaped  glandular  bodies  composed  of  two  quite  different  organs. 
In  the  lower  vertebrates  these  two  parts  are  entirely  separated  from  one  another 

Fig.  1077. — The  Suprarenal  Glands,  Ventral  View. 


but  in  man  and  the  mammals  they  have  become  joined  together  one  within  the 
other.  The  external  cortical  portion,  of  unknown  function,  is  developed  from  the 
mesoderm.     The  internal  medullary  portion  is  derived  from  the  sympatho- 

FiG.  1078. — The  Suprarenal  Glands,  Dorsal  .View. 

Marga  superior 

Apex 

suprarenalis 


Facies  posterior, 


'Facies  posterior  — t— 


Basis  gl.  suprarenalis 


chromaffin  tissues  and  thus  from  the  ectoderm  in  common  with  the  sympathetic 
nervous  system.  This  part  of  the  suprarenal  glands  is  known  to  produce  an 
internal  secretion  which  reaches  the  general  circulation  through  the  veins  and 


1324   THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

whose  principal  function  seems  to  be  to  aid  in  keeping  up  the  tone  and  activity  of 
the  muscle  and  other  tissues  innervated  by  the  sympathetic  system. 

Situation. — The  glands  are  deeply  placed  in  the  epigastric  region  (fig.  1080) 
lying  in  the  dorsal  and  cephalic  part  of  the  abdominal  cavity,  one  on  either  side  of 
the  vertebral  column  in  variable  relation  with  the  upper  extremity  of  the  kidney 
of  the  corresponding  side. 

Rarely  they  retain  the  fcetal  relation,  capping  the  superior  extremity  of  the  kidney  and 
extending  a  little  upon  both  medial  and  lateral  borders.  More  frequently  (especially  on  the 
left)  they  are  placed  more  upon  the  medial  borders  of  the  kidneys,  extending  (on  the  left)  as 
far  caudal  as  the  hilus,  sometimes  coming  in  contact  with  the  renal  vessels.  Aii  intermediate 
position  is  often  found,  especially  on  the  right.  In  the  high  positions  the  suprarenals  may  be 
on  a  level  with  the  tenth  intercostal  space  or  eleventh  rib.  In  the  low  positions  they  may 
extend  as  far  caudally  as  the  first  lumbar  vertebra.  The  left  is  usually,  but  not  always,  a 
little  higher  than  the  right,  corresponding  to  the  position  of  the  kidneys. 

Fixation. — The  suprarenals,  enclosed  in  the  renal  adipose  capsules,  are  attached 
to  the  renal  fascia  by  connective-tissue  strands  and  are  loosely  bound  by  connect- 
ive tissue  to  the  kidneys.  The  attachment  to  the  kidneys  is,  however,  so  loose 
that  the  suprarenals  are  not  dislocated  when  the  kidneys  are  displaced.  In 
addition  to  the  attachments  common  to  them  and  to  the  kidneys,  they  are  joined 
by  connective-tissue  bands  to  the  diaphragm,  vena  cava,  and  liver  on  the  right 
side  and  to  the  diaphragm,  aorta,  pancreas  and  spleen  on  the  left.  They  have  also 
additional  means  of  fixation  through  the  arteries,  veins,  and  nerve  fibres  which 
enter  and  leave  them,  and  through  the  parietal  peritoneum  which  in  places 
covers  their  ventral  surfaces. 

Fig.  1079. — Diagrammatic  Section  op  the  Suprarenal  Gland. 


Size  and  weight. — The  size  of  the  suprarenals  is  subject  to  considerable 
variation  within  physiological  limits,  in  some  cases  being  relatively  twice  as  large 
as  in  others.  The  two  glands  are  rarely  of  the  same  size,  the  right  being  more 
often  the  smaller. 

Proportionately  they  are  much  larger  in  the  foetus  and  embryo  than  in  the  adult,  but  they 
do  not  decrease  in  size  in  old  age.  They  appear  to  be  slightly  lighter  in  women  than  in  men. 
The  average  weight  in  the  adult  is  from  4  to  54  grams.  As  a  rule,  they  measure  about  30  mm. 
in  height;  7  or  8  mm.  in  thickness;  and  have  a  breadth  at  the  base  of  about  45  mm.  They 
augment  in  volume  during  digestion  and  also  increase  in  size  during  the  acute  infectious 
diseases  and  in  intoxications  such  as  uremia. 

Colour  and  consistency. — The  suprarenal  glands  as  seen  from  the  surface 
have  a  yellowish  or  brownish-yellow  colour.  Upon  section  the  colour  of  the 
surface  layer  appears  a  little  darker  while  the  central  part  of  the  gland  appears 
greyish  or,  if  it  contains  much  blood,  of  a  reddish  colour.  If  some  httle  time  has 
elapsed  since  death,  the  central  part  of  the  suprarenal  may  be  almost  black  in 
colour. 

The  glands  are  very  fragile  and  softer  in  consistency  than  the  thyroid  or  thymus.  As  a 
rule,  they  are  harder  and  more  resistant  than  the  fat  of  the  adipose  capsule  and  may  be  thus 
readily  detected  in  it. 

Form. — The  suprarenal  glands  are  markedly  flattened  dorso-ventrally.  Their 
surfaces  are  roughened  by  irregular  tubercles  and  furrows.  They  vary  consider- 
ably in  shape  (figs.  1077,  1078).  The  right  gland  is  usually  somewhat  triangular 
in  outline  while  the  left  is,  as  a  rule,  semilunar.  Each  gland  has  an  anterior  and  a 
posterior  surface,  a  base  and  an  apex,  a  medial  and  a  superior  margin. 

The  anterior  surface  [facies  anterior]  may  be  either  convex  or  concave,  and 


THE  SUPRARENAL  GLANDS 


1325 


look  ventro-laterally.  It  is  marked  by  a  distinct  transverse,  oblique,  or  nearly 
vertical  fissure,  the  hilus  suprarenalis.  At  this  point  a  small  artery  enters  and  the 
principal  suprarenal  vein  takes  exit  from  the  gland.  These  surfaces  are  in 
relation  with  different  organs  on  the  right  and  left  sides. 

The  anterior  surface  of  the  right  gland  is  in  the  greatest  part  of  its  extent  in  contact  with  the 
posterior  surface  of  the  hver,  upon  which  it  produces  the  suprarenal  impression.  The  medial 
edge  of  -this  surface  is  overlapped,  cephalioally  by  the  inferior  vena  cava  and  caudally  by  the 
duodenum.  The  gland  is  situated  between  the  two  layers  of  the  coronary  hgament,  in  most 
cases,  in  direct  contact  with  the  liver  to  which  it  is  bound  by  loose  connective  tissue;  but,  at 
times,  the  peritoneum  which  covers  the  ventral  surface  of  the  kidney  extends  for  a  greater  or  less 
distance  between  the  suprarenal  and  the  liver. 

The  anterior  surface  of  the  left  gland,  in  some  cases,  may  be  in  contact  in  its  cephalic  part 
with  the  left  lobe  of  the  liver  and  also,  at  times,  with  the  spleen.  The  middle  and  major  part 
lies  against  the  fundus  and  cardiac  end  of  the  stomach,  while  caudally  the  suprarenal  is  often 


Fig.  1080. — Ventral  View  of  the   Supbarenal  Glands,  in  Situ.      X  3.     (From  Toldt's 

Atlas.) 

Hepatic  veins  Diaphragm,  pars  lumbalis 

Left  suprarenal 


crossed  by  the  tail  of  the  pancreas  and  the  splenic  artery  and  vein.  The  whole  or  a  large  part  of 
the  anterior  surface  of  the  left  suprarenal  is  covered  by  the  parietal  peritoneum  of  the  omental 
bursa. 

The  posterior  surface  [facies  posterior]  of  both  the  suprarenals  is  distinctly 
smaller  than  the  anterior  surface.     It  is  flat  or  convex  and  looks  dorso-medially. 

It  is  in  relation  with  the  lumbar  part  of  the  diaphragm,  to  which  it  is  bound  by  connective 
tissue,  but  from  which  it  is  separated  by  an  extension  of  the  renal  adipose  capsule. 

The  base  [basis  gl.  suprarenalis]  is  a  narrow  elongated  surface  distinctly 
hollowed  out,  which  lies  in  contact  with  the  superior  extremity  of  the  kidney  or  its 
medial  margin,  cephalic  to  the  hilus. 

This  surface  looks  dorsally,  laterally,  and  somewhat  caudally  with  the  result  that  it  extends 
farther  on  the  anterior  surface  than  on  the  posterior  surface  of  the  kidney. 

The  medial  border  [margo  medialis]  is  sharp,  thin,  and  irregularly  convex.  It 
extends  more  or  less  vertically  to  meet  the  superior  border. 

On  the  right  it  hes  dorsal  to  the  inferior  vena  cava  cephalically  and  to  the  duodenum  caudally 
and  is  close  to,  if  not  in  contact  with,  the  sympathetic  cceliac  ganglion.  On  the  left  the  medial 
border  lies  dorsal  to  the  stomach  and  caudally  may  be  crossed  by  the  pancreas  and  splenic 
vessels.     It  is  in  close  proximity  to  the  aorta  and  the  coeliac  sympathetic  ganghon. 

The  superior  border  [margo  superior]  is  sharp  and  thin  and  differs  somewhat 
on  the  two  sides. 


1326    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 

On  the  right  it  is  irregular,  straight  or  convex,  and  extends,  dorsal  to  the  liver,  obliquely 
cephalo-medially  to  meet  the  medial  border  in  a  more  or  less  acute  point,  apex  suprarenalis, 
which  is  directed  cephaUcally  and  somewhat  medially.  On  the  left  the  superior  border  is 
irregularly  convex  in  shape  and  nearly  horizontal  in  direction.  It  passes  gradually  over  into 
the  medial  border  without  the  intervention  of  any  distinct  apex.  It  is  dorsal  to  the  stomach 
and  in  some  cases  comes  into  contact  with  the  spleen. 

Accessory  suprarenal  glands  [gl.  suprarenales  accessoriEe]  are  often  foimd  in  the  connective 
tissue  in  the  neighbourhood  of  the  principal  organs.  They  are  also  sometimes  found  in  the 
kidney  near  the  internal  spermatic  veins  and  in  the  region  of  the  sexual  glands.  The  structures 
recorded  as  accessory  suprarenal  glands  may  be  complete  suprarenal  glands  composed  of  the 
cortex  and  medulla  or  they  may  be  composed  of  the  cortex  only.  Masses  of  chromaffin  tissue 
representing  the  medulla  are  sometimes  spoken  of  as  accessory  suprarenals  but  these  more 
properly  belong  with  the  chromaffin  system. 

Complete  absence  of  the  suprarenal  glands  has  been  recorded  only  in  monsters  with  grave 
cranial  and  cephafic  defects.  Absence  of  one  gland  has  been  found  and  the  fusion  of  the  two 
has  also  been  noted. 

Structure. — The  suprarenal  glands  are  surrounded  by  a  thin  and  tough  fibrous 
capsule  composed  mainly  of  white  fibrous  connective  tissue.  From  the  capsule 
numerous  trabeculse  are  given  off  which  pervade  the  gland  and  form  septa  between 
the  groups  and  rows  of  cells.  Within  the  capsule  the  suprarenal  is  composed  of 
an  external  firmer  yellowish  layer,  the  cortex  [substantia  corticalis],  and  an  internal 
softer  whitish  layer,  the  medulla  [substantia  meduUaris]  (fig.  1079). 

On  section  the  cortex  is  seen  to  form  by  far  the  greater  part  of  the  gland  and  it  is  marked 
radially  from  the  centre  toward  the  surface  by  darker  and  lighter  streaks.  In  its  deepest 
part  it  is  brownish  yellow  or  red  and  is  usually  slightly  torn  where  it  joins  the  medulla.  As 
frequently  found  at  autopsy  the  cortex  is  separated  from  the  medulla  by  a  sUt  filled  with  a 
soft  dark  brown  or  blackish  mass  caused  by  the  breaking  down  of  the  deeper  layer  of  the  cortex. 
The  medulla  is  a  greyish,  spongy,  vascular  mass  which  often  because  of  its  blood  content  appears 
of  a  reddish  or  reddish-brown  colour. 

The  cortical  portion  of  the  gland  is  subdivided  into  a  superficial,  glomerular  portion, 
zona  glomerulosa;  an  intermediate,  fascicular  portion,  zona  fasciculata;  and  an  internal 
reticular  portion,  zona  reticulata,  according  to  the  peculiar  grouping  of  the  gland  cells  in  these 
respective  areas. 

In  the  glomerular  zone  the  cells  are  of  irregular  columnar  shape,  and  grouped  in  coiled 
columns.  In  the  fascicular  zone  the  cells,  which  are  of  polyhedral  shape,  are  arranged  in  more 
or  less  regular  parallel  columns,  while  in  the  reticular  zone  the  cells  form  trabecute  or  groups. 
The  reticular  connective-tissue  framework,  continuous  with  the  capsule,  surrounds  the  cell 
masses  and  cell  columns  of  the  several  zones.  The  cells  of  the  medulla  show  an  affinity  for 
chromic  acid — chromaffin  cells — and  are  grouped  in  irregular  masses  separated  by  septa  of  the 
reticulum  and  venous  spaces.  The  arteries  form  a  close-meshed  plexus  in  the  capsule  from 
which  branches  run  more  or  less  parallel  toward  the  medulla  forming  a  network  around  the 
cell  columns  of  the  glomerular  and  fascicular  zones.  This  opens  into  a  venous  plexus  of  wide 
calibre  in  the  reticular  zone,  which  is  connected  with  the  vessels  of  the  medulla.  Small  medul- 
lary arteries  pass  through  the  cortex  without  branching  to  end  in  a  venous  plexus  in  the  medulla. 
The  abundant  wide-meshed  venous  sinuses  in  the  medulla  (sinusoids)  join  to  form  small 
central  veins  which  converge  towai'd  the  centre  of  the  medulla  to  form  the  large  central  vein. 

Vessels  and  nerves. — The  suprarenal  glands  are  richly  supplied  with  vessels. 
The  arteries  are  three — superior,  middle  and  inferior. 

From  the  inferior  phrenic  artery,  the  superior  suprarenal  artery  arises  and  passes  toward  the 
superior  border  of  the  gland.  From  the  aorta  the  middle  suprarenal  artery  takes  origin  between 
the  coehac  and  superior  mesenteric  arteries  and  passes  toward  the  medial  border  of  the  supra- 
renal. It  is  a  branch  of  this  artery  which  is  usually  found  at  the  hilus  along  with  the  central 
vein.  From  the  renal  artery  the  inferior  suprarenal  artery  arises  and  reaches  the  suprarenal 
near  its  base.  These  three  arteries  anastomose  with  one  another  and  form  a  plexus  in  the 
capsule  of  the  suprarenal  from  which  the  arteries  for  the  interior  of  the  gland  are  derived. 

The  large  central  vein  from  the  medulla  passes  through  the  cortex  to  emerge  at  the  hilus 
as  the  suprarenal  vein,  vena  suprarenalis.  The  right  vein  opens  usually  into  the  inferior  vena 
cava,  where  there  is  a  valve,  the  left  into  the  left  renal  vein.  There  may  also  be  small  branches 
connecting  with  the  phrenic  or  the  right  renal  vein. 

The  lymphatics  of  the  suprarenals  are  very  numerous  and  are  represented  by  a  superficial 
plexus  in  the  capsule  and  a  deep  plexus  in  the  medulla.  These  are  connected  by  numerous 
anastomoses.  They  pass  medially  and  converge  into  a  number  of  trunks  on  each  side  which 
empty  into  lymph-glands  situated  along  the  aorta  near  the  origin  of  the  renal  arteries.  On  the 
left  side  there  is  also  the  communication  through  the  diaphragm  with  a  posterior  mediastinal 
gland. 

The  nerves  are  derived  chiefly  from  the  coeliac  and  renal  plexuses  but  include  filaments 
from  the  splanchnics,  and  according  to  some  authors  from  the  phrenic  and  vagus  nerves  also. 
These  numerous  fine  twigs  connect  with  the  gland  in  many  different  places  and  form  a  rich 
plexus.  Branches  are  distributed  to  the  capsule,  to  the  cortical  substance,  and  to  the  medullary 
substance.     Groups  of  sympathetic  ganglion  cells  are  found  in  the  medullary  part  of  the  gland. 

Development. — The  suprarenal  glands  of  mammals  have  their  origin  from  two  sources. 
The  cortical  mesodermic  portion  of  the  glands  arises  in  early  embryos  as  buds  extending  from 


THE  CAROTID  BODY  1327 

the  mesothelium  on  both  sides  of  the  root  of  the  mesentery  into  the  mesoderm  ventral  to  the 
aorta.  A  little  later  these  become  definite  organs  completely  separated  from  the  coelomic 
epithelium  and  are  soon  vasoularised,  but  the  central  vein  does  not  become  visible  until  con- 
siderably later.  The  suprarenal  glands  after  their  separation  from  the  peritoneum  form  a 
ridge  on  either  side  of  the  posterior  wall  of  the  ca4om  medial  to  the  mesonephros.  Some  little 
time  after  the  origin  of  the  cortical  portion  of  the  gland  has  undergone  cellular  differentiation 
and  has  become  surrounded  by  a  delicate  capsule,  the  medullary  portion  is  formed  by  the 
migration  of  masses  of  sympatho-chromaffin  cells  from  the  medial  side  toward  the  centre  of  the 
organ  so  that  they  surround  the  central  vein  as  the  anlage  of  the  medullary  nucleus.  They 
penetrate  the  cortical  portion  of  the  gland  as  development  proceeds  and  become  completely 
surroimded  by  it.  These  migrating  masses  are  entirely  or  for  the  most  part  of  chromaffin 
formative  cells  derived  from  the  ectoderm.  They  are  clearly  differentiated  from  the  cortical 
cells  by  their  small  size  and  darker  colour,  in  stained  sections.  Migration  of  these  cell  masses 
into  the  gland  seems  to  be  continued  even  after  birth.  The  differentiation  of  the  cortex  into 
three  layers  occurs  late  in  development.  The  suprarenal  glands  are  relatively  large  in  foetal 
life;  and  their  relation  to  the  kidneys  is  secondarily  acquired. 

THE  GLOMUS  CAROTICUM 

The  carotid  bodies  [glomera  carotica]  are  small  ovoid  or  spherical  bodies 
found  at  or  near  the  point  where  the  common  carotid  arteries  divide  into  the  inter- 
nal and  external  carotids  (fig.  1081).  They  are  usually  on  the  dorsal  and  medial 
side  of  the  angle  of  bifurcation  of  the  arteries.     There  is  ordinarily  one  body  on 

Fig.  1081. — The  Glomus  Caroticum  (Carotid  Body).  (From  Testut,  after  Prince- 
teau.)  1,  Carotid  body;  2,  3,  4,  common,  external  and  internal  carotids;  5,  int.  jugular;  7,  inf. 
cervical  .sympathetic  ganglion;  8,  vagus. 


each  side,  5  or  6  mm.  in  length  and  2  or  3  mm.  in  thickness.  It  is  reddish-yellow 
in  colour  and  is  attached  to  the  carotid  by  fibrous  tissue  and  by  the  vessels  and 
nerves  which  enter  it.  A  small  special  fibrous  band  may  sometimes  be  recog- 
nised binding  it  to  the  common,  external  or  internal  carotid  artery. 

The  carotid  body  or  gland  is  composed  of  two  essential  parts:  (1)  round,  oval,  or  polyhedral 
epithelial  cells  which  contain  chromaffin  granules,  and  are  bound  together  by  a  mass  of  fibrous 
connective  tissue;  and  (2)  a  rich  plexus  of  capillaries  and  sinusoids  forming  a  mesh.  Large 
lymph-vessels  surround  the  outside  of  the  gland.  The  carotid  gland  has  a  very  abundant 
nerve  supply,  mostly  from  the  sympathetic  system,  and  ganglion  cells  are  foimd  in  it.  It  may 
receive  twigs  from  the  superior  laryngeal,  hypoglossal,  or  glossopharyngeal  nerves,  as  recorded 
by  some  observers. 

The  size  of  the  carotid  body  varies  considerably.  At  times  the  carotid  bodies  are  absent;  in 
other  cases  they  are  so  small  that  they  can  be  detected  only  in  microscopic  sections;  occasionally 
they  are  8  mm.  in  length  by  4  or  5  mm.  in  thickness.  Rarely  the  carotid  bodies  may  be  broken 
up  into  two  or  more  smaller  masses  boimd  together  by  connective  tissue.  The  carotid  body 
may  be  larger  in  old  individuals  due  to  an  increase  in  the  connective  tissue  or  vascular  elements 
with  a  corresponding  decrease  in  the  epithehal  cells.  The  origin  is  probably  from  sympatho- 
chromaffin  cells  but  some  investigators  believe  that  they  are  derived  from  the  endothehum  of  the 
blood-vessels  and  others  that  they  arise  from  the  endoderm  of  a  branchial  pouch. 


1328    THE  SKIN,  MAMMARY  GLANDS  AND  DUCTLESS  GLANDS 
Figs.  1082  and  1083. — Aortic  Paraganglia.     (Zuckerkandl.) 

Aorta 


Sympathetic  trunk- 


Aortic  paraganglia^ 


Left  renal  artery 


inferior  mesenteric  artery 


-  —  Plexus  aorticus 


\ifc* 


Common  iliac  artery 


Vena  cava  int.        Aorta 


«*# 


Right  paraganglion  - 


■Left  renal  vein 


Ureter 

Left  paraganglion 


Inferior  mesenteric  artery 


Plexus  aorticus 


'"Common  iliac  artery 


REFERENCES  FOR  SKIN  AND  DUCTLESS  GLANDS 
THE  AORTIC  PARAGANGLIA 


1329 


The  abdominal  chromaffin  bodies,  the  paraganglia  aortica,  or  paraganglia 
lumbalia,  are  situated  on  each  side  of  the  abdominal  aorta  near  the  point  of  origin 
of  the  inferior  mesenteric  artery  (figs.  1082,  1083).  They  are  elongated,  flat- 
tened, ovoid  bodies,  softer  and  greyer  than  the  lymphatic  glands  and  extremely 
variable  in  size. 

They  measure,  as  a  rule,  between  6  and  12  mm.  in  length,  although  occasionally  as  long  as 
30  mm.  or  as  short  as  1  mm.  They  may  be  connected  by  transverse  bands  in  front  of  the 
aorta  or  occur  as  scattered  nodules  in  this  situation.  They  are  intimately  related  to  the  aortic 
sympathetic  plexus  and  at  least  one  of  them  is  uniformly  found.  They  consist  of  a  mass  of 
chromaffin  cells  surrounded  by  a  rich  capillary  plexus  and  contain  many  nerve  fibres  and  nerve 
cells. 

THE  GLOMUS     COCCYGEUM 

The  coccygeal  body  [glomus  coccygeum]  is  a  small,  spherical  greyish-red  body 
consisting  of  a  median  unpaired  mass  2  to  3  mm.  in  diameter,  single  or  divided 
into  three  to  six  connected  nodules.     It  is  placed  immediately  ventral  to  the  tip 

FiQ.  1084. — Coccygeal  Gland,  in  Sittt.  1,  Sacrum;  2,  coccyx;  3,  coccygeal  gland;  4, 
middle  sacral  artery;  5,  6,  sacral  sympathetic;  7,  ganglion  impar.;  8,  last  sacral;  9,  coccygeal 
nerve;  10,  gluteus  maximus;  11,  ischio-coccygeus;  12,  levator  ani;  13,  ano-coccygeal  raphe. 
(Testut.) 


of  the  coccyx,  imbedded  in  fat  and  in  relation  with  the  terminal  branch  or  branches 
of  the  medial  sacral  artery,  with  the  ischio-coccygeal  muscles,  and  fibres  of  the 
sympathetic  nervous  system  (fig.  1084). 

It  is  composed  of  groups  of  epithelial  cells  bound  together  by  a  mass  of  fibrous  tissue  and 
containing  a  plexus  of  sinusoidal  capillary  vessels  in  intimate  relation  with  the  cells.  Numerous 
nerve  fibres  also  enter  the  gland.  It  is  not  certain  that  the  cells  are  chromaffin  in  character  or 
that  the  coccygeal  body  has  an  internal  secretion. 

A.  References  for  the  skin  and  mammary  gland. — General  and  topographic:  Quain's 
Anatomy,  11th  ed.,  vol.  ii,  pt.  1;  Testut,  Traits  d'Anatomie  Humaine,  4th  ed .;  Poirier-Charpy, 
Traits  d'Anatomie,  vol.  v;  Rauber-Kopsch,  Lehrbuoh  der  Anatomie,  9th  ed.;  Bardeleben, 
Handbuch  der  Anatomie,  vol.  v,  pt.  1;  Merkel,  Topographische  Anatomie;  Corning,  Lehrbuoh 
der  topographischen  Anatomie.  Development:  Keibel  and  Mall,  Human  Embryology.  Skin: 
Heidenhain,  Anat.  Hefte.,  vol.  xxx;  Kean  (finger  prints),  Jour.  Amer.  Med.  Assoc,  vol.  xlvii; 
Unna  (blood  and  lymph),  Arch.  f.  mikr.  Anat.,  vol.  Lx.xii;  Botezat  (nerves)  Anat.  Anz.,  vol. 
xxxiii.  Nails:  Branca,  Annales  de  Dermat.  et  SyphQis,  1910;  Mammary  glands;  Kerr,  Buck's 
Ref.  Hand.  Med.  Sci.  (Breast)  vol.  4,  1914. 

B.  References  for  the  ductless  glands. — General  and  topographic:  Quain's  Anatomy, 
11th  ed. ;  Testut,  Trait6  d'Anatomie  Humaine,  4th  ed.,  vol.  iv;  Poirier-Charpy,  Traite  d'Anatomie 
vol.  iv.;  Rauber-Kopsch,  Lehrbuch  der  Anatomie,  9th  ed.;  Merkel,  Topographische  Anatomie; 
Corning,  Lehrbuch  der  topographischen  Anatomie,  3rd  ed.  Development:  Keibel  and  Mall, 
Human  Embryology.  Spleen:  Shepherd,  Jour.  Anat.  and  Physiol.,  vol.  x.xxvii;  Mall,  Amer. 
Jour.  Anat.,  vol.  ii.  Thyreoid:  Marshall,  Jour.  Ansit.  and  Physiol.,  vol.  xxix.  Parathyreoids: 
Forsyth,  Brit.  Med.  Jour.,  1907;  Rulison,  Anat.  Rec,  vol.  iii;Halsted  and  Evans,  Annals  of  Surg., 
vol.  xlvi.  Thymus:  Hammar,  Erbge.  d.  Anat.  u.  Entwick.,  Bd.,  xix.  Suprarenal  glands: 
Gerard,  Georges  et  Maurice,  Bull.  Mem.  Soc.  Anat.  Paris,  1911,  (6)  T.  13;  Ferguson,  J.  S., 
Amer.  Jour.  Anat.,  vol.  v,  1905.  Carotid  body:  Gomez, .L.  P.,  Am.  .tour.  Med.  Sci.,  vol.  cxxxvi; 
Aortic  paraganglia;  Zuckerkandl,  Verhandl.  d.  Anat.  Gesell.,  15th  Versamm.,  1901. 


I 


SECTION  XIII 

CLINICAL  AND  TOPOGRAPHICAL 
ANATOMY 


Revised  for  the  Fifth  Edition 
Bt  JOHN  MORLEY,  Ch.M.,  F.R.C.S. 

HONORARY     SURGEON,     ANCOAT's     HOSPITAL,    MANCHESTER;    LECTURER     IN     CLINICAL 
ANATOMY,     MANCHESTER     UNIVERSITY 

THE  HEAD 

IN  describing  the  clinical  and  topographical  relations,  the  divisions  of  the  body- 
will  be  successively  considered  in  the  following  order:  headj  neck,  thorax, 
abdomen,  pelvis,  back,  upper  and  lower  extremities. 

The  bony  landmarks  of  the  head  will  first  be  considered,  followed  by  a  separate 
description  of  the  cranium  and  the  face. 

Bony  landmarks. — These  should  be  studied  with  the  aid  of  a  skull,  as  well  as 
on  the  hving  subject.  Beginning  in  front  is  the  nasion,  a  depression  at  the  root  of 
the  nose,  and  immediately  above  it,  the  glabella,  a  slight  prominence  joining  the 
two  supracihary  arches.  These  points  mark  the  remains  of  the  frontal  suture,  and 
the  junction  of  the  frontal,  nasal,  and  superior  maxillary  bones  and  one  of  the  sites 
of  a  meningocele.  In  the  middle  line,  behind,  is  the  external  occipital  protuber- 
ance, or  inion,  the  thickest  part  of  the  vault,  and  corresponding  internally  with 
the  meeting-point  of  six  sinuses.  A  line  joining  the  inion  and  glabella  corresponds 
to  the  sagittal,  and  occasionally  the  frontal,  suture,  the  falx  cerebri,  the  superior 
sagittal  sinus,  widening  as  it  runs  backward,  and  the  longitudinal  fissure  of  the 
brain.  From  the  inion  the  superior  nuchal  hues  pass  laterally  toward  the  upper 
and  back  part  of  the  base  of  the  mastoid  processes,  and  indicate  the  first  or  so- 
called  horizontal  part  of  the  transverse  (lateral)  sinus. 

This  vessel  usually  presents  a  varying  curve  upward  and  runs  in  the  tentorium.  The  second 
or  sigmoid  portion  turns  downward  on  the  inner  surface  of  the  mastoid,  then  forward,  and  lastly 
downward  again  to  the  jugular  foramen,  thus  describing  the  double  curve  from  which  this 
part  takes  its  name.  In  the  jugular  foramen  the  vessel  occupies  the  posterior  compartment; 
its  junction  with  the  internal  jugular  is  dilated  and  forms  the  bulb.  A  line  curved  downward 
and  forward  from  the  upper  and  back  part  of  the  base  of  the  mastoid,  reaching  two-thirds  of 
the  way  down  toward  the  ape.x,  will  indicate  the  second  part  of  the  sinus.  The  spot  where  it 
finally  curves  inward  to  the  bulb  would  be  about  1.8  cm.  (J  in.)  below  and  behind  the  meatus. 
The  two  portions  of  the  transverse  sinus  meet  at  the  asterion  laterally;  at  the  entry  of  the 
superior  petrosal  sinus  medially.  The  right  transverse  sinus,  the  larger,  is  usually  a  continua- 
tion of  the  superior  sagittal  sinus,  and,  therefore,  receives  blood  chiefly  from  the  cortex  of  the 
brain;  the  left,  arising  in  the  straight  sinus,  drains  the  interior  of  the  brain  and  the  basal  ganglia. 
Each  transverse  sinus  receives  blood  from  the  temporal  lobe,  the  cerebellum,  diploe,  tympanic 
antrum,  internal  ear,  and  two  emissary  veins,  the  mastoid  and  posterior  condylar. 

About  6 . 2  cm.  (2|  in.)  above  the  external  occipital  protuberance  is  the  lambda, 
or  meeting  of  the  sagittal  and  lambdoidal  sutures  (posterior  f ontanelle,  small  and 
triradiate  in  shape) .  It  is  useful  to  remember,  as  guides  on  the  scalp  to  the  above 
two  important  points,  that  the  lambda  is  on  a  level  with  the  supraciUary  ridges, 
and  the  external  occipital  protuberance  on  one  with  the  zygomatic  arches. 

Below  the  external  occipital  protuberance,  between  it  and  the  foramen  magnum,  an  occip- 
ital, the  commonest  form  of  cranial  meningoceles,  makes  its  appearance.  It  comes  through 
the  median  fissure  in  the  cartilaginous  part  of  the  squamous  portion  of  the  bone. 

1331 


I 


1332  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

The  point  of  junction  of  the  occipital,  parietal,  and  mastoid  bones,  the  asterion, 
is  placed  about  3 . 7  cm.  (1|  in.)  behind  and  1 . 2  cm.  (|  in.)  above  the  centre  of  the 
auditory  meatus  (fig.  1085).  It  indicates  the  site  of  the  posterior  lateral  fon- 
tanelle  and  just  below  it  the  superior  nuchal  line  terminates.  The  bregma,  or 
junction  of  the  coronal,  sagittal,  and,  in  early  life,  the  frontal  suture  (anterior  f on- 
tan  elle,  large  and  lozenge-shaped),  lies  just  in  front  of  the  centre  of  a  line  drawn 
transversely  over  the  cranial  vault  from  one  pre-auricular  point  to  the  other  (fig. 
1090) .  The  bregmatic  f  ontanelle  normally  closes  before  the  end  of  the  second  year. 
The  lambdoid  fontanelle  is  closed  at  birth.  The  pterion,  or  junction  of  the  frontal 
and  sphenoid  in  front,  parietal  and  squamous  bones  behind,  lies  in  the  temporal 
fossa,  3.7  to  5  cm.  (IJ  to  2  in.)  behind  the  zygomatic  process  of  the  frontal,  and 
about  the  same  distance  above  the  zygoma  (fig.  1085).  This  spot  also  gives  the 
position  of  the  trunk  and  the  anterior  and  larger  division  of  the  middle  meningeal 
artery  (fig.  1090),  the  Sylvian  point  and  divergence  of  the  limbs  of  the  lateral 
(Sylvian)  fissure,  the  insula  (island  of  Reil),  and  middle  cerebral  artery.  It, 
further,  corresponds  to  the  anterior  lateral  fontanelle.  On  the  side  of  the  skull 
the  zygomatic  arch,  the  temporal  ridge,  and  external  auditory  meatus  need  atten- 
tion. That  important  landmark,  the  zygomatic  arch,  wide  in  front  where  it  is 
formed  by  the  zygomatic  (malar),  narrowing  behind  where  it  joins  the  temporal, 
gives  off  here  three  roots,  the  most  anterior  marked  by  the  eminentia  articularis, 
in  front  of  the  mandibular  (glenoid)  fossa,  the  middle  behind  this  joint,  while  the 
posterior  curves  upward  and  backward  to  be  continuous  with  the  temporal  ridge. 
Within  the  zygomatic  arch  lie  two  fossae  separated  by  the  infra-temporal  (ptery- 
goid) ridge :  above  is  the  temporal,  with  the  muscle  and  deep  temporal  vessels  and 
nerves;  below  is  the  infra-temporal  or  zygomatic  fossa,  with  the  lower  part  of  the 
temporal  muscle,  the  two  pterygoids,  the  internal  maxillary  vessels,  and  the  man- 
dibular division  of  the  fifth.  To  the  upper  border  of  the  zygomatic  arch  is  attached 
the  temporal  fascia,  to  its  lower,  the  masseter.  Its  upper  border  marks  the  level 
of  the  lower  lateral  margin  of  the  cerebral  hemisphere.  A  point  corresponding  to 
the  middle  root  of  the  zygoma,  immediately  in  front  of  the  tragus,  and  on  a  level 
with  the  upper  border  of  the  bony  meatus,  is  called  the  pre-auricular  point. 
Here  the  superficial  temporal  vessels  and  the  auriculo-temporal  nerve  cross  the 
zygoma,  and  a  patient 's  pulse  may  be  taken  by  the  anaesthetist.  The  lower  end  of 
the  central  (Rolandic)  fissure  lies  5  cm.  (2  in.)  vertically  above  this  point.  The 
temporal  ridge,  giving  origin  to  the  temporal  fascia,  starts  from  the  zygomatic  proc- 
ess of  the  frontal,  and  becoming  less  distinct,  curves  upward  and  backward  over 
the  lower  part  of  that  bone,  crosses  the  coronal  suture,  traverses  the  parietal  bone, 
curving  downward  and  backward  to  its  posterior  inferior  angle.  Here  it  passes 
on  to  the  temporal,  and  passing  forward  over  the  external  auditory  meatus,  is 
continuous  with  the  posterior  root  of  the  zygoma.  Below  the  root  of  the  zygoma 
will  be  felt  the  temporo-mandibular  joint,  and  when  the  mouth  is  opened,  the  con- 
dyle will  be  felt  to  glide  forward  on  the  eminentia  articularis,  leaving  a  well-marked 
depression  behind. 

The  external  auditory  meatus,  measured  from  its  opening  on  the  concha  to  the  membrane, 
is  about  2.5  cm.  (1  in.)  in  length;  if  from  the  tragus,  3.7  cm.  (1^  in.).  Its  long  axis  is  directed 
medially  and  a  little  forward  with  a  slight  convex  curve  upward,  most  marked  in  its  centre. 
Between  the  summit  of  this  curve  and  the  membrane  is  a  sUght  recess  in  which  foreign  bodies 
may  lodge.  The  lumen  is  widest  at  its  commencement,  narrowest  internally.  To  bring  the 
cartilaginous  portion  in  line  with  the  bony,  the  pinna  should  be  drawn  well  upward  and  back- 
ward. In  the  bony  portion  the  skin  and  periosteum  are  intimately  blended,  thus  accounting 
for  the  readiness  with  which  necrosis  occui's.  The  sensibility  of  the  meatus  is  explained  by 
the  two  branches  sent  by  the  auriculo-temporal  nerve.  The  fact  that  the  deeper  part  is  supplied 
by  the  auricular  branch  of  the  vagus  explains  the  vomiting  and  cough  occasionally  met  with  in 
affections  of  the  meatus. 

The  anterior  inferior  angle  of  the  parietal  bone,  and  its  great  importance  as  a  landmark, 
have  already  been  noted.  The  posterior  inferior  angle  of  tliis  bone  (grooved  by  the  transverse 
(lateral)  sinus)  lies  a  httle  above  and  behind  the  base  of  the  mastoid,  on  a  level  with  the  roots 
of  the  zygoma  (fig.  1085).  Just  below  and  in  front  of  the  tip  of  the  mastoid  the  transverse 
process  of  the  atlas  can  be  made  out  in  a  spare  subject. 

In  front,  the  circumference  of  the  bony  orbit  can  be  traced  in  its  whole  extent. 
The  supraorbital  notch  lies  at  the  junction  of  the  medial  and  intermediate  thirds  of 
the  supraorbital  arch.  When  this  notch  is  a  complete  foramen,  its  detection  is 
much  less  easy.  To  its  medial  side  the  supratrochlear  nerve  and  frontal  arterd 
cross  the  supraorbital  margin;  like  the  supraorbital,  this  nerve  and  vessel  lie,  at 


THE  CRANIUM 


1333 


first,  in  close  relation  with  the  periosteum.  The  frontal  artery  is  one  of  the  chief 
blood-supplies  to  flaps  taken  from  the  forehead.  Owing  to  the  paper-like  thin- 
ness of  the  bones  on  the  medial  wall  of  the  orbit,  e.  g.,  lacrimal,  ethmoid,  and 
body  of  sphenoid,  and  the  mobihty  of  the  skin,  injuries  which  are  possibly  pene- 
trating ones,  as  from  a  slate-pencil,  ferrule,  etc.,  are  always  to  be  looked  upon  with 
suspicion.  After  a  period  of  latency  of  symptoms,  infection  of  the  membranes 
and  frontal  abscess  have  often  followed.  Above  the  supraorbital  margin  is  the 
supraciliary  arch,  and  higher  still  the  frontal  eminence  [tuber  frontale]. 

FiQ.  1085. — The  Skull,  showing  Kronlein's  Method  of  Ckaniocerebral  Topography. 


THE  CRANIUM 

Under  this  heading  will  be  considered  the  scalp,  the  bony  sinuses,  cranio- 
cerebral topography  and  the  hypophysis. 

The  scalp. — The  importance  of  the  scalp  is  best  seen  from  an  examination 
of  its  layers  (fig.  1086).  These  are — (1)  skin;  (2)  subcutaneous  fat  and  fibrous 
tissue;  (3)  the  epicranius  (occipito-frontalis)  and  aponeurosis;  (4)  the  sub- 
aponeurotic layer  of  connective  tissue;  (5)  the  pericranium. 

The  first  three  layers  are  connected  and  move  together.  The  thick  skin 
supported  by  the  dense  fibrous  subcutaneous  layer  and  epicranial  aponeurosis,  is 
well  adapted  to  protect  the  underlying  skull  from  the  effects  of  trauma,  and  in 
this  connection  the  mobility  of  the  first  three  layers  on  the  subaponeurotic  areolar 
tissue  is  important.  A  scalp  wound  does  not  gape  widely  unless  it  involves  the 
epicranial  aponeurosis,  in  which  case  it  involves  the  subjacent  "dangerous  area" 
of  the  scalp,  so-called  because  pus  in  this  laj^er  maj^  spread  widely  underneath 
the  scalp  and  even  give  meningeal  infection  by  spreading  through  the  diploic  or 
emissary  veins.  In  the  process  of  scalping  (whether  performed  by  the  knife  or 
by  the  hair  being  caught  in  machinery),  separation  takes  place  at  this  sub- 
aponeurotic layer  which  is  loose,  delicate  and  devoid  of  fat. 

The  numerous  sebaceous  glands  frequently  give  rise  to  cj'sts  in  the  scalp. 


1334 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


The  epicranius  and  aponeurosis  have  been  described  elsewhere  (p.  336). 

The  pericranium  differs  from  periosteum  elsewhere  in  that  it  gives  little 
nourishment  to  the  bone  beneath,  which  derives  most  of  its  blood-supply  from 
the  meningeal  vessels.  After  necrosis  of  the  skull  there  is  no  tendency  to  the 
formation  of  an  involucrum  of  new  subperiosteal  bone  as  in  the  long  bones. 
The  pericranium  is  firmly  adherent  to  the  sutures  of  the  skull  bones,  so  that  any 
subpericranial  effusion  of  blood  or  pus  is  limited  by  the  sutures. 

Of  the  vessels  of  the  scalp,  the  arteries,  arising  in  the  anterior  region  from 
the  internal,  in  the  posterior  from  the  external,  carotid,  are  peculiar  in  their 
position.  Thus  they  he  superficial  to  the  deep  fascia,  which  is  here  represented 
by  the  aponeurosis  (fig.  1086).  From  this  position  arises  the  fact  that  a  large 
flap  of  scalp  may  be  separated  without  perishing,  as  it  carries  its  own  blood- 
vessels. From  the  density  of  the  layer  in  which  the  vessels  run  they  cannot 
retract  and  are  difficult  to  seize,  haemorrhage  thus  being  free.  Finally,  from 
their  position  over  closely  adjacent  bone,  ill-applied  pressure  may  easily  lead  to 
sloughing.  A  practical  point  with  regard  to  the  veins  is  given  below.  The 
lymphatics  from  the  front  of  the  scalp  drain  into  the  anterior  auricular  and 
parotid,  those  behind  into  the  posterior  auricular,  occipital  and  deep  cervical 
nodes.     The  nerves  are  derived  from  all  three  divisions  of  the  trigeminus,  from  the 

Fig.  1086. — Section  through  the  Scalp,  Skull,  and  Duka  Mater.     (Tillaux.) 


Skin  and  superficial 

fascia  with 

^  hair  bulbs  and  sebace- 
glands 
/  Fat  pellets 

Epicranial  aponeu- 


Skull:  diploic  tissue 


facial  (motor)  and  also  from  three  branches  of  the  second  and  third  cervical. 
The  supply  from  the  fifth  explains  the  neuralgia  in  acute  iritis,  glaucoma,  and 
herpes  frontahs,  and  also  the  pains  shooting  up  from  the  front  of  the  ear  in  late 
cancer  of  the  tongue. 

The  emissary  veins. — These  are  communications  between  the  sinuses  within, 
and  the  veins  outside,  the  cranium.  Most  of  them  are  temporary,  corresponding 
to  the  chief  period  of  growth  of  the  brain.  Thus  in  early  life,  when  the  develop- 
ment of  the  brain  has  to  be  very  rapid,  owing  to  the  approaching  closure  of  its 
case,  a  free  escape  of  blood  is  most  essential,  especially  in  children,  with  their 
sudden  explosions  of  laughter  and  passionate  crying! 

The  gravity  of  these  emissary  veins  and  their  free  communications  with  others 
are  shown  by  the  readiness  Avith  which  they  become  the  seat  of  thrombosis,  and 
thus  of  blood-poisoning,  in  cranial  injuries,  erysipelas,  infected  wounds  of  the  scalp, 
and  necrosis  of  the  skull.     They  include  the  following: 

1.  Vein  through  the  foramen  OEecum,  between  the  anterior  extremity  of  the  superior  sagittal 
sinus  and  the  nasal  mucous  membrane.  The  value  of  this  temporary  outlet  is  well  seen  in  the 
timely  profuse  epistaxis  of  children.  Other  more  permanent  communications  between  the  skuD 
cavity  arid  nasal  mucous  membrane  pass  through  the  ethmoid  foramina.  The  fact  that  the 
nasal  mucous  membrane  is  loose  and  ill-supported  on  the  nasal  conchas  ( turbinate  bones) 
allows  its  vessels  to  give  way  readily,  and  thus  forms  a  salutary  safeguard  to  the  brain,  warding 
off  many  an  attack  of  apoplexy.     2.  Vein  thi-ough  the  mastoid  foramen,  between  the  transverse 


THE  BONY  SINUSES  1335 

(lateral)  sinus  and  the  posterior  auricular  and  occipital  veins.  This  is  the  largest,  the  most 
constant,  and  the  most  superficial  of  the  emissary  veins.  Hence  the  old  rule  of  applying 
blisters  or  leeches  over  it  in  cerebral  congestion.  3.  Vein  through  the  posterior  superior  angle 
of  the  parietal  between  the  superior  sagittal  sinus  and  the  veins  of  the  scalp.  4.  Vein  through 
the  condyloid  foramen  between  the  transverse  (lateral)  sinus  and  the  deep  veins  of  the  neck. 
5.  Vein  through  the  hypoglossal  canal  between  the  occipital  sinus  and  the  deep  veins  of  the 
neck.  6.  Ophthalmic  veins  communicating  with  the  cavernous  sinus  and  the  angular  vein. 
These  veins  may  be  the  source  of  fatal  blood-poisoning,  by  conveying  out  of  reach  septic 
material,  in  acute  periostitis  of  the  orbit,  or  in  osteitis,  of  dental  origin,  of  the  jaws.  7.  Minute 
veins  through  the  foramen  ovale  between  the  cavernous  sinus  and  the  pharyngeal  and  pterygoid 
veins.  8.  Communications  between  the  frontal  diploic  and  supraorbital  veins,  between  the 
anterior  temporal  diploic  and  deep  temporal  veins,  and  between  the  posterior  temporal  and 
occipital  diploic  veins  and  the  transverse  sinus.  In  addition  to  the  veins  specially  mentioned, 
the  scalp  and  sinuses  communicate  by  numerous  diploic  veins,  by  those  in  the  inter-sutural 
membrane,  and  thi'ough  sutures  before  their  obliteration,  as  already  explained. 

Structure  of  cranium. —  Two  layers  and  intervening  cancellous  tissue.  Each 
layer  has  special  properties.  The  outer  gives  thickness,  smoothness,  and  uni- 
formity, and,  above  all,  elasticity.  The  inner  is  whiter,  thinner,  less  regular — 
e.  g.  the  depressions  for  vessels.  Pacchionian  bodies,  dura  mater,  and  brain. 
The  diploe,  formed  by  absorption  after  the  skull  has  attained  a  certain  thickness, 
reduces  the  weight  of  the  skull  without  proportionately  reducing  its  strength,  and 
provides  a  material  which  will  prevent  the  transmission  of  vibrations. 

A  blow  on  the  head  may  fracture  the  internal  layer  only,  the  external  one  and  diploe  escap- 
ing. This  is  difficult  to  diagnose,  and  thus  it  is  impossible  to  judge  of  the  severity  of  a  fracture 
from  the  state  of  the  external  layer.  This  may  be  whole,  or  merely  cracked,  while  the-internal 
shows  many  fragments,  which  may  set  up  meningitis  or  other  mischief.  It  is  usual  to  find  more 
extensive  splintering  of  the  inner  than  of  the  outer  layer  (table). 

The  average  thickness  of  the  adult  skull-cap  is  about  5  mm.  (\  in.).  (Holden.)  The 
thickest  part  is  at  the  external  occipital  protuberance,  where  the  bone  is  often  1.8  cm.  (|  in.) 
in  thickness.  The  thinnest  part  of  the  skull  vault  is  over  the  temporal  part  of  the  squamous. 
The  extreme  fragility  of  the  skull  here  is  partly  compensated  for  the  by  thickness  of  the  soft 
parts;  these  two  facts  are  always  to  be  remembered  in  the  diagnosis  of  a  fracture  of  the  skull 
here,  after  a  slight  injury.  Other  weak  spots  are  the  medial  wall  of  the  orbit,  the  cerebellar 
fossae,  and  that  part  of  the  middle  fossa  corresponding  to  the  glenoid  cavity. 

Anatomical  conditions  tending  to  minimise  the  effects  of  violence  inflicted  upon  the  skull. — 
(1)  The  density  and  mobility  of  the  scalp.  (2)  The  dome-like  shape  of  the  skull.  This  is  cal- 
culated to  bear  relatively  hard  blows  and  also  to  allow  them  to  glide  off.  (3)  The  number  of 
bones  tends  to  break  up  the  force  of  a  blow.  (4)  The  sutures  interrupt  the  transmission  of 
violence.  (5)  The  inter-sutural  membrane  (remains  of  fcetal  periosteum)  acts,  in  early  life, 
as  a  linear  buffer.  (6)  The  elasticity  of  the  outer  layer  (table).  (7)  The  overlapping  of  some 
bones,  e.  g.  the  parietal  by  the  squamous;  and  the  alternate  bevelling  of  adjacent  bones,  e.  g.  at 
the  coronal  suture.  (8)  The  presence  of  ribs,  or  groins,  e.  g.  (a)  from  the  crista  galli  to  the 
internal  occipital  protuberance;  (b)  from  the  root  of  the  nose  to  the  zygoma;  (c)  the  temporal 
ridge  from  orbit  to  mastoid;  (d)  from  mastoid  to  mastoid;  (e)  from  external  occipital  protu- 
berance to  th?  foramen  magnum.  (9)  Buttresses,  e.  g.  zygomatic  processes  and  the  greater 
wing  of  the  sphenoid.     (10)  The  mobility  of  the  head  upon  the  spine. 

THE  BONY  SINUSES 

Frontal. — When  well  developed,  the  frontal  sinuses  may  reach  5  cm.  (2  in.) 
upward  and  3.7  cm.  (1|  in.)  laterally,  occupying  the  greater  part  of  the  vertical 
portion  of  the  frontal  bone.  When  very  small,  they  scarcely  e.xtend  above  the 
nasal  process.  In  any  case,  they  are  rarely  symmetrical.  The  average  dimen- 
sions of  an  adult  frontal  sinus  are  3.7  cm.  (IJ  in.)  in  height,  2.5  cm.  (1  in.)  in 
breadth,  and  1.8  cm.  (f  in.)  in  depth.  (Logan  Turner.)  The  sinuses  are  sep- 
arated by  a  septum.  The  posterior  wall  is  very  thin.  Each  sinus  narrows 
downward  into  the  infundibulum.  This  is  'deeply  placed,  at  the  back  of  the 
cavity,  behind  the  frontal  (nasal)  process  of  the  maxilla  and  near  the  medial  wall 
of  the  orbit.  Its  termination  in  the  middle  meatus  is  about  on  a  level  -mth  the 
palpebral  fissure.'     (Thane  and  Godlee.)     Its  direction  is  backward. 

The  communication  of  these  sinuses  with  the  nose  accounts  for  the  frontal  headache,  the 
persistence  of  polypi  and  ozsena,  and  the  fact  that  a  patient  with  a  compound  fracture  opening 
up  the  sinuses  can  blow  out  a  flame  held  close  by. 

To  open  the  frontal  sinus,  while  the  incision  which  leaves  the  least  scar  is  one  along  the 
shaved  eyebrow,  superficial  laterally  so  to  avoid  the  supraorbital  nerve  and  vessels,  running  a 
little  downward  at  the  medial  end,  it  is  always  to  be  remembered  that,  where  the  sinuses  are 
little  developed,  this  or  a  median  incision  may  open  the  cranial  cavity.  To  avoid  this  compli- 
cation the  sinus  should  always  be  opened  at  a  spot  vertically  above  the  medial  angle. 

The  development  of  these  by  the  twentieth  or  twenty-fifth  year  may  render  a  fracture 


1336 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


here  much  less  grave  in  the  adult  than  would  otherwise  be  the  case,  the  inner  layer  (table),  if  now 
separated  from  the  outer,  protecting  the  brain.  Mr.  Hilton  showed  that  the  absence  of  any 
external  prominence  here  does  not  necessarily  imply  the  absence  of  a  sinus,  as  this  may  be  formed 
by  retrocession  of  the  internal  layer.  In  old  people  these  sinuses  may  enlarge  by  the  inner 
layer  following  the  shrinking  brain.  Again,  prominence  of  the  supracOiary  and  frontal 
eminences  does  not  necessarily  point  to  the  existence  of  a  sinus  at  all,  being  due  merely  to  a 
heaping  up  of  bone. 

The  mastoid  cells  are  arranged  in  two  groups,  of  the  utmost  importance  in  that 
frequent  and  fatal  disease,  inflammation  of  the  middle  ear: — (A)  The  upper,  or 
'antrum,'  present  both  in  early  and  late  life,  horizontal  in  direction,  closely  adja- 
cent to  and  communicating  with  the  tympanum.  (B)  The  lower,  or  vertical. 
This  group  is  not  developed  in  early  life. 

A.  Tympanic  antrum  (fig.  1088). — This  is  a  small  chamber  lying  behind  the 
tympanum,  into  the  upper  and  back  part  of  which  (epitympanic  recess)  it  opens. 
Its  size  varies,  especially  with  age.  Almost  as  large  at  birth,  it  reaches  its  maxi- 
mum (that  of  a  pea)  about  the  third  or  fourth  year.  After  this  its  size  usually 
diminishes  somewhat,  owing  to  the  development  of  the  encroaching  bone  around 

Fig.  1087. — Tempobal  Bone,  showing  Suprambatal  Triangle.     (Barr.) 
The  lower  part  of  the  transverse  sinus  is  here  placed  too  far  back  to  be  relied  upon  with  con- 
stant accuracy. 


Root  of  zygoma 


Suprameatat 

triangle 
Position  for 
~^         perforating 
vertical  cells 


it.  Its  roof,  or  tegmen,  is  merely  the  backward  continuation  of  the  tegmen 
tympani.  The  level  of  this  is  indicated  by  the  posterior  root  of  the  zygoma. 
'The  level  of  the  floor  of  the  adult  skull  at  the  tegmen  antri  is,  on  an  average,  less 
than  one-fourth  of  an  inch  above  the  roof  of  the  external  osseous  meatus;  in 
children  and  adolescents,  from  one-sixteenth  to  one-eighth  of  an  inch.'  (Mac- 
ewen.)  In  early  life,  when  the  bony  landmarks,  e.  g.  the  suprameatal  crest  (fig. 
1087),  are  little  marked,  the  level  of  the  upper  margin  of  the  bony  meatus  will  be 
the  safest  guide  to  avoid  opening  the  middle  fossa. 

The  lateral  wall  of  the  antrum  is  formed  by  a  plate  descending  from  the 
squamous  bone.  This  is  very  thin  in  early  life,  but  as  it  develops  by  deposit 
under  the  periosteum,  the  depth  of  the  antrum  from  the  surface  increases. 
Macewen  gives  the  average  of  the  depth  as  varying  from  one-eighth  to  three- 
fourths  of  an  inch.  The  thinness  of  the  outer  wall  in  early  life  is  of  practical 
importance.  It  allows  of  suppuration  making  its  way  externally — subperiosteal 
mastoid  abscess.  This  will  be  facihtated  by  any  delay  in  the  closure  of  the  petro- 
and  masto-squamosal  sutures,  by  which  this  thin  plate  blends  with  the  rest  of  the 
temporal  bone.     Further,  by  the  path  of  veins  running  through  these  sutures  or 


THE  TYMPANIC  ANTRUM 


1337 


their  remnants,  infection  may  reach  such  sinuses  as  the  inferior  petrosal.  The 
sutures  normally  close  in  the  second  year  after  birth.  Through  the  floor,  the 
antrum  communicates  with  the  lower  or  vertical  cells  of  the  mastoid.  This  floor 
is  on  a  lower  level  than  the  opening  into  the  tympanum,  and  thus  drainage  of  an 
infected  antrum  is  difficult,  fluid  finding  its  way  more  readily  into  the  lower  cells. 
Behind  the  mastoid  antrum  and  cells  is  the  bend  of  the  sigmoid  part  of  the  trans- 
verse (lateral)  sinus,  with  its  short  descending  portion  (fig.  1087).  The  average 
distance  of  the  sinus  from  the  superior  meatal  triangle  is  1  cm.  (f  in.).  It  may  be 
further  back;  on  the  other  hand,  it  may  come  within  2  mm.  (y\  in.)  from  the 
meatus,  and  even  overlap  the  outer  wall  of  the  antrum. 

Fig.  1088. — The  Mastoid  Antrum  and  Cells.  (Jacobson  and  Steward.) 
1.  Posterior  root  of  zygoma  forming  the  supramastoid  or  suprameatal  crest  and  upper 
part  of  Macewen's  triangle.  2.  Antrum,  and  in  front  of  it,  the  epitympanic  recess.  3.  Vertical 
cells  of  the  mastoid.  4.  Ridge  on  the  inner  wall  of  the  tympanum,  caused  by  the  facial  canal. 
5.  Fenestrse  on  inner  wall  of  tympanum,  indicated  in  shadow.  6.  A  deficiency  present  in  the 
tegmen  tympani,  enlarged  with  a  small  osteotrite  to  emphasise  the  thinness  of  the  roof  of  the 
antrum  and  tympanum.     7.  Cells  extending,  in  this  case,  even  into  the  root  of  the  zygoma. 


The  exact  position  of  the  antrum,  a  little  above  and  behind  the  external  auditory  meatus 
is  represented  by  Macewen's  'suprameatal  triangle.'  This  is  a  triangle  bounded  by  the  posterior 
root  of  the  zygoma  above,  the  upper  and  posterior  segment  of  the  bony  external  meatus  below, 
and  an  imaginary  line  joining  the  above  boundaries  (fig.  1087).  "Roughly  speaking,  if  the  orifice 
of  the  external  osseous  meatus  be  bisected  horizontally,  the  upper  half  would  be  on  the  level 
of  the  mastoid  antrum.  If  this  segment  be  again  bisected  vertically,  its  posterior  half  would 
again  correspond  to  the  junction  of  the  antrum  and  middle  ear,  and  immediately  behind  this 
lies  the  suprameatal  fossa.'  (Macewen.)  When  opening  the  antrum  through  this  triangle, 
the  operator  should  work  forward  and  medially,  so  as  to  avoid  the  transverse  sinus  (fig.  1087) ; 
while,  to  avoid  the  facial  nerve  (fig.  10S7),  he  should  hug  the  root  of  the  zygoma  and  the  upper 
part  of  the  bony  meatus  as  closely  as  possible.  The  level  of  the  base  of  the  brain  will  be  a  few 
lines  above  the  posterior  root  of  the  zygoma  (fig.  1089)  and  about  6  mm.  (j  in.)  above  the  roof 
of  the  bony  meatus.     (Macewen.) 


1338  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

B.  The  lower  or  vertical  cells  of  the  mastoid  are  developed  later  than  is  the 
antrum,  and  vary  much  in  their  contents.  The  condition  of  the  mastoid  cells 
varies  very  widely.  They  may  be  numerous  (fig.  1088)  or  few.  In  the  latter 
case  they  are  replaced  by  diploe,  or  by  bone  which  is  unusually  dense,  without 
necessarily  any  pathological  change.  Hence  mastoids  have  been  classified  as 
pneumatic,  diploetic,  or  sclerosed. 

As  part  of  the  surgical  anatomy  of  this  most  important  region,  the  different  paths  by  which 
infection  of  the  tympanum  and  antrum  may  travel  should  be  glanced  at.  The  most  important 
are: — (1)  Upward:  either  by  advancing  caries  or  by  infection  of  veins  going  to  the  superior 
petrosal  sinus,  or  through  the  tegmina  to  the  membranes;  an  abscess  in  the  overlying  temporal 
lobe,  usually  the  middle  and  back  part.  (2)  Backward :  the  transverse  (lateral)  sinus  and 
cerebellum  (abscess  of  the  front  and  outer  part  of  the  lateral  lobe)  are  reached  in  the  same  ways 
as  those  given  above,  the  mastoid  vein  being  the  one  chiefly  affected  here.  Macewen  has  shown 
that  the  bony  wall  of  the  sinus,  like  those  of  the  tegmina  and  the  aqueduct  of  Fallopius,  may  be 
naturally  imperfect.  (3)  Downward :  where  the  vertical  cells  are  well  developed  (fig.  929) 
mischief  may  reach  the  mastoid  notch  and  cause  deep-seated  inflammation  beneath  the  sterno- 
mastoid.  (v.  Bezold's  abscess.)  (4)  Lateralward:  the  explanation  of  this,  in  early  life,  has 
been  given  above.  (.5)  Medialward :  the  facial  nerve,  or  by  the  fenestra  ovahs;  the  labyrinth  is 
now  in  danger.  When  the  internal  ear  and  auditory  nerve  are  affected,  infection  finds  another 
path  to  the  cerebellar  fossa. 

The  sphenoidal  sinuses  are  less  important  surgically,  but  these  points  should  be  remem- 
bered:— (1)  Fracture  through  them  may  lead  to  bleeding  from  the  nose,  which  is  thus  brought 
into  communication  with  the  middle  fossa;  (2)  the  communication  of  their  mucous  membrane 
with  that  of  the  nose  may  explain  the  inveteracy  of  certain  cases  of  polypi  and  ozaena;  (3)  here 
and  in  the  frontal  sinuses  very  dense  exostoses  are  sometimes  formed.  Before  any  operative 
attack  on  these  sinuses  is  undertaken,  their  most  important  relations  should  be  remembered. 
Thus  above  are  the  olfactory  and  optic  nerves,  the  pituitary  body,  and  front  of  the  pons. 
Externally  lie  the  cavernous  sinus  and  superior  orbital  (sphenoidal)  fissure.  Below  is  the  roof 
of  the  nose. 

The  ethmoidal  and  maxillary  sinuses  are  considered  later  in  connection  with  the  Nose. 
See  also  the  sections  on  Osteology  and  Respiratory  System. 

CRANIO-CEREBRAL  TOPOGRAPHY 

To  make  as  clear  as  possible  the  points  of  practical  importance  which  have,  of 
late  years,  been  put  on  a  definite  basis,  and  which  the  surgeon  may  have  to  recall 
and  act  upon  at  very  short  notice,  cranio-cerebral  topography  will  be  spoken  of 
under  the  following  headings:  A.  Relation  of  the  brain  as  a  whole  to  the  skull, 
B.  Relation  of  the  chief  sulci  and  gyri  to  the  skull.  C.  Localisation  of  the 
chief  sulci  and  gyri.  Before  alluding  to  the  above,  it  is  necessary  to  say  distinctly 
that  the  following  surface-markings  and  points  of  guidance  are  only  approxi- 
mately reliable,  for  the  following  reasons:  (1)  In  two  individuals  of  the  same 
age  and  sex  the  sulci  and  convolutions  are  never  precisely  alike.  (2)  The  rela- 
tions of  the  convolutions  and  sulci  to  the  surface  vary  in  different  individuals. 
(3)  That  as  the  surface  area  of  the  scalp  and  outer  aspect  of  the  skull  are  greater 
than  the  surface  area  of  the  brain,  and  as  the  convexities  do  not  tally,  lines  drawn 
on  the  scalp  or  skull  cannot  always  correspond  precisely  to  cerebral  convolutions 
or  sulci.  It  results  from  the  above  that  when  a  definite  area  of  the  surface  is  said 
to  correspond  accurately  in  any  individual  to  a  definite  area  of  the  brain  surface, 
this  result  has  been  correlated  from  many  examinations;  and  that  as  surface- 
markings,  shape,  and  processes  of  skull  and  arrangement  of  surface  are  all  liable 
to  variations  in  different  individuals,  the  surgeon  must  allow  for  these  variations 
by  removing  more  than  that  definite  area  of  skull  which  is  said  to  correspond 
exactly  to  that  part  of  the  brain  which  he  desires  to  expose. 

A.  Relation  of  the  brain  as  a  whole  to  the  skull  (figs.  1089,  1091). — To  trace 
the  lower  level  of  each  cerebral  hemisphere  on  the  skull,  the  chalk  would  start  from 
the  lower  part  of  the  glabella;  thence  the  line  representing  the  lower  borders  of  the 
frontal  lobe  pursues  a  course,  slightly  curved  upward,  about  0.8  cm.  (^  in.) 
above  the  supraorbital  margin;  next,  crossing  the  temporal  crest  about  1.2  cm. 
(i  in)  above  the  zygomatic  (external  angular)  process,  it  passes  not  quite  hori- 
zontally but  descending  slightly  to  a  point  in  the  temporal  fossa  just  below  the 
tip  of  the  great  wing  of  the  sphenoid  (pterion),  2.5  cm.  (1  in.)  behind  the  zygo- 
matic process.  From  this  point  the  line  of  the  level  of  the  brain,  now  convex 
forward  and  corresponding  to  the  anterior  extremity  of  the  temporal  lobe, 
would  dip  down,  still  within  the  great  wing  of  the  sphenoid,  to  about  the  centre 
of  the  zygoma.     Thence  the  line  of  the  lower  border  of  the  temporal  lobe  would 


CRANIO-CEREBRAL  TOPOGRAPHY 


1339 


travel  along  the  upper  border  of  this  process  about  6  mm.  (J  in.)  above  the  roof 
of  the  external  auditory  meatus  (fig.  1089),  and  thence  just  above  the  base  of 
the  mastoid  and  the  posterior  inferior  angle  of  the  parietal,  and  so  along  the 
linea  nuchse  suprema,  and  corresponding  to  the  tentorium  and  horizontal  part 
of  the  transverse  (lateral)  sinus,  to  the  external  occipital  protuberance. 

The  upper  margin  of  each  hemisphere  would  be  represented  by  a  line  drawn 
from  just  below  the  glabella,  sufficiently  to  one  side  of  the  middle  line  to  allow  for 
the  falx  and  superior  sagittal  sinus,  to  one  immediately  above  the  superior  external 
occipital  protuberance  and  inion. 

B.  Relation  of  the  chief  fissures  and  convolutions  to  the  skull.  C.  Local- 
isation of  the  chief  sulci  and  gyri.     These  headings  will  be  taken  together. 

It  will  be  well  first  to  indicate  the  position  of  the  chief  sutures  which  mark  off 
the  parietal  bone,  under  which  lies  that  part  of  the  brain  which  is  most  important 
to  the  surgeon — the  motor  area.  The  upper  limit  of  the  bone  will  be  indicated  by 
the  line  already  spoken  of  as  giving  the  upper  margin  of  the  hemisphere — the 
sagittal  line,  or  Sagittal  suture.      The  anterior  limit  of  the  parietal  bone,  formed 

Fig.  1089. — The  Outline  of  the  Brain  and  its  Fissures  in  Relation  to  the  Sutures 
OF  THE  Skull.  (Cunningham.) 
s.M.  Supraciliary  margin  of  the  cerebrum,  i.l.m.  Infero-lateral  margin  of  the  cerebrum. 
L.s.  Position  of  highest  part  of  the  arch  of  the  transverse  sinus.  R.  Central  sulcus  (Fissure  of 
Rolando),  s^.  Anterior  horizontal  limb  of  lateral  fissure,  s^  Anterior  ascending  limb  of 
lateral  fissure,  s^  Posterior  horizontal  limb  of  lateral  fissure,  p.b.  Opercular  portion  of  the 
inferior  frontal  convolution,  p.t.  Triangular  portion  of  the  inferior  frontal  'convolution. 
P.O.  Orbital  portion  of  the  inferior  frontal  convolution. 


by  the  coronal  suture,  may  be  traced  thus :  The  point  where  it  leaves  the  sagittal 
suture  (the  bregma)  will  be  found  by  drawing  a  line  from  a  point  just  in  front  of 
the  external  auditory  meatus  (the  pre-auricular  point)  (fig.  1085)  straight  upward 
on  to  the  vertex;  from  this  point  a  line  drawn  downward  and  forward  to  the 
middle  of  the  zygomatic  arch  would  indicate  that  of  the  coronal  suture.  Under 
this  suture  lie  the  posterior  extremities  of  the  three  frontal  convolutions;  for  the 
frontal  lobe  lies  not  only  under  the  frontal  bone,  but  extends  backward  under  the 
anterior  part  of  the  parietal,  the  central  sulcus  (fissure  of  Rolando) ,  which  separates 
the  frontal  from  the  parietal  lobe,  lying  from  3.7  to  5  cm.  (1|  to  2  in.)  behind  the 
coronal  suture  at  its  upper  extremity  and  about  2.5  cm.  (1  in.)  at  its  lower. 

The  squamoso-parietal  suture,  which  marks  the  lower  border  of  the  anterior  two-thirds 
of  the  parietal  bone,  is  not  so  easy  to  define,  owing  to  the  irregularity  and  variations  of  its  curve. 
Its  highest  point  is  usually  4.3  cm.  (If  in.)  above  the  zygoma. 

The  lambdoid  suture,  which  forms  the  posterior  boundary  of  the  parietal  bone,  will  be 
marked  out  by  a  line  which  starts  from  a  point  (lambda)  about  6.2  cm.  (2i  in.)  above  the 
external  occipital  protuberance,  and  runs  downward  and  forward  to  a  point  on  a  level  with 
the  zygoma,  3.7  cm.  (IJ  in.)  behind  and  1.2  cm.  (J  in.)  above  the  centre  of  the  meatus. 


1340 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


The  position  of  the  chief  sulci  will  now  be  given: — 

Lateral  (Sylvian)  fissure  (fig.  1089). — The  point  of  appearance  of  this,  on 
the  outer  side  of  the  brain,  practically  corresponds  to  the  pterion  (p.  1332,  fig. 
1085) — a  point  which  lies  in  the  temporal  fossa,  about  3.7  cm.  (1|  in.)  behind  the 
zygomatic  process  and  about  the  same  distance  above  the  zygoma.  From  this 
point  the  lateral  fissure,  which  here  separates  the  frontal  and  parietal  from  the 
temporal  lobe,  runs  backward  and  upward,  ascending  gently,  at  first  in  the  line 
of  the  squamo-parietal  suture,  then  crossing  this  suture  about  its  centre  and 
thence,  ascending  more  rapidly,  it  climbs  up  to  the  temporal  ridge,  to  end  1.8  cm. 
(f  in.)  below  the  parietal  eminence.  Its  termination  is  surrounded  by  the 
supramarginal  convolution,  to  which  the  parietal  eminence  corresponds  with 
sufficient  accuracy.  Such  being  the  surface-marking  of  the  chief  or  posterior 
horizontal  limb  of  the  lateral  fissure  (s^,  fig.  1089),  it  remains  to  indicate  briefly 
the  two  shorter  limbs  which  bound  the  inferior  frontal  convolution,  which,  on  the 
left  side,  contains  the  centre  for  speech  (Broca's  convolution),  and  corresponds 
to  a  point  l3ang  three  fingers'  breadth  vertically  above  the  centre  of  the  zygo- 
matic arch.  (Stiles.)  Of  these,  the  anterior  horizontal  (s^,  fig.  1089)  runs  for- 
ward across  the  termination  of  the  coronal,  just  above  the  line  of  the  spheno- 
parietal suture.     The  ascending  limb   (s^,  fig.   1089)   runs  upward  for  about 


Fig.  1090. — Lateral  View  op  the  Skull,  Showing  the  Topogeaphy  of  the  Middle 
Meningeal  Artery  and  the  Transverse  Sinus. 


Anterior  branch 

of  middle 

meningeal  art. 

Posterior 
branch' of 
middle  menin- 
geal art. 


2.5  cm.  (1  in.)  just  behind  the  termination  of  the  coronal  suture,  or  5  cm.  (2  in.) 
behind  the  zygomatic  process. 

The  central  sulcus  (fissure  of  Rolando). — This  most  important  fissure,  in 
front  of  which,  in  the  precentral  convolution  of  the  frontal  lobe,  lie  the  motor 
centres  for  the  opposite  side  of  the  body,  is  situated  under  the  parietal  bone. 
It  may  be  marked  out  with  sufficient  precision  in  the  following  way  (Thane): 
The  sagittal  line,  from  glabella  to  external  occipital  protuberance,  is  bisected, 
and  a  point  1.2  cm.  (Jin.)  behind  the  centre  represents  the  superior  Rolandic  point. 
From  this  point  a  line  drawn  downward  and  forward  9  cm.  (3|  in.)  long,  at  an  angle 
of  67|°  with  the  sagittal  line  (i.  e.,  |  of  a  right  angle)  will  represent  the  central 
sulcus.     The  lower  extremity  of  this  line  is  known  as  the  inferior  Rolandic  point. 

This  method  is  open  to  the  objection  that  it  only  apphes  to  the  average  adult  skull,  and  not 
to  skulls  of  all  sizes.  To  obviate  this  difficulty  the  method  of  Kronlein  may  be  employed  in 
addition  (fig.  1085).  A  base  line  BL  is  drawn  through  the  lower  border  of  the  orbit  and  the 
upper  border  of  the  external  acustic  meatus.  Parallel  to  this  an  upper  horizontal  Une  UH  is 
marked  out  at  the  level  of  the  upper  margin  of  the  orbit.  Three  hues  vertical  to  the  base  line 
are  now  drawn,  (1)  at  the  posterior  border  of  the  mastoid  process  MRi  (2)  through  the  condyle 
of  the  lower  jaw  (CR2),  and  (3)  from  the  mid-point  of  the  zygoma  (ZS).  The  point  Ri,  where 
the  first  vertical  joins  the  sagittal  sutiu'e  is  the  superior  Rolandic  point.  The  point  S  where 
the  third  vertical  ZS  cuts  the  line  UH  marks  the  junction  of  the  three  hmbs  of  the  lateral  fissure. 
A  line  joining  Ri  and  S  will  cut  the  second  vertical  CR2  at  the  inferior  Rolandic  point,  Rj. 


CRANIO-CEREBRAL  TOPOGRAPHY 


1341 


The  posterior  limb  of  the  lateral  fissure  also  may  be  represented  by  a  line  bisecting  the  angle 
RiSH  and  ending  behind  at  the  point  S^  where  it  cuts  the  vertical  MRi. 

Some  further  points  in  the  surgical  anatomy  of  the  cranium  must  be  referred  to: — The  mid- 
dle meningeal  artery.  This  vessel,  entering  the  middle  fossa  by  the  foramen  spinosum,  grooves 
the  great  wing  of  the  sphenoid  and  divides  into  two  branches.  The  anterior  grooves  the 
anterior  inferior  angle  of  the  parietal  bone,  and  is  then  continued  upward  and  slightly  back- 
ward between  the  coronal  suture  and  central  sulcus  (fig.  1090),  almost  to  the  vertex;  the  posterior 
branch  takes  a  lower  level,  running  backward  under  the  squ.imous  bone  to  supply  the  parietal 
and  anterior  part  of  the  occipital  bones.  If  a  skull,  bisected  antero-posteriorly,  be  held  up  to 
the  light,  it  will  be  seen  how  thin  are  the  bones  over  the  chief  branches  of  this  vessel,  thus 
accounting  for  the  slight  violence  sometimes  sufficient  to  rupture  it.  The  groove  it  occupies 
in  the  parietal  is  sometimes  converted  into  a  canal.  A  wounded  artery  retracting  here  may  be 
very  difficult  to  secure.     The  veins  which  accompany  the  artery  and  which  lie  lateral  to  it 

Fig.  1091.- — Cerebral  Topography  and  Localization.     (Gushing,  prom  Keen's  Surgekt.) 


in  the  groove  are  thin-walled  and  sinus-like  before  they  open  into  the  spheno-parietal  sinus, 
another  explanation  of  the  obstinacy  of  this  haemorrhage.  According  to  the  point  of  rupture, 
three  hsematomata  should  be  remembered  (Kronlein),  anterior  or  fronto-temporal;  middle, 
or  temporo-parietal;  and  posterior,  or  parieto-occipital.  The  first  two  are  much  the  most 
frequent,  and  exposure  of  the  pterion,  with  free  removal  of  the  adjacent  bone,  will  suffice  for 
dealing  with  them. 

Drainage  of  the  lateral  ventricle. — (1)  Where  the  anterior  fontanelle  is  closed,  Poirier  and 
Keen  have  opened  the  inferior  cornu  through  the  middle  temporal  convolution,  the  pin  of 
the  trephine  being  placed  3.1  cm.  (IJ  in.)  behind  the  external  auditory  meatus,  and  about  the 
same  distance  above  Reid's  base-line  which  is  drawn  from  the  lower  margin  of  the  orbit  through 
the  mid-point  of  the  external  auditory  meatus.     The  needle  should  here  be  directed  to  a  point 


1342  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

about  5  cm.  (2  in.)  above  the  opposite  ear.  (2)  Kocher's  point  for  draining  the  lateral  ventricle 
is  taken  over  the  frontal  lobe  2.5  cm.  from  the  median  line  and  3  cm.  in  front  of  the  upper 
Rolandic  point.     The  needle  is  passed  downward  and  a  little  backward  to  a  depth  of  4  or  5  cm. 

Up  to  this  point  the  outside  of  the  cranium  has  been  mainly  considered;  it  remains  to  draw 
attention  to  some  of  the  chir.f  points  in  the  sjirgical  anatomy  of  the  interior,  especially  ot  the 
base.  The  three  fossae  are  of  paramount  importance  in  fracture.  In  the  anterior  fossa 
the  delicacy  of  parts  of  the  floor,  the  connection  of  this  with  the  nose  and  orbit,  and  the  exact 
adaptation  of  its  irregular  surface  to  that  of  the  frontal  lobes,  no  'water-bed'  intervening,  are 
the  chief  points.  Thus  the  slightness  of  a  fatal  fissure,  the  frequent  presence  of  bruising  after 
a  blow  perhaps  on  the  occiput,  which  has  been  considered  to  have  caused  only  concussion,  the 
characteristic  palpebral  hemorrhage,  and  the  infection  of  a  fracture  here  are  all  explained, 
together  with  the  possibility  and  gravity  of  a  fracture  here  from  a  severe  blow  on  the  nose.  In 
the  middle  fossa  the  frequency  of  fractures  is  explained  by  the  facts  that  while  here,  as  in  the 
other  fossae,  a  fracture  often  radiates  down  from  the  vertex,  the  overlying  vault  being  a  region 
often  struck,  the  base  is  weakened  by  numerous  foramina  and  fissures.  Further,  the  resisting 
power  of  the  petrous  bone  must  be  lessened  by  the  cavities  for  the  internal  ear,  the  carotid, 
and,  to  a  less  degree,  by  the  jugular  fossa.  For  fluids  to  escape  through  the  external  meatus, 
the  dura,  the  prolongation  of  the  arachnoid  into  the  internal  meatus,  the  membrani  tympani, 
and  probably  the  internal  ear,  must  all  be  injured.  The  presence  of  the  middle  meningeal  artery 
(fig.  1090)  and  the  cavernous  sinus  in  this  fossa  must  also  be  remembered,  especially  in  such 
operations  as  that  on  the  Gasserian  ganglion.  Posterior  fossa :  It  is  not  sufficiently  recognised 
that  fractures  here  are,  owing  to  the  anatomy  of  the  parts,  in  some  respects  the  most  important 
of  all.  It  is  here  that  a  small  fissure-fracture,  ultimately  fatal,  with  severe  occipital  and  frontal 
bruising  and  some  intradural  hemorrhage,  has  been  so  often  overlooked,  especially  in  the 
drunken.  This  is  explained  by  the  supposed  strength  of  the  bone,  this  being  really  very  thin  in 
places,  by  the  thickness  of  the  soft  parts,  and  the  abundance  of  hair.  Further,  there  is  no  very 
apparent  escape  of  cerebral  contents  as  in  the  anterior  and  middle  fosse.  Blood,  etc.,  may 
trickle  into  the  pharynx  far  back,  or  a  deep-seated  eochymosis  coming  up  after  two  days,  under 
the  muscles  about  the  mastoid  process,  may  call  attention  to  the  damage  within. 

Dura  mater. — The  outer  layer  of  this  membrane  acts  as  a  periosteum,  by  bringing  blood- 
vessels to  the  bone  while  the  inner  layer  supports  the  brain.  The  influence  of  its  partitions  and 
its  damping  effect  on  vibrations  is  great  in  blows  on  the  head.  Its  varying  adhesions,  according 
to  site  and  age,  must  be  remembered.  Thus  while  it  is  intimately  connected  over  the  base 
with  its  adhesions  to  the  different  foramina,  it  is  more  loosely  connected  with  the  vault,  as  is 
shown  in  middle  meningeal  hemorrhage.  In  early  and  later  life  the  closeness  of  its  connection 
with  the  bones  is  also  more  marked.     It  is  united  to  the  inter-sutural  membranes. 

Finally,  the  existence  of  the  cerebro-spinal  fluid  with  its  power  of  lessening  the  evil  of 
vibrations  and  its  aid  in  regulating  infra-cranial  pressure,  must  be  borne  in  mind.  The  chief 
collections,  in  which  the  subarachnoid  meshwork  is  almost  absent,  are  met  with  in  front  and 
behind  the  medulla.  That  in  front,  also  lying  under  the  pons,  Hilton's  'water-bed,'  sends 
a  prolongation  forward  to  the  optic  chiasma,  but  does  not  extend  under  the  frontal  or  temporal 
lobes.  The  collection  behind  lies  between  the  medulla  and  under  surface  of  the  cerebellum. 
Here,  by  the  foramen  of  Magendie,  the  intra-ventricular  cavities  communicate  with  the  sub- 
arachnoid space  of  the  spinal  cord. 

THE  HYPOPHYSIS  CEREBRI 

The  hypophysis  (pituitary  body)  which  has  now  become  of  great  clinical 
importance,  consists  of  a  pars  anterior  and  pars  intermedia  derived  from  the 
buccal  ectoderm,  and  a  posterior  pars  nervosa  formed  by  a  downgrowth  from 
the  floor  of  the  third  ventricle.  The  gland  lies  in  the  fossa  hypophyseos  of  the 
sphenoid  bone,  and  an  enlargement  of  it,  apart  from  general  skeletal  and  nutri- 
tional effect  due  to  anomalies  of  its  internal  secretions,  will  cause  pressure  on 
the  cavernous  sinus  on  each  side,  and  on  the  optic  chiasma  above.  It  will  also 
expand  the  fossa  hypophyseos,  pushing  down  its  floor  at  the  expense  of  the 
sphenoidal  air  sinus.  Such  enlargements  may  be  detected  by  lateral  radiograms. 
The  normal  size  of  the  adult  hypophyseal  fossa  (fig.  1097)  is  10-12  mm.  from 
before  backward  and  8  mm.  from  above  downward  (Keith). 

The  hypophysis  may  be  exposed  surgically  either  by  turning  the  nose  to  one  side,  and  remov- 
ing the  upper  part  of  the  septum  and  floor  of  the  sphenoidal  sinus,  or  by  Cushing's  method,  in 
which  a  sublabial  incision  is  made  in  the  vestibule  of  the  mouth,  and  through  it  the  mucosa  is 
then  separated  from  each  side, of  the  nasal  septum  back  to  the  sphenoidal  sinus.  A  strip  of 
septum  is  removed,  and  also  the  floor  of  the  sphenoidal  sinus,  after  which  the  hypophyseal  fossa 
is  opened  and  the  gland  e.xposed  (fig.  1097).* 

THE  FACE 

The  topics  included  under  this  heading  are  the  arteries,  parotid  region,  nerves, 
mandible  and  maxilla,  orbit,  mouth,  palate  and  nose. 

The  outhne  of  the  different  bones — nasal,  upper  and  lower  jaws,  zygomatic 
■*  H.  Gushing.     The  Pituitary  Body  and  its  Disorders,  1912. 


THE  FACE 


1343 


and  zygoma — can  be  readily  traced.  The  last  mentioned  and  the  glabella  are 
alluded  to  on  pp.  1331  and  1332;  and  the  canine  fossa  should  be  identified  as  one 
of  the  antral  routes.  The  delicacy,  laxity,  and  vascularity  of  the  skin  are  of  great 
importance  in  all  operations,  while  the  abundance  of  large  gland  orifices  accounts 
for  the  frequency  of  lupus  here. 

Arteries. — The  supraorbital  artery  can  be  felt  beating  just  above  its  notch 
(junction  of  medial  with  lateral  two-thirds  of  supraorbital  margin);  the  little 
frontal  artery  is  of  importance,  as  it  nourishes  the  flap  when  a  new  nose  is  taken 
from  the  forehead;  the  superficial  temporal,  accompanied  by  the  auriculo-temporal 
nerve,  can  be  felt  where  it  crosses  the  root  of  the  zygoma  just  in  front  of  the  tragus, 
its  anterior  branch  about  3.1  cm.  (1|  in.)  above  and  behind  the  zygomatic  process 
of  the  frontal;  the  occipital,  accompanied  by  the  great  occipital  nerve  (fig.  450), 
pulsates  to  the  medial  side  of  the  centre  of  a  line  drawn  from  the  occipital  protu- 
berance to  the  mastoid  process;  the  posterior  auricular,  rather  deeply,  between  the 
auricle  and  the  mastoid  process.     The  external  carotid  lies  behind  the  ascending 

Fig.  1092. — Surface  Relations  of  Vessels  and  Nerves  in  Lateral  View  op  the  Face 

AND  Neck. 


Supraorbital  n. 


Supratrochlear  n. 


Infratrochlear  n. 

External  nasal  n. 
Infraorbital  n. 

Buccal  n. 

Ext.  maxillary  art. 

Mental  n. 

Post,  belly  of 

digastric 

Ant.  belly  of 

digastric 

Thyreoid  cartilage 

Common  carotid 

art. 

Thyreoid  gland 


External  auditory 

meatus 
Facial  nerve  (in  red) 

Parotid  gland  (yellow) 
Sternomastoid 


Accessory  nerve 
Ext.  jugular  vein 


ramus  of  the  jaw.  The  external  maxillary  (fig.  1093)  crosses  the  jaw  just  in  front 
of  the  masseter;  if  divided,  both  ends  must  be  secured  here.  It  can  be  felt  again 
a  little  behind  the  angle  of  the  mouth,  just  beneath  the  mucous  membrane  (it 
here  gives  off  the  labial  branches,  which  can  also  be  felt,  lying  deeply,  if  the  lip 
is  taken  between  the  finger  and  thumb) ;  and  again  by  the  side  of  the  nose,  as  it 
runs  up  to  Ithe  angulusoculi.  The  small  angular  branch  is,  from  its  position, 
always  troublesome  to  secure.  To  trace  the  course  of  the  external  maxillary 
artery  a  line  should  be  drawn  from  a  point  a  little  above  and  lateral  to  the  tip  of 
the  great  cornu  of  the  hyoid  to  the  lower  part  of  the  anterior  border  of  the  masse- 
ter, and  thence  to  one  lateral  to  and  above  the  angle  of  the  mouth,  and  so  onward, 
lateral  to  the  angle  of  the  nose,  up  to  the  medial  angle.  The  anterior  facial  vein 
takes  a  straight  course  behind  the  tortuous  external  maxillary  artery.  The 
absence  of  valves  and  its  communication  by  the  angular  and  ophthalmic  veins 
with  the  cavernous  sinus,  and,  by  the  deep  facial,  with  the  pterygoid  plexus,  are 
of  grave  importance  in  infective  thrombosis.  The  external  jugular  vein  will  be 
mentioned  later. 

Parotid  region. — A  line  drawn  from  the  lower  border  of  the  meatus  to  a  point 
midway  between  the  nose  and  upper  lip  gives  the  level  of  the  parotid  duct,  which 


1344 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


opens  into  the  mouth  opposite  the  second  molar  tooth.  The  level  of  the  duct, 
somewhat  inconstant,  would  be  usually  about  a  finger^s  breadth  below  the 
zygoma.  It  is  accompanied  by  the  transverse  facial  artery  above,  and  the 
infraorbital  branch  of  the  facial  nerve  below. 

The  sheath  of  the  parotid,  continuous  with  those  of  the  masseter  and  sterno-mastoid,  is 
strong  enough  to  cause  most  exquisitely  painful  tension  when  inflammation  of  the  gland  is 
present,  and,  together  with  the  presence  of  deep  processes  of  the  gland  in  connection  with  the 


Fig.  1093. — Scheme  op  the  External  Maxillary  (Facial)  Artery.     (Walsham.) 


Orbicularis  ocuU  muscl 


Transverse  facial  artery 
M.  quadr.  labii  sup 

(caput  zygom.) 
Zygoma ticus  muscle 


Buccinator  muscle 

Masseteric  branch 

Masseter  muscle 

Stylo  -phar  ynge  u  i 

Stylo-glossus  muscle 
Ascending  palatine 
branch 
Tonsillar  branch 

External  maxillary 

artery 

External  carotid 

artery 

Posterior  belly  of 

digastric  muscle 

Lingual  artery 


Frontal  branch  of  ophthal- 
mic artery 

Nasal  branch  of  ophthal- 
mic artery 


-Angular  artery 
M.  quadr.  labii 
■  sup.  (caput  ang.) 
Infraorbital  artery 
Caput  infraorb. 
■Lat.  nasal  artery 
Caninus  muscle 

—Artery  of  septum 

Superior  labial 

artery 

Risonus  muscle 


Infenor  labial  artery 

Mental  branch  of  inferior 

alveolar  artery 
Quadratus  labii  inferioris 

muscle 
Inferior  labial  artery 
Triangularis  muscle 

Submental  artery 
branches  to  submaxillary 


Anterior  belly  of  digastric 
Mylo-hyoid  muscle 


■Hyo-glossus  muscle 


'Hypoglossal  nerve 


mandibular  (glenoid)  cavity  and  styloid  process,  to  explain  the  deep  burrowing  of  pus  which 
may  take  place  into  the  pharynx  and  pterygoid  region.  The  relation  of  the  capsule  to  growths, 
innocent  or  malignant,  of  the  parotid  is  also  important  (See  figs.  S65,  1092). 

The  parotid  region  would  be  thus  mapped  out  (fig.  1096).  Above  by  the  pos- 
terior two-thirds  of  the  zygoma;  below,  by  a  line  corresponding  to  the  posterior 
belly  of  the  digastric  (fig.  1096) ;  behind,  are  the  external  auditory  meatus,  mastoid, 
and  sterno-mastoid.  In  front  the  gland  and  socia  parotidis  overlap  the  posterior 
part  of  the  masseter,  to  a  variable  degree  (fig.  1096). 


THE  FACE  1345 

Sensory  nerves. — -The  cutaneous  nerve  areas  of  the  face  are  shown  in  fig.  774. 
The  supraorbital  nerve,  the  main  sensory  branch  of  the  ophthalmic,  emerges  from 
the  orbit  with  its  companion  artery  through  the  notch  (occasionally  a  foramen) 
at  the  junction  of  the  medial  third  and  lateral  two-thirds  of  the  supraorbital 
margin.  A  line  drawn  from  the  supraorbital  notch  downward  across  the  interval 
between  the  bicuspid  teeth  will  cross  the  infraorbital  foramen  from  which  emerges 
the  infraorbital  nerve,  the  main  terminal  division  of  the  maxillarj^,  at  a  point 
1  cm.  below  the  orbital  margin.  The  mental  foramen,  the  point  of  exit  of  the 
mental  nerve,  a  branch  of  the  inferior  alveolar,  is  found  on  a  prolongation  of  the 
same  line  midway  between  the  upper  and  lower  margins  of  the  mandible  in  the 
adult.  In  the  infant  in  whom  the  alveolar  element  of  the  jaw  is  relatively 
large,  the  mental  foramen  is  nearer  the  lower  margin,  while  in  the  edentulous 
jaw  of  old  age  it  is  found  much  nearer  the  upper  margin. 

In  trephining  to  expose  the  inferior  alveolar  (dental)  nerve,  one  of  the  common 
seats  of  neuralgia  and  one  in  which  a  peripheral  operation  is  justified  from  the 
results,  the  ascending  ramus  is  opened  midway  between  its  anterior  and  posterior 
borders,  on  a  level  with  the  last  molar. 

The  semilunar  ganglion  lies  at  a  depth  of  5.5-6  cm.  (2i  in.)  upder  the  eminentia  articularia 
at  the  base  of  the  zygoma.  In  exposing  it  for  the  purpose  of  excision  for  intractable  neuralgia 
the  following  structures  are  encountered:  (1)  Skin  and  superficial  fascia  with  branches  of  the 
superficial  temporal  artery;  (2)  temporal  fascia  and  muscle  with  deep  temporal  vessels;  (3) 
squamous  bone  and  great  wing  of  sphenoid,  which  are  trephined,  the  floor  of  the  middle  fossa 
being  gouged  away ;  (4)  middle  meningeal  vessels  and  dura  mater.  By  elevating  the  dura  mater 
and  superimposed  temporal  lobe,  and  securing  the  middle  meningeal  artery,  the  ganglion  is 
exposed,  lying  in  a  separate  compartment  [cavum  Meckelii]  of  the  dura,  which  contains  cerebro- 
spinal fluid.  The  motor  nerve  of  the  muscles  of  mastication  lies  on  the  lower  and  medial 
aspect  of  the  ganglion,  and  should  not  be  divided. 

Injection  of  the  mandibular  nerve  with  alcohol,  by  means  of  a  long  stout  hypodermic  needle 
is  practised  in  cases  of  intractable  neuralgia  as  an  alternative  to  excision  of  the  semilunar  gang- 
lion. A  vertical  line  is  drawn  on  the  cheek  downward  from  the  junction  of  the  posterior  and 
middle  thirds  of  the  zygomatic  arch,  and  the  needle  is  entered  on  this  line  at  a  point  1.5  cm. 
from  the  lower  border  of  the  zygoma.  It  is  directed  upward  and  medially  so  as  to  pass  through 
the  lowest  part  of  the  mandibular  notch.  If  the  mouth  is  opened  the  notch  is  depressed  and  more 
room  gained.  The  needle  impinges  first  against  the  inferior  surface  of  the  great  wing  of  the 
sphenoid  bone,  and  when  the  point  is  lowered  a  little  it  engages  in  the  foramen  ovale  at  a  depth 
of  4-4,5  cm.  In  most  cases  the  needle  can  be  passed  thi'ough  the  foramen  ovale  into  the  semi- 
lunar gangUon.     (Harris.)* 

The  maxillary  nerve  may  be  injected  by  passing  a  needle  along  the  floor  of  the  orbit  from  its 
infero-lateral  angle  in  a  direction  backward  and  sUghtly  medially  to  the  foramen  rotundum 
which  lies  4.5  cm.  from  the  surface. 

Facial  nerve. — In  the  petrous  bone  the  course  of  this  nerve  is  first  outward 
and  forward,  then,  having  entered  the  facial  canal,  backward  and  downward 
along  the  medial  wall  of  the  tympanum,  above  the  fenestra  ovalis.  Emerging 
from  the  stylo-mastoid  foramen  the  nerve  takes  first  the  line  of  the  posterior 
belly  of  the  digastric,  running  forward  and  a  little  downward  from  the  anterior 
border  of  the  mastoid  where  this  meets  the  auricle.  (Godlee.)  Entering  at 
once  the  posterior  part  of  the  parotid,  it  crosses  the  neck  of  the  mandible  at  the 
level  of  the  lower  border  of  the  tragus. 

The  frequent  paralysis  of  this  nerve  may  thus  depend  upon — (1)  cerebral  causes;  (2)  dis- 
ease of  or  injm-y  to  the  petrous  portion;  (.3)  affections  after  its  exit— BeU's  paralysis.  A  diag- 
nosis may  be  arrived  at  by  attention  to  the  following.  In  cerebral  disease  the  lower  part  of  the 
face  is  chiefly  affected,  the  eyelids  usually  escaping.  In  aU  the  other  forms  the  whole  side  of 
the  face  is  paralysed.  Hemiplegia  of  the  opposite  side  of  the  body  and  paralysis  of  the  sixth 
nerve  are  usually  present.  In  petrous  paralysis,  owing  to  involvement  of  the  chorda  tympani, 
there  may  be  interference  with  the  saliva  and  taste,  affecting  especially  the  anterior  part  of  the 
tongue.  The  auditory  nerve  may  also  be  affected.  Here  and  in  (3)  there  will  be  a  histor}'  of 
disease  or  injury.  In  complete  paralysis  the  smooth  side  of  the  face  and  forehead,  the  absence 
of  power  of  expression,  to  frown,  to  blow,  or  whistle,  the  open  eyelids  and  epiphora,  and  subse- 
quent liability  to  mischief  in  the  cornea,  the  di-opping  of  the  angle  of  the  mouth  and  dribbling 
of  saUva,  the  interference  with  mastication  from  paralysis  of  the  buccinator,  are  the  chief  points. 

Mandible. — Dislocation  of  the  temporo-mandibular  joint  is  referred  to  on 
p.  217.  In  the  usual  dislocation,  from  muscular  action,  the  jaw  is  suddenly 
brought  forward  against  the  anterior  part  of  the  capsule,  which  tends,  bj!-  the 
action  of  the  depressors,  to  give  way;  the  elevators  then  pull  up  the  mandible,  a 
sequence  that  must  be  remembered  in  reduction.     In  the  commonest  fracture  of 

*  Lancet,  Jan.  23,  1912. 


1346  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

the  mandible — unilateral,  near  the  mental  foramen — the  larger  anterior  fragment 
will  be  pulled  by  the  depressors  downward  and  medially,  the  smaller  posterior  one 
upward  and  usually  lateral  to  the  other  fragment. 

Maxilla. — The  boundaries  of  the  maxillary  sinus  (antrum)  are  of  much  im- 
portance. The  base  of  this  irregularly  pyramidal  cavity  corresponds  to  the 
middle  and  inferior  meatuses  on  the  lateral  wall  of  the  nose;  toward  the  upper 
and  back  part  is  the  opening  into  the  middle  meatus.  The  apex  runs  laterally 
toward  the  zygomatic  process.  The  roof  is  formed  by  the  orbital  plate  with  the 
infraorbital  nerve  and  vessels  anteriorly;  the  floor  by  the  junction  of  the  alveolar 
arch,  carrying  the  first  molars  (and  often  the  bicuspids),  with  the  hard  palate. 
It  may  be  pierced  by  the  roots  of  the  second  bicuspid  or  first  and  second  molar 
teeth.  Anteriorly,  the  antrum  is  bounded  by  the  canine  fossa;  posteriorly  it  is 
in  relation  with  the  zygomatic  fossa.  The  cavity,  present  at  birth,  increases 
gradually  up  to  the  twelfth  year. 

The  chief  paths  of  infection  are  through  the  teeth  (especially  the  first  and  second  molar), 
the  nose,  and  frontal  sinus.  The  obstinacy  of  inflammation  here  is  explained  by  the  site  of  the 
opening,  high  up  on  the  medial  wall,  and  thus  inadequate  drainage,  by  the  imperfectly  multi- 
locular  cavity  of  the  interior  and  its  rigid  walls.  The  chief  sites  for  opening  the  antrum  are — (a) 
thi'ough  the  sockets  of  the  first  or  second  molars;  (b)  through  the  canine  fossa,  after  the  reflec- 
tion of  mucous  membrane  has  been  detached,  midway  between  the  roots  of  the  teeth  and  the 
infraorbital  foramen  (this  path  gives  more  room) ;    (c)  through  the  inferior  meatus  of  the  nose. 

THE  ORBIT  AND  EYE 

The  bony  orbit  is  a  pyramidal  fossa  with  its  base  at  the  orbital  margin  and  its 
apex  at  the  optic  foramen.  The  medial  walls  of  the  two  orbits  are  approximately 
parallel,  but  the  lateral  walls  diverge  as  they  are  traced  forward  and  lie  at  right 
angles  to  each  other.  The  thin  floor  which  is  formed  mainly  by  the  maxilla  and 
corresponds  to  the  roof  of  the  maxillary  sinus,  is  readily  destroyed  by  growths 
extending  up  from  the  sinus  and  in  the  process  pressure  on  the  infraorbital 
nerve  is  apt  to  cause  pain  referred  to  the  cheek.  The  roof  formed  by  the 
orbital  plate  of  the  frontal  bone  is  also  thin,  and  foreign  bodies  thrust  into  the 
orbit  may  perforate  it  and  enter  the  frontal  lobe  of  the  cerebrum.  The  medial 
wall  is  chiefly  constituted  by  the  lacrimal  and  lamina  papyracea  of  the  ethmoid, 
both  very  thin  bones.  This  wall  is  readily  destroyed  by  malignant  growths  of  the 
nose. 

Injuries  of  the  medial  wall  such  as  may  be  associated  with  fractures  of  the  nose  bring  the 
ethmoidal  air  cells  into  communication  with  the  cellular  tissue  of  the  orbit.  The  latter  may  thus 
be  distended  with  air  on  attempting  to  blow  the  nose. 

The  lateral  wall  is  formed  in  its  anterior  third  by  the  zygomatic  bone,  which 
separates  the  or"bit  from  the  zygomatic  fossa.  The  posterior  two-thirds  formed 
by  the  sphenoid  bone  separate  the  orbit  from  the  temporal  lobe  of  the  brain  in 
the  middle  cranial  fossa.  The  orbit  communicates  with  the  cranimn  by  the 
optic  foramen,  which  transmits  the  optic  nerve  and  ophthalmic  artery  and  the 
superior  orbital  fissure  through  which  pass  all  the  other  vessels  and  nerves  of  the 
orbit. 

In  cases  of  fracture  of  the  base  of  the  skuU  involving  the  anterior  clinoid  process,  a  traumatic 
communication  (arterio-venous  aneurysm)  may  be  formed  between  the  internal  carotid  artery 
and  cavernous  sinus,  behind  the  apex  of  the  orbit,  giving  rise  to  pulsating  exophthalmos. 

The  orbital  margin  is  larger  in  the  transverse  than  in  the  vertical  direction, 
and  consequently  there  is  more  space  on  either  side  than  above  and  below  be- 
tween it  and  the  eyeball  which  is  nearly  spherical.  The  eyeball  lies  nearer  to  the 
medial  than  to  the  lateral  margin  and  hence  foreign  bodies  more  commonly 
penetrate  the  orbit  to  the  lateral  side  of  the  eye. 

Behind  the  fascia  bulbi,  the  eyeball  rests  on  a  mass  of  soft  loose  orbital  fat  in 
which  foreign  bodies  may  be  hidden  for  a  considerable  time. 

The  structure  of  the  eyelids. — The  different  layers  are  of  much  practical 
importance.  (1)  The  skin  is  delicate  and  fatless,  and  contains  pigment,  the 
object  of  this  being  to  protect  the  eye  from  bright  light.  It  helps  to  explain  the 
'dark  circles'  of  later  life.  (2)  Areolar  tissue.  Owing  to  its  looseness  and 
delicacy,  this  is  very  liable  to  infiltration,  as  in  oedema  and  erysipelas.     (3) 


THE  ORBIT  AND  EYE 


1347 


Orbicularis.  Paralysis  of  this,  tiie  palpebral  portion,  leads  to  epipiiora,  tiie 
puncta  being  no  longer  kept  in  their  normal  baclcward  direction  against  the 
conjunctiva.  (4)  Palpebral  fascia,  reaching  from  the  orbit  to  the  tarsal  cartilage. 
This  is  usually  strong  enough  to  prevent  haemorrhage,  due  to  fractured  base  of 
skull,  becoming  subcutaneous.  (5)  Levator  palpebr^e.  (6)  Tarsal  plate;  in 
reality,  densely  felted  fibrous  tissue.  (7)  Tarsal  (Meibomian)  glands,  lashes, 
and  sebaceous  follicles. 

I  Localised  inflammation  starting  in  any  of  these  last  three  structures,  especially  the  last,  will 
cause  a  'stye.'  The  frequency  with  which  the  lid-border  is  the  seat  of  that  most  troublesome 
chronic  inflammation,  blepharitis,  and  its  result,  'blear  eye,'  is  e.xplained  by  these  anatomical 
points.  Its  circulation  is  terminal  and  slow;  half  skin  and  half  mucous  membrane,  it  is  moister 
and  more  liable  to  local  irritation  than  the  skin;  while  its  numerous  glands  readily  partici- 
pate in  any  inflammation. 

Fig.  1094. — Sagittal  Section  Thkough  the  Uppek  Eyelid.     (After    Waldeyer  and  Fuchs.) 

^    Conjunctiva  near  fornix 
/    Anterior  layer  of  insertion 
"~    of  levator  palpebrffl 
superioris 
■  Superior  tarsal  muscle 
*  Miiller 

3  from  levator  passing 
tlirough  orbicularis  to  skin 


Cutaneous  surface 
just  above  supe- 
rior palpebral  fold 


Orbicularis  fibres,  r.nt_ 

across                       [\ 
Sweat-gland -\^ — 


--Supei 
/  of  I 

/--—Fibre 


Fine  hair  with  sebaceous 
gland  at  its  base 


Ciliary  gland  of  MoU 
Cilium 


^^—  Mucous  glands 


—  Mucous  gland 


_    Tarsal  (Meibomian)  gland 
-  -Musculus  ciliaris  Riolani 

'""Posterior  edge  of  lid-margin 
Opening  of  duct  of  tarsal  gland 


(8)  The  conjunctiva.  To  trace  this  important  membrane,  the  lids  should  be 
everted,  when  the  following  will  be  noted.  The  conjunctiva  over  the  tarsal  part 
of  the  lid  is  closely  adherent,  and  through  it  a  series  of  nearly  straight,  parallel, 
light  yellow  lines  and  granules,  the  tarsal  glands,  can  be  seen.  Owing  to  their 
position  here  (fig.  1094)  and  to  avoid  scarring,  a  tarsal  cyst  is  always  opened  on  its 
conjunctival  surface. 

Beyond  the  tarsi,  the  palpebral  conjunctiva  is  thicker  and  freely  movable 
owing  to  the  abundant  lax  submucous  tissue.  Underlying  vessels  are  visible 
here.  Leaving  the  eyelid  the  conjunctiva  is  reflected  onto  the  eyeball  at  the 
fornix.  Into  the  lateral  part  of  the  upper  fornix  open  the  ducts  of  the  lacrimal 
gland.  The  bulbar  conjunctiva  is  continued  over  the  front  of  the  ej^eball  to  the 
corneal  margin.  It  is  thin  and  contains  fine  vessels  which  are  distinguished  from 
subjacent  episcleral  vessels  by  the  fact  that  they  move  with  the  conjunctiva. 


1348 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


These  conjunctival  vessels,  derived  from  the  lacrimal  and  palpebral  arteries,  become  very- 
visible  in  conjunctivitis.  In  deep  inflammation  affecting  .the  iris  and  ciliary  body,  the  episcleral 
branches  of  the  anterior  ciliary  arteries  (which  are  derived  from  the  muscular  and  lacrimal 
arteries)  become  engorged  and  are  visible  as  a  pink  circumcorneal  zone  of  congestion,  deeply 
situated  under  the  conjunctiva.  These  branches  take  a  large  share  in  the  nutrition  of  the  cornea, 
and  are  responsible  for  the  vascularity  of  pannus  and  the  'salmon  patches'  of  interstitial 
keratitis. 

The  conjunctival  nerves  for  the  upper  lid  and  bulbar  part  of  the  membrane,  and  the  nerves 
to  the  cornea,  are  supplied  by  the  ophthalmic  division  of  the  trigeminal.  The  maxillary  divi- 
sion of  this  nerve  sUpphes  the  lower  palpebral  conjunctiva. 

The  differing  structure  of  the  palpebral  and  ocular  portions  has  important  bearings.  Thus 
the  palpebral  conjunctiva  is  thick,  highly  vascular  and  sensitive.  To  this  vasovilarity  we  owe  the 
chemosis,  or  hot,  red,  tense  swelling  of  purulent  ophthalmia.  The  exquisite  suffering  of  the  same 
disease,  or  that  caused  by  a  foreign  body,  is  explained  by  the  numerous  nerve-papillje  and  end- 
bulbs.  To  the  thickness  and  abundance  of  the  connective  tissue  are  due  the  contraction  and 
permanent  thickening  which  may  occur  in  granular  lids.  The  so-called  granulations,  met  with 
in  this  disease  on  the  palpebral  conjunctiva,  are  really  little  nodules  of  hypertrophied  lymphoid 
follicles,  or  mucous  glands,  which  abound  here. 

Immediately  under  the  bulbar  conjunctiva,  between  it  and  the  sclerotic,  lies  the  anterior 
part  of  the  fascia  bulbi  (of  Tenon).     This  fibrous  membrane  forms  a  sheath  for  the  posterior 


Pig.  1095.- 


-The  Lacrimal  Apparatus  and  Naso-lacrimal  Duct. 
(Bristles  are  introduced  into  the  puncta  lacrimalia.) 


(Bellamy.) 


Medial  wall  of  maxillary  sinus 


Lacrimal  sac 
Medial  palpebral  ligament 


Valvular  folds  in  naso-lacrimal  duct 


Lower  ndsiii  concha     Orifice  of  naso-lacrimal  duct 


five-sixths  of  the  eyeball,  and  is  intimately  connected  with  the  sheaths  of  the  extrinsic  muscles 
and  through  the  check  ligaments  with  the  orbital  walls.  Together  with  the  conjunctiva  it 
must  be  opened  in  the  operation  of  tenotomy  for  strabismus,  and  after  division  of  a  rectus  tendon 
the  muscle  retains  some  control  over  the  eye  through  its  connection  with  the  fascia  bulbi.  In 
enucleation  of  the  eyeball  both  conjunctiva  and  fascia  bulbi  are  divided  around  the  cornea, 
where  they  are  intimately  blended.  In  removal  of  the  upper  jaw  the  attachment  of  the  sus- 
pensory ligament  of  this  fascia  must  always  be  left  if  possible,  for  otherwise  the  eyeball  will  tend 
to  fall  forward  and  the  cornea  suffer  from  its  exposure  (Lockwood).  Finally  the  cavity  between 
the  two  layers  of  the  capsule  is  continuous  with  the  extensions  of  the  cerebral  membranes  along 
the  optic  nerve,  i.  e.,  with  the  subarachnoid  space. 

For  an  account  of  the  intrinsic  and  extrinsic  muscles  of  the  eye  the  reader  is  referred  to  the 
section  on  the  Eye.  Reference  may  be  made  here,  however,  to  the  part  played  by  certain  fibres 
of  the  cervical  sympathetic  system.  Emerging  from  the  cord  at  the  fh-st  and  second  thoracic 
segments,  the  communicating  fibres  pass  up  the  sympathetic  chain  in  the  neck  to  cell  stations 
in  the  superior  cervical  ganglion.  Thence  continuing  onward  tltrough  the  carotid  canal  and 
superior  orbital  fissure,  they  supply  (1)  the  dilator  muscle  of  the  u'is,  (2)  the  unstriped  muscle 
element  in  the  eyelids,  and  (3)  smooth  muscle  fibres,  deoribed  by  Sappey,  in  the  check  ligaments 
and  fascia  bulbi.  Paralysis  of  the  cervical  sympathetic  nerve  in  the  neck,  usually  in  its  lowest 
part,  by  trauma  or  the  pressure  of  a  malignant  growth,  causes  therefore  (1)  narrowing  of  the 
pupil,  (2)  narrowing  of  the  palpebral  fissure  (pseudo-ptosis),  and  (3)  enophthalmos. 

The  lacrimal  gland  lies  in  a  hollow  at  the  supero-lateral  angle  of  the  orbit, 
protected  by  the  zygomatic  process  of  the  frontal  bone.  It  is  not  palpable  nor- 
mally.    Its  lower  or  palpebral  portion  rests  on  the  lateral  third  of  the  fornix 


THE  MOUTH 


1349 


conjunctivse,  into  which  the  numerous  ducts  open,  and  it  may  be  seen  through  the 
conjunctiva  on  everting  and  raising  the  upper  lid. 

The  position  of  the  lacrimal  puncta  should  be  noted;  owing  to  their  backward  direction, 
the  lids  must  be  previously  everted.     The  puncta  are  kept  open  by  a  minute  fibrous  ring. 

Each  is  situated  on  a  minute  papilla  at  the  junction  of  the  medial  and  straight  third  of 
the  lid  with  the  lateral  curved  two-thirds.  Close  to  the  medial  angle,  in  addition  to  the  puncta 
and  papillae,  should  be  noted  the  caruncula  lacrimalis,  with  its  delicate  haii's,  and  the  plica 
semilunaris,  which  corresponds  to  the  third  eyelid  of  certain  birds. 

The  lacrimal  sac  is  a  most  important  part  of  the  lacrimal  apparatus,  from  its 
disfiguring  diseases;  it  lies  in  a  bony  groove,  between  the  nasal  process  of  the 
maxilla  and  the  lacrimal  bone.  The  medial  palpebral  ligament  crosses  it  a  little 
above  its  centre  (fig.  1095) .  Thus  two-thirds  of  the  sac  are  below  the  ligament, 
and  in  suppuration  the  opening  is  made  below  it  also.  The  angular  artery  ascends 
on  the  nasal  side  of  the  sac. 

The  manipulation  of  a  probe  along  the  lacrimal  passages  should  thus  be  practised: — the 
lower  lid  being  drawn  laterally  and  downward  by  the  thumb,  the  probe  is  passed  vertically  into 
the  punctum,  then  turned  horizontally  and  passed  on  till  it  reaches  the  medial  waU  of  the  sac. 
It  is  then  rotated  somewhat  forward,  raised  vertically,  and  pushed  gently  along  the  duct  down- 
ward, and  a  little  lateralward  and  backward,  till  the  floor  of  the  nose  is  reached,  the  operator 
aiming,  as  it  were,  for  the  site  of  the  first  molar  tooth.  The  naso-lacrimal  duct  extends  from 
the  lower  end  of  the  lacrimal  sac  to  the  inferior  meatus  of  the  nose  and  is  about  1 . 2  cm  (J  in.) 
in  length. 

If  the  eyes  are  opened  naturally,  the  greatest  part  of  the  cornea,  behind  it  the  iris,  with  the 
pupU  in  the  centre,  on  either  side  of  the  cornea  some  of  the  sclerotic,  the  semilunar  fold,  and 
caruncle  can  be  seen. 

THE  MOUTH 

The  lips. — When  the  whole  thickness  of  the  lip  is  incised  the  labial  artery 
will  be  found  lying  near  the  free  margin,  internal  to  the  orbicularis  muscle,  and 


Fig.  1096.— Side  op  the  Face  and  Mouth  Cmiti,  showing  the  Three  Salivakt  Glansd. 


Accessory  parotii 


Duct  of  accessory 
parotid 


Duct  of  parotid 


Frenulum  linguae. 


Sublingual  gland' 


Duct  of  submaxil 
lary  gland 

Mylo-hyoid  muscle. 


Masseter  muscle 


Posterior  belly  of 
digastric  muscle 


Submaxillary 
gland, 
drawn  backward 


■Hyoid  bo 


Deep  portion  of  submaxillary  gland 


between  it  and  the  mucosa.     There  is  a  very  free  anastomosis  between  the 
arteries  of  the  opposite  sides. 

If  the  tongue  be  raised,  the  under  surface  is  seen  to  be  smooth  and  devoid  of 
papillse.  In  the  middle  line  is  the  frenulum.  When  division  of  this  is  really 
required  in  tongue-tie,  the  scissors  should  be  kept  close  to  the  bone,  in  order  to 
avoid  the  ranine  vessels. 


1350 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


Of  these,  the  veins  can  be  seen  just  to  one  side;  the  arteries  are  close  by,  but  deeper.  Farther 
out  are  two  more  or  less  distinct  fringed  folds,  the  plica; l fimbria tse,  running  from  behind  forward 
and,  like  the  frenulum,  disappetiring  before  the  tip.  Between  these  and  the  frenulum  are  the 
small  apical  mucous  glands  of  Nuhn  or  Blandin.  Farther  back,  at  the  junction  of  the  mucous 
membrane  and  the  alveoli,  are  two  other  projections  of  the  mucosa,  the  sublingual;  under  these 
are  the  sublingual  glands,  the  ranine  veins,  and,  more  deeply,  Wharton's  duct  and  the  termina- 
tion of  the  lingual  nerve.  The  majoritj'  of  the  ducts  of  the  sublingual  gland  (Rivinian)  open  on 
the  sublingual  ridges.  A  single  larger  one,  Bartholin's,  opens  with  that  of  Wharton,  or  close  to 
it,  on  either  side  of  the  frenulum  (fig.  1096).  Dilatation  of  one  of  the  Rivinian  ducts,  more  fre- 
quently dilatation  of  a  muciparous  gland — and,  much  more  rarelj',  dilatation  of  Wharton's  duct 
— constitutes  a  'ranula.' 

The  submaxillary  gland  can  be  felt  nearer  the  angle  of  the  jaw,  lying  between 
its  fossa  and  the  mucous  membrane,  especially  if  pressure  is  made  from  outside. 
The  attachment  of  the  genio-glossi  can  be  felt  behind  the  symphysis:  the  division 
of  the  muscles  allows  the  tongue  to  come  well  out  of  the  mouth;  but  when  both 
have  to  be  divided,  the  tongue  loses  much  of  its  steadiness,  and  may  easily  fall 


Fig.  1097. — Sebtion  of  the  Skull  and  Brain  in  thp  Median  Plane.    (Braune.) 

Falx  cerebri 
Superior  sagittal  sinus 

Inferior  sagittal  sinus 

Corpus  caUosum 

Optic  chiasma 
Corpus  mammillare 

Occipital  lobe  of 


Torcular  Herophili 
Medulla  oblongata 


Posterior  ring  of  atlas 
Body  of  epistropheus  (axis) 


Thyreoid  gland 
Sterno-thyreoid  muscle' 


, Body  of  second  thoracic 

\  vertebra 


back  over  the  larynx  during  the  administration  of  the  anaesthetic  or,  later  on,  in 
sleep.  It  should  therefore  be  secured  forward  for  a  while  with  silk.  For  the 
same  reason,  in  removal  of  one-half  of  the  mandible,  part  of  this  muscular 
attachment  should  always  be  left,  if  possible. 

Turning  now  to  the  dorsum  of  the  tongue,  this  shows  two  distinct  parts:  one,  the  anterior 
two-thu'ds,  the  buccal,  is  rich  in  papiUic;  the  other,  the  posterior,  the  pharyngeal,  contains  abun- 
dant lymphoid  follicles  like  the  tonsil.  This  part  possesses  peculiar  sensibiUty,  as  shown  by 
movements  of  tongue  and  palate  when  a  depressor  is  placed  too  far  back.  The  two  parts 
are  separated  by  the  v -shaped  arrangement  of  the  vallate  papillEe,  with  the  apex  turned  back- 
ward. Immediately  behind  the  apical  vallate  papilla  is  a  small  pit,  the  foramen  cEecum 
which  represents  the  upper  remains  of  the  thyreoglossal  tract,  and  may  be  the  seat  of  lingual 
thyreoid  growths.  While  the  tongue  is  mainly  a  muscular  organ,  the  fine  fatty  connective  tissue 
in  the  septum  and  between  the  muscular  bundles  is  the  seat  of  that  dangerous  condition  acute 
glossitis,  and  of  gummatous  infiltration.  While  the  mouth  is  widely  open,  the  pterj^go-man- 
dibular  ligament  can  be  seen  and  felt  beneath  the  mucous  membrane,  behind  the  last  molar 
tooth.  Just  below  and  in  front  of  the  lower  attachment  of  this  ligament  the  lingual  nerve  can 
be  felt  lying  close  to  the  bone  below  the  last  molar.  The  simplest  and  surest  method  of  dividing 
the  nerve  here,  to  give  relief  from  pain  in  incurable  carcinoma  of  the  tongue,  is  to  draw  the  tongue 
out  of  the  mouth  and  expose  the  nerve  where  it  lies  superficially  under  the  mucous  membrane 
thus  made  prominent  between  the  side  of  the  tongue  and  the  gums,  the  centre  of  the  incision 


THE  TONSILS  1351 

being  opposite  to  the  last  molar  tooth.     (Roser,  L6ti6vant.)     In  cancer  of  the  tongue  pain  is 
often  referred  up  the  aurioulo-temporal  nerve  to  the  ear  and  side  of  head. 

Behind  the  last  molar  tooth  can  be  felt  the  coronoid  process,  and  higher  up, 
just  behind  and  medial  to  the  tooth,  the  pterygoid  hamulus  of  the  sphenoid. 
This  process  is  a  landmark  to  the  site  of  the  greater  palatine  foramen,  which  lies 
just  in  front  of  it,  and  which  transmits  the  greater  palatine  branch  of  the  descend- 
ing palatine  artery,  together  with  the  anterior  palatine  nerve.  The  vessel  and 
nerve  run  forward  in  grooves  on  the  lower  surface  of  the  palatine  process  of  the 
maxilla,  giving  off  anastomosing  branches  toward  the  middle  line,  and  join  at 
the  incisive  foramen  with  the  nasopalatine  artery. 

Their  position  must  be  remembered  in  raising  the  flaps  during  the  operation  for  closure  of 
a  cleft  in  the  hard  palate.  To  ensure  the  vitality  of  the  flaps  the  incisions  must  be  made  lateral 
to  the  vascular  arch,  close  to  and  pai'allel  with  the  upper  alveolus,  and  should  not  extend  be- 
yond a  point  opposite  to  and  just  medial  to  the  last  molar  tooth,  for  fear  of  encroaching  upon 
the  posterior  palatine  canal. 

When  the  teeth  are  clenched,  there  is  still  a  space,  communicating  between  the 
mouth  and  pharynx  behind  the  molar  teeth,  which  admits  a  medium-sized 
catheter.  When  a  patient  breathes  deeply  through  the  mouth  and  the  head  is 
thrown  back,  the  soft  palate  is  raised,  the  pillars  (arches)  separated;  the  uvula  and 
fauces,  with  the  anterior  and  posterior  pillars,  with  their  attachments,  the  tonsils, 
and  the  back  of  the  pharynx  are  exposed. 

This  portion  of  the  pharyngeal  mucous  membrane  would  lie  over  the  lower  part  of  the 
second  and  the  upper  part  of  the  third  cervical  vertebrae,  the  anterior  arch  of  the  atlas  corre- 
sponding to  the  level  of  the  posterior  nares,  and  the  body  of  the  epistropheus  (?ixis)  to  the  level 
of  the  soft  palate  (fig.  1097).  If  a  finger  be  introduced  past  the  soft  palate  to  this  part  of  the 
spine  and  turned  upward  and  downward,  it  is  possible,  with  the  aid  of  an  anfesthetic,  to  examine 
the  upper  four  or  five  and,  in  children,  six  vertebrse,  as  far  as  the  anterior  surfaces  of  their 
bodies.  'The  part  of  the  column  which  is  accessible  to  a  straight  instrument  introduced  through 
the  mouth  is  very  hmited,  extending,  in  the  adult,  from  the  lower  border  of  the  axis  to  the  middle 
or  lower  part  of  the  fourth  cervical  vertebra;  in  the  child,  owing  to  the  small  size  of  the  face,  it 
comprises  the  bodies  of  the  axis  and  of  the  third  cervical  vertebra.'  (Thane  and  Godlee,  from 
Chipault.)  The  distance  from  the  incisor  teeth  to  the  commencement  of  the  oesophagus  at 
the  cricoid  cartilage  is  15  cm.  (6  in.)  in  the  adult,  and  the  distance  from  the  teeth  to  the  cardiac 
orifice  of  the  stomach  is  48  to  50  cm.  (16  or  17  in.). 

The  lymphatic  drainage  of  the  face,  mouth,  and  tongue  is  given  on  pp.  712 
and  715. 

Tonsils. — The  relations  of  the  tonsils  should  be  carefully  examined.  Thus, 
they  are  separated  externally  by  the  superior  constrictor  and  pharyngeal  aponeuro- 
sis from  the  oscending  pharyngeal  and  internal  carotid  arteries.  The  latter  vessel 
lies  about  2.5  cm.  (1  in.)  behind  and  to  the  lateral  side  of  the  tonsil.  When 
serious  haemorrhage  follows  operations  here,  it  usually  comes  from  one  of  the 
numerous  tonsillar  branches  (fig.  448).  The  extent  to  which  the  tonsil  is  covered 
by  the  anterior  pillar,  how  far  it  projects  upward  beneath  the  soft  palate  or 
downward  into  the  pharynx,  have  all  important  bearings  on  the  mode  of  removal. 
Its  position  corresponds  to  a  point  a  little  above  and  in  front  of  the  angle  of  the 
jaw.  The  lateral  surface,  enclosed  by  an  imperfect  capsule  and  separated  from 
the  superior  constrictor  by  connective  tissue,  explains  how  an  enlarged  tonsil 
can  be  dragged  medialwarcl  by  a  vulsellum,  and  enucleated  after  an  incision  in  the 
mucous  membrane  around.  It  is  in  this  connective  tissue  that  severe  infective 
inflammation,  e.  g.,  after  scarlet  fever  or  an  imbedded  pipe-stem,  may  set  up 
haemorrhage  or  spreading  cellulitis,  retro-pharyngeal  or  otherwise. 

The  finger  introduced  downward  at  the  back  of  the  mouth,  especially  if  the  parts  are  ren- 
dered in  sensitive  by  local  anaesthetics,  feels  the  vallate  papilla,  the  lingual  and  laryngeal  surfaces 
of  the  epiglottis,  the  arytajno-epiglottidean  folds,  with  the  cuneiform  and  corniculate  cartilages. 
If  the  finger  be  moved  upward  behind  the  soft  palate  and  turned  upward  to  the  base  of  the  skull, 
and  then  forward,  it  will  feel  the  choanae  (posterior  nares),  separated  by  the  vomer.  Tlie  other 
boundaries  of  these  are,  laterally,  the  medial  pterygoid  plate  and  palate  bones;  above,  the  basi- 
sphenoid;  and  below,  the  horizontal  plate  of  the  palate  bone  and  the  inferior  nasal  spine. 
Within  each  nostril  would  be  felt  the  posterior  ends  of  the  two  lower  nasal  conchte  (turbinate 
bones);  above  and  behind  is  felt  the  basilar  process  of  the  skull,  the  vault  of  the  pharynx, 
and  the  bodies  of  the  upper  cervical  vertebree  (fig.  1097). 

The  size  of  the  choanae,  in  the  bony  skull  2.5  cm.  (Ijin.)  vertically  by  1.2  cm.  (J  in.),  and  the 
presence  of  anj^  adenoids,  are  especially  to  be  noted.  The  richness  of  the  naso-pharynx  in 
glandular  structures,  its  proneness  to  inflammation,  and  of  this  inflammation  to  spread  to  other 
parts, — e.  g.,  the  tympanum, — ^are  well  known.     The  finger  should  be  familiar  with  the  feel  of 


1352  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

adenoids — i.  e.,  hypertrophied  post-nasal  lymphatic  nodules — soft  bodies  of  irregular  shape 
blocking  up  the  naso-pharynx.  _  To  make  out  how  far  this  is  the  case,  it  is  well  to  take  the 
nasal  septum  as  the  starting-point. 

Pharyngeal  hypophyseal  remnants. — In  the  naso-pharyngeal  mucosa,  a  few  millimetres 
behind  the  posterior  border  of  the  vomer,  a  group  of  glandular  cells  may  be  found  on  micro- 
scopical examination  in  all  cases  (Haberfeld),  corresponding  in  histological  appearance  with  the 
pars  anterior  of  the  hypophysis.  These  cells  are  a  remnant  of  the  primitive  bud  that  grows 
toward  the  brain  in  front  of  the  bucco-pharyngeal  membrane  to  form  the  pars  anterior  of  the 
hypophysis.  In  some  cases  of  pituitary  disorder  they  give  rise  to  a  palpable  tumour  in  the  naso- 
pharynx. 

The  palate.- — Between  the  diverging  pillars  of  the  soft  palate  is  the  isthmus 
faucium,  bounded  above  by  the  free  margin  of  the  palate,  and  below  by  the 
dorsum  of  the  tongue.  The  space  between  the  arches  (pihars),  glossopalatine  and 
pharyngo-palatine,  with  attachments  denoted  by  their  names,  shallow  above, 
widens  and  deepens  below.  Of  its  lateral  boundaries,  the  posterior  pillars  come 
nearer  each  other  than  the  anterior.  The  coverings  of  the  hard  palate  are  chiefly 
mucous  membrane,  glands,  and  periosteum.  These  are  intimately  blended  by 
fibrous  septa,  as  in  the  superficial  layers  of  scalp  and  palm  of  the  hand.  Hence 
the  readiness  with  which  necrosis  takes  place  here. 

Hare-lip  and  cleft  palate. — Failure  of  union  between  the  mesial  nasal  process 
and  the  maxillary  process  of  the  embryo  gives  rise  to  the  deformity  known  as 
hare-lip. 

The  palate  is  developed  from  three  primitive  processes  growing  down  from  the  basis  cranii, 
viz.,  (1)  the  mesial  nasal  process  forming  the  premaxilla  which  lies  in  front  of  the  anterior  pala- 
tine foramen  and  bears  the  four  incisor  teeth,  (2)  and  (3)  the  maxillary  process  of  either  side. 
The  slighter  cases  of  failure  to  unite  affect  only  the  soft  palate  which  is  the  last  part  to  fuse. 
Complete  alveolar  cleft  palate,  which  occurs  combined  with  hare-lip  and  may  be  unilateral  or 
bilateral,  represents  more  serious  non-union.  In  this  condition  the  lateral  incisor  may  be  found 
either  on  the  medial  or  on  the  lateral  side  of  the  cleft,  which  is  explained  by  the  fact  that  thi& 
tooth  is  developed  in  the  groove  between  the  two  processes  (Keith). 

In  paring  the  edges  of  a  cleft  soft  palate,  the  following  structures  would  be,  successively, 
cut  through: — (1)  Oral  mucous  membrane;  (2)  submucous  tissue,  with  vessels,  nerves,  and 
glands;  (3)  glosso-palatine  muscle;  (4)  aponeurosis  of  tensor  palati;  (5)  anterior  fasciculus  of 
pharyngo-palatine;  (6)  levator  palati  and  uvular  muscles;  (7)  posterior  fasciculus  of  pharyngo- 
palatine;  (8)  submucous  tissue,  vessels,  nerves,  and  glands;  (9)  posterior  mucous  membrane. 
The  soft  palate  is  thicker  than  it  seems,  the  average  in  an  adult  being  6  mm.  (i  in.).  The 
muscles  widening  a  cleft  are  the  tensor  and  levator,  while  the  superior  constrictor  closes  it  in 
swallowing.  Of  the  arteries  of  the  palate,  from  the  external  maxillary  (facial),  ascending  pharyn- 
geal, and  internal  maxillary,  the  largest  is  the  descending  palatine  branch  of  the  last.  This 
emerges  from  the  posterior  palatine  canal  close  to  the  inner  side  of  the  last  molar  tooth. 

THE  NOSE 

On  the  face  the  outline  of  the  nasal  bones  can  be  easily  traced,  and  below  them 
the  lateral  nasal  cartilages,  flat  and  also  somewhat  triangular.  Below  these  are 
the  greater  alar  cartilages,  curved  and  so  folded  back  that  each  forms  a  lateral 
and  a  medial  plate.  Of  these,  the  medial  meet  below  the  septal  cartilage  to  form 
the  tip  of  the  nose,  while  the  lateral  curve  backward,  and,  together  with  dense 
masses  of  cellular  tissue  and  fat  and  accessory  cartilages,  form  the  alse. 

With  the  speculum,  especially  if  the  head  be  thrown  back  and  the  tip  of  the 
nose  drawn  up,  the  lower  part  of  the  septum,  floor  of  the  nose,  and  greater  portion 
of  the  inferior  concha  (turbinate  bone)  can  be  seen.  On  throwing  the  head 
further  back,  with  a  good  light  the  lower  margin  of  the  middle  concha  can  also 
be  made  out.  This  is  much  higher  up  and  nearly  on  a  level  with  the  root  of  the 
nasal  bone.  The  septum  often  deviates  to  one  side.  The  mucous  membrane 
over  it  is,  in  health,  dull  red  in  colour;  that  over  the  inferior  concha  is  thicker. 
The  anterior  extremity  of  the  latter  bone  is  about  1.8  cm.  (|  in.)  behind  the  nasal 
orifice,  while  the  opening  of  the  naso-lacrimal  duct  is  about  2.5  cm.  (1  in.)  behind 
and  about  1.8  cm.  (|  in.)  above  the  floor,  concealed  by  the  anterior  extremity  of 
the  inferior  concha.  The  opening  into  the  maxillary  sinus  (antrum)  is  situated  in 
about  the  centre  of  the  middle  meatus  and  2.5  cm.  (1  in.)  above  the  floor 

The  olfactory  area  of  the  mucous  membrane  extends  over  the  highest  concha 
(possibly  also  somewhat  lower)  and  corresponding  portions  of  the  septum.  The 
respiratory  portion  is  more  vascular  and  thicker,  especially  over  the  conchse.  It 
is  firmly  adherent  to  the  periosteum  and  perichondrium.  The  veins,  especially 
over  the  lower  conchse,  form  a  dense  plexus,  closely  resembling  cavernous  tissue. 


THE  NOSE 


1353 


This  fact  explains  the  severity  of  epistaxis,  and,  together  with  the  drainage  of 
blood  into  out-of-the-way  veins,  such  as  the  spheno-palatine  and  ethmoidal, 

Fig.  1098. — Section  of  the  Nose,  showing  the  Conch.*:  (Turbinate  Bones)  and  Meatuses 
WITH  THE  Openings  in  Dotted  Outline. 

Frontal  sinus 
Orifice  of  middle  ethmoidal  cells  , 


Superior  concna 
Orifice  of  the  posterior  ethmoidal  cells 
Orifice  of  the  sphenoidal  smus 
Sphenoidal  sinus 


Orifice  of  tuba  auditiva 


Orifice  of  frontal  sinus 


Upper  orifice  of 
naso-lacrimal 
duct 


Middle  concha 


Inferior  co.ncha       Orifice  of  the       Orifice  of  infundibulum 
maxillary  sinus 


Fig.  1099. — Section  showing  Bony  and  Cartilaginous  Septum. 
The  dotted  line  indicates  the  course  of  the  incisive  (anterior  palatine)  canal. 

Nasal  bone  Frontal  sinus 


Sphenoidal  sinus 


ve  between  sept; 
and  lateral  nasal 
cartilage 


Thickened  border  of  cartilage 
resting  upon  anterior  nasal  spine    Incisive 

papilla    Septal  cartilage 


Orifice  of  tuba  auditiva 
Soft  palate 


accounts  for  the  serious  results  which  may  follow  on  a  firmly  impacted  and  in- 
fected plug.     The  boundaries  of  the  posterior  nares  have  been  given  above. 


1354  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

About  1.2  cm.  (|  in.)  behind  tlie  posterior  extremities  of  tiie  inferior  conchse, 
just  above  the  level  of  the  hard  palate  (fig.  1097),  on  the  side  of  the  naso-pharynx, 
are  the  openmgs  of  the  tubce  auditivce  (Eustachian  tubes).  Oval  in  shape,  these 
are  bounded  above  and  behind  by  the  prominence  of  the  cartilage,  which  is  want- 
ing below,  thus  facilitating  the  entry  of  a  catheter.  The  lower  part  of  the  tube 
contains  in  early  life  lymphoid  tissue;  enlargement  of  this  explains  the  deafness 
in  certain  cases  of  adenoids.  At  the  upper  part  of  the  naso-pharynx,  on  the 
posterior  wall,  extending  down  laterally  as  far  as  the  tubae  auditivse,  is  the  col- 
lection of  lymphoid  tissue  known  as  the  pharyngeal  tonsil,  which  when  hypertro- 
phied,  plays  a  large  part  in  'naso-pharyngeal  adenoids.'  From  the  periosteum 
of  the  basi-sphenoid  and  basi-occipital  arise  naso-pharyngeal  fibromata. 

Nasal  septum. — The  structure  of  the  skeletal  element  of  the  septum,  which 
consists  of  the  septal  cartilage,  the  vertical  plate  of  the  ethmoid  and  the  vomer, 
is  shown  in  fig.  1099.  Slight  deviations  of  the  septum  to  one  side  are  common 
in  adults,  and  involve  mainly  the  cartilage  and  the  ethmoid  bone,  the  vomer 
being  but  little  affected  as  a  rule. 

The  convexity  is  most  commonly  on  the  right  side,  and  occlusion  of  the  nares  on  that  side 
with  unsightly  deflection  of  the  whole  nose,  results  in  some  cases  during  the  transition  from  the 
nfantile  to  the  adult  facial  conformation.  Too  extensive  removal  of  the  bony  septum  in  the 
operation  of  submucous  resection  for  the  relief  of  this  condition  may  cause  sinking  in  of  the 
bridge  of  the  nose.  More  often,  however,  this  is  due  to  the  destructive  effect  of  congenital 
syphilis. 

Accessory  sinuses. — The  communication  of  these  air  sinuses  with  the  nasal 
fossae  are  of  great  clinical  importance.  The  sphenoidal  sinus  opens  high  up  into 
the  spheno-ethmoidal  recess.  The  posterior  ethmoidal  sinuses  open  into  the 
superior  meatus  under  cover  of  the  superior  concha.  The  infundibulum  of  the 
frontal  sinus,  the  anterior  and  middle  ethmoidal  and  the  maxillary  sinus  all 
communicate  with  the  middle  meatus  under  cover  of  the  middle  concha.  The 
orifice  of  the  maxillary  sinus  lies  at  the  lowest  part  of  the  hiatus  semilunaris 
into  the  front  and  upper  end  of  which  the  frontal  sinus  opens.  Consequently 
infected  fluid  may  trickle  down  from  the  latter  into  the  maxillary  sinus.  The 
orifice  of  this  sinus  is  placed  high  up  in  its  medial  wall  so  that  fluid  does  not 
drain  away  from  it  readily  in  case  of  infection.  When  the  head  is  held  forward 
in  a  stooping  position  some  of  the  pus  or  mucus  may  escape  from  the  nostrils, 
since  in  this  position  the  fluid  contents  more  readily  reach  the  orifice. 

The  naso-Iacrimal  duct  which  carries  the  tears  into  the  nose  opens  into  the  front  and  upper 
part  of  the  inferior  meatus  under  cover  of  the  inferior  concha. 

THE  NECK 

The  topics  considered  in  the  neck  are  the  landmarks,  thyreoid  gland,  sterno- 
mastoid,  clavicle,  triangles  and  cervical  ribs. 

Bony  and  cartilaginous  landmarks. — The  body  of  the  hyoid  is  nearly  on  a 
level  with  the  angles  of  the  jaw,  and  the  interval  between  the  third  and  fourth 
cervical  vertebrae  (fig.  1097).  With  the  head  in  the  usual  erect  position  it  lies 
a  little  higher  than  the  chin.  It  divides  the  front  of  the  neck  into  supra-  and 
infra-hyoid  regions,  convenient  for  remembering  the  distribution  of  the  deep 
fascia.  On  either  side  of  the  body  are  the  great  cornua,  with  the  lesser  cornua 
attached  to  their  upper  borders  at  the  junction  with  the  body.  The  upper  borders 
of  these  are  the  guides  to  the  lingual  arteries.  The  outline  and  mobility  of  the 
body  and  the  great  cornua  are  easily  determined  by  relaxing  the  deep  fascia  and 
pushing  the  bone  over  to  the  opposite  side.  Below  the  hyoid  is  the  thyreo-hyoid 
space,  which  corresponds  with  the  epiglottis  and  the  upper  aperture  of  the 
larynx.  Thus,  if  the  throat  be  cut  above  the  hyoid,  the  mouth  will  be  opened 
and  the  tongue  cut  into;  if  the  thyreo-hyoid  space  be  cut,  the  pharynx  would  be 
opened  and  the  epiglottis  wounded  near  its  base.  In  the  former  case  the  lingual 
and  external  maxillary  are  the  most  likely  vessels  to  be  wounded ;  in  thyreo-hyoid, 
the  commonest  cut-throat,  the  superior  thyreoid  vessels,  and  the  superior  laryn- 
geal nerve.  The  projection  of  the  thyreoid  notch,  about  2.5  cm.  (1  in.)  below 
the  hyoid,  is  much  more  distinct  in  men  than  in  women  or  children.  It  does 
not  appear  before  puberty,  and  thus  flatness  of  the  thyreoid  must  be  expected 


^ 


THE  NECK  1355 

when  the  landmarks  for  tracheotomy  are  sought  for  in  children  with  short  fat 
necks. 

The  cricoid,  on  the  other  hand,  is  always  to  be  made  out.  It  corresponds  in  horizontal 
plane  to  the  following: — (1)  The  sixth  cervical  vertebra.  (2)  The  junction  of  pharynx  and 
oesophagus:  from  the  narrowing  of  the  tube  here,  foreign  bodies  may  lodge  at  this  point  and  cause 
dyspncea  by  pressing  on  the  air-tube  in  front.  The  cricoid  is  taken  as  the  centre  of  the  incision 
in  cesophagotomy,  and  also  for  ligature  of  the  common  carotid.  (3)  The  junction  of  larynx 
and  trachea.  (4)  The  crossing  of  the  omo-hyoid  over  the  common  carotid.  (5)  The  middle 
cervical  ganglion.  Above  the  cricoid  is  the  crico-thyreoid  rnembrane.  In  laryngotomy,  the 
deepest  part  of  the  incision  should  be  kept  to  the  middle  line  for  fear  of  injuring  the  crico- 
thyreoids,  and  as  near  the  cricoid  as  possible,  so  as  to  avoid  the  neighbourhood  of  the  vocal 
cords  and  the  small  crico-thyreoid  vessels.  The  space  is  always  small,  and,  after  middle  life, 
increasingly  rigid. 

The  distance  between  the  cricoid  and  the  manubrium  is  only  about  3.7  cm. 
(1|  in.).  When  the  neck  is  stretched,  about  1.8  cm.  (f  in.)  more  is  gained. 
Thus,  as  a  rule,  there  are  not  more  than  seven  or  eight  tracheal  rings  above  the 
sternum.  Of  these,  the  second,  third,  and  fourth  are  covered  by  the  thyreoid 
isthmus. 

The  parts  met  with  in  the  middle  line — (a)  above,  and  (6)  below,  the  isthmus — high  and 
low  tracheotomy — should  be  borne  in  mind:  (o)  Skin,  superficial  fascia,  branches  of  transverse 
cervical  and  infra-mandibular  nerves,  lymphatics,  cutaneous  arteries,  anterior  jugular  veins — 
with  their  transverse  branches  smaller  above — deep  fascia,  sterno-hyoids,  cellular  tissue,  supe- 
rior thyreoid  vessels,  and  pre-tracheal  layer  of  deep  fascia.  The  importance  of  this  last  is  two- 
fold, as,  first,  the  tube  in  tracheotomy  may  be  passed  between  it  and  the  trachea,  and  after  a 
wound  in  this  region  this  layer,  continuous  with  the  pericardium,  may  conduct  discharges  into 
the  mediastina,  (6)  The  surface  structures  are  much  the  same,  but  the  anterior  jugular  veins 
and  their  transverse  branches  are  much  larger.  The  inferior  thyreoid  veins  are  also  larger.  A 
thyreoidea  ima  may  be  present,  and  the  innominate  artery,  especially  in  children,  may  be  1.2 
cm.  (2  in.)  above  the  sternum.  The  trachea  is  also  smaller,  deeper,  and  less  steadied  by  muscles. 
The  thymus,  too,  in  young  children,  may  prove  a  difficulty.  Thus,  in  children,  the  high  opera- 
tion, incising  the  cricoid  and  crico-tracheal  membrane,  if  needful,  is  to  be  preferred.  The  cricoid 
is,  however,  not  to  be  incised,  if  possible;  the  higher  the  tube  is  inserted,  the  greater  the  irritation. 

The  suprasternal  notch,  between  the  sternal  heads  of  the  sterno-mastoids  in  on  a  level  with 
the  disc  between  the  second  and  third  thoracic  vertebrae.  Just  below  the  level  of  the  cricoid 
cartilage,  on  deep  pressure  at  the  anterior  border  of  the  sterno-mastoid  the  transverse  process  of 
the  sixth  cervical  vertebra  may  be  felt.  It  is  known  as  Chassaignac's  carotid  tubercle,  and  the 
common  carotid  may  be  compressed  against  it.  Compression  below  it  will  command  the 
vertebral  artery  as  well. 

The  thyreoid  gland  enclosed  in  a  capsule  of  deep  fascia  derived  from  the  pre- 
tracheal layer  (fig.  1070)  is  closely  connected  by  this  to  the  upper  trachea  and 
larynx.  The  upper  somewhat  pointed  extremity  of  each  lateral  lobe  reaches  to 
the  upper  and  back  part  of  the  thyreoid  cartilage;  here  enter  the  superior  thyreoid 
vessels.  The  lower  layer  and  rounded  extremity  reaches  to  the  fifth  or  sixth 
tracheal  ring;  its  posterior  and  lower  aspect  is  in  relation  to  the  inferior  thyreoid 
vessels  and  the  recurrent  nerve;  the  lateral  lobe,  posteriorly,  also  overlaps  the 
carotid  sheath,  which  may  be  infiltrated  in  malignant  disease  of  the  thyreoid. 
The  thyreoidea  ima  has  been  mentioned  above. 

The  isthmus  in  the  adult  is  opposite  to  the  second,  third,  and  fourth  tracheal  rings.  At 
its  upper  border  is  an  arterial  arch  formed  by  the  superior  thyreoids;  over  the  anterior  surface 
of  the  gland  and  isthmus  the  inferior  thyreoid  veins  take  origin  in  a  plexus.  The  upper  border 
of  the  thymus  (fig.  1100)  may  be  in  relation  with  the  lower  border  of  the  isthmus.  From  the 
upper  border  of  the  latter,  the  pyramidal  lobe,  especially  on  the  left  side,  is  often  present,  reach- 
ing by  a  pedicle  to  the  liyoid.  The  pyramidal  lobe,  when  present,  is  the  persistent  remnant  of 
the  thyreo-glossal  duct,  and  occasionally  cystic  outgrowths  persist  obstinately  as  remnants  of 
this  duct,  in  the  middle  line,  above,  behind,  and  below  (the  commonest  form)  the  hyoid  bone. 
In  short-necked  people  the  thyreoid  is  relatively  lower  in  relation  to  the  sternum,  and  en- 
largements of  the  gland  are  apt  to  become  mainly  intra-thoraeic.  An  enlargement  of  the 
thyreoid  is  liable  to  give  trouble  by  pressure  on  (1)  the  trachea,  which  is  compressed  laterally 
between  the  lateral  lobes;  (2)  the  oesophagus;  (3)  the  internal  jugular  vein  and  carotid  artery; 
(4)  the  reciu-rent  laryngeal  or  cervical  sympathetic  nerves. 

Parathyreoids. — These  small  glands,  about  the  size  of  a  pea,  vary  somewhat  in  number  and 
situation.  There  are  usually  four — t^A■o  behind  each  lateral  lobe.  The  upper  glands  lie  im- 
bedded in  the  capsule  of  the  thyreoid  about  the  junction  of  the  middle  and  upper  thirds  of  the 
lateral  lobes  on  the  posterior  aspect.  The  lower  pair  lie  nearer  the  lower  poles  of  the  lateral 
lobes,  sometimes  separated  from  them  by  a  distinct  interval.  Excision  of  all  the  parathyreoids 
gives  rise  to  tetany  in  animals. 

The  stemo-mastoid  is  the  landmark  for  several  important  operations.  Its 
medial  border,  the  thicker  and  better  marked  of  the  two,  overlaps  the  carotids; 


1356 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


the  common  carotid  corresponding,  as  far  as  the  upper  border  of  the  thyreoid, 
with  a  line  drawn  from  the  sterno-clavicular  joint  to  midway  between  the  mastoid 
process  and  the  angle  of  the  jaw.  The  artery  can  be  best  compressed  above  the 
level  of  the  cricoid,  as  here  it  is  less  deeply  covered.  The  student  should  recall 
the  deep  relations  of  the  sterno-mastoid,  which  he  may  classify  as  vessels,  nerves, 
muscles,  glands,  and  bones;  or,  according  to  their  position,  (1)  those  above  the 
level  of  the  angle  of  the  jaw;  (2)  those  between  the  angle  of  the  jaw  and  the  omo- 
hyoid; (3)  those  below  the  omo-hyoid. 

Of  the  two  heads  of  the  sterno-roastoid,  the  sternal  is  the  thicker  and  more  prominent,  the 
clavicular  the  wider.  A  stab  through  the  interval  wliich  lies  between  tlie  two  heads  might 
wound  the  bifurcation  of  the  innominate  on  the  right  side,  and  the  common  carotid  on  the  left, 
the  internal  jugular,  vagus,  and  phrenic  veins,  according  to  the  direction  of  the  wound. 

Fig.  1100. — Thymus  Gland  in  a  Child  at  Birth. 


r^~. 


Hyo-thyreoid  membrane 

Thyreoid  cartilage  [~;^^/ 


Sterno-thyreoid  muscle' 

Crico-thyreoid     ■^^;^-  w- 
membrane        ^^»^* 
Crico-thyreoid  muscle 


Thyreoid  gland 


Right  vagus  nerve 

Right  internal  jugular, 
vein 

Level  of  sternu 

Section  of  clavicle 

Section  of  first  rib 


Section  of  sternum 


^  Thyreo-hyoid  muscle 
I^VL  Omo-hyoid  muscle 


Cricoid  cartilage 
First  ring  of  trachea 


-r — Left  suspensory 
\        ligament 

Left  recurrent  nerve 


(Esophagus 

Left  innominate  vein 


Left  lobe  of  thymus 


Left  internal  mammary 
artery 


Pericardium 


Section  of  fifth  costal 
cartilage 


■Xiphoid  process 


The  anterior  jugular,  commencing  in  branches  from  the  submaxillary  and 
submental  regions,  descends  at  first  in  the  superficial  fascia  between  the  middle 
line  and  anterior  border  of  sterno-mastoid,  perforates  the  deep  fascia  just  above 
the  clavicle,  here  entering  Burns's  space  (p.  1361);  it  then  curves  laterally  to 
pass  beneath  both  origins  of  the  sterno-mastoid  a  little  above  the  clavicle,  to  end 
usually  in  the  external  jugular. 

When  distended,  a  large  communicating  branch  between  it  and  the  common  facial,  which 
runs  along  the  anterior  border  of  the  sterno-mastoid,  must  always  be  remembered  in  operations 
for  removal  of  glands,  etc.     The  varying  level  at  which  the  external  jugular  crosses  the  lateral 


THE  NECK 


1357 


border  of  the  clavicular  origin  must  be  remembered  in  such  operations  as  tenotomy  here.  These 
veins  vary  in  size  inversely  to  each  other;  the  anterior  jugulars  are  joined  by  numerous  trans- 
vesre  branches  and  become  larger  below.     They  have  no  valves. 

Of  the  chief  arteries  to  the  sterno-mastoid,  that  from  the  superior  thjrreoid  will  be  divided 
in  gature  of  the  common  carotid;  that  from  the  occipital  runs  with  the  spinal  accessory  nerve. 

Behind  the  stemo -clavicular  joint  lies  the  commencement  of  the  innominate 
veins,  the  bifurcation  of  the  innominate  artery  on  the  right,  and  the  common 
carotid  artery  on  the  left;  deeper  still  lie  the  pleura  and  lung. 

The  clavicle. — This  bone  can  be  felt  beneath  the  skin  in  its  whole  length. 
It  forms  the  only  bony  connection  between  the  upper  limbs  and  the  trunk.  As 
one  traces  it  laterally  toward  the  acromial  end,  it  rises  somewhat,  particularly 
in  children  and  in  subjects  of  good  muscular  development.  The  skin  over  it  is 
thin  but  very  mobile,  and  consequently  is  not  often  wounded.  The  most  im- 
portant posterior  relations  of  this  bone  are,  passing  from  the  medial  end  laterally, 
the  subclavian  vein,  the  subclavian  artery,  and  the  cords  of  the  brachial  plexus 
as  they  He  on  the  first  rib. 


Fig.  1101. — Anterior  and  Lateral  Cervicai,  Muscles. 


Stylo-glossus 
Hyo-glossus 

Mylo-hyoid 

Anterior  belly  of 
digastric 
Raphe  of  mylo- 
hyoid 


Thyreo-hyoid 

Inferior  constrictor 
Anterior  belly  of  omo- 
hyoid 

Sterno-hyoid 
Sterno-thyreoid 


The  vein  occupies  the  angle  between  the  first  rib  and  the  clavicle,  and  hence  is,  as  a  rule, 
the  first  structure  compressed  in  growths  of  this  bone.  The  artery  lies  on  a  deeper  plane  be- 
hind the  mid-point  of  the  clavicle,  and  the  nerve  cords  extend  a  little  further  laterally.  The 
Bubclavius  muscle  forms  a  protective  cushion  between  the  bone  and  these  important  structures, 
and  this  accounts  for  the  rarity  of  injury  to  them  in  fracture  of  the  clavicle.  Behind  the  medial 
half  of  the  clavicle  the  apex  of  the  lung  extends  upward  into  the  neck  toa  height  of  2. 5-3. 7  cm. 
(1-1 2  in.),  and  consequently  is  liable  to  be  wounded  by  a  stab  in  the  root  of  the  neck. 

Cervical  triangles. — In  front  of  the  sterno-mastoid  is  the  anterior  triangle, 
which  is  subdivided  into  three  smaller  triangles  by  the  digastric  muscle  above, 
and  the  anterior  belly  of  the  omo-hyoid  below  (fig.  1101).  These  smaller  tri- 
angles are  called,  from  above,  the  submaxillary,  the  superior  and  inferior  carotid 
triangles. 

The  submaxillary  or  digastric  triangle  is  bounded  above  by  the  jaw,  and  a  line 
drawn  back  to  the  mastoid  process;  below,  by  the  digastric  and  stylo-hyoid 
muscles;  and  in  front  by  the  middle  line  of  the  neck. 


1358  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

This  space  contains  the  submaxillary  gland,  and  embedded  in  the  gland  is  the  external 
maxillary  artery,  the  facial  vein  lying  superficial  to  the  gland;  deeper  than  the  gland  are  the 
submental  vessels  and  the  mylo-hyoid  vessels  and  nerve.  Posteriorly,  and  separated  from  the 
above  structures  by  the  styro-mandibular  ligament,  which  subdivides  the  triangle  into  a  sub- 
maxillary and  parotid  part,  is  the  upper  part  of  the  external  carotid  artery  running  up  into  the 
parotid  gland,  where  it  gives  off  its  two  terminal  and  the  posterior  auricular  branches.  More 
deeply  lie  the  internal  jugular  vein,  internal  carotid  artery,  and  the  vagus.  The  floor  of  the 
triangle  is  formed  by  the  mylo-hyoid,  hyo-glossus,  and  superior  constrictor.  The  lingual 
artery  may  be  tied  here,  or,  better,  in  order  to  get  behind  the  dorsalis  linguae,  close  to  its  origin, 
by  an  incision  similar  to  that  for  exposing  the  external  carotid. 

The  hypoglossal  is  a  guide  to  the  carotids  and  the  occipital  artery  at  the  lower  border  of  the 
digastric,  and  farther  forward,  to  the  subjacent  lingual,  from  which  it  is  separated  by  the 
hyo-glossus. 

The  superior  carotid  triangle  is  bounded  above  by  the  digastric,  below  by 
the  omo-hyoid,  and  behind  by  the  sterno-mastoid.  It  contains  the  upper  part  of 
the  common  carotid  and  its  branches,  the  external  being  at  first  somewhat 
anterior  to  the  internal.  All  the  branches  of  the  external  carotid,  save  the  three 
just  given,  are  found  in  this  space,  together  with  their  veins,  the  internal  jugular 
vein,  the  vagus  and  sympathetic  nerves,  and,  for  a  short  distance,  the  accessory, 
together  with  those  nerves  which  lie  in  front  of  and  behind  the  carotids. 

Ligature  of  the  common  carotid  is  usually  performed  at  the  'seat  of  election,'  where  the 
vessel  is  more  superficial,  above  the  omo-hyoid.  An  incision  with  its  centre  opposite  the  cricoid 
is  made  7.5  cm.  (3  in.)  long  in  the  line  of  the  carotid  artery.  The  deep  fascia  along  the  an- 
terior border  of  the  sterno-mastoid  having  been  divided,  the  cellular  tissue  beneath  is  opened  up, 
the  omo-hyoid  identified  and  drawn  down  or  divided.  The  sterno-mastoid  is  next  drawn  well 
laterally,  and  the  artery  felt  for.  At  this  stage,  such  veins  as  the  communication  between 
the  common  facial  and  the  anterior  jugular  and  the  superior  and  middle  th}Teoi_ds  may  give 
trouble.  The  sheath  is  next  opened  well  to  the  medial  side,  opposite  to  the  cricoid  cartilage, 
the  ascending  cervical,  when  seen,  being  avoided.  If  the  internal  jugular  be  distended,  it  may 
be  drawn  aside  with  a  blunt  hook,  or  pressure  made  lightly  in  the  upper  angle  of  the  wound. 
The  needle  should  be  passed  from  the  lateral  side  in  very  close  proximity  to  the  lateral  and  back 
part  of  the  artery,  so  as  to  avoid  the  vein  and  vagus.  Ligature  helow  the  omo-hyoid  is  rendered 
more  difficult  by  the  presence  of  the  anterior  jugular,  the  pretracheal  muscles,  an  overlapping 
thyreoid  gland,  especially  if  enlarged,  the  greater  depth  of  the  artery,  especially  pn  the  left  side 
and,  here  also,  the  closeness  of  the  internal  jugular.  The  collateral  circulation  is  given  at  p.  1360. 
Ligature  of  the  external  carotid,  otherwise  difficult,  is  rendered  very  simple  by  first  exposing  the 
bifurcation  of  the  common  carotid  artery,  the  incision  similar  to  the  last  being  prolonged  up- 
ward. Here  the  facial  and  lingual  veins  and  hypoglossal  nerve  cross  the  trunk,  over  which 
also  lie  some  of  the  deep  cervical  glands.  The  ligatiue  is  usually  placed  between  the  superior 
thyreoid  and  lingual  branches. 

Allusion  must  here  be  made  to  the  chief  structures  liable  to  be  met  with  in  operations 
on  the  neck.  These  are  the  internal  jugular,  the  accessory,  and  phrenic  nerves,  the  vagus 
and  hypoglossal,  the  thoracic  duct,  low  down  and  deep  on  the  left  side,  the  oesophagus  and 
recurrent  nerve  in  difficult  operations  on  the  thyreoid  gland.  Of  these,  the  internal  jugular  is, 
in  some  ways,  the  most  important.  Glands,  tuberculous  or  epitheliomatous,  are  often  adherent 
to  its  sheath,  especially  those  which  drain  the  submaxillary  group.  When  this  condition  is 
present  or  suspected,  it  is  always  well  to  begin  the  dissection  low  down  in  the  inferior  carotid 
triangle,  where  the  structures  are  probably  normal  and  the  landmarks  easy  to  identify.  In 
infective  thrombosis  of  the  transverse  sinus  the  internal  jugular  is  often  tied  opposite  to  the 
cricoid  cartilage,  being  either  divided  between  two  ligatures,  or,  if  the  thrombus  has  extended 
downward,  as  much  of  the  vein  as  is  possible  is  removed.  This  vein  contains  only  a  single  pair 
of  valves  low  down  in  the  neck.  In  all  operations  here  on  it  and  the  other  two  jugulars,  the 
risk  of  entry  of  air  is  to  be  remembered.  The  accessory  and  phrenic  nerves  are  alluded 
to  on  p.  1360. 

The  inferior  carotid  or  tracheal  triangle  is  bounded  above  by  the  omo-hyoid, 
behind  by  the  sterno-mastoid,  and  in  front  by  the  middle  line  of  the  neck.  It 
contains  the  lower  part  of  the  carotid  sheath  and  its  contents,  with,  behind^  it,  the 
inferior  laryngeal  nerve  and  inferior  thyreoid  vessels,  and  to  the  medial  side  the 
trachea,  thyreoid  gland,  and  oesophagus.  More  deeply  are  the  vertebral  vessels; 
on  the  left  side  is  the  thoracic  duct. 

The  position  of  the  branches  of  the  external  carotid  should  be  remembered. 
The  great  cornu  of  the  hyoid  and  the  ala  of  the  thyreoid  are  landmarks  for  the 
origin  of  most  of  them. 

The  superior  thyreoid,  arising  just  below  the  level  of  the  great  cornu  of  the  hyoid  bone, 
passes  downward  and  forward  to  the  back  part  of  the  thyreoid  cartilage  and  upper  part  of  the 
thyreoid  body.  Many  of  its  branches  are  important  in  surgery.  The  superior  laryngeal 
perforates  the  thyreo-hyoid  membrane.  The  sterno-mastoid  passes  laterally  into  the  middle 
of  the  muscle,  across  the  carotid  sheath.  The  crico-thyreoid  crosses  the  space  of  the  same  name 
just  below  the  lower  border  of  the  thyreoid  cartilage.     The  small  hyoid  branch  runs  to  the  lower 


THE  NECK  1359 

border  of  the  hyoid  bone.  Anastomosing  branches  of  the  superior  thyreoid  form  an  arch  along 
the  upper  border  of  the  isthmus.  The  Ungual  artery  arises  from  the  parent  trunk,  opposite  the 
tip  of  the  great  cornu  of  the  hyoid,  and  passes  forward  just  above  the  great  cornu,  crossed  by 
the  hypoglossal,  and  thence  to  the  side  of  the  tongue.  In  the  first  part  of  its  course,  before  it 
reaches  the  hyo-glossus,  it  is  curved,  at  first  ascending,  and  then,  having  descended  slightly, 
before  it  reaches  the  hyo-glossus,  and  while  it  lies  under  it,  its  curve  is  gentle,  with  the  concavity 
upward;  beyond  the  hyo-glossus,  as  it  lies  on  the  muscles  of  the  tongue  beneath  the  mucous 
membrane,  it  is  tortuous.  The  lingual  vein,  it  will  be  remembered,  does  not  run  with  its  artery, 
but  lies  superficial  to  the  hyo-glossus.  It  receives  the  two  small  venae  comitantes  which  run 
with  the  lingual  itself  just  before  it  crosses  the  common  carotid.  The  line  of  the  external 
maxillary  (facial)  artery  (fig.  1093),  which  often  arises  with  the  lingual,  has  been  given  on  p.  1343. 
The  occipital  artery,  starting  on  the  same  level  as  the  facial  (i.  e.,  at  a  point  a  little  above  and 
outside  the  tip  of  the  great  cornu  of  the  hyoid  bone),  follows  a  line  drawn  upward  and  laterally, 
first  to  the  interval  between  the  transverse  process  of  the  atlas  and  the  mastoid  process,  the 
former  bone  being  felt  just  below  and  in  front  of  the  tip  of  the  latter;  thence,  lying  in  the  occipital 
groove  of  the  mastoid,  the  artery  ascends  gradually,  enters  the  scalp,  together  with  the  great 
occipital  nerve,  a  little  medial  to  a  point  midway  between  the  external  occipital  protuberance 
and  the  mastoid  process,  to  follow,  tortuously  and  superficial  to  the  aponeurosis,  the  line  of  the 
lambdoid  suture. 

The  surface  marking  of  the  digastric  and  omo-hyoid,  which  subdivide  the  anterior  triangle 
into  the  three  smaller  subtriangles  above  described,  should  be  noted.  The  line  of  the  posterior 
belly  of  the  digastric  corresponds  to  one  drawn  from  the  apex  of  the  mastoid  process  to  a  point 
just  above  the  junction  of  the  great  cornu  and  body  of  the  hyoid  bone;  and  from  this  spot, 
which  gives  the  point  of  meeting  of  the  two  tendons,  one  slightly  curving  upward  to  a  point 
just  behind  the  symphysis  menti,  would  give  that  of  the  anterior  belly. 

To  trace  the  omo-hyoid,  a  line  should  be  drawn  from  the  lower  margin  of  the  side  of  the 
hyoid  bone  obliquely  downward,  so  as  to  cross  the  common  carotid  opposite  the  cricoid  carti- 
lage and  thence  curving  laterally  under  the  sterno-mastoid  at  the  junction  of  its  middle  and 
lower  thirds,  and  then  onward  and  still  laterally  parallel  with  and  a  little  above  the  clavicle, 
as  far  as  its  centre. 

Posterior  triangle. — This  shows  in  its  lower  part  a  wide<depression,  the  supra- 
clavicular fossa.  Here  the  brachial  plexus  may  be  felt,  and,  by  pressure  down- 
ward and  backward  immediately  behind  the  clavicle,  just  lateral  to  and  behind  the 
lateral  margin  of  the  sterno-mastoid,  the  pulsation  of  the  subclavian  artery  can  be 
stopped  against  the  first  rib. 

The  supra-clavicular  fossa  should  be  opened  out  by  depressing  the  arm,  and  parts  relaxed 
by  carrying  the  shoulder  forward  and  turning  the  head  to  the  same  side.  This  vessel  curves 
upward  and  laterally  from  behind  the  sterno-clavioular  joint  to  disappear  behind  the  centre  of 
the  clavicle,  the  highe.st  point  of  the  curve  being  1.2  to  2.5  cm.  (i  to  1  in.)  above  the  bone. 
The  artery  on  the  left  side  lies  more  deeply  than  the  right,  and  does  not  rise  so  high  into  the  neck. 
The  subclavian  vein  lies  at  a  lower  level,  separated  by  the  scalenus  anterior,  and  under  cover  of 
the  clavicle.  Into  the  above  curve  rise  the  pleura  and  lung.  The  pleura  must  be  expected  to 
rise  2.5  cm.  (1  in.)  above  the  clavicle,  behind  the  clavicular  head  of  the  sterno-mastoid. 

The  transverse  scapular  and  transverse  cervical  vessels  run  laterally,  parallel  with  the 
clavicle.  The  former  lies  behind  the  bone  and  subclavius ;  the  latter  also  runs  laterally  in  a  trans- 
verse direction,  across  the  root  of  the  neck,  but  on  a  slightly  higher  plane,  and  thus  a  little  above 
the  clavicle. 

Ligature  of  the  third  part  of  the  subclavian  is  best  performed  by  an  angular  incision,  the 
horizontal  portion  along  the  centre  of  the  clavicle,  and  the  vertical  one  along  the  posterior 
border  of  the  sterno-mastoid,  with  partial  division  of  this  and  the  trapezius  when  closely  ad- 
jacent. The  chief  points  to  bear  in  mind  are  the  venous  plexus  into  which  the  external  jugular, 
transverse  cervical,  transverse  scapular,  and  cephalic  veins  enter;  the  omo-hyoid  and  division 
of  the  fascia  which  ties  this  to  the  clavicle;  identification  of  the  lateral  margin  of  the  scalenus 
anterior  and  the  scalene  tubercle;  care  of  the  transverse  scapular  artery  and  the  descending 
branch  of  the  transverse  cervical.  The  needle  is  passed  from  above  downward  so  as  not  to  in- 
clude the  lowest  cord  of  the  brachial  plexus,  the  vein,  if  distended,  being  depressed  with  a  blunt 
hook.  If  the  nerve  to  the  subclavius  be  seen,  it  must  be  uninjured,  as  it  occasionally  forms  an 
important  part  of  the  phrenic.     The  collateral  circulation  is  given  at  p.  1360. 

Crossing  the  sterno-mastoid,  a  little  obliquely,  in  a  line  drawn  from  a  point 
just  below  and  behind  the  angle  of  the  jaw  which  marks  its  origin  in  the  union  of 
the  posterior  part  of  the  internal  maxillary  and  the  posterior  auricular  veins  to  the 
centre  of  the  clavicle,  runs  the  external  jugular  vein.  Above,  it  lies  between  the 
platysma  and  deep  fascia,  and  is  accompanied  by  the  group  of  superficial  cervical 
nodes  (p.  709).  About  3.7  cm.  (1|  in.)  above  the  clavicle  it  perforates  the  deep 
cervical  fascia,  its  coats  being  blended  with  the  opening.  Gentle  pressure  with  a 
finger  at  this  point  renders  the  vein  above  clearly  visible.  The  dilated  part 
between  this  point  and  the  subclavian  vein  is  called  the  sinus,  and  is  marked  by 
two  valves,  neither  of  which  is  usually  perfect. 

Opening  into  the  external  jugular,  in  the  middle  or  lower  third  of  its  course,  is  the  posterior 
external  jugular,  a  vessel  which  begins  in  the  occipital  region  superficially  and  runs  down  in  front 
of  the  anterior  border  of  the  trapezius,  across  the  posterior  triangle. 


1360  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

The  accessory  nerve,  having  crossed  the  transverse  process  of  the  atlas  at  a 
point  lying  a  little  below  and  in  front  of  the  apex  of  the  mastoid,  enters  the  ante- 
rior border  of  the  sterno-mastoid  at  about  the  junction  of  the  upper  and  middle 
thirds  of  the  muscle.  Having  traversed  the  muscle  obliquely,  it  leaves  it  usually 
at  a  point  a  little  lower  down,  pursues  a  similar  course  across  the  posterior  triangle 
and  disappears  under  the  anterior  border  of  the  trapezius,  to  enter  into  the  sub- 
trapezial  plexus  with  the  third  and  fourth  cervical  nerves. 

Above  it  is  accompanied  by  a  branch  from  the  occipital,  below  by  the  transverse  cervical 
artery.  It  is  always  seen  in  thorough  operations  on  the  upper  deep  cervical  glands.  The  nerve 
is  resected  in  spasmodic  torticollis,  and  in  recent  years  inveterate  facial  paralysis  has  been 
treated  by  anastomosing  the  facial  to  this  nerve  or  the  hypoglossal.  A  line  drawn  from  midway 
between  the  tip  of  the  mastoid  and  the  angle  of  the  mandible  along  the  above  given  course  of 
the  nerve  would  denote  its  position. 

Just  above  the  centre  of  the  sterno-mastoid,  the  small  occipital,  great  auricular,  and  cuta- 
neous cervical  nerves  emerge,  the  first  passing  upward  and  backward  to  the  scalp,  the  second 
upward  and  forward  across  the  upper  part  of  the  sterno-mastoid  to  the  ear,  and  the  last  turning 
straight  forward  to  the  front  of  the  neck.  The  small  occipital  and  great  auricular  are  often 
in  intimate  association  with  the  accessory  at  its  exit  from  the  muscle.  At  this  point  also  care 
must  be  taken  not  to  injure  the  nerve  in  removal  of  glands  from  the  posterior  triangle. 

The  phrenic  nerve,  taking  its  largest  root  from  the  fourth  cervical,  would 
begin  deeply  about  the  level  of  the  hyoid  bone;  thence  descending  under  the 
sterno-mastoid,  and,  passing  obliquely  medially  across  the  scalenus  anterior  (the 
posterior  borders  of  the  above  two  muscles  roughly  correspond  to  each  other  in 
the  lower  part  of  the  neck),  it  descends  under  the  subclavian  vein  and  clavicle  to 
enter  the  thorax. 

When  the  internal  j  ugular  is  distended,  its  lateral  border  will  be  liable  to  overlap  this  nerve. 
The  relations  of  the  scalenus  anterior  should  be  noted  here.  In  addition  to  the  plurenic,  which 
runs  with  a  slight  obliquity  medially  and  is  in  close  contact  with  the  muscle,  the  following  struc- 
tures cross  it  medio-laterally :  the  subclavian  vein  and  termination  of  the  external  jugular, 
the  transverse  scapular  and  transverse  cervical  vessels,  and  the  omo-hyoid.  At  its  medial 
margin  are  the  thyreo-cervical  trunk  and  vertebral  arteries,  and  over  them,  the  internal  jugular. 
Behind  it  are  the  subclavian  artery,  the  brachial  plexus,  and  pleura. 

The  level  of  the  brachial  plexus  (upper  border)  would  be  given  by  a  line  drawn 
from  the  cricoid  cartilage  to  the  centre  of  the  clavicle.  The  lowest,  medial  cord 
(eighth  cervical  and  first  thoracic,  giving  off  chiefly  the  ulnar,  medial  head  of 
median,  and  medial  antibrachial  cutaneous)  is  just  above  and  behind  the  sub- 
clavian artery.  Its  importance  in  ligature  of  the  artery  has  been  referred  to 
(p.  1359). 

In  paralys's  of  the  newly  born,  after  some  violent  manipulation,  it  is  usually  the  upper  and 
lateral  cord  (fifth  nerve,  and  axillary  and  median  chiefly)  which  suffers,  elevation  and  abduction 
at  the  shoulder  and  flexion  at  the  elbow-joint  being  lost. 

Collateral  circulation  after  ligature  of  the  common  carotid  (fig.  1102). — This  takes  place 
by  means  of  (1)  the  free  communication  which  exists  between  the  opposite  carotids,  both  with- 
out and  within  the  craniujm;  and  (2)  by  enlargement  of  the  branches  of  the  subclavian  artery  on 
the  same  side  as  that  on  which  the  carotid  has  been  tied.  Thus,  outside  the  cranium,  the  supe- 
rior and  inferior  thyreoids  are  the  chief  vessels  employed  (fig.  1102).  Within  the  cranium  the 
vertebral  replaces  the  internal  carotid. 

Collateral  circulation  after  ligature  of  the  second  and  third  parts  of  the  subclavian  (fig.  1102). 
— Here  the  following  three  sets  of  vessels  are  those  chiefly  employed: — 

The  transverse  scapular,  the  transverse  \  -.r^      /  The  thoraco-acromial,  infra-  and  sub- 
cervical,                                                      /  1      scapular,  and  circumflex  scapular. 

The  superior  intercostal,  the  aortic  inter-  1  ■, ,        (  The   lateral   thoracic   and   subscapular 

costals,  and  the  internal  mammary,       J  \      arteries. 

Numerous    unnamed    branches    passing  1 

through  the  axilla  from  branches  of  the  >  with         Branches  of  the  axillary, 
subclavian,                                                 J 

Deep  cervical  fascia. — The  arrangement  of  this  must  be  remembered — (a) 
above,  and  (5)  below,  the  hyoid  bone.     The  latter  is  far  more  important. 

(a)  Arrangement  above  the  hyoid  bone. — Here  two  chief  processes  can  be  made  out: — (i) 
one,  continuous  with  that  in  front  of  the  sterno-mastoid,  traced  upward  from  the  hyoid  bone, 
-encloses  the  submaxillary  gland,  passing  over  the  mylo-hyoid,  and,  ascending,  is  connected  with 
the  lower  border  of  the  mandible,  gives  off  the  masseteric  and  parotid  fascia,  and  is  attached 
to  the  lower  border  of  the  zygoma,  and,  more  posteriorly,  to  the  mastoid  and  linea  nuchse 
Buprema.  (ii)  A  special  process,  which  forms  the  stylo-mandibular  ligament,  is  important  in 
its  power  of  checking  over-action  of  the  external  pterygoid.  By  both  these  processes  the  ante- 
rior border  of  the  sterno-mastoid  is  tied  firmly  forward  to  the  mandible  about  its  angle,  and  more 
deeply  to  the  styloid  process.  This  renders  all  operations  under  the  upper  part  of  the  muscle, 
•e.  g.,  the  removal  of  glands,  extremely  difficult. 


THE  NECK 


1361 


(6)  Below  the  hyoid  bone. — The  importance  of  the  fascia  here  is  infinitely 
greater.  Four  layers  must  be  rememhored;  (i)  Superficial;  (ii)  pretracheal; 
(iii)  prevertebral;  (iv)  carotid,  (i)  Superficial.  This  starts  from  the  ligamentum 
nuchee,  encases  the  trapezius,  forms  the  roof  of  the  posterior  triangle  where  it  is 
perforated  by  branches  of  the  superficial  cervical  nerves  and  the  external  jugular 

Fig.  1102. — The  Collateral  Circulation  after  Ligature  of  the  Common  Carotid  and 

Subclavian  Arteries. 
(A  ligature  is  placed  on  the  common  carotid  and  on  the  third  portion  of  the  subclavian  artery.) 

Right  anterior  cerebral -fLi'l  ^^^*  anterior  cerebral 

J/'^\^ Anterior  communicating 

Internal  carotid -VV^ Post_  communicating 

Right  posterior  cerebral J  J  ?r^f\^ Left  posterior  cerebral 


Occipital 
Descending  branch  of  occipital 


External  carotid 

Superficial  branch  of  descending 

occipital 

Deep  branch"  ~ 


Anterior  spinal 


External  maxillary 
Lingual 


Superior  thyreoid 


Transverse 

cervical 
Descending  branch 
Acromical  branch 
Subscapular  branch — 

Su  praspinous      k. .. 

branch 

Anterior  circumflex 
Infraspini 

branch 

Post. 

circumflex 

Lateral  thoracic 

Subscapular' 

Circumfl 


Innominate 
Superior 
intercostal 
Left  com.  carotid 

Left  subclavian 
Sup.  thoracic 
Internal  mammary 


Anterior  intercostal 


vein.     Passing  on   it  encloses  the  sterno-mastoid;  and,  passing  over  the  anterior 
triangle,  it  meets  its  fellow  in  the  middle  line. 

jThin  behind,  it  is  thickened  anteriorly.  Behind  this  thickened  union  lie  the  anterior 
jugular  veins.  Below,  at  a  varying  distance  below  the  thyreoid  cartilage,  this  layer  divides 
into  two,  attached  to  the  front  and  back  of  the  manubrium.     Between  these   (Burns*s  space) 


1362 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


lie  some  fat,  a  small  gland,  a  communicating  branch  between  the  anterior  jugulars  and  a  small 
portion  of  the  veins,  and  the  sternal  heads  of  the  sterno-mastoids.  The  sheath  to  the  depressors 
of  the  hyoid  bone  is  partly  derived  from  this  layer,  partly  from  the  next.  Laterally,  this  layer 
gives  a  sheath  to  the  posterior  belly  of  the  omo-hyoid,  is  attached  to  the  clavicle,  and  passing  on, 
is  continuous  with  the  sheath  to  the  subclavius  and  coraoo-clavioular  fascia. 

(ii)  Pretracheal  or  middle.  This  lies  under  the  depressors  of  the  hyoid,  over 
the  trachea,  also  encasing  the  thyreoid  gland.  Farther  laterally  it  helps,  to- 
gether with  the  prevertebral,  to  form  the  carotid  sheath.  Traced  downward, 
the  pretracheal  layer  passes  over  the  trachea  into  the  thorax  (middle  mediastinum) 

As  it  descends,  it  encases  the  left  innominate  vein,  and  ends  by  blending  with  the  fibrous 
layer  of  the  pericardium.  Hilton  suggested  that  the  attachment  of  this  fascia  above,  and  that 
of  the  central  tendon  of  the  diaphragm  below,  to  the  pericardium  served  to  keep  this  sac  duly 
stretched,  and  so  prevented  any  pressure  of  the  lungs  upon  the  heart. 

Fia.  1103. — Section  of  Neck  through  the  Sixth  Cervical    Vertebra.     (Braune.) 


Larynx 


Pharynx 
Longns  colli 
Inferior  laryngeal 


Thyreo-arytaenoid 

Cricoarytaenoideus  lateralis 


Penrertebral  layer  of  deep  cervical  fascia 


FretTacheal  layer  of  deep  cervical  fascia 


Sup.  thyreoid  art. 
DesG  hypoglossi 
Sterno-mastoid 

Vagus 
Sym^thetic 
Phrenic 
Scale 
anterior 
Brachial  plexus 
Scalenus 
medius 
External 
jugular 
Part  of  articu- 
lar process 
Spinal 
accessory 


Sterno-hyoid,  just    posterior 
are  seen  the  thyreo-  and 
omo-hyoid  muscles 

Thyreoid  cartilage 

Muscular  process  of 

arytaenoid 
Cervical  fascia 

Thyreoid 

gland 
Common 
carotid 
Carotid  sheath 
Internal 
jugular 
Brachial 
plexus 
Scalenus  medius 
External  jugular 
Ihocostalis 

cervicis 
Scalenus  posterior 
Spinal  accessory 


Splenius 
Semispinalis  colli  and  multifidus 


Semispinalis  capitis 


Deep  cervical  vessels 


_rficial  layer  of  deep  cervical  fascia  on 
the  deep  aspect  of  the  trapezius  which 


it  here  encloses 


Sixth  cervical  vertebra 


(iii)  Prevertebral.  This  layer  passes  over  the  longus  colli  and  capitis  upward 
to  the  base  of  the  skull,  and  downward  over  the  longus  colli  behind  the  oesophagus 
into  the  posterior  mediastinum.  Laterally  it  helps  to  form  the  carotid  sheath, 
and,  lower  down,  gives  a  sheath  to  the  subclavian  artery  and  so  to  the  axil- 
lary, (iv)  The  carotid  sheath.  This  is  formed  by  septa  from  i,  ii,  and  iii,  meeting 
under  the  sterno-mastoid  (fig.  1103). 

The  following  uses  and  important  points  with  regard  to  the  anatomy  of  the  deep  cervical  fascia 
should  be  noted: — (A)  It  forms  certain  definitely  enclosed  spaces  in  which  pus  or  growths 
may  form,  and  by  the  walls  of  which  these  morbid  structures  may  be  tied  down  and  thus  rendered 
difficult  of  diagnosis,  while  their  increasing  pressure  may  embarrass  the  air-passages,  etc. 
Thus:  (1)  In  the  first  space,  which  lies  between  No.  1  and  the  skin,  the  structures  met  with, 
the  platysma  and  superficial  branches  of  the  cervical  plexus,  are  unimportant.  Any  abscess 
here  is  prone  to  extend,  but  superficially.  (2)  In  the  second  space,  between  the  superficial  and 
middle  layers,  lies  a  narrow  space  containing  loose  cellular  tissue  and  lymphatic  glands.  Sup- 
puration here  is  very  common,  but  usually  comes  forward.  (3)  This  is  the  largest  and  most 
important  of  all.     From  its  contents  it  has  been  called  the  visceral  compartment.     (Stiles.) 


THE  THORAX  1363 

It  is  bounded  in  front  by  the  middle,  and  behind  by  the  prevertebral  layer.  Its  contents  are — 
larynx,  trachea,  cesophagus,  thyreoid,  carotid  sheath,  glands;  and  below,  brachial  plexus,  sub- 
clavian artery,  and  abundant  loose  cellular  tissue  for  the  movements  of  the  neck.  Suppuration  is 
somewhat  rarer  here;  but  either  pus  or  growths,  if  oonfined  in  this  space,  may  have  baneful 
effects,  from  pressure,  or  from  their  tendency  to  travel  behind  the  sternum.  (4)  This  space 
between  the  prevertebral  layer  in  front  and  muscles  behind,  is  very  limited.  Retropharyngeal 
abscess  forms  here,  and  the  dyspnoea  it  causes  is  thus  explained.  The  origin  of  such  abscesses 
is  chiefly  twofold,  either  in  one  of  the  highest  deep  cervical  nodes,  e.  g.,  from  infection  of  the 
naso-pharynx  (p.  717),  or  from  disease  of  the  upper  cervical  vertebrae.  In  the  former  cases 
CStiles,  Chiene)  the  suppuration  will  be  in  front  of  the  prevertebral  fascia,  pointing  toward  the 
pharynx;  in  the  latter  behind  the  above  fascia,  spreading  laterally,  behind  the  carotid  sheath. 
In  making  his  incision,  now  along  the  posterior  border  of  the  sterno-mastoid,  the  surgeon  should 
keep  close  to  the  transverse  processes  of  the  vertebrae,  to  avoid!opening  the  visceral  compartment 
and  infecting  the  structures  in  it.  (B)  The  deep  cervical  fascia  gives  sheaths  or  canals  tc> 
certain  veins  which  perforate  it,  e.  g.,  the  external  jugular.  These  are  thus  kept  patent,  and  a. 
ready  passage  of  blood  ensured  from  the  head  and  neck.  Further,  this  fact  accounts  for  the 
readiness  with  which  air  may  enter  veins,  in  operations  low  down  in  the  neck.  The  carotid 
sheath  is  another  and  different  instance.  (C)  It  helps  to  resist  atmospheric  pressure.  (D) 
Hilton's  suggestion  as  to  its  action  on  the  pericardium  has  already  been  mentioned. 

The  lymphatic  nodes  of  the  head  and   neck  have  already   been  described. 
(See  Section  VI,  Lymphatic  System.) 

THE  THORAX 

The  bony  landmarks  of  the  thorax  will  be  discussed  first,  followed  by  the 
structures  of  the  thoracic  wall,  the  lungs  and  pleura,  and  finally  the  heart  and 
pericardium. 

Bony  landmarks. — The  top  of  the  sternum  corresponds  (in  inspiration)  to  the 
fibro-cartilage  between  the  second  and  third  thoracic  vertebrae,  and  is  distant 
about  6.2  cm.  (2|  in.)  from  the  spine.  In  the  newborn  child  it  corresponds  to 
the  middle  of  the  first  thoracic  vertebra  (Symington).  If  traced  downward,  the 
subcutaneous  sternum  presents  a  ridge  (sternal  angle  of  Louis)  opposite  to  the 
junction  of  the  manubrium  and  body,  and  the  second  costal  cartilages  on  either 
side;  this  ridge  usually  corresponds  to  the  disc  between  the  fourth  and  fifth 
thoracic  vertebrae.  At  the  lower  extremity  of  the  sternum  the  xiphoid  cartilage 
usually  retires  from  the  surface,  presenting  the  depression  of  the  epigastric  angle 
or  'pit  of  the  stomach.'  This  is  opposite  to  the  seventh  costal  cartilages  and  the 
expanded  upper  end  of  the  recti,  and  corresponds  to  the  tenth  thoracic  vertebra 
behind. 

Parts  behind  manubrium. — There  is  little  or  no  lung  behind  the  first  bone  of 
the  sternum,  the  space  being  occupied  by  the  trachea  and  large  vessels,  as  follows; 

The  left  innominate  vein  crosses  behind  the  sternum  just  below  its  upper  border.  Next 
come  the  great  primary  branches  of  the  aortic  arch.  Deeper  still  is  the  trachea,  dividing  into 
its  two  bronchi  opposite  to  the  junction  of  the  first  and  second  bones  of  the  sternum.  Deepest 
of  all  is  the  cesophagus.  About  2.5  cm.  (1  in.)  below  the  upper  border  of  the  sternum  is  the  high- 
est part  of  the  aortic  arch,  lying  on  the  bifurcation  of  the  trachea.     (Holden.)     (Fig.  1104). 

Sterno-clavicular  joint. — The  expanded  end  of  the  clavicle  and  the  lack  of 
proportion  between  this  and  the  sternal  facet,  on  which  largely  depends  the 
mobility  of  this,  the  only  joint  that  ties  the  upper  extremity  closely  to  the  trunk, 
can  be  easily  made  out  through  the  skin.  Its  strength,  considerable  when  the 
rarity  of  dislocation  compared  with  fracture  of  the  clavicle  is  considered,  depends 
mainly  on  its  ligaments,  the  buffer-bond  meniscus,  the  costo-clavicular  ligament, 
which  checks  excessive  upward  and  backward  movements,  and  the  fact  that  the 
elastic  support  of  the  first  rib  comes  into  play  in  strong  depression  of  the  shoulder 
as  in  carrying  a  weight.  The  relative  weakness  of  the  anterior  ligament  deter- 
mines the  greater  frequency  of  anterior  dislocation  of  the  clavicle  at  this  joint. 

Behind  the  joint  lie,  on  the  right  side,  the  innominate  artery,  right  innominate  vein,  and 
pleura;  on  the  left,  the  left  innominate  vein,  the  left  carotid,  and  the  pleura. 

Acromio -clavicular  joint. — On  tracing  the  clavicle  laterally,  it  is  found  to 
rise  somewhat  to  its  articulation  with  the  acromion.  This  joint  has  very  little 
mobility,  and  owes  its  protection  to  the  strong  conoid  and  trapezoid  ligaments 
hard  by.  Owing  to  the  way  in  which  the  joint-surfaces  are  bevelled,  that  of  the 
clavicle  looking  obliquely  downward,  and  resting  upon  the  acromion,  it  is  an 
upward  displacement  of  the  clavicle  which  usually  takes  place. 

Ribs. — In  counting  these,  the  position  of  the  second  is  denoted  by  the  trans- 


1364 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


verse  line  at  the  junction  of  the  manubrium  and  body  of  the  sternum.  It  is  well 
always  to  count  ribs  from  this  point  and  never  from  below,  as  the  twelfth  rib 
varies  in  size  and  may  be  obscured  by  the  sacro-spinalis  muscles.  The  nipple 
in  the  male,  lies  between  the  fourth  and  fifth,  nearly  an  inch  lateral  to  their 
cartilages.  The  lower  border  of  the  great  pectoral  corresponds  to  the  fifth  rib. 
The  seventh,  the  longest  of  the  ribs,  is  the  last  to  articulate  by  its  cartilage  with 
the  sternum.  When  the  arm  is  raised,  the  first  three  digitations  seen  of  the 
serratus  anterior  correspond  to  the  fifth,  sixth,  and  seventh  ribs.     The  ninth  rib 


Fig.   1104. — The  Abch  of  the  Aorta,  with  the  Pulmonary  Artery  and  Chief  Branches 

OF  THE  Aorta. 
(Modified  from  a  dissection  in  St.  Bartholomew's  Hospital  Museum.) 
Int.  jugular  v.^  Inferior  thyreoid  veins 


Transverse  cervical  a 

Transverse  scapular  a 

Right  inf.  laryng.  n 

Right  com.  carotid  a 

Subclavian  v 

Vagus  nerve 

Innominate  a  -"^^"^ 

Left  innominate  v 

Phrenic  nerve 

Superior  vena  cava 

Arch  of  aorta 

Right  bronchus 

Branch  of  right  pul- 
monary a. 

Branch  of  right  pul- 
monary V 
Right  pulmonary  a. 

Branch  of  right  pul- 
monary a. 
Branch  of  right  pul- 
monary V. 

Right  atrium 

Right  coronary  a. 

Thoracic  vertebra 

Azygos  vein 

Intercostal  vv. 

Intercostal  aa. 


Thyreoid  body 

Left  int.  jugular  v. 
Vagus  nerve 
Left  com.  carotid  a. 
Left  inf.  laryng.  n. 
Left  subclavian  a. 
Lelf  subclavian  v. 
Left  int.  mammary   v. 
Left  sup.  intercostal  v. 
Phrenic  nerve 
Vagus  nerve 
Recurrent  n. 
Lig.  arteriosum 
Left  pulmonary  a. 
Left  pulmonary  v. 
Left  bronchus 

Branch  of  left  pul- 
monary a. 
Pulmonary  a. 

Left  pulmonary  v. 
Left  coronary  a. 
Conus  arteriosus 

(Esophagus 
Thoracic  duct 
Thoracic  aorta 


is  the  most  oblique.  The  eleventh  and  twelfth  can  be  felt  lateral  to  the  sacro- 
spinalis.  Owing  to  the  obliquity  of  the  ribs,  their  sternal  ends  are  on  a  much 
lower  level  than  their  vertebral  extremities. 

'Thus  the  first  rib  in  front  corresponds  to  the  fourth  rib  behind,  the  second  to  the  si.xth, 
the  thu-d  to  the  seventh,  the  fourth  to  the  eighth,  the  fifth  to  the  ninth,  the  sixth  to  the  tenth, 
and  the  seventh  to  the  eleventh.  If  a  horizontal  line  be  drawn  round  the  body  from  before  back- 
ward at  the  level  of  the  inferior  angle  of  the  scapula,  while  the  arms  are  at  the  sides,  the  line  would 
cut  the  sternum  in  front  between  the  fourth  and  fifth  ribs,  the  fifth  rib  at  the  nipple  line,  and 
the  ninth  rib  at  the  vertebral  column.'  (Treves.)  The  most  frequently  broken  are  the  sixth, 
seventh,  and  eighth.  The  upper  four  and  the  two  lowest  ribs  are  best  covered  by  soft  parts, 
and,  in  the  case  of  the  former,  the  shoulder  and  arm  take  off  some  of  the  violence  that  would 
otherwise  reach  them.  The  way  in  which  the  ribs  are  embedded  in  the  soft  parts  (fig.  1106), 
and  the  fact  that  the  fragments  are  often  held  in  place  by  the  periosteum,  account  for  the  diffi- 
culty which  is  often  met  with  in  detecting  crepitus.  The  intercostal  spaces  are  wider  in  front 
than  behind.     The  three  upper  are  the  widest  of  all. 


THE  THORAX  1365 

Cervical  ribs. — It  occasionallj'  happens  that  the  rib  element  of  the  seventh 
cervical  vertebra,  normally  fused  with  the  true  transverse  process,  is  segmented  off 
as  a  separate,  though  usually  rudimentary,  rib.  This  anomaly  is  generally 
bilateral.  It  occurred  in  3  of  260  subjects  (1.16  per  cent.)  examined  by  Wingate 
Todd.* 

The  anterior  extremity  of  a  cervical  rib  may,  according  to  the  degree  of  its  development 
(1)  lie  free  amongst  the  scalene  muscles;  (2)  be  connected  with  the  sternum  by  a  hgameutous 
prolongation;  (3)  articulate  with  the  upper  surface  of  the  first  thoracic  at  about  its  centre  by 
a  synchondrosis,  or  (4)  form  a  complete  rib,  articulating  by  a  costal  cartilage  with  the  sternum. 

The  lowest  trunk  of  the  brachial  plexus  formed  by  the  eighth  cervical  and  first  thoracic 
roots,  the  subclavian  artery  and  less  commonly  the  subclavian  vein,  curve  over  the  upper 
surface  of  these  ribs.  The  abnormality  owes  its  clinical  importance  to  the  pressure  effects 
produced  on  the  nerve  trunk  in  a  small  proportion  of  the  cases.  This  pressure  is  manifested 
by  ( 1)  pain,  going  on  to  anaesthesia  down  the  medial  side  of  arm,  forearm  and  hand;  (2)  paralysis 
of  the  intrinsic  muscles  of  the  hand,  producing  the  main  en  griffe,  and  to  a  less  extent  of  the  mus- 
cles of  the  forearm;  (3)  vascular  effects  (anamia,  gangrene,  etc.),  manifested  chiefly  in  the  hand. 
Todd  has  shown  that  these  vascular  effects  are  not  due  to  mechanical  pressure  on  the  subclavian 
artery  by  the  cervical  rib  as  was  formerly  supposed,  but  are  trophic  lesions  of  the  sympathetic 
(vasomotor)  nerves.  The  vasomotor  nerves  to  the  arm  mainly  come  from  the  second  thoracic 
root  by  the  communication  it  gives  to  the  lowest  cord  of  the  brachial  plexus,  and  so  are  exposed 
to  pressure  from  the  rib. 

Fig.  1105. — Cervical  Ribs,  Viewed  from  Above.  ( X  i.)  NN,  Impression  for  Lowest 
Trunk  op  Brachial  Plexus.     AA,  Impression  for  Subclavian  Artery.     (T.  Wingate 

TODD.) 


The  same  investigator  has  shown  that  similar  symptoms  may  be  produced  occasionally  by 
a  first  thoracic  rib  in  cases  where  the  brachial  plexus  has  migrated  caudad.  In  the  living 
patient,  unless  a  radiogram  be  taken  showing  all  the  vertebroe  up  to  the  base  of  the  skuU,  it  is 
not  possible  with  precision  to  ascertain  with  which  vertebra  the  highest  rib  present  articulates. 

Structures  found  in  an  intercostal  space. — (1)  Skin;  (2)  superficial  fascia, 
with  cutaneous  vessels  and  nerves;  (3)  deep  fascia;  (4)  external  intercostal;  (5) 
cellular  interval  between  intercostals,  containing  trunks  of  intercostal  vessels  and 
nerves;  (6)  internal  intercostals;  (7)  thin  layer  of  fascia;  (8)  subpleural  connective 
tissue;  (9)  pleura  (fig.  1106). 

The  intercostal  arteries  are  nine  aortic  and  two  from  the  superior  intercostal.  An  aortic 
intercostal  having  given  off  its  dorsal  branch,  lying  beneath  the  pleura,  crosses  the  space  ob- 
liquely upward  to  gain  the  lower  border  of  the  rib  above,  enters  the  costal  groove  at  the  angle, 
and  runs  forward  between  the  intercostal  muscles  to  anastomose  with  the  anterior  intercostals 
from  the  internal  mammary  or  musculo-phrenic.  Hence  the  rule  of  making  the  incision  in 
empyema  above  the  upper  margin  of  the  lower  rib  and  in  front  of  the  angle.  Along  the  dorsal 
branch  a  vertebral  abscess  may  track  backward. 

Internal  mammary  artery.- — This  descends  behind  the  clavicle,  the  costal 
cartilages,  and  the  first  six  spaces,  about  1.2  cm.  (|  in.)  from  the  edge  of  the  ster- 
num. In  the  sixth  intercostal  space  it  divides  into  musculo-phrenic  and  superior 
epigastric  acteries.  Its  vense  comitantes  uniting  join  the  innominate  vein  of  the 
same  side.  A  punctured  wound  of  the  artery  is  most  easily  secured  in  the  second 
and  third  spaces;  below,  resection  of  part  of  a  costal  cartilage  will  be  needed. 

Structures  passing  through  the  upper  aperture  of  the  thorax. — If  a  section 
is  made  passing  through  the  manubrium  sterni,  upper  border  of  the  first  rib,  and 

*  Journal  of  Anatomy  and  Physiology,  Vol.  47,  1913. 


1366 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


upper  part  of  the  first  thoracic  vertebra,  the  following  structures  are  met  with : 
— (1)  In  the  middle  line.  Sterno-hyoid  and  sterno-thyreoid  muscles,  with  their 
sheaths  of  deep  cervical  fascia,  cellular  tissue  in  which  are  the  remains  of  the 
thymus  gland,  the  inferior  thyreoid  veins,  the  trachea  and  tracheal  fascia,  the 
oesophagus,  and  longus  colli  muscles.  Between  the  trachea  and  oesophagus  are 
the  recurrent  nerves.  (2)  On  each  side.  The  apex  of  the  lung,  covered  by  pleura, 
deep  cervical  fascia,  and  membranous  cervical  diaphragms  ("Sibson's  fascia") 
derived  from  the  scalenes,  rises  about  3.7  cm.  (1|  in.)  above  the  first  rib.  Between 
it  and  the  trachea  and  oesophagus  lie  the  following :  the  internal  mammary  artery, 
the  phrenic  nerve;  on  the  right  side,  the  innominate  vein  and  artery,  with  the 
vagus  between  the  two,  the  cardiac  nerves,  and  the  right  lymphatic  duct.  On 
the  left  side  are  the  common  carotid  and  subclavian  arteries,  with  the  left  vagus 
between  them,  the  cardiac  nerves  and  the  thoracic  duct.  Farthest  back  and 
on  each  side  are  the  trunk  of  the  sympathetic,  the  superior  intercostal  artery,  and 
the  first  thoracic  nerve. 

The  mamma. — This  lies  chiefly  on  the  pectoralis  major  and  slightly  on  the 
rectus  abdominis  and  serratus  anterior.  It  is  usually  described  as  reaching  from 
the  second  to  the  sixth  rib,  and  from  the  sternum  to  the  anterior  border  of  the 
axilla.  It  is  most  important  to  remember  that  the  breast  is  often  a  much  more 
extensive  structure  than  would  be  included  in  the  above  very  limited  description. 
Thus — (1)  the  gland  is  not  encapsuled  at  its  periphery,  its  tissue  branching  and 
breaking  up  here  to  become  continuous  with  the  superficial  fascia.     (Stiles.)     (2) 

Fig.  1106. — Section  op  the   Sixth  Left  Intercostal  Space,  at  the   Junction  of  the 
Anterior  and  Posterior  Thirds.     (Tillaux.) 


Intercostal  vein 

Intercostal  artery- 
Intercostal  nerve  - 
Serra  tus  anterior" 
Serratus  aponeurosis'" 
osis  covering  external  inter--. 
costal  muscle 
External  intercostal  muscle" 


— Aponeurosis  covering  the  internal 
intercostal  muscle 
Internal  intercostal  muscle 
— Pleura 


The  retinacula  cutis  contain  lymphatics  and,  sometimes,  mammary  tissue.  (3) 
There  is  a  lymphatic  plexus,  and,  often,  minute  lobules  of  gland  tissue,  in  the 
pectoral  fascia.  (Heidenhain.)  Fully  one-third  of  the  whole  mamma  lies 
posterior  and  lateral  to  the  axillary  border  of  the  pectoralis  major  so  that  it 
reaches  almost  to  the  mid-axillary  line.  That  part  of  the  upper  and  lateral 
quadrant  known  as  the  axillary  lobe  is  of  especial  importance  from  its  reach- 
ing into  close  vicinity  with  the  anterior  pectoral  group  of  axillary  nodes  (p.  719). 
In  the  male  the  nipple  is  usually  placed  in  the  fourth  space,  nearly  2.5  cm.  (1  in.) 
lateral  to  the  cartilages  of  the  fourth  and  fifth  ribs.  On  the  nipple  itself  open  the 
fifteen  or  twenty  ducts  which  dilate  beneath  it,  and  then  diverge  and  break  up 
for  the  supply  of  the  lobules.  The  skin  over  the  areola  is  very  adherent,  pig- 
mented, and  fatless.  Here  also  are  groups  of  little  swellings  corresponding  to 
large  sebaceous  follicles  and  areolar  glands.  The  skin  over  the  breast  is  freely 
movable,  and  united  to  the  fascia  which  encases  the  organ,  and  thus  to  the  inter- 
lobular connective  tissue,  by  bands  of  the  same  structure — the  retinacula  cutis. 
Under  the  breast,  and  giving  it  its  mobility,  is  a  cellulo-fatty  layer,  the  seat  of 
submammary  abscess. 

'  The  nerves  which  supply  the  breast  are  the  anterior  cutaneous  branches  of  the  second, 
third,'  foui'th,  and  fiftli  intercostal  nerves,  and  the  lateral  branches  of  the  last  three.  The 
connection  of  tliese  trunliS  serves  to  explain  the  diffusion  of  the  pain  often  observed  in  painful 
affections  of  the  breast.  Thus  pain  may  be  referred  to  the  side  of  the  chest  and  bacli  (along  the 
above  intercostal  trunks),  over  the  scapula,  along  the  medial  side  of  the  arm  (along  the  inter- 
costo-brachial  nerve),  or  up  into  the  neck.  The  gland  is  supplied  by  the  following  arteries :  the 
aortic  intercostals  of  the  second,  third,  fovirth,  and  fifth  spaces,  similar  intercostal  branches 
from  the  internal  mammary,  which  runs  outward,  two  small  branches  to  each  space,  perforating 
branches  from  the  same  vessel,  one  or  two  given  off  opposite  to  each  space,  the  long  thoracic  and 
external  mammary  (when  present)  from  the  axillary. 


THE  LUNGS 


1367 


The  lymphatics  have  aheady  been  described  (p.  721,  fig.  566). 

In  removal  of  the  breast  elliptical  incisions  will  usually  suffice  if  employed  on  wide  lines, 
and  if  attention  be  paid  to  the  following  points: — (1)  Those  details  in  the  surgical  anatomy 
already  referred  to,  especially  those  bearing  on  the  extensiveness  of  this  organ,  and  the  propor- 
tionate difference  between  seen  and  unseen  disease.  (2)  The  importance  of  removing  in  one 
continuous  piece  the  whole  breast,  all  the  skin  over  it,  the  costo-sternal  part  of  the  pectoralis 
major,  the  pectorahs  minor,  the  axillary  fat,  and  lymi^hatics. 

Outline  of  the  lungs.  Their  relation  to  the  chest-wall. — To  map  out  the 
lung,  a  line  should  be  drawn  from  the  apex,  a  point  about  2.5  cm.  (1  in.)  above  the 
clavicle,  a  little  lateral  to  the  sterno-mastoid  muscle,  at  the  junction  of  medial 
and  middle  thirds  of  clavicle,  obliquely  downward,  behind  the  sterno-clavicular 
joint,  to  near  the  centre  of  the  junction  of  the  first  and  second  bones  of  the  ster- 
num. Thence,  on  each  side,  a  line  should  be  drawn  slightly  convex  as  far  as  a 
similar  point  on  the  sternum  lying  opposite  the  articulation  of  the  fourth  chondro- 
sternal  joint.  On  the  right  side  the  line  may  be  dropped  as  low  as  the  sixth  chon- 
dro-sternal  joint;  on  the  left  the  incisura  cardiaca  may  be  shown  by  drawing  a 
vertical  line  along  the  middle  line  of  the  sternum,  from  the  level  of  the  medial 
extremities  of  the  fourth  costal  cartilages  to  the  lower  end  of  the  gladiolus,  and 

Fig.  1107. — Outline  op  the  Heart,  its  Valves,  the  Lungs  (shaded),  and  the  Pleura. 
(Holden.)     (Cf.  fig.  437.) 


by  carrying  two  other  lines,  from  the  extremities  of  the  first  line,  outward  so  as 
to  meet  at  a  point  over  the  heart's  apex  (Cunningham);  to  mark  this  gap,  a 
line  should  be  drawn  sloping  laterally  and  downward  from  the  fourth  chondro- 
sternal  articulation  across  the  foui'th  and  fifth  interspaces,  to  a  point  about 
3.7  cm.  (1|  in.)  below  the  left  nipple  (male)  and  2.5  cm.  (1  in.)  to  its  medial  side. 
This  point,  lying  in  the  fifth  space,  marks  the  apex  of  the  heart.  Thence  the  line 
curves  medially  to  the  sixth  costal  cartilage,  a  little  medial  to  its  chondro- 
sternal  junction,  and  in  the  lateral  vertical  line.  Thus  the  lower  part  of  the 
anterior  surface  of  the  right  ventricle  is  not  covered  by  lung.  The  lower  border 
of  the  lung  will  be  marked  on  the  right  side  by  a  line  drawn  from  the  sixth  chondro- 
sternal  articulation  across  the  side  of  the  chest  down  to  the  tenth  thoracic  spine. 
The  lower  border  of  the  left  lung  will  follow  a  similar  line,  starting  on  a  level 
with  a  similar  joint  (sixth  chondro-sternal  joint),  but  much  farther  laterally 
than  on  the  right  side,  i.  e.,  in  the  fifth  space,  about  7.5  cm.  (3  in.)  to  the  left 
of  the  middle  line,  or  a  point  corresponding  to  the  heart's  apex.  In  the  nipple- 
line  the  lung  crosses  the  sixth  rib,  in  the  mid-axillary  line  the  eighth,  and  opposite 


1368  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

the  angle  of  the  scapula  (the  arms  being  close  to  the  sides),  the  tenth  rib.  The 
position  of  the  great  fissure  in  each  lung  may  be  ascertained  approximately  by 
drawing  a  line  curving  downward  and  forward  from  the  second  thoracic  spine 
to  the  lower  border  of  the  lung  at  the  sixth  costal  cartilage;  and  the  smaller  fissure 
of  the  right  lung  extends  from  the  middle  of  the  foregoing  to  the  junction  of  the 
fourth  costal  cartilage  with  the  sternum.  It  will  be  seen  from  the  above  that 
there  is  little  lung  behind  the  manubrium.  The  connective  tissue  here  between 
the  lung  margins  contains  the  thymus,  large  up  to  the  age  of  puberty,  and,  later, 
its  remains.     The  hilus  (root)  of  the  lung  is  referred  to  on  p.  1230. 

The  pleura,  following  much  the  same  line  as  the  lung  above  and  in  front, 
reaches  lower  clown  laterally  and  behind.  Thus  the  two  sacs  starting  from  about 
2.5  cm.  (1  in.)  above  the  medial  third  of  the  clavicle  converge  toward  the  angle 
of  Louis  (p.  1238) ;  meeting  here,  they  descend  vertically,  the  left  overlapping  the 
right  slightly,  to  the  fourth  chondro-sternal  joint.  Hence  the  right  sac  descends 
behind  the  sternum  to  the  sterno-xiphoid  junction  and  sixth  chondro-sternal 
joint.  Thence,  as  it  curves  to  the  back  of  the  chest,  it  crosses  the  eighth  rib 
close  to  the  lateral  vertical  line  {vide  supra),  the  tenth  in  the  mid-axillary,  the 
eleventh  in  the  line  of  the  angle  of  the  scapula,  and  thence  toward  the  twelfth 
thoracic  vertebra.  On  the  left  side  the  pleura  parts  company  from  the  right  at  the 
level  of  the  fourth  chondro-sternal  junction,  deviating  laterally  and  downward 
across  the  fourth  and  fifth  interspaces;  it  then  turns  again  slightly  medially  to 
meet  the  sixth  costal  cartilage.  Thus,  as  in  the  case  of  the  lung,  but  to  a  less 
extent,  there  is  a  small  area  of  the  pericardium,  and,  under  it,  the  right  ventricle 
uncovered  by  the  pleura.  Over  the  side  and  back  of  the  chest,  along  its  dia- 
phragmatic reflection,  the  left  pleura  reaches  a  little  lower  than  the  right. 

The  deepest  part  of  the  pleural  sac  is  where  the  reflection  crosses  the  tenth  rib  or  tenth  space 
in  the  mid-axillary  line.  From  this  it  ascends  slightly  as  it  curves  back  to  the  spine.  (Cun- 
ningham.) The  relations  of  the  pleura  to  the  last  rib  are  of  much  importance  to  the  surgeon  in 
operations  on  the  kidney.  In  the  case  of  a  twelth  rib  of  ordinary  length,  the  pleural  reflection 
crosses  it  at  the  lateral  border  of  the  sacro-spinalis ;  when  a  rudimentary  last  rib  does  not  reach 
the  lateral  border  of  this  muscle,  an  incision  carried  upward  into  the  angle  between  the  eleventh 
rib  and  the  sacro-spinalis  will  open  the  pleural  sac.     (Melsome.) 

For  tapping  the  pleura  there  are  two  chief  sites: — (1)  The  sixth  or  seventh  space  in  front 
of  the  posterior  fold  of  the  axilla.  (2)  The  eighth  space  behind,  in  the  line  of  the  angle  of  the 
scapula.  For  the  incision  of  an  empyema  the  first  is  usually  chosen.  The  overlying  soft  parts 
are  not  thick,  the  interspace  is  wide  enough,  drainage  is  sufficient  (especially  if  part  of  the 
seventh  or  eighth  rib  be  resected),  and  this  site  is  free  from  the  objection  that  the  angle  of  the 
scapula  overlaps  the  seventh  and  eighth  ribs,  unless  the  arm  is  raised. 

Outline  of  the  heart.  Its  relation  to  the  chest-wall. — The  upper  limit  of 
the  heart  (base)  will  be  defined  by  a  line  crossing  the  sternum  a  little  above  the 
upper  border  of  the  third  costal  cartilage,  reaching  about  1.2  cm.  (J  in.)  to  the 
right  and  about  2.5  cm.  (1  in.)  to  the  left  of  the  sternum.  Its  apex  point  is  in  the 
fifth  space,  3.7  cm.  (1|  in.)  below  the  male  left  nipple,  and  2.5  cm.  (1  in.)  to  the 
medial  side.  This  point  will  be  at  7.5  cm.  (3  in.)  from  the  left  border  of  the 
sternum.  The  right  border  (right  atrium)  will  be  given  by  a  line,  slightly  convex 
laterally,  drawn  from  the  right  extremity  of  the  upper  border  to  the  right  sixth 
chondro-sternal  joint.  If  another  line,  slightly  convex  upward,  be  drawn 
onward  from  this  point  across  the  last  piece  of  the  sternum,  just  above  the 
xiphoid  cartilage,  to  the  apex,  it  will  give  the  lower  border  (margo  acutus  of  right 
ventricle),  which  rests  on  the  central  tendon  of  the  diaphragm.  The  left  border 
(margo  obtusus  of  left  ventricle)  will  be  given  by  a  line,  convex  to  the  left,  passing 
from  the  left  extremity  of  the  upper  border  to  the  apex,  medial  to  the  nipple- 
line.  This  line  should  be  7.5  cm.  (3  in.)  from  the  middle  of  the  sternum  at  the 
level  of  the  fourth  costal  cartilage.  The  base  of  the  heart  is  opposite  four  of 
the  thoracic  vertebrae,  viz.,  the  sixth,  seventh,  eighth,  and  ninth.  The  apex 
and  anterior  or  costo-sternal  surface  have  been  mentioned.  The  inferior  or 
diaphragmatic  surface  (chiefly  left  atrium  and  left  ventricle)  rests  upon  the 
diaphragm,  mainly  the  central  tendon,  to  which  the  intervening  pericardium 
is  connected,  and  is  thus  adjacent  to  the  liver  and  a  small  portion  of  the  stomach. 

If  a  circle  5  cm.  (2  in.)  in  diameter  be  described  around  a  point  midway  between  the  left 
nipple  and  the  lower  end  of  the  gladiolus,  it  will  define  with  sufficient  accuracy  for  practical 
purposes  that  part  of  the  heart  which  lies  immediately  behind  the  chest  wall,  and  which  is 
uncovered  by  lung  and  (in  part)  by  pleura.     (Latham.) 


THE  HEART  1369 

The  valves. — The  pulmonary  valves  (the  highest  and  most  superficial)  lie,  in 
front  of  the  aortic,  behind  the  third  left  chondro-sternal  joint,  and  opposite  to 
the  upper  border  of  the  third  costal  cartilage.  The  aortic  valves  lie  behind  and  a 
little  below  these,  opposite  to  the  medial  end  of  the  third  intercostal  space, 
and  on  a  level  with  the  lower  border  of  the  third  left  costal  cartilage.  The 
atrio -ventricular  openings  lie  at  a  somewhat  lower  level  than  that  of  the  aortic 
and  pulmonary.  Thus  the  tricuspid  valves  lie  behind  the  middle  of  the  sternum 
at  the  level  of  the  fourth  intercostal  space;  and  the  mitral  valves,  the  most  deeply 
placed  of  all,  lie  a  little  to  the  left  of  these,  behind  the  left  edge  of  the  sternum 
and  the  fourth  left  costal  cartilage  (fig.  1107;  also  cf.  fig.  437). 

'Thus  these  valves  are  so  situated  that  the  mouth  of  an  ordinary-sized  stethoscope  will 
cover  a  portion  of  them  all,  if  placed  over  the  juncture  of  the  third  intercostal  space,  on  the  left 
side,  with  the  sternum.  All  are  covered  by  a  thin  layer  of  lung;  therefore  we  hear  their  action 
better  when  the  breathing  is  for  a  moment  suspended.'     (Holden.) 

The  pericardium. — This  fibro-serous  sac,  occupying  the  middle  mediastinum, 
is  triangular  in  shape,  with  the  apex  upward.  Here  its  fibrous  layer  gives  mvest- 
ment  to  the  large  vessels,  except  the  inferior  cava.  It  is  also  continuous  with  the 
deep  cervical  fascia.  The  base,  connected  with  the  diaphragm,  has  been  referred 
to  above.  In  front  an  area  of  variable  size  (fig.  1107),  owing  to  the  divergence 
of  the  left  pleura,  is  in  contact  with  the  left  half  of  the  lower  part  of  the  sternum, 
and  more  or  less  of  the  medial  ends  of  the  fourth,  fifth,  and  sixth  costal  cartilages, 
here  forming  the  posterior  boundary  of  the  anterior  mediastinum.  Behind,  the 
pericardium  is  the  anterior  boundary  of  the  posterior  mediastinum,  and  is  in 
close  contact  with  the  oesophagus  and  aorta. 

Paracentesis  of  pericardium. — While  the  seat  of  election  must  here  remain  an  open  question, 
each  case  requiring  a  decision  for  itself,  the  one  most  suitable  on  the  whole  is  the  fifth  left  space, 
about  2.5  cm.  (1  in.)  from  the  sternum,  so  as  to  avoid  injury  to  the  internal  mammary  artery 
and  the  pleura,  of  which  the  line  of  reflection  has  been  shown  to  vary. 

In  incision  of  the  pericardium  to  establish  free  drainage,  a  portion  of  the  fifth  or  sixth  left 
costal  cartilage  should  be  carefully  resected,  the  internal  mammary  artery  tied,  the  trans- 
versus  thoracis  (triangularis  sterni)  scratched  through,  and  the  pleural  reflexion  pushed  aside. 

Relation  of  vessels  to  the  wall  of  the  thorax. — Aortic  arch. — The  ascending  part  of  the 
aorta  reaches  from  a  spot  behind  the  sternum,  a  little  to  the  left  of  the  centre,  on  a  level  with  the 
third  left  costal  cartilage,  to  the  upper  border  of  the  second  right  cartilage;  thus  it  passes  up- 
ward, backward,  and  to  the  right,  and  is  about  5  cm.  (2  in.)  long.  The  transverse  part  then 
crosses  backward  to  the  left  behind  the  sternum  (the  highest  part  of  the  arch  being  about  2.5 
cm.  (1  in.)  below  the  notch),  reaching  from  the  second  right  costal  cartilage  to  the  lower  border 
of  the  fourth  thoracic  vertebra  on  the  left  side.  This  part  recedes  from  the  surface,  and,  with 
the  next,  cannot  be  marked  out  on  the  surface.  The  third,  or  descending  part,  the  shortest 
of  the  three,  reaches  from  the  lower  border  of  the  fourth  to  that  of  the  fifth  thoracic  vertebra. 

Fig.  1104  will  remind  the  reader  of  many  of  the  pressure  symptoms  which  may  accompany 
an  aneurysm  of  the  aortic  arch;  e.  g.,  pressure  on  the  left  innominate  vein,  the  three  large  arte- 
ries, trachea,  and  left  bronchus,  recurrent  nerve,  oesophagus,  and  thoracic  duct.  In  aneurysm 
of  the  thoracic  aorta,  pain,  usually  unilateral,  referred  to  the  corresponding  intercostal  nerves, 
is  a  common  pressure  symptom. 

The  pulmonary  artery  lies  behind  the  left  side  of  the  sternum  and  its  junction  with  the  sec- 
ond and  third  costal  cartilages. 

Innominate  artery. — A  line  drawn  from  the  top  of  the  arch,  about  2 . 5  cm.  (1  in.)  below 
the  sternal  notch,  and  close  to  the  centre,  to  the  right  sterno-clavicular  joint,  will  give  the  line 
of  this  vessel. 

Left  common  carotid. — This  vessel  will  be  denoted  by  a  line  somewhat  similar  to  the  above, 
passing  from  the  level  of  the  arch  a  little  to  the  left  of  the  last  starting-point  to  the  left  sterno- 
clavicular joint. 

Left  subclavian  artery. — A  line  from  the  end  of  the  transverse  arch,  behind  the  left  of  the 
sternum,  straight  upward  to  the  clavicle,  delineates  the  vertical  thoracic  course  of  the  long  left 
subclavian  artery;  its  thoracic  portion  lies  behind  the  left  carotid. 

Innominate  veins. — The  left,  7.5  cm.  (3  in.)  long,  extends  very  obliquely  from  the  left 
sterno-olavicular  joint,  behind  the  upper  part  of  the  manubrium,  to  a  point  1.2  cm.  (|  in.)  to 
the  right  of  the  sternum,  on  the  lower  border  of  the  first  right  costal  cartilage.  The  right, 
about  2.5  cm.  (1  in.)  long,  descends  almost  vertically  to  the  above  point  from  the  right  sterno- 
clavicular joint. 

Venae  cavae. — The  superior  descends  from  the  point  above  given  for  the  meeting  of  the 
innominate  veins  in  the  first  intercostal  space,  close  to  the  sternum,  and  perforates  the  right 
atrium  on  a  level  with  the  third  costal  cartilage.  The  inferior  vena  cava. — The  opening  of  this 
vein  into  the  right  atrium  lies  under  the  middle  of  the  fifth  right  interspace  and  the  adjacent 
part  of  the  sternum. 

The  oesophagus. — The  relations  of  this  tube  in  its  cervical  and  thoracic 
portions  are  most  important,  e.g.,  to  the  trachea  and  left  bronchus;  the  vagi 
and  left  recurrent  nerve;  the  pleurae,  left  above  and  right  [below,  aorta,  and 


1370  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

pericardium.  Its  lymphatics  go  below  into  the  posterior  mediastinal  and  superior 
gastric  nodes;  above  into  the  lower  deep  cervical  nodes,  a  point  sometimes  diag- 
nostic in  malignant  disease. 

The  lumen  of  the  oesophagus  is  narrowed  at  three  points: — (1)  and  best  marked  at  the  cri- 
coid cartilage,  (2)  where  it  is  crossed  by  the  left  bronchus,  (3)  as  it  passes  through  the  dia- 
phragm. The  tube,  25  to  27  cm.  (10  to  11  in.)  long,  extends  from  the  sixth  cervical  to  the  lower 
■  border  of  the  tenth  thoracic  vertebra.  In  an  adult,  the  distance  from  the  incisor  teeth  to  the 
cricoid  is  about  15  cm.  (6  in.);  an  additional  7.5  cm.  (3  in.)  gives  the  level  of  the  crossing  of 
the  left  bronchus,  while  from  the  teeth  to  the  opening  in  the  diaphragm  would  be  from  41  to  43 
cm.  (16  to  17  in.).  To  expose  the  tube  in  the  neck  an  incision  is  made  on  the  left  side,  much 
as  for  the  higher  ligature  of  the  common  carotid,  but  carried  lower  down.  The  depressors  of 
the  hyoid  being  drawn  medially  or  divided,  the  pretracheal  fascia  is  opened,  which  allows  of 
the  overlapping  thyreoid  and  trachea  being  displaced  medially,  while  the  carotid  sheath  is  re- 
tracted laterally.  The  tracheal  rings  are  the  best  guide  to  the  oesophagus.  The  recurrent 
nerve  must  be  avoided. 

THE  ABDOMEN 

The  regions  and  subdivisions  will  first  be  considered,  the  abdominal  wall 
next,  and  finally  the  abdominal  cavity,  including  the  peritoneum  and  the  various 
organs. 

Subdivision  of  the  abdominal  cavity. — Certain  arbitrary  horizontal  and 
vertical  planes,  represented  by  lines  drawn  on  the  ventral  surface,  are  used  to 
subdivide  the  abdomen  for  topographical  purposes  (fig.  898).  A.  Horizontal 
planes.  (1)  Infracostal  through  the  lower  margins  of  the  tenth  costal  cartilages 
(the  lowest  part  of  the  costal  margin).  This  plane  crosses  the  body  of  the  third 
lumbar  vertebra.  (2)  Intertuhercular,  passing  through  the  tubercles,  prominent 
points  of  the  ihac  crests,  which  are  situated  about  5  cm.  (2  in.)  behind  the  anterior 
superior  spines.  This  plane  crosses  the  body  of  the  fifth  lumbar  vertebra. 
B.  Vertical  planes.  (1)  Median  vertical,  drawn  upward  in  the  middle  line 
from  the  symphysis  pubis.  (2)  Lateral  vertical,  drawn  upward  on  each  side 
parallel  to  the  former,  from  a  point  midway  between  the  anterior  superior  iliac 
spine  and  the  symphysis  pubis. 

These  lateral  lines  if  prolonged  upward  into  the  thorax  pass  rather  more  than  2.5  cm. 
(1  in.)  to  the  medial  side  of  the  male  nipple  and  meet  the  clavicle  a  little  medial  to  its  mid-point. 

According  to  the  BNA  system,  the  lateral  vertical  lines  are  slightly  curved,  extending 
upward  from  the  pubic  tubercle  on  each  side  along  the  lateral  margin  of  the  rectus  muscle 
(corresponding  to  the  linea  semilunaris). 

The  infracostal  and  intertuhercular  planes,  with  the  two  lateral  vertical 
planes  that  intersect  them  divide  the  abdomen  into  nine  regions: — three  median, 
viz.,  the  epigastric,  umbilical,  and  h3rpogastric  and  on  each  side  three  lateral,  viz., 
hypochondriac,  lumbar,  and  iliac  (fig.  898). 

Another  transverse  plane  of  practical  importance,  though  we  do  not  use  it  as  a  boundary 
of  the  abdominal  subdivisions,  is  represented  by  Addison's  transpyloric  line,  drawn  horizontally 
through  a  point  midway  between  the  umbilicus  and  the  sterno-xiphoid  junction  (or  midway 
between  the  symphysis  pubis  and  supra-sternal  notch).  It  crosses  the  spine  at  the  level  of 
the  first  lumbar  vertebra.  It  must  be  noted  that  the  pylorus  only  lies  in  this  plane  during 
life  when  the  subject  is  in  the  horizontal  position.  On  assuming  the  upright  position  the  pylorus 
falls  at  least  one  vertebra  lower.  The  sterno-xiphoid  plane,  drawn  horizontally  through  the 
junction  of  the  body  of  the  sternum  with  the  xiphoid,  outs  the  spine  at  the  disc  between  the 
ninth  and  tenth  thoracic  vertebrte,  and  the  umbilical  plane,  passing  through  the  umbilicus, 
crosses  the  disc  between  the  third  and  fourth  lumbar  vertebrae  (though  in  corpulent  subjects  it  is 
somewhat  lower). 

The    abdominal   wall.     Bony   and   muscular   landmarks. — The  linea   alba 

forms  a  perceptible  groove  in  the  middle  fine  from  the  xiphoid  cartilage  to  below 
the  umbilicus.  It  is  a  band  of  interlacing  fibres,  mostly  crossing  each  other  at 
right  angles,  that  forms  the  main  insertion  of  the  transversus  and  oblique 
muscles,  and  stretches  between  the  two  recti  muscles  from  xiphoid  cartilage  to 
symphysis.  It  is  on  the  average  1.2  cm.  (|  in.)  wide  above  the  umbilicus.  Below 
the  umbilicus  it  narrows  rapidly  and  becomes  merely  a  thin  fibrous  septum 
between  the  two  recti,  which  in  this  position  lie  close  together. 

In  its  broad  supra-umbilical  portion,  small  hernial  protrusions  of  subperitoneal  fat  often 
force  their  way  through  interstices  in  the  linea  alba,  and  true  peritoneal  sacs  may  be  drawn 
through  after  them.     The  linea  alba  is  not  very  vascular,  and  hence  was  at  one  time  the  favour- 


THE  ABDOMEN  1371 

ite  site  of  incisions  in  opening  the  abdominal  cavity.  Since  the  resulting  scar  is  weak  and 
yielding,  however,  it  is  now  more  customary  to  make  vertical  incisions  through  the  rectus 
sheath,  to  one  side  of  the  middle  line,  where  the  abdominal  wall  can  be  sutured  in  layers,  and 
an  incisional  hernia  prevented. 

The  umbilicus  lies  in  the  linea  alba  rather  below  its  centre.  It  is  somewhat 
prone  to  hernia  formation  (p.  1402)  and  is  occasionally  the  site  of  congenital 
fistulas,  which  may  originate  in  a  Meckel's  diverticulum  (p.  1376)  or  a  patent 
urachus. 

When  the  recti  are  thrown  into  contraction  the  linea  semilunaris  on  each  side 
is  made  evident  as  a  groove,  extending  with  a  slight  lateral  convexity  from 
the  tip  of  the  ninth  costal  cartilage,  where  the  lateral  vertical  line  meets  the  thoracic 
margin,  to  the  pubic  tubercle. 

The  contraction  of  the  recti  muscles  also  shows  up  the  three  lineae  transversae,  fibrous 
intersections  adherent  to  the  anterior  layer  of  the  sheath  of  the  rectus,  which  cros.?  the  substance 
of  the  muscle  (1)  at  the  umbilicus,  (2)  at  the  tip  of  the  xiphoid,  and  (3)  midway  between  the 
former  two.  A  tonic  contraction  of  one  or  both  recti  localised  to  one  of  these  segments  occa- 
sionally gives  rise  to  the  "phantom"  tumors  which  occur  in  some  hysterical  cases. 

The  linea  semilunaris  shares  the  disadvantages  of  the  linea  alba  as  a  site  for  incisions,  and 
there  is  the  further  danger  of  injury  to  the  nerve  supply  of  the  rectus,  which  may  involve  a 
diffuse  bulge  of  the  atrophied  muscle. 

In  tapping  the  bladder  above  the  pubes,  the  trocar  should  be  introduced  immediately  above 
the  pubes  and  driven  backward  and  a  little  downward.  In  this  operation,  and  in  suprapubic 
cystotomy,  the  retro-pubic  space  or  cavum  Retzii  is  opened.  This  is  bounded  in  front  by  the 
pubes  and  superior  fascia  of  the  urogenital  diaphragm,  behind  by  the  anterior  surface  of  the 
bladder.  Below  are  the  true  ligaments  of  this  viscus.  The  space  contains  fatty  tissue  and  veins, 
increasing  in  size  with  the  advance  of  life.  If  about  ten  ounces  of  fluid  are  injected  into  the 
bladder,  the  peritoneum  will  be  raised  sufficiently  to  allow  of  a  three-inch  incision  being  made 
between  the  recti  and  pyramidales  immediately  above  the  pubes.  The  transversalis  fascia  is 
thicker  below,  and  is  often  separated  from  the  linea  alba  by  fat,  which  must  not  be  mistaken 
for  the  extra-peritoneal  layer.  The  peritoneal  reflexion  is  loosely  connected  to  the  bladder 
and  can  always  be  peeled  upward. 

A  transverse  line  drawn  from  one  anterior  superior  iliac  spine  to  the  other  crosses  at  about  the 
level  of  the  top  of  the  promontory  of  the  sacrum.  Such  a  line  will  always  show  whether  the 
pelvis  is  horizontal  or  not.     (Holden.) 

The  inguinal  (Poupart's)  ligament  corresponds  to  a  line  drawn  with  a  slight 
curve  downward  between  the  anterior  superior  iliac  spine  and  the  pubic  tubercle. 
The  first  of  these  bony  prominences  corresponds  to  the  starting-point  of  the 
above  ligament,  the  attachment  of  the  fascia  lata  to  the  ilium,  the  meeting  of  the 
fleshy  and  aponeurotic  parts  of  the  external  oblique  (denoted  by  a  line  drawn 
upward  from  this  spine  to  the  ninth  costal  cartilage,  or  often  a  little  anteriorly 
to  these  points),  the  point  of  emergence  of  the  lateral  cutaneous  nerve  of  the 
thigh,  and  part  of  the  origins  of  the  internal  oblique,  transversus,  and  tensor 
fasciae  latae. 

The  pubic  tubercle  marks  the  lateral  pillar  (inferior  crus)  of  the  subcutaneous 
inguinal  (external  abdominal)  ring,  the  mouth  of  which  corresponds  to  the  crest 
of  the  pubes  lying  between  the  tubercle  and  the  symphysis.  The  neck  of  an 
inguinal  hernia  is  above  the  tubercle  and  Poupart's  ligament;  that  of  a  femoral 
hernia  below  and  lateral  to  the  tubercle,  and  below  the  same  hgament.  The  ring, 
and  especially  its  lateral  pillar,  can  easily  be  felt  by  invaginating  the  scrotal  skin 
with  a  finger,  and  pushing  upward  and  laterally.  In  a  female  patient,  if  the  thigh 
be  abducted,  the  tense  tendon  of  tlu'  adductor  longus  will  lead  up  to  the  site  of  the 
ring.  The  abdominal  inguinal  (internal  abdominal)  ring  is  situated  about  1.2  cm. 
(J  in.)  above  the  centre  of  Poupart's  ligament;  oval  in  shape,  and  nearly  vertical 
in  direction,  it  has  the  arching  fibres  of  the  transversus  above  it,  and  to  its 
medial  side  the  inferior  epigastric  artery,  lying  behind  the  spermatic  cord.  The 
pulsations  of  this  vessel  here  guide  the  finger  in  the  insertion  of  the  uppermost 
deep  sutures  in  radical  cure  of  hernia.  The  canal  runs  obliquely  downward  and 
forward  between  the  two  rings.  In  the  adult  it  is  about  3.7  cm.  (1^  in.)  long,  but 
in  early  life,  and  in  adults  with  a  large  hernia  dragging  upon  the  parts,  the  two 
rings  are  much  nearer,  and  may  be  one  behind  the  other.  For  the  anatomy  of 
inguinal  hernia  see  p.  1304. 

Vessels  in  the  abdominal  wall. — The  three  superficial  branches  of  the  com- 
mon femoral,  the  external  pudic,  epigastric,  and  circumfiex  iliac,  supply  the  lowest 
part  of  the  abdominal  wall  and  the  adjacent  groin  and  genitals.  The  others 
that  have  to  be  remembered  are  the  inferior  epigastrics  and  the  epigastric  branch 


1372  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

of  the  internal  mammary,  the  deep  circumflex  iliacs,  the  last  two  intercostals,  and 
the  abdominal  branches  of  the  lumbar  arteries. 

Of  these,  the  infei'ior  epigastric  is  the  most  important;  its  course  will  be  marked  out  by  a 
line  drawn  from  a  point  just  medial  to  the  centre  of  the  inguinal  ligament,  upward  and  medially 
to  the  medial  side  of  the  abdominal  ring,  and  thence  to  a  point  about  midway  between  the  pubes 
and  umbilicus,  forming  the  lateral  boundary  of  Hesselbach's  triangle  (fig.  1121).  Here  the 
vessel,  which  at  first  lies  between  the  peritoneum  and  fascia  transversalis,  perforates  the  latter 
and,  passing  over  the  semicircular  line  (fold  of  Douglas)  enters  the  sheath  of  the  rectus.  It  then 
runs  upward,  closely  applied  to  the  back  of  that  muscle,  and,  a  little  above  the  level  of  the 
umbilicus,  divides  into  branches  which  anastomose  with  the  epigastric  branch  of  the  internal 
mammary. 

One  superficial  vein  in  the  abdominal  wall  needs  especial  mention,  the  thoraco-epigastric, 
joining  the  veins  of  the  chest,  e.  g.,  the  long  thoracic  above  with,  the  superficial  epigastric 
below.  Its  valves  directing  the  blood  downward  below  and  upward  above  (Stiles)  may  be 
rendered  incompetent  when  this  vessel  is  enlarged,  as  in  interference  with  the  portal  vein,  mth 
which  it  communicates  by  a  vein  in  the  round  ligament,  or  in  blocking  of  the  inferior  vena  cava. 

Lymphatics. — It  is  sufficiently  correct  to  say  here  that  those  above  the  umbilical  line  go 
to  the  axillary,  and  those  below  that  line  to  the  inguinal  nodes. 

Nerves. — The  lower  seven  intercostals  and  the  ilio-hypogastric  and  ilio- 
inguinal supply  the  abdominal  wall.  The  sixth  and  seventh  intercostals  supply 
the  skin  over  the  upper  epigastrium;  the  eighth,  the  area  of  the  middle  linea 
transversa;  the  tenth,  that  of  the  imibilicus ;  the  last  thoracic,  ilio-inguinal  and  ilio- 
hypogastric, the  region  above  Poupart's  ligament,  and  that  of  the  pubes.  The 
ilio-hypogastric  supplies  the  skin  over  the  subcutaneous  inguinal  (external 
abdominal)  ring;  the  ilio-inguinal  that  over  the  cord  and  scrotum.  The  last 
thoracic  and  ilio-hypogastric  cross  the  iHac  crest  to  supply  the  skin  of  the  buttock. 

The  diaphragm. — The  upper  limit  of  the  diaphragm  rises  to  the  following 
levels  in  full  expiration:  Its  central  tendon  to  about  the  lower  end  of  the  body  of 
the  sternum,  or  the  seventh  chondro-sternal  joint;  the  right  half  to  the  fifth  rib, 
or  about  1  cm.  (|  in.)  below  the  nipple;  the  left  half  not  rising  quite  so  high,  i.  e., 
to  the  fifth  space,  or  2.5  cm.  (1  in.)  below  the  nipple. 

Topographical  relations  of  abdominal  viscera. — These  will  include  the 
peritoneum,  liver  and  bile  passages,  stomach,  spleen,  pancreas,  intestines, 
kidneys  and  ureters,  and  large  abdominal  vessels. 

The  peritoneal  spaces. — The  peritoneum  presents  certain  potential  spaces, 
determined  by  its  various  reflections  from  the  parietes  and  abdominal  viscera. 
In  these  spaces  collections  of  fluid  such  as  abscesses  or  extravasations  from  hollow 
viscera  or  blood  vessels  may  collect  and  become  shut  off  by  adhesions  or  overflow 
in  various  directions  into  neighbouring  spaces.  The  transverse  mesocolon  and 
great  omentum  together  form  a  shelf  transversely  placed,  which  divides  the  greater 
sac  into  two  main  divisions — supra-omental  and  infra-omental. 

The  supra-omental  region,  in  which  the  various  forms  of  subphrenic  abscess  are  found,  con- 
tains the  following  fossa;  (Barnard).*  (1)  Right  subphrenic,  between  the  right  lobe  of  the  liver 
and  right  cupola  of  the  diaphi-agm,  bounded  toward  the  median  line  by  the  falciform  ligament, 
and  behind  by  the  coronary  ligament.  It  communicates  below  with  (2)  the  subhepatic  fossa 
or  right  renal  pouch  (Morison),  which  is  bounded  above  by  the  visceral  surface  of  the  liver,  and 
below  by  the  mesocolio  shelf  and  right  kidney.  It  extends  from  the  right  lateral  abdominal 
wall,  its  most  capacious  part,  across  the  median  line  under  the  left  lobe  of  the  liver,  and  on  its 
posterior  aspect  lie  the  upper  pole  of  the  right  kidney,  epiploic  foramen,  and  anterior  surface  of 
small  omentum.  (3)  The  left  subphrenic,  also  known  as  the  anterior  perigastric  fossa,  lies 
between  the  left  dome  of  the  diaphragm  above,  and  the  left  lobe  of  liver,  stomach,  spleen  and 
omentum  below.  It  is  bounded  on  the  right  by  the  falciform  ligament  which  lies  somewhat  to 
the  right  of  the  median  line.  (4)  The  omental  bursa  may  be  regarded  as  a  diverticulum  from 
the  subhepatic  fossa  with  which  it  communicates  by  the  epiploic  foramen.  Abscesses  in  this 
sac  are  rare,  but  occasionally  laceration  of  the  pancreas  which  is  closely  related  to  it  behind 
gives  rise  to  a  collection  of  pancreatic  juice  and  blood  in  the  lesser  sac,  known  as  a  pancreatic 
pseudo-cyst  (Jordan  Lloyd). 

The  infra-omental  region  is  subdivided  in  its  abdominal  part  into  (1)  right  and  (2)  left 
compartments  by  the  attachment  of  the  root  of  the  mesentery  to  the  spine,  descending  from  the 
duodeno-jej  unal  flexure  downward  into  the  right  iliac  fossa.  These  fossae  communicate  with  the 
supra-omental  regions  in  the  neighbourhood  of  the  hepatic  and  splenic  flexm-es  of  the  colon 
respectively,  and  below  with  (3)  the  pelvis.  The  deepest  level  of  the  peritoneum  lining  the  pelvis 
constitutes  in  the  male  the  recto-vesioal,  and  in  the  female  the  recto-vaginal  fossa  (pouch  of 
Douglas). 

It  should  be  noted  that  with  a  patient  in  the  supine  position,  owing  to  the  contour  of  the 
psoas  muscles  and  the  anterior  convexity  of  the  lumbar  spine,  any  fluid  above  the  pelvic  brim 
will  tend  to  gravitate  into  the  subphrenic  spaces  across  the  flexures  of  the  colon  which  lie  far 
back  in  the  loins.  This  is  undesii-able  in  view  of  the  great  absorbing  power  of  the  subphrenic 
lymphatics,  and  may  be  obviated  by  propping  the  patient  in  a  half-sitting  position. 

*  Barnard,  H.  L.,  Brit.  Med.  Journal,  Feb.  15,  1908. 


THE  STOMACH  1373 

Viscera  behind  the  linea  alba. — From  above  downward  there  are  the  follow- 
ing:— (Ij  Above  the  umbiUcus — the  left  lobe  of  the  liver,  the  stomach,  the 
transverse  colon,  part  of  the  great  omentum,  the  pancreas,  and  cceliac  (solar) 
plexus.  (2)  Below  the  umbilicus — the  rest  of  the  great  omentum,  covering  in 
the  small  intestines  and  their  mesentery.  In  the  child,  the  bladder  occupies  a 
partly  abdominal  position;  and  in  the  adult,  the  same  viscus,  if  distended,  will 
rise  out  of  the  pelvis  and  displace  the  above  structures,  raising  the  peritoneum 
until,  if  distended  half  way  to  the  umbilicus,  there  is  an  area  of  nearly  5  cm. 
(2  in.)  safe  for  operations  above  the  symphysis.  The  gravid  uterus  also  rises 
behind  the  linea  alba. 

The  liver  (figs.  914,  941,  and  1125). — In  the  erect  position,  the  anterior  thin 
margin  of  the  liver  projects  about  1  cm.  (|  in.)  below  the  costal  cartilages,  but 
can  only  be  made  out  with  difficulty  in  this  position.  It  may  also  be  displaced 
downward  by  pleuritic  effusion  or  tight  lacing.  The  liver  is  also,  proportion- 
ately, much  larger  in  small  children. 

Of  the  three  more  accessible  surfaces,  the  right  lateral  is  opposite  the  seventh  to  the  eleventh 
intercostal  arches,  separated  from  them  by  the  pleura,  the  thin  base  of  the  lung,  and  the  dia- 
phragm. The  superior  surface  is  accurately  fitted  with  its  right  and  left  portions  into  the  hol- 
lows of  the  diaphragm,  a  slightly  depressed  area  intervening  which  corresponds  to  the  central 
tendon.  Its  level  corresponds  to  that  of  the  diaphragm  given  above.  On  the  left  side,  in  the 
adult,  the  limit  of  the  left  lobe  will  be  in  the  fifth  interspace,  about  7.5  cm.  (3  in.)  from  the  ster- 
num. The  antericr  surface  is  in  contact  with  the  diaphragm,  costal  arches,  and,  between  them, 
the  xiphoid  cartilage,  and,  below,  with  the  abdominal  wall.  Both  the  superior  and  anterior 
siu'faoes  are  subdivided  by  the  falciform  ligament,  an  important  point  in  subphrenic  suppura- 
tion. In  the  right  hypochondrium  the  anterior  margin  corresponds  to  the  lower  margin  of 
the  thorax;  but  in  the  epigastric  region,  running  obhquely  across  from  the  ninth  right  to  the 
eighth  left  costal  cartilage,  it  crosses  the  middle  line  about  a  hand's  breadth  below  the  sterno- 
xiphoid  articulation  (Godlee),  or  half-way  between  the  sterno-xiphoid  j unction  and  umbiUcus, 
i.e.,  in  the  transpyloric  line  (fig.  914).  Behind,  the  anterior  margin,  following  the  right  lateral 
surface  within  the  costal  arches,  crosses  the  last  rib  toward  the  level  of  the  eleventh  thoracic 
spine.  In  the  anterior  border,  a  little  to  the  right  of  the  median  vertical  plane,  is  the  umbilical 
notch,  where  the  falciform  and  round  ligaments  meet.  Still  further  to  the  right,  and  just  to  the 
left  of  the  mid-Poupart  plane,  is  the  fundus  of  the  gall-bladder. 

Gall-bladder  and  bile  passages. — The  fundus  of  the  gall-bladder,  situated  in  a 
fossa  on  the  under  surface  of  the  right  lobe  of  the  liver,  and  having  the  quadrate 
lobe  to  its  left,  lies  opposite  to  the  right  ninth  costal  cartilage,  close  to  the  lateral 
edge  of  the  rectus.  This  point  corresponds  to  the  site  of  intersection  of  the  lateral 
vertical  and  transpyloric  lines.  It  is  in  contact  with  the  hepatic  flexure  of  the 
colon  and  the  first  piece  of  the  duodenum,  into  either  of  which,  but  particularly 
the  latter,  large  gall-stones  impacted  in  the  neck  of  the  gall-bladder  occasionally 
ulcerate.  A  distended  gall-bladder  as  it  enlarges  tends  to  take  a  line  obliquely 
from  the  above  point  where  it  emerges  from  under  the  costal  margin  toward  the 
umbilicus. 

The  long  axis  of  the  gall-bladder  is  directed  from  the  fundus  backward  and  upward.  The 
cystic  duct  runs  from  the  neck  downward  and  forward  in  the  gastro-hepatic  omentum,  and  so 
forms  an  acute  angle  with  the  gall-bladder.  A  spiral  fold  of  mucous  membrane  at  the  junction 
of  the  two,  which  fulfils  the  function  of  keeping  the  lumen  open  for  the  flow  of  bile,  adds  to  the 
difficulty  of  passing  a  bougie  from  the  gall-bladder  down  into  the  common  duct. 

The  hepatic  and  cystic  ducts  join  in  the  right  free  margin  of  the  gastro-hepatic  omentum 
to  form  the  common  bile-duct,  7.5  cm.  (3  in.)  in  length,  which  as  it  runs  down  to  open  into  the 
duodenum  presents  four  distinct  stages.  (1)  It  first  lies  in  the  free  edge  of  lesser  omentum  in 
front  of  the  epiploic  foramen,  with  the  hepatic  artery  to  the  medial  side,  and  the  portal  vein 
behind  them  both.  (2)  Behind  the  first  part  of  the  duodenum  with  the  gastro-duodenal  artery 
accompanying  it.  (3)  In  a  deep  groove  in  the  head  of  the  pancreas,  between  that  gland  and 
the  posterior  aspect  of  the  second  part  of  the  duodenum.  The  pancreatic  tissue  siurounds  it 
completely  in  75  per  cent,  of  cases,  (Bunger)  hence  the  jaundice  that  occurs  in  chronic  inter- 
stitial pancreatitis.  (4)  Piercing  the  muscular  waU  of  the  duodenum  obliquely  it  ends  by 
joining  the  main  duct  of  the  pancreas  at  the  ampulla  of  Vater  and  opening  into  the  second  part 
of  the  duodenum  by  a  common  orifice.  This  orifice,  situated  on  the  postero-medial  aspect  of 
the  gut,  rather  below  the  centre  of  the  second  portion,  is  raised  on  a  small  papilla  and  is  nar- 
rower than  the  lumen  of  the  common  duct. 

The  stomach. — The  study  of  this  organ  by  rendering  its  contents  opaque  with 
bismuth  salts  and  projecting  its  shadow  by  X-rays  on  a  fluorescent  screen,  has 
greatly  modified  the  conception  of  its  shape  and  position  formed  from  post- 
mortem and  operative  observations.  Examined  post-mortem,  or  at  operations 
under  general  ansesthesia  it  forms  a  flaccid  sac  with  its  long  axis  directed  from  the 
fundus  obliquely  downward,  forward,  and  to  the  right.     Seen  under  X-rays, 


1374  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

with  the  patient  standing  upright,  the  cardiac  portion  (the  fundus  and  body 
together)  is  vertical,  and  the  smaller  pyloric  portion  is  directed  backward  and  to 
the  right  and  slightly  upward  (fig.  1125).  The  most  fixed  point  is  the  cardiac 
orifice. 

The  cardiac  orifice  lies  under  the  seventh  left  costal  cartilage  2  cm.  (f  in.)  from  the  sterno- 
xiphoid  junction  at  a  depth  of  about  10  cm.  (4  in.)  from  the  surface.  Behind,  this  point  corre- 
sponds to  the  tenth  thoracic  vertebra. 

The  pyloric  orifice  hes  in  the  transpyloric  plane  when  the  patient  is  recumbent,'but  when  the 
patient  is  standing  it  falls  to  the  level  of  the  second  or  third  lumbar  vertebra,  or  lower  still 

Fig.  1108. — Photograph  op  an  Empty  Stomach.     (J.  S.  B.  Stopford.) 


when"any  transient  faintness  or  nausea  causes  loss  of  muscular  tone  (Barclay).  The  pylorus  is 
slightly  to  the  right  of  the  middle  line  in  the  empty  stomach.  As  the  stomach  fiUs  it  descends 
farther  and  moves  a  little  farther  to  the  right.  The  lesser  curvature  presents  a  definite  notch  at 
the  junction  of  the  cardiac  and  pyloric  portions  of  the  stomach — the  incisura  angularis..  The 
greater  curvature  reaches  the  umbihoal  plane  in  the  erect  posture,  even  when  the  stomach  is 
empty.  When  the  viscus  is  full  tliis  curvature  lies  distinctly  below  this  plane,  being  lower  in 
women  than  in  men  (Hertz).  The  ■pyloric  portion  of  the  full  stomach  is  directed  backward 
and  a  httle  upward,  as  the  distended  pyloric  vestibule  moves  further  to  the  right  than  the  pyloric 
orifice  and  lies  on  an  anterior  plane.  In  the  recumbent  posture  the  greater  curvature  hes  above 
the  umbihcal  plane,  even  when  moderately  distended,  and  the  stomach  is  more  obliquely  placed. 
The  fundus  invariably  contains  gas,  even  when  the  stomach  contains  no  food,  in  which  case  the 
organ  forms  a  contracted  J-shaped  tube  (fig.  1108).  In  extreme  distention  the  left  dome  of  the 
diaphragm  is  so  pushed  up  by  the  fundus  that  it  lies  at  a  level  as  high  as  or  even  higher  than  the 


THE  INTESTINES  1375 

right  dome  (Hertz).  The  pressure  thus  exerted  on  the  heart  accounts  for  the  dyspnoea  and 
cardiac  pain  so  often  associated  with  flatulence.  The  position  of  the  pyloric  sphincter  is  shown 
on  the  outer  surface  by  a  very  constant  venous  ring  runrling  toward  both  lesser  and  greater 
curvatures  in  the  subserous  layer  at  right  angles  to  the  long  axis  of  the  pyloric  canal  (Moynihan). 

In  connection  with  the  extravasation  of  contents  that  results  from  perforating  ujcers  of  the 
stomach,  a  knowledge  of  the  subphrenic  peritoneal  fossaj  is  important  (p.  1372).  Perforation 
is  rare  on  the  posterior  surface  since  it  is  less  mobile  than  the  anterior,  and  protective  adhesions 
form  readily.  When  it  does  occur,  extravasation  into  the  omental  bursa  results,  and  suzih  a 
perforation  is  exposed  by  turning  up  transverse  colon  and  stomach  and  incising  the  transverse 
meso-colon.  Perforation  on  the  anterior  surface  usually  gives  rise  to  general  peritonitis,  but  in 
the  less  sarious  cases  an  abscess  may  form  localised  to  (l)  the  right  subphrenic  space,  (2)  the 
subhepatic  fossa,  or  (3)  the  left  subphrenic  space,  according  to  the  situation  of  the  ulcer  on  the 
stomach. 

The  Spleen  (fig.  1127;  see  also  figures  in  Sections  IX  and  XII). — This  lies  very 
obliquely  in  the  left  hypochondrium,  its  long  axis  corresponds  closely  with  the  line 
of  the  tenth  rib.  It  is  placed  opposite  the  ninth,  tenth,  and  eleventh  ribs  exter- 
nally, being  separated  from  these  by  the  diaphragm;  and  medially  it  is  connected 
with  the  great  end  of  the  stomach.  Below,  it  overlaps  slightly  the  lateral  border 
of  the  left  kidney  (fig.  1127).  Its  highest  point  is  on  a  level  with  the  spine  of 
the  ninth  thoracic,  and  its  lowest  with  that  of  the  eleventh  thoracic  vertebra. 
Its  upper  pole  is  distant  about  3.7  (1|  in.)  from  the  median  plane  of  the  body,  and 
its  lower  pole  about  reaches  the  mid-axillary  line  on  the  same  rib.  (Godlee.) 
In  the  natural  condition  it  cannot  be  felt;  but  if  enlarged,  its  notched  anterior 
margin  extends  downward  toward  the  umbilicus,  and  is  both  characteristic  and 
readily  felt. 

The  pancreas. — The  head  of  the  pancreas  lies  in  the  hollow  formed  by  the 
three  parts  of  the  duodenum,  on  the  bodies  of  the  second  and  third  lumbar 
vertebrae.  The  inferior  vena  cava  lies  behind  it.  The  neck,  body,  and  tail  of 
the  pancreas  pass  obliquely  to  the  left  and  slightly  upward,  crossing  respectively 
the  commencement  of  the  portal  vein,  the  aorta,  and  the  left  kidney.  The  root 
of  the  transverse  mesocolon  is  attached  to  the  anterior  margin  of  the  gland,  so 
that  its  supero-anterior  surface  is  related  to  the  omental  bursa,  and  its  inferior 
surface  to  the  greater  sac.  The  importance  of  this  relation  in  the  formation 
of  pancreatic  pseudo-cysts  has  been  referred  to  above. 

Pancreatic  ducts. — The  main  duct,  the  duct  of  Wirsung,  opens  into  the  common  ampulla  of 
Vater  with  the  bile  duct.  This  ampuUa  usually  opens  into  the  gut  by  a  narrow  orifice  raised 
on  a  small  papilla.  A  gaU-stone  impacted  in  the  ampulla  may  cause  a  flow  of  bile  backward 
along  the  duct  of  Wirsung,  and  so  give  rise  to  acute  pancreatitis  (Opie).  The  small  accessory 
duct  of  Santorini  opens  into  the  duodenum  independently  about  2  cm.  higher  up.  It  often 
anastomoses  with  the  larger  duct  in  the  substance  of  the  gland. 

Accessory  nodules  of  pancreatic  tissue  are  occasionally  met  with  in  the  walls  of  the  stomach 
or  small  intestine  at  diff'erent  regions. 

A  cyst  originating  in  the  pancreas  may  "point"  toward  the  anterior  abdominal  wall  by 
three  routes: — (1)  Above  the  stomach  through  the  lesser  omentum;  (2)  between  stomach  and 
transverse  colon  through  the  great  omentum;  (3)  below  the  transverse  colon  through  the  trans- 
verse mesocolon.  The  posterior  aspect  of  the  head  of  the  gland,  with  the  third  part  of  the 
common  bile  duct  may  be  exposed  by  incising  the  peritoneum  on  the  lateral  margin  of  the  second 
part  of  the  duodenum,  and  turning  the  gut  medially  toward  the  middle  line. 

Intestines.  (A)  Small. — The  average  length  of  the  small  intestine  is  about 
6.85  m.  (22|  ft.),  though  the  length  as  measured  post  mortem  varies  considerably 
with  the  degree  of  contraction  of  the  longitudinal  muscular  coat.  The  duodentma 
is  about  25  cm.  (10  in.)  in  length.  Of  the  remaining  portion  the  upper  two-fifths 
constitute  the  jejunum  and  the  lower  three-fifths  the  ileum,  though  this  division 
is  quite  arbitrary.  Cases  are  recorded  in  which  patients  have  survived  the  re- 
moval of  over  5  m.  (16  ft.)  of  small  intestine. 

The  first  part  -of  the  duodenum  extends  from  the  pylorus  on  the  first  or  second  lumbar  ver- 
tebra, backward  and  to  the  right.  It  ends  near  the  upper  pole  of  the  right  kidney  and  on  the 
medial  side  of  the  neck  of  the  gaU-bladder,  by  turning  down  to  form  the  less  mobile  second  -part, 
which  descends  in  front  of  the  hilum  of  the  right  kidney  to  the  level  of  the  third  lumbar  vertebra. 
The  third  part  of  the  duodenum  crosses  the  body  of  the  third  lumbar  vertebra  horizontally  in 
the  infracostal  plane,  and  then  turns  up  obliquely  to  the  left  side  of  the  spine  and  ends  at  the 
level  of  the  upper  border  of  the  second  lumbar  vertebra  in  the  duodeno-jejunal  flexure.  The 
first  part  is  the  most  mobile,  since  it  is  covered  back  and  front  by  peritoneum  in  the  first  half 
of  its  course.  The  second  part  has  a  peritoneal  covering  in  front  onlj'  and  is  devoid  of  it  where 
it  is  crossed  by  the  commencing  transverse  colon.  The  third  part  is  covered  by  peritoneum 
in  front  except  where  the  superior  mesenteric  vessels  pass  across  it  to  join  the  commencement  of 
the  mesentery.  It  is  probably  the  constricting  effect  of  these  vessels  on  the  duodenum  that 
gives  rise  to  the  acute  dilatation  of  the  stomach  which  occasionally  follows  abdominal  operations. 


1376  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

The  duodeno-jejunal  flexure,  which  hes  on  the  left  side  of  the  body  of  the  second  lumbar 
vertebra,  immediately  below  the  body  of  the  pancreas,  is  held  up  to  the  right  crus  of  the  dia- 
phragm by  a  band  of  fibro-muscular  tissue  known  as  the  suspensory  ligament  of  Treitz.  Some  of 
the  fibres  of  this  structui-e  are  continued  onward  into  the  root  of  the  mesentery.  It  is  not  found 
in  pronogxade  animals.  The  duodeno-jejunal  flexure  is  the  commonest  site  of  traumatic  rup- 
ture of  the  small  intestine,  since  it  is  the  point  of  union  of  a  fixed  and  a  freely  movable  portion 
of  the  gut. 

In  the  operation  of  posterior  gastro-enterostomy  the  duodeno-jejunal  flexm'e  is  readily 
found  by  passing  the  hand  along  the  under  surface  of  the  transverse  meso-colon  to  the  left  side 
of  the  spine,  the  omentum  and  colon  being  turned  upward.  The  first  coil  of  the  jejunum  is 
anastomosed  to  the  posterior  wall  of  the  stomach,  which  is  exposed  by  making  an  opening  in 
the  transverse  meso-colon. 

In  some  cases  the  first  few  centimetres  of  the  jejunum  are  found  to  be  fused  between  the 
layers  of  the  transverse  meso-colon.  Certain  peritoneal  fossas  are  often  found  on  the  left  side 
of  the  flexure.  They  may  give  rise  to  retro-peritoneal  hernia  and  strangulation  of  intestine. 
The  duodenal  fossaj  are  described  on  p.  1164. 

Jejunum  and  ileum. — The  mesentery  contains  between  its  two  peritoneal 
layers  the  superior  mesenteric  vessels  and  their  intestinal  branches,  the  superior 
mesenteric  plexus,  lacteals  and  many  lymph  nodes  on  their  course.  These 
nodes  are  frequently  enlarged  in  abdominal  tuberculosis  in  children  (tabes 
mesenterica) .  The  attached  border  of  the  mesentery  may  be  marked  out 
on  the  surface  by  a  line  drawn  from  just  below  the  transpyloric  plane  and  a  little 
to  the  left  of  the  middle  line  (the  duodeno-jejunal  flexure),  which  curves  downward 
and  to  the  right  to  end  in  the  iliac  fossa  at  the  junction  of  the  intertubercular 
and  right  lateral  vertical  lines  (the  ileo-caecal  valve). 

Meckel's  diverticulum  which  is  present  in  about  2  per  cent,  of  subjects  (Treves)  is  found  in 
the  free  border  of  the  ileum  30  cm.  to  1  m.  (1  to  3  ft.)  above  the  ileo-caecal  valve.  It  is  a  remains 
of  the  vitello-intestinal  duct.  It  is  usually  a  blind  conical  pouch  some  6  to  9  cm.  long  with  a 
free  extremity,  but  may  be  attached  to  the  umbihcus  by  a  fibrous  cord.  This  cord  may  cause 
acute  intestinal  obstruction  by  strangulating  a  coil  of  gut,  or  the  diverticulum  may  be  invag- 
inated  and  form  the  starting-point  of  an  intussusception. 

The  presence  of  aggregated  lymph  nodules  (Peyer's  patches)  in  the  lower  part  of  the  ileum 
accounts  for  the  fact  that  tuberculous  ulcers  and  perforating  typhoid  ulcers  are  almost  confined 
to  this  part  of  the  gut. 

Intestinal  localisation. — It  often  happens  that  the  surgeon  wishes  to  ascertain 
roughly  to  what  part  of  the  small  intestine  a  given  coil  presenting  in  a  wound 
belongs.  The  variations  in  length  of  the  small  intestine  and  the  considerablf 
range  of  movement  of  the  coils  during  peristalsis  render  the  problem  difficult, 
but  it  may  be  stated  as  a  general  rule  that  the  upper  third  of  the  intestine  lies 
in  the  left  hypochondrium  and  is  not  usually  encountered  in  a  wound;  the 
middle  third  occupies  the  middle  part  of  the  abdomen,  and  the  lower  third  lies 
in  the  pelvis  and  right  iliac  fossa  (Monks).  The  jejunum  is  thicker  walled  and 
more  vascular  than  the  ileum.  The  lumen  steadily  diminishes  as  we  pass 
downward,  hence  foreign  bodies  such  as  gall-stones  that  pass  through  the  jeju- 
num are  apt  to  become  impacted  in  the  lower  ileum. 

The  most  reliable  indications  of  the  level  of  a  given  coil  are  found,  however,  on  inspection 
of  the  mesentery  and  its  blood-vessels  (see  fig.  482  in  Section  V).  Opposite  the  upper  part  of 
the  bowel  the  mesenteric  arteries  are  arranged  in  a  series  of  large  primary  anastomosing  loops. 
From  these  the  vasa  recta  run  to  the  gut  3  to  5  cm.  long,  straight  and  unbranched.  Passing 
downward  toward  the  lower  end,  the  single  large  primary  loops  give  place  to  smaller  and  more 
numerous  secondary  loops  arranged  in  layers  coming  nearer  and  nearer  to  the  bowel.  Hence 
the  vasa  recta  become  shorter.  They  become  also  less  regular  and  more  branched,  and  in  the 
lower  third  of  the  small  intestine  are  less  than  1  cm.  in  length.  The  mesenteric  fat  in  the  upper 
third  never  reaches  quite  to  the  free  edge  of  the  meusentery,  so  that  clear  transparent  spaces 
are  left  near  the  bowel.  In  the  lower  third  the  fat  usually  occupies  the  whole  of  the  mesentery 
right  up  to  the  intestine,  and  makes  it  thicker  and  more  opaque.* 

The  average  width  of  the  mesentery,  from  its  root  at  the  posterior  parietes  to  the  bowel 
is  20  cm.  (8  in.)  and  the  longest  part  lies  between  2  and  8  m.  from  the  duodenum  (Treves). 
The  ileum  is  freely  movable  on  a  long  mesentery  down  to  the  ileo-C£ecal  region.  In  some  cases 
however  a  congenital  fusion  of  the  leit  half  of  the  mesentery  with  the  parietal  peritoneum  near 
the  pelvic  brim  binds  the  bowel  down  a  few  inches  above  the  ileo-ca3cal  valve,  and  has  been  said  to 
give  rise  to  symptoms  of  intestinal  stasis.     (Flint,!  Gray,  and  Anderson.) 

(B)  Large  intestine.  Ileo-csecal  region. — The  position  of  the  ileo-csecal 
valve  may  be  marked  on  the  surface  by  the  junction  of  the  intertubercular  and 
right  lateral  vertical  lines,  though  it  is  often  found  considerably  lower.  It  is 
situated  on  the  postero-medial  aspect  of  the  caecum.     The  caecum,  which  is  the 

*  Monks:  Trans.  Araer.  Surg.  Assoc,  1913. 

t  Bulletin,  Johns  Hopkins  Hospital,  Oct.,  1912. 


i 


THE  INTESTINES 


1377 


blind  extremity  of  the  colon  lying  below  the  horizontal  level  of  the  ileo-caecal 
valve,  is  approximately  6.2  cm.  (2|  in.)  in  both  vertical  and  transverse  diameters, 
though  its  size  varies  much  with  the  degree  of  distention.  It  lies  usually  in 
contact  with  the  anterior  abdominal  wall  above  the  lateral  half  of  the  inguinal 
ligament.  The  orifice  of  the  appendix  (vermiform  process)  lies  some  2  cm.  below 
the  ileo-cEecal  valve.  The  caecum  is  completely  covered  by  peritoneum  as  a 
rule,  though  exceptionally  its  posterior  surface  is  bound  down  in  the  right  iliac 
fossa. 

The  axial  rotation  of  the  midgut  and  descent  of  the  OEeeum  that  normally  take  place  dui'ing 
intra-u,terine  life  (p.  1168)  are  occasionally  not  completed,  with  the  result  that  the  cfficum  and 
appendix  may  be  found  above  and  to  the  left  of  the  umbilicus,  or  less  uncommonly  just  below 

Fig.  1109. — -Blood-vessels  of  the  Ileo-c.eal  Region.     (From  Kelly). 


the  right  lobe  of  the  liver  (3  per  cent.,  Alglave),  when  an  attack  of  appendicitis  may  simulate 
inflammation  of  the  gall-bladder.  On  the  other  hand  certain  cases  occur  in  which  the  CEBCum 
descends  unusually  far,  proceeding  downward  and  medially  until  it  becomes  a  pelvic  organ 
whenever  the  bladder  and  rectum  are  empty.  This  pelvic  position  of  the  ca;cum  is  found  in 
10  per  cent,  of  infants  (G.  M.  Smith).* 

In  the  commonest  form  of  intussusception,  the  ileo-caecal  valve  and  lower  ileum  are  pro- 
lapsed into  the  colon  and  carried  down  by  the  force  of  peristalsis  toward  the  anus.  The  valve 
in  these  cases  forms  the  apex  of  the  intussusceptum,  however  far  it  travels. 

*  Anat.  Record,  vol.  5,  1911,  p.  549. 


1378  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

The  vermiform  process  (appendix)  is  developed  at  the  apex  of  the  caecum, 
and  persistence  of  the  apical  appendix  of  foetal  type,  is  not  uncommon.  The 
fact  that  all  three  tsenis  coli  converge  at  the  base  of  the  appendix  is  an  anatomical 
reminder  of  its  primitive  position.  The  anterior  tsenia  is  of  great  service  in  opera- 
tions on  the  appendix,  since  by  following  it  down  from  the  colon  the  base  of  the 
appendix  can  alwaj^s  be  found.  The  adult  position  of  the  base  of  the  appendix 
on  the  postero-medial  aspect  of  the  caecum  is  due  to  the  disproportionate  growth 
of  the  lateral  saccule  of  the  caecum  which  comes  to  form  the  apparent  caecal  apex. 

The  appendix  averages  10  cm.  (4  in.)  in  length  in  the  adult.  The  position  of  its  base  only 
is  at  all  constant.  It  lies  distinctly  below  MoBurney's  point,  which  is  midway  between  the 
umbilicus  and  the  right  anterior  superior  iliac  spine.  This  point  is  often  the  seat  of  greatest 
tenderness  in  appendicitis.  The  appendix  itself  may  be  found  (1)  pointing  upward  and  to  the 
left  toward  the  spleen,  behind  the  terminal  ileum  and  mesentery;  (2)  hanging  over  the  pelvic 
brim,  in  which  position  tenderness  on  rectal  examination  or  pain  on  micturition  results  when 
the  organ  is  inflamed;  (3)  in  the  retro-colic  fossa;  and  (4)  with  its  tip  projecting  to  the  right  of 
the  csecum  in  the  right  lateral  paracolic  fossa,  where  it  causes  tenderness  when  inflamed  close 
to  the  anterior  superior  ihac  spine.  The  course  and  to  some  e.xtent  the  gravity  of  abscesses 
originating  in  the  appendix  will  depend  upon  the  position  the  inflamed  organ  is  occupying  at 
the  time  of  perforation. 

The  artery  of  the  appendix  derived  from  the  posterior  branch  of  the  ileo-eoUo  reaches  it  by 
running  down  behind  the  end  of  the  ileum.  It  raises  a  fold  of  peritoneum  called  the  mesen- 
terioluin  or  mesoappendix.  Very  rai-ely  the  artery  comes  from  the  anterior  branch  of  the 
ileo-colic. 

The  tmnice  coli  referred  to  above  as  converging  on  the  base  of  the  appendix  contribute  its 
longitudinal  muscular  coat.  The  inner  circular  coat  is  thicker,  but  along  the  attachment  of 
the  mesenteriole  certain  gaps  for  the  passage  of  lymph  and  blood-vessels  occur  in  the  muscular 
coats.  Through  these  gaps  infection  may  easily  spread  from  the  mucosa  to  the  peritoneum 
(Lockwood). 

The  appendix  is  essentially  a  lymph  gland  and  has  been  called  the  "abdominal  tonsil." 
The  lymph  follicles  he  in  the  submucosa.  They  are  poorly  developed  at  birth  but  reach 
their  fuU  development  within  the  first  few  weeks  of  extra-uterine  hfe  (Berry).*  ObUteration 
of  the  lumen  is  common  but  is  inflammatory  in  origin,  and  not,  as  was  once  thought,  a  change 
normal  in  advanced  age. 

Pericsecal  fossa. — In  addition  to  the  mesentery  of  the  appendix  certain  other  folds  of  per- 
itoneum are  usually  present  at  the  ileo-cffical  junction:  (1)  the  ileo-colic  or  anterior  vascular 
fold  (fig.  1109)  containing  the  anterior  branch  of  the  ileo-cohc  arterj^;  (2)  the  ileo-caecal,  or 
bloodless  fold  of  Treves,  running  from  the  lower  border  of  ileum  onto  the  ciEcum.  The  appen- 
dix may  be  in  a  fossa  behind  either  of  these  folds.  It  may  also  be  found  in  the  retro-colic  fossa 
lying  behind  the  cfficum  and  commencement  of  ascending  colon. 

The  colon  is  readily  distinguished  from  the  small  intestine  by  its  three  lon- 
gitudinal taeniae  and  saccules  and  by  the  appendices  epiploicse,  which  are  devel- 
oped before  birth. 

The  ascending  colon  runs  with  a  slight  lateral  convexity  upward  from  its 
junction  with  the  caecum  to  the  hepatic  flexure  which  lies  under  the  ninth 
right  costal  cartilage  at  the  level  of  the  second  lumbar  vertebra  and  in  contact 
with  the  anterior  surface  of  the  right  kidnej^  and  the  lower  surface  of  the  right 
lobe  of  the  liver.  It  lies  lateral  to  the  right  lateral  vertical  plane.  This  de- 
scription is  only  true  of  an  ascending  colon  examined  by  X-raj^s  in  the  recumbent 
position.  When  the  patient  stands  up,  the  flexure  sinks  to  the  infracostal 
plane  (third  lumbar  vertebra)  or  even  lower.  As  the  colon  ascends  in  the  angle 
between  the  quadratus  lumborum  and  psoas,  it  also  passes  backward  at  an  angle 
of  51°  ■ndth  the  horizontal,  as  may  be  seen  in  a  sagittal  section  through  the  right 
half  of  the  abdomen  (Coffey). f  The  caecum  and  ascending  colon  are  distended 
as  a  rule  with  fluid  contents  and  gas,  and  form  the  widest  part  of  the  colon. 

The  variations  in  the  peritoneal  attachments  of  the  colon,  which  are  of  growing  clinical 
importance,  are  explained  by  its  mode  of  development  (p.  1179).  During  intra-uterine  Ufe 
after  rotation  of  the  midgut  round  an  axis  formed  by  the  superior  mesenteric  vessels,  there  is 
a  stage  in  which  the  colon  has  almost  assumed  its  permanent  position  in  the  abdomen  but  is 
still  provided  with  a  free  mesocolon  for  both  ascending  and  descending  parts.  This  represents 
the  normal  condition  of  quadruped  mammals.  In  the  normal  human  individual  this  stage  is 
transient,  and  before  birth  the  ascending  and  descending  colons  lose  their  mesenteries  by 
fusion  of  the  posterior  layers  with  the  parietal  peritoneum.  Meanwhile  the  great  omentum, 
formed  by  a  bulging  out  of  the  primitive  dorsal  mesogastrium,  fuses  with  the  transverse  colon 
and  its  mesocolon.  The  extent  of  these  processes  of  fusion  varies,  particularly  as  far  as  the 
ascending  and  descending  colons  are  concerned.  Thus  only  52  per  cent,  of  adults  have  neither 
ascending  nor  descending  mesocolons  (the  normal  condition).  A  mesocolon  is  found  on  the 
left  side  in  36  per  cent,  of  all  cases  and  on  the  right  side  in  26  per  cent.  (Treves).     In  only  a 

*  Journ.  Anat.  and  Phys.,  vol.  35,  1900,  S3. 

t  Surgery,  Gynecology  and  Obstetrics,  vol.  15,  1912,  p.  390. 


i 


THE  KIDNEYS  1379 

small  proportion  (1.8  per  cent.,  however,  does  the  true  primitive  type  of  ascending  mesocolon 
persist,  continuous  with  the  mesentery  of  the  small  intestine  (G.  M.  Smith).  Such  an  anomaly 
renders  the  patient  liable  to  volvulus  of  the  ileo-0£ecal  region.  In  the  common  types  of  in- 
complete fusion  of  its  peritoneal  attachments  the  colon  is  inadequately  adapted  to  the  upright 
position  and  is  predisposed  to  ptosis.  A  layer  of  peritoneum  sometimes  found  passing  down- 
ward and  medially  from  the  parietes  in  the  right  flank  onto  the  front  of  the  ascending  colon, 
known  as  Jackson's  pericolic  membrane,  is  probably  due  to  persistence  of  an  early  stage  in  the 
development  of  the  great  omentum,  which  passes  to  the  right  across  the  ascending  colon  to 
join  with  the  parietal  peritoneum  before  the  descent  of  the  cjecum  is  complete,  and  so  is  the  most 
primitive  agent  in  fixing  the  proximal  colon  back  in  the  right  loin.  This  membrane  is  usually 
associated  with  a  congenitaUy  mobile  ascending  colon  (Morle}^.* 

At  the  hepatic  flexure  the  colon  bends  forward  and  to  the  left,  leaving  the  front  of  the  kidney 
to  which  it  is  fixed,  and  crossing  the  second  part  of  the  duodenum.  In  the  region  of  the  flexure 
three  inconstant  peritoneal  folds  are  met  with  giving  it  additional  attachment  to  the  neigh- 
bouring parts,  viz.,  (1)  the  phreno-colic  and  less  commonly  (2)  the  hepalo-colic  and  (3)  cysto- 
colic  hgaments  (Testut).  Thej'  must  not  be  confused  with  pathological  adhesions  acquired 
after  birth. 

The  transverse  colon  is  freely  mobile  except  at  its  extremities.  It  crosses  the 
abdomen  with  a  convexity  downward  and  forward,  being  separated  from  the 
anterior  abdominal  wall  in  the  middle  region  by  the  great  omentum. 

At  the  mid-line  it  usuaUy  lies  near  the  umbihcal  plane  in  the  recumbent  posture,  consider- 
ably lower  in  the  erect,  but  may  be  found  anywhere  from  the  infra-costal  plane  to  the  pubes, 
depending  on  the  tonicity  of  the  stomach.  Its  main  artery,  the  middle  colic  branch  of  the 
superior  mesenteric,  must  be  avoided  carefully  in  the  operations  of  gastro-enterostomy  and  gas- 
trectomy, since  hgature  of  it  causes  gangrene  of  the  transverse  colon. 

The  splenic  flexure  lies  far  back  in  the  left  hypochondrium  and  is  considerably 
higher  than  the  hepatic  flexure.  It  is  in  contact  with  the  lower  end  of  the  spleen, 
and  is  almost  invariably  held  firmly  in  position  by  its  -phreno-colic  ligament, 
derived  from  the  left  extremity  of  the  great  omentum. 

The  descending  colon  is  of  narrower  calibre  than  the  preceding  parts  and 
usually  is  found  firmly  contracted  and  empty.  It  passes  downward  and  forward 
in  the  angle  between  the  psoas  and  quadratus  lumborum  and  obliquely  across 
to  the  right  the  iliac  fossa  to  end  in  the  sigmoid  or  pelvic  colon.  The  lower  part 
of  the  descending  colon,  from  the  iliac  crest  to  the  pelvic  brim,  is  often  termed 
the  iliac  colon. 

In  its  upper  part  it  hes  in  front  of  the  convex  lateral  margin  of  the  left  kidney.  The  varia- 
tions in  its  peritoneal  attachments  have  been  referred  to  above  (p.  1242).  The  operation  of 
lumbar  colostomy,  common  in  pre-antiseptic  days,  was  performed  through  an  incision  in  the 
back  parallel  with  the  last  rib.  The  colon  lies  2.5  cm.  (1  in.)  to  the  lateral  side  of  the  edge  of 
the  sacro-spinalis,  between  the  twelfth  rib  and  ihac  crest.  The  occurrence  of  a  mesocolon  here 
was  a  common  source  of  difficulty  in  gaining  access  to  the  bowel  without  opening  the  peritoneum. 

The  pelvic  colon  (also  known  as  the  sigmoid  or  omega  loop  (Treves),  is  almost 
as  long  as  the  transverse  colon,  and  forms  a  loop,  the  two  ends  of  which,  at  the 
pelvic  brim  and  at  the  front  of  the  third  sacral  vertebra  respectively,  are  placed 
somewhat  closely  together.  The  loop  is  thus  anatomicallj^  predisposed  to  axial 
rotation,  and  is  the  commonest  seat  of  volvulus  in  the  whole  intestinal  tract. 

On  the  left  and  inferior  aspect  of  the  pelvic  mesocolon  near  its  base,  a  small  peritoneal 
fossa  {intersigmoid)  is  usually  found  in  the  angle  formed  by  the  root  of  the  mesocolon  and 
the  parietal  peritoneum.  It  occasionaUy  contains  an  internal  hernia  which  may  become 
strangulated. 

The  upper  part  of  the  pelvic  colon  is  frequently  brought  out  and  opened  tlirough  an  inci- 
sion in  the  left  iliac  region  to  form  an  artificial  anus  in  cases  of  inoperable  growth  of  the 
rectum. 

In  advanced  life,  and  in  the  chronically  constipated,  certain  diverticula  of  mucous  membrane 
are  occasionally  met  with  which  project  through  the  vascular  gaps  of  the  muscular  coat  into 
the  bases  of  the  appendices  epiploicse  in  this  region,  and  also  between  the  layers  of  the  pelvic 
mesocolon.  They  often  contain  foecal  concretions  and  may  become  inflamed  or  even  perforate, 
forming  an  abscess  in  the  left  ihac  fossa,  f 

The  junction  of  pelvic  colon  and  rectum  opposite  the  third  sacral  vertebra  forms  a  more  or 
less  acute  angle  and  constitutes  the  narrowest  part  of  the  colon.     It  is  a  frequent  site  of  stricture. 

The  kidneys. — These  lie  at  the  back  of  the  abdominal  cavity  so  deeply  in  the 
hypochondriac  and  epigastric  region  as  to  be  beyond  palpation  in  most  individuals, 
unless  enlarged  or  unduly  mobile.  The  lower  end  of  the  right  being  slightly 
lower  than  its  fellow,  encroaches  in  health  upon  the  lumbar  and  umbilical 
regions,  and  may  be  palpable  on  deep  inspiration  in  spare  subjects.     These 

*  Lancet.     Dec,  1913. 

t  McGrath:  Surgery,  Gynecology  and  Obstetrics,  vol.  15,  1912,  -129. 


1380 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


organs  lie  much  higher  and  nearer  to  the  vertebrae  than  is  usually  supposed  to  be 
the  case,  the  upper  two-thirds  of  the  right  and  all  the  left  kidney  being  behind 
the  ribs.  Relatively  to  the  vertebra3,  the  kidneys  lie  along  the  sides  of  the  last 
thoracic  and  the  first  three  lumbar. 

To  mark  them  in  from  the  front  the  following  points  should  be  noted:  The  upper  extremity 
of  the  right  should  reach  as  high  up  as  the  seventh  costal  cartilage,  the  left  up  to  the  sixth,  on 
either  side  close  to  the  costo-chondral  and  inter-cliondral  junctions.  This  level  will  corre- 
spond to  one  half  way  between  the  sterno-xiphoid  and  transpyloric  lines.     The  lower  end. 

Fig.  1110. — Renal  Fascia,  as  seen  in  Cross-section. 
Aorta  and  vena  cava 


Anterior  layer  of  renal  fascia 


Peritoneum 
Posterior  layer  of  renal  fascia 


about  11  cm.  (4|  in.)  below  this  point,  would  be  opposite  to  the  subcostal  line;  that  of  the  right 
kidney  is  usually  lower,  and  may  encroach  upon  the  umbilical  line.  For  practical  piu'poses 
the  hilus  is  opposite  a  point  on  the  anterior  abdominal  wall,  a  finger's  breadth  medial  to  the  tip 
of  the  ninth  costal  cartilage  (Stiles),  or  the  junction  of  the  transpyloric  and  lateral  vertical 
lines.  The  importance  of  the  relation  of  the  last  rib  has  been  mentioned  at  p.  1245.  The 
lateral  vertical  line  has  one-third  of  the  kidney  to  its  lateral  side,  and  two-thirds  to  its  medial 
side.  The  shortest  distance  between  the  two  kidneys,  obliquely  placed  so  as  to  be  closer  above, 
'at  the  upper  part  of  their  medial  borders'  (Thane  and  Godlee),  measures  about  6.2  cm.  (2|  in.). 
On  the  posterior  surface  of  the  body  the  ividney's  boundaries  are  indicated  by  the  following: 
— (1)  A  line  parallel  with,  and  2.5  cm.  (1  in.)  from,  the  mid-line,  between  the  lower  edge  of  the  tip 

Fig.  1111. — Renal  Fascia,  as  seen  in  Sagittal  Section. 
-Lung 


Suprarenal  gland 
—Kidney 

■Anterior  layer  of  renal  fascia 


Posterior  layer  of  renal  fascia 


of  the  spinous  process  of  the  eleventh  thoracic  and  the  lower  edge  of  the  spinous  process  of  the 
third  lumbar  vertebra;  (2)  and  (3)  lines  drawn  from  the  top  and  bottom  of  this  line  laterally, 
at  right  angles  to  it,  for  7  cm.  (2f  in.);  (4)  a  line  parallel  to  the  first,  and  connecting  the  ex- 
tremities of  (2)  and  (3).     Within  this  parallelogram  the  kidney  lies  (Morris). 

The  chief  relations  of  the  kidneys  are: — posteriorly — quadratus  lumborum, 
psoas,  diaphragm,  last  thoracic,  ilio-hypogastric,  and  ilio-inguinal  nerves.  The 
twelfth  rib  lies  behind  both,  the  right,  as  a  rule,  not  reaching  above  the  upper 
border.  The  left  often  reaches  the  eleventh  rib.  The  pleural  reflection  usually 
crosses  the  twelfth  rib  obliquely  reaching  below  its  neck.  Anteriorly — The 
liver,  right  colic  flexure  and  second  part  of  the  duodenum  (figs.  956  and  1009),  on 


THE  URETER 


1381 


the  right  side.     The  liver,  and  stomach  above,  the  body  of  the  pancreas  and  spleen 
over  the  centre,  and  the  descending;  colon  over  the  lower  part  of  the  left  kidney. 

The  attachments  of  the  specialised  fibrous  sheets  known  as  the  renal  fascia 
are  shown  in  figs.  1110  and  1111. 

The  anterior  and  posterior  layers  are  seen  to  be  continuous  above  and  laterally.  Medially 
and  below  they  remain  separate  and  it  is  in  this  dii-ection  that  the  abnormally  movable  kidney 
travels.  The  fatty  tissue  between  the  kidney  and  the  renal  fascia  is  known  as  the  perinephric 
fat;  that  outside  the  fascia  is  the  paranephi'ic  fat. 

The  kidneys  are  maintained  in  position  by  (1)  the  vascular  pedicle;  (2)  fatty 
capsule  and  fascia;  (3)  above  all  by  the  intra-abdominal  pressure. 

Failure  to  ascend  during  development  from  its  original  position  near  the  pelvic  brim  to 
its  normal  level  accounts  for  certain  cases  of  movable  kidney  of  congenital  origin.     In  these  cases 

Fig.  1112. — The  Abdominal  Aorta  and  Vena  Cava  Inferior, 


Gall-bladder 

Hepatic  duct 

Cystic  duct 

common  bile  duct 

Portal  vein  — 

Gastro-duodenal  br 

Right  gastric  art. 

Hepatic  artery 

Right  suprarenal  vein 

Inferior  suprarenal 
artery 

Renal  artery 
Renal  vem 

Inferior  vena  cava 

Kidney        ij 

Right  spermatic  vein 


Right  spermatic  artery 

Quadratus  lumborum 
muscle 

Lumbar  artery 
and  vein 
Uieteric       branch     of  — 
spermatic  artery 


Middle  sacral  vessels. 


Left  lobe  of  Uver 

(Esophagus 

Left  phrenic  artery 

Right  phrenic  artery 

Superior  suprarenal 
Left  gastric  artery 
Inferior  suprarenal 
Splenic  artery 

Left  phrenic  vein 
Left  suprarenal  vein 
Superior  mesenteric 

artery 
Kidney 

Ureteric  branch  of  renal 
Left  spermatic  vein 

Ureter 

Left  spermatic  artery 


Inferior  mesenteric 

artery 

Ureteric  branch  of 

spermatic 


Ureteric  branch  of 
common  iliac 

iliac  artery 


External  iliac  artery 
Hypogastric  artery 


the  renal  artery  may  take  origin  from  the  common  iliac  artery.  An  accessory  renal  artery 
running  into  the  lower  end  of  the  kidney  from  the  aorta  may  cause  kinking  of  the  ureter  and  is 
a  not  uncommon  cause  of  hydronephrosis. 

The  suprarenal  glands  are  not  so  firmly  attached  to  the  kidneys  as  to  the 
diaphragm;  hence  they  are  not  encountered  in  operations  for  movable  kidney  and 
are  not  removed  in  nephrectomy. 

Brode]  has  shown  that  incisions  into  the  kidney  should  be  made  rather  behind  its  convex 
border  (Brodel's  bloodless  line).  Occasionally  fusion  of  the  lower  poles  occurs  during  develop- 
ment across  the  middle  hue  of  the  body,  and  a  single  horseshoe  kidney  results,  with  double 
ureter  and  vascular  supply. 

The  ixreter. — On  an  average  30  cm.  (12  in),  long,  this  tube  descends  almost 
vertically  in  its  abdominal  course  on  the  psoas  muscle.     It  is  crossed  obUquely 


1382  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

by  the  spermatic  or  ovarian  vessels.  It  crosses  the  brim  of  the  pelvis  just  in 
front  of  the  bifurcation  of  the  common  iliac,  and  descends  on  the  side  wall  of  the 
pelvis  in  front  of  the  hypogastric  artery. 

The  abdominal  part  of  the  ureter  may  be  exposed  extraperitoneally  by  an  extension  for- 
ward of  the  usual  lumbar  renal  incision.  It  is  found  lying  between  peritoneum  and  psoas 
3.7  cm.  (IJ  in.)  from  the  middle  line  and  when  the  peritoneum  is  stripped  from  the  posterior 
abdominal  wall  the  ureter  is  invariably  carried  with  it. 

Aorta  and  iliac  arteries. — The  aorta  enters  the  abdomen  opposite  the  last 
thoracic  vertebra,  a  point  12  to  15  cm.  (5  to  6  in.)  above  the  umbilicus,  or  rather 
above  the  mid-point  between  the  infrasternal  depression  and  the  umbilicus 
(Thane  and  Godlee),  and  thence,  lying  to  the  left  of  the  mid-line,  divides  into  the 
two  common  iliacs  opposite  the  disc  between  the  third  and  fourth  lumbar  vertebrae, 
or  opposite  the  body  of  the  fourth  lumbar  vertebra.  This  point  is  about  2.5 
cm.  (1  in.)  below  and  to  the  left  of  the  umbilicus,  and  on  a  level  with  a  line 
drawn  across  the  highest  part  of  the  iliac  crest.  A  line  drawn  from  this  point, 
with  a  slight  curve  laterally,  to  just  medial  to  the  centre  of  Poupart's  ligament, 
will  give  the  line  of  the  iliac  arteries;  the  upper  third  of  this  line  giving  the  aver- 
age length  of  the  common  iliac.  The  relation  of  the  common  iliac  veins  is  shown 
in  fig.  1112.  The  right,  much  shorter  than  its  fellow,  lies  at  first  behind  and 
then  somewhat  lateral  to  its  artery.  The  left  is  at  first  to  the  medial  side  of 
its  artery,  and  then  behind  the  right.  At  the  upper  part  of  the  fifth  lumbar 
vertebra  behind  and  lateral  to  the  right  artery,  the  vena  cava  begins. 

The  site  of  some  of  the  branches  of  the  aorta  may  be  thus  approximately 
remembered  as  follows:  The  cceliac  artery  is  given  off  immediately  after  the  aorta 
has  perforated  the  diaphragm;  directly  below  this  is  the  superior  mesenteric 
artery.  About  2.5  cm.  (1  in.)  lower  down,  or  7.5  cm.  (3  in.)  above  the  umbilicus, 
the  renal  arteries  are  given  off.  About  2.5  cm.  (1  in.)  above  the  umbilicus  would 
be  the  level  of  the  inferior  mesenteric  artery.  The  relation  of  the  above  vessels  to 
the  transpyloric  line  (p.  1153)  is  as  follows:  (Stiles.)  The  cceliac  artery  is  two 
fingers'  breadth,  the  superior  mesenteric  one,  above  the  line,  the  renal  arteries  are 
a  finger's  breadth  below  it.  The  origin  of  the  inferior  mesenteric  is  midway  be- 
tween the  transpyloric  and  intertubercular  lines. 

Collateral  circulation  after  ligature  of  the  common  iliac. — The  chief  vessels  here  are: — 

ABOVE.  BELOW. 

Pubic  branch  of  inferior  epigastric  with  Pubic  branch  of  obturator. 

Internal  mammary  and  lower  intercostals  with  Inferior  epigastric. 

Lumbar  with  Ilio-lumbar  and  circumflex  iUac. 

Middle  sacral  with  Lateral  sacral  and  superior  gluteal. 

Superior  haemorrhoidal  with  Inferior  and  middle  haemorrhoidal. 

Ovarian  with  Uterine 
Collateral  circulation  after  ligature  of  the  external  iliac : — 

Internal  mammary,  lower  intercostals,  1         ■, .  t  <■    ■  •      *  • 

and  lumbar.  /  "^'^^  Inferior  epigastric. 

Ilio-lumbar,  lumbar,  and  gluteal  with  Deep  circumflex  iUao. 

Internal  and  external  circumflex  with  Superior  and  inferior  gluteal  (sciatic). 

Perforating  branches  of  profunda  with  Inferior  gluteal  (comes  nervi  ischiadici) . 

Circumflex  and  epigastric  with  Obturator. 

External  pudic  with  Internal  pudic. 

Collateral  circulation  after  ligature  of  the  internal  iliac : — 

Branches  of  profunda  with  Inferior  gluteal  (sciatic). 

Inferior  mesenteric  with  Hismorrhoidal  arteries. 

Vessel  of  opposite  side  with  Pubic  branch  of  obturator. 

Branches  of  opposite  side  with  Branches  of  pudic. 

Superior  and  inferior  gluteal  (sciatic)              with  Circumflex  and  perforating  of  profunda. 

Middle  sacral  with  Lateral  sacral. 

lUo-lumbar  and  superior  gluteal  with  Circumflex  iUac. 

THE  PELVIS 

The  male  pelvis  will  be  considered  first,  then  the  female  pelvis,  and  finally  a 
section  on  hernia. 

The  Male  Pelvis 

The  topics  under  this  heading  will  be  considered  in  the  following  order: 
boundaries  and  subdivisions,  scrotum  and  testis,  ductus  deferens  and  spermatic 


THE  MALE  PELVIS 


1383 


cord,  penis  and  urethra,  prostate,  bladder,  ischio-rectal  fossa,  rectum  and  anal 
canal. 

Bony  boundaries. — These  are  the  same  in  either  sex.  Above  and  in  front  is 
the  symphysis  pubis,  rounded  off  by  the  subpubic  ligament;  diverging  downward 
and  laterally  from  this  point  on  either  side  are  the  rami  of  the  pubes  and  ischia, 
ending  at  the  tuberosities  of  the  latter.  In  the  middle  line  behind  is  the  apex  of 
the  coccyx,  and  reaching  from  this  to  the  tuberosities  are  the  sacro-tuberous  (great 
sacro-sciatic)  ligaments,  to  be  felt  by  deep  pressure,  with  the  lower  border  of  the 
gluteus  maximus  overlapping  them. 

The  depth  of  the  perineum  varies  greatly — from  5  to  7. .5  cm.  (2  to  3  in.)  in  the  posterior 
and  lateral  part  to  2.5  cm.  (1  in.)  or  less  in  front.  In  the  middle  hne,  extending  longitudinally 
through  the  perineum,  is  the  raphe,  the  guide  to  the  urethra,  and  'the  line  of  safety'  (on  account 
of  the  small  size  of  the  vessels  here)  for  operations  on  it. 


Fig. 


1113. — ^Thb  Male  Perineum.     (Modified  from  Hirschfeld  and  Leveilld.) 
Bulbo-cavernosus 

Superficial  layer  of  uro-genital  trigone 
Ischio-cavernosus 

Muscles  of  thigh 


Post.  fern,  cutaneous  ni  rv 

Permeai  nerve  |         i 
Inferior  haemorrhoidal  nerve 
Cutaneous  branch  of  fourth  sacral 


Gluteus  maximus 
Tuberosity  of  ischium 
Sacro-tuberous  ligament 
Superficial  transversus  perinei 


Sphincter  ani  externus 


Subdivisions. — An  imaginary  line  drawn  transversely  across  the  perineum 
from  one  tuber  ischii  to  its  fellow  divides  the  lozenge-shaped  space  into  two 
triangles — (1)  An  anterior,  or  uro-genital;  and  2)  a  posterior,  or  rectal.  The 
pelvic  floor  includes  an  upper  or  pelvic  diaphragm  (formed  by  the  levator  ani  and 
coccygeus  on  each  side)  and  a  lower  incomplete  uro-genital  diaphragm  (or  trigone) . 

The  pelvic  diaphragm  (figs.  1113,  1114,  1115;  see  also  figs.  397,  399,  400) 
isYmade  up  of  the  levator  ani  coccygeus  muscles.  It  is  somewhat  funnel- 
shaped.  When  viewed  from  above  or  below  (fig.  395),  its  fibres  are  seen  to  form 
horseshoe-like  loops,  arising  on  either  side  anteriorly,  and  passing  posteriorly 
backward  around  the  uro-genital  apertures  to  be  inserted  chiefly  in  the  mid-line 
posteriorly.  The  pelvic  diaphragm  serves  primarily  for  the  support  of  the 
abdominal  viscera.  For  a  detailed  description  of  these  muscles,  as  well  as  those 
of  the  uro-genital  diaphragm,  see  section  on  the  Muscular  System. 


1384 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


The  xiro-genital  diaphragm  (or  trigone)  (fig.  400),  the  lower  diaphragm  of  the 
pelvic  floor,  is  both  morphologically  and  functionally  different  from  the  upper. 
The  uro-genital  diaphragm  is  a  sphincter  muscular  layer,  derived  (with  the  sphincter 
ani  externus)  from  the  primitive  sphincter  cloacae.  The  uro-genital  diaphragm  is 
composed  of  superior  and  inferior  fascial  layers,  enclosing  the  membranous  urethra, 
the  sphincter  urethrae  membranacese  and  the  transversus  perinei  profundus. 
Superficial  to  the  uro-genital  diaphragm  is  the  superficial  perineal  interspace 
(fig.  400).  This  is  covered  by  the  superficial  perineal  (CoUes')  fascia,  and  in- 
cludes the  crura  and  bulb  of  the  corpora  cavernosa,  with  associated  muscles, 
vessels  and  nerves. 

The  space  in  the  pelvic  floor  on  each  side  below  the  pelvic  diaphragm  is  the 
ischio-rectal  fossa  (figs.  399, 400, 1114).  In  the  posterior  or  rectal  triangle,  where 
the  urogenital  diaphragm  is  absent,  the  ischio-rectal  fossae  form  large  wedge-shaped 
spaces.  The  lowei-  wall  or  base  is  formed  chiefly  by  the  corresponding  skin  and 
superficial  fascia,  and  partly  by  the  external  sphincter  ani ;  the  medial  wall  by  the 

Fia.  1114. — Coronal  Section  of  the  Ischio-rectal  Fossa.    (G.  Elliot  Smith.) 


Falciform  process 


muscles  (levator  ani  and  coccygeus)  and  inferior  fascia  of  the  pelvic  diaphragm; 
the  lateral  wall  by  the  obturator  internus  muscle,  with  the  corresponding  obturator 
fascia  (with  Alcock's  canal,  incluchng  the  pudic  vessels  and  nerves) .  The  apex  of 
the  fossa  is  above,  where  medial  and  lateral  walls  meet.  The  narrow  fibrous  roof 
strip  joining  the  medial  and  lateral  walls  just  above  the  level  of  the  internal 
pudic  vessels  and  nerves  has  been  called  the  lamina  terminalis  (Elliot  Smith, 
fig.  1114).  Posteriorly  the  fossa  is  bounded  by  the  gluteus  maximus  and  lig. 
sacro-tuberosum.  Anteriorly  on  each  side  the  ischio-rectal  fossae  extend  as  narrow 
spaces  between  the  pelvic  diaphragm  above,  the  uro-genital  diaphragm  below,  and 
the  pelvic  wall  laterally  (figs.  400,  401,  402). 

Contents. — The  ischio-rectal  fossa  is  filled  with  loose  adipose  tissue  continuous  with  the 
subcutaneous  fat  of  the  buttock.  It  is  traversed  by  the  inferior  htemorrhoidal  branches  of 
the  internal  pudic  artery,  with  the  associated  veins  and  nerves,  passing  to  the  external  anal 
sphincter,  the  skin  and  the  adjacent  mucosa.  The  superficial  vessels  and  nerves,  as  the)' 
run  forward  to  pierce  the  superficial  perineal  fascia,  lie  in  this  space,  as  well  as  the  inferior 
clunial  (perforating  cutaneous)  branches  and  branches  of  the  fom'th  sacral  nerve.     The  inferior 


THE  MALE  PELVIS  1385 

hemorrhoidal  veins  traverse  the  fossa  obUquely  from  the  lateral  wall  downward  and  medially. 
They  are  usually  somewhat  dilated  near  the  anal  orifice,  and  when  morbidly  enlarged  constitute 
the  condition  known  as  htemorrhoids  ("piles")-  The  inner  opening  of  an  ana!  fistula  caused 
by  the  bursting  of  an  ischio-rectal  abscess  into  the  gut  is  usually  within  2  cm.  of  the  anal  margin, 
between  the  internal  and  external  sphincters. 

The  central  point  of  the  perineum  is  in  the  adult  nearly  an  inch  (2.5  cm.)  in 
front  of  the  anus,  or  midway  between  the  centre  of  the  anus  and  root  of  the  scro- 
tum. Here  the  following  structures  meet,  viz.,  the  levatores  ani,  the  two  trans- 
verse perineal  muscles,  the  bulbo-cavernosus,  and  the  sphincter  ani. 

The  comparative  weakness  of  the  attachment  of  the  sphincter  ani  in  front,  i.  e.,  not  into  a 
bony  point,  is  important  in  the  division  of  it,  as  in  operation  for  fistula.  The  sphincter  should 
never  be  cut  through  anteriorly,  especially  in  women,  where  its  attachment  here,  blending  with 
the  sphincter  vaginae,  is  a  very  weak  one.  This  point  also  corresponds  to  the  centre  of  the 
lower  margin  or  base  of  the  uro-genital  diaphi'agm  (triangular  ligament).  Its  development 
varies  much  in  different  bodies.  A  little  in  front  of  this  point  is  the  bulb,  with  the  corpus 
spongiosum  passing  forward  from  it.  This  would  also  be  the  level  of  the  artery  of  the  bulb, 
so  that  in  lithotomy  the  incision  should  always  begin  below  this  point.  A  knife  introduced 
at  the  central  point,  and  carried  backward  and  very  sUghtly  upward,  shoiild  enter  the  mem- 
branous urethra  just  in  front  of  the  prostate,  e.  g.,  iu  median  lithotomy  and  Cock's  external 
urethrotomy.     If  pushed  more  deeply,  it  would  enter  the  neck  of  the  bladder. 

In  median  lithotomy,  an  incision  3.7  cm.  (I5  in.)  long  is  made  tlirough  the  central  tendinous 
point  and  raphe,  so  as  to  hit  the  membranous  urethra.  The  following  structures  are  divided: — • 
Skin  and  fasciae;  some  of  the  most  anterior  fibres  of  the  external  sphincter  ani;  raphe  and 
central  tendinous  point;  minute  branches  of  transverse  perineal  vessels  and  nerves;  base  of 
uro-genital  diaphragm  Ln  centre;  membranous  m'ethra  and  constrictor  urethras. 

The  attachments  and  arrangements  of  the  superficial  fascia  (fig.  1115)  must  be 
traced  and  remembered.  If  the  two  layers  of  which  it  consists,  the  superficial 
alone  extends  over  both  urethral  and  rectal  triangles  alike,  and  is  continuous  with 
the  similar  structures  in  adjacent  regions,  the  only  difference  being  that,  if  traced 
foward  into  the  scrotum  and  penis,  it  loses  its  fat,  and  contains  dartos  fibres. 
The  deeper  layer,  found  only  over  the  urethral  triangle,  is  called  the  fascia  of  CoUes 
(fig.  1115).  Attached  at  the  sides  to  the  rami  of  the  pubes,  behind  to  the  base  of 
the  uro-genital  trigone  or  diaphragm,  and  open  in  front,  it  forms  the  superficial 
wall  of  a  somewhat  triangular  pouch,  limited  behind  by  the  uro-genital  trigone, 
and  containing  the  superficial  vessels,  nerves,  and  muscles,  the  bulb,  adjacent 
part  of  the  urethra,  and  crura  of  the  penis.  Owing  to  this  space  being  closed  behind 
and  open  in  front,  and  to  its  containing  the  above  structures,  fluids  extravasated 
within  this  space  will  obviously  tend  to  make  their  way  forward  into  the  scrotum, 
penis,  and  lower  part  of  the  abdominal  wall. 

The  uro-genital  triangle  is  subdivided  into  two  planes  by  the  inferior  fascia  of 
the  uro-genital  diaphragm  and  fascia  of  Colles.  The  structures  in  the  swperficial 
-plane,  between  the  uro-genital  diaphragm  and  the  fascia  of  Colles,  have  been 
given  above.  Those  in  the  deeper,  i.  e.,  between  the  two  layers  of  fascia  of  the 
diaphragm,  are — (1)  The  membranous  urethra;  (2)  deep  transverse  perineal 
muscle  and  sphincter  of  the  membranous  urethra;  (3)  the  bulbo-urethral  (Cow- 
per's)  glands;  (4)  and  (5)  part  of  the  pudic  artery  and  nerve,  and  branches. 

The  scrotum. — The  skin  of  the  scrotum  is  thin  and  delicate  so  that  when 
distended,  as  by  a  hydrocele  in  the  tunica  vaginalis,  it  is  remarkably  translucent. 
Attached  to  its  deep  aspect  is  a  layer  of  involuntary  muscle,  the  dartos.  When 
the  dartos  is  contracted,  as  under  the  influence  of  cold,  the  scrotal  skin  becomes 
rugose. 

To  this  tendency  to  wrinkling,  with  consequent  irritation  from  retained  dirt,  and  the 
presence  of  many  sweat  glands  the  frequency  of  epithehoma  in  this  part  is  due.  The  dartos  is 
apt  to  cause  inversion  of  the  skin  in  wounds  of  the  scrotum,  but  this  difficulty  in  suturing  may 
be  counteracted  by  the  application  of  a  hot  sponge,  which  relaxes  the  muscle. 

The  superficial  fascia  of  the  scrotum  is  continuous  with  the  fascia  of  Colles  and  the  super- 
ficial fascia  of  the  penis.  Hence  extravasation  of  urine  under  the  fascia  of  Colles's  balloons  the 
scrotum  and  penis.  The  laxity  of  the  areolar  tissue  under  the  dartos  accounts  for  the  great 
swelling  that  occurs  in  cedema  of  this  part. 

The  lymphatics  of  the  scrotum,  important  by  reason  of  the  e.\ten.sion  of 
scrotal  cancer,  drain  into  the  superficial  inguinal  nodes.  Those  from  the  anterior 
aspect  nearest  the  median  raph6  run  to  the  supero-lateral  glands  of  this  group, 
within  a  few  cm.  of  the  anterior  superior  spine.* 

*  Morley:     Lancet,  1911  (ii),  p.  1545. 


1386 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


The  numerous  large  sebaceous  glands  that  are  found  in  the  skin  of  the  scrotum  may  give 
rise  to  cysts  or  adenomata.  The  deeper  layers  of  the  scrotum  are  derived  from  the  abdom- 
inal wall,  being  brought  down  by  the  processus  vaginalis  in  the  descent  of  the  testis. 

Testis  and  epididymis. — The  left  testis,  the  first  to  descend,  lies  somewhat 
lower  in  the  scrotum,  and  this  fact  is  one  reason  of  the  frequency  with  which  a 


Fig.  1115. — The  Arteries  of  the  Perineum. 


Perineal  vesseli 


-cavernosus 


Colles's  fascia,  turned  back 


Ischio-cavernosus 

Transverse  perineal  vessels 
Cut  edge  of  uro-genital 
trigone 
Perineal  nerve  giving  off 
transverse  branch 

Pudic  vessels 


Dorsal  artery  of  penis 
Deep  artery  of  penis 


Artery  of  bulb 
Bulbo-urethral  gland 
Pudic  artery 

Sacro -tuberous  ligament 

Levator  ani 

External  sphincter  ani 

Gluteus  maximus 


Fig 


Symphysis  pub: 


Transverse  fold 
Vesicula  seminalis 

rJ-Ductus  ejaculatorius 
L  Prostate 

^—External  sphincter 
f- Internal  sphincter 

.External  sphincter 


varicose  condition  of  the  spermatic  veins  occurs  on  the  left  side.  On  palpation 
the  Smooth  firm  body  of  the  testis,  pressure  on  which  causes  the  characteristic 
"testicular  sensation"  can  be  felt  to  lie  in  front  of  and  rather  medially  to  the 
epididymis.  The  three  parts  of  the  latter^  the  caput  above,  the  body,  and  the 
Cauda  epididymidis  below,  can  also  be  distinguished.     Running  upward  from  the 


THE  TESTIS  1387 

back  of  the  epididymis  to  the  subcutaneous  inguinal  ring  the  spermatic  cord  can 
be  felt.  The  bulk  of  the  cord  is  made  up  of  its  coverings,  of  which  the  cremaster 
muscle  is  the  most  considerable,  and  of  the  pampiniform  plexus  of  veins.  On  roll- 
ing the  cord  between  the  finger  and  thumb  the  ductus  deferens  can  be  felt  like 
a  piece  of  whipcord  in  the  posterior  part. 

The  ductus  (vas)  deferens  is  thickened  and  nodular  in  tuberculous  epididymitis.  In  vari- 
cocele the  dilated  and  elongated  veins  of  the  pampiniform  plexus  feel  on  palpation  like  a  bag 
of  worms  in  the  scrotum.  It  is  important  that  the  student,  before  studying  diseased  con- 
ditions, should  make  himself  familiar  with  the  feel  of  the  normal  parts  as  mentioned  above  and 
be  able  to  identify  them. 

Underneath  the  visceral  layer  of  the  tunica  vaginalis,  the  body  of  the  testis  is  covered  by 
a  dense  fibrous  layer,  the  tunica  albuginea,  which  accounts  for  the  small  extent  of  swelling  in 
orchitis  as  compared  with  epididymitis.  The  lymphatics  of  the  testis  run  up  in  the  spermatic 
cord  through  the  inguinal  canal,  and  accompanying  the  spermatic  vessels  end  in  the  lumbar 
lymph  nodes,  below  the  level  of  the  renal  arteries.  These  nodes  may  be  reached  and  removed 
along  with  the  vessels  by  making  an  incision  in  the  loin  above  the  inguinal  (Poupart's) 
ligament,  and  stripping  the  peritoneum  off  the  posterior  abdominal  wall. 

On  the  right  side  of  the  perineum  (left  side  of  this  figure)  CoUes's  fascia  has  been  turned  back 
to  show  the  superficial  vessels.  On  the  left  side  the  superficial  vessels  have  been  cut  away  with 
the  anterior  layer  of  the  uro-genital  trigone  to  show  the  deep  vessels. 

The  epididymis  is  the  convoluted  first  part  of  the  duct  of  the  testis,  about  6  m.  (20  feet) 
in  length.  Its  three  portions  are  in  differing  connection  with  the  testis.  Thus  the  cauda  is 
held  in  place  by  connective  tissue,  the  body  by  the  same  medium;  the  caput  by  the  vasa  efferentia. 
Thus,  when  tubercular  disease  begins  here,  the  testis  itself  is  more  likely  to  be  early  involved. 

Ductus  deferens. — -The  two  extremities  and  the  course  of  this  involve  several  practical 
points.  About  4.5  cm.  (18  in.)  long,  it  begins,  convoluted  at  first  and  with  a  distinct  bend 
upward,  in  the  cauda  epididymidis.  It  thence  passes  almost  vertically  upward  at  the  back  of 
the  testis  and  cord  to  the  tubercle  of  the  pubes.  Entering  the  canal,  it  lies  on  the  grooved  upper 
aspect  of  the  inguinal  (Poupart's)  ligament,  and  then  under  the  arching  fibres  of  the  internal 
oblique  and  transversus,  upon  the  transversalis  fascia.  Its  position,  characteristic  feel,  and 
yellowish  aspect  are'  well-known  guides  in  operations  for  varicocele  and  hernia,  while  it  is  always 
to  be  isolated  and  palpated  when  tubercular  disease  below  is  suspected.  Leaving  the  canal 
by  the  abdominal  inguinal  ring,  it  hooks  round  the  inferior  epigastric  artery  and  then  descends 
into  the  pelvis  over  the  external  iliac  vessels.  Continuing  its  course  downward  and  backward 
over  the  side  of  the  pelvis,  it  arches  backward  over  the  side  of  the  bladder,  superficial  to  the 
obliterated  hypogastric  artery,  and  then  deep  to  the  ureter.  The  two  ducts  now  help  to  form 
the  lateral  boundaries  of  the  external  trigone,  between  the  base  of  the  bladder  and  the  rectum. 
They  here  become  dilated  and  sacculated  and  then  contract  again  to  empty  into  the  ejaculatory 
ducts. 

The  vesiculae  seminales  are  diverticula  growing  out  from  the  lower  end  of  the  deferential 
ducts  at  an  acute  angle,  one  on  each  side.  They  lie  below  and  lateral  to  the  deferential  ducts 
and  are  related  in  front  to  the  base  of  the  bladder  and  posterior  surface  of  the  prostate,  behind 
to  the  rectum,  and  above  to  the  reoto-vesical  pouch  of  peritoneum,  which  also  descends  to  cover 
the  upper  part  of  their  posterior  aspect.  The  normal  vesiculae  seminales  can  scarcely  be  dis- 
tinguished from  the  base  of  the  bladder  on  rectal  palpation,  but  when  diseased,  as  in  tuberculous 
or  gonorrhoeal  vesiculitis,  are  enlarged  and  indurated  and  can  be  detected  readily. 

The  ejaculatory  ducts,  formed  by  the  union  of  the  vesicular  and  deferential  duct  of  each 
side,  are  2-2. .5  cm.  in  length.  The  first  few  millimeters  of  their  course  is  extra-prostatic,  and 
then  entering  the  posterior  surface  of  the  prostate  they  run  side  by  side  downward  and  forward 
through  the  gland,  close  to  the  middle  line,  to  open  into  the  urethra  on  the  colliculus  seminalis 
at  either  side  of  the  opening  of  the  prostatic  sinus.  It  is  by  these  little  ducts  that  infection 
travels  from  the  urethra  to  the  vesiculas  and  epididymis  in  gonorrhoea. 

Descent  of  the  testis. — -The  testis  is  developed  between  the  tenth  and  twelfth  thoracic 
segments  of  the  embryo,  and  subsequently  moves  downward.  By  the  third  month  of  intra- 
uterine life  it  descends  into  the  iliac  fossa;  from  the  fourth  to  the  seventh  month  it  hes  at  the 
abdominal  inguinal  ring;  during  the  seventh  month  it  passes  obliquely  through  the  abdominal 
wall  by  the  inguinal  canal;  by  the  eighth  month  it  lies  at  the  subcutaneous  inguinal  ring,  and  it 
reaches  the  fundus  of  the  scrotum  about  the  time  of  birth.  The  left  testis  is  slightty  earlier 
than  the  right  in  all  these  stages.  The  descent  referred  to  is  due  in  part  to  the  common  descent 
of  organs,  associated  with  the  descent  of  the  diaphragm,  but  mainly  to  the  gubernaculum.  This 
is  a  mass  of  fibro-muscular  tissue  that  forms  under  the  inguinal  fold  (or  plica  gubernalrix)  of 
peritoneum  below  the  testis  as  it  lies  in  the  iliac  fossa,  and  in  the  mesorchium.  It  grows  down 
obliquely  through  the  abdominal  wall  from  a  point  lateral  to  the  inferior  epigastric  artery,  and 
tunnels  out  a  passage  for  the  testis.  As  it  travels  down  into  the  scrotum  it  carries  in  front  of 
it  three  layers  of  investing  fascia  derived  from  the  abdominal  wall,  viz.,  e.xternal  spermatic 
fascia  from  the  external  oblique,  cremasteric  from  internal  oblique  and  transversus  muscles, 
and  infundibuliform  fascia  from  the  transversalis  fascia.  The  gubernaculum  is  attached  above 
to  the  peritoneum  and  the  posterior  aspect  of  the  testis,  and  by  its  subsequent  contraction  it 
draws  down  into  the  scrotum  first  a  diverticulum  of  peritoneum,  the  processus  vaginalis,  and 
secondly  the  testis,  which  projects  into  the  processus  from  behind  just  as  it  did  into  the 
coelom. 

Shortly  after  birth,  obliteration  of  the  processus  vaginalis  should  occur,  commencing  at 
the  deep  abdominal  ring  and  immediately  above  the  testis.  The  part  of  the  processus  between 
these  two  points  disappears  completely.  The  lowest  part,  surrounding  the  testis,  persists  as 
the  tunica  vaginalis.     Failure  of  obliteration,  if  complete,   leaves  a  congenital  hernial  sac;  if 


1388 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


only  the  upper  part  perists,  and  does  not  communicate  with  the  tunica  vaginalis,  it  is  called  a 
funicular  sac.  Cysts  originating  in  the  processus  vaginalis  between  the  upper  and  lower 
points  of  primary  occlusion  are  known  as  encysted  hydrocele  of  the  cord. 

tTndescended  testis. — It  occasionally  happens  that  descent  of  the  testis  fails  on  one  or 
both  sides,  and  in  these  cases  the  organ  may  remain,  (1)  in  the  iliac  fossa,  (2)  in  the  inguinal 
canal,  or  (3)  at  the  subcutaneous  ring.  Deprived  of  the  protection  normally  afforded  against 
injury  bj^  the  scrotum  and  tunica  vaginalis,  the  misplaced  testis  is  subject  to  trauma,  shows  a 
tendency  to  torsion  of  its  pedicle  owing  to  its  long  mesorohium,  and  sometimes  becomes  the 
seat  of  malignant  disease.  A  funicular  hernial  sac  is  generally  present.  Such  testes  are  atro- 
phic and  functionally  deficient,  and  it  is  probably  owing  to  their  small  size  at  an  early  stage  that 
the  gubernaculum  fails  to  gain  a  hold  on  them.  It  has  been  shown  by  Bevan*  that  in  unde- 
scended testis  the  ductus  deferens  is  usually  long  enough  to  allow  the  organ  to  be  placed  in  the 
bottom  of  the  sci-otum  by  the  surgeon  without  tension  provided  that  the  spermatic  artery  and 
pampiniform  plexus  of  veins  are  divided.  The  blood-supply  of  the  organ  is  then  entirely 
derived  frotn  the  deferential  artery,  a  branch  of  the  superior  vesical.  In  rare  cases  the  testis 
descends  in  a  wrong  direction  (ectopia  testis)  and  comes  to  he  in  the  perineum,  over  Scarpa's 
triangle,  or  on  the  pubes. 

Penis. — The  subcutaneous  tissue  of  the  penis,  as  on  the  scrotum,  is  devoid 
of  fat  and  the  delicate  skin  is  very  mobile  and  distensible,  hence  the  ballooning 
of  these  parts  in  extravasation  of  urine  or  cedema.  The  fascia  penis  is  continuous 
with  CoUes's  fascia. 

In  radical  amputation  of  the  penis  for  malignant  disease  the  whole  organ,  including  the 
crura,  is  removed  through  an  incision  that  splits  the  scrotum,  and  the  stump  of  the  corpus 
spongiosum  (corpus  cavernosum  urethras)  is  brought  out  into  the  perineum  behind  the  scrotum. 

The  preputial  orifice  varies  greatly  in  size.     Normally  large  enough  to  allow  easy  retrac- 

FiG.  1117. — Cross-section  op  Penis. 

Dorsal  artery  y  |       /Deep  dorsal  ^ 


Tunica  albuginea 


Tunica  albuginea- 


Corpus  cavernosum  penis 

Fibrous  sheatli  of  penis 


Artery 


Urethra 
Corpus  cavernosum  urethrse  (spongiosum) 

tion  of  the  prepuce  from  off  the  glans,  it  is  frequently  so  small  that  retraction  is  impossible 
and  it  may  even  cause  difficulty  in  micturition.  The  mobility  of  the  skin  over  the  penis  must 
be  borne  in  mind  in  the  operation  of  circumcision,  and  care  taken  lest  too  much  of  the  prepuce 
be  removed,  leaving  insufficient  skin  to  cover  the  penis.  In  this  operation  the  vessels  from  which 
bleeding  occurs  lie,  (1)  on  the  dorsum,  (2)  in  the  frenum. 

Congenital  malformations  of  penis. — At  an  early  stage  of  development  the  urethra  opens 
on  the  inferior  aspect  of  the  penis  behind  the  glans.  After  the  ingi-owth  of  epithelium  that 
forms  the  glandular  urethi-a,  this  primitive  meatus  should  close.  Occasionally,  however,  it 
persists,  and  the  glandular  urethra  is  represented  by  a  groove  on  the  under  aspect  of  the  glans. 
In  these  cases  of  hypospadias  the  glans  is  flexed  on  the  penis  and  the  prepuce  is  deficient  IdbIow 
and  has  a  pecuhar  "hooded"  appearance.  In  epispadias  the  upper  wall  of  the  m-ethra  and 
corresponding  part  of  the  corpora  cavernosa  are  absent.  This  condition  is  usually  present 
in  cases  of  ectopia  vesicas. 

The  male  urethra  is  about  20  cm.  (8  in.)  in  length,  consisting  of  the  cavernous 
portion,  16  cm,  (6|  in.),  membranous  1  cm.  (|  in.)  and  prostatic  3  cm.  (IJ  in.). 
The  narrowest  part  is  the  external  orifice,  and  next  to  it  the  membranous 
urethra.  The  prostatic  urethra  is  the  widest  and  most  dilatable.  The  bulbous 
urethra,  just  in  front  of  the  uro-genital  diaphragm,  is  wider  than  the  rest  of  the 
penile  portion,  but  since  it  forms  the  most  dependent  spot  in  the  fixed  part  of 
the  urethra  (from  bladder  to  suspensory  ligament  of  penis) ,  it  is  specially  prone 
to  gonorrhoeal  stricture.  Behind  the  bulb,  the  urethra  narrows  suddenly  as  it 
passes  through  the  uro-genital  diaphragm  and  contraction  of  the  sphincters  of 

*  Journ.  Amer.  Med.  Assoc,  vol.  41,  1903,  p.  718. 


THE  PROSTATE  1389 

the  membranous  urethra  may  here  give  additional  difficulty  in  the  passage  of 
a  catheter. 

False  passages  most  commonly  occur  through  the  floor  of  the  bulb  on  account  of  this, 
difficulty  in  entering  the  membranous  urethi-a.  The  point  of  a  small  catheter  may  also  be 
caught  in  the  following  apertm'es:  (1)  The  lacuna  magna  in  the  roof  of  the  fossa  navicularis 
of  the  glandular  urethra;  (2)  other  crypts  or  lacunae  in  the  penile  part,  mostly  situated  in  the 
upper  wall;  (3)  the  prostatic  sinus  in  the  floor  of  the  prostatic  urethra  about  its  centre.  With 
the  penis  raised  the  urethra  presents  a  simple  cm-ve  under  the  symphysis  with  the  proportions 
of  an  ordinary  silver  catheter. 

It  is  in  the  region  of  the  uro-genital  diaphragm  that  the  urethra  is  most  liable  to  be  damaged 
by  a  fall  or  blow,  and  the  urine  extravasated  as  a  result  will  be  beneath  CoUes's  fascia.  In 
rupture  of  the  membranous  urethra  urine  may  find  its  way  in  front  of  the  inferior  fascia  of  the 
uro-genital  diaphragm  by  coexisting  injury  to  this,  or  tlirough  openings  in  the  vessels,  etc.; 
in  a  few  such  cases  urine  will  make  its  way  backward  behind  the  fascia  into  the  space  of 
Retzius,  ascending  thence  between  the  peritoneum  and  transversahs  fascia.  The  attachment 
of  the  deep  layer  of  superficial  fascia  to  the  base  of  the  m-o-genital  diaphragm  accounts  for  the 
fact  that  urine  extravasated  from  a  ruptured  m'ethra  or  thi-ough  an  opening  behind  a  stricture 
passes  not  backward  into  the  anal  triangle,  but  forward  onto  the  scrotum  and  abdominal  wall. 

The  prostate  consists  of  a  mass  of  racemose  glandular  tubules  imbedded 
in  a  fibro-muscular  stroma,  that  surrounds  the  first  part  of  the  urethra  and  lies 
below  the  neck  of  the  bladder.  Its  base  is  intimately  connected  with  the  bladder 
by  the  continuation  of  vesical  and  urethral  mucous  membrane  and  by  the  inser- 
tion of  the  outer  longitudinal  muscular  coat  of  the  bladder  into  the  gland.  The 
inner  circular  muscle  fibres  of  the  bladder  become  specialised  round  the  internal 
urethral  orifice  to  form  the  internal  sphincter. 

Adenomatous  enlargements  of  the  gland  usually  grow  upward  through  this  sphincter  which 
is  thus  dilated  and  pushed  aside,  so  that  the  glandular  growth  is  covered  only  by  vesical  mucous 
membrane. 

The  apex  of  the  prostate  hes  at  the  level  of  the  lower  border  of  the  pubic 
symphysis  and  1.5  cm.  behind  it.  It  is  firmly  fixed  to  the  superior  fascia  of  the 
uro-genital  diaphragm  (deep  layer  of  the  uro-genital  trigone)  and  here  the  urethra 
leaves  it  to  become  the  membranous  part.  The  anterior  surface  directed 
vertically  lies  2  cm.  behind  the  lower  part  of  the  pubic  symphysis  in  relation  to 
the  prostatic  plexus  of  veins;  and  from  it  the  dense  pubo-prostatic  ligaments 
run  forward  on  either  side  to  the  pubes.  The  posterior  surface  is  in  contact  with 
the  rectum,  through  the  anterior  wall  of  which  it  may  be  palpated  4  cm.  (I5  in.) 
above  the  anal  margin.  It  is  separated  from  the  rectum  by  the  two  layers  of 
the  recto-vesical  septum  (Elliot  Smith).*  The  lateral  surfaces  are  supported 
by  the  anterior  fibres  of  the  levator  ani,  from  which,  however,  they  are  separated 
on  each  side  by  a  dense  mass  of  fibrous  tissue  in  which  the  pudendal  (prostatic) 
plexus  of  veins  is  imbedded. 

The  prostatic  urethra  traverses  the  gland  nearer  the  anterior  than  the  pos- 
terior surface,  with  a  slight  forward  concavity.  Its  floor  is  placed  posteriorly 
and  presents  an  eminence,  the  colliculus  seminalis,  about  the  centre  of  which  is 
the  orifice  of  the  prostatic  sinus,  on  either  side  of  which  open  the  common  ejacu- 
latory  ducts.  The  prostate  is  indefinitely  divided  into  two  lateral  lobes.  The 
fissure  uniting  them  across  the  middle  line  in  front  of  the  urethra  (the  anterior 
commissure)  is  fibro-muscular  and  contains  no  glandular  tissue.  Behind  the 
urethra  the  lateral  lobes  are  continuous  and  the  portion  of  gland  Ijang  between 
bladder,  ejaculatory  ducts  and  urethra  has  been  erroneouslj^  termed  the  "middle 
lobe."  Though  not  a  separate  lobe  anatomically,  adenomatous  hypertrophy 
of  this  part  is  common,  when  it  projects  up  into  the  bladder,  and  prevents  the 
proper  emptying  of  that  organ. 

Capsule  and  sheath  of  the  prostate. — In  senile  enlargement  of  the  prostate  removal  may  be 
effected  by  the  suprapubic  or  by  the  perineal  route.  In  the  former,  the  bladder  is  opened 
above  the  pubes,  the  mucous  membrane  lying  over  the  gland  as  it  projects  into  the  bladder  is 
scratched  through  behind,  and  with  the  finger  the  whole  adenomatous  mass  is  enucleated. 
This  process  usually  involves  tearing  out  the  whole  of  the  prostatic  m-ethra,  and  the  ejaculatory 
ducts.  The  parts  left  behind  consist  of  (1)  the  "capsule"  which  is  simply  the  outer  part  of 
the  gland  proper  stretched  over  the  adenomatous  mass,  and  consists  of  fibro-muscular  tissue 
with  a  few  flattened  glandular  tubules  (C.  Wallace). f  Outside  this  (2)  the  fibrous  "sheath" 
is  derived  from  the  visceral  layer  of  pelvic  fascia,  in  which  is  imbedded,  on  the  anterior  and 
lateral  aspects  of  the  gland,  the  prostatic  plexus.     Since  these  veins  are  not  torn  there  is  com- 

*  Studies  in  Anatomy  of  the  Pelvis.     Journ.  Anat.  and  Physiol.,  vol.  42,  190S. 
t  C.  Wallace.     Prostatic  Enlargement,  1907. 


1390  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

paratively  little  hfemorrhage.  In  the  perineal  operation  the  posterior  surface  of  the  gland  is 
exposed  by  cutting  through  the  perineum  between  the  bulb  and  external  sphincter  ani,  and 
dividing  the  attachment  of  the  recto-m-ethi-al  muscle  to  the  m-o-genital  diaphragm  and  its  in- 
ferior fascia.  This  exposes  the  back  of  the  recto-vesioal  septum  (aponeurosis  of  DenonvilKers) 
which  is  split  at  its  base,  opening  up  the  reoto-prostatic  space  of  Proust.  By  a  longitudinal 
incision  into  the  prostate  on  each  side  the  adenomatous  lateral  lobes  may  be  enucleated  sepa- 
rately, and  it  is  claimed  without  injury  to  the  urethra  or  ejaeulatory  ducts  (Hugh  Young).* 

The  bladder  lies  above  the  pubic  symphysis  at  birth  and  so  is  mainly  an 
abdominal  organ.  The  anterior  surface,  in  contact  with  the  abdominal  wall, 
has  no  peritoneal  covering,  but  posteriorly  the  peritoneal  reflection  descends  to 
cover  the  posterior  surface  of  the  prostate,  which  is  relatively  lower  than  in  the 
adult. 

The  adult  bladder  when  empty  forms  a  pyriform  contracted  organ  behind  the  symphysis, 
and  bounding  the  retro-pubic  space  of  Retzius  posteriorly.  Into  this  space  urine  is  extrava- 
sated  in  extra-peritoneal  rupture  of  the  bladder,  and  may  mount  up  behind  the  abdominal  wall 
in  the  extra-peritoneal  tissue.  The  space  is  closed  below  by  the  pubo-pro.stafic  ligaments  and 
prostatic  plexus  of  veins.  In  distention,  the  neck  of  the  bladder  and  prostate  being  relatively 
fixed  and  immovable,  the  free  a-pex  rises  up  into  the  abdomen.  As  it  does  so  it  raises  the  peri- 
toneum off  the  abdominal  wall,  so  that  in  moderate  distention  5  cm.  (2  in.)  of  abdominal  wall 
above  the  pubes  are  free  of  peritoneum,  and  the  bladder  may  be  tapped  here  safely.  The  upper 
surface  and  a  little  of  the  posterior  are  covered  by  peritoneum,  which  is  also  related  to  the  upper 
halves  of  the  vesiculae  seminales.  Below  the  recto-vesioal  pouch  the  base  of  the  bladder  pre- 
sents a  small  triangular  area  in  contact  with  rectum,  bounded  by  the  peritoneal  cul-de-sac  above, 
the  converging  deferential  ducts  on  each  side  and  the  prostate  below.  Tlirough  this  triangle 
which  is  rather  expanded  in  distention  of  the  bladder,  puncture  per  rechmi  was  formerly  prac- 
tised. The  infero-lateral  surfaces  are  slung  up  by  the  levator  ani  as  by  a  hammock.  The  inte- 
rior of  the  bladder  can  be  examined  by  the  cystoscope  in  the  living  patient.  The  mucous  mem- 
brane is  loose  and  ruQ;ose  in  contraction,  except  over  the  trigone  at  the  base,  the  angles  of 
which  are  formed  by  the  ureteric  orifices  and  the  internal  meatus.  The  mucosa  here  is  firmly 
adherent  to  the  muscular  coat  and  smooth.  In  hypertrophy  of  the  bladder-muscle  from  ob- 
struction, a  fasciculated  appearance  of  the  mucosa  is  seen  and  possibly  diverticula  between 
the  bands  of  muscle. 

Rectum  and  anal  canal. — The  rectum  proper  extends  from  the  end  of  the 
pelvic  colon,  opposite  the  third  sacral  vertebra,  to  the  upper  end  of  the  narrow 
anal  canal,  which  runs  downward  and  backward  almost  at  right  angles  to  the 
rectum  and  is  3-4  cm.  in  length.  The  commencement  of  the  rectum  lies  13-14 
cm.  (5-5|  in.)  above  the  anus  in  the  adult.  This  point  is  marked  internally 
by  an  infolding  of  the  mucosa  on  the  right  and  anterior  wall  and  to  some  extent 
of  the  circular  muscle  fibres,  due  to  the  angle  at  which  the  free  pelvic  colon  turns 
into  the  fixed  rectum.  This  shelf  of  mucous  membrane  is  known  as  the  upper 
transverse  fold  (first  valve  of  Houston). 

Under  normal  conditions  the  rectum  does  not  form  a  reservoir  for  faecal  material,  which 
is  stored  in  the  lower  end  of  the  pelvic  colon,  above  the  upper  transverse  fold,  leaving  the 
rectum  empty  except  in  defsecation.  The  rectum  proper  is  subdivided  into  two  compartments 
by  the  inferior  transverse  fold  on  the  anterior  wall  (third  or  great  valve  of  Houston),  situated 
8-9  cm.  (3-3i  in.)  above  the  anus  at  the  level  of  the  anterior  cul-de-sac  of  the  peritoneum,  and 
resulting  from  the  adaptation  of  the  rectum  to  the  hollow  of  the  sacrum.  This  can  usually 
be  made  out  on  digital  examination.  The  other  transverse  folds  are  inconstant  and  only 
present  on  great  distention. 

The  rectum  and  anal  canal  may  be  divided  into  three  regions:  (1)  peritoneal 
from  the  third  sacral  vertebra  to  the  lower  transverse  fold  and  anterior  reflexion 
of  peritoneum  onto  bladder  or  vagina;  (2)  infraperitoneal  (rectal  ampulla) 
below  this  and  above  the  levator  ani;  (3)  anal  canal,  below  the  level  of  the 
levator  ani,  constriction  b3r  which  marks  it  off  from  the  ampulla  and  converts 
it  into  an  antero-posterior  slit. 

The  mucous  membrane  of  the  rectum  proper  is  redundant  and  mobUe  and  of  a  bright  pink 
colour  as  seen  by  the  sigmoidoscope.  It  is  dotted  over  by  rectal  pits,  visible  to  the  naked  eye, 
containing  lymphoid  follicles,  and  by  the  smaller  and  more  numerous  Lieberkhiin's  glands. 
In  the  peritoneal  chamber  the  mucosa  is  transversely  plicated.  In  the  rectal  ampulla  it  presents 
longitudinal  folds  in  which  lie  branches  of  the  superior  hfemorrhoidal  vessels.  These  longi- 
tudinal folds,  known  as  the  rectal  columns,  converge  into  the  anal  canal,  and  end  at  the  level 
of  the  anal  valves  half  way  down  the  canal,  each  uniting  two  adjacent  valves.  The  anal  valves 
probably  represent  the  original  cloacal  membrane,  dividing  the  proctoda^um  (formed  from  the 
epiblast)  from  the  hypoblastic  hindgut,  and  persistence  of  this  membrane  gives  one  form  of 
imperforate  anus  (Wood  Jonesf).  The  tearing  down  of  a  valve  by  hard  faeces  may  be  a  cause 
of  anal  fissure,  etc.  (Ball).     The  mucous  membrane  of  the  anal  canal  is  more  firmly  adherent 

*  Studies  on  Hypertrophy  and  Cancer  of  the  Prostate.     J.  H.  H.  Reports,  vol.   14,   1906. 
t  Brit.  Med.  Journal,  Dec.  14,  1904. 


FEMALE  GENITAL  ORGANS  1391 

to  the  underlying  muscular  coat  than  that  of  the  rectum,  hence  in  prolapse  the  mucosa  of  the 
rectal  ampulla  is  the  first  to  be  extruded. 

Peritoneal  relations. — The  peritoneal  chamber  of  the  rectum  has  no  covering  of  peritoneum 
behind,  and  the  peritoneum,  at  first  covering  its  first  aspect  and  sides,  leaves  the  sides 
obliquely  and  finally  is  reflected  onto  the  base  of  the  bladder  (or  the  vaginal  fornix  in  the 
female),  at  the  level  of  the  inferior  rectal  fold,  8  cm.  from  the  anus. 

Blood-supply. — (1)  The  superior  hsemorrhoidal  artery,  a  continuation  of  the  inferior  me- 
senteric, reaches  the  rectum  behind,  via  the  pelvic  meso-colon  and  bifurcates  at  once.  The  two 
branches  run  round  on  either  side  below  the  peritoneal  reflection;  giving  ofl^  secondary  branches 
that  pierce  the  muscular  coat  about  the  level  of  the  inferior  transverse  fold,  or  anterior  perit- 
oneal reflection.  Joining  the  submucous  layer,  these  arteries  run  down  in  the  rectal  columns 
to  the  anal  canal,  where  they  anastomose  with  (2)  the  middle  hsemorrhoidal  arteries,  branches 
of  the  hypogastric  (internal  iliac)  and  (3)  the  inferior  hasmorrhoidal  branches  of  the  internal 
pudendal.  The  veins  correspond.  Their  free  anastomosis  in  the  hsemorrhoidal  plexus  under 
the  rectal  columns,  the  union  afforded  here  between  the  portal  and  systemic  veins,  the  absence 
of  valves  in  the  superior  hsemorrhoidal  veins,  and  the  constriction  they  are  subject  to  in  passing 
through  the  muscular  coat,  are  some  of  the  anatomical  causes  of  the  frequency  of  haemorrhoids. 

The  branches  of  the  superior  hremorrhoidal  artery  to  the  rectum  anastomose  but  little 
with  one  another,  as  compared  with  the  sigmoid  arteries  to  the  pelvic  colon.  The  main  trunk 
of  the  superior  hsemorrhoidal  usually  receives  a  large  anastomotic  branch  from  the  lowest 
sigmoid  artery  1-2  cm.  below  the  sacral  promontory,  upon  which  the  upper  part  of  the  rectum 
is  dependent  for  its  blood-supply  after  ligature  of  the  superior  haemorrhoidal.  Hence  in  high 
excision  of  the  rectum  it  is  important  to  place  the  ligature  on  the  superior  hsemorrhoidal  above 
the  sacral  promontory  if  sloughing  of  the  gut  is  to  be  avoided.* 
For  lymphatics  of  the  rectum  see  p.  735. 

Supports  of  the  rectum. — The  anal  canal  is  fixed  by  its  attachment  to  the  levator  ani  and 
perineal  body.  After  division  of  the  perineal  body  and  recto-urethral  muscle  in  front,  the 
rectum  is  readily  separable  from -the  back  of  the  prostate  and  recto-vesical  septum.  When 
the  levator  ani  has  been  divided  on  each  side  and  the  peritoneum  opened,  as  in  the  perineal 
operation  for  excision  of  the  rectum,  the  gut  cannot  be  pulled  down  freely.  The  hand  passed 
up  behind  it  in  the  hollow  of  the  sacrum  meets  on  each  side  with  a  dense  fibrous  layer  running 
from  the  sacrum  opposite  the  third  foramen  onto  the  side  of  the  rectum.  This  is  the  rectal 
stalk  (Elliot  Smith)  and  consists  of  dense  fibrous  tissue  round  the  nervi  erigentes  from  second, 
third  and  fourth  sacral  foramina  and  the  middle  haemorrhoidal  vessels.  It  lies  about  2.5  cm. 
above  the  levator  ani,  and  after  division  of  it  the  bowel  is  easily  freed,  so  that  the  whole  of  the 
rectum  and  part  of  the  pelvic  colon  may  be  drawn  out  at  the  perineum  without  tension. 

Rectal  examination. — The  following  points  can  be  made  out  by  the  finger  introduced  into 
rectum: — (1)  The  thickened,  roll-like  feel  of  a  contracted  external  sphincter;  (2)  the  narrower, 
more  expanded,  internal  sphincter  extending  upward  for  2.5  cm.  (1  in.)  from  this;  (3) 
the  rectal  insertion  of  the  levatores  ani,  which  here  narrows  somewhat  the  lumen  of  the  gut; 
(4)  above  the  anal  canal,  with  its  contrasting  capaciousness,  is  the  more  or  less  dilated  rectum 
proper;  (5)  the  condition  of  the  ischiorectal  fossse  on  either  side;  (6)  the  membranous  urethra  in 
front,  especially  if  a  staff  has  been  introduced;  the  instrument  now  occupies  the  middle  line, 
and  has  the  normal  amount  of  tissue  between  it  and  the  finger,  thus  differing  from  one  in  a 
false  passage  (in  a  child  an  instrument  is  especially  distinct);  (7)  just  beyond  the  sphincters,  or 
3.7  cm.  (1|  in.)  within  the  anus,  lies  the  prostate;  (8)  converging  toward  the  base  of  the  prostate, 
and  forming  the  sides  of  the  triangular  space,  are  the  vesiculse  seminales  and  ejaculatory  ducts. 
These  can  rarely  be  felt  unless  diseased  and  enlarged;  any  enlargement  of  the  sacculated  ends 
of  the  deferential  ducts  is  much  more  perceptible;  (9)  it  is  within  this  triangular  space  that  the 
elasticity  of  a  distended  bladder  can  be  felt.  (10)  Usually  the  lowest  of  the  transverse  folds 
(folds  of  Houston),  semilunar  in  form  and  about  1.2  cm.  (J  in.)  in  width,  can  be  made  out  (fig. 
1116).  (11)  Behind,  the  coccyx  and  its  degree  of  pliability  and  the  lower  part  of  the  sacrum. 
It  may  also  be  possible  to  feel  enlarged  sacral  nodes  and  a  growth  from  the  other  pelvic 
bones. 

The  above  examination  refers  chiefly  to  the  male.^  It  remains  to  refer  to  rectal  examination 
in  the  female.  Anteriorly,  the  soft  perinseal  body  and  recto-vaginal  septum  will  be  met  with, 
and,  through  the  latter,  the  cervix  and  os  uteri,  and,  higher  up,  the  lower  part  of  the  cervix  uteri. 
More  laterally  the  ovaries  may  be  felt,  but  the  uterine  or  Fallopian  tubes,  unless  enlarged  and 
thickened,  are  not  to  be  made  out.  The  student  should  be  familiar  with  the  feel  of  a  healthy 
recto-uterine  or  recto-vesical  pouch,  according  to  the  sex,  and  the  coils  of  intestine  which  it 
may  contain,  so  as  to  be  able  to  contrast  this  with  any  collection  of  inflammatory  or  other 
fluid  or  mischief  descending  from  the  upper  pelvis,  e.  g.,  from  the  vermiform  appendix.  Pos- 
teriorly, certain  structures  are  met  with  in  either  sex.  After  a  very  short  interval  (sphincter 
and  ano-ooccygeal  body)  the  finger  reaches  the  tip  of  the  coccyx  and  explores  the  hollow  of  the 
sacrum.  On  each  side  are  the  ischial  tuberosity  and  wall  of  the  true  pelvis.  The  finger 
hooked  lateralward  and  upward,  comes  on  the  border  of  the  falciform  process  of  the  sacro- 
tuberous  (great  sacro-sciatic)  ligament,  passing  between  the  above-mentioned  bones. 

FEMALE  GENITAL  ORGANS 

The  external  organs  will  be  considered  first,  followed  by  the  internal.  Under 
the  external  organs  are  included,  for  convenience  sake,  the  labia  majora  and 
minora  at  the  sides;  and,  in  the  middle  line,  from  above  downward — (1)  The 
glans  clitoridis  with  its  prepuce;  (2)  the  vestibule;  (3)  the  urethral  orifice;  (4)  the 

*  H.  Hartmann.     Annals  of  Surgery,  Dec,  1909. 


1392  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

vaginal  orifice  with  the  hymen  or  its  remains;  (5)  the  fossa  navicularis;  (6)  the 
fourchette;  (7)  the  sldn  over  the  base  of  the  perineal  body. 

These  parts  have  been  described  elsewhere,  and  only  those  points  which  are  of 
importance  in  a  clinical  examination  will  be  alluded  to  here. 

The  labia  majora  are  two  thick  folds  of  skin,  covered  with  hair  on  their  outer 
surface,  especially  above,  where  they  unite  {anterior  com7nissure)  in  the  mons 
Veneris.  They  contain  fat,  vessels,  and  dartos,  but  become  rapidly  thinner 
below,  where  they  are  continuous  at  the  front  of  the  perineum  (their  posterior 
commissure). 

When  the  above  folds  are  drawn  aside,  the  labia  minora,  or  nymphae,  appear, 
not  projecting,  in  a  healthy  adult,  beyond  the  labia  majora.  They  are  small 
folds  of  skin,  which  meet  above  in  the  prepuce  of  the  clitoris,  and  below  blend 
with  the  labia  majora  about  their  centre.  Sometimes,  especially  in  nulliparae, 
they  unite  posteriorly  to  form  a  slight  fold,  the  fourchette. 

The  glans  clitoridis,  covered  by  its  prepuce,  occupies  the  middle  line  above. 
Below  it  comes  the  vestibule,  a  triangular  smooth  surface  of  mucous  mem- 
brane, bounded  above  by  the  clitoris,  below  by  the  upper  margin  of  the  vaginal 
orifice,  and  laterally  by  the  labia  minora.  In  the  middle  line  of  the  vestibule 
and  toward  its  lower  part,  about  12  mm.  (J  in.)  below  the  glans  clitoridis,  and  25 
mm.  (1  in.)  above  the  fourchette,  is  the  meatus  or  opening  of  the  urethra  (figs. 
1034,  1037). 

The  vaginal  orifice  lies  in  the  middle  line  between  the  base  of  the  vestibule 
above,  and  the  fossa  navicularis  below.  Its  orifice  is  partially  closed  in  the  virgin 
by  a  fold  of  mucous  membrane,  the  hymen  (fig.  1037).  This  is  usually  crescentic 
in  shape  attached  below  to  the  posterior  margin  of  the  vaginal  orifice,  and  with 
a  free  edge  towards  the  base  of  the  vestibule.  In  some  cases  it  is  diaphragmatic 
i.  e.  attached  all  around,  but  perforated  in  the  centre  (fig.  1037). 

The  schrivelled  remains  of  the  hymen  probably  constitute  the  carunculse 
hymenales.  On  either  side  of  the  vaginal  orifice,  at  it  lower  part,  lie  the  racemose, 
muciparous,  vestibular  glands  (glands  of  Bartholin),  situated  beneath  the  super- 
ficial perineal  fascia  and  sphincter  vaginae.  Their  ducts  run  slightly  upward  and 
open,  external  to  the  attachment  of  the  hymen,  within  the  labia  minora.  In 
relation  to  the  upper  two-thirds  of  the  vaginal  orifice,  placed  between  the  uro- 
genital diaphragm  behind  and  the  sphincter  vaginae  in  front,  are  the  vascular 
bulbs  of  the  vestibule,  rupture  of  which  produces  pudendal  hfematocele. 

Fourchette  and  fossa  navicularis. — The  fourchette,  as  stated  above,  is  the 
posterior  commissure  of  the  labia  minora.  Normally  the  inner  aspect  of  this  is 
in  contact  with  the  lower  surface  of  the  hymen.  When  the  fourchette  is  pulled 
down  by  the  finger,  a  shallow  depression  is  seen,  the  fossa  navicularis,  with  the 
fourchette  for  its  posterior,  and  the  hymen  for  its  anterior,  boundary. 

Internal  organs. — The  examinations  through  the  vagina  and  anus  will  be 
considered  first,  followed  by  uterus  and  appendages,  ovary  and  ureter. 

Examination  per  vaginam. — The  finger,  introduced  past  the  gluteal  cleft, 
perineum,  and  fourchette,  comes  upon  the  elliptical  orifice  of  the  vagina,  and  notes 
how  far  it  is  patulous  or  narrow;  the  presence  or  otherwise  of  any  spasm  from  the 
adjacent  muscles;  then,  passing  into  the  canal  itself,  the  presence  or  absence  of 
rugae,  a  naturally  moist  or  a  dry  condition  are  observed.  In  the  anterior  wall  the 
cord-like  urethra  can  be  rolled  between  the  finger  and  the  symphysis ;  and  further 
up  than  this,  if  a  sound  be  passed,  the  posterior  wall  of  the  bladder.  The  anterior 
wall  of  the  vagina  is  about  6.7  cm.  (2|  in.)  long.  The  posterior  wall,  7.5  cm.  (3 
in.)  long,  forms  the  recto-vaginal  septum,  and  through  it  any  faeces  present  in 
the  bowel  are  easily  felt.  The  cervix  uteri  is  next  felt  for  in  the  roof  of  the  vagina, 
projecting  downward  and  backward  in  a  line  drawn  from  the  umbilicus  to  the 
coccyx.  Besides  its  direction,  its  size,  shape,  mobility,  and  consistence  should  be 
noted.  The  os  uteri  should  form  a  dimple  or  fissure  in  the  centre  of  the  cervix. 
Of  its  two  lips,  the  posterior  is  the  thicker  and  more  fleshy  feeling  of  the  two. 
The  vaginal  culs-de-sac  or  fornices  are  next  explored.  These  should  be  soft  and 
elastic,  giving  an  impression  to  the  finger  similar  to  that  when  it  is  introduced 
into  the  angles  of  the  mouth.  Any  resistance  felt  here  may  be  due  to  scars, 
swellings  connected  with  the  uterus  (displacements  or  myomata),  effusions  of 
blood  or  inflammatory  material,  and,  in  the  case  of  the  lateral  culs-de-sac,  a 
displaced  or  enlarged  ovary,  or  dilatations  of  the  Fallopian  tubes.  The  posterior 
cul-de-sac  is  much  deeper  than  the  anterior,   and,   owing  to  the  peritoneum 


THE  OVARY 


1393 


descending  upon  the  posterior  wall  of  the  vagina,  when  the  finger  is  placed  here 
it  is  only  separated  from  the  peritoneal  sac  by  the  vaginal  wall  and  pelvic  fascia. 
In  examination  of  the  pelvic  organs  the  bimanual  method,  by  which  one  hand 
on  the  hypogastric  region,  pushes  them  down  and  steadies  them  as  well,  is  always 
to  be  employed  to  complete  an  examination. 

The  uterus  and  appendages. — The  normal  non-gravid  uterus  is  usually 
anteflexed  and  anteverted  so  as  to  lie  with  its  long  axis  approximately  at  right 
angles  to  that  of  the  vagina.  Its  position  varies  considerably  with  the  degree 
of  distention  of  the  bladder  in  front  and  of  the  rectum  behind.  The  distance 
from  external  os  to  fundus,  as  estimated  by  the  passage  of  a  sound  is  in  the 
adult  virgin  uterus  5.5  cm.  of  which  3  cm.  belong  to  the  cervix  and  2.5  cm.  to  the 
body.  In  the  empty  multiparous  uterus  the  total  length  of  the  cavity  is  6  cm., 
2.5  cm.  comprising  the  neck  and  3.5  cm.  the  body. 

Peritoneal  relations. — In  front  the  peritoneum  is  reflected  from  the  uterus  to  form  the 
utero-vesical  pouch  at  the  level  of  the  isthmus.  Behind  it  covers  not  only  the  uterus  but  the 
posterior  fornix  of  the  vagina,  before  turning  off  onto  the  front  of  the  rectum.  Laterally  the 
peritoneum  leaves  the  uterus  and  passes  on  to  the  lateral  pelvic  wall  as  a  large  twofold  partition 
fig.  1118),  the  broad  ligament. 


Fig.  1118. — Sagittal  Section  of  the  Bhoad  Ligament. 


Graafian  follicles 
of  ovary 


Mesovarium 


Mesometrium 
Posterior  surface 


Uterine  veins 


Base  of  ligament 


The  broad  ligament,  bearing  in  its  upper  border  the  uterine  tube,  in  front  the  round  ligament 
and  behind  the  ovary,  consists  of  (1)  an  upper  thin  part,  the  mesosalpinx  lying  above  the 
attachment  of  the  mesovarium,  and  containing  the  ovarian  vessels  and  the  epoophoron,  and 
below  this  (2)  the  thicker  mesometrium,  between  the  layers  of  which  is  a  dense  mass  of  fibrous 
tissue  surrounding  the  uterine  artery. 

The  anterior  aspect  of  the  cervix  below  the  utero-vesical  pouch  of  peritoneum,  is  readily 
separable  from  the  bladder  with  which  it  lies  in  contact,  and  the  peritoneum  may  be  raised  oil 
the  uterus  with  ease  in  the  lower  part  of  its  attachment  both  front  and  back.  Over  the  upper 
part  of  the  body  and  fundus,  however,  the  peritoneal  covering  is  firmly  adherent,  and  cannot 
be  dissected  off. 


The  ovary,  attached  by  its  hilum  to  the  mesovarium,  lies  in  a  fossa  at  the 
back  of  the  lateral  wall  of  the  pelvis  just  between  the  diverging  external  ihac  and 
hypogastric  vessels.  To  feel  it  the  finger  should  be  pushed  well  up  in  the  side  of 
the  vagina  toward  the  lateral  wall  of  the  pelvis.  On  the  abdominal  surface  its 
position  corresponds  to  the  middle  of  a  line  drawn  from  the  anterior  superior 
ihac  spine  of  that  side  to  the  opposite  pubic  tubercle  (Rawlings). 


1394  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

The  lymphatics  of  the  ovary  follow  the  ovarian  veins  (see  p.  745). 

Supports  of  the  uterus. — The  great  mobility  of  the  body  of  the  uterus  has  been  referred 
to  above.  The  organ  derives  its  support  almost  entu'ely  from  the  attachments  of  the  cervix 
and  vaginal  fornices.  These  rest  on  the  pelvic  floor,  formed  by  the  levator  ani  and  perineal 
body  which  support  them  the  more  efficiently  since  the  long  axis  of  the  vagina  is  at  right  angles 
to  that  of  the  uterus.  Above  the  pelvic  diaphragm  the  cervix  is  held  up  to  the  pelvic  walls  by 
strong  specialised  bands  of  fibro-muscular  tissue  running  in  both  antero-posterior  and  trans- 
verse directions.  The  chief  of  these,  lying  in  the  base  of  the  broad  ligaments  is  a  fibrous  sheath 
sm-rounding  the  uterine  artery  as  it  descends  medially  from  the  hypogastric.  In  the  antero- 
posterior direction  the  utero-vesical  ligaments  hold  up  the  cervix  to  the  pubes  in  front  and  the 
sacro-uterine  ligaments  bind  it  to  the  anterior  aspect  of  the  sacrum  behiind.  While  firmly 
supporting  the  uterus  these  bands  are  elastic,  and  so  do  not  fix  it  rigidly,  but  allow  of  the  cervix 
being  drawn  downward  by  traction  with  vulsellum  forceps. 

For  lymphatics  of  uterus  and  vagina  see  p.  745. 

The  ureter. — The  pelvic  portion  of  this  duct  is  of  special  importance  in  opera- 
tions on  the  uterus  and  upper  vagina.  It  crosses  the  brim  of  the  pelvis  on  either 
side  at  the  biftu-cation  of  the  common  ihac  artery,  or  just  in  front  of  it,  and 
descends  on  the  side  waU  in  front  of  the  hypogastric  artery,  crossing  the  ob- 
literated umbilical  'and  obturator  arteries.  Curving  forward  and  medially  it 
passes  under  the  base  of  the  broad  ligament,  where  the  uterine  artery  crosses 
above  it,  and  so  gains  the  lateral  angle  of  the  bladder  by  passing  across  in  rela- 
tion to  the  lateral  fornix  of  the  vagina.  In  the  base  of  the  broad  ligament  the 
ureter  lies  about  2  cm.  (f  in.)  from  the  side  of  the  cervix,  and  this  relation  must 
be  borne  in  mind  in  excision  of  the  uterus. 

Pelvic  floor. — The  pelvic  floor  of  the  female  corresponds  in  general  to  that 
of  the  male  (see  p.  1383).  There  are,  however,  important  differences,  due  to  the 
sexual  organs.  The  urogenital  diaphragm  is  relatively  smaller  in  area,  due  to  per- 
foration by  the  vagina.  The  pelvic  diaphragm  is  also  correspondingly  modified, 
and  the  pubo-coccygeus  component  is  more  strongly  developed  (see  section  on 
Musculature.)     The  ischio-rectal  fossa  is  similar  to  that  of  the  male  (p.  1384). 

HERNIA 

Three  varieties  of  hernia  will  be  considered,  inguinal,  femoral,  and  umbilical 

PARTS  CONCERNED  IN  INGUINAL  HERNIA 

In  inguinal  hernia,  as  in  femoral  and  umbilical,  there  is  a  weak  spot  in  the  ab- 
dominal wall — one  weakened  for  the  needful  passage  of  the  testicle  from  within 
to  outside  the  abdomen  (p.  1387).  The  parts  immediately  concerned  are  the  two 
inguinal  rings,  subcutaneous  (external)  and  abdominal  (internal),  and  the  canal. 
Now,  it  must  be  remembered  at  the  outset  that  the  rings  and  canal  are  only 
potential — they  do  not  exist  as  rings  or  canal  save  when  opened  up  by  a  hernia, 
or  when  so  made  by  the  scalpel.  The  canal  is  merely  an  oblique  slit  or  flat-sided 
passage.  The  subcutaneous  and  abdominal  rings  are  so  intimately  blended  with 
the  structures  that  pass  through  them,  and  so  filled  by  them,  that  they  are  potential 
rings  only. 

The  subcutaneous  inguinal  (external  abdominal)  ring. — This  is  usually 
described  as  a  ring :  it  is  really  only  a  separation  or  gap  in  the  aponeurosis  of  the 
external  oblique,  by  which  in  the  male  the  testicle  and  cord,  and  in  the  female 
the  round  ligament  by  which  the  uterus  is  kept  tilted  a  little  foward,  pass  out 
from  the  abdomen.  The  size  of  this  opening,  the  development  and  strength  of  its 
crura  or  pillars,  the  fascia  closing  the  ring — all  vary  extremely.  Formation :  by 
divergence  of  two  fasciculi  of  the  external  oblique  aponeurosis.  Boundaries :  two 
crura — (1)  Superior,  the  smaller,  attached  to  the  symphysis  and  blending  with  the 
suspensory  ligament  of  the  penis;  (2)  inferior,  stronger,  attached  to  the  pubic 
tubercle  and  blending  with  the  inguinal  ligament,  and  so  with  the  fascia  lata.  On 
this  inferior,  stronger  crus  rests  the  cord  (and  so  the  weight  of  the  testicle)  or 
round  ligament.  Shape :  triangular  or  elliptical,  with  the  base  downward  and 
medially  toward  the  pubic  crest. 

Intercrural  fibres  (intercolumnar  fascia)  (external  spermatic  fascia). — This,  derived  from 
the  lower  part  of  the  aponeurosis  of  the  external  oblique,  ties  the  two  crm'a  together,  and,  being 
continued  over  the  cord,  prevents  there  being  any  ring  here,  unless  made  with  a  scalpel.  This 
is  the  rule  in  the  body:  when  any  structure  passes  through  an  opening  in  a  fibrous  or  muscular 


INGUINAL  HERNIA 


1395 


layer,  it  carries  with  it  a  coating  of  tissue  froro  that  layer;  e.  g.,  the  inferior  cava  passing  through 
its  foramen  in  the  diaphi-agm,  and  the  membranous  uretlu-a  thi'ough  the  uro-genital  diaphragm. 
Effect  of  position  of  the  thigh  on  the  ring.— As  the  lower  crus  is  blended  with  Poupart's 
hgament,  and  as  the  fascia  lata  is  connected  with  this,  movements  of  the  thigh  will  affect  the 
rmg  much,  making  it  tighter  or  looser.  Thus  extension  and  abduction  of  the  thigh  stretch 
the  crura  and  close  the  ring.  In  flexion  and  adduction  of  the  thigh  the  crura  are  relaxed;  and 
this  is  the  position  in  which  reduction  of  a  hernia  is  attempted.  In  flexion  and  abduction  of 
the  thigh,  the  rmg  is  open;  and  this  is  the  position  in  which  a  patient  should  sit,  with  thighs 
widely  apart,  to  try  on  a  tru.ss,  and  cough  or  strain  downward,  as  in  rowing.  If  the  hernia  is 
now  kept  up,  the  truss  is  satisfactory. 

_  Helping  to  protect  this  most  important  spot,  and  preventing  its  being  more  than  a  potential 
rmg,  are  not  only  the  two  crura  and  the  intercrural  fibres,  but  also  a  structure  which  has  been 
called  a  thu-d  or  posterior  pillar,  namely,  the  reflected  inguinal  ligament.  This  has  its  base 
above  at  the  lower  part  of  the  linea  alba,  where  it  joins  its  fellow  and  the  aponeurosis  of  the 
external  oblique,  and  its  apex  downward  and  laterally,  where,  having  passed  behind  the  medial 
crus  it  blends  with  the  lacunar  (Gimbernat's)  ligament.     Again,  the  falx  inguinalis  (the  con- 

FiG.  1119. — The  Parts  concerned  in  Inguinal  Hernia. 
(From  a  dissection  in  the  Hunterian  Museum.) 
External  oblique,  cut  and  turned  back  Internal  oblique  External  oblique 


Falx  inguinalis 


Poupart's  (inguinal)  hgament 


Reflected  inguinal  ligament 


joined  tendon  of  the  internal  oblique  and  transversahs),  curving  mediaUy  and  downward  to 
be  attached  to  the  ilio-pectmeal  hne  and  spine,  is  a  most  powerful  protection,  behind,  to  what 
13  otherwise  a  weak  spot  and  a  potential  ring. 

Inguinal  canal.— This  is  not  a  canal  in  the  usual  sense,  but  a  chink  or  flat- 
sided  passage  m  the  thickness  of  the  abdominal  wall.  The  descriptions  of  the 
canal  usually  given  apply  rather  to  the  diseased  than  to  the  healthy  state.  It 
was  a  canal  once,  and  for  a  time  only,  i.  e.,  in  the  later  months  of  fcetal  life  (p.  1387). 
It  remains  weak  for  a  long  time  after,  but  only  a  vestige  of  it  remains  in  the  well- 
made  adult. 

Length.— In  very  early  life  there  is  no  canal;  one  ring  lies  directly  behind  the 
other,  so  as  to  facilitate  the  easy  passage  of  the  testis.  In  the  adult  it  measures 
about  37  mm.  (l^  in.)  in  length,  this  lengthening  being  brought  about  by  the 
growth  and  separation  of  the  alse  of  the  pelvis.  This  increased  obliquity  gives 
additional  safety.  On  the  other  hand,  a  large  hernia  has  not  only  opened  \^^dely 
the  canal  and  rings,  but  it  has  pulled  them  close  together,  and  one  behind  the  other 
thus  not  only  rendering  repair  much  more  difficult,  but  also  the  path  to  the 


1396  CLINICAL  AND  TOPOGRAPHICAL    ANATOMY 

peritoneal  sac  shorter  and  more  direct.     Direction.— From  the  abdominal  to  the 
subcutaneous  ring,  downward,  forward,  and  medially.  -^  •  in  , 

Boundaries.— For  convenience  sake,   certain  hmits   (largely  artifacial)  have 

been  named : —  ,  ,  ,        i,  i       j.  iu 

(1)  Floor. — This  is  best  marked  near  the  outlet,  where  the  cord  rests  on  the 
grooved  upper  margin  of  the  inguinal  (Poupart's)  and  the  lacunar  (Gimbernat's) 
lio-ament.  The  meeting  of  the  transversalis  fascia  with  this  hgament  forms  the 
floor  (2)  i?oo/.— The  apposition  of  the  muscles  and  the  arched  border  of  the 
internal  oblique  and  transversus.  (3)  Anterior  wall— Skin,  superficial  fascia, 
external  oblique  for  all  the  way.  Internal  oblique,  i.  e.,  that  part  arising  from 
Poupart's  ligament,  for  the  lateral  third  or  so.  To  a  slight  extent,  the  trans- 
versus and  the  cremaster.  (4)  Posterior  wall.—For  the  whole  extent,  transversalis 
fascia,  extraperitoneal  tissue,  and  peritoneum.  For  the  medial  two-thirds,  con- 
joined tendon  of  internal  oblique  and  transversus,  and  the  lateral  edge  of  the 
reflected  inguinal  hgament,  when  developed. 

Fig.  1120. — Dissection  of  Inquinai,  Canal.     (Wood.) 


^  %%\W  ,  ^' 


External  oblique, 
(turned  down) 


11       >  Internal  oblique 
Transversus 


Falx  inguinalis  (con- 
VTMW      1  I  joined  tendon) 

\  VWi     I  I  Reflected  ligament 

^■— ^-^  1  j (triangular  fascia) 

Cremaster 


The  transversalis  fascia  is  thicker  and  better  marked  at  its  attachments  below;  these  are- 
fa)  laterally,  to  medial  lip  of  iliac  erest;  (b)  to  the  ingmnal  ligament  between  the  anterior- 
superior  spine  and  the  femoral  vessels,  where  it  joins  the  fascia  ihaca;  (c)  opposite  the  femoral 
vessels  it  Tlso  joins  the  fascia  iliaca,  and  forms  with  it  a  funnel-shaped  sheath;  (d)  mecbal  to  the 
femoral  vessels  the  fascia  transversalis  is  attached  to  the  terminal  (.^'l°-Pe«t>,^^f ) J^^^'  ^^^J^f, 
the  conjoined  tendon,  with  which  it  blends.  The  falx  ingmnahs  {conjoined  tendon)  needs  special 
reference  It  is  foriied  by  the  lower  fibres  of  the  internal  oblique  and  transversus  (arciform 
fibres)  arching  downward  over  the  cord  to  be  inserted  into  the  crest  and  spme  and  the  termmai 
aho-pectineal)  line.  The  fibres  of  the  internal  oblique  become  increasingly  tendmous  as  they 
descend,  and  this,  with  the  fact  that  below  they  give  off  the  cremaster,  may  «ause  some  difficulty 
in  theh-  identification  when  it  is  desked  to  unite  them  to  the  upper  surface  of  Poupart  s  liga- 
ment in  the  operation  of  radical  cure. 

The  abdominal  inguinal  (internal  abdominal)  ring.— It  has  already  been  said 
that  the  term  'ring'  is  here  misapplied  except  in  an  artiflcial  sense,  as  when  an 
opening  is  made  by  a  scalpel;  or  in  abnormal  conditions  when  a  hernial  sac  is 
present.  The  abdominal  ring  is  not  a  ring  in  the  least,  but  merely  a  tunnel- 
shaped  expansion  of  the  transversahs  fascia,  which  the  cord  carries  on  with  it  as 
it  escapes  from  the  abdomen. 


INGUINAL  HERNIA 


1397 


Site. — Midway  between  the  anterior  superior  iliac  spine  and  pubic  tubercle. 
Shape :  oval,  with  the  long  diameter  vertical.  Boundaries :  centre  of  inguinal 
(Poupart's)  ligament,  about  12  mm.  (|  in.)  below.  Medially,  the  inferior 
epigastric  artery  (fig.  1121);  the  position  of  this  vessel,  by  its  pulsation,  is  an  im- 
portant guide  to  the  insertion  of  the  highest  sutures  between  the  arciform  fibres 
and  the  inguinal  ligament.  Owing  to  the  artery  lying  to  the  medial  side,  the 
incision,  in  cutting  to  relieve  the  deep  constriction  of  an  inguinal  hernia,  should 
always  be  made  directly  upward,  so  as  to  avoid  the  above  vessel.  A  large  ob- 
lique hernia  may  so  have  altered  the  relations  of  the  parts,  including  the  artery, 
that  it  is  difficult  to  decide  whether  the  hernia  is  oblique  or  direct.  The  above 
incision  will  be  safe,  because,  iia  either  case,  parallel  to  the  vessel. 
Coverings. — There  are  two  chief  forms  of  inguinal  hernia : — 
A.  The  cominon  form:  lateral,  or  oblique. — Lateral,  because  it  appears 
(at  the  abdominal  ring)  lateral  to  the  inferior  epigastric  artery.  Oblique, 
because  it  traverses  the  whole  of  the  inguinal  canal,  entering  it  at  its  inlet  and 
leaving  it  at  its  outlet.  This  form  is  usually  congenital  in  origin,  and  is  due  to 
non-obliteration  of  the  processus  vaginalis  in  infancy. 

Fia.  1121. — Dissection  of  the  Lower  Part  of  the  Abdominal  Wall  from  within,  the 
Peritoneum  having  been  removed.     (Wood.) 


order  of  the  poste- 
rior   part    of    the 
sheath  of  the  rec- 
tus (fold  of  Doug- 
Fascia  transversal- -^ ■ —  ^ 

Inferior  epigastr: 
artery 


Ductus  (vas)  deferens 


Spermatic  vessels 


Obliterated  hypo- 
gastric artery 
"■  Lymphatics  in 
femoral  ring 


External  iliac  artery 


B.  Rarer  form :  medial,  or  direct. — Medial,  because  it  appears  medial  to  the 
inferior  epigastric  artery.  Direct,  because,  instead  of  making  its  way  down  the 
whole  oblique  canal,  it  comes  by  a  short  cut,  as  it  were,  only  into  the  lower  part 
of  the  canal,  and  then  emerges  by  the  same  opening  as  the  other. 

A.  Oblique  inguinal  hernia. — This  possesses  its  coverings  as  follows: — 

(1)  At  the  abdominal  ring,  or  inlet,  it  obtains  three: — (a)  Peritoneum;  (6)  extra-peritoneal 
fat;  (c)  iiifuiidibuliform  fascia,  or  the  vaginal  process  of  transversalis  fascia  prolonged  at  this 
spot  along  the  cord. 

(2)  In  the  canal  it  obtains  one.  As  it  emerges  beneath  the  lower  border  of  the  internal 
oblique  it  gets  some  fibres  from  the  cremaster. 

(3)  At  the  subcutaneous  ring,  or  outlet,  the  hernia  obtains  three,  viz.:  (a)  Intercrura 
fibres  (interoolumnar  fascia) ;  (b)  superficial  fascia;  and  (c)  skin. 

B.  Direct  inguinal  hernia. — This  does  not  come  through  the  abdominal  ring,  but,«making 
its  waj'  through  the  posterior  wall  of  the  lower  third  of  the  canal,  either  through  the  medial  or 
intermediate  inguinal  fossa.  Its  coverings,  therefore,  vary  slightly  with  its  mode  of  exit  (vide 
infra). 

Hitherto  the  two  forms  of  inguinal  hernia  have  been  considered  from  the  superficial  aspect, 
that  in  which  they  are  met  with  in  practice.     The  inguinal  region  should  also  be  studied  as  to 


1398  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

the  posterior  aspect  of  its  so-called  rings  and  canal,  as  these  have  to  bear  the  early  stress  of  a 
commencing  hernia.  It  is  against  this  aspect  that  a  piece  of  omentum  or  intestine  is  constantly 
and  insidiously  pressing  and  endeavoui'ing  to  make  its  way  out.  Furthermore,  when  either  of 
the  above  constituents  of  hernia  have  made  their  way  a  little  farther,  and  got  out  into  the  ab- 
dominal ring  or  into  the  canal,  the  patient  is  no  longer  sound. 

On  the  posterior  wall  are  certain  cords  and  depressions,  marking  off  regions  which  corre- 
spond to  those  on  the  surface.  Thus,  there  are  three  prominent  cords  and  three  fossae 
(fig.  1121). 

Three  cords — (1)  Median,  or  urachus;  (2)  lateral,  or  the  obliterated  hypogastric  arteries. 

(1)  Median,  or  urachus.  This  interesting  foetal  relic,  the  intra-abdominal  part  of  the 
allantois,  passes  up  between  the  apex  of  the  bladder  and  the  umbilicus. 

(2)  The  obliterated  hypogastric  arteries.  These,  the  remains  of  vessels  which  during 
foetal  life  carry  the  impure  blood  of  the  foetus  out  to  the  mother  through  the  umbilicus,  run 
up  and  join  the  urachus  at  the  umbilicus. 

In  relation  to  these  cords  are  the  following  fossae : — (a)  A  medial  one,  between  the  virachus 
and  the  obliterated  hypogastric  artery.  This  corresponds,  on  the  anterior  surface,  to  the 
subcutaneous  inguinal  (external  abdominal)  ring.  Through  this  fossa  comes  the  commonest 
form  of  direct  inguinal  hernia,  (ft)  Between  the  obliterated  hypogastric  artery  and  the  inferior 
epigastric  artery,  which  runs  upward  and  medially  to  form  the  lateral  boundary  of  Hessel- 
bach's  triangle,  is  an  intermediate  fossa.  This  is  the  smallest  of  all.  The  rarer  form  of  direct 
hernia  comes  tlirough  here,  (c)  The  lateral  fossa  is  lateral  to  the  inferior  epigastric  artery.  It 
is  the  most  distinct  of  the  three,  from  the  way  in  which  the  cord  or  round  ligament  passes  down 
within  a  glove-like  vaginal  process  of  the  transversalis  fascia.  This  fossa  corresponds  to  the 
abdominal  ring. 

The  coverings  of  a  direct  hernia  may  now  be  considered,  together  with  the  two-fold  manner 
of  exit  of  this  hernia.  It  only  traverses  the  lower  part  of  the  canal,  making  its  way  through 
either  the  medial  or  the  intermediate  inguinal  pouch,  (i)  The  commonest  form,  coming 
through  the  medial  inguinal  pouch,  either  pushes  its  way  through  or  stretches  before  it  the  falx 
inguinalis.  Its  coverings  are: — (1)  Peritoneum;  (2)  extra-peritoneal  fat;  (3)  transversalis  fascia; 
(4)  falx  inguinalis  (unless  this  is  suddenly  burst  through);  (5)  (6)  (7).  At  the  subcutaneous 
ring  the  three  coverings  are  the  same  as  in  the  oblique  variety,  (ii)  This  rarer  form  of  direct 
hernia  comes  through  the  intermediate  inguinal  pouch.  As  a  rule,  the  falx  inguinalis  does  not 
reach  over  this  fossa.  The  coverings  will  be  the  same  as  in  the  last,  with  two  exceptions — 
there  is  no  falx  inguinalis,  and  the  cremasteric  fascia,  if  well  developed,  will  be  present. 

Varieties  of  inguinal  hernia  according  to  the  condition  of  the  vaginal  process  of  peritoneum. 
— Inguinal  herniEe  have  above  been  classified  according  to  tlieir  relation  to  the  deep  epigastric 
artery.  It  remains  to  allude  to  the  arrangement  of  these  same  hernias  according  to  the  varying 
condition  of  the  processus  vaginalis.  This  pouch  of  peritoneum,  which  paves  the  way  for  the 
passage  of  the  testis  before  this  organ  makes  its  start,  eventually  becomes  the  parietal  layer 
(p.  1387)  of  the  tunica  vaginalis  below,  in  this  fashion:  During  the  first  few  weeks  after  birth 
the  process  becomes  obliterated  at  two  spots — one  near  the  abdominal  ring,  and  one  just 
above  the  testis.  The  obliterative  process,  commencing  first  above  and  descending,  and  then, 
ascending  from  below,  the  shrivelling  continues  until  nothing  is  lett  save  the  tunica  vaginalis 
below.     The  following  are  possible  hernial  results  of  an  imperfect  obliteration  of  the  process: — 

(1)  If  the  process  does  not  close  at  all,  a  descending  hernia  is  called  congenital.  This  may 
make  its  way  into  the  scrotum.     The  testis  is  now  enveloped  and  concealed  by  the  hernia. 

(2)  If  the  process  is  closed  only  above,  i.  e.,  near  the  abdominal  ring,  two  varieties  may  be 
met  with,  the  infantile  and  the  infantile  encysted.  In  the  infantile,  owing  to  pressure  above,  the 
weak  septum  gradually  yields  and  forms  a  sac  behind  the  unobliterated  lower  part  of  the  pro- 
cessus funiculo-vaginalis.  Thus  three  layers  of  peritoneum  may  now  be  met  with  in  an  opera- 
tion, the  two  of  the  incompletely  obliterated  tunica  vaginalis,  and  the  proper  sac  of  the  hernia. 
In  the  encysted  infantile  variety  the  hernial  pressure  causes  the  septum  to  yield  and  form  a  sac 
projecting  into,  not  behind,  the  incompletely  obliterated  tunica  vaginalis.  Here,  theoretically, 
two  layers  of  peritoneum  will  be  met  with.  Another  variety  of  such  an  encysted  hernia  may 
be  produced  by  rupture,  not  stretching,  of  the  above-mentioned  septum. 

(3)  If  the  processus  vaginalis  be  closed  below  and  not  above,  a  patent  tubular  process  of 
peritoneum  will  lead  down  as  far  as  the  top  of  the  testis.  Any  hernia  into  this  process  is  called 
a  hernia  into  the  funicular  process.  All  these  varieties  save  the  congenital  and  hernia  into  the 
funicular  process  are  rare  in  practice.  Other  practical  points  are  that  all  hernise  in  children  and 
young  adults  are  probably  of  congenital  origin,  and,  therefore,  the  weakness  is  often  bilateral, 
though  it  may  not  be  so  palpably.  This  applies  to  both  sexes.  Again  in  hernia  of  sudden 
origin  into  the  funicular  process  with  narrow  surroundings,  strangulation  may  be  very  acute. 

Inguinal  hernia  in  the  female. — The  inguinal  canal  in  women  is  smaller  and  narrower  than 
in  men.  Inguinal  hernia  is,  therefore,  less  common  in  the  female  sex,  and  occurs  in  patients  who 
happen  to  be  tlie  subjects  of  an  unobliterated  processus  vaginalis,  which  extends  for  a  varying 
distance  along  the  round  ligament,  and  is  called  the  canal  of  Nuok.  Inguinal  hernia  in  the 
female  is,  therefore,  always  congenital.  It  is,  practically,  always  of  the  oblique  variety,  and 
travels  along  the  round  ligament  toward  the  labium  majus.  Its  coverings  will  be  the  same  as 
those  of  the  oblique  variety  in  the  male,  save  that  the  cremaster,  as  a  distinct  muscle,  is  absent, 
and  any  fibres  of  the  internal  oblique  which  may  be    present  are  but  little  developed. 

FEMORAL  HERNIA 

Parts  concerned  in  femoral  hernia. — (1)  Skin  and  superficial  fascia  of  groin. 
— The  latter  consists  of  two  layers:  (a)  Superficial  layer  of  superficial  fascia. — 

Fatty,  met  with  over  the  whole  groin,  and  continuous  with  the  superficial  fascia 


FEMORAL  HERNIA 


1399 


of  the  rest  of  the  body,  (b)  Deep  layer  of  superficial  fascia. — Thin  and  mem- 
branous, only  met  with  over  the  lower  third  of  the  abdominal  wall  and  to  the 
medial  side  of  the  groin. 

It  is  continuous  through  the  scrotum  with  the  deep  layer  of  the  superficial  fascia  of  the 
perineum.  Just  below  the  inguinal  hgament  it  is  joined  to  the  fascia  lata.  From  these  two 
facts  it  results  that  in  rupture  or  giving  way  of  the  urethra  the  extravasated  urine  may  come 
forward  by  way  of  the  genitals  (p.  13S5)  and  from  the  continuity  of  the  fascia  make  its  way  on 
to  the  abdomen,  but  not  down  on  to  the  thigh. 

Between  the  two  layers  of  superficial  fascia  lie  the  superficial  nodes  of  the  groin,  the  super- 
ficial branches  of  the  common  femoral  artery,  one  or  two  cutaneous  nerves,  and  some  veins 
descending  to  the  fossa  ovahs  to  join  the  great  saphenous  vein. 

(2)  Inguinal  (Poupart's)  ligament. — This  is  also  known  as  the  crural  arch,  a 
misnomer,  as  'crus'  means  leg.  A  description  of  its  shape  and  attachments  is 
given  on  p.  1371.  Owing  to  the  connection  of  the  fascia  lata  to  its  lower  border, 
the  fossa  ovalis  (saphenous  opening),  which  is  situated  in  the  fascia  lata,  and  has 
its  upper  cornu  blending  with  the  inguinal  ligament,  will  be  affected  by  movements 
of  the  thigh,  much  as  is  the  subcutaneous  inguinal  (external  abdominal)  ring, 
being  tightened  and  stretched  when  the  limb  is  extended  and  abducted,  relaxed 
when  it  is  adducted  and  flexed. 


Fig.  1122. — The  LAnrNi?  ekneath  the  Inguinal  Ligament.     (Lookwood.) 


— ■    Inguinal  ligament 
Muscular  lacuna 

Ilio-pectineal  Hgament^l 

1  \  \  \ 

Vascular  lacuna 
Hio-pectineal  eminenc 

Cooper's  ligament 
Lacunar  ligament 

Spermatic  cord 


The  parts  beneath  the  ligament  which  block  up  the  gap  between  it  and  the 
innominate  bone  are  of  the  utmost  importance  in  preventing  the  escape  of  a 
femoral  hernia  (fig.  1122). 

The  different  structures  are  arranged  in  three  compartments  (fig.  1122), 
named  latero-medially : — A.  lateral,  iliac,  or  muscular;  B.  central,  or  vascular; 
and  C.  medial,  or  pectineal.  Of  these,  the  first  is  the  largest;  the  second  or 
intermediate  one  lies  slightly  nearer  to  the  inguinal  ligament  than  the  other  two ; 
while  the  medial  compartment  differs  from  the  other  two  by  not  communicating 
with  the  pelvis,  being  closed  above  {vide  infra). 

(A)  The  lateral,  or  iliac,  compartment  is  bounded  in  front  by  the  inguinal  ligament  and  the 
iliac  fascia,  which  is  here  blending  with  it,  behind  by  the  ihum,  laterally  by  this  bone  and  the 
sartorius,  and  medially  by  the  ilio-pectineal  septum,  which,  descending  from  the  blending 
of , the  iliac  fascia  and  the  inguinal  ligament  above,  passes  down  to  the  iUo-pectineal  eminence, 
and  thence  to  the  medial  aspect  of  the  front  of  the  capsule  of  the  hip-joint.  This  compartment 
transmits  the  ilio-psoas  and  femoral  (anterior  crural)  and  lateral  cutaneous  nerves.  (B)  The 
vascular  compartment  is  bounded,  in  front,  by  the  inguinal  ligament  and  the  transversahs 
fascia,  which  here  blends  with  it,  forming  the  so-called  deep  crui'al  arch,  and  at  the  same  time 


1400  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

descends  on  to  the  front  of  the  femoral  sheath.  The  posterior  boundary,  Cooper's  ligament,  is 
formed  by  the  meeting  of  the  ilio-pectineal  septum  laterally  and  the  pectineal  fascia  or  sheath — 
medially  the  lacunar  (Gimbernat's)  ligament,  and  laterally  the  ilio-pectineal  septum.  This 
intermediate  compartment  transmits  the  ex  ernal  iliac  vessels  and  the  lumbo-inguinal  nerve. 
This  lies  to  the  lateral  side  of  the  artery,  the  vein  medially.  Between  the  vein  and  the  base  of 
the  lacunar  ligament  is  the  femoral  canal  (vide  infra).  (C)  The  medial  or  pectineal  compart- 
ment is  bounded  by  the  pectineal  fascia,  continuous  with  the  pubic  part  of  the  fascia  lata,  and 
behind  by  the  pubic  ramus.  It  lodges  the  upper  end  of  the  pectineus  muscle,  and  the  handle  of 
a  scalpel  passed  upward  along  the  muscle  would  be  prevented  from  passing  into  the  pelvis  by  the 
lacunar  ligament  and  the  blending  of  the  pectineal  fascia  with  the  upper  border  of  the  pubic 
ramus. 

(3)  Lacunar  (Gimbernat's)  ligament. — This  is  merely  tlie  triangular  medial 
attachment  of  Poupart's  ligament.  Its  apex  is  attached  to  the  pubic  tubercle; 
of  its  three  borders,  the  base  is  free  toward  the  vein  and  the  femoral  canal. 
Its  upper  border  is  continuous  with  Poupart's  ligament;  its  lower  is  attached  to 
the  terminal  (ilio-pectineal)  line. 

(4)  Fascia  lata. — Two  portions  are  described  over  the  upper  part  of  the  thigh : 
■ — (a)  An  iliac,  lateral  and  stronger,  attached  to  the  inguinal  ligament  in  its  whole 
extent  and  lying  over  the  sartorius,  ilio-psoas,  and  rectus.  (6)  A  pubic,  medial, 
weaker,  and  much  less  well  defined,  is  attached  above  to  the  terminal  line  and 
the  tubercle  of  the  pubes.  The  upper  cornu  of  the  fossa  ovalis  is  at  the  lacunar 
ligament,  and  at  the  lower  cornu  the  two  portions  of  the  fascia  blend. 

Their  relation  to  the  femoral  vessels. — The  iliac  portion,  being  attached  along 
Poupart's  ligament,  passes  over  these.  The  pubic  portion,  fastened  down  over 
the  pectineus,  which  slopes  down  on  to  a  deeper  plane  than  the  adjacent  muscles, 
passes  behind  the  femoral  vessels  to  end  on  the  capsule  of  the  hip-joint. 

(5)  Fossa  ovaUs  (saphenous  opening). — This  is  not  an  opening,  but  an  oval 
depression,  situated  at  the  spot  where  the  two  parts  of  the  fascia  lata  diverge  on 
different  levels.  Though  the  fascia  lata  is  wanting  here,  there  is  no  real  opening, 
as  the  deficiency  is  made  up  by  the  deep  layer  of  superficial  fascia,  or  cribriform 
fascia,  which  fills  up  the  opening. 

Uses  of  the  fossa  ovalis  {saphenous  opening). — Though  a  weak  spot,  it  is  so  on  purpose  to 
transmit  the  saphenous  to  the  femoral  vein,  and  the  superficial  to  the  deep  lymphatics.  The 
depression  is  present  in  order  to  allow  the  saphenous  vein  to  be  protected  from  pressure  in 
flexion  of  the  thigh. 

Site. — At  the  medial  and  upper  part  of  the  thigh,  with  its  centre  3.7  cm.  (1 J  in.)  below  and 
lateral  to  the  tubercle  of  the  pubis. 

Diameters. — Vertically,  2.5  cm.  (1  in.),  by  1.2  or  1.8  cm.  (|  or  f  in.).  Shape:  oval,  with 
its  long  axis  downward  and  laterally.  Two  exlremities  or  cornua:  upper  blending  with  the 
lacunar  ligament;  lower,  where  the  two  parts  of  the  fascia  lata  meet.  Two  borders:  lateral  or  falci- 
form, also  known  as  the  ligament  of  Hey,  or  femoral  ligament.  Semilunar  in  shape,  arching 
downward  and  laterally  from  the  lacunar  ligament  to  the  inferior  cornu.  This  lies  over  the 
femoral  vessels,  and  is  adherent  to  thezn;  to  it  is  fixed  superficially  the  cribriform  fascia  {vide 
infra).  The  medial  border  is  much  less  prominent,  owing  to  the  weakness  of  the  pubic  part 
of  the  fascia  lata  which  forms  it. 

(6)  Femoral  sheath. — This  is  a  funnel-shaped  sheath,  carried  out  by  the 
femoral  vessels  under  Poupart's  ligament,  and  continuous  above  (in  front)  with 
the  transversalis  fascia  as  it  descends  to  the  ligament,  lining  the  inner  surface 
of  the  abdominal  wall;  and  (behind)  with  the  iliac  fascia,  and  below  continuous 
with  the  proper  sheath  of  the  femoral  vessels. 

It  is  not  only  funnel-shaped,  but  large  and  loose,  for  two  reasons: — {a)  That  there  be  plenty 
of  room  for  the  femoral  vein  and  the  slowly  moving  venous  current  in  it  to  ascend  without  com- 
pression; (b)  to  allow  all  the  movements  of  the  thigh  taking  place — flexion  and  extension — 
without  undue  stretching  of  the  vessels.  By  two  connective-tissue  septa  the  sheath  is  divided 
into  three  compartments — the  lateral  for  the  artery,  the  intermediate  for  the  vein,  and  the 
medial  one  for  the  femoral  canal  {vide  infra).  Thus  one  septum  lies  between  the  artery  and 
vein,  and  another  between  the  vein  and  the  femoral  canal. 

(7)  Femoral  canal. — Definition:  the  medial  division  of  the  femoral  sheath. 
The  fascia  transversalis  and  fascia  iliaca  meet  directly  on  the  lateral  side  of  the 
femoral  artery,  but  not  so  closely  on  the  medial  side  of  the  femoral  vein.  Hence 
a  space  exists  here,  perhaps  to  prevent  the  thin-walled  vein,  with  its  sluggish 
current,  being  pressed  upon,  but  it  is  merely  a  slight  gap — not  a  canal,  unless  so 
made  by  a  knife  or  by  the  dilating  influence  of  a  hernia. 

Length:  about  1.9  cm.  (J  in.).  Limits:  below,  fossa  ovalis;  above,  femoral  ring  {vide 
infra). 


FEMORAL  HERNIA 


1401 


Boundaries. — Laterally,  a  septum  between  it  and  the  vein;  medially,  base  of  the  lacunar 
ligament  and  meeting  of  fascia  iliaca  and  transversalis;  behind,  fascia  iliaca;  in  front,  fascia 
transversalis. 

Contents. — Cellular  tissue  and  fat,  continuous  with  extra-peritoneal  fatty  layer.  A  lym- 
phatic node,  which  is  inconstant.'  Lymphatics  passing  from  inguinal  nodes  to  those  in  the 
pelvis. 

(8)  Femoral  ring. — This  is  mainly  an  artificial  product.  It  is  the  upper  or 
abdominal  opening  of  the  femoral  canal.  Shape:  oval,  with  its  long  axis  trans- 
verse. It  is  larger  in  women.  Boundaries:  medially,  the  lacunar  ligament; 
laterally,  the  femoral  vein;  in  front,  the  inguinal  ligament  and  the  thickening 
of  the  transversahs  fascia  attached  to  it,  and  called  'the  deep  crural  arch'; 
behind  the  pectineus  and  Cooper's  ligament,  a  thickened  fascial  bundle  attached 

Fig.  1123. — Irregulahities  of  the  Obturator  Artery.     (After  Gray.) 
A 


External  iliac  artery 
External  iliac  vein 


Obturator  foramen 


—    Inferior  epigastric  artery 


Lymphatic  node  in  femoral  ring 

The  obturator  artery,  given  off 
from  the  external  iliac  with  the 
inferior  epigastric,  descends  to 
gain  the  obturator  foramen,  but 
at    a    safe    distance  from    the 


The  obturator  artery,  coming  off 
from  the  inferior  epigastric, 
takes  a  course  so  near  to  the 
femoral  ring  that  it  would  very 
likely  be  divided  by  the  bis- 
toury introduced  from  without 
to  divide  the  base  of  the  lacunar 
ligament,  the  cause  of  the  con- 
strictioii 


to  the  hnea  terminalis  (fig.  1122).  It  is  closed  by  the  septum  crurale,  which 
is  a  barrier  of  fatty  connective  tissue,  continuous  with  the  extra-peritoneal 
fatty  layer,  perforated  by  lymphatics  passing  upward  to  the  pelvic  nodes. 

Position  of  vessels  around  the  ring. — Laterally  the  femoral  vein;  above,  the 
epigastric  vessels  as  they  ascend  from  the  external  iliac  vessels,  pass  close  to  the 
upper  and  lateral  aspect  of  the  ring;  immediately  in  front  are  the  cord  and  sper- 
matic vessels  always  to  be  remembered  in  this  hernia  in  the  male;  toward  the 
medial  side  there  may  be  an  unimportant  anastomosis  between  the  epigastric 
artery  above  and  the  obturator  below. 

If  from  dilatation  of  the  above  anastomosis  the  obturator  artery  comes  off  abnormally 
from  the  inferior  epigastric,  it  will  descend,  and  usually  does  so,  close  to  the  junction  of  the  ex- 
ternal iliac  and  common  femoral  vein,  and  thus  to  the  lateral  and  so  the  safe,  side  of  the  ring 
(fig.  1123,  A).  In  a  very  few  cases  it  curves  more  mediallj',  close  to  the  lacunar  ligament,  and 
thus  to  the  medial  side  of  the  ring,  and  is  then  in  great  danger  (fig.  1123,  B).     In  two  out  of 


1402  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

every  five  cases  the  obturator  arises  from  the  inferior  epigastric.  In  about  thirty-seven  per 
cent,  of  the  eases  with  such  an  origin  the  artery  either  crosses  or  courses  along  the  side  of  the 
ring.     (Cunningham.) 

Course  of  femoral  hernia. — At  first  this  is  downward  in  the  femoral  canal.  A  pouch  of 
peritoneum  having  been  gradually,  after  repeated  straining,  coughing,  etc.,  pushed  through  the 
weak  spot,  the  femoral  ring,  further  weakened  perhaps,  together  with  all  the  parts  in  the  fem- 
oral arch,  by  child-bearing,  some  extra  effort  will  force  intestine  or  omentum  into  this  pouch  and 
thus  form  a  hernia.  Thus  formed,  femoral  hernia  passes  at  first  downward  in  the  femoral  canal 
as  far  as  the  fossa  ovaUs,  but,  as  a  rule,  does  not  go  farther  downward  on  the  thigh,  but  mounts 
forward  and  upward,  and  somewhat  laterally,  even  reaching  the  level  of  the  inguinal  ligament. 
The  reasons  for  this  change  of  position  are: — (1)  The  narrowing  of  the  femoral  sheath,  funnel- 
like, i.  e.,  wide  above,  but  narrowed  below;  (2)  the  unyielding  nature  of  the  lower  margin  of  the 
fossa  ovalis;  (3)  the  fact  that  this  margin  and  the  lateral  border  are  united  to  the  femoral  sheath; 
(4)  the  constant  flexion  of  the  thigh;  (.5)  the  fact  that  vessels  (cliiefly  veins)  and  lymphatics 
descend  to  the  fossa  ovaUs,  the  veins  to  join  the  saphenous  vein  and  the  lymphatics  to  join 
the  deeper  group;  these  descending  vessels  serve  to  loop  upward  or  suspend  a  femoral  hernia, 
and  thus  prevent  its  further  course  downward. 

Coverings  of  a  femoral  hernia. — (A)  At  the  upper  or  femoral  ring  it  obtains 
peritoneum,  extra-peritoneal  fat,  and  septum  femorale  (crurale). 

(B)  In  the  canal,  a  coating  of  the  femoral  sheath. 

(C)  At  the  external  opening,  further  coverings  of  cribriform  fascia,  skin, 
and  superficial  fascia  are  added. 

Some  of  these  may  be  deficient  by  the  hernia  bursting  through  them,  or  they  may  be  matted 
together.  Sir  A.  Cooper  thought  this  especially  likely  to  occur  with  the  layer  of  femoral  sheath 
and  septum  crurale,  to  which  he  gave  the  name  oi  fascia  propria. 

The  relations  of  an  inguinal  and  femoral  hernia  respectively  to  the  pubic  tubercle  are  of 
importance  in  distinguishing  between  them  clinically.  If  a  finger  is  placed  on  the  pubic  tubercle 
a  hernia  that  lies  above  and  medial  to  it  will  be  inguinal,  one  below  and  lateral  to  it  wiU  be 
femoral. 

Radical  cure  of  femoral  hernia. — The  close  proximity  of  the  femoral  vein  always  intro- 
duces difficulty  in  the  introduction  of  the  deep  sutures  for  closure  of  the  crural  ring.  Any  clo- 
sure below  this  point  is  certain  to  be  inefiicient.  The  safest  and  simplest  method  is  to  feel 
for  the  pulsation  of  the  femoral  artery,  and  make  allowance  for  the  vein  on  its  medial  side.  The 
latter  vessel  is  then  protected  by  the  finger-tip  passed  up  the  femoral  canal,  so  that  its  dorsum 
rests  against  the  vein  and  its  tip  upon  the  linea  terminalis.  The  sutures  are  then  passed  so 
as  to  pick  up  the  ilio-peotineal  fascia  and  its  thickened  part.  Cooper's  ligament,  below,  and  the 
deep  crural  arch  and  Poupart's  ligament  above  (fig.  1122).  Thus,  when  tightened,  they  draw 
the  anterior  and  posterior  boundaries  of  the  ring  together.     (Lockwood,  Bassini.) 

PARTS  CONCERNED  IN  UMBILICAL  HERNIA 

A  hernial  protrusion  at  the  umbilicus,  or  exomphalos,  may  occur  at  three 
distinct  periods  of  life,  according  to  the  anatomy  of  the  part.  Any  account  of 
umbilical  hernia  would  be  incomplete  without  an  attempt  to  explain  how  this 
region,  originally  a  most  distinct  opening,  is  gradually  closed  and  changed  into 
a  knotty  mass  of  scar,  the  strongest  point  in  the  abdominal  wall. 

During  the  first  weeks  of  foetal  life,  in  addition  to  the  urachus,  umbilical 
arteries,  and  vein,  some  of  the  mesentery  and  a  loop  of  the  intestine  pass  through 
the  opening  to  occupy  a  portion  of  the  body  cavity  situated  in  the  umbilical  cord, 
later  on  returning  to  the  abdominal  cavity.  Occasionally  this  condition  persists, 
owing  to  failure  of  development,  and  the  child  is  born  with  a  large  hernial  swell- 
ing outside  the  abdomen,  imperfectly  covered  ^vith  skin  and  peritoneum.  To 
tlais  condition  the  term  congenital  umbilical  hernia  should  be  applied. 

Later  on  in  foetal  life  it  is  the  umbilical  vessels  alone  which  pass  through  this 
opening.  At  birth  there  is  a  distinct  ring,  which  can  be  felt  for  some  time  after 
in  the  flaccid  walls  of  an  infant's  belly.  If  this  condition  persist,  a  piece  of 
intestine  may  find  its  way  through,  forming  the  condition  which  should  be  known 
as  infantile  umbilical  hernia. 

This  condition  is  not  uncommon.  Why  it  is  not  more  frequently  met  with 
is  explained  by  the  way  in  which  this  ring  of  infancy  is  closed  and  gradually 
converted  into  the  dense  mass  of  scar  tissue  so  familiar  in  adult  life.  This  is 
brought  about — (1)  by  changes  in  the  ring  itself;  (2)  by  changes  in  the  vessels 
which  pass  through  it. 

(1)  Changes  in  the  ring  itself. — The  umbilical  ring  is  surrounded  by  a  sphincter-like 
arrangement  of  elastic  fibres,  best  seen  during  the  first  few  days  of  extra-uterine  life,  on  the 


THE  BACK  1403 

posterior  aspect  of  the  belly  wall.  In  older  infants  these  fibres  lose  their  elasticity,  become 
more  tendinous,  and  then  shrink  more  and  more.  As  they  contract  they  divide,  as  by  a  liga- 
ture, the  vessels  passing  through  the  ring,  thus  accounting  for  the  fact  that  the  cord,  wher- 
ever divided,  drops  off  at  the  same  spot  and  without  bleeding. 

(2)  Changes  in  the  vessels  themselves. — When  blood  ceases  to  traverse  these,  their  lumen 
contains  clots,  their  muscular  tissue  wastes,  while  the  connective  tissue  of  their  outer  coat 
hypertrophies  and  thickens.  Thus,  the  umbilical  vessels  and  the  umbilical  ring  are,  alike, 
converted  into  scar  tissue,  which  blends  together.  This  remains  weak  for  some  time,  and  may 
be  distended  by  a  hernia  (infantile). 

Finally,  we  have  to  consider  the  state  of  the  umbilicus  in  adult  life.  The  very  dense, 
unyielding,  fibrous  knot  shows  two  sets  of  fibres: — (1)  Those  decussating  in  the  middle  line; 
and  (2)  two  sets  of  circular  fibrous  bundles  which  interlace  at  the  lateral  boundaries  of  the 
ring.  The  lower  part  of  the  ring  is  stronger  than  the  upper.  In  other  words,  umbilical  hernia 
of  adult  life,  when  it  comes  through  the  ring  itself  and  not  at  the  side,  always  comes  through 
the  upper  part.  In  the  lower  three-fourths  of  the  umbilicus  the  umbihcal  arteries  and  urachus 
are  firmly  closed  by  matting  in  a  firm  knot  of  scar  tissue;  in  the  upper  there  is  only  the  umbil- 
ical vein  and  weaker  scar.  To  the  lower  part  run  up  the  umbilical  arteries  and  the  urachus. 
Owing  to  the  rapid  growth  of  the  abdominal  wall  and  pelvis  before  puberty,  and  the  fact 
that  the  urachus  and  the  umbilical  arteries,  being  of  soar  tissue,  elongate  with  difficulty,  the 
latter  parts  depress  the  umbilicus  by  reason  of  their  intimate  connection  with  its  lower  half. 

Owing  to  the  usual  exit  of  an  umbilical  hernia  of  adult  life  being  through  the  upper  part  of 
the  ring,  the  constricting  edge  in  strangulation  should  be  sought  below  and  divided  downward. 
As  pointed  out  by  Mr.  Wood,  it  is  here  that  the  dragging  weight  of  the  hernial  contents  and  the 
weight  of  the  dress  tend  to  produce  the  chief  results  of  strangulation.  An  incision  here  also 
gives  better  drainage  if  required. 

Coverings  of  an  umbilical  hernia. — These,  more  or  less  matted  together,  are : — 
(1)  Skin;  (2)  superficial  fascia,  which  loses  its  fat  over  the  hernia;  (3)  prolonga- 
tion of  scar  tissue  of  the  umbilicus  gradually  stretched  out;  (4)  transversalis 
fascia;  (5)  extra-peritoneal  fatty  tissue;  (6)  peritoneum.  If  the  hernia  come 
through  above  the  umbilicus,  or  just  to  one  side,  the  coverings  will  be  much  the 
same;  but,  instead  of  the  layer  from  the  umbilical  scar,  there  will  be  one  from  the 
linea  alba. 

Strangulated  umbilical  hernia  of  adult  life. — In  this,  the  most  fatal  of  the  strangulated 
hernise  ordinarily  met  with,  the  following  are  practical  points  in  the  surgical  anatomy: — 1.  The 
coverings,  including  the  sac,  are  always  thin,  at  times  so  markedly  so  that  the  intra-peritoneal 
contents  are  practically  subcutaneous.  2.  The  sac  is  multilocular,  and  one  or  more  of  its  cham- 
bers may  he  very  deep.  3.  The  contents  are  numerous,  viz.,  omentum,  often  voluminous  and 
adherent,  transverse  colon,  and  later  in  the  history,  small  intestine.  4.  The  contents  are  often 
adherent  to  the  sac  and  each  other,  thus  explaining  the  irreduoibility.  5.  The  long  duration 
of  the  presence  of  the  transverse  colon  with  its  stouter  walls  accounts  for  the  period,  often  pro- 
longed, in  which  warning  evidence  of  incarceration  precedes  that  of  strangulation.  6.  The 
communication  with  the  peritoneal  sac  is  direct,  short,  and  during  a  prolonged  operation,  free. 
Infection  is  thus  readily  brought  about. 

THE  BACK 

The  surface  form  and  landmarks  of  the  back  will  be  considered  first,  followed 
by  the  relations  of  skeleton,  muscles,  viscera  and  nervous  system. 

Median  furrow. — This  is  more  or  less  marked  according  to  the  muscular 
development,  lying  between  the  trapezii  and  semispinales  capitis,  in  the  cervical 
region,  and  the  sacro-spinales  lower  down.  The  lower  end  of  the  furrow  corre- 
sponds to  the  interval  between  the  spines  of  the  last  lumbar  and  the  first  sacral 
vertebra.     (Holden.) 

Vertebral  spines. — Those  of  the  upper  cervical  region  are  scarcely  to  be  made 
out  even  by  deep  pressure.  That  of  the  axis  may  be  detected  in  a  thin  subject. 
Over  the  spines  of  the  middle  three  cervical  vertebrae  is  normally  a  hollow,  owing 
to  these  spines  receding  from  the  surface  to  allow  of  free  extension  of  the  neck. 
The  seventh  cervical  is  prominent,  as  its  name  denotes.  Between  the  skull  and 
atlas,  or  between  the  atlas  and  epistropheus,  a  pointed  instrument  might  pene- 
trate, especially  in  flexion  of  the  neck. 

Of  the  thoracic  spines,  the  first  is  the  most  prominent,  more  marked  than  that  of  the  last 
cervical;  the  tliird  should  iDe  noted  as  on  a  level  with  the  medial  end  of  the  scapular  spine,  and 
in  some  cases  with  the  bifurcation  of  the  trachea;  that  of  the  seventh  with  the  lower  angle  of 
the  scapula;  that  of  the  twelfth  with  the  lowest  part  of  the  trapezius  and  the  head  of  the  twelfth 
rib.     The  obliquity  and  overlapping_  of  the  thoracic  spines  are  to  be  remembered. 

Of  the  lumbar  spines,  the  most  important  are  the  second,  which  corresponds  to  the  termi- 
nation of  the  cord,  and  the  fourth,  which  marks  the  highest  part  of  the  iliac  crests  and  the 
bifurcation  of  the  abdominal  aorta.  The  lumbar  spines  project  horizontally,  and  correspond 
with  the  vertebral  bodies.     The  third  is  a  little  above  the  umbilicus. 


1404 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


Owing  to  the  obliquity  of  the  thoracic  spines,  most  of  them  do  not  tally  with  the  heads  of 
the  correspondino;  ribs.  Thus,  the  spine  of  the  second  corresponds  with  the  head  of  the  third 
rib ;  the  spine  of  the  third  with  the  head  of  the  fourth  rib ;  and  so  on  till  we  come  to  the  eleventh 
and  twelfth  vertebrae,  which  do  tally  with  then*  corresponding  ribs.     (Holden.) 

The  lower  ribs  may  be  felt  lateral  to  the  sacro-spinalis  but  in  counting  them 
from  below  it  must  be  remembered,  as  pointed  out  by  Holl,  that  in  quite  a 

Fig.  1124. — Diagram  and  Table  showing    the  Approximate   Relation  to  the  Spinal 

Nerves  of  the  various  Motor,  Sensory,  and  Reflex  Functions  of  the  Spinal  Cord. 

(Arranged  by  Dr.  Gowers  from  anatomical  and  pathological  data.) 

.,\^    i  MOTOR  SENSORY  REFLEX 


St  erno -mastoid 
Trapezius 


\  Serratus 
j  Shoulder 
Arm  \  muse. 


Flexors,  Mp 

Extensors,  knee 
Adductors 


Muscles  of  leg  mov- 
ing foot 


I7eck  and  scalp 
Neck  and  shoulder 


I  Shoulder 

Arm 


Front  of  thorax 


I  Buttock,  upper 
part 


[•  Groin  and  scrotum 
(front) 

Lateral  side 


Medial  side 
Leg,  medial  side 
Buttock,  lower 


Back  of  thigh 
Leg    ) 

and     >  except  medial 
[foot    J    part 

1  Perineum  and  anus 


[Scapular 


■  Cremasteric 

I  1 

J    I  Knee-joint 


Foot-clonus 
Plantar 


considerable  percentage  the  last  rib  is  so  abnormally  short  that  it  does  not  reach 
as  far  as  the  lateral  border  of  the  sacro-spinalis;  or  is  so  rudimentary  as  to  re- 
semble a  transverse  process  (consequently  the  only  safe  method  of  counting  ribs 
is  from  above).  In  these  cases  the  lower  end  of  the  pleura  maj^  pass  from  the 
lower  part  of  the  twelfth  thoracic  vertebra,  almost  horizontally  to  the  lower  edge 
of  the  eleventh,  rib. 


THE  BACK 


1405 


Muscles. — The  student  will  remember  the  greater  number  and  complexity  and  the  numerous 
tendons  of  the  muscles  which  run  up  on  either  side  of  the  spines;  the  firmness  and  inextensibility 
of  their  sheaths;  the  large  amount  of  cellular  tissue  between  them;  and  the  fact  that  toward  the 
nape  of  the  neclc  these  muscles  lie  exposed  instead  of  being  protected  in  gutters,  as  is  the  case 
below:  all  these  anatomical  points  explain  the  extreme  painfulness  and  obstinacy  of  sprains 
here. 

Trapezius. — To  map  out  this  muscle,  the  arm  should  be  raised  to  a  right  angle  with  the 
trunk.  The  external  occipital  protuberance  should  be  dotted  in,  and  the  superior  nuchal  line 
passing  out  from  this;  below,  the  twelfth  thoracic  spine  should  be  marked;  and  laterally,  the 
lateral  third  of  the  clavicle  and  the  commencement  of  the  scapular  spine.  Then  a  line  should 
be  drawn  from  the  protuberance  vertically  downward  to  the  twelfth  thoracic  spine;  a  second 
from  about  the  middle  of  the  superior  nuchal  line  to  the  posterior  and  lateral  third  of  the 
clavicle;  and  a  third  from  the  last  thoracic  spine  upward  and  laterally  to  the  root  of  the  spine 
of  the  scapula. 


Fig.  1125. — Relations  of  the  Abdominal  Visceba  to  the  Antbbiob  Body  Wall. 


Lateral  yertical  (mid- 
clavicular) line 


Sterno-xiphoid  line 


Addison*s  "trans- 
pyloric"  line 


Infracostal  line 


Hiac  colon 
Intertubercular  line 


Cfficum  and  vermiform  process 


Latissimus  dorsi. — The  arm  being  raised  above  a  right  angle,  the  spines  of  the  sLxth  thoracic 
and  the  third  sacral  vertebra  should  be  marked;  then  the  outer  Up  of  the  crest  of  the  Uium,  the 
lower  two  or  three  ribs,  the  lower  angle  of  the  scapula,  and  the  posterior  fold  of  the  axiUa,  and 
finally  the  intertubercular  (bicipital)  gi-oove  should  all  be  marked. 

A  vertical  line  from  the  sixth  thoracic  to  the  thu-d  sacral  spine  will  give  the  spinal  origin  of 
the  muscle.  Another  from  the  thu-d  sacral  spine  to  a  point  on  the  iliac  crest,  2.5  cm.  (1  in.)  or 
more  lateral  to  the  edge  of  the  sacro-spinalis,  will  give  the  origin  of  the  muscle  from  the  sheath 
of  the  sacro-spinalis  and  the  ilium.  A  line  from  the  sixth  thoracic  spine,  almost  transversely 
at  first,  with  increasing  slight  obliquity  over  the  inferior  angle  of  the  scapula  to  the  axilla  and 
intertubercular  groove,  will  mark  the  upper  border  of  the  muscle.  Another  very  oblique  line 
from  the  point  of  the  iliac  crest  upward  and  laterally  to  the  axilla  will  give  the  lower  border 
and  the  tapering  triangular  apex  of  the  insertion.  The  muscle  may  be  attached  to  the  angle 
of  the  scaptila,  or  separated  from  it  by  a  bursa. 


1406 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


Triangle  of  Petit. — This  small  space  lies  above  the  crest  of  the  ihum,  at  about 
its  centre,  bounded  by  the  anterior  edge  of  the  latissimus  behind  and  the  posterior 
border  of  the  external  obhque,  in  front.  Through  this  gap,  when  the  muscles 
are  weak,  a  lumbar  abscess  occasionally,  and  very  rarely,  a  lumbar  hernia,  may 
appear. 

Origin  of  spinal  nerves. — It  is  very  important  to  remember  the  relations  of 
these  to  the  vertebral  spines,  in  determining  the  results  of  disease  or  injury  of  the 
cord  and  the  parts  thereby  affected.  The  above  relations  may  be  given  briefly 
as  follows: — 

The  origins  of  the  eight  cervical  nerves  correspond  to  the  cord  between  the 
occiput  and  the  sixth  cervical  spine.     The  upper  six  thoracic  come  off  between 

Fig.  1126. — Chief  Arterial  Anastomoses  on  the  Scapula. 
(From  a  dissection  in  the  Hunterian  Museum.) 
Supra-spinatus     Transverse  scapular  artery 


Descending  branch  of  transversa  colli  artery 

Rhomboideus  minor 
Levator  scapulae 


Infra-spinatus 

Triceps,  cut 

Deltoid,  insertion 
Deltoid 


Trapezius 

Rhomboideus  major 

Teres  major  I 

[Teres  major,  insertion 
Circumflex  scapular  artery    Posterior  circumflex  artery 


the  above  spine  and  that  of  the  fifth  thoracic  vertebra.  The  origins  of  the 
lower  six  thoracic  nerves  correspond  to  the  interval  between  the  fourth  and  the 
tenth  thoracic  spines.  The  five  lumbar  arise  opposite  the  eleventh  and  twelfth 
thoracic  spines;  and  the  origins  of  the  five  sacral  correspond  to  the  first  lumbar 
spines.  The  diagram  and  table  (fig.  1124),  arranged  by  Dr.  Gowers  from 
anatomical  and  pathological  data,  show  the  relations  of  the  origins  of  the  nerves 
to  their  exits  from  the  vertebral  canal,  and  the  regions  supplied  by  each. 

Scapula,  its  muscles  and  arterial  anastomoses. — Amongst  the  landmarks 
in  the  back,  the  student  should  be  careful  to  trace  the  angles  and  borders  of  the 
scapula  as  far  as  these  are  accessible.  The  upper  border  is  the  one  most  thickly 
covered.  With  the  hands  hanging  down,  the  upper  (medial)  angle  corresponds 
to  the  upper  border  of  the  second  rib;  the  lower  angle  to  the  seventh  intercostal 
space;  and  the  root  of  the  spine  of  the  scapula  to  the  interval  between  the  third 
and  fourth  thoracic  spines. 


THE  BACK 


1407 


The  axillary  border  of  the  scapula,  covered  by  the  latissimus  dorsi  and  teres  major,  may 
best  be  palpated  with  the  arm  hanging  to  the  side.  The  vertebral  border  is  brought  into 
prominence  by  placing  the  hand  on  the  opposite  shoulder.  This  border  is  held  in  apposition 
with  the  thorax  by  the  serratus  anterior;  consequently  in  paralysis  of  that  muscle,  supplied  by 
the  long  thoracic  nerve  (5,  6,  and  7  C),  it  becomes  unduly  prominent,  giving  rise  to  "winged 
scapula."  Fig.  1126  shows  the  chief  arteries  around  the  scapula.  The  anastomoses  on  the 
acromial  process  between  the  transverse  scapular  (supra-scapular)  thoraoo-acromial,  and 
circumflex  humeral  arteries  are  not  shown.  The  numerous  points  of  ossification,  primary  and 
secondary,  by  which  this  bone  is  developed  explain,  in  part,  the  frequency  of  cartilaginous  and 
other  growths  here. 

The  anatomy  of  the  loin  behind,  the  ilio-costal  region,  is  of  prime  importance,  owing  to  the 
numerous  operations  here.  The  lateral  border  of  the  sacro-spinalis  and  quadratus  lumborum 
may  be  indicated  on  the  surface  thus.  (Stiles.)  That  of  the  sacro-spinalis  by  drawing  a  line 
from  a  point  on  the  Oiac  crest  8.2  cm.  (Sj  in.)  (four  fingers'-breadth)  from  the  middle  line  up- 
ward and  slightly  laterally  to  the  angles  of  the  ribs.  That  of  the  quadratus  passing  upward 
and  sUghtly  medially  Ues  a  little  lateral  to  that  of  the  sacro-spinahs  (erector)  at  the  crest, 

Fig.  1127. — Relations  of  the  Abdominal  Viscera  to  the  Posterior  Body  Wall. 


and  a  little  medial  to  it  at  the  twelfth  rib.  The  ascending  and  descending  colon  lie  in  the 
slightly  depressed  angle  between  the  two  muscles.  The  iho-costal  region  varies  greatly  in 
space  according  to  the  length  of  the  lower  ribs,  shape  of  the  chest,  and  development  of  the  ihac 
crest.  An  incision  here — that  for  exploration  of  the  kidney  may  be  taken  as  the  type — would  be 
an  oblique  one,  about  10  cm.  (4  in.)  long,  starting  in  the  angle'between  the  twelfth  rib  and  the 
sacro-spinahs  muscle  and  passing  forward  and  downward  toward  the  anterior  extremity  of 
the  iliac  crest.  In  its  upper  part  the  incision  should  lie  1.2  cm.  (J  in.)  below  the  tweltfh  rib. 
The  anterior  fibres  of  the  latissimus  dorsi  are  divided  behind,  the  posterior  ones  of  the  external 
oblique  in  front.  The  yellowish-white  lumbar  fascia  now  comes  into  view,  and  is  the  first 
important  landmark.  It  and  the  fibres  of  the  internal  oblique  and  transversus  which  arise 
from  it  are  next  carefully  divided.  The  last  thoracic  nerve  and  lowest  intercostal  artery  may 
also  require  division.  If  the  latter  is  cut  close  to  the  rib,  the  htemorrhage  is  troublesome.  The 
transversalis  fascia  remains  to  be  divided.     To  avoid  the  peritoneum,  the  deeper  part  of  the 


1408  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

incisions  should  always  be  made  from  behind  forward.  If  more  room  is  required,  as  in  large 
growths  or  in  exploration  of  the  ureter,  the  incision  must  be  prolonged  beyond  the  iliac  crest, 
the  lumbo-ilio-inguinal  incision  of  Morris. 

Viscera. — Several  of  these,  which  can  be  mapped  in  behind — viz.,  the  kidneys, 
spleen,  etc. — have  been  already  mentioned  (pp.  1375,  1379). 

The  commencement  of  the  trachea  and  oesophagus  has  been  given  in  front  as 
corresponding  to  the  sixth  cervical  vertebra.  If  examined  from  behind,  this 
point,  o-sving  to  the  obliquity  of  the  spines,  would  be  a  httle  lower  down.  The 
trachea,  about  12.5  cm.  (5  in.)  long,  descending  in  the  middle  line,  bifurcates 
opposite  to  the  interval  between  the  third  and  fourth  thoracic  spines  (or  fourth 
and  fifth  bodies).  The  bronchi  enter  the  lungs  at  about  the  level  of  the  fifth 
thoracic  spine,  the  right  being  the  shorter,  wider,  and  more  horizontal.  The 
root  of  the  lung  is  opposite  to  the  fourth,  fifth,  and  sixth  dorsal  spines,  midway 
between  these  and  the  vertebral  border  of  the  scapula.  The  structures  in  it  are 
the  bronchus,  pulmonary  artery,  two  pulmonary  veins,  bronchial  vessels,  lymph- 
atics, and  nerves.  The  phrenic  nerve  is  in  front,  the  posterior  pulmonary  plexus 
behind.  On  the  right  side  the  superior  vena  cava  is  in  front,  the  vena  azygos 
(major)  arching  over  the  root  at  the  level  of  the  fourth  thoracic  vertebra.  On 
the  left  side  the  aorta  arches  over  the  root,  and  the  thoracic  aorta  descends 
behind  it.  The  oesophagus,  about  25  cm.  (10  in.)  in  length,  starting  in  the 
middle  line,  curves  twice  to  the  left,  at  first  gradually  at  the  root  of  the  neck; 
from  this  point  it  tends  to  regain  the  middle  line  up  to  the  fifth  thoracic  vertebra; 
thence  finally  turns  again,  and  more  markedly  to  the  left,  and  passes  through  the 
diaphragm  opposite  to  the  tenth,  entering  the  stomach  here  or  at  the  eleventh 
thoracic  vertebra  (ninth  or  tenth  thoracic  spine).  In  the  thorax  this  tube  tra- 
verses first  the  superior,  then  the  posterior,  mediastinum.  At  three  spots,  i.  e., 
its  commencement,  where  it  is  crossed  by  the  left  bronchus,  and  at  the  cardiac 
orifice,  it  presents  narrowings.  The  relations  of  this  tube  to  the  pleura,  peri- 
cardium, aorta,  vagi,  and  thoracic  duct  are  important  in  the  ulceration  of 
malignant  disease  and  infected  bodies,  and  in  the  passage  of  instruments. 

The  aorta  reaches  the  left  side  of  the  vertebral  column,  with  its  arch  just  above 
the  fourth  thoracic  spine,  and  thence  descends  on  the  front  of  the  column,  with  a 
shght  tendency  to  the  left,  to  bifurcate  opposite  the  fourth  lumbar  spine. 

The  spinal  cord. — This,  about  45  cm.  (18  in.)  long,  extends  from  the  foramen 
magnum  to  the  junction  between  the  first  and  second  lumbar  vertebrae.  Up  to 
the  third  month  of  foetal  life  it  reaches  to  the  sacral  end  of  the  vertebral  canal ; 
later,  owing  to  the  more  rapid  growth  of  the  bony  wall,  its  lower  limit  is  at  birth 
opposite  the  third  lumbar  vertebra.  The  dura  mater  is  continued,  as  a  sheath, 
as  low  as  the  second  sacral  vertebra.  It  is  anchored  above  to  the  upper  cervical 
vertebrae  and  the  foramen  magnum,  and  below,  as  the  filum  terminale,  to  the  peri- 
osteum of  the  coccyx.  The  deficiency  of  the  spinous  processes  and  laminae  of  the 
fourth  and  fifth  pieces  of  the  sacrum  allows  of  infection,  e.  g.,  of  a  bed-sore  reach- 
ing the  membranes,  and  so  the  cord.  The  arachnoid  and  pia  of  the  cord  are 
continuous  above  with  those  of  the  brain. 

The  parts  of  the  column  most  exposed  to  injury  are  the  thoraco-lumbar  and  cervico-thoraoic 
partly  because  here  more  mobile  parts  are  joined  to  those  which  are  more  fixed,  and  also  from 
the  amount  of  leverage  exerted  on  the  thoraco-lumbar  region,  and,  in  the  case  of  the  upper 
region,  because  this  is  affected  by  violence  exerted  on  the  head.  The  chief  provisions  for  pro- 
tection of  the  cord  are  the  number  of  bones  and  joints  which  allow  of  movement  without  serious 
weakening,  the  thi'ee  om-ves  and  columns,  cervical,  thoracic,  and  lumbar,  ensuring  bending 
before  breaking;  the  large  amount  of  cancellous  tissue  and  the  number  and  structure  of  the 
intervertebral  discs  all  tending  to  damp  vibrations;  the  large  size  of  the  theca  vertebrahs  and  the 
way  in  which  the  cord,  anchored  and  slung  by  the  thirty-one  pairs  of  nerves  and  the  Ugamenta 
denticulata,  about  twenty  in  number,  occupies  neutral  ground  in  the  centre  of  the  canal  as 
regards  injury  directly  and  indirectly  applied. 

In  lumbar  puncture  (Quincke)  as  a  means  of  diagnosis  or  of  relieving  pressure 
advantage  is  taken  of  the  fact  mentioned  above  that  the  theca  extends  below  the 
cord. 

A  line  drawn  joining  the  highest  points  of  the  iliac  crests  crosses  the  fourth  lumbar  spine. 
The  needle  is  inserted  in  the  median  line  between  the  third  and  fom-th  or  the  fourth  and  fifth 
spines,  and  directed  forward  and  slightly  upward.  The  back  must  be  flexed  as  fully  as  possible 
in  order  to  widen  the  interspinous  spaces.  The  needle  is  passed  to  a  depth  of  about  5  cm.  (2  in.) 
in  an  adult,  or  1.8  cm.  (f  in.)  in  an  infant.  In  the  supine  position  the  lowest  part  of  the  sub- 
arachnoid space  ia  in  the  mid-thoracic  region,  and  an  anaesthetic  fluid,  non-diffusible  and  of  a 


THE  SHOULDER  AND  ARM  1409 

higher  specific  gravity  than  the  cerebro-spina)  fluid,  will  tend  to  gravitate  there  (Barker). 
The  level  of  the  anaesthesia  can  be  varied  by  raising  the  pelvis  or  the  shoulders  to  diiferent 
levels. 

The  following  table,  from  Holden  and  Windle,  with  additions,  will  be  found  very  useful  in 
determining  the  relation  of  numerous  viscera  and  other  structiires  to  the  bodies  of  the  vertebrse. 

VERTEBRAL  LEVELS 

Cervical 

First.     Level  of  hard  palate. 

Second.     Level  of  free  edge  of  upper  teeth. 

Second  and  third.     Superior  cervical  ganglion  of  sympathetic. 

Fourth.     Hyoid  bone.     Upper  aperture  of  larynx. 

Fifth.  Thyreoid  cartilage  and  rima  glottidis.  Between  this  and  the  last  would  be  the 
bifurcation  of  the  common  carotid. 

Sixth.  Cricoid  cartilage.  Ending  of  pharynx  and  larynx.  Consisting  of  the  fused  fifth 
and  sixth  ganglia,  the  middle  cervical  ganglion  is  usually  opposite  this  vertebra.  Here  the 
omo-hyoid  crosses  the  common  carotid,  and  at  this  spot,  the  seat  of  election,  the  centre  of  the 
incision  for  tying  this  vessel  is  placed.  At  this  level  the  inferior  thyreoid  passes  behind  the 
carotid  trunk. 

Seventh.  Inferior  cervical  ganglion.  Apex  of  lung.  Arch  of  thoracic  duct  oyer  apex  of 
lung,  outward  and  downward  to  termination. 

Thoracic 

First.  Summit  of  arch  of  subclavian.  (Godlee.)  The  height  of  this  varies.  Usually 
it  is  from  1.2  to  2.5  cm.  (J  to  1  in.)  above  the  clavicle.  It  is  always  in  close  relation  with  the 
cervical  pleura. 

Second.  Level  of  episternal  notch.  This  is  usually  opposite  the  fibro-cartilage  between 
the  second  and  third.     Bifurcation  of  innominate.     (Godlee.) 

Third.  Beginning  of  superior  cava,  at  junction  of  first  right  costal  cartilage  with  sternum. 
Highest  part  of  aortic  arch,  about  2.5  cm.  (1  in.)  below  notch. 

Fourth.  Bifurcation  of  trachea.  Second  piece  of  aortic  arch,  extending  from  upper  border 
of  second  right  costal  cartilage,  reaches  spine.  Arch  of  vena  azygos.  The  superior  medias- 
tinum is  bounded  behind  by  the  upper  four  thoracic  vertebrae.  Louis'  angle,  junction  of  manu- 
brium and  gladiolus.     Thoracic  aorta  begins. 

Fifth  to  ninth.     Base  of  heart. 

Sixth.  Pulmonary  and  aortic  valves,  opposite  third  left  costal  cartilage  at  its  sternal  junc- 
tion, in  front.  Commencement  of  aorta  and  pulmonary  artery.  End  of  superior  cava,  third 
right  chondro-sternal  junction  in  front. 

Seventh.     Mitral  orifice. 

i  Eighth.     Tricuspid  orifice. 

Ninth.  Lower  level  of  manubrium  and  sterno-xiphoid  fine  (at  lower  border).  Opening 
in 'diaphragm  for  inferior  vena  cava  (lower  border). 

Tenth.  Level  of  tip  of  xiphoid  cartilage.  Lower  limit  of  lung  posteriorly.  Upper  limit 
of  Uver  comes  to  the  surface  posteriorly.  QDsophagus  passes  through  diaphragm.  Cardiac 
orifice  of  stomach  (sometimes).     Upper  limit  of  spleen.  . 

Eleventh.     Lower  border  of  spleen.     Suprarenal  gland.     Cardia  (sometimes). 

Twelfth.  Lowest  part  of  pleura.  Aorta  passes  through  diaphragm  (lower  border). 
Coeliac  artery  (lower  border),     tipper  end  of  kidney. 

Lumbar 

First.  Superior  mesenteric  arteries.  Pancreas.  Pelvis  of  kidney.  Renal  arteries. 
Transpyloric  Line.     (Addison.) 

Second.  Spinal  cord  ends  at  junction  of  first  and  second.  Duodeno-jejunal  flexure.  Re- 
ceptaculum  (cisterna)  chyli.     Lower  end  of  left  kidney. 

Third.     Umbilicus,  opposite  disc  between  third  and  fourth.     Lower  end  of  right  kidney. 

Fourth.     Bifurcation  of  aortic  arch.     Highest  part  of  iliac  crest. 

Fifth.     Commencement  of  superior  vena  cava. 

Sacral 

Third.  End  of  pelvic  colon  and  beginning  of  first  piece  of  rectum  proper.  Lower  Umit 
of  spinal  membranes. 

Fifth.     Reflexion  of  recto-vesical  pouch  of  peritoneum  2.5  cm.  (1  in.)  above  base  of  prostate. 

Coccyx  (tip).  2.5  cm.  (1  in.)  below  this  commencement  of  anal  canal.  Termination  of 
filum  terminale. 

THE  UPPER  EXTREMITY 

THE  SHOULDER  AND  ARM 

The  surface  form  and  landmarks  of  the  upper  extremity  will  first  be  considered 
followed  by  the  various  regions  of  the  shoulder,  arm,  forearm  and  hand. 


1410 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


General  surface  form.    Landmarks. — The  following  surface -marks,  of  the 

greatest  importance  in  determining  the  nature  of  shoulder  injuries,  can  be  made 
out  here: — The  clavicle  in  its  whole  extent,  the  acromion  process,  the  great 
tuberosity,  and  upper  part  of  the  shaft  of  the  humerus.  Much  less  distinctly, 
the  position  of  the  coracoid  process  in  the  infraclavicular  fossa  and  the  head  of 
the  humerus  through  the  axilla  can  be  made  out.  The  anterior  margin  of  the 
clavicle,  convex  medially  and  concave  laterally,  can  be  made  out  in  its  whole 
extent,  the  bone,  if  traced  laterally,  being  found  not  to  be  horizontal,  but  rising 
somewhat  to  its  junction  with  the  acromion.  The  stemo-  and  acromio-clavicu- 
lar  joints  have  been  referred  to  at  p.  1363. 

The  frequency  of  fracture  of  the  clavicle  is  explained  chiefly  by  its  exposure  to  shocks  of  varied 
kinds  from  the  upper  extremity,  inseparable  from  the  out-rigger-like  action  of  the  bone  and  its 
early  ossification.  On  the  other  hand,  the  main  safeguards  are  the  elasticity  and  curves  of  the 
bone,  the  way  in  which  it  is  embedded  in  muscles  which  will  damp  vibrations,  and  the  buffer- 
bond  fibro-cartilages  at  either  extremity.  The  looseness  and  toughness  of  the  overlying  skin 
explain  the  rarity  of  compound  fracture  here.  The  junction  of  the  two  curves  is  the  weakest 
spot  and  the  usual  site  of  fracture.  The  weight  of  the  limb  acting  through  the  coraco-olavicular 
ligaments  and  overcoming  the  trapezius  is  the  chief  factor  in  the  downward  displacement;  the 
pectoralis  minor  and  serratus  anterior  acting  on  the  scapula  draw  the  acromial  fragment  for- 
ward. The  tip  of  the  acromion,  when  the  arm  hangs  by  the  side  with  the  hand  supinated,  is  in 
the  same  Mne  as  the  lateral  condyle  and  the  styloid  process  of  the  radius.  On  the  medial  side, 
the  head  and  medial  condyle  of  the  humerus  and  the  styloid  process  of  the  ulna  are  in  the  same 
line.  Thus  the  great  tuberosity  looks  laterally,  the  head  medially,  and  the  lesser  tuberosity  some- 
what forward.     Between  the  two  tuberosities  runs  the  intertubercular  (bicipital)  groove,  which, 

Fig.  1128. — Transverse  Section  THRoncH  the  Right  Shoulder-joint,  showing  the 
Stkucturbs  in  contact  with  it.     (Braune.) 


Acromion- 

Supra-spinatus 

Trapezius 


Teres  minor 

Teres  major' 
Latissimus  dorsi' 


Deltoid 
Pectoralis  major 

ji  of  subscapularis  blended 

with  the  scapular  ligament 
Coraco-brachialis  and  short  head  of  biceps 


with  the  arm  in  the  above  position,  looks  directly  forward.  In  thin  subjects  its  lower  part 
can  be  defined.  Its  position  can  be  marked  with  sufficient  accuracy  by  a  Hne  running  down- 
ward from  the  acromion  in  the  long  axis  of  the  humerus.  Besides  the  tendon  and  its  synovial 
sheath,  the  insertion  of  the  latissimus  dorsi,  the  humeral  branch  of  the  thoraco-acromial  artery, 
and  the  anterior  circumflex  artery  run  in  the  groove.  When  the  fingers  are  placed  on  the  acro- 
mion and  the  thumb  in  the  axilla,  the  lower  edge  of  the  glenoid  cavity  can  be  felt;  and  if  the 
humerus  be  rotated  (the  elbow-joint  being  flexed),  the  head  of  the  humerus  can  be  felt  also. 

The  characteristic  roundness  of  the  shoulder  is  due  to  the  great  tuberosity 
lying  under  the  deltoid  (fig.  1130).  In  dislocation  the  loss  of  this  roundness  is 
due  to  the  absence  of  the  head  and  tuberosity  and  consequent  projection  of  the 
acromion. 

This  normal  projection  of  the  deltoid  renders  it  impossible  to  place  a  flat  straight  body  in 
contact  with  both  the  acromion  and  the  lateral  epicondyle  at  the  same  time  (Hamilton's  dis- 
location test).  Below  the  junction  of  the  lateral  and  middle  thirds  of  the  clavicle,  between 
the  contiguous  origins  of  the  pectoralis  major  and  deltoid,  is  the  infraclavicular  fossa,  in  which 
lie  the  cephalic  vein,  the  deltoid  branch  of  the  thoraco-acromial  artery,  and  a  lymphatic  node 
which  may  be  involved  in  obstinate  tuberculosis  of  the  cervical  groups.  On  pressing  deeply 
here,  the  coracoid  process  can  be  made  out  if  the  muscles  are  relaxed,  and  the  axillary  artery 
compressed  against  the  second  rib. 

On  raising  the  arm  and  abducting  it,  the  different  parts  of  the  deltoid  can  often  be  made  out 
— viz.,  fibres  from  the  lower  border  of  the  spine  of  the  scapula,  the  lateral  edge  of  the  acromion, 
and  the  lateral  third  or  more  of  the  front  of  the  clavicle;  the  characteristic  knitting  of  the  surface 


THE  AXILLARY  FOSSA 


1411 


owing  to  the  presence  of  fibrous  septa  continuous,  alike,  with  the  skin  and  the  sheath  of  the 
muscle  and  the  tendinous  septa  which  separate  the  muscular  bundles,  will  also  be  seen.  The 
muscle  will  be  marked  out  by  a  base-line  reaching  along  the  above  bony  points,  and  two  sides 
converging  from  its  extremities  to  the  apex,  a  point  on  the  lateral  surface  of  the  humerus,  about 
its  centre.  In  paralysis  of  the  deltoid,  the  humerus  being  no  longer  braced  up  against  the 
scapula,  the  finger-tips  can  be  placed  between  it  and  the  acromion. 

To  map  out  the  pectoralis  major,  a  line  should  be  drawn  down  the  lateral  aspect  of  the 
sternum  as  far  as  the  sixth  costal  cartilage,  and  then  two  others  marking  the  borders  of  the 
muscle — the  upper  corresponding  to  the  medial  border  of  the  deltoid,  the  lower  starting  from 
the  sixth  cartilage,  and  the  two  converging  to  the  folded  tendon,  which  is  inserted  as  a  double 

Fig.  1129. — The  Shoulder- joint,  as  shown  by  the  Rontgen-bays. 


layer  into  the  lateral  tubercular  (bicipital)  ridge.  The  pectoralis  minor  will  be  marked  out  by 
two  lines,  from  the  upper  border  of  the  third  and  the  lower  border  of  the  fifth  rib,  just  lateral 
to  their  cartilages,  and  meeting  at  the  coracoid  process.  The  lower  line  gives  the  level  of  the 
long  thoracic  artery;  the  upper,  where  it  meets  the  line  of  the  axillary  artery,  that  of  the  thoraco- 
acromial. 

When  the  arm  is  abducted  and  the  humerus  rotated  a  httle  laterally,  the  prominence  of  a 
well-developed  coraco-brachialis  comes  into  view;  a  Une  drawn  from  the  centre  of  the  clavicle 
along  the  medial  border  of  this  muscle  to  its  insertion  into  the  humerus  gives  the  Une  of  the 
axillary  artery. 

Axillary  fossa. — The  boundaries  of  this  space  anterior,  posterior,  medial,  or 
thoracic,  lateral  or  humeral,  apex  and  base,  with  the  structures  forming  them  and 


1412 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


the  vessels  and  nerves  in  relation  to  them,  must  be  remembered.  The  chief  vessels 
are  the  axillary  on  the  lateral  wall,  brought  into  prominence  when  the  arm  is 
abducted,  as  in  removal  of  the  mamma,  and  the  subscapular  on  the  posterior  wall. 
The  apex  is  felt,  when  the  finger  is  pushed  upward  in  an  operation  here,  to  be 
bounded  by  the  clavicle  in  front,  the  first  rib  behind,  and  the  coracoid  some- 
what laterally.  The  base  is  concave,  owing  to  the  coraco-clavicular  (costo- 
coracoid)  membrane  as  it  descends  to  blend  with  the  sheath  of  the  pectoralis 
minor,  giving  also  a  process  to  the  axillary  fascia  which  unites  the  anterior 
and  posterior  boundaries.     This  process  also  sends  septa  to  the  skin. 

An  axillary  abscess,  always  to  be  opened  early  to  avoid  subsequent  interference  with  the 
movements  of  the  shoulder,  is  reached  by  an  incision  on  the  medial  wall,  midway  between  the  an- 
terior and  posterior  boundaries,  so  as  to  avoid  the  long  thoracic  and  subscapular  vessels,  respec- 
tively, the  back  of  the  knife  being  directed  toward  the  lateral  wall.  The  only  vessel  on  this  wall 
is  the  superior  thoracic,  which  lies  high  up.  Additional  safety  is  given  by  the  use  of  Hilton's 
method.  For  exploration  of  the  axilla  the  best  incision  is  an  angular  one,  the  two  limbs  being 
placed  in  a  line  with  the  anterior  margin  of  the  great  pectoral,  and  in  the  line  of  the  axillary 
vessels.  This  runs  from  a  point  on  the  centre  of  the  clavicle  (the  limb  being  at  a  right  angle 
to  the  trunk)  to  the  medial  margin  of  the  coraco-brachialis.  If  this  be  obliterated  by  swelling, 
the  above  line  should  be  prolonged  to  the  middle  of  the  bend  of  the  elbow,  which  will  give  the 
guide  to  the  brachial  also.  Collateral  circulation.  If  the  first  part  of  the  artery  be  tied,  the 
channels  are  the  same  as  in  ligature  of  the  third  part  of  the  subclavian  {q.v.).  In  ligature 
of  the  third  part  of  the  axillary,  if  the  ligature  be  above  the  circumflex  arteries,  the  chief  vessels 
concerned  are  the  transverse  scapular  (suprascapular)  and  thoraco-acromial  above   and  the 


Fig.  1130. — Diagrammatic  Section  op  Shoulder  through  the  Intertuberculab 
(Bicipital)  Groove.     (Anderson.) 


Deltoid 
Subacromial  bursa 

Capsule  of  shoulder-joint 
Long  tendon  of  bicepE 

Synovial  membrane  lining  cap- 
sule and  biceps  tendon 


Glenoid  lip  (ligament) 


Glenoid  cavity 


Glenoid  lip  (ligament) 

Inner    fold   of    capsule   and 
synovial  membrane 


—  Humerus 


posterior  circumflex  below.  If  the  ligature  be  below  the  circumflex,  the  anastomoses  will  be 
those  concerned  in  ligature  of  the  brachial  above  the  profunda  (p.  1414).  The  lymphatic 
nodes  in  the  axilla  have  been  mentioned  at  p.  719,  (fig.  566). 

The  depression  of  the  axillary  fossa  is  best  marked  when  the  arm  is  raised  from  the  side 
to  an  angle  of  about  45°,  and  when  the  muscles  bounding  it  in  front  and  behind  are  contracted. 
.  In  proportion  as  the  arm  is  raised,  the  hollow  becomes  less,  the  head  of  the  humerus  now  pro- 
jecting into  it.  When  the  folds  are  relaxed  by  bringing  the  arm  to  the  side,  the  fingers  can  be 
pushed  into  the  space  so  as  to  examine  it. 

The  axiUary  (circumflex)  nerve  and  posterior  circumflex  vessels  wind  around  the  humerus 
under  the  deltoid;  a  hne  drawn  at  a  right  angle  to  the  humerus  and  a  little  above  the  centre 
of  this  muscle  marks  their  position  on  the  surface. 

To  trace  the  synovial  membrane  of  the  shoulder -joint  is  a  comparatively 
simple  matter  (fig.  11.30).  Covering  both  aspects  of  the  free  edge  of  the  glenoid 
ligament,  it  lines  the  inner  aspect  of  the  capsule,  whereb.y  it  reaches  the  articular 
margin  of  the  head  of  the  humerus;  there  is  a  distinct  reflection,  below,  from  the 
capsule  on  to  the  humeral  neck  before  the  rim  of  the  cartilage  is  reached. 

An  extensive  protrusion  of  synovial  membrane  takes  place  in  the  form  of  a  synovial  bursa, 
at  the  medial  and  anterior  part  of  the  capsule,  near  the  root  of  the  coracoid  process  under  the 
tendon  of  the  subscapularis.  Another  protrusion  takes  place  between  the  two  tuberosities 
along  the  intertubercular  groove,  as  low  as  the  insertion  of  the  pectoralis  major.  A  third 
synovial  protrusion  may  be  seen,  but  not  frequently,  at  the  lateral  or  posterior  aspect,  in  the 
form  of  a  bursa,  under  the  infra-spinatus  tendon.  Thus  the  continuity  of  the  capsule  is  inter- 
rupted by  two  and  sometimes  three  synovial  protrusions. 


THE  SHOULDER-JOINT 


1413 


Shoulder-joint. — The  frequency  of  dislocations  here,  nearly  equal  to  those  of 
all  the  other  joints  put  together,  calls  attention  to  the  points  contributing  to  make 
the  joint  alike  insecure  and  safe.  Strength  is  given  by  (1)  the  intimate  blending 
of  the  short  scapular  muscles,  especially  the  subscapularis  with  the  capsule;  (2) 
the  coraco-acromial  vault;  (3)  atmospheric  pressure;  (4)  the  long  tendon  of  the 
biceps;  (5)  the  elasticity  of  the  clavicle;  (6)  the  mobility  of  the  scapula.  The 
weakness  of  the  joint  is  readily  explained  by  its  free  mobility,  the  want  of  corre- 
spondence between  the  articular  surfaces,  its  exposure  to  injury,  and  the  length  of 
the  humeral  lever.  The  rent  in  the  capsule  is  usually  anterior  and  below,  and  to 
this  spot  the  head  of  the  humerus  must  be  made  to  return.  While  dislocations  are 
usually  primarily  subglenoid,  owing  to  the  above  part  of  the  capsule  being  the 
thinnest  and  least  protected,  they  take  usually  a  secondarily  forward  direction, 


Fig.  1131. — Posterior  View  of  the  Scapular  Muscles  and  Triceps. 


Supraspinatus 


The  X  mark  indicates 
where  the  radial 
nerve  leaves  the  long 
head  of  the  triceps 
and  passes  under  the 
outer  head  to  gain 
the  groove. 


as  the  triceps  prevents  the  head  passing  backward.  In  addition  to  the  above 
features  of  the  lower  part  of  the  capsule,  laxity  is  here  also  a  marked  feature,  to 
allow  of  free  abduction  and  elevation.  This  movement  wall  be  accordingly  much 
checked  by  any  inflammatory  matting  of  this  part  of  the  capsule. 

The  best  incision  for  exploring  the  joint  is  one  commencing  midway  between  the  coracoid 
and  acromion  processes  and  carried  downward  parallel  with  the  anterior  fibres  of  the  deltoid. 
The  cephaUc  vein  and  biceps  tendon  are  to  be  avoided.  If  drainage  is  needed,  it  must  be 
BuppUed  by  a  counter-incision  behind.  This  may  be  made  along  the  posterior  border  of  the 
deltoid,  part  of  its  humeral  attachment  being  detached  if  necessary.  The  axillary  (circumflex) 
nerve  must  be  avoided  in  the  upper  part  of  the  incision. 


1414 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


The  shaft  of  the  humerus  is  well  covered  by  muscles  in  the  greater  part  of  its 
extent,  especially  above.  Below  the  insertion  of  the  deltoid,  the  lateral  border  of 
the  bone  can  be  traced  downward  into  the  lateral  supracondyloid  ridge.  The 
medial  border  and  ridge  are  less  prominent. 

Attached  to  these  ridges  and  borders  are  the  intermuscular  septa,  each  lying  between  the 
triceps  and  brachiaUs  (anterior),  and  the  lateral  one  giving  origin  to  the  brachio-radialis  (supi- 
nator longus)  and  extensor  carpi  radialis  longus  as  well.  The  medial  extends  up  to  the  insertion 
of  the  coraco-braohialis,  the  lateral  to  that  of  the  deltoid.  The  lateral  septum  is  perforated  by 
the  anterior  part  of  the  profunda  vessels  and  the  radial  (musculo-spiral)  nerve,  the  medial  by  the 
superior  and  posterior  branch  of  the  inferior  ulnar  collateral  (anastomotica  magna)  artery  and 
the  ulnar  nerve. 

The  biceps  has  a  two-fold  attachment  above  and  below.  The  former  is  of  much  importance 
in  steadying  the  various  movements,  especially  the  upward  one,  and  in  harmonising  the  simul- 
taneous flexion  and  extension  of  the  shoulder-  and  elbow-joints.  (Cleland.)  The  lacertus 
fibrosus  curving  downward  and  medially  with  its  semilunar  edge  upward,  across  the  termina- 
tion of  the  brachial  artery,  strengthens  the  deep  fascia  and  the  origin  of  the  flexors  of  the  fore- 
arm. The  two  heads  unite  in  the  lower  third  of  the  arm.  The  tendon,  before  its  insertion, 
becomes  twisted,  the  lateral  border  becoming  anterior. 


Fig.  1132. — Cross-Section  through  the  Middle  of  the  Right  Arm.     (Heath.) 


Musculo-cutaneous  nerve 
Brachialis 


Hadial  nerve 
Profunda  vessels 


Biceps 

Brachial  vessels 


Triceps,  with  fibrous  intersection 


Superior  ulnar  collateral  vessels 


On  either  side  of  the  well-known  prominence  of  the  biceps  is  a  furrow.  Along 
the  lateral  ascends  the  cephahc  vein.  The  medial  corresponds  to  the  line  of  the 
basilic  vein  which  lies  superficial  to  the  deep  fascia  below  the  middle  of  the  arm, 
and  superficial  and  medial  to  the  brachial  vessels  and  median  nerve. 

The  strength  of  such  muscles  as  the  deltoid,  and  their  intimate  connection  with  the  peri- 
osteum of  the  humerus,  account  for  fracture  of  this  bone  by  muscular  action  being  more  common 
than  elsewhere.  The  presence  of  muscular  tissue  between  the  fragments,  together  with  de- 
ficient immobiUzation,  explains  the  fact  that  ununited  fractures  are  also  most  common  in  the 
humerus.  The  best  incisions  for  exploring  the  humerus,  e.  g.,  in  acute  necrosis,  etc.,  are  (a) 
for  the  upper  portion,  the  two  already  mentioned  along  the  anterior  and  posterior  borders  of  the 
deltoid.  In  the  latter  case  the  presence  of  the  radial  (musculo-spiral)  nerve  in  the  deeper  part 
of  the  wound  must  be  remembered;  (6)  for  the  lower  end  one  parallel  with  the  lateral  inter- 
muscular septum,  deepened  between  the  brachialis  and  brachio-radialis. 

A  line  drawn  along  the  medial  edge  of  the  biceps  from  the  insertion  of  the  teres 
major  to  the  middle  of  the  bend  of  the  elbow  corresponds  to  the  brachial  artery. 
In  the  upper  two-thirds,  this  artery  can  be  compressed  against  the  bone  by  pres- 
sure laterally;  in  its  lower  third  the  humerus  is  behind  it,  and  pressure  should  be 
made  backward.  The  presence  of  the  median  nerve  will  interfere  with  any  pro- 
longed digital  pressure  applied  in  the  middle  of  the  arm. 


THE  ARM 


1415 


In  ligature  of  the  artery  here  the  line  extends  from  the  mid-axillary  region  above,  prolonged 
to  the  centre  of  the  front  of  the  elbow.  The  only  structures  seen  should  be  the  medial 
edge  of  the  biceps,  the  basilic  vein,  and  the  median  nerve.  The  profunda  comes  off  2.5  cm. 
(1  in.)  below  the  teres  major,  having  the  same  relation  to  the  heads  of  the  triceps;  thus,  it  first 
lies  on  the  long  head,  behind  the  axillary  and  brachial  arteries,  then  between  the  long  and 
medial  heads,  and  next,  in  the  groove,  between  the  medial  and  lateral  heads,  and  courses  with 
the  radial  (musculo-spiral)  nerve  (fig.  1132);  the  nutrient  artery  arises  opposite  the  middle 
of  the  humerus;  in  many  cases  it  arises,  on  the  back  of  the  arm,  from  the  profunda;  the  superior 
ulnar  collateral  (inferior  profunda)  below  the  middle,  and  courses  with  the  ulnar  nerve  through 
the  intermuscular  septum  to  the  back  of  the  medial  condyle.  The  inferior  ulnar  collateral 
(anastomotica  magna)  is  given  off  from  2.5  to  5  cm.  (1  to  2  in.)  above  the  bend  of  the  elbow. 
Fig.  1138  will  show  the  collateral  circulation  after  ligature  of  the  brachial,  according  as  the 
vessel  is  tied  above  or  below  the  superior  profunda,  or  below  the  superior  ulnar  collateral. 

The  centre  of  the  arm  is  a  landmark  for  many  anatomical  structures.  On  the 
lateral  side  is  the  insertion  of  the  deltoid;  on  the  medial,  that  of  the  coraco- 
brachialis.  The  basilic  vein  and  the  medial  brachial  cutaneous  nerve  (nerve  of 
Wrisberg)  here  perforate  the  deep  fascia,  going  in  reverse  directions.  The  supe- 
rior ulnar  collateral  is  here  given  off  from  the  brachial  and  joins  the  ulnar  nerve; 
the  median  nerve  also  crosses  the  artery,  and  the  ulnar  nerve  leaves  the  medial 
side  of  the  vessel  to  pass  to  the  medial  aspect  of  the  limb. 

The  brachialis  can  be  mapped  out  by  two  pointed  processes  which  surround  the  insertion 
of  the  deltoid,  pass  downward  into  lines  corresponding  to  the  two  intermuscular  septa,  and  then 
converge  over  the  front  of  the  elbow  to  their  insertion  into  the  coronoid  process. 

The  median  nerve  (lateral  head,  5th.  6th,  7th  C;  medial  head,  Sth  C.  and  1st  T.)  can  be 
traced  by  a  line  drawn  from  the  lateral  side  of  the  third  part  of  the  axillary  and  first  part  of  the 
brachial  artery,  across  this  latter  vessel  about  its  centre,  and  then  along  its  medial  border  to 
the  forearm,  where  it  passes  between  the  two  heads  of  the  pronator  teres. 

Fia.  1133. — Cross-Section  through  the  Elbow.    ( X  1/2).    (After  Braune.) 

Tendon  of  biceps.-  _,  '^^        ;::^^^\'ff^  -Pronator  teres 

Brachio-radiahs        /  [-i.  ^^     \^<r      _    Median  nerve 

Extensor  carpi  radialis  longus  -  ^Mf^^^^'    '*''*t^'  -  *''*  Vv 

-Ulnar  collateral  ligament 

'ff^      -Ulnar  nerve 

^  — Olecranon 

Anconeus ^^N5v""^3  ^~~^~^^^^ 

-Tendon  of  triceps 


Radial  ; 

Brachialis - 


"Flexor  carpi  radialis 


The  ulnar  nerve  (Sth  C.  and  1st  T.)  lies  to  the  medial  side  of  the  above  arteries  as  far  as 
the  middle  of  the  arm,  where  it  leaves  the  brachial  to  course  more  medially  and  perforate  the 
medial  intermuscular  septum  together  with  the  superior  and  posterior  branch  of  the  inferior 
ulnar  collateral  and  so  get  to  the  back  of  the  medial  condyle.  A  line  drawn  from  the  medial 
border  of  the  coraco-brachialis,  where,  in  the  upper  part  of  its  course,  the  nerve  is  in  close  rela- 
tion with  the  medial  side  of  the  axillary  and  brachial  arteries,  to  the  back  of  the  medial  condyle, 
will  indicate  its  course.  Low  down,  the  nerve  is  in  the  medial  head  of  the  triceps,  and  may  be 
injured  in  operations  here. 

The  radial  (musculo-spiral)  nerve  (5th,  6th,  7th,  and  Sth  C.)  can  be  traced  by  a  line  begin- 
ning behind  the  third  part  of  the  axillary  artery,  then  carried  vertically  down  behind  the  upper- 
most part  of  the  brachial,  and  then,  just  below  the  posterior  border  of  the  axilla,  curving  back- 
ward behind  the  humerus  and  slightly  downward  just  below  the  insertion  of  the  deltoid.  Thus, 
passing  from  laterally  and  from  before  backward  in  its  groove,  accompanied  by  the  profunda 
vessels,  first  the  trunk,  and  then  the  smaller  anterior  division,  it  again  comes  to  the  front  by 
perforating  the  lateral  intermuscular  septum  at  a  point  about  opposite  to  the  junction  of  the 
middle  and  lower  thirds  of  the  arm,  and  passes  down  in  front  of  the  lateral  supracondyloid 
ridge,  lying  here  between  the  brachio-radialis  and  brachialis  anterior,  to  the  level  of  the  lateral 
condyle,  in  front  of  which  it  divides  into  the  superficial  (radial)  and  deep  (posterior  interos- 
seous) radials.  The  former  of  these  accompanies  the  radial  artery  to  the  front  of  the  arm,  the 
latter  travels  backward  to  the  back  of  the  forearm.  A  line  from  the  lateral  condyle  to  the 
insertion  of  the  deltoid  indicates  the  lateral  intermuscular  septum. 

In  addition  to  injuries  caused  by  fracture,  the  nerve  may  be  injured  in  crutch  pressure, 
the  sleep  of  intoxication,  use  of  an  Esmaroh's  bandage,  or  the  careless  reduction  of  a  dislocated 
shoulder  with  the  foot  in  the  axilla.  To  expose  the  nerve  the  incision  begins  below,  over  the 
lateral  intermuscular  septum,  where  it  lies  between  the  brachio-radialis  and  brachialis  (anterior). 
Hence  the  incision  is  prolonged  freely  upward  and  backward  toward  the  posterior  border  of  the 
deltoid. 

On  the  back  of  the  arm  is  the  triceps  muscle,  with  its  three  heads  and  tendon 
of  insertion,  all  brought  into  relief  in  a  muscular  subject  when  the  forearm  is 
strongly  extended.     Of  the  three  heads,  the  medial  is  the  least  distinct,  arising 


1416 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


below  the  groove  (musculo-spiral)  for  the  radial  (musculo-spiral)  nerve,  reaching 
to  each  intermuscular  septum,  and  tapering  away  above  as  high  as  the  teres  major. 
Most  of  the  fibres  of  this  head  lie  deeply.  The  lateral  head,  arising  above  the 
groove  as  high  as  the  great  tuberosity,  appears  in  strong  relief  just  below  the 
deltoid;  while  the  middle  or  long  head,  arising  from  the  scapula  just  below  the 
glenoid  cavity,  appears  between  the  teres  muscles.  The  tendon  of  insertion, 
passing  into  the  upper  and  back  part  of  the  olecranon  over  a  deep  bursa,  is  shown 
by  a  somewhat  depressed  area.  On  the  lateral  side,  an  important  expansion  to 
the  fascia  over  the  anconeus  is  given  off. 

Fig.  1134, — The  Elbow-Joint,  as  Shown  by  the  Rontgen-hats. 


) 


In  the  ossification  of  the  humerus  the  epiphyses  are  of  first  importance.  The  upper, 
consisting  of  those  for  tlie  head  and  two  tuberosities,  wliich  form  one  about  the  seventh  year, 
blends  with  the  shaft  between  the  twentieth  and  twentj'-fittli  years.  Separation  usually  takes 
place  at  an  earlier  date,  this  being  explained  by  the  fact  that  the  cone-like  arrangement  by  which 
the  diaphysis  fits  into  the  cap  of  the  epiphysis  becomes  more  marked  toward  the  date  of  union, 
and  thus  tends  to  prevent  displacement.  (Thomson.)  The  lower  epiphysis.  The  condition 
of  this  varies  with  the  degree  of  coalescence  of  its  four  centres.  The  first  and  chief,  that  for  the 
capitulum  (second  or  third  year),  unites  with  those  for  the  trochlea  and  lateral  epicondyle  soon 
after  puberty,  and  forms  an  epiphysis  which  joins  with  the  shaft  at  about  sixteen.  The  epi- 
physis for  the  medial  epicondyle  appears  at  the  fifth  year  and  unites  with  the  shaft  at  the 
eighteenth.  Injury  to  this  epiphysis  may  damage  the  ulnar  nerve  and  open  the  elbow-joint. 
Thus,  at  and  after  puberty,  there  are  two  chief  epiphyses  to  remember  here: — (a)  the  larger, 
consisting  of  capitular,  trochlear,  and  lateral  epicondyle  centres.  This  is  almost  entirely  intra- 
articular; (6)  the  smaller,  that  for  the  medial  epicondyle;  the  extent  to  which  this  is  intra-artic- 
ular  varies.     The  structures  that  would  be  divided  in  an  amputation  at  the  centre  of  the  arm 


THE  ELBOW 


1417 


are  shown  in  fig.  1132.  The  chief  points  needing  attention  are: — (1)  To  leave  as  much  of 
the  lever  of  the  humerus  as  possible;  (2)  clean  section  of  the  large  nerves,  the  radial  (musoulo- 
spiral)  in  its  groove  being  especially  liable  to  be  frayed  by  the  saw;  (3)  the  difference  between  the 
amount  of  retraction  of  the  free  biceps  in  front,  and  the  triceps  behind,  fixed  to  the  bone  and 
septa. 

THE  ELBOW 

The  bony  points,  epicondyles,  olecranon,  and  head  of  radius,  andtheir  relation 
to  one  another,  should  be  carefully  studied.  The  medial  epicondyle  is  the  more 
prominent  of  the  two,  is  directed  backward  as  well  as  medially,  and  lies  a  little 
above  its  fellow.  Above  it  can  be  traced  upward  the  supracondyloid  ridge  and 
corresponding  intermuscular  septum.  The  lateral  epicondyle  is  more  rounded,  and 
thus  less  prominent;  below,  and  a  little  behind  it,  the  head  of  the  radius  can  be  felt 
moving  under  the  capitulum  when  the  forearm  is  supinated  and  flexed.  A  depres- 
sion marks  this  spot  and  corresponds  to  the  interval  between  the  anconeus  and 
brachio-radialis  and  extensor  carpi  radialis  longus;  at  the  back,  the  upper  part 
of  the  olecranon  is  covered  by  the  triceps.  The  lower  part  is  subcutaneous,  and 
separated  from  the  skin  by  a  bursa.  If  the  thumb  and  second  finger  be  placed  on 
the  epicondyles  and  the  index  on  the  tip  of  the  olecranon,  and  the  forearm  com- 
pletely extended,  the  tip  of  the  olecranon  rises  so  as  to  be  on  the  line  joining  the 
two  epicondyles.     In  flexion  at  a  right  angle,  the  olecranon  is  below  the  line  of  the 


Fig.  1135. — Longitudinal  Section  of  the  Elbow-joint.     (One-half.)     (Braune.) 


Extensor  carpi  ulnaris 


Radial  nerve 
inr  \  \ 'Brachio-radialis 


— Supinator 
■Extensor  carpi  radialis  longus 


epicondyles,  and  in  complete  flexion  quite  in  front  of  them.  Between  the  medial 
epicondyle  and  olecranon  is  a  pit,  in  which  lie  the  ulnar  nerve  and  the  anastomosis 
between  the  inferior  ulnar  collateral  and  the  posterior  ulnar  recurrent  arteries. 
The  coronoid  process  is  so  well  covered  by  muscles,  vessels,  and  nerves  that  its 
position  cannot  be  distinctly  made  out. 

The  synovial  membrane  of  the  elbow-joint  communicates  with  that  of  the  superior  radio- 
ulnar. Hence  the  facility  with  which  tuberculous  disease  may  be  set  up  after  neglected  falls 
on  the  hand,  in  early  life.  At  this  time  the  weakness  of  the  annular  (orbicular)  ligament  leads 
to  its  being  easily  injured.  Swelling,  due  to  effusion  into  the  joint,  appears  on  either  side  of  the 
triceps  tendon,  and  soon  obliterates  the  depression  below  the  lateral  epicondyle.  The  simplest 
incision  for  an  infected  elbow-joint  is  a  vertical  one,  on  the  lateral  side  of  the  olecranon.  A 
superficial  swelling  over  the  tip  of  the  olecranon  is  due  to  effusion  into  the  bursa  between  the 
soft  parts  and  that  bone.  A  deeper,  less  easily  defined  swelling  in  the  same  region  is  due  to 
inflammation  of  the  bursa  between  the  olecranon  and  the  triceps.  A  swelling  on  the  medial 
side  of  the  elbow-joint,  if  painful  and  accompanied  by  inflammation  of  the  skin,  may  be  due 
to  mischief  in  the  epitrochlear  lymphatic  node  situated  just  above  the  medial  epicondyle,  and 
receiving  lymphatics  from  the  medial  border  of  the  forearm  and  the  two  medial  fingers. 

The  hollow  in  front  of  the  elbow. — The  delicacy  of  the  skin  here  must  always  be  borne  in 
mind  in  the  application  of  splints.  Owing  to  the  insidious  rapidity  with  which  pressure  may  set 
up  ischaemic  paralysis,  anterior  angular  splints  are  always  to  be  used  with  caution.     The  M-like 


1418 


CLINICAL  AXD  TOPOGRAPHICAL  AX  ATOMY 


arrangement  of  the  superficial  veins  as  usually  described  is  by  no  means  constant  (fig.  1136), 
The  median  basilic  is  the  vein  usually  chosen  for  venesection,  owing  to  its  larger  size  and  its 
being  firmly  supported  by  the  subjacent  bicipital  fascia  which  separates  it  from  the  brachial 
artery;  but  the  median  cephalic  is  the  safer.  The  median  basilic  is  crossed  by  branches  of 
the  medial  antibrachial  (internal)  cutaneous  nerve,  while  those  of  the  musculo-cutaneous  lie 
under  the  median  cephalic.  In  the  semiflexed  position,  the  fold  of  the  elbow  is  seen,  a  little 
above  the  level  of  the  joint.  This  forms  the  base  of  the  triangular  fossa  below  the  elbow,  the 
lateral  side  corresponding  to  the  brachio-radialis,  the  medial  to  the  pronator  teres,  and  the 
apex  to  the  meeting  of  these  muscles.  The  tendon  of  the  biceps  can  be  easih'  made  out  in  the 
centre  of  the  fossa,  giving  off  above  the  lacertus  fibrosus  from  its  medial  side  to  fasten  down  the 
flexors  of  the  forearm.  Under  the  tendon  on  its  medial  side  lie  the  bracliial  artery  and  the 
median  nerve,  a  little  medial  to  it,  for  a  short  distance.  The  radial  nerve  (musculo-spiral)  lies 
outside  the  fossa,  between  the  brachio-radialis  and  the  brachialis  (anterior),  and  gives  off  its  two 


Fig.  1136. — The  Bend  of  the  Ei^ow  with  the  Superficial  Veins. 
(From  a  dissection  by  Dr.  Alder  Smith  in  the  Museum  of  St.  Bartholomew's  Hospital.) 


Median  nerve 
Posterior  branch,  of  in- 
ferior ulnar  collateral 
Branches   of    medial 
anti-brachial 
cutaneous  nerve  ■ 

Posterior  ulnar  vein 


Brachialis 
Anterior  branch  of  in- 
ferior ulnar  collateral 
Anterior  ulnar  vein 
Median  basilic  vein 


Tendon  of  biceps 
Lacertus  fibrosus 


Deep  median  vein 
Ulnar  artery 


Pronator  teres 


Biceps 

Vena  comitans  of 

brachial  artery 
Basilic  vein 

Brachialis 

Cephalic  vein 

Brachial  artery 

Lateral  anti- 
brachial cuta- 
neous nerve 

Radial  n.  and  as- 

,  cending  branch 
of  radial  recur- 
rent artery 

Radial  vein 

Median  cephalic 

Ascending  br.  of 
radial  recurrent 
Superficial  radial 

nerve 

Radial  recurrent 

artery 

Bra  chio  -ra  diali  s 


Median  vein 

Superficial 
radial 
nerve 


terminal  branches  in  front  of  the  lateral  epicond^'le.      The  brachial  usually  bifurcates  oppo- 
site to  the  neck  of  the  radius. 

The  arterial  anastomoses  about  the  elbow-joint  are  as  follows:  The  radial  recurrent  runs  up 
unaer  cover  of  the  brachio-radialis  to  anastomose  with  the  anterior  branch  of  the  profunda 
on  the  front  of  the  lateral  condyle.  The  posterior  interosseous  recurrent  ascends,  between  the 
supinator  and  the  anconeus,  to  anastomose  on  the  back  of  the  lateral  condyle  with  the  posterior 
branch  of  the  profunda.  It  further  joins,  by  a  large  anastomotic  arch  across  the  back  of  the 
joint,  with  the  inferior  ulnar  collateral  (anastomofic  magna)  and  posterior  ulnar  recurrent. 
The  anterior  ulnar  recurrent  passes  upward  on  the  brachialis  to  join  the  anterior  part  of  the 
inferior  ulnar  collateral  under  the  pronator  teres,  on  the  front  of  the  medial  epicondyle.  The 
posterior  ulnar  recin-rent  makes  for  the  interval  between  the  back  of  the  medial  epicondyle 
and  the  olecranon,  to  join  with  the  superior  and  the  posterior  branch  of  the  inferior  ulnar 
collateral. 

It  will  be  seen  that  the  inferior  ulnar  collateral  (anastomotica  magna)  is  the  artery  most 
largely  employed,  distributing  branches  everywhere,  save  to  the  front  of  the  lateral  epicondyle. 


THE  FOREARM 


1419 


THE  FOREARM 

Bony  landmarks. — The  -posterior  border  of  the  ulna  can  be  easily  traced  down 
from  the  olecranon  to  the  back  of  the  styloid  process;  the  bone  becomes  somewhat 
rounded  below,  and  lies  between  the  flexor  and  extensor  carpi  ulnaris.  The  tip  of 
the  styloid  process  corresponds  to  the  medial  end  of  the  line  of  the  wrist-joint.  The 
radius  is  covered  above  by  the  brachio-radialis  and  radial  extensors  of  the  carpus, 
and  the  outline  of  the  bone  is  less  easily  followed.  Its  styloid  process  is  readily 
made  out  below  a  finger 's  breadth  above  the  thenar  eminence.  It  is  placed  about 
1.2  cm.  (I  in.)  lower  than  that  of  the  styloid  process  of  the  ulna. 

Thus,  a  line  drawn  straight  between  the  two  processes  would  fall  a  little  below  that  of  the 
wrist-joint,  this  being  shown  by  a  line  drawn  between  the  two  processes  forming  a  slight  curve, 
with  its  conoa\'ity  downward  (corresponding  to  the  concavity  of  the  lower  surface  of  the  radius 
and  fibro-cartilage)  about  1.2  cm.  (5  in.)  above  the  straight  Une  given  above. 

The  radial  styloid  process  is  covered  by  the  abductor  longus  and  extensor  brevis  polhcis, 
while  farther  out  Ues  the  extensor  pollicis  longus.     Between  the  styloid  process  of  the  ulna  and 


Fig.  1137. — The  Brachial  Artery  at  the  Bend  of  the  Elbow. 
(From  a  mounted  specimen  in  the  Anatomical  Department  of  Trinity  College,  Dubhn.) 


Posterior  branch  of   medial 

antibrachial    cutaneous 

nerve 
Anterior    branch    of    medial 

antibrachial    cutaneous 

nerve 


Biceps  muscle 


Brachial  artery 

Branch  to  pronator  teres 
Lacertus  fibrosus,  cut 

Pronator  teres  muscle 

Median  nerve 

Ulnar  artery 


Branch    of    radial  nerve  J 
supinator  longus 

Superficial  radial  nerve 

Radial  recurrent  artery  an 
deep  radial  nerve 

Tendon  of  biceps 
Musculo-cutaneous  nerve 

Brachio-radialis  muscle 

Radial  artery 


the  rounded  head  is  the  groove  for  the  extensor  carpi  ulnaris.  The  bones  are  nearest  to  each 
other  in  complete  pronation,  and  farthest  apart  in  complete  supination.  On  section,  the  bones 
are  found  at  every  point  nearer  to  the  back  than  to  the  front  of  the  limb,  but  increasingly  so 
above.  'The  lower  the  section  proceeds  down  the  Umb,  the  less  will  the  bones  be  covered  at  the 
sides,  and  the  more  equally  wUl  the  soft  parts  be  distributed  about  the  anterior  and  posterior 
aspects  of  the  Umb.  It  will  be  noticed  that  where  one  bone  is  the  more  substantial,  the  other 
is  the  more  slender,  as  near  the  elbow  and  wrist;  and  that  it  is  about  the  centre  of  the  limb 
that  the  two  are  most  nearly  of  equal  strength.'  (Treves.)  When  the  Hmb  is  pronated,  the 
interosseous  space  is  narrowed;  in  supination  and  the  mid-position  it  is  widened  out.  In 
pronation,  both  styloid  processes  can  be  distinctly  made  out;  in  supination,  that  of  the  radius 
is  the  more  distinct,  as  now  the  skin  and  soft  parts  are  stretched  and  raised  over  that  of  the  ulna. 


about 


,  —  ..w  ..   ^.-^. ^  „...^  ..„..,  j^..,.  to  aie  oLicLuiicu  iiuu  lai&eu  uvei  mat  oi  tuc  Luua. 

Joints. — The  position  of  the  superior  radio-ulnar  joint  is  marked  by  a  dimple 
)ut  12  mm.  (I  in.)  below  the  lateral  epicondyle.     The  inferior  can  just  be  felt, 


1420 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


when  the  forearm  is  pronated,  between  the  head  of  the  ulna  and  lower  end  of  the 
radius.  The  recessus  sacciformis  here  may  be  enlarged  in  rheumatic  and  other 
affections.  The  interosseous  membrane  not  only  ties  the  bones  together  and 
gives  attachment  to  muscles,  but  in  falls  on  the  hand  it  enables  the  ulna  to  partici- 
pate in  the  shock. 

The  following  are  important  points  with  regard  to  the  bones.  Common  fractures.  Ole- 
cranon.— This  usually  takes  place  at  the  constricted  centre  of  the  semilunar  (greater  sigmoid) 
notch  or  the  junction  of  the  olecranon  with  the  shaft.  A  fall  is  here  the  usual  cause,  and 
the  heavier  the  fall,  the  more  frequently  is  the  fracture  nearer  the  shaft,  though  displacement  is 
now  likely  to  be  slight,  owing  to  the  abundance  of  fibrous  and  muscular  structures  on  both  sides 

Fig    1138. — Diagram  of  the  Anastomoses  op  the  Beachial  Artery. 
(MacCormac  and  Anderson.) 


Thoraco-acromial 
Long  thoracic 


Anterior  curcumfl' 
Posterior  circumflex' 


Superior  radial  collateral  (i 
sively  large) 


Middle  collateral 


Radial  collateral- 


Superior  ulnar  collateral 


Radial  recurrent- 


Subscapular 
Circumflex  scapular 


ulnar  collateral 

Transverse  branch  of  inferior 

ulnar  collateral 
Anastomosis  of  anterior  ulnar  recurrent 
th  inferior  ulnar  collateral 


Anterior  ulnar  recurrent 
Posterior  ulnar  recurrent 


Posterior  interosseous  from  common  interosseous  of  ulnar 


of  the  fracture.  The  shaft  of  one  or  both  hones.  Usual  site,  about  the  middle  or  a  little  below  it, 
fracture  of  the  radius  being  more  frequent  from  its  connection  with  the  hand.  In  these  fractures 
the  chief  muscular  agencies  are — (1)  the  extensors  and  flexors  in  drawing  the  lower  fragment  or 
fragments  upward,  forward,  or  backward,  according  to  the  direction  of  the  fracture;  (2)  the 
biceps  in  drawing  the  upper  fragment  of  the  radius  upward;  (3)  the  influence  of  the  pronator 
teres,  if  the  fracture  is,  as  usual,  below  it,  and  (4)  that  of  the  quadratus  in  drawing  the  lower 
fragments  together.  Thus  the  chief  practical  points  are — (a)  the  reduction  of  displacement, 
whether  antero-posterior  or  lateral;  (6)  the  greater  the  number  of  fragments,  the  greater  the 
tendency  to  union  across  the  interosseous  space,  with  its  embarrassing  results,  and  the  greater 
the  need  of  a  supinated  position  in  the  setting;  (c)  the  risk  of  gangrene  here  from  the  faciUty 
with  which  the  vessels  are  compressed  against  the  contiguous  bones,  especially  in  flexion  of 
the  forearm;  and  the  consequent  need  of  attention  to  the  width  of  the  splints  and  the  bandaging; 
(d)  the  readiness  with  which  ischsemic  paralysis  may  rapidly  and  insidiously  be  caused.  Colles' 
fracture.     Here,  after  a  fall  on  the  hand,  the  radius  gives  way  usually  at  its  weakest  part,  about 


THE  FOREARM 


1421 


Fig.  1139. — The  Arteries  of  the  Forearm  with  the  Superficial  Volar  Arch. 


Tendon  of  biceps 

Lacertus  fibrosus  of  biceps 

Radial  recurrent  artery 

Brachio-radialis 

Superficial  radial  nerve 
Radial  artery 


Flexor  pollicis  longus 


Pronator  quadrati 

Radial  artery  winding  to  back 
of  wrist  under  extensors  of 
thumb 


Superficial  volar  br. 
Superficial  volar  arch 


Brachial  artery 
Basilic  vein 


Median  nerve 
Inferior  ulnar  collateral 
Brachial  artery 

Medial  epicondyle 


Ulnar  artery 

Pronator  teres 
Flexor  carpi  ulnaris 

Flexor  digitorum  sublimis 
Flexor  carpi  radialis 
Palmaris  longus 

Median  nerve 

Flexor  digitorum  sublimis 

Ulnar  artery 

Pisiform  bone 

Transverse  carpal  ligament 
Palmaris  brevis 


1422 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


18  mm.  (f  in.)  above  its  extremity,  where  the  narrow  compact  tissue  is  suddenly  expanding 
into  cancellous.  There  is  frequently  impaction  of  the  upper  into  the  lower  fragment.  There 
is  a  three-fold  displacement  of  the  lower  fragment: — (1)  It  is  driven  and  drawn  upward  and 
backward.  (2)  It  is  rotated  so  that  its  articular  surface  looks  somewhat  backward.  (3)  It 
is  drawn  to  the  radial  side.  The  chief  causes  of  the  discreditable  stiffness  often  allowed  to  result 
are  non-reduction  of  the  deformity,  adhesions  in  the  opened  wrist-joint,  teno-synovitis,  and 
prolonged  immobilisation. 

Separation  of  epiphysis. — This  may  take  place  in  the  radius  up  to  about  the  age  of  eighteen: 
it  is  commoner  before.  Its  possible  importance  in  interfering  with  the  symmetry  of  the  growth 
of  the  bones  is  obvious.  Here,  as  in  CoUes'  fracture,  the  level  of  the  styloid  processes  of  the 
radius  and  ulna,  and  the  correspondence  of  the  two  styloid  processes  of  the  radii,  are  important 
in  diagnosis.  Exposure  of  the  bones.  In  the  case  of  ununited  fracture  or  necrosis  the  radius 
may  be  reached — (o)  Behind,  by  an  incision  in  a  line  drawn  from  the  lateral  epicondyle  to  the 
back  of  the  radius.  The  field  opened  here  lies  between  the  brachio-radialis  and  the  radial 
extensors  on  the  one  side,  and  the  common  extensor  on  the  other.     Care  must  be  taken  of  the 


Fig.  1140. — Distribution  of  CuTANEOtrs  Nerves  on  the  Anterior  and  Posterior  Aspects 
OP  the  StrpERiOR  Extremity. 


Supra-acromial 


Medial  anti- 

brachial 

cutaneous 


osto- 

brachial 
Twig  of  medial 

antibrachial 

cutaneous 
Dorsal 

antibrachial 

cutaneous 

Musculo- 
cutaneous 
(lateral  anti- 
brachial 
cutaneous) 


Lateral 

brachial 

cutaneous 


Dorsal  anti- 
brachial 
cutaneous 


Musculo 

cutaneous II 

(lateral  anti-       | 
brachial       I 
cutaneous) 


deep  radial  (posterior  interosseous)  nerve.  (6)  In  front.  The  incision  here  lies  in  the  sulcus 
between  the  brachio-radialis  and  the  flexors.  The  pronator  teres  and  the  flexor  subUmis  must, 
in  part,  be  detached  from  the  radius.  If  more  room  is  required  to  reach  an  injured  upper 
extremity  of  the  radius,  the  incision  will  descend  from  above  the  lateral  epicondyle  in  the  groove 
between  the  anconeus  and  common  extensors.  In  the  detachment  of  the  supinator  the  deep 
radial  nerve  will  again  need  attention.  The  ulna  is  more  easily  reached  by  an  incision  between 
the  flexor  and  extensor  carpi  ulnaris.  In  removal  of  the  lower  part  of  the  bones  for  myeloid 
sarcoma  or  osteitis,  the  ulna  is  reached  in  the  interval  last  mentioned.  The  radius  is  best 
exposed  by  an  incision  between  the  brachio-radialis  and  extensor  carpi  radialis  longus,  the  super- 
ficial radial  nerve  being  the  guide.  (Morris.)  Finally,  the  so-called  'carrying  angle'  of  the 
forearm  deserves  mention.  In  extension  the  bones  of  the  forearm  are  not  in  a  straight  line  with 
the  humerus,  but  directed  sUghtly  laterally,  the  angle  at  the  elbow-joint  being  obtuse,  and  open 
laterally.  This  angle  is  so  named  from  its  facilitating  carrying  objects  during  walking.  In 
flexion  the  forearm  is  deflected  somewhat  toward  the  middle  line,  mouth,  etc.  These  properties 
are  liable  to  be  lost  under  many  and  widely  different  conditions,  of  wliich  injuries  to  the  epiphyses 
of  the  humerus,  badly  united  fractures  of  the  forearm,  and  osteoarthritis  of  the  elbow-joint  are 
instances. 


THE  FOREARM 


1423 


Soft,  parts. — Along  the  lateral  border,  of  the  forearm  descend  the  brachio- 
radialis  and  radial  extensors  of  the  carpus,  fleshy  above,  tendinous  below.  About 
3.7  cm.  (I5  in.)  above  the  styloid  process  of  the  radius,  a  fleshy  swelling  directed 
obliquely  downward  and  forward  from  behind,  across  this  lateral  border  of  the 
forearm,  denotes  the  extensors  of  the  thumb  crossing  those  of  the  carpus. 

Along  the  medial  border  is  the  fleshy  mass  of  the  pronator  teres  and  flexors,  the 
ulna  being  covered  by  the  flexor  carpi  ulnaris  and  flexor  profundus.  The  tendon 
of  the  pronator  is  inserted  into  the  radius  a  little  below  its  centre — a  point  of  im- 
portance in  the  treatment  of  fractures  and  in  amputation.  The  flexor  carpi  ul- 
naris tendon  can  be  felt  just  above  the  wrist  making  for  the  pisiform  bone;  and 
just  lateral  to  it  lies  the  ulnar  artery,  about  to  pass  over  the  transverse  carpal  (ante- 
rior annular)  ligament. 

The  course  of  the  artery  is  denoted  by  the  lower  two-thirds  of  a  hne  drawn  from  the 
front  of  the  medial  epicondyle  to  the  lateral  edge  of  the  pisiform  bone.  From  the  bifurcation 
of  the  brachial,  a  line  drawn  to  meet  the  former  at  the  junction  of  its  middle  and  upper  third 
marks  the  upper  part  of  the  artery,  here  thickly  covered  by  muscles.  In  ligature  of  the  artery 
in  the  middle  of  the  forearm,  the  white  line  and  sulcus  between  the  flexor  carpi  ulnaris  and  sub- 
limis  must  be  identified.  A  small  muscular  branch  will  often  lead  down  to  the  artery.  The 
line  of  the  ulnar  nerve  is  one  drawn  from  the  interval  between  the  medial  epicondyle  and  the 


Fig.  1141. — Section  through  the  Middle  of  the  Right  Forearm.     (Heath.) 


Brachio-radialis 

Supinator 
Extensor  carpi  radialis  longus  _^ 
and  brevis  W 

Abductor  pollicis  longus 


l|pf- Flexor  digitorum  sublimis 
Flexor  carpi  ulnaris 


Extensor  digitorum 

Extensor  carpi  ulnar 
Posterior  interosseous  vessels  and  deep  radial  nerve  |      Median  nerv 
Extensor  pollicis  longus 


Ulnar  vessels  and  nerve 
Flexor  digitorum  profundus 


olecranon  to  the  medial  side  of  the  ulnar  artery  just  above  the  wrist.  The  nerve  joins  the  artery 
at  the  junction  of  the  upper  and  middle  thirds  of  the  forearm.  The  median  nerve  runs  in  a 
hne  drawn  from  the  medial  side  of  the  brachial  artery,  in  the  elbow  triangle,  to  a  point  beneath, 
or  just  to  the  medial  side  of,  the  palmaris  longus  at  the  mid-point  of  the  front  of  the  wrist.  The 
radial  artery  will  be  marked  by  a  line  drawn  from  the  centre  of  the  bend  of  the  elbow  (where  the 
brachial  artery  divides  opposite  to  the  neck  of  the  radius)  to  a  point  just  medial  to  the  radial 
styloid  process  descending  along  the  medial  edge  of  the  brachio-radialis.  The  muscular  interval 
is  that  between  the  brachio-radialis  and  pronator  teres  above,  and  the  flexor  carpi  radialis  below. 
The  superficial  radial  nerve  will  be  marked  by  the  same  line  (it  lies  just  lateral  to  the  artery)  for 
its  upper  two-thirds;  it  then  leaves  the  artery  about  7.5  cm.  (3  in.)  above  the  wrist-joint,  and 
passes  to  tiie  back  of  the  forearm  under  the  tendon  of  the  brachio-radialis.  The  volar  inter- 
osseous artery  runs  down  on  the  interosseous  membrane  and  passes  to  the  back  of  the  fore- 
arm by  perforating  it  below,  having  passed  behind  the  pronator  quadratus.  The  dorsal 
interosseous  lies  between  the  superficial  and  deep  extensors.  These  small  arteries  reinforce 
the  palmar  through'  the  carpal  arches,  and  thus  bring  down  blood  after  ligature  of  the  trunks 
above. 

The  front  of  the  forearm  is  supplied  by  the  miiscido-cutaneous  on  the  lateral, 
and  the  medial  aniibrachial  (internal)  cutaneous  on  the  medial,  side;  just  above 
the  wrist  the  palmar  cutaneous  branches  of  the  median  and  ulnar  perforate  the 
deep  fascia  (fig.  1140).     The  back  of  the  forearm  is  supplied  by  the  radial  (mus- 


1424  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

culo-spiral)  and  posterior  branches  of  the  musculo-cutaneous  laterally,  and  the 
posterior  branches  of  the  medial  antibrachial  cutaneous  medially  (fig.  1140). 

The  lymphatics  of  the  upper  extremity  are  superficial  and  deep;  the  former 
run  with  the  superficial  veins,  the  latter  with  the  deep  vessels.  Occasionally  a 
few  small  nodes  occur  below  the  elbow.  The  epitrochlear  nodes  lie  upon 
the  basilic  vein,  a  little  above  the  medial  epicondyle  and  draining  the  fourth  and 
fifth  digits.  The  majority  of  the  lymphatics  open  into  the  axillary  nodes,  and 
terminate,  on  the  left  side  in  the  thoracic  duct,  on  the  right  in  the  lymphatic  duct. 
A  few,  accompanying  the  cephahc  vein,  reach  the  subclavian  or  infraclavicular 
nodes,  and  thus  communicate  with  the  lymphatics  of  the  neck. 

It  will  be  well  briefly  to  consider  here  the  chief  results  of  paralysis  of  the  main 
nerves  of  the  upper  extremity. 

Paralysis  of  the  median  nerve. — (a)  In  forearm:  Loss  of  pronation,  (fe)  At  ivrisl:  Dimin- 
ished flexion  1111(1  tciidciicy  toward  ulnar  adduction,  (c)  In  the  hand:  Power  of  grasp  is  lessened 
especially  in  the  tliunili  and  lateral  two  fingers.  Owing  to  the  loss  of  flexion  in  the  phalanges 
of  these  fingers  the  phalanges  are  liable  to  become  overextended  by  the  action  of  the  extensors 
and  interossei.  The  thumb  remains  extended,  adducted,  and  closely  applied  to  the  index,  the 
human  characteristic  being  thus  lost,  and  the  '  ape's  hand'  of  Duchenne  being  produced.  Sensa- 
tion will  be  lost  over  the  palmar  aspect  of  the  thumb  and  lateral  two  and  one-half  fingers  and 
over  the  distal  ends  of  the  same  fingers,  to  a  varying  degree,  according  to  the  sensory  distribution 
of  the  median  and  other  cutaneous  nerves.  The  above  apphes  to  lesions  of  the  trunk.  If  the 
nerve  be  injured  at  the  wrist,  flexion  of  the  wrist  and  fingers  is  less  interfered  with. 

Paralysis  of  the  ulnar  nerve. — (a)  At  wrist:  Power  of  flexion  is  diminished  and  that  of  ulnar 
adduction  lost.  (&)  In  the  hand:  Power  of  grasp  will  be  lessened  in  the  ring  and  little  fingers. 
The  interossei  will  be  powerless  to  abduct  or  adduct  the  fingers,  and  there  will  be  marked  wasting 
of  the  interosseous  spaces  and  hypothenar  eminence.  The  thumb  cannot  be  adducted.  After 
a  time,  from  paralysis  of  the  lumbricals  and  interossei,  the  hand  becomes  'clawed' — the  first 
phalanges  overextended,  and  the  second  and  third  flexed  (main  en  griff e).  Sensation  will  be 
lessened  over  the  area  supplied  by  the  nerve. 

Paralysis  of  the  radial  (musculo-spiral)  nerve. — (a)  In  the  forearm  This  is  flexed,  ex- 
tension being  impossible.  The  forearm  is  pronated,  supination  being  impossible  save  by  biceps, 
which  acts  now  most  strongly  on  a  flexed  elbow-joint,  (b)  In  the  wrist:  This  is  dropped,  owing 
to  the  loss  of  extension,  (c)  hi  the  hand:  The  thumb  is  flexed  and  adducted.  Some  slight 
power  of  extension  of  the  second  and  third  phalanges  of  the  fingers  remains  by  means  of  the 
lumbricales  and  interossei.  Sensation  is  impaired  over  the  posterior  and  lateral  aspect  of  the 
forearm  and  lost  to  a  varying  extent  over  the  distribution  of  the  radial  on  the  back  of  the  hand. 

Paralysis  of  the  deep  radial  (posterior  interosseous)  nerve. — The  evidence  here  is  somewhat 
similar  to  that  just  given,  but  with  the  following  differences,  (o)  In  the  forearm:  There  is  no 
loss  of  extension,  and  the  loss  of  supination  is  less  as  the  brachio-radialis  is  not  paralysed,  (b) 
At  the  wrist:  The  'drop'  and  loss  of  extension  are  not  so  marked,  as  the  extensor  carpi  radiahs 
longus  escapes.     Sensation :  There  is  no  loss. 

Paralysis  of  the  musculo-cutaneous  nerve. — Forearm:  Power  of  flexion  is  impaired,  owing 
to  complete  paralysis  of  the  biceps  and  partial  of  the  brachialis  (anterior).  Sensation:  This  is 
impaired  over  the  lateral  aspect  of  the  forearm,  both  back  and  front. 

Amputation  of  forearm. — The  'mixed'  method  by  skin-flaps  roundly  arched  and  circular 
division  of  the  soft  parts,  the  dorsal  flap  being  the  longer,  is  the  most  generally  applicable.  The 
bones  should  always  be  sawn  below  the  pronator  teres,  when  possible.  In  sawing  them  they 
must  be  kept  parallel,  the  limb  being  in  the  supinated  position.  As  the  radius  is  the  less  securely 
held  above,  it  is  well  to  complete  the  section  of  this  bone  first.  The  relative  position  of  the  ves- 
sels has  been  indicated  above  (p.  1423,  and  figs.  1139  and  1141). 

THE  WRIST  AND  HAND 

Bony  points. — On  the  medial  side  the  styloid  pi'ocess  and,  further  laterally,  the 
head  of  the  ulna  can  be  made  out.  On  the  lateral  side,  the  radial  styloid  process 
descends  about  1.2  cm.  (|  in.)  lower  than  that  of  the  radius,  and  is  somewhat  ante- 
rior to  it.  Abduction  of  the  hand  is  thus  less  free  than  adduction.  Between  the 
apex  of  the  styloid  process  and  the  ball  of  tlie  thumb  a  bony  ridge  can  be  felt,  with 
some  difficulty,  formed  by  the  tubercle  of  the  navicular  and  the  ridge  of  the  greater 
multangular  (trapezium).  At  the  base  of  the  hypothenar  eminence  the  pisiform 
can  be  more  readily  distinguished.  The  hook  of  the  hamatum  (unciform)  lies  below 
and  to  the  radial  side  of  the  pisiform.  On  the  front  of  the  metacarpo-phalangeal 
joint  of  the  thumb,  the  sesamoid  bones  can  be  distinguished. 

At  the  back  of  the  wrist  and  hand  the  triquetrum  (cuneiform)  bone  can  be  felt 
below  the  head  of  the  ulna;  and  more  toward  the  middle  line  tlie  prominence  of 
the  capitatum  (os  magnum),  which  supports  the  third  or  longest  digit. 

A  line  drawn  from  the  base  of  the  fifth  metacarpal  bone  to  the  radio-carpal  joint,  slightly 
curved  downward,  will  give  the  line  of  the  carpo-metacarpal  joints.  (Windle.)  When  the 
fingers  are  flexed,  it  will  be  seen  that  in  each  case  it  is  the  proximal  bone  which  forms  the  prom- 


THE  WRIST  AND  HAND 


1425 


inence ;  thus,  the  knuckle  is  formed  by  the  head  of  the  metacarpal,  the  interphalangeal  prominence 
by  the  head  of  the  first  phalanx,  and  the  distal  one  by  the  head  of  the  second.  _  Thus,  the  joint 
in  each  case  lies  below  the  prominence,  the  distal  joint  being  2  mm.  {^t  in.),  the  interphalangeal 
4  mm.  (i  in.),  and  the  metacarpo-phalangeal  8  mm.  (3  in.)  below  its  prominence. 

Skin  and  skin-folds. — The  skin  over  the  palm  is  thickened  over  the  heads  of 
the  metacarpal  bones  and  hypothenar  eminence,  thinner  over  the  thenar.  It  is 
peculiar  in  its  absence  of  sebaceous  glands  and  hair-follicles;  hence  the  absence  of 
boils  and  sebaceous  cysts.  It  is  intimately  connected  with  the  palmar  fascia, 
hence  the  chief  difficulty  in  operations  when  this  is  contracted.  Over  the  pulp 
of  the  digits  the  skin  is  closely  connected  with  the  periosteum  of  each  ungual 
phalanx.  The  importance  of  this  is  alluded  to  under  the  heading  of  whitlow 
(vide  infra). 

Skin -folds :  two  or  three  of  these  are  seen  on  the  palmar  surface  of  the  wrist :  two  lower  down, 
and  usually  close  together,  and  one  less  well  marked,  a  little  higher  up  upon  the  forearm.  None 
of  these  corresponds  exactly  to  the  wrist-joint  (fig.  1142).  The  lowest  'precisely  crosses  the  arch 
of  the  OS  magnum  in  the  line  of  the  third  metacarpal  bone'  (Tillaux),  and  is  not  quite  l.S  cm. 
(f  in.)  below  the  arch  of  the  wrist-joint.  It  is  about  1.2  cm.  (5  in.)  above  the  carpo-metacarpal 
joint  line,  and  indicates  very  fairly  the  upper  border  of  the  transverse  carpal  (anterior  annular) 
ligament. 

'Of  the  many  creases  in  the  skin  of  the  palm,  three  require  especial  notice.  The  first  starts 
at  the  wrist,  between  the  thenar  and  hypothenar  eminences,  and,  marking  off  the  former  emi- 


FiG.  1142. 


-Relation  of  the  Volar  Arches  to  the  Folds  op  the  Palm. 
Tillaux.) 


(Modified  from 


nence  from  the  palm,  ends  at  the  lateral  border  of  the  hand  and  at  the  base  of  the  index-finger. 
The  second  fold  is  slightly  marked.  It  starts  from  the  lateral  border  of  the  hand,  where  the 
first  fold  ends.  It  runs  obliquely  medially  across  the  palm,  with  a  marked  inclination  toward 
the  wrist,  and  ends  at  the  lateral  Hmit  of  the  hypothenar  eminence.  The  third,  lowest,  and  best 
marked  of  the  folds  starts  from  the  little  elevation  opposite  the  cleft  between  the  index  and 
middle  fingers,  and  runs  nearly  transversely  to  the  ulnar  border  of  the  hand,  crossing  the  hypo- 
thenar eminence  at  the  upper  end  of  its  lower  fourth.  The  first  fold  is  produced  by  the  adduc- 
tion of  the  thumb;  the  second,  mainly  by  the  bending  simultaneously  of  the  metacarpo-phalan- 
geal joints  of  the  first  and  second  fingers;  and  the  third  by  the  flexion  of  the  three  medial  fingers. 
The  second  fold,  as  it  crosses  the  third  metacarpal  bone,  about  corresponds  to  the  lowest  part 
of  the  superficial  volar  arch.  The  third  fold  crosses  the  necks  of  the  metacarpal  bones,  and 
indicates  pretty  nearly  the  upper  limits  of  the  synovial  sheaths  for  the  flexor  tendons  of  the 
three  lateral  fingers.  A  httle  way  below  this  fold,  the  palmar  aponeurosis  breaks  up  into  its 
four  slips,  and  midway  between  the  fold  and  the  webs  of  the  fingers  lie  the  metacarpo-phalan- 
geal joints.  Of  the  transverse  folds  across  the  fronts  of  the  fingers,  corresponding  to  the  meta- 
carpo-phalangeal and  interphalangeal  joints,  the  highest  is  placed  nearly  IS  mm.  (f  in.)  below 
its  corresponding  joint.  The  middle  folds  are  multiple  for  all  the  fingers,  and  are  exactly 
opposite  to  the  first  interphalangeal  joints.  The  distal  creases  are  single,  and  are  placed  a  little 
above  the  corresponding  joints.  There  are  two  single  creases  on  the  thumb  cori-esponding 
to  the  two  joints,  the  higher  crossing  the  metacarpo-phalangeal  joint  obhquely.  The  free  edge 
of  the  web  of  the  fingers,  measured  from  the  palmar  surface,  is  about  1.8  cm.  (f  in.)  from  the 
metacarpo-phalangeal  joints.     (Treves.) 

_  The  superficial  volar  arch,  formed  by  the  ulnar  anastomosing  with  the  super- 
ficial volar,  or  radialis  indicis,  will  be  shown  by  a  line  descending  to  the  radial  side 


1426 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


of  the  pisiform  bone,  and  then,  a  Httle  lower,  curving  across  the  palm  on  a  line  with 
the  thumb  when  outstretched  at  right  angles  with  the  index-finger.  The  four 
common  digital  arteries,  the  main  branches  of  the  superficial  arch,  run  downward 
along  the  interosseous  spaces,  and  bifurcate  12  mm.  (J  in.)  above  the  webs  of  the 
fingers;  the  most  medial  digital  does  not  bifurcate. 

The  digital  arteries  then  descend  along  the  sides  of  the  fingers  under  the  digital  nerves, 
giving  ofi  twigs  to  the  sheath  of  the  tendons,  which  enter  by  apertures  in  it,  and  run  in  the 
vincula  vasculosa.  It  is  owing  to  the  readiness  with  which  these  tiny  twigs  are  strangled  by 
inflammation  that  sloughing  of  the  tendon  takes  place  so  readily  and  irreparably.  Throughout 
its  course  the  superficial  volar  arch  deserves  its  name.     It  is  only  covered  by  the  palmaris 

Fig.  1143. — Anastomoses  and  Distribution  op  the  Arteries  of  the  Hand. 

Volar  interosseous  - 
Radial  artery  - 

Volar  radial  carpal 
Superficial  vola 


Dorsal  radial  carpal 
Radial  artery  at  wrist 

First  dorsal 
metacarpal 
Second  d 
metacarpal 

Princeps  polli 
First    dorsal    meta- 
carpal   (branch  to 
index) 

Radialis  indicis     ,     ,     ,,       ,,  ,,     ,,      ^^      ,  ^^r  ,  i^      i*x       ^— .c^    ^»  . 

Common   volar 
digitals 

Dorsal    meta- 
carpals 
Common   volar 
digital 


Dorsal  digital 

Volar  digital 

First  dorsal  branch  of  volar  digital 


Second  dorsal  branch  of  volar  digital 


Anastomosis  of  volar  digital  arteries 
about  matrix   of   nail  and  pulp  of 


brevis  and  central  part  of  the  palmar  fascia.  Beneath  it,  medio-laterally  are  the  flexor  brevis 
and  opponens  digiti  quinti,  the  digital  branches  of  the  ulnar  and  median  nerves,  and  the  flexor 
tendons  and  lumbricales. 

The  deep  volar  arch,  formed  by  the  radial  and  communicating  branch  of  the 
ulnar,  lies  about  1 . 2  cm.  (|  in.)  nearer  to  the  wrist  than  the  superficial.  It  is  not 
so  curved  as  the  superficial  arch,  and  rests  upon  the  interossei  and  metacarpal 
bones  just  below  their  bases.  The  structures  separating  it  from  the  superficial 
arch  have  been  already  given. 

Owing  to  the  frequency  of  wounds  here,  the  relation  of  the  structures  in  front  of 
the  wrist  is  most  important.     The  radial  artery  lies  between  the  tendon  of  the 


THE  WRIST  AND  HAND 


1427 


brachio-radialis  and  flexor  carpi  radialis.  Next  to  this  tendon  is  the  palmaris 
longus,  when  present.  At  the  mid-point  of  the  front  of  the  wrist  and  usually 
under  the  palmaris  longus  is  the  median  nerve.  To  the  medial  side  of  the  palmaris 
longus  is  the  flexor  sublimis,  the  tendons  for  the  middle  and  ring-finger  being  in 
front.  The  tendon  of  the  flexor  carpi  ulnaris  is  most  medial  and  between  this  and 
the  superficial  flexor  of  the  finger  the  ulnar  nerve  and  vessels  have  come  up  into  a 
superficial  position. 


Fig.  1144. — The  Superficial  Muscles  op  the  Palm  of  the  Hand. 


Flexor  carpi  radialis 


Abductor  pollicis  longus 

Opponens  pollicis 

Abductor  pollicis  brevis 


Flexor  pollicis  brevis 


Flexor  digitorum 
profundus 


Fasciae  and  sheaths. — The  transverse  and  dorsal  carpal  (annular)  ligaments 
bind  down  and  hold  in  place  the  numerous  tendons  about  the  wrist.  The  trans- 
verse carpal  (anterior  annular) ,  when  healthy,  cannot  be  detected.  It  is  attached 
to  the  pisiform  and  triquetral  (cuneiform)  bones  on  the  medial,  and  to  the  na- 
vicular and  greater  multangular  (trapezium)  on  the  lateral,  side. 


1428 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


The  ulnar  nerve  and  vessels,  the  superficial  volar,  and  palmar  cutaneous  branches  of  the 
median  and  ulnar  pass  over  it.  The  ulnar  artery  and  nerve  are  especially  protected  by 
their  position  between  the  pisiform  and  hook  of  the  hamate  (unciform),  and  also  by  a 
process  of  the  flexor  carpi  ulnaris,  which  passes  to  the  transverse  ligament,  thus  forming  a 
kind  of  tunnel.  The  flexor  carpi  radialis  passes  through  a  separate  sheath  formed  by  the  liga- 
ments and  the  groove  in  the  greater  multangular;  while  beneath  the  Hgaments  lie  the  flexor 
tendons,  the  median  nerve,  and  accompanying  artery.  Attached  to  its  upper  border  is  the 
deep  fascia  of  the  forearm,  and  to  its  lower  the  palmar  fascia  and  the  palmaris  longus  tendon, 
while  from  the  lateral  and  medial  parts  arise  some  of  the  thenar  and  hypothenar  muscles.  The 
upper  border  of  the  transverse  carpal  ligament  corresponds  to  the  lower  of  the  two  lines  which 

Fig    1145. — The  Deeper  Muscles  of  the  Palm  of  the  Hand. 


—  Abductor  poUicis  longus 
Flexor  carpi  radialis 
Extensor  poUicis  brevis 

Abductor  pollicis  brevis 


Opponens  pollicis 


Abductor  pollicis 

brevis 
.Flexor  pollicis 
brevis 

Adductor  pollicis 


cross  the  wrist  just  above  the  thenar  and  hypothenar  eminences.  The  large  synovial  sheath, 
for  all  the  flexors  of  the  fingers,  reaches  beneath  and  below  the  transverse  ligaments  as  far  as 
the  middle  of  the  palm,  and  above  the  wrist  for  3.7  to  5  cm.  (1 J  to  2  in.). 

The  dorsal  carpal  (posterior  annular)  ligament  is  attached  to  the  back  of  the 
lateral  margin  of  the  radius  above  the  styloid  process,  and  medially  to  the  back  of 
the  styloid  process  of  the  ulna,  the  triquetrum  and  pisiform.  Its  direction  is 
obhque,  being  higher  on  the  radial  side.  It  contains  six  tendon-compartments,  of 
which  four  are  on  the  radius. 

The  most  lateral  contains  the  long  abductor  and  short  extensor  of  the  thumb;  the  second 
the  two  radial  extensors  of  the  carpus;  the  third,  the  extensor  pollicis  longus;  this  deep  and  narrow 
groove  can  be  identified  when  the  hand  is  extended,  by  its  prominent  lateral  margin;  the  fourth 
transmits  the  extensor  communis  and  extensor  indicis  proprius;  the  fifth,  lying  between  the 


THE  WRIST  AND  HAND 


1429 


Fig.  1146. — Section  throttgh  Region  of  Wrist,  a  Little  above  the  Joint.     Kight  Side, 
Upper  Half  of  the  Section.     (Tillaux.) 

Flexor  carpi  radialis         Flexor  pollicis  longus 
Flexor  sublimis 


Radial  artery 
Brachio -radialis 


Flexor  profundus 

Pronator  quadratus 


Superficial  radial  nerve 


Abductor  pollicis  longus 
Extensor  brevis  pollicis 


Extensor  carpi  radialis 

longus 
Extensor  carpi  radialis 

brevis 


Extensor  pollicis  longus 


Ulnar  artery,  and  nerve 


Volar  interosseous  artery 


Flexor  carpi  ulnaris 


Extensor  com' 
-    munis  and  indicis 
Radius  Extensor  digiti  quinti 


Extensor  carpi  ulnaris 


Fig.  1147. — Region  of  the  Wrist,  as  Shown  by  the  ROntgen-rays. 


1430 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


radius  and  ulna,  the  extensor  digiti  quinti;  and  the  sixth,  lying  just  lateral  to  the  styloid  process 
of  the  ulna,  the  extensor  carpi  ulnaris.  The  sheaths  for  the  last  two  extensors  are  the  only  ones 
which  follow  the  tendons  of  their  insertion,  the  others  ending  at  a  varying  distance  below  the 
carpal  ligament.  The  lower  border  of  the  dorsal  carpal  corresponds  to  the  upper  margin  of  the 
transverse  carpal  ligament. 

Fig.  1148. — Thansverse  Section  of  the  Wrist  through  the  Middle  op  the  Pisifohm  Bone. 

Sheath  of  flexores  sublimis  and  profundus  digitorum  and  flexor  pollicis  longus 
enclosed  by  the  transverse  carpal  ligament 
Cut  tendon  of  palmaris  longus     Ulnar  nerve 

Lunate  bone    |  I  Ulnar  vessels 


Sheath  for  flexor  carpi  radialis 
Radial  origin  of  transverse 

carpal  ligament  ^ 

Sheath    for    abductor  longus  and  J,    " 


Sheath  of  extensor  carpi  ulnaris 


Sheath  of  extensores  carpi  radialis,  longus  and  brevis 


Sheath  of  extensor  communis  and  indicis 

Lunatu 


Sheath  of  extensor  digiti  quinti 
Triquetn 
Hamatum 


Fig.  1149. — Diagram  of  the  Great  Palmar  Bursa. 


Ulnar  portion  of  palmar  bursa 
Radial  portion  of  palmar  bursa 


Transverse  carpal  ligament 


Deep  transverse 
ligament 


The  palmar  aponeurosis,  by  its  strength,  toughness,  numerous  attachments, 
and  intimate  connection  with  the  superficial  fascia  and  skin  is  well  adapted  to  pro- 
tect the  parts  beneath  from  pressure. 

The  thenar  and  hypothenar  muscles  are  enclosed  in  two  processes,  which  are  thinner  so  as 
not  to  interfere  with  the  contraction  of  the  subjacent  muscles.     The  central  part,  pointed  above 


THE  WRIST  AND  HAND 


1431 


at  its  attachment  to  the  carpal  ligament,  spreads  out  fan-like  below,  and  gives  off  four  sKps, 
each  of  which  bifurcates  into  two  processes,  which  are  attached  to  the  sides  of  the  first  phalanx 
of  each  finger  and  into  the  superficial  transverse  ligament  of  the  web  and  the  deeper  one  which 
ties  the  heads  of  the  metacarpal  bones  together.  Transverse  fibres  pass  between  the  processes 
into  which  each  of  the  four  slips  bifurcates,  and  thus  form  the  beginning  of  the  theca,  which  is 
continued  down  the  finger  to  the  base  of  the  last  phalanx.  It  is  the  contraction  of  the  palmar 
aponeurosis,  especially  of  the  slip  to  the  two  medial  fingers,  which  gives  rise  to  Dupuytren's 
contraction.  The  theca  is  strong  opposite  the  first  two  phalanges  (hgamentum  vaginale), 
weak  and  loose  opposite  the  joints  (ligamentum  annulare).  The  density  of  this  osseo-fibrous 
tunnel  and  its  close  proximity  to  the  digital  nerves  explain  the  pain  in  thecal  inflammation. 
Its  tendency  to  gape  widely  after  section  is  to  be  remembered  in  amputations  through  infected 
parts. 

Sjraovial  membranes. — Beneath  the  transverse  carpal  ligament  lie  two 
synovial  sacs,  one  for  the  flexor  pollicis  longus,  and  one  for  the  superficial  and 
deep  flexors  of  the  fingers.  They  extend  above  the  transverse  ligament  for  rather 
more  than  2.5  cm.  (1  in.).  The  two  sacs  may  communicate.  A  compound 
palmar  ganglion  has  an  hour-glass  outline,  the  transverse  carpal  ligament  forming 
the  constriction. 

The  creaking  sensation  in  teno-synovitis  and  that  of  'melon-seed'  bodies  often  present  in 
tuberculosis  here  is  well  known.  The  sheath  for  the  long  flexor  of  the  thumb  reaches  to  the 
base  of  the  last  phalanx.  That  for  the  finger-flexors  gives  off  four  processes.  The  one  for  the 
little  finger  also  reaches  to  the  base  of  the  last  phalanx.  Those  for  the  index-,  middle,  and  third 
fingers  end  about  the  middle  of  the  metacarpal  bones.     Traced  from  the  insertions  of  the  flexor 


sublimis  and  profundus 
Ulnar  vessels  and  nerve 


Palmaris  brevis 

iHypothenar  muscles 


Fig.  1150. — Section  op  Cabpus  through  the  Hamate  Bone 
(BeUamy,  after  Henle.) 
Median  nerve 
Flexor  pollicis  longus    Flex' 
Flexor  carpi  radialis 
Thenar  muscles 
Base  of  first  metacarpal  bone 


Abductor  pollicis  longus- 
Greater  multangular- 
Extensor  pollicis  brevi 
Radial  vessel 
Extensor  carpi  radialis  longus — 


(Two-thirds.) 


Lesser  multangulai 
Extensor  carpi  radialis  brevis 

Capita  turn 
Extensor  indicis 


Extensor  carpi  ulnaris 

Extensor  digiti  quinti 
Hamatum 
Extensor  digitorun 
proprius 


profundus,  the  digital  synovial  sheaths  extend  upward  into  the  palm  as  far  as  the  bifurcation 
of  the  palmar  fascia  (p.  1430),  i.  e.,  into  a  point  about  opposite  to  the  necks  of  the  metacarpal 
bones,  denoted  on  the  surface  by  the  crease  which  corresponds  to  the  flexion  of  the  fingers. 
Thus,  about  1  -  2  cm.  (|in.)  separates  the  sheaths  of  the  lateral  three  fingers  from  the  large  syno- 
vial sac  beneath  the  transverse  carpal  ligament.  There  is  no  synovial  sheath  beneath  the  pulp 
of  the  fingers  or  thumb,  this  part  lying  on  the  periosteum  of  the  last  phalanx. 

This  has  an  important  bearing  on  whitlow.  Infection  here  may  be  merely  subcuticular, 
or  deeper,  in  the  latter  case  from  the  connection  of  the  skin  with  the  periosteum  here  existing 
the  bone  is  soon  affected,  and  necrosis  keeps  up  a  tedious  ulcer.  As  the  two  centres  of  the  pha- 
lanx do  not  unite  till  about  the  twentieth  year,  the  distal  one  only  requires  removal;  as  the 
flexor  sheath  only  reaches  to  the  insertion  of  the  flexor,  i.  e.,  into  the  proximal,  part  of  the  bone, 
both  sheath  and  tendon  may  escape  implication.  Higher  up  along  the  fingers  whitlow  may  be 
cellulo-cutaneous  or  thecal.  While  the  continuity  of  the  synovial  sheath  in  the  httle  finger  and 
thumb  (fig.  1149)  renders  infection  here  more  dangerous,  the  short  gap  between  the  digital 
and  the  palmar  sacs  is  readily  traversed  by  acute  infection,  with  all  the  grave  results  of 
thecal  suppuration. 

Suppuration  in  the  hand  owes  much  of  its  gravity  to  the  possibility  of  infection  of  the  syno- 
vial tendon  sheaths  and  consequent  sloughing  of  the  tendons.  At  the  same  time  it  is  now 
recognised  that  unless  these  sheaths  are  primarily  infected  pus  collects  at  first  in  certain  jioten- 
tial  spaces,  more  or  less  well  defined,  in  the  looser  connective  tissue  of  the  hand.  One  of  these, 
known  as  the  middle  palmar  space  (Kanavel*)  is  situated  on  the  front  of  the  metacarpals  of 
the  middle  and  ring  fingers,  and  lies  deeply  between  the  flexor  tendons  and  the  interosseous 
muscles.     Continuations  of  this  potential  space  extend  downward  along  the  lumbrical  muscles 

*  Kanavel,  A.  B.:  Infections  of  the  Hand,  1912. 


( 


1432 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


on  the  radial  side  of  the  three  medial  fingers,  and  may  lead  pus  from  the  palm  to  the  subcutane- 
ous tissue  of  these  fingers  or  vice  versa.  A  second  potential  compartment,  the  thenar  space 
(Kanavel)  lies  in  front  of  the  index  metacarpal,  between  the  flexors  of  the  index-finger  and  the 
adductor  transversus  poUicis.  As  in  the  former  space,  the  corresponding  lumbrical  muscle  pro- 
longs it  down  to  the  radial  side  of  the  index -finger. 

Distention  of  the  middle  pahnar  space  with  pus  leads  to  obliteration  of  the  hollow  of  the 
palm  and  a  variable  extension  of  the  swelling  along  the  radial  side  of  the  three  medial  fingers. 
Distention  of  the  thenar  space  follows  the  thenar  eminence,  obliterates  the  adduction  crease  of 

Fig.  1151. — Tendons  trpoN  the  Doksum  of  the  Hand. 
(The  dorsal  expansion  or  aponeuiotic  sheath  has  not  been  removed.) 


Abductor  polUcis  longus 
Extensor  pollicis  brevis 


Dorsal  carpal  ligament 


Extensor  carpi  ulnaris 


Extensor  digitorum  communis 


Extensor  digiti  quinti 


Extensor  indicis  proprius 


Attachment  of  extensor 
digitorum  communis 
to  third  phalanx 


the  thumb,  and  may  extend  down  the  radial  side  of  the  index-finger.  There  is  not  in  either  case 
the  extreme  tenderness  and  pain  on  passive  extension  of  the  fingers  that  is  characteristic  of 
infection  of  the  synovial  sheaths.  The  pus  is  best  evacuated  by  an  incision  on  the  radial  side 
of  the  finger  most  affected,  a  little  beliind  the  web,  sinus  forceps  being  passed  along  the  lumbrical 
muscle  into  the  palm,  so  as  to  avoid  opening  and  infecting  the  synovial  sheaths. 

It  must  be  remembered  also  that  infection  of  the  above  fascial  spaces  may  take  place 
secondarily,  by  the  bursting  into  them  of  pus  from  the  synovial  tendon  sheaths. 


THE  WRIST  AND  HAND 


1433 


Deeper  are  the  articular  synovial  sacs,  five  in  number: — (1)  Between  the 
interarticular  cartilage  and  the  head  of  the  ulna;  (2)  between  the  radius  and  the 
interarticular  cartilage  above,  and  the  navicular  and  lunate  and  triquetrum 
below;  (3)  between  the  greater  multangular  and  first  metacarpal  bone;  (4)  be- 
tween the  pisiform  and  the  triquetral  bone;  (5)  between  the  two  rows  of  carpal 
bones,  sending  two  processes  upward  between  the  three  bones  of  the  upper  row, 
and  three  downward  between  the  four  of  the  lower  row;  these  three  processes  being 
also  continued  below  into  the  medial  four  carpo-metacarpal  and  three  inter- 
metacarpal joints. 

Beneath  the  palmar  aponeurosis  covering  the  thenar  eminence  are  the  following  structures: — 
Superficial  volar  artery,  abductor  pollicis  brevis,  opponens  pollicis,  radial  head  of  short  flexor, 
tendon  of  long  flexor,  ulnar  head  of  short  flexor,  first  volar  metacarpal  arteries,  metacarpal  bone 
of  the  thumb,  with  the  tendon  of  the  flexor  carpi  radialis  and  greater  multangular. 

Beneath  the  central  part  of  the  palmar  aponeurosis  are  the  superficial  arch  and  its  digital 
branches;  the  ulnar  and  median  nerves,  with  their  branches;  the  lle.xors,  superficial  and  deep, 
with  their  synovial  sheath;  and  the  lumbricales;  then  a  layer  of  connective  tissue  (the  only 


Fig.  1152. — Diagrams  Illustrating  the  Insertions  of  the  Extensor,  Litmbrical  and 
Interosseous  Muscles  op  the  Right  Hand.  A,  Index  finger.  B,  Middle  finger.  C,  Ring 
finger.  D,  Little  finger.  IL,  2L,  3L,  4L,  Lumbricales.  1D9,  2D9,  3E)9,  4D9,  dorsal  interossei. 
1P9,  2P9,  3P9,  palmar  (volar)  interossei.  EC,  Extensor  communis  digitorum.  E9,  Extensor 
indicis  proprius.  EMD,  Extensor  digiti  quinti  proprius.  AMD,  abductor  digiti  quinti  (Willan : 
Anat.  Anz.  Bd.  42,  1912.) 


Riont 


structure,  together  with  the  deep  layer  of  fascia  over  the  interossei,  which  prevents  matter  pent 
in  by  the  palmar  aponeurosis  from  making  its  way  back  out  through  the  dorsum),  the  deep 
arch,  the  interossei,  and  the  metacarpal  bones. 

In  the  hypothenar  eminence  under  the  fascia  are  part  of  the  ulnar  artery  and  nerve,  the  ab- 
ductor and  flexor  brevis  digiti  quinti,  the  opponens,  the  deep  branch  of  the  ulnar  artery  and 
nerve,  and  the  fifth  metacarpal  bone. 

The  back  of  the  wrist  and  hand. — The  dorsal  carpal  (posterior  annular)  liga- 
ment has  already  been  described.  On  the  lateral  side  is  the  so-called  'snuff-box 
space'  (tabatiere  anatomique  of  Cloquet),  a  triangular  hollow,  bounded  toward  the 
radius  by  the  long  abductor  and  short  extensor  of  the  thumb,  and  toward  the 
ulna  by  the  long  extensor.  The  navicular  and  greater  multangular,  ^dth  their 
dorsal  ligaments,  form  the  floor.  In  the  roof  lie  the  radial  vein  and  branches  of  the 
radial  nerve.  More  deeply  is  the  artery,  following  a  line  from  the  apex  of  the 
styloid  process  to  the  back  of  the  interosseous  space. 

The  different  tendons  have  already  been  given.  Between  the  first  two  metacarpal  bones  is 
the  first  dorsal  interosseous  muscle,  wliich  forms  a  fleshy  projection  against  the  radial  side  of 
the  index  metacarpal,  when  the  thumb  and  index  are  pressed  together.  On  its  palmar  aspect 
is  the  adductor  polUcis.  Wasting  of  the  former  muscle  is  a  ready  indication  of  injury  or  disease 
of  the  ulnar  nerve. 


1434  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

The  skin  on  the  dorsum,  by  its  laxity,  readily  allows  of  cedema,  this  being  sometimes  evi- 
dence of  pressure  on  the  axillary  vein  by  carcinomatous  deposits.  The  dorsal  venous  arch 
receives  the  digital  plexuses,  and  from  it  the  radial  and  posterior  ulnar  veins  ascend.  The  me- 
dian vein  begins  in  plexuses  at  the  root  of  the  thumb  and  the  front  of  the  wrist. 

Ganglia  are  common  on  the  dorsum,  in  connection  with  the  extensors  of  the  fingers  and  the 
thumb.  While  usually  due  to  a  weakening  of  the  sheath  and  protrusion  of  this  and  the  synovial 
membrane,  such  swellings  may  be  due  to  a  projection  of  the  articular  synovial  membrane. 
Owing  to  the  laxity  of  the  skin,  the  slight  vascularity,  the  size  of  the  tendons,  their  connection 
with  joint-capsules  and  with  each  other,  which  fixes  them,  the  dorsum  of  the  wrist  is  the  'seat 
of  election,'  for  tendon-anastomosis  and  other  operations.  Metacarpo-phalangeal  dislocation. 
This  ocom's  in  the  thumb  and  the  index-finger  especially.  The  chief  cause  in  the  difficulty  in 
reduction  is  the  glenoid  ligament.  This,  in  reality  a  fibro-cartilaginous  plate,  is  blended  with 
the  lateral  ligaments  on  the  palmar  aspect  of  the  joint,  and  is  firmly  attached  to  the  phalanx, 
but  more  loosely  to  the  metacarpal.  Thus  when  dislocation  occurs  in  violent  hyperextension, 
the  metacarpal  attachment  of  the  glenoid  ligament  gives  way  and  it  is  carried  by  the  phalanx 
over  the  head  of  the  metacarpal  bone.  In  the  case  of  the  thumb,  the  buttonhole-like  slit  with 
which  the  two  heads  of  the  flexor  brevis,  now  displaced,  embrace  the  head  of  the  metacarpal, 
the  contraction  of  the  other  short  muscles,  and,  occasionally,  a  displaced  long  flexor,  are  addi- 
tional causes.  In  the  case  both  of  the  thumb  and  finger,  tilting  the  phalanx  well  back  on  the 
dorsum  of  the  metacarpal  and  then  combined  pressure  with  the  thumbs  forward  against  the 
base  of  the  phalanx,  when  this  is  sharply  flexed,  will  with  an  anaesthetic,  be  usually  successful. 
The  thumb  should  he,  first,  adduoted  into  the  palm. 

THE  LOWER  EXTREMITY 

HIP  AND  THIGH 

The  various  segments  of  the  lower  extremity  will  be  successively  considered  as 
follows:  hip  and  thigh,  knee  and  leg,  ankle  and  foot. 

Bony  landmarks. — Many  of  these,  such  as  the  anterior  superior  iliac  spine  and 
crest  of  the  ilium  and  the  tubercle  of  the  pubis,  have  already  been  mentioned. 
The  relative  length  of  the  limbs  is  obtained  by  carrying  the  measure  from  the  an- 
terior superior  spine  to  the  tip  of  the  corresponding  medial  malleolus.  The  pelvis 
must  be  horizontal  and  the  limbs  parallel.  The  share  taken  by  the  femur  and 
tibia  respectively  is  estimated  by  finding  the  transverse  sulcus  which  marks  their 
meeting-point. 

The  head  and  shaft  of  the  femur  are  well  covered  in,  save  in  the  emaciated.  The  head 
lies  just  below  Poupart's  ligament,  under  the  ilio-psoas,  and  a  little  to  the  outer  side  of  the  centre 
of  that  ligament.  A  line  drawn  horizontally  laterally  from  the  pubic  tubercle  will  cross  the  lower 
part  of  the  head.  All  the  head  and  the  front  of  the  neck,  but  only  two-thirds  of  the  back,  are 
within  the  capsule;  this  intra-capsular  position  of  the  upper  epiphysis,  which,  appearing  at  the 
first  year,  does  not  unite  till  eighteen  or  twenty,  accounts  largely  for  the  extreme  gravity  of 
acute  epiphysitis  here.  The  structure  of  the  neck,  i.  e.,  the  two  sets  of  lamellae,  vertical  to  sup- 
port the  weight,  transverse  and  intersecting  in  order  to  meet  the  puU  of  the  muscles,  and  the  wast- 
ing of  these  after  middle  life,  has  an  important  influence  on  injuries.  The  strong  process, 
femoral  spur  or  calcar  (Merkel)  which,  arising  from  the  compact  tissue  on  the  medial  and  under 
side  of  the  neck,  just  above  the  lesser  trochanter,  spreads  laterally  toward  the  trochanteric 
(digital)  fossa,  also  affords  strength,  and  its  degeneration  probably  plays  an  important  part  in 
the  fractures  of  the  neck. 

Hip-joint. — The  chief  points  of  surgical  importance  are  the  following: — The 
capsule  shows  fibres  chiefly  longitudinal  in  front,  circular  behind.  Of  the  former, 
the  ilio-femoral  or  inverted  Y-shaped  hgament  descends  fi-om  the  anterior  inferior 
spine  to  the  two  extremities  of  the  anterior  intertrochanteric  line.  It  not  only 
checks  extension  and  strengthens  the  front  of  the  joint,  but  it  keeps  the  pelvis  and 
trunk  propped  forward  on  the  heads  of  the  femurs,  thus  preventing  waste  of  mus- 
cular action.  It  is  joined  on  the  medial  side  by  the  pubo-capsular  ligament, 
which  checks  abduction.  Between  the  two  is  the  medial  part  of  the  front  cap- 
sule, and  here  the  ilio-psoas  bursa  may  communicate  with  the  joint.  This  fact 
must  be  remembered  in  tuberculous  disease  of  the  psoas,  and  the  presence  of  this 
bursa  explains  certain  deep-seated  swellings  in  the  front  of  the  joint  in  adults. 
Behind,  the  ischio-femoral  is  the  strongest  part  of  the  capsule,  its  fibres  blending 
with  the  circular  and  weaker  part  of  the  capsule  here.  Dislocation  usually 
occurs  at  the  posterior,  lower  and  medial  part  of  the  joint.  It  is  to  be  noted  that 
in  full  extension  and  flexion  the  head  of  the  femur  is  in  contact  with  the  weakest 
spot  in  the  capsule,  in  front  and  behind,  respectively.  From  the  deep  aspect  of 
the  capsule  fibres  pass  up  at  the  line  of  reflection  of  the  synovial  membrane  on  to 
the  neck- — the  cervica,!  Hgaments  of  Stanley.     In  intracapsular  fracture  these 


THE  HIP  AND  THIGH 


1435 


fibres  keep  the  fragments  together;  hence  one  need  of  gentle  handling;  their 
softening  may  explain,  a  little  later,  an  increase  in  the  shortening. 

Exploration  of  the  joint. — This  is  usually  effected  by  an  oblique  incision  downward  and 
slightly  medially  between  the  sartorius  and  rectus  medially  and  the  gluteus  medius  and  minimus 
laterally.  A  branch  of  the  ascending  division  of  the  lateral  cu-oumflex  is  the  only  artery  met 
with.  In  tapping  the  joint  the  puncture  is  made  in  the  same  line,  2  or  3  inches  below  the 
anterior-superior  spine.  'If  the  instrument  is  pushed  upward,  medially,  and  backward  beneath 
the  rectus,  it  will  pass  into  the  joint  a  little  above  the  anterior  intertrochanteric  Kne.     (Stiles.) 

Fig.  1153. — Region  of  the  Hip-joint,  as  Shown  by  the  Rontgen-rays. 


Trochanter  major. — This  valuable  landmark  is  most  prominent  when  the  limb 
is  rotated  medially  or  adducted;  it  lies  at  the  bottom  of  a  depression  when  the 
femur  is  everted. 

The  chief  structure  of  importance  between  it  and  the  skin  is  the  upper  part  of  the  insertion 
of  the  gluteus  maxim  us,  that  going  to  the  fascia  lata,  and  the  bursa  beneath  the  muscle.  Tliis  is 
often  multilocular.  It  is,  not  very  uncommonly,  the  seat  of  tubercular  inflammation  which 
readily  invades  the  cancellous  tissue  of  the  trochanter.  The  top  of  the  great  trochanter  is 
about  1.8  cm.  (f  in.)  below  the  level  of  the  femoral  head,  and,  when  the  femur  is  extended  is  a 
little  below  the  centre  of  the  hip-joint.     This  part  of  the  bone  is  covered  by  the  gluteus  medius. 


1436 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


The  slightness  of  the  prominence  of  the  great  trochanter  in  the  living  subject  compared  with  that 
in  the  skeleton  is  explained  by  fig.  1154,  which  shows  how  the  descending  gluteus  medius  and 
minimus  fill  up  the  space  between  the  ilium  and  trochanter.  To  examine  the  great  trochanter, 
the  thigh  should  be  abducted,  so  as  to  relax  the  strong  fascia  lata  passing  upward  over  the  tensor 
and  glutei  to  the  iliac  crest. 

Nelaton's  line. — This  useful  guide  is  a  line  drawn  from  the  anterior  superior 
spine  of  the  ilium  to  the  most  prominent  part  of  the  tuberositj^  of  the  ischium.  In 
normal  limbs,  the  top  of  the  great  trochanter  just  touches  this  line.  In  dislocation, 
fractures  of  the  neck,  and  in  wasting  of  the  neck,  as  in  osteo-arthritis,  the  relation 
of  the  trochanter  to  Nelaton's  line  becomes  altered. 

The  top  of  the  gi'eat  trochanter  is  a  guide  in  Adams's  operation  for  division  of  the  neck  of  an 
ankylosed  femur,  the  puncture  being  made  and  the  saw  entered  2.5  cm.  (1  in.)  above  and  about 
the  same  distance  in  front  of  this  point.  Owing  to  the  fact  that  in  many  cases  of  ankylosis 
the  neck  is  destroyed,  the  above  operation  has  been  largely  replaced  by  the  simpler  and  more 
widely  applicable  Gant's  osteotomy  just  below  the  great  trochanter,  from  the  lateral  side. 


Fig.  1154.- 


-Transverse  Section  op  the  Hip-Joint  and  its  Relations. 
(One-third.)     (Braune.) 


External  iliac  artery 


Gluteus  minimus 
Gluteus  medius 


;  Obturator  internus' 


Adductor  magnus 


Obturator  externus — -^ 


Adductor  longus-^ 
'Adductor  brevis ■ 


Bryant's  triangle. — Bryant  makes  use  of  the  following  in  deciding  the  position  of  the  great 
trochanter.  The  patient  being  flat  on  his  back  (1)  a  line  is  dropped  vertically  on  to  the  couch 
from  the  anterior  superior  spine;  (2)  from  the  top  of  the  great  trochanter  a  straight  Hne  in  the 
long  axis  of  the  thigh  is  drawn  to  meet  the  first;  (3)  to  complete  the  triangle,  a  line  is  drawn  from 
the  anterior  superior  spine  to  the  top  of  the  trochanter.  This  line  is  practically  Nelaton's. 
The  second  line  will  be  found  diminished  on  the  damaged  or  diseased  side. 

Muscular  prominences. — The  tensor  fasciw  latoe  forms  a  prominence  beginning  just  lateral 
to  the  sartorius  and  reaching  downward  and  somewhat  backward  to  the  strong  fascia  lata, 
7.5  to  10  cm.  (3  to  4  in.)  below  the  great  trochanter.  Below  this  point,  as  far  as  the  lateral  con- 
dyle of  the  tibia,  the  strong  ilio-libial  band  can  be  felt.  Like  the  inverted  Y-shaped  Ugament, 
this  band  is  a  powerful  saving  of  muscular  action  in  maintaining  the  erect  position.  At  the  in- 
sertion of  the  tensor  fascis  lata3  it  bifurcates  into  two  layers,  which  enclose  the  muscle.  The 
superficial  is  attached  to  the  iliac  crest  and  the  sheath  of  the  gluteus  medius;  the  deep  blends  with 
the  capsule  and  the  reflected  head  of  the  rectus.  This  deeper  layer  is  perforated  by  the  ascend- 
ing branch  of  the  lateral  circumflex.  The  ilio-tibial  band  is  a  guide  for  reaching  the  femur 
(p.  1334).  The  sartorius,  the  chief  landmark  of  the  thigh,  forming  a  boundary  of  the  femoral 
trigone  (Scarpa's  triangle),  the  adductor  (Hunter's)  canal,  and  the  popUteal  space,  can  be  readily 
brought  into  view  by  the  patient's  raising  his  limb  slightly  rotated  laterally.  In  the  middle  line 
the  rectus  muscle  stands  out  in  bold  relief,  with  its  tendon  of  insertion  and  the  patella,  when  the 


THE  HIP  AND  THIGH 


1437 


leg  is  extended.  On  either  side  of  this  muscle  is  a  furrow,  and  on  either  side,  again,  of  this 
furrow  the  vasti  become  prominent.  Between  the  vastus  medialis  and  adductor  muscles  is  a 
depression  indicating  the  adductor  canal.  At  the  upper  and  medial  third  of  the  thigh,  if  the 
limb  be  abducted,  the  upper  part  of  the  adductor  longiis  comes  into  strong  reUef .  On  the  medial 
side  below,  above  the  knee-joint,  the  vertical  fibres  of  the  adductor  magnus  end  in  a  powerfxil 
tendon  coming  down  to  the  adductor  tubercle  (fig.  1159).  This  replaces  here  the  medial  inter- 
muscular septum,  and  the  insertion  of  the  tendon  marks  the  level  of  the  lower  epiphysial  Hne 
of  the  femur.  At  the  lateral  and  back  part  of  the  thigh  the  vastus  lateralis  is  separated  from  the 
biceps  by  a  groove  which  indicates  the  lateral  intermuscular  septum.  Of  these  septa,  prolonga- 
tions inward  from  the  fascia  lata  to  the  linea  aspera,  the  lateral  lies  between  the  vastus  lateraUs 
and  the  biceps.  It  reaches  from  the  lateral  tuberosity  of  the  femur  to  the  insertion  of  the  gluteus 
maximus.  Just  above  the  condyle  it  is  perforated  by  the  superior  lateral  articular  vessel  and 
nerve.     The  medial  septum  extends  from  the  adductor  tubercle  to  the  trochanter.     It  is  weak  in 


Fig.  1155. — The  Muscles  attached  to  the  Pdbes. 
(From  a  dissection  in  the  Hunterian  Museum.) 

External  oblique-- 


Rectus  abdominis' 


Rectus  abdominis 
Pectineus 


Adductor  longus 
Adductor  brevis 


Adductor  longus 


Corpora  cavernosa  —  \A  ^ 

Adductor  brevis ; 
adductor  magnus 
and  obturator 
externus 
Corpus  spongiosum 
(cavernosum 
urethrse) 

Transversus 

perinei  prof. 

Bulb-cavernosus 


Obturator 
externus 
Adductor  magnus 
Gracilis 

Ischio-cavernosus 
Transversus  perinaei 


Central  tendinous  point 


Sphincter  ani 


comparison,  and  separates  the  adductor  from  the  vastus  mediaUs.  A  third,  the  weakest  of  all, 
separates  the  adductor  and  the  hamstrings.  The  fascia  lata  has  the  same  effect  as  that  in  the 
neck  in  causing  pus  to  burrow,  especially  downward,  and  in  rendering  the  diagnosis  of  swellings 
beneath  it  difficult.  Thickest  above  and  on  the  lateral  aspect,  and  again  about  the  bony  promi- 
nences at  the  knee-joint,  at  both  of  which  sites  it  receives  accessions  from  muscles,  it  is  divided 
into  iliac  and  pubic  portions.  The  former  is  attached  behind  to  sacrum  and  coccyx,  iliac  crest 
and  the  inguinal  hgament,  terminal  Una  and  pubic  tubercle.  Here  it  blends  with  the  pubic 
portion,  which  is  connected  with  the  pubic  arch.  At  the  fossa  ovaUs  (saphenous  opening)  the 
two  may  be  said  to  separate,  the  iliac  forming  the  upper  cornu  and  lateral  falciform  margin, 
and  descending  over  the  femoral  vessels  and  extensors.  The  pubic,  much  thinner,  forms  the 
medial  margin  of  the  fossa,  and  descends  obliquely  over  the  pectineus  and  adductor  longus 
behind  the  vessels,  to  blend  with  the  sheath  of  the  ilio-psoas  and  capsule  of  the  hip-joint. 


( 


1438 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


The  inguinal  (Poupart's)  ligament. — The  abdomen  is  separated  from  the 
thigh  by  a  fold,  best  marked  in  flexion — the  inguinal  furrow.  In  this,  pressure 
detects  the  meeting  of  the  aponeurosis  of  the  external  oblique  and  the  fascia  lata, 
i.  e.,  Poupart's  ligament,  extending  between  the  anterior  superior  spine  of  the  ilium 
and  the  tubercle  (spine)  of  the  pubes.  The  line  representing  it  should  be  drawn 
slightly  convex  downward,  o^ving  to  the  attachment  of  the  deep  fascia.  It  forms 
the  base  of  the  femoral  trigone;  its  medial  attachment  blends  with  the  triangular 
lacunar  (Gimbernat's)  ligament.  The  parts  passing  under  the  inguinal  ligament 
and  their  arrangement  have  been  given  at  p.  1399,  fig.  1122. 


-Diagram  of  Arteries  of  Thigh. 

Ilio-lumbar  artery 


Common  femoral 

Deep  femoral  (profunda) 
Descending  branch  of  lateral  circumflex 


Inferior  lateral  articular 

Posterior  tibial  recurrent  (from 

anterior  tibial) 

Anterior  tibial  recurrent 

Superior  fibular 

Anterior  tibial, 


Common  iliac  artery 

Inferior  epigastric 
Hypogastric,  dividing  into  anterior 
and  posterior  trunks 

External  iliac 
Obturator 
Inferior  gluteal 
Internal  pudic 

Lower  terminal  branch  of  medial 

circumflex 
Superficial  femoral  (muscular 
branches  omitted) 


Perforating  branches  of  deep  femoral, 
forming  anastomotic  loops  and  sup- 
plying posterior  muscles 


Superior  medial  articular 


Inferior  medial  articular  (sural  arteries 

arising  below  this  omitted) 
Posterior  tibial 


The  femoral  trigone  (Scarpa's  triangle)  (fig.  1159). — Immediately  below  the 
inguinal  ligament  a  hollow  is  seen  corresponding  to  this  region,  the  lateral  and 
medial  boundaries  of  which  are  brought  into  view  when  the  limb  is  raised,  the 
adductor  longus  especially  when  the  limb  is  abducted,  and  the  sartorius  when  the 
thigh  is  flexed  and  the  limb  extended  and  rotated  laterally.  The  floor  of  the 
femoral  trigone  is  not  horizontal,  the  plane  of  the  medial  part  being  very  oblique. 
It  is  formed  latero-medially  by  the  ilio-psoas,  pectineus,  adductor  brevis  (slightly), 
and  adductor  longus. 

A  psoas  abscess  descending  below  the  inguinal  ligament  usually  does  so  on  the  lateral  aspect 
of  the  femoral  vessels;  if  the  sheath  gives  way,  or  if  the  abscess  follows  the  profunda  artery,  it 
will  pass  beneath  the  adductor  longus  and  point  toward  the  medial  side  of  the  thigh.     (Taylor.) 


THE  HIP  AND  THIGH 


1439 


Fig.  1157. — Section  of  the  Right  Thigh  at  the  Apex  of  the  Femoral^Trigone.      (Heath.) 

Femoral  vessels 


Sartorius 
Lateral  cutaneous  nerve 


Profunda  vessels 

Adductor  longus 

Superficial  part  of  obturator  nerve 


Rectus  femoris 

Femoral  nerve 
Lateral  circumflex- 
vessels  \ii 
Tensor  fa 


Vastus  laterali 


Gracilis 
^\.f        Pectineus 

C^ld Adductor  brevis 

^\'^1| Deep  part  of  obturator 

-f-^H  nerve 

""Vv Adductor  magnus 

Semi-membranosus 


:nii-tendinosus 
Posterior  cutaneous  nerve 
Sciatic  nerve 


Fig.  ,1158. — Superficial  Dissection  of  the  front  of  the  Thigh. 
(Hirschield  and  Leveill6.) 


Inguinal  ligament 


Anterior  cutaneous  nerve 


Anterior  cutaneous  nerve 
Branch  to  sartorius 


Lateral  cutaneous  nerve  — 


Anterior  cutaneous  nerve 


Superficial  branches  of 

femoral  artery 
Femoral  artery 
Femoral  vein 
Anterior  cutaneous  nerve 


Great  saphenous  vein 
Anterior  cutaneous  nerve 


■Anterior  cutaneous  nerve 


Anterior  cutaneous  nerve 


Patellar  branch  of 
saphenous  nerve 


Saphenous  nerve 


( 


1440 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


If  it  simulate  a  femoral  hernia,  examination  of  the  back  and  the  fact  that  the  sweUing  is  below 
the  fossa  ovahs  will  prevent  mistakes.  Three  nerves  come  into  the  thigh  between  the  pelvis 
and  Poupart's  ligament,  i.  e.,  the  lumbo-inguinal  (genito-crural)  in  the  femoral  sheath,  the 
femoral  (anterior  crural)  between  the  iliacus  and  psoas  and  the  lateral  cutaneous  close  to  the 
lateral  attachment  of  the  inguinal  ligament. 

The  obturator  nerve  divides  into  two  in  the  obturator  foramen,  the  two  divi- 
sions being  separated  by  some  fibres  of  the  obturator  externus,  and  lower  down  by 
the  adductor  brevis.  The  relations,  course,  and  distribution  of  this  nerve,  in  the 
medial  fibres  of  the  psoas,  over  the  sacro-iliac  joint  and  under  the  ilio-pelvic  or 
sigmoid  colon  (Hilton),  through  the  obturator  foramen  with  its  branches  (from 
the  superficial  division)  through  the  cotyloid  notch  to  the  hip,  and  (from  the  deep) 


Fig.  1159. — Femoral  and  Obtubator  Nerves. 
Femoral  vein  Femoral  artery 


(Ellis.) 


Pectineus 

Obturator  (anterior  div.) 

Obturator  (posterior 

division)  \.\ >'  i  1 

Adductor  longus — r  — f 


Adductor  brevis 


Saphenous 
—  Nerve  to  vastus  medialis 


Adductor  magnus 
'Geniculate  branch  of  obturator 

Semi-membranosus 


Adductor  longus 
Femoral  artery 


Genu  suprema  artery 
Patellar  branch  of  saphenous 


along  the  popliteal  artery  to  the  knee,  and  others  to  the  lower  third  of  the  thigh, 
and  sometimes  the  upper  and  medial  aspect  of  the  leg  (Hilton),  may  be  of  much 
surgical  importance,  e.  g.,  in  carcinoma  of  the  bowel,  disease  of  the  sacro-iliac  and 
hip-joints,  growths  of  the  pelvis,  and  the  rare  obturator  hernia.  The  distribution 
of  the  cutaneous  nerves  is  shown  in  fig.  1158.  Lying  superficially  in  the  base  of 
the  trigone,  the  inguinal  lymphatic  nodes  can  be  detected  in  a  thin  person  (fig. 
1172). 

The  fossa  ovalis  (saphenous  opening). — The  depression  corresponding  to  this 
Is  placed  just  below  the  lacunar  (Gimbernat's)  ligament,  with  which  its  upper  ex- 
tremity blends.     Its  centre  is  about  3.7  cm.  (11  in.)  below  and  also  lateral  to  a 


THE  THIGH 


1441 


line  dropped  vertically  from  the  pubic  tubercle.  This  and  the  other  structures 
concerned  in  femoral  hernia  are  fully  described  under  this  section  (vide  supra, 
p.  1398).     The  course  of  the  great  saphenous  vein  is  given  below,  p.  1456. 

Line  of  femoral  artery. — A  line  drawn  from  the  mid-point  between  the  anterior 
superior  spine  and  the  symphysis  pubis  to  the  adductor  tubercle  will  correspond 
with  the  course  of  this  vessel.  The  sartorius  usually  crosses  it  10  cm.  (  3  to  4  in.) 
below  the  inguinal  (Poupart's)  ligament.  The  profunda  artery  arises  usually 
3.7-5  cm.  (1|  to  2  in.)  below  Poupart's  ligament. 

The  incision  for  tying  tiie  femoral  in  the  femoral  trigone  should  be  about  7.5  cm.  (3  in.) 
long,  in  the  Kne  of  the  artery,  and  begins  about  7.5  cm.  (3  in.)  below  the  inguinal  ligament,  and 
runs  over  the  apex  of  the  triangle.  The  femur  is  flexed  slightly,  abducted  and  rotated  laterally. 
The  fascia  lata  being  divided,  the  sartorius,  readily  recognised  by  its  direction,  is  drawn  later- 
ally. The  closely  subjacent  sheath  must  be  opened  on  its  lateral  side.  Structures  that  may 
be  seen  are  a  vein  joining  the  great  saphenous,  the  anterior  cutaneous,  saphenous  nerve,  and 
that  to  the  vastus  medialis.     The  collateral  circulation  (fig.  1156)  is  mainly  through  the  following 


Fig.  1160. — Section  of  Thigh  through  upper  Part  of  Hunter's  Canal.     (W.  A.) 


Saphenous  nerve. 
Femoral  artery,  with 
small  venee  comit- 
antes  (femoral  vein 
deeper) 

Sheath  of  vessels 


Great  saphenousvein 


Superficial  fascia 

Deep  fascia  contin- 
ued over  back  of 
thigh  as  superficial 
layer  of  deep  fascia 


Deep   layer  of  deep 
fascia  (muscular 
aponeurosis) 


Vein 


channels: — (1)  The  lateral  and  medial  circumflex  above,  with  the  genu  suprema  and  lower 
muscular  branches  of  the  femoral,  and  the  articular  of  the  popliteal.  (2)  The  perforating 
branches  of  the  profunda  above,  with  the  vessels  below  first  given.  (3)  The  comes  nervi  iscliia- 
dici  with  the  articular  of  the  popKteal. 

The  femoral  vein  Ues,  below  the  inguinal  ligament,  immediately  to  the  medial  side  of  the 
artery.  From  this  point  on  the  vein  gets  to  a  somewhat  deeper  plane,  though  stOl  very  close  to 
the  artery,  and  gradually  inclining  backward,  lies  behind  its  companion  at  the  apex  of  the  tri- 
angle, and  below  lies  somewhat  laterally  to  it. 

From  the  apex  of  the  femoral  trigone  (Scarpa's  triangle)  a  depression  runs 
down  along  the  medial  aspect  of  the  thigh,  corresponding  to  the  groove  already 
mentioned  between  the  vastus  medialis  muscle  and  the  adductors.  Along  this 
groove  lies  the  sartorius,  and  beneath  it  the  adductor  (Hunter's)  canal,  a  triangu- 
lar inter-muscular  gap  with  its  apex  toward  the  linea  aspera,  and  its  base  or  roof 
formed  by  the  fibrous  expansion  which  ties  together  its  boundaries,  viz.,  the  adduc- 
tor longus  and  magnus  and  the  vastus  medialis. 

The  vein,  which  in  the  upper  part  of  the  canal  lies  behind  the  artery,  separating  it  from 
the  three  adductors,  lower  down  inclines  more  and  more  to  the  lateral  side.  The  saphenous  nerve 
lies  also  in  the  canal,  but  not  in  the  sheath.  The  above-mentioned  space  terminates  at  about 
the  junction  of  the  middle  and  lower  thirds  of  the  thigh,  in  the  opening  in  the  adductor  magnua 


( 


1442  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

by  which  the  artery  enters  the  upper  and  medial  part  of  the  pophteal  space.  The  saphenous, 
the  largest  branch  of  the  femoral  nerve,  having  crossed  the  femoral  vessels  latero-mediaUy, 
accompanies  them  as  far  as  the  opening  in  the  adductor  magnus.  Here  it  perforates  the  aponeu- 
rotic roof,  and  is  prolonged  under  the  sartorius,  accompanied  by  the  superficial  part  of  the  genu 
suprema  artery,  to  perforate  the  fascia  lata  between  the  sartorius  and  gracilis,  and  run  with  the 
great  saphenous  vein  at  the  upper  and  medial  part  of  the  leg. 

Pressure  may  be  applied  to  the  femoral  artery — (1)  Immediately  below  the  inguinal  liga- 
ment: it  should  here  be  directed  backward  so  as  to  compress  the  vessel  against  the  brim  of  the 
pelvis  and  the  capsule  of  the  hip-joint;  (2)  at  the  apex  of  the  femoral  trigone  the  pressure  here 
being  directed  laterally  and  a  little  backward,  so  as  to  command  the  vessel  against  the  bone; 
(3)  in  the  adductor  canal  the  pressure  should  be  directed  laterally  with  the  same  object.  Care 
must  be  taken,  especially  above,  to  avoid  the  vein,  which  lies  very  close  to  the  artery,  and  also 
the  femoral  nerve,  which  enters  the  thigh  about  1.2  cm.  (J  in.)  outside  the  artery,  and  at  once 
breaks  up  into  its  branches,  superficial  and  deep. 

In  ligature  of  the  femoral  artery  in  Hunter's  canal,  the  line  of  the  incision,  in  the  middle 
third  of  the  thigh,  must  exactly  follow  that  of  the  vessel.  It  is  frequently  made  too  lateral, 
exposing  the  vastus  medialis.  Branches  of  the  saphenous  vein  being  removed,  the  fascia  lata 
is  slit  up  and  the  sartorius  identified  by  its  fibres  descending  medially.  Those  of  the  vastus 
medialis  are  less  oblique  and  are  directed  downward  and  laterally.  The  sartorius  having  been 
drawn  to  the  medial  side,  usually,  the  aponeurotic  roof  of  the  canal  is  opened,  and  the  femoral 
sheath  identified.  The  vein,  here  posterior  and  to  the  lateral  side,  is  closely  coimected  to  the 
artery. 

The  close  contiguity  of  the  femoral  artery  and  vein  accounts  for  the  comparative  frequency 
of  arterio-venous  aneurysms  especially  in  the  upper  part,  where  the  vessels  are  easily  wounded. 
Their  superficial  position  here  further  accounts  for  the  facility  with  which  mahgnant  disease, 
e.  g.,  epitheKomatous  glands,  may  cause  fatal  ha;morrhage.  Access  to  the  femur.  This  is  best 
attained  on  the  lateral  side  of  the  shaft  along  the  line  of  the  lateral  intermuscular  septum 
(fig.  1160),  the  biceps  being  pulled  backward,  and  the  vastus  lateralis  detached  anteriorly.  On 
the  medial  side  the  bone  may  be  exposed  by  an  incision  starting  from  a  point  midway  between 
the  inner  margin  of  the  patella  and  the  adductor  tubercle  and  passing  obliquely  upward  and 
laterally,  but  the  parts  here  are  more  vascular.  Fractures  of  the  shaft  usually  occur  about  the 
centre.  The  main  tendency  to  displacement  is  of  the  lower  fragment  upward  by  the  ham- 
strings. The  upper  fragment  is  anterior;  this  is  especially  marked  in  the  upper  third,  owing  to 
the  action  of  the  iho-psoas,  which  also  rotates  the  upper  fragment  laterally.  In  the  lower  third 
the  forward  curve  of  the  femur  and  its  more  superficial  position  explain  the  fact  that  it  is  here  that 
compound  fractures  of  the  femur  may,  occasionally,  occur.  Ossification.  The  unstable 
nature  of  the  tissues  about  the  upper  epiphysis,  which  appears  at  the  end  of  the  first  year  and 
unites  about  eighteen,  and  the  frequency  of  tuberculous  disease  in  early  life  are  well  known. 
In  the  lower  epiphysis  ossification  begins  before  birth,  a  point  of  medico-legal  importance  in 
deciding  whether  a  newly  born  child  has  reached  the  full  period  of  uterine  gestation.  From  this 
epiphysis,  the  level  of  which  is  denoted  by  a  line  drawn  horizontally  laterally  from  the  adductor 
tubercle,  and  the  vascular  growing  tendon  of  the  adductor  magnus — the  origin  of  an  exostosis 
is  not  uncommon.  Displacement  of  this  epiphysis  (it  unites  about  twenty)  in  boj'hood  and  adol- 
escence is  a  grave  injury  from  the  immediate  risk  of  the  popliteal  vessels.  The  mischief  is 
usually  done  by  overextension  of  the  leg,  as  when  this  is  caught  in  a  rapidly  moving  carriage- 
wheel;  the  epiphysis  is  carried  forward  in  front  of  the  diaphysis,  the  lower  end  of  which  is  directed 
backward,  endangering  the  vessels  which  are  posterior  and  closely  adjacent. 

Amputation  through  the  thigh. — This  is  usuaUj'  performed  in  the  lower  third,  by  anterior 
and  posterior  flaps,  the  former  being  the  longer,  so  as  to  ensure  a  scar  free  from  pressure,  and 
circular  division  of  the  muscles,  vessels,  and  nerves.  The  vessels  requiring  attention  are  the 
femoral,  which  lie  at  the  medial  side,  and  the  more  posteriorly,  the  lower  the  amputation;  the 
descending  branch  of  the  lateral  circumflex,  and  the  termination  of  the  profunda  near  the 
linea  aspera.  The  femoral  artery  has  a  marked  tendency  to  retract  in  the  adductor  canal. 
Care  should  be  taken  not  to  include  the  saphenous  nerve  when  the  femoral  vessels  are  tied,  and 
to  cut  the  sciatic  cleanly  and  high  up.  When  amputation  has  to  be  performed  in  the  upper 
third  of  the  thigh,  the  tendency  of  the  ilio-psoas  to  flex  the  shortened  limb  and  thus  bring  the 
sawn  femur  against  the  end  of  the  stump  must  be  remembered,  and  met  by  keeping  the  patient 
propped  up  and  the  stump  as  horizontal  as  possible.  Some  of  the  structures  now  divided  are 
shown  in  fig.  1160. 

The  buttocks.  Bony  landmarks. — The  finger  readily  traces  the  whole  outline 
of  the  iliac  crest.  Behind,  it  terminates  in  the  posterior  superior  iliac  spine, 
which  corresponds  in  level  to  the  second  sacral  spine  and  the  centre  of  the  sacro- 
iliac joint.    (Holden.) 

The  third  sacral  spine  marks  the  lowest  limit  of  the  spinal  membranes  and  the  cerebro- 
spinal fluid;  it  also  corresponds  to  the  upper  border  of  the  great  sacro-sciatic  notch.  The  first 
piece  of  the  coccyx  corresponds  to  the  spine  of  the  ischium.  (Windle.)  Its  apex  is  in  the  furrow 
just  behind  the  last  piece  of  the  rectum. 

The  tuberosities  of  the  ischium  are  readily  felt  by  deep  pressure  on  either  side 
of  the  anus.  In  the  erect  position  they  are  covered  by  the  lower  margin  of  the 
gluteus  maximus.  In  sitting  they  are  protected  by  tough  skin,  fasciae,  with  coarse 
fibrous  fat,  and  often  by  a  bursa  known,  according  to  the  patients  in  whom  it  be- 
comes enlarged,  as  weaver's,  coachman's,  lighterman's,  drayman's  bursa.     The 


THE  THIGH 


1443 


skin  of  the  buttock  is  coarse  and  difficult  to  cleanse  satisfactorily.     The  abun- 
dance of  sebaceous  glands  accounts  for  the  frequency  of  boils  here. 

Gluteus  maximus. — The  'fold  of  the  buttock'  neither  corresponds  accurately 
to,  nor  is  caused  by,  the  lower  margin  of  this  muscle.  Thus,  medially,  it  lies  below 
the  lower  margin  of  the  muscle,  as  it  runs  laterally  it  crosses  it,  and  comes  to  lie 
on  the  muscle.  The  fold  is  really  due  to  creasing  of  the  skin  adherent  here  to  the 
coarsely  fibro-fatty  tissue  over  the  tuber  ischii  during  extension.  But  in  early  hip 
disease,  in  which  flexion  of  the  joint  is,  with  wasting  of  the  muscle,  almost  unvary- 
ingly present,  the  fold  disappears  with  well-known  rapidity.  The  prominence  of 
the  buttock  is  mainly  due  to  the  gluteus  maximus,  especially  behind  and  below, 
and  in  less  degree  to  the  other  two  glutei  in  front.  Under  the  lower  edge  of  the 
gluteus  maximus  the  edge  of  the  sacro-tuberous  (great  sacro-sciatic)  ligament  can 
be  felt  on  deep  pressure. 

To  mark  out  the  upper  border  of  the  gluteus  maximus  a  line  is  drawn  from  a  point  on  the 
ihac  crest  5  cm.  (2  in.)  in  front  of  the  posterior  superior  spine,  downward  and  laterally  to  the 
back  of  the  great  trochanter.  The  lower  border  is  marked  out  by  a  second  hne  drawn  from  the 
side  of  the  coccyx  parallel  with  the  former,  and  ending  over  the  linea  aspera  at  the  junction  of 
the  upper  and  middle  thirds  of  the  thigh.  It  must  be  remembered  that  only  the  lower  and  inter- 
nal fibres  of  the  muscle  are  inserted  into  the  gluteal  ridge  on  the  femur.     The  greater  part  of 

Fig.  1161. — Section  through  the  Hip  and  Gluteal  Region.     (One-third.) 


SartoriuE 
Reflected  tendon 

of  rectus  \ 

Psoas  and  iliacus 
and  bursa       v 
Femoral  nerve^. 

Common  femoral.^ 
artery 
Common  femoral  vein^ 

Profunda  vessels^'     y'^ 


Se 


Gracili 

membranosus 

Adductor  brevls 

Semi-tendinosus 

Obturator  externus 

Adductor  magnu^-f-  — 

Adductor  longus 


Gluteus  maximu: 
Gluteus  medius 


Gluteus  minimus 


Sciatic  nerve  and  infe- 
rior gluteal  vessels 


Biceps 
Quadratus  femoris 


it  is  inserted  into  the  fascia  lata  and  ilio-tibial  band  and  so  Into  the  lateral  condyle  of  the  tibia. 
Weakness  of  the  gluteus  maximus  and  tensor  fasciae  lata;,  with  consequent  laxity  of  the  ilio- 
tibial  band,  gives  rise  to  abnormal  side-to-side  passive  mobility  at  the  knee-joint  in  full  extension. 


-The  following  superficial  nerves  can  be  marked  in  over 


Nerves  and  vessels, 
the  buttock  (fig.  1182). 

Behind  the  great  trochanter,  branches  of  the  lateral  cutaneous;  coming  down  over  the  crest, 
the  lateral  cutaneous  branch  of  the  last  thoracic  (about  in  a  line  with  the  great  trochanter), 
and  behind  this  the  lateral  branch  of  the  ilio-hypogastric.  Two  or  three  oiTsets  of  the  posterior 
primary  branches  of  the  lumbar  nerves  cross  the  hinder  part  of  the  ihac  crest  at  the  lateral 
margin  of  the  sacro-spinahs.  Two  or  three  twigs  from  the  posterior  divisions  of  the  sacral 
nerves  pierce  the  gluteus  maximus  close  to  the  coccyx  and  sacrum,  and  ramify  laterally.  Fi- 
nally, over  the  lower  border  of  the  gluteus  maximus,  turn  upward  branches  of  the  posterior 
cutaneous  (small  sciatic)  and  its  perineal  branch  (inferior  pudendal),  and  the  fourth  sacral 
nerve. 

Sciatic  nerve  (figs.  1162,  1163). — The  point  of  emergence  below  the  gluteus 
maximus  and  the  track  of  this  nerve  (fourth  and  fifth  lumbar  and  first  three  sacral 
nerves)  will  be  given  by  a  line  drawn  from  a  spot  a  little  medial  to  the  middle  of 
the  space  between  the  great  trochanter  and  the  tuber  ischii  to  the  lower  part  of 
the  back  of  the  thigh,  where  it  usualty  divides  into  the  tibial  and  common  peroneal 
(internal  and  external  popliteal)  nerves. 


{ 


1444 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


To  stretch  the  nerve,  an  incision  about  tliree  inches  long  is  made  in  the  line  of  the  nerve, 
beginning  about  3.7  cm.  (IJ  in.)  below  the  gluteus  maximus.  The  long  head  of  the  biceps  which 
covers  the  nerve  trunk  and  which  is  descending  mediolaterally,  is  drawn  medially.  If  the 
nerve  is  exposed  lower  down,  the  interval  between  the  hamstrings  is  identified  and  these  muscles 
drawn  aside.  The  perineal  branch  of  the  posterior  cutaneous  (inferior  pudenal)  perforates 
the  deep  fascia  about  2.5  cm.  (1  in.)  in  front  of  the  tuber  ischii,  and  turns  forward  to  supply  the 
genitals. 

Superior  gluteal  artery. — If  a  line  be  drawn  from  the  posterior  superior  spine  to  the  apex 
of  the  great  trochanter,  the  limb  being  slightly  flexed  and  rotated  medially,  the  point  of  emer- 
gence of  the  artery  from  the  upper  part  of  the  great  sacro-sciatic  notch  will  correspond  with  the 
junction  of  the  upper  and  middle  third  of  this  line.  (MacCormao.)  The  gluteal  nerve  emerges 
immediately  below  the  artery,  and  sends  branches  into  the  deeper  portion. 

Inferior  gluteal  (sciatic)  and  pudic  arteries. — The  limb  being  rotated  medially,  a  line  is 
drawn  from  the  posterior  superior  spine  to  the  lateral  part  of  the  tuber  ischii.  The  point  of  exit 
of  the  above  arteries  will  correspond  to  the  junction  of  the  middle  and  lower  thirds  of  this  line. 
(MacCormac.) 

THE  KNEE 

Bony  landmarks. — The  patella,  the  condyles  of  the  femur,  the  condyles  and 
tuberosity  of  the  tibia,  the  head  of  the  fibula,  are  all  easily  examined. 


Fig.  1162. — The  Gluteal  Region,  with  the  Superior  and  Inferior  Gluteal  and  Pudic 

Arteries. 
Gluteus  medius,  turned  up 


■  gluteal  nerve 
Gluteus  maximus,  cut 
Medial  circumflex  artery 
Obturator  externus  , 


Insertion  of  gluteus  medius 
Lateral  circumflex  artery 


Gluteus  minimus 

Muscular  branches  of  inferior  gluteal  artery 
Deep  branch  of  superior  gluteal  artery 
Superior  gluteal  nerve 


Piriformis  perforated  by  peroneal 
portion  of  sciatic  nerve 


Cut  edge  of  gluteus 


Insertion  of 
gluteus  maximus 

First  perforating  artery 

Quadratus  femoris 
Branch  of  internal  circumflex  artery 
Obturator  internus  with  the  two  gemelli 


Pudic  artery  and  nerve 
Inferior  gluteal  artery 
Biceps 
Semi-tendinosus 
Semi-membranosus 
Posterior  cutaneous  nerve 

comitans  nervi  ischiadic! 
Tibial  portion  of  sciatic  nerve 
Perineal  branch  of  posterior  cutaneous 


Perineal  portion  of  sciatic 
(From  a  dissection  by  W.  J.  Walsham  in  St.  Bartholomew's  Hospital  Museum.) 
The  muscular  branch  of  the  inferior  gluteal  (sciatic)  artery  has  been  drawn  inward  over  the 
tuber  ischii  with  the  reflected  origin  of  the  gluteus  maximus  muscle. 


The  patella. — ^The  limb  being  supported  in  the  straight  position,  and  the  exten- 
sor muscles  relaxed,  the  natural  range  of  mobility  laterally  of  the  patella  can  be 
estimated.     This  is  interfered  with  by  muscular  action  in  inflammatory  conditions. 


J 


THE  KNEE 


1445 


or  by  early  tuberculous  ulceration  of  the  contiguous  cartilages.  The  niunerous 
longitudinal  strise  or  sulci  on  the  anterior  surface  of  this  bone  can  now  also  be 
detected.  In  these  are  embedded  tendinous  bundles  of  the  rectus,  so  as  to  give 
firmer  leverage.  The  fact  that  these  fibres,  thus  tied  down,  are  liable  after  stretch- 
ing and  tearing  to  fold  in  between  the  ends  of  the  bone  after  fracture,  is  a  ready 
explanation  of  the  difficulty  of  ensuring  bony  union  here.  (Macewen.)  The 
patella  is  separated  from  the  tibia  by  a  pad  of  fat  and  a  deep  bursa,  save  at  its 
insertion.  Owing  to  the  lowest  part  of  the  patella  being  thus  separated  from  the 
joint  by  fat,  fracture  here  does  not,  necessarily,  open  the  joint. 

The  bone  has  the  following  relation  to  the  femur  in  different  positions: — (1)  In  extension,  the 
patella  rises  over  the  condyles,  and  in  full  extension  only  the  lower  third  of  its  articular  surface 
rests  upon  that  of  the  condyles;  its  upper  two-thirds  lies  upon  the  bed  of  fat  which  covers  the 


Fig. 


1163. — Deep  Dissection  of  the  Gluteal  Region. 
Hunterian  Museum.) 


(From  a  preparation  in  the 


Gluteus  medms 


Gluteus  minimus 

Piriformis,  divided 

into    two    by    the, 

sciatic 

Great  trochanter 

Obturator  externus 
Quadratus  femons 

Fascial  insertion  of 
gluteus 


Horizontal  fibres  of 
adductor  magnus 


Sciatic  foramen 
(notch) 

Gluteal  nerve  sup- 
plying portions  of 
gluteus  medius 

Gluteus  ] 


Obturator  internus. 
Below  is  the  infe- 
rior gemellus.  The 
superior  gemellus 
is  absent 


Sciatic  nerve.  Under  it, 
oblique  fibres  of  adduc- 
tor magnus  are  seen 


lower  and  front  part  of  the  femur.  (2)  In  extreme  flexion,  as  the  prominent  anterior  surface 
of  the  condyles  affords  leverage  to  the  quadriceps,  the  patella  needs  to  project  very  httle;  thus, 
only  its  upper  third  is  in  contact  with  the  femur,  its  lower  two-thu-ds  now  resting  on  the  pad  of 
fat  between  it  and  the  tibia.  (3)  In  semiflexion  the  middle  third  of  the  patella  rests  upon  the 
most  prominent  part  of  the  condyles.  (Humphry.)  While  the  bone  now  affords  the  greatest 
amount  of  leverage  to  the  quadriceps,  it  is  also  submitted  to  the  greatest  amount  of  strain  from 
this  muscle,  which  is  acting  almost  at  a  right  angle  to  the  long  axis  of  the  patella.  This  position 
may  therefore  be  called  the  'area  of  danger,'  as,  in  a  sudden  and  violent  contraction,  the  patella 
may  be  snapped  across  by  muscular  action,  aided  by  the  resistance  given  by  the  condyles,  in 
the  same  way  as  a  stick  is  snapped  across  the  knee.     The  amount  of  separation  of  the  fragments 


i 


1446 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


in  a  fracture  of  the  patella  is  due  chiefly  to  the  extent  to  which  the  lateral  tendinous  expansions 
of  the  vasti  are  torn;  to  a  less  degree  to  the  haemorrhage  from  the  numerous  articular  vessels 
(p.  1452)  and  synovial  effusion.  The  lower  fragment  is  usually  the  smaller,  and  its  fractured 
surface  tilted  forward;  that  of  the  upper  one  usually  looks  backward. 

The  patella,  the  largest  of  the  sesamoid  bones,  ossifies  by  a  centre  which  appears  from  the 
third  to  the  fifth  year.  The  process  is  completed  about  puberty.  The  rareness  with  which 
necrosis  and  caries  occur  here,  when  the  exposed  situation  of  the  bone  is  remembered,  is  partly 

Fig.  1164. — Knee-joint  as  Shown  by  the  ROntgen-rays,  Antero-posterior  View. 


explained  by  the  density  of  its  tissue,  especially  in  front,  and  the  intimate  blending  of  the  rectus 
fibres  with  its  periosteum.  When  the  knee-joint  is  bent,  the  trochlear  surface  of  the  femur  can 
be  made  out,  with  some  difficulty,  underneath  the  quadriceps  expansion.  The  upper  and  lateral 
angle  of  this  surface  forms  a  useful  landmark  (Godlee)  as  a  line  drawn  from  it  to  the  adductor 
tubercle  marks  the  level  of  the  lower  epiphysis  of  the  femur. 

Dislocation  of  the  patella. — The  following  anatomical  facts  account  for  this  taking  place 
much  more  frequently  laterally: — (1)  The  medial  edge  of  the  patella  is  more  prominent,  and 
thus  more  exposed  to  injury;  it  is  also  well  supported,  as  is  seen  when,  the  parts  being  relaxed,  the 


THE  KNEE 


1447 


fingers  are  insinuated  beneath  each  border.  (2)  The  pull  of  the  extensor  upon  the  patella, 
ligamentum  patella;,  and  tibia  is  somewhat  laterally,  as  the  tibia  is  directed  a  little  laterally 
to  the  femur,  to  meet  the  medial  direction  of  this  bone;  the  femora  being  directed  medially  here, 
to  bring  the  knee-joints  nearer  the  centre  of  gravity,  and,  so,  counterbalance  their  wide  separa- 
tion above  at  the  pelvis.  The  lateral  pull  of  the  quadriceps  upon  the  patella  is,  in  all  normal 
action  of  the  muscle,  counteracted  by  the  space  taken  in  the  trochlear  surface  by  the  lateral 
condyle,  this  being  wider  and  creeping  up  higher,  and  having  a  more  prominent  and  thus  pro- 
tective lip.     In  violent  contraction,  however,  these  counteracting  points  may  be  overcome. 

The  condyles  of  the  femur  and  tibia. — It  should  be  noted  that  on  the  medial 
side  the  prominence  of  the  medial  epicondyle  of  the  femur  is  well  marked,  and  that 

Fig.  1165. — Knee-joint  as  shown  by  the  Rontgen-rats,  Lateral  View. 


of  the  tibia  is  less  so,  while  on  the  lateral  side  this  condition  is  reversed.  Descend- 
ing to  the  lateral  condyle  of  the  tibia,  the  ilio-tibial  band  of  the  fascia  lata  can  be 
traced.  The  more  distinct  lateral  condyle  is  a  good  landmark  for  opening  the 
joint  in  amputation  and  excision.  It  also  indicates  the  lower  level  of  the  synovial 
membrane  of  the  knee-joint. 

Farther  back  are  the  biceps  and  fibular  collateral  (long  external  lateral)  Ugament.  The  gap 
onjthe  medial  side  between  the  femoral  and  tibial  condyles  is  the  place  for  feeling  for  a  displaced 
medial  fibro-oartilage  in  'internal  derangement'  of  the  knee,  and  also  for  'lipping'  in  suspected 
osteoartliritis.  On  each  femoral  epicondyle,  posteriorly,  in  a  thin  subject,  can  be  felt  its  tubercle, 
which  gives  attachment  to  the  collateral  ligament.  Owing  to  their  being  placed  behind  the 
■  centre  of  the  bone,  these  ligaments  become  tight  in  extension.     On  the  upper  and  posterior 


{ 


1448 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


part  of  the  medial  femoral  epicondyle  the  adductor  tubercle  and  the  vertical  tendon  of  the  ad- 
ductor magnus  can  be  felt  during  flexion.  This  bony  point  is  a  guide  to  the  lower  epiphysis, 
the  ossification  of  which  and  its  occasional  exostosis  have  been  mentioned  at  p.  1442.  The 
medial  aspect  of  this  epicondyle  faces  practically  in  the  same  direction  as  the  head  of  the  femur. 

Ligamentum  patellae  and  tuberosity  of  tibia. — These,  in  a  well-formed  leg, 
should,  with  the  centre  of  the  ankle-joint,  be  all  in  the  same  straight  line,  a  useful 
point  in  the  adjustment  of  fractures.  (Holden.)  Behind  the  upper  half  of  the 
ligament  is  the  infrapatellar  pad  of  fat;  below,  the  lower  half  is  separated  from  the 
tibia  by  a  deep  bursa.  The  tuberosity  (tubercle)  of  the  tibia  is  on  a  level  with  the 
head  of  the  fibula. 

[Prepatellar  bursa. — This  usually  protects  the  lower  part  of  the  patella  and  upper  part  of 
the  ligamentum  pateUaj.  It  is  liable  to  be  enlarged  in  those  who  habitually  kneel  much,  the 
enlargement  being  either  fluid  or  solid,  and  occasionally,  in  tertiary  syphilis.  Its  close  connec- 
tion with  the  patella  and,  at  the  sides,  with  the  joint  itself,  is  to  be  remembered  in  infective 
inflammations  of  the  bursa.  Usually  the  deep  fascia,  passing  off  from  the  sides  of  the  patella 
upward  to  the  thigh  and  downward  to  the  leg,  serves  to  conduct  inflammation  away  from  the 
joint. 

Synovial  membrane  (fig.  1167). — This,  the  largest  of  the  synovial  membranes, 
forms  a  short  cul-de-sac  above  the  patella,  between  the  quadriceps  extensor  and  the 
front  of  the  femur,  this  process  reaching  about  2.5  cm.  (1  in.)  above  the  trochlear 
surface  of  the  femur.     At  its  highest  point  this  cul-de-sac  communicates  with  an- 


FiG.  1166. — Horizontal  Section  of  the  Knee-joint. 

Prepatellar  bursa 


(One-half.)     (Braune.) 


Fibular  collateral  lig. 
Lateral  condyle  of  femur 


Tibial  n.  ' 
Semimembranosus 


Tibial  collateral  lig. 
Medial  condyle  of  femur 
M.  sartorius 


Great  saphenous  vein 
f!^^'         ^Gastrocnemius,  medial  head 
Tendon  of  gracilis 
Tendon  of  semitendlnosus 


other  synovial,  bursa-like  sac  lying  between  the  quadriceps  and  front  of  the  femur. 
Thus,  synovial  membrane  will  usually  be  met  with  6.2  cm.  (2|  in.)  or  more  above 
the  trochlear  surface  or  the  upper  border  of  the  patella  when  the  limb  is  extended. 
Flexing  the  joint  draws  the  membrane  down  very  slightly.  During  extension,  the 
above  pouch  is  supported  by  the  articularis  genu  (subcrureus) .  Traced  down- 
ward, the  membrane  reaches  the  level  of  the  head  of  the  tibia,  being  separated  in 
the  middle  line  from  the  upper  part  of  the  ligamentum  patellae  by  fat.  It  here 
gives  off  to  the  intercondyloid  notch  the  patellar  synovial  fold  (ligamentum  mu- 
cosum),  with  its  free  lateral  prolongations,  the  alar  folds  (ligamenta  alaria). 
These  three  so-called  ligaments  contain  fat,  the  processes  not  only  padding  gaps, 
but  also  meeting  concussions. 

The  enlargement  of  these  processes,  under  conditions  not  yet  understood,  may  certainly 
be  a  cause  of  'internal  derangement,'  and  simulate  a  loosened  meniscus.  But  the  synovial 
membrane  of  this  joint  is  not  only  the  largest:  it  is  also  the  most  complicated,  a  fact  accounting 
for  the  grave  peril  of  infective  arthritis,  and  the  well-known  difficulty  of  effective  drainage  and 
cleansing  this  joint.  Thus  'it  passes  over  the  gi-eater  portion  of  the  crucial  ligaments,  but  the 
posterior  surface  of  the  posterior  crucial,  which  is  connected  by  means  of  fibro-areolar  tissue 
to  the  front  of  the  ligamentum  postioum,  and  the  lower  portions  of  both  crucial  ligaments,  where 
they  are  united  together,  of  course  cannot  receive  a  complete  covering  from  the  membrane., 
(Morris.) 

From  the  above  ligaments  the  membrane  is  conducted,  lining  the  lower  part 
of  the  capsule  and  other  ligaments,  to  the  semilunar  cartilages,  first  over  their 


THE  KNEE  1449 

upper  surfaces  to  their  free  borders,  and  then  along  their  under  surfaces  to  the 
tibia.  Between  the  lateral  of  these  and  the  upper  and  back  part  of  the  tibia  is  a 
prolongation  of  the  synovial  membrane  to  facilitate  the  play  of  the  popliteus 
tendon. 

Finally,  amid  the  complications  of  this  synovial  membrane,  its  communication  with  some 
of  the  bursae  mentioned  below,  and  occasionally  with  the  superior  tibio-fibular  joint,  is  to  be 
borne  in  mind.  In  effusion  the  bony  prominences  are  obliterated,  and  the  patella  'floats.' 
The  knee-joint  is  easUy  opened  by  free  lateral  incisions  lying  midway  between  the  margins  of 
the  patella  and  the  tuberosities  of  the  condyles,  drainage-tubes  being  passed  so  as  to  meet  above 
the  patella.  The  above-mentioned  complications  of  the  synovial  membrane  show  that  such 
drainage  wiU  be  often  inadequate.  By  passing  a  director  to  the  back  of  the  joint  and  cutting 
down  upon  it  carefully  from  the  popliteal  space,  better  drainage  will  be  given,  but  opening  the 
joint  by  an  anterior  flap  is  needed  where  the  above  fail,  and,  even  then,  cleansing  of  the  numerous 
deep  recesses  is  obviously  difficult. 

Structures  on  the  head  of  the  tibia. — From  before  backward  these  are: — 
(1)  Transverse  ligament.  (2)  Anterior  end  of  medial  meniscus  (fibro-cartilage). 
(3)  Lower  attachment  of  anterior  crucial.  (4)  Anterior  end  of  lateral  meniscus 
blending  with  (3).  (5)  Posterior  extremity  of  lateral  meniscus  giving  off  a  strong 
process  to  posterior  crucial.  (6)  Posterior  extremity  of  medial  meniscus.  (7) 
Posterior  crucial  ligament.  Menisci. — These  serve  as  buffer-bonds  and  cushions 
between  the  contiguous  bones.  The  more  frequent  displacement  of  the  medial  is 
explained  by — (a)  its  greater  fixity,  and,  therefore,  its  feeling  strains  more.  Thus, 
in  addition  to  weaker  attachments  to  the  coronary  and  transverse  ligaments,  it  is 
connected  all  along  its  convex  border  with  the  inside  of  the  capsule,  and  strongly 
with  the  tibial  collateral  ligament.  The  lateral  meniscus,  on  the  other  hand,  is 
more  weakly  attached  to  the  capsule,  especially  opposite  to  the  popliteus  tendon, 
and  has  no  tie  to  the  fibular  collateral  ligament.  (&)  When,  in  the  erect  position, 
the  knee-joint  is  rotated  laterally  and  slightly  flexed,  a  common  position,  an 
especial  strain  is  thrown  upon  the  very  important  tibial  collateral  ligament,  and 
from  the  above-mentioned  connection,  on  the  medial  meniscus  also. 

Position  of  knee-joint  in  disease. — In  inflammatory  effusion,  the  position  which  best 
accommodates  the  collection  of  fluid  is  one  of  moderate  flexion,  the  ligaments  being  now  mainly 
relaxed.  Later  on,  when  the  ligaments  are  softened,  the  hamstrings  obstinately  displace  the 
leg  backward,  the  tibia  being  rotated  laterally  by  the  biceps.  The  antero-posterior  displacement 
is  always  more  marked  than  the  lateral.  In  straightening  an  anchylosed  joint,  the  resistance  of 
the  shortened  lateral,  crucial,  and  posterior  ligaments,  and  the  facility  with  which  a  softened 
upper  epiph.ysial  line  of  tlie  tibia  may  give  way,  must  never  be  forgotten.  Erasion  and  excision. 
— The  extent  and  comphcations  of  the  synovial  membrane  render  attention  to  the  following 
points  imperative: — (1)  Free  exposure  of  the  joint  usuaUy  by  an  anterior  curved  incision,  the 
medial  extremity  of  which  must  not  damage  the  great  saphenous  vein.  (2)  The  extent  of  the 
pouch  under  the  quadriceps,  it  may  be  for  5  cm.  (2  in.)  above  the  patella,  and  the  lateral  recesses 
under  the  vasti.  The  pouches  at  the  back  of  the  joint  are  far  more  difficult  to  deal  with,  viz., 
the  partial  covering  of  the  posterior  crucial  ligament,  the  proximity  of  the  popliteal  artery, 
the  pouches  in  relation  to  the  popUteus,  gastrocnemii,  and  back  of  the  femoral  condyles.  In 
erasion,  the  cartilage  and  bone,  where  diseased,  are  removed  with  a  gouge.  Owing  to  the 
removal,  in  addition  to  the  synovial  membrane,  of  the  fibro-cartilages,  and  crucial  ligaments, 
and  the  damage  to  lateral  and  patellar  ligaments,  there  is  a  most  obstinate  tendency  to  flexion 
afterward.  In  excision,  to  avoid  injury  to  the  epiphysis,  the  section  of  the  femur  should  not 
pass  higher  than  through  the  upper  third  of  the  trochlear  surface.  Of  the  tibia,  only  12  mm. 
(J  in.)  should  be  removed. 

Genu  valgum. — Here  the  natural  angle  at  which  the  femur  inclines  medially  to  the  tibia 
is  increased.  As  shown  by  the  late  v.  Mikulicz,  this  is  due  to  an  abnormal  growth  downward 
of  the  medial  part  of  the  femoral  diaphysis,  the  epiphysial  line  being  gradually  altered  from 
one  at  right  angles  to  the  shaft  to  one  which  runs  obliquely  from  without  downward  and  medially. 
The  femur  is  not  only  elongated  on  its  medial  side,  but  bent  at  its  lower  end,  the  concavity  of 
the  curve  being  lateral.  Other  changes  have  to  be  remembered.  Pes  valgus  very  commonly 
coexists,  and  in  the  tibia  there  may  be  a  compensatory  curve,  the  concavity  being  medial, 
in  the  lower  third,  or  an  analogous  alteration  in  the  line  of  the  upper  epiphysis  may  be  present, 
its  direction  being  no  longer  at  a  right  angle  with  the  shaft,  but  obhque.  In  Sir  W.  Macewen's 
supra-condyloid  osteotomy,  a  longitudinal  incision,  about  3.7  cm.  (IJ  in.)  long  is  made  where 
the  following  lines  meet,  viz.,  one  transverse,  a  finger's  breadth  above  the  upper  margin  of  the 
lateral  condyle,  and  one  longitudinal,  1.2  cm.  (J  in.)  in  front  of  the  adductor  magnus  tendon. 
The  bone  is  divided  in  front  of  the  genu  suprema  and  above  the  superior  medial  articular  artery, 
above  the  epiphysial  line  and  behind  the  upward  extension  of  the  synovial  membrane  under  the 
quadriceps. 

The  following  bursae  about  the  knee-joint  must  be  remembered.  Some,  it 
will  be  seen,  are  much  more  constant  than  others : — 


( 


1450 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


A.  In  front. — (1)  One  between  the  patella  and  skin,  the  bursa  prepatellaris  subcutanea 
(fig.  1167);  (2)  a  deeper  one  between  the  ligamentum  patellse  and  the  upper  part  of  the  tibia; 
(3)  between  the  skin  and  the  lower  part  of  the  tuberosity  of  the  tibia.     This  is  not  constant. 

B.  On  the  medial  side. — (1)  One  between  the  medial  head  of  the  gastrocnemius  and  medial 
condyle,  often  extending  between  the  above  muscle  and  the  semi-membranosus.  This  is  the 
largest  of  the  burs^  about  the  knee-joint,  and,  after  adult  life,  usually  communicates  with  the 
knee-joint.  But,  owing  to  the  narrow  communication,  it  is  rarely  possible,  when  the  parts  are 
relaxed  by  flexion  of  the  joint,  to  empty  the  cyst.  For  its  removal  a  straight  incision  is  made 
over  the  most  prominent  part  of  the  swelling,  its  neck  found  by  drawing  aside  the  tendons.  A 
ligature  is  then  pushed  high  up  around  the  neck,  and  the  cyst  cut  away.  (2)  One  superficial 
to  the  tibial  (collateral)  ligament,  between  it  and  the  tendon  of  the  sartorius,  gracilis,  and  semi 


Fig.  1167. — Vertical  Section  op  the  Knee-joint  in  the  Anteeo-posterior  Direction. 
(The  synovial  bursa  usually  present  above  the  upper  synovial  cul-de-sac  is  not  shown.) 
(The  bones  are  somewhat  drawn  apart.)     (After  Braune.) 


M.  vastus  lateralis 


M.  vastus  inter- 
medius 


Synovial  cavity 


Prepatellar  bursa 


Anterior  crucial  lig, 

Lig.  patella 


M.  gastrocnemius 


M.  tibialis  post 


tendinosus  (3)  One  beneath  the  ligament,  between  it  and  the  tendon  of  the  semi-membrano- 
sus. (4)  One  between  the  medial  condyle  of  the  tibia  and  the  semi-membranosus.  (5)  One 
between  the  semi-membranosus  and  semi-tendinosus.  Of  the  above  bursae,  the  first  two  alone 
are  constant.      The  second  and  third  are  often  one  bursa  prolonged. 

C.  On  the  lateral  side. — (1)  One  between  the  lateral  head  of  the  gastrocnemius  and  the 
condyle;  (2)  one  superficial  to  the  fibular  collateral  ligament  between  it  and  the  biceps  tendon; 
(3)  one  under  the  ligament  between  it  and  the  popliteus  tendon;  (4)  one  between  the  popHteua 
tendon  and  the  lateral  condyle  of  the  femur.  This  is  usually  a  diverticulum  from  the  synovial 
membrane. 

The  following  explanations  may  be  given  of  an  inflamed  knee-joint  usually  taking  the 
flexed  position: — -(1)  By  experimental  injections,  Braune  found  that  the  capacity  of  the  synovial 
sac  reaches  its  maximum  with  a  definite  degree  of  flexion,  i.  e.,  at  an  angle  of  twenty-five  degrees. 


THE  POPLITEAL  SPACE 


1451 


(2)    As  the  same  nei-ves  supply  the  synovial  membrane  and  the  muscles   which  act  upon  the 
joint,  reflex  spasm  of  the  flexors  will  help  to  explain  the  flexed  position.     (HQton.) 

Anastomoses  around  the  front  and  sides  of  the  knee-joint. — The  most  impor- 
tant of  these  take  the  form  of  three  transverse  arches.  (1)  The  highest  passes 
through  the  quadriceps  fibres  just  above  the  upper  edge  of  the  patella.  It  is 
formed  by  a  branch  from  the  deep  division  of  the  genu  suprema  (anastomotica 
magna)  and  one  from  the  lateral  circumflex  and  superior  lateral  articular.  The 
middle  and  lowest  arches  lie  under  the  ligamentum  patellte.  (2)  The  middle  arch, 
formed  by  branches  from  the  genu  suprema  and  superior  medial  articular  on  the 
medial  side,  and  the  inferior  lateral  articular,  on  the  lateral,  runs  in  the  fatty  tissue 

Fig.  1168. — Side  View  of  the  Popliteal  Artebt. 
(From  a  dissection  in  the  Hunterian  Museum.) 


Femoral  artery  and 

Branches  of  the  med 
cutaneous 

Sartoriu 


Genu  suprema  artery 


Vertical  fibres  of  the 
adductor  magnus         — 
Popliteal  artery 


Vastus  medialis 
Cut  edg.^  of  fascia  lata 


close  to  the  apex  of  the  patella.  (3)  The  lowest  arch  lies  on  the  tibia  just  above 
its  tuberosity,  and  results  from  the  anastomosis  of  the  recurrent  tibial  and 
the  inferior  medial  articular.  Seven  arteries  thus  take  place  in  this  series  of 
anastomoses. 

POPLITEAL  SPACE 

In  flexion,  the  hollow  of  this  space  appears;  in  extension  it  is  obliterated  and 
its  boundaries  are  ill-defined  the  only  ones  now  to  be  made  out  being  the  semi- 
tendinosus  and  the  biceps. 

Popliteal  tendons. — When  the  knee  is  a  little  bent  and  the  foot  rests  on  the  ground,  the 
following  can  be  made  out:— on  the  lateral  aspect,  behind  the  ilio-tibial  band,  and  descending  to 
the  prominence  on  the  lateral  side  of  the  head  of  the  fibula,  is  the  tendon  of  the  biceps.     This 


i 


1452 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


prominence  also  gives  attachment  to  the  fibular  collateral  ligament,  which  splits  the  tendon 
into  two  parts.  IJehind  is  the  apex  (styloid  process)  from  which  the  posterior  part  of  the 
fibular  collateral  ligament  arises.  Parallel  and  close  to  the  medial  border  of  the  tendon,  the 
peroneal  nerve  descends,  as  a  rounded  cord,  to  cross  the  neck  of  the  fibula  and  enter  the  peroneus 
iongus.  In  tenotomy  of  the  biceps  an  open  incision  should  be  employed  to  avoid  injiary  to 
the  nerve  and  insure  the  division  of  any  contracted  fascial  bands.  On  the  medial  side  the  ten- 
dons are  thus  arranged:  Nearest  to  the  middle  of  the  popliteal  space  is  the  long  and  more  slender 
tendon  of  the  semi-tendinosus;  next,  the  thicker  tendon  of  the  semi-membranosus;  this  and  the 
gracilis,  which  comes  next,  appear  as  one  tendon,  but  by  a  little  manipulation  the  finger  can  be 
made  to  sink  into  the  interval  between  the  semi-membranosus,  with  its  thick  rounded  border 
laterally  and  the  gracilis  medially.  The  sartorius  can  easily  be  thrown  into  relief  on  the  medial 
side  of  the  joint  by  telling  the  patient  to  raise  the  leg  extended,  the  limb  being  rotated  laterally 
and  one  leg  crosses  over  the  other. 

Popliteal  vessels. — The  artery  traverses  this  space  from  above  downward, 
appearing  beneath  the  semi-membranosus,  a  little  to  the  medial  side  of  the  middle 
line,  and  then  passing  down  in  the  centre  of  the  space  to  the  interval  between  the 
gastrocnemii.     Its  course  corresponds  with  a  line  drawn  from  the  medial  side  of  the 

Fig.  1169. — Deep  View  of  the  Popliteal  Space.     (Hirsohfeld  and  LeveiM.) 


Adductor  magnus 

Popliteal  vein 

Popliteal  artery 

Tibial  nerve 

Vastus  medialis 

Superior  medial  articular  artery 

Tendon  of  semi-membranosuE 


Medial  h. 
Inferior  r 


ad  of  gastrocnenuus 

ledial  articular  artery 

Popliteal  vein 

Popliteus 


Tendon  of  plantaris 


Vastus  lateralis 
Sciatic  nerve 

Short  head  of  biceps 

Peroneal  nerve 

Long  head  of  biceps,  cut 
Lateral  head  of  gastrocnemius 

Lateral  cutaneous  crural  nerve 


Gastrocnemius 


Small  saphenous  vein  and 


hamstrings  to  the  centre  of  the  lower  part  of  the  space.  The  artery  bifurcates  on 
the  level  of  a  line  corresponding  to  the  tuberosity  of  the  tibia.  It  lies  on  the  pop- 
liteal surface  of  the  femur,  the  oblique  popliteal  ligament  and  the  popliteus.  It 
is  the  second  of  these  structures  which  usually  prevents  popliteal  aneurism  and 
abscess  from  making  their  way  into  the  joint. 

The  popliteal  vein,  intimately  adherent  to  the  artery,  lies  to  the  lateral  side  above,  but 
crosses  to  its  medial  side  below.  The  popliteal  sheath  is  also  unusually  strong.  The  tibial 
nerve  crosses  the  artery  in  the  same  direction  as  the  vein,  by  which  it  is  separated  from  the 
artery.  This  nerve  is  the  direct  continuation  of  the  sciatic  nerve  (fig.  1 169),  and  enters  more  into 
the  space  than  its  fellow  branch.  The  close  relation  of  the  vein  and  nerve  explains  the  early 
stiffness  of  the  knee,  the  pains  below,  often  called  'rheumatic,'  and  the  oedema,  in  popliteal 
aneurism;  also  the  pulsation  of  swelUngs  not  aneurismal. 

The  superior  articular  arteries  (fig.  1169)  course  laterally  and  medially  immediately  above 
the  femoral  condyles;  the  way  in  which  they  cUng  closely  to  the  bone  here  is  one  provision  to  pre 
vent  overstretching  of  the  artery;  the  inferior  ones  lie  j  ust  above  the  head  of  the  fibula  and  below 
the  medial  condyle  of  the  tibia  (fig.  1169).  The  deep  part  of  the  genu  suprema  artery  runs  in 
front  of  the  tendon  of  the  adductor  magnus;  the  superficial  with  the  saphenous  nerve. 

The  popliteal  artery  may  be  ligatured — (A)  Behind,  in  the  upper  part  of  the  popHteal 
space,  just  after  its  emergence  from  under  the  semi-membranosus.     Here,  for  a  short  space 


THE  LEG  1453 

of  about  2.5  cm.  (1  in.),  the  vessel  is  comparatively  superficial  after  division  of  the  fasciae.  The 
nerve  is  generally  seen  first,  and,  with  the  vein,  must  be  drawn  laterally.  The  needle  should  be 
passed  from  the  vein.  (B)  From  the  front,  at  the  medial  side.  The  thigh  being  flexed,  ab- 
ducted, and  rotated  laterally,  a  free  incision  is  made  parallel  and  just  behind  the  adductor 
magnus  tendon,  commencing  at  the  junction  of  the  middle  and  lower  third  of  the  thigh.  The 
sartorius  and  the  hamstrings  are  drawn  backward,  and  the  adductor  magnus  forward.  Care 
must  be  taken  of  the  genu  suprema  (fig.  1168).  The  space  between  the  hamstrings  and  the 
adductor  magnus  being  carefully  opened  up,  the  artery  will  be  found  in  fatty  areolar  tissue. 
The  vein  and  tibial  nerve  are  on  the  lateral  side  of  the  vessel.  The  needle  is  passed  in  latero- 
medially.     The  collateral  circulation  (fig.  1156)  depends  chiefly  on  the  genu  suprema. 

The  small  saphenous  vein  perforates  the  roof  of  the  popliteal  space  in  its  lower  part.  As 
a  rule,  it  is  not  visible,  unless  enlarged. 

The  popliteal  nodes  are  not  to  be  felt  unless  enlarged. 

Bursse  in  the  popliteal  space. — These  have  been  already  spoken  of  (p.  1449). 

THE  LEG 

The  skin. — The  proneness  of  the  skin  to  dermatitis  in  the  lower  third  of  the 
medial  and  front  aspect  of  the  leg  as  a  result  of  varicose  veins  is  well  known.  The 
close  contiguity  of  the  periosteum  to  the  skin  here  accounts  for  the  difficulty  in 
healing  chronic  ulcers  whose  callous  base  has  become  fixed  to  the  periosteum,  and 
the  frequency  with  which  the  upper  fragment  of  a  fractured  tibia  perforates  the 
skin. 

Bony  landmarks. — From  the  tuberosity  (tubercle)  of  the  tibia  descends  the 
anterior  border  or  'shin. '  This  soon  becomes  sharp,  and  continues  so  for  its  upper 
two-thirds ;  in  the  lower  third  it  disappears,  to  be  overlaid  by  the  extensor  tendons. 
It  is  curved  somewhat  laterally  above  and  medially  below.  The  medial  border  can 
also  be  felt  from  the  medial  condyle  to  the  medial  malleolus.  Between  these  two 
borders  lies  the  medial  surface,  subcutaneous  save  above,  where  it  is  covered  by 
the  three  tendons  of  insertion  of  the  gracilis  and  semi-tendinosus,  and,  overlying 
them,  that  of  the  sartorius.  The  tibia  is  narrowest  and  weakest  at  the  junction  of 
the  middle  and  lower  thirds,  the  most  common  site  of  fracture.  Behind  the 
medial  malleolus,  part  of  the  groove  for  and  the  tendon  of  the  tibialis  posterior  can 
be  felt. 

The  head  of  the  fibula  can  be  felt  distinctly,  but  the  shaft  soon  becomes  buried 
amongst  muscles  till  about  7.5  cm.  (3  in.)  above  the  lateral  malleolus,  where  the 
bone  expands  into  a  large  triangular  subcutaneous  surface. 

This  lies  between  the  peroneus  tertius  and  the  other  two  peronei.  The  peroneus  longus 
overlaps  the  brevis,  especially  in  the  upper  two-thirds  of  the  leg.  In  the  lower  thii'd  the  brevis 
tends  to  become  anterior  (fig.  1173).  Behind  the  lateral  malleolus  these  tendons  descend  to  the 
foot  in  a  groove  on  its  posterior  border.  The  shaft  of  the  fibula  is  placed  on  a  plane  posterior 
to  that  of  the  tibia,  and  curves  backward  in  a  du-ection  reverse  to  that  of  the  tibia. 

Muscular  compartments  and  prominences. — When  the  muscles  of  the  leg  are 
thrown  into  action  by  dorsi-flexion  and  plantar  flexion  of  the  foot  or  by  standing 
on  the  toes,  several  groups  of  muscles  stand  out  on  the  surface,  owing  to  certain 
compartments,  and  the  origin  of  certain  muscles  from,  and  their  separation  by,  the 
deep  fascia,  which  knits  the  surface  into  corresponding  elevations  and  depressions. 
The  bones  and  the  two  peroneal  septa  divide  the  leg  into  four  compartments. 

These  are,  medio-laterally : — (1)  A  medial,  corresponding  to  the  medial  sm-face  of  the  tibia. 
(2)  An  anterior,  between  the  crest  of  the  tibia  and  the  anterior  peroneal  septum,  attached 
to  the  antero-lateral  border  of  the  fibula,  and  separating  the  extensors  from  the  peronei.  Its 
surface-marking  would  be  a  line  from  the  front  of  the  head  of  the  fibula  to  the  front  of  the 
lateral  malleolus.  In  this  anterior  compartment  lie  the  extensor  muscles  and  origin  of  the 
peroneus  tertius,  and  the  anterior  tibial  vessels  and  nerves.  (3)  A  lateral  or  peroneal  com- 
partment, lying  between  the  anterior  and  posterior  peroneal  septum,  the  latter  being  attached 
to  the  postero-lateral  border  of  the  fibula,  and  separating  the  peronei  from  the  calf  and  deep 
flexors.  This  peroneal  compartment,  a  narrow  one,  contains  the  two  chief  peronei  and  the 
peroneal  (external  popUteal)  nerve  and  its  three  divisions.  (4)  Much  the  largest,  this,  the 
posterior,  lies  between  the  posterior  peroneal  septum  and  the  medial  border  of  the  tibia,  and 
contains  the  calf  and  deep  flexor  muscles,  the' posterior  tibial  vessels  and  nerves,  and  the 
peroneal  artery  and  its  posterior  branch. 

The  space  between  the  tibia  and  fibula  in  front  is  mainly  occupied  by  the  fleshy  belly  of  the 
tibialis  anterior;  lateral  to  this,  and  much  less  prominent,  is  the  narrower  extensor  digitorum 
longus;  lateral  to  this,  again,  are  the  peronei  longus  and  brevis.  Lower  down,  in  an 
interval  between  the  tibialis  and  the  extensor  of  the  toes,  the  extensor  hallucis,  here  almost 
entirely  tendinous,  comes  to  the  surface.  Behind,  the  prominence  of  the  calf  is  mainl}'  formed 
by  the  gastrocnemius.     On  the  patient's  rising  on  tip-toe,  the  tendo  Achillis   starts  into  relief 


{ 


1454 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


from  about  the  middle  of  the  leg.  Of  the  two  heads  of  the  gastrocnemius,  the  medial  is  seen 
to  be  the  larger.  On  either  side  of  the  tendon,  but  more  distinctly  on  the  lateral  side,  where  it  is 
less  overlapped  by  the  gastrocnemius,  the  soleus  comes  into  view.  Its  muscular  fibres  are 
continued  on  the  deep  surface  of  the  tendon  to  within  a  short  distance  of  the  heel.  Between 
the  tendon  and  the  upper  part  of  the  os  calois  is  a  bursa,  oocasionaUy  the  seat  of  effusion,  as 
in  gonorrhoea. 

The  bones. — Their  relative  position  and  curves  have  been  mentioned  (p.  1453).  Access. — 
That  to  the  tibia  is  easy  along  the  medial  aspect.  The  fibula  is  best  explored  by  a  free  incision 
along  the  line  of  the  posterior  peroneal  septum,  which  lies  between  the  peronei  and  the  muscles 
at  the  back  (p.  1453).  The  presence  of  the  superficial  peroneal  (musculo-cutaneous)  nerve  per- 
forating the  deep  fascia  in  the  lower  third  below  and  that  of  the  common  peroneal  (external 
popliteal)  in  relation  to  the  neck  of  the  fibula  above,  must  be  remembered.     Fractures. — When, 

Fig.  1170. — Anastomoses  op  Tibial  Arteries. 
J 


Anterior  tibial  recurren 


Posterior  tibial,  giving  off  muscular  and 
medullary  branches 


Anastomosis  of  medial  malleolar  of —  (l_\ 
anterior  tibial  with  posterior  medial 
malleolar 

Medial  calcanean 
Medial  and  lateral  plantar 


Popliteal 

Anterior  tibial,  giving  off  posterior  tibial 
recurrent  and  superior  fibular  before 
piercing  interosseous  membrane  and 
anterior  tibial  afterward 


Lateral  malleolar  of  anterior  tibial 
joining  posterior  peroneal 


as  is  most  frequent,  the  tibia  gives  way  from  indirect  violence,  the  fracture  is  usually  at  the 
weakest  spot,  or  the  junction  of  the  middle  and  lower  thirds.  The  line  of  obliquity  is  generally 
marked,  and  from  above  downward  and  forward.  The  lower  fragment,  pulled  upward  by  the 
powerful  calf  muscles,  rides  behind  the  upper,  which  projects  forward  under  the  skin.  The 
fibula,  bending  more  than  the  tibia,  snaps  at  a  higher  level.  Tenderness  on  pressure  is  the  best 
guide  here,  as  it  is  in  suspected  fractures  of  the  upper  tibia,  transverse  from  direct  violence. 
The  most  common  variety  of  fracture  of  the  fibula  is  that  called  after  Pott,  complicated  with 
displacement  of  the  foot.  Here,  from  abduction  of  the  foot,  a  severe  strain  is  thrown  upon  the 
deltoid  ligament,  which  gives  way;  the  talus  (astragalus)  is  pressed  against  the  lateral  malleolus, 
and  the  inferior  tibio-fibular  ligaments  resisting,  the  fibula  yields  5  to  7  cm.  (2  to  3  in.)  above  the 
anlde,  the  upper  end  of  the  lower  fragment  being  usually  displaced  toward  the  tibia.  If  the 
deltoid  ligament  is  strong,  the  strain  often  tears  off  the  medial  malleolus.  The  medial  margin 
of  the  foot  is  turned  toward  the  ground,  the  lateral  raised.  The  foot  is  also  displaced  backward. 
On  the  medial  side  of  the  ankle  there  is  a  marked  projection  of  the  lower  end  of  the  tibia;  higher 


THE  LEG 


1455 


up,  on  the  lateral  side,  a  depression  where  the  fibula  is  broken.  The  need  of  replacing  the^foot 
and  the  weight-bearing  talus  (astragalus)  accurately,  the  fact  that  the  ankle-joint  is  opened  and 
the  numerous  tendons  iikety  to  be  matted  are  the  chief  points  to  bear  in  mind.  In  Dupuytren^s 
fracture  there  is  not  only  fracture  of  the  lower  end  of  the  fibula,  but  the  inferior  tibio-fibular 
ligaments  are  now  torn.     The  foot  is  displaced  upward  and  laterally,  together  with  the  lower 

Fig.  1171. — The  Anterior  Tibial  Artery,  Dorsal  Artery  of  the  Foot,  and  Perforating 
Branch  of  the  Peroneal  Artery,  and  Their  Bbanches. 


Superior  medial  articular  artery 


Inferior  medial  articular  artery 


Anterior  tibial  recurrent  artery 


Anterior  tibial  artery 


Tibialis  anterior  muscle 


Deep  peroneal  nerve 


Extensor  hallucis  longus 


Medial  malleolar  artery 


Crucial  ligament- 
Dorsalis  pedis  artery. 

Innermost  tendon  of  extensor  digi- 
torum  brevis 

Deep  plantar  branch 
First  dorsal  metatarsal  artery 


Superior  lateral  articular  artery 
Inferior  lateral  articular  artery 


—Extensor  digitorum  longus 


Perforating  peroneal  artery 
Lateral  malleolar  artery 


Peroneus  brevis  muscle 
Extensor  digitorum  brevis,  cut 


Arcuate  branch 

Dorsal  metatarsal  artery 


end  of  the  fibula.  Epiphyses.—The  upper  one  of  the  tibia  appears  shortly  before  birth  and 
includes  the  condyle  and  tuberosity.  It  does  not  fuse  with  the  shaft  till  the  age  of  twenty  or 
later.  This  fact  and  the  powerful  strain  of  the  rectus  on  this  epiphysis  explain  the  obscure 
pain  sometimes  complained  of  in  young  adults  much  given  to  atliletics,  over  the  tibial  tuberosity. 
The  lower  epiphysis,  including  the  medial  malleolus,  appears  in  the  second  and  joins  about  the 
eighteenth  year.     Separation  here  is  not  very  uncommon  up  to  puberty.     In  osteotomy  of  the 


i 


1456 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


tibia,  simple  or  cuneiform,  when  the  curve  is  antero-posterior  as  well  as  lateral,  the  close  vicinity 
of  the  tibiaUs  anterior  tendon  to  the  lateral  border  of  the  crest  must  be  remembered,  and  when 
the  fibula  does  not  yield  to  careful  force,  it,  also,  must  be  divided,  or  damage  may  be  done  to 
the  superior  and  inferior  tibio-fibular  Ugaments,  or  to  the  epiphyses  of  the  bones. 


Fig.  1172. — The  Superficial  Veins  and  Lymphatics  of  the  Left  Lower  Limb. 


Superficial  lymphatics  from 
lateral  wall  of  abdomen 

Superficial  lymphatics  from 
lower  and  anterior  walls 
of  abdomen 


Superficial  epigastric  vein' 


Common  femoral  vein 


Superficial  subinguinal  lym- 
phatic nodes 
External  pudendal  veir 


Accessory  saphenous  vein 


Great  saphenous  vein 


> 


Medial  malleolus 
Dorsal  venous  arch 


Superficial  inguinal  lym- 
phatic glands 
Superficial  circumflex 
iliac  vein 


Vessels. — The  saphenous  veins  should  be  carefully  traced,  owing  to  the  tend- 
ency of  these  and  their  branches  to  become  varicose.     The  great  saphenous 


THE  LEG 


1457 


(figs.  1158,  1172),  having  passed  from  the  arch  on  the  dorsum  over  the  medial 
malleolusjf'runs  up  close  to  the  medial  border  of  the  tibia,  where  it  is  to  be  avoided 
*in  ligature  of  the  posterior  tibial,  to  the  back  of  the  medial  condyle;  here  this  ves- 
sel is  to  be  remembered  in  operations  on  the  knee-joint;  then  upward  along  the 
thigh,  over  the  roof  of  the  adductor  (Hunter's)  canal,  to  the  fossa  ovalis  (saphe- 

FiG.  1173. — Relations  of  the  Popliteal  Artery  to  Bones  and  Muscles. 


Superior  lateral  articular  artery  • 

Tibial  nerve  - 

Fibular  lateral  ligament  - 

Inferior  lateral  articular  artery  . 

Popliteus  - 

Muscular  branch  to  soleus  " 
Soleu 
Anterior  tibial  artery 

Peroneus  longus  • 
Peroneal  artery  ■ 


Branch  of  tibial  nerve  to  flexor 
hallucis  longus 


Flexor  hallucis  longus  —^ 


Cutaneous  branch  of  peroneal  artery 

Peroneus  brevis  . 
Continuation  of  peroneal  artery  - 


Superior  medial  articular  artery 

■  Popliteal  artery 

■  Posterior  ligament  of  knee 

Azygos  articular  artery 
Semi -membrano  SUB 

-  Inferior  medial  articular  artery 

-  Muscular  branch 

.  Tibialis  posterior 
■  Tibial  nerve 

Muscular  branch  of  tibial  nerve  to 
flexor  digitorum  longus 

.  Flexor  digitorum  longus 


Posterior  tibial  artery 


Tibialis  posterior 


Communicating  branch 
Laciniate  ligament 


Calcaneus  , 


Internal  calcaneal  artery 


nous  opening)  (p.  1440  and  fig.  1172),  where  it  joins  the  femoral  by  perforating 
the  cribriform  fascia  and  the  femoral  sheath.  Four  to  six  valves  are  present 
chieily  in  the  upper  part. 

rpntJi'nf'?hrfh^°ul^''?u''  °''-f^^  ^?  T^^'^'^  thrombosis  is  most  Hkely  to  occm-,  reaches  from  the 
h»?„  ,f  fi  I  ^u  *°  t'^l^i'ldle  of  the  leg.  (Bemiett.)  The  saphenous  nerve  joins  the  vein 
below  the  knee,  having  been  under  the  sartorius  above  this  point  (fig.  1159  and  1160)      The 


i 


1458 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


surface-marking  of  the  upper  part  of  the  vein  is  a  line  drawn  from  the  posterior  border  of  the 
sartorius  or  the  adductor  tubercle  to  the  lower  part  of  the  fossa  ovalis.  The  small  saphenous 
vein  passes  behind  the  lateral  malleolus,  runs  upward  over  the  middle  of  the  calf,  and  joins  the 
popliteal  by  perforating  the  deep  fascia  in  the  lower  part  of  the  popliteal  space.  This  vein  is 
accompained  by  the  medial  sural  cutaneous  (external  saphenous)  nerve  throughout  its  course. 

The  popliteal  artery  bifurcates  at  the  lower  border  of  the  popliteus,  about  on 
a  level  with  the  tuberosity  of  the  tibia.  About  5  cm.  (2  in.)  lower  down  the  pero- 
neal artery  comes  off  from  the  posterior  tibial  (fig.  1173). 

The  course  of  the  posterior  tibial  corresponds  with  a  line  drawn  from  the  centre 
of  the  lower  part  of  the  popliteal  space  to  a  point  midway  between  the  tip  of  the 
medial  malleolus  and  the  medial  edge  of  the  calcaneus. 

In  the  lower  third,  the  artery  becomes  more  superficial,  passing  from  beneath  the  calf 
muscles,  lying  between  the  tendo  Achillis  and  medial  border  of  the  tibia,  and  covered  only  by 
the  skin,  deep  fascia,  and,  lower  down,  by  the  laciniate  (internal  annular)  ligament.  It  is  here, 
in  its  close  relation  to  the  tendons  of  the  tibialis  posterior  and  flexor  digitorum  longiis,  that  it 
is  liable  to  be  injured  in  the  older  methods  of  tenotomy.  The  nerve  is  medial  above,  lateral 
below  (fig.  1173). 

Ligature  of  the  posterior  tibial  in  the  middle  of  the  leg. — The  following  are  the  chief  points 
in  the  technique.     An  incision,  7.5  to  10  cm.  (3  to  4  in.)  long,  is  made  1.2  em.  (J  in.)  behind  the 


Fig.  1174. — Upper  Segment  of  a  Section  of  the  Right  Leg  in  the  Upper  Third.     (Heath.) 


Tibialis  anterior 
Extensor  digitorum  longus 

AAnterior  tibial  vessels  and 
deep  peroneal  nerve 

Peroneus  longus 

Flexor  hallucis  longus 
Soleus  with  fibrous  intersection. 

Gastrocnemius 


Tibialis  posterior 
Flexor  digitorum  longus 


Lateral  sural  cutaneous  nerve 


Small  saphenous 


Posterior  tibial  vessesls  and  tibial  nerve 


medial_border  of  the  tibia,  to  avoid  the  trunk  of  the  great  saphenous.  The  deep  fascia  being 
freely  opened,  the  medial  head  of  the  gastrocnemius  is  drawn  backward.  The  tibial  attachment 
of  the  soleus,  thus  exposed,  is  out  through  carefully,  so  as  to  allow  of  identification  of  its  central 
membranous  tendon,  which  must  not  be  confused  with  the  deep  intermuscular  septum  over 
the  flexor.  Any  sural  vessels  are  now  tied.  The  above-mentioned  special  septum  is  next 
made  out,  passing  between  the  bones  (vertical  Une  descending  from  oblique  hne  of  tibia  and 
oblique  line  of  fibula).  On  division  of  this  septum  the  nerve  usually  comes  into  view,  the  artery 
lying  more  laterally.  The  needle  is  passed  from  the  nerve;  the  vense  comitantes  may  be  in- 
cluded. The  muscles  should  now  be  fully  relaxed  by  flexion  of  knee  and  plantar  flexion  of  foot. 
The  ligature  will  be  placed  below  the  peroneal  artery. 

The  course  of  the  anterior  tibial  artery  corresponds  with  a  line  drawn  from  a 
point  midway  between  the  lateral  condyle  of  the  head  of  the  tibia  and  the  head  of 
the  fibula  to  one  on  the  centre  of  the  ankle-joint. 

This  line  corresponds  to  the  lateral  border  of  the  tibialis  anterior  and  the  interval  between  it 
and  the  extensor  digitorum  longus  (figs.  1170  and  1171).  This  is  shown  when  the  first  of  these 
muscles  is  thrown  into  action.  The  accompanying  nerve  is  in  front  in  the  middle  third  of  the 
leg,  lateral  above  and  below. 

Ligature  of  the  anterior  tibial  artery  at  the  junction  of  the  upper  and  middle  thirds  of  the 
leg.  The  limb  being  flexed  and  rotated  medially,  an  incision  is  made,  7.5  to  10  cm.  (3  to  4  in.) 
long,  in  the  line  of  the  artery,  distant  2.5  cm.  (1  in.)  or  more  (according  to  the  size  of  the  leg) 
from  the  crest,  and  beginning  about  5  cm.  (2  in.)  below  the  head  of  the  tibia.  If,  on  exposure 
of  the  deep  fascia,  the  intermuscular  septum  between  the  tibialis  and  long  extensor  of  the  toes 


THE  ANKLE  1459 

is  not  well  defined,  the  fascia  must  be  freely  slit  up  in  the  line  of  the  artery,  and  the  sulcus  felt 
for.  A  small  muscular  artery  may  lead  down  to  the  trunk.  The  foot  is  now  dorsiflexed  and  the 
artery  sought  for  deep  on  the  interosseous  membrane.  The  nerve  should  be  drawn  to  the 
outer  side.     The  venas  comitantes  may  be  included  in  the  ligature. 

In  senile  gangrene  the  liabiUty  of  the  tibial  arteries  to  disease  and  consequent  thrombosis 
and  interference  with  the  collateral  cu-eulation  accounts  both  for  the  extension  of  the  disease 
and  the  difficulty  in  detecting  pulsation. 

The  peroneal  artery,  given  off  from  the  posterior  tibial  about  an  inch  below 
the  popliteus,  or  two  inches  below  the  head  of  the  fibula,  runs  deeply  along  the 
medial  border  of  this  bone,  covered  by  the  flexor  hallucis  longus,  the  nerve  to 
which  accompanies  the  vessel. 

It  gives  off  the  anterior  peroneal,  through  the  interosseous  membrane,  to  the  front  of  the 
lateral  malleolus  about  an  inch  above  the  level  of  the  ankle-joint.  Its  continuation,  as  the  pos- 
terior peroneal,  runs  behind  the  malleolus,  to  join  the  anastomosis  about  the  ankle-joint. 

Tlie  nutrient  artery  of  the  tibia  arises  from  the  posterior  tibial  near  its  commencement.  It 
is  the  largest  of  all  the  nutrient  arteries  to  the  shafts  of  long  bones;  that  for  the  fibula  comes  from 
the  peroneal. 

As  a  general  rule,  in  amputation  2.5  cm.  (1  in.)  below  the  head  of  the  fibula,  only  one  main 
artery — the  popliteal — is  divided.  In  amputations  5  cm.  (2  in.)  below  the  head  of  the  fibula, 
two  main  arteries — the  anterior  and  posterior  tibials — are  divided.  In  amputations  7.5  cm. 
(3  in.)  below  the  head,  three  main  arteries — the  two  tibials  and  the  peroneal — are  divided. 
(Holden.) 

In  an  amputation  through  the  middle  of  the  leg,  the  anterior  tibial  artery  would  be  found 
cut  on  the  interosseous  membrane  between  the  tibialis  anterior  and  the  extensor  hallucis  longus, 
the  deep  peroneal  nerve  here  lying  in  front  of  the  vessel.  The  posterior  tibial  would  be  between 
the  superficial  and  deep  muscles  at  the  back  of  the  leg  lying  on  the  tibialis  posterior,  its  nerve 
being  to  the  lateral  side.     The  peroneal  would  be  close  to  the  fibula  in  the  flexor  hallucis  longus. 

The  superficial  peroneal  (musculo-cutaneous)  nerve,  having  passed  through 
the  peroneus  longus  and  then  between  the  peroneus  longus  and  peroneus  brevis, 
perforates  the  deep  fascia  in  the  lower  third  of  the  leg  in  the  line  of  the  septum 
between  the  peronei  and  extensors.  Directly  after,  it  divides  into  its  two  terminal 
branches. 

Amputation  of  the  leg. — To  give  one  instance  only,  amputation  'at  the  seat  of  election, 
or  a  hand's-breadth  below  the  knee-joint,  will  be  alluded  to.  Lateral  skin-flaps  and  circular 
division  of  the  muscles  give  an  excellent  result  in  hospital  practice  where  the  various  conditions 
which  call  for  such  a  step  are  usually  met  with.  The  above  name  was  given  because  the  pressure 
of  the  body  is  well  carried  on  the  prominences  about  the  knee-joint,  especially  the  tuberosity 
of  the  tibia,  when  the  patient  walks  with  the  knee  flexed  on  a  'bucket'  artificial  limb.  Thus  the 
scar,  being  central,  is  here  not  of  importance.  Two  broadly  oval  lateral  flaps  of  skin  and  fasciae 
are  raised,  and  the  remaining  soft  parts  severed  down  to  the  bones  with  circular  sweeps  of  the 
knife.  In  sawing  the  bone,  the  smaller  size  of  the  fibula  and  its  position  behind  the  tibia  must 
be  remembered.  It  is  well,  in  order  to  ensure  complete  division  of  the  fibula  first,  to  roll  the 
limb  well  over  on  its  medial  side,  and  place  the  saw  well  down  on  the  lateral  side.  The  parts 
cut  thi'ough  are  shown  in  fig.  1174. 

THE  ANKLE 

Bony  landmarks. — The  following  are  the  differences  between  the  two  malleoli : 
The  medial  is  the  more  prominent,  shorter,  and  is  placed  more  anteriorly  than  the 
lateral,  being  a  little  in  front  of  the  centre  of  the  joint.  The  lateral  descends 
lower  by  about  1.2  cm.  (|  in.),  and  thus  securely  locks  in  the  joint  on  this  side; 
it  is  opposite  to  the  centre  of  the  ankle-joint,  being  placed  about  1.2  cm.  (|  in.) 
behind  its  fellow. 

Owing  to  the  lateral  malleolus  descending  lower  than  the  medial,  in  Syme's  and  Pirogoff's 
amputations  the  plantar  incision  should  run  between  the  tip  of  the  lateral  malleolus  and  a  point 
1.2  cm.  (J  in.)  below  that  of  the  medial  one.  When  a  fracture  is  set,  or  a  dislocation  adjusted, 
the  medial  edge  of  the  patella,  the  medial  malleolus,  and  the  medial  side  of  the  great  toe  are 
useful  landmarks  and  should  be  in  the  same  vertical  plane,  regard  being  paid  at  the  same  time 
to  the  corresponding  points  in  the  opposite  limb.     (Holden.) 

On  the  posterior  aspect  of  the  medial  malleolus  is  a  groove  for  the  tibialis  pos- 
terior and  flexor  digitorum  longus,  the  first  named  being  next  the  bone.  The  tip 
and  borders  of  the  process  give  attachment  to  the  deltoid  ligament.  The  anterior 
border  and  tip  of  the  lateral  malleolus  give  attachment  to  the  anterior  talo-fibular 
and  calcaneo-fibular  ligaments  respectively,  the  posterior  talo-fibular  arising  from 
a  pit  behind  and  below  the  articular  facet.  The  posterior  border  is  grooved  for 
the  two  peronei.  The  line  of  the  ankle-joint  corresponds  to  one  about  1.2  cm. 
(I  in.)  below  the  tip  of  the  medial  malleolus  drawn  across  the  anterior  aspect. 


{ 


1460 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


Effusion  or  tuberculous  thickening  shows  itself  first  in  front,  between  the  medial  malleolus 
and  tibialis  anterior  and  between  the  peroneus  tertius  and  lateral  malleolus  and  then  behind, 
where  it  fills  up  the  hollow  between  the  tendo  Achillis  and  the  two  malleoli.  Owing  to  the  thin- 
ness of  the  transverse  crural  (anterior)  ligament,  the  extensor  sheaths  are  easOy  affected  in 
neglected  tuberculous  disease.  Owing  to  the  way  in  which  the  joint  is  locked  in,  it  is  not  easy 
to  open  and  drain  an  infected  ankle-joint  satisfactorily.     Removal  of  a  portion  of  the  lateral 

Fig.  1175. — Branches  of  the  Common  Peroneal  Nerve. 


Common  peroneal  nerve' 
Recurrent  articular' 


Superficial  peroneal 
Branch  to  peroneus  longus- 


Branch  to  extensor, 
digitorum  longus 


Branch  to  peroneus  brevis 


Superficial  peroneal- 


Intermediate  dorsal  cutaneous- 


Lateral  dorsal  cutaneous" 


Deep  peroneal  nerve 


Anterior  tibial  artery 


Tibialis  anterior 


Deep  peroneal  nerve 
Medial  dorsal  cutaneous 


Deep  peroneal  (lateral  division) 


—  Deep  peroneal  (medial  division) 


malleolus  subperiosteally,  leaving  the  tip  and  calcaneo-fibular,  will  admit  of  the  insertion  of  a 
tube  and  good  drainage  if  the  foot  is  so  slung  as  to  keep  its  lateral  aspect  dependent. 

Tendons. — (A)  In  front  of  ankle. — ^Latero-medially  are — (1)  The  tibialis 
anterior,  the  largest  and  most  medial.  This  tendon  appears  in  the  lower  third  of 
the  leg,  lying  just  under  the  deep  fascia,  close  to  the  tibia;  then,  crossing  over  the 


THE  ANKLE 


1461 


lower  end  of  this  and  the  ankle-joint,  it  passes  over  the  medial  side  of  the  tarsus, 
to  be  inserted  into  the  medial  and  lower  part  of  the  first  cuneiform  and  the  ad- 
jacent part  of  the  first  metatarsal.  (2)  The  extensor  hallucis  longus.  This  ten- 
don, concealed  above,  appears  low  down  in  a  line  just  lateral  to  the  last,  and  then, 
crossing  over  the  termination  of  the  anterior  tibial  vessels  and  nerves  (to  which 
its  muscular  part  lies  lateral),  it  descends  along  the  medial  part  of  the  dorsum  to 
be  inserted  into  the  base  of  the  last  phalanx  of  the  great  toe.  (3)  and  (4)  The 
extensor  digitorum  longus  and  peroneus  tertius  enter  a  common  sheath  in  the 
transverse  crural  ligament.     The  former  then  divides  into  four  tendons,  which 

Fig.  1176. — Lateral  View  op  the  Ankle  Region,  as  Shown  by  the  ROntgbn-rats 


run  to  the  four  lateral  toes.     The  peroneus  tertius  is  inserted  into  the  upper 
surface  of  the  base  of  the  fifth  (often  also  the  fourth)  metatarsal  bone. 

(B)  Behind. — The  tendo  Achillis,  the  thickest  of  all  tendons,  begins  near  the 
middle  of  the  leg,  in  the  junction  of  the  tendons  of  the  gastrocnemii  and,  a  little 
lower,  (p.  1453)  the  soleus.  Very  broad  at  its  commencement,  it  gradually  nar- 
rows and  becomes  very  thick.  About  3 . 7  cm.  (1|  in.)  from  the  heel,  or  about  the 
level  of  the  medial  malleolus,  is  its  narrowest  point.  After  this  it  again  expands 
sHghtly,  to  be  inserted  into  the  middle  of  the  back  part  of  the  calcaneus.  The 
long  tendon  of  the  plantaris  runs  along  its  medial  side,  to  blend  with  it  or  to  be  at- 
tached to  the  calcaneus.     On  either  side  of  the  tendo  Achillis  are  well-marked 


{ 


1462 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


furrows  below.  Along  the  medial,  the  tendon  of  the  tibialis  posterior  and  the 
posterior  tibial  vessels  and  nerve  come  nearer  the  surface.  Along  the  lateral, 
the  small  saphenous  vein  (more  superficially)  ascends  from  behind  the  lateral 
malleolus. 

(C)  On  the  medial  side. — The  tendon  of  the  tibialis  posterior,  which  has  pre- 
viously crossed  from  the  interspace  between  the  bones  of  the  leg  to  the  medial  side, 
lies  behind  the  inner  edge  of  the  tibia  above  the  medial  malleolus,  then  behind  this, 
being  here  under  the  flexor  digitorum  longus,  the  two  tendons  having  become  super- 
ficial on  the  medial  side  of  the  ten  do  Achillis.  It  then  passes  forward  over  the 
deltoid  and  under  the  laciniate  (internal  annular)  ligament  between  the  medial 
malleolus  and  the  sustentaculum  tali,  and  then  below  and  close  to  the  plantar  cal- 

FiG.  1177. — Horizontal  Section  through  the  Lower  Part  of  the  leg.     (After  Braune.) 


Deep  peroneal  n. 

Ant.  tibial  vessels 

M.  extensor  digitorum  com. 


Tendon  of  peroneus  longus 
M.  peroneus  brevis 
M.  flexor  hailucis  longus  —         \ 


Sural  nerv 


Tendon  of  ant.  tibial 

M  extensor  hailucis  longus 


Tendon  of  post,  tibial 

Tendon  of  flexor  longus  digitorum 


Tendo  calcaneus  (Achillis) 


caneo-navicular  ligament  {vide  infra) ,  and  so  to  its  insertion,  by  numerous  slips, 
into  the  tarsus  and  metatarsus,  especially  the  tuberosity  of  the  navicular.  The 
tendon  of  the  flexor  hailucis  longus  cannot  be  felt.  Having  passed  medially  from 
the  fibula,  it  crosses  the  lower  end  of  the  tibia  in  a  separate  furrow,  then  grooves 
the  backof  the  talus,  and  passes  under  the  sustentaculum  tali  on  its  way  to  its 
insertion. 

The  arrangement  of  the  structures  at  the  medial  ankle  from  above  downward,  and  medio- 
laterally,  is  as  follows  (fig.  1177): — tibialis  posterior,  flexor  digitorum  longus,  companion  vein, 
posterior  tibial  artery,  companion  vein,  tibial  nerve,  flexor  hailucis  longus.  The  tibiales  pos- 
terior and  anterior  turn  the  sole  mediaUy,  antagonising  the  peronei.     They  also  bear  a  large 


THE  ANKLE  1463 

share  in  maintaining  the  longitudinal  arch  of  the  foot.  The  flexors  not  only  act  upon  the  toes, 
but  aid  the  calf  muscles  in  straightening  the  foot  upon  the  leg  in  walking  or  standing  upon  tip- 
toe; hence  the  value  of  educating  them  in  cases  of  flat-foot. 

(D)  Tendons  on  the  lateral  aspect. — The  tendons  of  the  two  peronei,  which 
arise  from  the  fibula  between  the  extensor  digitorum  longus  and  flexor  hallucis 
longus,  pass  behind  the  lateral  malleolus,  the  brevis  being  nearer  to  the  bone  (fig. 
1177).  They  then  pass  forward  over  the  lateral  surface  of  the  calcaneus,  sepa- 
rated by  the  peroneal  tubercle  when  present,  and  diverge. 

The  brevis — the  upper  one — passes  to  the  projection  at  the  base  of  the  fifth  metatarsal; 
the  longus,  lying  below  the  brevis  on  the  calcaneus,  winds  round  the  lateral  border  of  the  foot, 
grooving  the  lateral  border  and  under  surface  of  the  cuboid.  Finally,  crossing  the  sole  obliquely 
forward  and  medially,  it  is  inserted  into  the  adjacent  parts  of  the  first  cuneiform  and  the  back 
part  and  under  surface  of  the  first  metatarsal.  While  in  connection  with  the  under  surface  of 
the  cuboid,  this  tendon  is  covered  in  by  a  sheath  from  the  long  plantar  ligament,  and  often 
contains  a  sesamoid  bone.  The  two  peronei  evert  the  foot,  as  is  seen  in  talipes  valgus  and  in 
fracture  of  the  lower  end  of  the  fibula;  the  peroneus  longus  aids  in  the  support  of  the  arch  of  the 
foot  (p.  1466),  and,  by  keeping  the  great  toe  on  the  ground,  is  important  in  the  third  stage  of 
walking,  skating,  etc. 

Annular  ligaments  and  synovial  membranes  of  tendons. — These  strap-like 
bands  of  deep  fascia,  which  serve  to  keep  the  above  tendons  in  position,  are  three 
in  number,  viz.: — 

(A)  Lateral. — This,  the  superior  peroneal  retinaculum,  extends  from  the  tip 
of  the  lateral  malleolus  to  the  lateral  surface  of  the  calcaneus.     It  keeps  the  two 

Fig.  1178. — Relations  op  Parts  behind  the  Medial  Malleolus.     (Heath.) 


Tendo  Achillis 

Tibialis  posterior 

Flexor  digitorum  longus 

Cruciate  Ugament  7^-i^       '  li'-f'CJ' ■    Posterior  tibial  artery 


Tibialis  posterior 
Tibialis  anterior 


Tibial  nerve 


Fezor  digitorum  longus 


peronei  in  place,  and  surrounds  them  behind  the  fibula  in  one  sheath  with  a  single 
synovial  sac,  which  extends  upward  into  the  leg  for  3 . 7  cm.  (1|  in.),  and  sends  two 
processes  into  the  two  sheaths  in  which  the  tendons  lie  on  the  calcaneus.  Farther 
on,  while  in  relation  with  the  cuboid,  the  peroneus  longus  has  a  second  synovial 
sheath. 

(B)  Medial. — This,  the  laciniate  ligament,  crosses  from  the  medial  malleolus 
to  the  medial  surface  of  the  calcaneus.  Beneath  it  are  the  following  canals : — (1) 
For  the  tibialis  posterior.  This  tendon-sheath  is  lined  by  a  sj^novial  membrane 
extending  from  a  point  3.7  cm.  (1|  in.)  above  the  malleolus  to  the  navicular.  (2) 
For  the  flexor  digitorum  longus.  The  synovial  sheath  of  this  tendon  is  separate 
from  that  of  the  closely  contiguous  tibialis  posterior.  It  extends  upward  into  the 
leg  about  as  high  as  the  sheath  just  given.  It  reaches  down  into  the  sole  of  the 
foot;  but  where  the  tendon  subdivides  to  enter  the  thecse,  each  of  these  is  lined  by 
a  separate  synovial  sheath.  Next  comes  (3)  a  wide  space  for  the  posterior  tibial 
vessels  and  nerve;  and,  lastly,  (4)  a  canal,  like  the  other  two,  with  a  separate 
synovial  sheath,  for  the  tendon  of  the  flexor  hallucis  longus.  The  lower  margin  of 
this  annular  ligament  gives  an  attachment  to  the  abductor  hallucis  and  blends 
with  the  plantar  fascia.  The  medial  calcaneal  vessels  and  nerve  perforate  the 
ligament. 


\ 


1464  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 

(C)  Anterior  annular  ligament. — This  is  a  double  structure.  (1)  Upper 
(transverse  crural  ligament),  above  the  level  of  the  ankle-joint,  and  tying  the 
tendons  down  to  the  lower  third  of  the  leg,  passes  transversely  between  the  ante- 
rior crest  of  the  tibia  and  fibula.  Here  is  one  sheath  only,  with  a  synovial  mem- 
brane for  the  tibialis  anterior.  (2)  Lower,  over  the  ankle-joint.  This  band,  the 
cruciate  ligament,  is  arranged  like  the  letter  -<,  placed  thus.  It  is  attached  by  its 
root  to  the  calcaneus,  and  by  its  bifurcations  to  the  medial  malleolus  and  plantar 
fascia. 

This  arrangement  of  the  branches  of  this  ligament  is  not  constant.  In  this,  the  lower 
annular  ligament,  there  are  usually  three  sheaths  with  separate  synovial  membranes — the 
most  medial  (the  strongest  in  each)  for  the  tibialis  anterior,  the  next  for  the  extensor  halluois 
longus,  and  the  third  common  to  the  extensor  communis  and  peroneus  tertius.  The  extensor 
digitorum  brevis  has  a  partial  origin  from  this  ligament. 

Points  in  tenotomy  and  guides  to  the  tendons. — The  tendo  Achillis  should  be  divided 
about  3.7  cm.  (If  in.)  above  its  insertion,  its  narrowest  point,  which  is  about  on  a  level  with  the 
medial  malleolus.  The  knife  should  be  introduced  on  the  medial  side  and  close  to  the  tendon, 
so  as  to  avoid  the  posterior  tibial  artery  (fig.   1178). 

The  tibialis  anterior  may  be  divided  about  25  mm.  (1  in.)  above  its  insertion  into  the  first 
cuneiform,  a  point  which  is  below  the  level  of  its  synovial  sheath.  The  tendon  has  here  the 
dorsalis  pedis  on  its  lateral  side,  but  separated  by  the  tendon  of  the  extensor  hallucis  longus. 
The  knife  is  introduced  on  this  side. 

The  tibialis  posterior. — The  usual  rule  for  dividing  this  tendon  is  to  take  a  spot  5  cm. 
(2  in.)  above  the  medial  malleolus,  and  as  accurately  as  possible  midway  between  the  anterior 
and  medial  borders  of  the  leg.  This  point  will  give  the  medial  margin  of  the  tibia,  in  close  ap- 
position to  which  the  tendon  is  lying,  and  is  a  point  at  which  the  tendon  is  rather  farther  from 
the  artery  than  it  is  below,  and  is  also  above  the  commencement  of  its  synovial  sheath.  A 
sharp-pointed  knife  is  used  first  to  open  the  sheath  freely,  and  then  a  blunt-pointed  one  to 
divide  the  tendon.     The  flexor  digitorum  longus  is  usually  cut  at  the  same  time. 

Owing  to  the  risk  of  injury  to  the  posterior  tibial  vessels,  the  difficulty  of  ensuring  division 
of  the  tendons,  the  following  open  method  is,  nowadays,  superior,  being  more  certain,  and  ad- 
mitting of  division  of  ligaments,  e.  g.,  talo-navicular  and  anterior  part  of  deltoid  (syndesmotomy 
of  Parker),  which  are  always  contracted  in  advanced  talipes  equino-varus.  A  V-shaped  flap 
with  its  apex  over  the  first  metatarsal  bone,  and  its  two  limbs  starting,  the  lower  below  the 
margin  of  the  plantar  fascia  on  a  line  with  the  medial  malleolus,  the  upper  from  a  point  over 
the  head  of  the  talus,  is  turned  backward.  The  plantar  fascia  is  divided,  the  tibiaUs  anterior  is 
found,  near  its  insertion,  under  the  upper  hp  of  the  wound,  the  tibialis  posterior  and  the  flexor 
digitorum  longus  in  the  lower,  the  former  close  to  the  navicular.  If  necessary,  the  calcaneo- 
and  talo-navicular  and  anterior  part  of  the  deltoid  ligaments  can  be  divided  also. 

Peronei. — The  peronei  longus  and  brevis  may  be  divided  5  cm.  (2  in.)  above  the  lateral 
malleolus,  so  as  to  be  above  the  level  of  their  synovial  sheath.  The  knife  should  be  inserted 
very  close  to  the  bone,  so  as  to  pass  between  the  fibula  and  the  tendons.  Division  below  the 
ateral  malleolus  by  a  small  flap  is  easier. 

THE  FOOT 

Bony  landmarks. — The  following  are  of  the  greatest  practical  importance 
owing  to  the  operations  which  are  performed  upon  the  foot. 

(A)  Along  the  medial  aspect  of  the  foot  are  the  following  :■ — 

(1)  Medial  tuberosity  of  the  calcaneus;  (2)  medial  malleolus;  (3)  2.5  cm. 
(1  in.)  below  the  malleolus,  the  sustentaculum  tali;  (4)  about  2.5  cm.  (1  in.)  in 
front  of  the  medial  malleolus,  and  a  little  lower,  is  the  tuberosity  of  the  navicular, 
the  medial  guide  in  Chopart's  amputation,  the  gap  between  it  and  the  susten- 
taculum being  filled  by  the  calcaneo-navicular  ligament  and  the  tendon  of  the 
tibialis  posterior,  in  which  there  is  often  a  sesamoid  bone;  (5)  the  first  cuneiform; 
(6)  the  base  of  the  first  metatarsal;  and  (7)  the  head  of  the  same  bone,  with  its 
sesamoid  bones  below.     (Holden). 

(B)  Along  the  lateral  aspect  are : — (1)  The  lateral  tuberosity  of  the  calcaneus; 
(2)  the  lateral  malleolus;  (3)  the  peroneal  tubercle  of  the  calcaneus  (when  pres- 
ent), 2.5  cm.  (1  in.)  below  the  malleolus,  with  the  long  peroneal  tendon  below  it, 
and  the  short  one  above;  (4)  the  projection  of  the  anterior  end  of  the  calcaneus, 
and  the  calcaneo-cuboid  joint,  midway  between  the  tip  of  the  lateral  malleolus  and 
the  base  of  the  fifth  metatarsal  bone;  (5)  the  base  of  the  fifth  metatarsal  bone;  (6) 
the  head  of  this  bone.  The  greater  process  of  the  calcaneus  and  the  muscular 
origin  of  the  short  extensor  lie  between  the  peroneus  brevis  and  tertius. 

Levels  of  joints  and  lines  of  operations. — The  line  of  the  ankle-joint  has  been  given  at 
p.  1459.  That  of  the  talo-calcaneal  joint — the  limited  lateral  movements  of  the  foot  take 
place  here  and  at  the  medio-tarsal  joint — corresponds,  on  the  lateral  side,  to  a  point  a  little  in 
front  of  the  lateral  malleolus  and  midway  between  it  and  the  peroneal  tubercle;  on  the  medial 


THE  FOOT 


1465 


side,  to  one  just  above  the  sustentaculum  tali.  In  Syme's  amputation  through  the  ankle-joint, 
the  incision  starts  from  the  tip  of  the  lateral  malleolus,  and  is  then  carried,  pointing  a  little  back- 
ward toward  the  heel,  across  the  sole  to  a  point  1.2  em.  (i  in.)  below  the  medial  malleolus. 
The  chief  supply  to  the  heel-flap  is  from  the  medial  calcaneal.  Care  should  be  taken  to  divide 
the  posterior  tibial  below  its  bifurcation  and  not  to  prick  this  vessel  afterward. 

In  Pirogoff's  amputation  the  incision  begins  and  ends  at  the  same  points,  but  is  carried 
straight  across  the  sole.  In  each  amputation  the  extremities  of  the  above  incision  are  joined 
by  one  going  directly  across  the  ankle-joint,  which  lies  about  1.2  cm.  (5  in.)  above  the  tip  of  the 
internal  malleolus. 

In  Chopart's  medio-tarsal  amputation,  which  passes  between  the  talus  and  the  navicular 
on  the  medial  side,  and  the  calcaneus  and  the  cuboid  on  the  lateral,  the  line  of  the  joints  to  be 
opened  would  be  one  drawn  across  the  dorsum  from  a  point  just  behind  the  tuberosity  of  the 
navicular  to  a  point  corresponding  to  the  calcaneo-cuboid  joint,  just  midway  between  the  tip 
of  the  lateral  malleolus  and  the  base  of  the  fifth  metatarsal  bone.  The  convexity  of  the  plantar 
flap  should  reach  to  a  point  2.5  cm.  (1  in.)  behind  the  heads  of  the  metatarsal  bones.  Owing 
to  the  tendency  of  the  unbalanced  action  of  the  calf  muscles  to  tilt  up  the  calcaneus  and  thus 
thi'ow  the  scar  down  into  the  line  of  pressure,  the  powerful  tibialis  anterior  tendon  and  those  of 
the  extensors  should  be  carefully  stitched  into  the  tissues  of  the  sole  flap. 

In  Lisfranc's,  or  Hey's,  or  the  tarso -metatarsal  amputation,  the  bases  of  the  fifth  and  first 
metatarsals  must  be  defined.  The  first  of  these  can  always  be  detected,  even  in  a  stout  'or 
swollen  foot;  on  the  medial  side  the  joint  between  the  first  cuneiform  and  the  first  metatarsal 


Fig.  1179. — Vektical  Section  through  the  Cuneiform  and  Cuboid  Bones.     (One-half.) 
Dorsalis  pedis  vessels  and  nerve 
Extensor  hallucis  longus 


First  cuneiform 
Tibialis  anterior 


Second  cuneiform 

I  Third  cuneiform 

,  Extensor  digitorum  brevis 
,  Dorsal  aponeurosis 
I  Cuboid 
I  Peroneus  tertius 


Abductor  ballucus 
Medial  plantar  vessels  and  nerve 
Abductor  hallucis 

Flexor  hallucis  longus 
Plantar  fascia 
Flexor  digitorum  longus 


Abductor  digiti  quinti 

Lateral  plantar  vessels  and  nerve 
Tendon  of  peroneus  longus 


Flexor  digitorum  brevis 


bone  lies  3.7  cm.  (IJ  in.)  in  front  of  the  navicular  tuberosity.  In  opening  the  joint  between  the 
second  metatarsal  and  the  middle  cuneiform,  its  position  (the  base  of  the  former  bone  projecting 
upward  on  to  a  level  6  or  8  mm.  (|  or  5  in.)  above  the  others),  and  the  way  in  which  it  is  locked 
in  between  its  fellows  and  the  cuneiform  bones,  must  be  remembered.  The  convexity  of  the 
plantar  flap  here  reaches  the  heads  of  the  metatarsal  bones. 

In  marking  out  the  flaps  for  the  amputation  of  the  great  toe,  the  large  size  of  the  head  of 
the  first  metatarsal,  and  the  importance  of  leaving  this  so  as  not  to  diminish  its  supporting 
power  and  the  treading  width  of  the  foot,  and  thus  of  marking  out  flaps  sufficiently  long  and 
large,  must  be  borne  in  mind.  The  dorsal  incision  should  begin  3.7  cm.  (1|  in.)  above  the  web. 
The  line  of  the  joint  is  a  httle  distal  to  the  centre  of  the  ball  of  the  toe  (fig.  1181).  The  sesa- 
moid bones  should  be  left,  so  as  not  to  endanger  the  vitaUty  of  the  flaps.  In  amputation  of 
the  other  toes,  the  line  of  their  metatarso-phalangeal  joints  lies  a  full  inch  above  the  web. 

Bursse  and  synovial  membranes. — The  synovial  sheath  of  the  extensor  hal- 
lucis longus  extends  from  the  front  of  the  ankle,  over  the  instep,  as  far  as  the  meta- 
tarsal bone  of  the  great  toe.  There  is  generally  a  bursa  over  the  instep,  above,  or 
it  may  be  below,  the  tendon. 

There  is  often  an  irregular  bursa  between  the  tendons  of  the  extensor  digitorum  longus 
and  the  projecting  end  of  the  talus  over  which  the  tendons  play.  There  is  much  friction  here. 
It  is  well  to  be  aware  that  this  bursa  sometimes  communicates  with  the  joint  of  the  head  of  the 
talus.  (Holden.)  There  is  a  deep  synovial  bursa  between  the  tendo  Achillis  and  the  cal- 
caneus. Numerous  other  bursie  may  appear  over  any  of  the  bony  points  in  the  foot,  especially 
when  they  are  rendered  over-prominent  by  morbid  conditions. 

Synovial  membranes. — In  addition  to  that  of  the  ankle-joint,  there  are  six 
synovial  membranes  in  the  tarsus,  viz.: — (1)  Talo-calcaneal,  peculiar  to  these 


i 


1466 


CLINICAL  AND  TOPOGRAPHICAL  ANATOMY 


bones;  (2)  talo-calcaneo-navicular,  common  to  these  bones  and  the  navicular; 
(3)  between  the  calcaneus  and  the  cuboid;  (4)  between  the  cuboid  and  the  lateral 
two  metatarsals;  (5)  between  the  first  cuneiform  and  the  first  metatarsal;  (6)  a 
comphcated  and  extensive  one,  which  branches  out  between  the  navicular  and 
cuneiform  bones;  between  the  cuneiforms;  between  the  third  cuneiform  and  the 
cuboid ;  between  the  second  and  third  cuneiform  and  the  second  and  third  meta- 
tarsal bones;  and  between  the  second  and  third  and  the  third  and  fourth  meta- 
tarsal bones. 


Fig.  1180. — Superficial  Nerves  in  the  Sole  of  the  Foot.     (Ellis.) 


Abductor  hallucis- 


Flexor  digitorum  brevis' 
Medial  plantar  nerva 
Medial  plantar  artery. 


Proper  plantar  digital 

nerve  to  medial  side 

of  hallux 


Abductor  minimi  digiti 


Lateral  plantar  artery 
Lateral  plantar  nerve 


Proper  plantar  digital 
branches  of  the 
lateral  plantar 


Proper  plantar  digital 
branches  of  the 
medial  plantar 


Dorsal  artery. — The  line  of  this  is  from  the  centre  of  the  ankle-joint  to  the 
upper  part  of  the  first  interosseous  space. 

On  its  medial  side  is  the  tendon  of  the  extensor  hallucis  longus ;  on  its  lateral,  the  most  medial 
tendon  of  the  extensor  digitorum  longus.  It  is  crossed  by  the  most  medial  tendon  of  the  extensor 
brevis.     The  origin  of  this  muscle  should  be  noted  on  the  lateral  and  fore  part  of  the  calcaneus. 

Cutaneous  nerves  (fig.  1182). — The  sites  of  these,  numerous  on  the  dorsum 
of  the  foot,  are  as  follows: — The  superficial  peroneal  (musculo -cutaneous)  nerve, 
having  perforated  the  fascia  in  the  lower  third  of  the  leg,  divides  into  two  chief 
branches,  medial  and  lateral,  which  supply  all  the  toes  save  the  lateral  part  of  the 
little,  and  the  adjacent  sides  of  the  first  and  second.  The  deep  peroneal  becomes 
cutaneous  in  the  first  space,  and  is  distributed  to  the  contiguous  sides  of  the  above- 


THE  FOOT 


1467 


mentioned  toes.  The  sural  nerve  runs  with  the  small  saphenous  vein  below  the 
malleolus,  and  supphes  all  the  lateral  border  of  the  foot  and  the  lateral  side  of 
the  little  toe.  The  saphenous  nerve,  coursing  with  the  great  saphenous  vein  in 
front  of  the  medial  malleolus,  supplies  the  medial  border  of  the  foot  as  far  as  the 
middle  of  the  instep.  The  cutaneous  nerves  to  the  sole  (from  the  medial  calcaneal, 
medial,  and  lateral  plantar)  are  shown  in  fig.  1180. 

Plantar  arteries. — The  line  of  the  medial  would  be  one  drawn  from  the  bifur- 
cation of  the  posterior  tibial,  or  about  midway  between  the  tip  of  the  medial  mal- 
leolus and  the  medial  border  of  the  heel,  to  the  middle  of  the  plantar  surface  of  the 
great  toe.  The  course  of  the  lateral  plantar  runs  in  a  line  drawn  from  the  bifur- 
cation, first  obhquely  across  the  foot  to  a  point  a  little  medial  to  the  medial  side  of 
the  base  of  the  fifth  metatarsal,  and  thence  obliquely  across  the  foot  till  it  reaches 
the  first  space  and  joins  with  a  communicating  branch  from  the  dorsal  artery.  It 
thus  crosses  the  foot  twice.     In  the  first  part,  it  is  more  superficial,  in  the  second 


Fig.  1181. — Longitudinal  Section  of     Foot.     (One-third.)     (Braune.) 

Tendo  AchiUis 
Posterior  tibial  vessels  , 
Talus      and  nerve 

Kavicular 
First  cuneiform 

Extensor  hallucis  longi 


Flexor  hallucis  longus 
Flexor  hallucis  brevis 

Lumbricalis 


Calcaneus 
Abductor  digiti  (juinti 
Lateral  plantar  vessels  and  nerve 
Quadratus  plantse 


Flexor  digitorum  brevis      Flexor  digitorum  communis 
Medial  plantar  nerve 


very  deep ;  it  here  forms  the  plantar  arch,  and  is  only  separated  from  the  bases  of 
the  metatarsals  by  the  interossei. 

The  anastomosing  branches  about  the  ankle-joint  are  shown  in  figs.   1170 
and  1171. 


Tarsal  bones. — The  chief  surgical  points  about  these  is  the  frequency  with  which  they  are 
diseased  and  their  changes  in  taHpes.  Frequency  of  disease. — This  is  explained,  chiefly, 
by  their  delicate  structure  and  the  fact  that  on  the  aspect  in  which  they  are  most  exposed  to 
injury  the  soft  parts  are  scanty.  Disease  once  started,  often  by  slight  injury,  finds  in  the  ter- 
minal circulation  of  the  parts,  and  the  frequent  want  of  rest,  other  contributing  causes.  The 
numerous  and  complicated  synovial  membranes  mentioned  above  explain  the  extension  of  the 
disease.  The  calcaneus  is  the  only  bone  in  which  mischief  is  likely  to  remain  limited.  The 
presence  of  an  epiphysis  to  this  bone  appearing  about  the  age  of  ten  and  joining  at  puberty 
is  to  be  remembered  as  a  starting-point  of  disease  here.  Talipes. — To  take  one  instance,  a  case 
of  talipes  equino-varus,  of  congenital  origin  and  confirmed  degree,  the  following  are  the  chief 
structural  changes  which  should  have  been  obviated  and  now  have  to  be  met,  given  briefly. 
Calcaneus. — This  is  elevated  posteriorly,  and  rotated  so  that  its  long  axis  is  du"ected  obliquely 
medially.  Talus. — The  inclination  of  the  neck  medially  is  much  increased,  and  the  whole  bone 
protruded  from  the  ankle-joint.  According  to  some,  the  neck  is  increased  in  length.  Navicular. 
— This  is  displaced  medially  so  that  it  articulates  with  the  medial  side  of  the  head  of  the  talus, 
and  its  tuberosity  may  form  a  facet  on  the  medial  malleolus.  Cuboid. — The  dorsal  surface  of 
this  is  displaced  downward,  and  bears  much  of  the  pressure  in  wall^ing.  Tendons. — Those 
chiefly  shortened  are  the  tendo  AchiUis  and  those  of  the  tibials  and  flexor  digitorum  longus. 
The  tendo  AchiUis  is  displaced  medially.  Ligaments. — Those  on  the  lateral  side  are  stretched, 
those  on  the  medial,  especially  the  anterior  part  of  the  deltoid,  the  dorsal  talo-navicular  and  the 
plantar  calcaneo-navicular  ligaments  are  shortened.  The  plantar  fascia  is  also  shortened, 
together  with  the  abductor  hallucis,  which  arises  from  it. 


i 


1468  CLINICAL  AND  TOPOGRAPHICAL  ANATOMY      ■ 

ARCHES  OF  THE  FOOT 

These  are  two — the  longitudinal  and  the  transverse. 

(A)  Longitudinal  arch  (fig.  1181). — This  is  by  far  the  most  important.  Ex- 
tent :  From  the  heel  to  the  heads  of  the  metatarsal  bones.  The  toes  do  not  add 
much  to  the  strength  and  elasticity  of  the  foot.  (Humphry.)  They  enlarge  its 
area  and  adapt  it  to  inequalities  of  the  ground,  are  useful  in  climbing,  and  in 
giving  an  impulse  to  the  step  before  the  foot  is  taken  from  the  ground,  in  the  third 
stage  of  walking.  Two  pillars. — The  late  Professor  Humphry  laid  stress  on  the 
important  differences  between  these  two: — (1)  Posterior  pillar:  This  consists  of 
the  calcaneus  and  hinder  part  of  the  talus,  viz.,  only  two  bones  in  order  to  secure 
solidity,  and  to  enable  the  calf-muscles  to  act  directly  upon  the  heel,  without  any 
of  that  loss  of  power  which  would  be  brought  about  by  many  moving  joint-sur- 
faces. (2)  Anterior  pillar:  Here  there  are  many  bones  and  joints  to  provide  (a) 
elastic  springiness,  and  (6)  width.  This  anterior  pillar  may  again  be  divided  into 
two:  (a)  A  medial  pillar,  very  elastic,  consisting  of  the  talus,  navicular,  three 
cuneiforms,  and  three  medial  metatarsals.  (6)  A  lateral,  formed  by  the  cuboids 
and  two  lateral  metatarsals.  This  is  stronger  and  less  elastic,  and  tends  to  but- 
tress up  the  medial  pillar.  Keystone :  This  is  represented  by  the  summit  of  the 
trochlear  surface  of  the  talus. 

It  differs  from  the  keystones  in  ordinary  arches  in  the  following  important  particulars 
(Humphry) :  (a)  in  not  being  wedge-shaped;  (6)  in  not  being  so  placed  as  to  support  and  receive 
support  from  the  two  halves  of  the  arch:  in  front  the  talus  does  fulfil  this  condition  by  fitting 
into  the  navicular;  behind,  it  overlaps  the  calcaneus  without  at  all  supporting  it;  (c)  this  arch 
and  the  support  of  its  keystone  largely  depend  on  ligaments  and  tendons;  (d)  it  is  a  mobile 
keystone :  to  give  it  chances  of  shifting  its  pressure,  and  so  obtaining  rest,  its  equilibrium  is  not 
always  maintained  in  one  position. 

(B)  Transverse  arch  (fig.  1179). — This  is  best  marked  about  the  centre  of  the 
foot,  at  the  instep,  along  the  tarso-metatarsal  joints.  This,  as  well  as  the  longitu- 
dinal arch,  yields  in  walking,  and  so  gives  elasticity  and  spring. 

Uses  of  the  arches. — (1)  They  give  combined  elasticity  and  strength  to  the  tread.  Thus 
they  give  firmness,  free  quickness,  and  dignity,  both  in  standing  and  walking,  instead  of  what 
we  see  in  their  absence,  viz.,  the  lameness  of  an  artificial  limb,  and  the  shufHing  or  hobbhng 
which  goes  with  tight  boots,  deformed  toes,  flat-foot,  bunions,  corns,  etc.;  (2)  they  protect  the 
plantar  vessels,  nerves,  and  muscles;  (3)  they  add  to  man's  height;  (4)  they  make  his  gait  a  per- 
fect combination  of  plantigrade  and  digitigrade,  as  is  seen  in  man's  walking,  when  he  uses  first 
the  heel,  then  all  the  foot,  and  then  the  toes.     (Hiimphry.) 

Maintenance  of  the  arch. — (1)  Plantar  fascia. — -This  is  (a)  a  binding  tie  between  the  pillars 
of  the  longitudinal  arch;  (6)  it  protects  the  structures  beneath;  (c)  it  is  a  self-regulating  ligament 
and  protection.  Thus,  having  a  quantity  of  muscular  tissue  attached  to  its  upper  and  back 
part,  is  constantly  responds  by  the  contraction  of  this,  to  the  amount  of  any  pressure  made  upon 
the  foot.  (2)  Plantar  calcaneo-navicular  ligament. — This  is  a  thick  tie-plate  of  fibro-cartil- 
aginous  tissue,  partly  elastic,  hence  called  the  'spring-ligament,'  attached  to  the  anterior  margin 
of  the  sustentaculum  tali  and  under  surface  of  navicular.  It  is  thickest  at  its  medial  side,  where 
it  blends  with  the  anterior  part  of  the  deltoid  ligament,  and  below,  where  the  tibialis  posterior, 
passing  into  the  sole,  is  in  contact  with  the  ligament  and  gives  much  support  to  the  head  of  the 
talus  and  the  navicular,  while  it  assists  the  power  and  spring  of  this  ligament  {vide  infra).  The 
dropping  of  the  talus  and  navicular  and  their  projection  on  the  medial  side  in  flat-foot  are  largely 
due  to  the  giving  way  of  the  above  ligament.  (3)  Calcaneo-cuboid  ligaments,  (o)  Long; 
(b)  short. — 'These  ligaments  are  the  main  support  of  the  lateral,  firm,  and  less  elastic  part  of  the 
longitudinal  arch.  (4)  Tibialis  posterior. — The  reason  of  this  muscle  having  so  many  insertions 
below  is  to  brace  together  the  tarsal  bones,  and  to  prevent  their  separation  when,  in  treading, 
the  elastic  anterior  pillar  tends  to  widen  out.  Of  these  numerous  offsets,  that  to  the  navicular 
is  the  most  important.  Thus  it  strengthens  the  calcaneo-navicular  ligament  by  blending  with 
it,  and  thus  supports  the  arch  at  a  trying  time.  By  coming  into  action  when  the  heel  is  raised, 
this  tendon  helps  the  calcaneo-navicular  ligament  to  support  the  head  of  the  talus,  and  to  main- 
tain the  arch  of  the  foot  when  the  weight  of  the  body  is  thrown  forward  on^to  the  instep.  In 
other  words,  the  tibialis  posterior  comes  into  play  just  when  the  heaviest  of  its  duties  is  devolving 
upon  this  ligament,  viz.,  when  the  heel  is  being  raised,  and  the  body-weight  is  being  thrown 
over  the  instep  on  to  the  opposite  foot.  (5)  Peroneus  longus. — This  raises  the  lateral  pillar, 
and  steadies  the  lateral  side  of  the  arch.  Further,  by  its  strong  process  attached  to  the  first 
metatarsal  bone,  it  keeps  the  great  toe  strapped  down  firmly  against  the  ground;  thus,  keeping 
down  the  anterior  pillar  of  the  longitudinal  arch,  it  aids  the  firmness  of  the  tread.  (Humphry.) 
(6)  Tibialis  anterior. — This  braces  up  the  keystone  of  the  arch.  Thus,  by  keeping  up  the  first 
cuneiform,  it  maintains  the  navicular,  and  so  indirectly  the  talus  in  situ. 

Fig.  1172  will  remind  the  reader  of  the  arrangement  of  the  superficial  lym- 
phatics of  the  lower  extremity.  These  follow  chiefly  the  saphenous  veins,  and 
enter  the  inguinal  nodes,  except  those  from  the  lateral  aspect  of  the  heel  which 


THE  LOWER  LIMB 


1469 


drain  into  the  popliteal  lymph-nodes  .  The  superficial  lymphatics  of  the  buttock 
enter  the  lateral,  and  those  over  the  adductor  muscles  the  most  medial  group  of 
the  inguinal  glands. 

The  deep  lymphatics  of  the  lower  limb,  comparatively  few  in  number,  follow 
the  course  of  the  deeper  vessels.  After  passing  through  some  four  or  five  glands 
deeply  placed  about  the  popliteal  vessels  (these  glands  also  receive  the  lymphatics 
along  the  small  saphenous  vein),  the  lymph  is  carried  up  by  lymphatics  along  the 
femoral  artery  to  the  deep  inguinal  nodes;  one  very  often  occupies  the  femoral 
canal. 

Fig.  1182  shows  the  distribution  of  the  superficial  nerves  on  both  aspects  of  the 
limb. 


Fig.  1182.- 


-DlSTRIBUTION  OF  CuTANEOUS  NerVES  ON  THE  POSTERIOR  AND  AnTEEIOB  ASPECTS 

OF  THE  Inferior  Extremity. 


Posterior 

branches 

of  lumbar 

nerves 
Posterior 

branclies 

of  sacral 

nerves 
Perforating 

cutaneous  of 

fourth  sacral 
Perineal 

branch  of 

posterior 

cutaneous 
Branch  of 

posterior 

cutaneous 
Obturator 


Branch  of 
femoral 
nerve 


Twigs  from 
saphenous 


Cutaneous 
branch  of 
peroneal 


Superficial 
peroneal 


Deep 
peroneal 


Paralysis  of  the  nerves  of  the  lower  extremity. — Ttie  student  sliould  take  this  opportunity 
of  considering  from  the  surgical  anatomy  the  results  of  paralysis  of  the  nerve  chiefly  affected, 
viz.,  the  great  sciatic  and  its  branches.  Sciatic:  The  limb  hangs  flail-like,  much  in  the  position 
of  one  affected  with  advanced  infantile  paralysis.  In  addition  to  the  results  of  paralysis  of  its 
two  divisions,  flexion  at  the  knee  will  be  lost,  owing  to  paralysis  of  the  hamstrings.  Peroneal 
(external  popliteal)  nerve:  The  extensors  and  psronei  being  paralysed  the  foot  drops,  it  cannot  be 
dorsiflexed  at  the  ankle  nor  abducted  at  the  medio-tarsal  joint.  Adduction  at  the  latter  joint 
is  impaired  owing  to  paralysis  of  the  tibialis  anterior.  The  arch  of  the  foot  is  largely  lost  owing 
to  paralj'sis  of  the  peroneus  longus.  Slight  extension  of  the  two  distal  phalanges  of  the  four 
lateral  toes  is  still  possible  by  means  of  the  interossei.  Sensation  is  impaired  over  the  distribu- 
tion of  the  medial  sural  cutaneous  deep,  and  superficial  peroneal  nerves.  Tibial  (internal 
popliteal)  nerve:  Here  the  calf  muscles,  the  flexors,  and  the  muscles  of  the' sole  of  the  foot  are 
paralysed.     The  ankle  cannot  be  plantar-flexed. 


i 


INDEX 

Bold-face  type  indicates  the  more  complete  descriptions 


Abdomen,  1142 

clinical  anatomy  of,  1370 
landmarks  of,  1370 
lymphatic  nodes  of,  730 
lymphatics  of,  730 
morphology  of,  1144 
muscles  acting  on,  503 
regions,  1142,  1370 
Abdominal  aorta,  690,  1382,  1408 
branches,  591 
aortic  plexus  of  nerves,  1045 
branches  of  vagus,  958 
fossaj,  430 

(inguinal)  rings,  429,  430,  1371,  1394,  1396 
portion  of  ureter,  1248 
wall,  lymphatics  in^  733 
superficial  veins  m,  683 
Abducens,  934 

nucleus  of,  826 
Abduction,  321 

Abductor  acoessorius  digiti  quinti,  499 
digiti  quinti  (foot),  454,  498 

(hand),  404 
hallucis,  496 

longus,  482 
ossis  metatarsi  quinti,  499 
pollicis  brevis,  406,  407 

longus  (extensor  ossis  metacarpi  pollicis), 
392,  393 
Aberrant  artery  of  aorta,  590 

spinal  ganglia,  965 
Abnormalities  (see  individual  organs). 
Aocessorius  ad  fiexorem  digitorem  profundum, 
402 
of  gluteus  minimus,  462 
(ilio-costalis  dorsi),  416 
Accessory  (spinal  accessory)  nerve,  958 
Acervulus  cerebri,  846 
Acetabular  artery,  608 
foramen,  174 
notch,  174 
Acetabulum,  169,  173 
Acoustic  area,  814 

(auditory)  nerve,  949,  1096 

nuclei  of,  823 
meatus  (see  "Auditory  Meatus"), 
(medullary)  strix,  814,  824 
Acromial  branches  of  posterior  circumflex  hu- 
meral artery,  573 
of  thoraco-acromial  artery,  571 
of  transverse  scapular  artery,  565 
(scapular)  e.xtremity  of  clavicle,  141 
Aoromio-clavicular  joint,  251,  1363 
Acromion  angle,  144 

process,  144 
Acromio-thoracio  axis,  671 
Action  of  muscles  (see  corresponding  muscle). 
Adam's  apple,  1211 
Addison's  transpyloric  line,  1153,  1370 
Adduction,  321 

Adductor  brevis,  453,  471,  474 
(Hunter's)  canal,  468,  618,  1441 
digiti  secundi,  498 
hallucis,  454,  496,  498 
longus,  453,  471,  472,  1437 


Adductor  magnus,  453,  471,  474,  1437 

(medial)  group  of  thigh  muscles,  453 

minimus,  474 

pollicis,  407,  408 

tubercle  of  femur,  181 
Adenoids,  naso-pharyngeal,  1130,  1354 
Adipose  body,  pararenal,  1243 

capsule  of  kidney,  1242 

folds  of  pleura,  1237 
Aditus  of  larynx,  1222,  1223 
Adminiculum  lineae  albse,  427 
Adrenals  (see  "Suprarenal  glands"). 
Aeby's  division  of  bronchial  branches,  1232 
Agger  nasi,  88,  1206 

Aggregated  follicles  (Peyer's  patches),  704 
Air-cells,  mastoid,  72 
Air-sacs,  1232 
Ala  of  central  lobule  of  cerebellum,  806 

cinerea  (trigonum  vagi),  814 
nucleus  of,  820 
Alse  of  frontal  bone,  60 

nasi,  1201 
Alar  folds,  291 

(lateral   occipito-odontoid   or   check)   liga- 
ments, 223 

(lower  lateral)  nasal  cartilages,  greater,  1201 
lesser,  1202 

processes  of  ethmoid,  81 
Alcock's  canal,  441,  445,  1384 
Alimentary   tract,   lymphatics   of,    699,    733, 

1168 
Ali-sphenoid  centre,  67,  119 
AUantois,  13,  1253 
Alopecia,  1293 

Alveolar  (dental)  artery,  inferior,  548 
posterior  superior,  549 
anterior  superior,  549 

canals,  87 

ducts,  1232 

(dental)  nerves,  938 
inferior,  941 
superior,  938 

periosteum,  1119 

point,  109 

part  of  mandible,  96 
maxilla,  87,  90 

saccules  (air-sacs),  1153 

veins,  646 
Alveoli  (air-cells),  1232 
Alveus,  877 

of  limbic  lobe,  868,  869 
Amastia,  1301 
Amnion,  9,  10 
Ampulla,  of  ductus  (vas)  deferens,  1257 

lactiferous,  1302 

phrenica,  1142 

recti,  1176 

of  semicircular  canals,  80 

of  tubs  uterinse  (Fallopian  tubes),  1270 

of  Vater,  1188 
Ampullae,  membranous,  1095 

of  splenic  arterioles,  1312 
Ampullar  branches  of  vestibular  ganglion,  950 
Anipullary  crista,  1095 

sulcus,  1095 
Amputation  at  centre  of  the  arm,  1416 

Chopart's  medio-tarsal,  1465 


I 


1472 


INDEX 


Amputation  of  foot,  1465 

of  forearm,  1424 

of  great  toe,  1465 

of  leg,  1459 

Pirogoff's,  1465 

Syme's,  1465 

tarso-metatarsal  (Hey's  or  Lisfranc's),  1465 

through  thigh,  1442 
Amygdala  (tonsil)  of  cerebellum,  807 
Amygdaloid  nucleus,  881 

of  lateral  ventricle,  877 
Amyloid  tubercle  of  lateral  ventricle,  877 
Anal  canal,  1177 

surgical  anatomy  of,  1390 

valves,  1177,  1390 
Anapophysis,  38 
Anastomosis   of   arteries    (see   corresponding 

artery).  , 

Anastomotic  branch  of  facial  nerve,  944 

(perforating)  of  middle  meningeal  arterj', 

548 
ulnar,  of  superficial  radial  nerve,  987 
Anastomotica  magna  artery  (genu  suprema), 

621 
Anatomical  neck  of  humerus,  147 
Anatomy,  definition  of,  1 

of  fourth  ventricle,  812 
Anconeus,  374,  377,  379 

internus,  402 
Andersch,  ganglion  of,  951 
Angle  (s),  acromion,  144 

cephalo-auricular,  1084 

of  fissure  of  Rolando,  860 

infrasternal,  139 

of  Louis,  139 

lumbo-saoral,  43 

of  mandible,  86 

of  maxilla,  88 

of  occipital  bone,  53 

of  parietal  bone,  57,  1332 

of  rib,  127 

sacro-vertebral,  39,  43 

of  scapula,  143 

of  sternum,  133,  139 

subscapular,  145 
Angular  artery,  540 

gyrus,  863 

motion  of  joints,  214 

process,  lateral  (zygomatic),  60 
medial,  60 

vein,  643 
Angulus  Ludovici,  139 
Ankle,  annular  ligaments,  1463 

bony  landmarks  of,  1459 

clinical  anatomy  of,  1459 

synovial  membranes  of  tendons  at,  1463 

tendons  at,  1460 
Ankle-joint,  297 

arterial  supply,  300 

ligaments  of,  298 

movements,  300 

muscles  acting  upon,  301 

nerve-supply,  299 

synovial  membrane  of,  299 
Annular  ligaments  of  ankle,  1463 

of  superior  radio-ulnar  joint,  262 
of  trachea  and  bronchi,  1227 
of  wrist,  387 
Annulus(i)  fibrosi  of  heart,  518 

fibrosus,  318 

inguinalis  abdominalis,  430 
subcutaneous,  430 

iridis  major,  1054 
minor,  1054 

tendineus  communis,  1067 

of  tympanic  membrane,  1087 

urethral,  1253 


Ano-coccygeal  nerves,  1018 
Anomalous  (muscle  of  nose),  335 
Ano-rectal  lymphatic  nodes,  735 
Ansa  hypoglossi,  953,  974,  979 

lenticularis,  880 

subclavia  (ansa  Vieussenii),  1036 
Antagonists  (muscles),  322 
Anthelix,  1082 

Antibrachial  cutaneous  branch  (external),  dor- 
sal, of  radial  nerve,  985 

cutaneous  nerve,  lateral,  987 
(internal)  medial,  984 

interosseous  nerve,  dorsal,  986 

fascia,  384 

vein,  median,  667 
Anti-tragicus,  1084 
Antitrago-helicine  fissure,  1084 
Antitragus,  1082 
Antrum  cardiacum,  1142 

of  Highmore  (maxillary),  87,  90,  111,  1346 

maxOlary,  77,  79,  1274 

pyloric,  of  stomach,  1151 

tympanic  (mastoid),  72,  73,  78,  1092,  1336 
Anus,  1177 

clinical  anatomy  of,  1390 

development  of,  1179 

lymphatics  of,  735 

sphincters  of,  448 
Aorta,  529,  586,  590 

abdominal,  690,  1382,  1408 
branches,  591 

arch  of,  530 

ascending,  529 

descending,  586 

development,  633 

relations  of,  1369,  1382 

semilunar  valves  of,  517 

thoracic,  586,  1369 

variations,  637,  638 
Aortic  arch,  530 

intercostal  arteries,  588 

isthmus,  531 

paraganglia,  1329 

septum,  527 

sinuses  (of  Valsalva),  518,  530 

spindle,  531 
Aortico-renal  ganglion,  1043 
Apertura  pyriformis,  108,  112 
Aperturae  cutis,  1282 
Apertures,  anterior  nasal  (nares),  108,  1200 

of  larynx,  1222 

palpebral,  1052 

of  pelvis,  175,  176 

posterior  nasal  (choanae),  1206 

superior  thoracic,  138,  1365 
Apex  of  arytsenoid  cartilage,  124 

of  fibula,  190 

of  heart,  508 

linguaj,  1106 

of  lung,  1230,  1233 

of  nose,  1200 

of  patella,  185 

of  prostate,  1264,  1389 

of  thyreoid  lobes,  1315 

of  suprarenal  gland,  1326 
Apical  dental  (suspensory)  ligament,  223 
Aphasia,  motor,  894 

sensory,  894 
Aponeuroses,  314,  317 

Aponeurosis  of  epicranius  (occipito-frontalis), 
337 

palmar,  387,  1430 

pharyngeal,  1130 

plantar,  492 
Apophysis  of  femur,  184 
Apparatus,  lacrimal,  1078 

olfactory,  1049 


J 


INDEX 


1473 


Appendages  of  skin,  1290 
cutaneous  glands,  1296 
hair  (pili),  1290 
mammary  glands,  1299 
nails  (ungues),  1293 
Appendices  epiploicae,  1170 

vesiculosi  (hydatids  of  Morgagni),  1269 
Appendicular  artery,  598,  1378 

skeleton,  139 
Appendix  epididymidis,  1257 

testis  (hydatid  of  Morgagni),  1257 
ventricular,  of  larynx,  1223 
vermiform,  1173,  1378 
Aquaeductus  cerebri  (Sylvii),  834 

vestibuli,  72,  80,  117 
Aqueduct  of  Fallopius  (facial  canal),  72 
Aqueous  chambers,  1064 

humor,  1052 
Arachnoid  granulations  (Pacchionian  bodies), 
649,  919 
membrane,  771,  917 
cranial,  918 
spinal,  919 

vessels  and  nerves  of,  920 
Arantius,  ventricle  of,  813 
Arbor  vitK  of  cerebellum,  809 
Arch  of  aorta,  530 
branches  of,  532 
costal,  139 

of  cricoid  cartilage,  1210 
deep  volar,  586,  639,  1426 

venous,  671 
dental,  1123 
digital  venous,  667 
dorsal  venous  (foot),  684 
jugular  venous,  648 
lateral  lumbo-costal,  437 
medial  lumbo-costal,  437 
parieto-occipital,  863 
plantar,  627 
pubic,  176 
superciliary,  59,  108 
superficial  volar,  582,  639,  1425 

venous,  671 
tarsal,  inferior,  554 

superior,  554 
venous,  plantar,  687 
of  vertebrse,  30 
zygomatic,  1332 
Arches,  of  atlas,  32,  33 
branchial,  17 
of  the  foot,  1468 
palatine,  1132 
Architecture  of  heart,  518 
Archoplasm,  5 
Arciform  process,  466 
Arcs,  reflex,  768 

Arcuate  (metatarsal)  artery),  632 
crest  of  arytajnoid  cartilage,  1212 
fibres  of  medulla  oblongata, 
external,  800,  818 
internal,  815,  817 
ligament,  external,  437 
internal,  437 
of  symphysis  pubis,  239 
renal  arteries,  1247 
Arcus  tendineus,  317,  440 

fascise  pelvis  (white  line),  440 
Area(s)  acustica,  814 

association,  of  cerebral  cortex,  894 
auditory  (cochlear),  of  cerebral  cortex,  893 
of  Broca  (area  parolfactoria),  858,  865 
cortical,  of  speech,  894 
dangerous,  of  the  leg,  1457 

of  scalp,  1333 
gustatory,  of  cerebral  cortex,  894 
olfactory,  of  cerebral  cortex,  893 


Area(s),  olfactory,  of  nasal  cavity,  1049 
plumiformis  (of  Retzius),  814 
postrema  of  Retzius,  814 
somsesthetic,  of  cerebral  cortex,  893 
surface,  of  telencephalon,  853 
visual,  of  cerebral  cortex,  893 
Areas,  cutaneous,  of  face,  1018 
of  lower  extremity,  1024 
of  neck,  1019 
of  scalp,  1018 
of  trunk,  1020 
of  upper  limb,  1022 
of  distribution  of  spinal  nerves,  970 
functional,  of  cerebral  cortex,  893 
Areola  of  mammary  gland,  1300,  1304 

secondary,  1304 
Areolar  glands  (of  Montgomery),  1304 
Arm,  centre  of,  as  a  surgical  landmark,  1414 
fasciaj  of,  377 
musculature  of,  362,  374 
veins  of,  667 
Arnold's  bundle,  832,  889 
ganglion,  963 
nerve,  956 
Arrectores  pilorum,  1293 
Arteria  aberrans  of  aorta,  590 
of  superior  intercostal,  568 
centralis  retinae,  553,  1065 
princeps  pollicis,  586 
radialis  indicis,  586 
septi  nasi,  541 
Arterial  supply  of  bones  and  joints  (see  corre- 
sponding bone  or  articulation), 
system,   morphogenesis  and  variations  of, 
633 
ArterioliE  rectae  of  kidney,  1247 
Artery  (see  also  "Blood-vessels"). 
Artery  (ies),  527 
aberrant,  568,  590 
accessory  (small)  meningeal,  548 
pudendal,  610,  639 
renal,  638 
acetabular,  608 

acromio-thoracic  (thoraco-acromial),  571 
angular,  540,  541 
anterior  central  of  medulla,  908 
cerebral,  554,  562 
ciliary,  553,  1065 
circumflex  humeral,  572 
communicating,  555,  562 
conjunctival,  553 
deep  temporal,  548 
ethomidal,  554 
inferior  cerebellar,  561 
intercostal,  588 
interosseous,  of  forearm,  1423 
mediastinal,  567 
perforating,  620 
peroneal,  626,  640,  1459 
scrotal  (or  labial),  620 
spinal,  561,  792,  638 
superior  alveolar  (dental),  549 
tibial,  629,  640,  1458 

recurrent,  632 
tympanic,  547 
aorta,  529,  586,  637,  638 
aortic  intercostals,  588 
appendicular,  598,  1378 
arcuate  (metatarsal),  632 
articular,  of  knee-joint,  622,  1452 
ascending  cervical,  564 
pharyngeal,  537 
palatine,  540 
of  auricle  (of  ear),  1084 
axillary,  569,  1412 
azygos,  of  vagina,  610 
basilar,  561 


1474 


INDEX 


Artery(ies),  brachial,  573,  640,  1414 
of  brain,  555,  905 
bronchial,  588,  638,  1234 
buccal,  548 

of  bulb  of  urethra,  613 
caroticotympanic,  552 
central  or  ganglionic,  906 

of  pons,  908 
of  cerebellum,  907 
of  cerebral  hemorrhage  (Charcot),  562,  906 

peduncles,  907 
chorioid,  554,  908 
ciliary,  553,  1065 
circumflex  (dorsal)  scapular,  572 
of  the  clitoris,  613 
deep,  614 
dorsal,  614 
casliao,  593,  638 
common  carotid,  533 
digital,  582 
iliac,  603 

interosseous,  of  forearm,  577 
coronary,  519 
cortical  cerebral,  906 
costo-cervical  trunk,  568 
cystic,  595 
deep  auricular,  547 
cervical,  568 
circumflex  iliac,  616 
lingual,  540 

plantar  (communicating),  633 
deferential,  610 
descending  palatine,  549 
dorsal  of  foot,  line  of,  1466 
digital  (foot),  633 

(hand),  586 
interosseous  (metatarsal),^633 

of  forearm,  579 
lingual,  539 
metacarpal,  586 
metatarsal  (interosseous),  633 
nasal,  554 

perforating,  of  palm,  586 
radial  carpal,  585 
thoracic  (thoraco-dorsal),  572 
ulnar  carpal,  580 
recurrent,  577 
dorsalis  hallucis,  633 

pedis,  632 
episcleral,  553 

of  external  acoustic  (auditory)  meatus,  1086 
carotid,  536,  1343 
iliac,  614 

maxillary  (facial),  540,  638,  1343;] 
pudendal  (pudic),  619 
spermatic,  615 
striate,  906 'I 
femoral,  616,  1441 
common,  616 
superficial,  616 
fibular  nutrient,  626 
of  the  fraenum,  540 
frontal,  554,  1343 
gastro-duodenal,  594 
genu  suprema  (anastomotica  magna),  621, 

640 
gluteal,  608 
hepatic,  594 

of  humerus,  nutrient,  576 
hypogastric  (internal  iliac),  605,  639 
ilio-colic,  598 
ilio-lumbar,  606 
inferior  alveolar  (dental),  548 
(deep)  epigastric,  614,  639 
gluteal,  609,  639,  1444 
haimorrhoidal,  613 
labial  (coronary),  541 


Artery(ies),  inferior  laryngeal,  564 
lateral  articular,  623 
medial  articular,  622 
mesenteric,  602,  638 
pancreatico-duodenal,  596 
phrenic,  592,  638 
quadrigeminate,  907 
suprarenal,  598 
thyreoid,  564 
tympanic,  537 
ulnar  collateral,  576 
vesical,  609 
infraorbital,  549,  1075 
innominate,  532,  1369 
internal  auditory,  561 
carotid,  549 
mammary,  566 
maxillary,  645,  638 
pudendal  (pudic),  610,!639 
spermatic,  598,  638,  1259 
striate,  906 
intercostals,  588,  638 
interosseous  recurrent,  580 
intestinal,  596 
jejunal  and  iliac,  598 
lacrimal,  552 

lateral  circumflex,  620,^640 
malleolar,  632 
palpebral,  552 
plantar,  627,  640 
posterior  malleolar,  626 
sacral,  607 
tarsal,  632 
thoracic,  571 
left  colic,  603 

common  carotid,  533 

iliac,  605 
coronary,  520 
gastric,  593 
gastro-epiploic,  595 
pulmonary,  529 
subclavian,  556 
superior  suprarenal,*592,il326 
lenticulo-optic,  562 
lenticulo-striate,  562 
of  lig.  teres  uteri,  615 
lingual,  539 

long  posterior  ciliary ,""553,  1065 , 
lowest  lumbar  (ima),  603 
lumbar,  593,  638 
major  palatine,  549 
masseteric,  548 
medial  circumflex,  620,  640 
malleolar,  632 
palpebral,  554 
plantar,  629 
tarsal,  632 
median,  of  forearm,  578,  639 
of  medulla  oblongata,  908 
meningeal,  917 
middle  or  azygos,  623 
cerebral,  555,  562 
colic,  598 
collateral,  576 
hsemorrhoidal,  610 
meningeal,  547,  1341 
quadrigeminate,  907 
sacral,  603 
suprarenal,  598,  638 
temporal,  545 
vesical,  609 
minor  palatine,  649 
musoulo-phrenic,  567 
nutrient  of  femur,  621 
of  humerus,  576 
of  radius  and  ulna,  579 
of  tibia,  626,  1459 


INDEX 


1475 


Artery  (ies),  obturator,  608,  639 
occipital,  642,  638,  1343 
oesophageal,  588 
omphalo-mesenterio,  638 
ophthalmic,  552,  638,  1074 
ovarian,  602 
parietal,  543 
peduncular,  907 
of  penis,  613 
deep,  614 
dorsal,  614 
perforating,  of  the  profunda,  620 
pericardiac  (of  aorta),  588 
pericardio-phrenic,  567 
perineal,  613,  639 
peroneal,  626,  640,  1459 
plantar  digital,  628 

metatarsal,  628 
popUteal,  621,  640,    1452 
posterior  auricular,  543,  1343 
central  of  medulla,  908 
cerebral,  561 
circumflex  humeral,  573 
communicating,  554 
conjunctival,  554 
deep  temporal,  548 
ethmoidal,  553 
inferior  cerebellar,  561 
meningeal,  537 
peroneal,  626 
scapular,  565 
scrotal  (labial),  613 
spinal,  561,  792 
superior  alveolar  (dental),  549 
tibial,  624,  640,1458 
recurrent,  632 
princeps  cervicis,  543 

poUicis,  586 
profunda  or  deep  femoral,  620,  640 
(superior)  profunda  of  arm,  576 
axillaris,  640 
proper  digital,  582 

heptaic,  595 
of  pterygoid  canal  (Vidian),  549 
pulmonary,  528,  1234 
of  quadrigeminate  bodies,  907 
radial,  582,  1423 
collateral,  576 
recurrent,  583 
at  wrist,  584 
radialis  indicis,  586 
renal,  598,  638 
of  retina,  central,  1065 
right  cohc,  598 
common  iliac,  605 
coronary,  519 
gastric,  594 
gastro-epiploic,  595 
pulmonary,  529 
subclavian,  557 
superior  suprarenal,  592 
saphenous,  621 
sciatic,  609,  640 

short  posterior  ciliary,  553,  1066 
sigmoid,  603 
spheno-palatine,  549 
spinal,  590 
splenic,  595 
stapedial,  638 
sternocleidomastoid,  542 
stylo-mastoid,  544 
subclavian,  556,  638 
subcostal,  588 
subungual,  540 
submental,  541 
subscapular,  571 
superficial  cervical,  566 


Artery(ies),  superficial  circumflex  iliac,  618  ' 
epigastric,  618 
temporal,  545,  1343 
superior  cerebellar,  561 
epigastric,  567 
gluteal,  608,  1444 
hajmorrhoidal,  603 
intercostal,  568 
labial  (coronary),  641 
laryngeal,  538 
lateral  articular,  622 
medial  articular,  622 
mesenteric,  696,  638 
pancreatico-duodenal,  595 
phrenic,  590 
quadrigeminate,  907 
thoracic,  570 
thyreoid,  638,  638 
tympanic,  548 
ulnar  collateral,  576 
vesical,  609 
supraorbital,  552,  1343 
suprarenal,  1326 

suprascapular  (transverse  scapular),  564 
sural,  622 
systemic,  529 
temporal,  545,  548,  1343 
testicular,  601 
thoraco-aoromial,  571 
of  thymus,  567 
thyroidea  ima,  533 

transverse  cervical  (transversa  colli),  565. 
638  ''         ' 

facial,  545 
scapular,  564,  638   ' 
of  tympanic  cavity,  1091 
ulnar,  576,  1423 
umbilical,  609 
urethral,  613 
uterine,  610 
vaginal,  610 
variations  of,  637,  639 
vertebral,  559,  638 

of  vertebral  canal,  590 
vesical,  609 
Vidian,  549 

volar  interosseous  of  forearm,  677,  639 
metacarpal,  586 
radial  carpal,  584 
ulnar  carpal,  580 
recurrent,  577 
zygomatico-orbital,  545 
Arthrodial  diarthroses,  212 
Articular  arteries  of  knee-joint,  622,  1452 
branches  of  auriculo-temporal  nerve,  941 
of  common  peroneal  (external  popliteal) 

nerve,  1013 
of  deep  peroneal  (anterior  tibial)  nerve 

1015 
of  genu  suprema  artery,  621 
of  obturator  nerve,  1004 
of  popliteal  artery,  623 
of  posterior  circumflex  humeral  arterv 
573  ^' 

of  profunda  artery,  621 
of  tibial  (internal  popliteal)  nerve,  1010 
of  transverse  scapular  artery,  565 
capsules  of  acromio-olavicular  joint,  251 
of  articulation  of  atlas  with  occiput,  218 
of  atlanto-dental  joint,  222 
of  capitular  articulation,  241 
of  carpo-metacarpal  joint  of  thumb,  273 
of  costo-transverse  articulation,  243 
of  hip-joint,  277 
of  inferior  radio-ulnar  joint,  264 
of  knee-joint,  287 
of  lateral  atlanto-epistrophic  joint,  231 


1476 


INDEX 


Articular  capsules  of  mandibular  articulation, 
215 
of  medial  tarso-metatarsal  articulation, 

308  ^      , 

of  metacarpo-phalangeal  joint  of  thumb, 

275 
of  shoulder-joint,  254 
of  sterno-costo-olavicular  joint,  248 
of  tibio-fibular  union,  295 
of  vertebral  joints,  228 
cartilage,  211 

of  shoulder-joint,  255 
disc  of  aoromio-olavicular  joint,  251 
of  inferior  radio-ulnar  joint,  264 
of  mandibular  articulation,  216 
of  sterno-costo-clavicular  joint,  249 
furrows  of  skin,  1284 
nerve,  recurrent,  of  leg,  1013 
process  of  vertebrae,  31 
processes  of  vertebrae,  ligaments  conneotmg, 

228 
rete,  of  knee,  622 
Articular  tubercle  of  temporal  bone,  71 

veins  of  mandibular  joint,  646 
Articularis  genu  (subcrureus),  470 
Articulation  (s) ,  2 1 1 

acromio-clavicular,  250 
ankle,  297 

of  anterior  parts  of  tarsus,  303 
arycorniculate,  1215 
atlanto-epistrophic,  220,  221 
of  atlas  with  occiput,  218 
of  auditory  ossicles,  1090 
of  bodies  of  vertebrse,  225 
calcaneo-cuboid,  306 
carpal,  268 

carpo-metacarpal,  272 
classification  of,  212 
constituents  of,  211 
costo-capitular,  241 
costo-chondral,  245 
costo-transverse,  243 
costo-vertebral,  241 
crico-arytaenoid,  1214 
crico-thyreoid,  1213 
cuboideo-navicular,  303 
oubo-metatarsal,  308 
ouneo-cuboid,  304 
cuneo-navicular,  304 
elbow,  258 
front  of  thorax,  244 
hip,  276,  1434 
incudo-malleolar,  1090 
incudo-stapedial,  1090 
interchondral,  246 
intercoccygeal,  238 
intercuneiform,  304 
intermetacarpal,  273 
intermetatarsal,  309 
interphalangeal,  of  fingers,  276 

of  toes,  310 
intersternal,  244 
knee,  284 
mandibular,  215 
of  lower  limb,  276 
medio-carpal,  270 

medio-tarsal  (transverse  tarsal)  305 
metacarpo-phalangeal,  274 

of  thumb,  275 
metatarso-phalangeal,  310 
movements  of,  213 
occipito-epistrophic,  223 
of  ossicles  of  ear,  1090 
of  i)elvis,  234 

radio-carpal  (wrist-joint),  265 
radio-ulnar,  261,  1419 
sacro-coccygeal,  237 


Articulation  (s),  sacro-vertebral,  232 
shoulder,  253,  1413 
of  the  skull,  215 

between  skull  and  vertebral  column,  218 
sterno-costal,  245 
sterno-costo-clavicular,      248, 
1363 
synarthrosis,  212 
talo-navicular,  305 
tarsal,  301 

tarso-metatarsal,  307 
tibio-fibular,  295 
transverse  tarsal,  305 
of  the  trunk,  224 
of  upper  extremity,  248 
of  vertebral  column,  225 
Ary-oorniculate  articulation  (synchondrosis), 

1215 
Ary-epiglottic  fold,  1221 

muscle,  1220 
Ary-membranosus  muscle,  1220 
Arytaenoid  cartilages,  1211 
Arytaenoideus  obliquus,  1220 

transversus,  1219 
Ary-vocalis  muscle  of  Ludwig,  1220 
Ascending  aorta,  529 
cervical  artery,  564 
colon,  1173,  1379 
lumbar  veins,  662,  663 
palatine  artery,  541 
pharyngeal  artery,  537 
Association  areas  of  cerebral  cortex,  894 
frontal,  894 
occipito-temporal,  894 
parietal,  894 
fibres  of  spinal  cord,  789 
system  of  cerebral  hemisphere,  890 
Asterion,  101,  1332 
Asternal  ribs,  127 
Astragalus  (talus),  192 
Athelia,  1301 
Atlanto-dental  articular  capsule,  222 

articulation,  220 
Atlanto-epistrophic  articulation,  220 
central,  221 
lateral,  221 
ligaments,  anterior,  221 
posterior,  221 
Atlanto-mastoid  muscle,  422 
Atlanto-occipital  articular  capsule,  218 
articulation,  218 
ligaments,  anterior,  218 
posterior,  218 
Atlas  and  epistropheus,  joints  between,  220 
description,  32 
development  of,  46 
with  occiput,  articulation  of,  218 
Atria  of  heart,  508,  511 

of  lungs,  1232 
Atrial  musculature,  518 
Atrial  plexus,  1041 

Atrio-vetnricular  bundle   (of  His),  517,  519, 
627 
orifice  (ostium  venosum)  of  left  side,  514 
of  right  side,  513 
Atrium  of  heart,  612,  514 

of  middle  nasal  meatus,  1206 
Attachments  and  origin  of  cranial  nerves,  929 
of  spinal  nerves,  964 
topography  of,  966 
Attic  of  middle  ear,  77 
AttoUens  aurem,  337 
Attrahens  aurem,  337 

Auditory   (cochlear)   area  of  cerebral  cortex, 
893 
artery,  internal,  661 
conduction  paths,  900 


INDEX 


1477 


Auditory  foramen,  125 

meatus,  external,  75,  108,  1084,  1332 

internal,  72,  117 
(cochlear)  nen^e,  949,  950 
(Eustachian)  tube,  1092 

pharyngeal  aperture  of,  1130 
veins,  internal,  652,  657 
Auerbach,  plexus  of,  1030,  1046,  1168 
Auricle  (pinna)  of  ear,  1082 

cutaneous  areas  of,  1019 

lymphatics  of,  714 

vessels  and  nerves,  1084 
of  heart,  508 
Auricular  artery,  deep,  547 

posterior,  543,  1343 
branches,    anterior,    of    auriculo-temporal 
nerve,  941 

of  great  auricular  nerve,  973 

of  occipital  artery,  543 

of  posterior  auricular  artery,  544 

of  small  occipital  nerve,  977 

of  superficial  temporal  artery,  545 

of  vagus,  956 
cartilage,  1084 
fissure,  75,  108 
lymph-nodes,  anterior,  709 

posterior,  709 
muscles,  337 
nerve,  great,  978 

posterior,  944 
point,  101 

sulcus,  posterior,  1083 
tubercle  (tubercle  of  Darwin),  1083 
veins,  anterior,  646 

posterior,  647 
Auricularis  anterior  (attrahens  aurem),  337 
posterior  (retrahens  aurem),  337 
superior  (attoUens  aurem),  337 
Auriculo-frontalis  muscle,  337 
Auriculo-temporal  nerve,  941 
Axial  set  of  bones,  27 

skeleton,  27,  29 
Axillary  arch,  374 
artery,  569 

collateral  circulation,  1412 

parts,  569,  570 
fascia,  370,  371 

fossa,  clinical  anatomy  of,  1411 
lymphatic  nodes,  719 
(circumflex)  nerve,  984 
vein,  671 
Axis  (epistropheus),  33,  47 
cceliac,  593 
of  eyeball,  1055 
of  heart,  509 
of  pelvis,  176 
of  scapula,  145 

th}'reoid  (thyreocervical  trunk),  564 
Axones,  762 

motor  (efferent),  764 
sensory  (afferent),  762 
sheaths  of,  766 
of  spinal  cord,  777 
terminations  of,  762 
Azygos  artery  of  vagina,  610 
(major)  vein,  662 
minor  (hemiazygos)  vein,  662 
tertia  (accessory  hemiazygos)  vein,  663 

B 

Back  of  hand,  1433 

clinical  anatomy  of,  1403 

muscles  (spinal),  410 
Baillarger,  stripes  of,  879 
Band,  diagonal,  of  Broca,  866 

ilio-tibial,  457,  458 


Band,  ilio-trochanteric,  280 

moderator,  of  heart,  516 

tendino-trochanteric,  280 
Barba,  1290 
Bars,  hyoid,  119 

mandibular,  119 

metamorphosis  of  branchial  or  visceral,  119 

thyreoid,  119 
Barthohn,  duct  of,  1278,  1892 

glands  of,  1278,  1392 
Basal  ganglia,  878 

vein,  657 
Base  of  arytsenoid  cartilage,  1211 

of  cranium,  103,  113 

of  encephalon,  794 

of  heart,  508 

line,  Reid's,  1341 

of  lungs,  1229,  1233 

of  nose,  1200 

of  prostate,  1264,  1389 

of  skull,  external,  103 

of  suprarenal  gland,  1325 

of  thyreoid  lobes,  1315 
Basi-bregmatic  axis,  112 
Basi-cranial  axis,  112 
Basi-facial  axis,  112 
Basi-hyal,  100,  119 
Basilar  artery,  561 

groove,  54 

plexus  of  veins,  651 

sulcus  of  pons,  804 
Basilic  vein,  667 

median  (median  cubital),  667 
Basion,  108,  112 
Basi-occipital,  119 
Basi-pharyngeal  canal,  63,  67 
Basis  (pes)  pedunculi,  840 

cranii,  interna,  113 
Basi-sphenoid  centre,  67,  119 
Basivertebral  veins,  666 
Bechterew's  bundle,  784 

nucleus  of  vestibular  nerve,  823 
•  Bell,  external  respiratory  nerve  of,  982 
Belly  of  muscle,  314 
Bertin,  bones  of,  67 

columns  of,  1246 
Biceps  brachii,  374,  379,  382 
relations,  1414 

femoris,  453,  475 
Bicipital  groove,  148 

muscles,  314 
Bicuspid  teeth,  1121 

(mitral)  valve,  515,  516 
Bifurcation  of  trachea,  1225 
Bile-duct,  common,  1188,  1373 
Bile-passages,  1186 
Bipenniform  muscles,  315 
Birth,  bones  of  skull  at,  120 
Biventer  cervicis,  418 
Biventral  lobe  of  cerebellum,  807 
Bladder  (urinary),  1249 

surgical  anatomy  of ,f  1390 
Blandin,  glands  of,  1110 
Blood-vascular  system,  507 

of  small  intestine,  1166 

of  spinal  cord,  792 

of  stomach,  1155 
Blood-vessels     (see     also     "Arteries"     and 
"Veins"). 

of  abdominal  wall,  1371 

of  brain,  905 

of  cerebellum,  907 

ciliary,  1065 

of  conjunctiva,  1348 

of  ductus  deferens,  1259 

around  elbow,  1418 

of  eyeball,  1065 


1478 


INDEX 


Blood-vessels  of  eyelids,  1078 

of  face,  1343 

of  Fallopian  tube,  1270 

of  female  external  genitals,  1278 

of  heart,  519 

of  kidney,  1247 

of  large  intestine,  1179 

of  larynx,  1224 

of  lips  and  cheeks,  1104 

of  liver,  1185 

of  lungs,  1234 

of  lymph-glands,  706 

of  mammary  glands,  1305 

of  nose,  1203,  1208 

of  oesophagus,  1141 

of  orbit  1074 

of  ovary,  1269 

of  palate,  1106 

of  parathyreoids,  1319 

of  parotid,  1115 

of  penis,  1262 

of  pericardium,  523 

of  pharynx,  1138 

of  pleura,  1239 

of  prostate  1265 

of  rectum,  1391 

retinal,  1065 

of  scalp,  1334 

of  scrotum,  1255 

of  skin,  1288 

of  spleen,  1312 

of  sublingual  gland,  1117 

of  submaxillary  gland,  1116 

of  suprarenal  glands,  1326 

of  teeth,  1124 

of  testis  and  appendages,  1256 

of  thymus,  1322 

of  thyreoid  gland,  1316 

of  tongue,  1111 

of  trachea  and  bronchi,  1228 

of  ureter,  1249 

of  urinary  bladder,  1253 

of  uterus,  1274 

of  vagina,  1276 

of  vulva,  1192 
Bochdalek,  ganglion  of,  939 
Body(ies)  of  axis  (epistropheus),  33 

carotid,  1327 

ciliary,  1060 

coccygeal,  1329 

of  corpus  callosum,  852 

of  epididymis,  1256 

of  femur,"  178 

of  fornix,  869 

of  gall-bladder,  1187 

geniculate,  834,  845 

of  hyoid  bone,  99 

inferior  quadrigeminate,  839 

of  ischium,  171 

(central  portion)  of  lateral  ventricles,  875 

of  Luys,  884 
mammillary,  871 

of  nails,  1294 

Nissl,  766 

Pacchionian,  919 

of  pancreas,  1195 

pararenal  adipose,  1243 

of  penis,  1260 

pineal,  845 

pituitary,  848,  1352 

of  pubis,  172 

of  radius,  153 

restiform,  810 

of  medulla  oblongata,  800 

of  rib,  127 
of  scapula,  141 
of  sphenoid,  62 


Body(ies)  of  sternum,  133 

of  stomach,  1151 

superior  quadrigeminate,  825,  841 
•  of  sweat  gland,  1297 

of  thymus,  1320 

of  tongue,  1106 

of  ulna,  157 

of  urinary  bladder,  1250 

of  uterus,  1271 

of  vertebra,  30 

vitreous,  1064 

Wolffian,  1278 
Bone(s),  astragalus  (talus),  191,  192 

of  Bertin  (sphenoidal  conchce),  67 

calcaneus,  191,  195 

capitate  (os  magnum),  159,  163 

carpal,  159 

clavicle,  139 

cotyloid,  173 

coxal  (os  innominatum),  169 

cuboid,  191,  199 

cuneiform,  161,  191,  197 

epipteric,  68,  101 

ethmoid,  81 

of  the  face,  51 

femur,  198 

fibula,  189 

fifth  metacarpal,  167 

fifth  metatarsal,  203 

first  metacarpal,  165 

first  metatarsal,  201 

of  foot  as  a  whole,  205 

fourth  metacarpal,  167 

fourth  metatarsal,  203 

frontal,  59 

greater  multangular  (trapezium),  159,  162 

hamate  (unciform),  159,  163 

humerus,  146 

hyoid,  99 

incus,  79,  119 

innominate,  169 

inferior  nasal  concha,  84 

interparietal  (inca  bone),  57 

lacrimal,  85 

lesser  multangular  (trapezoid),  159,  162 

of  limbs,  homology  of,  206 

of  the  lower  extremity,  169 

lunate  (semilunar),  159,  161 

malar,  93 

malleus,  79,  119 

mandible,  95 

maxilla,  87 

metacarpal,  164 

metatarsal,  200 

of  middle  ear,  79 

nasal,  86 

navicular  (scaphoid),  159,  160,  191,  196 

occipital,  51 

of  orbit,  109 

palate,  91 

parietal,  57 

patella,  184 

phalanges,  167,  203 

pisiform,  159,  162 

pre-maxilla,  89 

radius,  152 

ribs,  126 

scapula,  141 

second  metacarpal,  166 

second  metatarsal,  202 

sesamoid,  168,  204,  275,  317 

of  the  skull,  51 
at  birth,  120 
morphology  of,  117 

sphenoid,  62 

stapes,  80,  119 

styloid,  168 


INDEX 


1479 


Bone(s),  suprasternal,  133 
talus  (astragalus),  191,  192 
tarsal,  191 
temporal,  68 
at  birth,  122 
mastoid  portion,  68,  71 
petrous  portion,  68,  72 
squamous  portion,  68,  70 
tympanic  portion,  69,  70,  75 
third  metacarpal,  166 
third  metatarsal,  202 
of  thorax,  126 
tibia,  185 

triquetral  (cuneiform),  159,  161 
turbinate,  67,  83,  84 
of  tympanum,  79 
ulna,  155 

of  upper  extremity,  139 
vomer,  85 
Wormian,  68 
zygomatic,  93 
Bony  boundaries  of  perineum,  1383 
landmarks  of  abdomen,  1370 
of  the  ankle,  1459 
of  the  buttocks,  1442 
of  elbow,  1417 
of  the  foot,  1464 
of  forearm,  1419 
of  head,  1331 
of  the  knee,  1447 
of  the  leg,  1453 
of  the  hip  and  thigh,  1434 
ot  thorax,  1363 
of  wrist  and  hand,  1424 
sinuses  of  skull,  1335 
Borders  (see  individual  organs). 
Boundaries  (see  individual  parts). 
Bowman's  membrane,  1060 
Brachia  conjunctiva  (superior  cerebellar  pe- 
duncles), 831,  840 
Brachial  artery,  573,  640,  1414 
branches,  575 
collateral  circulation,  1414 
(internal)   cutaneous  branch,  posterior,   of 

radial  nerve,  985 
cutaneous  nerve,  lateral,  985 

medial,  983 
fascia,  377 

group  of  axillary  Ivmphatic  nodes,  719 
plexus,  980 
branches,  982 
cords  of,  981 
relations  of,  981,  1360 
terminal  branches  of,  985 
venae  comitantes,  671 
Brachialis,  374,  380,  382 

surface  markings  of,  1415 
Brachio-cephalic  (innominate)  veins,  641 
Brachio-radialis  (supinator  radii  longus),  387, 

388 
Brachium  conjunctivum,  812 
inferior,  834 
superior,  834 
pontis,  811 
Brain  (encephalon),  792 
blood-supply  of,  905 
cerebral  hemispheres,  850 
cerebrum,  833 
cerebellum,  804 
diencephalon  (inter-brain),  843 
isthmus  rhombencephali,  832 
medulla  oblongata,  799 
meninges  of,  908 
mesencephalon  (mid-brain),  833 
pons  (Varoli),  804 
prosencephalon  (fore-brain),  843 
rhombencephalon,  799 


Brain,  telencephalon  (end-brain),  847 

topography  of,  903,  1338 
Branches  (see  corresponding  vessel  or  nerve). 
Branchial  arches,  17 

bars,  metamorphosis  of,  119 
grooves,  17 
Branchiomerism,  16,  17 
Breast,  female  (mammary  gland),  1299 

male,  1305 
Bregma,  101,  112,  1332 
Brim  of  pelvis,  175 
Broad  (lateral)  ligaments  of  uterus  (alse  ves- 

pertilionis),  1267,  1393 
Broca's  area,  858,  865 
convolution,  858 
diagonal  band,  866 
Bronchi,  1226,  1231,  1408 
Bronchial  arteries,  588,  638,  1234 
branches,  Aeby's  division  of,  1232 

of  internal  mammary  artery,  567 
(pulmonary)  branches  of  vagus,  957 
glands,  1231 

lymphatic  nodes,  725,  1225 
tubes,  branching  of,  1231 
veins,  664,  666,  1234 
Bronchioles,  1232 

Broncho-oesophageal  muscle,  1141,  1228 
Bronchus,  eparterial,  1232 

hyparterial,  1232 
Brunner's  glands,  1166 
Bryant's  triangle,  1436 
Buccal  branches  of  cervico-facial  nerve,  945 
artery,  548 
nerve,  long,  939 
veins,  646 
Buccinator,  334 

(long  buccal)  nerve,  939 
set  of  facial  lymph-nodes,  711 
Bulb(s) ,  artery  of,  613 
of  hair,  1292 

of  internal  jugular  vein,  659 
olfactory,  758,  865 

of  posterior  cornu  of  lateral  ventricle,  876 
of  urethra,  1262 
Bulbar  plexus,  1041 
Bulbi  vestibuh,  1277 
Bulbo-cavernosus  443,  450 

in  female  (sphincter  vaginae),  451 
Bulbo-urethral  (Cowper's)  glands,  1265 
Bulbous   corpuscles    (end-bulbs   of   Krause), 

1290 
Bulbus  aortae,  530 
Bulla,  ethmoidal,  84.  Ill,  1205 
Bundle,  Arnold's,  832,  889 
atrio-ventricular  (of  His),  517,  519,  527 
commissural,  788 
Helweg's  (Bechterew's),  784 
posterior  longitudinal,  817 
Tiirk's,  832,  890 
of  Vicq  d'Azyr,  871 
Burdach's  column  of  spinal  cord,  781 
Bursa(Ee)  anguli  mandibuli,  1288 
anserina,  474 
of  anterior  ilio-femoral  musculature,  456 

thigh  muscles,  471 
of  the  arm,  subcutaneous,  377 

muscular,  379,  383 
of  back  of  leg,  486,  491 
bicipito-radialis,  383 
cubitalis  interossea,  383 
of  dorsal  arm  muscles,  379 
epicondyli  medialis  dorsalis,  379 
of  facialis  musculature,  330 
of  foot,  500,  1465 

of  forearm  and  hand,  384,  395,  403 
of  front  muscles  of  leg,  483 
gluteofemorales,  462 


1480 


INDEX 


Bursa(ae),  hyoid,  1217 
iliaca  subtendinea,  457 
iliopeotinea,  456 
of  infra-hyoid  muscles,  353 
infrapatellaris  profunda,  471 

subcutanea,  466 
intermetacarpophalangese,  395 
intermetatarsophalangeae,  500 
intratendinea  olecrani,  379 
ischiadiea  musculi  glutei  maximi,  462 
of  ischio-pubo-femoral  musculature,  464 
of  medial  thigh  muscles,  474 
mucosEe,  313,  318 
subcutaneous,  1288 
subfascial,  318 
submuscular,  318 
subtendinous,  318 
musculi  abductoris  pollicis  longi,  395 
anconei,  379 

bicipitis  femoris  inferior,  476 
superior,  476 
gastrocnemiahs,  476 
coraco-brachialis,  383 
extensoris  carpi  radialis  brevis,  395 
ulnaris,  395 
pollicis  longi,  395 
flexoris  carpi  radialis,  403 

ulnaris,  403 
gastroenemii  lateralis,  486 

medialis,  486 
infraspinati,  370 
latissimi  dorsi,  370 
obturatoris  externi,  464 

interni,  464 
pectinei,  474 
peetoralis  majoris,  374 
piriformis,  462 
quadrati  femoris,  464 
recti  femoris  (inferior),  471 

(superior),  471 
sartorii  propria,  471 
semimembranosus,  476 
sterno-hyoidei,  353 
subscapularis,  370 
supinatoris,  395 
teretis  majoris,  370 
thyreo-hyoidei,  353 
omentalis  (lesser  sac)  1146,  1372 
of  pectoral  muscles,  374 
pharyngeal,  1130 

of  posterior  iho-femoral  musculature,  476 
praepatellaris  subcutanea,  466 
subfascialis,  466 
subtendinea,  471 
prepatellar,  1288,  1448 
of  shoulder  musculature,  369 
sinus  tarsi,  483 
subacromialis,  369 
subcutanea  acromialis,  365 
caloanea,  477 

digitorum  dorsales,  384,  1288 
epicondyli  lateralis,  377 

medialis,  377 
infrapatellaris,  1288 
malleoli  medialis  et  lateralis,  477 
metacarpo-phalangea  dorsalis,  384,  1288 
olecrani,  377,  384 
prementalis,  330 
prominentiiB  laryngse,  330 
sacralis,  1288 
troohanterioa,  1288 
tuberositatis  tibiae,  477 
submammary  (retromammary),  1303 
subtendinea    musculi    extensoris    hallucis 
longi,  483 
olecrani,  379 
supracoracoidea,  370 


Bursa(ae),  suprapatellaris,  471 
synovial,  313,  318 
tendinis  calcanei,  486 

musculi  tibialis  anterioris,  483 
of  ventral  arm  muscles,  383 
Bursa  tendinum  musculi  extensoris  digitorum 
communis,  395 
of  trapezius,  350 

trochanterica  musculi  glutei  maximi,  462 
medii  anterior,  462 

posterior,  462 
minimi,  462 
subcutanea,  457 
Buttocks,  bony  landmarks  of,  1442 
clinical  anatomy  of,  1442 
nerves  of,  1443 


Caecum  (caput  coH),  1170 

cupular,  1096 

topography  of,  1376 

variations  of,  1171 

vestibular,  1096 
Calamus  scriptorius,  812 
Calcaneal  pillar,  205 

Caleanean  branches,  lateral,  of  sural  nerve, 
1013 
of  peroneal  artery,  lateral,  626 
of  posterior  tibial  artery,  medial,  626 

nerves,  medial,  1010 
Caloaneo-cuboid  articulation,  306 

ligaments,  306,  307 
Calcaneo-fibular  ligament,  299 
Calcaneo-metatarsal  ligament    492, 
Calcaneo-navicular  ligament,  lateral,  302,  305 

plantar  (spring),  305 
Calcaneo-plantar  cutaneous  nerves,  1010 
Calcaneus  (os  calcis),  191,  195 
Calcar  avis  (hippocampus  minor),  864,  868 

femorale,  184 
Calcarine  fissure,  864 
Calcification  of  bones,  27 

of  teeth,  1126 
Callosal  convolutions,  868 
Calloso-marginal  fissure,  857,  859 
Calyces  of  kidney,  1246 

of  ureter,  1248 
Camper's  fascia,  425 
Canal(s),  accessory  palatine,  103 

adductor  (Hunter's),  468,  618,  1441 

Alcock's,  441,  445 

alveolar,  87 

anal,  1177 

basi-pharvngeal,  63 

carotid,  73,  108 

central,  of  spinal  cord,  775 

of  cervix,  1272 

ethmoidal,  61,  83,  110,  113,  126 

facial  (Fallopian),  72,  73,  77,  78 

femoral  (crural),  468 

gubernacular,  l06 

of  Huguier,  75,  77,  108 

hyaloid,  1064 

hypoglossal,  117 

inferior  dental,  96 

infra-orbital,  87,  126 

inguinal,  424,  430 

clinical  anatomy  of,  1395 

lateral  semicircular,  78 

mandibular  (inferior  dental),  96,  126 

palatine,  92 

of  Petit,  1064 

pharyngeal,  66,  92,  103 

posterior  palatine,  126 

pterygoid  (Vidian)  canal,  103,  107,  108,  126 

pterygo-palatine,  88,  92,  103 


INDEX 


1481 


Canal (s),  pyloric,  1152 
sacral,  42 
of  Schlemm,  1059 
semicircular,  80,  1092 
zygomatico-facial,  126 
zygomatico-orbital,  94 
Canaliculi,  carotico-tympanic,  74 
Canaliculus  coohlese  (ductus  perilvmphaticus), 
73,  81,  108 
innominatus,  65 
mastoid,  73 
tympanic,  73,  108 
Canalis  musculo-tubarius,  73,  77,'[108 

facialis,  hiatus  of,  116 
Canine  fossa,  87 

teeth,  1120 
Caninus  (levator  anguli  oris),  332 
Capillaries,  lymphatic,  697 
Capilh,  1290 

Capitate  (os  magnum)  bone,  159,  163 
Capitular  (oosto-central)  articulation,  241 

ligaments  of  tibio-fibular  union,  295 
Capitulum  of  humerus,  150 
Capsular  ligament  of  elbow-joint,  258 

(perirenal)  branches  of  renal  arteries,  598 
Capsule,  articular,  acromio-clavicular,  251 
atlanto-dental,  222 
atlanto-epistrophic,  221 
atlanto-occipital,  218 
of  capitular  articulation,  241 
carpo-metacarpal  of  thumb,  273 
costo-transverse,  243 
crico-thyreoid,  1213 
of  hip-joint,  277 
of  knee-joint,  287 
of  mandibular  articulation,  215 
of  medial  tarso-metatarsal  joint,  308 
of  metacarpo-phalangeal  joint  of  thumb, 

275 
of  shoulder-joint,  254 
of  sterno-costo-clavicular  joint,  248 
of  tibio-fibular  union,  295 
of  vertebral  joints,  228 
external  (telencephalon),  881,  888 
Glisson's,  675,  1186 
glomerular,  1246 

internal  (telencephalon),  878,  886 
of  kidney,  1242,  1303 
of  prostate,  1265,  1389 
of  suprarenal  gland,  1326 
Tenon's,  1073 

surgical  importance  of,  1348 
of  thyreoid  gland,  1316 
Caput  angulare  (levator  labii  superioris  alseque 
nasi),  332 
infraorbitale  (levator  labii  superioris),  332 
zygomatioum  (zygomaticus  minor),  332 
Cardia  of  stomach,  1151 
Cardiac  branches  of  vagus,  957 
fossa  of  lungs,  1229 
ganglion  (of  Wrisberg),  1041 
nerve,  inferior,  1037 
middle,  1036 
superior  cervical,  1036 
notch  of  left  lung,  1229 
portion  of  stomach,  1151,  1374 
plexus,  1041 
vein,  anterior,  521 
great,  520 
middle,  520 
small  cardiac,  521 
smallest  cardiac,  521 
Carina  tracheae,  1225 
urethral,  1275,  1278 
Carotico-clinoid  foramen,  65 
Carotico-tympanic  artery,  552 
canaliculi,  74 


Carotieo    branches    from    tympanic    plexus, 

951,  961 
Carotid  arteries,  common,  533 

collateral  circulation,  536,  1360 
external,  533,  536,  1343 
branches,  536 
relations,  536 
internal,  533,  549 
variations,  637 
canal,  73,  108 
gland  (body),  550,  1327 
groove,  64 

nerves,  external,  1036 
internal,  960,  1033 
plexus  of  nerves,  common,  1036  \\ 
external,  1036 
internal,  1033 
ridge,  73 
sheath,  1362  _ 
triangle,  inferior  (tracheal),  1358 

superior,  1358 
(anterior)  wall  of  tympanic  cavity,  1054 
Carpal  arch  (rete),  volar,  581 
artery,  dorsal  radial,  585 
dorsal  ulnar,  580 
volar  radial,  584 
volar  ulnar,  581 
bones,  ossification  of,  164 
head  of  adductor  pollicis,  408 
joints,  268,  269 

(annular)  ligaments  of  wrist,  1427 
rete,  dorsal,  579,  586 
Carpo-metacarpal  joints,  272 

of  the  thumb,  273 
Carpus,  description  of,  159,  270 

ligaments,  384,  387 
Cartilage  (s),  211 
alar,  1201,  1202 
articular,  of  shoulder-joint,  255 
arytenoid,  1211 
auricular,  1084 
corniculate  (Santorini),  1212 
costal,  130 
cricoid,  1210 

cuneiform  (Wrisberg),  1213 
epiglottic,  1212 

interarytasnoid  (procricoid),  1213,  1218 
of  larynx,  1209 
lateral  nasal,  1201 
Meckel's,  98,  119 
nasal,  120 
periotic,  117 
septal  nasal,  1202 
sesamoid  nasal,  1202 

laryngeal,  1213 
sphenotic,  117 
thyreoid,  1210 
tracheal,  1227 
varieties,  211 
vomero-nasal,  1203 
Cartilaginous  plate  (pelvic  joints),  ear-shaped, 

235 
CartUago  triticea,  1217 
Caruncle,  lacrimal,  1052,  1055 

sublingual,  1117 
Carunculte   hymenales    (myrtiformes),    1275, 

1392 
Cauda  equina,  772 

helicis,  1084 
Caudate  branch  of  middle  cerebral  artery,  562 
(Spigelian)  lobe  of  liver,  1184 
nucleus,  877,  879 
process  of  liver,  1184 
Cavernous  nerves  of  clitoris,  1047 
of  penis,  1047 
plexus  of  nasal  conchse,  1208 
of  nerves,  1033 


1482 


INDEX 


Cavernous   (spongy)  portion  of  male  urethra, 

1264,  1388 
sinus,  652,  691 
Caves,  Meckel's,  916 
Cavity,  body,  14 
epidural,  911 
glenoid,  of  scapula,  143 
of  larynx,  1220 
lesser  sigmoid,  of  ulna,  157 
mediastinal,  1239 
nasal,  1203 
oral,  1100 
of  orbit,  1066 
pelvic,  175 
pericardial,  522 
pleural,  1236 
of  radius,  sigmoid,  154 
subarachnoid,  918 
subdural,  912 
thoracic,  1235 
of  tooth,  1118 
tympanic,  77,  1088 
of  ulna,  greater  sigmoid,  156 
of  uterus,  1271 
Cavum  conchas,  1082 

pelvis  subperitoneale,  448 
Retzii,  1250,  1371 
Cellifugal  processes  of  neurone,  762 
Cellipetal  processes  of  neurone,  762 
Cells,  4 

chromaffin,  1323 
ependymal,  768 
ethmoidal,  83,  84,  111,  1207 
Golgi,  in  cerebellum,  809 
gustatory,  1050 
olfactory,  1051 
mastoid,  1092,  1336 
of  Purkinje,  809 
stellate,  809 
Cementum  of  teeth,  1119 
Central  (ganglionic)  arteries  of  cerebrum,  906 

of  medulla  oblongata,  908 
branches  of  cerebral  arteries,  562,  563 
canal  of  spinal  cord,  775 
connections  of  cranial  nerves,  818 

of  abducens,  934 

of  cochlear,  824 

of  facial  nerve,  825,  946 

of  glosso-palatine,  825,  947 

of  glosso-phar\ns<"il,  820,  952 

of  hypoglossal,  820,  '.).") 4 

of  masticator,  829,  94-_' 

of  oculo-motor,  838,  933 

of  olfactory,  873,  929 

of  optic,  848,  931 

of  spinal  accessory,  820,  959 

of  trigeminus,  826,  935 

of  trochlear,  837,  934 

of  vagus,  820,  958 

of  vestibular,  823,  950 
gyrus,  anterior  (ascending  frontal  convolu- 
tion), 857 

posterior  (ascending  parietal),  861 
lobe  or  insula,  856 
lobule  of  cerebellum,  806 
nervous  system,  751 
point  of  perineum,  1385 
sulcus  (fissure  of  Rolando),  859,  1340 

angle  of,  860 

inferior  genu.  860 

in  foetus,  860 

of  insula,  857 

superior  genu,  860 
tendon  of  perineum,  449 
veins  of  retina,  659 
Centres,  association,  of  cerebral  cortex,  894 
Centrum  semiovale,  886 


Centrum  (body)  of  vertebrse,  30 
Cephalic  index,  117 
plexus,  gangliated,  959 
portion  of  sympathetic  trunk,  1033 
vein,  667,  671 
Cephalo-auricular  angle,  1084 
Cerato-cricoid  ligaments,  1213 

muscle,  1218 
Cerato-hyal  center,  100 

segment,  119 
Cerebellar  artery,  anterior  inferior,  561,  907 
posterior  inferior,  561,  907 
superior,  561,  907 
notches,  805,  915 
peduncle,  inferior,  810 

superior,  812,  831 
tract,  direct,  of  Flechsig,  784 
veins,  657 
Cerebello-olivary  fibres,  817 
Cerebellum  (hind  brain),  804 
ala  of  central  lobule,  806 
anterior  medullary  velum  of,  812 
arbor  vitse  of,  809 
biventral  lobe,  807 
blood-vessels  of,  907 
brachium  pontis,  811 
conjunctivum,  812 
central  lobule  of,  806 
conduction  paths  of,  899 
cortex  of,  809 
culmen  of,  806 
declive  (clivus),  806 
dentate  nucleus  of,  810 
external  features,  808 
fissures,  805 
flocculus,  807 

peduncle  of,  807 
folium  vermis  (cacuminis),  806 
fourth  ventricle,  anatomy  of,  812 
functions  of,  832 
gross  divisions  of,  805 
hemispheres  of,  805 
inferior  vermis,  808 
internal  structure  of,  808 
lingula  of,  806 
lobes  and  lobules,  805 
montioulus,  806 
nodule  of  inferior  vermis,  808 
notch  of,  805 
nuclei  of,  809,  810 
peduncles  of,  810 
posterior  medullary  velum,  808 
pyramid  of  vermis,  808 
sulci  of,  805 
superior  vermis  of,  806 
tentorium  of,  804 
tonsil  (amygdala)  of,  807 
tuber  vermis,  808 
uvula  of  vermis,  808 
vallecula  of,  807 
veins  of,  908 
vermis  of,  805,  807 
Cerebral  arteries,  anterior,  554,  562 
branches,  562 
middle,  556,  562 
posterior,  561,  562 
commissure,  anterior,  871 

inferior,  842,  890 
cortex,  879 

cornu  ammonis,  879 
functional  areas  of,  893 
structure  of,  879 
hemispheres,  850 

caudate  nucleus,  877 
corpus  striatum,  868,  879 
cortex  of,  852,  879,  893 
gyri  of,  852 


INDEX 


1483 


Cerebral  hemispheres,  lateral  ventricle,  873 
lobes  of,  853 

central  (insula),  856 
frontal,  857 
occipital,  863 
parietal,  860 
temporal,  854 
rhinencephalon,  864 
sulci  of,  852 
path  for  cranial  nerves,  895 
peduncles  (crura),  833,  835 

arteries  of,  907 
veins,  644,  657 

central  or  deep  (ganglionic),  655 
great  (of  Galen),  657 
inferior,  655 
internal,  657 
middle,  655 
superior,  654 
Cerebro-spinal  fasciculus,  lateral,  783 
ventral,  788 
fluid,  920,  1342 
path,  895 
Cerebrum,  833 
mesencephalon  (mid-brain),  833 
prosencephalon  (fore-brain),  843 
diencephalon  (inter-brain),  843 
telencephalon  (end-brain),  847 
Cerumen,  1085,  1298 
Ceruminous  glands,  1085,  1297 
Cervical  artery,  ascending,  564 
deep,  668 
superficial,  566 
transverse,  565 
branches  of  uterine  artery,  610 
chains  of  lymphatic  nodes,  deep,  714 
enlargement  of  spinal  cord,  772 
fascia,  external,  347 

middle,  350 
ganglion  of  sympathetic,  inferior,  1036 
middle,  1036 
superior,  960,  1035 
loop  (ansa  hypoglossi),  953,  974 
muscle,  330 
nerves,  971,  974 

anterior  primary  divisions,  974 
posterior  primary  divisions,  971 
plexus,  974 

ascending  branches  of,  977 
deep  branches  of,  978 
descending  branches  of,  978 
posterior,  of  Cruveilhier,  971 
superficial  branches  of,  977 
supra-clavicular  branches  of,  978 
transverse  branch,  978 
portion  of  external  maxillary  artery,  540 
of  internal  carotid  artery,  550 
of  sympathetic  trunk,  1033 

construction  of,  1037 
of  vertebral  artery,  559 
ribs,  131,  1365 
triangles,  1357 
vein,  deep,  661 
veins,  transverse,  672 
vertebra;,  description  of,  31 
development  of,  47 
Cervicalis  ascendens,  416 
Cervico-facial  nerve,  945 
Cervix  of  uterus,  1271 
Chains  of  nerurones,  768 
Chambers  of  the  eye,  1064 
Charcot's  artery  of  cerebral  hemorrhage,  562, 

906 
Check  (alar)  ligaments,  223 

of  eyeball,  1072 
Cheek,  1103 
Chiasma,  optic,  848,  849 


Choanaj    (posterior   nares),    107,    112,    1130, 

1206,  1351 
Chondro-cranium,  117 
Chondro-humeralis  (epitrochlearis),  374 
Chondro-glossus,  346 
Chopart's  medio-tarsal  amputation,  1465 
Chorda  tympani  nerve,  826,  946,  948 
Chorda  tendinse,  515 
Chords  of  Willis,  649 
Chorio-capillaris,  1055 
Chorioid,  1057,  1060 
artery,  554,  908 

branches  of  posterior  cerebral  artery,  563 
fissure,  868 
glomus,  876 
plexus  of  fourth  ventricle,  922 

of  lateral  ventricle,  875,  877,  924 
tela  of  fourth  ventricle,  758,  812 

of  third  ventricle,  923 
vein,  657 
Chorioidal  arteries  of  medulla  oblongata,  908 
fissure,  1080 

lamina,  epithelial,  876,  924 
membrane,  1052 
Chorion,  10 

Chromaffin  bodies,  1329 
cells,  1323 
system,  1323 
Chromatin,  5 
Cilia,  1290 

Ciliary  arteries,  anterior,  1065 
long  posterior,  1065 
short  posterior,  1065 
body,  1060 
ganglion,  961,  1076 
branches,  961 
roots,  932,  937,  961,  1033 
glands  (glands  of  Moll),  1078,  1297 
muscle,  1057,  1060 
nerves  of  eyeball,  1064,  1076 
long,  937 
short,  961,  1076 
processes,  1057 
veins,  658 
Cingulum,  867,  890 

of  teeth,  1120,  1121 
Circle  of  Willis  (circulus  arteriosus),  555 
Circular  sinus,  651 

sulcus  (limiting  sulcus  of  Reil),  857 
Circulation,  collateral,  of  axillary  artery,  1412 
of  brachial  artery,  1414 
of  common  carotid  artery,  1360 

iliac  arteries,  1382 
of  external  iliac  artery,  1382 
of  femoral  artery,  1441 
of  internal  iliac  artery,  1382 
of  popliteal  artery,  1453 
of  subclavian  artery,  1360 
fcEtal,  695 
pulmonary,  507 
systemic,  507 
Circulus  arteriosus  major,  1065 
minor,  1065 
tonsillaris,  952 
Circumanal  glands,  1297 
Circumduction,  215 
Circumferential  cartilage,  211 
Circumflex  artery,  lateral,  620,  640 
medial,  620,"  640 
femora!  veins,  690 
humeral  artery,  anterior,  572 

posterior,  573 
iliac  arterj',  deep,  616 
superficial,  618 
vein,  deep,  683 
superficial,  684 
nerve,  985 


1484 


INDEX 


Circumflex  (dorsal)  scapular  artery,  572 

veins,  671 
Circumvallate  papillae  of  tongue,  1106 
Cisterna  basalis,  918 

cerebello-medullaris  (cisterna  magna),  919 
chyli,  726 
pontis,  918 
subarachnoid,  918 
superior,  919 
Clarke's  column  of  spinal  cord,  776 
Classification  of  articulations,  212 

of  muscles,  319 
Claustrum,  880 
Clava,  801 

Clavicle,  139,  1357,  1410 
ossification  of,  141 
structure  of,  141 
Clavicular  branch  of  thoraco-aoromial  artery, 

571 
Cleft,  middle  ear,  77 
palate,  1106,  1352 
Clinical  and  topographical  anatomy,  1331 
of  abdomen,  1370 
of  back,  1403 
of  head,  1331 
of  lower  extremity,  1434 
of  neck,  1354 
of  pelvis,  1382 
of  thorax,  1363 
of  upper  extremity,  1409 
Clinoid  process,  anterior,  65,  116 
middle,  65,  116 
posterior,  63,  116 
Clitoris,  1277 
artery  of,  613 
cavernous  nerves  of,  1047 
deep  artery  of,  614 
dorsal  artery  of,  614 

vein  of,  1018 
lymphatics  of,  745 
Clivus,  117 

Cloaca,  1179,  1253,  1278 
Clunial  (gluteal)  branches,  inferior,  of  poste- 
rior femoral  cutaneous  nerve,  1007 
nerve,  inferior  medial   (perforating  cutan- 
eous), 1007 
middle,  973 
superior,  973 
Coats  of  the  eyeball,  1058 
Coccygeal  body,  1329 
cornua,  43 
foveola,  1284 
ganglion,  1040 
ligament,  911 
nerves,  973 

posterior  primary  division  of,  973 
rudimentary,  964 
plexus,  1018 
vertebras,  42 

development  of,  49 
Coccygeus,  440,  448 
Coccyx,  30,  42 

muscles  of,  448 
Cochlea,  81,  1092 
Cochlear  area  of  cerebral  cortex,  893 

duct  (membranous  cochlea,  or  scala  media), 

1090 
fenestra,  1089 
nerve,  824 
nuclei  of,  824 
Cochleariform  process,  1089 
Coeliac  artery  (axis),  593,  638 
branches  of  vagus,  958 
(semilunar)  ganglia,  1043 
lymphatic  nodes,  730 
plexus  of  nerves,  1043 
Coelom,  14 


Colic,  artery,  left,  603 
middle',  598 
right,  598 
flexures,  1173,  1379 
(basal)  surface  of  spleen,  1310 
veins,  677,  678 
Collateral  artery,  inferior  ulnar,  576 
middle,  576 
radial,  576 
superior  ulnar,  576 
branch  of  intercostal  arteries,  588 
circulation  of  axillary  artery,  1412 
of  brachial  artery,  1414 
of  common  carotid  artery,  536,  1360 

iliac  arteries,  605,  1382 
of  external  iliac  artery,  1382 
of  femoral  artery,  1441 
of  internal  iliac  artery,  1382 
of  popliteal  artery,  1453 
of  subclavian  artery,  1360 
eminence,  868,  877 
fissure,  864 

trigone  of  lateral  ventricle,  876 
Collecting  renal  tubule,  1246 
Colles'  fascia,  445 

fracture,  1420 
CoUiouli,  inferior,  834,  839 

superior,  841 
Colliculus  of  arytaenoid,  1212 
facialis,  815 

seminalis  (verumontanum),  1263,  1389 
Colloid  of  thvreoid  gland,  1316 
Colon,  ascending,  1173,  1378 
descending,  1174,  1379 
iliac,  1174 
pelvic,  1174,  1379 
sigmoid,  1174,  1379 
transverse,  1174,  1379 
Colostrum,  1303 

Column  anterior  of  spinal  cord,  786 
Burdach's,  781 
Clarke's,  776 
GoU's,  781 

lateral  of  spinal  cord,  782. 
posterior  of  spinal  cord,  780 
vertebral,  29,  43 
Columna  rugarum,  1275 
Columns,  anterior,  of  fornix,  870 
rectal  (of  Morgagni),  1177,  1390 
renal  (of  Bertin),  1246 
Comedo,  1298 

Comma-shaped  fasciculus,  782 
Commissural  branches  of  sympathetic,  1032 
bundle,  788 

fibres  of  white  substance  of  spinal  cord,  779 
system  of  fibres,  of  telencephalon,  890 
Commissure,  769 

anterior  cerebral,  848,  871,  890 

grey,  of  spinal  cord,  775 

habenular,  872,  885,  890 

hippocampal,  869,  890 

inferior  cerebral  (Gudden's),  842,  850,  890 

middle  cerebral,  844 

optic,  849 

posterior,  of  cerebrum,  835,  890 

of  vulva,  1276 
supramammillary,  871,  '890 
white,  of  spinal  cord,  776 
Common  bile-duct  (ductus  choledochus),  1188 
carotid  artery,  533 
branches,  536 

collateral  circulation,  536,  1360 
in  the  neck,  533 
relations,  533,  534,  1369 
thoracic  portion  of  left,  533 
digital  arteries,  582 
veins  (foot),  684 


INDEX 


1485 


Common  digital  veins,  volar,  671 
facial  vein,  644,  646 
femoral  artery,  616 
iliac  arteries,  603,  605 

collateral  circulation,  605 
veins,  679 

interosseous  artery  of  forearm,  570 
Communicans  cervicalis,  974 

fibularis,  1013 
Communicating  artery,  anterior,  555,  562 

posterior,  554 
Comparative  anatomy  of  large  intestine,  1180 
of  lips  and  cheeks,  1104 
of  liver  and  gall-bladder,  1 192 
of  palate,  1106 
of  pancreas,  1197 
of  peritoneum,  1151 
of  salivary  glands,  1117 
of  stomach,  1160 
of  teeth,  1127 
of  tongue,  1112 
of  tonsOs,  1138 
Compartments  under  inguinal  ligament,  1399 
Complexus,  412,  417 
Compound  bones,  27 
Compressor  bulbi  proprius,  450 
hemisphserium  bulbi,  451 
venae  dorsalis,  451 
Conarium,  845 
Concha,  1082 

eminence  of,  1083 
Concha;,  nasal,  83,  84,  1205 

sphenoidal,  64,  67 
Conchal  (inferior  tiarbinate)  crest,  88,  92 
Conduction  paths,  auditory,  900 
involving  cerebellum,  899 
of  nervous  system,  summary  of,  895 
methods  of  determining,  779 
of  olfactory  apparatus,  902 
of  optic  apparatus,  900 
vestibular,  899 
Condylar  foramen  (canal),  54 
fossa,  54,  108 

process  of  mandible,  96,  97 
tubercle  of  mandible,  97 
Condylarthroses,  213 
Condyles,  29 
of  femur,  182 
of  femur  and  tibia,  1447 
of  mandible,  97 
of  occipital  bone,  54,  108 
third  occipital,  56 
of  tibia,  185 
Condyloid  emissary  veins,  652 
Cone,  elastic,  of  larynx,  1215 
Conical  papillte  of  tongue,  1106 
Conjoined   tendon   of  internal  oblique   and 

transversalis,  435 
Conjugate  diameter  of  pelvic  inlet,  175 
Conjunctiva,  1054,  1347 
lymphatics  of,  698,  712 
ocular,  1054 
palpebral,  1054 
Conjunctival  arteries,  anterior,  553 
posterior,  554 
sac,  1054 

semilunar  fold  of,  1055 
veins,  658 
Connecting  fibro-cartilage,  211 
Connections,  central,  of  cranial  nerves,  818 
(for  individual  nerves,  see  "Central  con- 
nections"), 
cortical,  of  thalamus,  883 
of  nuclei  of  corpus  striatum,  880 
Conoid  ligament,  251 

tubercle,  140 
Constituents  of  articulations,  211 


Constrictor  laryngis,  1218 
radicis  penis,  450 
vaginEe,  449 
Constrictors  of  pharynx,  1137 
Construction  of  nervous  system,  762 
Conus  arteriosus,  516 

meduUaris,  771 
Convoluted  renal  tubules,  1246 
Convolutions,  cerebral,  852 
Cooper's  ligament,  1400 
Coraco-acromial  hgament,  252 
Coraco-brachialis,  374,  379,  381 
Coraco-clavicular  union,  251 
arterial  supply,  251 
ligaments,  251 
movements,  252 
nerve-supply,  251 
(costo-coracoid)  fascia,  371 
Coraco-humeral  ligament,  255 
Coracoid    (suprascapular  or   superior   trans- 
verse) ligament,  253 
process  of  scapula,  144 
(conoid)  tubercle,  140 
Cord,  oblique,  262 
spermatic,  1259,  1387 
spinal,  751,  771 

clinical  anatomy,  1408 
external  morphology  of,  771 
internal  structure  of,  775 
Cords  of  brachial  plexus,  917 
ganghated,  neurones  of,  755 
vocal  (gee  "Vocal  folds"). 
Corium,  1286 

Cornea,  1052,  1054,  1056,  1069,  1065 
Comiculate  cartilages  (of  Santorini),  1212 

tubercle  (of  Santorini)  of  larynx,  1221 
Corniculo-pharyngeal  ligament,  1218 
Cornu  ammonis,  868,  879 
Cornua  of  fascia  lata,  467 

of  fossa  ovalis  (saphenous  opening),  467 
of  hyoid  bone,  99,  100 
of  lateral  ventricles,  873,  874,  876 
of  sacrum,  40 
of  thyreoid  cartilage,  1211 
Cornucopise,  923 
Corona  cilaris,  1060 
glandis,  1260 
iridis,  1054 
radiata,  887 

ocoipito-thalamic  (optic)  radiation  of,  888 
Coronal  suture,  57,  101,  1339 
Coronary  arteries,  519 
ligaments  of  knee-joint,  290 

of  liver,  1184 
plexuses  of  nerves,  1041 
sinus,  521 

valve  (of  Thebesius)  of,  512 
sulcus  of  heart,  510 
(gastric)  vein,  675 
veins,  520 
Coronoid  fossa  of  humerus,  150 
process  of  mandible,  97,  1351 
of  ulna,  156 
Corpora  albicantia,  844,  1269 
cavernosa  of  clitoris,  1277 

penis,  1260 
mammillaria  (albicantia),  844 
quadrigemina,  834 
quadrigemina-thalamus  path,  786 
Corpus  adiposum  buocse,  1103,  1104 
callosum,  851 
body  of,  852 
forceps  major,  890 

minor,  890 
genu,  851 
peduncle  of,  866 
radiation  of,  851,  890 


1486 


INDEX 


Corpus  callosum,  rostral  lamina  of,  852 
rostrum  of,  852 
spleuium  of,  852 
striffi  of,  851 
sulcus  of,  867 
cavernosum  urethras  (corpus  spongiosum), 

1261 
Highmori,  1256 
mammae,  1302 
papillare  of  skin,  1286 
spongiosum  (cavernosum  urethrae),  1261 
striatum,  879 

caudate  nucleus  of,  879 
connections  of  nuclei  of,  880 
internal  capsule  of,  886 
lenticular  nucleus  of,  879 
trapezoideum,  824 
Corpuscles,  bulbous  (of  Krause),  1290 
genital,  1290 
colostrum,  1303 

concentric  (Hassal's)  of  thymus,  1321,  1322 
Golgi-Mazzoni,  1290 
lamellous  (Vater-Paoinian),  1290 
renal  (Malpighian),  1246 
Ruffini,  1290 
salivary,  1132 
splenic  (Malpighian),  1311 
tactile  (Meissner),  1290 
Corrugator  cutis  ani,  445 

muscle,  336 
Cortex,  cerebellar,  809 
cerebral,  879 

functional  areas  of,  893 
of  kidney,  1246 
of  lens  of  eye,  1062 
of  suprarenal  gland,  1326 
of  thymus,  1321 
Corti,  organ  of,  1096 

Cortical  branches  of  cerebral  arteries,  562,  563 
(superficial)  cerebral  veins,  654 
connections  of  thalamus,  883 
Cortico-pontine  fibres,  811 
Costal  arch,  139 

branch,  lateral,  of  internal  mammary  ar- 
tery, 567 
cartilages,  130 
Costal  groove,  127 
pleura,  1237 
processes,  38 

tuberosity  of  clavicle,  140 
Costo-axUlary  veins,  671 
Costo-central  (capitular)  articulation,  241 

ligaments,  241 
Costo-cervical  arterial  trunk,  568 
Costo-ohondral  joints,  245 
Costo-clavicular  (rhomboid)  ligament,  249 
Costo-eoracoid  fascia,  371 

ligament,  371 
Costo-coracoideus,  374 
Costo-mediastinal  sinus,  1238 
Costo-transverse  articulations,  243 
arterial  supply,  244 
ligaments  of,  243 
middle  (neck),  243 
posterior  (tubercular),  243 
superior,  243 
movements,  244 
nerve-supply,  244 
foramen,  32,  127 
of  atlas,  33 
Costo-xiphoid  ligament,  244,  245 
Costo-vertebral  articulations,  241 

groove,  138 
Cotunnius,  nerve  of,  962 
Cotyloid  bone,  173 
fibro-cartilage,  281 
fossa,  169 


Cowper's  (cremasteric)  fascia,  426,  434,  1254 

glands,  1265 
Coxal  bone  (os  innominatum),  169 

ossification  of,  174 
Cranial  arachnoid,  918 
cavity,  floor  of,  112 

relations  of  brain  to  walls  of,  903 
dura  mater,  913 
fossa,  anterior,  113 

middle,  116 

posterior,  116 

surgical  anatomy  of,  1342 
nerves,  927 

abducens,  934 

central  connections  of,  818 

cochlear,  950 

facial,  943 

glosso-palatine,  946 

glosso-pharyngeal,  951 

hypoglossal,  952 

masticator,  942 

oculo-motor,  931 

olfactory,  929 

optic,  930 

paths  of,  cerebral,  895 
short  reflex,  898 

spinal  accessory,  958 

superficial  attachments  of,  929 

terminal,  929 

trigeminus,  934 

trochlear,  933 

vagus,  954 

vestibular,  949 
pia  mater,  922 
subdural  cavity,  917 
venous  lacunae,  649 

sinuses,  649,  692,  916 
Cranio-cerebral  topography,  903,  1338 
Cranio-mandibular    musculature,    325,    338, 

341 
Cranium,  51 

clinical  anatomy  of,  1333 
measurements  of,  117 
remnants  of  cartilaginous,  124 
Cremaster,  423,  434,  1254 
external,  1259 
internal,  1254,  1259 
Cremasteric  branches  of  internal  spermatic 

arteries,  501 
fascia    (external    spermatic,    or    Cowper's 
fascia),  426,  434,  1254 
Crest(s),  29 

arcuate,  of  arytaenoid  cartilage,  1212 

conchal,  88,  92 

ethmoidal,  92 

external  occipital,  52 

of  fibula,  190 

frontal,  60 

of  greater  tuberosity  of  humerus,  148 

of  Uium,  169 

incisor,  90 

inferior  turbinate,  92 

internal  occipital,  53 

interosseous,  of  radius,  153 

of  ulna,  157 
intertrochanteric,  178 
lacrimal,  posterior,  85 
nasal,  90 
neural,  754 
obturator,  173 
of  scapula,  144 
sphenoidal,  63 
superior  turbinate,  92 
of  tibia,  anterior,  188 
transverse,  72 
Cribriform  lamina,  119 
plate  of  ethmoid,  81 


INDEX 


1487 


Crico-arytaenoid  articulation,  1214 

ligament,  1214 
Crico-arytaenoideus  lateralis,  1219 

posterior,  1218 
Cricoid  cartilage,  1210 
Crico-pharyngeal  ligament,  1218 
Crico-thyreoid  articulation,   1213 
ligament,  1215 
muscles,  1218 
Crico-tracheal  ligament,  1218 
Crista,  ampullary,  950,  1095 
galli,  81,  113 

supraventricularis,  516,  527 
terminalis,  513 
urethralis,  1263 
vestibuli,  80 
Crista}  of  matrix  unguis,  1295 

of  skin,  1284 
Crossed  pyramidal  tract,  783 
Crown  of  tooth,  1117 
Crucial  anastomosis,  620 

ligament  of  atlanto-epistrophic  joint,  222 
ligaments  of  knee-joint,  288 
Cruciate  ligament  of  leg  (lower  part  of  anterior 
annular  ligament),  479 
of  fingers,  387 
Crura  of  anthelix,  1083, 
of  cerebrum,  833,  835 
clitoridis,  1277 
of  diaphragm,  437 
of  fornix,  868 

of  greater  alar  nasal  cartilages,  1202 
of  penis,  1261 
of  stapes,  80 
Crural  canal,  468 
fascia,  477 
nerve,  anterior,  1001 
interosseous  1010 
Crureus,  468,  470 
Cruro-pedal  muscles,  486 
Crus  of  helix,  1082,  1083 
Cruveilhier,  posterior  cervical  plexus  of,  971 
Cryptorohism,  1257 
Crypts  of  iris,  1054 

of  Lieberktihn,  1166,  1177,  1390 
of  lingual  tonsil,  1107 
of  palatine  tonsil,  1132 
Crystalline  lens  of  eye,  1052,  1057,  1061 
Cubital   lymphatic   node,  superficial    (supra- 
trochlear), 719 
Cuboid,  191,  199 
Cuboideo-navicular  ligaments,  303  ' 

union,  303 
Cubo-metatarsal  joint,  309 

ligaments,  309 
Culmen  of  cerebellum,  806 
Cuneiform  bones,  159,  161,  191,  197 
first  (medial,  197 
third  (lateral,)  198 
second  or  middle,  197 
cartilages  (of  Wrisberg),  1213 
tubercle  (of  Wrisberg)  of  larynx,  1221 
Cuneo-cuboid  articulation  304 
Cuneo-lingual  gyrus,  anterior,  864 

posterior,  864 
Cuneo-navicular  articulation,  304 
Cuneus,  864 
Cupola  of  pleura,  1237 
Cupular  CEecum,  1096 

portion  of  epitympanic  recess,  1090 
Curvatures  of  spinal  column,  43 
of  stomach,  1152,  1374 
greater,  1152 
lesser,  1152 
Cusps  of  atrio-ventricular  valves,   516 
Cutaneous  areas  of  face,  1018 
of  lower  extremity,  1024 


Cutaneous  areas  of  neck,  1019 
of  pinna  (auricle),  1019 
of  scalp,  1018 
of  trunk,  1020 
of  upper  limb,  1022 
branches  of  anterior  ethmoidal  artery,  554 
of  intercostal  arteries,  589,  590 
(communicans  fibularis)  of  common  pero- 
neal nerve,  1013 
of  deep  circumflex  iliac  artery,  616 
dorsal    antibrachial   (external)   of    radial 

nerve,  987 
of  ilio-hypogastric  nerve,  995 
lateral,  of  thoracic  nerves,  995 
of  median  nerve,  992 
plantar,  of  medial  plantar  nerve,  1010 
posterior   brachial    (internal),    of    radial 
nerve,  985 
femoral  cutaneous  nerve,  1007 
of  sacral  plexus,  1007 
of  superficial  peroneal   (musculo-cutane- 

ous)  nerve,  1015 
of  superior  epigastric  artery,  567 
(medial  sural   cutaneous   or  tibial   com- 
municating) of  tibial  nerve,  1010 
of  ulnar  nerve,  990 
glands,  1296 
glomiform,  1296 
sebaceous,  1298 
nerves,  anterior  of  abdomen,  996 
of  femoral  nerve,  1003 
calcaneo-plantar,  1010 
of  foot,  lateral  dorsal,  1013 

surface  markings,  1466 
intermediate  dorsal,  of  leg,  1015 
lateral,  1000 
of  abdomen,  995 
sural,  1013 
medial  antibrachial  (internal),  934 
brachial,  983 
dorsal,  of  leg,  1015 
sural,  1010 
posterior  femoral  (small  sciatic),  1007 
superficial  cervical,  978 
rete  arteriosum,  1289 
veins,  1289 
Cuticle  (epidermis),  1285 
Cutis,  1285,  1286 
Cymba  conchse,  1082 
Cystic  artery,  595 
duct,  1187 
vein,  677 
Cysto-colic  ligament,  1379 
Cytomorphosis,  7 
Cytoplasm,  5 


"Dangerous  area"  of  leg,  1457 

of  scalp,  1333 
Dartos,  1254,  1260 
Darwin,  tubercle  of,  1083 
Deciduous  (milk)  teeth,  1126 

times  of  eruption,  1127 
Declive  of  cerebellum,  806 
Decussation,  fountain,  842 
of  lemnisci,  815 
of  pyramids,  799,  815 

of  superior   cerebellar   peduncles    (brachia 
conjunctiva),  840 
Deferential  artery,  610 

plexus  of  nerves,  1047 
Deiters'  nucleus,  823 
Deltoid  branch  of  profunda  artery,  576 
of  thoraco-acromial  artery,  571 
(internal     lateral)     ligament      of     ankle- 
joint,  298 
surface  markings,  1410 


1488 


INDEX 


Deltoideus,  365 

Delto-peotoral  lymphatic  nodes,  719 
Dendrites,  762 
Dens  (odontoid  process),  33 
Dental  arches,  1123 
branches,  inferior,  of  inferior  dental  plexus, 
941 
superior,  of  superior  dental  plexus,    938 

canal,  inferior,  96,  126 

nerves,  938,  941 
inferior,  941 
superior,  938 
Dentary  centre,  98 
Dentate  fascia,  868 

gyrus,  868 

nucleus  of  cerebellum,  810 

sutures,  212 
Dentine,  1118 

Denticulate  ligament,  920,  921 
Depressor  alfe  nasi,  334 

anguli  oris,  333 

labii  inferioris,  332 

septi  nasi,  334 
Derma  (oorium),  1286 
Descemet,  membrane  of,  1060 
Descendens  cervicalis  (hypoglossi),  953,  974, 

979 
Descending  aorta,  586 

brandies  of  cervical  plexus,  978 
of  lateral  circumflex  artery,  543 
(princeps  cervicis)  of  occipital  artery,  543 
of  spheno-palatine   (Meckel's)   ganglion, 

963 
of  transverse  cervical  artery,  565 

colon,  1174,  1379 

palatine  artery,  549 
Descent  of  the  testis,  1257,  1387 
Development  of  anus,  1179 

of  arteries,  633 

of  articulations  (joints),  213 

of  bones,  27  (see  also  the  individual  bones) 

of  brain,  754 

of  central  sulcus  (fissure  of  Rolando),  860 

of  oorium,  1290 

of  diaphragm,  120 

of  ear,  1096 

of  epidermis,  1286 

of  eye,  lOSO 

of  face,  18 

of  hairs,  1293 

of  heart,  523 

of  hypophysis  cerebri,  848 

of  kidney,  1248 

of  large  intestine,  1179 

of  larynx,  1225 

of  limbs,  20 

of  lips  and  cheeks,  1104 

of  liver,  1189 

of  lungs,  1235 

of  lymphatic  system,  706 

of  lymph-nodes,  707 

of  mammary  gland,  1306 

of  muscles,  316 

of  nails,  1296 

of  nerve  fibres,  758 

of  nervous  system,  754 

of  nose,  18,  1208 

of  oesophagus,  1141 

of  oral  cavity,  1102 

of  palate,  1105 

of  palato-pharyngeal  muscles,  1137 

of  pancreas,  1195 

of  parathyreoid  glands,  1319 

of  pericardium,  527 

of  peritoneum,  1144 

of  pharynx,  1138 

of  reproductive  organs,  1278 


Development  of  salivary  glands,  1117 
of  sebaceous  glands,  1298 
of  skull,  117 
of  small  intestine,  1168 
of  spleen,  1312 
of  stomach,  1157 
of  suprarenal  glands,  1326 
of  sweat  glands,  1297 
of  teeth,  1124 
of  thymus,  1322 
of  thyreoid  gland,  1318 
of  tongue,  1112 
of  tonsils,  1133 
of  tympanum,  80 
of  urinary  bladder,  1253 
of  veins,  690 

of  ventricles  of  brain,  758 
of  vermiform  process,  1179 
of  vertebra3,  45 
of  viscera,  18 
Diagonal  sulcus,  858 
band  of  Broca,  866 
Diameters  of  the  pelvis,  175,  177 
Diaphragm,  425,  436,  1372 . 
crura,  437 

and  heart,  recession  of,  20 
lymphatics,  725,  728 
pelvic,  440,  1383 
urogenital,  440,  1383 
Diaphragraa  pelvis  (Meyer),  440 

sella;,  848,  915 
Diaphragmatic  pleura,  1237 
lymph  nodes,  725,  736 
pelvic  fascia,  442,  447 
plexuses  of  nerves,  1044 
surface  of  heart,  509 

of  lung,  1229 

of  spleen,  1308 
Diaphysis,  28 
Diapophyses,  51 
Diarthroses,  212 
heteromorphic,  283 
homomorphic,  212 
Diencephalon  (interbrain),  758,  843 
Digastric  fossa,  95 
muscles,  314 
triangle,  1357 
Digastricus,  343,  344 
Digestive  system,  1099 

abdomen,  1142 

intestines,  1161 

liver,  1180 

mouth,  1100 

oesophagus,  1138 

pancreas,  1192 

peritoneum,  1145 

pharynx,  1129 

stomach,  1151 
Digital  arteries,  common  (hand),  582 

dorsal  (foot),  633 

plantar,  628 

proper  (hand),  582 
branches,  dorsal,  of  ulnar  nerve,  990 

of  medial  plantar  nerve,  1011 

volar,  of  ulnar  nerve,  991 
fossa  of  epididymis,  1255 

of  femur,  178 

of  fibula,  191 
nerves,  common  plantar,  1011,  1013 

common  volar,  of  hand,  991 

dorsal,  of  foot,  1013 
of  hand,  987,  990 

proper  plantar,  1011,  1013 

volar,  of  hand,  992 
veins  (foot),  dorsal,  684 

plantar,  common,  684 

volar  (hand),  671 


INDEX 


1489 


Digital  venous  arch  (hand),  667 
Digitations,  hippocampal,  877 
Dilator  naris  anterior,  335 
posterior,  335 

pupilte,  1061 
Dimples  of  skin,  1285 
Diploe,  veins  of,  648 
Direct  cerebellar  tract  of  Flechsig,  784 

pyramidal  tract,  788 
Disc,    articular,    of    the    aoromio-clavicular 
joint,  251 
of  inferior  radio-ulnar  articulation,  264 
of  mandibular  articulation,  216 
of  the  sterno-costo-clavicular  joint,  249 

optic,  1055 
Dislocation  of  mandible,  1345 

metaoarpo-phalangeal,  1434 

of  patella,  1446 
Diverticula,  intestinal,  1170,  1379 
Diverticulum,  Meckel's,  1169 
Dolichopellie  pelvis,  177 
Dorsalis  hallucis  artery,  633 

pedis  artery,  632 
Dorso-epitrochlearis,  379 
Dorsum  of  foot,  muscles  of,  492 

of  ilium,  165 

of  nose,  1200 

of  penis,  1260 

sellte  (epihippi),  63,  116 

of  tongue,  1106 
Douglas'  fold,  427 

(recto-uterine  or  recto-vaginal)  pouch,  1148, 
1267 
Duct(s),  alveolar,  1232 

of  Bartholin,  1117 

cochlear,  1096 

common  bile,  1188 

cystic,  1187 

efferent  of  testis,  1256 

ejaculatory,  1257,  1263,  1387 

endolymphatic,  1094 

of  epididymis,  1256 

of  gall-bladder,  1188,  1373 

of  Gartner,  1275 

hepatic,  1187 

of  lacrimal  gland,  excretory,  1047 

lactiferous,  1302 

of  mammary  glands,  1302 

MilUerian,  1257,  1267,  1279 

naso-lacrimal,  1080,  1205,  1349 

pancreatic  (of  Wirsung),  1194,  1375 
accessory  (of  Santorini),  1195 

papillary  (of  Bellini),  1246 

paraurethral  (of  Skene),  1277 

of  parotid  gland  (Stenson's),  1115,  1343 

right  lymphatic,  '728 

of  Rivinus,  1117 

semicircular,  1094 

of  sublingual  gland,  1117 

of  submaxillary  gland  (Wliarton's),  1116 

of  sweat  glands,  1297 

thoracic,  726 

thyreo-glossal,  1318 

utriculo-saccular,  1094 

Wolffian,  1248,  1267,  1278 
Ductless  glands,  1306 

aortic  paraganglia,  1329 

chromaffin  system,  ,1323 

glomus  caroticum,  1325 
ooccygeum,  1329 

parathyreoid  glands,  1318 

spleen,"  1306 

suprarenal  glands,  1323 

thymus,  1319 

thyreoid  gland,  1312 
Ductuli  aberrantes  (of  epididymis),  1257 
Ductus  arteriosus  (Botalli),  528 


Ductus     oholedochus     (common     bile-duct), 
1188 
(vas)  deferens,  1257,  1259,  1387 
(canaliculi)  lacrimales,  1079 
perilymphaticus,  81 

reuniens  of  membranous  labyrinth,  1094 
venosus,  675,  694 
Duodenal  fossa;,  1164 
papQla;,  1164,  1195 
veins,  677 
Duodeno-jejunal  flexTire,  1152,  1376 
Duodenum,  1161,  1375 
lymphatics  of,  734 
parts  of,  1161 
Dupuytren's  fracture,  1455 
Dura  mater,  771,  910 
blood-vessels  of,  917 
cranial,  913 
filum  of,  911 
nerves  of,  917 
spinal,  911 
surgical  anatomy  of,  1342 


Ear,  1082 

development  of,  1096 

internal,  1092 

middle,  1086 

muscles  of,  337,  1084 

ossicles  of,  79,  1090 

vessels  and  nerves,  1084,  1086,  1091,  1096 
Ectoderm,  10 

Ehrenritter,  ganglion  of,  951 
Ejaculatory  duct,  1257,  1263,  1387 
Elastic  cone  of  larynx,  1215 

membrane  of  larynx  (Lauth),  1215 
Elbow,  clinical  anatomy  of,  1417 
Elbow-joint,  258 

arterial  anastomoses  around,  1418 
supply  of,  261 

ligaments  of,  258 

movements  of,  201 

muscles  acting  upon,  261 

nerve-supply  of,  261 

synovial  membrane  of,  261 
Elevations  of  skin,  1284 
Eleventh  thoracic  vertebra,  39 
Elliptical  recess  (fovea  hemielliptica),  80 
Embryonic  disc,  9,  10,  11 
Eminence  of  auricle,  1083 

collateral,  868,  877 

frontal,  59,  108 

hypoglossal,  814 

ilio-pectineal,  169 

medial,  of  floor  of  fourth  ventricle,  813 

parietal,  57 

pyramidal,  of  temporal  bone,  77 
Eminentia  arcuata,  78,  116 
Emissary  veins,  647,  649,  652,  916 
mastoid,  647 
parietal,  649 
of  scalp,  1334 
Enamel,  1118  _ 
Enarthrodial  diarthroses,  213 
Encephalon,  751,  792 

blood-supply  of,  905 

divisions  of,  796 
Endocardium,  508 
Endoderm,  10 
Endognathion  centre,  91 
Endolymph,  1093 
Endolymphatic  duct,  1094 

sac,  1094 
Endometrium,  1274 
Endomysium,  315 
Endo-pelvic  fascia  (recto-vesical),  442,  447 


1490 


INDEX 


Endothoracic  fascia,  1235 
Enlargements  of  spinal  cord,  772 
Ensiform  process  (metasternum),  132,  134 
Eparterial  bronchus,  1232 
Ependymal  cells,  768,  846 
Ephippial  diarthroses,  212 
Epicardium,  508 
Epicondyles  of  femur,  183 

of  humerus,  151 
Epicranial  aponeurosis,  337 

musculature,  336 
Epicranio-temporalis,  337 
Epicranius  (occipito-frontalis),  336 
Epidermis,  (cuticle),  1285 
Epididymal  branches  of  int.  spermatic  ar- 
teries, 601 
Epididymis,  1266,  1386 
Epidural  cavity,  911 

Epigastric  artery,  inferior  (deep),  614,  639 
superficial,  618 
superior,  567 

lymphatic  nodes,  732,  733 

plexus,  1043 

region,  1143 

veins,  inferior,  683 
superficial,  684 
superior,  666 
Epiglottic  cartilage,  1212 

tubercle,  1212,  1222 

vallecula,  1221 
Epihyal  segment  of  styloid  process,  119 
Epimysium,  316 
Epiphyseal  cartilages,  28 

lines,  28 
Epiphyses,  28  (see  also  individual  bones). 
Epiphysis  (pineal  body),  758,  834,  845 
Epiploic  foramen  (of  Winslow),  1147 

or  omental  branches  of  epiploic  arteries,  595 
Epipteric  bones,  68,  101,  119 
Episcleral  arteries,  553 

veins,  659 
Epispadias,  1388 
Epistropheus,  description  of,  33 
Epithalamus,  845 
Epithelial  chorioid  lamina,  924 
Epithelium  lentis,  1064 
Epitrochleo-olecranonis    (anconeus  internus), 

402 
Epitym  panic  recess,  78 
Eponychium,  1294,  1296 
Epoophoron,  1269 
Equator  of  eyeball,  1055 

of  lens  of  eye,  1062 
Erector  penis  (or  olitoridis),  451 

spinas,  412,  414 
Eruption  of  teeth,  1127 
Ethmoid,  81 

at  birth,  124 

cells,  83,  111,  1207 
Ethmoidal  artery,  anterior,  554 
posterior,  553 

branches  of  anterior  ethmoidal  artery,  554 
of  posterior  ethmoidal  artery,  553 

bulla.  111,  1205 

canals,  61,  83,  110,  113,  126 

(superior  turbinate)  crest,  92 

fissure,  113 

infundibulum,  1205 

nerve,  anterior,  936,  937 
posterior,  937 

notch,  61 

process,  85 

spine,  63,  113 

veins,  659 
Ethmo-turbinals,  119 
Ethmo-vomerine  region  of  skull,  117 
Eustachian  tube,  74,  1089,  1092 


Eustachian  tube,  openings  of,  1130,  1354 

valve,  512 
Excretory  ducts  of  lacrimal  gland,  1079 
Exoccipital,  119 
Exognathion  centre,  91 
Expiration,  muscles  which  affect,  248 
Extension  (of  muscles),  321 
Extensor  carpi  radialis  acoessorius,  391 
brevis,  388,  389 
intermedius,  391 
longus,  387,  388 
ulnaris,  388,  391 
communis  pollicis  et  indicis,  394 
digiti  annularis,  395 

quinti  proprius  (extensor  minimi  digiti), 
388,  391 
digitorum  brevis  (foot),  454,  492 
(hand),  395 
communis,  388,  391 
longus,  453,  480,  481 
group  of  arm  muscles,  377 
hallucis  brevis,  482,  492 
longus,  453,  480,  482 
indicis  proprius,  392,  394 
medii  digiti,  395 
ossis  metacarpi  pollicis   (abductor  pollicis 

longus),  393 
pollicis  brevis,  392,  394 
longus,  392,  394 
Extremity,  lower,  bones  of,  169 

clinical  and  topographical  anatomy  of, 

1434 
lymphatics  of,  746 
upper,  bones  of,  139 

clinical  and  topographical  anatomy  of, 

1409 
lymphatics,  719,  1424 
Extrinsic  muscles  of  tongue,  345 
Eye,  1051 
blood-vessels  of,  1031 
clinical  anatomy  of,  1346 
crystalline  lens,  1052 
development  of,  1080 
eyelids,  1053,  1076 
general  surface  view,  1052 
lymphatics  of  orbit,  715 
nerves  of,  1064,  1348 
Eyeball,  (bulbus  ocuh),  1-055 
blood-vessels  of,  1065 
equator  of,  1055 
hemispheres  of,  1057 
insertions  of  muscles,  1056 
muscles  of,  501,  1067 
nerves  of,  1064 
poles  of,  1055 
Eyelashes  (cilia),  1053,  1347 
Eyelids,  1053,  1076 
blood-vessels  of,  1078 
clinical  anatomy,  1346 
glands  of,  1078 
lymphatics  of,  712,  1078 
nerves  of,  1078 
structure  of,  1077 


Face,  bones  of,  51 

clinical  anatomy,  1342 

cutaneous  areas  of,  1018 

development  of,  18 

lymphatic  vessels  of,  712 

muscles  of,  324,  329,  501 

veins  of,  643 
Facial  (external  maxillary)  artery,  540,  1343 

branches  of  great  auricular  nerve,  978 

(Fallopian)  canal,  72,  77,  78 

lymph-nodes,  709,  711 


INDEX 


1491 


Facial  nerve,  943,  946,  1345 
nucleus  of,  825 
paralysis  of,  1345 

portion  of  external  maxillary  artery,  540 

vein,  anterior,  643,  1343 
common,  644,  646 
posterior  (temporo-maxillary),  644 
transverse,  646 
Facialis,  musculature,  324,  329,  501 
Falciform  ligament  of  liver,  1185 

margin  of  fascia  lata,  467 

process  of  great  sacro-soiatic  ligament,  236 
Fallopian  canal,  72,  77,  78 

tubes,  1269 
Fallopius,  aqueduct  of  (facial  canal),  72 
Falx  cerebelU,  915 

cerebri,  914 

inguinalis  (conjoined  tendon  of  internal  ob- 
lique and  transversalis),  436,  1396 
Fascia(8B)  antibrachial,  384 

of  arm,  377 

axillary,  370,  371 

brachial,  377 

bulbi  (Tenon's  capsule),  1073,  1348 

Camper's,  425 

Colles',  425 

coraco-clavicular  (costo-coracoid),  371 

cranio-mandibular,  339 

cremasteric  (Cowper's),  426,  434,  1254 

cribrosa,  467 

crural,  477 

of  deep  musculature  of  shoulder  girdle,  356 

deep  cervical,  1360 

deep  palmar,  387 

dentate,  868 

diaphragmatic  pelvic,  442,  447 

endo-pelvic  (recto-vesical),  442,  447 

endothoracica,  1235 

external  cervical,  347 
spermatic,  1387 

of  foot,  491 

of  forearm  and  hand,  384 

of  hand,  1427 

of  head  and  neck,  329 

hypothenar,  387 

iliac,  455,  466 

of  ilio-femoral  musculature,  455 

ilio-peotineal,  455,  466 

of  infrahyoid  musculature,  350 

intercolumnar  (external  spermatic),  1304 

interpterygoid,  339 

of  ischio-pubo-femoral  musculature,  463 

lata,  454,  457,  466,  1400,  1436 

lateral  pharyngeal,  339 

of  leg,  477 

lingual,  346 

lumbar,  436 

lumbo-dorsal,  414,  428 

masseteric,  339 

middle  cervical,  350 

muscle,  313 

of  musculature  of  shoulder,  365 

nuchae,  414 

obturator,  439,  463 

of  orbit,  1071 

palpebral,  1071 

parietal  (pelvic),  447 

parotid,  339,  348,  1114 

of  pectoral  muscles,  371 

of  pelvis,  muscular,  443,  446,  447 
subcutaneous,  445 

penis,  1260 

plantar,  1468 

of  posterior  group  of  ilio-femoral  muscles, 
457 

of  prevertebral  musculature,  355 

prostatico-perineal,  447 


Fascia  (ae)  psoas,  455 
renal,  1242 

of  scalene  musculature,  353 
Scarpa's,  425,  445 
of  scrotum,  1385 
semilunar,  382 
Sibson's,  129,  356,  1237 
of  spinal  musculature,  413 
superficial,  313 

permeal  (Colles'),  446,  1385 

of  shoulder  girdle,  347 
of  supra-hyoid  musculature,  344 
temporal,  339 
thenar,  387 
of  thigh,  466 
thoraco-abdominal  musculature,  425 

subcutaneous,  425 
transversalis,  426 
triangular,  430 

of  upper  limb  musculature,  363 
of  urogenital  diaphragm,  445 
of  wrist,  1427 

transversi  of  palmar  aponeurosis,  387 
Fas ci cuius  (i),  769 

anterior  marginal,  786 

comma-shaped,  782 

cuneatus  (Burdach's  column),  781 

gracilis  (Goll's  column),  781 

inferior  longitudinal,  892 

intermediate,  784 

lateral  cerebro-spinal,  783 

mammillo-mesen  cephalic     (tegmento-mam- 

millary  or  mammillo-peduncular),  871 
mammilio-thalamic,  871,  883 
medial  longitudinal,  817,  842 
oblique,  804 
oooipito-frontal,  892 
pedunculo-mammillary,  849 
proprii,  769 
proprius,  dorsal,  782 

lateral,  782 

ventral,  786 
retroflexus  of  Meynert,  841,  843,  872,  886 
rubro-spinal,  786 
spino-cerebellar,  dorsal,  784 
spino-olivary  (Helweg's  bundle),  784 
sulco-marginal,  788 
superficial  ventro-lateral  (spino-cerebellar), 

784 
superior  longitudinal,  892 
■uncinate,  891 
ventral  cerebrospinal,  788 
vestibulo-spinal,  786 
Fasciola  cinerea,  868 
Fauces,  isthmus  of,  1100,  1130,  1131 
Female,  reproductive  organs,  1265 
clinical  anatomy  of,  1391 
development  of,  1278 
external  (vulva),- 1276 
lymphatics  of,  744,  1278 
ovaries,  1238 

tubffi  uterinse  (Fallopian  tubes),  1269 
uterus,  1271 
vagina,  1274 

vessels  and  nerves  of,  1278 
urethra,  1278 
Femoral  artery,  616,  1441 

branches,  618 

collateral  circulation,  1441 

common,  616 

profunda  or  deep,  620,  640 

superficial,  616 
canal  (crural  canal),  468,  1400 
cutaneous  nerve,  posterior  (small  sciatic), 

1007 
hernia,  1398 
(anterior  crural)  nerve,  1001 


1492 


INDEX 


Femoral  plexus  of  nerves,  1045 

ring,  466,  1401 

septum,  466 

sheath,  1400 

trigone  (Scarpa's  triangle),  467,  1438 

vein,  690,  1441 
tributaries,  690 
Femoro-tibial  muscle,  486 
Femoro-popliteal  vein,  685,  693 
Femur,  178 

clinical  anatomy  of,  1434,  1442 

condyles  of,  1447 

ossification  of,  184 

trochanters  of,  178 
Fenestra  cochleae  (rotunda),  73,  1089 

vestibuli  (ovalis),  73,  1089 
Ferrein,  pyramid  of,  1246 
Fibras  propriae,  890 
Fibres,  arcuate,  817 

association,  of  telencephalon,  890,  893 
of  white  substance  of  spinal  cord,  779 

of  cerebellar  cortex,  809 

cerebello-olivary,  817 

of  cerebral  cortex,  879 

commissural  system  of,  890 

external  arcuate,  of  medulla  oblongata,  800 

interorural  (intercolumnar  fascia),  430 

internal  arcuate,  815 

muscles,  315 

nerve,  767 

development  of,  758 

projection,  of  telencephalon,  886 

sympathetic,  970,  1029 

visceral  afferent,  970 
efferent,  970 
Fibro-cartQages,  cotyloid,  281 

interosseous,  244 

interpubic,  240 

intervertebral,  225,  238 

semilunar,  289 

triangular  (articular  disc),  264 
Fibula,  description  of,  189,  1454 

ossification  of,  191 
Fibular  branch  of  posterior  tibial  artery,  626 

collateral  ligament,  286 

nutrient  branch  of  peroneal  artery,  626 
Fibulo-calcaneus  medialis,  491 
Fibulo-tibialis,  486 
Fifth  ventricle  (cavity  of  septum  pellucidum), 

872 
Fila  radicularia,  775',  964 
Filaments,  root,  of  spinal  nerves,  775 

of  pons,  lateral,  804 
Filiform,  papillae  of  tongue,  1106 
Filum  of  dura  mater,  911 

terminale,  771,  721 
Fimbria,  868,  877 

ovarica,  127 
Fimbriae  of  tubae  uterinae   (Fallopian  tube), 

1270 
Fimbriate  folds  of  tongue,  1107 
Fimbrio-dentate  sulcus,  868 
Fingers,  4 

muscles  acting  on,  505 
Fissura  prima,  866 

serotina,  865 
Fissure(s),  anterior  median,  772 

antitrago-helicine,  1084 

auricular,  75,  108 

calcarine,  864 

calloso-marginal,  857,  859 

of  cerebellum,  805 

of  cerebrum,  852 

chorioid,  1080 

collateral,  855,  864 

ethmoidal,  113 

external  parieto-occipital,  862 


Fissure(s),  Glaserian,  71,  77 

hippocampal  or  (chorioid),  868 

horizontal  (of  cerebellum),  805 

inferior  orbital  (spheno-maxillary),  102, 109, 
126 

lateral  (Sylvian),  850,  855,  1340 

of  liver,  1183 

longitudinal,  of  cerebrum,  850 

of  lung,  1230,  1234 

oral,  HOC 

parieto-occipital,  860,  864 

petro-tympanic,  71,  77,  108,  126 

portal,  1183 

posterior  median,  of  medulla  oblongata,  801 

postlimbic,  863 

pterygo-maxillary,  102 

pterygo-palatine,  102 

retrotonsillar,  of  cerebellum,  807 

of  Rolando,  859,  1340 

semilunar  (of  cerebellum),  805 

spheno-maxillary,  102,  109 

of  spinal  cord,  772 

superior  orbital  (sphenoidal),  65,  109,  116' 
125 

of  Sylvius,  850,  855 

of  telencephalon,  853 

transverse,  of  cerebrum,  850 

tympano-mastoid,  71,  75,  108 

umbilical,  of  liver,  1183 
Flechsig,  direct  cerebellar  tract  of,  784 

secondary  optic  radiation  of,  890 
Flexion  of  muscles,  321 
Plexor  accessorius,  454,  495 
longus  digitorum,  491 

carpi  radialis,  396,  398 

brevis  (radio-carpeus),  403 
ulnaris,  396,  398 

brevis  (ulno-earpeus),  402 

digiti  quinti  brevis    (foot),   454,   498,   499 
(hand),  404 

digitorum  brevis,  454,  493 
longus,  454,  486,  489 
profundus,  401 
Flexor  digitorum  profundus,  401 
sublimis,  399 

group  of  arm  muscles,  379 

haUucis  brevis,  454,  496,  497 
longus,  454,  486,  490 

poUicis  brevis,  407,  408 
longus,  402 
Flexure(s)  of  duodeno-jejunal,  1376 

of  duodenum,  1161 

left  cohe  (splenic),  1174,  1379 

of  rectum,  1176 

right  colic  (hepatic),  1173,  1379 
Floating  ribs,  127 
Floccular  fossa,  73 
Flocculus  of  cerebellum,  807 

peduncle  of,  807 
Floor  of  cranial  cavitj',  112 

of  fourth  ventricle,  813 

pelvic,  1384 
in  female,  1394 
Fluid,  cerebro-spinal,  920  1342 
Flumma  pilorum,  1291 
Fcetal  circulation,  695 

skull,  general  characters  of,  120 
Fold(s),  adipose,  of  pleura,  1237 

alar,  291 

ary-epiglottic,  1221 

of  Douglas,  427 

of  duodenum,  1164 

glosso-epiglottic,  1220 

inferior  palpebral,  1053 

neural,  754 

patellar,  290 

recto-uterine,  1274 


INDEX 


1493 


Fold(s),  semilunar,  of  conjunctiva,  1055 

of  skm,  1284 

sublingual,  1116 

superior  palpebral,  1053 

transverse    (Houston's),   of  rectum,    1177, 
1390 

of  tympanic  mucous  membrane,  1089 

ventricular,  of  larynx,  1222 

vocal,  1223 
Foliate  papUlse  of  tongue,  1106 
Folium  vermis  (cacuminis)  of  cerebellum,  806 
Follicles,  Graafian,  1269 

of  hair,  1292 

lingual,  1107 

lymph,  704 
Fontana,  spaces  of,  1060 
Fontanelle(s),  sagittal,  59 

of  skull,  120 
Foot,  amputations  of,  1465 

arches  of,  1468 

arteries  of,  627,  631 

bones  of,  191,  205,  1467 

bony  landmarks  of,  1464 

bursae  of,  1465 

clinical  anatomy  of,  1464 

cutaneous  nerves  of,  1466 

muscles  acting  on,  at  ankle-joint,  505 

musculature  of,  491 

synovial  membranes  of,  1465 

talipes,  1467 
Foramen(ina),  29 

acetabular,  174 

apicis  dentis,  1118 

auditory,  125    ■ 

caecum,  61,  113,  1318 
of  ethmoid,  81 
of  medulla  oblongata,  799 
(Morgagni)  of  tongue,  1106 

carotico-olinoid,  65 

condylar,  54 

costo-transverse,  127 

of  diaphragma  sellae,  916 

epiploic  (foramen  of  Winslow),  1147 

greater  palatine,  106 

hypoglossal,  54,  108,  125 

incisive,  89 

inferior  dental,  96 

infra-orbital,  87,  1345 

intervertebral,  30 

intraventricular  (Monroi),  847,  874 

jugular,  74,  108,  117,  125 

laoerum,  63,  74,  108,  116 

lesser  palatine,  106 

of  Magendie,  813 

magnum,  51,  56,  108,  117,  125 

mandibular  (inferior  dental),  96 

mastoid,  72,  108,  117 

mental,  95 
palatine,  106 

of  Monro,  847,  874 

of  nerves  of  skull,  125 

of  norma  facialis,  108 

obturator  (thyreoid),  174 

optic,  63,  64,  110,  116,  125 

ovale,  66,  116,  125 
of  Pacchioni,  116 

papillaria,  1246 

parietal,  57 

petro-sphenoidal,  125 
.   pharyngeal,  126 

rotundum,  65,  103,  116,  125 

sacral,  40 

scapular,  142 

of  Scarpa,  89,  106,  126 

spheno-palatine,  93,  103,  111,  126 

spinosum,  65,  116 

of  Stenson,  89,  106 


roramen(ina),  sternal,  133 

stylo-mastoid,  73,  108,  126 

supra-orbital,  60 

supratrochlear,  150 

thyreoid  (thyreoid  cartilage),  1211 

trigeminal,  125 

venae  cavae,  438 

venarum  minimarum  (Thebesii),  514 

vertebral,  31 

Vesalii,  65,  116 

zygomatioo-temporal,  126 
Forceps  major,  876 
Forearm,  clinical  anatomj-  of,  1419 

common  fractures  of  bones  of,  1420 

joints  of,  1419 

muscles  of,  362 

musculature  of,  383 

nerves  of,  1423 

synovial  tendon  sheaths  of,  395,  403 

vessels  and  nerves  of,  1423 
Fore-brain,  843 
Formation,  reticular,  816 
Fornix,  anterior  pillars  (columns)  of,  870 

body  of,  869 

conjunctival,  1054,  1347 

fibres  of,  869,  870,  871,  890 

of  Limbic  lobe,  868 

pharyngeal,  1130 

posterior  pillars  (crura),  868 

transverse,  869,  890 

of  vagina,  1275 
Fossa (e),  abdominal,  430 

anterior  cranial,  113 

of  anthelix,  1082 

axillary,  clinical  anatomy  of,  1411 

canine,  87 

cardiac,  of  lung,  1229 

condylar,  54,  108 

coronoid,  150 

cotyloid,  169 

digastric,  95 

digital,  of  femur,  178 
of  fibula,  191 

ductus  venosi,  1183 

duodenal,  1164 

of  femur,  intercondyloid,  182 

floocular,  73 

of  gall-bladder,  1183 

glenoid,  29 

of  humerus,  coronoid,  150 
olecranon,  150 
radial,  151 

hypophyseos,  63,  116 

iliac,  170 

ileo-caecal,  1172 

ileo-colic,  1172 

ilio-pectineal,  467 

incisive,  87 

incisor,  95 

infraspinous,  142 

infra-temporal  (zygomatic),  101,  1332 

interpeduncular,  835 

intersigmoid,  1175 

ischio-rectal,  441,  445,  1384 

jugular,  73,  108 

lacrimal,  61,  109 

mandibular,  108 

mastoid,  72 

middle  cranial,  116 

nasal,  108,  110 

navicularis,  1264,  1277,  1392 

olecranon,  150 

ovalis  (of  heart),  512 

(saphenous  opening),  467,  1400,  1440 

ovarica,  1268 

paraduodenal  (Landzert),  1164 

pericardial,  1172,  1378 


1494 


INDEX 


Fossa(e),  posterior  cranial,  116 

pterygoid,  66,  107 

pterygo-palatine  (spheno-maxillary),  102 

radial,  151 

rhomboidea,  802 

of  Rosenmueller,  1130 

scaphoid,  54,  55,  66,  95,  107 

of  skull,  surgical  anatomy  of,  1342 

spheno-maxillary  (pterygo-palatine),  102 

subareuata,  73,  117 

subscapular,  141 

supraspinous,  141 

supratonsillar,  1132 

Sylvian,  854 

temporal,  101 

triangular,  of  auricle,  1082 
of  elbow,  1418 

trochanteric  or  digital,  178 

trochlear,  61 

venee  cavEe,  1183 

vermiform,  53,  108,  117 

zygomatic,  101,  1332 
Fossula  cochlearis,  72 

petrosa,  73 

vestibularis,  72 
Fountain  decussation  (Forel),  842 
Fourchette,  1276,  1392 
Fourth  ventricle,  812 
anatomy  of,  812 
chorioid  plexus  of,  922 
floor  of,  813 
roof  of,  812 
tela  chorioidea  of,  922 
Fovea  of  arytaenoid  cartilages,  1212 

centralis,  1055 

of  femur,  178 

hemielliptica,  80 

hemisphserica,  80 

inferior,  of  floor  of  fourth  ventricle,  814 
superior  of,  floor  of  fourth  ventricle,  815 

inguinalis,  430 

pterygoidea,  97 

sublingualis,  95 

umbilical,  1284 
Foveola  palatina,  1104 
Fracture  or  fractures  of  bones  of  the  leg,  1454 

doUes',  1420 

common,  of  bones  of  forearm,  1420 

Dupuytren's,  1455 

of  mandible,  1345 

of  olecranon,  1420 

Pott's,  1454 
Freckles,  1283 
Frenulum  of  anterior  medullary  velum,  832 

clitoridis,  1277 

of  ileo-caecal  valve,  1172 

of  penis,  1260 

of  tongue,  1107,  1349 

veli,  812,  835 
Frenum  (duodenal),  1164 
Frequency  of  disease  of  tarsal  bones,  1396 
Frontal  artery,  554,  1343 

association  area,  894 

bone  at  birth,  123 
description  of,  59 

branches  of  anterior  ethmoidal  artery,  554 
of  superficial  temporal  artery,  545 

convolution,  ascending,  851 

crest,  60 

eminences,  59,  108 

gyrus,  inferior,  858 
middle,  858 
superior,  857 

lobe,  857 

nerve,  936,  1075 

notch,  60 

operculum,  856 


Frontal  pole,  850 

pontile  path  (Arnold's  bundle),  832,  840, 
889 

process  of  maxilla,  87,  88 

sinus,  59,  61,  1207,  1335 

spine,  (nasal),  60 

sulcus,  inferior,  858 
middle,  858 
superior,  858 

suture,  59 

vein,  644 
Frontal  vein,  644 

diploic,  648 
Frontalis,  337 
Fronto-ethmoidal  cells,  84 
Fronto-marginal  sulcus,  858 
Fronto-nasal  plate,  117 

process,  119 
Fronto-sphenoidal  process,  95 
Functional  areas  of  cerebral  cortex,  893 
Functions  of  cerebellum,  832 

of  muscle  groups,  500 
Fundiform  hgament  of  penis,  427 
Fundus  of  gall-bladder,  1187 

of  stomach,  1151,  1374 

uterus,  1271 
Fungiform  papillse  of  tongue,  1106 
Funiculi  of  nerves,  769 

spinal  cord,  774,  780 
Funiculus,  anterior,  775,  786 

cuneatus  of  medulla  oblongata,  801 

gracilis  of  medulla  oblongata,  801 

lateral,  775,  782 

posterior,  774,  780 

separans,  814 
Furcal  nerve,  998 
Furrow,  29 

Furrows,  articular,  of  skin,  1284 
Fusiform   gyrus    (occipito-temporal  convolu- 
tion), 855,  864 

muscles,  315 


Galea  aponeurotica   (epicranial  aponeurosis), 

337 
Galen,  veins  of,  923 
Gall-bladder,  1187 

clinical  anatomy  of,  1372 

ducts  of,  1187,  1188,  1372 
Ganglion  (ia),  aberrant  spinal,  965 

of  Andersch,  951 

aortico-renal,  1043 

basal,  878 

of  Bochdalek,  939 

cardiac  (ganglion  of  Wrisberg),  1041 

ciliary,  961,  1033,  1076 

ooccygeum  impar,  1032,  1040 

coeliac  (semilunar),  1043 

(neural)  crest,  754 

first  thoracic,  1038 

geniculate,  826,  947 

inferior  cervical,  1036 

interpeduncular  (von  Gudden's),  843,  872, 
885 

jugular    (superior),    of    glosso-pharyngeus, 
957 
of  vagus,  954,  956 

of  glosso-pharyngeus,  951 

middle  cervical,  1036 

nodosum  (ganglion  of  trunk),  954,  956 

otic  (Arnold's),  963 

petrosal,  951 

phrenic,  1044 

renal,  1044 

of  root  of  vagus,  956 

roots  of,  959 


INDEX 


1495 


Ganglion  (ia),  second  thoracic,  1038 

semilunar  (Gasserian),  826,  938,  1345 

spheno-palatine  (Meckel's),  962 

spinal,  964 

spiral,  of  cochlea,  950 

splanchnic,  1039 

submaxillary,  963 

superior  cervical,  sympathetic,  960,  1035 
jugular,  or  Ehrenritter's,  951 
mesenteric,  1043,  1045 

sympathetic,  959,  1032 
of  head,  959 

of  synovial  sheaths,  1434 

terminal,  930 

of  trunk  of  vagus,  956 

of  Valentine,  939 

vestibular,  823,  950 

of  Wrisberg,  cardiac,  498 
Gangliated  cephalic  plexus,  959 

nerve  trunks  (cords),  755,  1029,  1032 
Ganglionic    branches    of    middle    meningeal 

artery,  548 
Gartner,  duct  of,  1275 
Gasserian    (semilunar)    ganglion,     826,    935, 

1345 
Gastric  artery,  left,  593 
right,  594 

branches  of  epiploic  arteries,  595 
of  vagus,  958 

lymphatic  nodes,  730,  734 

plexus  of  nerves,  anterior,  958 
inferior,  1045 
posterior,  958 
superior  (coronary),  1045 

surface  of  spleen,  1309 
Gastrocnemius,  453,  484,  485 
Gastro-duodenal  artery,  594 
Gastro-epiploic  artery,  left,  595 
right,  595 

vein,  left,  675 
right,  675 
Gastro-hepatic  ligament,  1150 
Gastro-phrenic  ligament,  1150 
Gastro-splenic  (gastro-lienal)  ligament 

(omentum),  1150,  1310 
Gastroptosis,  1160 
Gemellus  inferior,  464 

superior,  464 
Gemmules,  762 
Genial  tubercles,  95 
Geniculate  bodies,  834,  845 

ganglion,  826,  949 
Geniculo-tympanio  branch  of  glosso-palatine, 

951,  961 
Genio-glossus,  346 
Genio-hyoideus,  343,  344 
Genio-pharyngeus,  346 
Genital  corpuscles,  1290 

ridge,  1267,  1278 

swellings,  1279 

tubercle,  1279 
Genitalia,  female,  external,  1276 
clinical  anatomy  of,  1391 

male,  1253 
Genito-femoral    (genito-crural)    nerve,    1000, 

1260 
Genu  of  corpus  callosum,  851 

of  facial  canal,  78 

inferior,  of   central  sulcus   (fissure  of  Rol- 
ando), 860 

of  internal  capsule    (telencephalon),  887 

superior,  of  central  sulcus  (fissure  of  Rol- 
ando), 860 

suprema  artery,  621,  640 

valgum,  1449 
Germ  laj'ers,  9 
Gimbernat's  hgament,  424,  429,  466,  1400     • 


Gingival  branches,  inferior,  of  inferior  dental 
plexus,  941 
superior,  of  superior  dental  plexus,  939 
Ginglymi  diarthroses,  213 
Girdle,  pelvic,  207 

shoulder,  207 
Glabella,  60,  101,  109,  1331 
Gladiolus  (mesosternum),  132 
Gland(s),  1099 

broncliial,  1231 

Brunner's,  1166 

bulbo-uretliral  (Cowper's)  1265 

carotid,  550,  1327 

ceruminous,  1297 

ciliary  (of  Moll),  1078,  1297 

circumanal,  1297 

ductless,  1306 

of  eyeUds,  1078 

glomiform,  1296 

greater  vestibular  (of  Bartholin),  1278, 1392 

Henle's  1078 

I&ause's,  1078 

lacrimal,  1079,  1348 

lingual,  1108 

lesser  vestibular,  1278 

of  Lieberkuehn,  1166,  1177,  1390 

of  lips  and  cheeks,  1103 

lymphatic,  704 
intercolated,  706 

mammary,  1299 

of  Montgomery,  1304 

mucous,  of  larynx,  1224 

nasal,  1208 

of  Nuhn  or  Blandin,  1110, 

olfactory,  1208 

para-thyreoid,  1318,  1355 

parotid,  348,  1113 
accessory,  1114 

preputial,  1298 

prostate,  1264 

salivary,  1113 

sebaceous,  1298 

of  skin,  1296 

of  small  intestine,  1166 

of  palate,  1104 

sublingual,  1116 

submaxillary,  1116,  1350 

sudoriferous  (sweat), 1296 

suprarenal,  1323 

accessory,  1326 

tarsal  (Meibomian),  1054,  1078 

thymus,  1319 

thyreoid,  1312 
accessory,  1315 
clinical  anatomy  of,  1355 

tracheal,  1227 

urethral  (of  Littrg),  1264 

Zeiss's,  1078 
Glandular  branches  of  external  maxiUarj',  541 

of  inferior  thyreoid  artery,  564 
Glans  clitoridis,  1277 

of  penis,  1260 
Glaserian  fissure,  71,  77 
Gleno-humeral  bands,  254 

ligament,  255 
Glenoid  cavity  of  scapula,  143 

fossa,  29 

ligament,  (lip)  255 

of  metacarpo-phalangeal  joints,  294 

lip  of  shoulder-joint,  255 

of  hip-joint  (cotyloid  fibro-cartilage),  281 
Gliding  motion  of  joints,  214 
Glisson's  capsule,  675,  1186 

paUidus,  880 
Glomerular  capsule,  1246 

layer  of  olfactory  bulb,  866 
Glomeruli  of  olfactory  nerves,  929 


1496 


INDEX 


Glomiform  glands,  1296 
Glomus  caroticum  (carotid  gland),  1327 
choroideum,  876 
cocoygeum,  1040,  1329 
Glosso-epiglottic  folds,  1220 

ligament  1218 
Glosso-hyal  process,  99 
Glosso-palatine  arches,  1132 

nerve,  826,  946 
Glosso-palatinus  (palato-glossus),  lldo 
Glosso-pharyngeal  nerves,  820,  951 
Glottis,  1223 

Gluteal  arteries,  608,  1444 
branches,  609 
superior,  608 
inferior,  609,  639 
branches  of  internal  pudendal  artery,  613 

of  posterior  femoral  cutaneous  nerve,  1007 
line,  anterior,  170 
inferior,  166 
posterior,  170 
nerve,  inferior,  1007 

superior,  1007 
tuberosity  of  femur,  178 
veins,  inferior  680 
superior,  680 
Gluteus  maximus,  453,  457,  459 
surface  marking,  1443 
medius,  453,  457,  461 
minimus,  453,  457,  461 
Golgi  cells  in  cerebellum,  809 
Golgi-Mazzoni  corpuscles,  1290 
GolUs  column,  781 
Gomphosis  sutures,  212 
Gonion,  112,  113 
Gower's  tract,  784 
Graafian  follicles,  1269 
Gracilis,  453,  471,  472 
Granular  layer  of  cerebellar  cortex,  809 
Granulations,  arachnoid,  649,  919 
Great  auricular  nerve,  978 
cardiac  vein,  520 
omentum,  1149 
(anterior)  palatine  nerve,  963 
prevertebral  plexuses  of  nerves,  1010 
(internal)  saphenous  vein,  684,  1456 
splanchnic  nerve,  1038 
superficial  petrosal  nerve,  948 
trochanter  of  femur,  178,  1435 
Greater  alar    (lower  lateral)  nasal  cartilages, 
1201 
curvature  of  stomach,  1152 
multangular  (trapezium)  bone,  162 
occipital  nerve,  971 
palatine  foramina,  106 

canals,  92 
tuberosity  of  humerus,  147  ,    ,•   n 

vestibular    glands     (glands    of    Bartholm), 
1278,  1392 
Grey  commissure  of  spinal  cord,  775    _  ■ 
rami  communicantes  of  sympathetic   sys- 
tem, 1030 
substance,  central,  of  niesencephalon,  836 
of  pons  (nuclei  pontis),  831 
of  nervous  system,  768 
of  spinal  cord,  775 
Groove  of  atlas,  33 
basilar,  54 
bony,  29 
carotid,  64 
costal,  127 
costo-vertebral,  138 
of  cuboid,  peroneal,  199 
infra-orbital,  87 
intertubercular  (bicipital),  148 
lacrimal,  85,  87,  110 
mylo-hyoid,  96 


Groove,  neural,  754 
obturator,  172 
occipital,  72 
optic,  63,  113 

for  radial  nerve  (musoulo-spiral),  149 
sacral,  41 
sigmoid,  72 
Grouping  of  muscles  according  to  function,  500 
Growth,  prenatal,  22 
of  the  organs,  25 
of  the  parts,  24 
of  the  systems,  25 
Gubernacular  canals,  106 
Gubernaculum  testis,  1257,  1387 
Gudden's  commissure  (inferior  cerebral  com- 
missure), 842,  850,  890 
Guftis,  1119 

lymphatics  of,  715 
Gustatory  area  of  cerebral  cortex,  894 
cells,  1051 
organ,  1051 
Gynecomastia,  1305 
Gyrus  (i)  Andres  Retzii,  868 
ambiens,  865 
angular,  863 
anterior  central,  857 
cuneo-lingual,  843 
orbital,  858 
breves  (precentral  gyri),  857 
of  cerebellum,  804 
of  cerebrum,  852 
cinguli  (cingulum),  867 
cunei,  864 
cuneo-lingual,  864 
deep  annectant,  860 
dentate,  868 
epicallosus,  868 
external  orbital,  838 
fornicatus,  867 

cinguli  (cingulum),  867 
hippocampus,  868 
isthmus  of,  867 
fusiform    (occipito-temporal    convolution), 

855,  864 
hippocampal,  868 
inferior  frontal,  858 

temporal,  855 
lateral  occipital,  863 
olfactory,  865 
orbital,  859 
lingual,  855,  864 
longus,  857 
marginal,  858 
medial  olfactory,  866 

orbital,  858 
middle  frontal,  858 

temporal,  855 
orbital,  858 

origin  of,  853  ■  ^  in   oci 

posterior  central  (ascending  parietal),  86 J. 

orbital,  858 
post-parietal,  863 
profundi,  852 
rectus,  858 

semilunar,  865  , 

subcallosal   (peduncle  of  corpus  callosum). 

866 
submarginal,  858 
superior  frontal,  857 

occipital,  863 

parietal,  862 

temporal,  854 
supracallosal,  868 
supramarginal,  863 
transitivus,  852 
transverse  temporal,  855 
•  uncinatus,  868 


INDEX 


1497 


H 


Habenulse,  846 

Habenular  commissure,  846,  872,  885,  890 

nucleus,  872,  885 

trigone,  835 
Habenulo-peduncular  tract,  873 
Hajmolymph  nodes,  708 
Haemorrhoidal  artery,  inferior,  613,  1391 
middle,  610,  1391 
superior,  603,  1091 
of  middle  sacral  artery,  603 

nerves,  inferior,  1017 
middle,  1017 
superior,  1045 

plexus  of  nerves,  middle,  1045,  1046 
superior,  1045 
of  veins,  683,  1391 
Hairs  (pili),  1290 

development  of,  1293 
olfactory,  1050 
Hamate  (unciform)  bone,  159,  163 
Hamular  process  of  sphenoid,  66,  106,  1351 
Hamulus,  81,  163 
Hand,  bony  points  of,  1424 

clinical  anatomy  of,  1424 

fascia  of,  1427 

muscles  acting  on,  at  wrist,  504 

musculature  of,  363,  383,  403 

skin-folds  of,  1425 

synovial  membranes  of,  1431 
Hard  palate,  1104 
Hare-lip,  1352 
Harmonic  sutures,  212 
Hassal's  corpuscles  of  thymus,  1322 
Head  of  axis,  33 

of  bone,  29 

bony  landmarks  of,  1331 

clinical  and  topographical  anatomy  of,  1331 

deep  lymphatic  nodes  of,  714 
vessels  of,  714 

of  epididymis,  1256 

lymphatics  of,  709 

of  muscle,  314 

muscles  acting  on,  502 

musculature  of,  323 

of  pancreas,  1192 

process,  11 

sympathetic  ganglia  of,  959 
Heart,  508 
Heart,  atria  of,  511 

development  of,  623 

foetal,  695 

ventricles  of,  516 

lymphatics  of,  701,  730,  522 

muscle  of,  518 

nerves  of,  522 

relation  to  chest-wall,  523,  1368 

vessels  of,  519 
Heister,  valve  of,  1187 
Helicis  major,  1084 

minor,  1084 
Helicotrema,  81 
Helix,  1083 

Helweg's  (Bechterew's)  bundle,  784 
Hemiazygos  vein  (azygos  minor),  662 

accessory,  663 
Hemispheres  of  cerebellum,  805 

cerebral,  850 
Henle,  loop  of,  1246 
Henle's  glands,  1078 
Hepatic  artery,  594 

branches  of  superior  epigastric  artery,  567 

of  vagus,  958 

duct,  1187 

(right  coUc)  flexure,  1173,  1379 

lymphatic  nodes,  730,  736,  1186 


Hepaticlymphatics,  1186 

plexus  of  nerves,  1045 

veins,  675 
Hepato-oolic  ligament,  1379 
Hepato-duodenal  ligament,  1150,  1185 
Hernia,  congenital,  1255,  1387,  1398 

femoral,  1394 

into  the  funicular  process,  1255,  1398 

infantile,  1398 

inguinal,  1255,  1394,  1398 

scrotal,  1255 

surgical  anatomy  of,  1394 

umbilical,  adult,  1402 
Hesselbach,  ligament  of,  430 

triangle  of,  1398 
Hey's  amputation,  1465 
Hiatus,  accessory,  116 

aorticus  of  diaphragm,  437 

canalis  facialis,  73,  116 

cesophageus,  437 

sacralis,  40 

semilunaris  of  middle  nasal  meatus,  1205 
Highest  nuchal  line,  52 

Highmore,  antrum  of,  87,  90,  111,  1206,  1346 
Hilus  of  kidney,  1242 

of  lungs,  1229,  1230 

of  ovary,  1268 

of  spleen,  1309 

of  suprarenal  glands,  1325 
Hind-brain,  804 
Hip,  musculature  of,  453,  454 
Hip-joint,  276 

arterial  supply,  282 

ligaments  of,  277 

lymphatics  of,  750 

movements  of,  282 

muscles  acting  upon,  283 

nerve-supply,  282 

relations,  282 

surgical  anatomy  of,  1435 
Hippocampal  branch  of  posterior  communi- 
cating artery,  554 

commissure  (psalterium  or  b'ra),  869,  890 

digitations,  877 

(ohorioid)  fissure,  868 

gyrus,  868 
Hippocampus,  868 

gyrus  of,  868 

major,  868,  877 

minor  (calcar  avis),  864,  868,  876 
Hirci,  1290 

Homologies  of  parts  in  sexes,  1280 
Homology  of  the  bones  of  the  limbs,  206 
Horizontal  fissure  of  cerebellum,  805 
Horner's  muscle,  336,  1078 
Horns  of  spinal  cord,  776 
Houston's  folds  of  rectum,  1177,  1390 
Huguier,  canal  of,  75,  77,  108 
Hum.eral  artery,  anterior  circumflex,  572 

posterior  circumflex,  573 
Humerus,  description  of,  146 

clinical  anatomy  of,  1410,  1414 

nutrient  artery  of,  576 

ossification  of,  161,  1416 

tuberosities  of,  147 
Humor,  aqueous,  1052,  1064 

vitreous,  of  eye,  1052,  1064 
Hunter's  (adductor)  canal,  468,  1441 
Hyaloid  canal  (canal  of  Cloquet),  1064 

membrane,  1064 
Hydatid  of  Morgagni,  1257,  1269 
Hymen,  1276,  1392 
Hyo-epiglottic  ligament,  1218 
Hyo-glossal  membrane,  346 
Hj'o-glossus,  346 
Hyoid  bars,  119 

bone,  99,  119 


1498 


INDEX 


Hyoid  bone  at  birth,  124 
cornua  of,  99,  100 
muscles  acting  on,  501 
branch  of  lingual  artery,  540 

of  superior  thyreoid  artery,  538 
bursa,  1217 
Hyo-mandibular  muscles,  325 
Hyo-temporal  muscles,  325 
Hyo-thyreoid  ligament,  1217 

membrane,  1217 
Hyparterial  bronchus,  1232 
Hypertrichosis,  1290 
Hypertrophy  of  nails,  1296 
Hypochondriac  region,  1143 
Hypochordal  bar,  51 

Hypogastric  (internal  iliac)  artery,  605,  638 
branches,  606,  639 
lymphatic  nodes,  732 
plexuses  of  nerves,  1045 
region,  1143 
(internal  iliac)  vein,  679 
tributaries,  680 
Hypoglossal  eminence  (trigonum  hypoglossi), 
814 
foramen  (canal),  54,  108,  117,  125 
(cervical)  loop,  974,  979 
nerve,  952 

central  connections,  820,  954 
nucleus  of,  820 
Hypomalar,  95 

Hypophyseal  fossa  (sella  turcica),  63 
Hypophysis  cerebri,  758,  847,  848,  1342 

development  of,  848 
Hypospadias,  1280,  1388 
Hypothalamic  nucleus  (body  of  Luys),  884 

sulcus,  (sulcus  of  Monro),  847 
Hypothalamus,  881 

optic  portion  of,  847 
Hypothenar  fascia,  387 
Hypo-tympanic  recess,  77 


Ileo-csecal  fossa,  1172 
(colic)  valve,  1172 
region,  1376 
Ileo-colic  artery,  598 
fossa,  1172 
vein,  677 
Ileum,  1165,  1376 

Iliac  arteries,  collateral  circulation,  605,  1382 
common,  603,  605,  638 
deep  circumflex,  616 
external,  614,  638 
superficial  circumflex,  618 
branch  of  ilio-lumbar  artery,  607 
(nutrient)  branch  of  obturator  artery,  608 
colon,  1174,  1379 
fascia,  455,  466 
fossa,  170 
lymphatic  nodes,  common,  731 

external,  732 
plexus  of  nerves,  1045 
spines,  169 
vein,  external,  683 

internal  (hypogastric),  679 
veins,  common,  679 
Iliacus,  455 

minor,  455 
Ilio-cocoygeus,  440,  448 
Ilio-costal  region,  1407 

Ilio-costalis    cervicis     (cervicalis   asoendens), 
416 
dorsi  (accessorius),  416 
lumborum,  416 
Ilio-femoral  ligament,  278 
musculature,  454 


Ilio-hypogastric  nerve,  998 
Ilio-inguinal  nerve,  1000 
Ilio-lumbar  artery,  606 
ligament,  233 
vein,  680 
Iho-pectineal  eminence,  169 
fascia,  455,  466 
fossa,  467 
line,  173 
Ilio-tibial  band,  457,  458,  1436 
Ilio-trochanteric  band,  280 
Ilium,  169 
crest  of,  169 
tuberosity  of,  171 
Inca  bone,  (interparietal),  57 
Incisive  branch  of  inferior  alveolar  (dental) 
artery,  548 
foramen,  89 
fossa,  87 
papilla,  1104 
sutures,  106 
Incisivus  labii  inferioris,  332 

superioris,  332 
Incisor  crest,  90 
fossa,  95 
teeth,  1120 
Incisura,  29 

apiois  cordis,  510 
interarytsenoidea,  1222 
Incisure,  anterior,  of  auricle,  1082 
antitragic,  1082 
of  Santorini,  1085 
terminal  (auricle),  1084 
Incudo-maUeolar  articulation,  1090. 
Incudo-stapedial  articulation,  1090 
Incus,  79,  119 

ligaments  of,  1091 
Index,  cephalic,  117 
pelvic,  177 
thoracic,  139 
Induseum  griseum,  868 
Infra-clavicularis,  374 
Infraglenoid  tubercle  of  scapula,  143 
Infrahyoid  musculature,  327,  350 

portion  of  external  cervical  fascia,  347 
Infra-omental  region  of  peritoneum,  1372 
Infra-orbital  artery,  549,  1075 

branches  of  cervico-facial  nerve,  945  , 
canal,  87,  103,  126 
foramen,  87,  1345 
groove,  87 
nerve,  937,  939 
plex-us,  937,  939,  945 
process,  95 
sulcus,  1284 
vein,  646 
Infraspinatus,  368 

Infraspinous  branches  of  posterior    scapular 
artery,  566 
of  transverse  scapular  artery,  565 
fossa,  142 
Infra-temporal  (zygomatic)  fossa,  101,  1332 

ridge,  65 
Infratrochlear  nerve,  936,  937 
Infra-vomerine  center,  71 
Infundibula  (ureter),  1248 
Infundibular  recess,  848 
Infundibulo-pelvic  ligament,  1267 
Infundibulum  of  cerebrum,  848 
of  ethmoid,  83 

in  middle  nasal  meatus.  111,  1205 
of  tuba?  uterinte  (Fallopian  tubes),  1270 
Inguinal     abdominal     (internal     abdominal) 
ring,  430,  1371,  1396 
branches  of  femoral  artery,  620 
canal,  424,  430,  1371,  1395 
hernia,  1255,  1394,  1398 


INDEX 


1499 


Inguinal  (Poupart's)  ligament,  424,  429,  1371, 
1399,  1438 
reflected  (triangular)  fascia,  430,  1395 
lymphatic  nodes,  746 
ring,  subcutaneous   (external  abdominal), 

429,  1371,  1394 
(iliac)  regions,  1143 
Inion,  101,  1331 

Inlet  or  brim  (superior  aperture)  of  pelvis,  175 
Innominate  artery,  532,  637,  1369 

branches,  532 
Innominate  canal  (canaliculus),  65 
bone,  169 

(brachio-cephalic)  veins,  641,  691,  692 
relations  to  thoracic  wall,  1369 
Inscriptio  tendinea,  317,  430 
Insertion  of  muscles,  314  (see  also  individual 

muscles) 
Inspiration,  muscles  which  affect,  247 
Insula  (island  of  Reil),  856 
Integument,  1281 
Interarticular  cartilage,  211 

ligament  (capitular  articulation),  241 

(sterno-costal  joint),  245 
menisci  (semilunar  ftbro-cartilages),  289 
Interarytffinoid    (procricoid)    cartilage,    1213, 

1218 
Inter-brain,  843 
Intercalated  lymph-nodes,  706 
Intercapitular  veins  (hand),  667 

(foot),  684 
Intercarpal  ligaments,  269 
Interchondral  articulation,  246 
arterial  supply,  247 
capsule  of,  247 
movements,  247 
nerves,  247 
Interclavicular  ligament,  248 

notch,  133 
Intercoccygeal  joints,  238 
Intercondyloid  fossa  of  femur,  182 
eminence  of  tibia,  185 
fossae  of  tibia,  185 
tubercles,  185 
Intercostal   branches   of   internal   mammary 
artery,  567 
arteries,  588 

superior,  568 
branches  of  musculo-phrenic  artery,  567 
ligaments,  external,  423,  432 
lymphatics,  724,  728 
muscles,  function  of,  422 
nerves,  thoracic,  995 
spaces,  139 
veins,  664 
Intercostales  externi,  423,  432 

interni,  423,  433 
Intercosto-brachial  (interc osto- humeral) 

nerve,  995 
Intercrural  (intercolumnar)  fibres  of  external 

obhque,  430,  1394 
Intercuneiform  articulation,  304 
Interfascial  (Tenon's)  space,  715 
Interfoveolar  ligament,  430,  435 
Interior  of  skull,  112 
Interlobar  fissure  of  lungs,  1230 
Intermediate  cell  mass,  15 
crus  of  diaphragm,  437 
fasciculus  (mixed  lateral  zone),  784 
plex-us,  1041 
Intermetacarpal  articulations,  273 
Intermetatarsal  joints,  309 
Intermuscular  septa,  314 
of  foot,  492 
of  leg,  477 
of  thigh,  468 
septum  of  arm,  lateral,  377 


Intermuscular  septum  of  arm,  medial,  377 
Interossei  dorsales  (foot),  499 
(hand),  410 
plantares,  499 
volares  (hand),  409 
Interosseous  arteries  of  foot,  633 
of  forearm,  577,  579,  1423 
artery,  of  forearm,  common,  577 
dorsal,  579 
volar,  577,  639 
crest  of  fibula,  190 
of  radius,  153 
of  tibia,  188 
of  ulna,  157 
crural  nerve,  1010 

ligaments,  anterior  talo-calcaneal  joint,  302 
inferior,  tibio-fibular  articulation,  297 
intercuneiform  joints,  304 
middle  tarso-metatarsal  joints,  308 
of  middle  tibio-fibular  union,  296 
of  pelvic,  articulations,  235 
of  posterior  talo-calcaneal  joint,  301 
superior,  tibio-fibular  joint,  295 
membrane  of  forearm,  263,  264,  1420 
muscles  of  foot,  454,  499 

of  hand,  409 
nerve,  posterior,  986 

volar  (anterior),  992 
recurrent  artery,  580 
Interparietal  bone,  119 

sulcus  (intraparietal),  861 
Interpeduncular  fossa,  835 

nucleus  (ganglion),  843,  885 
Interphalangeal  articulations  of  fingers,  276 

of  toes,  310 
Interpterygoid  fascia,  339 
Interpubic  fibro-cartilage,  240 
Intersigmoid  fossa,  1175 
Interspinal  muscles  (interspinals),  412,  419 
Interspinous  ligaments,  231 
Intersternal  joints,  244 
Intertragic  notch,  1082 
Intertransversarii,  412,  417 
Intertransverse  ligaments,  231 
muscles,  anterior  and  lateral,  356 
dorsal,  412 
Intertrochanteric  crest,  178 
Intertubercular  (bicipital),  groove,  148 
Intervaginal  space  of  optic  nerve,  1073 
Interventricular  foramen  (foramen  of  Monro), 
847,  874 
septum,  516 
Intervertebral  articulation,  ligaments  of,  225 
fibro-cartilages,  225,  238 
veins,  666 
Intestinal  arteries,  596 
veins,  677 
lymphatic  trunk,  731 
Intestines,  clinical  anatomy  of,  1375 
large,  1170,  1376 
lymphatics  of,  734 
small,  1161,  1375 
Intracranial  portion  of  internal  carotid  artery, 
550 
of  vertebral  artery,  560 
Intralabial  muscles,  331 
Intraparietal  sulcus,  861 
Intrinsic  muscles  of  great  toe,  495 
of  larynx,  1218 
of  httle  toe,  498 
of  tongue,  1110 
Introduction,  1 

Intumescentia  tympanica,  951 
Involution  of  mammary  gland,  1303 
Iris,  1052,  1054,  1060,  1065. 
Ischial  spine,  172 
Ischio-bulbosus  muscle,  451 


1500 


INDEX 


Ischio-capsular  ligament,  278 
Ischio-cavernosus  (erector  penis),  443,  451 
Iseliio-femoralis,  461 
Ischio-pubicus  (Vlacovitoh),  450 
Ischio-pubo-femoral  musculature,  463 
Ischio-rectal  fossae,  441,  445,  1384 
Ischium,  171 

Island  of  Reil  (insula  or  central  lobe),  865 
Isthmus,  aortic,  531 

of  Fallopian  tubes,  1290 

of  fauces,  1100,  1352 

of  gyrus  fornicatus,  867 

pharyngeal    (faucium),    1100,    1130,    1131, 
1352 

of  rhombeneophalon,  758,  832 

of  thymus,  1321 

of  thyreoid  gland,  1313 

of  tuba  auditiva  (Eustachian  tube),  1092 

of  uterus,  1271 
Iter  chordae  anterius,  126 
posterius,  78,  126 


Jacobson,  nerve  of,  951,  961 

organ  of,  1057,  1204 
Jejunal  and  Oiac  branches  of  superior  mesen- 
teric artery,  598 
Jejuno-ileum,  lymphatics  of,  734 
Jejunum,  1165,  1376 
Joint-furrows,  1284 
Joints  (see  "Articvdations"). 
Jugular  foramen,  74,  108,  117,  125 
fossa,  73,  108 

ganglion   (superior)   of    glosso-pharyngeal, 
951 
of  vagus,  954,  956 
nerve,  960,  1035 
(interclavicular)  notch,  133 
process,  54,  108 
vein,  anterior,  648 
line  of,  1356 
external,  646,  1359 
internal,  659,  691 
posterior  external,  648 
venous  arch,  648 
Jugum  sphenoidale,  67 


K 


Kidneys,  1241,  1379 

clinical  anatomy  of,  1379 

development  of,  1247 

lymphatics  of,  701,  737,  1247 

position  and  relations  of,  1243,  1380 

structure,  1246 

surfaces  of,  1243 

variations  and  comparative,  1247 

vessels  and  nerves  of,  1247 
Knee-joint,  284 

anastomoses  around,  1457 

arterial  supply,  291 

bursae  around,  1449 

clinical  anatomy  of,  1449 

ligaments  of,  284 

lymphatics  of,  750 

movements  of,  292 

muscles  acting  upon,  295 

nerve-supply,  292 

relations,  292 

synovial  membrane  of,  290,  1448 
Krause,  end-bulbs  of,  1290 

glands  of,  1078 
Kronlein's  method  for  topography  of  brain, 

1340 


Labia  (see  also  "Lips"). 

of  cervix  uteri,  1272 

majora,  1276,  1392 

minora  (nymphae),  1277,  1392 
Labial  arteries  (of  mouth),  541 

(or  scrotal)  arteries,  anterior,  620 
posterior,  613 

branches,  inferior,  of  mental  nerve,  941 
superior,  of  maxillary  nerve,  939 

nerves,  anterior,  1000 
posterior,  1017 

tubercle,  1102 

veins  (of  mouth)  644 
(of  vulva),  683,  684 
Labyrinth  of  ethmoid,  82 

membranous,  1092 

osseous,  80 
Lacertus  fibrosus  (semilunar  fascia),  382 
Lacrimal  apparatus,  1079 

clinical  anatomy  of,  1346 

artery,  552 

bone,  85 

at  birth,  124 

branch  of  dorsal  nasal  artery,  554 
of  middle  meningeal  artery,  548 

canal,  1080 

caruncle,  1052,  1055 

crest,  85,  110 

ductus  (canaliculi),  1079 

fossa,  61,  109 

gland,  1079,  1348 

groove,  85,  87,  110 

nerve,  936,  1075 

papilla,  1054 

process,  85 

puncta,  1079,  1349 

sac,  1080,  1349 

tubercle,  88 

vein,  659 
Lacrimo-ethmoidal  cells,  84 
Laciniate  ligament  (internal  annular)  of  leg, 

480 
Lactiferous  duct,  1254 

sinus  (ampulla),  1254 
Lacuna(8e)  laterales,  649 

magna,  1264 

of  Morgagni  (urethral),  1264 

musculorum,  466 

vasorum,  466 

venous,  of  dura,  916 
Lacunar   (Gimbernat's)    ligament,    424,  429, 

466,  1400 
Lalognosis,  894 
Lambda,  101,  1331 
Lambdoid  suture,  57,  101 
Lamellous  corpuscles  of  (Vater,  or  Pacinian), 

1290 
Lamina(Ee),  anterior  elastic,  of  cornea,  1060 

basal  (vitreous),  of  chorioid,  1060 

basilaris  of  membranous  labyrinth,  1096 

of  cerebellum,  medullary,  808 

chorio-capillaris,  1060 

cribriform,  119 

cribrosa  solera,  930,  1055,  1059,  1073 

of  temporal  bone,  92 

of  cricoid  cartilage,  1210 

epithelial  chorioid,  876,  924 

fusca,  1059 

mediastinales,  1237 

medullary,  of  lenticular  nucleus,  880 
of  thalamus,  882 

papyracea  (os  planum),  83 

posterior  elastic,  of  cornea,  1060 

quadrigemina,  833 

rostal,  of  corpus  callosum,  852 


INDEX 


1501 


Lamina  of  septum  pellucidum,  812 
spiralis,  81 

suprachoroidea,  1057,  1060 
terminalis,  (of  brain),  848 

(of  isohio-rectal  fossa),  1384 
of  thyreoid  cartilage,  1210 
tragi,  1084 

of  tuba  auditiva,  1092 
of  vertebrEe,  30 
Landmarks  of  abdomen,  1370 
bony  of  the  ankle,  1459 

of  the  buttocks,  1442 

of  cranium  and  scalp,  1333 

of  elbow,  1417 

of  the  foot,  1464 

of  forearm,  1419 

of  the  knee,  1447 

of  neck,  1354 

of  the  leg,  1453 

of  thigh  and  hip,  1434 

of  wrist  and  hand,  1424 
Langerhans,  islets  of,  1195 
Lanugo,  1290 
Large  intestine,  1170 

anus,  1177 

blood-vessels  of,  1179 

caecum  or  caput  coli,  1170,  1377 

clinical  anatomy  of,  1376 

colon,  1173,  1378 

development  of,  1179 

lymphatics  of,  1179 

nerves  of,  1179 

rectum,  1176 

variations  and  comparative,  1130 

vermiform  process  (appendix),  1173,  1378 
Laryngeal  artery,  superior,  538 

inferior,  564 
nerve,  inferior,  957 

superior,  956 
pharynx,  1134 
prominence,  1211 
veins,  inferior,  659 

superior,  659 
ventricle,  1222 
Larynx,  1209 

cartilages  of,  1209 
cavity  of,  1220 
development  of,  1225 
joints  of,  1213 
lymphatics  of,  719,  1224 
muscles  of,  326,  501,  1218 
vessels  and  nerves  of,  1224 
vocal  folds  (cords),  1223 
Latissimo-condjdoideus  (dorso-epitrochlearis), 

379 
Latissimus  dorsi,  368 

clinical  anatomy  of,  1405 
Law  of  developmental  direction,  12 
Laxator  tympani  muscle,  79 
Left  atrium  of  heart,  514 
colic  artery,  603 

vein,  678 
common  carotid  artery,  533 

iliac  artery,  605 
coronary  artery,  520 
gastric  artery,  593 
gastro-epiploic  artery,  595 

vein,  677 
innominate  vein,  641 
lower  bronchial  artery,  588 
pulmonary  artery,  529 

veins,  529 
subclavian  artery,  556 
upper  bronchial  artery,  588 
ventricle  of  heart,  516,  517 
Leg,  bony  landmarks  of,  1453 
clinical  anatomy  of,  1453 


Leg,  fasciae  of,  497 

nauscles  acting  on,  505 
muscular  compartments,  1453 
musculature  of,  453,  477 
vessels  of,  1456 
Lemnisci,  decussation  of,  815 
of  medulla  oblongata,  815 
Lemniscus,  831,  839 
lateral,  816,  831,  839 
medial,  816,  831,  839 
nucleus  of,  824,  839 
Lens,  crystalline,  1052,  1057,  1062 
Lens-capsule,  1057 
Lenticular  nucleus,  878,  879 
process  of  incus,  79 
papillte  of  tongue,  1106 
Lenticulo-optic  artery,  562 
Lenticulo-striate  arterjf,  562 
Lesser  alar  (sesamoid)  nasal  cartilages,  1202 
curvature  of  stomach,  1152 
multangular  (trapezoid)  bone,  159,  162 
(gastro-hepatio)  omentum,  1150,  1185 
palatine  foramina,  106 
sac  of  peritoneum,  1148 
sigmoid  cavity  of  ulna,  157 
splanchnic  nerve,  1039 
tuberositj'  of  humerus,  147 
Levator  ani,  440,  448 
claviculae,  359 
cushion,  1130 
epiglottidis,  347 
labii  superioris,  322 

alaeque  nasi,  332 
menti,  334 

palpebrae  superioris,  1068 
penis,  451 
scapulffi  356,  359 
of  thyreoid  gland,  1315 
veli  palatini,  1137 
Levatores  costarum,  423,  432 

longi,  432 
Levels,  vertebral,  1409 
Lieberkiihn,  (crypts)  glands  of,  1166,  1177, 

1390 
Lienal  plexTis  of  nerves,  1045 
Lieno-renal  ligament,  1310 
Lieutaud,  vesical  trigone  of,  1252 
Ligament (s)  (see  also  "Ligamentum"),  211 
alar  (occipito-dental  or  check),  223 
of  ankle-joint,  298,  1463 
annular,  at  ankle,  1463 
of  finger,  387    ^ 

of  superior  radio-ulnar  joint,  262 
of  trachea  and  bronchi,  1227 
of  wrist,  387 
anterior,  of  ankle,  298 
annular  (wrist),  387 
atlanto-epistrophic,  221 
atlanto-occipital,  218 
crucial,  288 
longitudinal,  227 
medio-carpal,  270 

oblique  (lateral  occipito-atlantal),  219 
sacro-coccygeal,  234 
sacro-iliac,  234 
of  symphysis  pubis,  239 
talo-calcaneal,  302 
talo-fibular,  299 
apical  dental  (suspensory),  223 
arcuate  (subpubic),  239 
connecting  articular  processes  vertebrae,  228 
Cooper's,  1400 

of  articulation  of  atlas  with  occiput,  218 
of  atlanto-epistrophic  joint,  221 
of  auricle  (of  ear),  1084 
uniting  bodies  of  vertebrae,  225 
broad  (lateral),  of  uterus,  1267,  1393 


1502 


INDEX 


Ligament(s)  of  ealcaneo-cuboid  joint,  306 
calcaneo-fibular,  299 
calcaneo-metatarsal,  492 
of  capitular  (oosto-oentral)  articulation,  241 
capsular,  of  elbow-joint,  258 
carpal  (annular),  1427 
of  carpo-metacarpal  joints,  272 
of  the  carpus,  dorsal,  384 

transverse,  387 

volar,  387 
cerato-oricoid,  1213 
check,  of  eyeball,  1072 
coccygeal,  911 
CoUes',  430 
conoid,  251 
coraco-acromial,  252 
coraco-clavioular,  251 
coraco-humeral,  255 
corniculo-pharyngeal,  1218 
coronary,  of  knee-joint,  290 

of  liver,  1184 
costo-clavicular,  (rhomboid),  249 
of  oosto-transverse  articulation,  243 
costo-xiphoid,  244,245 
crioo-arytaenoid,  1214 
crico-pharyngeal,  1218 
crico-tracheal,  1218 
crucial,  of  central  atlanto-dental  joint,  222 

of  knee-joint,  288 
cruciate,  of  leg,  479 

of  fingers,  387 
of  cuboideo-navicular  union,  303 
of  cubo-metatarsal  joint,  308 
of  cuneo-ouboid  articulation,  304 
of  cuneo-navicular  articulation,  304 
cysto-oolic,  1379 
deltoid  (of  ankle-joint),  298 
denticulate,  920,  921 
dorsal  intercarpal,  269 
of  elbow-joint,  258 
external  arcuate,  437 

intercostal,  423,  432 

lateral,  of  knee-joint,  286 
falciform,  of  liver,  1185 
fibular  collateral,  286 
of  first  row  of  carpal  bones,  269 
fundiform  (superficial  suspensory)  of  penis, 

427 
gastro-hepatic,  1150,  1185 
gastro-phrenic,  1150 

gastro-splenic,  (gastro-lienal),  1150,  1310 
Gimbernat's,  424,  429,  466 
gleno-humeral,  255 
glenoid  (lip),  255 
glosso-epiglottic,  1218 
hepato-colic,  1379 
hepato-duodenal,  1150,  1185 
Hesselbach's,  430 
of  hip-joint,  277 
hyo-epiglottic,  1218 
hyo-thyreoid,  1217 
ilio-lumbar,  238 
ilio-femoral,  278 
immediate,  225 
of  incus,  1091 

inferior  interosseous,  (tibio-fibular),  297 
of  inferior  radio-ulnar  joint,  264 
inferior  sacro-iliac,  235 

transverse,  (spino-glenoid),  253 
infundibulo-pelvic,  1267 
inguinal  (Poupart's),  424,  429,  1371,  1399, 

1438 
interarticular,  241,  245 
interclavicular,  248 
of  intercuneiform  joint,  304 
interfoveolar,  430,  435 
intermediate,  225 


Ligarnent(s)  of  intermetacarpal  joints,  273 
of  intermetatarsal  joints,  309 
internal  arcuate,  437 

lateral,  of  knee-joint,  286 

of  mandibular  articulation,  215 
interosseous,  cubo-metatarsal  joint,  309 

anterior  talo-calcaneal,  302 

intercuneiform  joints,  304 

intermediate  tarso-metatarsal  joint,  308 

metacarpal,  269 

of  pelvic  articulations,  235 

of  posterior  talo-calcaneal  joint,  301 
of  interphalangeal  joints,  fingers,  276 

of  toes,  311 
interspinous,  231 
of  intersternal  joints,  244 
intertransverse,  231,  238 
of  intervertebral  articulation,  227 
of  knee-joint,  284 

(internal  annular)  laciniate,  of  leg,  480 
ischio-capsular,  278 

lacunar  (Gimbernat's)  424,  429,  466,  1400 
of  larynx,  1213 
lateral,  of  ankle-joint,  299 

calcaneo-navicular,  302,  305 

hyo-thyreoid,  1217 

malleolar,  anterior,  296 
posterior,  297 

sacro-coccygeal  (intertransverse),  238 
of  left  vena  cava,  521,  523 
of  liver,  1184 

malleolar  (of  tympanum),  1091 
of  mandibular  articulation,  215    , 
medial  palpebral,  1052 
median  crico-thyreoid,  1215 

hyo-thyreoid,  1217 
of  medio-carpal  joint,  270 
of  metacarpo-phalangeal  joints,  274,;_275 
of  metatarso-phalangeal  joints,  310 
of  mid  radio-ulnar  union,  262 
middle  costo-transverse,  243 

tibio-fibular  (interosseous),  296 
morphology  of,  213 
neck,  243 
oblique,  of  mid  radio-ulnar  union,  262 

popliteal  (hgament  of  Winslow),  287 
occipito-cervical,  223 
uniting  occiput  and  epistropheus,' 223 
orbito-tarsal,  1071 
of  ossicles  of  ear,  1090 
ovarian,  1269 
patellar,  471 

of  pelvic  articulations,  234 
piso-hamate,  269 
piso-metacarpal,  269 
phreno-cohc  or  costo-colic,  1150, 1174, 1310, 

1379 
phrenico-lienal  (lieno-renal)  ,'1310 
plantar,  1468 

calcaneo-ouboid,  307 

calcaneo-navicular,  302,  305 
accessory,  310 

long,  307 
pulmonary,  1236 
posterior,  of  ankle-joint,  298 

annular  (wrist),  384 

atlanto-epistrophic,  221 

atlanto-occipital,  218 

costo-transverse,  243 

crucial  (of  knee),  288 

longitudinal,  227 

(dorsal)  medio-carpal,' 270 

sacro-iliac,  234 

of  symphysis  pubis,  239 

of  talo-calcaneal  joint,  301 

talo-fibular,  299 
Poupart's,  424,  429,n371 


INDEX 


1503 


Ligament  (s),  proper  scapular,  252 
pubo-prostatic  (pubo-vesical),  1252 
radial  collateral,  261,  267 
radiate  of  anterior  costo-central  or  stellate, 
242 

of  medio-carpal  joint,  270 

sterno-costal,  245 
of  radio-carpal  joint,  266 
of  radio-ulnar  joints,  261,  264 
reflected  inguinal  (triangular  fascia),  430 
rhomboid  (costo-clavioular),  249 
round,  of  uterus,  1274 

of  liver,  1185 
of  sacro-coccygeal  articulation,  238 
sacro-lumbar,  232 

saoro-spinous  or  small  sacro-sciatic,  236 
sacro-tuberous,  235 
of  sacro-vertebral  articulations,  232 
of  second  row  of  carpal  bones,  270 
of  shoulder-joint,  254 
between  skull  and  vertebral  column,  218 
spheno-mandibular,  217 
spino-glenoid  (inferior  transverse),  253 
connecting  spinous  processes  of  vertebrae, 

229 
spiral,  of  cochlea,  1096 
spring,  305 
sterno-clavicular,  248 
of  sterno-costal  joints,  245 
of  sterno-costo-clavicular  articulation,  248 
sterno-pericardial,  522 
stylo-hyoid,  99 

stylo-mandibular  (stylo-maxillary),  217 
superficial  transverse,  387 
superior  costo-transverse,  243 

interosseous,  tibio-fibular  joint,  295 

sacro-iliac,  234 

sterno-costal,  245 

transverse    (coracoid   or   suprascapular), 
253 
supraspinous,  230,  238 
suspensory,  of  Cooper,  1303 

of  the  eyeball,  1072,  1348 

of  lens  of  eye,  1057,  1064 

of  ovary,  1269 

of  penis,  427,  1260 

of  Treitz,  1164,  1376 
of  symphysis  pubis,  238 
talo-calcaneal,  302 
of  talo-navicular  joint,  305 
temporo-mandibular,  215 
thyreo-epiglottic,  1215 
thyreoid,  1314 
tibial  collateral,  286 
tibio-fibular,  295 
transverse,    of   central    atlanto-epistrophic 

joint,  222 
crural,  479 

dorsal  (medio-carpal  joint),  270 
-  of  heads  of  metatarsal  bones,  309 

of  hip-joint,  280 

humeral,  256 

of  knee-joint,  289 

of  pubis,  446 
connecting  transverse  processes  of  vertebrae, 

231 
trapezoid,  251 
triangular,  of  liver,  1185 
tubercular  (posterior  costo-transverse),  243 
ulnar  collateral,  259,  266 
umbilical,  1250,  1252 
uniting  laminae  of  vertebrae,  229 
of  urinary  bladder,  1252 
utero-sacral,  1274 
vaginal,  317 
vaginal  (fingers),  387 
ventricular  of  larynx,  1215 


Ligament(s),  vocal,  1215 

volar  accessory  (glenoid),  274 
intercarpal,  269 
radio-carpal,  266 
Ligamenta  denticulata,  911 

flava,  229 
Ligamentous  branch  of  ovarian  artery ,"[  602 
Ligamentum (a)  alaria  (knee-joint),  291 

ano-coccygeum,  449 

arteriosum,  628,  531 

breve,  399,  401 

dentioulatum,  920,  921 

epididymis,  1255 

interfoveolare,  430 

longum,  399,  401 

rauoosum  (knee-joint),  290 

nuchas,  231,  414 

patellae,  285,  1448 

pectinatum  iridis,  1060 

sacro-iliaoa,  anteriora,  177,  234 

teres,  280 

of  liver,  675,  1185 

(round  ligament)  of  uterus,  1274 

venosum  of  liver,  675,  1185 

Winslowii,  287 
Ligature  of  anterior  tibial  artery,  1458 

of  brachial  artery,  1414 

of  common  carotid  artery,  1358 

of  femoral  artery,  1441 

in  Hunter's  canal,  1442 

of  popUteal  artery,  1452 

of  posterior  tibial  artery,  1458 

of  third  part  of  subclavian  artery,  1359 

of  ulnar  artery,  1423 
Ligula  (taenia  ventriculi  quarti),  813 
Limbic  lobe,  865,  866 
Limbous  sutures,  212 
Limbs,  cutaneous  areas  of,'1020,  1022,',1024 

development  of,  20 
Limbus  of  cornea,  1025 

fossae  ovalis,  511 

sphenoidalis,  63 

of  tympanic  membrane,  1087 
Limen  of  insula,  857,  865 

nasi,  1204 
Limiting  sulcus  of  floor  of  fourth  ventricle,  813 
Line(s)  (see  also  "Linea"). 

(striae)  albicantes,  1283,  1384 

bony,  29 

of  femur,  intertrochanteric,  178 
sph-al,  178 

of  fibula,  oblique,  190 
secondary  obUque,  190 

gluteal,  170 

ilio-pectineal,  173 

mylo-hyoid,  95 

Nflaton's,  1436 

oblique,  of  mandible,  95 
of  radius,  154 
of  thyreoid,  124 

popliteal,  189 

of  scapula,  oblique,  142 

supra-condylar,  of  femur,  181 

temporal  (ridges),  57,  60,  1332 

transpyloric  (Addison's),  1153,  1370 

trapezoid  (oblique),  140 

of  ulna,  oblique,  157 
LLaea  alba  of  abdomen,  427,  1370 
viscera  behind,  1373 

aspera,  178 

pectinea  of  femur,  181 

semiciroularis,  427 

semilunaris  of  abdomen,  1371 

splendens,  921 

suprema  (highest  nuchal  line),  52 
Lingual  artery,  539 
branches,  539 


1504 


INDEX 


Lingual  (gustatory)  branch  of  inferior  alveolar 
(dental)  artery,  548 
of  glosso-pharyngeal  nerve,  952 
of  facial  nerve,  944  ^ 

fascia,  346 

follicles,  1107  ■' 

gyrus,  864 
nerve,  940,  1350 
papillae,  1160 
plexus  of  nerves,  1036 
tonsil,  1107 
veins,  660 
Lingula  cerebelli  (luigula  vermis),  806,  831 
of  left  lung,  1229 
of  mandible,  96 

of  sphenoid,  64  > 

of  Wrisberg,  942 
Lips,  1102,  1349 

of  Eustachian  aperture,  1130 
glenoid,  255 

of  ileo-c£ecal  valve,  1172 
lymphatics  of,  713 
variations  and  comparative,  1172 
vocal,  1223 
Lisfranc,  amputation  of,  1465 
Lissauer,  marginal  zone  of,  782 
Little  finger,  muscles  of,  404 
Littr6,  glands  of  (urethral),  1264 
Liver,  1180 

blood-vessels  of,  1185 

clinical  anatomy  of,  1373 

development  of,  1189 

ductus    oholedochus    (common    bile-duct), 

1188 
gall-bladder,  1187 
ligaments  of,  1184 
lobes  and  fissures  of,  1180 
lymphatics  of,  699,  736 
topography  of,  1373 
Liver,  surfaces  and  borders  of,  1181 
variations  and  comparative,  1190 
Lobe(s),  biventral,  807 
central,  856 
of  cerebellum,  805 
frontal,  857 

inferior  semilunar,  of  cerebellum,  807 
limbic,  865,  866 
of  liver,  1183 
of  lungs,  1230 
of  mammary  gland,  1302 
occipital,  863 
olfactory,  865 
■parietal,  860 
of  prostate,  1265 

pyramidal,  of  thyreoid  gland,  1314 
quadrangular,  806 

superior  semilunar  of  cerebellum,  806 
of  telencephalon,  853 
temporal,  of  cerebrum,  854 
of  thymus,  1320 
of  thyreoid  gland,  1313 
uvular,  of  cerebellum,  791 
Lobule  of  auricle  of  ear,  1083 
central,  of  cerebellum,  806 
of  cerebellum,  805 
inferior  parietal,  863 
paracentral,  857,  863 
quadrate,  863 
splenic,  1312 
superior  parietal,  862 
of  testis,  1256 
of  thymus,  1321 
of  thyreoid  gland,  1316 
Lobulus  epididymis  (conus  vasculosus),  1256 
Locus  caeruleus  of  floor  of  fourth  ventricle, 

815,  829 
Loewenthal's  tract,  786 


Longissimus  capitis  (trachelo-mastoid),  416 
cervicis  (transversalis  cervicis),  416 
dorsi,  416 
Longitudinal  arch  of  foot,  1468 
bundle,  posterior,  817 
fasciculus,  inferior,  892 
medial,  817,  842 
nucleus  of,  871 
superior,  892 
fissure  of  cerebrum,  850 
ligament  of  intervertebral  articulation,  227 
(sagittal)  sinuses,  649,  650 

striEe  of  corpus  callosum,  851,  892 

of  hippocampus,  871 
vertebral  veins,  665 
Longitudinalis  hnguse  inferior  medius,  347 
Longus  capitis  (rectus  capitis  anterior  major), 
355 
colli,  355 
Loop,  cervical  (hypoglossal),  953,  979 

Henle's,  1246 
Louis,  angle  of,  139 
Lower  extremity,  articulations  of,  276 
clinical  anatomy  of,  1434 
cutaneous  areas  of,  1024 
fasciie  of,  454 
lymphatics  of,  746,  748 
musculature  of,  452 
Lowest  lumbar  (lumbalis  ima)  artery,  603 
Lumbar  arteries,  593,  638 
lowest  (ima),  603 
branch  of  ilio-lumbar  artery,  607 
enlargement  of  spinal  cord,  772 
fascia,  436 
lymphatic  nodes,  730 

trunks,  730 
muscle,  436 
nerves,  973,  996 

posterior  primary  divisions,  973 
plexus,  998 

branches  of,  998 
composition  of  nerves  of,  998 
situation  of,  998 
portion  of  sympathetic  system,  1039 
puncture  (Quinclve),  1408 
regions,  1143 
ribs,  132 
veins,  675 

ascending,  662,  663 
vertebrse,  37 
description,  37 
development  of,  48 
Lumbo-costal  arch,  lateral,  437 

medial,  437 
Lumbo-dorsal  fascia,  414,  428 
Lumbo-inguinal    (crural)    branch    of   genito- 
femoral nerve,  1000 
Lumbo-sacral  angle,  43 
plexus,  996 
trunk,  1005 
Lumbricales  (foot),  454,  495 

(hand),  408,  409 
Lunate  (semilunar)  bone,  159,  161 
Lungs  (pulmones),  1228 
clinical  anatomy  of,  1367 
development  of,  1235 
form  of,  1228 
lobes  of,  1230 
lymphatics  of,  729,  1235 
surfaces  of,  1229 
topography  of,  1233,  1367 
variations  of,  1235 
vessels  and  nerves  of,  1234 
Lunula  of  nails,  1295 

of  semilunar  valves,  517 
Luys,  body  of,  884 
Lymph,  movement  of,  702 


INDEX 


1505 


Lymphatic  capillaries,  697,  698 

duct,  right  (terminal  collecting),  728 
follicle,  70-1 

nodes    (glands)    of    abdomen    and    pelvis, 
730 

ano-rectal,  735  - 

anterior  auricular,  709 
mediastinal,  724 

axillary,  719 

bronchial,  725,  1226 

buccinator,  711 

coeliac,  730 

common  iliac,  731 

deep  cervical  chain,  714 

delto-pectoral,  719 

development  of,  707 

diaphragmatic,  725,  736 

epigastric,  732,  733 

external  iliac,  732 

facial,  709,  711 

gastric,  730,  734 

of  head  and  neck,  709,  714 

hepatic,  730,  736 

hypogastric,  732 

inferior  deep  cervical,  714 

inguinal,  746 

internal  mammary,  724 

intercostal,  724 

of  larynx,  1224 

of  lower  extremity,  746 

lumbar,  730 

mesenteric,  731 

meso-colic,  734 

occipital,  709 

parietal,  of  thorax,  724 

parotid,  709 

of  pelvis,  730 

popliteal,  748 

post-aortic,  731 

posterior  mediastinal,  725 
auricular,  709 

pre-aortic,  730 

pulmonary,  725 

sacral,  733 

splenic,  730,  736 

structure  of,  704 

subinguinal,  746 

submaxillary,  709 

submental,  711 

superficial  cubital  (supratrochlear), 
719,1 

superior  deep  cervical,  714 

supramaxillary,  711 

of  thorax,  deep,  724 
visceral,  724 

umbilical,  733 

of  upper  extremity,  719 
system,  697 

general  anatomy  of,  697 
special  anatomy  of,  709 
development  of,  706 
of  eyeball,  1065 
of  orbit,  1076 
vessels,  702,  705 

of  abdomen  and  pelvis,  733 
of  eyelids,  1078 
of  face,  712 
of  head,  712,  714 
of  hip-joint,  750 
of  knee-joint,  750 
of  lower  extremity,  748 
of  neck,  712,  714 
of  CESophagus,  730,  1141 
regeneration  of,  707 
structure  of,  702 
of  thorax,  deep,  725 
superficial,  723 
95 


Lymphatic  vessels  of  upper  extremity,  deep, 
721 
superficial,  721 
Lymphatics  of  abdomen  and  pelvis,  730 

in  abdominal  wall,  1372 

of  alimentary  tract,  699,  733 

of  anus,  735 

of  auricle  (of  ear),  714,  1084 

of  brain,  714 

capillaries,  697 

of  clitoris,  745 

of  conjunctiva,  698,  712 

of  diaphragm,  728 

of  digestive  tract  in  head  and  neck,  715  ' 

of  ductus  deferens  and  seminal  vesicles,  744 

of  duodenum,  734 

of  excretory  organs,  737 

of  external  auditory  meatus,  714,  1086 

of  the  eye,  715,  1065 

of  eyelids,  712 

of  Fallopian  tube,  745,  1270 

of  female  external  genitals,  744,  1278 

of  gums,  715 

of  head  and  neck,  709 

of  heart,  522,  701,  730 

of  ileooEeoal  region,  734 

intercostal,  728 

of  jejuno-ileum,  734 

of  kidney,  737,  1247 

of  large  intestine,  734,  1179 

of  larynx,  719,  1224 

of  lips,  713 

of  liver,  736,  1186 

of  lower  extremity,  746,  1468 

of  lungs,  729,  1235 

of  mammary  gland,  723,  1305 

of  nasal  cavities,  717,  1208 

of  neck,  709 

of  nose,  712,  1203,  1208 

of  ovary,  745,  1269 

of  palate,  717 

of  pancreas,  736,  1195 

of  parotid  gland,  1115 

of  penis,  744,  1262 

offpharynx,  717,  1138 

of  pleura,  1239 

of  prostate,  739,  1265 

of  rectum  and  anus,  735 

of  reproductive  organs,  male,  742 

of  scalp,  712 

of  scrotum,  742,  1255,  1385 

of  shoulder-joint,  723 

of  skin,  698,  1289 

of  small  intestine,  1168 

of  spleen,  736,  1312 

of  stomach,  734,  1156 

of  suprarenal  glands,  738,  1326 

of  teeth,  1124 

of  testis,  744,  1256,  1387 

of  thoracic  muscles,  723 

of  thorax,  723 

of  thj'reoid  gland,  719,  1317 

of  thymus,  729,  1322 

of  tongue,  715,  1111 

of  tonsils,  1138 

of  trachea  and  bronchi,  699,  1228 

of  tubae  (Fallopian  tubes),  1270 

of  upper  extremity,  719,  1424 

of  ureter,  738,  1249 

of  urethra,  female,  742 
male,  744 

of  urinary  bladder,  739,  1253 

of  uterus,  745,  1274 

of  vagina,  745,  1276 

of  vulva,  744,  1278 
Lymph-follicles,  704 
Lymph-nodes,  704 


1506  INDEX 


Lymphoglan dulse,  704 
Lymphoid  organs,  704 
Lyra,  hippocampal,  869 

M 

Macewen's  suprameatal  triangle,  1337 
Macula  aoustica  saoouli,  950,  1094 
utriculi,  1093 
lutea  (yellow  spot),  1055,  1057 
Magendie,  foramen  of,  813 
Major  sublingual  duct   (of  Bartholin),   1117 

palatine  artery,  549 
Malar  bone,  93 

branches  of  maxUlary  nerve,  938 

of  temporo-facial  nerve,  945 
tubercle,  95 
tuberosity,  93 
Male  mammary  gland,  1305 
pelvis,  1382 

reproductive  organs,  1263,  1386 
Malleolar  artery,  lateral,  632 
medial,  632 

posterior  lateral  artery,  626 
folds  of  tympanic  mucous  membrane,  1089 
ligaments,  anterior  lateral,  296 
posterior  lateral,  297 
of  ossicles  of  ear,  1091 
prominence  of  tympanic  membrane,  1087 
recesses   of   tympanic  mucous  membrane, 

1089 
rete,  lateral,  626,  632 

medial,  626,  632 
stria  of  tympanic  membrane,  1087 
Malleoli,  clinical  anatomy  of,  1451 
lateral,  191 
medial,  189 
Malleus,  79,  119 
Malpighi,  pyramids  of,  1246 
Malpighian  corpuscle  (renal),  1246 

(splenic),  1311 
Mammary  artery,  external,  1305 
internal,  566,  1365 
cutaneous   branches    of   aortic   intercostal 

arteries,  590 
gland  (mamma),  1299 
clinical  anatomy  of,  1366 
line  (ridge),  1306 
lymphatics  of,  723,  1305 
in  male,  1305 

vessels  and  nerves  of,  1305 
plexiis  of  nerves,  internal,  1037 
veins,  internal,  666 
venous  plexus,  671 
MammiUary  bodies,  843,  871 

process,  38 
MammUlo-mesencephalic  fasciculus,  871 
Mammillo-thalamic  fasciculus,  871,  883 
Mandible  (lower  jaw),  95 
age  changes  in,  99 
at  birth,  124 
ossification  of,  98 
surgical  anatomy  of,  1345 
Mandibular  bars,  119 
branches  of  cervico-faoial  nerve,  946 
(inferior  dental)  canal,  96,  126 

foramen,  96 
fossa,  108 
nerve   (third  division  of  trigeminus),  939, 

1345 
(sigmoid)  notch,  96,  97 
portion  of  internal  maxillary  artery,  546 
spine,  96 
Manubrium  of  malleus,  79 

sterni  (presternum),  132,  133 
Margin,  falciform,  of  fascia  lata,  467 
of  lungs,  1229,  1233 


Marginal  gyrus,  858 
sinuses,  650 
zone  of  Lissauer,  782 
Marge  aoutus  of  heart,  510 

obtusus,  510 
Marshall,  obhque  vein  of,  521,  523 
Massa  intermedia,  844 
Masseter  muscle,  338,  341 
Masseteric     branch    of    external    maxillary 
artery,  541 
artery,  548 
fascia,  339 
nerve,  943 
veins,  644,  646 
Mastication,  muscles  of,  325 
Masticator  nerve,  829,  942 
Mastoid  antrum  (see  "Tympanic  antrum"), 
branch  of  great  auricular  nerve,  978 
of  occipital  artery,  543 
of  small  occipital  nerve,  977 
of  stylo-mastoid  artery,  544 
canaliculus,  73 
cells,  72,  1092,  1336 
foramen,  72,  108,  117 
(supra-meatal)  fossa,  72 
notch  (digastric  fossa),  72 
process,  72,  108 

development  of,  76 
Mater,  dura,  771 

pia,  771 
Maxilla,  86,  1346 
at  birth,  124 
ossification  of,  91 
Maxillary  artery,  external,  540,  638,  1343 
internal,  545,  638 
nerve  (second  division  of  trigeminus),  937 
plexus  of  nerves,  external,  1036 

internal,  1036 
process  of  inferior  turbinate,  85 

of  palate  bone,  92 
sinus  (antrum  of  Highmore),  87,  90,  111, 

1206,  1346 
vein,  internal,  646 
Maxillo-ethmoidal  cells,  84 
Maxillo-turbinates,  119 
Meatal  branch  of  stylomastoid  artery,  544 
Meatus,  external  auditory  (acoustic),  75,  108, 
1084,  1332 
internal  auditory,  72,  117 
naso-pharyngeus,  1206 
of  nose,  83,  111,  1205 
Meckel's  cartilage,  98,  119 
caves,  916 
diverticulum,  1169 
ganglion,  962 
Median  antibrachial  vein,  667,  668 
artery  of  forearm,  578,  639 
basilic  (cubital)  vein,  667,  669 
cephalic  vein,  668 
crico-thyreoid  ligament,  1215 
cubital  vein,  667 

fissure  of  spinal  cord,  anterior,  772 
hyo-thyreoid  ligament,  1217 
nerve,  991,  1423 

results  of  paralysis  of,  1424 
sulcus  of  floor  of  fourth  ventricle,  813 
Mediastinal  artery,  anterior,  567 
branches  of  aorta,  590 
lymphatic  nodes,  anterior,  724 

posterior,  725 
pleura,  1237 
septum,  1239 
surface  of  lungs,  1229 
veins,  664,  667 
Mediastinum,  20,  1228,  1239 
divisions,  1239 
testis  (corpus  Highmori),  1256 


INDEX 


1507 


Medio-oarpal  joint,  270 
arterial  supply,  270 
ligaments,  270 
movements  of,  271 
muscles  acting  upon,  270 
nerve-supply  of,  270 
Medulla  of  kidney,  1246 
oblongata,  799 

blood-vessels  of,  908 

central  connections  of  cranial  nerves  in, 

818 
ventral  aspect  of,  799 
of  suprarenal  gland,  1321 
of  thymus,  1326 
Medullary  cavity,  28 
lamina  of  lenticular  nucleus,  880 

of  thalamus,  882 
laminae  of  cerebellum,  808 
ray  of  kidney,  1246 
sheaths,  759 
strise,  acoustic,  824 
velum,  anterior  (superior),  812 
posterior,  808 
MeduUated  fibres,  760,  767 
Medullation  of  fasciculi  of  spinal  cord,  order 

of,  791 
Meibomian  glands,  1054,  1078 
Meissner,  tactile  corpuscles  of,  1290 

plexus  of,  1030,  1045 
Membrana  sacciformis,  265 
Membrane  (s).  Bowman's,  1060 
choroidal,  1052 
of  Descemet,  1060 
elastic,  of  larynx,  1215 
hyaloid,  1064 
hyo-glossal,  346 
hyo-thyreoid,  1217 
interosseous,  of  forearm,  1420 

of  mid-radio-uLnar  union,  263,  264 
of  middle  tibio-fibular  union,  295 
pharyngeal,  1102 
quadrangular  of  larynx,  1215 
secondary  tympanic,  1089,  1096 
Shrapnell's,  1087 

synovial,  211;  (see  also  the  individual  ar- 
ticulations) 
Membrane,  tectorial,  223 
tympanic,  1086 

vestibular  (membrane  of  Reissner),  1096 
Membranous  ampullae,  1095 
cochlea,  1095 
cranium,  117 
labyrinth,  1092 
nasal  septum,  511 
semicircular  canals,  1094 
urethra,  1264,  1388 
Meningeal  artery,  accessory  (small),  548 
arteries,  917 
middle,  547 

surgical  anatomy  of,  1341 
posterior,  537 
branches  of  anterior  ethmoidal  artery,  554 
of  maxillary  nerve,  middle  (recurrent) 

937 
of  occipital  artery,  543 
of  ophthalmic  nerve,  recurrent,  935 
of  posterior  ethmoidal  artery,  553 
of  spinal  nerve-trunks  (recurrent),  970 
of  vagus,  956 
of  vertebral  artery,  560 
plexus  of  nerves,  1036 
veins,  646,  917 
Meninges,  908 
arachnoid,  917 
dura  mater,  910 
pia  mater,  920 
relation  to  spinal  nerves,  965 


Meningoceles,  1331 
Menisci,  interarticular,  289 
Mental  branch  of  inferior  alveolar   (dental) 
artery,  548 

foramen,  95 

muscle,  334 

nerve,  941 

protuberance,  95 

spine,  95 

tubercle,  95 
Mentalis  (levator  menti),  334 
Mento-labial  sulci,  1284 
Meridians  of  eyeball,  1055 
Mesatipellio  pelvis,  177 
Mesencephalon,  758,  833 

blood-vessels  of,  907 

external  features  of,  834 

internal  structure  of,  836,  843 
Mesencephalic  root  of  masticator  nerve,  836, 
942 

nucleus  of,  829 
Mesencephalo-  or  tecto-spinal  tract,  786,  842 
Mesenteric  artery,  inferior,  602,  638 
superior,  596,  638 

ganglion,  superior,  1043,  1045 

lymphatic  nodes,  731 

plexus  of  nerves,  inferior,  1045 
superior,  1045 

vein,  inferior,  678 
superior,  677 
Mesenteriolum,  of  appendix,  1173 
Mesentery,  1165,  1376 

development  of,  19 
Mesethmoid,  119 
Meso-colic  lymphatic  nodes,  734 
Meso-colon,  1174,  1175 
Mesoderm,  10,  14 
Mesognathion  centre,  91 
Meso-metrium,  1267 

Meso-nephros  (Wolffian  body),  16,  1256,  1278 
Meso-palatine  suture,  89,  106 
Meso-salpinx,  1267 
Meso-scapula,  145 
Meso-sternum,  132 
Mesotendons,  318 
Mesovarium,  1267 
Metacarpal  arteries,  dorsal,  586 
volar,  586 

bones,  164 

union  of  heads  of,  274 

head  of  adductor  polUcis,  408 

veins,  dorsal,  667 
volar,  671 
Metacarpo-phalangeal  joints,  274 

of  thumb,  275 
Metacarpus,  ossification  of,  168 
Metamerism,  15 

of  cranial  musculature,  327 
Metamorphosis  of  branchial   (visceral)  bars, 

119 
Metanephros,  1278 
Metasternum,  132 
Metatarsal  artery,  dorsal,  633 
plantar,  628 

bones,  200 

union  of  heads  of,  309 

piUar,  205 

veins,  plantar,  687 
Metatarso-phalangeal  articulations,  310 
Metatarsus,  200 

Metathalamus  (geniculate  bodies),  845 
Metopic  suture,  69,  101 
Meynert,  fasciculus  retroflexus,  843,"  885 
Micromastia,  1301 
Mid-brain,  833 
Middle  alveolar  canal,  87 

(azygos)  articular  artery,  623 


1508 


INDEX 


Middle  cardiac  nerve,  1036 
vein,  520 

cerebral  artery,  555,  562 
vein,  655 

clinoid  process,  65 

coat  of  eye,  1060 

colic  artery,  598 

collateral  (branch,  of  profunda)  artery,  576 

constrictor  of  pharynx,  1137 

costo-transverse  (neck  or  interosseous)  liga- 
ment, 243 

cranial  fossa,  116 
Middle  ear,  77,  1086 

ethmoidal  cells.  111 

hsemorrhoidal  artery,  610 

meatus  of  nose.  111 

meningeal  artery,  547,  1341 
veins,  646 

nasal  conchae,  83 

palatine  foramina,  106 

peduncle  of  cerebellum,  811 

sacral  artery,  603 
vein,  679 

suprarenal  arteries,  598 

temporal  artery,  545 

thalamic  branch  of  posterior  communicating 
artery,  554 

thyreoid  vein,  661 

umbilical  ligament,  1250 
Mid-radio-ulnar  union,  262 
Milk,  1303 

teeth,  1126 
Minor  palatine  arteries,  549 

sublingual  ducts  (of  Rivini),  1117 
Mitral  cells  of  olfactory  bulb,  866 

(bicuspid)  valve,  515,  516 
Moderator  band  of  heart,  516 
Modiolus,  81 
Molars,  1121 

Molecular  layer  of  cerebellar  cortex,  809 
Moll,  glands  of,  1078 
Monro,  foramen  of,  847,  874 

sulcus  of,  847 
Mons  pubis  (veneris),  1276 
Montgomery,  glands  of,  1304 
Monticulus  of  cerebellum,  806 
Morgagni,  columns  of,  1177 

hydatid  of,  1257,  1269 

lacunse  of,  1264 

sinus  of,  1137 

ventricle  of,  1222 
Morphogenesis,  7  (see  also  "Development") 
Morphological  axis  of  scapula,  145 
Morphology       (see       also        "Comparative 
Anatomy") 

of  alimentary  canal,  1099 

of  joints,  213 

of  musculature  of  head  and  neck,  323 
of  pelvic  outlet,  444 

of  skull,  117 

of  spinal  cord,  external,  771 

of  the  testis,  1256 

of  the  vertebrEe,  serial,  50 
Morula,  9 
Motor  aphasia,  894 

area  of  speech,  894 

roots  (see  individual  nerves) 
TMouth,  1100 

clinical  anatomy  of,  1349 

muscles  of,  332 
Movements  of  joints,  214  (see  also  individual 

articulations) 
Mullerian  duct,  1257,  1267,  1279 
Multangular  bone   (trapezium)  greater,   159, 
162 
(trapezoid)  lesser,  159,  162 
Multifidus,  412,  419 


Multipenniform  muscle,  315 
Muscle(s)  (see  also  "Musculature") 
abductor  aocessorius  digiti  quinti  (foot),  499 
digiti  quinti  (foot),  454,  498 

(hand),  404 
hallucis,  454,  496 

longus,  482 
ossis  metatarsi  quinti,  499 
poUicis  brevis,  406,  407 

longus  (extensor  ossi  metaoarpi  polli- 
cis),  392,  393 
abnormal,  of  front  of  leg,  482 
of  back  of  leg,  491 

of  volar  side  of  forearm  and  wrist,  392 
accessorius  ad  flexorem  digitorum  profun- 
dum  (forearm),  402 
of  gluteus  minimus,  462 
of  spinal  musculature,  416 
accessory  peroneal,  484 
acting  upon  joints  (see  individual  articula- 
tion) 
adductor  brevis,  453,  471,  474 
digiti  secundi,  498 
hallucis,  454,  496,  498 
longus,  453,  471,  472,  1437 
magnus,  453,  471,  474,  1437 
minimus,  474 
poUicis,  407,  408 
anconeus,  374,  377,  379 

internus,  402 
of  the  angle  of  the  mouth,  332 
anomalus,  335 
antagonists,  322 

anterior  and  lateral  intertransverse,  356 
antitragus,  1084 
articularis  genu,  470 
atlanto-mastoid,  422 
attached  to  the  tendons  of  flexor  digitorum, 

longus,  495 
attachments  of  bones  (see  individual  bones) 
of  auricle  (of  ear),  337,  1084 
auricularis  anterior  (attrahens  aurem),  337 
posterior  (retrahens  aurem),  337 
superior  (attollens  aurem),  337 
auriculo-frontalis,  337 
ary-epiglottic,  1220 
ary-membranosus,  1220 
arytaenoideus  obliquus,  1220 

transversus,  1218 
ary-vocalis,  of  Ludwig,  1220 
belly  of,  314 

biceps  brachii,  374,  379,  382,  1414 
biceps  femoris,  453,  475 
bicipital,  314 
bipenniform,  315 
biventer  cervicis,  418 
brachialis,  374,  380,  382 
braohio-radialis    (supinator    radii    longus), 

387,  388 
broncho-oesophageal,  1141,  1248 
buccinator,  334 
bulbo-cavernosus,  443,  450 

in  female,  (sphincter  vaginae),  450,  1278 
oaninus,  332 
caput  angulare,  332 
infraorbitale,  332 
zygomaticum,  332 
cerato-cricoid,  1218 
cervical,  330 
cervicalis  ascendens,  416 
chondro-humeralis  (epitrochlearis),  374 
chondro-glossus,  346 
ciliaris  Riolani,  1077 
ciliary,  1057,  1060 
classification  of,  319 
coooygeus,  440,  448 
complexus,  412,  417 


INDEX 


1509 


Musole(s),  compressor  bulbi  proprius,  450 
hemisphseriura  bulbi,  451 
venae  dorsalis,  451 
constrictor  laryngis,  1218 
radicis  clitoridis,  451 
penis,  450 
vaginae,  449,  451 
ooraco-brachialis,  374,  379,  381 
corrugator,  336 
cutis  ani,  445 
costo-coraooideus,  374 
cremaster,  423,  434,  1254,  1259 
crico-arytEenoideus  lateralis,  1219 

posterior,  1218 
crico-thyreoid,  1218 
crureus,  468,  470 
cruro-pedal,  486 
deltoideus,  364,  365,  1410 
depressor  alae  nasi,  334 
anguli  oris,  333 
labii  inferioris,  332 
septi  nasi,  334 
diaphragm,  425,  436 
digastric  variety  of,  314 
digastricus,  343,  344 
dilator  naris  anterior,  335 
posterior,  335 
pupilte,  1061 
divisions  of,  316 
of  dorsum  of  foot,  492 
epicranio-temporalis,  337 
epicranius,  336 
epitrochleo-olecranonis  (anconeus  internus), 

402 
erector  spinas,  414 

extensor  carpi  radialis  accessorius,  391 
brevis,  388,  399 
intermedius,  391 
longus,  387,  388 
ulnaris,  388,  391 
communis  pollicis  et  indicis,  394 
digiti  annularis,  395 

quinti  proprius,  388,  391 
digitorum  brevis  (foot),  454,  492 
(hand),  395 
communis,  388,  391 
longus,  453,  480,  481 
hallucis  brevis,  482,  492 
longus,  453,  480,  482 
indicis  proprius,  392,  394 
medii  digiti,  395 
minimi  digiti,  388,  391 
ossis  metacarpi  pollicis,  392,  393 
poDicis  brevis,  392,  394 
longus,  392,  394 
erector  penis  (clitoridis),  443,  451 
fascite,  313 
femoro-tibial,  486 
fibulo-calcaneus  medialis,  491 
fibulo-tibialis  (peroneo-tibialis),  486 
finer  structure  of,  315 
flexor  accessorius  (digitorum  longus),  491 
(quadratus  plantae),  495 
carpi  radialis,  396,  398 

brevis  (radio-carpeus),  403 
ulnaris,  396,  398 

brevis  (ulno-carpeus),  402 
digiti  quinti  brevis  (foot),  454,  498,  499 

(hand),  404 
digitorum  brevis  (foot),  454,  493 
longus  (leg),  454,  486,  489 
profundus,  401 
sublimis,  399 
hallucis  brevis,  454,  496,  497 

longus,  454,  486,  490 
pollicis  brevis,  407,  408 
longus,  402 


Muscle  (s),  of  front  of  leg,  480 
frontalis,  337 

fusiform,  315 
gastrocnemius,  453,  484,  485 
gemellus  inferior,  464 

superior,  464 
genio-glossus,  346 
genio-hyoideus,  343,  345 
genio-pharyngeus,  347 
glosso-palatinus  (palato-glossus),  1135 
gluteus  maximus,  443,  457,  459 

medius,  457,  461 

minimus,  457,  461 
gracilis,  453,  471,  472 
gross  structure  of,  314 
grouped  according  to  function,  500 
head  of,  314 
helicis  major,  1084 

minor,  1084 
Horner's,  336 
hyo-glossus,  346 
iliacus,  455 

minor,  456 
ilio-coccygeus,  440,  448 
ilio-costalis   cervicis  (cervicalis  ascendens), 
416 

dorsi  (accessorius),  416 

lumborum,  416 
incisivus  labii  inferioris,  332 

superioris,  332 
incisure  helicis  (Santorini),  1084 
inferior  constrictor  of  pharynx,  1136 

oblique,  1068 
infra-clavicularis,  374 
infraspinatus,  364,  368 
insertion  of,  314 
intercostales  externi,  423,  432 

interni,  423,  433 
internal  cremaster,  1254,  1259 
interossei  dorsales  (foot),  454,  499 
(hand),  410 

plantares,  454,  499 

volares  (hand),  409 
interspinal,  412,  419 
intertransversarii,  417 
intralabial,  331 
ischio-bulbosus,  451 
ischio-cavernosus  (erector  penis  or  clitoris) 

443,  451 
isohio-femoraUs,  461 
isohio-pubicus  (Vlacovitch),  450 
of  larynx,  1218 
latissimo-condyloideus       (dorso-epitrochle- 

aris),  379 
laxator  tympani,  79 
latissimus  dorsi,  364,  368,  1405 
levator  anguli  oris,  332 

ani,  440,  448 

clavioulae,  359 

epiglottidis,  347 

labii  superioris,  332 
alaeque  nasi,  332 

menti,  334 

palpebrae  superioris,  1068 

scapulae,  356,  369 

veli  palatini,  1137 
levatores  costarum,  423,  432 

longi,  432 
of  little  finger,  404 
longissimus  capitis  (trachelo-mastoid),  416 

cervicis  (transversalis  cervicis),  416 

dorsi,  416 
longitudinalis  superior  and  inferior,  1110 
linguae  inferior  medius,  347 
longus  capitis,  355 

colli,  355 
lumbar,  436 


1510 


INDEX 


Muscle (s),  lumbricales  (foot),  454,  495 

(hand),  408 
masseter,  341 
meatalis,  334 

middle  constrictor  of  pharynx,  1137 
multifidus,  412,  419 
multipenniform,  315 
mylo-hyoideus,  343,  344 
nasalis,  334 

pars  alaris  (depressor  alse  nasi),  334 

pars  transversa  (compressor  naris),  334 
nerves  of,  318 
nomenclature  of,  319 
number  of,  315 

obliquus  abdominis  externus,  423,  432 
interaus,  423,  434 

auriculae,  1084 

capitis  inferior,  412,  420 
superior,  412,  420 
obturator  externus,  453,  463,  464 

internus,  453,  463 
occipitalis,  337 

minor,  337 
occipito-frontalis,  336 
occipito-scapularis,  359 
ocular,  1068 

action,  1068 
omo-hyoideus,  351 

opponens  digiti  quinti  (foot),  454,  498,  499 
(hand),  404,  405 

hallucis,  498 

poUicis,  407,  408 
oral,  331 
orbicularis  oculi,  336,  1077 

oris,  331 
of  orbit,  324,  325,''1067 
orbital  (of  Mueller),  1071 
origin  of,  314 
of  ossicles  of  ear,  1091 
palmaris  brevis,  404 

longus,  396,  398 
papillary,  515,  516,  517 
pectineus,  453,  471,  472 
pectoral  group,  362,  370,  372 

abnormal,  374 
pectoralis  major,  370,  372,  1411 

minimus,  374 

minor,  370,  373,  1411 
pectoro-dorsalis  (axillary  arch),  374 
periorbital,  335 

peroneo-calcaneus  internus,  491 
peroneo-tibialis,  486 
peroneus  brevis,  453,  483 

digiti  quinti,  484 

longus,  453,  483 

tertius,  453,  480,  482 
pharyngo-palatinus    (palato-pharyngeus), 

1136 
of  pharynx,  1134 
physiology  of,  320 
piriformis,  467,  461 
plantaris,  454,  484,  485 
platysma,  330 
pleuro-cesophageal,  1141 
polygastric,  314 
popliteus,  454,  486 
procerus,  336 
pronator  quadratus,  402 

teres,  395,  396 
psoas  major,  455 

minor,  455,  456 
pterygoideus  externus,  342 

internus,  342 
pubo-cavernosus  (levator  penis),  452 
pubo-coccygeus,  440,  448 
pubo-peritonealis,  436 
pubo-rectalis,  440,  448 


Muscle  (s),  pubo-transversaUs,  436 
pyramidalis,  424,  431 

auriculae  (Jungi),  1084 

nasi,  336 
quadrate,  332 
quadratus  femoris,  453,  463,  464 

labii  inferioris,  332 
superioris,  332 

lumborum,  425,  436 

plantse  (flexor  accessorius),  454,  495 
quadriceps  femoris,  453,  468,  470 
radio-carpeus,  403 
recti,  of  eye,  1068 
recto-cocoygeus,  449,  1177 
recto-uterine,  1252 
recto-vesical,  1252 
rectus  abdominis,  422,  424,  430 

acessorius,  471 

capitis  anterior  (minor),  356 
major,  355 
lateralis,  356 
posterior  major,  417,  419 
minor,  412,  419 

femoris,  468,  470,  1436 
relation  to  the  skin,  313 
retrahens  aurem,  337 
rhomboideus  major,  356,  358 

minor,  356,  358 
risorius,  333 
rotatores,  412,  419 
sacro-coccygeus  anterior,  448 

posterior,  448 
sacro-spinalis  (erector  spinae),  412,  414 
sartorius,  453,  468,  1436 
scalenus  anterior,  353 

medius,  354 

minimus,  355 

posterius,  354 
scansorius,  462 
scapulo-clavicularis,  374 
semimembranosus,  453,  475,  476 
semispinalis  capitis  (complexus),  412,  417 

cervicis,  419 

dorsi,  419 
semitendinosus,  453,  475,  476 
serratus  anterior,  356,  359 

posterior  inferior,  423,  431 
superior,  423,  431 
of  shoulder  musculature,  362,  365 
of  soft  palate,  1134 
of  sole  of  foot,  493 
soleus,  454,  484,  485 

accessorius,  485,  491 
sphincter  ani,  externus,  441,  449 
internus,  1177 

of  bladder,  1253 

pupdlae,  1061 

urethrae  (membranaceae),  449 

urogenitalis,  442,  449 

vagina;,  451,  1278 
spinalis  capitis  (biventer  cervicis),  418 

cervicis,  412,  417 

dorsi,  412,  417 
splenius  capitis,  414 

cervicis,  414 
accessorius,  414 
stapedius,  1091 
sternalis,  374 

sterno-chondro-scapularis,  374 
sterno-clavioularis,  374 
sterno-cleido-mastoid,  347,  349 
sterno-hyoideus,  351 
sterno-thyroideus,  351 
stylo-glossus,  346 
stylo-hyoideus,  343,  344 
stylo-pharyngeus,  1137 
subanconeus,  378 


INDEX 


1511 


Muscle  (s),  subclavius,  370,  373 
subcostales,  423,  434 
suborureus,  470 
subcutaneous,  313 
suboccipital,  328,  412,  419 
subscapularis,  364,  369 

minor,  369 
superior  constrictor  of  pharynx,  1137 

obUque,  1068 

tarsal  (Mueller's),  1068 
supinator  (brevis),  392 

radii  longus,  388 
supracostales,  432,  433 
supraspinatus,  364,  368 
synergists,  322 
tail  of,  314 
tarsal,  1072,  1078 
temporalis,  341 

superficialis,  337 
tensor  capsularis  artioulationis  metacarpo- 
phalangei  digiti  quinti,  406 

fascise  dorsalis  pedis,  482 
lata;  457,  459,  1436 
suralis,  476 

lamina;  posterioris  vaginae  musculi  recti 
abdominis,  436 

laminae  posterioris  vagina;  musculi  recti 
et  fasciae  transversalis  abdominis,  436 

ligamenti  annularis  anterior,  393 
posterior,  393 

tarsi  (Horner's),  336 

tympani,  1089,  1091 

veil  palatini,  1137 
tenuissimus,  475 
teres  major,  364,  369 

minor,  364,  367 
of  thigh,  453,  464 
of  the  thumb,  406 
thyreo-arytaenoideus  (externus),  1219 

internus  (m.  vooalis),  1220 

obliquus,  1220 

superior,  1220 
thyreo-epiglottic,  1220 
thyreo-hyoideus,  351 
tibialis  anterior,  453,  480,  1468 

posterior,  453,  486,  490,  1468 

secundus    (tensor   of   capsule   of   anlde- 
_  joint),  491 
tibio-astragalus  anticus,  482 
of  tongue,  345,  346,  1110 
trachelo-mastoid,  416 
tragicus,  1084 
transversalis  cervicis,  416 
transverso-spinal,  412,  419 
transversus  abdominis,  424,  435 

auriculae,  1084 

linguae,  1110 

menti,  333 

nuoh^,  337 

perinei  profundus,  442,  449,  1278 
superficialis,  444,  452,  1278 

thoracis  (triangularis  sterni),  424,  434 

vaginae  (Fiihrer),  449 
trapezius,  347,  349,  1405 
triangularis,  (depressor  anguli  oris),  333 

sterni,  424,  434 
triceps  brachii,  374,  377,  378,  1416 

surae,  484 
ulnaris  digiti  quinti,  392 
ulno-carpeus,  402 
unci-pisiformis,  403 
unipenniform,  315 
uvula;,  1137 
variation  in,  320 
vastus  intermedins  (crureus),  468,  470 

lateralis  (vastus  externus),  468,  470 

medialis  (vastus  internus),  468,  470 


Muscle(s),  ventricular,  of  larynx,  1220 

vertebro-ocoipital,  417 

verticahs  linguae,  1111 

vessels  of,  319 

vocaUs,  1220 

zygomaticus,  333 
minor,  332 
Muscular  process  of  arytaenoid,  1211 

veins  (of  orbit),  658 
Musculature  (see  also  "Muscles"),  313 

of  the  arm,  362,  374,  377,  379 

cranio-mandibular,  338,  341 

epicranial,  336 

of  expiration,  248 

external  genital,  450 

facialis,  324,  329,  380,  501 

of  forearm  and  hand,  362,  383,  387 

of  foot,  454,  492 

functional  groups,  600 

of  hand,  363,  403 

of  head,  neck,  and  shoulder  girdle,  323 

of  heart,  518 

of  the  hip,  453,  454 

of  inspiration,  247 

of  leg,  453,  477,  480 

of  lower  limb,  452 

of  mastication  and  swallowing,  325 

of  neck,  327 

of  pelvic  outlet,  439,  448 

prevertebral,  328,  355 

of  respiration,  503 

of  shoulder  girdle,  327,  347,  363 

spinal,  410,  412 

of  thigh,  453,  468 

thoracic-abdominal,  422,  430 

of  the  upper  limb,  360 
Musculi  papillares,  515,  516,  517 

pectinati  (heart),  513 
Musculo-cutaneous  nerve,  987,  1014,  1459 

results  of  paralysis,  1424 
Musculo-phrenic  artery,  567 
Musculo-spiral  groove,  149 

(radial)  nerve,  985 
results  of  paralysis  of,  1424 
Musculus  ciliaris  Riolani,  1077 

interfoveolaris,  435 

uvulae,  1137 

vocalis,  1220 
Myelencephalon,  799 

Mylo-hyoid  branch  of  inferior  alveolar  (dental) 
artery,  548 
nerve,  943 

groove,  96 

line  95 
Mylo-'hyoideus,  343,  344 
Myocardium,  508,  518 
Myometrium,  1274 

N 

Nail-bed,  1295 
Nails  (ungues),  1293 
Nail-wall,  1294 
Nares,  1200 

posterior  (choana;),  107,  112,  1206 
Nasal  aperture,  anterior,  108 
bones  at  birth,  124 
description  of,  86 
branches  of  anterior  ethmoidal  artery,  554 
nerve,  937 
of  infra-orbital  artery,  549 
of  maxillary  nerve,  939 
of  posterior  ethmoidal  artery,  553 
of  spheno-palatine  artery,  549 
(Meckel's)  ganghon,  962 
cartilages,  1201 
cavity,  1203 


1512 


INDEX 


Nasal  conchae  (turbinate  bones),  83,  84,  1205 

crest,  90 

fossa?,  IDS,  110 

glands,  1208 

meatuses,  1205 

muscles,  324,  334,  501 

notch,  60,  87 

pharynx,  1130 

septum,  cartilaginous,  1204,  1354 
membranous,  1204 
osseous.  111,  1354 

sinuses,  accessory,  1354 

spine,  anterior,  60,  87,  90,  112 
posterior,  91 

vein,  external,  644 
Nasalis,  muscle,  334 

pars  transversa  (compressor  naris),  334 

pars  alaris  (depressor  alse  nasi),  334 
Nasion,  109,  1331 
Naso-ciliary  (nasal)  nerve,  936 
Naso-frontal  vein,  658 
Naso-lacrimal  duct.  111,  1080,  1205,  1349 
Naso-palatine  nerve  (of  Cotunnius),  962 
Naso-pharyngeal  adenoids,  1130,  1354 

meatus,  1206 
Navicular  (scaphoid)  bone,  159,  160,  191,  196 
Neck  af  axis,  33 

cutaneous  areas  of,  1019 

deep,  lymphatic  nodes  of,  714 
vessels  of,  714 

fascia;  of,  347,  1360 

of  gall-bladder,  1187 

landmarks,  1354 

ligament,  243 

lymphatics  of,  709 

musculature  of,  323,  327 

of  penis,  1260 

superficial  lymph-nodes  of,  709 

surgical  anatomy  of,  1354 

of  teeth,  1117i 

triangles  of,  1357 
NiSlaton's  line,  1436 
Nephrotome,  16 
Nerve  (s),  769 

in  abdominal  wall,  1372 

accessory  (spinal),  958,  1360 

abducens,  934,  1075 

accessory  obturator,  1005 

acoustic  (auditory),  949,'?1096 

to  adductor  magnus,  1009 

ano-coccygeal,  1018 

anterior  crural,  1001 

cutaneous  of  abdomen,  995 

of  thigh,  1003 
ethmoidal,  936,  937 
interosseus,  992 
labial,  1000 
palatine,  963 
scrotal,  1000 

superior  alveolar  (dental)  ,'^938 
tibial,  1015 

of  Arnold,  956 

to  artioularis  genu  (suborureus),^1003 

of  auricle  of  ear,  1084 

auriculo-temporal,  941 

axillary  (circumflex),  984 

to  biceps  femoris,  1009 

bronchial  (pulmonary),  957 

buccinator  (long  buccal),  939 

cardiac,  522 

cavernous,  of  penis,  1047 
of  clitoris,  1047 
cervical,  971,  974 

cervico-faoial,  945 

chorda  tympani,  826,  946,  948 

ciliary,  of  eyeball,  937,  1064,  1076 

circumflex,  984 


Nerve(s),  coccygeal,  973 
cochlear  or  auditory,  950 

nucleus  of,  624 
common  peroneal  (external  popliteal),  1013 

plantar  digital,  1011 
communicans  cervicalis,  974 

fibularis,  1013 
of  conjunctiva,  1348 
of  Cotunnivis,  962 
cranial,  927 

nuclei  in  medulla  oblongata,  818 
of  cranial  dura  mater,  917 
cranio-spinal,  926 
cutaneous,  of  face,  1345 

of  foot,  1466 

of  forearm,   1423 

of  lower  extremity,  distribution  of,  1024, 
1469 

of  thigh,  1025 
perforating,  1007 
deep  peroneal  (anterior  tibial),  1015,  1466 
radial  (posterior  interosseous),  985,  986 

temporal,  943 
descendens  cervicalis,  953,  974 
dorsal  antibrachial  interosseus,  986 

digital,  of  foot,  1013 
of  hand,  986,  990 

of  ductus  deferens,  1259 

of  penis  (or  clitoris),  1018 

scapular  (nerve  to  rhomboids),  982 

thoracic,  984 
of  external  acoustic  (auditory)  meatus,  1086 

carotid,  1036 

popliteal,  1013 
to  external  pterygoid  muscle,  943 
external  respiratory,  of  Bell,  982 

superficial  petrosal,  1036 
of  eyeball,  1064 
of  evelids,  1078 
facial,  943,  1345 

nucleus  of,  825 
of  female  external  genitalia,  1278 
femoral  (anterior  crural),  ICJOl 
fibres,  development  of,  758 
fifth  cervical,  971 

cranial  (trigeminus),  934 
first  cervical,  971,  974 

thoracic,  994 
to  flexor  carpi  radialis,  992 
ulnaris,  990 

digitorum  longus,  1010 
profundus,  990 
sublimis,  992 

hallucis  longus,  1010 
foramina  of  skull,  125 
fourth  cervical,  971,  975 
frontal,  935,  1075 
furcal,  998 

geniculo-tympanic,  948 
to  genio-glossus,  954 
to  genio-hyoid,  954,  976 
genito-femoral  (genito-crural),  1000 
glosso-palatine,  946 

nucleus  of,  825 
glosso-pharyngeal,  951 

nucleus  of,  820 
great  auricular,  978 

(anterior)  palatine,  963 

splanchnic,  1038 

superficial  petrosal,  948 
greater  occipital,  971 
of  heart,  522 
to  hyo-glossus,  954 
hypoglossal,  952,  1111 

nucleus  of,  820 
ilio-hypogastric,  998 
ilio-inguinal,  1000 


INDEX 


1513 


Nerve(s),  inferior  alveolar  (dental),  941 

cardiac,  957,  1037 

clunial  (gluteal),  1007 

hsemorrhoidal,  1017 

(or  recurrent)  laryngeal,  957 

medial   clunial    (perforating   cutaneous), 
1007 

vesical,  1017,  1047 
infra-orbital,  937,  939,  1345 
infratroohlear,  936,  937 
intercosto-brachial    (intercosto-humeral), 

995 
intermediate  dorsal  cutaneous,  of  leg,  1015 
intermedius,  825 
internal  carotid,  960,  1033 

pterygoid  muscle,  939,  943 
interosseous  crural,  1010 
ischiadicus,  1008 
of  Jacobson,  951,  961 
jugular,  960,  1035 
of  kidney,  1247 
lacrimal,  936,  1075 
of  large  intestine,  1178 
of  larynx,  1225 
last  thoracic,  995 
lateral  anterior  thoracic,  983 

antibrachial  cutaneous,  987 

cutaneous,  1000 
of  abdomen,  995 
brachial,  985 
dorsal,  1013 
sural,  1013 

plantar,  1012 
least  splanchnic,  ,1039 
lesser  internal  cutaneous,  983 

splanchnic,  1039 
to  levator  scapula;,  979 
lingual,  940,,  1111,  1350 
of  lips  and  cheeks,  1104 
of  liver,  1186 
long  ciliary',  937 

(middle")  subscapular,  984 

thoracic,  982 
to  longus  capitis,  979 

colli,  979 
of  lower  extremity,  paralysis  of,  1469 
lower  subscapular,  984 
lumbar,  973,  995 

of  lumbar  plexus,  composition  of,  998 
of  lungs,  1235 
of  lymphatic  vessels,  702  ' 
of  mammary  gland,  1305 
mandibular  (third  division  of  trigeminus), 

939,  1345 
masseteric,  943 
masticator,  942 

nucleus  of,  829 
maxillary,  937,  1076,  1345 
medial  anterior  thoracic,  983 

antibrachial   (internal)  cutaneous  nerve, 
984 

brachial  cutaneous,  983 

calcaneal    (calcaneo-plantar    cutaneous), 
1010 

dorsal  cutaneous,  of  leg,  1015 

plantar,  1010 

sural  cutaneous,  1010 
median,  991,  1415 
mental,  941 
middle  cardiac,  1036 

clunial,  973 

hajmorrhoidal,  1017  a 

(recurrent)  meningel,  937 

(external)  palatine,  948,  963 

(long)  subscapular,  984 

superior  alveolar  (dental),  938 
of  muscles,  318 


Nerve(s),  musculo-cutaneous,  987,  1459 

results  of  paralysis,  1424 
musculo-spiral,  985 
to  mjdo-hyoid,  943 
naso-ciliary  (nasal),  936,  1076 
naso-palatine,  962 
of  nose,  1203,  1208 
obturator,  1003,  1440 

accessory,  1005 
to  obturator  internus,  1007 
oculomotor,  835,  838,  931,  1075 

nucleus  of,  837 
of  oesophagus,  958,  1141 
olfactory,  865,  929 
to  omo-hyoid,  953,  976 
ophthalmic,  1075 
optic,  848,  930,  1052,  1073 
of  orbit,  1075 
of  ovary,  1269 
of  palate,  1105 
to  palmaris  longus,  992 
of  pancreas,  1195 
of  parotid  gland,  1115 
to  peetineus,  1002 
of  penis,  1262 
pericardiac,  957 
perineal,  1017 
peroneal,  1469 
phrenic,  979 

relations,  1360 
to  piriformis,  1007 
of  pleura,  1239 
pneumogastrio  (vagus),  954 
to  popliteus,  1010 
posterior  auricular,  944 

belly  of  digastric,  944 

brachial  cutaneous,  985 

ethmoidal,  937 

femoral  cutaneous  (small  sciatic),  1007 

inferior  nasal,  963 

interosseus,  986 

(small)  palatine,  963 

scrotal  (labial)  nerves,  1017 

superior  alveolar  (dental),  938 

thoracic,  982 
to  pronator  teres,  992 
proper  plantar  digital,  1011 

volar  digital,  992 
of  prostate,  1265 
pudio  (pudendal),  1017 
to  quadratus  femoris,  1007 
radial  (musculo-spiral),  985,  1415 
to  rectus  capitis  anterior  (minor),  979 
lateralis,  979 

femoris,  1003 
recurrent  articular,  of  leg,  1013 

(inferior  laryngeal),  957 
to  rhomboids,  982 
roots,  769 

rudimentary  coccygeal,  964 
sacral,  973,  1006 

of  sacral  plex-us,  composition  of,  1006 
saphenous,  1003,  1467 
to  sartorius,  1002 
to  scalene  muscles,  978 
sciatic  (n.  ischiadicus),  1008,  1443,  1469 
of  scrotum,  1255 
to  semimembranosus,  1009 
to  semitendinosus,  1009 
seventh  cranial  (facial),  943,  1345 
short  subscapular,  984 
of  skin,  1289 
of  small  intestine,  1168 

occipital,  977 

palatine,  948 

sciatic,  1007 

superficial  petrosal,  951 


1514 


INDEX 


Nerve(s),  smallest  occipital,  971 
to  soleus,  1010 
spheno-palatine,  938 
spinal,  964 

accessory,  958 
nucleus  of,  820 

origin  of,  1406 
spinous  (recurrent),  939 
of  spleen,  1312 
to  stapedius  muscle,  944 
to  sterno-mastoid,  978 
to  sterno-thyreoid,  963 
of  stomach,  1156 
to  stylo-glossus,  954 
to  stylo-hyoid,  944 
to  subclavius,  983 
sublingual,  941 

gland,  1116 
of  submaxillary  gland,  1117 
suboccipital,  971 
subscapular,  984 
superficial  cervical  cutaneous,  978 

peroneal    (musculo-cutaneous),    1014, 
1459,  1466 

radial  (radial),  986 
superior  alveolar,  938 

cardiac,\957 

cervical  cardiac,  1036 

clunial,  973 

gluteal,  1007 

hsemorrhoidal,  1045 

laryngeal,  956 

vesical,  1047 
supra-acromial,  978 
supraclavicular,  978 
supra-orbital,  935,  1345 
of  suprarenal  glands,  1326 
suprascapular,  982 
supratrochlear,  936 
sural  (external  or  short  saphenous),  1013, 

1467 
of  teeth,  1124 
temporo-facial,r945 
tenth    cranial    (vagus    or   pneumogastric), 

954 
terminalis,  929 
thoracic,  971,'  994 

intercostal,  995 
thoraco-abdominal,  995 
thoraco-dorsal  (middle  or  long)    subscapu- 
lar, 984 
of  thymus,  1322 
to  thyreo-hyoid,  953,  976 
of  thyreoid  gland,  1318 
tibial,  1009,  1469 

communicating,  1010 
to  tongue,  1111 
of  trachea  and  bronchi,  1228 
to  trapezius,  979 
trigeminus,  934 

nuclei  of,  826 
trochlear,  835,  837,  933,  1075 

nucleus  of,  837 
trunks,  gangliated,  1029,  1032 
of  tubsE  uterina3  (Fallopian  tubes),  1270 
tympanic,  961 
of  tympanic  cavity,  1091 
ulnar,  987,  1415 

anastomotic,  987 

collateral,  985 
upper  (short)  subscapular,  984 
of  ureter,  1249 
of  urinary  bladder,  1253 
of  uterus,  1274 
of  vagina,  1017,  1276 
vagus  or  pneumogastric,  954 

nucleus  of,  820 


Nerve(s),  to  vastus  intermedius  (crureus),  1003 
lateralis,  1003 
mediahs,  1003 

vestibular,  949 
nuclei,  823 

Vidian,  962 

volar  digital,  of  hand,  992 
(anterior)  interosseous,  992 

of  Wrisberg,  946,  983 

zygomatic,  938,  1076 

zygomatico-facial  (malar),  938 

zygomatioo-temporal,  938 
Nerve-foramina  of  the  skull,  125 
Nerve-supply  of  muscles  (see  "Nerves;"  also 

corresponding  muscles,  articulations,  etc.) 
Nerve-trunks,  gangliated,  1029,  1032 

mixed,  965 

spinal,  primary  divisions  of,  944,  967,  970 
Nervous  system,  751 
central,  751,  770 
construction  of,  762 
development  of,  754 
general   summary  of  some  of  principal 

paths  of  the  nervous  system,  895 
peripheral,  754,  924 
sympathetic,  1026 
Nervus  intermedius,  825 
Neural  branches  of  spinal  arteries,  590 

crest,  754 

folds,  754 

groove,  10,  11,  754 

plate,  11,  754 

tube,  14,  754 
Neuraxis,  762 
Neurenteric  canal,  11 
Neurilemma,  761 
Neuroblasts,  755 
Neuro-central  suture,  45 
Neuro-fibrillfe,  765 
Neuroglia,  759,  767 
Neuroglia,  759,  767 
Neuro-muscular  spindle,  764 
Neurone,  755,  762 

chains,  768 

structure  of,  765 

systems  of  spinal  cord,  777 
Neurones  of  cerebral  path  for  cranial  nerves, 
895 

of  cerebro-spinal  path,  895 
Nipple  of  mammary  gland,  1300,  1304 
Nissl  bodies,  766 
Node(s),  atrio-ventricular,  519 

haemolymph,  708 

lymph(atic)  (see  "Lymphatic  nodes") 
Nodulus  Arantii,  517 

of  cerebellum,  808 
Nomenclature,  anatomical,  1 

of  muscles,  319 
Non-medullated  fibres,  767 
Norma  basilaris,  skull,  103 

facialis  of  skull,  108 

lateralis,  skull,  101 

occipitalis,  skull,  101 

verticalis,  skull,  100 
Nose,  1200 

cartilages  of,  1201 

clinical  anatomy  of,  1352 

development  of,  1208 

lymphatics  of,  712 

meatuses  of,  1205 

muscles  of,  334 

nostril  (nares),  1200 

olfactory  area  (region),  1050 

sinuses  connecting  with,  1206 

vessels  and  nerves,  1203,  1208 
Notch,  29 

acetabular,  174 


INDEX 


1515 


Notch,  cardiac,  of  left  lung,  1229 

of  cerebellum,  805 

ethmoidal,  61 

frontal,  60 

great  scapular,  137 
sciatic,  172 

intertragic,  1082 

jugular  (interclavicular),  133 

mandibular  (sigmoid),  96,  97 

mastoid,  72 

nasal,  60,  87 

pancreatic,  1194 

posterior  cerebellar,  915 

preoccipital,  861 

pterygoid,  66 

radial  (lesser  sigmoid  cavity)  of  ulna,  157 

of  Rivinus,  77 

scapular,  142 

semilunar  (greater  sigmoid  cavity)  of  ulna, 
156 

small  sciatic,  172 

spheno-palatine,  91,  93 

of  spleen,  1311 

supra-orbital,  60 

temporal,  868 

tentorial,  915 

thyreoid,  1210,  1211 

of  tibia,  popliteal,  185 

tympanic,  77 

ulnar  (sigmoid  cavity)  of  radius,  154 
Notochord,  11 

Notochordal  region  of  skull,  117 
Nuchal  line,  highest,  52 
inferior,  52 
superior,  52 
Nuck,  canal  of,  1398 
Nucleus(i),  abducens  nerve,  826 

accessory  olivary,  817 

of  the  ala  cinerea,  820 

ambiguus,  822 

amygdalae,  881 

amygdaloid,  of  lateral  ventricle,  877 

arcuatus,  818 

Bechterew's,  823 

caudate,  877,  879 

of  cerebellum,  809 

of  cochlear  nerve,  824  ■ 

of  cranial  nerves  in  meduUa  oblongata,  818 

Deiters's,  823 

dentate,  of  cerebellum,  810 

dorsal  efferent,  of  cochlear  nerve,  824 
of  vagus,  822 

dorsalis  (Clarke's  column),  776 

of  Edinger  and  Westphal,  838 

emboliformis  of  cerebellum,  810 

of  facial  nerve,  825 

fastigii  (roof  nucleus)  of  cerebellum,  810 

funiculi    cuneati    (of    Burdach's    column), 
801,  815 
gracihs;(of  GoU's  column),  801,  815 

globosus  of  cerebellum,  810 

of  glosso-palatine  nerve,  825 

of  glosso-pharyngeus,  820 

habenular,  872,  885 

of  hypoglossal  nerve,  820 

hypothalmio,  884 

incertus  of  floor  of  fourth  ventricle,  815 

of  inferior  colliculus,  839 

inferior  olivary,  of  medulla  oblongata,  817 

intercalatus,  814 

interpeduncular   (Von  Gudden),   843,  872, 
885 

of  lateral  lemniscus,  824,  839 
of  thalamus,  845 

of  lens  of  eye,  1062 

lenticular,  878,  879 

lentiformis,  857 


Nucleus  of  masticator  nerve,  829 

of  medial  longitudinal  fasciculus,  843,  871 

medial  thalamic,  845 

of  mesencephalic  root  of  trigeminus  nerve, 

829 
of  oculomotor  (or  third)  nerve,  837 
pontis,  831 
pulpy,  226 
red,  840 
respiratory,  822 
salivatorius,  826,  947 
of  scapula,  139 
Schwalbe's,  823 
of  solitary-tract,  820 
of  spinal  accessory  nerve,  820 

tract,  826 
spinahs,  823 
Stilling's,  776 
of  superior  colliculus,  842 
superior  olivary,  824 
of  termination,  770 
of  thalamus,  871,  882 
trapezoidei,  824 
of  trigeminus  nerve,  826 
of  trochlear  (or  fourth)  nerve,  837 
of  vagus  or  pneumogastric,  820 
vasomotor,  822 
ventral  cochlear,  824 
vestibularis,  823 
Number  of  muscles,  315 
Nutrient  arteries  of  femur,  621 

of  fibula,  626 

of  humerus,  576 

of  radius  and  ulna,  679 

tibial,  626,  1459 
branch  of  obturator  artery,  608 

of   posterior  circumflex   humeral   artery, 
573 

of  transverse  scapular  artery,  565 
Nymphaj  (labia  minora),  1277,  1392 

O 

ObeUon,  101 
Obex,  802,  813 

Obhque  diameter  of  pelvic  inlet,  175 
fasciculus,  804 
head  of  adductor  hallucis,  498 

of  adductor  poUicis,  408 
ligament  (mid-radio-ulnar  union),  262 
line  of  clavicle,  140 
of  fibula,  190 
of  mandible,  95 
of  radius,  154 

posterior,  154 
of  scapula,  142 
of  thyreoid  cartilage,  1211 
of  ulna,  157 
muscle  of  eye,  inferior,  1068 

superior,  1068 
popliteal  ligament  (hgamentum  Winslowii), 

287 
sinus  of  pericardium,  523 
vein  of  left  atrium  (of  Marshall),  521,  623, 
691 
Obliquus  abdominis  externus,  423,  432 
internus,  423,  434 
capitis  inferior,  412,  420 
superior,  412,  420 
Oblong  fovea  of  aryta;noid,  1212 
Obturator  artery,  608,  639 
crest   173 

externus,  453,  463,  464 
fascia,  439,  463 
(thyreoid)  foramen,  174 
groove,  172 
internus,  453,  463 


1516 


INDEX 


Obturator  nerve,  1003,  1440 
accessory,  1005 
vein,  680 
Occipital  artery,  542,  638,  1343 
bone,  51 

articulations  of,  56 
at  birth,  121 
ossification  of,  56 
branches  of  occipital  artery,  543 
of  posterior  auricular  artery,  545 

nerve,  944 
of  small  occipital  nerve,  977 
condyle,  third,  56 
condyles,  108 
crest,  external,  52 
internal,  53,  117 
groove,  72 
gyri,  863 
lobe,  863 

lymph-nodes,  709 
nerve,  greater,  971 
small,  977 
smallest,  971 
point,  101,  112 
pole,  850 
pontile  fibres,  840 
portion  of  vertebral  artery,  560 
protuberance,  external,  52,  101 

internal,  53 
sinus,  650 
sulci,  862,  863 
suture,  101 
vein,  647 
diploic,  648 
Occipitalis,  337 

minor,  337 
Occipito-atlantal  articulation,  218 

ligaments,  219 
Occipito-cervioal  ligament,  223 
Occipito-epistrophic  articulation,  223 
Occipito-frontal  fasciculus,  892 
Occipito-frontalis,  336 
Ocoipito-mastoid  suture,  101 
Occipito-mesencephalic  path   (Flechsig's  sec- 
ondary optic  radiation),  890 
Occipito-pontile  path,  832 
Occipito-scapularis,  359 
Occipito-temporal  association  area,  894 

convolution,  864 
Oocipito-thalamic  (optic)  radiation,  888 
Occiput  and  atlas,  ligaments  uniting,  218 
Ocular  conjunctiva,  1054 

muscles,  325,  1067 
Oculomotor  nerves,  835,  838,  931 
nucleus  of,  837 
sulcus,  835 
Odontoid  process  (dens)  of  axis,  33 
(Esophageal  arteries,  588 

branches  of  inferior  thyreoid  artery,  564 
of  left  gastric  artery,  594 
of  vagus,  958 
plexuses,  954,  955 
veins,  661,  664 
(Esophagus,  1138 

clinical  anatomy  of,  1369,  1408 
development  of,  1141 
lymphatic  vessels  of,  730,  1141 
variations  and  comparative,  1141 
vessels  and  nerves  of,  1141 
Olecranon  fossa  of  humerus,  150 

process  of  ulna,  156 
Olfacto-mammillary  tract,  873 
Olfacto-mesencephalic  tract,  873 
Olfactory  apparatus,  1049 
area  of  cerebral  cortex,  893 

(region)  of  nasal  mucous  membrane,  1049, 
1352 


Olfactory  brain,  864 

bulb,  758,  865,  1050 

cells,  1050 

conduction  path,  902 

glands,  1208 

groove,  1206 

gyrus,  lateral,  865 
medial,  866 

layer  of  olfactory  bulb,  866 
lobe,  865 

nerve,  865,  929 

central  connections,  929 

organ,  1049,  1208 

region  of  nasal  cavity,  1208 

strias  (gyri),  865,  866 

sulcus,  858 

tract,  758,  865,  893 
development  of,  758 

trigone  (tubercle),  865 

ventricle,  866 
Olivary,  nuclei,  accessory,  817 
inferior,  817 
superior,  824 
Olives  of  medulla  oblongata,  800 
Omental  branches  of  epiploic  arteries,  595 

bursa  (lesser  sac),  1146,  1372 
Omentum,  great,  1149 

lesser  (gastro-hepatic),  1160,  1185 
Omo-hyoideus,  351 
Omphalo-mesenteric  artery,  638 
Opercula  of  insula,  856 
Operculum  proper,  854,  856 

temporal,  854,  866     ■ 
Ophryon,  109,  112 
Ophthalmic  artery,  552,  638,  1074 
branches,  552 

division  of  trigeminus  (fifth  nerve),  936, 1075 

veins,  658,  659,  1075 
Ophthalmo-meningeal  vein,  655 
Opisthion,  107,  108 

Opponens  digiti  quinti  (foot),  454,  498,  499 
(hand),  404,  405 

hallucis,  498 

pollicis,  407,  408 
Optic-acoustic  reflex  path,  840,  842 
Optic  apparatus,  conduction  paths  of,  900 

chiasma,  847,  848,  849 

cup,  1080 

disc,  1055 

foramen,  63,  64,  110,  116,  125 

groove,  63,  116 

nerve,  848,  930,  1052,  1073 
sheaths  of,  931,  1073 
papilla  of,  1055 

portion  of  hypothalamus,  847 

radiation,  888 

Flechsig's  secondary,  890 

recess,  848 

tracts,  849 

vesicle,  758,  1080 
Ora  serrata,  1057 
Oral  cavity,  1100 

development  of,  1102 

fissure,  (rima  oris),  1100 

fossa,  1102 

muscles,  331 

orifice,  muscles  of,  501 

pharynx,  1130 

vestibule,  1100 
Orbicular  tubercle  of  incus,  79 
Orbicularis  ciliaris,  1060 

ocuU,  336,  1097 

oris,  331 
Orbit,  108,  109,  1332,  1346 

fascije  of^  107l 

lymphatic  system  of,  1076 

muscles  of,  325,  1067 


INDEX 


1517 


Orbital  branch  of  middle  meningeal  artery,  548 

branches  of  maxillary  nerve,  938 

of  spheno-palatine   (Meckel's)   ganglion, 
963 

fissure,  inferior,  109,  126 
superior,  65,  109,  116,  125 

gyri,  858 

muscle  of  Muller,  1071 

periosteum,  1071 

plates,  61 

process  of  malar  bone,  94 
of  palate  bone,  91,  93 

sulci,  858 

wings  of  sphenoid,  64 
Orbito-sphenoid  centre,  67,  119 
Organ  (s),  4 

of  Giraldes,  1257 

of  Jacobson,  951,  961,  1051,  1204 

lymphoid,  704 

olfactory,  1049,  1208 

reproductive,  male,  1253 
female,  1265 

of  special  sense,  1049 

spiral  (organ  of  Corti),  1096 

of  taste,  1051 

urinary,  1241 
Orifice,  atrio-ventricular,  of  heart,  513,  514 

external  urethral,  1264 

of  stomach,  1151,  1374 

(os)  of  uterus,  1271 
Origin  of  muscles,   314    (see  also   individual 
muscles) 

of  spinal  nerves,  964 
Os  calcis  (calcaneus),  191,  195 

centrale,  164,  208 

innominatum,  169 

Japonicum,  95 

linguae,  99 

planum,  83 

trigonum,  194,  199 

uteri,  1271 

Vesalianum,  199 
Osseous  labyrinth,  80 

part  of  tuba  auditiva  (Eustachian  tube) ,  1092 

portion    of    external    acoustic     (auditory) 
meatus,  1085 
Ossicles  of  ear,  79,  1090 
articulations,  1090 
ligaments,  1090 
muscles,  1091 
Ossification  of   bones,  27    (see   also   the   in- 
dividual bones") 
Osteogenesis,  27 
Osteology,  27 

Ostium  abdominale  of  tuba?  uterinae  (Fallo- 
pian tubes),  1270 

venosum  (atrio-ventrioular  orifice),  513,  514 
Otic  (Arnold's)  ganglion,  963 
Otoconia  (otoliths),  1095 
Outlet  (interior  aperture)  of  pelvis,  176 
Ovarian  arteries,  602 
branches,  602 

branches  of  uterine  artery,  610 

ligaments,  1269 

plexuses  of  nerves,  1045 

veins,  674 
Ovaries,  1268 

clinical  anatomy  of,  1393 

lymphatics  of,  701,  745,  1269 

vessels  and  nerves  of,  1269 
Ovula  Nabothi,  1274 
Ovum,  segmentation  of,  9 


Pacchionian  bodies  (arachnoid  granulations), 

649,  919 
Pacchionius,  foramen  ovale  of,  116 


Pacinian  corpuscles,  1290 
Palate,  1104 
bone,  91 

at  birth,  124 
development  of,  1106 
hard,  1104 
lymphatics  of,  717 
muscles  acting  on,  502 
soft,  326,  1104 
surgical  anatomy  of,  1352 
Palatine  arches,  1132 

branch  of  ascending  pharyngeal  artery,  537 
artery,  ascending,  541 

descending,  549 
major,  549 
canals,  92,  103,  126 

accessory,  103 
foramina,  106 
nerve,  great  (anterior),  963 
middle  (external),  948,  963 
posterior  (small),  948,  963 
process  of  maxilla,  87,  88 
tonsil,  1132 

variations  and  comparative,  1106 
vein,  644 

superior,  646 
Palato-ethmoidal  cells,  84 
Palm,  muscles  acting  on,  504 
Palmar  aponeurosis,  387,  1430 
arch,  (see  "Volar  arch") 
cutaneous  branch  of  median  nerve,  992 

of  ulnar  nerve,  990 
fascia,  deep,  387 
Palmaris  brevis,  404 

longus,  398 
Palpebra,  inferior,  1053 

superior,  1053 
Palpebral  aperture,  1052 
arteries,  lateral,  552 
branches  of  infratrochlear  nerve,  937 
of  maxillary  nerve,  inferior,  939 
of  ophthalmic  artery,  palpebral,  552 
of  supra-orbital  artery,  553 
conjunctiva,  1054,  1078 
fascia,  1071 
folds,  1053 

ligament,  medial,  1052,  1078 
raphe,  lateral,  1078 
veins,  644,  658 
Pampiniform  plexus,  674,  1259 
Pancreas,  1192 

blood-supply  of,  1195 
development  of,  1195 
lymphatics  of,  699,  736,  1195 
topographic,  1375 
variations  and  comparative,  1197 
Pancreatic  branches  of  splenic  artery,  595 
duct  (canal  of  Wirsung),  1194,  1375 
accessory  (of  Santorini),  1195 
Pancreatico-duodenal  artery,  inferior,  596 
superior,  595 
vein,  675,  677 
Panniculus  adiposus,  313,  1287 

carnosus,  313 
Papilla,  duodenal,  1164,  1195 
hair,  1292 
incisive,  1104 
of  kidney,  1246 
lacrimal,  1054 

(nipple)  of  mammary  glands,  1300,  1304 
optic,  1055 
Papillae  of  skin,  1286 

of  tongue,  1106 
Papillary  ducts  (of  Bellini),  1246 
muscles  of  heart,  515,  516,  517 
process  of  liver,  1184 
Paracentral  lobule,  857,  858,  863 


1518 


INDEX 


Paradidymis  (organ  of  Giraldes),  1257 
Paraduodenal  fossa,  1164 
Paraganglia,  1323 

aortic  (lumbalia),  1329 
Paralysis  of  deep   radial    (posterior   interos- 
seous) nerve,  results  of,  1424 
of  facial  nerve,  1345 
of  median  nerve,  results  of,  1424 
of  musculo-cutaneous  nerve,  1424 
of  nerves  of  lower  extremity,  1469 
of  radial  (musculo-spiral)  nerve,  1424 
of  ulnar  nerve,  results  of,  1424 
Paramedial  sulcus,  858 
Parametrium,  1274 
Paranasal  sinuses,  1206 
Parapophysis,  51 
Pararenal  adipose  body,  1243 
Parasinoidal  sinuses,  919 
Para-thyreoid  glands,  1318 
Paraurethral  ducts,  1277 
Parietal  association  area,  894 
bones,  57 

at  birth,  123 
branches  of  abdominal  aorta,  592 
of  hypogastric  artery,  606 
(posterior  temporal)  of  superficial  tem- 
poral artery,  545 
of  thoracic  aorta,  588 
eminence,  57 
emissary  vein,  649 
fascia  of  pelvis,  447 
foramen,  57 
lobe,  860 
lobule,  inferior,  863 

(gyrus)  superior,  862 
lymphatic  nodes  of  thorax,  724 
peduncle  of  thalamus,  8  S3 
pleura,  1237 
Parieto-mastoid  suture,  101 
Parieto-ocoipital  arch,  863 

fissure,  860,  864 
Parolfactory  area  (Broca's  area),  858,  865 

sulci,  865,  866 
Paroophoron,  1269 

Parotid  branches  of  auriculo-temporal  nerve, 
941,  961 
of  superficial  temporal  artery,  545 
fascia,  339,  348,  1114 
gland,  348,  1113 
accessory,  1114 
duct  (Stenson's),  1115,  1343 
lymph-nodes,  709 
veins,  644,  646 
vessels  and  nerves,  1115 
plexus  (pes  anserinus),  945 
region,  1343 
Pars  alaris  (depressor  alee  nasi),  334 
ciliaris  retinae,  1061 
fixa  of  penis,  1260,  1264 
flaccida  (Shrapnell's  membrane),  1087 
glabra  of  Ups,  1104 
intercartilaginea,  1223 
intermedia  of  facial  nerve,  946 

(of  Kobelt),  1278 
intermembranacea,  1223 
Ubera  of  penis,  1260,  1264 
tensa,  1087 

transversa  (compressor  naris),  334 
villosa  of  lips,  1104 
Parumbilical  veins,  678 
Patches,  Peyer's,  704,  1166 
Patella,  184 

clinical  anatomy  of,  1444 
Patellar  fold  (ligamentum  mucosum),  290 
ligament,  47l 
plexus,  1001 
rete,  622 


Paths,  auditory  conduction,  900 
cerebral,  for  cranial  nerves,  895 
cerebro-spinal,  895 

conduction,  involving  cerebellum,  899 
of  olfactory  apparatus,  902 
of  optic  apparatus,  900 
summary  of,  895 
frontal  pontile  (Arnold's  bundle),  832,  889 
occipito-mesencephalic,  890 
occipito-pontile,  832 
optic,  900 

optic-acoustic  reflex,  840 
short  reflex,  of  cranial  nerves,  898 
spino-cerebral,  895 
of  spinal  cord,  short  reflex,  895 
temporal  pontile  (Turk's  bundle),  832,  840, 

890 
vestibular,  899 
Pecten  of  pubis,  173 
Pectineo-femoral  band,  278 
Pectineus,  453,  471,  472 

Pectoral     (descending)    branch     of    anterior 
circumflex  humeral  artery,  573 
branch  of  thoraco-acromial  artery,  571 
group,  of  muscles,  362,  370 

of  axillary  lymphatic  nodes,  720 
Pectoralis  major,  372 

surface  markings,  1411 
minor,  373 

surface  markings,  1410 
minimus,  374 
Pectoro-dorsalis  (axillary  arch),  374 
Pedicles  of  axis,  34 
of  lumbar  vertebrae,  37 
of  vertebrae,  30 
Peduncles  of  cerebellum,  810,  831 
of  cerebrum,  833,  835 
of  corpus  callosum,  866 
of  flocculus,  807 
of  superior  olive,  825 
of  thalamus,  880,  883 
Peduncular  tract,  transverse,  835 
Pedunculi  conarii,  846 
Pelvic  articulations,  234 
ligaments  of,  234 
diaphragm,  440,  448,  1383 
fasciae,  446 

clinical  anatomy  of,  1385 
floor  in  female,  1394 

in  male,  1383 
girdle,  207 
index,  177 

inlet,  diameters  of,  175 
measurements,  177 
outlet,  176 

muscles  of,  439 
colon,  1174,  1379 
plexuses  of  nerves,  1046 
portion  of  ureter,  1248 
splanchnics,  1017,  1040,  1046 
Pelvis,  articulations  of,  234 
axis  of,  176 

description  of,  175,  1382 
differences  according  to  sex,  177 
inlet  (superior  aperature)  of,  175 
lymphatics  of  730,  733 
major  (false),  175 
measurements,  177 
minor  (true),  175 
muscles  acting  on,  505 
outlet  (inferior  aperature) ,  176 
renal,  1248 
of  ureter,  1247 

visceral  lymphatic  vessels  of,  733 
Penis,  1260 
artery  of,  613 
cavernous  plexus  of,  1047 


INDEX 


1519 


Penis,  deep  artery  of,  614 
dorsal  artery  of,  614 

nerves  of,  1018 
lymphatics  of,  744,  1262 
surgical  anatomy  of,  1388 
vessels  and  nerves  of,  1262 
Perforated  substance,  anterior,  847,  866 

posterior,  835,  844 
Perforating    branches    of    deep    volar    arch, 
586 

of  lateral  plantar  artery,  628 
of  the  profunda,  620 
of   internal   mammary  artery,  567 

maxillary  artery,  529 
of  peroneal  artery,  626 
veins,  690 
Pericsecal  fossa;,  1172,  1378 
Pericardiac  branches  of  aorta,  588 
of  internal  mammary  artery,  567 
of  phrenic  nerve,  979 
Pericardial  branches  of  vagus,  956 
cavity,  522 

development  of,  527 
lymph-capillaries  of,  702 
pleura,  1237 
Pericardio-phrenic  artery,  567 
Pericardium,  522 
development,  20,  525 
surgical  anatomy,  1369 
vessels  of,  523 
Perichondrium,  28 
Pericranium,  1334 
Perilymph,  1092 
Perilymphatic  space  of  membranous  labyrinth, 

1095 
Perimetrium,  1274 
Perimysium  internum  (endomysium),  315 

externum  (epimysium,)  316 
Perineal  artery,  613,  639 
fascia,  superficial,  445 
nerve,  1017 
Perineum,  1383 

central  tendon  of,  449 
muscles  acting  on,  503 
surgical  anatomy  of,  1385 
triangles  of,  1383 
Periorbita,  1071 
Periorbital  muscles,  335 
Periosteal  branches  of  supra-orbital  artery, 

553 
Periosteum,  28 

lymph-capOlaries  of,  701 
Periotic  capsule,  69,  117 

cartilages,  117 
Peripheral,  nervous  system,  754,  924 
cranio-spinal  system,  926 
sympathetic  system,  926,  1026 
Peritoneal    branches    of    superior    epigastri-c 
artery,  567 
cavity,  lymphatic  capillaries  of,  702 
Peritoneum,  1141 

clinical  and  topographical  anatomy  of,  1372 
development  of,  1144,  1151 
of  rectum,  1177 
spaces  of,  1372 
sections,  1146 

variations  and  comparative,  1151 
vessels  and  nerves,  1151 
Permanent  teeth,  times  of  eruption  of,  1127 
Peroneal  artery,  626,  640,  1459 

anterior  (perforating),  626,  1459 
posterior,  626 
groove  of  cuboid,  199 
muscles,  accessory,  484 
nerve,  common  (external  popliteal),  1013 
results  of  paralysis  of,  1469 
deep,  (anterior  tibial),  1015,  1466 


Peroneal   nerve,  superficial  (musculo-cutane- 

ous),  1014,  1459,  1466 

retinacula,  480 

vein,  688 
Peronei  muscles,  tenotomy  of,  1464 

accessory,  484 
Peroneo-caloaneus  internus(of  Macalister),  491 
Peroneo-tibialis,  486 
Peroneus  brevis,  453,  483 

digiti  quinti,  484 

longus,  453,  483,  1468 

tertius,  453,  480,  482 
Perpendicular  plate  (mesethmoid)  of  ethmoid, 

82 
Pes  anserinus,  945 

hippocampi,  877 

pedunculi,  840 
Petiole  of  epiglottic  cartilage,  1212 
Petit,  canal  of,  1064 

triangle  of,  434,  1406 
Petrosal  branch  of  middle  meningeal  artery, 
548 

ganglion,  951 

nerve,  external  superficial,  1036 
great  superficial,  948 
small  superficial,  951 

portion  of  internal  carotid  artery,  550 

process,  posterior,  63 

sinuses,''652 
Petro-mastoid,  119 
Petro-sphenoidal  foramen,  125 
Petro-squamous  sinus,  653 

(squamo-mastoid)  suture,  71 
Petro-tympanic    (Glaserian),    fissure   71,    77, 

108,  126 
Petrous  portion  of  temporal  bone,  68,  72 
Peyer's  patches,  704,  1166 
Phalanges  of  fingers,  167 

ossification  of,  168,  204 

third,  terminal,  or  ungual,  168,  204 

of  toes,  203 
Pharyngeal  aponeurosis,  1130 

arterj',  ascending,  537,  638 

branches  of  ascending  pharyngeal  artery, 
537 
of  inferior  thyreoid  artery,  564 
of  glosso-pharyngeal  nerves,  951 
of   spheno-palatine   (Meckel's)  ganglion, 

963 
of  vagus,  956 

bursa,  1130 

(pterygo-palatine)  canal,  66,  92,  103 

foramen,  126 

hypophyseal  remnants,  1352 

sthmus  (faucial),  1130,  1131 

membrane,  1102 

ostium  of  tuba  auditiva,  1092 

plexus  of  nerves,  956,  1036 
of  veins,  659 

recess,  1130 

tonsil,  1130,  1354 

tubercle,  54,  108 

veins,  659 
Pharyngo-palatine  arches,  1132 
Pharyngo-palatinus  (palato-pharjmgeus), 

1136 
Pharynx,  1128 

development,  1138 

laryngeal,  1134 

lymphatics  of,  717,  113S 

muscles  of,  325,  502,  1134 

nasal,  1130 

oral,  1130 

variations  and  comparative,  1138 

vessels  and  nerves,  113S 
Philtrum,  1102,  1284 
Phrenic  arteries,  inferior,  692,  638 


1520 


INDEX 


Phrenic  arteries,  superior,  590 

branches  of  musculo-phrenic  artery,  567 

of  superior  epigastric  artery,  567 
ganglion,  1044 
nerve,  979 

relations  of,  1360 
(diaphragmatic)  plexuses  of  nerves,  1044 
veins,  inferior,  675 
superior,  667 
Phrenico-oostal  sinus,  1237 
Phreno-colic  ligament,  1150,  1174,  1310,  1379 
Phrenicohenal  (lienorenal)  ligament,  1310 
Physiology  of  muscles,  320,  323 
Pia  mater,  771,  920 
cranial,  922 
spinal,  921 
Pigment  of  iris,  1061 
retinal,  1062 
of  skin,  1286 
Pillars  of  the  foot,  205,  1468 
of  fornix,  anterior,  870 
posterior,  868 
Pineal  body,  845 
Pinna  (see  Auricle) 
Piriformis,  453,  457,  461 
Pirogoff's  amputation,  1465 
Pisiform  bone,  159,  162 
Pits,  olfactory,  1050 

rectal,  1390 
Pituitary  body,  848,  1342 
Plane  or  arthrodial  diarthroses,  212 
Plantar  aponeurosis,  492 
arch,  627 

arteries,  lines  of,  1467 
artery,  deep  (communicating),  633 
lateral,  627,  640 
medial,  629 
calcaneo-cuboid    (short  plantar)   ligament, 

307,  1468 
calcaneo-navicular  ligament,  1468 
digital  (collateral)  arteries,  628 

branches,  proper,  of  medial  plantar  nerve, 

1011 
nerves,  common,  1011,  1013 

proper,  1011,  1013 
veins,  684 
fascia,  492,  1468 
ligaments,  307,  1468 

accessory,  310 
metatarsal  arteries,  628 

veins,  687 
nerve,  lateral,  1009,  1012 

medial,  1009,  1010 
venous  arch,  687 
rete,  684 
Plantaris,  454,  484,  485 
Planum  popliteum,  181 
Plate,  cribriform,  of  ethmoid,  81 
fronto-nasal,  117 
neural,  754 
olfactory,  1050 
orbital,  61 

perpendicular,  of  ethmoid,  82 
pterygoid,  66 
tympanic,  108 
Platypelhc  pelvis,  177 
Platysma,  330 
Pleura,  1236 
blood-vessels  of,  1239 
clinical  anatomy  of,  1368 
development  of,  20 
lymphatics  of,  701,  1239 
nerves  of,  1239 
Pleural  cavity,  1236 
reflection,  lines  of,  1237 
sinuses,  1237 
vilh,  1237 


Pleurapophysis,  51 

Plexuses  of  nerves,  abdominal  aortic,  1045 
anterior  pulmonary,  957 
atrial,  1041 

of  Auerbach,  757,  1030 
brachial,  980 

line  of,  1360 
bulbar,  1041 
cardiac,  1041 
cavernous,  1033 

of  penis  (or  clitoris),  1047 

of  cephalic  ganglia,  960 
cervical,  974 
coccygeal,  1018 
coeliac,  1043 
common  carotid,  1036 
coronary,  1041 
deferential,  1047 
external  carotid,  1036 

maxillary  (facial),  1036 
femoral,  1045 
gangliated  cephalic,  959 
hepatic,  1045 
hypogastric,  1045 
iliac,  1045 
inferior  dental,  941 

gastric,  1045 

mesenteric,  1045 
infra-orbital,  937,  939,  945 
internal  carotid,  1033 

mammary,  1037 

maxillary  1036 
intermediate,  1041 
lingual,  1036 
lumbar,  998 
lumbo-sacral;  996 
of  Meissner,  757,  1030 
meningeal,  1036 
middle  hajmorrhoidal,  1046 
myentericus  (plexus  of  Auerbach),  1045 
cesophageal,  954,  955 
ovarian,  1045 
parotid,  945 
patellar,  1001 
pelvic,  1046 
pharyngeal,  956,  1036 
phrenic  (diaphragmatic),  1044 
popliteal,  1045 
posterior  cervical,  of  Cruveilhier,  971 

oesophageal,  954 

pulmonary,  954,  955,  957 
pulmonary,  1043 

prevertebral,  755,  1029,  1032,  1040 
prostatic,  1047 
pudendal,  1016 
renal,  1044 
sacral,  1006 
spermatic,  1045,  1260 
splenic  (lienal),  1045 
submucosus  (plexus  of  Meissner),  1045 
subsartorial,  1003 
subtrapezial,  979 
superior  dental,  939 

gastric  (coronary),  1045 

haemorrhoidal,  1045 

mesenteric,  1045 

thyreoid,  1036 
thoracic  aortic,  1038 
suprarenal,  1044 
tympanic,  951,  961,  1033,  1089 
utero-vaginal,  1047 
vertebral,  1037 
vesical,  1047 

of  veins,  anterior  sacral,  679 
basilar.  651 
chorioid,  of  fourtli  ventricle,  922 

of  lateral  ventricle,  924 


INDEX 


1521 


Plexuses  choroid  of  third  ventricle,  924 
chorioidea,  875,  877 
hsemorrhoidal,  683 
of  internal  carotid,  653 
mammary,  671 
pampiniform,  674,  1259 
pharyngeal,  659 
pterygoid,  682 
thyreoideus  impar,  660 
utero-vaginal,  683 
vertebral,  664 
vesical,  683 
Plica(86)  ciliares,  1057 
ciroulares,  1165 
epigastrioa,  430 
fimbriata,  430 
incudis,  1090 

lacrimalis  (Hasneri),  1080,  1205 
longitudinalis  duodeni,  1189 
palatinsB  transversa;,  1104,  1106 
palmataa,  1272 
salpingo-pharyngea,  1130 
salpingo-palatina,  1130 
semilunaris,  1053,  1170 
triangularis,  1132,  1133 
of  tympanic  membrane,  1087 
umbilicalis  lateratis,  430 
ureterioa,  1252 
Pneumogastrie  nerve,  954 
Point(s),  alveolar,  109 
auricular,  101 
central,  of  perineum,  1385 
occipital,  101 
pre-auricular,  1332 
Bolandic,  1340 
subnasal,  109 
Poles,  of  cerebral  hemispheres,  850 
of  eyeball,  1055 
of  lens  of  eye,  1062 
Polygastric  muscles,  314 
Polymastia,  1301 
Polytheha,  1301 
Pons  (Varoli),  804 

basilar  sulcus  of,  804 
blood-vessels  of,  90S 
brachia  conjunctiva  (superior  cerebellar 

peduncles),  831 
grey  substance  of,  831 
internal  structure  of,  815,  829 
lemniscus  (fillet)  in,  831 
Pontile  path,  frontal,  832,  840,  889 

temporal  (Turk's  bundle),  832,  890 
Pontine  branches  of  basilar  artery,  561 

sulci,  804 
Popliteal  artery,  621,  640,  1452 
collateral  circulation,  1453 
ligament,  oblique,  287 
line,  189 

lymphatic  nodes,  748 
nerve,  external,  1013 

internal,  1009 
nerves,  paralysis  of,  1469 
plexus  of  nerves,  1045 
space,  clinical  anatomy  of,  1451 
vem,  688,  1452 
accessory,  689 
Pophteus,  454,  486 
Pore,  canal,  1051 
of  skin,  1285 
sudoriferous,  1297 
taste,  1051 
Porta  hepatis,  1183 
Portal  fissure  of  liver,  1183 
vein,  528,  675 
development,  694 
tributaries,  675 
veins,  accessory,  678 


Position    of   organs    (see    corresponding    Or- 
gan) 
Post-aortic  lymphatic  nodes,  731 
Post-auditory  process,  122 
Post-central  branches  of  spinal  arteries,  590 
sulcus,  inferior,  861,  862 
superior,  861,  862 
Post-glenoid  process,  71 
Post-limbic  fissure,  863 
Post-malar,  95 

Post-nodular  sulcus  of  cerebellum,  808 
Post-parietal  gyrus,  863 
Post-scapula,  145 
Post-sphenoid  centre,  67 
Pott's  fracture,  1454 
Pouch  of  Douglas,  1148,  1267,  1274 

of  Prussak,  1089 

recto-uterine    (recto-vaginal),    1148,    1267, 
1274 

recto-vesical,  1148 

of  Troltsch,  1089 
Poupart's  ligament,  424,  429,  1371,  1399,  1438 
Precuneus  (quadrate  lobe),  863 
Prjeputium  clitoridis,  1277 

penis,  1260 
Praevesical  space  (cavum  Retzii),  1250 
Pre-aortic  lymphatic  nodes,  730 
Pre-auricular  point,  1332 
Precentral  sulcus,  807,  857 
Preglenoid  tubercle,  71 
Pre-laminar  branches  of  spinal  arteries,  590 
Premalar,  95 
Premaxilla,  89,  91,  119 
Premolars,  1121 
Preoccipital  notch,  861 
Pre-palatine  centre,  91 
Prepatellar  bursa,  1448 
Prepuce,  1260 
Pre-scapula,  145 
Pre-sphenoid  centre,  67,  119 
Presternum,  132 
Prevertebral  musculature,  328,  355 

plexuses,  755,  1029,  1032,  1040 
Primary  curvatures  of  spinal  column,  43 

divisions  of  spinal  nerve-trunk,  967 
anterior,  968 
posterior,  967 
Primitive  groove,  10 

node,  11 

pit,  10 

streak,  10 
Princeps  cervicis  artery,  543 

pollicis  artery,  586 
Procerus  (pyramidalis  nasi),  336 
Process (es),  accessory  (of  vertebra),  38 

acromion,  144 

alar,  of  ethmoid,  81 

alveolar,  87,  90 

anterior  clinoid,  65,  116 

arciform,  466 

caudate,  of  liver,  1184 

cihary,  1057 

cochleariform,  1089 

condylar,  of  mandible,  96 

coracoid,  of  scapula,  144 

coronoid  of  mandible,  96,  1351 

ensiform,  132,  134 

ethmoidal,  85 

external  auditory,  75 

frontal,  of  maxilla,  87,  88 

fronto-nasal,  119 

fronto-sphenoidal,  95 

glosso-hyal,  99 

hamular,  66,  106 

infra-orbital,  95 

jugular,  54,  108 

lacrimal,  85 


1522 


INDEX 


Process(es),  lenticular,  of  incus,  79 
mastoid,  72,  108 

maxillary  of  inferior  nasal  concha,  84 
of  palate  bone,  92 
middle  cHnoid,  65,  116 
muscular,  of  arytEenoid  cartilage,  1211 
orbital,  of  malar  bone,  94 

of  palate  bone,  91,  93 
palatine,  87,  88 
posterior  clinoid,  63,  116 

petrosal,  63 
post-glenoid,  71 
pterygoid,  62,  66 
pyramidal,  of  palate  bone,  91,  92 
sphenoidal,  of  palate  bone,  91,  92 
styloid,  70,  73,  75,  108 
of  fibula,  190 
of  radius,  155 

of  third  metacarpal  bone,  166 
of  ulna,  158 
supracondylar,  149 
temporal,  of  malar  bone,  95 
trochlear,  195 
unciform,  163 
uncinate,  of  ethmoid,  83 
vaginal  of  sphenoid,  63,  66 
of  temporal,  75 
vermiform,  1378 

vocal,  of  arytenoid  cartilage,  1212 
xiphoid,  132,  134 
zygomatic,  70,  87,  88 
Processus  cochleariformis,  77 
Folii,  79 
globulares,  119 
gracilis,  79 
marginalis,  95 
tubarius,  66 

uncinatus  (of  Winslow),  1194 
vaginalis,  1387 
Profunda  (superior)  artery,  576 
axillaris  artery,  640 
(deep)  femoral  artery,  620,  640 
branches,  620 
vein,  690 
Projection  fibres  of  white  substance  of  telen- 
cephalon, 886,  889 
Prominence,  laryngeal,  1211 
Promontory  in  cochlea,  81,  1089 

of  temporal  bone,  73 
Pronation,  321 
Pronator  quadratus,  402 
ridge  of  ulna,  157 
teres,  395,  396 
Proper  digital  arteries,  582 
plantar  digital  nerves,  1011 
scapular  ligaments,  252 
volar  digital  nerves  of  hand,  992 
veins,  671 
Prosencephalon  (fore-brain),  843 
external  features  of  843 
internal  structure  of,  878 
Prostate,  1264 

lymphatics  of,  700,  739 
surgical  anatomy  of,  1389 
vessels  and  nerves  of,  1265 
Prostatic  branches  of  inferior  vesical  artery, 
608 
plexus  of  nerves,  1047 
portion  of  urethra,  1263,  1265,  1388 
Prostatic   utriculus    (sinus   pocularis,   uterus 

masoulinus),  1263 
Prostatico-perineal  fascia,  447 
Protoplasm,  5 

Protuberance,  external  occipital,  52 
internal  occipital,  52 
mental,  95 
Prussak,  pouch  of,  1089 


Psalterium,  hippocampal,  869 
Psuedo-hermaphroditism,  1230 
Psoas  abscess,  1438 
fascia,  455 
major,  455 
minor,  455 
Pterion,  101,  1332 
Pterygoid,  accessory,  342 
branches  of  internal  maxillary  artery,  548 
(Vidian)  canal,  103,  107,  108,  126 
fossa,  66,  107 

hamulus  (of  sphenoid),  66,  1351 
muscles,  338,  342 
notch,  66 
plate,  lateral  66 

medial,  66 
plexus  of  veins,  646 

portion  of  internal  maxillary  artery,  546 
processes,  62,  66 
tubercle,  66 
veins,  646 
Pterygoideus  externus,  338,  342 

internus,  338,  342 
Pterygo-maxillary  fissure,  102 
Pterygo-palatine   (pharyngeal)   canal,  88,  92, 
103 
fissure,  102 

(spheno-m  axillary)  fossa,  102 
portion  of  internal  maxillary  artery,  546 
Pubes,  1290 
Pubic  arch,  176 

branch  of  inferior  epigastric  artery,  615 
of  obturator  artery,  608 
Pubis,  172 

symphysis,  238 
tubercle  (spine)  of,  172 
Pubo-capsular  (pectineo-femoral)  band,  278 
Pubo-cavernosus  (levator  penis),  451 
Pubo-coccygeus,  440,  448 
Pubo-peritonealis,  436 
Pubo-prostatic  hgaments,  middle,  1252 
Pubo-rectalis,  440,  448 
Pubo-transversalis,  436 
Pubo-vesical  ligaments,  1252 
Pudendal  (pudic)  artery,  610,  639 
accessory,  638 
(superficial)  external,  619 
internal,  610,  639 
nerve,  1017 
long,  1007 
vein,  external,  684 
internal,  681 
plexus  of  nerves,  1016 
of  veins,  682,  683 
Pulmonary  artery,  528,  1234 
circulation,  507 
left,  529 
relations,  1369 
right,  529 
variations,  637 
branches  of  vagus,  957 
ligament,  1236 
lymphatic  nodes,  725 
(visceral)  pleura,  1236 
plexus,  anterior,  957,  1043 

posterior,  954,  955,  957,  1043 
(semilunar)  valves,  517 
veins,  529,  1234 
Pulp  of  tooth,  1118 
Pulpa  lienis,  1311 
Pulpy   nucleus   of   intervertebral  fibro-cartU- 

ages,  226 
Pulvinar  of  thalamus,  845,  889 
Puncta  lacrimalia,  1054,  1079,  1349 
PupO,  1054 
Purkinje  cells,  809 
fibres  of  heart,  516 


INDEX 


1523 


Putamen,  880 

Pyloric  antrum  of  stomach,  1151 

canal,  1152 

portion  of  stomach,  1151 

vein,  675 
Pylorus,  1152,  1374 
Pyramidal  eminence  of  temporal  bone,  77 

fasciculi  of  pons,  830 

fibres,  840,  889 

lobe  of  thyreoid  gland,  1314 

process  of  palate  bone,  91,  92 

tract,  anterior  or  direct,  788 
crossed,  783 
Pyramidalis,  424,  431 

nasi,  336 
Pyramids  of  Ferrein,  1246 

of  Malpighi  (renal),  1246 

of  medulla  oblongata,  783,  799 
decussation  of,  815 
structure  of,  815 

of  vermis,  808 

vertebral,  43 


Quadrangular  lobe  of  cerebellum,  806 

membrane  of  larynx,  1215 
Quadrate  lobe,  of  liver,  1184 

muscles,  332 
Quadratus  femoris,  453,  463,  464 
.     labii    inferioris    (depressor    labii 
inferioris),  332 
superioris,  332 
lumborum,  425,  436,  1407 
plantae  (flexor  accessorius),  454,  495 
Quadriceps  femoris,  453,  468,  470 
Quadrigeminate  arteries,  907 
body,  inferior,  834,  839 
superior,  825,  834,  841 
Quadrigemino-pontile  fibres,  841 

R 

Radial  artery,  582 

in  palm  (deep  volar  arch),  586 
at  the  wrist,  584 
carpal  artery,  dorsal,  585 

volar,  584 
collateral  ligament,  261,  267 
fossa  of  humerus,  151 
(musculo-spiral)  nerve,  985 
hne  of,  1415,  1423 
results  of  paralysis  of,  1424 
deep  (posterior  interosseous),  985 

results  of  paralysis  of,  1424 
superficial  (radial),  987 
notch  (lesser  sigmoid  cavity)  of  ulna,  157 
recurrent  artery,  583 
vena)  comitantes,  671 
Radialis  indicis  artery,  586 
Radiate  (anterior   costo-central   or  stellate) 
ligament,  242 
sterno-oostal  ligament,  anterior,  245 
Radiation  of  corpus  eollosum,  851 
Flechsig's  secondary  optic,  890 
occipito-thalamic  (optic),  888 
Radicular  veins,  792,  908 
Radio-carpal  or  wrist-joint,  265 
arterial  supply  of,  267 
ligaments  of,  266 
movements  of,  267 
muscles  acting  upon,  268 
nerve-supply,  267 
relations  of,  267 
Radio-carpeus  muscle,  403 
Radio-ulnar  joint,  inferior,  263,  419 
mid,  262 

superior,  262,  1419 
ligaments,  262,  264 


Radius,  152 

clinical  anatomy  of,  1419,  1422 
Ramus(i)  bronchial,  1231 

colli  (infra-mandibular  branch),  of  cervico 
facial  nerve,  946 

communicantes,  969,  1030,  1037 

of  fissure  of  Sylvius,  856 

of  ischium,  172 

isthmi  faucium,  940 

Knguales,  954 

of  mandible,  95 

of  pubis,  172 
Ranvier,  nodes  of,  761,  767 
Raphe  of  palate,  1104 

lateral  palpebral,  1078 

scrotal,  1254 
Receptaeulum  (cisterna)  chyli,  726 
Recess(es),  elUptical,  80 

epitympanic,  78 

hypo-tympanie,  78 

infundibular,  848 

optic,  848 

pharyngeal,  1130 

spheno-ethmoidal,  1206 

spherical,  80 

supra-pineal,  847 

of  tumpanic  mucous  membrane,  1089 
Recessus  ellipticus  (fovea  hemielliptioa),  80 

sphajricus  (fovea  hemisphaerica),  80 
Rectal  branches  of  lateral  sacral  arteries,  608 
(hsemorrhoidal)  of  middle  sacral  arteries, 

columns  (of  Morgagni),  1177,  1390 
examination,  1391 
pits,  1390 
sinuses,  1177 
stalk,  1391 
triangle,  440,  1383 
Recto-uterine  folds,  1274 

pouch  (of  Douglas),  1267,  1274 
Recto-vaginal  pouch  of  peritoneum,  1148 
Recto-veslcal  pouch  of  peritoneum,  1148 
Rectum,  1176 

clinical  anatomy  of,  1390 
lymphatics  of,  735 
supports  of,  1391 
Rectus  abdominis,  422,  424,  430 
accessorius,  471 
capitis  anterior  (minor),  356 
lateralis,  356 
major,  355 

posterior  major,  412,  419 
minor,  412,  419 
femoris,  468,  470,  1436 
Recurrent  artery,  anterior  tibial,  632 
dorsal  ulnar,  577 
interosseous,  580 
posterior  tibial,  632 
radial,  583 
volar  ulnar,  577 
articular  nerve  of  leg,  1013 
branches  of  deep  volar  arch,  586 
of  lacrimal,  552 
of  spinal  nerve-trunks,  970 
of  vagus  nerve,  956 
meningeal  branch  of  maxillary  nei-ve,  937 

of  ophthalmic  nerve,  935 
(inferior  laryngeal)  nerve,  957 
Red  nuclei,  840 

References  for  articulations,  311 
blood-vascular  system  ,''696 
digestive  system,  1197" 
ductless  glands,  1329 
lymphatic  system,  750 
morphogenesis,  25 
musculature,  506 
nervous  system,  1047 


1524 


INDEX 


References  for  osteology,  209 
respiratory  system,  1240 
skin  and  mammary  glands,  1329 
special  sense  organs,  1098 
urogenital  system,  1280 
Reflected  inguinal  ligament  (CoUes'  ligament, 

triangular  fascia),  1395 
Reflex  paths  of  cranial  nerves,  898 
of  spinal  cord,  895 
optic  acoustic,  840 
Regeneration  of  lymphatics,  707 
Region,  ilio-costal,  1406 
parotid,  1343 
of  skull,  anterior,  108 
inferior,  103 
lateral,  101 
posterior,  101 
superior,  100 
Regions  of  abdomen,  1142,  1370 
Reil,  island  of  (insula),  856 
Reissner,  membrane  of,  1096 
Relations    of     organs     (see     correspondmg 

organs) 
Renal  arteries,  598,  638 
accessory,  638 
branches  of  lumbar  arteries,  693 

of  vagus,  958 
columns  (of  Bertin),  1246 
(Malpighian)  corpuscles,  1246 
fascia,  1242 
ganglia,  1044 
pelvis,  1248 

plexuses  of  nerves,  1044 
pyramids  (of  Malpighi),  1246 
surface  of  spleen,  1309 
tubules,  1246 
veins,  673 
Reproductive  organs,  development  of,  1278 
female,  1265 
male,  1253 

lymphatics  of,  742,  744 
Respiration,  1199 

musculature,  247,  248,  503 
Respiratory  nerve  of  Bell,  external,  982 
nucleus,  822 
system,  1196 
larynx,  1209 
lungs,  1228 

mediastinal  septum,  1239 
nose,  1200 
pleura},  1236 
thoracic  cavity,  1235 
trachea  and  bronchi,  1225 
region  of  nose,  1208,  1352 
Restiform  body,  800,  810 
fibres  of,  830 
in  pons,  830 
Rate  arteriosum,  cutaneous,  1289 
sub-papillary,  1289 
articular  of  knee,  622 
canalis  hypoglossi,  650,  665 
dorsal  carpal,  579,  585 
venous  (foot),  684 
(hand),  667 
foraminis  ovalis,  646 
lateral  malleolar,  626,  632 
medial  malleolar,  626,  632 
patellar,  622 
plantar  venous,  684 
testis,  1256 
volar  carpal,  579,  581 
Retia  venosa  vertebrarum,  665 
Reticular   formation   of   medulla   oblongati 
816 

layer  of  thalamus,  882 

of  pons,  816 

of  spinal  cord,  776 


Retina,  1051,  1057,  1061 
Retinacula,  1287 
mammaj,  1303 
pateUse  laterale,  471 
mediale,  471 
peroneal,  480 
tendinum,  317 
Retinal  arteries,  1065 
pigment  layer,  1057 
veins,  1065 
Retractors  of  the  lips,  332 
Retrahens  aurem,  337 
Retro-pubic  space  (of  Retzius),  1371 
Retrotonsillar  fissure  of  cerebellum,  807 
Rhinencephalon,  864 
Rhombencephalon,  758 
isthmus  of,  832 

summary  of  principal  structures  in,  833 
Rhomboid  fossa,  802 

ligament  (costo-clavioular),  249 
muscles,  nerve  to,  982 
Rhomboideus  major,  356,  358 

minor,  356,  358 
Ribs,  120 

asternal  or  false,  127 
bicipital,  132 
cervical,  131,  1365 
clinical  anatomy  of,  1363,  1404 
eleventh,  130 
first,  128 
floating,  127 
lumbar,  132 
ossification  of,  130 
pecuUar,  128 
second,  129 
sternal  (true),  127 
tenth,  129 
twelfth,  130 

typical  characters  of,  127 
variations  of,  131 
vertebral,  127 
vertebro-chondral,  127 
vertebro-sternal,  127 
Ridge  (s),  carotid,  73 
genital,  1267,  1278 
nfra-temporal,  65 
lateral  supracondylar,  149 
medial  supracondylar,  149 
pronator,  of  ulna,  157 
transverse,  of  palate,  1104,  1106 
temporal,  71 
Right  atrium  (auricle)  of  heart,  512 
branch  of  hepatic  artery,  595 
bronchial  artery,  588 
colic  artery,  598 
common  iliac  artery,  605 
coronary  artery,  519 

branches,  519 
gastric  artery,  594 
gastro-epiploic  artery,  595 

vein,  677 
innominate  vein,  641 
lymphatic  duct,  728 
pulmonary  artery,  529 

veins,  529 
superior  intercostal  vein,  664 
terminal  branch  of  hepatic  artery,  589 

collecting  lymphatic  duct,  728 
ventricle  of  heart,  516 
Rima  glottidis,  1223 
oris,  1100 
palpebrarum,  1052 
pudendi,  1276 

vestibuli,  1222  .     ,  ,.  ,        ,    ,  , 

RinK(s),  abdominal  ingumal  (mternal  abdom- 
inal), 430,  1371,  1396 
femoral,  466,  1401 


INDEX 


1525 


Rings,  subcutaneous  inguinal  (external  abdom- 
inal), 429,  1371,  1394 

tonsillar  (Waldeyer's),  1133 
Risorius,  333 
Rivinus,  notch  of,  77 
Rolandic  angle,  860 

points,  1340 
Rolando,  fissure  of,  859,  1340 

gelatinous  substance  of,  776 
Root(s)  of  Arnold's  or  otic  ganglion,  963 

canal  of  tooth,  1118  ' 

of  ciliary  ganglion,  long,  937 
short,  932 

filaments  of  spinal  nerves,  775,  964 

of  hair,  1292 

of  lungs,  1229,  1230,  1234,  1408 

of  nails,  1294 

of  nose,  1200 

of  optic  tracts,  849 

of  penis,  1260 

of  spheno-palatine  (Meckel's)  ganglion,  962 

of  spinal  nerves,  771,  964 

of  teeth,  1117 

of  tongue,  1107 
Rosenmtiller,  fossa  of,  1130 
Rostral  lamina  of  corpus  calloum,  852 

sulci,  858 
Rostrum  of  corpus  callosum,  852 

of  sphenoid,  63 
Rotation,  215,  321 
-Rotatores,  breves,  412,  419 

longi,  412,  419 
Round  ligament  liver,  1185 

of  uterus,  1274 
Rubro-spinal  fasciculus,  786 
Ruffini,  corpuscles  of,  1290 
RugsB  of  vagina,  1275 


Sac,  conjunctival,  1054 

endolymphatic,  1094 

lacrimal,  1080,  1349 

lesser,  1148 

synovial,  313 
Saccular  branch  of  vestibular  ganghon,  950 
Saccule  of  membranous  labyrinth,  1093 
Sacculo-ampullar  division  of  vestibular  nerve, 

950 
Sacral  arteries,  lateral,  607 
middle,  603 

branches,  lateral  of  middle  sacral  artery,  603 

canal,  42 

cornua,  40 

foramina,  40 

groove,  41 

hiatus,  40 

lymphatic  nodes,  733 

nerves,  973,  1006 

plexus,  1006 

composition  of  nerves  of,  1006 
of  veins,  anterior,  679 

portion  of  sympathetic  system,  1040 

veins,  lateral,  680 
middle,  679 

vertebrae,  development  of,  48 
Sacro-coccygeal  articulation,  237 

ligament,  anterior,  238 
deep  posterior,  238 
superficial  posterior,  238 
Sacro-coccygeus,  anterior,  448 

posterior,  448 
Sacro-iliac  articulation,  234 

ligaments,  anterior,  234 

inferior,  235 

posterior,  234 

superior,  234 


Sacro-lumbar  ligament,  232 

Sacro-spinaUs  (erector  spinas),  412,  414,  1407 

Sacro-spinous  or  small  sacro-sciatic  ligament, 

236 
Sacro-tuberous  (great  or  posterior  sacro-sciatic) 

ligament,  235 
Sacro-vertebral  angle,  39,  43 

articulations,  232 
Sacrum,  description  of,  30,  39 

sex  and  racial  differences  of,  42 
Sagittal  fontaneUe,  59 

sinus,  inferior,  650 
superior,  649 

sulcus,  60 

suture,  57,  101 
Salivary  corpuscles,  1132 

glands,  1113 

development  of,  1117 
variations  and  comparative,  1117 
Salivatory  nucleus,  826,  947 
Santorini,  cartilages  of,  1212 

duct  of,  1195 

incisures  of,  1085 
Saphenous  artery,  621 

nerve,  1003,  1467 

external  or  short,  1010,  1013 

opening  (fossa  ovaUs),  467,  1400,  1440 

vein,  accessory,  684 

great  (internal),  684,  1456 
small  (ex-ternal),  684,  1458 
Sarcolemma,  315 
Sartorius,  453^  468,  1436 
Scala  media,  1096 

tympani,  81,  1096 

vestibuli,  81,  1096 
Scalene  musculature,  328,  353 

tubercle,  129 
Scalenus  anterior,  353 

medius,  354 

minimus,  355 

posterior,  354 
Scalp,  1333 

cutaneous  areas  of,  1018 

lymphatics  of,  712 
Scansorius,  462 
Soapha  of  auricle  of  ear,  1083 
Scaphoid  bone,  159,  160 

fossa,  55,  66,  107 
Scapula,  141 

clinical  anatomy  of,  1406 
Scapular  artery,  circumflex  (dorsal),  572 
posterior,  565 
transverse  (suprascapular),  564  • 

foramen,  142 

nerve,  dorsal,  982 

notch,  142 

veins,  transverse,  648 
Seapulo-clavicular  union,  250 
Scapulo-clavicularis,  374 
Scarf-skin  (epidermis),  1285 
Scarpa,  fascia  of,  425,  445 

foramina  of,  89,  106,  126 

triangle  of,  467,  1438 
Schindylesis  sutures,  212 
Schlemm,  canal  of,  1059 
Schwalbe,  nucleus  of,  823 
Sciatic  artery,  609,  640 

nerve  (N.  ischiadious),  1008,  1443 
results  of  paralysis  of,  1469 
small,  1007 

notch,  great,  172 
small,  172 
Scleral  sulcus,  1054 
Sclera,  1052,  1056,  1058 
Sclerotome,  15 

Scrotal  (or  labial)  arteries,  anterior,  620 
posterior,  613 


1526 


INDEX 


Scrotal  nerves,  anterior,  1000 
posterior,  1017 
veins,  684 
Scrotum,  12ol 

lymphatics  of,  698,  742,  1255 
surgical  anatomy  of,  1385 
vessels  and  nerves  of,  1255 
Scutum,  1089 
Sebaceous  glands,  1298 
Sebum  cutaneum,  1298 

palpebrale,  1054 
Secondary  tympanic  membrane,  1089,  1096 
Sections  of  peritoneum,  1146 
Segmentation  of  the  ovum,  9 
Sella  turcica,  63,  113 
Seraioanalis  m.  tensoris  tympani,  74 
Semicircular  canals,  78,  80 

ducts    (membranous   semicircular   canals), 
3094 
Semilunar  bone,  159,  161 
fascia,  382 
fibro-cartilages,  289 
fissures  of  cerebellum,  805 
fold  of  conjunctiva,  1055 
of  large  intestine,  1170 
ganglia,  1043 

(Gasserian)  ganglion,  826,  936,  1345 
gyrus,  865 
lobe,  inferior,  of  cerebellum,  807 

superior,  of  cerebellum,  806 
notch  (greater  sigmoid  cavity),  156 
valves,  aortic,  517 
pulmonary,  517 
Semimembranosus,  453,  475,  476 
Seminal  vesicles,  1257 
Seminiferous  tubules,  1256 
SemispinaUs  capitis  (complexus),  412,  417 
cervicis,  412,  419 
dorsi,  412,  419 
Semitendinosus,  453,  475,  476 
Sense,  organs  of  special,  1049 
Sensory  aphasia,  894 

axones,  762 
Sensory-motor  area  of  cerebral  cortex,  893 
Septa,  intermuscular,  314 

of  thigh,  468 
Septal  branches  of  spheno-palatine  artery,  549 

nasal  cartilage,  1202 
Septulse  of  mediastinum  testis,  1256 
Septum  aortic,  527 

of  arm,  intermuscular,  377 
atriorum,  511 
canalis  musculotubarii,  73 
femoral,  466 

of  foot,  intermuscular,  492 
of  heart,  membranous,  511,  527 
interventricular,  516 
of  leg,  intermuscular,  477 
linguae,  346 
mediastinal,  1239 
nasal.  111,  1204,  1354 
Septum  pellucidum,  872 
cavity  of,  872 
laminaj  of,  872 
of  penis,  1261 

posticum  of   Schwalbe    (subarachnoid  sep- 
tum), 919 
sigmoid,  341 
sphenoidal,  62 
transversum,  20 
Serial  morphology  of  vertebrae,  50 
Serrate  sutures,  212 
Serratus  anterior  (magnus),  356,  359 
posterior  inferior,  423,  431 
superior,  423,  431 
Sesamoid  bones,  68,  205,  275,  317 
cartilages  of  larynx,  1213 


Sesamoid  nasal  cartilages,  1202 
plate,  plantar,  310 
tibial  and  fibular,  209 
ulnar  and  radial,  209 
Seventh  cervical  vertebra?,  34 

cranial  nerve  (facial),  943,  1345 
Shaft  of  bones,  29   (see   also  the    individual 
bones) 
of  hair,  1292 
Sheath  (s),  carotid,  1362 
femoral,  1400 
medullary,  759 
of  optic  nerve,  931 
of  parotid  gland,  1344 
primitive,  761 
of  prostate,  1389 
of  rectus  muscle,  427 
of  hair  roots,  1292 

synovial  tendon,  317,  318, 403, 483, 484,  491 
Shoulder,  clinical  anatomy  of,  1409 

musculature  of,  323,  363,  503 
Shoulder-blade  (scapula),  141 
Shoulder-girdle,  207 
Shoulder-joint,  253 
arterial  supply,  257 
clinical  anatomy  of,  1413 
ligaments  of,  254 
lymphatics  of,  723 
movements  of,  257 
muscles  acting  upon,  258 
nerve-supply  of,  357 
synovial  membrane,  255,  1412 
Shrapnell's  membrane,  1087 
Sibson's  fascia,  129,  355,  1237 
Sigmoid  artery,  603 
cavity  of  radius,  154 
of  ulna,  greater,  156 
lesser,  157 
colon,  1174,  1379 
groove,  72 
notch,  96,  97 
septum,  341 
sinus,  652 
vein,  678 
Sinuses,  accessory  nasal,  1354 
aortic  (of  Valsalva),  518 
bony,  of  skull,  1335 
cavernous,  652,  691 
cervical,  17 
circular,  651 

connecting  with  nose,  1354 
coronary,  521 
costo-mediastinal,  1238 
cranial  venous,  649,  692,  916 
of  dura  mater,  649 
epididymidis  (digital  fossa),  1255 
frontal,  59,  61,  1207,  1335 
inferior  petrosal,  652 

sagittal  (longitudinal),  650 
interoavernosus,  651 
of  kidney,  1242 
lactiferous,  1302 
longitudinal  vertebral,  665 
mammarum,  1299 

marginal,  650  v  ■  o-r 

maxillaris  (antrum  of  Highmore),  87,  90, 

111,  1206,  1354 
of  Morgagni,  1137  _ 
oblique,  of  pericardium,  523 
occipital,  650 
paranasal,  1206 
parasinoidal,  919 

of  pericardium,  transverse,  523,  527 
petro-squamous,  653 
phrenico-costal,  1237 
pleural,  1237 
of  portal  vein,  675 


INDEX 


1527 


Sinuses,  rectal,  1177 
sigmoid,  652 

sphenoidal,  62,  1207,  1338 
spheno-parietal,  653 
straight,  650 
superior  petrosal,  652 

sagittal  (longitudinal),  649 
tarsi,  195 

transverse  (lateral),  651 
tympanic,  1089 
uro-genital,  1279 
of  Valsalva,  518,  530 
venarum,  513 
venosus,  of  heart,  525 
of  sclera  (Sohlemn),  1059 
Sinusoids,  672,  675 
Skeleton,  27 

appendicular,  139 
axial,  29 
Skene,  ducts  of,  1277 
Skin,  1281 
appendages  of,  129 
cerium,  1286 

development  of,  1286,  1290 
epidermis,  1285 
lymphatics  of,  698,  1289 
muscle-fibres  of,  1288 
tela  subcutanea  (superficial  fascia),  1287 
vessels  and  nerves,  1288 
Skin-folds  of  wrist  and  hand,  1425 
Skull,  appendicular  elements  of,  117 
articulations  of,  215 
at  birth,  120 
bones  of,  51 
bony  landmarks,  1331 

sinuses  of,  1335 
fcetal,  general  characters,  120 
interior  of,  112 
morphology  of,  117 
nerve-foramina  of,  125 
regions  of,  anterior  (norma  facialis),  108 
inferior  (norma  basalis),  103 
lateral  (norma  lateralis),  101 
posterior  (norma  occipitalis),  101 
superior  (norma  verticalis),  100 
topography  of,  1338 
as  a  whole,  160 
Small  cardiac  vein,  521 
intestine,  1161,  1375 
blood-supply,  1166 
clinical  anatomy  of,  1375 
development  of,  1168 
duodenum,  1161 
ileum  and  jejunum,  1165 
lymphatics  of,  1168 
nerves  of,  1168 
(accessory)  meningeal  artery,  548 
occipital  nerve,  977 
palatine  nerve,  948 
(external)  saphenous  vein,  684,  1458 
sciatic  nerve,  1007 
superficial  petrosal  nerve,  951 
Smaller  palatine  canals,  92 
Smallest  cardiac  vein,  521 

occipital  nerve,  971 
Snuff-box  space  (tabati^re  anatomique),  1433 
Soft  palate,  1104 
muscles  of,  326 
Solar  plex-us,  1043 
Sole  of  foot,  muscles  of,  493 
Soleus,  454,  484,  485 

accessorius,  491 
Solitary  follicles,  704 

glands  of  small  intestine,  1166 
tract,  820 
Somresthetic  (sensory-motor)  area  of  cerebral 
cortex,  893 


Somites,  mesodermic,  14,  15 
Space(s),  Burns',  1356 
of  Fontana,  1060 
intercostal,  139 

interfascial  (Tenon's),  715,  1073 
popliteal,  1451 
praevesical,  1250 
snuff-box,  1433 
subarachnoid,  771 
subdural,  771 
Special  sense,  organs  of,  1049 
Speech,  cortical  areas  of,  894 
Spermatic  artery,  external,  615 
internal,  698,  638,  1259 
branch,  external,  of  genito-femoral  nerve, 

1000 
cord,  1254,  1269,  1387 
fascia,  external,  1387 
plexus  of  nerves,  1045 
veins,  674,  1259 
Spermatozoa,  1256 

Spheno-ethmoidal     branch     of     naso-ciliary 
(nasal)  nerve,  937 
cells,  84 
recess,  1206 
Sphenoid,  62 

at  birth,  122 
Sphenoidal  conchas  (turbinate  bones),  64,  67 
at  birth,  124 
development  of,  119 
crest,  63 

(superior  orbital)  fissure,  65,  109,  116,  126 
process  of  palate  bone,  91,  92 

of  septal  cartilage,  1203 
septum,  62 
sinuses,  62,  1207 
Spheno-mandibular  ligament,  217 
Spheno-maxillary  fissure,  102,  109,  126 

fossa,  102 
Spheno-palatine  artery,  549 
nerve,  938 
foramen,  93,  103,  111,  126 
(Meckel's)  ganglion,  962 
branches,  962 
roots,  962 
notch,  91,  93 
vein,  646 
Spheno-parietal  sinus,  653 
Sphenotic  cartilage,  117 
Spherical  recess,  80 
Sphincter  ani  externus,  441,  449 
internus,  1 177 
tertius,  1177 
internal,  of  urinary  bladder,  1253,  1389 
pupillae  (iridis),  1061 
urethras  (in  female),  449 

membranaceae,  449 
urogenitalis,  442,  449 
vaginaj,  1276,  1278 
Spigelian  lobe  of  liver,  1184 
Spinal  accessory  nerve,  958 
nucleus  of,  820 
arachnoid,  919 
artery,  anterior,  561,  638,  792 

posterior,  561,  792 
branches  of  aortic  intercostal  arteries,  590 
of  deep  cervical  artery,  568 
of  Uio-lumbar  artery,  607 
of  lateral  sacral  arteries,  60S 
of  superior  intercostal  arteries,  568 
of  vertebral  artery,  560 
cord,  751,  771 

blood  supply  of,  792 
central  canal  of,  775 
clinical  anatomy  of,  1408 
external  morphology  of,  771 
internal  structure  of,  775 


1528 


INDEX 


Spinal  cord,  meninges  of,  908 

summary  of,  788 

surface  of,  772 

systems  of  neurones  in,  777 

terminal  ventricle,  775 
dura  mater,  911 
ganglia,  964 

aberrant,  965 

neurones  of,  755 
musculature,  410 
nerves,  964 

aberrant  ganglia,  965 

areas  of  distribution  of,  970 

attachment  of,  964 

Cauda  equina,  966 

course  of,  965 

filia  radicularia,  965 

ganglion  of,  964 

origm  of,  964 

roots  of,  964 

topography  of  attachment  of,  966,  1406 
nerve-trunks,  anterior  primary  divisions,  968 

meningeal  (recurrent)  branch  of,  970 

posterior  primary  divisions,  967,  970 

rami  communicantes,  969 
pia  mater,  921 
(inferior)     portion     of     (spinal)     accessory 

nerve,  958 
tract,  of  trigeminus  nerve,  828 
veins,  anterior,  665 

posterior,  665 
Spinalis  capitis  (biventer  cerviois),  418 
cervicis,  412,  417 
dorsi,  412,  417 
Spindle,  aortic,  531 

neuromuscular,  764 
Spine  (s),  29 

anterior  nasal,  87,  90,  112 

ethmoidal,  63,  113 

frontal  (nasal),  60 

of  helix,  1084 

of  ilium,  169 

ischial,  172 

mandibular,  96 

mental,  95 

nasal  (frontal),  60 

posterior,  91 
of  pubis,  172 
of  scapula,  141,  144 
of  sphenoid,  65,  108 
suprameatal,  72 

of  tibia  (iatercondyloid  eminence),  185 
vertebral,  1403 
Spino-cerebellar  fasciculi,  784 

path,  985 
Spino-mesencephalic  (spLno-tectal)  tract,  786, 

842 
Spino-olivary  fasciculus,  784 
Spino-thalamic  tract,  786 
Spinous  process  of  epistropheus,  34 

of  seventh  cervical  vertebra,  34 

of  vertebra:,  31 

ligaments  connecting,  229 
Spiral  canal  of  cochlea,  81 
ganglion  of  cochlea,  950 
ligament  of  cochlea,  1096 
line  of  femur,  178 
organ  (organ  of  Corti),  1096 
valve  (of  Heister),  1187 
Splanchnic  ganglion,  1039 
nerve,  great,  1038 

least,  1039 

lesser,  1039 

pelvic,  1017,  1040,  1046 
Spleen  (lien),  1306 
development,  1312 
lymphatics,  736,  1312 


Spleen,  topography  of,  1310,  1375 

variations,  1310 

vessels  and  nerves,  1312 
Splenic  artery,  595 

branches  of  vagus,  958 

(left  colic)  flexure,  1174,  1379 

lobules,  1312 

lymphatic  nodes,  730,  736 

(lienal)  plexus  of  nerves,  1045 

pulp,  1311 

vein,  677 
Splenium  of  corpus  callosum,  852 
Splenius,  412,  414 

capitis,  414 

cervicis,  414 
accessorius,  414 
Spongioblasts,  755 
Spot,  yellow,  of  fundus  oculi,  1055 

of  larynx,  1223 
Spring  ligament,  305 
Squamous  portion  of  temporal  bone,  68 

sutures,  212 
Stapedial  fold,  1090 

artery,  638 
Stapedic  branch  of  stylo-mastoid  artery,  544 
Stapedius,  1091 

nerve  to,  944 
Stapes,  80,  119 
Stellate  cells  of  cerebellar  cortex,  809 

figures  of  lens  of  ej'e,  1063 

ligament,  242 
Stem  of  fissure  of  Sylvius,  855 
Stenson's  duct,  1115,  1343 

foramina,  89,  106 
Stephanion,  101 

Sternal  branches  of  internal  mammary  artery, 
567 

foramen,  133 

synchondrosis,  133 
Sternalis,  374 
Sternebras,  132 

Sterno-chondro-scapularis,  374 
Sterno-clavicular  joint,  surgical  anatomy  of, 
1363 

ligaments,  248 
Sterno-clavicularis,  374 
Sterno-cleido-mastoid  artery,  542 
Sterno-cleido-mastoideus,  347,  349 
Sterno-costal  articulations,  245 
ligaments,  245 

surface  of  heart,  510 
Sterno-oosto-clavicular  articulation,  248 
ligaments  of,  248 
movements  of,  250 
Sterno-hj'oideus,  3i51 

Sterno-mastoid  branch  of  superior  thyreoid 
artery,  538 

as  a  landmark,  1355 

vein,  660 
Sterno-pericardial  ligaments,  522 
Sterno-thyreoideus,  351 
Sterno-xiphoid  plane,  1370 
Sternum,  132 

abnormaUties  of,  138 

angle  of,  133,  139 

body  of,  133 

development  of,  135 
StUling's  nucleus,  776 
Stomach,  1151 

blood-vessels  of,  1151 

clinical  anatomy  of,  1373 

comparative,  1160 

development  of,  1157 

lymphatics  of,  734,  1156 

nerves  of,  1156 

peristalsis  of,  1159 

position  and  relations,  1153 


INDEX 


1529 


Stro/ight  (collecting),  renal  tubule,  1167 

sinus,  450 
Stratum  album  medium,  842 
profundum,  842 
cinereum,  842 
corneum,  1286 
unguis,  1295 
germinativum  (Malpighii),  1286,  1295 
granulosum,  1286 
lemnisci,  825,  839,  842 
lucidum,  1286 

opticum  (stratum  album  medium),  842 
zonale,  839,  842,  845,  881 
Streeter,  nucleus  incertus  of,  815 
Strias  acustica(ae),  814 

(linete)  albicantes,  1283,  1304 

intermediate  olfactory,  865 

Lancisii,  851,  871 

lateral  longitudinal,  of  corpus  callosum,  851 

longitudinal,  of  corpus  callosum,  851,  892 

of  hippocampus  871 
medial  longitudinal,  of  corpus  callosum,  851 
medullares  acustici,  824 

(pineales)  of  thalami,  846,  872 
olfactory,  865,  866 

terminalis   thalami    (ttenia   semicircularis), 
845,  892 

of  thalamus,  873,  881,  892 
transverse,  of  corpus  callosum,  852 
Striate  arteries,  external,  906 

internal,  906 
Stripes  of  Baillarger,  879 

Structure  of  organs  (see  corresponding  organ) 
Stylo-glossus,  346- 

Stylo-hyal  portion  of  styloid  process,  75,  119 
Stylo-hyoid  ligaments,  99 
Stylo-hyoideus,  343,  344 
Styloid  bone,  168 
process,  70,  73,  75,  77,  108 
of  fibula,  190 
of  radius,  155 

of  third  metacarpal  bone,  166 
of  ulna,  158 
Stvlo-mandibular  (stylo-maxillary)  ligament, 

217 
Stylo-mastoid  branch  of  posterior  auricular 
artery,  544 
foramen,  73,  108,  126 
vein,  646 
Stylo-pharyngeus,  1137 
Subanconeus,  378 
Sub-arachnoid  cavity  or  space,  771,  919 

cisternas,  918 
Subcallosal  gyrus  (peduncle  of  corpus  callo- 
sum), 866 
sulcus,  866 
Subclavian  artery,  556 

collateral  circulation,  1360 
left,  556 

relations,  556,  558,  1369 
right,  557 
variations,  638 
group  of  axillary  lymphatic  nodes,  719 
sulcus,  of  lung,  1229 
vein,  671 
Subclavius,  373 
Subcostal  artery,  588 
Subcostales,  423,  434 
Subcrureus,  470 

Subcutaneous  dorsal  veins  of  penis,  684 
inguinal    (external   abdominal)    ring,    429, 

1371,  1394 
muscles,  313 
of  hand,  404 
Subdural  cavity,  912,  917 
space  of  spinal  cord,  771 
Subfascial  bursse  mucosae,  318 


Subiculum  of  the  promontory,  1089 
Sublingual  artery,  540 

caruncle,  1116,  1117 

fold,  1116 

gland,  1116 
ducts  of,  1117 
vessels  and  nerves,  1117 

lymphatic  nodes,  746 

nerve,  941 

vein,  660 
Submammary  (retromammary)  bursa;,  1303 
Submarginal  gyrus,  858 
Submaxillary  ganglion,  963 
roots,  963,  1036 

gland,  1115,  1350 

duct  of  (Wharton's)    1116 
vessels  and  nerves,  1116 

lymph-nodes,  709 

portion  of  external  cervical  fascia,  347 

(digastric)  triangle,  1357 
Submental  artery,  541 

set  of  facial  lymph-nodes,  711 

vein,  644 
Submuscular  bursa;  mucosae,  318 
Subnasal  point,  109,  112 
Suboccipital  muscles,  412,  419 

nerve,  971 
Subparietal  sulcus  (postlimbic  fissure),  863 
Subphrenic  area  of  peritoneum,  1372 
Subsartorial  plexus,  1003 
Subscapular  angle,  145 

artery,  571 

branches  of  posterior  scapular  artery,  566 
of  transverse  scapular  arterj',  565 

fossa,  141 

group  of  axillary  lymphatic  nodes,  720 

nerves,  984 

vein,  671 
Subscapularis,  369 

minor,  369 
Substance,  anterior  perforated,  847,  866 

central  grey,  of  mesencephalon,  836 
of  medulla,  818 

gelatinous,  central,  of  spinal  cord,  776 
of  Rolando,  776 

grey,  of  pons,  831 

of  nervous  system,  768 
of  spinal  cord,  775 
of  telencephalon,  879 

posterior  perforated,  835,  844 

white,  nervous  system,  768 
of  spinal  cord,  775,  777 
of  telencephalon,  885 
Substantia  alba,  768 

corticalis,  1293 

grisea,  768,  818 

medullaris,  1293 

nigra,  836,  840 

reticularis  alba  (Ai'noldi),  868 
Subtendinous  bursa;  mucosse,  318 
Subtrapezial  plexus,  979 
Sudoriferous  glands  (sweat-glands),  1296 

pore,  1297 
Sulco-marginal  fasciculus,  788 
Sulcus(i),  29 

ampullary,  1095 

antero-inferior,  807 

antero-intermediate,  774 

antero-lateral,  773 

auricular,  1082 

basilar,  of  pons,  804 

breves,  857 

central  (fissure  of  Rolando),  859,  1340 

of  cerebellum,  805 

of  cerebrum,  852 

cinguli  (calloso-marginal  fissure),  857,  858, 
869 


1530 


INDEX 


Sulcus(i),  circular,  857 
coronarius,  510 
of  corpus  callosum,  867 
of  crus  of  helix,  1084 
cunei,  864 
diagonal,  858 
fimbrio-dentate,  868 
of  floor  of  fourth  ventricle,  813 
fronto-marginal,  858 
of  heart,  510,  511 
hypothalamic,  847 
inferior  frontal,  858 
postcentral,  861,  862 
temporal,  855 
infra-orbital,  1284 
interparietal  (intraparietal),  861 
lateral  occipital,  863 
matricis  unguis,  1294 
median  subcallosal,  866 
mento-labial,  1284 
middle  frontal,  858 

temporal,  855 
of  Monro,  847 
oculomotor,  835 
olfactory,  858 
orbital,  858 
parallel,  855 
para-medial,  858 
parolfactory,  865 
pontine,  804 

postcentral  of  cerebellum,  806,  861,  862 
posterior  median,  772 
postero-inferior,  807 
postero-intermediate,  773 
postero-lateral,  773 
post-nodular,  808 
pre-auricularis,  177 
precentral,  807,  857 
rostral,  858 
sagittal,  60 
scleral,  1054 
of  skin,  1284 
of  spinal  cord,  772 
subclavian,  of  lung,  1229 
subparietal,  863 
superior  frontal,  858 
postcentral,  861,  862 
temporal  855 
supra-orbital,  1284 
of  telencephalon,  853 
terminalis  of  tongue,  1106 
of  heart,  511 
transverse  occipital,  862,  863 

temporal,  855 
transversus,  69,  108 
of  anthelix,  1083 
tympanicus,  75 
Supercilia,  1290 
Superciliary  arch,  59,  108 
Supination,  321 
Supinator  (brevis),  392 

radii  longus,  388 
Supracallosal  gyrus,  868 
Supra-clavicular  branches  of  cervical  plexus, 
978 
nerves,  978 

portion    of    brachial  plexus,   branches    of, 
982 
Supra-condylar  lines,  181 
process,  149 
ridge,  lateral,  149 
medial,  149 
Supracostales,  anterior,  433 

posterior,  432 
Supraglenoid  tubercle  of  scapula,  144 
Supra-hyoid  musculature,  325,  344 
Supramammillary  commissure,  871,  890 


Supra-mandibular    branch    of    cervico-facial 

nerve,  946 
Supramarginal  gyrus,  863 
Supra-maxillary    set    of  facial  lymph-nodes, 

711 
Supra-meatal  fossa,  72 
spine,  72 

triangle,  Macewen's,  1337 
Supra-occipital,  119 

Supra-omental  region  of  peritoneum,  1372 
Supra-orbital  artery,  552,  1343 
branches,  553 
border,  60 
nerve,  935 
notch,  60 
sulcus,  1284 
vein,  644 
Suprapineal  recess,  847 
Suprarenal  artery,  inferior,  598 
middle,  598" 
superior,  592 
glands,  1323,  1381 

accessory  (of  Marchand),  1326 
development,  1326 
lymphatics,  701,  738 
vessels  and  nerves  of,  1326 
plexuses  of  nerves,  1044 
veins,  673 
Suprascapular    (transverse    cervical)    artery, 
564 
(coracoid  or  superior  transverse)  ligament, 

253 
nerve,  982 
Supraspinatus,  368 

Supraspinous  branches  of  posterior  scapular 
artery,  566 
of  transverse  scapular  artery,  565 
fossa,  141 
ligament,  230,  238 
Suprasternal  bones,  133 
Supratonsilar  fossa,  1132 
Supratragic  tubercle,  1082 
Supratrochlear  branch  of  frontal  nerve,  936 
foramen,  150 
lymphatic  node,  719 
Sural  branches  of  popliteal  artery,  622 

(ex-ternal  or  short  saphenous)  nerve,  1010, 
1013,  1467 
Surfaces  of  organs  (see  corresponding  organ). 
Surgical  anatomy  of  organs  (see  corresponding 

organ). 
Suspensorius  duodeni,  1164,  1376 
Suspensory  ligament  of  Cooper,  1303 
of  the  eyeball,  1072,  1348 
of  lens  of  eye,  1057,  1064 
(apical    dental)    of    occipito-epistrophic 

articulation,  223 
of  ovary,  1269 
of  penis,  427,  1260 
of  Treitz,  1164,  1376 
Sustentaculum  hepatis,  1174 
lienis,  1174 
tali,  195 
Suture(s),  212 

of  anterior  cranial  fossa,  113 
coronal,  57,  101,  1339 
frontal,  59 
incisive,  106 
lambdoid,  57,  101,  1339 
meso-palatine,  89,  106 
metopic,  59,  101 
neuro-central,  45 
of  norma  facialis,  108 
occipital,  101 
occipito-mastoid,  101 
parieto-mastoid,  101 
petro-squamous,  71 


INDEX 


1531 


Suture(s),  sagittal,  57,  101,  1339 
squamoso-parietal,  1339 
transverse,  108 
palatine,  106 
of  vertex  of  skull,  101 
Swallowing,  muscles  of,  325 

process  of,  1137 
Sweat-glands,  1296 
Swellings,  genital,  1279 
Sylvian  fossa,  854 

point,  856 
Sylvius,  aqueduct  of,  834 

fissure  of,  850,  855,  134,0 
Syme's  amputation,  1465 
Sympathetic  fibres,  970,  1029 
nerves  of  orbit,  1076,  1348 
relations  of  spinal  cord,  789 
system,  959,  1026 
construction  of,  1030 
ganglia  of,  959 
origin  of,  1029 

prevertebral  plexuses  of,  1029 
trunks,  1032,  1033 
Symphysis  of  mandible,  95 
pubis,  238 

ligaments  of,  238 
Synapses,  762,  765 
Synarthroses,  212 
Synchondroses,  212 

sternal,  133 
Syncytium,  759 
Syndesmoses  (synarthroses),  212 

tympano-stapedial,  1090 
Synergists,  322 
Synovial  bursse,  313,  318 

membrane,    211    (see    also    corresponding 

articulations) 
sheaths  (vaginae  mucosae  tendinum),  378 
tendon-sheaths,  317 

of  forearm  muscles,  395,  403 
of  leg  muscles,  483,  484,  491 
System,  association,  of  hemisphere,  890 
blood-vascular,  507 
chromaffin,  1333 
digestive,  1099 
of  fibres,  commissural,  890 
lymphatic,  697 
nervous,  751 

central,  751,  770 
peripheral,  754,  924 
sympathetic,  1026 
neurone,  777,  895 
respiratory,  1199 
urogenital,  1241 
Systemic  arteries,  529 
circulation,  507 
veins,  640 


Tabatifere  anatomique  (of  Cloquet),  1433 
Table  showing  relations  of  cervical  and  thora- 
cic nerves  to  branches  of  brachial 
plex-us,  993 
of  lumbar  and  sacral  nerves  to  branches 
of  lumbar  and  sacral  plexuses  and  to 
pudic  nerve,  1016 
of  muscles  of  lower  extremity  to  nerves 
of  lumbar  and  sacral  plexuses,  1016 
of  muscles  of  upper  extremity  to  cervi- 
cal nerves,  993 
of  vertebral  levels,  1409 
of  distribution  of  spinal  nerves    (Cow- 
ers'), 969 
Tactile  corpuscles  (Meissner),  1290 
Tsenia  chorioidea,  844 
fimbria,  868,  877 


Taenia  fornicis,  868 
pontis,  855 

semicircularis,  845,  873 
thalami,  846,  872 
Tail  of  caudate  nucleus,  877 
of  epididymis,  1256 
of  muscle,  314 
of  pancreas,  1194 
Talipes,  1467 
Talo-calcaneal  union,  301 
Talo-fibular  ligament,  anterior,  299 

posterior,  299 
Talo-navicular  articulation,  305 

ligament,  306 
Talus  or  astragalus,  191,  192 
Tan,  1283 

Tangential  layer  of  fibres  of  cortex,  879 
Tapetum  of  posterior  cornu  of  lateral  ventricle, 

876 
Tarsal  arch,  inferior,  554 
superior,  554 
arteries,  medial,  632 
bones,  191 

clinical  anatomy  of,  1467 
branches  of  dorsalis  pedis  artery,  632 
elements,  accessory,  199 
(Meibomian)  glands,  1054,  1298 
joints,  301 

transverse,  305 
muscles,  1072,  1078 
Tarso-metatarsal  articulation,  308 
Tarsus,  191 

anterior  articulations  of,  303 
of  eyelids,  1053,  1077 
Taste,  organ  of,  1051 
Taste-buds,  1051 
Taste-pores,  1051 
Tectorial  membrane,  223 
Teeth,  1117 
canine,  1120 
deciduous  or  milk,  1126 
incisor,  1119 
molars,  1121 

premolar  or  bicuspid,  1121 
times  of  eruption,  1127 
variations  and  comparative,  1127 
vessels  and  nerves,  1124 
Tegmen  tympani,  77 
Tegmento-mammUlary  fasciculus,  871 
Tegmentum  of  pons,  830 
Tela  chorioidea,  758 
of  fourth  ventricle,  922 
subcutanea  (superficial  fascia),  313,  1287 
of  the  abdomen,  425 
of  the  arm,  377 
of  the  back,  413 
of  the  forearm  and  hand,  384 
of  the  foot,  491 
of  gluteal  region,  457 
of  head  and  neck,  347 
of  leg,  477 

of  pectoral  region,  371 
of  the  perineum,  445 
of  shoulder,  365 
of  thigh,  466 

of  thoracic-abdominal  musculature,  425 
Telencephalon,  758,  847 
gyri,  fissures  and  sulci,  852 
lobes,  853 

central  (insula),  856 
frontal,  857 
occipital,  863 
parietal,  860 
rhinencephalon,  864 
temporal,  854 
projection  fibres  of,  886 
Telodendria  of  axones,  762 


1532 


INDEX 


Temporal  artery,  anterior  deep,  54S 
middle,  545 
posterior  deep,  548 
superficial,  545,  1343 
bone,  68 

at  birth,  122 

mastoid  portion  of,  68,  71 
petrous  portion  of,  68,  72 
squamous  portion  of,  68,  70 
tympanic  portion  of,  69,  70,  75 
branches,  superficial,  of  auriculo-temporal 
nerve,  942 
of  maxillary  nerve,  938 
of  temporo-facial  nerve,  945 
fascia,  339 
fossa,  101 
gyrus,  inferior,  855 
middle,  855 
superior,  854 
lines  (ridges),  57,  60,  71,  1332 
lobe  of  cerebrum,  854 

operoula  of,  854 
nerves,  deep,  943 
notch,  868 
pole,  850 

pontile  path  (Ttirk's  path),  832,  840,  890 
process  of  malar  bone,  95 
sulcus,  middle,  855 

superior,  855 
vein,  deep,  646 
diploic,  648 
middle,  646 
superficial,  646 
wings  of  sphenoid,  65 
Temporalis  muscle,  338,  341 

superficialis,  337 
Temporo-facial  nerve,  945 
Temporo-malar   branch   of   maxillary  nerve, 

938  . 

Tempo ro-maxillary  (posterior  facial)  vein,  644 
Tendino-trochanteric  band,  280 
Tendo  Achillis,  485    ■ 
Tendon(s),  314,  317 
at  the  ankle,  1460 
conjoined,  435 
of  the  conus,  518 
popliteal,11451 
of  the  quadriceps,  471 
Tendon-sheaths,  317 

of  forearm  muscles,  395,  403 
of  leg  muscles,  483,  484,  491 
Tenon's  capsule,  1073,  1348 

space,  715 
Tensor   capsularis   articulationis   metacarpo- 
phalangei  digiti  quinti,  406 
of  the  capsule  of  the  ankle-joint,  491 
fasciae  dorsalis  pedis,  482 
latffi,  457,  459  ,1436 
suralis,  476 
laminas    posterioris    vaginas    musculi    recti 
abdominis,  436 
posterioris  vaginae  musculi  recti  et  fasciae 
transversalis  abdominis,  436 
ligamenti  annularis  anterior,  393 

posterior,  393 
tarsi,  (Horner's  muscle),  336 
tympani,  1089,  1091 
vaginae  femoris   (tensor  fasciae  latae),  457, 

459,  1436 
veli  palatini,  1137 
Tentorial    (recurrent   meningeal)    branch    of 
ophthalmic  nerve,  935 
notch,  915 
Tentorium  cerebelli,  914 
Tenuissimus,  475 
Teres  major,  369 
minor,  369 


Terminal  branches  (see  corresponding  artery 
or  nerve) 
incisure  (auricle),  1084 
nerve,  929 

stria,  of  thalamus,  873 
sulcus,  1106 

vein  (of  corpus  striatum),  657 
ventricle  of  spinal  cord,  775 
Testes,  1255,  1386 
descent  of,  1257,  1387 
lymphatics  of,  700,  744,  1256,  1387 
Testicular  arteries,  601 
Tetrahedral-shaped  spleen,  1310 
Thalamencephalon,  844 
Thalami,  758,  844 
Thalamo-olivary  tract,  817,  830 
Thalamo-spinal  tract,  786 
Thalamus,  881 
anterior  tubercle  (nucleus)  of,  845,  882 
cortical  connections  of,  883 
medullary  lamina  of,  882 
nuclei  of,  871,  882,  883 
peduncles  of,  880,  883 
pulvinar  of,  882 
stratum  zonale,  881 
stria  terminahs  of,  845,  881,  892 
stria;  meduUares,  872 
Thebesius  foramina  of,  514 

valvula  of,  512 
Theoa  folhouli,  1292 
Thenar  fascia,  387 
Thigh,  bony  landmarks  of,  1434 
fasciae  of,  466 
muscles,  453,  464 
acting  on,  505 
muscular  prominences  of,  1436 
Third  occipital  condyle,  56 
part  of  axillary  artery,  570 
of  subclavian  artery,  558 
ventricle  of  brain,  846 
chorioid  plexuses  of,  924 
Thoracic  aorta,  586,  1369 
aortic  plexus,  1038 
aperture,  superior,  138 
artery,  dorsal,  (thoraco-dorsal) ,  572 
lateral,  571 
superior,  570 
cavity,  1235 
duct,  726 
ganglia,  1038 
intercostal  nerves,  995 
muscles,  lymphatics,  923 
nerves,  971,  994 

lateral  anterior,  983 
medial  anterior,  983 
long,  982 
posterior,  982 
portion  of  left  subclavian  artery,  556 
of  sympathetic  system,  1037 
of  thymus,  1321 
vein,  lateral,  671 
vertebrae,  description  of,  30,  36 
peculiar,  36 
Thoracic-abdominal  musculature,  422 
fasciae  of,  425 
muscles  of,  430 
nerves,  995 
Thoraco-acromial     (acromio-thoracic     axis), 
artery,  571 
vein,  671 
Thoraco-dorsal  (middle  or  long)  subscapular 

nerve,  984 
Thoraco-epigastric  vein,  671,  1372 
Thorax,  126 

articulations  at  front  of,  244 
bony  landmarks,  1363 
clinical  anatomy  of,  1363 


INDEX 


1533 


Thorax,  deep  veins  of,  665 
lymphatics  of,  723,  724,  725 
movements  of,  247 
as  a  whole,  138 
Thumb,  muscles  of,  406 

acting  on,  504 
Thymic  arteries,  567 

veins,  661 
Thymus,  1319 

corpuscles  of,  1321 
cortex  of,  1321 
development  of,  1322 
lymphatics  of,  729,  1322 
medulla  of,  1321 
vessels  (and  nerves)  of,  1322 
Thyreo-arytsenoideus  externus,  1219 
internus  (m.  vocalis),  1220 
obhquus,  1220 
superior,  1220 
Thyreocervical  trunk  (thyreoid  axis),  564 
Thyreo-epiglottic  ligament,  1215 

muscle,  1220 
Thyreo-glossal  duct,  1318 
Thyreo-hyal  centre,  100 

segment,  119 
Thyreo-hyoideus,  351 
Thyreoid  artery,  inferior,  564 
superior,  538,  638 
bars,  119 
cartilage,  1210 
gland,  1312 
accessory,  1315 
clinical  anatomy  of,  1355 
development  of ,  1318 
lymphatics  of,  699,  719,  1317 
laminae,  1210 
hgament,  1314 
vessels,  1316 
notch,  inferior,  1211 

superior,  1210 
plexus  of  nerves,  inferior,  1036 

superior,  1Q36 
tubercle,  inferior,  1211 

superior,  1211 
veins,  660,  661,  1317 
Thyreoidea  ima  artery,  533 

vein,  661 
Tibia,  185,  1454 
condyles  of  femur  and,  1447 
epiphyses  of,  1435 
structures  on  head  of,  1449 
tuberosity  of,  and  ligamentum  patellaj,  1448 
Tibial  artery,  anterior,  629,  640,  1458 
posterior,  624,  640,  1458 
collateral  ligament,  286 
communicating  nerve,  1010 
nerve  (internal  popliteal),  1009 
paralysis  of,  1469 
anterior,  1015 
posterior,  1009 
nutrient  artery,  626,  1459 
recurrent  artery,  anterior,  632 

posterior,  632 
veins,  anterior,  688 
posterior,  688 
Tibialis  anterior,  453,  480,  1468 
tenotomy,  1464 
posterior,  454,  486,  490,  1468 
secundus  (tensor  of  capsule  of  ankle-joint), 
491 
Tibio-astragalus  anticus,  482 
Tibio-fibular  ligaments,  295 

union,  295 
Tigroid  masses,  766 
Tissues,  4 

Toes,  muscles  acting  on,  506 
Tomes'  fibrils  and  sheath,  1118 


Tongue,  1106 

development  of,  1112 

glands  of,  1108 

lymphatics  of,  715 

muscles  of,  325,  345,  346,  502,  1110 

papillaj,  1106 

surgical  anatomy  of,  1350 

variations  and  comparative,  1112 

vessels  and  nerves,  1111 
Tonsil  (amygdala)  of  cerebellum,  807 
Tonsillar  branch  of  external  maxillary  artery, 
541 
of  ascending  palatine,  541 
of  glosso-pharyngeal  nerve,  952 

fossEe,  1131,  1132 

ring  (Waldeyer's),  1133 
TonsUs,  lingual,  1107 

lymphatics  of,  1132 

palatine,  1132,  1351 

pharyngeal,  1130,  1354 

variations  and  comparative,  1138 

vessels  of,  1132 
Topography  of  attachment  of  spinal  nerves, 
966 

of  brain,  general,  793,  1338 

of  organs  (see  corresponding  organ) 
Torcular  Herophili,  650 
Torus  tubarius,  1130 
Trabecute  (carnese)  cordis,  516 

lienis,  1311 
Trabecular  region  of  skull,  117 
Trachea,  1225,  1408 

lymphatics  of,  699,  1228 

vessels  and  nerves,  of  1228 
Tracheal  branches  of  inferior  thyreoid  artery, 
564 

cartilages,  1227 

glands,  1227 

veins,  661 
Trachelo-mastoid,  416 
Tract,  anterior  or  direct  pyramidal,  788 

crossed  pyramidal,  7S3 

direct  cerebellar  (Flechsig),  784 

Gower's,  784 

habenulo-peduncular,  873 

Loewenthal's,  786 

mesencephalo-(tecto-)  spinal,  786,  842 

olfacto-mammillary,  873 

olfacto-mesencephalic,  873 

olfactory,  758,  865,  893 

optic,  849 

solitary,  820 

spinal,  nucleus  of,  826 
of  trigeminus  nerve,  828 

spino-mesencephalic      (spino-teotal),      786, 
842 

spino-thalamic,  786 

thalamo-olivary,  817,  830 

thalamo-spinal,  786 

transverse  peduncular,  835 

ventral  vestibulo-spinal,  786 
Tractus  ilio-pubicus,  430 

ilio-tibialis,  457,  458 

spino-teotalis,  786 
Tragi,  1290 
Tragus,  1082 

Trans-pyloric  line  (Addison),  1153,  1370 
Transyersalis  cervicis,  416 

fascia,  426 
Transverse  arch  of  foot,  1468 

carpal   (anterior  annular)  ligaments,   1427 

cervical  (transversa  coUi)  artery,  565,  638 
veins,  672 

colon,  1174 

crest,  72 

crural  ligament  of  leg  (upper  part  of  anterior 
annular  ligament),  479 


1534 


INDEX 


Transverse  diameter  of  pelvic  inlet,  175 
facial  artery,  545 

vein,  646 
fissure  of  cerebrum,  850 
(Houston's)  folds  of  rectum,  1177,  1390 
fornix,  869,  890 
humeral  ligament,  256 
ligament  of  central  atlanto-epistrophic,  222 
of  heads  of  metatarsal  bones,  309 
hip-joint,  280 

inferior  (spino-glenoid),  253 
of  knee-joint,  289 
of  pubis,  446 

superior  (coracoid,  or  suprascapular),  253 
nasal  branch  of  dorsal  nasal  artery,  554 
palatine  suture,  106 
processes  of  atlas,  33 
of  vertebrte,  31 

ligaments  connecting,  231 
scapular  (suprascapular)  artery,  664,  638 

veins,  648 
(lateral)  sinus,  651,  1331 

of  pericardium,  523,  527 
strise  of  corpus  callosum,  851 
sulci,  108 
suture,  108 
Transverso-spinal  muscles,  412,  419 
Transversus  abdominis,  424,  435 

group  of  lateral  division  of  thoraco-abdomi- 

nal  muscles,  434 
menti,  333 

nuchae  (occipitalis  minor),  337 
•perinei  profundus,  442,  449 

superficialis,  444,  452 
thoracis  (triangularis  sterni),  424,  434 
vaginae  (Fvihrer),  449 
Trapezium,  159,  162 
Trapezius,  347,  349 

clinical  anatomy,  1405 
Trapezoid  bone,  159,  162 
ligament,  251 
(obhque)  line,  140 
Treitz,  suspensory  ligament  of,  1164,  1376 
Triangle,  Bryant's,  1436 
Hesselbach's,  1398 
inferior  carotid  (tracheal),  1358 
Macewen's  suprameatal,  1337 
of  neck,  posterior,  1359 
of  Petit,  434,  1406 
rectal,  440,  1383 
Scarpa's  467,  1438 
submaxillary  (digastric),  1357 
superior  carotid,  1358 
urogenital,  440,  1383,  1385 
Triangles,  cervical,  1357 

of  perineum,  1383 
Triangular  fascia,  430 
fibro-cartilage,  264 
fossa  of  auricle,  1082 
fovea  of  aryta^noid,  1212 
ligament,  urogenital  diaphragm,  442,  1384 
(lateral)  ligaments  of  liver,  1185 
Triangularis  (depressor  anguli  oris),  333 

sterni,  424,  434 
Tributaries  of  veins  (see  corresponding  vein) 
Triceps  brachii,  374,  377,  378 
surface  markings,  1416 
surse,  484 
Tricuspid  valve,  515,  516 
Trigeminal  foramen,  125 

impression,  73 
Trigeminus  nerve,  934 
nuclei  of,  826 
spinal  tract  of,  828 
Trigona  fibrosa,  518 

Trigone,  collateral,  of  lateral  ventricle,  876 
femoral,  Scarpa's  triangle,  467,  1438 


Trigone  of  lemniscus,  832,  835 

of  Lieutaud,  1252 

olfactory,  865 

urogenital,  442,  446,  1384 

vesical  (of  Lieutaud),  1252 
Trigonum  lumbale  (triangle  of  Petit),  434 
Triquetral  (cuneiform),  bone,  159,  161 
Trochanter,  great,  178 

third,  181 
Trochanteric  of  digital  fossa,  178 
Trochanters  of  femur,  178 

clinical  anatoiny  of,  1435 
Trochlea,  318,  1068 

of  humerus,  150 

of  talus,  193 
Trochlear  branches  of  supra-orbital  artery, 
553 

fossa,  61 

nerve,  835,  837,  933 

process,  195 
Troltsch,  pouches  of,  1089 
True    ligaments    of    bladder    and    prostate, 

1252 

synchondroses,  212 
Trunk,  articulations  of,  224 

costo-cervical  arterial,  568 

cutaneous  areas  of,  1020 

lumbo-sacral,  1005 

lymphatic,  intestinal,  731 
lumbar,  730 

sympathetic,  gangliated,  1029,  1032 

thyreocervical,  564 
Tuba  auditiva   (Eustachian  tube)   74,   1089, 

1092,  1354 
Tubae  uteriuEe  (Fallopian  tubes),  1269 
lymphatics  of,  700,  745,  1270 
vessels  and  nerves,  1270 
Tubal  branch  of  ovarian  artery,  602 

branches  of  uterine  artery,  610 
Tube,  auditory,  (Eustachian),  74,  1089,  1092, 
1354 

neural,  754 
Tuber  caloanei,  196 

einereum,  847,  848 

omentale,  1184 

vermis,  808 
Tubercle(s),  29 

adductor,  of  femur,  181 

amygdaloid,  of  lateral  ventricle,  877 

anterior  of  thalamus,  845,  882 

articular,  of  temporal  bone,  71 
of  atlas,  32 

auricular  (tubercle  of  Darwin),  1083 

of  calcaneus,  anterior,  195 

condylar,  of  mandible,  97 

coracoid  (conoid)  of  clavicle,  140 

cornioulate,  of  larynx,  1221 

cuneiform,  of  larynx,  1221 

of  epiglottis,  1212,  1222 

of  femur,  cervical,  178 

genial,  95 

genital,  1279 

inferior  thyreoid,  1211 

intervenosum  (of  Lower),  513 

labial,  1102 

lacrimal,  88 

malar,  95 

mental,  95 

olfactory,  865 

pharyngeal,  54,  108 

preglenoid,  71 

pterygoid,  66 

(spine)  of  pubis,  172 

for  the  quadratus,  178 

of  rib,  127 

scalene,  129 

of  scapula,  infraglenoid,  143 


INDEX 


1535 


Tubercles,  of  scapula,  supraglenoid,  144 
superior  thyreoid,  1211 
supratragic,  1082 
of  thoracic  vertebrse,  37 
Tubercular    (posterior  costo-transverse)  liga- 
ment, 243 
Tuberculum  aeustioum,  815 
cuneatum,  801 

intervenosum  (of  Lower),  513 
jugulare,  54 
sella;,  63,  116 
Tuberosity,  29 
of  calcaneus,  196 
of  clavicle,  costal,  140 
of  cuboid,  199 
of  femur,  gluteal,  178 
of  fifth  metatarsal  bone,  203 
of  first  metatarsal  bone,  201 
of  humerus,  greater,  147 

lesser,  147 
of  ilium,  171 
of  ischium,  172 
malar,  93 

of  maxilla,  87,  92,  106 
of  navicular  (scaphoid),  161,  196 
of  radius,  152 
of  tibia,  185 
of  ulna,  156 

ungual  (of  third  phalanx),  168 
Tubes,  Fallopian,  1269 
Tubules,  renal,  1246 
seminiferous,  1256 
Tubuli  recti,  1256 
Tunica  albuguiea  of  testis,  1256 
of  penis,  1260 
of  spleen,  1311 
propria  of  corium,  1286 
serosa  of  spleen,  1310 

vaginalis  communis  (internal  spermatic  or 
infundibuliform  fascia),  1254,  1259 
propria,  1254 
vasculosa  (of  testis),  1256 
Turbinate  bones  (conchse)  83,  84,  1205 

sphenoidal,  64,  67 
Turk's  bundle,  832,  890 
Tympanic  antrum,  72,  73,  78,  1092,  1336 
artery,  anterior,  547 
inferior,  537 
superior,  548 
bone,  at  birth,  123 
branch  of  petrosal  ganglion,  951 

of  stylo-mastoid  artery,  544 
canaheulus,  73,  108 
cavity,  77,  1088 

vessels  and  nerves,  1091 
walls  of,  1088 
membrane,  1086 

secondary,  1089,  1096 
mucous  membrane,  1089 
nerve,  961 
notch,  77 

ostium  of  tuba  auditiva,  1092 
plate,  108 

plexus,  951,  961,  1033,  1089 
portion  of  temporal  bone,  69,  75 
sinus,  1089 
sulcus,  75 
veins,  696 
Tympano-hyal  portion  of  styloid  process,  75, 

119 
Tympano-mastoid  (auricular)  fissure,  71,  75, 
Tympano-petrosal  branch  of  tympanic  plexus, 

961 
Tympano-stapedial  syndosmosis,  1090 
Tympanum,  77 
bones  of,  79 
development  of,  80 


U 


IHna,  155 

clinical  anatomy  of,  1419,  1422 
Ulnar  anastomotic  branch  of  superficial  radial 
nerve,  987 

arterj^  576,  640,  1423 
vena3  comitantes,  671 

collateral  artery,  inferior,  576 
superior,  576 
nerve,  985 

collateral  ligament,  259,  266 

nerve,  987 

line  of,  1415,  1423 
results  of  paralysis,  1424 

notch  (sigmoid  cavity)  of  radius,  154 

recurrent  artery,  volar,  577 
Ulno-carpeus,  492 
Ultimobranchial  bodies,  1318 
Umbilical  artery,  609 

fissure  of  liver,  1183 

fovea,  1284 

hernia,  1402 

hgaments,  1250,  1252 

lymphatic  nodes,  733 

notch,  1182 

plane,  1370 

recess,  675 

region,  1143 

vein,  675,  680 
Umbilicus,  clinical  anatomy  of,  1371 
Umbo  of  tympanic  membrane,  1087 
Unciform  bone,  159 

process,  163 
Uncinate  fasciculus,  891 

process  of  ethmoid,  83 
Unci-pisiformis,  403 
Uncus,  868 
Ungual  phalanges,  168 

process  of  third  phalanx,  168 
Ungues  (nails),  1293 
Union,  coraco-clavicular,  251 

cuboideo-navicular,  303 

of  heads  of  metacarpal  bones,  274 

of  metatarsal  bones,  309 

of  radius  with  ulna,  261 

scapulo-clavicular,  250 

talo-oalcaneal,  301 

tibio-fibular,  295 
Unipenniform  muscle,  315 
Urachal  branch  of  superior  vesical  artery,  609 
Urachus,  1250,  1252,  1253,  1398 
Ureter,  1248 

clinical  anatomy  of,  1381,  1394 

lymphatics  of,  738,  1249 

portions  of,  1248 

vessels  and  nerves  of,  1249 

variations  and  development  of,  1249 
Ureteral  branches  of  renal  arteries,  598 
of  internal  spermatic  artery,  601 
of  ovarian  arteries,  602 
Ureteric  branches  of  superior   vesical   artery, 

609 
Urethra,  female,  1277,  1278 

lymphatics  of,  742 

male,  1262,  1388 
lymphatics  of,  740 

surgical  anatomy  of,  1389 
Urethral  annulus,  1253 

artery,  613 

bulb,  artery  of,  613 

carina,  1276,  1278 

glands  (of  Littr6),  1264 

lacuna3  (of  Morgagni),  1264 

orifice  of  bladder,  1263 
Urinary  bladder,  1249 
development  of,  1253 


1536 


INDEX 


Urinary  bladder,  parts  of,  1250 
lymphatics  of,  700,  739,  1249 
vessels  and  nerves  of,  1253 
organs,  1241 
bladder,  1249 
kidneys,  1241 
ureters,  1249 
Urogenital  diaphragm,  440,  449 
sinus,  1279 
system,  1241 
triangle,  440,  1383,  1385 
trigone  (triangular  ligament),  442,  1384 
Uterine  artery,  610 

branch  of  ovarian  artery,  602 
veins,  683 
Utero-sacral  ligaments,  1274 
Utero-vaginal  plexus  of  nerves,  1047 

of  veins,  683 
Uterus  (womb),  1271 

clinical  anatomy  of,  1393 
lymphatics  of,  700,  745,  1274 
masculinus,  1263 
vessels  and  nerves  of,  1274 
Utricle,  1093 

Utricular  branch  of  vestibular  ganglion,  950 
Utriculo-ampullar  division  of  vestibular  nerve, 

950 
Utriculo-sacoular  duct,  1094 
Utriculus,  prostatic,  1263 
Uvula  of  palate,  1104,  1106,  1137 
of  urinary  bladder,  1252 
of  vermis,  808 


Vagina,  1274,  1277 

clinical  anatomy  of,  1392 
lymphatics  of,  745,  1276 
vessels  and  nerves  of,  1276 
Vagina  fibrosa  tendinis,  317 
musculi  flexoris  hallucis  longi,  491 
flexorum  digitorum  longi,  491 
tibialis  posterior,  491 
tendinis  musculi  extensoris   carpi  ulnaris, 
395 
digiti  quinti,  395 
hallucis  longi,  483 
pollicis  longi,  395 
flexoris  carpi  radialis,  403 

pollicis  longi,  403 
peronsei  longi  plantaris,  484 
tibialis  anterioris,  483 
tendinum   musculorum   abductoris   pollicis 
longi  et  extensoris  pollicis  brevis,  395 
extensoris  digitorum  communis  et  ex- 
tensoris indicis,  395 
longi,  483         .     '    .    . 
extensorum  carpi  radialium,  395 
flexorum  communium,  403 
peroneorum  communis,  484 
VaginEE  mucosa}  tendinum,  318 
tendinum  digitales,  491 

musculorum  flexorum  digitorum,  403 
Vaginal  artery,  610 
ligaments,  317 
of  finger,  387 
nerves,  1017 

of  sphenoid,  63,  66 

of  temporal  bone,  76 

Vagus  (pneumogastric),  954 

nucleus  of,  820,  822 
Valentine,  ganglion  of,  939 
Vallate    (circumvallate)    papillis    of    tongue, 

1106 
Vallecula  cerebelli,  807 
epiglottic,  1107,  1221 
Sylvii,  856 


Valsalva,  sinus  of,  518,  530 
Valve  (s),  anal,  1177,  1390 
of  aorta,  semilunar,  517 
atrio-ventricular,  515 
bicuspid  (mitral),  515 
of  fossa  navicularis,  612 
of  Heister,  1187 
(folds)  of  Houston,  1390 
ileo-caical  (colic),  1172 
mitral,  515 

pulmonary  semilunar,  517 
sinus  coronarii,  512 

(of  Thebesius),  612 
tricuspid,  515 
of  veins,  528 

venfe  cavaj  (Eustachian),  512 
Valvula  foraminis  ovalis,  512 
Variability,  25 
Variations  of  blood-vessels,  508 

arteries,  637,  639 

veins,  69 
of  organs  (see  corresponding  organ) 
Vas  aberrans,  640 

(ductus)  deferens,  1257 
Vasa  aberrantia  hepatis,  1184 
brevia,  696 
vasorum,  628 
Vascular  coat  of  eye,  1060 
Vaso-motor  nuclei,  822 
Vastus  intermedins  (crureus),  468,  470 
lateralis  (vastus  externus),  468,  470 
medialis  (vastus  internus),  468,  470 
Vater,  ampulla  of,  1188 

corpuscles  of,  1290 
Vein(s)  (see  also  "Vena"),  528 
of  abdominal  wall,  superficial,  683 
accessory  cephalic,  667 

hemiazygos  (azygos  tertia),  663 

popliteal,  689 

portal,  678 
•  saphenous,  684 
angular,  643 
anterior  auricular,  646 

bronchial,  666 

cardiac,  521 

external  spinal,  792 

facial,  643,  1343 

jugular,  648,  693 

mediastinal,  667 

parotid,  644 

tibial,  688 
articular  of  mandible,  646 
ascending  lumbar,  662,  663 
of  auricle  (of  ear),  1084 
axillary,  671 

azygos  (major),  662,  693 
basal,  657 
basilic,  667 
basivertebral,  666 
brachial  vense  comitantes,  671 
of  brain,  663 
bronchial,  1234 
buccal,  646 

cardiac  (coronary),  620 
central  (ganglionic),  666 

of  retina,  659 
cephalic,  667,  671 

accessory,  667 
cerebellar,  657,  908 
cerebral,  654 
chorioid,  657 
ciliary,  658 
circumflex,  671 

of  cochlear  canaliculus,  652,  658 
common  facial,  644,  646,  693 

iliac,  699 

volar  digital,  671 


INDEX 


1537 


Vein(s),  condyloid  emissary,  652 
conjunctival,  658 
coronary  (gastric),  675 
of  corpus  striatum,  657 
cortical  or  superficial  cerebral,  654 
costo-axillary,  671 
cutaneous,  1289 
cystic,  677 
deep  (ganglionic),  655 

cervical,  661 

circumflex  iliac,  683 

of  clitoris,  683 

temporal,  646 
of  the  diploe,  648 
dorsal  digital  (foot),  684 

of  clitoris;  683 

lingual,  660 

metacarpal,  667 

metatarsal,  684 

of  penis,  681 
duodenal,  677 
of  the  ear,  667 

emissary,  647,  649,  652,  916,  1334 
episcleral,  659 
ethmoidal,  659 
of  external  acoustic  (auditory)  meatus,  1086 

iliac,  683 

jugular,  646,  693 

nasal,  644 

pudendal,  684 
femoral,  690 

vena3  comitantes,  690 
femoro-popliteal,  685,  693 
frontal,  644 

diploic,  648 
great  cerebral  (of  Galen),  657,  923 

cardiac,  520 

(internal)  saphenous,  684,  693 
hajmorrhoidal  plexus  of,  683 
of  head  and  neck,  642,  693 
superficial,  643 
deep,  648 
of  heart,  520 
hemiazygos  (azygos  minor),  662 

accessory,  663 
hepatic,  675 

hypogastric  (internal  iliac),  679 
ileo-colic,  677 
ilio-lumbar,  680 
inferior  alveolar  (dental),  646 

cerebellar,  657 

cerebral,  655 

epigastric,  683 

gluteal  (sciatic),  680 

hemorrhoidal,  683 

labial,  644 

laryngeal,  659 

mesenteric,  678 

ophthalmic,  646,  659 

palpebral,  644 

phrenic,  675 

thyreoid,  661 
infra-orbital,  646 

innominate  (brachio-cephalic),  641,  691,  692 
intercapitular  (hand),  667 

of  foot,  684 
intercostal,  664 
internal  auditorj',  652,  657 

cerebral,  657 

jugular,  659,  691,  693 

mammary,  666 

maxillary,  646 

pudendal;  681 

spinal,  792 
intervertebral,  666 
Intestinal,  677 
labial  (of  mouth),  644 


Vein(s),  labial  (of  vulva),  683,  684 
lacrimal,  659 
lateral  circumflex,  690 

sacral,  680 

thoracic,  671 
left  colic,  678 

gastro-epiploio,  677 

superior  intercostal,  664 
lingual,  660 

of  lower  extremity,  683,  693 
lumbar,  675 

of  Marshall,  oblique,  521,  523 
masseteric,  644,  645 
mastoid  emissary,  647,  652 
medial  perforating,  690 
median  antibrachial,  667,  668 

basilic,  669 

cephalic,  668 

cubital,  667 

of  medulla,  908 
of  medulla  oblongata,  657,  908 
meningeal,  917 
middle  cardiac,  520 

cerebral,  655 

colic,  677 

hajmorrhoidal,  683 

meningeal,  646 

sacral,  679 

temporal,  646 
morphogenesis  and  variations,  690 
muscular  (of  orbit),  658 
of  nasal  cavities,  657 
naso-frontal,  658 
oblique  (of  Marshall),  of  left   atrium.  521, 

623 
obturator,  680 
occipital,  647 
oesophageal,  661,  662 
ophthalmic,  658,  659,  1075  . 
ophthalmo-meningeal,  655 
of  orbit,  658 
ovarian,  674 
palatine,  644 
palpebral,  658 
pancreatic,  677 
pancreatico-duodenal,  677 
parietal  emissary,  649 
parumbilioal,  678 
pericardiac,  666 
of  pharynx,  659 
plantar,  digital,  684 

metatarsal,  687 
of  pons,  657,  908 
popliteal,  688 
portal,  528,  675 

development  of,  694 
posterior  auricular,  647 

bronchial,  664 

external  jugular,  648 
spinal,  792 

facial  (temporo-maxillary ) ,  644 

labial,  683 

of  left  ventricle,  521 

mediastinal,  664 

parotid,  646 

superior  alveolar  (dental),  646 

tibial,  688 
profunda  or  deep  femoral,  690 
proper  volar  digital  (hand),  671 
pterygoid  plexiis  of,  646 
pulmonary,  529,  1235 
pyloric,  675 

radial  vena;  comitantes,  671 
radicular,  792,  908 
renal,  673,  693 
right  colic,  677 

gastro-epiploic,  677 


1538 


INDEX 


Vein(s),  right  colic,  superior  intercostal,  664 
sigmoid,  678 
scrotal,  684 
small  cardiac,  521 

(external)  saphenous,  684,  693 
smallest  cardiac,  521 
spermatic,  674,  1259 
spheno-palatine,  646 
spinal,  665 
splenic,  677,  1312 
sterno-mastoid,  660 
stylo-mastoid,  646 
subclavian,  671 

subcutaneous  dorsal  of  penis,  684 
sublingual,  660 
submental,  644 
subscapular,  671 
superficial,  in  abdominal  wall,  683 

circumflex  iliac,  684 

epigastric,  684 

of  lower  extremity,  683 

temporal,  646 

of  upper  extremity,  667 
superior  cerebellar,  657 

cerebral,  654 

epigastric,  666 

gluteal,  680 

hsemorrhoidal,  683 

labial,  644 

laryngeal,  659 

mesenteric,  677 

ophthalmic,  658 

palatine,  646 

palpebral,  644 

phrenic,  667 

thyreoid,  660 
supra-orbital,  644 
suprarenal,  673 
systemic,  640 
temporal  (of  diploe),  648 
temporo-maxillary  (posterior  facial),  644 
terminal  (of  corpus  striatum),  657 
thoraoo-acromial,  671 
thoraoo-epigastric,  671,  1372 
of  thorax,  662 
thymic,  661 
thyreoid,  660,  1317 
thyreoidea  ima,  661 
tracheal,  661 
transverse  cervical,  672 

facial,  646 

scapular  (suprascapular),  648 
tympanic,  646 

cavity,  1091 
ulnar  venae  comitantes,  671 
umbilical,  675,  680 
of  upper  extremity,  667 

development  of,  692 
uterine,  683 
vermian,  908 
vertebral,  661,  664 
Vesalian,  646 
volar  metacarpal,  671 
Velum,  anterior  (superior)  medullary,  812 
interpositum,  847,  923 
of  palate,  1104 
posterior  medullary,  808 
Vena  canaliculi  cochleae,  652,  658 
cava,  inferior,  672 

development  of,  693 

superior,  641 

development,  690 
centralis  retinae,  1065 
cerebri  magna  (Galeni),  657 
comitans  n.  hypoglossi,  660 
septi  pellucidi,  657 
Venae  cava?,  relation  to  thoracic  wall,  1369 


Venae  cavffi  comitantes,  528 

vorticosa;,  659,  1057,  1065 
Venous  arch,  digital  (hand),  667 

lacunae  of  dura,  916 

plexuses,  vertebral,  664 

sinus  of  sclera,  1059 

sinuses,  cranial,  528,  649,  916 
Ventricle(s)  of  Arantius,  813 

of  brain,  development  of,  758 

fifth,  872 

fourth,  812 

of  heart,  left,  516,  517 
right,  516 

of  larynx  (ventricle  of  Morgagni),  1222 

lateral,  of  cerebral  hemisphere,  873 
drainage  of,  1341 

olfactory,  866 

terminal,  of  spinal  cord,  775 

third,  of  brain,  846 

Verga's,  869 
Ventricular  appendix  (laryngeal  saccule),  1223 

folds  (false  vocal  cords),  1222 

ligament  of  larynx,  1215 

musculature,  518 

muscle  of  larynx,  1220 
Ventro-lateral  fasciculus,  superficial,  770 
Verga's  ventricle,  869 
Vermiform  process  (appendix),  1173,  1378 

fossa,  53,  117 
Vermis  of  cerebellum,  805 

furrowed  bands  of  uvula  of,  808 

inferior,  807,  808 

pyramid  of,  808 

superior,  806 

tubes,  808 

uvula  of,  808 
Vernix  caseosa,  1299 
Vertebra  prominens,  35 

structure  of,  45 
Vertebra(a3),  29 

articulations  of  bodies  of,  225 

cervical,  30,  31 

coccygeal,  30,  42 

lumbar,  30,  39 

ossification  of,  45 

thoracic  (dorsal),  30,  36 
Vertebral  artery,  559,  638 

articulations,  225 

branches  of  lumbar  arteries,  593 

canal  (spinal),  31 
arteries  of,  590 
venous  plexuses  of,  664 

column,  29 
as  a  whole,  43 

foramen,  31 

groove,  43 

levels,  1409 

ligaments,  228 

notches,  30 

plexus  of  nerves,  1037 

portion  of  vertebral  artery,  560 

spines,  1403 
Vertebro-occipital  muscle,  412,  417 
Vertex  of  urinary  bladder,  1250 
Vesalian  vein,  646 
Vesahus,  foramen  of,  66,  116 
Vesical  arteries,  inferior,  609 
middle,  609 
superior,  609 

branch  of  obturator  artery,  608 

nerves,  inferior,  1017,  1047 
superior,  1047 

plexus  of  nerves,  1047 
of  veins,  683 

portion  of  ureter,  1249 

vein,  661 
Vesicle(s),  brain,  755 


INDEX 


1539 


Vesicles,  optic,  758 

of  thyreoid  gland,  1316 
Vesicula;  seminales,  1257,  1387 

lymphatics,  744 
Vessels     (see     "Blood-vessels,"     "arteries," 

"veins,"  "lymphatic  vessels"). 
Vestibular  branch  of  stylo-mastoid  artery,  544 

csecum,  1096 

conduction  paths,  899 

fenestra,  73,  1089 

ganglion  (gangUon  of  Scarpa),  823,  950 

glands,  1278 

membrane  (membrane  of  Reissner),  1096 

nerve,  949 
nuclei  of,  823 

slit,  1222 
Vestibule  (of  temporal  bone),  80 

of  larynx,  1221 

of  nose,  1204 

oral,  1100 

of  vagina,  1277,  1392 
Vestibulo-spinal  fasciculus,  786 
VibrisssB,  1204,  1290 
Vicq  d'Azyr,  bundle  of,  871 
Vidian  artery,  549 

canal,  103,  107,  108,  126 

nerve  (n.  canalis  pterygoidei),  962 
Villi,  pleural,  1237 

of  small  intestine,  1166 
Vincula  tendinum,  399,  401 
Visceral  bars,  metamorphosis  of,  119 

lymphatic  nodes  of  thorax,  724 

vessels  of  abdomen,  and  pelvis,  733 
Visual  area  of  cerebral  cortex,  893 
Vitreous  body  or  humor  of  eye,  1052,  IO64 

lamina  of  chorioid,  1026 
Vocal  folds  (cords),  false,  1222 
true,  1223 

ligaments,  1215 

lip,  1223 

muscle,  1220 

process  of  arytenoid  cartilage,  1212 
Volar  arch,  deep,  586,  639,  1426 
venous,  671 
superficial,  682,  639,  1425 
venous,  671 

artery,  superficial,  584 

carpal  rete  (arch),  579,  581 

digital  veins,  671 

interosseous  artery  of  forearm,  577 

(anterior)  interosseous  nerve,  992 

ligament,  accessory  (or  glenoid),  274 

metacarpal  arteries,  586 
veins,  671 

musculature,  363 

perforating  branches  of  radial  artery,  586 

radial  carpal  artery,  584 

(anterior)  radio-carpal  ligament,  266 

ulnar  carpal  artery,  580 
Vomer,  85 

Vomero-nasal  organ  (of  Jaoobson),  1051,  1204 
Vortices  of  hair,  1291 
Vulva  (external  female  genitalia),  1276 

W 

Waldeyer's  tonsillar  ring,  1133 
Wallerian  degeneration,  780 
Wharton's  duct,  1116 


White  commissures  of  spinal  cord,  776 

ramus  communicans,  1030 

substance  of  nervous  system,  768 
of  spinal  cord,  775,  777 
of  telencephalon,  885 
Whitlow,  1431 
Willis,  circle  of  (circulus  arteriosus),  555 

chords  of,  649 
Wings  of  sphenoid,  62 

great  or  temporal,  65 

small  or  orbital,  64 
Winslow,  foramen  of,  1147 
Wirsung,  duct  of,  1194 
Wisdom  teeth,  1122 
Wolffian  body,  1278 

duct,  1248,  1267,  1278 
Word-blindness,  895 
Wormian  bone,  68 
Wrinkles  of  skin,  1284 
Wrisberg,  cardiac  ganglion  of,  1041 

cartilages  of,  1213 

lingula  of,  942 

nerve  of,  946,  983 
Wrist,  bony  points  of,  1424 

clinical  anatomy  of,  1424 
Wrist-joint,  265 


Xiphoid  branch  of  superior  epigastric  artery, 
567 
process,  132,  134 


Yellovc  spot  (macula  lutea),  1055 

of  larvnx,  1223 
Yolk-sac,  10,  13 


Zeiss's  glands,  1078 
Zinn,  ligament  of,  1067 
Zona  fasoiculata,  1326 
glomerulosa,  1326 
reticulata,  1326 
Zone(s),  marginal,  of  Lissauer,  782 

mixed  lateral,  784 
Zonula  oiliaris,  1064 
Zonular  spaces,  1064 
Zygapophysis,  57 
Zygomatic  arch,  1332 
bone  (malar),  93 

at  birth,  124 
branches  of  lacrimal  artery,  552 

(orbital  or  temporo-malar)  of  maxillary 

nerve,  938 
(malar)  of  temporo-facial  nerve,  945 
fossa,  101,  1332 
process,  70,  87,  88 
Zygomatico-facial  (malar)  branch  of  maxillary 
nerve,  938 
canals,  126 
Zygomatioo-orbital  artery,  545 

canals,  94 
Zygomatico-temporal   (temporal)    branch   of 
maxillary  nerve,  938 
foramen,  126 
Zygomaticus  (zygomaticus  major),  333 
minor,  332 


COLUMBIA  UNIVERSITY  LIBRARIES  (hsLstx) 

QM  23  IV183  1914  C.1 

Morris's  human  anatomy 


2002191202 


QM27j 


Hvunan  anatomy 


UBz 
1914 


MAR  2  0  1944      '=i^'  <>   (^-^J^^<^  T)r 


'\ 


